Analysis of ductile damage and fracture under reverse loading

Abstract

This paper investigates the influence of reverse and cyclic loading on the damage and fracture behavior of the aluminum alloy EN-AW 6082-T6. A series of uniaxial tension–compression and shear tests with newly designed shear specimen has been performed to analyze the development of plastic deformations and damage under different stress conditions. In addition, several monotonic uniaxial tension and compression tests are conducted to detect the strength-differential (SD) effect. Hence, combined hardening law is incorporated into the hydrostatic-stress-sensitive yield function to predict irreversible deformations under cyclic loading. A newly defined strain triaxiality is proposed to describe the strain state and to reveal the damage evolution processes. To accurately model cyclic plasticity, strain triaxiality is incorporated into the extended Voce strain hardening, and the angle parameter between effective back stress and reduced stress is added to Chaboche’s kinematic hardening. Furthermore, a modified anisotropic stress-state-dependent continuum damage model is considered to evaluate the damage and fracture evolution processes. Additionally, the digital image correlation (DIC) technique is applied to measure the strain fields during the experiment. Numerical simulations are used to predict the distribution of stresses and strains. Finally, the distribution and amount of damage are used to explain the fracture behavior detected by scanning electron microscopy (SEM) pictures taken in the critical parts of the specimens. SEM images and numerically predicted damage stains confirm that the different failure modes depend on the loading history.