MODIFIED EPOXY FORMULATION FOR IMPROVING THE FRACTURE-RESISTANCE OF FILAMENT-WOUND PRESSURE-VESSELS

A modified epoxy composition for filament winding of pressure vessels was investigated. The system consisted of a DGEBA-type DER 332 epoxy r esin, an aliphatic amine T-403 hardener, and an amine-terminated ATBN 1300X16 toughening agent. The design goal was to achieve a toughened s ystem, with processing characteristics suitable for filament winding. The product should have an improved fracture toughness, with minimal s acrifice of its thermal and mechanical properties and general performa nce. Specifically it was sought to develop a composite material lamina te in which the damaged zone caused by a high-energy penetrating impac t is localized. The selected epoxy system was investigated in its bulk state with respect to its theological, thermal, mechanical, and morph ological behavior. Further testing included adhesive shear strength, c omposite tensile and shear strength, and fracture analysis. The ATBN m odification of the epoxy system achieved most of the design objectives including pot life, glass transition temperature and ductility of the bulk epoxy, and improved fracture mechanism, with minimal sacrifice o f the mechanical properties of the composite. This was achieved becaus e of the ATBN contribution, both as a crosslinking agent and as a toug hener. Morphological studies revealed the presence of a rubbery globul ar phase of 1 mu m diameter, dispersed uniformly in the epoxy matrix, which was formed when ATBN was added. Fractured composite specimens sh owed that a better interfacial adhesion of the matrix to the fibers wa s achieved in the modified formulation.