Load history effects on fatigue crack growth threshold for Ti–6Al–4V and Ti-17 titanium alloys

Load history effects on room temperature fatigue-crack-growth threshold measurement are evaluated for titanium alloys Ti–6Al–4V and Ti-17. Baseline thresholds are determined by the use of a conventional load-shedding technique. Load history is synthesized by precracking at ΔK levels with Kmax greater than the subsequently measured threshold. Threshold for the latter is defined as the first notice of crack propagation under increasing ΔK, constant R, step loading. An empirical overload model is developed to account for precracking history on the threshold. Stress relief annealing after precracking and prior to threshold measurement is demonstrated to eliminate load history effects on rising ΔK, constant R, step loading threshold measurement, and to be comparable to that made using load shedding, but with considerable time saving.