1、Designation: D7615/D7615M 11Standard Practice forOpen-Hole Fatigue Response of Polymer Matrix CompositeLaminates1This standard is issued under the fixed designation D7615/D7615M; the number immediately following the designation indicates theyear of original adoption or, in the case of revision, the
2、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 practice provides instructions for modifying staticopen-hole tensile and compressive strength test method
3、s todetermine the fatigue behavior of composite materials sub-jected to cyclic tensile or compressive forces, or both. Thecomposite material forms are limited to continuous-fiber rein-forced polymer matrix composites in which the laminate isboth symmetric and balanced with respect to the test direct
4、ion.The range of acceptable test laminates and thicknesses aredescribed in 8.2.1.2 This practice supplements Test Methods D5766/D5766M and D6484/D6484M with provisions for testingspecimens under cyclic loading. Several important test speci-men parameters (for example, fatigue force(stress) ratio) ar
5、enot mandated by this practice; however, repeatable resultsrequire that these parameters be specified and reported.1.3 This practice is limited to test specimens subjected toconstant amplitude uniaxial loading, where the machine iscontrolled so that the test specimen is subjected to repetitiveconsta
6、nt amplitude force (stress) cycles. Either engineeringstress or applied force may be used as a constant amplitudefatigue variable. The repetitive loadings may be tensile, com-pressive, or reversed, depending upon the test specimen andprocedure utilized.1.4 The values stated in either SI units or inc
7、h-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Combiningvalues from the two systems may result in non-conformancewith the standard.1.4.1 Within the text the inch-pou
8、nd units are shown inbrackets.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 limitation
9、s prior to use.2. Referenced Documents2.1 ASTM Standards:2D883 Terminology Relating to PlasticsD3878 Terminology for Composite MaterialsD5229/D5229M Test Method for Moisture AbsorptionProperties and Equilibrium Conditioning of Polymer Ma-trix Composite MaterialsD5766/D5766M Test Method for Open-Hole
10、 TensileStrength of Polymer Matrix Composite LaminatesD6484/D6484M Test Method for Open-Hole CompressiveStrength of Polymer Matrix Composite LaminatesE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical TestingE83 Practice for Verification and Class
11、ification of Exten-someter SystemsE122 Practice for Calculating Sample Size to Estimate,With Specified Precision, 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 Practi
12、ce for Verification of Constant Amplitude Dy-namic Forces in an Axial Fatigue Testing SystemE739 Practice for Statistical Analysis of Linear or Linear-ized Stress-Life (S-N) and Strain-Life (e-N) Fatigue DataE1309 Guide for Identification of Fiber-ReinforcedPolymer-Matrix Composite Materials in Data
13、basesE1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in DatabasesE1823 Terminology Relating to Fatigue and Fracture Test-ing3. Terminology3.1 DefinitionsTerminology D3878 defines terms relatingto high-modulus fibers and their composites. TerminologyD883 defines
14、 terms relating to plastics. Terminology E6 definesterms relating to mechanical testing. Terminology E1823defines terms relating to fatigue. Terminology E456 and1This practice is under the jurisdiction of ASTM Committee D30 on CompositeMaterials and is the direct responsibility of Subcommittee D30.0
15、5 on Structural TestMethods.Current edition approved Jan. 1, 2011. Published February 2011.DOI: 10.1520/D7615_D7615M-11.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer
16、 to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.Practice E177 define terms relating to statistics. In the event ofa conflict between terms, Terminology D3878 shall havepreced
17、ence over the other standards.NOTE 1If the term represents a physical quantity, its analyticaldimensions are stated immediately following the term (or letter symbol) infundamental dimension form, using the following ASTM standard sym-bology for fundamental dimensions, shown within square brackets: M
18、for mass, L for length, T for time, u for thermodynamic temperature,and nd for non-dimensional quantities. Use of these symbols is restrictedto analytical dimensions when used with square brackets, as the symbolsmay have other definitions when used without the brackets.3.2 Definitions of Terms Speci
19、fic to This Standard:3.2.1 constant amplitude loading, nin fatigue, a loadingin which all of the peak values of force (stress) are equal andall of the valley values of force (stress) are equal.3.2.2 fatigue loading transition, nin the beginning offatigue loading, the number of cycles before the forc
20、e (stress)reaches the desired peak and valley values.3.2.3 force, P MLT2, nthe total force carried by a testspecimen.3.2.4 force (stress) ratio, R nd, nin fatigue loading, theratio of the minimum applied force (stress) to the maximumapplied force (stress).3.2.5 frequency, f T1, nin fatigue loading,
21、the number offorce (stress) cycles completed in 1 s (Hz).3.2.6 nominal value, na value, existing in name only,assigned to a measurable property for the purpose of conve-nient designation. Tolerances may be applied to a nominalvalue to define an acceptable range for the property.3.2.7 peak, nin fatig
22、ue loading, the occurrence where thefirst derivative of the force (stress) versus time changes frompositive to negative sign; the point of maximum force (stress)in constant amplitude loading.3.2.8 residual strength, ML-1T-2, nthe value of force(stress) required to cause failure of a specimen under q
23、uasi-static loading conditions after the specimen is subjected tofatigue loading.3.2.9 run-out, nin fatigue, an upper limit on the numberof force cycles to be applied.3.2.10 spectrum loading, nin fatigue, a loading in whichthe peak values of force (stress) are not equal or the valleyvalues of force
24、(stress) are not equal (also known as variableamplitude loading or irregular loading).3.2.11 valley, nin fatigue loading, the occurrence wherethe first derivative of the force (stress) versus time changesfrom negative to positive sign; the point of minimum force(stress) in constant amplitude loading
25、.3.2.12 wave form, nthe shape of the peak-to-peak varia-tion of the force (stress) as a function of time.3.3 Symbols:A = Cross-sectional area of a specimenK = specimen chord stiffness, P/dKi= specimen chord stiffness prior to fatigue cyclesKN= specimen chord stiffness after N fatigue cyclesD = speci
26、men hole diameterh = specimen thicknessN = number of constant amplitude cyclesDN= change in chord stiffness after N fatigue cyclesP = force carried by specimenPmaxq= peak force under quasi-static loading for measure-ment of stiffnessPminq= valley force under quasi-static loading for mea-surement of
27、stiffnessw = specimen widthd = crosshead or extensometer translationsalt= alternating open hole stress during fatigue loadingsohm= maximum cyclic open hole stress magnitude,given by the greater of the absolute values ofsmaxand sminsmax= value of stress corresponding to the peak value offorce (stress
28、) under constant amplitude loadingsmaxq= value of stress corresponding to the peak value offorce (stress) under quasi-static loading for mea-surement of stiffness, given by the greater of theabsolute values of smaxand 0.5 3sminsmean= mean normal stress during fatigue loadingsmin= value of stress cor
29、responding to the valley valueof force (stress) under constant amplitude loadingsminq= value of stress corresponding to the valley valueof force (stress) under quasi-static loading formeasurement of stiffness, given by the greater ofthe absolute values of sminand 0.5 3smax4. Summary of Practice4.1 I
30、n accordance with Test Methods D5766/D5766M orD6484/D6484M, but under constant amplitude fatigue loading,perform a uniaxial test of an open-hole specimen. Cycle thespecimen between minimum and maximum axial forces(stresses) at a specified frequency. At selected cyclic intervals,determine the specime
31、n stiffness from a force versus deforma-tion curve obtained by quasi-statically loading the specimenthrough one tension, compression or tension-compressioncycle as applicable. Determine the number of force cycles atwhich failure occurs (or at which a predetermined change inspecimen stiffness is obse
32、rved), for a specimen subjected to aspecific force (stress) ratio and stress magnitude.5. Significance and Use5.1 This practice provides supplemental instructions forusing Test Methods D5766/D5766M or D6484/D6484M toobtain open-hole fatigue data for material specifications, re-search and development
33、, material design allowables, andquality assurance. The primary property that results is thefatigue life of the test specimen under a specific loading andenvironmental condition. Replicate tests may be used to obtaina distribution of fatigue life for specific material types, lami-nate stacking seque
34、nces, environments, and loading conditions.Guidance in statistical analysis of fatigue data, such as deter-mination of linearized stress life (S-N) curves, can be found inPractice E739.5.2 This practice can be utilized in the study of fatiguedamage in a polymer matrix composite open-hole specimensuc
35、h as the occurrence of microscopic cracks, fiber fractures, ordelaminations. The change in strength associated with fatigueD7615/D7615M 112damage may be determined by discontinuing cyclic loading toobtain the static strength using Test Methods D5766/D5766Mor D6484/D6484M.NOTE 2This practice may be u
36、sed as a guide to conduct variableamplitude loading. This information can be useful in the understanding offatigue behavior of composite structures under spectrum loading condi-tions, but is not covered in this standard.5.3 Factors that influence open-hole fatigue response andshall therefore be repo
37、rted include the following: material,methods of material fabrication, accuracy of lay-up, laminatestacking sequence and overall thickness, specimen geometry,specimen preparation (especially of the hole), specimen con-ditioning, environment of testing, type of support fixture,specimen alignment and g
38、ripping, test frequency, force (stress)ratio, normal stress magnitude, void content, and volumepercent reinforcement. Properties that result include the fol-lowing:5.3.1 Specimen stiffness versus fatigue life curves for se-lected normal stress values.5.3.2 Normal stress versus specimen stiffness cur
39、ves atselected cyclic intervals.5.3.3 Normal stress versus fatigue life curves for selectedstress ratio values.6. Interferences6.1 Force (Stress) RatioResults are affected by the force(stress) ratio under which the tests are conducted. Experiencehas demonstrated that reversed (tension-compression) f
40、orceratios are critical for fatigue-induced damage in open holespecimens, with fully reversed tension-compression (R = 1)being the most critical force ratio (1)3.6.2 Loading FrequencyResults are affected by the loadingfrequency at which the test is conducted. High cyclic rates mayinduce heating with
41、in the specimen that may cause variationsin specimen temperature and properties of the composite asdiscussed in 11.3.2. The temperature of the specimen should bemonitored, and the frequency should be kept low enough toavoid significant temperature variations, unless that is a factorto be studied dur
42、ing the test. For example, loading frequenciesup to 5Hz have been used successfully. Varying the cyclicfrequency during the test is generally not recommended, as theresponse may be sensitive to the frequency utilized and theresultant thermal history.6.3 EnvironmentResults are affected by the environ
43、men-tal conditions under which the tests are conducted. Laminatestested in various environments can exhibit significant differ-ences in both strength and failure mode. Experience hasdemonstrated that elevated temperature, humid environmentsare generally critical for open hole fatigue-induced damage
44、(1).However, critical environments must be assessed indepen-dently for each material system, stacking sequence and loadingcondition tested.6.4 Method of Stiffness MeasurementResults are affectedby the method used to monitor specimen stiffness. Force versusdeformation data provide an indication of sp
45、ecimen stiffnesschange due to damage formation. However, the accuracy ofsuch measurements is affected by factors such as strainindicator accuracy, signal noise, gage length and extensometerslippage, extensometer placement/location, grip slippage, andload frame stiffness (for crosshead deflection dat
46、a), and soforth.6.5 Hole PreparationResults are affected by the holepreparation procedures.6.6 OtherAdditional sources of potential data scatter aredocumented in Test Methods D5766/D5766M and D6484/D6484M.7. Apparatus7.1 General ApparatusGeneral apparatus shall be in ac-cordance with Test Method D57
47、66/D5766M Configuration Afor tension-tension fatigue loading, and in accordance with TestMethod D6484/D6484M Procedure A for tension-compressionand compression-compression fatigue loading. The micrometeror gage used shall be capable of determining the hole diameterto 6 0.025 mm 6 0.001 in.7.2 Testin
48、g MachineIn addition to the requirements de-scribed in Test Methods D5766/D5766M or D6484/D6484M,the testing machine shall be in conformance with Practice E467and shall satisfy the following requirements:7.2.1 Drive Mechanism and ControllerThe velocity of themovable head shall be capable of being re
49、gulated under cyclicforce (stress) conditions. The drive mechanism and controllershall be capable of imparting a continuous loading wave formto the specimen. It is important to minimize drift of the fatigueloading away from the maximum and minimum values.Achieving such accuracy is critical in the development ofreliable fatigue life data since small errors in loading mayresult in significant errors in fatigue life. It is recommendedthat the test controller be equipped with a Test Amplitudecontroller, capable of monitoring the fatigue forces
