Fatigue behaviors of a titanium alloy in the VHCF regime based on a vibration‐based bending fatigue test

Abstract

A vibration-based bending fatigue test based on electrodynamic shaker is conducted in order to study the high cycle and very high cycle fatigue (VHCF) behaviors of a titanium alloy TC17 with a sort of novel specimens. After obtaining a full S-N curve covering the lifetime up to 10 9 cycles, several fatigue crack initiation and failure process modes are revealed based on the observation of the fracture surfaces. Especially, the statistical distribution characteristics of the fatigue lifetime and some relevant factors are discussed. The results indicate that the obtained S-N curve does not exhibit a plateau region in the VHCF regime. And the present crack initiation mechanism involves the facets formed by the primary α-phase cleavage and the development of microcracks.Moreover, the scatter of the fatigue lifetime can be obviously influenced by the resonance frequency range of the specimens.

A Novel Ultrasonic Fatigue Test and Application in Bending Fatigue of TC4 Titanium Alloy

“…Finally, the ultrasonic bending fatigue test and the ultrasonic axial fatigue test obtained 19 and 14 valid data, respectively, as shown in Table 2. It can be seen from the fitting curve in Figure 8 that the S-N curve under bending load shows a continuous decline [40,41], and does not show the "step" characteristics of high-strength steel [26,42]. This is consistent with the existing research results.…”

“…The values of σ 0 , a, and b of the ultrasonic fatigue specimen were 206.79, 3.38, and 1.26 × 1013, respectively; and the values of σ 0 , a, and b of the ultrasonic axial fatigue specimen were 235, 7.57, and 3.07 × 1020, respectively. It can be seen from the fitting curve in Figure 8 that the S-N curve under bending load shows a continuous decline [40,41], and does not show the "step" characteristics of high-strength steel [26,42]. This is consistent with the existing research results.…”

“…Highmagnification images of the crack initiation site are shown in Figure 11b,d; there are numerous small facets are indicated by yellow arrows. Other flexural studies have also reported this phenomenon of internal crack initiation [23,33,41]. It is thought that at lower stress amplitudes, the influence of the stress gradient on the bending test is small.…”