Comparative experimental study on the measurement of type-Ⅰ dynamic stress intensity factor using different distance strain gages

Based on the linear elastic fracture mechanics theory,the difference of the measurement of type-Ⅰ dynamic stress intensity factor (DSIF) using different distance strain gages was analyzed. The three-point bending tests under impact loading were performed using strain gage method. When the orientation angles between stain gage and crack track were at specific acute and obtuse,the strain field in the vicinity of crack tip can be described by a two-parameter formula,which was related with the crack velocity and distance between strain gage and crack. Combining the strain- time curves of analytical solation and experimental test,an equation for calculating the value of DSIF was derived. The detailed comparisons and discussions of the values of DSIF obtained by simultaneous strain gage and dynamic caustics tests were presented. The results showed that there was an excellent agreement in the values of DSIF between strain gage and dynamic caustics tests when the strain gage was placed within the valid locations. The tests analysis indicated that the difference of DSIF between strain gage and dynamic caustics methods increased with the increase of distance between strain gage and crack. The results provide an experimental basis for a further application of strain gage method in the research of fracture properties of rock-like materials.