Fatigue threshold behavior of α-phase copper alloys in desiccated air: modulus effects

The effects of load ratio (R) in the range of 0.1–0.9 on fatigue threshold behavior of three α-phase copper alloys were studied. Three commercial alloys of nominal composition Cu–30Ni, Cu–30Zn and 90Cu–7Al–2Fe were tested. Threshold values (ΔKth) of these Cu-alloys decreased linearly with increasing R-ratio. Differences in elastic modulus (E) exerted a clear and significant effect on the threshold behavior, i.e., higher E promoted higher thresholds for the whole tested range of R-ratios. Good correlation was found between E and the threshold level under closure-free conditions, i.e., high R-ratio. Roughness-induced closure and crack micro-deflection appeared to dominate the threshold behavior.