Alignment of Nickel Coated Carbon Fibers by Magnetic Field during Cure of Polymer Composites

Abstract

Carbon fibers are widely used as reinforcement in polymer-matrix composites due to their excellent mechanical properties combined with their lightweight. Coating of short carbon fibers with nickel not only preserves the desired specific mechanical properties of both the fiber and the resulting composite but also improves their electrical conductivity and magnetic properties. The short fibers may be randomly dispersed in composites to exhibit isotropic behavior. However, controlling the orientation of the fiber reinforcement can improve the performance of the composite such as electrical conductivity, modulus, and strength in the loading direction. In this study, the alignment of nickel coated carbon (NiC) fibers by a magnetic field during cure of an epoxy resin is explored. For this purpose, the effects of several parameters such as field strength (10-50 mT) and fibers length (0.1 and 0.25 mm) on the degree of fiber alignment within composites are investigated using scanning confocal microscopy and image analysis techniques. The 0.1 mm long fibers started to align along the direction of magnetic field at around 10 mT. The degree of alignment was enhanced at about 30 mT which enabled the NiC fibers to interact easily with each other and build NiC fiber networks. Furthermore, when a higher magnetic field of 50 mT is applied, in addition to the rotation and network formation, pronounced migration of fibers towards the magnetic poles was observed. In addition, under the same magnetic field of 30 mT, longer fibers (0.25 mm) reached a higher degree of alignment.