Evaluation of the effect of sizing levels on transverse flexural and shear strengths of carbon/epoxy composites

Abstract

The effect of fiber sizing levels on shear and transverse flexural strengths of epoxy-sized Grafil XAS carbon fibers/Epon 828 epoxy matrix composite materials has been studied. The results of short-beam shear and transverse flexural tests suggest that an optimum sizing level exists that yields maximum short-beam shear and transverse flexural strengths. Among the three types of fibers studied (unsized, 0.7 and 1.2 wt%) the best sizing level is 0.7 wt%. Scanning electron microscopy of failure surfaces was used to verify that the strength maxima were the result of failure moving away from the interface and into the matrix. The statistical analysis of the results shows that the SBS and TF strengths were significantly different for the composite made of fibers with different sizing level. Thus, control over sizing level is important for improved composite performance.