Abstract

The equivalent stress hypotheses allow us to compare an arbitrary stress state with a uni-dimesional one. These hypotheses are empirical, so some plausibility criteria are needed. Diversity of such criteria shows that the hypotheses of strength are still being developed. However as a whole they can be systemised. Six modelling principles are suggested, leading to a small number of “all-purpose ” models. These models contain well-established hypotheses and can be applied to different material classes. The various forms of the meridian being of practical relevance can be received for these models. Unlike the known models, here the rotational, triangular or hexagonal symmetry in the deviatoric plane can be obtained independently from the compressibility. Meaningful are only the models with trigonal symmetry. In order to compute the parameters of the models a simple optimisation routine as well as certain constraints are proposed. 1.