Abstract: 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.

Key words: rock mechanics, type-I crack, strain gage method, dynamic stress intensity factor