| Recently,train is running faster and faster,and considering the stability and security,Seamless Welded Rails(SWR) are used as the train orbits gradually. The temperature of the rails will vary with weather.So that the rails may release the energy due to the metal characteristic of expanding or contracting with temperature,there is some badly distortion in the SWR,worsly occurring accidents on expanding orbits.The Portrait Thermal Stress(PTS) of the SWR should be monitored in some parts regularly,as to avoid such accident. For solving this problem,there are several ways of measuring the PTS of the SWR at present,such as Demarcating Path Length,Strain and Stress,Magnetic Induction Measurement and Ultrasonic Measurement. However, portable,universal and effective instruments or methods don't appear up to now in China.This article describes a way of special ultrasonic system which monitors thermal stress in seamless welded rails.This monitoring system is a non destructive testing system,which adopts AVR MCU and high-precise time chip processing as the core of it,and adopts the Critically Refracted Longitudinal wave as the object of measuring.My studying focuses on the theory of the monitoring system,which will be listed in this arctile:According to the Snell theory, the theory of motivating of Critically Refracted Longitudinal wave is described in details,and the finite element software is used to emulate the propagating course.The formulas of calculating the PTS of SWR are taken from the acoustoelasticity theory,and the calculating the parameters is introduced.According to assemble materials, three kinds of ways of monitoring the PTS of SWR using Critically Refracted Longitudinal wave are described,which are measuring the sound-time in changeless distance, Ultrasonic Critical-angle Refractomery and frequency spectrum,the first way of ways is used in this experiment system.The factors,which effect the monitoring system,are assaid in some degree based... |
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