EFFECT OF PRELOAD ON JOINT ROTATION CONSTANT OF CONVENTIONAL AEROSPACE BOLTED JOINTS

Airframe assembly with axial bolted joints in flange configuration is subjected to combined loading of axial load, bending moment and shear force. Structural Integrity of full-scale airframe assemblies is evaluated by conducting full-scale bend load test and by measurement of Joint Rotation Constant (JRC) at different joints to estimate natural frequencies, mode shapes and global deflections accurately and also to classify the joints. Structural integrity, JRC and class of joints primarily depend on type of joint and its preload. Experiments are carried out on axial bolted joint configurations with Pipe and Airframe sections. Effect of preload on JRC at both joints is studied at different torque levels with increasing bending moment. Reduction in measured JRC is observed with increasing preload at Pipe section as well as Airframe section joints. Measured JRC values at both joints have shown decreasing trend with increasing BM for initial preloads before showing increasing trend for higher preloads. Initially, no variation in measured frequencies of first three modes is observed with increasing preload followed by mild increase before showing no variation again for higher preloads for Airframe section joint. The behavior of JRC at different preloads with increasing bending moment indicates how the modal parameters of the assembly and deflections are expected to behave for various preloads.