ASTM D4680-98(2011)
(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's 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.
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 standard. The values given in parentheses are mathematical conversions to SI units that are provided for information only and are not considered standard.
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)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: D4680 − 98 (Reapproved 2011)
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 2.2 ASTM Adjuncts:
Compression-Shear Creep Test Apparatus
1.1 This test method covers the determination of time-
dependent properties of structural adhesives in wood-to-wood
3. Terminology
bonds when specimens are subjected to shearing stresses at
3.1 Definitions:
various levels of static load, constant temperature, and relative
3.1.1 Many terms in these test methods are defined in
humidity. Apparatus and procedures are provided for direct
Terminology D907.
measurementoftime-dependentsheardeformation(creep)and
3.1.2 creep, n—the dimensional change with time of a
time to failure of adhesive bonds under static load. Guidelines
material under load, following the initial instantaneous elastic
forselectingtestconditions,methodsforcalculatingcreeprate,
or rapid deformation. Creep at room temperature is sometimes
creep strain, creep modulus, and extrapolation of time to
called cold flow.
failure, are given along with methods of presenting these data.
3.1.3 creep modulus, n—the ratio of initial applied stress to
1.2 Thevaluesstatedininch-poundunitsaretoberegarded
creep strain.
as standard. The values given in parentheses are mathematical
3.1.4 creep strain, n—the total strain, at any given time,
conversions to SI units that are provided for information only
produced by the applied stress during a creep test.
and are not considered standard.
3.1.4.1 Discussion—In this test method, creep strain is
1.3 This standard does not purport to address all of the
calculated by dividing displacement at any given time by the
safety concerns, if any, associated with its use. It is the
estimated apparent thickness of the adhesive bondline.
responsibility of the user of this standard to establish appro-
3.1.5 rate of creep, n—the slope of the creep-time curve at
priate safety and health practices and determine the applica-
a given time.
bility of regulatory limitations prior to use.
3.1.6 shear stress, n—thestresscomponenttangentialtothe
plane on which the forces act, that is, in the plane of the bond
2. Referenced Documents
line.
2.1 ASTM Standards:
3.1.7 strain, n—the unit change, due to stress, in the size or
D143Test Methods for Small Clear Specimens of Timber
shape of a body referred to its original size or shape.
D905Test Method for Strength Properties of Adhesive
3.1.8 stress, n—the force exerted per unit area at a point
Bonds in Shear by Compression Loading
within the plane.
D907Terminology of Adhesives
D2016Methods of Test for Moisture Content of Wood
4. Significance and Use
(Withdrawn 1987)
4.1 Creep data that are obtained over a relatively short
period of time in this test method can provide a measure of an
1 adhesivebond’sabilitytowithstandstaticloadinginshearover
This test method is under the jurisdiction of ASTM Committee D14 on
Adhesives and is the direct responsibility of Subcommittee D14.30 on Wood arelativelylongperiodoftime.Creepmeasurementsaremade
Adhesives.
over a range of expected service conditions, including level of
Current edition approved April 1, 2011. Published April 2011. Originally
stress, temperature, relative humidity, and duration of load.
approved in 1987. Last previous edition approved in 2004 as D4680–98(2004).
Creep rate, creep strain, and creep modulus are calculated at
DOI: 10.1520/D4680-98R11.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
the various service conditions.
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
The last approved version of this historical standard is referenced on Available from ASTM International Headquarters. Order Adjunct No.
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 (2011)
4.2 Creep data can be used to (1) predict performance of an returntheloadedapparatustothetestenvironment.Sincethere
adhesiveunderlong-termloading,(2)characterizeanadhesive, are no significant changes in temperature before or after
(3) compare adhesives with each other and against loading, no adjustments are needed in the spring.
specifications, and (4) design structural members fabricated 5.3.2 Thecreep-testapparatusismadeofcorrosion-resistant
with an adhesive.
components so that it can be used in high-temperature and
humidenvironmentsforprolongedperiodswithoutconcernfor
4.3 Time-to-failure data provide a measure of the ultimate
damaging the apparatus or interfering with the effectiveness of
load-carrying ability of an adhesive bond as a function of time
the test.
at various levels of stress, temperature, and relative humidity.
5.3.3 Thecreep-testapparatushasbeencompactlydesigned
4.4 With proper caution, time-to-failure data derived from
withitsload-applyingmechanismbuilt-in.Thus,severalofthe
relativelyshortloadingperiodscanbeextrapolatedtoestimate
units may be stacked on racks in a small environmental
theusefulservicelifeofanadhesiveatworkinglevelsofstatic
chamber such as an oven, incubator, or humidity cabinet. The
stress. This property may also be used with creep data to
apparatus may be transferred from one exposure chamber to
accomplish purposes listed in 4.2.
another, or may be removed from an exposure chamber for
4.5 This test method is a research tool intended for devel-
measurements without disturbing the specimen under static
opment or evaluation of new adhesives and new product
load.
designs. The researcher may select from suggested tests those
5.3.4 The creep-test apparatus shown in Fig. 1 has a
that are appropriate. However, creep and time-to-failure tests
microswitch mounted at its base which is activated when the
are nonroutine and can be time-consuming and expensive, so
creep specimen fails. A small pin is located in the lower
tests must be selected with care.
specimen seat which is driven against the microswitch when
the failed specimen strikes it. The microswitch must be
4.6 The apparatus and procedures may be suitable for
connected to an automatic timer-recorder.
measuring creep properties of adhesives on substrates other
than wood, such as metal, plastic, and glass, but such consid-
5.4 Automatic Timer-Recorder—If creep or time-to-failure
erations are not within the scope of this test method.
measurements are to be made, an automatic and multi-channel
timer-recorder is connected to the microswitch on each creep-
5. Apparatus
test apparatus. The timer-recorder is capable of automatically
5.1 Testing Machine—A testing machine, or other suitable scanning the several connected circuits at selected intervals of
loading machine, capable of applying compression loads from time. When the creep specimen fails and activates the
0 to 5000 lbf (22 kN) and cross-head speeds from 0.01 to 0.40 microswitch, the timer-recorder automatically records the time
in./min (0.3 to 10.2 mm/min) is sufficient for this test method. at which the circuit is broken.
A minimum vertical space of 20 in. (508 mm) is required to
5.5 Microscope—A microscope is required to measure dis-
compress the loading spring in the creep-test apparatus.
placement of scribe marks across the two adherends of a
5.2 Compression Shearing Tool—The testing machine is
specimen as creep occurs. Accurate measurements are also
equipped with a shearing tool capable of applying a uniformly required for bondline thicknesses. Make measurements to the
distributed compression load to the loading ledges of the
nearest 0.001 mm (0.0004 in.). A linear traveling binocular
block-shear specimen. A shearing tool equipped with a self- microscope is ideally suited to creep measurements; however,
aligning seat in the shearing blade ensures uniform loading.
a microscope fitted with an appropriately graduated scale is
satisfactory. An objective lens of at least 7× magnification is
5.3 Creep-Test Apparatus—Staticloadsshallbeappliedand
required.
maintained on block-shear specimens by means of the
5,4
compression-loadedcreep-testcylindershowninFig.1. The
5.6 Environmental Chambers—Control of temperature and
apparatus is spring-loaded and can sustain any load up to the
relative humidity is required in creep tests of adhesive bonds
design capacity of the spring. This particular spring has a
on wood substrates. Temperature has a profound effect on
design load of 2300 lbf (10 kN); however, others of greater or
creep properties of adhesives. Humidity also affects creep of
less capacity may be substituted. Varying spring capacities
certain adhesives, but it can also affect dimensional change in
with outside diameters no greater than the cylinder inside
woodadherends.Conditioningequipmentshouldbecapableof
diameter are available.
maintainingaconstanttemperaturewithin 63.0°F(61.7°C)of
5.3.1 For creep tests above room temperature, it is not
theset-pointandconstantrelativehumiditywithin 65%ofthe
necessary to adjust the spring or load to compensate for the
set-point at a given temperature.
effects of changing temperature. It is only necessary that the
apparatus, with included specimen, be preconditioned to the
6. Materials
test temperature before the test load is applied to the spring.
6.1 Adherends—Selectsugarmaple(Acersaccharum)asthe
The preheated apparatus must be wrapped with a piece of
standard adherend material with the grain of the wood straight
flexible thermal insulation material while the test load is
andparalleltothedirectionofshearandfreeofalldefectssuch
applied to the specimen. After loading and measurements,
as knots, splits, and discolorations. Sugar maple is a uniformly
textured and high-density wood preferred in creep tests be-
cause it is less likely to deform near the bondline or fail in the
Thiscreep-testapparatusmaybepurchasedfromHullMachineShop,P.O.373,
Hull, GA30646, or other suitable suppliers. wood before the test is completed.
D4680 − 98 (2011)
FIG. 1 Creep Test Apparatus
6.1.1 Sugar maple adherend material has a minimum spe- specific wood species. However, it should be recognized that
cificgravityof0.65(basedonoven-dryweightandvolume).A woodsthatarelessuniformintextureandlowerindensitythan
method for selecting maple blocks at this specific gravity, sugar maple, are more likely to deform and fail prematurely.
including appropriate adjustments in specific gravity for vari- 6.1.3 When conducting creep and time-to-failure tests, it is
ous moisture contents, is described in the Appendix of Test important not to overload the adherend and cause deformation
Method D905. If more complete procedures are required for at the bondline or failure in the wood before the test is
refereed tests, specific gravity may be determined in accor- completed.Asaguidetoselectingmaximumlevelsofstress,it
dance with Section 116 of Test Methods D143. is recommended that the load not exceed the average shear
6.1.2 Any other species of wood may be used as adherend strength parallel-to-grain for the species of wood when ad-
material, particularly in those cases where it is necessary to justed for any change in moisture content from 12%.Average
know the creep behavior of an adhesive in contact with a shear strengths at 12% moisture content for sugar maple and
D4680 − 98 (2011)
other species of wood are presented in Table4-2 of the Wood Fig. 2. Use the test adhesive to bond the two hard maple
Handbook. For moisture contents other than 12%, it will be adherends together.The shear area is 1.00 by 1.00 in. (2.54 by
2 2
necessary to adjust shear strengths by the formula described in 2.54 cm), equalling 1.00 in. (6.45 cm ).
pp. 4-32 and 4-33 of the Wood Handbook.
7.2 The finished specimen for creep tests has well-defined
6.1.4 Should premature failures occur in the wood after
scribe marks on each side of the specimen for measuring
mean strength values have been adjusted for moisture content,
displacement of the two adherends as creep takes place.
then the 5% exclusion limit may be used to select the
7.3 Scribe marks are not necessary for specimens intended
maximum level of stress for a particular species of wood. The
for the time-to-failure tests.
maximum level of stress S is determined by the follow-
max0.05
ing equation:
7.4 Number of Specimens:
7.4.1 Test at least ten specimens at each set of test
S 5 S 21.645~0.14S ! (1)
max0.05 m m
conditions, that is, each combination of stress level,
where S is the mean shear strength parallel-to-grain as
m
temperature, and relative humidity, for either creep test or
presented in Table4-2 of the Wood Handbook.
time-to-failure test. It is suggested that at least one test joint
6.2 Adhesives—Creep properties of any adhesive can be assembly (contains twelve specimens) be prepared for each
measured on any species of wood as long as the level of shear
combination of test conditions.
stress does not exceed the shear strength of the wood in the 7.4.2 Randomlyassignthetenspecimensforeachsetoftest
specimen.
conditions to that set from the entire lot of specimens prepared
for testing of a given adhesive.
7. Test Specimens
7.4.3 For many adhesives, measured creep properties will
7.1 The standard specimen for both creep and time-to- be highly variable, and ten specimens may not be a large
enoughsampletogiveahighdegreeofconfidencetothemean
failure tests shall be the block-shear specimen illustrated in
of a measured property. Creep tests generally are expensive
and time-consuming, and a specimen count of ten represents a
6 practical compromise.
Wood Handbook: Wood As An Engineering Material, USDA Agriculture
Handbook 72,rev.,U.S.ForestProductsLab.,1974,Table4-2andp.4-32and4-33. 7.4.4 If it is determined from experimental evidence that a
AvailablefromU.S.GovernmentPrintingOfficeSuperintendentofDocuments,732
reasonable degree of confidence can be given to a mean by
N. Capitol St., NW, Mail Stop: SDE, Washington, DC 20401.
FIG. 2 Block-Shear Specimen for Creep and Time To Failure Tests
D4680 − 98 (2011)
using a lesser number of specimens, then it is permissible to givenin8.1.Conditionthemtherefor7daystoensurethatthe
use the lesser number. moisture content has
...
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