1、Designation: D 6873/D6873M 08Standard Practice forBearing Fatigue Response of Polymer Matrix CompositeLaminates1This standard is issued under the fixed designation D 6873/D6873M; 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 (e) indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice provides instructions for modifying staticbearing test methods to determine the fatigue behavio
3、r ofcomposite materials subjected to cyclic bearing forces. 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 direction.The range of acceptable test laminates and thicknesses
4、aredescribed in 8.2.1.2 This practice supplements Test Method D 5961/D 5961M with provisions for testing specimens under cyclicloading. Several important test specimen parameters (for ex-ample, fastener selection, fastener installation method, andfatigue force/stress ratio) are not mandated by this
5、practice;however, repeatable results require that these parameters bespecified 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 repetitiveconstant amplitude force (str
6、ess) 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 inch-pound unitsare to be
7、regarded separately as standard. Within the text theinch-pound units are shown in brackets. The values stated ineach system are not exact equivalents; therefore, each systemmust be used independently of the other. Combining valuesfrom the two systems may result in nonconformance with thestandard.1.5
8、 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. Referenced Docu
9、ments2.1 ASTM Standards:2D 883 Terminology Relating to PlasticsD 3878 Terminology for Composite MaterialsD 5229/D 5229M Test Method for Moisture AbsorptionProperties and Equilibrium Conditioning of Polymer Ma-trix Composite MaterialsD 5961/D 5961M Test Method for Bearing Response ofPolymer Matrix Co
10、mposite LaminatesE4 Practices for Force Verification of Testing MachinesE6 Terminology Relating to Methods of Mechanical Test-ingE 122 Practice for Calculating Sample Size to Estimate,With Specified Precision, the Average for a Characteristicof a Lot or ProcessE 177 Practice for Use of the Terms Pre
11、cision and Bias inASTM Test MethodsE 456 Terminology Relating to Quality and StatisticsE 467 Practice for Verification of Constant Amplitude Dy-namic Forces in an Axial Fatigue Testing SystemE 739 Practice for Statistical Analysis of Linear or Linear-ized Stress-Life ( S-N) and Strain-Life (e-N) Fat
12、igue DataE 1309 Guide for Identification of Fiber-ReinforcedPolymer-Matrix Composite Materials in DatabasesE 1434 Guide for Recording Mechanical Test Data of Fiber-Reinforced Composite Materials in DatabasesE 1823 Terminology Relating to Fatigue and Fracture Test-ing3. Terminology3.1 DefinitionsTerm
13、inology D 3878 defines terms relatingto high-modulus fibers and their composites. TerminologyD 883 defines terms relating to plastics. Terminology E6defines terms relating to mechanical testing. TerminologyE 1823 defines terms relating to fatigue. Terminology E 456and Practice E 177 define terms rel
14、ating to statistics. In the1This practice is under the jurisdiction of ASTM Committee D30 on CompositeMaterials and is the direct responsibility of Subcommittee D30.05 on Structural TestMethods.Current edition approved March 1, 2008. Published April 2008. Originallyapproved in 2003. Last previous ed
15、ition approved in 2003 as D 6873-03.2For 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 to the standards Document Summary page onthe ASTM website.1Copyright ASTM Internati
16、onal, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.event of a conflict between terms, Terminology D 3878 shallhave precedence over the other standards.NOTE 1If the term represents a physical quantity, its analyticaldimensions are stated immediately following th
17、e term (or letter symbol) infundamental dimension form, using the following ASTM standard sym-bology for fundamental dimensions, shown within square brackets: Mfor mass, L for length, T for time, u for thermodynamic temperature,and nd for non-dimensional quantities. Use of these symbols is restricte
18、dto analytical dimensions when used with square brackets, as the symbolsmay have other definitions when used without the brackets.3.2 Definitions of Terms Specific to This Standard:3.2.1 bearing force, P MLT-2, nthe total force carried bya bearing coupon.3.2.2 constant amplitude loading, nin fatigue
19、, a loadingin which all of the peak values of force (stress) are equal andall of the valley values of force (stress) are equal.3.2.3 fatigue loading transition, nin the beginning offatigue loading, the number of cycles before the force (stress)reaches the desired peak and valley values.3.2.4 force (
20、stress) ratio, R nd, nin fatigue loading, theratio of the minimum applied force (stress) to the maximumapplied force (stress).3.2.5 frequency, f T-1, nin fatigue loading, the numberof force (stress) cycles completed in 1 s (Hz).3.2.6 hole elongation, D L, nthe permanent change inhole diameter in a b
21、earing coupon caused by damage forma-tion, equal to the difference between the hole diameter in thedirection of the bearing force after a prescribed loading and thehole diameter prior to loading.3.2.7 nominal value, na value, existing in name only,assigned to a measurable property for the purpose of
22、 conve-nient designation. Tolerances may be applied to a nominalvalue to define an acceptable range for the property.3.2.8 peak, nin fatigue loading, the occurrence where thefirst derivative of the force (stress) versus time changes frompositive to negative sign; the point of maximum force (stress)i
23、n constant amplitude loading.3.2.9 residual strength, ML-1T-2, nthe value of force(stress) required to cause failure of a specimen under quasi-static loading conditions after the specimen is subjected tofatigue loading.3.2.10 run-out, nin fatigue, an upper limit on the numberof force cycles to be ap
24、plied.3.2.11 spectrum loading, nin fatigue, a loading in whichthe peak values of force (stress) are not equal or the valleyvalues of force (stress) are not equal (also known as variableamplitude loading or irregular loading).3.2.12 valley, nin fatigue loading, the occurrence wherethe first derivativ
25、e of the force (stress) versus time changesfrom negative to positive sign; the point of minimum force(stress) in constant amplitude loading.3.2.13 wave form, nthe shape of the peak-to-peak varia-tion of the force (stress) as a function of time.3.3 Symbols:d = fastener or pin diameterD = specimen hol
26、e diameterh = specimen thicknessk = calculation factor used in bearing equations todistinguish single-fastener tests from double-fastener testsLg= extensometer gage lengthN = number of constant amplitude cyclesP = force carried by specimend = crosshead translationD = hole elongationsalt= alternating
27、 bearing stress during fatigue loadingsbrm= maximum cyclic bearing stress magnitude, givenby the greater of the absolute values of smaxandsminsmax= value of stress corresponding to the peak value offorce (stress) under constant amplitude loadingsmaxq= value of stress corresponding to the peak value
28、offorce (stress) under quasi-static loading for mea-surement of hole elongation, given by the greaterof the absolute values of smaxand 0.5 3sminsmean= mean bearing stress during fatigue loadingsmin= value of stress corresponding to the valley valueof force (stress) under constant amplitude loadingsm
29、inq= value of stress corresponding to the valley valueof force (stress) under quasi-static loading formeasurement of hole elongation, given by thegreater of the absolute values of sminand 0.5 3smax4. Summary of Practice4.1 In accordance with Test Method D 5961/D 5961M, butunder constant amplitude fa
30、tigue loading, perform a uniaxialtest of a bearing specimen. Cycle the specimen betweenminimum and maximum axial forces (stresses) at a specifiedfrequency. At selected cyclic intervals, determine the holeelongation either through direct measurement or from a force(stress) versus deformation curve ob
31、tained by quasi-staticallyloading the specimen through one tension-compression cycle.Determine the number of force cycles at which failure occurs,or at which a predetermined hole elongation is achieved, for aspecimen subjected to a specific force (stress) ratio and bearingstress magnitude.5. Signifi
32、cance and Use5.1 This practice provides supplemental instructions forusing Test Method D 5961/D 5961M to obtain bearing fatiguedata for material specifications, research and development,material design allowables, and quality assurance. The primaryproperty that results is the fatigue life of the tes
33、t specimenunder a specific loading and environmental condition. Repli-cate tests may be used to obtain a distribution of fatigue life forspecific material types, laminate stacking sequences, environ-ments, and loading conditions. Guidance in statistical analysisof fatigue data, such as determination
34、 of linearized stress life(S-N) curves, can be found in Practice E 739.5.2 This practice can be utilized in the study of fatiguedamage in a polymer matrix composite bearing specimen. Theloss in strength associated with fatigue damage may bedetermined by discontinuing cyclic loading to obtain the sta
35、ticstrength using Test Method D 5961/D 5961M.NOTE 2This practice may be used as a guide to conduct spectrumD 6873/D6873M 082loading. This information can be useful in the understanding of fatiguebehavior of composite structures under spectrum loading conditions, but isnot covered in this standard.5.
36、3 Factors that influence bearing fatigue response and shalltherefore be reported include the following: material, methodsof material fabrication, accuracy of lay-up, laminate stackingsequence and overall thickness, specimen geometry, specimenpreparation (especially of the hole), fastener-hole cleara
37、nce,fastener type, fastener geometry, fastener installation method,fastener torque (if appropriate), countersink depth (if appropri-ate), specimen conditioning, environment of testing, time attemperature, type of mating material, number of fasteners, typeof support fixture, specimen alignment and gr
38、ipping, testfrequency, force (stress) ratio, bearing stress magnitude, voidcontent, and volume percent reinforcement. Properties thatresult include the following:5.3.1 Hole elongation versus fatigue life curves for selectedbearing stress values.5.3.2 Bearing stress versus hole elongation curves at s
39、e-lected cyclic intervals.5.3.3 Bearing stress versus fatigue life curves for selectedhole elongation values.6. Interferences6.1 Force (Stress) RatioResults are affected by the force(stress) ratio under which the tests are conducted. Specimensloaded under tension-tension or compression-compressionfo
40、rce (stress) ratios develop hole elongation damage on oneside of the fastener hole, whereas specimens loaded undertension-compression force (stress) ratios can develop damageon both sides of the fastener hole. Experience has demonstratedthat reversed (tension-compression) force ratios are critical f
41、orbearing fatigue-induced hole elongation, with fully reversedtension-compression (R = 1) being the most critical forceratio (1-3).36.2 Loading FrequencyResults are affected by the loadingfrequency at which the test is conducted. High cyclic rates mayinduce heating due to friction within the joint,
42、and may causevariations in specimen temperature and properties of thecomposite. Varying the cyclic frequency during the test isgenerally not recommended, as the response may be sensitiveto the frequency utilized and the resultant thermal history.6.3 Fastener Torque/Pre-loadResults are affected by th
43、einstalled fastener pre-load (clamping pressure). Laminates canexhibit significant differences in hole elongation behavior andfailure mode due to changes in fastener pre-load under bothtensile and compressive loading. Experience has demonstratedthat low fastener torque/clamp-up is generally critical
44、 forbearing fatigue-induced hole elongation. (1, 2, 4). It should benoted that in some instances, low torque testing of single shearspecimens has proven unsuccessful due to loosening of thefastener nut/collar during fatigue loading caused by deforma-tion of the pin/bolt.6.4 Debris BuildupResults are
45、 affected by the buildup offiber-matrix debris resulting from damage associated with holeelongation. The presence of debris may mask the actual degreeof hole elongation, and can increase both the friction forcetransfer and temperature within the specimen under fatigueloading. Experience has demonstr
46、ated that non-reversed forceratios (especially compression-compression force ratios) ex-hibit greater debris buildup than reversed force ratios, and thathole elongation can be most accurately determined if debris isremoved prior to hole elongation measurement (1,2,4). There-fore, cleaning the specim
47、en hole(s) prior to measurement isrecommended to ensure conservatism of hole elongation data.6.5 EnvironmentResults are affected by the environmen-tal conditions under which the tests are conducted. Laminatestested in various environments can exhibit significant differ-ences in both hole elongation
48、behavior and failure mode.Experience has demonstrated that elevated temperature, humidenvironments are generally critical for bearing fatigue-inducedhole elongation (1-4). However, critical environments must beassessed independently for each material system, stackingsequence, and torque condition te
49、sted.6.6 Fastener-Hole ClearanceBearing fatigue test resultsare affected by the clearance arising from the differencebetween hole and fastener diameters. Small changes in clear-ance can change the number of cycles at which hole elongationinitiates, and can affect damage propagation behavior (1). Forthis reason, both the hole and fastener diameters must beaccurately measured and recorded. A typical aerospace toler-ance on fastener-hole clearance is +75/-0 m +0.003/-0.000in. for structural fastener holes.6.7 Fastener Type/Hole PreparationRes
