Abstract

Strength theory deals with the strength of material under the complex stress state (bi-axial stress or tri- axial stress). Sometimes, it is referred to as the yield criterion in metallic mechanics and computational mechanics, or as the failure criterion in rock-soil mechanics and concrete mechanics. Great effort has been devoted to the formulation of strength theories, failure criteria, yield criteria and many versions of these have been presented during the past 100 years (Zyczkowski, 1981; Yu, 2002). From the 1950s to the 1970s, the von Mises criterion was considered the best. The von Mises criterion, however, is only suitable for those materials that have identical strength both in tension and compression, and shear yield stresses equal to ?_y = 0.577?_y, where ?_y is shear yield strength and ?_y is uni-axial yield strength of materials.