# Mechanical Performance of Polymer Materials for Low-Temperature Applications
## 3 Results and Discussion  
### Effect of Temperature on Tensile Properties  
This section describes the experimental results of mechanical tensile tests at different temperatures and strain rates performed on PVDF, PE, and ABS specimens. In engineering applications, deformation and reduction in cross-sectional area of a specimen are very small and can be neglected. Thus, the cross-sectional area was assumed to be constant during deformation, and the nominal stress was the load divided by the initial cross-section of the specimen. The strain means nominal strain defined as the variation amount of the measured displacement by the extensometer divided by the initial gauge length. Figure 3 shows the nominal stress-strain curves obtained with PVDF, PE, and ABS at a constant strain rate of \(10^{-3}\) s\({}^{-1}\) at different temperatures. All the tested polymers exhibited an increase in the tensile strength and Young's modulus with a decrease in temperature from \(25\,^{\circ}\mathrm{C}\) to \(-100\,^{\circ}\mathrm{C}\). Further, reduction of the elongation and toughness was observed below \(0\,^{\circ}\mathrm{C}\) as the tensile properties deteriorated. These results are similar to those of an early study of the tensile mechanical properties of PVDF [25]. These observations indicate that the properties of thermoplastic polymers demonstrate a significant variation with in-service conditions such as dependence on temperature and strain rate [30]. The low-temperature tensile testing revealed that, compared with PE, PVDF had better capacity, such as strength. Furthermore, the variation of toughness was much less likely to occur when reducing the temperature. As prior tensile tests demonstrated, tensile stress-strain curves for ABS exhibited a temperature dependency, and the results of the tensile test also revealed that the tensile strength and elastic modulus increased with the decrease in temperature, but  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Material**} & \multirow{2}{*}{**Temperature (\({}^{\circ}\)C)**} & \multirow{2}{*}{**Strain Rate (s\({}^{-1}\))**} & \multicolumn{2}{c}{**UTM Speed (mm/min)**} \\ \hline
1 & & 25 & \(10^{-3}\) & 3 \\
2 & & 0 & \(10^{-3}\) & 3 \\
3 & & \(-50\) & \(10^{-4}\) & 0.3 \\
4 & PE 100 & \(-50\) & \(10^{-3}\) & 3 \\
5 & &  
the elongation and modulus of toughness showed little change. Figure 4 presents the shape of the fractured specimens of PVDF at different temperatures. The failure characteristic was different for each specimen at the end of tests at different temperatures. Further, as the temperature decreased, a narrow shape and whitened area became less common. The arrows in Figure 4 indicate the height of the whitened area during the tensile test, and limited necking occurs in the fracture plane. However, the fracture at low temperatures occurs before the necking. Accordingly, the brittleness of the specimens is considered to increase as the temperature decreases. Further, Figure 5 also presents the failure types of the PE specimens according to temperature. The tensile test specimen at room temperature appeared with fairly agglomerated fibers and a torn form compared to that in the testing at low temperatures. However, as the temperature dipped below 0\({}^{\circ}\), the properties were weakened, and the polymer fibers were stiffened. In addition, the height of the necked area was confirmed to have a short length, and the fracture surfaces flattened out at low temperatures. Figure 6 presents the failure type of the ABS specimens and the whitened area due to necking. A narrow shape appears in the specimen at 25 \({}^{\circ}\)C, but such shapes do not occur below 0 \({}^{\circ}\)C.