Transverse Liquid Composite Moulding Processes for Advanced Composite Material Manufacturing

Abstract

Many recent developments in Liquid Composite Moulding (LCM) processes have focused on the benefits of transverse (through-thickness) flow to reduce the impregnation path. The fluid flows in the same direction as the preform deformation, so the complex coupling between flow and deformation, known as hydrodynamic compaction, leads to a non-uniform fibre volume fraction distribution in the wet region. This type of behaviour occurs in a wide variety of manufacturing processes and experimental characterisation techniques involving through-thickness impregnation of fibrous reinforcements, such as Compression Resin Transfer Moulding (CRTM), permeability measurement systems and Resin Transfer Pressing (RTP). A comprehensive numerical model is developed based on the fully coupled, non-linear, time-dependent governing equations to predict the homogenisation time, fluid pressure, effective stress, and fibre volume fraction distribution for a general transverse resin impregnation/compression process. Detailed analysis of transverse permeability measurement systems is carried out, and the true permeability relation is extracted from measurements of the apparent permeability by removing the effects of hydrodynamic compaction. Commonly made assumptions, such as quasi-steady flow and uniform through-thickness deformation, introduce significant errors in manufacturing process predictions. It is shown that the fully coupled governing equations must be used when modelling processes involving direct contact between the tool and preform. Optimal resin-to-reinforcement ratios are determined using the developed model to minimise the processing time and resin wastage. A Physics-Informed Neural Network (PINN) is used to simulate the simple case of transverse compression of a saturated preform, with solution times of less than 1 ms, to explore the applicability of machine learning to composite manufacturing simulations. Furthermore, viscoelastic compaction models are implemented into simulations to capture the interaction between hydrodynamic compaction behaviour and viscoelastic effects. When a saturated stack is held at a constant thickness, the total load decreases due to the equilibration of fluid pressure and viscoelastic stress relaxation. Viscoelastic simulations were found to significantly improve the accuracy of predictions compared to elastic models. The comprehensive analysis given in this thesis provides an in-depth understanding of various aspects of the flow and deformation in transverse impregnation/compression processes.