Experimental Validation of Local and Global Force Simulations for Rigid Tool Liquid Composite Moulding Processes

Abstract

Resin Transfer Moulding (RTM) and Compression RTM (CRTM) are two manufacturing processes used to produce fibre-reinforced composite components. Significant previous research has been carried out on simulation of flow in such processes, allowing optimisation of cycle times and void formation. However, little work exists on predicting tooling forces. Accurate simulation of tooling forces will allow optimal mould tool design and selection of appropriate peripheral equipment. It is also necessary to allow simulation of more complex semi-flexible mould processes such as RTM Light. This research has focussed on experimental validation of local and global force simulations during RTM and CRTM process cycles. Comprehensive characterisation studies were undertaken on a Chopped Strand Mat (CSM) reinforcement; two compaction stress models and a permeability relationship were characterised. A study was undertaken to determine the friction coefficient between glass-fibre reinforcements and typical mould surfaces. The friction coefficient is required to calculate the influence of the shear component of reinforcement compaction stress in non-planar geometries. Processing parameters had little impact on the friction coefficient, validating use of a simple model in simulation. Fabric reinforcements subjected to in-plane shear, such as when draped in non-planar moulds, respond differently to unsheared fabrics. The effect of in-plane shear on the reinforcement compaction stress is studied for plain-weave and biaxial-stitched fabrics. Both materials exhibit increasing reinforcement compaction stress with increasing shear angle, however the stress increases significantly more for the plain-weave than for the stitched fabric. A simple model was proposed to account for this increase; however the accuracy of the model is limited. Comprehensive RTM and CRTM studies were undertaken for planar and non-planar geometries using CSM. Simulated force traces showed very good agreement to experimental results, trends such as increasing clamping force with increasing fibre volume fraction and compression speed captured well. Flow front progression and cycle times were also well predicted. The viscoelastic reinforcement compaction model performed significantly better than the mixed-elastic model. Force control during secondary compression of CRTM showed significant benefits for both geometries; reducing required clamping force significantly for only small increases in cycle time. Simulation again showed very good agreement to experiment.