In-plane shear mechanical properties of SiC/SiC ceramic matrix composites Study of test methods

Ceramic matrix composites（CMCs）, as outstanding high-temperature structural materials, have found extensive application in aero engines. Consequently, it is crucial to conduct research on high-temperature mechanical property test methods and ascertain these properties to broaden CMC applications in the aerospace sector. The double-in-plane shear test scheme recommended by the national military standard GJB 10311—2021 often results in high calculated average shear stress in the gauge area due to stress concentration at the incision, leading to significant deviations between in-plane shear modulus test results and those of the V-notch shear test. To address this, a novel in-plane shear mechanical property test method has been developed by integrating the digital image correlation method（DIC） with the double-incision shear test. Compared to the V-notch shear test, this method boasts a smaller test fixture and specimen size, making it more suitable for high-temperature in-plane shear testing. To mitigate the impact of stress concentration at the incision, finite element model updating（FEMU） is proposed, constructing an objective function based on the variance between the average in-plane shear strain and numerically calculated strain in the DIC-measured gauge area. This allows for iterative determination of the material’s in-plane shear modulus. For engineering application convenience, the material’s in-plane shear modulus and strength can be obtained by varying the specimen’s incision depth during testing. The feasibility of this test method and the reliability of its results are further validated using SiC/SiC orthogonal laminated ceramic matrix composites. Results indicate that the proposed experimental method can simultaneously determine the in-plane shear modulus and strength of CMCs. The SiC/SiC ceramic matrix composites exhibit typical yield points in their in-plane shear stress-strain behavior, with post-yield shear behavior characterized by linear strain strengthening.