FATIGUE-CRACK GROWTH FROM SMALL SURFACE CRACKS IN TRANSFORMATION-TOUGHENED CERAMICS

A theoretical model based on the theory of complex potentials and disl ocation formalism is used to simulate the fatigue crack growth of smal l cracks in a transformation-toughened ceramic. Assuming power-law cra ck growth in which the growth rate depends on the effective stress int ensity at the crack tip instead of the applied stress intensity, it is shown that the crack growth rate decreases with the applied stress in tensity in the initial stage of fatigue crack growth. This is in agree ment with existing experimental evidence for the growth of small crack s in Mg-PSZ. Nem experimental results obtained by in situ observation in a scanning electron microscope of a similar material confirm this b ehavior. The numerical results also confirm the plausibility of using the steady-state toughness value obtained from quasi-static crack grow th as a normalizing parameter in the power-law for fatigue crack growt h.