Strength and Toughness of Continuous‐Alumina‐Fiber‐Reinforced Glass‐Matrix Composites

Unidirectional, continuous‐fiber composites were fabricated using polycrystalline alumina fibers and four different silicate glass matrices of differing thermal expansion. Fracture toughness measurements, strength measurements, and fractographic analysis of failed specimens are used to identify the failure mechanism. Results show that the elastic modulus mismatch between the matrix and the fibers shields the reinforcing fibers from matrix crack extension, thereby increasing composite toughness without fiber pullout. Fractographic analysis shows that fiber shielding leads to fiber failure ahead of matrix crack. Composite toughness increases linearly with increases in the residual compressive stress in the matrix phase. Ultimate composite strengths are dependent upon thermal‐expansion‐induced residual stresses and fiber strength.