Mechanisms of fatigue-crack propagation in ductile and brittle solids

摘要

The mechanisms of fatigue-crack propagation areexamined with particular emphasis on the similarities anddifferences between cyclic crack growth in ductile materials, suchas metals, and corresponding behavior in brittle materials, such asintermetallics and ceramics. This is achieved by considering theprocess of fatigue-crack growth as a mutual competition betweenintrinsic mechanisms of crack advance ahead of the crack tip (e.g.,alternating crack-tip blunting and resharpening), which promotecrack growth, and extrinsic mechanisms of crack-tip shieldingbehind the tip (e.g., crack closure and bridging), which impede it.The widely differing nature of these mechanisms in ductile andbrittle materials and their specific dependence upon the alternatingand maximum driving forces (e.g., #DELTA#K and K_(max)provide a useful distinction of the process of fatigue-crackpropagation in different classes of materials; moreover, it providesa rationalization for the effect of such factors as load ratio andcrack size. Finally, the differing susceptibility of ductile and brittlematerials to cyclic degradation has broad implications for theirpotential structural application; this is briefly discussed withreference to lifetime prediction.