1993 年 42 巻 479 号 p. 962-968
The dynamic stress intensity factor of fast propagating cracks was calculated from the measured data of crack tip position versus time, through numerical simulation with an improved finite difference method. The data were obtained with a measuring system consisting of ladder gages and a digital wave memory unit. The cracks were propagated in the double-cantilever beam type specimens machined from the model material, polymethyl methacrylate(PMMA). The specimens were in various sizes where the ratio of initial crack length to specimen size was kept constant. The dynamic stress intensity factor decreased at the beginning of the crack propagation phase, remained almost unchanged in the next stage, and increased in the third stage. The above mentioned result appeared in all sizes of specimens, in common. But, after the third stage the behavior of the stress intensity factor varied with the specimen geometry. The characteristic values of the dynamic stress intensity factor in the process of the crack propagation and arrest were illustrated and investigated with respect to the following parameters: the specimen size, the initiation stress intensity factor, and the crack jump distance. The specimen size mainly affects the scatter of the results: the larger specimen gives the result with a smaller scatter.