Nonlinear analysis formulation > Failure criteria > Mohr-Coulomb and Tresca criterions

In principal stress space, this criterion takes the form of an irregular hexagonal cone. This criterion can be written in principal stresses as:

		(152)

where the principal stresses are given by:

		(153)

and where the "mean" and "deviator" stresses are

		(154)

The invariants s and t are:

		(155)

		(156)

Substituting for

and

from (59) gives the function:

		(157)

The Tresca criterion is obtained from (63) by putting

to give:

		(158)

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