# Recovery Behavior of Fe-Based Shape Memory Alloys under Different Restraints
## 4 Result and Discussion
### Fe-SMA Behavior under Partial Restraint  
Table 3 shows the activation test results as the FSMA-A and FSMA-C specimens with 0.04 pre-strain were heated to 200 \({}^{\circ}\)C under different contact temperatures. The comparison of temperature-recovery stress curves under partial restraint for FSMA-A and FSMA-C are presented in Figures 10 and 11. The recovery strains for the FSMA-A specimen constrained at 120 \({}^{\circ}\)C and 160 \({}^{\circ}\)C during heating were 0.00242 and 0.00401. Also, the recovery strain constrained at 200 \({}^{\circ}\)C was 0.00627 which is 65% of the recovery strain under free restraint. The recovery strain grew as the contact temperature mounted. In Figure 10a, when the heating temperature reached 200 \({}^{\circ}\)C, the stresses in the FSMA-A constrained at 120 \({}^{\circ}\)C and 160 \({}^{\circ}\)C were 101 MPa and 52 MPa. The recovery strain (\(\sigma_{m,T}\)) decreased approximately 48.06 MPa as the contact temperature increased by 40 \({}^{\circ}\)C. Even though the temperature for each restraint point was set differently in the FSMA-A specimen, the short-term relaxation was small in both cases due to the steady maximum recovery stress (\(\sigma_{m}\)) and final recovery stress (\(\sigma_{f}\)). The final recovery stresses constrained at a heating of 120 \({}^{\circ}\)C and 160 \({}^{\circ}\)C were 396 MPa and 347 MPa. As the contact temperature increased, the final recovery stress (\(\sigma_{f}\)) decreased by 49 MPa. In the cooling phase, the recovery strains for the FSMA-A specimen constrained at 120 \({}^{\circ}\)C and 160 \({}^{\circ}\)C were 0.00752 and 0.00818. These are nearly 78.7% and 85.6% of the total value when compared to the value under the  
Figure 9: Elastic shortening due to recovery stress of Fe-SMA. free restraint. As presented in Figure 9(b), the final recovery stresses constrained at 120 \({}^{\circ}\)C and 160 \({}^{\circ}\)C after cooling were 173 MPa and 114 MPa which are roughly 33.5% and 22.1% of the value compared to the value from the one under the rigid restraint. In the case of the FSMA-C specimen, the recovery strains constrained at 120 \({}^{\circ}\)C and 160 \({}^{\circ}\)C during heating were 0.00692 and 0.01088. Also, the recovery strain constrained at 200 \({}^{\circ}\)C was 0.01531 which is 77.4% of the recovery strain under the free restraint. Like the FSMA-A specimen, the recovery strain increased when the contact temperature mounted. As shown in Figure 10(a), the stresses in the specimen constrained at 120 \({}^{\circ}\)C and 160 \({}^{\circ}\)C were 105 MPa and 81 MPa when the heating temperature arrived at 200 \({}^{\circ}\)C. The recovery strain (\(\sigma_{m,T}\)) decreased as the contact temperature increased. However, short-term relaxation developed in accordance with the variation in the maximum recovery stress (\(\sigma_{m}\)) and final recovery stress (\(\sigma_{f}\)). The maximum recovery stresses constrained at 120 \({}^{\circ}\)C and 160 \({}^{\circ}\)C in heating were 351 MPa and 325 MPa. Subsequently, the final recovery stresses became 310 MPa and 273 MPa. As the contact temperature increased, the maximum recovery stress and final recovery stress decreased. In the cooling phase, the recovery strains for the FSMA-C specimen constrained at 120 \({}^{\circ}\)C and 160 \({}^{\circ}\)C were 0.01769 and 0.01852 which are nearly 89.5% and 93.7% of the value compared to the values under free restraint. As described in Figure 10(b), the maximum recovery stress and final recovery stress in the cooling phase were comparable. The recovery stress decreased in accordance with the decrease of the contact temperature and the final recovery stresses constrained at 120 \({}^{\circ}\)C and 160 \({}^{\circ}\)C were 40.5% and 29.2% from the recovery stress in the specimen under initially restraint condition.