1、Designation: C 1332 01 (Reapproved 2007)Standard Test Method forMeasurement of Ultrasonic Attenuation Coefficients ofAdvanced Ceramics by Pulse-Echo Contact Technique1This standard is issued under the fixed designation C 1332; the number immediately following the designation indicates the year ofori
2、ginal adoption or, in the case of revision, 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 test method describes a procedure for measurementof ultr
3、asonic attenuation coefficients for advanced structuralceramic materials. The procedure is based on a broadbandbuffered piezoelectric probe used in the pulse-echo contactmode and emitting either longitudinal or shear waves. Theprimary objective of this test method is materials characteriza-tion.1.2
4、The procedure requires coupling an ultrasonic probe tothe surface of a plate-like sample and the recovery of succes-sive front surface and back surface echoes. Power spectra ofthe echoes are used to calculate the attenuation spectrum(attenuation coefficient as a function of ultrasonic frequency)for
5、the sample material. The transducer bandwidth and spectralresponse are selected to cover a range of frequencies andcorresponding wavelengths that interact with microstructuralfeatures of interest in solid test samples.1.3 The purpose of this test method is to establish funda-mental procedures for me
6、asurement of ultrasonic attenuationcoefficients. These measurements should distinguish and quan-tify microstructural differences among solid samples andtherefore help establish a reference database for comparingmaterials and calibrating ultrasonic attenuation measurementequipment.1.4 This test metho
7、d applies to monolithic ceramics and alsopolycrystalline metals. This test method may be applied towhisker reinforced ceramics, particulate toughened ceramics,and ceramic composites provided that similar constraints onsample size, shape, and finish are met as described herein formonolithic ceramics.
8、1.5 This test method sets forth the constraints on samplesize, shape, and finish that will assure valid attenuationcoefficient measurements. This test method also describes theinstrumentation, methods, and data processing procedures foraccomplishing the measurements.1.6 This test method is not recom
9、mended for highly attenu-ating materials such as very thick, very porous, rough-surfacedmonolithics or composites. This test method is not recom-mended for highly nonuniform, heterogeneous, cracked, defec-tive, or otherwise flaw-ridden samples that are unrepresentativeof the nature or inherent chara
10、cteristics of the material underexamination.1.7 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 regulat
11、ory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 1331 Test Method for Measuring Ultrasonic Velocity inAdvanced Ceramics with Broadband Pulse-Echo Cross-Correlation MethodE 664 Practice for the Measurement of theApparentAttenu-ation of Longitudinal Ultrasonic Waves by Immersi
12、onMethodE 1316 Terminology for Nondestructive ExaminationsE 1495 Guide for Acousto-Ultrasonic Assessment of Com-posites, Laminates, and Bonded Joints2.2 ASNT Document:Recommended Practice SNT-TC-1A for NondestructiveTesting Personnel Qualification and Certification32.3 Military Standard:MIL-STD-410
13、Nondestructive Testing Personnel Qualifica-tion and Certification42.4 Additional references are cited in the text and at end ofthis test method.3. Terminology3.1 Definitions of Terms Specific to This Standard:1This test method is under the jurisdiction of ASTM Committee C28 onAdvanced Ceramics and i
14、s the direct responsibility of Subcommittee C28.03 onPhysical Properties and Performance.Current edition approved Aug. 1, 2007. Published August 2007. Originallyapproved in 1996. Last previous edition approved in 2001 as C 133201.2For referenced ASTM standards, visit the ASTM website, www.astm.org,
15、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 NondestructiveTesting (ASNT), P.O. Box28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:
16、/www.asnt.org.4Available from Standardization Documents Order Desk, DODSSP, Bldg. 4,Section D, 700 Robbins Ave., Philadelphia, PA 19111-5098, http:/www.dodssp.daps.mil.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.1 acoustic im
17、pedance (Z)a property (1)5defined by amaterials density, p, and the velocity of sound within it, v,where Z = rv.3.1.2 attenuation coeffcient (a)decrease in ultrasoundintensity with distance expressed in nepers (Np) per unitlength, herein, a = ln(I0/ I)/d, where a is attenuationcoefficient, d is path
18、 length or distance, I0is original intensityand I is attenuated intensity (2).3.1.3 attenuation spectrumthe attenuation coefficient, a,expressed as a function of ultrasonic frequency, f, or plotted asa versus f, over a range of ultrasonic frequencies within thebandwidth of the transducer and associa
19、ted pulser-receiverinstrumentation.3.1.4 back surfacethe surface of a test sample which isopposite to the front surface and from which back surfaceechoes are returned at normal incidence directly to the trans-ducer.3.1.5 bandwidththe frequency range of an ultrasonicprobe, defined by convention as th
20、e difference between thelower and upper frequencies at which the signal amplitude is 6dB down from the frequency at which maximum signalamplitude occurs. The frequency at which the maximumoccurs is termed the center frequency of the probe or trans-ducer.3.1.6 broadband transduceran ultrasonic transd
21、ucer ca-pable of sending and receiving undistorted signals over a broadbandwidth, consisting of thin damped piezoelectric crystal in abuffered probe (search unit).3.1.7 buffered probean ultrasonic search unit as defined inTerminology E 1316 but containing a delay line or buffer rod towhich the piezo
22、element, that is, transducer consisting of apiezoelectric crystal, is affixed. The buffer rod separates thepiezoelement from the test sample (see Fig. 1).3.1.8 buffer rodan integral part of a buffered probe orsearch unit, usually a quartz or fused silica cylinder thatprovides a time delay between th
23、e excitation pulse from thepiezoelement and echoes returning from a sample coupled tothe free end of the buffer rod.3.1.9 free surfacethe back surface of a solid test sampleinterfaced with a very low density medium, usually air or othergas, to assure that the back surface reflection coefficient equa
24、ls1 to a high degree of precision.3.1.10 frequency (f)number of oscillations per second ofultrasonic waves, measured in megahertz, MHz, herein.3.1.11 front surfacethe surface of a test sample to whichthe buffer rod is coupled at normal incidence (designated as testsurface in Terminology E 1316).3.1.
25、12 inherent attenuationultrasound energy loss in asolid as a result of scattering, diffusion, and absorption. Thisstandard assumes that the dominant inherent losses are due toRayleigh and stochastic scattering (2) by the material micro-structure, for example, by grains, grain boundaries, and mi-crop
26、ores. Measured ultrasound energy loss which, if notcorrected, may include losses due to diffraction, individualmacroflaws, surface roughness, couplant variations, and trans-ducer defects.3.1.13 reflection coeffcient (R)measure of relative inten-sity of sound waves reflected back into a material at a
27、ninterface, defined in terms of the acoustic impedance of thematerial in which the sound wave originates (Z0) and theacoustic impedance of the material interfaced with it (Zi),where R =(Zi Z0)/(Zi+ Z0)2.3.1.14 test sample a solid coupon or material part thatmeets the constraints needed to make the a
28、ttenuation coeffi-cient measurements described herein, that is, a test sample orpart having flat, parallel, smooth, preferably ground/polishedopposing (front and back) surfaces and having no discreteflaws or anomalies that are unrepresentative of the inherentproperties of the material.3.1.15 transmi
29、ssion coeffcient (T)measure of relative in-tensity of sound waves transmitted through an interface,defined in terms of the acoustic impedance of the material inwhich the sound wave originates (Z0) and the acoustic imped-ance of the material interfaced with it ( Zi), where T =(4ZiZ0)/(Zi+ Z0)2so that
30、 R + T =1.3.1.16 wavelength (l)distance that sound (of a particularfrequency) travels during one period (during one oscillation), l= v/f, where v is the velocity of sound in the material andwhere velocity is measured in cm/s, and wavelength in cm,herein.3.2 Other terms used in this test method are d
31、efined inTerminology E 1316.4. Summary of Test Method4.1 This test method describes a procedure for determininga materials inherent attenuation coefficient and attenuationspectrum by means of a buffered broadband probe operating inthe pulse-echo contact mode on a solid sample that has smooth,flat, p
32、arallel surfaces.4.2 The procedure described in this test method involvesdigital acquisition and computer processing of ultrasonic echowaveforms returned by the test sample. Test sample con-straints, probing methods, data validity criteria, and measure-ment corrections are prescribed herein.5. Signi
33、ficance and Use5.1 This test method is useful for characterizing materialmicrostructure or measuring variations in microstructure thatoccur because of material processing conditions and thermal,mechanical, or chemical exposure (3). When applied to mono-lithic or composite ceramics, the procedure sho
34、uld reveal5The boldface numbers in parentheses refer to a list of references at the end ofthis standard.FIG. 1 Cross Section of Buffered Broadband Ultrasonic ProbeC 1332 01 (2007)2microstructural gradients due to density, porosity, and grainvariations. This test method may also be applied to polycry
35、s-talline metals to assess variations in grain size, porosity, andmultiphase constituents.5.2 This test method is useful for measuring and comparingmicrostructural variations among different samples of the samematerial or for sensing and measuring subtle microstructuralvariations within a given samp
36、le.5.3 This test method is useful for mapping variations in theattenuation coefficient and the attenuation spectrum as theypertain to variations in the microstructure and associatedproperties of monolithic ceramics, ceramic composites andmetals.5.4 This test method is useful for establishing a refer
37、encedatabase for comparing materials and for calibrating ultrasonicattenuation measurement equipment.5.5 This test method is not recommended for highly attenu-ating monolithics or composites that are thick, highly porous,or that have rough or highly textured surfaces. For thesematerials Practice E 6
38、64 may be appropriate. Guide E 1495 isrecommended for assessing attenuation differences amongcomposite plates and laminates that may exhibit, for example,pervasive matrix porosity or matrix crazing in addition tohaving complex fiber architectures or thermomechanical deg-radation (3). The proposed AS
39、TM Standard Test Method forMeasuring Ultrasonic Velocity in Advanced Ceramics(C 1331) is recommended for characterizing monolithic ceram-ics with significant porosity or porosity variations (4).6. Personnel Qualifications6.1 It is recommended that nondestructive evaluation/examination personnel appl
40、ying this test method be qualified inaccordance with a nationally recognized personnel qualifica-tion practice or standard such asASNT SNT-TC-1A, MILSTD410, or a similar document. The qualification practice orstandard used and its applicable revision(s) should be specifiedin a contractual agreement.
41、6.2 Knowledge of the principles of ultrasonic testing isrequired. Personnel applying this test method shall be experi-enced practitioners of ultrasonic examinations and associatedmethods for signal acquisition, processing, and interpretation.6.3 Personnel shall have proficiency in computer program-m
42、ing and signal processing using digital methods for time andfrequency domain signal analysis. Familiarity with the Fouriertransform and associated spectrum analysis methods for ultra-sonic signals is required.7. Apparatus7.1 The instrumentation and apparatus for pulse-echo con-tact ultrasonic attenu
43、ation coefficient measurement shouldinclude the following (see Fig. 2). Appropriate equipment canbe assembled from any of several suppliers.7.1.1 Buffered Probe, meeting the following requirements:7.1.1.1 The probe should have a center frequency thatcorresponds to an ultrasonic wavelength that is le
44、ss than onefifth of the thickness, d, of the test sample.7.1.1.2 The probe bandwidth should match the bandwidth ofreceived echoes. This may require transducer bandwidths offrom 50 to 200 MHz.7.1.1.3 The probe should be well constructed, carefullyselected, and shown to be free of internal defects and
45、 structuralanomalies that distort received echoes.7.1.1.4 The frequency spectra of the first two echoes re-turned by the free end of the buffer should be essentiallygaussian (bell shaped).7.1.2 Buffer Rod, with length that results in a time delay$3times the interval between two successive echoes fro
46、m theback surface of the test sample. This imposes a limit on the testsample thickness if the buffer rod length is fixed or predeter-mined by design.7.1.3 Couplant, meeting the following requirements:7.1.3.1 The couplant should be a fluid such as glycerine oran ultrasonic gel that will not corrode,
47、damage, or be absorbedby the test sample or part being examined.7.1.3.2 The couplant film or couplant layer thickness shouldbe much less than the ultrasound wavelength in the couplant atthe probes center frequency.FIG. 2 Block Diagram of Computer System for Ultrasonic Signal Acquisition and Processi
48、ng for Pulse-Echo Attenuation MeasurementC 1332 01 (2007)37.1.3.3 Ideally, to avoid echo distortions, the acoustic im-pedance of the couplant should be between that of the bufferrod material and test sample (5). With fluid couplants, justreducing the couplant layer thickness is usually more practica
49、lthan impedance matching by changing the fluid. For example,if glycerine is used between a fused quartz buffer and a steelsample, the couplant layer thickness should be less than 1 m.7.1.3.4 Dry coupling, for example, with an elastomer or thindeformable polymer film, may be used provided that echodistortions or phase inversions are avoided by acoustic imped-ance matching (5) and by substantially reducing the couplantlayer thickness.7.1.4 Pulser-Receiver, having a bandwidth exceeding thatof the probe by a factor of 1.5 to 2 and including theprobe/transd
