The bending deformation of magnesium oxide

Abstract

The plastic deformation of MgO in pure bending is accomplished by the motion of dislocations, which, relative to the beam geometry, can be classified in two groups. The dislocations in the first, and classically accepted, group all have Burgers vectors with a component normal to the neutral axis of the beam. These form what is described as two-dimensional slip. The dislocations in the second group all have Burgers vectors with no component normal to the neutral axis although the planes in which they lie are normal to the neutral axis and at 45° to the sides of the beam. Consequently, we cannot wholly define slip in a beam deformed in this mode in a single plane, but must consider it relative to all three dimensions of the beam. Therefore it is defined as three-dimensional slip. Beams which deformed in the three-dimensional mode work-hardened more rapidly than beams which deformed in the two-dimensional mode alone. This increased work-hardening rate is due to the complex stresses created in the plane of the beam cross section and not to dislocation intersections or to the production of point defects.