High Specific Energy Absorption Research Articles

Parametric design of multi-cell thin-walled structures for improved crashworthiness with stable progressive buckling mode

Thin-walled single and multi-cell structures are an ongoing topic of interest in the field of crashworthiness, due to their wide range of applications in automotive and aerospace industry as lightweight energy-absorbing structures in crash environments. This work presents a new five-cell cross-section that merges high performance multi-cell and twelve-edge cross-sections from previous research, and compares its performance to four- and nine-cell square cross-sections. Super Folding Element (SFE) theory and Finite Element Analysis (FEA) in LS-DYNA are used to analyze cross-sections and found to have good agreement. The LS-DYNA environment is validated with physical testing. The geometry of the cross-sections is varied in order to find maximal values of the performance parameters specific energy absorption (SEA) and crush force efficiency (CFE) under stable progressive buckling mode and constraints for manufacturability. The nine- and five-cell cross-sections ultimately out-perform the four-cell cross-section, with the nine-cell having the highest SEA and CFE, though the five-cell design has a significantly lower (47%) mean crush force (Pm) for only an 11% and 14% loss in SEA and CFE respectively. As a final refinement, the geometry was varied across these two high-performing cross-sections to create equivalent mean crush forces to the four-cell cross-section, which showed the five-cell cross-section to have an improved SEA and better mass efficiency over the nine-cell under a mean crush force constraint.

Three-Dimensional High-Entropy Alloy-Polymer Composite Nanolattices That Overcome the Strength-Recoverability Trade-off.

Mechanical metamaterials with three-dimensional micro- and nanoarchitectures exhibit unique mechanical properties, such as high specific modulus, specific strength, and energy absorption. However, a conflict exists between strength and recoverability in nearly all the mechanical metamaterials reported recently, in particular the architected micro/nanolattices, which restricts the applications of these materials in energy storage/absorption and mechanical actuation. Here, we demonstrated the fabrication of three-dimensional architected composite nanolattices that overcome the strength-recoverability trade-off. The nanolattices under study are made up of a high-entropy alloy-coated (14.2-126.1 nm in thickness) polymer strut (approximately 260 nm in the characteristic size) fabricated via two-photon lithography and magnetron sputtering deposition. In situ uniaxial compression inside a scanning electron microscope showed that these composite nanolattices exhibit a high specific strength of 0.027 MPa/kg m3, an ultrahigh energy absorption per unit volume of 4.0 MJ/m3, and nearly complete recovery after compression under strains exceeding 50%, thus overcoming the traditional strength-recoverability trade-off. During multiple compression cycles, the composite nanolattices exhibit a high energy loss coefficient (converged value after multiple cycles) of 0.5-0.6 at a compressive strain beyond 50%, surpassing the coefficients of all the micro/nanolattices fabricated recently. Our experiments also revealed that, for a given unit cell size, the composite nanolattices coated with a high entropy alloy with thickness in the range of 14-50 nm have the optimal specific modulus, specific strength, and energy absorption per unit volume, which is related to a transition of the dominant deformation mechanism from local buckling to brittle fracture of the struts.

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.

Influence of fabric architecture on crushing behavior of semi-hexagonal composite structures under axial loading

This paper reports the mechanical response of semi-hexagonal part with three different multi-layer reinforcements. Unidirectional, plain woven and orthogonal fabric under quasi-static axial compression were considered. Meso-scale finite element numerical models with failure criterion were also established to simulate the onset and development of internal damage during the compression process. There were two different crush-failure modes occurring in the crush tests of the three different composite samples: a splaying mode for samples with unidirectional fabric, a buckling mode for samples with 3D orthogonal woven fabric and a mixture mode of both buckling and splaying for samples with the plain woven fabric. The samples reinforced by unidirectional fiber have the highest specific energy absorption and lowest peak loading, whereas the samples by 3D orthogonal fabric present the lowest specific energy absorption and highest peak loading. It was also demonstrated by a numerical model that the existence of Z-binder suppresses the delamination by restraining the expanding of warp and weft yarns. The comparison of numerical results and experimental data indicates that the structure of reinforcement has a significant role in the mechanical performance of textile composite.

Design and production of filament-wound composite square tubes

Composite square tubes have gained increasing attention as energy absorbers due to their high specific energy absorption capacity and long stroke. One of the key important issues for producing filament-wound composite square tubes demands both windability and uniform coverage of winding patterns. Based on the analytic geometry, the spatial relation between the feed eye and the mandrel was outlined and the kinematic equations for coupling the motion of the mandrel and the feed eye were derived. Consequently, a design method for small-angle winding of composite square tubes was proposed, taking the non-slippage condition of winding trajectories into account. A periodically geodesic winding theory was presented and its winding error for various initial winding points was analyzed. The designed fiber patterns were then applied to the practical production of a composite square tube with small winding angles. The results show that the present design method for filament-wound square tubes is accurate and reliable. The obtained kinematic equations and motion laws of the feed eye and the mandrel satisfy the basic winding principle and manufacturability of filament-wound composite square tubes. The present method is able to provide a useful tool for design and production of composite square tubes.

Design of Epoxy based Resin Composites for Automotive Applications: A Case Study on IC Engine Valve Guide

The present attempt in this project is to reduce the vibrations, temperature due to friction, noise and weight of I C engine valve guide by replacing conventional metal valve guide with composite valve guide. Composite materials have been used in automotive components because of their properties such as low weight, high specific stiffness, corrosion resistance, ability to produce complex shapes, high specific strength and good impact energy absorption etc. The Internal combustion engine valve guides are the parts that support the valves in the cylinder head, besides this it keeps lubricating oil from getting sucked into the combustion chamber past the intake valve stem, it keeps exhaust gases from getting into the crankcase past the exhaust valve stem and it also keeps the valve face in perfect alignment with the valve seat. A valve guide test rig is indigenously fabricated. Valve guides are manufactured using the developed composite material (Resin ARL-136, Hardener AH-126 and 4 vol% WS2), on a CNC lathe. The performance of the developed composite guide under varied conditions of speeds, that is, fixed change in rpm and modulated changes in rpm is assessed. Noise, temperature and vibrations are measured. The experimental data revealed that contribution of composite guide in respect of acceleration, velocity and displacement components of vibration is not substantial. A substantial reduction in noise levels is seen. As far as temperature rise due to friction is concerned maximum components fail at elevated temperatures, with composite guides the temperature generated due to friction at higher speeds is less, a considerable weight reduction is also observed.

Energy Absorption of Pultruded Glass-Graphite/Epoxy Hybrid Composites under High Strain-Rate Induced Transverse Tension

This paper focuses on the dynamic tensile response of glass-graphite/epoxy composites illustrating improvement in energy absorption through hybridization. The dynamic response and energy absorption characteristics of pultruded hybrid combinations of glass and graphite fibers in an epoxy matrix subjected to induced transverse tension at high strain-rate in a modified Split Hopkinson Pressure Bar (SHPB) apparatus, are presented. Transverse tensile strength was determined by diametral compression of disc samples (Brazilian indirect tensile test method). Diametral crack initiation and strain to failure were monitored with a Shimadzu HPV-2 high-speed video camera at a recording speed of 500,000 fps and Digital Image Correlation (DIC). Adequate measures were taken to ensure that initiation of specimen failure occurred at the exact center of the disc specimen, and propagated through the diameter along the compressive loading axis, for the induced transverse tension tests to be valid. A study of the strength and specific energy absorption demonstrates the benefits of hybridization. Under induced transverse tensile loading condition, the pure glass/epoxy (GL60) exhibited higher strength than pure graphite/epoxy (GR60). Pure graphite/epoxy (GR60) has higher specific energy absorption capacity than pure glass/epoxy (GL60) in transverse tension. Among all hybrids, GR30 has the highest specific energy absorption under transverse tension. Overall, hybrid GL48, with 48% low-cost glass fibers in the inner core and 12% high-cost graphite fibers in outer shell, was found to exhibit better performance under induced transverse tension at high strain-rates, showing the benefits of hybridization.

Multi-objective optimization of tapered tubes for crashworthiness by surrogate methodologies

In this paper, the single and multi-objective optimization of thin-walled conical tubes with different types of indentations under axial impact has been investigated using surrogate models called metamodels. The geometry of tapered thin-walled tubes has been studied in order to achieve maximum specific energy absorption (SEA) and minimum peak crushing force (PCF). The height, radius, thickness, tapered angle of the tube, and the radius of indentation have been considered as design variables. Based on the design of experiments (DOE) method, the generated sample points are computed using the explicit finite element code. Different surrogate models including Kriging, Feed Forward Neural Network (FNN), Radial Basis Neural Network (RNN), and Response Surface Modelling (RSM) comprised to evaluate the appropriation of such models. The comparison study between surrogate models and the exploration of indentation shapes have been provided. The obtained results show that the RNN method has the minimum mean squared error (MSE) in training points compared to the other methods. Meanwhile, optimization based on surrogate models with lower values of MSE does not provide optimum results. The RNN method demonstrates a lower crashworthiness performance (with a lower value of 125.7% for SEA and a higher value of 56.8% for PCF) in comparison to RSM with an error order of 10-3. The SEA values can be increased by 17.6% and PCF values can be decreased by 24.63% by different types of indentation. In a specific geometry, higher SEA and lower PCF require triangular and circular shapes of indentation, respectively.

Hybrid panels from woven Kevlar® and Dyneema® fabrics against ballistic impact with wearing flexibility

.This paper reports on a study of hybrid ballistic panels consisting of plain-woven fabrics made from Kevlar® and Dyneema®, aiming to achieve protective and flexible ballistic panels. Experimental and numerical approaches were adopted for this research. Ballistic penetration tests indicated that the single-phase Kevlar® fabric panels was more energy absorbent than that of the Dyneema® fabric panels at low areal density. When the areal density reached around 1.4 kg/m2, the Kevlar® woven fabric panels started to outperform the Dyneema® counterpart in terms of energy absorption. Accordingly, hybrid panels from the two types of fabrics were engineered and such panels were associated to the higher specific energy absorption than the single-phase panels. It was also found that placing the Kevlar® fabric layer close to the impact face and the Dyneema® fabric layers towards the back face resulted in an improvement of around 16% in ballistic performance over the panels constructed in the reverse sequence. In this investigation, the optimum ratio of the two types of fabrics in hybrid panels was found to be 1:1.

Evaluation of axially-crushed cellular truss structures for crashworthiness

ABSTRACTThin-walled tubes have long been used as energy absorbing structures, owing to their high specific energy absorption (SEA) capacity. But, they are associated with substantial high values of peak crush force (PCF). A high PCF results in a high deceleration pulse on the critical components and/or the passengers. This poses serious safety concerns. Even the use of triggers and grooves do not reduce the PCF considerably. To achieve improvement on the safety aspect, the research on the crashworthiness of the cellular truss structures was conducted in this paper. Finite element simulation model was developed by using ABAQUS/Explicit software and validated experimentally with structures fabricated through additive manufacturing. The truss structures were compared to the thin-walled tubes on the basis of their mass, SEA and PCF values. For an equal amount of energy absorption, while the truss structures had a higher mass, the PCFs were lowered significantly. The PCFs decreased at a rate 1.5 to 4.5 times faster than the corresponding decrease in SEAs. The example of the crash box showed that the drop in PCF due to the use of truss structure resulted in a reduction of around 5g deceleration at the cost of 1 kg of additional mass.

An energy dissipating mechanism for crushing square aluminium/CFRP tubes

A platen with cutting blades was introduced as a new energy dissipating mechanism to simultaneously cut and crush square bare CFRP tubes and CFRP tubes wrapped externally with aluminium sheets. The specially designed and manufactured platens with four round tip blades, four sharp tip blades and eight round tip blades were used to reduce the initial peak crushing force and increase the energy absorption of CFRP tubes. Notches were introduced at one end of tubes to control the location of the initial failure. Experimental results showed that the deformation mode of CFRP tubes and aluminium sheet-wrapped CFRP tubes that were crushed by platens with blades was a combination of splaying progressive and transverse shearing failure mode. More damage was observed to CFRP plies when tubes were crushed by using round tip blades. Tubes cut and crushed by a platen with eight round tip blades had a lower initial peak crushing force, higher mean crushing force, larger energy absorption and higher specific energy absorption in comparison with counterpart tubes crushed by flat platens. A comparison between the new trigger mechanism proposed in this study (cutting blades) and other different trigger mechanisms used in published literature was made.

A numerical study of temperature effect on the penetration of aluminum foam sandwich panels under impact

Abstract The aluminum foam sandwich is a composite structure with light weight and high specific energy absorption under impact. However, penetrated behaviors of the composite structures at elevated temperatures still remain unclear. A systematic numerical model of the aluminum foam sandwich was developed with the nonlinear, finite element program ABAQUS. In this model, a constitutive relation of aluminum foam with temperature effects was put forward based on uniaxial compressive tests. Subsequently, a failure criterion including both average stress and von Mises stress is obtained through compression, tension and penetration experiments at elevated temperatures. Besides, the eroding contact ensures the touch between the punch and foam core. The numerical model well captured the penetrative process well including the failure features and force-time curves at elevated temperatures. Meanwhile, the energy and max force of aluminum foam sandwich with different mass ratios are discussed. The results disclosed strong temperature effects on the penetrated behaviors of aluminum foam sandwich plates, and reveal the changes of failure modes at elevated temperatures.

Diffusion Bonding in Fabrication TA2 Sheets Enhanced Aluminum Foam Sandwich

Aluminum foam sandwiches (AFSs) served as sheet materials have enormous marketing potential for their interesting combinations of excellent properties, such as low density, high specific strength, energy absorption and thermal insulation. In this paper, transient liquid phase (TLP) bonding method was used to prepare pure titanium sheet enhanced AFS (TS-AFS). Fabricated TS-AFS with the dimension of 80×80×18 mm3 presented uniform foam core, and bubbles ranged from 0 mm to 2 mm occupied the most area of cross section. Thickness of interface layer increased with the increase in the holding time. Additionally, metallic compounds of Al20CaTi2 and Al2Ti were detected at the bonding joint.

Microstructure and strength correlation of pure Al and Al-Mg syntactic foam composites subject to uniaxial compression

The microstructure and quasi-static compression of glass cenospheres/aluminum matrix syntactic foams (AMSFs) with three t/R ratio cenospheres (t/R=0.043, 0.052 and 0.064) and three different matrices (cp-Al, 5A03 and 5A06) were investigated. The compression strength and energy absorption of foams were found to increase with t/R ratio and Mg in matrix. The strengthening mechanisms were attributed to the nature properties of cenospheres and the thickness of high strength interfacial reaction MgAl2O4 forming. Two models were provided to predict the quasi-static properties of AMSFs considering the factors including physical properties of matrix and cenospheres, volume fraction of cenospheres, composition changing of matrix and thickness of interfacial reaction coating caused by interfacial reaction between matrix and cenopsheres. The predictions for peak stress, plateau stress, energy absorption capacity and specific energy absorption of AMSFs showed good agreement with experimental data. The Al-Mg syntactic foams in this study exhibited high specific energy absorption (56Jg−1) and specific plateau strength (94MPacm−3g−1).

Cutting and crushing of square aluminium/CFRP tubes

Square CFRP tubes were wrapped externally with aluminium sheets and crushed quasi-statically in the axial direction to investigate the effect of aluminium sheet-wrapping on the energy absorption of CFRP tubes. Moreover, a specially designed and manufactured platen with cutting blades was employed, as a new energy dissipating mechanism, to simultaneously cut and crush both CFRP tubes and aluminium sheet-wrapped CFRP tubes. Notches were introduced at one end of some tubes which were crushed by a platen with blades to control the location of the failure. Experimental results showed that the deformation mode of CFRP tubes and aluminium sheet-wrapped CFRP tubes that were crushed by a flat platen or by a platen with blades was a combination of splaying progressive and transverse shearing failure mode. By wrapping CFRP tubes with aluminium sheets and using cutting blades, the mean crushing force and energy absorption increased by up to 70%. The crushing response of tubes without notches crushed by a platen with blades was similar to those tubes crushed by flat platens. Tubes with notches crushed by a platen with blades had a lower initial peak force, higher mean crushing force, larger energy absorption and higher specific energy absorption in comparison with counterpart tubes crushed by flat platens.

Crashworthiness analysis and optimization of fourier varying section tubes

Thin-walled structures are widely used as energy absorption devices for their proven advantages on lightweight and crashworthiness. However, a majority of studies have being focus on exploring separately the crashworthiness of the thin-walled structure with a specific geometric section, such as circular, square, hexagon, octagon etc., and little research has investigated the relationship of crashworthiness among thin-walled structures with different sections systematically. This paper utilizes Fourier series expansion to generate a series of novel sectional configurations, namely Fourier varying sectional tubes (FVSTs), to look into their advantages of crashworthiness, thereby developing some FVSTs with highest possible energy absorption capacity. Based on the validated finite element (FE) models, parametric analysis is conducted to investigate the effects of cross-sectional configuration, perimeter and thickness of FVSTs on collapse mode and energy absorption. The results showed that the collapse modes of FVSTs are fairly sensitive to cross-sectional configuration, perimeter and wall thickness. Of these FVSTs generated, the highest specific energy absorption (SEA) increases 77.54% by increasing perimeter and 69.73% by decreasing wall thickness. Finally, a discrete optimization based on the orthogonal arrays is conducted to obtain the optimal FVST for maximizing SEA under the constraint of the initial peak crushing force (IPCF). The optimized FVSTs are of superior crashworthiness and great potential as an energy absorber.

Analysis of Structural Configurations for Assessment of Crashworthiness

Crashworthiness of an energy absorbing (EA) structural member depends on its geometric configuration and material. Different structural configurations can be conceived to enhance performance of crashworthiness in design of safety systems in automobiles. Specific energy absorption (SEA) is often regarded as an important parameter in assessing crashworthiness and is commonly adopted in majority of research conducted in developing a variety of EA structures. Major limitation in most EA structures is that they exhibit high initial peak force and low stroke efficiency. This paper presents an analysis of few new structural configurations for EA structures that essentially meet all important parameters of crashworthiness such as high crash force efficiency (CFE), stroke efficiency (SE) and SEA. The structures are made of aluminium alloy AA7005 in T6 state. The relative merits of each configuration are discussed and a best one is recommended for improved crashworthiness.

Development of carbon fibre‐reinforced plastic (CFRP) crash absorbers with stable crushing behaviour considering the connection to the bumper system

Crash absorbers made of fibre‐reinforced plastics becoming more and more popular to reduce the mass in the front section of cars. Various research projects analysed the high specific energy absorption and the stable crushing behaviour of this material, however without examining the connection to other car body components. This paper focuses on the connection of the crash absorbers to the bumper system, particularly regarding to the crushing behaviour. An initial step focused on the development of a crash absorber made of carbon‐fibre‐reinforced plastic, which shows similar energy absorption compared to absorbers made of aluminium. A following step investigated various connection concepts using a drop tower. These first connection concepts resulted in unstable crushing behaviour. The finite element simulation of the tests delivered additional information about the reasons for the insufficient crushing behaviour. Subsequently, a simulation of various connection concepts turned out suitable connection concepts. A final drop tower test investigated the best connection concept. The developed connection system shows similar to the unmodified crash absorber stable crushing behaviour.

Highly effective energy dissipation system based on one-dimensionally arrayed short single-walled carbon nanotubes

In this paper, the impact energy dissipation characteristics of one-dimensional (1D) short single-walled carbon nanotube (SWNT) system are investigated via molecular dynamics (MD) simulation. It is found that 1D SWNT system has good force mitigation performance and extraordinarily high specific energy absorption (SEA) upon high-speed impact in the absence of plasticity, which is 1 to 2 orders advantageous over macroscale impact protection devices and structures. Moreover, a simple model based on the theorem of momentum can give an accurate prediction of force mitigation effect. The mechanism of this non-plastic impact energy dissipation lies in the transformation of impact energy to the kinetic and potential energy of SWNT molecules. Similar to macroscopic metallic rings, SWNTs can buckle under large force, which in fact enhances force mitigation capability of the system. A continuum model is established, able to predict the critical forces of SWNTs of different radii. Finally, system performance upon impact speeds in a broader range and the influence of parameters such as system length and SWNT radius are discussed. This work may be instructive to the design of novel impact energy mitigation system at nanoscale.

Crushing behavior of new designed multi-cell members subjected to axial and oblique quasi-static loads

A new design of multi-cell devices was proposed in this paper, and evaluated in terms of crashworthiness capability under quasi-static axial and oblique (9°, 18° and 27°) loading. The structures studied in the present paper were single and multi-cell members made up of two straight columns with the same shape of cross-section connected together by several ribs. They included several sectional configurations such as triangle, square, hexagon and circle with different scales (i.e. 0, 0.25, 0.5, 0.75 and 1). Finite element code LS-DYNA was used to simulate the crashworthiness behavior of the proposed members under quasi-static loads. Several crashworthiness indicators including SEA, Fmax and CFE were obtained at different crushing angles for all the columns, and a powerful decision making method known as COPRAS was then implemented to choose the best energy absorber with the criteria of having higher specific energy absorption and lower initial peak force. From the COPRAS calculations, the multi-cell members with inner tube and scale number of 0.5 were selected as the better energy absorbers, and the column with circular cross-section was also found to be the best energy absorbing device.