Effect of Nonproportional Loadings on Ductile Fracture: Experiments and analysis
Shamik Basu (Texas A&M University), Amine Benzerga (Texas A&M University)
Crack initiation and growth: methods, applications, and challenges
Wed 9:00 - 10:30
Barus-Holley 161
This study aims at understanding the effects of load path changes on the fracture locus of ductile materials. Guided by previous theoretical analyses, we design an experimental program to probe the path-dependence of the fracture locus of mild steel under axisymmetric loading conditions. Under such circumstances, failure occurs by microvoid growth to coalescence, as confirmed by post-mortem fractography. Following the literature, the fracture locus is given in terms of a strain to failure versus a strain-weighted average of stress triaxiality. The strain to failure was recorded for each loading path and the locus relating it to average triaxiality was constructed. This process was repeated for a set of non-proportional loading paths. By way of comparison, a fracture locus that best represents proportional loadings was also determined using notched bar experiments. Finite element calculations were used to determine the evolution of stress triaxiality at failure locations. A large number of families of step loading were also studied employing theoretical calculations using a void growth model with a simple failure criterion. The findings indicate that there is generally no one-to-one relationship between the average loading triaxiality and the strain to failure. In addition, variations of the latter due to nonproportional loadings can be so large that care should be taken in using fracture criteria based on a hydrostatic-stress dependent critical strain.