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Out-of-Autoclave Processing of Composite Prepregs - A major paradigm shift is presently occurring in the design and manufacture of commercial aircraft. Traditional metallic designs are being replaced by composite designs, as witnessed by the present development of the Boeing 787 and the Airbus A-350-XWB. These new aircraft require new design tools, new methods of inspection and analysis, and new methods of manufacture. In particular, to meet future demand, production rates must increase 3-to-4-fold. While composite aerospace parts are traditionally manufactured by autoclave processing and high pressures, autoclave processing is not compatible with the target production rates, and thus new manufacturing methods must be developed that are both faster and less costly. Vacuum bag only prepregs (VBO) have been formulated that permit part manufacture at much lower pressures than autoclaves (achievable with vacuum bags), yet reportedly yield equivalent properties. However, a major concern associated with vacuum bag processing is that the lower pressures will lead to increased frequency of voids, the Achilles heel of composite laminates. In this project, we investigate fundamental issues associated with void evolution in VBO prepregs, focusing on the effects of basic process parameters such as moisture content, solvent content, fabric architecture, ply drop-offs, and breathe-out distances. A major question we are attempting to address is the primary cause of voids, and what practices are most likely to prevent them.

High moisture contents lead to porosity in composite laminates produced from VBO prepregs