4. Result and Discussion
Tensile tests were performed to investigate the effect of sandwich composites in additive manufacturing. The effects on various outer shells, raster angle, and layer thickness at fabrication were also measured. All of the experiments were carried out exactly as instructed. As specified in the experimental design, After tensile testing, broken test specimens are shown in Figure.1. All the samples were broken in different ways along the infill direction during the loading.
<<< Figure.1 ASTM Standard Tensile Tested 3D printed Specimens >>>
To generate main plots, the mean of each parameter at all levels was used. The maximum mean value indicates the optimized parameters for tensile strength, and the significance of the parameters was determined using Analysis of Variance (ANOVA). The interaction of process parameters on tensile strength was investigated in this analysis. The main plot effect demonstrates the direct impact of independent parameters, whereas the interaction effect demonstrates the combined impact of two parameters. The main tensile strength plot for FDM printed PLA specimens is shown in Figure.2. Tensile strength decreases with increasing layer thickness and number of shells, but increases with increasing raster angle. The PLA mean plot analysis shows that a raster angle of 90 (Level 3), a layer thickness of 0.1 (Level 1), and a number of shells of 3 produce the best results. The mean plot for PLA analysis also reveals that the raster angle has the greatest influence on tensile strength, followed by layer thickness and the number of shells.
<<< Figure.2 Main Plots for printed samples a)PLA, b)PLA/Al2O3, c)PLA/Cu, d)PLA/CF, e)PLA/Al2O3-SW, f)PLA/Cu-SW & g) PLA/CF-SW>>>
The PLA/ceramic composite main pot demonstrates that tensile strength decreases with increasing layer thickness and the number of shells. increases as the raster angle increases. When compared to PLA, PLA/Ceramic has slightly higher strength for a layer thickness of 0.2 (Level 2) but lower strength for the number of shells (Level 1). PLA/Copper composite plots show that the tensile strength varies similarly to PLA but has less strength than PLA and PLA/Ceramic composites.
PLA/Carbon fibre composite plots show that tensile strength varies similarly to PLA for raster angle input parameters, but with less tensile strength. The layer thickness and number of shells provide nearly equal strength across all levels (Level 1 to Level 3). The PLA-PLA/Ceramic sandwich mean plots show a similar variation for the input parameter but show improved tensile strength over PLA at all levels (Level 1 to Level 3).A PLA-PLA/Copper sandwich mean plot shows a similar variation in tensile strength for input parameters such as PLA, but shows significant improvement over PLA. A mean plot of a PLA-PLA/Carbon fiber sandwich reveals that the sandwich is unaffected by layer thickness and behaves like PLA, but the tensile strength increases as the number of shells from all levels increases (Level 1 to Level 3).
It is also necessary to determine the parameters that have a significant impact on the tensile strength of the specimen. ANOVA (analysis of variance) was used to identify the most significant parameters affecting the response parameter in terms of percentage. The statistical significance of individual parameters has been represented by the p-value. According to Taguchi et al. [36], the p-value for the 95 percent confidence level should be less than 0.05. The ANOVA result for tensile strength means data is shown in Table.6, which shows that the p-value of the raster angle, layer thickness, and the number of shells (all input parameters) was less than 0.05 for all materials. However, the number of shells has a p-value greater than 0.05 for the material PLA/Carbon fiber composites, and the raster angle has a p-value greater than 0.05 for the material PLA-PLA/CF sandwich.
<< < Table.7 ANOVA table for Experimental Results>>>
As a result of these factors having a statistically significant effect on tensile strength, the confidence interval for PLA material was 96.26%, for PLA/Ceramic composite was 94.08 %, for PLA/Copper composite was 95.03 %, for PLA/Carbon fiber composites was 95.24 %, for PLA-PLA/Ceramic sandwich was 94.09 %, for PLA-PLA/Copper sandwich was 92.36 %, and for PLA-PLA/CF sandwich was 95.08%. As a result, the raster angle (greater than 34 %.) is the most influenced parameter for PLA, PLA/Ceramic-composite, PLA/Carbon fiber, and PLA-PLA/Ceramic sandwich. The layer thickness has the greatest influence on the tensile strength of the PLA-PLA/Copper sandwich and the PLA-PLA/Carbon fiber sandwich. The number of shells has the greatest influence on the tensile strength in PLA/copper composites.