Experimental and theoretical studies of a bolted joint excited by a torsional dynamic load

This paper presents the experimental work on a single joint rig and the analytical models for representing the experimental results. A bolted joint connecting two beams is shaken at two resonant frequencies. These experiments have illustrated microslip and macroslip phenomena from measurements taken locally to the joint interface in the time domain. Hysteresis loops of the torque versus the relative angular displacement of the joint have been generated from the time-domain data of the rig subjected to multiple bolt preloads and amplitudes of excitation. Damping behaviour evolving from linear viscous type to nonlinear frictional type is clearly shown in the plots of the hysteresis loops and the frequency spectra of the relative angular displacement of the joint. As microslip in the joint develops, the hysteresis loops deviate from an ellipse and the contribution from superharmonics in the frequency spectra becomes stronger. The presence of odd superharmonics in the frequency spectra seems to suggest that the nonlinearity due to friction in the joint can be represented by a cubic stiffness term. The Jenkins-element model for the friction torque in the joint has been used to fit the hysteresis loops of the experimental joint.