## 3 Results and Discussion
### Material Property of the Sample  
The samples were weighted using the electrical analytical balance (FA2004), of which the precision was 0.1 mg. Together with the volume of the dynamic test plates, the density of each sample was determined. Based on [PERSON]'s law, the elastic modulus of the samples was obtained. According to the equation \(\mathrm{G}\ =\mathrm{E}/2(1\ +\ \upsilon)\), the ME plates' shear elastic modulus could be determined, where \(\upsilon\) is Poisson ratio, and \(\upsilon\) = 0.36 [32]. Table 2 summarizes the average measured material properties of each type of dynamic test samples. Since \(\mathrm{E}_{0.4}\), \(\mathrm{L}_{0.15}\) and \(\mathrm{X}_{0}\) were fabricated with the same processing parameters, they had the same properties. It can be seen that the wider the extrusion width is, the larger the material property of the corresponding samples will be. This can be explained that the bonding area between adjacent extruded filaments will be decreased when the extrusion width decreases, as seen from the comparison between Figure 5a,b, leading to the deterioration of bonding strength. There would be more thermal cycles and more non-uniform thermal gradients, leading to more distortions, deformations and non-uniformities of the extruded filament (as shown from Figure 6a,b), which is a major reason for the bonded layers' poor quality [27], and thus worse bonding quality. In addition, decreasing extrusion width would increase the bonding gap between the filaments of the cross section, generating more defects such as delamination, internal pores and void structures. Therefore, decreasing extrusion width will deteriorate the material property of the ME product. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Order**} & \multirow{2}{*}{**Sample**} & **Average Elastic** & **Average Shear** & **Average Density** & **Poisson’s Ratio** \\  & & **(MPa)** & **(MPa)** & **(g/cm\({}^{3}\))** & **Ratio** \\ \hline
**1** & \(\mathrm{E}_{0.4}\), \(\mathrm{L}_{0.15}\) and & 18.8 & 6.91 & 0.92 & \\
**2** & \(\mathrm{E}_{0.3}\) & 18.5 & 6.80 & 0.91 & \\
**3** & \(\mathrm{E}_{0.2}\) & 18.0 & 6.62 & 0.91 & \\
**4** & \(\mathrm{L}_{0.2}\) & 19.3 & 7.10 & 0.92 & \\
**5** & \(\mathrm{L}_{0.1}\) & 18.1 & 6.65 & 0.91 & \\
**6** & \(\mathrm{Z}_{0}\) & 17.1 & 6.29 & 0.90 & \\
**7** & \(\mathrm{O}_{0}\) & 17.6 & 6.47 & 0.93 & \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Average material properties of material extrusion (ME) samples. Figure 5: _Cont._  
Decreasing layer height can reduce the samples' material property. When layer height is decreased, the number of layers needed to fabricate the sample will increase, resulting in the increase of bonding layers and thermal cycles, which further lead to more distortions and non-uniformities in the sample, as shown in Figure 6c. The bonding quality and strength between extruded filaments became worse. In addition, the defects like porosity, gap, separation, etc. would increase in the sample, as shown in Figure 5c. Therefore, the material property of the sample will be decreased when the layer height is reduced. The samples built in the X direction had larger material properties than those built in other directions. As the build direction changed from X to Z, more layers were required to manufacture the part, resulting in more bonding layers, thermal cycles and distortions (Figure 6d, the distortion occurred due to high non-uniform temperature gradient between the bottom and the top layers during the printing). The bonding quality and strength would be reduced (see Figure 5d), and thus the material properties of the built part were deteriorated. Figure 5: Scanning electron microscope (SEM) micrograph of the sample’s cross section. (**a**) Sample E\({}_{0.4}\) (or L\({}_{0.15}\), X\({}_{0}\)); (**b**) Sample E\({}_{0.2}\); (**c**) Sample L\({}_{0.1}\) and (**d**) Sample Z\({}_{0}\). Figure 6: Surface SEM observation of the sample.