3.1. Simple strain-state-independent fracture criteria
Strain-state-independent criteria often specify a critical equivalent, principal or thinning strain as a fixed parameter. Because of the differences among strain types, these criteria will behave differently when plotted in diagrams such as the FLD shown in Fig. 1. To illustrate this behavior, J2 plasticity with proportional loading is assumed. The strain types can then be calculated using the stress ratio α as follows: