1、Designation: E2884 131E2884 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
2、of revision, 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 NOTESection 2 was corrected editorially in June 2104.1. Scope Scope*1.1 This guide covers the use of co
3、nformable eddy current sensor arrays for nondestructive examination of electricallyconducting materials for discontinuities and material quality. The discontinuities include surface breaking and subsurface cracksand pitting as well as near-surface and hidden-surface material loss. The material quali
4、ty includes coating thickness, electricalconductivity, magnetic permeability, surface roughness and other properties that vary with the electrical conductivity or magneticpermeability.1.2 This guide is intended for use on nonmagnetic and magnetic metals as well as composite materials with an electri
5、callyconducting component, such as reinforced carbon-carbon composite or polymer matrix composites with carbon fibers.1.3 This guide applies to planar as well as non-planar materials with and without insulating coating layers.1.4 UnitsThe values stated in SI units are to be regarded as standard. The
6、 values given in parentheses are mathematicalconversions to inch-pound units that are provided for information only and are not considered standard.1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this s
7、tandard to establish appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.6 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the
8、Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2E543 Specification for Agencies Performing Nondestructive TestingE1316 Termin
9、ology for Nondestructive ExaminationsE2338 Practice for Characterization of Coatings Using Conformable Eddy-Current Sensors without Coating ReferenceStandards2.2 ASNT Documents:3SNT-TC-1A Recommended Practice for Personnel Qualification and Certification in Nondestructive TestingANSI/ASNT-CP-189 Sta
10、ndard for Qualification and Certification of NDT Personnel2.3 AIA Standard:4NAS 410 Certification and Qualification of Nondestructive Testing Personnel2.4 Department of Defense Handbook:MIL-HDBK1823A Nondestructive Evaluation System Reliability Assessment1 This guide is under the jurisdiction of AST
11、M Committee E07 on Nondestructive Testing and is the direct responsibility of Subcommittee E07.07 on ElectromagneticMethod.Current edition approved June 1, 2013Nov. 1, 2017. Published June 2013December 2017. Originally approved in 2013. Last previous edition approved in 2013 asE288413.131. DOI: 10.1
12、520/E2884-13E01.10.1520/E2884-17.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 Available from American So
13、ciety for Nondestructive Testing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.4 Available from Aerospace Industries Association of America, Inc. (AIA), 1000 Wilson Blvd., Suite 1700, Arlington, VA 22209-3928, http:/www.aia-aerospace.org.(Replacement standar
14、d for MIL-STD-410.)This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that user
15、s consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshoh
16、ocken, PA 19428-2959. United States12.5 ISO Standards:5ISO 9712 Non-destructive TestingQualification and Certification of NDT Personnel3. Terminology3.1 DefinitionsFor definitions of terms relating to this guide refer to Terminology E1316.3.2 Definitions of Terms Specific to This Standard:3.2.1 B-Sc
17、ana method of data presentation utilizing a horizontal base line that indicates distance along the surface of amaterial and a vertical deflection that represents a measurement response for the material being examined.3.2.2 C-Scana method of data presentation which provides measurement responses for
18、the material being examined intwo-dimensions over the surface of the material.3.2.3 conformablerefers to an ability of sensors or sensor arrays to conform to non-planar surfaces without significant effectson the measurement results, or with effects that are limited to a quantifiable bound.3.2.4 dept
19、h of sensitivitydepth to which the sensor response to features or properties of interest exceeds a noise threshold.3.2.4.1 DiscussionThe depth of sensitivity is generally can be larger or smaller than the depth of penetration since it incorporates a comparisonbetween the signal obtained from a featu
20、re as well as measurement noise, whereas the depth of penetration refers to the decreasein field intensity with distance away from a test coil.3.2.5 discontinuity-containing reference standarda region of the material under examination or a material having electro-magnetic properties similar to the m
21、aterial under examination for which a discontinuity having known characteristics is present.3.2.6 discontinuity-free reference standarda region of the material under examination or a material having electromagneticproperties similar to the material under examination for which no discontinuities are
22、present.3.2.7 drive windinga conductor pattern or coil that produces a magnetic field that couples to the material being examined.3.2.7.1 DiscussionThe drive winding can have various geometries, including: 1) a simple linear conductor that is placed adjacent to a one-dimensionalarray of sensing elem
23、ents; 2) one or multiple conducting loops driven to create a complex field pattern; and 3) multiple conductingloops with a separate loop for each sensing element.3.2.8 insulating shimsconformable and substantially non-conducting or insulating foils that are used to measure effects ofsmall lift-off e
24、xcursions on sensor response.3.2.9 lift offnormal distance from the plane of the conformable sensor winding conductors to the surface of the conductingmaterial under examination.3.2.10 model for sensor responsea relation between the response of the sensor (for example, impedance magnitude and phaseo
25、r real and imaginary parts) and properties of interest (for example, electrical conductivity, magnetic permeability, lift-off, andmaterial thickness) for at least one sensing element and at least one drive winding.3.2.10.1 DiscussionThese model responses may be obtained from database tables and may
26、be analysis-based or empirical.3.2.11 sensing elementa means for measuring the magnetic field intensity or rate of change of magnetic field intensity, suchas an inductive coil or a solid-state device.3.2.11.1 DiscussionThe sensing elements can be arranged in one or two-dimensional arrays. They can p
27、rovide either an absolute signal related to themagnetic field in the vicinity of the sense element or a differential signal.3.2.12 spatial half-wavelengthspacing between the conductors of a linear drive winding with current flow in oppositedirections.5 Available from International Organization for S
28、tandardization (ISO), ISO Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,Switzerland, http:/www.iso.org.E2884 1723.2.12.1 DiscussionThis spacing affects the depth of sensitivity. The spatial wavelength equals two times this spacing. For a circular drive winding,th
29、e effective spatial half-wavelength is equal to the drive winding diameter.3.2.13 system performance verificationthe use of a measurement of one or more response values, typically physical propertyvalues, for a reference part to confirm that the response values are within specified tolerances to val
30、idate the system standardizationand verify proper instrument operation.4. Summary of Guide4.1 The examination is performed by scanning a conformable eddy current sensor array over the surface of the material ofinterest, with the sensor array energized with alternating current of one or more frequenc
31、ies. The electrical response from eachsensing element of the eddy current sensor array is modified by the proximity and local condition of the material being examined.The extent of this modification is determined by the distance between the eddy current sensor array and the material beingexamined, a
32、s well as the dimensions and electrical properties (electrical conductivity and magnetic permeability) of the material.The presence of metallurgical or mechanical discontinuities in the material alters the measured impedance of the eddy current senseelements. While scanning over the material, the po
33、sition at each measurement location should be recorded along with the responseof each sensing element in the sensor array. The measured responses and location information can then be used, typically in theform of a displayed image (C-scan (3.2.2) or in the form of a plot (B-scan (3.2.1), to determin
34、e the presence and characteristicsof material property variations or discontinuities.4.2 The eddy current sensor arrays used for the examination are flexible and, with a suitable backing layer, can conform to bothflat and curved surfaces, including fillets, cylindrical surfaces, etc. The sensor arra
35、y can have a variety of configurations. Theseinclude: 1) a linear drive conductor that is energized by the instrument alternating current and a linear array of absolute senseelements positioned parallel to the drive conductor; 2) a complex drive conductor that produces a desired field pattern at eac
36、hsensing element; and 3) individual drive conductors associated with each sensing element.Associated with each sense element areone or more measurement responses that reflect the local material condition at each location over the surface. The sensor arraysmay be used with models for the sensor respo
37、nse and appropriate algorithms to convert measured responses for each sensingelement into physical properties, such as lift-off, electrical conductivity, magnetic permeability, coating thickness, and/or substratethickness. Baseline values for these measurement responses or physical properties are us
38、ed to ensure proper operation during theexamination while local variations in one or more of these properties can be used to detect and characterize the discontinuity. Forexample, although, an impedance magnitude or other sensing element response can be used without a model to determine thepresence
39、of a flaw, a measurement of the lift-off at each sensing element location ensures that the sensor is conforming properlyto the surface. Also, a position measurement capability, such as a rolling position encoder, can be used to measure location in thescan direction and ensure that sufficient data re
40、solution is achieved. Visual or audio signaling devices may be used to indicate theposition of the discontinuity.5. Significance and Use5.1 Eddy current methods are used for nondestructively locating and characterizing discontinuities in magnetic or nonmagneticelectrically conducting materials. Conf
41、ormable eddy current sensor arrays permit examination of planar and non-planar materialsbut usually require suitable fixtures to hold the sensor array near the surface of the material of interest, such as a layer of foambehind the sensor array along with a rigid support structure.5.2 In operation, t
42、he sensor arrays are standardized with measurements in air and/or a reference part. Responses measured fromthe sensor array may be converted into physical property values, such as lift-off, electrical conductivity, and/or magneticpermeability. Proper instrument operation is verified by ensuring that
43、 these measurement responses or property values are withina prescribed range. Performance verification on reference standards with known discontinuities is performed periodically.5.3 The sensor array dimensions, including the size and number of sense elements, and the operating frequency are selecte
44、dbased on the type of examination being performed. The depth of penetration of eddy currents into the material under examinationdepends upon the frequency of the signal, the electrical conductivity and magnetic permeability of the material, and somedimensions of the sensor array. The depth of penetr
45、ation is equal to the conventional skin depth at high frequencies but is alsorelated to the sensor array dimensions at low frequencies, such as the size of the drive winding and the gap distance between thedrive winding and sense element array. For surface-breaking discontinuities on the surface adj
46、acent to the sensor array, highfrequencies should be used where the penetration depth is less than the thickness of the material under examination. For subsurfacediscontinuities or wall thickness measurements, lower frequencies and larger sensor dimensions should be used so that the depthof penetrat
47、ion is comparable to the material thickness.5.4 Insulating layers or coatings may be present between the sensor array and the surface of the electrically conducting materialunder examination. The sensitivity of a measurement to a discontinuity generally decreases as the coating thickness and/or lift
48、-offincreases. For eddy current sensor arrays having a linear drive conductor and a linear array of sense elements, the spacing betweenE2884 173the drive conductor and the array of sense elements should be smaller than or comparable to the thickness of the insulating coating.For other array formats
49、the depth of sensitivity should be verified empirically.5.5 Models for the sensor response may be used to convert responses measured from the sensor array into physical propertyvalues, such as lift-off, electrical conductivity, magnetic permeability, coating thickness, and/or substrate thickness. Fordetermining two property values, one operational frequency can be used. For nonmagnetic materials and examination for crack-likediscontinuities, the lift-off and electrical conductivity should be determined. For magnetic materials, when the electricalco
