Bolted Joints under Sustained Loading

A study of bolted structural joints under sustained loads (1,000 hours) was made to determine long-term joint slip. Joints representative of antenna structural joints were used. These joints were coated with galvanize, Inorganic Zinc primer, red oxide zinc chromate primer, and mill scale. Interference bolts and hexhead bolts of two different grades were used (ASTM A325 and ASTM A490). The bolted structural joints were tested for long-term static shear stress, long-term static shear stress with a superimposed transverse vibration, and a short-term static shear stress with repetitive load reversals. The effects of such variables as joint and fastener coatings, bolt design, strength level shear, tension stress, and balanced design tension-shear rates were studied. All of the faying surfaces tested reached a steady-state rate of slip under sustained loads. The amount and degree of total slip and slip rate were dependent principally on joint shear stress, faying-surface coating, and bolt type.