The Mathematical Analysis of Electromagnetic Fields around Surface Cracks in Metals
The work described in this paper arises from a program for the detection and measurement of surface cracks in metals carried out at University College London. The instrument which was developed for the purpose, the Crack Microgauge, employs the acpd (alternating current potential difference) method. An alternating electric current at a frequency of 6 kHz is applied to the specimen, and the instrument measures the voltage between the probe terminals which are applied to the surface of the specimen. By examining the variation of the voltage readings with position on the surface and, in particular, the jump in readings obtained when the probe crosses the crack, the crack can be detected and features of its geometry deduced. The correlation between instrument readings and information about the crack geometry must be made by use of a theoretical model of the electromagnetic field produced in the crack neighborhood. The authors have been principally concerned in the study of this mathematical problem. In this paper we have attempted to bring together in summary form the most significant results arising from the studies on several different projects.
KeywordsFatigue Crack Crack Depth Skin Depth Normal Crack Crack Geometry
Unable to display preview. Download preview PDF.
- Auld, B.A., Muennemann, F. and Winslow, D.K., 1982, Observation of fatigue crack closure effects with the ferromagnetic resonance eddy current probe, J. Nondestr. Eval., to appear.Google Scholar
- Collins, R., Michael, D.H. and Ranger, K.B., 1981, The a.c. field around a plane semi-elliptical crack in a metal surface, in: “Proceedings of Thirteenth Symposium on Nondestructive Evaluation”. San Antonio, TX.Google Scholar
- Dover, W.D.,Charlesworth, F.D.W., Taylor, K.A., Collins, R. and Michael, D.H., 1980, A.c. field measurement: theory and practice, in: “The measurement of crack length and shape during fracture and fatigue”. C.J. Beevers, ed., Engineering Materials Advisory Service, Warley, U.K.Google Scholar
- Dover, W.D., Charlesworth, F.D.W., Taylor, K.A., Collins, R. and Michael, D.H., 1981, The use of a.c. field measurements to determine the shape and size of a crack in a metal, in: “Eddy current characterization of materials and structures”, G. Birnbaum and G. Free, eds, American Society for Testing and Materials, Philadelphia, PA.Google Scholar
- Kahn, A.H., 1981, Impedance changes produced by a crack in a plane surface, Review of Progress in Quantitative NDE, Vol. 1, D.O. Thompson and D.E. Chimenti (eds.), Plenum Pub. Corp., NY, 1982.Google Scholar
- Michael, D.H., Collins, R., and Dover, W.D., 1982, Detection and measurement of cracks in threaded bolts with an a.c. potential difference method, Proc. Roy. Soc. London, to appear.Google Scholar
- Mirshekar-Syahkal, D., Michael, D.H. and Collins, R., 1981, Parasitic voltages induced by artificial flaws when measured using the a.c, field technique, J. Nondestr. Eval., 2, 3 /4.Google Scholar
- Mirshekar-Syahkal, D., Collins, R. and Michael, D.H., 1982, The influence of skin depth on crack measurement by the a.c. field technique, J. Nondestr. Eval., 3, 2.Google Scholar
- Muennemann, F., Auld, B.A., Fortunko, C.M. and Padget, S.A., 1982, Inversion of eddy current signals in a non-uniform probe field, these proceedings.Google Scholar