1、Designation: D 5528 01 (Reapproved 2007)3Standard Test Method forMode I Interlaminar Fracture Toughness of UnidirectionalFiber-Reinforced Polymer Matrix Composites1This standard is issued under the fixed designation D 5528; the number immediately following the designation indicates the year oforigin
2、al adoption or, in the case of revision, the year 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.1NOTEAdded research report reference to Section 14 editorially in March 2008.
3、2NOTECorrected Eq. 3 in July 2008.3NOTEEq. 3 was rewritten for clarification in August 2009.1. Scope1.1 This test method describes the determination of theopening Mode I interlaminar fracture toughness, GIc, of con-tinuous fiber-reinforced composite materials using the doublecantilever beam (DCB) sp
4、ecimen (Fig. 1).1.2 This test method is limited to use with compositesconsisting of unidirectional carbon fiber and glass fiber tapelaminates with brittle and tough single-phase polymer matri-ces. This limited scope reflects the experience gained inround-robin testing. This test method may prove use
5、ful forother types and classes of composite materials; however,certain interferences have been noted (see 6.5).1.3 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informationonly.1.4 This standard may involve hazardous materials, opera-tions,
6、and equipment.1.5 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.2
7、. Referenced Documents2.1 ASTM Standards:2D 883 Terminology Relating to PlasticsD 2651 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 Comp
8、osite MaterialsD 5229/D 5229M Test Method for Moisture AbsorptionProperties and Equilibrium Conditioning of Polymer Ma-trix Composite MaterialsE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE 122 Practice for Calculating Sample Size to
9、 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 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a T
10、est Method3. Terminology3.1 Terminology D 3878 defines 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.
11、 In the event ofconflict between terms, Terminology D 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.1This test method is under
12、 the jurisdiction of ASTM Committee D30 onComposite Materials and is the direct responsibility of Subcommittee D30.06 onInterlaminar Properties.Current edition approved May 1, 2007. Published June 2007. Originallyapproved in 1994. Last previous edition approved in 2001 as D 5528 01.2For referenced A
13、STM 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.(a) with piano hinges (b) with loading blocksFIG. 1 Double Cantilever Beam Spe
14、cimen1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.2 Mode I interlaminar fracture toughness, GIcthecritical value of G for delamination growth as a result of anopening load or displacement.3.2.3 energy release rate, Gthe loss o
15、f energy, dU, in thetest specimen per unit of specimen width for an infinitesimalincrease in delamination length, da, for a delamination growingunder a constant displacement. In mathematical form,G 521bdUda(1)where:U = total elastic energy in the test specimen,b = specimen width, anda = delamination
16、 length.3.3 Symbols:3.3.1 A1slope of plot of a/b versus C1/3.3.3.2 adelamination length.3.3.3 a0initial delamination length.3.3.4 bwidth of DCB specimen.3.3.5 Ccompliance, d/P, of DCB specimen.3.3.6 CVcoefficient of variation, %.3.3.7 dadifferential increase in delamination length.3.3.8 dUdifferenti
17、al increase in strain energy.3.3.9 E11modulus of elasticity in the fiber direction.3.3.10 E1fmodulus of elasticity in the fiber directionmeasured in flexure.3.3.11 Flarge displacement correction factor.3.3.12 Gstrain energy release rate.3.3.13 GIcopening Mode I interlaminar fracture tough-ness.3.3.1
18、4 hthickness of DCB specimen.3.3.15 Llength of DCB specimen.3.3.16 L8half width of loading block.3.3.17 mnumber of plies in DCB specimen.3.3.18 Nloading block correction factor.3.3.19 NLpoint at which the load versus opening dis-placement curve becomes nonlinear.3.3.20 nslope of plot of Log C versus
19、 Log a.3.3.21 Papplied load.3.3.22 Pmaxmaximum applied load during DCB test.3.3.23 SDstandard deviation.3.3.24 tdistance from loading block pin to center line oftop specimen arm.3.3.25 Ustrain energy.3.3.26 VISpoint at which delamination is observed visu-ally on specimen edge.3.3.27 Vffiber volume f
20、raction, %.3.3.28 dload point deflection.3.3.29 Deffective delamination extension to correct forrotation of DCB arms at delamination front.3.3.30 Dxincremental change in Log a.3.3.31 Dyincremental change in Log C.4. Summary of Test Method4.1 The DCB shown in Fig. 1 consists of a rectangular,uniform
21、thickness, unidirectional laminated composite speci-men containing a nonadhesive insert on the midplane thatserves as a delamination initiator. Opening forces are applied tothe DCB specimen by means of hinges (Fig. 1a) or loadingblocks (Fig. 1b) bonded to one end of the specimen. The endsof the DCB
22、are opened by controlling either the openingdisplacement or the crosshead movement, while the load anddelamination length are recorded.4.2 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 postproc
23、essed. Instanta-neous delamination front locations are marked on the chart atintervals of delamination growth. The Mode I interlaminarfracture toughness is calculated using a modified beam theoryor compliance calibration method.5. Significance and Use5.1 Susceptibility to delamination is one of the
24、majorweaknesses of many advanced laminated composite structures.Knowledge of a laminated composite materials resistance tointerlaminar fracture is useful for product development andmaterial selection. Furthermore, a measurement of the Mode Iinterlaminar fracture toughness, independent of specimen ge
25、-ometry or method of load introduction, is useful for establish-ing design allowables used in damage tolerance analyses ofcomposite structures made from these materials.5.2 This test method can serve the following purposes:5.2.1 To establish quantitatively the effect of fiber surfacetreatment, local
26、 variations in fiber volume fraction, and pro-cessing and environmental variables on GIcof a particularcomposite material.5.2.2 To compare quantitatively the relative values of GIcfor composite materials with different constituents.5.2.3 To develop delamination failure criteria for compositedamage t
27、olerance and durability analyses.6. Interferences6.1 Linear elastic behavior is assumed in the calculation ofG used 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, wh
28、ich is typically the specimen thickness for theDCB test.6.2 In the DCB test, as the delamination grows from theinsert, a resistance-type fracture behavior typically developswhere the calculated GIcfirst increases monotonically, and thenstabilizes with further delamination growth. In this test method
29、,a resistance curve (R curve) depicting GIcas a function ofdelamination length will be generated to characterize theinitiation and propagation of a delamination in a unidirectionalspecimen (Fig. 2). The principal reason for the observedresistance to delamination is the development of fiber bridging(
30、1-3).3This fiber bridging mechanism results from growing thedelamination between two 0 unidirectional plies. Becausemost delaminations that form in multiply laminated compositestructures occur between plies of dissimilar orientation, fiberbridging does not occur. Hence, fiber bridging is considered
31、tobe an artifact of the DCB test on unidirectional materials.Therefore, the generic significance of GIcpropagation values3The boldface numbers in parentheses refer to the list of references at the end ofthis test method.D 5528 01 (2007)32calculated beyond the end of the implanted insert is question-
32、able, and an initiation value of GIcmeasured from theimplanted insert is preferred. Because of the significance of theinitiation point, the insert must be properly implanted andinspected (8.2).6.3 Three definitions for an initiation value of GIchave beenevaluated during round-robin testing (4). Thes
33、e include GIcvalues determined using the load and deflection measured (1)at the point of deviation from linearity in the load-displacementcurve (NL), (2) at the point at which delamination is visuallyobserved on the edge (VIS) measured with a microscope asspecified in 7.5, and (3) at the point at wh
34、ich the compliancehas increased by 5 % or the load has reached a maximum value(5 %/max) (see Section 11). The NL GIcvalue, which istypically the lowest of the three GIcinitiation values, isrecommended for generating delamination failure criteria indurability and damage tolerance analyses of laminate
35、d com-posite structures (5.2.3). Recommendations for obtaining theNL point are given in Annex A2. All three initiation values canbe used for the other purposes cited in the scope (5.2.1 and5.2.2). However, physical evidence indicates that the initiationvalue corresponding to the onset of nonlinearit
36、y (NL) in theload versus opening displacement plot corresponds to thephysical onset of delamination from the insert in the interior ofthe specimen width (5). In round-robin testing of AS4/PEEKthermoplastic matrix composites, NL GIcvalues were 20 %lower than VIS and 5 %/max values (4).6.4 Delaminatio
37、n growth may proceed in one of two ways:(1) by a slow stable extension or (2) a run-arrest extension inwhich the delamination front jumps ahead abruptly. Only thefirst type of growth is of interest in this test method. Anunstable jump from the insert may be an indication of aproblem with the insert.
38、 For example, the insert may not becompletely disbonded from the laminate, or may be too thick,resulting in a large neat resin pocket, or may contain a tear orfold. Furthermore, rapid delamination growth may introducedynamic effects in both the test specimen and in the fracturemorphology. Treatment
39、and interpretation of these effects isbeyond the scope of this test method. However, because crackjumping has been observed in at least one material in which theguidelines for inserts (see 8.2) were not violated, the specimensare unloaded after the first increment of delamination growthand reloaded
40、to continue the test. This procedure induces anatural Mode I precrack in the DCB specimen. The firstpropagation GIcvalue is referred to as the Mode I precrack GIc.6.5 Application to Other Materials, Layups, and Architec-tures:6.5.1 Toughness values measured on unidirectional compos-ites with multipl
41、e-phase matrices may vary depending upon thetendency for the delamination to wander between variousmatrix phases. Brittle matrix composites with tough adhesiveinterleaves between plies may be particularly sensitive to thisphenomenon resulting in two apparent interlaminar fracturetoughness values: on
42、e associated with a cohesive-type failurewithin the interleaf and one associated with an adhesive-typefailure between the tough polymer film and the more brittlecomposite matrix.6.5.2 Nonunidirectional DCB configurations may experi-ence branching of the delamination away from the midplanethrough mat
43、rix cracks in off-axis plies. If the delaminationbranches away from the midplane, a pure Mode I fracture maynot be achieved as a result of the structural coupling that mayexist in the asymmetric sublaminates formed as the delamina-tion grows. In addition, nonunidirectional specimens mayexperience si
44、gnificant anticlastic bending effects that result innonuniform delamination growth along the specimen width,particularly affecting the observed initiation values.6.5.3 Woven composites may yield significantly greaterscatter and unique R curves associated with varying toughnesswithin and away from in
45、terlaminar resin pockets as thedelamination grows. Composites with significant strength ortoughness through the laminate thickness, such as compositeswith metal matrices or 3D fiber reinforcement, may experiencefailures of the beam arms rather than the intended interlaminarfailures.7. Apparatus7.1 T
46、esting MachineA properly calibrated test machineshall be used that can be operated in a displacement controlmode with a constant displacement rate in the range from 0.5to 5.0 mm/min (0.02 to 0.20 in./min). The testing machine shallconform to the requirements of Practices E4. The testingmachine shall
47、 be equipped with grips to hold the loadinghinges, or pins to hold the loading blocks, that are bonded tothe specimen.7.2 Load IndicatorThe testing machine load-sensing de-vice shall be capable of indicating the total load carried by thetest specimen. This device shall be essentially free from inert
48、ialag at the specified rate of testing and shall indicate the loadwith an accuracy over the load range(s) of interest of within61 % of the indicated value.7.3 Opening Displacement IndicatorThe opening dis-placement may be estimated as the crosshead separation,provided the deformation of the testing
49、machine, with thespecimen grips attached, is less than 2 % of the openingdisplacement of the test specimen. If not, then the openingdisplacement shall be obtained from a properly calibratedexternal gage or transducer attached to the specimen. Thedisplacement indicator shall indicate the crack opening dis-placement with an accuracy of within 61 % of the indicatedvalue once the delamination occurs.FIG. 2 Delamination Resistance Curve (R Curve) from DCB TestD 5528 01 (2007)337.4 Load Versus Opening Displacement RecordAn X-Yplotter, or
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