Characteristics of mode I fatigue crack growth of aged prestrained carbon steel

The fatigue crack growth property of prestrained carbon steels was investigated to predict the fatigue life of the structures and mechanical parts, the materials of which were prestrained by metal working such as machining, pressing, and forging. In this study, the relationship between the ultimate tensile strengthσ B of prestrained specimens and the crack growth rate dl/dN is the focus. The following results were obtained. Under the large-scale yielding (LSY) condition, there is a correlation between dl/dN and σB, where the dl/dN versus σnal characteristics are determined by σB regardless of the degree of prestrain. Under the small-scale yielding (SSY) condition, dl/dN appears to be determined by the stress intensity factor range ΔK rather than σB, in comparison with the case under the LSY condition. In addition, the relationship between σB and the cyclic yield strength σyc is discussed in terms of the cyclic stress-strain characteristics of prestrained 0.1% carbon steel and other nonstrained carbon steels. It is considered that σB represents the material resistance against the plastic deformation by which fatigue cracks propagate regardless of the existence of prestrain.