Abstract：Structural components in the fields of aviation, aerospace, weapons, and energy are often subjected to repeated impacts of small loads (or small energies). This type of load is different from the single-pulse impact of large energy and the conventional low-strain-rate fatigue, which is called impact fatigue. Because the energy-based impact fatigue test methods can only detect the relation between impact energy and fatigue life, the industrial application of impact fatigue test results in structural design and performance evaluation has been limited. Therefore, this paper focuses on exploring a new impact fatigue loading method. First, based on a brief review of the development of the existing impact fatigue test methods, this paper affirms the superiority of the stress wave method based on the Hopkinson bar principle, and raises the problem of non-constant amplitude loading in the impact fatigue tests. The waveform generated by the Hopkinson bar is controllable and measurable, which is beneficial to realizing constant-amplitude cyclic loading. Then, three impact fatigue loading techniques (namely the one-wave, two-wave, and three-wave techniques) based on the Hopkinson bar are proposed. The feasibility of these methods is verified through experiments, focusing on studying whether there is a non-constant amplitude loading problem caused by secondary loading. The three-wave technique is found to be the most effective impact fatigue loading method because it could achieve constant amplitude loading and obtain comprehensive test data. Finally, a constant-amplitude dynamic shear fatigue test method is developed using the three-wave technique. The impact fatigue performance tests are carried out on the TC4 titanium alloy. The test loading frequency is 0.1 Hz, and the test strain rate ranges from 6800/s to 8400/s. It is proved that this method can realize dynamic shear fatigue testing of metal materials at the strain rate level of 103/s. This study provides a new idea for the constant-amplitude impact fatigue test. By changing the forms of the specimen and the loading bars, the impact fatigue loading of other loading modes (such as tension, compression, etc.) can also be realized.
2024, Vol. 45 
