PSI - Issue 78

Angelo Masi et al. / Procedia Structural Integrity 78 (2026) 686–693

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Table 1. Nominal displacement history adopted for the cyclic test.

Target

Amplitude (% dy)

Displacement d [mm]

Frequency [Hz]

No. of cycles

1 2 3 4 5 6 7 8 9

25% 50% 75%

0.9 1.8 2.7 3.6 5.4 7.2 9.0

0.139 0.069 0.046 0.034 0.023 0.017 0.014 0.012 0.010 0.008 0.006

4 4 4 4 4 4 4 4 4 4 4

100% 150% 200% 250% 300% 333% 450% 600%

10.8

12

10 11

16.2 21.6

The system is instrumented with: • Template Matching Method bases on object detection algorithms (Open CV platform) applied to videos with high frame rates (60 fps) recorded during the test. • LVDTs to measure global and local displacements: Fig. 3 shows an LVDT that measures the horizontal displacement of the steel arm used to apply the load to the SPEAD device and other four LVDTs that acquire the deformations near the hourglasses (two on each SPEAD device tested simultaneously). The force value is obtained as a result of measuring the load cell. All sensors are synchronised to enable high-resolution (50 Hz sampling) acquisition of force-displacement cycles, and to detect local damage phenomena such as yielding, pinching or buckling of steel components, as well as steel low-cycle fatigue strength phenomena.

Fig. 3. Test equipment and sensors’ layout.

Figure 4 shows the cyclic response (Fig. 4a) and the envelop curve (Fig. 4b) in terms of the total force (applied at the top of the device, see Fig. 3) as a function of the registered drift (the ratio between the upper horizontal LVDT