On the hysteretic nature of variable-amplitude fatigue crack growth

Local Stress-Strain (LSS) approach as applied in notch fatigue analysis is extended to the fatigue crack in order to simulate the effect of variable-amplitude loading on near-tip stress and strain. Simulated near-tip stress-strain response appears to explain load sequence sensitivity of near-threshold fatigue crack growth. This observation is supported by fractographic evidence of near-threshold variable-amplitude fatigue crack in an Al-Cu alloy under closure-free conditions.