Dislocation motion in MgO crystals under plate impact

Abstract

Dislocation dynamics in MgO single crystals is studied by means of plate impact experiments in which specimens are subjected to stress pulses of 214 to 376 MPa resolved shear stress with duration in the range of 0.09 to 0.23μsec. Dislocation structures in the recovered crystals are observed by an etch pit technique and by transmission electron microscopy. Etch pit studies show that inclusions play a role in the generation of interior glide bands and that there is a 20 to 40-fold increase in dislocation densities outside the glide bands. Assuming the average dislocation velocity is approximately proportional to the applied stress the drag coefficient for MgO at dislocation velocities of 1 to 2 km sec−1 is observed to be 5×10−5 Nsec m−2. Transmission electron microscopy determines the spacing and curvature of dislocations in glide bands.