含不同角度穿透裂纹板拉伸断裂的有限元模拟

对含不同预置角度穿透裂纹板受拉伸断裂过程进行了数值模拟.选用增量型弹塑性本构关系,采用自编有限元程序求解虚功原理方程,裂纹扩展参照了LS-DYNA商业计算软件处理断裂问题的单元失效方法,考核了不同幅值载荷和预置裂纹角度的影响,给出了不同时刻等效应力云图和指定点的应力、应变随时间变化曲线.计算结果表明:当应力波在板中传播时,会在裂纹尖端引起应力集中,板产生垂直裂纹和水平裂纹.垂直裂纹扩展垂直于加载方向,水平裂纹扩展平行于加载方向,两者均与预置裂纹角度无关.板上不同位置的应力变化仅和相对裂尖位置相关,而与预置裂纹角度无关.相对裂尖位置、与板边界距离和加载位置是影响应变随时间变化的主要因素.当载荷幅值较小时,不会出现裂纹扩展.当载荷幅值较大时,聚集在裂纹尖端的应变能需较长时间才能释放,这会影响水平裂纹的出现时间.

Response of elastic-plastic plate embedded cracks at different orientation under impact load

Three-dimensional computation was carried out on the dynamic response of metal plate embedded at the different inclined cracks under parallel impact load.To describe the elastic-plastic material,an increase type of constitutive relationship was adopted and governing equation in Lagrangian form was solved by finite element method(FEM).Referring to LS-DYNA commercial code,six types of failure criteria based on stress and strain respectively indicate the fatigued elements which represent the cracks.During the loading,stress waves are generated which propagate inwards the plate and lead to the stress concentration around the crack tips.Meanwhile,new cracks are formed evolving from the crack tips.In contrast to the loading,the vertical cracks propagate perpendicularly and the parallel ones propagate horizontally.But these new cracks are independent of the inclination of the embedded cracks.The stress time history at each point in the plate is approximately related to the distance to the tips and either independent of the crack inclination.Moreover,the distances to the tips and plate frontier,and loading walls mainly affect the local strain time history.This means that the local strain is determined by the time integration of the plate loading.If the load amplitude is below a threshold value,the cracks do not prolong further.Otherwise,it takes a long time to release the strain energy concentrated around the tips,which postpones the appearance of the parallel cracks.