1、Designation: D 6671/D 6671M 06Standard Test Method forMixed Mode I-Mode II Interlaminar Fracture Toughness ofUnidirectional Fiber Reinforced Polymer Matrix Composites1This standard is issued under the fixed designation D 6671/D 6671M; the number immediately following the designation indicates theyea
2、r of original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of lastreapproval. A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes the determination of inter
3、-laminar fracture toughness, Gc, of continuous fiber-reinforcedcomposite materials at various Mode I to Mode II loadingratios using the Mixed-Mode Bending (MMB) Test.1.2 This test method is limited to use with compositesconsisting of unidirectional carbon fiber tape laminates withbrittle and tough s
4、ingle-phase polymer matrices. This testmethod is further limited to the determination of fracturetoughness as it initiates from a delamination insert. Thislimited scope reflects the experience gained in round robintesting. This test method may prove useful for other types oftoughness values and for
5、other classes of composite materials;however, certain interferences have been noted (see Section 6).This test method has been successfully used to test thetoughness of both glass fiber composites and adhesive joints.1.3 The values stated in either SI units or inch-pound unitsare to be regarded separ
6、ately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.4 This standard does not purport to address all of thesafety concerns
7、, 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 883 Terminology Relating to PlasticsD 265
8、1 Guide for Preparation of Metal Surfaces for Adhe-sive BondingD 2734 Test Methods for Void Content of Reinforced Plas-ticsD 3171 Test Methods for Constituent Content of CompositeMaterialsD 3878 Terminology for Composite MaterialsD 5229/D 5229M Test Method for Moisture AbsorptionProperties and Equil
9、ibrium Conditioning of Polymer Ma-trix Composite MaterialsD 5528 Test Method for Mode I Interlaminar FractureToughness of Unidirectional Fiber-Reinforced PolymerMatrix CompositesE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE 122 Prac
10、tice for Calculating Sample Size to Estimate,With a Specified Tolerable Error, the Average for aCharacteristic of a Lot or ProcessE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 456 Terminology Relating to Quality and Statistics3. Terminology3.1 Terminology D 3878 defines
11、 terms relating to high-modulus fibers and their composites. Terminology D 883defines terms relating to plastics. Terminology E6 definesterms relating to mechanical testing. Terminology E 456 andPractice E 177 define terms relating to statistics. In the event ofconflict between terms, Terminology D
12、3878 shall have prece-dence over the other terminology standards.3.2 Definitions of Terms Specific to This Standard:3.2.1 crack opening mode (Mode I)fracture mode inwhich the delamination faces open away from each other andno relative crack face sliding occurs.3.2.2 crack sliding mode (Mode II)fract
13、ure mode inwhich the delamination faces slide over each other in thedirection of delamination growth and no relative crack faceopening occurs.3.2.3 mixed-mode fracture toughness, Gcthe critical valueof strain energy release rate, G, for delamination growth inmixed-mode.1This test method is under the
14、 jurisdiction of ASTM Committee D30 onComposite Materials and is the direct responsibility of Subcommittee D30.06 onInterlaminar Properties.Current edition approved March 1, 2006. Published March 2006. Originallyapproved in 2001. Last previous edition approved in 2004 as D 6671/D 6671M 04e1.2For ref
15、erenced 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 page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, We
16、st Conshohocken, PA 19428-2959, United States.3.2.4 mixed-mode ratio, GI/GIIthe ratio of Mode I strainenergy release rate to Mode II strain energy release rate.3.2.5 mode mixture, GII/Gfraction of Mode II to totalstrain energy release rate. The mixed-mode ratio, GI/GII,isattimes referred to instead
17、of the mode mixture.3.2.6 Mode I strain energy release rate, GIthe loss ofstrain energy associated with Mode I deformation in the testspecimen per unit of specimen width for an infinitesimalincrease in delamination length, da, for a delamination growingunder a constant displacement.3.2.7 Mode II str
18、ain energy release rate, GIIthe loss ofstrain energy associated with Mode II deformation in the testspecimen per unit of specimen width for an infinitesimalincrease in delamination length, da, for a delamination growingunder a constant displacement.3.2.8 strain energy release rate, Gthe loss of stra
19、inenergy, dU, in the test specimen per unit of specimen width foran infinitesimal increase in delamination length, da, for adelamination growing under a constant displacement. In math-ematical form,G 51 dUbda(1)where:a = delamination length, mm in.,b = width of specimen, mm in.,G = total strain ener
20、gy release rate, kJ/m2in.-lbf/in.2, andU = total elastic strain energy in the test specimen, N-mmin.-lbf.3.3 Symbols:a = delamination length, mm in.ao= initial delamination length, mm in.a1-25= propagation delamination lengths, mm in.b = width of specimen, mm in.bcal= width of calibration specimen,
21、mm in.c = lever length of the MMB test apparatus, mm in.cg= lever length to center of gravity, mm in.C = compliance, d/P, mm/N in./lbfCcal= calibration specimen compliance, d/P, mm/N in./lbfCsys= system compliance, d/P, mm/N in./lbfCV = coefficient of variation, %E11= longitudinal modulus of elastic
22、ity measured in tension,MPa psiE22= transverse modulus of elasticity, MPa psiEcal= modulus of calibration bar, MPa psiE1f= modulus of elasticity in the fiber direction measured inflexure, MPa psiG = total strain energy release rate, kJ/m2in.-lbf/in.2G13= shear modulus out of plane, MPa psiG12= shear
23、 modulus in plane, MPa psiGI= opening (Mode I) component of strain energy releaserate, kJ/m2in.-lbf/in2GII= shear (Mode II) component of strain energy releaserate, kJ/m2in.-lbf/in2GII/G = mode mixtureGc= total mixed-mode fracture toughness, kJ/m2in.-lbf/in2Gcest= estimated value of total mixed-mode
24、fracture tough-ness, kJ/m2in.-lbf/in2h = half thickness of test specimen, mm in.L = half-span length of the MMB test apparatus, mm in.m = slope of the load displacement curve, N/mm lb/in.mcal= slope of the load displacement curve from calibrationtest, N/mm lbf/in.P = applied load, N lbfP5 %/max= cri
25、tical load at 5 %/max point of loading curve, NlbfPest= estimated value of critical load, N lbfPg= weight of lever and attach apparatus, N lbfPnl= critical load at nonlinear point of loading curve, N lbfPtab= expected load on the loading tab, N lbfPvis= critical load when delamination is observed to
26、 grow, NlbfSD = standard deviationt = thickness of calibration bar, mm in.U = strain energy, N-mm in.-lbfV = fiber volume fraction, %a = mode mixture transformation parameter for setting leverlengthb = non-dimensional crack length correction for mode mix-turex = crack length correction parameter,xE1
27、111G13H3 2 2SG1 1GD2Jd = load point deflection, mm in.dest= estimated load point deflection, mm in.dmax= maximum allowable load point of deflection, mmin.G = transverse modulus correction parameter,G1.18=E11E22G134. Summary of Test Method4.1 The Mixed-Mode Bending (MMB) test apparatus shownin Fig. 1
28、 is used to load split laminate specimens to determinethe delamination fracture toughness at various ratios of ModeI to Mode II loading. The composite test specimen, shown inFig. 2, consists of a rectangular, uniform thickness, unidirec-tional laminated composite specimen, containing a nonadhe-sive
29、insert at the midplane which serves as a delaminationinitiator. Loading forces are applied to the MMB specimen viatabs that are applied near the ends of the delaminated section ofFIG. 1 MMB ApparatusD 6671/D 6671M 062the specimen and through rollers that bear against the specimenin the nondelaminate
30、d region. The base of the MMB apparatusholds the specimen stationary while the MMB lever loads thespecimen. The base attaches to the bottom specimen tab andalso bears on the specimen near the far end with a roller. Thelever attaches to the top tab and bears down on the specimenhalfway between the ba
31、se roller and the tabs. The lever rolleracts as a fulcrum so by pushing down on the lever arm oppositethe tab, the tab is pulled up. The length of the lever arm, c, canbe changed to vary the ratio of the load pulling on the tab to theload bearing through the roller thus changing the mode mixtureof t
32、he test. The load shall be applied to the lever such that theload remains vertical during the loading process. To reducegeometric nonlinear effects as a result of lever rotation, thelever shall be loaded such that the height of loading is slightlyabove the pivot point where the lever attaches to the
33、 testspecimen (1, 2).34.2 A record of the applied load versus opening displace-ment is recorded on an x-y recorder, or equivalent real-timeplotting device or stored digitally and post-processed. Theinterlaminar fracture toughness, Gc, and mode mixture, GII/G,are calculated from critical loads read f
34、rom the load displace-ment curve.5. Significance and Use5.1 Susceptibility to delamination is one of the majorweaknesses of many advanced laminated composite structures.Knowledge of the interlaminar fracture resistance of compos-ites is useful for product development and material selection.Since del
35、aminations can be subjected to and extended byloadings with a wide range of mode mixtures, it is importantthat the composite toughness be measured at various modemixtures. The toughness contour, in which fracture toughnessis plotted as a function of mode mixtures (see Fig. 3), is usefulfor establish
36、ing failure criterion used in damage toleranceanalyses of composite structures made from these materials.5.2 This test method can serve the following purposes:5.2.1 To establish quantitatively the effects of fiber surfacetreatment, local variations in fiber volume fraction, and pro-cessing and envir
37、onmental variables on Gcof a particularcomposite material at various mode mixtures,5.2.2 To compare quantitatively the relative values of Gcversus mode mixture for composite materials with differentconstituents, and5.2.3 To develop delamination failure criteria for compositedamage tolerance and dura
38、bility analyses.5.3 This method can be used to determine the followingdelamination toughness values:5.3.1 Delamination InitiationTwo values of delaminationinitiation shall be reported: (1) at the point of deviation fromlinearity in the load-displacement curve (NL) and (2)atthepoint at which the comp
39、liance has increased by 5 % or the loadhas reached a maximum value (5 %/max) depending on whichoccurs first along the load deflection curve (see Fig. 4). Eachdefinition of delamination initiation is associated with its ownvalue of Gcand GII/G calculated from the load at thecorresponding critical poi
40、nt. The 5 %/Max Gcvalue is typicallythe most reproducible of the three Gcvalues. The NL value is,however, the more conservative number. When the option ofcollecting propagation values is taken (see 5.3.2), a thirdinitiation value may be reported at the point at which thedelamination is first visuall
41、y observed to grow on the edge ofthe specimen. The VIS point often falls between the NLand the5 %/Max points.5.3.2 Propagation OptionIn the MMB test, the delamina-tion will grow from the insert in either a stable or an unstablemanner depending on the mode mixture being tested. As anoption, propagati
42、on toughness values may be collected whendelaminations grow in a stable manner. Propagation toughnessvalues are not attainable when the delamination grows in anunstable manner. Propagation toughness values may be heavilyinfluenced by fiber bridging which is an artifact of thezero-degree-type test sp
43、ecimen (3-5). Since they are oftenbelieved to be artificial, propagation values must be clearlymarked as such when they are reported. One use of propagationvalues is to check for problems with the delamination insert.Normally, delamination toughness values rise from the initia-tion values as the del
44、amination propagates and fiber bridging3The boldface numbers in parentheses refer to a list of references at the end ofthis standard.FIG. 2 MMB Test VariablesFIG. 3 Mixed-Mode Summary GraphFIG. 4 Load-Displacement CurvesD 6671/D 6671M 063develops. When toughness values decrease as the delaminationgr
45、ows, a poor delamination insert is often the cause. Thedelamination may be too thick or deformed in such a way thata resin pocket forms at the end of the insert. For accurateinitiation values, a properly implanted and inspected delami-nation insert is critical (see 8.2).5.3.3 Precracked ToughnessUnd
46、er rare circumstances,toughness may decrease from the initiation values as thedelamination propagates (see 5.3.2). If this occurs, the delami-nation should be checked to insure that it complies with theinsert recommendations found in 8.2. Only after verifying thatthe decreasing toughness was not due
47、 to a poor insert, shouldprecracking be considered as an option. With precracking, adelamination is first extended from the insert in Mode I, ModeII, or mixed mode. The specimen is then reloaded at the desiredmode mixture to obtain a toughness value.6. Interferences6.1 Linear elastic behavior is ass
48、umed in the calculation ofGcused in this test method. This assumption is valid when thezone of damage or nonlinear deformation at the delaminationfront, or both, is small relative to the smallest specimendimension, which is typically the specimen thickness for theMMB test.6.2 The application to othe
49、r materials, layups, and architec-tures is the same as described in Test Method D 5528.6.3 The nonlinear (NL) initiation value of toughness isnormally the more conservative value, but a few materials haveexhibited lower propagation toughness values, particularly inthe high Mode II regime. In the high Mode II regime, thedelamination growth is often unstable, precluding propagationtoughness values from being determined. The use of initiationtoughness values could result in nonconservative
