高应变率载荷下纯钛的非连续冲击疲劳失效模型及其微观机理

The fatigue failure behavior of structural materials under repeated impact loads has always attracted much attention. Mastering its damage accumulation process and evolution mechanism at the micro-scale is the fundamental way to understand the impact fatigue failure mechanism. Due to the complexity of the impact fatigue load itself and the limitations of the current experimental equipment, there are still major problems in the study of impact fatigue failure of materials. Therefore, pure titanium was used as the research object and a strain-controlled impact fatigue life test was designed based on the traditional split Hopkinson tension bar system. The strain-controlled impact fatigue life test was achieved by changing the length of the striker, and the amplitude of the incident wave needed to be kept at the same level when using different striker tests. The relationship between strain amplitude and impact fatigue life was analyzed. The impact fatigue interruption experiments of 5 times, 10 times and 20 times were carried out with 100 mm bullets. The microstructure of the samples after different impact times were characterized by electron backscatter diffraction (EBSD) and then the quasi-static mechanical properties were tested. The fracture morphology after impact fatigue failure was observed by scanning electron microscope (SEM). The cyclic hardening/softening law and its microscopic evolution mechanism of pure titanium during impact fatigue failure were studied. The results show that the strain-controlled impact fatigue life test can be realized by changing the striker length. The Manson-Coffin fatigue life model can better reflect the relationship between impact fatigue life and strain amplitude of pure titanium. Moreover, pure titanium exhibits cyclic hardening during impact fatigue failure, which is mainly due to the combined effect of fine grain strengthening caused by twin deformation and strain hardening caused by plastic deformation during fatigue. Finally, the impact fatigue damage of pure titanium is mainly manifested as the loss of deformation ability.