Increase In Specific Energy Absorption Research Articles

A Synergistic Approach Combining Surface Enhancement and Buckling Modes for Improved Axial Crushing Performance of Thin-Walled Tubes

Abstract In this study, thin-walled tubes were circumferentially strengthened by plasticity ball burnishing of critical locations determined from buckling mode analysis. Axial crush test results revealed that the surface-treated (ST) tubes increased localized yield strength, attained superior crashworthiness performance, and triggered predictable deformation modes according to the buckling modes of the tubes. Numerical analysis was performed and successfully validated with the experiment at 90% prediction accuracy. The treated tube ST-4 with the 12th buckling mode outperformed a conventional tube with an increase in specific energy absorption (SEA) and crush force efficiency (CFE) by up to 70% while sustaining a low increase in initial peak force (IPF). Furthermore, the tube demonstrated a greater rate of energy dissipation compared to tubes with conventional surface-treated patterns at the same level of surface-treated area. The crashworthiness performance improved as the surface-treated area ratio increased. A theoretical model was developed for the surface-treated tube based on fundamental deformation kinematics, predicting mean crushing force and total energy absorption with acceptable accuracy. The findings strongly suggest that the proposed surface-enhanced tubes have great potential to be used as energy-absorbing structures in crashworthiness applications.

A ribbed strategy disrupts conventional metamaterial deformation mechanisms for superior energy absorption

ABSTRACT Enhancing energy absorption in mechanical metamaterials has been a focal point in structural design. Traditional methods often include introducing heterogeneity across unit cells. Herein, we propose a straightforward ribbed strategy to achieve exceptional energy absorption. We demonstrate our concept through modified body-centered cubic (BCC) and face-centered cubic (FCC) ribbed truss-lattice metamaterials (BCCR and FCCR). Using stainless-steel 316L samples, compression tests indicate a 111% and 91% increase in specific energy absorption (SEA) for BCCR and FCCR, respectively, along with an enhancement in compression strength by 61.8% and 40.7%. Deformation mechanisms are comprehensively elucidated through both finite element analysis and theoretical calculations. The mitigation of stress concentration at nodes, redistribution of load transfer pathways within struts, and introduction of multiple plastic hinges collectively contribute to increased energy absorption and higher compression strength. Using rein-based polymer samples, the ribbed truss-lattice metamaterials also exhibit exceptional damage tolerance, experiencing only a 15% loss in maximum strength after cyclic compression at 20% strain, while maintaining a 73% higher SEA compared to their non-ribbed counterpart. This strategy extends beyond the discussed structures, presenting itself as a generic approach to enhance plateau strength and SEA.

Energy absorption characteristics of asymmetric tree-like fractal gradient hierarchical structures

Bionic gradient hierarchy design as a design method that can effectively improve the structural crashworthiness, but its current research only focuses on the symmetric fractal method related to the discussion. In view of this, this article carries out the innovative design and research of asymmetric tree-like fractal gradient hierarchy structure (ATFGHS). The results show that the crashworthiness of the structure can be greatly improved by using the asymmetric tree-like fractal gradient hierarchy design method. Specifically, the ATFGHS-P3 showed a 98% increase in energy absorption (EA), a 98% increase in specific energy absorption (SEA), and an 84% increase in crush force efficiency (CFE) compared to a conventional hexagonal multicellular tube. The completion of this study provides valuable insights into the design and optimization of novel lightweight thin-walled energy-absorbing structures.

In-plane dynamic impact mechanical properties of novel bi-directional hierarchical honeycomb

A novel bi-directional hierarchical honeycomb is proposed. A finite element numerical model was constructed using Abaqus/Explicit, the model's accuracy was verified, and a series of in-plane impact studies were carried out. Firstly, the mechanical properties of axial impact were analyzed for different bi-directional hierarchical honeycombs. The results show that the mechanical properties of NBHH-h1h22h3-III and NBHH-h1h2h3h4-IV are the best and almost identical. Subsequently, the mechanical properties of NBHH-XhxYhy-IIs with different layers were analyzed. Research results show that NBHH-h33h4-II has a 77.96 % increase in specific energy absorption (SEA) compared to NBHH-h13h2-II, and NBHH-h13h2-II has a 116.02 % increase in SEA compared to NBHH-3h1h2-II. A parametric study of NBHHs was conducted. The mechanical properties of NBHHs with different layer ratio coefficients were analyzed, and it was found that the mechanical properties of NBHHs with l2 = 12 and k = 0.2 are the best. Finally, the effects of wall thickness and velocity on NBHHs were analyzed. Increasing the wall thickness appropriately can effectively improve the impact resistance of the structure. Bi-directional hierarchical design provides a practical reference for enhancing the in-plane mechanical properties of honeycombs.

Crashworthiness properties of square hierarchical multicellular tube under axial impact

A new square hierarchical multicellular tube design is introduced, and the crashworthiness of various square hierarchical multicellular tubes with identical wall thickness and mass is systematically analyzed using validated numerical models. The study explores the impact of parameters such as layer level, wall thickness, and impact load angle on the structure’s impact resistance. Additionally, the impact resistance of square hierarchical multicellular tubes is compared to that of conventional square multicellular tubes with the same wall thickness. The findings reveal that the proposed square hierarchical multicellular tube effectively mitigates peak crushing forces and enhances crushing force efficiency under the same mass. Specifically, the third-order square hierarchical multicellular (SHMT-3) tube exhibits a 48.23% increase in specific energy absorption and a 75.14% improvement in crushing force efficiency. Notably, the peak crushing force decreases by 15.40% compared to that of the square tube. Under identical wall thickness, the crush force efficiency of SHMT-3 reaches 89.51%, marking a 125.21% improvement compared to square tube. Overall, the comprehensive crashworthiness of square hierarchical multicellular tubes surpasses that of traditional square multicellular tubes. These results contribute valuable insights for innovatively designing new hierarchical multicellular tube structures.

Mechanical property enhancement in additively manufactured NiTi double-asymmetric honeycombs with bioinspired graded design

ABSTRACT The cuttlebone is known for its ability to possess high specific stiffness, progressive failure and lightweight from the porous chambered structure. Inspired by the microstructural characteristics of cuttlebone and incorporating the wall gradient design, a series of double-asymmetric honeycombs were designed and processed by LPBF. Results indicated that bionic structural units with the junction design can maintain the integrity of the residual parts after local buckling and failure, improving the load-bearing capacity. The double-asymmetric honeycomb with gradation parameter α = 2/3 achieved a maximum specific compressive strength of 70.64 MPa cm3/g. As α decreases, there is an increase in specific energy absorption and a narrowing of the hysteresis loop. The as-build honeycomb had undergone stress-induced martensite transformation during compression. The dissipated mechanical energy (ME) decreased with the increasing cycle number and the decreasing α. The results provide design guidelines and process strategies for developing high-performance honeycombs.

Evaluation of Automotive Bio-Composites Crash Box Performance

In the automotive industry, sustainable materials, such as bio-composites, are progressively being adopted due to their lightweight feature, which reduces vehicle weight, fuel consumption and pollutants emissions. Bio-composites are renewable and biodegradable, making them more environmental-friendly. However, limited investigations into the use of bio-composites in crash box applications have indicated that they lack the impact strength to fully absorb collision energy. This study aims to compare the crashworthiness performance of crash boxes made from OPEFB fiber/epoxy and kenaf fiber/epoxy composites, with conventional steel and carbon fiber/epoxy using LS-DYNA quasi-static simulations. Six different crash box designs are proposed: square, hexagonal, decagonal, hexagonal 3-cell, hexagonal 6-cell, and decagonal 10-cell structure, to evaluate the effect of these designs on crash box performance. The results show that bio-composite crash boxes are inferior to traditional materials in terms of energy absorption and specific energy absorption, but they yield better performance in crush force efficiency. In terms of design, decagonal 10-cell structure produces the highest specific energy absorption and energy absorption for bio-composites. Hence, optimization is performed on the OPEFB fibre/epoxy decagonal 10-cell crash box, aiming to increase energy absorption capability by varying the thickness, perimeter, and length of the crash box. The design is optimized by increasing thickness and maintaining length and perimeter. Compared to the original design, the optimized design improves energy absorption by 59% and specific energy absorption by 19%. The optimized design is then subjected to both quasi-static and impact loading tests, revealing that the optimized OPEFB fibre/epoxy crash box design exhibits 44% lower energy absorption than steel under quasi-static load, but it demonstrates a 56% increase in crush force efficiency and a 6 % increase in specific energy absorption. Under impact load, it shows a 91% increase in specific energy absorption compared to the traditional square steel crash box.

Mechanical responses and energy absorption characteristics of a novel functionally graded voxel lattice structure

Functionally graded lattice structures have attracted considerable interest owing to their superior mechanical performance compared to traditional uniform structures. In this paper, a novel voxel lattice unit cell with multiple symmetrical struts was designed, and graded lattice structures with variable densities were proposed. Quasi-static compression tests and numerical simulations were conducted to investigate mechanical responses, deformation modes, and energy absorption abilities. The results demonstrated that graded design enabled tunable deformation and a significant 20.3 % increase in specific energy absorption compared to uniform structures. This study expands the design space of functionally graded lattice structures and highlights their significance in practice.

Crashworthiness of Additively Manufactured Lattice Reinforced Thin-Walled Tube Hybrid Structures

In this paper, a new hybrid structure of body-centered cubic lattice-filled thin-walled tube is designed, and the hybrid structure specimens of one-piece printing and split-printing are prepared by laser melting technique. The deformation mode and energy absorption characteristics of the new hybrid structure are investigated by experiments and numerical simulations. Under axial compression, the one-piece printed hybrid structure forms more wrinkles with smaller wavelengths, and the specific energy absorption increases by 12.14% compared with the split-printed structure; under transverse compression, the one-piece printed structure does not show the separation of the thin-walled tube from the lattice, and the specific energy absorption increases by 134.83% compared with the split-printed structure. It is worth noting that the designed hybrid structure has a 112.60% (580.15%) increase in specific energy absorption under axial compression (under transverse compression) compared to the empty tube. The effects of wall thickness, lattice density, and loading rate on the crashworthiness of the hybrid structure were investigated using a validated finite element model. This paper provides a new idea for the preparation of lightweight and high-strength energy-absorbing structures.

High Frictional Coated Multi-Layer Ballistic Fabrics for High Velocity and Hypervelocity Impact Protection

Increasing the inter-fiber friction of ballistic fabrics is crucial for improving their impact shielding performance. Shear thickening fluid (STF) impregnation is commonly used to improve inter-fiber friction, but it has several fundamental shortcomings. Polymer coating, with its superior properties, can be an ideal material for increasing the friction coefficient of fabrics. Our study aimed to evaluate the effectiveness of the coating process in enhancing the energy absorption mechanism within and among the fabric layers. Additionally, we investigated the capability of a multi-layer coated fabric system for hypervelocity impact shielding and spall liners. Our findings demonstrated the effectiveness of the coating process in improving the ballistic limit of the fabric system. Coated fabrics showed a 19.6% and 23.4% increase in specific energy absorption compared to pristine fabrics. We conducted hypervelocity impact experiments with impact velocities between 1.9 km/s to 2.1 km/s using a triple bumper system. The front bumper generated a debris cloud, the back bumper comprised the coated fabrics, and the third bumper acted as a witness plate. We compared the area of impact on the witness plate and the penetration area to estimate the efficiency of the coated fabrics. Our results showed that the coated fabrics had a higher area of impact with lower intensity of damage and a decrease in the penetration area compared to pristine fabrics with similar areal densities, indicating excellent impact shielding performance.

On the Use of a Hybrid Metallic-Composite Design to Increase Mechanical Performance of an Automotive Chassis

Thanks to the introduction of high-performance composite materials, 'metal replacement' approaches are successfully gaining ground even in the most challenging engineering applications. Among these, one of the most recent application challenges is improving the driving range of Battery Electric Vehicles (BEVs) by adopting innovative materials to lighten the mass of structural components, thus reducing energy requirements and enabling the use of smaller and less expensive batteries. Hence, in the present work, the employment of laminated composite panels in an electric minibus chassis is investigated as an effective way to reduce the global mass of the chassis’ structure and, at the same time, to increase its structural performances in terms of torsional stiffness and crashworthiness. By replacing specific steel tubulars with carbon-fiber-reinforced polymer (CFRP) laminated composite structures, different chassis configurations were numerically developed and detailed simulations to compare both masses and mechanical responses were carried out. The paper proves that with this approach it is possible to lighten the chassis up to 9%, while achieving a 7% increase in torsional stiffness and a 9% increase in Specific Energy Absorption (SEA).

Experimental investigation on the quasi-static structural properties of carbon fibre/metal hybrids processed by roll forming

Carbon Fibre Reinforced Metal Hybrid (CFRMH) materials combine high specific strength and stiffness with excellent fatigue resistance and damage tolerance. They are a potential solution for lightweight automotive crash and structural components, but their application is limited due to the lack of cost-effective manufacturing technologies. This study presents a new method for the manufacture of long steel components that are reinforced with a carbon fibre patch via roll forming, a low-cost sheet metal forming process that is heavily applied in the automotive industry. For this, CFRMH sheets are first produced in a hot press and then roll-formed to hollow components that are structurally tested in a 3-point bending test. The material deformation after roll forming and the failure modes after the structural tests are analysed with optical microscopy. The results of this study show that part quality and forming defects after roll forming depend on the carbon fibre orientation and the forming temperature. Depending on the carbon fibre layup, an increase in specific energy absorption of more than 45.6% was achieved compared to the sole steel counterpart. This was related to an intact adhesion at the carbon fibre–steel interface after roll forming, which allowed the carbon fibre patch to effectively absorb the deformation energy. The results suggest that roll forming presents a low-cost alternative for metal hybrid part production with significant potential to reduce weight and increase the structural performance of future automotive components.

Crashworthiness design of hexagonal tubes using self-similar inspired structures

In this paper, we focus on the design of multi-cell hexagonal tubes filled with self-similar inspired multi-cell tubes with a different layout. The effect of the hierarchy design, layout optimization and the number of self-similar inspired substructures were numerically investigated. The multi-criteria decision-making method (COPRAS) is used to evaluate crashworthiness. The results show that the self-similar inspired substructures filled in the edge middle of the multi-cell hexagonal tubes provide a higher crushing force and specific energy absorption than those filled in the corner of these multi-cell tubes for both 0th and 1st order multi-cell hexagonal tubes. The crushing force and the specific energy absorption increase with the hierarchy and the number of substructures. The max specific energy absorption of 2nd order multi-cell hexagonal tubes with two self-similar inspired substructures is 2.82 times higher than that of the 1st order multi-cell hexagonal tubes with one self-similar inspired substructure. It is found that the crashworthiness of these multi-cell tubes can be further enhanced by optimizing the cross-sectional topology. The current study provides a new approach to optimizing the crashworthiness of self-similar inspired structures for engineering applications.

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.

Processing of in-situ aluminium foam-filled stainless steel tube with foam-tube bonding for enhanced crashworthiness

This work aims to achieve superior mechanical properties in in-situ aluminium foam-filled stainless steel 316L tubes by promoting good bonding between the foam and the tube. Towards this end, the stainless steel tubes (inner surface) were electroplated with copper before in-situ foam-filling. Detailed microstructural studies were conducted at the foam/tube interface. In-situ foam-filled tube specimens were subjected to uniaxial compression and three-point bend testing. The axial compression and bending performance of the in-situ foam-filled tubes were compared with ex-situ foam-filled tubes and in-situ foam-filled tubes produced without copper coating. The deformed samples were sectioned and analysed to understand the deformation modes. The results show that copper coating is very effective in promoting good bonding between the foam and the tube during in-situ foaming, leading to considerable improvement in the mechanical performance of the foam-filled tubes. Ex-situ-heat processed (ex-situ-HP) foam-filled tubes (FFTs) and in-situ-uncoated (in-situ-UC) FFTs were found to display approximately 34 % and 46 % increase in specific energy absorption (SEA) as compared to empty-HP tubes. Electroplating of the inner surface of the steel tube with copper before in-situ foam-filling was found to promote good metallurgical bonding between the foam and the steel tube. Because of the enhanced foam-tube bonding, the in-situ-copper coated (in-situ-CC) FFTs were found to display ~61 % and 10 % higher SEA as compared to the empty-HP and in-situ-UC FFTs, respectively. The deformation mechanisms in foam-filled tubes are discussed in detail.

Sandwich structures with repairable cores based on truncated cube cells

With dramatic increase in 3D printing applications in industry, sandwich panels with 3D printed cores have gained a lot of attention recently. In harmony with global movement towards sustainability and low-carbon emission industries, sandwich panels with easy-to-repair and cost-effective cores would be very attractive structures. In this regard, implementing separated cells for constructing lattice structures instead of using back-to-back lattice structures makes repairing local damages in the core easier and more cost-effective. Ideally, a damaged cell can be replaced with an intact new cell without the need to change the whole core structure. In this study, mechanical responses of a single truncated cube unit cell, a well-known geometry for constructing regular lattices has been studied analytically, numerically, and experimentally. Analytical relationships were derived for stiffness, yield stress, and Poisson's ratio of a single unit cell. Samples were 3D printed and tested mechanically in large deformation regime. A good agreement between results from analytical derivations, numerical simulations, and experiments was observed. It was shown that an equilateral truncated cube structure has a yield stress at least twice of that for a simple cube structure. Three types of repairable sandwich panels with different uniform core densities as well as four graded cores were studied as well. The functionally graded sandwich panels presented the best performance while considering both energy absorption capacity and mass. The best functionally graded sandwich panels (Type 4) showed an increase in specific energy absorption (SEA) by almost 21% and a decrease in maximum displacement by 2.5% with respect to the second-ranking best option.

High-velocity impact resistance of doubly curved sandwich panels with re-entrant honeycomb and foam core

This work describes the high-velocity impact behavior of doubly curved sandwich panels. The sandwich panels are manufactured using carbon/fiber epoxy composite face sheets, polyurethane foam core and 3D-printed PLA plastic cellular auxetic (re-entrant) honeycombs. High-velocity impact tests are carried out by using a single-stage air gas gun test machine. A spherical steel projectile with the radius of 5 mm is impacted to the center of the specimens with the speed of 100 m/s. The experimental data are used to validate explicit finite element models of the doubly curved structures. An analytical model is also developed for the ballistic limit of the flat and doubly curved sandwich panels, and the analytical results are compared to those obtained from the numerical ones. Parametric numerical analyses of the high-speed impact of the curved sandwich panels are then carried out considering various radii of curvature of the panels. The results show that the energy absorption is increased as the curvature is decreased for the panels with both foam and re-entrant core. In addition, the core configuration provides a key role in the impact resistance of the sandwich panels. Re-entrant models show an increase in specific energy absorption (SEA) compared to the foam core types.

A novel class of bioinspired composite via ultrasound-assisted directed self-assembly digital light 3D printing

The advent of advanced manufacturing technologies brings about the possibilities of novel materials with potentially unprecedented material properties. Through ultrasound-assisted directed self-assembly digital light processing, we present a novel class of composite – the discontinuous interpenetrating-phase composite (d-IPC) – where the cellular filler phase is based on lines of particle assemblies, as opposed to continuous materials. Through yttria particle doping, we fully illustrate the unique microstructural-specific mechanical properties of the d-IPC. Despite being fully bulk and having a similar density (1.18 g/cm3) and strength (68 MPa) as the matrix polymer, it presents an additional plateau-deformation behaviour under large compressive strains and hence a 218% increase in specific energy absorption up to 37 J/g. The enabling mechanism is derived from the peculiar discontinuous and macroscopically aligned particle-based struts which do not contribute to a notable diminution of strength but can yet modulate high-strain deformation via induction of progressive localized failures. The concept of d-IPC is also extendable to solid fillers of all materials, morphology, and reasonable sizes, allowing the d-IPC to be highly customizable with multifunctional potentials. Through this work, we also aim to demonstrate the potentials of using advanced microstructural-controllable manufacturing techniques to achieve conceptually new and advanced composite materials.

Study on compression load and energy absorption characteristics of glass fiber honeycomb tube

In terms of the deficiency of the existing research on the compression load and energy absorption characteristics of composite structures, a glass fiber honeycomb tube with different thickness and different cell number was proposed. The static compression test was carried out by universal testing machine. The results show that the failure forms of honeycomb tube are fiber fracture damage, fiber layer delamination and their composite forms. The peak compression load and total energy absorption increase with the increase of cell number and thickness, and the specific energy absorption increase only with the increase of thickness. The compression peak load of single-cell honeycomb tube with wall thickness of 0.4 mm is the smallest, which is 2.21 KN; and the compression peak load of eight-cell honeycomb tube with wall thickness of 1.2 mm is the largest, which is 91.48 KN. The corresponding total energy absorption is 25.16 J and 2257.57 J respectively; the corresponding specific energy absorption is 8.38 J/g and 45.06 J/g respectively.

Effect of smoke treatment on flexural strength of bamboo hierarchical structure

Despite bamboo’s noteworthy durability, the incidental effects of smoke treatment on the mechanical properties of bamboo culms, including its underlying mechanisms, have not been fully investigated. This study investigated the effects of smoke treatment on the flexural strength of Madake bamboo’s (Phyllostachys bambusoides) hierarchical structure. Results in small clear specimens displayed an asymmetrical flexural behaviour regardless of the applied treatment, and the parameters of flexural strain and specific energy absorption, demonstrated by modulus of elasticity and modulus of rupture, were found to differ. Concerning compression, parenchyma cells had good ability to absorb large deformation, indicated by their large increase in specific energy absorption. In addition, a distinct difference was found between smoke-treated bamboo and untreated bamboo as the capacity of its outermost fibres to withstand greater tensile load was impaired, indicated by the reduction in flexural strain. Thermal degradation caused an increase in the hydrophobicity of bamboo’s outermost layers, thereby engendering higher brittleness in the smoked bamboo. This work highlights critical changes in the mechanical properties of smoked bamboo, which can be addressed in future studies to improve its strength as a sustainable construction material.