Strain Rate Effect in the Single-Fiber-Fragmentation Test

摘要

The single fiber fragmentation test (SFFT) has been widely used to characterize the interface in fiber-reinforced polymers. The purpose of the work reported here was to determine the effect of strain rate on the fiber fragment lengths obtained in the SFFT. Three materials systems were used to make single-fiber-composite speci-mens: E-glass fiber/polycarbonate matrix, AS4-carbon fiber/polycarbonate matrix, and AU4-carbon fiber/polycarbonate matrix. The fiber-matrix adhesion in all three systems is based on physisorption rather than chemisorption. Each system wastested at strain rates ranging over four orders of magnitude. Results are reported in terms of fragment length, the dependent variable in this study, which is inversely related to the quality of the interface. It was expected that the fragment length would show a systematic decrease with increasing strain rate, but the expected trend was not found. Although the polycarbonate matrix exhibited rate-dependentviscoelastic behavior typical of amorphous polymers below T_g the fragment length at saturation did not show a statistically significant variation with strain rate for any of the three materials systems. A major contributor to the lack of observedeffect was the inherent random variability associated with the SFFT; random van-ability in average fragment length was equal or greater than the 190/0 effect of ratepredicted for ideal elastic systems with no debonding at the interface. In addition, considerable interfacial debonding occurred during the SFFT, not surprising for in-terfaces based on physisorption alone. Debonding interferes with transfer of applied load from matrix to fiber, and would thus interfere with transfer of the effect of rate from matrix to fiber. A tensile impact test developed previously was also performed on single-fiber composite specimens made from the same three materials systems. The results of the impact tests differed from those obtained at controlled strain-rates for only two of the materials systems.