Determination of the optimal impregnation velocity in Resin Transfer Molding by capillary rise experiments and infrared thermography

Void minimization is an important issue in Resin Transfer Molding (RTM) because concentrated porosity can significantly decrease the quality of final composite parts. The injection stage is critical, since the impregnation of the fibers can generate voids by entrapment of residual air. The optimal velocity of the flow front in RTM injections can be determined by capillary rise experiments carried out through the fibrous reinforcement. Classical wicking investigation techniques are based on the visualization of the liquid front during the capillary rise, which can be enhanced by fluorescence. However, this technique can only be applied to transparent fibers such as glass. For this reason, a new approach based on InfraRed Thermography (IRT) is proposed in this paper for non-transparent carbon fibers. An inverse algorithm is used to estimate the optimal velocity of the flow front during resin injection from the thermal images obtained by IRT. This new experimental method was validated by comparison with capillary rise experiments carried out by fluorescence through glass fibers, after which it was applied to carbon fibers in order to determine the optimal impregnation velocity.