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.