The number of cycles is important in the definition of both fatigue types. If the life is between 103 and 105 cycles, we are in a low cycle fatigue case. For this kind of fatigue, the material is loaded with stress level that produces macroscopic plastic strain. For the second fatigue kind, high cycle fatigue, the material only suffers microscopic plastic strain and the number of cycles can reach several millions.
Once the parameters have been introduced, it is necessary to define the failure criteria for the end of the test.
The complete breaking of the specimen.
The decrease of the maximum load, the maximum stress or the elastic modulus, due to the existence of cracks.