"Defect control in OOA processing of composite prepregs" - Composite parts for commercial aircraft are traditionally manufactured using high-pressure autoclave processing of prepregs (carbon fiber pre-impregnated with epoxy resin). In recent decades, however, the use of composite parts for aircraft has increased, and aircraft markets have grown, creating demand to increase production rates. To meet this demand and to allow for the production of large composite parts (e.g., wings and fuselage), alternative production methods are required. There are several drawbacks to autoclave processing, including a large capital investment, long cycle time, high cost of the nitrogen gas used to pressurize the vessel, size limitations, and poor energy efficiency. New out-of-autoclave processing methods (OOA) have been developed to address these drawbacks. One such method is vacuum-bag-only (VBO) processing of prepregs, a technique that involves only atmospheric pressure to consolidate parts. VBO processing presents a potential solution for the manufacture of larger parts at faster rates using conventional layup and placement tools. However, before VBO methods can be employed for primary structure, the quality of VBO-processed parts must be shown to be equivalent to autoclave-cured parts. The elimination of high external pressures during the cure cycle removes safeguards in the manufacturing process, resulting in the need for strict protocols in the layup and cure of VBO parts. In this work, we assess the feasibility of VBO processing for aerospace components, performing a systematic study of the effect of process parameters on the quality of VBO parts. Particular attention if directed to the mechanisms of void formation and growth in prepreg-processed carbon fiber composites, as these are not well understood. The objective is to determine the causes and mechanisms of void formation. This knowledge will enable better control of defects and thus lead to production of higher quality parts. An additional objective of the work is to determine the feasibility of low-pressure VBO processing for large-scale structural components. Parametric effects considered include resin moisture content, chemical aging of the material, and the evolution of volatile components during cure.