含单侧预制裂纹梁的冲击动态断裂过程试验研究

利用动焦散线试验方法研究了冲击下预制裂纹梁的动态断裂行为,对比分析了冲击荷载作用下单裂纹与双裂纹试件的应力强度因子、扩展轨迹以及速度、加速度等参数的变化规律。试验结果表明:冲击荷载作用下,含双裂纹且主裂纹在冲击点正下方的试件起裂时间最早,裂纹扩展后期朝向次裂纹方向发生较小的偏移;含Ⅰ型单裂纹的试件起裂时间次之,裂纹扩展路径呈直线;含双裂纹且两条裂纹均偏置于冲击点的试件起裂时间最晚,扩展过程中发生明显的曲裂现象。同时,裂纹扩展过程中曲裂现象越严重,裂纹扩展的最大速度就越小。在落锤冲击试件到试件断裂的整个阶段,应力强度因子一直表现出振荡变化。含双裂纹的试件,在主裂纹扩展中期,次裂纹上的应力强度因子有一个快速下降的过程。

Dynamic fracture tests for a beam containing unilateral pre-existing cracks under impact loads

By means of experimental method of dynamic caustics, this study compared the dynamic fracture behaviors such as stress intensity factor and the extension tracks, velocity and acceleration of cracks between precast beams with single crack and double cracks under the impact load. The experiment results indicate the following findings. When the impact point is directly upon the main crack, the double-crack beam cracks the earliest, with a extension track of the main crack slightly deviates to the secondary crack in the late stage of cracking extension; Latter comes the single-crack beam of I-type, with a straight extension track of the main crack; the double-crack beam cracks the latest with bending fracture obviously, when the impact point are upon neither of the cracks. The more serious of bending fracture phenomenon during the process of crack extension, the smallest of the maximum velocity. During the whole cracking process which is between the tacking places of the impact load and the fracture of the precast beams, the stress intensity factors vary with time in oscillation. The stress intensity factors of the secondary crack on the double-crack beam decrease dramatically in the middle stage of cracking extension.