ISOGEOMETRIC ANALYSIS OF BUCKLING AND POST-BUCKLING BEHAVIOR OF VARIABLE ANGLE TOW COMPOSITE LAMINATES

Variable-angle tow (VAT) composites can significantly improve structural stability and load-carrying capacity by introducing spatially varying fiber paths. However, after discretization, conventional finite element methods often have difficulty ensuring the smoothness and continuity of curved fiber trajectories. To address this issue, this study investigates the buckling and post-buckling behavior of VAT composite laminates based on isogeometric analysis (IGA). In terms of methodology, a buckling analysis model for VAT composite laminates is established by combining the Reissner-Mindlin plate theory, and geometric nonlinear analysis is further introduced to develop a three-dimensional curved shell element suitable for large-deformation post-buckling analysis. On this basis, the LaRC03 failure criterion and a stiffness degradation model are incorporated to describe the initiation and evolution of fiber and matrix damage during the post-buckling stage. The effectiveness of the proposed method is validated through several numerical examples, including isotropic plates, straight-fiber composite laminates, and VAT composite laminates. The effects of the pre-buckling stress field and fiber path parameters on the buckling performance and post-buckling response of the structures are also analyzed. The results show that the proposed method can accurately predict the buckling loads and mode shapes under uniaxial compression, pure shear, and combined compression–shear loading conditions, and can effectively capture the complete structural response from buckling to post-buckling and ultimately to damage-induced failure. Compared with conventional finite element methods, IGA can achieve stable and accurate results with fewer degrees of freedom, demonstrating superior convergence and computational efficiency. In addition, the boundary conditions and fiber path parameters have significant effects on the buckling and post-buckling responses of the structures, and their coupled influence determines, to some extent, the load-carrying capacity and failure modes of VAT composite laminates.