Effect of slip distribution on the fracture behaviour of magnesium oxide single crystals

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Abstract
The tensile deformation of chemically polished magnesium oxide crystals has been correlated with the distribution of slip at the onset of plastic flow. If two slip bands, generated on orthogonal {110} planes, happen to intersect to nucleate a crack before other slip bands develop nearby, then the crack so formed is unstable and the crystal completely brittle. If, however, there is a higher density of slip sources cracks can become stabilized by adjacent slip bands and the crystals continue to deform. Sometimes slip is confined to a single slip band which expands laterally to fill the entire gauge length, these crystals are extremely ductile. The fracture behaviour of a given crystal depends critically upon the relative orientation, number, thickness and spacing between slip bands. The density of slip may be increased artificially when dislocation sources are injected into the crystal surface by sprinkling with carborundum before loading. Such crystals are always ductile in tension. A similar treatment for crystals to be bent leads to a profound change in their fracture behaviour.

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