Single-fiber push-out tests performed with a Berkovich and a flat-end indenter tip were conducted on the same SiC/PyC/SiC ceramic matrix composite sample for comparison. Push-out measurements were stopped at different stages during the experiment for a detailed microscopic analysis of the front and back side of the sample, to investigate the progression of failure during push-out process. The microscopic analyses reveal differences from the established interpretations which are crucial for quantitative evaluation of interface properties. Based on the microscopic findings, a modified loading schedule comprising unloading-reloading cycles is proposed, which provides access to the dissipative and nondissipative energy contributions during push-out test. A new energy-based approach is presented which allows for the determination of the interfacial fracture toughness, without assumptions regarding the stress distribution along the interface to be made. Presuming stable crack growth along the complete debonding length, the interfacial fracture toughness of the sample investigated amounts to 44 ± 9 J/m 2 .

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For mechanical characterization of interfacial properties in fiber-reinforced ceramic matrix composites by single-fiber push-out tests, a determination of the relevant crack area is required. In established evaluation methods, the relevant crack area is approximated by the total cylindrical fiber surface of the pushed fiber. This concept disregards that stable crack propagation, which is relevant for prediction of macromechanical behavior, may occur on just part of the fiber-matrix interface area. In the present publication, a new approach to quantify the relevant crack area is presented, enabling a more reliable determination of the interfacial fracture toughness of ceramic matrix composites.The new concept is applied to SiC-fiber reinforced SiC-matrix composites with pyrocarbon fiber coatings (SiC/PyC/SiC) produced via chemical vapor infiltration technique. The occurrence of stable and unstable crack growth, as predicted in literature, can be verified experimentally. A strong correlation between PyC fiber coating thickness and interfacial fracture toughness is found.

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