Multiscale analysis and validation of elastic constitutive relations for 2.5D shallow orthogonal woven C_f/SiC composites under multiple directions loading

The 2.5D woven carbon fiber reinforced silicon carbide CMC overcomes the shortcomings of weak interlayer bonding in 2D fabrics and performance degradation caused by yarn buckling in 3D fabrics. By interweaving warp and weft yarns, this method achieves simultaneous improvement in in-plane performance and interlaminar strength, resulting in more stable mechanical properties for CMCs in complex aerospace environments. However, current research on CMC fabrics predominantly focuses on 2D and 3D structures, leaving the constitutive relationship of 2.5D woven C_f/SiC under isotropic stress loads insufficiently studied. To address this gap, this research employed 2.5D shallow orthogonal woven C_f/SiC fabrics (2.5D-SO-C_f/SiC) as the subject and adopted a sequential multiscale approach to establish its constitutive model. In the model establishment process, theoretical analysis, numerical simulation, and experiment testing were integrated to characterize and formulate the elastic response model under diverse mechanical loading conditions. Through theoretical research and finite element calculations, this study established the numerical relationship between the macroscopic material properties of 2.5D-SO-C_f/SiC and the properties of its constituent materials across multiple scales, culminating in a final mesoscale constitutive model. The validity and accuracy of the proposed model were verified via macroscopic experiments on specimens subjected to mechanical loads in multiple directions.