Determining the state of stress in the narrow section of Arcan test specimens, by the FEM method

Abstract

Mohr-Coulomb failure criterion is used to establish the failure conditions under a compound state of stress. According to this criterion, materials failure is produced to a certain combination of normal and shear stresses. Arcan type tests are an easy way to study the specimens behavior in pure and mixed mode (tensile & shear) respectively. The fixture allows an ARCAN sample to be rotated at 15° increments from 0° to 90° to produce different amounts of mode-mixt during loading; with 0° being pure tension/compression loading to 90° being pure shear loading. The Arcan method, like the Iosipescu method, uses specimens with a predetermined breaking section. A condition for material testing is that the stress in the narrow section to be as uniform as possible. This depends on the shape and depth of the notch. Starting from apriori knowledge about Iosipescu specimen, the modelling will be carried in FEM software to optimize the shape of the specimen, in order to obtain more uniform stress in cross section, A FEM is performed for Iosipescu specimen, designed for pure shear, when it is mounted in Arcan device, so it is need to be studied for some complex states of stress. The studied material is aluminum alloy type 7075, used in aerospace industry. This analysis is necessary before the tests are carried out, in order to adopt an appropriate form of the specimens.