Measuring method and process analysis of void formation conditions for resin matrix composites

For fiber reinforced resin matrix composites, void is a common defect which can seriously deteriorate the properties of composite parts. Voids form and grow during composite fabrication, so the processing parameters must be carefully controlled to avoid this defect. In hot melt prepreg/autoclave process, hygroscopic water absorbed by prepreg is believed to be the main source of voids, especially for zero resin bleeding cases, because hygroscopic water and water vapour bubbles can not be effectively removed without sufficient resin flow. For this case, Springer and Kardos believed that resin pressure must be larger than a critical value to prevent the initiation and growth of water vapour bubble. Kardos et al established a simple expression to calculate the critical resin pressure for circular bubbles: