ASTM C908
Tape Sealant Yield Strength Test Fixture
ASTM C908 Tape Sealant Fixture – Universal Grip Data Sheet (PDF)
ASTM C908 is a laboratory method for determining the yield strength of preformed tape sealants such as butyl and polyisobutylene glazing tapes. Sealant manufacturers, glazing suppliers and building product labs use it for specification and quality control. Universal Grip supplies a C908 test fixture that holds the substrate plates in alignment on a universal testing machine.
What ASTM C908 Measures
Preformed tape sealants are tacky, deformable solids that work under compression between two surfaces. ASTM C908 loads a tape specimen assembled between rigid substrates at a controlled rate and identifies the yield value from the load-deformation curve. The result reflects the tape's resistance to flow, along with its cohesive and adhesive bonding behavior and the stiffness of the compound. It is a comparative index for specification and QC rather than a simulation of in-service performance.
How the ASTM C908 Test Works
-
Assemble the tape specimen between the rigid substrate plates as the standard describes.
-
Condition the assembled specimens before testing.
-
Mount the plates in the fixture so they stay aligned with the load axis.
-
Load the specimen at the specified controlled rate.
-
Determine the yield value from the load-deformation record and report it with the failure appearance.
Specimens and Setup
-
Cut tape to the required length without stretching or distorting its cross-section.
-
Keep substrate surfaces clean and dry so the bond is consistent between specimens.
-
Apply the tape and assemble plates the same way every time; assembly pressure affects results.
-
Record tape width, thickness and substrate material for each test series.
-
Refer to the current edition of ASTM C908 for exact specimen dimensions, conditioning and rate.
Universal Grip ASTM C908 Fixture
-
1 kN standard capacity, a low-capacity design sized for soft tape sealant forces; higher capacities on request
-
Rigid substrate plates sized to the specimen to hold tape geometry
-
Aligned holders keep loading consistent across the bond
-
Steel and aluminum construction with corrosion-resistant finish
-
Quick specimen changeover for test series
-
Clevis pin or threaded adapter to suit your electromechanical test frame
Applications
-
Preformed tape sealant quality control
-
Glazing tape specification
-
Butyl and polyisobutylene tape development
-
Incoming material inspection
Related Standards and Products
Send us your tape width and thickness, substrate material and frame connection, and we will quote a C908 fixture. Request a quote
ASTM C908 FAQ
What does yield strength mean for a tape sealant?
It is the load level at which the tape stops resisting and begins to flow, read from the load-deformation curve. Because tape sealants are viscoelastic, the value depends strongly on rate and temperature, so always test at the conditions the standard specifies.
Is ASTM C908 used for cured glazing gaskets?
No. C908 is written for preformed tape sealants, the tacky, uncured tapes used in glazing and construction joints. Cured elastomeric gaskets and sealants are covered by other ASTM C24 methods, so check which standard your specification calls out.
What substrate plates are used?
The fixture uses rigid substrate plates sized to the specimen. Specify the substrate material your specification requires when ordering, since adhesion to aluminum, glass or other surfaces can change the result.
Why is the fixture rated only 1 kN?
Tape sealants yield at low loads, and a low-capacity fixture and load cell give better resolution of the yield point. Higher capacities are available if you also test stiffer materials on the same setup.
Will it fit my test machine?
Yes. The fixture is supplied with a clevis pin or threaded adapter to match your electromechanical universal testing machine. Include your frame make and connection type when requesting a quote.