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Information on the growth of fatigue cracks in engineering structures is necessary for the prediction of service lives of structures subjected to fatigue loading. Thus, considerable work has been done to develop fatigue crack propagation laws. To determine the primary material parameters affecting fatigue crack growth, a review and analysis of existing fatigue crack propagation data were conducted.
The results show that the primary factor affecting fatigue crack growth rates in high yield strength steels, titanium, and aluminum is the applied energy release rate range, ΔGI, in psi ∙inches. The stress intensity factor, KI, can be related to GI by using the modulus of elasticity; consequently, crack growth rates usually are expressed in terms of ΔKI for a particular material. However, the primary factor affecting fatigue crack growth rate is ΔGI. Crack growth rates also can be expressed in terms of the crack opening displacement range, Δδ, because GI can be related to δ. By using a critical strain, crack extension criterion, analysis of crack propagation behavior for these metals suggests that a change to accelerated crack growth rates occurs when δ reaches a value of 1.6 × 10-3 in.
cracking (fracturing), crack propagation, strain energy methods, fatigue (materials), corrosion fatigue, stress corrosion, cyclic loads, stress cycle, ductility, tensile properties, yield strength, pressure vessels, structural steels, titanium alloys, aluminum alloys
Applied Research Laboratory, U.S. Steel Corp., Monroeville, Pa.