Fracture of A12O3 in Combined Tension/Torsion: I, Experiments

Combined tension/torsion tests were performed on solid A1₂O₃ rods at principal stress ratios σ₂/σ₁ of 0 (pure tension), -0.17, -0.38, -0.78, and -1.0 (pure torsion). The tensile principal stress at fracture σ₁ increased with increasing compressive principal stress σ₂, resulting in a higher strength in torsion than uniaxial tension. The ratio σ₁ (torsion)σ₁ (tension) was 1.31 for A1₂O₃, 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.