Numerical model of relaxation during vacuum-assisted resin transfer molding (VARTM)

The inherent economic and environmental advantages of a vacuum-assisted resin transfer molding (VARTM) composite manufacturing process have caused an increase in the number of applications and generated research activity within the industry. Unfortunately, a variation in part thickness is introduced during the impregnation stage of a vacuum-infused flexible mold process, leading to a predictable and undesirable reduction in mechanical properties. It will be shown that the fluid pressure gradient established during the infusion phase directly results in a gradient in part thickness. The severity of the thickness gradient depends on the magnitude of the imposed pressure and the behavior of the underlying fibrous material. This report examines this behavior through the development of an efficient numerical model. An equilibrium relationship between external confining pressure, reinforcement response, and internal resin pressure is proposed and implemented within the context of a specific implicit finite element-based procedure. A detailed description of the original algorithm provides the background for the insertion of the new equilibrium constraint. This report also includes a discussion of important issues such as information recovery and adaptive time-step procedures. The result is a simple numerical tool capable of simulating the infusion process. The new procedure is validated through a comparison with known analytic one-dimensional models and also used to obtain solutions to an important class of axisymmetric examples.