Fig. 2 Flow chart of the computer program developed in the present work
With an increase in the load cycles, (1) the total cracked area\(\ A_{C}\) increases, (2) the supporting ligament area decreases, (3) the current stresses increase, (4) the two adjacent tips of some neighboring cracks approach and (5) the extent of the plastic zones ahead of the tips of some cracks is altered. As a consequence, the tip of a crack may either advance or stop propagating. Thus, the adjacent tips of neighboring two cracks either stop their advance at a distance or the two cracks coalesce.
In the case of a CAL, the following two scenarios are possible. Should the amplitude of the applied stress be greater than the fatigue limit of the material, fracture of the specimen takes place after the application of some load cycles when the ligament area becomes unable to support the current applied maximum stress. The second scenario happens when applied stress amplitude is less than the fatigue limit of the material. In this case, all existing cracks stop their propagation after a number of loading cycles and the specimen remains unbroken after a number of loading cycles greater than\({\ 10}^{7}\).
The program was run to trace possible events of fatigue growth behavior of the existing surface cracks due to the application of one of the loading patterns listed in Table 1. In this case, the possibility is to have the first scenario. Different specimens were randomly configured and virtually tested.