Investigation of sapphire strength across the scales

Abstract

The strength of sapphire across several length scales has been studied by micro-cantilever bending tests on specimens with the a-plane perpendicular to the main loading direction. The combined machining of two types of FIB (Ga and plasma Xe) is used to produce specimens with a wide range of dimensions, with specimen heights ranging from a few microns to several tens of microns. All specimens exhibit a fracture surface along m-planes. These micro-bending strength results are compared with macroscopic bending results obtained on the same sample with the same orientation. A marked size effect is observed on the measured strength, ranging from around 20 GPa at the micrometric scale down to 650 MPa for macroscopic specimens. A comparison with data from literature on sapphire samples of different size is made. Statistical models are found unable to capture the size effect on the entire range of sample sizes.