Higher Damping Ratio Research Articles

Mechanical Properties of the Cortex in Older Adults and Relationships With Personality Traits.

Aging and neurodegeneration impact structural brain integrity and can result in changes to behavior and cognition. Personality, a relatively stable trait in adults as compared to behavior, in part relies on normative individual differences in cellular organization of the cerebral cortex, but links between brain structure and personality expression have been mixed. One key finding is that personality has been shown to be a risk factor in the development of Alzheimer's disease, highlighting a structure-trait relationship. Magnetic resonance elastography (MRE) has been used to noninvasively study age-related changes in tissue mechanical properties because of its high sensitivity to both the microstructural health and the structure-function relationship of the tissue. Recent advancements in MRE methodology have allowed for reliable property recovery of cortical subregions, which had previously presented challenges due to the complex geometry and overall thin structure. This study aimed to quantify age-related changes in cortical mechanical properties and the relationship of these properties to measures of personality in an older adult population (N = 57; age 60-85 years) for the first time. Mechanical properties including shear stiffness and damping ratio were calculated for 30 bilateral regions of the cortex across all four lobes, and the NEO Personality Inventory (NEO-PI) was used to measure neuroticism and conscientiousness in all participants. Shear stiffness and damping ratio were found to vary widely across regions of the cortex, upward of 1 kPa in stiffness and by 0.3 in damping ratio. Shear stiffness changed regionally with age, with some regions experiencing accelerated degradation compared to neighboring regions. Greater neuroticism (i.e., the tendency to experience negative emotions and vulnerability to stress) was associated with high damping ratio, indicative of poorer tissue integrity, in the rostral middle frontal cortex and the precentral gyrus. This study provides evidence of structure-trait correlates between physical mechanical properties and measures of personality in older adults and adds to the supporting literature that neurotic traits may impact brain health in cognitively normal aging.

Mechanical characteristics of new mesh-type elastic plate under different temperatures and vehicle dynamics loads

The dynamic characteristics of the elastic plate are affected by changes in ambient temperature. In this study, tensile tests of rubber materials at different temperatures were conducted, revealing that rubber materials exhibit significant nonlinearity and sensitivity at low temperatures. Finite element models of Groove Elastic Plate (GEP) and New Mesh-Type Elastic Plate (NMTEP) were established, incorporating the corresponding rubber material parameters to simulate temperature effects. The stress, deformation, stiffness, and damping characteristics of the two types of elastic plates were analyzed under varying temperature conditions. Finite element calculations show that NMTEP maintains better structural stability, lower static/dynamic stiffness, and a higher damping ratio at low temperatures. Additionally, dynamic calculations indicate that temperature variations significantly impact the track system's dynamic performance. The vibration and wheel-rail forces for NMTEP are significantly lower than those for GEP under all temperature conditions, suggesting that NMTEP is more conducive to vehicle safety and stability at low temperatures.

Experiment on MICP-solidified calcareous sand with different rubber particle contents and sizes

Microbially induced calcite precipitation (MICP) is a new environmentally friendly technology, with the ability to improve the mechanical properties of calcareous sand. Rubber is a high-compressibility material with a higher damping ratio than that of calcareous sand. In this study, calcareous sand was replaced by equal volume contents (0%, 1%, 3%, 5%, 7%, and 9%) and different sizes (0–1, 1–2, and 2–3 mm) of rubber, and a series of water absorption and unconfined compressive strength (UCS) tests were conducted on MICP-solidified rubber–calcareous sand (MRS). The results showed that the water absorption is reduced when the rubber content is larger. The UCS of 0–1-mm MRS decreased with the increase in rubber content. For 1–2-mm and 2–3-mm MRS, the UCS was improved by 11.30% and 15.69%, respectively, compared with the clean sand. Adding rubber promoted the formation of calcium carbonate, but the strength and stiffness of rubber particles were lower than those of the calcareous sand. Therefore, higher rubber content weakened the sand frame bearing system, and the UCS decreased when the rubber content was more than 5%. Moreover, a large amount of 0–1-mm rubber led to the increase in transverse deformation of the samples, which caused the acceleration of the destruction of the sand structure. The water absorption of 0–1-mm MRS was higher than that of 1–2-mm and 2–3-mm MRS, but the UCS of 0–1-mm MRS was lower. The best rubber size is 1–2 mm and 2–3 mm, and the best rubber content is 3%–5%. The outcome of this study may, in the authors’ view, prove beneficial in improving the strength of calcareous sand when it is reinforced by MICP-combined rubber.

Preparation and properties of silica fume@polyure-thane urea cement composites

In this study, a new material was synthesized by compounding silica fume and polyurethane urea, which is used to evaculate the vibration reduction performance of concrete. The mechanical and damping properties of silica fume@ polyurethane urea (SF@PUU) reinforced cement paste were investigated. Also, FT-IR, XRD, TG analysis, and SEM are included. The results indicated that SF@PUU leads to the production of high damping ratio cement pastes. The damping capacities of SF@PUU cement composites, where the damping mechanism included internal, external, and multiphase friction within the cement matrix. Additionally, SF@PUU created a constrained-layer damping structure in cement paste to improve the damping properties. The review confirmed that SF@PUU subjected to proper treatments can be as the replacement to cement in concrete or as a damping filler. However, more investigation is required into the dimensional stability and durability of SF@PUU-based concrete.

Numerical Investigation of the Seismic Performance of an Innovative Type of Buckling-Restrained Brace (BRB)

Previous studies have demonstrated that the inclusion of tire-derived aggregate (TDA) enhances the damping, ductility, and toughness of concrete mixtures. The effectiveness of tire-derived aggregate as a ductile material with a higher damping ratio and lower density in buckling-restrained braces has been examined at California State University’s Structures Laboratory (CSU). Through experimental and theoretical investigations, this study compares the structural application of buckling-restrained braces with TDA and with conventional concrete infill subjected to various ground motions as well as artificial excitations. The evaluations include modeling a full-scale experimental setup equipped with a single-leg BRB utilizing ETABS 2016 and OpenSees 2000 software. The effectiveness of the application is demonstrated through a comparison of accelerations, displacements, stiffness, and damping ratios between TDA and concrete filling. Additionally, a design guideline for TDA-filled buckling-restrained braced frames is provided.

The influence of steel reinforcements on static rigidity of epoxy granite spindle head for dynamic performance enhancement of machining center: Experiments and finite element simulation

Machine tool structures are subjected to continuous distortions and unwanted vibrations during machining. The structures should have excellent static and dynamic properties to minimize the adverse effects due to vibration. Cast iron is generally used as a structural material for machine tools owing to its higher structural rigidity and moderate damping properties. The lack of desired dynamic properties results in poor surface finish of the machined components. Epoxy granite is a resin mineral-based composite found to provide superior damping ability but it has lesser material stiffness. Steel reinforcements are more appropriate to enhance the static rigidity of epoxy granite structures. The cast iron spindle head of the vertical machining center is considered for the present study. Static structural analysis has been performed by finite element analysis and the results are considered as a benchmark for the design of epoxy granite spindle head. Multiple design configurations of steel reinforcements are evolved through topology optimization to achieve improved stiffness with a higher damping ratio. A model which exhibited higher stiffness with minimum steel has been proposed for fabrication. A 1:2 scaled model of the proposed configuration has been fabricated using epoxy granite. Experimental modal analysis and numerical static analyses have been carried out and the results are compared to those of cast iron spindle head. A significant reduction in mass and deformation of the epoxy granite spindle head by 22% and 57%, respectively, was observed compared to that of cast iron spindle head.

The Dynamic Behaviour of Symmetrical Laminated Nano-composite Containing Equal Numbers of Glass and Carbon Fibre Layers

Fibre-reinforced polymer composite has many uses in structural components that required high strength, stiffness, and damping capacity. Cross and quasi-laminated epoxy composites with and without nano Al2O3 were used in this investigation to determine flexural modulus, natural frequency, damping ratio, and mode shapes by using analytical, experimental, and numerical (ANSYS) methods. It was demonstrated that adding 2 % nano Al2O3 improved the flexural modulus and the damping ratio while decreased the natural frequency. Cross number 2 and quasi number 2 had the highest natural frequency for cross and quasi laminate groups which are equal to 23.5 Hz and 20.25 Hz experimentally, respectively. On the other hand, the higher damping ratio was achieved for cross number 1 with nano Al2O3 and quasi number 2 with nano Al2O3 for both cross and quasi laminates, which are equal to 0.707 % and 0.693 %, respectively. The flexural modulus and damping ratio are inversely related to each other. However, the novelty in this article is that by adding two glass plies at the outer surface of quasi group laminate the flexural modulus, natural frequency, and damping ratio are increased simultaneously, as in the configurations quasi number 2 and quasi number 2 with nano Al2O3 in comparison with quasi number 1 and quasi number 1 with nano Al2O3.

A Modeling Framework to Develop Materials with Improved Noise and Vibration Performance for Electric Vehicles

The automotive and aerospace industries increasingly use lightweight materials to improve performance while reducing fuel consumption. Lightweight materials are frequently used in electric vehicles (EVs). However, using these materials can increase airborne and structure-borne noise. Furthermore, EV noise occurs at high frequencies, and conventional materials have small damping. Thus, there is an increasing need for procedures that help design new materials and coatings to reduce the transferred and radiated noise at desired frequencies. This study pioneered new techniques for microstructure modeling of coated and uncoated materials with improved noise, vibration, and harshness (NVH) performance. This work uses the microstructure of materials to study their vibration-damping capacity. Images from an environmental scanning electron microscope (ESEM) show the microstructure of a sample polymer and its coating. Tensile tests and experimental modal analysis were used to obtain the material properties of the polymer for microstructure modeling. The current work investigates how different microstructure parameters, such as fiberglass volume fraction and orientation, can change the vibration performance of materials. The damping ratio in the study was found to be affected by changes in both the direction and volume ratio of fiberglass. Furthermore, the effects of the coating are investigated in this work. Through modal analysis, it was observed that increasing the thickness of aluminum and aluminum bronze coatings caused a rightward shift in resonance frequency. Coatings with a thickness of 2 mm were found to perform better than those with lower thicknesses. Furthermore, the aluminum coating resulted in a greater shift in frequency than the aluminum bronze coating. Additionally, the coating with a higher damping ratio (i.e., aluminum bronze) significantly reduced the amplitude of surface velocity due to excitation, particularly at higher frequencies. This study provides engineers with an understanding of the effects of layer coating on the NVH performance of components and a modeling approach that can be used to design vehicles with enhanced noise and vibration performance.

Fea modelling perforated pattern fiber woven roving 4 elastomeric isolator (PFWREI)

Earthquakes can cause lateral displacements due to the movement of the earth's plates. Earthquake vibrations may induce shocks in structures; if the building structure can't sustain the shocks caused by earthquake forces, it might be damaged. Therefore, so that an earthquake does not cause damage to the building structure, it must consider the magnitude of the earthquake force. To decrease the effects of an earthquake, a base isolator can be put in place to absorb and spread the earthquake's energy before it gets into the building. The base isolator is often made of rubber and a steel plate, although the cost of production and weight of the base isolator is high. Type 4 fiberglass woven roving will be used to produce a prototype to reduce the overall production cost of a base isolator. A hole pattern will be applied to the fiber in two design variations, pattern-1 and pattern-2. The fiber holes are made so that the rubber can fill the gaps. The purpose is to make the base isolator components stick together tightly. The FEA Abaqus program will assess the fiber pattern variations to discover the most effective hole pattern modifications for reducing seismic force. The results indicated that pattern-1 had a higher damping ratio than pattern-2.

Thermo-Mechanical Properties of Carbon Nanotube Yarns With High Energy Dissipation Capabilities

Abstract Carbon nanotube yarns (CNTYs) are porous hierarchical fibers that exhibit a strong property-structure relationship. The morphology and structure of dry-spun CNTYs are characterized and correlated with their quasi-static and dynamic mechanical properties. These characterizations include assessment of the CNTY homogeneity by means of Raman spectroscopy mapping, determination of linear density and porosity, atomic force microscopy, and dedicated measurements of the statistical distribution of the yarn’s diameter. Tensile testing of CNTYs yielded a specific strength of 0.21–0.34 N/tex, and a specific elastic modulus of 3.59–8.06 N/tex, depending on the gage length. While the strength is weakly sensitive to the gage length, the elastic modulus depends on the gage length. The importance of subtracting the machine compliance for the determination of the CNTY’s elastic modulus is highlighted, since the error can reach up to 28%. Dynamic mechanical analysis shows that the CNTY is a stiff material with an extraordinary high damping ratio, which increases with temperature and reaches ∼0.6 at 60 °C. In addition, the CNTY presents a frequency-stiffening behavior in the 18–48 Hz range, with storage modulus (E′) and loss modulus (E″) which increase ∼2.5 times (E′) and ∼7 times (E″) at 48 Hz.

Passive walking biped robot model with flexible viscoelastic legs

To simulate the complex human walking motion accurately, a suitable biped model has to be proposed that can significantly translate the compliance of biological structures. In this way, the simplest passive walking model is often used as a standard benchmark for making the bipedal locomotion so natural and energy efficient. This paper is devoted to a presentation of the application of internal damping mechanism to the mathematical description of the simplest passive walking model with flexible legs. This feature can be taken into account by using the viscoelastic legs, which are constituted by the Kelvin–Voigt rheological model. Then, the update of the impulsive hybrid nonlinear dynamics of the simplest passive walker is obtained based on the Euler–Bernoulli’s beam theory and using a combination of Lagrange mechanics and the assumed mode method, along with the precise boundary conditions. The main goal of this study is to develop a numerical procedure based on the new definition of the step function for enforcing the biped start walking from stable condition and walking continuously. In our previous work, it was shown that the period-one gait cycle can be produced by adding the proportional damping model with high damping ratio to the elastic legs. The present paper overcomes the practical limitations of this damping model and similarly demonstrates the stable period-one gait cycles for the viscoelastic legs. The study of the influence of various system parameters is carried out through bifurcation diagrams, highlighting the region of stable period-one gait cycles. Numerical simulations clearly prove that the overall effect of viscoelastic leg on the passive walking is efficient enough from the viewpoint of stability and energy dissipation.

Effects of magnitude and distance on spectral and pseudospectral acceleration proximities for high damping ratio

Effects of magnitude and distance on spectral and pseudospectral acceleration proximities for high damping ratio

Influence of Rubber Inclusion on the Dynamic Response of Rail Track

Heavier and faster trains have motivated researchers to seek better ways to absorb the increasing amount of energy imparted to rail foundations and mitigate track deterioration. In recent years, resilient rubber products have attracted more attention due to the high level of damping and the associated energy absorbing capacity of rubber. However, because rubber granules have lower shear strength and higher compressibility compared with natural rock aggregates, a better understanding of how rubber inclusions can influence the track system is imperative, especially before putting these recycled resilient materials into practice. In this paper, the performance of rail track incorporating an alternative subballast layer, i.e., a synthetic energy absorbing layer (SEAL) consisting of a mixture of granulated rubber and mining waste is evaluated through large-scale prismoidal triaxial tests and a computational dynamic model. It is revealed that the amount of granulated rubber in SEAL composites has a significant influence on the dynamic behavior of the track. Fundamentally, increasing the amount of rubber within SEAL leads to a higher vertical deformation, increased energy absorbing capacity, and a higher damping ratio and vibration level, while reducing the ballast degradation, track stiffness, and lateral movement (dilation) of the track. It has been found that 10% of rubber by mass is the optimal amount of rubber to be included in SEAL. This amount of rubber will ensure that a ballasted track can efficiently reduce the dynamic contact pressure at the interface between different track layers (i.e., sleeper, ballast, subballast, and subgrade), and reduce the lateral spread (dilation) and breakage of ballast without generating excess vibration and settlement comparing with traditional track materials.

Characterization of energy dissipative cushions made of Ni–Ti shape memory alloy

Earthquake-resistant design of structures requires dissipating seismic energy by deformations of structural members or additional fuse elements. Owing to its easy-to-produce, plug-and-play, high equivalent damping ratio, and large displacement capacity characteristics, energy dissipative steel cushions (SCs) were found to be an efficient candidate for this purpose. However, similar to other conventional metallic dampers, residual displacement after a strong shaking is the most notable drawback of the SCs. In this work, cushions produced from Ni–Ti shape memory alloy (SMA) are evaluated numerically by experimentally verified finite element models to assess their impact on the performance of earthquake-resistant structures. Furthermore, a reinforced concrete testing frame is retrofitted with energy dissipative steel and Ni–Ti cushions. Performance of the frames (e.g. dissipated energy by the cushions, hysteretic energy to input energy ratio, maximum drift, and residual drift) with different types of cushions are evaluated by nonlinear response history analyses. The numerical results showed that the SCs are effective to reduce peak responses, while Ni–Ti cushions are more favorable to reduce residual drifts and deformations. Hence, a hybrid system, employing the steel and SMA cushions together, is proposed to reach optimal seismic performance.

Gaussian quantum particle swarm optimization-based wide-area power system stabilizer for damping inter-area oscillations

PurposeThe extensive increase in power demand has challenged the ability of power systems to deal with small-signal oscillations such as inter-area oscillations, which occur under unseen operating conditions. A wide-area measurement system with a phasor measurement unit (PMU) in the power network enhances the observability of the power grid under a wide range of operating conditions. This paper aims to propose a wide-area power system stabilizer (WAPSS) based on Gaussian quantum particle swarm optimization (GQPSO) using the wide-area signals from a PMU to handle the inter-area oscillations in the system with a higher degree of controllability.Design/methodology/approachIn the design of the wide-area stabilizer, a dead band is introduced to mitigate the influence of ambient signal frequency fluctuations. The location and the input signal of the wide-area stabilizer are selected using the participation factor and controllability index calculations. An improved particle swarm optimization (PSO) technique, namely, GQPSO, is used to optimize the variables of the WAPSS to move the unstable inter-area modes to a stable region in the s-plane, thereby improving the overall system stability.FindingsThe proposed GQPSO-based WAPSS is compared with the PSO-based WAPSS, genetic algorithm-based WAPSS and power system stabilizer. Eigenvalue analysis, time-domain simulation responses and performance index analysis are used to assess performance. The various evaluation techniques show that GQPSO WAPSS has a consistently good performance, with a higher damping ratio, faster convergence with fewer oscillations and a minimum error in the performance index analysis, indicating a more stable system with effective oscillation damping.Originality/valueThis paper proposes an optimally tuned design for the WAPSS with a wide-area input along with a dead-band structure for damping the inter-area oscillations. Tie line power is used as the input to the WAPSS and optimal tuning of the WAPSS is performed using an improved PSO algorithm, known as Gaussian quantum PSO.

Non-linear mechanical properties and dynamic response of silicon nitride bioceramic

Natural spinal tissues have unique dynamic properties and it is crucial to investigate the full dynamic response of spinal implants and related biomedical materials to ensure compatibility with the host tissue. Silicon nitride is a promising bioceramic for spinal implants. In this study, the mechanical properties and dynamic response of silicon nitride were comprehensively evaluated using novel and efficient testing methods, at both the material and structural level. The correlation between mechanical properties and porosity was investigated and the results showed that Young's modulus and compressive strength decreased non-linearly as porosity increased. Both the compressive strength (100.35±3.39MPa) and fracture toughness (1.06±0.06MPa⋅m1/2) of the porous silicon nitride samples (~70% porosity) can be considered sufficient for load bearing purposes as a substitute for trabecular bone. Moreover, the results from a drop tower test showed that the average ultimate strength of the scaffolds under an impact loading was significantly lower than the strength under quasi-static compression. Nevertheless, this value is still comparable to that of trabecular bone. Regarding damping capacity, the results of free damped vibration tests of cantilever beams showed that a silicon nitride beam has a higher damping ratio (0.17%±0.01%) than a zirconia beam (0.13%±0.01%), which indicates that ceramics with similar Young's moduli can have different energy dissipating capacities. However, both dense and porous silicon nitride showed a low energy dissipation, substantially lower than natural spinal tissues. Overall, dense silicon nitride possesses a high stiffness, and altering the porosity of silicon nitride is one option to tailor its mechanical properties towards those of trabecular bone, however, more effort is required to increase its damping capacity, if this is a desired trait.

Design of PI controller parameters of a CSI‐fed SCIM drive ensuring high damping ratio and maximum system stability

AbstractThe control scheme for an electric motor drive is generally implemented by involving proportional‐integral (PI) controllers in current and speed feedback control loops. A good design of PI controller parameters has always been a challenging task for control system design engineers. This paper describes the D‐decomposition method for the design of the parameters of involved DC‐link current and speed PI controllers in closed‐loop scheme of a pulse width‐modulated, current source inverter (CSI)‐fed squirrel‐cage induction motor drive. The PI controllers ensure the stable operation of CSI‐fed induction motor in natural unstable operating region of its torque‐slip characteristic. In order to achieve smoother speed tracking performance with minimum overshoot/undershoot, the damping ratio has been pre‐specified while designing the PI controller parameters using the D‐decomposition method. Simulation results have been presented to confirm the design and have been compared with the results already published.

On passive damping in machine tool hybrid structural parts

Hybrid materials combining steel or cast iron with fibre or particle composites have a good potential for lightweight machine tool structural design with high damping ratio. These materials are analyzed in the paper with a focus on damping improvement of structural components and machine tool assemblies. Fibre composites and particle composites were selected as the lightweight elements for the hybrid machine tool structure. The fibre composites were designed as low-density, high stiffness-oriented reinforcements, which were bonded to build metal structural parts conventionally. The particle composites were applied as filler materials into the hollows of the metal structural parts. Both composite structures presented a possibility to reduce the mass of the component due to the reduction of wall thickness (fibre composite) or removal of heavy ribbing (particle composites) and to influence the parts’ static and dynamic stiffness. Hybrid structures, combining the light-weight elements with cast iron or welded steel, were designed and tested in case studies using experimental modal analysis methods. Experimental modal analysis was used as the main approach for identification of the damping ratio on a basic coupon level, followed by testing of structural parts in a stand-alone configuration and ending with a structural part assemblies testing. Both particle composites and fibre composites were successful in improving the damping ratio of single structural parts. However, the damping ratio of the hybrid component mounted into an assembly configuration shows only less significant improvement. The presented results demonstrate importance of the damping caused in the connecting interfaces.

On the dynamic response of a poroelastic medium subjected to a moving load based on nonlocal Biot theory

Based on classical Biot poroelastic theory and nonlocal elastic theory, an analytical model for investigating the dynamic responses of saturated porous materials subjected to a moving load is proposed. The displacement and stress fields in the frequency and wavenumber domains are obtained through Fourier transform. Then, the double inverse Fourier transform is applied to the obtained displacement and stress solutions to give the results in the time–space domain. The influences of the nonlocal parameter and load moving speed on the displacement field are discussed in detail. The influence of the nonlocal parameter on the displacement is enhanced with increasing load moving speed. Furthermore, the increase in the nonlocal parameter results in a decrease of the “resonance-like” frequency in a saturated material, reducing the critical load moving speed. The influence of the damping ratio is also investigated; as expected, a higher damping ratio always reduces the displacement. Finally, the influences of the nonlocal parameter on the pore pressure and permeability are presented.

Damping ratio maximization in thickness direction using viscoelastic and structural materials based on constrained layer damping

Constrained layer damping (CLD) is a typical application known to exhibit high damping. However, the damping ratio generally attains its maximum value when the applied surface is fully covered with the damping material. In this study, a method is proposed of topology optimization in the thickness direction using viscoelastic and constrained materials based on CLD in order to obtain a higher damping ratio. A mathematical formulation is proposed of the material interpolation functions of the store elastic modulus, loss elastic modulus, Poisson's ratio and density. As a result of the optimization using a cantilever beam, the damping ratio obtained in the optimal layout is 1.44 times higher than that in conventional CLD. The higher damping in the optimal layout can be attributed to compression of the viscoelastic material by the slits, and a decrease in the flexural rigidity caused by the taper and the longitudinally extending part of the slits.