Rate effects on the mechanical response of magnesium aluminate spinel

► Spinel specimens were tested under both compression and equibiaxial flexural conditions. ► The strength was rate dependent for both loading conditions. ► The failure on ring-on-ring specimens was initiated from central area. ► Fracture toughness tests were attempted by using Chevron notch and surface crack methods. The uniaxial compressive, biaxial flexural strength and fracture toughness of a polycrystalline transparent MgAl 2O 4 spinel were characterized over a wide range of loading rates. The flexural tests were carried out by means of ring-on-ring equibiaxial bending, while the fracture toughness was determined by four-point bending on samples with Chevron notch (CN) configuration. The surface crack (SC) method was also attempted in determining the fracture toughness. Quasi-static experiments were conducted on a servohydraulic testing machine, while the high-rate experiments were performed on a modified Kolsky bar. Results showed that both the failure strength and fracture toughness of the spinel were rate sensitive. Edge beveling in sample preparation did not affect the ring-on-ring flexural strength significantly, and the failure initiation sites were found to be inside the loading ring area regardless of edge conditions. Fracture toughness tests following ASTM standard were largely affected by the inherent coarse microstructure of this material.