A feasibility study on monitoring of weld fatigue crack growth based on coda wave interferometry (CWI)

Abstract

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.