The mechanisms of fatigue-crack propagation in ceramics and intermetallic materials are examined through a comparison of cyclic crack-growth behavior in ductile and brittle materials.This is achieved by considering crack growth as 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.The widely differing nature of these mechanisms and their specific dependence upon the alternating and maximum driving forces (e.g. DELTA K and K_max) provide a useful distinction of the process of fatigue-crack propagation in these different classes of materials.
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