Fatigue Crack Thresholds

Abstract

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.

Fatigue Crack Growth Experiments of Resonating Micro-Samples

“…The measured values for the threshold are between 3.7-3.9. They are smaller than those of bulk materials measured with conventional methods, but comparable to data obtained with ultrasonic techniques [8]. No effect on crack growth behavior is believed to occur on fcc materials at higher frequencies, at least for frequencies less than 300 Hz as in these experiments.…”

Fatigue crack growth behaviour of ferrite–bainite dual phase steels

“…Minakawa and McEvily 13 have reported that the fatigue threshold of AISI 1018 steel (0?15-0?20C) at R50?05 is 6?0 MPa m 1/2 . On the basis of the comparison of the order of the estimated DK th for the FBDP steels with that of low carbon steel 23 at the similar R ratio, one can infer that the developed steels possess higher DK th than low carbon steels; however, the estimated results are comparable to DK th values of the mild steel or 1018 steel at low positive R ratios.…”

“…where M is the applied bending moment (5Pl), P is the applied load, l is the distance between loading point and location of crack, B is the breadth of the specimen, W is the width of the specimen and An attempt has been made to assess the appropriateness of the order of the estimated DK th values of the investigated FBDP steels with those reported for other steels tested under similar R ratios. McEvily 23 has reported that the threshold value for a low carbon steel at an R ratio of 21?0 is 3?8 MPa m 1/2 and the DK th is 6?6 MPa m 1/2 at R50?13 for mild steel. Minakawa and McEvily 13 have reported that the fatigue threshold of AISI 1018 steel (0?15-0?20C) at R50?05 is 6?0 MPa m 1/2 .…”

Characterizing the Fatigue Damage in a Martensitic Spring Steel

“…Especially, the stages of crack initiation and short crack propagation can account for up to 90% of the fatigue life in the high cycle fatigue regime, leading to a particular interest in investigating these stages of fatigue damage evolution. [1] Furthermore, it is extremely important to understand the mechanisms of crack initiation and short crack propagation for lifetime predictions of structures which are not fail safe, as their failure can cause a catastrophic damage.Many studies have shown, that crack initiation often occurs at slip bands (see for example, the studies by Christ, McEvily, Efthymiadis et al, and Hong et al [1][2][3][4] ) and that short crack propagation is strongly influenced by the local microstructure, leading to an oscillating crack propagation rate (see for example, the studies by Christ, McEvily, Miller, and Yang et al [1,2,5,6] ). However, until now, just a few studies have investigated the fatigue damage evolution in a martensitic steel and the corresponding impact of the complex martensitic microstructure on the crack initiation and the short crack propagation.…”

“…Many studies have shown, that crack initiation often occurs at slip bands (see for example, the studies by Christ, McEvily, Efthymiadis et al, and Hong et al [1][2][3][4] ) and that short crack propagation is strongly influenced by the local microstructure, leading to an oscillating crack propagation rate (see for example, the studies by Christ, McEvily, Miller, and Yang et al [1,2,5,6] ). However, until now, just a few studies have investigated the fatigue damage evolution in a martensitic steel and the corresponding impact of the complex martensitic microstructure on the crack initiation and the short crack propagation.…”