Fatigue Crack Growth Rate Studies on High-Strength Low-Alloy Steel under Different Loading Conditions

The fatigue crack growth rate of 0.3C–CrMoV (ESR) steel has been investigated on parent metal and weld under sinusoidal and block loading conditions to simulate the proof pressure testing and service conditions of rocket motor case. Parent metal exhibited higher resistance to fatigue crack propagation at lower stress intensities during sinusoidal loading, and as the stress intensity increased, the crack propagation rates in weld and parent were almost identical. Block loading introduced a plastic zone ahead of the crack tip, retarding the crack propagation rates. During block loading with continuous increase in stress intensity levels, crack growth rates were slow compared to the specimens tested at different ranges of initial stress intensity levels. The Paris’ law constants C and m were evaluated.