Abstract
AbstractAn investigation has been carried out concerning the effects of moisture on the mechanical properties of a unidirectionally reinforced aramid/epoxy composite; specifically, Kevlar 49‐Fiberite 934. (Fiberite 934 is a 350°F‐cure epoxy composed primarily of tetraglycidyl methylene dianaline and hardened by diaminodiphenyl sulfone.) Absorption of water has been found to plasticize the resin so as to produce a decrease in the glass transition temperature from, 210°C to 150°C, and this plasticization serves to increase substantially the room‐temperature ductility of the resin. Moisture also serves to increase the static tensile strength, of the laminate, presumably by enhancing resin ductility and making the composite more forgiving of local flaws and fiber misalignments. The moisture‐induced enhancement of static strength is observed to carry over to an increase in fatigue lifetime at a given stress, although the fraction of ultimate tensile strength lost per decade of fatigue loading is the same in wet and dry materials. It is concluded that the mechanism of fatigue damage—probably a form of fiber abrasion—is unaffected by moisture, but the fatigue resistance of the wet composite is improved by virtue of its increased static strength.
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