ASTM D4680-98(2004)
(Test Method)Standard Test Method for Creep and Time to Failure of Adhesives in Static Shear by Compression Loading (Wood-to-Wood)
Standard Test Method for Creep and Time to Failure of Adhesives in Static Shear by Compression Loading (Wood-to-Wood)
SIGNIFICANCE AND USE
Creep data that are obtained over a relatively short period of time in this test method can provide a measure of an adhesive bond’ability to withstand static loading in shear over a relatively long period of time. Creep measurements are made over a range of expected service conditions, including level of stress, temperature, relative humidity, and duration of load. Creep rate, creep strain, and creep modulus are calculated at the various service conditions.
Creep data can be used to (1) predict performance of an adhesive under long-term loading, (2) characterize an adhesive, (3) compare adhesives with each other and against specifications, and ( 4) design structural members fabricated with an adhesive.
Time-to-failure data provide a measure of the ultimate load-carrying ability of an adhesive bond as a function of time at various levels of stress, temperature, and relative humidity.
With proper caution, time-to-failure data derived from relatively short loading periods can be extrapolated to estimate the useful service life of an adhesive at working levels of static stress. This property may also be used with creep data to accomplish purposes listed in 4.2.
This test method is a research tool intended for development or evaluation of new adhesives and new product designs. The researcher may select from suggested tests those that are appropriate. However, creep and time-to-failure tests are nonroutine and can be time-consuming and expensive, so tests must be selected with care.
The apparatus and procedures may be suitable for measuring creep properties of adhesives on substrates other than wood, such as metal, plastic, and glass, but such considerations are not within the scope of this test method.
FIG. 1 Creep Test Apparatus
SCOPE
1.1 This test method covers the determination of time-dependent properties of structural adhesives in wood-to-wood bonds when specimens are subjected to shearing stresses at various levels of static load, constant temperature, and relative humidity. Apparatus and procedures are provided for direct measurement of time-dependent shear deformation (creep) and time to failure of adhesive bonds under static load. Guidelines for selecting test conditions, methods for calculating creep rate, creep strain, creep modulus, and extrapolation of time to failure, are given along with methods of presenting these data.
1.2 The values stated in inch-pound units are to be regarded as the standard. The SI units are given in parentheses are for information only.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Standards Content (Sample)
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Designation:D4680–98(Reapproved2004)
Standard Test Method for
Creep and Time to Failure of Adhesives in Static Shear by
Compression Loading (Wood-to-Wood)
This standard is issued under the fixed designation D4680; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope Compression-Shear Creep Test Apparatus
1.1 This test method covers the determination of time-
3. Terminology
dependent properties of structural adhesives in wood-to-wood
3.1 Definitions—Many terms in these test methods are
bonds when specimens are subjected to shearing stresses at
defined in Terminology D907.
various levels of static load, constant temperature, and relative
3.1.1 creep—the dimensional change with time of a mate-
humidity. Apparatus and procedures are provided for direct
rial under load, following the initial instantaneous elastic or
measurementoftime-dependentsheardeformation(creep)and
rapid deformation. Creep at room temperature is sometimes
time to failure of adhesive bonds under static load. Guidelines
called cold flow.
forselectingtestconditions,methodsforcalculatingcreeprate,
3.1.2 creep modulus—the ratio of initial applied stress to
creep strain, creep modulus, and extrapolation of time to
creep strain.
failure, are given along with methods of presenting these data.
3.1.3 creep strain—the total strain, at any given time,
1.2 Thevaluesstatedininch-poundunitsaretoberegarded
produced by the applied stress during a creep test.
as the standard. The SI units are given in parentheses are for
3.1.3.1 Discussion—In this test method, creep strain is
information only.
calculated by dividing displacement at any given time by the
1.3 This standard does not purport to address all of the
estimated apparent thickness of the adhesive bondline.
safety concerns, if any, associated with its use. It is the
3.1.4 rate of creep—the slope of the creep-time curve at a
responsibility of the user of this standard to establish appro-
given time.
priate safety and health practices and determine the applica-
3.1.5 shear stress—the stress component tangential to the
bility of regulatory limitations prior to use.
plane on which the forces act, that is, in the plane of the bond
2. Referenced Documents line.
2 3.1.6 strain—the unit change, due to stress, in the size or
2.1 ASTM Standards:
shape of a body referred to its original size or shape.
D143 Test Methods for Small Clear Specimens of Timber
3.1.7 stress, n—the force exerted per unit area at a point
D905 Test Method for Strength Properties of Adhesive
within the plane.
Bonds in Shear by Compression Loading
D907 Terminology of Adhesives
4. Significance and Use
D2016 Test Methods for Moisture Content of Wood
4.1 Creep data that are obtained over a relatively short
2.2 ASTM Adjuncts:
period of time in this test method can provide a measure of an
adhesivebond’sabilitytowithstandstaticloadinginshearover
This test method is under the jurisdiction of ASTM Committee D14 on
arelativelylongperiodoftime.Creepmeasurementsaremade
Adhesives and is the direct responsibility of Subcommittee D14.30 on Wood
over a range of expected service conditions, including level of
Adhesives.
stress, temperature, relative humidity, and duration of load.
Current edition approved April 1, 2004. Published April 2004. Originally
approved in 1987. Last previous edition approved in 1998 as D4680–98. DOI:
Creep rate, creep strain, and creep modulus are calculated at
10.1520/D4680-98R04.
the various service conditions.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
3 4
Withdrawn. The last approved version of this historical standard is referenced Available from ASTM International Headquarters. Order Adjunct No.
on www.astm.org. ADJD4680. Original adjunct produced in 1987.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D4680–98 (2004)
4.2 Creep data can be used to (1) predict performance of an The preheated apparatus must be wrapped with a piece of
adhesiveunderlong-termloading,(2)characterizeanadhesive, flexible thermal insulation material while the test load is
(3) compare adhesives with each other and against specifica-
applied to the specimen. After loading and measurements,
tions, and ( 4) design structural members fabricated with an
returntheloadedapparatustothetestenvironment.Sincethere
adhesive.
are no significant changes in temperature before or after
4.3 Time-to-failure data provide a measure of the ultimate
loading, no adjustments are needed in the spring.
load-carrying ability of an adhesive bond as a function of time
5.3.2 Thecreep-testapparatusismadeofcorrosion-resistant
at various levels of stress, temperature, and relative humidity.
components so that it can be used in high-temperature and
4.4 With proper caution, time-to-failure data derived from
humidenvironmentsforprolongedperiodswithoutconcernfor
relativelyshortloadingperiodscanbeextrapolatedtoestimate
damaging the apparatus or interfering with the effectiveness of
theusefulservicelifeofanadhesiveatworkinglevelsofstatic
the test.
stress. This property may also be used with creep data to
5.3.3 Thecreep-testapparatushasbeencompactlydesigned
accomplish purposes listed in 4.2.
withitsload-applyingmechanismbuilt-in.Thus,severalofthe
4.5 This test method is a research tool intended for devel-
units may be stacked on racks in a small environmental
opment or evaluation of new adhesives and new product
chamber such as an oven, incubator, or humidity cabinet. The
designs. The researcher may select from suggested tests those
apparatus may be transferred from one exposure chamber to
that are appropriate. However, creep and time-to-failure tests
another, or may be removed from an exposure chamber for
are nonroutine and can be time-consuming and expensive, so
measurements without disturbing the specimen under static
tests must be selected with care.
load.
4.6 The apparatus and procedures may be suitable for
measuring creep properties of adhesives on substrates other 5.3.4 The creep-test apparatus shown in Fig. 1 has a
than wood, such as metal, plastic, and glass, but such consid-
microswitch mounted at its base which is activated when the
erations are not within the scope of this test method.
creep specimen fails. A small pin is located in the lower
specimen seat which is driven against the microswitch when
5. Apparatus
the failed specimen strikes it. The microswitch must be
5.1 Testing Machine— A testing machine, or other suitable
connected to an automatic timer-recorder.
loading machine, capable of applying compression loads from
5.4 Automatic Timer-Recorder—If creep or time-to-failure
0 to 5000 lbf (22 kN) and cross-head speeds from 0.01 to 0.40
measurements are to be made, an automatic and multi-channel
in./min (0.3 to 10.2 mm/min) is sufficient for this test method.
timer-recorder is connected to the microswitch on each creep-
A minimum vertical space of 20 in. (508 mm) is required to
test apparatus. The timer-recorder is capable of automatically
compress the loading spring in the creep-test apparatus.
scanning the several connected circuits at selected intervals of
5.2 Compression Shearing Tool—The testing machine is
time. When the creep specimen fails and activates the mi-
equipped with a shearing tool capable of applying a uniformly
croswitch, the timer-recorder automatically records the time at
distributed compression load to the loading ledges of the
which the circuit is broken.
block-shear specimen. A shearing tool equipped with a self-
5.5 Microscope—A microscope is required to measure dis-
aligning seat in the shearing blade ensures uniform loading.
placement of scribe marks across the two adherends of a
5.3 Creep-TestApparatus—Staticloadsshallbeappliedand
specimen as creep occurs. Accurate measurements are also
maintained on block-shear specimens by means of the
5,4
required for bondline thicknesses. Make measurements to the
compression-loadedcreep-testcylindershowninFig.1. The
nearest 0.001 mm (0.0004 in.). A linear traveling binocular
apparatus is spring-loaded and can sustain any load up to the
microscope is ideally suited to creep measurements; however,
design capacity of the spring. This particular spring has a
a microscope fitted with an appropriately graduated scale is
design load of 2300 lbf (10 kN); however, others of greater or
less capacity may be substituted. Varying spring capacities satisfactory. An objective lens of at least 73 magnification is
required.
with outside diameters no greater than the cylinder inside
diameter are available.
5.6 Environmental Chambers—Control of temperature and
5.3.1 For creep tests above room temperature, it is not
relative humidity is required in creep tests of adhesive bonds
necessary to adjust the spring or load to compensate for the
on wood substrates. Temperature has a profound effect on
effects of changing temperature. It is only necessary that the
creep properties of adhesives. Humidity also affects creep of
apparatus, with included specimen, be preconditioned to the
certain adhesives, but it can also affect dimensional change in
test temperature before the test load is applied to the spring.
woodadherends.Conditioningequipmentshouldbecapableof
maintainingaconstanttemperaturewithin 63.0°F(61.7°C)of
theset-pointandconstantrelativehumiditywithin 65%ofthe
Thiscreep-testapparatusmaybepurchasedfromHullMachineShop,P.O.373,
Hull, GA 30646, or other suitable suppliers. set-point at a given temperature.
D4680–98 (2004)
FIG. 1 Creep Test Apparatus
6. Materials Method D905. If more complete procedures are required for
refereed tests, specific gravity may be determined in accor-
6.1 Adherends—Select sugar maple (Acer saccharum)as
dance with Section 116 of Test Methods D143.
the standard adherend material with the grain of the wood
6.1.2 Any other species of wood may be used as adherend
straight and parallel to the direction of shear and free of all
material, particularly in those cases where it is necessary to
defectssuchasknots,splits,anddiscolorations.Sugarmapleis
know the creep behavior of an adhesive in contact with a
a uniformly textured and high-density wood preferred in creep
specific wood species. However, it should be recognized that
testsbecauseitislesslikelytodeformnearthebondlineorfail
woodsthatarelessuniformintextureandlowerindensitythan
in the wood before the test is completed.
sugar maple, are more likely to deform and fail prematurely.
6.1.1 Sugar maple adherend material has a minimum spe-
cificgravityof0.65(basedonoven-dryweightandvolume).A 6.1.3 When conducting creep and time-to-failure tests, it is
method for selecting maple blocks at this specific gravity, important not to overload the adherend and cause deformation
including appropriate adjustments in specific gravity for vari- at the bondline or failure in the wood before the test is
ous moisture contents, is described in the Appendix of Test completed.Asaguidetoselectingmaximumlevelsofstress,it
D4680–98 (2004)
FIG. 2 Block-Shear Specimen for Creep and Time To Failure Tests
is recommended that the load not exceed the average shear 7. Test Specimens
strength parallel-to-grain for the species of wood when ad-
7.1 The standard specimen for both creep and time-to-
justed for any change in moisture content from 12%.Average
failure tests shall be the block-shear specimen illustrated in
shear strengths at 12% moisture content for sugar maple and
Fig. 2. Use the test adhesive to bond the two hard maple
other species of wood are presented in Table4-2 of the Wood
adherends together.The shear area is 1.00 by 1.00 in. (2.54 by
2 2
Handbook. For moisture contents other than 12%, it will be
2.54 cm), equalling 1.00 in. (6.45 cm ).
necessary to adjust shear strengths by the formula described in
7.2 The finished specimen for creep tests has well-defined
pp. 4-32 and 4-33 of the Wood Handbook.
scribe marks on each side of the specimen for measuring
6.1.4 Should premature failures occur in the wood after
displacement of the two adherends as creep takes place.
mean strength values have been adjusted for moisture content,
7.3 Scribe marks are not necessary for specimens intended
then the 5% exclusion limit may be used to select the
for the time-to-failure tests.
maximum level of stress for a particular species of wood. The
7.4 Number of Specimens:
maximum level of stress S is determined by the
max0.05
7.4.1 Test at least ten specimens at each set of test condi-
following equation:
tions,thatis,eachcombinationofstresslevel,temperature,and
S 5 S 21.645~0.14S ! (1) relative humidity, for either creep test or time-to-failure test. It
max0.05 m m
is suggested that at least one test joint assembly (contains
where S is the mean shear strength parallel-to-grain as
m
6 twelve specimens) be prepared for each combination of test
presented in Table4-2 of the Wood Handbook.
conditions.
6.2 Adhesives—Creep properties of any adhesive can be
7.4.2 Randomlyassignthetenspecimensforeachsetoftest
measured on any species of wood as long as the level of shear
conditions to that set from the entire lot of specimens prepared
stress does not exceed the shear strength of the wood in the
for testing of a given adhesive.
specimen.
7.4.3 For many adhesives, measured creep properties will
be highly variable, and ten specimens may not be a large
enoughsampletogiveahighdegreeofconfidencetothemean
Wood Handbook: Wood As An Engineering Material, USDA Agriculture
of a measured property. Creep tests generally are expensive
Handbook 72,rev.,U.S.ForestProductsLab.,1974,Table4-2andp.4-32and4-33.
and time-consuming, and a specimen count of ten represents a
AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,732
N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401. practical compromise.
D4680–98 (2004)
7.4.4 If it is determined from experimental evidence that a givenin8.1.Conditionthemtherefor7daystoensurethatthe
reasonable degree of confidence can be given to a mean by moisture content has stabilized before creep tests begin. If
using a lesser number of specimens, then it is permissible to creep tests are to be conducted at equilibrium moisture
use the lesser number. conditions other than those in
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