Page 96 - MSAM-2-4

Materials Science in Additive Manufacturing 3D-printed composite auxetic structures

Figure 6. Display of printed test specimens.

A B which had weak regions at joints. With a 4.75% increase
in weight, rotating rigid FR1 was endowed with 2.69 times
tensile modulus and 2.77 times tensile strength, compared
with the specimen without reinforcing fibers. Similar
improvements can also be found in rotating rigid FR2 and
rhombus FR.
Due to the anisotropy of carbon fiber, the printing
direction has a great impact on the tensile properties of
specimens. This can be illustrated by the comparison
between re-entrant FR1 and re-entrant FR2. Although
Figure 7. Evaluation of Poisson’s ratio via tensile test. (A) Uniaxial tensile
test. (B) Images of deformation of the test specimen, from which we can re-entrant FR2 was infilled with a higher percentage of
obtain the axial and lateral strain. fibers, the tensile strength of re-entrant FR2 was lower
than that of re-entrant FR1 because the fiber direction in
of tensile modulus and strength. As shown in Figure 10, re-entrant FR2 was perpendicular to the loading direction,
the location of failure is consistent with the layout of stress while the fiber direction in re-entrant FR1 was parallel
concentrations. with the loading direction. On the other hand, the tensile
modulus was weakly correlated to the printing direction.
3.2. Effect of continuous fibers on tensile behavior The addition of fiber composites increased the tensile
The continuous carbon fiber has prominent performance modulus of re-entrant FR2, which had the highest tensile
in stiffness and strength. In this work, only two layers modulus of 189.25MPa among the specimens since it has
of continuous carbon fibers were infilled in the auxetic the highest fiber composite content. A similar trend also
structures. The tensile modulus and tensile strength were happened to rotating rigid FR3. Although infilled with
calculated based on stress-strain curves (Figure 11B, 2.27% fiber composites, the rotating rigid FR3 achieved a
Figure 12B, Figure 13B) and summarized in Table 2. tensile strength increase of only 13%, which is much lower
Results showed that a weight increase of less than 20% than the strength improvements observed in the other two
resulted in a significant increase in tensile modulus and reinforcing specimens.
tensile strength. The reinforcing effect was conspicuous, The continuous reinforcing fibers significantly
especially for rotating rigid and rhombus structures, improved the tensile properties of test specimens.

Volume 2 Issue 4 (2023) 6 https://doi.org/10.36922/msam.2159