1、Designation: D 6476 08Standard Test Method forDetermining Dynamic Air Permeability of Inflatable RestraintFabrics1This standard is issued under the fixed designation D 6476; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year
2、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. Scope1.1 This test method covers the procedures used to deter-mine under dynamic airflow conditions the high pressurepermeab
3、ility of permeable, uncoated fabrics typically used forinflatable restraints. For the determination of air permeabilityof inflatable restraint fabrics under low pressure conditions atsteady-state air flow, refer to Test Method D 737.1.2 Procedures and apparatus other than those stated in thistest me
4、thod may be used by agreement of purchaser andsupplier with the specific deviations from the standard ac-knowledged in the report.1.3 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system are not exact equivalents; therefor
5、e, each systemmust be used independently of the other.1.4 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
6、of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 123 Terminology Relating to TextilesD 737 Test Method for Air Permeability of Textile FabricsD 1776 Practice for Conditioning and Testing TextilesD 2904 Practice for Interlaboratory Testing of a Textile TestMethod th
7、at Produces Normally Distributed DataD 6799 Terminology Relating to Inflatable RestraintsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 For all terminology relating to D13.20, Inflatable re-straints, refer to Terminology D 6799.3.1.
8、1 The following terms are relevant to this standard:average dynamic air permeability (ADAP), dynamic air per-meability (DAP), cushion, exponent of dynamic air permeabil-ity (EXP, ) inflatable restrain, inflator, module, standard atmo-sphere for testing textiles3.2 For all other terms related to text
9、iles, see TerminologyD 123.4. Summary of Test Method4.1 A volume of dessicated compressed air at known vol-ume and pressure passes through a fabric specimen into thestandard atmosphere for testing textiles. During the portion ofthe test cycle which simulates airbag inflation, the pressuredifferentia
10、l pressure across the specimen rises to a valuecorresponding to a peak inflation pressure. During the portionof the test cycle which simulates airbag deflation, the pressuredifferential drops to 0 kPa as the air passes through thespecimen. The time to reach the maximum pressure and thesubsequent tim
11、e to correspond to similar times in an airbagdeployment.4.2 Software algorithms integral to the apparatus smoothout the pressure data and determine the values for ADAP andEXP.5. Significance and Use5.1 For matters relating to lot acceptance of commercialshipments and conformity to specification or o
12、ther standard,refer to Section 13 of this test method.5.2 This test method is useful in the selection and designvalidation of permeable, uncoatable fabrics used in inflatablerestraint cushions. The dynamic conditions and higher pressuredifferentials of this test method may better simulate theinflati
13、on and deflation cycle of an airbag module duringdeployment than do the steady-state conditions of Test MethodD 737.5.2.1 Only uncoated, permeable fabrics should be used. Useof coated fabrics may yield invalid results and potentiallydamage the test apparatus.5.3 Within the limits of variance express
14、ed in Section 12,this test method is useful for design validation and may besuitable for incorporation in a material specification or for lotacceptance testing of commercial shipments. Caution is ad-vised on very low permeability fabrics or with the 200 cm3.1This test method is under the jurisdictio
15、n of ASTM Committee D13 on Textilesand is the direct responsibility of Subcommittee D13.20 on Inflatable Restraints.Current edition approved July 1, 2008. Published July 2008. Originally approvedin 2000. Last previous edition approved in 2005 as D 647605.2For referenced ASTM standards, visit the AST
16、M 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.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, Unite
17、d States.size test heat because between-laboratory precision as pre-sented in Section 12 may be as high as 21 %.5.4 This test method may be used for materials other thaninflatable restraint fabrics which experience dynamic air per-meability in sudden bursts. In such cases, the physical appa-ratus or
18、 its software algorithms may require modification toprovide suitability for use.5.5 Due to the split-second time interval for testing, thepressure versus time data is subject to recording anomalies andelectronic noise. The data should be digitally filtered to obtainthe underlying smooth pressure cur
19、ve prior to data analysis.The software in the apparatus includes a reliable algorithmboth to smooth the curve and to determine the exponent of airpermeability.5.6 It is inherent in the design and operation of thisequipment that major components key to the calibration andmeasurements are specific to
20、the individual test head. The sizeor permeability measuring range of the test head is typicallychosen to correspond to the fabric specimen to be tested. Theprecision of this test method is highly dependent on the size ofthe test head. The precision of the data collected using one testhead should be
21、used to estimate the precision of data collectedusing a different test head, even on the same apparatus.5.7 It is mandatory that fabric specimens be conditioned andtested in standard atmosphere for testing textiles.6. Apparatus6.1 Removable Test Head, containing a Pressure Vessel ofknown volume capa
22、ble of being charged pneumatically from 0to no less than 400 kPa (0 to no less than 58 psi) with atolerance of 6 3.0 %, of sufficient volume to challengeadequately the fabric being tested, equipped with a solenoidrelease valve mechanism, a test chamber, and a circular orificewith an area of 50 cm2;
23、and equipped with a means ofmeasuring and adjusting the pressure range in increments of 1kPa (0.1 psi), a minimum range between pressure set points of5 kPa (1 psi) and rise and fall ranges in ms sufficient to meetthe conditions of a material specification for dynamic airpermeability testing of infla
24、table restraint fabrics.6.2 Pressure Transducers and Rigid Wall Pickup Tubes,suitable for measuring the pressure differential of the fabricspecimen in a range sufficient to meet the conditions of amaterial specification for dynamic air permeability testing ofinflatable restraint fabrics, with a tole
25、rance of 6 2 %, mountedin a static or low pressure area in the test fixture that does notinterfere with airflow.6.3 Air Compressor and Air Desiccating Cartridge, capableof charging the pressure vessel in the test head to the specifiedpressure up to 400 kPa.6.4 Mounting Fixture, capable of retaining
26、the fabric speci-men over the test orifice without stretching the specimen andwithout air leakage at the periphery of the test area.6.5 Electrical Firing Pulse Source, suitable for actuating theinflation and for communicating with the data acquisitionsystem dependent on an electrical signal.6.6 Data
27、 Acquisition System, suitable for recording theoutput of the pressure transducers versus elapsed time ofairflow.6.7 Filter Requirements, data sampling rate, transducerfrequency response, and amplifier frequency response shall besuch that minimal effect on accuracy of the data occurs. Theaccuracy of
28、the pressure transducers, amplifiers, and timerswithin the test apparatus shall be calibrated to within 6 3%.7. Sampling7.1 Dynamic air permeability testing is a destructive testand therefore necessitates sampling procedures if used inconjunction with lot acceptance of commercial shipments.7.2 Lot S
29、ample:7.2.1 For acceptance testing, the lot size is the quantity offabric finished in one production day or as agreed uponbetween the purchaser and the supplier.7.2.2 Unless otherwise agreed upon between the purchaserand the supplier, take as a lot sample all the rolls in acommercial shipment. Consi
30、der the rolls to be the primarysampling units.7.3 Laboratory Sample7.3.1 An entire roll of fabric or a full-width cut from the endof a roll within a lot sample constitutes a laboratory sample.7.4 Test Specimens:7.4.1 Test specimens are the pieces of fabric that actuallyundergo testing. Cut or mark s
31、pecimens from the end of eachroll of fabric in the laboratory sample, as indicated in thematerial specification or equivalent. Cut 165mm by 330 mmrectangular specimens from the full-width fabric sample, ormark similarly sized areas across the full-width fabric samplewithout cutting individual specim
32、ens.7.4.2 If areas of full width fabric are tested without cuttingindividual specimens, position test areas representing a broaddistribution across the length and width, preferably along thediagonal of the laboratory sample, and no nearer the edge thanone tenth its width.8. Conditioning8.1 Precondit
33、ion test specimens in accordance with PracticeD 1776 or as agreed upon between the the purchaser and thesupplier.8.2 Prior to testing, bring the test specimens to moistureequilibrium at ambient atmospheric pressure, at 21 6 1C (706 2F), and at 65 6 2 % relative humidity, unless directed todo otherwi
34、se by an agreement by the purchaser and supplier.8.3 Equilibrium is considered to have been reached whenthe increase in mass of the specimen in successive weighingsmade at intervals of not less than 2 h does not exceed 0.1 % ofthe mass of the specimen.9. Procedure9.1 Select and condition specimens i
35、n accordance with 8.1.9.2 Mount the fabric specimen on the test fixture, ensuringthat the retention mechanism clamps the fabric tightly withminimal tension and without damage or wrinkling.9.3 Perform all system calibrations.9.4 Enter the specimen number into recording portions ofthe data acquisition
36、.9.5 Ensure the pressure vessel is pressurized with desiccatedair to a pressure sufficiently high to test the specimen within thepressure ranges specified.D64760829.6 In accordance with the applicable material specificationor laboratory guideline, select and install the appropriate testhead for the
37、fabric type to be measured.9.7 Preset the start, upper, and lower pressure limits.9.8 Establish data acquisition system response to pressureinputs.9.9 Initiate the starting sequence and note the response ofthe data acquisition system to verify successful airflow.9.10 Record maximum differential pres
38、sure in kPa (psi),time to maximum pressure in ms, or whatever data points arerequired by the material specification.9.11 Remove the specimen from the test stand and mark itas having been tested.9.12 On the test report, record the data required by thematerial specification.NOTE 1The unit of permeabil
39、ity commonly used for ADAP measure-ment is mm/s. A velocity of 1 mm/s is the mathematical equivalent of apermeability of 0.1 cm3/(cm2.s). Permeability and velocity are consideredinterchangeable terms.10. Equipment Calibration10.1 For inflatable restraints, all test equipment used inaccordance with t
40、hese test methods shall be certified forcalibration annually by an independent agency or equipmentmanufacturer whose results are traceable to the NationalInstitute of Science and Technology (NIST) or other nationalstandards laboratory. The test parameters of the equipmentshall be tested within the o
41、perating ranges covered in thematerial specification or equivalent document.11. Report11.1 State that the tests were conducted in accordance withthis test method for determining the dynamic air permeabilityof inflatable restraints fabrics.11.1.1 If deviation from this test method occurred, anyrefere
42、nce to this test method shall state: “Testing was per-formed in accordance with ASTM D 6476, with the followingchanges:”11.2 The purchaser and supplier shall determine the exactform of the test report. Unless otherwise specified, report thefollowing information:11.2.1 Fabric designation,11.2.2 Lot i
43、dentification,11.2.3 Date of report,11.2.4 Name of person certifying report,11.2.5 Relevant specification,11.2.6 Number of specimens used in each test,11.2.7 Tests performed and data obtained,11.2.8 Laboratory conditions if other than standard, and11.2.9 Deviations from standard procedures and appar
44、atus.12. Precision and Bias12.1 BiasFor multifilament fabrics such as those used forinflatable restraints, there is no standard reference materialavailable to serve as an accepted standard value for dynamic airpermeability testing. In the absence of a known true value, theaccuracy of this test metho
45、d cannot be determined.12.2 The analysis of precision of test results using this testmethod is meaningful both within-laboratory and between-laboratory with multiple operators.12.3 An Interlaboratory Test3was planned and conductedon uncoated fabrics covering a range of permeabilities typi-cally used
46、 in inflatable restraint cushions in accordance withPractice E 691 and Practice D 2904. For inflatable restraintfabrics, the typical range of permeabilities is between zero and10 cfm when measured in accordance with Test Method D 737.Two variables, ADAP and EXPONENT were studied. Analysiswas done us
47、ing SAS 6.1, PROC. GLM, and PROC.VARCOMP. Three components of variance - single-operator,within-laboratory, and between-laboratory - were statisticallycalculated to determine precision of this test method.12.4 Precision of ADAPFor the components of variancelisted in Table 1, two averages of observed
48、 values should beconsidered significantly different at the 95 % probability levelif the difference equals or exceeds the critical differences listedin Table 212.4.1 Primary source of variance of ADAP is betweenlaboratories.12.4.2 The critical differences for ADAP values as a percentof the ADAP avera
49、ge at the 95 % probability level for singleoperator, within laboratory, and between laboratory generally3A research report detailing the interlaboratory test is available from ASTMHeadquarters. Request RR:D131104.TABLE 1 Components of Variance as Standard Deviations,Percentage PointsADAP Single-Operator Within-Laboratory Between-LaboratoryMaterial A:420 d. Nylon200 cc. Head466 mm/sAverage ADAP6.15 % 0.00 % 4.13 %Material B:650 d. Polyester200 cc. Head525 mm/sAverage ADAP2.78 % 0.00 % 3.83 %Material C:420 d. Nylon400 cc. Head799 mm/sAverage ADAP3.67 % 0.00 % 0.00 %Material D:630
