Quantitative measuring method and influencing factors of void formation conditions in thermosetting resins

An off-line measuring method of void formation conditions was designed based on the characteristics of the hot press process for resin matrix composites and the mechanism of void formation controlled by diffusion. This method can quantitatively determine the relation between resin pressure and porosity. By means of this method, the effects of gel temperature, relative moisture and resin pressure on void formation conditions in two epoxy systems were studied, including void content, morphology and distribution. The modified Kardos void model was compared with the experiments. The results indicate that the method can be used to simulate the void formation process caused by hygroscopic moisture in the hot press process, and it has good repeatability. The evolution of resin pressure vs porosity follows the exponential decay function. Moreover, the gel temperature and relative moisture have great effects on porosity, while the resin type influences porosity, morphology and distribution of voids remarkably. The study provides an important measuring method and experimental evidence for void defect control in composites during the hot press process.