Ductile damage and fracture characterizations in bi-cyclic biaxial experiments

Abstract

This paper discusses novel extremely low-cycle bi-cyclic biaxial reverse experiments with large strains. Various tests with tension-compression-tension (TCT) shear cyclic loads, superimposed by either non-reverse or reverse cyclic loading patterns, are newly designed to investigate the plastic, damage, and fracture behavior. These experiments fill the gaps in carrying out complex reverse loading by utilizing 4mm thick biaxially loaded cruciform specimens. The deformed specimens in different loading stages are examined metallographically with micrographs to elucidate the influence of loading histories on the occurrence and evolution of micro-defects. In addition, scanning electron microscopy (SEM) is also used to analyze the fractured surfaces and verify the anisotropic damage mechanism. An advanced anisotropic cyclic plastic-damage continuum model is utilized to characterize the material behavior, including the Bauschinger effect, the stress-differential effect and the non-hardening effect after shear reverse loading as well as stress-state-induced damage mechanisms. Due to the utilization of the digital image correlation (DIC) technique, the numerical results can be compared with the experimental ones in both load–displacement curves and strain fields, respectively. The elastic strain triaxiality and strain Lode parameter are introduced, providing a novel perspective for analyzing the cyclic loading experiments.