Fracture prediction under nonproportional loadings by considering combined hardening and fatigue-rule-based damage accumulation

Abstract

To predict fracture initiation in ductile material under nonproportional loadings, an approach considering combined hardening and a fatigue-rule-based damage accumulation law was investigated. Eleven complex nonproportional experiments, including torsion-tension tests, compression-torsion tests, and uniaxial tension-compression cyclic tests were performed. Finite element analysis was conducted on the experimental data to extract information on essential local fractures, such as stress triaxiality and the Lode parameter. The Chaboche combined hardening model was tuned to capture the material hardening characteristics, ensuring a reliable description of the hardening behavior compared with the isotropic hardening assumption. In addition, the inclusion of fracture locus was proposed to determine the predeformation effect on damage evolution. Combined with the fatigue-rule-based damage accumulation laws, the damage evolution can consider the variable strain history. Thus, fatigue-rule-based damage accumulation, together with the combined hardening law, considerably improved the ability to predict fracture onset in cases of torsion-tension loading with respect to the integral-based damage accumulation law.