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Abstract This paper mainly concerns effects of the auxetic structure on the crash performances in terms of the axial crash force, specific energy absorption, and deceleration, which are evaluated with the conventional and honeycomb structures. Based on the systematic design procedure, the re-entrant units for the auxetic structure are regularly arranged in the tube wall, which are produced by the additive manufacturing with SUS316L metal powder. Under the low impact condition, the auxetic does not only exhibit higher specific energy absorption, but also demonstrate substantially low deceleration due to effect of the densification during the axial crash compared with the conventional tube. Furthermore, while the honeycomb tube demonstrates oscillating behavior in the deceleration, the auxetic tube tends to maintain steady deceleration after the first peak during the axial crash, which is able to guarantee enhanced damping performances under the low impact condition. [ABSTRACT FROM AUTHOR]

Lattice truss reinforced honeycombs (LTRHs), termed honeytubes, were developed based on a hybrid design of micro-lattice truss and square honeycomb topologies. Carbon fiber reinforced composite and polymer LTRHs were fabricated using different manufacturing approaches. Out-of-plane compression tests were performed on the LTRHs, and the properties were compared with the conventional square honeycombs. The stiffness and strength values of composite LTRHs didn’t surpass those of composite square honeycombs due to the manually induced defects. On the other hand, polymeric LTRHs with perfect geometries were stiffer and stronger than the corresponding polymeric square honeycombs. A parametric study of the buckling resistance was carried out via finite element analysis, and the results indicated that hollow lattice stiffens honeycombs and increases the resistance to buckling, while the specific properties of honeytubes depend on their geometrical parameters. Moreover, the crush force efficiency and specific energy absorption were greater than those of square honeycombs and hollow lattice. This work demonstrates that hybrid designs that capitalize on micro-topologies can populate vacant regions in mechanical property charts, and provide increased energy absorption as crushing protection structures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spinal interbody cages adapted for an auxetic, and honeycomb using standard CAD software operations and manufactured with SLM. • Auxetic-based cages exhibit higher strength properties than honeycomb-based cages. • The stiffness of the auxetic cages is comparable to stiffness of human cortical bone. • The honeycomb cages exhibit lower value of Young's modulus closer to that for vertebrae. This paper presents a method for modeling a biomedical device by adaptation a commercially available interbody cage for an auxetic metamaterial and honeycomb structure using standard operations in Computer-Aided design software. The mechanical properties of experimental prototypes of Ti-6Al-4 V cages made by selective laser melting using computer modeling (finite element analysis), static and low-cycle fatigue compression tests (up to 3500 cycles) are characterized. 3D printed cells with structures with an angle of inclination between cell edges of less than 90˚ (auxetic metamaterial) are shown to exhibit higher static compressive strength and fatigue resistance than cells based on structures with an angle of inclination greater than 90˚ (honeycomb structure). The changes in the inclination angle differently affect to the porosity and consequently to mechanical behavior of auxetic metamaterial and honeycomb structure. The Young modulus of the auxetic-based interbody cage is 6.68 ± 0.28 GPa and comparable to the elastic modulus of human cortical bone. The honeycomb-based cage exhibits lower values of Young modulus (1.19 ± 0.03 GPa) close to that of trabecular bone and vertebrae. Importantly, the auxetic-based cage is not destroyed after 3500 cycles under 14 kN load with residual deformations ≤ 1 % (0.21 ± 0.10 mm displacements). [ABSTRACT FROM AUTHOR]

Integrated lightweight metastructures with microwave absorption and mechanical properties are of great significance in practical applications, but so far relevant study is still lacking. In this paper, an integrated lightweight gradient honeycomb metastructure (GHM) was proposed using 3D printing and screen printing technologies. Using the equivalent circuit method (ECM), we provided an in-depth analysis of how to broaden the absorption bandwidth and derived the mathematical formula of the equivalent resistance of the hexagon loop. The simulation results reveal that the proposed metastructure has the characteristics of broadband absorption, polarization insensitivity, oblique incidence stability, and radar cross section (RCS) suppression in the operating frequency range. The measured results are in good agreement with the simulation ones. In addition, the compression test results show that the metastructure has good compression strength. This work provides a route to achieve integrated metastructures with thin, lightweight, excellent absorption and mechanical properties. [ABSTRACT FROM AUTHOR]

• A kind of two-layer oblique honeycomb sandwich structure of flaky carbonyl iron powder/photosensitive resin composites with high precision was prepared by liquid crystal display (LCD) 3D printing method. • The structure is beneficial to improve the microwave absorption strength, and has the characteristics of light weight and low material consumption. • LCD 3D printing technology has the advantages of high precision, free forming and less time consumption. Carbonyl iron powder (CIP) is one of the most widely used magnetic loss absorbents due to its high saturation magnetization, strong wave absorption performance and low cost. However, CIP has a very high density (7.86 g/cm2) and requires a high addition amount (more than 50 wt%) when used as a microwave absorbing filler, which leads to high weight and low mechanical properties of the composite. Taking the diverse attenuation mechanisms during the electromagnetic energy conversion process into considerations, this paper designs a two-layer oblique honeycomb sandwich structure, which was prepared by liquid crystal display (LCD) 3D printing. This structure combines porous structure with strong absorbing materials to achieve strong electromagnetic wave (EMW) absorption performance at low concentrations and improve mechanical properties. When the inclined honeycomb core angle is 15° with only 15 wt% FCIP addition, the EMW absorption and mechanical properties of the composite are significantly improved compared with the full-filled structure. [ABSTRACT FROM AUTHOR]

Re-entrant honeycombs are one type of lightweight cellular materials with superior energy absorption and impact resistance. Yet, the mechanical properties of re-entrant honeycombs need to be further improved due to its bending-dominated deformation mechanism. In this study, we designed a novel stretching-dominated re-entrant honeycomb by combining the structural hierarchy and auxetic cellular configurations. Such hierarchical re-entrant honeycomb (H-ReH) is manufactured through fine-resolution 3D printing technique. The mechanical behavior and deformation mechanism of the designed H-ReH has been investigated through combined digital image correlation and finite element simulation. The 3D-printed H-ReHs exhibit enhanced specific stiffness, specific initial-buckling strength, structural stability and specific energy absorption capacity due to the uniquely combined deformation mechanisms. A competition between the 1st order and the 2nd order hierarchy has been revealed, which governs the mechanical properties of the H-ReHs. These findings provide thorough understandings and facilitate future design of lightweight but robust cellular materials. [ABSTRACT FROM AUTHOR]

Cellular auxetic materials possess a negative Poisson's ratio (NPR) and attractive mechanical properties; however, these materials are limited by their low stiffness and strength and strong anisotropy. To address these issues, we developed a novel auxetic honeycomb with a fully triangular architecture inspired by the anti-tetra chiral configuration. The new stretch-dominant structure was fabricated using a three-dimensional printing process. The resulting deformation behavior of the triangular auxetic honeycomb structure was compared with that predicted from finite element (FE) simulations; these revealed an NPR and high stiffness, in which the ratio of specific stiffness to specific density was 0.12. The simulations allowed for an NPR in both the longitudinal and transverse directions concurrently. Based on the mechanism revealed by the FE simulations, the novel triangular honeycomb can be tuned to have the same behavior in two orthogonal directions, while retaining high stiffness and an NPR. [ABSTRACT FROM AUTHOR]

This paper reports the failure and recovery mechanisms of 3D-printed lightweight honeycomb composites. Through this experimental study, we demonstrate the enhanced mechanical performance of 3D-printed composite structures and their ability for shape recovery under heat excitation. The remarkable mechanical performance of the reinforced honeycombs draws from the combination of the structural geometry and the tailored material composition. The results show that the addition of continuous fibers enables the honeycomb structure to avoid catastrophic failure even at high levels of deformation, which allows the shape memory effect to be activated and nearly 87% percent of the initial structural shape to be recovered. Moreover, the reinforced honeycombs exhibit enhanced properties: the specific energy absorption and specific stiffness of the reinforced honeycombs are up to 2 times greater than those of the conventional honeycombs. These enhanced mechanical properties combined with the controllable shape recovery of the 3D-printed structures can be used in the design of novel energy absorbing and protective material systems, biomedical devices, and actuators. [ABSTRACT FROM AUTHOR]

To systematically and comprehensively investigate the in-plane compression behavior of star-triangular honeycomb (STH) under quasi-static load, a group of specimens were fabricated by additive manufacturing technology and a compression test was carried out. The results show that the deformation of STH is stable, and negative Poisson's ratio (NPR) effect is obvious in the 1-direction. However, this effect is weakened in the 2-direction. Subsequently, numerical simulation models were established to understand the small and large deformation behaviors of STH in detail. In accordance with the deformation mechanism of STH in different directions, theoretical analysis models were developed to predict their elastic modulus and Poisson's ratio, and the results were highly consistent with the numerical simulation results. Detailed parameter analysis shows that the influence of inclined angle θ on the elastic modulus and Poisson's ratio of STH is more obvious than that of t / l. Additionally, with the increase in the inclined angle, the deformation of STH has no obvious difference in the 1-direction while it is considerably different in the 2-direction. When the strain is small, the plateau stress of STH with the same cell-wall angle α is similar in different directions. Then, the value of plateau stress and duration of the plateau stage varies greatly with the increase of compression strain. Finally, the energy absorption capacity of STH in different directions was compared. The results show that the energy absorption capacity of STH in the 2-direction is much higher than that in the 1-direction. Furthermore, two energy-absorbing stages appear in the compression process of STH, among which the energy contribution of the second stage occupies the largest proportion. This study aims to provide guidelines for the engineering application of STH. [ABSTRACT FROM AUTHOR]