Eddy current (EC) testing is the most commonly used method to inspect near-surface cracks in railheads. Monitoring surface defects periodically is important to assess the track quality for serving daily operations. Nevertheless, despite being used in many countries, this method has limitations when characterizing cracks under the rail surface. Theoretically, EC testing is unreliable for the inspection of many cracks situated too close to each other in a concentrated location. This study has aimed to prove these limitations. EC signals from inspected cracks were compared with real crack profile parameters, i.e. depth and area, which were delivered by slicing the inspected cracked spots into 0.65 mm-thick pieces. The results show that the EC signal responses to the parameters of area and depth may lead to misleading measurements of the near-surface crack depth in the railhead. For instance, a shallower crack with a larger area can generate a higher EC signal response than a deeper crack with a smaller area. Another important conclusion is that the EC testing in this experiment could not be used to measure densely located cracks, which are those near-surface cracks which are typically found in a rail track.

涡流 (EC) 测试是检查轨头近表面裂纹的最常用方法。定期监测表面缺陷对于评估服务日常运营的轨道质量非常重要。然而，尽管在许多国家使用这种方法，但在表征钢轨表面下的裂纹时仍存在局限性。从理论上讲，EC 测试对于检查集中位置中彼此过于靠近的许多裂纹是不可靠的。本研究旨在证明这些局限性。来自检查裂纹的 EC 信号与真实裂纹轮廓参数（即深度和面积）进行了比较，这些参数是通过将检查裂纹点切成 0.65 毫米厚的碎片来传递的。结果表明，EC 信号对面积和深度参数的响应可能导致对轨头近表面裂纹深度的测量产生误导。例如，面积较大的较浅裂纹比面积较小的较深裂纹可以产生更高的 EC 信号响应。另一个重要结论是，本实验中的 EC 测试无法用于测量密集位置的裂纹，这些裂纹是通常在铁轨中发现的近表面裂纹。