- Email: [email protected]
Three dimensional modeling of the DC potential drop method using finite element and boundary element analysis
N DT Abstracts 50264 Saka, M.; Yuasa, D.; Abe, H.; Sugino, K. Nondestructive characterization of bifurcated crack by potential d r o p technique Nondestructive Testing Evaluation, Vol. 7, No. !-6, pp. 61-72. (1992) A method was presented for the nondestructive evaluation of a crack bifurcated from a horizontal crack in a rail. The method was based on the measurement of the difference and distribution of d.c. electrical potential on the top surface of the rail. First, a problem of current flow in a plate, which contained horizontal and bifurcated cracks and was subjected to a uniform current was analyzed numerically by using a 2-D finite element method. The potential distribution on the measuring surface of the plate was obtained for various combinations of the cracks. The potential distribution showed a remarkable change in its slope just above both ends of the horizontal crack. Also the relation between the vertical component of the bifurcated crack and the total potential difference above the horizontal crack was revealed to be independent of the combinations of the cracks. Next, in order to characterize the cracks in actual rail based on the 2-D numerical analysis, a method was introduced for obtaining a rectangular section electrically equivalent to the section of actual rail. Finally, it was verified by experiments using rail specimens that the cracks were characterized quantitatively through the present numerical results together with the use of the equivalent section.
Surface crack configuration can be detected by the DC Potential Drop Method. A belch processing program for the determination of surface crack configuration has been developed. The production of the mesh element has been considerably improved by the introduction of a three dimension boundary fit transformation coordinate system. The curved grid can he automatically changed to correspond to the actual crack shape, according to the comparison of the ~ u r e d potential difference distribution and the analyzed one. The results of application to the simulated surface crack showed good agreement between the analyzed crack configuration and the actual one. 52562 Saka, M.; Yuasa, D.; Abe, H.; Sugino, K. Nondestructive characterization of bifurcated
crack
by
potential drop technique Nondestructive Characterization of Materials V, Karuizawa (Japan), 27- 30 May 1991. pp, 61-72. Edited by T. Kishi, T. Saito, C. Ruud and R. Green. lketani Science and Technology Foundation (1993) A method was presented for the nondestructive evaluation of a crack bifurcated from a horizontal crack in a rail. The method was based on the ~ u r e m e n t of the difference and distribution of d.c. electrical potential on the top surface of the rail. First, a problem of current flow in a plate, which contained horizontal and bifurcated cracks and was subjected to a uniform current, was analyzed numerically by using a 2-D finite element method. Next, in order to characterize, the cracks in actual rail based on the 2-D numerical analysis, a method was introduced for obtaining a rectangular section electrically equivalent to the section of actual rail. Finally, it was verified by experiments using rail specimens that the cracks were characterized quantitatively through the present numerical results together with the use of the equivalent section.
50104 Blitz,J. Electrical and magnetic methods of nondestructive testing Adam Hilger 237 pp, (1991) This book gives a comprehensive account of the electrical and magnetic methods of nondestructive testing, it begins with a discussion of the requirements for nondestructive testing and the Criteria for the choice of a given method. This is followed by a summary of the general theory relating to electrical and magnetic testing techniques. Specific methods are then discussed. Several chapters are devoted to eddy current and flux-leakage techniques. Other tests such as the microwave and potential drop methods are also included. Some useful programs for eddy current impedance analyses are given in the appendix. These programs are in BASIC and can be run on inexpensive personal computers.
52049 Hognest~l H Measurement of mechanical stress a n d fatigue in steel by c o m p a r i n g potential drop curves between contact points at different magnetization of the area under test Patent Cooperation Treaty No. WO 9,218,839 (29 Oct. 1992)
48753 Nath, S.; Lord, W.; Rudolphi, TJ. Hybrid numerical methods for electromagnetic NDE Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (United States), 15-20 Jul. 1990. Voi. 10 A, pp. 317-324. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press ( 199 ! ). ISBN 0-306-43903-4. This paper reports the results of an ongoing study to examine the relative advantages of boundary element and finite element methods and also proposes hybrid formulation. The boundary element method (BEM) is based on the Green's function approach and is feasible only when the material properties are homogeneous. This technique is ideal if one is interested only in the boundary solution or at selected interior points, or if one is modeling an infinite domain. On the other hand, the finite element method (FEM) can handle non-linear and anisotropie materials extremely well and generates a full field solution in the whole region, thus making it convenient to study the physics of the phenomenon and the energy/defect interactions. In the AC potential drop (ACPD) method, a uniform alternating current at low frequency is applied to a specimen, and the potential is measured across the probe. By examining the variation of the potential when the probe straddles the crack, the crack can he detected and the features of its geometry deduced. A crack microgauge instrument has been developed for laboratory and in-service inspection and has been used for measuring stress induced cracks, fatigue cracks in welded joints or in the threaded region of bolts and other components.
Nath, S.; Rudoiphi, T.J.; Lord, W. Three dimensional modeling of the DC potential d r o p method using finite element and boundary element analysis 51520
Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 28 Jul. - 2 Aug. 1991. Vol. 1 IA, pp. 553-560. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1992) Finite element (FE) and boundary element (BE) methods of numerical analysis have been utilized in the solution of numerous electromagnetic nondestructive evaluation (NDE) phenomena. This research is part of an endeavor to compare and contrast FE and BE methods as applied to electromagnetic NDE. In particular, this paper presents a three dimensional FE and BE model of the DC Potential drop method to characterize fatigue cracks. The next few sections describe the principle of the DC Potential drop (DCPD) method and its applications, the FE and BE formulations, data obtained from modeling a compact tension specimen, and finally, some conclusions.
Hognestad, H. New method for determining absolute stress in ferromagnetic steel via potential drop measurements 50519
Materials Science and Technology, Vol. 8, No. 7, pp. 649-651 (Jul. 1992) A technique has been developed in which transient potential drop signals are obtained during initial and anhysterctic magnetisation. From these, a deviation curve can be obtained that reflects the absolute stress not only in small test specimens, but also in large steel structures. However, further investigations and experimental work are required before an instrument for reliable measurement can be of practical value. The use of deviation curves to indicate structural changes during fatigue before cracks develop, may also be a possible application of the new technique.
48752 Topp, D.A.; Dover, W.D. Review of A C P D / A C F M c r a c k m e a s u r e m e n t systems Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (United States), 15o20 Jul. 1990. Vol. 10 A. pp. 301-308. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1991). 1SBN 0-306-43903-4. The alternating current potential drop (ACPD) method was developed in response to a need for a nondestructive testing method for monitoring crack shape. By contrast, the alternating current field measurement (ACFM) technique allow cracks to he detected and reliable accurate measurements of their size to he made. The development of both these techniques is reviewed in this paper, together with a discussion of appropriate applications.
50518 Schone, D.; Aurich, D. M e a s u r i n g c r a c k p r o p a g a t i o n (In G e r m a n : English Abstract) Materiaiprufung, Vol. 34, No. 7-8, pp. 224-227 (Jul.-Aug. 1992) DC and AC potential drop methods are well-approved for monitoring crack initiation and propagation in electrical conductive materials. In this article, two systems for automatic, continuous crack length measurements with direct current are presented. Their application to the low-cycle fatigue testing of steel specimens is described. By integration over several cycles, it was possible to measure the potential with an accuracy of 0.5 mu V, corresponding to a crack length resolution of 0.05 ram.
48527 Nath, S.; Rudolphi, T.I.; Lord, W. C o m p a r a t i v e study of finite-element and boundary-element analyses of the DC potential d r o p m e t h o d Materials Evaluation, Vol, 50, No. 1, pp. 51-55 (Jan. 1992)
69
Surface crack configuration can be detected by the DC Potential Drop Method. A belch processing program for the determination of surface crack configuration has been developed. The production of the mesh element has been considerably improved by the introduction of a three dimension boundary fit transformation coordinate system. The curved grid can he automatically changed to correspond to the actual crack shape, according to the comparison of the ~ u r e d potential difference distribution and the analyzed one. The results of application to the simulated surface crack showed good agreement between the analyzed crack configuration and the actual one. 52562 Saka, M.; Yuasa, D.; Abe, H.; Sugino, K. Nondestructive characterization of bifurcated
crack
by
potential drop technique Nondestructive Characterization of Materials V, Karuizawa (Japan), 27- 30 May 1991. pp, 61-72. Edited by T. Kishi, T. Saito, C. Ruud and R. Green. lketani Science and Technology Foundation (1993) A method was presented for the nondestructive evaluation of a crack bifurcated from a horizontal crack in a rail. The method was based on the ~ u r e m e n t of the difference and distribution of d.c. electrical potential on the top surface of the rail. First, a problem of current flow in a plate, which contained horizontal and bifurcated cracks and was subjected to a uniform current, was analyzed numerically by using a 2-D finite element method. Next, in order to characterize, the cracks in actual rail based on the 2-D numerical analysis, a method was introduced for obtaining a rectangular section electrically equivalent to the section of actual rail. Finally, it was verified by experiments using rail specimens that the cracks were characterized quantitatively through the present numerical results together with the use of the equivalent section.
50104 Blitz,J. Electrical and magnetic methods of nondestructive testing Adam Hilger 237 pp, (1991) This book gives a comprehensive account of the electrical and magnetic methods of nondestructive testing, it begins with a discussion of the requirements for nondestructive testing and the Criteria for the choice of a given method. This is followed by a summary of the general theory relating to electrical and magnetic testing techniques. Specific methods are then discussed. Several chapters are devoted to eddy current and flux-leakage techniques. Other tests such as the microwave and potential drop methods are also included. Some useful programs for eddy current impedance analyses are given in the appendix. These programs are in BASIC and can be run on inexpensive personal computers.
52049 Hognest~l H Measurement of mechanical stress a n d fatigue in steel by c o m p a r i n g potential drop curves between contact points at different magnetization of the area under test Patent Cooperation Treaty No. WO 9,218,839 (29 Oct. 1992)
48753 Nath, S.; Lord, W.; Rudolphi, TJ. Hybrid numerical methods for electromagnetic NDE Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (United States), 15-20 Jul. 1990. Voi. 10 A, pp. 317-324. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press ( 199 ! ). ISBN 0-306-43903-4. This paper reports the results of an ongoing study to examine the relative advantages of boundary element and finite element methods and also proposes hybrid formulation. The boundary element method (BEM) is based on the Green's function approach and is feasible only when the material properties are homogeneous. This technique is ideal if one is interested only in the boundary solution or at selected interior points, or if one is modeling an infinite domain. On the other hand, the finite element method (FEM) can handle non-linear and anisotropie materials extremely well and generates a full field solution in the whole region, thus making it convenient to study the physics of the phenomenon and the energy/defect interactions. In the AC potential drop (ACPD) method, a uniform alternating current at low frequency is applied to a specimen, and the potential is measured across the probe. By examining the variation of the potential when the probe straddles the crack, the crack can he detected and the features of its geometry deduced. A crack microgauge instrument has been developed for laboratory and in-service inspection and has been used for measuring stress induced cracks, fatigue cracks in welded joints or in the threaded region of bolts and other components.
Nath, S.; Rudoiphi, T.J.; Lord, W. Three dimensional modeling of the DC potential d r o p method using finite element and boundary element analysis 51520
Review of Progress in Quantitative Nondestructive Evaluation, Brunswick, Maine (United States), 28 Jul. - 2 Aug. 1991. Vol. 1 IA, pp. 553-560. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1992) Finite element (FE) and boundary element (BE) methods of numerical analysis have been utilized in the solution of numerous electromagnetic nondestructive evaluation (NDE) phenomena. This research is part of an endeavor to compare and contrast FE and BE methods as applied to electromagnetic NDE. In particular, this paper presents a three dimensional FE and BE model of the DC Potential drop method to characterize fatigue cracks. The next few sections describe the principle of the DC Potential drop (DCPD) method and its applications, the FE and BE formulations, data obtained from modeling a compact tension specimen, and finally, some conclusions.
Hognestad, H. New method for determining absolute stress in ferromagnetic steel via potential drop measurements 50519
Materials Science and Technology, Vol. 8, No. 7, pp. 649-651 (Jul. 1992) A technique has been developed in which transient potential drop signals are obtained during initial and anhysterctic magnetisation. From these, a deviation curve can be obtained that reflects the absolute stress not only in small test specimens, but also in large steel structures. However, further investigations and experimental work are required before an instrument for reliable measurement can be of practical value. The use of deviation curves to indicate structural changes during fatigue before cracks develop, may also be a possible application of the new technique.
48752 Topp, D.A.; Dover, W.D. Review of A C P D / A C F M c r a c k m e a s u r e m e n t systems Review of Progress in Quantitative Nondestructive Evaluation, La Jolla, California (United States), 15o20 Jul. 1990. Vol. 10 A. pp. 301-308. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1991). 1SBN 0-306-43903-4. The alternating current potential drop (ACPD) method was developed in response to a need for a nondestructive testing method for monitoring crack shape. By contrast, the alternating current field measurement (ACFM) technique allow cracks to he detected and reliable accurate measurements of their size to he made. The development of both these techniques is reviewed in this paper, together with a discussion of appropriate applications.
50518 Schone, D.; Aurich, D. M e a s u r i n g c r a c k p r o p a g a t i o n (In G e r m a n : English Abstract) Materiaiprufung, Vol. 34, No. 7-8, pp. 224-227 (Jul.-Aug. 1992) DC and AC potential drop methods are well-approved for monitoring crack initiation and propagation in electrical conductive materials. In this article, two systems for automatic, continuous crack length measurements with direct current are presented. Their application to the low-cycle fatigue testing of steel specimens is described. By integration over several cycles, it was possible to measure the potential with an accuracy of 0.5 mu V, corresponding to a crack length resolution of 0.05 ram.
48527 Nath, S.; Rudolphi, T.I.; Lord, W. C o m p a r a t i v e study of finite-element and boundary-element analyses of the DC potential d r o p m e t h o d Materials Evaluation, Vol, 50, No. 1, pp. 51-55 (Jan. 1992)
69