1、Designation: D 5528 01 (Reapproved 2007)Standard 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 oforigina
2、l adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method describes the determination of theopening Mode I
3、 interlaminar fracture toughness, GIc, of con-tinuous fiber-reinforced composite materials using the doublecantilever beam (DCB) specimen (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 sing
4、le-phase polymer matri-ces. This limited scope reflects the experience gained inround-robin testing. This test method may prove useful 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 th
5、estandard. The values given in parentheses are for informationonly.1.4 This standard may involve hazardous materials, opera-tions, 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 stand
6、ard 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 2651 Guide for Preparation of Metal Surfaces for Adhe-sive BondingD 2734 Test Methods f
7、or 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 Equilibrium Conditioning of Polymer Ma-trix Composite MaterialsE4 Practices for Force Ver
8、ification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE 122 Practice 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 Methods
9、E 456 Terminology Relating to Quality and StatisticsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test Method3. Terminology3.1 Terminology D 3878 defines terms relating to high-modulus fibers and their composites. Terminology D 883defines terms relating to pla
10、stics. 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 3878 shall have prece-dence over the other terminology standards.3.2 Definitions of Terms Specific to This
11、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 the jurisdiction of ASTM Committee D30 onComposite Materials and is the direct responsibility of Subcommittee D30.06 onInterlaminar Properties.Current edition a
12、pproved May 1, 2007. Published June 2007. Originallyapproved in 1994. Last previous edition approved in 2001 as D 5528 01.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, ref
13、er to the standards Document Summary page onthe ASTM website.(a) with piano hinges (b) with loading blocksFIG. 1 Double Cantilever Beam Specimen1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.2.2 Mode I interlaminar fracture toughn
14、ess, GIcthecritical value of G for delamination growth as a result of anopening load or displacement.3.2.3 energy release rate, Gthe loss of energy, dU, in thetest specimen per unit of specimen width for an infinitesimalincrease in delamination length, da, for a delamination growingunder a constant
15、displacement. In mathematical form,G 521bdUda(1)where:U = total elastic energy in the test specimen,b = specimen width, anda = delamination 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 Cc
16、ompliance, d/P, of DCB specimen.3.3.6 CVcoefficient of variation, %.3.3.7 dadifferential increase in delamination length.3.3.8 dUdifferential 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.
17、11 Flarge displacement correction factor.3.3.12 Gstrain energy release rate.3.3.13 GIcopening Mode I interlaminar fracture tough-ness.3.3.14 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 co
18、rrection 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 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 of
19、top 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 fraction, %.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 c
20、hange 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 thickness, unidirectional laminated composite speci-men containing a nonadhesive insert on the midplane thatserves as a delamination initiator. Opening forces ar
21、e 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 are opened by controlling either the openingdisplacement or the crosshead movement, while the load anddelamination length are recorded.4.2 A record of the applie
22、d load versus opening displace-ment is recorded on an X-Y recorder, or equivalent real-timeplotting device or stored digitally and postprocessed. Instanta-neous delamination front locations are marked on the chart atintervals of delamination growth. The Mode I interlaminarfracture toughness is calcu
23、lated using a modified beam theoryor compliance calibration method.5. Significance and Use5.1 Susceptibility to delamination is one of the majorweaknesses of many advanced laminated composite structures.Knowledge of a laminated composite materials resistance tointerlaminar fracture is useful for pro
24、duct development andmaterial selection. Furthermore, a measurement of the Mode Iinterlaminar fracture toughness, independent of specimen ge-ometry or method of load introduction, is useful for establish-ing design allowables used in damage tolerance analyses ofcomposite structures made from these ma
25、terials.5.2 This test method can serve the following purposes:5.2.1 To establish quantitatively the effect of fiber surfacetreatment, local variations in fiber volume fraction, and pro-cessing and environmental variables on GIcof a particularcomposite material.5.2.2 To compare quantitatively the rel
26、ative values of GIcfor composite materials with different constituents.5.2.3 To develop delamination failure criteria for compositedamage tolerance and durability analyses.6. Interferences6.1 Linear elastic behavior is assumed in the calculation ofG used in this test method. This assumption is valid
27、 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 theDCB test.6.2 In the DCB test, as the delamination grows from theinsert, a resistance-type fracture behavior typica
28、lly developswhere the calculated GIcfirst increases monotonically, and thenstabilizes with further delamination growth. In this test method,a resistance curve (R curve) depicting GIcas a function ofdelamination length will be generated to characterize theinitiation and propagation of a delamination
29、in a unidirectionalspecimen (Fig. 2). The principal reason for the observedresistance to delamination is the development of fiber bridging(1-3).3This fiber bridging mechanism results from growing thedelamination between two 0 unidirectional plies. Becausemost delaminations that form in multiply lami
30、nated compositestructures occur between plies of dissimilar orientation, fiberbridging does not occur. Hence, fiber bridging is considered tobe an artifact of the DCB test on unidirectional materials.Therefore, the generic significance of GIcpropagation values3The boldface numbers in parentheses ref
31、er to the list of references at the end ofthis test method.D 5528 01 (2007)2calculated beyond the end of the implanted insert is question-able, and an initiation value of GIcmeasured from theimplanted insert is preferred. Because of the significance of theinitiation point, the insert must be properl
32、y implanted andinspected (8.2).6.3 Three definitions for an initiation value of GIchave beenevaluated during round-robin testing (4). These 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 p
33、oint at which delamination is visuallyobserved on the edge (VIS) measured with a microscope asspecified in 7.5, and (3) at the point at which 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 thr
34、ee GIcinitiation values, isrecommended for generating delamination failure criteria indurability and damage tolerance analyses of laminated 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 ci
35、ted in the scope (5.2.1 and5.2.2). However, physical evidence indicates that the initiationvalue corresponding to the onset of nonlinearity (NL) in theload versus opening displacement plot corresponds to thephysical onset of delamination from the insert in the interior ofthe specimen width (5). In r
36、ound-robin testing of AS4/PEEKthermoplastic matrix composites, NL GIcvalues were 20 %lower than VIS and 5 %/max values (4).6.4 Delamination 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 the
37、first type of growth is of interest in this test method. Anunstable jump from the insert may be an indication of aproblem with the insert. 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 orfol
38、d. Furthermore, rapid delamination growth may introducedynamic effects in both the test specimen and in the fracturemorphology. Treatment 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 theg
39、uidelines for inserts (see 8.2) were not violated, the specimensare unloaded after the first increment of delamination growthand reloaded 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
40、.6.5 Application to Other Materials, Layups, and Architec-tures:6.5.1 Toughness values measured on unidirectional compos-ites with multiple-phase matrices may vary depending upon thetendency for the delamination to wander between variousmatrix phases. Brittle matrix composites with tough adhesiveint
41、erleaves between plies may be particularly sensitive to thisphenomenon resulting in two apparent interlaminar fracturetoughness values: one associated with a cohesive-type failurewithin the interleaf and one associated with an adhesive-typefailure between the tough polymer film and the more brittlec
42、omposite matrix.6.5.2 Nonunidirectional DCB configurations may experi-ence branching of the delamination away from the midplanethrough matrix 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
43、 that mayexist in the asymmetric sublaminates formed as the delamina-tion grows. In addition, nonunidirectional specimens mayexperience significant anticlastic bending effects that result innonuniform delamination growth along the specimen width,particularly affecting the observed initiation values.
44、6.5.3 Woven composites may yield significantly greaterscatter and unique R curves associated with varying toughnesswithin and away from interlaminar resin pockets as thedelamination grows. Composites with significant strength ortoughness through the laminate thickness, such as compositeswith metal m
45、atrices or 3D fiber reinforcement, may experiencefailures of the beam arms rather than the intended interlaminarfailures.7. Apparatus7.1 Testing MachineA properly calibrated test machineshall be used that can be operated in a displacement controlmode with a constant displacement rate in the range fr
46、om 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 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-s
47、ensing de-vice shall be capable of indicating the total load carried by thetest specimen. This device shall be essentially free from inertialag 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 Ope
48、ning Displacement IndicatorThe opening dis-placement may be estimated as the crosshead separation,provided the deformation of the testing machine, with thespecimen grips attached, is less than 2 % of the openingdisplacement of the test specimen. If not, then the openingdisplacement shall be obtained
49、 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)37.4 Load Versus Opening Displacement RecordAn X-Yplotter, or similar device, shall be used to make a permanentrecord during the test of load versus opening displacement atthe point of load application. Alternatively, the data may best
