Abstract
The effects of the mean stress-intensity factor, Km, and the range of the stress intensity, ΔK, on crack propagation phenomena in the Al-alloy RR 58 have been studied using contoured double-cantilever beam specimens providing a constant stress-intensity factor for all crack lengths.
Based on the experimental data available, a relationship of the following form, between the cyclic crack growth rate, da/dN, and the tensile loading levels, has been proposed:
where ΔK = (Kmax - Kmin); Kmax, Kmin and Km are the maximum, minimum and mean values of the stress-intensity factor; ΔKth is the threshold value of ΔK for crack propagation; K1C is the critical fracture toughness in plane strain conditions; A and α arc constants. In tests at room temperature (21 °C) in laboratory air and at a loading frequency of 0.15 Hz, it was found that ΔKth decreased with increasing values of K m , α was equal to 1.36 and A equalled 3.16 times 10-5(in/cycle).
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