Investigation of a Weld Crack in Eddy Current Testing Using the Finite Element Method

摘要

Surface-breaking cracks in welds can be detected with the eddy current method. However, the experimental evaluation of the method for example in terms of probability of detection is often carried out with the use of test pieces including fatigue cracks and manufactured notches. There is a need to understand the difference between, on one hand, cracks formed in welds and, on the other hand, fatigue cracks or notches. Here, this difference is studied by evaluation of the characteristics of a weld crack by the use of a mathematical model. The finite element method is used in order to predict eddy current signal responses to cracks. The crack is described as a surface in the model where a boundary condition is applied corresponding to an electrically isolating layer. It is shown that the complex geometry of the crack can be included in the finite element model. The weld cracks studied here are showing a larger signal response compared to closed cracks. A larger volume of the damage is expected to be responsible for the increased impedance response which can be even larger than the response encountered from the interaction with an artificially created notch of equal size.