Prior-to-failure extension of flaws under monotonic and pulsating loadings: Inelastic fatigue
An equation governing the prior to failure crack propagation is proposed. For a rate-sensitive solid containing two-dimensional crack and subject to the tensile mode of fracture, the differential equations are integrated numerically for the loads increasing monotonically in time. The resulting integral curves sigma = sigma(l) and l = l(t), i.e. load vs. crack length and length vs. time, indicate that the growth of cracks in the subcritical range is strongly rate dependent. The fatigue growth, viewed as a sequence of slow growth periods, is simulated on an EAI 380 analogue computer. The fourth power law proposed by Paris is confirmed only within a certain range of high-cycle fatigue propagation and for a rate-insensitive solid. For a more pronounced rate dependency, induced by the viscosity of a solid and/or in the proximity of the final instability point, the growth is markedly enhanced.