Design of Experiments is a buzz phrase that came out of QS9000 programs. The experiments chosen should have basis in sound engineering. If failure is predicted after a long series of load cycles, then the testing should be performed in the same manner. Loads should not exceed the actual load in service. Test temperature should be realistic. Rest time should be realistic unless a cooling fan is introduced to moderate temps during rapid cycling.
I have toyed around with concepts of degradation factors. How do you demonstrate required life if the lifetime is 20 years or more? The answer can be arrived at in a reasonable time if you: increase the oper temp, reduce the lube, increase the load, etc. It is pure conjecture at this point how to arrive at the degradation factors. This is good material for advanced study.