Impact Absorber Research Articles

Mechanical and Thermal Properties of Aged Helmet Outer Shells Made of Acrylonitrile-Butadiene-Styrene

Acrylonitrile-butadiene-styrene (ABS) material is widely used as a protective rigid shell and impact absorber in bike helmets, providing vital protection against head injuries under specific working conditions. However, ABS aging in helmets could affect the safety factor of helmets and shorten the service life. Exploring the transformation during aging process for real assembled helmets made of ABS out shells is crucial for the investigation and fabrication of high performance helmets. Herein, the effect of long-term aging on the physical properties of practical helmets made of ABS outer shells has been discussed systematically. Four different types of helmets were subjected to different aging conditions, i.e., outdoor environment, ultraviolet exposure, hot air, and humid-heat conditions. The impact property and stiffness tests were carried out as a function of aging time and aging conditions. The measured helmets were capable of meeting engineering tolerances when aged under outdoor, ultraviolet, and hot air conditions, and could deliver competitive mechanical performance to their pristine helmets. Yet, after aging under humid-heat for 800 h, the helmets showed an obvious decrease in impact strength, gloss, and stiffness. The influence of different aging conditions was further investigated by thermal and spectral characterizations. The study might provide some valuable advice for helmet performance evaluation.

On the broadband efficacy of impact absorbers

An impact absorber is a small, typically spherical, device placed freely into a cavity of the structure whose vibrations are to be mitigated. The device is particularly effective when it synchronizes with a target mode. The resulting strong impacts induce dissipation in the contact region and/or scattering of energy to high-frequency modes (and dissipation outside the contact region). As the synchronization can in principle take place at an arbitrary target frequency, impact absorbers are commonly claimed to have broadband efficacy. The present work reveals that this capacity is surprisingly limited. A taut string is considered under random excitation with a Gaussian-bell-curve-type power spectral density. It is shown that the fundamental mode dominates the displacement response even when the half power bandwidth spans only modes 29 to 37. Consequently, the absorber tends to synchronize with the fundamental mode, and energy is distributed to higher-frequency modes, reducing the displacement (root-mean-square) level. Even when the spectrum is cut off outside this bandwidth, or one of the high-order modes is subjected to harmonic near-resonant forcing, the fundamental mode is still prominent in the displacement response. In those cases, the reduction of the displacement level is marginal. Perhaps more critically, the energy transfer to high frequencies has a detrimental effect on the stress level, and the impacts cause sudden stress spikes, typically exceeding the linear limit cases (no/fixed absorber). Interestingly, the non-synchronized and less regular response typical for larger clearances is observed to trigger significant high-to-low energy transfer, which can have a beneficial effect on the stress level.

Impact Buffering Characteristics of One-Dimensional Elastic-Plastic Composite Granular Chain.

Considering the elastic-plastic deformation, the wave propagations and energy transmissions of the one-dimensional three-segment composite granular chain are studied. The axial symmetry model for elastic-perfectly plastic materials is built by using the finite element method. Six materials with different yield strengths are selected for the adjustable segment. The results show that the repeated loading and unloading behaviors, as well as the wave propagations in the elastic-plastic granular chain, are complex and significantly different from those in the purely elastic granular chain. The yield strength of the granular materials in the adjustable segment has significant effects on energy dissipation and wave velocity, which could be used to design the impact buffer. The studies show that taking lower yield strength for the adjustable part than the non-adjustable part, the energy dissipation could be increased, and the wave velocity could be reduced, then the arrival time of the impact waves could be delayed. These characteristics of the elastic-plastic granular chain could be used to design metamaterials for impact absorbers in impact protection.

Characterization of magnetorheological fluids based on capillary magneto-rheometer

Magnetorheological fluids (MRFs) are a class of smart magnetic controlled materials whose rheological properties can be controlled by a magnetic field. These materials have advantages of short response time, high dynamic range and low energy consumption. Due to their excellent properties, MRFs have a widely application potential in the field of impact mitigation. As the shear rate dependent viscosity of MRFs is astonishing for the shear thinning effect, thus it is crucial to study the rheological properties cross a wide range of shear rates for guiding the design and application of MRFs based adaptive impact absorbers. Commercial rotational rheometers are usually used to test the rheological properties of MRFs, but their range of measuring shear rates are limited. Commercial capillary rheometers are designed to measure the rheological behavior over a wide range of shear rates, but they’re usually lack of ability to measure with magnetic field. In order to study the rheological properties of MRFs under higher shear rate and applied magnetic field, a lab-made speed-controlled capillary magneto-rheometer is developed in the presnt work; The expressions for equivalent shear rate and apparent viscosity of MRFs under the dimensional constraint of the set-up are derived. In addition, the theoretical expression of shear rate of MRFs is modified by Rabinowitsch correction. Then, the rheological properties of three particle volume fractions (10%, 15%, and 20%)of MRFs with different magnetic field strengths (6 mT, 13 mT, 20 mT, and 25 mT)are tested and analyzed, and the rheological characteristic curves of MRFs with shear rate range of 101s−1–105s−1 are obtained with the normalized characterization using Mason number. According to the experimental results, the MRFs show an obvious shear thinning phenomenon as shear rate increases, and in the Mason number based normalized characterization, the curves of different particle volume fractions are collapse to a master curve.

An investigation of the effect of structural parameters on the impact properties of sandwich-structured shock absorbers

The purpose of this study is to develop an impact absorber with a core made of sustainable textile waste as an alternative to the conventional honeycomb structure. In this case, the core structure is made of cotton fiber webs recycled from denim waste, and the outer shell is made of polypropylene plates reinforced with carbon, jute, and E-glass woven fabrics. Production of the sandwich structure is carried out using the hot press method. In addition to the fabric types and layer sequences utilized in the outer shell, the geometry of the core structure is altered, and their effect on the drop-weight impact resistance is examined. The prominent results emphasize that the use of high-performance fabrics in the outer shell facing the outer surface increases the impact resistance, and the sizes of the holes to be obtained in the core structure should be optimized in order to be effective in energy absorption. The results reveal that these developed sandwich structures can constitute a promising alternative for the automotive industry.

Kinetic Walking Energy Harvester Design for a Wearable Bowden Cable-Actuated Exoskeleton Robot.

Over the past few decades, wearable exoskeletons of various forms have been developed to assist human activities or for rehabilitation of movement disorders. However, sustainable exoskeletons with efficient energy harvesting devices still have not been fully explored. In this paper, we propose the design of a lightweight wearable Bowden-cable-actuated soft exoskeleton robot with energy harvesting capability. Unlike previous wearable exoskeletons, the presented exoskeleton uses an electromagnetic generator to both harvest biomechanical energy and to output mechanical torque by controlling an operation mode relay switch based on a human’s gait. Moreover, the energy-harvesting module also acts as a knee impact absorber for the human, where the effective damping level can be modulated in a controlled manner. The harvested energy is regulated and stored in super capacitors for powering wireless sensory devices when needed. The experimental results show an average of a 7.91% reduction in thigh muscle activity, with a maximum of 3.2 W of electric power being generated during movement downstairs. The proposed design offers important prospects for the realization of lightweight wearable exoskeletons with improved efficiency and long-term sustainability.

Axial crushing of auxetics tube manufactured by 3D printing of poliamide reinforced with short carbon fibre

Additive manufacturing, and more specifically FFF (Fused Filament Fabrication), makes it possible to manufacture complex designs that are difficult to manufacture using conventional processes that improve the mechanical behaviour of the component. In the present work, the axial impact behaviour of cylindrical tubes with a reentrant auxetic structure has been characterized. The material used is a polyamide 6 reinforced with short carbon fibre. As a reference, a solid thickness tube with the same outer diameter and mass as the tube with the auxentic structure has been designed. The main result is that the auxetic structure not only improves the specific absorption capacity, but also allows a progressive collapse thanks to the design and location of fault initiators. For this reason, 3D printing technologies have very attractive properties for the design of impact absorbers in the transport sector.

Predictive design of impact absorbers for mitigating resonances of flexible structures using a semi-analytical approach

Analytical conditions are available for the optimum design of impact absorbers (or Vibro-Impact Nonlinear Energy Sinks) for the special case where the host structure is well described as a rigid body. Accordingly, the analysis relies on the assumption that the impacts cause immediate dissipation in the contact region, which is modeled in terms of a coefficient of restitution (Newton’s impact law) that is assumed to be known and fixed. When a flexible host structure is considered instead, the impact absorber not only dissipates energy at the time instances of impact, but, and perhaps more importantly, it inflicts nonlinear energy scattering between structural modes. Hence, it is crucial to account for such nonlinear energy transfers yielding energy redistribution within the modal space of the structure. In the present work, we develop a design approach for flexible host structures. We consider the case of a forced excitation near primary resonance with a well-separated mode. We demonstrate that the time scales of the impact and the resonant vibration can be decoupled. On the long time scale, the dynamics of the host structure can be properly reduced to the fundamental harmonic of the resonant mode. A light impact absorber responds to this enforced motion, and we show that the conventional Slow Invariant Manifold of the dynamics is recovered for the commonly considered regime of two symmetric impacts per period. On the short time scale of the impact dynamics, the contact mechanics and elasto-dynamics must be finely resolved. We show that it is sufficient to run a numerical simulation of a single impact event with representative pre-impact velocity. From this short-time simulation, we derive an effective modal coefficient of restitution and the properties of the contact force pulse, needed to approximate the behavior on the long time scale. We derive a closed-form expression of the periodic resonant response and establish that the design problem can be reduced to four dimensionless parameters. We demonstrate the approach for the numerical example of a cantilevered beam with a spherical impact absorber. We conclude that the proposed semi-analytical procedure enables deep qualitative understanding of the problem and, at the same time, yields a quantitatively accurate prediction of the optimum design.

Application of an inventive problem solving approach for developing new generation vehicle crash boxes

Abstract In frontal crashes, the most important parts that absorb the kinetic energy of the vehicle by plastic deformation are impact absorbers. Efforts are underway to develop innovative impact absorbers to keep the impact of the accident on drivers and passengers to a minimum. The TRIZ (theory of inventive problem solving) approach was used in the product development process of an impact absorber. TRIZ is a creative and systematic problem-solving method that can be used for the development of the next generation of products and systems. TRIZ tools such as ideality, technical contradictions formulation, inventive principles, s-field analysis, and scientific effects were used to achieve ideal final results (IFR). The solutions obtained are evaluated in terms of applicability/ manufacturing, cost, lightweight and patentability. This study generated a new standardized solution in Turkey.

Simulation of the behavior of lattice structured impact absorbers manufactured by additive manufacturing

Thin-walled tubes are widely used as impact absorbers in transportation structures, due to their high efficiency in absorbing longitudinal impact loads. This study focuses on the investigation of the effect of squared lattice infill in the crashworthiness efficiency of thin-walled aluminum tube. The tube and infill were modeled as an additively manufactured integrated part. Impact analysis was performed using finite element method (FEM), considering empty and filled tubes with different combinations of thicknesses for tube walls and lattice structure. The inclusion of lattice infill changed the crashworthiness efficiency of the energy absorber. Filled tubes presented increased energy absorption and higher values of peak and mean force levels. Tube crushing mode and crushing efficiency were also affected by infill configuration.

High-rate nanofluidic energy absorption in porous zeolitic frameworks.

Optimal mechanical impact absorbers are reusable and exhibit high specific energy absorption. The forced intrusion of liquid water in hydrophobic nanoporous materials, such as zeolitic imidazolate frameworks (ZIFs), presents an attractive pathway to engineer such systems. However, to harness their full potential, it is crucial to understand the underlying water intrusion and extrusion mechanisms under realistic, high-rate deformation conditions. Here, we report a critical increase of the energy absorption capacity of confined water-ZIF systems at elevated strain rates. Starting from ZIF-8 as proof-of-concept, we demonstrate that this attractive rate dependence is generally applicable to cage-type ZIFs but disappears for channel-containing zeolites. Molecular simulations reveal that this phenomenon originates from the intrinsic nanosecond timescale needed for critical-sized water clusters to nucleate inside the nanocages, expediting water transport through the framework. Harnessing this fundamental understanding, design rules are formulated to construct effective, tailorable and reusable impact energy absorbers for challenging new applications.

Armadillo modelled foldable motorcycle helmet: A preliminary design concept for rider in Indonesia

Safety is an important thing while riding a bicycle or motorcycle. Using a helmet is one of the solutions to increase safety of the rider, but sometimes people are too lazy to bring the helmet because of its big size. In the present work, a foldable helmet adopting the Armadillo concept was proposed to make people feel more comfortable in carrying the helmet. The design also follows the safety standard required by the SNI (Indonesia National Standard). A locking system for the folding mechanism is discussed, and a honeycomb foam for impact absorber is considered in the design. As a result, the proposed foldable helmet can have a reduction volume of 23.75% compared with the non-foldable one. This work is expected to contribute to the innovative engineering design field.

Development of Carbon Fiber Composite Impact Absorber with Integrated Hydraulic Damper

Development of Carbon Fiber Composite Impact Absorber with Integrated Hydraulic Damper

MODELLING THE PROCESS OF DAMPING LONGITUDINAL LOADS IN TRANSPORT SYSTEMS USING ROLLER IMPACT ABSORBERS

Background. In this work, for a defect-free transportation of large-sized structures by rail, a new damping system for longitudinal dynamic loads is proposed. Its operation is based on the use of roller impact absorbers. The relevance of this work is explained by significant volumes of damaged and destroyed structures at the transportation stage.Objective. The goal is to develop a mathematical model of the process of damping longitudinal loads in a transport system with roller impact absorbers. The paper considers an extreme version of the dynamic loading of a transport system in the process of its collision with a railway stopper car.Methods. Based on the Appel formalism for non-holonomic systems, kinematic and dynamic equations of motion of the transport system are formulated that describe the process of damping longitudinal loads. The obtained equations were numerically integrated using the developed program. Using it, a series of numerical experiments was carried out with varying parameters of the transport system. Results. The main regulatory parameters of roller impact absorbers, which significantly affect the quality of their functioning, are determined. The laws of their influence on the dynamic state of transported goods are established. A quantitative assessment of the effectiveness of the use of roller impact absorbers to reduce dynamic loads on transported structures.Conclusions.It has been established that dynamic loads on transported goods can be reduced by more than 14 times compared with the existing traditional schemes and methods of securing structures. The main conclusion is made: in order to significantly reduce the level of longitudinal transport loads on the transported goods, their fixation relative to the wagons should be carried out in a “movable-adjustable” way (in contrast to the traditional “hard” method).

THE INFLUENCE OF THE STIFFNESS OF THE ELEMENTS OF RAIL DAMPING ON THE PARAMETERS OF THE MULTI-MASS WAGON–TRACK VIBRATORY SYSTEM

The task of achieving the increase in the weight and velocity of trains being core objective for most railways is inherently associated with solving problems of improving the dynamic qualities of wagons and locomotives during their interaction with the upper structure of the railway track. The strength and stability of rolling stock against derailment in various climatic zones should be ensured together with minimizing operating costs.Analysis of the reliability and performance of the wagon–track system can be conducted based on multivariate dynamic calculations of mathematical models and through experimental studies of dynamic vibrations. Currently, the issues of the influence of changes in the elastic-hysteresis properties of various impact absorber materials under the action of temperature factors on the elements of a multi-mass vibratory system remain insufficiently studied. The purpose of the research described in the article was to analyze the dynamic processes taking place in a multi-mass wagon–track vibratory system under the influence of changes in stiffness and internal friction coefficients of a damping rail component depending on a type of structural material and ambient temperature.The research resulted in elaborating model of multi-mass vibratory wagon–track system. Multivariate model calculations were carried out regarding various stiffness and internal friction parameters of damping elements situated under the rail; the parameters being selected from experimentally constructed dynamic hysteresis. The work presents results of calculations of the reaction forces and deviations in the elements of the vibratory system depending on temperature, type of material, thickness and design of damping elements.

Impact and particle vibration absorbers optimal design

Impact and particle vibration absorbers optimal design

Design of and Research of Impact Absorber Based on Synthetic Material

This paper carries out the design and research work of related testing equipment, and successfully develop a vertical deformation measuring instrument based on the surface layer of synthetic material. The design principle is that simulates the human body by dropping a weight of a certain mass from a prescribed height according to the law of conservation of energy movement process. In the whole process, the potential energy of the object has converted into kinetic energy, and the test piece forms an impact. The energy data absorbed by the test sample is collected by the impact sensor, and the sensor is sampled at a high frequency using a high-speed data collector and divided into its transmission to the computer system. Then the computer system records, analyses, processes, and calculates the collected data in real time, and displays the pressure change curve of the entire impact process, and finally calculates the impact absorption value of the tested surface during the entire process.

A multi-objective optimization of energy absorption properties of thin-walled circular tube with combined bar extrusion under quasi-static axial loading: Experiments and numerical simulation

Thin-walled tubes are one of the most popular impact absorbers. Recently, some methods have been proposed to improve crush performance parameters of the thin-walled tube such as filling by foam, modifying geometry etc. Each method has its advantages and disadvantages. It is still a challenge for crashworthy designers to design an efficient energy-absorbing system which has all the necessary requirements. Therefore, the present paper aims to introduce a new design technique which is a combination of bar extrusion and thin-walled circular tube. The crushing behavior of the new proposed energy absorber was studied both experimentally and numerically. Finite element models were developed to estimate the force-displacement curve and the folding shapes of the tube. The numerically predicted load-displacement curve and the calculated crush performance parameters were verified using experimental measurements. Moreover, a parametric study was performed to investigate the effects of different parameters on the proposed energy absorber response. According to the results, the percentage increases in energy absorption (Ea) capacity and specific energy absorption (SEA) for the proposed energy absorber were 39.02% and 14.37% respectively compared to the thin-walled tube. In order to determine the optimized geometric parameters of the proposed energy absorber, a multi-objective optimization technique was implemented. Based on the response surface methodology (RSM), Ea and SEA increased 245.5% and 246.3% for the optimum proposed energy absorber. The predictive models for Ea and SEA were obtained by polynomial equations.

Dynamic Mechanical Compression Impulse of Lithium-Ion Pouch Cells

Strain rate sensitivity has been widely recognized as a significant feature of the dynamic mechanical properties of lithium-ion cells, which are important for their accurate representation in automotive crash simulations. This research sought to improve the precision with which dynamic mechanical properties can be determined from drop tower impact testing through the use of a diaphragm to minimize transient shock loads and to constrain off-axis motion of the indenter, specialized impact absorbers to reduce noise, and observation of displacement with a high speed camera. Inert pouch cells showed strain rate sensitivity in an increased stiffness during impact tests that was consistent with the poromechanical interaction of the porous structure of the jellyroll with the liquid electrolyte. The impact behaviour of the inert pouch cells was similar to that of an Expanded Polypropylene foam (EPP), with the exception that the inert pouch cells did not show hysteretic recovery under the weight of the indenter. This suggests that the dynamic mechanical behaviour of the inert pouch cells is analogous to a highly damped foam.

Suppression of multiple modal resonances of a cantilever beam by an impact damper

Impact dampers are usually used to suppress single mode resonance. The goal of this paper is to clarify the difference when the impact damper suppresses the resonances of different modes. A cantilever beam equipped with the impact damper is modeled. The elastic contact of the ball and the cantilever beam is described by using the Hertz contact model. The viscous damper between the ball and the cantilever beam is modeled to consume the vibrational energy of the cantilever beam. A piecewise ordinary differential-partial differential equation of the cantilever beam is established, including equations with and without the impact damper. The vibration responses of the cantilever beam with and without the impact damper are numerically calculated. The effects of the impact absorber parameters on the vibration reduction are examined. The results show that multiple resonance peaks of the cantilever beam can be effectively suppressed by the impact damper. Specifically, all resonance amplitudes can be reduced by a larger weight ball. Moreover, the impacting gap is very effective in suppressing the vibration of the cantilever beam. More importantly, there is an optimal impacting gap for each resonance mode of the cantilever beam, but the optimal gap for each mode is different.