Cantilever Pull-Off Test and Static Design Load

Cantilever pull-off tests were conducted at ambient (23 ± 2°C) and at elevated (82 ± 2°C) temperatures in the laboratory as well as under exposure to outdoor climate using dead loads attached to cantilever beams with the displacement force acting on metal buttons of two different diameters (20 and 50 mm) attached to float glass plates with the TSSA film adhesive (see Fig. 12 for a sche­matic of the test equipment configuration).

Test specimens were prepared by bonding stainless steel buttons of differ­ent diameters with the TSSA (і mm film thickness prior to compression) to standard (uncoated) float glass coupons in a typical autoclave process used for the production of laminated glass at BGT Bischoff Glastechnik Bretten (Ger­many). The following procedure was used for the manufacture of the point­fixing specimens:

1. Clean glass and steel surface using dow corning r40 cleaner.

2. Apply Dow Corning® 92-023 primer on both glass and steel surfaces.

3. Remove polyester film cover on one side of the structural silicone film adhesive and place the steel button on the film adhesive.

4. Cut the excess of film adhesive around the button.

5. Remove second polyester cover from the adhesive and place button with the film adhesive face on glass.

6. Using manual load equipment, place pressure of approximately 0.7 MPa on the button for a short period of time (10 s).

7. Place glass vertically with attached buttons in standard autoclave pro­cess for laminated glass, run at 13 bar and 140° C for 4 h.

8. Cut glass by water jet to generate individual test specimens.

The above process conditions were chosen primarily based on their suitabil­ity to fit into a standard glass lamination process.

In the laboratory, cantilever pull-off tests were conducted at ambient cli­mate (23 ± 2°C, 50 ± 5% relative humidity) and at elevated temperature climate (82 ± 2°C, relative humidity not controlled); in the latter case by placing the whole test apparatus into a forced-convection oven. Test specimens with 50 mm diameter buttons were exposed to two dead loads by placing weights of 55 N for 56 days and 81.3 N for 59 days, respectively, at the free end of a cantilever of 320 mm length. It is estimated that these loads correspond to a maximum stress of 1.17 and 1.68 MPa, respectively, in the structural silicone film adhesive (see calculation method provided in the Appendix). No failure occurred during the test and only reversible, elastic elongation of the film adhesive was observed with a displacement of about 2 mm registered on the ruler scale (having 1 mm graduation which allows readings within 0.5 mm). No differences were observed between tests run at ambient and elevated temperatures.

Test specimens with 20 mm diameter buttons were exposed to two dead loads by placing weights of 3.5 N for 56 days and 5.1 N for 59 days, respectively, at the free end of a cantilever of 222 mm length. It is estimated that these loads correspond to a maximum stress of 0.65 and 1.02 MPa, respectively, in the structural silicone film adhesive. No failure occurred during the test and only re­versible, elastic elongation of the film adhesive was observed with a displace­ment of about 1 mm registered on the ruler scale (having 1 mm graduation which allows readings within 0.5 mm). No differences were observed between tests run at ambient and elevated temperatures.

Only test specimens with 50 mm diameter buttons were exposed simultane­ously to outdoor weathering and to a dead load by placing a weight of 80 N at the end of a cantilever of 370 mm length. The test apparatus was installed in southern Germany facing south at an inclination angle of 24° (see Fig. 13). It is estimated that the force of 80 N corresponds to a maximum stress of 1.87 MPa in the structural silicone film adhesive.

The outdoor exposure test was started on 3 Jan. 2011 and no failure has been observed until now (150 days of exposure). Furthermore, no creep has been observed over this period of time beyond the initial elastic response of the specimen (resulting in a displacement of about 1 mm on the gauge).