Mechanical characterization of uncoated and coated ceramic matrix composite (CMC) across manufacturing stages using static and fracture test

Static (tensile, compression and flexural) tests on uncoated and SiC surface coated CMC produced via Liquid Silicon Infiltration (LSI) were performed at room temperature on two layup [0°/90°]4 and [45°/-45°]4. A detailed comparison of mechanical properties across all manufacturing stages (CFRP, C/C, uncoated and coated CMC) were performed to evaluate the evolution of mechanical properties before and after pyrolysis and after silicon infiltration. The CFRP stage generally exhibited the highest mechanical strengths, except for the [0°/90°]4 compressive response, for which the coated CMC achieved the highest value. Further optical microscopic images were taken of fractured samples to better analyze the failure mechanism. An increase of 42 % in compressive strength is found for coated CMC as compared with uncoated CMC. Fracture tests on final coated CMC composite were performed to evaluate mode I and mode II fracture energies and fracture toughness values to understand the fracture mechanism using DCB, ENF and SENB tests. Static studies showed better compressive strength and tension-controlled brittle failure, whereas the progressive softening in the fracture load–displacement responses indicated significant resistance to shear-induced crack propagation. These combined mechanical findings suggest that damage tolerance in LSI-based CMCs is governed by internal microstructural toughening mechanisms.