| Elevated temperature mechanical properties and failure behavior of an $alpha$-alumina/aluminum composite were studied in tension and fatigue. Effects of the test temperature and isothermal exposure on the stress-strain curve, tensile strength, and fatigue lifetime were investigated. Characteristics of the fracture surfaces and the changes of failure mode as a function of temperature were analyzed.;Test temperature affects the transition point from Stage I to Stage II on the stress-strain curve of longitudinal composite by altering the residual stress distribution. Low-temperature treatment or tensile prestraining method was found to extend the composite Stage I region by introducing compressive residual stress in the matrix.;The longitudinal specimens retained room temperature tensile strength of 520 MPa up to $175spcirc$C; strength then decreased with increasing test temperature due to the reduction of matrix strength and the reduction in fiber-matrix adhesion. At temperature near the matrix melting point, fiber degradation by chemical reaction becomes significant. At low temperatures, dimple patterns around the broken fibers on the composite fracture surfaces are a result of interacting fiber fracture and subsequent necking down of the ductile matrix. At high temperature, the fracture mode is characterized by the shear failure of the matrix.;At room temperature, fracture in the transverse direction is caused primarily by matrix rupture and some fiber splitting; at $400spcirc$C, failure occurs predominantly by interfacial debonding. The degree of the interfacial failure is increased after isothermal exposure. In addition, the decrease in tensile strength is caused by matrix softening and void formation at the interface.;Fatigue resistance of the composites is insensitive to the test temperature up to $175spcirc$C. In general, fracture surfaces for the tension and fatigue tests are similar at corresponding test temperatures; however, initiation and propagation of the fatigue cracks were identified from the patterns on the fracture surfaces in the longitudinal specimens at room temperature. |
