Notched Fracture Behavior of an Oxide/Oxide Ceramic‐Matrix Composite

Abstract

The fracture behavior of an oxide/oxide ceramic-matrix composite, alumina/alumina-silica (Nextel610/AS), was investigated at 23°and 950°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°and 950°C. The effect of temperature on the notched strength was significant. Net section failure stress decreased 50% when temperature was increased from 23°to 950°C. Observations of damage progression indicated that the reduction in notch strength with temperature was associated with self-similar crack growth at 950°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.

Developments in Oxide Fiber Composites

“…These changes are correlated with coarsening of matrix porosity and extensive sintering to the fiber surface. Analogous changes are obtained at elevated temperatures and in notched specimens 53,54 . The retained strength of the system with the mullite–alumina matrix remains essentially unchanged upto 1200°C.…”

New porous silicon carbide composite reinforced by intact high-strength carbon fibres

“…27,28 They have as yet been investigated mainly for materials with oxide fibres and oxide matrix (oxide/oxide composites). 3,[24][25][26][27][28][29][30][31] It is concluded that the function of the highly porous matrix material is to isolate fibres from cracks within the matrix. 3,29 The fracture behaviour is referred to the damage effects of the matrix material and the consequence for neighbouring fibres.…”

“…The mechanical properties of these materials are determined by the fibres and the material is therefore characterised as "fibre-dominated". [24][25][26] It is assumed that matrices with a low stiffness do not take over axial forces from the fibres to a substantial extent. Consequently, stress redistribution between fibres is limited, and so the strength and fracture toughness are lower than those of composites with stiff matrices.…”

Strength and Notch Sensitivity of Porous‐Matrix Oxide Composites

“…Notwithstanding progress in the development of fiber coatings and environmental barrier coatings for use with SiC/SiC composites, oxide systems remain top contenders for applications requiring long service lives (>10 4 h) in oxidizing environments, albeit at operating temperatures (about 1200°C) that are some 100–200 K below the targeted levels for SiC/SiC. This has motivated numerous activities in material development and assessment in industrial 1–5 and government laboratories, 6–12 as well as academia 13–19 …”