1、Designation: D 6115 97 (Reapproved 2004)Standard Test Method forMode I Fatigue Delamination Growth Onset of UnidirectionalFiber-Reinforced Polymer Matrix Composites1This standard is issued under the fixed designation D 6115; the number immediately following the designation indicates the year oforigi
2、nal 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 determines the number of cycles (N)for the ons
3、et 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
4、method 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 th
5、eexperience 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 D 5528).1.3 The values stated in SI units are to be regarded asstandard. The values provided in
6、 parentheses are for informa-tion 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 and health practices and determine the applica-bility of regulatory l
7、imitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 883 Terminology Relating to PlasticsD 2584 Test Method for Ignition Loss of Cured ReinforcedResinsD 2651 Guide for Preparation of Metal Surfaces for Adhe-sive BondingD 2734 Test Method for Void Content of Reinforced Plas-ticsD 3171
8、 Test Method 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 MaterialsD 5528 Test Method for Mode I Interlaminar FractureToughness of Unidirec
9、tional Fiber-Reinforced PolymerMatrix CompositesE 4 Practices for Force Verification of Testing MachinesE 6 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 Proce
10、ssE 177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE 456 Terminology Relating to Quality and StatisticsE 467 Practice for Verification of Constant Amplitude Dy-namic Loads on Displacements in an Axial Load FatigueTesting SystemE 691 Practice for Conducting an Interlaboratory
11、 Study toDetermine the Precision of a Test MethodE 739 Practice for Statistical Analysis of Linear or Linear-ized Stress-Life (S-N) and Strain-Life (e-N ) Fatigue Data1This specification is under the jurisdiction of ASTM Committee D30 onComposite Materials and is the direct responsibility of Subcomm
12、ittee D30.06 onInterlaminar Properties.Current edition approved Mar. 1, 2004. Published March 2004. Originallyapproved in 1997. Last previous edition approved in 1997 as D 6115 97.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org
13、. 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, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.E 1049 Practices for Cycle Co
14、unting in Fatigue AnalysisE 1150 Definitions Relating to Fatigue33. Terminology3.1 Terminology D 3878 defines terms relating to high-modulus fibers and their composites. Terminology D 883defines terms relating to plastics. Terminology E 6 definesterms relating to mechanical testing. Terminology E 45
15、6 andPractice E 177 define terms relating to statistics. DefinitionE 1150 defines terms relating to fatigue. In the event of conflictbetween terms, Terminology D 3878 shall have precedenceover the other terminology standards.3.2 Definitions of Terms Specific to This Standard:3.2.1 crack opening mode
16、 (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 of delaminationgrowth from an implanted thin insert.3.2.3
17、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 toughness, GIcthecritical value of G for delamination growth becau
18、se 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 constant displacement. In math-ematical form:G 521bdUda(1)w
19、here: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 specimen.3.3.5 CVcoefficient of variation, %.3.3.6 dainfinit
20、esimal 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 GIcavaverage values of GIcfrom the quasi-statictests.3.3.12
21、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 elapsed fatigue cycles.3.3.16 Naapplication dependent value of
22、 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 of fatigue cycles for the value of Pmaxat N = 1 to decrease
23、 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.3.3.25 Ustrain energy.3.3.26 Vffiber volume fraction, %.3.3.2
24、7 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 dmmminimum value of cyclic displacement.3.3.32 Deffective delamina
25、tion 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 D 5528.4.2 The DCB specimen is cycled between a minimum andmaximum
26、 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 growth occurs, Na, is recorded. The mode I cyclicstrain e
27、nergy release rate, for example the maximum value,GImaxis calculated using a modified beam theory or othermethods described in Test Method D 5528. By testing severalspecimens a relationship is developed between GImaxand Nafor the chosen frequency.3Withdrawn.FIG. 2 GN CurveD 6115 97 (2004)25. Signifi
28、cance 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 productdevelopment and material selection. Furthermore, a me
29、asure-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 used in damage tolerance analyses of compositest
30、ructures 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 of a particularcomposite material.5.2.2 To co
31、mpare 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. Interferences6.1 Linear elastic behavior is assume
32、d 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 for theDCB test.6.2 As the delamination grows
33、 under fatigue, fiber bridgingobserved in quasi-static testing (see Test Method D 5528) mayalso occur. Fiber bridging inhibits the fatigue delaminationgrowth resulting in slower growth rates than if there was nobridging. This results in artificially high threshold values wherethe delamination ceases
34、 to grow or grows very slowly.4Inaddition, 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 large changes in the delami-nation growth ra
35、te. 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 that delamination growth will not occuruntil N
36、acycles 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 delamination was visually observed to grow a
37、tthe 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 approximately equivalent to a 5 % decrease in them
38、aximum cyclic load). The three techniques gave differentresults but the N1%avalue is typically the lowest of the threevalues5and is recommended for generating a conservativecriterion for avoiding onset of fatigue delamination growth indurability and damage tolerance analyses of laminated com-posite
39、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 may occur in the composite. Toavoid these e
40、ffects, 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 frequency shall be reported.6.5 The displacement r
41、atio, 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 be consid-ered by using the corrections giv
42、en in the Annex of TestMethod D 5528.6.6 The application to other materials, lay-ups and architec-tures is described in Test Method D 5528.7. Apparatus7.1 Testing MachineA properly calibrated test machineshall be used that can be operated in a displacement controlmode. The testing machine shall conf
43、orm to the requirementsof Practices E 4 and E 467. 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 be capable of indicating the total load c
44、arried 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 shallnot be less than 10 % of the full scale of
45、 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 may be estimated as the crosshead separa
46、tion 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 properly calibrated external gage or transduc
47、er 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 D 5528.4Martin, R. H. and Murri, G. B., “Characterization of Mode I and Mod
48、e IIDelamination Growth and Thresholds in AS4/PEEK Composites,” CompositeMaterials: Testing and Design (9th Volume), ASTM STP 1059, S. P. Garbo, Ed.,1990, pp. 251270.5Preliminary data from D30.06 round robin.D 6115 97 (2004)38. Sampling and Test Specimens8.1 The test specimen dimensions and load int
49、roduction areas described in Test Method D 5528.8.2 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 available Pmaxmay be determined thus:Pmax5ba
