Determining the Influence of Temperature on Longitudinal Stresses in Rails Using the Acoustoelasticity Effect

Abstract

Railway track control is one of the main works necessary to ensure the safety of passenger and freight traffic, both in our country and abroad. In modern conditions, ensuring trouble-free operation of the railway is associated with solving the problems of determining longitudinal stresses in rails caused by the long length of the long-welded rails, increasing the speed of transportation, increasing cargo turnover and the influence of ambient temperature. Longitudinal stresses in rails are greatly influenced by temperature. Due to the lack of temperature compensation in the fixed long-welded rails, rail lashes cannot freely expand and contract when it changes. Exceeding the permissible longitudinal stresses in rails can cause the appearance and development of fatigue cracks, destruction of the rail track and emergency situations, which can lead to their temperature release, loss of stability and bending. Therefore, modern methods of non-destructive testing and diagnostic microprocessor systems are being developed, software for them is being improved. Among the well-known methods of non-destructive testing, acoustic methods (ultrasonic and aku-stoelasticity effect) are most widely used, which make it possible to control stresses in rails during the movement of freight and passenger trains. Principle of action of the effect of acoustoelasticity is based on the dependence of longitudinal stresses on the speed, amplitude and frequency of elastic ultrasonic waves. In this work, the effect of temperature on longitudinal stresses in rails was determined. Using the acoustoelasticity effect, longitudinal, transverse and transformed waves were recorded under normal conditions, as well as at positive and negative ambient temperatures. The main measured parameter is the propagation time of the ultrasonic signal from the emitter to the receiver through the section of the rail. Studies have shown that elastic wave velocities decrease when the rail material is heated and are determined mainly by the temperature relationships of the elastic moduli. Temperature affects residual stresses in rails, which can lead to the occurrence and development of defects. The information obtained during the control of the rails was recorded in the Akusto-1 microprocessor system, operating on the basis of the acoustoelasticity effect. Tensometry was used to confirm the results obtained by this system. Stress control was carried out by a certified multi-channel microprocessor strain gauge system MMTS-64.01 accuracy class 0,2. Proposed is a scheme for control of longitudinal mechanical stresses in rails using longitudinal, transverse and transformed waves. To control the height of the rail, a separate-combined direct converter was additionally installed between the radiating and receiving inclined converters. The developed acoustic control method based on the acoustoelasticity effect makes it possible to determine mechanical stresses in rails with an error not exceeding 10 %, which is permissible for its practical use on the railway.