Study on mechanism of crack propagation of sapphire single crystals of four different orientations under impact load and static load

Abstract Sapphire has a wide range of applications due to its excellent physical properties. Sapphire is a typical anisotropic material, whose parts are usually employed in the complex conditions, including static and dynamic load. The mechanism of crack propagation under different loading conditions has important significance for successful application of sapphire. In this study, impact and static load tests have been performed on the A-plane, C-plane, M-plane and R-plane of sapphire by the high frequency cyclic impact test device, respectively. The force signals applied to sapphire have been obtained under different test conditions. The crack propagation has been analyzed based on the fracture morphology of specimen. It is found that sapphire will quickly crack and break under impact load, and then enter the fatigue stage. In the static load indentation tests, the force applied to sapphire seems to increase linearly with the linear increase of load, but this relationship is not yet linear in the unloading procedure. The crack propagation is affected by the crystal orientation, which leads to different characteristics of the surface morphology of the different crystal orientations sapphire after fracture. So four different models of crack system are proposed for A-plane, C-plane, M-plane and R-plane respectively. In addition, the three-dimensional morphology of sapphire is observed by a white-light interferometer. It seems that the Hertzian cone crack occurs only on the R-plane sapphire after impact load, but it cannot be sure whether the cone crack occurs when impacting A-, C-, and M-planes sapphire.