THE FRACTURE TOUGHNESS OF IMPURE MGO CRYSTALS.
CARNEGIE INST OF TECH PITTSBURGH PA DEPT OF METALLURGY AND MATERIALS SCIENCE
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When cracks are propagated through impure MgO crystals in a series of small jumps, the force needed to initiate successive jumps decreases as the crack grows in the manner predicted by a Griffith energy balance, in which an effective, or fracture surface energy is substituted for the true surface energy of the crystal. Fracture surface energies in the range 1000 to 3000 ergssq cm are obtained. Examination of the fracture surfaces shows that many dislocations are introduced by the crack as it comes to the end of a jump. The measured fracture surface energy represents the release of elastic energy which is needed to re-start a crack from a plastically deformed configuration. When the crack divides the crystal into unequal instead of equal parts, a different pattern of slip occurs at its tip, which leads to a higher fracture surface energy. Author
- Ceramics, Refractories and Glass