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UBC Theses and Dissertations

Behaviour of resin voids in out-of-autoclave prepreg processing Wells, Jeremy


Resin in prepreg contains small bubbles called resin voids. These voids are isolated from the laminate inter-connected breathing network and cannot be removed by vacuum debulk. Initially these voids contribute negligibly to porosity; however, they may grow and contribute significantly to porosity by vapourization of dissolved volatile species and/or ideal gas expansion particularly in low pressure out-of-autoclave (OOA) processes. Modern advanced prepregs have low volatile content except for moisture due to the hygroscopic property of epoxy. The goal of this study is to investigate the behaviour of resin voids and determine the mechanisms and processing conditions that cause resin void growth. The first part of this study investigates the growth of resin voids in neat resin specimens under controlled temperature, resin pressure and moisture content. Neat resin was vacuum bagged on a glass tool and visually observed in-situ by use of a digital microscope. A criterion that predicts the critical resin pressure below which resin voids can grow due to moisture vapourization was tested for two separate moisture contents and accurately predicts the onset of resin void growth. Additionally, resin voids were observed to contribute significantly to porosity in the very low resin pressure regime due to ideal gas expansion. The results indicate that resin pressure is a critical parameter for mitigating resin void porosity. The second part of this study investigates resin void growth in laminates by stimulating moisture vapourization and/or ideal gas expansion and comparing them to a porosity free baseline. In order to isolate the effect of resin voids, laminates were fully evacuated before cure. Reduced resin pressure, increased moisture content and increased cure temperature were tested parameters. Laminates were laid up on a glass tool and observed and recorded in-situ. Both surface and bulk porosity were measured for each laminate. In-situ observations and resin pressure correlate well with porosity results based on the resin void growth mechanisms investigated for all test conditions except increased cure temperature. Possible explanations for the discrepancy are discussed. Resin pressure was seen as a critical parameter in porosity management and the concept of a minimum resin pressure is proposed and discussed.

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