Page 61 - ESAM-1-2

Engineering Science in
Additive Manufacturing Multi-material additive manufacturing of metals

approach, Wei et al. simulated the MMAM of SS316L/W the series arrangement due to its stress–strain plateau,
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bimetallic structures using MM-LPBF, treating the bottom reduced fracture, and consistent plastic deformation. FEM
layer material as a substrate (Figure 16E). At the SS316L/W successfully predicted this behavior. Similarly, Zhang et
interface (top of Figure 16C), good wettability with the W al. investigated a Ti-6AL-4V/CuA/Al-Cu-Mg MMAM
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substrate was observed, and the cross-sectional melt pool gyroid lattice structure (Figure 17B) fabricated using
view (right-hand side) indicated that W did not melt and MM-LPBF. FEM analysis of a unit cell showed that the
no elemental mixing occurred. However, at the W/SS316L highest levels of equivalent stress and strain occurred at
interface (bottom of Figure 16E), the SS316L appeared the center of the inclined struts, indicating shear fracture.
on top of W rather than beneath it. This was attributed to Due to the differences in strength and stiffness between the
high energy density resulting in keyhole mode melting, Al-rich and Ti-rich regions, the upper portion of the lattice
as seen in the bottom right-hand side of Figure 16E. The deformed prior to the lower portion.
application of excess heat is due to significant differences Likewise, FEA-based compression testing on a
in thermal properties between SS316L and W. In a similar P21/SS316L bimetallic cylindrical structure fabricated
approach using CFD–DEM based methods, Wimmer using MM-LDED revealed significant stress and strain
et al. conducted a numerical simulation of melt accumulation during the test (Figure 17C). Stress
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pool dimensions in SS/Al and compared the results to concentration occurred around the circumference of
experimental data (Figure 16F), utilizing a meshless SPH the P21 region as ∆h percentage increased, while strain
method. primarily accumulated on the SS316L side. Throughout
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5.2. Mechanical behavior computational analysis the test, it was observed that the softer material absorbed
a larger portion of the strain, whereas the harder material
Finite element modeling (FEM) of MMAM structures is bore the majority of the stress. This behavior is clearly
crucial for predicting the mechanical behavior of complex depicted in the color intensity gradients in Figure 17A-C. It
designs, thereby supporting the optimization of material should be noted that due to limitations in software flexibility
distribution. Recent studies have applied and advanced and adaptability for AM structures—including bimetallic
various modeling software tools to address the structural or systems—models typically assume smooth surfaces (i.e.,
thermal qualification of designs using FEM. The presence neglecting surface roughness), the absence of defects or
of dissimilar materials with contrasting mechanical and porosity, and ideal, crack-free interfaces. As a result, FEA
thermal properties introduces complex residual stresses, results often exhibit notable discrepancies when compared
especially near the interface. FEM enables detailed with experimental data. Griffis et al. performed site-
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analysis of elastic and plastic deformation, residual stress specific MM structural FEM using local material properties
accumulation, interfacial stress distribution, and potential in the MM-LPBF bimetallic fusion zone, modeling the
failure mechanisms under various loading conditions. This interfacial region as an effective third material. Their FEA
modeling approach provides insights into the structural method was used to inform a localized redesign of the
reliability of MM structures and is essential for identifying fusion zone geometry to interlock material regions and
stress concentration zones and guiding design strategies improve the global pull-apart strength of the interface.
to mitigate defects such as warping, delamination, and Few studies have applied MM structural modeling
cracking. While most of these studies have been validated from a computational topology optimization design
using multi-polymeric structures, 201,202 due to the relative perspective. Giraldo-Londona et al. developed a multi-
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ease of fabrication compared to metallic structures, objective algorithm for the joint design of MM structures,
only a few have shown the capability of modeling and considering both structural and thermal load cases.
verifying metallic MMAM structures. McDonnell et al. For comprehensive reviews on multiobjective topology
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and Zhang et al. fabricated MMAM lattice structures optimization in MMAM component design, readers are
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using SS316L/17-PH and Ti-6Al-4V/CuA/Al-Cu-Mg, referred to Zhang et al. and Sanders et al., who provide
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respectively. McDonell et al. constructed a bimetallic detailed theoretical insights into the development of MM
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lattice structure composed of BCC and octet truss topology optimization algorithms.
architectures using MM-LPBF, with horizontal and vertical
material separations (Figure 17A). It was observed that 6. Discussion and future direction
the deformation behavior and stress–strain response of
the bimetallic lattice—featuring a combination of ductile 6.1. Feedstock recyclability and build material cross-
and brittle metals—varied with lattice arrangement. contamination
The parallel bimetallic lattice structure demonstrated Post-processing and recycling procedures for parts
superior energy-absorption performance compared to produced via metal AM using powder feedstock present

Volume 1 Issue 2 (2025) 29 doi: 10.36922/ESAM025180010