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Materials Science in Additive Manufacturing Cast and 3D-printed fiber orientations

were printed. One batch included fibers, while the other printing parameters follow the matching criteria and the
batch did not. Both flexural properties of the printed fiber fibers exhibit a high degree of directional distribution,
mixture and the non-fiber mixture were tested (Figure 25), the flexural strength and deflection distance of the printed
and improvement ratios of flexural stress (σ) and deflection fiber mixture can increase by up to 180% and 380%,
distance (δ) were adopted to characterize the impact respectively, compared to the printed non-fiber mixture.
of fiber orientation on the mechanical performance, as In the case of printing Parameter A that follows the
expressed by Equation XV. matching criteria, the fibers align well within the printed
’
Increment ratio of flexural stress = filament, as discussed in Sections 3.3 and 4. However,
for printing Parameters B and C, which do not follow
’ the matching criteria, the fibers tend to exhibit a lower
Increment ratio of deflection distance = (XV)
degree of directional distribution within the printed
filaments, as discussed in Section 4. Consequently, the
Figure 26 presents the relative improvement ratios of
mechanical performance. As shown in Figure 26, when the flexural properties of the specimens printed using printing
Parameter A surpass those of Parameters B and C.
6. Conclusions

In this work, a comprehensive investigation was conducted
to assess the impacts of boundary constraints and flow
fields on fiber orientation. First, analytical models and CFD
simulations were developed to predict fiber orientation based
on boundary constraints and flow fields. Subsequently, both
cast and printed specimens were prepared to investigate the
impacts of boundary constraints and flow fields on fiber
Figure 25. Experimental setups for mechanical performance test of
printed specimens. orientation and mechanical performance. The analysis of
fiber orientation relied on the fluorescence image processing
method and µ-CT scan, while mechanical performance was
evaluated through tensile and flexural properties assessment.
The results reveal that the fibers of cast specimens
prepared using the DC process exhibit a higher degree of
directional fiber orientation, attributed to the well-aligned
flow field generated by the DC process. In addition, the
mechanical performance of DC specimens is superior to
that of specimens prepared through the RC process.
In the case of printed specimens, when they are
fabricated with printing parameters following the matching
criteria, the cross-section of printed filaments matches the
dimensions of the nozzle opening, resulting in well-aligned
flow streamlines. Consequently, fibers exhibit a higher
degree of directional orientation, aligning with the printing
direction. However, when specimens are fabricated with
printing parameters that do not follow the matching
Figure 26. The improvement in the mechanical performance of printed criteria, fibers tend to have a random orientation, which is
specimens with various printing configurations. limited by the boundary constraints of printed filaments.

Table 3. Testing run for the 3D‑printed specimens The findings in this work have practical significance
for both cast and printed FRCs. By controlling the
Run No. A B C fiber orientation through adjustments in the printing
Pumping speed (mm/s) 650 1 650 2 650 2 parameters, it becomes possible to enhance the mechanical
Nozzle movement speed (mm/s) 66.7 1 53.3 2 40 2 performance of components, enabling them to withstand
1 The pairs of printing parameters follow the matching criteria. greater loads. Furthermore, structures requiring specific
2 The pairs of printing parameters that do not follow the matching criteria. directional performance, such as those needing directional

Volume 2 Issue 3 (2023) 15 https://doi.org/10.36922/msam.1603