An experimental study on the strain-rate-dependent compressive and tensile response of an alumina ceramic

This research article studied the strain-rate-dependent mechanical response of a CeramTec Alotec 98% alumina ceramic under uniaxial compression and indirect tension loadings. Mechanical testing was carried out using a load frame for quasi-static strain rates and a split-Hopkinson Pressure Bar (SHPB) for dynamic strain rates combined with the digital image correlation (DIC) technique and ultra-high-speed photography to investigate strain-rate-dependent failure behavior. Furthermore, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, electron backscatter diffraction, and X-ray microscopy was applied to determine the microstructural and failure features before and after experiments (e.g., elemental composition, grain size, voids, and impurities). Experimental results showed that the strength in compression was >10 × higher than those in tension. In addition, a strain-rate-sensitivity of strength on compression (linear fit slope of 0.68) was greater than in tension (0.39), and this was believed to be associated with crack growth and interaction, manifested as differences in measured crack speeds between the compression (2.5 ± 1.3 km/s) and tension (5.9 ± 2.1 km/s) cases. Post-mortem analysis of fracture surfaces revealed that intergranular fracture was more likely to appear in quasi-static loading and transgranular fracture in dynamic loading in alumina, with compression generating more micro-cracks as expected. Overall, this paper provides new comparative strain-rate-dependent strength and crack speed measurements of compression and tension, which serve as important inputs for future computational/numerical model development and validation.