Specific Energy Absorption Capacity Research Articles

Enhancing crashworthiness characteristics of modified hexagonal honeycomb structural panels through stretching and bending of ribs

The effects of stretching and bending of concave, convex, and horizontal ribs on the energy absorption characteristics of modified hexagonal honeycomb structural panels are investigated under in-plane quasi-static compression loading conditions. In this regard, five hierarchical modified structural panel configurations were fabricated using polylactic acid material (PLA) via a fused filament 3D printer, ensuring uniform wall thickness in the 1.5–2 mm range. The panels included the regular hexagonal panel (RHP), regular hexagonal panel with concave rib (RHCP), regular hexagonal panel with convex rib (RHXP), regular hexagonal panel with concave and horizontal ribs (RHCRP), and regular hexagonal panel with convex and horizontal ribs (RHXRP). In-plane quasi-static compressive loading tests were conducted to analyze crush resistance characteristics, and buckling modes of the modified honeycomb panels were examined through experimental and finite element analysis procedures. The result indicates that the specific energy absorption capacity (SEA) of RHXRP is increasing significantly compared to the SEA capacity of other categories of the structures. The changes in failure modes and increased crush energy absorption characteristics of modified RHP with the introduction of concave, convex, and horizontal ribs are elaborated.

Backing plate material selection for optimizing joint performance in friction stir welded aluminium honeycomb

Aluminium honeycomb core is a thin-walled cellular structure extensively used in crash resistance applications in automotive industry. To overcome current challenges in adhesive-bonded honeycomb, new fabrication route using micro friction stir lap welding has been proposed. With a specific energy absorption capacity as high as 28.2 kJ/kg in flatwise impact testing, fabricated honeycomb demonstrated its potential for industrial applications. The structure exhibited no weld cracks or cell wall delamination, unlike adhesive-bonded honeycombs. However, in friction stir welding of thin sheets (0.5 mm), achieving an optimized heat input is challenging due to limited scope for variation in process parameter and tool design. Therefore, control of heat outflow by proper selection of backing plate material is the alternative approach for achieving desirable joint performance. Experiments with backing plates having a range of thermal diffusivities demonstrated that joint produced with mild steel backplate exhibited maximum shear-tensile strength. Conversely, joint with aluminium backplate exhibited poor plastic flow of material. Effective sheet thickness and lap width were predominantly affected by heat accumulation in weld, resulting in different failure modes.

A novel anti-missing-rib lozenge lattice metamaterial with enhanced mechanical properties

In this work, a novel anti-missing-rib lozenge lattice metamaterial (ALLM) is designed. Besides, its mechanical properties are enhanced by introducing lateral and longitudinal auxiliary ribs. The mechanical properties and elasto-plastic deformation behaviors of the proposed metamaterials are systematically investigated through quasi-static compression experiments and finite element analysis. The results show that the designed ALLM exhibits distinct negative Poisson’s ratio (NPR) characteristics and superior specific energy absorption (SEA) capacity. The novel design concurrently enhances the stiffness while preserving the inherent NPR of ALLM. The effects of missing-rib lozenge subunit rotation angles, auxiliary rib configuration, and ligament width on the deformation patterns, energy absorption, stiffness, and NPR of the resulting metamaterials are investigated by parametric analysis. This study provides a reference for the design of tunable lozenge grid missing-rib lattice metamaterials.

Comparative failure behavior of metal honeycomb structures under bending: A finite element-based study

In recent years, metallic honeycomb structures have been popularly researched due to their significant influence on structural strength and rigidity. In this study, the bending response of multi-cellular beam structures with four (hollow tube (HT), square (Squ), hexagonal (Hex) and octagonal (Octa) and Re-entrant honeycomb (ReH)) cross-sections are numerically investigated. Furthermore, using the nonlinear finite element codes LS-DYNA, a comparative study of the energy absorption characteristics between structures with auxetic and non-auxetic beam cross-sections was carried out. The ReH specimen used in the finite element (FE) validation study was manufactured using the Direct metal laser sintering (DMLS) additive manufacturing method to accommodate the complex geometries. FE method analysis are carried out to systematically investigate the influence of the geometrical configuration and identify the failure mechanism on the bending performance. The results show that in the HT structure, an upper corner fracture occurred because of folding in the contact area of the indenter. For Squ, Hex and Octa beam structures, failure occurs due to localized stress caused by buckling in the cell walls.On the other hand, the cross-sectional area of ReH structure tends to shrink under the bending load. Thus, the influence of the local buckling effect could be minimized despite the high displacements. This situation has ensured that the reduction in the moment of inertia of the cross-section remains limited. Furthermore, the specific energy absorption (SEA) capacity of the ReH beam significantly performed 11.3, 3.76 and 1.77 times better than the multi-cellular beam with Hex, Squ and Octa honeycomb beams, respectively. Accordingly, it was understood that the failure of the re-entrant cross-section under severe deformation was more limited than the others. This study is expected to contribute to evaluating the load-bearing capacity of metallic honeycomb structures, including understanding the failure process.

Investigation of Energy Absorbing and Damage Behavior of Gyroid and Diamond Cell Based Lattice Structures Manufactured through Powder Bed Fusion Technology

Cellular porous structures are used as an alternative to blocking structures in in-dustrial fields where multi-functionality and mechanical efficiency are necessary. Many industries, such as automotive, aerospace and defense, utilize the benefits of these structures due to their high specific strength, outstanding noise and vibration damping abilities, thermal shielding, and superior specific energy absorption capacities. This study aims to reveal energy absorbing behavior and deformation mechanisms under compression load of Gyroid and Diamond cell based triply periodic minimal surface (TPMS) structures manufactured by powder bed fusion (PBF) technology. The TPMS lattice structures fabricated using AlSi10Mg material were designed in different relative densities according to cell wall thickness and cell number. Crushing behaviors of these structures were numerically investigated with a commercial Ls-Dyna finite elements (FE) software. The numerical results were obtained in a good agreement with the experimental data. The FE analysis facilitated understanding of the deformation damage mechanisms and stress distribution on the cell surfaces of the TPMS lattice structures designed with different relative densities. The findings of the study demonstrated that peak stress values computed during crushing of the TPMS lattice structures go up significantly with increasing relative density. Crush force efficiency (CFE) and energy absorption capacity of the TPMS lattice structures remarkably varied depending on deformation damage mechanisms occurred during crushing process. The highest CFE values for the Diamond and Gyroid cell-based lattice structures was obtained as 54% and 51%, respectively. Moreover, it was found that specific energy absorption capacity of the Diamond cell based TPMS lattice structures is 50% more than that of the Gyroid cell based TPMS lattice structures with close relative densities.

Numerical Prediction of the Yield Surface of a Chiral Auxetic Structure

For today's requirements, the material itself is often not sufficient anymore. This leads to structural cellular materials and metamaterials, which allow for more degrees of freedom by a strong structure–property relationship. Auxetic structures investigated in this contribution belong to metamaterials. Auxetic metamaterials show huge advantages in their properties, e.g., an enhanced specific energy absorption capacity (SEAC) as well as a negative Poisson's ratio, combined with a very high stiffness‐to‐weight ratio. Experimental probing of these structures is very challenging, hence, up to now, auxetic materials have only been investigated in uniaxial, bending, or shear loading. But for an industrial application, the knowledge of the multiaxial yield behavior is inevitable. For the first time, the present study deals with the numerical probing of the yield surface for a chiral auxetic structure applying multiaxial loading. The changes in Poisson's ratio, SEAC, and the resulting nonconvex yield surface are studied numerically. It shows that the highest specific energy absorption capacities are reached under compression load cases while higher stiffnesses and yield stresses are achieved under tensile loading. There is a strong structure–property relationship and load case dependency for Poisson's ratio as well as for the SEAC.

Reinforcement of 3D‐Printed Re‐Entrant Structures using Additional Supports under Three‐Point Bending, Experimental and Numerical Analyses

Because of the significant effect of geometry on the mechanical properties of auxetic structures, this work focuses on enhancing the re‐entrant hexagonal honeycomb properties, as an auxetic cellular structure with widespread use, by modifying its unit cell's geometry. Herein, six novel structures with additional struts added as supports to the structure are designed to improve the specific energy absorption capacity and flexural modulus. The results reveal that adding supports significantly increases the maximum force tolerated by the structure in the same undergone displacement as the conventional re‐entrant. Furthermore, the findings indicate that honeycombs with concave curved supports outperform conventional re‐entrant honeycombs, showing a significant enhancement in flexural modulus (Ef) by ≈282%, energy absorption, and specific energy absorption by over 297%. Moreover, angle support structures demonstrate outstanding outcomes compared to simple straight supports and single‐support structures. Additionally, a parametric study is carried out using the validated finite‐element model to analyze the influence of the supports’ thickness and radius as well as the distance between the middle of the unit cell and the support (L3) in honeycombs with concave curved supports and the β angle of angle supports in the double‐angle support structures.

Crushing response of triply periodic minimal surface structures fabricated by investment casting and powder bed fusion method

Cellular materials, serving as alternatives to solid materials in applications demanding high mechanical efficiency and versatility, bring significant advantages to industries like automotive and aerospace. With attributes such as impressive strength-to-weight ratios, noise dampening, thermal shielding, and energy absorption, these materials are valuable assets. This study focuses on probing the energy absorption and deformation behavior of gyroid based triply periodic minimal surface (TPMS) structures under quasi-static compression. These gyroid structures, produced using AlSi10Mg through both investment casting and powder bed fusion (PBF) techniques, were designed at varying relative densities (7.5%, 11.2%, and 14.8%), adjusting cell wall thickness and cell numbers. Crushing response of these structures was also analyzed numerically using a commercial LS-DYNA finite element software. The study's findings indicate that gyroid structures printed through the PBF technique display around 150% greater specific energy absorption (SEA) capacity than those created using the investment casting method. However, the crush force efficiency of casted gyroid structures surpasses that of printed gyroid structures by 25%, owing to reduced peak stress values at the onset of crush dam

Mechanical design and energy absorption performances of novel plate-rod hybrid lattice structures

Hybrid lattice structures, integrating diverse structural components from fundamental lattice topologies, have attracted significant attention for their exceptional mechanical properties encompassing elastic modulus, yield stress, and energy absorption. To amalgamate the lightweight characteristics of rod structures with the robust mechanical properties of plate structures, a novel plate-rod hybrid lattice (PRHL) with controllable geometrical parameters and higher energy absorption was proposed and fabricated via the Selective Laser Sintering technique. In the PRHL design, the hybrid rod structure, interlinked with the center of each surface of the semi-open Octet plate lattice (SOPL), mutually provides support and deformation constraints. To identify the mechanical properties of PRHL, quasi-static uniaxial compression tests of PRHL samples sintered by Polylactic Acid powder were carried out. In comparison to SOPL, the newly proposed PRHL demonstrates an approximate 13.4% improvement in initial crush stress and an 18.5% increase in specific energy absorption capacity. Furthermore, numerical simulations incorporating the effect of printing orientation were performed to analyze the deformation mechanism of the PRHL structures. The present study also underscores the capacity to fine-tune the mechanical properties of PRHLs by regulating the plate thickness, rod diameter and excavated hole diameter.

Flexural Behavior of Bidirectionally Graded Lattice

This study aims to investigate the flexural behavior of newly designed bidirectionally graded lattice beams with body‐centered cubic unit cells made of stainless steel 316 L. Uniform and unidirectionally graded lattice beams are also studied for comparison. All the lattice beams are fabricated by electron beam melting and tested under quasi‐static bending loads. The experimental results reveal that the flexural stiffness and strength of bidirectional lattice beams are higher than those of both the uniform and unidirectional counterparts. The unidirectional lattice beams display the lowest strength owing to the easier collapse of thinner lattice layers on the impact side with the indenter. Finite element models, developed and validated using the experimental results, are used to evaluate the effects of the density gradient and the loading velocity on the performance of bidirectional lattice beams. The parametric study shows that the flexural stress and the specific energy absorption capacity of bidirectional functionally graded lattice beams increase with increasing loading velocity and can be enhanced by manipulating the layer density gradient.

Modeling, testing, and optimization of novel lattice structures for enhanced mechanical performance

Cellular materials have drawn increasing interest in numerous applications due to their promising specific stiffness, strength and energy absorption capacity. In this work, a variety of rather novel lattice topologies pertinent to additive manufacturing are derived and examined. A number of these are derived by free-domain and constrained domain topology optimization procedures, while others are inspired by the triply periodic minimum surface (TPMS) sheet-based topologies. The topology optimization module utilized a single objective function of minimizing strain energy under linear elastic conditions. A total of fifteen different lattice topologies are investigated numerically, including both novel and conventional topologies (e.g. strut-based lattices) and their effective elastic properties are determined with respect to relative density through finite element analysis (FEA). Based on the preliminary FEA results, a number of these topologies are selected of which tessellated lattice structures are fabricated through laser powder bed fusion (LPBF) additive manufacturing technique out of Nylon thermoplastic material. The tessellated lattice structures are experimentally tested in compression and their mechanical performance, including uniaxial modulus, yield strength, and energy absorption capacity (EAC), is assessed. FEA simulations have been conducted using an elastic-plastic constitutive model for the Nylon base material. Both the experimental and numerical results reveal that the mechanical performance of the novel tube-based TPMS lattice P-100 and the combined loading (CL) topology derived through free-domain topology optimization surpasses all other topologies. P-100 uses a primitive TPMS with equal-length tubular connections in each direction, where the tubular length percentage compared to the primitive lattice size is 100%, while CL lattice topology is a free domain topology optimized under compressive loads on the centers of faces, edges, and vertices toward the center. The innovative lattice topologies proposed in the current study, particularly the P-100 and CL topologies, can become crucial in applications where it is necessary to improve the energy absorption capacity, such as sandwich panel cores, supports, and infills for 3D printed components.

Butterfly lattice materials for controllable multi-stage energy absorption

Energy absorption properties of cellular materials have gained increasing interest due to their superior performance and immense design space. This paper introduces a novel lattice material with a Butterfly configuration that has controllable multi-stage crushing behavior and high specific energy absorption capacity. A theoretical model is developed to predict the plateau stress, elastic modulus and critical strain of each stage, in order to obtain the multi-stage stress-strain curve. Compression experiments and the finite element modelling are also carried out to validate the theoretical model. Theoretical and experimental results show that the Butterfly lattice material has more than two crushing stages and a specific energy absorption property comparable to the traditional stretching-dominated lattice material. Finally, effects of topology configuration, cell number, and geometrical parameter on the energy absorption behavior are analyzed. It is found that the length of the vertical beam dramatically influences the plateau load and deformation behavior of each stage.

Mechanical response of functionally graded lattices with different density grading strategies

This paper explains the quasi-static compressive behaviour of functionally graded lattices made of polyamide PA11 by multi jet fusion (MJF). The effects of various unit cell topologies such as body-centred cubic (BCC), rhombic dodecahedron (RD), and octet (OT) unit cells, as well as different stacking configurations were examined to achieve bi-directional and uni-directional grading in the lattice structures. Moreover, the strut diameters of the lattices were changed to obtain different relative density grading. The experimental results showed that topology grading played a dominant role in tuning the deformation patterns, stress-strain curves, and the energy absorption capacity of the lattice structures. Based on the numerically simulated results obtained from the validated finite element models, a semi-empirical formula was subsequently developed to predict the plateau stress of the studied FG lattices. Further numerical studies on the effects of the loading direction and the cell arrangement showed that the specific plateau stress and specific energy absorption capacity of the lattices compressed along the loading direction (z) were higher than those when they were compressed in the lateral (x) direction. Additionally, the cell arrangement predominately affected the deformation patterns and stress-strain curves. The findings of this study revealed that desired crushing performance of lattice structures can be achieved through functional grading of cell topologies, and it can be further enhanced by incorporating strut diameter grading.

3D printed bending-stretching coupled non-self-similar hierarchical cellular topology under in-plane loading

Ultralight hierarchical metamaterial is a type of promising structure in aerospace and transportation applications owing to the high stiffness/strength to density ratio. Though some hierarchical topologies with distinct in-plane configurations have been reported, the topology with superior mechanical behaviors under plastic deformation is urgent to be tailored. The present study develops a novel bending-stretching coupled Non-Self-Similar Hierarchical Topology (NSSHT) via additive fabricating methodology, and gives an insight into the mechanical responses and energy absorption capacities. It is identified that the softening post initial peak stress is triggered by the bending of the oblique membrane in the first order unit cell when edge length ratio (γ) is low, while by the initial rotation of second order unit cell when γ is high. Compared to the quasi-static measurements, the dynamic specific initial peak stress of NSSHT with uniform wall thickness (η= 1) was enhanced up to 131.9%. The deformation modes at distinct stress stages are different under quasi-static and dynamic loads. For specific energy absorption capacity, the NSSHT with non-uniform wall thickness behaves better, and the majority is dissipated at stress enhancement stage. The developed novel hierarchical structures enable to provide a wider spectrum of choices for tailoring high-performance lightweight components.

In-plane bending performance of novel negative Poisson’s ratio structures and its enhancement through the application of shape optimization method

NPR structures possess unique mechanical characteristics rendering them attractive for various engineering applications. However, their low in-plane stiffness limits their structural applications. The present study proposes a two-fold solution to overcome this issue. Firstly, new negative Poisson’s ratio (NPR) structures were designed with improved NPR thereby yielding better performance than the conventional NPR structures. Secondly, shape optimization was applied to the structures, whereby material was redistributed in each cell according to the applied load. The bending performance of structures was evaluated through Finite Element Method, duly validated, and quantified in terms of their flexural stiffness and energy absorption capacity. According to the results, the newly proposed structures offered higher performance than the conventional structure, i.e., 37–213 % stiffness and 9–37 % specific energy absorption capacity. This improvement further increased by many folds when shape optimization was applied to the structures, i.e., 427 % stiffness and 151 % specific energy absorption as compared to unoptimized conventional structures. This study reveals that the bending performance of NPR structures can be enhanced by improving the cell design/NPR and invoking shape optimization. The results detailed herein study can serve as a guideline to realize further improvements.

Mechanical performance of Bio-Inspired Gyroid and Primitive concrete structures under combined compression and torsion Loads: A discrete element method study

Bioinspired lightweight Primitive and Gyroid structures are two well-known TPMS (triply periodic minimal surface) cellular structures. These structures have been shown to possess high specific strength and energy absorption capacity, and thus hold great promise for a range of prefabricated civil engineering applications. As a result, concrete cellular TPMS structures have garnered the attention of researchers. However, prior to this study, no investigation has been carried out on the mechanical properties and failure patterns of concrete Primitive and Gyroid structures under coupled compressive and torsional loads. This lack of knowledge on the behaviour of these structures can lead to safety concerns in construction projects. To better understand the mechanical behaviour of Primitive and Gyroid structures under combined compression and torsion, the discrete element method (DEM) is adopted to simulate the TPMS structures. Both linear contact and nonlinear softbond contact models are utilized to simulate the brittle mechanical behaviour of concrete material. After validating the DEM parameters using published experimental data, the DEM models are subjected to coupled compressive and torsional loads to study their compressive and torsional bearing capacity and cracking patterns. The results indicate that the Primitive based structures outperform the Gyroid based structures in terms of both compressive and torsional resistance. The study is the world's first to reveal that a compressive load enhances the ultimate torsional bearing capacity of TPMS structures, but a torsional load reduces their compressive bearing capacity. Additionally, the loading conditions have little impact on the cracking patterns of the four TPMS structures.

Mechanical performance of carbon fiber‐reinforced polymer cellular structures manufactured via fused filament fabrication

AbstractThis article investigates the mechanical behavior of polyamide and carbon fiber‐reinforced (CFR) polyamide structures produced by Fused Filament Fabrication. CFR improves solid polyamide's tensile strength and modulus by more than 200% and 800%, respectively. The enhancement is highest in the parallel raster due to the alignment of the fibers in the printing direction. The compression tests of gyroid, honeycomb, and Voronoi cellular structures revealed the effect of geometry and fiber reinforcement on energy absorption performance. CFR gyroid infill offers the best performance with a specific energy absorption capacity reaching 10 kJ/kg and an efficiency close to 50%. Fiber reinforcement improves energy absorption by a factor of four or higher while increasing the weight by only 10%. The energy absorption capacity of the reinforced polyamide offers enormous potential for developing new lightweight load‐bearing and impact‐absorbing structures.

Crushing behaviour of corrugated tilted honeycomb core inspired by plant stem

In this study, a new corrugated tilted honeycomb (CTH) core for sandwich structure is proposed by implementing the corrugated and tapered shape inspired by plant stems. Its crushing responses and energy absorption capacity are numerically investigated by using finite element software LS-DYNA. This study aims to propose an effective energy-absorbing core with a high energy-absorbing capacity and high crushing force efficiency. The crushing and energy absorption efficiencies of the proposed CTH cores are evaluated by comparing them with those of the commercially available cores such as square honeycomb core and aluminium foam of the same mass. The crushing performances of each core are evaluated by using the key indicators of the energy-absorbing structure such as the peak crushing force (PCF), mean crushing force (MCF), crushing force efficiency (CFE), and the specific energy absorption capacity (SEA). The effects of the crushing speed, tilted angle, and relative density on the crushing behaviour of the proposed CTH core are also investigated. It is found that under various crushing speeds, the proposed CTH core has a lower PCF, a higher MCF, CFE, and SEA than the conventional square honeycomb core and aluminium foam of the same mass. Furthermore, the CTH core has higher CFE and SEA than most of the existing structural forms of cores with similar relative density. The CTH core with two corrugations (C2) has a significantly improved SEA, which is four times higher than aluminium foam, up to 142% higher than the primitive structure, and 46% higher than the square antiprism structure, showing an excellent performing core for the energy-absorbing sandwich structures.

Experimental and numerical investigation on energy absorbing characteristics of empty and cellular filled composite crash boxes

Composite structures have been used in the automotive and aircraft industries because of their superior properties such as specific energy absorption ability, lightweight and crashworthiness. This paper aims to determine energy absorbing and deformation behaviours of composite crash boxes designed in different geometries by an innovative approach. The hand-layup vacuum bagging method was utilized to produce the composite crash boxes, which were developed with three different outer wall geometries (square, hexagon, and cylinder), and cellular filled square and hexagonal interiors. Carbon fibre reinforced polymer (CFRP) material was used in fabrication of the crash boxes. Experimental and numerical studies were conducted to investigate the energy absorbing and deformation behaviours under static compression load of the composite crash boxes. A commercial finite elements (FE) software (Ls-Dyna) was used for the numerical model. The study's findings revealed that cellular-filled composite crash boxes perform significantly better in terms of energy absorption performance. It was observed that filling an empty square type composite crash box with hexagonal cells increased the box's specific energy absorption capacity by around 140%.

Experimental and numerical investigation on enhancing capped-end tube energy absorption capacity by orifice effect

This work proposes a method of energy absorption via phase change material (PCM)-filled circular tubes with caps and orifices on their end surfaces. As a novel method of energy absorption, energy absorbers were filled with a squeezable material. These filled tubes were anticipated to offer superior energy absorption performance than hollow tube systems thanks to energy dissipation during material squeezing through orifices. It has been experimentally studied how these tubes react when crushed by quasi-static lateral force. We used a hemi-cylindrical indenter to laterally compress the samples. Using systematic case design (SCD) and finite element (FE) method, we were able to provide guidelines for the effect of geometrical parameters of filled tubes to be employed as energy absorbers under lateral compression. Commercial FE analysis software (LS-Dyna) was used to develop the FE model, which was then validated by experimental results. Specific energy absorption capacity (SE) and force-displacement curves of filled tubes were derived as a function of geometrical parameters including thickness, diameter, and orifice size. A parametric studywas conducted to evaluate the principal and interactive effects of geometrical factors on the SE. In conclusion, we proposed an empirical formulation of energy absorption as a function of geometrical factors for a PCM-filled capped-end tube that can predict energy absorption with more than 95% accuracy. Validation was further achieved by comparison with analytical method.