Microstructural Crack Tip Plasticity Controlling Small Fatigue Crack Growth

Abstract

In this chapter, we present a metallurgical–mechanical mechanism-based strategy for the design of fatigue-resistant metals. Specifically, we elucidate the importance of the metallurgical microstructure in a mechanical singular field (crack tip). The fatigue crack growth resistance is controlled through the crack tip “plasticity”, and the effect of the associated microstructure becomes significant when the crack is “small (or short)”. More importantly, the resistance to small crack growth determines a major portion of fatigue life and strength. Therefore, the microstructural crack tip plasticity is a key breakthrough to the development of fatigue-resistant metals. As successful examples of this concept, we introduce the effects of grain refinement, martensitic transformation, strain aging, dislocation planarity enhancement, and microstructure heterogeneity on small fatigue crack growths.