1、Designation: E2884 17Standard Guide forEddy Current Testing of Electrically Conducting MaterialsUsing Conformable Sensor Arrays1This standard is issued under the fixed designation E2884; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revisi
2、on, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This guide covers the use of conformable eddy currentsensor arrays for nondestructive examination of
3、electricallyconducting materials for discontinuities and material quality.The discontinuities include surface breaking and subsurfacecracks and pitting as well as near-surface and hidden-surfacematerial loss. The material quality includes coating thickness,electrical conductivity, magnetic permeabil
4、ity, surface rough-ness and other properties that vary with the electrical conduc-tivity or magnetic permeability.1.2 This guide is intended for use on nonmagnetic andmagnetic metals as well as composite materials with anelectrically conducting component, such as reinforced carbon-carbon composite o
5、r polymer matrix composites with carbonfibers.1.3 This guide applies to planar as well as non-planarmaterials with and without insulating coating layers.1.4 UnitsThe values stated in SI units are to be regardedas standard. The values given in parentheses are mathematicalconversions to inch-pound uni
6、ts that are provided for informa-tion only and are not considered standard.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practi
7、ces and deter-mine the applicability of regulatory limitations prior to use.1.6 This international standard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and
8、Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E543 Specification for Agencies Performing NondestructiveTestingE1316 Terminology for Nondestructive Examinations2.2 ASNT Documents:3SNT-TC-1A Recommended Pra
9、ctice for Personnel Qualifi-cation and Certification in Nondestructive TestingANSI/ASNT-CP-189 Standard for Qualification and Certifi-cation of NDT Personnel2.3 AIA Standard:4NAS 410 Certification and Qualification of NondestructiveTesting Personnel2.4 Department of Defense Handbook:MIL-HDBK1823A No
10、ndestructive Evaluation System Re-liability Assessment2.5 ISO Standards:5ISO 9712 Non-destructive TestingQualification and Cer-tification of NDT Personnel3. Terminology3.1 DefinitionsFor definitions of terms relating to thisguide refer to Terminology E1316.3.2 Definitions of Terms Specific to This S
11、tandard:3.2.1 B-Scana method of data presentation utilizing ahorizontal base line that indicates distance along the surface ofa material and a vertical deflection that represents a measure-ment response for the material being examined.3.2.2 C-Scana method of data presentation which pro-vides measure
12、ment responses for the material being examinedin two-dimensions over the surface of the material.1This guide is under the jurisdiction of ASTM Committee E07 on Nondestruc-tive Testing and is the direct responsibility of Subcommittee E07.07 on Electro-magnetic Method.Current edition approved Nov. 1,
13、2017. Published December 2017. Originallyapproved in 2013. Last previous edition approved in 2013 as E2884131. DOI:10.1520/E2884-17.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume inform
14、ation, refer to the standards Document Summary page onthe ASTM website.3Available fromAmerican Society for Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.4Available from Aerospace Industries Association of America, Inc. (AIA), 1000Wilson
15、 Blvd., Suite 1700,Arlington, VA22209-3928, http:/www.aia-aerospace.org.(Replacement standard for MIL-STD-410.)5Available from International Organization for Standardization (ISO), ISOCentral Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,Geneva, Switzerland, http:/www.iso.org.*A
16、 Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization establ
17、ished in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.13.2.3 conformablerefers to an ability of sensors or sensorarrays to conform to non-planar surfaces without
18、 significanteffects on the measurement results, or with effects that arelimited to a quantifiable bound.3.2.4 depth of sensitivitydepth to which the sensor re-sponse to features or properties of interest exceeds a noisethreshold.3.2.4.1 DiscussionThe depth of sensitivity can be largeror smaller than
19、 the depth of penetration since it incorporates acomparison between the signal obtained from a feature as wellas measurement noise, whereas the depth of penetration refersto the decrease in field intensity with distance away from a testcoil.3.2.5 discontinuity-containing reference standarda regionof
20、 the material under examination or a material having elec-tromagnetic properties similar to the material under examina-tion for which a discontinuity having known characteristics ispresent.3.2.6 discontinuity-free reference standarda region of thematerial under examination or a material having elect
21、romag-netic properties similar to the material under examination forwhich no discontinuities are present.3.2.7 drive windinga conductor pattern or coil that pro-duces a magnetic field that couples to the material beingexamined.3.2.7.1 DiscussionThe drive winding can have variousgeometries, including
22、: 1) a simple linear conductor that isplaced adjacent to a one-dimensional array of sensing ele-ments; 2) one or multiple conducting loops driven to create acomplex field pattern; and 3) multiple conducting loops with aseparate loop for each sensing element.3.2.8 insulating shimsconformable and subs
23、tantially non-conducting or insulating foils that are used to measure effectsof small lift-off excursions on sensor response.3.2.9 lift offnormal distance from the plane of the con-formable sensor winding conductors to the surface of theconducting material under examination.3.2.10 model for sensor r
24、esponsea relation between theresponse of the sensor (for example, impedance magnitude andphase or real and imaginary parts) and properties of interest(for example, electrical conductivity, magnetic permeability,lift-off, and material thickness) for at least one sensing elementand at least one drive
25、winding.3.2.10.1 DiscussionThese model responses may be ob-tained from database tables and may be analysis-based orempirical.3.2.11 sensing elementa means for measuring the mag-netic field intensity or rate of change of magnetic fieldintensity, such as an inductive coil or a solid-state device.3.2.1
26、1.1 DiscussionThe sensing elements can be arrangedin one or two-dimensional arrays. They can provide either anabsolute signal related to the magnetic field in the vicinity ofthe sense element or a differential signal.3.2.12 spatial half-wavelengthspacing between the con-ductors of a linear drive win
27、ding with current flow in oppositedirections.3.2.12.1 DiscussionThis spacing affects the depth of sen-sitivity. The spatial wavelength equals two times this spacing.For a circular drive winding, the effective spatial half-wavelength is equal to the drive winding diameter.3.2.13 system performance ve
28、rificationthe use of a mea-surement of one or more response values, typically physicalproperty values, for a reference part to confirm that theresponse values are within specified tolerances to validate thesystem standardization and verify proper instrument operation.4. Summary of Guide4.1 The exami
29、nation is performed by scanning a conform-able eddy current sensor array over the surface of the materialof interest, with the sensor array energized with alternatingcurrent of one or more frequencies. The electrical responsefrom each sensing element of the eddy current sensor array ismodified by th
30、e proximity and local condition of the materialbeing examined. The extent of this modification is determinedby the distance between the eddy current sensor array and thematerial being examined, as well as the dimensions andelectrical properties (electrical conductivity and magnetic per-meability) of
31、 the material. The presence of metallurgical ormechanical discontinuities in the material alters the measuredimpedance of the eddy current sense elements. While scanningover the material, the position at each measurement locationshould be recorded along with the response of each sensingelement in th
32、e sensor array. The measured responses andlocation information can then be used, typically in the form ofa displayed image (C-scan (3.2.2) or in the form of a plot(B-scan (3.2.1), to determine the presence and characteristicsof material property variations or discontinuities.4.2 The eddy current sen
33、sor arrays used for the examinationare flexible and, with a suitable backing layer, can conform toboth flat and curved surfaces, including fillets, cylindricalsurfaces, etc. The sensor array can have a variety of configu-rations. These include: 1) a linear drive conductor that isenergized by the ins
34、trument alternating current and a lineararray of absolute sense elements positioned parallel to the driveconductor; 2) a complex drive conductor that produces adesired field pattern at each sensing element; and 3) individualdrive conductors associated with each sensing element. Asso-ciated with each
35、 sense element are one or more measurementresponses that reflect the local material condition at eachlocation over the surface. The sensor arrays may be used withmodels for the sensor response and appropriate algorithms toconvert measured responses for each sensing element intophysical properties, s
36、uch as lift-off, electrical conductivity,magnetic permeability, coating thickness, and/or substratethickness. Baseline values for these measurement responses orphysical properties are used to ensure proper operation duringthe examination while local variations in one or more of theseproperties can b
37、e used to detect and characterize the disconti-nuity. For example, although, an impedance magnitude or othersensing element response can be used without a model todetermine the presence of a flaw, a measurement of the lift-offat each sensing element location ensures that the sensor isconforming prop
38、erly to the surface. Also, a position measure-ment capability, such as a rolling position encoder, can be usedE2884 172to measure location in the scan direction and ensure thatsufficient data resolution is achieved. Visual or audio signalingdevices may be used to indicate the position of the discont
39、i-nuity.5. Significance and Use5.1 Eddy current methods are used for nondestructivelylocating and characterizing discontinuities in magnetic ornonmagnetic electrically conducting materials. Conformableeddy current sensor arrays permit examination of planar andnon-planar materials but usually require
40、 suitable fixtures tohold the sensor array near the surface of the material ofinterest, such as a layer of foam behind the sensor array alongwith a rigid support structure.5.2 In operation, the sensor arrays are standardized withmeasurements in air and/or a reference part. Responses mea-sured from t
41、he sensor array may be converted into physicalproperty values, such as lift-off, electrical conductivity, and/ormagnetic permeability. Proper instrument operation is verifiedby ensuring that these measurement responses or propertyvalues are within a prescribed range. Performance verificationon refer
42、ence standards with known discontinuities is performedperiodically.5.3 The sensor array dimensions, including the size andnumber of sense elements, and the operating frequency areselected based on the type of examination being performed.The depth of penetration of eddy currents into the materialunde
43、r examination depends upon the frequency of the signal,the electrical conductivity and magnetic permeability of thematerial, and some dimensions of the sensor array. The depthof penetration is equal to the conventional skin depth at highfrequencies but is also related to the sensor array dimensions
44、atlow frequencies, such as the size of the drive winding and thegap distance between the drive winding and sense elementarray. For surface-breaking discontinuities on the surfaceadjacent to the sensor array, high frequencies should be usedwhere the penetration depth is less than the thickness of the
45、material under examination. For subsurface discontinuities orwall thickness measurements, lower frequencies and largersensor dimensions should be used so that the depth ofpenetration is comparable to the material thickness.5.4 Insulating layers or coatings may be present between thesensor array and
46、the surface of the electrically conductingmaterial under examination. The sensitivity of a measurementto a discontinuity generally decreases as the coating thicknessand/or lift-off increases. For eddy current sensor arrays havinga linear drive conductor and a linear array of sense elements,the spaci
47、ng between the drive conductor and the array of senseelements should be smaller than or comparable to the thicknessof the insulating coating. For other array formats the depth ofsensitivity should be verified empirically.5.5 Models for the sensor response may be used to convertresponses measured fro
48、m the sensor array into physical prop-erty values, such as lift-off, electrical conductivity, magneticpermeability, coating thickness, and/or substrate thickness. Fordetermining two property values, one operational frequencycan be used. For nonmagnetic materials and examination forcrack-like discont
49、inuities, the lift-off and electrical conductiv-ity should be determined. For magnetic materials, when theelectrical conductivity can be measured or assumed constant,then the lift-off and magnetic permeability should be deter-mined. The thickness can only be determined if a sufficientlylow excitation frequency is used where the depth of sensitivityis greater than the material thickness of interest. For determin-ing more than two property values, measurements at operatingconditions having at least two depths of penetration should beused; these dif
