The effects of waveshape on the fatigue crack growth rate (da/dN) and fracture mode in Waspaloy have been studied. The main effects are: (i) at high frequency (0.25 Hz) growth rates are insensitive to waveshape, (ii) at low frequency (0.0033 Hz) a greater contribution to the growth rate is indicated for the ramp-up and dwell components of the waveform when compared to the ramp-down time, (iii) increasing growth rate and proportion of intergranular fracture is observed with increasing crack opening time, t{sub}(opening) the period within a cycle when the crack surfaces are open. Analysis of the fatigue data using different waveform configurations has shown that better correlation between growth rate and fracture mode is observed when t{sub}(opening) rather than t{sub}(total) is used as the basis for a mechanism map.
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