Fracture characteristics of Al2O3/YAG composite at room temperature to 2023Â K

The fracture behavior of the notched unidirectionally solidified eutectic Al2O3/YAG composite was investigated by tensile test at room temperature to 2023 K, and the results were analyzed by the finite element method. The stress-strain behavior, notched strength and the fracture toughness were strongly dependent on temperature and displacement speed. The specimens fractured in a brittle manner at low temperatures and at high displacement speeds but in a ductile manner accompanying plastic deformation at high temperatures and at low displacement speeds. The notched strength for a given displacement speed of 10−7 m/s increased with increasing temperature from 132 MPa at 1873 K to 153 MPa at 1923 K, and then decreased to 133 and 110 MPa at 1973 and 2023 K, respectively. Also the notched strength for a given temperature of 2023 K increased with decreasing displacement speed from 67 MPa at the displacement speed of 10−5 m/s to 124 MPa at 10−6 m/s, and then decreased to 110 and 72 MPa at 10−7 and 10−8 m/s, respectively. The stress distribution and the plastic zone size ahead of the notch were calculated by a finite element method using the dependence of flow stress on temperature and displacement speed. Based on the calculation result, the experimentally observed increase in the notched strength with increasing temperature and decreasing displacement speed up to the maximum value could be accounted for by the increase in plastic zone size ahead of the notch. Also, the observed decrease in notched strength with further increasing temperature and decreasing displacement speed could be accounted for by the decrease in the stress carrying capacity of the yielded ligament.