| 1. |
- Andersson, Robin, 1986, et al.
(författare)
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An efficient approach to the analysis of rail surface irregularities accounting for dynamic train–track interaction and inelastic deformations
- 2015
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Ingår i: Vehicle System Dynamics. - : Informa UK Limited. - 1744-5159 .- 0042-3114. ; 53:11, s. 1667-1685
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Tidskriftsartikel (refereegranskat)abstract
- A two-dimensional computational model for assessment of rolling contact fatigue induced by discrete rail surface irregularities, especially in the context of so-called squats, is presented. Dynamic excitation in a wide frequency range is considered in computationally efficient time-domain simulations of high-frequency dynamic vehicle-track interaction accounting for transient non-Hertzian wheel–rail contact. Results from dynamic simulations are mapped onto a finite element model to resolve the cyclic, elastoplastic stress response in the rail. Ratcheting under multiple wheel passages is quantified. In addition, low cycle fatigue impact is quantified using the Jiang–Sehitoglu fatigue parameter. The functionality of the model is demonstrated by numerical examples.
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| 2. |
- Andersson, Robin, 1990, et al.
(författare)
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EMBRACE: The emotion sharing bracelet
- 2015
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Ingår i: Proceedings of SIDeR’15 – student interaction design research conference.
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Konferensbidrag (refereegranskat)abstract
- In this study we present Embrace; a wearable device that explores the potential of wearable technology harnessing the affordance of human form and deformable displays. We research new ways of communicating with loved ones in order to improve the experience of connectedness when they are apart. Embrace is a wearable device in the form of a bracelet that shares emotion between peers by providing both visual and haptic feedback. Other devices like smartphones and tablets have a rigid form and material. In contrast, the deformable display used in Embrace enables the user to wear the technology seamlessly on the body. The haptic feedback for sharing emotions is believed to provide a different experience since the physical sensation is more close to feeling heartbeats, hugs, and skin contact, compared to only visual information of today’s mobile devices.
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| 3. |
- Andersson, Robin, 1986, et al.
(författare)
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Evaluation of stress intensity factors under multiaxial and compressive conditions using low order displacement or stress field fitting
- 2018
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Ingår i: Engineering Fracture Mechanics. - : Elsevier BV. - 0013-7944. ; 189, s. 204-220
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Tidskriftsartikel (refereegranskat)abstract
- A methodology for evaluation of stress intensity factors from the asymptotic displacement (or stress) fields at a crack front is proposed. The methodology strives to be of practical use in conjunction with commercial FE-codes, also when approaches such as XFEM are employed. To this end, the matching of the fields is carried out through a minimalistic, low order, ansatz of the displacement and stress fields. As demonstrated, the proposed methodology can deal with multiaxial loading of curved crack fronts in three-dimensional bodies. The methodology shows good accuracy also for compressive loading when crack face friction can be neglected.
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| 4. |
- Andersson, Robin, 1986, et al.
(författare)
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Integrated analysis of dynamic vehicle-track interaction and plasticity induced damage in the presence of squat defects
- 2015
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Ingår i: Proceedings of the 10th International International Conference on Contact Mechanics and Wear of Rail/Wheel Systems, Colorado Springs, USA, August-September 2015.
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Konferensbidrag (refereegranskat)abstract
- Despite significant efforts, the mechanisms behind the formation of squats – a form of rolling contact fatigue damage – are not fully understood. This study employs numerical simulations to investigate the propensity of squat initiation in the vicinity of small, isolated rail surface irregularities. Time domain dynamic vehicle–track interaction analysis is used to obtain wheel–rail contact stress distributions, which are mapped onto a continuum finite element model that accounts for plastic deformation of the rail material. The evaluated stress and strain fields are quantified using two RCF impact measures: accumulated effective strain and the Jiang-Sehitoglu multiaxial low cycle fatigue parameter. It is shown that the RCF impact increases with increasing size of the surface irregularity and that clustering of irregularities might strongly promote RCF. The friction coefficient is identified as a very influential parameter. Further, the effect of variations in friction along the rail is evaluated. It is shown that a short rail section of low friction results in fairly high RCF impact.
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| 5. |
- Andersson, Robin, 1986, et al.
(författare)
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Integrated analysis of dynamic vehicle–track interaction and plasticity induced damage in the presence of squat defects
- 2016
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Ingår i: Wear. - : Elsevier BV. - 0043-1648. ; 366-367:SI, s. 139-145
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Tidskriftsartikel (refereegranskat)abstract
- Despite significant efforts, the mechanisms behind the formation of squats – a form of rolling contact fatigue (RCF) damage – are not fully understood. This study employs numerical simulations to investigate the propensity of squat initiation in the vicinity of small, isolated rail surface irregularities. Time-domain dynamic vehicle–track interaction analysis is used to obtain wheel–rail contact stress distributions, which are mapped onto a continuum finite element model that accounts for plastic deformation of the rail material. The evaluated stress and strain fields are quantified using two RCF impact measures: accumulated effective strain and the Jiang–Sehitoglu multiaxial low cycle fatigue parameter. It is shown that the RCF impact increases with increasing size of the surface irregularity and that clustering of irregularities might strongly promote RCF. The friction coefficient is identified as a very influential parameter and also the effect of variations in friction along the rail is evaluated.
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| 6. |
- Andersson, Robin, 1986, et al.
(författare)
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Numerical assessment of the loading of rolling contact fatigue cracks close to rail surface irregularities
- 2020
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Ingår i: Fatigue and Fracture of Engineering Materials and Structures. - : Wiley. - 8756-758X .- 1460-2695. ; 43:5, s. 947-954
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Tidskriftsartikel (refereegranskat)abstract
- Rolling contact fatigue damage of railway rails in the form of squats, characterised by local depressions and cracks located at the rail surface, has been linked to the occurrence of local rail surface irregularities. This study concerns rolling contact fatigue cracks in the vicinity of fairly smooth surface irregularities, here denoted dimples. The influence of factors such as dimple geometry, cluster effects, and crack size is evaluated. To this end, dynamic vehicle–track simulations featuring realistic wheel and rail profiles are employed to characterise the dynamic impact during a wheel passage. The contact load in the vicinity of the dimples is then mapped onto a 3D finite element model of a rail section containing a crack in the rail head. The crack loading is finally quantified by multimodal stress intensity factors. The analyses establish that also shallow dimples might have a significant impact on the crack loading. This effect is increased for larger or multiple irregularities but decreases as the crack grows.
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| 7. |
- Andersson, Robin, 1986, et al.
(författare)
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Numerical investigation of crack initiation in rails and wheels affected by martensite spots
- 2018
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Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 114, s. 238-251
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Tidskriftsartikel (refereegranskat)abstract
- White etching layers (WELs) in the form of thermally induced martensite spots are often associated to so-called stud defects on rail surfaces and so-called rolling contact fatigue clusters on wheel treads. These defects might promote further material deterioration of rails and wheels and it is thus of importance to deepen the knowledge regarding their initiation mechanisms. The aim of this study is to gain insight into the problem by making qualitative assessments of different operational scenarios, involving various axle loads and amount of friction. To this end, this paper considers crack initiation, quantified through the Jiang–Sehitoglu low cycle fatigue criterion, in the vicinity of pre-existing WELs (in the form of martensite spots) subjected to varying contact load conditions. Three-dimensional finite element analyses are conducted to model phase transformations as well as the resulting residual stresses. It is seen that the contact pressure magnitude and WEL thickness affect the results only moderately, while the traction coefficient has a significant detrimental influence. It is furthermore seen that occasional wheel passages that are off-set in the lateral direction with respect to the WEL spot’s centre might be responsible for crack initiation on the gauge corner side of the rail surface.
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| 8. |
- Andersson, Robin, 1986
(författare)
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Squat defects and rolling contact fatigue clusters - Numerical investigations of rail and wheel deterioration mechanisms
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Squat defects, a type of localised rolling contact fatigue damage appearing on rail surfaces with rail break as an ultimate consequence, have concerned infrastructure managers for the last couple of decades. In recent years similar types of defects—so-called studs—that are visually resembling squats, have started to appear. In contrast to conventional rolling contact fatigue of rails, these defects are associated with a thin surface layer of brittle material—a "white etching layer". The wheel counterpart of squats/studs are called "rolling contact fatigue clusters". Despite significant research efforts, the exact initiation mechanisms of the defects are still unknown and it is difficult to relate the occurrence of squats/studs and rolling contact fatigue clusters to specific operational scenarios. The current work aims to deepen the understanding of squat/stud and rolling contact fatigue cluster initiation by comparing and ranking predicted damage from various potential causes of initiation under different operational scenarios. Special emphasis is put on local surface irregularities. These are studied using dynamic vehicle–track interaction simulations to evaluate the impact of e.g. irregularity size, vehicle velocity, wheel–rail friction conditions and position relative to a sleeper. It is seen that surface irregularities might cause substantial fatigue impact. Rolling contact fatigue initiation connected to operational scenarios of specific interest are studied more in detail by mapping dynamic contact stresses from simulations of vehicle–track interaction to finite element models for subsequent stress analyses and ranking of operational scenarios via ratchetting response and low cycle fatigue impact. Among the results, it is seen that larger irregularities and higher wheel–rail friction promote higher fatigue impact. In order to study the influence of irregularity geometry when macroscopic cracks are present, dynamic contact stresses are mapped onto finite element models of a cracked rail head. The severity is assessed using an equivalent stress intensity factor, which is seen to increase with the size of the irregularity. This effect holds also for clusters of irregularities. It is furthermore seen that even a shallow irregularity can make a substantial impact. The influence of white etching layers is investigated by simulating thermally induced phase transformations occurring in spots on rail and wheel surfaces, subjected to subsequent mechanical loading. The influence of axle load and wheel–rail friction is investigated with respect to fatigue impact. It is seen that the axle load has a rather low influence whereas an increased frictional loading increases the fatigue impact considerably.
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| 9. |
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| 10. |
- Andersson, Robin, 1986
(författare)
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Surface defects in rails - Potential influence of operational parameters on squat initiation
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Despite significant efforts throughout the last decades, the mechanisms behind the formation of squats — a form of rolling contact fatigue (RCF) damage in rails — are not fully understood. Proposed causes of initiation involve, but are not limited to, small initial rail surface irregularities which yield high contact stresses, rail corrugation and varying friction conditions. To complicate matters further, a very similar rail defect — the stud — has started to appear during the last ten years. This defect lacks common signs of RCF initiated damage, such as large scale plastic deformations, and is commonly found in connection with so-called white etching layers.The first paper of this thesis (Paper A) concerns a simplified two-dimensional model which is used to evaluate the dynamic interaction between a train and a flexible track. Wheel–rail contact stresses (and the resulting contact forces) are used to make assessments of the RCF impact due to rail surface irregularities under varying operational conditions. Excitation due to isolated rail defects and rail corrugation are considered. Differences in predicted RCF impact using a two-dimensional and a (computationally more expensive) three-dimensional contact model are investigated.A computational framework for more detailed RCF assessment is also established (Paper B). Wheel–rail contact stresses from the dynamic vehicle–track model are used as prescribed loads imposed onto a refined continuum finite element model of a rail section. This makes it possible to compute resulting stress and strain fields in the rail material. The propensity of RCF initiation is quantified using accumulated strain and the Jiang–Sehitoglu fatigue parameter.Finally (in Paper C), the aforementioned computational framework is utilised to perform detailed analyses of interesting operational scenarios that have been identified in Paper A. Further, the influence of interacting surface irregularities and varying friction conditions along the rail are investigated.The aim of this thesis is to increase the knowledge regarding squat initiation by means of numerical modelling. Such an improved understanding of squat initiation will also be beneficial in order to understand and mitigate the corresponding form of damage occuring on wheels — so called RCF clusters.
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| 11. |
- Andersson, Robin, 1986, et al.
(författare)
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The influence of rail surface irregularities on contact forces and local stresses
- 2015
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Ingår i: Vehicle System Dynamics. - : Informa UK Limited. - 1744-5159 .- 0042-3114. ; 53:1, s. 68-87
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Tidskriftsartikel (refereegranskat)abstract
- The effect of initial rail surface irregularities on promoting further surface degradation is investi-gated. The study concerns rolling contact fatigue formation, in particular in the form of the so-calledsquats. The impact of surface irregularities in the form of dimples is quantified by peak magnitudesof dynamic contact stresses and contact forces. To this end simulations of two-dimensional (laterextended to three-dimensional) vertical dynamic vehicle–track interaction are employed. The mostinfluencing parameters are identified. It is shown that even very shallow dimples might have a largeimpact on local contact stresses. Peak magnitudes of contact forces and stresses due to the influenceof rail dimples are shown to exceed those due to rail corrugation.
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| 12. |
- Hakonen, Aron, 1970, et al.
(författare)
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Dimer-on-mirror SERS substrates with attogram sensitivity fabricated by colloidal lithography.
- 2015
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Ingår i: Nanoscale. - : Royal Society of Chemistry (RSC). - 2040-3364 .- 2040-3372. ; 7:21
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Tidskriftsartikel (refereegranskat)abstract
- Nanoplasmonic substrates with optimized field-enhancement properties are a key component in the continued development of surface-enhanced Raman scattering (SERS) molecular analysis but are challenging to produce inexpensively in large scale. We used a facile and cost-effective bottom-up technique, colloidal hole-mask lithography, to produce macroscopic dimer-on-mirror gold nanostructures. The optimized structures exhibit excellent SERS performance, as exemplified by detection of 2.5 and 50 attograms of BPE, a common SERS probe, using Raman microscopy and a simple handheld device, respectively. The corresponding Raman enhancement factor is of the order 10(11), which compares favourably to previously reported record performance values.
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| 13. |
- Jonsson, Robin, 1986, et al.
(författare)
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Engaging the missing actor : lessons learned from an age-management intervention targeting line managers and their HR partners
- 2023
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Ingår i: Journal of Workplace Learning. - : Emerald Group Publishing Ltd.. - 1366-5626. ; 35:9, s. 177-196
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Tidskriftsartikel (refereegranskat)abstract
- Purpose – This study aims to describe and evaluate the impact of a participatory age-management intervention on the knowledge, awareness and engagement of line managers and their HR partners from six health-care organizations in Sweden.Design/methodology/approach – The learning workshops consisted of lectures, discussions, feedback and exchange of experiences with colleagues and invited experts. A total of 19 participants were interviewed six months after the final workshop, and qualitative thematic analysis was used to analyze the transcribed interviews.Findings – The intervention design produced promising results in improving line managers’ and HR partners’ knowledge and increasing awareness and engagement. On some occasions, the participants also initiated changes inorganizational policies and practices. However, the intervention primarily became a personal learning experience as participants lacked resources and mandates to initiate change in their daily work. To stimulate engagement and change at the organizational level, the authors believe that an intervention must receive support from higher managers, be anchored at the workplace and be aligned with the organization’s goals; moreover, participants must be provided with sufficient resources and mandates to coordinate the implementation of age-management strategies.Practical implications – Prolonged working life policies and skill shortages are affecting organizations and societies, and for many employers, there are strong reasons for developing strategies to attract, recruit and retain older workers.Originality/value – This study offers lessons and guidance for future workplace interventions to attract, recruit and retain older workers
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| 14. |
- Jonsson, Robin, 1986, et al.
(författare)
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Organizational Hindrances to the Retention of Older Healthcare Workers.
- 2020
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Ingår i: Nordic Journal of Working Life Studies. - : Det Kgl. Bibliotek/Royal Danish Library. - 2245-0157. ; 10:1, s. 41-58
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Tidskriftsartikel (refereegranskat)abstract
- The Swedish healthcare sector is currently experiencing recruitment difficulties combined with increasing demand for healthcare services. This study accordingly seeks knowledge of the obstacles to and opportunities for retaining older employees in the Swedish healthcare sector. Results of interviews with line managers and human resource (HR) partners indicate that the informants have positive attitudes toward older healthcare workers in general, particularly acknowledging their contributions based on long experience and skill. However, line managers’ high workload, the absence of age-management strategies, and universal HR policies not conducive to older workers’ individual needs are considered obstacles to retention on an organizational level. To retain older healthcare workers and maintain their ability and motivation, the healthcare sector and especially HR strategies need to be more proactive in addressing these issues, and formalized policies are required in order to benefit from the potential labor reserve that older employees constitute.
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| 15. |
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Proceedings of the symposium Woodworking Tools and Techniques – Past, Present and Future, Stockholm 16-19 September 2022
- 2023
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Proceedings (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- The 3rd Swedish Symposium on Furniture Technology& Design was held in Stockholm the 16th through the19th of September 2022, this time arranged by MalmstensAlumni in collaboration with the Swedish History Museum,Skokloster Castle and LiU Malmstens.Contents:Foreword page 6Ulf Brunne, Chairman, Malmstens AlumniWoodworking Tools and Techniques – Technical and Aesthetical Aspects of Furniture Design and Cabinetmaking through the Ages page 7Johan Knutsson, Professor in Furniture Culture LiU Malmstens, SwedenFrom Tool Marks to Work Practises page 14Hans Piena, Curator of Domestic Culture, Dutch Open Air Museum, The NetherlandsCharacteristics of Japanese Woodworking Tools page 21Kenji Komatsu, Woodworker/Artist, Wood Workshop BYHAND, JapanA Reconstruction of an Early 16th Century Tondo Frame page 29Iskander Breebaart, Senior Furniture Conservator Rijksmuseum, The NetherlandsWave Mouldings and Ornamental Lathe page 37Josephine Erckrath, Cabinetmaker and Furniture Conservator Møbelarkitekt Tyge Axel Holm, DenmarkDutch Moulding Planes from Skokloster Castle, Sweden page 42Jaap Boonstra, Furniture Conservator, Amsterdam Museum, The Netherlands, Pol Bruijs, Furniture Conservator, Private Practise, The NetherlandsMahogany Spheres – Reconstruction of an Artistically Crafted Element of a Writing Cabinet by the Berlin Ebenist Joseph Schneevogl (1795–1864) page 54Prof. Dr. Angelika Rauch, University of Applied Sciences, Potsdam, GermanyDipl.-Rest. Jörg Weber, Head of Workshop, University of Applied Sciences Potsdam, GermanyConstruction Features that are Typical for Marquetry Cabinets by Jan van Mekeren page 60Paul van Duin, Head of Furniture Conservation, Rijksmuseum, The NetherlandsIskander Breebaart, Senior Furniture Conservator, Rijksmuseum, The NetherlandsAustralian Timbers and Contemporary Woodworking page 68Evan Dunstone, Dunstone Design, AustraliaWoodworking as Means for Understanding and Developing the Human-Technology Relationship – Discussed Through the Work of Cabinet Maker Thomas Tempte page 74Andreas Nobel, Professor in Furniture Design LiU Malmstens, SwedenThe Future of Furniture Craft Education – a Churchill Fellowship page 80Joseph Bray, Head of Wood School Sylva Foundation, UKApplied Information Technology and Mathematics in Woodturning page 86Ulf Jansson, Engineer and Woodturner Private Practise, Sweden
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| 16. |
- Saroukhani, S., et al.
(författare)
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On statistical strain and stress energy bounds from homogenization and virtual testing
- 2015
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Ingår i: European Journal of Mechanics, A/Solids. - : Elsevier BV. - 0997-7538. ; 51, s. 77-95
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Tidskriftsartikel (refereegranskat)abstract
- Computational homogenization for quasistatic stress problems is considered, whereby the macroscale stress is obtained via averaging on Statistical Volume Elements (SVE:s). The variational "workhorse" for the subscale problem is derived from the presumption of weak micro-periodicity, which was proposed by Larsson et al. (2011). Continuum (visco)plasticity is adopted for the mesoscale constituents, whereby a pseudo-elastic, incremental strain energy serves as the potential for the updated stress in a given time-increment. Strict bounds on the incremental strain energy are derived from imposing Dirichlet and Neumann boundary conditions, which are defined as suitable restrictions of the proposed variational format. For this purpose, both the standard situation of complete macroscale strain control and the (less standard) situation of macroscale stress control are considered. Numerical results are obtained from "virtual testing" of SVE:s in terms of mean values and a given confidence interval, and it is shown how these properties converge with respect to the SVE-size for different prescribed macroscale deformation modes and different statistical properties of the random microstructure. In addition, the upper and lower bounds for a sequence of increasing strain levels, for a fixed SVE-size, are used as "data" for the calibration of a macroscopic elastic-plastic constitutive model.
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