Based on experiments on marble

red sandstone and granite

their ultimate envelope can be averaged as straight lines. With these lines

their slope and bonding stress can be calculated. Two hardening parameters should be decided by data of some points on stress-strain curve before peak strength. According to experiments

the occurrence of failure isn’t far away from phase change

so the phase change parameter can’t be computed by Desai’s method. The authors think that taking a value of a little greater than 2 is appropriate. When back predicting stress-strain curve

the authors proposed a simple and applicable method

regarded the end of initial compression phase as initial condition to calculate initial hardening parameter and trajectory of plastic strains.