APPLICATION OF THE MICROBOND TECHNIQUE - EFFECTS OF HYGROTHERMAL EXPOSURE ON CARBON-FIBER EPOXY INTERFACES

The authors have used the microbond technique to study the effect of hygrothermal exposure on carbon-fiber/epoxy microcomposites. Immersion of T300/Epon 828 or AS4/Epon 828 composites in water at 80-degrees-C for several hours resulted in lower interfacial shear strengths for both materials within the first hour of exposure. After 6h in hot water, the interfacial shear strength of T300/Epon 828 samples was reduced by 41% while the AS4/Epon 828 samples suffered a loss of 20% in interfacial strength. The frictional component of the sheared droplet sliding along the fiber after debonding was twice its original value for AS4/Epon 828 composites while the frictional component of T300/Epon 828 fibers tripled for the same exposure to hot/wet conditions. X-ray photoelectron spectroscopy indicated little change in the concentration of functional surface groups on the fibers following hygrothermal exposure. The diminution in shear strength is probably related to plasticization of the resin by water as well as reduction in mechanical interlocking pressures arising from thermal expansion mismatching of the fiber and matrix.