The growth behavior of surface of surface fatigue crack under random loadings is investigated in 2024-T4 aluminum alloy. For fatigue testing and data acquisition, the system based on personal computers si developed, and pseudo random histories are generated by computer simulation method. Crack length and crack closure are measured by unloading elastic compliance technique.
The crack opening point is almost constant during a block of pseudo random loadings composed of 500 cycles and crack opening stress intensity factor Kop is found to be controlled by the maximum stress intensity range pair among the random load history. The growth rates of surface fatigue crack under random loadings can be well expressed in terms of the effective stress intensity range Keff accounting for crack closure.
