| With the initial production of advanced composites, the use of composite materials has been growing rapidly in many industrial fields. The major impact has been with the weight-sensitive aerospace applications, where high strength/stiffness-to-weight ratios are very important factors. Conventionally, composites structure fabrication was conducted by hand lay-up and subsequent autoclave-based curing processes. However, the demand for cost-effective and efficient composite manufacturing is growing and thus perpetuating the replacement of existing hand lay-up processing. Automated fiber placement draws special attention for its low cost potential, flexible, and automated process. This fiber placement was investigated through the Function Block Diagram approach, and as a result, it was concluded that two sub-processes, heat towpreg and compact towpreg , are opportunity areas for better fiber placement process. This dissertation develops a heat transfer model with new heating alternatives for the heat towpreg sub-process and analyzes compaction force with a currently used pneumatic mechanism for the compact towpreg sub-process.; A linear composite towpreg was modeled with uniform material properties in one-dimension along the thickness. Thereafter, a heat transfer model between the towpreg and heating tools such as hot gas, fluid, and rigid contact heat sources, was developed. The simulation results show that a rigid contact heating is an outstanding heating alternative from both manufacturing and energy-efficiency standpoints. The manufacturing speed of rigid contact-heating, with a constant heating temperature of 200°C is at least thirty times faster than the manufacturing speed with hot-air heating with a convective heat transfer coefficient of 260 W/m2/°C. Energy efficiency of rigid heating is at least thirteen times better than the efficiency of hot air heating.; To further develop the rigid contact heating, a conceptual model of a linear two-dimensional finite element roller was employed along radial and angular directions. The roller was modeled with a transparent Pyrex tube coated with Teflon on the outer surface and a radiant heating filament coil inside. From a static-heating simulation of the roller model, the results showed an overshoot of 45.68°C and a rise time of 0.32 seconds with an ON/OFF controller. (Abstract shortened by UMI.)... |
