TESTING SIMULATION
A virtual test starts with one of the above configured specimens. The
specimen is subjected to a cyclic axial load corresponding to the
parameters given for one of the experiments listed in Table 1.
Consequently, some grains are plastically deformed. A grain is
considered experiencing plastic deformation when the current applied
stress is greater than its yield stress.
The extents of the monotonic and cyclic plastic zones ahead of the tip
of a crack are assumed given by either (1) carefully calculated extents
based on fracture mechanics concepts in terms of crack length, applied
stress and yield stresses of the grains located ahead of the tip or (2)
the extent of plasticity within the grains located ahead of the tip,
whichever is greater. The applied load and the extents of the crack tip
plastic zones calculate corresponding maximum and cyclic crack tip
opening displacements which are, then, used for the calculation of the
advance rate of the considered tip. The details of those calculations
are given elsewhere 37.
All existing tips are subjected to the above calculations. An increment
of load cycles is accommodated to capture the earliest event out of (1)
a maximum tip advance of 0.1μm, (2) a maximum approach of
adjacent tips of two neighboring cracks of 0.1 μm (3) the
earliest merge of two approaching tips and (4) the instant of changing
the applied load as given in Table 1. The resulting advance of the tips
updates their coordinates within the surface grains. With the updated
configuration of the existing cracks, a computational loop terminates.
The flow chart of a computer software devised to follow and repeat the
above algorithm for further computational loops is shown in Fig. 2.