1、Designation: D 7337/D7337M 07Standard Test Method forTensile Creep Rupture of Fiber Reinforced Polymer MatrixComposite Bars1This standard is issued under the fixed designation D 7337/D7337M; the number immediately following the designation indicates theyear of original adoption or, in the case of re
2、vision, the 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 test method outlines requirements for tensile creeprupture testing of fiber reinforced polym
3、er matrix (FRP)composite bars commonly used as tensile elements in rein-forced, prestressed, or post-tensioned concrete.1.2 Data obtained from this test method are used in designof FRP reinforcements under sustained loading. The procedurefor calculating the one-million hour creep-rupture capacity is
4、provided in Annex A1.1.3 The values stated in either SI units or inch-pound unitsare to be 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 o
5、ther. Combining valuesfrom the two systems may result in nonconformance with thestandard.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 practice
6、s and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 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
7、-trix Composite MaterialsD 7205/D 7205M Test Method for Tensile Properties ofFiber Reinforced Polymer Matrix Composite BarsE4 Practices for Force Verification of Testing MachinesE 456 Terminology Relating to Quality and StatisticsE 1012 Practice for Verification of Test Frame and Speci-men Alignment
8、 Under Tensile and Compressive AxialForce Application3. Terminology3.1 Terminology in D 3878 defines terms relating to high-modulus fibers and their composites. Terminology in D 883defines terms relating to plastics. Terminology in E 6 definesterms relating to mechanical testing. Terminology in E 45
9、6defines terms relating to statistics and the selection of samplesizes. In the event of a conflict between terms, Terminology inD 3878 shall have precedence over the other terminologystandards.3.2 Definitions of Terms Specific to This Standard:3.2.1 anchor, na protective device placed on each end of
10、a bar, between the bar and the grips of the tensile testingapparatus, to prevent grip-induced damage. Usually used onbars with irregular surfaces, as opposed to flat strips wherebonded tabs are more typical.3.2.2 anchoring section, nthe end parts of the specimenwhere an anchor is fitted to transmit
11、the forces from the testingapparatus to the test section.3.2.3 bar, na linear element, often with surface undula-tions or a coating of particles that promote mechanical inter-lock with concrete.3.2.4 creep, ntime-dependent deformation (or strain) un-der sustained force (or stress).3.2.5 creep ruptur
12、e, nmaterial failure caused by sustainedforce (or stress) over time.3.2.6 creep rupture capacity, nthe force at which failureoccurs after a specified period of time from initiation of asustained force. The predicted force causing failure at 1 millionhours is referred to as the million-hour creep rup
13、ture capacity.This capacity is determined by the method described in theAnnex.3.2.7 creep rupture strength, nthe stress causing failureafter a specified period of time from initiation of a sustainedforce.3.2.8 creep rupture time, nthe lapsed time between thestart of a sustained force and failure of
14、the test specimen.1This test method is under the jurisdiction of ASTM Committee D30 onComposite Materials and is the direct responsibility of Subcommittee D30.05 onStructural Test Methods.Current edition approved Aug. 1, 2007. Published September 2007.2For referenced ASTM standards, visit the ASTM w
15、ebsite, 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 International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United S
16、tates.3.2.9 failure, nrupture of the bar under test into twoseparate pieces.3.2.10 force ratio, nthe ratio of a constant sustained forceapplied to a specimen to its tensile capacity as determinedaccording to Test Method D 7205/D 7205M.3.2.11 grid, na two-dimensional (planar) or three-dimensional (sp
17、atial) rigid array of interconnected FRP barsthat form a contiguous lattice that can be used to reinforceconcrete. The lattice can be manufactured with integrallyconnected bars or constructed of mechanically connectedindividual bars. The grid bar elements have transverse dimen-sions typically greate
18、r than 3 mm 0.12 in.3.2.12 nominal cross-sectional area, na measure of cross-sectional area of a bar, determined over at least one represen-tative length, used to calculate stress.3.2.13 representative length, nthe minimum length of abar that contains a repeating geometric pattern that, placedend-to
19、-end, reproduces the geometric pattern of a continuousbar (usually used in reference to bars having surface undula-tions for enhancing interlock with concrete).3.2.14 surface undulation, nvariation in the area, orienta-tion, or shape of cross-section of a bar along its length,intended to enhance mec
20、hanical interlock between a bar andconcrete, made by any of a number of processes such as, forexample, indentation, addition of extra materials, and twisting.3.2.15 test section, nthe portion of a specimen betweenthe anchoring sections of the test specimen.3.3 Symbols:a1, b1= empirical constantsA =
21、nominal or standard cross-sectional area of a bar, seeTest Method D 7205/D 7205MFr= stress carried by specimen at rupturePr= force carried by specimen at rupturet = time, hoursYc= creep rupture trend line4. Summary of Test Method4.1 This test method consists of measuring the time torupture of a bar
22、subjected to a constant tensile force. Multipleforce levels are specified by the method so that a relationshipbetween force and time-to-failure can be derived.5. Significance and Use5.1 This method for investigating creep rupture of FRP barsis intended for use in laboratory tests in which the princi
23、palvariable is the size or type of FRP bars, magnitude of appliedforce, and duration of force application. Unlike steel reinforc-ing bars or prestressing tendons subjected to significant sus-tained stress, creep rupture of FRP bars may take place belowthe static tensile strength. Therefore, the cree
24、p rupture strengthis an important factor when determining acceptable stresslevels in FRP bars used as reinforcement or tendons in concretemembers designed to resist sustained loads. Creep rupturestrength varies according to the type of FRP bars used.5.2 This test method measures the creep rupture ti
25、me ofFRP bars under a given set of controlled environmentalconditions and force ratios.5.3 This test method is intended to determine the creeprupture data for material specifications, research and develop-ment, quality assurance, and structural design and analysis.The primary test result is the mill
26、ion-hour creep rupturecapacity of the specimen.5.4 Creep properties of reinforced, post-tensioned, or pre-stressed concrete structures are important to be considered indesign. For FRP bars used as reinforcing bars or tendons, thecreep rupture shall be measured according to the method givenherein.6.
27、Interferences6.1 GrippingThe method of gripping has been known tocause premature creep rupture in bars. Anchors, if used, shallbe designed in such a way that the creep rupture capacity canbe achieved without excessive slip throughout the length of theanchor during the test.6.2 System AlignmentExcess
28、ive bending may cause pre-mature failure. Every effort shall be made to eliminate bendingfrom the test system. Bending may occur due to misalignmentof the bar within anchors or grips or associated fixturing, orfrom the specimen itself if improperly installed in the grips orif it is out-of-tolerance
29、due to poor specimen preparation. SeePractice E 1012 for verification of specimen alignment undertensile loading.6.3 Measurement of Cross-Sectional AreaThe nominalcross-sectional area of the bar is measured by immersing aprescribed length of the specimen in water to determine itsbuoyant weight. Bar
30、configurations that trap air during immer-sion (aside from minor porosity) cannot be assessed using thismethod. This method may not be appropriate for bars that havelarge variations in cross-sectional area along the length of thebar.6.4 Test ConditionsCreep rupture is highly dependentupon environmen
31、tal conditions such as, for example, tempera-ture, humidity, and chemical agents. Every effort shall be madeto test FRP bars for creep rupture under tightly controlled andmonitored conditions (see Sections 7, 10 and 11 for require-ments).7. Apparatus7.1 The testing apparatus shall be capable of appl
32、ying andmaintaining a force on the specimen within 61 % of thedesired sustained force.7.2 Test ApparatusUse a testing apparatus with a forcecapacity in excess of the tensile capacity of the specimen andcalibrated according to Practices E4.7.3 AnchorsAnchors, if used, shall be in accordance withTest
33、Method D 7205/D 7205M.7.4 Temperature ControlThe temperature of the test en-vironment shall be maintained at the specified temperature62C 64F during the test period. If no temperature isspecified, maintain the temperature at 23C 73F.7.5 Environmental Test ChamberAn environmental testchamber may be r
34、equired for test environments other thanambient testing laboratory conditions. For environments wheretemperature is specified, the chamber shall be capable ofmaintaining the required temperature to within 62C 64F.In addition, the chamber may have to be capable of maintain-ing environmental condition
35、s such as fluid exposure or relativehumidity during the test. For environments where relativeD 7337/D7337M 072humidity is specified, the chamber shall be capable of main-taining the required humidity to within 610 %RH.8. Sampling and Test Specimens8.1 Specimens shall be representative of the lot or
36、batchbeing tested. For grid-type FRP specimens, linear test speci-mens may be prepared by cutting away extraneous material insuch a way as not to affect the performance of the part to beused. Leaving a minimum 2 mm 0.08 in. projection of thecross bars is recommended. In the test section of the speci
37、men,no postproduction machining, abrading, or other such process-ing is permitted. Such processing may be used in the anchoringsections to promote bond of the rod to the anchoring device.8.2 During the sampling and preparation of test specimens,all deformation, heating, outdoor exposure to ultraviol
38、et light,and other conditions possibly causing changes to the materialproperties of the specimen shall be avoided, unless theseconditions are specified as part of the test procedure.8.3 The length of the specimen shall be in accordance withTest Method D 7205/D 7205M.8.4 The cross-sectional area of t
39、he specimen shall be deter-mined in accordance with either of the two methods describedin Test Method D 7205/D 7205M: nominal area or standardarea.8.5 If a specimen fails at or slips out of an anchoringsection, an additional test shall be performed on a separatespecimen taken from the same lot as th
40、e failed specimen.8.6 A 100 mm 4 in. long specimen of the bar shall be usedto determine the average moisture content of the as-received oras-conditioned bar before the start of creep rupture testing. Theaverage moisture content shall be determined according toProcedure D, section 3.2.2, of Test Meth
41、od D 5229/D 5229M.8.7 A 100 mm 4 in. long traveler specimen of the samecross-section geometry and appropriate size (but withoutanchors) shall be used to determine the average moisturecontent of each bar after creep rupture testing. The ends ofcreep rupture specimens and traveler specimens shall be s
42、ealedwith a water resistant sealant such as a high grade, room-temperature curing epoxy to avoid end effects. The averagemoisture content shall be determined according to ProcedureD, section 3.2.2, of Test Method D 5229/D 5229M.9. Test Matrix9.1 The quasi-static tensile strength of the bars as deter
43、-mined by Test Method D 7205/D 7205M is used as a basis forselecting the applied tensile forces for creep rupture tests. Ateach given force ratiofor example, 80 %, 70 %, 60 % of thetensile strengththe applied force must be maintained con-stant until failure occurs while the time elapsed to rupture o
44、feach test specimen is recorded.NOTE 1The selection of force ratios is dependent on the fiberarchitecture and fiber volume fraction for the bar. Material systems with ahigh resistance to creep rupture (for example, carbon FRP composite) willnecessitate the selection of closely-spaced force ratios at
45、 stress levelsapproaching 100 % of the quasi-static tensile strength. Material systemswith less resistance to creep rupture (for example, glass FRP composite)will necessitate the selection of widely-spaced force ratios.9.2 A minimum of four force ratios are required (see Fig.A1.1 for example). A min
46、imum of 5 valid test results arerequired for each force ratio. For the entire group of testsreported, the range between the longest and shortest recordedrupture times shall be at least three decades. Data fromspecimens that break before the applied tensile force is fullyapplied to the specimen shall
47、 be disregarded.NOTE 2It is suggested that additional specimens be tested at eachforce ratio, especially for those force ratios that require long times torupture.9.2.1 The highest force ratio shall be selected such that atleast four specimens in this group ruptures at a time of greaterthan 1 h.NOTE
48、3The highest force is specified with the aim of minimizing theeffects of the initial loading ramp on the creep rupture time.9.2.2 The lowest force ratio shall be selected such that atleast one specimen in this group ruptures at a time of greaterthan 8000 h.NOTE 4The lowest force is specified with th
49、e aim of limiting theextent of extrapolation required to determine the one million hour creeprupture capacity.9.2.3 The remaining force ratios shall be roughly equallyspaced in relation to the highest and lowest force ratiosdetermined in 9.2.1 and 9.2.2, respectively.10. Conditioning10.1 The recommended pre-test condition is effective mois-ture equilibrium at a specific relative humidity as establishedby Test Method D 5229/D 5229M; however, if the test re-questor does not explicitly specify a pre-test conditioningenvironment, no conditi
