Energy Absorbing Structures Research Articles

Anti-blast analysis and design of a sacrificial cladding with graded foam-filled tubes

Foam-filled tubes are excellent energy absorption structures for impact resistance, and graded foam may have superiority for the design of anti-blast sacrificial cladding. The anti-blast response of density-graded foam-filled tubes as a core layer is investigated numerically and theoretically. Mesoscopic finite element models for graded foam-filled tubes are constructed, and their constant-velocity compression and anti-blast performance are simulated. One-dimensional analytical shock models based on an empirical force–displacement relationship are developed to analyze the axial collapse wave propagation in graded foam-filled circular tubes. Single-/double-wave deformation patterns are observed for graded foam-filled tubes under blast loading, especially the negatively graded foam-filled tubes with gradient parameters close to zero may also show a single-wave deformation pattern. The results demonstrate that the negatively graded foam-filled tube with a small density gradient is a good choice to design anti-blast sacrificial cladding with a small critical length and a low transmitted force. A contour map of the critical length required to absorb the impulse of blast loading for different gradient parameters and diameter-thickness ratios of the outer tube is established. This study proposes a new design guideline for superior blast resistance structures in engineering applications.

Towards an Ideal Energy Absorber: Relating Failure Mechanisms and Energy Absorption Metrics in Additively Manufactured AlSi10Mg Cellular Structures under Quasistatic Compression

A designer of metallic energy absorption structures using additively manufactured cellular materials must address the question of which of a multitude of cell shapes to select from, the majority of which are classified as either honeycomb, beam-lattice, or Triply Periodic Minimal Surface (TPMS) structures. Furthermore, there is more than one criterion that needs to be assessed to make this selection. In this work, six cellular structures (hexagonal honeycomb, auxetic and Voronoi lattice, and diamond, gyroid, and Schwarz-P TPMS) spanning all three types were studied under quasistatic compression and compared to each other in the context of the energy absorption metrics of most relevance to a designer. These shapes were also separately studied with tubes enclosing them. All of the structures were fabricated out of AlSi10Mg with the laser powder bed fusion (PBF-LB. or LPBF) process. Experimental results were assessed in the context of four criteria: the relationship between the specific energy absorption (SEA) and maximum transmitted stress, the undulation of the stress plateau, the densification efficiency, and the design tunability of the shapes tested—the latter two are proposed here for the first time. Failure mechanisms were studied in depth to relate them to the observed mechanical response. The results reveal that auxetic and Voronoi lattice structures have low SEA relative to maximum transmitted stresses, and low densification efficiencies, but are highly tunable. TPMS structures on the other hand, in particular the diamond and gyroid shapes, had the best overall performance, with the honeycomb structures between the two groups. Enclosing cellular structures in tubes increased peak stress while also increasing plateau stress undulations.

Influence of curvy stiffeners on the axial crushing response of 3D-printed polymer composite cylindrical tubular structures

Fused deposition modeling, is one of the highly efficient layer-wise additive manufacturing techniques that have shown great prospective in fabricating the energy-absorbing structures as per the designed geometry with appreciable accuracy. In this research study, the axial crushing performance of various polymer and polymer composite-based cylindrical tubular structures with different types of curved stiffeners is investigated experimentally. Four design configurations were proposed for the cylindrical tube with curved stiffeners and all the tubular samples were fabricated through fused deposition modeling-based 3D printing technique. Subsequently, quasi-static axial crushing tests were performed for the successfully fabricated tubes and their axial crushing characteristics were determined and compared. Overall results indicated that the P/CF-CCS1 configuration shows highly improved energy absorption efficiency than the other tube configurations considered in this study. Cylindrical tubes with curvy stiffeners show a more stabilized crushing response with better energy absorption capability in all of the proposed tube configurations.

On Crashworthiness and Energy-Absorbing Mechanisms of Thick CFRP Structures for Railway Vehicles.

This study aims to provide important guidelines for the crashworthiness design of composite energy-absorbing structures, especially railway vehicles. An experimental and numerical investigation was carried out to explore the crushing response of circular composite tubes reinforced with plain woven carbon fiber-reinforced polymers (CFRP). Quasi-static and dynamic axial crushing tests were performed on CFRP tubes with an inner diameter of 100 mm and a nominal wall thickness of 12 mm. Experimental results showed that increasing loading velocity led to a 21.8% reduction in specific energy absorption (from 99.7 kJ/kg to 78.7 kJ/kg) but had negligible influence on failure modes. Finite element models were also established and validated against the experimental results using ABAQUS/Explicit software. The effects of several different parameters such as the number of shell layers, friction coefficient, and interface properties on the simulated results, were also investigated and analyzed. A small variation in these parameters could change the total energy absorption of CFRP tubes. The comparisons between the predicted and experimental results indicated that a finite element model with 10 shell layers could effectively replicate the crushing response. In addition, the simulated results indicated that the damage of tubal wall materials dominated the major energy-absorbing mechanisms of CFRP tubes under quasi-static loads, which was 69.1% of the total energy. The energy dissipated by friction effects between the loading platen and the crushed fronds was 24.1% of the total energy. The increase in the loading velocity led to a decrease in the composite damage energy except for friction energy, resulting in a decrease in the total energy absorption.

Mechanical behaviors of multidimensional gradient gyroid structures under static and dynamic loading: A numerical and experimental study

Sophisticated gradient designs in natural materials are usually desired in man-made cellular materials with the aim to achieve multifunction and improve structural performance. However, many natural structures are still difficult to mimic due to their complex gradient designs. In this paper, a novel design strategy is proposed for generating multi-dimensional gradient gyroid structures, which have the ability to mimic complex gradient pore characteristics. The novel design strategy is based on the topological constants instead of thickness, cell size and porosity. Moreover, it adopted the interpolation function to bridge the gap between adjacent pore gradients. Five gradient gyroid structures from one-dimensional, two-dimensional to three-dimensional (1D, 2D to 3D) space were generated as examples using this design method. A numerical method is developed to assess the mechanical response of proposed structures incorporating the rate-dependent properties under varying impact loading velocity. Functionally graded metallic gyroid structures were fabricated using selective laser melting and its experimental results were used to validate the numerical model under both quasi-static and dynamic compression. Then the load-bearing capacity of these gradient gyroid structures under different loading velocities was investigated. According to the results from the numerical analysis, the gradient design of gyroid structures has a substantial impact on the deformation modes and load-bearing capacity. Gradient design in gyroid structures is capable of providing excellent specific energy absorption and demonstrates tremendous promise for managing deformation behaviors. 3D gradient design exhibits the best loading bearing capacity among 1D, 2D gradient ones and traditional triply periodic minimal surface structures (including gyroid, diamond, Primitive, F-Koch and IWP). The multidimensional gradient design strategy proposed in this study showed the ability to mathematically control the complex gradient pore characteristics, which can be applied to the design of functionally graded structures for efficient energy absorption also in modern composite structures.

Parametric analysis on axial compression performance of bio-inspired porous lattice structures

The porous lattice structures (PLSs) have the advantages of excellent mechanical properties and light weight. Inspired by the structural shape of lotus root, this work proposes four lotus root-shaped bio-inspired PLSs (BPSs), which are triangular BPS (TBPS), quadrangular BPS (QBPS), pentagonal BPS (PBPS) and hexagonal BPS (HBPS). The axial compression properties of these BPSs are investigated. All of these four structures have uniform structural stiffness and excellent energy absorption properties. They exhibit stable deformation modes of X-shape and single-headed axe. In addition, the effects of geometric parameters and cell arrangements on the compression performance of these BPSs are investigated. The BPSs with different geometric parameters show various deformation modes such as single-headed axe, double-headed axe, sun and turtle shapes. The BPSs with different cell arrangements exhibit rich deformation modes such as crescent, dart, X and V shapes. Their cells show the deformation modes of axial crushing and bending, and the axial crushing deformation mode is more conducive to obtaining stable compression performance. Furthermore, the sample of QBPS is manufactured through 3D printing, and the compression experiment is performed to verify the simulation model. These results show that the BPSs are excellent energy-absorbing structures that have wide application prospects.

Lattice Structure Design Method Aimed at Energy Absorption Performance Based on Bionic Design

To obtain the lattice structure with excellent energy absorption performance, the structure of loofah inner fiber is studied to develop bionic design of lattice structure by experiment and simulation analysis method. From the compression experiment about the four bionic multi-cell lattice structures (bio-45, bio-60, bio-75, and bio-90) and VC lattice structures, we found that all are made of PLA and fabricated by the fused deposition modeling (FDM) 3D printer. The comprehensive performance of bio-90 lattice structure is the best in the performance of the specific volume energy absorption (SEAv), the effective energy absorption (EA), and the specific energy absorption (SEA). Based on the experimental result, the energy absorption performance of bio-90 lattice structure is then studied by the simulation analysis of influence on multiple parameters, such as the number of cells, the relative density, the impact velocity, and the material. The results can provide a reference for the design of highly efficient energy absorption structures.

Safety Assessment and Crash Compatibility of Heavy Quadricycle under Frontal Impact Collisions

An electric heavy quadricycle, categorized as an L7e vehicle, is an alternative solution for sustainable mobility with a lower carbon footprint and high energy consumption efficiency. However, accidental crashes of quadricycles with larger vehicle opponents can cause extensive damage to their structures and fatal injury to the occupants due to their geometry drawback in limited space in the front crumple zone. This work investigates the crashworthiness performance and safety assessment of the L7e vehicle under rigid wall crash tests and crash compatibility in car-to-car collisions with a sedan and an SUV. Crash scenarios are simulated using a nonlinear finite element analysis via LS-DYNA to evaluate structural crashworthiness and occupant injuries of a hybrid III 50th percentile male dummy. The compatible vertical alignment of the primary energy-absorbing structure substantially affects the safety of the quadricycle under a frontal crash. A secondary energy-absorbing component should be adapted to the L7e vehicle to achieve vertical alignment with different vehicle sizes. In addition, the typical rigid-wall frontal crash test at 50 kph considerably underestimates the structural damage and occupant injury of the L7e vehicle compared to car-to-car collisions. Thus, additional crash tests representing car-to-car collisions that account for the car’s smaller size and lighter mass should be included in the safety regulation for the L7e vehicle.

Characterization of penetrate and interpenetrate tessellated cellular lattice structures for energy absorption

Recently, cellular lattice structures are gaining research attention due to their lightweight and high energy absorption. Interpenetrated lattice structure is a combination of two or more regular lattices with the same volume and without any contact at the unit level. The interpenetrated tessellated lattice (I-PTL) structures are better known for load sharing and energy absorption applications. In the current research, regular unit cell lattices such as cubic, beam lattice, body-centered cubic, and octahedron are considered to fabricate penetrated and interpenetrated cellular lattice structures and tested for energy absorption on quasi-static loading. These structures were fabricated using a Vat polymerization three-dimensional printer and tested as per the American Society for Testing and Materials (ASTM) standards, and the results were compared with numerical simulation using ANSYS. The penetrated tessellated lattice structural and I-PTL behavior deliver energy transfer controlled by the surface and solid joint interactions. The enhancement in mechanical properties is observed with the controllable compliance and specific energy absorption of the lattice structure.

Crushing behaviours and energy absorption characteristics of square antiprisms structure against flatwise crushing

In this study, a type of thin-walled energy absorber named square antiprisms (SAP) is proposed, which can be used as a core of cladding “sandwich” panel design for improving crashworthiness. Three types of SAP structure, i.e. open SAP, half-enclosed SAP and all-enclosed SAP are studied. The purpose of this unique geometric structure is to increase the energy absorption capacity of the thin-walled structure while maintaining a uniform collapsing resistance under various crush loading rates as compared with other existing conventional thin-walled structures (i.e. cylindrical tube, square tube), and folded square dome shaped structure proposed recently [50]. A unit cell of standard Miura-origami folding core is numerically simulated and calibrated with the experimental results. Good agreement on the peak and average crushing force between numerical results and experimental data is achieved. The calibrated numerical model is then used to simulate the structural response of thin-walled energy-absorbing structures under various loading rates. The collapse modes and the energy absorption capacity including average and peak stress, energy absorption, crush force efficiency and densification strain are compared among these structures. The proposed open SAP structure shows good energy absorption characteristics under quasi-static loading and dynamic loading by yielding low initial peak stress, big crush force efficiency, large densification strain and more uniform collapsing. In addition, unlike the existing typical axial crashed thin-walled energy absorber, the SAP structure show shows insensitivity to the medium and low crushing speed (no more than 63 km/s) in terms of initial peak stress and uniformity ratio. Compared with the existing typical thin-walled structures, the proposed SAP structure demonstrates a superior performance to most of the axially loaded thin-walled components, indicating a potential application as an energy absorber.

Lessons from nature: 3D printed bio-inspired porous structures for impact energy absorption – A review

As a result of their mechanical characteristics, biological structures often provide inspiration for the development of high-performance mechanical structures. Nevertheless, traditional production processes are often incapable of precisely reproducing the intricate and exquisite nature of biological systems. Modern additive manufacturing techniques provide a pathway to the creation of materials with complex patterns that are inspired by biological processes. In this paper, we identify the different types of biomimetic porous structures seen in nature, many of which are composite structures, and categorise them. We also identify the natural species with porous structures and illustrate their functions. In addition, this review paper presents how these porous structures have been mimicked for engineering applications. Figures are shown to demonstrate the scale (meso, micro, and nano) at which the porous structures are emulated. As biological porous structures have been successfully mimicked into synthetic materials using additive manufacturing (AM), we classify the types of 3D printing with respect to impact loading applications and describe the various types of additive manufacturing processes used to manufacture biomimetic porous structures. This review paper will be of interest to academics looking to design innovative lightweight porous composite structures and use emerging technologies to investigate their energy absorption properties, which have a wide range of engineering applications.

Conversion of low density polyethylene foams into auxetic metamaterials

AbstractCellular polymers, such as polyethylene foams, are commonly used in the packaging industry. These materials have short service life and generate a high volume of waste after use. In order to valorize this waste and produce added‐value applications, it is proposed to convert these materials into highly efficient energy absorption structures. This was done by modifying the original cellular morphology of the foams (spheroidal or polygonal) into a re‐entrant structure to produce auxetic materials. This work presents an optimized process combining mechanical compression and solvent vapor evaporation‐condensation leading to low density foams (77–200 kg/m3) having negative Poisson's ratios (NPR). Three series of recycled low density polyethylene (LDPE) foams with an initial density of 16, 21, and 36 kg/m3 were used to optimize the processing conditions in terms of treatment temperature, time, and pressure. From all the samples prepared, a minimum Poisson's ratio of −3.5 was obtained. To further characterize the samples, the final foam structure was analyzed to relate with mechanical properties and compare with conventional foams having positive Poisson's ratios. The results are discussed using tensile properties and energy dissipation which were shown to be highly improved for auxetic foams. Overall, the resulting foams can be used in several applications such as sport and military protection equipment.

Topometry Optimization of Energy Absorbing Structure through Targeting Force-Displacement Method considering Tailor Rolled Blank Process

Inspired by topometry optimization, this work proposed a new design approach that mixed of targeting force-displacement (TFD) method and tailor rolled blank (TRB) process for thin-walled energy absorption structures, which has vast applied prospects in the aerospace and automotive industries. This method not only overcomes manufacturing difficulty caused by the TFD method based on topometry optimization but also provides a new idea for TRB energy absorption structure. The optimized results can be transferred to the computer aided design environment without additional postprocessing. Firstly, a uniform thickness constraint is introduced to make the designed structure have constant thickness distribution along desired direction; topometry optimization is carried out to use TFD method. Secondly, a method that can automatically divide the design domain is developed. The adjacent elements with smaller thickness differences are merged to form TRB subdomains based on the optimization results of forestep, and the TFD method is used again. Finally, TRB finite element modeling codes is developed. According to the second step, modeling of the transition zone is added to finally form the TRB structure that meets the requirements of manufacturing. This method is used to optimize the crashworthiness of the thin-walled tube under axial and oblique loading. Numerical results demonstrate the effectiveness of this method. Therefore, this method can be used to design high-efficiency energy absorber on aircraft or automobile, such as the strut of aircraft and energy absorption box of automobile.

Crashworthiness of lantern-like lattice structures with a bidirectional gradient distribution

Oblique impact loading conditions strongly influence the crashworthiness of energy-absorbing structures. In the present work, inspired by the distribution characteristics of spider webs, a bidirectional gradient configuration of cell wall thickness was introduced to enhance the crashworthiness of lattice structures based on the functional similarity of longitudinal gradient distribution and lateral gradient distribution. A comparative study of different gradient configurations was carried out using the finite element (FE) simulations. It was found that the longitudinal gradient distribution was beneficial to improve the comprehensive energy absorption capacity of the lattice structure, especially under small-angle impact conditions. With the increase of impact angle, the effect of the lateral gradient distribution on the stability of energy absorption became more prominent. In comparison to the uniform structure and the single gradient structure, the lattice structure with the positive longitudinal gradient and the negative lateral gradient distribution exhibited great potential in enhancing the energy absorption capacity and reducing the peak crushing force. A detailed parametric study was executed to explore the effects of the gradient layer number and the gradient thickness increment of the bidirectional gradient distribution on the comprehensive energy absorption capacity and energy absorption stability of the structure under multi-angle impact conditions. The findings of this research provide valuable guidelines to design bio-inspired lattice structures subjected to complex loading conditions.

Research on Optimization Design of Key Energy-Absorbing Structure of a Helicopter Seat Based on Human–Seat Coupling System

During the process of emergency landing, the energy of the impact in the vertical direction is dissipated through the deformation of the structure. The landing load is transferred to the spine of the occupant through the landing gear, the fuselage and finally the seat. This can cause serious damage to the human body. Since the seat is in direct contact with the human body, the energy absorption capacity of the seat is the most direct manifestation of the Crashworthiness of the helicopter. The solutions proposed in the paper may reduce the impact of the seat on the spine of the occupant during the collision by optimizing the key energy-absorbing structure. Taking the seat of the H135 helicopter as a case, the mechanical model of the human–seat coupling system, which is based on the theories of energy methods and structural mechanics, is simplified. Additionally, the simulation was considered reasonable by comparing the simulation results with the results of crashworthiness tests. On the basis of the above, the optimization of the key energy-absorbing structure of the seat was completed by using Latin hypercube sampling and the kriging model. Overall, the optimization effectively enhanced the crashworthiness of this helicopter seat and provided a solution for the passive safety design of aviation seats.

Optimization of Anti-Impact Energy Absorption Structure of Hydraulic Support

Rock bursts are a frequent occurrence in deep coal mining, and reducing the risk of rock bursts is necessary for the safe and efficient mining of coal. As honeycomb structures have good impact resistance, the design suggests that a honeycomb structure is adopted in the roof. A mechanical model of the hydraulic support is established, and the influence of geometric parameters on the impact resistance of the honeycomb structure is studied. Finally, the orthogonal test method was used to analyze the influence and weight of the geometric parameters on the anti-impact performance of the honeycomb structure with hydraulic leg stress and roof displacement as the evaluation indexes. This paper provides a new design idea for the research and development of an impact resistance hydraulic support in the underground coal mine, which is significant in ensuring coal mine safety.

Correlation Study between the Mechanical Property of the Square Cone Energy-Absorbing Structure and Collision Energy Distribution for Urban Rail Trains

In order to study the influence of the square cone energy-absorbing structure of urban rail trains on the collision energy distribution of trains during the collision process, an eight-marshalling train crash dynamics model was established, and the force–displacement energy-absorbing characteristic curve of the anti-climbing structure was obtained through a full-scale impact experiment. According to the characteristics of the curve, the influence of the initial peak force, the platform force and the slope of the platform force of the anti-climbing energy-absorbing device on the energy absorption of the train collision under a 25 km/h condition was studied. Based on this, the multi-objective genetic algorithm was used to optimize the overall energy distribution scheme of the train. The results showed that the changes in the initial peak force, the platform force and the slope of the platform force will lead to changes in the energy absorption of the four-section moving train and the four-section stationary train that are closer to the collision interface, and the other is almost unchanged. Through the optimized design, the energy absorption of the head car impact interface is increased by 0.74%, the energy absorption of the first impact interface of the middle cars is reduced by 3.36% and the third impact interface of the middle cars is increased by 9.17%. The distribution of the collision energy of the train is more reasonable. At the same time, the deformation of the middle car body is reduced, and the utilization efficiency of the overall energy-absorbing structure of the train is improved.

Study on energy absorption characteristics of expansion tube with light magnesium alloy

This paper proposed a lightweight magnesium alloy expansion energy-absorbing structure. The structure adopts lightweight materials, which can greatly reduce its own weight on the basis of ensuring energy absorption performance. Firstly, the geometric model of structure is designed and the corresponding physical prototype is processed. The theoretical model of magnesium alloy expansion tube is studied, and the main mechanical response is analyzed. Then the structural mechanical properties are studied by quasi-static compression test. Combined with the theoretical model, several typical deformation stages in expanding are analyzed. The effects of geometric parameters on the energy absorption performance are studied. The results show that with the increase of die angle, die expansion size and tube thickness, the maximum peak force, average force, energy absorption and specific energy absorption increase. Then the test results are compared with the corresponding theoretical steady force to verify the applicability of the theoretical model. The theoretical values are basically in good agreement with the experimental values. The error of all results is within 10%. Finally, comparing the characteristics of magnesium alloy, aluminum alloy and steel energy absorbing tube with the same quality, it is concluded that the specific energy absorption of magnesium alloy structure is 31.6% and 4.1% higher than that of steel and aluminum respectively, and magnesium alloy tube has higher specific energy absorption.

Efficient crash structure design for road traffic accidents of tomorrow

Energy absorbing structures (EAS) play a vital role in automotive crash mitigation systems and save countless lives each year. Innovative EAS design ideas such as cross-sectional geometry is an area under intense research as evidenced by a large number of publications in recent years. It is however very difficult to directly compare the efficiency of the design suggestions due to parameter variation. This paper identifies designs with the highest potential, introduces an efficient reduced order modelling methodology and provides the first comprehensive unbiased benchmark. Critical evaluation of results reveal that some designs have inherent issues not previously reported, whilst others demonstrate significant potential for improving EAS performance compared to “conventional” designs.

Sandwich structure with negative Poisson’s ratio of periodic rectangular tube: Mechanical properties and energy absorption

Due to its unique deformation form, Negative Poisson’s ratio sandwich structure has excellent energy absorption, but the low load capacity limits its engineering applications. In this paper, we design a new negative Poisson’s ratio rectangular tube periodic sandwich structure. There are many beams in this structure which appear plastic hinges when compressed. After further compression, the rectangular tube wall buckles and the core shrinks inward, which realizes that the structure exhibits high-performance energy absorption ability and excellent mechanical properties. Three-dimensional finite element model of sandwich structure with negative Poisson’s ratio of periodic rectangular tube quasi-static compression test and low-velocity impact were investigated by the use of ABAQUS/Explicit software. The accuracy of the simulation method was verified by the comparison of test and simulation results. Based on the validated numerical models were further investigated to comprehensively understand the influence of rectangular tube unit cell wall thickness ( t) and cell height ( h) on the load capacity and energy absorption capacity of the specimen. The energy absorption capacity and mechanical properties of the proposed negative Poisson’s ratio sandwich structure could be enhanced by optimizing the design of rectangular tube unit cell wall thickness ( t) and rectangular tube unit cell height ( h). The present findings offer insights into the application of negative Poisson’s ratio sandwich structure impact energy-absorbing structures in aerospace, automotive and other fields.