References of "International Journal of Plasticity"
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See detailA generic anisotropic continuum damage model integration scheme adaptable to both ductile damage and biological damage-like situations
Mengoni, Marlène ULg; Ponthot, Jean-Philippe ULg

in International Journal of Plasticity (in press)

This paper aims at presenting a general versatile time integration scheme applicable to anisotropic damage coupled to elastoplasticity, considering any damage rate and isotropic hardening formulations ... [more ▼]

This paper aims at presenting a general versatile time integration scheme applicable to anisotropic damage coupled to elastoplasticity, considering any damage rate and isotropic hardening formulations. For this purpose a staggered time integration scheme in a finite strain framework is presented, together with an analytical consistent tangent operator. The only restrictive hypothesis is to work with an undamaged isotropic material, assumed here to follow a J2 plasticity model. The only anisotropy considered is thus a damage-induced anisotropy. The possibility to couple any damage rate law with the present algorithm is illustrated with a classical ductile damage model for aluminium, and a biological damage-like application. The later proposes an original bone remodelling law coupled to trabecular bone plasticity for the simulation of orthodontic tooth movements. All the developments have been considered in the framework of the implicit non-linear finite element code Metafor (developed at the LTAS/MN2L, University of Liège, Belgium - www.metafor.ltas.ulg.ac.be). [less ▲]

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See detailA one phase thermomechanical model for the numerical simulation of semi-solid material behavior. Application to thixoforming
Koeune, Roxane; Ponthot, Jean-Philippe ULg

in International Journal of Plasticity (2014), 58

This work deals with the development of an appropriate constitutive model for semi-solid thixoforming processes of metallic alloys. These processes rely on a very specific material behavior called ... [more ▼]

This work deals with the development of an appropriate constitutive model for semi-solid thixoforming processes of metallic alloys. These processes rely on a very specific material behavior called thixotropy that can be displayed by some metallic alloys heated up to their semi-solid state. It is a particular evolutionary behavior which is characterized by a solidlike behavior at rest and a liquid flow during shearing, thus by a decrease of the viscosity and of the resistance to deformation while sheared. An original one-phase thermo-elasto-viscoplastic constitutive model has been developed. The basic idea is to extend the classical isotropic hardening and viscosity models beyond the solid state by considering two more non-dimensional internal scalar parameters. The semi-solid state is treated as a particular case, and one of the main features of the proposed constitutive model is that it remains valid over a wide range of temperatures, starting from room temperature to above the liquidus in a continuous manner, thus allowing a continuous transition between classical solid and fluid behavior. Another feature is that, after the forming step, it is possible to simulate the cooling down of the component back to room temperature using the elastic–viscoplastic model. So it is possible to estimate residual stresses, something that is definitely impossible while using a fluid-like model or a rigid viscoplastic approach. The presented model is illustrated and validated by means of representative numerical applications, as two different extrusion tests are carried out and the computed predictions are compared to experimental results. [less ▲]

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See detailA combined incremental-secant mean-field homogenization scheme with per-phase residual strains for elasto-plastic composites
Wu, Ling ULg; Noels, Ludovic ULg; Adam, Laurent et al

in International Journal of Plasticity (2013), 51

This paper presents an incremental secant mean-fi eld homogenization (MFH) procedure for composites made of elasto-plastic constituents. In this formulation, the residual stress and strain states reached ... [more ▼]

This paper presents an incremental secant mean-fi eld homogenization (MFH) procedure for composites made of elasto-plastic constituents. In this formulation, the residual stress and strain states reached in the elasto-plastic phases upon a fi ctitious elastic unloading are considered as starting point to apply the secant method. The mean stress fields in the phases are then computed using secant tensors, which are naturally isotropic and enable to de fine the Linear-Comparison-Composite. The method, which remains simple in its formulation, is valid for general non-monotonic and non-proportional loading. It is applied on various problems involving elastic, elasto-plastic and perfectly-plastic phases, to demonstrate its accuracy compared to other existing MFH methods. [less ▲]

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See detailOn the numerical integration of rate independent single crystal behavior at large strain
Ben Bettaieb, Mohamed; Débordes, Olivier; Dogui, Abdelwaheb et al

in International Journal of Plasticity (2012), 32-33

This paper presents a new numerical algorithm for the integration of the constitutive equations of a single crystal for finite rate-independent elastoplastic strains. The algorithm addressed in this paper ... [more ▼]

This paper presents a new numerical algorithm for the integration of the constitutive equations of a single crystal for finite rate-independent elastoplastic strains. The algorithm addressed in this paper is dedicated to face-centered-cubic (FCC) crystal structures. Its first feature is a much more efficient and more accurate integration scheme of the constitutive equations compared to previous attempts. This scheme is based on a fully implicit integration procedure, yet it may be transformed easily into an explicit scheme. Determining the set of active slip systems is performed by the use of a combinatorial search procedure, and the determination of the slip rates of the different active slip systems is based on the fixed point method. The second feature of this algorithm stems from the original method used to solve the ambiguity of the possible non-uniqueness of the set of active slip systems. A robust method, based on a small positive perturbation of the critical shear stresses, is proposed to overcome this difficulty. It is worth mentioning that the algorithm developed in this paper is not limited to one particular hardening law or to FCC crystal structures. Rather, it can be used and extended to various hardening laws and crystal structures (e.g. BCC or HCP. . .) in a straightforward manner. The authors demonstrate the performance of the proposed algorithm and illustrate its accuracy and efficiency through various numerical simulations at the single crystal and polycrystal scales. The predicted results obtained from those simulations were compared with those obtained using other numerical techniques and algorithms (i.e., a pseudo-inversion technique and an explicit algorithm). Our numerical predictions are also compared with some numerical and experimental results from other papers. The response of the polycrystal was computed by using the proposed algorithm combined with Taylor’s homogenization scheme, which is used to compute the overall polycrystalline behavior. The paper ends with a statistical study of the influence of the perturbation technique on the response prediction for a single crystal and a polycrystal. [less ▲]

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See detailFinite element analysis of the free surface effects on the mechanical behavior of thin nickel polycrystals
Keller, Clément ULg; Hug, eric; Habraken, Anne ULg et al

in International Journal of Plasticity (2012), 29

The miniaturization of metallic samples has been proved to deeply affect their mechanical properties leading to a softening or a hardening effect depending on the order of the dimension reduction. The ... [more ▼]

The miniaturization of metallic samples has been proved to deeply affect their mechanical properties leading to a softening or a hardening effect depending on the order of the dimension reduction. The objective of this work is to provide new numerical results which explain the softening mechanisms on the mechanical behavior for nickel polycrystals which have been experimentally characterized by the authors in a previous published paper (Keller et al., 2011). Based on a strain gradient crystalline plasticity model identified for nickel, simulations of tensile tests were performed for samples with different thicknesses and grain sizes. The simulations correctly reproduce the softening effect linked to a decrease in the thickness and in the number of grains across the thickness. The analysis of the plasticity mechanisms shows that the softening is due to surface effects which are discussed in terms of grain orientations, dislocation mean free path and long-range back-stress. The model also predicts a hardening mechanism for further dimension reduction if the samples have only grain boundaries perpendicular to the tensile direction. In this case, the modification of the mechanical behavior is due to strain gradients formation. [less ▲]

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See detailMicrostructural size effects on mechanical properties of high purity nickel
Keller, Clément ULg; Hug, E.; Feaugas, X.

in International Journal of Plasticity (2011), 27

The aim of this article is to provide experimental results in order to understand the microstructural size effects which occur with a decrease in the thickness of polycrystalline nickel samples from 3.2 ... [more ▼]

The aim of this article is to provide experimental results in order to understand the microstructural size effects which occur with a decrease in the thickness of polycrystalline nickel samples from 3.2 mm to 12.5 lm. The influence of the thickness, grain size and ratio thickness to grain size on the mechanical properties and strain hardening were investigated by mechanical tests and TEM observations. The results show the presence of three different domains of mechanical behaviour: polycrystalline, multicrystalline and quasi-single crystalline depending on the thickness and on the number of grains across the thickness. The transition between the three domains is due to the occurrence of surface effects involving a decrease in the long-range internal backstress revealed by the TEM observations. [less ▲]

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See detailRotation of axes for anisotropic metal in FEM simulations
Duchene, Laurent ULg; Lelotte, Thomas; Flores, Paulo et al

in International Journal of Plasticity (2008), (24), 397427

For the FE simulations relying on elasto-plastic models based on anisotropic yield locus description, it is important for the simulation accuracy to follow a Cartesian reference frame, where the yield ... [more ▼]

For the FE simulations relying on elasto-plastic models based on anisotropic yield locus description, it is important for the simulation accuracy to follow a Cartesian reference frame, where the yield locus is expressed. The classical formulations like the Hill 1948 model keep a constant shape of the yield locus when other texture based yield loci regularly update their shape. However in all these cases, the rotation of the Cartesian reference frame must be known. For simple shear tests performed on steel sheets, experimental displacements provide the actual updated position of initial orthogonal grids. The initial and final texture measurements give information on the average crystals rotation. For Hill constitutive law and texture based models, this paper compares the experimental results with different ways to follow the Cartesian reference frame: the co-rotational method, an original method based on the constant symmetric local velocity gradient and the Mandel spin computed by four different methods. [less ▲]

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See detailModel Identification and FE Simulations Effect of Different Yield Loci and Hardening Laws in Sheet Forming
Flores, Paulo; Duchene, Laurent ULg; Bouffioux, Chantal ULg et al

in International Journal of Plasticity (2007), 23(3), 420-449

The bi-axial experimental equipment [Flores, P., Rondia, E., Habraken, A.M., 2005a. Development of an experimental equipment for the identification of constitutive laws (Special Issue). International ... [more ▼]

The bi-axial experimental equipment [Flores, P., Rondia, E., Habraken, A.M., 2005a. Development of an experimental equipment for the identification of constitutive laws (Special Issue). International Journal of Forming Processes] developed by Flores enables to perform Bauschinger shear tests and successive or simultaneous simple shear tests and plane strain tests. Flores investigates the material behavior with the help of classical tensile tests and the ones performed in his bi-axial machine in order to identify the yield locus and the hardening model. With tests performed on one steel grade, the methods applied to identify classical yield surfaces such as [Hill, R., 1948. A theory of the yielding and plastic flow of anisotropic materials. Proceedings of the Royal Society of London A 193, 281–297; Hosford, W.F., 1979. On yield loci of anisotropic cubic metals. In: Proceedings of the 7th North American Metalworking Conf. (NMRC), SME, Dearborn, MI, pp. 191–197] ones as well as isotropic Swift type hardening, kinematic Armstrong–Frederick or Teodosiu and Hu hardening models are explained. Comparison with the Taylor–Bishop–Hill yield locus is also provided. The effect of both yield locus and hardening model choices is presented for two applications: plane strain tensile test and Single Point Incremental Forming (SPIF). [less ▲]

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See detailLength changes and texture prediction during free end torsion test of copper bars with FEM and remeshing techniques
Duchene, Laurent ULg; El Houdaigui, Fouad; Habraken, Anne ULg

in International Journal of Plasticity (2007), 23(8), 1417-1438

FEM numerical simulations of the experimental free end torsion tests [Toth, L.S., Jonas, J.J., Daniel, D., Bailey, J.A., 1992. Texture development and length changes in copper bars subjected to free end ... [more ▼]

FEM numerical simulations of the experimental free end torsion tests [Toth, L.S., Jonas, J.J., Daniel, D., Bailey, J.A., 1992. Texture development and length changes in copper bars subjected to free end torsion. Textures Microstruct. 19, 245–262] of copper cylindrical bars were analysed in the present study. The self-made Finite Element (FE) code LAGAMINE was used to compute numerical prediction of the Swift effect, i.e. the lengthening of the cylinder during the torsion. The material behaviour was represented by an interpolation law [Habraken, A.M., Ducheˆne, L., 2004. Anisotropic elasto-plastic finite element analysis using a stress–strain interpolation method based on a polycrystalline model. Int. J. Plasticity 20 (8–9), 1525–1560] linked with a Taylor polycrystal plasticity model either based on a strain rate insensitive or a visco-plastic crystal plasticity model. The influence of texture evolution was analysed. A torsion dedicated remeshing technique was developed to allow very large strain simulations. Predicted axial lengthening and predicted textures were compared to experimental measurements. A good agreement was obtained for shear strain up to 2.0. The Swift effect related angular shift of the pole figure maxima from symmetrical orientations was reproduced correctly. [less ▲]

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See detailAnisotropic elasto-plastic finite element analysis using a stress-strain interpolation method based on a polycrystalline model
Habraken, Anne ULg; Duchene, Laurent ULg

in International Journal of Plasticity (2004), 20(Issue 8-9), 1525-1560

This paper describes a stress–strain interpolation method to model the macroscopic anisotropic elasto-plastic behavior of polycrystalline materials. Accurate analytical descriptions of yield loci derived ... [more ▼]

This paper describes a stress–strain interpolation method to model the macroscopic anisotropic elasto-plastic behavior of polycrystalline materials. Accurate analytical descriptions of yield loci derived from crystallographic texture [Int. J. Plasticity 19 (2003) 647; J. Phys. IV France 105 (2003) 39] are an interesting alternative to finite element models, where the macroscopic stress is provided by an averaging of microscopic stresses computed on a set of representative crystallites [Acta Metal 22 (1985) 923; Int. J. Plasticity 5 (1989) 67]. The parameters of the analytical functions modeling the yield locus are identified by comparison with a high number of stress tensors computed, for instance, by the well-known Taylor model [J. Inst. Metal 62 (1938) 307]. This identification method depends on the crystallographic texture and should be applied each time that the plastic strain has induced a significant texture evolution. The stress–strain interpolation method accurately describes the anisotropic material behavior in a narrow stress direction defined by only five stress points. The cost of texture updating is then greatly reduced compared to a full analytical function of the yield locus. After the mathematical description of the stress–strain interpolation method, its validity is demonstrated on two non-radial strain paths. The simulations of a deep drawing experiment allow comparing model predictions and measurements. Accuracy and CPU time of the interpolation stress–strain method are judged against two other models, respectively based on a complete analytical yield locus and on the averaging of crystallite stresses. [less ▲]

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See detailUnified stress update algorithms for the numerical simulation of large deformation elasto-plastic and elasto-viscoplastic processes
Ponthot, Jean-Philippe ULg

in International Journal of Plasticity (2002), 18(1), 91-126

This paper is concerned with unified stress update algorithms for elastoplastic and elasto-viscoplastic constitutive equations for metals submitted to large deformations. We present here a newly developed ... [more ▼]

This paper is concerned with unified stress update algorithms for elastoplastic and elasto-viscoplastic constitutive equations for metals submitted to large deformations. We present here a newly developed time integration algorithm which is, in the case of J2 flow theory material behavior, an extension to the viscoplastic range of the classical radial return algorithm for plasticity. The resulting unified implicit algorithm is both efficient and very inexpensive. Moreover, if there is no viscosity effect (rate-independent material) the presented algorithm degenerates exactly into the classical radial return algorithm for plasticity. (C) 2002 Elsevier Science Ltd. All rights reserved. [less ▲]

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