The modified Tresca criterion is one of the early criteria proposed to describe the yielding of polymers.
On the contrary, modified Tresca criterion gives better prediction of the yield locus of the annealed PP-based polymers (PPH-160, PP/10POE-160).
As for the parameters of the modified Tresca criterion ([tau].sub.T.sup.o] and [[Mu].sub.T]) which has been shown to better describe the yield behavior of annealed materials, [[tau].sub.T.sup.o] increases with thermal treatment consistently with the increase in [[sigma].sup.y] while the yield stress pressure sensitivity coefficient slightly increases with annealing (Table 4).
10 the relevant envelope of the modified Tresca criterion of the PPH-160 is constructed using Eq.