冲击载荷下材料动态断裂参数的有限元计算

Finite Element Calculation of Dynamic Fracture Parameters of Material Under Impact Load

材料在冲击载荷下的行为不同于静态载荷作用下的行为。然而,由于动态断裂问题的复杂性,即使象三点弯曲试样,也还没有获得裂纹尖端动态应力强度因子的解析表达式。为了满足理论分析和实验工作的需要,采用LS-DYNA有限元软件,对三点弯曲试样在冲击载荷作用下(包括正弦、线性和不规则载荷历程)的动态过程进行了有限元分析,获得了裂纹尖端的动态应力应变场和裂纹尖端区域节点力和位移与时间的关系曲线。基于虚拟裂纹闭合技术(VCCT),提出了在冲击载荷作用下裂纹结构能量释放率和动态应力强度因子的计算方法,得到了不同冲击载荷下三点弯曲试样的能量释放率GI和动态应力强度因子KId与时间的关系曲线。结果表明:该方法得到的有限元计算结果与实验吻合较好,且具有较高精度,文中提出的方法可用于动态断裂参数的计算。

The behaviors under impact condition are different from the ones under quasi-static condition. However, because of the complexity of dynamic fracture problems, the analytical result of stress intensity factor of such simple sample as three point bending beam hasn＇ t been determined. To satisfy the request of theoretical and experimental analysis, the finite element method program LS-DYNA is used to analyse the dynamic process （including the sine, linear, anomalistic progress） of three point bending beam under impact load. The dynamic stress, strain field at crack tip and corresponding curves of force-time and displacement-time in the area of crack tip are obtained. The method of determining the energy release rate and dynamic stress intensity factor under impact load is obtained by virtual crack closure method, the curve of G1 （ energy release rate） vs. time, KId （ dynamic stress intensity factor ） vs. time under different impact loads are calculated, and according to KId -time curves the corresponding dynamic stress intensity factor of the extend time which is determined by experimental method in the literature, called dynamic fracture toughness,is determined. The results got by FEM are compared with the experimental results and show good agreement with experimental data, and more it has higher precision. As a result, this method can be used to the computtion of dynamic fracture parameters.