Selected mechanical properties of symmetrically (plusmn;45deg;) reinforced 16hyphen;lamina graphite/epoxy composites have been found to be affected by subhyphen;Tgannealing. Postcured specimens of Thornel 300 graphite/Narmco 5208 epoxy were subhyphen;Tgannealed at 140thinsp;deg;C for ca. 10, 102, 103, 104, and 105min, with a prior quenching from aboveTg. The ultimate tensile strength strainhyphen;tohyphen;break, and static toughness of the composite materials were found to decrease as a function of subhyphen;Tgannealing time. No weight loss was observed during the subhyphen;Tgannealing. The timehyphen;dependent change in properties can be explained on the basis of physical aging which is related to free volume decrease in the nonhyphen;equilibrium glassy state of network epoxies. The results imply possible changes in composite properties with service time.
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