Which one of the following statements is not correct regarding theories of failure?
- AThe cause of failure depends on the properties of the material.
- BIn case of brittle materials, the maximum principal stress theory should be used.
- CFor ductile materials, the maximum shear stress theory gives good approximation.
- DThe cause of failure is not dependent on the stress system to which it is subjected.Correct
Solution
Concept
Applicability of failure theories
Step-by-step solution
1. Failure depends on both the material and the stress system. 2. Brittle materials: maximum principal stress theory. 3. Ductile materials: maximum shear stress (Tresca) or distortion energy theory. 4. So the statement that failure does not depend on the stress system is wrong.
Explanation
A failure theory relates the combined stress state to the simple tension test. The result clearly depends on how the stresses are combined, i.e. on the stress system.
Why the other options are wrong
Statements (a), (b) and (c) are standard.
Shortcut
Brittle → Rankine; ductile → Tresca/von Mises.
Common mistake
Choosing a correct statement in a "not correct" question.
Correct answer: D) The cause of failure is not dependent on the stress system to which it is subjected.