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)
>>>