The Ultimate Flexural Strength of Fiber-Reinforced Ceramic Matrix Composite: A Multiscale Approach

This paper tackles the important issue of the flexural strength of continuous fiber-reinforced ceramic composite. Estimates of the flexural strength of 2D woven SiC/SiC composite are extracted from symmetric and asymmetric 3-point bending test results using three independent approaches: (1) the equations of elastic beam theory for homogeneous solids, (2) finite element analysis of the stress state, (3) stress–strain relations in the tensile outer surface of specimens. Furthermore, the flexural strength is predicted from the ultimate tensile strength using a bundle failure model based on the fracture of the critical filament. It is shown that the equation of elastic beam theory significantly overestimates the flexural strength of the 2D SiC/SiC (620 MPa), while the alternate approaches and the predictions from the ultimate tensile strength converged to ≈340 MPa. The variability of strength data was approached using the construction of p-quantile diagrams that provide an unbiased assessment of the normal distribution function. Pertinent Weibull parameters are derived using the first moment equations. Important trends in the effects of the size, stress gradient, tension–flexure relations, strength of critical filament in a tow, and populations of critical flaws are established and discussed.