Remotely Detecting Damage in Critical Structural Bolted Joints

novel remote non-destructive inspection and evaluation (N I&E) method for detecting and quantifying damage in critical bolted joints on military and commercial structures is proposed. The NDI&E method utilizes remotely located impedance sensor to periodically monitor changes in the structural stiffness, mass and damping. Damage to the joint fasteners or connection materials causes direct changes in the overall joint stiffness and damping. Mass changes also occur but are usually of lower order significance. The impedance sensors consist of small piezoelectric patches that are used to directly measure the structure's dynamic response. Because the sensors are very lightweight, robust, and inexpensive, they can be readily located at critical inspection points over an entire structure. With the sensors in place, the structural integrity can be inspected [remotely from outside the structure, and the resulting signals can be integrated into control systems. Recent advances in signal processing techniques may yield additional concise information pertaining to the nature of the damage. The method can potentially save millions of dollars on inspection and operation costs over the life of a structure.