1、Designation: D 7248/D 7248M 08Standard Test Method forBearing/Bypass Interaction Response of Polymer MatrixComposite Laminates Using 2-Fastener Specimens1This standard is issued under the fixed designation D 7248/D 7248M; the number immediately following the designation indicates theyear of original
2、 adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method determines the uniaxial bearing/bypassinteraction
3、response of multi-directional polymer matrix com-posite laminates reinforced by high-modulus fibers by eitherdouble-shear tensile loading (Procedures A and C) or single-shear tensile or compressive loading (Procedure B) of atwo-fastener specimen. The scope of this test method is limitedto net sectio
4、n (bypass) failure modes. Standard specimenconfigurations using fixed values of test parameters are de-scribed for each procedure. A number of test parameters maybe varied within the scope of the standard, provided that theparameters are fully documented in the test report. Thecomposite material for
5、ms are limited to continuous-fiber ordiscontinuous-fiber (tape or fabric, or both) reinforced com-posites for which the laminate is balanced and symmetric withrespect to the test direction. The range of acceptable testlaminates and thicknesses are described in 8.2.1.1.2 This test method is consisten
6、t with the recommendationsof MIL-HDBK-17, which describes the desirable attributes ofa bearing/bypass interaction response test method.1.3 The two-fastener test configurations described in thistest method are similar to those in Test Method D 5961/D 5961M as well as those used by industry to investi
7、gate thebearing portion of the bearing/bypass interaction response forbolted joints, where the specimen may produce either a bearingfailure mode or a bypass failure mode. Should the testspecimen fail in a bearing failure mode rather than the desiredbypass mode, then the test should be considered to
8、be a bearingdominated bearing/bypass test, and the data reduction andreporting procedures of Test Method D 5961/D 5961M shouldbe used instead of those given in this standard.1.4 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. Within the text theinch
9、-pound units are shown in brackets. The values stated ineach system are not exact equivalents; therefore, each systemmust be used independently of the other. Combining valuesfrom the two systems may result in nonconformance with thestandard.1.5 This standard does not purport to address all of thesaf
10、ety 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:2D 792 Test Methods for Density
11、and Specific Gravity (Rela-tive Density) of Plastics by DisplacementD 883 Terminology Relating to PlasticsD 2584 Test Method for Ignition Loss of Cured ReinforcedResinsD 2734 Test Methods for Void Content of Reinforced Plas-ticsD 3171 Test Methods for Constituent Content of CompositeMaterialsD 3878
12、Terminology for Composite MaterialsD 5229/D 5229M Test Method for Moisture AbsorptionProperties and Equilibrium Conditioning of Polymer Ma-trix Composite MaterialsD 5687/D 5687M Guide for Preparation of Flat CompositePanels with Processing Guidelines for Specimen Prepara-tionD 5766/D 5766M Test Meth
13、od for Open-Hole TensileStrength of Polymer Matrix Composite LaminatesD 5961/D 5961M Test Method for Bearing Response ofPolymer Matrix Composite LaminatesD 6484/D 6484M Test Method for Open-Hole CompressiveStrength of Polymer Matrix Composite LaminatesD 6742/D 6742M Practice for Filled-Hole Tension
14、andCompression Testing of Polymer Matrix Composite Lami-nates1This test method is under the jurisdiction of ASTM Committee D30 onComposite Materials and is the direct responsibility of Subcommittee D30.05 onStructural Test Methods.Current edition approved Sept. 1, 2008. Published October 2008. Origi
15、nallyapproved in 2007. Last previous edition approved in 2007 as D 7248/D 7248M-07.2For 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 standards Document Summary pa
16、ge onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.E4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE83 Practice for Verification and Classification of
17、 Exten-someter SystemsE 122 Practice for Calculating Sample Size to Estimate,With Specified Precision, the Average for a Characteristicof a Lot or ProcessE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 456 Terminology Relating to Quality and StatisticsE 1309 Guide for Ide
18、ntification of Fiber-ReinforcedPolymer-Matrix Composite Materials in DatabasesE 1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in Databases2.2 Other Document:MIL-HDBK-17 Polymer Matrix Composites, Vol 1, Sec-tion 733. Terminology3.1 DefinitionsTerminology D 387
19、8 defines terms relatingto high-modulus fibers and their composites. TerminologyD 883 defines terms relating to plastics. Terminology E6defines terms relating to mechanical testing. TerminologyE 456 and Practice E 177 define terms relating to statistics. Inthe event of a conflict between terms, Term
20、inology D 3878shall have precedence over the other documents.NOTE 1If the term represents a physical quantity, its analyticaldimensions are stated immediately following the term (or letter symbol) infundamental dimension form, using the following ASTM standard sym-bology for fundamental dimensions,
21、shown within square brackets: Mfor mass, L for length, T for time, u for thermodynamic temperature,and nd for non-dimensional quantities. Use of these symbols is restrictedto analytical dimensions when used with square brackets, as the symbolsmay have other definitions when used without the brackets
22、.3.2 Definitions of Terms Specific to This Standard3.2.1 gross bypass stress, fgr_bypML-1T-2, nthe grossbypass stress for tensile loadings is calculated from the totalforce bypassing the fastener hole.3.2.2 net bypass stress, fnet_bypML-1T-2, nthe net by-pass stress for tensile loading is calculated
23、 from the forcebypassing the fastener hole minus the force reacted in bearingat the fastener.NOTE 2For compressive loadings the gross and net bypass stressesare equal and are calculated using the force that bypasses the fastener hole(since for the compressive loading case the bearing stress reaction
24、 is onthe same side of the fastener as the applied force, the force reacted inbearing does not bypass the fastener hole).NOTE 3Several alternate definitions for gross and net bypass stresshave been used historically in the aerospace industry. Comparison of datafrom tests conforming to this standard
25、with historical data may need toaccount for differences in the bypass definitions.3.2.3 bearing area, L2, nthe area of that portion of aspecimen used to normalize applied loading into an effectivebearing stress; equal to the diameter of the fastener multipliedby the thickness of the specimen.3.2.4 b
26、earing chord stiffness, EbrML-1T-2, nthe chordstiffness between two specific bearing stress or bearing strainpoints in the linear portion of the bearing stress/bearing straincurve.3.2.5 bearing force, P MLT2, nthe in-plane force trans-mitted by a fastener to a specimen at the fastener hole.3.2.6 bea
27、ring strain, ,brnd, nthe normalized hole de-formation in a specimen, equal to the deformation of thebearing hole in the direction of the bearing force, divided bythe diameter of the hole.3.2.7 bearing strength, Fxbr_bypML-1T-2, nthe value ofbearing stress occurring at the point of bypass (net sectio
28、n)failure.3.2.8 bearing stress, sbrML-1T-2, nthe bearing forcedivided by the bearing area.3.2.9 diameter to thickness ratio, D/h nd, nin a bearingspecimen, the ratio of the hole diameter to the specimenthickness.3.2.9.1 DiscussionThe diameter to thickness ratio may beeither a nominal value determine
29、d from nominal dimensions oran actual value determined from measured dimensions.3.2.10 edge distance ratio, e/D nd, nin a bearingspecimen, the ratio of the distance between the center of thehole and the specimen end to the hole diameter.3.2.10.1 DiscussionThe edge distance ratio may be eithera nomin
30、al value determined from nominal dimensions or anactual value determined from measured dimensions.3.2.11 nominal value, na value, existing in name only,assigned to a measurable quantity for the purpose of conve-nient designation. Tolerances may be applied to a nominalvalue to define an acceptable ra
31、nge for the quantity.3.2.12 offset bearing strength, FxbroML-1T-2, nthevalue of bearing stress, in the direction specified by thesubscript, at the point where a bearing chord stiffness line,offset along the bearing strain axis by a specified bearing strainvalue, intersects the bearing stress/bearing
32、 strain curve.3.2.12.1 DiscussionUnless otherwise specified, an offsetbearing strain of 2 % is to be used in this test method.3.2.13 width to diameter ratio, w/D nd, nin a bearingspecimen, the ratio of specimen width to hole diameter.3.2.13.1 DiscussionThe width to diameter ratio may beeither a nomi
33、nal value determined from nominal dimensions oran actual value, determined as the ratio of the actual specimenwidth to the actual hole diameter.3.2.14 ultimate bearing strength, FxbruML-1T-2, nthevalue of bearing stress, in the direction specified by thesubscript, at the maximum force capability of
34、a bearingspecimen.3.2.15 ultimate gross bypass strength, Fxgr_bypML-1T-2,nthe value of gross bypass stress, in the direction specifiedby the subscript, at the maximum force capability of thespecimen.3.2.16 ultimate net bypass strength, Fxnet_bypML-1T-2,nthe value of net bypass stress, in the directi
35、on specified bythe subscript, at the maximum force capability of the specimen.3.3 Symbols:A = cross-sectional area of a specimen3Available from Standardization Documents Order Desk, Bldg. 4 Section D, 700Robbins Ave., Philadelphia, PA 19111-5098, Attn: NPODS.D 7248/D 7248M 082CV = coefficient of var
36、iation statistic of a sample populationfor a given property (in percent)d = fastener or pin diameterD = specimen hole diametere = distance, parallel to applied force, from hole center toend of specimen; the edge distanceExbr= bearing chord stiffness in the test direction specifiedby the subscriptf =
37、 distance, parallel to applied force, from hole edge to endof specimenFxbr_byp= bearing stress at the ultimate bypass strength inthe test direction specified by the subscriptFxgr_byp_c= ultimate compressive gross bypass strength inthe test direction specified by the subscriptFxgr_byp_t= ultimate ten
38、sile gross bypass strength in the testdirection specified by the subscriptFxnet_byp_c= ultimate compressive net bypass strength in thetest direction specified by the subscriptFxnet_byp_t= ultimate tensile net bypass strength in the testdirection specified by the subscriptg = distance, perpendicular
39、to applied force, from hole edgeto shortest edge of specimenh = specimen thicknessk = calculation factor used in bearing equations to distin-guish single-fastener tests from double-fastener testsLg= extensometer gage lengthn = number of specimens per sample populationP = force carried by test specim
40、enPf= force carried by test specimen at failurePmax= maximum force carried by test specimen prior tofailuresn-1= standard deviation statistic of a sample population fora given propertyw = specimen widthxi= test result for an individual specimen from the samplepopulation for a given propertyx = mean
41、or average (estimate of mean) of a samplepopulation for a given propertyd = extensional displacement = general symbol for strain, whether normal strain or shearstrainbr= bearing strainsbr= bearing stressw = specimen widthdcsk= countersink depthdfl= countersink flushness (depth or protrusion of the f
42、as-tener in a countersunk hole)4. Summary of Test Method4.1 Bearing/Bypass ProceduresDefinition of the uniaxialbearing/bypass interaction response requires data for varyingamounts of bearing and bypass forces at a fastener hole. Fig. 1shows a typical composite laminate bearing/bypass interactionFIG.
43、 1 Illustration of FHT, FHC, Bearing and Bearing/Bypass Bolted Joints Data and Bearing/Bypass Interaction Diagram (Refs 1-3)D 7248/D 7248M 083diagram (Refs 1-3),4along with illustrative data from varioustest types. Data from Practice D 6742/D 6742M and TestMethod D 5961/D 5961M define the 100 % bypa
44、ss and bearingends of the interaction diagram. Rationale for the baselinebearing/bypass specimen geometry and fastener torques aregiven in 6.7 and 6.8. Procedures A and B of this test methodprovide data in the bypass/high bearing region, while Proce-dure C provides data in the bypass/low bearing reg
45、ion. Morecomplicated test setups have been used to develop data acrossthe full range of bearing/bypass interaction. This test method islimited to cases where the bearing and bypass loads are alignedin the same direction. It is also limited to uniaxial tensile orcompressive bypass loads. Test procedu
46、res for cases where thebearing and bypass loads act at different directions, or caseswith biaxial or shear bypass loads are outside the scope of thisstandard.4.1.1 Ultimate strength for all procedures is calculatedbased on the specimen gross cross-sectional area, disregardingthe presence of the hole
47、. While the hole causes a stressconcentration and reduced net section, it is common industrypractice to develop notched design allowable strengths basedon gross section stress to account for various stress concentra-tions (fastener holes, free edges, flaws, damage, and so forth)not explicitly modele
48、d in the stress analysis. This is consistentwith the ASTM D30 test methods for open and filled holetension and compression strength (Test Methods D 5766/D 5766M, D 6484/D 6484M, and Practice D 6742/D 6742M).4.2 Procedure A, Bypass/High Bearing Double Shear:4.2.1 Aflat, constant rectangular cross-sec
49、tion test specimenwith two centerline holes located near the end of the specimen,as shown in the test specimen drawings of Figs. 2 and 3,isloaded at the hole in bearing. The bearing force is normallyapplied through a close-tolerance, lightly torqued fastener (orpin) that is reacted in double shear by a fixture similar to thatshown in Figs. 4 and 5. The bearing force is created by pullingthe assembly in tension in a testing machine. The differencefrom a standard “bearing” test is that the expected primaryfailure mod
