Fracture toughness of fiber‐polymer interfaces estimated from single fiber peel tests

Single fibers of carbon, glass, and DuPont Kevlar have been embedded to about half their diameters in an epoxy resin and then peeled off. The work of fracture GI can be estimated from the peel force by a simple formula, so long as the fibers are fully elastic during the peel process. This was true with glass, which had GI = 140 Jm−2 and carbon with GI = 60 Jm−2. With Kevlar, inelastic effects obscured the results. The effect of water on the glass epoxy interface was readily shown. Carbon, however, required high temperature water at the interface to cause significant losses. Strong acids at 25°C had about the same effect as water at 90°C. Organic fluids such as kerosene had very little effect. Similar environmental effects could also be detected with Kevlar, though further work is required here to separate out the inelastic contribution.