## 2 Materials and Methods
### Sample Preparation  
To determine the single effect of the processing parameter on tensile property, three kinds of dense-structure samples were fabricated by an ME device (D-force V2) according to ISO 527-2-2012 (International standard, plastics determination of tensile properties Part 2: test conditions for molding and extrusion plastics), as the schematic shown in Figure 1a. The first kind could be divided into three types, and they had different extrusion widths (a certain width of the filament extruded from the nozzle), which were separately 0.4, 0.3 and 0.2 mm. These samples were represented by T\({}_{\text{E0.4}\_i}\), T\({}_{\text{E0.3}\_i}\) and T\({}_{\text{E0.2}\_i}\). The second kind had another three types of samples built with different layer heights, which were 0.2, 0.15 and 0.1 mm. They were represented by T\({}_{\text{L0.2}\_i}\), T\({}_{\text{L0.15}\_i}\) and T\({}_{\text{L0.1}\_i}\). The third kind of samples also had three different types, whose build directions were X, Z and Oblique, individually represented by T\({}_{\text{X0\_i}}\), T\({}_{\text{Z0\_i}}\) and T\({}_{\text{O0\_i}}\). It is noted that only one processing parameter was set different from the original (or default) type of samples (i.e., T\({}_{\text{E0.4}\_i}\), T\({}_{\text{L0.15}\_i}\) and T\({}_{\text{X0\_i}}\)) for each other type based on fractional factorial design. Details of the processing parameter settings are provided in Table 1. To ensure the reliability and repeatability of the measurements, more than ten samples of each type were fabricated (thus, \(i>10\)). Figure 1: Two-dimensional drawing of the samples. (**a**) Tensile test sample and (**b**) dynamic test sample. For the dynamic characteristic, another three kinds of dense-structure samples were fabricated with the same ME device, as the schematic shown in Figure 1b. They were also fabricated based on fractional factorial design, with the three processing parameters (i.e., extrusion width, layer height and build direction) individually set to the values shown in Table 1. These samples were separately represented by E0.4\(j\), E0.3\(j\), E0.2\(j\), L0.2\(j\), L0.15\(j\), L0.1\(j\), X0\(j\), _Z0\(j\) and O0\(j\), (_j_ = 1-5). It is noted that TE0.4\(j\), E0.4\(j\), T1.0.15\(j\), L0.15\(j\), TX0\(j\) and X0\(j\) were fabricated with the same processing parameters (the default values). All the samples mentioned above were made of polylactic acid (PLA [32], environmentally friendly material, having good workability and forming stability). Apart from only one single processing parameter set different for each type of samples, all the others were set the same, such as printing speed (moving speed of the printing head during the manufacturing process, set as 60 mm/s), extruder temperature (the temperature of the extruder to heat the filament to molten state, set as 200 \({}^{\circ}\)C), etc. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \begin{tabular}{c} **Sample** \\ _(i \(>\) 10)_ \\ _(j = 1–5)_ \\ \end{tabular}  & \begin{tabular}{c} **Extrusion** \\ **Width (mm)** \\ \end{tabular}  & \begin{tabular}{c} **Layer Height** \\ **(mm)** \\ \end{tabular}  & \begin{tabular}{c} **Build Direction** \\ **Section** \\ \end{tabular}  & \begin{tabular}{c} **Longitudinal** \\ **Contours** \\ \end{tabular}  \\ \hline TE0.4\(j\) & 0.4 & 0.15 & \begin{tabular}{c} X direction (0\({}^{\circ}\)) \\ \end{tabular}  & Extrusion width & 3 \\ E0.4\(j\) & & & & & & \\ TE0.3\(j\) & 0.3 & 0.15 & \begin{tabular}{c} X direction (0\({}^{\circ}\)) \\ \end{tabular}  & Extrusion width & 4 \\ TE0.2\(j\) & & 0.2 & 0.15 & \begin{tabular}{c} X direction width \\ \end{tabular}  & 6 \\ \hline T1.0.2\(j\) & 0.4 & 0.2 & \ \begin{tabular}{c} X direction width \\ \end{tabular}  & 3 \\ T1.0.15\(j\) & 0.4 & 0.15 & X direction (0\({}^{\circ}\)) & Extrusion width & 3 \\ T1.0.15\(j\) & & & & & \\ T1.0.15\(j\) & & & & & \\ T1.0.15\(j\) & & & & & \\ T1.0.1\(j\) & 0.4 & 0.1 & & & \\ L0.1\(j\) & & & & & \\ \hline T2.0\(i\) & & & & & \\ T2.0 & 0.4 & 0.15 & \begin{tabular}{c} X direction width \\ \end{tabular}