Crack growth was studied in sapphire on both the m-plane and the r-plane (rhombohedral twin plane). Crack growth on the m-plane fit a power law function of stress intensity factor and an Arrhenius function of temperature. Crack growth on r-plane double torsion specimens was irregular. Spurts of growth on the r-plane were mixed with propagation on rough surfaces. Control of crack growth was not possible. Our studies suggest that r-plane fracture requires a lower KI than that on the m-plane. We suggest that propagation on the r-plane may be associated with twinning at the crack tip during or prior to crack growth.
Composites, Advanced Ceramics, Materials, and Structures, Annual Conference | 26th | | American Ceramic Society