High-frequency vibrations on the compaction of dry fibrous reinforcements

Liquid Composite Molding (LCM) is a composite manufacturing technique, in which a dry fibrous reinforcement is placed inside a mold, impregnated with a liquid resin and cured. During the fabrication process, the fibrous preform is subject to through-thickness and in-plane deformations. These deformations may affect the quality of the components and their mechanical performance. Hence, the compaction behavior of the reinforcement is crucial in order to predict its deformation during processing. The present work deals with the first stage of LCM manufacturing, during which the dry preform is draped into the rigid base mold and then compressed during closure of the upper mold. Under traditional manufacturing conditions, the preform is subjected to a single static compressive load. In the current study, controlled vibrations are applied to the preform before static compaction. These vibrations have a strong impact on nesting and on the further static compaction behavior of the reinforcement. The scope of this investigation is to study the influence of vibration parameters such as amplitude and frequency on the compaction of continuous fiber beds used to reinforce high-performance composites. Mechanical tests were performed using a special DMA instrument that allows characterizing the dynamic compaction of fibrous reinforcements at high frequency.