Dynamic stress/strain response of the interphase in polymer matrix composites

The interphases. of various sized E-glass-fiber/epoxy-amine systems were te sted at displacement rates in the range of 230 to 2450 mum/sec using a new experimental technique (dynamic micro-debonding technique). The fiber syste ms include unsized, epoxy-amine compatible sized, and epoxy-amine incompati ble sized glass fibers. A data reduction scheme was developed to relate the force vs. displacement response obtained from the dynamic micro-debonding technique to interphase shear stress/strain response. The stress/strain cur ves and interphase shear modulus values were obtained from these composite systems under average shear strain rates (ASSR) in the range of 215-3278 (1 /s). The results showed that the magnitude of the interphase shear modulus was sizing and strain rate dependent In all cases, the shear modulus was fo und to be more compliant than the bulk matrix. The two sized fiber systems exhibited the highest strain rate sensitivity, with modulus increasing abou t threefold over the range studied. In addition, the rate dependent behavio r of the model interphase materials were determined using the dynamic mecha nical analysis (DMA) technique. The model interphase materials closely rese mble the interphase that forms on unsized and compatible sized fibers. Mast er curves relating the flexural storage modulus to strain rate were constru cted based on the time-temperature superposition principle from DMA frequen cy sweep measurements. The DMA measured results are consistent with the dyn amic micro-debonding test results, providing confidence in the test method as a reliable technique for characterizing the high strain rate properties of the interphase in composites.