BACKGROUND

Abstract: Results are compared for several different sets of 4-point flexure strength measurements on sapphire as a function of crystal orientation and temperature. The only consistent trend is that strength drops rapidly with increasing temperature when the c-axis of the crystal is the principal axis of tension and compression. Using Grafoil between sapphire and the load fixture increases the apparent strength of specimens whose principal axis is c by a factor of 2–3, but has little effect on other crystallographic orientations. The rate of crack propagation on the m-plane of sapphire increases by 7 orders of magnitude between 20 and 600ºC