Fatigue induced cracks in welds may result in the failure of welded structures and therefore it is important to detect the fatigue crack in the early stage. In this paper, we proposed a coda wave interferometry (CWI)-enabled fatigue cracks detection method using piezoceramic transducers. Because of its high sensitivity to the tiny change in the medium, the CWI method employs the multiple scattered coda waves to detect the slight change of welding fatigue cracks. Firstly, a theoretical model is developed by combining the CWI theory with the acoustoelastic effect. The derivation shows that there is a linear relationship between the crack width change and the coda wave relative velocity variation. To verify the correctness of the derived result, the CWI technique is applied to the detection of micro fatigue cracks of three butt welded specimens under fatigue loading. Experimental results show that the relative velocity variation of coda wave increases linearly with the increase of the width of welding fatigue cracks. In addition, energy-based active sensing (EAS) approach was also used as a comparison. Compared with the EAS method, the CWI technique is more sensitive to slight changes of welding fatigue cracks and therefore holds a great potential for the monitoring of micro fatigue crack in the early stage.

焊缝中的疲劳诱导裂纹可能导致焊接结构失效，因此早期检测疲劳裂纹非常重要。在本文中，我们提出了一种使用压电陶瓷换能器的尾波干涉测量 (CWI) 疲劳裂纹检测方法。由于CWI方法对介质的微小变化具有较高的灵敏度，因此采用多次散射尾波来检测焊接疲劳裂纹的微小变化。首先，将CWI理论与声弹性效应相结合，建立了理论模型。推导表明，裂纹宽度变化与尾波相对速度变化之间存在线性关系。为了验证导出结果的正确性，将CWI技术应用于疲劳载荷下三个对接焊接试样的微疲劳裂纹检测。实验结果表明，随着焊接疲劳裂纹宽度的增加，尾波的相对速度变化呈线性增加。此外，还使用了基于能量的主动传感（EAS）方法作为比较。与EAS方法相比，CWI技术对焊接疲劳裂纹的细微变化更为敏感，因此在早期监测微疲劳裂纹方面具有很大的潜力。