Summarising, the proposed formulation(1)needs the specification of the current values of , which have to be specified through suitable hardening laws, and parameters Rh; nd; nc ; kR; βe0 ; βc0 and kc . Table 2 shows the full range of possibilities in the choice of parameters for the different shapes that surface (1) is able to reproduce. For any shape either in the meridian and the deviatoric representation, there is one parameterthat is irrelevant for the definition of the shape. It should be noted that the only non null parameter for obtaining the Matsuoka and Nakai (1974) criterion is nd=1
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