Study On Permeability Of Fiber Perform In LCM

Liquid Composite Molding ( LCM ) is a close operation whereby a dry preform is placed between matched moulds and impregnated with a liquid resin. It has been representing the promising development direction of composites manufacturing techniques with high quality and low cost due to its outstanding operation for large structure or function parts with complex geometry in one step. With the aid of National 863 Plan, the measurement, calculation and influence factors of fiber perform permeability in LCM were studied in this paper. And the corresponding computer simulations for LCM filling process were also conducted.Regarding the LCM filling process as the Newton fluid through fibrous reinforcements, the permeability of preform determines the saturating of resin in fiber, and has effects on the curing process and the quality of products. Based on the Darcy's law, the theoretical model of permeability measurement was established. And the influence of different testing methods and major process parameters such as fabric structure, fiber volume fraction, injection pressure, flow rate and resin viscosity on preform permeability were investigated in details. It was found that the permeability of fibrous reinforcement mainly lied on the preform architecture. The distribution of void region and fiber volume fraction in the perform had important effects on permeability. The increasing injection pressure and flow rate could improve the permeability for the shorter filling time while the influence of testing methods and resin viscosity were relatively smaller.The local permeabilities under the conditions of the most common draping defects including edge effect and shear deformation in LCM were studied. According to the experiment of influences of fiber structures and the width of edge channel on flow filling, it was found that even a small gap(l or 2mm) between the preform and the mold edge could also disrupt the flow pattern, which evidently changed the local permeability of preform. The fillingprocess was simulated using the permeability for different edge width predicted by A. Hammami or Poiseuille model, which shown good agreement with the experiment results. It was also found the main direction of permeability rotated after shearing and the permeability decreased with the increasing of shearing angle. The excellent prediction of shearing permeability by the Lai-Young model provided theoretical support for the numerical filling simulations in complex parts.As one of the basic study in LCM, the permeability of fiber perform is a key to the control of flow pattern and the filling simulation. This research is dedicated to investigate the relationship between the permeability and technical parameters and solve the defect of low producing efficiency due to inadequate impregnating and filling in LCM, which provide theoretical support and practical guidance for procedure design and manufacture to enhance the controllable capability. It also has significant influence on the development of composites manufacturing techniques with high quality and low cost.