1、Designation: D4680 98 (Reapproved 2011)Standard Test Method forCreep and Time to Failure of Adhesives in Static Shear byCompression Loading (Wood-to-Wood)1This standard is issued under the fixed designation D4680; the number immediately following the designation indicates the year oforiginal adoptio
2、n 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 covers the determination of time-dependent properties of s
3、tructural adhesives in wood-to-woodbonds when specimens are subjected to shearing stresses atvarious levels of static load, constant temperature, and relativehumidity. Apparatus and procedures are provided for directmeasurement of time-dependent shear deformation (creep) andtime to failure of adhesi
4、ve bonds under static load. Guidelinesfor selecting test conditions, methods for calculating creep rate,creep strain, creep modulus, and extrapolation of time tofailure, are given along with methods of presenting these data.1.2 The values stated in inch-pound units are to be regardedas standard. The
5、 values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.3 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
6、 establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D143 Test Methods for Small Clear Specimens of TimberD905 Test Method for Strength Properties of AdhesiveBonds in Shear by Compressio
7、n LoadingD907 Terminology of AdhesivesD2016 Test Methods for Moisture Content of Wood32.2 ASTM Adjuncts:Compression-Shear Creep Test Apparatus43. Terminology3.1 DefinitionsMany terms in these test methods aredefined in Terminology D907.3.1.1 creep, nthe dimensional change with time of amaterial unde
8、r load, following the initial instantaneous elasticor rapid deformation. Creep at room temperature is sometimescalled cold flow.3.1.2 creep modulus, nthe ratio of initial applied stress tocreep strain.3.1.3 creep strain, nthe total strain, at any given time,produced by the applied stress during a cr
9、eep test.3.1.3.1 DiscussionIn this test method, creep strain iscalculated by dividing displacement at any given time by theestimated apparent thickness of the adhesive bondline.3.1.4 rate of creep, nthe slope of the creep-time curve ata given time.3.1.5 shear stress, nthe stress component tangential
10、 to theplane on which the forces act, that is, in the plane of the bondline.3.1.6 strain, nthe unit change, due to stress, in the size orshape of a body referred to its original size or shape.3.1.7 stress, nthe force exerted per unit area at a pointwithin the plane.4. Significance and Use4.1 Creep d
11、ata that are obtained over a relatively shortperiod of time in this test method can provide a measure of anadhesive bonds ability to withstand static loading in shear overa relatively long period of time. Creep measurements are madeover a range of expected service conditions, including level ofstres
12、s, temperature, relative humidity, and duration of load.Creep rate, creep strain, and creep modulus are calculated atthe various service conditions.4.2 Creep data can be used to (1) predict performance of anadhesive under long-term loading, (2) characterize an adhesive,1This test method is under the
13、 jurisdiction of ASTM Committee D14 onAdhesives and is the direct responsibility of Subcommittee D14.30 on WoodAdhesives.Current edition approved April 1, 2011. Published April 2011. Originallyapproved in 1987. Last previous edition approved in 2004 as D4680 98 (2004).DOI: 10.1520/D4680-98R11.2For r
14、eferenced 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.3Withdrawn. The last approved version of this historical standard i
15、s referencedon www.astm.org.4Available from ASTM International Headquarters. Order Adjunct No.ADJD4680. Original adjunct produced in 1987.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.(3) compare adhesives with each other and again
16、st specifica-tions, and (4) design structural members fabricated with anadhesive.4.3 Time-to-failure data provide a measure of the ultimateload-carrying ability of an adhesive bond as a function of timeat various levels of stress, temperature, and relative humidity.4.4 With proper caution, time-to-f
17、ailure data derived fromrelatively short loading periods can be extrapolated to estimatethe useful service life of an adhesive at working levels of staticstress. This property may also be used with creep data toaccomplish purposes listed in 4.2.4.5 This test method is a research tool intended for de
18、vel-opment or evaluation of new adhesives and new productdesigns. The researcher may select from suggested tests thosethat are appropriate. However, creep and time-to-failure testsare nonroutine and can be time-consuming and expensive, sotests must be selected with care.4.6 The apparatus and procedu
19、res may be suitable formeasuring creep properties of adhesives on substrates otherthan wood, such as metal, plastic, and glass, but such consid-erations are not within the scope of this test method.5. Apparatus5.1 Testing MachineA testing machine, or other suitableloading machine, capable of applyin
20、g compression loads from0 to 5000 lbf (22 kN) and cross-head speeds from 0.01 to 0.40in./min (0.3 to 10.2 mm/min) is sufficient for this test method.A minimum vertical space of 20 in. (508 mm) is required tocompress the loading spring in the creep-test apparatus.5.2 Compression Shearing ToolThe test
21、ing machine isequipped with a shearing tool capable of applying a uniformlydistributed compression load to the loading ledges of theblock-shear specimen. A shearing tool equipped with a self-aligning seat in the shearing blade ensures uniform loading.5.3 Creep-Test ApparatusStatic loads shall be app
22、lied andmaintained on block-shear specimens by means of thecompression-loaded creep-test cylinder shown in Fig. 1.5,4Theapparatus is spring-loaded and can sustain any load up to thedesign capacity of the spring. This particular spring has adesign load of 2300 lbf (10 kN); however, others of greater
23、orless capacity may be substituted. Varying spring capacitieswith outside diameters no greater than the cylinder insidediameter are available.5.3.1 For creep tests above room temperature, it is notnecessary to adjust the spring or load to compensate for theeffects of changing temperature. It is only
24、 necessary that theapparatus, with included specimen, be preconditioned to thetest temperature before the test load is applied to the spring.The preheated apparatus must be wrapped with a piece offlexible thermal insulation material while the test load isapplied to the specimen. After loading and me
25、asurements,return the loaded apparatus to the test environment. Since thereare no significant changes in temperature before or afterloading, no adjustments are needed in the spring.5.3.2 The creep-test apparatus is made of corrosion-resistantcomponents so that it can be used in high-temperature andh
26、umid environments for prolonged periods without concern fordamaging the apparatus or interfering with the effectiveness ofthe test.5.3.3 The creep-test apparatus has been compactly designedwith its load-applying mechanism built-in. Thus, several of theunits may be stacked on racks in a small environ
27、mentalchamber such as an oven, incubator, or humidity cabinet. Theapparatus may be transferred from one exposure chamber toanother, or may be removed from an exposure chamber formeasurements without disturbing the specimen under staticload.5.3.4 The creep-test apparatus shown in Fig. 1 has amicroswi
28、tch mounted at its base which is activated when thecreep specimen fails. A small pin is located in the lowerspecimen seat which is driven against the microswitch whenthe failed specimen strikes it. The microswitch must beconnected to an automatic timer-recorder.5.4 Automatic Timer-RecorderIf creep o
29、r time-to-failuremeasurements are to be made, an automatic and multi-channeltimer-recorder is connected to the microswitch on each creep-test apparatus. The timer-recorder is capable of automaticallyscanning the several connected circuits at selected intervals oftime. When the creep specimen fails a
30、nd activates the micro-switch, the timer-recorder automatically records the time atwhich the circuit is broken.5.5 MicroscopeA microscope is required to measure dis-placement of scribe marks across the two adherends of aspecimen as creep occurs. Accurate measurements are alsorequired for bondline th
31、icknesses. Make measurements to thenearest 0.001 mm (0.0004 in.). A linear traveling binocularmicroscope is ideally suited to creep measurements; however,a microscope fitted with an appropriately graduated scale issatisfactory. An objective lens of at least 73 magnification isrequired.5.6 Environmen
32、tal ChambersControl of temperature andrelative humidity is required in creep tests of adhesive bondson wood substrates. Temperature has a profound effect oncreep properties of adhesives. Humidity also affects creep ofcertain adhesives, but it can also affect dimensional change inwood adherends. Cond
33、itioning equipment should be capable ofmaintaining a constant temperature within 63.0F (61.7C) ofthe set-point and constant relative humidity within 65 % of theset-point at a given temperature.6. Materials6.1 AdherendsSelect sugar maple (Acer saccharum)asthe standard adherend material with the grain
34、 of the woodstraight and parallel to the direction of shear and free of alldefects such as knots, splits, and discolorations. Sugar maple isa uniformly textured and high-density wood preferred in creeptests because it is less likely to deform near the bondline or failin the wood before the test is c
35、ompleted.6.1.1 Sugar maple adherend material has a minimum spe-cific gravity of 0.65 (based on oven-dry weight and volume).Amethod for selecting maple blocks at this specific gravity,including appropriate adjustments in specific gravity for vari-ous moisture contents, is described in the Appendix of
36、 TestMethod D905. If more complete procedures are required for5This creep-test apparatus may be purchased from Hull Machine Shop, P.O. 373,Hull, GA 30646, or other suitable suppliers.D4680 98 (2011)2refereed tests, specific gravity may be determined in accor-dance with Section 116 of Test Methods D1
37、43.6.1.2 Any other species of wood may be used as adherendmaterial, particularly in those cases where it is necessary toknow the creep behavior of an adhesive in contact with aspecific wood species. However, it should be recognized thatwoods that are less uniform in texture and lower in density than
38、sugar maple, are more likely to deform and fail prematurely.6.1.3 When conducting creep and time-to-failure tests, it isimportant not to overload the adherend and cause deformationat the bondline or failure in the wood before the test iscompleted.As a guide to selecting maximum levels of stress, iti
39、s recommended that the load not exceed the average shearstrength parallel-to-grain for the species of wood when ad-justed for any change in moisture content from 12 %. Averageshear strengths at 12 % moisture content for sugar maple andother species of wood are presented in Table 4-2 of the WoodHandb
40、ook.6For moisture contents other than 12 %, it will benecessary to adjust shear strengths by the formula described inpp. 4-32 and 4-33 of the Wood Handbook.66.1.4 Should premature failures occur in the wood aftermean strength values have been adjusted for moisture content,then the 5 % exclusion limi
41、t may be used to select the6Wood Handbook: Wood As An Engineering Material, USDA AgricultureHandbook 72, rev., U.S. Forest Products Lab., 1974, Table 4-2 and p. 4-32 and 4-33.Available from U.S. Government Printing Office Superintendent of Documents, 732N. Capitol St., NW, Mail Stop: SDE, Washington
42、, DC 20401.FIG. 1 Creep Test ApparatusD4680 98 (2011)3maximum level of stress for a particular species of wood. Themaximum level of stress Smax0.05is determined by thefollowing equation:Smax0.055 Sm2 1.6450.14Sm! (1)where Smis the mean shear strength parallel-to-grain aspresented in Table 4-2 of the
43、 Wood Handbook.66.2 AdhesivesCreep properties of any adhesive can bemeasured on any species of wood as long as the level of shearstress does not exceed the shear strength of the wood in thespecimen.7. Test Specimens7.1 The standard specimen for both creep and time-to-failure tests shall be the block
44、-shear specimen illustrated inFig. 2. Use the test adhesive to bond the two hard mapleadherends together. The shear area is 1.00 by 1.00 in. (2.54 by2.54 cm), equalling 1.00 in.2(6.45 cm2).7.2 The finished specimen for creep tests has well-definedscribe marks on each side of the specimen for measuri
45、ngdisplacement of the two adherends as creep takes place.7.3 Scribe marks are not necessary for specimens intendedfor the time-to-failure tests.7.4 Number of Specimens:7.4.1 Test at least ten specimens at each set of test condi-tions, that is, each combination of stress level, temperature, andrelati
46、ve humidity, for either creep test or time-to-failure test. Itis suggested that at least one test joint assembly (containstwelve specimens) be prepared for each combination of testconditions.7.4.2 Randomly assign the ten specimens for each set of testconditions to that set from the entire lot of spe
47、cimens preparedfor testing of a given adhesive.7.4.3 For many adhesives, measured creep properties willbe highly variable, and ten specimens may not be a largeenough sample to give a high degree of confidence to the meanof a measured property. Creep tests generally are expensiveand time-consuming, a
48、nd a specimen count of ten represents apractical compromise.7.4.4 If it is determined from experimental evidence that areasonable degree of confidence can be given to a mean byusing a lesser number of specimens, then it is permissible touse the lesser number.8. Conditioning of Materials and Specimen
49、s8.1 Condition hard maple boards at 73 6 3F (23 6 1.7C)and 65 6 2 % relative humidity until they reach moistureequilibrium (approximately 12 % moisture content), as indi-cated by no further significant changes in weight. Use TestMethods D2016 for guidance to determine when equilibriumhas been reached. Other relative humidities may be substitutedas long as (1) the wood reaches equilibrium between 10 and12 % moisture content, (2) the alternative conditions aresubstituted consistently throughout the test method, and (3) theFIG. 2 Block-Shear Specimen for Creep
