Peculiarities of prolonged plastic deformation of MgO crystals in the stress field of concentrated load

The peculiarities of the prolonged plastic deformation phenomenon occurred under microindentation on (001) plane of MgO crystals were investigated by a technique of acoustic emission signal registration for both cases of penetrating and removing of the indentor into/out of sample surface. The quantitative relation between the changes of the slip-line square and crack size and the number of acoustic emission signals arising at the indentor removal was established. The latter correlation conforms the relaxation nature of the prolonged deformation. More reliable mechanism of this phenomenon was proposed. The energy needed for such effect development is probably of the reactive pulse nature and is due to the reverse deformation recoil (return) during the indentor removal from the sample.