1、Designation: D6671/D6671M 06D6671/D6671M 13Standard 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 indic
2、ates theyear 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes the determinatio
3、n of interlaminar fracture toughness, Gc, of continuous fiber-reinforcedcomposite materials at various Mode I to Mode II loading ratios using the Mixed-Mode Bending (MMB) Test.1.2 This test method is limited to use with composites consisting of unidirectional carbon fiber tape laminates with brittle
4、 andtough single-phase polymer matrices. This test method is further limited to the determination of fracture toughness as it initiatesfrom a delamination insert. This limited scope reflects the experience gained in round robin testing. This test method may proveuseful for other types of toughness v
5、alues and for other classes of composite materials; however, certain interferences have beennoted (see Section 6). This test method has been successfully used to test the toughness of both glass fiber composites and adhesivejoints.1.3 The values stated in either SI units or inch-pound units are to b
6、e regarded separately as standard. The values stated in eachsystem may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from thetwo systems may result in non-conformance with the standard.1.4 This standard does not purport to address all of
7、the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating t
8、o PlasticsD2651 Guide for Preparation of Metal Surfaces for Adhesive BondingD2734 Test Methods for Void Content of Reinforced PlasticsD3171 Test Methods for Constituent Content of Composite MaterialsD3878 Terminology for Composite MaterialsD5229/D5229M Test Method for Moisture Absorption Properties
9、and Equilibrium Conditioning of Polymer Matrix CompositeMaterialsD5528 Test Method for Mode I Interlaminar FractureToughness of Unidirectional Fiber-Reinforced Polymer Matrix CompositesE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE122
10、 Practice for Calculating Sample Size to Estimate, With Specified Precision, the Average for a Characteristic of a Lot orProcessE177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE456 Terminology Relating to Quality and Statistics1 This test method is under the jurisdiction of
11、 ASTM Committee D30 on Composite Materials and is the direct responsibility of Subcommittee D30.06 on InterlaminarProperties.Current edition approved March 1, 2006Oct. 1, 2013. Published March 2006November 2013. Originally approved in 2001. Last previous edition approved in 20042006as D6671/D6671M 0
12、4D6671/D6671M 06.1 . DOI: 10.1520/D6671_D6671M-06.10.1520/D6671_D6671M-13.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the
13、ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users cons
14、ult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3.1 Terminology D3878
15、 defines terms relating to high-modulus fibers and their composites. Terminology D883 defines termsrelating to plastics.Terminology E6 defines terms relating to mechanical testing.Terminology E456 and Practice E177 define termsrelating to statistics. In the event of conflict between terms, Terminolo
16、gy D3878 shall have precedence over the other terminologystandards.NOTE 1If the term represents a physical quantity, its analytical dimensions are stated immediately following the term (or letter symbol) infundamental dimension form, using the following ASTM standard symbology for fundamental dimens
17、ions, shown within square brackets: M for mass,L for length, T for time, u for thermodynamic temperature, and nd for non-dimensional quantities. Use of these symbols is restricted to analyticaldimensions when used with square brackets, as the symbols may have other definitions when used without the
18、brackets.3.2 Definitions of Terms Specific to This Standard:3.2.1 crack opening mode (Mode I)fracture mode in which the delamination faces open away from each other and no relativecrack face sliding occurs.3.2.2 crack sliding mode (Mode II)fracture mode in which the delamination faces slide over eac
19、h other in the direction ofdelamination growth and no relative crack face opening occurs.3.2.3 mixed-mode fracture toughness, Gc M/T2the critical value of strain energy release rate, G, for delamination growthin mixed-mode.3.2.4 mixed-mode ratio, GI/GII ndthe ratio of Mode I strain energy release ra
20、te to Mode II strain energy release rate.3.2.5 mode mixture, GII/G ndfraction of Mode II to total strain energy release rate. The mixed-mode ratio, GI/ GII, is attimes referred to instead of the mode mixture.3.2.6 Mode I strain energy release rate, GI M/T2the loss of strain energy associated with Mo
21、de I deformation in the testspecimen per unit of specimen width for an infinitesimal increase in delamination length, da, for a delamination growing undera constant displacement.3.2.7 Mode II strain energy release rate, GII M/T2the loss of strain energy associated with Mode II deformation in thetest
22、 specimen per unit of specimen width for an infinitesimal increase in delamination length, da, for a delamination growing undera constant displacement.3.2.8 strain energy release rate, GG M/T2the loss of strain energy, dU, in the test specimen per unit of specimen widthfor an infinitesimal increase
23、in delamination length, da, for a delamination growing under a constant displacement. In mathematicalform,G 51 dUb da (1)G 521b dUda (1)where:a = delamination length, mm in.,b = width of specimen, mm in.,G = total strain energy release rate, kJ/m2 in.-lbf/in.2, andU = total elastic strain energy in
24、the test specimen, N-mm in.-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, mm in.c = lever length of the MMB test apparatus, mm in.cg = lever len
25、gth 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 of variation, %E11 = longitudinal modulus of elasticity measured in tension, MPa psiE22 = transverse modulus of elasticit
26、y, MPa psiEcal = modulus of calibration bar, MPa psiD6671/D6671M 132E1f = modulus of elasticity in the fiber direction measured in flexure, MPa psiG = total strain energy release rate, kJ/m2 in.-lbf/in.2G13 = shear modulus out of plane, MPa psiG12 = shear modulus in plane, MPa psiGI = opening (Mode
27、I) component of strain energy release rate, kJ/m2 in.-lbf/in2GII = shear (Mode II) component of strain energy release rate, kJ/m2 in.-lbf/in2GII/G = mode mixtureGc = total mixed-mode fracture toughness, kJ/m2 in.-lbf/in2Gcest = estimated value of total mixed-mode fracture toughness, kJ/m2 in.-lbf/in
28、2h = 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 calibration test, N/mm lbf/in.P = applied load, N lbfP5 %/max = critical load at 5 %/max point of lo
29、ading 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 = critical load when delamination is observed to grow, N lbfSD = standard d
30、eviationt = thickness of calibration bar, mm in.U = strain energy, N-mm in.-lbfV = fiber volume fraction, % = mode mixture transformation parameter for setting lever length = non-dimensional crack length correction for mode mixture = crack length correction parameter, E1111G13H322S 11D2J = load poin
31、t deflection, mm in.est = estimated load point deflection, mm in.max = maximum allowable load point of deflection, mm in. = transverse modulus correction parameter,1.18=E11E22G134. Summary of Test Method4.1 The Mixed-Mode Bending (MMB) test apparatus shown in Fig. 1 is used to load split laminate sp
32、ecimens to determine thedelamination fracture toughness at various ratios of Mode I to Mode II loading. The composite test specimen, shown in Fig. 2,consists of a rectangular, uniform thickness, unidirectional laminated composite specimen, containing a nonadhesive insert at themidplane which serves
33、as a delamination initiator. Loading forces are applied to the MMB specimen via tabs that are applied nearthe ends of the delaminated section of the specimen and through rollers that bear against the specimen in the nondelaminatedFIG. 1 MMB ApparatusD6671/D6671M 133region. The base of the MMB appara
34、tus holds the specimen stationary while the MMB lever loads the specimen. The base attachesto the bottom specimen tab and also bears on the specimen near the far end with a roller. The lever attaches to the top tab and bearsdown on the specimen halfway between the base roller and the tabs. The lever
35、 roller acts as a fulcrum so by pushing down on thelever arm opposite the tab, the tab is pulled up. The length of the lever arm, c, can be changed to vary the ratio of the load pullingon the tab to the load bearing through the roller thus changing the mode mixture of the test. The load shall be app
36、lied to the leversuch that the load remains vertical during the loading process. To reduce geometric nonlinear effects as a result of lever rotation,the lever shall be loaded such that the height of loading is slightly above the pivot point where the lever attaches to the testspecimen (1, 2).34.2 A
37、record of the applied load versus opening displacement is recorded on an x-y recorder, or equivalent real-time plottingdevice or stored digitally and post-processed. The interlaminar fracture toughness, Gc, and mode mixture, GII/G, are calculatedfrom critical loads read from the load displacement cu
38、rve.5. Significance and Use5.1 Susceptibility to delamination is one of the major weaknesses of many advanced laminated composite structures.Knowledge of the interlaminar fracture resistance of composites is useful for product development and material selection. Sincedelaminations can be subjected t
39、o and extended by loadings with a wide range of mode mixtures, it is important that the compositetoughness be measured at various mode mixtures. The toughness contour, in which fracture toughness is plotted as a function ofmode mixtures (see Fig. 3), is useful for establishing failure criterion used
40、 in damage tolerance analyses of composite structuresmade from these materials.5.2 This test method can serve the following purposes:5.2.1 To establish quantitatively the effects of fiber surface treatment, local variations in fiber volume fraction, and processingand environmental variables on Gc of
41、 a particular composite material at various mode mixtures,5.2.2 To compare quantitatively the relative values of Gc versus mode mixture for composite materials with differentconstituents, and5.2.3 To develop delamination failure criteria for composite damage tolerance and durability analyses.5.3 Thi
42、s method can be used to determine the following delamination toughness values:5.3.1 Delamination InitiationTwo values of delamination initiation shall be reported: (1) at the point of deviation fromlinearity in the load-displacement curve (NL) and (2) at the point at which the compliance has increas
43、ed by 5 % or the load hasreached a maximum value (5 %/max) depending on which occurs first along the load deflection curve (see Fig. 4). Each definitionof delamination initiation is associated with its own value of Gc and GII/G calculated from the load at the corresponding criticalpoint. The 5 %/Max
44、 Gc value is typically the most reproducible of the three Gc values. The NL value is, however, the more3 The boldface numbers in parentheses refer to a list of references at the end of this standard.FIG. 2 MMB Test VariablesFIG. 3 Mixed-Mode Summary GraphD6671/D6671M 134conservative number. When the
45、 option of collecting propagation values is taken (see 5.3.2), a third initiation value may be reportedat the point at which the delamination is first visually observed to grow on the edge of the specimen. The VIS point often fallsbetween the NL and the 5 %/Max points.5.3.2 Propagation OptionIn the
46、MMB test, the delamination will grow from the insert in either a stable or an unstable mannerdepending on the mode mixture being tested. As an option, propagation toughness values may be collected when delaminationsgrow in a stable manner. Propagation toughness values are not attainable when the del
47、amination grows in an unstable manner.Propagation toughness values may be heavily influenced by fiber bridging which is an artifact of the zero-degree-type testspecimen (3-5). Since they are often believed to be artificial, propagation values must be clearly marked as such when they arereported. One
48、 use of propagation values is to check for problems with the delamination insert. Normally, delamination toughnessvalues rise from the initiation values as the delamination propagates and fiber bridging develops. When toughness values decreaseas the delamination grows, a poor delamination insert is
49、often the cause. The delamination may be too thick or deformed in sucha way that a resin pocket forms at the end of the insert. For accurate initiation values, a properly implanted and inspecteddelamination insert is critical (see 8.2).5.3.3 Precracked ToughnessUnder rare circumstances, toughness may decrease from the initiation values as the delaminationpropagates (see 5.3.2). If this occurs, the delamination should be checked to insure
