On Predictive Evaluation of Sub-Objectives for Quality Assurance of Vacuum Assisted Resin Infusion of Large Composite Structures

Vacuum assisted molding technologies for the manufacture of composite structures have become more and more popular in the last decade in many industries due to their simplicity, relatively low cost and speed of preparation for production. However, their distribution is limited due to the low stability of the achieved quality indicators (limited porosity, the required proportion of the reinforcing component, geometry accuracy), which requires a large number of experimental tests of the process, as well as the use of very complex and laborious computer modeling methods to obtain information on a rational strategy (number and location of gates and runners for resin injection and vacuum vents) and process conditions (temperature, pressure, time). The presented work proposes a technology for computer modeling of the process, based on the formulation and the finite elements implementation of a coupled problem, including the Cahn-Hilliard, Richards, thermal kinetics-convection-diffusion and heat transfer equations to describe evolution of the porous perform filling by the resin taking into account its cure with a preliminary assessment of the process quality sub-objectives before the start of the post-filling stage, when the thermosetting resin begins to solidify. After analyzing a large group of process variants, the time instant for performing such a forecast and the composition of sub-objectives were determined, the values of which allow obtaining with sufficient accuracy valid estimates of the resin filling, fiber volume fraction of the preform, the spatial distribution and the average value of porosity in the molded part just before the transition of the resin from a liquid to a gelatinous state. A significant reduction in the computation time for the simulation, achieved through the use of preliminary estimates of partial quality criteria, ensures the effective use of the developed product in optimization systems to minimize the unfilled preform volume during vacuum infusion processes before the resin solidification.