Principle Stresses: Example 2

Question:

The direct stresses acting on an element of material, on orthogonal planes, are 85N/mm^2 (tensile) and 45N/mm^2 (tensile) together with a shear stress of 15N/mm^2. What is the factor of safety according to the

a) Tresca yield criterion

b) von-Mises yield criteria

The material has a tensile yield stress of 240N/mm^2 and v=0.3.

Answer:

a) Tresca:

As both stress values are positive, the second stress figure is set to zero to comply with Tresca Yield Criteria.

b) von-Mises: