Abstract: Based on the twin shear stress theory, a new smooth ridge corner model of generalized twin shear stress criterion is proposed in this paper. This new smooth ridge model gives a close estimate of experimental data, reflects the influence of intermediate principal stress and the required characteristics concerning smoothness, convexity, symmetry, etc. The results of researches show that the three parameter criterion of William-Warnke and some other criteria are not a smooth Mohr-Coulomb surface, but a smooth ...