Question

(A) Describe how fatigue damage happens in a ductile material. Draw sketches if needed. (B) If we maintain a constant stress σ-0.9G (GIs the yield strength) on a steel, will fatigue damage happen? Why?

Answer 1

A) Fatigue failure in ductile materials : When material undergo repeatedly applied loads after a certain amount of plastic deformation, a neck forms in the tensile test specimen, the force for further deformation decreases and, finally, the piece breaks. When fracture occurs after extensive plastic deformation, the test piece fails by ductile fracture.

B) No fatigue failure will not occur. As under constant loading stress below yield stress failure will not occur.

Fatigue can only be happen under cyclic loading not under constant applied load.