Propagation of a slant crack under impact studied by caustics

In the present paper the propagation of a slant crack under an impact load was studied by the method of caustics. An air gun was employed for the production of the load pulse. It was concluded that the steady crack velocity increases linearly with the angle of crack inclination, reaching a maximum value when the initial crack is normal to the load direction. The crack starts to propagate in the presence of both K_I- and K_II-stress intensity factors. The K_II-factor has a maximum value of one-tenth of the K_I-factor and an oscillatory character. This becomes zero in the first third of the crack-path, as the crack tends, gradually, to follow its final direction, normal to the direction of the applied pulse. An apparently distinctive effect relating the crack velocities and stress intensity factors may be concluded from the experimental results. For the same values of K_I and K_II, the crack propagates in some cases with different velocities, depending, apparently, on the initial crack inclination. It is believed that it is related to the validity of energy fracture-criteria and requires further study.