Endre søk
Begrens søket
1234567 151 - 200 of 3271
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 151.
    Andreasson, Eskil
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Jönsson, Joel
    Tetra Pak, SWE.
    Advancements in package opening simulations2014Inngår i: Procedia Materials Science / [ed] Zhang, Z; Skallerud, B; Thaulow, C; Ostby, E; He, J, Elsevier, 2014, Vol. 3, s. 1441-1446Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The fracture mechanical phenomenon occurring during the opening of a beverage package is rather complex to simulate. Reliable and calibrated numerical material models describing thin layers of packaging materials are needed. Selection of appropriate constitutive models for the continuum material models and how to address the progressive damage modeling in various loading scenarios is also of great importance. The inverse modeling technique combined with video recording of the involved deformation mechanisms is utilized for identification of the material parameters. Large deformation, anisotropic non-linear material behavior, adhesion and fracture mechanics are all identified effects that are needed to be included in the virtual opening model. The results presented in this paper shows that it is possible to select material models in conjunction with continuum material damage models, adequately predicting the mechanical behavior of failure in thin laminated packaging materials. Already available techniques and functionalities in the commercial finite element software Abaqus are used. Furthermore, accurate descriptions of the included geometrical features are important. Advancements have therefore also been made within the experimental techniques utilizing a combination of microCT-scan, SEM and photoelasticity enabling extraction of geometries and additional information from ordinary experimental tests and broken specimens. Finally, comparison of the experimental opening and the virtual opening, showed a good correlation with the developed finite element modeling technique.

  • 152.
    Andreasson, Eskil
    et al.
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    Kao-Walter, Sharon
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    Ståhle, Per
    Micro-mechanisms of a laminated packaging material during fracture2014Inngår i: Engineering Fracture Mechanics, ISSN 0013-7944, E-ISSN 1873-7315, Vol. 127Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The micro-mechanisms of fracture in a laminate composed of an aluminium foil and a polymer film are considered in this study. The laminates as well as the individual layers, with and without premade centre-cracks, were tensile tested. Visual inspection of the broken cross-sections shows that failure occurs through localised plasticity. This leads to a decreasing and eventually vanishing cross-section ahead of the crack tip for both the laminate and their single constituent layers. Experimental results are examined and analysed using a slip-line theory to derive the work of failure. An accurate prediction was made for the aluminium foil and for the laminate but not for the freestanding polymer film. The reason seems to be that the polymer material switches to non-localised plastic deformation with significant strain-hardening.

  • 153.
    Andreasson, Eskil
    et al.
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    Mehmood, Nasir
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    Kao-Walter, Sharon
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    Trouser tear tests of two thin polymer films2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Trouser tear testing has been concerned in this research work. A polypropylene film and a low density polyethylene film used in the packaging industry are considered. The experimental trouser tear tests showed different results for both materials when they were subjected to load in different material directions. Therefore the hypothesis was verified, that the in-plane material orientation/alignment induced during manufacturing, hence creating anisotropic in-plane mechanical properties, also affects the tearing behavior. A brittle-like failure was shown in the polypropylene film while the low density polyethylene presented a highly ductile behavior. The two polymer films can be classified as one low-extensible and one high-extensible material according to the test method utilized. Material parameters in the principal material directions i.e. manufacturing direction and cross direction were extracted from the experimental tests for further numerical studies. Scanning electron microscope was used for micromechanical and fractographical analysis of the crack tip and crack surfaces created during the tests. The methods discussed will help classify different groups of materials and can be used as a predictive tool for the crack initiation and crack propagation path in packaging material, especially thin polymer films.

  • 154.
    Andreasson, Eskil
    et al.
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    Mehmood, Nasir
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    Mao, Tan
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    An Experimental, Numerical and SEM Study of Fracture in a Thin Polymer Film2014Inngår i: MATERIALS STRUCTURE & MICROMECHANICS OF FRACTURE VII, Trans Tech Publications Inc., 2014, Vol. 592-593, s. 225-+-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Observations and analysis of samples from scanning electron microscopic (SEM) micrographs has been concerned in this work. The samples originate from fractured mechanical mode I tensile testing of a thin polymer film made of polypropylene used in the packaging industry. Three different shapes of the crack; elliptical, circular and flat, were used to investigate the decrease in load carrying capacity. The fracture surfaces looked similar in all studied cases. Brittle-like material fracture process was observed both by SEM micrographs and the experimental mechanical results. A finite element model was created in Abaqus as a complementary tool to increase the understanding of the mechanical behaviour of the material. The numerical material models were calibrated and the results from the simulations were comparable to the experimental results.

  • 155.
    Andreasson, Eskil
    et al.
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    Mehmood, Nasir
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    Mao, Tan
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    Kao-Walter, Sharon
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    Experimental and Numerical fracture of cracks emanating from different types of flaws in thin polymer films2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Fracture mechanical Mode I tensile testing has been performed on an oriented polyproplyne film used in packaging industry. Physical Tensile testing for the continuum material has been performed to observe the material strength and to extract continuum material properties for numerical analysis. Fracture mechanical testing of different shaped notches is performed to observe the failure initiation in the material. A brittle-like failure was shown in the polypropylene film while the low density polyethylene presented a highly ductile behavior. A finite element method (FEM) strategy has been successfully developed to perform numerical analysis of polymer films. The developed FEM model gives an accurate and approximate method to compare and analyze the experimental and numerical results. The obtained results have shown a very fine similarity under theoretical, experimental and numerical analysis. Depending on crack geometry different shape crack effects showed the transferability of localized stresses at different points around the crack. Fracture surface and fracture process is analyzed using scanning electron microscope (SEM). Brittle failure with small deformation and presence of small voids and their coalescence has also been shown in SEM micrographs for LDPE material. The methods discussed will help classify different groups of materials and can be used as a predictive tool for the crack initiation and crack propagation path in packaging material, especially thin polymer films.

  • 156.
    Andreasson, Eskil
    et al.
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för maskinteknik.
    Persson, Leo
    Jacobsson, Henrik
    Nordgren, Johan
    Integrating Moldflow and Abaqus in the Package Simulation Workflow2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Tetra Pak has used numerical simulation tools for plastic injection molding (Moldflow) and structural analysis (Abaqus/Implicit and Abaqus/Explicit) for many years. Today these two simulation tools are used independently of each other without any coupling. How these two disciplines can be combined to better predict the mechanical response of a polymer component is presented in this work. The manufacturing process, in this case injection molding, creates the mechanical properties of the produced polymer part. Process settings, material selection and molding tool geometry affect the polymer flow, material orientation and rate of crystallinity. A method to build a layered finite element model in Abaqus using results from Moldflow simulations regarding crystallinity growth and molecular orientation is proposed. Relatively simple material models were utilized and assigned for each individual material layer through the thickness in the polymer part. These constitutive models were derived phenomenologically from experimental test results and could adequately capture both the microscopic and the macroscopic behavior in a more realistic way. The numerical results showed a good agreement with the experimental results, both regarding visual appearance and force/displacement response.

  • 157. Angantyr, Anders
    et al.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    A pareto-based genetic algorithm search approach to handle damped natural frequency constraints in turbo Generator rotor system design2004Inngår i: Journal of engineering for gas turbines and power, ISSN 0742-4795, E-ISSN 1528-8919, Vol. 126, nr 3, s. 619-625Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The detailed design of a turbo generator rotor system is highly constrained by feasible regions for the damped natural frequencies of the system. A major problem for the designer is to find a solution that fulfills the design criterion for the damped natural frequencies. The bearings and some geometrical variables of the rotor are used as the primary design variables in order to achieve a feasible design. This paper presents an alternative approach to search for feasible designs. The design problem is formulated as an optimization problem and a genetic algorithm (GA) is used to search for feasible designs. Then, the problem is extended to include another objective (i.e., multiobjective optimization) to show the potential of using the optimization formulation and a Pareto-based GA in this rotordynamic application. The results show that the presented approach is promising as an engineering design tool

  • 158. Angantyr, Anders
    et al.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Optimization of a rotor-bearing system with an evolutionary algorithm2004Inngår i: 10th International Symposium on Transport Phenomena and Dynamics of Rotating Machinery: ISROMAC-2004 / [ed] Dieter Bohn, Aachen: Inst. of steam and gas turbines, RWTH , 2004Konferansepaper (Fagfellevurdert)
  • 159. Angantyr, Anders
    et al.
    Andersson, Johan
    Linköping University.
    Aidanpää, Jan-Olov
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Constrained optimization based on a multiobjective evolutionary algorithm2003Inngår i: The 2003 congress on evolutionary computation: CEC 2003, Piscataway, NJ: IEEE Communications Society, 2003, s. 1560-1567Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A criticism of Evolutionary Algorithms (EAs) might be the lack of efficient and robust generic might be the lack of officient and robust generic methods to handle constraints. The most widespread approach for constrained search problems is to use penalty methods. EAs have received increased interest during the last decade due to the ease of handling multiple objectives., A constrained Optimization problem or an unconstrained multiobjective problem may in principle be two different ways to pose the same underlying I problem. In this paper an alternative approach for the constrained optimization problem is presented. The method is a variant of a multiobjective real coded Genetic Algorithm (CA) inspired by the penalty approach. It is evaluated on six different constrained single objective problems found in the literature. The results show that the proposed method performs well in terms of efficiency, and that it is rohust for a majority of the test problems.

  • 160.
    Ankarberg, Martin
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Industriell Produktion.
    Jilnö, Erik
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Industriell Produktion.
    Redesign of Gas Hydraulic Suspension for Product Service System: A Master Thesis Work at Strömsholmen AB2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In these times, when manufacturing firms wonder how to integrate products and services into innovative offerings, how should products be designed to be of most value? This study is the investigation of this question for the manufacturing firm Strömsholmen AB, which designs gas springs and hydraulic suspension. The research has led to interviews of personnel to identify challenges and a workshop to generate new service ideas. By analyzing a specific gas hydraulic suspension product, this study shows that designing for product service systems (PSS) with a life-cycle perspective specifically for manufacturing, assembly, delivery, use, maintenance and remanufacturing, can greatly reduce costs and open up for innovative PSS business models. Using Design for Assembly, Design for Disassembly, Design for Serviceability and Design for Remanufacturing shows how concrete improvements to a product can be made. Improvements that show the potential of a redesign for the gas hydraulic suspension. Integrating products and services and pursuing the ideas and methods of this thesis, will ultimately make Strömsholmen better prepared to differentiate, to stay competitive, to deepen customer relations and to gain greater profits long-term.

  • 161.
    Antonatos, Alexandros
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Marina system.
    Parametric FE-modeling of High-speed Craft Structures2012Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The primary aim of the thesis was to investigate aluminum as building material for high speed craft, study the hull structure design processes of aluminum high speed craft and develop a parametric model to reduce the modeling time during nite element analysis. An additional aim of the thesis was to study the degree of validity of the idealizations and the assumptions of the semi-empirical design methods by using the parametric model.

    For the aluminum survey, a large amount of scientic papers and books related to the application of aluminum in shipbuilding industry were re-viewed while for the investigation of hull structure design, several designs of similar craft as well as all the classication rules for high speed craft were examined. The parametric model was developed on Abaqus nite ele-ment analysis software with the help of Python programming language. The study of the idealizations and the assumptions of the semi-empirical design methods was performed on a model derived by the parametric model with scanltings determined by the high speed craft classication rules of ABS.

    The review on aluminum showed that only specic alloys can be applied on marine applications. It also showed that the eect of reduced mechanical properties due to welding could be decreased by introducing new welding and manufacturing techniques. The study regarding the hull structure de-sign processes indicated that high speed craft are still designed according to semi-empirical classication rules but it also showed that there is ten- dency of transiting on direct calculation methods. The developed paramet-ric model does decrease the modeling time since it is capable of modeling numerous structural arrangements. The analysis related to the idealizations and the assumptions of the semi-empirical design methods revealed that the structural hierarchy idealization and the method of dening boundary by handbook type formulas are applicable for the particular structure while the interaction eect among the structural members is only possible to be studied by detailed modeling techniques.

  • 162.
    Aoki, S.
    et al.
    Tokyo Institute of Technology, Department of Mechanical and Environmental Informatics.
    Amaya, K.
    Tokyo Institute of Technology, Department of Mechanical and Environmental Informatics.
    Noguchi, T.
    Tokyo Institute of Technology, Department of Mechanical and Environmental Informatics.
    Ståhle, P.
    Luleå tekniska universitet.
    Sundin, Karl-Gustaf
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Identification of elastic/visco-plastic material constants under impact loading2000Inngår i: IUTAM Symposium on Field Analysis for Determination of Material Parameters - Experimental and Numerical Aspects :: proceedings of the IUTAM Symposium held in Abisko National Park, Kiruna, Sweden, July 31 - August 4, 2000 / [ed] P. Ståhle, Dordrecht: Encyclopedia of Global Archaeology/Springer Verlag, 2000Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A method for identifying the material constants of an elastic/visco-plastic meterial under tensile impact loading is proposed. In this method, the Kalman filter and the finite element method are used together with a few test data. To obtain data for high strain rates, notched specimens are employed, because arbitrarily shaped specimens are available in this method. To increase the accuracy of identification, a test under a relatively low strain rate is needed in addition to a test under a high strain rate. The optimum strain rate is determined in such a way that the largest eigen value of the covariance matrix of the estimated parameters becomes minimum. A numerical simulation in performed to demonstrate the validity and usefulness of this method

  • 163.
    Appelquist, Ellinor
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW. KTH, Centra, SeRC - Swedish e-Science Research Centre.
    Imayama, Shintaro
    KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Revisiting the stability analysis of the flow over a rotating diskManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Local linear stability analysis applied to the rotating-disk flow is discussed.This flow case is an exact similarity solution to the cylindrical incompressible Navier–Stokes equations also called the von K ́arm ́an flow. The laminar mean velocity profiles are obtained by solving the resulting ordinary differential equations assuming the flow is axisymmetric and time independent. Two stability-analyses methods are used to investigate the local linear stability of this flow: i)the ‘shooting method’; and ii) the ‘Chebyshev polynomial method’. This theoretical investigation focuses on convectively unstable disturbances. Results obtained from the two methods are compared and the methods are shown togive similar results. These theoretical results are also compared with direct numerical simulations and experimental results showing good agreement.

  • 164.
    Appelquist, Ellinor
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Schlatter, Philipp
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Alfredsson, P. Henrik
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Lingwood, Rebecca
    KTH, Skolan för teknikvetenskap (SCI), Mekanik.
    Transition to turbulence in the rotating-disk boundary-layer flow with stationary vorticesArtikkel i tidsskrift (Fagfellevurdert)
  • 165.
    Appelsved, Peter
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Investigation of Mechanical Properties of Thermoplastics with Implementations of LS-DYNA Material Models.2012Independent thesis Advanced level (degree of Master (One Year)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The increased use of thermoplastics in load carrying components, especially in the automotive industry, drives the needs for a better understanding of its complex mechanical properties. In this thesis work for a master degree in solid mechanics, the mechanical properties of a PA 6/66 resin with and without reinforcement of glass fibers experimentally been investigated. Topics of interest have been the dependency of fiber orientation, residual strains at unloading and compression relative tension properties. The experimental investigation was followed by simulations implementing existing and available constitutive models in the commercial finite element code LS-DYNA.

    The experimental findings showed that the orientation of the fibers significantly affects the mechanical properties. The ultimate tensile strength differed approximately

    50% between along and cross flow direction and the cross-flow properties are closer to the ones of the unfilled resin, i.e. the matrix material. An elastic-plastic model with Hill’s yield criterion was used to capture the anisotropy in a simulation of the tensile test. Residual strains were measured during strain recovery from different load levels and the experimental findings were implemented in an elastic-plastic damage model to predict the permanent strains after unloading. Compression tests showed that a stiffer response is obtained for strains above 3% in comparison to tension. The increased stiffness in compression is although too small to significantly influence a simulation of a 3 point bend test using a material model dependent of the hydrostatic stress.

  • 166.
    Ardekani, Mehdi Niazi
    et al.
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Costa, Pedro
    Breugem, Wim Paul
    Brandt, Luca
    KTH, Centra, SeRC - Swedish e-Science Research Centre. KTH, Skolan för teknikvetenskap (SCI), Centra, Linné Flow Center, FLOW.
    Numerical study of the sedimentation of spheroidal particles2016Inngår i: International Journal of Multiphase Flow, ISSN 0301-9322, E-ISSN 1879-3533, Vol. 87, s. 16-34Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The gravity-driven motion of-rigid particles in a viscous fluid is relevant in many natural and industrial processes, yet this has mainly been investigated for spherical particles. We therefore consider the sedimentation of non-spherical (spheroidal) isolated and particle pairs in a viscous fluid via numerical simulations using the Immersed Boundary Method. The simulations performed here show that the critical Galileo number for the onset of secondary motions decreases as the spheroid aspect ratio departs from 1. Above this critical threshold, oblate particles perform a zigzagging motion whereas prolate particles rotate around, the vertical axis while having their broad side facing the falling direction. Instabilities of the vortices in the wake follow when farther increasing the Galileo number. We also study the drafting kissing-tumbling associated with the settling of particle pairs. We find that the interaction time increases significantly for non-spherical particles and, more interestingly, spheroidal particles are attracted from larger lateral displacements. This has important implications for the estimation of collision kernels and can result its increasing clustering in suspensions of sedimenting spheroids.

  • 167.
    Arkman, Jonas
    et al.
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Boo, Christofer
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Hållfasthetslära. Linköpings universitet, Tekniska högskolan.
    Design och dimensionering av momentskärmsstativ för provflygning av JAS39 Gripen: Konceptverifiering med hjälp av handberäkningar och FEM2013Independent thesis Basic level (degree of Bachelor), 10,5 poäng / 16 hpOppgave
    Abstract [sv]

    Det här projektet har genomförts på uppdrag av Saab, med syftet att designa och dimensionera ett stativ för infästning av en momentskärm. Denna momentskärm används vid provflygning av JAS39 Gripen för att vid behov upphäva ett okontrollerat tillstånd som kan inträffa vid tester av spinnfall och högalfaflygningar.

    Det arbete som presenteras i den här rapporten är en del av ett större projekt där målet har varit att ta fram ett stativ. I den här rapporten presenteras analyser som har gjorts dels med handbokslösningar och klassisk hållfasthetslära, dels med FE-programmet Ansys för att kontrollera att det slutgiltiga konceptet uppfyller samtliga givna krav.

    Vid dimensioneringen har ett iterativt arbetssätt använts, det har byggt på att först ta fram ett grundläggande koncept och sedan förbättra detta under projektets gång. Efter varje iteration har analyser gjorts av resultatet för att verifiera stativets funktion. För att inte påverka flygegenskaperna mer än nödvändigt har det även varit viktigt att minimera stativets vikt. Projektet har resulterat i ett koncept av titanlegeringen Ti-6Al-4V med en vikt på 67,7 kg.

  • 168.
    Arrell, Douglas
    et al.
    Siemens Industrial Turbomachinery AB, Finspång.
    Hasselqvist, Magnus
    Siemens Industrial Turbomachinery AB, Finspång.
    Sommer, C
    ABB Technology Ldt, Heidelberg, Germany.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska högskolan.
    On TMF damage, degradation effects, and the associated TMin influence on TMF test results in γ/γ′ alloys2004Inngår i: Proceedings of the International Symposium on Superalloys / [ed] Green K.A., Pollock T.M., Harada H., Howson T.E., Reed R.C., Schirra J.J., Walston S., Warrendale, PA, USA: The Minerals, Metals and Materials Society, TMS , 2004, s. 291-294Konferansepaper (Annet vitenskapelig)
  • 169.
    Asghar, Raja Babar
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik.
    Optimization as a Thermodynamic System2010Independent thesis Advanced level (degree of Master (Two Years)), 30 poäng / 45 hpOppgave
    Abstract [en]

    As we know that nature made the things optimized in all point of views, also it is supposed that nature works under some evolutionary process.

    Since there was no such Evolutionary Structural Optimization (ESO) method having strong mathematical background, that’s why these are not much reliable. The purpose of this thesis work is a little effort to introduce such an ESO method having a strong mathematical background.

    In this thesis work Optimization as a thermodynamic system, we are introducing a new method for topology optimization by using concept of Free Energy and Dissipation Potential from non-smooth thermodynamics system. For better understanding we may call it as Evolutionary Structural Topology Optimization (ESTO), and this project work is done in the following steps.

    An evolution problem is formulated in terms of free energy and dissipation potential for a non-smooth thermodynamical system. Free energy is taken as an objective function for a general structural optimization problem. Derivation of a well posed evolution problem for which evolution is such that objective function always decreases. An optimality criteria method is derived for given evolution problem and it is implemented in a FEM program TRINITAS. And the behaviour of the so called evolutionary parameters such as Forward and Backward plastic constants is analyzed.

  • 170.
    Asgharzadeh, Mohammadali
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Faleskog, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    A model for precipitation strengthening accounting for variations of particlesize and spacing based on strain gradient plasticity in 3D2018Manuskript (preprint) (Annet vitenskapelig)
  • 171.
    Asgharzadeh, Mohammadali
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Faleskog, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    A shearing/looping transition model for precipitation strengthening2018Manuskript (preprint) (Annet vitenskapelig)
  • 172.
    Asgharzadeh, Mohammadali
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Faleskog, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Strengthening effects of particle-matrix interaction analyzed by anaxi-symmetric model based on strain gradient plasticity2018Manuskript (preprint) (Annet vitenskapelig)
  • 173.
    Asgharzadeh, Mohammadali
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Faleskog, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Dahlberg, Carl F. O.
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    A 3D model for the analysis of plastic flow properties of randomly-distributed particles2018Manuskript (preprint) (Annet vitenskapelig)
  • 174.
    Ashwear, Nasseradeen
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Vibration Frequencies as Status Indicators for Tensegrity Structures2014Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

     Applications of vibration structural health monitoring (VHM) techniques are increasing rapidly. This is because of the advances in sensors and instrumentation during the last decades. VHM uses the vibration properties to evaluate many civil structures during the design steps, building steps and service life.

    The stiffness and frequencies of tensegrity structures are primarily related to the level of pre-stress. The present work investigates the possibilities to use this relation in designing, constructing and evaluating the tensegrity structures.

    The first part of the  present work studies the improvement of current models for resonance frequency simulation of tensegrities by introducing the bending behaviour of all components, and by a one-way coupling between the axial force and the stiffness. From this, both local and global vibration modes are obtained. The resonance frequencies are seen as non-linearly dependent on the pre-stress level in the structure, thereby giving a basis for diagnosis of structural conditions from measured frequencies. The new aspects of tensegrity simulations are shown for simple, plane structures but the basic methods are easily used also for more complex structures.

    In the second part, the environmental temperature effects on vibration properties of tensegrity structures have been investigated, considering primarily seasonal temperature differences (uniform temperature differences). Changes in dynamic characteristics due to temperature variations were compared with the changes due to decreasing pre-tension in one of the cables. In general, it is shown that the change in structural frequencies made by temperature changes could be equivalent to the change made by damage (slacking). Different combinations of materials used and boundary conditions are also investigated. These are shown to have a significant impact on the pre-stress level and the natural frequencies of the tensegrity structures when the environment temperature is changed.

  • 175.
    Ashwear, Nasseradeen
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Vibration-based Assessment of Tensegrity Structures2016Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Vibration structural health monitoring (VHM) uses the vibration properties to evaluate many civil structures during the design steps, building steps and service life.The whole function, expressed by stiffness and frequencies of tensegrity structures are primarily related to the level of pre-stress. The present work investigates the possibilities to use this relation in designing, constructing and evaluating the tensegrity structures.One of the aims of the thesis was to improve the current models for resonance frequency simulation of tensegrities. This has been achieved by introducing the bending behaviour of all components, and by a one-way coupling between the axial force and the stiffness.The environmental temperature effects on vibration properties of tensegrity structures have been also  investigated. Changes in dynamic characteristics due to temperature variations were compared with the changes due to decreasing pre-tension in one of the cables. In general, it is shown that the change in structural frequencies coming from temperature changes could of several magnitude as those from damage.Coinciding natural frequencies and low stiffness are known issues of tensegrity structures. The former can be an obstacle in VHM, while the later normally limits their uses in real engineering applications. It has been shown that the optimum self-stress vector of tensegrity structures can be chosen such that their lowest natural frequency is high, and separated from others.The environmental temperature effects on vibration properties of tensegrity structures were revisited to find a solution such that the natural frequencies of the tensegrity structures are not strongly affected by the changes in the environmental temperature. An asymmetric self-stress vector can be chosen so that the criterion is fulfilled as well as possible. The level of pre-stress can also be regulated to achieve the solution. The last part of this thesis, services as a summary of the work.

  • 176.
    Ashwear, Nasseradeen
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Reducing effects from environmental temperature on the natural frequencies of tensegrity structuresInngår i: Journal of Sound and Vibration, ISSN 0022-460X, E-ISSN 1095-8568Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    n vibration health monitoring, dynamic properties such as natural frequencies and mode shapes are used as tools for assessing the structures health condition.~They are, however, also affected by environmental conditions like wind, humidity and temperature changes. Of particular importance is the change of the environmental temperature, and it is the most commonly considered environmental variable that influences the vibration health monitoring algorithms.~This paper discusses how the tensegrity structures can be designed such that some of their lowest natural frequencies are less sensitive to the temperature changes. A genetic algorithm is used to solve the optimization problem. In the form-finding stage, an asymmetric self-stress vector can be chosen so that the criterion is fulfilled as well as possible. The level of pre-stress can also be regulated to achieve the solution, particularly when a symmetric self-stress vector is chosen.

  • 177.
    Ashwear, Nasseradeen
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Eriksson, Anders
    KTH, Skolan för teknikvetenskap (SCI), Mekanik, Strukturmekanik.
    Vibration health monitoring for tensegrity structures2017Inngår i: Mechanical systems and signal processing, ISSN 0888-3270, E-ISSN 1096-1216, Vol. 85, s. 625-637Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Tensegrities are assembly structures, getting their equilibrium from the interaction between tension in cables and compression in bars. During their service life, slacking'in their cables and nearness to buckling in their bars need to be monitored to avoid a sudden collapse. This paper discusses how to design the tensegrities to make them feasible for vibrational health monitoring methods. Four topics are discussed; suitable finite elements formulation, pre-measurements analysis to find the locations of excitation and sensors for the interesting modes, the effects from some environmental conditions, and the pre-understanding of the effects from different slacking scenarios.

  • 178.
    Asnafi, Nader
    Volvo Car Components Corporation/Industrial Development Centre, Olofström, Sweden.
    Analytical modelling of tube hydroforming1999Inngår i: Thin-walled structures, ISSN 0263-8231, E-ISSN 1879-3223, Vol. 34, nr 4, s. 295-330Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The automotive industry has shown a growing interest in tube hydroforming during the past years. The advantages of hydroforming (less thinning, a more efficient manufacturing process etc.) can, for instance, be combined with the high strength of extra high strength steels, which are usually less formable, to produce structural automotive components which exhibit lower weight and improved service performance. Design and production of tubular components require knowledge about tube material behaviour and tribological effects during hydroforming and how the hydroforming operation itself should be controlled. These issues are studied analytically in the present paper. Hydroforming consists of free forming and calibration. Only the so-called free forming is treated here. The analytical models constructed in this paper are used to show what the limits are during the free forming, how different material and process parameters influence the loading path and the forming result, and what an experimental investigation into hydroforming should focus on. The present study was a part of a larger investigation, in which finite-element simulations and experiments were also conducted. The results of these simulations and experiments will be accounted for in coming papers.

  • 179.
    Asnafi, Nader
    Gränges Technology, Finspång, Sweden.
    On springback of double-curved autobody panels2001Inngår i: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 43, nr 1, s. 5-37Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The springback of double curved autobody panels is studied theoretically and experimentally. Both steel and aluminum sheets are included in this investigation. The obtained results show that the springback is decreased with increasing binder force, increasing curvature, increasing sheet thickness and decreasing yield strength. This paper comprises also a discussion on the plastic strains and their influence on the springback.

  • 180.
    Asnafi, Nader
    Industrial Development Center/Volvo Cars Body Components, Olofström, Sweden .
    On Springback of Double-Curved Autobody Panels1998Inngår i: Proceedings, working groups meeting - IDDRG, International Deep Drawing Research Group: Genval, Benelux, June 15 - 16, 1998, 1998Konferansepaper (Annet vitenskapelig)
  • 181.
    Asnafi, Nader
    Swedish Institute for Metals Research, Stockholm, Sweden.
    On Springback of Double-Curved Autobody Panels, Part I: Theoretical Treatment1996Rapport (Annet vitenskapelig)
  • 182.
    Asnafi, Nader
    Swedish Institute for Metals Research, Stockholm, Sweden.
    On Springback of Double-Curved Autobody Panels, Part II: Experimental Analysis1996Rapport (Annet vitenskapelig)
  • 183.
    Asnafi, Nader
    Örebro universitet, Institutionen för naturvetenskap och teknik.
    Proceedings of the International Conference on Mechanical, Electric and Industrial Engineering (MEIE2018)2018Konferanseproceedings (Fagfellevurdert)
  • 184.
    Asnafi, Nader
    et al.
    Sapa Profiles/Sapa Technology, Finspång, Sweden.
    Nilsson, T.
    Sapa Profiles/Sapa Technology, Finspång, Sweden.
    Lassl, G.
    Volvo Car Corp..
    Automotive tube bending and tubular hydroforming with extruded aluminium profiles2000Inngår i: SAE technical paper series, ISSN 0148-7191, artikkel-id 2670Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Side Member Left and Side Member Right, which go from bumper to bumper, were at the focus in the present study. These side members were produced using straight round (hollow with a circular cross-section) extruded aluminium profiles as tube material. The tubes were bent and hydroformed. Rotary-draw bending yielded the best result. A spread within 8 mm after bending was found to be acceptable provided that the bent tube was hydroformed with a high maximum internal pressure (1300 bars in this study). Pressure-assisted tool (hydroforming tool) closure should be preferred. Such a tool closure prevents formation of buckles, which may be difficult to straighten out completely during hydroforming. Planeness and parallelity of the press tables and adapters play a significant role, as far as the spread and inplaneness of hydroformed components are concerned. The hydroforming tool must be matched in the press that actually will be used. Proper evacuation (of particularly air) is essential, especially in long hydroforming tools. All cross sections must be deformed at least 2% (average perimeter enlargement), if the hydroformed components are to exhibit a reasonable spread. The critical (fracture) cross-sections predicted by finite-element simulation correspond to those found in practical tests. However, the finite-element simulation was not able to predict formation of wrinkles at the tube ends caused by excessively large strokes. Such wrinkles were obtained in practice.

  • 185.
    Aspsjö, Philip
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Industriell teknik.
    Spännkraft på bandavskrapare: Utredning och konstruktion2013Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [en]

    This thesis was performed at Vendig AB which is a company that develops and sells products such as belt scrapers for conveyor. The thesis is divided into two parts, one part where it´s investigated which tension force is required to tighten Vendig AB´s scraper Hampus against the belt in a correct way. The second part is called mechanical design and here a new and more compact tension device is developed.

    Field studies has been conducted at a couple of Vendig AB´s costumers to get a knowledge base about how Vendig AB´s products are used, how they function and the environment they operate in. During one of the field studies the force between the scraper and the belt was measured. The result from the measurements, together with a report from LKAB [1], were evaluated and summarized in a table. The required force was recalculated for all different version of the scraper.

    After the tension force had been investigated the old tension device was evaluated and a requirement specification for a new was compiled in collaboration with Vendig AB´s group of technology. A number of concepts where then developed using the concept generator tool SCAMPER. One concept conformed very well to the requirement specification and was further developed. The concept was dimensioned by simulations in CAD, and basic drawings were made. The design solutions where discussed with suppliers and the design was updated. Finally a prototype was ordered to test and evaluate the concept. The tests revealed shortcomings in the prototype which has been evaluated and solutions has been discussed.

  • 186.
    Athanasiou, Vasileios
    Linköpings universitet, Institutionen för medicin och hälsa, Avdelningen för radiologiska vetenskaper. Linköpings universitet, Hälsouniversitetet.
    Estimation and modelling of fMRI BOLD response2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    One of the current topics of research in neuroimaging techniques is related to explaining and modelling the Blood Oxygen Level Dependent (BOLD) responses. BOLD responses are estimated by processing functional Magnetic Resonance Imaging (fMRI) data. BOLD responses are caused by hemodynamic responses to neural activity which alter the levels of blood oxygenation at local brain regions. The main aims of the current thesis were to i) develop and examine methods regarding BOLD response estimation from the visual cortex and the frontal cortex of human brain and to ii) develop a model in order to explain the physiological mechanisms which cause the estimated BOLD responses.

    In order to satisfy the main aims, fMRI data were provided by the Center of Medical Imaging and Visualization (CMIV). The provided fMRI data consist of fMRI brain measurements of twelve healthy human subjects who were subjected to visual stimulation. By processing the fMRI data, Regions Of Interest (ROIs) were extracted at the anatomical sites of the visual cortex and the frontal cortex. Afterwards, the fMRI data were manipulated in order to extract BOLD responses from the visual cortex and the frontal cortex. Various methods were developed and compared in terms of which technique provided well representative BOLD responses.       

    Subsequently, a model was developed by using software Wolfram Mathematica 9 in order to explain the physiological mechanisms of the estimated BOLD responses at the visual and the frontal cortex. The model aimed to solve for oxygen concentration in blood plasma as blood flows from the arterial part to the venous part of the blood circulation system through a capillary. Oxygen outward diffusion through the capillary wall and oxygen concentration at the extravascular environment were modelled as well. Blood plasma oxygen concentration was turned into hemoglobin oxygen saturation (Sa ) through hemoglobin oxygen dissociation curve and Henry’s law for gases. As a result, the Sa  was estimated through modelling for oxygen concentration in blood plasma. Finally, the developed model ended to a system with input the fractional change of Cerebral Blood Flow (CBF) velocity and Cerebral Metabolic Rate of Oxygen (CMR ) and as output a proportional signal to the BOLD response. By simulating for different scenarios of fractional changes of CBF velocity and CMR  and by comparing the resulted BOLD responses to the estimated ones, it was attempted to explain for the physiological mechanisms which caused the BOLD responses at the anatomical sites of the visual and frontal cortex.

  • 187.
    Austrell, Per-Erik
    et al.
    Division of Structural Mechanics, Lund Institute of Technology.
    Kari, LeifKTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Constitutive Models for Rubber IV: proceedings of the 4th European Conference for Constitutive Models for Rubber, ECCMR 2005, Stockholm, Sweden, 27-29 June 20052005Collection/Antologi (Fagfellevurdert)
    Abstract [en]

    The unique properties of elastomeric materials are taken advantage of in many engineering applications. Elastomeric units are used as couplings or mountings between stiff parts. Examples are shock absorbers, vibration insulators, flexible joints, seals and suspensions etc.

     

    However, the complicated nature of the material behavior makes it difficult to accurately predict the performance of these units, using for example finite element modelling. It is therefore necessary that the constitutive model accurately capture relevant aspects of the mechanical behavior.

     

    The latest development concerning constitutive modelling of rubber is collected in these proceedings. It is the fourth ECCMR-European Conference on Constitutive Modelling in a series on this subject.

     

    Topics included in this volume are, Hyperelastic models, Strength, fracture & fatigue, Dynamic properties & the Fletcher-Gent effect, Micro-mechanical & statistical approaches, Stress softening, Viscoelasticity, Filler reinforcement, and Tyres, fiber & cord reinforced rubber.

  • 188.
    Autioniemi, J
    et al.
    Lapland University of Applied Sciences.
    Autioniemi, M
    Lapland University of Applied Sciences.
    Casselgren, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Konttaniemi, H
    Lapland University of Applied Sciences.
    Sukuvaara, T
    FMI-Arctic Research Centre, Sodankylä.
    Ylitalo, R
    FMI-Arctic Research Centre, Sodankylä.
    Intelligent Road2015Rapport (Annet vitenskapelig)
    Abstract [en]

    Project Intelligent Road is a common effort of four main partners: Rovaniemi University of Applied Sciences (RAMK), Luleå Technical University (LTU), Finnish Meteorological Institute (FMI), Kaakkois-Suomen ELY-keskus (KaS ELY) – and representatives of business sector of the region. The overall objective of the project is to support the development of business community in Northern Scandinavian region by testing and improvement of existing innovative products concerned with road safety provision in Nordic weather conditions. The specific objective of the project is to create a demo of sustainable and marketable Intelligent Road System providing location-based short-term road weather information to the road user passing by the area. Target Groups, which are directly and positively affected by the project are businesses and above mentioned project partners. All these actors have exclusive know-how in the area and are each equally important for the implementation of the project and its success. Final beneficiaries of this project are business community of the Northern Scandinavian Region; Ministry of Transport and Communications of Finland, represented by KaS ELY and Finnish Transport Safety Agency; Swedish Ministry of Enterprise, Energy and Communications; and of course local municipalities, as Luleå Municipality, and road users.

  • 189.
    Axelsson, Emil
    et al.
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Maskinteknisk produktframtagning (MTEK).
    Källner, David
    Högskolan i Halmstad, Akademin för ekonomi, teknik och naturvetenskap, Maskinteknisk produktframtagning (MTEK).
    Plastgranulat Extruder2016Independent thesis Basic level (university diploma), 5 poäng / 7,5 hpOppgave
  • 190.
    Axelsson Paulsson, Victor
    Uppsala universitet, Teknisk-naturvetenskapliga vetenskapsområdet, Tekniska sektionen, Institutionen för teknikvetenskaper, Industriell teknik.
    Konstruktion av dumpervagn: Från beställning till underlag2015Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [en]

    This thesis describes the design of a tipping trailer, from a company’s demands andrequests to complete manufacturing documentation. The design is developed for thecompany Abexor AB in Östersund that produces tipping trailers. The product issupposed to be used by Abexors customer to transport cargos of different kinds,such as gravel, stone, dirt, etc.The work commenced with a meeting at the company where demands were set.After that a pre-study was conducted to find out what traffic rules were required forthe trailer to be allowed to be driven on roads. Similar products were examined tosee how the trailer could be designed. The pre-study was followed by an idea andconcept generation. Nine different concepts were generated and the best werechosen for continued work.The concepts that were chosen resulted in a design in CAD were considerationswere taken for dimensions, traffic rules and function. Manufacturing documentationand a list of components to be bought were generated.In the section discussion and conclusions you can see what the thesis has resulted in.It’s also described what could have been done different and guidelines for futuredevelopment have been made.

  • 191.
    Azar, Amin S.
    et al.
    SINTEF Mat & Chem, Oslo, Norway.
    Svensson, Lars-Erik
    Högskolan Väst, Institutionen för ingenjörsvetenskap, Avd för industriell produktion.
    Nyhus, Bård
    SINTEF Mat & Chem, Oslo, Norway.
    Effect of crystal orientation and texture on fatigue crack evolution in high strength steel welds2015Inngår i: International Journal of Fatigue, ISSN 0142-1123, E-ISSN 1879-3452, Vol. 77, s. 95-104Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the present study, electron backscattered diffraction is used to analyze the fatigue crack evolution in a high strength steel weld that was loaded cyclically in the plastic regime. Three prominent regions of a fatigue crack are investigated separately: crack tip, crack trajectory and crack initiation. Taylor and Schmid factors are mapped with respect to the defined loading matrix. Possible effective mechanisms are proposed based on the local plasticity properties like lattice rotation and misorientation. The analyses of the crack tip and trajectory regions show that although the critical resolved shear stresses in some regions are low, small deformation resistance of these regions can compromise the dislocation immobility and cause local fracture. It is shown that if the crack grows transgranularly, at least one side of the crack may show low lattice rotation or strain equivalent values, which indicates the relaxation of elastic stresses after fracture. The crack initiation is determined to be dominantly controlled by transcrystalline mechanism of initiation that takes place under plastic loading conditions. It is also shown that the secondary < 123 >11 (1) over bar type of slip systems were the most activated under such loading conditions. (C) 2015 Elsevier Ltd. All rights reserved.

  • 192.
    Azeez, Ahmed
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Mekanik och hållfasthetslära.
    Effect of dwell time on stress intensity factor of ferritic steel for steam turbine applications2018Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In the transition from conventional to green energy production resources, steam turbines are used to satisfy the lack of energy during peaks in the demand times and the limited access of renewable resources. This type of usage for steam turbines makes them operate on a flexible schedule, which leads to unpredictable issues related to shorter component life and faster crack propagation. Thus, the steam turbine components must be examined to determine their specific life period. This will help set proper maintenance intervals and prevent unexpected failures. For that, thermo-mechanical fatigue (TMF) testing is used, where a specimen made of the same material as the turbine component is subjected to both temperature and load variation. The specimen is pre-cracked to investigate the crack propagation behavior, which is the focus of this study.

    This thesis work concentrates on simulating the TMF cycle for the steam turbine casing component. The material is 9%-10%Cr ferritic steel. The aim is to understand the material behavior during crack propagation and to predict a useful testing parameter. The method provided in this work discusses two cases, both are out-of-phase (OP) TMF tests with strain control. The maximum and minimum temperatures for the cycle are 600 ˚C and 400 ˚C respectively, while the maximum and minimum strain levels are 0 and  respectively. The study will investigate different , which is the maximum compressive strain level. Case 1 has a dwell time at the maximum temperature only, while case 2 has dwell times at both maximum and minimum temperatures. The method utilizes the stress intensity factor (SIF) to characterize the crack tip conditions. Also, it uses Paris' law to estimate the duration of the tests. For simplification, only the elastic behavior of the material is considered.

    The results obtained show no effect of using different pre-crack lengths due to the strain control condition. Minor effects can be observed by using different dwell times, however very short dwell times must be avoided to produce reliable results. A recommended dwell time of 5 minutes could be used, since longer dwell times will make the test prohibitively time-consuming. The compressive strain levels used in the work shows large effects on the results. Using low compressive strain values will produce a very long time for the tests, while very high compressive strains produce large plasticity. Thus, high compressive strains must be avoided since the SIF describes cracks for only elastic or near elastic cases. Also, small compressive strain levels in case 2 should not be used since it will lead to results like case 1. This is due to the small creep effect at the minimum temperature. Finally, compressive strain levels of 0.6 %, 0.5 % and 0.4 % are recommended for case 1, while only 0.6 % compressive strain level is recommended for case 2.

    This thesis contributes to the fields of solid mechanics, fracture mechanics and the use of TMF testing, where a recommended set of testing parameters are provided.

  • 193.
    AZİZOĞLU, YAĞIZ
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Micromechanical Numeric Investigation of Fiber Bonds in 3D Network Structures.2014Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In manufacturing of paper and paperboard, optimized fiber usage has crucial importance for process efficiency and profitability. Dry strength of paper is one of the important quality criteria, which can be improved by adding dry strength additive that affect fiber to fiber bonding. This study is using the micromechanical simulations which assist interpretation of the experimental results concerning the effect of strength additives.

    A finite element model for 3D dry fiber network was constructed to study the effect of bond strength, bond area and the number of bonds numerically on the strength of paper products. In the network, fibers’ geometrical properties such as wall thickness, diameter, length and curl were assigned according to fiber characterization of the pulp and SEM analyses of dry paper cross-section. The numerical network was created by depositing the fibers onto a flat surface which should mimic the handsheet-making procedure. In the FE model, each fiber was represented with a number of quadratic Timoshenko beam elements where fiber to fiber bonds were modelled by beam-to-beam contact. The contact model is represented by cohesive zone model, which needs bond strength and bond stiffness in normal and shear directions. To get a reasonable estimate of the bond stiffness, a detailed finite element model of a fiber bond was used. Additionally, the effect of different fiber and bond geometries on bond stiffness were examined by this model since the previous work [13] indicated that the bond stiffness can have a considerable effect on dry strength of paper.

    The network simulation results show that the effect of the strength additive comes through improving the bond strength primarily. Furthermore, with the considered sheet structure, both the fiber bond compliance and the number of bonds affect the stiffness of paper. Finally, the results of the analyses indicated that the AFM measurements of the fiber adhesion could not be used directly to relate the corresponding changes in the bond strength.

    The fiber bond simulation concluded that fiber wall thickness has the most significant effect on the fiber bond compliance. It was also affected by micro-fibril orientation angle, bond orientation and the degree of pressing.

  • 194.
    Azizoğlu, Yağız
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Luleå University of Technology.
    Modeling of Cold Pilgering of Tubes2017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Cold pilgering is a challenging tube forming process in terms of modeling due to the complexity in kinematic of tools, friction condition and material behavior. The process development has mostly been based on simple formulas and costly full-scale tryouts. The aim in this study is to develop validated Finite element models of cold pilgering to increase the understanding of influence of the process parameters on the produced tubes.

    In the course of this thesis, three-dimensional mechanical and thermo-mechanical Finite element models of cold pilgering were developed. The commercial code MSC.Marc was used in the simulations. General 3D models are needed to be able to capture asymmetric deformation in cold pilgering. It was found that tool deflections together with elastic deformation of roll dies have considerable influence on the rolling force. Furthermore, the strain rate and temperature effects on the response of the material and thereby on the rolling force were evaluated.

  • 195.
    Azizoğlu, Yağız
    et al.
    Högskolan Dalarna, Akademin Industri och samhälle, Materialteknik. Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Gärdsback, Mattias
    Sandvik Materials Technology, R&D, Sandviken..
    Sjöberg, Bengt
    Sandvik Materials Technology, R&D, Sandviken..
    Lindgren, Lars-Erik
    Luleå University of Technology.
    Finite element analysis of cold pilgering using elastic roll dies2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    A finite element model of cold pilgering with elastic roll dies have been developed and used to investigate the influence of roll die deformation on the material flow, contact region, roll separating force and tube dimensions. Full scale experiments were performed to validate the contact surface and tube dimensions. The results show that the influence of roll die flattening is not significant on the contact length. However, elastic deformation of roll die has strong influence on both the wall thickness reduction and roll separating force. Thus it is recommended to consider elasticity of roll dies when forces and tube dimensions are estimated.

  • 196.
    Azizoğlu, Yağız
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Gärdsback, Mattias
    Sandvik Materials Technology, R&D, Sandviken.
    Sjöberg, Bengt
    Sandvik Materials Technology, R&D, Sandviken.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Finite Element Analysis of cold pilgering using elastic roll dies2017Inngår i: Procedia Engineering, ISSN 1877-7058, E-ISSN 1877-7058, Vol. 207, s. 2370-2375Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A finite element model of cold pilgering with elastic roll dies have been developed and used to investigate the influence of roll die deformation on the material flow, contact region, roll separating force and tube dimensions. Full scale experiments were performed to validate the contact surface and tube dimensions. The results show that the influence of roll die flattening is not significant on the contact length. However, elastic deformation of roll die has strong influence on both the wall thickness reduction and roll separating force. Thus it is recommended to consider elasticity of roll dies when forces and tube dimensions are estimated.

  • 197.
    Babu, Bijish
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Swerea MEFOS AB.
    Mechanism-based flow stress model for Ti-6Al-4V: applicable for simulation of additive manufacturing and machining2018Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Ti-6Al-4V has remarkable properties such as high specific mechanical properties (viz. stiffness, strength, toughness, fatigue resistance), corrosion resistance, biocompatibility etc. These properties make it attractive for applications in aerospace, chemical industry, energy production, surgical implants, etc. Many of these applications have to satisfy high requirements on mechanical properties, which are directly affected by the microstructure. Therefore, it is essential to understand as well as to model the microstructure evolution during manufacturing as well as in-service. Furthermore, this alloy has a narrow temperature and strain rate window of workability.

    This work was initiated as part of a project aimed at performing finite element simulations of a manufacturing process chain involving hot forming, welding, machining, additive manufacturing and heat treatment of Ti-6Al-4V components within the aerospace industry. Manufacturing process chain simulations can compute the cumulative effect of the various processes by following the material state through the whole chain and give a realistic prediction of the final component. Capacity to describe material behavior in a wide range of temperatures and strain rates is crucial for this task.

    A material model based on the dominant deformation mechanisms of the alloy is assumed to have a more extensive range of validity compared to an empirical relationship. Explicit dislocation dynamics based models are not practically feasible for manufacturing process simulation, and therefore the concept of dislocation density, (length of dislocations per unit volume) developed by (Kocks1966; Bergström, 1970) is followed here. This mean field approach provides a representation of the average behavior of a large number of dislocations, grains, etc. Conrad (1981) studied the influence of various factors like solutes, interstitials, strain, strain rate, temperature, etc., on the strength and ductility of titanium systems and proposed a binary additive relationship for its yield strength. The first component relates to long-range interactions and second short-range relates to lattice resistance for dislocation motion. For high strain rate deformation, this short-range term is extended to include the effects of a viscous drag given by phonon and electron drag (Lesuer et al. 2001).  Immobilisation of dislocation by pile-ups gives hardening and remobilization/annihilation by dislocation glide and climb gives restoration. Globularization is also considered to restore the material. The material model is calibrated using isothermal compression tests at a wide range of temperatures and strain rates. Compression tests performed using Gleeble thermo-mechanical simulator is used at low-strain rates and split-Hopkins pressure bar is used at high strain rates for calibration.

    During additive manufacturing depending on the temperature, heating/cooling rates, Ti-6Al-4V undergoes allotropic phase transformation. This transformation results in a variety of textures that can give different mechanical properties.  Based on the texture (Semiatin et al., 1999b; Seetharaman and Semiatin, 2002; Thomas et al., 2005) identified few microstructural features that are relevant to the mechanical properties. The three separate alpha phase fractions; Widmanstatten,  grain boundary, Martensite, and the beta-phase fraction are included in the current model. However, since the strengthening contributions of these individual alpha phases are not known, a linear rule of mixtures for the total alpha-beta composition is developed. This model is calibrated using continuous cooling tests performed by Malinov et al. 2001 with differential scanning calorimeter at varying cooling rates.  

    This mechanism-based model is formulated in such a way that it can be implemented in any standard finite element software. In the current work, this is implemented as subroutines within MSC Marc and used for simulation of hot-forming and additive manufacturing. 

  • 198.
    Babu, Bijish
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Charles, Corinne
    Department of Industrial Production, Högskolan Väst, Trollhättan.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Physically Based Constitutive Model of Ti-6Al-4V for Arbitrary Phase Composition2018Inngår i: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The principal challenge in producing aerospace components using Ti-6Al-4V alloy is to employ the optimum process window of deformation rate and temperature to achieve desired material properties. Qualitatively understanding the microstructure-property relationship is not enough to accomplish this goal. Developing advanced material models to be used in manufacturing process simulation is the key to compute and optimize the process iteratively. The focus in this work is on physically based flow stress models coupled with microstructure evolution models. Such a model can be used to simulate processes involving complex and cyclic thermo-mechanical loading.

  • 199.
    Babu, Bijish
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Swerea MEFOS.
    Lundbäck, Andreas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Simulation of additive manufacturing of Ti-6Al-4V using a coupled physics-based flow stress and microstructure modelManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Simulating the additive manufacturing process of Ti-6Al-4V is very complex owing to the microstructural changes and allotropic transformation occurring during its thermo-mechanical processing. The alpha-phase with a hexagonal close pack structure is present in three different forms; Widmanstatten, grain boundary, and Martensite. A metallurgical model that computes the formation and dissolution of each of these phases is used in this work. Furthermore, a physically based flow-stress model coupled with the metallurgical model is applied in the simulation of direct energy deposition additive manufacturing case.

  • 200.
    Babu, Bijish
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Svoboda, Ales
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Ghassemali, Ehsan
    School of Engineering, Jönköping University..
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Dislocation density based plasticity model extended to high strain rate deformation of Ti-6Al-4VManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    One of the main challenges in the simulation of machining is accurately describing the material behavior during severe plastic deformation at strain rates ranging six orders of magnitude and temperature between room temperature to nearly melting temperature. High strain rate measurements are performed using Split-Hopkinson Pressure Bar (SHPB) technique at a range of temperatures. The temperature change during deformation is included by computing the plastic work converted to heat energy. A physics-based material model published earlier (Babu and Lindgren, 2013) is extended in this paper to include the high strain rate mechanisms of phonon and electron drag. Characterization of the microstructure is performed using Electron Backscatter Diffraction (EBSD), and a novel method is proposed in this work to quantify the extent of globularization which is compared with model predictions.

1234567 151 - 200 of 3271
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf