Fault Detection Method of Bolt-joint Using Acceleration and Impedance

Abstract

It is necessary to ensure the structural safety of various structures by on-line monitoring of the damages of their bolt-joints. This is an experimental study for the reliable health monitoring of bolt-joints using both acceleration-based global monitoring technique for assessing the global condition of the structure and impedance-based local monitoring technique for small damage estimation. Acceleration and impedance-based damage tests were performed for a specimen composed of bolt-joints. The tightening torque of the bolts was loosened gradually. For global monitoring, the joint damage due to bolt looseness is evaluated by using the modal characteristic and neural network technique obtained from measured acceleration. For local monitoring, the condition of the joint is estimated by measuring the impedance signal for the same bolt loosened state. As a result of applying the acceleration-based technique, it has been found that a damage location can be estimated if the bolt looseness progresses to more than a certain degree, while the damage index increases with the increase in bolt looseness. Further, as a result of applying the impedance-based method, the small damage can be clearly identified by using the damage index. The damage index increases as the degree of bolt looseness increases. The combination of the two techniques may lead to more reliable monitoring.