The use of carbon nanofibers for thermal residual stress reduction in carbon fiber/epoxy laminated composites

Carbon nanofibers (CNFs) were incorporated into an epoxy matrix with three weight fractions of 0.1%, 0.5% and 1% which were then reinforced with unidirectional carbon fibers (CFs) to fabricate laminated composites with cross-ply configuration. Thermomechanical analysis and tensile tests of the specimens were carried out to characterize thermal and mechanical properties of CNF/epoxy composites and compare them with the behavior of the neat resin. Characterization showed that the coefficient of thermal expansion (CTE) of the epoxy matrix is significantly reduced by adding small amounts of CNF. CNFs also moderately increase the Young's modulus of the epoxy. The slitting method was used for the measurement of residual stresses in cross-ply CF/epoxy and CNF-reinforced CF/epoxy laminates. It involves cutting a narrow slit progressively from one surface of the laminate, and measuring the released strains at the other surface. The results showed that the addition of 0.1%, 0.5% and 1 wt.% CNF leads to 4.4%, 18.8% and 25.1% reductions in residual stress, respectively. These findings confirm that CNFs possess excellent potential to be used as a thermal expansion compensator for the modification of the thermal behavior of the epoxy matrix and the reduction of the thermal residual stresses in the fiber/epoxy laminated composites. (C) 2013 Elsevier Ltd. All rights reserved.