Research on Constant-Amplitude Impact Fatigue Test Method Based on Hopkinson Bar
Structural components in the fields of aviation,aerospace,weapons,and energy are often subjected to repeated impacts of small loads(or low energy).This type of load is different from the single-pulse impact of high 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 perform-ance 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 existing impact fatigue test methods,this pa-per affirms the superiority of the stress wave method based on the Hopkinson bar principle,and raises the problem of non-constant amplitude loading in impact fatigue tests.The waveform generated by the Hop-kinson bar is controllable and measurable,which is beneficial to realizing constant-amplitude cyclic load-ing.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 meth-od because it can achieve constant amplitude loading and obtain comprehensive test data.Finally,a con-stant-amplitude dynamic shear fatigue test method is developed using the three-wave technique.Impact fa-tigue 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 in other loading modes(such as tension,compression,etc.)can also be real-ized.
impact fatigueHopkinson barstress waveconstant amplitudedynamic test techniques
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