Mechanics and mechanisms of fatigue damage and crack growth in advanced materials

The mechanisms of fatigue-crack propagation in ceramics and intermetallics are examined through a comparison of cyclic crack-growth behavior in ductile and brittle materials. Crack growth is considered to be a mutual competition between intrinsic mechanisms of crack advance ahead of the crack tip, which promote crack growth, and extrinsic mechanisms of crack-tip shielding behind the tip, which impede it. In this paper, we examine and model the widely differing nature of these mechanisms, with emphasis on behavior in ceramics at ambient and elevated temperatures, and compare their specific dependencies upon the alternating and maximum driving forces (e.g., ΔK and K max), thereby providing a useful distinction of the process of fatigue-crack propagation in these different classes of materials.