Specific Energy Absorption Research Articles

Closed-cell Polyurethane In-situ Foaming Hofneycomb for Enhanced Energy Absorption and Water Intrusion Resistance

To achieve novel core with high energy absorption and strong water intrusion resistance, a composite structure was created by employing in-situ foaming of closed-cell polyurethane (PU) in a honeycomb structure. Experimental, theoretical, and finite element analyses revealed that the in-situ foaming technique increased the honeycomb's energy absorption by 312.84% and improved impact efficiency by 61.45% while maintaining specific energy absorption (SEA). Remarkably, this composite structure surpassed the energy absorption capacity of individual honeycomb and foam. The coupling gain ratio introduced by the foam increases within a certain range as the honeycomb cell size decreases and wall thickness increases, with little influence from the foam's mechanical properties. Water intrusion, leading to ice formation at low temperatures, drastically reduced honeycomb SEA by 94.61% and impaired mechanical properties significantly. Closed-cell PU in-situ foaming provided exceptional water intrusion resistance, preserving the honeycomb's mechanical performance, including energy absorption and SEA.

Nonlinear Mechanical Properties of Irregular Architected Materials

Abstract Architected materials have received increasing attention due to their exotic mechanical properties including ultra-high stiffness-to-weight ratio, strength, energy absorption, and toughness. Typically, their mechanical properties and deformation behavior arise from the periodically tessellated unit cells. Although periodicity in conventional architected materials promises homogeneity and predictability in mechanical behaviors, it imposes a strong restriction on the design space of architected materials. Inspired by biomaterials, aperiodic and disordered designs significantly expand the design space and have been proven effective in controlling and optimizing linear elastic properties. Taking a step further, here we focus on the nonlinear properties of irregular lattice materials under large deformation, including the stress–strain curve and specific energy absorption. Such materials are generated by a nature-inspired virtual growth program that assembles predefined geometric building blocks in a stochastic yet controllable manner. The nonlinear properties are analyzed through quasi-static compression experiments and large-scale numerical simulations. Based on the well-agreed experimental and numerical results, through the lens of machine learning techniques, the nonlinear properties show a strong correlation with the appearance frequency of the building blocks and their local connectivity, regardless of the nondeterministic nature of the microstructures. A practical constitutive model is proposed for future developments such as generative design and engineering application. Our research offers valuable insights and serves as an inspiration for deeper exploration into the intricate structure–property relationships within materials with aperiodic and disordered microstructures.

Crashworthy Performance of Sustainable Filled Structures Using Recycled Beverage Cans and Eco-Friendly Multi-Cell Fillers

The recycling of resources is an important measure to achieve circular economy and sustainable development. In this paper, a sustainable filled structure was proposed and realized by combining recycled empty beverage cans with eco-friendly multi-cell fillers. Quasi-static axial compressions were carried out to characterize the energy absorption performance and synergistic effect of the filled tubes. Experimental results showed that the crashworthiness of sustainable filled structures varied with both filling densities and materials. With the increase in filling density, the specific energy absorption of the filled tubes presented an upward trend. With the variation in filling materials, the filled tubes exhibited different crashworthiness performances. The PLA multi-cell filled tube could withstand larger external force and exhibited higher SEA values, with a maximum value of 9.64 J/g. The PLAS multi-cell filled tube showed excellent loading stability and lower ULC value, with a minimum value of 10%. These findings provided valuable insights for designing novel sustainable energy absorption structures.

A Novel Approach for Fabricating In Situ Aluminum Foam‐Filled Carbon Steel Tubes via Hot‐Dip Aluminizing

Herein, a new process combining hot‐dip aluminizing (HDA) technology with melt foaming method is developed to prepare in situ aluminum foam‐filled AISI 1020 tubes with metallurgical bonding which has the advantages of low production cost and wide range of product sizes. Detailed microstructural characterization is performed at the foam/tube interface of in situ foam‐filled tubes (FFTs). Quasistatic compressive experiments are carried out to investigate deformation behavior and mechanical properties of ex situ and in situ FFTs with and without HDA pretreatment (in situ‐HDA FFTs and in situ‐without HDA FFTs). The results indicate that HDA pretreatment effectively improves the wettability between the steel tube and the aluminum melt, enhancing the interfacial bonding quality between the two. Under compressive loading, in situ‐HDA FFTs axially deform in an efficient mixed mode, showing superior energy absorption capability as compared to the empty heat treatment (empty‐HT) tubes. Specifically, in situ‐HDA FFTs have the highest specific energy absorption of an average of 16.6 kJ kg−1 which is 13% higher than the average value of ex situ‐HT FFTs.

Energy absorption characteristics of asymmetric tree-like fractal hierarchical circular tubes under axial impact

A circular tube structure with asymmetric tree-like fractal hierarchical properties, known as asymmetric tree-like fractal hierarchical circular tubes (ATFH), was designed by combining an asymmetric tree-like fractal hierarchical structure with a single circular tube. The crashworthiness of this structure under axial impact was investigated using an experimentally validated LS-DYNA finite element model. Results showed that the Specific Energy Absorption (SEA) of ATFH-L4 tubes improved by 17.65%, 51.21%, 39.85%, 20.37%, 10.45%, and 44.81% compared to BBT, CMT, CT, GBCT-L3, HCT-P, and MCT tubes, respectively. The study of energy absorption performance of ATFH tubes at different fractal positions revealed that ATFH-L2-B6/8, ATFH-L3-B6/8, and ATFH-L4-B5/8 exhibited superior energy absorption properties. These findings demonstrate that the asymmetric tree-like fractal hierarchical structure design can enhance structural crashworthiness. The results provide an effective guide for designing multi-cellular structures with high energy absorption efficiency.

Stiff, lightweight, and programmable architectured pyrolytic carbon lattices via modular assembling

Recent advances in additive manufacturing have enabled the creation of three-dimensional (3D) architectured pyrolytic carbon (PyC) structures with ultrahigh specific strength and energy absorption capabilities. However, their scalability is limited by reduced strength at larger sizes. Here we introduce a modular assembling approach to scale up PyC lattice structures while retaining strength. Three assembling mechanisms—adhesive, Lego-adhesive, and mechanical interlocking—are explored, demonstrating notably increased specific compressive strength and modulus as size increases, driven by energy release from assembly joint fractures. Practical application is demonstrated by using assembled PyC lattices as the core of an aerospace sandwich structure, significantly enhancing indentation resistance compared to conventional aramid paper honeycomb core. The method also enables versatile designs, including curved structures for space debris protection and bio-scaffold applications. This scalable approach offers a promising pathway for integrating PyC structures into large-scale engineering applications requiring superior mechanical properties and programmability in complicated shape design.

Revisiting the safety limit in magnetic nanoparticle hyperthermia: insights from eddy current induced heating.


Magnetic nanoparticle hyperthermia (MNH) emerges as a promising therapeutic strategy for cancer treatment, leveraging alternating magnetic fields (AMFs) to induce localized heating through magnetic nanoparticles (MNPs). However, the interaction of AMFs with biological tissues leads to non-specific heating caused by eddy currents, triggering thermoregulatory responses and complex thermal gradients throughout the body of the patient. While previous studies have implemented the Atkinson-Brezovich limit to mitigate potential harm, recent research underscores discrepancies between this threshold and clinical outcomes, necessitating a re-evaluation of this safety limit. Therefore, in this study, through electromagnetic (EM) simulations, the complex interaction between AMFs and anatomical models was investigated. 
Approach. 
In particular, we considered a circular coil configuration placed at different positions along the craniocaudal axis of various anatomical human models. The excitation current was normalized, at different frequencies, to meet the basic restriction of local 10g-averaged specific energy absorption rate (SAR) in the human models, as defined by the exposure guidelines of the International Commission on Non-Ionizing Radiation Protection (ICNIRP 2020) and the standard IEC 60601-2-33 of the International Electrotechnical Commission (IEC 2022). 
Main Results. 
The resulting permissible magnetic field strength values for the reference levels set by ICNIRP (2020) for occupational and general public exposure, emerged to be up to approximately 1.4 and 3 times less than that defined in the Atkinson-Brezovich limit. The widely used limit was found to align more closely with the first level of controlled operating mode defined in IEC 60601-2-33 (IEC 2022). 
Significance. 
The results indicate that the permissible magnetic field amplitude during MNH treatment should be much lower than that in the Atkinson-Brezovich limit. This study offers valuable insights into the role of computational simulations in advancing the potential to establish a reliable metric for safety evaluation and monitoring within the clinical framework of MNH.

Compression performance of 3D-printed ant-inspired lattice structures: An innovative design approach

In this study, three different ant-inspired lattice design types: single, double, and inverted double structures were considered due to ants’ excellent load-carrying weight ratio. Lattice structures were fabricated using the 3D printing method and polylactic acid filament was used as a printing material. The true blueprint images of the ant were used to obtain the parametric dimensions of the ant-inspired lattice structure. Hence, the presented innovative method for designing lattice structures can be a promising option for industrial sectors requiring high-strength structures. The quasi-static axial compression tests were conducted to evaluate the compression performance of the novel lattice structures. The compression performance of ant-inspired single lattice structures was compared based on specific force, specific energy absorption, and specific stiffness at different height values. The deformation stages and damage regions of ant-inspired lattice structures were analyzed to identify their critical regions during compression tests. The results indicated that as the height value increased, there was a notable decrease in specific force, specific energy absorption, and specific stiffness, along with buckling damage in the ant-inspired single lattice structures. Among the three design types, the ant-inspired inverted double lattice structure showed better compression performance compared to the ant-inspired double lattice structure; however, the ant-inspired single lattice structure with a height of 30 mm exhibited the highest overall compression performance.

Effect of curvature angle and structural configurations on dynamic performance of honeycomb sandwich structures

The aim of this study is to investigate the effects of curve angle and structural parameters on ballistic performance of honeycomb sandwich structures. In the study, high-velocity impact simulations were performed in LS DYNA finite element program to investigate the effects of honeycomb structural parameters, curve angle, residual velocity, specific energy absorption (SEA) and damage mechanism. Progressive damage analysis based on the combination of cohesive zone model (CZM) and bilinear traction-separation law was performed. The ballistic limit value increased by 41.9% when the facesheet thickness increased by two times. When the cell wall thickness increased by five times, the ballistic limit value increased by 13.3%. When the core height was two times increased, the ballistic limit velocity value increased by 2.076 times. Although the ballistic limit velocity value of the CFRP Facesheet and Aluminum (Al) core sandwich structure is 7.14% lower than the all Al specimen, the SEA value is 9.47% higher. When the curve angle increases from 0˚ to 180˚, the ballistic limit value decreases by 22.8%. In general, this study provides useful information about the design of ballistic structures, parameters affecting their performance and their effects.

Development of impact characteristics response model for combined tube expansion axial splitting module

Combined tube-expansion and axial splitting mechanism yields excellent force-displacement characteristic and high stroke efficiency. In this paper, a mathematical model to estimate and optimise impact response of such mechanism was developed, to correlate the impact response to the module dimensional parameters, i.e. diameter-to-thickness ratio, D1/t and expansion ratio, D2/D1 and other design parameters such as material strength, expansion angle, and friction coefficient. Accurate finite element (FE) analysis, validated with experimental results were performed to generate results sufficient to form a response surface model (RSM). The current mathematical model successfully captured the effect of expansion ratio, thickness ratio, and initial diameter of the tube, with R 2 of 0.99 for specific energy absorbed and 0.81 for mean crushing force throughout 80 data points. A case study was also presented which shows the result comparison between numerical and the proposed model, yielding error below 1% difference for mean and peak crushing force, total energy absorbed, specific energy absorbed (SEA), stroke and crushing force efficiencies. The model has also been implemented in an optimisation for railway vehicle case study using the proposed mathematical model. The current research found that the combined module could reach SEA and stroke efficiency values of 29.74 kJ/kg and 0.99, respectively, significantly better than most of the metallic-based impact energy absorbing mechanisms.

Origami-inspired auxetic structures: Design and performance in quasi-static and dynamic loading

Auxetic metamaterials have gained attention due to their unique mechanical properties. Integrating origami structures with cellular structures can significantly enhance their energy absorption capacity under mechanical loads. This study develops a novel auxetic structure by combining a curved origami design with the cross-petal auxetic structure. The structure’s behavior under in-plane compressive loading is analyzed using finite element simulations and validated through experimental testing of 3D-printed specimens. The effects of loading rates (quasi-static, low-, medium-, and high-velocity) and geometrical parameters on energy absorption are examined through parametric studies. Structure grading, based on unit cell wall thickness, is also investigated to enhance performance. Finally, the proposed structure’s energy absorption is compared with two common auxetic metamaterials (reentrant and chiral) under various loading conditions. Results indicate deformation becomes more localized with increased loading velocity, with the proposed design achieving a 70% improvement in energy absorption over non-origami designs and a 16% enhancement through grading. The main contribution of this study is the creation of a hybrid structure combining curved origami and cross-petal auxetic designs, achieving a 70% improvement in energy absorption. The dual plateau stress region and graded design further enhance performance, positioning it as an innovative solution for impact protection and soft robotics. The proposed structure exhibits up to 7.56 times higher specific energy absorption under quasi-static loading compared to reentrant and chiral designs, maintaining superior performance at higher loading velocities.

Functionally graded sustainable lattice structures: Insights into material grading and lattice hybridization

This novel work presents the investigation of functionally graded lattice structures (FGLS) based on polylactic acid (PLA) and wood-reinforced PLA (WPLA) composite. The synergistic effect of a multi-material system and hybridization of two different primitive lattices (Gyroid and Schwarz primitive (SP)) on compressive strength, specific energy absorption (SEA) and stiffness was studied. The findings of the study revealed that the hybrid FGLS fabricated combining the Gyroid lattice of PLA and SP lattice of WPLA (PLA-G/WPLA-SP) exhibits the highest values of stiffness, SEA, and compressive strength.

Development and Performance Evaluation of an Auxetic Yield Metal Damper for Enhanced Seismic Energy Dissipation

In this study, a new auxetic yield metal (AYM) damper is introduced for the first time based on the application of the auxetic structure. The performance of the proposed system is investigated via nonlinear finite element analysis by using ABAQUS commercial code. These types of steel dampers are fabricated from mild steel plate with elliptical holes and dissipate energy through the inelastic deformation of the constitutive material. To assess the capability of the proposed AYM damper, a set of nonlinear quasi-static finite element analyzes has been conducted on the damper with various geometric parameters. To ensure that the numerical models accurately predict the responses of AYM dampers, experimental validation techniques were employed. This validation confirms the models' sufficient accuracy in representing the dampers' behavior. According to the results, the proposed AYM damper exhibits a low yield displacement, stable hysteretic loops, a good range of ductility, and a high energy dissipating capacity. The specific energy absorption and ductility of the proposed auxetic damper are 32.5J/kg and 59, respectively. With its ductile behavior, this damper can dissipate a large amount of earthquake input energy. Furthermore, it is found that the use of proposed auxetic dampers in the steel frame, increases the hardness, strength and ductility of the frame and the energy absorption increased by 210%.

Design Method of Gyroid Lattice Structure Based on the Load Paths Direction and Capacity

The Design of lattice structures with triply periodic minimal surface (TPMS) can improve the specific stiffness, strength, heat dissipation, and energy absorption functions of their physical structures. The load-transferred law in the structure can serve as a crucial basis for the design, including the distribution and anisotropy of the unit cells. In this paper, a design method based on load paths is proposed and a series of Gyroid lattice structures with variable density cells, variable direction cells, and combination of variable density and direction cells, are designed with better mechanical properties. The load paths within a given structure are extracted to explicitly provide the load-transferred law. The capacity of the load paths is then proposed to guide the distribution of the cells, and a mapping relationship with the parameters controlling the porosity is established. The lattice structures with variable density cells are designed. Afterwards, the pointing stress vectors of the load paths is defined as the main load-transferred direction in the local region to guide the direction of the cells. Based on the anisotropic behavior of the Gyroid cells, the direction setting principles are formulated, and the lattice structures with variable direction cells are designed. Furthermore, a model generation method is proposed, and the Gyroid lattice structures that combine variable density and direction cells are implemented. Two models are applied to validate the proposed method, including a two-dimensional three-point bending beam and a three-dimensional supporting beam. The obtained results show that for the same porosity, both the variable density and variable direction designs of Gyroid cells allow to improve the mechanical properties. The variable density design outperforms the variable direction design. In addition, the Gyroid lattice structures combining variable density and direction cells have significantly higher performance, which indicates that the proposed design method can more effectively increase the load-bearing performance.

Crushing and energy absorption behavior of self-similar nested hierarchically hexagonal honeycomb

To enhance the impact resistance of honeycomb structures, this article proposes a novel self-similar nested honeycomb structure (SNHRH) by incorporating self-similar ribs within the honeycomb framework. Finite element simulations and experimental validations were conducted using Abaqus software. The results from the out-of-plane crushing tests demonstrate that the SNHRH exhibits superior energy absorption capabilities compared to conventional honeycomb structures, hierarchical multifunctional chiral metamaterials, and spider-web hierarchical honeycombs. Furthermore, the enhanced energy absorption characteristics of the SNHRH-1 are not merely attributable to the incorporation of internal cytokinetic elements; rather, they arise from the interactions among these internal components, which result in more pronounced plastic deformation at the intersections. To further elucidate the impact of geometric parameters on the crashworthiness of the proposed honeycomb structure, this study analyzes the significant effects of relative density, rib angle, and thickness ratio distribution. The accuracy of the finite element simulation results was verified through compression tests. The findings indicate that relative density is positively correlated with energy absorption, specific energy absorption, initial peak crash force, and crushing force efficiency. An increase in relative density corresponds to higher energy absorption and specific energy absorption while maintaining constant wall thickness. Notably, within the same type of honeycomb structure, higher orders exhibit improved energy absorption performance. Specifically, the energy absorption of SNHRH-4 was found to be 88.63% greater than that of SNHRH-1.

Crashworthiness Analysis of a Novel Double‐Filled Hierarchical Hexagonal Tube Subjected to Axial Impact

This article presents a novel double‐filled hierarchical hexagonal (DHH) tube. An Abaqus finite element model is utilized to investigate the crashworthiness of this structure under axial impact. A numerical analysis explores the energy absorption (EA) performance across varying different inner hexagon side lengths, fractal orders, and tube masses. The results indicate that specific EA (SEA) increases with the hierarchical order, with the SEA of the second‐order DHH tubes being 9.22–24.70% higher than that of conventional single‐layered hexagonal tubes and 39.20–43.30% greater than that of conventional single‐filled hierarchical tubes. The DHH structure demonstrates optimal performance with an inner hexagon side lengths of 15 mm, achieving the highest SEA across different parameters. This study provides valuable insights for designing hierarchical multicell double tubes with improved EA efficiency.

Bionic Inner-Tapered Energy Absorption Tube Featuring Progressively Enhanced Fold Deformation Mode.

Slender tubes are in high demand owing to their lightweight and outstanding energy absorption. However, conventional slender tubes are prone to catastrophic failures such as Euler's buckling under axial load. Interestingly, growing bamboos overcome this similar dilemma via a unique tapered intine in the internodes, which endows them with excellent energy absorption. Inspired by this finding, a bionic inner-tapered tube (BITT) was designed to enhance the energy absorption of slender tubes under axial load. The special energy absorption (SEA) was evaluated via a quasi-static axial compression test. Then, theoretical calculation and finite element analysis were carried out to analyze the energy absorption mechanisms. The results reveal that the tapered inner wall induces a progressively enhanced fold deformation mode for BITT, which not only prevents buckling failure and decreases initial peak crushing load but also improves the energy absorption efficiency by increasing plastic deformation. The influences of taper and length-diameter ratio on the axial energy absorption of BITT are explored. Finally, the bionic square array (BSA) and bionic hexagon array (BHA) are fabricated by taking BITT as the basic structural unit, which significantly improves the main energy absorption performance indicators under axial load.

Mechanical Properties of a Stability‐Enhancing Honeycomb with Double‐Platform Stresses and Variable Stiffness

Herein, a stability‐enhancing honeycomb (SEH) is designed based on the diabolo‐shaped honeycomb (DSH). SEH is obtained by adding wedge‐shaped parts to the DSH, which improves the stability of honeycomb deformation. The inclusion of the variable stiffness region imparts variable stiffness properties to the honeycomb. The combined effect of the variable stiffness region and the wedge‐shaped part eliminates the buckling phenomenon during honeycomb deformation. The results demonstrate that the honeycomb generates double‐platform stresses during deformation, and the specific energy absorption (SEA) increases rapidly after entering the variable stiffness region. The effects of the variable stiffness region, wedge‐shaped part, and crossbar length on the mechanical properties of SEH are analyzed using a finite‐element model, which is validated through compression experiments. Adjusting the variable stiffness region changes the strain of the variable stiffness. Modifying the wedge‐shaped part affects the magnitude and corresponding strain of the second plateau stress in the honeycomb. As the length of the crossbar increases, the stress and SEA gradually decrease. This article provides a design concept for variable stiffness honeycombs and offers insights to improve their effectiveness in protective engineering.

Study on the mechanical properties of the thin-walled double circular tube filled with a novel NPR lattice core based on the concave rotating mechanism

Abstract This study presents a thin-walled double circular tube filled with a novel negative Poisson’s ratio(NPR) lattice core based on the concave rotating mechanism. The unit cell of the NPR lattice core is constructed by replacing each inclined side of a concave hexagon with a smaller concave hexagon with an identical geometry aspect ratio. The single cell is arrayed to obtain a two-dimensional honeycomb structure, and then curling and mirroring operations are utilized to get a circular tube structure. Compressive deformation and load-displacement response of NPR lattice core with different concave angles are analyzed by FEM. To validate with numerical results, the NPR lattice core samples are prepared using 3D printing technology and subjected to quasi-static uniaxial compression experiments. Then, the thin-walled double circular tube filled with the NPR lattice core(FDCT) is established. The load-displacement relationship and energy absorption characteristics are analyzed, and the effects of two angle parameters on the specific energy absorption of the structure are discussed. The results show that an increase in the concave angle decreases the rigidity of the NPR lattice core. When subject to compression, all models show NPR effects, with minimum and maximum Poisson's ratios of -0.29 and -0.5, respectively. For FDCT, it is found that the interaction between the core layer and the tube wall enhances the structure's energy absorption performance. Changes in the core layer angle parameters affect the energy absorption of the FDCT structure, where increasing the concave angle improves the energy absorption efficiency of the structure. In contrast, the effect of the rotational angle is not significant.

Tunable mechanical performance of nanoporous energy absorption composite material

Abstract Nanofluidic energy absorption materials (NEAs) represent smart and efficient energy absorption composite materials in the ever-growing application of advanced protective structures. In this paper, an integrated experimental and molecular dynamics simulation study is conducted on the NEAs (ZSM-5/water) to investigate the tunable strategy of mechanical performance and energy absorption by considering the microstructural, mechanical, and thermal factors. The results demonstrate that the NEAs is an efficient and tunable liquid spring-like volume memory material. The typical NEAs show superior energy absorption capacity, achieving a specific energy absorption of 5.17 J/cm³ and an energy absorption ratio of 1.14 J/cm³ per cycle. Compared with insensitivity of the loading rate, the solid-fluid mass ratio is confirmed to significantly affect energy absorption performance, with an optimal ratio of approximate 1. Temperature is validated as an effective in-situ tunable parameter for NEAs in terms of both infiltration and energy absorption properties, with only slight effect on exfiltration. The critical infiltration pressure and specific energy absorption decrease by 23% and 40% as temperature increase from 25°C to 80°C. The gas-fluid interaction based energy absorption mechanism under high temperatures is proposed according to the comparison between experimental results and molecular dynamics simulations. The findings in this work will provide novel materials solutions for the intelligent energy absorption protective structures.