Viscoelastic Components Research Articles

Viscoelastic study of cement and emulsified asphalt mortar under temperature variations based on a novel variable-order fractional Maxwell model

Cement and emulsified asphalt (CA) mortar is a critical viscoelastic component of ballastless track systems, exhibiting pronounced temperature sensitivity. However, accurately predicting the mechanical responses of CA mortar due to temperature fluctuations remains a challenge. This work proposes a novel variable-order fractional Maxwell (VOFM) model to investigate the viscoelastic properties of CA mortar under temperature variations. The VOFM model is numerically solved using a time-varying coefficient ladder (TVL) model. The VOFM model is validated by comparing with both numerical integration methods and experimental data. The basic properties of the VOFM model, the viscoelastic responses of CA mortar under varying temperatures and alternating stress are systematically investigated. The results show that the mechanical properties of VOFM model agree with the FM model when time-dependent parameters of the VOFM model correspond to that of the FM model. Moreover, high temperatures have a promoting effect on the deformation of CA mortar under both alternating and constant stress conditions. The peak amplitude of CA mortar strain under practical varying temperature and stress loading correlates with the trend of temperature changes.

Finite element analysis of 2.5D packaging processes based on multi-physics field coupling for predicting the reliability of IC components

The 2.5D packaging technology is a high–performance method for electronic packaging. This study addresses the reliability issues of 2.5D packaging during the manufacturing process. A multi–physics field coupling Finite Element Method (FEM) has been developed, combined with sub–modeling techniques, to investigate the curing of underfill adhesive, the curing of Epoxy Molding Compound (EMC), and the reflow soldering between the interposer and substrate in a 2.5D packaging entity during various manufacturing procedures. The focus is on the thermo–mechanical–chemical behavior of viscoelastic components within the packaging structure, as well as the viscoplastic characteristics of the micro solder balls and microbumps. A systematic analysis is conducted on the warpage deformation and stress distribution of the 2.5D packaging at crucial time points. The results demonstrate that after curing, the overall warpage of the packaging exhibits a ‘concave’ warpage profile. Additionally, as the thickness of the EMC above the chip increases, the warpage value of the packaging also increases. The warpage value defined by linear elasticity is larger than that defined by viscoelasticity. The maximum Von Mises stress value in the key areas of the submodel is greater than the maximum Von Mises stress value in the corresponding key areas of the global model. After reflow soldering, the stress concentration in the micro solder balls occurs at the edge of the micro solder ball array. The maximum stress values for each component of the packaging are observed in the interface areas between the components. Packaging components that undergo the curing process have notably higher warpage and Von Mises stress values than those that do not undergo the curing process. The simulation method established in this study can accurately predict the warpage deformation and stress distribution state of 2.5D packaging, providing significant engineering application value for process optimization and reliability enhancement of 2.5D packaging in the production process.

Rutting and fatigue behavior of neat and nanomodified asphalt mixture with SiO2 and TiO2

Modern asphalt technology has adopted nanomaterials as an alternative option to assert that asphalt pavement can survive harsh climates and repeated heavy axle loading during service life and prolong pavement life. This work aims to elucidate the behavior of the modified asphalt mixture fracture model and assess the fatigue and Rutting performance of Hot Mix Asphalt (HMA) mixes using the outcomes of indirect Tensile Strength (IDT), Semicircular bend (SCB) and rutting resistance; for this, a single PG (64−16) nanomodified asphalt binder with 5 % SiO2 and TiO2 have been investigated through a series of laboratory tests, including: Resilient modulus, Creep compliance, and tensile strength, SCB, and Flow Number (FN) to study their potential role of these nanomaterials to improve the rutting characteristics and fatigue life of wearing asphalt mixture at different temperatures. The outcome of this study revealed the positive role of these materials in enhancing mixture IDT characteristics, fracture energy, and viscoelastic deformation component of crack propagation; on the other hand, at higher temperatures, the modified mixture exhibited a superior performance in reducing the permanent deformation of asphalt mixture with SiO2 followed by TiO2 as compared to neat asphalt mixture.

Physical phenomena during nanoindentation deformation of amorphous glassy polymers

We identify for visco-elasto-plastic (VEP) glassy polymers, physical phenomena during Berkovich nanoindentation, a locally imposed deformation. Live visuals via in situ nanoindentation indicate mainly sink-in during loading, with pile-up after unloading. Scanning Probe Microscopy (SPM) indicates significant volume conserving upflow below the tip, for these high ν, compliant materials, with compliance correlated high geometric fractional contact, hcΔhmΔ∼0.86−0.95. We adapt the ideal conical indentation framework to VEP Berkovich nanoindentation, to calculate the contact area and visually depict the upflow and the displacement paths, in the material. The combination of SPM and P−h data, indicates a mixed comparison with uniaxial modulus and yield stress, with conventionally defined hardness, H<3σy, and nanoindentation modulus, EN>E. By rationally removing viscoelastic (VE) effects from the loading P−h data, we find instant, zero-time hardness HL0>3σy. We apply the power law model to only the recovery onset, to estimate pure elastic recovery. We then deconvolute the VEP nanoindentation into the conventional EP (elasto-plastic) and elastic contributions, isolating the VE component. Constraint-induced sink-in, pile-up and VE recovery of the highly yielded tip-apex region, mirror the converse constrained deformation effects, governing the trends in the conventional EP EN and HL0 estimates for glassy polymers.

Multiscale modeling for viscoelasticity of woven CFRP considering preforming and curing effects via finite element and long-short term memory analysis

The constitutional model is crucial to model the complex response of woven carbon fiber reinforced plastics (CFRPs) during curing. This study developed a multiscale modeling method to describe the viscoelastic behavior of preformed woven CFRP parts during curing. The essence of the viscoelastic modeling lies in the stiffness matrix, which was predicted via the long-short term memory (LSTM) model. A library of viscoelastic stiffness components for the LSTM model was created through finite element method (FEM) on mesoscopic representation volume elements (RVEs). Specifically, FEM models for RVEs with different configurations were established first, and then utilized for virtual relaxation tests to build the stiffness component library for the woven CFRP. Afterwards, the LSTM model was embedded into the material model for FEM at the part-level. Finally, the prediction accuracy of the multiscale modeling method for viscoelasticity of the woven CFRP samples was validated by experiments with the average error of 6.62%.

Lightweight silicon and glass composites with submicron viscoelastic interlayers and unconventional combinations of stiffness and damping

The necessity of stiff structural materials with advanced damping characteristics has arisen naturally along with the technological evolution. However, despite ever-growing demand, the achievement of stiff materials with high damping factor remains challenging because of the antagonistic nature of the two properties. Here, this challenge is accomplished by exploiting the non-affine deformation of laminated composites paired with the dissipative nature of the viscoelastic phase. Guided by a finite element design analysis, composites with flat submillimeter stiff layers and submicron viscoelastic interlayers are fabricated. The viscoelastic component consists of a prudently chemically architectured comb-like polydimethylsiloxane (PDMS) elastomer that properly adheres to the stiff silicon or glass layers, strong enough to withstand repeated dynamic cycles. The composites are fabricated using an unconventional but simple stacking route based on the diffusion of a platinum catalyst precursor into a reactive solvent-free PDMS melt. The fabricated composites, Si/PDMS and glass/PDMS, exhibit an elastic modulus higher than common monolithic glass, they are as light as glass but have about four orders of magnitude higher loss factor. The composites markedly outperform numerous customary materials, they escape the Ashby limit for mechanical damping – stiffness trade-off, and their exceptional combinations of properties are maintained over a broad range of temperatures and frequencies.

Thermomechanical EBM‐based modeling of time‐dependent creep behavior in semicrystalline polymers: Competitive viscoelastic impact of amorphous and crystalline sections

AbstractIn this study, the creep behavior of semicrystalline polymers was investigated based on time‐dependent thermomechanical characteristics of the amorphous and crystalline sections. To this end, different equivalent box models (EBMs) with simple or complex structures were designed to interconnect the system components and cover all of their likely interactions. To induce time‐dependency to the model, a variety of viscoelastic models (e.g., Maxwell, Kelvin–Voigt, Maxwell representation of standard linear viscoelastic [SLV] model, Kelvin representation of SLV model, Burger and developed Bingham–Norton) were incorporated with the EBM structures as its crystalline/amorphous components. A specific strategy was devised in order to separately indicate the particular effects of crystalline and amorphous sections along with stress concentration on the temperature‐dependent creep behavior of the system. This approach combined with validating the theoretical data against the creep test results, performed at 20, 40, and 60°C, helped to indicate the most efficient structure for EBM and the best applicable viscoelastic model component. Accordingly, based on the findings of the present study, it was revealed that the series arrangement of the amorphous and crystalline model components, represented by the Burger viscoelastic model, could provide the best predictions regarding the temperature‐dependent creep in semicrystalline polymers.Highlights Creep behavior of semicrystalline polymers at different temperatures. Representing the crystalline and amorphous sections using viscoelastic models. Evaluating different interactions in the semicrystalline polymers using EBMs. Comparison of the efficiency of different viscoelastic model components in EBM. Distinct impact of crystalline and amorphous sections on the system properties.

Improving the prediction of turbulent kinetic energy for drag reduction in turbulent viscoelastic pipe flow

Reducing turbulence in pipe flows using polymer additives is crucial for industrial applications like crude oil, water, and sewage transportation. While previous research has accurately predicted friction factor and velocity profiles, none has fully understood turbulent kinetic energy (TKE) behavior in such fluids. Authors are now focusing on exploring turbulence models to better understand the TKE behavior. In this research, we have introduced a model to improve the behavior of TKE in a modified generalized Newtonian fluid (GNF). The developed model aims to simulate the viscoelastic effects of fluids that result in drag reduction in turbulent pipe flow. The work is noteworthy as it integrates turbulence and viscoelastic components, offering a comprehensive understanding of the phenomenon. By incorporating the rheological properties of viscoelastic fluids and replacing the damping function with a non-Newtonian alternative proposed by Cruz and Pinho, the Launder–Sharma k–ε turbulence model is now suitable for simulating dilute non-Newtonian viscoelastic fluids. The viscoelastic aspect of the model employs the modified GNF model. The developed model has been subjected to simulations using the computational fluid dynamics software. The results obtained for fluid TKE demonstrate a significant improvement in comparison to our previous research and the findings of other researchers. Furthermore, the model's prediction for the Darcy friction factor has been enhanced, resulting in an average error of only 3.71% in this section. It is noteworthy that the model consistently maintains a high level of accuracy in predicting other essential flow parameters such as mean axial velocity and Reynolds stresses. The provided model advances our understanding of viscoelastic fluid behavior in turbulent pipe flow by applying the modified GNF model.

Human Gastric Organoid-Derived Mucus Shares Key Properties with Native Gastric Mucus and Inhibits Motility of Helicobacter pylori

To prevent and treat gastric disease caused by Helicobacter pylori, it is crucial to understand the role of the stomach’s first line of defense: the gastric mucus layer. Gastric mucus is a complex hydrogel that has been studied extensively in animal models, and multiple groups have collected and purified porcine gastric mucus to yield pure solutions of mucin proteins. However, purified mucin—the functional viscoelastic component of mucus—cannot accurately recapitulate the molecular complexity of mucus in its entirety since it lacks salts, lipids, electrolytes, and other proteins. Additionally, access to human samples for functional analyses remains a critical barrier to mucus research. Therefore, the objective of this study was to engineer sterile human gastric mucus in vitro to evaluate its translational potential to native mucus (NM), for further study of interactions between mucus and H. pylori bacteria. In vivo, H. pylori use flagellar motility to traverse the mucus layer and colonize the underlying epithelium. We hypothesize that the microarchitecture and gel-forming capacity of our lab-grown mucus (LGM) significantly restrict H. pylori motility. Inspired by previous studies, we developed and optimized a protocol for the in vitro production of sterile LGM using epithelial monolayers derived from human gastric organoids and cultured at an air-liquid interface. This mucus could be easily harvested and did not require purification or processing. Additionally, mucus production was maintained for over one month, demonstrating the robustness of our culture system. Mass spectrometry and size exclusion chromatography revealed that the LGM has a molecular composition similar to that of native mucus. Further, we have confirmed with cryo-scanning electron microscopy that the LGM has a characteristic honeycomb structure with similar pore size distributions to those found in native mucus. Rheometric frequency sweeps demonstrated comparable, predominantly elastic gel behavior in both LGM and NM samples. Acid flow experiments in a 2D Hele Shaw cell have also demonstrated that LGM enables viscous fingering—a previously studied hydrodynamic phenomenon typical of mucus gels that is thought to be involved in gastric acid transport mechanisms in vivo. Finally, live imaging and particle tracking were used to quantify the motility of H. pylori in the LGM. Compared to liquid media, the LGM caused a significant decrease in H. pylori swimming speed. Overall, our human gastric lab-grown mucus recapitulates key functions of native mucus and will enable future investigations into gastric mucus pathophysiology and H. pylori infection. NIH Grants: R01 GM131408-01 &amp; UL1 TR002319. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Comparative analysis of ventricular stiffness across species.

Investigating ventricular diastolic properties is crucial for understanding the physiological cardiac functions in organisms and unraveling the pathological mechanisms of cardiovascular disorders. Ventricular stiffness, a fundamental parameter that defines ventricular diastolic functions in chordates, is typically analyzed using the end-diastolic pressure-volume relationship (EDPVR). However, comparing ventricular stiffness accurately across chambers of varying maximum volume capacities has been a long-standing challenge. As one of the solutions to this problem, we propose calculating a relative ventricular stiffness index by applying an exponential approximation formula to the EDPVR plot data of the relationship between ventricular pressure and values of normalized ventricular volume by the ventricular weight. This article reviews the potential, utility, and limitations of using normalized EDPVR analysis in recent studies. Herein, we measured and ranked ventricular stiffness in differently sized and shaped chambers using exvivo ventricular pressure-volume analysis data from four animals: Wistar rats, red-eared slider turtles, masu salmon, and cherry salmon. Furthermore, we have discussed the mechanical effects of intracellular and extracellular viscoelastic components, Titin (Connectin) filaments, collagens, physiological sarcomere length, and other factors that govern ventricular stiffness. Our review provides insights into the comparison of ventricular stiffness in different-sized ventricles between heterologous and homologous species, including non-model organisms.

Experiment, Simulation, and Theoretical Investigation of a New Type of Interlayer Connections Enhanced Viscoelastic Damper

A conventional plate-type viscoelastic damper (VED) can easily crack at the interfaces of steel plates and viscoelastic components. In the present work, grooved VEDs, which are a new type of interfacial enhanced VEDs with interfacial grooves, are designed to improve the damping capacity and anti-cracking ability of conventional dampers. The dynamic property experiments of the normal and grooved VEDs are carried out and the interfacial cracking failure of the VEDs are simulated and analyzed by using bilayer cohesive constitutive model with ABAQUS. The grooved VED exhibits excellent dynamic performance and energy dissipation capacity at different temperatures, frequencies, and displacement amplitudes. Experiments and finite element analysis prove that the energy dissipation performance and interfacial bonding strength of the grooved VED are effectively improved. A modified fractional standard linear solid model, in which the Payne effect and temperature–frequency equivalent principle are combined and implemented, is proposed. This model can portray the influence of the excitation displacement, surrounding temperature and external excitation frequency on damper properties at the same time. The fillers and molecular chains affections at micro- and meso-scale are also taken into account. The model’s numerical calculations and experimental results comparisons present that the modified fractional standard linear solid model has sufficient accuracy and performs well in depicting the dynamic properties of the interfacial grooved VED. The errors between the theoretical and experimental values of [Formula: see text] and [Formula: see text] for the grooved VED are mostly within 20% at representative conditions. The interfacial groove structures can well enhance the interfacial bonding and improve the service life of conventional dampers. The modified fractional standard linear solid model is simple and has clear physical meanings for each macro/micro parameters, making it convenient for application in engineering practice. The present research is of great significance in improving the work stability of VEDs and promoting the application of viscoelastic damping technology.

Effect of temperature on dynamic and steady-state shear rheological properties of Jambolan (Syzygium cumini) pulp

Jambolan is an exotic fruit rich in phenolic compounds with many health benefits. The study of fruit's rheological properties plays key roles in its industrial processing and obtainment of products. The present work evaluated the time-dependent and steady-state shear rheological properties of Jambolan pulp at several temperatures. The Jambolan pulp presented thixotropy as a time-dependent property and also showed shear thinning behaviour with yield stress in the steady shear measurements. The Figoni-Shoemaker and Hershel-Buckley models adequately described both the product rheological phenomena. During the oscillatory analysis, the pulp showed some viscoelastic properties, increasing when the oscillatory frequency (ω) increased. All previous parameters also verified the impact of the temperature. The increment in temperature resulted in a reduction in consistency levels. In the temperature range studied, the viscoelastic solid component presented higher values than the viscous component. The thixotropic phenomenon and the presence of the yield stress can be related to this. Viscoelastic moduli decreased with the increase in temperature. When relevant, the Arrhenius’ Activation Energy of some model parameters were calculated. The data obtained are applicable for future studies, to improve industrial process design, and to evaluate food properties.

Numerical study of electrically conducting MHD fluids in a vertical channel with Jeffrey fluid flow and first order chemical reaction

This research paper explores the influence of first order chemical reaction on sustainable properties of electrically conducting magnetohydrodynamic (MHD) fluids in a vertical channel with the unique characteristics of Jeffrey fluid flow. The mathematical model of MHD flow with Jeffrey fluid and chemical reaction incorporates the impacts of viscous dissipation, Joule heating and a non-Newtonian fluid model with viscoelastic properties in the flow regions. The governing equations of the flow field were solved using finite difference method and impacts of flow parameters on the flow characteristics are discussed numerically using graphical representation. It’s revealed that increasing Jeffrey parameter results to decline in the velocity field profiles. Also, species concentration field profiles decline with higher values of destruction chemical reaction parameter. The findings of this study have significant implications in various engineering applications, including energy generation, aerospace engineering, and materials processing. Additionally, the inclusion of Jeffrey fluid flow introduces a viscoelastic component, enhancing the complexity of the fluid dynamics.

Estimating intracranial parameters using an inverse mathematical model with viscoelastic elements that closely predicts complex ICP morphologies

The quantitative relationship between arterial blood pressure (ABP) and intracranial pressure (ICP) waveforms has not been adequately explained. We hypothesized that the ICP waveform results from interferences between propagating and reflected pressure waves occurring in the cranium following the initiating arterial waveform. To demonstrate cranial effects on interferences between waves and generation of an ICP waveform morphology, we modified our previously reported mathematical model to include viscoelastic elements that affect propagation velocity. Using patient data, we implemented an inverse model methodology to generate simulated ICP waveforms in response to given ABP waveforms. We used an open database of traumatic brain injury patients and studied 65 pairs of ICP and ABP waveforms from 13 patients (five pairs from each). Incorporating viscoelastic elements into the model resulted in model-generated ICP waveforms that very closely resembled the measured waveforms with a 16-fold increase in similarity index relative to the model with only pure elasticity elements. The mean similarity index for the pure elasticity model was 0.06 ± 0.12 SD, compared to 0.96 ± 0.28 SD for the model with viscoelastic components. The normalized root mean squared error (NRMSE) improved substantially for the model with viscoelastic elements compared to the model with pure elastic elements (NRMSE of 2.09% ± 0.62 vs. 15.2% ± 4.8, respectively). The ability of the model to generate complex ICP waveforms indicates that the model may indeed reflect intracranial dynamics. Our results suggest that the model may allow the estimation of intracranial biomechanical parameters with potential clinical significance. It represents a first step in the estimation of inaccessible intracranial parameters.

A new method to characterize the nonlinear magneto-viscoelasticity behavior of magneto-active elastomers under large amplitude oscillatory axial (LAOA) loading

The nonlinear viscoelasticity of magneto-active elastomers (MAEs) under large amplitude oscillatory shear (LAOS) loading has been extensively characterized. A reliable and effective methodology, however, is lacking for such characterizations under large amplitude oscillatory axial (LAOA) loading. This is partly due to complexities associated with experimental compression mode characterizations of MAEs and in-part due to their asymmetric stress–strain behavior leading to different elastic moduli during extension and compression. This study proposes a set of new nonlinear measures to characterize nonlinear and asymmetric behavior of MAEs subject to LAOA loading. These include differential large/zero strain moduli and large/zero strain-rate viscosity, which could also facilitate physical interpretations of the inter- and intra-cycle nonlinearities observed in asymmetric and hysteretic stress–strain responses. The compression mode stress–strain behavior of MAEs was experimentally characterized under different magnitudes of axial strain (0.025 to 0.20), strain rate (frequency up to 30 Hz) and magnetic flux density (0 to 750mT). The measured stress–strain responses were decomposed into elastic, viscous and viscoelastic stress components using Chebyshev polynomials and Fourier series. The stress decomposition based on Chebyshev polynomials permitted determination of equivalent nonlinear elastic and viscous stress components, upon which the proposed measures were obtained. An equivalent set of Fourier coefficients was also obtained for estimating equivalent elastic/viscous stress, thereby facilitating faster calculation of the proposed material measures. The proposed methodology is considered to serve as an effective tool for deriving constitutive models for describing nonlinear and asymmetric characteristics of MAEs.

Evaluating a polymicrobial biofilm model for structural components by co-culturing Komagataeibacter hansenii produced bacterial cellulose with Pseudomonas aeruginosa PAO1

A polymicrobial biofilm model of Komagataeibacter hansenii and Pseudomonas aeruginosa was developed to understand whether a pre-existing matrix affects the ability of another species to build a biofilm. P. aeruginosa was inoculated onto the preformed K. hansenii biofilm consisting of a cellulose matrix. P. aeruginosa PAO1 colonized and infiltrated the K. hansenii bacterial cellulose biofilm (BC), as indicated by the presence of cells at 19 μm depth in the translucent hydrogel matrix. Bacterial cell density increased along the imaged depth of the biofilm (17-19 μm). On day 5, the average bacterial count across sections was 67 ± 4 % P. aeruginosa PAO1 and 33 ± 6 % K. hansenii. Biophysical characterization of the biofilm indicated that colonization by P. aeruginosa modified the biophysical properties of the BC matrix, which inlcuded increased density, heterogeneity, degradation temperature and thermal stability, and reduced crystallinity, swelling ability and moisture content. This further indicates colonization of the biofilm by P. aeruginosa. While eDNA fibres - a key viscoelastic component of P. aeruginosa biofilm - were present on the surface of the co-cultured biofilm on day 1, their abundance decreased over time, and by day 5, no eDNA was observed, either on the surface or within the matrix. P. aeruginosa-colonized biofilm devoid of eDNA retained its mechanical properties. The observations demonstrate that a pre-existing biofilm scaffold of K. hansenii inhibits P. aeruginosa PAO1 eDNA production and suggest that eDNA production is a response by P. aeruginosa to the viscoelastic properties of its environment.

Analysis of energy dissipation in non-linear viscoelastic beam in skew bending

This paper deals with the problem of analyzing the energy dissipation in a non-linear viscoelastic beam structural component made of a functionally graded material. The beam is in skew bending. The viscoelastic model used for dealing with the beam mechanical behaviour is set-up by combining of linear as well as non-linear springs and dashpots. The viscoelastic model is under strains which change in time on sinusoidal law. The material properties of the viscoelastic model are distributed smoothly along the thickness of the beam structure. The energy dissipation in the beam is due to dashpots which are parts of the viscoelastic model. Therefore, the strain energy dissipation density is derived by analyzing the stresses and strains in the dashpots. Then the strain energy dissipation density is integrated in the volume of the beam in order to obtain solution of the dissipated energy. The solution is applied for investigating the change of the dissipated energy due to variation of the properties of the model and the loading conditions of the beam.

DESIGN OF VISCO-ELASTIC SUPPORTS FOR TIMOSHENKO CANTILEVER BEAMS

The appropriate design of supports, upon which beams are usually placed as structural components in many engineering scenarios, has substantial significance in terms of both structural efficacy and cost factors. When beams experience various dynamic vibration effects, it is crucial to contemplate appropriate support systems that will effectively adapt to these vibrations. The present work investigates the most suitable support configuration for a cantilever beam, including viscoelastic supports across different vibration modes. Within this particular framework, a cantilever beam is simulated using beam finite elements. The beam is positioned on viscoelastic supports, which are represented by simple springs and damping elements. These supports are then included in the overall structural model. The equation of motion for the beam is first formulated in the temporal domain and then converted to the frequency domain via the use of the Fourier Transform. The basic equations used in the frequency domain are utilized to establish the dynamic characteristics of the beam by means of transfer functions. The determination of the ideal stiffness and damping coefficients of the viscoelastic components is achieved by minimizing the absolute acceleration at the free end of the beam. In order to minimize the objective function associated with acceleration, the nonlinear equations derived from Lagrange multipliers are solved using a gradient-based technique. The governing equations of the approach need partial derivatives with respect to design variables. Consequently, analytical derivative equations are formulated for both the stiffness and damping parameters. The present work introduces a concurrent optimization approach for both stiffness and damping. Passive constraints are established inside the optimization problem to impose restrictions on the lower and higher boundaries of the stiffness and damping coefficients. On the other hand, active constraints are used to ascertain the specific values of the overall stiffness and damping coefficients. The efficacy of the established approach in estimating the ideal spring and damping coefficients of viscoelastic supports and its ability to provide optimal support solutions for various vibration modes have been shown via comparative experiments with prior research.

A Novel Viscoelastic-Friction Model for the Multiphase Hysteretic Behavior of Aluminum Foam/Polyurethane Interpenetrating Phase Composite Damper

An aluminum foam/polyurethane interpenetrating phase composite damper (AF/ PUCD) can perform multi-functional energy dissipation to address different seismic hazards due to its multiphase hysteretic behavior. To improve the design of AF/PUCDs in engineering structures, a highly effective model based on the real deformation of an AF/PUCD is needed to describe its multiphase hysteretic behavior. In this paper, a novel viscoelastic-friction model composed of a viscoelastic component and a friction component is constructed. The hysteretic responses in each phase under various external excitations are described through the different combinations of the viscoelastic component and friction component. The unknown model parameters are identified through the Universal Global Algorithm (UGO). The model results are compared with the experimental results and the results from the Modified Bouc–Wen model and Optimum model. The comparative results show that the viscoelastic-friction model has a higher accuracy in capturing the multiphase hysteresis of AF/PUCD and predicting the boundary of each phase when the AF/PUCD is subjected to various cyclic excitations. Therefore, the viscoelastic-friction model is a good candidate for the design of AF/PUCDs applied in vibration control structures.

Experimental and analytical study of a seismic energy dissipation device made of butterfly-shaped steel plates and viscoelastic pads

This paper presents the seismic performance of a new hybrid seismic damper combining a metallic and viscoelastic damper. Two damper specimens with different configurations were tested under cyclic loading to investigate their hysteretic response to increasing loading. A curve-fitting procedure based on genetic algorithm was developed to make an analytical model for viscoelastic dampers based on the test results, and the analytical model of the hybrid damper was constructed by combining the individual models of the metallic-yielding damper and the viscoelastic damper. Both hybrid damper configurations exhibited a high energy dissipation capacity due to the complementary behavior of their components at different loading displacements. The viscoelastic component showed a relatively higher energy-dissipation capacity but a lower strength at small displacements. In comparison, the butterfly-shaped metallic yielding component exhibited a lower energy-dissipation capacity but higher strength at the same displacement. Conversely, the opposite was true at large displacements. The effectiveness of the damper was further investigated by retrofitting a four-story case study structure. Based on the test and the analysis results, it was concluded that the proposed hybrid damper has the potential to enhance the seismic performance of structures by increasing their strength and energy dissipation capacity, and that the developed analytical model turned out to simulate the nonlinear behavior of the damper adequately.