Accurate characterisation and modelling of the nonlinear bending behaviour of non-crimp fabrics for composite process simulations

Simulation of the manufacturing processes of composite structures is being used increasingly to obtain defect-free manufacturing and investigate the effects of process parameters. The manufacturing of wind turbine blades (WTB) is considered in this work. The general trend in the industry is to form stacks of bindered non-crimp fabrics (NCFs) simultaneously to decrease the processing times. These stacks are referred to as preforms. On the other hand, forming of multi-layered fabrics may cause wrinkling (fibre waviness), which in WTBs can cause a knockdown in the strength of up to 66% for some wrinkle configurations [1]. To predict fibre wrinkling, the bending behaviour of the fabric materials needs to be accurately characterised and modelled [2]. Numerous methods for characterising the bending stiffness of fabric materials have been studied in the literature, but they all suffer from either expensive equipment or uncertainties in the data processing schemes [3]. Furthermore, most conventional models of fabric materials consider a constant bending stiffness, which causes the size of the wrinkles to be overpredicted [4], as shown in Figure 1. In the current work, an experimental methodology for automatic and reliable characterisation of fabric bending stiffness is presented together with a model that is capable of accurately simulating the nonlinear bending response of fabric materials