<title>Ultrasonic measurement of stress in pin and hanger connections</title>

Abstract

Pin and hanger connections can sometimes lock up due to corrosion. As the stresses in the connection are cycled due to thermal expansion and contraction of the bridge, fatigue cracking and failure may occur. We constructed an apparatus to simulate a locked-up pin and hanger connection. It consists of a 12 tooth spline bolted to the base of a mechanical testing machine. Hangers were mounted on the spline, which constrains their ends against rotation. The free ends of the hangers were loaded by the test machine's piston. We performed proof of concept tests of a method to detect stresses in pin and hanger connections prior to cracking. The method uses the fact that stress causes change in sound velocity. We propagated shear waves polarized parallel and perpendicular to the hanger axis. The normalized difference in shear wave velocities is called the birefringence. We measured the birefringence near the outer fibers of the hangers, at midsection. We simulated 3 scenarios: continuous monitoring of hanger status; intermittent monitoring from a known initial state; measurement with no a priori knowledge of hanger status. Good agreement with strain gauge data was obtained for all three scenarios.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.