579 research outputs found
A study of the Yld2004 yield function and one extension in polynomial form: A new implementation algorithm, modeling range, and earing predictions for aluminum alloy sheets
No full textAs shown recently in (Soare and Barlat, 2010. Convex polynomial yield functions. J. Mech., Phys. Solids, 58, 1804-1818), the principal values based yield function Yld2004, proposed in (Barlat et al., 2005. Linear transformation based anisotropic yield function. Int. J. Plast., 21, 1009-1039), is polynomial for integer exponents. Based on this observation, a new algorithm is proposed for implementing symmetric yield functions formulated in terms of principal values. The algorithm is tested here by simulating with a commercial FE code the cylindrical deep drawing of two aluminum sheets. It is found that the classical description of the in-plane directional properties of the sheet (uniaxial r-values and yield stresses), even if modeled correctly by the yield function, is not sufficient for a unique characterization of the predicted earing profile. For certain combinations of the directional properties the r-value in biaxial stressing has to be considered for a correct calibration of the material model. This in turn requires a finer detail in yield surface modeling and, to achieve it, an ad-hoc extension of Yld2004 is constructed. In combination with the proposed implementation algorithm, the extension is shown to be a useful research tool, having some interesting modeling capabilities and satisfactory FE runtime. (C) 2011 Elsevier Masson SAS. All rights reserved.X1156sciescopu
A Shear Fracture Criterion to Predict Limit Strains in Sheet Metal Forming
No full textPresent work examines a mathematical model to predict the onset of shear fracture in the industrial processes of sheet metal forming such as biaxial stretching. Historically, sheet metal formability has been assessed by simple testing such as the Erichsen test. Lately, the concept of experimental Forming Limit Curve, FLC, was developed to evaluate formability. The Forming Limit Diagram shows the FLC which is the plot of principal strains in the sheet metal surface, epsilon(1) and epsilon(2), occurring at critical points obtained in the laboratory formability tests or in the fabrication process. Two types of undesirable failure mechanisms can occur in sheet metal forming operations: local necking and shear fracture. Therefore, two kinds of limit strain curves can be plotted: the local necking limit curve FLC-N and the shear fracture limit curve FLC-S. The D-Bressan shear instability criterion model proposed for the theoretical prediction of forming limit strain curve owing to the onset of local necking, FLC-N, in sheet metal forming is reformulated to predict the shear fracture strain limit, FLC-S, of sheet metal forming operations. Shear fracture is anticipated to initiate in the direction of pure shear when the shear stress attains some critical value. The Barlat Yld2000-2d anisotropic yield function proposed by Barlat et al. is employed and the material is assumed to display both planar and normal anisotropy. The new approach investigate the influence of mechanical plastic properties such us the plastic anisotropy parameters, pre-strain and work hardening coefficient in sheet metal formability. Some experimental and theoretical results of forming limit curve for aluminium obtained from present model for two values of the power coefficients a = 5 and 6 are shown. The relevant issues related with the FLC-S is presented and discussed.X1111sciescopu
Orthotropic yield criteria for description of the anisotropy in tension and compression of sheet metals
No full textIn this paper, yield functions describing the anisotropic behavior of textured metals are proposed. These yield functions are extensions to orthotropy of the isotropic yield function proposed by Cazacu et al. (Cazacu, O., Plunkett, B., Barlat, F., 2006. Orthotropic yield criterion for hexagonal close packed metals. Int. J. Plasticity 22, 1171-1194). Anisotropy is introduced using linear transformations of the stress deviator. It is shown that the proposed anisotropic yield functions represent with great accuracy both the tensile and compressive anisotropy in yield stresses and r-values of materials with hcp crystal structure and of metal sheets with cubic crystal structure. Furthermore, it is demonstrated that the proposed formulations can describe very accurately the anisotropic behavior of metal sheets whose tensile and compressive stresses are equal. It was shown that the accuracy in the description of the details of the flow and r-values anisotropy in both tension and compression can be further increased if more than two linear transformations are included in the formulation. If the in-plane anisotropy of the sheet in tension and compression is not very strong, the yield criterion CPB06ex2 provides a very good description of the main trends. (c) 2007 Elsevier Ltd. All rights reserved.X11144132sciescopu
Mechanical behaviour of TWIP steel under shear loading
No full textTwinning induced plasticity steels (TWIP) are very good candidate for automotive industry applications because they potentially offer large energy absorption before failure due to their exceptional strain hardening capability and high strength. However, their behaviour is drastically influenced by the loading conditions. In this work, the mechanical behaviour of a TWIP steel sheet sample was investigated at room temperature under monotonic and reverse simple shear loading. It was shown that all the expected features of load reversal such as Bauschinger effect, transient strain hardening with high rate and permanent softening, depend on the prestrain level. This is in agreement with the fact that these effects, which occur during reloading, are related to the rearrangement of the dislocation structure induced during the pre-deformation. The homogeneous anisotropic hardening (HAH) approach proposed by Barlat et al. (2011) [1] was successfully employed to predict the experimental results.110Ysciescopu
Earing predictions based on asymmetric nonquadratic yield function
No full textA nonquadratic yield function (Yld96; Barlat, F., Maeda, Y., Chung, K., Yanagawa, M., Brem, J.C., Hayashida, Y., Lege, D.J. Matsui, K., Murtha, S.J., Hattori, S., Becker, R.C., Makosey, S., 1997. Yield function development for aluminium alloy sheet. J. Mech. Phys. Solids, 45, 1727) which simultaneously accounts for the anisotropy of uniaxial yield stresses and r values was newly implemented in a finite element code. Yield surface shapes, yield stress and r-value directionalities of Yld96 were investigated and compared with those of the previous yield function, Yld91 (Barlat, F,, Lege, D,J., Brem, J.C. 1991a. A six-component yield function for anistropic metals. Int. J. Plasticity, 7, 693). Complete formulations for Yld96 implementation and the calculation of coefficients were also discussed for the convenient use of Yld96. A 2090-T3 aluminum alloy sheet sample was modeled and earing formation during a cup drawing test was simulated using the FEM code. The results of earing and thickness strain profiles were compared with the results obtained with Yld91. Investigations were further carried out with a translated yield surface to account for the strength differential effect observed in this material. Computation results with the translated yield surface were in very good agreement with experimental results. It was shown that the yield surface shape and translation have a significant influence on the prediction of the cup height profile during the drawing of a circular blank. (C) 2000 Elsevier Science Ltd. All rights reserved
Study on plastic flow localization prediction using a physically-based hardening model
No full textThe present paper aims at a detailed analysis of sheet metal formability using the physically-based hardening model accounting for the evolution of the anisotropic work-hardening induced by the microstructural evolution at large strains of Teodosiu and Hu (1995) [9]. The onset of localized necking is simulated by an advanced sheet metal forming limit model which connects, through the Marciniak-Kuczinsky analysis, the respective microstructural hardening model with the phenomenological anisotropic yield criterion Yld2000-2d (Barlat et al., 2003) [17]. Linear and complex strain paths are taken into account. The selected material is a DC06 steel sheet. An exhaustive study on the evolution of internal variables of the microstructural hardening model under such loadings is presented. The origin of the increase/decrease of formability under specific strain path changes is discussed. (C) 2011 Elsevier B.V. All rights reserved.X1132sciescopu
The formability of twinning-Induced plasticity steels predicted on the base of Marciniak-Kuczynski theory
No full textThe purpose of this work is to predict and analyze the formability of twinning - induced plasticity steels through the Marciniak-Kuczynski (MK) theory with emphasis on the solutions for improving the prediction results. The selected constitutive equations involve the Yld00-2d of Barlat et al. (2003) plane stress yield function, the Swift strain-hardening power law and the dislocation density based constitutive model proposed by Kim et al. (2013), taking into account the dislocation glide, twinning and dynamic strain aging. Three types of high manganese content TWIP steels sheet were selected. To understand the formability of the TWIP steel and the factors influencing it, a sensitive study on the effect of the mechanical properties of the TWIP steel on the MK theory concept and the predicted forming limits is performed. Using the dislocation density based microstructural model, the deformation twinning effect and the contribution of dynamic strain aging to the FLDs of TWIP steel is analyzed. The relevant influence of the sharpness of the yield surface in the biaxial stretching region in the prediction of FLDs of TWIP steels is highlighted. The extended MK model can be adapted to predict the forming limits of the TWIP steels by using an unusual high initial geometrical defect imposed by their high strain hardening. In this way it was showed that the MK theory cannot be applied for predicting the forming limits of TWIP steels unless by applying imperfection factors that are not physically reasonable. Therefore, new failure models are required for TWIP steel.11Nsciescopu
Convolute cut-edge design for a circular cup based on FEM and an analytical approach
No full textA convolute cut-edge design was developed for a single step cup drawing operation in order to produce an earless cup profile. An iterative procedure, based on the finite element method and a constant strain method using a new anisotropic yield function (Barlat et al., called Yld2004-18p), was used to design a convolute shape for an earless target cup height. A simplified analytical approach that relates the earing profile to r-value directionality was presented in this work. R-value directionality was included with the incompressible condition from the compressive mode at the rim. The result obtained from the iterative procedure was compared with the one from the analytical approach suggested. It is proven that both Yld2004 model and the simplified analytical method provide an accurate prediction of the convolute cut-edge shape. © 2007 American Institute of Physics
A new model for FLD prediction based on advanced constitutive equations
No full textAn advanced sheet metal forming limit model is developed. Using the Marciniak-Kuczinsky analysis, this approach intends to join advantages of physics-based aspects of plasticity with advantages of phenomenological material description. It aims thus at connecting the most advanced physically-based hardening model accounting for the evolution of the anisotropic work hardening induced by the microstructural evolution at large strains of Teodosiu and Hu (1995) with the advanced phenomenological anisotropic yield criterion Yld2000-2d (Barlat et al. Int J Plast 19: 1297-1319, 2003). Two deep-drawing quality sheet metals are selected: a bake-hardening steel (BH) and AA6016-T4 aluminium alloy. Linear and complex strain paths are taken into account. By comparing the simulated and experimental results the model is validated.X11810sciescopu
Numerical integration algorithm of updated homogeneous anisotropic hardening model through finite element framework
No full textIn this work, an updated version of the homogeneous anisotropic hardening (HAH20) model proposed by Barlat et al. (2020) is implemented into a finite element framework through a stress integration algorithm. To improve the convergence of this model inside the integration algorithm, the algorithmic step sizes of the solution variable increments are controlled by the line-search method. The HAH20 implementation is validated by comparing the simulation results obtained from the finite element analysis with those calculated by stand-alone HAH20 code. In addition, the simulation results of tests, including strain path changes such as tension-compression and cross-loading, are compared with experimental measurements, and the effectiveness of the step size control in the current HAH20 model is investigated. The performance of the implemented algorithm is analyzed through convergence maps for critical strain path change simulations. (C) 2020 Elsevier B.V. All rights reserved.11Nsciescopu
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