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).
NASA and the U. S. Air Force are looking to improve space borne telescopes by reducing mirror
weight. One commonly attempted solution is to fabricate Carbon Fiber Reinforced Polymer
(CFRP) mirrors using a mirror replication technique. These attempts have been hindered by the
well-known fiber print-through phenomenon. The resulting sinusoidal surface distortion is fiber
print-through, where chemical and thermal shrinkage during cure have been hypothesized to be
the dominant causes. Although successful mitigation of fiber print-through via a polished resin
layer method has been proven, an additional resin layer reduces the heat transfer through the
mirror thickness that would be necessary for high-energy laser applications and also carries
The purpose of this research was to quantify the dominating causes of fiber print-through and its
contribution to the total surface roughness of a composite (where total roughness includes the
elements of print-through and other surface anomalies that contribute to diffuse reflection). In
order to quantify the causes of fiber print-through, a number of CFRP samples with varying fiber
type, diameter and cure schemes were fabricated. The dominating causes of fiber print-through
were then found by measuring fiber print-through, via microscopic interferometry, and
determining which variables had the greatest influence on print-through.
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, the effects of fiber print-through create an unacceptable surface roughness on replicated CFRP mirrors. In order to mitigate fiber print-through, two methods of generating a polishable resin layer were investigated. The first method employs the application of resin films to the CFRP surface. The second, unconventional method generates a co-cured resin layer using a magnetic fiber migration approach. A final polishing step was used to attain optical quality surface features on all of the replicated specimens. Replicated resin films with thicknesses ≥ 0.25 mm sufficiently mitigate fiber print-through. Room temperature and high temperature cure resins were polished below 50 Å rms surface roughness (1 μm to 1mm bandwidth) or better. The magnetic fiber migration technique was suitable for eliminating fiber print-through. Replicated magnetic fiber laminates were polished to within specular quality as well.