Fracture of A1 2 O 3 in Combined Tension/Torsion: I, Experiments

Combined tension/torsion tests were performed on solid A1 2 O 3 rods at principal stress ratios σ 2 /σ 1 of 0 (pure tension), ‐0.17, ‐0.38, ‐0.78, and ‐1.0 (pure torsion). The tensile principal stress at fracture σ 1 increased with increasing compressive principal stress σ 2 , resulting in a higher strength in torsion than uniaxial tension. The ratio σ 1 (torsion)σ 1 (tension) was 1.31 for A1 2 O 3 , in general agreement with limited torsional data for brittle materials in the literature. Brittle fracture data in the tension‐compression quadrant of principal stress space show an interesting dichotomy since strengthening is observed in torsional investigations, whereas weakening is observed for pressurized‐tube studies. This difference may be either a pressurized‐tube test artifact or a real effect due to the presence of stress gradients.