Notched fracture behavior of an oxide/oxide ceramic-matrix composite

The fracture behavior of an oxide/oxide ceramic-matrix composite, alumina/alumina-silica (Nextel610/AS), was investigated at 23 degrees and 950 degrees C using a single edge notched specimen geometry with clamped ends. Crack growth and damage progression were monitored during the tests using optical microscopy, ultrasonic C-scans, and crack mouth opening displacement, The net section strength of Nextel610/AS was less than the unnotched ultimate tensile strength. The failure mode was nonbrittle with considerable nonlinear deformation prior to and after the peak load at 23 degrees and 950 degrees C. The effect of temperature on the notched strength was significant. Net section failure stress decreased 50% when temperature was increased from 23 degrees to 950 degrees C, Observations of damage progression indicated that the reduction in notch strength with temperature was associated with self-similar crack growth at 950 degrees C, Ultrasonic C-scans were found to be an effective method of monitoring damage progression. Ultrasonic attenuation ahead of the notch tip was correlated with surface matrix cracks and exposed fiber lengths on the fracture surface.