1、Designation: D 7006 03Standard Practice forUltrasonic Testing of Geomembranes1This standard is issued under the fixed designation D 7006; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parent
2、heses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice provides a summary of equipment andprocedures for ultrasonic testing of geomembranes using thepulse echo method.1.2 Ultrasonic wave prop
3、agation in solid materials is corre-lated to physical and mechanical properties and condition ofthe materials. In ultrasonic testing, two wave propagationcharacteristics are commonly determined: velocity (based onwave travel time measurements) and attenuation (based onwave amplitude measurements). V
4、elocity of wave propagationis used to determine thickness, density, and elastic properties ofmaterials. Attenuation of waves in solid materials is used todetermine microstructural properties of the materials. In addi-tion, frequency characteristics of waves are analyzed to inves-tigate the propertie
5、s of a test material. Travel time, amplitude,and frequency distribution measurements are used to assess thecondition of materials to identify damage and defects in solidmaterials. Ultrasonic measurements are used to determine thenature of materials/media in contact with a test specimen aswell. Measu
6、rements are conducted in the time-domain (timeversus amplitude) or frequency-domain (frequency versusamplitude).1.3 Measurements of one or more ultrasonic wave transmis-sion characteristics are made based on the requirements of thespecific testing program.1.4 This standard does not purport to addres
7、s 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 Documents2.1 ASTM Standards:D 4437 Practice f
8、or Determining the Integrity of FieldSeams Used in Joining Flexible Polymeric SheetGeomembranesD 4545 Practice for Determining the Integrity of FactorySeams Used in Joining Manufactured Flexible SheetGeomembranesD 4883 Test Method for Density of Polyethylene by theUltrasound TechniqueE 1316 Terminol
9、ogy for Nondestructive Examinations3. Terminology3.1 Definitions:3.1.1 geomembrane, nan essentially impermeable geo-synthetic composed of one or more synthetic sheets.3.1.2 atmosphere for testing geomembranes, nair main-tained at a relative humidity of 50 to 70 % and a temperatureof 21 6 1C.3.1.3 Fo
10、r definitions of terms related to ultrasonic testing,refer to Terminology E 1316.4. Summary of Practice4.1 Mechanical waves are introduced to a geomembranefrom a surface of the material using an ultrasonic transducer.Transmission characteristics of the waves in the geomembraneare determined. The mea
11、sured characteristics are used toevaluate certain properties and condition of geomembranes.5. Significance and Use5.1 This practice covers test arrangements, measurementtechniques, sampling methods, and calculations to be used fornondestructive evaluation of geomembranes using ultrasonictesting.5.2
12、Wave velocity may be established for particulargeomembranes (for specific polymer type, specific formula-tion, specific density). Relationships may be established be-tween velocity and both density and tensile properties ofgeomembranes. An example of the use of ultrasound fordetermining density of p
13、olyethylene is presented in TestMethod D 4883. Velocity measurements may be used todetermine thickness of geomembranes (1, 2).2Travel time andamplitude of transmitted waves may be used to assess thecondition of geomembranes and to identify defects in geomem-branes including surface defects (for exam
14、ple, scratches, cuts),inner defects (for example, discontinuities within geomem-branes), and defects that penetrate the entire thickness ofgeomembranes (for example, pinholes) (3, 4). Bonding be-tween geomembrane sheets can be evaluated using travel time,velocity, or impedance measurements for seam
15、assessment1This practice is under the jurisdiction of ASTM Committee D35 on Geosyn-thetics and is the direct responsibility of Subcommittee D35.10 on Geomembranes.Current edition approved Dec. 1, 2003. Published January 2004.2The boldface numbers in parentheses refer to the list of references at the
16、 end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.(5-10). Examples of the use of ultrasonic testing for determin-ing the integrity of field and factory seams through travel timeand velocity measurements (resulting
17、in thickness measure-ments) are presented in Practices D 4437 and D 4545, respec-tively. An ultrasonic testing device is routinely used forevaluating seams in prefabricated bituminous geomembranesin the field (11). Integrity of geomembranes may be monitoredin time using ultrasonic measurements.NOTE
18、1Differences may exist between ultrasonic measurements andmeasurements made using other methods due to differences in testconditions such as pressure applied and probe dimensions. An example isultrasonic and mechanical thickness measurements.5.3 The method is applicable to testing both in the labora
19、-tory and in the field for parent material and seams. The testdurations are very short as wave transmission throughgeomembranes occurs within microseconds.6. Apparatus6.1 The test equipment consists of a single transducer (bothtransmitter and receiver); a pulse generator; a pulse receiver(includes a
20、mplifier and filters for noise reduction); electroniccircuits to measure and record waveforms, to measure wavetravel time, to measure wave amplitudes, and to displayreceived signals; electronic circuitry to time and synchronizeall instrument functions; and connecting cables. The testapparatus is sho
21、wn in Fig. 1.6.2 Piezoelectric transducers are effective for wave trans-mission. Compressional waves (P-waves, longitudinal waves)shall be used for ultrasonic testing of geomembranes. A spacershall be used to obtain good near surface resolution and toeliminate near field effects for accurate measure
22、ment of ultra-sonic wave propagation characteristics in geomembranes. Aplastic spacer has been found to be effective for geomem-branes. The thickness of the spacer shall be at least twice thethickness of the test specimen. The thickness of the spacer shallbe less than 5 to 10 times the thickness of
23、the test geomem-brane. For testing geomembranes with various thicknesses, usethe material with the largest thickness for selection of thethickness of the spacer. The spacer shall be sufficiently large tocover the active surface area of the transducer to ensure that thewaveform generated is fully tra
24、nsmitted to the test specimenthrough the spacer. The center frequency of the transducer shallbe between 1 and 20 MHz (a 10 MHz transducer has beenfound to be effective). Focused transducers shall be used fortextured geomembranes to ensure measurements are made overessentially a “point” on the test m
25、aterial. Other means may alsobe used if high frequency mechanical waves can be generatedwith these devices.6.3 Pulse generator shall generate pulses of electrical energythat activate the transducer. Pulsers that generate spike orsquare wave type voltage pulses have been found to beeffective for test
26、ing geomembranes.6.4 The receiver shall amplify and filter the signal receivedby the transducer after the waves have been transmittedthrough a test sample.6.5 Electronic circuitry shall be used to measure travel timeof waves in a test sample. The circuitry shall allow fordetermination of travel time
27、s with a precision equal to or betterFIG. 1 Test ApparatusD7006032than 0.1 s. If attenuation and amplitude measurements aredesired, instrumentation shall be used to record the waveformsreceived from a test material. The circuitry shall allow fordetermination of amplitudes with a precision equal to o
28、r betterthan 1 mV. Electronic circuitry may also be used to displayreceived signals. Analog to digital converters and computer-ized signal acquisition and analysis setups have been found tobe effective for testing geomembranes.6.6 Electronic circuitry shall be used to time and synchro-nize all instr
29、ument functions to eliminate uncertainty in thedetermination of wave transit times.NOTE 2The apparatus listed here has been found to be effective fortesting geomembranes. Ultrasonic testing of materials is a well establishedfield and other types of devices may also be used for testing geomem-branes.
30、 Details for various test arrangements and examples of devicesproduced by various manufacturers are available in (12). Effectiveness ofalternative devices shall be demonstrated prior to their routine use forgeomembranes.7. Materials7.1 A coupling agent shall be used to ensure good contactbetween the
31、 transducer and test specimen. Coupling agentsinclude water, commercial ultrasonic couplants, oil, petroleumjelly, grease, glycerin, propylene glycol, or other viscous fluids.Water has been used effectively on flat surfaces. More viscousmaterials may be used on inclined surfaces.8. Sampling and Test
32、 Specimens8.1 Test specimens shall be cut such that a distance greaterthan 10 times the thickness of the specimen shall be leftbetween the transducer and the edges of the specimen in everydirection.8.2 In field testing, measurements shall be taken at locationsthat are at a distance greater than 10 t
33、imes the thickness of thespecimen from the edges of the geomembrane sheet in anydirection.NOTE 3Seam inspection tests may be conducted at locations closer tothe edge of geomembranes than specified in 8.2. Effectiveness of the nearedge measurements shall be demonstrated prior to their routine use toe
34、nsure that potential edge reflections do not interfere with measurementsthrough the thickness of geomembranes.9. Calibration9.1 The electronic equipment shall be calibrated to ensureaccurate determination of the transit time. Calibration bars orblocks with known thicknesses and wave transmission vel
35、oci-ties shall be used for calibration procedures.10. Conditioning10.1 For baseline measurements (i.e., measurements used toestablish baseline ultrasonic properties for a particulargeomembrane), specimens shall be exposed to the standardatmosphere for testing geomembranes for a period sufficient tor
36、each moisture and temperature equilibrium. Exposure for 24 hhas been found to be effective for reaching equilibrium.10.2 Tests can be conducted at conditions outside the rangefor standard atmosphere conditions for various applicationssuch as field measurements. For these measurements, speci-mens sha
37、ll be in moisture and temperature equilibrium withtheir surrounding environment.NOTE 4Correction factors shall be used if comparisons are to be madebetween standard and nonstandard testing conditions. Correction factorsare determined by taking measurements at nonstandard conditions andnormalizing th
38、ese by the measurements conducted at standard conditions.10.3 Surface PreparationThe surface of the test geomem-brane shall be free of excessive dust, particles, and any othermaterials that may interfere with wave transmission. Thesurface of geomembranes may be cleaned with a damp cloth toensure a c
39、lean measurement surface prior to testing.11. Procedure11.1 Ultrasonic measurements in geomembranes shall beconducted using the pulse echo test method. In this method,ultrasonic waves are sent and received from one surface of atest specimen using one or two transducers. A single transducershall be u
40、sed in the measurements of geomembranes.11.2 Ultrasonic measurements on geomembranes may betaken using two test arrangements. In both arrangements, thetransducer shall be orthogonal to the test geomembrane.11.2.1 Arrangement AIn this arrangement the transducerassembly is placed over the test geomemb
41、rane. The transducerassembly consists of the ultrasonic transducer and the spacer.Apply a small amount of couplant between the transducer andthe spacer to ensure that the two units are in good contact withno air gaps. Then, apply a small amount of couplant on thesurface of the geomembrane at the mea
42、surement location.Place the transducer assembly on the geomembrane leaving athin film of couplant between the assembly and the geomem-brane. Ensure that the transducer assembly is in good contact(i.e., no air gaps) with the geomembrane. A small load may bepermanently attached on top of the transduce
43、r to provide goodcontact with the geomembrane and ensure that the transducer isperfectly orthogonal to the test specimen. This arrangement ispresented in Fig. 2a.11.2.2 Arrangement BIn this arrangement the transducerassembly is placed below the test geomembrane. Apply a smallamount of couplant betwe
44、en the transducer and the spacer toensure that the two units are in good contact with no air gaps.Then, apply a small amount of couplant on the top surface ofthe spacer. Place the geomembrane over the spacer leaving athin film of couplant between the spacer and the geomembrane.Ensure that the geomem
45、brane is in good contact (i.e., no airgaps) with the transducer assembly. This arrangement ispresented in Fig. 2b. In this arrangement, no pressure is appliedto the geomembrane. Pressure can affect the thickness of thegeomembrane, which can affect the travel time in the geomem-brane. This arrangemen
46、t is applicable when the underside of ageomembrane is accessible.NOTE 5Commercially available “delay line” transducers can be usedin Test Arrangement A. These transducers have plastic spacers attached tothe ultrasonic units. Use of these types of transducers has been found to beeffective for testing
47、 geomembranes. Commercially available immersiontransducer setups can be used in Test Arrangement B. In these setups awater resistant transducer is placed at a certain depth in a water bath. Thespecimen is placed directly on the surface of water at a fixed distanceaway from the transducer. The water
48、between the specimen and thetransducer acts as the spacer. These systems are particularly effective forfocused transducers. Care must be taken not to leave the test specimen incontact with water for extended periods of time when using these setups.D7006033Test specimens shall not be exposed to water
49、 for more than 30 min duringa test.11.2.3 If comparisons will be made between ultrasonicmeasurements, similar test arrangements shall be used. Inparticular, the pressure applied to a geomembrane during theultrasonic tests shall be the same for comparative analyses.11.2.4 The gain and frequency response characteristics ofthe receiver shall be kept constant within a test program andbetween test programs if comparisons will be made.11.3 Subsequent to proper placement of the specimen andthe transducer assembly, take a measurement by sending andreceiving pulses in the geomembrane.
