1、Designation: E 1495 02 (Reapproved 2007)Standard Guide forAcousto-Ultrasonic Assessment of Composites, Laminates,and Bonded Joints1This standard is issued under the fixed designation E 1495; the number immediately following the designation indicates the year oforiginal adoption or, in the case of re
2、vision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This guide explains the rationale and basic technologyfor the acousto-ultrasonic (AU) method. Gui
3、delines are givenfor nondestructive evaluation (NDE) of flaws and physicalcharacteristics that influence the mechanical properties andrelative strength of composite structures (for example,filament-wound pressure vessels), adhesive bonds (for ex-ample, joints between metal plates), and interlaminar
4、andfiber/matrix bonds in man-made composites and natural com-posites (for example, wood products).1.2 This guide covers technical details and rules that mustbe observed to ensure reliable and reproducible quantitativeAU assessments of laminates, composites, and bonded struc-tures. The underlying pri
5、nciples, prototype apparatus, instru-mentation, standardization, examination methods, and dataanalysis for such assessments are covered. Limitations of theAU method and guidelines for taking advantage of its capa-bilities are cited.1.3 The objective of AU is to assess subtle flaws andassociated stre
6、ngth variations in composite structures andbonded joints. Discontinuities such as large voids, disbonds, orextended lack of contact at interfaces can be assessed by otherNDE methods such as conventional ultrasonics.1.4 Additional information may be found in the publicationscited in the list of refer
7、ences at the end of this guide. Thereferenced works provide background on research, applica-tions, and various aspects of signal acquisition, processing, andinterpretation.1.5 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.6
8、 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 and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Docu
9、ments2.1 ASTM Standards:2E 543 Specification for Agencies Performing Nondestruc-tive TestingE 1316 Terminology for Nondestructive Examinations2.2 ASNT Standard:3ANSI/ASNT CP-189 Standard for Qualification and Certi-fication of Nondestructive Testing PersonnelSNT-TC-1A Recommended Practicem for Perso
10、nnel Quali-fications and Certification in Nondestructive Testing2.3 AIA Document:4NAS-410 Certification and Qualification of NondestructiveTesting Personnel3. Terminology3.1 Definitions:3.1.1 acousto-ultrasonics (AU)a nondestructive examina-tion method that uses induced stress waves to detect and as
11、sessthe diffuse defect states, damage conditions, and variations ofmechanical properties of an examination structure. The AUmethod combines aspects of acoustic emission (AE) signalanalysis with ultrasonic materials characterization methods(Terminology E 1316).3.1.2 Additional related definitions may
12、 be found in Termi-nology E 1316.3.2 Definitions of Terms Specific to This Standard:3.2.1 stress wave factor (SWF)a generic measure of therelative energy loss (attenuation) or propagation efficiency ofstress waves generated by the AU method. There are many1This guide is under the jurisdiction of AST
13、M Committee E07 on Nondestruc-tive Testing and is the direct responsibility of Subcommittee E07.04 on AcousticEmission Method.Current edition approved July 1, 2007. Published July 2007. Originally approvedin 1992. Last previous edition approved in 2002 as E 1495 - 02.2For referenced ASTM standards,
14、visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available fromAmerican Society for Nondestructive Testing (ASNT), P.O. Box28518, 1711 Arling
15、ate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.4Available from Aerospace Industries Association of America, Inc. (AIA), 1000Wilson Blvd., Suite 1700,Arlington, VA22209-3928, http:/www.aia-aerospace.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 194
16、28-2959, United States.ways to define and calculate the SWF. Several of these aredescribed in Section 11 of this guide.4. Summary of Guide4.1 GeneralTwo probes are attached to a sample in asend-receive configuration. One (a pulsed sending probe) isoptimized for wave generation, while the other (a re
17、ceivingprobe) is optimized for signal sensing. The probes are attachedto the sample surface at normal incidence. The usual, and oftenmost practical, configuration has piezoelectric probes, a senderand receiver, on the same side of the examination part (1).5Measurements are performed by allowing ultr
18、asonic stresswaves to interact with a volume of material between theprobes. The waves are modified by the material microstructureand morphology (2).4.2 PrincipleThe AU method measures the relative effi-ciency of stress wave propagation in a material. The dominantattribute measured is stress wave att
19、enuation. Lower attenua-tion, a high SWF value, means better stress wave energytransmission for many composites and, therefore, better trans-mission and redistribution of dynamic strain energy. Moreefficient strain energy transfer and strain redistribution duringloading or impact corresponds to incr
20、eased strength andfracture resistance in composite structures and adhesive bonds.A lower SWF usually indicates regions in which strain energyis likely to concentrate and result in crack growth and fracture(3).4.3 Structure Configuration EffectsIn monolithic platesand homogeneous composite slabs, the
21、 SWF will exhibit signalattenuation effects due to variations in microstructure, mor-phology, porosity, cure state, microcrack populations, etc. (4).A lower SWF typically corresponds to regions of higherattenuation. In laminated structures or bonded joints, however,interfaces and bondlines can produ
22、ce either lower or higherSWF values, depending on the bond quality (5). Delaminatedregions can produce higher SWF values because more energyis reflected or channeled to the receiving probe.4.4 In-Plane MeasurementsOffsetting probes enables thecollection of stress wave reverberations that have travel
23、edin-plane from sender to receiver. It is therefore possible tomeasure in-plane, mechanical property variations in principalload directions in fiber-reinforced laminates or adhesivelybonded joints (that is, properties such as interlaminar shearstrength and adhesive bond strength).4.5 Signal Collecti
24、on CriterionWith the AU method,instead of singling out specific echoes, all of the multiplereverberations, including signals from internal reflectors andscatterers, are collected and analyzed together. Even withpulse-echo or through-transmission configurations, all stresswave reflections and reverbe
25、rations in a local volume ofmaterial are collected and evaluated, as in backscatter,forward-scatter, and diffuse field analysis.4.6 Wavelength CriterionIn composite panels or bondedplates, the sender should produce wavelengths that are com-parable to or less than the panel or plate thickness. Suitab
26、lewavelengths are those passed by the examination piece atfrequencies equal to or greater than the sending probe centerfrequencies.5. Significance and Use5.1 GeneralConventional ultrasonics should be consid-ered first for the detection of overt flaws such as delaminationsin composites. Thereafter, A
27、U should be considered for com-posites that are proved to be free of major flaws or disconti-nuities. The AU method is intended almost exclusively forassessing the collective effects of dispersed defects and sub-critical flaw populations. These are material aberrations thatinfluence AU measurements
28、and also underlie mechanicalproperty variations, dynamic load response, and impact andfracture resistance.5.2 Specific AdvantagesThe AU method can be used toevaluate composite laminate and bond quality using access toonly one surface as, for example, the exterior surface ofpressure vessels. It is un
29、necessary to utilize angle beam fixturesbecause the method can always be applied with probes atnormal incidence. The method can be applied using drycoupling with elastomer pads attached to the probes, and thereis no need to immerse the examination object in water.5.3 General ApplicationsThe AU metho
30、d was devised toassess diffuse discontinuity populations and any associatedchanges of the mechanical properties of composites andcomposite-like materials. The AU method has been used toevaluate fiber-reinforced composites (6), composite laminates(7), filament-wound pressure vessels (8), adhesive bon
31、ds (9),paper and wood products (10), and cable and rope (11). Themethod has been shown to be particularly practical for assess-ing the strength of adhesively bonded joints. It has also beenshown to be useful for assessing microporosity (12), micro-cracking (13), hydrothermal aging (14), and damage p
32、roducedby impacts (15) and fatigue (16).6. Basis of Application6.1 Personnel Qualification6.1.1 If specified in the contractual agreement, personnelperforming examinations to this standard shall be qualified inaccordance with a nationally recognized NDT personnel quali-fication practice or standard
33、such as ANSI/ASNT CP-189,SNT-TC-1A, NAS-410, or a similar document and certified bythe employer or certifying agency, as applicable. The practiceor standard used and its applicable revision shall be identifiedin the contractual agreement between the using parties.6.2 Qualification of Nondestructive
34、Agencies6.2.1 If specified in the contractual agreement, NDT agen-cies shall be qualified and evaluated as described in PracticeE 543. The applicable edition of Practice E 543 shall bespecified in the contractual agreement.6.3 Proper application of the AU method requires theinvolvement of an NDE spe
35、cialist to plan and guide theexamination procedure. Knowledge of the principles of ultra-sonic examination is required. Personnel applying AU shouldbe experienced practitioners of conventional ultrasonic andacoustic emission examination and associated methods forsignal acquisition, processing, and i
36、nterpretation.5The boldface numbers in parentheses refer to the list of references at the end ofthis guide.E 1495 02 (2007)26.4 Particular emphasis should be placed on personnelhaving proficiency in computer signal processing and the useof digital methods for time and frequency domain signalanalysis
37、. Familiarity with ultrasonic spectrum analysis usingdigital Fourier transforms is mandatory. Spectral distribution,multiple regression, and pattern recognition analyses andadaptive learning procedures are important.6.5 Application of the AU method also requires proficiencyin developing and designin
38、g reference standards. The develop-ment of reference standards is needed for each type of materialand configuration to be examined. Because AU measurementsare relative and comparative, experimental examinations con-firmed by destructive testing are needed to avoid ambiguities inthe interpretation of
39、 results.7. Limitations7.1 GeneralThe AU method possesses the limitationscommon to all ultrasonic methods that attempt to measureeither absolute or relative attenuation. When instrument set-tings and probe configurations are optimized for AU, they areunsuitable for conventional ultrasonic flaw detec
40、tion.7.2 Signal Reproducibility FactorsTheAU results may beaffected adversely by the following factors: (1) improperselection of type and amount of couplant, (2) couplant thick-ness variations and bubbles, (3) specimen surface roughnessand texture, (4) probe misalignment and insufficient pressure,(5
41、) probe resonances and insufficient damping, and (6) insuf-ficient instrument bandwidth.8. Standardization8.1 Self-StandardizationThe sender and receiver probescan be used to verify each other. Deficiencies in the instrumen-tation and probe response become evident by comparing theresults with the st
42、andard waveforms established previously fora reference item. Commercial ultrasonic probes andAE sensorsrespond to deformation (stress) waves in a complex fashionthat involves both normal and in-plane displacements of theexamination sample surface. Although it is possible to stan-dardize such probes
43、in an absolute sense, even sensors of thesame design and specification should be treated as unique anddefinitely noninterchangeable.8.2 Stress Wave Factor NormalizationRegardless of howthe SWF is defined, it is practical to normalize it relative tosome standard value, for example, the maximum value
44、foundfor the optimum condition of a representative material sampleor structure. This is appropriate where many nominally iden-tical articles will be examined.8.3 Reference StandardsNormalization of the SWF is thefirst step toward establishing a reference standard. The secondstep is to fabricate a se
45、t of samples exhibiting the full range ofexpected material conditions and flaw states. One of thesesamples should represent the optimum condition of the mate-rial. This procedure should be followed by the development ofbenchmark structures that can be used as comparative stan-dards.9. System Configu
46、ration9.1 Standard ConfigurationFour possible AU probe con-figurations are shown in Fig. 1. With the probes on the sameside of a panel, examination proceeds by holding the probes ina fixture and moving them as a unit to cover the examined area.For zero offset between probes, the configuration reduce
47、s toeither the pulse-echo or through-transmission mode, as shownin Fig. 1 (b) and (d) respectively. The prototype apparatusdepicted in Fig. 2 illustrates the essential features of a standardconfiguration.9.2 ProbesTwo classes of piezoelectric probes are appro-priate: (1) resonant and non-resonant AE
48、 sensors, and (2)damped broadband ultrasonic probes. Resonant AE sensorshave more sensitivity, but the signals transmitted by the testpiece may be of sufficient strength such that sensitivity is not aproblem. One reason for avoiding resonant sensors is that theyFIG. 1 Four Possible AU Probe Configur
49、ationsE 1495 02 (2007)3have ringdown characteristics that may be difficult to separatefrom the multiple reflections transmitted by the examinationsample.9.2.1 Probe BandwidthNon-resonant AE sensors have aflatter frequency response curve than resonant sensors. Thisresponse characteristic should be exploited in AU because itwould render a truer signal over a wider bandwidth. Anotherapproach is to use the bandwidth response of damped broad-band ultrasonic probes. Good results can be obtained withbroadband ultrasonic probes working as both senders andreceivers. For m
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