ASTM D4680-98
(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)
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 This standard does not purport to address all of the safety problems, 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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Designation: D 4680 – 98
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 D 4680; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope 3.1.1 creep—the dimensional change with time of a mate-
rial under load, following the initial instantaneous elastic or
1.1 This test method covers the determination of time-
rapid deformation. Creep at room temperature is sometimes
dependent properties of structural adhesives in wood-to-wood
called cold flow.
bonds when specimens are subjected to shearing stresses at
3.1.2 creep modulus—the ratio of initial applied stress to
various levels of static load, constant temperature, and relative
creep strain.
humidity. Apparatus and procedures are provided for direct
3.1.3 creep strain—the total strain, at any given time,
measurement of time-dependent shear deformation (creep) and
produced by the applied stress during a creep test.
time to failure of adhesive bonds under static load. Guidelines
3.1.3.1 Discussion—In this test method, creep strain is
for selecting test conditions, methods for calculating creep rate,
calculated by dividing displacement at any given time by the
creep strain, creep modulus, and extrapolation of time to
estimated apparent thickness of the adhesive bondline.
failure, are given along with methods of presenting these data.
3.1.4 rate of creep—the slope of the creep-time curve at a
1.2 The values stated in inch-pound units are to be regared
given time.
as the standard. The SI units are given in parentheses are for
3.1.5 shear stress—the stress component tangential to the
information only.
plane on which the forces act, that is, in the plane of the bond
1.3 This standard does not purport to address all of the
line.
safety concerns, if any, associated with its use. It is the
3.1.6 strain—the unit change, due to stress, in the size or
responsibility of the user of this standard to establish appro-
shape of a body referred to its original size or shape.
priate safety and health practices and determine the applica-
3.1.7 stress, n—the force exerted per unit area at a point
bility of regulatory limitations prior to use.
within the plane.
2. Referenced Documents
4. Significance and Use
2.1 ASTM Standards:
4.1 Creep data that are obtained over a relatively short
D 143 Methods of Testing Small Clear Specimens of Tim-
2 period of time in this test method can provide a measure of an
ber
adhesive bond’s ability to withstand static loading in shear over
D 905 Test Method for Strength Properties of Adhesive
3 a relatively long period of time. Creep measurements are made
Bonds in Shear by Compression Loading
over a range of expected service conditions, including level of
D 907 Terminology of Adhesives
4 stress, temperature, relative humidity, and duration of load.
D 2016 Test Methods for Moisture Content of Wood
Creep rate, creep strain, and creep modulus are calculated at
3. Terminology the various service conditions.
4.2 Creep data can be used to (1) predict performance of an
3.1 Definitions—Many terms in these test methods are
adhesive under long-term loading, (2) characterize an adhesive,
defined in Terminology D 907.
(3) compare adhesives with each other and against specifica-
tions, and ( 4) design structural members fabricated with an
adhesive.
This test method is under the jurisdiction of ASTM Committee D14 on
4.3 Time-to-failure data provide a measure of the ultimate
Adhesives and is the direct responsibility of Subcommittee D14.30 on Wood
load-carrying ability of an adhesive bond as a function of time
Adhesives.
Current edition approved May 10, 1998. Published March 1999. Originally
at various levels of stress, temperature, and relative humidity.
published as D 4680 – 87. Last previous edition D 4680 – 92.
4.4 With proper caution, time-to-failure data derived from
Annual Book of ASTM Standards, Vol 04.10
relatively short loading periods can be extrapolated to estimate
Annual Book of ASTM Standards, Vol 15.06.
Annual Book of ASTM Standards, Vol 04.09. the useful service life of an adhesive at working levels of static
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D4680–98
FIG. 1 Creep Test Apparatus
stress. This property may also be used with creep data to 5. Apparatus
accomplish purposes listed in 4.2.
5.1 Testing Machine— A testing machine, or other suitable
4.5 This test method is a research tool intended for devel-
loading machine, capable of applying compression loads from
opment or evaluation of new adhesives and new product
0 to 5000 lbf (22 kN) and cross-head speeds from 0.01 to 0.40
designs. The researcher may select from suggested tests those
in./min (0.3 to 10.2 mm/min) is sufficient for this test method.
that are appropriate. However, creep and time-to-failure tests
A minimum vertical space of 20 in. (508 mm) is required to
are nonroutine and can be time-consuming and expensive, so
compress the loading spring in the creep-test apparatus.
tests must be selected with care.
5.2 Compression Shearing Tool—The testing machine is
4.6 The apparatus and procedures may be suitable for
measuring creep properties of adhesives on substrates other equipped with a shearing tool capable of applying a uniformly
than wood, such as metal, plastic, and glass, but such consid- distributed compression load to the loading ledges of the
erations are not within the scope of this test method.
D4680–98
block-shear specimen. A shearing tool equipped with a self- nearest 0.001 mm (0.0004 in.). A linear traveling binocular
aligning seat in the shearing blade ensures uniform loading. microscope is ideally suited to creep measurements; however,
5.3 Creep-Test Apparatus—Static loads shall be applied and a microscope fitted with an appropriately graduated scale is
maintained on block-shear specimens by means of the satisfactory. An objective lens of at least 73 magnification is
compression-loaded creep-test cylinder shown in Fig. 1. The required.
apparatus is spring-loaded and can sustain any load up to the
5.6 Environmental Chambers—Control of temperature and
design capacity of the spring. This particular spring has a
relative humidity is required in creep tests of adhesive bonds
design load of 2300 lbf (10 kN); however, others of greater or on wood substrates. Temperature has a profound effect on
less capacity may be substituted. Varying spring capacities
creep properties of adhesives. Humidity also affects creep of
with outside diameters no greater than the cylinder inside certain adhesives, but it can also affect dimensional change in
diameter are available.
wood adherends. Conditioning equipment should be capable of
5.3.1 For creep tests above room temperature, it is not maintaining a constant temperature within 63.0°F (61.7°C) of
necessary to adjust the spring or load to compensate for the
the set-point and constant relative humidity within6 5 % of the
effects of changing temperature. It is only necessary that the set-point at a given temperature.
apparatus, with included specimen, be preconditioned to the
test temperature before the test load is applied to the spring.
6. Materials
The preheated apparatus must be wrapped with a piece of
6.1 Adherends—Select sugar maple (Acer saccharum)as
flexible thermal insulation material while the test load is
the standard adherend material with the grain of the wood
applied to the specimen. After loading and measurements,
straight and parallel to the direction of shear and free of all
return the loaded apparatus to the test environment. Since there
defects such as knots, splits, and discolorations. Sugar maple is
are no significant changes in temperature before or after
a uniformly textured and high-density wood preferred in creep
loading, no adjustments are needed in the spring.
tests because it is less likely to deform near the bondline or fail
5.3.2 The creep-test apparatus is made of corrosion-resistant
in the wood before the test is completed.
components so that it can be used in high-temperature and
6.1.1 Sugar maple adherend material has a minimum spe-
humid environments for prolonged periods without concern for
cific gravity of 0.65 (based on oven-dry weight and volume). A
damaging the apparatus or interfering with the effectiveness of
method for selecting maple blocks at this specific gravity,
the test.
including appropriate adjustments in specific gravity for vari-
5.3.3 The creep-test apparatus has been compactly designed
ous moisture contents, is described in the Appendix of Test
with its load-applying mechanism built-in. Thus, several of the
Method D 905. If more complete procedures are required for
units may be stacked on racks in a small environmental
refereed tests, specific gravity may be determined in accor-
chamber such as an oven, incubator, or humidity cabinet. The
dance with Section 116 of Methods D 143.
apparatus may be transferred from one exposure chamber to
6.1.2 Any other species of wood may be used as adherend
another, or may be removed from an exposure chamber for
material, particularly in those cases where it is necessary to
measurements without disturbing the specimen under static
know the creep behavior of an adhesive in contact with a
load.
specific wood species. However, it should be recognized that
5.3.4 The creep-test apparatus shown in Fig. 1 has a
woods that are less uniform in texture and lower in density than
microswitch mounted at its base which is activated when the
sugar maple, are more likely to deform and fail prematurely.
creep specimen fails. A small pin is located in the lower
6.1.3 When conducting creep and time-to-failure tests, it is
specimen seat which is driven against the microswitch when
important not to overload the adherend and cause deformation
the failed specimen strikes it. The microswitch must be
at the bondline or failure in the wood before the test is
connected to an automatic timer-recorder.
completed. As a guide to selecting maximum levels of stress, it
5.4 Automatic Timer-Recorder—If creep or time-to-failure
is recommended that the load not exceed the average shear
measurements are to be made, an automatic and multi-channel
strength parallel-to-grain for the species of wood when ad-
timer-recorder is connected to the microswitch on each creep-
justed for any change in moisture content from 12 %. Average
test apparatus. The timer-recorder is capable of automatically
shear strengths at 12 % moisture content for sugar maple and
scanning the several connected circuits at selected intervals of
other species of wood are presented in Table 4-2 of the Wood
time. When the creep specimen fails and activates the mi-
Handbook. For moisture contents other than 12 %, it will be
croswitch, the timer-recorder automatically records the time at
necessary to adjust shear strengths by the formula described in
which the circuit is broken.
pp. 4-32 and 4-33 of the Wood Handbook.
5.5 Microscope—A microscope is required to measure dis-
6.1.4 Should premature failures occur in the wood after
placement of scribe marks across the two adherends of a
mean strength values have been adjusted for moisture content,
specimen as creep occurs. Accurate measurements are also
then the 5 % exclusion limit may be used to select the
required for bondline thicknesses. Make measurements to the
5 6
This creep-test apparatus may be purchased from Hull Machine Shop, P.O. 373, Wood Handbook: Wood As An Engineering Material, USDA Agriculture
Hull, GA 30646, or other suitable suppliers. Detailed working drawings of the Handbook 72, rev., U.S. Forest Products Lab., 1974, Table 4-2 and p. 4-32 and 4-33.
apparatus are available from ASTM, 100 Barr Harbor Drive, PO Box C700, West Available from the Superintendent of Documents, U.S. Govt. Printing Office,
Conshohocken, PA 19428–2959. Order ADJ4680. Washington, DC 20402.
D4680–98
FIG. 2 Block-Shear Specimen for Creep and Time To Failure Tests
maximum level of stress for a particular species of wood. The is suggested that at least one test joint assembly (contains
maximum level of stress S is determined by the twelve specimens) be prepared for each combination of test
max0.05
following equation: conditions.
7.4.2 Randomly assign the ten specimens for each set of test
S 5 S 2 1.645~0.14S ! (1)
max0.05 m m
conditions to that set from the entire lot of specimens prepared
where S is the mean shear strength parallel-to-grain as
m
for testing of a given adhesive.
presented in Table 4-2 of the Wood Handbook.
7.4.3 For many adhesives, measured creep properties will
6.2 Adhesives—Creep properties of any adhesive can be
be highly variable, and ten specimens may not be a large
measured on any species of wood as long as the level of shear
enough sample to give a high degree of confidence to the mean
stress does not exceed the shear strength of the wood in the
of a measured property. Creep tests generally are expensive
specimen.
and time-consuming, and a specimen count of ten represents a
practical compromise.
7. Test Specimens
7.4.4 If it is determined from experimental evidence that a
7.1 The standard specimen for both creep and time-to- reasonable degree of confidence can be given to a mean by
failure tests shall be the block-shear specimen illustrated in using a lesser number of specimens, then it is permissible to
Fig. 2. Use the test adhesive to bond the two hard maple use the lesser number.
adherends together. The shear area is 1.00 by 1.00 in. (2.54 by
2 2
8. Conditioning of Materials and Specimens
2.54 cm), equalling 1.00 in. (6.45 cm ).
7.2 The finished specimen for creep tests has well-defined
8.1 Condition hard maple boards at 73 6 3°F (23 6 1.7°C)
scribe marks on each side of the specimen for measuring
and 65 6 2 % relative humidity until they reach moisture
displacement of the two adherends as creep takes place.
equilibrium (approximately 12 % moisture content), as indi-
7.3 Scribe marks are not necessary for specimens intended
cated by no further significant changes in weight. Use Test
for the time-to-failure tests.
Methods D 2016 for guidance to determine when equilibrium
7.4 Number of Specimens:
has been reached. Other relative humidities may be substituted
7.4.1 Test at least ten specimens at each set of test condi- as long as (1) the wood reaches equilibrium between 10 and
tions, that is, each combin
...
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