Simultaneous characterization of preform expansion and permeability in vacuum assisted resin infusion

Abstract

Vacuum assisted resin infusion (VARI) is a composite manufacturing process, in which a fibrous reinforcement is laid out in a mold, and then sealed under a vacuum bag. The preform is compressed under vacuum and a liquid polymer resin is infused into the mold cavity. A characterization of compressibility and permeability is required to get accurate predictions of infusion times and thickness of final parts. A new experimental methodology is developed to simultaneously characterize the preform expansion and permeability of fibrous reinforcements during infusion. It is implemented in a one-dimensional rectangular workbench by impregnating the preform with silicone oil. Pressure sensors measure the liquid pressure, and the reinforcement thickness is acquired by linear variable displacement transducers (LVDTs). The flow rate is also recorded with a scale. The expansion of the wetted reinforcement and permeability can be modeled by power laws as a function of pressure and fiber volume content, respectively. For isotropic preforms, a single experiment provides all the information needed to simulate the flow and predict the infusion time, the thickness and pressure. To validate this new characterization approach, the results of two infusions are successfully compared with numerical simulations.