Improved Fatigue Strength Adhesive Part II. Adhesive Optimization.

摘要

In spite of their high static strengths over a wide temperature range, present 350 F service adhesive systems must be limited in maximum structural design loadings to as little as 30% of static ultimate strength if fatigue lives in the order of 10 to the 7th power cycles are required. This situation has limited the use of high temperature adhesives in bonding such fatigue resistant materials as graphite-epoxy composites. However, addition of high strength, high modulus fibers, such as graphite, to the adhesive system has been found to improve the fatigue durability of such assembles. An increase in allowable fatigue loading was demonstrated in the initial portion of this contract by addition of PWA, a graphite fiber fabric, to ADX-653, a 350 F service system. The adhesion of resin to fiber, the effect of resin and fiber modulus, and the influence of fiber volume content and bondline thickness were examined. The fatigue resistance of the ADX-653/PWA combination, as measured by a single load test, was doubled by the application of a silane finishing agent to the graphite surface prior to resin impregnation. A five-fold increase in the expected bond lifetime under advanced fighter aircraft spectrum fatigue testing was demonstrated using the PWA reinforced ADX-653 system as compared to a state of the art nylon fabric supported system.