The precursor decay relation in plate impact experiments by a longitudinal wave is studied on the basis of the elastodynamics of dislocations. The material is modeled as an elastic continuum containing a distribution of dislocation loops. The waves radiated from the dislocations as they are hit by the incident wave result in the decay of the latter at the wave front. The response of the instruments is considered finite, so that the decay is calculated at a time Dgr;tbehind the front. The loops are assumed small, i.e., of radius agr;0∼0 (c1Dgr;t) so that the wavelets emanated from the whole loop have the time to contribute to the decay. The loops are assumed to lie on a plane which makes an angle with the direction of propagation of the incident front and they are set in motion of uniform radial expansion by the incident front. The fundamental solution from each loop is obtained asymptotically and the precursor decay is obtained by superposition of all the loops that had the time to contribute. The obtained precursor decay relation is a modified Orowan’s relation since it is of the same form as that obtained by using Orowan’s formula but with a correction factor which depends on the dislocation velocity and configuration (curvature and orientation).
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