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The strength realized in a composite depends in part on its ability to arrest its nascent flaws and cracks. A theory for glass fiber-resin bonding is developed based on a restrained resin layer in the interphase region, an interfacial mechanism for resistance to crack penetration through the glass surface, and the segregation of resin-glass bonds of a strong, hydrolysis-resistant type to the alkali-free, silica “islands” on the glass surface.
In well-bonded glass fiber-resin composites, the initial effects of water are to stiffen the interphase resin layer and to create a pressure at the interface through the formation of water pockets on the glass surface. Stiffening the resin interphase layer weakens its ability to absorb the stress of a crack tip penetrating from the resin to the interface, thereby lowering composite strength resistance. The long term effect of the water layer is twofold. It creates a pressure tending to pry off the resin layer from the silica islands. It also furnishes a reservoir for the solution of aqueously soluble ions, that is, it acts to dissolve certain of the silicate areas and undermine the silica islands and thereby break the glass-resin bonds from the glass filament mass.
composites, solid mechanics, glass fibers, crosslinking, polymers, bonding, effect of water, interfaces, interphase region, crack propagation, restrained resin layer, water films, aqueous attack, unsaturated polyester, epoxy, E-glass, evaluation, tests
Eakins, W J
Consultant, South Woodstock, Vt.