Identifying Joint Dynamics in Bolted Cantilevered Systems Under Varying Tightening Torques and Torsional Excitations

Objectives: This paper characterizes how joint stiffness and damping parameters for a bolted cantilevered beam change with different number of bolts, different tightening torques on each, and with different levels of torsional excitations. Such characterization is unaddressed in the literature and is our modest contribution to the state-of-the-art. Another modest contribution is to propose and demonstrate the use of an alternative method of identifying joint characteristics using the harmonic balance method. Methods: A cantilevered beam was torsionally excited at its free end using a modal shaker and the relative displacements across the bolted connection were measured. Experiments were conducted in a temperature-controlled environment. Experiments for all configurations were repeated in a randomized order. Results: System dynamics were observed to be strongly dependent on the level of excitation, tightening torques, and number of bolts at the interface. Parameters identified using the harmonic balance method were found to agree with those identified using the standard and established method of using hysteresis loops. Identified parameters were used to predict the dynamic behavior of another assembled system which had a similar bolted connection, thus validating the identification. Conclusions: Experimental setup and procedures described are simple and the methods of identification robust. Our results suggest that the harmonic balance method is a viable alternate method for joint parameter identification that is not very sensitive to signal processing and conditioning. Our methods and findings can guide other researchers and practitioners interested in the dynamics of assemblies with bolted joints.