Fiber print-through mitigation technique for composite mirror replication

Abstract

The quickest method for generating a lightweight composite optic is to replicate an optical-quality glass tool onto a carbon-fiber-reinforced polymer (CFRP). However, fiber print-through creates an unacceptable sinusoidal surface roughness on replicated CFRP mirrors; chemical and thermal shrinkage during cure are commonly hypothesized to be the dominant causes. In order to mitigate fiber print-through, two methods of generating a polishable resin layer were investigated. The first method employs the application of a resin film to the CFRP surface. The second method, which is a more unconventional approach, generates a cocured resin layer using magnetic fibers. The latter approach is being developed to eliminate the application of additional resin layers to the CFRP surface, since additional layers present structural disadvantages.It was found that the magnetic fiber technique is comparable to the conventional approach in mitigating fiber print-through. Due to the presence of a 0.25-mm-thick buffer above the reinforcing phase, a final polishing step was used to attain optical quality features on all of the replicated specimens. CFRP and magnetic fiber samples were polished to within 50-Å rms roughness (1-µm to 1-mm bandwidth).