Effects of molecular relaxation behavior on sized carbon fiber-vinyl estermatrix composite properties

The mechanical and viscoelastic properties of unidirectional vinyl-ester ca rbon fiber composites were investigated. A cooperativity analysis of the co mposites was performed on storage (E') and loss modulus (E ") master curves obtained from dynamic mechanical analysis. The temperature sensitivity of the horizontal logarithmic shift factors (log a(T)), cooperativity, obtaine d from E' data, was found to vary with the sizing used to pretreat the carb on fibers. The observed variations in the experimental trends in cooperativ ity with fiber sizing for the composite materials were found to deviate sig nificantly from theory. However, the trends in tensile and apparent shear s trength of the composites matched the observed qualitative trends in viscoe lastic cooperativity obtained from the storage modulus master curves. These results may suggest that the viscoelastic and ultimate mechanical properti es of a composite material are related. However, several inconsistencies we re observed when comparing the E " and E' data which should also be conside red in the interpretation of the experimental results. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.