Fabricating high-quality VARTM laminates by magnetic consolidation: experiments and process model

Abstract

In recently developed magnet assisted composite manufacturing (MACM) processes, a magnetic consolidation pressure is applied on composite laminates by a set of permanent magnets during fabrication. This magnetic pressure was shown to provide considerable benefits such as increased fiber volume fraction, improved mechanical properties, and reduced void content in wet lay-up/vacuum bag processes. In this article, the effectiveness of MACM to fabricate high-quality vacuum assisted resin transfer molding (VARTM) laminates is investigated and a new, transient process model for MACM is introduced. Towards this goal, 6-, 12-, and 18-ply, random mat E-glass/epoxy composite laminates were fabricated by placing Neodymium Iron Boron (NdFeB) permanent magnets on the vacuum bag either after or before the resin infusion. In both scenarios, the magnetic pressure was shown to considerably improve surface quality, reduce laminate thickness, and increase fiber volume fraction to above 50%. The flexural strength of the 6-, 12-, and 18-ply laminates was improved by more than 28%, 23%, and 11%, respectively. The flexural modulus was also enhanced substantially, at least by 41%, 34%, and 23%, for the same set of laminates. Applying the magnets before infusion increased the filling time due to decreased fabric permeability, and consequently reduced the process-induced voids to under 1%, while the laminates made by conventional VARTM contained up to 6% voids. The transient magnetic consolidation model developed for this process is shown to accurately predict the fiber volume fraction and final laminate thickness for all the fabricated laminates.