Fatigue crack growth rate behaviour of 9310 steel under constant- and variable-amplitude loading

Fatigue-crack-growth experiments were performed on compact, C(T), specimens made of 9310 steel utilizing constant-amplitude loading and single-spike overloads. The specimens were subjected to a broad spectrum of load ratios (0.1 ≤ R ≤ 0.9). Various loading sequences were implemented to obtain near threshold test data including compression pre-cracking with constant amplitude, load reduction, and the ASTM E-647 load-reduction method. The results were compared with existing literature on thinner C(T) specimens. Notable load-history effects were observed within the threshold regime. The ΔK-rate test data exhibited a strong correlation over a wide range in rates when analyzed using FASTRAN, a life-prediction software, using a plane-strain constraint factor (α = 2.5). Additionally, under variable-amplitude loading, a transition from plane-strain to plane-stress behaviour was essential to align with the test results.