Study On CT Specimen Dynamic Fracture Based On Hopkinson Tension Bar Device

The dynamic fracture problem of material is much more complex than quasi-static fracture problem, and the inertial effects during the test create a great difficulty for measuring fracture parameters. Thus, the experimental study of metallic material dynamic fracture has an extremely important significance for the accurate calculation of dynamic fracture toughness.In this paper, a combination of experimental and numerical simulation methods were conducted for the research of impact tensile fracture of the compact tension specimens under stress loading, and the balancing problem of compact tension specimens under wave loading was studied. The main work of this paper includes the following:Firstly, the improved Hopkinson device was used to test the dynamic fracture property of the 2A12T4 aluminum alloy compact tension specimens. The corresponding waveform parameters were obtained by the resistance strain gauges attached to the rods, and also the stress parameters at the crack tip were measured by the strain gauge, thus the effect of three different stress waves on dynamic response of the specimen was investigated. The tests demonstrated the parameters of incident wave, reflected wave, transmitted wave and the parameters of the crack tip stress were extracted. The phenomena about the crack initiation point did not appear when the specimen was balancing were observed during the test. It provided a new way to study the subsequent issues.Then,the Abaqus finite element analysis software was adopted to simulate the loading process of the compact tension specimen under the stress wave loading with the measured incident wave as the loading condition. In this paper, the rationality of the experiment with split Hopkinson device was verified and the stress at each time point and each symmetry point was compared and analyzed. The results indicated that: the internal dynamic stress equilibrium of the specimen produced gradually in this simulation, and the crack appeared after the specimen balancing, which verified the reliability of the experiment.Finally, the effect of different incident wave on dynamic fracture of compact tension specimen was studied by numerical method,the results indicated: The crack point could appear after specimen dynamic balance by changing the waveform of the incident wave,which was obtained by the observation of the stress cloud and comparison of crack propagation direction. This study laid the foundation for the study of dynamic fracture of compact tension specimens in the future.