Energy Absorbing Structures Research Articles

Evaluation of crushing and energy absorption characteristics of bio-inspired nested structures

Abstract Mimicking anatomical structures like bone can aid in the development of energy absorbing structures that can achieve desirable properties. Accordingly, this study presents the analysis of tubular nested designs inspired by Haversian bone architecture. Based on this design philosophy, a total of 18 nested tube designs with various geometrical configurations were developed. Within each design, the effect of reinforcement walls on the crashworthiness performance is also analysed. A finite element model, validated using quasi-static experimental tests, was used to study the crashworthiness performance and progressive deformation of the nested system. Based on the results, a multi-criteria decision-making method known as Technique of Order Preference by Similarity to Ideal Solution (TOPSIS) was employed to determine the most suitable cross-section that features high energy absorption and low impact force. Consequently, the study identified a nested tube configuration that exhibits superior crashworthiness and high energy absorbing characteristics. The bio-inspired design methodology presented in this study allows the exploitation of variable nested geometries for the development of high-efficiency energy absorbing structures.

Mechanical performance of bio-inspired corrugated tubes with varying vertex configurations

Thin-walled metal tubes are the most widely used energy-absorption structures in various industries. Bionics can help engineers to design novel tubular structures to achieve outstanding crashworthiness performance. Inspired by the unique microstructure of a horse-hoof-wall and the concept of vertex-based hierarchy, a novel bio-inspired corrugated tube and its derivative structures with varying vertex configurations were proposed in this paper. Quasi-static compression test and finite element simulation were employed to investigate the mechanical behaviors of these bio-inspired tubes. The results showed that these bio-inspired tubes exhibit good crashworthiness performance, especially in terms of their weight force efficiencies. Moreover, by applying a complex proportional assessment method, the tube with regular octagon vertex configuration was selected as the optimum one among these bio-inspired tubes. A theoretical model was developed to predict the mean crushing force of the proposed tubes. In conclusion, the horse-hoof-wall inspired tubes exhibit a novel perspective on providing superior mechanical properties and pave a way of applications of bio-inspired engineering structures.

Experimental and numerical investigations on the energy-absorption of a bending-straightening structure

This paper introduces an energy-absorption structure which dissipates energy utilising the ‘bending-straightening’ process and the friction of a thin metal plate. Three repeated tensile tests were carried out to investigate the force and energy characteristics of the structure. Different loading methods and loading rates of the simulation were studied and the numerical model was verified. Furthermore, the effects of the metal plate thickness, width, the central distance of the structure and the friction coefficient on the energy-absorption of the absorber were studied systematically. The results show that the structure is of good test reproducibility and the loading process is steady. The stable tensile force (STF) and the dissipated energy increase with the rising of the structural parameters significantly. With some of the engineering improvements, the absorber can be implemented in the seat anti-impact structure and this work can provide guidelines for the design and analysis for engineering applications.

Multi-cell energy-absorbing structures with hollow columns inspired by the beetle elytra

In this work, we propose a new type of thin-walled energy-absorbed structure with hollow columns that possesses a design inspired by the beetle elytra. The failure mode of the bionic thin-walled structures is firstly discussed by developing a theoretical model. The energy absorption properties of these bio-inspired multi-cell thin-walled structures have been then investigated using nonlinear finite element simulations. The values of the specific energy absorption and the crushing force effectiveness have been evaluated for different structures with parametrized column nested configurations. Dynamic impact simulations of multi-cell tubes with different columns nested modes, wall thickness and impact angles have been performed, and the results discussed.

A computational study on the crushing behaviour of aluminium capped cylindrical tubes subjected to oblique load

Light-weight tubular structures have been employed as an ideal energy absorbing elements in aircraft manufacturing industries for their superior energy absorbing capability. The present article discusses about the numerical investigations on the oblique crushing behavior and energy absorption performance of various aluminum capped cylindrical tubes. Numerical models were developed with ABAQUS/CAE® code to predict the deformation behaviour of the proposed tubes under oblique impact force. The deformation response of proposed aluminium tube structures was related with the conventional cylindrical (simple) tubes and the results revealed that aluminium capped cylindrical tubes absorbed more impact energy than the conventional cylindrical tubes. The overall outcomes exposed that the proposed aluminium capped cylindrical tubes are remarkable as energy absorbing structures in dissipating impact energy in the oblique direction.

Numerical investigation on the effect of wall thickness on quasistatic crushing properties of nylon honeycomb structure

Honeycomb structures are extensively used energy-absorbing structures in the airplane, spacecraft and automobile body parts. The critical parameters that influence the aggregate energy absorption are cell size, wall thickness and node length. However, wall thickness is a crucial determining factor for crushing and buckling. The type of failure manifested to the crushing of the cells can be predicted with unit cell buckling. The current work investigated on quasistatic crushing properties of honeycomb structure by varying unit cell wall thickness and at constant cell size of 10 mm. The out of plane quasistatic compression test of nylon honeycomb core of various wall thicknesses i.e 1, 1.1, 1.2, 1.3, 1.4 and 1.5 mm is carried out using ANSYS 14 simulation. The results obtained from the test are in close agreement with unit cell buckling analysis for predicting the mode of failure. The ultimate compressive strength of 1.5 mm cell is observed to be 1.4 folds higher than that of 1 mm cell. The energy absorption obtained from load-displacement graph during compression test indicates the proportional relationship between wall thickness and energy absorption. High energy absorption ability for 1.5 mm wall thickness core infers superior crushing strength enables to use as energy-absorbing devices, where lightweight and strength are the prime concern.

High rate damage of composite material for modelling of energy absorbing structures

This paper proposes an approach for the modeling of crushing behavior of absorbing structural components, made of fiber-reinforced composite material. The effect of strain rate dependency of material properties is in the focus of this research, thus proposed material model is based on introduction of damage parameters, and high rate behavior is expressed in terms of damage rate. Stress-strain response of typical carbon fiber-reinforced composite to a wide range of impact loading rates provides data for calibration of the proposed model. Abaqus explicit solver with implemented user material model is used for direct 3D finite element simulation of impact with tubular specimen. Impact initiation process is considered in details to explain initial peak appearance on load diagram not only caused by the tube chamfer failure with consequent transfer of crushing process to a regular tubular zone, but also as effect of strain-rate dependency. Simulation shows a good agreement with typical load-displacement curves and crashworthiness values.

Performance Evaluation of Dampers Under Dynamic Impact Based on Magnetic Field FE and CFD

It is necessary to install a damping energy absorbing structure for a certain type of naval gun test shell without projectile belt. Applicable high-performance dampers currently include viscoelastic colloidal damper and magnetorheological damper, and two kinds of special dampers for test shells have been designed and manufactured. In order to evaluate the mechanical properties of these two dampers under dynamic impact, a one-way coupling numerical method was proposed for simulation and analysis. Quasi-static experiments were used to verify the model based on magnetic field finite element (FE) and computational fluid dynamics (CFD). The model is also characterized by passive dynamic mesh and user-defined functions (UDF) based on C language. The results showed that the CFD models of both dampers were accurate. Though the colloidal damper is simpler in structure and lower in the cost, the MR damper has more significant damping and higher energy absorption ratio under impact. Compared with colloidal damper, MR damper is characterized by long working time, multiple vortices, chaotic streamlines and more uniform temperature distribution. When the power was continuously applied, the velocity of the impacted MR damper dropped to zero within 80ms, and the piston finally stopped at a stroke of 1.3mm. The colloidal damper reset within 8ms, and the reset velocity was 1.1m/s. In this study, the performance evaluation results of the two dampers were obtained, and the latest numerical methods for the mechanical performance analysis of colloidal dampers and MR dampers under dynamic impact were provided.

Finite element investigations on the effect of stiffeners in polygonal tubes under axial impact

Multi-cell tubular structures are gaining much interest in the crashworthiness field, owing to their extensive applications in automotive vehicles as lightweight energy-absorbing structures in collision events. The current paper examines the numerical simulation of axial impact loading of thin-walled aluminium multi cellular polygonal tube of different configurations. Nonlinear impact simulations were performed on multi cellular polygonal tubes using finite element ABAQUS/CAE explicit code to examine the influence of stiffeners. From the overall results obtained, the crashworthiness performance of the proposed multi cellular tubes of various configurations were compared. Moreover, square section multi-cellular tubes were retained as most prominent for higher specific energy absorption. This type of structures was found to be effective one to improve the crashworthiness performance during impact events.

Multi-objective optimization of crashworthiness of vehicle front longitudinal beam

Front longitudinal beam (FLB) is an important structure for the analysis of force transmission and energy absorption path in different crashing scenarios. In the present paper, the finite element (FE) model of a full-scale vehicle yun-100 Zotye is employed to explore the energy absorption of FLB, and aiming at its poor energy absorption problem, circular beam was used as the original topology optimization space of FLB. The advantages of both static and dynamic topology optimization methods are fully considered, and a variable density method is combined with a hybrid cellular automaton (HCA) method. The substructure dissipated energy and force for frontal crash in a full-scale vehicle are obtained at a speed of 13.8 m/s. The maximum stiffness in axial is obtained through the static topology optimization method and the maximum energy-absorbing structure of FLB which is satisfied with axial strength obtained through the dynamic topology optimization method. According to the results of topology optimization, a multi-cell thin-walled structure is interpreted as the novel FLB. A parametric study on geometric parameters is also performed to explore their effects on crashing characteristics of novel FLB, and it is found that they significantly influenced the crashworthiness of multi-cell thin-walled structure (especially the absorption of energy). Furthermore, in order to maximize the characteristics of novel FLB, a multi-objective optimization process is carried out using non-dominated sorting genetic algorithm (NSGA-II). The optimized FLB after multi-objective optimization is applied to Zotye of 100% vehicle frontal crash. The results showed that the peak value of acceleration decreased by 10.3% and the mass of the optimized FLB reduced to 0.59 kg. It indicated that the optimized FLB manifested excellent crashworthiness and better protective characteristics.

An improved plastically dilatant unified viscoplastic constitutive formulation for multiscale analysis of polymer matrix composites under high strain rate loading

Polymer matrix composites are commonly used to fabricate energy-absorbing structures expected to experience impact loading. As such, a detailed understanding of the dynamic response of the constituent materials is necessary. Since the rate, temperature, and pressure dependence of carbon fiber reinforced polymer matrix composites are primarily manifestations of the rate, temperature, and pressure dependence of the polymer matrix, it is crucial that the constitutive behavior of the matrix be accurately characterized. In this work, an existing unified viscoplastic constitutive formulation is extended to ensure thermodynamic consistency and to more accurately account for the tension-compression asymmetry observed in the response of polymeric materials. A new plastic potential function is proposed, and elementary loading conditions are utilized to determine relations between model constants to ensure nonnegative plastic dissipation, a necessary thermodynamic requirement. Expressions for plastic Poisson's ratios are derived and are bounded by enforcing nonnegative plastic dissipation. The model is calibrated against available experimental data from tests conducted over a range of strain rates, temperatures, and loading cases on a representative thermoset epoxy; good correlation between simulations and experimental data is obtained. Temperature rises due to the conversion of plastic work to heat are computed via the adiabatic heat energy equation. The viscoplastic polymer model is then used as a constitutive model in the generalized method of cells micromechanics framework to investigate the effects of matrix adiabatic heating on the high strain rate response of a unidirectional composite. The thermodynamic consistency of the model ensures plastic dissipation can only cause an increase in temperature. Simulation results indicate significant thermal softening due to the conversion of plastic work to heat in the composite for matrix dominated deformation modes.

Novel design of closed-cell foam structures for property enhancement

Cellular materials, such as foams, can be used as load bearing members in civil construction and as protective energy absorbing structures for personnel and equipment. In the present study, novel lightweight closed-cell structures were designed, and their mechanical properties and collapse mechanisms were investigated through a combination of experimental validation and finite element (FE) simulations. Selected porous structure designs were manufactured from acrylonitrile butadiene styrene (ABS) using additive manufacturing technology. These 3D printed structures were subjected to quasi-static loading to determine the dependence of their elastic and plastic responses from their topological features. Deformation mechanisms were elucidated through quasi-static compression experiments and FE modelling. The appropriate distribution of the base material in the designed closed-cell structures inherits the merits of uniform stress distribution and large deformations that lead to reaching high strengths and desirable energy absorption efficiencies. The effects of relative density and cell shape were studied in detail from elastic loading through the large plastic strain densification regions. The effects of cellular architecture on deformation mechanisms and energy absorption capabilities demonstrated the possibility of enhancing energy absorption efficiencies with appropriate design criteria. Based on the experimental and numerical analyses, the most efficient energy absorbing closed-cell structure was proposed.

Crashworthiness of Nomex® honeycomb-filled anti-climbing energy absorbing devices

To investigate the energy-absorption characteristics of thin-walled metals and Nomex® honeycomb composite structures, Nomex® honeycombs with five different specifications were applied to anti-climbing energy absorbing devices. Based on compression tests on Nomex® honeycombs, the equivalent numerical model for honeycombs was verified. A finite element model (FEM) for anti-climbing energy absorbing devices was established in Hypermesh. On this basis, the effects of parameters of different honeycombs on absorbed energy of energy-absorbing structure were analysed through LS-DYNA. The results showed that the energy absorption capacity of the anti-climbing energy absorbing devices mainly depended on honeycomb and thin-walled tubes. A Type-2 model exhibited the highest energy absorption capacity, at about 362 kJ, ACT1-3.2-144 honeycomb and thin-walled tubes absorbed energies of 198 and 149 kJ, respectively, which accounted for more than 95% of the total energy absorbed by the whole structure. The results also revealed that the corresponding average buffer force (484 kN) and the maximum peak buffer force (1226 kN) of the Type-2 model were also much greater than those of the other four structures. The buffer force of the Type-2 model remained within 300 to 1000 kN.

Significance of material constitutive model and forming parameters on the crashworthiness performance of capped cylindrical tubular structures

An accuracy of crushing performance indicators is critical to evaluate in finite element crushing simulations particularly for the press-formed capped tubular energy absorbing structures. It is essential to select the appropriate material constitutive model and to incorporate the forming parameters into the finite element crushing model as a vital input. Hence in the present article, the influence of various material constitutive models and forming (multi-stage deep drawing) parameters on the axial crashworthiness characteristics of thin-walled capped cylindrical tubes were investigated numerically. Both forming and crushing simulations were executed by nonlinear finite element LS-DYNA® code. The forming parameters such as thickness distribution, residual stress, and effective plastic strain were mapped to a finite element crushing model of the tube. The numerical predictions of the thickness distribution and final deformed profiles of the capped cylindrical tubes are correlated with the experiments. The results revealed that the forming parameters have a substantial effect on the crushing performance of the deep drawn capped cylindrical tubes. As a result of these analyses, the thickness and strain predictions strengthens the tube and significantly influenced the crushing performance indicators such as initial peak crushing force, mean crushing force, and the energy absorbing capacity.

Numerical and experimental studies on compressive behavior of Gyroid lattice cylindrical shells

In this paper, Gyroid lattice cylindrical shell (LCS) specimens were designed by a newly proposed mapping methodology and were fabricated by selective laser melting (SLM) technology. Their energy absorption and deformation modes were investigated through quasi-static compression tests. A finite element model (FEM) was proposed, which was validated by the experimental results, for a further study on the compressive behavior of the Gyroid LCS. Based on the numerical study, it was found that Gyroid LCS showed superior energy absorption to the hexagonal LCS and triangular LCS with the same density. In addition, a parametric study indicated that main energy absorption factors, namely total energy absorption, specific energy absorption and mean crushing load, were in power function relationship with the relative density. Finally, it was found that thickness gradient and geometric gradient had significant effects on the failure modes of Gyroid LCS under compression. The research in this paper is expected to provide some guidance for the design of energy absorption devices or structures.

Experimental verification and optimization research on the energy absorption abilities of beetle elytron plate crash boxes

To develop a new type of biomimetic sandwich plate crash box inspired by beetle elytra (referred to as the beetle elytron plate (BEP) crash box) with a better energy absorption capability, we conducted experimental verification and optimization research on two methods proposed in our previous studies: changing the amplitude (A) of the deformation leading line predicted by the finite element method and setting the trabeculae in the middle of the honeycomb walls. The following results were determined. (1) The method of increasing A to reduce the peak force of the BEP crash box is effective, whereas the latter method is invalid. (2) The latter method is invalid because the unit structure (the BEP crash box) is different from the multivariate structure (the BEP) used to determine the prediction due to the change of constraint condition on the trabeculae provided by the honeycomb walls. (3) An optimum A of 1.0 is proposed for BEP crash boxes with better energy absorption abilities and more stable successively laminated deformation. Specifically, the main peak force of the BEP crash box is approximately the same as that of the conventional one, while the structural energy absorption (SEA) and load uniformity (LU) of BEP crash boxes are at least 3 times and between only one-third and one-fourth those of conventional crash box, respectively, meaning that BEP crash boxes can be directly used to replace conventional one and to significantly improve security. Thus, these results provide an experimental basis for further research on BEP crash boxes.

Modelling of composite energy absorbing structures for automotive load-bearing systems

Due to the increasing demands for environmental friendliness and fuel economy of cars, the task of reducing their weight is becoming topical. One of the promising ways to solve this problem is the use of composite materials for the manufacture of automotive body. The body of the car is subjected not only to static and slowly changing dynamic loads, but also can be subjected to impact loading. Therefore, it is necessary to assess the effectiveness of the use of composite materials for the manufacture of elements responsible for energy absorption. The paper analyzes the features of energy absorption during the destruction of composite structures, describes the ongoing processes and gives recommendations on the design of composite front rails. To assess the effectiveness of the composite front rail, a simulation of process of its crushing is carried out. To confirm the performance of the design, a crash test of a car with a composite energy absorbing structure is simulated. The applicability and high efficiency of composite energy absorber are confirmed

Crashworthiness study on hybrid energy absorbers as vertical struts in civil aircraft fuselage designs

This research concerns the crashworthiness study and enhancement of commercial aircraft fuselage structures by incorporating crushable hybrid energy absorbers to work as vertical struts. To assess their contribution on a representative aircraft structure, a numerical simulation of a Boeing 737-200 drop test is developed and validated with experimental data available in the literature. The fuselage section is then simulated both with and without the fuel tank, showing more harmful effects for the latter scenario. The numerical model accurately captures the experiment’s collapse process with low artificial energy ratios. Later, four vertical hybrid energy absorbers designed for programmed and progressive collapse, are added in the cargo compartment, connecting the underfloor beams and the frames. Different designs and positions are studied, combining aluminum tubes with square and circular cross-sections, filled with a core made from a GFRP skeleton and foam extrusions. Acceleration graphs show a reduction in passenger injury levels from severe to moderate according to an Eiband diagram when energy absorbers are fitted. Energy trends from the hybrid absorbers are also monitored, with dissipation of up to 10 kJ of the fuselage’s kinetic energy through plastic deformation and collapse. Results also show a significant improvement on the global crashworthiness of the fuselage, leading to an increase in plastic dissipation by the frames from 76 kJ to 122 kJ and a reduction on the accelerations up to 50% when the energy-absorbing structures are added.

Experimental study of a honeycomb energy-absorbing device for high-speed trains

Aluminium honeycomb is a light weight, thin-walled material with a typical multi-cellular construction and a good strength-to-weight ratio. Therefore, aluminium honeycomb can be used as an energy-absorbing device for high-speed trains. Due to its large mass and high operating speed, a high-speed train can generate large impact energy. Thus, an energy-absorbing device with a greater energy absorption capability must be designed for high-speed trains. To reduce the aerodynamic drag, the cross-sectional area of a high-speed train is limited. Therefore, a honeycomb energy-absorbing device should be designed in such a way that it is longer than the traditional energy-absorbing devices; however, this may lead to bending, destruction and uncontrollable deformation of the honeycomb; these factors are not conducive for energy absorption. In this paper, a sleeve structure was designed for high-speed trains, and a crash experiment of the energy-absorbing structure showed that the bending and destruction of the honeycomb energy-absorbing device are effectively suppressed compared with the ordinary honeycomb energy-absorbing structure. Moreover, the fluctuation of the crash force was smaller and the crash force is more stable than the traditional thin-walled energy-absorbing structure. Therefore, the deformation instability problem of the ordinary honeycomb energy-absorbing structure and the crash force fluctuation problem of the traditional thin-walled energy-absorbing structure can be solved. Then, a crash experiment and simulation involving a high-speed train with improved honeycomb energy-absorbing device was carried out, and the results showed that the deformation of the end of the train body was stable and controllable, and the train body deceleration satisfied the collision standard EN15227.

On lateral compression of circular aluminum, CFRP and GFRP tubes

Thin-walled structures made of lightweight materials, e.g. aluminum, fiber reinforced composites, have been increasingly used as energy absorption structures in vehicles. This work aimed to characterize the lateral crushing behaviors of circular aluminum, glass fiber reinforced plastics (GFRP) and carbon fiber reinforced plastics (CFRP) tubes with different geometric configuration such as diameter-to-thickness (D/T) ratio or thickness. In the experimental investigation, four different D/T ratios varied from 10.78 to 48.02 were considered here for the aluminum, GFRP and CFRP tubes. Crushing behaviors such as force-displacement curves, deformation histories, and crushing force were quantified. The experimental results revealed that the load carrying capacities, energy absorption (EA) and specific energy absorption (SEA) of the circular tubes decline with increasing D/T ratio. It was found that better crashworthy characteristics of thicker composites, with a smaller D/T ratio, were due to the more favorable failure modes occurring throughout lateral compression. The lateral crashworthy performance of the GFRP tubes was marginally better than that of the CFRP counterparts. Due to ductile behavior of aluminum tubes and brittle behavior of composites, aluminum tubes showed much better lateral crashworthiness than that of the composite counterparts. Moreover, with the increase in the D/T ratio, aluminum tubes exhibited greater advantage on crashworthiness than the composite tubes. On the basis of the experimental data, explicit finite element analysis was further carried out for modeling the lateral crushing behavior of aluminum, GFRP and CFRP tubes. The numerical results were in good agreement with the experimental data, demonstrating the validity of these finite element (FE) models in predicting lateral crushing responses of aluminum, GFRP and CFRP tubes. The proposed FE models can be exploited to further study similar thin-walled metal and composite structures for design optimization.