A Multiscale framework for simulating large-curvature bending response of thin fibre composite structures with incremental shell stiffness updating

Abstract

The nonlinear bending stiffness of thin carbon-fibre woven composites is critical in the design of deployable space structures, yet it is not represented in conventional analytical or numerical design frameworks. Although this nonlinear bending response has been experimentally observed and characterised, a generalised modelling strategy that can systematically incorporate it into structural-scale simulations remains limited. This thesis proposes a multi-scale numerical framework, supported by user-defined subroutines, to embed bending stiffness nonlinearity into finite element models and to predict the response of thin woven composite structures undergoing large deformations. At the meso-scale, the curvature-dependent bending stiffness was extracted from a previously developed and experimentally validated in-house representative unit-cell model, incorporating material plasticity and progressive damage. Building on this input, a macro-scale modelling approach was developed in this thesis using a UGENS user-defined subroutine to embed the curvature-dependent stiffness into structural simulations. The framework was applied to flat coupons and singly curved configurations, including tape springs, to assess the influence of bending stiffness degradation on global structural behaviour. Numerical predictions were validated against analytical solutions and experimental results reported in the literature. The proposed approach accurately reproduced the nonlinear bending moment response and the global deformation behaviour of both flat and curved structures, including complex response features such as bifurcations. Overall, the thesis demonstrates a practical and reliable modelling route for incorporating bending stiffness degradation in thin woven composite structures, enabling improved analysis and design of advanced space structures.