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To assess the long-term durability of advanced composite joints, the localized creep response of a quasi-isotropic ([45/0/–45/90]2s), graphite fiber/polymer matrix (G40-800/5260) composite laminate subjected to bolt-bearing loads at ambient and elevated temperatures was investigated. Monotonic tension tests and static creep tests were performed on single-hole bolted joints at temperatures of 23, 100, and 150°C. The influence of lateral constraint on the creep response was studied by performing creep tests with bolt clampup torques of 5.65 N·m and a “finger-tight” level. While the ultimate monotonic bearing strength was affected only marginally by temperature, substantial changes in the initial joint stiffness and the hole elongation at fracture were observed in the monotonie tests as the temperature was increased. In the creep tests, significant time-dependent hole elongations were observed at high bearing stress levels and temperatures, with the creep component of the hole elongation found to exceed 5% of the original hole diameter in one case. The lateral constraint had a large influence on the creep behavior of the joints. As the clampup torque was reduced from 5.65 N·m to a finger-tight level, the rate of hole elongation increased by a factor of 2 to 4, indicating the importance of maintaining high clampup conditions in bolted laminate joints. A simple empirical expression was proposed to model the creep behavior of the joints. This expression correlated the experimental data reasonably well and is useful for indicating trends in the creep response of bolted laminate joints.
composite materials, fracture (materials), laminates, bolted joints, creep (materials), elevated temperature, hole elongation, bearing strength, bolt torque
Assistant professor, North Dakota State University, Fargo, ND
Professor, University of Iowa, Iowa City, IA