Hwang Young-In, Lee Hyosung, Kim Yong-Il, Kim Ki-Bok
Non-destructive Evaluation Team, Safety Measurement Institute, Korea Research Institute of Standards and Science, 267 Gajeong-ro, Yuseong-gu, 34113 Daejeon, Republic of Korea.
Department of Measurement Engineering, University of Science and Technology, 217, Gajeong-ro, Yuseong-gu, 34113 Daejeon, Republic of Korea.
J Nondestr Eval. 2022;41(3):63. doi: 10.1007/s10921-022-00895-w. Epub 2022 Sep 8.
Non-destructive stress measurement by ultrasonic testing is based on calculating the acoustoelastic modulus obtained from the relationship between material stress and sound wave velocity. A critically refracted longitudinal (L) wave, which is a bulk longitudinal wave penetrating below and parallel to the surface below an effective depth, is most suitable for ultrasonic stress measurement tests because it exhibits a relatively large change in travel time in response to a change in stress. In particular, the residual stress distribution through the thickness of the subject can be calculated if transducers of different frequencies are applied because of the characteristic of propagation to different depths of penetration depending on the frequency. The main purpose of this study was to visualize the internal or residual stress distribution through the thickness of rails using L waves. To this end, L probes with different center frequencies were designed and manufactured, and the residual stress values of an unused railroad rail and two used railroad rails operated under different conditions were calculated. This was done using the ultrasonic signals received from each probe, of which the distributions were mapped. Through these mapping results, different residual stress values could be calculated according to the depth. The differences in residual stress generation and distribution according to the conditions surrounding the contact between train wheels and rails, and their characteristics, were visualized and analyzed. As a result, it could be concluded that the non-destructive evaluation technique using L waves could detect differences in the residual stress of a rail, and thus can be used to measure the residual stress of the rail accurately.
通过超声检测进行无损应力测量是基于计算从材料应力与声波速度之间的关系获得的声弹性模量。临界折射纵波（L波）是一种穿透到有效深度以下并与该深度以下的表面平行的体纵波，最适合用于超声应力测量测试，因为它在应力变化时传播时间会有相对较大的变化。特别是，如果应用不同频率的换能器，由于其传播特性会根据频率穿透到不同深度，因此可以计算出被测对象厚度方向上的残余应力分布。本研究的主要目的是利用L波可视化钢轨厚度方向上的内部应力或残余应力分布。为此，设计并制造了具有不同中心频率的L探头，并计算了一根未使用的铁轨以及两根在不同条件下运行的使用过的铁轨的残余应力值。这是通过从每个探头接收到的超声信号来完成的，并绘制了这些信号的分布图。通过这些映射结果，可以根据深度计算出不同的残余应力值。可视化并分析了根据车轮与钢轨接触周围条件产生的残余应力及其分布的差异，以及它们的特性。结果可以得出结论，使用L波的无损评估技术可以检测钢轨残余应力的差异，因此可用于准确测量钢轨的残余应力。
