Enhancement by Metallic Tube Filling of the Mechanical Properties of Electromagnetic Wave Absorbent Polymethacrylimide Foam

Abstract

By the addition of a carbon-based electromagnetic absorbing agent during the foaming process, a novel electromagnetic absorbent polymethacrylimide (PMI) foam was obtained. The proposed foam exhibits excellent electromagnetic wave-absorbing properties, with absorptivity exceeding 85% at a large frequency range of 4.9–18 GHz. However, its poor mechanical properties would limit its application in load-carrying structures. In the present study, a novel enhancement approach is proposed by inserting metallic tubes into pre-perforated holes of PMI foam blocks. The mechanical properties of the tube-enhanced PMI foams were studied experimentally under compressive loading conditions. The elastic modulus, compressive strength, energy absorption per unit volume, and energy absorption per unit mass were increased by 127.9%, 133.8%, 54.2%, and 46.4%, respectively, by the metallic tube filling, and the density increased only by 5.3%. The failure mechanism of the foams was also explored. We found that the weaker interfaces between the foam and the electromagnetic absorbing agent induced crack initiation and subsequent collapses, which destroyed the structural integrity. The excellent mechanical and electromagnetic absorbing properties make the novel structure much more competitive in electromagnetic wave stealth applications, while acting simultaneously as load-carrying structures.

Effect of Absorbent Foam Filling on Mechanical Behaviors of 3D-Printed Honeycombs

“…Unlike empty honeycomb under L-direction (L-EH), the absorbent-foam-filled honeycomb ( Figure 4 a, L-FH-1) under L-direction exhibited foam-like features, i.e., the three typical regions, namely linear, plateau, and densification regions [ 38 ]. Figure 4 a shows that absorbent-foam-filling led to a significant reinforcement of the compressive performance, as compared with the empty honeycomb.…”

“…Typical specimens of empty honeycomb and absorbent-foam-filled honeycomb were shown in Figure 2 . The electromagnetic-wave absorption of the absorbent PMI foam and PLA 3D-printed honeycomb based on metamaterial absorber were measured in earlier studies [ 8 , 38 ]. The PLA 3D-printed honeycomb with resistive films and carbon-based absorbent PMI foam exhibited excellent electromagnetic-wave-absorption properties.…”

“…Therefore, the purpose of present study was to design a hybrid structure with excellent mechanical performance and electromagnetic-wave-absorption properties, based on previous study [ 8 , 38 ]. The absorbent polymethacrylimide (PMI) foam with absorptivity exceeding 85% at a large frequency range of 4.9–18 GHz and 3D-printed honeycomb with absorptivity exceeding 90% at a large frequency range of 3.53–24.00 GHz were offered.…”

Polymeric Foams

“…The authors demonstrated the efficient formation of conductive networks by using both types of fibers during foaming, resulting in specific EMI shielding effectiveness values from 10 to 60 dB. In the same way, Yan and co-workers [18] have considered the development of polymethacrylimide (PMI) foams with improved EMI shielding performance, focusing on EMI absorption, by adding electromagnetic absorbers during foaming, and combining said foam with metallic tubes to guarantee proper compressive performance, thereby creating a component that could find interesting applications in electromagnetic wave stealth load-carrying structural applications. Abbasi and co-workers [19] have developed microcellular polyetherimide (PEI) nanocomposite foams containing low amounts of graphene nanoplatelets, being able to reach high electrical conductivities while significantly reducing density, which could enable their use in cutting-edge sectors such as aerospace or telecommunications for applications requiring electrostatic discharge (ESD) or EMI shielding.…”

Effects of Aluminum Foam Filling on Compressive Strength and Energy Absorption of Metallic Y-Shape Cored Sandwich Panel

“…The foam-filled corrugated panel has also been demonstrated to have enhanced blast resistance behavior compared with empty panels [31]. Besides foam filling, metallic [32][33][34] and composite [35,36] tubes are also effective in enhancing the strength and energy absorption of metallic foams [32], polymeric foams [33,35,36], and aluminum honeycombs [34]. In conclusion, foam filling and tube enhancement are two effective methods of increasing the specific strength and energy absorption of lattice and foam structures.…”