Local strain accumulation in fatigue crack propagation process of Ti‐6Al‐4V alloy

Abstract

Fatigue crack growth behaviours of the titanium alloy Ti‐6Al‐4V, with two different microstructures, at different maximum stresses were identified by digital image correlation technique. Full‐field strains were monitored around fatigue cracks after consecutive cycles in fatigue crack growth experiments. Results indicated that the Ti‐6Al‐4V alloy with a bi‐modal microstructure had a better fatigue resistance than that with a primary‐α microstructure. Typical behaviours of small cracks and the evolution of multi‐scale fatigue cracks were clarified. The strain accumulations around the micro‐notch and fatigue crack increased with increasing number of load cycles. On the basis of von Mises strain mapping, it was found that crack growth rate could be characterized by crack‐tip plastic zone size.

Crack initiation and propagation from geometric microdefects: Experiment and transition fatigue behavior

“…No facet feature is observed in the initiation region, displaying the typical failure type of “surface‐without‐facets.” 33 Meanwhile, radial stripes emanate around the microdefect. The generated stripes can be attributed to the laceration and are indicative of crack deflection through the propagation process 34 . Distribution and direction of the stripes are clearly presented in the stream‐type chart, as displayed in Figure 5C, which is generated from image binarization data of dash line area in Figure 5B.…”

“…The generated stripes can be attributed to the laceration and are indicative of crack deflection through the propagation process. 34 Distribution and direction of the stripes are clearly presented in the stream-type chart, as displayed in Figure 5C, which is generated from image binarization data of dash line area in Figure 5B.…”

Short review on multiscale short fatigue crack growth model

“…[31][32][33] When it comes to large-scale yielding, it is beyond the capacity of LEFM. Several studies [33][34][35] have demonstrated that the size of plastic zone is comparable with crack length in the initial stage of crack propagation. In the very beginning, the initial crack propagation is a large-scale yielding problem.…”