Warpage prediction and elimination in filament-wound and fiber-placed composite shells

Filament winding and fiber placement are becoming common manufacturing processes throughout the aerospace industry for both launch vehicle and aircraft structures. The promise of significant weight reduction, compared to metallic structures, along with the advantages of automation, including reduced cost and increased quality control, make these attractive structural solutions. Recent demonstrations include: the Combined Experiments (CEP) sub-orbital demonstration flight, Boeing's Sea Launch orbital vehicle, and the Beach Starship. These vehicles employed filament winding or fiber placement manufacturing processes and substantiated large performance gains. However, as with many new technology development programs unforeseen complications often arise. In filament winding the tooling is generally in the form of a plug that has the composite fibers filament wound or fiber placed on the outer surface. Once the parts are released from the tooling they can demonstrate significant warpage. In many cases this warpage is large enough to make the part unusable. As the aerospace industry develops the need for larger composite structures with both the requirements of high performance and reduced manufacturing cost, understanding and controlling part warpage becomes an ever increasing necessity.; This research has identified the residual stresses responsible for the large distortions. It will be shown that the stresses develop during manufacturing and result from cure consolidation. The magnitude is dependent on manufacturing parameters including cure pressure, winding tension, and material characteristics (i.e., pre-preg fiber volume fraction, resin viscosity, etc.).; In this dissertation a systematic procedure, or methodology, is developed to eliminate the processing induced warpage. This is accomplished by first developing a through-thickness strain model based on fiber/resin cure consolidation and tooling thermal expansions. The strain model is then integrated with classical laminate theory and solutions for predicting and eliminating warpage obtained. The warpage elimination is accomplished by developing manufacturing tension control techniques that reduce and alter the residual stress profile to eliminate stress couples. The accuracy of the warpage prediction and elimination techniques are verified with experimental procedures. It was found that the predictions were accurate and the warpage could be reduced and eliminated in most cases.