大理岩I–II复合型动态断裂的实验研究

 利用霍普金森压杆系统对几何相似的3种尺寸(f50 mm，f130 mm，f200 mm)中心直裂纹平台巴西圆盘大理岩试样进行了3种加载角(载荷方向与裂纹线的夹角分别为0°，10°和19°)的径向冲击实验，采用实验–数值方法确定复合型动态断裂的I，II型应力强度因子时间历程曲线KI(t)和KII(t)，以及起裂时刻tf的复合比(KI(tf)/KII(tf))。在100 μs加载时间内试样尺寸对复合比会产生影响：对于静态情况为I–II复合型加载的10°加载角，在动态加载时，f50 mm尺寸试样仍处于复合型加载，而f130 mm，f200 mm尺寸试样已经处于II型加载，产生这种差异的原因是应力波与裂纹面相互作用产生的扰动。岩石I，II型动态断裂韧度(KId，KIId)均存在尺寸效应，而且KIId比KId的尺寸效应更为显著，对此现象从能量的角度给出解释。考虑裂纹尖端应力场Williams特征展开式的第一非奇异常数项，T应力对动态应力强度因子的计算并无影响，但对复合型动态断裂的开裂角有一定的影响。

AN EXPERIMENTAL STUDY OF MIXED-MODE I-II DYNAMIC FRACTURE OF MARBLE

A diametrical impact experiment with three loading angles(the angles between loading direction and crack line are 0°，10° and 19°respectively) was performed for the geometrically similar cracked straight through flattened Brazilian disc specimens of three sizes(f50 mm，f130 mm，f200 mm) by split Hopkinson pressure bar system. Time-history curves of stress intensity factors(KI(t) and KII(t)) of mixed-mode I-II dynamic fracture，as well as the mode mixture ratio(KI(tf)/KII(tf)) at the initial time of fracture，were determined by experimental numerical method. Within loading time of 100 μs，the mode mixture ratio is affected by the size of specimen：when loading angle is 10°，in which the static condition is mixed-mode loading，the specimen of f50 mm is still in the state of mixed-mode loading，and so is under the dynamic loading condition；however，the f130 mm and f200 mm specimens are in the state of mode II loading. The difference is caused by the disturbance of interaction of stress wave and crack surfaces. Rock fracture toughness of both modes I and II(KId and KIId) has size effect；and the size effect of KIId is much more remarkable than that of KId，which can be explained from the viewpoint of energy. Considering the first nonsingular constant term in Williams series expansion of stresses near the crack tip，T stress has no effect on the computation of dynamic stress intensity factor，however it affects the crack initiation angle for the mixed-mode dynamic fracture.