Prediction of elastic properties of 2D biaxial and triaxial braided composites multi-scale RVE models using the finite element method

Accurate prediction of the elastic constants of braided composites has become increasingly critical, yet the complex geometry of these materials remains challenging for evaluating stiffness. To address this challenge, a novel multiscale finite-element representative volume element (RVE) framework was developed to predict the elastic behavior of two-dimensional biaxial and triaxial braided composites. An analytical approach was first derived to calculate the minimal curved unit-cell dimensions regardless of braid diameter for the three main patterns as a function of curvature angle and yarn pitch length of the braid structure. Subsequently, periodic RVEs were generated to capture the mechanical properties of the resulting composites. Periodic boundary conditions were applied under six independent loading modes to extract the complete anisotropic stiffness tensor. The resulting predictions were validated through uniaxial tensile tests and also three-point bending experiments to confirm the model's robustness under combined stress states, showing an error margin of less than 8% compared to numerical results. A qualitative comparison of maximum principal stress contours further validated the RVE's capability to replicate anisotropic load paths and shear coupling. Taken together, the proposed multiscale RVE–FEM methodology is demonstrated to be a reliable, physics-based tool for the design and optimization of braided composite structures.