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Hydra has a tubular bilayered epithelial body column with a dome-shaped head on one end and a foot on the other. Hydra lacks a permanent mouth: its head epithelium is sealed. Upon neuronal activation, a mouth opens at the apex of the head which can exceed the body column diameter in seconds, allowing Hydra to ingest prey larger than itself. While the kinematics of mouth opening are well characterized, the underlying mechanism is unknown. We show that Hydra mouth opening is generated by independent local contractions that require tissue-level coordination. We model the head epithelium as an active viscoelastic nonlinear spring network. The model reproduces the size, timescale and symmetry of mouth opening. It shows that radial contractions, travelling inwards from the outer boundary of the head, pull the mouth open. Nonlinear elasticity makes mouth opening larger and faster, contrary to expectations. The model correctly predicts changes in mouth shape in response to external forces. By generating innervated : nerve-free chimera in experiments and simulations, we show that nearest-neighbour mechanical signalling suffices to coordinate mouth opening. Hydra mouth opening shows that in the absence of long-range chemical or neuronal signals, short-range mechanical coupling is sufficient to produce long-range order in tissue deformations.

[Abstract]: The use of adhesives in the marine sector is rather limited at the time being, but their use in specific areas of the ship would be an advantage due, among other things, to their low weight and low stress concentration along the bonding joint. The aim of this work is to predict the long-term behaviour of the material, as this is a critical factor when using adhesive as a bonding method in ships, since its durability must be guaranteed throughout a previously defined life cycle. This can be predicted by applying the time–temperature superposition principle (TTS), which involves carrying out a test at different temperatures for each specimen, considerably reducing the test time. Two types of experiments have been carried out according with operation modes in dynamic mechanical analysis (DMA): a dynamic frequency sweep and a stationary creep test under constant stress, to check the behaviour of the adhesive under both dynamic and sustained loading. The master curve for the frequency study will be constructed in such a way as to cover the whole range of relevant vibrations that can occur on the vessel, while that for the creep test the curve obtained covers a range of 25 years, which is usually used as the minimum service life in shipbuilding. For both, a temperature range from room temperature to the maximum operating temperature of the material established by the manufacturer shall be studied.

A macroscopic constitutive model, the Porous Eindhoven Glass Polymer (Porous EGP) model, is presented to describe the deformation behavior of cavitated rubber toughened polymers under multiaxial loading conditions. It is shown that the proposed macroscopic constitutive model is able to describe the non-linear pre-yield regime, strain rate dependence, post-yield behavior (strain softening and hardening) and void evolution for loading conditions ranging from shear to equi-triaxial (pure triaxial) tension and compression. The Porous EGP model is a combination of a well established non-linear viscoelastic viscoplastic model, the Eindhoven Glassy Polymer (EGP) model, and the modified Gurson model. The Gurson model is adopted to determine the equivalent stress and plastic rate of deformation tensor making it depending on the void volume fraction, deviatoric and hydrostatic stress. The macroscopic constitutive model is developed based on the response of realistic 3D representative volume elements (RVEs) containing randomly positioned mono-disperse inclusions. The constitutive behavior of the matrix phase in this full-field model is described by the EGP model, and the cavitated inclusions are idealized as voids. Their response is studied for a range of void volume fractions, multiaxial loading conditions, strain rates and thermodynamic states. The yield behavior of the heterogeneous material depends non-linearly on the macroscopic hydrostatic stress. This response is well captured with the proposed macroscopic constitutive model.

Sustainability has become a paramount concern in modern research, aligning with global efforts to reduce carbon emissions and embrace circular economy principles. The mentioned imperative extends to the field of pavement engineering, where the widening of existing pavements, a common practice to accommodate increasing traffic demands, necessitates sustainable solutions. The current thesis addresses the pressing need for pavement engineering practices that align with ambitious sustainability goals while ensuring structural integrity and performance. Drawing upon the context of countries like the Netherlands, striving for zero carbon emissions and full circularity by 2030, the research explores avenues for sustainable pavement widening. This involves optimizing designs to minimize material usage, reduce emissions, incorporate recyclable materials, and extend the lifespan of road infrastructure. The challenges posed by non-uniform settlements and stress concentrations at widening joints are investigated, highlighting the importance of accurate material modelling and interface characterization. Motivated by the need for sustainable pavement solutions, the research aims to guide decision-making in pavement design towards environmental sustainability while meeting functional requirements. The scope encompasses FEM models, EVP behaviour of asphalt surfaces, base layer variations, interface modelling, and comparative analyses between 2D and 3D models. The current study undertakes a thorough examination of the implications of pavement widening on stress concentrations, material behaviour, and interface modelling, aiming for development of more sustainable and resilient pavement designs. Employing a comprehensive research framework encompassing theoretical modelling and numerical simulations, the study seeks to elucidate the issues inherent in widened pavement structures. The main thesis objective is the development of an elasto-visco, Civil Engineering

High density polyethylene (HDPE) can show viscoelastic-viscoplastic behaviors under monotonic loads and a stress softening after reloading under cyclic ones. This sets a challenge in simultaneously representing such response in material constitutive models. In addition, due to the adoption of novel accelerated tests at higher temperatures, e.g., 95 degrees C, the need for a higher temperature calibration is motivated. Therefore, the objective of this study is threefold: (i) to investigate the capability of the three network viscoplastic (TNV) model in capturing HDPE thermo-viscoplasticity under monotonic and cyclic loads, (ii) to report observations on HDPE at various strain-rates and temperatures from 23 degrees C to 95 degrees C including the alpha-relaxation region (iii) to explore the ratcheting behavior of HDPE, i.e., cyclic creep. The FEA analysis based on the calibrated TNV model was successfully able to predict the HDPE behavior under static, quasi-static and dynamic loads. The predicted strain range Delta epsilon and midrange strain epsilon s of the cyclic creep showed good agreements. This implies that the TNV model can be a reliable candidate for HDPE engineering assessments. Findings of this work will have many industrial applications, e.g., products manufacturers or resin producers, in which HDPE is used under complex loads. Similar procedures can be followed for other thermoplastics which lays the basis for establishing a standard calibration guideline., QC 20230214

Peristaltic pump technology is widely used wherever relatively low, highly-accurately dosed volumetric flow rates are required and where fluid contamination must be excluded. Thus, typical fields of application include food, pharmaceutical, medical technology and analytics. In certain cases, when applied in conjunction with polymer-based tubing material, supplied peristaltic flow rates are reported to deviate from expected set flow rates relevantly. Said deviations are related to i) chosen tube material, ii) total over all time of the pump cycles exerted on applied polymer tubes and iii) applied frequency of pump revolutions. This work presents a fast, dynamic, 2D Multiphysics simulation method, which significantly reduces the considered deviations by serving as the basis for elaborating an a priori operational setpoint correction. The numerical solver encompasses laminar fluid dynamics, geometric restrictions provided by peristaltic pump operation, as well as viscoelastic tube material properties and tube material fatigue effects. Within this work, a considerable variety of validation experiments and application examples of the novel methodology will be presented.

As an environmental-friendly material with eligible mechanical properties, FFRP (Flax Fiber Reinforced Polymer) composites are being widely studied and used in the construction industry. This paper presents an investigation of the effect of environmental humidity on the viscoelastic properties of FFRP. Frequency sweep tests are conducted, and results are re-organized by the Time-Temperature Superposition Principle (TTSP). The Huet-Sayegh viscoelastic model is introduced to describe the relationship between viscoelastic properties and loading frequency. The fractional derivative is applied to the model for more accurate results. It is found both storage modulus and loss modulus decrease with the increase of relative humidity. However, the loss factor does not have a monotonical correlation with the relative humidity of the environment. In general, it can be concluded both the capacity of FFRP to store and dissipate the energy decreases over the hygroscopicity absorption in the air, but there is no specific relationship between the amount of their reduction.

Every moment of every day, at least hundreds of thousands of tires roll across a surface throughout the world. Tires are indisputably important in our daily life. The tire's primary component is rubber, which consumes energy when it rotates on a substrate due to the viscoelastic material's internal friction: a phenomenon referred to as rolling resistance. The interaction between the tire and the road surface is one of the most intricate and crucial phenomena in an automobile, because it is responsible for creating forces, moments, and deformation in the tire. Additionally, the road's roughness interacts with the tire and contributes significantly to its performance. This dissertation aims to develop a comprehensive physics-based model for predicting the rolling resistance of a viscoelastic material due to dynamic deformations caused by tire rotation using an analytical approach. The model was developed by proposing a Gaussian wave function propagating across a tire circumference's viscoelastic medium. The wave function was selected to describe the displacement field produced by tire-road interaction. Additionally, by adopting a multi-scale modeling technique, the model was upgraded to estimate rolling resistance while taking into account surface roughness at all length scales, from macroscopic to microscopic. Additionally, another mathematical model was developed using the Fourier series approach to evaluate the steady-state stress response and energy dissipation for any harmonic and non-harmonic periodic strain signals. Additionally, the dissertation strove to build a continuum damage mathematical model using a combined testing/modeling methodology to predict the aging of Styrene-Butadiene Rubber (SBR) after continuous exposure to the atmosphere. The obtained model was developed through the implementation of optimization techniques while formulating a mathematical model, which was then combined with a physics-based model to predict rolling resistance while taking i

The increase of new and ever more stringent emission legislation has brought about with it a surge in the demand for more sustainable automotive solutions. This has particularly been the case for automobiles, including heavy-duty vehicles like trucks and buses, with internal combustion engines, which now require the design and manufacturing of more durable and reliable components. An important component of internal combustion engine automobiles, which helps achieve this target, is the exhaust after-treatment system. Exhaust after-treatment systems are usually equipped with some type of catalytic converter, treating the combustion gases from the engine exhaust manifold to reduce the concentration of pollutants. The catalytic converter assembly usually consists of an assembly of an outer metallic canning, an inner substrate and a packaging mat in between the two. The packaging mat, commonly known as the support mat, is an important component in the assembly, protecting the ceramic substrate from road induced and thermal loads, thereby preventing any damage to the latter. This thesis involves further development of a finite element model for the support mat that could be used in catalytic converter simulations with a reasonable degree of accuracy and reliability. In line with this objective, the characteristic mechanical response of the mat is first studied through a series of material tests: namely compression, friction, and shear tests. Different non-linear material models like hyperfoam, hyperelastic and viscoelastic models, are then created in ABAQUS to simulate the mat behaviour in the tests. The material model correlating most closely with the test is then implemented in the simulation of the assembly process, canning of a catalytic converter. This report includes the material tests conducted on the mats in new and aged condition, findings of the characteristic response of the mats in these tests as well as the constitutive material modelling and finite element s

The dynamic behaviour of a novel anisotropic cellular micro-structural geometry derived from the basic symmetric Kelvin cell is discussed for varying relative density. The cells are arranged in a cubic array and the dynamic response is studied in a classical seismic mass setup using beam elements to represent the ligaments of the cell. The eigenfrequencies and the eigenmodes of the cellular array are computed together with forced response simulations where a proportional damping model of the Young's modulus for the cell ligaments is assumed. The frequency dependence of the damping is based on a fractional derivative representation. Using a recently developed inversion method, equivalent, homogenised solid material models of the cellular array are discussed with the associated equivalent elastic properties given in terms of the 21 elastic constants of the Hooke's tensor. For the equivalent solid material models, the eigenfrequencies and eigenmodes are computed, and forced response simulations are performed assuming the same type of proportionality in the damping as the cellular array, for the same seismic mass setup. The correlation, between the eigenfrequencies and the eigenmodes, shows an overall interesting agreement between the cellular and the equivalent solid model for the quite complex deformation shapes observed. The forced response results indicate that the equivalent solid modelling accurately represents the global dynamics of the anisotropic cellular array, but needs to be further refined when local shearing deformation within the individual cells starts to be dominating., QC 20221024

Wormlike micellar solutions possess complex rheology: when exposed to a flow field, the wormlike micelles may orientate, stretch, and break into smaller micelles. Entangled wormlike micellar solutions exhibit shear banding characteristics: macroscopic bands with different local viscosities are organized and stacked along the velocity gradient direction, leading to a non-monotonic flow curve in simple shear. We present a systematic analysis of four commonly used constitutive models that can predict a non-monotonic flow curve and potentially describe the rheology of entangled wormlike micellar solutions with shear-banding characteristics: the Johnson–Segalman, the Giesekus, the thixotropic viscoelastic, and the Vasquez–Cook–McKinley (VCM) models. All four constitutive models contain a stress diffusion term, to account for a smooth transition between the shear bands and ensure a uniqueness of the numerical solution. Initially, the models are fitted to shear and extensional experimental data of a shear-banding wormlike micellar solution. Subsequently, they are employed to solve three non-homogeneous flows: the Poiseuille flow in a planar channel, the flow in a cross-slot geometry, and the flow past a cylinder in a straight channel. Each of these flows exposes the wormlike micellar solution to different flow kinematics (shear, extensional, and mixed), revealing different aspects of its rheological response. The predictive capability of each model is evaluated by directly comparing the numerical results to previously published experimental data obtained from microfluidic devices with corresponding flow configurations. While all the models can describe qualitatively the characteristic features observed experimentally in the benchmark flows, such as plug-like velocity profiles and elastic instabilities, none of them yields a quantitative agreement. Based on the overall performance of the models and also accounting for their differing numerical complexity, we conclude that t, source:https://www.sciencedirect.com/science/article/pii/S0377025722000891

Due to the viscoelastic nature of polymeric matrix, polymer composites exhibit time-dependent degradation in modulus and strength. The former is exhibited as time-dependent increase in strain under constant loading, known as creep. Upon unloading, this viscoelastic strain will recover completely if enough time is allowed. During cyclic loading the time for recovery may not be enough resulting in partial recovery. The effect of this partial recovery on subsequent creep and recovery has hardly been studied in the past and hence is the focus of this thesis. Numerous parameters are known to influence the creep response of viscoelastic materials, namely: the magnitude and rate of application of the load, temperature, creep duration. However, the influence of recovery duration, particularly in the case of cyclic creep loading, is more limited. Hence, the objective of this thesis was to investigate the effect that the recovery duration had on the cyclic creep response of a unidirectional carbon fibre reinforced polymer composite. Utilizing creep durations of 20s and 40s, and recovery durations varying from 1s to 80s, manufactured composite samples were subjected to cyclic creep loading conditions at two stress levels (8 / 0.1 MPa, 12.5 / 0.5 MPa) and four temperatures (room temperature, 80 oC, 120 oC, 180 oC). The maximum recorded strain during creep and recovery durations increased with the number of cycles for a given set of loading conditions and their magnitude decreased with increase in recovery duration for a given cycle. The unrecovered strain and the unrecovered stored energy at the end of each loading cycle increased with the number of cycles but decreased with recovery duration for a given cycle. The test temperature did not alter this effect of creep recovery duration; however, the magnitude of strains (creep, recovered, and unrecovered) increased with increase in test temperature. Similar effect was observed with applied peak load. Based on these results, it ca

Wave attenuation, filtering and guiding is an ongoing topic of scientific research, as there are many opportunities for improvement of existing solutions in modern industry. One of the recent advancements has been made with the use of non-reciprocal metamaterials.Certain properties of metamaterials have made them suitable for use in various engineering fields. In this study, we investigate non-reciprocal wave propagation behavior in coupled thin beams phononics, due to time-modulation of material properties and axial loads. We compare the results for the beams which are interconnected with Winkler’s type of elastic layers and elastic or viscoelastic Pasternak layers. An analytic approach is used to discover directional band gaps and investigate wave propagation through these systems of beams, at relevant excitation frequencies. The proposed framework can be exploited in further analysis of phononic systems based on multiple beams coupled through different mediums and structural elements modeled with higher-order beam theories.

Introducing ionic liquids (ILs) into ultra-high molecular polyethylene (UHMWPE) is a promising approach to improving the processibility of UHMWPE. To have a comprehensive understanding of the role of ILs in affecting the properties and molecular structures of UHWMPE, we conducted a systematic study on the viscoelastic behaviours of UHMWPE/IL composites with various ILs content at room temperature. Stress relaxation tests were performed under constant tensile strain (epsilon(0) = 0.47%). Constant strain-rate tests were also performed at five strain rates over the range of 2 x 10(-3) s(-1) to 1.7 x10(-1) s(-1). To have deeper insights into the phenomena and the structure-property relationship, theoretical modelling based on the generalized Maxwell model was employed to study the time-dependent relaxation modulus. The modelling results suggest decreased elasticity and viscosity by the addition of ILs, indicating weakened bonding and enhanced motions of chain segments. Moreover, experimental yield stresses from the constant strain-rate tests were modelled by the cooperative model, which is based on the Eyring's activation theory and takes the cooperative motion of chain segments into accounts. Analysis of the modelling results also shows that ILs increased the effective volume and decreased the energy barrier required to activate chain motions, confirming the enhanced mobilities of chain segments of UHMWPE by the addition of ILs.

This study examines the failure modeling of materials exhibiting nonlinear behavior and reduced dimension structures using peridynamic (PD) theory. Among the existing PD models, PD constitutive correspondence approach is adopted in the development. PD correspondence approach offers a way to use constitutive equations from classical continuum mechanics by defining a nonlocal deformation gradient tensor. However, using the original definition of deformation gradient leads to spurious oscillations in the solution. This work uses a bond-associated deformation gradient with the peridynamic differential operator to eliminate these oscillations. The numerical modeling assumes the quasi-static loading conditions, and the solution is obtained using the implicit technique with the Intel PARDISO solver using the exact tangent stiffness matrix. PD models are systematically developed for rubber-like materials, polymers exhibiting high stretch, and epoxy adhesives. The force density vectors for rubber materials are derived using the neo-Hookean constitutive equation. The weak form of PD equilibrium is used to impose the boundary conditions directly on the last layer of material points. Stretch-based criterion is used to eliminate interaction during failure simulations. The validity for predicting damage is demonstrated through simulations of experiments concerning progressive damage growth in pre-notched styrene-butadiene rubber sheets. The formulation is then extended for the polymer that can sustain high stretches. Anand’s model and Talamini-Mao-Anand’s model are used to derive force density vectors. The fidelity of this PD model for predicting large deformation, progressive damage, and rupture is established by comparison with experimental measurements of polymer sheets with defects under displacement-controlled tensile loading. To model epoxy adhesives, a viscoelastic material model in the presence of finite deformation is employed to derive the force density vectors. The rel

Tidsberoende effekter, såsom krypning, krympning och stålrelaxation, är ofta svåra att prediktera när det kommer till förspända betongkonstruktioner. Krypning som ett fenomen är komplicerat och förenklas därför i gällande byggnormer (Eurocode), för att underlätta konstruktörens arbete. När det gäller etappvis spännarmerade betongbroar har dessa förenklingar visat sig ge felaktiga prognoser av de tidsberoende effekterna. Syftet med denna uppsats är att modellera dessa effekter i ett kommersiellt Finita Element program och därmed skapa en pålitlig rutin för framtida arbete inom området. En djupgående undersökning gjordes kring olika krypmodeller och hur de kan implementeras. De tillgängliga metoderna i det valda programmet utvärderades med ett enkelt lastfall. En fallstudie av Jiang Jin Bridge, en etappvis spännarmerad betongbro i Chongqing, Kina, genomfördes sedan. Genom att implementera krypmodellen och analysera den valda bron över en tidsperiod på 10 år kunde modellens tillförlitlighet ökas. Tre krypmodeller, tidshärdande, töjningshärdande och en viskoelastisk modell, jämfördes med hur krypning beaktas i den nuvarande byggnormen (Eurocode). Den viskoelastiska modellen valdes som den mest lämpliga, den gav de mest exakta resultaten samtidigt som den var lättare att implementera. Genom att analysera Jiang Jin Bridge med denna modell visades det att den kunde användas för större och mer komplexa konstruktioner. Resultatet av fallstudien stärker tillförlitligheten hos den viskoelastiska krypmodellen. Modellering av bron med skalelement gav en mer exakt beskrivning av nedböjningshistoriken jämfört med när balkelement användes. Beteendet kan dock inte förklaras fullständigt med hjälp av krypmodellen och andra tidsberoende effekter såsom förluster i spännkablar behöver undersökas vidare. En förenklad kalibrering visade att nedböjningshistoriken kunde beskrivas mer exakt genom att ändra de tidsberoende förlusterna för de förspända spännkablarna., Long-term effects, such as creep, shrinkage, and steel relaxation, are often difficult to predict for prestressed concrete structures. Creep as a phenomenon is complicated to describe and is therefore simplified in the current building standards, to better accommodate the designer. When dealing with segmentally constructed prestressed concrete bridges, these simplifications have shown to provide inaccurate predictions of the long-term effects. The aim of this Master's Thesis is to model these effects in a commercial Finite Element Analysis (FEA) program and to establish a reliable routine for future work in the area. A thorough investigation of previous work were conducted regarding creep models and how they are implemented. The available methods in the program of choice were evaluated using a simple load case. A case study of the Jiang Jin Bridge, a prestressed concrete box girder bridge in Chongqing, China, was then performed. By implementing the chosen creep model in a long-term analysis for the case study the reliability of the model was increased. Three creep models, time hardening, strain hardening, and a viscoelastic model, was compared to the current building code (Eurocode). The viscoelastic model was chosen to be the most appropriate, as it provided the most accurate results while also being easier to implement. By analysing the Jiang Jin Bridge with this model, it was shown that it could be used for larger and more complex structures. The result of the case study strengthens the reliability of the viscoelastic creep model. Modelling the bridge with shell elements provided a more accurate description of the deflection history, compared to when beam elements were used. The behaviour cannot, however, be fully explained by using the creep model, and other time-dependant losses such as steel relaxation needs to be investigated further. A simplified calibration showed that the deflection history could be more accurately described by modifying the time-dependent, Tidsberoende effekter såsom krypning är svåra att prediktera, och vanligtvis används förenklade metoder vid dimensionering av betongkonstruktioner. Förenklade metoder har dock visat sig vara otillräckliga vid projektering av etappvis spännarmerade betongbroar. Examensarbetet undersöker olika modeller för krypning och hur dessa kan implementeras i numerisk analys. De olika modellerna jämförs och utvärderas inledningsvis i ett mycket renodlat exempel. Vidare används Jiang Jin Bridge som en fallstudie för att utvärdera en viskoelastisk krypmodell. Analysen visar att det är fullt möjligt att modellera långtidseffekter för etappvis efterspända betongbroar. En jämförelse mellan uppmätta och uppskattade deformationer visade dock på viss avvikelse. En kalibrering av tidsberoende förluster i spännarmeringen (stålrelaxation) kunde justera för denna avvikelse.

This document constitutes the user manual for tBeam, standalone software for the analysis of energy dissipation in pavements under moving vehicles. tBeam was developed as part of the improvement of modeling capabilities for environmental life cycle assessment of pavements being conducted by the University of California Pavement Research Center for the California Department of Transportation. tBeam is finite element based, employing multi-layered three-node Timoshenko beam elements resting on a viscoelastic Winkler foundation. It provides an approximation of the deflection bowl of pavements and the energy dissipated in pavement structures when subjected to loads moving at constant velocities. tBeam supports two loading options: a uniform pressure (per unit length) applied to a segment at the center of the beam, and a rolling rigid wheel. To achieve numerical efficiency the load-beam-foundation system is represented relative to a moving coordinate system attached to the moving load. The higher efficiency is made possible because, in this framework, an observer attached to the moving coordinate system perceives a “static” state (i.e., independent of time). The standalone tBeam software serves two purposes. First, to provide developers of pavement LCA tools a “guide” as to how to integrate tBeam technology into their program. To this end, the “main” of tBeam can be used as “guide” for integrating tBeam capabilities within the LCA tool. Second, tBeam capabilities are relevant to pavement research in general. Thus, it could represent a useful addition to the toolset for pavement viscoelastic mechanics.

An earthquake directly affects a structure by increasing the energy within the structural system. A significant portion of this energy can be dissipated by the introduction of structural control systems. Several structural control systems such as passive, active and semi-active control systems are gaining importance nowadays in the earthquake resistant design of structures.  viscous damper (VD) is a type of passive energy dissipation device, which operates on the principle of fluid flow through orifices. This type of damper has found numerous applications in the military and aerospace industry from many years. Recently, in the civil engineering field, high capacity fluid viscous dampers have found commercial applications on buildings and bridges subjected to seismic and/or wind storm inputs. VDs use inertial flows, where oil is forced through small orifices at high speeds, in turn generating high damping force. In the present study, the effectiveness of fluid viscous dampers in reducing the responses of a structure under seismic excitations is evaluated analytically using non-linear time history analysis. A twenty story reinforced concrete structure with square plan is considered in this study. Acceleration time histories of Indian seismic zone III,IV and zone V are used for the analysis. The analysis is carried out using the computer package ETABS 2015. The analysis results confirmed that a significant reduction in the responses such as displacements and other forces is possible with the introduction of fluid viscous dampers and hence it can be used as an alternative to the conventional ductility based design method of earthquake.

We develop a viscoelastic generalization of the elastic Eshelby inclusion solution, where the inclusion and surrounding matrix are two different viscoelastic solids and the inclusion's eigenstrain is a time-periodic oscillatory input. The solution exploits the Correspondence Principle of Linear Viscoelasticity and a Discrete Fourier Transform to efficiently capture the steady-state oscillatory behavior of the 3-D mechanical fields. The approach is illustrated here in the context of the recently-developed in vitro Cell-in-Gel system, where an isolated live cardiomyocyte (the inclusion) is paced to contract periodically within a soft hydrogel (the matrix), for the purpose of studying the effect of mechanical load on biochemical signals that regulate contractility. The addition of viscoelasticity improves the fidelity of our previous elastic Eshelby inclusion analysis of the Cell-in-Gel system by accounting for the time-varying fields and the resulting hysteresis and dissipated mechanical energy. This mathematical model is used to study the parametric sensitivities of the relative stiffness of the inclusion, the inclusion's aspect ratio (slenderness), and the cross-link density of the hydrogel matrix.

The viscoelastic properties of rubber materials are caused by the combination of the dual response as an elastic solid and a viscous fluid. This behavior yields in time-dependent mechanical properties; thus, phenomena such as stress relaxation, creep, energy dissipation, hysteresis, and strain rate are observed. In this study, three different carbon black-reinforced natural rubber compounds were experimentally evaluated under stress relaxation and several linear phenomenological constitutive models were fitted to evaluate their viscoelastic parameters. It was observed that both the elastic and viscous parameters increase in a non-linear relation as the strain and carbon black content increase, and the viscous parameters were dependent on the configuration of the model. The Maxwell and Zener models exhibited fitting values of 76.08 and 95.10%, respectively, while the Wiechert model showed the best fitting values and can be adequately used to estimate the relaxation process of carbon black-reinforced natural rubber applications., Las propiedades viscoelásticas del caucho son debidas a la combinación de la respuesta dual como un sólido elástico y un fluido viscoso. Este comportamiento produce propiedades mecánicas dependientes del tiempo; observando fenómenos como la relajación de esfuerzos, fluencia, disipación de energía, histéresis y tasa de deformación. En este estudio, se evaluaron experimentalmente tres compuestos diferentes de caucho natural reforzado con negro de humo sometidos a relajación de esfuerzos y se ajustaron varios modelos constitutivos fenomenológicos lineales para evaluar sus parámetros viscoelásticos. Se observó que tanto los parámetros elásticos como viscosos aumentan en una relación no lineal a medida que aumenta la deformación y el contenido de negro de humo, y los parámetros viscosos dependen de la configuración del modelo. Los modelos Maxwell y Zener exhibieron valores de ajuste de 76.08 y 95.10% respectivamente, mientras que el modelo de Wiechert mostró los mejores valores de ajuste y puede usarse adecuadamente para estimar el proceso de relajación de las aplicaciones de caucho natural reforzado con negro de humo.

The physiological processes of cells and tissues are regulated not only by biochemical and electrical signaling but also by mechanics. The mechanical microenvironment is involved in the progression of diseases and is one of the key elements in fabricating physiologically relevant 3D tissues. The complexity of biological tissue structure leads to complex mechanical behavior. However, our ability to characterize the mechanical properties of biomaterials is limited due to technical challenges. Mechanosensation of brain cells and the mechanical microenvironment of brain tissue are relevant for healthy functioning, neurodevelopment, neurodegenerative diseases, and regeneration. There are many challenges associated with the mechanical testing of brain tissue such as restricted access to the brain, lack of available material, difficult sample preparation procedures, and preservation of its viability. Furthermore, mechanical testing can be performed at various scales, from single cells to the whole organ and with various mechanical testing modalities. As seen from previous studies, variation of the experimental parameters contribute to the observed variability in mechanical data. Finally, understanding which structural components of tissues and cells give rise to certain mechanical behavior remains an unmet objective. To address above mentioned issues, three objectives were set for this thesis: Objective 1: Develop indentation setup and protocols to measure mechanical properties of the brain slices in a reproducible manner. Novel indentation protocols using ferrule-top indentation device are established in this thesis. Chapter 2 introduces contact mechanics theory. As there are many different models available, general guidelines are given for selecting indentation profiles for soft tissue measurements. Chapter 3 shows experimental observations when indenting on the brain slices such as the influence of the indentation-depth, indentation-speed, oscillatory-ramp, dynamic mech

This study introduces a design procedure for improving an individual’s footwear comfort with body weight index and activity requirements by customized three-dimensional (3D)-printed shoe midsole lattice structure. This method guides the selection of customized 3D-printed fabrications incorporating both physical and geometrical properties that meet user demands. The analysis of the lattice effects on minimizing the stress on plantar pressure was performed by initially creating various shoe midsole lattice structures designed. An appropriate common 3D printable material was selected along with validating its viscoelastic properties using finite element analysis. The lattice structure designs were analyzed under various loading conditions to investigate the suitability of the method in fabricating a customized 3D-printed shoe midsole based on the individual’s specifications using a single material with minimum cost, time, and material use.

To ensure the shelf life of a semiconductor, the integrated circuits are usually embedded in an epoxy molding compound (EMC) to shield it from stress and corrosion. The EMC is a viscoelastic material and is categorized as a thermoset. Working with viscoelastic material appose a challenge due to the cure-induced warpage. Warpage is a deformation that reduces stress resistance and can also make for assembly issues. Being able to predict the warpage accurately is an essential part of the electronics industry. To simulate the warpage, the finite element method is usually used. The Research Institutes of Sweden (RISE) in Piteå, which focuses on composites, have created a solver and corresponding material definition for simulating the curing process of a viscoelastic material. In this thesis, the solver created by RISE was investigated to see how well it could predict the warpage during the curing of an EMC. The investigation consisted of reproducing the simulating conducted by Lin et al. in the article "Modeling and Characterization of Cure-Dependent Viscoelasticityof Molded Underfill in Ultrathin Packages" where the curing of an ultrathin flip-shipChip-Scale Package (fcCSP) was simulated. The result will be reproduced using the simulating program LS-Dyna and both the RISE material definition and an build-in material definition will be simulated to see the difference. From the investigation, we could conclude that although the result from the article was unobtainable, the RISE model could predict the warpage more accurately which shows the importance of the cure shift factor. The investigation also found that the RISE model has some implementation errors for the stress-strain calculations in the RISE model. In conclusion, the RISE model was able to predict the warpage in a desired way, but more studies need to be created to ensure the model’s accuracy for the correct warpage magnitude.

Hospital Acquired Infections and equipment contamination are some of the biggest issues faced by the healthcare industry worldwide. These infections generally range from mild to life threatening human infections which lead to increased costs and prolonged hospitalization time. The primary factor which caused these issues were biofilm forming bacteria which are able to withstand medications and defend themselves from various cleaning procedures. Another aspect which make these bacteria troublesome is that they are able to hide inside the biofilm, thus evading a lot of diagnostic tests. The methods used to detect these biofilms are unfortunately toxic to cells and cannot be used in vivo. Though there is enough data on the formation of biofilm on abiotic surfaces, the data present on the biophysical properties, structural organizations within the biofilm or their viscoelastic properties is very limited. In this master’s degree project, a dynamic monitoring platform is made for 2 different strains of the Salmonella Enteritidis bacteria where their structural and biophysical properties was investigated. Each strain lacks either curli or cellulose which are major components responsible for proper biofilm formation so performing these experiments on them gave us important information on how their properties get affected over time. Bacterial growth monitoring for all the strains were performed by measuring the absorbance every hour over a period of 5h and it was observed that all the strains had a very similar growth pattern until the end of the 4th hour after which they showed very mild differences. The next set of experiments involved using an eQCM to monitor the formation of biofilm on the surface of a quartz chip over 48h. There were differences observed in the biofilm formation pattern and mass deposition which provided clues as to how the biofilm formation and their viscoelastic properties are affected due to the mutations. This led to finding further clues regarding

Decellularized extracellular matrix is a tissue-specific biomaterial that recapitulates the complexity of the inherent tissue environment to elicit cellular response. Here, a multi-material decellularized liver (dLM)-based bioink with gelatin is developed and polyethylene glycol crosslinking is used to enhance the viscoelasticity of the dLM. We evaluated the necessity of a post-printing secondary cross-linker mushroom tyrosinase to improve robustness and long term stability. We further demonstrate it's biocompatibility using liver specific gene analysis of HepG2 cells., Part of ISBN 9781733419031QC 20230614

Dynamic shear modulus and damping ratio of soil serve as indispensable basic data for the seismic design on important engineering projects. It is known that damping is one of the dynamic soil parameters describing the process of inelastic energy loss of a seismic wave traveling through a medium. However, damping is influenced by several mechanisms in soils that are not understood thoroughly to allow sufficient modeling. At small strain levels the material damping is related to the frequency-independent hysteretic damping which appears as hysteresis loop in the stress-strain diagram. The energy dissipated in the material during one cycle of a harmonic oscillation can be calculated by the inside area of this hysteresis loop. Laboratory tests such as low-frequency torsional shear or cyclic triaxial tests make use of the stress-strain behavior and determine the damping ratio directly from this hysteresis loop. Established techniques to determine the material damping ratio are mostly based on the measurement of the spatial decay of surface waves caused by the dissipation of energy (material damping) and the spreading of the wavefronts over an increasing area (geometrical damping). The approach presented considers the fact that geometrical damping has no influence on the phase velocity of body waves and likewise the dispersion curve and therefore apply the multi-channel spectral analysis of seismic downhole data to determine the damping ratio. This approach is based on the work of Meza-Fajardo and Lai, 2007 which showed the possibility of determining material damping ratio spectrum entirely from in situ phase velocity measurements of P- and S-waves. They proposed a model of energy dissipation in soils based on linear viscoelastic material behavior. A distinctive feature of this linear viscoelasticity theory is that the parameters phase velocity, the attenuation coefficient and damping ratio are functions of frequency. The approach is demonstrated on a downhole data set of

In this paper we present a computational model to simulate surface waves on photo-responsive liquid crystal thin films under dynamic illumination. The influence of light attenuation is included to model the dynamic photo-mechanical response as a result of the forward (trans to cis) and the backward (cis to trans) isomerization of the embedded azobenzene molecules. The viscoelastic nature of the liquid crystal films is also estimated and incorporated in this study. The temporal response of the material under static spot illumination is analyzed first to understand the underly- ing mechanisms behind the observed response. The relation between the fraction of transformed molecules and the macroscopic light induced strains and stresses through the thickness is investi- gated to establish the significance of light attenuation. Subsequently, the model liquid crystal film is exposed to a rectangular illumination waveform to simulate a moving light source and thereby generate surface waves. Results are presented that relate the wave attributes, (i.e., the amplitude, frequency and phase lag) to the time scales associated with the moving light source, the molecular trans-cis isomerization reaction and the viscoelastic response of the material. A design guideline for producing surface waves with specific features (amplitude, phase) is presented.

Cervical disc replacement (CDR) is a motion-preserving surgical procedure for treating patients with degenerative disorders. Numerous reports of first generation CDR “ball-and-socket” articulating devices have shown satisfactory clinical results. As a result, CDR devices have been safely implemented in the surgeon's armamentarium on a global scale. However, only minor design improvements have been made over the last few years, as first generation CDRs devices were based on traditional synovial joint arthroplasty designs. As a consequence, these articulating designs have limited resemblance to the complex kinematic behavior of a natural disc. This has driven the development of deformable viscoelastic CDR devices to better mimic the biomechanical behavior of a natural disc. As a result, several viscoelastic CDR devices have been developed in recent years that vary in terms of materials, design and clinical outcomes. Since these viscoelastic CDR devices are fairly new, their weaknesses and strengths, which are related to their design characteristics, have not been well described. Therefore, this literature review discusses design related advantages and disadvantages of deformable viscoelastic CDR devices. As such, this paper can provide insight for surgeons and engineers on specific design characteristics of several viscoelastic devices and could potentially help to develop and design future implants. Eleven viscoelastic CDR devices were identified. An extensive database search on the devices’ tradenames in Medline and PubMed was performed next. The devices were categorized based on common design characteristics to give an overview of both category and device specific complications and advantages. Overall, literature shows that most of these viscoelastic CDR devices can provide motion in all six degrees-of-freedom and have a variable center of rotation. Nevertheless, the viscoelastic materials used do not have an extensive history in orthopedics, so the long-term mater

The use of certain polymers is actively being examined as means to passively reduce the damaging effects of impact loading. With uncertainty of the dynamic environments in which these materials achieve optimal performance, a further investigation is necessary to analyze the dynamic behavior of the viscoelastic material as loading rate varies. This study was conducted using a polymeric Split-Hopkinson pressure bar while using electromagnetic velocity gauges for measuring stress-strain data to obtain material characteristics of the test specimens. Frequency domain characteristics were obtained by fitting a rheological model to test data. Strain-rates observed during the study were on the order of 10^3 1/s. A polymeric Split-Hopkinson pressure bar was used instead of a conventional elastic bar to reduce the impedance mismatch with the test specimens. Electromagnetic velocity gauges were employed to justifiably neglect the dispersion and attenuation effects that accompany the use of viscoelastic bars.

Introduction: A critical step in biomaterial selection effort is the determination of material as well as the biological properties of the target tissue. Previously, the selection of biomaterials and carriers for dental pulp regeneration has been solely based on empirical experience. Methods: In this study, first, the linear, viscoelastic material functions and compressive properties of miniature pig dental pulp were characterized using small-amplitude oscillatory shear and uniaxial compression at a constant rate. They were then compared with the properties of hydrogels (ie, agarose, alginate, and collagen) that are widely used in tissue regeneration. Results: The comparisons of the linear viscoelastic material functions of the native pulp tissue with those of the 3 hydrogels revealed the gel-like behavior of the pulp tissue over a relatively large range of time scales (ie, over the frequency range of 0.1-100 rps). At the constant gelation agent concentration of 2%, the dynamic properties (ie, storage and loss moduli and the tan delta) of the collagen-based gel approached those of the native tissue. Under uniaxial compression, the peak normal stresses and compressive moduli of the agarose gel were similar to those of the native tissue, whereas alginate and collagen exhibited significantly lower compressive properties. Conclusions: The linear viscoelastic and uniaxial compressive properties of the dental pulp tissue reported here should enable the more appropriate selection of biogels for dental pulp regeneration via the better tailoring of gelation agents and their concentrations to better mimic the dynamic and compressive properties of native pulp tissue.

Cellulose nanocrystals (CNCs) reinforced polyvinyl alcohol (PVA)‐based hydrogels with high water content and tunable mechanical properties that can be molded in to any desired shape are presented in this work. Freeze thawing of PVA‐CNC solutions in a mixed solvent system of dimethyl sulfoxide and water enabled to produce a set of physically crosslinked hydrogels with tunable mechanical properties. It was observed that the composition of the solvent altered the mechanical properties and network structure in the hydrogel systems. Differential scanning calorimetry was used to understand the thermal events behind solvent effect on the properties of the hydrogel. Optical microscopy results suggest that these hydrogels possess a macroporous structure. Furthermore, dynamic viscoelastic analysis and axial compression tests have shown that the viscoelastic and mechanical compression properties of the hydrogels improved upon reinforcement with CNC. Overall, the hydrogel enjoys appealing properties as a synthetic biomaterial for soft tissue applications., Title in thesis list of papers: Role of solvent on structure, viscoelasticity and mechanical compressibility in nanocellulose-reinforced poly (vinyl alcohol) hydrogels

Analysis of nonlocal axial vibration in a nanorod is a crucial subject in science and engineering because of its wide applications in nanoelectromechanical systems. The aim of this paper is to show how these vibrations can be modelled within the framework of port-Hamiltonian systems. It turns out that two port-Hamiltonian descriptions in physical variables are possible. The first one is in descriptor form, whereas the second one has a non-local Hamiltonian density. In addition, it is shown that under appropriate boundary conditions these models possess a unique solution which is non-increasing in the corresponding ‘energy’, i.e., the associated infinitesimal generator generates a contraction semigroup on a Hilbert space, whose norm is directly linked to the Hamiltonian.

Airborne Composites Automation recently installed an automation product line that creates flat thermoplastic laminates intended for consumer electronics industry. However, due to the composite nature of the material and the process parameters, the final product is deformed, as a result of internal residual stresses. The purpose of this thesis is to use Finite Element Analysis methods in order to build up digital twins of the composite laminates undergoing the manufacturing process composed by several pressing cycles in order to predict their final warpage. Hence, this work aims at characterizing and predicting the real cause for warpage, offering an opportunity to minimizing it. Since the parameterization of the simulations is automated, this work is a first step towards the use of data-driven methods that enable analysis and design of future laminates under different process parameters.

Cartilage repair remains a major challenge and treatment of osteochondral defects generally results in inferior quality fibrous repair tissue. This study aims to elaborate on the work of Korthagen et al. who developed a thermoplastic polyurethane and polyetherketoneketone implant to treat osteochondral defects. Although promising results were found, Korthagen et al. encountered difficulties binding the neo-tissue to the elastomer part of the implant. The goal of this study is therefore to test potential solutions to improve cell binding properties of the elastomer in vitro, and to optimize the elastomers mechanical properties to mimic native articular cartilage. The newly produced elastomer showed encouraging cell binding properties with multiple cells types. In addition, 3D printing and punching holes in the elastomer part of the implant both have great potential in creating porosity to physically anchor the neo-tissue. The optimal diameter of vertically aligned punched holes was found to be 319 $\mu$m. Not only provides this diameter optimal circumstances for cartilage to grow into, it also optimizes anchoring potential. Besides that, 3D printing efforts were found to be promising in creating both excellent cell facilitating properties as well as mechanical properties mimicking that of native articular cartilage. Both punched and 3D printed elastomer samples were tested for toxicity and immune response. Both tests delivered excellent results and no sign of toxicity or adverse immune response was detected. These results combined with the excellent cell binding properties of the elastomer strengthens our confidence in favorable future in vivo outcomes., Jointsphere, Biomedical Engineering | Tissue Biomechanics and Implants

Every day, roads are submitted to greater stresses. Thereby, additives have been incorporated to asphalt mixtures to enhance pavements performance. The purpose of this experimental study is to characterize for the first time, to date, the viscoelastic properties of asphalt samples modified with recycled rubber —from used vehicles tires— and asphaltite in the same mixture, at different temperatures and frequencies. All with the aim of optimizing the material properties and coming up with a proposal to an environmental issue: discarded vehicles tires and their after-service use. The stiffness of briquettes was analyzed by axial compression test. The results were principally represented in Black Space and Cole-Cole plot and indicate a substantial increase in stiffness and elasticity of the modified asphalt throughout the whole temperature range. This shows that the simultaneous addition of these two ingredients to the bitumen is a favorable alternative in road construction using asphalt pavements., Constantemente, las carreteras están sometidas esfuerzos cada vez mayores. Así pues, diversos aditivos se han incorporado a las mezclas asfálticas para mejorar el desempeño de los pavimentos. Este estudio busca caracterizar por primera vez, a la fecha, propiedades viscoelásticas de briquetas de asfalto modificado con caucho reciclado de llantas de automóviles en desuso y asfaltita en una misma mezcla, a diferentes temperaturas y frecuencias. La mezcla propuesta busca optimizar las propiedades del material y al mismo tiempo plantear una solución a una problemática medioambiental. La rigidez de las muestras fue analizada mediante pruebas de compresión axial. Los resultados, representados principalmente en el Espacio de Black y la gráfica Cole-Cole, muestran un incremento considerable en la rigidez y la elasticidad del asfalto modificado en todo el rango de temperaturas. Esto expone que la adición simultánea de los dos componentes al asfalto resulta una alternativa favorable al construir carpetas asfálticas.