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

Abstract

The very high cycle fatigue (VHCF) problems of thin-plate structures are usually caused by high-frequency vibrations. This paper proposes an accelerated fatigue test method based on ultrasonic loading technology in order to develop a feasible bending testing method and explore the bending fatigue characteristics of thin-plate structures in the VHCF regime. A new bending fatigue specimen with an intrinsic frequency of 20 kHz was designed based on cantilever bending through finite element simulation. It was verified by the axial load test with R = −1. The results showed that the method could effectively transfer the dangerous cross-section at the first-order cantilever bending restraint to the internal part of the specimen, thereby making the fracture location independent of the complex stresses. The linear relationship between the vibration amplitude and the maximum stress was also verified using strain measurements. Furthermore, the S-N curves and fracture morphology for different loading types were consistent with conventional studies to a certain extent, which indicated that the design of the bending test model was reasonable.

The Gradient Effect on Cyclic Behavior of 316L Stainless Steel in the Ultrasonic Bending Test

“…The nanoindentation hardness was finally converted to Vickers hardness by formula calculation [21]. An ultrasonic bending fatigue system with a loading frequency of 20 kHz and a stress ratio of R = −1 was used in this experiment [22], as shown in Figure 4. The test loading direction was along the Z-axis, as shown in Figure 3.…”

“…Intermittent loading mode (110 ms of loading time followed by 800 ms of rest time) and cooled compressed air were employed to mitigate thermal effects during testing. An ultrasonic bending fatigue system with a loading frequency of 20 kHz and a stress ratio of R = −1 was used in this experiment [22], as shown in Figure 4. The test loading direction was along the Z-axis, as shown in Figure 3.…”