Experimental Characterization of the Effect of a Spray Adhesive on the Velocity of Impregnation of a Resin on Carbon Fiber Fabrics Utilizing the VARTM Manufacturing Technique

The effect of a spray rubber adhesive frequently used in liquid composite molding (LCM) processes on the longitudinal velocities during the impregnation of resin on thin (2–3 mm) carbon fiber preforms is reported. Experimental observations show that application of this adhesive invariably results in a lower mold filling time when compared to the corresponding observations in the same laminated configurations without adhesive. That is notwithstanding the greater delay in the resin flow front at the rigid mold surface. These effects were systematically observed in single and multi-fiber stacks. Fill-up time differences up to 30 % and flow front delayed distances up to 37 % were observed between preforms with and without the spray rubber adhesive. Moreover, predictions made through Darcy’s law for resin front flow position with time are in good agreement with our experimental observations. Given this agreement between theory and experiments, we identify that the average longitudinal front flow velocity is directly proportional to the overall longitudinal preform permeability to porosity ratio ( K / Ø ). Our experimental observations suggest that the bonding between plies provided by the spray adhesive effectively increases the preform resistance to resin flow through two mechanisms 1) a reduction on the K/Ø ratio which in turn causes an increase on the resin front velocity at the top of the preform and reduces mold filling time, and 2) a simultaneous reduction on the through thickness permeability which in combination with the reduction on longitudinal permeability causes a larger delay in the resin flow front advance at the rigid mold with respect to the front advance at the top of the preform. Given these mechanisms for increased flow resistance, this paper closes with some cautionary comments regarding the possibility of detrimental effects on the mold filling and quality of the final product resulting from the use of the spray adhesive on thicker laminates.