Role of microstructures on the growth of long fatigue cracks

An analysis is presented to understand the role of microstructures on the two crack growth driving force parameters, K_max* and ΔK^th*, without invoking the extrinsic crack closure concepts. Microstructural variables considered are: grain size, precipitates and stacking fault energy. It is shown that K_max* is strongly affected by the scale of the microstructure, such as grain size or precipitate spacing. For each case, the mode of slip deformation and environment affects the fatigue resistance as represented by K_max*. However, the microstructures seem to have a smaller effect on ΔK_th*. Also, the enhanced planarity of slip from the reduction in stacking fault energy has a pronounced effect on K_max* when compared with the materials deforming under homogeneous slip.