PSI - Issue 64

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

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activation was conducted in the climate chamber for the convenience of later investigation of the pre-stress loss due to elevated temperature. The strain gauges were zeroed before steps 1, step 2 and step 3, but not before step 4.

3.3. Measurements One strain gauge (SG01) and seven thermocouples were employed to monitor the strain and temperature variations throughout and after the activation process. Fig. 2illustrates the placement of these sensors. The strain gauge was positioned on the glass surface, maintaining 50 mm from the edge of the glass pane. Five thermocouples (TC01-TC05) were embedded within the adhesive. Two additional thermocouples (TC06 and TC07) were installed on the surface of the top and bottom Fe-SMAs.

4. Thermocouples and strain gauge locations for the activation tests.Results and discussions 4.1. Step 1: activation at 160ºC

In step 1, L_ac1 was subjected to heating up to 160 °C followed by cooling down to room temperature. The temperature development and strain measurements obtained during this process are illustrated in Fig. 3. The temperature in the anchorage zone did not exceed 30 °C, confirming minimal impact on the mechanical properties of the adhesive in this area, thereby ensuring the shear force transfer ability of the anchorage zone. The measurement of the strain gauge lasted for 20 hours. The strain values obtained for the two tested specimens after all components cooled back to room temperature were - 71.1 μm/m and -81.2 μm/m , as shown in Fig. 3(b). These negative values indicated compression resulting from the SME of the Fe-SMA after the activation process.

Fig. 3. (a) Temperature vs. time and (b) strain vs. time during and after activation when the activation temperature was 160 °C.

4.2. Step 2: activation at 200º C To further utilize the SME of the Fe-SMA, the activation length (L_ac1) of the Fe-SMA was subjected to a second activation at 200 °C. This approach aimed to recover a higher pre-strain and potentially achieve a higher corresponding pre-stress. The temperature and strain measurements obtained during and after the activation process are depicted in Fig. 4. During the activation, the temperature of the anchorage part increased to approximately 40 °C, which remained below the glass transition temperature of SikaPower®-1277 (around 67 °C). Although the increased temperature up