Strengths of Sapphire Crystals
THE strength of single crystals of entirely brittle materials should depend on the presence of stress raising flaws. Internally these could be formed by static dislocation arrays, voids or inclusions of foreign material. On the surface the flaws could be formed by mechanical damage or by surface steps as suggested by Marsh1.
The ultimate strength of solids
AbstractThere is an upper limit to the mechanical strength of any material under any particular test conditions. This limit is known as the ideal strength. The present paper attempts to define the ideal strength as closely as is presently possible. To this end, a brief account is first given of some of the highest strengths recorded experimentally. Then follows a short account of the published theoretical calculations of the ideal strength. Finally, the theoretical and experimental values are compared, and it is shown that in several instances these differ by less than a factor 2x. Resume Il existe une limite superieure de la resistance mecanique de tout rnateriau pour des conditions d'essai donnees. On donne a cette limite le nom de resistance ideale. Dans l'article, on tente de definir la resistance ideale de la maniere la plus precise qu'il soit possible de la faire avec les connaissances actuelles. A cette fin, on presente d'abord un sommaire de quelqu'unes des plus hautes resistances determinees expe...
Growth and Defect Structure of Sapphire Microcrystals
Examination of small euhedral crystals of α‐Al2O3 (sapphire) that were observed following oxidation of aluminum and an aluminum alloy in wet hydrogen at high temperatures showed that growth probably occurs by decomposition of AlO on an Al2O3 surface. Rapid growth occurs on the tips of needles and the edges of platelets at lattice steps formed by intersection of hollow screw dislocations with these surfaces. Screw dislocations were detected by x‐ray measurement of the lattice twist they produce in the needle‐like crystals or ``whiskers.'' Needles were bent to elastic strains of over 2% corresponding to a strength of 1011 dyne cm−2.