# Recovery Behavior of Fe-Based Shape Memory Alloys under Different Restraints
## 4 Result and Discussion  
### Mechanical Properties of Fe-SMA  
Figure 5 and Table 4 compare the stress-strain curves by the direct tensile tests and present a summary of the direct tensile test results. The ultimate strain and strength for the FSMA-A specimen are 0.22556 and 1140 MPa, respectively. The ultimate strengths for the FSMA-B and FSMA-C specimens, which have different chemical compositions from the FSMA-A, are reduced by 3% and 5% compared to the FSMA-A specimen. The ultimate strength for the FSMA-C specimen that has an additional heat treatment decreased by 2.33% compared to the FSMA-B specimen that has the same chemical composition as the FSMA-C specimen. It is thought that the internal stress from the work hardening is released/eliminated during the heat treatment which leads to a strength reduction [17]. The ultimate strain for the FSMA-B and FSMA-C specimens increased by 74.5% and 75.2% when compared to the FSMA-A specimen. The high ultimate stress and low strain in the FSMA-A specimen is considered to be the effect of dispersion hardening and grain refinement from Titanium carbide in the work hardening process [18, 19]. The elastic modulus for the specimens was determined by a stress-strain curve that was in a range between 0 and 130 MPa. The elastic modulus for each type of specimen is 125, 126.14 and 123 GPa. This is thought to be the effect of chemical elements such as nickel, titanium or carbon in each specimen which is insignificant on the elastic modulus. In Fe-SMA, the yield point is ambiguous due to the nonlinear behavior from the phase transformation from the austenite phase to the martensite phase and plastic deformation [20]. So, the yield point of the Fe-SMA was determined using a 0.2% offset method. The yield stress of the FSMA-A specimen was 599 MPa and the yield stress for the FSMA-B and FSMA-C specimens increased to 36.6% and 31.6% with respect to the FSMA-A.  
Figure 4: Description of partial restraint(**a**) Stress-strain relationship, (**b**) Strain-temperature relationship  
\begin{table}
\begin{tabular}{p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt} p{42.7 pt}} \hline \hline \multirow{2}{*}{**Specimen**} & **Type of SMA** & \begin{tabular}{c} **Constraint** \\ **Temperature** \\ **(°C)** \\ \end{tabular} & \begin{tabular}{c} **Strain at** \\ **Constraint** \\ **Point** \\ \end{tabular} & \begin{tabular}{c} **Recovery Strain** \\ **at Constraint** \\ **Point** \\ \end{tabular} & \
\begin{tabular}{c} **Maximum** \\ **Recovery Stress**, \\ **(MPa)** \\ \end{tabular} &
\begin{tabular}{c} **Final Recovery** \\ **Stress** \\ **(MPa)** \\ \end{tabular} \\ \hline A-120H & \multirow{4}{*}{FSMA-A} & 120(Heat) & 0.02791 & 0.00242 & 399 & 396.01 \\ \cline{2-6} A-160H & & 160(Heat) & 0.02632 & 0.00401 & 347 & 347 \\ \cline{2-6} A-200H & & 200(Heat) & 0.02406 & 0.00627 & 302 & 298 \\ \cline{2-6} A-160C & & 160(Cool) & 0.02281 & 0.00752 & 173 & 173 \\ \cline{2-6} A-120C & & 120(Cool) & 0.02215 & 0.00818 & 114 & 114 \\ \cline{2-6} C-120H & & 120(Heat) & 0.02543 & 0.00692 & 351 & 310 \\ \cline{2-6} C-160H & & 160(Heat) & 0.02147 & 0.01088 & 325 & 273 \\ \cline{2-6} C-200H & & 200(Heat) & 0.01703 & 0.01531 & 267 & 248 \\ \cline{2-6} C-160C & & 160(Cool) & 0.01465 & 0.01769 & 168 & 163 \\ \cline{2-6} C-120C & & 120(Cool) & 0.01382 & 0.01852 & 118 & 117 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Details of variable and summary of activation test result under partial restraint.  
Therefore, while the FSMA-A type is suitable for being applied to structural components which carry a large load, the FSMA-B and FSMA-C types may be more effectively employed in structural components that require a high ductility.