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Mechanical Behavior of Samhire
Author(s) -
CONRAD HANS
Publication year - 1965
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1965.tb14711.x
Subject(s) - materials science , frank read source , slip (aerodynamics) , dislocation , plasticity , sapphire , tearing , ultimate tensile strength , composite material , crystal twinning , stress intensity factor , strain rate , condensed matter physics , glide plane , crystallography , dislocation creep , fracture mechanics , thermodynamics , optics , chemistry , physics , laser , microstructure
The present state of the knowledge of the mechanical behavior of sapphire is reviewed. Sapphire deforms plastically at temperatures above 900°C, the most common mode of deformation being slip on the basal plane in the 〈110〉 direction. Under certain conditions, however, slip may occur on prism planes or twinning may occur. A yield point is often observed, which appears to be related to the multiplication of dislocations by a mechanism controlled by the motion of dislocations through the lattice, rather than by the tearing of dislocations from an impurity (or defect) atmosphere. The dynamics of yielding and flow is similar and can be expressed by either of two thermally activated equations. In one, the effect of stress is principally on the pre‐exponential factor; in the other, its effect is principally on the activation energy. There are insufficient data to permit a positive decision between the two, or to positively identify the rate‐controlling dislocation mechanism. For 60°‐oriented crystals fracture generally occurs on a plane approximately normal to the tensile stress and the fracture surface is conchoidal. In the range 1100° to 1500°C, the tensile fracture stress decreases with increase in plastic strain, independent of temperature and strain rate. The mechanism of failure in this case seems to be the interaction of edge dislocations with pre‐existing cracks.