A closed form solution for flow during the vacuum assisted resin transfer molding process

A closed form solution to the flow of resin in vacuum assisted resin transf er molding process (VARTM) has been derived. VARTM is used extensively for affordable manufacturing of large composite structures. During the VARTM pr ocess, a highly permeable distribution medium is incorporated into the pref orm as a surface layer. During infusion, the resin flows preferentially acr oss the surface and simultaneously through the preform giving rise to a com plex flow front. The analytical solution presented here provides insight in to the scaling laws governing fill times and resin inlet placement as a fun ction of the properties of the preform, distribution media and resin. The f ormulation assumes that the flow is fully developed and is divided into two regimes: a saturated region with no crossflow and a flow front region wher e the resin is infiltrating into the preform from the distribution medium. The flow front region moves with a uniform velocity. The law of conservatio n of mass and Darcy's Law for flow through porous media are applied in each region. The resulting equations are nondimensionalized and are solved to y ield the flow front shape and the development of the saturated region. It i s found that the flow front is parabolic in shape and the length of the sat urated region is proportional to the square root of the time elapsed. The r esults thus obtained are compared to data from full scale simulations and a n error analysis of the solution was carried out. It was found that the tim e to fill is determined with a high degree of accuracy while the error in e stimating the flow front length, d, increases with a dimensionless paramete r epsilon =K(2xx)h(2)(2)/K(2yy)d(2). The solution allows greater insight in to the process physics, enables parametric and optimization studies and can reduce the computational cost of full-scale 3-dimensional simulations. A p arametric study is conducted to establish the sensitivity of flow front vel ocity to the distribution media/preform thickness ratio and permeabilities and preform porosity. The results provide insight into the scaling laws for manufacturing of large scale structures by VARTM. [S1087-1357(00)02002-5].