Citation: Nath, S.D.; Nilufar, S.
Performance Evaluation of Sandwich
Structures Printed by Vat
Photopolymerization. Polymers 2022,
14, 1513. https://doi.org/10.3390/
polym14081513
Academic Editors: Alberto
Campagnolo and Alberto Sapora
Received: 7 March 2022
Accepted: 6 April 2022
Published: 8 April 2022
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Article
Performance Evaluation of Sandwich Structures Printed by
Vat Photopolymerization
Shukantu Dev Nath and Sabrina Nilufar *
School of Mechanical, Aerospace, and Materials Engineering, Southern Illinois University Carbondale,
Carbondale, IL 62901, USA; shukantudev.nath@siu.edu
* Correspondence: sabrina.nilufar@siu.edu
Abstract:
Additive manufacturing such as vat photopolymerization allows to fabricate intricate
geometric structures than conventional manufacturing techniques. However, the manufacturing
of lightweight sandwich structures with integrated core and facesheet is rarely fabricated using
this process. In this study, photoactivatable liquid resin was used to fabricate sandwich structures
with various intricate core topologies including the honeycomb, re-entrant honeycomb, diamond,
and square by a vat photopolymerization technique. Uniaxial compression tests were performed
to investigate the compressive modulus and strength of these lightweight structures. Sandwich
cores with the diamond structure exhibited superior compressive and weight-saving properties
whereas the re-entrant structures showed high energy absorption capacity. The fractured regions
of the cellular cores were visualized by scanning electron microscopy. Elastoplastic finite element
analyses showed the stress distribution of the sandwich structures under compressive loading, which
are found to be in good agreement with the experimental results. Dynamic mechanical analysis
was performed to compare the behavior of these structures under varying temperatures. All the
sandwich structures exhibited more stable thermomechanical properties than the solid materials
at elevated temperatures. The findings of this study offer insights into the superior structural and
thermal properties of sandwich structures printed by a vat photopolymerization technique, which
can benefit a wide range of engineering applications.
Keywords:
vat photopolymerization; sandwich panels; cellular core structures; dynamic mechanical
analysis
1. Introduction
Sandwich panels are generally constructed with two facesheets separated by low-
density core cellular structures. The facesheets and the core can be made of different or
the same material. The mechanical properties of a sandwich panel depend mostly on the
topology of the core cellular structures as well as the materials of the core and facesheets,
and the geometry of the panel. The material of the facesheets and the topology of the
cellular structure can be chosen according to the application of the panel, such as structural
rigidity [
1
], energy absorption capacity [
2
], vibration and acoustic attenuation [
3
], thermal
insulation property [
4
], etc. Sandwich panels are extensively utilized in airplane wings
and bodies, lightweight sportswear, marine and military applications, thermal insulative
walls/roofs, vibration absorbing materials, and automotive parts [5–10].
Foams are first studied as the core materials among all other core types of sandwich
panels [
11
]. Foams are an excellent choice for compressive loading [
12
–
14
] but they offer
poor bending performance due to their bending-dominated architecture [
15
], and exhibit
prominent size effects [
16
]. Later, the randomly porous foam cores are replaced by defined
periodic cellular architectures. Among those, the most studied shape is the conventional
honeycomb structure. Honeycomb core is lightweight, strong, and a high energy absorbent
in the out-of-plane direction [
17
–
20
]. Rectangular and diamond shapes are also commonly
Polymers 2022, 14, 1513. https://doi.org/10.3390/polym14081513 https://www.mdpi.com/journal/polymers
