Subcritical crack growth in CVI SiCf/SiC composites at elevated temperatures: dynamic crack growth model

Abstract A dynamic crack-growth model has been developed to predict slow crack growth in ceramic composites containing nonlinear, creeping fibers in an elastic matrix. Mechanics for frictional bridging and nonlinear fiber-creep equations are used to compute crack extension dynamically. Discrete, two-dimensional fiber bridges are employed, which allows separate bridge “clocks”, to compute slow crack-growth rates for composites containing Nicalon-CG and Hi-Nicalon fibers. Predictions for activation energies, time-temperature exponents, crack lengths, and crack-velocity data for composites in bending at 1173 K to 1473 K in inert environments are in good agreement with experimental data. In addition, calculated creep strains in the bridges agree with experimental damage-zone strains. The implications of multiple-matrix cracking are discussed.