Background

Continuous welded rails (CWR) are subjected to thermal effects that may lead to buckling or fracture during warm or cold seasons, respectively. The modal characteristics (frequency and mode shapes) of CWR may reveal important information about the thermal stress that can be used to prevent rail failures.

Objective

The primary objective of this study is to prove a contactless method to monitor the vibration and to extract the modal characteristics of rails using a high-speed camera and advanced image processing. This study is the first step towards a general noninvasive monitoring paradigm aimed at measuring axial stress in CWR.

Methods

To prove the principles of the proposed paradigm, a finite element model of an unrestrained rail segment under varying length, boundary conditions, and axial stresses was formulated. The results of the model were then used to interpret the experimental results relative to a 2.4 m-long rail subjected to compressive loading–unloading cycles. During the experiment, the rail was subjected to the impact of an instrumented hammer and the triggered vibration was recorded with a high-speed camera. The videos were then processed using the phase-based displacement extraction, motion magnification, as well as dynamic mode decomposition techniques to extract the modal characteristics of the specimen.

Results

The results show that the frequencies extracted from the images matched well those obtained with two conventional accelerometers bonded to the rail while the mode shapes extracted from the videos matched those predicted numerically. Additionally, the numerical analysis enabled the interpretation of some unexpected experimental results.

Conclusions

The results presented here proved that the proposed method to infer axial stress in CWR requires proper modeling in order to link the modal characteristics of the rails to the axial stress. In the future, the finite element formulation presented here will be expanded to model CWR under given cross-ties and fasteners conditions in order to link the modal characteristics of the rail of interest to its axial stress.

中文翻译：

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非接触式监测轨道振动的方法

背景

连续焊接的钢轨（CWR）受到热影响，分别可能在温暖或寒冷的季节导致屈曲或断裂。CWR的模态特征（频率和模态形状）可能会揭示有关热应力的重要信息，这些信息可用于防止轨道故障。

客观的

这项研究的主要目的是证明一种非接触式方法，该方法使用高速相机和先进的图像处理技术来监测振动并提取轨道的模态特征。这项研究是迈向旨在测量CWR轴向应力的通用无创监测范例的第一步。

方法

为了证明所提出范式的原理，建立了在变化的长度，边界条件和轴向应力下无约束的钢轨节段的有限元模型。然后，将模型的结果用于解释相对于2.4 m长的轨道的压缩压缩-卸载循环的实验结果。在实验过程中，钢轨受到了仪器锤的冲击，并使用高速摄像机记录了触发的振动。然后使用基于相位的位移提取，运动放大以及动态模式分解技术对视频进行处理，以提取样本的模态特征。

结果

结果表明，从图像中提取的频率与用两个传统的加速度计粘结在轨道上获得的频率匹配得很好，而从视频中提取的模式形状与数值预测的那些匹配。此外，数值分析还可以解释一些意想不到的实验结果。

结论

此处给出的结果证明，所提出的推断CWR中轴向应力的方法需要适当的建模，以便将钢轨的模态特性与轴向应力联系起来。将来，此处给出的有限元公式将在给定的横梁和紧固件条件下扩展到CWR模型，以便将目标轨道的模态特性与其轴向应力联系起来。