应变片法确定Ⅰ型裂纹动态应力强度因子试验研究

Experimental research on determination of dynamic stress intensity factor of type-Ⅰ crack using strain gage method

基于扩展裂纹尖端附近应变场分析,采用冲击载荷作用的三点弯曲梁进行试验,开展了应变片法确定Ⅰ型裂纹动态应力强度因子的研究。明确了应变片与裂纹扩展方向之间朝向角为特定锐角和钝角条件下,动态裂纹尖端附近的归一化应变采用与裂纹扩展速度、应变片黏贴位置相关的二项式来表示,给出了二项式的相关系数确定过程和动态应力强度因子计算式。结果表明,二项式的理论计算的应变与时间关系变化曲线与试验实测相吻合;选取曲线最大值两侧3/4峰值处的时间差为特征时间△t时,理论计算结果与实测的应变与时间关系一致性较高;选用理论计算和试验实测的应变与时间关系变化曲线最大值,结合计算式,确定Ⅰ型裂纹动态应力强度因子,同时,与采用动焦散线法计算的结果进行对比,验证了应变片法确定Ⅰ型裂纹动态应力强度因子的可行性。研究过程为应变片法在岩石断裂力学特征量的测定提供了理论基础。

In this study, three-point bending beam tests were carried out under impact load. Dynamic stress intensity factor（DSIF） of type-Ⅰ crack was determined by using the strain gauge method, which considered the stress field near the tip of propagating crack. When the orientation angle between strain gauge and the crack path was at specific acute and obtuse angle, the normalised strain around a propagating crack could be clearly described by a two-parameter formula, which was related to the velocity of propagating crack and the location of the strain gauge. Furthermore, the corresponding coefficient and DSIF formula were also given. The results show that the strain-time curve obtained by the theoretical method is in good agreement with experimental data. When characteristic time△t is chosen at the time span of 3/4 peak strain before and after the peak value of strain-time curve, the consistency of theoretical calculations and experimental results is relatively high. DSIF is calculated by using the theoretical and experimental peak value of the strain-time curve. Meantime, the dynamic caustics method is applied for the determination of DSIF of type-Ⅰcrack and the obtained results verify the feasibility of the strain gauge method as well. In conclusion, this study provides an effective theoretical basis for the application of strain gauge method in the determination of dynamic fracture properties for rock mass.