Page 41 - MSAM-1-4

Materials Science in Additive Manufacturing Acoustic performances of SC lattices fabricated by DLP

One of the critical properties is acoustic performance, fabricated through template replication processing. A good
including sound absorption and sound insulation, which agreement between the numerical and experimental
is highly structural-dependent for lattice material. In the results was observed. The model was also used alongside
history of AM development, various technologies emerged the TMM with minor modifications to model the sound
to overcome the difficulties of the AM processes. They can absorption properties of functionally graded metal foams
be divided into three large groups, mainly liquid-based, with a finite number of layers with great accuracy .
[18]
powder-based, and solid-based processes. In general, the A less conventional approach in the acoustic modeling of
liquid-based processes use photosensitive polymers as lattice structures is to view such lattices as resonant materials
raw materials and ultraviolet (UV) light as energy source. similar to Helmholtz resonators [19,20] and microperforated
These liquid-based technologies generally have some panels (MPP) [21,22] . In a recent work on the sound absorption
advantages, such as cost-effectiveness, high dimension performances of microlattices, the sound and energy
accuracy, good surface finish, and a wide range of available absorption of four classes of plate and truss microlattices
materials. But they also have some shortcomings, such based on the faced-centered cubic (FCC) crystal structure
as post-processing requirements, relatively small build were investigated . Sound absorption measurements on
[23]
volumes, and no multi-materials capability. For solid- metal lattice samples of various geometries and the number of
based processes such as material extrusion, thermoplastics layers revealed that there exist various numbers of resonance
filaments and metal wires are primarily used as base peaks with absorption coefficients near one. The number of
materials, and heat energy or electron beams are used as an resonance peaks in the frequency range corresponds to the
energy source. The advantages of these processes include number of layers, with the first peak occurring at the lower
multi-material parts fabrication, ease of structure removal frequencies when the number of layers is increased. It was
and minimal material wastage. However, these processes proposed in the work that the modeling of the characteristic
tend to suffer from relatively poor dimensional accuracies impedance based on a modification of major research work
and surface finishes, limited material choices and relatively by Maa et al. , which assumes the cavities as a set of micro-
[21]
high energy consumption. In addition, as for powder- perforations, was a viable method that can model such
based technologies, they mainly exploit the high-energy lattices with great accuracies.
laser and electron beam as an energy source and powder
form material including thermoplastics and metals, with From the above case studies, the mechanisms of sound
the latter being the more common class of materials. These propagation and dissipation can be modeled by methods
technologies can present fast, with no support structure, that may vary significantly in physics. It takes a trained
large build volume and have additional part function researcher in the acoustics community to determine with
processing. Furthermore, due to the lack of development, confidence the most appropriate mathematical model
the materials are limited and surface finish and accuracy to model the acoustic properties of lattice structures of a
are relatively poor, and the energy consumption is the particular geometry, especially if the geometry is novel.
highest among the total technologies, which are the Even for the same lattice design, the physics of sound
main disadvantages of the powder-based processes. The propagation can vary widely with changes in its design
detailed information for liquid-, solid-, and powder-based parameters such as unit cell size and strut width. Such
technologies are summarized in Supplementary Text 1 (in difficulty in determining the most appropriate modeling
Supplementary File). approach arises as there is very few concrete acoustics
design guidelines dedicated to lattice structures in the
While the complex interior structure of engineered
lattices makes it difficult to analyze their acoustic literature.
properties, there exist many mathematical models that In this work, the acoustic properties of truss lattice
aim to characterize the sound absorption or transmission structures based on the simple cubic (SC) crystal structure
properties of porous materials. These models include were investigated. Many samples of SC-Truss lattices of
the classical Delany-Bazley (DB) model , the Johnson- varying unit cell lengths and strut radii were fabricated
[8]
Champoux-Allard model [1,9] , the Biot theory [10,11] , and the using vat photopolymerization and their sound absorption
transfer matrix method (TMM) [12,13] . Furthermore, the properties were measured using an impedance tube. This
parameters for the above models may be obtained through work also investigated the use of both the DB model and
measurements, analytical, or empirical methods [1,14-16] . the TMM with resonator theory, referred to herein as the
For instance, research on the sound absorption efficiency multi-layered micropore-cavity (MMC) model, to model the
of IN625 foams has been proposed by Zhai et al. The sound absorption performances of the SC-Truss lattices and
[17]
classical DB model using a tetrakaidekahedral unit cell was compared them with the experimental results. Thereafter,
employed to predict the performance of foams, which are some numerical models and guidelines were proposed to

Volume 1 Issue 4 (2022) 2 https://doi.org/10.18063/msam.v1i4.22