A study on determining true stress-strain curve for anisotropic materials with rectangular tensile bars

摘要

Recently, a method has been proposed for determining material true stress-strain curve with rectangular tensile bars up to localized necking. In the proposed method, material true stress-strain curve can be directly calculated from the load versus thickness reduction (at the minimum cross-section) curve. The method was established based on the finite element (FE) analysis for isotropic materials. In this study, this method has been extended for materials with isotropic elastic properties but anisotropic plastic properties. Two cases, transverse anisotropy and planar anisotropy, have been considered. Hill's anisotropic material model implemented in ABAQUS was applied for the study. More than 30 three dimensional FE analyses of rectangular specimens with different anisotropy value, hardening exponent and cross-section aspect ratio have been carried out. It is shown that the relation between thickness reduction and total area reduction of a given cross-section is influenced by material plastic anisotropy. It is, however, found that the anisotropic effect on the thickness-area reduction relation can be normalized by the width to thickness strain increment ratio r, and a modified thickness-area reduction relation is proposed and numerically and experimentally verified. One practical problem in tensile test is that it is difficult to predict the necking location. In this regard, a study on the sensitivity of initial notch geometry has been carried out. It is found that for a fixed initial notch radius, the percentage of error is approximately equal to the percentage of initial width reduction. The accuracy of using large initial width reduction can be improved by using large notch radius. (C) 2001 Elsevier Science Ltd. All rights reserved. [References: 11]