Page 50 - MSAM-3-1

Materials Science in Additive Manufacturing Adhesion study for multi-material 3D printing

Another critical component of the methodology Table 2. Material combinations tested in this work
involved the investigation of material deposition order
Material B
Material A
and its effect on interlaminar adhesion properties. We Sample Interface design (printed first) (printed last)
types
systematically prepared and tested samples using two
distinct printing sequences, specifically varying the order 1 No modification cPLA TPU
in which cPLA and TPU were printed. This variation 2 TPU cPLA
aimed to ascertain the influence of print order on the bond 3 Low profile mechanical cPLA TPU
quality between cPLA and TPU. In Figure 2, “Material 4 interlocking TPU cPLA
A” and “Material B” refer to cPLA and TPU, respectively, 5 Top infill modification cPLA TPU
whose printing order was alternated as detailed in the 6 TPU cPLA
subsequent paragraph and summarized in Table 2.
Abbreviations: cPLA: conductive polylactic acid; TPU: Thermoplastic
The first set of samples was fabricated by initiating polyurethane.
the print with the cPLA, subsequently followed by the
deposition of the TPU layer. This sequence prioritizes the Table 3. Print settings for different print filaments
placement of the rigid material as the foundational layer. Settings Materials
Conversely, the second set of samples reversed this order,
starting with TPU as the base, on which cPLA was printed. cPLA TPU
The test coupons were fabricated through a modified E3D Nozzle temperature (°C) 200 235
ToolChanger on a standard glass heated bed. A 0.6 mm Print speed (mm/s) 70 50
nozzle was used to print cPLA filaments, whereas a standard Nozzle size (mm) 0.6 0.4
0.4 mm nozzle was used to print the TPU-based filaments. Part cooling fan yes no
A larger nozzle was used for cPLA filament to ensure Infill percentage 20% 15%
good printability as the cPLA filament tends to clog when
a smaller nozzle is used. The printing parameters used in Infill pattern Grid Gyroid
this work were adopted from the settings recommended Number of perimeter lines 2 2
by the respective manufacturers. Table 3 summarizes the Abbreviations: cPLA: conductive polylactic acid; TPU: Thermoplastic
print settings that were used to print each material. polyurethane.

2.3. Mechanical tests multi-material test coupons high-resolution images of the fracture surfaces post-
The tensile test was conducted in accordance with ASTM tensile testing. This visual inspection facilitated a
D638 with some slight modifications using a universal comparative assessment of the macroscopic features
testing machine (AGX plus 10 kN, Shimadzu). For the across different coupon types, providing immediate
tensile test, a strain rate of 2 mm/min was used. The force visual cues to the nature of the bond failure, such as
required to pull the sample until it failed was recorded adhesive or cohesive fracture patterns.
over time. The tensile stress was calculated based on the (ii) Micro-CT analysis: We utilized a Bruker SkyScan
smallest cross-sectional area of the tensile coupons where 1173 micro-CT scanner to probe deeper into the
the interface between the two materials was situated. internal structures in three dimensions. This non-
Five samples were used for the tensile test to ensure the destructive technique allowed us to construct
statistical significance of the results. With three different detailed 3D representations of the internal coupon
types of interfaces and two print orders, there were structure, including any voids, delamination, or
altogether six different coupons that have been tested, and other imperfections that contributed to the failure.
they are summarized in Table 2. The parameters set for the micro-CT scans included
a source voltage of 80 kV, source current of 60 µA,
2.4. Characterization of failure mode of the tensile image pixel size of 17.47 µm, exposure time of 850 ms,
coupons and rotation steps of 1°.
The characterization of the fracture modes for the tensile (iii) Surface roughness characterization: A Keyence VX‑100
coupons was performed using optical microscopy, micro- non-contact 3D laser scanning microscope was used
computed tomography (micro-CT) analysis, and surface to quantitatively measure the surface roughness at
roughness characterization to gain both qualitative and the interface. The surface topography data acquired
quantitative insights into the failure mechanisms: through this method were critical for understanding
(i) Optical microscopy: For the initial qualitative the role of surface roughness in interlaminar
analysis, an optical camera was employed to capture adhesion. Specific parameters measured, including

Volume 3 Issue 1 (2024) 5 https://doi.org/10.36922/msam.2672