Shock-absorbing Capacity Research Articles

Vulnerability to climate change among the Changpa pastoral nomads of Leh-Ladakh

Pastoral nomads of the Himalayan region are the least responsible but most threatened by climate change. Therefore, the present study was conducted to analyze vulnerability to climate change among the randomly selected 200 Changpa pastoral nomads of Leh-Ladakh. A vulnerability to climate change index was developed underlying the principle of IPCC by using 18 household-level indicators of bio-physical and societal importance. The study indicated that the average vulnerability scores of Changpa pastoral nomads were positive, which indicated their shock-absorbing capacity to extreme climatic conditions, whereas 32% of the households were extremely vulnerable. But vulnerability index score of 7.50% of households was negative, which indicated their inability to cope with the extreme climatic conditions. Hence, immediate attentions are required to formulate better adaptation strategies to improve the adaptive capacity of the vulnerable Changpa pastoral nomads to changing climate conditions.

Development of novel magnetorheological dampers with low-speed sensitivity for flying car suspensions

As urban traffic environments continue to grow in complexity, there is an urgent need for a versatile mode of transportation that seamlessly transitions between terrestrial and aerial mobility. In conventional magnetorheological damper (CMRD), the magnetorheological fluid flowing through the narrow annular gap between the piston and cylinder in CMRD results in a damping force directly proportional to velocity. As velocity increases, the damping force rises sharply, posing a significant risk to the vehicle’s mechanical structure and passenger safety. This velocity sensitivity restricts their applications primarily to standard commercial vehicle suspension systems. They face significant challenges when it comes to high-speed impact scenarios. To overcome this limitation, enhance the shock-absorbing capacity of flying cars, ensure passenger safety, and improve passenger comfort during the landing phase, this study introduces a novel magnetorheological damper (NMRD) with unique internal channel structure embedded in a circular permanent magnet. In road travel mode, NMRD maintains a wide dynamic range. During high-speed impact landing, when the impact force exceeds the threshold, the pressure relief channel opens, effectively reducing the peak impact force. This feature greatly expands the application range of magnetorheological dampers. The researches included simulations of the electromagnetic induction phenomenon within the piston, The pressure relief damping force inside the NMRD valve was accurately measured by using material testing system, the peak force and peak acceleration experienced by the two dampers during impact were tested using a dedicated drop hammer apparatus. These tests demonstrate that the NMRD exhibits superior impact resistance performance compared to CMRD. This highlights the promising potential for the NMRD’s application within the suspension systems of flying cars.

Macroeconomic Indicators and Pakistan’s Banking Industry’s Shock Absorbing Capacity A Case Study of Conventional and Islamic Banks

Macroeconomic Indicators and Pakistan’s Banking Industry’s Shock Absorbing Capacity A Case Study of Conventional and Islamic Banks

The effects of material and structural properties of the periodontal ligament in mechanical function of tooth-PDL-bone complex in dental trauma: A sensitivity study using finiteelement analysis

Periodontal ligament (PDL) plays a crucial role in transferring load from tooth to its adjacent bone, and its role is more pronounced in case of trauma, due to its shock-absorbing character, which has not been fully understood yet. Different constitutive models have correlated mechanical function of PDL with its anisotropic, inhomogeneous, non-linear elastic nature, and it was variably modeled using Finite Element (FE) simulations of dental trauma. Furthermore, since capturing accurate dimension of PDL is difficult, various thicknesses were considered for PDL in FE reconstruction process. In this study, the sensitivity of FE analyses to variation in mechanical properties, including a large range of elastic properties for a linear elastic model, also a hyper-elastic material model, and various thicknesses of PDL was investigated by developing a CT-based FE model of tooth-PDL-bone complex. Results of this study highlighted the crucial role of PDL in absorption and dissipation of energy, as well as in stress distribution within alveolar bone during dental trauma. It was observed that as Young's modulus of PDL decreases and its thickness increases, its shock-absorbing capacity would be escalated. Moreover, it was found that inclusion of PDL reduces the maximum von Mises stress exerted on the alveolar bone by about 60% in some areas, compared to the case in which the PDL is absent. Results of this work underscore the need of presenting comprehensive constitutive models to describe mechanical behavior of PDL, with the goal of understanding the behavior of a tooth-PDL-bone complex in pathological conditions, such as trauma.

Improving light-cured intermediate resin for hard and space mouthguard using a glass fiber.

A light-cured intermediate material is useful for fabricating a hard insert and a buffer space mouthguard (H&SMG). However, it requires improvement in its mechanical properties and shock-absorbing capacity. The aim of this study was to evaluate the mechanical properties of two prototype light-cured intermediate materials reinforced with glass fibers, and the impact absorption capacity and durability of H&SMGs made with the prototype intermediate materials. Two prototype materials containing long and microlength glass fibers in a light-cured intermediate material, Innerframe LC®, for H&SMG, were fabricated and tested. A three-point bending test was performed for evaluation of the mechanical properties. In addition, a shock absorption test was conducted using a customized pendulum impact testing machine to evaluate the H&SMGs' impact absorption capacity and durability. Long and microlength glass fibers significantly improved flexural modulus and strength. H&SMGs made with these two glass fiber-containing materials had high impact absorption capacity against both low and high impact forces, while the mouthguards made with long glass fiber materials had the best results. Long and microlength glass fibers with the prototype materials improved the mechanical properties of Innerframe LC® and the impact absorption capacity and durability of H&SMGs. H&SMGs made with the long glass fiber prototype materials had the best performance.

Stainless steel wave spring as vibration absorber for motorcycle: Design simulation and analysis

In the ongoing world, everyone has been using the shock absorber as an essential component in most places like load carriers, large structures, and automobiles. This shock absorber plays a crucial role in the vehicle suspension to absorb the major shocks. So, if we absorb the shocks more efficiently, we can reduce the damage to the vehicle body, passenger and also, we can give a comfortable drive to the driver. In the suspension system, spring is the major part to absorb shocks through spring energy. So, if we use different springs or if we can modify the existing spring with better efficiency then we can increase the shock-absorbing capacity. Based on these ideas, I worked on the comparative analysis between coil spring shock absorber and wave spring shock absorber using stainless steel material under static structural and random vibrational analysis. Through these results, we can understand how effectively the wave spring shock absorber can replace the coil spring absorber in terms of load and deformation. In the end, we can find the effectiveness of springs under different random obstructions using the PSD concept in Ansys. This work can be helpful to mono shock absorber bikes and in other places where springs are required at low space areas. If we replace the coil spring with a wave spring with the same length, we can absorb more vibrations at a more comfortable level for the drivers.

Fiber Loading of Date Palm and Kenaf Reinforced Epoxy Composites: Tensile, Impact and Morphological Properties

Date palm fiber (DPF) and kenaf fiber were reinforced in epoxy having various fiber loading 40%, 50%, and 60% by weight. These hybrid samples were manufactured by hot press technique and then characterized for tensile, impact, and morphological behavior to evaluate the ratio of fibers in the hybrid composites; the addition of kenaf improved the tensile properties, Scanning Electron Microscopy (SEM) revealed the interfacial bonding of fiber/matrix, and dispersion and void content in composites. Impact test studies reflected the effect of natural fiber with epoxy, level of stress transfer from matrix to reinforced material, and reinforced material’s role in absorbing the impacts. It showed that 50% of DPF had the best shock-absorbing capacity. The obtained results indicated that 30% DPF in hybrid composite showed improved tensile properties and homogeneous distribution of fiber without void content; however, 50% DPF loading in hybrid composites had the best impact properties.

Injectable and Crosslinkable PLGA-Based Microribbons as 3D Macroporous Stem Cell Niche.

Poly(lactide-co-glycolide) (PLGA) has been widely used as a tissue engineering scaffold. However, conventional PLGA scaffolds are not injectable, and do not support direct cell encapsulation, leading to poor cell distribution in 3D. Here, a method for fabricating injectable and intercrosslinkable PLGA microribbon-based macroporous scaffolds as 3D stem cell niche is reported. PLGA is first fabricated into microribbon-shape building blocks with tunable width using microcontact printing, then coated with fibrinogen to enhance solubility and injectability using aqueous solution. Upon mixing with thrombin, firbornogen-coated PLGA microribbons can intercrosslink into 3D scaffolds. When subject to cyclic compression, PLGA microribbon scaffolds exhibit great shock-absorbing capacity and return to their original shape, while conventional PLGA scaffolds exhibit permanent deformation after one cycle. Using human mesenchymal stem cells (hMSCs) as a model cell type, it is demonstrated that PLGA μRB scaffolds support homogeneous cell encapsulation, and robust cell spreading and proliferation in 3D. After 28 days of culture in osteogenic medium, hMSC-seeded PLGA μRB scaffolds exhibit an increase in compressive modulus and robust bone formation as shown by staining of alkaline phosphatase, mineralization, and collagen. Together, the results validate PLGA μRBs as a promising injectable, macroporous, non-hydrogel-based scaffold for cell delivery and tissue regeneration applications.

Trends in tourism under economic uncertainty

We use the gravity model to examine the causal link between economic policy uncertainty (EPU) and inbound tourism (ITM) in the United Kingdom. The results for the full sample demonstrate that EPU Granger causes ITM. This finding shows that association is misappropriated due to structural changes. We apply the time-varying rolling window technique to revisit the dynamic association between EPU and ITM. The findings for the subsamples indicate that EPU has a negative effect on ITM. In contrast, ITM has a positive effect on EPU in the subsamples. These results support the gravity model, which states that as EPU increases, the level of ITM decreases. The results have noteworthy implications for policymakers in the form of consistency in policies and short-term shock forecasting that is capable of greater shock-absorbing capacity to lessen the revocation of tourist programs. A stable exchange rate regime in the destination country will make tourism cheaper and more attractive to tourists. Decision-makers should consider time-varying attributes to establish tourism activities for effective and accurate predictions.

Fretting Wear Resistance of Titanium Foam Developed by Powder Metallurgy Route

Titanium foam is a promising material for bio-implant application because of its capability of minimizing the stress shielding effect at the interface between implant and host bone, in addition to its higher strength and weight ratio and shock absorbing capacity as compared to solid titanium and its alloys. In the present study, titanium foam has been developed by powder metallurgy route under optimum processing conditions with and without addition of cenosphere as space holder. Followed by the development of titanium foam (with and without addition of cenosphere), characterization and fretting wear behavior (kinetics and mechanism) has been studied using tungsten carbide as counter body. A detailed study of wear behavior shows that there is a significant decrease in wear rate due to fretting wear in porous titanium with 20 wt% cenosphere addition as compared to as received Ti6Al4V, porous titanium with 10 wt% cenosphere and without cenosphere. Coefficient of friction was also found to be reduced in porous titanium with cenosphere addition and 10 wt% cenosphere added titanium showed a maximum reduction in coefficient of friction. The mechanism of wear was found to vary with cenosphere content in the matrix.

Financial Stability Assessment for EU Candidate Countries and Potential Candidates

This paper reviews and assesses financial stability challenges in countries preparing for EU membership, i.e. Albania, Bosnia and Herzegovina, Kosovo, Montenegro, North Macedonia, Serbia and Turkey. The paper mainly focuses on the period since 2016 (unless the analysis requires a longer time span) and on the banking sectors that dominate financial systems in this group of countries. For the Western Balkans, the paper analyses recent trends in financial intermediation, as well as the two main challenges that have been identified in the past. Asset quality continues to improve, but the share of non-performing loans is still high in some countries, while regulatory, legal and tax impediments are still to be resolved in most cases. High unofficial euroisation is a source of indirect credit risk for countries with their own national legal tender, which calls for continued efforts to promote the use of domestic currencies in the financial system. At the same time, banking systems seem less prone to financial stress from maturity mismatches than certain EU peers. These risks are met with a solid shock-absorbing capacity in the Western Balkans, as exemplified by robust capital and liquidity buffers. Turkey experienced a period of heightened financial stress during 2018 and, while its banking system appears to have sufficient buffers to absorb shocks overall, significant forex borrowing of corporates and high rollover needs of banks in foreign exchange on the wholesale market constitute considerable financial stability risks. JEL Classification: F31, F34, F36, G15, G21, G28

Capital controls as shock absorbers

The recent global financial crisis has resuscitated the debate on the relevance of capital controls as effective policy instruments. This paper contributes to this debate by studying the shock-absorbing capacity of capital controls. Using a recently developed capital control dataset for a panel of 33 emerging market economies, I show that output in economies with stricter capital inflow controls responds significantly less to global credit supply shocks, whereas capital outflow controls have no significant shock-absorbing capacity. Leverage is significantly lower in economies enacting stricter capital inflow controls, suggesting that financial frictions play a role in driving the shock-absorbing capacity of inflow controls.

In Vitro Shock Absorption Tests on Implant-Supported Crowns: Influence of Crown Materials and Luting Agents.

To investigate the force absorption capacity of implant-supported crowns made of different restorative materials and connected to abutments with different luting agents. Molar crowns were milled of different computer-aided design/computer-aided manufacture materials (n = 8 crowns per material): polymethyl methacrylate, polyether ether ketone, composite, lithium disilicate, titanium, and zirconia. Crowns were mounted on titanium implant replicas using different luting agents: uncemented, temporarily cemented (zinc oxide-eugenol cement), conventionally cemented (zinc oxide phosphate cement), and adhesively bonded. As a reference, one implant replica was tested without a crown. Force absorptions of the different combinations of crown materials and luting agents were determined by applying an increasing force (0 to 250 N) on the occlusal crown surface and measuring the resulting force below the implant. Mean curves of applied and resulting forces up to 200 N were determined (six measurements per group), and slopes were calculated. Statistical analysis was performed (one-way analysis of variance, Bonferroni post hoc test, α = .05). Significant (P < .001) differences in the applied and resulting forces were found between the crown materials that were uncemented, temporarily cemented, cemented, and adhesively bonded. Materials with higher moduli of elasticity (ceramics, titanium) showed steeper slopes of the force curves and lower shock-absorbing capacity than resin-based materials, but were influenced more by the luting agents. The damping effects of resin-based materials were higher in combination with all cementation and luting modes. Shock absorption tests exhibited a strong material-dependent damping behavior of implant-supported crowns. The shock-absorbing capacity of crown materials with high moduli of elasticity may benefit from conventional cementation.

Experiments on shock-absorbing capacity of granular matter under impact load

Granular matter is a complex energy dissipation system. The friction and the viscous contacts among particles can dissipate effectively the system energy caused by external impact load. The force chain structure in granular system can extend the local impact in spatial dimension and expand the instantaneous impact in temporal dimension, thus to obtain the effective shock-absorbing effect. To investigate the absorbing capacity of granular matter under an impact load, in the present study, we develop an experimental system, in which a rock ball impacts granular matter in a cylinder under gravity, and the impact force on the cylinder bottom is measured with three load cells. The influences of particle size, material propery, thickness of granular matter on shock-absorbing capacity are discussed. The results show that irregular particles have more shock absorbing capacity, while the large-size particles have a slightly higher shock absorbing capability than the small-size particles. The thickness of granular matter, H, is a key parameter to affect the shock-absorbing. Critical thickness, Hc, is obtained in the experiments. The shock-absorbing capacity of granular matter is enhanced with H increasing when HHc, while H has little influence on shock-absorbing when H&gt;Hc. The resutls above are obtained with constant impact energy. Critical thickness Hc should be a function of impact energy and will be determined in the next study. With the experiments on shock-absorbing capacity of granular matter, it can reveal basic mechanical behaviors of granular materials and be applied in mechanical vibration absorptions.

Study on Shock-Absorbing Capacity of Roadside Safety Devices Made by Porous Ultra-High Molecular Weight Polyethylene

The porous Ultra-high Molecular Weight Polyethylene (UHMWPE) is designed to fabricate the roadside safety devices fixed on the conventional metal or concrete road highway guardrails. When the UHMWPE with pores is shocked, the material is compressed because the pores are closed and much energy is absorbed. Next, elastic deformation and plastic deformation happen further under the stress, kinetic energy is transformed into deformation energy further. The cushioning capacity of UHMWPE will be improved when the pores are induced. Then the vehicles will not be destroyed seriously when they bounce. On the other hand, it will be convenient to fix the roadside safety devices on the conventional metal or concrete road highway guardrails and the cost must be lower than changing the whole guardrails. Experimental results indicate that: UHMWPE exhibited excellent shock-absorbing capacity and it was a promising roadside safety material.

The Potential for Brain Injury on Selected Surfaces Used by Cheerleaders

Although playground surfaces have been investigated for fall impact attenuation, the surfaces that cheerleaders use have received little attention. To determine (1) the critical height for selected surfaces used by cheerleaders at or below which a serious head impact injury from a fall is unlikely to occur, (2) the critical heights for non-impact-absorbing surfaces for comparison purposes, and (3) the effect of soil moisture and grass height on g(max) (which is defined as the multiple of g [acceleration due to gravity at the earth's surface at sea level: ie, 32.2 feet x s(-1) x s(-1)] that represents the maximum deceleration experienced during an impact) and the Head Injury Criterion (HIC) at the critical height for a dry grass surface. Observational study. A local cheerleading gym, indoor locations within the authors' institution, and various outdoor locations. g(max), HIC, and critical height. Critical heights for the surfaces tested ranged from 0.5 ft (0.15 m) for concrete and vinyl tile installed over concrete to more than 11 ft (3.35 m) for a spring floor. Increases in grass height and soil moisture resulted in an increase in the critical height for grass surfaces. Only spring floors and 4-in (0.10-m)-thick landing mats placed on traditional foam floors had critical heights greater than 10.5 ft (3.20 m), thus providing enough impact-absorbing capacity for performance of 2-level stunts. The potential for serious head impact injuries can be minimized by increasing the shock-absorbing capacity of the surface, decreasing the height from which the person falls, or both. Cheerleaders and cheerleading coaches should use the critical heights reported in this study to compare the relative impact-absorbing capacities of the various surfaces tested, with critical height as an indicator of the impact-absorption capacity of the surface. The findings of this study can be used to select the most appropriate surface for the type of maneuver to be performed, based on the maximum height expected to be achieved by the cheerleader(s) during execution of the maneuver. Cheerleaders should not perform maneuvers at heights that exceed the critical height for the surface on which they are performing.

LOW VELOCITY IMPACT OF COMPOSITE CROP STRAW PANELS

Abstract The shock behaviour of crop straw reinforced composites with unsaturated polyester epoxy was studied. In this research an attempt has been made to design and manufacture protective composite vests for soldiers. The low velocity impact loading was generated by a drop weight impact machine with drop heights varying from 100 to 200 mm. The drop mass used in these experiments was 15 kg. The shock-absorbing capacity of the vests was found to be strongly affected by straw type, straw weight percentage per unit volume of composite panel (the permanent composite volume of the panel is equal to 434.2 cm3), and broken short rounded straight steel wire to straw weight ratio. This research concerns the evaluation of all the low velocity drop weight test parameters such as peak dynamic force, duration time, and impulse due to free falling of drop mass at different impact energies: 1.5, 2.25, and 3 J. In addition, indentation parameters such as contact force and absorbed energy could be evaluated. Mathematical models describing these parameters are presented in a form that can be easily predicted. The predicted shock-absorbing capacity shows good agreement with the experimental results. In addition, the optimum tailoring variables affecting the shock-absorbing performance of the composite vest system could be determined.

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In the present investigation, an experimental dental arch model fabricated in epoxy was assayed in Kratos universal testing machine to study the mechanical behavior of ethylene and vinyl acetate copolymer (EVA) in the form of mouthguard for sports and flat plate. The following variables were considered: thickness (3 and 4-mm plates), temperature (room and mouth temperature) and presence/absence of artificial saliva. Mechanical properties of EVA were tested under compressive strength: apparent absorbed energy (J.mm-1), maximum tension (N.mm-1), maximum dislocation (mm) and maximum strength (N). Data were recorded and modeled mathematically. Regarding the absorbed energy, maximum tension and maximum force, it was verified that the higher the thickness of the mouthguards, the better the results of force dissipation and redirection to the system and to several regions of the dental arch. In the presence of saliva and close to mouth temperature, the material responded positively to these alterations, resenting increased ductibility as well as improved mechanical responses. Regarding maximum dislocation, it was observed a better accommodation of the occlusion under conditions that simulate those observed in the oral environment. In conclusion, EVA proved to be an adequate material for fabrication of mouthguards and interocclusal splints. In addition, EVA showed good results in force dissipation and demonstrated a shock-absorbing capacity and a great protection potential.

Dynamic Analysis of a Container with a Single Layer of Drums Mounted on a Railroad Car Suffering Collision

Dynamic analysis has been performed with a new Type of 20' box container qualified as an industrial package Type 2 and 3 and as a Type A container. In the model for a numerical collision experiment the container was partially loaded with 21 × 1000 kg drums, arranged along three parallel rows forming a single layer. One of the aims in the container development was to achieve a system that could transport cargoes with a variable number of drums stacked in changeable configurations, while ensuring the safety of the container for dynamic forces that could arise during normal conditions of transport. This led to the design of an interchangeable tray for the drums that can easily be handled and loaded into the container, together with passive restraining devices that prevent this assembly from moving inside the container when subjected to dynamic forces. The container system is designed to withstand accelerations of up to 6g in the longitudinal direction. These can be expected during normal switchyard operations at collision speeds of about 13 km.h−1. In the dynamic analysis, initially the collision speed is assumed to be low, but then it is gradually increased until damaging forces are observed. For moderate collision speeds <10 km.h−1) the shock absorbers of the railroad and ram car remain fully functional. However, at speeds exceeding 10 to 11 km.h−1 the shock absorbers reach their full travel capacity, and a true impact occurs. At this point, the forces on the walls of the container, caused by the inertia of the cargo, grow rapidly with the speed of the collision, depending on how well the tray support system functions in its shock-absorbing capacity. One result of the calculations is that stiff support systems are not capable of absorbing the impact forces once the critical velocity of 10 km.h−1 is exceeded, since the forces quickly grow beyond even the design strength of a new 20' box container of 500 kN. In comparison the design strength of a today's IP 2/IP 3 container is only approx. 80 kN. In the numerical experiments, it was observed that a soft cushioning support tray system like the one developed by CORROBESCH/STM has excellent shock absorbing characteristics. By contrast, a rigid support system, or worse, no support system at all, is likely to produce impact forces at normal conditions of transport capable of endangering the container walls.

Shock absorbency of factors in the shoe/heel interaction--with special focus on role of the heel pad.

The heel pad acts as a shock absorber in walking and in heel-strike running. In some patients, a reduction of its shock-absorbing capacity has been connected to the development of overuse injuries. In this article, the shock absorption of the heel pad as well as external shock absorbers are studied. Individual variation and the effect of trauma and confinement on the heel pad were specifically investigated. Drop tests, imitating heel impacts, were performed on a force plate. The test specimens were cadaver heel pads (n = 10); the shoe sole component consisted of ethyl vinyl acetate (EVA) foam and Sorbothane inserts. The shock absorption was significantly greater in the heel pad than in the external shock absorbers. The mean heel pad shock absorption was 1.1 times for EVA foam and 2.1 times for Sorbothane. The shock absorption varied by as much as 100% between heel pads. Trauma caused a decrease in the heel pad shock absorbency (24%), whereas heel pad confinement increased the shock absorbency (49% in traumatized heel pads and 29.5% in nontraumatized heel pads). These findings provide a biomechanical rationale for the clinical observations of a correlation between heel pad shock absorbency loss and heel strike-dependent overuse injuries. To increase shock absorbency, confinement of the heel pad should be attempted in vivo.