# A Smart Rehabilitation Glove Based on Shape-Memory Alloys for Stroke Recovery
## 4 Results and Discussion  
### SMA Properties  
The smart rehabilitation glove uses SMA wires as the actuation part, and the performance of the SMA wires is shown in Figure 3. Figure 3a shows the stress-strain curve of the SMA wires under tensile testing until fracture. The curve exhibits the characteristic mechanical behavior of SMAs, including an initial elastic deformation stage, followed by a stress plateau region associated with stress-induced martensitic transformation, and a subsequent stress-hardening stage dominated by plastic deformation. The material reaches its maximum load-bearing capacity at approximately 1600 MPa, before undergoing fracture at a strain of around 16%. These results indicate that the SMA undergoes significant stress-induced phase transformation during tension, and ultimately fails at a high-stress level, which guarantees that the SMA wires can provide a stable and sufficient driving force for the rehabilitation glove. In Figure 3b-d, the stress-strain curves of SMA wires under different applied strains (3%, 5%, and 7%) exhibit characteristic pseudoelastic behavior. When the applied stress reaches the critical phase-transformation stress, a stress plateau appears due to the stress-induced B2\(\rightarrow\)B19\({}^{\prime}\) martensitic transformation. The critical stress for phase transformation (\(\sigma_{\rm c}\)) is approximately 350 MPa. As the applied strain increases, the hysteresis loop becomes more pronounced, indicating enhanced energy dissipation. Upon unloading, most of the strain is recovered, with a residual strain that can be fully restored through heating. Figure 3: (**a**) The stress–strain curve of SMA wires under tensile testing until fracture. (**b–d**) The stress–strain curves of SMA wires under different strains of 3%, 5%, and 7%. Figure 4a illustrates the phase transformation of the SMA induced by temperature. During the cooling process, a single exothermic peak is observed, corresponding to the phase transformation from B2 to B19\({}^{\prime}\) martensite. Conversely, the heating process exhibits a prominent endothermic peak, indicating the reverse transformation from the martensitic phase to the austenitic phase. The phase-transformation temperatures were determined using the double-tangent method, yielding A\({}_{\rm s}\) = 35.1 \({}^{\circ}\)C, A\({}_{\rm f}\) = 46.5 \({}^{\circ}\)C, M\({}_{\rm s}\) = 24.1 \({}^{\circ}\)C, and M\({}_{\rm f}\) = 13.4 \({}^{\circ}\)C. Here, A\({}_{\rm s}\) and A\({}_{\rm f}\) denote the start and finish temperatures of the austenitic transformation, whereas M\({}_{\rm s}\) and M\({}_{\rm f}\) correspond to the start and finish temperatures of the martensitic transformation. Figure 4b shows the stress-strain curves of the SMA wires at a fixed strain of 5% under different temperatures (\(-\)15 \({}^{\circ}\)C, 15 \({}^{\circ}\)C, 45 \({}^{\circ}\)C, and 75 \({}^{\circ}\)C). As the temperature increases, the plateau stress rises, indicating that higher critical stress is required for phase transformation. These results highlight the temperature dependence of the pseudoelastic behavior of SMAs. The temperature-strain curves of the SMA wires under different stresses are shown in Figure 4c. As the stress increases, the phase-transformation temperatures of the SMA wires increase accordingly. The phase-transformation temperatures at 300 MPa were determined by the double-tangent method to be A\({}_{\rm s}\) = 62.1 \({}^{\circ}\)C, A\({}_{\rm f}\) = 72.3 \({}^{\circ}\)C, M\({}_{\rm s}\) = 55.6 \({}^{\circ}\)C, and M\({}_{\rm f}\) = 43.2 \({}^{\circ}\)C. As shown in Figure 4c, the recovery strain is about 6%. SMA wire actuation tests were conducted at stresses of 150 MPa, 200 MPa, and 300 MPa (Figure 4d), with incrementally increasing current values from 0 to 60 mA and back to 0 mA. The experiments reveal that under 150 MPa stress, applying approximately 20 mA allows the temperature of the SMA wire to reach the phase-transformation value, initiating contraction. As the current increases, the amount of SMA strain increases.