Identification of bolted joints through laser vibrometry

We present a new technique for identifying the dynamics of bolted joints. The technique relies on the comparison of the overall dynamics of the bolted structure to that of a similar but unbolted one. The difference in the dynamics of the two systems can be attributed solely to the joint; modeling this difference in the dynamics enables us to construct a nonparametric model for the joint dynamics. Noncontacting, laser vibrometry is utilized to experimentally measure the structural responses with increased accuracy and to perform scans of the structural modes at fixed frequency. A numerical algorithm is then developed to post-process the experimental data and identify the joint force. Theoretical calculations are first used to validate the technique, which is then utilized to identify a practical joint. Experimental force-displacement plots at the joint reveal clear hysteresis loops which, in turn, can be used to estimate the damping dissipation at the joint. Moreover, experimental frequency responses and scans of the mode shapes of the bolted structure reveal nonproportional damping and nonlinear effects due to micro-impacts of the connected beams at the bolted joint.