Growth Rate of Small Surface-Cracks in Age Hardening Cu-Ni-Si Alloy under Cyclic Stressing

Stress-controlled fatigue tests were conducted on round-bar specimens to understand the fatigue behavior of precipitate-strengthened Cu–6Ni–1.5Si alloy. The cracks were initiated at the grain boundaries, followed by growth along the crystallographic slip planes in the adjacent grains. The crack growth data of plain specimens exhibited a large scatter, resulting in a difficulty of the measurement of crack growth rate. To evaluate the small-crack growth rate of the alloy, the plain specimens with a small blind hole as the crack starter were fatigued. The crack growth rate of small cracks from the hole was uniquely determined by a term σanl and the material constant, n, was 5.3. The term σanl with n = 5.3 was applied to the plain specimen, showing good applicability of the term to small cracks in the plain specimen.