| 1. |
- Alfredsson, Bo, et al.
(författare)
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Numerical analysis of plasticity effects on fatigue growth of a short crack in a bainitic high strength bearing steel
- 2016
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Ingår i: International Journal of Fatigue. - : Elsevier. - 0142-1123 .- 1879-3452. ; 92, s. 36-51
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Tidskriftsartikel (refereegranskat)abstract
- Plasticity effects on fatigue growth were simulated for a physically short crack. The material description comprised the Drucker-Prager yield surface, non-associated flow rule and non-linear combined hardening. The simulated development of the growth limiting parameter agreed with the experimental crack behaviour with early rapid propagation followed by a transition to slow R-controlled growth. The crack was open to the tip without any crack face closure throughout all load cycles. Instead compressive residual stresses developed at the unloaded tip which supplied an explanation to the slow rate of the propagated short crack in this bainitic high strength bearing steel. The material's strength differential effect was the key difference explaining why compressive residual stresses instead of crack face closure was responsible for the short crack effect in this material.
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| 2. |
- Johansson, Ulrika, 1974-, et al.
(författare)
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Assembly of functionalized silk together with cells to obtain proliferative 3D cultures integrated in a network of ECM-like microfibers
- 2019
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 9, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- Tissues are built of cells integrated in an extracellular matrix (ECM) which provides a three-dimensional (3D) microfiber network with specific sites for cell anchorage. By genetic engineering, motifs from the ECM can be functionally fused to recombinant silk proteins. Such a silk protein, FN-silk, which harbours a motif from fibronectin, has the ability to self-assemble into networks of microfibers under physiological-like conditions. Herein we describe a method by which mammalian cells are added to the silk solution before assembly, and thereby get uniformly integrated between the formed microfibers. In the resulting 3D scaffold, the cells are highly proliferative and spread out more efficiently than when encapsulated in a hydrogel. Elongated cells containing filamentous actin and defined focal adhesion points confirm proper cell attachment to the FN-silk. The cells remain viable in culture for at least 90 days. The method is also scalable to macro-sized 3D cultures. Silk microfibers formed in a bundle with integrated cells are both strong and extendable, with mechanical properties similar to that of artery walls. The described method enables differentiation of stem cells in 3D as well as facile co-culture of several different cell types. We show that inclusion of endothelial cells leads to the formation of vessel-like structures throughout the tissue constructs. Hence, silk-assembly in presence of cells constitutes a viable option for 3D culture of cells integrated in a ECM-like network, with potential as base for engineering of functional tissue.
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| 3. |
- Linares Arregui, Irene, et al.
(författare)
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Elastic-plastic characterization of a high strength bainitic roller bearing steel-experiments and modelling
- 2010
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Ingår i: International Journal of Mechanical Sciences. - : Elsevier BV. - 0020-7403 .- 1879-2162. ; 52:10, s. 1254-1268
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Tidskriftsartikel (refereegranskat)abstract
- Monotonic and cyclic deformations were studied for a high strength bainitic roller bearing steel. The temperature of 75 °C corresponded to normal roller bearing conditions. The materials showed hydrostatic influence on yielding, but no or marginal influence of plastic deformation on density change. Therefore, a linear elastic constitutive model with pressure dependent yielding, non-associated flow rule, combined non-linear kinematic and isotropic hardening was necessary to characterize the cyclic behaviour. A stepwise process is detailed for determining the material parameters of the pressure dependent model, where particular attention was placed on the hardening parameters. One set of parameters was sufficient to describe all tested load ranges including compressive ratchetting. Some comparative tests were performed at room temperature, 150 °C and on martensitic specimens at 75 °C. The temperature influence was limited to the isotropic hardening parameters.
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| 4. |
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| 5. |
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| 6. |
- Linares Arregui, Irene, 1981-
(författare)
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Mechanical behaviour of a roller bearing steel : Strength differential effect, low temperature creep and propagation of short cracks
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Fatigue cracks in bearings either initiate from the surface or from an inclusion below the rolling contact surface. Then, short cracks start to propagate. Short crack grow at considerably faster rates than long cracks subjected to a nominally equivalent stress intensity factor range. One of the explanations for the difference in growth behaviour between short and long cracks is the development of plastic deformation at the advancing crack tip. In order to investigate this effect, the analysis of short crack propagation at bearing loads requires understanding of the fundamental material behaviour. This thesis presents the material characterisation of a bainitic high strength bearing steel, where the yield stress in tension was lower than in compression. This phenomenon is called strength differential effect (SDE). The work studies the influence of the SDE on the cyclic plastic properties, the elastic behaviour of the material, low temperature creep. These mechanical properties are quantified and modelled using continuum models.Paper A focused on the characterisation of the SDE which was modelled using a Drucker-Prager yield surface and a non-associated flow rule. The cyclic mechanical properties were quantified and modelled using combined non-linear hardening.In paper B the elastic behaviour of the material was studied; the material showed non-linear elastic behaviour in uniaxial tension and compression. The elastic modulus was higher in compression than in tension at high stress levels. On the other hand, the cyclic torsion experiments showed that the stress-strain elastic relation in shear was linear. A non-linear elastic model was proposed.Low temperature creep was studied in Paper C, where the creep strains were quantified in tension and compression. The material showed higher creep strains in tension than in compression for the same stress level and the influence of the SDE in low temperature creep was analysed.The short crack growth in the bainitic steel was analysed through simulations in Paper D. The material model described in Paper A was implemented in a material subroutine. The simulations captured the development of plastic strains as the short crack becomes long. The material model could qualitatively describe the experiment results, where the change in rate as the crack advanced from short to long was ascribed to the growing plastic zone ahead of the crack tip.
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| 7. |
- Linares Arregui, Irene, et al.
(författare)
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Non-linear elastic characterisation of a high strength bainitic roller bearing steel
- 2013
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Ingår i: International Journal of Mechanical Sciences. - : Elsevier. - 0020-7403 .- 1879-2162. ; 68, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- A small but not negligible non-linear elastic behaviour was detected when investigating cyclic uniaxial push-pull experiments on a high strength bainitic steel. Cyclic torsion experiments led to the conclusion that the shear modulus was relatively constant. A non-linear elastic model was implemented where the bulk modulus was extended with a second order term related to the elastic dilatation and where the shear modulus was constant. The material presented a strength differential effect (SDE), with larger yield stress in compression than in tension. Consequently, the non-linear elastic model was combined with a plasticity model that incorporated a Drucker-Prager yield surface, non-associated flow rule and combined non-linear hardening. Expressions that include non-linear elasticity were derived for the elastic-plastic hardening and the compliance tensors. The extended material model predicted the elastic-plastic results from cyclic push-pull experiments. Also, a phenomenological analysis of the cyclic elastic response showed isotropic damage in the elastic moduli. The steady-state damage increased linearly with the cyclic plastic strain range.
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| 11. |
- Xie, Meng, et al.
(författare)
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Secondary ossification center induces and protects growth plate structure
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Ingår i: eLIFE. - 2050-084X.
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Tidskriftsartikel (refereegranskat)abstract
- Growth plate and articular cartilage constitute a single anatomical entity, but later separate into two distinct structures by the formation of secondary ossification center (SOC). The reason for such spatial separation remains unknown. Here, we demonstrate that evolutionarily SOC first appears in amniotes. Mathematical modelling reveals that SOC reduces mechanical stress within the growth plate. Analysis of mammals with specialized extremities reveals that SOC size correlates with the extent of mechanical demands. Ex and in vivo experiments demonstrate that SOC allows epiphyseal chondrocytes to withstand a several-fold higher load before activation of the YAP-p73 signalling pathway and caspase-dependent apoptosis, with hypertrophic chondrocytes being the most load-sensitive cells. Atomic force microscopy shows that hypertrophic chondrocytes are the least mechanically stiff cells within the growth plate. Altogether, these findings suggest that SOC is evolved to protect epiphyseal chondrocytes, especially the hypertrophic chondrocytes, from the high mechanical stress encountered in the terrestrial environment.
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| 12. |
- Xie, Meng, et al.
(författare)
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Secondary ossification center induces and protects growth plate structure
- 2020
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Ingår i: eLIFE. - : ELIFE SCIENCES PUBLICATIONS LTD. - 2050-084X. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Growth plate and articular cartilage constitute a single anatomical entity early in development but later separate into two distinct structures by the secondary ossification center (SOC). The reason for such separation remains unknown. We found that evolutionarily SOC appears in animals conquering the land - amniotes. Analysis of the ossification pattern in mammals with specialized extremities (whales, bats, jerboa) revealed that SOC development correlates with the extent of mechanical loads. Mathematical modeling revealed that SOC reduces mechanical stress within the growth plate. Functional experiments revealed the high vulnerability of hypertrophic chondrocytes to mechanical stress and showed that SOC protects these cells from apoptosis caused by extensive loading. Atomic force microscopy showed that hypertrophic chondrocytes are the least mechanically stiff cells within the growth plate. Altogether, these findings suggest that SOC has evolved to protect the hypertrophic chondrocytes from the high mechanical stress encountered in the terrestrial environment.
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