Papers by Keyword: Plastic Anisotropy

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Authors: Yu Guo An, Henk Vegter, Louisa Carless
Abstract: Recently, many flexible constitutive equations have been proposed for sheet forming simulations. However, various mechanical tests are required to determine the many material parameters needed for such models. In the present work, effort has been made to investigate the correlation between the polycrystal plasticity based yield loci and those determined from mechanical tests, in order to define yield functions easily and accurately with minimum amount of experimental work. The results for different materials indicate that, in many cases, the Hill’48 deviates significantly from the measured yield loci. The yield loci derived from measured texture and polycrystal plasticity perform better than the Hill’48 yield function in general. Based on the two yield loci derived from the Taylor full constraint model and the Pancake model, a new combined model is proposed. The new model uses the averaged biaxial points of the two models but keeps the shape of the yield loci derived from the Taylor full constraint model in the stretching regime. The stress factors in the uniaxial and shear mode are calculated by averaging the stress factors of the two models. The proposed new description has been validated using several steel grades.
Authors: Paul van Houtte, Jerzy Gawad, Philip Eyckens, Albert van Bael, Giovanni Samaey, Dirk Roose
Abstract: Cup drawing of sheet material (carbon steel DC06 and aluminium alloy AA3103-O) is simulated using a Finite Element (FE) method configured as a hierarchical multi-scale model. It performs a two-way simulation of the interactions between the metal flow and the crystallographic textures of the polycrystalline material. In this, the evolution of the deformation textures is simulated by the Taylor and ALAMEL models, and this in every integration point of the FE mesh. The resulting textures have been compared with experimentally measured ones at different positions within the work-piece. An anisotropic constitutive model is used based on the Facet model identified from the current texture in every location by means of the Taylor and/or ALAMEL model. The updating procedure has been highly optimized. Simulated and experimental results (cup profiles, deformation textures) are compared. The effect of texture updating is assessed.
Authors: Elena Lyamina, Gow Yi Tzou, Shao Yi Hsia
Abstract: The paper concerns with an effect of plastic anisotropy on the load required to deform hollow cylinders between two parallel, rough dies. It is assumed that the material obeys Hill’s quadratic yield criterion and its associated flow rule. The friction stress is supposed to be proportional to the corresponding shear yield stress, including the maximum friction law as a special case. The kinematically admissible velocity field is chosen such that the stress field following from the associated flow rule satisfies the boundary condition at the plane of symmetry. Moreover, this velocity field is singular in the vicinity of the friction surface. Therefore, in the case of the maximum friction law the friction law is satisfied, again if the associated flow rule is combined with the velocity field. A significant effect of plastic anisotropy on the limit load is illustrated.
Authors: Sansot Panich, Vitoon Uthaisangsuk, Surasak Suranuntchai, Suwat Jirathearanat
Abstract: Plastic behavior of advanced high strength steel sheet of grade TRIP780 (Transformation Induced Plasticity) was investigated using three different yield functions, namely, the von Mises’s isotropic, Hill’s anisotropic (Hill’48), and Barlat’s anisotropic (Yld2000-2d) criterion. Uniaxial tensile and balanced biaxial test were conducted for the examined steel in order to characterize flow behavior and plastic anisotropy in different stress states. Additionally, disk compression test was performed for obtaining the balanced r-value. According to the different yield criteria, yield stresses and r-values were calculated for different directions and then compared with experimental data. To verify the modeling accuracy, a hole expansion test was carried out experimentally and numerically by FE simulation. Stress-strain curve from the biaxial test was described using voce and swift hardening models. Punch load and stroke, final hole radius, and strain distribution on specimen surface along the hole circumference and the specimen diameter in rolling and transverse directions were determined and compared with the experimental results. It was found that the simulations applying Yld2000-2d yield function provided an acceptable agreement. Consequently, it is noted that the anisotropic yield potential significantly affects the accuracy of the predicted deformation behavior of sheet metal subjected to hole expanding load.
Authors: Shun Ying Zhang, Lionel Leotoing, Dominique Guines, Sandrine Thuillier
Abstract: Bron and Besson yield criterion has been used to investigate the plastic anisotropic behavior of an aluminum alloy AA5086. The parameters of this anisotropic yield model have been identified by two different methods: a classical one, considering several homogeneous conventional experiments and an exploratory one, with only biaxial test. In this paper, the parameter identification with conventional experiments has been carried out with uniaxial tensile tests and simple shear tests in different orientations to the rolling direction and with a hydraulic bulge test. For comparison’s sake, Hill’s 48 yield function has also been calibrated analytically from uniaxial tensile tests. Numerical simulation for the cross biaxial test has been carried out with the anisotropic parameters identified from the conventional tests. From this simulation, the principle strains along a specified path in the gauge area of the cruciform specimen have been evaluated. A good agreement is observed between experimental and numerical values of principal strains for a large range of strain paths.
Authors: Natsuko Sugiura, Naoki Yoshinaga
Abstract: Electro-deposited pure iron has a very sharp and isotropic <111>//ND fiber texture and a needle shaped grain elongated in the ND. This pure iron exhibits an r-value of over 7, and it is difficult to explain such a high r-value only from the texture. Specific {110} plane slips, which are perpendicular to the sheet surface, exclusively act in this material and this limitation of the active slip system is the main mechanism behind the extraordinarily high r-value. Thus, tensile deformation by this slip system doesn’t require a decrease in thickness. In this study, the mechanism of this slip system limitation is investigated. Because both the {110} slip plane and grain boundary are perpendicular to the sheet surface, the slip plane can easily connect with adjacent grains. This good continuity of slip plane with adjacent grain may have an influence on the choice of slip system.
Authors: Ivaylo N. Vladimirov, Yalin Kiliclar, Vivian Tini, Stefanie Reese
Abstract: The paper discusses the application of a newly developed coupled material model of finite anisotropic multiplicative plasticity and continuum damage to the numerical prediction of the forming limit diagram at fracture (FLDF). The model incorporates Hill-type plastic anisotropy, nonlinear Armstrong-Frederick kinematic hardening and nonlinear isotropic hardening. The numerical examples investigate the simulation of forming limit diagrams at fracture by means of the so-called Nakajima stretching test. Comparisons with test data for aluminium sheets display a good agreement between the finite element results and the experimental data.
Authors: Natsuko Sugiura, Naoki Yoshinaga
Abstract: Electro-deposited pure iron has a quite sharp and isotropic <111>//ND fiber texture and a needle-shaped grain elongated in ND. This pure iron shows an r-value exceeding 7, which is difficult to explain from the texture alone. In this study the deformation behavior of electro-deposited pure iron was investigated to reveal the mechanism behind the extremely high r-value. The post-deformation surface slip lines indicated that the particular <110> plane slips, which are perpendicular to ND, exclusively act in the specimen. The tensile deformation caused by this slip system does not require any decrease in thickness, hence the extraordinary high r-value is mainly attributable to this limitation of the active slip system. Presumably, the needle-shaped microstructure affected the limitation of the slip system.
Authors: D. Gloaguen, Emmanuel Girard, Ronald Guillén
Abstract: Complementary methods have been used to analyse residual stresses in zirconium alloy tubes which were manufactured by cold rolling : X-ray diffraction and scale transition model. A modified elasto-plastic self-consistent model (EPSC) has been used to simulate the experiments and exhibits agreement with experimental data. X-ray diffraction analysis in rolling direction shows opposite stress values for {10 14 } and { 2022} planes respectively. The measured strains were generated by an anisotropic plastic deformation. Plastic incompatibility stress on X-ray measurements should be taken into account so as to make a correct interpretation of the experimental data.
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