Edge Crack Detection: A Theoretical and Experimental Study

Detection of cracks close to an edge by conventional eddy current techniques is difficult, owing to the significant background signal from the edge. It is necessary to develop methods for minimizing the effect of the background signal, thereby increasing the probability of detection. The edge signal is known to be influenced by a number of factors and it is essential to characterize these in order to minimize its influence. This study aims at developing a good understanding of these factors so as to facilitate the development of such techniques. A boundary element method (BEM) approach was used to model the signal due to the edge and to compare with experimental measurements. Experiments were conducted on electro-discharge machined (EDM) slots in the vicinity of an edge using both absolute and differential probes. The influence of orientation of a differential probe on the signal from the crack and the edge was also studied. We report on the development of improved methods to reduce the influence of signal due to the edge by appropriate use of differential probes and with the aid of signal processing. An inexpensive physical technique which results in a improved detectability was also developed

Automatic Generation and Execution of Eddy Current Scan Plans

Eddy current inspection is highly sensitive to the position of the probe relative to the component being scanned. Ensuring that the probe maintains a constant lift-off and remains perpendicular to the surface being scanned is very import to the scanning process, as the signal strength is best under the these constraints. Variations of tilt or lift-off during a scan can introduce large, spurious signals that may mask flaw indications. Earlier work on scan automation used the probe signal to control the lift-off variations so that a constant lift-off could be maintained over a non-planar surface[1]. The present study focuses on achieving probe perpendicularity and constant lift-off all through a given scan, to attain accurate and rep eatable eddy current measurements.</p

Modeling Eddy Current Crack Signals of Differential and Reflection Probes

The efforts of past several years have resulted in development of an eddy current model [1–8], using the boundary element method (BEM). As of last year, the BEM algorithm based on the Hertz potential approach [1–3] was shown to be effective in dealing with complex part and probe geometry [4–6], and particularly in modeling crack signals [7–9]. Previously, the modeling capabilities were demonstrated mostly with absolute probes. This year, the focus has been shifted toward on crack signals of differential and reflection probes

Edge Crack Detection: A Theoretical and Experimental Study

Detection of cracks close to an edge by conventional eddy current techniques is difficult, owing to the significant background signal from the edge. It is necessary to develop methods for minimizing the effect of the background signal, thereby increasing the probability of detection. The edge signal is known to be influenced by a number of factors and it is essential to characterize these in order to minimize its influence. This study aims at developing a good understanding of these factors so as to facilitate the development of such techniques. A boundary element method (BEM) approach was used to model the signal due to the edge and to compare with experimental measurements. Experiments were conducted on electro-discharge machined (EDM) slots in the vicinity of an edge using both absolute and differential probes. The influence of orientation of a differential probe on the signal from the crack and the edge was also studied. We report on the development of improved methods to reduce the influence of signal due to the edge by appropriate use of differential probes and with the aid of signal processing. An inexpensive physical technique which results in a improved detectability was also developed.</p

Eddy Current Flow Near an Edge: A Comparison between Stratton-Chu and Magnetic Potential Formulations

This paper presents a comparative study of two different boundary integral equation (BIE) formulations applicable to eddy current (EC) problems.</p

Automatic Generation and Execution of Eddy Current Scan Plans

Eddy current inspection is highly sensitive to the position of the probe relative to the component being scanned. Ensuring that the probe maintains a constant lift-off and remains perpendicular to the surface being scanned is very import to the scanning process, as the signal strength is best under the these constraints. Variations of tilt or lift-off during a scan can introduce large, spurious signals that may mask flaw indications. Earlier work on scan automation used the probe signal to control the lift-off variations so that a constant lift-off could be maintained over a non-planar surface[1]. The present study focuses on achieving probe perpendicularity and constant lift-off all through a given scan, to attain accurate and rep eatable eddy current measurements.</p

Progress in Eddy Current Modeling via the Boundary Element Method

For the past several years, we have been developing an eddy current model, using the boundary element method (BEM). Last year, in particular, a BEM algorithm based on the Hertz potential approach was found and shown to be effective in dealing with complex part geometry, while keeping the computational resource requirement to a minimum [1–3]. This paper concerns a further extension of the model to include cracks.</p