The Mohr-Coulomb stress criterion is based on the Mohr-Coulomb theory also known as the Internal Friction theory. This criterion is used for brittle materials with different tensile and compressive properties. Brittle materials do not have a specific yield point and hence it is not recommended to use the yield strength to define the limit stress for this criterion.
This theory predicts failure to occur when:
s1 ≥ sTensileLimit if s1 > 0 and s3 > 0
s3 ≥ - sCompressiveLimit if s1 < 0 and s3 < 0
s1 / sTensileLimit + s3 / sCompressiveLimit < 1 if s1 ≥ 0 and s3 ≤ 0
The factor of safety is given by:
Factor of Safety (FOS) = {s1 / sTensileLimit + s3 / sCompressiveLimit} (-1)