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In this paper, we propose double-arrowed auxetic metamaterials (DAMs) featuring bidirectional wall thickness gradients. Their crushing behavior under low-velocity impact is systematically investigated using a validated finite element (FE) model. The results show that the bidirectional gradient design effectively improves the transverse necking effect observed in uniform DAMs. The bidirectional gradient configuration contributes to improved energy absorption and impact strength. Specifically, there is a 60.7% increase in specific energy absorption (SEA) and a 40.5% improvement in plateau stress, compared to uniform DAMs. Furthermore, the bidirectional gradient configuration reduces the initial peak stresses generated during the dynamic crushing process and exhibits higher crash load efficiency (CLE).

This study investigates the specific energy absorption (SEA) capacity and auxetic behavior of the PCSs subjected to the low-velocity impact (LVI). VeroWhite resin is selected as the base material. Instead of traditional energy absorption studies conducted across varying loading velocities or cyclic layers, we investigate the PCSs’ energy absorption capacity through a parametric study employing an orthogonal design. Three structural geometric parameters are considered as factors, with each factor comprising four levels. The orthogonal table yields 16 unique combinations, corresponding to 16 PCSs with distinct geometries. The collective SEA assessment of these combinations identifies the “optimum combination”, whose exceptional SEA capacity demonstrates the feasibility of the proposed approach for tailoring the SEA properties of cellular structures. Additionally, the findings reveal that incorporating a convex feature into the geometry of conventional re-entrant honeycomb structures significantly influences their energy absorption capabilities. This work introduces a new and simple method for conducting parametric studies on the mechanical properties of cellular structures, enabling the identification of peak values. The employed strategy also holds promise for investigating the acoustic and thermal properties of honeycomb structures.

A novel structure resembling plant stems, termed bio-inspired fractal plant stems multi-cellular circular tubes (BFPMC), was developed by incorporating fractal plant stem characteristics into smaller circular tubes within larger ones. The crashworthiness of this structure under axial impact was investigated using a validated LS-DYNA finite element model. The energy absorption performance of BFPMC tubes, varying in the number of branches, fractal orders, and inner circular diameters, was numerically studied. The numerical findings reveal a 19.27% increase in specific energy absorption (SEA) for BFPMC with $D_i=30$mm compared to $D_i=0$mm, indicating that filling a single circular tube can enhance the structure’s impact resistance. Subsequently, structural parameters conducive to excellent energy absorption characteristics were determined for various combinations of a number of branches, fractal order, and inner circle diameter parameters. These results offer valuable insights for designing multi-cellular double tubes with high energy absorption efficiency.

To enhance the crashworthiness of thin-walled structures, this study proposes a self-similar nested hierarchical hexagonal tube. This innovative design incorporates the hierarchical technique into the structural configuration of hexagonal thin-walled tubes. Numerical analysis, conducted using a validated finite element model, reveals that the proposed self-similar nested hierarchical hexagonal tube (SNHHT) significantly enhances energy absorption compared to traditional hexagonal tubes, maintaining consistent wall thickness and mass conditions. Particularly noteworthy is the improvement in energy absorption indexes under the same mass condition, with SNHHT-4 demonstrating enhancements of up to 76.45% and 86.84% in energy absorption and crushing force efficiency, respectively, while concurrently achieving a 4.11% reduction in initial peak crash force. Subsequently, a parametric study exploring wall thickness, shape factor, and various rib thicknesses was performed to investigate structural crashworthiness. Finally, employing the simplified super-folded element method, the theoretical formulation of mean crushing force was derived, and its accuracy was validated through numerical simulations.

Due to the high energy absorption capability and excellent bending strength of the sandwich panels, they are mostly preferred as protective structures against explosive blast attacks. The evaluation of their blast-mitigation characteristics through experiments is highly dangerous, costly, time-consuming, and polluting for the environment. Therefore, in this presented work, a series of numerical analyses were performed to evaluate the blast mitigation of the outstanding sandwich panels with honeycomb, corrugated, auxetic, and foam cores. The masses of sandwich panels were kept constant, and their areal densities were maintained constant throughout the study to effectively compare their performance under identical air blast loading conditions. To apply the air blast loads to the designed sandwiches, 1–3kg of spherical-shaped trinitrotoluene charges were used for a 100mm stand-off distance. The sandwiches are made of high-strength AL-6XN steel and crushable aluminum foam. The rate-dependent Johnson–Cook constitutive model of plasticity and the crushable foam model with volumetric hardening were used for the evaluation of sandwich panels’ plastic deformations. The findings of the work depicted that the honeycomb core is more efficient than the other core structures of the same masses because the sandwich panels with honeycomb core provide smaller back skin deflections, globalized core crushing, and higher core energy absorption than the other sandwich panels for extreme conditions of air blast loading.

Negative stiffness (NS) structures have singular mechanical properties and potential applications in various scenarios. A corrugated tube (CT) and an NS lattice structure (NLS) composed of CTs and connection plates are proposed. The mechanical properties of CT and NLS under axial compression are investigated by experiments and simulations. The deformation modes of CT and NLS are layer-by-layer folding of structural layers. The influences of geometric parameters on the compression performance of CT and NLS have been studied. Through a reasonable design of the thickness of upper and lower conical structures, CT and NLS can exhibit periodic changes in peak and valley forces during the compression process, resulting in significant NS behavior. In addition, the increase of CT’s number does not significantly affect the NS effect, and the load-carrying capacity of NLS increases significantly as the number of CT increases. The energy absorption (EA) and peak force values of NLS-$4\times 4$, NLS and NLS-$2\times 2$ are approximately 16, 9, and 4 times those of CT-3.0-0.6-f0.5, and the EA value of an NLS model is the sum of the EA values of its all CTs. In addition, the effects of geometric parameters on the mechanical properties of NLS are systematically investigated. With reasonable parameter values, NLS exhibits strong NS effect and excellent EA capacity.

The integration of smart materials with metamaterials offers significant research value in additive manufacturing. This paper proposes a novel approach combining shape memory polymers (SMP) with zero Poisson’s ratio (ZPR) metamaterials to create better space-filling, lightweight, and high-energy absorbing materials. A cellular structure with three deformation processes was designed by adjusting the rib arm lengths of the ZPR lattice AuxHex, forming a 3D gradient structure. The cellular units were also prepared using the dual-nozzle fusion filament printing technique, and the energy absorption and shape recovery properties of various hierarchical gradient structures, compared to the uniform structure, were simulated and analyzed using the viscoelastic intrinsic model. The results indicate that all gradient structures exhibit superior energy absorption capabilities compared to uniform materials, with the energy absorption performance of the optimal gradient material being 44.32% higher than that of the nongradient material, and they also enhance the shape recovery performance to some extent. Furthermore, it was observed that when a lattice layer, which avoids internal rib contact throughout the compression process, is positioned in the middle layer, it harmonizes the deformation of the upper and lower layers, thereby improving overall stability. This configuration enhances both energy absorption and partial shape recovery performance, offering a novel approach for the design of smart material assemblies with graded metamaterial structures. This study provides a new perspective and methodology for the future design of supergradient smart material collections.

Crashworthiness research has attracted significant attention, focusing on evaluating deformation behavior and selecting composite material components that act as energy-absorbing devices. Among the available composite materials, carbon fibers can absorb high energy during a crash. This paper presents the initial concept of the design application of a carbon fiber Belleville spring. The proposed design of the mechanism is directed to reduce the extent of the impact. An analytical approach is followed to calculate the energy absorbed during a crash. The parametric study is conducted for a different range of load $22250\le F\le 27000$N to predict which spring material absorbs maximum energy. The impact on the occupant side is minimum by the finite element approach. A brief overview of the spring’s energy absorption capability is provided through Ansys, and a correlation is proposed, which helps predict the value of Energy for different loads.

The low frequency vibration energy absorption properties of granular materials have been investigated on an Invert Torsion Pendulum (ITP). The energy absorption rate of granular material changes nonlinearly with amplitude under low frequency vibration. The frequency of ITP system increases a little with granular materials in the holding cup. The vibration frequency of ITP system does not change with time.

This paper deals with the crash energy absorption and the local buckling characteristics of the expansion tube during the tube expanding processes. In order to improve energy absorption capacity of expansion tubes, local buckling characteristics of an expansion tube must be considered. The local buckling load and the absorbed energy during the expanding process were calculated for various types of tubes and punch shapes with finite element analysis. The energy absorption capacity of the expansion tube is influenced by the tube and the punch shape. The material properties of tubes are also important parameter for energy absorption. During the expanding process, local buckling occurs in some cases, which causes significant decreasing the absorbed energy of the expansion tube. Therefore, it is important to predict the local buckling load accurately to improve the energy absorption capacity of the expansion tube. Local buckling takes place relatively easily at the large punch angle and expansion ratio. Local buckling load is also influenced by both the tube radius and the thickness. In prediction of the local buckling load, modified Plantema equation was used for strain hardening and strain rate hardening. The modified Plantema equation shows a good agreement with the numerical result.

A nonlinear elasto-plastic phenomenological constitutive model for aluminum alloy foams subjected to quasi-static and dynamic compression is proposed. The six-parameter model can fully capture the three typical features of stress-strain response, i.e., linearity, plasticity-like stress plateau, and densification phases. Moreover, the parameters of the model can be systematically varied to describe the effect of initial density of foams that may be responsible for changes in yield stress and hardening-like or softening-like behavior at various strain rates. The experimental results at various loading rates are provided to validate the model. It is shown that the proposed model can be used in the selection of the optimal-density and energy absorption foam for a specific application based on certain design criteria.

In this study, an arbitrary shaped acoustic omnidirectional absorber (AOA) is achieved for absorbing incoming acoustic/elastic waves in the ambient environment. Using the transformation acoustics theory, we present a theoretical framework for two-dimensional acoustic path guidance around arbitrary shapes for which the material parameters in the transformed space can be obtained analytically. Results indicate that the transformed space is distorted rather than compressed; numerical simulations confirm that these absorbers exhibit a remarkably large absorption and that the proposed method can control acoustic absorption for arbitrary geometries of interest. This method can potentially be applied to sound absorption and noise control.

The current scenario focuses on lightweight and better energy-absorbing structural materials for critical engineering applications in aerospace, automobiles, marine, electronic, and implant materials for biomedical industries. The magnesium-based syntactic foams are the preferred choice of material in the same category due to their lightweight, higher plateau strength, better damping characteristics, and excellent energy absorption behavior. Many works were reported based on the polymer and aluminum-based syntactic foams and their developments. However, the rapidly increasing interest in magnesium-based syntactic foams and the adoption of the applications are still at a nascent stage. This proposed review work comprehensively insights the magnesium-based syntactic foam; various hollow filler material usages and summarizes the influence of physical and mechanical behavior on processing routes and future research opportunities for applications.

Blast-resistant structures are traditionally designed with solid materials of huge weight to resist blast loads. This not only increases the construction costs, but also undermines the operational performance. To overcome these problems, many researchers develop new designs with either new materials or new structural forms, or both to resist the blast loads. Friction damper, as a passive energy absorber, has been used in earthquake-resistant design to absorb vibration energy from cyclic loading. The use of friction damper in blast-resistant design to absorb high-rate impact and blast energy, however, has not been well explored. This study introduces a new sandwich panel equipped with rotational friction hinge device with spring (RFHDS) between the outer and inner plates to resist the blast loading. This device RFHDS, as a special sandwich core and energy absorber, consists of rotational friction hinge device (RFHD) and spring. The RFHD is used to absorb blast energy while the spring is used to restore the original shape of the panel. This paper studies the mechanism of RFHD by using theoretical derivation and numerical simulations to derive its equivalent force–displacement relation and study its energy absorption capacity. In addition, the energy absorption and blast loading resistance capacities of the sandwich panel equipped with RFHDS are numerically investigated by using Ls-Dyna. It is found that the proposed sandwich panel can recover, at least partially its original configuration after the loading and thus maintain its operational and blast-resistance capability after a blasting event. In order to maximize the performance of the proposed sandwich panel, parametric calculations are carried out to study the performance of RFHDS and the sandwich panels with RFHDS. The best performing sandwich panel with RFHDS in resisting blast loadings is identified. This sandwich panel configuration might be employed to mitigate blast loading effects in structural sandwich panel design.

Metastructures are extensively used in aerospace engineering. In the present work, a high-strength structure was designed based on a reentrant hexagonal honeycomb (RHH) by topology optimization. To generate a negative Poisson’s ratio (NPR) effect, topologically optimized cells were alternately arranged with RHH cells to obtain a hybrid hexagonal honeycomb (HHH). In comparison with other NPR structures, this structure had superior energy absorption characteristics. In addition, the mechanical properties and deformation behavior of this structure were analyzed. Finally, single, double, and triple functional gradients were introduced into the HHH. It was found that the introduction of functional gradients improved the energy absorption capacity of the structure, and that the energy absorption capacity increased with the increase in the number of functional gradients.

In this paper, we propose a new multicellular design of assembled multi-frusta with alternate orientations and varied taper angles for effective energy absorption applications. Extensive crush test experiments, comprehensive finite-element simulations and analytical modeling were carried out to evaluate the energy absorption performance of the newly proposed multicellular assemblies. The performances of these assemblies are calibrated against conventional assembly of uniform tubes. Two aspects of the work were parametrically examined. The first was concerned with the effect of the frusta taper angle, while the second was concerned with the multi-frusta layout on the energy absorption of the proposed multi-frusta assembled structures. The results reveal that the face centered square layout with an appropriately selected taper angle possesses the optimal high specific energy absorption, low peak force, and smooth crushing force curve, which makes it a crashworthy device.

In this paper, two center-symmetric chiral honeycombs (CSCH-1 and CSCH-2) were designed through a center-symmetric approach. Corresponding samples were prepared using 3D printing technology, and in-plane impacts were carried out under quasi-static experiments with the conventional chiral honeycomb (CH). The experimental results show that CSCH-1 and CSCH-2 have better load-bearing capacity and energy-absorbing properties than CH. The mean stress of the two increased by 40% and 60%, and the energy absorption (EA) increased by 92.10% and 101.90%, respectively, compared to CH. Furthermore, the design of CSCH-2 effectively controls the expansion and deformation of the structure, and shows better negative Poisson’s ratio effect. Subsequent finite element modeling was performed using the finite element software Abaqus/Explicit, and the accuracy of the finite element model was verified. Furthermore, the in-plane impact mechanical behavior of CH, CSCH-1, and CSCH-2 was investigated at different impact velocities, various nodal circle radii, and different orthogonal array ratios.

This paper introduces a biomimetic gradient hierarchical multicellular structure consisting of two tree-like fractal variants: one based on vertex connections (HCV) and the other based on wall connections (HCW). We investigate their mechanical behavior and deformation through numerical simulations. Our findings reveal that, irrespective of whether they have the same wall thickness or mass, second-order and third-order structures exhibit superior energy absorption capacity (EA) and crushing force efficiency (CFE) compared to first-order structures, resulting in significantly enhanced crashworthiness performance. In the case of HCV structures with identical wall thickness, the third-order structure outperforms the first-order structure by 79.73% in specific energy absorption (SEA) and by 38.51% in CFE. Similarly, for HCW structures, the third-order variant surpasses the first-order one by 45.57% in SEA and 28.39% in CFE. We also conduct a parametric study, exploring the influence of inner circle diameter, fractal coefficient, and fractal angle on the crashworthiness of biomimetic gradient hierarchical multicellular structures. We identify the optimal fractal coefficient and inner diameter distribution range for HCV when the fractal angle is 60${}^{\circ }$. Lastly, we compare these structures with traditional multicellular tubes, demonstrating that biomimetic gradient hierarchical multicellular tubes achieve up to 50.34% higher SEA and 55.13% higher CFE. The results of this study offer valuable design insights for developing lightweight and efficient energy-absorbing structures.

This paper presents the investigations made on the effect of impact response of glass fiber-reinforced epoxy nanocomposites. The laminates are prepared using 6 layers of glass woven roving mates of 610 gsm and MMT clay content varied from 0%, 1%, 3% and 5%. The prepared composite laminates were subjected to low-velocity impact with energy of 18 J. The methodology used for the impact test is based on the ASTM D3029 standard. During these impact tests, load–time histories, Peak load and absorbed energy were recorded by load cell. The incorporation of 1% and 3% nanoclay lead to higher load bearing capacity and energy absorption. Damages produced on the front and back surfaces of the samples were analyzed by visual inspection methods and scanning electron microscope.

Thin-walled structures are used in automotive industry due to their excellent lightweight and crashworthiness properties. This paper proposes a vertex fractal multi-cell hexagonal structure to develop a novel lightweight energy absorber. Experimental analysis and numerical modeling are performed to investigate the crashworthiness of the fractal multi-cell hexagonal structures. The numerical results indicate that fractal configurations and geometrical parameters of the fractal hexagonal structure have significant effect on the crashworthiness. In addition, the multi-objective design optimization is performed to seek the optimal crashworthiness parameters and explore the optimal crashworthiness of the fractal hexagonal structure. The results show that the fractal multi-cell hexagonal structure outperforms non-fractal hexagonal structure.