Abstract: The transmitted caustics experimental system has been used to conduct the dynamic caustics research about the propagation law of cracks and the poly methyl methacrylate (PMMA) plates have been employed to make model specimens. The results have shown that: 1) All the b endpoints of the prefabricating cracks propagate under the action of the stress wave and generally extend along the horizontal direction with a phenomenon of warping seen from the propagation path; 2) As the dip angle θchanges, the extension displacement of b endpoint has the rule of variation between increasing and decreasing, and the extensiondisplacement curve is generally symmetrical about the linear θ=0° from -45° to 45°, but it has an apparent difference from -75° to -45° and 45° to 75°; 3) When θ=-45°, θ=0° and θ=60° theextensiondisplacement curve reaches the peak values of 22, 31 and 36 mm respectively, and reaches the low values of 9 mm and 11 mm when θ=±30°; 4) The change curve of stress intensity factor K_Ⅰ^d and the change curve of energy release rate G have a similar trend, which are both at a peak value at first, then the repeated oscillation change with peak value for several times; 5) The values of stress intensity factor and energy release rate are closely related to energy, which means the displacement of corresponding crack is larger when the values both have a relatively higher level, otherwise it is small relatively.

Key words: static-dynamic load, crack angle, dynamic caustics, stress intensity factor, energy release rate