Dislocation Activity, Stable Crack Motion, and the Warm‐Prestressing Effect in Magnesium Oxide

Abstract

Four‐point bend tests were performed on precracked single‐crystal MgO specimens at different temperatures and strain rates. A large amount of stable crack growth before fracture occurred; etching revealed dislocations in the crack advance region. We believe that dislocation sources near the crack tip emit loops, producing shielding and antishielding dislocations; the latter promote crack advance by a repeated microcleavage mechanism. “Warm‐prestressing” experiments, which improve the room‐temperature fracture toughness by dislocation shielding, were performed. There was a prestress below which no “warmprestressing effect” (WPSE) was exhibited and the magnitude of the WPSE increased with increasing prestressing temperature.