NiTi合金动态断裂过程的实验和数值方法研究

The study of experimental and numerical methods for dynamic fracture process of NiTi alloy

为获得Ni Ti合金的动态起裂韧度和动态扩展速度与动态加载率之间的定量变化规律。利用分离式霍普金森压杆(SHPB)测试系统对单边三点弯曲试样(SENB)进行冲击加载试验,采用实验-有限元相结合的方法,获得动态断裂参数随时间的变化规律。SENB试样裂纹起裂时刻和裂纹扩展速度由粘贴在裂纹尖端的裂纹扩展计(CPG)测定。采用上述方法和数据获得Ni Ti合金的I型动态起裂韧度和动态扩展速度。实验结果表明:裂纹扩展计测得的起裂时刻与粘贴在同一试样上的监裂应变片测得的结果基本相符,因此可以利用裂纹扩展计代替传统的监裂应变片来监测裂纹起裂时刻,并获得Ni Ti合金的起裂韧度。同时,可以利用裂纹扩展计(CPG)获得裂纹动态扩展过程,绘制出裂纹扩展速度与时间的关系曲线,从而探讨Ni Ti合金的动态断裂韧度和裂纹扩展速度与动态加载率之间的定量变化规律。

To obtain a quantitative change rule between the dynamic initial fracture toughness, dynamic crack propagation speed and dynamic loading rate of NiTi alloy, an impact loading test was conducted on single edge notched three-point bending （SENB） specimens with the split Hopkinson pressure bar （SHPB） test system based on the experimental-FEM method to figure out the variation rules of dynamic fracture parameters of NiTi alloy. The time of crack initiation and the crack extension speed were measured by the crack propagation gauge （CPG） pasted near the crack tip of the specimen. It is feasible to measure the initiation fracture toughness and crack propagation speed of Type I NiTi alloy by taking the aforementioned method. According to the test results： the crack initiation time displayed on the CPG is roughly in line with the result on the crack strain gage pasted on the same specimen. So the CPG can be used as crack strain gage, which can also measure the fracture toughness of NiTi alloy. In addition, the dynamic crack propagation process can be obtained with the CPG. According to the dynamic crack propagation process, the relation curve between crack propagation speed and time can be drawn out. In this way, the quantitative change rule between the dynamic fracture toughness, dynamic crack propagation speed and dynamic loading rate of NiTi alloy can be worked out.