Near-tip residual stress as an independent load interaction mechanism

Closure-free intrinsic threshold stress intensity, Delta Kth,i, varies significantly as a unique function of near-tip residual stress. It does so in equal measure in 5 mm and 50 mm thick compact tension specimens. Specially designed load sequences employing marker loads are employed to fractographically characterize the effect of load history on fatigue crack growth rate under closure-free conditions in 7075-T6 Al-alloy. Observed variations correlate with Delta Kth,i, confirming that near-tip residual stress operates as an independent load interaction mechanism. A certain 'micro latency' before crack arrest due to increased Delta Kth,i is investigated under different gaseous environments through experiments involving hold time.