Composite sandwich structures offer several advantages such as reduced weight, highbending/torsion stiffness, superior thermal insulation and excellent acoustic damping overconventional structural materials. One failure mechanism in a composite sandwich structure isthe debonding of the composite facesheets from the core structure. A well-formed adhesive filletat the interface of the honeycomb core cell walls and the laminate is a significant factor inpreventing bond failure. Improved adhesion strength with a well-formed adhesive fillet at theinterface of the honeycomb core walls and laminate is the aim of sandwich compositemanufacturing, and is one area of investigation in this work. Out-of-autoclave (OOA) processingof composites offers several key benefits compared to autoclave processing such as lowermanufacturing cost resulting from a lower capital cost and lower energy consumption. In thepresent work, the effects of moisturized adhesive film, core type, material system and variablelevels of vacuum on adhesive fillet formation are evaluated. Aluminum honeycomb and ventedaluminum honeycomb are used as core materials in this study. Two material systems of prepregsand adhesive films, Cycom 5320 prepreg with FM 309-1M adhesive, and MTM45-1 prepregwith MTA-241/PK13 adhesive are used to manufacture the panels and evaluate the performance.A quantitative investigation of the adhesive fillet geometry is carried out for all the panels.Manufactured panels are evaluated for peel strength and flatwise tensile strength in accordancewith ASTM standards. Various combinations of core material, moisture content, material systemand vacuum level are evaluated for effects on adhesive strength and adhesive foaming.
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