1、Designation: D6671/D6671M 131Standard Test Method forMixed Mode I-Mode II Interlaminar Fracture Toughness ofUnidirectional Fiber Reinforced Polymer Matrix Composites1This standard is issued under the fixed designation D6671/D6671M; the number immediately following the designation indicates theyear o
2、f 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 () indicates an editorial change since the last revision or reapproval.1NOTECharacters in equations 2, 3, 10, 12, 13, and 1721 corrected edi
3、torially in May 2015.1. Scope1.1 This test method describes the determination of inter-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 comp
4、ositesconsisting of unidirectional carbon fiber tape laminates withbrittle and tough single-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 robin
5、testing. This test method may prove useful for other types oftoughness values and for 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 joint
6、s.1.3 The values stated in either SI units or inch-pound unitsare to be regarded separately 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-conformancewit
7、h the standard.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 of regulatory limitations prior to use.
8、2. Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsD2651 Guide for Preparation of Metal Surfaces forAdhesiveBondingD2734 Test Methods for Void Content of Reinforced PlasticsD3171 Test Methods for Constituent Content of CompositeMaterialsD3878 Terminology for Composite Ma
9、terialsD5229/D5229M Test Method for MoistureAbsorption Prop-erties and Equilibrium Conditioning of Polymer MatrixComposite MaterialsD5528 Test Method for Mode I Interlaminar FractureTough-ness of Unidirectional Fiber-Reinforced Polymer MatrixCompositesE4 Practices for Force Verification of Testing M
10、achinesE6 Terminology Relating to Methods of Mechanical TestingE122 Practice for Calculating Sample Size to Estimate, WithSpecified Precision, the Average for a Characteristic of aLot or ProcessE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE456 Terminology Relating to Qual
11、ity and Statistics3. Terminology3.1 Terminology D3878 defines terms relating to high-modulus fibers and their composites. Terminology D883 de-fines terms relating to plastics. Terminology E6 defines termsrelating to mechanical testing. Terminology E456 and PracticeE177 define terms relating to stati
12、stics. In the event of conflictbetween terms, Terminology D3878 shall have precedenceover the other terminology standards.NOTE 1If the term represents a physical quantity, its analyticaldimensions are stated immediately following the term (or letter symbol) infundamental dimension form, using the fo
13、llowing ASTM standard sym-bology for fundamental dimensions, 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 sym
14、bolsmay have other definitions when used without the brackets.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.1This test method is under the jurisdictio
15、n of ASTM Committee D30 onComposite Materials and is the direct responsibility of Subcommittee D30.06 onInterlaminar Properties.Current edition approved Oct. 1, 2013. Published November 2013. Originallyapproved in 2001. Last previous edition approved in 2006 as D6671/D6671M 06.DOI: 10.1520/D6671_D66
16、71M-13E01.2For 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 page onthe ASTM website.Copyright ASTM International, 100 Barr Harbor Drive
17、, PO Box C700, West Conshohocken, PA 19428-2959. United States13.2.2 crack sliding mode (Mode II)fracture mode in whichthe delamination faces slide over each other in the direction ofdelamination growth and no relative crack face opening occurs.3.2.3 mixed-mode fracture toughness, GcM/T2the criti-ca
18、l value of strain energy release rate, G, for delaminationgrowth in mixed-mode.3.2.4 mixed-mode ratio, GI/GIIndthe ratio of Mode Istrain energy release rate to Mode II strain energy release rate.3.2.5 mode mixture, GII/G ndfraction of Mode II to totalstrain energy release rate. The mixed-mode ratio,
19、 GI/ GII,isattimes referred to instead of the mode mixture.3.2.6 Mode I strain energy release rate, GIM/T2the lossof strain energy associated with Mode I deformation in the testspecimen per unit of specimen width for an infinitesimalincrease in delamination length, da, for a delamination growingunde
20、r a constant displacement.3.2.7 Mode II strain energy release rate, GIIM/T2theloss of strain energy associated with Mode II deformation inthe test specimen per unit of specimen width for an infinitesi-mal increase in delamination length, da, for a delaminationgrowing under a constant displacement.3.
21、2.8 strain energy release rate, G M/T2the loss of strainenergy, 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 521bdUda(1)where:a = delamination length, mm i
22、n.,b = width of specimen, mm in.,G = total strain energy 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
23、 specimen, mm in.bcal= width of calibration specimen, mm in.c = lever length of the MMB test apparatus, mm in.cg= lever length to center of gravity, mm in.C = compliance, /P, mm/N in./lbfCcal= calibration specimen compliance, /P, mm/N in./lbfCsys= system compliance, /P, mm/N in./lbfCV = coefficient
24、of variation, %E11= longitudinal modulus of elasticity 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.
25、2G13= shear modulus out of plane, MPa psiG12= shear modulus in plane, MPa psiGI= opening (Mode I) component of strain energy releaserate, kJ/m2in.-lbfin2GII= shear (Mode II) component of strain energy releaserate, kJ/m2in.-lbfin2GII/G = mode mixtureGc= total mixed-mode fracture toughness, kJ/m2in.-l
26、bf/in2Gcest= estimated value of total mixed-mode fracturetoughness, kJ/m2in.-lbfin2h = 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/
27、mm lbf/in.P = applied load, N lbfP5 % max= critical load at 5 %max point of loading curve,N lbfPest= 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= c
28、ritical load when delamination is observed to grow, NlbfSD = standard deviationt = thickness of calibration bar, mm in.U = strain energy, N-mm in.-lbfV = fiber volume fraction, % = mode mixture transformation parameter for setting leverlength = non-dimensional crack length correction for mode mix-tu
29、re = crack length correction parameter,E1111G13H3 2 2S11D2J = load point deflection, mm in.est= estimated load point deflection, mm in.max= maximum allowable load point of deflection, mmin. = transverse modulus correction parameter,1.18=E11E22G134. Summary of Test Method4.1 The Mixed-Mode Bending (M
30、MB) test apparatus shownin Fig. 1 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 spe
31、cimen, containing a nonadhe-sive 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 ofthe specimen and through rollers that bear against the specimenD6671/D6671M 1312in the n
32、ondelaminated 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 be
33、tween the base 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
34、 mixtureof the 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 att
35、aches to the 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
36、loads read from 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 selecti
37、on.Since delaminations 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 usefulf
38、or establishing 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-cessi
39、ng and environmental 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 tolera
40、nce and durability 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 wh
41、ich the compliance 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 c
42、ritical point. The 5 %Max Gcvalue is typi-cally the most reproducible of the three Gcvalues. The NLvalue is, however, the more conservative number. When theoption of collecting propagation values is taken (see 5.3.2), athird initiation value may be reported at the point at which thedelamination is f
43、irst visually observed to grow on the edge ofthe specimen.TheVIS 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,
44、propagation toughness values may be collected when3The boldface numbers in parentheses refer to a list of references at the end ofthis standard.FIG. 1 MMB ApparatusFIG. 2 MMB Test VariablesFIG. 3 Mixed-Mode Summary GraphFIG. 4 Load-Displacement CurvesD6671/D6671M 1313delaminations grow in a stable m
45、anner. 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 specimen (3-5). Since they are oftenbelieved to be artificial, propagation
46、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 delamination propagates and fiber bridgingdevelops. When toughness values de
47、crease as the delaminationgrows, 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
48、.3.3 Precracked ToughnessUnder 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 decr
49、easing toughness was not due 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 assumed in the calculation ofGcused in this test method. This assumption is valid when thezone of damage or nonline
