Abstract
Microscopic and macroscopic surface fatigue crack propagation studies were carried out under periodic overstressing with Ti-6Al-4V alloy. Relatively small acceleration of crack propagation (less than 10 times) occurred when the crack length was of macroscopic scale more than 200μm. The fracture surface morphology showed that the crack propagated in zigzag manner similarly to the cases of macroscopic cracks with large acceleration in carbon steels and aluminum alloys reported previously. The acceleration was compared with that of through-thickness cracks as well as macroscopic and microscopic surface cracks in steels and aluminum alloys reported previously. A relatively good correlation was obtained in terms of the tensile strength-Young's modulus ratio σB/E and the acceleration became larger as σB/E became smaller. The surface crack growth rate in Ti-6Al-4V alloy, steels and aluminum alloy under constant amplitude loading agreed well with each other and with the through-thickness crack growth rate in different materials published in literature in the ΔKeff/E diagram.
