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 stydy, the relationship between the ultimate tensile strength σ_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 σ_B, where the dl/dN versus σ_aⁿl characteristics are determined by σ_B 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 σ_B, in comparison with the case under the LSY condition. In addition, the relationship between σ_B and the cyclic yield strength σ_yc 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 σ_B represents the material resistance against the plastic deformation by which fatigue cracks propagate regardless of the existence of prestrain.