PSI - Issue 79

Girolamo Costanza et al. / Procedia Structural Integrity 79 (2026) 9–16

13

Displacement-controlled testing investigated three displacement levels: ± 1 . 25 mm , ± 2 . 5 mm , and ± 5 mm to evalu ate displacement-dependent superelastic activation and energy dissipation characteristics. Cyclic loading protocols included both tension-compression loops and reverse loading sequences to assess material stability and identify po tential training e ff ects. Data post-processing employed numerical integration techniques to quantify energy dissipation through hysteretic loop area calculation, while SEA calculations enabled configuration comparison independent of geometric scaling e ff ects.

2.6. Performance Metrics and Calculation Methods

Comprehensive performance evaluation required systematic quantification of key seismic device characteristics through standardized calculation methodologies. Figure 4 presents a typical force-displacement hysteretic loop ob tained experimentally from cyclic testing. This section illustrates the determination of all performance metrics from experimental data.

Fig. 4. Representative force-displacement hysteretic loop (L-shaped Ni-Ti assembly, 5mm displacement, 25°C)

Energy dissipation capacity was determined through numerical integration of hysteretic loops using the trapezoidal rule method. The energy dissipated per cycle corresponds to the area enclosed by the force-displacement hysteretic loop, calculated as: E diss = Fdx ≈ n i = 1 F i + F i + 1 2 ( x i + 1 − x i ) (1) where F represents the applied force and x the corresponding displacement. This discrete approximation enables accurate energy quantification from experimental force-displacement data pairs. Specific abssorbed energy (SEA) provided configuration-independent performance comparison by normalizing total energy dissipation to active material volume. For individual L-shaped sheet configurations, the active volume was calculated as V sheet = 2 × s × b × l , where s , b , and l represent sheet thickness, width, and length respectively. Combined sheet-spring assemblies required summation of sheet and spring volumes: V total = V sheets + V springs = 2 × s × b × l + 2 × π r 2 wire × L wire (2) where r wire and L wire denote wire radius and total wire length in the helical spring configuration. Peak force capacity was identified as the maximum absolute force magnitude throughout the loading cycle, repre senting the device’s maximum load-bearing capability. Sti ff ness characterization employed linear regression analysis of the initial elastic loading region to determine the force-displacement slope, providing quantitative assessment of structural rigidity.