PSI - Issue 64

Zhikang Deng et al. / Procedia Structural Integrity 64 (2024) 400–408 Zhikang Deng / Structural Integrity Procedia 00 (2019) 000 – 000

407

8

for in the design stage. One solution would be to use mechanical anchoring of the Fe-SMA tendons in metal shoes at the end of the specimens instead of the adhesive anchorage. Hereby, a temporary softening of the adhesive due to elevated temperatures would not lead to non-recoverable pre-stress loss. Table 3 Corrected measured strain , total mechanical strain and coresponding stress values for the two specimens Properties Step 1 Step 2 Step 3 Step 4

[μm/m] [MPa] [μm/m] [MPa]

AC01 AC02 AC01 AC02 AC01 AC02 AC01 AC02

-71.1 -81.2

-33.6 -30.1

132.9 132.8

327.2 276.8

-5.0 -5.7

-2.4 -2.1

9.3 9.3

22.9 19.3

-71.1 -81.2

-104.7 -111.3

28.2 21.5

222.5 165.5

-5.0 -5.7

-7.3 -7.8

2.0 1.5

15.6 11.6

5. Conclusions This contribution discussed the effect of activation temperature on the temperature development in the adhesive and on the pre-stress generation in the glass substrate when Fe-SMA strips adhesively bonded to glass panels were activated at 160 ºC and 200 ºC. Furthermore, the effect of service temperatures of 50 ºC and 80 ºC on the pre-stress loss in the glass substrate was also investigated. The following conclusions can be drawn: (1) Activation test at 160 °C: • An average compressive strain of -76.2 μm/m was obtained with an activation temperature of 160 °C. The generated average pre-stress was -5.4 MPa. • The temperature in the anchorage zone did not exceed 30 °C, confirming the integrity of the anchorage zone at this activation temperature. (2) Activation test at 200 °C: • The compressive strain was further increased by an average of - 31.9 μm/m when the activation temperature was raised to 200 °C. The pre-stress can be further increased by an average of -2.3 MPa. • The maximum temperature in the anchorage zone was approximately 40 °C, which remained below the glass transition temperature of SikaPower®-1277. • No damage of glass or adhesive failure was observed during the activation process, indicating the feasibility of activation at 200 °C using electrical resistive heating. (3) Pre-stress loss due to elevated temperatures: • Elevated service temperatures (50 °C and 80 °C) led to complete pre-stress loss in the bonded joints. The research findings indicated promising prospects for pre-stressing glass elements using adhesively bonded Fe-SMA strips. This investigation, in which the activation process was deemed critical, demonstrated the feasibility of activating Fe-SMA strips, adhesively bonded on glass panels, at temperatures of 160 °C and 200 °C. Moreover, the study established the pre-stress loss due to elevated service temperatures, hence measures should be taken to prevent high-temperature increase due to direct sun exposure, etc. Otherwise, the pre-stressing effect would be fully lost. Further investigations should prioritize exploring the effects of multiple temperature cycles, humidity and UV exposures on the glass-to-Fe-SMA bonded joints. Understanding their impact is crucial for assessing the long-term reliability of such strengthening concepts.