Investigation into fatigue reliability of MSD structure by modifiable division of cyclic loading method

MSD (Multiple Site Damage) can cause the structure strength to degrade, which may lead to a catastrophic failure. In order to avoid the failure, the crack growth and reliability of the MSD structure in its whole life cycle should be exactly evaluated. In this paper, assuming that the fracture toughness and stress intensity factor of the MSD structure follow the lognormal distribution, a multiple-crack propagation reliability model of the MSD structure is constructed by combining the stress-strength interference model and the second boundary theory. In view of two influencing factors related to the crack growth of the MSD structure, a recursion relation of crack growth length under fatigue load is deduced. Then, by drawing on the modifiable division of the cyclic loading method, a calculation method of the failure probability of the MSD structure with changing load cycles is proposed. Finally, by analyzing and calculating a MSD panel with collinear hole-edge cracks under far-field uniform load, the variation trends of the failure probability of the MSD panel with fatigue load cycles are obtained, and the calculation results are compared with the experimental ones. It is found that the proposed method can reflect the failure trends of the MSD panel more accurately.