Abstract: An experimental-numerical method for measuring dynamic crack propagating veloc-ities under stress wave loading is established in this paper. The experiments of thethree-point bend specimen are done on the improved Hopkinson bar. Deflection ofloading point, dynamic load and instantaneous crack length ave measured, then crackpropagating velocities are calculated. Experiments on 40Cr steel show that the resultsgiven by this method have a good agreement with that obtained by the resistance frac-ture gage method. Therefore this method is feasible for measuring crack propagatingvelocities under high loading rate and will have wide application.

Key words: stress wave loading, dynamic fracture,