Modeling and Simulation of Dry-spot dynamics in Liquid Composite Molding in two dimensions

Kurzfassung

Fibre-reinforced plastics are in high demand by wide range of industries. Liquid Composite Molding process used in the manufacturing of Fibre-reinforced plastic materials deals with the injection of resin into the dry-fibre. The flow of resin during the injection is caused by pressure difference. A complete impregnation of the dry-fibres with resin in the injection phase of the composite manufacturing process is undoubtedly an important factor. The manufacturing process seems to become difficult with the increase in complexities of part geometry, and can result in air-entrapments on the fibre. Experiment shows that the large macroscopic air-entrapment (dry-spot) formed during a pressure driven injection phase of a Liquid Composite Molding (LCM) process, disperses into smaller voids, and is completely removed in an occurring injection procedure. Therefore, occurrence of dry-spot alone cannot decide the material quality. The behaviour of the dry-spot should be investigated. An understanding of the dry-spot dynamics may facilitate the reusability of the previously disregarded injection strategy. The thesis discusses the numerical simulation of dry-spot dynamics in LCM process and investigates the dependency of simulation parameters to simulate the approximate closing time of dry-spot. Due to the low flow velocities and porous nature of the fibre, two-phase simulation of air-resin system is based on the pressure-saturation approach formulated using Darcys law. The relative permeability model takes into account the influence on the flow of each phase in the presence of the other phase. Numerical investigations showed that the user-defined relative permeability values (maximum attainable relative permeability of each phase and power coefficient value) associated with the relative permeability models have a high influence on the numerical simulation. The choice of the best relative permeability model and the optimization of the parameters based on simulation condition is a necessity for approximating the experimental results. The consistency of the optimized parameters is verified for its sensitivity with changes to simulation input parameters and showed good agreement with experimental results. However, the computational time associated with the best fitting relative permeability model and optimized parameters is considerably very high. With a view to possibly improve the simulation results of a computationally faster relative permeability model, the pressure-saturation equations are modified with the introduction of air-fraction term [44]. This provides an additional term apart from relative permeability terms, to control the numerical simulation. The numerical results showed good relation between approximating experimental observation and low computational cost. This motivates the use of numerical researches on the topic of dry-spot dynamics in the case of high fibre volume content materials.