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  • 3301.
    Pettersson, Jens
    et al.
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Maskinteknik.
    Larsson, Tom
    Högskolan i Jönköping, Tekniska Högskolan, JTH, Maskinteknik.
    Utvecklingsarbete av avfallspress2017Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    In this thesis a further development of Orwak AB’s existing product, TOM, has been developed. The product is a trash bin that compresses the waste the user dumps to reduce the volume of the trash. A machine like this is called a waste compactor. The problems which had been revealed was that the user could not toss the waste during the compression process and the existing compression system was not optimally designed.The project started with a requirement specification that was made together with the company to create clear guidelines about what should be done. A GANTT-schedule was also made to know what and when everything was going to be performed. The work then proceeded with a pilot study, followed by a method called Brainstorming that is used to develop new ideas. The concepts was then screened through both feedback from the company and a method called Pughs matrix. Finally, only a few concepts remained and was further developed in the 3D-modelling program Solid Works.The final result became a new compression system and a new type of disposal hatch. The new compression system is driven by an electrical actuator that is connected to one of the arms in the so called “scissor lift solution”. By using this type of solution, the compression system became more compact and at the same time reduced the compression time due to the high gearing. The new disposal hatch looks like a type of garage door and occupies less space inside the machine. The hatch also has a magnetic switch that offers a safe solution to toss waste during the compression process.The project has only developed concept solutions in CAD that can be further developed by the company. No calculations or tests has been done on the concepts due to the limited time frame and an agreement with the company.

    Fulltekst (pdf)
    fulltext
  • 3302.
    Pettersson, Kjell
    et al.
    KTH, Tidigare Institutioner (före 2005).
    Kese, Kwadwo
    KTH, Tidigare Institutioner (före 2005).
    Efsing, Pål
    KTH, Tidigare Institutioner (före 2005).
    Studies on Delayed Hydride Cracking of Zircaloy Cladding1999Inngår i: Ninth International Symposium on Environmental Degradation of Materials in Nuclear Power Systems—Water Reactors / [ed] S Bruemmer, P Ford, G Was, 1999Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Occasionally Zircaloy fuel cladding fail by forming long axial splits which lead to substantial releases of fission products. Postirradiation examinations of failed fuel suggested that Delayed Hydride Cracking (DHC) could be the mechanism. Tests on unirradiated cladding were used in order to develop a test method for irradiated cladding. These tests showed that unirradiated cladding was sensitive to DHC and that the threshold stress intensity factor for crack growth decreased and the maximum crack growth rate increased with increasing yield strength. The subsequent tests on irradiated cladding showed that it had about the same properties as unirradiated cladding with a similar yield strength. The cracking mechanism was studied with metallographic and fractographic examinations. The observations suggest that the cause of cracking is re-orientation of hydride plates in the vicinity of the crack tip from a plane perpendicular to the plane of the crack to an orientation parallel with the crack. This reduces the local fracture toughness to a value below the applied K and the crack grows until it is arrested in material where the re-orientation has not yet taken place. The driving force for re-orientation is the stress field at the crack tip, and as expected from such a mechanism the observed temperature dependence of cracking is consistent with the combined activation energies for hydrogen diffusion and solubility in Zircaloy. A recent study of the effect of hydride plates oriented perpendicular to the stress in uniaxial tests indicates however that these have no effect on ductility at temperatures above 100°C, while the DHC tests were conducted at 200 and 300CC. The exact mechanism of cracking is therefore still something of a mystery. 

  • 3303.
    Pettersson, Robert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Simulation of Human Movements through Optimization2012Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Optimization has been used to simulate human neural control and resulting movement patterns. The short term aim was to develop the methodology required for solving the movement optimization problem often arising when modelling human movements. A long term aim is the contribution to increased knowledge about various human movements, wherein postures is one specific case. Simulation tools can give valuable information to improve orthopeadic treatments and technique for training and performance in sports. In one study a static 3D model with 30 muscle groups was used to analyse postures. The activation levels of these muscles are minimized in order to represent the individual’s choice of posture. Subject specific data in terms of anthropometry, strength and orthopedic aids serve as input. The specific aim of this part was to study effects from orthopedic treatment and altered abilities of the subject. Initial validation shows qualitative agreement of posture strategies but further details about passive stiffness and anthropometry are needed, especially to predict pelvis orientation. Four studies dealt with movement optimization. The main methodological advance was to introduce contact constraints to the movement optimization. A freetime multiple phase formulation was derived to be able to analyse movements where different constraints and degrees of freedom are present in subsequent phases of the movements. The athletic long jump, a two foot high jump, a backward somersault and rowing were used as applications with their different need of formulation. Maximum performance as well as least effort cost functions have been explored. Even though it has been a secondary aim in this work the results show reasonable agreement to expected movements in reality. Case specific subject properties and inclusion of muscle dynamics are required to draw conclusions about improvements in the sport activity, respectively.

    Fulltekst (pdf)
    fulltext
  • 3304.
    Pettersson, Robert
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Movement optimization of multibody system subjected to contact constraint with application to long jumpInngår i: Journal of Biomechanics, ISSN 0021-9290, E-ISSN 1873-2380Artikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    Optimization is a useful method to study control in biomechanical systems. At the same time the optimization limits and requires consideration of computational cost, degrees of freedom and sensitivity of constraints. Here the athletic long jump has been studied as a multibody system, seeking an optimal take-off technique. The model was based on rigid links, joint actuators and a wobbling mass. The contact to the ground was modelled as a spring-damper system with tuned properties. The movement in the degrees of freedom representing physical joints was described over contact time through two fifth-order polynomials, with a variable transition time, while the motion in the degrees of freedom of contact and wobbling mass was integrated forward in time, as a consequence. Muscle activation variables were then optimized in order to maximize ballistic flight distance. The optimization determined contact time, end configuration, activation and interaction with the ground from an initial configuration. The simulation used initial velocities from recorded jumps(Athens,Muraki) and anatomical data from referred experiments were complemented by assumed reasonable data. A sensitivity study was performed for important basic parameters. The results from optimization show a reasonable agreement with experimentally recorded jumps.

  • 3305.
    Pettersson, Robert
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Free-time optimization of targeted movements based on temporal FE approximation2010Inngår i: Proc. CST 2010, 2010Konferansepaper (Fagfellevurdert)
  • 3306.
    Pettersson, Robert
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Free-time optimization of targeted movements based on temporal finite element approximation2010Inngår i: Proceedings of the Tenth International Conference on Computational Structures Technology, Civil-Comp Ltd , 2010, Vol. 93Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Previous work by the authors has shown that temporal finite element approximations can be used for the representation of targeted optimal control problems, and that a weak equilibrium formulation leads to robust and efficient simulations. A free-time formulation is now introduced to increase the degree of freedom in finding optimal movement. The timescale parameter in relation to the objective function is discussed and verified by numerical examples. For movements with partial contact multiple phases with different mechanical properties are included. The free-time formulation allows these phases to be determined by the optimization. A three-phase two-foot high jump is simulated where the movement optimization finds a prior motion preparing for the subsequent phases with different mechanical properties.

  • 3307.
    Pettersson, Robert
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Optimisation of multiple phase human movements2013Inngår i: Multibody system dynamics, ISSN 1384-5640, E-ISSN 1573-272X, Vol. 30, nr 4, s. 461-484Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    When simulating human movements it is frequently desirable to optimise multiple phase movements where the phases represent, e.g., different contact conditions. The different constraints are usually acting in parts of the movements and their time durations are in most cases unknown. Therefore a multiple phase free-time optimisation method is formulated in this work, with phase times included as variables. Through a temporal finite element approach, a discrete representation is derived and a nonlinear optimisation algorithm solves for the rather high number of variables (similar to 6000) and constraints (similar to 15000) in the presented numerical problem. A four degrees of freedom test problem, representing a standing high jump, is solved in order to test some basic aspects. A more realistic problem shows its performance in its intended applications, biomechanical simulations. This is a sagittal eight degrees of freedom model for a human backward somersault, including preparing movement, flight phase and landing. The numerical performance as well as some application specific results are discussed. The method description is general and applicable to other movements in its presented format.

  • 3308.
    Pettersson, Robert
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Optimization of multiple phase human movementsInngår i: Multibody system dynamics, ISSN 1384-5640, E-ISSN 1573-272XArtikkel i tidsskrift (Annet vitenskapelig)
    Abstract [en]

    When simulating human movements it is frequently desirable to optimize multiple phase movements where the phases represent, e.g., different contact conditions. The different constraints are usually acting in parts of the movements and their time durations are in most cases unknown. Therefore a multiple phase free-time optimization method is formulated in this work, with phase times included as variables. Through a temporal finite element approach, a discrete representation is derived and a nonlinear optimization algorithm solves for the rather high number of variables (∼ 6000) and constraints (∼ 15000) in the presented numerical problem. The method is applied to a test problem and a more realistic problem in order to test some basic aspects as well as to see its performance in its intended applications, biomechanical simulations. First a four degrees of freedom test problem, representing a standing high jump, is solved. Then a sagittal eight degrees of freedom model is used with application to a human backward somersault, including preparing movement, flight phase and landing. The numerical performance as well as some application specific results are discussed. The method description is general and applicable to other movements in its presented format.

  • 3309.
    Pettersson, Robert
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Nordmark, Arne
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Simulation of rowing in an optimization context2014Inngår i: Multibody system dynamics, ISSN 1384-5640, E-ISSN 1573-272X, Vol. 32, nr 3, s. 337-356Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Competitive rowing requires efforts close to the physiological limits, where oxygen consumption is one main aspect. The rowing event also incorporates interactions between the rower, the boat and oars, and water. When the intention is to improve the performance, all these properties make the sport interesting from a scientific point of view, as the many variables influencing the performance form a complex optimization problem. Our aim was to formulate the rowing event as an optimization problem where the movement and forces are completely determined by the optimization, giving at least qualitative indications on good performance. A mechanical model of rigid links was used to represent rower, boat and oars. A multiple phase cyclic movement was simulated where catch slip, driving phase, release slip and recovery were modeled. For this simplified model, we demonstrate the influence of the stated mathematical cost function as well as a parameter study where the optimal performance is related to the planned average boat velocity. The results show qualitatively good resemblance to expected movements for the rowing event. An energy loss model in combination with case specific properties of rower capacities, boat properties, and rigging was required to draw qualitative practical conclusions about the rowing technique.

  • 3310.
    Pettersson, Simon
    et al.
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET).
    Miranda, Andersson
    Högskolan i Halmstad, Sektionen för ekonomi och teknik (SET).
    VEVA Multifunctional Spindlering2013Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [en]

    Our thesis is made in collaboration with Autoliv Sweden and the department Global Development Seatbelt in Vårgårda.

    Autoliv was founded in 1953 by two brothers from Vårgårda. Since then, they have become world leading in automotive safety and cooperates with several major automotive companies.

     

    The aim of the project was to evaluate a concept that Adrian Bud for Global Development Seatbelt department in Vårgårda had come up with. The concept aims to simplify the design and reduce the number of parts in an adaptive load limiter (LLA). With a reduction in the number of parts, the price for the LLA would decrease and also make assembly easier.

     

    An LLA adjusts the chest compression from the seatbelt in a crash sequence. This helps reducing the injury that might result from such chest compressions in a crash. The load limiter ensures that the slowdown of the body is done in a smooth manner by adjusting the amount of belt released.

     

    Our concept evaluation has included conceptual design, primary design, visualization of design in Catia V5 and FEM analysis. Finally prototypes were built with the help of Autolivs central workshop and tests were performed at Autoliv. The report also includes analyzes of the results, recommendations for the continuation of work and development and a critical review of the evaluation.

    Fulltekst (pdf)
    VEVA Multifunctional Spindlering
  • 3311.
    Pham, Quoc Tuan
    et al.
    Blekinge Institute of Technology, Sweden.
    Islam, Md Shafiqul
    Blekinge Institute of Technology, Sweden.
    Barlo, Alexander
    Blekinge Institute of Technology, Sweden.
    Sigvant, Mats
    Volvo Cars, Sweden; Blekinge Institute of Technology, Sweden.
    Pérez Caro, Lluís
    RISE Research Institutes of Sweden, Material och produktion, Tillverkningsprocesser.
    Trana, Kristoffer
    Volvo Cars, Sweden.
    Modeling the strain localization of shell elements subjected to combined stretch–bend loads: Application on automotive sheet metal stamping simulations2023Inngår i: Thin-walled structures, ISSN 0263-8231, E-ISSN 1879-3223, Vol. 188, artikkel-id 110804Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study presents a modeling approach for predicting strain localization during sheet metal stamping processes focused on automotive engineering applications. The so-called stretching-to-bending ratio, ρ, is proposed to characterize the loading conditions acting on an element during stamping processes. Then, localized strain or necking strain is suggested to be a function of ρ. Different stretch–bending tests with different tool radii, i.e., R3, R6, R10, and R50 are conducted for two automotive sheet metals, DP800 and AA6010, to identify their forming limits under combined stretch–bend loads. The calibrated necking limit curve of the AA6016 sheet is then employed in AutoForm R10 software to predict the necking and failure of a stamped panel. Agreement with the experimental observation of failure positions of the panel validates the usefulness of the proposed modeling approach in practice. 

  • 3312.
    Phan, Tra
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Bader, Sebastian
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Oelmann, Bengt
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för elektronikkonstruktion.
    Performance of an electromagnetic energy harvester with linear and nonlinear springs under real vibrations2020Inngår i: Sensors, E-ISSN 1424-8220, Vol. 20, nr 19, artikkel-id 5456Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The introduction of nonlinearities into energy harvesting in order to improve the performance of linear harvesters has attracted a lot of research attention recently. The potential benefits of nonlinear harvesters have been evaluated under sinusoidal or random excitation. In this paper, the performances of electromagnetic energy harvesters with linear and nonlinear springs are investigated under real vibration data. Compared to previous studies, the parameters of linear and nonlinear harvesters used in this paper are more realistic and fair for comparison since they are extracted from existing devices and restricted to similar sizes and configurations. The simulation results showed that the nonlinear harvester did not generate higher power levels than its linear counterpart regardless of the excitation category. Additionally, the effects of nonlinearities were only available under a high level of acceleration. The paper also points out some design concerns when harvesters are subjected to real vibrations. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.

    Fulltekst (pdf)
    fulltext
  • 3313.
    Phiri, Tapiwanashe
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Björkman, Niklas
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Simmulating pullout forces in particleboard2019Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Pull-out forces of screws and connectors in particleboard are particularly important when designing for strength and, or assembly in the furniture industry. The aim of this thesis was to develop a simulation model of particleboard that can predict pull-out forces of screws better than the currently used simulation model at IKEA of Sweden. The developed model was validated against experimental results from pull-out tests carried out by IKEA.

    Material properties for particleboard are determined from experiments previously carried out at IKEA test labs unless stated otherwise in the report. The authors did not carry out any tests. In order to simulate the pull-out forces of a screw, the finite element method was employed, simulation models from three different material models selected from the Finite Element Analysis (FEA) software LS-DYNA. The first material model considered Mat_143, a wood material model based on the Hashin failure criterion and used to develop simulation model 1. The second material considered, Mat_122 3D, based on Hill’s plasticity theory, was used with Mat_Add_Generalised_Damage to allow for incremental damage accumulation and failure. This was simulation model 2. The third one, Mat_221 which represents an orthotropic material with simplified damage, was used to develop simulation model 3.

    Experimental test results for tensile test, bending test, shear test and, finally, the screw pull-out test was used to validate the simulation models. Before the scale validation, a single hexahedral element was simulated to evaluate the accuracy of the simulation models and to get a better understanding of the limitations of the material models. A mesh type and convergence study was carried out where it was concluded that the first- and second-order hexahedral and tetrahedral elements could be employed for the full model simulations, giving a sufficiently accurate result, i.e. matching the experimental results by at least 86%. An element size range of 1-3 mm was enough for quasi-static load cases and while an element size range 0.15-3 mm was relevant for dynamic load cases. Model 1 was abandoned when it was discovered the material model was not suitable for predicting material behaviour other than that of wood for a large mesh.

    The remaining two simulation models were evaluated for tensile, shear and bending load cases. Simulation model 2 predicted both tensile and bending forces with an accuracy of 99% or higher, and predicted shear forces with an accuracy of 86%. Simulation model 3 predicts both tensile and shear forces with an accuracy of 98% or higher and predicted bending forces with an accuracy of 86%.

    For the screw pull-out test, simulation models 2 and 3 under-predicted the pull-out forces significantly due to premature shear failure.iiiThe currently used particleboard simulation model is referred to as simulation model 4 throughout the report. Simulation model 4 was the most accurate simulation model for predicting pull-out forces in particleboard.

    Fulltekst (pdf)
    Simulating pull-out fracture in particleboard
    Fulltekst (pdf)
    fulltext
  • 3314.
    Phounglamcheik, Aekjuthon
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Wang, Liang
    SINTEF Energy Research, Torgarden, Trondheim, Norway.
    Romar, Henrik
    Research Unit of Sustainable Chemistry, Oulu University, Oulu, Finland.
    Kienzl, Norbert
    BEST—Bioenergy and Sustainable Technologies GmbH, Graz, Austria.
    Broström, Markus
    Department of Applied Physics and Electronics, Umeå University, 901 87 Umeå, Sweden.
    Ramser, Kerstin
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Skreiberg, Øyvind
    deSINTEF Energy Research, P.O. Trondheim, Norway.
    Umeki, Kentaro
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Effects of Pyrolysis Conditions and Feedstocks on the Properties and Gasification Reactivity of Charcoal from Woodchips2020Inngår i: Energy & Fuels, ISSN 0887-0624, E-ISSN 1520-5029, Vol. 34, nr 7, s. 8353-8365Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pyrolysis conditions in charcoal production affect yields, properties, and further use of charcoal. Reactivity is a critical property when using charcoal as an alternative to fossil coal and coke, as fuel or reductant, in different industrial processes. This work aimed to obtain a holistic understanding of the effects of pyrolysis conditions on the reactivity of charcoal. Notably, this study focuses on the complex effects that appear when producing charcoal from large biomass particles in comparison with the literature on pulverized biomass. Charcoals were produced from woodchips under a variety of pyrolysis conditions (heating rate, temperature, reaction gas, type of biomass, and bio-oil embedding). Gasification reactivity of produced charcoal was determined through thermogravimetric analysis under isothermal conditions of 850 degrees C and 20% of CO2. The charcoals were characterized for the elemental composition, specific surface area, pore volume and distribution, and carbon structure. The analysis results were used to elucidate the relationship between the pyrolysis conditions and the reactivity. Heating rate and temperature were the most influential pyrolysis parameters affecting charcoal reactivity, followed by the reaction gas and bio-oil embedding. The effects of these pyrolysis conditions on charcoal reactivity could primarily be explained by the difference in the meso- and macropore volume and the size and structural order of aromatic clusters. The lower reactivity of slow pyrolysis charcoals also coincided with their lower catalytic inorganic content. The reactivity difference between spruce and birch charcoals appears to be mainly caused by the difference in catalytically active inorganic elements. Contrary to pyrolysis of pulverized biomass, a low heating rate produced a higher specific surface area compared with a high heating rate. Furthermore, the porous structure and the reactivity of charcoal produced from woodchips were influenced when the secondary char formation was promoted, which cannot be observed in pyrolysis of pulverized biomass.

  • 3315.
    Pilthammar, Jan
    et al.
    Volvo Cars, Sweden; Blekinge Institute of Technology, Sweden.
    Skåre, Thomas
    RISE Research Institutes of Sweden, Material och produktion, Tillverkningsprocesser.
    Galdos, L.
    Mondragon Unibertsitatea, Spain.
    Frojdh, K.
    Proximion AB, Sweden.
    Ottosson, Peter
    RISE Research Institutes of Sweden, Material och produktion, Tillverkningsprocesser.
    Wiklund, Daniel
    RISE Research Institutes of Sweden, Material och produktion, Tillverkningsprocesser.
    Carlholmer, Jonathan
    RISE Research Institutes of Sweden, Material och produktion, Tillverkningsprocesser.
    Sigvant, M.
    Volvo Cars, Sweden; Blekinge Institute of Technology, Sweden.
    Ohlsson, M.
    RISE Research Institutes of Sweden.
    Argandoña, E. Sáenz de
    Mondragon Unibertsitatea, Spain.
    Abbasi, F.
    Mondragon Unibertsitatea, Spain.
    Sarasua, O.
    Fagor Arrasate S. Coop, Spain.
    Garro, A.
    Koniker S. Coop, Spain.
    Rutgersson, W.
    Cascade control AB, Sweden.
    New press deflection measuring methods for the creation of substitutive models for efficient die cambering2021Inngår i: IOP Conference Series: Materials Science and Engineering, ISSN 1757-8981, E-ISSN 1757-899X, Vol. 1157, artikkel-id 012076Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cost and time for die tryout are significant within the car industry, and elastic deflections of dies and presses are most commonly not considered during the virtual die design and forming simulation phase. Because of this, active surfaces of stamping dies are only cambered based on previous experiences of tool types and presses. However, almost all stamping dies and presses are unique, and available experiences are not valid for new materials. Partners within the Eureka SMART Advanced Manufacturing research project CAMBER have developed advanced deflection measuring devices to quantify the elastic deformations of presses. Using these measurements, cambering methodologies can be utilized in sheet metal forming simulations. Important breakthroughs in recent years enabling the cambering methodology consists of efficient simulation strategies for full scale simulations with elastic dies and optimization techniques for creating substitutive press structures based on measurements. Furthermore, modern press deflection measurement methods are beneficial in applications such as Industry 4.0, predictive maintenance, product quality control, etc. through a more advanced understanding and live monitoring of the press system.

  • 3316. Pilthammar, Johan
    et al.
    Sigvant, Mats
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Hansson, Mårten
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Pálsson, Einar
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Rutgersson, Wilhelm
    Cascade Control AB, SWE.
    Characterizing the Elastic Behaviour of a Press Table throughTopology Optimization2017Inngår i: Journal of Physics: Conference Series / [ed] Volk W., Institute of Physics Publishing (IOPP), 2017, Vol. 896, artikkel-id 012101Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Sheet metal forming in the car industry is a highly competitive area. The use ofdigital techniques and numerical methods are therefore of high interest for reduced costs andlead times. One method for reducing the try-out phase is virtual rework of die surfaces. Thevirtual rework is based on Finite Element (FE) simulations and can reduce and support manualrework. The elastic behaviour of dies and presses must be represented in a reliable way in FEmodelsto be able to perform virtual rework. CAD-models exists for nearly all dies today, butnot for press lines. A full geometrical representation of presses will also yield very large FEmodels.This paper will discuss and demonstrate a strategy for measuring and characterizing apress table for inclusion in FE-models. The measurements of the elastic press deformations iscarried out with force transducers and an ARAMIS 3D optical measurement system. The presstable is then inverse modelled by topology optimization using the recorded results as boundaryconditions. Finally, the press table is coupled with a FE-model of a die to demonstrate itsinfluence on the deformations. This indicates the importance of having a reliable representationof the press deformations during virtual rework.

  • 3317.
    Pilthammar, Johan
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Sigvant, Mats
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Islam, Md. Shafiqul
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Schill, M.
    Dynamore Nord, Sweden.
    Sjoblom, S.
    Blekinge Tekniska Högskola. student.
    Sjoblom, V.
    Blekinge Tekniska Högskola. student.
    Lind, M.
    Blekinge Tekniska Högskola. student.
    An overview of Methods for Simulating Sheet Metal Forming with Elastic Dies2023Inngår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP / [ed] Asnafi, N Lindgren, LE, IOP PUBLISHING LTD , 2023, Vol. 1284, artikkel-id 012054Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Sheet metal forming (SMF) simulations are traditionally carried out with rigid active forming surfaces. This means that the elasticity and dynamics of presses and die structures are ignored. The only geometries of the tools included in the simulations are the active forming surfaces. One reason for this simplification is the large amount of computational power that is required to solve finite element (FE) models that incorporates elastic stamping dies. Another reason is the lack of die CAD models before the later stages of stamping projects. Research during the last couple of decades indicated potential large benefits when including elastic dies in SMF simulations. For example, for simulating die try-out or for Digital Twins of presses and dies. Even though the need and potential benefits of elastic dies in simulations are well known it is not yet implemented on a wide scale. The main obstacles have been lacking data on presses and dies, long simulation times, and no standardized implementation in SMF software. This paper presents an overview of existing methods for SMF simulations with elastic dies and discuss their respective benefits and drawbacks. The survey of methods shows that simulation models with elastic tools will be needed for detailed analyses of forming operations and also for purposes like digital twins. On the other hand, simplified and robust models can be developed for non-FEA users to carry out simple one-step compensation of tool surfaces for virtual spotting purposes. The most promising and versatile method from the literature is selected, modified, and demonstrated for industrial sized dies.

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  • 3318.
    Pilthammar, Johan
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Sigvant, Mats
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Islam, Md. Shafiqul
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Schill, M.
    Dynamore Nord, Sweden..
    Sjoblom, S.
    Blekinge Tekniska Högskola. student.
    Sjoblom, V.
    Blekinge Tekniska Högskola. student.
    Lind, M.
    Blekinge Tekniska Högskola. student.
    Three Industrial Cases of Sheet Metal Forming Simulations with Elastic Dies2023Inngår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP / [ed] Asnafi, N Lindgren, LE, IOP PUBLISHING LTD , 2023, Vol. 1284, artikkel-id 012055Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Previous research and experience points to many advantages if sheet metal forming is simulated with elastic dies. Some areas that are enabled by simulations with elastic dies are virtual spotting, improved digital twins, and improved production support. A promising method was selected from the literature, and after important modifications it is deemed to be fast and robust for simulating industrial sized dies. The method consists of meshing die solids with a coarse mesh to represent the structural behaviour of the die. The forming surfaces are then represented by a fine shell mesh connected to the solid mesh by tied contacts with an offset. With additional modifications to reduce solver time this yields a robust and flexible way of modelling sheet metal forming with elastic dies. There is an increase in preprocessing and simulation time compared to using rigid tools, but industrial dies can now be modeled within an hour and solved within a working day. It is also easy to update the model by replacing separate parts such as die solids or forming surfaces. One of the main criteria in favor of the selected approach is the realistic modeling of blankholder and cushion systems. In this paper simulations of three industrial cases are demonstrated: one case of virtual die spotting and two cases of production support. The three cases demonstrate the importance and potential of using elastic dies during virtual die tryout, production support, and for cases like digital twins and production control.

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  • 3319.
    Pilthammar, Johan
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Skare, T.
    RISE IVF AB, Div Mat & Prod, SWE.
    Galdos, L.
    Mondragon Unibertsitatea ESP.
    Frojdh, K.
    Proximion AB, SWE.
    Ottosson, P.
    RISE IVF AB, Div Mat & Prod, SWE.
    Wiklund, D.
    RISE IVF AB, Div Mat & Prod, SWE.
    Carlholmer, J.
    RISE IVF AB, Div Mat & Prod, SWE.
    Sigvant, Mats
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Ohlsson, M.
    RISE IVF AB, Div Mat & Prod, SWE.
    Saenz de Argandona, E.
    Mondragon Unibertsitatea, ESP.
    Abbasi, F.
    Mondragon Unibertsitatea, ESP.
    Sarasua, O.
    Fagor Arrasate S Coop, ESP.
    Garro, A.
    Koniker S Coop, ESP.
    Rutgersson, W.
    Cascade Control AB, SWE.
    New press deflection measuring methods for the creation of substitutive models for efficient die cambering2021Inngår i: INTERNATIONAL DEEP-DRAWING RESEARCH GROUP CONFERENCE (IDDRG 2021) / [ed] Liewald, M, Karadogan, C, IOP PUBLISHING LTD , 2021, Vol. 1157, artikkel-id 012076Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Cost and time for die tryout are significant within the car industry, and elastic deflections of dies and presses are most commonly not considered during the virtual die design and forming simulation phase. Because of this, active surfaces of stamping dies are only cambered based on previous experiences of tool types and presses. However, almost all stamping dies and presses are unique, and available experiences are not valid for new materials. Partners within the Eureka SMART Advanced Manufacturing research project CAMBER have developed advanced deflection measuring devices to quantify the elastic deformations of presses. Using these measurements, cambering methodologies can be utilized in sheet metal forming simulations. Important breakthroughs in recent years enabling the cambering methodology consists of efficient simulation strategies for full scale simulations with elastic dies and optimization techniques for creating substitutive press structures based on measurements. Furthermore, modem press deflection measurement methods are beneficial in applications such as Industry 4.0, predictive maintenance, product quality control, etc. through a more advanced understanding and live monitoring of the press system.

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  • 3320.
    Pilthammar, Johan
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Wall, Johan
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Sigvant, Mats
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Framework for Simulation-Driven Design of Stamping Dies Considering Elastic Die and Press Deformations2017Inngår i: PROCEEDINGS OF THE 20TH INTERNATIONAL ESAFORM CONFERENCE ON MATERIAL FORMING (ESAFORM 2017) / [ed] Brabazon D.,Ul Ahad I.,Naher S., American Institute of Physics (AIP), 2017, Vol. 1896, artikkel-id 010001Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Sheet metal forming (SMF) simulations are used extensively throughout the development phase of industrialstamping dies. In these SMF simulations, the die and press are normally considered as rigid. Previous research has howevershown that elastic deformation in these parts has a significant negative impact on process performance. This paperdemonstrates methods for counteracting these negative effects, with a high potential for improved production support anda reduced lead time through a shorter try-out process. A structural finite element model (FE-model) of a simplified die isstudied. To account for elastic deformation, the blankholder surfaces are first virtually reworked by adjusting the nodalpositions on the die surfaces attaining a pressure distribution in accordance to the design phase SMF simulations with rigidsurfaces. The elastic FE-model with reworked surfaces then represents a stamping die in running production. The die isnow assumed to be exposed to changed process conditions giving an undesired blankholder pressure distribution. Thechanged process conditions could for example be due to a change of press line. An optimization routine is applied tocompensate the negative effects of the new process conditions. The optimization routine uses the contact forces acting onthe shims of the spacer blocks and cushion pins as optimization variables. A flexible simulation environment usingMATLAB and ABAQUS is used. ABAQUS is executed from MATLAB and the results are automatically read back intoMATLAB. The suggested optimization procedure reaches a pressure distribution very similar to the initial distributionassumed to be the optimum, and thereby verifying the method. Further research is needed for a method to transform thecalculated forces in the optimization routine back to shims thicknesses. Furthermore, the optimization time is relativelylong and needs to be reduced in the future for the method to reach its full potential.

  • 3321.
    Pintado, P.
    et al.
    Univ Castilla La Mancha, Dept Mech Engn, Ave Camilo Jose Cela S-N, E-13071 Ciudad Real, Spain..
    Ramiro, C.
    Univ Castilla La Mancha, Dept Mech Engn, Ave Camilo Jose Cela S-N, E-13071 Ciudad Real, Spain..
    Berg, Mats
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Spårfordon. KTH, Skolan för teknikvetenskap (SCI), Centra, VinnExcellence Center for ECO2 Vehicle design. KTH, Skolan för teknikvetenskap (SCI), Centra, Järnvägsgruppen, JVG.
    Morales, A. L.
    Univ Castilla La Mancha, Dept Mech Engn, Ave Camilo Jose Cela S-N, E-13071 Ciudad Real, Spain..
    Nieto, A. J.
    Univ Castilla La Mancha, Dept Mech Engn, Ave Camilo Jose Cela S-N, E-13071 Ciudad Real, Spain..
    Chicharro, J. M.
    Univ Castilla La Mancha, Dept Mech Engn, Ave Camilo Jose Cela S-N, E-13071 Ciudad Real, Spain..
    Miguel de Priego, J. C.
    Patentes Talgo, Paseo Tren Talgo 2, Madrid 28290, Spain..
    Garcia, E.
    Univ Castilla La Mancha, Dept Mech Engn, Ave Camilo Jose Cela S-N, E-13071 Ciudad Real, Spain..
    On the mechanical behavior of rubber springs for high speed rail vehicles2018Inngår i: Journal of Vibration and Control, ISSN 1077-5463, E-ISSN 1741-2986, Vol. 24, nr 20, s. 4676-4688Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    There are many engineering design problems that call for rubber components as the best solution. Vulcanized rubber has found its way into all sorts of devices, from the universal automobile pneumatic tire to the ubiquitous compliant bushing. Some high-speed rail vehicle suspensions make use of rubber, not only in the air spring itself, but also in the auxiliary spring. The mechanical characteristics of this component influence vehicle dynamics and, therefore, accurate spring models with which to conduct dynamic analysis would make for powerful design tools. Nevertheless, the mechanical behavior of rubber defies simple modeling on account of stress relaxation, creep, set, viscosity, internal friction, and nonlinear stress-strain relations. Despite the advances in the micromechanical understanding of these phenomena, as well as in the macroscopic modeling of rubber spring behavior, there is ample room for refinement, and this is precisely the goal of this paper. The mechanical behavior of a particular rubber spring for high speed rail vehicles has been characterized. The results reveal the necessary components of the model, and suggest the appropriate procedure for parameter extraction. Our model proposal consists of three elements in parallel: a nonlinear elastic spring; a soft friction element; and a Maxwell viscous component. The characterization procedure takes into account both stress relaxation and nonlinear elasticity. The proposed model accurately reproduces experimental results and may then be used with confidence in any type of numerical simulation. Nevertheless, for this statement to be true, the problem of numerical softening potentially induced by soft friction models should be resolved. The paper will show that a trailing moving average filter, seamlessly tied to the model, wipes out the softening effect.

  • 3322.
    Piroti, Shwana
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Eriksson, Jesper
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Friction Modeling in FE Simulation: Identification of Friction Model Parameters in Airbag and Crash Dummy Head Contact through Simulation and Experimental Data Response Correlation2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Motor vehicle-traffic accidents are a common cause of traumatic brain injuries, resulting in severe and sustaining disabilities, or even fatality. In an effort to mitigate injuries related to vehicle crashes, various safety systems such as the occupant airbag has been implemented. In angled impacts, occupant interaction with the airbags can lead to head rotation, and during recent years head rotation has been emphasized as an important contributor to head injury risk. Therefore, for prediction of head injury risk in crash simulations it is important to correctly model the friction force which arises in the contact between occupants and the car interior. The aim of this thesis is therefore to study the friction within such a system. More specifically, the analysis is focusing on dummy head to airbag interaction and to correlate a three parameter friction model for this contact pair, as well as a one parameter model currently used by Volvo Car Group, with measured laboratory test data in the software LS-DYNA.A preliminary study in LS-DYNA was conducted to determine the configuration of the laboratory setup consisting of a statically inflated customized driver airbag and a crash dummy head being launched to impact the airbag. The laboratory test data was analyzed using linear regression and Students T-test to identify the influence of parameters on the measured responses. The simulation model was then modified to represent the laboratory setup, prior to an optimization study performed to correlate simulation and laboratory test data responses. Lastly, an evaluation study was made to test whether or not the proposed friction model could improve occupant crash simulations.It was found in the thesis study that the friction force had a large effect on the rotation of the head around the vertical axis (z−axis in the anatomical coordinate system of the head). The experimental data showed that the internal pressure of the airbag had little effect on the response. This was likely due to the studied pressures being large enough for the airbag to be so stiff that no plowing effect of the dummy head moving through the airbag fabric could be seen. Furthermore, results from the optimization study indicated that the model correlation was improved when a three parameter friction model with velocity dependence was used. This implies that the friction coefficient is dependent on the velocity. It was also shown that material properties affecting friction behavior vary between different crash dummy heads, as well as different surface coating. Both dummy T-shirt fabric and grease paint resulted in significantly lower surface friction.Due to the difference in friction for different dummy heads, a single set of friction model parameter values that describes the friction behavior of all crash dummy heads does not exist. The study finds that when sliding is present in a contact, a three parameter model for describing the friction improves the correlation, as it can account for the velocity dependence of the friction in the contact. In contrast, when sliding is not present the one parameter and the three parameter model give similar results.Keywords: friction, velocity dependent friction coefficient, finite element analysis, car crash simulation, Volvo Cars, crash test dummy head, driver airbag, LS-DYNA, laboratory testing, optimization study.

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  • 3323.
    Plos, Mario
    et al.
    Chalmers University of Technology, Sweden.
    Shu, Jiangpeng
    Chalmers University of Technology, Sweden.
    Lundgren, Karin
    Chalmers University of Technology, Sweden.
    Zandi, Kamyab
    RISE., SP – Sveriges Tekniska Forskningsinstitut, CBI Betonginstitutet AB.
    A multi-level structural assessment strategy for analysis of RC bridge deck slabs2016Inngår i: IABSE Congress Stockholm 2016: Challenges in Design and Construction of an Innovative and Sustainable Built Environment, IABSE c/o ETH Hönggerberg , 2016, s. 1559-1566Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A multi-level structural assessment strategy for evaluation of response and load carrying capacity of reinforced concrete bridges deck slabs are presented [1]. The strategy is based on the principle of successively improved analysis methods in structural assessment. It provides a structured approach to the use of simplified as well as advanced non-linear finite element analysis methods. The proposed methods were used for analysis of previously tested slabs subjected to bending and shear type of failures. As expected, the advanced methods gave an improved understanding of the structural response and were capable of demonstrating higher, yet conservative, predictions of the load-carrying capacity. The proposed strategy clearly provides the engineering community a framework for using successively improved structural analysis methods for enhanced assessment in a straightforward manner.

  • 3324.
    Poddar, Satyasarathi
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Farkostteknik och Solidmekanik, Hållfasthetslära.
    Rate-dependent effects on the mechanical behaviour of paper2023Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    It is established that paper properties depend on the loading rate. The rule of thumb is that the in-plane strength and stiffness increases about 10\%, when the strain rate increases by a factor of 10. Converting of paperboard into packages requires creasing of the paperboard followed by folding to make 3 dimensional packages. Crease response is controlled by in-plane properties, which contribute to the loading and the spring back of the crease which gives the paperboard its final geometry. 

    This work aims to characterize the rate and time dependent properties of paper, done by tensile testing at high strain rates of up-to 100 000 mm/min using an electro-mechanical testing machine. Also investigated in this work are the rate dependence and characterization of the plies for a deeper understanding of the contributing factors to this rate dependence. At the end of this work the aim is to retrieve the rate dependent behavior of the materials and compare them with the existing rule of thumb.

    In this work it was concluded that the rule of thumb is accurate for the ultimate strength of the material in the strain rate range of 10^4 to 10^1 strains/second. It was also observed that stiffness of the material increases, but at a rate lower than the stated rule of thumb.

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  • 3325. Polzer, S.
    et al.
    Gasser, T. Christian
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Swedenborg, J.
    Bursa, J.
    The Impact of Intraluminal Thrombus Failure on the Mechanical Stress in the Wall of Abdominal Aortic Aneurysms2011Inngår i: European Journal of Vascular and Endovascular Surgery, ISSN 1078-5884, E-ISSN 1532-2165, Vol. 41, nr 4, s. 467-473Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objectives: The role of the intraluminal thrombus (ILT) in abdominal aortic aneurysm (AAA) rupture is controversial, and it is still not clear if an ILT increases or decreases AAA rupture risk. Specifically, signs of bleeding in the ILT are considered to increase AAA rupture risk. to further explore this hypothesis, intact AAAs (n = 4) with clear signs of fissures in the ILT, identified by computed tomography angiography (CTA) were investigated. Methods: Two different cases of ILT fissuring were investigated, where (1) ILT fissures were extracted directly from the CTA data and (2) a hypothetical fissure was introduced in the otherwise-intact ILT tissue. Wall stress distributions were predicted based on detailed Finite Element (FE) models. Results: ILT fissures extracted from CTA data locally increase the mechanical stress in the underlying wall by up to 30%. The largest impact on wall stress was observed if the ILT crack reaches the aneurysm wall, or if it involves large parts of the ILT. By contrast, a concentric failure in the medial ILT, which does not reach the aneurysm wall, has almost no impact on wall stress distribution. Hypothetical ILT fissures that connect the lumen with the wall cause a twofold increase of the stress in the underlying wall. Conclusions: ILT fissures increase the stress in the underlying wall, whereas regions other than that remain unaffected. If ILT fissures reach the wall or involve large parts of the ILT, the resulting increase in wall stress could possibly cause AAA rupture.

  • 3326.
    Polák, Jaroslav
    et al.
    Institute of Physics of Materials, Academy of Sicences of Czech Republic, Brno.
    Petrás, Roman
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Heczko, Milan
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Kruml, Tomás
    Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno.
    Chai, Guocai
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. Sandvik Materials Technology, Sandviken, Sweden.
    Evolution of the Cyclic Plastic Response of Sanicro 25 Steel Cycled at Ambient and Elevated Temperatures2016Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 83, nr 1, s. 75-83Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cyclic plastic response of the austenitic heat resistant steel Sanicro 25 has been studied during strain controlled low cycle fatigue tests performed at ambient and at elevated temperature. Simultaneously with the cyclic hardening/softening curves hysteresis loops during cyclic loading were analyzed using generalized statistical theory of the hysteresis loop. The probability density distribution function of the internal critical stresses, the effective saturated stress and their evolution during cycling were derived for various strain amplitudes. The internal dislocation structure and the surface relief at room and at elevated temperature were studied and correlated with the cyclic stress–strain response and the evolution of the probability density function of the internal critical stresses.

  • 3327.
    Popov Popov, Nikita
    Högskolan i Skövde, Institutionen för ingenjörsvetenskap.
    Design and preliminary finite element analysis of structural frame of a double base for an infant child restraint system.2015Independent thesis Basic level (degree of Bachelor), 15 poäng / 22,5 hpOppgave
    Abstract [en]

    Child restraint systems (CRS) are used for protection of the child in case of car accident. These systems have been found to have a difficult installation process that in many cases can cause greater loads on the child and as a consequence can lead to an increased risk of injury and a reduction in safety. The problems are even more significant in cases of families with two or more children and in small cars with lack of available space. Misuse and its causes are identified from literature as well as from surveys and market research. The design guidelines are gathered from existing CRS designs. Currently available automotive and CRS fastening systems are studied. A specific methodological approach is used for project development. A new concept for a child restraint system is introduced. The main aims are the design proposal of a double ISOFIX base for two children, reduction in the misuse of the CRS, improving the user experience and achieving technological, societal and environmental contributions. The second aspect is to verify the structure of the double base by means of preliminary finite-element analysis using the case of a frontal collision in accordance to current approval testing procedures. Al 2024 is chosen for design by the material selection performed in order to optimize the structure in relation to strength and weight. The finite-element preliminary static analysis is performed employing shell elements. The results are analysed with respect to the mesh convergence. In addition a linearized buckling check is carried out. Finally, the achieved results are discussed in comparison with initial assumptions and goals and future work is suggested.

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  • 3328.
    Pouransari, Zeinab
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Numerical studies of turbulent flames in wall-jet flows2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The present thesis deals with the fundamental aspects of turbulent mixing and non-premixed combustion in the wall-jet flow, which has a close resemblance to many industrial applications. Direct numerical simulations (DNS) of turbulent wall-jets with isothermal and exothermic reactions are performed. In the computational domain, fuel and oxidizer enter separately in a nonpremixed manner and the flow is compressible, fully turbulent and subsonic. The triple “turbulence-chemistry-wall” interactions in the wall-jet flow have been addressed first by focusing on turbulent flow effects on the isothermal reaction, and then, by concentrating on heat-release effects on both turbulence and flame characteristics in the exothermic reaction. In the former, the mixing characteristics of the flow, the key statistics for combustion and the near-wall effects in the absence of thermal effects are isolated and studied. In the latter, the main target was to identify the heat-release effects on the different mixing scales of turbulence. Key statistics such as the scalar dissipation rates, time scale ratios, two-point correlations, one and two-dimensional premultiplied spectra are used to illustrate the heat release induced modifications. Finer small mixing scales were observed in the isothermal simulations and larger vortical structures formed after adding significant amounts of heat-release. A deeper insight into the heat release effects on three-dimensional mixing and reaction characteristics of the turbulent wall-jet flow has been gained by digging in different scales of DNS datasets. In particular, attention has been paid to the anisotropy levels and intermittency of the flow by investigating the probability density functions, higher order moments of velocities and reacting scalars and anisotropy invariant maps for different reacting cases. To evaluate and isolate the Damkohler number effects on the reaction zone structure from those of the heat release a comparison between two DNS cases with different Damkohler numbers but a comparable temperature rise is performed. Furthermore, the wall effects on the flame and flow characteristics, for instance, the wall heat transfer; the near-wall combustion effects on the skin-friction, the isothermal wall cooling effects on the average burning rates and the possibility of formation of the premixed mode within the non-premixed flame are addressed. The DNS datasets are also used for a priori  analysis, focused on the heat release effects on the subgrid-scale (SGS) statistics. The findings regarding the turbulence small-scale characteristics, gained through the statistical analysis of the flow have many phenomenological parallels with those concerning the SGS statistics. Finally, a DNS of turbulent reacting wall-jet at a substantially higher Reynolds number is performed in order to extend the applicability range for the conclusions of the present study and figuring out the possible differences.

    Fulltekst (pdf)
    Thesis
  • 3329.
    Pouransari, Zeinab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Biferale, L.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Statistical analysis of the velocity and scalar fields in reacting turbulent wall-jets2015Inngår i: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 27, nr 2, s. 025102-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The concept of local isotropy in a chemically reacting turbulent wall-jet flow is addressed using direct numerical simulation (DNS) data. Different DNS databases with isothermal and exothermic reactions are examined. The chemical reaction and heat release effects on the turbulent velocity, passive scalar, and reactive species fields are studied using their probability density functions (PDFs) and higher order moments for velocities and scalar fields, as well as their gradients. With the aid of the anisotropy invariant maps for the Reynolds stress tensor, the heat release effects on the anisotropy level at different wall-normal locations are evaluated and found to be most accentuated in the near-wall region. It is observed that the small-scale anisotropies are persistent both in the near-wall region and inside the jet flame. Two exothermic cases with different Damkohler numbers are examined and the comparison revealed that the Damkohler number effects are most dominant in the near-wall region, where the wall cooling effects are influential. In addition, with the aid of PDFs conditioned on the mixture fraction, the significance of the reactive scalar characteristics in the reaction zone is illustrated. We argue that the combined effects of strong intermittency and strong persistency of anisotropy at the small scales in the entire domain can affect mixing and ultimately the combustion characteristics of the reacting flow.

  • 3330.
    Pouransari, Zeinab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Brethouwer, Geert
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Direct Numerical Simulation of a Turbulent Reacting Wall-Jet2011Inngår i: Direct and large-eddy simulation VIII, 2011, s. 345-350Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The turbulent wall-jet includes a number of interesting fluid mechanics phenomena with close resemblance to many mixing and combustion applications. During the last decades, both DNS (Ahlman et al., 2007; Ahlman et al., 2009), and LES (Dejoan & Leschziner, 2005) have been used to study the turbulent wall-jet. Ahlman et al. (2009) performed DNS of nonisothermal turbulent wall jets. Earlier in 2007, Ahlman et al. investigated turbulent statistics and mixing of a passive scalar for an isothermal case by means of DNS. The first three-dimensional DNS of a reacting turbulent flow was performed by Riley et al. (1986) who simulated a single reaction of two scalars, without heat release, for a mixing layer. Recently, Knaus et al. (2009) studied the effect of heat release in non-premixed reacting shear layers (Knaus & Pantano, 2009).

  • 3331.
    Pouransari, Zeinab
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    Vervisch, Luc
    INSA de Rouen.
    Fuchs, Laszlo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Processteknisk strömningsmekanik.
    Johansson, Arne V.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Turbulens.
    DNS analysis of wall heat transfer and combustion regimes in a turbulent nonpremixed wall-jet flameManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Understanding the heat-release effects on the wall heat transfer in turbulent reacting flows, i.e. heat transfer with or without significant density variation, is essential for a wide variety of industrial flows, especially combustion problems. The present study focuses on the wall heat transfer and the near-wall reaction characteristics. The heat-release effects on the wall heat transfer and skin friction coefficients are investigated using three-dimensional direct numerical simulations of a turbulent reacting wall-jet flow with and without heat release. Reductions in the skin-friction coefficient are observed in the exothermic case, compared to the isothermal one, and the underlying mechanism is explained. The absolute wall heat flux also increases, while the corresponding Nusselt number decreases with increasing heat release. Furthermore, the wall effects on the near-wall average burning rate are assessed. It is found that the isothermal cold wall results in an appreciable decrease of the burning rate in the exothermic cases. We observed indications that the wall increases the chances for the development of the premixed mode and its occurrence is very fast in the wall normal direction.

  • 3332.
    Prabhu, Nikhil
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Material parameter identification of a thermoplastic using full-field calibration2020Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Finite element simulation of thermoplastic components is gaining importance as the companies aim to avoid overdesign of the components. Cost of the component can be minimized by using an adequate amount of material for its application. Life of the component, in a particular application, can be predicted as early as during its design phase with the help of computer simulations. To achieve reliable simulation results, an accurate material model which can predict the material behaviour is vital. Most material models consist of a number of material parameters that needs to be fed into them. These material parameters can be identified with the inputs from physical tests. The accuracy of the data extracted from the physical tests, however, remains the base for the aforementioned process.

    The report deals with the implementation of optical measurement technique such as Digital Image Correlation (DIC) in contrast with the conventional extensometers. A tensile test is conducted on a glass fibre reinforced thermoplastic specimen, according to ISO 527-2/1A, to extract the experimental data with the help of DIC technique. The material behavior is reproduced within a finite element analysis software package LS-DYNA, with the combination of elastoplastic model called *MAT_024 and stress state dependent damage and failure model called GISSMO. The tensile test is performed under quasi-static condition to rule out the strain rate dependency of the thermoplastic material. The mesh sensitivity of the damage model is taken into account with the element size regularization.

    The thesis concerns setting up a routine for material parameter identification of thermoplastics by full-field calibration (FFC) approach. Also, comparison of the strain field in the specimen, obtained through the newly set up routine against the regular non-FFC i.e. extensometer measurement routine. The major objective being, through the comparisons, a qualitative assessment of the two routines in terms of calibration time vs. gain in simulation accuracy. Material models obtained through both the routines are implemented in three-point and four-point bending simulations. The predicted material behaviors are evaluated against experimental tests.

    Fulltekst (pdf)
    fulltext
  • 3333.
    Prigent, Yoann
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Mallol, Pau
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Tibert, Gunnar
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    A classical lamination model of bi-stable woven composite tape-springs2011Inngår i: Proceedings of the 24th Nordic Seminar on Computational Mechanics / [ed] Jouni Freund and Reijo Kouhia, Department of Civil and Structural Engineering, Aalto University , 2011, s. 51-54Konferansepaper (Fagfellevurdert)
    Abstract [en]

    This extended abstract presents the work done so far on modeling woven composite materials, specifically two carbon fiber reinforced plastics materials: twill and plain weave. The material model has been initially verified against data available in a database.

    Fulltekst (pdf)
    fulltext
  • 3334. Prot, V.
    et al.
    Skallerud, B.
    Sommer, G.
    Holzapfel, Gerhard A.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Biomekanik.
    On modelling and analysis of healthy and pathological human mitral valves: Two case studies2010Inngår i: JOURNAL OF THE MECHANICAL BEHAVIOR OF BIOMEDICAL MATERIALS, ISSN 1751-6161, Vol. 3, nr 2, s. 167-177Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Biomechanical data and related constitutive modelling of the mitral apparatus served as a basis for finite element analyses to better understand the physiology of mitral valves in health and disease. Human anterior and posterior leaflets and chordae tendinae from an elderly heart showing no disease and a hypertrophic obstructive cardiomyopathic heart (HOCM) were mechanically tested by means of uniaxial cyclic extension tests under quasi-static conditions. Experimental data for the leaflets and the chordae tendinae showed highly nonlinear mechanical behaviours and the leaflets were anisotropic. The mitral valve from the HOCM heart exhibited a significantly softer behaviour than the valve from the healthy one. A comparison with porcine data was included because many previous mitral modelling studies have been based on porcine data. Some differences in mechanical response were observed. Material parameters for hyperelastic, transversely isotropic constitutive laws were determined. The experimental data and the related model parameters were used in two finite element studies to investigate the effects of the material properties on the mitral valve response during systole. The analyses showed that during systole the mitral valve from the HOCM heart bulged into the left atrium by taking on the shape of a balloon, whereas the anterior leaflet of the healthy valve remained in the left ventricle.

  • 3335. Prus, C.
    et al.
    Vinuesa, Ricardo
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Stabilitet, Transition, Kontroll. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Tembras, E.
    Mestres, E.
    Ramirez, J. P. Berro
    Impact simulation and optimisation of elastic fuel tanks reinforced with exoskeleton for aerospace applications2017Inngår i: International Journal of Crashworthiness, ISSN 1358-8265, E-ISSN 1754-2111, Vol. 22, nr 3, s. 271-293Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The main subject of the study is the impact simulation of an elastic fuel tank reinforced with a polymer exoskeleton. Thanks to its lightweight and failure resistance, this type of design shows potential to be used in aerospace applications. The simulation emulates a drop test from the height of 20 m on a rigid surface, in accordance with Military Handbook testing guidelines for fuel tanks. The focus is on providing an example of modelling and solving this type of problems. The computational methods are tested on a generic model of a rectangular prismatic tank with rounded edges. The walls of the tank are made of orthotropic fabric reinforced polymer. The simulation is performed for a 70% and a 100% water-filled tank. All calculations are performed using the Altair HyperWorks 13.0 software suite, in particular, the nonlinear RADIOSS solver and OptiStruct Solver and Optimiser. The fluid inside the tank is modelled using the SPH (Smoothed Particle Hydrodynamics) approach. The model serves as a basis for establishing a design optimisation procedure, aiming at reduction of mass of the tank components while ensuring structural integrity. The main insights of the current study are the successful modelling of the liquid and the air inside the tank by means of smoothed-particle hydrodynamics elements, and the structural optimisation methodology of a composite fuel tank.

  • 3336.
    Pujante, J.
    et al.
    Fundaci´o CTM Centre Tecnol`ogic, Pla¸ca de la Ci`encia 2, Spain .
    Garcia-Llamas, E.
    Fundaci´o CTM Centre Tecnol`ogic, Pla¸ca de la Ci`encia 2, Spain .
    Golling, Stefan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Fundaci´o CTM Centre Tecnol`ogic, Pla¸ca de la Ci`encia 2, Spain .
    Casellas, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Fundaci´o CTM Centre Tecnol`ogic, Pla¸ca de la Ci`encia 2, Spain .
    Microstructural and mechanical study of press hardening of thick boron steel sheet2017Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 896, artikkel-id 012085Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Press hardening has become a staple in the production of automotive safetycomponents, due to the combination of high mechanical properties and form complexity itoffers. However, the use of press hardened components has not spread to the truck industrydespite the advantages it confers, namely affordable weight reduction without the use of exoticmaterials, would be extremely attractive for this sector.The main reason for this is that application of press hardened components in trucks impliesadapting the process to the manufacture of thick sheet metal. This introduces an additionallayer of complexity, mainly due to the thermal gradients inside the material resulting inthough-thickness differences in austenitization and cooling, potentially resulting in complexmicrostructure and gradient of mechanical properties.This work presents a preliminary study on the press hardening of thick boron steel sheet.First of all, the evolution of the sheet metal during austenitization is studied by means ofdilatometry tests and by analysing the effect of furnace dwell time on grain size. Afterwards,material cooled using different cooling strategies, and therefore different effective cooling rates, isstudied in terms of microstructure and mechanical properties. Initial results from finite elementsimulation are compared to experimental results, focusing on the phase composition in throughthickness direction.Results show that industrial-equivalent cooling conditions do not lead to gradientmicrostructures, even in extreme scenarios involving asymmetrical cooling.

  • 3337.
    Pujante, Jaume
    et al.
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència, 2, 08243 Manresa (Spain).
    Frómeta, David
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència, 2, 08243 Manresa (Spain).
    Garcia-Llamas, Eduard
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència, 2, 08243 Manresa (Spain).
    Gimenez, Maria
    Autotech Engineering Spain (Gestamp), Autotech Poligono Industrial Ca N'Estella, Passatge Edison 4, 08635 St. Esteve Sesrovires (Spain).
    Casellas, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära. Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència, 2, 08243 Manresa (Spain).
    Hot Stamped Aluminium for Crash-Resistant Automobile Safety Cage Applications2021Inngår i: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 1016, s. 445-452Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hot stamping, also known as press hardening in the context of sheet steel, has steadily gained relevance in the automotive industry, starting off as a specialist application and turning into a staple technique in the production of safety cage products in little more than a decade. However, despite the weight reduction offered by martensitic steels, further improvement could be obtained by substituting these components by high-performance aluminium. In this regard, the very same process of hot stamping could be employed to attain the required combination of shape complexity and mechanical properties at a reasonable cost for mass-market application, if the limitations imposed by cycle time and process window could be overcome. In this work, the feasibility of hot stamping of 6000-series aluminium alloy sheet is studied, first in dilatometry experiments and later in semi-industrial conditions in a pilot facility. A cycle time shortening strategy is employed, and compared to the conventional thermal cycle in terms of implementation and obtained results. In addition to basic characterization, aluminium thus processed is studied in terms of fracture toughness, in order to obtain data relevant to crashworthiness that can be readily compared with alternative materials.

  • 3338.
    Pujante, Jaume
    et al.
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència 2, Manresa, 08243, Spain; Department of Science and Material Engineering, Universitat Politècnica de Catalunya, Av. Eduard Maristany 10-14, Barcelona, 08019, Spain.
    Garcia-Llamas, Eduard
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència 2, Manresa, 08243, Spain.
    Ramírez, Giselle
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència 2, Manresa, 08243, Spain.
    Cuadrado, Nuria
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència 2, Manresa, 08243, Spain; Department of Science and Material Engineering, Universitat Politècnica de Catalunya, Av. Eduard Maristany 10-14, Barcelona, 08019, Spain.
    Ademaj, Agim
    METAKUS Automotive GmbH, Fehrenberger Straße 1a, Baunatal, 34225, Germany.
    Vilaseca, Montserrat
    Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència 2, Manresa, 08243, Spain.
    Casellas, Daniel
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära. Eurecat, Centre Tecnològic de Catalunya, Unit of Metallic and Ceramic Materials, Plaça de la Ciència 2, 08243 Manresa, Spain.
    Wear Mechanisms in Press Hardening: An Analysis through Comparison of Tribological Tests and Industrial Tools2023Inngår i: Lubricants, E-ISSN 2075-4442, Vol. 11, nr 5, artikkel-id 222Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Press hardened components have become widespread in the automotive industry in structural and crash-resistant applications, thanks to the combination of the complex shapes and high mechanical properties obtained. However, the press hardening of coated boron steel results in severe adhesive-based wear, with tool maintenance being required in as few as 3000 cycles. The current industrial implementation of press hardening is defined to work around this phenomenon. While this aspect has been studied by different authors, most of the literature deals with laboratory-scale tribosimulators, leaving an open question into how this knowledge transfers to macroscopic effects on the industrial process. In this work, wear in press hardening is studied by comparing the results obtained in laboratory conditions with a pilot-scale line, and finally, with wear mechanisms observed on industrial tools. The aim of this study is to consolidate the current knowledge about the micro-mechanisms involved, and to understand to what extent the existing tests reproduce the actual mechanisms observed in the press floor. The results show how material transfer mainly happens as an accumulation of dust compacted into initial defects on the tool surface. Moreover, this mechanism is effectively reproduced in laboratory tribosimulators and pilot environments, showing a similar morphology to wear on industrial tools. The work sheds light on the underlying causes of wear, and its potential mitigation strategies.

    Fulltekst (pdf)
    fulltext
  • 3339.
    Pujari-Palmer, Michael
    et al.
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Robo, Céline
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Persson, Cecilia
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Procter, Philip
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Engqvist, Håkan
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Tillämpad materialvetenskap.
    Influence of cement compressive strength and porosity on augmentation performance in a model of orthopedic screw pull-out2018Inngår i: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 77, s. 624-633Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Disease and injuries that affect the skeletal system may require surgical intervention and internal fixation, i.e. orthopedic plate and screw insertion, to stabilize the injury and facilitate tissue repair. If the surrounding bone quality is poor the screws may migrate, or the bone may fail, resulting in screw pull-out. Though numerous studies have shown that cement augmentation of the interface between bone and implant can increase screw holding strength in bone, the physical properties of cement that influence pull-out force have not been investigated. The present study sought to determine how the physical properties of calcium phosphate cements (CPCs), and the strength of the biological or synthetic material surrounding the augmented screw, affected the corresponding orthopedic screw pull-out force in urethane foam models of healthy and osteoporotic bone (Sawbones). In the simplest model, where only the bond strength between screw thread and cement (without Sawbone) was tested, the correlation between pull-out force and cement compressive strength (R2 = 0.79) was weaker than correlation with total cement porosity (R2 = 0.89). In open pore Sawbone that mimics “healthy” cancellous bone density the stronger cements produced higher pull-out force (50-60% increase). Higher strength, lower porosity, cements also produced higher pull-out forces (50-190% increase) in Sawbones with cortical fixation if the failure strength of the cortical material was similar to (bovine tibial bone), or greater than (metal shell), actual cortical bone. This result is of particular clinical relevance where fixation with a metal plate implant is indicated, as the nearby metal can simulate a thicker cortical shell and, thereby, increase the pull-out force of screws augmented with stronger cements. The improvement in pull-out force was apparent even at low augmentation volumes of 0.5 ml (50% increase), which suggest that in clinical situations where augmentation volume is limited the stronger, lower porosity CPCs may still produce a significant improvement in screw holding strength. When correlations of all the tested models were compared both cement porosity and compressive strength accurately predicted pull-out force (R2=1.00, R2=0.808), though prediction accuracy depended upon the strength of the material surrounding the Sawbone. The correlations strength was low for bone with no, or weak, cortical fixation. Higher strength and lower porosity CPCs also produced greater pull-out force (1-1.5 kN) than commercial CPC (0.2-0.5kN), but lower pull-out force than PMMA (2-3 kN). The results of this study suggest that the likelihood of screw fixation failure may be reduced by selecting calcium phosphate cements with lower porosity and higher bulk strength, in patients with healthy bone mineral density and/or sufficient cortical thickness. This is of particular clinical relevance when fixation with metal plates is indicated, or where the augmentation volume is limited.

  • 3340.
    Punnam, Pradeep Reddy
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Dundeti, Chitendar Reddy
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    A Finite Element Analysis of Crack Propagation in Interface of Aluminium Foil - LDPE Laminate During Fixed Arm Peel Test.2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    This thesis deals with numerical simulation of a peel test with an Aluminium foil and Low Density Poly-Ethylene (LDPE) laminate. This work investigates the effects of the substrate thickness and studies the influences of interfacial strength and fracture energy of the cohesive zone between the Aluminium and LDPE. This study evaluates the proper guidelines for defining cohesive properties. A numerical cohesive zone model was created in ABAQUS. Continuum tensile tests were performed to extract LDPE material properties. The aluminium properties were found in literature. After acquiring material parameters, the simulation continued with studying the effects of changing interfacial strength, geometric parameters and fracture energy. The results were obtained in the form of root rotations and the force displacement response was studied carefully. It was validated by comparison to the traction separation curve.

    Fulltekst (pdf)
    BTH2017Punnam
  • 3341.
    Pupurs, A.
    et al.
    Riga Tech Univ, Latvia.
    Sahbi Loukil, Mohamed
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten. RISE Res Inst Sweden, Sweden.
    Marklund, E.
    RISE Res Inst Sweden, Sweden.
    Varna, J.
    Riga Tech Univ, Latvia; Lulea Univ Technol, Sweden.
    Mattsson, D.
    RISE Res Inst Sweden, Sweden.
    Transverse Crack Initiation in Thin-Ply Laminates Subjected to Tensile Loading at Low and Cryogenic Temperatures2024Inngår i: Mechanics of composite materials, ISSN 0191-5665, E-ISSN 1573-8922, s. 1049-1064Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Laminates with ultra-thin plies is a promising new development for polymeric composite materials expected to provide superior resistance to intralaminar crack propagation. The ply thickness effect on the crack initiation stress that according to some theoretical studies on fiber/matrix debonding does not depend on the ply thickness was investigated. Ultra-thin ply carbon fiber/epoxy cross-ply laminates subjected to tensile loading at room, -50, and -150 degrees C temperatures relevant for cryogenic fuel storage, aeronautical, and aerospace applications were studied. The stochastic nature of the crack initiation stress in the 90 degrees-plies was analyzed using Weibull strength distribution. The results obtained show delayed transverse crack initiation only in the thinnest plies with a clear trend that the scale parameter is much larger. This thickness effect on initiation is different than that for crack propagation which is observable in much larger ply thickness range. Regarding crack propagation, it was found that in most cases even at very high applied strain levels (1.5%) only a few transverse cracks have propagated from the specimen edges to its middle.

  • 3342.
    Pupurs, Andrejs
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Laboratory of Experimental Mechanics of Materials, Riga Technical University, Kipsalas 6B, 1048, Riga, Latvia.
    Loukil, Mohamed
    Department of Polymer Materials and Composites, RISE Research Institutes of Sweden, Bröderna Ugglas gata Hus 208, 581 88, Linköping, Sweden; Division of Engineering Materials, Linköping University, 581 83, Linköping, Sweden.
    Varna, Janis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap. Laboratory of Experimental Mechanics of Materials, Riga Technical University, Kipsalas 6B, 1048, Riga, Latvia.
    Digital Image Correlation (DIC) Validation of Engineering Approaches for Bending Stiffness Determination of Damaged Laminates2022Inngår i: Applied Composite Materials, ISSN 0929-189X, E-ISSN 1573-4897, Vol. 29, nr 5, s. 1937-1958Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    During the last decade new models for bending stiffness prediction of damaged composite laminates have been proposed in the literature advancing the earlier developed engineering approaches in accuracy and in complexity. However, experimental data for validation of complex analytical or engineering models are almost non-existent in the literature. In the present work a detailed experimental study was performed to investigate the bending stiffness reduction of composite cross-ply laminates with evolving micro-damage. Intralaminar cracks and local delaminations in the bottom surface 90-degree layer of carbon/epoxy and glass/epoxy cross-ply laminates were introduced in 4-point bending tests. Digital Image correlation (DIC) technique was used to experimentally determine the midplane curvature. The accuracy of beam theory for bending stiffness determination was assessed. The measured bending stiffness reduction with respect to transverse crack density was also compared with FEM predictions. The results show that the beam theory gives slightly underestimated curvature at low deflections, whereas at large deflections the beam theory overestimates the curvature and the moment-curvature relation becomes nonlinear. Nevertheless, the overall agreement between beam theory and DIC-based results is still very good, which leads to conclude that beam theory based data reduction schemes have sufficient accuracy for predicting bending stiffness even for highly damaged laminates.

  • 3343.
    Pärlstrand, Anders
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Ultrasonic measurement and analysis of screw elongation2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    Based on the customers' increasing demands on the precision of the preload in a screw joint Atlas Copco is investigating the opportunity to integrate ultrasonic technologies in their industrial tools in order to be able to measure the screw elongation and thereby preload. The preload in a screw joint is important when trying to optimize the joint in terms of weight and life time. The ultrasonic technology for preload measurements has two large advantages; the technique requires only access to the screw head and it is completely independent of the friction in the joint which enables more accurate measurements of the preload. In ultrasonic preload measurements the time of flight is measured (i.e. time for ultrasonic waves to travel through the screw). The time can be transformed into length and elongation by use of the sound velocity. Of importance in this calculation is to take the so called acoustoelastic effect into account which predicts a lower longitudinal wave velocity with increasing tensile stress. The purpose of this master thesis is to develop a method that can predict screw elongations from ultrasonic measurements. Finite element simulations showed that the acoustoelastic ultrasonic constant only depend on the ratio between the clamp length and the screw diameter up to a certain degree of accuracy. A function of type =∙ ∙ where a, b and c are real-valued constants and = is the clamp length () divided by the screw diameter () fits the data well. However, the ultrasonic measurements showed some deviations from the theoretical predictions.

    Fulltekst (pdf)
    fulltext
  • 3344.
    Pääjärvi, Simon
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Rotor Dynamic Modeling of Hydropower Rotors by 3D-Finite Element Analysis2022Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    By using the rotor dynamic capabilities of Simcenter Nastran Rotordynamics, an eigenvalue analysis of 3D-finite element models of the Jeffcott rotor and the overhung rotor were conducted and compared to the results with beam-based, lumped parameter models. The first two critical speeds of the Jeffcott rotor were estimated with variations of 3.9 and 6.4%. The first three critical speeds of the overhung rotor were estimated with 8.5, 6.7 and 6.5% variations, respectively. The Jeffcott rotor was also analysed with different element configurations: Solid elements, axisymmetric Fourier elements, beam/solids and all beam elements. The Fourier elements were the most appropriate option for axisymmetric rotors regarding computational time and accuracy.

    Tilting pad journal bearings were simulated and validated against data from Vattenfall's facilities in Älvkarleby, where a vertical rotor is connected to two four-pad tilting pad journal bearings. The bearing formulation was defined in a Fortran based subroutine, which acquires the rotor's speed and position to supply a bearing load vector in Simcenter Nastran's transient solver. The experimental rig was also modelled to include the rotor/stator interaction. The force and displacement orbits at the bearings were replicated adequately concerning experimental data, where a maximum deviation of 20.8% and 9.8% were observed for the forces in x and y-directions. 

    A 3D-finite element model and a beam based finite element model were compared for an actual hydropower unit, which aimed to investigate the mode extraction procedure and how high mass, elastic rotor components influence the system's dynamics. Consistent rotor modes were identified at frequencies within 15% deviation, where the maximum deviation occurred in the upper range frequency pairs. Convergence between the models was observed for the static, lower range frequencies when considering a rigid generator rotor in the 3D finite element model. The outcome is consistent with the model assumptions and underlines that the beam based model cannot capture specific contributions from elastic rotor components.

    3D-finite element analysis is a viable option when considering non-axisymmetric and complex rotors. High mass, non-rigid components must be analysed  in this manner as their dynamic contributions may not be captured with other approaches. Intricate and non-rigid supporting structures are also suitable for 3D modelling to properly reflect the stator-rotor interaction. It is a delicate matter to pinpoint when these conditions occur, and modelling decisions must be therefore be substantiated by simulations and experimental validation.

    Fulltekst (pdf)
    fulltext
  • 3345.
    Pääjärvi, Simon
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Simulation of Vertical Rotors by 3D-Finite Element Modelling2022Inngår i: Svenska Mekanikdagar 2022 / [ed] Pär Jonsén; Lars-Göran Westerberg; Simon Larsson; Erik Olsson, Luleå tekniska universitet, 2022Konferansepaper (Fagfellevurdert)
    Fulltekst (pdf)
    fulltext
  • 3346.
    Pérez Caro, Lluís
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Swerea IVF AB.
    Modelling of Forming and Welding in Alloy 7182017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The reduction of fuel consumption and carbon dioxide emissions are currently a key factor for the aviation industry due to major concerns about climate change and more restrictive environmental laws. One way to reduce both fuel consumption and CO2 emissions is by significantly decreasing the vehicle’s weight while increasing engine's efficiency. In order to meet these requirements, the European aero engine industry is continuously focusing on alternative manufacturing methods for load carrying structures in advanced materials, such as titanium and nickel-based superalloys. Alternatively to traditional large-scale single castings, new manufacturing methods involve sheet metal parts, small castings and forgings assembled by welding. These new manufacturing methods allow more flexible designs in which each part is made of the most suitable material state, leading to several advantages such as reduction of product cost and weight while increasing engine's efficiency. Nickel-based superalloys are widely used in the aero engine industry, typically constituting up to 50% of the total weight of the aircraft engine. Due to their excellent material properties at high temperatures in severe corrosive environments, these superalloys are employed most extensively in the hot sections of gas turbine engines for both military and civil aircrafts with running temperatures up to 650°C.

    In this thesis, a manufacturing process chain including forming and welding in the nickelbased superalloy 718 is studied. The main focus in the work lies on determining the thermomechanical properties, modelling and simulation of cold forming, study forming limits based on Nakazima tests for forming limit curves (FLC) and applying a damage and failure criterion. The work also comprises a brief study on hot forming. Finally, modelling of a subsequent welding procedure is included where residual stresses from the forming simulation are used to predict shape distortions due to the welding procedure. The results are compared with experimental observations.

    The cold forming procedure of a double-curved component made of alloy 718 is studied using FE-analyses and forming tests. The same geometry was used to produce a hot forming tool. During forming tests at room temperature, micro cracks and open cracks were observed in the draw bead regions, not indicated when formability is assessed using a forming limit curve (FLC). Standard material models such as von Mises or Barlat Yld2000-2D were not capable of accurately predict the behaviour of the material after the point of diffuse necking, making the prediction of damage and failure during forming a challenge. The GISSMO damage model was therefore calibrated and used to predict material failure in forming of alloy 718. Tensile, plane strain, shear and biaxial tests at room temperature are performed up to fracture and continuously evaluated using Digital Image Correlation (DIC) by ARAMIS™. In this work, the GISSMO damage model is coupled with the anisotropic Barlat Yld2000-2D material model for forming simulations in alloy 718 at room temperature using LS-DYNA. Numerical predictions are able to accurately predict failure on the same regions as observed during the experimental forming tests. Comparisons of the distribution of damage on one of the draw beads between simulations and damage measurements by acoustic emission indicate that higher damage values correspond to bigger micro cracks. Numerical FE-predictions of the cold forming and subsequent welding procedure shows that the welding procedure further increases the shape distortions. This was found to agree with experimental observations.

    Fulltekst (pdf)
    fulltext
  • 3347.
    Pérez Caro, Lluís
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Forming group OSAS, Industrial Development Centre in Olofström AB, Vällaregatan 30, Olofström.
    Marth, Stefan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Schill, Mikael
    DYNAmore Nordic AB, Linköping.
    Odenberger, Eva-Lis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Forming group OSAS, Industrial Development Centre in Olofström AB, Vällaregatan 30, Olofström.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Calibration of a damage and fracture model for alloy 7182016Inngår i: Advancements in Theoretical and Applied Plasticity: Proceedings of PLASTICITY ’16: The Twenty Second International Symposium on Plasticity and its Current Applications / [ed] Akhtar S. Khan, Fulton, Maryland 20759-0591, USA: NEAT PRESS , 2016, s. 223-225Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Nickel-based superalloys are primarily used in the hot sections of aircraft engines because they can maintain their mechanical properties and chemical stabilities at high temperatures under severe corrosive environments i.e. for a long time. In order to simulate forming procedures in Alloy 718 sheets, the GISSMO damage and failure model is coupled with both isotropic von Mises and anisotropic Barlat YLD2000 material models in the finite element code LS-DYNA. In this study, the calibration of the GISSMO model for forming simulations at room temperature is discussed. The calibration requires failure strains for different stress states as a function of triaxiality, which are obtained by testing six different specimen geometries up to fracture. Numerical predictions will be compared with experimental observations from forming tests.

  • 3348.
    Pérez Caro, Lluís
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Division of Materials and Production, RISE IVF AB, Vällaregatan 30, SE-293 38 Olofström, Sweden.
    Odenberger, Eva-Lis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Division of Materials and Production, RISE IVF AB, Vällaregatan 30, SE-293 38 Olofström, Sweden.
    Schill, Mikael
    DYNAmore Nordic AB, Brigadgatan 5, SE-587 58 Linköping, Sweden.
    Niklasson, Fredrik
    GKN Aerospace Engine Systems Sweden, SE-461 38 Trollhättan, Sweden.
    Åkerfeldt, Pia
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Materialvetenskap.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Springback prediction and validation in hot forming of a double-curved component in alloy 7182021Inngår i: International Journal of Material Forming, ISSN 1960-6206, E-ISSN 1960-6214, Vol. 14, nr 6, s. 1355-1373Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The demands associated with the production of advanced parts made of nickel-base superalloys are continuously increasing to meet the requirements of current environmental laws. The use of lightweight components in load-carrying aero-engine structures has the potential to significantly reduce fuel consumption and greenhouse gas emissions. Furthermore, the competitiveness of the aero-engine industry can benefit from reduced production costs and shorter development times while minimizing costly try-outs and increasing the efficiency of engines. The manufacturing process of aero-engine parts in superalloys at temperatures close to 950 °C produces reduced stamping force, residual stresses, and springback compared to traditional forming procedures occurring at room temperature. In this work, a hot forming procedure of a double-curved component in alloy 718 is studied. The mechanical properties of the material are determined between 20 and 1000 °C. The presence and nature of serrations in the stress–strain curves are assessed. The novel version of the anisotropic Barlat Yld2000-2D material model, which allows the input of thermo-mechanical data, is used in LS-DYNA to model the behaviour of the material at high temperatures. The effect of considering the stress-relaxation data on the predicted shape distortions is evaluated. The results show the importance of considering the thermo-mechanical anisotropic properties and stress-relaxation behaviour of the material to predict the final geometry of the component with high accuracy. The implementation of advanced material models in the finite element (FE) analyses, along with precise process conditions, is vital to produce lightweight components in advanced materials of interest to the aerospace industry.

    Fulltekst (pdf)
    fulltext
  • 3349.
    Pérez Caro, Lluís
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Division of Materials and Production, RISE IVF AB, Vällaregatan 30, SE-293 38, Olofström, Sweden.
    Odenberger, Eva-Lis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Division of Materials and Production, RISE IVF AB, Vällaregatan 30, SE-293 38, Olofström, Sweden.
    Schill, Mikael
    DYNAmore Nordic AB, Brigadgatan 5, SE-587 58, Linköping, Sweden.
    Steffenburg-Nordenström, Joachim
    GKN Aerospace Engine Systems Sweden, SE-461 38, Trollhättan, Sweden.
    Niklasson, Fredrik
    GKN Aerospace Engine Systems Sweden, SE-461 38, Trollhättan, Sweden.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Prediction of shape distortions during forming and welding of a double-curved strip geometry in alloy 7182020Inngår i: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 107, nr 7-8, s. 2967-2981Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The finite-element method (FEM) has considerably contributed to the development of more advanced manufacturing methods for metal structures. The prediction of the final shape of a component is of great interest to the manufacturing industry. In addition to its inherent difficulties, the presence of various types of processes in the manufacturing chain may dramatically increase the level of demand. Therefore, including all steps of the manufacturing process in the simulations is key to being successful. This has been done for a long time in the stamping industry, which involves sequences of forming, trimming, and springback. However, more complex manufacturing procedures, that include assembling of formed parts with forgings and castings via welding, have been modeled with simplifications, resulting in a reduced prediction accuracy. This hinders the compensation of accumulated shape distortions based on the simulation results. One such example is the fabrication of aero-engine structures, in which the history from the forming procedure has not been considered in subsequent welding and heat treatment analyses. In the present study, a double-shaped part manufactured from alloy 718 is formed at 20 °C and laser-welded using the bead-on-plate procedure. The coupling of different manufacturing analyses, including cold forming, trimming, result mapping, welding, cooling, and springback, is achieved using LS-DYNA. Additionally, the effect of adding the GISSMO damage model in the forming simulation is studied. The results of the forming analysis are used as inputs for the material model *MAT_CWM in the welding simulation. The anisotropic thermomechanical properties of alloy 718 are determined at temperatures up to 1000 °C. Encouraging agreement is found between the model predictions and the results of forming and welding tests. The findings underscore the importance of including the material history and accurate process conditions along the manufacturing chain to both the prediction accuracy of shape distortions, and to the potential of the industry.

  • 3350.
    Pérez Caro, Lluís
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. RISE IVF AB.
    Schill, Mikael
    DYNAmore Nordic AB.
    Haller, Kristian
    AcousticAgree AB.
    Odenberger, Eva-Lis
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. RISE IVF AB.
    Oldenburg, Mats
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Damage and fracture during sheet-metal forming of alloy 7182020Inngår i: International Journal of Material Forming, ISSN 1960-6206, E-ISSN 1960-6214, Vol. 13, s. 15-28Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Forming nickel-based superalloy aero-engine components is a challenging process, largely because of the risk of high degree of springback and issues with formability. In the forming tests conducted on alloy 718 at room temperature, open fractures are observed in the drawbead regions, which are not predicted while evaluating the formability using the traditional forming-limit diagram(FLD). This highlights the importance of an accurate prediction of failure during forming as, in some cases, may severely influence the springback and thereby the accuracy of the predicted shape distortions, leading the final shape of the formed component out of tolerance. In this study, the generalised incremental stress-state dependent damage model (GISSMO) is coupled with the isotropic von Mises and the anisotropic Barlat Yld2000-2D yield criteria to predict the material failure in the forming simulations conducted on alloy 718 using LS-DYNA. Their effect on the predicted effective plastic strains and shape deviations is discussed. The failure and instability strains needed to calibrate the GISSMO are directly obtained from digital image correlation (DIC) measurements in four different specimen geometries i.e. tensile, plane strain, shear, and biaxial. The damage distribution over the drawbeads is measured using a non-linear acoustic technique for validation purposes. The numerical simulations accurately predict failure at the same regions as those observed in the experimental forming tests. The expected distribution of the damage over the drawbeads is in accordance with the experimental measurements. The results highlight the potential of considering DIC to calibrate the GISSMO in combination with an anisotropic material model for forming simulations in alloy 718.

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