Page 99 - ESAM-1-1

Engineering Science in
Additive Manufacturing Mechanical property of metal-based IPC

for its excellent mechanical properties, was selected as and 75 MPa, respectively. The model was discretized
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the matrix material for the truss lattices. Following the using 4-node linear tetrahedron elements (C3D4),
completion of printing, the as-printed metal specimens with mesh sizes of 0.3 mm for the truss microlattices
underwent post-processing procedures, including the and 0.5 mm for the epoxy resin after considering mesh
removal of residual powder, stress relief treatment, convergence. General contact conditions were applied,
ultrasonic cleaning, and drying in a convection oven. assigning dynamic and static friction coefficients of 0.2 and
0.15, respectively.
2.2.2. Epoxy infiltration

The IPC specimens for each structure were fabricated 2.3.3. Evaluation indicators
through a vacuum epoxy infiltration method, as shown To quantitatively evaluate the compressive performance
in Figure 1B. The epoxy resin was prepared by mixing of the metamaterials, total energy absorption (TEA),
EPOLAM 2040 resin with the hardener at a weight ratio SEA, and compressive strength were introduced as key
of 100:39. The SLM-fabricated metal lattice specimens performance indicators. TEA represents the total energy
were then placed in custom-designed molds, which were absorbed during deformation, whereas SEA normalizes
subsequently filled with thoroughly mixed epoxy resin. this value by the specimen mass. Energy absorption
To eliminate trapped air and ensure complete infiltration, efficiency (EAE) is introduced to identify the densification
the molds underwent a vacuum treatment at −0.1 MPa point. Beyond the final EAE peak, the structure exhibits
for 30 min. This process was repeated 3 times. Then, the significant hardening. Compressive strength refers to the
molds were placed in an oven for thermal curing at 80°C maximum stress that the metamaterials can sustain before
for 30 min, allowing the epoxy resin to solidify properly. failure. The mathematical definitions of these evaluation
After curing, excess resin was removed, and the specimens indicators are summarized as follow:
were carefully cut and polished to achieve the final IPC d
metamaterials. TEA 0 F xdx() (I)
2.3. Evaluation methods SEA = TEA/m, (II)
2.3.1. Mechanical testing EAE = TEA/F (x), (III)
Quasi-static compression tests were performed using Where d and F(x) represent the compression distance
the Shimadzu AG25-TB testing machine (Shimadzu and instantaneous load during the quasi-static tests, and m
Corporation, Japan). The specimens were positioned denotes the specimen mass.
between two rigid plates, with the upper plate applying
downward compression at a strain rate of 0.001/s until the 3. Results and discussion
structure fully collapsed, according to ISO 13314:2011. 3.1. Compressive response
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Three independent repeat experiments were conducted for
each specimen to ensure the consistency and reliability of Figure 2 illustrates the mechanical response and indicators
the statistical results. The compressive load-displacement for various metamaterials. Figure 2A-C present the
data were recorded throughout the testing process, while engineering stress-strain relationships and von Mises
the deformation behavior was captured using a digital stress distribution patterns of the truss metamaterials
camera. The data were presented with standard deviations (FCC, FCCR, and FCCH).
at the 95% confidence interval. All three truss microlattices exhibit a layer-by-layer
catastrophic collapse behavior with fractures primarily
2.3.2. Finiment element analysis method occurring at the node positions. Due to structural disorder
To complement the experimental tests, finite element caused by damage, the subsequent von Mises stress is
analysis (FEA) was performed using Abaqus/CAE 2022 distributed predominantly near the fractured locations.
(Dassault Systèmes Simulia Corp., USA). The simulation The FCCR unit cell demonstrates a more uniform
setup replicated the experimental conditions by placing stress distribution, indicating the positive role of ribs in
the lattice metamaterials between two rigid plates. With optimizing the load flow path. In contrast, the failure of
the kinetic energy to internal energy ratio considered to be diagonal struts results in the loss of connectivity between
<5%, the loading velocity was set to 1 m/s to ensure quasi- the inner small-scale geometry and the overall structure
static deformation conditions. Material properties for in the FCCH microlattice. This causes excessive stress
Ti-6Al-4V and epoxy resin were assigned based on their to concentrate on the thinner external struts, which are
respective densities 4.42 g/cm³ and 1.18 g/cm³, Young’s designed to maintain constant relative density, leading to
moduli 110 GPa and 2 GPa, and yield strengths 880 MPa premature structural collapse.

Volume 1 Issue 1 (2025) 4 doi: 10.36922/esam.8554