## 3 Results and Discussion  
### Pre-Straining of Fe-SMA  
Stress-strain responses on different pre-strain levels are shown in Figure 6. The variance of the stress-strain responses at each pre-strain level on Figure 6 might be because of the microstructure changes due to the initial defects during alloy casting and the temperature difference during pressing [10]. Moreover, in contrast with the mechanical behavior of a normal steel material, no distinguished yielding point was shown on behavior of the Fe-SMA material as shown in Figure 6. This is because the Fe-SMA shows the plastic deformation and the phase transformation from austenite phase to martensite phase during the activation of the SME by resistive electronic heating [10]. Due to difficulty in defining the stress-induced transformation (\(\sigma_{0.2}\)) on the stress-strain diagram of the Fe-SMA, 0.2% offset point was arbitrarily set to define the modulus of elasticity, which shows the averaged modulus of elasticity of 133 GPa and the averaged stress induced transformation of 463 MPa. The stresses at the fracture of the Fe-SMA were 640 MPa, 691 MPa, 697 MPa, and 742 MPa at 2%, 4%, 6% and 8% of the pre-straining levels, respectively, which shows the increasing stresses by the averaged 5.1%. The stress and strain results are summarized in Table 4.  
After the strain of the specimen reached the target pre-strain level, the load was removed at a rate of 0.25 mm/min until the residual stress became zero to measure the residual strain. As shown in Figure 6, at the beginning of the unloading, the stress was reduced from the ultimate stress to 60% with same inclination of the initial modulus of elasticity, and the strain was recovered by the reverse transformation as pseudoelastic strain [9; 22]. The residual strains of the specimens were 1.07%, 2.90%, 4.72% and 6.52% for 2% to 8% of pre-strains, respectively, which shows 1.19% of the average recovered strain. The relationship between the recovered strain and pre-strain values showed a linear tendency with a slope and an intercept of 0.9234 and \(-\)0.7696, respectively. Around 99.5% of recovered strain values can be explained by the pre-strain values with the mentioned linear tendency.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Specimen** & **Pre-Strain** & **Recovered Strain** & **Maximum Stress** & **Recovery Temperature** & **Recovery Stress** \\ \cline{2-5}  & **(\%)** & **(\%)** & **(MPa)** & **(\({}^{\circ}\)C)** & **(MPa)** \\ \hline PS2-T100 & 1.94 & 1.02 & 644.80 & 114.6 & 287.06 \\ PS2-T130 & 1.91 & 1.05 & 641.85 & 130.7 & 322.37 \\ PS2-T160 & 1.96 & 1.03 & 636.11 & 163.4 & 358.08 \\ PS2-T190  
To investigate the effect of the pre-strain levels on the modulus of elasticity of the Fe-SMA, the un-loaded Fe-SMAs after being stretched up to the target strain were heated to induce the recovery stress and were re-loaded with the direct tensile test. Figure 7 shows the modulus of elasticity of 120.93 GPa, 108.90 GPa, 97.82 GPa and 88.22 GPa, respectively. The modulus of elasticity was decreased by an average of 9.3% with increase in the pre-strains from 2% to 8%. At 2% pre-strained Fe-SMA, modulus of elasticity of the Fe-SMA with activated SME was 120.93 GPa, which is lower than the 173 GPa reported in [32].