## 4 Experimental Results and Discussion  
### Effect of Print Parameter on Mechanical Property of 3D-Printed CFRCs  
The influence of the main effect of three factors and the second-order interaction effect on the stress of the specimen is analyzed using Minitab19. On the Pareto graph, the reference line for statistical significance is drawn at the dotted line, where it is the (1-\(\alpha\)/2) fractional place of the T-distribution of the degree of freedom equal to the degree of freedom of the error term. When the standardized effect of the factor is greater than the value at the dotted line, it indicates that the factor is a significant factor. It can be seen from the normal and Pareto diagrams that the printing layer thickness and printing speed significantly affect the tensile stress of the print tensile specimen, as shown in Figure 5a,b. Secondly, the variance analysis of the factors affecting the mechanical properties of the tensile parts also shows that the printing layer thickness and printing speed of the fiber-reinforced nozzle can significantly affect the maximum tensile stress because their \(p\) values are less than 0.05.  
Using the Origin 2021 software, the 3D color-mapped surface with projection is drawn using the fiber print layer thickness as the x-axis, the fiber print speed as the y-axis, and the maximum tensile stress as the z-axis, as shown in Figure 5c. It can be seen that within the parameters explored in the test, the slower the printing speed, the smaller the print layer thickness and the greater the maximum tensile stress the specimen can withstand. The maximum tensile stress obtained in the test at the slowest fiber printing speed of 250 mm/min and the minimum fiber printing layer thickness of 0.05 mm was 189.52 MPa. The printing temperature at this time was 210 \({}^{\circ}\)C. According to the above test results, the optimal process parameters of this independent extrusion 3D printer were determined: fiber printing layer thickness of 0.05 mm, fiber printing nozzle speed of 250 mm/min, and fiber printing nozzle temperature of 210 \({}^{\circ}\)C.  
Take the data of significant factor as layer thickness and maximum tensile stress of the specimens to make scatter diagram, as shown in Figure 5d. It can be seen that the smaller the layer thickness, the better the mechanical properties of the specimen. It is again confirmed by test 15 and test 16 that the lower the layer thickness, the higher the maximum tensile stress can be at the same temperature and speed.  
It can be seen from test 12 and test 14 that for the same fiber print layer thickness, the same fiber print temperature, and the same fiber print line width, test 12 with a lower fiber print speed has a higher tensile stress. As can be seen from Table 4, the average maximum tensile stress at the three center points is 161.65 MPa. It has the same fiber printing temperature, fiber printing layer thickness, and fiber printing speed as test 17, and the difference only lies in whether there is overlap between adjacent fibers, and it can be seen that the experimental group with fiber overlap can take more tensile stress. It can also be seen from test 12 and test 13 that the experimental group with fiber overlap was subjected to greater fracture stress. It is tentatively determined that the degree of fiber overlap has an effect on the maximum tensile stress.  
Figure 4: Reinforced fiber layer placement diagram with layer thickness of 0.1 mm, 0.15 mm.