Small fatigue crack growth behavior of titanium alloy TC4 at different stress ratios

Abstract

In this paper, the small fatigue crack behavior of titanium alloy TC4 at different stress ratios was investigated. Single‐edge‐notch tension specimens were fatigued axially under a nominal maximum stress of 370 MPa at room temperature. Results indicate that fatigue cracks in TC4 initiate from the interface between α and β phases or within α phase. More than 90% of the total fatigue life is consumed in the small crack initiation and growth stages. The crack growth process of TC4 can be divided into three typical stages, ie, microstructurally small crack stage, physically small crack stage, and long crack stage. Although the stress ratio has a significant effect on the total fatigue life and crack initiation life at constant σmax, its effect on crack growth rate is indistinguishable at R = −0.1, 0.1, and 0.3 when crack growth rate is plotted as a function of ∆K.

Effects of Different Materials on Residual Stress Fields of Blade Damaged by Foreign Objects

“…The damage caused by foreign objects is different from notches through low-speed and quasi-static impact. The stress concentration and microstructure deformation caused by foreign object damage (FOD) have an important influence on the fatigue life of the blade [ 3 , 4 ]. Additionally, the tensile residual stress generated in blades by FOD may expedite the propagation rate of fatigue cracks, ultimately leading to a reduction in blade fatigue strength and potential fatigue failure; this significantly hinders the safe operation of gas turbines [ 5 ].…”

Experimental Studies into the Analysis Required for the Durability Assessment of 7075 and 6061 Cold Spray Repairs to Military Aircraft

“…At this stage, it should be noted that the growth of small naturally occurring lead cracks, i.e., the cracks that determine the operational life of a component [31][32][33], which see the environment often grow in a near exponential fashion [26,[31][32][33][34][35][36][37] and follow a da/dN versus ∆K curve that is essentially a Paris-like crack growth equation with a small fatigue threshold. Furthermore, for small cracks growing in laboratory air, there are minimal R ratio effects [26,30,[37][38][39][40][41][42]. (The relationship between the long crack and the small crack da/dN versus ∆K curves, for cracks that are growing in air, is discussed in [38].)…”