Simulation of non-linear bending behavior of ultra-thin woven composites

Abstract

Ultra-thin woven fibre composites are commonly used to design self-deployable space struc- tures subjected to large deformations. Accurate prediction of their folding and deployment behaviour is crucial for optimising space structures. Recent studies have suggested that in thin woven composites made of one to two layers, the material exhibits a significant reduction in bending stiffness at high curvatures, resulting in a non-linear moment-curvature response, but the phenomenon lacks comprehensive evidence. This study confirms the reported bending stiffness reduction by capturing the complete moment-rotation response from its initial stiffness to failure via a single experimental procedure conducted on coupons. Several approaches are used to construct the bending response from the experimental studies, and their effectiveness is evaluated. The observed experimental response is then captured using a representative unit cell-based homogenised numerical model which is proposed by previous researchers. The model is used to assess the effects of geometrical non-linearities and the material non-linearities of tows on the bending response. The meso-mechanical bendingresponsealignswellwiththeexperimentalvalues. Themeso-scalebendingresponse is incorporated into macro-scale simulations via a user-defined section stiffness. Comparison of simulated results with column bending test results obtained through physical experiments shows that the proposed model is capable of accurately predicting the non-linear bending response. The study shows a significant variation in bending stiffness reduction at large curvatures when updating the stiffness matrix in comparison to the simulation performed only with a constant stiffness matrix. Incorporating this change of stiffness is critical for predicting the amount of energy stored for deployment as well as the force required for folding the structure.