1、Designation: E2661/E2661M 10Standard Practice forAcoustic Emission Examination of Plate-like and Flat PanelComposite Structures Used in Aerospace Applications1This standard is issued under the fixed designation E2661/E2661M; the number immediately following the designation indicates the yearof origi
2、nal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers acoustic emission (AE) examina-tion or moni
3、toring of panel and plate-like composite structuresmade entirely of fiber/polymer composites.1.2 The AE examination detects emission sources andlocates the region(s) within the composite structure where theemission originated. When properly developed AE-based cri-teria for the composite item are in
4、place, the AE data can beused for nondestructive examination (NDE), characterizationof proof testing, documentation of quality control or fordecisions relative to structural-test termination prior to comple-tion of a planned test. Other NDE methods may be used toprovide additional information about
5、located damage regions.For additional information see Appendix X1.1.3 This practice can be applied to aerospace compositepanels and plate-like elements as a part of incoming inspection,during manufacturing, after assembly, continuously (duringstructural health monitoring) and at periodic intervals d
6、uringthe life of a structure.1.4 This practice is meant for fiber orientations that includecross-plies, angle-ply laminates or two-dimensional wovenfabrics. This practice also applies to 3-D reinforcement (forexample, stitched, z-pinned) when the fiber content in the thirddirection is less than 5 %
7、(based on the whole composite).1.5 This practice is directed toward composite materials thattypically contain continuous high modulus greater than 20 GPa3 Msi fibers.1.6 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system
8、 may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is therespon
9、sibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2E543 Specification for Agencies Performing Nondestruc-tive TestingE976 Guide for Determining
10、the Reproducibility of Acous-tic Emission Sensor ResponseE1067 Practice for Acoustic Emission Examination of Fi-berglass Reinforced Plastic Resin (FRP) Tanks/VesselsE1106 Test Method for Primary Calibration of AcousticEmission SensorsE1316 Terminology for Nondestructive ExaminationsE1781 Practice fo
11、r Secondary Calibration of AcousticEmission SensorsE2533 Guide for Nondestructive Testing of Polymer MatrixComposites Used in Aerospace Applications3. Terminology3.1 DefinitionsSee Terminology E1316 for general termi-nology applicable to this practice.3.2 Definitions of Terms Specific to This Standa
12、rd:3.2.1 characteristic damage statetransverse matrix crack-ing during the virgin loading of a composite; often resulting inreaching a limit of the crack density prior to reaching failure.Results in a reduction of stiffness of the composite. Foradditional information see X1.2.3.2.2 flat panel compos
13、iteany fiber reinforced compositelay-up consisting of laminas (plies) with one or more orienta-tions with respect to some reference direction that result in atwo-dimensionally flat article of finite thickness (typicallyrelatively thin).3.2.3 plate-like compositeany fiber-reinforced compositelay-up c
14、onsisting of laminas (plies), which is not strictly flat,but for purposes of the AE examination, can be considered asa two-dimensional (2-D) structural plate for wave propagation1This practice is under the jurisdiction of ASTM Committee E07 on Nonde-structive Testing and is the direct responsibility
15、 of Subcommittee E07.04 onAcoustic Emission Method.Current edition approved June 1, 2010. Published July 2010.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the st
16、andards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.and for location of the region of AE source origin. Applies fora minimum radius of curvature of greater than about2m(6ft),so curvature d
17、oes not change group velocities.3.2.4 quasi-isotropic lay-upa plate where the group ve-locities of both the fundamental modes have been shown to beindependent of propagation direction. For example: +45/-45/0/90s3.3.2.5 wideband AE sensorswideband (broadband) AEsensors, when calibrated according to E
18、1106 or E1781, exhibitdisplacement or velocity response over several hundred kHzwith a coefficient of variation of the response in dBs that doesnot exceed 10 %.3.2.6 wideband-based (modal) AE techniquesAE tech-niques with wideband AE sensors that subject waveforms ofthe signals to combined time and
19、frequency analysis to obtainmode-based arrival times (for source location calculations) andmodal amplitudes for potential source identification. Note thatmode-based arrival times can also be obtained with resonantsensors, but only at certain experimentally determined frequen-cies.4. Summary of Pract
20、ice4.1 This practice consists of subjecting flat composite pan-els or plate-like composite structures to loading or stressingwhile monitoring with sensors that are sensitive to AE (tran-sient displacement waves) caused by the creation of micro-damage, growing flaws and friction-based sources. For ad
21、di-tional information see X1.3.4.2 This practice provides an approach to determine thelocal regions of origin of theAE sources and any potential localregions of large accumulation(s) of AE sources.4.3 This practice can provide an approach to use AE-basedcriteria to determine the significance of flaw
22、s.5. Significance and Use5.1 This AE examination is useful to detect micro-damagegeneration, accumulation and growth of new or existing flaws.The examination is also used to detect significant existingdamage from friction-based AE generated during loading orunloading of these regions. The damage mec
23、hanisms that canbe detected include matrix cracking, fiber splitting, fiberbreakage, fiber pull-out, debonding and delamination. Duringloading, unloading and load holding, damage that does not emitAE energy will not be detected.5.2 When the detected signals from AE sources are suffi-ciently spaced i
24、n time so as not to be classified as continuousAE, this practice is useful to locate the region(s) of the 2-D testsample where these sources originated and the accumulation ofthese sources with changing load and/or time.5.3 The probability of detection of the potential AE sourcesdepends on the natur
25、e of the damage mechanisms, flawcharacteristics and other aspects. For additional informationsee X1.4.5.4 Concentrated damage in fiber/polymer composites canlead to premature failure of the composite item. Hence, the useof AE to detect and locate such damage is particularlyimportant.5.5 AE-detected
26、flaws or damage concentrated in a certainregion may be further characterized by other NDE techniques(for example, visual, ultrasonic, etc.) and may be repaired asappropriate. Repair procedure recommendations and the sub-sequent examination of the repair are outside the scope of thispractice. For add
27、itional information see X1.5.5.6 This practice does not address sandwich core, foam coreor honeycomb core plate-like composites due to the fact thatcurrently there is little in the way of published work on thesubject resulting in a lack of a sufficient knowledge base.5.7 Refer to Guide E2533 for add
28、itional information abouttypes of defects detected by AE, general overview of AE asapplied to polymer matrix composites, discussion of theFelicity ratio (FR) and Kaiser effect, advantages and limita-tions, AE of composite parts other than flat panels, and safetyhazards.6. Basis of ApplicationPersonn
29、el QualificationContractual Agreement6.1 The following items are subject to contractual agree-ment between the parties using or referencing this practice.6.2 Personnel QualificationUnless contractually agreedotherwise, personnel performing examinations to this practiceshall be qualified in accordanc
30、e with a nationally or interna-tionally recognized NDT personnel qualification practice orstandard such asANSI/ASNT-CP-189, SNT-TC-1A, NAS-410,or a similar document. They shall be certified by the employeror certifying agency, as applicable. The practice or standardused and its applicable revision s
31、hall be identified in thecontractual agreement between the using parties.6.3 Qualification of Nondestructive AgenciesUnless con-tractually agreed otherwise, NDT agencies shall be qualifiedand evaluated as described in E543. The applicable edition ofE543 shall be specified in the contractual agreemen
32、t.6.4 Procedure and TechniquesThe procedures and tech-niques to be utilized shall be as specified in the contractualagreement. In particular, the contractual agreement should statewhether full monitoring of the test sample is required or if onlypartial monitoring of certain expected critical areas i
33、s required.6.5 Timing of ExaminationThe timing of examinationshall be in accordance with 1.3, unless otherwise specified.6.6 Reporting CriteriaReporting criteria for the examina-tion results shall be in accordance with Section 12, unlessotherwise specified.7. Apparatus7.1 Refer to Fig. 1 for a typic
34、al AE system block diagramshowing key components.7.2 AE Sensors:7.2.1 The selection of a wideband or resonant sensor isdescribed here. For information on the frequency content ofAEwaves see X1.6. For a scientific method to select sensors whosebest frequency response corresponds to the frequency rang
35、e ofthe highest amplitudes of the AE waves see X1.7.3Lei Wang, F.G. Yuan, “Group velocity and characteristic wave curves of Lambwaves in composites: Modeling and experiments,” Composites Science and Tech-nology 67 (2007) 13701384.E2661/E2661M 1027.2.1.1 Wideband sensors can be used along with wavefo
36、rmrecording to enhance AE data analysis by the application ofwideband-based AE techniques. A wideband sensor should bechosen with relatively flat response (E1106 or E1781) fromabout 50 kHz to 400 kHz. For additional information see X1.7for plates less than 2-mm thick and X1.8.7.2.1.2 If resonant sen
37、sors are used, the best choice is asensor with its primary resonance in the lower portion of a 50kHz to 400 kHz frequency band. Sensors with a lowerfrequency resonance of about 25 kHz to 50 kHz can be used toincrease sensor spacing (for example when a limited number ofAE channels are available see E
38、1067) in AE testing ofcomposites, but such sensors increase the likelihood thatunwanted extraneous noise will be recorded. To minimize theeffects of airborne noise the lower resonant-frequency sensorscan be wrapped with sound absorbing material.7.2.2 Sensors should be shielded against electromagneti
39、cinterference (EMI) through proper design practice or differen-tial (anti-coincidence) element design, or both.7.2.3 Sensors should have omni-directional response, withdirectional variations not exceeding 4 dB from the averagepeak response of the set of sensors.7.3 Sensor Couplant:7.3.1 The sensors
40、must be acoustically coupled (to removeair from between the sensor face and the composite surface)directly to the test sample. Commercially available couplantsfor ultrasonic flaw detection may be used. Silicone-basedhigh-vacuum grease has been found to be particularly suitable,but it may not be desi
41、rable for all test locations and all testsamples. Adhesives may also be used. Note: the sensorattachment procedure as well as the couplant or adhesive mayrequire approval prior to sensor installation due to specialrequirements for materials placed in contact with compositestructures (compatibility a
42、nd/or contamination control).7.3.2 Couplant selection should be made to minimizechanges (for example, drying out of the couplant or movementof the couplant due to gravity over the range of test tempera-tures and test time duration) in coupling sensitivity during acomplete examination.7.4 Sensor Atta
43、chment Apparatus:7.4.1 AdhesivesVarious adhesives can be used to attachsensors and provide acoustic coupling. The bond line createdby the adhesive must be much thinner than the shortestwavelengths of interest. Adhesives such as two-part epoxies,silicone adhesives, and cyanoacrylates have been succes
44、sfullyused for attaching sensors. Sensors attached with some adhe-sives can be difficult to remove without damaging the sensor orthe examination sample. Also, due to the larger design defor-mations of composite materials (relative to metals designed tooperate in their elastic range), adhesively bond
45、ed sensors maydebond during test sample stressing or during thermal cyclingof the test sample.7.4.2 TapeElastic adhesive tapes have been successfullyused for mounting transducers (for example, taping the sensorsto one side of a large composite panel).7.4.3 Elastic BandsAn elastic band (for example,
46、rubberbands) can be placed over the sensor and anchored to the testsample to hold sensors in place.7.4.4 Spring LoadedSensors may be spring loadedagainst the test sample by fixturing (that does not generateextraneous noise during testing). Such mounting must be ableFIG. 1 AE System Block DiagramE266
47、1/E2661M 103to accommodate the deformation of the test sample withoutlosing acoustic coupling.7.4.5 It is generally unacceptable to modify a composite bymachining a “flat” to mount a sensor (creates potential dam-age). Thus, with surfaces that are rough, or have curvature, orboth, it is typical that
48、 the sensors will have less sensitivity thanwhen they are mounted on flat and smooth surfaces.7.4.6 This practice does not address the use of waveguidesfor fiber/polymer composites.7.5 System Cabling:7.5.1 Sensor CableAE systems typically use a standardlow noise shielded coaxial cable that is not su
49、sceptible totriboelectric noise (from mechanical movement of the cable)for this connection, due to its ability to shield the low levelsignal out of the sensor from electromagnetic interference. Thecable should be kept short, 1-2 m 3-6 ft, to reduce attenuationof the signal, to reduce the length of cable possibly exposed toelectromagnetic interference and to create the best signal-to-noise ratios. If it is absolutely necessary to use a longer lengthduring testing, the effect of the longer length on the attenuationof signal amplitudes should be evaluated (f
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