ASTM C961-15(2024)

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: C961 − 15 (Reapproved 2024)
Standard Test Method for
Lap Shear Strength of Sealants
This standard is issued under the fixed designation C961; 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 4. Summary of Test Method
4.1 The sealant is placed between two glass substrates. The
1.1 This test method covers a laboratory procedure for
sample is placed in a tensile tester and pulled at a constant rate
determining the lap shear strength of sealants. It also provides
to failure. The maximum shear force and mode of failure is
information on the adhesive bond of the sealants to the tested
noted. Maximum shear stress is calculated and reported.
substrates.
1.2 The values stated in SI units are to be regarded as the
5. Significance and Use
standard. The values given in parentheses are for information
5.1 Sealants are generally subjected to longitudinal and
only.
lateral shear stresses in end use applications. This test method
1.3 This standard does not purport to address all of the
measures the cohesive strength of sealants when subjected to
safety concerns, if any, associated with its use. It is the
shear stresses, and also provides information regarding the
responsibility of the user of this standard to establish appro-
adhesive bond to the substrates being tested.
priate safety, health, and environmental practices and deter-
mine the applicability of regulatory limitations prior to use.
6. Apparatus
1.4 The subcommittee with jurisdiction of this standard is
6.1 Sealant Applicator or Oven, capable of maintaining the
not aware of any similar or equivalent ISO standard.
sealant within 62.8 °C (65 °F) of the specified temperature.
1.5 This international standard was developed in accor-
6.2 Substrates, of annealed glass that are 25.4 mm wide by
dance with internationally recognized principles on standard-
76.2 mm long and 6.35 mm thick (1 by 3 by 0.25 in.). Other
ization established in the Decision on Principles for the
substrates may be used when specified (Fig. 1).
Development of International Standards, Guides and Recom-
6.3 Template, to provide 3.18 mm ( ⁄8-in.) sealant thickness
mendations issued by the World Trade Organization Technical
(Fig. 2).
Barriers to Trade (TBT) Committee.
6.4 Hot Knife or Spatula.
2. Referenced Documents
6.5 Tension Testing Machine, capable of pulling a specimen
at a rate of 12.7 mm (0.5 in.)/min.
2.1 ASTM Standards:
C717 Terminology of Building Seals and Sealants
7. Sampling
3. Terminology
7.1 Sealant shall be free of external surface contaminants
such as talc, oil, dust, and moisture. Handling of the sealant
3.1 Definitions—Refer to Terminology C717 for definitions
surfaces in contact with the substrate shall be minimized.
of the following terms used in this test method: adhesive
7.2 A 1.0 kg (2.2-lb) representative sample shall be taken
failure, cohesive failure, sealant, standard conditions, and
from bulk stock for testing.
substrate.
8. Test Specimens
1 8.1 Prepare six test specimens from the bulk sample by
This test method is under the jurisdiction of ASTM Committee C24 on Building
Seals and Sealants and is the direct responsibility of Subcommittee C24.30 on using the applicator or the oven method.
Adhesion.
8.1.1 Applicator Method:
Current edition approved Jan. 1, 2024. Published January 2024. Originally
8.1.1.1 Clean the substrate surface with soap and water
approved in 1981. Last previous edition approved in 2015 as C961–15. DOI:
followed by a water rinse and solvent wipe with methyl ethyl
10.1520/C0961-15R24.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
ketone (MEK).
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 NOTE 1—At the request of the sealant manufacturer, an alternative
the ASTM website. cleaning procedure may be used.
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C961 − 15 (2024)
9. Conditioning
9.1 Condition all test specimens at standard conditions for at
least 24 h prior to testing.
9.2 Additional conditioning may be done as specified by
mutual agreement between the purchaser and sealant manufac-
turer.
10. Procedure
10.1 Attach each specimen to the jaws of the tension testing
machine and separate at a crosshead speed of 12.7 mm (0.5
in.)/min to failure (separation) (Fig. 4). Align the testing
machine jaws to prevent cocking of test assembly.
10.2 Visually inspect and record the mode of bond failure
(cohesive or adhesive) and the approximate percentage of each.
10.3 Observe and record the maximum shear force in
newtons (or pounds-force).
11. Calculation
11.1 Calculate the maximum shear stress, S, as follows:
S 5 F/A (1)
Length
Dimension mm in.
where:
G, J 76.2 ± 0.25 (3.00± 0.01)
H, K, M 25.4 ± 0.25 (1.00 ± 0.01)
S = maximum shear stress, Pa (or lbf/in. ),
I, L 6.35 ± 0.10 (0.250± 0.004)
F = maximum shear force, N (or lbf), and
A = contact area of the specimen with one substrate, m (or
FIG. 1 Assembly of Test Sealant on Substrates
in. ).
11.2 Average the results of the six specimens tested.
8.1.1.2 Using an appropriate die or nozzle, apply a 25.4 mm
12. Report
by 25.4 mm (1 by 1-in.) layer of sealant onto one end of the
substrate surface at a thickness that when compressed will
12.1 Report t
...