Process-induced viscoelastic stress in composite laminates
International Nuclear Information System (INIS)
Stango, R.J.
1985-01-01
In recent years, considerable interest has developed in evaluating the stress response of composite laminates which is associated with cooling the material system from the cure temperature to room temperature. This research examines the fundamental nature of time-dependent residual-thermal stresses in composite laminates which are caused by the extreme temperature reduction encountered during the fabrication process. Viscoelastic stress in finite-width, symmetric composite laminates is examined on the basis of a formulation that employs an incremental hereditary integral approach in conjunction with a quasi-three dimensional finite element analysis. A consistent methodology is developed and employed for the characterization of lamina material properties. Special attention is given to the time-dependent stress response at ply-interface locations near the free-edge. In addition, the influence of cooling path on stress history is examined. Recently published material property data for graphite-epoxy lamina is employed in the analysis. Results of the investigation generally indicate that nominal differences between the thermoelastic and viscoelastic solutions are obtained. Slight changes of the final stress state are observed to result when different cooling paths are selected for the temperature history. The methodology employed is demonstrated to result in an accurate, efficient, and consistent approach for the viscoelastic analysis of advanced composite laminates
Estimation of piezoelastic and viscoelastic properties in laminated structures
DEFF Research Database (Denmark)
Araujo, A. L.; Soares, C. M. Mota; Herskovits, J.
2009-01-01
An inverse method for material parameter estimation of elastic, piezoelectric and viscoelastic laminated plate structures is presented. The method uses a gradient based optimization technique in order to solve the inverse problem, through minimization of an error functional which expresses...... the difference between experimental free vibration data and corresponding numerical data produced by a finite element model. The complex modulus approach is used to model the viscoelastic material behavior, assuming hysteretic type damping. Applications that illustrate the influence of adhesive material...
On the stabilization of viscoelastic laminated beams with interfacial slip
Mustafa, Muhammad I.
2018-04-01
In this paper, we consider a viscoelastic laminated beam model. This structure is given by two identical uniform layers on top of each other, taking into account that an adhesive of small thickness is bonding the two surfaces and produces an interfacial slip. We use viscoelastic damping with general assumptions on the relaxation function and establish explicit energy decay result from which we can recover the optimal exponential and polynomial rates. Our result generalizes the earlier related results in the literature.
Gramoll, K. C.; Dillard, D. A.; Brinson, H. F.
1989-01-01
In response to the tremendous growth in the development of advanced materials, such as fiber-reinforced plastic (FRP) composite materials, a new numerical method is developed to analyze and predict the time-dependent properties of these materials. Basic concepts in viscoelasticity, laminated composites, and previous viscoelastic numerical methods are presented. A stable numerical method, called the nonlinear differential equation method (NDEM), is developed to calculate the in-plane stresses and strains over any time period for a general laminate constructed from nonlinear viscoelastic orthotropic plies. The method is implemented in an in-plane stress analysis computer program, called VCAP, to demonstrate its usefulness and to verify its accuracy. A number of actual experimental test results performed on Kevlar/epoxy composite laminates are compared to predictions calculated from the numerical method.
THERMO-VISCOELASTIC CHARACTERIZATION OF POLYMER LAMINATE FILMS
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Eliza Truszkiewicz
2016-02-01
Full Text Available The investigated material - laminate is intended as a substrate for small electronic components, electrodes and printed circuits, which are processed onto the laminate prior to thermoforming. The placement of the electronic components and the connecting circuits must be carefully designed to prevent damage during the thermoforming. The thermo-viscoelastic behavior of a polymer laminate film was characterized by mechanical measurements to obtain data for material modeling. The strain was measured using digital image correlation. The film is anisotropic and is able to deform to strains up to 60%.
Large strain viscoelastic dissipation during interfacial rupture in laminated glass.
Elzière, Paul; Dalle-Ferrier, Cécile; Creton, Costantino; Barthel, Étienne; Ciccotti, Matteo
2017-02-22
In the dynamic rupture of laminated glass, it is essential to maximize energy dissipation. To investigate the mechanisms of energy dissipation, we have experimentally studied the delamination and stretching of a polymeric viscoelastic interlayer sandwiched between glass plates. We find that there is a velocity and temperature domain in which delamination fronts propagate in a steady state manner. At lower velocities, fronts are unstable, while at higher velocities, the polymer ruptures. Studying the influence of the interlayer thickness, we have shown that the macroscopic work of fracture during the delamination of the interlayer can be divided in two main components: (1) a near crack work of fracture which is related to the interfacial rupture and to the polymer deformation in the crack vicinity. (2) A bulk stretching work, which relates to the stretching of the interlayer behind the delamination front. Digital image correlation measurements showed that the characteristic length scale over which this stretching occurs is of the order of the interlayer thickness. Finally, an estimate of the bulk stretching work was provided, based on a simple uniaxial tensile test.
Şahan, Mehmet Fatih
2017-11-01
In this paper, the viscoelastic damped response of cross-ply laminated shallow spherical shells is investigated numerically in a transformed Laplace space. In the proposed approach, the governing differential equations of cross-ply laminated shallow spherical shell are derived using the dynamic version of the principle of virtual displacements. Following this, the Laplace transform is employed in the transient analysis of viscoelastic laminated shell problem. Also, damping can be incorporated with ease in the transformed domain. The transformed time-independent equations in spatial coordinate are solved numerically by Gauss elimination. Numerical inverse transformation of the results into the real domain are operated by the modified Durbin transform method. Verification of the presented method is carried out by comparing the results with those obtained by the Newmark method and ANSYS finite element software. Furthermore, the developed solution approach is applied to problems with several impulsive loads. The novelty of the present study lies in the fact that a combination of the Navier method and Laplace transform is employed in the analysis of cross-ply laminated shallow spherical viscoelastic shells. The numerical sample results have proved that the presented method constitutes a highly accurate and efficient solution, which can be easily applied to the laminated viscoelastic shell problems.
Viscoelastic behavior of human lamin A proteins in the context of dilated cardiomyopathy.
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Avinanda Banerjee
Full Text Available Lamins are intermediate filament proteins of type V constituting a nuclear lamina or filamentous meshwork which lines the nucleoplasmic side of the inner nuclear membrane. This protein mesh provides a supporting scaffold for the nuclear envelope and tethers interphase chromosome to the nuclear periphery. Mutations of mainly A-type lamins are found to be causative for at least 11 human diseases collectively termed as laminopathies majority of which are characterised by aberrant nuclei with altered structural rigidity, deformability and poor mechanotransduction behaviour. But the investigation of viscoelastic behavior of lamin A continues to elude the field. In order to address this problem, we hereby present the very first report on viscoelastic properties of wild type human lamin A and some of its mutants linked with Dilated cardiomyopathy (DCM using quantitative rheological measurements. We observed a dramatic strain-softening effect on lamin A network as an outcome of the strain amplitude sweep measurements which could arise from the large compliance of the quasi-cross-links in the network or that of the lamin A rods. In addition, the drastic stiffening of the differential elastic moduli on superposition of rotational and oscillatory shear stress reflect the increase in the stiffness of the laterally associated lamin A rods. These findings present a preliminary insight into distinct biomechanical properties of wild type lamin A protein and its mutants which in turn revealed interesting differences.
The role of nonlinear viscoelasticity on the functionality of laminating shortenings
Energy Technology Data Exchange (ETDEWEB)
Macias-Rodriguez, Braulio A.; Peyronel, Fernanda; Marangoni, Alejandro G.
2017-11-01
The rheology of fats is essential for the development of homogeneous and continuous layered structures of doughs. Here, we define laminating shortenings in terms of rheological behavior displayed during linear-to-nonlinear shear deformations, investigated by large amplitude oscillatory shear rheology. Likewise, we associate the rheological behavior of the shortenings with structural length scales elucidated by ultra-small angle x-ray scattering and cryo-electron microscopy. Shortenings exhibited solid-like viscoelastic and viscoelastoplastic behaviors in the linear and nonlinear regimes respectively. In the nonlinear region, laminating shortenings dissipated more viscous energy (larger normalized dynamic viscosities) than a cake bakery shortening. The fat solid-like network of laminating shortening displayed a three-hierarchy structure and layered crystal aggregates, in comparison to two-hierarchy structure and spherical-like crystal aggregates of a cake shortening. We argue that the observed rheology, correlated to the structural network, is crucial for optimal laminating performance of shortenings.
Blast Analysis of Laminated Glass Curtain Walls Equipped by Viscoelastic Dissipative Devices
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Chiara Bedon
2012-09-01
Full Text Available Nonlinear numerical simulations are reported for a conventional unitized laminated glass curtain wall subjected to high- and low-level air blast loading. The studied curtain wall, spanning floor to floor, consisted of a laminated glass panel, a continuous bead of structural silicone sealant, a split screw spline frame and four rigid brackets. Firstly, a linear elastic FE-model (M01 is presented to investigate dynamic stresses and deflections due to explosion, by taking into account geometrical nonlinearities. Since, in similar glazing systems, it is important to take into account the possible cracking of glass lites, a second model (M02, calibrated to previous experimental data, is proposed. In it, glass behaves as a brittle-elastic material, whereas an elastoplastic characteristic curve is assumed for mullions. As a result, the design explosion seriously affects the main components of the curtain wall, especially the bead of silicone. To address these criticalities, additional viscoelastic (VE devices are installed at the frame corners (M03. Their effectiveness explains the additional deformability provided to the conventional curtain wall, as well as the obvious dissipation of the incoming energy due to blast loading. Structural and energy capabilities provided by devices are highlighted by means of numerical simulations.
Amabili, Marco; Balasubramanian, Prabakaran; Breslavsky, Ivan; Ferrari, Giovanni; Tubaldi, Eleonora
2018-03-30
In case of direction-dependent viscoelasticity, a simplified formulation of the three-dimensional quasi-linear viscoelasticity has been obtained manipulating the original Fung equation. The experimental characterization of the static hyperelastic behaviour, the relaxation, the dynamic modulus and the loss factor of woven Dacron from a commercial aortic prosthesis has been performed. An 11% difference of the reduced relaxation (after infinite time) between axial and circumferential directions has been observed for the woven Dacron. A very large increase in stiffness is obtained in case of harmonic loading with respect to the static loading. These findings are particularly relevant for dynamic modelling of currently used aortic grafts. Copyright © 2018 Elsevier Ltd. All rights reserved.
Time-dependent ultrasound echo changes occur in tendon during viscoelastic testing.
Duenwald-Kuehl, Sarah; Kobayashi, Hirohito; Lakes, Roderic; Vanderby, Ray
2012-11-01
The viscoelastic behavior of tendons has been extensively studied in vitro. A noninvasive method by which to acquire mechanical data would be highly beneficial, as it could lead to the collection of viscoelastic data in vivo. Our lab has previously presented acoustoelasticity as an alternative ultrasound-based method of measuring tendon stress and strain by reporting a relationship between ultrasonic echo intensity (B mode ultrasound image brightness) and mechanical behavior of tendon under pseudoelastic in vitro conditions [Duenwald, S., Kobayashi, H., Frisch, K., Lakes, R., and Vanderby Jr, R., 2011, "Ultrasound Echo is Related to Stress and Strain in Tendon," J. Biomech., 44(3), pp. 424-429]. Viscoelastic properties of the tendons were not examined in that study, so the presence of time-dependent echo intensity changes has not been verified. In this study, porcine flexor tendons were subjected to relaxation and cyclic testing while ultrasonic echo response was recorded. We report that time- and strain history-dependent mechanical properties during viscoelastic testing are manifested in ultrasonic echo intensity changes. We also report that the patterns of the echo intensity changes do not directly mimic the patterns of viscoelastic load changes, but the intensity changed in a repeatable (and therefore predictable) fashion. Although mechanisms need further elucidation, viscoelastic behavior can be anticipated from echo intensity changes. This phenomenon could potentially lead to a more extensive characterization of in vivo tissue behavior.
Yan, Bo; Ren, Juan; Zheng, Xi; Liu, Yue; Zou, Qingze
2017-12-01
Study of the dynamic evolutions of cell viscoelasticity is important as during cell activities such as cell metastasis and invasion, the rheological behaviors of the cells also change dynamically, reflecting the biophysical and biochemical connections between the outer cortex and the intracellular structures. Although the time variations of the static modulus of cells have been investigated, few studies have been reported on the dynamic variations of the frequency-dependent viscoelasticity of cells. Measuring and monitoring such dynamic evolutions of cells at nanoscale can be challenging as the measurement needs to meet two objectives inherently contradictory to each other-the measurement must be broadband (to cover a large frequency spectrum) but also rapid (to capture the time-elapsed changes). In this study, we exploited a recently developed control-based nanomechanical protocol of atomic force microscope to monitor in real time the dynamic evolutions of the viscoelasticity of live human prostate cancer cells (PC-3 cells) and study its dependence on myosin activities. We found that the viscoelasticity of PC-3 cells, followed the power law, and oscillated at a period of about 200 s. Both the amplitude and the frequency of the oscillation strongly depended on the intracellular calcium and blebbistatin-sensitive motor proteins.
Xiao, Hanguang; Tan, Isabella; Butlin, Mark; Li, Decai; Avolio, Alberto P
2017-06-01
Experimental investigations have established that the stiffness of large arteries has a dependency on acute heart rate (HR) changes. However, the possible underlying mechanisms inherent in this HR dependency have not been well established. This study aimed to explore a plausible viscoelastic mechanism by which HR exerts an influence on arterial stiffness. A multisegment transmission line model of the human arterial tree incorporating fractional viscoelastic components in each segment was used to investigate the effect of varying fractional order parameter (α) of viscoelasticity on the dependence of aortic arch to femoral artery pulse wave velocity (afPWV) on HR. HR was varied from 60 to 100 beats/min at a fixed mean flow of 100 ml/s. PWV was calculated by intersecting tangent method (afPWV Tan ) and by phase velocity from the transfer function (afPWV TF ) in the time and frequency domain, respectively. PWV was significantly and positively associated with HR for α ≥ 0.6; for α = 0.6, 0.8, and 1, HR-dependent changes in afPWV Tan were 0.01 ± 0.02, 0.07 ± 0.04, and 0.22 ± 0.09 m/s per 5 beats/min; HR-dependent changes in afPWV TF were 0.02 ± 0.01, 0.12 ± 0.00, and 0.34 ± 0.01 m/s per 5 beats/min, respectively. This crosses the range of previous physiological studies where the dependence of PWV on HR was found to be between 0.08 and 0.10 m/s per 5 beats/min. Therefore, viscoelasticity of the arterial wall could contribute to mechanisms through which large artery stiffness changes with changing HR. Physiological studies are required to confirm this mechanism. NEW & NOTEWORTHY This study used a transmission line model to elucidate the role of arterial viscoelasticity in the dependency of pulse wave velocity on heart rate. The model uses fractional viscoelasticity concepts, which provided novel insights into arterial hemodynamics. This study also provides a means of assessing the clinical manifestation of the association of pulse wave velocity and heart rate
Said-Houari, Belkacem
2012-03-01
In this paper, we consider a viscoelastic wave equation with an absorbing term and space-time dependent damping term. Based on the weighted energy method, and by assuming that the kernel decaying exponentially, we obtain the L2 decay rates of the solutions. More precisely, we show that the decay rates are the same as those obtained in Lin et al. (2010) [15] for the semilinear wave equation with absorption term. © 2011 Elsevier Inc.
Erdel, Fabian; Baum, Michael; Rippe, Karsten
2015-02-01
The eukaryotic cell nucleus harbours the DNA genome that is organized in a dynamic chromatin network and embedded in a viscous crowded fluid. This environment directly affects enzymatic reactions and target search processes that access the DNA sequence information. However, its physical properties as a reaction medium are poorly understood. Here, we exploit mobility measurements of differently sized inert green fluorescent tracer proteins to characterize the viscoelastic properties of the nuclear interior of a living human cell. We find that it resembles a viscous fluid on small and large scales but appears viscoelastic on intermediate scales that change with protein size. Our results are consistent with simulations of diffusion through polymers and suggest that chromatin forms a random obstacle network rather than a self-similar structure with fixed fractal dimensions. By calculating how long molecules remember their previous position in dependence on their size, we evaluate how the nuclear environment affects search processes of chromatin targets.
THE INFLUENCE OF VISCOELASTICITY ON VELOCITY-DEPENDENT RESTITUTIONS IN THE OBLIQUE IMPACT OF SPHERES
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Emanuel Willert
2017-08-01
Full Text Available We analyse the oblique impact of linear-viscoelastic spheres by numerical models based on the Method of Dimensionality Reduction and the Boundary Element Method. Thereby we assume quasi-stationarity, the validity of the half-space hypothesis, short impact times and Amontons-Coulomb friction with a constant coefficient for both static and kinetic friction. As under these assumptions both methods are equivalent, their results differ only within the margin of a numerical error. The solution of the impact problem written in proper dimensionless variables will only depend on the two parameters necessary to describe the elastic problem and a sufficient set of variables to describe the influence of viscoelastic material behaviour; in the case of a standard solid this corresponds to two additional variables. The full solution of the impact problem is finally determined by comprehensive parameter studies and partly approximated by simple analytic expressions.
Cochrane, Alexander P.; Merrett, Craig G.; Hilton, Harry H.
2014-12-01
The advent of new structural concepts employing composites in primary load carrying aerospace structures in UAVs, MAVs, Boeing 787s, Airbus A380s, etc., necessitates the inclusion of flexibility as well as viscoelasticity in static structural and aero-viscoelastic analyses. Differences and similarities between aeroelasticity and aero-viscoelasticity have been investigated in [2]. An investigation is undertaken as to the dependence and sensitivity of aerodynamic and stability derivatives to elastic and viscoelastic structural flexibility and as to time dependent flight and maneuver velocities. Longitudinal, lateral and directional stabilities are investigated. It has been a well established fact that elastic lifting surfaces are subject to loss of control effectiveness and control reversal at certain flight speeds, which depend on aerodynamic, structural and material properties [5]. Such elastic analyses are extended to linear viscoelastic materials under quasi-static, dynamic, and sudden and gradual loading conditions. In elastic wings one of the critical static parameters is the velocity at which control reversal takes place (VREVE). Since elastic formulations constitute viscoelastic initial conditions, viscoelastic reversal may occur at speeds VREVstatic, dynamic, and sudden and gradual loading conditions. In elastic wings the critical parameter is the velocity at which control reversal takes place (VREVE). Since elastic formulations constitute viscoelastic initial conditions, viscoelastic reversal may occur at speeds VREVflexibility and time dependent material properties (viscoelasticity) on aerodynamic derivatives and on lateral, longitudinal, directional and spin stability derivatives. Cases of both constant and variable flight and maneuver velocities are considered. Analytical results for maneuvers involving constant and time dependent rolling velocities are analyzed, discussed and evaluated. The relationships between rolling velocity p and aileron angular
Memory-dependent derivatives theory of thermo-viscoelasticity involving two-temperature
Energy Technology Data Exchange (ETDEWEB)
Ezzat, M. A. [Alexandria University, Alexandria (Egypt); El-Bary, A. A. [Arab Academy for Science and Technology, Alexandria (Egypt)
2015-10-15
A new model of two-temperature generalized thermo-viscoelasticity theory based on memory-dependent derivative is constructed. The equations of the new model are applied to one-dimensional problem of a half-space. The bounding surface is taken to be traction free and subjected to a time dependent thermal shock. Laplace transforms technique is used. A direct approach is applied to obtain the exact formulas of heat flux, temperature, stresses, displacement and strain in the Laplace transform domain. Application is employed to our problem to get the solution in the complete form. The considered variables are presented graphically and discussions are made.
Time dependent viscoelastic rheological response of pure, modified and synthetic bituminous binders
Airey, G. D.; Grenfell, J. R. A.; Apeagyei, A.; Subhy, A.; Lo Presti, D.
2016-08-01
Bitumen is a viscoelastic material that exhibits both elastic and viscous components of response and displays both a temperature and time dependent relationship between applied stresses and resultant strains. In addition, as bitumen is responsible for the viscoelastic behaviour of all bituminous materials, it plays a dominant role in defining many of the aspects of asphalt road performance, such as strength and stiffness, permanent deformation and cracking. Although conventional bituminous materials perform satisfactorily in most highway pavement applications, there are situations that require the modification of the binder to enhance the properties of existing asphalt material. The best known form of modification is by means of polymer modification, traditionally used to improve the temperature and time susceptibility of bitumen. Tyre rubber modification is another form using recycled crumb tyre rubber to alter the properties of conventional bitumen. In addition, alternative binders (synthetic polymeric binders as well as renewable, environmental-friendly bio-binders) have entered the bitumen market over the last few years due to concerns over the continued availability of bitumen from current crudes and refinery processes. This paper provides a detailed rheological assessment, under both temperature and time regimes, of a range of conventional, modified and alternative binders in terms of the materials dynamic (oscillatory) viscoelastic response. The rheological results show the improved viscoelastic properties of polymer- and rubber-modified binders in terms of increased complex shear modulus and elastic response, particularly at high temperatures and low frequencies. The synthetic binders were found to demonstrate complex rheological behaviour relative to that seen for conventional bituminous binders.
Time and Temperature Dependence of Viscoelastic Stress Relaxation in Gold and Gold Alloy Thin Films
Mongkolsuttirat, Kittisun
Radio frequency (RF) switches based on capacitive MicroElectroMechanical System (MEMS) devices have been proposed as replacements for traditional solid-state field effect transistor (FET) devices. However, one of the limitations of the existing capacitive switch designs is long-term reliability. Failure is generally attributed to electrical charging in the capacitor's dielectric layer that creates an attractive electrostatic force between a moving upper capacitor plate (a metal membrane) and the dielectric. This acts as an attractive stiction force between them that may cause the switch to stay permanently in the closed state. The force that is responsible for opening the switch is the elastic restoring force due to stress in the film membrane. If the restoring force decreases over time due to stress relaxation, the tendency for stiction failure behavior will increase. Au films have been shown to exhibit stress relaxation even at room temperature. The stress relaxation observed is a type of viscoelastic behavior that is more significant in thin metal films than in bulk materials. Metal films with a high relaxation resistance would have a lower probability of device failure due to stress relaxation. It has been shown that solid solution and oxide dispersion can strengthen a material without unacceptable decreases in electrical conductivity. In this study, the viscoelastic behavior of Au, AuV solid solution and AuV2O5 dispersion created by DC magnetron sputtering are investigated using the gas pressure bulge testing technique in the temperature range from 20 to 80°C. The effectiveness of the two strengthening approaches is compared with the pure Au in terms of relaxation modulus and 3 hour modulus decay. The time dependent relaxation curves can be fitted very well with a four-term Prony series model. From the temperature dependence of the terms of the series, activation energies have been deduced to identify the possible dominant relaxation mechanism. The measured
Sun, Wei; Wang, Zhuo; Yan, Xianfei; Zhu, Mingwei
2018-01-01
The mechanical parameters of viscoelastic materials, such as storage modulus and loss factor, have frequency-dependent characteristic and the combination of different polymers usually exhibits various mechanical characteristics, which make the identification of the mechanical parameters of viscoelastic materials become a routine and challenging task. In this study, based on the measured resonance frequencies and frequency response functions (FRFs) of a viscoelastic damping plate, an inverse approach was developed to identify the aforementioned parameters with frequency-dependent characteristic. An analysis model was established with both the viscoelastic material damping and the remaining equivalent viscous damping considered. A response surface method was provided to achieve the matching calculation, which can identify the storage modulus and loss factor simultaneously. A cantilever plate attached with ZN_1 viscoelastic material was chosen to demonstrate the proposed method and the measured and the predicted FRFs were compared with the purpose of assessing the rationality of identification results. The results show that the loss factor of viscoelastic materials would be overestimated if only the material damping was included in the analysis model.
Energy Technology Data Exchange (ETDEWEB)
Cochrane, Alexander P. [Aerospace Engineering Department, University of Glasgow, University Avenue, Glasgow, Lanarkshire (United Kingdom); Merrett, Craig G. [Mechanical and Aerospace Engineering Department, Carleton Univ., 1125 Col. By Dr., Ottawa, ON (Canada); Hilton, Harry H. [Aerospace Engineering Department in the College of Engineering and Private Sector Program Division at the National Center for Supercomputing Applications, University of Illinois at Urbana-Champaign, 104 South Wright Street, Urbana, IL 61801 (United States)
2014-12-10
The advent of new structural concepts employing composites in primary load carrying aerospace structures in UAVs, MAVs, Boeing 787s, Airbus A380s, etc., necessitates the inclusion of flexibility as well as viscoelasticity in static structural and aero-viscoelastic analyses. Differences and similarities between aeroelasticity and aero-viscoelasticity have been investigated in [2]. An investigation is undertaken as to the dependence and sensitivity of aerodynamic and stability derivatives to elastic and viscoelastic structural flexibility and as to time dependent flight and maneuver velocities. Longitudinal, lateral and directional stabilities are investigated. It has been a well established fact that elastic lifting surfaces are subject to loss of control effectiveness and control reversal at certain flight speeds, which depend on aerodynamic, structural and material properties [5]. Such elastic analyses are extended to linear viscoelastic materials under quasi-static, dynamic, and sudden and gradual loading conditions. In elastic wings one of the critical static parameters is the velocity at which control reversal takes place (V{sub REV}{sup E}). Since elastic formulations constitute viscoelastic initial conditions, viscoelastic reversal may occur at speeds V{sub REV<}{sup ≧}V{sub REV}{sup E}, but furthermore does so in time at 0 < t{sub REV} ≤ ∞. The influence of the twin effects of viscoelastic and elastic materials and of variable flight velocities on longitudinal, lateral, directional and spin stabilities are also investigated. It has been a well established fact that elastic lifting surfaces are subject to loss of control effectiveness and control reversal at certain flight speeds, which depend on aerodynamic, structural and material properties [5]. Such elastic analyses are here extended to linear viscoelastic materials under quasi-static, dynamic, and sudden and gradual loading conditions. In elastic wings the critical parameter is the velocity at
Thermoviscoelastic characterization and prediction of Kevlar/epoxy composite laminates
Gramoll, K. C.; Dillard, D. A.; Brinson, H. F.
1990-01-01
The thermoviscoelastic characterization of Kevlar 49/Fiberite 7714A epoxy composite lamina and the development of a numerical procedure to predict the viscoelastic response of any general laminate constructed from the same material were studied. The four orthotropic material properties, S sub 11, S sub 12, S sub 22, and S sub 66, were characterized by 20 minute static creep tests on unidirectional (0) sub 8, (10) sub 8, and (90) sub 16 lamina specimens. The Time-Temperature Superposition-Principle (TTSP) was used successfully to accelerate the characterization process. A nonlinear constitutive model was developed to describe the stress dependent viscoelastic response for each of the material properties. A numerical procedure to predict long term laminate properties from lamina properties (obtained experimentally) was developed. Numerical instabilities and time constraints associated with viscoelastic numerical techniques were discussed and solved. The numerical procedure was incorporated into a user friendly microcomputer program called Viscoelastic Composite Analysis Program (VCAP), which is available for IBM PC type computers. The program was designed for ease of use. The final phase involved testing actual laminates constructed from the characterized material, Kevlar/epoxy, at various temperatures and load level for 4 to 5 weeks. These results were compared with the VCAP program predictions to verify the testing procedure and to check the numerical procedure used in the program. The actual tests and predictions agreed for all test cases which included 1, 2, 3, and 4 fiber direction laminates.
Rühl, Andreas
2017-01-01
The thesis investigates a polymeric laminate consisting of poly(methyl methacrylate) (PMMA) and thermoplastic polyurethane (TPU) experimentally and numerically with regard to its impact behaviour and applicability. After a basic characterization of the monolithic materials, PMMA-TPU-PMMA laminates were subjected to impact loadings at velocities up to 5 m/s using threepoint bending and dart impact tests. Based on the experimental basis, different material models for the Finite Element simulation are presented, which are able to capture the time and temperature dependent behaviour of the laminate. Final validation experiments, consisting of head-dummy impacts at 10 m/s on automotive side windows, were conducted for PMMA and the laminate in order to investigate their applicability as glass substitution products. The Content Introduction · Fundamentals · Experimental Investigation · Material Modelling of PMMA · Material Modelling of TPU · Simulation of PMMA-TPU Laminate · Component Tests and Validation · S...
Ropers, Steffen
2017-01-01
Within the scope of this work, Steffen Ropers evaluates the viscoelastic and temperature-dependent nature of the bending behavior of thermoplastic composite sheets in order to further enhance the predictability of the draping simulation. This simulation is a useful tool for the development of robust large scale processes for continuously fiber-reinforced polymers (CFRP). The bending behavior thereby largely influences the size and position of wrinkles, which are one of the most common processing defects for continuously fiber-reinforced parts. Thus, a better understanding of the bending behavior of thermoplastic composite sheets as well as an appropriate testing method along with corresponding material models contribute to a wide-spread application of CFRPs in large scale production. Contents Thermoplastic Prepregs Draping Simulation of Thermoplastic Prepregs Bending Characterization of Textile Composites Modeling of Bending Behavior Target Groups Researchers and students in the field of polymer, lightweight,...
Lamin A/C-dependent interaction with 53BP1 promotes cellular responses to DNA damage
DEFF Research Database (Denmark)
Gibbs-Seymour, Ian; Markiewicz, Ewa; Bekker-Jensen, Simon
2015-01-01
damage. Lamins A/C regulate 53BP1 levels and consequently lamin A/C-null HDF display a 53BP1 null-like phenotype. Our data favour a model in which lamins A/C maintain a nucleoplasmic pool of 53BP1 in order to facilitate its rapid recruitment to sites of DNA damage and could explain why an absence...
International Nuclear Information System (INIS)
Fietier, Nicolas; Deville, Michel O.
2003-01-01
This paper presents the development of spectral element methods to simulate unsteady flows of viscoelastic fluids using a closed-form differential constitutive equation. The generation and decay Poiseuille planar flows are considered as benchmark problems to test the abilities of our computational method to deal with truly time-dependent flows. Satisfactory results converging toward steady-state regimes have been obtained for the flow through a four-to-one planar abrupt contraction with unsteady algorithms. Time-dependent simulations of viscoelastic flows are prone to numerical instabilities even for simple geometrical configurations. Possible methods to improve the numerical stability of the computational algorithms are discussed in view of the results carried out with numerical simulations for the flows through a straight channel and the four-to-one contraction
International Nuclear Information System (INIS)
Ghayesh, Mergen H.; Amabili, Marco; Farokhi, Hamed
2013-01-01
In the present study, the coupled nonlinear dynamics of an axially moving viscoelastic beam with time-dependent axial speed is investigated employing a numerical technique. The equations of motion for both the transverse and longitudinal motions are obtained using Newton’s second law of motion and the constitutive relations. A two-parameter rheological model of the Kelvin–Voigt energy dissipation mechanism is employed in the modelling of the viscoelastic beam material, in which the material time derivative is used in the viscoelastic constitutive relation. The Galerkin method is then applied to the coupled nonlinear equations, which are in the form of partial differential equations, resulting in a set of nonlinear ordinary differential equations (ODEs) with time-dependent coefficients due to the axial acceleration. A change of variables is then introduced to this set of ODEs to transform them into a set of first-order ordinary differential equations. A variable step-size modified Rosenbrock method is used to conduct direct time integration upon this new set of first-order nonlinear ODEs. The mean axial speed and the amplitude of the speed variations, which are taken as bifurcation parameters, are varied, resulting in the bifurcation diagrams of Poincaré maps of the system. The dynamical characteristics of the system are examined more precisely via plotting time histories, phase-plane portraits, Poincaré sections, and fast Fourier transforms (FFTs)
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz
2000-01-01
The 3D-LIM has as yet been used to simulate the following two three-dimensional problems. First, the method has been used to simulete for viscoelastic end-plate instability that occurs under certain conditions in the transient filament stretching apparatus for pressure sensitive adhesives...... (polymeric melts) and polymeric solutions. Secondly, the 3D-LIM has also been applied to calculate the inflation of a thick sheet of a polymer melt into an elliptic cylinder. These problems all include free surfaces. As the governing equations are solved for the particle positions, the motion of surfaces can...... be followed easily even in 3D viscoelastic flow....
Moore, M.; Ziaei-Rad, S.; Salehi, H.
2013-02-01
In this study, the stability characteristics and thermal response of a bistable composite plate with different asymmetric composition were considered. The non-linear finite element method (FEM) was utilized to determine the response of the laminate. Attention was focused on the temperature dependency of laminate mechanical properties, especially on the thermal expansion coefficients of the composite graphite-epoxy plate. Also the effect of including the resin layers on the stability characteristics of the laminate was investigated. The effect of the temperature on the laminate cured configurations in the range of 25°C to 180°C and -60°C to 40°C was examined. The results indicate that the coefficient of thermal expansions has a major effect on the cured shapes. Next, optical microscopy was used to characterize the laminate composition and for the first time the effect of including the resin layers on the actuation loads that causes snapping behavior between two stable shapes was studied. The results obtained from the finite element simulations were compared with experimental results and a good correlation was obtained. Finally, the stability characteristics of a tapered composite panel were investigated for using in a sample winglet as a candidate application of bistable structures.
Czech Academy of Sciences Publication Activity Database
Minster, Jiří; Micka, Michal
2012-01-01
Roč. 2, č. 1 (2012), s. 81-89 ISSN 2161-6221 R&D Projects: GA AV ČR(CZ) IAA200710801 Institutional support: RVO:68378297 Keywords : microindentation * numerical simulation * viscoelastic characteristics Subject RIV: JJ - Other Materials
Segall, P.
2017-12-01
Distinguishing magma chamber pressurization from relaxation of a viscoelastic aureole surrounding the chamber based on geodetic measurements has remained challenging. Elastic models with mass inflow proportional to the pressure difference between the chamber and a deep reservoir predict exponentially decaying flux. For a spherical chamber surrounded by a Maxwell viscoelastic shell with pressure dependent recharge, the surface deformation is the sum of two exponentials (Segall, 2016). GPS displacements following eruptions of Grímsvötn, Iceland in 2004 and 2011 exhibit rapid post-eruptive inflation (time scale of 0.1 yr), followed by inflation with a much longer time constant. Markov Chain Monte Carlo inversion with the viscoelastic model shows the GPS time series can be fit with viscosity of 2e16 Pa-s, and a relatively incompressible magma, B = beta_c/ (beta_m + beta_c) > 0.6, where beta_m and beta_c are chamber and magma compressibility. The latter appears to conflict with the ratio of erupted volume to geodetically inferred source volume change, rv 10, obtained for the best fitting spherical (Mogi ) source (Hreinsdóttir, 2014). Since rv = 1/B, this implies a relatively compressible melt, B 0.1. Reexamination of the co-eruptive GPS and tilt data with the more general ellipsoidal model of Cervelli (2013), reveals that the best fitting sources are oblate (b/a 3), deeper, and with larger volume changes, rv 3, relative to spherical models. Oblate magma chambers are consistent with seismic tomography. FEM calculations including free surface effects lead to even larger co-eruptive volume changes, smaller rv and hence larger B. I conclude that the data are consistent with rapid post-eruptive inflation driven by viscoelastic relaxation with a relatively incompressible magma, although other interpretations will be discussed.
Bocchieri, Robert Thomas
One important factor in the durability of polymeric composites is their loss in stiffness over time due to many softening mechanisms, including nonlinear viscoelasticity, viscoplasticity and damage. Damage here refers to all ply-level microstructural changes such as matrix cracking, fiber-matrix debonding and shear yielding. This dissertation uses the theory previously established by Schapery (1999) to develop experimental and data analysis methods for isolating these softening effects. Schapery's constitutive theory is first tailored for a continuous fiber composite and evaluated for creep/recovery loading where nonlinear viscoelasticity, viscoplasticity and damage growth have a significant effect on strain. Numerical methods, implementing a Genetic Algorithm, are developed to fit material parameters in the recovery equations. This method successfully fits simulated recovery data with hereditary damage effects, but was not implemented on real data due to the unusually complex recovery behavior of the material studied. A method of Acoustic emission monitoring and waveform analysis is developed as a means for tracking two of the primary damage mechanisms in these materials, matrix-cracking and fiber/matrix debond. With direct monitoring, the extent of damage in the material does not need to be inferred from its effect on the stress-strain response. Unidirectional 30°, 45° and 90° coupons of a rubber-toughened carbon/epoxy are monitored in this way for various loading histories. A method of comparing waveforms from different samples is also suggested. An interpretation of the AE data is pro posed based on an initial population of existing flaws. Then a cumulative distribution function (CDF) of microcracking is defined and used to study effects of stress history. After developing an idealized model of the material consisting of two viscoelastic phases, a single loading parameter, which is theoretically independent of loading history and derived from viscoelastic
Time-dependent solution for reorientation of rotating tidally deformed visco-elastic bodies
Hu, Haiyang; van der Wal, Wouter; Vermeersen, Bert
2017-04-01
Many icy satellites or planets contain features which suggest a (past) reorientation of the body, such as the tiger stripes on Enceladus and the heart-shaped Sputnik Planum on Pluto. Most of these icy bodies are tidally locked and this creates a large tidal bulge which is about three times of its centrifugal (equatorial) bulge. To study the reorientation of such rotating tidally deformed body is complicated and most previous studies apply the so-called fluid limit method. The fluid limit approach ignores the viscous response of the body and assumes that it immediately reaches its fluid limit when simulating the reorientation due to a changing load. As a result, this method can only simulate cases when the change in the load is much slower than the dominant viscous modes of the body. For other kinds of load, for instance, a Heaviside load due to an impact which creates an instant relocation of mass, it does not give us a prediction of how the reorientation is accomplished (e.g. How fast? Along which path?). We establish a new method which can give an accurate time-dependent solution for reorientation of rotating tidally deformed bodies. Our method can be applied both semi-analytically or numerically (with finite element method) to include features such as lateral heterogeneity or non-linear material. We also present an extension of our method to simulate the effect of a fossil bulge. With our method, we show that reorientation of a tidally deformed body driven by a positive mass anomaly near the poles has a preference for rotating around the tidal axis instead of towards it, contrary to predictions in previous studies. References Hu, H., W. van der Wal and L.L.A. Vermeersen (2017). A numerical method for reorientation of rotating tidally deformed visco-elastic bodies. Journal of Geophysical Research: Planets, doi:10.1002/2016JE005114, 2016JE005114. Matsuyama, I. and Nimmo, F. (2007). Rotational stability of tidally deformed planetary bodies. Journal of Geophysical
Directory of Open Access Journals (Sweden)
Yuxiang Wang
Full Text Available Although the skin's mechanical properties are well characterized in tension, little work has been done in compression. Here, the viscoelastic properties of a population of mouse skin specimens (139 samples from 36 mice, aged 5 to 34 weeks were characterized upon varying specimen thickness, as well as strain level and rate. Over the population, we observed the skin's viscoelasticity to be quite variable, yet found systematic correlation of residual stress ratio with skin thickness and strain, and of relaxation time constants with strain rates. In particular, as specimen thickness ranged from 211 to 671 μm, we observed significant variation in both quasi-linear viscoelasticity (QLV parameters, the relaxation time constant (τ1 = 0.19 ± 0.10 s and steady-state residual stress ratio (G∞ = 0.28 ± 0.13. Moreover, when τ1 was decoupled and fixed, we observed that G∞ positively correlated with skin thickness. Second, as steady-state stretch was increased (λ∞ from 0.22 to 0.81, we observed significant variation in both QLV parameters (τ1 = 0.26 ± 0.14 s, G∞ = 0.47 ± 0.17, and when τ1 was fixed, G∞ positively correlated with stretch level. Third, as strain rate was increased from 0.06 to 22.88 s-1, the median time constant τ1 varied from 1.90 to 0.31 s, and thereby negatively correlated with strain rate. These findings indicate that the natural range of specimen thickness, as well as experimental controls of compression level and rate, significantly influence measurements of skin viscoelasticity.
Wang, Yuxiang; Marshall, Kara L; Baba, Yoshichika; Lumpkin, Ellen A; Gerling, Gregory J
2015-01-01
Although the skin's mechanical properties are well characterized in tension, little work has been done in compression. Here, the viscoelastic properties of a population of mouse skin specimens (139 samples from 36 mice, aged 5 to 34 weeks) were characterized upon varying specimen thickness, as well as strain level and rate. Over the population, we observed the skin's viscoelasticity to be quite variable, yet found systematic correlation of residual stress ratio with skin thickness and strain, and of relaxation time constants with strain rates. In particular, as specimen thickness ranged from 211 to 671 μm, we observed significant variation in both quasi-linear viscoelasticity (QLV) parameters, the relaxation time constant (τ1 = 0.19 ± 0.10 s) and steady-state residual stress ratio (G∞ = 0.28 ± 0.13). Moreover, when τ1 was decoupled and fixed, we observed that G∞ positively correlated with skin thickness. Second, as steady-state stretch was increased (λ∞ from 0.22 to 0.81), we observed significant variation in both QLV parameters (τ1 = 0.26 ± 0.14 s, G∞ = 0.47 ± 0.17), and when τ1 was fixed, G∞ positively correlated with stretch level. Third, as strain rate was increased from 0.06 to 22.88 s-1, the median time constant τ1 varied from 1.90 to 0.31 s, and thereby negatively correlated with strain rate. These findings indicate that the natural range of specimen thickness, as well as experimental controls of compression level and rate, significantly influence measurements of skin viscoelasticity.
Wong, W L E; Joyce, T J; Goh, K L
2016-04-01
The mechanical response of skin to external loads is influenced by anisotropy and viscoelasticity of the tissue, but the underlying mechanisms remain unclear. Here, we report a study of the main effects of tissue orientation (TO, which is linked to anisotropy) and strain rate (SR, a measure of viscoelasticity), as well as the interaction effects between the two factors, on the tensile properties of skin from a porcine model. Tensile testing to rupture of porcine skin tissue was conducted to evaluate the sensitivity of the tissue modulus of elasticity (E) and fracture-related properties, namely maximum stress (σU) and strain (εU) at σU, to varying SR and TO. Specimens were excised from the abdominal skin in two orientations, namely parallel (P) and right angle (R) to the torso midline. Each TO was investigated at three SR levels, namely 0.007-0.015 s(-1) (low), 0.040 s(-1) (mid) and 0.065 s(-1) (high). Two-factor analysis of variance revealed that the respective parameters responded differently to varying SR and TO. Significant changes in the σU were observed with different TOs but not with SR. The εU decreased significantly with increasing SR, but no significant variation was observed for different TOs. Significant changes in E were observed with different TOs; E increased significantly with increasing SR. More importantly, the respective mechanical parameters were not significantly influenced by interactions between SR and TO. These findings suggest that the trends associated with the changes in the skin mechanical properties may be attributed partly to differences in the anisotropy and viscoelasticity but not through any interaction between viscoelasticity and anisotropy.
Wang, Yuxiang; Marshall, Kara L.; Baba, Yoshichika; Lumpkin, Ellen A.; Gerling, Gregory J.
2015-01-01
Although the skin’s mechanical properties are well characterized in tension, little work has been done in compression. Here, the viscoelastic properties of a population of mouse skin specimens (139 samples from 36 mice, aged 5 to 34 weeks) were characterized upon varying specimen thickness, as well as strain level and rate. Over the population, we observed the skin’s viscoelasticity to be quite variable, yet found systematic correlation of residual stress ratio with skin thickness and strain, and of relaxation time constants with strain rates. In particular, as specimen thickness ranged from 211 to 671 μm, we observed significant variation in both quasi-linear viscoelasticity (QLV) parameters, the relaxation time constant (τ1 = 0.19 ± 0.10 s) and steady-state residual stress ratio (G∞ = 0.28 ± 0.13). Moreover, when τ1 was decoupled and fixed, we observed that G∞ positively correlated with skin thickness. Second, as steady-state stretch was increased (λ∞ from 0.22 to 0.81), we observed significant variation in both QLV parameters (τ1 = 0.26 ± 0.14 s, G∞ = 0.47 ± 0.17), and when τ1 was fixed, G∞ positively correlated with stretch level. Third, as strain rate was increased from 0.06 to 22.88 s−1, the median time constant τ1 varied from 1.90 to 0.31 s, and thereby negatively correlated with strain rate. These findings indicate that the natural range of specimen thickness, as well as experimental controls of compression level and rate, significantly influence measurements of skin viscoelasticity. PMID:25803703
Energy Technology Data Exchange (ETDEWEB)
Kanagawa, Y.; Murakami, S.; Mizobe, T. [Nagoya University, Nagoya (Japan). Faculty of Engineering; Fujii, T. [Daihatsu Motor Co. Ltd., Osaka (Japan)
1997-07-15
A constitutive model for describing the inelastic deformation of unidirectional and symmetric angle-ply CFRP (Carbon Fiber Reinforced Plastics) laminates is developed. The kinematic hardening creep flow law of Malinin and Khadjinsky and the evolution equation of Armstrong and Frederick are extended to describe the creep deformation of anisotropic materials. In order to express anisotropic hardening, back stress taking account of anisotropic inelastic strain sensitivity is incorporated into the creep constitutive equation. Then, the resulting model is applied to analyze the time-dependent inelastic deformation of symmetric angle-ply laminates. Comparison between the prediction and the experimental observation shows that the present model can describe well the time-dependent inelastic behavior under different loadings. 12 refs., 10 figs.
Viscoelastic properties of differentiating blood cells are fate- and function-dependent.
Directory of Open Access Journals (Sweden)
Andrew E Ekpenyong
Full Text Available Although cellular mechanical properties are known to alter during stem cell differentiation, understanding of the functional relevance of such alterations is incomplete. Here, we show that during the course of differentiation of human myeloid precursor cells into three different lineages, the cells alter their viscoelastic properties, measured using an optical stretcher, to suit their ultimate fate and function. Myeloid cells circulating in blood have to be advected through constrictions in blood vessels, engendering the need for compliance at short time-scales (minutes, compared to undifferentiated cells. These findings suggest that reduction in steady-state viscosity is a physiological adaptation for enhanced migration through tissues. Our results indicate that the material properties of cells define their function, can be used as a cell differentiation marker and could serve as target for novel therapies.
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz
2000-01-01
A new technique for the numerical 3D simulation of time dependent flow of viscoelastic fluid is presented. The technique is based on a Lagrangian kinematics description of the fluid flow. The fluid is described by the Rivlin Sawyer integral constitutive equation. The method (referred to as the 3D...... Lagrangian Integral Method) is a finite element method where Galerkons method is used for solving the governing equation in rectangular coordinates numerically. In the present implementation the velocity and pressure fields are approximated with tri-linear and constant shape functions, respectivly.The 3D LIM......) and polymeric solutions. Secondly, the 3D-LIM has also been applied to calculate the inflation of a thick sheet of a polymeric melt into a elliptic cylinder. These problems all include free surfaces. As the governing equations are solved for the particle positions, the motion of surfaces can be followed easily...
Zhu, Lin-Fa; Kim, Soo; Chattopadhyay, Aditi; Goldberg, Robert K.
2004-01-01
A numerical procedure has been developed to investigate the nonlinear and strain rate dependent deformation response of polymer matrix composite laminated plates under high strain rate impact loadings. A recently developed strength of materials based micromechanics model, incorporating a set of nonlinear, strain rate dependent constitutive equations for the polymer matrix, is extended to account for the transverse shear effects during impact. Four different assumptions of transverse shear deformation are investigated in order to improve the developed strain rate dependent micromechanics model. The validities of these assumptions are investigated using numerical and theoretical approaches. A method to determine through the thickness strain and transverse Poisson's ratio of the composite is developed. The revised micromechanics model is then implemented into a higher order laminated plate theory which is modified to include the effects of inelastic strains. Parametric studies are conducted to investigate the mechanical response of composite plates under high strain rate loadings. Results show the transverse shear stresses cannot be neglected in the impact problem. A significant level of strain rate dependency and material nonlinearity is found in the deformation response of representative composite specimens.
Sugino, Naoto; Nakajima, Shinya; Kameda, Takao; Takei, Satoshi; Hanabata, Makoto
2017-08-01
Silicone elastomers ( polydimethylsiloxane _ PDMS) are widely used in the field of imprint lithography and microcontactprinting (μCP). When performing microcontactprinting, the mechanical properties of the PCMS as a base material have a great influence on the performance of the device. Cellulose nanofibers having features of high strength, high elasticity and low coefficient of linear expansion have attracted attention in recent years due to their characteristics. Therefore, three types of crystalline cellulose having different molecular weights were added to PDMS to prepare a composite material, and dynamic viscoelasticity was measured using a rheometer. The PDMS with the highest molecular weight crystalline cellulose added exhibited smaller storage modulus than PDMS with other molecular weight added in all temperature ranges. Furthermore, when comparing PDMS to which crystalline cellulose was added and PDMS which is not added, the storage modulus of PDMS to which cellulose was added in the low temperature region was higher than that of PDMS to which it was not added, but it was reversed in the high temperature region It was a result. When used in a low temperature range (less than 150 ° C.), it can be said that cellulose can function as a reinforcing material for PDMS.
Energy Technology Data Exchange (ETDEWEB)
HAMMERAND,DANIEL C.; KAPANIA,RAKESH K.
2000-05-01
A triangular flat shell element for large deformation analysis of linear viscoelastic laminated composites is presented. Hygrothermorheologically simple materials are considered for which a change in the hygrothermal environment results in a horizontal shifting of the relaxation moduli curves on a log time scale, in addition to the usual hygrothermal loads. Recurrence relations are developed and implemented for the evaluation of the viscoelastic memory loads. The nonlinear deformation process is computed using an incremental/iterative approach with the Newton-Raphson Method used to find the incremental displacements in each step. The presented numerical examples consider the large deformation and stability of linear viscoelastic structures under deformation-independent mechanical loads, deformation-dependent pressure loads, and thermal loads. Unlike elastic structures that have a single critical load value associated with a given snapping of buckling instability phenomenon, viscoelastic structures will usually exhibit a particular instability for a range of applied loads over a range of critical times. Both creep buckling and snap-through examples are presented here. In some cases, viscoelastic results are also obtained using the quasielastic method in which load-history effects are ignored, and time-varying viscoelastic properties are simply used in a series of elastic problems. The presented numerical examples demonstrate the capability and accuracy of the formulation.
Non linear viscoelastic models
DEFF Research Database (Denmark)
Agerkvist, Finn T.
2011-01-01
Viscoelastic eects are often present in loudspeaker suspensions, this can be seen in the displacement transfer function which often shows a frequency dependent value below the resonance frequency. In this paper nonlinear versions of the standard linear solid model (SLS) are investigated. The simu......Viscoelastic eects are often present in loudspeaker suspensions, this can be seen in the displacement transfer function which often shows a frequency dependent value below the resonance frequency. In this paper nonlinear versions of the standard linear solid model (SLS) are investigated...
Gutierrez-Lemini, Danton
2014-01-01
Engineering Viscoelasticity covers all aspects of the thermo- mechanical response of viscoelastic substances that a practitioner in the field of viscoelasticity would need to design experiments, interpret test data, develop stress-strain models, perform stress analyses, design structural components, and carry out research work. The material in each chapter is developed from the elementary to the advanced, providing the background in mathematics and mechanics that are central to understanding the subject matter being presented. The book examines how viscoelastic materials respond to the application of loads, and provides practical guidelines to use them in the design of commercial, military and industrial applications. This book also: · Facilitates conceptual understanding by progressing in each chapter from elementary to challenging material · Examines in detail both differential and integral constitutive equations, devoting full chapters to each type and using both forms in ...
Directory of Open Access Journals (Sweden)
Mikaël Barboteu
2016-01-01
Full Text Available We consider a mathematical model which describes the dynamic evolution of a viscoelastic body in frictional contact with an obstacle. The contact is modelled with a combination of a normal compliance and a normal damped response law associated with a slip rate-dependent version of Coulomb’s law of dry friction. We derive a variational formulation and an existence and uniqueness result of the weak solution of the problem is presented. Next, we introduce a fully discrete approximation of the variational problem based on a finite element method and on an implicit time integration scheme. We study this fully discrete approximation schemes and bound the errors of the approximate solutions. Under regularity assumptions imposed on the exact solution, optimal order error estimates are derived for the fully discrete solution. Finally, after recalling the solution of the frictional contact problem, some numerical simulations are provided in order to illustrate both the behavior of the solution related to the frictional contact conditions and the theoretical error estimate result.
Elastomer-metal laminate armor
Gamache, R.M.; Giller, C.B.; Montella, G.; Fragiadakis, D.; Roland, C.M.
2016-01-01
The article of record as published may be found at http://dx.doi.org/10.1016/j.matdes.2016.08.072 A study was carried out of pressure wave transmission and the ballistic penetration of steel substrates incorporating a front-face laminate, the latter consisting of alternating layers of thin metal and a soft polymer; the latter undergoes a viscoelastic phase transition on impact. The ballistic properties of laminate/steel structures are substantially better than conventional military armor. ...
Marques, Severino P C
2012-01-01
This text is a guide how to solve problems in which viscoelasticity is present using existing commercial computational codes. The book gives information on codes’ structure and use, data preparation and output interpretation and verification. The first part of the book introduces the reader to the subject, and to provide the models, equations and notation to be used in the computational applications. The second part shows the most important Computational techniques: Finite elements formulation, Boundary elements formulation, and presents the solutions of Viscoelastic problems with Abaqus.
Welch, K.; Mousavi, S.; Lundberg, B.; Strømme, M.
2005-09-01
A newly developed method for determining the frequency-dependent complex Young's modulus was employed to analyze the mechanical response of compacted microcrystalline cellulose, sorbitol, ethyl cellulose and starch for frequencies up to 20 kHz. A Debye-like relaxation was observed in all the studied pharmaceutical excipient materials and a comparison with corresponding dielectric spectroscopy data was made. The location in frequency of the relaxation peak was shown to correlate to the measured tensile strength of the tablets, and the relaxation was interpreted as the vibrational response of the interparticle hydrogen and van der Waals bindings in the tablets. Further, the measured relaxation strength, holding information about the energy loss involved in the relaxation processes, showed that the weakest material in terms of tensile strength, starch, is the material among the four tested ones that is able to absorb the most energy within its structure when exposed to external perturbations inducing vibrations in the studied frequency range. The results indicate that mechanical relaxation analysis performed over relatively broad frequency ranges should be useful for predicting material properties of importance for the functionality of a material in applications such as, e.g., drug delivery, drug storage and handling, and also for clarifying the origin of hitherto unexplained molecular processes.
Embedded adhesive connection for laminated glass plates
DEFF Research Database (Denmark)
Hansen, Jens Zangenberg; Poulsen, S.H.; Bagger, A.
2012-01-01
The structural behavior of a new connection design, the embedded adhesive connection, used for laminated glass plates is investigated. The connection consists of an aluminum plate encapsulated in-between two adjacent triple layered laminated glass plates. Fastening between glass and aluminum...... is ensured using a structural adhesive. At first, the elastic and viscoelastic material properties of the adhesive are identified where the influence of load-rate and failure properties are also examined. Through an inverse analysis using the finite element method, the experimental observations...... usage in a design situation. The embedded connection shows promising potential as a future fastening system for load-carrying laminated glass plates....
Shape Optimization of Unconstrained Viscoelastic Layers Using Continuum Finite Elements
Lumsdaine, A.; Scott, R. A.
1998-09-01
Of the many methods available for achieving effective vibration damping, adding viscoelastic lamina is a significant technique for vibration and reduction. Recently, the desire to apportion this material in a way that will take the greatest advantage of its dissipative characteristics has led to studies in optimization. Optimal design for viscoelastically damped laminated beams and plates undergoing harmonic excitation has been examined in the literature, both for constrained and unconstrained damping layers. However to the authors' knowledge, previous optimization studies have not used continuum based finite elements to model the structure, as is done here. The problem examined is the shape optimization of an unconstrained damping layer on an elastic structure, assuming a constant volume of damping material as a design constraint. The objective is to minimize the peak displacement. Several boundary conditions are examined for beam and plate type structures. The peak displacement and the loss factor of the optimized structure are compared with the uniform layer structure. Also, results obtained using realistic (frequency dependent) and constant viscoelastic material data are compared. The structures are modelled using continuum based elements in the ABAQUS Finite Element Code. The optimization code uses a Sequential Quadratic Programming algorithm. For most of the structures examined, order of magnitude improvement is seen as a result of optimizing the shape of the damping layer. Peak displacements are reduced by up to 98%. These results are quite robust, with the optimized damping layer achieving significantly better damping performance for a wide variety of cases examined.
Narooei, K; Arman, M
2018-03-01
In this research, the exponential stretched based hyperelastic strain energy was generalized to the hyper-viscoelastic model using the heredity integral of deformation history to take into account the strain rate effects on the mechanical behavior of materials. The heredity integral was approximated by the approach of Goh et al. to determine the model parameters and the same estimation was used for constitutive modeling. To present the ability of the proposed hyper-viscoelastic model, the stress-strain response of the thermoplastic elastomer gel tissue at different strain rates from 0.001 to 100/s was studied. In addition to better agreement between the current model and experimental data in comparison to the extended Mooney-Rivlin hyper-viscoelastic model, a stable material behavior was predicted for pure shear and balance biaxial deformation modes. To present the engineering application of current model, the Kolsky bars impact test of gel tissue was simulated and the effects of specimen size and inertia on the uniform deformation were investigated. As the mechanical response of polyurea was provided over wide strain rates of 0.0016-6500/s, the current model was applied to fit the experimental data. The results were shown more accuracy could be expected from the current research than the extended Ogden hyper-viscoelastic model. In the final verification example, the pig skin experimental data was used to determine parameters of the hyper-viscoelastic model. Subsequently, a specimen of pig skin at different strain rates was loaded to a fixed strain and the change of stress with time (stress relaxation) was obtained. The stress relaxation results were revealed the peak stress increases by applied strain rate until the saturated loading rate and the equilibrium stress with magnitude of 0.281MPa could be reached. Copyright © 2017 Elsevier Ltd. All rights reserved.
Borcherdt, R. D.
2007-12-01
General theoretical solutions for Rayleigh- and Love-Type surface waves in viscoelastic media describe physical characteristics of the surface waves in elastic as well as anelastic media with arbitrary amounts of intrinsic absorption. In contrast to corresponding physical characteristics for Rayleigh waves in elastic media, Rayleigh- Type surface waves in anelastic media demonstrate; 1) tilt of the particle motion orbit that varies with depth, and 2) amplitude and volumetric strain distributions with superimposed sinusoidal variations that decay exponentially with depth. Each characteristic is dependent on the amount of intrinsic absorption and the chosen model of viscoelasticity. Distinguishing characteristics of anelastic Love-Type surface waves include: 1) dependencies of the wave speed and absorption coefficient on the chosen model and amount of intrinsic absorption and frequency, and 2) superimposed sinusoidal amplitude variations with an exponential decay with depth. Numerical results valid for a variety of viscoelastic models provide quantitative estimates of the physical characteristics of both types of viscoelastic surface waves appropriate for interpretations pertinent to models of earth materials ranging from low-loss in the crust to moderate- and high-loss in water-saturated soils.
Hogea, Cosmina S; Armstrong, William D
2002-11-01
The paper develops a one-dimensional magneto-elastic model of a magnetostrictive fiber actuated polymer matrix composite material which accounts for a strong viscoelastic response in the polymer matrix. The viscoelastic behavior of the composite polymer matrix is modeled with a three parallel Maxwell element viscoelastic model, the magnetoelastic behavior of the composite fibers is modeled with an anhysteric directional potential based domain occupation theory. Example calculations are performed to identify and explain the dynamical behavior of the composite. These calculations assume that a constant stress and the oscillating magnetic field are applied in the fiber longitudinal direction. The inclusion of matrix viscosity results in an apparent hysteresis loop in the magnetization and magnetostriction curves even though the model does not include magnetoelastic hysteresis in the fibers. The apparent hysteresis is a consequence of the interaction of the time varying fiber stress caused by matrix viscosity with a multidomain state in the fiber. The small increase in fiber longitudinal compressive stress due to matrix viscosity under increasing field inhibits the occupation of domains with magnetization orientations near the fiber longitudinal [112] direction. As a consequence, the summed longitudinal magnetization and magnetostriction is reduced as compared to the decreasing field limb.
A Damage-Dependent Finite Element Analysis for Fiber-Reinforced Composite Laminates
Coats, Timothy W.; Harris, Charles E.
1998-01-01
A progressive damage methodology has been developed to predict damage growth and residual strength of fiber-reinforced composite structure with through penetrations such as a slit. The methodology consists of a damage-dependent constitutive relationship based on continuum damage mechanics. Damage is modeled using volume averaged strain-like quantities known as internal state variables and is represented in the equilibrium equations as damage induced force vectors instead of the usual degradation and modification of the global stiffness matrix.
Barboro, Paola; D'Arrigo, Cristina; Diaspro, Alberto; Mormino, Michele; Alberti, Ingles; Parodi, Silvio; Patrone, Eligio; Balbi, Cecilia
2002-10-01
Using quantitative immunoelectron microscopy we show here that when the nuclear matrix is isolated from rat hepatocytes in the presence of an inhibitor of RNase activity both lamins and the nuclear mitotic apparatus protein (NuMA) preferentially localize within the electron-dense domains of the internal nuclear matrix (INM). After RNA digestion NuMA undergoes a sharp depletion, while labeling by an antibody against lamins A and C within the electron-transparent regions increases, suggesting that a subset of lamin epitopes is masked by the interaction with RNA. We were able to explain this result by visualizing for the first time a thin web of lamin protofibrils which connects the electron-dense regions. Confirmation of these changes has been obtained by immunoblot analysis and confocal microscopy. As RNA digestion results both in the release of NuMA and in the collapse of the INM, we propose that a fraction of nuclear RNA brings about the association of NuMA islands with a lamin scaffold and that this interaction is required to maintain the latter in a state of high molecular dispersion.
Amri, Manel; Touil-Boukoffa, Chafia
2015-09-01
The role of nitric oxide (NO) in host defense against Echinococcus granulosus larvae was previously reported. However, NO production by NOS2 (inducible NO synthase) is counteracted by the expression of Arginase. In the present study, our aim is to evaluate the involvement of the laminated layer (external layer of parasitic cyst) in Arginase induction and the protoscoleces (living and infective part of the cyst) survival. Our in vitro results indicate that this cystic compound increases the Arginase activity in macrophages. Moreover, C-type lectin receptors (CLRs) with specificity for mannan and the TGF-β are implicated in this effect as shown after adding Mannan and Anti-TGFβ. Interestingly, the laminated layer increases protoscoleces survival in macrophages-parasite co-cultures. Our results indicate that the laminated layer protects E. granulosus against the NOS2 protective response through Arginase pathway, a hallmark of M2 macrophages. Copyright © 2015 Elsevier B.V. All rights reserved.
DEFF Research Database (Denmark)
Nielsen, Michael Wenani; Hattel, Jesper Henri; Løgstrup Andersen, Tom
2012-01-01
In this work, a cure hardening instantaneous linear elastic (CHILE) model and a path dependent (PD) constitutive approach are compared, for the case of modelling strain build-up during curing of a thick composite laminate part. The PD approach is a limiting case of viscoelasticity with path...... dependency on temperature and cure degree. Model predictions are compared to experimentally determined in-situ strains, determined using FBG sensors. It was found that both models offer good approximations of internal strain build-up. A general shortcoming is the lack of capturing rate-dependent effects...
Directory of Open Access Journals (Sweden)
Nicole Reisinger
Full Text Available Laminitis is one of the most common diseases in horses. It is not only painful for the animal, but also has a significant financial impact on the equine industry. This multifactorial disease affects the connective tissue of the hoof. However, the pathogenesis of laminitis is still not fully understood. Endotoxins, also known as lipopolysaccharides (LPS, and bacterial exotoxins seem to play an important role during the development of laminitis. The aim of our study was to investigate the effect of increasing LPS concentrations (0, 2.5, 5, 10, and 100 μg/mL on cell viability of isolated epidermal and dermal hoof cells as well as on the tissue integrity of hoof explants. Furthermore, glucose, acetic acid, lactic acid, and propionic acid concentrations in explant supernatants were measured to evaluate the energy metabolism in the hoof tissue. LPS did not exhibit cytotoxic effects on epidermal or dermal cells. Force required to separate LPS treated hoof explants decreased in a concentration dependent manner. Specifically, explants incubated with 10 and 100 μg/mL needed significantly less force to separate compared to control explants. Lactic acid concentrations were significantly decreased in explants incubated with 5, 10, or 100 μg/mL LPS, while glucose, acetic acid and propionic acid concentrations were unaffected by LPS treatment. Our study indicates that LPS has no cytotoxic effect on epidermal and dermal cells isolated from hoof tissue, but impairs integrity of hoof explants. In addition, LPS led to an alteration of the lactic acid production in the lamellar tissue. Since our data highlight that LPS can affect the integrity of the equine hoof tissue in vitro, endotoxins should be further explored for their contribution to facilitate the development of laminitis.
Visco-piezo-elastic parameter estimation in laminated plate structures
DEFF Research Database (Denmark)
Araujo, A. L.; Mota Soares, C. M.; Herskovits, J.
2009-01-01
A parameter estimation technique is presented in this article, for identification of elastic, piezoelectric and viscoelastic properties of active laminated composite plates with surface-bonded piezoelectric patches. The inverse method presented uses experimental data in the form of a set...... determining the material parameters for the best fit. The solution of the inverse problem is obtained by gradient-based optimization techniques, through constrained minimization of an error functional, which expresses the deviation of the numerical model's response with respect to the experimentally measured...... data. Results are presented for the estimation of elastic, piezoelectric and viscoelastic properties in laminated plates....
Multi-scale simulation of viscoelastic fiber-reinforced composites
Staub, S.; Andrä, H.; Kabel, M.; Zangmeister, T.
2012-01-01
This paper presents an effective algorithm to simulate the anisotropic viscoelastic wbehavior of a fiber-reinforced composite including the influence of the local geometric properties, like fiber-orientation and volume fraction. The considered composites consist of a viscoelastic matrix which is reinforced by elastic fibers. The viscoelastic composite behavior results anisotropic due to the local anisotropic fiber-orientations. The influence of the local time-dependent viscoelastic properties...
Energy Technology Data Exchange (ETDEWEB)
Zhang, Da Peng; Lei, Yong Jun; Shen, Zhi Bin [College of Aerospace Science and Engineering, National University of Defense Technology, Changsha (China); Wang, Cheng Yuan [Zienkiewicz Centre for Computational Engineering, College of Engineering, Swansea University, Swansea Wales (United Kingdom)
2017-01-15
Vibration responses were investigated for a viscoelastic Single-walled carbon nanotube (visco-SWCNT) resting on a viscoelastic foundation. Based on the nonlocal Euler-Bernoulli beam model, velocity-dependent external damping and Kelvin viscoelastic foundation model, the governing equations were derived. The Transfer function method (TFM) was then used to compute the natural frequencies for general boundary conditions and foundations. In particular, the exact analytical expressions of both complex natural frequencies and critical viscoelastic parameters were obtained for the Kelvin-Voigt visco-SWCNTs with full foundations and certain boundary conditions, and several physically intuitive special cases were discussed. Substantial nonlocal effects, the influence of geometric and physical parameters of the SWCNT and the viscoelastic foundation were observed for the natural frequencies of the supported SWCNTs. The study demonstrates the efficiency and robustness of the developed model for the vibration of the visco-SWCNT-viscoelastic foundation coupling system.
International Nuclear Information System (INIS)
Zhang, Da Peng; Lei, Yong Jun; Shen, Zhi Bin; Wang, Cheng Yuan
2017-01-01
Vibration responses were investigated for a viscoelastic Single-walled carbon nanotube (visco-SWCNT) resting on a viscoelastic foundation. Based on the nonlocal Euler-Bernoulli beam model, velocity-dependent external damping and Kelvin viscoelastic foundation model, the governing equations were derived. The Transfer function method (TFM) was then used to compute the natural frequencies for general boundary conditions and foundations. In particular, the exact analytical expressions of both complex natural frequencies and critical viscoelastic parameters were obtained for the Kelvin-Voigt visco-SWCNTs with full foundations and certain boundary conditions, and several physically intuitive special cases were discussed. Substantial nonlocal effects, the influence of geometric and physical parameters of the SWCNT and the viscoelastic foundation were observed for the natural frequencies of the supported SWCNTs. The study demonstrates the efficiency and robustness of the developed model for the vibration of the visco-SWCNT-viscoelastic foundation coupling system
Simulation of Transient Viscoelastic Flow
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz; Hassager, Ole
1993-01-01
The Lagrangian kinematic description is used to develop a numerical method for simulation of time-dependent flow of viscoelastic fluids described by integral models. The method is shown to converge to first order in the time step and at least second order in the spatial discretization. The method...
Williams, Robert K.; Paranthaman, Mariappan; Chirayil, Thomas G.; Lee, Dominic F.; Goyal, Amit; Feenstra, Roeland
2002-01-01
A laminate article comprises a substrate and a biaxially textured (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer over the substrate, wherein 0article can include a layer of YBCO over the (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer. A layer of CeO.sub.2 between the YBCO layer and the (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer can also be include. Further included can be a layer of YSZ between the CeO.sub.2 layer and the (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer. The substrate can be a biaxially textured metal, such as nickel. A method of forming the laminate article is also disclosed.
Viscoelastic behaviour of pumpkin balloons
Gerngross, T.; Xu, Y.; Pellegrino, S.
2008-11-01
The lobes of the NASA ULDB pumpkin-shaped super-pressure balloons are made of a thin polymeric film that shows considerable time-dependent behaviour. A nonlinear viscoelastic model based on experimental measurements has been recently established for this film. This paper presents a simulation of the viscoelastic behaviour of ULDB balloons with the finite element software ABAQUS. First, the standard viscoelastic modelling capabilities available in ABAQUS are examined, but are found of limited accuracy even for the case of simple uniaxial creep tests on ULDB films. Then, a nonlinear viscoelastic constitutive model is implemented by means of a user-defined subroutine. This approach is verified by means of biaxial creep experiments on pressurized cylinders and is found to be accurate provided that the film anisotropy is also included in the model. A preliminary set of predictions for a single lobe of a ULDB is presented at the end of the paper. It indicates that time-dependent effects in a balloon structure can lead to significant stress redistribution and large increases in the transverse strains in the lobes.
Energy Technology Data Exchange (ETDEWEB)
Duband-Goulet, Isabelle; Woerner, Stephanie [Laboratoire du Stress et Pathologies du Cytosquelette, Universite Paris Diderot-Paris 7, CNRS, Institut de Biologie Fonctionnelle et Adaptative, 4 rue M.A. Lagroua Weill Halle, 75205 Paris cedex 13 (France); Gasparini, Sylvaine [Laboratoire de Biologie Structurale et Radiobiologie, URA CNRS 2096, Commissariat a l' Energie Atomique Saclay, 91190 Gif-sur-Yvette (France); Attanda, Wikayatou [Laboratoire du Stress et Pathologies du Cytosquelette, Universite Paris Diderot-Paris 7, CNRS, Institut de Biologie Fonctionnelle et Adaptative, 4 rue M.A. Lagroua Weill Halle, 75205 Paris cedex 13 (France); Konde, Emilie; Tellier-Lebegue, Carine [Laboratoire de Biologie Structurale et Radiobiologie, URA CNRS 2096, Commissariat a l' Energie Atomique Saclay, 91190 Gif-sur-Yvette (France); Craescu, Constantin T. [INSERM U759, Institut Curie/Universite de Paris-Sud, 91405 Orsay Cedex (France); Gombault, Aurelie [Laboratoire du Stress et Pathologies du Cytosquelette, Universite Paris Diderot-Paris 7, CNRS, Institut de Biologie Fonctionnelle et Adaptative, 4 rue M.A. Lagroua Weill Halle, 75205 Paris cedex 13 (France); Roussel, Pascal [Institut Jacques Monod, UMR 7592, Universite Paris Diderot-Paris 7, CNRS, 15 rue Helene Brion, 75205 Paris (France); Vadrot, Nathalie; Vicart, Patrick [Laboratoire du Stress et Pathologies du Cytosquelette, Universite Paris Diderot-Paris 7, CNRS, Institut de Biologie Fonctionnelle et Adaptative, 4 rue M.A. Lagroua Weill Halle, 75205 Paris cedex 13 (France); Oestlund, Cecilia; Worman, Howard J. [Department of Medicine and Department of Pathology and Cell Biology, College of Physicians and Surgeons, Columbia University, New York, NY (United States); and others
2011-12-10
Lamins A and C are nuclear intermediate filament proteins expressed in most differentiated somatic cells. Previous data suggested that prelamin A, the lamin A precursor, accumulates in some lipodystrophy syndromes caused by mutations in the lamin A/C gene, and binds and inactivates the sterol regulatory element binding protein 1 (SREBP1). Here we show that, in vitro, the tail regions of prelamin A, lamin A and lamin C bind a polypeptide of SREBP1. Such interactions also occur in HeLa cells, since expression of lamin tail regions impedes nucleolar accumulation of the SREBP1 polypeptide fused to a nucleolar localization signal sequence. In addition, the tail regions of A-type lamin variants that occur in Dunnigan-type familial partial lipodystrophy of (R482W) and Hutchison Gilford progeria syndrome ( Increment 607-656) bind to the SREBP1 polypeptide in vitro, and the corresponding FLAG-tagged full-length lamin variants co-immunoprecipitate the SREBP1 polypeptide in cells. Overexpression of wild-type A-type lamins and variants favors SREBP1 polypeptide localization at the intranuclear periphery, suggesting its sequestration. Our data support the hypothesis that variation of A-type lamin protein level and spatial organization, in particular due to disease-linked mutations, influences the sequestration of SREBP1 at the nuclear envelope and thus contributes to the regulation of SREBP1 function.
Numerical solution methods for viscoelastic orthotropic materials
Gramoll, K. C.; Dillard, D. A.; Brinson, H. F.
1988-01-01
Numerical solution methods for viscoelastic orthotropic materials, specifically fiber reinforced composite materials, are examined. The methods include classical lamination theory using time increments, direction solution of the Volterra Integral, Zienkiewicz's linear Prony series method, and a new method called Nonlinear Differential Equation Method (NDEM) which uses a nonlinear Prony series. The criteria used for comparison of the various methods include the stability of the solution technique, time step size stability, computer solution time length, and computer memory storage. The Volterra Integral allowed the implementation of higher order solution techniques but had difficulties solving singular and weakly singular compliance function. The Zienkiewicz solution technique, which requires the viscoelastic response to be modeled by a Prony series, works well for linear viscoelastic isotropic materials and small time steps. The new method, NDEM, uses a modified Prony series which allows nonlinear stress effects to be included and can be used with orthotropic nonlinear viscoelastic materials. The NDEM technique is shown to be accurate and stable for both linear and nonlinear conditions with minimal computer time.
A Viscoelastic Constitutive Law For FRP Materials
Ascione, Luigi; Berardi, Valentino Paolo; D'Aponte, Anna
2011-09-01
The present study deals with the long-term behavior of fiber-reinforced polymer (FRP) materials in civil engineering. More specifically, the authors propose a mechanical model capable of predicting the viscoelastic behavior of FRP laminates in the field of linear viscoelasticity, starting from that of the matrix material and fiber. The model is closely connected with the low FRP stress levels in civil engineering applications. The model is based on a micromechanical approach which assumes that there is a perfect adhesion between the matrix and fiber. The long-term behavior of the phases is described through a four-parameter rheological law. A validation of the model has also been developed by matching the predicted behavior with an experimental one available in the literature.
Emanuel, Kaj S; van der Veen, Albert J; Rustenburg, Christine M E; Smit, Theodoor H; Kingma, Idsart
2018-03-21
The mechanical behaviour of the intervertebral disc highly depends on the content and transport of interstitial fluid. It is unknown, however, to what extent the time-dependent behaviour can be attributed to osmosis. Here we investigate the effect of both mechanical and osmotic loading on water content, nucleus pressure and disc height. Eight goat intervertebral discs, immersed in physiological saline, were subjected to a compressive force with a pressure needle inserted in the nucleus. The loading protocol was: 10 N (6 h); 150 N (42 h); 10 N (24 h). Half-way the 150 N-phase (24 h), we eliminated the osmotic gradient by adding 26% poly-ethylene glycol to the surrounding fluid. For 62 additional discs, we determined the water content of both nucleus and annulus after 6, 24, 48, or 72 h. The compressive load was initially counterbalanced by the hydrostatic pressure in the nucleus. The load forced 4.3% of the water out of the nucleus, which reduced nucleus pressure by 44(±6)%. Reduction of the osmotic gradient disturbed the equilibrium disc height, and a significant loss of annulus water content was found. Remarkably, pressure and water content of the nucleus pulposus remained unchanged. This shows that annulus water content is important in the response to axial loading. After unloading, in the absence of an osmotic gradient, there was substantial viscoelastic recovery of 53(±11)% of the disc height, without a change in water content. However, for restoration of the nucleus pressure and for full restoration of disc height, restoration of the osmotic gradient was needed. Copyright © 2017 Elsevier Ltd. All rights reserved.
Lerch, Bradley A.; Arnold, Steven M.
2014-01-01
In support of an effort on damage prognosis, the viscoelastic behavior of Ti-6Al-4V (Ti-6-4) was investigated. This report documents the experimental characterization of this titanium alloy. Various uniaxial tests were conducted to low load levels over the temperature range of 20 to 538 C to define tensile, creep, and relaxation behavior. A range of strain rates (6x10(exp -7) to 0.001/s) were used to document rate effects. All tests were designed to include an unloading portion, followed by a hold time at temperature to allow recovery to occur either at zero stress or strain. The titanium alloy was found to exhibit viscoelastic behavior below the "yield" point and over the entire range of temperatures (although at lower temperatures the magnitude is extremely small). These experimental data will be used for future characterization of a viscoelastic model.
Arefi, Mohammad; Zenkour, Ashraf M.
2017-09-01
In this paper, size-dependent free vibration analysis of a sandwich nanoplate is presented. The sandwich nanoplate is including an elastic nano core and two piezo-electro-magnetic face-sheets as sensor and actuator actuated by electric and magnetic potentials. The sandwich nanoplate is resting on visco-Pasternak's foundation. Hamilton's principle is employed to derive the governing equations of motion based on Kirchhoff plate and nonlocal elasticity theory. The numerical results are presented to study the influence of important parameters of the problem such as applied electric and magnetic potentials, nonlocal parameter and visco-Pasternak's parameters. Furthermore, the influence of various boundary conditions is discussed on the vibration characteristics of the sandwich nanoplate.
Khan, Zeeshan; Khan, Muhammad Altaf; Siddiqui, Nasir; Ullah, Murad; Shah, Qayyum
2018-01-01
Wire coating process is a continuous extrusion process for primary insulation of conducting wires with molten polymers for mechanical strength and protection in aggressive environments. In the present study, radiative melt polymer satisfying third grade fluid model is used for wire coating process. The effect of magnetic parameter, thermal radiation parameter and temperature dependent viscosity on wire coating analysis has been investigated. Reynolds model and Vogel's models have been incorporated for variable viscosity. The governing equations characterizing the flow and heat transfer phenomena are solved analytically by utilizing homotopy analysis method (HAM). The computed results are also verified by ND-Solve method (Numerical technique) and Adomian Decomposition Method (ADM). The effect of pertinent parameters is shown graphically. In addition, the instability of the flow in the flows of the wall of the extrusion die is well marked in the case of the Vogel model as pointed by Nhan-Phan-Thien.
The rheological properties of microfibrillated cellulose (MFC) produced from agricultural residue corn stover were investigated. The corn stover MFC gels exhibited concentration-dependent viscoelastic properties. Higher corn stover MFC concentrations resulted in stronger viscoelastic properties. Th...
The rheological properties of microfibrillated cellulose (MFC) produced from agricultural residue corn stover were investigated. The corn stover MFC gels exhibited concentration-dependent viscoelastic solid properties. Higher corn stover MFC concentrations resulted in stronger viscoelastic propertie...
Directory of Open Access Journals (Sweden)
Liu Qimao
2018-02-01
Full Text Available This paper proposes an assumption that the fibre is elastic material and polymer matrix is viscoelastic material so that the energy dissipation depends only on the polymer matrix in dynamic response process. The damping force vectors in frequency and time domains, of FRP (Fibre-Reinforced Polymer matrix laminated composite plates, are derived based on this assumption. The governing equations of FRP laminated composite plates are formulated in both frequency and time domains. The direct inversion method and direct time integration method for nonviscously damped systems are employed to solve the governing equations and achieve the dynamic responses in frequency and time domains, respectively. The computational procedure is given in detail. Finally, dynamic responses (frequency responses with nonzero and zero initial conditions, free vibration, forced vibrations with nonzero and zero initial conditions of a FRP laminated composite plate are computed using the proposed methodology. The proposed methodology in this paper is easy to be inserted into the commercial finite element analysis software. The proposed assumption, based on the theory of material mechanics, needs to be further proved by experiment technique in the future.
Viscoelastic guidance of resuscitation
DEFF Research Database (Denmark)
Stensballe, Jakob; Ostrowski, Sisse R; Johansson, Pär I
2014-01-01
the use of viscoelastic hemostatic assays to guide trauma resuscitation. RECENT FINDINGS: Viscoelastic hemostatic assays such as thrombelastography and rotational thrombelastometry have shown to reduce bleeding, transfusion of fresh frozen plasma and platelets, and possibly mortality in different surgical...... populations. In trauma care, viscoelastic hemostatic assays allows for rapid and timely identification of coagulopathy and individualized, goal-directed transfusion therapy. As part of the resuscitation concept, viscoelastic hemostatic assays seem to improve outcome also in trauma; however, there is a need...... for randomized clinical trials to confirm this. SUMMARY: We are moving toward avoiding coagulopathy by individualized, goal-directed transfusion therapy, using viscoelastic hemostatic assays to guide ongoing resuscitation of actively bleeding patients in a goal-directed manner....
Directory of Open Access Journals (Sweden)
Alexandre Ottaviani
2009-02-01
Full Text Available Both genetic and epigenetic alterations contribute to Facio-Scapulo-Humeral Dystrophy (FSHD, which is linked to the shortening of the array of D4Z4 repeats at the 4q35 locus. The consequence of this rearrangement remains enigmatic, but deletion of this 3.3-kb macrosatellite element might affect the expression of the FSHD-associated gene(s through position effect mechanisms. We investigated this hypothesis by creating a large collection of constructs carrying 1 to >11 D4Z4 repeats integrated into the human genome, either at random sites or proximal to a telomere, mimicking thereby the organization of the 4q35 locus. We show that D4Z4 acts as an insulator that interferes with enhancer-promoter communication and protects transgenes from position effect. This last property depends on both CTCF and A-type Lamins. We further demonstrate that both anti-silencing activity of D4Z4 and CTCF binding are lost upon multimerization of the repeat in cells from FSHD patients compared to control myoblasts from healthy individuals, suggesting that FSHD corresponds to a gain-of-function of CTCF at the residual D4Z4 repeats. We propose that contraction of the D4Z4 array contributes to FSHD physio-pathology by acting as a CTCF-dependent insulator in patients.
Directory of Open Access Journals (Sweden)
Giulia Ognibene
2018-03-01
Full Text Available Electrospun veils from copolyethersulfones (coPES were prepared as soluble interlaminar veils for carbon fiber/epoxy composites. Neat, resin samples were impregnated into coPES veils with unmodified resin, while dry carbon fabrics were covered with electrospun veils and then infused with the unmodified epoxy resin to prepare reinforced laminates. The thermoplastic content varied from 10 wt% to 20 wt%. TGAP epoxy monomer showed improved and fast dissolution for all the temperatures tested. The unreinforced samples were cured first at 180 °C for 2 h and then were post-cured at 220 °C for 3 h. These sample showed a high dependence on the curing cycle. Carbon reinforced samples showed significant differences compared to the neat resin samples in terms of both viscoelastic and morphological properties.
A Thermodynamic Theory Of Solid Viscoelasticity. Part 1: Linear Viscoelasticity.
Freed, Alan D.; Leonov, Arkady I.
2002-01-01
The present series of three consecutive papers develops a general theory for linear and finite solid viscoelasticity. Because the most important object for nonlinear studies are rubber-like materials, the general approach is specified in a form convenient for solving problems important for many industries that involve rubber-like materials. General linear and nonlinear theories for non-isothermal deformations of viscoelastic solids are developed based on the quasi-linear approach of non-equilibrium thermodynamics. In this, the first paper of the series, we analyze non-isothermal linear viscoelasticity, which is applicable in a range of small strains not only to all synthetic polymers and bio-polymers but also to some non-polymeric materials. Although the linear case seems to be well developed, there still are some reasons to implement a thermodynamic derivation of constitutive equations for solid-like, non-isothermal, linear viscoelasticity. The most important is the thermodynamic modeling of thermo-rheological complexity , i.e. different temperature dependences of relaxation parameters in various parts of relaxation spectrum. A special structure of interaction matrices is established for different physical mechanisms contributed to the normal relaxation modes. This structure seems to be in accord with observations, and creates a simple mathematical framework for both continuum and molecular theories of the thermo-rheological complex relaxation phenomena. Finally, a unified approach is briefly discussed that, in principle, allows combining both the long time (discrete) and short time (continuous) descriptions of relaxation behaviors for polymers in the rubbery and glassy regions.
Sensitivity Analysis of Viscoelastic Structures
Directory of Open Access Journals (Sweden)
A.M.G. de Lima
2006-01-01
Full Text Available In the context of control of sound and vibration of mechanical systems, the use of viscoelastic materials has been regarded as a convenient strategy in many types of industrial applications. Numerical models based on finite element discretization have been frequently used in the analysis and design of complex structural systems incorporating viscoelastic materials. Such models must account for the typical dependence of the viscoelastic characteristics on operational and environmental parameters, such as frequency and temperature. In many applications, including optimal design and model updating, sensitivity analysis based on numerical models is a very usefull tool. In this paper, the formulation of first-order sensitivity analysis of complex frequency response functions is developed for plates treated with passive constraining damping layers, considering geometrical characteristics, such as the thicknesses of the multi-layer components, as design variables. Also, the sensitivity of the frequency response functions with respect to temperature is introduced. As an example, response derivatives are calculated for a three-layer sandwich plate and the results obtained are compared with first-order finite-difference approximations.
Optimal Design of Laminated Composite Beams
DEFF Research Database (Denmark)
Blasques, José Pedro Albergaria Amaral
This thesis presents an optimal design framework for the structural design of laminated composite beams. The possibility of improving the static and dynamic performance of laminated composite beam through the use of optimal design techniques motivates the investigation presented here. A structural....... Furthermore, the devised beam model is able account for the different levels of anisotropic elastic couplings which depend on the laminate lay-up. An optimization model based on multi-material topology optimization techniques is described. The design variables represent the volume fractions of the different...... design of laminated composite beams. The devised framework is applied in the optimal design of laminated composite beams with different cross section geometries and subjected to different load cases. Design criteria such as beam stiffness, weight, magnitude of the natural frequencies of vibration...
Göçer, A.; Nair, F.; Karamış, M. B.
2018-01-01
In this study, it is aimed to produce a layered composite structure with Al sheath and Al / B4C cored by extrusion technique and to characterize the mechanical and micro structure of the products. In the production of composite billets, powder in tube (PIT) method was used. In this method, Al7075 (ø 30 mm) tube is filled with Al2124 / B4C powder mixtures. The semi-finished composite billets were sintered at 500 ° C for 1 hour and extruded at the extrusion ratios of R = 14 R = 9 and R = 6.25 at the same temperature to obtain circular cross-section rods. The density changes, hardness distributions and sheath-core section ratios of these bars were determined. The changes of these values depending on the extrusion rate and B4C ratio were investigated. It is also revealed in the micro structure changes depending on these ratios.
Soft Matter Lubrication: Does Solid Viscoelasticity Matter?
Putignano, Carmine; Dini, Daniele
2017-12-06
Classical lubrication theory is unable to explain a variety of phenomena and experimental observations involving soft viscoelastic materials, which are ubiquitous and increasingly used in e.g. engineering and biomedical applications. These include unexpected ruptures of the lubricating film and a friction-speed dependence, which cannot be elucidated by means of conventional models, based on time-independent stress-strain constitutive laws for the lubricated solids. A new modeling framework, corroborated through experimental measurements enabled via an interferometric technique, is proposed to address these issues: Solid/fluid interactions are captured thanks to a coupling strategy that makes it possible to study the effect that solid viscoelasticity has on fluid film lubrication. It is shown that a newly defined visco-elasto-hydrodynamic lubrication (VEHL) regime can be experienced depending on the degree of coupling between the fluid flow and the solid hysteretic response. Pressure distributions show a marked asymmetry with a peak at the flow inlet, and correspondingly, the film thickness reveals a pronounced shrinkage at the flow outlet; friction is heavily influenced by the viscoelastic hysteresis which is experienced in addition to the viscous losses. These features show significant differences with respect to the classical elasto-hydrodynamic lubrication (EHL) regime response that would be predicted when solid viscoelasticity is neglected. A simple yet powerful criterion to assess the importance of viscoelastic solid contributions to soft matter lubrication is finally proposed.
Viscoelastic behavior of discrete human collagen fibrils
DEFF Research Database (Denmark)
Svensson, René; Hassenkam, Tue; Hansen, Philip
2010-01-01
Whole tendon and fibril bundles display viscoelastic behavior, but to the best of our knowledge this property has not been directly measured in single human tendon fibrils. In the present work an atomic force microscopy (AFM) approach was used for tensile testing of two human patellar tendon...... on the strain. The slope of the viscous response showed a strain rate dependence corresponding to a power function of powers 0.242 and 0.168 for the two patellar tendon fibrils, respectively. In conclusion, the present work provides direct evidence of viscoelastic behavior at the single fibril level, which has...
Shape oscillations of a viscoelastic drop
International Nuclear Information System (INIS)
Khismatullin, Damir B.; Nadim, Ali
2001-01-01
Small-amplitude axisymmetric shape deformations of a viscoelastic liquid drop in microgravity are theoretically analyzed. Using the Jeffreys constitutive equation for linear viscoelasticity, the characteristic equation for the frequency and decay factor of the shape oscillations is derived. Asymptotic analysis of this equation is performed in the low- and high-viscosity limits and for the cases of small, moderate, and large elasticities. Elastic effects are shown to give rise to a type of shape oscillation that does not depend on the surface tension. The existence of such oscillations is confirmed by numerical solution of the characteristic equation in various regimes. A method for determining the viscoelastic properties of highly viscous liquids based upon experimental measurements of the frequency and damping rate of such shape oscillations is suggested
Topology optimization of viscoelastic rectifiers
DEFF Research Database (Denmark)
Jensen, Kristian Ejlebjærg; Szabo, Peter; Okkels, Fridolin
2012-01-01
An approach for the design of microfluidic viscoelastic rectifiers is presented based on a combination of a viscoelastic model and the method of topology optimization. This presumption free approach yields a material layout topologically different from experimentally realized rectifiers...
Viscoelastic behavior of discrete human collagen fibrils
DEFF Research Database (Denmark)
Svensson, Rene; Hassenkam, Tue; P, Hansen
2010-01-01
on the strain. The slope of the viscous response showed a strain rate dependence corresponding to a power function of powers 0.242 and 0.168 for the two patellar tendon fibrils, respectively. In conclusion, the present work provides direct evidence of viscoelastic behavior at the single fibril level, which has...
Hübner, S; Eam, J E; Hübner, A; Jans, D A
2006-01-15
Lamins, members of the family of intermediate filaments, form a supportive nucleoskeletal structure underlying the nuclear envelope and can also form intranuclear structures. Mutations within the A-type lamin gene cause a variety of degenerative diseases which are collectively referred to as laminopathies. At the molecular level, laminopathies have been shown to be linked to a discontinuous localization pattern of A-type lamins, with some laminopathies containing nuclear lamin A aggregates. Since nuclear aggregate formation could lead to the mislocalization of proteins interacting with A-type lamins, we set out to examine the effects of FLAG-lamin A N195K and R386K protein aggregate formation on the subnuclear distribution of the retinoblastoma protein (pRb) and the sterol responsive element binding protein 1a (SREBP1a) after coexpression as GFP-fusion proteins in HeLa cells. We observed strong recruitment of both proteins into nuclear aggregates. Nuclear aggregate recruitment of the NPC component nucleoporin NUP153 was also observed and found to be dependent on the N-terminus. That these effects were specific was implied by the fact that a number of other coexpressed karyophilic GFP-fusion proteins, such as the nucleoporin NUP98 and kanadaptin, did not coaggregate with FLAG-lamin A N195K or R386K. Immunofluorescence analysis further indicated that the precursor form of lamin A, pre-lamin A, could be found in intranuclear aggregates. Our results imply that redistribution into lamin A-/pre-lamin A-containing aggregates of proteins such as pRb and SREBP1a could represent a key aspect underlying the molecular pathogenesis of certain laminopathies.
Keenan, R.
1985-01-01
Two-piece unit heats and presses protective layers to form laminate. Rubber diaphragm between upper and lower vacuum chambers alternates between neutral position and one that presses against solar-cell array, supplying distributed force necessary to press layers of laminate together. Encapsulation helps to protect cells from environment and to ensure long panel life while allowing efficient generation of electricity from Sunlight.
DYNAMIC DEFORMATION THE VISCOELASTIC TWOCOMPONENT MEDIUM
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V. S. Polenov
2015-01-01
Full Text Available Summary. In the article are scope harmonious warping of the two-component medium, one component which are represent viscoelastic medium, hereditary properties which are described by the kernel aftereffect Abel integral-differential ratio BoltzmannVolterr, while second – compressible liquid. Do a study one-dimensional case. Use motion equation of two-component medium at movement. Look determination system these equalization in the form of damped wave. Introduce dimensionless coefficient. Combined equations happen to homogeneous system with complex factor relatively waves amplitude in viscoelastic component and in fluid. As a result opening system determinant receive biquadratic equation. Elastic operator express through kernel aftereffect Abel for space Fourier. With the help transformation and symbol series biquadratic equation reduce to quadratic equation. Come to the conclusion that in two-component viscoelastic medium exist two mode sonic waves. As a result solution of quadratic equation be found description advance of waves sonic in viscoelastic two-component medium, which physical-mechanical properties represent complex parameter. Velocity determination advance of sonic waves, attenuation coefficient, mechanical loss tangent, depending on characteristic porous medium and circular frequency formulas receive. Graph dependences of description advance of waves sonic from the temperature logarithm and with the fractional parameter γ are constructed.
Isolation of nanoscale exosomes using viscoelastic effect
Hu, Guoqing; Liu, Chao
2017-11-01
Exosomes, molecular cargos secreted by almost all mammalian cells, are considered as promising biomarkers to identify many diseases including cancers. However, the small size of exosomes (30-200 nm) poses serious challenges on their isolation from the complex media containing a variety of extracellular vesicles (EVs) of different sizes, especially in small sample volumes. Here we develop a viscoelasticity-based microfluidic system to directly separate exosomes from cell culture media or serum in a continuous, size-dependent, and label-free manner. Using a small amount of biocompatible polymer as the additive into the media to control the viscoelastic forces exerted on EVs, we are able to achieve a high separation purity (>90%) and recovery (>80%) of exosomes. The size cutoff in viscoelasticity-based microfluidics can be easily controlled using different PEO concentrations. Based on this size-dependent viscoelastic separation strategy, we envision the handling of diverse nanoscale objects, such as gold nanoparticles, DNA origami structures, and quantum dots. This work was supported financially by National Natural Science Foundation of China (11572334, 91543125).
Impact load time histories for viscoelastic missiles
International Nuclear Information System (INIS)
Stoykovich, M.
1977-01-01
Generation of the impact load time history at the contact point between a viscoelastic missile and its targets is presented. In the past, in the case of aircraft striking containment shell structure, the impact load history was determined on the basis of actual measurements by subjecting a rigid wall to aircraft crash. The effects of elastic deformation of the target upon the impact load time history is formulated in this paper. The missile is idealized by a linear mass-spring-dashpot combination using viscoelastic models. These models can readily be processed taking into account the elastic as well as inelastic deformations of the missiles. The target is assumed to be either linearly elastic or rigid. In the case of the linearly elastic target, the normal mode theory is used to express the time-dependent displacements of the target which is simulated by lumped masses, elastic properties and dashpots in discrete parts. In the case of Maxwell viscoelastic model, the time-dependent displacements of the missile and the target are given in terms of the unknown impact load time history. This leads to an integral equation which may be solved by Laplace transformation. The normal mode theory is provided. Examples are given for bricks with viscoelastic materials as missiles against a rigid target. (Auth.)
Postseismic surface deformations due to lithospheric and asthenospheric viscoelasticity
Cohen, S. C.
1979-01-01
This paper proposes a model for postseismic surface deformations by attributing them to lithospheric and asthenospheric viscoelasticity. The model predicts that the deformations due to lithospheric viscoelasticity depend on the decrease in the effective shear modulus acting long after the lithospheric relaxation compared to that acting immediately following the earthquake. While such deformations are generally smaller than those associated with asthenospheric viscoelasticity, they occur on a shorter time scale and may be in opposite direction to both the motion occurring at the time of the earthquake and that occurring as the asthenospheric relaxation occurs.
Dynamic Viscoelasticity of Individual Bacterial Cells
Vadillo-Rodriguez, Virginia; Dutcher, John
2009-03-01
We have used an AFM-based approach to probe the mechanical properties of single bacterial cells (gram-negative Escherichia coli K12) by applying a constant compressive force to the cell under fluid conditions while measuring the time-dependent displacement (creep) of a colloidal AFM tip due to the viscoelastic properties of the cell. We observed that the cells exhibited a viscoelastic solid-like behavior with retarded elasticity, i.e. both an instantaneous and a delayed elastic deformation, which is well described by a three-parameter mechanical model. Using the best fit parameter values, we have calculated the dynamic viscoelastic behavior of the cells over a wide range of frequencies based on a numerical time-frequency transform technique and we have compared the calculated behavior with that measured experimentally. Comparison of the results obtained for E. coli with previously reported data on the mechanical properties of others gram-negative cells and their isolated surface layers suggests that the elastic component of the cell viscoelastic response is dominated by the properties of the peptidoglycan layer, whereas the viscous component likely arises from the liquid-like character of the cell membranes.
Viscoelastic fingering with a pulsed pressure signal
International Nuclear Information System (INIS)
Corvera Poire, E; Rio, J A del
2004-01-01
We derive a generalized Darcy's law in the frequency domain for a linear viscoelastic fluid flowing in a Hele-Shaw cell. This leads to an analytic expression for the dynamic permeability that has maxima which are several orders of magnitude larger than the static permeability. We then follow an argument of de Gennes (1987 Europhys. Lett. 2 195) to obtain the smallest possible finger width when viscoelasticity is important. Using this and a conservation law, we obtain the lowest bound for the width of a single finger displacing a viscoelastic fluid. When the driving force consists of a constant pressure gradient plus an oscillatory signal, our results indicate that the finger width varies in time following the frequency of the incident signal. Also, the amplitude of the finger width in time depends on the value of the dynamic permeability at the imposed frequency. When the finger is driven with a frequency that maximizes the permeability, variations in the amplitude are also maximized. This gives results that are very different for Newtonian and viscoelastic fluids. For the former ones the amplitude of the oscillation decays with frequency. For the latter ones on the other hand, the amplitude has maxima at the same frequencies that maximize the dynamic permeability
Current perpendicular to plane giant magnetoresistance in laminated nanostructures
International Nuclear Information System (INIS)
Vedyayev, A.; Zhukov, I.; Dieny, B.
2005-01-01
We theoretically studied spin-dependent electron transport perpendicular-to-plain (CPP) in magnetic laminated multilayered structures by using Kubo formalism. We took into account not only bulk scattering, but the interface resistance due to both specular and diffuse reflection and also spin conserving and spin-flip processes. It was shown that spin-flip scattering at interfaces substantially reduces the value of giant magnetoresistance (GMR). This can explain the experimental observations that the CPP GMR ratio for laminated structures only slightly increases as compared to non-laminated ones even though lamination induces a significant increase in CPP resistance
Viscoelasticity of multicellular surfaces.
Pajic-Lijakovic, Ivana; Milivojevic, Milan
2017-07-26
Various modeling approaches have been applied to describe viscoelasticity of multicellular surfaces. The viscoelasticity is considered within three time regimes: (1) short time regime for milliseconds to seconds time scale which corresponds to sub-cellular level; (2) middle time regime for several tens of seconds to several minutes time scale which corresponds to cellular level; and (3) long time regime for several tens of minutes to several hours time scale which corresponds to supra-cellular level. Short and middle time regimes have been successfully elaborated in the literature, whereas long time viscoelasticity remains unclear. Long time regime accounts for collective cell migration. Collective cell migration could induce uncorrelated motility which has an impact to energy storage and dissipation during cell surface rearrangement. Uncorrelated motility influences: (1) volume fraction of migrating cells, (2) distribution of migrating cells, (3) shapes of migrating cell groups. These parameters influence mechanical coupling between migrating and resting subpopulations and consequently the constitutive model for long time regime. This modeling consideration indicates that additional experimental work is needed to confirm the feasibility of constitutive models which have been applied in literature for long time regime as: (1) relaxation of stress and strain, (2) storage and loss moduli as the function of time, (3) distribution of migrating cells. Copyright © 2017 Elsevier Ltd. All rights reserved.
Fractional viscoelastic beam under torsion
Colinas-Armijo, N.; Cutrona, S.; Di Paola, M.; Pirrotta, A.
2017-07-01
This paper introduces a study on twisted viscoelastic beams, having considered fractional calculus to capture the viscoelastic behaviour. Further another novelty of this paper is extending a recent numerical approach, labelled line elementless method (LEM), to viscoelastic beams. The latter does not require any discretization neither in the domain nor in the boundary. Some numerical applications have been reported to demonstrate the efficiency and accuracy of the method.
Ivins, E. R.; Unti, T. W. J.; Phillips, R. J.
1982-01-01
It has long been known that the earth behaves viscoelastically. Viscoelasticity may be of importance in two aspects of mantle convection, including time-dependent behavior and local storage of recoverable work. The present investigation makes use of thermal convection in a box as a prototype of mantle flow. It is demonstrated that recoverable work can be important to the local mechanical energy balance in the descending lithosphere. It is shown that, even when assuming large viscoelastic parameters, an inherent time-dependence of viscoelastic convection appears only in local exchanges of mechanical energy. There is no strong exchange between buoyant potential energy and recoverable strain energy in the Rayleigh number range investigated. The investigation is mainly concerned with viscoelastic effects occurring on a buoyant time scale. It is found that viscoelastic effects have a negligible influence on the long term thermal energetics of mantle convection.
VISCOELASTIC MODELS OF TIDALLY HEATED EXOMOONS
International Nuclear Information System (INIS)
Dobos, Vera; Turner, Edwin L.
2015-01-01
Tidal heating of exomoons may play a key role in their habitability, since the elevated temperature can melt the ice on the body even without significant solar radiation. The possibility of life has been intensely studied on solar system moons such as Europa or Enceladus where the surface ice layer covers a tidally heated water ocean. Tidal forces may be even stronger in extrasolar systems, depending on the properties of the moon and its orbit. To study the tidally heated surface temperature of exomoons, we used a viscoelastic model for the first time. This model is more realistic than the widely used, so-called fixed Q models because it takes into account the temperature dependence of the tidal heat flux and the melting of the inner material. Using this model, we introduced the circumplanetary Tidal Temperate Zone (TTZ), which strongly depends on the orbital period of the moon and less on its radius. We compared the results with the fixed Q model and investigated the statistical volume of the TTZ using both models. We have found that the viscoelastic model predicts 2.8 times more exomoons in the TTZ with orbital periods between 0.1 and 3.5 days than the fixed Q model for plausible distributions of physical and orbital parameters. The viscoelastic model provides more promising results in terms of habitability because the inner melting of the body moderates the surface temperature, acting like a thermostat
VISCOELASTIC MODELS OF TIDALLY HEATED EXOMOONS
Energy Technology Data Exchange (ETDEWEB)
Dobos, Vera [Konkoly Thege Miklos Astronomical Institute, Research Centre of Astronomy and Earth Sciences, Hungarian Academy of Sciences, H-1121 Konkoly Thege Miklós út 15-17, Budapest (Hungary); Turner, Edwin L., E-mail: dobos@konkoly.hu [Department of Astrophysical Sciences, Princeton University, 08544, 4 Ivy Lane, Peyton Hall, Princeton, NJ (United States)
2015-05-01
Tidal heating of exomoons may play a key role in their habitability, since the elevated temperature can melt the ice on the body even without significant solar radiation. The possibility of life has been intensely studied on solar system moons such as Europa or Enceladus where the surface ice layer covers a tidally heated water ocean. Tidal forces may be even stronger in extrasolar systems, depending on the properties of the moon and its orbit. To study the tidally heated surface temperature of exomoons, we used a viscoelastic model for the first time. This model is more realistic than the widely used, so-called fixed Q models because it takes into account the temperature dependence of the tidal heat flux and the melting of the inner material. Using this model, we introduced the circumplanetary Tidal Temperate Zone (TTZ), which strongly depends on the orbital period of the moon and less on its radius. We compared the results with the fixed Q model and investigated the statistical volume of the TTZ using both models. We have found that the viscoelastic model predicts 2.8 times more exomoons in the TTZ with orbital periods between 0.1 and 3.5 days than the fixed Q model for plausible distributions of physical and orbital parameters. The viscoelastic model provides more promising results in terms of habitability because the inner melting of the body moderates the surface temperature, acting like a thermostat.
Modeling electrically active viscoelastic membranes.
Directory of Open Access Journals (Sweden)
Sitikantha Roy
Full Text Available The membrane protein prestin is native to the cochlear outer hair cell that is crucial to the ear's amplification and frequency selectivity throughout the whole acoustic frequency range. The outer hair cell exhibits interrelated dimensional changes, force generation, and electric charge transfer. Cells transfected with prestin acquire unique active properties similar to those in the native cell that have also been useful in understanding the process. Here we propose a model describing the major electromechanical features of such active membranes. The model derived from thermodynamic principles is in the form of integral relationships between the history of voltage and membrane resultants as independent variables and the charge density and strains as dependent variables. The proposed model is applied to the analysis of an active force produced by the outer hair cell in response to a harmonic electric field. Our analysis reveals the mechanism of the outer hair cell active (isometric force having an almost constant amplitude and phase up to 80 kHz. We found that the frequency-invariance of the force is a result of interplay between the electrical filtering associated with prestin and power law viscoelasticity of the surrounding membrane. Paradoxically, the membrane viscoelasticity boosts the force balancing the electrical filtering effect. We also consider various modes of electromechanical coupling in membrane with prestin associated with mechanical perturbations in the cell. We consider pressure or strains applied step-wise or at a constant rate and compute the time course of the resulting electric charge. The results obtained here are important for the analysis of electromechanical properties of membranes, cells, and biological materials as well as for a better understanding of the mechanism of hearing and the role of the protein prestin in this mechanism.
Viscoelastic Properties of Polymer Blends
Hong, S. D.; Moacanin, J.; Soong, D.
1982-01-01
Viscosity, shear modulus and other viscoelastic properties of multicomponent polymer blends are predicted from behavior of individual components, using a mathematical model. Model is extension of two-component-blend model based on Rouse-Bueche-Zimm theory of polymer viscoelasticity. Extension assumes that probabilities of forming various possible intracomponent and intercomponent entanglements among polymer molecules are proportional to relative abundances of components.
Mashayekhi, Somayeh; Miles, Paul; Hussaini, M. Yousuff; Oates, William S.
2018-02-01
In this paper, fractional and non-fractional viscoelastic models for elastomeric materials are derived and analyzed in comparison to experimental results. The viscoelastic models are derived by expanding thermodynamic balance equations for both fractal and non-fractal media. The order of the fractional time derivative is shown to strongly affect the accuracy of the viscoelastic constitutive predictions. Model validation uses experimental data describing viscoelasticity of the dielectric elastomer Very High Bond (VHB) 4910. Since these materials are known for their broad applications in smart structures, it is important to characterize and accurately predict their behavior across a large range of time scales. Whereas integer order viscoelastic models can yield reasonable agreement with data, the model parameters often lack robustness in prediction at different deformation rates. Alternatively, fractional order models of viscoelasticity provide an alternative framework to more accurately quantify complex rate-dependent behavior. Prior research that has considered fractional order viscoelasticity lacks experimental validation and contains limited links between viscoelastic theory and fractional order derivatives. To address these issues, we use fractional order operators to experimentally validate fractional and non-fractional viscoelastic models in elastomeric solids using Bayesian uncertainty quantification. The fractional order model is found to be advantageous as predictions are significantly more accurate than integer order viscoelastic models for deformation rates spanning four orders of magnitude.
DEFF Research Database (Denmark)
Ormarsson, Sigurdur; Steinnes, Jan Roar
2014-01-01
There is a need of more advanced analysis for studying how the long-term behaviour of glued laminated timber structures is affected by creep and by cyclic variations in climate. A beam theory is presented able to simulate the overall hygro-mechanical and visco-elastic behaviour of (inhomogeneous)...
Viscoelastic behavior of discrete human collagen fibrils
DEFF Research Database (Denmark)
Svensson, Rene; Hassenkam, Tue; P, Hansen
2010-01-01
Whole tendon and fibril bundles display viscoelastic behavior, but to the best of our knowledge this property has not been directly measured in single human tendon fibrils. In the present work an atomic force microscopy (AFM) approach was used for tensile testing of two human patellar tendon...... fibrils. Fibrils were obtained from intact human fascicles, without any pre-treatment besides frozen storage. In the dry state a single isolated fibril was anchored to a substrate using epoxy glue, and the end of the fibril was glued on to an AFM cantilever for tensile testing. In phosphate buffered...... on the strain. The slope of the viscous response showed a strain rate dependence corresponding to a power function of powers 0.242 and 0.168 for the two patellar tendon fibrils, respectively. In conclusion, the present work provides direct evidence of viscoelastic behavior at the single fibril level, which has...
Acoustic wave rectification in viscoelastic materials
Tanaka, Yukihiro; Shimomura, Yukito; Nishiguchi, Norihiko
2018-03-01
We have numerically investigated the propagation of acoustic waves in a periodic array of triangular holes embedded in a matrix composed of viscoelastic materials, such as polymers, using an extended finite-difference time-domain method. Although the viscoelasticity of the substrate in acoustic wave rectifiers smears out the fine structures observed at the transmission rate, the rectifying effect of acoustic waves survives. Moreover, the transmittance for longitudinal wave incidence broadly shows a vivid rectification effect in a wide frequency range when the difference between the velocities of longitudinal and transverse waves is large. In addition, the extreme sensitivity of shear rate with respect to time (or frequency) gives rise to the marked modulation of the frequency dependence of the transmission rate.
Rotation of a synchronous viscoelastic shell
Noyelles, Benoît
2018-03-01
Several natural satellites of the giant planets have shown evidence of a global internal ocean, coated by a thin, icy crust. This crust is probably viscoelastic, which would alter its rotational response. This response would translate into several rotational quantities, i.e. the obliquity, and the librations at different frequencies, for which the crustal elasticity reacts differently. This study aims at modelling the global response of the viscoelastic crust. For that, I derive the time-dependence of the tensor of inertia, which I combine with the time evolution of the rotational quantities, thanks to an iterative algorithm. This algorithm combines numerical simulations of the rotation with a digital filtering of the resulting tensor of inertia. The algorithm works very well in the elastic case, provided the problem is not resonant. However, considering tidal dissipation adds different phase lags to the oscillating contributions, which challenge the convergence of the algorithm.
Viscoelastic behaviour of cold recycled asphalt mixes
Cizkova, Zuzana; Suda, Jan
2017-09-01
Behaviour of cold recycled mixes depends strongly on both the bituminous binder content (bituminous emulsion or foamed bitumen) and the hydraulic binder content (usually cement). In the case of cold recycled mixes rich in bitumen and with low hydraulic binder content, behaviour is close to the viscoelastic behaviour of traditional hot mix asphalt. With decreasing bituminous binder content together with increasing hydraulic binder content, mixes are characteristic with brittle behaviour, typical for concrete pavements or hydraulically bound layers. The behaviour of cold recycled mixes with low content of both types of binders is similar to behaviour of unbound materials. This paper is dedicated to analysing of the viscoelastic behaviour of the cold recycled mixes. Therefore, the tested mixes contained higher amount of the bituminous binder (both foamed bitumen and bituminous emulsion). The best way to characterize any viscoelastic material in a wide range of temperatures and frequencies is through the master curves. This paper includes interesting findings concerning the dependency of both parts of the complex modulus (elastic and viscous) on the testing frequency (which simulates the speed of heavy traffic passing) and on the testing temperature (which simulates the changing climate conditions a real pavement is subjected to).
Relativistic viscoelastic fluid mechanics.
Fukuma, Masafumi; Sakatani, Yuho
2011-08-01
A detailed study is carried out for the relativistic theory of viscoelasticity which was recently constructed on the basis of Onsager's linear nonequilibrium thermodynamics. After rederiving the theory using a local argument with the entropy current, we show that this theory universally reduces to the standard relativistic Navier-Stokes fluid mechanics in the long time limit. Since effects of elasticity are taken into account, the dynamics at short time scales is modified from that given by the Navier-Stokes equations, so that acausal problems intrinsic to relativistic Navier-Stokes fluids are significantly remedied. We in particular show that the wave equations for the propagation of disturbance around a hydrostatic equilibrium in Minkowski space-time become symmetric hyperbolic for some range of parameters, so that the model is free of acausality problems. This observation suggests that the relativistic viscoelastic model with such parameters can be regarded as a causal completion of relativistic Navier-Stokes fluid mechanics. By adjusting parameters to various values, this theory can treat a wide variety of materials including elastic materials, Maxwell materials, Kelvin-Voigt materials, and (a nonlinearly generalized version of) simplified Israel-Stewart fluids, and thus we expect the theory to be the most universal description of single-component relativistic continuum materials. We also show that the presence of strains and the corresponding change in temperature are naturally unified through the Tolman law in a generally covariant description of continuum mechanics.
Relativistic viscoelastic fluid mechanics
International Nuclear Information System (INIS)
Fukuma, Masafumi; Sakatani, Yuho
2011-01-01
A detailed study is carried out for the relativistic theory of viscoelasticity which was recently constructed on the basis of Onsager's linear nonequilibrium thermodynamics. After rederiving the theory using a local argument with the entropy current, we show that this theory universally reduces to the standard relativistic Navier-Stokes fluid mechanics in the long time limit. Since effects of elasticity are taken into account, the dynamics at short time scales is modified from that given by the Navier-Stokes equations, so that acausal problems intrinsic to relativistic Navier-Stokes fluids are significantly remedied. We in particular show that the wave equations for the propagation of disturbance around a hydrostatic equilibrium in Minkowski space-time become symmetric hyperbolic for some range of parameters, so that the model is free of acausality problems. This observation suggests that the relativistic viscoelastic model with such parameters can be regarded as a causal completion of relativistic Navier-Stokes fluid mechanics. By adjusting parameters to various values, this theory can treat a wide variety of materials including elastic materials, Maxwell materials, Kelvin-Voigt materials, and (a nonlinearly generalized version of) simplified Israel-Stewart fluids, and thus we expect the theory to be the most universal description of single-component relativistic continuum materials. We also show that the presence of strains and the corresponding change in temperature are naturally unified through the Tolman law in a generally covariant description of continuum mechanics.
On thermal edge effects in composite laminates
Herakovich, C. T.
1976-01-01
Results are presented for a finite-element investigation of the combined influence of edge effects due to mechanical and thermal mismatch in composite laminates with free edges. Laminates of unidirectional boron/epoxy symmetrically bonded to sheets of aluminum and titanium were studied. It is shown that interlaminar thermal stresses may be more significant than the interlaminar stresses due to loading only. In addition, the stresses due to thermal mismatch may be of the same sign as those due to Poisson's mismatch or they may be of opposite sign depending upon material properties, stacking sequence, and direction of loading. The paper concludes with a brief discussion of thermal stresses in all-composite laminates.
Modelling nonlinear viscoelastic behaviours of loudspeaker suspensions-like structures
Maillou, Balbine; Lotton, Pierrick; Novak, Antonin; Simon, Laurent
2018-03-01
Mechanical properties of an electrodynamic loudspeaker are mainly determined by its suspensions (surround and spider) that behave nonlinearly and typically exhibit frequency dependent viscoelastic properties such as creep effect. The paper aims at characterizing the mechanical behaviour of electrodynamic loudspeaker suspensions at low frequencies using nonlinear identification techniques developed in recent years. A Generalized Hammerstein based model can take into account both frequency dependency and nonlinear properties. As shown in the paper, the model generalizes existing nonlinear or viscoelastic models commonly used for loudspeaker modelling. It is further experimentally shown that a possible input-dependent law may play a key role in suspension characterization.
Viscoelasticity using reactive constrained solid mixtures.
Ateshian, Gerard A
2015-04-13
This study presents a framework for viscoelasticity where the free energy density depends on the stored energy of intact strong and weak bonds, where weak bonds break and reform in response to loading. The stress is evaluated by differentiating the free energy density with respect to the deformation gradient, similar to the conventional approach for hyperelasticity. The breaking and reformation of weak bonds is treated as a reaction governed by the axiom of mass balance, where the constitutive relation for the mass supply governs the bond kinetics. The evolving mass contents of these weak bonds serve as observable state variables. Weak bonds reform in an energy-free and stress-free state, therefore their reference configuration is given by the current configuration at the time of their reformation. A principal advantage of this formulation is the availability of a strain energy density function that depends only on observable state variables, also allowing for a separation of the contributions of strong and weak bonds. The Clausius-Duhem inequality is satisfied by requiring that the net free energy from all breaking bonds must be decreasing at all times. In the limit of infinitesimal strains, linear stress-strain responses and first-order kinetics for breaking and reforming of weak bonds, the reactive framework reduces exactly to classical linear viscoelasticity. For large strains, the reactive and classical quasilinear viscoelasticity theories produce different equations, though responses to standard loading configurations behave similarly. This formulation complements existing tools for modeling the nonlinear viscoelastic response of biological soft tissues under large deformations. Copyright © 2015 Elsevier Ltd. All rights reserved.
Laminate armor and related methods
Chu, Henry S; Lillo, Thomas M; Zagula, Thomas M
2013-02-26
Laminate armor and methods of manufacturing laminate armor. Specifically, laminate armor plates comprising a commercially pure titanium layer and a titanium alloy layer bonded to the commercially pure titanium outer layer are disclosed, wherein an average thickness of the titanium alloy inner layer is about four times an average thickness of the commercially pure titanium outer layer. In use, the titanium alloy layer is positioned facing an area to be protected. Additionally, roll-bonding methods for manufacturing laminate armor plates are disclosed.
EB curable laminating adhesives
International Nuclear Information System (INIS)
Matsuyama, Asao; Kobayashi, Masahide; Gotoh, Sakiko
1992-01-01
New developed solvent free EB curable laminating adhesives have two liquid components, A with hydroxy and acryloyl group, B with isocyanate and acryloyl group in a molecule. These EB laminating adhesives do not need any aging process, which is a big advantage, and are very suitable for environment, safety, and health because of no heating process and solvent free formulas. And we have made basic research about the relation of peel strength or heat seal strength versus Tg of cured film, elongation at break, elastic modulus, and so on. Basic specifications of the new developed adhesives are shown. (author)
Dielectrophoresis of spermatozoa in viscoelastic medium.
Koh, James Boon Yong; Marcos
2015-07-01
Knowledge of spermatozoa motility is important in selecting suitable spermatozoa for assisted reproduction procedures. By considering the internal sliding force within an active filament, its shape in a viscoelastic Oldroyd-B fluid subjected to nonuniform electric field is presented. The resulting velocity is a function of the beating pattern and DEP force, which is dependent on the spermatozoon's morphology as well as the gradient of the mean square electric field. Finally, the velocities of the X- and Y-spermatozoa are compared under various conditions of nonuniform electric field and viscoelasticity of the medium. The presence of DEP force alters their velocities to different extents, giving an 84% level of confidence for selecting spermatozoon that contains the chromosome leading to a female. Therefore, a nonuniform electric field can be used not only to sort and select spermatozoa of desired morphology, but also for gender selection. Moreover, we found that sorting in a viscoelastic fluid medium is more effective as the effect of DEP on the spermatozoa velocity is enhanced by an order of magnitude. © 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim.
Lubrication of soft viscoelastic solids
Pandey, Anupam; Karpitschka, Stefan; Venner, Cornelis H.; Snoeijer, Jacobus Hendrikus
2015-01-01
Lubrication flows appear in many applications in engineering, biophysics, and in nature. Separation of surfaces and minimisation of friction and wear is achieved when the lubrication fluid builds up a lift force. In this paper we analyse soft lubricated contacts by treating the solid walls as viscoelastic: soft materials are typically not purely elastic, but dissipate energy under dynamical loading conditions. We present a method for viscoelastic lubrication and focus on three canonical examp...
Theory of viscoelasticity an introduction
Christensen, R
1982-01-01
Theory of Viscoelasticity: An Introduction, Second Edition discusses the integral form of stress strain constitutive relations. The book presents the formulation of the boundary value problem and demonstrates the separation of variables condition.The text describes the mathematical framework to predict material behavior. It discusses the problems to which integral transform methods do not apply. Another topic of interest is the thermoviscoelastic stress analysis. The section that follows describes the heat conduction, glass transition criterion, viscoelastic Rayleigh waves, optimal str
Directory of Open Access Journals (Sweden)
M.R. Mofakhami
2008-01-01
Full Text Available In this paper sound transmission through the multilayered viscoelastic air filled cylinders subjected to the incident acoustic wave is studied using the technique of separation of variables on the basis of linear three dimensional theory of elasticity. The effect of interior acoustic medium on the mode maps (frequency vs geometry and noise reduction is investigated. The effects of internal absorption and external moving medium on noise reduction are also evaluated. The dynamic viscoelastic properties of the structure are rigorously taken into account with a power law technique that models the viscoelastic damping of the cylinder. A parametric study is also performed for the two layered infinite cylinders to obtain the effect of viscoelastic layer characteristics such as thickness, material type and frequency dependency of viscoelastic properties on the noise reduction. It is shown that using constant and frequency dependent viscoelastic material with high loss factor leads to the uniform noise reduction in the frequency domain. It is also shown that the noise reduction obtained for constant viscoelastic material property is subjected to some errors in the low frequency range with respect to those obtained for the frequency dependent viscoelastic material.
Finite element reduction strategy for composite sandwich plates with viscoelastic layers
Directory of Open Access Journals (Sweden)
Adriana Amaro Diacenco
2012-01-01
Full Text Available Composite materials have been regarded as a convenient strategy in various types of engineering systems such as aeronautical and space structures, as well as architecture and light industry products due to their advantages over the traditional engineering materials, such as their high strength/stiffness relation characteristics and their anti-corrosion properties. This paper is devoted to the finite element modeling of composite laminated structures incorporating viscoelastic materials to the problem of vibration attenuation. However, the typically high dimension of large finite element models of composite structures incorporating viscoelastic materials makes the numerical processes sometimes unfeasible. Within this context, emphasis is placed on a general condensation strategy specially adapted for the case of viscoelastically damped structures, in which a constant (frequency- and temperature-independent reduction basis to be enriched by static residues associated to the applied loads and the viscoelastic forces is used. After presenting the theoretical foundations, the numerical applications of composite plates treated by viscoelastic materials are addressed, and the main features of the methodology are discussed.
Finite element reduction strategy for composite sandwich plates with viscoelastic layers
Directory of Open Access Journals (Sweden)
Adriana Amaro Diacenco
2013-04-01
Full Text Available Composite materials have been regarded as a convenient strategy in various types of engineering systems such as aeronautical and space structures, as well as architecture and light industry products due to their advantages over the traditional engineering materials, such as their high strength/stiffness relation characteristics and their anti-corrosion properties. This paper is devoted to the finite element modeling of composite laminated structures incorporating viscoelastic materials to the problem of vibration attenuation. However, the typically high dimension of large finite element models of composite structures incorporating viscoelastic materials makes the numerical processes sometimes unfeasible. Within this context, emphasis is placed on a general condensation strategy specially adapted for the case of viscoelastically damped structures, in which a constant (frequency- and temperature-independent reduction basis to be enriched by static residues associated to the applied loads and the viscoelastic forces is used. After presenting the theoretical foundations, the numerical applications of composite plates treated by viscoelastic materials are addressed, and the main features of the methodology are discussed.
Photovoltaic module and laminate
Energy Technology Data Exchange (ETDEWEB)
Bunea, Gabriela E.; Kim, Sung Dug; Kavulak, David F.J.
2018-04-10
A photovoltaic module is disclosed. The photovoltaic module has a first side directed toward the sun during normal operation and a second, lower side. The photovoltaic module comprises a perimeter frame and a photovoltaic laminate at least partially enclosed by and supported by the perimeter frame. The photovoltaic laminate comprises a transparent cover layer positioned toward the first side of the photovoltaic module, an upper encapsulant layer beneath and adhering to the cover layer, a plurality of photovoltaic solar cells beneath the upper encapsulant layer, the photovoltaic solar cells electrically interconnected, a lower encapsulant layer beneath the plurality of photovoltaic solar cells, the upper and lower encapsulant layers enclosing the plurality of photovoltaic solar cells, and a homogenous rear environmental protection layer, the rear environmental protection layer adhering to the lower encapsulant layer, the rear environmental protection layer exposed to the ambient environment on the second side of the photovoltaic module.
Energy Technology Data Exchange (ETDEWEB)
Liu, J.C. [College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058 (China); Zhang, Y.Q., E-mail: cyqzhang@zju.edu.cn [College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058 (China); State Key Laboratory of Mechanical Structural Strength and Vibration, Xi' an Jiaotong University, Xi' an 710049 (China); Fan, L.F. [College of Architecture and Civil Engineering, Beijing University of Technology, Beijing 100084 (China)
2017-04-11
The general equation for transverse vibration of double-viscoelastic-FGM-nanoplate system with viscoelastic Pasternak medium in between and each nanoplate subjected to in-plane edge loads is formulated on the basis of the Eringen's nonlocal elastic theory and the Kelvin model. The factors of the structural damping, medium damping, small size effect, loading ratio, and Winkler modulus and shear modulus of the medium are incorporated in the formulation. Based on the Navier's method, the analytical solutions for vibrational frequency and buckling load of the system with simply supported boundary conditions are obtained. The influences of these factors on vibrational frequency and buckling load of the system are discussed. It is demonstrated that the vibrational frequency of the system for the out-of-phase vibration is dependent upon the structural damping, small size effect and viscoelastic Pasternak medium, whereas the vibrational frequency for the in-phase vibration is independent of the viscoelastic Pasternak medium. While the buckling load of the system for the in-phase buckling case has nothing to do with the viscoelastic Pasternak medium, the buckling load for the out-of-phase case is related to the small size effect, loading ratio and Pasternak medium. - Highlights: • Vibration of double-viscoelastic-FGM-nanoplate system under in-plane edge loads is investigated. • Biaxial buckling of the system with simply supported boundary conditions is analyzed. • Explicit expression for the vibrational frequency and buckling load is obtained. • Impacts of viscoelastic Pasternak medium on vibrational frequency and buckling load are discussed. • Influences of structural damping, small size effect and loading ratio are also considered.
Micromechanics Models for Viscoelastic Plain-Weave Composite Tape Springs
DEFF Research Database (Denmark)
Kwok, Kawai; Pellegrino, Sergio
2017-01-01
The viscoelastic behavior of polymer composites decreases the deployment force and the postdeployment shape accuracy of composite deployable space structures. This paper presents a viscoelastic model for single-ply cylindrical shells (tape springs) that are deployed after being held folded...... homogenization leads to the lamina relaxation ABD matrix. The accuracy of the proposed model is verified against the experimentally measured time-dependent compliance of single lamina in either pure tension or pure bending. Finite element simulations of single-ply tape springs based on the proposed model...
Viscoelasticity of Edam cheese during its ripening
Directory of Open Access Journals (Sweden)
Šárka Nedomová
2010-01-01
Full Text Available Series of the indentation of the ball (10 mm in diameter by the constant speed into blocks of Edam cheese has been conducted. The indentation tests were performed at different speeds (1, 5, 10, 20 and 100 mm/min, and the corresponding force–displacement responses were fitted with an analytical solution to obtain the time-dependent constants and the instantaneous force–displacement response. The measurement has been performed for the cheeses of different stages of their maturity. The dependence of the indentation force on the penetration depth has been evaluated. This dependence can be fitted by a polynom. The indentation force decreases with cheese fat content. It increases with the loading rate. Its value also decreases with the time of the cheese ripening. The recently proposed method for the indenation of the ball into viscoelastic solids has been used for our data analysis. This procedure, which needs the use of the numeric methods, enables to obtain stress relaxation moduli, which describe the viscoelasticity of the tested materials. The obtained moduli describe the stage of the cheese maturity.
Numerical solution of transient viscoelastic flow
DEFF Research Database (Denmark)
Hassager, Ole; Rasmussen, Henrik K.; Szabo, Peter
1996-01-01
A number of applications of the Lagrangina kinematic specification in the simulation of transient viscoelastic flows are shown.......A number of applications of the Lagrangina kinematic specification in the simulation of transient viscoelastic flows are shown....
Dynamic-mechanical response of graphite/epoxy composite laminates and neat resin
Yang, P.; Carlsson, L.; Sternstein, S. S.
1983-01-01
Dynamic mechanical measurement results are presented for the case of carbon fiber-reinforced, epoxy matrix composite laminates subjected to loading perpendicular to the lamination plane, as well as for neat epoxy resin under the same conditions, where temperatures ranged between 20 and 200 C and deformation levels lie within the linear viscoelastic region. In-phase and out-of-phase stiffnesses are found to become superposed, forming master curves that cover a 12-decade frequency range. The application of a master curve scaling procedure shows that the in-phase stiffness has the same shape, and out-of-phase stiffness has the same dispersion, for all laminates irrespective of stacking sequence and are, in turn, nearly identical to those for the neat epoxy resin. An empirical function is found for the relaxation modulus which, when converted to a dynamic modulus, yields good overall agreement for both of the dynamic stiffness components as a function of frequency.
A theory of piezoelectric laminates
International Nuclear Information System (INIS)
Giangreco, E.
1997-01-01
A theory of piezoelectric laminates is rationally derived from the three-dimensional Voigt theory of piezoelectricity. The present theory is a generalization to piezoelectric laminates of the Reissner-Mindlin-type layer-wise theory of elastic laminates. Both a differential formulation and a variational formulation of the piezoelectric laminate problem are presented. The proposed theory is adopted in the analysis of simple problems, in order to verify its effectiveness. The results it provides turn out to be in good agreement with the results supplied by the Voigt theory of piezoelectricity
Simulations of flow induced ordering in viscoelastic fluids
Santos de Oliveira, I.S.
2012-01-01
In this thesis we report on simulations of colloidal ordering phenomena in shearthinning viscoelastic fluids under shear flow. Depending on the characteristics of the fluid, the colloids are observed to align in the direction of the flow. These string-like structures remain stable as long as the
TERFENOL-D Lamination Process Cost Reduction
National Research Council Canada - National Science Library
Slaughter, Julie
1998-01-01
The process of manufacturing laminated TERFENOL-D is costly and time consuming. This Phase I study was aimed at reducing the reject rate of the current lamination process and thus reducing the cost of laminated TERFENOL-D...
Extensional rheometer based on viscoelastic catastrophes outline
DEFF Research Database (Denmark)
2014-01-01
The present invention relates to a method and a device for determining viscoelastic properties of a fluid. The invention resides inter alia in the generation of viscoelastic catastrophes in confined systems for use in the context of extensional rheology. The viscoelastic catastrophe is according ...... to the invention generated in a bistable fluid system, and the flow conditions for which the catastrophe occurs can be used as a fingerprint of the fluid's viscoelastic properties in extensional flow....
SYNTHESIS OF VISCOELASTIC MATERIAL MODELS (SCHEMES
Directory of Open Access Journals (Sweden)
V. Bogomolov
2014-10-01
Full Text Available The principles of structural viscoelastic schemes construction for materials with linear viscoelastic properties in accordance with the given experimental data on creep tests are analyzed. It is shown that there can be only four types of materials with linear visco-elastic properties.
Viscoelastic modes in chiral liquid crystals
Indian Academy of Sciences (India)
Viscoelastic properties of liquid crystals are very important for applications like display technology. However, there are not many direct techniques to study them. In this review, we describe our studies on the viscoelastic modes of some chiral liquid crystals using dynamic light scattering. We discuss viscoelastic modes ...
On the flexoviscous behavior in viscoelastic materials
Fu, John Y.
2011-01-01
A phenomenological model on the relationship between viscoelasticity and flexoelectricity is proposed to address the electromechanical coupling under rheological processes in viscoelastic materials. Our theoretical studies show that some observed ferroelectric phenomena in certain viscoelastic materials, like polymer films, may not be intrinsic material behavior.
Prabhakar-like fractional viscoelasticity
Giusti, Andrea; Colombaro, Ivano
2018-03-01
The aim of this paper is to present a linear viscoelastic model based on Prabhakar fractional operators. In particular, we propose a modification of the classical fractional Maxwell model, in which we replace the Caputo derivative with the Prabhakar one. Furthermore, we also discuss how to recover a formal equivalence between the new model and the known classical models of linear viscoelasticity by means of a suitable choice of the parameters in the Prabhakar derivative. Moreover, we also underline an interesting connection between the theory of Prabhakar fractional integrals and the recently introduced Caputo-Fabrizio differential operator.
Interrogating the viscoelastic properties of tissue using viscoelastic response (VISR) ultrasound
Selzo, Mallory Renee
Affecting approximately 1 in 3,500 newborn males, Duchenne muscular dystrophy (DMD) is one of the most common lethal genetic disorders in humans. Boys with DMD suffer progressive loss of muscle strength and function, leading to wheelchair dependence, cardiac and respiratory compromise, and death during young adulthood. There are currently no treatments that can halt or reverse the disease progression, and translating prospective treatments into clinical trials has been delayed by inadequate outcome measures. Current outcome measures, such as functional and muscle strength assessments, lack sensitivity to individual muscles, require subjective effort of the child, and are impacted by normal childhood growth and development. The goal of this research is to develop Viscoelastic Response (VisR) ultrasound which can be used to delineate compositional changes in muscle associated with DMD. In VisR, acoustic radiation force (ARF) is used to produce small, localized displacements within the muscle. Using conventional ultrasound to track the motion, the displacement response of the tissue can be evaluated against a mechanical model. In order to develop signal processing techniques and assess mechanical models, finite element method simulations are used to model the response of a viscoelastic material to ARF excitations. Results are then presented demonstrating VisR differentiation of viscoelastic changes with progressive dystrophic degeneration in a dog model of DMD. Finally, clinical feasibility of VisR imaging is demonstrated in two boys with DMD.
Seismic Wave Propagation in Layered Viscoelastic Media
Borcherdt, R. D.
2008-12-01
Advances in the general theory of wave propagation in layered viscoelastic media reveal new insights regarding seismic waves in the Earth. For example, the theory predicts: 1) P and S waves are predominantly inhomogeneous in a layered anelastic Earth with seismic travel times, particle-motion orbits, energy speeds, Q, and amplitude characteristics that vary with angle of incidence and hence, travel path through the layers, 2) two types of shear waves exist, one with linear and the other with elliptical particle motions each with different absorption coefficients, and 3) surface waves with amplitude and particle motion characteristics not predicted by elasticity, such as Rayleigh-Type waves with tilted elliptical particle motion orbits and Love-Type waves with superimposed sinusoidal amplitude dependencies that decay exponentially with depth. The general theory provides closed-form analytic solutions for body waves, reflection-refraction problems, response of multiple layers, and surface wave problems valid for any material with a viscoelastic response, including the infinite number of models, derivable from various configurations of springs and dashpots, such as elastic, Voight, Maxwell, and Standard Linear. The theory provides solutions independent of the amount of intrinsic absorption and explicit analytic expressions for physical characteristics of body waves in low-loss media such as the deep Earth. The results explain laboratory and seismic observations, such as travel-time and wide-angle reflection amplitude anomalies, not explained by elasticity or one dimensional Q models. They have important implications for some forward modeling and inverse problems. Theoretical advances and corresponding numerical results as recently compiled (Borcherdt, 2008, Viscoelastic Waves in Layered Media, Cambridge University Press) will be reviewed.
Lamins, laminopathies and disease mechanisms
Indian Academy of Sciences (India)
2011-07-08
Jul 8, 2011 ... Lamins are major structural proteins of the nucleus and are essential for nuclear integrity and organization of nuclear functions. Mutations in the human lamin genes lead to highly degenerative genetic diseases that affect a number of different tissues such as muscle, adipose or neuronal tissues, or cause ...
Dynamical problem of micropolar viscoelasticity
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging Solutions)
The dynamic problem in micropolar viscoelastic medium has been investigated by employing eigen value approach after applying Laplace and Fourier transformations. An example of infinite space with concentrated force at the origin has been presented to illustrate the application of the approach. The integral transforms ...
Dynamical problem of micropolar viscoelasticity
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging Solutions)
gen (1969). They discussed the propagation condi- tions and growth equations governing the propa- gation of waves in micropolar viscoelastic medium. Cicco and Nappa (1998) discussed a ... Following Eringen (1967) the constitutive relations and the field equations in ... Cartesian co-ordinates system (x, y, z). To analyze.
Failure criteria for viscoelastic materials
Knauss, W. G.
1974-01-01
Research projects concerned with developing a theory of fracture of materials are discussed. The effects of the geometry of the structure and the loads acting on the structure as they influence the failure process are analyzed. The effects of the viscoelastic deformation characteristics of the bulk elastomer on failure behavior are examined. Additional material parameters which control the fracture process are identified.
Influence of viscoelasticity on bubble coalescence in wormlike micellar solutions
Chandran Suja, Vineeth; Kannan, Aadithya; Andrew Kubicka, Bruce; Fuller, Gerald
2017-11-01
The stability of bubbles against coalescence in wormlike micellar (WLM) solutions is of importance for many industries. The viscoelasticity of the WLM solutions plays a key role in the bubble stability and can be tuned to change the various stages in the drainage of the thin film between bubbles leading to coalescence. Using a single bubble thin film interferometric technique, we have studied the influence of WLM solution (CTAB /Sodium Salicylate) viscoelasticity on the three stages of thin film drainage- the fluid entrainment, dimple formation and its stability, and the transition to a black film prior to coalescence. The fluid entrained decreased with a decrease in the viscoelastic moduli. The bubble also deformed resulting in the formation of a dimple. The dimple formation and its washout depends on the viscoelastic properties of the solution. For lower surfactant concentration, the dimples were seen to become unstable and have larger washout velocities. Further, depending on the relaxation time of the WLM solution, complex washout dynamics involving rapid dimple deceleration, recoil and oscillatory washouts are observed. As the film thins further, we observe stark step-wise transition to a black film, as opposed to pure surfactant systems that exhibit multiple steps.
Hygrothermal effects on the tensile strength of carbon/epoxy laminates with molded edges
Directory of Open Access Journals (Sweden)
Cândido Geraldo Maurício
2000-01-01
Full Text Available The interlaminar stresses are confined to a region near the free edge. Therefore, the laminate stacking sequence and the free edge finishing are some of the factors that affect the strength of the laminate and limit its life. The use of molded edges eliminates the need for trimming and machining the laminates edges thus improving productivity. However, this fabrication technique may have a detrimental effect on the laminate strength for certain stacking sequences. This effect in the presence of moisture has not been characterized. This work presents the results of a comparative study of the resistance to delamination of laminates with machined edges and molded edges. Additionally, two environmental conditions were considered: dry laminates and laminates saturated with moisture. The tensile strength of the laminates were measured and micrographs were used to analyze the microstructure of the laminates near the free edges. It is concluded that the mechanical properties of advanced composites depend on the environmental conditions and the fabrication techniques used to produce the laminates. Therefore, it is necessary to account for these factors when experimentally determining the design allowables.
Mechanical vibration of viscoelastic liquid droplets
Sharp, James; Harrold, Victoria
2014-03-01
The resonant vibrations of viscoelastic sessile droplets supported on different substrates were monitored using a simple laser light scattering technique. In these experiments, laser light was reflected from the surfaces of droplets of high Mw poly acrylamide-co-acrylic acid (PAA) dissolved in water. The scattered light was allowed to fall on the surface of a photodiode detector and a mechanical impulse was applied to the drops using a vibration motor mounted beneath the substrates. The mechanical impulse caused the droplets to vibrate and the scattered light moved across the surface of the photodiode. The resulting time dependent photodiode signal was then Fourier transformed to obtain the mechanical vibrational spectra of the droplets. The frequencies and widths of the resonant peaks were extracted for droplets containing different concentrations of PAA and with a range of sizes. This was repeated for PAA loaded water drops on surfaces which displayed different values of the three phase contact angle. The results were compared to a simple model of droplet vibration which considers the formation of standing wave states on the surface of a viscoelastic droplet. We gratefully acknowledge the support of the Leverhulme trust under grant number RPG-2012-702.
Local linear viscoelasticity of confined fluids.
Hansen, J S; Daivis, P J; Todd, B D
2007-04-14
In this paper the authors propose a novel method to study the local linear viscoelasticity of fluids confined between two walls. The method is based on the linear constitutive equation and provides details about the real and imaginary parts of the local complex viscosity. They apply the method to a simple atomic fluid undergoing zero mean oscillatory flow using nonequilibrium molecular dynamics simulations. The method shows that the viscoelastic properties of the fluid exhibit dramatic spatial changes near the wall-fluid boundary due to the high density in this region. It is also shown that the real part of the viscosity converges to the frequency dependent local shear viscosity sufficiently far away from the wall. This also provides valuable information about the transport properties in the fluid, in general. The viscosity is compared with predictions from the local average density model. The two methods disagree in that the local average density model predicts larger viscosity variations near the wall-fluid boundary than what is observed through the method presented here.
Viscoelasticity of colloidal polycrystals doped with impurities
Louhichi, Ameur; Tamborini, Elisa; Oberdisse, Julian; Cipelletti, Luca; Ramos, Laurence
2015-09-01
We investigate how the microstructure of a colloidal polycrystal influences its linear visco-elasticity. We use thermosensitive copolymer micelles that arrange in water in a cubic crystalline lattice, yielding a colloidal polycrystal. The polycrystal is doped with a small amount of nanoparticles, of size comparable to that of the micelles, which behave as impurities and thus partially segregate in the grain boundaries. We show that the shear elastic modulus only depends on the packing of the micelles and varies neither with the presence of nanoparticles nor with the crystal microstructure. By contrast, we find that the loss modulus is strongly affected by the presence of nanoparticles. A comparison between rheology data and small-angle neutron-scattering data suggests that the loss modulus is dictated by the total amount of nanoparticles in the grain boundaries, which in turn depends on the sample microstructure.
Sternstein, S. S.; Yang, P.
1983-01-01
A new test geometry, referred to as centro-symmetric deformation (CSD), is proposed for characterizing the viscoelastic behavior of the matrix of carbon-epoxy laminates. The sample consists of a thin disk, typically 6-14 plies thick, having a nominal diameter of 30 mm. The disk is freely supported on a circular anvil; the load is applied to the center of the disk using an 8-mm-diameter ball bearing nosepiece. The CSD test geometry provides viscoelastic dispersion data which are independent of the angular orientation of the sample. The test geometry is sufficiently sensitive to matrix changes to allow its use for postcuring, humidity, crosslink density, and other matrix change studies. Test results are presented for a carbon-epoxy laminate.
"Subclinical" laminitis in dairy cattle.
Vermunt, J J
1992-12-01
In dairying countries worldwide, the economic importance of lameness in cattle is now recognised. Laminitis is regarded as a major predisposing factor in lameness caused by claw disorders such as white zone lesions, sole ulcer, and heel horn erosion. The existence of subclinical laminitis was first suggested in the late 1970s by Dutch workers describing the symptoms of sole haemorrhages and yellowish-coloured, soft sole horn. In an attempt to clarify some of the confusing and often conflicting terminology, the literature on laminitis is reviewed. Disturbed haemodynamics, in particular repeated or prolonged dilation of arteriovenous anastomoses, have been implicated in the pathogenesis of both equine and bovine laminitis. Some characteristics of the vascular system of the bovine claw which may be of importance in the pathophysiology of the subclinical laminitis syndrome are therefore discussed. Clinical observations suggest that subclinical laminitis is a multifactorial disease. The different factors that are or may be involved in its aetiology vary in complexity and severity according to the management protocol of the animals. The possible involvement of subclinical laminitis in claw lesions is assessed.
Directory of Open Access Journals (Sweden)
Luciane Maria Laskoski
2016-03-01
Full Text Available ABSTRACT: Laminitis is a severe podal affection, which pathophysiology remains partially renowned. Ischemic, enzymatic, metabolic and inflammatory mechanisms are connected to the development of laminar lesions. However, few therapeutic measures are effective to prevent or control the severity of acute laminitis and its prodromal stage, which often determines serious complications such as rotation and/or sinking of the distal phalanx and even the loss of hoof. The purpose of this study is to compile the actual knowledge in respect to the pathophysiology and treatment of equine laminitis.
Subclinical laminitis in dairy heifers.
Bradley, H K; Shannon, D; Neilson, D R
1989-08-19
By causing poorer horn quality, subclinical laminitis is considered to be a major predisposing cause of other hoof problems, particularly sole ulcers in newly calved heifers. In this study the hind hooves of 136 female Friesian/Holstein cattle aged between four months and two years were examined to discover at what age the signs of subclinical laminitis appeared. Sole haemorrhages were found in the hoof horn of calves as young as five months. The consistent finding of these lesions in heifers of all ages indicated that subclinical laminitis of varying degree was a common condition during the early growing period of young dairy heifers.
Towbin, B D; Meister, P; Pike, B L; Gasser, S M
2010-01-01
Chromatin is nonrandomly distributed in nuclear space, yet the functional significance of this remains unclear. Here, we make use of transgenes carrying developmentally regulated promoters to study subnuclear gene positioning during the development of Caenorhabditis elegans. We found that small transgenes (copy number ≤50) are randomly distributed in early embryonic nuclei, independent of promoter activity. However, in differentiated tissues, these same transgenes occupied specific subnuclear positions: When promoters are repressed, transgenes are found at the nuclear periphery, whereas active, developmentally regulated promoters are enriched in the nuclear core. The absence of specific transgene positioning in embryonic nuclei does not reflect an absence of proteins that mediate perinuclear sequestration: Embryonic nuclei are able to sequester much larger transgene arrays (copy number 300-500) at the periphery. This size-dependent peripheral positioning of gene arrays in early embryos correlates with the accumulation of heterochromatic marks (H3K9me3 and H3K27me3) on large arrays. Interestingly, depletion of nuclear lamina components caused release of arrays from the nuclear envelope and interfered with their efficient silencing. Our results suggest that developmentally silenced chromatin binds the nuclear lamina in a manner correlated with the deposition of heterochromatic marks. Peripheral sequestration of chromatin may, in turn, support the maintenance of silencing.
Matrix elasticity regulates lamin-A,C phosphorylation and turnover with feedback to actomyosin.
Buxboim, Amnon; Swift, Joe; Irianto, Jerome; Spinler, Kyle R; Dingal, P C Dave P; Athirasala, Avathamsa; Kao, Yun-Ruei C; Cho, Sangkyun; Harada, Takamasa; Shin, Jae-Won; Discher, Dennis E
2014-08-18
Tissue microenvironments are characterized not only in terms of chemical composition but also by collective properties such as stiffness, which influences the contractility of a cell, its adherent morphology, and even differentiation. The nucleoskeletal protein lamin-A,C increases with matrix stiffness, confers nuclear mechanical properties, and influences differentiation of mesenchymal stem cells (MSCs), whereas B-type lamins remain relatively constant. Here we show in single-cell analyses that matrix stiffness couples to myosin-II activity to promote lamin-A,C dephosphorylation at Ser22, which regulates turnover, lamina physical properties, and actomyosin expression. Lamin-A,C phosphorylation is low in interphase versus dividing cells, and its levels rise with states of nuclear rounding in which myosin-II generates little to no tension. Phosphorylated lamin-A,C localizes to nucleoplasm, and phosphorylation is enriched on lamin-A,C fragments and is suppressed by a cyclin-dependent kinase (CDK) inhibitor. Lamin-A,C knockdown in primary MSCs suppresses transcripts predominantly among actomyosin genes, especially in the serum response factor (SRF) pathway. Levels of myosin-IIA thus parallel levels of lamin-A,C, with phosphosite mutants revealing a key role for phosphoregulation. In modeling the system as a parsimonious gene circuit, we show that tension-dependent stabilization of lamin-A,C and myosin-IIA can suitably couple nuclear and cell morphology downstream of matrix mechanics. Copyright © 2014 Elsevier Ltd. All rights reserved.
Viscoelastic-gravitational deformation by a rectangular thrust fault in a layered earth
International Nuclear Information System (INIS)
Rundle, J.B.
1982-01-01
Previous papers in this series have been concerned with developing the numerical techniques required for the evaluation of vertical displacements which are the result of thrust faulting in a layered, elastic-gravitational earth model. This paper extends these methods to the calculation of fully time-dependent vertical surface deformation from a rectangular, dipping thrust fault in an elastic-gravitational layer over a viscoelastic-gravitational half space. The elastic-gravitational solutions are used together with the correspondence principle of linear viscoelasticity to give the solution in the Laplace transform domain. The technique used here to invert the displacements into the time domain is the Prony series technique, wherein the transformed solution is fit to the transformed representation of a truncated series of decaying exponentials. Purely viscoelastic results obtained are checked against results found previously using a different inverse transform method, and agreement is excellent. A series of results are obtained for a rectangular, 30 0 dipping thrust fault in an elastic-gravitational layer over viscoelastic-gravitational half space. Time-dependent displacements are calculated out to 50 half space relaxation times tau/sub a/, or 100 Maxwell times 2tau/sub m/ = tau/sub a/. Significant effects due to gravity are shown to exist in the solutions as early as several tau/sub a/. The difference between the purely viscoelastic solution and the viscoelastic-gravitational solutions grows as time progresses. Typically, the solutions with gravity reach an equilibrium value after 10--20 relaxation times, when the purely viscoelastic solutions are still changing significantly. Additionally, the length scaling which was apparent in the purely viscoelastic problem breaks down in the viscoelastic-gravitational problem
Fukahata, Yukitoshi; Matsu'ura, Mitsuhiro
2017-12-01
The viscoelastic deformation of an elastic-viscoelastic composite system is significantly different from that of a simple viscoelastic medium. Here, we show that complicated transient deformation due to viscoelastic stress relaxation after a megathrust earthquake can occur even in a very simple situation, in which an elastic surface layer (lithosphere) is underlain by a viscoelastic substratum (asthenosphere) under gravity. Although the overall decay rate of the system is controlled by the intrinsic relaxation time constant of the asthenosphere, the apparent decay time constant at each observation point is significantly different from place to place and generally much longer than the intrinsic relaxation time constant of the asthenosphere. It is also not rare that the sense of displacement rate is reversed during the viscoelastic relaxation. If we do not bear these points in mind, we may draw false conclusions from observed deformation data. Such complicated transient behavior can be explained mathematically from the characteristics of viscoelastic solution: for an elastic-viscoelastic layered half-space, the viscoelastic solution is expressed as superposition of three decaying components with different relaxation time constants that depend on wavelength.
Fukahata, Yukitoshi; Matsu'ura, Mitsuhiro
2018-02-01
The viscoelastic deformation of an elastic-viscoelastic composite system is significantly different from that of a simple viscoelastic medium. Here, we show that complicated transient deformation due to viscoelastic stress relaxation after a megathrust earthquake can occur even in a very simple situation, in which an elastic surface layer (lithosphere) is underlain by a viscoelastic substratum (asthenosphere) under gravity. Although the overall decay rate of the system is controlled by the intrinsic relaxation time constant of the asthenosphere, the apparent decay time constant at each observation point is significantly different from place to place and generally much longer than the intrinsic relaxation time constant of the asthenosphere. It is also not rare that the sense of displacement rate is reversed during the viscoelastic relaxation. If we do not bear these points in mind, we may draw false conclusions from observed deformation data. Such complicated transient behavior can be explained mathematically from the characteristics of viscoelastic solution: for an elastic-viscoelastic layered half-space, the viscoelastic solution is expressed as superposition of three decaying components with different relaxation time constants that depend on wavelength.
Insulin resistance and laminitis in horses
Horn, Isabella
2009-01-01
Laminitis is a common painful condition in horses that often has a poor outcome. The aetiology of laminitis has been widely studied, but still not completely understood. There is some evidence that pasture associated laminitis is one of the most common forms of laminitis , and this is most likely associated with underlying endocrine dysfunction i.e. insulin resistance. However, what the prevalence of insulin resistance in horses presented with laminitis is, that is currently unknown and it ha...
Dynamic Electromechanical Response of a Viscoelastic Dielectric Elastomer under Cycle Electric Loads
Directory of Open Access Journals (Sweden)
Junjie Sheng
2018-01-01
Full Text Available Dielectric elastomer (DE is able to produce large electromechanical deformation which is time-dependent due to the viscoelasticity. In the current study, a thermodynamic model is set up to characterize the influence of viscoelasticity on the electromechanical and dynamic response of a viscoelastic DE. The time-dependent dynamic deformation, the hysteresis, and the dynamic stability undergoing viscoelastic dissipative processes are investigated. The results show that the electromechanical stability has strong frequency dependence; the viscoelastic DE can attain a larger stretch in the dynamic response than the quasistatic actuation. Furthermore, with the decreasing frequency of the applied electric load, the viscoelastic DE system will present dynamic stability evolution from an aperiodic motion to the quasiperiodic motion. The DE system may also experience a stability evolution from a single cycle motion to multicycle motion with the increasing relaxation times. The value and variation trend of the amplitude of the stretch are highly dependent on the excitation frequency and the relaxation time.
The forward undulatory locomotion of Ceanorhabditis elegans in viscoelastic fluids
Shen, Amy; Ulrich, Xialing
2013-11-01
Caenorhabditis elegans is a soil dwelling roundworm that has served as model organisms for studying a multitude of biological and engineering phenomena. We study the undulatory locomotion of nematode in viscoelastic fluids with zero-shear viscosity varying from 0.03-75 Pa .s and relaxation times ranging from 0-350 s. We observe that the averaged normalized wavelength of swimming worm is essentially the same as that in Newtonian fluids. The undulatory frequency f shows the same reduction rate with respect to zero-shear viscosity in viscoelastic fluids as that found in the Newtonian fluids, meaning that the undulatory frequency is mainly controlled by the fluid viscosity. However, the moving speed Vm of the worm shows more distinct dependence on the elasticity of the fluid and exhibits a 4% drop with each 10-fold increase of the Deborah number De, a dimensionless number characterizing the elasticity of a fluid. To estimate the swimming efficiency coefficient and the ratio K =CN /CL of resistive coefficients of the worm in various viscoelastic fluids, we show that whereas it would take the worm around 7 periods to move a body length in a Newtonian fluid, it would take 27 periods to move a body length in a highly viscoelastic fluid.
Viscoelastic-Viscoplastic Modelling of the Scratch Response of PMMA
Directory of Open Access Journals (Sweden)
G. Kermouche
2013-01-01
Full Text Available This paper aims at understanding how to model the time-dependent behavior of PMMA during a scratch loading at a constant speed and at middle strain levels. A brief experimental study is first presented, consisting of the analysis of microscratches carried out at various scratching velocities and normal loads. The loading conditions have been chosen in such a way that neither (viscoelasticity nor (viscoplasticity of the PMMA may be neglected a priori. The main analyzed parameter is the tip penetration depth measured during the steady state. Then, a finite element model is used to investigate the potential of classical elastic-viscoplastic constitutive models to reproduce these experimental results. It is mainly shown that these models lead to unsatisfying results. More specifically, it is pointed out here that the time-independent Young modulus used in such models is not suitable. To take into account this feature, a viscoelastic-viscoplastic model based on the connection in series of a viscoelastic part with a viscoplastic part is proposed. It is shown that it leads to more acceptable results, which points out the importance of viscoelasticity in the scratch behavior of solid polymers.
Viscoelastic performance of dielectric elastomer subject to different voltage stimulation
Sheng, Junjie; Zhang, Yuqing; Liu, Lei; Li, Bo; Chen, Hualing
2017-04-01
Dielectric elastomer (DE) is capable of giant deformation subject to an electric field, and demonstrates significant advantages in the potentially application of soft machines with muscle-like characteristics. Due to an inherent property of all macromolecular materials, DE exhibits strong viscoelastic properties. Viscoelasticity could cause a time-dependent deformation and lower the response speed and energy conversion efficiency of DE based actuators, thus strongly affect its electromechanical performance and applications. Combining with the rheological model of viscoelastic relaxation, the viscoelastic performance of a VHB membrane in a circular actuator configuration undergoing separately constant, ramp and sinusoidal voltages are analyzed both theoretically and experimentally. The theoretical results indicated that DE could attain a big deformation under a small constant voltage with a longer time or under a big voltage with a shorter time. The model also showed that a higher critical stretch could be achieved by applying ramping voltage with a lower rate and the stretch magnitude under sinusoidal voltage is much larger at a relatively low frequency. Finally, experiments were designed to validate the simulation and show well consistent with the simulation results.
Dynamic viscoelastic models of human skin using optical elastography
International Nuclear Information System (INIS)
Kearney, Steven P; Khan, Altaf; Dai, Zoujun; Royston, Thomas J
2015-01-01
A novel technique for measuring in vivo human skin viscoelastic properties using optical elastography has been developed. The technique uses geometrically focused surface (GFS) waves that allow for wide bandwidth measurements of the wave field. An analytical solution for the case of a radiating annular disk surface source was fit to experimentally measured GFS waves, enabling an estimate of the frequency-dependent surface wavenumber, which can then be related to the dynamic shear modulus. Several viscoelastic models were then fit to the dynamic shear modulus dispersion curve. Viscoelastic models were evaluated based on their overall quality of fit and variability amongst healthy volunteers. An Ecoflex phantom was used to validate the procedure and results by comparison to similar studies using the same type of phantom. For skin results, it was found that the ‘α’ parameters from the fractional models had the least variability, with coefficients of variability of 0.15, and 0.16. The best fitting models were the standard linear solid, and the fractional Voigt, with a mean fit correlation coefficient, R 2 , of 0.93, 0.89, respectively. This study has demonstrated the efficacy of this new method, and with larger studies the viscoelastic skin models could be used to identify various skin diseases and their response to treatment. (paper)
PIV and DNS analyses of viscoelastic turbulent flows behind a rectangular orifice
International Nuclear Information System (INIS)
Tsukahara, Takahiro; Motozawa, Masaaki; Tsurumi, Daisei; Kawaguchi, Yasuo
2013-01-01
Highlights: • Viscoelastic fluid turbulence in relaxing and non-equilibrium flow is investigated. • Numerical and experimental results of viscoelastic turbulent orifice flow are provided. • DNS result using Giesekus model agrees well with the experimental one by surfactant solution. • Formation of Kelvin–Helmholtz vortices behind the orifice weakens in viscoelastic flows. • Highly viscoelastic flow reduces the form drag, but increases the skin friction due to extra stress. -- Abstract: We performed PIV (particle image velocimetry) measurements and DNS (direct numerical simulations) on turbulent orifice flows for the Newtonian fluid and viscoelastic fluids, and compared their results with emphasis on turbulence statistics and vortical motions just behind the orifice rib. In the experiment, a cationic surfactant solution of CTAC (cetyltrimethyl ammonium chloride) was chosen as the viscoelastic fluid that is known to provide substantial drag reduction in the case of smooth-wall turbulence. In the viscoelastic flows, the formation of the Kelvin–Helmholtz vortices emanating from the orifice edge was found to be attenuated compared to the Newtonian case, resulting in the suppression of turbulent eddies and Reynolds shear stress behind the orifice. However, the variation of the drag depended on the Reynolds number and the surfactant concentration (or the Weissenberg number): that is, the drag-reducing effect can be achieved only in limited conditions or low Reynolds-number flows. Although DNS results was found to be in qualitative agreement with the experimental data, we discussed also inconsistency between the experimental and DNS results
Laskoski, Luciane Maria; Valadão, Carlos Augusto Araújo; Dittrich, Rosangela Locatelli; Deconto, Ivan; Faleiros, Rafael Resende
2016-01-01
ABSTRACT: Laminitis is a severe podal affection, which pathophysiology remains partially renowned. Ischemic, enzymatic, metabolic and inflammatory mechanisms are connected to the development of laminar lesions. However, few therapeutic measures are effective to prevent or control the severity of acute laminitis and its prodromal stage, which often determines serious complications such as rotation and/or sinking of the distal phalanx and even the loss of hoof. The purpose of this study is to c...
Implementation of viscoelastic Hopkinson bars
Directory of Open Access Journals (Sweden)
Govender R.
2012-08-01
Full Text Available Knowledge of the properties of soft, viscoelastic materials at high strain rates are important in furthering our understanding of their role during blast or impact events. Testing these low impedance materials using a metallic split Hopkinson pressure bar setup results in poor signal to noise ratios due to impedance mismatching. These difficulties are overcome by using polymeric Hopkinson bars. Conventional Hopkinson bar analysis cannot be used on the polymeric bars due to the viscoelastic nature of the bar material. Implementing polymeric Hopkinson bars requires characterization of the viscoelastic properties of the material used. In this paper, 30 mm diameter Polymethyl Methacrylate bars are used as Hopkinson pressure bars. This testing technique is applied to polymeric foam called Divinycell H80 and H200. Although there is a large body of of literature containing compressive data, this rarely deals with strain rates above 250s−1 which becomes increasingly important when looking at the design of composite structures where energy absorption during impact events is high on the list of priorities. Testing of polymeric foams at high strain rates allows for the development of better constitutive models.
Viscoelastic-electromagnetism and Hall viscosity
Hidaka, Yoshimasa; Hirono, Yuji; Kimura, Taro; Minami, Yuki
2012-01-01
We introduce a kind of electromagnetism, which we call viscoelastic-electromagnetism, to investigate viscoelastic transport phenomena. It is shown that Cartan's formalism of general relativity is essential for viscoelastic theory, and then the corresponding electric and magnetic fields are regarded as a velocity gradient and a Burgers vector density, respectively. As an application of this formalism, the Streda formula for the Hall viscosity is obtained.
Water evaporation on highly viscoelastic polymer surfaces.
Pu, Gang; Severtson, Steven J
2012-07-03
Results are reported for a study on the evaporation of water droplets from a highly viscoelastic acrylic polymer surface. These are contrasted with those collected for the same measurements carried out on polydimethylsiloxane (PDMS). For PDMS, the evaporation process involves the expected multistep process including constant drop area, constant contact angle, and finally a combination of these steps until the liquid is gone. In contrast, water evaporation from the acrylic polymer shows a constant drop area mode throughout. Furthermore, during the evaporation process, the drop area actually expands on the acrylic polymer. The single mode evaporation process is consistent with formation of wetting structures, which cannot be propagated by the capillary forces. Expansion of the drop area is attributed to the influence of the drop capillary pressure. Furthermore, the rate of drop area expansion is shown to be dependent on the thickness of the polymer film.
Shape recovery of viscoelastic beams after stowage
DEFF Research Database (Denmark)
Kwok, Kawai
2015-01-01
The deployment of viscoelastic structures that have been held stowed for a given time duration can be formulated as a viscoelastic boundary value problem in which the prescribed condition switches from constant displacement to constant traction. This paper presents closed-form expressions...... for the load relaxation and shape recovery of a linear viscoelastic beam subject to such time-varying constraints. It is shown that a viscoelastic beam recovers to its original shape asymptotically over time. The analytical solutions are employed to investigate the effect of temperature and stowage time...
Modeling of Shock Propagation and Attenuation in Viscoelastic Components
Directory of Open Access Journals (Sweden)
R. Rusovici
2001-01-01
Full Text Available Protection from the potentially damaging effects of shock loading is a common design requirement for diverse mechanical structures ranging from shock accelerometers to spacecraft. High damping viscoelastic materials are employed in the design of geometrically complex, impact-absorbent components. Since shock transients are characterized by a broad frequency spectrum, it is imperative to properly model frequency dependence of material behavior over a wide frequency range. The Anelastic Displacement Fields (ADF method is employed herein to model frequency-dependence within a time-domain finite element framework. Axisymmetric, ADF finite elements are developed and then used to model shock propagation and absorption through viscoelastic structures. The model predictions are verified against longitudinal wave propagation experimental data and theory.
Influence of support viscoelastic properties on the structural wave propagation
International Nuclear Information System (INIS)
Park, Jun Hong
2007-01-01
The dissipation of the structural vibration energy at viscoelastic supports is an efficient method of reducing modal resonances and consequent noise and fatigue related problems. The support stiffness has significant impact on the modal characteristics. The dissipation capabilities of the viscoelastic support depend on its stiffness. Methods to optimally tune this support stiffness are proposed in this study. The characteristic mechanical impedance for structural vibration is obtained from wave propagation analysis and non-reflecting boundary conditions. The wave propagation is analyzed near the supports installed at edges, middle of a structure, and for the tuned vibration absorber. The dependence of the optimal stiffness on the location and mass of the supports is identified. A simple analytical solution for optimal support stiffness for maximum dissipation of propagating vibration energy at supports is presented
Estimation of adhesive bond strength in laminated safety glass using guided mechanical waves
Huo, Shihong
Laminated safety glass is used in the automobile industry and in architectural applications. Laminated safety glass consists of a plastic interlayer, such as a layer of poly vinyl butyral (PVB) or Butacite, surrounded by two adjacent glass plates. The glass can be float glass, plate glass, tempered glass, or sheet glass, and the plastic interlayer is made of a viscoelastic material with relatively high damping. The level of adhesive bond strength between the plastic interlayer and the two adjacent glass plates has a significant role in the penetration resistance against flying objects and is a critical parameter towards ensuring the proper performance of safety glass. Therefore, estimation and control of adhesive bond levels in laminated safety glass is a critical issue. There are several destructive testing procedures used to quantify the adhesion level in laminated safety glass. These tests include the tension test, the peel test, the impact test, and the pummel test. All these tests have drawbacks including the pummel test method, which has been the most widely used in industry for over 80 years. The primary drawbacks of the pummel test method are that it is destructive and subjective (i.e., involves individual human judgment), which precludes this method for use as an on-line test method for quality control. Consequently, a quantitative nondestructive testing method to evaluate adhesion levels would be an asset to the laminated safety glass industry. In this study, adhesion levels in laminated safety glass samples, i.e., windshields, have been assessed using the guided mechanical wave method. To study the adhesive bond strength analytically, the imperfect interfaces between the plastic interlayer and the two adjacent glass plates in laminated safety glass are modeled using a bed of longitudinal and shear springs, and their stiffness characteristics are estimated using fracture mechanics and atomic force microscopy (AFM) surface measurements. The atomic force
Viscoelasticity of Brownian Carbon Nanotubes in PDMS Semidilute Regime
MARCEAU, Sandrine; DUBOIS, Philippe; FULCHIRON, René; CASSAGNAU, Philippe
2009-01-01
The objective of the present paper is to investigate the linear viscoelasticity of diluted suspension of MWNT spread in PDMS. Specifically, we focus our attention on both the CNT relaxation in semidilute conditions and the concept of percolation threshold for such system. Finally, the results, and mainly the concentration dependence of the zero-shear viscosity and mean relaxation time, will be discussed within the Doi−Edwards theory framework on molecular dynamic of rigid rods in a semi...
Posnansky, Oleg P.
2014-12-01
In this work we introduce a 2D minimal model of random scale-invariant network structures embedded in a matrix to study the influence of microscopic architecture elements on the viscoelastic behavior of soft biological tissue. Viscoelastic properties at a microscale are modeled by a cohort of basic elements with varying complexity integrated into multi-hierarchic lattice obeying self-similar geometry. It is found that this hierarchy of structure elements yields a global nonlinear frequency dependent complex-valued shear modulus. In the dynamic range of external frequency load, the modeled shear modulus proved sensitive to the network concentration and viscoelastic characteristics of basic elements. The proposed model provides a theoretical framework for the interpretation of dynamic viscoelastic parameters in the context of microstructural variations under different conditions.
Magnetic and viscoelastic response of elastomers with hard magnetic filler
International Nuclear Information System (INIS)
Kramarenko, E Yu; Chertovich, A V; Semisalova, A S; Makarova, L A; Perov, N S; Khokhlov, A R; Stepanov, G V
2015-01-01
Magnetic elastomers (MEs) based on a silicone matrix and magnetically hard NdFeB particles have been synthesized and their magnetic and viscoelastic properties have been studied depending on the size and concentration of magnetic particles and the magnetizing field. It has been shown that magnetic particles can rotate in soft polymer matrix under applied magnetic field, this fact leading to some features in both magnetic and viscoelastic properties. In the maximum magnetic field used magnetization of MEs with smaller particles is larger while the coercivity is smaller due to higher mobility of the particles within the polymer matrix. Viscoelastic behavior is characterized by long relaxation times due to restructuring of the magnetic filler under the influence of an applied mechanical force and magnetic interactions. The storage and loss moduli of magnetically hard elastomers grow significantly with magnetizing field. The magnetic response of the magnetized samples depends on the mutual orientation of the external magnetic field and the internal sample magnetization. Due to the particle rotation within the polymer matrix, the loss factor increases abruptly when the magnetic field is turned on in the opposite direction to the sample magnetization, further decreasing with time. Moduli versus field dependences have minimum at non-zero field and are characterized by a high asymmetry with respect to the field direction. (paper)
Sorting Nexin 6 Enhances Lamin A Synthesis and Incorporation into the Nuclear Envelope
González-Granado, Jose M.; Navarro-Puche, Ana; Molina-Sanchez, Pedro; Blanco-Berrocal, Marta; Viana, Rosa; de Mora, Jaime Font; Andrés, Vicente
2014-01-01
Nuclear lamins are important structural and functional proteins in mammalian cells, but little is known about the mechanisms and cofactors that regulate their traffic into the nucleus. Here, we demonstrate that trafficking of lamin A, but not lamin B1, and its assembly into the nuclear envelope are regulated by sorting nexin 6 (SNX6), a major component of the retromer that targets proteins and other molecules to specific subcellular locations. SNX6 interacts with lamin A in vitro and in vivo and links it to the outer surface of the endoplasmic reticulum in human and mouse cells. SNX6 transports its lamin A cargo to the nuclear envelope in a process that takes several hours. Lamin A protein levels in the nucleus augment or decrease, respectively, upon gain or loss of SNX6 function. We further show that SNX6-dependent lamin A nuclear import occurs across the nuclear pore complex via a RAN-GTP-dependent mechanism. These results identify SNX6 as a key regulator of lamin A synthesis and incorporation into the nuclear envelope. PMID:25535984
Sorting nexin 6 enhances lamin a synthesis and incorporation into the nuclear envelope.
Directory of Open Access Journals (Sweden)
Jose M González-Granado
Full Text Available Nuclear lamins are important structural and functional proteins in mammalian cells, but little is known about the mechanisms and cofactors that regulate their traffic into the nucleus. Here, we demonstrate that trafficking of lamin A, but not lamin B1, and its assembly into the nuclear envelope are regulated by sorting nexin 6 (SNX6, a major component of the retromer that targets proteins and other molecules to specific subcellular locations. SNX6 interacts with lamin A in vitro and in vivo and links it to the outer surface of the endoplasmic reticulum in human and mouse cells. SNX6 transports its lamin A cargo to the nuclear envelope in a process that takes several hours. Lamin A protein levels in the nucleus augment or decrease, respectively, upon gain or loss of SNX6 function. We further show that SNX6-dependent lamin A nuclear import occurs across the nuclear pore complex via a RAN-GTP-dependent mechanism. These results identify SNX6 as a key regulator of lamin A synthesis and incorporation into the nuclear envelope.
Observation of viscoelastic displacement recovery after microindentation
Czech Academy of Sciences Publication Activity Database
Minster, Jiří; Novák, Z.
2011-01-01
Roč. 15, č. 3 (2011), s. 317-325 ISSN 1385-2000 R&D Projects: GA AV ČR(CZ) IAA200710801 Institutional research plan: CEZ:AV0Z20710524 Keywords : quasi-homogenous and quasi-isotropic viscoelastic material * microindentation * viscoelastic compliance * interferometry * creep recovery Subject RIV: JI - Composite Materials Impact factor: 1.109, year: 2011
Viscoelastic modes in chiral liquid crystals
Indian Academy of Sciences (India)
2015-11-27
Nov 27, 2015 ... Viscoelastic properties of liquid crystals are very important for applications like display technology. However, there are not many direct techniques to study them. In this review, we describe our studies on the viscoelastic modes of some chiral liquid crystals using dynamic light scattering. We discuss ...
experimental viscoelastic characterization of corn cob composites ...
African Journals Online (AJOL)
Dr Obe
static radial compression, determine a viscoelastic or rheological model for the tested corn cob samples, and investigate the effects of moisture content and rate of loading on the viscoelastic constants that characterize the ... exchange of kinetic energy on that scale. As any other model, mechanical models give at most part ...
Analytical study for deformability of laminated sheet metal
Directory of Open Access Journals (Sweden)
Mohammed H. Serror
2013-01-01
Full Text Available While a freestanding high-strength sheet metal subject to tension will rupture at a small strain, it is anticipated that lamination with a ductile sheet metal will retard this instability to an extent that depends on the relative thickness, the relative stiffness, and the hardening exponent of the ductile sheet. This paper presents an analytical study for the deformability of such laminate within the context of necking instability. Laminates of high-strength sheet metal and ductile low-strength sheet metal are studied assuming: (1 sheets are fully bonded; and (2 metals obey the power law material model. The effect of hardening exponent, volume fraction and relative stiffness of the ductile component has been studied. In addition, stability of both uniform and nonuniform deformations has been investigated under plane strain condition. The results have shown the retardation of the high-strength layer instability by lamination with the ductile layer. This has been achieved through controlling the aforementioned key parameters of the ductile component, while the laminate exhibits marked enhancement in strength–ductility combination that is essential for metal forming applications.
Analytical study for deformability of laminated sheet metal.
Serror, Mohammed H
2013-01-01
While a freestanding high-strength sheet metal subject to tension will rupture at a small strain, it is anticipated that lamination with a ductile sheet metal will retard this instability to an extent that depends on the relative thickness, the relative stiffness, and the hardening exponent of the ductile sheet. This paper presents an analytical study for the deformability of such laminate within the context of necking instability. Laminates of high-strength sheet metal and ductile low-strength sheet metal are studied assuming: (1) sheets are fully bonded; and (2) metals obey the power law material model. The effect of hardening exponent, volume fraction and relative stiffness of the ductile component has been studied. In addition, stability of both uniform and nonuniform deformations has been investigated under plane strain condition. The results have shown the retardation of the high-strength layer instability by lamination with the ductile layer. This has been achieved through controlling the aforementioned key parameters of the ductile component, while the laminate exhibits marked enhancement in strength-ductility combination that is essential for metal forming applications.
Using lamb waves tomonitor moisture absorption thermally fatigues composite laminates
Energy Technology Data Exchange (ETDEWEB)
Lee, Jae Sun; Cho, Youn Ho [School of Mechanical Engineering, Pusan National University, Busan (Korea, Republic of)
2016-06-15
Nondestructive evaluation for material health monitoring is important in aerospace industries. Composite laminates are exposed to heat cyclic loading and humid environment depending on flight conditions. Cyclic heat loading and moisture absorption may lead to material degradation such as matrix breaking, debonding, and delamination. In this paper, the moisture absorption ratio was investigated by measuring the Lamb wave velocity. The composite laminates were manufactured and subjected to different thermal aging cycles and moisture absorption. For various conditions of these cycles, not only changes in weight and also ultrasonic wave velocity were measured, and the Lamb wave velocity at various levels of moisture on a carbon-epoxy plate was investigated. Results from the experiment show a linear correlation between moisture absorption ratio and Lamb wave velocity at different thermal fatigue stages. The presented method can be applied as an alternative solution in the online monitoring of composite laminate moisture levels in commercial flights.
Axial Dynamic Stiffness of Tubular Piles in Viscoelastic Soil
DEFF Research Database (Denmark)
Bayat, Mehdi; Andersen, Lars Vabbersgaard; Ibsen, Lars Bo
2016-01-01
Large offshore wind turbines are f0W1ded on jacket structures. In this study, an elastic full-space jacket structure foundation in an elastic and viscoelastic medium is investigated by using boundary integral equations. The jacket structure foundation is modeled as a hollow, long circular cylinder......-resonance are presented .in series of Bessel's function. Important responses, such as dynamic stiffness and phase angle, are compared for different values of the loss factor as the material damping, Y0W1g's modulus and Poisson's ratio in a viscoelastic soil. Results are verified. with known results reported...... in the literature. It is observed that the dynamic stiffness fluctuates with the loss factor, and the turning point is independent of the loss factor while the turning point increases with load frequency. It is seen that the non-dimensional dynamic stiffness is dependent on Young's modulus and Poisson's ratio...
Transient behaviour of a polymer dragged through a viscoelastic medium.
Vandebroek, Hans; Vanderzande, Carlo
2014-09-21
We study the dynamics of a polymer that is pulled by a constant force through a viscoelastic medium. This is a model for a polymer being pulled through a cell by an external force, or for an active biopolymer moving due to a self-generated force. Using the Rouse model with a memory dependent drag force, we find that the center of mass of the polymer follows a subballistic motion. We determine the time evolution of the length and the shape of the polymer. Through an analysis of the velocity of the monomers, we investigate how the tension propagates through the polymer. We discuss how polymers can be used to probe the properties of a viscoelastic medium.
Codimension zero laminations are inverse limits
Lozano Rojo, Álvaro
2013-01-01
The aim of the paper is to investigate the relation between inverse limit of branched manifolds and codimension zero laminations. We give necessary and sufficient conditions for such an inverse limit to be a lamination. We also show that codimension zero laminations are inverse limits of branched manifolds. The inverse limit structure allows us to show that equicontinuous codimension zero laminations preserves a distance function on transversals.
Visualization and Theoretical Analysis for Instabilities of Viscoelastic Flow
Kometani, Hideo; Kitajima, Hidetoshi; Matsumura, Takumi; Suga, Takanori; Kanai, Toshitaka
The flow instabilities of polymer melts known as viscoelastic fluid were discussed in this report. Especially the occurrence mechanisms of two typical flow instabilities of “Shark Skin” and “Melt Fracture” were experimentally analyzed and the occurrence criteria for the flow instabilities were clarified with the viscoelastic flow simulation. As for “Shark Skin” region, the surface roughness at the die exit was observed without the pressure fluctuation and the flow pattern fluctuation at the wall vicinity in the die land. This result indicates that “Shark Skin” occurs at the die exit. As for “Melt Fracture” region, the periodical oscillation of the flow pattern and the periodical pressure fluctuation corresponding to the periodical distortion of the extrudate were recognized in the die land without the periodical oscillation of the flow pattern and the periodical pressure fluctuation in the reservoir (entry region of the die land). This result indicates that “Melt Fracture” is initiated at the die entry and occurs in the die land. Furthermore with the viscoelastic flow simulation, it was confirmed that the occurrence of “Shark Skin” depends on the wall shear stress and the occurrence of “Melt Fracture” depends on the maximum normal stress of flow direction.
Lamin A reassembly at the end of mitosis is regulated by its SUMO-interacting motif
International Nuclear Information System (INIS)
Moriuchi, Takanobu; Kuroda, Masaki; Kusumoto, Fumiya; Osumi, Takashi; Hirose, Fumiko
2016-01-01
Modification of proteins with small ubiquitin-related modifier (SUMO; SUMOylation) is involved in the regulation of various biological processes. Recent studies have demonstrated that noncovalent associations between SUMOylated proteins and co-operative proteins containing SUMO-interacting motifs (SIMs) are important for the spatiotemporal organization of many protein complexes. In this study, we demonstrate that interactions between lamin A, a major component of the nuclear lamina, and SUMO isoforms are dependent on one of the four SIMs (SIM3) resided in lamin A polypeptide in vitro. Live cell imaging and immunofluorescence staining showed that SIM3 is required for accumulation of lamin A on the chromosomes during telophase, and subsequent evaluation of a panel of deletion mutants determined that a 156-amino acid region spanning the carboxyl-terminal Ig-fold domain of lamin A is sufficient for this accumulation. Notably, mutation of SIM3 abrogated the dephosphorylation of mitosis-specific phosphorylation at Ser-22 of lamin A, which normally occurs during telophase, and the subsequent nuclear lamina reorganization. Furthermore, expression of a conjugation-defective SUMO2 mutant, which was previously shown to inhibit endogenous SUMOylation in a dominant-negative manner, also impaired the accumulation of wild type lamin A on telophase chromosomes. These findings suggest that interactions between SIM3 of lamin A and a putative SUMO2-modified protein plays an important role in the reorganization of the nuclear lamina at the end of mitosis. - Highlights: • Lamin A interacts with SUMO2 via a SUMO-interacting motif (SIM) in the Ig domain. • SIM3 of lamin A is responsible for chromosomal accumulation during telophase. • A 156-aa region spanning the Ig domain is sufficient for chromosomal accumulation. • Accumulation of lamin A is required for timely dephosphorylation on chromosomes. • A putative SUMO2-modified protein may mediate chromosomal accumulation of lamin
Lamin A reassembly at the end of mitosis is regulated by its SUMO-interacting motif
Energy Technology Data Exchange (ETDEWEB)
Moriuchi, Takanobu; Kuroda, Masaki; Kusumoto, Fumiya; Osumi, Takashi; Hirose, Fumiko, E-mail: fhirose@sci.u-hyogo.ac.jp
2016-03-01
Modification of proteins with small ubiquitin-related modifier (SUMO; SUMOylation) is involved in the regulation of various biological processes. Recent studies have demonstrated that noncovalent associations between SUMOylated proteins and co-operative proteins containing SUMO-interacting motifs (SIMs) are important for the spatiotemporal organization of many protein complexes. In this study, we demonstrate that interactions between lamin A, a major component of the nuclear lamina, and SUMO isoforms are dependent on one of the four SIMs (SIM3) resided in lamin A polypeptide in vitro. Live cell imaging and immunofluorescence staining showed that SIM3 is required for accumulation of lamin A on the chromosomes during telophase, and subsequent evaluation of a panel of deletion mutants determined that a 156-amino acid region spanning the carboxyl-terminal Ig-fold domain of lamin A is sufficient for this accumulation. Notably, mutation of SIM3 abrogated the dephosphorylation of mitosis-specific phosphorylation at Ser-22 of lamin A, which normally occurs during telophase, and the subsequent nuclear lamina reorganization. Furthermore, expression of a conjugation-defective SUMO2 mutant, which was previously shown to inhibit endogenous SUMOylation in a dominant-negative manner, also impaired the accumulation of wild type lamin A on telophase chromosomes. These findings suggest that interactions between SIM3 of lamin A and a putative SUMO2-modified protein plays an important role in the reorganization of the nuclear lamina at the end of mitosis. - Highlights: • Lamin A interacts with SUMO2 via a SUMO-interacting motif (SIM) in the Ig domain. • SIM3 of lamin A is responsible for chromosomal accumulation during telophase. • A 156-aa region spanning the Ig domain is sufficient for chromosomal accumulation. • Accumulation of lamin A is required for timely dephosphorylation on chromosomes. • A putative SUMO2-modified protein may mediate chromosomal accumulation of lamin
Laser cutting of Kevlar laminates
Energy Technology Data Exchange (ETDEWEB)
VanCleave, R.A.
1977-09-01
An investigation has been conducted of the use of laser energy for cutting contours, diameters, and holes in flat and shaped Kevlar 49 fiber-reinforced epoxy laminates as an alternate to conventional machining. The investigation has shown that flat laminates 6.35 mm thick may be cut without backup by using a high-powered (1000-watt) continuous wave CO/sub 2/ laser at high feedrates (33.87 mm per second). The cut produced was free of the burrs and delaminations resulting from conventional machining methods without intimate contact backup. In addition, the process cycle time was greatly reduced.
Continuous jute fibre reinforced laminated paper composite
Indian Academy of Sciences (India)
Plastic bags create a serious environmental problem. The proposed jute fibre reinforced laminated paper composite and reinforcement-fibre free paper laminate may help to combat the war against this pollutant to certain extent. The paper laminate, without reinforcement fibre, exhibited a few fold superiority in tensile ...
Catherine M. Marx; Russell C. Moody
1981-01-01
A total of 180 small Douglas FirâLarch (DF-L) or Southern Pine (SP) glued-laminated beams were evaluated to determine the tension lamination quality necessary to obtain desired design stresses. The test beams had either the regular laminating grades of L1 DF-L/No. 1D SP or the special 302-24 laminating grade as tension laminations. Because an initial set of SP beams...
Dynamics of a supercritical composite shaft mounted on viscoelastic supports
Montagnier, O.; Hochard, C.
2014-01-01
The damping in a carbon fiber reinforced plastic (CFRP) laminate is greater than that which occurs in most metallic materials. In the supercritical regime, the damping can trigger unstable whirl oscillations, which can have catastrophic effects. The vibrations occurring in a supercritical composite drive shaft are investigated here in order to predict instabilities of this kind. A simply supported carbon/epoxy composite tube mounted on viscoelastic supports is studied, using an approximation of the Rayleigh-Timoshenko equation. The damping process is assumed to be hysteretic. The composite behavior is described in terms of modulus and loss factor, taking homogenized values. The critical speeds are obtained in several analytical forms in order to determine the effects of factors such as the rotatory inertia, the gyroscopic forces, the transverse shear and the supports stiffness. Assuming that the hysteretic damping can be expressed in terms of the equivalent viscous model, the threshold speed is obtained in the form of an analytical criterion. The influence of the various factors involved is quantified at the first critical speed of a subcritical composite shaft previously described in the literature. The influence of the coupling mechanisms on the unsymmetrical composite laminate and the end fittings is also investigated using a finite element model. None of these parameters were found to have a decisive influence in this case. Those having the greatest effects were the transverse shear and the supports stiffness. The effects of the composite stacking sequence, the shaft length and the supports stiffness on the threshold speed were then investigated. In particular, drive shafts consisting only of ±45° or ±30° plies can be said to be generally unstable in the supercritical regime due to their very high loss factors.
Structure-induced nonlinear viscoelasticity of non-woven fibrous matrices.
Rizvi, Mohd Suhail; Pal, Anupam; Das, Sovan Lal
2016-12-01
Fibrous materials are widely utilized as tissue engineering scaffolds for tissue regeneration and other bioengineering applications. The structural as well as mechanical characteristics of the fibrous matrices under static and dynamic mechanical loading conditions influence the response of the cells. In this paper, we study the mechanical response of the non-woven fibrous matrices under oscillatory loading conditions and its dependence on the structural properties of fibrous matrix. We demonstrate that under oscillatory shear and elongation, the fibrous matrices demonstrate nonlinear viscoelasticity at all strain amplitudes. This is contrary to the behavior of other soft polymeric materials for which nonlinearity in the viscoelastic response vanishes for small strains. These observations suggest that despite their prevalence, the measures of linear viscoelasticity (e.g., storage and loss moduli) are inadequate for the general description of the viscoelastic nature of the fibrous materials. It was, however, found that linear viscoelastic nature of fibrous matrices for small amplitudes is restored when a pre-stretch is applied to the fibrous matrix along with oscillatory strains. Further, we also explored the influence of the structural properties of the fibrous matrices (fiber orientation, alignment and curvature) on their viscoelastic nature.
Analysis of viscoelastic behavior of a filled elastomer under action of different loads
Directory of Open Access Journals (Sweden)
Gligorijević Nikola I.
2017-01-01
Full Text Available Mechanical properties of viscoelastic filled polymers strongly depend on temperature and strain rate and vary for several orders of magnitude. During service life, a viscoelastic body, especially carboxy-terminated polybutadiene (CTPB composite solid rocket propellant grain, is subjected to many stress-inducing loads. Its structural integrity analysis (hereafter: “structural analysis”, unlike elastic bodies, is quite complex and sometimes impossible under the action of just a single load. An even greater problem occurs when multiple different types of loads act simultaneously. This study is based on a complete uniaxial mechanical characterization of a viscoelastic CTPB composite rocket propellant, made in MTI- -Belgrade, whose results were used for the analysis of the propellant grain reliability. Through an example, this paper shows a behavior of the viscoelastic propellant grain when it is subjected to extremely different environmental loads at the same time. Similar explicit examples are difficult to found in the literature, except in the form of recommended principles for analysis. It is shown that the tensile strength under the action of fast load due to the pressure may be almost 20 times greater than the tensile strength under the slow temperature load. A probabilistic approach is presented in evaluation the reliability and service life. An example is shown for a rocket propellant grain as a viscoelastic body. The presented principles of the analysis can be applied to any arbitrary viscoelastic body in other areas.
An analysis of 3D anisotropic–viscoelastic forward modeling and dissipation
International Nuclear Information System (INIS)
Yang, Chunying; Li, Xiang-Yang; Wang, Yun
2015-01-01
The anisotropic–viscoelastic wave equation is a generalized expression of a transversely isotropic–viscoelastic medium. The viscoelastic horizontal–tranverse isotropic (HTI) medium is a special case. Considering the horizontal symmetry axis of viscoelastic HTI media, we develop elasticities and wave equations for preserving its transverse isotropy. To model anisotropic–viscoelastic wave propagation, we apply the fourth-order Runge–Kutta and Fourier pseudospectral method to discretize the wave equation. The convolutional perfectly matched layer (CPML) absorbed boundary condition is applied to the 3D modeling algorithm and the result shows that it absorbs reflected energy efficiently. We present three models to investigate anisotropic–viscoelastic waves. Two half-space models demonstrate the azimuthal attenuation, which appears both on the PP and PSv wave. The quality factor is greater along the fracture direction for both the PP and PSv waves. Analysis shows that frequency-dependent amplitude attenuation behaves differently along the fracture azimuth. This demonstates that we can use this property for reservoir detection. (paper)
Transient viscoelasticity study of tobacco mosaic virus/Ba2+ superlattice
2014-01-01
Recently, we reported a new method to synthesize the rod-like tobacco mosaic virus (TMV) superlattice. To explore its potentials in nanolattice templating and tissue scaffolding, this work focused the viscoelasticity of the superlattice with a novel transient method via atomic force microscopy (AFM). For measuring viscoelasticity, in contrast to previous methods that assessed the oscillating response, the method proposed in this work enabled us to determine the transient response (creep or relaxation) of micro/nanobiomaterials. The mathematical model and numerical process were elaborated to extract the viscoelastic properties from the indentation data. The adhesion between the AFM tip and the sample was included in the indentation model. Through the functional equation method, the elastic solution for the indentation model was extended to the viscoelastic solution so that the time dependent force vs. displacement relation could be attained. To simplify the solving of the differential equation, a standard solid model was modified to obtain the elastic and viscoelastic components of the sample. The viscoelastic responses with different mechanical stimuli and the dynamic properties were also investigated. PMID:24994956
Stress Wave Propagation in Viscoelastic-Plastic Rock-Like Materials
Directory of Open Access Journals (Sweden)
Liu Lang
2016-05-01
Full Text Available Rock-like materials are composites that can be regarded as a mixture composed of elastic, plastic, and viscous components. They exhibit viscoelastic-plastic behavior under a high-strain-rate loading according to element model theory. This paper presents an analytical solution for stress wave propagation in viscoelastic-plastic rock-like materials under a high-strain-rate loading and verifies the solution through an experimental test. A constitutive equation of viscoelastic-plastic rock-like materials was first established, and then kinematic and kinetic equations were then solved to derive the analytic solution for stress wave propagation in viscoelastic-plastic rock-like materials. An experimental test using the SHPB (Split Hopkinson Pressure Bar for a concrete specimen was conducted to obtain a stress-strain curve under a high-strain-rate loading. Inverse analysis based on differential evolution was conducted to estimate undetermined variables for constitutive equations. Finally, the relationship between the attenuation factor and the strain rate in viscoelastic-plastic rock-like materials was investigated. According to the results, the frequency of the stress wave, viscosity coefficient, modulus of elasticity, and density play dominant roles in the attenuation of the stress wave. The attenuation decreases with increasing strain rate, demonstrating strongly strain-dependent attenuation in viscoelastic-plastic rock-like materials.
Ramo, Nicole L.; Puttlitz, Christian M.
2018-01-01
Compelling evidence that many biological soft tissues display both strain- and time-dependent behavior has led to the development of fully non-linear viscoelastic modeling techniques to represent the tissue’s mechanical response under dynamic conditions. Since the current stress state of a viscoelastic material is dependent on all previous loading events, numerical analyses are complicated by the requirement of computing and storing the stress at each step throughout the load history. This requirement quickly becomes computationally expensive, and in some cases intractable, for finite element models. Therefore, we have developed a strain-dependent numerical integration approach for capturing non-linear viscoelasticity that enables calculation of the current stress from a strain-dependent history state variable stored from the preceding time step only, which improves both fitting efficiency and computational tractability. This methodology was validated based on its ability to recover non-linear viscoelastic coefficients from simulated stress-relaxation (six strain levels) and dynamic cyclic (three frequencies) experimental stress-strain data. The model successfully fit each data set with average errors in recovered coefficients of 0.3% for stress-relaxation fits and 0.1% for cyclic. The results support the use of the presented methodology to develop linear or non-linear viscoelastic models from stress-relaxation or cyclic experimental data of biological soft tissues. PMID:29293558
Directory of Open Access Journals (Sweden)
Bohan Liu
2014-01-01
Full Text Available PolyVinyl Butyral (PVB film is now widely used in automotive industry and architectures serving as the protective interlayer. The dynamic modulus of PVB is measured through systematic experiments based on Dynamic Mechanical Analysis (DMA method at various temperatures, heating rates, and vibration frequencies. Further, viscoelasticity of PVB influenced by time and temperature is systematically studied. Fitted empirical formulas describing the relationship between glass transition temperature and frequency, as well as the heating rate of PVB, are established. The master curve of PVB at 293 K is suggested based on the experiment data as to express the dynamic modulus variation at various frequencies in a wider range. Constitutive behavior of PVB is then analyzed based on Generalized Maxwell (GM model and Fractional Derivative (FD model, respectively. It is shown that PVB has higher efficiency of energy dissipation in its high energy absorption state, while both fifth-order GM model and FD model can characterize the viscoelasticity of PVB at glassy transition area. Results may offer useful fundamental experimental data and important constitutive characteristics of PVB and shed lights on further studies on viscoelasticity behavior of PVB and energy mitigation ability of laminated glass.
Directory of Open Access Journals (Sweden)
Tai-Hong Cheng
2015-01-01
Full Text Available Composite materials are increasingly used in wind blade because of their superior mechanical properties such as high strength-to-weight and stiffness-to-weight ratio. This paper presents vibration and damping analysis of fiberreinforced composite wind turbine blade with viscoelastic damping treatment. The finite element method based on full layerwise displacement theory was employed to analyze the damping, natural frequency, and modal loss factor of composite shell structure. The lamination angle was considered in mathematical modeling. The curved geometry, transverse shear, and normal strains were exactly considered in present layerwise shell model, which can depict the zig-zag in-plane and out-of-plane displacements. The frequency response functions of curved composite shell structure and wind blade were calculated. The results show that the damping ratio of viscoelastic layer is found to be very sensitive to determination of magnitude of composite structures. The frequency response functions with variety of thickness of damping layer were investigated. Moreover, the natural frequency, modal loss factor, and mode shapes of composite fiber reinforced wind blade with viscoelastic damping control were calculated.
Normalization of Impact Energy by Laminate Thickness for Compression After Impact Testing
Nettles, A. T.; Hromisin, S. M.
2013-01-01
The amount of impact energy used to damage a composite laminate is a critical parameter when assessing residual strength properties. The compression after impact (CAI) strength of impacted laminates is dependent upon how thick the laminate is and this has traditionally been accounted for by normalizing (dividing) the impact energy by the laminate's thickness. However, when comparing CAI strength values for a given lay-up sequence and fiber/resin system, dividing the impact energy by the specimen thickness has been noted by the author to give higher CAI strength values for thicker laminates. A study was thus undertaken to assess the comparability of CAI strength data by normalizing the impact energy by the specimen thickness raised to a power to account for the higher strength of thicker laminates. One set of data from the literature and two generated in this study were analyzed by dividing the impact energy by the specimen thickness to the 1, 1.5, 2, and 2.5 powers. Results show that as laminate thickness and damage severity decreased, the value which the laminate thickness needs to be raised to in order to yield more comparable CAI data increases.
Transient waves in visco-elastic media
Ricker, Norman
1977-01-01
Developments in Solid Earth Geophysics 10: Transient Waves in Visco-Elastic Media deals with the propagation of transient elastic disturbances in visco-elastic media. More specifically, it explores the visco-elastic behavior of a medium, whether gaseous, liquid, or solid, for very-small-amplitude disturbances. This volume provides a historical overview of the theory of the propagation of elastic waves in solid bodies, along with seismic prospecting and the nature of seismograms. It also discusses the seismic experiments, the behavior of waves propagated in accordance with the Stokes wave
Viscoelastic Relaxation Modulus Characterization Using Prony Series
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Juliana E. Lopes Pacheco
Full Text Available AbstractThe mechanical behavior of viscoelastic materials is influenced, among other factors, by parameters like time and temperature. The present paper proposes a methodology for a thermorheologically and piezorheologically simple characterization of viscoelastic materials in the time domain based on experimental data using Prony Series and a mixed optimization technique based on Genetic Algorithms and Nonlinear Programming. The text discusses the influence of pressure and temperature on the mechanical behavior of those materials. The results are compared to experimental data in order to validate the methodology. The final results are very promising and the methodology proves to be effective in the identification of viscoelastic materials.
Damping Analysis of Cylindrical Composite Structures with Enhanced Viscoelastic Properties
Kliem, Mathias; Høgsberg, Jan; Vanwalleghem, Joachim; Filippatos, Angelos; Hoschützky, Stefan; Fotsing, Edith-Roland; Berggreen, Christian
2018-04-01
Constrained layer damping treatments are widely used in mechanical structures to damp acoustic noise and mechanical vibrations. A viscoelastic layer is thereby applied to a structure and covered by a stiff constraining layer. When the structure vibrates in a bending mode, the viscoelastic layer is forced to deform in shear mode. Thus, the vibration energy is dissipated as low grade frictional heat. This paper documents the efficiency of passive constrained layer damping treatments for low frequency vibrations of cylindrical composite specimens made of glass fibre-reinforced plastics. Different cross section geometries with shear webs have been investigated in order to study a beneficial effect on the damping characteristics of the cylinder. The viscoelastic damping layers are placed at different locations within the composite cylinder e.g. circumferential and along the neutral plane to evaluate the location-dependent efficiency of constrained layer damping treatments. The results of the study provide a thorough understanding of constrained layer damping treatments and an improved damping design of the cylindrical composite structure. The highest damping is achieved when placing the damping layer in the neutral plane perpendicular to the bending load. The results are based on free decay tests of the composite structure.
Anisotropy in the viscoelastic response of knee meniscus cartilage.
Coluccino, Luca; Peres, Chiara; Gottardi, Riccardo; Bianchini, Paolo; Diaspro, Alberto; Ceseracciu, Luca
2017-01-26
The knee meniscus is instrumental to stability, shock absorption, load transmission and stress distribution within the knee joint. Such functions are mechanically demanding, and replacement constructs used in meniscus repair often fail because of a poor match with the surrounding tissue. This study focused on the native structure-mechanics relationships and on their anisotropic behavior in meniscus, to define the target biomechanical viscoelastic properties required by scaffolds upon loading. To show regional orientation of the collagen fibers and their viscoelastic behavior, bovine lateral menisci were characterized by second harmonic generation microscopy and through time-dependent mechanical tests. Furthermore, their dynamic viscoelastic response was analyzed over a wide range of frequencies. Multilevel characterization aims to expand the biomimetic approach from the structure itself, to include the mechanical characteristics that give the meniscus its peculiar properties, thus providing tools for the design of novel, effective scaffolds. An example of modeling of anisotropic open-cell porous material tailored to fulfill the measured requirements is presented, leading to a definition of additional parameters for a better understanding of the load transmission mechanism and for better scaffold functionality.
A Comparison of Viscoelastic Properties of Three Root Canal Sealers
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Malihe Pishvaei
2013-01-01
Full Text Available Objective: Handling of endodontic sealers is greatly dependent on their elasticity and flow ability. We compared the viscoelastic properties of three root canal sealers.Materials and Methods: AH Plus (Dentsply, De Trey, Konstanz, Germany, Endofill (Dentsply Hero, Petrópolis, Rio de Janeiro, Brazil and AH26 (Dentsply, De Trey, Konstanz, Germany were mixed according to the manufacturers' instructions. The resulted pastes were placed on the plate of a rheometer (MCR 300, Anton-Paar, Graz, Austria. The experiments were performed at 25˚C and 37˚C. Viscoelastic properties of the sealers including loss modulus (G", storage modulus (G´ and complex viscosity (η* were studied using dynamic oscillatory shear tests. The shear module versus frequency (from 0.01 to 100 S-1 curves were gained using frequency deformation sweep test. Three samples of each material were examined at each temperature. The mean of these three measurements were recorded.Results: The storage modulus of AH plus was higher than its loss modulus at two temperatures. Endofill exhibited a crossover region in which the storage modulus crosses the loss modulus in both temperatures. At 25ºC the loss modulus of AH26 was higher than the storage modulus (G">G¢. In contrast, at 37ºC G¢was greater than G² (G¢>G². Both shear modules of AH Plus and Endofill decreased as the temperature raised from 25ºC to 37ºC. On the contrary, the loss modulus and storage modulus of AH26 increased at 37ºC.Conclusion: In both test temperatures, AH Plus behaved like viscoelastic solids and Endofill exhibited a gel-like viscoelastic behavior. AH26 at 25ºC behaved like liquids, while at 37ºC it was an elastic solid-like material
The theory of viscoelastic crack propagation and healing
International Nuclear Information System (INIS)
Greenwood, J A
2004-01-01
Classical fracture mechanics applied to a viscoelastic material states that the critical stress-intensity factor at which the crack propagates depends on the instantaneous elastic modulus of the solid, and provides no mechanism for a speed dependence of the apparent surface energy. This suggests that any speed dependence must be because surface energy itself is speed-dependant. Schapery (1975) has explained how by using the Barenblatt concept of fracture mechanics, involving surface forces instead of surface energy alone, a dependence of the apparent surface energy on the crack speed is found. Here, Schapery's principles are applied to the particular case of a Maugis-Dugdale surface force law and a three-element viscoelastic solid to find the complete dependence of the apparent surface energy, both in fracture and in crack healing, on the crack velocity. To a good approximation, the apparent surface energy in crack healing is the reciprocal of the energy for fracture. Simple approximate equations relating the crack speed to the stress-intensity factor are given
The theory of viscoelastic crack propagation and healing
Energy Technology Data Exchange (ETDEWEB)
Greenwood, J A [University Engineering Department, Trumpington Street, Cambridge CB2 1PZ (United Kingdom)
2004-09-21
Classical fracture mechanics applied to a viscoelastic material states that the critical stress-intensity factor at which the crack propagates depends on the instantaneous elastic modulus of the solid, and provides no mechanism for a speed dependence of the apparent surface energy. This suggests that any speed dependence must be because surface energy itself is speed-dependant. Schapery (1975) has explained how by using the Barenblatt concept of fracture mechanics, involving surface forces instead of surface energy alone, a dependence of the apparent surface energy on the crack speed is found. Here, Schapery's principles are applied to the particular case of a Maugis-Dugdale surface force law and a three-element viscoelastic solid to find the complete dependence of the apparent surface energy, both in fracture and in crack healing, on the crack velocity. To a good approximation, the apparent surface energy in crack healing is the reciprocal of the energy for fracture. Simple approximate equations relating the crack speed to the stress-intensity factor are given.
Multiscale modeling of damage in multidirectional composite laminates
Singh, Chandra Veer
90°-plies. The predictions agree well with published experimental data as well as independent FE computations. Limited parametric studies are performed to show usability of SDM for more general laminates. To predict the initiation and growth of intralaminar cracks, an energy based model is proposed in which these cracks initiate and multiply when the work required to form new set of cracks exceeds a laminate dependent critical energy release rate. The approach requires determination of average crack opening and sliding displacements at varying crack spacing. This task is performed through a suitable 3-D FE analysis. In case of off-axis ply cracking, a mixed mode fracture criterion is utilized, where the critical energy release rates in normal and shear modes are determined by fitting the damage model with the experimental data for a reference laminate. The predictions from the model for [0/+/-theta4/01/2]s and [0/90/∓45]s laminates show remarkable agreement with the experimental results. The methodology and the results covered in this dissertation will be of interest to mechanics of materials researchers as well as to engineers in industry where composite materials for structural applications are of interest.
Understanding viscoelasticity an introduction to rheology
Phan-Thien, Nhan
2017-01-01
This book presents an introduction to viscoelasticity, in particular, to the theories of dilute polymer solutions and dilute suspensions of rigid particles in viscous and incompressible fluids. These theories are important, not just because they apply to practical problems of industrial interest, but because they form a solid theoretical base upon which mathematical techniques can be built, from which more complex theories can be constructed, to better mimic material behaviour. The emphasis of this book is not on the voluminous current topical research, but on the necessary tools to understand viscoelasticity. This is a compact book for a first year graduate course in viscoelasticity and modelling of viscoelastic multiphase fluids. The Dissipative Particle Dynamics (DPD) is introduced as a particle-based method, relevant in modelling of complex-structured fluids. All the basic ideas in DPD are reviewed. The third edition has been updated and expanded with new results in the meso-scale modelling, links between...
Viscoelastic model of tungsten 'fuzz' growth
International Nuclear Information System (INIS)
Krasheninnikov, S I
2011-01-01
A viscoelastic model of fuzz growth is presented. The model describes the main features of tungsten fuzz observed in experiments. It gives estimates of fuzz growth rate and temperature range close to experimental ones.
Dynamics and Stability of Rolling Viscoelastic Tires
Energy Technology Data Exchange (ETDEWEB)
Potter, Trevor [Univ. of California, Berkeley, CA (United States)
2013-04-30
Current steady state rolling tire calculations often do not include treads because treads destroy the rotational symmetry of the tire. We describe two methodologies to compute time periodic solutions of a two-dimensional viscoelastic tire with treads: solving a minimization problem and solving a system of equations. We also expand on work by Oden and Lin on free spinning rolling elastic tires in which they disovered a hierachy of N-peak steady state standing wave solutions. In addition to discovering a two-dimensional hierarchy of standing wave solutions that includes their N-peak hiearchy, we consider the eects of viscoelasticity on the standing wave solutions. Finally, a commonplace model of viscoelasticity used in our numerical experiments led to non-physical elastic energy growth for large tire speeds. We show that a viscoelastic model of Govindjee and Reese remedies the problem.
Thermal Effects on the Compressive Behavior of IM7/PET15 Laminates
Walker, Sandra Polesky
2003-01-01
The effect of changing operating temperature on the compressive response of IM7/PETI5 composite laminates is investigated within this paper. The three temperatures evaluated for this study were 129 C, 21 C, and 177 C, a spectrum from cryogenic to an elevated operating temperature. Laminate compressive strength property testing was conducted using the Wyoming Combined Load Compression fixture to generate strength data at the three operating temperatures of interest for several lay-ups. A three-dimensional finite element analysis model of a [90/0]8s composite laminate subject to compressive loading is developed. The model is used to study the key attributes of the laminate that significantly influence the state of stress in the laminate. Both the resin rich layer located between lamina and the thermal residual stresses present in the laminate due to curing are included in the analysis model. For the laminate modeled, the effect of modeling temperature dependent material properties was determined to be insignificant for the operating temperatures studied. Simply using the material properties measured at the operating temperature of interest was sufficient for predicting stresses accurately in a linear analysis for the current problem. The three-dimensional analysis results revealed that the application of an applied compressive axial load in the 0-degree direction decreased the interlaminar stresses present in the laminate initially due to curing. Therefore, failure was concluded not be attributable to the interlaminar stresses in the composite laminate being studied when a compressive load is applied. The magnitude of the measured laminate compressive strength change with a change in temperature is concluded to be dominated by the change in the lamina compressive axial strength with a change in temperature.
Fully coupled heat conduction and deformation analyses of visco-elastic solids
Khan, Kamran
2012-04-21
Visco-elastic materials are known for their capability of dissipating energy. This energy is converted into heat and thus changes the temperature of the materials. In addition to the dissipation effect, an external thermal stimulus can also alter the temperature in a viscoelastic body. The rate of stress relaxation (or the rate of creep) and the mechanical and physical properties of visco-elastic materials, such as polymers, vary with temperature. This study aims at understanding the effect of coupling between the thermal and mechanical response that is attributed to the dissipation of energy, heat conduction, and temperature-dependent material parameters on the overall response of visco-elastic solids. The non-linearly viscoelastic constitutive model proposed by Schapery (Further development of a thermodynamic constitutive theory: stress formulation, 1969,Mech. Time-Depend. Mater. 1:209-240, 1997) is used and modified to incorporate temperature- and stress-dependent material properties. This study also formulates a non-linear energy equation along with a dissipation function based on the Gibbs potential of Schapery (Mech. Time-Depend. Mater. 1:209-240, 1997). A numerical algorithm is formulated for analyzing a fully coupled thermo-visco-elastic response and implemented it in a general finite-element (FE) code. The non-linear stress- and temperature-dependent material parameters are found to have significant effects on the coupled thermo-visco-elastic response of polymers considered in this study. In order to obtain a realistic temperature field within the polymer visco-elastic bodies undergoing a non-uniform heat generation, the role of heat conduction cannot be ignored. © Springer Science+Business Media, B. V. 2012.
Enhanced active swimming in viscoelastic fluids
Riley, Emily E; Lauga, Eric Jean-Marie
2014-01-01
Swimming microorganisms often self propel in fluids with complex rheology. While past theoretical work indicates that fluid viscoelasticity should hinder their locomotion, recent experiments on waving swimmers suggest a possible non-Newtonian enhancement of locomotion. We suggest a physical mechanism, based on fluid-structure interaction, leading to swimming in a viscoelastic fluid at a higher speed than in a Newtonian one. Using Taylor's two-dimensional swimming sheet model, we solve for the...
VISCOELASTIC STRUCTURAL MODEL OF ASPHALT CONCRETE
Directory of Open Access Journals (Sweden)
V. Bogomolov
2016-06-01
Full Text Available The viscoelastic rheological model of asphalt concrete based on the generalized Kelvin model is offered. The mathematical model of asphalt concrete viscoelastic behavior that can be used for calculation of asphalt concrete upper layers of non-rigid pavements for strength and rutting has been developed. It has been proved that the structural model of Burgers does not fully meet all the requirements of the asphalt-concrete.
Recent advances in elasticity, viscoelasticity and inelasticity
Rajagopal, KR
1995-01-01
This is a collection of papers dedicated to Prof T C Woo to mark his 70th birthday. The papers focus on recent advances in elasticity, viscoelasticity and inelasticity, which are related to Prof Woo's work. Prof Woo's recent work concentrates on the viscoelastic and viscoplastic response of metals and plastics when thermal effects are significant, and the papers here address open questions in these and related areas.
Jeans instability in a viscoelastic fluid
International Nuclear Information System (INIS)
Janaki, M. S.; Chakrabarti, N.; Banerjee, D.
2011-01-01
The well known Jeans instability is studied for a viscoelastic gravitational fluid using generalized hydrodynamic equations of motions. It is found that the threshold for the onset of instability appears at higher wavelengths in a viscoelastic medium. Elastic effects playing a role similar to thermal pressure are found to lower the growth rate of the gravitational instability. Such features may manifest themselves in matter constituting dense astrophysical objects.
Van De Camp, W.; Dhallé, M. M.J.; Warnet, L.; Wessel, W. A.J.; Vos, G. S.; Akkerman, R.; Ter Brake, H. J.M.
2017-01-01
The paper describes a temperature-dependent extension of the classical laminate theory (CLT) that may be used to predict the mechanical behaviour of Fibre Metal Laminates (FML) at cryogenic conditions, including crack initiation. FML are considered as a possible alternative class of structural
An inelastic constitutive equation of fiber reinforced plastic laminates
Energy Technology Data Exchange (ETDEWEB)
Kanagawa, Y.; Murakami, S.; Mizobe, T. [Univ. of Nagoya (Japan). Dept. of Mechanical Engineering
1998-01-01
A constitutive model for describing the time-dependent inelastic deformation of unidirectional and symmetric angle-ply CFRP (carbon Fiber Reinforced Plastics) laminates is developed. The kinematic hardening creep law of Malinin and Khadjinsky and the evolution equation of Armstrong and Frederick are extended to describe the creep deformation of initially anisotropic materials. In particular, the evolution equations of the back stresses of the anisotropic material were formulated by introducing a transformed strain tensor, by which the expression of the equivalent strain rate of the anisotropic material has the identical form as that of the isotropic materials. The resulting model is applied to analyze the time-dependent inelastic deformation of symmetric angle-ply laminates. Comparison between the predictions and the experimental observations shows that the present model can describe well the time-dependent inelastic behavior under different loadings.
Directory of Open Access Journals (Sweden)
R. Jayendiran
2015-02-01
Full Text Available This work focuses on evaluating the time-dependent non-linear ferroelastic behaviour of 1-3 piezocomposites under pure uni-axial compressive stress loading condition. An experimental setup is developed to study the influence of high-stress levels on the stress-strain and stress-polarization behaviour of 1-3 piezocomposites. The electro-elastic effective properties of 1-3 piezocomposites are measured experimentally based on IEEE standard and compared with the proposed numerical model using finite-element software ABAQUS. The time-dependent effective properties are evaluated using viscoelastic model and it is incorporated into a 3D micromechanical model to predict the viscoelastic behaviour of 1-3 piezocomposites under mechanical loading. The simulated results are compared with the viscoelastic behaviour of 1-3 piezocomposites obtained from experiments.
Laser Speckle Rheology for evaluating the viscoelastic properties of hydrogel scaffolds
Hajjarian, Zeinab; Nia, Hadi Tavakoli; Ahn, Shawn; Grodzinsky, Alan J.; Jain, Rakesh K.; Nadkarni, Seemantini K.
2016-01-01
Natural and synthetic hydrogel scaffolds exhibit distinct viscoelastic properties at various length scales and deformation rates. Laser Speckle Rheology (LSR) offers a novel, non-contact optical approach for evaluating the frequency-dependent viscoelastic properties of hydrogels. In LSR, a coherent laser beam illuminates the specimen and a high-speed camera acquires the time-varying speckle images. Cross-correlation analysis of frames returns the speckle intensity autocorrelation function, g2(t), from which the frequency-dependent viscoelastic modulus, G*(ω), is deduced. Here, we establish the capability of LSR for evaluating the viscoelastic properties of hydrogels over a large range of moduli, using conventional mechanical rheometry and atomic force microscopy (AFM)-based indentation as reference-standards. Results demonstrate a strong correlation between |G*(ω)| values measured by LSR and mechanical rheometry (r = 0.95, p 0.08) over a large range (47 Pa – 36 kPa). In addition, |G*(ω)| values measured by LSR correlate well with indentation moduli, E, reported by AFM (r = 0.92, p rheology and micro-indentation in assessing hydrogel viscoelastic properties at multiple frequencies and small length-scales. PMID:27905494
Tian, Fei; Zhang, Wei; Cai, Lili; Li, Shanshan; Hu, Guoqing; Cong, Yulong; Liu, Chao; Li, Tiejun; Sun, Jiashu
2017-09-12
The microfluidic passive control of microparticles largely relies on the hydrodynamic effects of the carrier media such as Newtonian fluids and viscoelastic fluids. Yet the viscoelastic/Newtonian interfacial effect has been scarcely investigated, especially for high-resolution particle separation. Here we report a microfluidic co-flow of Newtonian (water or PBS) and viscoelastic fluids (PEO) for the size-dependent separation of microparticles. The co-flow condition generates a stable viscoelastic/Newtonian interface, giving rise to the wall-directed elastic lift forces that compete with the center-directed lift forces, and efficiently hinders the migration of microparticles from the Newtonian to the viscoelastic fluid in a size-dependent manner. An almost complete separation of a binary mixture of 1 μm and 2 μm polystyrene particles is achieved by the co-flow of water and a very dilute PEO solution (100 ppm), whereas the sole use of water or PEO could not lead to an efficient separation. This co-flow microfluidic system is also applied for the separation of Staphylococcus aureus (1 μm) from platelets (2-3 μm) with >90% efficiencies and purities.
Lamin in inflammation and aging.
Tran, Joseph R; Chen, Haiyang; Zheng, Xiaobin; Zheng, Yixian
2016-06-01
Aging is characterized by a progressive loss of tissue function and an increased susceptibility to injury and disease. Many age-associated pathologies manifest an inflammatory component, and this has led to the speculation that aging is at least in part caused by some form of inflammation. However, whether or not inflammation is truly a cause of aging, or is a consequence of the aging process is unknown. Recent work using Drosophila has uncovered a mechanism where the progressive loss of lamin-B in the fat body upon aging triggers systemic inflammation. This inflammatory response perturbs the local immune response of the neighboring gut tissue and leads to hyperplasia. Here, we will discuss the literature connecting lamins to aging and inflammation. Copyright © 2016 Elsevier Ltd. All rights reserved.
Optimization of Laminated Composite Structures
DEFF Research Database (Denmark)
Henrichsen, Søren Randrup
allows for a higher degree of tailoring of the resulting material. To enable better utilization of the composite materials, optimum design procedures can be used to assist the engineer. This PhD thesis is focused on developing numerical methods for optimization of laminated composite structures....... The first part of the thesis is intended as an aid to read the included papers. Initially the field of research is introduced and the performed research is motivated. Secondly, the state-of-the-art is reviewed. The review includes parameterizations of the constitutive properties, linear and geometrically...... of the contributions of the PhD project are included in the second part of the thesis. Paper A presents a framework for free material optimization where commercially available finite element analysis software is used as analysis tool. Robust buckling optimization of laminated composite structures by including...
The Development of Laminated Armor
1948-09-27
unsaturated alkyd . Initially, two commercially available rigid polyester resins were examined, namely, Plaskon 920 and Laminac 4125. Laminac 4125 had a com...combination under various conditions of resin content and molding pressures. The binders employed in this study were restricted, exclusively, to the...low-pressure polyester resins which are commonly employed in laminate fabrication. In addition to their ready adaptability, they offer the advantage
Impact damages modeling in laminated composite structures
Directory of Open Access Journals (Sweden)
Kreculj Dragan D.
2014-01-01
Full Text Available Laminated composites have an important application in modern engineering structures. They are characterized by extraordinary properties, such as: high strength and stiffness and lightweight. Nevertheless, a serious obstacle to more widespread use of those materials is their sensitivity to the impact loads. Impacts cause initiation and development of certain types of damages. Failures that occur in laminated composite structures can be intralaminar and interlaminar. To date it was developed a lot of simulation models for impact damages analysis in laminates. Those models can replace real and expensive testing in laminated structures with a certain accuracy. By using specialized software the damage parameters and distributions can be determined (at certain conditions on laminate structures. With performing numerical simulation of impact on composite laminates there are corresponding results valid for the analysis of these structures.
Lamin A reassembly at the end of mitosis is regulated by its SUMO-interacting motif.
Moriuchi, Takanobu; Kuroda, Masaki; Kusumoto, Fumiya; Osumi, Takashi; Hirose, Fumiko
2016-03-01
Modification of proteins with small ubiquitin-related modifier (SUMO; SUMOylation) is involved in the regulation of various biological processes. Recent studies have demonstrated that noncovalent associations between SUMOylated proteins and co-operative proteins containing SUMO-interacting motifs (SIMs) are important for the spatiotemporal organization of many protein complexes. In this study, we demonstrate that interactions between lamin A, a major component of the nuclear lamina, and SUMO isoforms are dependent on one of the four SIMs (SIM3) resided in lamin A polypeptide in vitro. Live cell imaging and immunofluorescence staining showed that SIM3 is required for accumulation of lamin A on the chromosomes during telophase, and subsequent evaluation of a panel of deletion mutants determined that a 156-amino acid region spanning the carboxyl-terminal Ig-fold domain of lamin A is sufficient for this accumulation. Notably, mutation of SIM3 abrogated the dephosphorylation of mitosis-specific phosphorylation at Ser-22 of lamin A, which normally occurs during telophase, and the subsequent nuclear lamina reorganization. Furthermore, expression of a conjugation-defective SUMO2 mutant, which was previously shown to inhibit endogenous SUMOylation in a dominant-negative manner, also impaired the accumulation of wild type lamin A on telophase chromosomes. These findings suggest that interactions between SIM3 of lamin A and a putative SUMO2-modified protein plays an important role in the reorganization of the nuclear lamina at the end of mitosis. Copyright © 2016 Elsevier Inc. All rights reserved.
International Nuclear Information System (INIS)
Gorospe, Alking; Nisay, Arman; Shin, Hyung-Seop
2014-01-01
Highlights: • I c degradation behavior under transverse tension loading in different CC tape structure. • Weibull distribution analysis applied on delamination mechanism of CC tape. • Delamination mechanism on CC tapes depending on copper lamination type. • SEM and WDS mapping analysis of delamination sites under transverse loading. - Abstract: Laminated HTS coated conductor (CC) tapes having a unique multi-layer structure made them vulnerable when exposed to transverse loading. Electromechanical transport properties of these CC tapes can be affected by excessive transverse stresses. Due to the coefficient of thermal expansion (CTE) mismatch and incompatibility among constituent materials used in coil applications, delamination among layers occurs and causes critical current, I c degradation in the CC tapes. In this study, the delamination behaviors in copper (Cu) solder-laminated CC tapes by soldering and surround Cu-stabilized ones by electroplating under transverse tension loading were investigated. Similarly to the surround Cu-stabilized CC tapes in our previous reports, the Cu solder-laminated CC tapes also showed an abrupt and gradual I c degradation behavior. However, the Cu solder-laminated CC tapes showed different delamination morphologies as compared to the surround Cu-stabilized CC tapes; the superconducting side and the substrate side of the Cu solder laminated CC tapes were totally separated by delamination. On the other hand, the brass laminate did not show any significant effect on the delamination strength when it is added upon the surround Cu-stabilized CC tapes
Paradigm shifts in understanding equine laminitis
Patterson-Kane, J.C.; Karikoski, N.P.; McGowan, C.M.
2018-01-01
Laminitis, one of the most debilitating conditions of all equids, is now known to be the result of several systemic disease entities. This finding, together with other recent developments in the field of laminitis research, have provoked a rethink of our clinical and research strategies for this condition. First, laminitis is now considered to be a clinical syndrome associated with systemic disease (endocrine disease, sepsis or systemic inflammatory response syndrome, SIRS) or altered weight ...
Viscoelastic properties of polymer composites during processing
O'Brien, Daniel James
Residual stresses that are induced during processing of polymer matrix composites lead to warpage of structural parts and can produce microcracks and other forms of damage. Process models that track the development of residual stresses in composites during processing have received growing attention in recent years. An accurate and easy to implement simulation will help lower the manufacturing cost by enabling engineers to predict and prevent the warpage in parts due to residual stress. The critical feature of a process model is the development of an accurate material model to predict mechanical properties throughout the entire manufacturing cycle. Material models are very complex since the matrix changes from a fluid to a viscoelastic solid at the end of cure. In this work several aspects of the curing, viscoelastic, and cure shrinkage behavior of an aerospace grade epoxy resin were characterized and modeled for the purpose of composites process modeling. Measurement of matrix viscoelastic properties during cure was accomplished through two experimental approaches, each suited to a particular range of cure states. To investigate the material behavior during later stages of cure after gelation, small beam specimens were tested in three-point bending. During early stages of curing, samples were examined by shearing the material between parallel plates in a rheometer. Specimens for each configuration were manufactured at several cure states and tested at a range of temperatures. These data were used to develop a material model to predict the relaxation modulus of the matrix at any time during cure. Additionally, moire interferometry was successfully applied to the measurement of the viscoelastic Poisson's ratio of the matrix through its entire glassy-to-rubbery transition. The matrix viscoelastic material models were then used to predict composite viscoelastic properties and correlated with experimental results. In addition, the viscoelastic shrinkage behavior of the
Viscoelastic Fluid-Structure Interactions
Dey, Anita; Rothstein, Jonathan; Modarres-Sadeghi, Yahya
2015-11-01
When a flexible object such as an elastic sheet is placed perpendicular to the flow of a Newtonian fluid, the structure can oscillate due to the shedding of separated vortices at high Reynolds numbers. If the same flexible object is placed in non-Newtonian flows, however, the structure's response is still unknown. Unlike Newtonian fluids, the flow of viscoelastic fluids can become unstable at infinitesimal Reynolds numbers due to a purely elastic flow instability. In this talk, we will discuss the fluid-structure interaction between a wormlike micelle solution at high Weissenberg number and a flexible elastic sheet in cross flow. Elastic flow instabilities have been observed for wormlike micelle solutions in a number of flows. Here we will study what happens when elastic flow instabilities occur in the vicinity of a thin flexible polymer sheet. We will show that the time varying fluid forces exerted on the structure can grow large enough to cause a structural motion which can in turn feed back into the flow to modify the flow instability. The static and dynamic responses of the flexible sheet will be presented for a series of flexible sheets oriented at different angles to the flow direction, for varying fluid flow rates, and for varying fluid compositions and properties. In addition, measurements of velocity profiles and flow-induced birefringence will be presented in order to quantify the time variation of the flow field and the state of stress in the fluid.
The management of equine acute laminitis
Directory of Open Access Journals (Sweden)
Mitchell CF
2014-12-01
Full Text Available Colin F Mitchell, Lee Ann Fugler, Susan C Eades Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA Abstract: Laminitis is an extremely painful condition resulting in damage to the soft tissues anchoring the third phalanx to the hoof, which can result in life-threatening debilitation. Specific therapy is not available. The most important principles of therapy include aggressive nutritional and medical management of primary disease processes, cryotherapy, anti-inflammatory therapy, pain management, and biomechanical support. This review focuses on the principles of evidenced-based therapies. Keywords: laminitis treatment, laminitis biomechanics, laminitis pain
Field performance of stress-laminated highway bridges constructed with glued laminated timber
J.P. Wacker
2004-01-01
This paper summarizes the field performance of three stress-laminated deck timber bridges located in Wisconsin, New York, and Arizona. The deck superstructures of these single-span highway bridges is comprised of full-span glued laminated timber (glulam) beam laminations manufactured with southern pine, hem fir/red maple combination, and/or Douglas fir lumber species....
SPH modeling and simulation of spherical particles interacting in a viscoelastic matrix
Vázquez-Quesada, A.; Ellero, M.
2017-12-01
In this work, we extend the three-dimensional Smoothed Particle Hydrodynamics (SPH) non-colloidal particulate model previously developed for Newtonian suspending media in Vázquez-Quesada and Ellero ["Rheology and microstructure of non-colloidal suspensions under shear studied with smoothed particle hydrodynamics," J. Non-Newtonian Fluid Mech. 233, 37-47 (2016)] to viscoelastic matrices. For the solvent medium, the coarse-grained SPH viscoelastic formulation proposed in Vázquez-Quesada, Ellero, and Español ["Smoothed particle hydrodynamic model for viscoelastic fluids with thermal fluctuations," Phys. Rev. E 79, 056707 (2009)] is adopted. The property of this particular set of equations is that they are entirely derived within the general equation for non-equilibrium reversible-irreversible coupling formalism and therefore enjoy automatically thermodynamic consistency. The viscoelastic model is derived through a physical specification of a conformation-tensor-dependent entropy function for the fluid particles. In the simple case of suspended Hookean dumbbells, this delivers a specific SPH discretization of the Oldroyd-B constitutive equation. We validate the suspended particle model by studying the dynamics of single and mutually interacting "noncolloidal" rigid spheres under shear flow and in the presence of confinement. Numerical results agree well with available numerical and experimental data. It is straightforward to extend the particulate model to Brownian conditions and to more complex viscoelastic solvents.
Viscoelastic effects on frequency tuning of a dielectric elastomer membrane resonator
International Nuclear Information System (INIS)
Zhou, Jianyou; Jiang, Liying; Khayat, Roger E.
2014-01-01
As a recent application of dielectric elastomers (DEs), DE resonators have become an alternative to conventional silicon-based resonators used in MEMS and have attracted much interest from the research community. However, most existing modeling works for the DE resonators ignore the intrinsic viscoelastic effect of the material that may strongly influence their dynamic performance. Based on the finite-deformation viscoelasticity theory for dielectrics, this paper theoretically examines the in-plane oscillation of a DE membrane resonator to demonstrate how the material viscoelasticity affects the actuation and frequency tuning processes of the resonator. From the simulation results, it is concluded that not only the applied voltage can change the natural frequency of the resonator, but also the inelastic deformation contributes to frequency tuning. Due to the viscoelasticity of the material, the electrical loading rate influences the actuation process of the DE resonator, while it has little effect on the final steady frequency tuned by the prescribed voltage within the safety range. With the consideration of the typical failure modes of the resonator and the evolution process of the material, the tunable frequency range and the safe range of the applied voltage of the DE membrane resonator with different dimension parameters are determined in this work, which are found to be dependent on the electrical loading rate. This work is expected to provide a better understanding on the frequency tuning of viscoelastic DE membrane resonators and a guideline for the design of DE devices
Viscoelasticity of subcortical gray matter structures.
Johnson, Curtis L; Schwarb, Hillary; D J McGarry, Matthew; Anderson, Aaron T; Huesmann, Graham R; Sutton, Bradley P; Cohen, Neal J
2016-12-01
Viscoelastic mechanical properties of the brain assessed with magnetic resonance elastography (MRE) are sensitive measures of microstructural tissue health in neurodegenerative conditions. Recent efforts have targeted measurements localized to specific neuroanatomical regions differentially affected in disease. In this work, we present a method for measuring the viscoelasticity in subcortical gray matter (SGM) structures, including the amygdala, hippocampus, caudate, putamen, pallidum, and thalamus. The method is based on incorporating high spatial resolution MRE imaging (1.6 mm isotropic voxels) with a mechanical inversion scheme designed to improve local measures in pre-defined regions (soft prior regularization [SPR]). We find that in 21 healthy, young volunteers SGM structures differ from each other in viscoelasticity, quantified as the shear stiffness and damping ratio, but also differ from the global viscoelasticity of the cerebrum. Through repeated examinations on a single volunteer, we estimate the uncertainty to be between 3 and 7% for each SGM measure. Furthermore, we demonstrate that the use of specific methodological considerations-higher spatial resolution and SPR-both decrease uncertainty and increase sensitivity of the SGM measures. The proposed method allows for reliable MRE measures of SGM viscoelasticity for future studies of neurodegenerative conditions. Hum Brain Mapp 37:4221-4233, 2016. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.
Linear viscoelastic characterization from filament stretching rheometry
DEFF Research Database (Denmark)
Wingstrand, Sara Lindeblad; Alvarez, Nicolas J.; Hassager, Ole
Traditionally, linear viscoelasticity is measured using small amplitude oscillatory shear flow. Due to experimental difficulties, shear flows are predominately confined to the linear and mildly nonlinear regime. On the other hand, extensional flows have proven more practical in measuring viscoela......Traditionally, linear viscoelasticity is measured using small amplitude oscillatory shear flow. Due to experimental difficulties, shear flows are predominately confined to the linear and mildly nonlinear regime. On the other hand, extensional flows have proven more practical in measuring...... viscoelasticity well into the nonlinear regime. Therefore at present, complete rheological characterization of a material requires two apparatuses: a shear and an extensional rheometer. This work is focused on developing a linear viscoelastic protocol for the filament stretching rheometer (FSR) in order...... to measure both linear and nonlinear dynamics on a single apparatus. With a software modification to the FSR motor control, we show that linear viscoelasticity can be measured via small amplitude squeeze flow (SASF). Squeeze flow is a combination of both shear and extensional flow applied by axially...
Mechanical properties of multifunctional structure with viscoelastic components based on FVE model
Hao, Dong; Zhang, Lin; Yu, Jing; Mao, Daiyong
2018-02-01
Based on the models of Lion and Kardelky (2004) and Hofer and Lion (2009), a finite viscoelastic (FVE) constitutive model, considering the predeformation-, frequency- and amplitude-dependent properties, has been proposed in our earlier paper [1]. FVE model is applied to investigating the dynamic characteristics of the multifunctional structure with the viscoelastic components. Combing FVE model with the finite element theory, the dynamic model of the multifunctional structure could be obtained. Additionally, the parametric identification and the experimental verification are also given via the frequency-sweep tests. The results show that the computational data agree well with the experimental data. FVE model has made a success of expressing the dynamic characteristics of the viscoelastic materials utilized in the multifunctional structure. The multifunctional structure technology has been verified by in-orbit experiments.
DEFF Research Database (Denmark)
Drozdov, Aleksey; Christiansen, Jesper de Claville; Sanporean, Catalina-Gabriela
2012-01-01
Purpose – The purpose of this paper is to perform experimental investigation and constitutive modeling of the viscoelastic and viscoplastic behavior of metallocene catalyzed polypropylene (mPP) with application to lifetime assessment under conditions of creep rupture. Design/methodology/approach ......Purpose – The purpose of this paper is to perform experimental investigation and constitutive modeling of the viscoelastic and viscoplastic behavior of metallocene catalyzed polypropylene (mPP) with application to lifetime assessment under conditions of creep rupture. Design...... an arbitrary three-dimensional deformation with small strains, and its parameters are found fitting the observations. Findings – Crystalline structure and molecular architecture of polypropylene strongly affect its time and rate-dependent behavior. In particular, time-to-failure of metallocene catalyzed...... in long-term creep tests. Keywords Metallocene catalyzed polypropylene, Viscoelasticity, Viscoplasticity, Creep rupture, Constitutive modeling, Elastoplastic analysis, Viscosity, Creep, Physical properties of materials Paper type Research paper...
Non-Linear Finite Element Analysis of Viscoelastic Materials
National Research Council Canada - National Science Library
Negaard, Gordon
1998-01-01
.... It would be useful if viscoelastic materials could be used to damp the vibration of such structures, however the behavior of a viscoelastic material in an extremely high g-loading is not well understood...
Parametric imaging of viscoelasticity using optical coherence elastography
Wijesinghe, Philip; McLaughlin, Robert A.; Sampson, David D.; Kennedy, Brendan F.
2015-03-01
We demonstrate imaging of soft tissue viscoelasticity using optical coherence elastography. Viscoelastic creep deformation is induced in tissue using step-like compressive loading and the resulting time-varying deformation is measured using phase-sensitive optical coherence tomography. From a series of co-located B-scans, we estimate the local strain rate as a function of time, and parameterize it using a four-parameter Kelvin-Voigt model of viscoelastic creep. The estimated viscoelastic strain and time constant are used to visualize viscoelastic creep in 2D, dual-parameter viscoelastograms. We demonstrate our technique on six silicone tissue-simulating phantoms spanning a range of viscoelastic parameters. As an example in soft tissue, we report viscoelastic contrast between muscle and connective tissue in fresh, ex vivo rat gastrocnemius muscle and mouse abdominal transection. Imaging viscoelastic creep deformation has the potential to provide complementary contrast to existing imaging modalities, and may provide greater insight into disease pathology.
Instability of an oscillator moving along a thin ring on a viscoelastic foundation
Lu, T.; Metrikine, A.
2017-01-01
The stability of an oscillator uniformly moving along a thin ring that is connected to an immovable axis by a distributed viscoelastic foundation has been studied. The dynamic reaction of the ring to the oscillator is represented by a frequency and velocity dependent equivalent stiffness. The
DEFF Research Database (Denmark)
Nielsen, Michael Wenani; Schmidt, Jacob Wittrup; Hattel, Jesper Henri
2012-01-01
Bragg grating sensors are used to monitor process-induced strains during vacuum infusion of a thick glass/epoxy laminate. The measured strains are compared with predictions from a cure hardening instantaneous linear elastic (CHILE) thermomechanical numerical model where different mechanical boundary...... predicts the experimental transverse strains well when a tied boundary condition at the tool/part interface is used and the tool thermal expansion is taken into account. However, the CHILE approach is shown to overestimate residual strains after demoulding because of the shortcomings of the model...... conditions are employed. The accuracy of the CHILE model in predicting process-induced internal strains, in what is essentially a viscoelastic boundary value problem, is investigated. A parametric study is furthermore performed to reveal the effect of increasing the laminate thickness. The numerical model...
Viscoelasticity and plasticity mechanisms of human dentin
Borodin, E. N.; Seyedkavoosi, S.; Zaitsev, D.; Drach, B.; Mikaelyan, K. N.; Panfilov, P. E.; Gutkin, M. Yu.; Sevostianov, I.
2018-01-01
Theoretical models of viscoelastic behavior and plastic deformation mechanisms of human dentin are considered. Using the linear viscoelasticity theory in which creep and relaxation kernels have the form of fraction-exponential functions, numerical values of instantaneous and long-time Young's moduli and other characteristics of dentin viscoelasticity under uniaxial compression are found. As dentin plastic deformation mechanisms, mutual collagen fiber sliding in the region of contact of their side surfaces, separation of these fibers from each other, and irreversible tension of some collagen fibers, are proposed. It is shown that the second mechanism activation requires a smaller stress than that for activating others. The models of plastic zones at the mode I crack tip, which correspond to these mechanisms, are studied. It is shown that the plastic zone size can increase from a few hundreds of nanometers to hundreds of micrometers with increasing applied stress.
Viscoelastic love-type surface waves
Borcherdt, Roger D.
2008-01-01
The general theoretical solution for Love-Type surface waves in viscoelastic media provides theoreticalexpressions for the physical characteristics of the waves in elastic as well as anelastic media with arbitraryamounts of intrinsic damping. The general solution yields dispersion and absorption-coefficient curves for the waves as a function of frequency and theamount of intrinsic damping for any chosen viscoelastic model.Numerical results valid for a variety of viscoelastic models provide quantitative estimates of the physicalcharacteristics of the waves pertinent to models of Earth materials ranging from small amounts of damping in the Earth’s crust to moderate and large amounts of damping in soft soils and water-saturated sediments. Numerical results, presented herein, are valid for a wide range of solids and applications.
Broadband nanoindentation of glassy polymers: Part I Viscoelasticity
Joesph E. Jakes; Rod S. Lakes; Don S. Stone
2012-01-01
Protocols are developed to assess viscoelastic moduli from unloading slopes in Berkovich nanoindentation across four orders of magnitude in time scale (0.01-100 s unloading time). Measured viscoelastic moduli of glassy polymers poly(methyl methacrylate), polystyrene, and polycarbonate follow the same trends with frequency (1/unloading time) as viscoelastic moduli...
A Thermodynamic Theory of Solid Viscoelasticity. Part II:; Nonlinear Thermo-viscoelasticity
Freed, Alan D.; Leonov, Arkady I.; Gray, Hugh R. (Technical Monitor)
2002-01-01
This paper, second in the series of three papers, develops a general, nonlinear, non-isothermal, compressible theory for finite rubber viscoelasticity and specifies it in a form convenient for solving problems important to the rubber, tire, automobile, and air-space industries, among others. Based on the quasi-linear approach of non-equilibrium thermodynamics, a general nonlinear theory of differential type has been developed for arbitrary non-isothermal deformations of viscoelastic solids. In this theory, the constitutive equations were presented as the sum of a rubber elastic (equilibrium) and a liquid type viscoelastic (non-equilibrium) terms. These equations have then been simplified using several modeling and simplicity arguments.
Freed, Alan; Leonov, Arkady I.
2002-01-01
This paper, the last in the series, continues developing the nonlinear constitutive relations for non-isothermal, compressible, solid viscoelasticity. We initially discuss a single integral approach, more suitable for the glassy state of rubber-like materials, with basic functionals involved in the thermodynamic description for this type of viscoelasticity. Then we switch our attention to analyzing stability constraints, imposed on the general formulation of the nonlinear theory of solid viscoelasticity. Finally, we discuss specific (known from the literature or new) expressions for material functions that are involved in the constitutive formulations of both the rubber-like and glassy-like, complementary parts of the theory.
Surface energy and viscoelasticity influence caramel adhesiveness.
Wagoner, Ty B; Foegeding, Edward Allen
2017-08-26
Adhesion is an important textural attribute that directs consumer eating patterns and behaviors and can be a negative attribute during food processing. The objectives of this study were to modify caramel formulation and compare adhesion to different materials to quantify the influence of surface energetics and viscoelasticity on caramel adhesiveness. Mechanical adhesion was viewed in the context of pressure sensitive tack theory, where adhesion is controlled by viscoelasticity of the adhesive material and the surface energy relationship of material and probe. Caramel samples varied in total amount of fat and protein, and mechanical adhesion was measured using a series of materials with total surface energies of 39.7-53.2 mJ/m 2 . Adhesiveness decreased as fat and protein content increased, with a significant effect of total surface energy. Viscoelasticity was modeled using creep recovery data fit to a four-element Burger mechanistic model. Burger model parameters representing retarded elasticity correlated strongly with adhesiveness. The results suggest two zones of adhesion based on formulation, one driven by both surface energy relationships-most notably dispersive and total surface energy-and viscoelasticity, and the other driven solely by viscoelasticity. Relationships between mechanical properties and adhesion have been explored but are still not well understood, and could aid in the design of food products with a controlled level of adhesion. The results of this study indicate the importance of considering material surface energy when measuring mechanical adhesion or texture profile analysis. Understanding the relationships between viscoelastic behavior and adhesion can be used to make inferences on perceived texture. © 2017 Wiley Periodicals, Inc.
The laminA/NF-Y protein complex reveals an unknown transcriptional mechanism on cell proliferation.
Cicchillitti, Lucia; Manni, Isabella; Mancone, Carmine; Regazzo, Giulia; Spagnuolo, Manuela; Alonzi, Tonino; Carlomosti, Fabrizio; Dell'Anna, Maria Lucia; Dell'Omo, Giulia; Picardo, Mauro; Ciana, Paolo; Capogrossi, Maurizio C; Tripodi, Marco; Magenta, Alessandra; Rizzo, Maria Giulia; Gurtner, Aymone; Piaggio, Giulia
2017-01-10
Lamin A is a component of the nuclear matrix that also controls proliferation by largely unknown mechanisms. NF-Y is a ubiquitous protein involved in cell proliferation composed of three subunits (-YA -YB -YC) all required for the DNA binding and transactivation activity. To get clues on new NF-Y partner(s) we performed a mass spectrometry screening of proteins that co-precipitate with the regulatory subunit of the complex, NF-YA. By this screening we identified lamin A as a novel putative NF-Y interactor. Co-immunoprecipitation experiments and confocal analysis confirmed the interaction between the two endogenous proteins. Interestingly, this association occurs on euchromatin regions, too. ChIP experiments demonstrate lamin A enrichment in several promoter regions of cell cycle related genes in a NF-Y dependent manner. Gain and loss of function experiments reveal that lamin A counteracts NF-Y transcriptional activity. Taking advantage of a recently generated transgenic reporter mouse, called MITO-Luc, in which an NF-Y-dependent promoter controls luciferase expression, we demonstrate that lamin A counteracts NF-Y transcriptional activity not only in culture cells but also in living animals. Altogether, our data demonstrate the occurrence of lamin A/NF-Y interaction and suggest a possible role of this protein complex in regulation of NF-Y function in cell proliferation.
Natural fabric sandwich laminate composites: development and ...
Indian Academy of Sciences (India)
Home; Journals; Bulletin of Materials Science; Volume 40; Issue 1 ... Natural fabrics; jute; linen; sandwich laminate; mechanical properties; fractographic analysis. ... In this work, eco-friendly natural fabric sandwich laminate (NFSL) composites are formulated using jute and linen-fabric-reinforced epoxy with different layer ...
Hybrid natural element method for viscoelasticity problems
Zhou, Yan-Kai; Ma, Yong-Qi; Dong, Yi; Feng, Wei
2015-01-01
A hybrid natural element method (HNEM) for two-dimensional viscoelasticity problems under the creep condition is proposed. The natural neighbor interpolation is used as the test function, and the discrete equation system of the HNEM for viscoelasticity problems is obtained using the Hellinger-Reissner variational principle. In contrast to the natural element method (NEM), the HNEM can directly obtain the nodal stresses, which have higher precisions than those obtained using the moving least-square (MLS) approximation. Some numerical examples are given to demonstrate the validity and superiority of this HNEM. Project supported by the Natural Science Foundation of Shanghai, China (Grant No.13ZR1415900).
Crack growth in linearly viscoelastic media
International Nuclear Information System (INIS)
Huang, N.C.
1991-01-01
A computational method for the analysis of initiation and quasi-static extension of a crack in a linearly viscoelastic medium subjected to a tensile mode of deformation is presented. A fracture process zone of Dugdale type is assumed in front of the crack tip. Viscoelastic and viscoplastic deformations of the fracture process zone are analyzed, and crack initiation and crack growth are considered to follow a fracture criterion of critical energy release rate. Examples are given for demonstration of the computational method. (orig.)
Wind turbine blade with viscoelastic damping
Sievers, Ryan A.; Mullings, Justin L.
2017-01-10
A wind turbine blade (60) damped by viscoelastic material (54, 54A-F) sandwiched between stiffer load-bearing sublayers (52A, 52B, 56A, 56B) in portions of the blade effective to damp oscillations (38) of the blade. The viscoelastic material may be located in one or more of: a forward portion (54A) of the shell, an aft portion (54D) of the shell, pressure and suction side end caps (54B) of an internal spar, internal webbing walls (54C, 54E), and a trailing edge core (54F).
Viscoelastic Pavement Modeling with a Spreadsheet
DEFF Research Database (Denmark)
Levenberg, Eyal
2016-01-01
The aim herein was to equip civil engineers and students with an advanced pavement modeling tool that is both easy to use and highly adaptive. To achieve this, a mathematical solution for a layered viscoelastic half-space subjected to a moving load was developed and subsequently implemented...... in a spreadsheet environment. The final program can consider up to five fully bonded layers, each isotropic, homogeneous and weightless. The top layer (as well as others if desired) is linear viscoelastic, while the remaining layers are linear elastic. The load is applied vertically to the surface of the system...
Isoprenylation is required for the processing of the lamin A precursor
International Nuclear Information System (INIS)
Beck, L.A.; Hosick, T.J.; Sinensky, M.
1990-01-01
The nuclear lamina proteins, prelamin A, lamin B, and a 70-kD lamina-associated protein, are posttranslationally modified by a metabolite derived from mevalonate. This modification can be inhibited by treatment with (3-R,S)-3-fluoromevalonate, demonstrating that it is isoprenoid in nature. We have examined the association between isoprenoid metabolism and processing of the lamin A precursor in human and hamster cells. Inhibition of 3-hydroxy-3-methylglutaryl coenzyme A reductase by mevinolin (lovastatin) specifically depletes endogenous isoprenoid pools and inhibits the conversion of prelamin A to lamin A. Prelamin A processing is also blocked by mevalonate starvation of Mev-1, a CHO cell line auxotrophic for mevalonate. Moreover, inhibition of prelamin A processing by mevinolin treatment is rapidly reversed by the addition of exogenous mevalonate. Processing of prelamin A is, therefore, dependent on isoprenoid metabolism. Analysis of the conversion of prelamin A to lamin A by two independent methods, immunoprecipitation and two-dimensional nonequilibrium pH gel electrophoresis, demonstrates that a precursor-product relationship exists between prelamin A and lamin A. Analysis of R,S-[5-3H(N)]mevalonate-labeled cells shows that the rate of turnover of the isoprenoid group from prelamin A is comparable to the rate of conversion of prelamin A to lamin A. These results suggest that during the proteolytic maturation of prelamin A, the isoprenylated moiety is lost. A significant difference between prelamin A processing, and that of p21ras and the B-type lamins that undergo isoprenylation-dependent proteolytic maturation, is that the mature form of lamin A is no longer isoprenylated
Dipolar Interaction and Magneto-Viscoelasticity in Nanomagnetic Fluid.
Basheed, G A; Jain, Komal; Pathak, Saurabh; Pant, R P
2018-04-01
We investigate the effect of dilution on dipolar interaction with linear and non-linear rheological properties of kerosene based magnetic fluid. The steady-state behavior demonstrate a shear thinning behavior and corroborated with a power law, (η = c γ ˙ n + η∞) exponent, n ≤ 1. The shear-induced-breakup (separation) of nanoparticles and the yielding behavior has been explained by Bingham model. Moreover, the magnetoviscous effect showed an initial increase at low shear rate and decrease at higher shear rate. Further, specific viscosity (ηF)-versus-Mason number (Mn) shows a perfect scaling at lower Mn (≤10-4) confirming negligible thermal and colloidal forces. Whereas, at higher Mn (≥10-3) deviation from collapse indicates the dominance of Brownian forces acting on nanofluids. The magnetic field dependent elastic (G') and viscous (G″) modulus reveal a crossover from viscoelastic-to-viscous behavior of nanofluid at critical concentration. Finally, we compare viscoelastic results with De Gans diagonal scaling theory to correlate the functional dependence of storage and loss modules with different particle volume concentration.
Wettability of graphene-laminated micropillar structures
Bong, Jihye; Seo, Keumyoung; Park, Ji-Hoon; Ahn, Joung Real; Ju, Sanghyun
2014-12-01
The wetting control of graphene is of great interest for electronic, mechanical, architectural, and bionic applications. In this study, the wettability of graphene-laminated micropillar structures was manipulated by changing the height of graphene-laminated structures and employing the trichlorosilane (HDF-S)-based self-assembly monolayer. Graphene-laminated micropillar structures with HDF-S exhibited higher hydrophobicity (contact angle of 129.5°) than pristine graphene thin film (78.8°), pristine graphene-laminated micropillar structures (97.5°), and HDF-S self-assembled graphene thin film (98.5°). Wetting states of the graphene-laminated micropillar structure with HDF-S was also examined by using a urea solution, which flowed across the surface without leaving any residues.
Wettability of graphene-laminated micropillar structures
International Nuclear Information System (INIS)
Bong, Jihye; Seo, Keumyoung; Ju, Sanghyun; Park, Ji-Hoon; Ahn, Joung Real
2014-01-01
The wetting control of graphene is of great interest for electronic, mechanical, architectural, and bionic applications. In this study, the wettability of graphene-laminated micropillar structures was manipulated by changing the height of graphene-laminated structures and employing the trichlorosilane (HDF-S)-based self-assembly monolayer. Graphene-laminated micropillar structures with HDF-S exhibited higher hydrophobicity (contact angle of 129.5°) than pristine graphene thin film (78.8°), pristine graphene-laminated micropillar structures (97.5°), and HDF-S self-assembled graphene thin film (98.5°). Wetting states of the graphene-laminated micropillar structure with HDF-S was also examined by using a urea solution, which flowed across the surface without leaving any residues
Rayleigh–Lamb wave propagation on a fractional order viscoelastic plate
Meral, F. Can; Royston, Thomas J.; Magin, Richard L.
2011-01-01
A previous study of the authors published in this journal focused on mechanical wave motion in a viscoelastic material representative of biological tissue [Meral et al., J. Acoust. Soc. Am. 126, 3278–3285 (2009)]. Compression, shear and surface wave motion in and on a viscoelastic halfspace excited by surface and sub-surface sources were considered. It was shown that a fractional order Voigt model, where the rate-dependent damping component that is dependent on the first derivative of time is replaced with a component that is dependent on a fractional derivative of time, resulted in closer agreement with experiment as compared with conventional (integer order) models, such as those of Voigt and Zener. In the present study, this analysis is extended to another configuration and wave type: out-of-plane response of a viscoelastic plate to harmonic anti-symmetric Lamb wave excitation. Theoretical solutions are compared with experimental measurements for a polymeric tissue mimicking phantom material. As in the previous configurations the fractional order modeling assumption improves the match between theory and experiment over a wider frequency range. Experimental complexities in the present study and the reliability of the different approaches for quantifying the shear viscoelastic properties of the material are discussed. PMID:21361459
Changes in large pulmonary arterial viscoelasticity in chronic pulmonary hypertension.
Directory of Open Access Journals (Sweden)
Zhijie Wang
Full Text Available Conduit pulmonary artery (PA stiffening is characteristic of pulmonary arterial hypertension (PAH and is an excellent predictor of mortality due to right ventricular (RV overload. To better understand the impact of conduit PA stiffening on RV afterload, it is critical to examine the arterial viscoelastic properties, which require measurements of elasticity (energy storage behavior and viscosity (energy dissipation behavior. Here we hypothesize that PAH leads to frequency-dependent changes in arterial stiffness (related to elasticity and damping ratio (related to viscosity in large PAs. To test our hypothesis, PAH was induced by the combination of chronic hypoxia and an antiangiogenic compound (SU5416 treatment in mice. Static and sinusoidal pressure-inflation tests were performed on isolated conduit PAs at various frequencies (0.01-20 Hz to obtain the mechanical properties in the absence of smooth muscle contraction. Static mechanical tests showed significant stiffening of large PAs with PAH, as expected. In dynamic mechanical tests, structural stiffness (κ increased and damping ratio (D decreased at a physiologically relevant frequency (10 Hz in hypertensive PAs. The dynamic elastic modulus (E, a material stiffness, did not increase significantly with PAH. All dynamic mechanical properties were strong functions of frequency. In particular, κ, E and D increased with increasing frequency in control PAs. While this behavior remained for D in hypertensive PAs, it reversed for κ and E. Since these novel dynamic mechanical property changes were found in the absence of changes in smooth muscle cell content or contraction, changes in collagen and proteoglycans and their interactions are likely critical to arterial viscoelasticity in a way that has not been previously described. The impact of these changes in PA viscoelasticity on RV afterload in PAH awaits further investigation.
Changes in Large Pulmonary Arterial Viscoelasticity in Chronic Pulmonary Hypertension
Wang, Zhijie; Lakes, Roderic S.; Golob, Mark; Eickhoff, Jens C.; Chesler, Naomi C.
2013-01-01
Conduit pulmonary artery (PA) stiffening is characteristic of pulmonary arterial hypertension (PAH) and is an excellent predictor of mortality due to right ventricular (RV) overload. To better understand the impact of conduit PA stiffening on RV afterload, it is critical to examine the arterial viscoelastic properties, which require measurements of elasticity (energy storage behavior) and viscosity (energy dissipation behavior). Here we hypothesize that PAH leads to frequency-dependent changes in arterial stiffness (related to elasticity) and damping ratio (related to viscosity) in large PAs. To test our hypothesis, PAH was induced by the combination of chronic hypoxia and an antiangiogenic compound (SU5416) treatment in mice. Static and sinusoidal pressure-inflation tests were performed on isolated conduit PAs at various frequencies (0.01–20 Hz) to obtain the mechanical properties in the absence of smooth muscle contraction. Static mechanical tests showed significant stiffening of large PAs with PAH, as expected. In dynamic mechanical tests, structural stiffness (κ) increased and damping ratio (D) decreased at a physiologically relevant frequency (10 Hz) in hypertensive PAs. The dynamic elastic modulus (E), a material stiffness, did not increase significantly with PAH. All dynamic mechanical properties were strong functions of frequency. In particular, κ, E and D increased with increasing frequency in control PAs. While this behavior remained for D in hypertensive PAs, it reversed for κ and E. Since these novel dynamic mechanical property changes were found in the absence of changes in smooth muscle cell content or contraction, changes in collagen and proteoglycans and their interactions are likely critical to arterial viscoelasticity in a way that has not been previously described. The impact of these changes in PA viscoelasticity on RV afterload in PAH awaits further investigation. PMID:24223157
Rate-dependent mode I interlaminar crack growth mechanisms in graphite/epoxy and graphite/PEEK
Gillespie, J. W., Jr.; Carlsson, L. A.; Smiley, A. J.
1987-01-01
In this paper the mode I fracture behavior of graphite/epoxy and graphite/PEEK composites is examined over four decades of crosshead rates (0.25-250 mm/min). Straight-sided double-cantilever-beam specimens consisting of unidirectional laminates were tested at room temperature. For graphite/epoxy the load-deflection response was linear to fracture, and stable slow crack growth initiating at the highest load level was observed for all rates tested. In contrast, mode I crack growth in the graphite/PEEK material was often unstable and showed stick-slip behavior. Subcritical crack growth occurring prior to the onset of fracture was observed at intermediate displacement rates. A mechanism for the fracture behavior of the graphite/PEEK material (based on viscoelastic, plastic, and microcrack coalescence in the process zone) is proposed and related to the observed rate-dependent phenomena.
Cartagena, Alexander; Raman, Arvind
2014-03-04
The measurement of viscoelasticity of cells in physiological environments with high spatio-temporal resolution is a key goal in cell mechanobiology. Traditionally only the elastic properties have been measured from quasi-static force-distance curves using the atomic force microscope (AFM). Recently, dynamic AFM-based methods have been proposed to map the local in vitro viscoelastic properties of living cells with nanoscale resolution. However, the differences in viscoelastic properties estimated from such dynamic and traditional quasi-static techniques are poorly understood. In this work we quantitatively reconstruct the local force and dissipation gradients (viscoelasticity) on live fibroblast cells in buffer solutions using Lorentz force excited cantilevers and present a careful comparison between mechanical properties (local stiffness and damping) extracted using dynamic and quasi-static force spectroscopy methods. The results highlight the dependence of measured viscoelastic properties on both the frequency at which the chosen technique operates as well as the interactions with subcellular components beyond certain indentation depth, both of which are responsible for differences between the viscoelasticity property maps acquired using the dynamic AFM method against the quasi-static measurements. Copyright © 2014 Biophysical Society. Published by Elsevier Inc. All rights reserved.
Gravitational Instability of Cylindrical Viscoelastic Medium ...
Indian Academy of Sciences (India)
symmetric cylinder of viscoelastic medium permeated with non uniform ... plasma (SCP) and weakly coupled plasma (WCP). The non uniform mag- netic field and rotation are considered to act along the axial direction of the cylinder. ... disperse, cold gas to collapse was given by Sir James Jeans (1902) and now known.
Viscoelastic properties of cellular polypropylene ferroelectrets
Czech Academy of Sciences Publication Activity Database
Gaal, M.; Bovtun, Viktor; Stark, W.; Erhard, A.; Yakymenko, Y.; Kreutzbruck, M.
2016-01-01
Roč. 119, č. 12 (2016), s. 1-12, č. článku 125101. ISSN 0021-8979 R&D Projects: GA ČR GA15-08389S Institutional support: RVO:68378271 Keywords : ferroelectrets * viscoelastic properties * ultrasonic Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.068, year: 2016
Gravitational Instability of Cylindrical Viscoelastic Medium ...
Indian Academy of Sciences (India)
because of possible applications to various objects like white dwarf matter, inte- rior of heavy planets, atmosphere of neutron star and ultra cold neutral plasma. Prajapati & Chhajlani (2013) studied the linear self-gravitational instability of finitely conducting magnetized viscoelastic fluid using the GH model and discussed.
Seismic Analysis of a Viscoelastic Damping Isolator
Directory of Open Access Journals (Sweden)
Bo-Wun Huang
2015-01-01
Full Text Available Seismic prevention issues are discussed much more seriously around the world after Fukushima earthquake, Japan, April 2011, especially for those countries which are near the earthquake zone. Approximately 1.8×1012 kilograms of explosive energy will be released from a magnitude 9 earthquake. It destroys most of the unprotected infrastructure within several tens of miles in diameter from the epicenter. People can feel the earthquake even if living hundreds of miles away. This study is a seismic simulation analysis for an innovated and improved design of viscoelastic damping isolator, which can be more effectively applied to earthquake prevention and damage reduction of high-rise buildings, roads, bridges, power generation facilities, and so forth, from earthquake disaster. Solidworks graphic software is used to draw the 3D geometric model of the viscoelastic isolator. The dynamic behavior of the viscoelastic isolator through shock impact of specific earthquake loading, recorded by a seismometer, is obtained via ANSYS finite element package. The amplitude of the isolator is quickly reduced by the viscoelastic material in the device and is shown in a time response diagram. The result of this analysis can be a crucial reference when improving the design of a seismic isolator.
Experimental Viscoelastic Characterization of Corn Cob Composited ...
African Journals Online (AJOL)
The nature of viscoelasticity in biomateria1s and the techniques for characterizing their rheological properties were reviewed. Relaxation tests were performed with cylindrical samples of corn cob composites which were initially subjected to radial compression. It was found that a Maxwell model composed of two simple ...
Viscoelasticity promotes collective swimming of sperm
Tung, Chih-Kuan; Harvey, Benedict B.; Fiore, Alyssa G.; Ardon, Florencia; Suarez, Susan S.; Wu, Mingming
From flocking birds to swarming insects, interactions of organisms large and small lead to the emergence of collective dynamics. Here, we report striking collective swimming of bovine sperm, with sperm orienting in the same direction within each cluster, enabled by the viscoelasticity of the fluid. A long-chain polyacrylamide solution was used as a model viscoelastic fluid such that its rheology can be fine-tuned to mimic that of bovine cervical mucus. In viscoelastic fluid, sperm formed dynamic clusters, and the cluster size increased with elasticity of the polyacrylamide solution. In contrast, sperm swam randomly and individually in Newtonian fluids of similar viscosity. Analysis of the fluid motion surrounding individual swimming sperm indicated that sperm-fluid interaction is facilitated by the elastic component of the fluid. We note that almost all biological fluids (e.g. mucus and blood) are viscoelastic in nature, this finding highlights the importance of fluid elasticity in biological function. We will discuss what the orientation fluctuation within a cluster reveals about the interaction strength. Supported by NIH Grant 1R01HD070038.
On viscoelastic instability in polymeric filaments
DEFF Research Database (Denmark)
Rasmussen, Henrik Koblitz; Hassager, Ole
1999-01-01
The 3D Lagrangian Integral Method is used to simulate the effects of surface tension on the viscoelastic end-plate instability, occuring in the rapid extension of some polymeric filaments between parallel plates. It is shovn that the surface tension delays the onset of the instability. Furthermore...
Stationary thermal convection in a viscoelastic ferrofluid
Energy Technology Data Exchange (ETDEWEB)
Laroze, D., E-mail: david.laroze@gmail.co [Max Planck Institute for Polymer Research, D 55021 Mainz (Germany); Instituto de Alta Investigacion, Universidad de Tarapaca, Casilla 7D, Arica (Chile); Martinez-Mardones, J. [Instituto de Fisica, Pontificia Universidad Catolica de Valparaiso, Casilla 4059, Valparaiso (Chile); Perez, L.M. [Departamento de Ingenieria Metalurgica, Universidad de Santiago de Chile, Av. Bernardo OHiggins 3363, Santiago (Chile); Rojas, R.G. [Instituto de Fisica, Pontificia Universidad Catolica de Valparaiso, Casilla 4059, Valparaiso (Chile)
2010-11-15
We report theoretical and numerical results on convection for a magnetic fluid in a viscoelastic carrier liquid. We focus in the stationary convection for idealized boundary conditions. We obtain explicit expressions of convective thresholds in terms of the control parameters of the system. Close to bifurcation, the coefficients of the corresponding amplitude equation are determined analytically. Finally, the secondary instabilities are performed.
Changes in protein solubility, fermentative capacity, viscoelasticity ...
African Journals Online (AJOL)
The use of frozen dough remedied availability of fresh bread. However, bread elaborated from frozen dough has less volume and texture is firmer. This study evaluates how storage affects the protein solubility, fermentative capacity and viscoelasticity of frozen dough. In addition to examining the effects of storage on the ...
Viscoelastic properties of the false vocal fold
Chan, Roger W.
2004-05-01
The biomechanical properties of vocal fold tissues have been the focus of many previous studies, as vocal fold viscoelasticity critically dictates the acoustics and biomechanics of phonation. However, not much is known about the viscoelastic response of the ventricular fold or false vocal fold. It has been shown both clinically and in computer simulations that the false vocal fold may contribute significantly to the aerodynamics and sound generation processes of human voice production, with or without flow-induced oscillation of the false fold. To better understand the potential role of the false fold in phonation, this paper reports some preliminary measurements on the linear and nonlinear viscoelastic behavior of false vocal fold tissues. Linear viscoelastic shear properties of human false fold tissue samples were measured by a high-frequency controlled-strain rheometer as a function of frequency, and passive uniaxial tensile stress-strain response of the tissue samples was measured by a muscle lever system as a function of strain and loading rate. Elastic moduli (Young's modulus and shear modulus) of the false fold tissues were calculated from the measured data. [Work supported by NIH.
García-Pelagio, Karla P.; Bloch, Robert J.; Ortega, Alicia; Gonzalez-Serratos, Hugo
2008-08-01
Costameres at the sarcolemmal skeletal myofibers transmit the lateral force generated by myofibrils from them to the extracellular matrix. We used an elastimeter method by which sucking pressure is applied through a micropipette to the surface membrane of single mice myofibers of the Extensor digitorum longus to measure the viscoelasticity of the sarcolemma-costamere complex as a function of sarcomere length (SL). Constant suction pressure applied to the sarcolemma generated a sarcolemmal-costamere-myofibril bleb of variable height depending on the sucking pressure and SL. It took some time for the bleb to reach a stable height after applying the pressure. This time delay indicates that the sarcolemma-costamere-myofibril system acts as a viscoelastic system. We undertook the present experiments to measure the height stabilization time of the bleb at different sarcomere lengths from which we estimated the viscoelastic parameters of the system. The time course of the bleb formation was biphasic and reached a plateau between 3.5 to 1.3 and 4.9 to 3.5 min for normal and dystrophic mice respectively depending on SL of 3.0 to 5.6 μm. Based on a Maxwell-Voigt system we found the viscoelastic parameters such as viscosity, friction coefficient and the costameres (k) and sarcolemma (k1) elasticity constants.
Nanoscale Viscoelasticity of Extracellular Matrix Proteins in Soft Tissues: a Multiscale Approach
Miri, Amir K.; Heris, Hossein K.; Mongeau, Luc; Javid, Farhad
2013-01-01
We propose that the bulk viscoelasticity of soft tissues results from two length-scale-dependent mechanisms: the time-dependent response of extracellular matrix proteins (ECM) at the nanometer scale and the biophysical interactions between the ECM solid structure and interstitial fluid at the micrometer scale. The latter was modeled using the poroelasticity theory with an assumption of free motion of the interstitial fluid within the porous ECM structure. Following a recent study (Heris, H.K., Miri, A.K., Tripathy, U., Barthelat, F., Mongeau, L., 2013. Journal of the Mechanical Behavior of Biomedical Materials), atomic force microscopy was used to perform creep loading and 50-nm sinusoidal oscillations on porcine vocal folds. The proposed model was calibrated by a finite element model to accurately predict the nanoscale viscoelastic moduli of ECM. A linear correlation was observed between the in-depth distribution of the viscoelastic moduli and that of hyaluronic acids in the vocal fold tissue. We conclude that hyaluronic acids may regulate the vocal fold viscoelasticity at nanoscale. The proposed methodology offers a characterization tool for biomaterials used in vocal fold augmentations. PMID:24317493
Khan, Kamran
2012-11-09
We formulate a constitutive framework for biodegradable polymers that accounts for nonlinear viscous behavior under regimes with large deformation. The generalized Maxwell model is used to represent the degraded viscoelastic response of a polymer. The large-deformation, time-dependent behavior of viscoelastic solids is described using an Ogden-type hyperviscoelastic model. A deformation-induced degradation mechanism is assumed in which a scalar field depicts the local state of the degradation, which is responsible for the changes in the material\\'s properties. The degradation process introduces another timescale (the intrinsic material clock) and an entropy production mechanism. Examples of the degradation of a polymer under various loading conditions, including creep, relaxation and cyclic loading, are presented. Results from parametric studies to determine the effects of various parameters on the process of degradation are reported. Finally, degradation of an annular cylinder subjected to pressure is also presented to mimic the effects of viscoelastic arterial walls (the outer cylinder) on the degradation response of a biodegradable stent (the inner cylinder). A general contact analysis is performed. As the stiffness of the biodegradable stent decreases, stress reduction in the stented viscoelastic arterial wall is observed. The integration of the proposed constitutive model with finite element software could help a designer to predict the time-dependent response of a biodegradable stent exhibiting finite deformation and under complex mechanical loading conditions. © 2012 Springer-Verlag Wien.
Laminitis and the equine metabolic syndrome.
Johnson, Philip J; Wiedmeyer, Charles E; LaCarrubba, Alison; Ganjam, V K Seshu; Messer, Nat T
2010-08-01
Although much has been written about laminitis in the context of its association with inflammatory processes, recognition is growing that most cases of laminitis examined by veterinarians in private practice are those associated with pasture grazing, obesity, and insulin resistance (IR). The term 'endocrinopathic laminitis' has been adopted to classify the instances of laminitis in which the origin seems to be more strongly associated with an underlying endocrinopathy, such as either IR or the influence of corticosteroids. Results of a recent study suggest that obesity and IR represent the most common metabolic and endocrinopathic predispositions for laminitis in horses. IR also plays an important role in the pathogenesis of laminitis that develops when some horses or ponies are allowed to graze pastures at certain times of the year. The term equine metabolic syndrome (EMS) has been proposed as a label for horses whose clinical examination results (including both physical examination and laboratory testing) suggest heightened risk for developing laminitis as a result of underlying IR. Copyright (c) 2010 Elsevier Inc. All rights reserved.
Direct Composite Laminate Veneers: Three Case Reports
Directory of Open Access Journals (Sweden)
Bora Korkut
2013-05-01
Full Text Available Re-establishing a patient’s lost dental esthetic appearance is one of the most important topics for contemporary dentistry. New treatment materials and methods have been coming on the scene, day by day, in order to achieve such an aim. Most dentists prefer more conservative and aesthetic approaches, such as direct and indirect laminate veneer restorations, instead of full-ceramic crowns for anteriors where aesthetics is really important. Laminate veneers are restorations which are envisioned to correct existing abnormalities, esthetic deficiencies and discolorations. Laminate veneer restorations may be processed in two different ways: direct or indirect. Direct laminate veneers have no need to be prepared in the laboratory and are based on the principle of application of a composite material directly to the prepared tooth surface in the dental clinic. Indirect laminate veneers may be produced from composite materials or ceramics, which are cemented to the tooth with an adhesive resin. In this case report, direct composite laminate veneer technique used for three patients with esthetic problems related to fractures, discolorations and an old prolapsed restoration, is described and six-month follow-ups are discussed. As a conclusion, direct laminate veneer restorations may be a treatment option for patients with the esthetic problems of anterior teeth in cases similar to those reported here.
Predisposing factors of laminitis in cattle.
Vermunt, J J; Greenough, P R
1994-01-01
Laminitis is regarded as a major predisposing factor in lameness caused by claw disorders. Despite intensive study, both by experiment and by clinical observation, knowledge of the precise aetiology and pathogenesis of bovine laminitis is still incomplete. It is often hypothesized that changes in the micro-circulation of the corum (dermis) of the bovine claw contribute significantly to the development of laminitis; arteriovenous anastomoses (AVAs) playing a crucial role. Many factors have been implicated as contributing causes of laminitis in cattle; the disease has a multifactorial aetiology. The cause of laminitis should be considered as a combination of predisposing factors leading to vascular (AVAs in particular) reactivity and inhibition of normal horn synthesis. Nutrition, disease, management and behaviour appear to be closely involved in the pathogenesis of bovine laminitis. The major factors predisposing to laminitis in cattle, as reported or suggested in the literature, are reviewed, including systemic disease, nutrition (barley grain, protein, carbohydrate and fibre), management (housing, bedding and exercise), calving, season, age, growth, genetics, conformation and behaviour.
Structural feasibility of parallel-laminated veneer crossarms
John Youngquist; Frank Brey; Joseph Jung
1977-01-01
Experimentally and commercially produced laminated M-19 crossarms were tested by standard Rural Electrification Administration (REA) crossarm tests. The laminated crossarms, produced by laminating veneer and by laminating solid-sawn dimension stock, generally performed satisfactorily according to REA specified standards. Materials tested are described and results on...
Linear Viscoelasticity of Spherical SiO 2 Nanoparticle-Tethered Poly(butyl acrylate) Hybrids
Goel, Vivek
2010-12-01
The melt state linear viscoelastic properties of spherical silica nanoparticles with grafted poly(n-butyl acrylate) chains of varying molecular weight were probed using linear small amplitude dynamic oscillatory measurements and complementary linear stress relaxation measurements. While the pure silica-tethered-polymer hybrids with no added homopolymer exhibit solid-like response, addition of matched molecular weight free matrix homopolymer chains to this hybrid, at low concentrations of added homopolymer, maintains the solid-like response with a lowered modulus that can be factored into a silica concentration dependence and a molecular weight dependence. While the silica concentration dependence of the modulus is strong, the dependence on molecular weight is weak. On the other hand, increasing the amount of added homopolymer changes the viscoelastic response to that of a liquid with a relaxation time that scales exponentially with hybrid concentration. © 2010 American Chemical Society.
Viscoelastic gravel-pack carrier fluid
International Nuclear Information System (INIS)
Nehmer, W.L.
1988-01-01
The ability of a fluid to flow adequately into the formation during gravel-pack treatments is critical to achieving a good pack. Recent studies have indicated ''fish-eyes'' and/or ''microgels'' present in many polymer gelled carrier fluids will plug pore throats, leading to impaired leakoff and causing formation damage. Intensive manipulation of the polymer gelled fluid using shear and filter devices will help remove the particles, but it adds to the cost of the treatment in terms of equipment and manpower. Excessive shear will degrade the polymer leading to poor gravel suspension, while too little shear will cause filtration problems. A gelled carried fluid using a viscoelastic surfactant system has been found to leak off very efficiently to the formation, and cause no formation damage, without the use of shear/filter devices. Viscoelastic surfactant-base gelled fluids develop viscosity because of the association of surfactant moloecules into large rod-shaped aggregates. There is no hydration of polymer involved, so fish-eyes and microgels will not be formed in the viscoelastic fluid. A surfactant-base system having a yield point allows the gravel carrying properties to be much better than fluids gelled with conventional polymer systems (hydroxyethylcellulose [HEC]). For example, a gravel carried fluid gelled with 80 lb HEC/1,000 gal has a viscosity of about 400 cp at 170 sec/sup -1/; a viscoelastic surfactant-base system having only one-half the viscosity still flows into cores about four times more efficiently than the HEC-base fluid. The rheology, leakoff, formation damage and mixing properties of a viscoelastic, surfactant-base, gravel-pack carrier fluid are discussed
Meshfree modeling in laminated composites
Simkins, Daniel Craig
2012-09-27
A problem of increasing importance in the aerospace industry is in detailed modeling of explicit fracture in laminated composite materials. For design applications, the simulation must be capable of initiation and propagation of changes in the problem domain. Further, these changes must be able to be incorporated within a design-scale simulation. The use of a visibility condition, coupled with the local and dynamic nature of meshfree shape function construction allows one to initiate and explicitly open and propagate holes inside a previously continuous problem domain. The method to be presented naturally couples to a hierarchical multi-scale material model incorporating external knowldege bases to achieve the goal of a practical explicit fracture modeling capability for full-scale problems. © 2013 Springer-Verlag.
Shielding Effectiveness of Laminated Shields
Directory of Open Access Journals (Sweden)
B. P. Rao
2008-12-01
Full Text Available Shielding prevents coupling of undesired radiated electromagnetic energy into equipment otherwise susceptible to it. In view of this, some studies on shielding effectiveness of laminated shields with conductors and conductive polymers using plane-wave theory are carried out in this paper. The plane wave shielding effectiveness of new combination of these materials is evaluated as a function of frequency and thickness of material. Conductivity of the polymers, measured in previous investigations by the cavity perturbation technique, is used to compute the overall reflection and transmission coefficients of single and multiple layers of the polymers. With recent advances in synthesizing stable highly conductive polymers these lightweight mechanically strong materials appear to be viable alternatives to metals for EM1 shielding.
Interaction and deformation of viscoelastic particles: Nonadhesive particles
International Nuclear Information System (INIS)
Attard, Phil
2001-01-01
A viscoelastic theory is formulated for the deformation of particles that interact with finite-ranged surface forces. The theory generalizes the static approach based upon classic continuum elasticity theory to account for time-dependent effects, and goes beyond contact theories such as Hertz and that given by Johnson, Kendall, and Roberts by including realistic surface interactions. Common devices used to measure load and deformation are modeled and the theory takes into account the driving velocity of the apparatus and the relaxation time of the material. Nonadhesive particles are modeled by an electric double layer repulsion. Triangular, step, and sinusoidal trajectories are analyzed in a unified treatment of loading and unloading. The load-deformation and the load-contact area curves are shown to be velocity dependent and hysteretic
A note on adding viscoelasticity to earthquake simulators
Pollitz, Fred
2017-01-01
Here, I describe how time‐dependent quasi‐static stress transfer can be implemented in an earthquake simulator code that is used to generate long synthetic seismicity catalogs. Most existing seismicity simulators use precomputed static stress interaction coefficients to rapidly implement static stress transfer in fault networks with typically tens of thousands of fault patches. The extension to quasi‐static deformation, which accounts for viscoelasticity of Earth’s ductile lower crust and mantle, involves the precomputation of additional interaction coefficients that represent time‐dependent stress transfer among the model fault patches, combined with defining and evolving additional state variables that track this stress transfer. The new approach is illustrated with application to a California‐wide synthetic fault network.
Rusakov, V. V.; Raikher, Yu. L.
2017-09-01
The theory of orientational motion of a Brownian magnetic nanoparticle embedded in a viscoelastic medium and subjected to a time-dependent uniform magnetic field is developed. The rheology of the viscoelastic environment of the particle is modeled by the Jeffreys scheme, which under variation of a minimal number of parameters is able to resemble a wide range of soft materials: from a weakly structured (nearly Newtonian) polymer solution to a gel. It is shown that in the Jeffreys model, the diffusional orientational motion of a particle is a combination of two modes, which could be associated with a fast motion within the polymer mesh cell and a slow displacement that involves deformation of the mesh, respectively. The dependencies of the reference times of both relaxation modes on the Jeffreys viscous and elastic parameters and temperature are found. It turns out that in substantially viscoelastic media, the rate of the slow mode (it dominates in relaxation) quadratically depends on the matrix temperature. This effect does not have analogs in linearly viscous systems. For an ensemble of magnetic nanoparticles in viscoelastic and gel Jeffreys matrices: (1) the dynamic magnetic susceptibility is derived and evaluated both within an exact approach and in a simple approximation; (2) the problem of magnetic relaxometry, i.e., evolution of magnetization after step-wise turning off the field, is solved; (3) the specific power loss caused by viscous dissipation generated by the particles under an ac field is analyzed as a function of the rheological parameters. Results (1) and (2) provide simple models for magnetic nanorheology; consideration (3) advances the physics of magnetic hyperthermia in viscoelastic and gel-like media.
Amador Carrascal, Carolina; Chen, Shigao; Urban, Matthew W; Greenleaf, James F
2018-01-01
Ultrasound shear wave elastography is a promising noninvasive, low cost, and clinically viable tool for liver fibrosis staging. Current shear wave imaging technologies on clinical ultrasound scanners ignore shear wave dispersion and use a single group velocity measured over the shear wave bandwidth to estimate tissue elasticity. The center frequency and bandwidth of shear waves induced by acoustic radiation force depend on the ultrasound push beam (push duration, -number, etc.) and the viscoelasticity of the medium, and therefore are different across scanners from different vendors. As a result, scanners from different vendors may give different tissue elasticity measurements within the same patient. Various methods have been proposed to evaluate shear wave dispersion to better estimate tissue viscoelasticity. A rheological model such as the Kelvin-Voigt model is typically fitted to the shear wave dispersion to solve for the elasticity and viscosity of tissue. However, these rheological models impose strong assumptions about frequency dependence of elasticity and viscosity. Here, we propose a new method called Acoustic Radiation Force Induced Creep-Recovery (ARFICR) capable of quantifying rheological model-independent measurements of elasticity and viscosity for more robust tissue health assessment. In ARFICR, the creep-recovery time signal at the focus of the push beam is used to calculate the relative elasticity and viscosity (scaled by an unknown constant) over a wide frequency range. Shear waves generated during the ARFICR measurement are also detected and used to calculate the shear wave velocity at its center frequency, which is then used to calibrate the relative elasticity and viscosity to absolute elasticity and viscosity. In this paper, finite-element method simulations and experiments in tissue mimicking phantoms are used to validate and characterize the extent of viscoelastic quantification of ARFICR. The results suggest that ARFICR can measure tissue
The role of neutrophils in equine laminitis.
Leise, Britta
2018-03-01
Equine laminitis is a devastating disease in which failure of the adhesion between the digital dermal and epidermal laminae at the basement membrane results in crippling lameness and structural damage to the foot of the horse. Laminitis occurring secondary to sepsis is known to result from a significant inflammatory response that includes leukocyte emigration into the lamellar tissue. These leukocytes, in particular the neutrophil, have been extensively evaluated in experimental models of sepsis-related laminitis in the horse. This review will discuss the relevant findings elucidated from these models and how these findings have affected the development of therapies used to treat this crippling disease.
Curing of Thick Thermoset Composite Laminates: Multiphysics Modeling and Experiments
Anandan, S.; Dhaliwal, G. S.; Huo, Z.; Chandrashekhara, K.; Apetre, N.; Iyyer, N.
2017-11-01
Fiber reinforced polymer composites are used in high-performance aerospace applications as they are resistant to fatigue, corrosion free and possess high specific strength. The mechanical properties of these composite components depend on the degree of cure and residual stresses developed during the curing process. While these parameters are difficult to determine experimentally in large and complex parts, they can be simulated using numerical models in a cost-effective manner. These simulations can be used to develop cure cycles and change processing parameters to obtain high-quality parts. In the current work, a numerical model was built in Comsol MultiPhysics to simulate the cure behavior of a carbon/epoxy prepreg system (IM7/Cycom 5320-1). A thermal spike was observed in thick laminates when the recommended cure cycle was used. The cure cycle was modified to reduce the thermal spike and maintain the degree of cure at the laminate center. A parametric study was performed to evaluate the effect of air flow in the oven, post cure cycles and cure temperatures on the thermal spike and the resultant degree of cure in the laminate.
Behaviour of Mechanically Laminated CLT Members
Kuklík, P.; Velebil, L.
2015-11-01
Cross laminated timber (CLT) is one of the structural building systems based on the lamination of multiple layers, where each layer is oriented perpendicularly to each other. Recent requirements are placed to develop an alternative process based on the mechanical lamination of the layers, which is of particular interest to our research group at the University Centre for Energy Efficient Buildings. The goal is to develop and verify the behaviour of mechanically laminated CLT wall panels exposed to shear stresses in the plane. The shear resistance of mechanically jointed CLT is ensured by connecting the layers by screws. The paper deals with the experimental analysis focused on the determination of the torsional stiffness and the slip modulus of crossing areas for different numbers of orthogonally connected layers. The results of the experiments were compared with the current analytical model.
Oseledec multiplicative ergodic theorem for laminations
Nguyên, Viêt-Anh
2017-01-01
Given a n-dimensional lamination endowed with a Riemannian metric, the author introduces the notion of a multiplicative cocycle of rank d, where n and d are arbitrary positive integers. The holonomy cocycle of a foliation and its exterior powers as well as its tensor powers provide examples of multiplicative cocycles. Next, the author defines the Lyapunov exponents of such a cocycle with respect to a harmonic probability measure directed by the lamination. He also proves an Oseledec multiplicative ergodic theorem in this context. This theorem implies the existence of an Oseledec decomposition almost everywhere which is holonomy invariant. Moreover, in the case of differentiable cocycles the author establishes effective integral estimates for the Lyapunov exponents. These results find applications in the geometric and dynamical theory of laminations. They are also applicable to (not necessarily closed) laminations with singularities. Interesting holonomy properties of a generic leaf of a foliation are obtained...
Laminate mechanics for balanced woven fabrics
Akkerman, Remko
2006-01-01
Laminate mechanics equations are presented for composites with balanced woven fabric reinforcements. It is shown that mimicking these textile composites with equivalent transversely isotropic (‘unidirectional’) layers requires disputable manipulations. Various micromechanics predictions of textile
Free edge effects in laminated composites
Herakovich, C. T.
1989-01-01
The fundamental mechanics of free-edge effects in laminated fiber-reinforced composites is examined, reviewing the results of recent experimental and analytical investigations. The derivation of the governing equations for the basic problem is outlined, including the equilibrium and mismatch conditions and the elasticity formulation, and experimental data on axial displacement and shear strain in angle-ply laminates are summarized. Numerical predictions of free-edge deformation and interlaminar and through-thickness stress distributions are presented for cross-ply, angle-ply, and quasi-isotropic laminates, and the mechanisms of edge damage and failure in angle-ply laminates are briefly characterized. Extensive diagrams, drawings, graphs, and photographs are provided.
Mechanical characterisation of structural laminated bamboo
Sharma, Bhavna; Bauer, Helene; Schickhofer, Gerhard; Ramage, Michael H.
2017-01-01
Low carbon construction materials are needed to reduce CO2 emissions in the built environment. Laminated bamboo is an example of such a material, however to be used in structural applications, fundamental mechanical properties are needed to establish the design values used in architecture and engineering practice. Recent studies on laminated bamboo have focused on the use of timber standards for small clear specimens, with little work published on structural scale testing. The presented work ...
Dynamic Response Research of U Shaped Pipe with Viscoelastic Damping Layer
Guo, Yajuan; Meng, Guang; Li, Hongguang
The frequency dependency property of viscoelastic material leads to the dynamic analysis of compound structures which are complex and costly. Furthermore, using commercial finite element software, it is difficult to carry out the dynamic response analysis with this characteristic. Based on finite element iterative and modal strain energy (MSE) method, a mode superposition algorithm was proposed to solve the dynamic response of viscoelastic damping structure in this paper. Through iterative and MSE method, the modal frequency and loss factor for each mode can be obtained. Before calculating the next order modal frequency, the modal mode and corresponding load are extracted and the response of node was calculated at first in this algorithm. As a consequence, the node displacement response can be solved by summarizing the response results of each independent mode in the required frequency range. Numerical calculation of U shaped pipe with viscoelastic damping layer illustrates that the method is simple and practical. Moreover, the simulations with this method agree quite well with the experimental derived results. In the meantime, the damping layer parameters study shows that the position of the damping layer has an obvious effect of reducing the vibration response of U shaped pipe, but the width of the damping layer has little influence. The procedure proposed in this paper can be extended to analyze other more complex structures with viscoelastic material.
Hayat, Tasawar; Ashraf, Muhammad Bilal; Alsulami, Hamed H; Alhuthali, Muhammad Shahab
2014-01-01
The objective of present research is to examine the thermal radiation effect in three-dimensional mixed convection flow of viscoelastic fluid. The boundary layer analysis has been discussed for flow by an exponentially stretching surface with convective conditions. The resulting partial differential equations are reduced into a system of nonlinear ordinary differential equations using appropriate transformations. The series solutions are developed through a modern technique known as the homotopy analysis method. The convergent expressions of velocity components and temperature are derived. The solutions obtained are dependent on seven sundry parameters including the viscoelastic parameter, mixed convection parameter, ratio parameter, temperature exponent, Prandtl number, Biot number and radiation parameter. A systematic study is performed to analyze the impacts of these influential parameters on the velocity and temperature, the skin friction coefficients and the local Nusselt number. It is observed that mixed convection parameter in momentum and thermal boundary layers has opposite role. Thermal boundary layer is found to decrease when ratio parameter, Prandtl number and temperature exponent are increased. Local Nusselt number is increasing function of viscoelastic parameter and Biot number. Radiation parameter on the Nusselt number has opposite effects when compared with viscoelastic parameter.
Effect of long-time immersion of soft denture liners in water on viscoelastic properties.
Iwasaki, Naohiko; Yamaki, Chisato; Takahashi, Hidekazu; Oki, Meiko; Suzuki, Tetsuya
2017-09-26
Aim of this study was to investigate the effect of long-time immersion of soft denture liners in 37°C water on viscoelastic properties. Six silicone-based and two acrylic resin-based soft denture liners were selected. Cylindrical specimens were stored in distilled water at 37°C for 6 months. Viscoelastic properties, which were instantaneous and delayed elastic displacements, viscous flow, and residual displacement, were determined using a creep meter, and analyzed with 2-way analysis of variance and Tukey's comparison (α=0.05). Viscoelastic properties and their time-dependent changes were varied among materials examined. The observed viscoelastic properties of three from six silicone-based liners did not significantly change after 6-month immersion, but those of two acrylic resin-based liners significantly changed with the increase of immersion time. However, the sum of initial instantaneous elastic displacement and delayed elastic displacement of two acrylic resin-based liners during 6-month immersion changed less than 10%, which might indicate clinically sufficient elastic performance.
Calculation of viscoelastic properties of edible films: application of three models
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CHANDRA Prabir K.
2000-01-01
Full Text Available The viscoelastic properties of edible films can provide information at the structural level of the biopolymers used. The objective of this work was to test three simple models of linear viscoelastic theory (Maxwell, Generalized Maxwell with two units in parallel, and Burgers using the results of stress relaxation tests in edible films of myofibrillar proteins of Nile Tilapia. The films were elaborated according to a casting technique and pre-conditioned at 58% relative humidity and 22ºC for 4 days. The testing sample (15mm x 118mm was submitted to tests of stress relaxation in an equipment of physical measurements, TA.XT2i. The deformation, imposed to the sample, was 1%, guaranteeing the permanency in the domain of the linear viscoelasticity. The models were fitted to experimental data (stress x time by nonlinear regression. The Generalized Maxwell model with two units in parallel and the Burgers model represented the relaxation curves of stress satisfactorily. The viscoelastic properties varied in a way that they were less dependent on the thickness of the films.
Zhou, Jianyou; Jiang, Liying; Khayat, Roger E.
2018-01-01
Elastomers are known to exhibit viscoelastic behavior under deformation, which is linked to the diffusion processes of the highly mobile and flexible polymer chains. Inspired by the theories of polymer dynamics, a micro-macro constitutive model is developed to study the viscoelastic behaviors and the relaxation process of elastomeric materials under large deformation, in which the material parameters all have a microscopic foundation or a microstructural justification. The proposed model incorporates the nonlinear material viscosity into the continuum finite-deformation viscoelasticity theories which represent the polymer networks of elastomers with an elastic ground network and a few viscous subnetworks. The developed modeling framework is capable of adopting most of strain energy density functions for hyperelastic materials and thermodynamics evolution laws of viscoelastic solids. The modeling capacity of the framework is outlined by comparing the simulation results with the experimental data of three commonly used elastomeric materials, namely, VHB4910, HNBR50 and carbon black (CB) filled elastomers. The comparison shows that the stress responses and some typical behaviors of filled and unfilled elastomers can be quantitatively predicted by the model with suitable strain energy density functions. Particularly, the strain-softening effect of elastomers could be explained by the deformation-dependent (nonlinear) viscosity of the polymer chains. The presented modeling framework is expected to be useful as a modeling platform for further study on the performance of different type of elastomeric materials.
Relationship between viscoelastic properties of soft denture liners and clinical efficacy
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Hiroshi Murata
2008-10-01
Full Text Available Soft denture liners are applied for denture wearers who cannot tolerate a hard-based denture due to a thin and non-resilient oral mucosa and/or severe alveolar resorption. This material distributes and absorbs masticatory forces by means of the cushioning effect. Clinical success of the materials depends both on their viscoelastic properties and on durability. Acrylic resins and silicones are mainly available for permanent soft liners. The acrylic permanent soft liners demonstrate viscoelastic behavior while silicone permanent soft liners demonstrate elastic behavior. The improvement in masticatory function is greater in dentures lined with the acrylic materials than in those lined with silicone products. However, the acrylic materials exhibit a more marked change in viscoelastic properties and loss of cushioning effect over time than silicones. From the standpoint of durability, the silicones are preferred. It is important to understand viscoelastic properties and durability of each soft denture liner and to select the material according to the clinical situations and purposes. The ideal permanent soft liners have a relatively high value of loss tangent and storage modulus, and high durability. Further research is necessary to develop the ideal soft denture liner.
Yuan, Dan; Zhang, Jun; Yan, Sheng; Peng, Gangrou; Zhao, Qianbin; Alici, Gursel; Du, Hejun; Li, Weihua
2016-08-01
In this work, particle lateral migration in sample-sheath flow of viscoelastic fluid and Newtonian fluid was experimentally investigated. The 4.8-μm micro-particles were dispersed in a polyethylene oxide (PEO) viscoelastic solution, and then the solution was injected into a straight rectangular channel with a deionised (DI) water Newtonian sheath flow. Micro-particles suspended in PEO solution migrated laterally to a DI water stream, but migration in the opposite direction from a DI water stream to a PEO solution stream or from one DI water stream to another DI water stream could not be achieved. The lateral migration of particles depends on the viscoelastic properties of the sample fluids. Furthermore, the effects of channel length, flow rate, and PEO concentration were studied. By using viscoelastic sample flow and Newtonian sheath flow, a selective particle lateral migration can be achieved in a simple straight channel, without any external force fields. This particle lateral migration technique could be potentially used in solution exchange fields such as automated cell staining and washing in microfluidic platforms, and holds numerous biomedical applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Hong, Xiaowei; Stegemann, Jan P; Deng, Cheri X
2016-05-01
Characterization of the microscale mechanical properties of biomaterials is a key challenge in the field of mechanobiology. Dual-mode ultrasound elastography (DUE) uses high frequency focused ultrasound to induce compression in a sample, combined with interleaved ultrasound imaging to measure the resulting deformation. This technique can be used to non-invasively perform creep testing on hydrogel biomaterials to characterize their viscoelastic properties. DUE was applied to a range of hydrogel constructs consisting of either hydroxyapatite (HA)-doped agarose, HA-collagen, HA-fibrin, or preosteoblast-seeded collagen constructs. DUE provided spatial and temporal mapping of local and bulk displacements and strains at high resolution. Hydrogel materials exhibited characteristic creep behavior, and the maximum strain and residual strain were both material- and concentration-dependent. Burger's viscoelastic model was used to extract characteristic parameters describing material behavior. Increased protein concentration resulted in greater stiffness and viscosity, but did not affect the viscoelastic time constant of acellular constructs. Collagen constructs exhibited significantly higher modulus and viscosity than fibrin constructs. Cell-seeded collagen constructs became stiffer with altered mechanical behavior as they developed over time. Importantly, DUE also provides insight into the spatial variation of viscoelastic properties at sub-millimeter resolution, allowing interrogation of the interior of constructs. DUE presents a novel technique for non-invasively characterizing hydrogel materials at the microscale, and therefore may have unique utility in the study of mechanobiology and the characterization of hydrogel biomaterials. Copyright © 2016 Elsevier Ltd. All rights reserved.
Ceramic laminates with tailored residual stresses
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Baudín, C.
2009-12-01
Full Text Available Severe environments imposed by new technologies demand new materials with better properties and ensured reliability. The intrinsic brittleness of ceramics has forced scientists to look for new materials and processing routes to improve the mechanical behaviour of ceramics in order to allow their use under severe thermomechanical conditions. The laminate approach has allowed the fabrication of a new family of composite materials with strength and reliability superior to those of monolithic ceramics with microstructures similar to those of the constituent layers. The different ceramic laminates developed since the middle 1970´s can be divided in two large groups depending on whether the development of residual stresses between layers is the main design tool. This paper reviews the developments in the control and tailoring of residual stresses in ceramic laminates. The tailoring of the thickness and location of layers in compression can lead to extremely performing structures in terms of strength values and reliability. External layers in compression lead to the strengthening of the structure. When relatively thin and highly compressed layers are located inside the material, threshold strength, crack bifurcation and crack arrest during fracture occur.
Las severas condiciones de trabajo de las nuevas aplicaciones tecnológicas exigen el uso de materiales con mejores propiedades y alta fiabilidad. La potencialidad de uso de materiales frágiles, como los cerámicos, en estas aplicaciones exige el desarrollo de nuevos materiales y métodos de procesamiento que mejoren su comportamiento mecánico. El concepto de material laminado ha permitido la fabricación de una nueva familia de materiales con tensiones de fractura y fiabilidad superiores a las de materiales monolíticos con microestructuras similares a las de las láminas que conforman el laminado. Los distintos materiales laminados desarrollados desde mediados de los años 70 se pueden
Paradigm shifts in understanding equine laminitis.
Patterson-Kane, J C; Karikoski, N P; McGowan, C M
2018-01-01
Laminitis, one of the most debilitating conditions of all equids, is now known to be the result of several systemic disease entities. This finding, together with other recent developments in the field of laminitis research, have provoked a rethink of our clinical and research strategies for this condition. First, laminitis is now considered to be a clinical syndrome associated with systemic disease (endocrine disease, sepsis or systemic inflammatory response syndrome, SIRS) or altered weight bearing rather than being a discrete disease entity. Next, laminitis associated with endocrine disease (endocrinopathic laminitis) is now believed to be the predominant form in animals presenting (primarily) for lameness. Third, the designation of laminitis as a primary and severe basement membrane pathology now requires revision. Instead, current data now proposes a variable subclinical phase associated with gross changes in the hoof capsule, with stretching and elongation of the lamellar cells an early and key event in the pathophysiology. These findings have fuelled new mechanistic hypotheses and research directions that will be discussed, together with their implications for future clinical management. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.
The nuclear lamins: flexibility in function.
Burke, Brian; Stewart, Colin L
2013-01-01
The nuclear lamina is an important structural determinant for the nuclear envelope as a whole, attaching chromatin domains to the nuclear periphery and localizing some nuclear envelope proteins. The major components of the lamina are the A-type and B-type lamins, which are members of the intermediate filament protein family. Whereas the expression of A-type lamins is developmentally regulated, B-type lamins, as a class, are found in all cells. The association of B-type lamins with many aspects of nuclear function has led to the view that these are essential proteins, and there is growing evidence suggesting that they regulate cellular senescence. However, B-type lamins are dispensable in certain cell types in vivo, and neither A-type nor B-type lamins may be required in early embryos or embryonic stem cells. The picture that is beginning to emerge is of a complex network of interactions at the nuclear periphery that may be defined by cell- and tissue-specific functions.
Viscoelasticity of Xenon near the Critical Point
Berg, Robert F.; Moldover, Michael R.; Zimmerli, Gregory A.
1999-01-01
Using a novel, overdamped, oscillator flown aboard the Space Shuttle, we measured the viscosity of xenon near the liquid-vapor critical point in the frequency range 2 Hz less than or equal to f less than or equal to 12 Hz. The measured viscosity divergence is characterized by the exponent z(sub eta) = 0.0690 +/- 0.0006, in agreement with the value z(sub eta) = 0.067 +/- 0.002 calculated from a two-loop perturbation expansion. Viscoelastic behavior was evident when t = (T - T(sub c))/T(sub c) less than 10(exp -5) and dominant when t less than 10(exp -6), further from T(sub c) than predicted. Viscoelastic behavior scales as Af(tau) where tau is the fluctuation decay time. The measured value of A is 2.0 +/- 0.3 times the result of a one-loop calculation. (Uncertainties stated are one standard uncertainty.)
Viscoelastic creep of high-temperature concrete
International Nuclear Information System (INIS)
Pfeiffer, P.A.; Marchertas, A.H.; Bazant, Z.P.
1985-01-01
Presented in this report is the analytical model for analysis of high temperature creep response of concrete. The creep law used is linear (viscoelastic), the temperature and moisture effects on the creep rate and also aging are included. Both constant and transient temperature as well as constant and transient moisture conditions are considered. Examples are presented to correlate experimental data with parameters of the analytical model by the use of a finite element scheme
International Nuclear Information System (INIS)
Favale, Nicolas O.; Sterin Speziale, Norma B.; Fernandez Tome, Maria C.
2007-01-01
Lamin A/C is the most studied nucleoskeletal constituent. Lamin A/C expression indicates cell differentiation and is also a structural component of nuclear speckles, which are involved in gene expression regulation. Hypertonicity has been reported to induce renal epithelial cell differentiation and expression of TonEBP (NFAT5), a transcriptional activator of hypertonicity-induced gene transcription. In this paper, we investigate the effect of hypertonicity on lamin A/C expression in MDCK cells and the involvement of TonEBP. Hypertonicity increased lamin A/C expression and its distribution to nucleoplasm with speckled pattern. Microscopy showed codistribution of TonEBP and lamin A/C in nucleoplasmic speckles, and immunoprecipitation demonstrated their interaction. TonEBP silencing caused lamin A/C redistribution from nucleoplasmic speckles to the nuclear rim, followed by lamin decrease, thus showing that hypertonicity induces lamin A/C speckles through a TonEBP-dependent mechanism. We suggest that lamin A/C speckles could serve TonEBP as scaffold thus favoring its role in hypertonicity
Static viscoelasticity of biomass polyethylene composites
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Keyan Yang
Full Text Available The biomass polyethylene composites filled with poplar wood flour, rice husk, cotton stalk or corn stalk were prepared by extrusion molding. The static viscoelasticity of composites was investigated by the dynamic thermal mechanical analyzer (DMA. Through the stress-strain scanning, it is found that the linear viscoelasticity interval of composites gradually decreases as the temperature rises, and the critical stress and strain values are 0.8 MPa and 0.03% respectively. The experiment shows that as the temperature rises, the creep compliance of biomass polyethylene composites is increased; under the constant temperature, the creep compliance decreases with the increase of content of biomass and calcium carbonate. The biomass and calcium carbonate used to prepare composites as filler can improve damping vibration attenuation and reduce stress deformation of composites. The stress relaxation modulus of composites is reduced and the relaxation rate increases at the higher temperature. The biomass and calcium carbonate used to prepare composites as filler not only can reduce costs, but also can increase stress relaxation modulus and improve the size thermostability of composites. The corn stalk is a good kind of biomass raw material for composites since it can improve the creep resistance property and the stress relaxation resistance property of composites more effectively than other three kinds of biomass (poplar wood flour, rice husk and cotton stalk. Keywords: Biomass, Composites, Calcium carbonate, Static viscoelasticity, Creep, Stress relaxation
Asymmetric facial skin viscoelasticity during climacteric aging
Piérard, Gérald E; Hermanns-Lê, Trinh; Gaspard, Ulysse; Piérard-Franchimont, Claudine
2014-01-01
Background Climacteric skin aging affects certain biophysical characteristics of facial skin. The purpose of the present study was to assess the symmetric involvement of the cheeks in this stage of the aging process. Methods Skin viscoelasticity was compared on both cheeks in premenopausal and post-menopausal women with indoor occupational activities somewhat limiting the influence of chronic sun exposure. Eighty-four healthy women comprising 36 premenopausal women and 48 early post-menopausal women off hormone replacement therapy were enrolled in two groups. The tensile characteristics of both cheeks were tested and compared in each group. A computerized suction device equipped with a 2 mm diameter hollow probe was used to derive viscoelasticity parameters during a five-cycle procedure of 2 seconds each. Skin unfolding, intrinsic distensibility, biological elasticity, and creep extension were measured. Results Both biological elasticity and creep extension were asymmetric on the cheeks of the post-menopausal women. In contrast, these differences were more discrete in the premenopausal women. Conclusion Facial skin viscoelasticity appeared to be asymmetric following menopause. The possibility of asymmetry should be taken into account in future studies of the effects of hormone replacement therapy and any antiaging procedure on the face in menopausal women. PMID:24748810
Crack Tip Parameters for Growing Cracks in Linear Viscoelastic Materials
DEFF Research Database (Denmark)
Brincker, Rune
In this paper the problem of describing the asymptotic fields around a slowly growing crack in a linearly viscoelastic material is considered. It is shown that for plane mixed mode problems the asymptotic fields must be described by 6 parameters: 2 stress intensity factors and 4 deformation...... intensity factors. In the special case of a constant Poisson ratio only 2 deformation intensity factors are needed. Closed form solutions are given both for a slowly growing crack and for a crack that is suddenly arrested at a point at the crack extension path. Two examples are studied; a stress boundary...... value problem, and a displacement boundary value problem. The results show that the stress intensity factors and the displacement intensity factors do not depend explicitly upon the velocity of the crack tip....
Boosman, R; Németh, F; Gruys, E
1991-07-01
This review deals with the features of clinical and subclinical laminitis in cattle. Prominent clinical signs of acute laminitis are a tender gait and arched back. The sole horn reveals red and yellowish discolourations within five days. In subacute and chronic cases clinical signs are less severe. In chronic laminitis the shape of the claws is altered. Laminitis is frequently followed by sole ulceration and white zone lesions. Blood tests showed no significant changes for laminitic animals. Arteriographic studies of claws affected by laminitis indicated that blood vessels had narrowed lumens. Gross pathology revealed congestion of the corium and rotation of the distal phalanx. Histopathologic studies indicate that laminitis is associated with changes of the vasculature. Peripartum management and nutrition are important factors in its aetiology. It is hypothesised that laminitis is evoked by disturbed digital circulation. In the pathogenesis of acute laminitis three factors are considered important: the occurrence of thrombosis, haemodynamic aspects of the corium, and endotoxins which trigger these pathologic events.
Scarf Repair of Composite Laminates
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Xie Zonghong
2016-01-01
Full Text Available The use of composite materials, such as carbon-fiber reinforced plastic (CFRP composites, aero-structures has led to an increased need of advanced assembly joining and repair technologies. Adhesive bonded repairs as an alternative to recover full or part of initial strength were investigated. Tests were conducted with the objective of evaluating the effectiveness of techniques used for repairing damage fiber reinforced laminated composites. Failure loads and failure modes were generated and compared with the following parameters: scarf angles, roughness of grind tool and number of external plies. Results showed that scarf angle was the critical parameter and the largest tensile strength was observed with the smallest scarf angle. Besides, the use of external plies at the outer surface could not increase the repairs efficiency for large scarf angle. Preparing the repair surfaces by sanding them with a sander ranging from 60 to 100 grit number had significant effect on the failure load. These results allowed the proposal of design principles for repairing CFRP structures.
Advanced glycation endproducts in horses with insulin-induced laminitis.
de Laat, M A; Kyaw-Tanner, M T; Sillence, M N; McGowan, C M; Pollitt, C C
2012-01-15
Advanced glycation endproducts (AGEs) have been implicated in the pathogenesis of cancer, inflammatory conditions and diabetic complications. An interaction of AGEs with their receptor (RAGE) results in increased release of pro-inflammatory cytokines and reactive oxygen species (ROS), causing damage to susceptible tissues. Laminitis, a debilitating foot condition of horses, occurs in association with endocrine dysfunction and the potential involvement of AGE and RAGE in the pathogenesis of the disease has not been previously investigated. Glucose transport in lamellar tissue is thought to be largely insulin-independent (GLUT-1), which may make the lamellae susceptible to protein glycosylation and oxidative stress during periods of increased glucose metabolism. Archived lamellar tissue from horses with insulin-induced laminitis (n=4), normal control horses (n=4) and horses in the developmental stages (6h, 12h and 24h) of the disease (n=12) was assessed for AGE accumulation and the presence of oxidative protein damage and cellular lipid peroxidation. The equine-specific RAGE gene was identified in lamellar tissue, sequenced and is now available on GenBank. Lamellar glucose transporter (GLUT-1 and GLUT-4) gene expression was assessed quantitatively with qRT-PCR in laminitic and control horses and horses in the mid-developmental time-point (24 h) of the disease. Significant AGE accumulation had occurred by the onset of insulin-induced laminitis (48 h) but not at earlier time-points, or in control horses. Evidence of oxidative stress was not found in any group. The equine-specific RAGE gene was not expressed differently in treated and control animals, nor was the insulin-dependent glucose transporter GLUT-4. However, the glucose transporter GLUT-1 was increased in lamellar tissue in the developmental stages of insulin-induced laminitis compared to control horses and the insulin-independent nature of the lamellae may facilitate AGE formation. However, due to the lack of
Viscoelastic material inversion using Sierra-SD and ROL
Energy Technology Data Exchange (ETDEWEB)
Walsh, Timothy [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Aquino, Wilkins [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Ridzal, Denis [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Kouri, Drew Philip [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); van Bloemen Waanders, Bart Gustaaf [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Urbina, Angel [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2014-11-01
In this report we derive frequency-domain methods for inverse characterization of the constitutive parameters of viscoelastic materials. The inverse problem is cast in a PDE-constrained optimization framework with efficient computation of gradients and Hessian vector products through matrix free operations. The abstract optimization operators for first and second derivatives are derived from first principles. Various methods from the Rapid Optimization Library (ROL) are tested on the viscoelastic inversion problem. The methods described herein are applied to compute the viscoelastic bulk and shear moduli of a foam block model, which was recently used in experimental testing for viscoelastic property characterization.
Differential geometry of viscoelastic models with fractional-order derivatives
International Nuclear Information System (INIS)
Yajima, Takahiro; Nagahama, Hiroyuki
2010-01-01
Viscoelastic materials with memory effect are studied based on the fractional rheonomic geometry. The geometric objects are regarded as basic quantities of fractional viscoelastic models, i.e. the metric tensor and torsion tensor are interpreted as the strain and the fractional strain rate, respectively. The generalized viscoelastic equations are expressed by the geometric objects. Especially, the basic constitutive equations such as Voigt and Maxwell models can be derived geometrically from the generalized equation. This leads to the fact that various viscoelastic models can be unified into one geometric expression.
The viscoelastic properties of the cervical mucus plug
DEFF Research Database (Denmark)
Kjær Bastholm, Sara; Becher, Naja; Stubbe, Peter Reimer
2013-01-01
The objective of this study was to characterize the viscoelastic properties of cervical mucus plugs (CMPs) shed during labor at term. Spontaneously shed cervical mucus plugs from healthy women in active labor, were tested. The viscoelastic properties of cervical mucus plugs were investigated...... with using frequency and stress sweep experiments within the linear viscoelastic region. Random-effects regression was used for statistical analysis. The CMPs are solid-like viscoelastic structures and the elastic modulus dominated the viscous modulus at all frequencies. These rheological characteristics...
The effect of surface roughness and viscoelasticity on rubber adhesion.
Tiwari, A; Dorogin, L; Bennett, A I; Schulze, K D; Sawyer, W G; Tahir, M; Heinrich, G; Persson, B N J
2017-05-21
Adhesion between silica glass or acrylic balls and silicone elastomers and various industrial rubbers is investigated. The work of adhesion during pull-off is found to strongly vary depending on the system, which we attribute to the two opposite effects: (1) viscoelastic energy dissipation close to an opening crack tip and (2) surface roughness. Introducing surface roughness on the glass ball is found to increase the work of adhesion for soft elastomers, while for the stiffer elastomers it results in a strong reduction in the work of adhesion. For the soft silicone elastomers a strong increase in the work of adhesion with increasing pull-off velocity is observed, which may result from the non-adiabatic processes associated with molecular chain pull-out. In general, the work of adhesion is decreased after repeated contacts due to the transfer of molecules from the elastomers to the glass ball. Thus, extracting the free chains (oligomers) from the silicone elastomers is shown to make the work of adhesion independent of the number of contacts. The viscoelastic properties (linear and nonlinear) of all of the rubber compounds are measured, and the velocity dependent crack opening propagation energy at the interface is calculated. Silicone elastomers show a good agreement between the measured work of adhesion and the predicted results, but carbon black filled hydrogenated nitrile butadiene rubber compounds reveal that strain softening at the crack tip may play an important role in determining the work of adhesion. Additionally, adhesion measurement under submerged conditions in distilled water and water + soap solutions are also performed: a strong reduction in the work of adhesion is measured for the silicone elastomers submerged in water, and a complete elimination of adhesion is found for the water + soap solution attributed to an osmotic repulsion between the negatively charged surface of the glass and the elastomer.
Teller, Sean S; Farran, Alexandra J E; Xiao, Longxi; Jiao, Tong; Duncan, Randall L; Clifton, Rodney J; Jia, Xinqiao
2012-10-01
The biomechanical function of the vocal folds (VFs) depends on their viscoelastic properties. Many conditions can lead to VF scarring that compromises voice function and quality. To identify candidate replacement materials, the structure, composition, and mechanical properties of native tissues need to be understood at phonation frequencies. Previously, the authors developed the torsional wave experiment (TWE), a stress-wave-based experiment to determine the linear viscoelastic shear properties of small, soft samples. Here, the viscoelastic properties of porcine and human VFs were measured over a frequency range of 10-200 Hz. The TWE utilizes resonance phenomena to determine viscoelastic properties; therefore, the specimen test frequency is determined by the sample size and material properties. Viscoelastic moduli are reported at resonance frequencies. Structure and composition of the tissues were determined by histology and immunochemistry. Porcine data from the TWE are separated into two groups: a young group, consisting of fetal and newborn pigs, and an adult group, consisting of 6-9-month olds and 2+-year olds. Adult tissues had an average storage modulus of 2309±1394 Pa and a loss tangent of 0.38±0.10 at frequencies of 36-200 Hz. The VFs of young pigs were significantly more compliant, with a storage modulus of 394±142 Pa and a loss tangent of 0.40±0.14 between 14 and 30 Hz. No gender dependence was observed. Histological staining showed that adult porcine tissues had a more organized, layered structure than the fetal tissues, with a thicker epithelium and a more structured lamina propria. Elastin fibers in fetal VF tissues were immature compared to those in adult tissues. Together, these structural changes in the tissues most likely contributed to the change in viscoelastic properties. Adult human VF tissues, recovered postmortem from adult patients with a history of smoking or disease, had an average storage modulus of 756±439 Pa and a loss tangent of 0
Directory of Open Access Journals (Sweden)
Ghani Razaqpur
2015-11-01
Full Text Available A new carbon fiber reinforced polymer (CFRP anchor is developed and tested to delay debonding in reinforced concrete (RC beams externally strengthened with FRP laminate/sheet. The C-shape anchor is made from a commercially available CFRP grid. The anchors legs are 95 mm long while the spacing between the legs is adjustable, depending on FRP laminate and beam widths. Nine full scale RC beams, 3.0 m long, 250 mm wide and 400 mm deep, were strengthened with CFRP laminate/sheet, with and without the C-anchor. The main test parameters were the type and amount of FRP laminate and the presence/absence of the anchor. Test results showed that beams with the anchor had generally 5%–10% higher debonding and failure load, and they reached higher deflection at failure than the companion beams without anchors. Although complete separation of the FRP laminate from the concrete was not observed in any of the beams with anchors, there was noticeable slip at failure at one end of the laminate. A significant outcome of the study is that anchors are effective in limiting the extent of debonding along the laminate, thus contributing to the flexural stiffness of the beam by reducing the extent of cracking and limiting the crack width along the beam. Finally, the anchor allowed the FRP to reach or exceed its theoretically allowable strain computed based on the American Concrete Institute (ACI Committee 440 recommendation while in none of the beams without anchors, the FRP reached its theoretically allowable strain.
Thompson, B. S.; Sung, C. K.
1986-12-01
The articulating members of linkage machinery must be designed and manufactured with high stiffness-to-weight ratios in order that these machine systems operate successfully in a high-speed mode. One approach to satisfying this criterion is to exploit the high specific stiffnesses of polymeric fibrous composite laminates. In this paper, results of mechanical tests of candidate materials are presented and the material constitutive behaviour classified. A variational theorem is then derived by using the Stieltjes convolution notation which enables the equations governing the geometrically-non-linear dynamic response of linkages fabricated in linear viscoelastic composite materials to be systematically established. The formulation includes inertial terms which couple the kinematic deformations of the link material with the kinematics governing the gross motion of the linkage being analyzed. This variational principle provides the basis for a finite element formulation in which the properties of the heterogeneous, two-constituent laminates are represented by a continuum model for a homogeneous single-constituent material. The predictive capability of this model is evaluated by simulating the vibrational response of both experimental four-bar linkages and also slider-crank mechanisms fabricated with simple link geometries, prior to comparing the computer results with experimental data from these laboratory mechanisms.
Processing, thermal and mechanical behaviour of PEI/MWCNT/carbon fiber nanostructured laminate
Santos, L. F. P.; Ribeiro, B.; Hein, L. R. O.; Botelho, E. C.; Costa, M. L.
2017-11-01
In this work, nanostructured composites of polyetherimide (PEI) with addition of functionalized multiwall carbon nanotube (MWCNT) were processed via solution mixing. After processing, these nanocomposites were evaluated by thermogravimetry (TGA), dynamic-mechanical analysis (DMA), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Subsequently, the nanocomposite was processed with carbon fibers by using hot compression molding. In order to evaluate interlaminar fracture strength, the processed laminates were mechanically evaluated by interlaminar shear strength (ILSS) and compression shear test (CST). Also, the Weibull distribution was employed to help in the statistical treatment of the data obtained from the mechanical tests. With regards to the fracture of the specimens, optical microscopy was used for the evaluation of the material. The addition of 1 wt% of MWCNT in the polymer matrix increased both thermal stability and viscoelastic behavior of the material. These improvements positively impacted the mechanical properties, generating a 16% and 58% increase in the short-beam strength and apparent interlaminar shear, respectively. In addition, it can be verified from morphological analysis of the fracture a change in the failure mode of the laminate by the incorporation of MWCNT. This behavior can be proven from CST test where there was no presence of the shear force by compression.
Relationship between viscoelastic properties of soft denture liners and clinical efficacy
Hiroshi Murata; Taizo Hamada; Shinsuke Sadamori
2008-01-01
Soft denture liners are applied for denture wearers who cannot tolerate a hard-based denture due to a thin and non-resilient oral mucosa and/or severe alveolar resorption. This material distributes and absorbs masticatory forces by means of the cushioning effect. Clinical success of the materials depends both on their viscoelastic properties and on durability. Acrylic resins and silicones are mainly available for permanent soft liners. The acrylic permanent soft liners demonstrate viscoelasti...
Sciumè, Giuseppe; Benboudjema, Farid
2017-05-01
A post-processing technique which allows computing crack width in concrete is proposed for a viscoelastic damage model. Concrete creep is modeled by means of a Kelvin-Voight cell while the damage model is that of Mazars in its local form. Due to the local damage approach, the constitutive model is regularized with respect to finite element mesh to avoid mesh dependency in the computed solution (regularization is based on fracture energy).
Nonlinear Viscoelastic Rheology and the Occurrence of Aftershocks
Shcherbakov, R.; Zhang, X.
2017-12-01
Aftershocks are ubiquitous in nature. They are the manifestation of relaxation phenomena observed in various physical systems. In one prominent example, they typically occur after large earthquakes. The observed aftershock sequences usually obey several well defined non-trivial empirical laws in magnitude, temporal, and spatial domains. In many cases their characteristics follow scale-invariant distributions. The occurrence of aftershocks displays a prominent temporal behavior due to time-dependent mechanisms of stress and/or energy transfer. There are compelling evidences that the lower continental crust and upper mantle are governed by various solid state creep mechanisms. Among those mechanisms a power-law viscous flow was suggested to explain the postseismic surface deformation after large earthquakes. In this work, we consider a slider-block model to mimic the behavior of a seismogenic fault. In the model, we introduce a nonlinear viscoelastic coupling mechanism to capture the essential characteristics of crustal rheology and stress interaction between the blocks and the medium. For this purpose we employ nonlinear Kelvin-Voigt elements consisting of an elastic spring and a dashpot assembled in parallel to introduce viscoelastic coupling between the blocks and the driving plate. By mapping the model into a cellular automaton we derive the functional form of the stress transfer mechanism in the model. We show that the nonlinear viscoelasticity plays a critical role in triggering of aftershocks. It explains the functional form of the Omori-Utsu law and gives physical interpretation of its parameters. The proposed model also suggests that the power-law rheology of the fault gauge and underlying lower crust and upper mantle controls the decay rate of aftershocks. To verify this, we analyze several prominent aftershock sequences to estimate their decay rates and correlate with the rheological properties of the underlying lower crust and mantle, which were estimated
Superpressure Balloon Design Using Nonlinear Viscoelasticity
Rand, James; Rand, James; Wakefield, David
Stratospheric balloon platforms are used extensively by scientists for a variety of purposes. The typical balloon used today is the zero pressure natural shape fabricated from a thin film of linear low density polyethylene. This material has been found to possess a variety of desirable characteristics suitable to this environment. This film will remain ductile at very low temperatures which will permit it to develop large strains if necessary to satisfy equilibrium considerations. However, in order to achieve long duration flight without significant changes in altitude, the balloon should be pressurized to the extent necessary to maintain constant volume during typical variations in temperature. In the past, pressurized balloons were fabricated from other materials in order to achieve significant increases in strength. Thin films of polyester or polyimide have been used to make relatively small spheres capable of long duration flight. Unfortunately, these materials do not have the ductility of polyethylene at low temperature and are somewhat more fragile and subject to damage. In recent years various organizations have attempted to use the characteristic shape of a pumpkin to limit the stresses in a balloon envelope to that which can be accommodated by laminated fabric materials. While developing the design, analysis and construction techniques for this type of system, the use of polyethylene has been successfully demonstrated to provide a reliable envelope. This shape is achieved by using high strength members in the meridional direction to carry the very high loads generated by the pressure. These so called "tendons" have very low elongation and serve to limit the deformation of the film in that direction. However, earlier designs attempted to limit the stresses in the circumferential direction by using a lobe angle to control the stress. Unfortunately this has led to a number of stability problems with this type of balloon. In order to control the stability of
Boundary-layer effects in composite laminates: Free-edge stress singularities, part 6
Wanag, S. S.; Choi, I.
1981-01-01
A rigorous mathematical model was obtained for the boundary-layer free-edge stress singularity in angleplied and crossplied fiber composite laminates. The solution was obtained using a method consisting of complex-variable stress function potentials and eigenfunction expansions. The required order of the boundary-layer stress singularity is determined by solving the transcendental characteristic equation obtained from the homogeneous solution of the partial differential equations. Numerical results obtained show that the boundary-layer stress singularity depends only upon material elastic constants and fiber orientation of the adjacent plies. For angleplied and crossplied laminates the order of the singularity is weak in general.
Yin, J. J.; Li, S. L.; Yao, X. L.; Chang, F.; Li, L. K.; Zhang, X. H.
2016-08-01
In order to analyze the lightning strike ablation damage characteristic of composite laminate with fastener, based on the energy-balance relationship in lightning strike, mathematical analysis model of ablation damage of composite laminate with fastener was constructed. According to the model, an effective three dimensional thermal-electrical coupling analysis finite element model of composite laminate with fastener suffered from lightning current was established based on ABAQUS, and lightning strike ablation damage characteristic was analyzed. Analytical results reveal that lightning current could conduct through the thickness direction of the laminate due to the existence of metallic fastener, and then distribute to all layers, finally conducted in-the-plane of each layer, conductive ability of different layup orientations depend on potential distribution and in-the-plane electrical conductivity along potential gradient declining direction; different potential boundaries correspond to different potential distribution in each layer, and result in conductive ability of different layup orientations was changed, then caused different lightning strike ablation damage distribution. According to the investigation in this paper, we can recognize the lightning strike ablation damage characteristic of composite laminate with fastener qualitatively.
Lamin A Is an Endogenous SIRT6 Activator and Promotes SIRT6-Mediated DNA Repair
Directory of Open Access Journals (Sweden)
Shrestha Ghosh
2015-11-01
Full Text Available The nuclear lamins are essential for various molecular events in the nucleus, such as chromatin organization, DNA replication, and provision of mechanical support. A specific point mutation in the LMNA gene creates a truncated prelamin A termed progerin, causing Hutchinson-Gilford progeria syndrome (HGPS. SIRT6 deficiency leads to defective genomic maintenance and accelerated aging similar to HGPS, suggesting a potential link between lamin A and SIRT6. Here, we report that lamin A is an endogenous activator of SIRT6 and facilitates chromatin localization of SIRT6 upon DNA damage. Lamin A promotes SIRT6-dependent DNA-PKcs (DNA-PK catalytic subunit recruitment to chromatin, CtIP deacetylation, and PARP1 mono-ADP ribosylation in response to DNA damage. The presence of progerin jeopardizes SIRT6 activation and compromises SIRT6-mediated molecular events in response to DNA damage. These data reveal a critical role for lamin A in regulating SIRT6 activities, suggesting that defects in SIRT6 functions contribute to impaired DNA repair and accelerated aging in HGPS.
Directory of Open Access Journals (Sweden)
Alicia Arjona
2015-11-01
Full Text Available Volcanic areas present a lower effective viscosity than usually in the Earth's crust. It makes necessary to consider inelastic properties in deformation modelling. As a continuation of work done previously by some of the authors, this work is concerned with the proof that the perturbed equations representing the viscoelastic-gravitational displacements resulting from body forces embedded in a layered Earth model leads to a well-posed problem even for any kind of domains, with the natural boundary and transmission conditions. A homogeneous or stratified viscoelastic half-space has often been used as a simple earth model to calculate the displacements and gravity changes. Here we give a constructive proof of the existence of weak solutions and we show the uniqueness and the continuous dependence with respect to the initial data of weak solutions of the dynamic coupled viscoelastic-gravitational field equations.
Dakshinamurthy, Devika; Gupta, Srinivasa
2018-04-01
Fused Deposition Modelling (FDM) is a fast growing Rapid Prototyping (RP) technology due to its ability to build parts having complex geometrical shape in reasonable time period. The quality of built parts depends on many process variables. In this study, the influence of three FDM process parameters namely, slice height, raster angle and raster width on viscoelastic properties of Acrylonitrile Butadiene Styrene (ABS) RP-specimen is studied. Statistically designed experiments have been conducted for finding the optimum process parameter setting for enhancing the storage modulus. Dynamic Mechanical Analysis has been used to understand the viscoelastic properties at various parameter settings. At the optimal parameter setting the storage modulus and loss modulus of the ABS-RP specimen was 1008 and 259.9 MPa respectively. The relative percentage contribution of slice height and raster width on the viscoelastic properties of the FDM-RP components was found to be 55 and 31 % respectively.
A viscoelastic, viscoplastic model of cortical bone valid at low and high strain rates.
Johnson, T P M; Socrate, S; Boyce, M C
2010-10-01
The stress-strain behavior of cortical bone is well known to be strain-rate dependent, exhibiting both viscoelastic and viscoplastic behavior. Viscoelasticity has been demonstrated in literature data with initial modulus increasing by more than a factor of 2 as applied strain rate is increased from 0.001 to 1500 s(-1). A strong dependence of yield on strain rate has also been reported in the literature, with the yield stress at 250 s(-1) having been observed to be more than twice that at 0.001 s(-1), demonstrating the material viscoplasticity. Constitutive models which capture this rate-dependent behavior from very low to very high strain rates are required in order to model and simulate the full range of loading conditions which may be experienced in vivo; particularly those involving impact, ballistic and blast events. This paper proposes a new viscoelastic, viscoplastic constitutive model which has been developed to meet these requirements. The model is fitted to three sets of stress-strain measurements from the literature and shown to be valid at strain rates ranging over seven orders of magnitude. 2010 Acta Materialia Inc. All rights reserved.
Creep damage index as a sensitive indicator of damage accumulation in thermoplastic laminates
Czech Academy of Sciences Publication Activity Database
Minster, Jiří; Šperl, Martin; Šepitka, J.
2018-01-01
Roč. 37, č. 3 (2018), s. 147-154 ISSN 0731-6844 Institutional support: RVO:68378297 Keywords : damage accumulation * thermoplastic laminate * cyclic tensile loading * time -dependent properties * microindentation Subject RIV: JL - Materials Fatigue, Friction Mechanics OBOR OECD: Audio engineering, reliability analysis Impact factor: 1.086, year: 2016 http://journals.sagepub.com/doi/pdf/10.1177/0731684417735184
Pickering, J.P.; Vancso, Gyula J.
2001-01-01
A commercial atomic force microscope (AFM) outfitted with a custom control and data acquisition system was used to investigate the adhesive nature of a viscoelastic polydimethylsiloxane (PDMS) network. Due to the complex dependence of the adhesion of this sample on factors such as indentation,
Analysis on and Optimization of a Circular Piezoelectric Composite Laminate for a Micro-Pump Driver
International Nuclear Information System (INIS)
Jia, Jianyuan; Wang, Weidong; Huang, Xinbo
2002-01-01
Among the various micro-pump actuation devices, piezoelectric composite laminate actuation has become an effective method. Due to lacking of analysis treatments, the design of this type micro-pump is in a great limitation. In this paper, an electromechanical-coupled mechanics model is established for the circle-flake micro-actuator. A kind of analysis and design method is presented that piezoelectric plate's radial strain induced by inverse piezoelectric effect is equivalently substituted with transverse stress on piezoelectric composite laminates. It is pointed out that the equivalent transverse load depends on the edge electric field distribution of parallel plate capacitor. The question has been solved that where the neutral plane in the piezoelectric composite laminates lies. Finally, an optimization design is developed on the radius ratio of piezoelectric-to-silicon plate radius by utilizing of FEA modeling
Master plot analysis of microcracking in graphite/epoxy and graphite/PEEK laminates
Nairn, John A.; Hu, Shoufeng; Bark, Jong Song
1993-01-01
We used a variational stress analysis and an energy release rate failure criterion to construct a master plot analysis of matrix microcracking. In the master plot, the results for all laminates of a single material are predicted to fall on a single line whose slope gives the microcracking toughness of the material. Experimental results from 18 different layups of AS4/3501-6 laminates show that the master plot analysis can explain all observations. In particular, it can explain the differences between microcracking of central 90 deg plies and of free-surface 90 deg plies. Experimental results from two different AS4/PEEK laminates tested at different temperatures can be explained by a modified master plot that accounts for changes in the residual thermal stresses. Finally, we constructed similar master plot analyses for previous literature microcracking models. All microcracking theories that ignore the thickness dependence of the stresses gave poor results.
Determination of Fracture Parameters for Multiple Cracks of Laminated Composite Finite Plate
Srivastava, Amit Kumar; Arora, P. K.; Srivastava, Sharad Chandra; Kumar, Harish; Lohumi, M. K.
2018-04-01
A predictive method for estimation of stress state at zone of crack tip and assessment of remaining component lifetime depend on the stress intensity factor (SIF). This paper discusses the numerical approach for prediction of first ply failure load (FL), progressive failure load, SIF and critical SIF for multiple cracks configurations of laminated composite finite plate using finite element method (FEM). The Hashin and Chang failure criterion are incorporated in ABAQUS using subroutine approach user defined field variables (USDFLD) for prediction of progressive fracture response of laminated composite finite plate, which is not directly available in the software. A tensile experiment on laminated composite finite plate with stress concentration is performed to validate the numerically predicted subroutine results, shows excellent agreement. The typical results are presented to examine effect of changing the crack tip distance (S), crack offset distance (H), and stacking fiber angle (θ) on FL, and SIF .
Axial Dynamic Stiffness of Tubular Piles in Viscoelastic Soil
Directory of Open Access Journals (Sweden)
Mehdi Bayat
2016-09-01
Full Text Available Large offshore wind turbines are founded on jacket structures. In this study, an elastic full-space jacket structure foundation in an elastic and viscoelastic medium is investigated by using boundary integral equations. The jacket structure foundation is modeled as a hollow, long circular cylinder when the dynamic vertical excitation is applied. The smooth surface along the entire interface is considered. The Betti reciprocal theorem along with Somigliana’s identity and Green’s function are employed to drive the dynamic stiffness of jacket structures. Modes of the resonance and anti-resonance are presented in series of Bessel’s function. Important responses, such as dynamic stiffness and phase angle, are compared for different values of the loss factor as the material damping, Young’s modulus and Poisson’s ratio in a viscoelastic soil. Results are verified with known results reported in the literature. It is observed that the dynamic stiffness fluctuates with the loss factor, and the turning point is independent of the loss factor while the turning point increases with load frequency. It is seen that the non-dimensional dynamic stiffness is dependent on Young’s modulus and Poisson’s ratio, whilst the phase angle is independent of the properties of the soil. It is shown that the non-dimensional dynamic stiffness changes linearly with high-frequency load. The conclusion from the results of this study is that the material properties of soil are significant parameters in the dynamic stiffness of jacket structures, and the presented approach can unfold the behavior of soil and give an approachable physical meaning for wave propagation.
Nuclear Actin and Lamins in Viral Infections
Cibulka, Jakub; Fraiberk, Martin; Forstova, Jitka
2012-01-01
Lamins are the best characterized cytoskeletal components of the cell nucleus that help to maintain the nuclear shape and participate in diverse nuclear processes including replication or transcription. Nuclear actin is now widely accepted to be another cytoskeletal protein present in the nucleus that fulfills important functions in the gene expression. Some viruses replicating in the nucleus evolved the ability to interact with and probably utilize nuclear actin for their replication, e.g., for the assembly and transport of capsids or mRNA export. On the other hand, lamins play a role in the propagation of other viruses since nuclear lamina may represent a barrier for virions entering or escaping the nucleus. This review will summarize the current knowledge about the roles of nuclear actin and lamins in viral infections. PMID:22590674
International Nuclear Information System (INIS)
Du, Ping; Lin, I-Kuan; Zhang, Xin; Lu, Hongbing
2010-01-01
Polydimethylsiloxane (PDMS)-based micropillars (or microcantilevers) have been used as bio-transducers for measuring cellular forces on the order of pN to µN. The measurement accuracy of these sensitive devices depends on appropriate modeling to convert the micropillar deformations into the corresponding reaction forces. The traditional approach to calculating the reaction force is based on the Euler beam theory with consideration of a linear elastic slender beam for the micropillar. However, the low aspect ratio in geometry of PDMS micropillars does not satisfy the slender beam requirement. Consequently, the Timoshenko beam theory, appropriate for a beam with a low aspect ratio, should be used. In addition, the inherently time-dependent behavior in PDMS has to be considered for accurate force conversion. In this paper, the Timoshenko beam theory, along with the consideration of viscoelastic behavior of PDMS, was used to model the mechanical response of micropillars. The viscoelastic behavior of PDMS was characterized by stress relaxation nanoindentation using a circular flat punch. A correction procedure was developed to determine the load–displacement relationship with consideration of ramp loading. The relaxation function was extracted and described by a generalized Maxwell model. The bending of rectangular micropillars was performed by a wedge indenter tip. The viscoelastic Timoshenko beam formula was used to calculate the mechanical response of the micropillar, and the results were compared with measurement data. The calculated reaction forces agreed well with the experimental data at three different loading rates. A parametric study was conducted to evaluate the accuracy of the viscoelastic Timoshenko beam model by comparing the reaction forces calculated from the elastic Euler beam, elastic Timoshenko beam and viscoelastic Euler beam models at various aspect ratios and loading rates. The extension of modeling from the elastic Euler beam theory to the
Time-Dependent Morphologies and Viscoelastic Properties of Block Copolymers.
1982-03-15
junc- tions). In their mathematical model, the observed tensile stress is a product of two functions, one accounting for the rigid behavior of the...weights, and hence varying fractions of interphase (7,8) In addition, SBS specimens swollen in isooctane and re-dried showed a significant lowering of
Reflection of plane micropolar viscoelastic waves at a loosely ...
Indian Academy of Sciences (India)
R. Narasimhan (Krishtel eMaging) 1461 1996 Oct 15 13:05:22
micropolar viscoelastic solid half-space is employed to study the reflection and transmission of plane waves at a loosely bonded interface between two dissimilar micropolar viscoelastic solid half-spaces. The amplitude ratios for various reflected and refracted waves are computed for a particular model for different values of.
Viscoelastic finite-element analysis of human skull - dura mater ...
African Journals Online (AJOL)
SERVER
2008-03-18
Mar 18, 2008 ... tensor; ij δ , the Kronecker delta;. )( tG , the shear relaxation function;. )( tK , the bulk relaxation function; )(t θ , the volumetric strain; t , the present time; τ , the past time. Human skull has the viscoelastic material (Charalambopoulos et al., 1998). Considering the viscoelasticity of human skull and dura mater ...
Modelling Viscoelasticity of Loudspeaker Suspensions using Retardation Spectra
DEFF Research Database (Denmark)
Ritter, Tobias; Agerkvist, Finn T.
2010-01-01
, the viscoelastic retardation spectrum, which provides a more fundamental description of the suspension viscoelasticity, is rst used to explain the accuracy of the empirical LOG creep model (Knudsen et al.). Then, two extensions to the LOG model are proposed which include the low and high frequency limit...
The dynamic viscoelasticity and plasticizer leachability of tissue conditioners.
Hong, Guang; Maeda, Takeshi; Murata, Hiroshi; Sasaki, Keiichi
2012-12-01
Dynamic viscoelasticity is one of the most important characteristics of tissue conditioners. Leaching of plasticizer from tissue conditioners may cause changes in the dynamic viscoelasticity of these materials. The purpose of this study was to determine the dynamic viscoelasticity and plasticizer leachability of commercial tissue conditioners. Five commercial tissue conditioners were used in this study: COE Comfort (CC), Fit Softer (FS), Hydro-Cast (HC), Soft Conditioner (SC) and Visco-Gel (VG). Five specimens of each material were stored in 37°C distilled water. The dynamic viscoelasticity and plasticizer leaching of each specimen were measured at 0, 1, 3, 7 and 14 days after immersion using a dynamic mechanical analyzer and high performance liquid chromatography. Data were analyzed using one-way anova and Student-Newman-Keuls test (α = 0.05). Significant differences in dynamic viscoelasticity and plasticizer leaching were found among the materials. The dynamic viscoelasticity of all materials increased or decreased significantly with time. Rapid changes in dynamic viscoelasticity were evident on day 1 after water immersion. The material CC recorded the highest level of plasticizer leaching. These results suggest that the dynamic viscoelasticity of commercial tissue conditioners is affected by plasticizer leaching. However, these effects are limited. © 2012 The Gerodontology Society and John Wiley & Sons A/S.
Reflection of plane micropolar viscoelastic waves at a loosely ...
Indian Academy of Sciences (India)
A solution of the ﬁeld equations governing small motions of a micropolar viscoelastic solid half-space is employed to study the reﬂection and transmission of plane waves at a loosely bonded interface between two dissimilar micropolar viscoelastic solid half-spaces. The amplitude ratios for various reﬂected and refracted ...
Effect of Viscoelasticity on Adhesion of Bioinspired Micropatterned Epoxy Surfaces
Castellanos, G.; Arzt, E.; Kamperman, M.M.G.
2011-01-01
The effect of viscoelasticity on adhesion was investigated for micropatterned epoxy surfaces and compared to nonpatterned surfaces. A two-component epoxy system was used to produce epoxy compositions with different viscoelastic properties. Pillar arrays with flat punch tip geometries were fabricated
Noise reduction of rotating machinery by viscoelastic bearing supports
Tillema, H.G.
2003-01-01
The demand for silent rolling bearing applications, such as electric motors and gearboxes, has resulted in an investigation of viscoelastic bearing supports. By placing a thin viscoelastic layer between the bearing outer ring and the surrounding structure, vibrations of the shaft-bearing arrangement
On the Abaqus FEA model of finite viscoelasticity
Ciambella, Jacopo; Destrade, Michel; Ogden, Ray W.
2013-01-01
Predictions of the QLV (Quasi-Linear Viscoelastic) constitutive law are compared with those of the ABAQUS viscoelastic model for two simple motions in order to highlight, in particular, their very different dissipation rates and certain shortcomings of the ABAQUS model.
Experimental Characterization of Innovative Viscoelastic Foams
Directory of Open Access Journals (Sweden)
Massimo Viscardi
2016-05-01
Full Text Available The evolutionary trend in the automotive industry has produced over time numerous performance and aesthetic innovations, however, the exponential development related to transportation technologies also introduced new requirements concerning the environmental impact [1]. The awareness of ecological issues has led to a reorganization of the evaluations and the vehicle design, currently aimed at reducing the problems that have emerged in empirical investigations and the parallel increase in environmental solutions. The vehicle renewal process involves targeted technical mutations both to observance of ecology as to the safety and comfort of the driver. New recyclable materials and more resistant have been developed in order to minimize the environmental impact of the vehicle even at the end of the operating life of its components, as well as solutions relating to the reduction of noise pollution generated as a response to the requirements of comfort. Modern research programs on a global scale have set themselves the objective of exploiting the potentiality of innovative technologies in the optimization of vehicles efficiency, the noise reduction and in the consequent reduction of fuel burn. One of the crucial topics in the greening of the new generation automotive sector is therefore the use and development of high vibro-acoustic performance materials. The goal of this research is properly focused on the analysis of viscoelastic materials appointed to increase the damping of the vibrations generated in a vehicle. The use of a viscoelastic material in this context is due to its high property to convert vibrational energy into heat, providing a significant dissipation of the vibrations. Trade-off analyses are performed in order define the stiffness and damping capacity of several viscoelastic foams with different thickness and density.
Energy Technology Data Exchange (ETDEWEB)
Miyano, Y.; Nakata, M.; Ishiguro, T. [Kanazawa Inst. of Tech., Ishikawa (Japan); Yamamoto, T. [Fukuoka Univ. (Japan)
1998-07-15
The time and temperature dependencies of static, creep, and fatigue fracture behavior of unidirectional CERP are investigated by 3-point bending tests in the direction parallel to fibers. The effects of time and temperature on the fracture behavior are investigated by the observation of fractured surface. The fracture behavior evaluated by the strength, deformation, and fractured surface varies markedly by the rate of loading and temperature irrespective of the forms of static, creep, and fatigue load. Regardless of the loading forms of static, creep, and fatigue, the same time-temperature equivalent law holds good between the time dependence and temperature dependence of the fracture behavior as that of dynamic behavior of the matrix resins. As a result, long-term behaviors of static, creep, and fatigue can be estimated by using the time-temperature equivalent law, and they can be compared and evaluated on the same time and temperature axes if each of the static test, creep test, and fatigue test are performed by varying the temperature. 9 refs., 13 figs., 1 tab.
Viscoelastic Analysis of Thermally Stiffening Polymer Nanocomposites
Ehlers, Andrew; Rende, Deniz; Senses, Erkan; Akcora, Pinar; Ozisik, Rahmi
Poly(ethylene oxide), PEO, filled with silica nanoparticles coated with poly(methyl methacrylate), PMMA, was shown to present thermally stiffening behavior above the glass transition temperature of both PEO and PMMA. In the current study, the viscoelastic beahvior of this nanocomposite system is investigated via nanoindenation experiments to complement on going rheological studies. Results were compared to neat polymers, PEO and PMMA, to understand the effect of coated nanoparticles. This material is based upon work supported by the National Science Foundation under Grant No. CMMI-1538730.
Transient vibration of thin viscoelastic orthotropic plates
Czech Academy of Sciences Publication Activity Database
Soukup, J.; Valeš, František; Volek, J.; Skočilas, J.
2011-01-01
Roč. 27, č. 1 (2011), s. 98-107 ISSN 0567-7718. [International Conference on Dynamical Systems - Theory and Applications /10./. Lodz, 07.12.2009-10.12.2009] R&D Projects: GA ČR GA101/07/0946 Institutional research plan: CEZ:AV0Z20760514 Keywords : transient vibration thin plate * orthotropic * general viscoelastic standard solid Subject RIV: BI - Acoustics Impact factor: 0.860, year: 2011 http://www.springerlink.com/content/hn67324178846n4r/
Direct and inverse scattering for viscoelastic media
International Nuclear Information System (INIS)
Ammicht, E.; Corones, J.P.; Krueger, R.J.
1987-01-01
A time domain approach to direct and inverse scattering problems for one-dimensional viscoelastic media is presented. Such media can be characterized as having a constitutive relation between stress and strain which involves the past history of the strain through a memory function, the relaxation modulus. In the approach in this article, the relaxation modulus of a material is shown to be related to the reflection properties of the material. This relation provides a constructive algorithm for direct and inverse scattering problems. A numerical implementation of this algorithm is tested on several problems involving realistic relaxation moduli
Topology optimization of laminated plates with prestress
DEFF Research Database (Denmark)
Pedersen, Niels Leergaard
2002-01-01
Laminated plates with different prestress in the layers are topology optimized. The objectives are to minimize the deflection due to the prestress or to minimize ordinary compliance. The prestress is accounted for by including the force equivalent to the prestressing and adding the initial stress...... stiffness matrix to the structural stiffness. The calculations of sensitivities are complicated not only by the prestress but also because we are dealing with laminates. The topology optimization problem is solved using a new penalization scheme as an alternative to the SIMP (power law) approach...
Properties of Chitosan-Laminated Collagen Film
Directory of Open Access Journals (Sweden)
Vera Lazić
2012-01-01
Full Text Available The objective of this study is to determine physical, mechanical and barrier properties of chitosan-laminated collagen film. Commercial collagen film, which is used for making collagen casings for dry fermented sausage production, was laminated with chitosan film layer in order to improve the collagen film barrier properties. Different volumes of oregano essential oil per 100 mL of filmogenic solution were added to chitosan film layer: 0, 0.2, 0.4, 0.6 and 0.8 mL to optimize water vapour barrier properties. Chitosan layer with 0.6 or 0.8 % of oregano essential oil lowered the water vapour transmission rate to (1.85±0.10·10–6 and (1.78±0.03·10–6 g/(m2·s·Pa respectively, compared to collagen film ((2.51±0.05·10–6 g/(m2·s·Pa. However, chitosan-laminated collagen film did not show improved mechanical properties compared to the collagen one. Tensile strength decreased from (54.0±3.8 MPa of the uncoated collagen film to (36.3±4.0 MPa when the film was laminated with 0.8 % oregano essential oil chitosan layer. Elongation at break values of laminated films did not differ from those of collagen film ((18.4±2.7 %. Oxygen barrier properties were considerably improved by lamination. Oxygen permeability of collagen film was (1806.8±628.0·10–14 cm3/(m·s·Pa and values of laminated films were below 35·10–14 cm3/(m·s·Pa. Regarding film appearance and colour, lamination with chitosan reduced lightness (L and yellowness (+b of collagen film, while film redness (+a increased. These changes were not visible to the naked eye.
Effects of viscoelasticity in the high Reynolds number cylinder wake
Richter, David
2012-01-16
At Re = 3900, Newtonian flow past a circular cylinder exhibits a wake and detached shear layers which have transitioned to turbulence. It is the goal of the present study to investigate the effects which viscoelasticity has on this state and to identify the mechanisms responsible for wake stabilization. It is found through numerical simulations (employing the FENE-P rheological model) that viscoelasticity greatly reduces the amount of turbulence in the wake, reverting it back to a state which qualitatively appears similar to the Newtonian mode B instability which occurs at lower Re. By focusing on the separated shear layers, it is found that viscoelasticity suppresses the formation of the Kelvin-Helmholtz instability which dominates for Newtonian flows, consistent with previous studies of viscoelastic free shear layers. Through this shear layer stabilization, the viscoelastic far wake is then subject to the same instability mechanisms which dominate for Newtonian flows, but at far lower Reynolds numbers. © Copyright Cambridge University Press 2012.
Correlation of Two Coupled Particles in Viscoelastic Medium
International Nuclear Information System (INIS)
Xie Baisong; Wu Haicheng; Yan Shiwei; Zhang Fengshou; Dulat, Sayipjamal
2006-01-01
Considering the viscoelastic memory effect, we study the correlated motion of two hydrodynamically coupled colloidal particles, each of which confined in a harmonic potential well, in a Kelvin-type and Maxwell-type viscoelastic medium. We find that viscoelastic relaxation plays a significant role in modifying the correlation, particularly the cross correlation. We also find that both the real and imaginary parts of the response function are significantly different from the viscous medium case. In particular there is a phase shift between the vanishing imaginary part and the maximal real part of the response function in a viscoelastic medium. In addition imaginary part of the cross correlation response function exhibits a net energy loss (gain) behavior when the elasticity parameter of the medium is larger (smaller) than the critical value for Kelvin (Maxwell) viscoelastic fluid. Some implication of our results and their connection with previous works are discussed.
Continuous jute fibre reinforced laminated paper composite and ...
Indian Academy of Sciences (India)
Plastic bags create a serious environmental problem. The proposed jute fibre reinforced laminated paper composite and reinforcement-fibre free paper laminate may help to combat the war against this pollutant to certain extent. The paper laminate, without reinforcement fibre, exhibited a few fold superiority in tensile ...
Cycling fiber metal laminates : Considerations, test setup and results
Müller, B.; Teixeira De Freitas, S.; Sinke, J.
2015-01-01
The development of fiber metal laminates to multi-functional materials by embedding heater elements in the laminate extends their field of application. Fiber metal laminates with embedded heater elements are likely to be used for the de- and anti-icing of leading edges in aircraft as they combine
Thermal cycling fiber metal laminates : Considerations, test setup and results
Müller, B.; Teixeira de Freitas, S.; Sinke, J.
2015-01-01
The development of fiber metal laminates to multi-functional materials by embedding heater elements in the laminate extends their field of application. Fiber metal laminates with embedded heater elements are likely to be used for the de- and anti-icing of leading edges in aircraft as they combine
Impact performance of two bamboo-based laminated composites
Huanrong Liu; Zehui Jiang; Zhengjun Sun; Yan Yan; Zhiyong Cai; Xiubiao Zhang
2017-01-01
The present work aims to determine the impact performance of two bamboo-based laminated composites [bamboo/poplar laminated composite (BPLC) and bamboo/ glass fiber laminated composite (BGFLC)] using lowvelocity impact tests by a drop tower. In addition, fracture characteristics were evaluated using computed tomography (CT). Results showed that BPLC presented better...
Locomotion of helical bodies in viscoelastic fluids: enhanced swimming at large helical amplitudes.
Spagnolie, Saverio E; Liu, Bin; Powers, Thomas R
2013-08-09
The motion of a rotating helical body in a viscoelastic fluid is considered. In the case of force-free swimming, the introduction of viscoelasticity can either enhance or retard the swimming speed and locomotive efficiency, depending on the body geometry, fluid properties, and the body rotation rate. Numerical solutions of the Oldroyd-B equations show how previous theoretical predictions break down with increasing helical radius or with decreasing filament thickness. Helices of large pitch angle show an increase in swimming speed to a local maximum at a Deborah number of order unity. The numerical results show how the small-amplitude theoretical calculations connect smoothly to the large-amplitude experimental measurements.
On the modelling of electro-viscoelastic response of electrostrictive polyurethane elastomers
Ask, A.; Menzel, A.; Ristinmaa, M.
2010-06-01
Electroactive polymers (EAP) deform under electric fields. This effect in fact generates various new fields of engineering applications of high technological interest. As an advantage, EAP may undergo deformations much larger than those capable by electroactive ceramics—however, to the price of acting at comparatively low forces. As common for polymers, EAP exhibit time-dependent material behaviour. The model proposed in this contribution, on the one hand, captures these electro-viscoelastic effects and, on the other hand, also nicely fits into iterative finite element formulations in order to simulate general boundary value problems. While the deformation itself as well as the electric potential are introduced as global degrees of freedom, the internal variables accounting for the viscous response are incorporated at the so-called local integration point level. Apart form calibrating the model against experimental data, a simple coupled finite element example is studied to show the applicability of the finite deformation electro-viscoelastic formulation proposed.
Correlating Viscoelasticity with Metabolism in Single Cells using Atomic Force Microscopy
Caporizzo, Matthew; Roco, Charles; Coll-Ferrer, Carme; Eckmann, David; Composto, Russell
2015-03-01
Variable indentation-rate rheometric analysis by Laplace transform (VIRRAL), is developed to evaluate Dex-Gel drug carriers as biocompatible delivery agents. VIRRAL provides a general platform for the rapid characterization of the health of single cells by viscoelasticity to promote the self-consistent comparison between cells paramount to the development of early diagnosis and treatment of disease. By modelling the frequency dependence of elastic modulus, VIRRAL provides three metrics of cytoplasmic viscoelasticity: low frequency stiffness, high frequency stiffness, and a relaxation time. THP-1 cells are found to exhibit a frequency dependent elastic modulus consistent with the standard linear solid model of viscoelasticity. VIRRAL indicates that dextran-lysozyme drug carriers are biocompatible and deliver concentrated toxic material (rhodamine or silver nanoparticles) to the cytoplasm of THP-1 cells. The signature of cytotoxicity by rhodamine or silver exposure is a frequency independent 2-fold increase in elastic modulus and cytoplasmic viscosity while the cytoskeletal relaxation time remains unchanged independent of cytoplasmic stiffness. This is consistent with the known toxic mechanism of silver nanoparticles, where mitochondrial injury leads to ATP depletion and metabolic stress causes a decrease of mobility within cytoplasm. NSF DMR08-32802, NIH T32-HL007954, and ONR N000141410538.
How Enzymes Work: A Look through the Perspective of Molecular Viscoelastic Properties
Directory of Open Access Journals (Sweden)
Hao Qu
2013-02-01
Full Text Available We present nanorheology measurements on the folded state of an enzyme that show directly that the (ensemble-averaged stress-strain relations are nonlinear and frequency dependent beyond 1-Å deformation. We argue that this frequency dependence allows for opening a nonequilibrium cycle in the force-deformation plane if the forward and backward conformational changes of the enzyme during catalysis happen at different speeds. Using a heuristic model for the experimentally established viscoelastic properties of the enzyme, we examine a number of general features of enzymatic action. We find that the proposed viscoelastic cycle is consistent with the linear decrease of the speed of motor proteins with load. We find a relation between the stall force and the maximum rate for enzymes (in general and motors (in particular. We estimate the stall force of the motor protein kinesin from thermodynamic quantities and estimate the maximum rate of enzymes from purely mechanical quantities. We propose that the viscoelastic cycle provides a framework for considering mechanochemical coupling in enzymes on the basis of possibly universal materials properties of the folded state of proteins.
3D printing of an interpenetrating network hydrogel material with tunable viscoelastic properties.
Bootsma, Katherine; Fitzgerald, Martha M; Free, Brandon; Dimbath, Elizabeth; Conjerti, Joe; Reese, Greg; Konkolewicz, Dominik; Berberich, Jason A; Sparks, Jessica L
2017-06-01
Interpenetrating network (IPN) hydrogel materials are recognized for their unique mechanical properties. While IPN elasticity and toughness properties have been explored in previous studies, the factors that impact the time-dependent stress relaxation behavior of IPN materials are not well understood. Time-dependent (i.e. viscoelastic) mechanical behavior is a critical design parameter in the development of materials for a variety of applications, such as medical simulation devices, flexible substrate materials, cellular mechanobiology substrates, or regenerative medicine applications. This study reports a novel technique for 3D printing alginate-polyacrylamide IPN gels with tunable elastic and viscoelastic properties. The viscoelastic stress relaxation behavior of the 3D printed alginate-polyacrylamide IPN hydrogels was influenced most strongly by varying the concentration of the acrylamide cross-linker (MBAA), while the elastic modulus was affected most by varying the concentration of total monomer material. The material properties of our 3D printed IPN constructs were consistent with those reported in the biomechanics literature for soft tissues such as skeletal muscle, cardiac muscle, skin and subcutaneous tissue. Copyright © 2017 Elsevier Ltd. All rights reserved.
Creep and Viscoelastic Behaviour of Human Dentin
Directory of Open Access Journals (Sweden)
T.Jafarzadeh
2004-03-01
Full Text Available Statement of Problem: Biomechanics of the human dentition is inherently complex.Purpose: The aim of this study is to investigate, in vitro, the creep and the recovery of dentin under static uniaxial compressive stress conditions.Materials and Methods: Specimens of cylindrical morphology were prepared from recently extracted non-carious lower molar teeth, such that the average tubule orientation was axial. Slides of mid- coronal dentin (parallel surfaces, height 1.8 mm were sectionedwith a slow speed diamond saw and then cut into cylindrical discs. Specimens were stored at 4ºC for 24h to restabilize water content. Creep data were then measured by LVDT axially in water for periods of 2h load + 2h recovery on 4 separate groups (n=6: at two stresses (10 & 18 MPa and at two temperatures: 37 & 60ºC. Maximum creep strain, permanent set,strain recovery and initial compressive modulus were reported.Results: Compliance values were also calculated and slight non-linearity found at 60ºC.Two-way ANOVA was performed on results. Dentin exhibited a linear viscoelastic response under 'clinical' compressive stress levels , with a maximum strain ~ 1% and highrecoverability: permanent set<0.3%.Conclusion: This established a performance standard for viscoelastic stability of restorative biomaterials, replacing human dentin.
Polymer engineering science and viscoelasticity an introduction
Brinson, Hal F
2015-01-01
This book provides a unified mechanics and materials perspective on polymers: both the mathematics of viscoelasticity theory as well as the physical mechanisms behind polymer deformation processes. Introductory material on fundamental mechanics is included to provide a continuous baseline for readers from all disciplines. Introductory material on the chemical and molecular basis of polymers is also included, which is essential to the understanding of the thermomechanical response. This self-contained text covers the viscoelastic characterization of polymers including constitutive modeling, experimental methods, thermal response, and stress and failure analysis. Example problems are provided within the text as well as at the end of each chapter. New to this edition: · One new chapter on the use of nano-material inclusions for structural polymer applications and applications such as fiber-reinforced polymers and adhesively bonded structures · Brings up-to-date polymer pro...
Static viscoelasticity of biomass polyethylene composites
Yang, Keyan; Cai, Hongzhen; Yi, Weiming; Zhang, Qingfa; Zhao, Kunpeng
The biomass polyethylene composites filled with poplar wood flour, rice husk, cotton stalk or corn stalk were prepared by extrusion molding. The static viscoelasticity of composites was investigated by the dynamic thermal mechanical analyzer (DMA). Through the stress-strain scanning, it is found that the linear viscoelasticity interval of composites gradually decreases as the temperature rises, and the critical stress and strain values are 0.8 MPa and 0.03% respectively. The experiment shows that as the temperature rises, the creep compliance of biomass polyethylene composites is increased; under the constant temperature, the creep compliance decreases with the increase of content of biomass and calcium carbonate. The biomass and calcium carbonate used to prepare composites as filler can improve damping vibration attenuation and reduce stress deformation of composites. The stress relaxation modulus of composites is reduced and the relaxation rate increases at the higher temperature. The biomass and calcium carbonate used to prepare composites as filler not only can reduce costs, but also can increase stress relaxation modulus and improve the size thermostability of composites. The corn stalk is a good kind of biomass raw material for composites since it can improve the creep resistance property and the stress relaxation resistance property of composites more effectively than other three kinds of biomass (poplar wood flour, rice husk and cotton stalk).
Viscoelastic Flow Modelling for Polymer Flooding
de, Shauvik; Padding, Johan; Peters, Frank; Kuipers, Hans; Multi-scale Modelling of Multi-phase Flows Team
2015-11-01
Polymer liquids are used in the oil industry to improve the volumetric sweep and displacement efficiency of oil from a reservoir. Surprisingly, it is not only the viscosity but also the elasticity of the displacing fluid that determine the displacement efficiency. The main aim of our work is to obtain a fundamental understanding of the effect of fluid elasticity, by developing an advanced computer simulation methodology for the flow of non-Newtonian fluids through porous media. We simulate a 3D unsteady viscoelastic flow through a converging diverging geometry of realistic pore dimension using computational fluid dynamics (CFD).The primitive variables velocity, pressure and extra stresses are used in the formulation of models. The viscoelastic stress part is formulated using a FENE-P type of constitutive equation, which can predict both shear and elongational stress properties during this flow. A Direct Numerical Simulation (DNS) approach using Finite volume method (FVM) with staggered grid has been applied. A novel second order Immersed boundary method (IBM) has been incorporated to mimic porous media. The effect of rheological parameters on flow characteristics has also been studied. The simulations provide an insight into 3D flow asymmetry at higher Deborah numbers. Micro-Particle Image Velocimetry experiments are carried out to obtain further insights. These simulations present, for the first time, a detailed computational study of the effects of fluid elasticity on the imbibition of an oil phase.
Dynamics of magnetic nanoparticles in viscoelastic media
Energy Technology Data Exchange (ETDEWEB)
Remmer, Hilke, E-mail: h.remmer@tu-bs.de [Institute of Electrical Measurement and Fundamental Electrical Engineering, TU Braunschweig, Braunschweig (Germany); Roeben, Eric; Schmidt, Annette M. [Institute of Physical Chemistry, Universität zu Köln, Köln (Germany); Schilling, Meinhard; Ludwig, Frank [Institute of Electrical Measurement and Fundamental Electrical Engineering, TU Braunschweig, Braunschweig (Germany)
2017-04-01
We compare different models for the description of the complex susceptibility of magnetic nanoparticles in an aqueous gelatin solution representing a model system for a Voigt-Kelvin scheme. The analysis of susceptibility spectra with the numerical model by Raikher et al. is compared with the analysis applying a phenomenological, modified Debye model. The fit of the models to the measured data allows one to extract the viscoelastic parameter dynamic viscosity η and shear modulus G. The experimental data were recorded on single-core thermally blocked CoFe{sub 2}O{sub 4} nanoparticles in an aqueous solution with 2.5 wt% gelatin. Whereas the dynamic viscosities obtained by fitting the model – extended by distributions of hydrodynamic diameters and viscosities – agree very well, the derived values for the shear modulus show the same temporal behavior during the gelation process, but vary approximately by a factor of two. To verify the values for viscosity and shear modulus obtained from nanorheology, macrorheological measurements are in progress. - Highlights: • Ac susceptibility spectra of CoFe2O4 nanoparticles in aqueous gelatin solution. • Analysis of spectra with different approaches of Voigt-Kelvin model. • Comparison of modified Debye model with numerical model. • Both models provide similar values for viscoelastic parameters.
Separable finite viscoelasticity: integral-based models vs. experiments
Jridi, Nidhal; Arfaoui, Makrem; Hamdi, Adel; Salvia, Michelle; Bareille, Olivier; Ichchou, Mohamed; Ben Abdallah, Jalel
2018-03-01
In the present paper, the predictive capabilities of some integral-based finite strain viscoelastic models under the time-strain separability assumption have been investigated through experimental data for monotonic, relaxation and dynamic shear loads, in time and frequency domains. This analysis is instigated by experimental investigation results on two vulcanized carbon black filled rubbers. A unified identification procedure has been deployed to all models to determine the constitutive parameters. The monotonic tests were performed to capture the rate dependent and the long-term response of the materials. For the purely hyperelastic response, we considered the proposed hyperelastic potential proposed in Abaqus for incompressible materials. Relaxation tests were intended to identify the time-dependent material properties, and completed with a dynamic mechanical analysis. Models under consideration are Christensen, Fosdick & Yu, a variant of BKZ model, and the Simo model implemented in Abaqus. In the time domain, for each test case and for each model, the nominal stress is hence compared to experimental data, and the predictive capabilities are then examined with respect to three polynomial hyperelastic potentials forms. The dynamic properties had been investigated in the frequency domain with respect to the frequency and predeformation dependencies, and then comparison conclusions have been drawn.
Merrett, Craig G.
indicates that the flutter condition should be taken when simple harmonic motion occurs and certain additional velocity derivatives are satisfied. 3. The viscoelastic material behavior imposes a flutter time indicating that the presence of flutter should be verified for the entire life time of a flight vehicle. 4. An expanded definition for instability of a lifting surface or panel. Traditionally, instability is treated as a static phenomenon. The static case is only a limiting case of dynamic instability for a viscoelastic structure. Instability occurs when a particular combination of flight velocity and time are reached leading to growing displacements of the structure. 5. The inclusion of flight velocity transients that occur during maneuvers. Two- and three-dimensional unsteady incompressible and compressible aerodynamics were reformulated for a time dependent velocity. The inclusion of flight velocity transients does affect the flutter and instability conditions for a lifting surface and a panel. The applications of aero-servo-viscoelasticity are to aircraft design, wind turbine blades, submarine's stealth coatings and hulls, and land transportation to name a few examples. One caveat regarding this field of research is that general predictions for an application are not always possible as the stability of a structure depends on the phase relations between the various parameters such as mass, stiffness, damping, and the aerodynamic loads. The viscoelastic material parameters in particular alter the system parameters in directions that are difficult to predict. The inclusion of servo controls permits an additional design factor and can improve the performance of a structure beyond the native performance; however over-control is possible so a maximum limit to useful control does exist. Lastly, the number of material and control parameters present in aero-servo-viscoelasticity are amenable to optimization protocols to produce the optimal structure for a given mission.
International Nuclear Information System (INIS)
Sultania, Minakshi; Yadaw, S.B.; Rai, J.S.P.; Srivastava, Deepak
2010-01-01
The effects of variation of styrene content on the thermal, mechanical and morphological behaviours of epoxy novolac vinyl ester resin (EVER)/glass fabric laminate have been investigated. The vinyl ester resin matrix was synthesized indigenously using epoxy novolac resin and methacrylic acid catalyzed by triphenylphosphine at a temperature of 85 deg. C in nitrogen atmosphere. Fourier-transform infra-red spectroscopic (FT-IR) analysis was used to see the structural changes during the synthesis of the EVER. Differential scanning calorimetric (DSC) technique was used to investigate the curing behaviour of the EVER matrix. Exothermic peaks (T p ) appeared in the range of 117-127 deg. C for all the samples of epoxy resin and EVERs. Thermal stability of the prepared samples was analyzed by dynamic thermogravimetric runs. The TG/DTG trace of epoxy showed two-step mass loss decomposition behaviour whereas that of vinyl ester resin exhibited a single step mass loss. Mechanical properties such as tensile, flexural and impact strengths of the prepared laminates were determined and it was found cured resin containing 40% styrene showed the best balance of properties and EVER/glass fabric laminates exhibited better properties as compared to the epoxy/glass fabric laminates Dynamic mechanical analyses of the samples were done to determine the viscoelastic properties. T g decreased significantly with increased styrene concentration due to increase in cross-linking density. Cross-sections of the cured samples, which failed during impact testing, have been critically studied through scanning electron microscopic (SEM) analysis to gain insight into the phase morphology.
Directory of Open Access Journals (Sweden)
A. V. Khohlov
2016-01-01
Full Text Available The article analyses a one-dimensional linear integral constitutive equation of viscoelasticity with an arbitrary creep compliance function in order to reveal its abilities to describe the set of basic rheological phenomena pertaining to viscoelastoplastic materials at a constant temperature. General equations and basic properties of its quasi-static theoretic curves (i.e. stress-strain curves at constant strain or stress rates, creep, creep recovery, creep curves at piecewise-constant stress and ramp relaxation curves generated by the linear constitutive equation are derived and studied analytically. Their dependences on a creep function and relaxation modulus and on the loading program parameters are examined.The qualitative properties of the theoretic curves are compared to the typical properties of viscoelastoplastic materials test curves to reveal the mechanical effects, which the linear viscoelasticity theory cannot simulate and to find out convenient experimental indicators marking the field of its applicability or non-applicability. The minimal set of general restrictions that should be imposed on a creep and relaxation functions to provide an adequate description of typical test curves of viscoelastoplastic materials is formulated. It is proved, in particular, that an adequate simulation of typical experimental creep recovery curves requires that the derivative of a creep function should not increase at any point. This restriction implies that the linear viscoelasticity theory yields theoretical creep curves with non-increasing creep rate only and it cannot simulate materials demonstrating an accelerated creep stage. It is also proved that the linear viscoelasticity cannot simulate materials with experimental stress-strain curves possessing a maximum point or concave-up segment and materials exhibiting equilibrium modulus dependence on the strain rate or negative rate sensitivity.Similar qualitative analysis seems to be an important
Tropicalized Lambda Lengths, Measured Laminations and Convexity
DEFF Research Database (Denmark)
C. Penner, R.
of the basic cell decomposition of Riemann's moduli space to other contexts for general moduli spaces of flat connections on a surface. In any case, this discussion drastically simplifies aspects of previous related studies as is explained. Furthermore, a new class of measured laminations relative to an ideal...
Prediction of fatigue damage in tapered laminates
DEFF Research Database (Denmark)
Raeis Hosseiny, Seyed Aydin; Jakobsen, Johnny
2017-01-01
. By increasing the cracks density, damage occurs when residual material properties reduce to a critical level. Residual strength and stiffness of simple laminates are assigned in a set of fatigue failure criteria to assess the remaining life of the components by increasing number of loading cycles. The mode...
Finite Element Anlaysis of Laminated Composite Plates
1988-09-01
4 B. THE PRINCIPLE OF VIRTUAL WORK .............. 4 C. LAMINATE THEORY ........................ 8 1. Introduction...described. The principle of virtual displacements is invoked to obtain equilibrium relations. B. THE PRINCIPLE OF VIRTUAL WORK In this section, we prove...that total internal virtual work is equal to total ex- ternal virtual work and equivalence of this principle to the minimum total potential energy
Recycling of Aluminum from Fibre Metal Laminates
Zhu, G.; Xiao, Y.; Yang, Y.; Wang, J.; Sun, B.; Boom, R.
2012-01-01
Recycling of aluminum alloy scrap obtained from delaminated fibre metal laminates (FMLs) was studied through high temperature refining in the presence of a salt flux. The aluminum alloy scrap contains approximately mass fraction w(Cu) = 4.4%, w(Mg) = 1.1% and w(Mn) = 0.6% (2024 aluminum alloy). The
Laminated Root Rot of Western Conifers
E.E. Nelson; N.E. Martin; R.E. Williams
1981-01-01
Laminated root rot is caused by the native fungus Phellinus weirii (Murr.) Gilb. It occurs throughout the Northwestern United States and in southern British Columbia, Canada. The disease has also been reported in Japan and Manchuria. In the United States, the pathogen is most destructive in pure Douglas-fir stands west of the crest of the Cascade Range in Washington...
[Laminitis in cattle: a literature review].
Lischer, C; Ossent, P
1994-10-01
Worldwide afflictions of the claws belong to the economically important diseases in dairy cattle. The significance of laminitis has gained importance in the last years since the condition is regarded as the most important predisposing factor for the development of lesions such as sole ulcer, white line disease and heel horn erosion. Apart from the clinical stages (acute, subacute, chronic, chronic-recurrent) there is also a subclinical form of laminitis which does not cause lameness. It is characterized by soft yellowish sole and heel horn with haemorrhages in the sole and along the white line. Laminitis is a multifactorial event in which nutrition, genetic disposition and the perinatal period, combined with the associated diseases of high-yielding cows, have a particular significance. Currently, two principally different hypotheses on the pathogenesis are discussed. The generally accepted theory bases on a disturbance in the microcirculation of the corium. According to the other theory the circulatory disturbances are secondary to changes which occur in the horn producing cells of the stratum basale of the epidermis. The predisposing factors and the pathogenesis of laminitis are discussed in the light of possible therapeutic and prophylactic measures.
Natural fabric sandwich laminate composites: development and ...
Indian Academy of Sciences (India)
Natural fabrics; jute; linen; sandwich laminate; mechanical properties; fractographic analysis. 1. Introduction. Owing to ecological necessities and strict regulations, incor- porating natural fibres in the place of synthetic fibres becomes inevitable for the manufacturers to accomplish new composite materials originated from ...
Nuclear Structures Surrounding Internal Lamin Invaginations
Czech Academy of Sciences Publication Activity Database
Legartová, Soňa; Stixová, Lenka; Laur, O.; Kozubek, Stanislav; Sehnalová, Petra; Bártová, Eva
2014-01-01
Roč. 115, č. 3 (2014), s. 476-487 ISSN 0730-2312 R&D Projects: GA MŠk(CZ) LD11020 Institutional support: RVO:68081707 Keywords : LAMINS * NUCLEAR PORES * CHROMATIN Subject RIV: BO - Biophysics Impact factor: 3.263, year: 2014
Doped LZO buffer layers for laminated conductors
Paranthaman, Mariappan Parans [Knoxville, TN; Schoop, Urs [Westborough, MA; Goyal, Amit [Knoxville, TN; Thieme, Cornelis Leo Hans [Westborough, MA; Verebelyi, Darren T [Oxford, MA; Rupich, Martin W [Framingham, MA
2010-03-23
A laminated conductor includes a metallic substrate having a surface, a biaxially textured buffer layer supported by the surface of the substrate, the biaxially textured buffer layer comprising LZO and a dopant for mitigating metal diffusion through the LZO, and a biaxially textured conductor layer supported by the biaxially textured buffer layer.
Lamin C and chromatin organization in Drosophila
Indian Academy of Sciences (India)
Drosophila lamin C (LamC) is a developmentally regulated component of the nuclear lamina. The lamC gene is situated in the fifth intron of the essential gene tout velu (ttv). We carried out genetic analysis of lamC during development. Phenotypic analyses of RNAi-mediated downregulation of lamC expression as well as ...
Natural fabric sandwich laminate composites: development and ...
Indian Academy of Sciences (India)
Sci., Vol. 40, No. 1, February 2017, pp. 139–146. c Indian Academy of Sciences. DOI 10.1007/s12034-016-1356-y. Natural fabric sandwich laminate composites: development and investigation ... studied by Gassan and Bledzki [17]. An investigation on the ... spread with the aid of a brush. Another layer of reinforce- ment in ...
Edge effects in angle-ply composite laminates
Hsu, P. W.; Herakovich, C. T.
1977-01-01
This paper presents the results of a zeroth-order solution for edge effects in angle-ply composite laminates obtained using perturbation techniques and a limiting free body approach. The general solution for edge effects in laminates of arbitrary angle ply is applied to the special case of a (+ or - 45)s graphite/epoxy laminate. Interlaminar stress distributions are obtained as a function of the laminate thickness-to-width ratio and compared to finite difference results. The solution predicts stable, continuous stress distributions, determines finite maximum tensile interlaminar normal stress and provides mathematical evidence for singular interlaminar shear stresses in (+ or - 45) graphite/epoxy laminates.
Directory of Open Access Journals (Sweden)
Vincent Olunloyo
2016-12-01
Full Text Available In this paper, we present an analytical method for solving a well-posed boundary value problem of mathematical physics governing the vibration characteristics of an internal flow propelled fluid-structure interaction where the pipeline segment is idealized as an elastic hollow beam conveying an incompressible fluid on a viscoelastic foundation. The effect of Coriolis and damping forces on the overall dynamic response of the system is investigated. In actuality, for a pipe segment supported at both ends and subject to a free motion, these two forces generate conjugate complex frequencies for all flow velocities. On employing integral transforms and complex variable functions, a closed form analytical expression is derived for the overall dynamic response. It is demonstrated that a concise mathematical expression for the natural frequency associated with any mode of vibration can be deduced from the algebraic product of the complex frequency pairs. By a way of comparative analysis for damping decrement physics reminiscent with laminated structures, mathematical expressions are derived to illustrate viscoelastic damping effects on dynamic stability for any flow velocity. The integrity of the analytical solution is verified and validated by confirming theresults in literature in appropriate asymptotic limits.
Microcracking in composite laminates under thermal and mechanical loading. Thesis
Maddocks, Jason R.
1995-01-01
Composites used in space structures are exposed to both extremes in temperature and applied mechanical loads. Cracks in the matrix form, changing the laminate thermoelastic properties. The goal of the present investigation is to develop a predictive methodology to quantify microcracking in general composite laminates under both thermal and mechanical loading. This objective is successfully met through a combination of analytical modeling and experimental investigation. In the analysis, the stress and displacement distributions in the vicinity of a crack are determined using a shear lag model. These are incorporated into an energy based cracking criterion to determine the favorability of crack formation. A progressive damage algorithm allows the inclusion of material softening effects and temperature-dependent material properties. The analysis is implemented by a computer code which gives predicted crack density and degraded laminate properties as functions of any thermomechanical load history. Extensive experimentation provides verification of the analysis. AS4/3501-6 graphite/epoxy laminates are manufactured with three different layups to investigate ply thickness and orientation effects. Thermal specimens are cooled to progressively lower temperatures down to -184 C. After conditioning the specimens to each temperature, cracks are counted on their edges using optical microscopy and in their interiors by sanding to incremental depths. Tensile coupons are loaded monotonically to progressively higher loads until failure. Cracks are counted on the coupon edges after each loading. A data fit to all available results provides input parameters for the analysis and shows them to be material properties, independent of geometry and loading. Correlation between experiment and analysis is generally very good under both thermal and mechanical loading, showing the methodology to be a powerful, unified tool. Delayed crack initiation observed in a few cases is attributed to a
Hou, T. H.
1985-01-01
High quality long fiber reinforced composites, such as those used in aerospace and industrial applications, are commonly processed in autoclaves. An adequate resin flow model for the entire system (laminate/bleeder/breather), which provides a description of the time-dependent laminate consolidation process, is useful in predicting the loss of resin, heat transfer characteristics, fiber volume fraction and part dimension, etc., under a specified set of processing conditions. This could be accomplished by properly analyzing the flow patterns and pressure profiles inside the laminate during processing. A newly formulated resin flow model for composite prepreg lamination process is reported. This model considers viscous resin flows in both directions perpendicular and parallel to the composite plane. In the horizontal direction, a squeezing flow between two nonporous parallel plates is analyzed, while in the vertical direction, a poiseuille type pressure flow through porous media is assumed. Proper force and mass balances have been made and solved for the whole system. The effects of fiber-fiber interactions during lamination are included as well. The unique features of this analysis are: (1) the pressure gradient inside the laminate is assumed to be generated from squeezing action between two adjacent approaching fiber layers, and (2) the behavior of fiber bundles is simulated by a Finitely Extendable Nonlinear Elastic (FENE) spring.
Calculation of neutron albedo from laminated semiinfinite media
International Nuclear Information System (INIS)
Dobrynin, Yu.L.; Mikaehlyan, L.A.; Skorokhvatov, M.D.
1978-01-01
A version of a laminated neutron detector with increased efficiency for recording external neutron fluxes by gamma-quanta from neutron capture is considered. The detector comprises two zones. The first zone constitutes an absorbent layer (europium oxide) 0.5 cm thick, and the second one is a moderator (water with gadolinium salt at the concentration of 0.8 g/l). Mono-energetic neutrons fall normally onto the detector surface. Neutron energy varied from 0.1 eV to MeV. The results of calculations of the integral numerical current albedo (INCA) of neutrons by the Monte Carlo method are presented. The INCA dependences on neutron energy are obtained for one moderator with different gadolinium contents; for the absorbent with the moderator containing and lacking the gadolinium. The resultant dependences are indicative of preferential capture of neutrons by the gadolinium in the moderator, this being more desirable for recording neutrons in the (n, γ) reaction
Recent progress of particle migration in viscoelastic fluids.
Yuan, Dan; Zhao, Qianbin; Yan, Sheng; Tang, Shi-Yang; Alici, Gursel; Zhang, Jun; Li, Weihua
2018-02-13
Recently, research on particle migration in non-Newtonian viscoelastic fluids has gained considerable attention. In a viscoelastic fluid, three dimensional (3D) particle focusing can be easily realized in simple channels without the need for any external force fields or complex microchannel structures compared with that in a Newtonian fluid. Due to its promising properties for particle precise focusing and manipulation, this field has been developed rapidly, and research on the field has been shifted from fundamentals to applications. This review will elaborate the recent progress of particle migration in viscoelastic fluids, especially on the aspect of applications. The hydrodynamic forces on the micro/nano particles in viscoelastic fluids are discussed. Next, we elaborate the basic particle migration in viscoelasticity-dominant fluids and elasto-inertial fluids in straight channels. After that, a comprehensive review on the applications of viscoelasticity-induced particle migration (particle separation, cell deformability measurement and alignment, particle solution exchange, rheometry-on-a-chip and others) is presented; finally, we thrash out some perspectives on the future directions of particle migration in viscoelastic fluids.
Viscoelasticity evaluation of rubber by surface reflection of supersonic wave.
Omata, Nobuaki; Suga, Takahiro; Furusawa, Hirokazu; Urabe, Shinichi; Kondo, Takeru; Ni, Qing-Qing
2006-12-22
The main characteristic of rubber is a viscoelasticity. So it is important to research the characteristic of the viscoelasticity of the high frequency band for the friction between a rubber material and the hard one with roughness, for instance, the tire and the road. As for the measurement of the viscoelasticity of rubber, DMA (dynamic mechanical analysis) is general. However, some problems are pointed out to the measurement of the high frequency band by DMA. Then, we evaluated the viscoelasticity characteristic by the supersonic wave measurement. However, attenuation of rubber is large, and when the viscoelasticity is measured by the supersonic wave therefore, it is inconvenient and limited in a past method by means of bottom reflection. In this report, we tried the viscoelasticity evaluation by the method of using complex surface reflection coefficient and we compared with the friction coefficient under wide-range friction velocity. As a result, some relationships had been found for two properties. We report the result that character of viscoelasticity of rubber was comparable to friction coefficient.
Exposing the nonlinear viscoelastic behavior of asphalt-aggregate mixes
Levenberg, Eyal; Uzan, Jacob
2012-05-01
In this study asphalt-aggregate mixes are treated as both viscoelastic and viscoplastic. Following a damage mechanics approach, a nonlinear viscoelastic constitutive formulation is generated from a linear formulation by replacing `applied stresses' with `effective viscoelastic stresses'. A non-dimensional scalar entity called `relative viscoelastic stiffness' is introduced; it is defined as the ratio of applied to effective viscoelastic stress and encapsulates different types of nonlinearities. The paper proposes a computational scheme for exposing these nonlinearities by uncovering, through direct analysis of any test data, changes experienced by the `relative viscoelastic stiffness'. In general terms, the method is based on simultaneous application of creep and relaxation formulations while preserving the interrelationship between the corresponding time functions. The proposed scheme is demonstrated by analyzing a uniaxial tension test and a uniaxial compression test (separately). Results are presented and discussed, unveiling and contrasting the character of viscoelastic nonlinearities in both cases. A conceptual viewpoint is offered to explain the observations, illustrating the requirements from any candidate constitutive theory.
Optical tracking of local surface wave for skin viscoelasticity.
Guan, Yubo; Lu, Mingzhu; Shen, Zhilong; Wan, Mingxi
2014-06-01
Rapid and effective determination of biomechanical properties is important in examining and diagnosing skin thermal injury. Among the methods used, viscoelasticity quantification is one of the most effective methods in determining such properties. This study aims to rapidly determine skin viscoelasticity by optically tracking the local surface wave. New elastic and viscous coefficients were proposed to indicate skin viscoelasticity based on a single impulse response of the skin. Experiments were performed using fresh porcine skin samples. Surface wave was generated in a single impulse using a vibrator with a ball-tipped device and was detected using a laser Doppler vibrometer. The motions along the depth direction were monitored using an ultrasound system. The ultrasound monitoring results indicated the multi-layered viscoelasticity of the epidermis and dermis. The viscoelastic coefficients from four healthy samples show a potential viscoelasticity variation of porcine skin. In one sample, the two coefficients were evidently higher than those in a healthy area if the skin was slightly burned. These results indicate that the proposed method is sensitive, effective, and quick in determining skin viscoelasticity. Copyright © 2014 IPEM. Published by Elsevier Ltd. All rights reserved.
Effect of viscoelasticity on adhesion of bioinspired micropatterned epoxy surfaces.
Castellanos, Graciela; Arzt, Eduard; Kamperman, Marleen
2011-06-21
The effect of viscoelasticity on adhesion was investigated for micropatterned epoxy surfaces and compared to nonpatterned surfaces. A two-component epoxy system was used to produce epoxy compositions with different viscoelastic properties. Pillar arrays with flat punch tip geometries were fabricated with a two-step soft lithography process. Adhesion properties were measured with a home-built adhesion tester using a spherical sapphire probe as a counter-surface. Compared to flat controls, micropatterned epoxy samples with low viscoelasticity (i.e., low damping factors) showed at least a 20-fold reduction in pull-off force per actual contact area for both low (E' = 2.3 MPa) and high (E' = 2.3 GPa) storage moduli. This antiadhesive behavior may result from poor contact formation and indicates that the adhesion performance of commonly used elastomers for dry adhesives (e.g., polydimethylsiloxane) is governed by the interfacial viscoelasticity. Adhesion significantly increased with increasing viscoelasticity. Micropatterned samples with high viscoelasticity showed a 4-fold reduction in adhesion for aspect ratio (AR) 1.1 patterns but a 2-fold enhancement in adhesion for AR 2.2 patterns. These results indicate that viscoelasticity can enhance the effect of surface patterning on adhesion and should be considered as a significant parameter in the design of artificial patterned adhesives. © 2011 American Chemical Society
Novel Remanufacturing Process of Recycled Polytetrafluoroethylene(PTFE)/GF Laminate
Xi, Z.; Ghita, O. R.; Johnston, P.; Evans, K. E.
2011-01-01
Currently, the PTFE/GF laminate and PTFE PCB manufacturers are under considerable pressure to address the recycling issues due to Waste Electrical and Electronic Equipment (WEEE) Directive, shortage of landfill capacity and cost of disposal. This study is proposing a novel manufacture method for reuse of the mechanical ground PTFE/Glass fibre (GF) laminate and production of the first reconstitute PTFE/GF laminate. The reconstitute PTFE/GF laminate proposed here consists of a layer of recycled sub-sheet, additional layers of PTFE and PTFE coated glass cloth, also covered by copper foils. The reconstitute PTFE/GF laminate showed good dielectric properties. Therefore, there is potential to use the mechanical ground PTFE/GF laminate powder to produce reconstitute PTFE/GF laminate, for use in high frequencies PCB applications.
Aluminum Laminates in Beverage Packaging: Models and Experiences
Directory of Open Access Journals (Sweden)
Gabriella Bolzon
2015-08-01
Full Text Available Aluminum laminates are among the main components of beverage packaging. These layered material systems are coupled to paperboard plies except in the cap opening area, where the human force limit sets a requirement on the material properties to allow open-ability and the mechanical characteristics are of particular interest. Experimental investigations have been carried out on this composite and on its components by either traditional or full-field measurement techniques. The interpretation of the collected data has been supported by the simulation of the performed tests considering either a homogenized material model or the individual laminate layers. However, different results may be recovered from similar samples due to physical factors like the material processing route and the embedded defectiveness. In turn, the conclusions may vary depending on the model assumptions. This contribution focuses on the physical effects and on the modeling of the large localized deformation induced by material singularities. This topic is discussed at the light of some experimental results.
Li, Chuanbin; Qin, Boyang; Gopinath, Arvind; Arratia, Paulo E; Thomases, Becca; Guy, Robert D
2017-10-01
Many important biological functions depend on microorganisms' ability to move in viscoelastic fluids such as mucus and wet soil. The effects of fluid elasticity on motility remain poorly understood, partly because the swimmer strokes depend on the properties of the fluid medium, which obfuscates the mechanisms responsible for observed behavioural changes. In this study, we use experimental data on the gaits of Chlamydomonas reinhardtii swimming in Newtonian and viscoelastic fluids as inputs to numerical simulations that decouple the swimmer gait and fluid type in order to isolate the effect of fluid elasticity on swimming. In viscoelastic fluids, cells employing the Newtonian gait swim faster but generate larger stresses and use more power, and as a result the viscoelastic gait is more efficient. Furthermore, we show that fundamental principles of swimming based on viscous fluid theory miss important flow dynamics: fluid elasticity provides an elastic memory effect that increases both the forward and backward speeds, and (unlike purely viscous fluids) larger fluid stress accumulates around flagella moving tangent to the swimming direction, compared with the normal direction. © 2017 The Author(s).
Macro-scale approach for rough frictionless multi-indentation on a viscoelastic half-space
DUBOIS, Guillaume; CESBRON, Julien; YIN, Hai Ping; ANFOSSO LEDEE, Fabienne
2011-01-01
This paper deals with the numerical study of frictionless viscoelastic tyre/road contact. The present macro-scale approach takes into account both the viscoelastic behaviour of the tyre and the roughness of the road surface by solving the contact problem between a rough multi-indentation surface and a viscoelastic half-space. The method relies on the fact that a viscoelastic solution can be instantaneously reduced to an elastic solution. A simplified description of viscoelastic material behav...
[Viscoelastic properties of relaxed papillary muscle at physiological hypertrophy].
Smoliuk, L T; Lisin, R V; Kuznetsov, D A; Protsenko, Iu L
2012-01-01
Viscoelastic properties of relaxed rat papillary muscles at physiological hypertrophy (intensive swimming for 5 weeks) have been obtained. It has been ascertained that viscoelastic properties of hypertrophied muscles are not significantly distinguished from those of control papillary muscles. A three-dimensional model of myocardial fascicle has been verified in compliance with experimental data of biomechanical tests of hypertrophied muscles. Elastic and viscous parameters of structural elements of the model negligibly differ from the parameters of the model of a control muscle. It is shown that physiological hypertrophy has a slight influence on viscoelastic properties of papillary muscles.
Thermal convection of viscoelastic shear-thinning fluids
International Nuclear Information System (INIS)
Albaalbaki, Bashar; Khayat, Roger E; Ahmed, Zahir U
2016-01-01
The Rayleigh–Bénard convection for non-Newtonian fluids possessing both viscoelastic and shear-thinning behaviours is examined. The Phan-Thien–Tanner (PTT) constitutive equation is implemented to model the non-Newtonian character of the fluid. It is found that while the shear-thinning and viscoelastic effects could annihilate one another for the steady roll flow, presence of both behaviours restricts the roll stability limit significantly compared to the cases when the fluid is either inelastic shear-thinning or purely viscoelastic with constant viscosity. (paper)
Love wave dispersion in anisotropic visco-elastic medium
Directory of Open Access Journals (Sweden)
G. GIR SUBHASH
1978-06-01
Full Text Available The paper presents a study on Love wave propagation in a anisotropic
visco-elastic layer overlying a rigid half space. The characteristic frequency
equation is obtained and the variation of the wave number with frequency
under the combined effect of visco-elasticity and anisotropy is analysed
in detail. The results show that the effect of visco-elasticity on the
wave is similar to that of anisotropy as long as the coefficient of anisotropy
is less than unity.
Homogenization theory for designing graded viscoelastic sonic crystals
International Nuclear Information System (INIS)
Qu Zhao-Liang; Ren Chun-Yu; Pei Yong-Mao; Fang Dai-Ning
2015-01-01
In this paper, we propose a homogenization theory for designing graded viscoelastic sonic crystals (VSCs) which consist of periodic arrays of elastic scatterers embedded in a viscoelastic host material. We extend an elastic homogenization theory to VSC by using the elastic-viscoelastic correspondence principle and propose an analytical effective loss factor of VSC. The results of VSC and the equivalent structure calculated by using the finite element method are in good agreement. According to the relation of the effective loss factor to the filling fraction, a graded VSC plate is easily and quickly designed. Then, the graded VSC may have potential applications in the vibration absorption and noise reduction fields. (paper)
Modelling Viscoelasticity of Loudspeaker Suspensions using Retardation Spectra
DEFF Research Database (Denmark)
Ritter, Tobias; Agerkvist, Finn T.
2010-01-01
It is well known that, due to viscoelastic eects in the suspension, the displacement of the loudspeaker increases with decreasing frequency below the resonance. Present creep models are either not precise enough or purely empirical and not derived from the basis of physics. In this investigation......, the viscoelastic retardation spectrum, which provides a more fundamental description of the suspension viscoelasticity, is rst used to explain the accuracy of the empirical LOG creep model (Knudsen et al.). Then, two extensions to the LOG model are proposed which include the low and high frequency limit...
Active-passive calibration of optical tweezers in viscoelastic media
DEFF Research Database (Denmark)
Fischer, Mario; Richardson, Andrew C; S Reihani, S Nader
2010-01-01
In order to use optical tweezers as a force measuring tool inside a viscoelastic medium such as the cytoplasm of a living cell, it is crucial to perform an exact force calibration within the complex medium. This is a nontrivial task, as many of the physical characteristics of the medium and probe......, e.g., viscosity, elasticity, shape, and density, are often unknown. Here, we suggest how to calibrate single beam optical tweezers in a complex viscoelastic environment. At the same time, we determine viscoelastic characteristics such as friction retardation spectrum and elastic moduli of the medium...
Numerical simulations of viscoelastic flows with free surfaces
DEFF Research Database (Denmark)
Comminal, Raphaël; Spangenberg, Jon; Hattel, Jesper Henri
2013-01-01
We present a new methodology to simulate viscoelastic flows with free-surfaces. These simulations are motivated by the modelling of polymers manufacturing techniques, such as extrusion and injection moulding. One of the consequences of viscoelasticity is that polymeric materials have a “memory......” of their past deformations. This generates some numerical difficulties which are addressed with the log-conformation transformation. The main novelty of this work lies on the use of the volume-of-fluid method to track the free surfaces of the viscoelastic flows. We present some preliminary results of test case...
Run-and-tumble-like motion of active colloids in viscoelastic media
Lozano, Celia; Ruben Gomez-Solano, Juan; Bechinger, Clemens
2018-01-01
Run-and-tumble motion is a prominent locomotion strategy employed by many living microorganisms. It is characterized by straight swimming intervals (runs), which are interrupted by sudden reorientation events (tumbles). In contrast, directional changes of synthetic microswimmers (active particles) are caused by rotational diffusion, which is superimposed with their translational motion and thus leads to rather continuous and slow particle reorientations. Here we demonstrate that active particles can also perform a swimming motion where translational and orientational changes are disentangled, similar to run-and-tumble. In our system, such motion is realized by a viscoelastic solvent and a periodic modulation of the self-propulsion velocity. Experimentally, this is achieved using light-activated Janus colloids, which are illuminated by a time-dependent laser field. We observe a strong enhancement of the effective translational and rotational motion when the modulation time is comparable to the relaxation time of the viscoelastic fluid. Our findings are explained by the relaxation of the elastic stress, which builds up during the self-propulsion, and is suddenly released when the activity is turned off. In addition to a better understanding of active motion in viscoelastic surroundings, our results may suggest novel steering strategies for synthetic microswimmers in complex environments.
Viscoelastic characterization of carbon fiber-epoxy composites by creep and creep rupture tests
International Nuclear Information System (INIS)
Farina, Luis Claudio
2009-01-01
One of the main requirements for the use of fiber-reinforced polymer matrix composites in structural applications is the evaluation of their behavior during service life. The warranties of the integrity of these structural components demand a study of the time dependent behavior of these materials due to viscoelastic response of the polymeric matrix and of the countless possibilities of design configurations. In the present study, creep and creep rupture test in stress were performed in specimens of unidirectional carbon fiber-reinforced epoxy composites with fibers orientations of 60 degree and 90 degree, at temperatures of 25 and 70 degree C. The aim is the viscoelastic characterization of the material through the creep curves to some levels of constant tension during periods of 1000 h, the attainment of the creep rupture envelope by the creep rupture curves and the determination of the transition of the linear for non-linear behavior through isochronous curves. In addition, comparisons of creep compliance curves with a viscoelastic behavior prediction model based on Schapery equation were also performed. For the test, a modification was verified in the behavior of the material, regarding the resistance, stiffness and deformation, demonstrating that these properties were affected for the time and tension level, especially in work temperature above the ambient. The prediction model was capable to represent the creep behavior, however the determination of the equations terms should be considered, besides the variation of these with the applied tension and the elapsed time of test. (author)
Micro-Mechanical Viscoelastic Properties of Crosslinked Hydrogels Using the Nano-Epsilon Dot Method.
Mattei, Giorgio; Cacopardo, Ludovica; Ahluwalia, Arti
2017-08-02
Engineering materials that recapitulate pathophysiological mechanical properties of native tissues in vitro is of interest for the development of biomimetic organ models. To date, the majority of studies have focused on designing hydrogels for cell cultures which mimic native tissue stiffness or quasi-static elastic moduli through a variety of crosslinking strategies, while their viscoelastic (time-dependent) behavior has been largely ignored. To provide a more complete description of the biomechanical environment felt by cells, we focused on characterizing the micro-mechanical viscoelastic properties of crosslinked hydrogels at typical cell length scales. In particular, gelatin hydrogels crosslinked with different glutaraldehyde (GTA) concentrations were analyzed via nano-indentation tests using the nano-epsilon dot method. The experimental data were fitted to a Maxwell Standard Linear Solid model, showing that increasing GTA concentration results in increased instantaneous and equilibrium elastic moduli and in a higher characteristic relaxation time. Therefore, not only do gelatin hydrogels become stiffer with increasing crosslinker concentration (as reported in the literature), but there is also a concomitant change in their viscoelastic behavior towards a more elastic one. As the degree of crosslinking alters both the elastic and viscous behavior of hydrogels, caution should be taken when attributing cell response merely to substrate stiffness, as the two effects cannot be decoupled.
Directory of Open Access Journals (Sweden)
Mikhail Popov
2016-12-01
Full Text Available Sliding friction can be reduced substantially by applying ultrasonic vibration in the sliding plane or in the normal direction. This effect is well known and used in many applications ranging from press forming to ultrasonic actuators. One of the characteristics of the phenomenon is that, at a given frequency and amplitude of oscillation, the observed friction reduction diminishes with increasing sliding velocity. Beyond a certain critical sliding velocity, there is no longer any difference between the coefficients of friction with or without vibration. This critical velocity depends on material and kinematic parameters and is a key characteristic that must be accounted for by any theory of influence of vibration on friction. Recently, the critical sliding velocity has been interpreted as the transition point from periodic stick-slip to pure sliding and was calculated for purely elastic contacts under uniform sliding with periodic normal loading. Here we perform a similar analysis of the critical velocity in viscoelastic contacts using a Kelvin material to describe viscoelasticity. A closed-form solution is presented, which contains previously reported results as special cases. This paves the way for more detailed studies of active control of friction in viscoelastic systems, a previously neglected topic with possible applications in elastomer technology and in medicine.
Sensing of fluid viscoelasticity from piezoelectric actuation of cantilever flexural vibration
Energy Technology Data Exchange (ETDEWEB)
Park, Jeongwon; Jeong, Seongbin; Kim, Seung Joon; Park, Junhong, E-mail: parkj@hanyang.ac.kr [Department of Mechanical Convergence Engineering, Hanyang University, Seoul 133-791 (Korea, Republic of)
2015-01-15
An experimental method is proposed to measure the rheological properties of fluids. The effects of fluids on the vibration actuated by piezoelectric patches were analyzed and used in measuring viscoelastic properties. Fluid-structure interactions induced changes in the beam vibration properties and frequency-dependent variations of the complex wavenumber of the beam structure were used in monitoring these changes. To account for the effects of fluid-structure interaction, fluids were modelled as a simple viscoelastic support at one end of the beam. The measured properties were the fluid’s dynamic shear modulus and loss tangent. Using the proposed method, the rheological properties of various non-Newtonian fluids were measured. The frequency range for which reliable viscoelasticity results could be obtained was 10–400 Hz. Viscosity standard fluids were tested to verify the accuracy of the proposed method, and the results agreed well with the manufacturer’s reported values. The simple proposed laboratory setup for measurements was flexible so that the frequency ranges of data acquisition were adjustable by changing the beam’s mechanical properties.
Dynamic viscoelasticity of protease-treated rice batters for gluten-free rice bread making.
Honda, Yuji; Inoue, Nanami; Sugimoto, Reina; Matsumoto, Kenji; Koda, Tomonori; Nishioka, Akihiro
2018-03-01
Papain (cysteine protease), subtilisin (Protin SD-AY10, serine protease), and bacillolysin (Protin SD-NY10, metallo protease) increased the specific volume of gluten-free rice breads by 19-63% compared to untreated bread. In contrast, Newlase F (aspartyl protease) did not expand the volume of the rice bread. In a rheological analysis, the viscoelastic properties of the gluten-free rice batters also depended on the protease categories. Principal component analysis (PCA) analysis suggested that the storage and loss moduli (G' and G″, respectively) at 35 °C, and the maximum values of G' and G″, were important factors in the volume expansion. Judging from the PCA of the viscoelastic parameters of the rice batters, papain and Protin SD-AY10 improved the viscoelasticity for gluten-free rice bread making, and Protin SD-NY effectively expanded the gluten-free rice bread. The rheological properties differed between Protin SD-NY and the other protease treatments.
Generalized Fractional Derivative Anisotropic Viscoelastic Characterization
Directory of Open Access Journals (Sweden)
Harry H. Hilton
2012-01-01
Full Text Available Isotropic linear and nonlinear fractional derivative constitutive relations are formulated and examined in terms of many parameter generalized Kelvin models and are analytically extended to cover general anisotropic homogeneous or non-homogeneous as well as functionally graded viscoelastic material behavior. Equivalent integral constitutive relations, which are computationally more powerful, are derived from fractional differential ones and the associated anisotropic temperature-moisture-degree-of-cure shift functions and reduced times are established. Approximate Fourier transform inversions for fractional derivative relations are formulated and their accuracy is evaluated. The efficacy of integer and fractional derivative constitutive relations is compared and the preferential use of either characterization in analyzing isotropic and anisotropic real materials must be examined on a case-by-case basis. Approximate protocols for curve fitting analytical fractional derivative results to experimental data are formulated and evaluated.
Heart valve viscoelastic properties - a pilot study
Directory of Open Access Journals (Sweden)
Kochová P.
2007-10-01
Full Text Available The effects of cryopreservation on the biological tissue mechanics are still largely unknown. Generalized Maxwell model was applied to characterize quantitatively the viscoelastic behavior of sheep mitral heart valve tissue. Three different groups of specimens are supposed to be tested: fresh tissue specimens (control group, cryopreserved allografts from tissue bank and allografts already used as tissue replacements taken from the animals approximately one year after the surgery. Specific aim of this study is to determine whether or not the treatment used for storage in tissue bank influences significantly the mechanical properties and behavior of the tissue. At the moment, only the first group of specimens was examined. The methodology presented in this paper proved suitable to complete the study.
Directory of Open Access Journals (Sweden)
Zhengchao Xie
2009-01-01
Full Text Available Due to the large number of design variables that can be present in complex systems incorporating visco-elastic damping, this work examines the application of genetic algorithms in optimizing the response of these structures. To demonstrate the applicability of genetic algorithms (GAs, the approach is applied to a simple viscoelastically damped constrained-layer beam. To that end, a finite element model (FEM derived by Zapfe, which was based on Rao's formulation, was used for a beam with constrained-layer damping. Then, a genetic algorithm is applied to simultaneously determine the thicknesses of the viscoelastic damping layer and the constraining layer that provide the best response. While the targeted response is ultimately at the discretion of the designer, a few different choices for the fitness function are shown along with their corresponding impact on the vibratory response. By integrating the FEM code within the GA routine, it is easier to include the frequency-dependence of both the shear modulus and the loss factors for the viscoelastic layer. Examples are provided to demonstrate the capabilities of the method. It is shown that while a multi-mode optimization target provides significant reductions, the response for that configuration is inferior to the response when only single-mode reduction is considered. The results also reveal that the optimum configuration has a lower response level than when a thick layer of damping material is used. By demonstrating the applicability of GA for a simple beam structure, the approach can be extended to more complex damped structures.
Hama, Brian; Mahajan, Gautam; Kothapalli, Chandrasekhar
2017-08-01
Exogenous delivery of cartilage extract is being explored as a promising candidate for knee arthritis treatment as it biomimics native cartilage tissue characteristics. In this study, we report on the rheological characterization of aqueous suspensions constituted from a powdered form of unhydrolyzed chicken sternum extract. The effect of particle size (as-received vs. milled), suspension fluid (water vs. PBS), and temperature (37°C vs. 4°C), on the viscoelastic properties of the sternum extract based particulate suspensions were evaluated. Results showed that these suspensions exhibit shear-thinning characteristics as shear rate (γ̇) increases, while viscosity (η), storage (G'), and loss (G″) moduli of the suspensions increased with increasing particulate loading (ϕ: 2.5-10wt%). Reducing the as-received particle size by milling decreased G', G, and η of the suspensions and increased the influence of ϕ on these properties, possibly due to improved particle packing. Replacing water with PBS had no significant effect on the rheological properties, but temperature reduction from 37°C to 4°C increased G', G", and η of the suspensions and lowered the impact of powder loading on viscoelastic properties. The suspension's time-dependent response was typical of viscoelastic materials, characterized by an asymptotical approach to a final stress (stress relaxation) or strain (creep). Results were fit to a power-law model for creep, a general relaxation model for exponential decay in stress, Carreau-Yasuda models for flow curves, and a two-parameter Liu model to identify the maximum powder loading (ϕ m ). Among the various forces involved in particle-particle interactions within these suspensions, electrostatic forces appeared to dominate the most. Such characterization of the viscoelastic nature of these suspensions would help in formulating stable injectable cartilage extract based therapeutics for in vivo applications. Copyright © 2017 Elsevier Ltd. All
Simulating the time-dependent behaviour of excavations in hard rock
CSIR Research Space (South Africa)
Malan, DF
2002-10-01
Full Text Available associated with using viscoelastic theory to simulate the time-dependent behaviour of hard rock, a viscoelastic convergence solution for the incremental enlargement of a tabular excavation is discussed. Data on the time dependent deformation of a tunnel...
Stagnation point flow and heat transfer for a viscoelastic fluid ...
Indian Academy of Sciences (India)
M REZA
2017-11-09
Newtonian fluid) on the surface of water. (viscous fluid) has motivated us to study this problem. In general, crude oils have different rheological properties based on dilution. For example, crude oil [15, 16] has viscoelastic prosperities.
Stability of non-linear constitutive formulations for viscoelastic fluids
Siginer, Dennis A
2014-01-01
Stability of Non-linear Constitutive Formulations for Viscoelastic Fluids provides a complete and up-to-date view of the field of constitutive equations for flowing viscoelastic fluids, in particular on their non-linear behavior, the stability of these constitutive equations that is their predictive power, and the impact of these constitutive equations on the dynamics of viscoelastic fluid flow in tubes. This book gives an overall view of the theories and attendant methodologies developed independently of thermodynamic considerations as well as those set within a thermodynamic framework to derive non-linear rheological constitutive equations for viscoelastic fluids. Developments in formulating Maxwell-like constitutive differential equations as well as single integral constitutive formulations are discussed in the light of Hadamard and dissipative type of instabilities.
Propagation of shear waves in viscoelastic medium at irregular boundaries
Chattopadhyay, Amares; Gupta, Shishir; Sharma, Vikash; Kumari, Pato
2010-04-01
The aim of the paper is to study the shear wave propagation in a viscoelastic layer over a semi-infinite viscoelastic half space due to irregularity in the viscoelastic layer. It is of great interest to study the propaga-tion of shear waves in the assumed medium having a non planar boundary due to its similarity to most of the real situations. The perturbation method is applied to find the displacement field. The effect of complex wave number on dissipation factor is analysed. Finally, as an application, the result obtained has been used to get the reflected field in viscoelastic layer when the shear wave is incident on an irregular boundary in the shape of parabolic irregularity as well as triangular notch. It is observed that the amplitude of this reflected wave decreases with increasing length of the notch, and increases with increasing depth of the irregularity.
Nonlinear Viscoelastic Mechanics of Cross-linked Rubbers
Freed, Alan D.; Leonov, Arkady I.; Gray, Hugh R. (Technical Monitor)
2002-01-01
The paper develops a general theory for finite rubber viscoelasticity, and specifies it in the form, convenient for solving problems important for rubber, tire and space industries. Based on the quasi-linear approach of non-equilibrium thermodynamics, a general nonlinear theory has been developed for arbitrary nonisothermal deformations of viscoelastic solids. In this theory, the constitutive equations are presented as the sum of known equilibrium (rubber elastic) and non-equilibrium (liquid polymer viscoelastic) terms. These equations are then simplified using several modeling arguments. Stability constraints for the proposed constitutive equations are also discussed. It is shown that only strong ellipticity criteria are applicable for assessing stability of the equations governing viscoelastic solids.
Large deflection of viscoelastic beams using fractional derivative model
International Nuclear Information System (INIS)
Bahranini, Seyed Masoud Sotoodeh; Eghtesad, Mohammad; Ghavanloo, Esmaeal; Farid, Mehrdad
2013-01-01
This paper deals with large deflection of viscoelastic beams using a fractional derivative model. For this purpose, a nonlinear finite element formulation of viscoelastic beams in conjunction with the fractional derivative constitutive equations has been developed. The four-parameter fractional derivative model has been used to describe the constitutive equations. The deflected configuration for a uniform beam with different boundary conditions and loads is presented. The effect of the order of fractional derivative on the large deflection of the cantilever viscoelastic beam, is investigated after 10, 100, and 1000 hours. The main contribution of this paper is finite element implementation for nonlinear analysis of viscoelastic fractional model using the storage of both strain and stress histories. The validity of the present analysis is confirmed by comparing the results with those found in the literature.
Artificial softness sensing - an automatic apparatus for measuring viscoelasticity
Kato, I.; Kudo, Y.; Ichimaru, K.
1975-01-01
Synthetic polymer models of several degrees of softness were subjected to standard creep tests to determine their viscoelastic characteristics. The automatic measuring apparatus and the theory of measurement used in modeling the human recognition of the softness factor are described.
A K-BKZ Formulation for Soft-Tissue Viscoelasticity
Freed, Alan D.; Diethelm, Kai
2005-01-01
A viscoelastic model of the K-BKZ (Kaye 1962; Bernstein et al. 1963) type is developed for isotropic biological tissues, and applied to the fat pad of the human heel. To facilitate this pursuit, a class of elastic solids is introduced through a novel strain-energy function whose elements possess strong ellipticity, and therefore lead to stable material models. The standard fractional-order viscoelastic (FOV) solid is used to arrive at the overall elastic/viscoelastic structure of the model, while the elastic potential via the K-BKZ hypothesis is used to arrive at the tensorial structure of the model. Candidate sets of functions are proposed for the elastic and viscoelastic material functions present in the model, including a regularized fractional derivative that was determined to be the best. The Akaike information criterion (AIC) is advocated for performing multi-model inference, enabling an objective selection of the best material function from within a candidate set.
Cyclic viscoelasticity and viscoplasticity of polypropylene/clay nanocomposites
DEFF Research Database (Denmark)
Drozdov, Aleksey; Christiansen, Jesper de Claville; Hog Lejre, Anne-Lise
2012-01-01
Observations are reported in tensile relaxation tests under stretching and retraction on poly-propylene/clay nanocomposites with various contents of filler. A two-phase constitutive model is developed in cyclic viscoelasticity and viscoplasticity of hybrid nanocomposites. Adjustable parameters...
Fatigue and fracture of fibre metal laminates
Alderliesten, René
2017-01-01
This book contributes to the field of hybrid technology, describing the current state of knowledge concerning the hybrid material concept of laminated metallic and composite sheets for primary aeronautical structural applications. It is the only book to date on fatigue and fracture of fibre metal laminates (FMLs). The first section of the book provides a general background of the FML technology, highlighting the major FML types developed and studied over the past decades in conjunction with an overview of industrial developments based on filed patents. In turn, the second section discusses the mechanical response to quasi-static loading, together with the fracture phenomena during quasi-static and cyclic loading. To consider the durability aspects related to strength justification and certification of primary aircraft structures, the third section discusses thermal aspects related to FMLs and their mechanical response to various environmental and acoustic conditions.
High energy impact on woven laminates
López-Puente, J.; Zaera, R.; Navarro, C.
2003-09-01
The influence of high velocity impacts on CFRPs was studied by launching Spherical steel masses, at velocities from 60 m/s to 550 m/s, against carbon fiber/epoxy woven laminates. The extension of the damage induced in the laminate was measured by C-Scan. Finite element numerical simulation of the impact test used a failure model based on the Chang-Chang model. A comparison was made of the damaged areas resulting from non-destructive inspection of the specimens and those predicted by numerical simulation. To conclue the analysis, an analytical model developed by Cantwell-Morton was used to calculate the residual velocity of the projectile after perforation. The residual velocities predicted by numerical and by analytical models, were also compared.
Gamma-quantum channeling in laminated structures
International Nuclear Information System (INIS)
Vinetskij, V.L.; Fajngol'd, M.I.
1979-01-01
The phenomenon of the neutral particle (gamma-quanta) channeling in a laminated system (a stack of layers with different electron densities, where the corresponding refraction index serves as a potential) is considered. The examination is carried out in the framework of geometrical optics. A case is analyzed when the quantum wavelength is less than the atomic radius (lambda 0 ). It is obtained that the maximum channeling angle is independent of the period of layers and for lambda=10 -9 -10 -10 cm it amounts to 10 -4 -10 -5 . The approximation under consideration can be applied for long-period systems, particularly, for amorphous media of light atoms, periodically doped with atoms of heavier elements (laminated minerals, disordered alloys, polymers, some plastics and so on). Chenneling in similar structures made of cylindrical layers is considered [ru
Investigation of transient cavitating flow in viscoelastic pipes
International Nuclear Information System (INIS)
Keramat, A; Tijsseling, A S; Ahmadi, A
2010-01-01
A study on water hammer in viscoelastic pipes when the fluid pressure drops to liquid vapour pressure is performed. Two important concepts including column separation and the effects of retarded strains in the pipe wall on the fluid response have been investigated separately in recent works, but there is some curiosity as to how the results for pressure and discharge are when column separation occurs in a viscoelastic pipe. For pipes made of plastic such as polyethylene (PE) and polyvinyl chloride (PVC), viscoelasticity is a crucial mechanical property which changes the hydraulic and structural transient responses. Based on previous developments in the analysis of water hammer, a model which is capable of analysing column separation in viscoelastic pipes is presented and used for solving the selected case studies. For the column-separation modelling the Discrete Vapour Cavity Model (DVCM) is utilised and the viscoelasticity property of the pipe wall is modelled by Kelvin-Voigt elements. The effects of viscoelasticity play an important role in the column separation phenomenon because it changes the water hammer fundamental frequency and so affects the time of opening or collapse of the cavities. Verification of the implemented computer code is performed for the effects of viscoelasticity and column separation - separately and simultaneously - using experimental results from the literature. In the provided examples the focus is placed on the simultaneous effect of viscoelasticity and column separation on the hydraulic transient response. The final conclusions drawn are that if rectangular grids are utilised the DVCM gives acceptable predictions of the phenomenon and that the pipe wall material's retarded behaviour strongly dampens the pressure spikes caused by column separation.
Linear Viscoelasticity, Reptation, Chain Stretching and Constraint Release
DEFF Research Database (Denmark)
Neergaard, Jesper; Schieber, Jay D.; Venerus, David C.
2000-01-01
A recently proposed self-consistent reptation model - alreadysuccessful at describing highly nonlinear shearing flows of manytypes using no adjustable parameters - is used here to interpretthe linear viscoelasticity of the same entangled polystyrenesolution. Using standard techniques, a relaxation......, and that incorporation ofconstraint release leads to the observed downturn. Constraintrelease has already been shown to be important in nonlinear flowsand for polydisperse systems, but is clearly shown here to benecessary to describe the linear viscoelasticity of monodispersesystems....
Nonlinear viscoelasticity and relaxation phenomena of polymer solids
Peng, S. T. J.; Landel, R. F.; Valanis, K. C.
1977-01-01
In the light of a three-chain model of statistical network theories of rubberlike elastic models, it is assumed that the free energy function of incompressible viscoelastic polymer solids is a separable, symmetric function of the principle stretch ratios and the hidden thermodynamic coordinates along the same directions. This assumption leads to a characterization of those viscoelastic polymer solids which exhibit the property of factorizability between the time and strain functions.
Quasi-Static Viscoelasticity Loading Measurements of an Aircraft Tire
Mason, Angela J.; Tanner, John A.; Johnson, Arthur R.
1997-01-01
Stair-step loading, cyclic loading, and long-term relaxation tests were performed on an aircraft tire to observe the quasi-static viscoelastic response of the tire. The data indicate that the tire continues to respond viscoelastically even after it has been softened by deformation. Load relaxation data from the stair-step test at the 15,000-lb loading was fit to a monotonically decreasing Prony series.
The management of equine acute laminitis
Mitchell CF; Fugler LA; Eades SC
2014-01-01
Colin F Mitchell, Lee Ann Fugler, Susan C Eades Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA, USA Abstract: Laminitis is an extremely painful condition resulting in damage to the soft tissues anchoring the third phalanx to the hoof, which can result in life-threatening debilitation. Specific therapy is not available. The most important principles of therapy include aggressive nutritional and medical management of primary disease pro...
Laminated multilayer sheet structure and its utilization
International Nuclear Information System (INIS)
Chiba, K.; Itoh, K.; Mitani, Y.; Sobajima, S.; Yonemura, U.
1980-01-01
A laminated multilayer sheet structure is described comprising (A) an opaque flexible sheet layer, and (B) a flexible layer laminated on the surface of layer (A) and composed of a transparent thermic ray reflecting layer (B 1 ) bonded to a transparent synthetic resin layer (B 2 ), said layer (B 1 ) being a transparent thermic ray reflecting layer composed of (I) a layer of a metal having a thickness of about 50 to about 600 A, said metal being selected from the group consisting of gold, silver, copper, aluminum and a mixture of alloy of at least two of said metals, and (II) a high refractive substance layer having a thickness of about 50 to about 600 A, of an oxide of titanium derived from a layer of an organic titanium compound of the formula Ti 1 O/sub m/R/sub n/, where R is alkyl of 1-20 carbon atoms, l=1-30, m=4+3(1-1), and n=4+2(1-1), and containing the organic residual moiety of the organic titanium compound, the amount of said organic residual moiety being 0.1 to 30% by weight based on the weight of the high refractive substance layer; or said layer (B 1 ) being a transparent semiconductive layer having a thickness of about 500 to about 5,000 a and being composed of a compound selected from the group consisting of indium oxide, tin oxide, cadmium oxide, antimony oxide, copper iodide, and a mixture of at least two of said compounds. A method is described for heat-insulating a room, which comprises applying to the surface of a floor, wall, ceiling or partition in the room a laminated multilayer sheet structure comprising (A) an opaque flexible sheet layer, and (B) a flexible layer laminated on the surface of layer (A) and composed of a transparent thermic ray reflecting layer (B 1 ) bonded to a transparent synthetic resin layer
Zvietcovich, Fernando; Rolland, Jannick P.; Grygotis, Emma; Wayson, Sarah; Helguera, Maria; Dalecki, Diane; Parker, Kevin J.
2018-02-01
Determining the mechanical properties of tissue such as elasticity and viscosity is fundamental for better understanding and assessment of pathological and physiological processes. Dynamic optical coherence elastography uses shear/surface wave propagation to estimate frequency-dependent wave speed and Young's modulus. However, for dispersive tissues, the displacement pulse is highly damped and distorted during propagation, diminishing the effectiveness of peak tracking approaches. The majority of methods used to determine mechanical properties assume a rheological model of tissue for the calculation of viscoelastic parameters. Further, plane wave propagation is sometimes assumed which contributes to estimation errors. To overcome these limitations, we invert a general wave propagation model which incorporates (1) the initial force shape of the excitation pulse in the space-time field, (2) wave speed dispersion, (3) wave attenuation caused by the material properties of the sample, (4) wave spreading caused by the outward cylindrical propagation of the wavefronts, and (5) the rheological-independent estimation of the dispersive medium. Experiments were conducted in elastic and viscous tissue-mimicking phantoms by producing a Gaussian push using acoustic radiation force excitation, and measuring the wave propagation using a swept-source frequency domain optical coherence tomography system. Results confirm the effectiveness of the inversion method in estimating viscoelasticity in both the viscous and elastic phantoms when compared to mechanical measurements. Finally, the viscoelastic characterization of collagen hydrogels was conducted. Preliminary results indicate a relationship between collagen concentration and viscoelastic parameters which is important for tissue engineering applications.
Wolff, Hans-Michael; Irsan; Dodou, Kalliopi
2014-08-01
We aimed to investigate the effect of solubility parameter and drug concentration on the rheological behaviour of drug-in-adhesive films intended for transdermal application. Films were prepared over a range of drug concentrations (5%, 10% and 20% w/w) using ibuprofen, benzoic acid, nicotinic acid and lidocaine as model drugs in acrylic (Duro-Tak 87-4287 and Duro-Tak 87900A) or silicone (Bio-PSA 7-4301 and Bio-PSA 7-4302) pressure sensitive adhesives (PSAs). Saturation status of films was determined using light microscopy. Viscoelastic parameters were measured in rheology tests at 32°C. Subsaturated films had lower viscoelastic moduli whereas saturated films had higher moduli than the placebo films and/or a concentration-dependent increase in their modulus. Saturation concentration of each drug in the films was reflected by decreasing/increasing viscoelastic patterns. The viscoelastic windows (VWs) of the adhesive and drug-in-adhesive films clearly depicted the effect of solubility parameter differences, molar concentration of drug in the adhesive film and differences in PSA chemistry. Drug solubility parameters and molar drug concentrations have an impact on rheological patterns and thus on the adhesive performance of tested pressure sensitive adhesives intended for use in transdermal drug delivery systems. Use of the Flory equation in its limiting form was appropriate to predict drug solubility in the tested formulations.
Karikoski, N P; Horn, I; McGowan, T W; McGowan, C M
2011-10-01
Endocrinopathic causes of laminitis may be a common underlying causative pathogenesis in first-opinion or field cases presenting with laminitis, as opposed to laminitis produced in inflammatory research models. This study aimed to determine whether evidence of an underlying endocrinopathy was present in horses presented for laminitis to a first-opinion/referral veterinary teaching hospital. A second aim was to compare the signalment of horses and ponies with laminitis with the equine hospital population during the same period. All horses presenting for laminitis at Helsinki University Equine Teaching Hospital, Finland, over a 16-month period were examined for an underlying endocrinopathy. Horses presenting for laminitis were compared with the hospitalized population over the same period. There were 36 horses presented for laminitis, and evidence of endocrinopathy was present in 89%. Of the horses showing an underlying endocrinopathy, one-third had a diagnosis of pituitary pars intermedia dysfunction, and two-thirds showed basal hyperinsulinemia indicative of insulin resistance, without evidence of hirsutism. Phenotypic indicators of obesity were present in 95% of horses with basal hyperinsulinemia without hirsutism. Compared with the hospital population during the same period, horses with laminitis associated with an underlying endocrinopathy were significantly older and more likely to be pony breeds. Our data support that endocrine testing should be performed on all cases of laminitis that do not have a clear inflammatory or gastrointestinal origin. Copyright © 2011 Elsevier Inc. All rights reserved.
Numerical analysis of laminated elastomer by FEM
International Nuclear Information System (INIS)
Mazda, T.; Shiojiri, H.
1993-01-01
A Computer code based on mixed finite element method was developed for three dimensional large strain analyses of laminated elastomers including nonlinear bulk stress vs. bulk strain relationships. The adopted element is the variable node element with maximum node numbers of 27 for displacements and 4 for pressures. At first, the displacements and pressures were calculated by the code using single element under various loading conditions. The results were compared with theoretical solutions and the both results' exactly coincided with each other. Next, the analyses of laminated elastomers subjected to axial loadings were conducted using both the new code and ABAQUS code, and the results were compared with the test results. The agreement of the results of the present code were better than ABAQUS code mainly due to the capability of handling wider range of material properties. Lastly, the shearing tests of laminated elastomers were simulated by the new code. The results were shown to be in good agreement with the test results. (author)
Peeling stress analysis of piezo-bonded laminated composite plate
Huang, Bin; Kim, Heung Soo
2012-04-01
A stress function based method is proposed to analyze the interlaminar stresses at the free edge of a piezo-bonded composite laminated structure. Two piezoelectric actuators are symmetrically surface bonded on composite laminate. Same electric fields are applied to the two symmetric piezoelectric actuators which can generate induced strain, resulting in pure extension on the laminated plate. The stresses that satisfy the traction-free boundary conditions at the free edge and at the top and bottom surfaces of the laminate were obtained by using the complementary virtual work principle. Cross-ply and angle-ply laminates were analyzed. To verify the proposed method, the stress concentrations predicted by the present method were compared with those analyzed by the finite element method. The results provided that the stress function based analysis of piezo-bonded laminated composite structure is an efficient and accurate method for initial design stage of piezo-composite structure.
Peter, Annette; Khandekar, Shaunak; Deakin, Janine E; Stick, Reimer
2015-11-01
Platypus (Ornithorhynchus anatinus) holds a unique phylogenetic position at the base of the mammalian lineage due to an amalgamation of mammalian and sauropsid-like features. Here we describe the set of four lamin genes for platypus. Lamins are major components of the nuclear lamina, which constitutes a main component of the nucleoskeleton and is involved in a wide range of nuclear functions. Vertebrate evolution was accompanied by an increase in the number of lamin genes from a single gene in their closest relatives, the tunicates and cephalochordates, to four genes in the vertebrate lineage. Of the four genes the LIII gene is characterized by the presence of two alternatively spliced CaaX-encoding exons. In amphibians and fish LIII is the major lamin protein in oocytes and early embryos. The LIII gene is conserved throughout the vertebrate lineage, with the notable exception of marsupials and placental mammals, which have lost the LIII gene. Here we show that platypus has retained an LIII gene, albeit with a significantly altered structure and with a radically different expression pattern. The platypus LIII gene contains only a single CaaX-encoding exon and the head domain together with coil 1a and part of coil1b of the platypus LIII protein is replaced by a novel short non-helical N-terminus. It is expressed exclusively in the testis. These features resemble those of male germ cell-specific lamins in placental mammals, in particular those of lamin C2. Our data suggest (i) that the specific functions of LIII, which it fulfills in all other vertebrates, is no longer required in mammals and (ii) once it had been freed from these functions has undergone structural alterations and has adopted a new functionality in monotremes. Copyright © 2015 Elsevier GmbH. All rights reserved.
Bayesian inference model for fatigue life of laminated composites
DEFF Research Database (Denmark)
Dimitrov, Nikolay Krasimirov; Kiureghian, Armen Der; Berggreen, Christian
2016-01-01
A probabilistic model for estimating the fatigue life of laminated composite plates is developed. The model is based on lamina-level input data, making it possible to predict fatigue properties for a wide range of laminate configurations. Model parameters are estimated by Bayesian inference....... The reference data used consists of constant-amplitude cycle test results for four laminates with different layup configurations. The paper describes the modeling techniques and the parameter estimation procedure, supported by an illustrative application....
Arteriographical and pathological changes in chronic laminitis in dairy cattle.
Boosman, R; Nemeth, F; Gruys, E; Klarenbeek, A
1989-07-01
The arteriographic appearance of 76 bovine hind digits, obtained from a slaughterhouse, was related to the macroscopic signs of chronic laminitis in the digits. There were statistically significant correlations between the macroscopic and the arteriographic appearance of the claws. Subsequent histological examination of the radiographically abnormal arteries revealed features indicative of arteriosclerosis. The results of this study indicate that chronic laminitis develops following a subclinical attack of laminitis due to a continous hypoperfusion of the digit.
Energy Saving Glass Lamination via Selective Radio-Frequency Heating
Energy Technology Data Exchange (ETDEWEB)
Shulman, Holly S.; Allan, Shawn M.
2009-11-11
This Inventions and Innovations program supported the technical and commercial research and development needed to elevate Ceralink's energy saving process for flat glass lamination from bench scale to a self-supporting technology with significant potential for growth. Radio-frequency heating was any un-explored option for laminating glass prior to this program. With significant commercial success through time and energy savings in the wood, paper, and plastics industries, RF heating was found to have significant promise for the energy intensive glass lamination industry. A major technical goal of the program was to demonstrate RF lamination across a wide range of laminate sizes and materials. This was successfully accomplished, dispelling many skeptics' concerns about the abilities of the technology. Ceralink laminated panels up to 2 ft x 3 ft, with four sets processed simultaneously, in a 3 minute cycle. All major categories of interlayer materials were found to work with RF lamination. In addition to laminating glass, other materials including photovoltaic silicon solar cells, light emitting diodes, metallized glass, plastics (acrylic and polycarbonate), and ceramics (alumina) were found compatible with the RF process. This opens up a wide range of commercial opportunities beyond the initially targeted automotive industry. The dramatic energy savings reported for RF lamination at the bench scale were found to be maintained through the scale up of the process. Even at 2 ft x 3 ft panel sizes, energy savings are estimated to be at least 90% compared to autoclaving or vacuum lamination. With targeted promotion through conference presentations, press releases and internet presence, RF lamination has gained significant attention, drawing large audiences at American Ceramic Society meetings. The commercialization success of the project includes the establishment of a revenue-generating business model for providing process development and demonstrations for
Energy Saving Glass Lamination via Selective Radio Frequency Heating
Energy Technology Data Exchange (ETDEWEB)
Allan, Shawn M.
2012-02-27
This project focused on advancing radio-frequency (RF) lamination technology closer to commercial implementation, in order to reduce the energy intensity of glass lamination by up to 90%. Lamination comprises a wide range of products including autoglass, architectural safety and innovative design glass, transparent armor (e.g. bullet proof glass), smart glass, mirrors, and encapsulation of photovoltaics. Lamination is also the fastest growing segment of glass manufacturing, with photovoltaics, architectural needs, and an anticipated transition to laminated side windows in vehicles. The state-of-the-art for glass lamination is to use autoclaves, which apply heat and uniform gas pressure to bond the laminates over the course of 1 to 18 hours. Laminates consist of layers of glass or other materials bonded with vinyl or urethane interlayers. In autoclaving, significant heat energy is lost heating the chamber, pressurized air, glass racks, and the glass. In RF lamination, the heat is generated directly in the vinyl interlayer, causing it to heat and melt quickly, in just 1 to 10 minutes, without significantly heating the glass or the equipment. The main purpose of this project was to provide evidence that low energy, rapid RF lamination quality met the same standards as conventionally autoclaved windows. The development of concepts for laminating curved glass with RF lamination was a major goal. Other primary goals included developing a stronger understanding of the lamination product markets described above, and to refine the potential benefits of commercial implementation. The scope of the project was to complete implementation concept studies in preparation for continuation into advanced development, pilot studies, and commercial implementation. The project consisted of 6 main tasks. The first dealt with lamination with poly-vinyl butyral (PVB) interlayers, which prior work had shown difficulties in achieving good quality laminates, working with Pilkington North
Energy Saving Glass Lamination via Selective Radio Frequency Heating
Energy Technology Data Exchange (ETDEWEB)
Allan, Shawn M; Baranova, Inessa; Poley, Joseph; Reis, Henrique
2012-02-27
This project focused on advancing radio-frequency (RF) lamination technology closer to commercial implementation, in order to reduce the energy intensity of glass lamination by up to 90%. Lamination comprises a wide range of products including autoglass, architectural safety and innovative design glass, transparent armor (e.g. bullet proof glass), smart glass, mirrors, and encapsulation of photovoltaics. Lamination is also the fastest growing segment of glass manufacturing, with photovoltaics, architectural needs, and an anticipated transition to laminated side windows in vehicles. The state-of-the-art for glass lamination is to use autoclaves, which apply heat and uniform gas pressure to bond the laminates over the course of 1 to 18 hours. Laminates consist of layers of glass or other materials bonded with vinyl or urethane interlayers. In autoclaving, significant heat energy is lost heating the chamber, pressurized air, glass racks, and the glass. In RF lamination, the heat is generated directly in the vinyl interlayer, causing it to heat and melt quickly, in just 1 to 10 minutes, without significantly heating the glass or the equipment. The main purpose of this project was to provide evidence that low energy, rapid RF lamination quality met the same standards as conventionally autoclaved windows. The development of concepts for laminating curved glass with RF lamination was a major goal. Other primary goals included developing a stronger understanding of the lamination product markets described above, and to refine the potential benefits of commercial implementation. The scope of the project was to complete implementation concept studies in preparation for continuation into advanced development, pilot studies, and commercial implementation. The project consisted of 6 main tasks. The first dealt with lamination with poly-vinyl butyral (PVB) interlayers, which prior work had shown difficulties in achieving good quality laminates, working with Pilkington North
The characterization of Mode I delamination failure in non-woven, multidirectional laminates
Chai, H.
1984-01-01
The uniform double cantilever beam test and SEM are presently used for the characterization of Mode I delamination behavior in fiber-reinforced epoxy laminates. Delamination failure assumes forms that depend on ply orientation, test specimen geometry, and matrix toughness, but the calculated fracture energy is noted to be heavily dependent on fracture surface morphology. A material property concept that is independent of both test specimen geometry and the orientation of the plies constituting the delaminating interface is elucidated, through the definition of interlaminar fracture solely in terms of an interlaminar separation that includes no fiber breakage or pull-out. This value, which dissipates the lowest possible amount of energy during crack growth, is the controlling factor for laminate toughness.
Boek, E. S.; Jusufi, A.; Löwen, H.; Maitland, G. C.
2002-10-01
Understanding how macroscopic properties depend on intermolecular interactions for complex fluid systems is an enormous challenge in statistical mechanics. This issue is of particular importance for designing optimal industrial fluid formulations such as responsive oilfield fluids, based on viscoelastic surfactant solutions. We have carried out extensive molecular dynamics simulations, resolving the full chemical details in order to study how the structure of the lamellar phase of viscoelastic surfactant solutions depends on the head group (HG) chemistry of the surfactant. In particular, we consider anionic carboxylate and quaternary ammonium HGs with erucyl tails in aqueous solutions together with their sodium and chloride counterions at room temperature. We find a strong HG dependence of the lamellar structure as characterized by suitable pair correlation functions and density distributions. The depth of penetration of water into the bilayer membrane, the nature of counterion condensation on the HGs and even the order and correlation of the tails in the lamellae depend sensitively on the chemical details of the HG. We also determine the compressibility of the lamellar system as a first step to using atom-resolved molecular dynamics in order to link the molecular and macroscopic scales of length and time. The results give important insight into the links between molecular details and surfactant phase structure which is being exploited to develop more systematic procedures for the molecular design and formulation of industrial systems.
Energy Technology Data Exchange (ETDEWEB)
Goyal, T. [Indian Institute of Technology Kanpur. Dept. of Aerospace Engineering, UP (India); Gupta, R. [Infotech Enterprises Ltd., Hyderabad (India)
2012-07-01
In this work, minimum weight-cost design for laminated composites is presented. A genetic algorithm has been developed for the optimization process. Maximum-Stress, Tsai-Wu and Tsai-Hill failure criteria have been used along with buckling analysis parameter for the margin of safety calculations. The design variables include three materials; namely Carbon-Epoxy, Glass-Epoxy, Kevlar-Epoxy; number of plies; ply orientation angles, varying from -75 deg. to 90 deg. in the intervals of 15 deg. and ply thicknesses which depend on the material in use. The total cost is a sum of material cost and layup cost. Layup cost is a function of the ply angle. Validation studies for solution convergence and weight-cost inverse proportionality are carried out. One set of results for shear loading are also validated from literature for a particular case. A Pareto-Optimal solution set is demonstrated for biaxial loading conditions. It is then extended to applied moments. It is found that global optimum for a given loading condition is a function of the failure criteria for shear loading, with Maximum Stress criteria giving the lightest-cheapest and Tsai-Wu criteria giving the heaviest-costliest optimized laminates. Optimized weight results are plotted from the three criteria to do a comparative study. This work gives a global optimized laminated composite and also a set of other local optimum laminates for a given set of loading conditions. The current algorithm also provides with adequate data to supplement the use of different failure criteria for varying loadings. This work can find use in the industry and/or academia considering the increased use of laminated composites in modern wind blades. (Author)
Characterization of Contact and Bulk Thermal Resistance of Laminations for Electric Machines
Energy Technology Data Exchange (ETDEWEB)
Cousineau, J. Emily [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Bennion, Kevin [National Renewable Energy Laboratory (NREL), Golden, CO (United States); DeVoto, Doug [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Mihalic, Mark [National Renewable Energy Laboratory (NREL), Golden, CO (United States); Narumanchi, Sreekant [National Renewable Energy Laboratory (NREL), Golden, CO (United States)
2015-06-30
The ability to remove heat from an electric machine depends on the passive stack thermal resistances within the machine and the convective cooling performance of the selected cooling technology. This report focuses on the passive thermal design, specifically properties of the stator and rotor lamination stacks. Orthotropic thermal conductivity, specific heat, and density are reported. Four materials commonly used in electric machines were tested, including M19 (29 and 26 gauge), HF10, and Arnon 7 materials.
Viscoelastic and fatigue properties of model methacrylate-based dentin adhesives
Singh, Viraj; Misra, Anil; Marangos, Orestes; Park, Jonggu; Ye, Qiang; Kieweg, Sarah L.; Spencer, Paulette
2010-01-01
The objective of the current study is to characterize the viscoelastic and fatigue properties of model methacrylate-based dentin adhesives under dry and wet conditions. Static, creep, and fatigue tests were performed on cylindrical samples in a 3-point bending clamp. Static results showed that the apparent elastic modulus of the model adhesive varied from 2.56 to 3.53 GPa in the dry condition, and from 1.04 to 1.62 GPa in the wet condition, depending upon the rate of loading. Significant diff...
DEFF Research Database (Denmark)
Ojanen, X.; Tanska, P.; Malo, M. K.H.
2017-01-01
Trabecular bone is viscoelastic under dynamic loading. However, it is unclear how tissue viscoelasticity controls viscoelasticity at the apparent-level. In this study, viscoelasticity of cylindrical human trabecular bone samples (n = 11, male, age 18–78 years) from 11 proximal femurs were......, utilizing the second order Prony series to depict viscoelasticity. FE simulations showed that tissue-level equilibrium elastic modulus (Eeq) increased with increasing crystallinity (r = 0.730, p =.011) while at the apparent-level it increased with increasing hydroxylysyl pyridinoline content (r = 0.718, p...... or simulated viscoelastic parameters at the tissue- and apparent-levels nor were the parameters related to tissue elasticity determined with SAM. However, only Eeq, g2 and relaxation time τ1 from simulated viscoelastic values were statistically different between tissue- and apparent-levels (p
Fibre-Metal Laminated Materials
Directory of Open Access Journals (Sweden)
Cristina Alia
2013-01-01
Full Text Available The adhesives used for applications in marine environments are subject to particular chemical conditions, which are mainly characterised by an elevated chlorine ion content and intermittent wetting/drying cycles, among others. These conditions can limit the use of adhesives due to the degradation processes that they experience. In this work, the chemical degradation of two different polymers, polyurethane and vinylester, was studied in natural seawater under immersion for different periods of time. The diffusion coefficients and concentration profiles of water throughout the thickness of the adhesives were obtained. Microstructural changes in the polymer due to the action of water were observed by SEM, and the chemical degradation of the polymer was monitored with the Fourier transform infrared spectroscopy (FTIR and differential scanning calorimetry (DSC. The degradation of the mechanical properties of the adhesive was determined by creep tests with Mixed Cantilever Beam (MCB specimens at different temperatures. After 180 days of immersion of the specimens, it was concluded that the J-integral value (depending on the strain implies a loss of stiffness of 51% and a decrease in the failure load of 59% for the adhesive tested.
Pettermann, Heinz E.; DeSimone, Antonio
2017-09-01
A constitutive material law for linear thermo-viscoelasticity in the time domain is presented. The time-dependent relaxation formulation is given for full anisotropy, i.e., both the elastic and the viscous properties are anisotropic. Thereby, each element of the relaxation tensor is described by its own and independent Prony series expansion. Exceeding common viscoelasticity, time-dependent thermal expansion relaxation/creep is treated as inherent material behavior. The pertinent equations are derived and an incremental, implicit time integration scheme is presented. The developments are implemented into an implicit FEM software for orthotropic material symmetry under plane stress assumption. Even if this is a reduced problem, all essential features are present and allow for the entire verification and validation of the approach. Various simulations on isotropic and orthotropic problems are carried out to demonstrate the material behavior under investigation.
Schäpe, Jens; Prausse, Steffi; Radmacher, Manfred; Stick, Reimer
2009-05-20
The nuclear lamina is part of the nuclear envelope (NE). Lamin filaments provide the nucleus with mechanical stability and are involved in many nuclear activities. The functional importance of these proteins is highlighted by mutations in lamin genes, which cause a variety of human diseases (laminopathies). Here we describe a method that allows one to quantify the contribution of lamin A protein to the mechanical properties of the NE. Lamin A is ectopically expressed in Xenopus oocytes, where it is incorporated into the NE of the oocyte nucleus, giving rise to a prominent lamina layer at the inner nuclear membrane. Nuclei are then isolated and probed by atomic force microscopy. From the resulting force curves, stiffness values are calculated and compared with those of control nuclei. Expression of lamin A significantly increases the stiffness of oocyte nuclei in a concentration-dependent manner. Since chromatin adds negligibly to nuclear mechanics in these giant nuclei, this method allows one to measure the contribution of individual NE components to nuclear mechanics.
Directory of Open Access Journals (Sweden)
Shepherd Duncan ET
2009-06-01
Full Text Available Abstract Background Articular cartilage is a viscoelastic material, but its exact behaviour under the full range of physiological loading frequencies is unknown. The objective of this study was to measure the viscoelastic properties of bovine articular cartilage at loading frequencies of up to 92 Hz. Methods Intact tibial plateau cartilage, attached to subchondral bone, was investigated by dynamic mechanical analysis (DMA. A sinusoidally varying compressive force of between 16 N and 36 N, at frequencies from 1 Hz to 92 Hz, was applied to the cartilage surface by a flat indenter. The storage modulus, loss modulus and phase angle (between the applied force and the deformation induced were determined. Results The storage modulus, E', increased with increasing frequency, but at higher frequencies it tended towards a constant value. Its dependence on frequency, f, could be represented by, E' = Aloge (f + B where A = 2.5 ± 0.6 MPa and B = 50.1 ± 12.5 MPa (mean ± standard error. The values of the loss modulus (4.8 ± 1.0 MPa mean ± standard deviation were much less than the values of storage modulus and showed no dependence on frequency. The phase angle was found to be non-zero for all frequencies tested (4.9 ± 0.6°. Conclusion Articular cartilage is viscoelastic throughout the full range of frequencies investigated. The behaviour has implications for mechanical damage to articular cartilage and the onset of osteoarthritis. Storage modulus increases with frequency, until the plateau region is reached, and has a higher value than loss modulus. Furthermore, loss modulus does not increase with loading frequency. This means that more energy is stored by the tissue than is dissipated and that this effect is greater at higher frequencies. The main mechanism for this excess energy to be dissipated is by the formation of cracks.
The ultratough peeling of elastic tapes from viscoelastic substrates
Afferrante, L.; Carbone, G.
2016-11-01
The peeling of an elastic thin tape from a flat smooth viscoelastic substrate is investigated. Based on a Green function approach and on the translational invariance, a closed form analytical solution is proposed, which takes into account the viscoelastic dissipation in the substrate material. We find that peeling is prevented from taking place, only when the external force is smaller than the one predicted by Kendall's formula for elastic tapes on rigid substrates. However, we also find that, regardless of the value of the applied force, steady state detachment may occur when the elastic tape is sufficiently stiff. In this case, the constant peeling velocity can be modulated by properly defining the geometrical parameters and the material properties of tape and viscoelastic foundation. On the other hand, for relatively high peeling angles or compliant tapes a threshold value of the peeling force is found, above which the steady-state equilibrium is no longer possible and unstable detachment occurs. The present study contributes to shed light on the behavior of pressure sensitive adhesives in contact with viscoelastic substrates like the human skin. At the same time, it can be considered a first step towards a better understanding of the effect of viscoelastic dissipation on the fracture behavior of solids.
Laminitis subclínica en bovinos
Franco, M. S.; Oliver, O. J.
2012-01-01
La laminitis subclínica es una entidad multifactorial que afecta a los bovinos especialmente en el periodo del periparto. Se caracteriza por la coloración amarilla de la suela, hemorragias de la suela, separación de la línea blanca y erosiones de talón. Se considera que es el mayor factor predisponente para la presentación de cojeras de pezuña a causa del debilitamiento del tejido corneo de la misma, lo que comrpromete el bienestar del animal y acarrea perdidas económicas directas e indirecta...
DEFF Research Database (Denmark)
Wu, Zhigang; Hjort, Klas; Wicher, Grzegorz
2008-01-01
A high viability microfluidic cell separation technique of high throughput was demonstrated based on size difference continuous mode hydrodynamic spreading with viscoelastic tuning. Using water with fluorescent dye as sample fluid and in parallel introducing as elution a viscoelastic biocompatibl...
Viscoelastic and thermal properties of woven sisal fabric reinforced natural rubber biocomposites
CSIR Research Space (South Africa)
John, MJ
2009-01-01
Full Text Available on the viscoelastic properties of the textile composites has also been examined. An investigation into the viscoelastic properties with thermal resistance and morphology of woven sisal fabric reinforced natural rubber composites is presented. The damping factor...
A MEMS lamination technology based on sequential multilayer electrodeposition
International Nuclear Information System (INIS)
Kim, Minsoo; Kim, Jooncheol; Herrault, Florian; Schafer, Richard; Allen, Mark G
2013-01-01
A MEMS lamination technology based on sequential multilayer electrodeposition is presented. The process comprises three main steps: (1) automated sequential electrodeposition of permalloy (Ni 80 Fe 20 ) structural and copper sacrificial layers to form multilayer structures of significant total thickness; (2) fabrication of polymeric anchor structures through the thickness of the multilayer structures and (3) selective removal of copper. The resulting structure is a set of air-insulated permalloy laminations, the separation of which is sustained by insulating polymeric anchor structures. Individual laminations have precisely controllable thicknesses ranging from 500 nm to 5 µm, and each lamination layer is electrically isolated from adjacent layers by narrow air gaps of similar scale. In addition to air, interlamination insulators based on polymers are investigated. Interlamination air gaps with very high aspect ratio (>1:100) can be filled with polyvinylalcohol and polydimethylsiloxane. The laminated structures are characterized using scanning electron microscopy and atomic force microscopy to directly examine properties such as the roughness and the thickness uniformity of the layers. In addition, the quality of the electrical insulation between the laminations is evaluated by quantifying the eddy current within the sample as a function of frequency. Fabricated laminations are comprised of uniform, smooth (surface roughness <100 nm) layers with effective electrical insulation for all layer thicknesses and insulator approaches studied. Such highly laminated structures have potential uses ranging from energy conversion to applications where composite materials with highly anisotropic mechanical or thermal properties are required. (paper)
Lateral testing of glued laminated timber tudor arch
Douglas R. Rammer; Philip Line
2016-01-01
Glued laminated timber Tudor arches have been in wide use in the United States since the 1930s, but detailed knowledge related to seismic design in modern U.S. building codes is lacking. FEMA P-695 (P-695) is a methodology to determine seismic performance factors for a seismic force resisting system. A limited P-695 study for glued laminated timber arch structures...
Three-dimensional free vibration analysis of thick laminated circular ...
African Journals Online (AJOL)
Dr Oke
Laminated circular plates are commonly used structural component having a broad application in aerospace, civil, mechanical, nuclear, electronic as well as marine ..... sufficient to obtain satisfactory convergence for first five frequency parameters of glass/epoxy laminated circular plates. It is seen that the first axisymmetric ...
Morphing of Bistable Composite Laminates Using Distributed Piezoelectric Actuators
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Marie-Laure Dano
2012-01-01
Full Text Available The use of bistable unsymmetric cross-ply laminates for morphing application has received growing attention in the last few years. So far, most studies use large rectangular piezoelectric Macro Fiber Composite (MFC patches bonded at the center of the laminate to induce snap-through. However, the use of large rectangular MFC patches bonded in the center of the laminates significantly influences the shape of the laminate by greatly reducing the curvature at the midsection of the laminate where the MFC patches are bonded. This paper presents a study where narrow cocured MFC strips distributed over the entire surface are used to induce snap-through of unsymmetric cross-ply laminates. This MFC configuration allows having a more uniform curvature in the laminate. Since the strips are bonded on both sides, reverse snap-through should be obtained. The study was both theoretical and experimental. A finite element nonlinear analysis was used to predict the two stable cylindrical configurations and the snap-through induced by MFC actuation. For the experimental study, a laminate-MFC structure was manufactured and tested. The shapes were measured using a 3D image correlation system as a function of applied voltage. Good correlations for the cylindrical shape and displacement field were observed.
Optimum design of laminated composite under axial compressive load
Indian Academy of Sciences (India)
In the present study optimal design of composite laminates, with and without rectangular cut-out, is carried out for maximizing the buckling load. Optimization study is carried out for obtaining the maximum buckling load with design variables as ply thickness, cut-out size and orientation of cut-out with respect to laminate.
Hole-thru-laminate mounting supports for photovoltaic modules
Wexler, Jason; Botkin, Jonathan; Culligan, Matthew; Detrick, Adam
2015-02-17
A mounting support for a photovoltaic module is described. The mounting support includes a pedestal having a surface adaptable to receive a flat side of a photovoltaic module laminate. A hole is disposed in the pedestal, the hole adaptable to receive a bolt or a pin used to couple the pedestal to the flat side of the photovoltaic module laminate.
Thickness effect in composite laminates in static and fatigue loading
Lahuerta Calahorra, F.
2017-01-01
Thick Laminates (above 6mm) are increasingly present in large composites structures such as wind turbine blades. Designs are based on static and fatigue coupon tests performed on 1-4mm thin laminates. However, a thickness effect has been observed in limited available experimental data. For this
Three-dimensional free vibration analysis of thick laminated circular ...
African Journals Online (AJOL)
Three-dimensional free vibration analysis of thick laminated circular plates. Sumit Khare, N.D. Mittal. Abstract. In this communication, a numerical analysis regarding free vibration of thick laminated circular plates, having free, clamped as well as simply-supported boundary conditions at outer edges of plates is presented.
Lamins, laminopathies and disease mechanisms: Possible role for ...
Indian Academy of Sciences (India)
2011-07-08
Jul 8, 2011 ... Lamins are major structural proteins of the nucleus and are essential for nuclear integrity and organization of nuclear functions. Mutations in the human lamin genes lead to highly degenerative genetic diseases that affect a number of different tissues such as muscle, adipose or neuronal tissues, or cause ...
Lamins, laminopathies and disease mechanisms: Possible role for ...
Indian Academy of Sciences (India)
Lamins are major structural proteins of the nucleus and are essential for nuclear integrity and organization of nuclear functions. Mutations in the human lamin genes lead to highly degenerative genetic diseases that affect a number of different tissues such as muscle, adipose or neuronal tissues, or cause premature ageing ...
Experimental and numerical analysis of thick embedded laminated glass connections
Santarsiero, Manuel; Bedon, Chiara; Louter, P.C.
2018-01-01
Laminated glass components are usually realized by bonding glass plates using interlayer polymers that develop adhesion forces during lamination. Recently, these adhesion forces have been used also to realize special adhesive connections for structural glass components and assemblies. The typical
Does oral prednisolone treatment increase the incidence of acute laminitis?
Jordan, V J; Ireland, J L; Rendle, D I
2017-01-01
It is accepted among equine practitioners that glucocorticoid treatment is a risk factor for the development of laminitis. However, there is little published evidence of a link between glucocorticoids and laminitis. To determine whether horses receiving oral prednisolone are at increased risk of laminitis. Retrospective case-control study. Clinical records of horses registered with the ambulatory service at Liphook Equine Hospital between January 2001 and November 2014 were reviewed retrospectively to identify horses that had received treatment with oral prednisolone. For each treated horse, 2 time-matched controls that received veterinary attention but were not treated with prednisolone were selected. Incidence of laminitis was compared between the 2 groups and factors associated with laminitis were assessed using Cox regression analysis. Of the 416 horses treated with prednisolone, 16 (3.8%) were diagnosed with laminitis subsequent to the initiation of prednisolone treatment with an overall incidence of 2.60 (95% CI 1.49-4.22) cases per 100 horse-years at risk. A total of 7 horses (1.7%) developed laminitis during the course of their treatment and 3 (0.7%) of the horses treated with prednisolone were ultimately subjected to euthanasia as a result of laminitis. A total of 46 (5.7%), of the 814 time-matched control horses were diagnosed with laminitis during the study period with an overall incidence of 3.46 (95% CI 2.54-4.62) cases per 100 horse-years at risk. Of these, 12 (1.5%) were subjected to euthanasia as a result of laminitis. There were no significant differences in the overall laminitis incidence rate (P = 0.8), incidence rate during prednisolone treatment (P = 0.09), or probability of laminitis (P = 0.3) between the 2 groups. Mean survival time was greater in the prednisolone than the control group. Equine metabolic syndrome and increasing age were associated with increased risk of laminitis. Administration of oral prednisolone did not increase the risk
VARIATIONALLY-BASED EFFECTIVE DYNAMIC THICKNESS FOR LAMINATED GLASS BEAMS
Directory of Open Access Journals (Sweden)
Jaroslav Schmidt
2017-11-01
Full Text Available Laminated glass, consisting of glass layers connected with transparent foils, has found its applications in civil, automotive, or marine engineering. Due to a high contrast in layer properties, mechanical response of laminated glass structures cannot be predicted using classical laminate theories. On the other hand, engineering applications demand easy-to-use formulas of acceptable accuracy. This contribution addresses such simplified models for free vibrations of laminated glass beams, with the goal to determine their natural frequencies and modal damping properties. Our strategy is to approximate the complex behavior of a laminated structure with that of an equivalent monolithic beam. Its effective thickness is determined by the variational method proposed by Galuppi and Royer-Carfagni for static problems, which we extended for modal analysis. We show that this new approach overcomes inaccuracies of the currently used dynamic effective thickness model by López-Aenlle and Pelayo.
Fatigue Performance of Composite Laminates After Low-velocity Impact
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LIANG Xiao-lin
2016-12-01
Full Text Available Compression-compression fatigue tests were carried out on T300/5405 composite laminates after low-velocity impact, compression performance of the laminates with different impact damages was studied together with its fatigue life and damage propagation under different stress levels, then the effects of impact energy, stress level and damage propagation on fatigue life of laminates were discussed. The results indicate that impact damage can greatly reduce the residual strength of laminates; under low fatigue load levels, the higher impact energy is, the shorter the fatigue life of laminates with impact damage will be; damage propagation undergoes two stages during the fatigue test, namely the steady propagation and the rapid propagation, accounting for 80% and 20% of the overall fatigue life, respectively; damage propagation rate decreases with the reduction of stress level.
The mechanical behavior of GLARE laminates for aircraft structures
Wu, Guocai; Yang, J.-M.
2005-01-01
GLARE (glass-reinforced aluminum laminate) is a new class of fiber metal laminates for advanced aerospace structural applications. It consists of thin aluminum sheets bonded together with unidirectional or biaxially reinforced adhesive prepreg of high-strength glass fibers. GLARE laminates offer a unique combination of properties such as outstanding fatigue resistance, high specific static properties, excellent impact resistance, good residual and blunt notch strength, flame resistance and corrosion properties, and ease of manufacture and repair. GLARE laminates can be tailored to suit a wide variety of applications by varying the fiber/resin system, the alloy type and thickness, stacking sequence, fiber orientation, surface pretreatment technique, etc. This article presents a comprehensive overview of the mechanical properties of various GLARE laminates under different loading conditions.
Modeling viscoelastic flow in a multiflux static mixer
Köpplmayr, T.; Miethlinger, J.
2014-05-01
We present a numerical and experimental study of the polymer flow in a multiflux static mixer. Various geometrical configurations are compared in terms of layer homogeneity. To evaluate the layer-forming process in different geometries, we applied a general and precise approach based on trajectory calculations for a large set of material points, followed by a statistical analysis. A simulation of viscous flow using the Carreau-Yasuda constitutive equation produced results which deviated from our experimental findings. Therefore, we used the Giesekus constitutive equation, taking into account viscoelastic effects, such as extrudate swell and secondary motions inside the mixer. Parallel plate rheometry was employed to collect dynamic mechanical data in the linear viscoelastic flow regime. Weissenberg numbers were calculated, and the maximum relaxation time in the obtained spectrum was limited to avoid divergence issues. The results of our study provide deeper insights into the layerforming process of viscoelastic melts in a multiflux static mixer.
Design of a rotary passive viscoelastic joint for wearable robots.
Carpino, Giorgio; Accoto, Dino; Di Palo, Michelangelo; Tagliamonte, Nevio Luigi; Sergi, Fabrizio; Guglielmelli, Eugenio
2011-01-01
In the design of wearable robots that strictly interact with the human body and, in general, in any robotics application that involves the human component, the possibility of having modular joints able to produce a viscoelastic behaviour is very useful to achieve an efficient and safe human-robot interaction and to give rise to emergent dynamical behaviors. In this paper we propose the design of a compact, passive, rotary viscoelastic joint for assistive wearable robotics applications. The system integrates two functionally distinct sub-modules: one to render a desired torsional stiffness profile and the other to provide a desired torsional damping. Concepts and design choices regarding the overall architecture and the single components are presented and discussed. A viscoelastic model of the system has been developed and the design of the joint is presented. © 2011 IEEE
Viscoelastic Plate Analysis Based on Gâteaux Differential
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Kadıoğlu Fethi
2016-01-01
Full Text Available In this study, it is aimed to analyze the quasi-static response of viscoelastic Kirchhoff plates with mixed finite element formulation based on the Gâteaux differential. Although the static response of elastic plate, beam and shell structures is a widely studied topic, there are few studies that exist in the literature pertaining to the analysis of the viscoelastic structural elements especially with complex geometries, loading conditions and constitutive relations. The developed mixed finite element model in transformed Laplace-Carson space has four unknowns as displacement, bending and twisting moments in addition to the dynamic and geometric boundary condition terms. Four-parameter solid model is employed for modelling the viscoelastic behaviour. For transformation of the solutions obtained in the Laplace-Carson domain to the time domain, different numerical inverse transform techniques are employed. The developed solution technique is applied to several quasi-static example problems for the verification of the suggested numerical procedure.
Experimental and numerical evaluation of viscoelastic sandwich beams
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Waldir Neme Felippe Filho
Full Text Available Abstract Viscoelastic materials can dissipate a large amount of energy when subjected to cyclic shear deformations, but they have low bearing capacity. Therefore they are often employed as a damping layer in sandwich structures. These sandwich structures present a high damping ratio and simple application. In order to design sandwich structures, many aspects ranging from computer modeling to laboratory testing should be considered. In this study, a test set of experiments were performed and results are compared with a numerical GHM (Golla, Hughes and Mc Tavish method based model, in order to establish a method to support viscoelastic sandwich beam design. In this way, starting from the dynamic properties of a viscoelastic material, a numerical model is used to evaluate the behavior of these structures. Comparisons with uncontrolled structures are also presented, showing the dissipative characteristics of this passive control.
Seismic mitigation of structures by using viscoelastic dampers
International Nuclear Information System (INIS)
Li, W.Q.; Tsai, C.S.
1994-01-01
In this paper, the characteristics of energy-absorbing capacities of the viscoelastic damper and its applications to the seismic mitigation of structures during earthquakes are studied. An innovative analystica model for the viscoelastic damper accounting for the earthquake-like and wind-like loadings and temperature effects, in good agreement with experimental results, and finite element formulations for the viscoelastic damper are presented. The applications of proposed methodology to a structure incoporating visoelastic dampers is examined while subjected to horizontal and vertical earthquake ground motions. Numerical results show that the responses of the structure equipped with added dampers to earthquake loadings are significantly reduced. The same concept can also be applied to many types of structures for vibration reductions. (orig.)
Lattice Boltzmann model for three-phase viscoelastic fluid flow
Xie, Chiyu; Lei, Wenhai; Wang, Moran
2018-02-01
A lattice Boltzmann (LB) framework is developed for simulation of three-phase viscoelastic fluid flows in complex geometries. This model is based on a Rothman-Keller type model for immiscible multiphase flows which ensures mass conservation of each component in porous media even for a high density ratio. To account for the viscoelastic effects, the Maxwell constitutive relation is correctly introduced into the momentum equation, which leads to a modified lattice Boltzmann evolution equation for Maxwell fluids by removing the normal but excess viscous term. Our simulation tests indicate that this excess viscous term may induce significant errors. After three benchmark cases, the displacement processes of oil by dispersed polymer are studied as a typical example of three-phase viscoelastic fluid flow. The results show that increasing either the polymer intrinsic viscosity or the elastic modulus will enhance the oil recovery.
Bifurcation and chaos of an axially accelerating viscoelastic beam
International Nuclear Information System (INIS)
Yang Xiaodong; Chen Liqun
2005-01-01
This paper investigates bifurcation and chaos of an axially accelerating viscoelastic beam. The Kelvin-Voigt model is adopted to constitute the material of the beam. Lagrangian strain is used to account for the beam's geometric nonlinearity. The nonlinear partial-differential equation governing transverse motion of the beam is derived from the Newton second law. The Galerkin method is applied to truncate the governing equation into a set of ordinary differential equations. By use of the Poincare map, the dynamical behavior is identified based on the numerical solutions of the ordinary differential equations. The bifurcation diagrams are presented in the case that the mean axial speed, the amplitude of speed fluctuation and the dynamic viscoelasticity is respectively varied while other parameters are fixed. The Lyapunov exponent is calculated to identify chaos. From numerical simulations, it is indicated that the periodic, quasi-periodic and chaotic motions occur in the transverse vibrations of the axially accelerating viscoelastic beam
Folding, stowage, and deployment of viscoelastic tape springs
DEFF Research Database (Denmark)
Kwok, Kawai; Pellegrino, Sergio
2013-01-01
This paper presents an experimental and numerical study of the folding, stowage, and deployment behavior of viscoelastic tape springs. Experiments show that during folding the relationship between load and displacement is nonlinear and varies with rate and temperature. In particular, the limit...... and propagation loads increase with the folding rate but decrease with temperature. During stowage, relaxation behavior leads to a reduction in internal forces that significantly impacts the subsequent deployment dynamics. The deployment behavior starts with a short, dynamic transient that is followed by a steady...... deployment and ends with a slow creep recovery. Unlike elastic tape springs, localized folds in viscoelastic tape springs do not move during deployment. Finite-element simulations based on a linear viscoelastic constitutive model with an experimentally determined relaxation modulus are shown to accurately...
Numerical Investigation of Corrugated Wire Mesh Laminate
Directory of Open Access Journals (Sweden)
Jeongho Choi
2013-01-01
Full Text Available The aim of this work is to develop a numerical model of Corrugated Wire Mesh Laminate (CWML capturing all its complexities such as nonlinear material properties, nonlinear geometry and large deformation behaviour, and frictional behaviour. Development of such a model will facilitate numerical simulation of the mechanical behaviour of the wire mesh structure under various types of loading as well as the variation of the CWML configuration parameters to tailor its mechanical properties to suit the intended application. Starting with a single strand truss model consisting of four waves with a bilinear stress-strain model to represent the plastic behaviour of stainless steel, the finite element model is gradually built up to study single-layer structures with 18 strands of corrugated wire meshes consistency and double- and quadruple-layered laminates with alternating crossply orientations. The compressive behaviour of the CWML model is simulated using contact elements to model friction and is compared to the load-deflection behaviour determined experimentally in uniaxial compression tests. The numerical model of the CWML is then employed to conduct the aim of establishing the upper and lower bounds of stiffness and load capacity achievable by such structures.
General dispersion and dissipation relations in a one-dimensional viscoelastic lattice
International Nuclear Information System (INIS)
Wang Wenqiang; Yu Jidong; Tang Zhiping
2008-01-01
We derive the general dispersion and dissipation relations for a one-dimensional viscoelastic lattice, demonstrate the relevance of these relations to viscoelastic fracture and phase transition, and show a procedure to determine the suitable mesh size in numerical simulation of stress waves propagating in viscoelastic continuum
Coffinier, Catherine; Jung, Hea-Jin; Nobumori, Chika; Chang, Sandy; Tu, Yiping; Barnes, Richard H; Yoshinaga, Yuko; de Jong, Pieter J; Vergnes, Laurent; Reue, Karen; Fong, Loren G; Young, Stephen G
2011-12-01
Neuronal migration is essential for the development of the mammalian brain. Here, we document severe defects in neuronal migration and reduced numbers of neurons in lamin B1-deficient mice. Lamin B1 deficiency resulted in striking abnormalities in the nuclear shape of cortical neurons; many neurons contained a solitary nuclear bleb and exhibited an asymmetric distribution of lamin B2. In contrast, lamin B2 deficiency led to increased numbers of neurons with elongated nuclei. We used conditional alleles for Lmnb1 and Lmnb2 to create forebrain-specific knockout mice. The forebrain-specific Lmnb1- and Lmnb2-knockout models had a small forebrain with disorganized layering of neurons and nuclear shape abnormalities, similar to abnormalities identified in the conventional knockout mice. A more severe phenotype, complete atrophy of the cortex, was observed in forebrain-specific Lmnb1/Lmnb2 double-knockout mice. This study demonstrates that both lamin B1 and lamin B2 are essential for brain development, with lamin B1 being required for the integrity of the nuclear lamina, and lamin B2 being important for resistance to nuclear elongation in neurons.
Aerobic fitness, hippocampal viscoelasticity, and relational memory performance.
Schwarb, Hillary; Johnson, Curtis L; Daugherty, Ana M; Hillman, Charles H; Kramer, Arthur F; Cohen, Neal J; Barbey, Aron K
2017-06-01
The positive relationship between hippocampal structure, aerobic fitness, and memory performance is often observed among children and older adults; but evidence of this relationship among young adults, for whom the hippocampus is neither developing nor atrophying, is less consistent. Studies have typically relied on hippocampal volumetry (a gross proxy of tissue composition) to assess individual differences in hippocampal structure. While volume is not specific to microstructural tissue characteristics, microstructural differences in hippocampal integrity may exist even among healthy young adults when volumetric differences are not diagnostic of tissue health or cognitive function. Magnetic resonance elastography (MRE) is an emerging noninvasive imaging technique for measuring viscoelastic tissue properties and provides quantitative measures of tissue integrity. We have previously demonstrated that individual differences in hippocampal viscoelasticity are related to performance on a relational memory task; however, little is known about health correlates to this novel measure. In the current study, we investigated the relationship between hippocampal viscoelasticity and cardiovascular health, and their mutual effect on relational memory in a group of healthy young adults (N=51). We replicated our previous finding that hippocampal viscoelasticity correlates with relational memory performance. We extend this work by demonstrating that better aerobic fitness, as measured by VO 2 max, was associated with hippocampal viscoelasticity that mediated the benefits of fitness on memory function. Hippocampal volume, however, did not account for individual differences in memory. Therefore, these data suggest that hippocampal viscoelasticity may provide a more sensitive measure to microstructural tissue organization and its consequences to cognition among healthy young adults. Copyright © 2017 The Authors. Published by Elsevier Inc. All rights reserved.
Some remarks on static, creep and fatigue flexural strength of satin woven CFRP laminates
Energy Technology Data Exchange (ETDEWEB)
Miyano, Y.; McMurry, M.K. [Kanazawa Institute of Technology (Japan); Muki, R. [Univ. of California, Los Angeles, CA (United States)
1995-12-31
This paper deals with the time-temperature dependent flexural strength of a satin-woven CFRP laminate having a matrix resin with a high glass transition temperature of T{sub g} = 236/C under static, creep and fatigue loading by 3-point bending tests. Static tests were conducted at various points in a wide range of deflection rates and temperatures. The creep and fatigue tests were carried out at various constant temperatures; the fatigue test was conducted at two frequencies. The results of the experimental study are as follows. The flexural strength of the CFRP laminates for all three loading types is time-temperature dependent even near room temperature well below T{sub g}. The time and temperature superposition principle for the matrix resin also holds for the flexural strength of the CFRP laminates. The fracture modes are almost the same for the three loading types under all conditions tested. Finally, we propose a method for predicting the flexural fatigue strength for a given number of cycles to failure at an arbitrary temperature, frequency and stress ratio based on the current experimental findings and considering the relationships among the static, creep and fatigue flexural strengths.
Geometrically Nonlinear Transient Response of Laminated Plates with Nonlinear Elastic Restraints
Directory of Open Access Journals (Sweden)
Shaochong Yang
2017-01-01
Full Text Available To investigate the dynamic behavior of laminated plates with nonlinear elastic restraints, a varied constraint force model and a systematic numerical procedure are presented in this work. Several kinds of typical relationships of force-displacement for spring are established to simulate the nonlinear elastic restraints. In addition, considering the restraining moments of flexible pads, the pads are modeled by translational and rotational springs. The displacement- dependent constraint forces are added to the right-hand side of equations of motion and treated as additional applied loads. These loads can be explicitly defined, via an independent set of nonlinear load functions. The time histories of transverse displacements at typical points of the laminated plate are obtained through the transient analysis. Numerical examples show that the present method can effectively treat the geometrically nonlinear transient response of plates with nonlinear elastic restraints.
Lubineau, Gilles
2013-11-01
A practical way to track the development of transverse cracking in a laminated composite is to monitor the change of its electrical resistance. Yet, the relations between transverse cracking and the global modification of resistivity is still unclear that makes difficult to interpret these non-destructive-testing results. Here, we introduce the homogenization process that defines at the meso scale an equivalent homogeneous ply that is energetically equivalent to the cracked one. It is shown that this equivalent ply mainly depends on the cracking level while it can be considered independent on the rest of the laminated structure. The direct consequence is that the meso scale is a pertinent one to perform the homogenization. Then, non-destructive electrical measurements can be considered as a reliable technique to access meso scale damage indicators. © 2013 Elsevier Ltd.
Optomechanical measurement of the role of lamins in whole cell deformability.
Kolb, Thorsten; Kraxner, Julia; Skodzek, Kai; Haug, Michael; Crawford, Dean; Maaß, Kendra K; Aifantis, Katerina E; Whyte, Graeme
2017-12-01
There is mounting evidence that the nuclear envelope, and particularly the lamina, plays a critical role in the mechanical and regulation properties of the cell and changes to the lamina can have implications for the physical properties of the whole cell. In this study we demonstrate that the optical stretcher can measure changes in the time-dependent mechanical properties of living cells with different levels of A-type lamin expression. Results from the optical stretcher shows a decrease in the deformability of cells as the levels of lamin A increases, for cells which grow both adherently and in suspension. Further detail can be probed by combining the optical stretcher with fluorescence microscopy to investigate the nuclear mechanical properties which show a larger decrease in deformability than for the whole cell. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Comparison of in vivo and ex vivo viscoelastic behavior of the spinal cord.
Ramo, Nicole L; Shetye, Snehal S; Streijger, Femke; Lee, Jae H T; Troyer, Kevin L; Kwon, Brian K; Cripton, Peter; Puttlitz, Christian M
2018-03-01
Despite efforts to simulate the in vivo environment, post-mortem degradation and lack of blood perfusion complicate the use of ex vivo derived material models in computational studies of spinal cord injury. In order to quantify the mechanical changes that manifest ex vivo, the viscoelastic behavior of in vivo and ex vivo porcine spinal cord samples were compared. Stress-relaxation data from each condition were fit to a non-linear viscoelastic model using a novel characterization technique called the direct fit method. To validate the presented material models, the parameters obtained for each condition were used to predict the respective dynamic cyclic response. Both ex vivo and in vivo samples displayed non-linear viscoelastic behavior with a significant increase in relaxation with applied strain. However, at all three strain magnitudes compared, ex vivo samples experienced a higher stress and greater relaxation than in vivo samples. Significant differences between model parameters also showed distinct relaxation behaviors, especially in non-linear relaxation modulus components associated with the short-term response (0.1-1 s). The results of this study underscore the necessity of utilizing material models developed from in vivo experimental data for studies of spinal cord injury, where the time-dependent properties are critical. The ability of each material model to accurately predict the dynamic cyclic response validates the presented methodology and supports the use of the in vivo model in future high-resolution finite element modeling efforts. Neural tissues (such as the brain and spinal cord) display time-dependent, or viscoelastic, mechanical behavior making it difficult to model how they respond to various loading conditions, including injury. Methods that aim to characterize the behavior of the spinal cord almost exclusively use ex vivo cadaveric or animal samples, despite evidence that time after death affects the behavior compared to that in a living
Wazir, Umar; Ahmed, Mai Hassan; Bridger, Joanna M; Harvey, Amanda; Jiang, Wen G; Sharma, Anup K; Mokbel, Kefah
2013-12-01
Lamin A/C (LMNA), lamin B1 (LMNB1) and lamin B receptor (LBR) have key roles in nuclear structural integrity and chromosomal stability. In this study, we have studied the relationships between the mRNA expressions of A-type lamins, LMNB1 and LBR and the clinicopathological parameters in human breast cancer. Samples of breast cancer tissues (n = 115) and associated non-cancerous tissue (ANCT; n = 30) were assessed using reverse transcription and quantitative PCR. Transcript levels were correlated with clinicopathological data. Higher levels of A-type lamins and LMNB1 mRNA expression were seen in ANCT. Higher lamin A/C expression was associated with the early clinical stage (TNM1 vs. TNM3 - 13 vs. 0.21; p = 0.0515), with better clinical outcomes (disease-free survival vs. mortality - 11 vs. 1; p = 0.0326), and with better overall (p = 0.004) and disease-free survival (p = 0.062). The expression of LMNB1 declined with worsening clinical outcome (disease-free vs. mortalities - 0.0011 vs. 0.000; p = 0.0177). LBR mRNA expression was directly associated with tumor grade (grade 1 vs. grade 3 - 0.00 vs. 0.00; p = 0.0479) and Nottingham Prognostic Index (NPI1 vs. NPI3 - 0.00 vs. 0.00; p = 0.0551). To the best of our knowledge, this is the first study to suggest such a role for A-type lamins, lamin B1 and LBR in human breast cancer, identifying an important area for further research.