Design Of Energy Absorber Research Articles

A novel design of thin-walled energy absorption structures with local surface nanocrystallization

A high-efficient energy absorption design in virtue of ultrasonic impact surface nanocrystallization treatment is proposed to enhance the crashworthiness of square thin-walled tubes. Due to significant improvement on mechanical characteristics within the treated areas, structural crashworthiness after surface nanocrystallization is significantly increased without the requirement of modifying configurations or mass. The results reveal that by optimizing local surface nanocrystallization layouts with a nanocrystallization area treatment ratio of approximately 50%, the specific energy absorption is enhanced by 64.29% as compared to the untreated tube. Experimental study validates that this technology is effective in the enhancement of the crashworthiness of square thin-walled tubes.

Design of porous and graded NiTi smart energy absorbers considering synthetic uncertainty in parameters

The synthetic uncertainty (SU) method is introduced and applied to the optimal design of energy absorbing NiTi shape memory alloy (SMA) bars. A sensitivity analysis for a large number of stochastic parameters identifies geometrical grading, porosity, and imposed maximum nominal stress as critical design parameters for the energy dissipation capacity of the bars. Parametric uncertainty on the optimal design of the energy absorber is incorporated and estimated through the SU formalism. The SU method provides a unified approach to discover the critical design parameters, quantify uncertainty, and optimally design a system around its extreme response (maximum or minimum). Therefore, the SU method is placed next to the robust design optimization (RDO) process, yet with a discovery component. It is found that variations in porosity and shape factor can significantly alter the stress-strain response and energy dissipation capacity. For a given value of maximum nominal stress, it is found that there exists an optimal combination of shape factor and porosity which maximizes the energy dissipation capacity of a tapered and porous NiTi bar.

Impact test and numerical simulation of typical sub-cargo fuselage section of civil aircraft

This paper deals with impact test and numerical investigations on the crashworthiness of the typical sub-cargo fuselage section of a civil aircraft. The sub-cargo fuselage section with three-frame and two-span is designed and manufactured, and the 3.95 m/s impact test is conducted to research the failure modes and impact response characteristics for the upside-down sub-cargo fuselage section. The impact process is simulated by using the LS-DYNA finite element code. The impact velocity, displacement, and acceleration response are compared, and a good agreement between test results and numerical simulation results is observed. The energy absorption characteristics and impact load transfer path are further studied based on the verified finite element model (FEM). The results show that the impact phases are characterized by the bending and twisting of fuselage frames, the bending of middle stanchions and C-channel stanchions, the pull-off failure and shear failure of rivets, and the two plastic hinges formed at the joints of C-channel stanchions and fuselage frames. The fuselage frames and middle stanchions are the main energy absorption components. The impact load is transmitted along with the fuselage frames, middle stanchions, and C-channel stanchions to the cargo cross beams, and the area of middle stanchions is the most important energy absorption design area.

On crashing behaviors of bio-inspired hybrid multi-cell Al/CFRP hierarchical tube under quasi-static loading: An experimental study

Bio-inspired structures have gained more and more concerns attributed to their unique enhancement in energy absorption capacity. This paper experimentally investigates the axial crushing behavior and energy absorption of a second-order hybrid multi-cell aluminum and CFRP (Al/CFRP) hierarchical tube under quasi-static loading. Five different configurations of the hierarchical tubes packing CFRP hollow tubes were designed. The quasi-static compression test was employed to investigate their crushing characteristics, axial collapse and energy absorption behaviors, and further compared with the Al hollow counterparts. The effects of different configurations involving the radial topology, the sub-tube number, the wall thickness, and the packing configuration were discussed in detail. The results reveal that the multi-cell tubes undergo a specific progressive folding collapse, and the energy absorption capability can be significantly improved for the hierarchical sections. The radial topology hardly affects the crashworthiness with the constant outer-tubular diameter and thickness. Additionally, both packing number and wall thickness conduce to improving the load-bearing capacities. By comparison with the specific multi-cell tube packing Al/CFRP sub-tubes, the hybrid tube packing net CFRP tubes own better crashworthiness and conduce to a wider range of applications in the design of automobile frames and energy absorbers.

Crashworthiness analysis of bionic thin-walled tubes inspired by the evolution laws of plant stems

Recently, bionic thin-walled structures have attracted widespread attention in automotive safety design because of their excellent crashworthiness behavior and weight efficiency. In this paper, inspired by the evolution laws and microstructure of plant stems, a group of bionic tubes with m parts and n layers (PmLnBTs) are proposed and investigated by theoretical prediction and numerical analysis. Theoretical models of PmLnBTs are developed to predict the specific energy absorption. Finite element model is conducted with LS-DYNA and validated by a quasi-static axial crushing experiment. The accuracy of the theoretical model is verified by numerical analysis, and the maximum relative error is less than 7%. Furthermore, parametric studies are conducted to investigate the effects of geometric parameters on the energy absorption capability of PmLnBTs. The results indicate that the PmLnBTs exhibit superior crashworthiness performance compared to traditional bi-tubular circle tubes. Moreover, when designing such a bionic energy absorber, it can effectively improve the crashworthiness performance by appropriately increasing the number of layers, reducing the outermost circle diameter or avoiding innermost circle diameter value too large or too small. The findings of this paper provide a guidance for the design of energy absorber with excellent energy absorption performance.

Modulation of multi-directional auxeticity in hybrid origami metamaterials

A novel origami metamaterial with programmable multi-directional auxeticity is proposed by hybridizing the concept of re-entrant honeycomb with the Miura pattern. Normal Miura-based origami metamaterials have been widely shown to exhibit negative in-plane Poisson's ratio. However, negative out-of-plane Poisson's ratio cannot be realized in these set of materials, essentially limiting their capability for prospective applications in many multi-functional devices and systems. Here we propose a hybrid Miura-based metamaterial that can show both in-plane and out-of-plane negative Poisson's ratios. More interestingly, we are able to program the Poisson's ratios to have mild to extreme auxeticity and map their mutual interaction as a function of the microstructural configuration. Besides the single-layer meta-sheets, we have shown that a class of multi-layer stacked metamaterial with uniform and graded configurations can be developed to achieve multi-objective functional goals. Theoretical and experimental analyses are combined in this paper to demonstrate the concepts of modulating multi-directional Poisson's ratios. The fundamental mechanics of the proposed origami based metamaterial being scale-independent, this novel class of deployable hybrid materials can be directly transferred for application in a range of milli-, micro-, and nanometer-size systems, essentially opening avenues for the design of energy absorbers, sensors, actuators, medical stents, catalysis, drug delivery systems, adaptive wings for next-generation of aircrafts and other deployable mechanical and electronic systems at multiple length-scales.

Dual damage criteria in a crash stop

This study proposes a method to apply dual criteria for the assessment of product damage based on the deceleration signal in a crash-stop incident. To evaluate the shock effects, a procedure is proposed to decompose the original crash signal into two components, i.e. an equivalent crash signal and a residual shock signal. The characteristics of crash signals are analysed in both time and frequency domains. It is found that the equivalent crash signal can represent the original crash signal if the dominant frequency (fn) of the product structure is relatively lower than the effective frequency (fs) of the crash signal, i.e. fnfs≤15. Otherwise, the original crash signal should be used in the assessment of product damage if fnfs>15. The dual damage criteria method is proposed by combing the maximum-acceleration vs. velocity-change (Amax-ΔV) diagram and shock response spectrum (SRS), i.e. the former can offer a lower bound of damage boundary on Amax-ΔV diagram while the latter can define an upper bound of damage boundary on SRS graph. The method of dual damage criteria is illustrated numerically using two types of cantilever beams, as an example. The proposed method can be applied with the critical SRS (Sc) method recommended in ASTM D3332-99 for the packaging design and test, and may also be considered in the design and test of other impact energy and shock absorbers in a crash-stop incident.

Effect of Extra Gas Amount on Liquid Outflow from Hydrophobic Nanochannels: Enhanced Liquid-Gas Interaction and Bubble Nucleation.

Understanding liquid motion in nanoenvironment is of fundamental importance in nanofluidics-based systems. While the liquid outflow from hydrophobic nanochannels can significantly affect system performance, its underlying mechanism remains unclear so far. Here, we present an experimental study of the gas-phase effect on liquid outflow behavior from hydrophobic nanochannels in a liquid nanofoam (LN) system. Four LN samples, consisting of same liquid-solid composition but different amounts of the gas phase, are characterized by cyclic quasi-static compression tests. A remarkable difference in the LN system reusability has been observed, indicating that the liquid outflow behavior is highly sensitive to the amount of the gas phase. As the gas amount increases, the degree of liquid outflow from hydrophobic nanochannels is considerably promoted. This promotive effect is because of the suppression of gas outflow and acceleration of bubble nucleation in the nanochannels. These fundamental findings open a new perspective on liquid outflow behavior and can facilitate the design of reusable nanofluidics-based energy absorbers.

Optimization of Foam-Filled Square Thin-Walled Aluminium Structures

Crash box are the structural part designed to absorb energy during crash and minimize the injury to passengers. Various design of energy absorbers has been introduced to unleash design with the best crashworthiness behavior. Foam-filled structures are one of the promising designs. In this study, foam-filled structure was investigated to increase the energy absorption capability and reduce the initial peak force simultaneously. Since most foam-filled structures tend to absorb more energy with high peak force, optimization of the energy absorbers is significant in obtaining the optimum design. Response surface methodology (RSM) has been dominant technique in crashworthiness optimization mainly because of it provides efficient and accurate solution. This paper focused on the optimization foam-filled columns with respect to thickness of the tube and length of foam to enhance energy absorptions and reduce initial peak force. The optimization results suggested by Design Expert software for impact test is 515.9 J for EA and 134.94kN for IPF value with the column thickness of 2.0mm and foam length of 185mm. For quasi-static test, the optimum solution value for EA and IPF are 864.5J and 88.33kN respectively with column thickness of 1.87mm and foam length of 200mm.

Design and evaluation of a shunted flexible piezoelectric damper for vibration control of cable structures

In this work a shunted flexible piezoelectric damping system is designed and numerically evaluated for the purpose of vibration attenuation of large deployable space cable structures. We propose a design of a tube-shaped flexible piezoelectric energy absorber consisting of multilayered PVDF sectors, which could be shunted with two types of passive electric circuits, i.e. the series resistance-inductance (LR) shunt and the series resistance-negative capacitance (NC-R) shunt. The compatible stiffness of the PVDF tube ensures an effective transformation of deformation from the vibrating cable to the energy absorber. For best performance we carried out optimization on the geometric parameters of the PVDF tube. By analysis we found that the optimal thickness of the PVDF tube is roughly 0.4 times of the inner tube radius. We optimized the shunt circuits and selected the appropriate distribution position of the damper in the flexible cable structures. The performance of the design was numerically evaluated based on three problems, namely the longitudinal vibration of a single-cable structure, the transverse vibration of a single-cable structure and the vibration of a cross-cable structure. Based on the results, we confirm the remarkable performance of the design. Being highly frequency dependent, the design with the LR shunt only works for one deformation mode at a time, e.g. bending or stretching. In contrast, the design with the NC-R shunt works for both modes as it has a much wider frequency band. The design with the LR shunt has better performance than the NC-R shunt when dealing with the stretching deformation mode only. For vibration with combined stretching and bending, however, the performance of both designs is equally good. This is because the NC-R shunt can work for both deformation modes simultaneously, and hence it shows great adaptability and application potential in vibration control of complex flexible space structures.

Influence of plain end-cap on the energy absorption characteristics of cylindrical tubular structures for lateral impact vehicle collisions

Thin-walled cylindrical tubes have been renowned as an ideal energy absorber in aerospace and automotive industries for their lightweight potential and extraordinary energy absorbing capability. In this research article, systematic investigations on the specific energy absorption characteristics and lateral crushing behaviour of deep drawn non-capped and plain end-capped cylindrical tubular structures were performed. Initially, finite element models were developed with ABAQUS/CAE® code to predict the deformation characteristics of the proposed tubes under quasi-static lateral compression. Subsequently, detailed experimental studies on the aluminium cylindrical tubes of various thickness (1.63 mm, 2.04 mm and 3.25 mm) under lateral quasi-static loading have been performed and the lateral crushing force-deformation histories obtained were analyzed. The lateral deformation response of the proposed tubes under impact lateral loading has been studied further and analyzed with the validated finite element model. Also, the impact crushing performance of the plain end-capped cylindrical tubes was related to the non-capped cylindrical tubes and within tested samples, the plain end-capped tubes absorbed 0.8–1.6 times more specific energy than the conventional non-capped cylindrical tubes. Finally, it was found that the plain end-capped tubular structures exhibit desirable force–deformation characteristics such as uniform crushing force with a long crush stroke and maximum energy which is very important in the design of energy absorbers for transverse direction.

In-plane crushing behavior and energy absorption design of composite honeycombs

Theoretical analysis and numerical simulation methods were used to study the in-plane crushing behavior of single-cell structures and regular and composite honeycombs. Square, hexagonal, and circular honeycombs were selected as honeycomb layers to establish composite honeycomb models in the form of composite structures and realize the complementary advantages of honeycombs with type I and type II structures. The effects of honeycomb layer arrangement, plastic collapse strength, relative density, and crushing velocity on the deformation mode, plateau stress, load uniformity, and energy absorption performance of the composite honeycombs were mainly considered. A semi-empirical formula for plateau stress and energy absorption rate per unit mass for the composite honeycombs was developed. The results showed that the arrangement mode of honeycomb layers is an important factor that affects their mechanical properties. Appropriately selecting the arrangement of honeycomb layers and the proportion of honeycomb layers with different structures in a composite honeycomb can effectively improve its load uniformity and control the magnitude of plateau stress and energy absorption capacity.

Porous Refractory Ceramics as a Protective Material in Explosive Loading of Metal Container

In this work, we tested experimentally refractory porous aluminosilicate ceramic materials as protective energy-absorbing design elements of naturalistic large-scale layouts of explosion-proof thin-walled metal containers. We showed that lightweight refractory porous aluminosilicate materials can be effectively used for an efficient (two or more times) increase in explosion-proof characteristics of the containers simultaneously with minimization of their mass and dimensions. These materials significantly reduce the impact of a shock wave and other damaging factors of explosives and explosive devices on the metal shell of the containers. We developed full-size models of explosion-proof containers with a diameter of 1.2 m that are capable of withstanding an explosion of explosive charge (TNT) with a weight of not less than 3.5 kg without being beyond the range of elastic deformation of the metal shell. The obtained results allow designing similar explosion-proof containers in a wide mass-scale range with predetermined explosion-proof characteristics without costly research and development. Solid refractory porous materials are promising for the development of nonstationary transported explosion-proof containers for the storage, transportation, and destruction of explosive materials and devices, since their application makes it possible to reduce the material consumption, weight, and dimensions of containers.

Principle, design and validation of a power-generated magnetorheological energy absorber with velocity self-sensing capability

Based on the structural design concept of ‘functional integration’, this paper proposes the principle of a power-generated magnetorheological energy absorber with velocity self-sensing capability (PGMREA), which realizes the integration of controllable damping mechanism and mechanical energy-electrical energy conversion mechanism in structure profile and multiple functions in function profile, including controllable damping, power generation and velocity self-sensing. The controllable damping mechanism consists of an annular gap and a ball screw. The annular gap fulfilled with MR fluid that operates in pure shear mode under controllable electromagnetic field. The rotational damping torque generated from the controllable damping mechanism is translated to a linear damping force via the ball screw. The mechanical energy-electrical energy conversion mechanism is realized by the ball screw and a generator composed of a permanent magnet rotor and a generator stator. The ball screw based mechanical energy-electrical energy conversion mechanism converts the mechanical energy of excitations to electrical energy for storage or directly to power the controllable damping mechanism of the PGMREA. The velocity self-sensing capability of the PGMREA is achieved via signal processing using the mechanical energy-electrical energy conversion information. Based on the principle of the proposed PGMREA, the mathematical model of the PGMREA is established, including the damping force, generated power and self-sensing velocity. The electromagnetic circuit of the PGMREA is simulated and verified via a finite element analysis software ANSYS. The developed PGMREA prototype is experimentally tested on a servo-hydraulic testing system. The model-based predicted results and the experimental results are compared and analyzed.

Energy absorption design study of subway vehicles based on a scaled equivalent model test

To obtain the characteristics of collision energy absorption and improve the passive safety of subway vehicles, the energy absorption design of subway vehicles was studied based on a one-seventh-scale model crash test. A full-size three-dimensional model of a subway vehicle was established using the multibody dynamics software MADYMO. The simulation results of the dynamics model were scaled down according to the similarity coefficients. By comparing the simulation results with the scaled model test results, the maximum error of deformation was 2.10 and 4.35% for the head car and the maximum deforming middle car, respectively, and the energy absorption error was found to be 8.75 and 5.70% for the head car and the maximum deforming middle car, respectively. The results indicate that the collision dynamics model of subway vehicles is relatively accurate. Next, based on this dynamics model, a full factorial experiment was designed to study the effects of the marshalling, mass and crushing tube’s plastic deformation platform force on the energy absorption of subway vehicles. The calculation results were fitted by multiple linear regression functions. Finally, the authors obtained the crash energy absorption formulas for the subway head car with an accuracy of 98.42% and for the maximum deforming middle car with an accuracy of 95.31%. These formulas can be applied to the preliminary design of subway vehicles and offer guiding significance for the parameter design of subway vehicles’ energy-absorbing devices.

Design, analysis, and assessment of energy absorbers

Design, analysis, and assessment of energy absorbers

A concept of smart multiaxial impact damper made of vacuum packed particles

The conceptual design of smart crash energy absorber made of Vacuum Packed Particles (VPP) is presented in this work. This structure is composed of granular material inside a plastomer sleeve. The absorber can change the flexural stiffness and as a result the amount of dissipated energy depending on the impact conditions. The special properties of the granular structure create the possibility of various applications as different working modes can be used. When the pressure inside is equal or higher than atmospheric pressure the system behaves similarly to a liquid, otherwise it has properties similar to viscoplastic solid. The physical properties of the structure may be rapidly changed by adjusting the pressure inside the system. Due to these properties Vacuum Packed Particles is considered to be a smart material.

Solving the mystery of China’s thousand-year-old wooden pagoda

The world’s oldest wooden pagoda was built with no nails nearly 1000 years ago in Yingxian, China. During the past ten centuries the 67 m tall building has survived countless earthquakes, thunderstorms and wars. To understand its remarkable structural resilience and durability, a comprehensive analysis has been carried out. This paper describes the particular features of the building, including the extensive use of strong but flexible, multi-layered ‘dougong’ brackets, semi-rigid timber joints and the lack of a structural connection to the foundation. These characteristics are then analysed to determine how they function under extreme loading. A combination of energy-absorbing design, good drainage, sound foundations and woodworm-eating swallows appears to explain its extraordinary longevity.

Development of high-performance energy absorption component based on the structural design and nanocrystallization

Over the past decades, to meet the ever-increasing energy-saving and environmental-friendly needs, light-weight vehicles, e.g., electric cars, have been widely advocated. Due to significant deterioration in the capability of energy dissipation, crashworthiness enhancement becomes again the most critical issue for the light-weighted vehicles. However, the design based on conventional structure has been more difficult, and the employment of high-strength materials induces much higher cost. To achieve both large safety margin and low cost, this study implemented both material enhancement and structure optimization in the energy absorber design. Since most light-weight structures involve thin-walled frames, the surface mechanical attrition treatment (SMAT), able to induce nanostructures in metals for strength enhancement without sacrificing ductility, is the perfect choice. Based on the structure of energy absorber, SMAT technology was intensively improved to take full advantage of the excellent performance of the advanced steel material and fulfill real-life application. Structure optimization was also explored through extensive experiments and numerical simulations. The final products was examined by real tests, and the results revealed that it was lighter, stronger and have high-safety impact levels compared to similar products on the present market as expected.

Effects of weld damage on the dynamics of energy-absorbing lanyards

Manufacturers recommend removing fall protection system components from service for any indication of weld spatter or tool damage; however, little is known about the specific effects of lanyard damage on fall arrest dynamics. Thirty-two energy-absorbing lanyards were drop tested after being damaged with weld spatter, plasma torches and cutting tools and compared with new, undamaged lanyards. Two lanyards damaged with a plasma torch failed completely without deploying the energy absorber while weld spatter damage and tool cuts, up to two-thirds through the width of the webbing, had no effect on fall arrest dynamics. The results highlight the catastrophic implications of high-temperature damage to lanyard webbing resulting from plasma torches – which require immediate removal from service. In addition, the integrated energy absorber design in bungee-style lanyards makes them more susceptible to damage anywhere along the length. We therefore recommended against bungee lanyards for ironworkers and welders.