1、Designation: D6115 97 (Reapproved 2011)Standard Test Method forMode I Fatigue Delamination Growth Onset of UnidirectionalFiber-Reinforced Polymer Matrix Composites1This standard is issued under the fixed designation D6115; 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 () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method determines the number of cycles (N)for the onset
3、of delamination growth based on the openingmode I cyclic strain energy release rate (G), using the DoubleCantilever Beam (DCB) specimen shown in Fig. 1. This testmethod applies to constant amplitude, tension-tension fatigueloading of continuous fiber-reinforced composite materials.When this test met
4、hod is applied to multiple specimens atvarious G-levels, the results may be shown as a GN curve, asillustrated in Fig. 2.1.2 This test method is limited to use with compositesconsisting of unidirectional carbon fiber tape laminates withsingle-phase polymer matrices. This limited scope reflects theex
5、perience gained in round robin testing. This test method mayprove useful for other types and classes of composite materials,however, certain interferences have been noted (see Section 6.5of Test Method D5528).1.3 The values stated in SI units are to be regarded asstandard. No other units of measurem
6、ent are included in thisstandard.1.3.1 ExceptionThe values provided in parentheses arefor information only.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 a
7、nd health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsD2584 Test Method for Ignition Loss of Cured ReinforcedResinsD2651 Guide for Preparation of Metal Surfaces for Adhe-sive Bonding
8、D2734 Test Methods for Void Content of Reinforced Plas-ticsD3171 Test Methods for Constituent Content of CompositeMaterialsD3878 Terminology for Composite MaterialsD5229/D5229M Test Method for Moisture AbsorptionProperties and Equilibrium Conditioning of Polymer Ma-trix Composite MaterialsD5528 Test
9、 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 TestingE122 Practice for Calculating Sample Size to Estimate,With Specified Precision,
10、the Average for a Characteristicof a Lot or ProcessE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE456 Terminology Relating to Quality and StatisticsE467 Practice for Verification of Constant Amplitude Dy-namic Forces in an Axial Fatigue Testing SystemE691 Practice for Cond
11、ucting an Interlaboratory Study toDetermine the Precision of a Test MethodE739 Practice for Statistical Analysis of Linear or Linear-ized Stress-Life (S-N) and Strain-Life (e-N) Fatigue DataE1049 Practices for Cycle Counting in Fatigue Analysis1This specification is under the jurisdiction of ASTM Co
12、mmittee D30 onComposite Materials and is the direct responsibility of Subcommittee D30.06 onInterlaminar Properties.Current edition approved Aug. 1, 2011. Published December 2011. Originallyapproved in 1997. Last previous edition approved in 2004 as D6115 97 (2004).DOI: 10.1520/D6115-97R11.2For refe
13、renced 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.FIG. 1 DCB Specimen with Piano Hinges1Copyright ASTM International, 10
14、0 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.E1150 Definitions of Terms Relating to Fatigue3. Terminology3.1 Terminology D3878 defines terms relating to high-modulus fibers and their composites. Terminology D883 de-fines terms relating to plastics. Terminology E6
15、 defines termsrelating to mechanical testing. Terminology E456 and PracticeE177 define terms relating to statistics. Definitions E1150defines terms relating to fatigue. In the event of conflictbetween terms, Terminology D3878 shall have precedenceover the other terminology standards.3.2 Definitions
16、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 andin which these faces do not undergo any relative sliding.3.2.2 cycles to onset of delamination growth, Nathe num-ber of fatigue cycles elapsed until the onset
17、 of delaminationgrowth from an implanted thin insert.3.2.3 fatigue delamination growth onset relationship,GNthe relationship between the peak cyclic value of strainenergy release rate to the number of fatigue cycles until theonset of delamination growth, Na.3.2.4 mode I interlaminar fracture toughne
18、ss, GIcthecritical value of G for delamination growth because of anopening load or displacement.3.2.5 strain energy release rate, Gthe 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
19、constant displacement. In math-ematical form:G 521bdUda(1)where:U = total elastic strain energy in the test specimen,b = specimen width, anda = delamination length.3.3 Symbols:3.3.1 adelamination length.3.3.2 a0initial delamination length.3.3.3 bwidth of DCB specimen.3.3.4 Ccompliance, d/P, of DCB s
20、pecimen.3.3.5 CVcoefficient of variation, %.3.3.6 dainfinitesimal increase in delamination length.3.3.7 dUinfinitesimal increase in strain energy.3.3.8 EIImodulus of elasticity in the fiber direction.3.3.9 Gstrain energy release rate.3.3.10 GIcopening mode I interlaminar fracture tough-ness.3.3.11 G
21、Icavaverage values of GIcfrom the quasi-statictests.3.3.12 GImaxmaximum or peak cyclic mode I strain en-ergy release rate.3.3.13 GNrelationship between the cyclic strain energyrelease rate and the number of cycles to onset of delaminationgrowth.3.3.14 hthickness of DCB specimen.3.3.15 Nnumber of ela
22、psed fatigue cycles.3.3.16 Naapplication dependent value of N at whichdelamination growth onset will occur.3.3.17 N1a%number of fatigue cycles for the value of Pmaxat N = 1 to decrease by 1 %.3.3.18 NaViSnumber of fatigue cycles at which the onsetof delamination growth is observed.3.3.19 N5a%number
23、of fatigue cycles for the value of Pmaxat N = 1 to decrease by 5 %.3.3.20 Papplied load.3.3.21 Pcrvalue of load at the onset of delaminationgrowth from the insert in the quasi-static tests.3.3.22 Pmaxmaximum cyclic load.3.3.23 Rratio of minimum and peak loads Pmin/Pmax.3.3.24 SDstandard deviation.3.
24、3.25 Ustrain energy.3.3.26 Vffiber volume fraction, %.3.3.27 dload point deflection.3.3.28 dcrvalue of displacement at the onset of delamina-tion growth from the insert in a quasi-static test.3.3.29 dmaxmaximum value of cyclic displacement.3.3.30 dmeanmean value of cyclic displacement.3.3.31 dmmmini
25、mum value of cyclic displacement.3.3.32 Deffective delamination extension to correct forrotation of DCB arms at delamination front.3.3.33 Davaverage value of D from the quasi-static tests.4. Summary of Test Method4.1 The Double Cantilever Beam (DCB) shown in Fig. 2 isdescribed in Test Method D5528.4
26、.2 The DCB specimen is cycled between a minimum andmaximum displacement, dmin, and dmax, at a specified fre-quency. For linear elasticity and small deflections (d/a 0.4)the displacement ratio, dmin/ dmax, is identical to the R-ratio.The number of displacement cycles at which the onset ofdelamination
27、 growth occurs, Na, is recorded. The mode I cyclicstrain energy release rate, for example the maximum value,GImaxis calculated using a modified beam theory or othermethods described in Test Method D5528. By testing severalspecimens a relationship is developed between GImaxand Nafor the chosen freque
28、ncy.FIG. 2 GN CurveD6115 97 (2011)25. 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 under fatigue loads is useful for productdevelopm
29、ent and material selection. Furthermore, a measure-ment of the relationship of the mode I cyclic strain energyrelease rate and the number of cycles to delamination growthonset, GN, that is independent of specimen geometry ormethod of load introduction, is useful for establishing designallowables use
30、d in damage tolerance analyses of compositestructures 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 environmental variables on GN
31、of a particularcomposite material.5.2.2 To compare quantitatively the relative values of GNfor composite materials with different constituents.5.2.3 To develop criteria for avoiding the onset of delami-nation growth under fatigue loading for composite damagetolerance and durability analyses.6. Inter
32、ferences6.1 Linear elastic behavior is assumed in the calculation ofG used in this test method. This assumption is valid when thezone of damage or non-linear deformation at the delaminationfront, or both, is small relative to the smallest specimendimension, which is typically the specimen thickness
33、for theDCB test.6.2 As the delamination grows under fatigue, fiber bridgingobserved in quasi-static testing (see Test Method D5528) mayalso occur. Fiber bridging inhibits the fatigue delaminationgrowth resulting in slower growth rates than if there was nobridging. This results in artificially high t
34、hreshold values wherethe delamination ceases to grow or grows very slowly.3Inaddition, the rate of change of the delamination growth rateversus the peak cyclic strain energy release rate for the DCB isvery high. Therefore, small variations in the peak cyclic strainenergy release rate will result in
35、large changes in the delami-nation growth rate. For these two reasons, this test method doesnot monitor the fatigue delamination growth rate. Instead, thistest method monitors the number of cycles until the onset ofdelamination growth from the end of a thin insert. A value ofG may be defined such th
36、at delamination growth will not occuruntil Nacycles have elapsed, where Nais defined by theapplication, Fig. 1.6.3 Three definitions to determine the number of cyclesuntil the onset of delamination growth were used during aninvestigative round robin. These include: (1) the number ofcycles until the
37、delamination was visually observed to grow atthe edge, NaViS;(2) the number of cycles until the compliancehad increased by 1 %, N1%a(this is approximately equivalent toa 1 % decrease in the maximum cyclic load; and (3) thenumber of cycles until the compliance has increased by 5 %,N5%a(this is approx
38、imately equivalent to a 5 % decrease in themaximum cyclic load). The three techniques gave differentresults but the N1%avalue is typically the lowest of the threevalues4and is recommended for generating a conservativecriterion for avoiding onset of fatigue delamination growth indurability and damage
39、 tolerance analyses of laminated com-posite structures. Because of the difficulties in visually moni-toring the end of a delamination during a fatigue test, the visualmethod is not included in this test method.6.4 The test frequency may affect results. If the test fre-quency is high, heating effects
40、 may occur in the composite. Toavoid these effects, frequency should be chosen to be between1 and 10 cycles per second (Hz) and should be chosen such thatthere is no temperature change of the specimen. Other testfrequencies may be used if they are more appropriate for theapplication. The test freque
41、ncy shall be reported.6.5 The displacement ratio, dmin/ dmax, may have a largeeffect on the results. Because the DCB specimen cannot betested in compression the displacement ratio must remainwithin the following range: 0 # dmin/dmax 1. The displace-ment ratio shall be reported. Large deflections may
42、 be consid-ered by using the corrections given in the Annex of TestMethod D5528.6.6 The application to other materials, lay-ups and architec-tures is described in Test Method D5528.7. Apparatus7.1 Testing MachineA properly calibrated test machineshall be used that can be operated in a displacement c
43、ontrolmode. The testing machine shall conform to the requirementsof Practices E4 and E467. The testing machine shall beequipped with grips to hold the loading hinges, or pins to holdthe loading blocks, that are bonded to the specimen.7.2 Load IndicatorThe testing machine load sensing de-vice shall b
44、e capable of indicating the total load carried by thetest specimen. This device shall be essentially free frominertia-lag at the specified rate of testing and shall indicate theload with an accuracy over the load range(s) of interest ofwithin 61 % of the indicated value. The peak cyclic load shallno
45、t be less than 10 % of the full scale of the load cell. Section8.2 details how to estimate the expected peak cyclic load. If thecurrent load cell capacity of the test stand is too large, a lowload capacity load cell may be placed in series.7.3 Opening Displacement IndicatorThe opening dis-placement
46、may be estimated as the crosshead separation oractuator displacement provided the deformation of the testingmachine, with the specimen grips attached, is less than 2 % ofthe maximum cyclic opening displacement of the test speci-men. If not, then the opening displacement shall be obtainedfrom a prope
47、rly calibrated external gage or transducer attachedto the specimen. The displacement indicator shall indicate thecrack opening displacement with an accuracy of within 61%of the indicated value once the delamination occurs.7.4 MicrometersAs described in Test Method D5528.3Martin, R. H. and Murri, G.
48、B., “Characterization of Mode I and Mode IIDelamination Growth and Thresholds in AS4/PEEK Composites,” CompositeMaterials: Testing and Design (9th Volume), ASTM STP 1059, S. P. Garbo, Ed.,1990, pp. 251 270.4Preliminary data from D30.06 round robin.D6115 97 (2011)38. Sampling and Test Specimens8.1 Th
49、e test specimen dimensions and load introduction areas described in Test Method D5528.8.2 An estimate of the values of Pmaxduring the longduration tests may be required to determine if a smaller loadcell is required, per Section 7.2. If quasi-static tests wereconducted on identical specimens to those to be fatigue tested,a value of Pmaxmay be estimated by assuming the lowest valueof peak cyclic strain energy release rate will be 10 % of GIc.Or,Pmax=0.1 Pcr, where Pcris the value used to calculate Gk.If this data is not avail
