Evaluation of thermally-aged carbon fiber/epoxy composites using acoustic emission, electrical resistance and thermogram

Interfacial and mechanical properties of thermal aged carbon fiber (CF) reinforced epoxy composites (CFRC) were evaluated using acoustic emission (AE), electrical resistance (ER), contact angle (CA) and thermogram measurements. Unidirectional (UD)-composites were aged at 200, 300, and 400 degrees C to produce different interfacial conditions. The interfacial degradation was identified by Fourier transform infrared (FT-IR) spectroscopy after the different thermal aging. AE and ER of UD composites were measured along 0, 30, 60 and 90 degrees directions. Changes in wavespeed, with thermal aging, were calculated using wave travel time from an AE source to AE sensor and changes in ER were measured. For a thermogram evaluation, the composites were laid upon on a hotplate and the increase in the surface temperature measured. Static contact angles were measured after different thermal aging and elapsed times to evaluate wettability. Tests of interlaminar shear strength (ILSS) and tensile strength at transverse directions were also performed to explore the effects of thermal aging on mechanical and interfacial properties. While thermal aging of CFRCs, at all three aging temperatures, was found to affect all of these properties, the changes were particularly evident for aging at 400 degrees C.