Controllable kilohertz impact fatigue loading functioned by cyclic stress wave of Hopkinson tension bar and its application for TC4 titanium alloy

Engineering materials are occasionally subjected to high-frequency impact fatigue in service. However, there are still gaps in the loading techniques that hinder the acquisition of sufficient experimental data. In this work, we developed a novel loading methodology based on stress wave guidance to achieve controllable impact fatigue of ∼ 1 kHz frequency. Hopkinson tension bar was modified first by introducing a highly mismatched wave impedance ratio of the incident bar over specimen, ensuring nearly total reflection of the incident stress waves and thereby generating successive stress waves to perform impact fatigue loading on specimen. Each unloading process was governed by specimen recovery within loading interval. Case study was conducted by experimenting TC4 titanium alloy at the frequency of 1,048 Hz. Meanwhile, each strain, stress and strain rate are measurable during loading and recovery cycle. Finally, the comparison with the results from non-impact fatigue of 5 Hz revealed that, at high stress amplitudes, the impact fatigue life of high-frequency is lower than that of the low-frequency non-impact fatigue. Both crack initiation and propagation mechanisms are influenced by load amplitude and frequency.