1、Designation: D 4680 98 (Reapproved 2004)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 D 4680; the number immediately following the designation indicates the year oforiginal adopt
2、ion 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 covers the determination of time-dependent properties o
3、f structural 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 adh
4、esive 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 the standa
5、rd. The SI units are given in parentheses are forinformation only.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 establish appro-priate safety and health practices and determine the app
6、lica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2D 143 Test Methods for Small Clear Specimens of TimberD 905 Test Method for Strength Properties of AdhesiveBonds in Shear by Compression LoadingD 907 Terminology of AdhesivesD 2016 Test Methods for Moisture
7、 Content of Wood2.2 ASTM Adjuncts:Compression-Shear Creep Test Apparatus33. Terminology3.1 DefinitionsMany terms in these test methods aredefined in Terminology D 907.3.1.1 creepthe dimensional change with time of a mate-rial under load, following the initial instantaneous elastic orrapid deformatio
8、n. Creep at room temperature is sometimescalled cold flow.3.1.2 creep modulusthe ratio of initial applied stress tocreep strain.3.1.3 creep strainthe total strain, at any given time,produced by the applied stress during a creep test.3.1.3.1 DiscussionIn this test method, creep strain iscalculated by
9、 dividing displacement at any given time by theestimated apparent thickness of the adhesive bondline.3.1.4 rate of creepthe slope of the creep-time curve at agiven time.3.1.5 shear stressthe stress component tangential to theplane on which the forces act, that is, in the plane of the bondline.3.1.6
10、strainthe 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 data that are obtained over a relatively shortperiod of time in this test method can p
11、rovide 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 ofstress, temperature, relative humidity, and duration of load.Creep rate, creep strain, and
12、 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,(3) compare adhesives with each other and against specifica-tions, and ( 4) design structural members fabricated wi
13、th 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-failure data derived fromrelatively short loading periods can be ext
14、rapolated 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 4.2.1This test method is under the jurisdiction of ASTM Committee D14 onAdhesives and is the direct responsibility of Subcommi
15、ttee D14.30 on WoodAdhesives.Current edition approved April 1, 2004. Published April 2004. Originallyapproved in 1987. Last previous edition approved in 1998 as D 4680 98.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Ann
16、ual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from ASTM International, 100 Barr Harbor Drive, PO Box C700,West Conshohocken, PA 194282959. Request No. ADJD4680.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700
17、, West Conshohocken, PA 19428-2959, United States.4.5 This test method is a research tool intended for devel-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
18、and can be time-consuming and expensive, sotests must be selected with care.4.6 The apparatus and procedures 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 meth
19、od.5. Apparatus5.1 Testing Machine A testing machine, or other suitableloading machine, capable of applying 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) i
20、s required tocompress the loading spring in the creep-test apparatus.5.2 Compression Shearing ToolThe testing machine isequipped with a shearing tool capable of applying a uniformlydistributed compression load to the loading ledges of theFIG. 1 Creep Test ApparatusD 4680 98 (2004)2block-shear specim
21、en. A shearing tool equipped with a self-aligning seat in the shearing blade ensures uniform loading.5.3 Creep-Test ApparatusStatic loads shall be applied andmaintained on block-shear specimens by means of thecompression-loaded creep-test cylinder shown in Fig. 1.4,3Theapparatus is spring-loaded and
22、 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 orless capacity may be substituted. Varying spring capacitieswith outside diameters no greater than the cylinder insidediameter are available.5.3.1 Fo
23、r creep tests above room temperature, it is notnecessary to adjust the spring or load to compensate for theeffects of changing temperature. It is only necessary that theapparatus, with included specimen, be preconditioned to thetest temperature before the test load is applied to the spring.The prehe
24、ated apparatus must be wrapped with a piece offlexible thermal insulation material while the test load isapplied to the specimen. After loading and measurements,return the loaded apparatus to the test environment. Since thereare no significant changes in temperature before or afterloading, no adjust
25、ments 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 andhumid environments for prolonged periods without concern fordamaging the apparatus or interfering with the effectiveness ofthe test.5.3.3 The creep-tes
26、t apparatus has been compactly designedwith its load-applying mechanism built-in. Thus, several of theunits may be stacked on racks in a small environmentalchamber such as an oven, incubator, or humidity cabinet. Theapparatus may be transferred from one exposure chamber toanother, or may be removed
27、from an exposure chamber formeasurements without disturbing the specimen under staticload.5.3.4 The creep-test apparatus shown in Fig. 1 has amicroswitch 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
28、microswitch whenthe failed specimen strikes it. The microswitch must beconnected to an automatic timer-recorder.5.4 Automatic Timer-RecorderIf creep or time-to-failuremeasurements are to be made, an automatic and multi-channeltimer-recorder is connected to the microswitch on each creep-test apparatu
29、s. The timer-recorder is capable of automaticallyscanning the several connected circuits at selected intervals oftime. When the creep specimen fails and activates the mi-croswitch, the timer-recorder automatically records the time atwhich the circuit is broken.5.5 MicroscopeA microscope is required
30、to measure dis-placement of scribe marks across the two adherends of aspecimen as creep occurs. Accurate measurements are alsorequired for bondline thicknesses. Make measurements to thenearest 0.001 mm (0.0004 in.). A linear traveling binocularmicroscope is ideally suited to creep measurements; howe
31、ver,a microscope fitted with an appropriately graduated scale issatisfactory. An objective lens of at least 73 magnification isrequired.5.6 Environmental ChambersControl of temperature andrelative humidity is required in creep tests of adhesive bondson wood substrates. Temperature has a profound eff
32、ect oncreep properties of adhesives. Humidity also affects creep ofcertain adhesives, but it can also affect dimensional change inwood adherends. Conditioning equipment should be capable ofmaintaining a constant temperature within 63.0F (61.7C) ofthe set-point and constant relative humidity within 6
33、5 % of theset-point at a given temperature.6. Materials6.1 AdherendsSelect sugar maple (Acer saccharum)asthe standard adherend material with the grain of the woodstraight and parallel to the direction of shear and free of alldefects such as knots, splits, and discolorations. Sugar maple isa uniforml
34、y 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 completed.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
35、 blocks at this specific gravity,including appropriate adjustments in specific gravity for vari-ous moisture contents, is described in the Appendix of TestMethod D 905. If more complete procedures are required forrefereed tests, specific gravity may be determined in accor-dance with Section 116 of T
36、est Methods D 143.6.1.2 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
37、in density thansugar 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
38、 of stress, itis 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 o
39、f the WoodHandbook.5For 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.56.1.4 Should premature failures occur in the wood aftermean strength values have been adjusted for moisture content,then the 5 %
40、 exclusion limit may be used to select themaximum level of stress for a particular species of wood. Themaximum level of stress Smax0.05is determined by thefollowing equation:4This creep-test apparatus may be purchased from Hull Machine Shop, P.O. 373,Hull, GA 30646, or other suitable suppliers.5Wood
41、 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, DC 20401.D 4680 98 (2004)3Smax
42、0.055 Sm2 1.6450.14Sm! (1)where Smis the mean shear strength parallel-to-grain aspresented in Table 4-2 of the Wood Handbook.56.2 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 thes
43、pecimen.7. Test Specimens7.1 The standard specimen for both creep and time-to-failure tests shall be the block-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
44、.2 The finished specimen for creep tests has well-definedscribe marks on each side of the specimen for measuringdisplacement 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 te
45、n specimens at each set of test condi-tions, that is, each combination of stress level, temperature, andrelative 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
46、.7.4.2 Randomly assign the ten specimens for each set of testconditions to that set from the entire lot of specimens 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 de
47、gree of confidence to the meanof a measured property. Creep tests generally are expensiveand time-consuming, and 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
48、 number of specimens, then it is permissible touse the lesser number.8. Conditioning of Materials and Specimens8.1 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
49、significant changes in weight. Use TestMethods D 2016 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) thesubstituted standard conditions are reported. If the facilities arenot available for conditioning wood to the 10 to 12 % moistureFIG. 2 Block-Shear Specimen for Creep and Time To Failure TestsD 4680 98 (2004)4content range,
