- Email: [email protected]
A reversing direct current potential drop system for detecting and sizing fatigue cracks along weld toes
N DT Abstracts McKeighan, P.C.; Tabrett, C.P.; Smith, D.J. The influence of crack deflection a n d bifurcation on DC
drop for a plate without crack, increment of the potential drop due to respective cracks which is calculated by assuming that the plate contains one of these cracks and a term representing the interaction between these cracks. The term is composed of multiplication of the increment of the potential drop due to respective cracks. The methodology is extended successively to calculate the potential drop for a crack in multiple cracking more than two. The inverse problem to evaluate the crack length is analyzed by comparing the potential drop calculated in this way with the measurement.
60320
potential drop calibration Symposium on Special Applications and Advanced Techniques for Crack Size Determination, Atlanta, Georgia (United States), 19 May 1993. pp. 51-66. (STP; 1251) Edited by J.J. Ruschau and J.K. Donald. ASTM (1995) (PCN) 04-0 i 2510-30. ISBN 0803120036 Finite element and analog techniques are used to assess the influence of abnormal crack morphologies on the potential drop (PD) response of an M(T) specimen. All crack geometries considered, including simply deflected, bifurcated, and periodic sawtooth morphologies, result in higher potentials than observed for an undetected crack. The greatest influence was observed with a bifurcated crack even with relatively short branch segment lengths.
59913 Takahashi, K.; Shoji, T. NDI of non-sintered a r e a in powder forged steel by means of alternative c u r r e n t potential d r o p (In Japanese, English abstract) Journal of JSNDI, Vol. 44, No. 9, pp. 736-743 (1995) By using alternative current potential drop (ACPD) method, potential drop of obliquely ground specimen was measured. The greater the ground thickness, which means the smaller the depth of non-sintered area (NSA), the smaller the potential drop normalized with that of the portion which has no surface defect. The ground thickness where the potential drop became constant correspond to the maximum depth where the NSA was observed by SEM observation on fractured surface. Hence, the depth of NSA can be given precisely by the ACPD non-destructively. Obvious relationship between tensile strength and normalized potential drop was observed.
60319 Jablonski, D.A. Measurement of multiple-site c r a c k i n g in simulated aircraft panels using AC potential drop Symposium on Special Applications and Advanced Techniques for Crack Size Determination, Atlanta, Georgia (United States), 19 May 1993. pp. 33-50. (STP; 1251) Edited by J.J. Ruschau and J.K. Donald. ASTM (1995) (PCN) 04-012510-30. ISBN 0803120036 The AC potential drop technique was applied to aluminum test specimens under fatigue cycling conditions as well as monotonic R-curve testing. Aluminum ALCLAD 2024 test specimens of three different specimen geometries were examined. Specimens with a single-hole were used to examine the effects of lead placement on the sensitivity of AC potential drop. Three-bole specimens were used to simulate multiple- site cracking from several holes. Riveted specimens containing one row of three rivets were used to examine multiple-site cracking from fasteners. Optimum current and potential lead geometries were determined for each specimen geometry. Relationships between the AC potential and crack length were determined for AC current frequencies of 3, 10, and 30 kHz. The sensitivity of AC potential drop in measuring crack initiation was investigated. The sensitivity was found to increase substantially with increasing AC current frequency,
Kim, H.; Shoji, T. Study on the evaluation of inclined crack by I C F P D technique 59912
(In Japanese, English abstract) Journal of JSNDI, Vol. 44, No. 9, pp. 730-735 (1995) A new technique using an alternative current has been developed for detecting and sizing of defects that are existing on surface, blind and inside in components. This technique is based that current is induced only in exploratory region by a straight induction wire flowing a constant &c., and potential drops are measured with potential pick-up pins of which a spacing is constant, 10mm. This technique is named by ICFPD (Induced Current Focusing Potential Drop). This paper describes the results of some inclined cracks evaluated by ICFPD technique. In the vicinity of defect, the potential drops are varied with the inclined angle and depth of defect because the distribution of the induced current is depended on the variation of the inclined angle and depth of defect.
60316 Frise, P.R.; Sahney, R. Selection of a potential d r o p crack measurement system for zirconium alloy specimens Insight, Vol. 38, No. 2, pp. 96-101 (Feb. 1996) The pressure tubes in Canadian CANDU heavy water nuclear reactors are made of cold-worked Zr-2.5 Nb. An experimental programme has been undertaken to develop a potential drop system to measure the size of flaws in this material when it is being evaluated for its fracture toughness properties using test specimens which have been removed from a reactor, or are about to be placed in service in a reactor. One direct current and two alternating current systems were evaluated and it was found that a localized direct current potential drop system gave satisfactory results on flat plate specimens of the material.
59465 Kanno, S.; Hayashi, M.; Miyazala', K.; Sanoh, J. M o n i t o r i n g of fatigue crack shape change in elevated t e m p e r a t u r e water by DC potential d r o p method Proceedings of the 13th International Conference on NDE in the Nuclear and Pressure Vessel Industries, Kyoto (Japan), 22-25 May 1995. pp. 267- 270. ASM International (1995) ISBN 0-87170-548-6 Fatigue surface crack shape is monitored by DC potential drop method (PDM). Since the number of PDM electrode wires are limited by the number of Connax seals in the simulated BWR environment test apparatus, newly developed PDM is employed for the crack growth measurement. Potential differences are measured between electrodes disposed at one side and one way of the surface crack and a pair of electrodes across the crack at its center. The number of PDM electrode wires can be reduced to almost one half compared with the conventional method. The crack shapes has been determined by the simplified method. The obtained surface crack shapes well agree with the measured ones analyzed from fracture surface.
Sadeghi, S,H.H.; Mirshekar-Syahkal, D. Two dimensional inversion of crack signal in surface electromagnetic field measurement technique 60123
Review of Progress in Quantitative Nondestructive Evaluation, Snowmass Village, Colorado (United States), 31 Jul.-5 Aug. 1994. Voi. 14A, pp. 275-282. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1995) ISBN 0-306-45062-3 In the methods of the surface magnetic field measurement (SMFM) and the induction ac potential-drop (IACPD), the surface field is produced by U-shaped wires or rectangular coils carrying high frequency currents. This paper quantifies the accuracy of the one-dimensional inversion technique for cracks of small aspect ratios and reports on a two- dimensional approach for inverting the SMFM and IACPD crack signals. In this connection, the one-dimensional method is first described. Then, the errors due to this 4nterpretation for circular-arc cracks are discussed using a set of computer simulated results. Finally, two- dimensional inversion curves for fatigue cracks with circular-arc shape are presented.
58915 Wojcik, A.G. Potential drop techniques for c r a c k characterisation Materials World, Vol. 3, No. 8, pp. 379-381 (Aug. 1995) AC and DC potential drop techniques can be used to characterise defects and monitor crack growth in a diverse range of applications. 58914 Yee, R.; Lambert, S.B. A reversing direct c u r r e n t potential drop system for detecting and sizing fatigue cracks along weld toes Journal of Testing and Evaluation, Vol. 23, No. 4, pp. 254-260 (Jul. 1995) Steel welded T-joints with 102 mm thick base plates were fatigue tested in three-point bending. A reversing direct current potential drop (DCPD) system was used to detect the initiation of multiple surface cracks along the transverse weld toes of these joints and to monitor the size and shape of fatigue cracks that developed from these cracks. Potential drop readings were obtained by fixed probes straddling the weld toes and normalized with respect to potential drop readings from a remote reference probe. The fixed-prohe arrangement was able to detect 0.4 mm to 1.0 mm deep surface cracks along the transverse weld toes of the T-joints. The 2D calibrations were able to predict the crack depth at the deepest points of these cracks to within + 10%.
59914 Liu, H.; Saka, M.; Abe, H.; Komura, L; Sakamoto, H. Simplified NDE of multiple cracks by means of the DC potential drop technique based on the analysis of c r a c k interactions (In Japanese, English abstract) Journal of JSNDI, Vol. 44, No. ! 1, pp. 875-881 (Nov. 1995) A method is proposed for simplified nondestructive evaluation of multiple cracks by means of the d.c. potential drop technique. Twodimensional multiple cracks are treated. First for a plate containing two cracks, a new methodology is introduced to calculate the potential drop between both sides of a crack, it is expressed as the sum of the potential
66
drop for a plate without crack, increment of the potential drop due to respective cracks which is calculated by assuming that the plate contains one of these cracks and a term representing the interaction between these cracks. The term is composed of multiplication of the increment of the potential drop due to respective cracks. The methodology is extended successively to calculate the potential drop for a crack in multiple cracking more than two. The inverse problem to evaluate the crack length is analyzed by comparing the potential drop calculated in this way with the measurement.
60320
potential drop calibration Symposium on Special Applications and Advanced Techniques for Crack Size Determination, Atlanta, Georgia (United States), 19 May 1993. pp. 51-66. (STP; 1251) Edited by J.J. Ruschau and J.K. Donald. ASTM (1995) (PCN) 04-0 i 2510-30. ISBN 0803120036 Finite element and analog techniques are used to assess the influence of abnormal crack morphologies on the potential drop (PD) response of an M(T) specimen. All crack geometries considered, including simply deflected, bifurcated, and periodic sawtooth morphologies, result in higher potentials than observed for an undetected crack. The greatest influence was observed with a bifurcated crack even with relatively short branch segment lengths.
59913 Takahashi, K.; Shoji, T. NDI of non-sintered a r e a in powder forged steel by means of alternative c u r r e n t potential d r o p (In Japanese, English abstract) Journal of JSNDI, Vol. 44, No. 9, pp. 736-743 (1995) By using alternative current potential drop (ACPD) method, potential drop of obliquely ground specimen was measured. The greater the ground thickness, which means the smaller the depth of non-sintered area (NSA), the smaller the potential drop normalized with that of the portion which has no surface defect. The ground thickness where the potential drop became constant correspond to the maximum depth where the NSA was observed by SEM observation on fractured surface. Hence, the depth of NSA can be given precisely by the ACPD non-destructively. Obvious relationship between tensile strength and normalized potential drop was observed.
60319 Jablonski, D.A. Measurement of multiple-site c r a c k i n g in simulated aircraft panels using AC potential drop Symposium on Special Applications and Advanced Techniques for Crack Size Determination, Atlanta, Georgia (United States), 19 May 1993. pp. 33-50. (STP; 1251) Edited by J.J. Ruschau and J.K. Donald. ASTM (1995) (PCN) 04-012510-30. ISBN 0803120036 The AC potential drop technique was applied to aluminum test specimens under fatigue cycling conditions as well as monotonic R-curve testing. Aluminum ALCLAD 2024 test specimens of three different specimen geometries were examined. Specimens with a single-hole were used to examine the effects of lead placement on the sensitivity of AC potential drop. Three-bole specimens were used to simulate multiple- site cracking from several holes. Riveted specimens containing one row of three rivets were used to examine multiple-site cracking from fasteners. Optimum current and potential lead geometries were determined for each specimen geometry. Relationships between the AC potential and crack length were determined for AC current frequencies of 3, 10, and 30 kHz. The sensitivity of AC potential drop in measuring crack initiation was investigated. The sensitivity was found to increase substantially with increasing AC current frequency,
Kim, H.; Shoji, T. Study on the evaluation of inclined crack by I C F P D technique 59912
(In Japanese, English abstract) Journal of JSNDI, Vol. 44, No. 9, pp. 730-735 (1995) A new technique using an alternative current has been developed for detecting and sizing of defects that are existing on surface, blind and inside in components. This technique is based that current is induced only in exploratory region by a straight induction wire flowing a constant &c., and potential drops are measured with potential pick-up pins of which a spacing is constant, 10mm. This technique is named by ICFPD (Induced Current Focusing Potential Drop). This paper describes the results of some inclined cracks evaluated by ICFPD technique. In the vicinity of defect, the potential drops are varied with the inclined angle and depth of defect because the distribution of the induced current is depended on the variation of the inclined angle and depth of defect.
60316 Frise, P.R.; Sahney, R. Selection of a potential d r o p crack measurement system for zirconium alloy specimens Insight, Vol. 38, No. 2, pp. 96-101 (Feb. 1996) The pressure tubes in Canadian CANDU heavy water nuclear reactors are made of cold-worked Zr-2.5 Nb. An experimental programme has been undertaken to develop a potential drop system to measure the size of flaws in this material when it is being evaluated for its fracture toughness properties using test specimens which have been removed from a reactor, or are about to be placed in service in a reactor. One direct current and two alternating current systems were evaluated and it was found that a localized direct current potential drop system gave satisfactory results on flat plate specimens of the material.
59465 Kanno, S.; Hayashi, M.; Miyazala', K.; Sanoh, J. M o n i t o r i n g of fatigue crack shape change in elevated t e m p e r a t u r e water by DC potential d r o p method Proceedings of the 13th International Conference on NDE in the Nuclear and Pressure Vessel Industries, Kyoto (Japan), 22-25 May 1995. pp. 267- 270. ASM International (1995) ISBN 0-87170-548-6 Fatigue surface crack shape is monitored by DC potential drop method (PDM). Since the number of PDM electrode wires are limited by the number of Connax seals in the simulated BWR environment test apparatus, newly developed PDM is employed for the crack growth measurement. Potential differences are measured between electrodes disposed at one side and one way of the surface crack and a pair of electrodes across the crack at its center. The number of PDM electrode wires can be reduced to almost one half compared with the conventional method. The crack shapes has been determined by the simplified method. The obtained surface crack shapes well agree with the measured ones analyzed from fracture surface.
Sadeghi, S,H.H.; Mirshekar-Syahkal, D. Two dimensional inversion of crack signal in surface electromagnetic field measurement technique 60123
Review of Progress in Quantitative Nondestructive Evaluation, Snowmass Village, Colorado (United States), 31 Jul.-5 Aug. 1994. Voi. 14A, pp. 275-282. Edited by D.O. Thompson and D.E. Chimenti. Plenum Press (1995) ISBN 0-306-45062-3 In the methods of the surface magnetic field measurement (SMFM) and the induction ac potential-drop (IACPD), the surface field is produced by U-shaped wires or rectangular coils carrying high frequency currents. This paper quantifies the accuracy of the one-dimensional inversion technique for cracks of small aspect ratios and reports on a two- dimensional approach for inverting the SMFM and IACPD crack signals. In this connection, the one-dimensional method is first described. Then, the errors due to this 4nterpretation for circular-arc cracks are discussed using a set of computer simulated results. Finally, two- dimensional inversion curves for fatigue cracks with circular-arc shape are presented.
58915 Wojcik, A.G. Potential drop techniques for c r a c k characterisation Materials World, Vol. 3, No. 8, pp. 379-381 (Aug. 1995) AC and DC potential drop techniques can be used to characterise defects and monitor crack growth in a diverse range of applications. 58914 Yee, R.; Lambert, S.B. A reversing direct c u r r e n t potential drop system for detecting and sizing fatigue cracks along weld toes Journal of Testing and Evaluation, Vol. 23, No. 4, pp. 254-260 (Jul. 1995) Steel welded T-joints with 102 mm thick base plates were fatigue tested in three-point bending. A reversing direct current potential drop (DCPD) system was used to detect the initiation of multiple surface cracks along the transverse weld toes of these joints and to monitor the size and shape of fatigue cracks that developed from these cracks. Potential drop readings were obtained by fixed probes straddling the weld toes and normalized with respect to potential drop readings from a remote reference probe. The fixed-prohe arrangement was able to detect 0.4 mm to 1.0 mm deep surface cracks along the transverse weld toes of the T-joints. The 2D calibrations were able to predict the crack depth at the deepest points of these cracks to within + 10%.
59914 Liu, H.; Saka, M.; Abe, H.; Komura, L; Sakamoto, H. Simplified NDE of multiple cracks by means of the DC potential drop technique based on the analysis of c r a c k interactions (In Japanese, English abstract) Journal of JSNDI, Vol. 44, No. ! 1, pp. 875-881 (Nov. 1995) A method is proposed for simplified nondestructive evaluation of multiple cracks by means of the d.c. potential drop technique. Twodimensional multiple cracks are treated. First for a plate containing two cracks, a new methodology is introduced to calculate the potential drop between both sides of a crack, it is expressed as the sum of the potential
66