Energy Absorbing Structures Research Articles

Fully foldable mechanical metamaterials with isotropic auxeticity and its generated multi-mode folding form

Abstract Auxetic materials, a type of mechanical metamaterial with negative Poisson's ratios, are potentially utilized in the realms of energy absorption and engineering structures. However, most of the existing auxetic materials either contain a large amount of rotational motion or still have gaps when fully folded, which is not conducive to lifting loads. Besides, their application is limited to flexible environments due to their single-folding mode. To overcome such limitations, a fully foldable mechanical metamaterial with isotropic auxeticity is proposed by utilizing the Sarrus mechanism, and its generated multi-mode folding form is obtained in this paper. Then, the DOF, bistability and kinematic characterizations are analyzed to show the performance of the proposed structures. Finally, the parameters of the proposed fully foldable mechanical metamaterials are discussed to simplify the structures. Some prototypes are fabricated to validate the effectiveness and performance of the proposed mechanical metamaterials. The proposed mechanical metamaterials have some merits, such as isotropic auxeticity, being fully folded to achieve dense compression, being bistable with load-bearing capacity, multi-mode folding form, and one-DOF, and they have versatile potential applications in complex environments requiring high-impact resistance and flexible adaptation.

Effect of fractal dimension on mechanical behaviour and energy absorption of Menger sponge-inspired fractal structures

The Fractal Dimension (FD) of Menger Fractal Cubes (MFCs) defines their intricate geometry, making them ideal for lightweight structural applications. However, the effect of FD on their structural behaviour is largely unexplored. This study examines AlSi7Mg MFC geometries formed through a recursive process, with densities ranging from 40 to 1958 kg/m³, corresponding to FDs ranging from 2.35 to 2.73. Compression tests and simulations revealed that higher fractal orders increased densification displacement, achieving up to 80 % compressibility, with multi-level extended plateau regions indicating enhanced energy absorption. The fourth-order MFC with an FD of 2.35 and a density of 40 kg/m³ showed a specific energy absorption (SEA) of 6 J/g, demonstrating its potential for weight-efficient, energy-absorbing structures. The outcomes of this study indicate that total energy absorbed increases with an increasing FD, while crush efficiency improves as FD decreases showing better crashworthiness. Moreover, the structures exhibited unique force-displacement responses tailored to their FD. These findings offer valuable insights into optimising thin-walled fractal structures for various engineering applications by adjusting the FD to fine-tune relative density and enhance mechanical performance.

Optimizing mechanical properties and pioneering biodegradable polymer blends for superior energy-absorbing structures used in sport helmets

Replacing elements made of conventional plastics (like polystyrene) with biodegradable substitutes is part of the trend of sustainable development and waste reduction. The manuscript covers issues related to the design, manufacturing and testing of sports helmet protective inserts made of biodegradable material. The FEM numerical simulations carried out by the authors allowed to determine the optimal desirable mechanical properties (Re = 8.5–65 MPa, E = 500–8000 MPa for 30 × 30 mm inserts; Re = 10.5–60 MPa, E = 500–7500 MPa for 48 × 48 mm inserts; Re = 13–95 MPa, E = 400–8500 MPa for 55 × 55 mm inserts) and geometric parameters (wall thickness equal to 0.2–0.5 mm, height of 20 mm), ensuring the formation of a plastic fold, which is the most effective energy-absorbing mechanism. The conducted quasi-static compression, bending and dynamic tensile strength tests allowed to determine blends with appropriate proportions of durable PLA with more plastic PBAT, PBS and TPS that meet the established criteria: PLA50PBAT50, PLA30PBAT70 and PLA30TPS70.

An adaptive bionic sensor: enhancing ankle joint tracking with high sensitivity and superior cushioning performance

Flexible sensors are renowned for their rapid responsiveness, high flexibility, and outstanding mechanical properties, making them ideal for applications in wearable devices, sports and health monitoring, and human-machine interfaces. To enhance the sensing performance of these flexible sensors, researchers have drawn inspiration from nature, creating various bionic microstructures. However, these structures often manifest in the macroscopic form of thin films, which do little to improve impact resistance and joint protection. In response, this work achieves a highly sensitive and impact-resistant pressure sensor by integrating bionic principles at both micro and macro levels. Specifically, at the micro level, a muscle-like hydrogel system consisting of MXene nanosheets incorporated into the double network of polyvinyl alcohol and sodium alginate matrix is selected. At the macro level, the bionic prototypes of mimosa leaves and durian spikes with good energy absorption structure, together with octopus’ sucker with good adsorption capacity are selected, and the synergistic construction of the three structures is realized through 3D printing methods. The obtained sensor has an appropriate response range, sensitivity and stability. More importantly, the displacement deformation of the hydrogel can be reduced by 91.22%, while its adhesion strength can be increased by 57.5% compared to the unstructured hydrogel. As a proof-of-concept, the proposed bionic flexible sensor can be used to monitor the motion status of the human ankle joint in real-time, thereby assisting users in making real-time judgments on gait health.

Study on crashworthiness of square frustum lattice structure under in-plane compression load

The direction of load on the component in engineering applications is often uncertain, so the excellent crashworthiness and smooth load transfer of energy-absorbing structures in various directions is of great application value. Square frustum lattice structure (SFLS) was proposed based on the control of cell deformation mode and the improvement of in-plane strength without increasing the overall mass. Compared with multi-cell tubes commonly used in engineering and origami-patterned structure with excellent performance in research, it is found that the SFLS shows high and stable energy absorption capacity with the same structural parameters. The SEA and CFE of SFLS are 1.7 times and 3.5 times of origami structure and multi-cell tube, respectively, and the fluctuation indicator of the force displacement curve of origami structure and multi-cell tube are 1.7 times and 2.7 times of that of SFLS. In-plane quasi-static compression experiment was carried out and the finite element model was verified. The results of parametric analysis and sensitivity show that, compared with the change of cell number and cell height, the crashworthiness of SFLS under in-plane compression was most sensitive to the ratio of side length, in the range of parameters studied, the maximum SEA value of SFLS can reach 79.35 J/g for k value equal to 0.3, while the best indicator of smoothness of force-displacement curve of SFLS is found at k equal to 0.5.

3D printing of biomimetic liquid crystal elastomers with enhanced energy absorption capacities

Spider dragline silks are noted for their unmatched toughness, which arises from their unique primary structure. However, the underlying mechanisms of this toughness have seldom been verified using synthetic structural materials. Liquid crystal elastomers (LCEs) are polymer networks with mechanical properties bearing high resemblances to those of spider silks, and are ideal material for mimicking the primary structure of spider silk and revealing its toughing mechanisms. This study introduces a LCEs-based energy absorption structure that mimics the primary structure of spider dragline silks via 3D printing method. This LCEs-based biomimetic structure offers superior toughness and energy absorption capabilities with a damping capacity of 90%, significantly surpassing that of both artificial and biological viscoelastic materials. We successfully demonstrated that the biological primary structure provides the highest energy absorption capacity than other structures. This superior energy absorption capability was examined through hysteresis tests and then validated through intuitive ball free-falling tests. The work will illuminate a new pathway in the development of kinetic energy buffering and absorption materials.

Crash resistance analysis and optimization of sponge like thin-walled pipes under multiple working conditions

The crashworthiness of bionic thin-walled structures has been the subject of considerable research interest. In this article, we emulate the bi-diagonal skeletal structure of deep-sea glass sponges and construct sponge-like multicellular thin-walled tubes (SLMTT) with a parameterized ratio of the number of two distinct single-celled organisms (CSS I and CSS II). Thin-walled sponge-like tubes of varying dimensions were manufactured using selective laser melting (SLM) technology. The crashworthiness of these structures was evaluated under axial compression, transverse compression, and three-point bending conditions through experimental and computational approaches, including parametric analyses of the inner and outer wall thicknesses. The results show that SLMTT I has better crashworthiness under the three working conditions, and the SEA of BLMESI is 40.9 and 26.13% higher than that of BLMESII. under transverse compression and three-point bending conditions, respectively. Finally, a multi-objective optimization design of SLMTT I under multiple operating conditions is carried out by the second generation of Non-dominated Sorting Genetic Algorithm (NSGA-II) with the aim of obtaining the ideal structure with maximum specific energy absorption and minimum initial peak crushing force. This study offers novel insights into the design of bionic energy-absorbing structures under diverse operational scenarios.

An insight into the quasi-static indentation and specific energy absorption performance of glass fiber-aluminum wire mesh hybrid laminates

This study investigates the quasi-static indentation (QSI), three points bending and Izod impact performance alongside with the damage evaluation of pure glass-fiber laminates (GG) and hybrid laminates with aluminum mesh of two configurations (A1 with Al-mesh at the surface layers and A2 with Al-mesh in the middle layers). The energy absorption capacity, bending performance, and impact strength of the hybrid laminates were found to be enhanced in terms of weight ratio. Hybrid laminates exhibited better energy absorption (17.95%) and impact resistance (up to 63.7%). A1 possessed increased ductility and less damage, whereas A2 offered superior bending strength and toughness. The proposed hybrid composites proved to be an effective choice for fields requiring lightweight, energy-absorbing structures.

Research on the energy absorption performance of lattice filling structures based on homogenization analysis technique

The lattice structure has great application prospects in the field of energy absorption, but the high cost of numerical analysis makes it difficult to carry out related structural designs. Therefore, this article studies the feasibility of the homogenization analysis technique for the analysis of energy absorption processes in lattice-filled structures. In the study, compression experiments and numerical simulations were conducted for four different types of unit cells (including periodic truss-lattice cells and triply periodic minimal surface (TPMS cells). In the experiments, two compression samples with different numbers of periods were designed for the same unit cell structure. The research shows that the homogenized numerical model takes a lot less time to run than the classical beam and shell element models. The results of the simulation are also in line with the data from the experiments. On the other hand, the material curve constructed based on a small number of unit cell samples has excellent analytical accuracy. This means that relevant research can obtain the material experimental data required for homogenized analysis using lattice samples with low manufacturing costs. Understanding these phenomena can provide a basis for the design of energy absorption structures.

Failure mechanism and crashworthiness optimization of variable stiffness nested origami crash box

In recent years, the study of the crashworthiness of lightweight and efficient thin-walled energy-absorbing structures has received increasing attention. In this work, 3D printing technology was adopted to create a nested origami crash box with stiffness variation, which was made of short carbon fiber reinforced nylon material. The structure effectively inhibits the development of failure behavior of short carbon fiber-reinforced nylon origami crash box due to material brittleness. The quasi-static compression experiment results indicate that compared to origami crash box, nested origami crash box improves by 40% in specific energy absorption and 50% in crash force efficiency, while the initial peak crushing force remains unchanged. The effects of three key geometrical parameters, namely dihedral angle, distance between tubes, and height difference on the damage mechanism of the nested origami crash box are discussed in detail using the finite element method, and the response surface model combined with the non-dominated sorting genetic algorithm II is used for multi-objective optimization. In this work, the concepts of origami theory and nested systems are integrated for the first time, aiming to achieve a stable and efficient energy-absorbing deformation mode by precisely modulating the stress transfer path of the structure and its stiffness. This work provides new ideas for the design and fabrication of novel lightweight energy-absorption boxes.

Investigation on the energy absorption characteristics of novel graded auxetic re-entrant honeycombs

In this work, innovative graded auxetic re-entrant honeycombs constructed by adjusting the geometric parameters of a core unit cell are proposed, and their deformation modes and energy absorption characteristics with different impact speeds are systematically investigated. The novel graded design utilizes structural hierarchy on the meso-scale and functional gradient on the macro-scale. The numerical simulation models are verified by comparing the experimental results. The results show that compared with the ungraded honeycomb (URH), one of the graded honeycombs (GRHs), named GRH1, can greatly improve the specific energy absorption by 36.4%, 10.8%, and 6.00% for the quasi-static, low, and high-speed impact at a strain of 0.6. At the same time, the initial peak stress of GRH1 is decreased by 43.2% and 27.1% compared with that of URH for low and high-speed impact, respectively. It could be indicated that the GRH1 was an ideal energy-absorbing structure. This work provides a new route for designing graded auxetic honeycombs with enough insight to understand the deformation mechanism of the structures, which could be used in lightweight buffer protective systems.

Energy absorption structure with negative stepped plateau force characteristics under quasi-static loads

The force-displacement curve is the key to determine the energy absorption performance. Customizing the force-displacement curve enables the design of more advanced and efficient energy absorption systems. In this paper, we introduce a negative stepped plateau force structure (NSPFS) design by combining crooked plate units with curved and straight combined cross-section (CSCC) units. First, the NSPFS is fabricated by using additive manufacturing technology, and a compression experiment is conducted to validate the design methodology. Then, a finite element model is developed and compared with the experimental results to verify its effectiveness. The peak force (PF) and mean crushing force (MCF) of the crooked plate unit are primarily controlled by wall thickness t1 and initial angle θ1. When θ1 = 1.146° and t1 = 1.0 mm of crooked plate unit, the lowest point of the plateau phase decreases by 84 % compared to the PF, and the ratio of PF to MCF is 4.9. When the PF of the crooked plate unit is greater than the PF of the CSCC unit, the structure has the characteristics of negative stepped plateau force. More phase plateau forces can be obtained when multiple NSPFS are compressed in series. When multiple NSPFS units are compressed in parallel, multi-phase continuous negative stepped plateau force can be achieved. Therefore, NSPFS allows for the customization of complex force-displacement curves through series and parallel design.

Similarity design method and multi-objective optimization of train energy-absorbing tube velocity distortion under axial impact

Thin-walled tubes are commonly used as crucial structures for energy absorption. It is an efficient and convenient research method to establish a small-scale model of the energy-absorbing thin-walled tube for experiments. However, due to the inevitable difference between the design velocity of the test and the actual velocity of the test, it cannot meet the traditional similarity theory. Because of this limitation, this article constructs a similarity design method for the velocity distortion of the multi-cell energy-absorbing tube at the front end of the train under axial impact. Firstly, according to the motion equation of the train system, the design criterion of the similar model under the velocity distortion is derived. Then, the collision mass correction factor is derived based on the elastic-plastic structural energy equation, aiming at the error of the collision peak force and the error of the collision time, the correction factor of the wall thickness of the energy absorbing tube is obtained based on the simulation analysis results. Finally, it is verified that the velocity distortion similarity model can accurately predict the dynamic response of the prototype, and reveals the influence of the mass and wall thickness correction factors on the error.

Research on the Energy-Absorbing and Cushioning Performance of a New Half-Bowl Ball Rubber Body in Tunnel Support

As coal mine underground operating conditions are harsh, strengthening and optimizing the support structure is conducive to the safety of mining work and personnel. Currently, underground support devices face problems such as poor environmental adaptability and unbalanced performance of shockproof and energy absorption. At the same time, the energy absorption mechanism and impact dynamic analysis of the support structure are still imperfect. This paper proposes a simple and effective bionic half-bowl spherical rubber energy-absorbing structure based on the actual production needs of coal mines, with energy-absorbing rubber as the main structural interlayer. A combination of experimental testing and simulation was used to reveal the dynamic response and mechanism of simulated energy absorption of a half-bowl-shaped rubber layer under different working conditions. Abaqus software was used to simulate and analyze the dynamic response of the half-bowl spherical rubber structure under the impact condition, and the simulation data were compared with the experimental results. In addition, the relationship between energy absorption and stress at the rubber structure and the base plate under different impact velocities was investigated. The results show that the simulated and experimental results of the rubber structure have almost the same pressure vs. time trend within 0.1 s at an impact velocity of 64 m/s, and there is no significant wear on the rubber surface after impact. Due to the energy-absorbing effect of the rubber structure, the maximum stress of the bottom member plate-2 of the mechanism is lower than 9 × 104 N. The maximum amount of compression of the half-bowl ball is 37.56 mm at an impact velocity of 64 m/s. The maximum amount of compression of the half-bowl ball is 37.56 mm.

Experimental and numerical study on CuO/ZnO-modified aramid fabric for ballistic and UV radiation protection

Aramid fabrics are widely used in bulletproof armor because of their excellent mechanical properties. Previous studies have shown that ultraviolet radiation has a negative effect on the mechanical properties of aramid yarn, so improving the mechanical properties and impact resistance of aramid fabrics under ultraviolet radiation has become a research focus. In this work, aramid fabric was modified with CuO and ZnO particles to improve its ballistic performance under ultraviolet radiation. The ballistic impact resistance response and microscopic failure mechanisms of aramid fabrics under ultraviolet radiation were analyzed in detail. Under ultraviolet radiation, the ballistic limit velocity (vbl) of the CuO/ZnO-modified aramid fabric was 185.1 % greater than that of a neat fabric with a similar areal density. The vbl of the single-layer modified fabric was 45.6 % greater than that of the two-layer neat fabrics. The decrease in the ballistic performance of the aramid fabric under ultraviolet radiation was attributed to surface damage caused by the fracture of the chemical structure of the fibers, which weakened the mechanical properties of the fabric. The numerical simulation results were highly consistent with the ballistic impact test results, and the error between the numerical simulation and experimental results was within 10 %. The effects of changes in the mechanical parameters of the fabrics on the protection mechanism and energy absorption structure during ballistic impact were investigated. The energy dissipation of the modified fabric was at least 147.7 % greater than that of the neat fabric, further explaining the significant improvement in the ballistic performance of CuO/ZnO-modified fabrics under ultraviolet radiation.

Crashworthiness and optimization design of additive manufacturing double gradient lattice enhanced thin-walled tubes under dynamic impact loading

It is of paramount importance to ensure the protection of both infrastructure and personnel in scenarios characterized by a high strain rate dynamic impact. In order to develop lighter weight and higher crashworthiness energy-absorbing structures, this paper incorporates the bionic design of lattice reinforced thin-walled tube structures in the form of double gradient, as a means of achieving the aforementioned objectives. Material mechanical properties and the designed structures at high strain rate were researched using Split Hopkinson Pressure Bar (SHPB) experiment. The effects of gradient form and gradient parameters on the deformation pattern and crashworthiness of lattice enhanced thin-walled tubes are researched by means of the validated finite element model and the experimentally fitted Johnson-Cook material model. The results indicate that the specific energy absorption of the double gradient lattice enhanced thin-walled tube (T3L3) is increased by 36.19 % and the peak crush force is reduced by 21.19 % compared to the lattice enhanced thin-walled tube without gradient. Finally, the multi-objective optimization analysis of the T3L3 with the objective of achieving the maximum SEA and minimum PCF is carried out by Response Surface Methodology (RSM) and Non-dominated Sorting Genetic Algorithm-II (NSGA-II) to find the Pareto optimal solution set. Double-gradient bionic structure offers a new idea for designing energy-absorbing structures under high-speed impact conditions.

A machine learning-based crashworthiness optimization for a novel pine cone-inspired multi-cell tubes under bending

Bionic tubes are of interest in vehicle engineering due to their superior crashworthiness potential. This study proposes a crashworthiness response investigation and machine learning-based multi-objective optimization of pine cone-inspired muti-celled tubes (PCMTs). The base computer PCMT model was correlated using existing experiments, followed by a dynamic response evaluation of different PCMT geometrical and thickness configurations to assess their structural performance. Surrogate models of these PCMTs were then constructed using machine learning algorithms, and their main and interaction effects were analyzed. A non-dominated sorting genetic algorithm II (NSGA-II) approach was employed to perform a multi-objective optimization. The results demonstrate that thickness change had more effect on the initial peak force (IPF) and the mean crushing force (MCF) than the specific energy absorption (SEA). Besides, due to the coupling effect, IPF, MCF and SEA of the optimal design solution of the PCMTs could reach a 36.82 %, 61.66 % and 72.95 % increase than the sum case, suggesting that embedding inner tubes could significantly increase energy absorption with a relative minor IPF increase. Moreover, the MCF and SEA of optimal design gave an average difference of 18.01 % and 5.91 % from the original tubes. PCMTs, therefore, could be used as an ideal energy absorption structure in the vehicle body structures.

Effect of Extrusion Ratio on Mechanical Behavior and Microstructure Evolution of 7003 Aluminum Alloy at High-Speed Impact.

The extrusion ratio (ER) is one of the most important factors affecting the service performance of aluminum profiles. In this study, the influence of ER on the mechanical behavior and microstructure evolution of 7003 aluminum alloy at high-speed impact with strain rates ranging from 700 s-1 to 1100 s-1 was investigated. The studied alloy with an ER of 56 formed coarse grain rings during the heat treatment. The microstructure of the alloys with ERs of 20 and 9 is relatively uniform. The results indicate that under high-speed impact, the mechanical response behavior of the 7003-T6 alloy with different ERs is different. For the alloy with an ER of 56, strain hardening is the main mechanism of plastic deformation. In contrast, a flow stress reduction occurs at middle deformation stage for the ones with ERs of 20 and 9 due to concentrated deformation, which is more significant in the alloy with an ER of 20. Under high-speed impact, the alloy with an ER of 56 undergoes uneven plastic deformation due to the presence of coarse grain rings. The deformation is mainly borne by the region of coarse grains near the edge, and the closer to the center, the smaller the deformation. The deformation of the alloys with ERs of 20 and 9 is relatively uniform, but exhibits localized concentrated deformation in the area near the edge. The significant plastic deformation within deformation band causes a local temperature rise, resulting in a slight decrease in flow stress after the peak. These results can provide reliable data support for the application of 7003 aluminum alloy in the vehicle body crash energy absorption structure.

Multi-Objective Optimization of Crashworthiness of Shrink Tube Energy Absorption Structure

By means of material testing, truck testing and numerical simulation, the structural parameters of the shrink tube anti-climb device for high-speed trains were determined. The effects of cone angle, tube thickness, friction coefficient and axial length of the friction cone on the crashworthiness of the shrink tube were studied, and the main causes were analyzed. Using cone angle and tube wall thickness as input variables, and peak crush force, mean crash force and specific energy absorption as crashworthiness indexes, a proxy model was constructed using a radial basis function. The global response surface methodology was adopted to optimize the design of the shrink tube’s structural parameters. The results showed that the crashworthiness of the shrink tube was positively correlated with the cone angle, the thickness of the shrink tube and the friction coefficient, and the influence decreased successively, while the influence was negatively correlated with the axial length of the friction cone, which had the least influence. Through the optimized design, the peak force of the shrink tube increased by only 5.41%, while the specific energy absorption increased by 31.03%. Additionally, the mean force was closer to the technical requirements of 600 kN, and the crashworthiness was optimized.

3D Printed Metamaterials for Energy Absorption in Motorsport Applications

In this study, various 3D printed metamaterials are investigated for application in energy absorbing structures in motorsports. Impact attenuating structures are used to decelerate vehicles and protect drivers in the event of a crash. Additive manufacturing enables complex plastic structures which can facilitate improved angular resistance and reduced weight and cost compared with traditional approaches. Metamaterials were 3D printed from PLA using commercially available equipment and include gyroid structures, a novel reinforced gyroid design and a lattice designed using finite-element analysis-based topology optimization. Compression testing was used to measure stress–strain response, compressive modulus, and energy absorption. This demonstrated gyroids and reinforced gyroids have ideal compressive behavior for high energy absorption under impact. The topology optimized metamaterial was found unsuitable for this application due to its high stiffness, revealing a weakness in traditional topology optimization approaches which are not catered to maximize energy absorption. The reinforced gyroid demonstrated the highest specific energy absorption and was used to manufacture an impact attenuator which demonstrated the potential to safely stop a hypothetical 300 kg vehicle crash. This work supports that gyroid-based structures can reduce weight, volume and cost over current materials in all motorsport categories, with improved safety from oblique crashes.