Fatigue crack closure evaluation with the potential method

Crack closure during crack propagation was measured with the potential method and the compliance technique for the titanium alloy Ti-6A1-4V. In vacuum with the potential method too high crack closure loads are evaluated due to an electrical contact of the roughened fracture surfaces. After a change in pressure from vacuum to 760 torr, after a decrease in mean load and after an overload cycle, the total amount of potential change during one cycle decreases gradually. This is due to the formation of an insulating oxide layer during the repeated mechanical contact.