The maximum normal stress criterion also known as Coulomb’s criterion is based on the Maximum normal stress theory. According to this theory failure occurs when the maximum principal stress reaches the ultimate strength of the material for simple tension.
This criterion is used for brittle materials. It assumes that the ultimate strength of the material in tension and compression is the same. This assumption is not valid in all cases.
For example, cracks decrease the strength of the material in tension considerably while their effect is far less smaller in compression because the cracks tend to close.
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:
σ1 >= σ limit , where σ1 is the maximum principal stress.
The Factor of Safety (FOS) is calculated as:
FOS = σ limit / σ1