Improved Energy Absorption Research Articles

Progress in the development of bead foams – A review

For a long time, the number of available bead foam variants limited to standard polymers which restricted their functionality mainly to packaging, thermal insulation (e.g. in construction) and shock absorption (e.g. in transportation). In particular, standard polymers such as expanded polystyrene, expanded polyethylene and expanded polypropylene were used for components requiring good insulating properties and high energy absorption at low cost. Mainly since the last two decades, new polymer variants have found their way into the world of bead foams and are currently adding further functionalities, such as sustainability, flame retardancy, increased thermal stability and enhanced mechanical performance (e.g. improvements in energy absorption and impact resistance). Versatile fields of application open up, revolutionizing both industry and design sectors. This review article emphasizes the special development progress of new bead foam variants and their processing technologies. Upcoming opportunities of digital methods for modelling and simulation are highlighted.

Pre-Tensioned CFRP Tubes for Improved Energy Absorption

The use of materials like CFRP has shot into prominence to achieve lightweight designs without compromising on structural integrity. Circular thin tubes are often employed in passenger cars as energy absorbers to absorb the impact energy during an accident. When such tubes are made of materials like CFRP it contributes to weight reduction besides leading to reduced fuel consumption. Also due to their lower weight, such tubes shall be capable of absorbing more energy per unit mass compared to metallic designs, which is defined as specific energy absorption capacity (SEA). Pre-stressing techniques are widely used by civil engineers across the globe to impart more stress/energy bearing capacity for the structures. Based on pre-stressing principles, the introduction of pre-tension during the fabrication stage for thin CFRP tubular structures has been experimentally studied to validate the applicability of pre-stress concepts for more SEA. The study investigates experimentally the additional advantage prestressing can bring for a CFRP tube in terms of SEA improvement.

Enhancement of tensile, flexural and ILSS properties of C-epoxy composites with the addition of ETBN toughener and Af-MWCNTs

The objective of this research is to develop a hybrid composite with a unique combination of features such as tensile, flexural and Interlaminar shear strength (ILSS) properties. It is a present need for components used in underwater, aerospace, defence and automotive applications, as parts are subjected to a variety of loading conditions, including tensile, bending and shearing. Carbon fibre reinforced epoxy (C-epoxy) composite is modified by adding epoxy terminated butadiene acrylonitrile (ETBN) liquid rubber and amino-functionalized multi-walled carbon nanotubes (Af-MWCNTs). With the addition of ETBN, the tensile, flexural and ILSS properties were improved by 38%, 46% and 80%, respectively. The addition of 0.5wt% of Af-MWCNTs improved the tensile and flexural strengths by a maximum of 59% and 61%, respectively. In contrast, the maximum improvement in ILSS of 120% was obtained at 1.0 wt.% of Af-MWCNTs. The unique combination of C-epoxy-ETBN-Af-MWCNTs led to the formation of the serrated surface at the fibre matrix interface, which caused improved energy absorption. The toughening mechanisms which are responsible for the improvement in properties are discussed and the results are validated through finite element analysis (FEA).

Mechanical testing of adhesive, self-piercing rivet, and hybrid jointed aluminum under tension loading

Joining technologies play a crucial role in facilitating vehicle weight reduction, while maintaining structural performance and vehicle crashworthiness. Adhesive and self-piercing rivet (SPR) joining have individually been assessed in joining multi-material structures including aluminum alloys; however, limitations include fixturing requirements for adhesive joints and non-uniform load distribution within SPR joints. Hybrid (adhesive-SPR) joining has been proposed to potentially address these limitations. Yet, there is limited data regarding the strength, stiffness and energy absorption of hybrid joints under tension loading, and a lack of quantitative comparisons between adhesive, SPR and hybrid joints. In the present study, adhesive, SPR and hybrid joints were created in aluminum H-shaped tension specimens and the joint morphologies were quantified. Joint strength, stiffness and energy absorption were compared for two aluminum sheet metal alloys and three sheet thicknesses. Adhesive joints exhibited higher strength (up to 20.5%) and stiffness (up to 422%) than SPR joints, while SPR joints demonstrated higher energy absorption (up to 352%). Hybrid joints in 3 mm sheet exhibited reduced strength and stiffness relative to adhesive joints. Importantly, hybrid joints for 1 and 2 mm sheet thicknesses demonstrated strength and stiffness comparable to adhesive joints (<8% difference), and improved energy absorption compared to adhesive (up to 336%) and SPR joints (up to 53.5%), enhancing the performance of the individual methods. The study results could facilitate identifying suitable joining method, sheet thickness and alloy type according to structural applications (e.g. intrusion prevention versus energy-absorbing structures), and support future adoption and improvement of hybrid joints.

Editorial: Mechanical Metamaterials: Cutting-Edge Metastructures

Challapalli et al. utilized machine learning to find cellular (lattice) structures with a high natural frequency to avoid resonance and high impact energy, demonstrating a 30-100% higher natural frequency and a 300% improvement in energy absorption. Their work shows the potential impact of machining learning on the design of metamaterials.Xiao et al. studied a new metastructure for morphing wing design to break through the technical challenge of small-scale aircraft. Their morphing wing design with soft pneumatic actuators and modified pantographic metastructures demonstrates spanwise and chordwise morphing capabilities, showing an engineering breakthrough of prototyping.These papers highlight some current engineering challenges of metamaterial design. This community will grow fast and impact the world through scientific findings and engineering breakthroughs. We hope that readers will enjoy reading these papers specially solicited for the community.Shanghai Jiao Tong University Xin-Lin Gao Southern Methodist University

Alloy Partitioning Effect on Strength and Toughness of κ-Carbide Strengthened Steels.

Alloy partitioning during heat treatment in a lightweight precipitation hardened steel was investigated using transmission electron microscopy and atom probe tomography. The mechanical properties are discussed as a function of the effect of solution treatment temperature and aging time, giving rise to variations in chemical modulation. A wrought lightweight steel alloy with a nominal composition of Fe-30Mn-9Al-1Si-1C-0.5Mo (wt. %) was solution-treated between 1173–1273 K and aged at 773 K. Lower solution treatment temperatures retained a finer grain size and accelerated age hardening response that also produced an improved work hardening behavior with a tensile strength of −1460 MPa at 0.4 true strain. Atom probe tomography indicated these conditions also had reduced modulation in the Si and Al content due to the reduced aging time preventing silicon from diffusing out of the κ-carbide into the austenite. This work provides the framework for heat-treating lightweight, age hardenable steels with high strength and improved energy absorption.

A mesh morphing computational method for geometry optimization of assembled mechanical systems with flexible components

In this paper an interactive computational methodology was developed assuming that shape and size optimization of flexible components can significantly improve energy absorption or storage ability in assembled systems with flexible components (AS-FC). A radial basis functions mesh morphing formulation in non-linear numerical finite element analysis, including contact problems and flow interaction, was adopted as optimal design method to optimize shape and size design parameters in AS-FC. Flexible components were assembled in finite element environment according to functional ISO-ASME tolerances specification; non-linear structural analysis with flow interaction analysis was performed. The results of the study showed that the proposed method allows to optimize the shape and size of the flexible components in AS-FC maximizing the system's ability to absorb or store energy. The potentiality of the method and its forecasting capability were discussed for the case study of an automotive crash shock in which the specific energy absorption was increased by over 40%. The case studied refers to a simple flexible component geometry, but the method could be extended to systems with more complex geometries.

Dynamic crushing of tailored honeycombs realized via additive manufacturing

Enhancing the energy absorption characteristics of a material/structure without compromising its strength and stiffness has been a longstanding challenge in the pursuit of lightweight engineering. Here, we introduce a novel tailoring strategy where the wall thickness of the honeycombs is bi-linearly graded along the out-of-plane direction to tune their energy absorption and impact resistance by varying two design parameters, the gradation parameter α and the normalized taper length η'. Based on the proposed scheme, hexagonal honeycombs of the same mass and varying parameters [α, η'] were designed and realized via Digital Light Processing (DLP) additive manufacturing. Low-velocity out-of-plane impact tests and dynamic FE calculations were performed to examine the collapse response of geometrically tailored honeycombs and assess their energy absorption characteristics and collapse mechanisms in relation to those observed in conventional (non-tailored) honeycombs of the same mass. The measurements and predictions revealed that the bi-linearly wall-thickness tailored honeycombs consistently outperform their non-tailored counterparts when the impact energy is high, reporting an increase in energy absorption as high as 250%. Such remarkable enhancement in energy absorption is attributed to a transition in the underlying collapse mechanism from global buckling mode to progressive crushing of the cell-walls. We also examined the impact response of honeycombs with periodic variations in cell-wall thickness and found that the latter structures collapse rapidly in an unstable manner, similar to what observed in conventional honeycombs, leading to limited capacity to dissipate the impact energy. With careful selection of the design parameters [α,η′], we experimentally demonstrate that bilinearly wall-thickness tailored honeycombs can exhibit simultaneous improvements in energy absorption and impact resistance, providing new opportunities for expanding the property space of honeycombs and opening the door for a wide range of applications.

WITHDRAWN: Improved energy absorption and post-impact characteristic of polyurethane foam sandwich composite

This article has been retracted at the request of the Editor. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal .

Improved energy absorption capacity of closed-cell aluminium foams by electroplating

ABSTRACT In the present study, hybrid closed-cell foams consisting of two materials with different ductilities were manufactured to improve the energy absorption capacity. The mechanical characteristics, deformation modes and energy absorption capacities of the foams were investigated. Furthermore, the energy absorption mechanisms of the hybrid foams were analysed. The results demonstrated a significant synergistic effect between the foams and coating with different ductilities during deformation. Their combination increased the densification strain and improved the energy absorption capacity of the samples. Among the specimens investigated, the Al/Zn–Cu(A) foam showed the best densification strain (0.75) and presented superior energy absorption capacities (energy absorption capacity per unit volume (U v) = 4.5 J cm–3; energy absorption capacity per unit mass (U m) = 8.4 J g–1). The intrinsic mechanism of energy absorption optimisation is a combination of the advantages of brittle and ductile deformation modes.

Affecting Factors of Partially Quenched S-shaped Products for the Improvement of Energy Absorption in Axial Crash

Affecting Factors of Partially Quenched S-shaped Products for the Improvement of Energy Absorption in Axial Crash

In-plane energy absorption characteristics of a modified re-entrant auxetic structure fabricated via 3D printing

Here, we present the in-plane energy absorption characteristics of modified re-entrant auxetic honeycombs realized via fused filament fabrication in conjunction with parametric analysis and geometry optimization. The influence and interaction effects of the geometrical parameters such as strut-length ratio and joint-angles on the stiffness, strength and energy absorption characteristics of modified re-entrant auxetic honeycombs were evaluated. Subsequently, Finite Element results obtained using ABAQUS/Explicit were corroborated with measured data. Deformation mode, stress-strain response and energy absorption behavior of an optimal re-entrant auxetic honeycomb were studied and compared with conventional re-entrant auxetic structure. Modified auxetic structure reveals an 36% improvement in the specific energy absorption capacity. Our analysis further indicates that due to the introduction of more nodes with low rotational stiffness, the failure strain of the modified re-entrant structure has increased resulting in improved energy absorption capacity.

Improving energy absorption capacity of foam concrete with gradient and layered architecture

The mechanical properties of foam concrete are significantly affected by its failure mode, closely related to its density and height-diameter ratio, and unfavorable failure mode would inevitably adversely affect its mechanical performance. To investigate the effect of density and height-diameter ratio on the failure modes, firstly a quasi-static compression test is carried out on the specimens with four densities (400, 600, 800, and 1000 kg/m3) and four height-diameter ratios (0.5, 1.0, 1.5, and 2.0). Most specimens exhibit unfavorable splitting failure, while only the specimens with low densities or small height-diameter ratios undergo crushing or shear failure. To improve the mechanical performance of foam concrete, especially the energy absorption capacity, measures including layered architecture, density gradient, and split plate are proposed and experimentally examined in the present study. The results show that sufficient density difference between adjacent foam concrete layers is able to effectively mitigate the propagation of cracks so as to significantly improve its mechanical performance. Moreover, steel split plate at the interface of adjacent foam concrete layers is capable of successfully stopping crack development among different layers, demonstrating superior energy absorption capacity. In addition, layer by layer crushing failure mode can be achieved through the synergy of density gradient and split plates to fill the demand of multi-level protection for important structural members.

Bio-inspired repeatable lattice structures for energy absorption: Experimental and finite element study

New and innovative lightweight materials are the key demands of the automotive and aerospace industry. Exceptional energy absorption properties can be obtained from designs with local-buckling characteristics. Inspired by many biological designs, bio-inspired structures exhibit a significant progress over the conventional lightweight structures. In this paper, the energy absorption behavior of lattice structures derived from the hexactinellida sea sponge Euplectella aspergillum is studied for the first time. The designed lattice structures are fused filament fabricated with thermoplastic polyurethane material. Energy absorption and deformation behavior are studied under quasi-static loading conditions. The effect of the strut thickness, relative density, and unit cell size on the energy absorption is studied both experimentally and numerically. The structures are designed to increase the energy absorption capacity with a stable plateau region without compromising the mean plateau stress. The bio-inspired lattice structures showed a local buckling other than the global buckling mode of deformation. The cyclic loading–unloading of the structures was also carried out to study their compressive behavior and repeatability. The structures underwent a softening effect over the first cycle and become stable from the second cycle onwards. Hence, the improved energy absorption capacity, stable post-yielding stress, and high mean value stress can be used to develop better energy absorbers.

Ballistic performance of synergistically toughened Kevlar/epoxy composite targets reinforced with multiwalled carbon nanotubes/graphene nanofillers

AbstractThe individual and synergistic effects of multi‐walled carbon nano tubes (MWCNT) and graphene nano‐platelets (GNP) on the ballistic performance (low and high velocity) of functionalized Kevlar reinforced polymer matrix composites have been investigated. Low‐velocity impact tests were carried out on the composite targets (6 layers) using a gas gun setup. Surface hardened conical nose projectiles of 10 mm diameter were used and the inlet velocity was in the range of 122–128 m/s. Similarly, high‐velocity ballistic impact experiments were conducted on the targets (24 layers) using a 9 mm full metal jacketed (FMJ) projectile with an initial velocity of 430 ± 15 m/s. Acid treatment was done to functionalize the Kevlar fiber surface. From the low‐velocity impact experiments, the hybrid targets had better ballistic resistance when compared to the unfilled and individually filled nanocomposites. A reduced projectile exit velocity, improved impact energy absorption (32.5 J), and an improved energy absorption percentage of 27.57 were observed for the hybrid combination. Similar improvements were observed during high‐velocity ballistic experiments which were evident from the fractographic analysis. The macroscopic investigation on the target containing both the nano‐fillers had the least penetration depth of 5.8 mm and a high damage area compared to the other targets. This is due to the addition of f‐MWCNT and f‐GNP which has increased the matrix toughening and functionalization of Kevlar which increased the interfacial bonding. In addition, the crack bridging property of CNTs and encapsulation behavior of graphene due to stacking has synergistically improved the overall toughness of the composites.

Post Tensioned CFRP tubes for improved energy absorption

Thin-walled tubes made of CFRP (Carbon fiber reinforced Polymer) are being increasingly used as CC (Crush Cans) due to their higher specific energy absorption capacity in the automotive domain for absorbing impact energy during a frontal crash. Finite element analysis (FEA) based computational methods have matured over the years with increased accuracy and acceptable correlation with experimental results. FEA-based computational studies when used appropriately can reduce the number of physical tests and prototypes required besides accelerating the overall cycle design time. The present work proposes an FEA based design validation approach for the evaluation of post-tensioned crush can design that can absorb more impact energy compared to a normal CFRP thin tube. The FEM based method uses a combination of multiple simulation techniques to predict the behavior of a post-tensioned tube. The post-tensioning in the present work has been proposed in the form of internal pressure for the thin tube. It was found that a safe value of pressure, when applied as a post-tensioning load, can improve the energy absorption capacity without increasing the weight of the tube.

Energy Absorption AZ31B using Quenching in Nano Fluid

This paper focuses on improving energy absorption through a series of heat treatment and quenching in medium, presence of nanoparticle. The characterisation of the experiment was to determine the suitable combination of composition factors: temperature, soaking time, and the medium that consist of nanoparticle on magnesium alloy surface structure to improve the energy absorption using quenching in nanofluids. The diameter and thickness of the specimen are 6 mm and 10 mm, respectively. All specimens undergo heat treatment based on the temperature of the furnace and the soaking time of the specimen in the furnace, which will be submerged into three medium distilled water, and the addition of a 0.1% wt carbon-nanotube (CNT) and 0.1% wt nano-silica. The addition of CNT and nano-silica shows an increment of 106.68%% and 59.30% for energy absorption, respectively, when compared to the controlled sample. Later microscopy has performed on the specimen to correlate the addition of nanoparticles in the heat treatment and improved energy absorption by EDS analysis on the material composition on the specimen’s surface. Therefore, this paper reveals factors of heat treatment and the presence of CNT and Nano silica effects on enhancing magnesium alloy energy absorption: UTS and yield strength using quenching method.

Enhanced compressive and energy absorption properties of braided lattice and polyurethane foam hybrid composites

Ultralight structures with excellent specific mechanical properties have been of great interest in the field of transportation. In this study, a new ultralight hybrid material composed of braided lattice (BL) composite tubes and polyurethane (PU) foam was developed. First, BL preforms were produced using a braiding process, and BL composites were subsequently manufactured by resin impregnation and curing. The BL composites were inserted into a PU foam to make a hybrid composite. The compressive behavior of these hybrid composites was experimentally characterized, focusing on the effect of the number of BL layers and their cross-sectional shapes and perimeters on the energy-absorbing behavior. Furthermore, finite element (FE) modeling was conducted to investigate the energy absorption mechanism in the hybrid composites. A good correlation between FE modeling and experimental results was achieved, indicating that the hybrid composites exhibited significantly improved energy absorption properties due to the synergistic effects between foam and BL, outperforming similar ultralight cellular structures in terms of crashworthiness.

Multi-objective optimization of a multi-cellular aluminum extruded crush rail subjected to dynamic axial and oblique impact loading conditions

This work presents a multi-objective shape optimization study of a multi-cellular aluminum extrusion subjected to dynamic axial and oblique (20° angled) impact loading conditions. Finite element models are developed, validated with experimental data, parameterized, and used to exhaust the design space using a full factorial design of experiments. An analysis of different energy absorption characteristics, such as axial and oblique mean crush force, crush efficiency, and oblique impact coefficient, are presented. A multi-objective optimization problem is defined to generate new solutions that dominate a baseline profile in all aspects of performance, which produced a geometry with up to 16% improvements in energy absorption. The parametric study is used to define the “true” Pareto front, which is the set of non-dominated designs and the solution to the optimization problem. The response surface methodology (RSM) is used to perform the multi-objective optimization analysis. The traditional RSM approach is compared to an adaptive surrogate-assisted response surface method (ASA-RSM) in their speed and ability to identify the true Pareto front correctly. Using the traditional metamodel constraint, the traditional RSM approach could only identify 18% of the true Pareto front using up to 8% of the design domain. After relaxing the constraint, the traditional RSM approach still required approximately 63% of the entire domain to identify 67% of the true Pareto front accurately. In comparison, the ASA-RSM approach was able to identify 84.5% of the true Pareto front using 42% of the entire domain. In some instances, the ASA-RSM approach correctly identified 100% of the true Pareto front by using as little as 18% of the domain. However, the ASA-RSM approach’s peak performance is dependent on the initial sampling and resulting metamodel. This study provides a comprehensive understanding of the performance gains of multi-objective optimization in the application of structural crashworthiness considering various loading conditions.

Multi-objective design optimization of additively manufactured lattice structures for improved energy absorption performance

This paper aims to improve the energy absorption performance of stiffness-optimized lattice structures by utilizing a multi-objective surrogate-based size optimization that considers the additive manufacturing (AM) constraints such as the minimum printable size. A truss optimization is first utilized at the unit cell level under static compressive loads for stiffness maximization and two optimized lattice configurations called the Face-Body Centered Cubic (FBCC) lattice and the Octet Cubic (OC) are obtained. A multi-objective size optimization process is then carried out to improve the energy absorption capabilities of those lattice designs using non-linear compression simulations with Nylon12 material to be fabricated by the Multi Jet Fusion (MJF) AM process. Thin plate spline (TPS) interpolation method is found to produce very high accuracy as the surrogate model to predict the highly nonlinear response surfaces of energy absorption objectives in the optimization. Compared to the lattice designs with uniform strut diameters, by using the optimization process, the maximum energy absorption efficiency ( EAEm) and the crush stress efficiency ( CSE) of the OC lattice design are further improved up to 33% and 37%, respectively. The FBCC lattice design is also found to have superior EAEm performance compared to the existing lattice types considered for fabricating by the MJF process in the literature.