Stress Dependence of Ultrasonic Guided Waves in Rails

Abstract

Most modern railways use continuous welded rails (CWRs). A major problem in these structures is the almost total absence of expansion joints, which can create severe issues such as buckling in hot weather and breakage or pulling apart in cold weather. To minimize these risks, CWRs are built by connecting track segments that are prestressed before welding. A related critical parameter is the rail neutral temperature (NT), which is defined as the temperature at which the net longitudinal force in the rail is zero. When the ambient temperature is higher or lower than the NT, the rail is under compression and tension, respectively. Knowledge of the NT provides a potential method for indirect measurement of the stress and load in the rail. Unfortunately, the measurement of the in situ stress (or NT) has been a long-standing challenge for railway owners and operators. This paper presents numerical results on the dynamic behavior of CWRs subjected to a static axial stress. The results show how ultrasonic guided waves are sensitive to variations in stress and could potentially be used to estimate the stress level or the NT in rails. The present work represents the initial concept phase of a research and development study funded by the FRA. The ultimate objective of this study is to develop and test a prototype system that uses noncontact dynamic sensing to measure in situ rail stress in motion at speeds up to 30 mph to determine rail NTs and the related incipient buckling risks in CWRs.