# Research and Implementation of Axial 3D Printing Method for PLA Pipes
## 4 Five-axis 3D Printing Platform Development and Test Verification
### Experimental Results and Analysis
#### 4.2.2 Mechanical Properties Test Samples and Experimental Design  
Mechanical tests were carried out to verify the effect of axial printing on the mechanical properties of pipe parts. Since there is no standard for the direct testing of pipe parts, the test samples were generated by simulating the axial printing path of pipe parts, and the mechanical testing experiments were conducted by using the plastic tensile property testing standard GB/T 1040.2-2006/ISO 527-2:1993, and the plastic bending property testing standard GB/T 9341-2008/ISO 178:2001. The printing material was PLA with the characteristics given in Table 1, and the testing machine was TY8000 series material  
Figure 16: Typical print sample: (**a**) Circular section and plane single segment curve, (**b**) Elliptic section and plane single segment curve, (**c**) Circular section and plane multi-segment curve, (**d**) Circular section and space curve. testing machine (Tianyuan Test Equipment Co., Ltd., Yangzhou, China). The size of the test sample is shown in Figure 17.  
Figure 17a is the standard sample for the tensile test, with a standard spacing of 80 mm, and Figure 17b is the standard sample for the three-point bending test, with a span of 50 mm. The thickness of the sample is 4 mm, and the thickness of the layer is 0.2 mm, which makes a total of 20 layers. To study the influence of axial printing on the mechanical properties of printed specimens, the number of layers printed along the radial path of the sample was determined according to the thickness of the actual supporting pipe, and the number of layers printed along the axial path of the sample was determined according to the thickness of the axial strengthening printing, as shown in Figure 18.  
To study the enhancement rule of the axial path on the mechanical properties, the radial path is gradually replaced with an axial path, and a set of samples is printed for every five layers replaced, that is, the number of axial path layers is 0, 5, 10, 15, 20 layers respectively, with five samples for each group. The samples with an axial path of zero layers were used as the control group, while the remaining samples were used as the experimental group. Figure 19 shows a localized view of a printed specimen. The lower part is the radial path of 10 layers, and the upper part is the axial path of 10 layers. The Tensile Test  
The standard sample was tensile tested at a rate of 2 mm/min, as shown in Figure 20.  
Figure 19: Local diagram of the experimental sample. Figure 17: Test sample size: (**a**) Tensile sample, (**b**) Three-point bending sample. Figure 18: The path direction. The stress-strain curve of the tensile test is shown in Figure 21.  
The average maximum tensile stress of the same set of samples, shown in Table 2. Standard deviation is depicted in brackets. The data in Table 2 are represented by a graph, as shown in Figure 22. The horizontal axis represents the number of layers printed in the axial direction, and the vertical axis represents the maximum stress value of the tensile experiment. Increasing the axial layers and the decreasing radial layers, the tensile stress of the print increases by an average of 2.6% for each additional layer of axial layers, which proves that the axial printing does have an enhancement effect, and the enhancement effect is also improved with the increase of the number of reinforcement layers. \begin{table}
\begin{tabular}{c c} \hline
**No. of Axial Layers** & **Maximum Tensile Stress (MPa)** \\ \hline
0 & 34.1 (3.8) \\
5 & 39.0 (2.6) \\
10 & 42.4 (1.0) \\
15 & 47.2 (2.8) \\
20 & 51.6 (1.5) \\ \hline \end{tabular}
\end{table} 
Table 2: Tensile test the maximum stress of each group. Figure 20: The tensile test. Figure 21: Tensile test stress-strain curve. It is essential to point out that, even when all the layers are in the axial direction, the maximum tensile stress given in the material specifications (Table 1) is not reached. These low tensile properties indicate the presence of voids between the deposited layers.