​Mechanical properties of sapphire crystals (2)

Mechanical properties of sapphire crystals (2)

The Poisson coefficient is 0.27-0.30, which is related to the crystallographic direction. The intensity characteristics of sapphire are structure-sensitive, and this fact essentially explains the difference in the measurements obtained by different authors. Lower Lower The temperature dependence of the critical cutting stress and the ruby-cut yield stress ratio at 90 and 60 degrees is shown in Figures 2.55-2.57.

 Activation energies E and activation volume V* are determined by stress τ* (Fig. 2.58). The temperature dependence of activation energies has two ranges: below 1,800 K, this is E*=335 -500 kJ/mol, while above 1,800 K, the activation/chemical energy increases to 3,350 kJ/mol. Based on the value of the activation/chemical energy, its temperature and stress-dependent properties, two mechanisms of plastic deformation in sapphire can be predicted . At temperatures up to 1,800 K, the thermal activation migration process on the Peierls-Navarro barrier occurs; at higher temperatures, dislocation climbing is more likely to occur.

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