In-situ study on compressive behaviors of different types of 3D SiC/SiC composites using X-ray computed tomography and digital image correlation

X-ray computed tomography (X-CT) and digital image correlation (DIC) are typical methods to capture in-situ, full-field information during mechanical tests. In this paper, above two methods are combined to conduct in-situ investigation on compressive behaviors of 3D 4-directional braided (denoted as 4D) and 3D stitched SiC/SiC composites, which has not been systematically studied in other works. The loading direction of stitched composites is parallel or vertical to the ply direction, denoted as P and V, respectively. DIC tests were first conducted to determine observation points corresponding to specific damage modes. Af-terwards, in-situ X-CT was utilized to acquire 3D images of internal microstructures during loading. Digital volume correlation (DVC) was subsequently performed to calculate defor-mation, and extract cracks induced by successive loading combined with image subtrac-tion. SEM was finally used to further illustrate failure mechanisms through examining fracture surfaces at the microscale. The results indicate that the preform patterns and loading directions both have an ineligible effect on mechanical behaviors of 3D SiC/SiC composites. More specifically, for 4D and P composites, inter-bundle and intra-bundle debonding, and fiber breakage resulted from bending and bucking account for eventual failure. Besides, damage of 4D composites show obvious global feature. Nevertheless, the main failure mode of V composites is interlayer matrix cracking and V composites exhibit higher strength. This work demonstrates that the integrated application of DIC, X-CT, DVC and image subtraction enables initial damage localization and visualization of microstructure-related damage evolution, providing an effective way for evaluating bearing capacity of composite structures. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).