Diffusion Models of Fatigue Crack Growth with Sequence Effects Due to Stationary Random Loading

摘要

A new fatigue crack growth model that includes load sequence effects is formulated. This model includes a load history dependent parameter, the reset stress, which reflects the state of residual compression at the crack tip. Unlike various models aimed at constant or block loads, this model includes constantly evolving crack closure effects under random amplitude loads. It is found to accurately predict crack growth of ASTM aluminum and SAE steel specimens. Simulation studies demonstrate the pronounced bias that may arise if these sequence effects are neglected. Simple analytical corrections for this bias are established, and show excellent agreement with simulation. These use a hierarchy of diffusion models on different time scales; e.g., steady-state reset stress models at various crack sizes. Higher-order statistics can also be found from numerical solution of the vector diffusion equations. 17 refs., 6 figs.