| 1. |
- Cannmo, Patrik, et al.
(författare)
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Modelling of plasticity and damage in a polycrystalline microstructure
- 1995
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Ingår i: International Journal of Plasticity. - 0749-6419 .- 1879-2154. ; 11:8, s. 949-970
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Tidskriftsartikel (refereegranskat)abstract
- The mesomechanical behavior of a polycrystalline microstructure subjected to monotonic and cyclic loadings is investigated. The analysis is based on a Voronoi polygonization strategy for generation of grains embedded in a contiguous matrix. The main emphasis is to investigate the interaction between the microconstituents and the failure processes along grain boundaries. A rational interface theory based on damage development coupled to inelastic slip and dilatation is developed. The theory uses the interface width as a constitutive parameter, which regularizes the theory of LEMAITRE [1992], that is restricted to perfect bond between grain and matrix. In a series of FE-analyses parameter variations were performed: The unit cell size (as compared to the average grain diameter), the grain-matrix area ratio, the interface width and constitutive parameters. It appears that the composite behavior can be designed as brittle or ductile solely depending on the strength and rate of damage development in the interfaces. A localization band was detected, and its orientation is in the range that is predicted within continuum theory.
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| 2. |
- Kajberg, Jörgen, et al.
(författare)
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High strain-rate tensile testing and viscoplastic parameter identification using microscopic high-speed photography
- 2004
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Ingår i: International journal of plasticity. - 0749-6419 .- 1879-2154. ; 20:4-5, s. 561-575
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Tidskriftsartikel (refereegranskat)abstract
- A combined experimental/numerical method for determination of constitutive parameters in high strain-rate material models is presented. Impact loading, using moderate projectile velocities in combination with small specimens (sub mm) facilitate tensional strain rates in the order of 104-105 s-1. Loading force is measured from one-dimensional wave propagation in a rod using strain gauges and deformation is monitored with a high-speed camera equipped with a microscope lens. A sequence of digital photographs is taken during the impact loading and the plastic deformation history of the specimen is quantified from the photographic record. Estimation of material parameters is performed through so called inverse modelling in which results from repeated FE-simulations are compared with experimental results and a best choice of constitutive parameters is extracted through an iterative optimisation procedure using the simplex method. Results are presented from a preliminary tension test of a mild steel (A533B) at a strain rate well over 104 s-1. The sensitivity of the evaluated material parameters to errors in measured quantities is studied. The method, especially the optical technique for measurement of deformation will be further developed.
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| 3. |
- Babu, Bijish, et al.
(författare)
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Dislocation density based model for plastic deformation and globularization of Ti-6Al-4V
- 2013
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 50, s. 94-108
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Tidskriftsartikel (refereegranskat)abstract
- Although Ti-6Al-4V has numerous salient properties, its usage for certain applications is limited due to the challenges faced during manufacturing. Understanding the dominant deformation mechanisms and numerically modeling the process is the key to overcoming this hurdle. This paper investigates plastic deformation of the alloy at strain rates from 0.001s−1 to 1s−1 and temperatures between 20° C and 1100° C. Pertinent deformation mechanisms of the material when subjected to thermo-mechanical processing are discussed. A physically founded constitutive model based on the evolution of immobile dislocation density and excess vacancy concentration is developed. Parameters of the model are obtained by calibration using isothermal compression tests. This model is capable of describing plastic flow of the alloy in a wide range of temperature and strain rates by including the dominant deformation mechanisms like dislocation pile-up, dislocation glide, thermally activated dislocation climb, globularization, etc. The phenomena of flow softening and stress relaxation, crucial for the simulation of hot forming and heat treatment of Ti-6Al-4V, can also be accurately reproduced using this model.
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| 4. |
- Babu, Bijish, Tec. Lic. 1979-, et al.
(författare)
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Physically Based Constitutive Model of Ti-6Al-4V for Arbitrary Phase Composition
- 2018
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Ingår i: International journal of plasticity. - 0749-6419 .- 1879-2154.
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
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| 6. |
- Balieu, Romain, et al.
(författare)
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A new thermodynamical framework for finite strain multiplicative elastoplasticity coupled to anisotropic damage
- 2015
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 70, s. 126-150
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Tidskriftsartikel (refereegranskat)abstract
- The thermodynamical framework of an elastoplastic model coupled to anisotropic damage is presented in this paper. In the finite strain context, the proposed model is based on the multiplicative decomposition of the strain gradient into elastic and plastic parts. The anisotropic degradation is introduced by means of a second order tensor and another intermediate configuration is introduced by fictitiously removing this degradation from the plastic intermediate configuration. To enhance the physical meaning of the Mandel-like stress measure work conjugated to the inelastic flow stated in this fictitious configuration, i.e. the "effective stress", a new damage rate tensor is defined with its associated push-forward and pull-back operations. The emphasis in this paper is placed on the description of the interesting properties of the novel definitions of the push-forward and pull-back operations which are discussed through a thermodynamical framework. Furthermore, a specific constitutive model with the plastic and damage flow rules deduced from the restrictions imposed by the second law of thermodynamics is discussed with an application on an asphalt concrete material where the anisotropic evolution of the damage is highlighted.
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| 7. |
- Barba, D., et al.
(författare)
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A thermodynamically consistent constitutive model for diffusion-assisted plasticity in Ni-based superalloys
- 2018
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Ingår i: International journal of plasticity. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0749-6419 .- 1879-2154. ; 105, s. 74-98
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
- Croné, Philip, et al.
(författare)
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Analytical prediction of yield stress and strain hardening in a strain gradient plasticity material reinforced by small elastic particles
- 2022
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 151, s. 103200-103200
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Tidskriftsartikel (refereegranskat)abstract
- The influence on macroscopic work hardening of small, spherical, elastic particles dispersedwithin a matrix is studied using an isotropic strain gradient plasticity framework. An analyticalsolution for strain hardening, i.e. the flow stress as a function of plastic strain, based ona recently developed model for initial yield strength is proposed. The model accounts forrandom variations in particle size and elastic properties, and is numerically validated againstFE solutions in 2D/3D unit cell models. Excellent agreement is found as long as the typicalparticle radius is much smaller than the material length scale, given that the particle volumefraction is not too large (< 10%) and that the particle/matrix elastic mismatch is within arealistic range. Finally, the model is augmented to account for strengthening contribution from shearable particles using classic line tension models and successfully calibrated againstexperimental tensile data on an ?? − 2.8??%?? − 0.16??%?? alloy.
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| 9. |
- Cui, Luqing, et al.
(författare)
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Dependence of microstructures on fatigue performance of polycrystals : A comparative study of conventional and additively manufactured 316L stainless steel
- 2022
-
Ingår i: International journal of plasticity. - : Elsevier. - 0749-6419 .- 1879-2154. ; 149
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Tidskriftsartikel (refereegranskat)abstract
- The fatigue properties and microstructural evolution of 316 L stainless steel (316LSS) manufactured by laser powder bed fusion (L-PBF) were systematically studied and compared with its wrought counterpart. The as-built L-PBF 316LSS shows a pronounced heterogeneity, not only structurally but also chemically, with a unique microstructure of highly serrated grain boundaries, bimodal grain structure, nano-precipitates, solidification cell structures, and chemical segregations. The microindentation test showed that the hardness of the as-built L-PBF 316LSS reached 2.589 GPa, which was about 1.6 times higher than that of the wrought solution annealed counterpart, and the sparser slip steps around indentations revealed its greater dislocation storage capability. The S-N curves indicated that the fatigue resistance of the as-built L-PBF 316LSS was significantly better than that of the wrought solution annealed samples, and this was ascribed to its unique microstructural characteristics, especially the pre-existing high-density dislocations and chemical microsegregation within cellular solidification features. Furthermore, the enhanced planar slip in L-PBF 316LSS by its unique microstructure, especially the formation of deformation twins, delays the strain localization and restrains slip band generation, thereby significantly inhibiting crack initiation, and contributing greatly to the fatigue performance. The unique cell structure appears to be more effective in improving the low-cycle fatigue performance of L-PBF 316LSS due to the enhanced ductility.
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| 10. |
- Cui, Luqing, et al.
(författare)
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New insights into the anisotropic ductility of additively manufactured Inconel 718
- 2023
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Ingår i: International journal of plasticity. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0749-6419 .- 1879-2154. ; 169
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Tidskriftsartikel (refereegranskat)abstract
- Anisotropic ductility in additively manufactured (AM) alloys, namely better ductility along the building direction (BD) has been extensively studied and traditionally attributed to the crystallographic texture. However, recent studies have shown significant ductility anisotropy in weakly or non-textured AM alloys, indicating that other factors may also play critical roles. To explore this, AM Inconel 718 with weak crystallographic texture was selected as the model material, and the in-situ high-energy X-ray diffraction tests together with multiscale microstructural characterization techniques were performed to explore the deformation micromechanisms. The results of this study, for the first time, revealed that the better ductility in the vertical specimen (loading parallel to BD) was partially due to the negative stress triaxiality factor (TF) of the {220} grains during plastic deformation, which results in the shrinkage or even healing of the microvoids. Furthermore, the & delta;-phase alignment in conjunction with grain boundary orientation were also proved to have a pronounced impact on the anisotropic ductility of AM alloys. On the other hand, though in the overall weak-textured microstructure, the proportion of 101 grains were marginally over other grains. Thus, the positive effect of {220} grains on ductility was stronger than the negative effect of {200} and {311} grains, contributing to the excellent failure elongation exceeding 12% for both samples. The findings of this study shed new light on the mechanisms underlying the anisotropic ductility of AM alloys and provide insight into strategies for enhancing their performance.
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| 11. |
- Dahlberg, Carl F. O., et al.
(författare)
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A deformation mechanism map for polycrystals modeled using strain gradient plasticity and interfaces that slide and separate
- 2013
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 43, s. 177-195
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Tidskriftsartikel (refereegranskat)abstract
- Small scale strain gradient plasticity is coupled with a model of grain boundaries that take into account the energetic state of a plastically strained boundary and the slip and separation between neighboring grains. A microstructure of hexagonal grains is investigated using a plane strain finite element model. The results show that three different microstructural deformation mechanisms can be identified. The standard plasticity case in which the material behaves as expected from coarse grained experiments, the nonlocal plasticity region where size of the microstructure compared to some intrinsic length scale enhances the yield stress and a third mechanism, active only in very fine grained microstructures, where the grains deform mainly in relative sliding and separation.
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| 12. |
- Dahlberg, Carl F. O., 1980-, et al.
(författare)
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Evolution of the length scale in strain gradient plasticity
- 2019
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Ingår i: International journal of plasticity. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0749-6419 .- 1879-2154. ; 112, s. 220-241
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Tidskriftsartikel (refereegranskat)abstract
- An equivalence is assumed between a microstructural length scale related to dislocation density and the constitutive length scale parameter in phenomenological strain gradient plasticity. An evolution law is formed on an incremental basis for the constitutive length scale parameter. Specific evolution equations are established through interpretations of the relation between changes in dislocation densities and increments in plastic strain and strain gradient. The length scale evolution has been implemented in a 2D-plane strain finite element method (FEM) code, which has been used to study a beam in pure bending. The main effect of the length scale evolution on the response of the beam is a decreased strain hardening, which in cases of small beam thicknesses even leads to a strain softening behavior. An intense plastic strain gradient may develop close to the neutral axis and can be interpreted as a pile-up of dislocations. The effects of the length scale evolution on the mechanical fields are compared with respect to the choice of length evolution equation.
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| 13. |
- Dahlberg, Carl F. O., 1980-
(författare)
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Spatial distribution of the net Burgers vector density in a deformed single crystal
- 2016
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Ingår i: International journal of plasticity. - : Elsevier. - 0749-6419 .- 1879-2154. ; 85, s. 110-129
-
Tidskriftsartikel (refereegranskat)abstract
- A two-dimensional deformation field on an indented single crystal, where the only nonzero lattice rotation occurs in the plane of deformation and only three effective in-plane slip systems are activated, is investigated both experimentally and numerically. ElectronBackscatter Diffraction (EBSD) is utilized to probe the lattice rotation field on the sample. The lattice rotation field is utilized to calculate the two non-zero components of Nye'sdislocation density tensor, which serves as a link between plastic and elastic deformation states. The enhanced accuracy of EBSD enabled measurements of the net Burgers vector density, and a new quantity β, which monitors the activity of slip systems in the deformed zone. The β-field is compared to the slip system activity obtained by analytical solution and also by crystal plasticity simulations. A qualitative comparison of the three methods confirms that the β-field obtained experimentally agrees with the slip system activity obtained analytically and by numerical methods.
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| 14. |
- Dahlberg, Carl, 1980-, et al.
(författare)
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Geometrically necessary dislocation density measurements associated with different angles of indentations
- 2014
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 54, s. 81-95
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Tidskriftsartikel (refereegranskat)abstract
- Experiments and numerical simulations of various angles of wedge indenters into face-centered cubic single crystal were performed under plane strain conditions. In the experiments, the included angles of indenters are chosen to be 60 degrees, 90 degrees and 120 degrees and they are indented into nickel single crystal into the < 00 (1) over bar > direction with its tip parallel to < 1 1 0 > direction, so that there are three effective in-plane slip systems on (1 1 0) plane. Indenters are applied 200 mu m in depth. The midsection of the specimens is exposed with a wire Electrical Discharge Machining (EDM) and the in-plane lattice rotations of the region around the indented area are calculated from the crystallographic orientation maps obtained from electron backscatter diffraction (EBSD) measurement. No matter which angles of indenters are applied, the rotation fields are very similar. There is a strong lattice rotation discontinuity on the line below the indenter tip. The magnitude of the lattice rotation ranges from -20 degrees to 20 degrees. Lower bounds on the Geometrically Necessary Dislocation (GND) densities are also calculated and plotted. The numerical simulations of the same experimental setup are performed. The simulation results of lattice rotation and slip rates are plotted and compared with the experimental result. There is high correlation between the experimental result and the numerical result.
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| 15. |
- Deng, Dunyong, 1989-, et al.
(författare)
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High Temperature Mechanical Integrity of Selective Laser Melted Alloy 718 Evaluated by Slow Strain Rate Tests
- 2021
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Ingår i: International journal of plasticity. - : Elsevier. - 0749-6419 .- 1879-2154. ; 140
-
Tidskriftsartikel (refereegranskat)abstract
- Strain rate dependent deformation behaviours of selective laser melted Alloy 718 (IN718) are systematically studied at 550 and 650 °C by slow strain rate testing, with a forged counterpart as a reference. Selective laser melted IN718 shows significant susceptibility to intergranular cavitation, resulting in ductility degradation with decreasing strain rate. Detailed fractography and cross section inspections are employed to identify the damage mechanisms. Creep rates are also estimated and compared with the conventional counterparts. The possible critical factors for the inferiority of time dependent damage resistance of selective laser melted IN718 are discussed.
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| 16. |
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| 17. |
- Dong, Zhihua, et al.
(författare)
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Influence of Mn content on the intrinsic energy barriers of paramagnetic FeMn alloys from longitudinal spin fluctuation theory
- 2019
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Ingår i: International journal of plasticity. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0749-6419 .- 1879-2154. ; 119, s. 123-139
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Tidskriftsartikel (refereegranskat)abstract
- First-principles calculations were performed to investigate the influence of Mn content on the intrinsic energy barriers (IEBs) of paramagnetic FeMn alloys with face-centered cubic (fcc) structure. The IEBs were derived from the free energies accounting for longitudinal spin fluctuations (LSFs). LSFs are demonstrated to be important for the quantitative description of IEBs and their alloying dependencies at finite temperature. The unstable stacking and unstable twinning fault energies of the fcc phase slightly decrease with Mn content, whereas the intrinsic stacking fault energy (gamma(fcc)(isf)) is predicted to monotonically increase. This latter finding contradicts the experimentally reported, local minimum of gamma(isf) in the fcc/hexagonal close-packed (hcp) coexistence region. The partitioning of Mn during the fcc/hcp phase transition is proposed to reconcile theory and experiment. Both temperature and impurities ([C] and Cr) hardly influence the monotonic concentration dependence of gamma(fcc)(isf) but considerably alter the magnitude. The fcc/hcp interfacial energy is nearly independent of Mn concentration in contrast to the parabolic dependence predicted in thermodynamic modeling. In contrast to the fcc phase, the estimated intrinsic stacking fault energy of the ideal hcp structure monotonically decreases with Mn content and temperature. A high twinnability is predicted at 450 K within the stability field of the paramagnetic fcc Fe-Mn alloys.
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| 18. |
- Dong, Zhihua, et al.
(författare)
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Plastic deformation modes in paramagnetic gamma-Fe from longitudinal spin fluctuation theory
- 2018
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Ingår i: International journal of plasticity. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0749-6419 .- 1879-2154. ; 109, s. 43-53
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Tidskriftsartikel (refereegranskat)abstract
- Using an efficient first-principles computational scheme, we calculate the intrinsic stacking fault energy (gamma(isf) ) and the unstable stacking fault energy (gamma(usf)) of paramagnetic gamma-Fe as a function of temperature. The formation energies are derived from free energies accounting for thermal longitudinal spin fluctuations (LSFs). LSFs are demonstrated to be important for the accurate description of the temperature-dependent magnetism, intrinsic and unstable stacking fault energies, and have a comparatively large effect on gamma(isf) of gamma-Fe. Dominated by the magneto-volume coupling at thermal excitations, gamma(isf) of gamma-Fe exhibits a positive correlation with temperature, while gamma(usf )declines with increasing temperature. The predicted stacking fault energy of gamma-Fe is negative at static condition, crosses zero around 540 K, and reaches 71.0 mJ m(-2) at 1373 K, which is in good agreement with the experimental value. According to the plasticity theory formulated in terms of the intrinsic and unstable stacking fault energies, twinning remains a possible deformation mode even at elevated temperatures. Both the large positive temperature slope of gamma(usf) and the predicted high-temperature twinning are observed in the case of austenitic stainless steels.
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| 19. |
- Fischer, Tim, et al.
(författare)
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Relating stress/strain heterogeneity to lath martensite strength by experiments and dislocation density-based crystal plasticity
- 2024
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 174
-
Tidskriftsartikel (refereegranskat)abstract
- To enhance the fundamental understanding for micromechanical lath martensite deformation, the microstructure as well as macro- and microscopic tensile properties of as -quenched 15-5 PH stainless steel are systematically analysed depending on the austenitisation temperature. Based on electron backscatter diffraction (EBSD) and backscattered electron (BSE) analysis, it is noted that the martensite morphology alters from a less defined to a more clearly defined parallel arrangement of the block and lath structure with increasing temperature. For an indepth quantification of the hierarchical boundary strengthening contributions in relation to local stress/strain heterogeneity, separate high-fidelity virtual microstructures are realised for the different scales (prior austenite grains, packets and blocks). This is consistent with the materials transformation process. The virtual microstructures are simulated employing the crystal plasticity finite element method (CPFEM) adapted for handling high dislocation density and encompassing all relevant strengthening mechanisms by boundaries, dislocations and solute atoms. While accurately capturing the measured size -dependent stress-strain behaviour, the simulations reveal in line with the experiments (Hall-Petch) that blocks are the most effective dislocation motion barrier, causing increased strain hardening and stress/strain heterogeneity. Furthermore, since strain localisation is predicted strongest in the distinct block structure, the experimentally observed early plastic material yielding is thought to be favoured here.
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| 20. |
- Fredriksson, Per, et al.
(författare)
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Size-dependent yield strength of thin films
- 2005
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 21:9, s. 1834-1854
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Tidskriftsartikel (refereegranskat)abstract
- Biaxial strain and pure shear of a thin film are analysed using a strain gradient plasticity theory presented by Gudmundson [Gudmundson, P., 2004. A unified treatment of strain gradient plasticity. Journal of the Mechanics and Physics of Solids 52, 1379-1406]. Constitutive equations are formulated based on the assumption that the free energy only depends on the elastic strain and that the dissipation is influenced by the plastic strain gradients. The three material length scale parameters controlling the gradient effects in a general case are here represented by a single one. Boundary conditions for plastic strains are formulated in terms of a surface energy that represents dislocation buildup at an elastic/plastic interface. This implies constrained plastic flow at the interface and it enables the simulation of interfaces with different constitutive properties. The surface energy is also controlled by a single length scale parameter, which together with the material length scale defines a particular material. Numerical results reveal that a boundary layer is developed in the film for both biaxial and shear loading, giving rise to size effects. The size effects are strongly connected to the buildup of surface energy at the interface. If the interface length scale is small, the size effect vanishes. For a stiffer interface, corresponding to a non-vanishing surface energy at the interface, the yield strength is found to scale with the inverse of film thickness.
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| 21. |
- Gudmundson, Peter, et al.
(författare)
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Isotropic strain gradient plasticity model based on self-energies of dislocations and the Taylor model for plastic dissipation
- 2019
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Ingår i: International journal of plasticity. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0749-6419 .- 1879-2154. ; 121, s. 1-20
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Tidskriftsartikel (refereegranskat)abstract
- A dislocation mechanics based isotropic strain gradient plasticity model is developed. The model is derived from self-energies of dislocations and the Taylor model for plastic dissipation. It is shown that the same microstructural length scale emerges for both the energetic and the dissipative parts of the model. Apart from a non-dimensional factor of the order of unity, the length scale is defined as the Burgers vector divided by the strain for initiation of plastic deformation. When the structural length scale approaches this microstructural length scale, strengthening effects result. The present model predicts an increased initial yield stress that is controlled by the energetic contribution. For larger plastic strains, the hardening is governed by the dissipative part of the model. The theory is specialized to the simple load cases of tension with a passivation layer that prohibits plastic deformation on the surfaces as well as pure bending with free and fixed boundary conditions for plastic strain. Simulations of initial yield stress for varying thicknesses are compared to experimental observations reported in the literature. It is shown that the model in a good way can capture the length scale dependencies. Also upper bound solutions are presented for a spherical void in an infinite volume as well as torsion of a cylindrical rod. The model is as well applied to derive a prediction for the Hall-Petch effect.
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| 22. |
- Hård af Segerstad, P., et al.
(författare)
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A constitutive equation for open-cell cellular solids, including viscoplasticity, damage and deformation induced anisotropy
- 2008
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 24:5, s. 896-914
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Tidskriftsartikel (refereegranskat)abstract
- A thermodynamically consistent approach is developed for modelling the response of an open-cell cellular solid at finite compressive strains. The cellular solid is considered as a network of struts, where each strut connects two vertex points. A hypothesis is proposed that the vertex points move affinely in the finite strain regime, where the struts buckle plastically. The strut deformation is assumed to be 1-dimensional and depend directly on the macroscopic deformation; thus the description of the strut response requires only a scalar valued response function. Owing to this simple ansatz it is possible to include multiple nonlinear mechanisms, such as hyperelasto-viscoplasticity and damage. The macrostress is obtained by averaging over a statistical ensemble of struts. The model has been implemented in the context of finite strains and damage coupled to viscoplastic Perzyna type behaviour. All model parameters may be determined by performing tests in simple compression. The model is well capable of reproducing data from compression experiments on various open-cell aluminium foams.
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| 23. |
- Hård af Segerstad, Per, 1977, et al.
(författare)
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Computational modelling of dissipative open-cell cellular solids at finite deformations
- 2009
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Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 25:5, s. 802-821
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Tidskriftsartikel (refereegranskat)abstract
- This study concerns the constitutive modelling of dissipative open-cell structural cellular solids under primarily finite compressive deformations and the corresponding non-linear finite element implementation. A thermodynamically consistent, mechanistic approach presented in Hard of Segerstad et al. [Hard of Segerstad, P., Larsson, R., Toll, S., 2008. A constitutive equation for open-cell cellular solids, including viscoplasticity, damage and deformation induced anisotropy. International Journal of Plasticity. 24, 896-914.] is adopted for modelling the initial linear-elastic response and the subsequent plateau behaviour. In these regions the cellular solid is considered as a network of struts, where each strut connects two vertex points. A hypothesis is proposed that the vertex points move affinely in the finite strain regime, where the struts buckle plastically. The strut deformation is further assumed to be one-dimensional and depend directly on the macroscopic deformation; thus the description of the strut response requires only a scalar valued response function. Owing to this simple ansatz, the introduction of multiple non-linear mechanisms, such as hyperelasto-viscoplasticity and damage becomes feasible for large scale computations. An additional hyperelastic volumetric response, activated near the point-of-compaction, is introduced for two reasons, (i) to capture the stiffness recovery at high compressive volumetric deformations, where the struts come into contact, and (ii) to prevent numerical instability. The model is implemented as a user defined constitutive driver in the implicit version of the finite element code ABAQUS and tested experimentally for an open-cell aluminium alloy foam (Duocel 6101-0,40 ppi). All material parameters are determined by a simple compression test, and subsequently used to simulate the indentation of a rigid sphere into a foam cylinder. The model accurately captures the experimental load-displacement relation and the deformed geometry. (C) 2008 Elsevier Ltd. All rights reserved.
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| 24. |
- Lin, Fengxiang, et al.
(författare)
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Transmission of {332}(113) twins across grain boundaries in a metastable β-titanium alloy
- 2018
-
Ingår i: International journal of plasticity. - : Elsevier. - 0749-6419 .- 1879-2154. ; 105, s. 195-210
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Tidskriftsartikel (refereegranskat)abstract
- Plastic deformation by dislocation slip and twinning is investigated in a metastable body centered cubic Ti-Mo alloy. Experimental crystal orientation maps show twin lamellae connected across grain boundaries, especially when they host low angle misorientation angles. A three-dimensional crystal plasticity based finite element model (CPFEM) is used to predict internal stresses due to deformation twinning. It is found that twin transmission across grain boundaries relaxes the strong back-stresses at the twin tip more than dislocation slip does. CPFEM predictions also indicate that the forward-stresses, which promote twinning in the adjacent grain, depend not only on the crystal misorientation angle but also on the misorientation axis, and the inclination of the grain boundary plane. © 2018 Elsevier Ltd.
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| 25. |
- Lindgren, Lars-Erik, et al.
(författare)
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Simulation of hydroforming of steel tube made of metastable stainless steel
- 2010
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Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 26:11, s. 1576-1590
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Tidskriftsartikel (refereegranskat)abstract
- The Olson-Cohen model for strain induced deformation, further developed by Stringfellow and others, has been calibrated together with a flow stress model for the plastic deformation of metastable stainless steel. Special validation tests for checking one of the limitations of the model have also been carried out. The model has been implemented into a commercial finite element code using a staggered approach for integrating the stress-strain relations with the microstructure model. Results from a thermo-mechanical coupled simulation of hydroforming of a tube have been compared with corresponding experiments. The agreement between experimental results of radial expansion and martensite fraction and the corresponding computed results is good.
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| 26. |
- Lindström, Thomas, et al.
(författare)
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Constitutive model of an additively manufactured ductile nickel-based superalloy undergoing cyclic plasticity
- 2020
-
Ingår i: International journal of plasticity. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0749-6419 .- 1879-2154. ; 132
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a transversely isotropic elasto-plastic model based on the multilinear Ohno-Wang model was developed to simulate the cyclic behaviour of an additively manufactured ductile nickel-based superalloy. The transverse isotropy was taken into account by the incorporation of a structural tensor in the modelling framework. To calibrate the model, a number of uniaxial isothermal low-cycle fatigue tests were carried out on smooth specimens manufactured in three different orientations with respect to the building platform. The test specimens were subjected to different strain ranges and load ratios, as well as four different temperatures, namely room temperature, 400 degrees C, 500 degrees C and 600 degrees C. By using a cycle jumping procedure, where the material properties are changed from virgin parameters to mid-life parameters, the mid-life behaviour, commonly used for fatigue life predictions, of the concerned material could be simulated with good agreements to the performed experiments. To validate the results, the maximum and minimum stress, as well as the plastic strain range and hysteresis area from the simulated mid-life hysteresis loops were compared to the values obtained from the experiments.
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| 27. |
- Norman, Viktor, et al.
(författare)
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On the micro- and macroscopic elastoplastic deformation behaviour of cast iron when subjected to cyclic loading
- 2019
-
Ingår i: International journal of plasticity. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0749-6419 .- 1879-2154. ; 115, s. 200-215
-
Tidskriftsartikel (refereegranskat)abstract
- The complicated constitutive behaviour of cast iron, involving a non-linear elastic regime, tension-compression stress asymmetry, varying elastic modulus and an inflection in the tension-to-compression hardening curve, is investigated using a micromechanical modelling approach. In this way, it is demonstrated that the abnormalities observed in the constitutive behaviour are qualitatively and quantitatively explained by the interaction behaviour between the matrix and graphite constituents. In initial tension, the absence of linearity is rationalised by the successive loss in load-carrying capacity of the graphite phase due to debonding, which in subsequent cycling, results in the opening and re-contact of the matrix-graphite interface. This effect is demonstrated to result in tension-compression asymmetry in stress and elastic modulus, as well as the inflection in tension-to-compression loading. The given model of explanation is validated by comparison to the experimentally acquired microscopic strain field in EN-GJV-400 at locations where stress concentrations are generated due to the matrix-graphite debonding, using high-resolution digital image correlation of scanning electron images.
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| 28. |
- Subasic, M., et al.
(författare)
-
Experimental investigation and numerical modelling of the cyclic plasticity and fatigue behavior of additively manufactured 316 L stainless steel
- 2024
-
Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 176
-
Tidskriftsartikel (refereegranskat)abstract
- This study addresses the critical need for a constitutive model to analyze the cyclic plasticity of additively manufactured 316L stainless steel. The anisotropic behavior at both room temperature and 300 °C is investigated experimentally based on cyclic hysteresis loops performed in different orientations with respect to the build direction. A comprehensive constitutive model is proposed, that integrates the Armstrong-Frederick nonlinear kinematic hardening, Voce nonlinear isotropic hardening and Hill's anisotropic yield criterion within a 3D return mapping algorithm. The model was calibrated to specimens in the 0° and 90° orientations and validated with specimens in the 45° orientation. A single set of hardening parameters successfully represented the elastoplastic response for all orientations at room temperature. The algorithm effectively captured the full cyclic hysteresis loops, including historical effects observed in experimental tests. A consistent trend of reduced hardening was observed at elevated temperature, while the 45° specimen orientation consistently exhibited the highest degree of strain hardening. The applicability of the model was demonstrated by computing energy dissipation for stabilized hysteresis loops, which was combined with fatigue tests to propose an energy-based fatigue life prediction model.
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| 29. |
- Wang, Bochao, et al.
(författare)
-
A visco-elastic-plastic constitutive model of isotropic magneto-sensitive rubber with amplitude, frequency and magnetic dependency
- 2020
-
Ingår i: International journal of plasticity. - : Elsevier. - 0749-6419 .- 1879-2154. ; 132
-
Tidskriftsartikel (refereegranskat)abstract
- A three-dimensional visco-elastic-plastic constitutive model of isotropic magneto-sensitive (MS) rubber with amplitude, frequency and magnetic dependency under a continuum constitutive framework is developed. MS rubber is akind of smart material mainly composed of a rubber matrix and magnetizable particles. Under a magnetic field, there is an increase of its dynamic modulus due to the interaction between the magnetic field and MS rubber, which is often referred to as the magnetic dependency of MS rubber. Experimental results reveal that besides the magnetic dependency, there is a frequency and amplitude dependency of its dynamic modulus. In specific, the modulus of MS rubber increases with increasing frequency and dereases with increasing strain amplitude. To depict the above properties and to consider the balance of energy in continuum mechanics framework, a new constitutive model consisting of a viscoelastic fractional derivative element, a bounding surface model in series with a neo-Hookean elastic model with magnetic sensitivity and a magnetic stress tensor term for MS rubber is proposed. The contribution of this constitutive model is that by using a free energy based method, with only eight material parameters, the amplitude, frequency and magnetic dependency of MS rubber can be reflected. After parameter identification, the simulationresults show a good agreement with those of measurements. Therefore, by utilizing the model proposed, the ability of approaching the dynamic behavior of MS rubber-based vibration reduction devices in the design phase is possible which contributes to the application of MS rubber in noise and vibration reduction area.
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| 30. |
- Wang, Bochao, et al.
(författare)
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Modelling the influence of magnetic fields to the viscoelastic behaviour of soft magnetorheological elastomers under finite strains
- 2023
-
Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 164
-
Tidskriftsartikel (refereegranskat)abstract
- Isotropic soft magneto-rheological elastomers (s-MRE) are polymer-based composites where magnetically soft particles are randomly distributed in the elastomer matrix. Under a magnetic field, a strong modulus magnetic stiffening effect and a magnetostriction performance is exhibited for isotropic s-MRE, offering a wide application potential in vibration control, soft robotics and haptic displays. In the last decades, substantial theoretical work has focused on modelling the magnetostriction behaviour of isotropic s-MRE. Modelling the influence of magnetic fields to the viscoelastic behaviour of isotropic s-MRE has received less attention, despite the magnetic-dependent viscoelasticity is an essential component of the observed magneto-mechanical response and of great importance for the application of isotropic s-MRE. To predict the magneto-mechanical coupling behaviour accurately and provide guidance for the design of isotropic s-MRE-based applications, a multiplicatively-typed magneto-hyperelastic free energy and a new type of process-dependent viscosity evolution law is proposed in this work. Afterwards, the ability of the model to predict the modulus magnetic stiffening effect and magnetic-dependent nonlinear viscoelastic behaviour of isotropic s-MRE is examined. Finally, three sets of finite element case studies are presented to illustrate the feasibility of the model-based simulation and guide the design of isotropic s-MRE-related applications.
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| 31. |
- Wei, Daixiu, et al.
(författare)
-
Si-addition contributes to overcoming the strength-ductility trade-off in high-entropy alloys
- 2022
-
Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 159
-
Tidskriftsartikel (refereegranskat)abstract
- Face-centered cubic single-phase high-entropy alloys (HEAs) containing multi-principal transition metals have attracted significant attention, exhibiting an unprecedented combination of strength and ductility owing to their low stacking fault energy (SFE) and large misfit parameter that creates severe local lattice distortion. Increasing both strength and ductility further is challenging. In the present study, we demonstrate via meticulous experiments that the CoCrFeNi HEA with the addition of the substitutional metalloid Si can retain a single-phase FCC structure while its yield strength (up to 65%), ultimate strength (up to 34%), and ductility (up to 15%) are simultaneously increased, owing to a synthetical effect of the enhanced solid solution strengthening and a reduced SFE. The dislocation behaviors and plastic deformation mechanisms were tuned by the addition of Si, which improves the strain hardening and tensile ductility. The present study provides new strategies for enhancing HEA performance by targeted metalloid additions.
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| 32. |
- Xu, W. W., et al.
(författare)
-
Atomic origins of the plastic deformation micro-mechanisms of ?/?? : FeCoNiAlTi high-entropy alloys
- 2022
-
Ingår i: International journal of plasticity. - : Elsevier BV. - 0749-6419 .- 1879-2154. ; 158, s. 103439-
-
Tidskriftsartikel (refereegranskat)abstract
- The gamma/gamma' FeCoNiAlTi high-entropy alloys (HEAs) break the strength-ductility trade-off and possess an excellent combination of strength and ductility. However, lack of atomic-level understanding of plastic deformation behaviors restricts the exploration of full capacities of the FeCoNiAlTi HEAs. By computing the generalized stacking fault energies (GSFEs) of the gamma and gamma' phases, the relationships between planar stacking faults and work-hardening capacities, and the effect of chemical concentration and grain orientation on the deformation mechanisms were explored in depth for the FeCoNiAlTi HEAs. Our results demonstrate that the multicomponent nature lowers the GSFEs of the matrix but enhances those of the precipitate to achieve the strength-ductility balance of the HEA. An active factor (epsilon) defined as gamma isf/gamma apb (gamma isf: intrinsic stacking fault energy, gamma apb: anti-phase boundary energy) was introduced to bridge activation of microbands (MBs) and planar stacking faults in the gamma/gamma' alloys. Tuning a suitable low epsilon around 0.2 is an efficient strategy for acquiring the extended MBs-induced plasticity. Analyzing the individual/synergetic contribution of the principal elements to the GSFEs-related properties, we find that increasing the amount of Co and Ti promotes the strength-ductility balance and facilitates the MB activation by altering the GSFEs of both gamma and gamma'. Based on our comprehensive analysis, it is concluded that raising the Co/Fe ratio or lowing the Al/Ti ratio benefits the achievement of the desired mechanical properties of the FeCoNiAlTi HEA.
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| 33. |
- Österlöf, Rickard, et al.
(författare)
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A finite strain viscoplastic constitutive model for rubber with reinforcing fillers
- 2016
-
Ingår i: International journal of plasticity. - : Elsevier. - 0749-6419 .- 1879-2154. ; 87, s. 1-14
-
Tidskriftsartikel (refereegranskat)abstract
- A three dimensional viscoplastic constitutive model for finite strains in a co-rotational explicit scheme is developed and implemented using finite elements that captures the amplitude dependency, commonly referred to as the Fletcher-Gent effect, and frequency dependency of rubber with reinforcing fillers. The multiplicative split of the deformation gradient is utilized and the plastic flow rule stems from an extension to finite strains of a boundary surface model with a vanishing elastic region. The storage and loss modulus for a 50 phr carbon black filled natural rubber are captured over a large range of strain amplitudes, 0.2-50% shear strain, and frequencies, 0.2-20 Hz. In addition, bimodal excitation is replicated accurately, even though this measurement data is not included when obtaining material parameters. This capability is essential when non-sinusoidal loading conditions are to be replicated. By separating the material and geometrical influence on the properties of a component, the design engineers have the capability to evaluate more concepts early in the design phase. This also reduces the need of complex prototypes for physical testing, thereby saving both time and money.
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| 34. |
- Ristinmaa, Matti
(författare)
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Cyclic plasticity model using one yield surface only
- 1995
-
Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419. ; 11:2, s. 163-181
-
Tidskriftsartikel (refereegranskat)abstract
- A time-independent plasticity model using only one yield surface and capable of predicting cyclic loading is presented. Memory points are defined to monitor the loading history; these memory points have the property that they can be created as well as disappear during the load history. The generalized plastic modulus is defined from these memory points in such a way that it will be continuous and provide a smooth transition from elastic to elastic-plastic behavior. The model is formulated for general pressure-insensitive plasticity. Because only one yield surface is used, this framework allows all types of yield functions to be easily implemented. For piecewise linear response, the concept of memory points may be interpreted in terms of the classic Mroz model. Moreover, a generalization of the Mroz model for a smoothly varying response can be made. As an important example of pressure-insensitive plasticity, the von Mises criterion is incorporated into the model to illustrate the response for different load situations. Of particular interest is cyclic hardening, mean stress relaxation, and ratchetting. A simple law for controlling the ratchetting is also introduced.
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| 35. |
- Runesson, Kenneth, et al.
(författare)
-
Discontinuous Bifurcations of Elasto-Plastic Solution at Plane Stress and Plane Strain
- 1991
-
Ingår i: International Journal of Plasticity. - 0749-6419. ; 7:1-2, s. 99-121
-
Tidskriftsartikel (refereegranskat)abstract
- Conditions for discontinuous bifurcations of the incremental fields in elastic-platic materials subjected to the condition of either plane stress or plane strain are derived and explicit expressions for the critical hardening modulus and the corresponding bifurcation directions are obtained for a quite general class of plasticity models. The only restriction is that the gradients of the yield function and plastic potential, that defines the nonassociated flow rule, have the same principal directions and that two of these directions are located in the plane of interest. Drucker-Prager's and Mohr-Coulomb's yield criteria are taken as typical for the behavior of pressure-dependent materials such as concrete and granular materials. For the latter criterion, results for plane strain have previously been obtained only for the very particular case when the intermediate principal stress is directed out-of-plane. These results are confirmed in this paper as a part of the investigation of the complete behavior.
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| 36. |
- Hallberg, Håkan, et al.
(författare)
-
A constitutive model for the formation of martensite in austenitic steels under large strain plasticity
- 2007
-
Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419. ; 23:7, s. 1213-1239
-
Tidskriftsartikel (refereegranskat)abstract
- A constitutive model for diffusionless phase transitions in elastoplastic materials undergoing large deformations is developed. The model takes basic thermodynamic relations as its starting point and the phase transition is treated through an internal variable (the phase fractions) approach. The usual yield potential is used together with a transformation potential to describe the evolution of the new phase. A numerical implementation of the model is presented, along with the derivation of a consistent algorithmic tangent modulus. Simulations based on the presented model are shown to agree well with experimental findings. The proposed model provides a robust tool suitable for large-scale simulations of phase transformations in austenitic steels undergoingz extensive deformations, as is demonstrated in simulations of the necking of a bar under tensile loading and also in simulations of a cup deep-drawing process.
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| 37. |
- Håkansson, Paul, et al.
(författare)
-
Comparison of isotropic hardening and kinematic hardening in thermoplasticity
- 2005
-
Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419. ; 21:7, s. 1435-1460
-
Tidskriftsartikel (refereegranskat)abstract
- A coupled thermo-mechanical problem is presented in this paper. The constitutive model is based on thermoplastic model for large strains where both kinematic and isotropic hardening are included. It is shown that a non-associated plasticity formulation enables thermodynamic consistent heat generation to be modeled, which can be fitted accurately to experimental data. In the numerical examples the effect of heat generation is investigated and both thermal softening and temperature-dependent thermal material parameters are considered. The constitutive model is formulated such that pure isotropic and pure kinematic hardening yield identical uniaxial mechanical response and mechanical dissipation. Thus, differences in response due to hardening during non-proportional loading can be studied. Thermally triggered necking is studied, as well as cyclic loading of Cook's membrane. The numerical examples are solved using the finite element method, and the coupled problem that arises is solved using a staggered method where an isothermal split is adopted.
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| 38. |
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| 39. |
- Håkansson, Paul, et al.
(författare)
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Thermomechanical response of non-local porous material
- 2006
-
Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419. ; 22:11, s. 2066-2090
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Tidskriftsartikel (refereegranskat)abstract
- A thermomechanical model of a porous material is presented. The constitutive model is based on the Gurson model, formulated within a thermodynamic framework and adapted to large deformations. The thermodynamic framework yields a heat equation that naturally includes the mechanical dissipation. To introduce a length scale, the Gurson model was enhanced through non-local effects of the porosity being taken into account. A numerical integration scheme of the constitutive model and the algorithmic stiffness tensor are derived. The integration of the plastic part of the deformation gradient is based on an exponential update operator, an eigenvalue decomposition is also being used to reduce the number of equations that need to be solved. The coupled problem that arises is dealt with by employing a staggered solution method. To examine the capabilities of the model, shear band formation in a thick disc and crack growth in a thick notched disc were investigated. (c) 2006 Elsevier Ltd. All rights reserved.
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| 40. |
- Jansson, Mikael, et al.
(författare)
-
On constitutive modeling of aluminum alloys for tube hydroforming applications
- 2005
-
Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419. ; 21:5, s. 1041-1058
-
Tidskriftsartikel (refereegranskat)abstract
- The increased interest in lightweight materials for automotive structures has also lead to a search for efficient forming methods that suit these materials. One attractive concept is to use hydroforming of aluminum tubes. The advantages of this forming method includes better tolerances, decreased number of parts and an increased range of forming options. By using FE simulations, the process can be optimized to reduce the risk for failure, i.e. bursting or wrinkling. However, extruded aluminum is highly anisotropic and it is crucial that the material model used for simulations is able to accurately describe this behavior. Also, tube hydroforming occurs predominantly in a biaxial stress state which should be considered in the material testing, where uniaxial tests are used extensively in the industry today. The present study accentuates the need for improved constitutive models. It is shown that a material model, which accurately describes the anisotropic behavior of aluminum tubes, can be obtained from simple and robust experiments.
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| 41. |
- Li, Hongjia, 1985, et al.
(författare)
-
Accounting for lattice coherency in a two-phase elastic-plastic self-consistent model for nickel-based superalloys
- 2018
-
Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419. ; 110, s. 248-271
-
Tidskriftsartikel (refereegranskat)abstract
- A 2-site elastic-plastic self-consistent (EPSC) model is developed and implemented in order to account for crystallographic texture development and grain morphology evolution under strong correlations between neighbor grains of different phases, both in space and orientation. Predictions of the model adequately fit the published in situ neutron diffraction data for nickel-based superalloys at ambient and elevated temperatures, in whichγandγ'phases exhibit exact cube-cube orientation relationship. Comparison with 2-site model (small strain algorithm, non-rotation scheme) and 1-site model (finite strain algorithm, co-rotation scheme) has been made, and the result shows that the present 2-site model (finite strain algorithm, rotation scheme) leads to better predictions in lattice strain evolution where both rotation of crystal lattice and correlation between inclusions are accounted for, especially when the applied strain is larger than 0.02 for transverse direction and0.05∼0.18for axial direction for the materials studied in this work. Based on a systematic study on the effects of grain-grain interaction and total grain number on the homogenized results, we found that transverse lattice strains ofγ(200) and/orγ'(100) are sensitive to the interplay betweenγ-γ'interaction and evolution of grain orientation distribution with deformation, while that ofγ(220) andγ'(110) are sensitive to the initial crystallographic texture.
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| 42. |
- Mirkhalaf, Mohsen, 1982, et al.
(författare)
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Modelling of the post yield response of amorphous polymers under different stress states
- 2017
-
Ingår i: International Journal of Plasticity. - 0749-6419. ; 88, s. 159-187
-
Tidskriftsartikel (refereegranskat)abstract
- In this contribution, an elasto-viscoplastic constitutive model based on the single mode EGP (Eindhoven Glassy Polymer) model is proposed to describe the deformation behaviour of solid polymers subjected to finite deformations under different stress states. The polymeric material examined in this work is a specific commercial grade of Bisphenol, a polycarbonate called Makrolon 2607, for which there were experimental results available in the open literature for: uniaxial compression, plane strain compression and tensile test on a dumbbell shape specimen. The material properties of the original model are determined and calibrated from a uniaxial compression-loading test. Then, several numerical examples under different stress states are presented to illustrate the limitations of the single mode EGP model. A more general elasto-viscoplastic model is proposed, which preserves the isotropy of the original model, using the lode angle parameter to distinguish shear-dominated stress states and capture the material post yield response. The numerical treatment of the model, including the state update procedure and also the consistent tangent operator, required for the finite implementation of the model within an implicit finite element scheme, is presented. A comprehensive set of numerical examples is employed to compare the predictions of the original and new models against experimental results and to investigate the effect of the proposed modifications. The numerical results show that the proposed model provides a closer agreement with experimental evidence and opens the possibility for computational simulations of amorphous polymers under different stress states.
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| 43. |
- Tillberg, Johan, 1980, et al.
(författare)
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On the role of material dissipation for the crack-driving force
- 2010
-
Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419. ; 26:7, s. 992-1012
-
Tidskriftsartikel (refereegranskat)abstract
- The thermodynamic setting for the formulation of the "crack-driving force" for a singular crack in conjunction with rate-independent material response is discussed. One key ingredient is the introduction of a fixed (absolute) configuration, relative to which both physical and (virtual) configurational and spatial changes can be described. Only quasistatic and isothermal conditions are considered in this paper. A variational framework is established for the rate of global energy dissipation (integrated over the whole material domain) due to the combined action of a (discrete) crack extension and continuum inelasticity, whereby the material time derivative of internal variables and the rate of crack extension are coupled. The classical assumption (previously adopted in the literature) is that there is no coupling, i.e. the internal variables are considered as fixed (material) fields just like an inhomogeneous material property. The other (extreme) assumption is that the internal variables fields are convected with the configurational motion due to the virtual crack extension. Both cases are investigated in this paper for a simple 2D example of an edge crack in a plate in a setting of small strains and hardening plasticity. In particular, we consider convergence issues from mesh refinement. (c) 2009 Elsevier Ltd. All rights reserved.
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| 44. |
- Wallin, Mathias, et al.
(författare)
-
Deformation gradient based kinematic hardening model
- 2005
-
Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419. ; 21:10, s. 2025-2050
-
Tidskriftsartikel (refereegranskat)abstract
- A kinematic hardening model applicable to finite strains is presented. The kinematic hardening concept is based on the residual stresses that evolve due to different obstacles that are present in a polycrystalline material, such as grain boundaries, cross slips, etc. Since these residual stresses are a manifestation of the distortion of the crystal lattice a corresponding deformation gradient is introduced to represent this distortion. The residual stresses are interpreted in terms of the form of a back-stress tensor, i.e. the kinematic hardening model is based on a deformation gradient which determines the back-stress tensor. A set of evolution equations is used to describe the evolution of the deforrnation gradient. Non-dissipative quantities are allowed in the model and the implications of these are discussed. Von Mises plasticity for which the uniaxial stress-strain relation can be obtained in closed form serves as a model problem. For uniaxial loading, this model yields: a kinematic hardening identical to the hardening produced by isotropic exponential hardening. The numerical implementation of the model is discussed. Finite element simulations showing the capabilities of the model are presented.
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| 45. |
- Yin, Z. Y., et al.
(författare)
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Micromechanical analysis of kinematic hardening in natural clay
- 2009
-
Ingår i: International Journal of Plasticity. - : Elsevier BV. - 0749-6419. ; 25:8, s. 1413-1435
-
Tidskriftsartikel (refereegranskat)abstract
- This paper presents a micromechanical analysis of the macroscopic behaviour of natural clay. A microstructural stress-strain model for clayey material has been developed which considers clay as a collection of clusters. The deformation of a representative volume of the material is generated by mobilizing and compressing all the clusters along their contact planes. Numerical simulations of multistage drained triaxial stress paths on Otaniemi clay have been performed and compared the numerical results to the experimental ones in order to validate the modelling approach. Then, the numerical results obtained at the microscopic level were analysed in order to explain the induced anisotropy observed in the clay behaviour at the macroscopic level. The evolution of the state variables at each contact plane during loading can explain the changes in shape and position in the stress space of the yield surface at the macroscopic level, as well as the rotation of the axes of anisotropy of the material.
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