Analysis of two parameter identification methods for original and modified Johnson-Cook fracture strains, including numerical comparison and validation of a new blue-brittle dependent fracture model for free-cutting steel 50SiB8

A non-linear relation between fracture strain and temperature is observed in Split Hopkinson Tension Bar (SHTB) tests for free-cutting steel 50SiB8 at high strains temperatures, due to blue-brittleness. fourth-degree polynomial function the thermal parts of original modified Johnson-Cook (JC) constitutive equation suggested corresponding parameters are identified. Fracture modelling not reported literature. characterized under quasi-static, isothermal, rate conditions using smooth notched tension specimens. For calculation JC parameters, two different parameter identification procedures, so-called forward backward methods performed, compared with each other explained detail. stress triaxiality factor model, method while proposed model. The effect blue-brittleness presented. Furthermore, FEM simulations based model experiments. In blue-brittle range, new adjusted shows more accurate results, regarding diameter strain. Additionally, this work introduces a combining Bai-Wierzbicki dependent models nonlinear effect, further experiments required order determine its parameters.