CONVEXITY OF SMOOTH YIELD SURFACE OF FRICTIONAL MATERIAL.

Various known smooth yield conditions which have a reduced degree of symmetry in the deviatoric cross section, similar to the Mohr-Coulomb criterion, have been recently reviewed by O. C. Zienkiewicz and G. N. Pande. Yet, the question of convexity of the yield surface, which is important for theoretical reasons as well as numerical applications, has apparently, not been examined. This question is addressed in the paper. It is found that while the yield criterion of K. J. William and E. P. Warnke is always convex, the yield criteria of G. Gudehus and of J. H. Argyris, et al. , are convex only for a certain range of material parameters. However, parameter values which fall outside this range might not be excluded for applications to frictional materials.