Growth of surface cracks under cyclic loading

Failures of thick structures such as aircraft components, automobiles components, buildings, etc. are usually caused by fatigue crack growth of part-through cracks (surface or comer cracks). The focus of the present investigation is on fatigue crack growth of semi-elliptical surface cracks, under constant amplitude loading and variable amplitude loading. The study includes experiments conducted on 7075-T6 aluminum alloy with a semi-elliptical surface crack to evaluate the growth of surface flaws under the influence of plasticity-induced closure, closure free surface flaws and surface flaws under flight simulated loading. The crack growth patterns will be compared with those predicted using a modified strip-yield model. The results from the constant amplitude tests conducted served as a benchmark for the strip-yield model, enabling determination of the required constraint factors at the surface and the deepest point of penetration. Work in the field of experimental uncertainty analysis will also be discussed in this investigation.