Homogenized response of ultra-thin woven fibre composites under flexural loading

Abstract

Design of large space structures is restricted due to the limited storage capacity of launch vehicles. Deployable structures made with ultra-thin woven fibre composites eliminates this bottleneck due to self-deploying nature. These structures can selfdeploy using the strain energy stored during elastic folding. Popularity of selfdeployable structures got increased due to their high strength, lightweight, and good

packaging properties. However, thin woven fibre composites undergo large

deformation during folding process due to the formation of high curvature, which causes reduction in bending stiffness. Hence, it is crucial to understand the mechanical

behaviour of these structures before implementing, in order to avoid unnecessary

failures. Numerical modelling techniques have become popular in this research area

due to the advancement of computational methods to obtain the mechanical properties

of thin woven fibre composites. Homogenised Kirchhoff plate-based representative unit cell modelling technique with solid elements is considered in this research. Corresponding ABD stiffness matrices are obtained with using virtual work principle, where the repetitive nature of woven fibre composites is represented by periodic boundary conditions. First, a series of micro-mechanical analyses is carried out to observe the influence of the relative positioning of tows on the mechanical properties of thin woven fibre composites. Various phase shifts between the plies have been considered in this research which might be originated from the inter-ply misalignment during the manufacturing stage. The outcomes of this parametric study clearly depict the variation in in-plane and out-of-plane properties extracted from the ABD stiffness matrices and describe the potential causes for the detected deviations between experimental and numerical results. Next, a resin embedded unit cell model is developed to predict the non-linear bending behaviour with degree of deformation. Initially, a geometrically linear analysis is carried out and then the analysis is extended to non-linear region to observe the moment-curvature response. Linear analysis results of extensional stiffness and Poisson’s ratio showed good agreement with the experimental results extracted from the literature. However, the out-of-plane properties and shear stiffness values were overpredicted. Similarly, non-linear analysis overpredicted the bending stiffness throughout the considered curvature range. Hence, the resin embedded unit cell model needs further improvements and modifications to accurately predict the out-of-plane properties, and capture the reduction in bending stiffness.