ASTM D7998-19

Standard Test Method for Measuring the Effect of Temperature on the Cohesive Strength Development of Adhesives using Lap Shear Bonds under Tensile Loading

SIGNIFICANCE AND USE
4.1 The test method enables strength values for wood and other materials bonded with an adhesive under a range of controlled bonding temperature, time, and pressure conditions to be evaluated. Bond formation and subsequent testing is affected in a coordinated fashion, and this enables transient strength values of sets of similar bond types to be explored with diverse parameters as independent variables. Principal among these variables is the temperature at which bonds are formed and the time that selected temperatures are maintained prior to testing. The use of controlled methods of adhesive application, the rapid attainment of stable bond formation conditions, and the rapid transition to the bond testing mode enables snapshots of bond strength to be attained as bonds progress from limited strength (or initial tack) to maximum strength. Derived data may be used to evaluate and compare the strength development characteristics of diverse types and formulations of adhesive. The method may thus be used to aid in tailoring and matching adhesives to the manufacture of diverse bonded products that involve heating.  
4.2 The method may also be used to evaluate the co-dependent effect of temperature and time on the degradation of sample bonds. Pressing temperatures up to 265°C (509°F) may be necessary for such investigations of thermal degradation. Specimens are pressed for a range of times and temperatures and very shortly thereafter tested either at elevated temperature or immediately following rapid forced air cooling. Alternatively, thermal damage of pre-formed bond samples may be evaluated by subjecting them to controlled temperature and time sequences prior to testing.  
4.3 The method may also be used to evaluate the effect of wood type and variability, or of non-wood materials, on bond strength development.  
4.4 By hermetically sealing the overlap region of sample bonds during their formation, the method may also be used to evaluate the effect of moisture and oth...
SCOPE
1.1 This test method concerns bonding and testing of wood adhesives and related adhesives using small scale tensile lap-shear samples in a manner that emphasizes transient cohesive strength as a function of bonding time and temperature.  
1.2 Use of thin adherends enables bondlines to be rapidly heated to elevated temperatures and maintained at those temperatures for a range of times at a controlled pressure before testing.  
1.3 Optional rapid forced air cooling of bonds after pressing and immediately before testing enables the effect of testing temperature on transient strength to be evaluated.  
1.4 Bond overlap distance is specified to ensure that failure occurs in the bondline rather than in unbonded portions of adherend strips, and also to minimize the effect of shear stress non-uniformity along the overlap during tensile testing.  
1.5 Standard wood or alternative non-standard materials must be of specified high quality and uniformity of structure and dimension to minimize variability of bonding and maximize stress transfer into the bonds during testing.  
1.6 The effect of wood variability and type, or of the properties of alternative non-wood materials, on bond strength development may be explored using the method.  
1.7 Optional hermetic sealing of bond overlaps during their heated pressing enables the effect of moisture on bonding to be evaluated.  
1.8 Thermal damage, either of pre-formed bonds or by prolonging bond forming times, may be evaluated as a function of time and elevated temperature using this test method.  
1.9 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.10 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, health, and environmental practices and determine the applicabil...

General Information

• Status: Published
• Publication Date: 31-May-2019
• ICS: 83.180 - Adhesives
• Technical Committee: D14 - Adhesives
• Drafting Committee: D14.30 - Wood Adhesives

Relations

• Replaces: ASTM D7998-15 - Standard Test Method for Measuring the Effect of Temperature on the Cohesive Strength Development of Adhesives using Lap Shear Bonds under Tensile Loading
• Effective Date: 01-Jun-2019
• Refers: ASTM E691-13 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-May-2013
• Refers: ASTM D907-12a - Standard Terminology of Adhesives
• Effective Date: 01-Jul-2012
• Refers: ASTM D907-12 - Standard Terminology of Adhesives
• Effective Date: 01-May-2012
• Refers: ASTM D907-11a - Standard Terminology of Adhesives
• Effective Date: 01-Dec-2011
• Refers: ASTM E691-11 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2011
• Refers: ASTM D907-11 - Standard Terminology of Adhesives
• Effective Date: 01-Jan-2011
• Refers: ASTM D907-08b - Standard Terminology of Adhesives
• Effective Date: 01-Oct-2008
• Refers: ASTM E691-08 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Oct-2008
• Refers: ASTM D907-08a - Standard Terminology of Adhesives
• Effective Date: 15-Aug-2008
• Refers: ASTM D907-08 - Standard Terminology of Adhesives
• Effective Date: 01-Mar-2008
• Refers: ASTM D907-06 - Standard Terminology of Adhesives
• Effective Date: 01-Dec-2006
• Refers: ASTM E691-05 - Standard Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
• Effective Date: 01-Nov-2005
• Refers: ASTM D907-05 - Standard Terminology of Adhesives
• Effective Date: 01-Apr-2005
• Refers: ASTM D907-05e1 - Standard Terminology of Adhesives
• Effective Date: 01-Apr-2005

Overview

ASTM D7998-19 is an international standard test method developed by ASTM International, focusing on the measurement of the effect of temperature on the cohesive strength development of adhesives using lap shear bonds under tensile loading. Primarily utilized for wood adhesives, this method is also applicable to adhesives for other bonded materials. By simulating various controlled bonding and testing conditions, the standard provides essential data on how adhesives develop strength under different thermal and environmental parameters.

Adhering to ASTM D7998-19 supports the evaluation and comparison of adhesive performance, aids in selecting suitable adhesives for manufacturing processes, and helps optimize production techniques that involve heat. This is especially relevant for industries where bond strength development during heating and cooling is critical to product integrity and performance.

Key Topics

• Bond Strength Development: Measures the transient and maximum cohesive strength of adhesive bonds at various temperatures and bonding durations.
• Controlled Test Conditions: Uses small-scale tensile lap-shear samples with precise control over temperature, time, and pressure to ensure reliable and reproducible results.
• Evaluation Variables: Allows independent variation of bonding temperature, bonding time, pressure, adherend type (e.g., different woods or non-wood materials), and moisture content.
• Moisture and Volatile Effects: Optional hermetic sealing of the overlap region permits the study of moisture and volatile compounds on bond strength.
• Thermal Degradation: Assesses bond strength loss due to prolonged exposure to elevated temperatures.
• Rapid Heating and Cooling: Thin adherends and forced air cooling enable rapid temperature transitions, simulating real-world manufacturing conditions.

Applications

ASTM D7998-19 offers significant practical value for industries and research settings, including:

• Adhesive Formulation Evaluation: Manufacturers can compare different adhesive types and formulations to determine suitability for thermally processed bonded products.
• Production Process Optimization: The method helps in tailoring pressing times and temperatures to achieve desired bond strength, improving throughput and product reliability.
• Quality Control: Provides standardized criteria for assessing batch-to-batch consistency in adhesive bonding performance.
• Material Research: Useful for investigating the influence of wood species variability or alternative adherend types on adhesive properties.
• Failure Analysis: Pinpoints thermal damage thresholds, helping resolve production or product failures related to adhesive bond degradation.
• Moisture Management: Enables targeted studies on how moisture content and volatile compounds impact adhesive curing and performance under heat.

Related Standards

Adhering to ASTM D7998-19 ensures alignment with several other ASTM standards relevant to adhesives and material testing:

• ASTM D907: Terminology of Adhesives - foundational terminology for interpreting test results and methodologies.
• ASTM E691: Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method - guidance on test precision and reproducibility.
• Other Standards for Adhesive Testing: Complementary methods for different adhesives, bond configurations, or test conditions.

Practical Value

Implementing ASTM D7998-19 in adhesive testing protocols delivers measurable improvements in product development, manufacturing quality, and research. It enhances reliability in applications where lap shear strength under variable thermal conditions is critical, such as engineered wood products, furniture manufacturing, and innovative composites. Compliance with this standard also supports market acceptance and regulatory requirements for thermally bonded products.

Key SEO keywords: ASTM D7998-19, adhesive strength test, cohesive strength development, lap shear bond, tensile loading, temperature effect on adhesives, wood adhesives, adhesive thermal degradation, moisture effects on bonding, rapid heating cooling adhesives, adhesive bond testing standard.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D7998 − 19
Standard Test Method for
Measuring the Effect of Temperature on the Cohesive
Strength Development of Adhesives using Lap Shear Bonds
under Tensile Loading
This standard is issued under the fixed designation D7998; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.10 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This test method concerns bonding and testing of wood
responsibility of the user of this standard to establish appro-
adhesives and related adhesives using small scale tensile
priate safety, health, and environmental practices and deter-
lap-shear samples in a manner that emphasizes transient
mine the applicability of regulatory limitations prior to use.
cohesive strength as a function of bonding time and tempera-
Some specific hazards statements are given in Section 10 on
ture.
Hazards.
1.2 Use of thin adherends enables bondlines to be rapidly
1.11 This international standard was developed in accor-
heated to elevated temperatures and maintained at those
dance with internationally recognized principles on standard-
temperatures for a range of times at a controlled pressure
ization established in the Decision on Principles for the
before testing.
Development of International Standards, Guides and Recom-
1.3 Optional rapid forced air cooling of bonds after pressing
mendations issued by the World Trade Organization Technical
and immediately before testing enables the effect of testing
Barriers to Trade (TBT) Committee.
temperature on transient strength to be evaluated.
2. Referenced Documents
1.4 Bond overlap distance is specified to ensure that failure
occurs in the bondline rather than in unbonded portions of
2.1 ASTM Standards:
adherend strips, and also to minimize the effect of shear stress
D907 Terminology of Adhesives
non-uniformity along the overlap during tensile testing.
E691 Practice for Conducting an Interlaboratory Study to
Determine the Precision of a Test Method
1.5 Standard wood or alternative non-standard materials
must be of specified high quality and uniformity of structure
3. Terminology
and dimension to minimize variability of bonding and maxi-
mize stress transfer into the bonds during testing.
3.1 See Terminology D907 for other terms related to adhe-
1.6 The effect of wood variability and type, or of the sives.
properties of alternative non-wood materials, on bond strength
3.2 Definitions of Terms Specific to This Standard:
development may be explored using the method.
3.2.1 adherend strip, n—one of two adherend pieces that
1.7 Optional hermetic sealing of bond overlaps during their constitute a test specimen.
heated pressing enables the effect of moisture on bonding to be
3.3 adhesive spread rate, n—the mass of adhesive applied
evaluated.
per unit surface area of the overlap region of the adherend.
1.8 Thermal damage, either of pre-formed bonds or by
3.4 contact heating, n—thetransferofheatenergytothetest
prolongingbondformingtimes,maybeevaluatedasafunction
specimen by the application of precisely temperature-
of time and elevated temperature using this test method.
controlled heads pressing on the test specimen’s surfaces with
1.9 The values stated in SI units are to be regarded as controlled force.
standard. No other units of measurement are included in this
3.5 forced air cooling, n—the rapid cooling of the overlap
standard.
region of a test specimen after bonding at elevated temperature
This test method is under the jurisdiction of ASTM Committee D14 on
Adhesives and is the direct responsibility of Subcommittee D14.30 on Wood
Adhesives. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
CurrenteditionapprovedJune1,2019.PublishedJuly2019.Originallyapproved contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
in 2015. Last previous edition approved in 2015 as D7998 – 15. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
D7998-19. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7998 − 19
by the controlled application of air jets onto both external faces
of the overlap portion of the specimen.
3.6 test specimen, n—the lap shear sample made up of an
adhesive between two pieces of adherend.
3.7 thermal damage, n—the decrease in measured bond
strengthduetoexposuretoaspecifiedelevatedtemperaturefor
a specified time.
3.8 transient bond strength, n—the strength of a partially
formed test specimen bond (sometimes referred to as “green
strength”) upon being tested.
4. Significance and Use
4.1 The test method enables strength values for wood and
other materials bonded with an adhesive under a range of
A typical test sample mounted in an apparatus for rapid bond heating and
controlled bonding temperature, time, and pressure conditions
pressing followed by bond pulling.
to be evaluated. Bond formation and subsequent testing is 3
FIG. 1 Typical Test Sample
affected in a coordinated fashion, and this enables transient
strength values of sets of similar bond types to be explored
with diverse parameters as independent variables. Principal
among these variables is the temperature at which bonds are
5. Apparatus
formed and the time that selected temperatures are maintained
5.1 Integrated Bond Forming and Testing Apparatus:
prior to testing. The use of controlled methods of adhesive
5.1.1 Sample Forming Function—A small laboratory scale
application, the rapid attainment of stable bond formation
apparatus that has two horizontally opposed temperature-
conditions, and the rapid transition to the bond testing mode
controlled pressing heads measuring approximately 25 by 25
enables snapshots of bond strength to be attained as bonds
mm (1.0 by 1.0 in.) is required. The heads must close
progress from limited strength (or initial tack) to maximum
synchronously to a controlled force and dwell time in order to
strength. Derived data may be used to evaluate and compare
form adhesively bonded specimens in a lap fashion. The
the strength development characteristics of diverse types and
specimens must be in line with the gripping mechanisms of the
formulations of adhesive. The method may thus be used to aid
apparatus (Fig. 1 and Fig. 2) and position stops must be
in tailoring and matching adhesives to the manufacture of
provided within those mechanisms to ensure accuracy of bond
diverse bonded products that involve heating.
overlap distance during sample positioning. Temperature con-
4.2 The method may also be used to evaluate the co-
trol of the pressing heads between ambient and 150°C (302°F)
dependent effect of temperature and time on the degradation of
must be maintained within 61.5°C (2.7°F). Pressing force
sample bonds. Pressing temperatures up to 265°C (509°F) may
must be controllable between 20 and 800 6 2 N (4.5 to 180 6
be necessary for such investigations of thermal degradation.
0.45 lbf), and press closure from the open position must be
Specimens are pressed for a range of times and temperatures
achievable within 2 s.
and very shortly thereafter tested either at elevated temperature
5.1.2 Bond Testing Function—For measuring transient bond
or immediately following rapid forced air cooling.
strengths, the apparatus requires an integrated mechanical
Alternatively, thermal damage of pre-formed bond samples
loading function which acts in an axis perpendicular to that of
may be evaluated by subjecting them to controlled temperature
the sample forming function. Automated gripping of the end
and time sequences prior to testing.
portions of test specimens is necessary to avoid any disruption
of partially formed bonds prior to their being pulled. The
4.3 The method may also be used to evaluate the effect of
apparatus must be capable of applying tensile testing force at a
wood type and variability, or of non-wood materials, on bond
controlled rate of 500 N/s 6 25 N/s (112 6 5.6 lbf/s) up to at
strength development.
least 1 kN (224 lbf), and load must be digitally sampled at a
4.4 By hermetically sealing the overlap region of sample
frequencyofnotlessthan2kHzduringsamplepullinginorder
bonds during their formation, the method may also be used to
to capture the peak load at bond failure with an accuracy of
evaluate the effect of moisture and other resident volatile fluids
6 2 N (0.45 lbf). The apparatus must be capable of affecting
on bond strength development.
the transition from press opening to the onset of pulling within
4.5 The method may also be used to evaluate the effect that 2 s. Alternatively, if forced air cooling is employed after press
the temperature at which variously formed bonds are tested has opening according toAlternative Test Method I and 5.1.3, then
on their strength. Controlled rapid forced air cooling immedi- the onset of pulling must be possible within2softhe cessation
ately after bond formation but before testing is necessary for of bond cooling.
such investigations. This approach may be employed to ex-
plore the thermoplastic characteristic of thermosetting adhe-
sives and also the strength of hot melt adhesives as a function
Manufactured and available from Adhesive Evaluation Systems, Inc., 155 SW
of pressing and testing temperatures. Madison Ave, Corvallis, OR 97333, www.adhesiveevaluationsystems.com.
D7998 − 19
FIG. 2 Schematic of the Bonding and Testing Concept
5.1.3 Rapid Bond Cooling Function—Bonds may be tested (0.787 6 0.02 in.) across the grain. The specified precision in
after rapid cooling to ambient temperature by employing length is required to ensure accuracy of overlap distance when
Alternative Method I, 9.1. A small retractable forced air the two adherend strips are mounted in the bond forming and
attachment is required to affect rapid and controlled tempera- testing apparatus.
ture reduction of test bonds when the pressing heads are
7. Adhesive Type and Application
retracted at the end of the bond forming stage and immediately
7.1 Adhesive Type—Awide range of adhesive types may be
prior to the bond pulling stage. The transition between press
opening and the activation of cooling must be achievable evaluated using this test method as long as they may be applied
in an accurate and uniform fashion onto the overlap portion of
within 2 s. The cooling function must be capable of reducing
the bondline temperature so as not to exceed 31°C (88°F) adherend strips. The method is well suited to the evaluation of
the effect of temperature on the strength development of
within 5 s. A possible cooling device is given in Fig. 3.
thermosetting adhesives. It may also be employed with hot
6. Adherend Type and Preparation
melt adhesives in accordance withAlternative Method III, 9.3.
Adhesive type and method of preparation must be reported.
6.1 Adherend Type—Unless otherwise noted in the report,
uniform, planar and defect-free hard maple (Acer saccharum
7.2 AdhesiveApplicationandSpreadRate—Awiderangeof
spp.) or European beech (Fagus sylvatica spp.) of 0.6 to 0.8
adhesive spread rates may be employed, depending upon the
2 2
mm (0.024 to 0.031 in.) thickness is to be used. The selected
adhesive type.Aspread rate of 50 6 5 g/m (6.14 lb/1000 ft )
thickness must be maintained within 6 0.04 mm (0.0016 in.)
is standard. A standard adhesive application method is not
and the measured thickness must be reported. The surfaces to
specified, but methods could include shielded spraying, contact
beadheredmustbeknife-cutandnotsanded.Otherspeciesand
or transfer printing, spatula, metered droplet deposition and
non-wood materials may be employed, and must be reported
dispersion methods, among others. Care should be taken to
fully. In such cases, thickness must be minimized to ensure
maximize uniformity of adhesive distribution over the bonding
rapid heat transfer into bondlines to achieve target tempera-
area. The application method employed and spread rate accu-
tures up to 150 6 2°C (302 6 3.6°F) within 15 s, while having
racy achieved must be reported in accordance with 7.3.
sufficient tensile strength to ensure failure in the bondline
7.3 Adhesive Spread Rate Measurement and Reporting—
rather than in the unbonded portions of adherend strips.
Weight gain of adherend strips due to adhesive application
6.2 Adherend Preparation—Wood or related material is to
using the reported method should be reported. Five randomly
be loosely stacked and equilibrated at 21 6 2°C (70 6 3.6°F)
selected strips are to be weighed before and after adhesive
and 50 6 5 % relative humidity for at least 12 h before
application over a measured area. Variability in the delay
adherend strips are cut to size. Photo-degradation due to
betweenadhesiveapplicationandweighingmustbeminimized
exposure to sunlight and UV light must be minimized. The
in order to minimize the effect of evaporation on the measure-
strips are to be cut from portions of wood veneer having clear
ment. In any case, this delay must not exceed 10 s. Mean and
grain to provide strips of 120 6 0.2 mm (4.724 6 0.008 in.)
standard deviation values of spread rate must be reported in the
2 2
length parallel to the grain 64° and width of 20 mm 6 0.5 mm
units of g/m (lb/1000 ft ).
8. Bond Formation and Testing
8.1 Bond Formation—Adherend pairs are to be mounted in
the bond forming and testing apparatus following the applica-
tion of adhesive to the endmost portion of one of the adherend
strips. A non-standard alternative is to apply adhesive to both
adherend strips.Abond overlap of 5 6 0.4 mm (0.197 6 0.016
in.) is standard (see 8.1.1). The delay between adhesive
application and closure of the heated pressing heads onto the
overlap should be 7 6 3 s in order to minimize the effects of
adhesive pre-cure, penetration and evaporation. Deviations
An attachment for rapid air-jet cooling which may be raised, activated and
from these limits must be reported, including when open
lowered automatically.
FIG. 3 Attachment for Rapid Air-jet Cooling assembly time is an independent variable. A pressing pressure
D7998 − 19
of 2 6 0.2 MPa (290 6 29 psi) is standard. This pressure temperatures. For testing efficiency, use of a minimum tem-
requires a force of 200 6 20 N (50 6 5 lbf) on the standard perature wh
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7998 − 15 D7998 − 19
Standard Test Method for
Measuring the Effect of Temperature on the Cohesive
Strength Development of Adhesives using Lap Shear Bonds
under Tensile Loading
This standard is issued under the fixed designation D7998; 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 (´) indicates an editorial change since the last revision or reapproval.
1. Scope
1.1 This test method concerns bonding and testing of wood adhesives and related adhesives using small scale tensile lap-shear
samples in a manner that emphasizes transient cohesive strength as a function of bonding time and temperature.
1.2 Use of thin adherends enables bondlines to be rapidly heated to elevated temperatures and maintained at those temperatures
for a range of times at a controlled pressure before testing.
1.3 Optional rapid forced air cooling of bonds after pressing and immediately before testing enables the effect of testing
temperature on transient strength to be evaluated.
1.4 Bond overlap distance is specified to ensure that failure occurs in the bondline rather than in unbonded portions of adherend
strips, and also to minimize the effect of shear stress non-uniformity along the overlap during tensile testing.
1.5 Standard wood or alternative non-standard materials must be of specified high quality and uniformity of structure and
dimension to minimize variability of bonding and maximize stress transfer into the bonds during testing.
1.6 The effect of wood variability and type, or of the properties of alternative non-wood materials, on bond strength
development may be explored using the method.
1.7 Optional hermetic sealing of bond overlaps during their heated pressing enables the effect of moisture on bonding to be
evaluated.
1.8 Thermal damage, either of pre-formed bonds or by prolonging bond forming times, may be evaluated as a function of time
and elevated temperature using this test method.
1.9 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.10 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. Some specific hazards statements are given in Section 1010 on Hazards.
1.11 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D907 Terminology of Adhesives
E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method
3. Terminology
3.1 See Terminology D907 for other terms related to adhesives.
3.2 Definitions of Terms Specific to This Standard:
This test method is under the jurisdiction of ASTM Committee D14 on Adhesives and is the direct responsibility of Subcommittee D14.30 on Wood Adhesives.
Current edition approved Sept. 15, 2015June 1, 2019. Published November 2015July 2019. Originally approved in 2015. Last previous edition approved in 2015 as
D7998 – 15. DOI: 10.1520/D7998-15.10.1520/D7998-19.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7998 − 19
3.2.1 adherend strip, n—one of two adherend pieces that constitute a test specimen.
3.3 adhesive spread rate, n—the mass of adhesive applied per unit surface area of the overlap region of the adherend.
3.4 contact heating, n—the transfer of heat energy to the test specimen by the application of precisely temperature-controlled
heads pressing on the test specimen’s surfaces with controlled force.
3.5 forced air cooling, n—the rapid cooling of the overlap region of a test specimen after bonding at elevated temperature by
the controlled application of air jets onto both external faces of the overlap portion of the specimen.
3.6 test specimen, n—the lap shear sample made up of an adhesive between two pieces of adherend.
3.7 thermal damage, n—the decrease in measured bond strength due to exposure to a specified elevated temperature for a
specified time.
3.8 transient bond strength, n—the strength of a partially formed test specimen bond (sometimes referred to as “green strength”)
upon being tested.
4. Significance and Use
4.1 The test method enables strength values for wood and other materials bonded with an adhesive under a range of controlled
bonding temperature, time, and pressure conditions to be evaluated. Bond formation and subsequent testing is affected in a
coordinated fashion, and this enables transient strength values of sets of similar bond types to be explored with diverse parameters
as independent variables. Principal among these variables is the temperature at which bonds are formed and the time that selected
temperatures are maintained prior to testing. The use of controlled methods of adhesive application, the rapid attainment of stable
bond formation conditions, and the rapid transition to the bond testing mode enables snapshots of bond strength to be attained as
bonds progress from limited strength (or initial tack) to maximum strength. Derived data may be used to evaluate and compare
the strength development characteristics of diverse types and formulations of adhesive. The method may thus be used to aid in
tailoring and matching adhesives to the manufacture of diverse bonded products that involve heating.
4.2 The method may also be used to evaluate the co-dependent effect of temperature and time on the degradation of sample
bonds. Pressing temperatures up to 265°C (509°F) may be necessary for such investigations of thermal degradation. Specimens
are pressed for a range of times and temperatures and very shortly thereafter tested either at elevated temperature or immediately
following rapid forced air cooling. Alternatively, thermal damage of pre-formed bond samples may be evaluated by subjecting
them to controlled temperature and time sequences prior to testing.
4.3 The method may also be used to evaluate the effect of wood type and variability, or of non-wood materials, on bond strength
development.
4.4 By hermetically sealing the overlap region of sample bonds during their formation, the method may also be used to evaluate
the effect of moisture and other resident volatile fluids on bond strength development.
4.5 The method may also be used to evaluate the effect that the temperature at which variously formed bonds are tested has on
their strength. Controlled rapid forced air cooling immediately after bond formation but before testing is necessary for such
investigations. This approach may be employed to explore the thermoplastic characteristic of thermosetting adhesives and also the
strength of hot melt adhesives as a function of pressing and testing temperatures.
5. Apparatus
5.1 Integrated Bond Forming and Testing Apparatus:
A typical test sample mounted in an apparatus for rapid bond heating and pressing followed by bond pulling.
FIG. 1 Typical Test Sample
D7998 − 19
FIG. 2 Schematic of the Bonding and Testing Concept
5.1.1 Sample Forming Function—A small laboratory scale apparatus that has two horizontally opposed temperature-controlled
pressing heads measuring approximately 25 by 25 mm (1.0 by 1.0 in.) is required. The heads must close synchronously to a
controlled force and dwell time in order to form adhesively bonded specimens in a lap fashion. The specimens must be in line with
the gripping mechanisms of the apparatus (Fig. 1 and Fig. 2) and position stops must be provided within those mechanisms to
ensure accuracy of bond overlap distance during sample positioning. Temperature control of the pressing heads between ambient
and 150°C (302°F) must be maintained within 61.5°C (2.7°F). Pressing force must be controllable between 20 and 800 6 2 N
(4.5 to 180 6 0.45lbf), 0.45 lbf), and press closure from the open position must be achievable within 2 s.
5.1.2 Bond Testing Function—For measuring transient bond strengths, the apparatus requires an integrated mechanical loading
function which acts in an axis perpendicular to that of the sample forming function. Automated gripping of the end portions of test
specimens is necessary to avoid any disruption of partially formed bonds prior to their being pulled. The apparatus must be capable
of applying tensile testing force at a controlled rate of 500N/s 500 N/s 6 25 N/s (112 6 5.6lbf/s) 5.6 lbf/s) up to at least 1kN
(224lbf), 1 kN (224 lbf), and load must be digitally sampled at a frequency of not less than 2 kHz during sample pulling in order
to capture the peak load at bond failure with an accuracy of 6 2N (0.45lbf). 6 2 N (0.45 lbf). The apparatus must be capable
of affecting the transition from press opening to the onset of pulling within 2 s. Alternatively, if forced air cooling is employed
after press opening according to Alternative Test Method I and 5.1.3, then the onset of pulling must be possible within 2 s of the
cessation of bond cooling.
5.1.3 Rapid Bond Cooling Function—Bonds may be tested after rapid cooling to ambient temperature by employing Alternative
Method I, 9.1. A small retractable forced air attachment is required to affect rapid and controlled temperature reduction of test
bonds when the pressing heads are retracted at the end of the bond forming stage and immediately prior to the bond pulling stage.
The transition between press opening and the activation of cooling must be achievable within 2 s. The cooling function must be
capable of reducing the bondline temperature so as not to exceed 31°C (88°F) within 5 s. A possible cooling device is given in
Fig. 3.
6. Adherend Type and Preparation
6.1 Adherend Type—Unless otherwise noted in the report, uniform, planar and defect-free hard maple (Acer saccharum spp.)
or European beech (Fagus sylvatica spp.) of 0.6 to 0.8 mm (0.024 to 0.031 in.) thickness is to be used. The selected thickness must
be maintained within 6 0.04 mm (0.0016 in.) and the measured thickness must be reported. The surfaces to be adhered must be
knife-cut and not sanded. Other species and non-wood materials may be employed, and must be reported fully. In such cases,
thickness must be minimized to ensure rapid heat transfer into bondlines to achieve target temperatures up to 150 6 2°C (302 6
3.6°F) within 15 s, while having sufficient tensile strength to ensure failure in the bondline rather than in the unbonded portions
of adherend strips.
An attachment for rapid air-jet cooling which may be raised, activated and lowered automatically.
FIG. 3 Attachment for Rapid Air-jet Cooling
Manufactured and available from Adhesive Evaluation Systems, Inc., 155 SW Madison Ave, Corvallis, OR 97333, www.adhesiveevaluationsystems.com.
D7998 − 19
6.2 Adherend Preparation—Wood or related material is to be loosely stacked and equilibrated at 21 6 2°C (70 6 3.6°F) and
50 6 5 % relative humidity for at least 12 h before adherend strips are cut to size. Photo-degradation due to exposure to sunlight
and UV light must be minimized. The strips are to be cut from portions of wood veneer having clear grain to provide strips of 120
6 0.2 mm (4.724 6 0.008 in.) length parallel to the grain 64° and width of 20 mm 6 0.5 mm (0.787 6 0.02 in.) across the grain.
The specified precision in length is required to ensure accuracy of overlap distance when the two adherend strips are mounted in
the bond forming and testing apparatus.
7. Adhesive Type and Application
7.1 Adhesive Type—A wide range of adhesive types may be evaluated using this test method as long as they may be applied
in an accurate and uniform fashion onto the overlap portion of adherend strips. The method is well suited to the evaluation of the
effect of temperature on the strength development of thermosetting adhesives. It may also be employed with hot melt adhesives
in accordance with Alternative Method III, 9.3. Adhesive type and method of preparation must be reported.
7.2 Adhesive Application and Spread Rate—A wide range of adhesive spread rates may be employed, depending upon the
2 2
adhesive type. A spread rate of 50 6 5 g/m (6.14 lb/1000 ft ) is standard. A standard adhesive application method is not specified,
but methods could include shielded spraying, contact or transfer printing, spatula, metered droplet deposition and dispersion
methods, among others. Care should be taken to maximize uniformity of adhesive distribution over the bonding area. The
application method employed and spread rate accuracy achieved must be reported in accordance with 7.3.
7.3 Adhesive Spread Rate Measurement and Reporting—Weight gain of adherend strips due to adhesive application using the
reported method should be reported. Five randomly selected strips are to be weighed before and after adhesive application over
a measured area. Variability in the delay between adhesive application and weighing must be minimized in order to minimize the
effect of evaporation on the measurement. In any case, this delay must not exceed 10 s. Mean and standard deviation values of
2 2
spread rate must be reported in the units of g/m (lb/1000ft(lb/1000 ft ).
8. Bond Formation and Testing
8.1 Bond Formation—Adherend pairs are to be mounted in the bond forming and testing apparatus following the application
of adhesive to the endmost portion of one of the adherend strips. A non-standard alternative is to apply adhesive to both adherend
strips. A bond overlap of 5 6 0.4 mm (0.197 6 0.016 in.) is standard (see 8.1.1). The delay between adhesive application and
closure of the heated pressing heads onto the overlap should be 7 6 3 s in order to minimize the effects of adhesive pre-cure,
penetration and evaporation. Deviations from these limits must be reported, including when open assembly time is an independent
variable. A pressing pressure of 2 6 0.2MPa 0.2 MPa (290 6 29 psi) is standard. This pressure requires a force of 200 6 20N
20 N (50 6 5lbf) 5 lbf) on the standard bond with a 20 by 5 mm (.787 by .196 in.) overlap. Deviations from this pressure may
be necessary, particularly to reduce compr
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