Work-piece length of the effect on stress and analysis of cracking-criterion under equal channel angular pressing

Abstract

Finite-element method (FEM) and experimental investigation of 2024 Al subjected to equal-channel angular pressing (ECAP) has been carried out. The maximum equivalent normal stress and the maximum shear stress at an optionally given displacement of ECAP have been obtained through FEM for various given initial length of ECAP samples. The cracking criterion for the materials subjected to ECAP is further discussed with the help of experimental investigation. It is observed that at all given displacement of ECAP, the maximum equivalent normal stress is always less than the ultimate tensile strength of materials for all ECAPed samples with various initial length, while the maximum shear stress is always present at the angular channel zone of ECAP die, and its value decreases with the decrease of initial length of ECAPed samples. When the used initial length is small enough, the computed maximum shear stress becomes less than the shear strength of the materials, which is in very good agreement with the experimental observation that the frequency of sample cracking is decreased greatly. It is concluded that the non-cracking criterion of the materials subjected to ECAP could be expressed as "the maximum shear stress is less than the shear strength of materials". It is also suggested that a rational research should be involved in the actual measurement of stress-strain curve and the optimization in the configuration of ECAP die, the technology of materials pretreatment and the length of samples based on the above-motioned non-cracking criterion.