Application of Ductile Fracture Criteria for the FLD Prediction of Steel Sheets

Abstract

This paper applies ductile fracture criteria for the formability prediction of various types of steel sheets to evaluate the accuracy of ductile fracture criteria on the prediction of forming limit diagrams (FLDs). The ductile fracture criteria studied in this paper include the Cockcroft criterion (1968), the Brozzo criterion (1972), the Oh criterion (1979), the Oyane-Sato criterion (1980), the Clift criterion (1990) and the Ko-Huh criterion (2007). The material properties and the experimental FLDs of 24 kinds of steel sheets are collected from researchers. Hosford79 yield function with normal anisotropy is utilized to model the yield surfaces of these steel sheets. The Hollomon equation is employed to describe the strain hardening behaviors. The material constants in the ductile fracture criteria are evaluated with the limited strains in the uniaxial tension state for Cockcroft criterion, Brozzo criterion, Oh criterion, Clift criterion and Ko-Huh criterion while the limit strains in both the uniaxial tension and plane strain tension conditions are used for the material constant evaluation in Oyane-Sato criterion. The FLDs are predicted with these ductile fracture criteria with linear strain paths. The predicted FLDs are compared with experimental data. The results show that the FLDs predicted from Oyane-Sato and Ko-Huh ductile fracture criteria match the experimental data well for the LHS FLDs while other ductile fracture criteria overestimate the limited strain in plane strain tension conditions. For the right hand side FLDs, all these ductile fracture criteria do not perform well compared with experimental FLDs.