The influence of variable amplitude loading on crack closure and notch fatigue behaviour

Smooth and notched 1045 steel specimens were tested under constant amplitude, R = −1 loading and under a variable amplitude load history consisting of periodic overloads followed by high R-ratio small cycles. The notched specimens exhibited a notch size effect under constant amplitude loading, but the effect was reduced in the long life region (defined as a fatigue life > 10 7 cycles) under the variable amplitude load history. A crack growth model that followed crack closure changes on a cycle-by-cycle basis adequately predicted fatigue life for the periodically overloaded notched specimens.