## 3 Results and Discussion
### Thermo-Mechanical Characterization of Composite  
The thermo-mechanical response of the prepared materials was investigated by TMA to observe the deflection in terms of displacement during the cooling and heating profile. In the investigated range (\(-\)150-150 \({}^{\circ}\)C), Ni-Ti ribbon displayed the deflection (\(L\)) in the maximum range of \(-\)1200 mm; however, on the coating of the polymer to one side, the surface leads to a deflection decrease towards \(-\)350 mm. This decrease in the behavior of the deflection contributes towards additional load in the three-point bending test.  
The decrease in deflection behavior was more significant after the coating on both sides, probably because on cooling and heating ranges polymer has significantly adhered to the substrate without any delamination or breakage.  
Figure 6 reports the deflection behavior in \(\Delta L\) as a function of the temperature and time for the Ni-Ti ribbon and PMMA composites, based on the definition of the coefficient of thermal expansion (CTE), it is clear that a large value corresponds to a phase change in the material. The change in the displacement of the Ni-Ti ribbon compared to composite shows a large difference due to the presence of the polymer coating on the surface of the alloy. The polymer coating acts as a back force, showing the good adhesion of the polymer during the heating and cooling cycles.  
Figure 5: Optical Micrograph (OM) images of the (**a**) Ni-Ti ribbon and (**b**) poly (methyl methacrylate)-Ni-Ti ribbon composite.  
The behavior of the hysteresis curve for the composite showed no significant difference in respect of the coating thickness on the one side and both side samples. The coefficient of thermal expansion remains unchanged for both of the composites. Figures 7 and 8 display the response of the Ni-Ti ribbon and composite as a function of the temperature and their corresponding expansion, respectively. The values are significantly reduced from the Ni-Ti ribbon. The polymer still sustains, during cooling and heating cycles, without any delamination from the Ni-Ti surface. The heating profile shows the combination of the austenite and martensitic peaks; as a result, a bi-furcated peak has been observed. On the cooling segment, the austenite and martensitic peaks, with the conversion from B\({}_{2}\) to R, and the B1\({}_{9}\)' combined peaks are observed. For the Ni-Ti ribbon-polymer composite, the values of the displacement (\(L\)) reduce in comparison to the Ni-Ti ribbon as a virgin sample response (Figure 7). As mentioned before, the polymer acts as a load to the Ni-Ti surface, which could backlog force.  
Figure 6: Displacement as a function of time and temperature for the Ni-Ti ribbon and PMMA composite.  
Figure 7: Thermomechanical analysis (TMA) curves of the Ni-Ti ribbon showing displacement (\(L\)) and the coefficient of thermal expansion (CTE) versus the temperature profile.  
The thickness of the composite increases with the load applied on the surface, and, as a result, the displacement response reduces. The rule of mixture applies here as the combined effect from the matrix polymer as well as the ribbon (Figure 8).  
The coefficient of thermal expansion (CTE) of the PMMA composite with one side showed the lower effect of PMMA on the functional behavior of the shape memory alloy (Figure 9).  
Figure 8: Hysteresis behavior of the PMMA-Ni-Ti composite (one side and both sides) surface as a function of the temperature.  
Figure 9: The coefficient of thermal expansion (CTE) response of the composite as a function of time.  
The peaks are more prominent during the cooling and heating segment. However, the coating of PMMA on both sides of the Ni-Ti ribbon induces some mechanical effects, and, as a result, the peaks are less prominent during the heating and cooling segment. The mechanical behavior of the composite during cooling and heating shows no delamination of the coating from the substrate.