The investigation on dynamic fracture behavour of materials under compressive-shear combined stress waves

In this paper, an improved plate impact experimental technique is presented for studying dynamic fracture mechanism of materials, under the conditions that the impacting loading is provided by a single pulse and the loading t ime is in the sub-microsecond range. The impacting tests are carried out on the pressure-shear gas gun. The loading rate achieved is dK/dt similar to 10(8) MPa m(1/2) s(-1). With the elimination of influence of the specimen b oundary, the plane strain state of a semi-infinite crack in an infinite ela stic plate is used to simulate the deformation fields of crack tip. The sin gle pulses are obtained by using the "momentum trap" technique. Therefore, the one-time actions of the single pulse are achieved by eradicating the st ress waves reflected from the specimen boundary or diffracted from the crac k surfaces. In the current study, some important phenomena have been observ ed. The special loading of the single pulse can bring about material damage around crack tip, and affect the material behavior, such as kinking and br anching of the crack propagation. Failure mode transitions from mode I to m ode II crack are observed under asymmetrical impact conditions. The mechani sms of the dynamic crack propagation are consistent with the damage failure model.