Synergism between fatigue and cyclic‐stress corrosion cracking: Electrochemically active surface area

Abstract

After over 50 years of research on the topic, researchers continue to consider how time-dependent environmental effects can be integrated with cycledependent fatigue crack growth rate (CGR) models. Early corrosion-fatigue (CF) model assumptions were that cycle-dependent CF and time-dependent stress corrosion cracking (SCC) contributions are separable, operate in parallel, are non-interacting. However, research has shown that CF and SCC may interact synergistically to produce CGRs greater than that obtained by simple summation. Proposed here is that CF and SCC mechanisms may interact synergistically as each is dependent on the electrochemically active surface area (E-ASA) at a crack tip. A phenomenological model is developed for the effects of crack tip strain rate, film-rupture, and repassivation rates on E-ASA. Analysis of hold-time CGR data provides a method of separating cyclic-and static-load hold-time effects on E-ASA. Five model parameters, each having physical interpretation, are found to have reasonable magnitudes.

Fatigue damage evolution and failure of pre‐corroded aluminum alloy 7075‐T651 under air and corrosion environments

“…Hall et al pointed that corrosion fatigue and stress corrosion cracking may interact synergistically as each is dependent on the electrochemically active surface area at a crack tip. Crack tip strain rate caused by fatigue stress can enhance crack growth rate for stress corrosion cracking by increasing the electrochemically active surface area at a crack tip 22 . Chen et al demonstrated that the crack growth rate first increase and then decrease with the increase of NaCl concentration for AA2024‐T3 in 2.00‐ to 5‐wt.% NaCl solution 23,24 ; this was attributed to the competition between crack tip closure and hydrogen embrittlement.…”