​Dynamic strength of sapphire crystal (4)

Dynamic strength of sapphire crystal (4)

It is known that the fastest rate at which a load travels through any material is equal to the speed of sound in that material, specifically (E/γ)1/2, where E is Young's modulus and γ is the density of the material. Sound in sapphire At medium velocities, the shock load conduction velocity can reach (1.04-1.12)•104 m/s, which is much higher than the speed of the bullet (300-850 m/s). Generally speaking, the behavior of the shock load lasts about 100 m/s. fractions of a second, while the energy exits from the impact point several orders of magnitude faster. At the instant of impact, a series of stress waves are emitted from the impact point. These waves reach the boundaries of the sample or bulk, twin sandwich or etc. and are reflected back, slowly weakening their intensity. The superposition of the direct and reflected waves results in the formation of standing waves, which create a sudden increase in stress at the antinode and cause damage to the sample. Therefore, the course of events will be determined by the sample shape and size, the place of impact and the structural integrity as well as the orientation of the crystal are determined by a process.

Figure 2.60 Behavior of sapphire with different orientations in impact test. The maximum impact energy is 7 J

Figure 2.60 shows the strength comparison of different crystallographically oriented sapphire samples grown by the same method. In fact, all specially heat-treated samples with (0001) orientation can withstand three to five shocks up to 7 J. R-oriented samples It was destroyed after the first impact, and only one third (112 0) of the oriented samples survived the test under the same test conditions.

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