Abstract:

The electromagnetic resonant fatigue crack propagation testing system is a device applied to test metal material fracture characteristics under the resonant condition, which is required to trace the system natural frequency and control the test load precisely during the fatigue crack growing process. So, it is necessary to analyze the system dynamic characteristics accurately during the fatigue crack propagation process. Accordingly, the electromagnetic resonant fatigue test vibration system model of three degree freedom with damping has been established, the stiffness of compact tension (CT) test specimen of different materials are calculated using finite element method, and the relation of CT specimen stiffness with crack propagation length has been obtained. The variation laws of system natural frequency, test load amplitude-frequency curve and resonance amplitude during the fatigue crack propagation process have been researched, and some related experiments also have been carried out. The experimental results show that the system natural frequency maximum deviation value between the theoretical and the experimental data is 1.9 Hz, and the system dynamic characteristics simulation results match well with the experimental results. Furthermore, the research results supply a theoretical foundation for the precise controll of electromagnetic resonant fatigue test load.

Key words: dynamic characteristics, fatigue crack propagation, finite element method, multi-degree freedom vibrating system, test load, electromagnetic resonant fatigue test