|
This paper presents an analysis of a bolted lap joint assembly using continuum wave models to examine the scattering of flexural waves across a joint under loss of torque preload. The motivation for this work is derived from monitoring the dynamics of large buildings and bridges to assess the level of damage in bolted or riveted assemblies following a severe loading condition. In the event of such a condition, these joints can loosen or fail completely creating a potentially hazardous environment for the general public while these structures are still in service. It has been suggested that using nondestructive techniques to monitor the health of these bolted connections to determine the extent of damage can minimize such risks to the public. This paper discusses such a health monitoring approach using local mechanical impedance models to characterize the non-linear joint dynamics of a bolted assembly. As the torque on the bolted assembly is varied, the local and global response of a fixed-fixed one- dimensional structure is studied. The loss of torque load is correlated with the changes seen in the local scattering dynamics of the bolted joint. Incoming and outgoing wave dynamics at the joint are separated to compute the frequency dependent local scattering matrix of the joint and determine its affect on the global system response as the torque on the bolted assembly is varied. Analytical results using the continuum wave descriptions of the structural dynamics are compared against experimental data on a beam fixed at both ends with a bolted lap joint located at its center. Using a least squares cost function between experimental and analytical transfer function data, an effective joint stiffness is obtained. Minimizing the cost function leads to an optimal solution for a parameterized model of the joint dynamics and attempts to account for possible non-linearities such as cubic springs, deadband, stiction and hysteresis. Piezoelectric actuators are used to excite the beam in bending. Strain sensor arrays are distributed on both sides of the joint to capture the local scattering properties of the joint as a function of torque load.
|
