High Energy Absorption Capacity Research Articles

An experimental study on the bending response of multi-layered fibre-metal-laminates

The combination of thin light metal sheets with fibre-reinforced thermoplastic layers in multi-layered fibre-metal-laminates advantageously combines the properties of both material classes. In this way, components can be developed which have both significantly increased specific properties (strength and stiffness with respect to density) and high energy absorption capacity compared with conventional design with mono materials. However, the structural behaviour of crash structures is decisively determined by material behaviour of the thermoplastic and metal constituents as well as the interface properties between both constituents and the corresponding delamination behaviour. To evaluate the structural response of multi-layered fibre-metal-laminates under highly dynamic loading conditions, Charpy tests were performed, where the test parameters, light metal material configuration, support length and laminate thickness, were varied. Moreover, the metal sheet surfaces were pre-treated by embossing to achieve different surface topologies. The influence of the different test parameters on the specific energy absorption capacity was characterised by the analysis of force–displacement curves.

Development of Family of Super Convergent Shear Deformable Finite Elements for the Analysis of Sandwich Beams with Soft Core

Sandwich structures are widely used in aerospace and naval industries as they are light in weight and have high energy absorption capacities. Sandwich beams with soft core are the most commonly used structures in many applications. Analysis of sandwich beams is the key in its design and the development of new family of super convergent shear deformable finite elements are presented in this article. In this article, formulation of three different Super Convergent shear deformable finite elements with 4, 7, and 10 degrees of freedom respectively, for analysis of the sandwich beams with soft core are presented. The formulation considers the top, bottom face sheets and core as separate entities and are coupled by beam kinematics. The performance of these elements are validated by results available in the published literature. The article highlights the issues with the traditional elements for modeling sandwich beams and the advantages of the elements developed, in particular wave propagation analysis, are addressed in this article.

Experimental Investigation of Tensile and Impact Behavior of Aramid-Natural Fiber Composite

Abstract For past few decades there is tremendous growth in science and technology which demands new materials. To meet such demands for materials, the world’s focus is towards emerging and promising field of Composite materials, the reason being is that composite materials are light weight and high strength to weight ratio when compared to most conventional metals. The main purpose of this paper is to investigate tensile and impact property of Aramid with natural fiber composite. Kevlar being the main reinforcement along with Neem/Kenaf and matrix is Epoxy resin. The main reason of choosing Kevlar as main reinforcement as it has good strength, high impact and high energy absorption capacity but Kevlar being quiet costlier so Kenaf and Neem is used alternatively to reduce the cost and to replace and substitute the Kevlar with natural fibers without affecting the impact resistance property. Mechanical properties such as tensile, impact are found and the results are plotted.

Mechanical behavior of gas metal arc AA6082-T6 weldments

A series of experiments have been conducted to determine the mechanical properties of AA6082-T6 plates which have been joined by means of the Gas Metal Arc technique. Hardness Vickers tests, bending tests, tensile tests, fatigue tests and Charpy V-notch tests have been carried out to characterize the joints. In addition, an accurate microstructure analysis of selected fracture surfaces has been done. From the tests it is concluded that HAZ softening brings to a reduction in strength with respect to the parent material. It has been noticed that there is a minimum value of hardness in the heat affected zone, that corresponds to the weakest part of the component. From the Charpy V-notch impact tests it has been observed that the material in the HAZ has the highest energy absorption capacity.

Influence of occlusal thickness of custom-made mouthguards on ventilatory parameters, rate of perceived exertion, and peak velocity attained during an incremental test

Custom-made mouthguards are used to prevent orofacial injuries arising from falls and knocks. It has been observed that thicker custom-made mouthguards transmit less force to the mouth owing to their higher energy absorption capacity. However, it is believed that thicker custom-made mouthguards can alter ventilation during exercise because of the higher resistance or restriction of oral airflow. The purpose of this study was to investigate if a thicker custom-made mouthguard (occlusal thickness of 5 mm; 5MG) alters ventilatory parameters, rate of perceived exertion (RPE), and peak velocity during an incremental test relative to a thinner custom-made mouthguard (occlusal thickness of 3 mm; 3MG) and no mouthguard (NoMG). Eleven male amateur contact team sports players completed three running incremental tests on different days. Each test was performed with either 3MG, 5MG, or without a mouthguard. The peak velocity during the incremental test was similar between the different conditions (14.9±0.6, 14.9±0.7, and 14.7±0.9 km·h-1 for NoMG, 3MG, and 5MG, respectively). Furthermore, no differences were found in the peaks of pulmonary oxygen uptake, minute ventilation and respiratory frequency, or second ventilatory threshold. RPE was higher when wearing 5MG than when running without a mouthguard only at the 12.5 km·h-1 stage (P=.03). These data indicate that wearing custom-made mouthguards with occlusal thicknesses between 3 mm and 5 mm does not alter ventilatory parameters at the end of an incremental test. Thus, custom-made mouthguards with an occlusal thickness of 5 mm should be preferred owing to their greater protection capacity.

Topology optimization-guided lattice composites and their mechanical characterizations

Optimization design assisted with advanced additive manufacturing techniques opens an effective gate for us to create novel, lightweight, mechanically robust cellular materials. Among them, lattice materials with an ordered cellular architecture have been known for their high mechanical properties, low density and energy absorption capacity. Limitedly, what kinds of topologic architecture have the best performance? And how could we obtain the optimized architecture? To answer them, we here took up two challenging tasks to achieve a novel compression-resistant lattice: ① The topology optimization method was introduced to design the optimized topologic architecture. ② Metallization was used to form lattice composites to further enhance the mechanical properties of pristine polymer. The topology optimization-guided lattice with only 20% volume of solid materials quite resembles the microstructure of cuttlebone, giving an indication of a good compression-resistant ability. Furthermore, the synthesized composites exhibit high specific compressive modulus of 5417.02 MPa kg−1 and energy absorption efficiency of 78%. By in situ compressive tests, digital image correlation, finite element simulation and fracture analysis, the deformation mechanism, and fracture modes were unambiguously revealed. The design strategies and findings shed light on the realization of advanced materials with tailored mechanical properties.

In-plane dynamic crushing behaviors of a novel auxetic honeycomb with two plateau stress regions

In order to obtain honeycomb structure with higher energy absorption capacity, a novel honeycomb is proposed by adding double arrowhead honeycomb (DAH) cells into star-shaped honeycomb (SSH), and therefore named as star-arrowhead honeycomb (SAH). An analytical model is built to investigate the in-plane elastic properties of the newly proposed honeycomb and the results are in good agreement with the finite element simulations. The in-plane dynamic crushing behaviors and energy absorption capabilities of SAH are studied systematically by finite element method and are compared with that of SSH and DAH. Two plateau stress regions in the stress–strain curves of SAH are observed under low-velocity impact loading, and the second plateau stress is over three times higher than the first one. The in-plane Poisson's ratio of SAH under static and high-velocity impact loading always shows negative value. However, the Poisson's ratio of SAH changes from negative to positive under low-velocity and medium-velocity impact loading. In addition, the Poisson's ratio of SSH and DAH are negative during the entire dynamic deformation processes. The results of finite element simulations show that SAH can absorb much more energy than SSH with the same relative densities under different impact velocities, especially under low-velocity impact loading. Furthermore, the effects of the cell wall thickness and the impact velocity on plateau stress of SAH are discussed, and therefore a deformation map is summarized. It can be concluded that SAH is a better choice for energy absorption. This study may provide a new design concept for the high performance honeycomb structure with multi plateau stress regions.

Experimental and numerical investigation into the crashworthiness of metal-foam-composite hybrid structures

To meet the growing demands for structural lightweight and safety, metal-foam-composite hybrid tubular sandwich structures, which combine low-cost metallic materials and high-strength composites with low-density cellular materials, have been recently introduced to be a class of energy absorber configurations for automotive engineering. This study proposed four different hybrid sandwich tubes and investigated their crashworthiness and performance to cost ratio under quasi-static axial condition. For a comparative purpose, individual carbon fiber reinforced plastic (CFRP) tube, aluminum tubes and aluminum foam were also tested here. From the energy absorption perspective, it is found that all the hybrid specimens exceeded the sum of the individual components. Of different configurations, specimen C-F-C (i.e. outer CFRP tube + aluminum foam + inner CFRP tube) had the highest energy absorption capacity (in energy absorption): 6.70 kJ, specific energy absorption (SEA): 37.32 kJ/kg, improvement of energy absorption: 39.1%, and material cost: 6.877 £, respectively. The specimen C-F-A (i.e. outer CFRP tube + aluminum foam + inner aluminum tube) exhibited the highest crushing force efficiency (0.87) and value-added performance of energy absorption (0.325 kJ/£). The specimen A-F-A (i.e. outer aluminum tube + aluminum foam + inner aluminum tube) exhibited the lowest peak crushing force (63.56 kN) and lowest material cost (2.227 £). Further, the finite element (FE) model was established to analyze the crashworthiness characteristics of hybrid sandwich tubes through validating the simulation results with the experimental data, which provided a basis for further parametric analysis and structural optimization.

Crashworthiness of hierarchical circular-joint quadrangular honeycombs

The new hierarchical circular-joint quadrangular honeycomb is proposed by iteratively replacing the edge-junctions of regular honeycomb with a circular joint. Firstly, the nonlinear finite element analysis is performed through LS-DYNA and the results are validated by experimental data. Then, analytical solutions to crushing resistance of the hierarchical honeycomb are obtained based on the Simplified Super Folding Element (SSFE) theory. The results between the numerical and analytical method are in good agreement, which indicates that the analytical solutions are reliable. Furthermore, parametric studies of the first and second hierarchical order structures are conducted numerically. The results show that the specific energy absorption of the first and second-order hierarchical honeycomb is improved by up to 81.8%, 115.3% respectively compared with the regular honeycomb. It is also found that the out-of-plane crashworthiness performance of the second-order hierarchical honeycomb can be enhanced by increasing relative density. However, the peak crushing force would also increase with the increase in relative density. The findings of this study show that the proposed hierarchical honeycomb is a structural configuration with high energy absorption capacity.

Evaluation of mild steel hollow and foam filled circular tubes under axial loading

AAF (Aluminium alloy foam) has turned out to be a beneficiary content in the automotive sector across the globe. It has been in applications due its light weight tendency and providing high strength and energy absorbing capacity. The content of paper marks a plot on the energy absorption capability of the AAF filled circular tubes. AlSi10Mg has been produced by the melt route method. Aluminium foam filled circular tubes, mild steel (MS) thin walled hollow tubes were tested under compression loading to note the energy absorption and deformation behavior. The compression was carried out with a strain rate of 0.1/s. FESEM tests was conducted to obtain the data at micro and macro levels. The test results portray that the foam filled circular tubes shows more energy absorption than the hollow (ERW) tubes at 0.1/s strain rate.

Metallic Glass Structures for Mechanical-Energy-Dissipation Purpose: A Review

Metallic glasses (MGs), a new class of advanced structural materials with extraordinary mechanical properties, such as high strength approaching the theoretical value and an elastic limit several times larger than the conventional metals, are being used to develop cellular structures with excellent mechanical-energy-dissipation performance. In this paper, the research progress on the development of MG structures for energy-dissipation applications is reviewed, including MG foams, MG honeycombs, cellular MGs with macroscopic cellular structures, microscopic MG lattice structures and kirigami MG structures. MG structures not only have high plastic energy absorption capacity superior to conventional cellular metals, but also demonstrate great potential for storing the elastic energy during cyclic loading. The deformation behavior as well as the mechanisms for the excellent energy-dissipation performance of varying kinds MG structures is compared and discussed. Suggestions on the future development/optimization of MG structures for enhanced energy-dissipation performance are proposed, which can be helpful for exploring the widespread structural-application of MGs.

The synergic influence of nano-silica and carbon nano tube on self-compacting concrete

The influence of nano-silica (NS), carbon nano-tube (CNT) and fly ash (FA) as solo, binary or ternary combination on fresh and hardened properties of self-compacting concretes (SCC) were investigated in this study. These materials were replaced with the certain portion of the cement. In scope of this study, the eight groups of mixes categorized into two categories with and without FA so that each category possessed a reference group and three other groups with only NS, CNT or both. Based on different previous studies, the optimum substitution percentages selected 2%, 0.08% and 40% for NS, CNT and FA, respectively. The slump-flow, V-Funnel and L-Box properties of the produced fresh concretes were investigated. Besides, compressive strength and flexural toughness properties of hardened concretes were determined and were compared with typical properties of SCC.Test results showed that NS worsened the fresh concrete properties due to its higher water demand, but in presence of FA, NS improved these properties significantly and removed segregation and bleeding effects of 40% FA. Also, the CNT substitution in concrete provided 20% increase in toughness index of SCC. According to test results, the mix with 2% NS, 0.02% CNT and 40% FA can be considered as the best SCC mix due to discussed specifications. Finally, besides all convenient fresh properties, by support of NS and CNT, the inclusion of high volume of FA enabled to sustainable construction and production of a more environment-friendly concrete with improved mechanical properties. Moreover, CNT resulted in more ductile concrete with higher energy-absorbing capacity.

Low-velocity impact behavior of composites reinforced with weft-knitted spacer glass fabrics

Structural parameters of fabrics influence the mechanical behaviour of fabric-reinforced composites. Weft-knitted spacer fabrics have high energy absorption capacity. In this paper, low-velocity impact behavior of composites reinforced with weft-knitted spacer fabrics has been studied using energy-balance method. The effect of fabric geometry on the impact behavior of composites was investigated. A theoretical model was generated to predict the energy dissipated through the impact, considering the structural parameters of fabrics as reinforcement of composites. For this purpose, dissipated energies due to contact, membrane and bending deformation of fabrics, and buckling deformation of spacer yarns were considered. In order to evaluate the proposed model, weft-knitted spacer fabrics with two types of spacer yarn's orientation were used as reinforcement of composites. Low-velocity impact examinations were performed using the drop hammer testing machine. The results showed that the model has about 12 and 13% error in prediction of dissipated energies of different samples. Comparison between theoretical and experimental results confirms that the proposed model is capable to predict the impact behavior of weft-knitted spacer fabric-reinforced composites.

Increasing the structural energy dissipation of laminated fibre composite materials by delamination control

In this paper an approach to increase the energy absorption capacity of laminated composites is investigated. The interlaminar interfaces of two different composite materials, a 2/2 twill weave of glass fibre reinforced polypropylene and a plain weave of carbon reinforced epoxy, are modified. Perforated, non adhesive polytetrafluorethylene (PTFE-) foils were interleaved between the composite layers leading to different interlaminar contact area (ICA) set-ups. The energy absorption capacity, impact resistance as well as the damage and failure behaviour, especially delamination, are evaluated in Charpy drop weight experiments. Based on the resulting force-displacement-response, initiation and propagation energies as well as the ductility index are evaluated. High speed camera imaging is used to correlate failure phenomena to structural response. It can be shown, that the failure behaviour of textile reinforced composites is significantly influenced by the interface modification concept. As a result, the delamination initiation and propagation is enhanced with lower ICA leading to higher energy absorption capacity on the one hand and higher propagation-to-initiation-energy-ratio on the other hand. Consequently, the already high energy absorption capacity of composite materials can be further increased up to 65% while the ductility index rises up to ten times.

Low-velocity impact behaviour of a shear thickening fluid (STF) and STF-filled sandwich composite panels

Sandwich composite panels (SCPs) with carbon fibre reinforced plastic (CFRP) facings are usually vulnerable to low-velocity transverse impact loading. In this study, a method is presented to improve the impact resistance and energy absorption capacity of CFRP-faced SCPs by filling them with a concentrated styrene/acrylate particle based shear thickening fluid (STF). First, for the STF alone, aspects of mechanical performance, namely rheological and low-velocity impact behaviours, were systematically examined. It was found that the critical shear stress of the STF was lower than that of silica particle based STF with a similar particle size and volume fraction, indicating that shear thickening was more easily achieved in the styrene/acrylate particle based STF. In addition, the STF exhibited much higher energy absorption capacity than an aluminium foam. Finally, low-velocity transverse impact experiments were performed on STF-filled SCPs with two core thicknesses, 7.2 mm and 12.7 mm. It was shown that the absorbed energy of the SCPs with a thin core increased by up to 99.3%, while the impact damage of SCPs with a thick core could be effectively suppressed on the back surface of the SCPs. The impact mechanism of the STF-filled SCPs is also discussed. This study provides a new method for the design of impact-resistant SCPs.

Preparation and Properties of C/C Hollow Spheres and the Energy Absorption Capacity of the Corresponding Aluminum Syntactic Foams.

The present study focuses on the preparation and characterization of lab-scale aluminum syntactic foams (ASFs) filled with hollow carbon spheres (HCSs). A new and original process for the fabrication of HCSs was explored. Firstly, expanded polystyrene beads with an average diameter of 6 mm and coated with carbon fibers/thermoset phenolic resin were produced by the “rolling ball” method. In the next step, the spheres were cured and post-cured, and then carbonized at 1050 °C under vacuum to form the HCSs. The porosity in the shell of the HCSs was decreased by increasing the number of impregnation–carbonization cycles. The aluminum syntactic foams were fabricated by casting the molten aluminum into a crucible filled with HCSs. The morphology of the hollow spheres before and after carbonization was investigated by scanning electron microscope (SEM). The compressive properties of the ASF were tested and the energy absorption capacities were calculated according to stress–strain curves. The results showed that the ASF filled with HCSs which had been treated by more cycles of impregnation–carbonization had higher energy absorption capacity. The aluminum syntactic foam absorbed 34.9 MJ/m3 (28.8 KJ/Kg) at 60% strain, which was much higher than traditional closed cell aluminum foams without particles. The HCSs have a promising future in producing a novel family of metal matrix syntactic foams.

Effects of aluminum foam filling on the low-velocity impact response of sandwich panels with corrugated cores

In this study, a closed-cell aluminum foam was filled into the interspaces of a sandwich panel with corrugated cores to form a composite structure. The novel structure is expected to have enhanced foam-filled cores with high specific strength and energy absorption capacity. An out-of-plane compressive load under low-velocity impact was experimentally and numerically carried out on both the empty and foam-filled sandwich panels as well as on the aluminum foam. It is found that the empty corrugated sandwich panel has poor energy absorption capacity due to the core member buckling compared to that of the aluminum foam. However, by the filling of the aluminum foam, the impact load resistance of the corrugated panel was increased dramatically. The loading-time response of the foam-filled panel performs a plateau region like the aluminum foam, which has been proved to be an excellent energy absorption material. Numerical results demonstrated that the aluminum foam filling can decrease the corrugated core member defects sensitivity and increase its stability dramatically. The plastic energy dissipation of the core member for the foam-filled panel is much higher than that of the empty one due to the reduced buckling wavelength caused by the aluminum foam filling.

Multi-objective optimization for designing a composite sandwich structure under normal and 45° impact loadings

Abstract With their lightweight character and high energy absorption capacity, composite sandwich structures have attracted increasing attention in the transportation industry. The aim of this work is to present a new approach to investigate and optimize a composite sandwich structure by taking into account both normal and 45° low-speed impact loadings. First, a finite element model considering elastic-plastic, damage, and failure behaviours of the composites by using continuum damage mechanics is developed and validated by a normal low-speed impact test. Second, dynamic effects of normal and 45° impacts on energy absorption and failure behaviours of the composite sandwich structures are investigated. Then, a parametric study is performed to systematically understand the influences of core depth and cell thickness on the impact resistance of the sandwich composite structures subjected to both normal and 45° impacts. In contrast to their metal counterparts, it is interestingly found that absorbed energy generally increases with cell thickness, with a small extent of fluctuation, whereas core depth jumps, and the energy absorption capacity remains almost steady under normal impact but varies irregularly under the 45° impact. Afterwards, a multi-objective optimization is performed to enhance the energy absorption under both normal and 45° loadings. The energy absorption capability of the optimal composite sandwich structure can remarkably be improved by 12.447% for normal impact, and 7.9% for 45° impact. This method provides a new manner and systematic guidance for designing a lightweight composite sandwich structure more practical for engineering application.

Experimental and numerical investigation on bending collapse of embedded multi-cell tubes

Traditional multi-cell tubes exhibit much higher energy absorption capacity and efficiency than single-cell tubes when subjected to axial or transverse loads. This work investigates the bending resistance of a type of composite multi-cell tubes, which is easily obtained by embedding a group of small single tubes into an enveloping tube. This type of embedded multi-cell tubes is flexible in sectional dimensions and shape, easily prepared and highly cost-effective. Three-point bending tests are first performed to investigate the bending behavior and response of embedded multi-cell tubes with different cell configurations. The influences of friction condition, end treatment and partially filling are also studied experimentally. Numerical simulation of the experiment is then carried out by employing the explicit finite element code LS-DYNA. The simulation results generally compare well with experiment. The quasi-static and dynamic bending responses of both embedded and traditional multi-cell tubes with almost the same sectional shape and dimensions are investigated numerically. The bending resistance of embedded multi-cell tubes is found to account for about 65–72% of corresponding traditional multi-cell tubes.

Crushing analysis for novel bio-inspired hierarchical circular structures subjected to axial load

Hierarchical structures are widely observed in nature, and used in engineering due to superior mechanical properties. In this paper, a novel hierarchical circular tube (HCT) by iteratively adding self-similar sub-circle at the junctions of the primary ribs is proposed to enhance structural crashworthiness performance. The finite element model of HCT is firstly established through LS-DYNA and validated via experiment testing. The energy absorption performance of different hierarchical HCTs is investigated under dynamic load. The hierarchical organization has remarkable potential to improve the crashworthiness behavior of thin-walled structure, especially, the 2nd order HCT exhibits significant advantages for energy absorption efficiency. Then, parametric designs are performed to explore the crashworthiness effect on main geometrical parameters of 2nd order HCT. Furthermore, theoretical model of 2nd order HCT is derived based on super folding element method, and obtain the good prediction accuracy for energy absorption and mean crushing force. To further obtain the optimal design of the 2nd order HCT, multi-objective optimization is performed by employing radial basis function (RBF) neural networks and multi-objective particle swarm optimization (MOPSO) algorithm. The several optimal structures are obtained under different peak crushing force (PCF). The findings of this research offer a new route of designing novel crashworthiness structure with high energy absorption capacity.