Question

1. What features distinguish fatigue fracture surfaces from monotonic fracture surfaces?

2. When might you expect fatigue fractures to look similar to monotonic fractures with the unaided eye?

3. Describe how you may get an indication of the magnitude of the cyclic stress and cycles to failure by looking at the fracture surface?

4. Identify a component where the control of fatigue crack nucleation life is most important and explain why?

5. Identify a component where the control of fatigue crack propagation life is most important and explain why?

Answer 1

1. The damage modes in cyclic loading (pulsating tension) were similar to those in monotonic tension except that an additional wear mechanism of damage, produced by cycling, was identified in the internal structure of the composite. Due to cyclic tensile loading, those fatigue damage modes developed slowly, leads to a gradual increase in cyclic elapsed strain and a decrease in composite modulus.