A TECHNIQUE FOR LOCALLY INCREASING SURFACE HEAT SPREADING AND THROUGH-THICKNESS THERMAL-CONDUCTIVITY OF GRAPHITE EPOXY LAMINATES/

The polymer matrix composite through-thickness thermal conductivity is particularly important in applications such as composite spaceborne e lectronics enclosures where the heat dissipation is primarily dependen t on thermal conduction to a heat sink. The spreading of heat at the c omposite surface and subsequent localized conduction in the through-th ickness direction down to high thermal conductivity fiber may be the k ey to designing a lightweight, thermally efficient enclosure. A finite element model was constructed of a composite with heat applied to a c entral area. The laminate consisted of a hybrid of high thermal conduc tivity pitch fiber/epoxy on the outside surfaces interlaminated with l ow thermal conductivity carbon fabric/epoxy. Three configurations were modeled: (A) a heat source in the middle, (B) Cu plating under the ce ntral heat source and (C) Cu plating under the heat source with a cent rally located hole that was also Cu plated. The model with Cu on the s urface under the heat source had a maximum surface temperature 35% low er than the model with no Cu to spread the heat. The model with a cent ral Cu plated hole had a maximum surface temperature 58% lower than th at with no Cu plating on the surface. Therefore, the surface Cu platin g with Cu plated hole spreads the heat and increases the through-thick ness thermal conductivity. Samples were prepared using the aforementio ned hybrid pitch fiber/epoxy interlaminated with carbon fabric/epoxy l aminates sandwiched between .015 mm thick Cu foil. In the fabricated s amples, all Cu (except that in the immediate vicinity of the heat sour ce) would be removed by etching. A drill size of 2.29 mm diameter and feed rate of 152 cm/min were selected to minimize pitch fiber damage a nd matrix smearing, which results in increased thermal resistivity. So me of the drilled holes were etched with sulfuric acid and Cu plated a nd some were just cleaned and Cu plated. SEM photomicrographs of the h oles and of the hole edges showed no appreciable increase in Cu adhere nce of the etched over the unetched samples. The unetched samples appe ared to have as intimate contact with the Cu as the etched samples. Th e etched samples had areas with thicker epoxy layers insulating the pi tch fibers from the Cu. The co-cured surface Cu foil with and without a Cu plated hole to spread the heat and increase through-thickness the rmal conductivity, respectively, are currently being incorporated into heat transfer test samples.