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RESEARCH PRODUCT

Strain rate effect in the single-fiber-fragmentation test

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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 specimens: 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 was tested 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-dependent viscoelastic 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 observed effect was the inherent random variability associated with the SFFT; random variability in average fragment length was equal or greater than the 19% effect of rate predicted for ideal elastic systems with no debonding at the interface. In addition, considerable interfacial debonding occurred during the SFFT, not surprising for interfaces 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 strainrates for only two of the materials systems.