4.2 Effect of Layer Thickness
The ANOVA table.6 shows that the p-value for layer thickness is less than 0.05 for all materials except PLA/CF. As a result, the layer thickness is statistically significant for the 95% confidence interval. Furthermore, the layer thickness increases while the tensile strength decreases. The maximum tensile strength was observed for the thinnest layer (Layer Thickness-Level 1). The lower layer thickness may result in more strands and more surface area for bonding between subsequent layers, resulting in higher tensile strength. Because of the higher bonding between the rasters, the high stiffness attained with lower layer height allows it to withstand more loads than others. When the layer height increases, fewer layers are required to complete the object, and the bonding between adjacent layers decreases, resulting in a decrease in load-withstanding capacity.
Figure.6 shows the stress-strain curve for layer thickness. It indicates that the increase in layer thickness reduces the tensile strength. Because of the increased layer thickness, there is less surface bonding between the layers, which leads to more voids, resulting in lower tensile strength, which can be observed clearly from the microscope examination as shown in figure.7. These details clearly show the good agreement between the observed results and the results reported by Coogan et al.[41]. Low extrusion pressure is induced on the layer at a high layer height, which may result in less bonding between the layers. In the opposite direction, as layer height decreased, bonding strength increased. Similarly, lower layer height exhibits high stiffness and high strain at break, as well as the presence of high pressure, developing more bonding and fewer voids. At high layer heights, more voids form and pave the way for brittle failure. At 100-micron layers, all materials, compositions, and sandwiches have higher tensile strength. The maximum tensile strength was observed for 100 microns’ layer thickness with 4 outer shells. On the other hand, for the 300 micron layer thickness also, the maximum tensile strength was observed for 4 outer shells. Figure 7 depicts a scanning electron microscopic image of a 100 mm layer thickness; fibers are pulled out in PLA/CF specimens and very few voids are observed in PLA/Cu specimens.
<<<Figure.6 Stress Strain Relationship for Various Layer Thicknesses (LT). a) 100 microns. b). 200 microns. c) 300 microns>>>
<<<Figure.7 Microscopic Examination of Various Layer thickness>>>
According to figure.8, at 100-micron layers, there were fewer voids between the adjacent layers, and higher necking was found. The 100-micron layer PLA/Al2O3/PLA sandwich has a maximum tensile strength of 59 MPa and an elongation of 12.5%. PLA/CF has a minimum tensile strength of 16 MPa at 300 micron layer thickness and an elongation of 6.2%. These findings show that increasing the layer thickness changes the mode of failure from ductile to brittle and improves brittleness. This brittleness may be caused by the introduction of more voids and less bonding in-between layers. At higher layer heights, crack propagation is transferred quickly between the layers, resulting in abrupt failure. This reduces tensile strength and causes brittle failure.
<<<Figure.8 Voids between the subsequent layers (Layer thickness/No. of Layers/Raster Angle)
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