Energy Absorbing Structures Research Articles

Finite element-based optimisation of an elastomeric honeycomb for impact mitigation in helmet liners

Finite element simulation was used to analyse the response of an elastomeric pre-buckled honeycomb structure under impact loading, to establish its suitability for use in helmet liners. A finite element-based optimisation was performed using a search algorithm based on a radial basis function. This approach identified optimisation configurations of a pre-buckled honeycomb structure, based on structural bounds subject to impact loading conditions. Furthermore, the influence of objective function, peak acceleration and head injury criterion was analysed with respect to the resultant mechanical behaviour of the structure. Numerical results demonstrate that this class of structure can exceed the performance threshold of a common helmet design standard and minimise the resultant injury index. Experimental testing, facilitated through laser sintering of thermoplastic polyurethane powder, validated the output of the numerical optimisation. When subject to initial impact loading, the fabricated samples satisfied their objective functions. Successive impact loading was performed to assess the performance and degradation. Samples optimised for peak acceleration demonstrated superior performance after stabilisation, relative to their initial response. The culmination of this study establishes a numerical design pathway for future optimisation of candidate structures for head impact protection. Furthermore, the optimised pre-buckled honeycomb structure represents a new class of energy absorbing structure, which can exceed the thresholds prescribed by the design standard.

Impact resistance and energy absorption ability of bio-mimetic thin-walled structures with hollow columns under impact loading

With the increasing damage of lives and properties caused by impact accidents, thin-walled tubes have been widely employed to make energy-absorbing structures in the field of automotive engineering due to their lightweight and energy absorption ability. In this work, we proposed three kinds of thin-walled bio-mimetic tubes inspired by horsetail plants and investigated the energy absorption abilities of the above structures with hollow columns under impact loading by means of the finite-element method. The effect of three factors, including column diameter, wall thickness, and impact angle, on the energy absorption characteristics of the bio-mimetic structure, is discussed. The primary outcome of this research is a design method for the use of thin-walled multi-cell tubes for an energy absorption device where impact loading is expected. It was also found that the energy absorption performances of the hexagonal structures are better than that of the triangular and quadrilateral ones. Moreover, the results revealed that the absorbed energy by thin-walled bio-mimetic structures shows more dependence on the impact angle than on the wall thickness of the tube.

Design Method Using Response Surface Model for CFRP Corrugated Structure under Quasistatic Crushing

The development of a carbon-fiber-reinforced plastic (CFRP) part is carried out by utilizing many experimental results in deciding the design. For this reason, the development period of a CFRP structure is long and an obstacle for commercialization. In this paper, multiple regression analysis is used to derive a response surface that estimates the generated load using the shape parameters of a corrugated collision energy absorbing structure to shorten the development period. To obtain the response surface, we conducted a quasistatic crushing experiment by using the length of linear portions (pitch) and the number of stacks (thickness) of a corrugated shape as parameters. When progressive crushing mode is observed, energy absorption efficiency decreases with the increase in pitch, and increases with the increase in the number of stacks. To discuss how energy absorption efficiency changes, a comparison examination is conducted using the derived response surfaces. Results indicate that specifications with high energy absorption efficiency can be accurately selected using the response surface of primary expression. In addition, differences in deformation mode were due to the influence of the stress at the corner portion of a part.

Reversed-Torsion-Type Crush Energy Absorption Structure and Its Inexpensive Partial-Heating Torsion Manufacturing Method Based on Origami Engineering

Abstract Current vehicle energy absorbers face two problems during a collision in that there is only a 70% collapse in length and there is a high initial peak load. These problems arise because the presently used energy-absorbing column has no deployment shrinkage function. It has been shown that a column called the Reversed Spiral Origami Structure (RSO) developed by Nojima solves the above two problems. However, in the case of the existing technology of the RSO, the forming cost of hydroforming is too expensive for application to a real vehicle structure. Therefore, a new structure imitating RSO, named the Reversed Torsion Origami Structure (RTO), has been developed, which has excellent energy absorption in simulation. Here, a manufacturing system is developed for the RTO cheaply. Excellent results are obtained also in a physical experiment. The RTO can replace conventional energy absorbers and is expected to be widely used in not only automobile structures but also building structures.

Machine learning prediction of mechanical properties of braided-textile reinforced tubular structures

Braided-textile composites have been applied in various engineering fields and used for high-efficiency energy absorbers to meet different loading requirements. However, it’s difficult to accurately forecast the mechanical properties of these braided-textile composites based on theoretical method, which is a big obstacle to the precise design of the energy-absorbing structure. In this research, carbon fiber reinforced composite (CFRC) tubular structures were fabricated by two-dimensional braided textiles, and 160 groups of orthogonal axial compression experiments were carried out.Axial compression behaviors of CFRC tubular structures, including peak force, mean crushing force, energy absorption, specific energy absorption, elastic modulus and other relevant parameters, were tested and collected in a database. The feed forward back propagation (FFBP) algorithm based on artificial neural network (ANN), as an algorithm with high convergence accuracy in machine learning (ML), was adapted to build a prediction model to forecast the overall axial compression properties of those CFRC tubular structures uncollected in the database. By a series of error analyses, the ML method was proven to have high accuracy in predicting the relevant mechanical properties within the range of orthogonal design groups. Although the relative error of marginal sample data (especially single-layer tubes) is large, the mean absolute error (MAE) of training set and test set is only about 5% and 10%, respectively. Our work demonstrates the potential of machine learning methods in predicting the overall mechanical properties and guiding the design of composite materials.

Out-of-plane impact analysis for a bioinspired sinusoidal honeycomb

The special energy-absorbing structure of beak protects the head of woodpecker from being hurt when pecking tree. Inspired by the micro wavy structure of the woodpecker beak, a novel bionic sinusoidal honeycomb is proposed and its crashworthiness performance is analyzed. Results show that the bionic sinusoidal honeycomb produces more folds than the conventional honeycomb under the same mass conditions, which greatly improves the energy absorption effect. Compared with the conventional honeycomb, although the initial peak crushing force of bionic sinusoidal honeycomb is generally higher (the change ranges from −1.64% to 11.84%), the specific energy absorption of all bionic sinusoidal honeycombs is much better (the increase ranges from 30.12% to 80.99%). Moreover, the bionic sinusoidal honeycomb has a better crush force efficiency when the amplitude is small. A comprehensive comparison of the impact resistance of the bionic sinusoidal honeycomb and conventional honeycomb shows that the proposed bionic sinusoidal honeycomb has better energy absorption and application scalability than the conventional honeycomb. Highlights A novel bionic sinusoidal honeycomb (BSH) is proposed based on woodpecker beaks The impact resistance of BSH is systematically studied using finite element analysis. Its specific energy absorption (SEA) can increase by 80.99% compared to conventional honeycomb. The SEA of BSH increases as the wall thickness increases, but it is weakly related to the amplitude and the wavenumber.

An Optimal Design of the Two-Staged Square Sectional Combined Energy Absorption Structure with Local Surface Nanocrystallization

An Optimal Design of the Two-Staged Square Sectional Combined Energy Absorption Structure with Local Surface Nanocrystallization

Finite element analysis of energy absorption characteristics for biomimetic thin-walled multi-cellular structure inspired by horsetails

Tubular thin-walled structure has attracted more and more attention because of its light weight and energy absorption characteristic, and has been widely applied to the fields of aerospace and automotive engineering. For millions of years, effective strategies in the biological tissues of nature creatures had evolved to synthesize structures that possess excellent mechanical properties. One impressive example is found in the internal morphology of horsetail plants. In this study, five kinds of the finite element model of multi-cellular thin-walled structures were established inspired by horsetails, and the energy absorption characteristics and crushing force efficiency of the above structures under axial impact loading were investigated by finite element method. Combined with the above bio-mimetic structures with good performance, a novel bio-mimetic multi-cellular thin-walled structure was proposed. The parameter study, including wall thickness, column diameter and impact angle were completed by numerical simulation method. The results show that the specific energy absorption and crushing force efficiency of the new proposed structure are 49.9 kJ/kg and 88.9% respectively, which are significantly higher than those of the conventional structure. The above bio-mimetic thin-walled structure inspired by horsetails can be applied in developing lightweight energy absorbing structure in the field of automotive or aircraft design.

Design of Hierarchical Architected Lattices for Enhanced Energy Absorption.

Hierarchical lattices are structures composed of self-similar or dissimilar architected metamaterials that span multiple length scales. Hierarchical lattices have superior and tunable properties when compared to conventional lattices, and thus, open the door for a wide range of material property manipulation and optimization. Using finite element analysis, we investigate the energy absorption capabilities of 3D hierarchical lattices for various unit cells under low strain rates and loads. In this study, we use fused deposition modeling (FDM) 3D printing to fabricate a dog bone specimen and extract the mechanical properties of thermoplastic polyurethane (TPU) 85A with a hundred percent infill printed along the direction of tensile loading. With the numerical results, we observed that the energy absorption performance of the octet lattice can be enhanced four to five times by introducing a hierarchy in the structure. Conventional energy absorption structures such as foams and lattices have demonstrated their effectiveness and strengths; this research aims at expanding the design domain of energy absorption structures by exploiting 3D hierarchical lattices. The result of introducing a hierarchy to a lattice on the energy absorption performance is investigated by varying the hierarchical order from a first-order octet to a second-order octet. In addition, the effect of relative density on the energy absorption is isolated by creating a comparison between a first-order octet lattice with an equivalent relative density as a second-order octet lattice. The compression behaviors for the second order octet, dodecahedron, and truncated octahedron are studied. The effect of changing the cross-sectional geometry of the lattice members with respect to the energy absorption performance is investigated. Changing the orientation of the second-order cells from 0 to 45 degrees has a considerable impact on the force–displacement curve, providing a 20% increase in energy absorption for the second-order octet. Analytical solutions of the effective elasticity modulus for the first- and second-order octet lattices are compared to validate the simulations. The findings of this paper and the provided understanding will aid future works in lattice design optimization for energy absorption.

Energy Absorption Performance of Bio-inspired Honeycombs: Numerical and Theoretical Analysis

Energy absorption performance has been a long-pursued research topic in designing desired materials and structures subject to external dynamic loading. Inspired by natural bio-structures, herein, we develop both numerical and theoretical models to analyze the energy absorption behaviors of Weaire, Floret, and Kagome-shaped thin-walled structures. We demonstrate that these bio-inspired structures possess superior energy absorption capabilities compared to the traditional thin-walled structures, with the specific energy absorption about 44% higher than the traditional honeycomb. The developed mechanical model captures the fundamental characteristics of the bio-inspired honeycomb, and the mean crushing force in all three structures is accurately predicted. Results indicate that although the basic energy absorption and deformation mode remain the same, varied geometry design and the corresponding material distribution can further boost the energy absorption of the structure, providing a much broader design space for the next-generation impact energy absorption structures and systems.

Clustering Analysis of Energy Consumption in the Countries of the Visegrad Group

The main purpose of this paper is to assess energy consumption with a breakdown into main sectors of the countries that belong to the Visegrad Group. The specific objectives aim to determine changes in energy absorption, its productivity, structure by sectors and to show the similarities of the Visegrad Group countries to the other EU states in terms of the sectoral energy absorption structure. All members of the Visegrad group, i.e., Poland, Hungary, Slovakia and the Czech Republic, were purposefully selected for the study as of 31 December 2018. The research period covered the years 1990–2018. The sources of gathered information were the literature on the subject and OECD data. The following methods were used for the analysis and presentation of materials: explanations, tabular and graphical depictions, descriptive statistics, dynamics indicators, and cluster analysis performed with the following methods: k-means, hierarchical agglomerative clusters and DIvisive ANAlysis (DIANA). There is a limited number of previous studies on the relationship between the national level of economic development and energy consumption in different sectors of industry. Additionally, there are no such analytical projects concerning EU states. The article fills the research gap in this area. It was established that the dynamics of productivity growth over the nine years (2010–2018) was similar in the countries of the Visegrad group and on average for the EU. This means that the members of the Visegrad group did not actually improve their energy efficiency as compared to the EU average. The reason may be the increasingly faster implementation of modern technologies in developed economies of Western Europe as compared to the developing countries, which include the members of the Visegrad group. The conversion of the economy had a very large impact on changing the structure of energy absorption by sector. Industry and agriculture lost their importance. On the other hand, the transport and service sectors benefited. As a result of the cluster analysis, all EU (European Union) states were divided into four groups. Poland, the Czech Republic, and Hungary found themselves in one group, along with most Western European countries. This may mean that the economies of these states have become unified with highly developed economic systems. Slovakia found itself in the group of states with a greater importance of industry. The study complements the contribution to the theory. From a practical point of view, it shows the impact of economic transformation on changes in energy consumption in individual sectors, which may be a model of transition in this area.

Analysis of energy absorption characteristics of corrugated top beams of anti-impact hydraulic supports

To enhance the inferior energy-absorption performance of a hydraulic support during coal mine rock burst, which leads to failure and damage, a framework including a kind of corrugated laminated energy-absorbing component on the top beam of the hydraulic support is developed. First, triangular, trapezoidal and sinusoidal corrugated core energy-absorbing structures are designed, and their mathematical models are established. Second, three kinds of corrugated core components are optimized to obtain the suitable structural parameters, and based on the findings, the energy-absorption characteristic curves of the three kinds of corrugated core components are obtained through a simulation analysis. The results show that the sinusoidal corrugated core exhibits the best energy-absorption effect among the single-layer corrugated components. Among the two-layer and four-layer corrugated core components, the triangular corrugated core arrangement is the optimal arrangement. The energy absorption of the three kinds of corrugated core components is correlated with the delamination. The results of the experiment and simulation are consistent. This study provides a theoretical basis and experimental reference for the design of energy-absorbing components for an anti-impact hydraulic support.

Design and experimental research on buffer protection of high-g penetrator for deep space exploration

Deep space exploration technology is an important development direction for scientific exploration. The penetrator method has been proposed as an inexpensive method of studying planetary bodies. The basic principle of this method is that the detection equipment carried by the high-speed penetrator hits a planetary body at a high speed and is buried up to several meters below the surface to carry out detection work. During the frictional collision process with the planets crust, the instantaneous acceleration peaks of the scientific payload (electronic instrumentation) are large. Shock protection of these payloads is necessary to improve their survival and mission success. In this paper, with the goal of improving the survival rate of scientific loads inside a penetrator, a penetrator with a multilayer energy-absorbing structure is developed, in which cushioning protection measures, such as an aluminum foam-filled corrugated tube(AFFT) structure, polyurethane rubber, and epoxy resin potting, are applied to the penetrator. Since the analysis of this process is a highly nonlinear problem, a numerical modeling method is the main approach in this paper. The LS-DYNA software platform was used to simulate the penetrators penetration process on a moon soil medium. The results obtained using empirical formulas and theoretical derivations were compared with the results of numerical analysis to ensure the accuracy of the penetration simulation model. The finite element model of the penetrator was then verified and modified by conducting shock response spectral experiments and shock simulations. The results showed that the spacer scheme had a positive effect on the impact isolation and energy absorption. In addition, this scheme provides an important reference for the design of the penetrator prototype to guarantee the success of subsequent ground rocket sled experiments.

Compression Experiment and Failure Analysis of Additive Manufactured Multi-Layer Lattice Sandwich Structure

The rapid development of additive manufacturing technology provides a new opportunity for the fabrication and research of multi-layer lattice sandwich structures, and thereby some excellent performances can be further discovered. Based on the manufacturing-experiment-analysis technical route, the failure mode of the additive manufactured aluminum multi-layer alloy lattice sandwich structure under quasi-static compression is systematically studied in this paper. Through the combination of experimental observation and finite element analysis, the complex failure mechanism of the multi-layer lattice sandwich structure is revealed. The results show that the multi-layer lattice sandwich structure under quasi-static compression conditions mainly manifests as a layer-by-layer failure mode of the internal lattice structure, which includes the yield, plastic buckling and material damage. At the same time, in comparison with the force–displacement curve and the structural deformation in the key locations, the analysis accuracy of the finite element model can be verified by the compression experiment. Based on the verified finite element model, the most significant influence of different face panel thicknesses, as well the rod radiuses and tilting angles on the energy absorption (EA) is identified via sensitivity analysis. Furthermore, size factors on the structural EA are revealed. This study can provide a helpful guidance for the design of multi-layer lattice sandwich structures in practical applications.

Twist and lock: nutshell structures for high strength and energy absorption.

Nutshells achieve remarkable properties by optimizing structure and chemistry at different hierarchical levels. Probing nutshells from the cellular down to the nano- and molecular level by microchemical and nanomechanical imaging techniques reveals insights into nature's packing concepts. In walnut and pistachio shells, carbohydrate and lignin polymers assemble to form thick-walled puzzle cells, which interlock three-dimensionally and show high tissue strength. Pistachio additionally achieves high-energy absorption by numerous lobes interconnected via ball-joint-like structures. By contrast, the three times more lignified walnut shells show brittle LEGO-brick failure, often along the numerous pit channels. In both species, cell walls (CWs) show distinct lamellar structures. These lamellae involve a helicoidal arrangement of cellulose macrofibrils as a recurring motif. Between the two nutshell species, these lamellae show differences in thickness and pitch angle, which can explain the different mechanical properties on the nanolevel. Our in-depth study of the two nutshell tissues highlights the role of cell form and their interlocking as well as plant CW composition and structure for mechanical protection. Understanding these plant shell concepts might inspire biomimetic material developments as well as using walnut and pistachio shell waste as sustainable raw material in future applications.

Crashworthiness analysis and multi-objective optimisation of a novel circular tube under three-point bending

A new excellent energy absorption structure named as leaf vein branched circular tubes (LVBCT) is proposed based on lotus leaf vein branched structure. The crashworthiness of LVBCT under lateral load is numerically studied by LS-DYNA. First, the numerical simulation model is established and compared with the existing experimental results to verify the feasibility. Meanwhile, the crushing behaviour of the regular circular tube is carried out for comparison. It can be found that the introduction of leaf vein branched characteristics can enhance the energy absorption capacity. Following that, the influence of structural parameterson the crashworthiness of LVBCT is systematically studied. Finally, based on polynomial regression model and non-dominated sorting genetic algorithm II (NSGA-II), the optimal design of LVBCT with different numbers of main-veins are carried out. Under the lateral load, the optimised LVBCT has a very good energy absorption performance, which can be used for vehicle external safety protection.

MECHANICAL PROPERTIES ANALYSIS OF A NEW ENERGY ABSORBING STRUCTURE WITH NEGATIVE STIFFNESS

As a kind of mechanical metamaterial with wide application prospect, negative stiffness structures show significant advantages in energy absorption, vibration attentuation, and noise reduction . However, their engineering applications are severely limited attributed to the low specific energy absorption efficiency and non-autonomous spring-back of negative stiffness structures with the speciality of multi-stability. In order to solve this problem, by means of cell configuration design, a new kind of three-dimensional negative stiffness structure with the characteristic of autonomous spring-back is proposed in this paper. For this negative stiffness cells in series, the self rebound of curved beams during the loading and unloading process is used to realize the cyclic loading and multiple reuse of the structure.The multi-stability is restrained by adding a groove of certain depth. The buckling mode is selected via the adjustment of side wall thickness. The difference between critical loads of negative stiffness is thus enlarged, accordingly, the energy absorption efficiency is significantly improved. Then in order to achieve high energy absorption under complex load environments, the gradient design of structure size is carried out, and a gradient negative stiffness structure is proposed. The energy absorption efficiency of gradient negative stiffness structure and uniform negative stiffness structure under different load cinditons is compared by finite element simulations. Analytical and numerical results reveal that for the newly developed negative stiffness structure, not only the feature of autonomous spring-back is achieved, but also the energy absorption ability is improved. Moreover, different critical load maximums for negative stiffness are obtained for the gradient structure due to different microstructure sizes, which makes it to exhibit better energy absorption efficiency on the basis of realizing autonomous spring-back under various impact load environments. The new energy-absorption structure proposed in this paper provides technical support for engineering applications such as vibration attenuation and structure reorganization.

Insight into the negative Poisson’s ratio effect of the gradient auxetic reentrant honeycombs

As an interesting energy-absorbing structure, auxetic reentrant honeycomb has attracted much attention in recent decades. Furthermore, due to the adjustable design in the configuration of the graded auxetic reentrant honeycomb (GARH), its mechanical performances were of greater designability and controllability. In this manuscript, compressive properties of the positive gradient auxetic honeycomb (PGAH) and negative gradient auxetic honeycomb (NGAH) were both investigated under different compression velocities. Meanwhile, the negative Poisson's ratio effects on the deformation behaviours and crushing stresses of the PGAH and NGAH were systematically studied. It was found that a new shrinkage deformation mechanism existed in the NGAH, which was different from the dynamic compressive properties of the PGAH and homogeneous auxetic honeycomb in the existing studies. Besides, the energy dissipation characteristics of both the PGAH and NGAH were also investigated. The results showed that, when under the medium and high compression velocities, the energy dissipation of the NGAH were 12.1 times and 7.41 times of those in the PGAH, respectively. It could be indicated that the NGAH was an ideal energy-absorbing structure.

Study on Automobile Front-End Structure Based on Pedestrian Leg Protection

According to the pedestrian leg protection regulations, a collision with the simplified finite element model of the leg was carried out on the basis of incorporating EPP foam materials with different foaming rates and cushioning into the simplified front-end structure of the car. The results show that the front-end foam energy-absorbing structure of the vehicle cannot meet the pedestrian leg protection regulations. This paper designs a thin-walled steel structure and applies it to the front-end structure of the vehicle. After collision simulation with a simplified finite element model of the leg, the pedestrian’s tibial acceleration, knee joint shear displacement and knee joint bending angle are compared and analyzed. Pedestrian leg injury parameters, the results show that thin-walled steel structure is more suitable for giving full play to the energy absorption effect in an environment with insufficient energy absorption space than foam energy absorption structure.

On the crashworthiness performance of novel hierarchical multi-cell tubes under axial loading

In recent years, the concept of hierarchy has been introduced into crashworthy design to explore an ultralight energy-absorbing structure with outstanding mechanical properties. In this study, a group of novel hierarchical multi-cell tubes (NHMTs) are proposed by replacing every sides of traditional multi-cell tubes with smaller square cells. The finite element model of NHMTs is first established and validated by experimental test. Then, the crashworthiness performance of NHMTs is analyzed and compared with taditional multi-cell tubes (TMTs). The results indicate that NHMTs exhibit superior crashworthiness behavior than TMTs and the hierarchical level has significant effect on the crashworthiness of NHMTs. Furthermore, in order to analyze energy absorption mechanism of NHMTs, the theoretical models of specific energy absorption (SEA) and mean crushing force (MCF) are established and validated. The result shows that the theoretical model of SEA and MCF can accurately predict the energy absorption behavior of NHMTs. This investigation offers a novel technique to design multi-cell tubes with excellent energy absorption capacity.