ASTM D4502-92(1998)e1

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e1
Designation: D 4502 – 92 (Reapproved 1998)
Standard Test Method for
Heat and Moisture Resistance of Wood-Adhesive Joints
This standard is issued under the fixed designation D 4502; 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.
e NOTE—Keywords were added editorially in March 1998.
1. Scope the Rating of Electrical Equipment
1.1 The purpose of this test method is to estimate the
3. Terminology
resistance of adhesive-bonded joints to thermal and hydrolytic
3.1 Definitions
degradation.
3.1.1 For definitions of terms used in this test method, refer
1.2 This test method is primarily for wood-to-wood joints
to Terminology D 907.
but may be applied to joints of wood to other materials.
3.2 shear strength, n—in an adhesive joint, the maximum
1.3 The effects of chemicals such as fire retardants, preser-
average stress when a force is applied parallel to the joint.
vatives, and extractives in the wood upon joint degradation
3.2.1 Discussion—In most adhesive test methods, the shear
resistance can be estimated.
strength is actually the maximum average stress at failure of
1.4 This test method does not account for the effects of
the specimen, not necessarily the true maximum stress in the
stress, the other principal degrading factor, nor does it account
material.
for cyclic or variable temperature or moisture levels.
1.5 This standard does not purport to address all of the
4. Summary of Test Method
safety concerns, if any, associated with its use. It is the
4.1 The degradation of adhesive joints is a physicochemical
responsibility of the user of this standard to establish appro-
process. The speed of degradation is related to the levels of
priate safety and health practices and determine the applica-
temperature, moisture (and other chemicals), and physical
bility of regulatory limitations prior to use.
stress to which the joint is exposed. This test method is based
2. Referenced Documents on the principles of chemical kinetics and uses the Arrehenius
temperature dependence relationship to estimate the long-term
2.1 ASTM Standards:
effects of heat and moisture at the service temperature.
D 897 Test Method for Tensile Properties of Adhesive
2 4.2 Specimens whose unaged properties have been esti-
Bonds
mated by control tests are subjected to an accelerated thermal
D 905 Test Method for Strength Properties of Adhesive
2 or hydrolytic aging environment in groups. Aging is acceler-
Bonds in Shear by Compression Loading
2 ated by using elevated temperature. Periodically, a group of
D 907 Terminology of Adhesives
specimens is removed from the aging environment and tested.
D 2304 Test Method for Thermal Endurance of Rigid Elec-
3 The estimated property after aging and the time of aging are
trical Insulating Materials
recorded. After several groups have been tested in this manner,
D 2307 Test Method for Relative Thermal Endurance of
3 the rate of property loss in the aging environment can be
Film-Insulated Round Magnet Wire
estimated. This basic experiment is repeated at several other
D 2339 Test Method for Strength Properties of Adhesives in
2 elevated temperatures, and the rates of property loss at those
Two-Ply Wood Construction in Shear by Tension Loading
temperatures estimated. The rate of property loss relationship
2.2 IEEE Standard:
to temperature is estimated. This relationship can be extrapo-
IEEE No. 1, General Principles for Temperature Limits in
lated to lower service temperatures for estimating service life.
4.3 This test method employs a smaller version of the Test
Method D 905 block shear specimen, but other shear strength
This test method is under the jurisdictioin of ASTM Committee D-14 on
Adhesives and is the direct responsibility of Subcommittee D14.70 on Construction
or tensile strength specimens may also be used.
Adhesives.
Current edition approved July 15, 1992. Published December 1992. Originally
e1
published as D 4502 – 85. Last previous edition D 4502 – 85 (1990) .
Annual Book of ASTM Standards, Vol 15.06.
Available from Institute of Electrical and Electronics Engineers, 345 East 47th
Annual Book of ASTM Standards, Vol 10.01.
St., New York, NY 10017.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
D 4502
5. Significance and Use perforated to permit free-flow of water vapor. It may be cut
from any material that is resistant to corrosion, heat, and
5.1 This test method can serve as a useful tool for durability
moisture. Perforated high-density hardboard has proven satis-
assessment and service life forecasting.
factory. The platform must be cut in half to pass through the
5.1.1 This test method can be used to measure the effects of
neck of the jar. An aging jar with platform is shown in Fig. 1.
heat and moisture and the effect of their interaction on
The jars must be placed in an aging oven, such as described in
adhesives and bonded joints. Knowledge of these effects is
5.1, to achieve the required temperature.
useful to an adhesive formulator or manufacturer. Moist heat
6.4 Water Baths—Constant-level water baths capable of
aging is particularly useful for determining the effects of acidic
control to within 0.5°C of the desired temperature are required.
adhesive systems on the hydrolysis of wood adherends.
The baths must be able to contain 100 specimens.
5.1.2 This test method provides a means of comparing the
6.5 Testing Machine—The testing machine shall have a
rate of degradation of an unknown adhesive-adherend combi-
capacity of not less than 3000 kg (6210 lbf) in compression.
nation to the rate of degradation of a known combination in
The machine shall be capable of maintaining a uniform rate of
thermal or hydrolytic aging environments. Such a comparison
loading such that the load may be applied with a continuous
can be useful to adhesive manufacturers for introducing a new
motion of the movable head to the maximum load at a rate of
product to the market and for helping designers selecting
10.0 6 5 mm/min (0.40 in./min) with a permissible variation
adhesives.
of + 0.5 %.
5.1.3 This test method does not duplicate any natural
6.6 Shearing Tool—A shearing tool similar to the tool
service environment, but it does provide a means of estimating
pictured in Test Method D 905 is satisfactory. The tool must
the service life of joints in similar environments. Service-life
have a self-aligning seat to ensure uniform lateral distribution
estimates are useful to designers of bonded structures or
of the load.
structures using bonded products.
5.2 Service-life estimates rely on the assumption that the
7. Materials
chemical degradation mechanism is the same at the elevated
7.1 Adhesive to Be Tested:
aging temperatures as at the service temperature. However, this
7.2 Joints—Wood for wood-to-wood joints or joints of
may not be true in every case. This possibility, together with
wood to metal or plastic shall be free of defects such as knots,
the variability in specimen preparation, in the aging exposures,
cracks, short-grain and sharp-grain deviations, or any discol-
and in the strength measurements, require that caution be used
orations or soft spots indicative of decay. Generally, a high-
in accepting the estimate of service life.
density uniform-textured wood is desirable so that the maxi-
6. Apparatus mum stress will be placed on the adhesive joint during testing.
The standard shall be hard maple (Acer saccharum or Acer
6.1 Aging Ovens—Ovens are required that are capable of
nigrum) having a minimum specific gravity of 0.65 (based on
control within 62 % of specified exposure temperature
oven-dry weight and volume). Other species may be used
throughout the chamber for extended periods of time (60.5°C
5 where evaluation of the adhesive’s performance in contact with
control is desirable). The ovens must be capable of operating
that species is a specific requirement.
at temperatures from 60 to 175°C. The oven must have an
7.3 Saturated Salt Solutions—A constant relative humidity
internal capacity for up to 100 specimens well-spaced and
at a given temperature can be maintained in sealed aging jars
supported on racks to allow free air flow.
by a saturated aqueous solution in contact with an excess of the
6.2 Environmental Chambers—Chambers for moist-heat
solid phase of a specific salt. Tables are available that show
aging must be capable of 60.5°C temperature and 0.5 %
relative humidities at given temperatures for many salts.
relative humidity control uniformly throughout the chamber.
Sodium chloride is recommended. A saturated solution of
The chamber must be capable of operating at temperatures
sodium chloride will produce a relative humidity of 73 to 76 %
from 60 to 90°C and relative humidity from 60 to 80 %. The
over the temperature range from 40 to 100°C. This translates to
chamber must have the capacity for up to 100 specimens
wood moisture content in the approximate range from 9 to
well-spaced and supported on racks to allow free air flow.
13 %.
6.3 Moist Aging Jars—Heat-resistant glass jars are required
to expose specimens to constant relative humidity and tem-
8. Test Specimens
perature over saturated salt solutions. Wide-neck canning jars
8.1 A modified block shear specimen (Fig. 2) is suggested.
with volumes of 3 ⁄2 L (1 gal), rubber gaskets, and clamp lids
The specimen is similar to the specimen of Test Method D 905,
have proven satisfactory at temperatures of 100°C (212°F) and
but its smaller size allows more specimens to fit in the aging
below. The jars must have a platform inside (without legs) to
chambers. Other specimens such as used in Test Method D 897
support specimens above the saturated salt solution. A 6-mm
or Test Method D 2339 are also satisfactory. If a type from Test
( ⁄4-in.) diameter bead of silicone sealant around the inside
Method D 2339 is selected, then use 6.5-mm ( ⁄4-in.) lumber
surface of the jar and about 5 cm (2 in.) above the bottom
for each lamina, and increase the specimen length to 130 mm
provides a ledge to support the platform. The platform must be
(5.1 in.) while maintaining the 25.4-mm (1-in.) overlap. Other
Millett, M. A., Western, L. J., and Booth, J. J., “Accelerated Aging of Cellulosic
Materials: Design and Application of a Heating Chamber,” TAPPI, Vol 50, No. 11, Dean, J. A., ed., Lange’s Handbook of Chemistry, 12th ed., McGraw-Hill Book
1967, pp 74A–80A. Co., Inc., 1978.
D 4502
FIG. 1 Moist Aging Jar with a Shelf for Aging Specimens Over a Saturated Salt Solution
bonded joints or products may also be tested if a suitable 8.3.2 After bonding, trim one edge and one end of each
specimen can be devised. panel. Then cut two rows of five specimens each from the 63
by 305-mm (2 ⁄2 by 12-in.) panels, as shown in Fig. 3, or four
8.2 Condition the wood at 23 6 2°C (73.4 + 3.6°F) and
relative humidity of either 30 or 65 %, or other conditions, rows of five specimens each from the 127 by 305-mm (5 by
12-in.) panels.
depending on the adhesive manufacturer’s requirement.
8.3 Prepare modified shear block specimens as described in
NOTE 2—The adhesive should be thoroughly cured by hot pressing,
Test Method D 905 with the following exceptions:
oven heating, high-frequency heating, or whatever method is appropriate.
Undercured adhesives cause unwanted results in the early stages of
8.3.1 Cut rough 1-in. (25.4-mm) lumber into 127 or 63 by
1 elevated temperature aging.
305-mm (5 or 2 ⁄2 by 12-in.) billets as required by Section 9.
Saw each billet in half through the thickness using a bandsaw.
8.4 Mark each specimen using a templet before cutting to
Joint the surface of each half that is to be bonded and plane to
indicate the panel and position in the panel.
8-mm ( ⁄16-in.) thickness. (Note 1) Bond the billets as described
in Test Method D 905. 9. Sampling
9.1 Sample Size:
NOTE 1—If during strength testing specimens fail in compression
9.1.1 If using the modified block shear specimen, prepare
parallel to the grain at the ends, the laminae thickness should be increased
5 3
from8mm( ⁄16 in.) to 9.5 mm ( ⁄8 in.) or greater, as necessary. the following numbers and sizes of panels, depending on the
D 4502
9.2.3 The distribution of specimens for subsequent data
analysis is summarized by the block experimental designs
shown in Table 4 for each of the experiments.
10. Procedure
10.1 Initial Strength:
10.1.1 Condition the control specimens to equilibrium
moisture content (EMC) at 23 + 2°C and 50 6 2 % relative
humidity or other conditions as agreed upon by the parties
involved. One to four weeks may be required to reach EMC,
depending on the beginning moisture content.
10.1.2 Test the specimens (after they reach EMC) in the
shear tool with the universal test machine crosshead moving at
10 + 0.05 mm/min (0.400 6 0.002 in./min). Store the speci-
mens in a plastic bag, or remove them one at a time from the
conditioned environment during testing. Record the strength
and estimated percentage of wood failure for each specimen.
10.2 Service Life Estimate:
10.2.1 Aging temperatures are given in Table 4. For a given
temperature/moisture condition, mount five groups (10 speci-
mens per group) on suitable racks for dry aging, place in jars
for moist aging, or string each group on stainless steel wire for
wet aging.
10.2.2 Estimate five aging intervals that will produce ap-
proximately equal strength decrements to a total strength loss
of 25 to 30 % from the initial strength for each of the five aging
temperatures. Previous aging experience may not be available,
FIG. 2 Modified Block Shear Specimen
especially for new adhesives. If this is the case, use the
approximate times given in Table 5.
NOTE 3—Twenty-five percent strength loss is a convenient level. Any
type of experiment to be performed (service life, rate compari-
amount of loss can be defined as failure as long as it is agreeable to the
son, or quality control):
parties requiring this test and it is defined in the report. Higher percentages
Service life estimation 10 panels,
of loss require longer exposure times.
127 by 305 mm
Rate comparison:
10.2.3 Place the five groups (see Note 4) in the aging
One adhesive/different exposures
exposure. At the end of the first aging interval, withdraw the
(10 panels, 127 by 305 mm)
Two adhesives/same exposure
first group of specimens, recondition to EMC, and test as
(10 panels, 63 by 305 mm)
described in 10.1.1 and 10.1.2. Based on this test, project the
(for each
...