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  • 301.
    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.

    Fulltekst (pdf)
    fulltext
  • 302.
    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.

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  • 303.
    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.

    Fulltekst (pdf)
    fulltext
  • 304.
    Azizoğlu, Yağız
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik. Dalarna University, Borlänge 781 77, Sweden.
    Gärdsback, Mattias
    Sandvik Materials Technology, Sandviken 811 81, Sweden.
    Yamanaka, Akinori
    Tokyo University of Agriculture and Technology, Department of Mechanical Systems Engineering, Tokyo 184-8588, Japan.
    Kuwabara, Toshihiko
    Tokyo University of Agriculture and Technology, Department of Mechanical Systems Engineering, Tokyo 184-8588, Japan.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Work hardening during alternating load directions of 316L SS2018Inngår i: Proceedings of the 17th International Conference on Metal Forming METAL FORMING 2018 September 16 – 19, 2018, Loisir Hotel Toyohashi, Toyohashi, Japan / [ed] Ken-ichiro Mori; Yohei Abe; Tomoyoshi Maeno, Elsevier, 2018, s. 1777-1784Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Understanding and modelling the plastic behavior of a material are essential for simulation and design of metal forming processes. Cold pilgering of tubes is a process with very complex strain history with alternating loading direction. This makes evaluation of the work hardening challenging. Cold deformation applied in a single direction predominantly exhibit work hardening, while changes of the loading direction may even cause softening in other directions. The influence of alternating loading directions on work hardening has been experimentally investigated for 316L stainless steel (SS). Cubic specimens were cut out from the preform of the tube. The specimens are subjected to uniaxial compressions in alternating directions along two perpendicular axes. From the results, a cyclic elastic-plastic constitutive model based on a Chaboche-type approach is calibrated and implemented in the commercial finite element code MSC.Marc.

  • 305.
    Azizoğlu, Yağız
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Temperature and plastic strain dependent Chaboche model for 316L used in simulation of Cold PilgeringManuskript (preprint) (Annet vitenskapelig)
  • 306.
    Azizoğlu, Yağız
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Sjöberg, Bengt
    Alleima Sverige AB, Sweden.
    Lindgren, Lars-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Hållfasthetslära.
    Modeling of cold pilgering of stainless-steel tubes2024Inngår i: Journal of Manufacturing Processes, ISSN 1526-6125, Vol. 112, s. 112-125Artikkel i tidsskrift (Fagfellevurdert)
  • 307.
    Azmeh, Saria
    et al.
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Hådén, Rasmus
    Mittuniversitetet, Fakulteten för naturvetenskap, teknik och medier, Institutionen för naturvetenskap.
    Utveckling av befintlig bäckenstol2020Independent thesis Basic level (degree of Bachelor), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Toalettstolen är en av de viktigaste delarna i badrummet. Utöver att fylla sin givna funktion, är det viktigt att toalettstolen passar in i rummet, håller i många år och lätt att både använda och rengöra. I vissa situationer kan det vara svårt att använda den vanliga toalettstolen, på grund av en sjukdom eller bara att man behöver gå på toa flera gånger under natten. Uppdraget givet av Eurotrade Wholesale AB har varit att utveckla en befintlig höj- och sänkbar bäckenstol vid användande av WC. För att klara av detta uppdrag har gruppen använts sig av designprocessen. Designprocessen består utav tre faser: analysfas, kreativ fas och genomförandefas. I början av arbetet tilldelades gruppen en prototypstol utgiven av Eurotrade Wholesale AB. Denna prototyp utvärderades med hjälp av användartest och aktivitetsanalys och därefter skapades en kravspecifikation i samråd med Eurotrade Wholesale AB. Arbetet fortlöpte med brainstorming och konceptskisser som senare utvärderades med hjälp av Pughs konceptsalsmatris. Det vinnande konceptet gick till vidareutveckling och därefter skapades två 3D modeller för att avsluta med simuleringstester i Solidworks. Efter en teoretisk aktivitetsanalys hade utfört på slutkonceptet kunde det konstateras att slutkonceptet kräver färre aktiviteter vid både användning och reglering. Det framtagna konceptet är även mer stabil än den givna prototypen och klarar av en högre last utifrån de simuleringar som har gjorts. Projektet syfte är uppfyllt och alla ska-krav har blivit uppnådda. Vid ett eventuellt fortsatt arbetet hade gruppen arbetat vidare uppfylla återstående två bör-krav. Det innebär en materialundersökning, för att bland annat utvärdera materialet, kolla om materialet är återvinningsbart och utvärdera hållfastigheten i sitsen, utvärdera priset för att se om produktionspriset <250 kr och ytterligare vidareutveckla slutkonceptet.

     

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  • 308.
    Babbepalli, Venkata Venu Sai Phani Ram
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik, Farkostteknik och Solidmekanik, Hållfasthetslära.
    Implementation of moisturedependent constitutive model for paperboard2020Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    There has been a considerable increase in the usage of paper products due to its sustainability in the product cycle. Many environmental and process variables can affect the mechanical behavior of paper from its making to finished products. Of these variables, moisture is of particular importance and strongly influences both papermaking, converting, and end-use of the paper products.

    Experimental investigations at different humidity levels reveals that normalized in-plane constitutive parameters, such as elastic parameters and the linear hardening modulus, in both MD and CD1) follow a linear relationship with normalized moisture ratio. This relation is found to be acceptable for a wide range of commercial paperboards. To capture this observation, a novel material model with orthotropic elasticity and anisotropic hardening2 is proposed. An associative flow rule for the evolution of plastic strain is proposed. The proposed flow rule is such that all stresses contribute to plastic flow rather than an effective stress. A simple version using anisotropic linear hardening is implemented. The mechanical properties, such as elastic parameters and hardening moduli are considered functions of the moisture ratio. An implicit variant of the material model is implemented in LS-DYNA®. The simulations with the proposed material model at different humidity levels follow the experimental results well for uniaxial loading, but discrepancies are obtained for simulation of biaxial loading tests.

    The moisture is assumed constant in the proposed model since the experiments are done in a moisture-controlled environment.

    Fulltekst (pdf)
    fulltext
  • 309.
    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. 

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  • 310.
    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.

  • 311.
    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.

  • 312.
    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.

  • 313. Backman, Anders
    et al.
    Bodin, Kenneth
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Högpresterande beräkningscentrum norr (HPC2N).
    Lacoursière, Claude
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Högpresterande beräkningscentrum norr (HPC2N).
    Servin, Martin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Democratizing CAE with Interactive Multiphysics Simulation and Simulators2012Konferansepaper (Annet vitenskapelig)
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  • 314.
    Backman, Sofi
    et al.
    Algoryx Simulation AB, Umeå, Sweden.
    Lindmark, Daniel
    Algoryx Simulation AB, Umeå, Sweden.
    Bodin, Kenneth
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Algoryx Simulation AB, Umeå, Sweden.
    Servin, Martin
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Algoryx Simulation AB, Umeå, Sweden.
    Mörk, Joakim
    Algoryx Simulation AB, Umeå, Sweden.
    Löfgren, Håkan
    Epiroc AB, Nacka, Sweden.
    Continuous Control of an Underground Loader Using Deep Reinforcement Learning2021Inngår i: Machines, E-ISSN 2075-1702, Vol. 9, nr 10, artikkel-id 216Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The reinforcement learning control of an underground loader was investigated in a simulated environment by using a multi-agent deep neural network approach. At the start of each loading cycle, one agent selects the dig position from a depth camera image of a pile of fragmented rock. A second agent is responsible for continuous control of the vehicle, with the goal of filling the bucket at the selected loading point while avoiding collisions, getting stuck, or losing ground traction. This relies on motion and force sensors, as well as on a camera and lidar. Using a soft actor–critic algorithm, the agents learn policies for efficient bucket filling over many subsequent loading cycles, with a clear ability to adapt to the changing environment. The best results—on average, 75% of the max capacity—were obtained when including a penalty for energy usage in the reward.

    Fulltekst (pdf)
    fulltext
  • 315.
    Baer, Máren Ingá
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Material- och solidmekanik.
    Crack propagation calculations in non-elastic metals2018Independent thesis Advanced level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [en]

    It is important to know the lifespan of a component, thus services can be planed. At Siemens Industrial Turbomachinery AB (SIT AB) develop and produce gas and steam turbines, the turbines are heavily strained by thermal and centrifugal forces during their life span which lead to cracking. Today there is no good crack propagation method for materials with large amount of plastic deformation and creep. At SIT a new method, ΔKBDCPP, has been developed that takes these phenomenon in consideration. It is assumed that the whole model has plastic material properties except circular elements at the crack front which have elastic properties. The new method is reviewed by doing simulations on a a specimen model in Franc3D together with the FE program Abaqus. There have been conducted thermo-mechanical fatigue (TMF) tests and 2D simulations on specimen to measure the crack propagation. The TMF tests where immitaded in new simulations with the method ΔKBDCPP. Forces, creep times, cycles and material data where emulated in the model and then simulated. The number of cycles per crack length for the isothermal simulations became higher then for the TMF tests. This is a expected result because the conditions are optimal during simulations, which they may not be during experimental test. The result of ΔKBDCPP are closer to the TMF test results then the 2D simulated ΔKeffective, another crack propagation calculation method. Additionally, out-of-phase (OP) simulations where carried out, in OP the maximum temperature and maximum stress do not coincide. When the temperature is at max the component is held in the minimum stress. For OP simulations the results became irregular, for one of the simulations the number of cycles per crack length became lower for the simulated specimen than for the TMF test, and contrariwise for the other OP simulation. However, it was concluded that the later was correct because the majority of the simulations, and all the isothermal simulations, gave this result. it also was the result for the isothermal simulations. One OP simulation was compared to a 2D simulation and here the method of ΔKBDCPP was also more accurate to the TMF tests. The method of ΔKBDCPP seem to function well however, the solving time for models with creep is long. A model with a small crack and creep is time consuming to simulate, which is a disadvantages.

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  • 316.
    Bagheri, R.
    et al.
    University of Zanjan, Iran.
    Ayatollahi, M.
    University of Zanjan, Iran.
    Mousavi, Mahmoud
    Aalto University, Finland.
    Analysis of cracked piezoelectric layer with imperfect non-homogeneous orthotropic coating2015Inngår i: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 93, s. 93-101Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Abstract The fracture problem for a medium composed of a cracked piezoelectric strip with functionally graded orthotropic coating is studied. The layer is subjected to anti-plane mechanical and in-plane electrical loading. In this paper, we first address, the problem of a screw dislocation located in a substrate which is imperfectly bonded to the coating. Then, in order to model the cracked piezoelectric layer, by means of the dislocation solution, we construct integral equations for the layer, in which the unknown variables are dislocation densities. These unknowns are determined through satisfaction of the boundary conditions on the crack faces. By use of the dislocation densities, the field intensity factors are determined. Several examples are presented to demonstrate the applicability of the proposed solution. ", keywords = Piezoelectric strip; Functionally graded layer; Imperfect bonding; Multiple cracks; Stress intensity factors, isbn = 0020-7403, doi=https://doi.org/10.1016/j.ijmecsci.2014.11.025

  • 317.
    Bagheri, R.
    et al.
    University of Zanjan, Iran.
    Ayatollahi, M.
    University of Zanjan, Iran.
    Mousavi, Mahmoud
    Aalto University, Finland.
    Analytical solution of multiple moving cracks in functionally graded piezoelectric strip2015Inngår i: Applied mathematics and mechanics, ISSN 0253-4827, E-ISSN 1573-2754, Vol. 36, nr 6, s. 777-792Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dynamic behaviors of several moving cracks in a functionally graded piezoelectric (FGP) strip subjected to anti-plane mechanical loading and in-plane electrical loading are investigated. For the first time, the distributed dislocation technique is used to construct the integral equations for FGP materials, in which the unknown variables are the dislocation densities. With the dislocation densities, the field intensity factors are determined. Moreover, the effects of the speed of the crack propagation on the field intensity factors are studied. Several examples are solved, and the numerical results for the stress intensity factor and the electric displacement intensity factor are presented graphically finally.

  • 318.
    Baghous, Nareg
    et al.
    Khalifa Univ Sci & Technol, Adv Digital & Addit Mfg ADAM Ctr, Abu Dhabi 127788, U Arab Emirates.;Khalifa Univ Sci & Technol, Sch Engn, Dept Mech Engn, POB 127788, Abu Dhabi, U Arab Emirates..
    Barsoum, Imad
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik. Khalifa Univ Sci & Technol, Adv Digital & Addit Mfg ADAM Ctr, Abu Dhabi 127788, U Arab Emirates.;Khalifa Univ Sci & Technol, Sch Engn, Dept Mech Engn, POB 127788, Abu Dhabi, U Arab Emirates..
    Al-Rub, Rashid K. Abu
    Khalifa Univ Sci & Technol, Adv Digital & Addit Mfg ADAM Ctr, Abu Dhabi 127788, U Arab Emirates.;Khalifa Univ Sci & Technol, Sch Engn, Dept Mech Engn, POB 127788, Abu Dhabi, U Arab Emirates..
    The effect of Lode parameter on the yield surface of Schoen's IWP triply periodic minimal surface lattice2022Inngår i: Mechanics of materials, ISSN 0167-6636, E-ISSN 1872-7743, Vol. 175, s. 104473-, artikkel-id 104473Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Owing to the advancements in additive manufacturing and increased applications of additively manufactured structures, it is essential to fully understand both the elastic and plastic behavior of cellular materials, which include the mathematically-driven sheet lattices based on triply periodic minimal surface (TPMS) that have received significant attention recently. The compressive elastic and plastic behaviors have been well established for many TPMS latticed structures, but not under multiaxial loading. Furthermore, TPMS lattices are compu-tationally expensive to model explicitly when used in latticing various structures for enhanced multi -functionality, and hence the need to develop accurate yield surfaces in order to capture their plastic behavior in a homogenized approach. The majority of previous yield surfaces developed for cellular materials originate from cellular foams, and limited attempts has been made to develop yield surfaces for TPMS lattices. In this study, a numerical modeling framework is proposed for developing the initial yield surface for cellular materials and is used to develop the initial yield surface for Schoen's IWP sheet-based TPMS cellular lattices. The effect of different loading conditions on the effective yield strength of the IWP sheet-based (IWP-s) TPMS lattice is numerically investigated, based on a single unit cell of IWP-s under fully periodic boundary conditions, assuming an elastic-perfectly plastic behavior of the base material, for relative densities (rho) ranging from 7% to 28%. In order to account for different loading conditions, the stress state is characterized in a generalized fashion through the Lode parameter (L). The effect of L is studied over a range of mean stress values (sigma m) to understand the effect of both L and sigma m on the effective yield strength. An initial yield surface is developed incorporating the effect of L, sigma m and rho, and is validated numerically showing rather good agreement. In the 3D principal stress space, the shape of the yield surface for the IWP-s lattice resembles the shape of a cocoa pod.

  • 319.
    Bahaloo, Hassan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Eidevåg, Tobias
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-41296 Gothenburg Sweden; Contamination and Core CFD, Volvo Car Corporation, SE-405 31 Gothenburg, Sweden.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Casselgren, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Abrahamsson, Per
    Technical Analysis, Fluid Mechanics, AFRY, Gothenburg, Sweden 412 63.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Ice Sintering: Dependence of Sintering Force on Temperature, Load, Duration, and Particle Size2022Inngår i: Svenska Mekanikdagar 2022 / [ed] Pär Jonsén; Lars-Göran Westerberg; Simon Larsson; Erik Olsson, Luleå tekniska universitet, 2022Konferansepaper (Fagfellevurdert)
  • 320.
    Bahaloo, Hassan
    et al.
    Department of Mechanical Engineering, University of New Hampshire, Durham.
    Li, Yaning
    Department of Mechanical Engineering, University of New Hampshire, Durham.
    Micropolar Modeling of Auxetic Chiral Lattices With Tunable Internal Rotation2019Inngår i: Journal of applied mechanics, ISSN 0021-8936, E-ISSN 1528-9036, Vol. 86, nr 4Artikkel i tidsskrift (Fagfellevurdert)
  • 321.
    Bahaloo, Hassan
    et al.
    Department of Mechanical and Industrial Engineering, Northeastern University, Boston, USA. Department of Mechanical and Industrial Engineering, Qatar University, Doha, Qatar.
    Papadopolus, Jim
    Department of Mechanical and Industrial Engineering, Northeastern University, Boston, USA. Department of Mechanical and Industrial Engineering, Qatar University, Doha, Qatar.
    Ghosh, Ranajay
    Department of Mechanical and Industrial Engineering, Northeastern University, Boston, USA.
    Mahdi, Elsadig
    Department of Mechanical and Industrial Engineering, Qatar University, Doha, Qatar.
    Vaziri, Ashkan
    Department of Mechanical and Industrial Engineering, Northeastern University, Boston, USA.
    Nayeb-Hashemi, Hamid
    Department of Mechanical and Industrial Engineering, Northeastern University, Boston, USA.
    Transverse vibration and stability of a functionally graded rotating annular disk with a circumferential crack2016Inngår i: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 113, s. 26-35Artikkel i tidsskrift (Fagfellevurdert)
  • 322.
    Bahaloohoreh, Hassan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Experiments and simulations on the mechanics of ice and snow2023Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this study, experiments and simulations were conducted to investigate ice and snow. The ice sintering force as a function of temperature, pressing force (contact load), contact duration, and particle size during the primary stage of sintering was formulated using experimental methods along with an approximate, semi-analytic, close-form solution. It was shown that the ice sintering force increases nearly linear with increasing external pressing force but best approximated as a power law for dependency on both contact duration and particle size. Moreover, the exponent of the power law for size dependence is around the value predicted by general sintering theory. The temperature dependence of the sintering force is highly nonlinear and follows the Arrhenius equation. It was observed that at temperatures closer to the melting point, a liquid bridge is observed upon these paration of the contacted ice particles. The ratio of ultimate tensile strength of ice to the axial stress concentration factor in tension is found as an important factor in determining the sintering force, and a value of nearly 1.1 MPa was estimated to best catch the sintering force of ice in different conditions. From the temperature dependency, the activation energy is calculated to be around 41.4 kJ/mol, which is close to the previously reported value. Also, the results for the sintering force suggest that smaller particles are “stickier” than larger particles. Moreover, cavitation and surface cracking is observed during the formation of the ice particles and these can be one of the sources for the variations observed in the measured ice sintering force values.

    The presence of a capillary bridge in contact between an ice particle and a "smooth" (or rough) Aluminum surface at relative humidity around 50% and temperatures below the melting point was experimentally demonstrated. Experiments were conducted under controlled temperature conditions and the mechanical instability of the bridge upon separation of the ice particle from the Aluminum surface with a constant speed was considered. It was observed that a liquid bridge with a more pronounced volume at temperatures near the melting point is formed. It was showen that the separation distance is proportional to the cube root of the volume of the bridge. The volume of the liquidbridge is used to estimate the thickness of the liquid layer on the ice particle and the estimated value was shown to be within the range reported in the literature. The thickness of the liquid layer decreases from nearly 56 nm at -1.7◦C to 0.2 nm at -12.7◦C. The dependence can be approximated with a power law, proportional to (TM − T)−β, where β < 2.6. We further observe that for a rough surface, the capillary bridge formation in the considered experimental conditions vanishes.

    The Discrete Element Method (DEM) was employed to simulate the filling behavior of dry snow. Snow as a heterogeneous, hot material which is constituted from spherical ice particles which can form bonds. The bonding behavior of ice particles is important in determining the macroscopic behavior of snow. The bond diameter of ice-ice contacts as a function of time, compressive load, and strain rate is used and a DEM for dry snow was developed and programmed in MATLAB. A beam element with implemented damage model was used in the simulation. The simulated parameters were macroscopic angle of repose, packing density, and surface conditions as a function of temperature and fillingrate. The DEM results were able to verify the existing published experimental data. The simulation results showed that angle of repose of snow decreased with decreasing the temperature, the surface became irregular due to particles rotation and re-arrangement for lower falling speeds of particles, and density increased with depth of deposition.

    Fulltekst (pdf)
    fulltext
  • 323.
    Bahaloohoreh, Hassan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Eidevåg, Tobias
    Department of Chemistry and Chemical Engineering, Chalmers University of Technology, SE-41296 Gothenburg, Sweden; Contamination and Core CFD, Volvo Car Corporation, SE-405 31 Gothenburg, Sweden.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Casselgren, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Forsberg, Fredrik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Abrahamsson, Per
    Technical Analysis, Fluid Mechanics, AFRY, Gothenburg 412 63, Sweden.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Ice sintering: Dependence of sintering force on temperature, load, duration, and particle size2022Inngår i: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 131, nr 2, artikkel-id 025109Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We present experiments along with an approximate, semi-analytic, close-form solution to predict ice sintering force as a function of temperature, contact load, contact duration, and particle size during the primary stage of sintering. The ice sintering force increases nearly linear with increasing contact load but nonlinear with both contact duration and particle size in the form of a power law. The exponent of the power law for size dependence is around the value predicted by general sintering theory. The temperature dependence of the sintering force is also nonlinear and follows the Arrhenius equation. At temperatures closer to the melting point, a liquid bridge is observed upon the separation of the contacted ice particles. We also find that the ratio of ultimate tensile strength of ice to the axial stress concentration factor in tension is an important factor in determining the sintering force, and a value of nearly 1.1 MPa can best catch the sintering force of ice in different conditions. We find that the activation energy is around 41.4KJ/mol41.4KJ/mol, which is close to the previously reported data. Also, our results suggest that smaller particles are “stickier” than larger particles. Moreover, during the formation of the ice particles, cavitation and surface cracking is observed which can be one of the sources for the variations observed in the measured ice sintering force.

    Fulltekst (pdf)
    fulltext
  • 324.
    Bajuri, M. N.
    et al.
    University of Oxford, England; University of Teknol Malaysia, Malaysia.
    Isaksson, Hanna
    Lund University, Sweden.
    Eliasson, Pernilla T.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Avdelningen för kliniska vetenskaper. Linköpings universitet, Medicinska fakulteten.
    Thompson, Mark S.
    University of Oxford, England.
    A hyperelastic fibre-reinforced continuum model of healing tendons with distributed collagen fibre orientations2016Inngår i: Biomechanics and Modeling in Mechanobiology, ISSN 1617-7959, E-ISSN 1617-7940, Vol. 15, nr 6, s. 1457-1466Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The healing process of ruptured tendons is problematic due to scar tissue formation and deteriorated material properties, and in some cases, it may take nearly a year to complete. Mechanical loading has been shown to positively influence tendon healing; however, the mechanisms remain unclear. Computational mechanobiology methods employed extensively to model bone healing have achieved high fidelity. This study aimed to investigate whether an established hyperelastic fibre-reinforced continuum model introduced by Gasser, Ogden and Holzapfel (GOH) can be used to capture the mechanical behaviour of the Achilles tendon under loading during discrete timepoints of the healing process and to assess the models sensitivity to its microstructural parameters. Curve fitting of the GOH model against experimental tensile testing data of rat Achilles tendons at four timepoints during the tendon repair was used and achieved excellent fits (0.9903 amp;lt; R-2 amp;lt; 0.9986). A parametric sensitivity study using a three-level central composite design, which is a fractional factorial design method, showed that the collagen-fibre-related parameters in the GOH model-kappa, k(1) and k(2)-had almost equal influence on the fitting. This study demonstrates that the GOH hyperelastic fibre-reinforced model is capable of describing the mechanical behaviour of healing tendons and that further experiments should focus on establishing the structural and material parameters of collagen fibres in the healing tissue.

  • 325. Balieu, R.
    et al.
    Lauro, F.
    Bennani, B.
    Delille, R.
    Matsumoto, T.
    Mottola, E.
    A fully coupled elastoviscoplastic damage model at finite strains for mineral filled semi-crystalline polymer2013Inngår i: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 51, s. 241-270Artikkel i tidsskrift (Fagfellevurdert)
  • 326.
    Balieu, Romain
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Byggvetenskap, Bro- och stålbyggnad.
    Modèle viscoélastique-viscoplastique couplé avec endommagement pour les matériaux polymères semi-cristallins2012Manuskript (preprint) (Annet vitenskapelig)
  • 327.
    Balieu, Romain
    et al.
    KTH, Skolan för arkitektur och samhällsbyggnad (ABE), Transportvetenskap, Väg- och banteknik.
    Lauro, F.
    Bennani, B.
    Haugou, G.
    Chaari, F.
    Matsumoto, T.
    Mottola, E.
    Damage at high strain rates in semi-crystalline polymers2015Inngår i: International Journal of Impact Engineering, ISSN 0734-743X, E-ISSN 1879-3509, Vol. 76, s. 1-8Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A specific damage characterization method using Digital Image Correlation for semi-crystalline polymers is proposed for a wide range of strain rates. This damage measurement is an extension of the SEE method [16] which was developed to characterize the behaviour laws at constant strain rates of polymeric materials. This procedure is compared to the well-known damage characterization by loss of stiffness technique under quasi-static loading. In addition, an in-situ tensile test, carried out in a microtomograph, is used to observe the cavitation phenomenon in real time. The different ways used to evaluate the damage evolution are compared and the proposed technique is also suitable for measuring the ductile damage observed in semi-crystalline polymers under dynamic loading.

  • 328.
    Banaem, Hossein Y
    et al.
    Tehran University of Medical Science.
    Ahmadian, Alireza
    Tehran University of Medical Science.
    Saberi, Hooshangh
    Tehran University of Medical Science.
    Daneshmehr, Alireza
    University of Tehran.
    Khodadad, Davood
    Tehran University of Medical Science.
    Brain tumor modeling: glioma growth and interaction with chemotherapy2011Inngår i: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 8285Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In last decade increasingly mathematical models of tumor growths have been studied, particularly on solid tumors which growth mainly caused by cellular proliferation. In this paper we propose a modified model to simulate the growth of gliomas in different stages. Glioma growth is modeled by a reaction-advection-diffusion. We begin with a model of untreated gliomas and continue with models of polyclonal glioma following chemotherapy. From relatively simple assumptions involving homogeneous brain tissue bounded by a few gross anatomical landmarks (ventricles and skull) the models have been expanded to include heterogeneous brain tissue with different motilities of glioma cells in grey and white matter. Tumor growth is characterized by a dangerous change in the control mechanisms, which normally maintain a balance between the rate of proliferation and the rate of apoptosis (controlled cell death). Result shows that this model closes to clinical finding and can simulate brain tumor behavior properly.

  • 329.
    Banaem, Hossein Yousefi
    et al.
    Department of Biomedical Engineering, Faculty of Advance Medical Technology, Isfahan University of Medical Science.
    Kermani, Saeed
    Department of Biomedical Engineering, Faculty of Advance Medical Technology, Isfahan University of Medical Science.
    Sarrafzadeh, Omid
    Department of Biomedical Engineering, Faculty of Advance Medical Technology, Isfahan University of Medical Science.
    Khodadad, Davood
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    An improved spatial FCM algorithm for cardiac image segmentation2013Inngår i: 13th Iranian Conference on Fuzzy Systems: IFSC 2013, Qazvin, Iran; 27-29 August 2013, Piscataway, NJ: IEEE Communications Society, 2013, artikkel-id 6675656Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Image segmentation is one of challenging field in medical image processing. Segmentation of cardiac wall is one of challenging work and it is very important step in evaluation of heart functionality by existing methods. For cardiac image analysis, Fuzzy C- Means (FCM) algorithm proved to be superior over the other clustering approaches in segmentation field. However, the nave FCM algorithm is sensitive to noise because of not considering the spatial information in the image. In this paper an improved FCM algorithm is formulated by incorporating the spatial domain neighborhood information into the membership function for clustering (ISFCM). In this paper we applied improved Fuzzy c-Means with spatial information for left ventricular wall segmentation. Obtained results showed that the proposed method can segment cardiac wall automatically with acceptable accuracy. The comparison of proposed method with nave FCM proved that ISFCM can segment with more accuracy than nave FCM.

  • 330.
    Bandari, Shiva Ram
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Investigation on Flow Control Valve by CFD Simulation2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    In a water distribution system, Flow Control Valve is used to control the flow rate in the pipeline connections. In this thesis, a fixed flow control valve is investigated to reduce the flow rate and set to deliver the pre-set flow of 5-6 LPM (litre per minute). Which helps to distribute the water for a maximum period and maintains the usage only for the drinking purpose. A geometry of FCV with a ball check valve is implemented, where the ball check helps to stop the back flow of the fluid from the valve. Detailed inspection of dynamic changes in pressure and flow velocity in the valve are conducted through simulation. The study of fluid properties describes the expected design and specifies the flow structure in the valve. The results of this project demonstrate a good performance of the design-build and influence the requirements. The obtained values in the simulation, analytical and experimental results are compatible, which concludes the survey of FCV is equipped to custom.

    Fulltekst (pdf)
    fulltext
  • 331. Banks-Sills, Leslie
    et al.
    Ståhle, Per
    Malmö högskola, Teknik och samhälle (TS).
    Svensson, Ingrid
    Eliaz, Noam
    Strain Driven Transport for Bone Modeling at the Periosteal Surface2011Inngår i: Mathematical Biosciences, ISSN 0025-5564, E-ISSN 1879-3134, Vol. 230, nr 1, s. 37-44Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Bone modeling and remodeling has been the subject of extensive experimental studies. There have been several mathematical models proposed to explain the observed behavior, as well. A different approach is taken here in which the bone is treated from a macroscopic view point. In this investigation, a one-dimensional analytical model is used to shed light on the factors which play the greatest role in modeling or growth of cortical bone at the periosteal surface. It is presumed that bone growth is promoted when increased amounts of bone nutrients, such as nitric oxide synthase (NOS) or messenger molecules, such as prostaglandin E2 (PGE2), seep out to the periosteal surface of cortical bone and are absorbed by osteoblasts. The transport of the bone nutrients is assumed to be a strain controlled process. Equations for the flux of these nutrients are written for a one-dimensional model of a long bone. The obtained partial differential equation is linearized and solved analytically. Based upon the seepage of nutrients out of the bone, the effect of loading frequency, number of cycles and strain level is examined for several experiments that were found in the literature. It is seen that bone nutrient seepage is greatest on the tensile side of the bone; this location coincides with the greatest amount of bone modeling

    Fulltekst (pdf)
    FULLTEXT01
  • 332.
    Banno, Yuki
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik. Department of Civil Engineering, Gifu University, Gifu, Japan.
    Kinoshita, K.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik.
    Numerical investigation of influence of under- and over- treatment on residual stress state induced by HFMI2021Inngår i: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 65, nr 11, s. 2135-2146Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This study aims to investigate influence of under- and over-treatment on residual stress state induced by HFMI numerically. Finite element simulations were performed using a flat plate model considering S355 where feed rate and the number of hits were varied. To reduce computational time, the mass scaling method was adopted to the simulations. In addition, in order to survey influence of surface removal on residual stress state, electropolishing was conducted after the HFMI simulation. Additional simulations were performed on bead on plate model considering JIS-SM400 in order to investigate applicability of isotropic hardening model for residual stress estimation. From the results, the mass scaling method can result in reducing computational time more than 90% with reasonable good estimation of the residual stresses.The investigations regarding under- and over-treatment reveal that high feed rate mainly influences residual stress state on the treated surface and the number of hits is independent of amount of induced residual stress. Surface removal after the simulation can result in slightly improving the accuracy of the estimated residual stresses. The simulations to bead on plate model give reasonable results in a depth of around 0.2 mm even when the residual stresses due to welding is disregarded. 

  • 333.
    Banno, Yuki
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Teknisk mekanik.
    Kinoshita, K.
    Ishikawa, T.
    Anami, K.
    Influence of grid blast on the fatigue strength improvement by peening2021Inngår i: Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations - Proceedings of the 10th International Conference on Bridge Maintenance, Safety and Management, IABMAS 2020, CRC Press/Balkema , 2021, s. 3165-3173Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this study, to evaluate the influence of grid blast following to the peening process on the fatigue strength improvement, residual stress measurement and fatigue tests have been conducted. Examined peening processes were UIT, PPP and HP with ICR apparatus. For the residual stress measurement, plate and on-bead specimens made of JIS-SM400, SBHS400, SBHS500 and SBHS700 were used, and X-ray diffraction method was applied to the measurement. The results concluded that the differences in the compressive residual stress distribution in the vicinity of peened area with and without blast are not so significant. For the fatigue tests, out-of-plane gusset welded joint specimens made of JIS-SM490 and SBHS500 were used. Fatigue tests were conducted under stress ratio R=0.0 and 0.5. Fatigue tests showed that fatigue strength of peened specimens with blast are almost the same as that of peened specimens without blast, and those results were observed independently of steel grade and of peening methods.

  • 334.
    Baptista, Marcia
    et al.
    University of Lisbon, Instituto Superior Tecnico,Lisbon, Portugal.
    Mishra, Madhav
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Henriques, Elsa
    University of Lisbon, Instituto Superior Tecnico,Lisbon, Portugal.
    Prendinger, Helmut
    National Institute of Informatics,Tokyo, Japan.
    Using Explainable Artificial Intelligence to Interpret RemainingUseful Life Estimation with Gated Recurrent UnitManuskript (preprint) (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    In engineering, prognostics can be defined as the estimation of the remaining useful life of a system given current and past condition. This field has drawn much attention from research, industry, and government as this kind of technology can help improve the efficiency and lower the costs of maintenance in a variety of technical applications. An approach to prognostics that has gained increasing attention is the use of datadriven methods. These methods typically use pattern recognition and machine learning to estimate the residual life of equipment based on historical data. Despite their promising results, a major disadvantage is that it is difficult to interpretthis kind of models i.e. to understand why a certain prediction of remaining useful life was made at a certain point in time. Model interpretability is however of crucial importance to facilitate the use of data-driven prognostics in domains such as aeronautics and energy, where certification is critical. To help address this issue, we use the Local Interpretable Modelagnostic Explanations (LIME) from the field of eXplainable Artificial Intelligence (XAI) to analyze the prognostics of a Gated Recurrent Unit (GRU) on the C-MAPSS data. We select the GRU as this is a deep learning model which a) has an explicit temporal dimension and b) has shown promising results in the field of prognostics. Our results suggest that it is possible to obtain information about feature importance of the GRU both globally (for the whole model) and locally (for a given RUL prediction.

    Fulltekst (pdf)
    Explainable Artificial Intelligence
  • 335.
    Baravdish, George
    et al.
    Linköpings universitet, Institutionen för teknik och naturvetenskap, Kommunikations- och transportsystem. Linköpings universitet, Tekniska fakulteten.
    Borachok, Ihor
    Ivan Franko Natl Univ Lviv, Ukraine.
    Chapko, Roman
    Ivan Franko Natl Univ Lviv, Ukraine.
    Johansson, Tomas
    Aston Univ, England.
    Slodicka, Marian
    Univ Ghent, Belgium.
    An iterative method for the Cauchy problem for second-order elliptic equations2018Inngår i: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 142, s. 216-223Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The problem of reconstructing the solution to a second-order elliptic equation in a doubly-connected domain from knowledge of the solution and its normal derivative on the outer part of the boundary of the solution domain, that is from Cauchy data, is considered. An iterative method is given to generate a stable numerical approximation to this inverse ill-posed problem. The procedure is physically feasible in that boundary data is updated with data of the same type in the iterations, meaning that Dirichlet values is updated with Dirichlet values from the previous step and Neumann values by Neumann data. Proof of convergence and stability are given by showing that the proposed method is an extension of the Landweber method for an operator equation reformulation of the Cauchy problem. Connection with the alternating method is discussed. Numerical examples are included confirming the feasibility of the suggested approach.

    Fulltekst (pdf)
    fulltext
  • 336.
    Barba, D.
    et al.
    Univ Oxford, England.
    Alabort, E.
    Univ Oxford, England.
    Garcia-Gonzalez, D.
    Univ Oxford, England.
    Moverare, Johan
    Linköpings universitet, Institutionen för ekonomisk och industriell utveckling, Konstruktionsmaterial. Linköpings universitet, Tekniska fakulteten.
    Reed, R. C.
    Univ Oxford, England.
    Jerusalem, A.
    Univ Oxford, England.
    A thermodynamically consistent constitutive model for diffusion-assisted plasticity in Ni-based superalloys2018Inngår i: International journal of plasticity, ISSN 0749-6419, E-ISSN 1879-2154, Vol. 105, s. 74-98Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An elasto-viscoplastic thermodynamically consistent constitutive model for diffusion-assisted phase transformations is presented here. The model accounts for the different deformation mechanisms, their time dependence, the crystal rotations produced by microtwin propagation and the chemistry-plasticity coupling occurring at high temperature. It is applied to the study of the chemically assisted microtwinning observed in Ni-based superalloys in the temperature range of 600-800 degrees C. The model parameters are calibrated against multi-directional mechanical data from tensile creep tests of single crystal superalloy MD2. The constitutive model is then implemented into a crystal plasticity finite element code to study the activation of the different deformation mechanisms within single crystal and polycrystalline aggregates. Doing so, a relation between the rotations of the crystal and the creep life of the different crystal orientations is established. The results eventually reveal the critical role of the strong anisotropy of microtwin formation on the asymmetric behavior of the alloy and its relevant role on the mechanical performance.

  • 337.
    Barbagallo, Mathias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Finnveden, Svante
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    A natural variational principle for Biot's equation: Waveguide FE and SEA of multilayered structures comprising porous materials2011Konferansepaper (Annet vitenskapelig)
  • 338.
    Barbagallo, Mathias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Finnveden, Svante
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    A self-adjoint variational principle for anisotropic viscoelastic Biot’s equations2013Inngår i: International Journal of Engineering Science, ISSN 0020-7225, E-ISSN 1879-2197, Vol. 63, s. 71-83Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A variational principle for anisotropic viscoelastic Biot’s equations of motion is presented. It is based upon an extended Hamilton’s principle, also valid for dissipative systems. Using this principle, a functional analogous to the Lagrangian is defined, starting from Biot’s variational formulation based on frame and fluid displacements. Then, a mixed displacement–pressure formulation is presented, which reduces the number of variables of response from six to four. The corresponding functional analogous to the Lagrangian is derived making full use of variational calculus. The derived functionals are self-adjoint and stationary for true motion.

  • 339.
    Barbagallo, Mathias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Finnveden, Svante
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Characterisation of a generic trim-panel: sound reduction index and material parameters2013Rapport (Annet vitenskapelig)
  • 340.
    Barbagallo, Mathias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Finnveden, Svante
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Spatial energy decay and indirect couplings in statistical energy analysis2010Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Spatial energy decay within elements affects the validity of SEA. This is particularly significant for chains of similar long well-connected structures such as ventilation ducts, fluid-filled pipes and rib-stiffened plates found in ships, aircraft and railway cars. The effects of spatial energy decay on the high frequency response of one-dimensional well-connected elements are herein studied by comparing calculations by an SEA, a spectral finite element method and an SEA-like model. An SEA only includes direct coupling loss factors (CLFs); conversely, an SEA-like model also contains indirect CLFs. At high frequencies, the spatial energy decay increases and SEA overestimates the energies in all elements away from the excitation. Moreover, the indirect CLFs in the SEA-like model have to be considered when evaluating the energy flows, as the accumulated spatial decay from the excitation to the observed point increases. Thus, SEA cannot predict the high frequency response of similar long well-connected elements and alternative formulations are needed.

  • 341.
    Barbagallo, Mathias
    et al.
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Finnveden, Svante
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Strukturakustik.
    Liu, Hao
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, MWL Marcus Wallenberg Laboratoriet.
    Statistical energy analysis of the sound transmission through layered panels using a variational formulation of the porous materialArtikkel i tidsskrift (Annet vitenskapelig)
  • 342.
    Barlo, Alexander
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Failure Prediction of Complex Load Cases in Sheet Metal Forming: Emphasis on Non-Linear Strain Paths, Stretch-Bending and Edge Effects2023Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    With the increased focus on reducing carbon emissions in today’s society, several industries have to overcome new challenges, where especially the automotive industry is under a lot of scrutiny to deliver improved and more environmentally friendly products. To meet the demands from customers and optimize vehicles aerodynamically, new cars often contain complex body geometries, together with advanced materials that are introduced to reduce the total vehicle weight. With the introduction of the complex body components and advanced materials,one area in the automotive industry that has to overcome these challenges is manufacturing engineering, and in particular the departments working with the sheet metal forming process. In this process complex body component geometries can lead to non-linear strain paths and stretch bending load cases, and newly introduced advanced materials can be prone to exhibit behaviour of edge cracks not observed in conventional sheet metals. This thesis takes it onset in the challenges seen in industry today with predicting failure of the three complex load cases: Non-Linear Strain Paths, Stretch-Bending,and Edge Cracks. Through Finite Element simulation attempts are made to accurately predict failure caused by aforementioned load cases in industrial components or experimental setups in an effort to develop post-processing methods that are applicable to all cases.

    Fulltekst (pdf)
    fulltext
  • 343.
    Barlo, Alexander
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Sigvant, Mats
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Kesti, V.
    SSAB Europe Oy, Finland..
    Islam, Md. Shafiqul
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Tuan Pham, Quoc
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Pilthammar, Johan
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Determination of Edge Fracture Limit Strain for AHSS in the ISO-16630 Hole Expansion Test2023Inngår i: 42ND CONFERENCE OF THE INTERNATIONAL DEEP DRAWING RESEARCH GROUP / [ed] Asnafi, N Lindgren, LE, IOP PUBLISHING LTD , 2023, Vol. 1284, artikkel-id 012027Konferansepaper (Fagfellevurdert)
    Abstract [en]

    With the increased demand for application of sustainable materials and lightweight structures, the sheet metal forming industry is forced to push existing materials to the limits. One area where this is particular difficult is when it comes to assessing the formability limit for sheet edges. For decades, the ISO-16630 Hole Expansion Test (HET) has been the industry standard for expressing the edge formability of sheet metals through the Hole Expansion Ratio (HER). However, in recent years, this test has been criticized for its high scatter in results for repeated experiments. This scatter has been suspected to be caused by the operator-reliant post-processing of the test, or variations in the cutting conditions for the different test specimens. This study investigates the impact of shifting the evaluation point of the test from the through-thickness crack to the onset of surface failure on the reported scatter, as well as performs inverse modeling of the Hole Expansion Test to obtain an edge limit strain value.

    Fulltekst (pdf)
    fulltext
  • 344.
    Barlo, Alexander
    et al.
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Sigvant, Mats
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Manopulo, Niko
    AutoForm Development GmbH, CHE.
    Islam, Md. Shafiqul
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Pilthammar, Johan
    Blekinge Tekniska Högskola, Fakulteten för teknikvetenskaper, Institutionen för maskinteknik.
    Failure Prediction of Automotive Components Utilizing a Path Independent Forming Limit Criterion2022Inngår i: Key Engineering Materials / [ed] Vincze G., Barlat F., Trans Tech Publications Inc., 2022, s. 906-916Konferansepaper (Fagfellevurdert)
    Abstract [en]

    An area in the automotive industry that receives a lot of attention today is the introduction of lighter and more advanced material grades in order to reduce carbon emissions, both during production and through reduced fuel consumption. As the complexity of the introduced materials and component geometries increases, so does the need for more complex failure prediction approaches. A proposed path-independent failure criterion, based on a transformation of the limit curve into an alternative evaluation space, is investigated. Initially, the yield criterion used for this transformation of the limit curve was investigated. Here it was determined that the criterion for the transformation could not be decoupled from the material model used for the simulation. Subsequently, the approach using the transformed limit curve was tested on an industrial case from Volvo Cars, but a successful failure prediction was not obtained. © 2022 The Author(s). Published by Trans Tech Publications Ltd, Switzerland.

    Fulltekst (pdf)
    fulltext
  • 345.
    Barrskog, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.), Hållfasthetslära (Avd.).
    Implementation of methods for computation of Tooth Interior Fatigue Fracture2017Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    For a company like Scania CV AB, a vast number of laws and regulations has to be considered when developing a truck. In the constant struggle to keep the generated noise below the allowed levels, the gears are made more slender and flexible. The slenderness in combination with case hardening has brought a new type of gear fracture into the light.The Tooth Interior Fatigue Fracture, TIFF. A 2D-method, and a tool for engineers, was developed in the early 2000’s. However, this tool did not provide sufficient accuracy andcompatibility with the current design process to be adopted by the engineers at Scania.This thesis expands on the current 2D-model and attempts to improve the accuracy by bringing the analysis to 3D. Furthermore, the computational tool is developed in Pythonto allow for a more streamlined interface with the current workflow.The proposed method approximates the tooth as a cantilever-beam, and is only evaluated for this case. However, the stresses are computed with good accuracy. The onlydiscrepancy is one of the stress components, where the error is about 50%. This error isderived from the decision to, in torsion, model the cross-section of the gear tooth as an ellipse. The method has potential to be incorporated into the current design process, but the accuracy of the stresses due to torsion has to be improved, and some of the equations has to be adapted before real gear geometries can be considered.

  • 346. Barsoum, I.
    et al.
    Faleskog, Jonas
    KTH, Skolan för teknikvetenskap (SCI), Hållfasthetslära (Inst.).
    Pingle, S.
    The effect of stress state on ductility in the moderate stress triaxiality regime of medium and high strength steels2012Inngår i: International Journal of Mechanical Sciences, ISSN 0020-7403, E-ISSN 1879-2162, Vol. 65, nr 1, s. 203-212Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Experiments on double notched tube specimens subjected to tension and torsion were conducted by Barsoum and Faleskog (2007) [8,9]. In this study a complementary experimental investigation was conducted on tensile round circumferentially notched bar specimens. The results from the current study were compared with the results from the double circumferentially notched tube specimens with stress triaxiality larger than 0.7 in order to asses the influence of the Lode parameter on ductility in the moderate stress triaxiality regime. The effective plastic strain, the stress triaxiality T and the Lode parameter L were determined at the center of the notch up to the point of onset of failure by means of finite element. The influence of the Lode parameter on the failure strain was significant for the high strength and low hardening material, whereas for the medium strength and high hardening material the influence of the Lode parameter was less distinguished. The experimental results were then analyzed with the micromechanical model proposed by Barsoum and Faleskog (2011) [15], which is based on the assumption that ductile failure is a consequence of that plastic deformation localizes into a band. The band consists of a square array of equally sized cells, with a spherical void located in the center of each cell, which allows for studying a single 3D unit cell with fully periodic boundary conditions. The unit cell is subjected to a proportional loading such that it resembles the stress state, in terms of T and L, from the experiments. The micromechanical model captures the experimental trend and the influence of L on ductility very well. It is found that the Lode parameter sensitivity increases by the combination of increase in the yield strength and decrease in strain hardening. The fractographical analysis reveals that this Lode parameter sensitivity is associated with the failure characteristics of the material.

  • 347.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Avancerade metoder för noggrannare dimensionering av svetsade konstruktioner2009Inngår i: Svetsen, ISSN 0039-7091, Vol. 68, nr 3Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
  • 348.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Fatigue Assessment of Cruciform Joints Welded with Different Methods2005Inngår i: IIW Doc. No. XIII-2074-05, 2005Konferansepaper (Annet vitenskapelig)
  • 349.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Fatigue design of welded structures: effect of weld quality and residual stresses, XIII-2312-102010Konferansepaper (Annet vitenskapelig)
  • 350.
    Barsoum, Zuheir
    KTH, Skolan för teknikvetenskap (SCI), Farkost och flyg, Lättkonstruktioner.
    Fatigue Strength of cruciform joints fabricated with different welding processes2007Inngår i: International Symposium on Integrated Design and Manufacturing of Welded Structures, Eskilstuna, 2007Konferansepaper (Annet vitenskapelig)
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