ASTM D3983-98

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Designation: D 3983 – 98
Standard Test Method for
Measuring Strength and Shear Modulus of Nonrigid
Adhesives by the Thick-Adherend Tensile-Lap Specimen
This standard is issued under the fixed designation D 3983; 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 E 83 Practice for Verification and Classification of Exten-
someters
1.1 This test method describes a method of measuring the
E 104 Practice for Maintaining Constant Relative Humidity
shear modulus and rupture stress in shear of adhesives in
by Means of Aqueous Solutions
bonded joints. The method employs lap-shear specimens with
E 229 Test Method for Shear Strength and Shear Modulus
wood, metal, or composite adherends, with adhesives having
of Structural Adhesives
shear moduli ranging up to 700 MPa (100 000 psi). This test
method is suitable generally for joints in which the ratio of
3. Terminology
adherend tensile modulus to adhesive shear modulus is greater
3.1 Definitions—For definitions of terms used in this test
than 300 to 1. It is not suitable for adhesives that have a high
method, refer to Terminologies E 6 and D 907.
shear modulus in the cured state and that also require elimina-
3.1.1 initial tangent modulus, n—the slope of the stress-
tion of volatile constituents during cure.
strain curve at the origin.
1.2 The values stated in SI units are to be regarded as
3.1.2 nominal stress, n—the stress at a point calculated on
standard. The values given in parentheses are for information
the net cross section by simple elastic theory without taking
only.
into account the effect on the stress produced by discontinuities
1.3 This standard does not purport to address all of the
such as holes, grooves, fillets, etc.
safety concerns, if any, associated with its use. It is the
3.1.3 normal stress, n—the stress component perpendicular
responsibility of the user of this standard to establish appro-
to a plane on which the forces act, that is, the plane of the
priate safety and health practices and determine the applica-
bondline.
bility of regulatory limitations prior to use.
3.1.4 proportional limit, n—the maximum stress that a
2. Referenced Documents material is capable of sustaining without significant deviation
from proportionality of stress to strain.
2.1 ASTM Standards:
3.1.5 secant modulus, n—the slope of the secant drawn
D 143 Methods of Testing Small Clear Specimens of Tim-
2 from the origin to any specified point on the stress-strain curve.
ber
3.1.5.1 Discussion—Modulus is expressed in force per unit
D 905 Test Method for Strength Properties of Adhesive
3 area (MPa, lb/in. , etc.).
Bonds in Shear by Compression Loading
3.1.6 shear modulus, n—the ratio of shear stress to corre-
D 907 Terminology of Adhesives
sponding shear strain below the proportional limit. (Compare
D 1151 Test Method for Effect of Moisture and Temperature
secant modulus.)
on Adhesive Bonds
3.1.6.1 Discussion—The term shear modulus is generally
D 2651 Guide for Preparation of Metal Surfaces for Adhe-
reserved for materials that exhibit linear elastic behavior over
sive Bonding
most of their stress-strain diagram. Many adhesives exhibit
E 6 Terminology Relating to Methods of Mechanical Test-
curvilinear or nonelastic behavior, or both, in which case some
ing
other term, such as secant modulus, may be substituted.
3.1.7 shear strain, n—the tangent of the angular change,
due to force, between two lines originally perpendicular to
This test method is under the jurisdiction of ASTM Committee D-14 on
Adhesives and is the direct responsibility of Subcommittee D14.70 on Construction
each other through a point in the body.
Adhesives.
3.1.7.1 Discussion—Shear strain equals adherend slip/
Current edition approved March 10, 1998. Published February 1999. Originally
adhesive layer thickness.
published as D 3983 – 81. Last previous edition D 3983 – 93.
Annual Book of ASTM Standards, Vol 04.10.
Annual Book of ASTM Standards, Vol 15.06.
4 5
Annual Book of ASTM Standards, Vol 03.01. Annual Book of ASTM Standards, Vol 11.03.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 3983
3.1.8 shear strength, n—in an adhesive joint, the maximum
average stress when a force is applied parallel to the joint.
3.1.8.1 Discussion—In most adhesive test methods, the
shear strength is actually the maximum average stress at failure
of the specimen, not necessarily the true maximum stress in the
material.
3.1.9 shear stress, n—the stress component tangential to the
plane of which the forces act, that is, the plane of the bondline.
3.1.9.1 Discussion—Nominal shear stress equals load/bond
area.
3.1.10 strain, n—the unit change due to force, in the size or
shape of a body referred to its original size or shape.
3.1.11 stress, n—the intensity at a point in a body of the
internal forces or components of force that act on a given plane
through the point.
3.1.12 stress-strain diagram, n—a diagram in which corre-
sponding values of stress and strain are plotted against each
other. Values of stress are usually plotted as ordinates (verti-
cally) and values of strain as abscissas (horizontally).
3.2 Definitions of Terms Specific to This Standard:
3.2.1 load, n—the force applied to the specimen at any
NOTE 1—The modulus is represented by the secant modulus line at
given time.
some load P less than the load to cause failure.
3.2.2 load-slip diagram, n—a diagram in which correspond-
FIG. 2 Load-Slip Diagram of Nonlinear Adhesive Under Cyclic
Low-Level Loading Showing Both Elastic and Viscoelastic
ing values of load and slip are plotted against each other.
Recovering Diagrams
Values of load are usually plotted as ordinates (vertically) and
values of slip as abscissas (horizontally).
3.2.2.1 Discussion—Stress-strain behavior is commonly re-
corded in the form of a load-slip diagram. The difference
between the two is simply one of scale. Load is divided by
bond area to obtain stress and slip is divided by adhesive layer
thickness to obtain strain. Examples of various types of
load-slip diagrams and modulus are shown in Figs. 1-3.
NOTE 1—The modulus may be represented by the initial tangent, the
secant drawn to the ultimate load, or the secant drawn to some interme-
diate load.
FIG. 3 Load-Slip Diagram of Adhesive Loaded to Failure
3.2.3 rate of strain, n—rate of slip per unit adhesive
thickness.
3.2.4 slip, n—the relative collinear displacement of the
adherends on either side of the adhesive layer in the direction
of the applied load.
3.3 Symbols:Symbols:
NOTE 1—Case load and unload diagrams and modulus line are congru-
3.3.1 c 5 half the overlap length 5 L/2, mm or in.
ent.
ˆ
3.3.2 G 5 estimate of shear modulus of adhesive, MPa or
FIG. 1 Load-Slip Diagram of Linear Elastic Adhesive Under Cyclic
Low-Level Loading psi.
D 3983
3.3.3 G 5 shear modulus of adhesive, MPa or psi. ties of adhesives. This thick adherend lap-shear test yields a
3.3.4 E 5 tensile modulus of adherend, MPa or psi. uniformity of stress distribution approaching that obtained in
3.3.5 t 5 thickness of adherend, mm or in. thin tubular butt joints subjected to torsion, which is considered
3.3.6h5 thickness of adhesive, mm or in. to be a condition of pure shear.
3.3.7 P 5 failure load for the bond, N or lbf. 5.2 The user is cautioned that pure shear strength cannot be
max
3.3.8 L 5 overlap length, mm or in. obtained by this test method, because some tensile and com-
2 2
3.3.9 A 5 bond area, mm or in. pression stresses and stress concentrations are present in the
3.3.10d5 adherend slip at load equivalent to 0.1 P , joint. The estimate of shear strength by this test method will be
max
mm or in. conservative. If pure shear strength is demanded, then Test
3.3.11 t¯ 5 maximum nominal shear stress sustained by Method E 229 should be used.
max
the bond, MPa or psi.
6. Equipment
4. Summary of Test Method
6.1 Test Machine— A tension test machine with electronic
load cell capacities of 0 to 100 and 0 to 1000 kg (0 to 200 and
4.1 Lap-shear specimens are prepared with the adhesive in
0 to 2000 lb) is satisfactory for this test method. The machine
question using selected adherends. The load-deformation prop-
should have a loading rate capability of 0 to 200 kg/min (0 to
erties of the specimens are measured under specific recom-
400 lb/min) or a crosshead movement rate of 0 to 1 mm/min (0
mended conditions to yield a “first estimate” of adhesive shear
to 0.040 in./min). Closed-loop control of load level and loading
modulus. This estimate is used to determine the optimized joint
rate, or crosshead position and movement rate, is desirable to
geometry for best attainable uniformity of stress distribution in
facilitate testing under controlled cyclic loading conditions. A
the joint. A second set of specimens is prepared having the
working space approximately 450 by 450 mm (18 by 18 in.) is
optimized joint geometry. The final values for load-
desirable to accommodate the specimen grips and the installa-
deformation properties are then measured under a variety of
tion of a chamber for environmental control. In-line tension
controlled environmental and experimental conditions.
grips, shown in Fig. 4, are used for transmitting the load to the
4.2 The test method is based upon the theoretical analysis
specimen.
by Goland and Reissner relating stress concentrations (that is,
6.2 Slip Gage and Signal Conditioner:
nonuniformity) in single-lap joints to the geometry of the joint
6.2.1 The shear strain in adhesive layers is usually small.
and the mechanical properties of the materials involved. The
Thin layers of relatively rigid adhesives (greater than 50 MPa
controlling factor in the Goland and Reissner equations is a
(7000 psi)) require an ASTM Class A extensometer. Class B-1
composite of essentially three ratios which can be manipulated
or B-2 extensometers suffice for thicker layers and more
to improve the stress uniformity in the joint, and thereby
flexible adhesives. Extensometer classes are described in
control the accuracy of measurement. Stress uniformity is
Practice E 83.
improved by (1) increasing the adherend tensile modulus in
6.2.2 A mechanical-electrical transducer, the linear variable
relation to the shear modulus of the adhesive, and by ( 2)
differential transformer (LVDT), is well suited for these tests.
increasing adherend and adhesive thickness while minimizing
The LVDT with suitable signal conditioning will satisfy the
overlap length. Because of these relationships, the practice was
requirements of Class B and A extensometers. They are rugged
developed to use high-modulus adherends in thick cross
enough to remain fastened to the specimen through failure if
sections.
the gage is properly designed.
5. Significance and Use 6.2.2.1 The LVDT should have a linear output over a
displacement range of 62.5 mm (60.10 in.) to accommodate
5.1 This test method is capable of providing shear modulus
adhesive layers varying in shear modulus and thickness.
and shear strength values for adhesives with accuracy suitable
6.2.2.2 The LVDT transducers with signal conditioner
for use by design engineers in predicting the characteristics of
should provide several ranges of displacement resolution—
building assemblies bonded with nonrigid adhesives. Adhesive
between 0.0005 and 0.5 mm/cm (5 3 10 and 0.05 in./m) of
formulators will also find the method useful during the
chart paper.
development of new adhesive systems. In general, the thick
6.2.3 The slip gage shall employ two LVDTs as described in
adherend lap-shear test is a useful tool in research during
6.2.2, positioned in such a manner as to measure and compen-
studies of both short- and long-term load-deformation proper-
sate for rotation of the adherends as well as slip.
6.2.4 A gage design that has been found to compensate
satisfactorily for adherend rotation is shown in Fig. 5, Fig.
Goland, M., and Reissner, E., “The Stresses in Cemented Joints,” Journal of
A1.1, and Fig. A1.2. The gage consists of three components:
Applied Mechanics, November 1944, pp. A17–A27.
FIG. 4 Incline Tension Grips with Specimen Bolted in Place Ready for Testing
D 3983
FIG. 5 Dual Transducer Slip Gage Mounted on a Thick Adherend Lap Specimen
the gage itself on which two LVDTs are mounted, the follower, 6.4.2 The combined test chamber and conditioning unit
and a gage block. The gage and follower attach to opposing should be capable of maintaining a constant temperature within
adherends by clamping knife edges. One knife edge on each the limits from 23 to 71 6 1°C (80 to 160 6 2°F), and constant
component may be advanced or retracted by a captive screw. relative humidity within the limits of 44 to 98 6 2 % at a given
The gage block is placed between the gage and follower to temperature.
align the knife edges. The gage is clamped to the stationary or
6.4.3 A suitable test chamber is described in Annex A2.
downward moving adherend and the follower to the upward
moving adherend, so the LVDT core moves out of the LVDT
7. Materials
during loading. This prevents damage to the LVDT upon
7.1 Adherend:
failure of the specimen. The follower is equipped with a
7.1.1 Wood—Hard maple (Acer saccharum or Acer nigrum)
knurled adjustment screw for each LVDT. These screws are
with a minimum specific gravity of 0.60 is the standard wood
used to null mechanically and electrically each LVDT prior to
adherend for this test method. Other dense species with
testing.
comparable modulus of elasticity such as yellow birch, Dou-
6.2.5 The slip gage shall be equipped with a switching and
glas fir, western hemlock, or southern pine may be used. The
signal-conditioning device to permit recording the signal from
lumber shall be of straight grain and free of defects, including
each LVDT individually or the sum of the signals.
knots, birdseye, short grain, decay, and any unusual discolora-
6.2.6 The LVDTs and slip gage components should be
tions within the shearing area. Criteria for lumber selection
fabricated of corrosion-resistant materials.
shall be those described in Test Method D 905.
6.3 X-Y Recorder— A general-purpose X-Y recorder with
7.2 Metal—Use cold-rolled steel or aluminum-alloy bar
inputs compatible with the outputs of the load cell and slip
stock, machined to a surface finish of 16 μin. or better in the
gage is required. The load is connected to the recorder of the
bond area, for adhesives that contain no volatil
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