Impact Attenuation Research Articles

MXene/polyurethane auxetic composite foam for electromagnetic interference shielding and impact attenuation

Lightweight electromagnetic interference (EMI) shielding and impact attenuating materials are vital to protect delicate components in portable electronics. While conductive foams are intriguing for lightweight EMI shielding, their impact attenuating properties remain unexplored. Herein, a MXene/auxetic polyurethane (MX/APU) composite foam is developed for multifunctional EMI shielding and impact attenuation. The MX/APU composite presents a superior EMI shielding effectiveness (SE) of 76.2 dB, 31.2% higher than its non-auxetic counterpart at the same density owing to the larger specific surface area arising from the auxetic structure. Given its ultralow density of 0.063 g cm−3, it yields a specific SE of 1210 dB cm3 g−1, placing it among the best candidates for lightweight applications. The negative Poisson’s ratio of MX/APU composite foam also delivers multifunctionalities of impact attenuation, reducing the peak force by 51.4% compared to a non-auxetic foam. This work provides a conceptually new approach to design lightweight multifunctional materials using auxetic structures.

Eco‐Friendly Electronics—A Comprehensive Review

AbstractEco‐friendliness is becoming an indispensable feature for electrical and electronic equipment to thrive in the competitive market. This comprehensive review is the first to define eco‐friendly electronics in its multiple meanings: power saving devices, end‐of‐life impact attenuators, equipment whose manufacturing uses green processing, electronics that use materials that minimize environmental and health risks, designs that improve lifespan, reparability, etc. More specifically, this review discusses eco‐friendly technologies and materials that are being introduced to replace the well‐established ones. This is done for all material classes (metals, polymers, ceramics, and composites). Manufacturing, recycling, and final product characteristics are discussed in their various interconnected aspects. Additionally, the concept of consciously planned obsolescence is introduced to address the paradoxical relationship between durability and efficiency. The overall conclusions are that there is an important global trend to make electronics more eco‐friendly. However, matching the performance and stability of well‐established materials and technologies seems to be the main barrier to achieve it. These new implementations can have detrimental or beneficial net impacts on the environment. Assessing their net outcome is challenging because their impacts are frequently unknown and the current evaluation methods (and tools) are incapable of comprehensively quantifying these impacts and generating reliable verdicts.

Influence of the Testing Procedure on the Value of the Impact Attenuation of Rail Fastening Systems: an Experimental Study

Railway superstructure components are subject to impact forces caused by irregularities in the rail and wheel or variations in the support stiffness. These imperfections lead to the premature and accelerated deterioration of the track and increase maintenance costs. Generally, to mitigate these dynamic loads, elastomeric rail pads are interposed between rails and sleepers. For each track section, the pad choice is made according to its stiffness, impact attenuation and cost. In this experimental study, eight types of rail pads were characterized using two procedures from EN 13146–3. The results revealed that the rail pad material and geometry affect the impact attenuation ability of the pad and the testing procedure affect the results. It was found that the preload applied is one of the parameters that most affects the impact attenuation value. Appling a preload of 50 kN during the impact attenuation test, which is suggested by the standard, affected this parameter by ranging from between ~2 and ~ 20, depending on the rail pad. Based on these results it is considered that EN 13146–3 should be updated.

Application of UHMWPE in energy-absorbing road safety systems

The article considers the possibility of using a polymer material based on ultra-high molecular weight polyethylene (UHMWPE) in energy-absorbing structures of road safety systems. To determine the mechanical and energy absorbing characteristics of the material, bench tests carried out on the material and element of the designed structure in the form of a thin-walled cylinder. The possibility of using UHMWPE in the actual design of the road safety system checked by creating a validated digital twin of the impact attenuator. Based on the simulation results, polymer and metal structures compared.

Features of Seismic Impact Attenuation of the Russian Platform and Ural Earthquakes

The article analyzes the macroseismic impact of earthquakes that occurred in the late 20th and early 21st centuries on the Russian Platform and in the Urals. The relationships between seismic intensity I, magnitude M, and hypocentral distance r, according to the Blake–Shebalin equation, were established for five regions of the study area. For the first time, the coefficients of individual macroseismic field equations for the Ural near-surface and deeper sources were obtained (h ≤ 1 km: b = 1.5, v = 2.43, c = 1.01; h > 1 km: b = 1.5, v = 2.9, c = 2.13). The possibility of using the Blake–Shebalin equation with average coefficients (b = 1.5, v = 3.5, c = 3) was confirmed for earthquakes in southern Russian Platform. The low attenuation of the intensity of Baltic Sea earthquakes is established for the Eastern Baltics. The coefficient v = 2.48 in the obtained equation is similar to v = 2.7 recommended for this territory in the new Russian and Interstate Standard “Earthquakes: Macroseismic Intensity Scale” (2019). However, the level of seismic impact according to the established equation is higher than that predicted by this standard. The reduced attenuation coefficients for earthquakes in the eastern Russian Platform and induced events (h ≤ 1 km) in the eastern Baltic Shield have been obtained: v = 2.3 and v = 3.02, respectively. However, due to the lack of field data, these results need to be refined. New dependences are recommended for more accurate prediction of seismic impact from earthquakes in these regions.

Design of crashworthy attenuator structures as a part of vehicle safety against impact: Application of waste aluminum can-based material

The impact attenuator is an essential system in both race cars and urban vehicles. The structure of an impact attenuator serves as a safety barrier between the impacted surface and the driver in an accident. Attenuator materials tend to have a high price; thus, alternative materials were explored in the current work, i.e., used cans from food and beverage containers. The study deployed a nonlinear finite element algorithm to calculate a series of impacts on the attenuator structures. The thickness of the cans and velocity of the impact were considered as the main parameters. Analysis results concluded that the attenuator's average energy was 16000 J for a can thickness of 1 mm. This value is more than two times the 0.5 mm thick used cans. The attenuator's new design was then matched with an attenuator regulation, and the results surpassed the standard value of 7350 J.

Experimental analysis and numerical optimization of a thermoplastic composite in crashworthiness

In this work, we present an experimental analysis and a numerical optimization study for the material parameter identification of an impact attenuator made of a brand new All-PP thermoplastic composite material subjected to an axial impact load. After an experimental characterization of the material, a Finite Element (FE) numerical model of the impact attenuator is created and simulated using the LS-DYNA explicit software. Subsequently, in order to capture the force-displacement trend of the crush experimental test, a fine-tuning of some relevant material parameters through surrogate-based optimization techniques is performed. The optimization process mainly consists of (1) defining a set of target points on the load-displacement curve where to evaluate the Mean Squared Error (MSE) between the numerical and the experimental values; (2) using a Design of Experiments technique to provide a sample set on which expensive deterministic simulations are performed; (3) constructing as many surrogate approximations as the number of target points in order to predict how the load values change over the parameters’ domain; (4) predicting an overall MSE surface that is optimized by means of a genetic algorithm in a sequential domain reduction iterative procedure. Results show a good agreement between the numerical and the experimental impact load and energy curves, and hence confirm that surrogate-based optimization is a valuable technique to refine the material parameters in the numerical simulation of composite structures.

Impact attenuation provided by older adult protective headwear products during simulated fall-related head impacts.

IntroductionWhile protective headwear products (PHP) are designed to protect older adults from fall-related head injuries, there are limited data on their protective capacity. This study’s goal was to assess the impact attenuation provided by commercially available PHP during simulated head impacts.MethodsA drop tower and Hybrid III headform measured the decrease in peak linear acceleration (g atten ) provided by 12 PHP for front- and back-of-head impacts at low (clinically relevant: 3.5 m/s) and high (5.7 m/s) impact velocities.ResultsThe range of g atten across PHP was larger at the low velocity (56% and 41% for back and frontal impacts, respectively) vs. high velocity condition (27% and 38% for back and frontal impacts, respectively). A significant interaction between impact location and velocity was observed (p < .05), with significantly greater g atten for back-of-head compared to front-of-head impacts at the low impact velocity (19% mean difference). While not significant, there was a modest positive association between g atten and product padding thickness for back-of-head impacts (p = .095; r = 0.349).ConclusionThis study demonstrates the wide range in impact attenuation across commercially available PHP, and suggests that existing products provide greater impact attenuation during back-of-head impacts. These data may inform evidence-based decisions for clinicians and consumers and help drive industry innovation.

Association between knee valgus and impact attenuation during single-leg landing

Association between knee valgus and impact attenuation during single-leg landing

A study of the impact attenuator

A study of the impact attenuator

Analysis of bicycle helmet damage visibility for concussion-threshold impacts

ABSTRACT Any helmet involved in an accident should be replaced, regardless of appearance after impact. However, consumer compliance and interpretation of this recommendation is unclear, for which there is additional ambiguity for lesser impacts. This study aims to investigate the relation between helmet damage visibility and lesser impacts in line with concussion. As a preliminary model, a commercially available road-style helmet was chosen. Twelve helmets underwent impact attenuation testing; four were dropped from the standard testing height of 2 m, and eight from lower drop heights (0.34 and 0.42 m) associated with the production of linear accelerations (90 and 100 g, respectively) consistent with the production of concussion. Expanded polystyrene damage was assessed via flat punch penetration testing. American adults were then polled on helmet damage visibility based upon before and after photos. All helmets demonstrated damage to the expanded polystyrene liner in the form of altered material properties. Helmets dropped from 2 m displayed significant changes in elastic buckling (p < .01) and densification behavior (p < .01) as compared with lower drop height results. Adverse change in elastic buckling behavior was found to increase linearly with drop height (p < .001). Damage visibility was significant for helmets dropped from a 2-meter height, however, such a relation among the helmets impacted at the threshold for concussion was lacking. These findings suggest that for the chosen helmet model, consumers may be unable to distinguish between new helmets and helmets with diminished protective abilities.

Design and Analysis of Honeycomb based Impact Attenuator

The main idea of this research work is to understand the energy absorbing capacity of cellular solids when used in application of automobile as a safety measure to protect the occupants and structure of the vehicle. The full scaled model of the proposed design of the impact attenuator would be an expensive approach to follow. To understand the mechanism of energy absorption in honeycomb structure two types of experimental test were carried out. The first test includes a simple compression test of honeycomb structure only. The second experimental test consist of a composite sandwich of glass fiber and honeycomb under high speed drop test. Using the simple compression test the mechanical properties of the honeycomb were extracted in the out of plane behavior and then results from experimental data were calibrated with the FEM model. It was observed that very similar results were obtained in Experimental and FEM methods. And finally, the full scaled model analysis was carried in FEM package of ANSYS using mechanical properties of honeycomb extracted in simple compression test.

Structure design, mathematical modeling and dynamical performance tests of a new viscoelastic elastomer damper

In order to improve the ride of passive suspension system for the military vehicles in all kinds of roads, a new viscoelastic elastomer damper with one-way throttle valve structure was designed, and its working principle was set forth. A variable rigidity Maxwell fluid model was used to model viscoelastic elastomer damper, and the resistance formulae of elastomer damper in the input process and return process were conducted respectively, the shock experiment proved that the shock experiments proved the reliability of mathematical modeling. Finally, the dynamical performance tests about the continuous impact test, durability test and attenuation performance test were carried out on the elastomer damper, and the experimental results have shown that the elastomer damper has good impact resistance and stability performance.

Experimental assessment of permeability variation with the compression of soft reticulated foams

The resistance to flow of imbibed fluids in soft porous structures subjected to compression can be a solution for impact attenuation. The mechanism, named ex-poro-hydrodynamic (XPHD) lubrication, is based on permeability variation with porosity, which, at its turn, depends on the compression degree of the porous structure. A literature survey revealed scarce information regarding the permeability of compressed reticulated foams or 3D fiber-based structures, used in XPHD applications. Moreover, the permeability depends on the fluid and its velocity. This paper presents experimental data of the permeability of glycerine for an in-plane, axisymmetric flow through a porous material subjected to various degrees of compression. The experiments were done on an in-house made radial permeameter with pressure differentials up to 6 bars. The experimental data was compared with the predicted results, using the well-known Kozeny-Carman equation and related formulations.

Detraining of specific neuromuscular qualities in elite footballers during COVID-19 quarantine

ABSTRACT The COVID-19 pandemic forced elite football leagues into extended breaks followed by prompt resumption of competition. Inadequate periods of on-pitch football-specific training may underlie the increased injury incidence reported following restart in a non-peer reviewed report. Detraining effects from isolated training are expected, but existing models do not completely describe the unprecedented conditions imposed by COVID-19. Providing insight into specific neuromuscular qualities affected by extended absence of football-specific training, we share countermovement jump performance and kinetic data from an elite team’s assessments pre and post 15 weeks of isolated training, and to contextualise these trends, off-season changes with no training. The isolated circuit resistance and aerobic interval training maintained jump height and Reactive Strength Indexmodified, but there were moderate magnitude (p = 0.01–0.04) changes in eccentric ‘yielding’ and landing ‘loading’ phase variables. These changes suggest a compromised initiation of countermovement deceleration, impact attenuation and altered coordination/motor control strategies or muscle-tendon properties. This analysis may have revealed kinetic markers specifically stimulated by football-specific training/competition, relevant to post-quarantine monitoring. Lower landing forces may reduce overuse injury risk, while yielding phase alterations suggest a negative effect on reactive performance, therefore the overall effect on vulnerability to injury is unclear.

Energy Absorption Enhancement for Multiple Impact Angles of a Rear Crash Attenuator

This research aims at developing a reliable finite element framework to investigate the specific energy absorption of a rear crash attenuator of an open-wheel-type IndyCar vehicle. The failure behavior was learnt based on various nonlinear finite element modeling techniques to simulate a crash as per regulations from the governing body of IndyCar, utilizing the continuum damage mechanics model. The sandwich structure material characterization for the tuning of the material model was done by the means of a correlation with experimental data and adjusting the non-physical input parameters in the software. Post-calibration, the development of the rear impact attenuator was performed with a finite element model. The failure modes were investigated for head-on and oblique impact angles. The specific energy absorption was determined for these configurations of impact by evaluating the force over the crushed displacement. The insights from the simulation were utilized to improve the overall specific energy absorption by 41.8% with a gradual deceleration value to that of the prescribed. Finally, the results were compared to the previous IndyCar structure and a new prototype was suggested with highlights of the refreshed results.

Impact Attenuator Optimum Design for a FSAE Racing Car by Numerical and Experimental Crash Analysis

One of the most important requirements of the Formula SAE (Society of Automotive Engineers) race car design competition is that the car structure must guarantee a high protection level in case of frontal impacts, by preventing intrusions into the driver foot zone or dangerous deceleration levels. These functions are mainly performed by the impact attenuators, which have to guarantee a high specific energy absorption capacity (SEA) and in order to preserve vehicle performances, have to be as light weighted as possible. The aim of this study is the design of an impact attenuator, to be mounted on a Formula SAE car, which main purpose is to obtain the optimal crash energy management, maximizing the absorbed energy and optimizing the geometry. The outcome of the study highlights that the absorber structure made up of honeycomb sandwich panels (primary energy absorbers), realized by means of different aluminium alloys employing an innovative design considering particular geometrical cavities within the structure, could lead to reduce the overall weight and to achieve a more progressive deformation during the impact.

Biomechanics of lower limb in badminton lunge: a systematic scoping review.

BackgroundBadminton is a popular sport activity in both recreational and elite levels. A lot of biomechanical studies have investigated badminton lunge, since good lunge performance may increase the chances to win the game. This review summarized the current trends, research methods, and parameters-of-interest concerning lower-extremity biomechanics in badminton lunges.MethodologyDatabases including Web of Science, Cochrane Library, Scopus, and PubMed were searched from the oldest available date to September 2020. Two independent authors screened all the articles and 20 articles were eligible for further review. The reviewed articles compared the differences among playing levels, footwear designs, and lunge directions/variations, using parameters including ground reaction forces, plantar pressure distribution, kinematics, and kinetics.ResultsElite badminton players demonstrated higher impact attenuation capability, more aggressive knee and ankle strategy (higher mechanical moment), and higher medial plantar load than amateur players. Footwear modifications can influence comfort perception and movement mechanics, but it remains inconclusive regarding how these may link with lunging performance. Contradicting findings in kinematics is possibly due to the variations in lunge and instructions.ConclusionsPlaying levels and shoe designs have significant effects on biomechanics in badminton lunges. Future studies can consider to use an unanticipated testing protocol and realistic movement intensity. They can study the inter-limb coordination as well as the contributions and interactions of intrinsic and extrinsic factors to injury risk. Furthermore, current findings can stimulate further research studying whether some specific footwear materials with structural design could potentially compromise impact attenuation, proprioception, and performance.

Experimental Research on the Mechanical Performance of the Bolted Rock under Lateral Impact Load: Effect of Prestress, Body Material, and Anchorage Style

In order to reveal the impact mechanical properties and their key influencing factors of the bolted rock under the lateral impact load, through the lateral drop hammer impact test, the time-history curve of impact force, axial force of the bolt, and surface strain of the sample under different combination types of influencing factors is obtained, and the whole process of deformation and failure of the bolted rock is recorded. The test results show that the material of the bolt has a significant influence on the impact force and axial force of the bolt. There is a positive correlation between bolt strength and impact peak and impact attenuation slope and a negative correlation between bolt strength and impact action time. The effect of prestress on the impact resistance of the bolted rock was also evaluated by the test which suggested that prestress of the bolt can significantly reduce both impact time and bolt axial force of the bolted rock but has limited effect on the impact force. It was also found that the time-history curve of the impact force of anchoring rock mass had significant difference with full-length anchoring and nonanchoring. Compared with the nonanchoring bolt, the full-length anchored rock mass has a larger impact peak and shorter action time, which means that the impact resistance of the full-length bolted rock has a certain degree of weakening. Through scientific research, determining the reasonable bolt material, prestress value, and anchorage style can improve the impact resistance of the sample.

An experimental study of glass fibre roving sizings and yarn finishes in high-performance GF-PA6 and GF-PPS composite laminates

In the present study a range of glass fibre (GF) coatings (roving sizings and yarn finishes) were investigated for the manufacture of high-performance composite laminates based on Polyamide 6 (PA6) and Polyphenylene Sulfide (PPS) matrices. Matrix compatibility and resulting composite performance of press-consolidated laminates was evaluated by macro-mechanical testing on the basis of 3-point flexural and short-beam-shear tests. Among the tested yarn finishes, γ-aminopropyltriethoxysilane (A-1100 aminosilane yarn finish) and chromium(III)methacrylate (Volan®A chromium yarn finish) stood out as highly efficient adhesion promoters for both PA6 and PPS. Flexural strength properties of laminates prepared from finished yarn fabrics (up to 770 MPa) surpassed industrial grade laminates. A GF-epoxy laminate yielded lower flexural strength (570 MPa) compared to the GF-PPS laminates at an identical fibre volume fraction of 56%. These findings exemplified that neat PA6 and PPS matrices require no further chemical modification, i.e. adhesion and resulting composite strength can be tailored most efficiently by fibre coating adaptation. SEM imaging further verified that PA6 and PPS polymers adhere strongly to specific glass fibre coatings. In contrast, laminates made from desized (uncoated) fabrics exhibited interfacial debonding, and hence the lowest laminate performance throughout. Additional compression, and compression after impact tests (50 J impact) revealed that laminates made from sized or finished fabrics boast superior impact attenuation when compared to their desized fabric counterparts.