Abstract: Near-threshold fatigue crack propagation behaviour of a cold-worked copper tested with distinct fa- tigue testing systems under different stress ratios has been investigated.The emphasis was placed on the evaluation of crack closure effect as well as the effective fatigue threshold,It was found that the fatigue threshold for R=0 is higher than those for R=-1 and R=0.4,for which almost the same threshold value was derived.Compared with the conventional closure evaluation method,the pro- posed new closure evaluation method can generally interpret the dependence of the fatigue thresh- old on stress ratio and loading condition,and leads to a higher and relatively constant effective fa- tigue threshold of about 3 MPa·m~(1/2) for the cold-worked copper at different stress ratios and loading conditions.

Key words: near-threshold fatigue, crack, stress ratio