Temperature- and displacement speed-dependence of notched strength at 1873-2023K of Alumina/YAG composite

The temperature- and displacement speed-dependence of unnotched and notched strengths at 1873-2023 K of directionally solidified eutectic Al ₂O₃/YAG (Yttrium-Aluminum Garnet with the composition of Y₃Al₅O₁₂) composite was investigated experimentally by tensile test and analytically by the finite element method. The notched specimens fractured in a brittle manner at low temperatures and at high displacement speeds, but in a ductile manner at high temperatures and at low displacement speeds. The notched strength increased, reaching maximum, and decreased with increasing temperature under a given displacement speed and with decreasing displacement speed under a given temperature. For the finite element analysis, the temperature dependence of the Young's modulus was measured to be 345-0.0361T (T: temperature, K) GPa and the temperature- and strain rate-dependence of the flows stress in the plastic deformation stage of unnotched specimens was estimated as {(strain rate)/(1.23×10 ⁵)}^1/5 exp{1.81×10⁴/T} from the reported data. From the comparison of the experimental- with analytical results, the increase in the notched strength with increasing temperature and decreasing displacement speed up to the maximum notched-strength value was accounted for by the increase in plastic zone size ahead of the notch. Also the decrease in notched strength with further increasing temperature and decreasing displacement speed was accounted for by the loss of the stress carrying capacity of the yielded ligament due to the softening.