The influence of the lode parameter on ductile failure strain in steel

In this study an experimental investigation was conducted on tensile round circumferentially notched bar specimens. The results were compared to the experimental result on double notched tube specimens subjected to tension and torsion conducted in [5]. The comparison was done for moderate stress triaxiality levels larger than 0.7 with the objective to assess the influence of the Lode parameter on the ductile failure strain. The effective plastic strain, the stress triaxiality T and the Lode parameter L were determined at the center of the notch up to the point of failure by means of finite element based on J2-plasticity. The influence of the Lode parameter on the failure strain was remarkable for the high strength and low hardening material, whereas for the medium strength and high hardening material the influence of the Lode parameter was less prominent. The experimental results were then analyzed with the micromechanical model proposed in [6-7] which is based on the assumption that ductile failure is a consequence of that plastic deformation localizing into a band of imperfections. It is found that the micromechanical model captures the experimental trend and thus the influence of L on the ductility very well. It is found that the Lode parameter sensitivity increases with increase in the yield strength. The fractographical analysis reveals that Lode parameter sensitivity is associated with the failure characteristics of the material.