Relation of interfacial adhesion in Kevlar®/epoxy systems to surface characterization and composite performance

A central problem in composite materials is the poorly understood relation between the nature of the surfaces at the fiber/matrix interface, the actual interfacial bond strength, and interface‐sensitive composite properties, in this study on the Kevlar®/epoxy composite system, the interface was varied chemically by fiber sizings. The sized and unsized fiber surfaces and the cured matrix surface were characterized by contact angle measurements. The interfacial shear strength was directly measured by single‐filament pull‐out tests of sized and unsized fibers in epoxy matrix. The shear strengths of the composites made with sized and unsized fibers were measured. The results from surface analysis, interfacial shear tests, and composite shear tests were consitent. This suggests that surface‐contact‐angle analysis and single‐filament pull‐out tests may be helpful in screening strength of the composite.