PSI - Issue 64

2078 Sizhe Wang et al. / Procedia Structural Integrity 64 (2024) 2075–2082 Author name / Structural Integrity Procedia 00 (2019) 000–000 during activation, and the activation length was half of the Fe-SMA length (i.e., = /2). Each specimen is designated with a label, wherein letter “A” indicates activation test, the subsequent number indicates the activation length, and the final part (if exists) indicates the repetitions. 2.2. Activation of Fe-SMA The activation of Fe-SMA was conducted after the specimens had cured for more than one week. The electrical resistive heating technique was used. The Fe-SMA activation parts were heated to a target temperature of 180 ℃. Fig. 2a shows the activation setup. Four copper connecters were customized, each of which had a contact area of 50 mm×10 mm with the Fe-SMA strips, and the copper connecters were fixed by the G-clamps which were isolated from the copper connectors. The Fe-SMA strips on both sides were connected as a series circuit. A computer-controlled electric power supply provided a current with a density of 6 A/mm 2 . The Fe-SMA anchorage parts were left unheated, with no special cooling measures employed. During the activation, six thermocouples were mounted on the specimens. T1‒T2 and T4‒T5 measured the temperatures of the activation parts of Fe-SMA strips on each side, respectively, T3 measured the temperature of the anchorage part of Fe-SMA strip, whereas T6 measured the temperature of the steel plate, as shown in Fig. 2b. When the maximum measured temperature reached 180 ℃, the power supply switched off automatically. Then the specimens stayed in air cooling to the room temperature. Four strain gauges SG1‒SG4 were mounted at the middle section on the steel plate to measure the strain caused by Fe-SMA prestress. The strain gauges were located at distances of 35 mm (SG3), 45 mm (SG2), 55 mm (SG4), and 65 mm (SG1), respectively, to the specimen centreline. 4

Copper connectors

SG1 SG2

SG3 SG4

T6

Steel plate

Fe-SMA strip

G-clamps

T3

T2 T1

T5 T4

Strain gauge (SG)

Thermocouple (T)

Copper connectors

Power supply

(a)

(b)

Fig. 2. Activation of Fe-SMA using electrical resistive heating technique. (a) Activation setup. (b) Layouts of strain gauges and thermocouples during activation process. 3. Experimental results Fig. 3 shows the typical temperature histories during the activation process . In approximately 20‒60 seconds, the electricity heated the Fe-SMA activation part to the target temperature of 180 ℃. However, the temperatures of the activation part were not always uniform. For example, in Fig. 3a, discrepancies between thermocouples T1, T2, T4, and T5 were observed. With the Fe-SMA strip length increasing, the temperature fields of the activation parts seemed to be more uniform. For example, in Fig. 3b, the temperature curves of T1, T2, T4, and T5 were more consistent. During the entire activation process, the maximum temperatures of the steel plates measured across all the specimens