Application to subcritical crack growth

This chapter explains how fracture mechanics can be applied to subcritical crack growth, primarily by environmentally-assisted cracking, creep, and fatigue. It describes in each case the development of a crack-growth relationship characterizing the velocity of a crack, with respect to time or number of cycles, as a function of the relevant governing parameter, which is generally the stress intensity factor, K, for environmentally-assisted cracking, a series of characterizing parameters for creep-crack growth, such as C∗, C(t), and C t , depending on the mode of creep deformation, and the alternating stress intensity, ΔK, for fatigue crack growth. In addition to a brief discussion of mechanisms, for fatigue, we further derive how the form of the crack-growth law, which is known as the Paris law, can change for ductile (e.g., metallic) vs. brittle (e.g., ceramic) materials. Finally, we show how such crack-growth relationships can be utilized to predict the lifetime of components or structures using the damage-tolerant life-prediction methodology.