Methodical Fiber Push‐In Indentation for Improved Statistical Assessment of Interfacial Shear Strength in CMCs

ABSTRACT Ceramic matrix composites (CMCs) are advanced materials known for their exceptional thermal stability, high strength‐to‐weight ratio, and resistance to oxidation and wear, making them ideal for aerospace and high‐temperature applications. CMCs mitigate the inherent brittleness of ceramics through fiber reinforcements. A weak fiber–matrix interface allows for crack bridging and fiber pullout to increase their toughness; however, their design complexity can limit the understanding of CMC behavior. Push‐in testing is a critical method used to evaluate the interfacial properties and mechanical performance of CMCs. This study focuses on the push‐in testing technique to assess the interfacial shear strength and debonding behavior of CMCs. The methodology involves applying a controlled load to a fiber or fiber bundle embedded in the ceramic matrix until debonding occurs. Key parameters such as load–displacement curves, interfacial shear strength, and energy absorption are analyzed to understand the material's performance under stress. In this study the tests were conducted using an instrumented nano‐indenter directly on the cross‐section of a SiC–SiC composite. Initially, the cross‐sections were optically imaged, and a custom Quantitative Microscopy (QM) tool was used to measure fiber radius and coating thickness before the indentation tests. A shear‐lag model was then used to estimate the sliding stress ( τ ) between the BN‐coated SiC fiber and the SiC matrix for a large number of fibers with varying radii and coating thicknesses to allow for statistical analysis.