Journal
COMPOSITE STRUCTURES
Volume 203, Issue -, Pages 11-17Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.compstruct.2018.06.123
Keywords
Prepreg; Surface tension; Capillary pressure; Transport phenomena; Electron microscopy
Categories
Funding
- Natural Sciences and Engineering Research Council of Canada (NSERC)
- Boeing Company
- Convergent Manufacturing Technologies
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Pre-impregnated sheets of advanced carbon fibers with highly viscous thermoset-based resin systems are commonly used in fabricating aerospace composite parts. As prepreg sheets are vacuum bagged and heated during processing, the resin slowly infiltrates in dry spots between fibers. Under vacuum condition, surface tension-induced capillary effects impose deep negative pressures on the liquid resin, leading to tensile stretching. A method is presented to quantify the capillary-induced negative pressure. During processing, samples are quenched to freeze the infiltration process before taking SEM images. Using image analysis and by invoking interfacial stress boundary condition, the pressure distribution is determined. Sub-micron radii of curvature at the resin interface were measured corresponding to local negative pressures up to several atmospheres and an average pressure of - 10 to -50 kPa. Effects of negative pressures on the state of material and on defects such as resin phase separation are discussed.
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