# Compressive Properties of Green Velvet Material Used in
## 3 Results  
### Load-Deformation Curve  
Figure 5 showed a typical load-deformation curve of the tested PLON blocks. The two typical phases, including Phase I (the first linear region) and Phase II (the densification region that exhibited nonlinearity behavior with a sharp increase in the material's stiffness), could be identified for all the load-deformation curves of the evaluated PLON materials. The PLON block has its deformation in the linear elasticity region, accounting for 30% of the entire deformation (as shown in Figures 5 and 6). Compared with PLON, the load-deformation curves of FPF and loofah blocks have three typical phases including Phase I (the first linear region), Phase II (the second linear portion, which belongs to the plateau region and exhibits reduced stiffness compared to the stiffness of Phase I) and Phase III (the densification region) [24]. The load-deformation curves of coir and latex exhibited two typical phases similar to those of PLON: linear elasticity and densification [25].  
Figure 6 showed typical load-deformation curves of the tested four PLON blocks with different densities. The average slopes of the two phases are respectively represented by K1 and K2. The least square linear regression technique is used to derive these slope values. The PLON block has its deformation in the linear elasticity region, accounting for 30% of the entire deformation (as shown in Figures 5 and 6). Table 1 summarized the ANOVA results obtained from the GLM procedure performed for each of the three evaluated properties of the PLON cushion. It was indicated that the main effects of PLON blocks with different densities on K1 and K2 values are statistically significant at the 5% significance level. Table 2 summarized the means of these average slope values and their comparisons were performed using the LSD multiple comparisons procedure. The mean comparison results indicated that the high-density PLON materials used in this experiment had significantly higher average slope values than the low density ones for K2, as was shown in Table 2. There were no significant differences among PLON blocks with densities of 20 kg/m\({}^{3}\) and 30 kg/m\({}^{3}\), but there were significant differences among PLON blocks with densities of 30 kg/m\({}^{3}\), 40 kg/m\({}^{3}\) and 50 kg/m\({}^{3}\) for K1, as was shown in Table 2.  
Figure 4: Mechanical test system diagram.  
Figure 5: A typical load-deformation curve of the tested PLON block.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline  & \multicolumn{2}{c}{**K1**} & \multicolumn{2}{c}{**K2**} \\ \cline{2-5}
**Source** & **F Value** & **_p Value_** & **F Value** & **_p Value_** \\ \hline PLON & 357.03 & \textless{}0.0001 & 31.54 & \textless{}0.0001 \\ \hline \hline \end{tabular}
\end{table}
Table 1: ANOVA results performed on three factors.  
Figure 6: Typical load-deformation curve of the tested PLON block with different densities: (**a**) 20 kg/m\({}^{3}\) PLON block’s typical load-deformation curve, (**b**) 30 kg/m\({}^{3}\) PLON block’s typical load-deformation curve, (**d**) 50 kg/m\({}^{3}\) PLON block’s typical load-deformation curve.  
The K1 value insignificantly increased when the density changed from 20 kg/m\({}^{3}\) to 30 kg/m\({}^{3}\), indicating that the K1 value was not sensitive to the change of low density. K1 values were more sensitive to density changes that range from 30 kg/m\({}^{3}\) to 50 kg/m\({}^{3}\). The K2 value increased as the density increased, indicating that stiffness increased with density. The 50 kg/m\({}^{3}\) PLON block had the largest K1 and K2 values and the maximum stiffness. The 20 kg/m\({}^{3}\) PLON block had the smallest K1 and K2 values and the minimum stiffness. The above results indicated that a sitter would feel the seat as significantly stiffer and has less sense of subsidence when sitting on a higher density PLON cushion.