​Dynamic strength of sapphire crystal (5)

Dynamic strength of sapphire crystal (5)

The depth of the defect layer formed on the surface of sapphire during mechanical processing, other things being equal, is related to the method of crystal growth and the grain structure. For example, crystals grown by the Verneuil and Stepanov method have a small grain structure elements, their defect layer depth is the greatest, and their relative strength and crack resistance are the lowest under shock loading (Fig. 2.63a).

In sapphire crystals, which have about 20% covalent bonds, all failure types are observed: brittle fracture, plastic rheology (the aforementioned failure) and shearing. Under central impact, brittle fracture occurs in the middle of the sample. Hearts were observed, but destruction of peripheral regions was not excluded (Fig. 2.63b).

The effective stress value of the cut was found to be related to the tension pulse shape and duration, the stress state of the medium and different physical factors such as temperature, initial microstructure, etc. So the cut strength is a function of many variables. Cut The energy criterion for failure is based on the work that must be cut in the expansion-wave interaction region and is accompanied by the contribution of elastic energy in the stretching pulse. If the elastic energy is sufficient to effect this process, the cut will occur.

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