Method for Determining Localized Instability Based on Strain Evolution

In the state of tensile stress, as the deformation increases, the plastic flow of the sheet metal changes from a stable state to a meta-stable state, and finally flows in an unstable state until it ruptures. Although the classic plastic instability theories can describe the instability behavior of materials, these instability theories are based on accurately obtaining the basic performance parameters of materials (such as n, r). However, the basic performance parameters of some materials are not constant and their changes are related to the course of strain, which brings certain difficulties to theoretical calculation of instability strain. Therefore, the classical plastic theory is combined with digital image correlation(DIC) technology to study the evolution law of different strain components in the neck shrinkage region, and the local instability criterion based on strain evolution is established. Finally, advanced high-strength dual-phase steels (DP780, DP980 and DP1180) are used as the research object to verify the validity of the localized instability criterion established. Subsequently, a method for determining the damage instability point based on the unity of time and space is proposed. © 2023 Chinese Mechanical Engineering Society. All rights reserved.