This article describes the types of closure mechanisms, including plasticity-induced, roughness-induced, oxide-induced, and fretting-debris-induced. It discusses test techniques used to establish a valid threshold value for aluminum alloy crack growth thresholds, steel crack growth thresholds, and titanium alloy crack growth thresholds. The near-threshold behavior of nickel-base superalloys is described. The article briefly reviews the threshold results for fiber-reinforced, whisker-reinforced, and particulate-re-inforced metal-matrix alloys. It explains the near-threshold fatigue crack propagation in welded joints and the fundamental considerations for modeling threshold behavior. The article concludes with a discussion on the effects of thresholds in the engineering design process.
A.J. McEvily, Fatigue Crack Thresholds, Fatigue and Fracture, Vol 19, ASM Handbook, By ASM Handbook Committee, ASM International, 1996, p 134–152, https://doi.org/10.31399/asm.hb.v19.a0002357
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