Energy Absorption Research Articles

Three-Dimensionally Printed K-Band Radar Stealth Lightweight Material with Lotus Leaf Structure.

K-band radar waves have high penetration and low attenuation coefficients. However, the wavelength of this radar wave is relatively short; thus, designing and preparing both broadband and wide-angle radar wave absorbers in this band presents considerable challenges. In this study, a resin-based K-band radar wave absorber with a biomimetic lotus leaf structure was designed and formed by UV curing. Here, microscale lotus leaf papillae and antireflection structures were prepared using a DLP 3D printer, and the contact angle between the material and water droplets was increased from 56° to 130°. In addition, the influence of the geometric parameters of the lotus leaf antireflection structure on the electromagnetic absorption performance and mechanical strength was investigated. After simulation optimization, the maximum electromagnetic loss of the lotus leaf structure 3D-printed sample was -32.3 dB, and the electromagnetic loss was below -10 dB in the 20.8-26.5 GHz frequency range. When the radar incidence angle was 60°, the maximum electromagnetic loss was still less than -10 dB. The designed lotus leaf structure has a higher mechanical energy absorption per unit volume (337.22 KJ/m3) and per unit mass (0.55 KJ/Kg) than commonly used honeycomb lightweight structures during the elastic deformation stage, and we expect that the designed structure can be used as an effective lightweight material for K-band radar stealth.

Theoretical prediction and experimental validation of flexural behaviour and failure modes of 3D-woven honeycomb sandwich panels

This study presents a novel approach to enhance the flexural performance of sandwich composite panels by introducing 3D-woven honeycomb (HC) composites as core material. The flexural performance and failure modes of these novel structures are compared with traditional aluminium honeycombs across various facesheet materials. Experimental findings are complemented by numerical analyses, while observed failure modes are compared with theoretical flexural failure modes. The results reveal that 3D-woven Kevlar HC cores demonstrate superior flexural stiffness and strength due to its integrated structure, while enhanced energy absorption is attributed to unique deformation mechanisms within the 3D-woven core. Failure modes observed in the experiments closely aligned with theoretical predictions, further validating the approach. Overall, the findings validate the potential of novel 3D-woven Kevlar HC cores as promising alternatives for lightweight, high-performance sandwich composite panels.

Programmable multi-stability of curved-crease origami structures with travelling folds

Multi-stable structures capable of rapid switching among different stable states have seen applications in various fields such as energy absorption, mechanical computing, and soft actuators. Curved-crease origami, which naturally involves simultaneous deformation of creases and facets, shows great potential in the development of multi-stable structures. However, upon loading, existing curved-crease origami structures tend to follow the same deformation mode as in the curved surface formation process which involves facets elastic bending, flattening, and reverse bending, thus leading to only two stable states. To achieve multi-stability, here we propose a series of curved-crease origami structures composed of planar facets and curved ones. Through a combination of experiments, numerical simulations, and analytical modelling, we demonstrate that the planar facets forming a Sarrus linkage guide the deformation mode of the curved ones, leading to the initiation and propagation of travelling folds in the curved facets. By transforming the travelling folds at specific positions into actual creases, we can achieve multiple stable states in a single structure. In addition, the number and positions of the stable states, as well as the initial peak force, can be programmed by varying the geometric parameters. Consequently, this work opens a new pathway for the development of generic multi-stable structures with programmable mechanical properties.

Rebound characteristics of flexible and stiff jute rubber/epoxy hybrid composite under low-velocity impact

This present work aims to assess the low-velocity impact response of novel configuration based on jute/rubber/epoxy flexible and stiff composites having varying layup sequences using an experimental study. The Charpy and drop weight impact tests are done according to the standards. Drop weight low-velocity impact test at an energy level of 15J was performed using a conical shape impactor. Carboxylated Nitrile Butadiene Rubber (XNBR) containing carbon fillers ( N330 and N550) consisting 35 phr concentration each is used in the stacking sequence of the composite due to its high toughness and energy dissipation property. During drop weight tests conducted at a 15J energy level, the flexible RJRJR composite exhibited a peak force of 486 N, whereas the stiffer RJEJR composite demonstrated a peak force of 1075 N. The flexible composite shows no damage for the energy level tested. However, the stiff composite made using epoxy in between jute layers fails due to the matrix cracking in the composite. The peak force and specific energy absorption is dependent on stacking configuration and increases with the addition of rubber interface in the stiff composite. The energy absorption of stiff composite is higher as compared to flexible composite as indicated by the peak force.

New 3D petal-like structures with lightweight, high strength, high energy absorption, and auxetic characteristics

A novel type of petal-like structure that exhibits superior mechanical properties, was proposed and fabricated by integrating advantages of metamaterial, multi-stage deformation, and high strength of fiber-reinforced composites. Compression testing and finite element analysis were first conducted on three petal-like structures formed with different angles and made from fiber-reinforced composites. The findings indicated that these composite-based multi-cell structures can also exhibit a satisfactory stress plateau stage through judicious structural design. After ensuring the structures' performance under quasi-static compression load, the impact resistance of the new structures was further examined. It was found that the structure's auxetic characteristics diminished under low-speed impact load. However, under a 20 J impact load, the structures exhibited energy absorption characteristics (SEA) that surpassed those of both conventional and other new auxetic structures by 8–40 times. These promising results demonstrate that the newly designed petal-like structures have high potential applications in various fields such as construction and automotive industries.

Experimental study on the ballistic performance of CFRP/AFB sandwich plate

Lightweight bulletproof plate is highly demanded in the field of security field. A novel plate of carbon fiber reinforced plate (CFRP)/aramid filament bundles (AFB) sandwich plate is manufactured through winding methods in this paper. The ballistic performance is evaluated and failure mechanism is explored on the designed six CFRP/AFB sandwich plates. It is found that the sandwich structure of 3-4 × 16 is the best structure by comprehensively considering the energy absorption, Coefficient of Variation(CV) and shaping difficulty, of which the v50 and the average energy absorption are 225.26 m/s and 150.60 J, respectively. In addition, for the case that the number of filaments in the first entanglement is more and the number of first entanglement in the secondary entanglement is less, the ballistic performance would be better. To the failure mechanism, the upper CFRP is damaged by shear failure and the bottom CFRP shows delamination and separation in the impact process. The filament bundle plate in the core layer is benefit in resistance to projectile impact and it fails mainly by the disintegration and bending. This novel CFRP/AFB sandwich plate is a new direction for producing ballistic proof plate.

Repairability of rubber-backed vitrimer composites under variations of impact damage

This study evaluates the effectiveness of rapid heat pressing repair on composites made of vitrimer matrix, a reshapable and recyclable polymer, subjected to varying degrees of impact damage. Two types of composites were fabricated for impact testing: randomly oriented glass fiber reinforced vitrimers (GFRV) and woven carbon fiber reinforced vitrimers (CFRV). Izod pendulum impact tests were conducted on samples along both the thickness and width. Impacts with varying energy levels were applied to induce different degrees of damage, allowing for the assessment of impact strength degradation and repair effectiveness. Additionally, a rubber adhesive layer was applied to the back of composites to quantitatively measure the increase in energy absorption and its effect on repair performance. The findings demonstrate the potential of rapid heat pressing repair in restoring the mechanical integrity of vitrimer composites and highlight the influence of a rubber adhesive layer in enhancing energy absorption and repair efficacy.

Failure mechanism and plastic hinge of RC joints under impact load acting on column ends

Impact loads often act on columns end during accidents such as vehicle impacts and terrorist attacks. The resulting deformations lead to a redistribution of internal forces in the member as well as a reduction in the load carrying capacity. The integrity of the core area of the joint is threatened, which could trigger a progressive collapse. This study numerically investigated the damage and deformation of reinforced concrete (RC) beam-column joints when they are impacted on the column end. The resistance mechanism of joints and the influence of impact location as well as impact velocity was explored. Besides, the deformation capacity of RC beam-column joints under impact loading was quantified using equivalent plastic hinges. It was found that the damage and plastic deformation is concentrated at the impacted column end. The horizontal reaction force at the beam end provides resistance and plays the role as a bearing. The column bottom reaction force is in the same direction as the impact force. However, it is much smaller than the beam end reaction force. The resistance mechanisms within the joints can be categorized into strut-and-tie near the loading point and arches in the mid-span of the beam and column. The core area rotates and has a significant lateral displacement towards the impact location, whether it is loaded at the beam end or the column end. As the impact location moves away from the core aera, the impacted column end exhibit more bending failure. With increasing impact velocity, the impact force, reaction force and total energy absorption of the joint increase. The deformation increases, with more damage occurring in the core area and spreading to the beam. In addition, the plastic curvature was used to describe the actual plastic deformation of the joints, whose maximum occurring at the interface where the impacted column end meets the core area. A formula for the equivalent plastic hinge length of RC joints was proposed, taking into account the effects of impact location and impact velocity.

Inverse design of cellular structures with the geometry of triply periodic minimal surfaces using generative artificial intelligence algorithms

Triply periodic minimal surfaces (TPMS) exhibit excellent mechanical and energy absorption properties due to their structural advantages. However, existing porous TPMS structural design methods are constrained to a forward process from structural parameters to mechanical properties. This study proposed an inverse design method that combines bidirectional generative adversarial networks (BiGAN) and mechanical performance targets, resulting in a combined TPMS structure of Primitive and IWP types with superior buffering and energy absorption capabilities. The results show that under a single load value target condition of the designed structure, the minimum deviation index (R2) between the load value corresponding to the displacement point and the target load value is only 0.987, and the maximum mean absolute percentage error (MAPE) is only 5.92 %. When considering the elastic modulus target, the approach successfully conducts two sets of combined structural designs meeting the requirements of both high and low elastic moduli. When targeting the specified load-displacement curve conditions, specifically when combining high elastic modulus with ascending plasticity, the designed structures exhibit an error of only 2.2 % compared to the target property. Moreover, the quasi-static uniaxial compression experiments conducted on additively manufactured designed structures confirm that the experimental curves match the target curves in terms of deformation trends and load value ranges. The success of this inverse design approach for cellular TPMS structures has the potential to expedite new structural material development processes.

Dye-Sensitized Solar Cells Characterization of Kitolod Leaves (Hippobroma longifora)

Energy from fossil fuels is decreasing day by day and also causes many environmental problems. In the current era, many environmentally friendly renewable energy sources have been developed, such as the development of DSSC (Dye Sensitized Solar Cells). DSSC is a technology that utilizes colored materials sourced from nature which are used as absorbers of sunlight energy to be converted into electrical energy. In this research, the synthesis and characterization of organic material from kitolod leaves as DSSC will be carried out. Kitolod leaves (Hippobroma longifora) are wild plants that usually grow in home gardens and rice fields. Kitolod leaves which have chlorophyll can support the absorption of sunlight if applied as a sensitizer in DSSC. The methods that will be used in this research are making TiO2 paste, dye solution preparation, electrolyte solution preparation, DSSC fabrication, testing and characterization. The tests that will be carried out are testing the TiO2 layer, dye absorption, and electric current. Meanwhile, the characterization that will be carried out is dye absorption using UV-Vis, and electric current using a potentiometer. From the results of light absorption shows that when the wavelength is 500 nm or the green light spectrum, the maximum light absorption by the chlorophyll of kitolod leaves is 1.78 (a.u.). The maximum voltage (Vm) and maximum current (Im) in daylight lamps have greater values ​​compared to warm white lamps. The highest efficiency of the solar light source is shown when the air mass is 1.5 (08.30-08.40). The time of DSSC immersion in dye also influences the resulting of Vm and Im values ​​which can be shown in that the Vm and Im values ​​of DSSC 2 (30 minutes) are greater than those of DSSC 1 (10 minutes). The results of open circuit voltage (Voc) and the short circuit current (Isc) in this research still need to be improved to produce better efficiency.

Effect of wheat bran filler particulates nettle fiber reinforced epoxy matrix composite − A novel material for thermal insulation application

This research examines the mechanical and thermal characteristics of composites made from nettle fiber-reinforced wheat bran filler particulate epoxy framework. It highlights the influence of different filler materials on the performance of these composites. A thorough examination of mechanical properties was carried out, focusing on the flexibility, bending strength, impact resistance, and Shore D hardness. The malleable quality was completely changed by adding a filler ingredient, reaching a peak of 51.36 MPa. The flexural strength reached 47.38 MPa, showing excellent ability to withstand loads. The assessment of affect quality reached a maximum of 13 kJ/m2, indicating high energy absorption and durability. The Shore D hardness, which indicates the surface’s ability to resist indentation, ranged from 52 to 61, indicating differences in the stiffness of the composite material. The addition of bran filler to this composite provides an ideal thermal conductivity value of 0.98 W/mK. The morphological properties of the composites were analysed using Scanning Electron Microscopy (SEM), which provided detailed insights into their internal structure. The SEM images revealed a uniform distribution of nettle filaments and bran fillers inside the epoxy matrix, with well-formed samples exhibiting strong fiber–matrix adhesion and minimal voids.

Shape memory sandwich structure with reprogrammable shape and mechanical properties

Sandwich structures are usually used in aerospace and automotive engineering fields. By selecting different core materials and panels, a large number of design strategies are proposed to obtain various types of sandwich structures for various applications. Here, we developed a kind of shape memory sandwich structure using shape memory foam and laminates. The sandwich structure can not only program its shape utilizing SME but also can adjust its mechanical properties by controlling its temperature or shape. The mechanical and thermal–mechanical properties of shape memory laminates, foam and sandwich structure were characterized, respectively. The energy absorption property and bending resistance of the shape memory sandwich structure after being programmed were studied by compression test and drop weight impact test. Shape programmable and mechanical properties adjustable suggest potential applications of this sandwich structure in an adjustable shock-absorbing interface and space deployable structure.

Thermoluminescence response of Ce doped CaTiO3 nanophosphor synthesized by hydrothermal method for gamma dosimetry

Abstract Nanocrystalline calcium titanate (CaTiO3) doped with cerium ions (0.02 mol%) was synthesized via hydrothermal method and its luminescent properties were studied for gamma dosimetry. For the synthesized samples, the best luminescent response was achieved after annealing at 700 °C for 8 h. The synthesis was confirmed via XRD technique yielding the cyrstallite size of 22 nm for the most intense peak (121). The surface morphology was studied via scanning electron microscopy (SEM) yielding the grain size of 12 µm. The strong IR absorptions appeared at 700 cm−1 and 712 cm−1 attributed to bending mode of vibrations changing angle between Ti–O–Ti for CaTiO3 and CaTiO3:Ce respectively, as confirmed via Fourier-Transform Infrared (FTIR) Spectroscopy. Thermoluminescent (TL) response of undoped and doped samples was studied by Mikrolab RA94 TLD Reader-Analyzer having heating rate 10 °C/s, for absorbed doses 0–20 mGy from 137Cs γ-source having a dose rate 100 mSv/h. The found values at 662 keV for the photon-sensing parameters, i.e., mass attenuation coefficients (μ/ρ), mass-energy attenuation coefficient (μ en/ρ), effective atomic number for photon interaction (Z eff,PI) and effective atomic number for total photon energy absorption (Z eff,PEA) were 0.07030882 cm2/g, 0.0280245 cm2/g, 13.9 and 13.4 respectively. Thus, synthesized nanophosphor has shown excellent thermoluminescent dosimetric response for gamma radiation sensing in the selected dose range.

A novel negative Poisson’s ratio structure with high Poisson’s ratio and high compression resistance and its application in magnetostrictive sensors

Currently, dead zones and low sensitivity have hindered the utilization of magnetostrictive sensors. In this paper, a new negative Poisson’s ratio structure inspired by an hourglass is proposed to provide a feasible idea for this problem. The novel negative Poisson’s ratio structure exhibits a high Poisson’s ratio and a high compression resistance. Theoretical studies have demonstrated that the structure’s performance is strongly dependent on four design parameters. The structure is analyzed and tested via finite element analysis simulation by changing the design parameters. This structure’s negative Poisson’s ratio can reach up to −1.004. It possesses a compressive strength of 1.83 kN and an energy absorption capacity of 8.72 J. A magnetostrictive sensor using the proposed negative Poisson’s ratio structure as the base realizes a 271.7 % sensitivity improvement. The problem of dead zones in magnetostrictive sensors can be also solved simultaneously. The proposed structure in this paper provides a feasible solution for further expanding the applications of magnetostrictive sensors.

Study on the energy absorption effect and impact resistance of a composite sandwich panel with carbon fiber reinforced re-entrant hexagonal honeycomb core with negative Poisson's ratio

Negative Poisson's ratio (NPR) structures have excellent energy absorption and buffering properties, but they generally have disadvantage of low specific strength, which restricts their wide applications. Therefore, in this study, the carbon fiber reinforced Nylon material (Nylon 12CF) was prepared and used to construct re-entrant hexagonal honeycomb NPR structure. The reinforced (Nylon 12CF) and unreinforced (Nylon 12) specimens were fabricated by 3D printing technology and tested quasi-statically. Then, the quasi-static of the reinforced and unreinforced re-entrant NPR structure and the impact analysis of the composite sandwich panel (CSP) with re-entrant NPR carbon fiber reinforced core are carried out by finite element method. The results show that the NPR structure reinforced with carbon fiber has 112.5% higher failure stress and 113.9% higher energy absorption efficiency than the unreinforced structure. The finite element simulation results are in good agreement with the experimental results. Under the impact load of a 5 kg object with different initial velocities, the maximum of the displacement of the back face sheet's center point of the CSP with reinforced NPR core is smaller than that of CSP with unreinforced NPR core, especially when the impact velocity is 20 m/s. At different initial impact velocities, the CSP of the reinforced NPR structure core all showed high impact resistance, which was about 1.4 times that of the unreinforced NPR structure core. This research provides new ideas for designing more efficient energy-absorbing and impact-resistant structures.

Fabrication of Energy Absorber by Alternative Stacking of Polyamides having Different Stiffness

Fabrication of Energy Absorber by Alternative Stacking of Polyamides having Different Stiffness

Impact response of additively manufactured density-graded open-cell foams

Additive manufacturing has made it possible to fabricate materials that were unachievable with traditional methods. This study focuses on understanding the deformation behavior and energy absorption mechanics of additively manufactured cellular materials with gradually varying densities. Foams have unique deformation behavior due to their intricate topology and composition, resulting in excellent energy dissipation capability. Varying the density can significantly influence their deformation response and improve energy absorption and impact resistance. Voronoi tessellation is employed to model the foams, as it effectively captures the cell morphology in foam structures and produces stochastic cellular topologies accurately. Resin-based additive manufacturing techniques are employed to fabricate cellular materials with varying density configurations for low-velocity and high-velocity impact experiments. The study demonstrates that density-graded foams effectively dissipate a broad spectrum of impact energies, surpassing uniform counterparts by transmitting reduced stress, especially at lower energy levels. This characteristic enhances their suitability for advanced energy absorption applications. The results also show that at high impact velocities, the direction of density gradation influences energy dissipation and peak stress transmission.

Crushing performance and energy absorption characteristics of aluminum/CFRP hybrid thin-walled tubes: Experimental and numerical investigations

This paper presents both experimental and numerical studies with the main purpose of exploring the crushing behavior of aluminum/CFRP hybrid thin-walled tubes under compression conditions. In particular, aluminum/CFRP tubes with 8, 10, and 12 layers of composites are considered, and the energy absorption characteristics are examined by quasi-static crushing experiments. An explicit finite element (FE) model is developed to investigate the axial crushing response and damage behavior of aluminum/CFRP tubes. Following validation against the experimental data, the developed FE model is applied to analyze the effects of number of layers and loading angles on the failure mechanism and energy absorption indexes of different tube configurations. The obtained results provide valuable insights into a practical energy absorption solution for aluminum/CFRP tubes subjected to crushing conditions, thereby contributing to the long-term development of the related industry.

Finite Element Modeling and Analysis of RC Shear Walls with Cutting-Out Openings

In recent decades, reinforced concrete (RC) shear walls have been one of the best structural solutions to resist lateral load in high-rise buildings. Shear wall openings are essential for preparations and architectural requirements, which weaken the wall, reducing bearing capacity, energy absorption, and stiffness while also causing stress concentrations. This paper presents a comprehensive finite element (FE) investigation of the behavior and performance of RC shear walls with openings and subjected to lateral loads. The study aims to evaluate the influence of various parameters, such as opening location, size, wall aspect ratio, axial load, and concrete strength, which affect the performance of shear walls. FE models were developed to simulate the seismic response of RC shear walls under the combined effect of constant axial and lateral loads. The obtained results from the FE model showed a successful validation using the experimental data available in the literature. The FE analysis results demonstrate that the inclusion of lower openings leads to a 25% decrease in the bearing capacity of the wall when compared to the upper openings. Moreover, it was observed that augmenting the sizes of the openings and the aspect ratios of the wall resulted in declines in the strength, stiffness, and energy absorption capacity of the wall while simultaneously enhancing the ductility and displacement of the RC shear walls.

Numerical study of composite structures behavior under ballistic impacts

The aim of this paper is to introduce a finite element study of the behavior of composite plates subjected to ballistic impacts. The work studies different configurations of laminated composite structures, with and without reinforcements, subjected to high-speed projectile impacts (400-1000 m/s). The investigation focuses on the response of different composite materials' stacking sequences, as well as the impact of epoxy carbon reinforced with carbon nanotubes and the behavior of hybrid sandwich structures made of Kevlar epoxy and glass epoxy. The purpose is to develop a strategy of composite material damage modelling, identify the effects of multi material hybridization, and the influence of reinforcement by carbon nanotubes, on the structures' resistance to ballistic impacts. Numerical simulation provides a detailed description of plate damage. Results show that composite plates with 2% carbon nanotubes (CNT) displays a better impact energy absorption compared to 1% CNT and plates without CNT. The study also revealed the hybridization sequences offering the greatest energy absorption.