Effect Of Internal Friction Research Articles

Phase transition induced anelasticity in Fe–Ga alloys with 25 and 27%Ga

Neutron diffraction and mechanical spectroscopy techniques were applied to study phase transitions in Fe–Ga alloys with 25 and 27 at.% Ga. The following sequences of phase transitions at continuous heating and subsequent cooling in the 20–900 °C temperature range were recorded: D03 → L12 (limited amount) → A2(B2) was recorded at heating and A2(B2) → D03 at cooling for Fe-24.8Ga alloy, and the D03 → L12 → D019 → A2(B2) was recorded at heating and A2(B2) → L12 at cooling for Fe-27.4Ga alloy. Thus, the difference in 2.6 at.%Ga between two studied compositions with D03 structure leads to their different structures after heating to 900 °C. These transition sequences determine different temperature dependencies of elastic and anelastic properties. The D03 → A2(B2) transition (in Fe-25Ga) does not lead to a well-pronounced anelastic effect, in contrast the D03 → L12 transition (in Fe-27Ga) generates internal stresses due to a different rate of an increase in the lattice parameter with temperature and leads to a well-pronounced transient internal friction effect.

Effect of Internal Friction and the Lamé Ratio on Stoneley Wave Propagation in Viscoelastic Media of Order 1

AbstractThe present work aims to study the propagation of Stoneley wave at the common interface of two distinct homogeneous viscoelastic semi-infinite media. The closed-form expression of the velocity equation has been obtained. The real part of the velocity equation corresponds to the phase velocity of Stoneley wave, whereas the imaginary part corresponds to the damped velocity associated with the Stoneley wave. The Lame ratio associated with Lame’s first constant for the upper/lower viscoelastic semi-infinite medium and the frictional parameter associated with the shear strain for the upper/lower viscoelastic semi-infinite medium have significant effects on the phase velocity and the damped velocity of Stoneley wave associated with a longitudinal/transversal wave in the upper/lower viscoelastic semi-infinite medium. Numerical computation and graphical illustration were carried out to highlight the important peculiarities of the problem. Moreover, as a special case, it was observed that the velocity equa...

Rheological model of Love wave propagation in viscoelastic layered media under gravity

Purpose – The purpose of this paper is to deal with the propagation of Love waves in inhomogeneous viscoelastic layer overlying a gravitational half-space. It has been observed velocity of Love waves depends on viscosity, gravity, inhomogeneity and initial stress of the layer. Design/methodology/approach – The dispersion relation for the Love wave in closed form is obtained with Whitaker’s function. Findings – The effect of various non-dimensional inhomogeneity factors, gravity factor and internal friction on the non-dimensional Love wave velocity has been shown graphically. The authors observed that the dispersion curve of Love wave increases as the inhomogeneity factor increases. It is seen that increment in gravity, inhomogeneity and internal friction decreases the damping phase velocity of Love waves but it is more prominent in case of internal friction. Originality/value – Surface plot of Love wave reveals that the velocity ratio increases with the increase of non-dimensional phase velocity and non-dimensional wave number. The above results may attract seismologists and geologists.

Electron-conformational transformations govern the temperature dependence of the cardiac ryanodine receptor gating

Temperature influences many aspects of cardiac excitation-contraction coupling, in particular, hypothermia increases the open probability (Popen) of cardiac sarcoplasmic reticulum (SR) Ca2+-release channels (ryanodine-sensitive RyR channels) rising the SR Ca2+ load in mammalian myocytes. However, to the best of our knowledge, no theoretical models are available for that effect. Traditional Markov chain models do not provide a reasonable molecular mechanistic insight on the origin of the temperature effects. Here in the paper we address a simple physically clear electron-conformational model to describe the RyR gating and argue that a synergetic effect of external thermal fluctuation forces (Gaussian–Markovian noise) and internal friction via the temperature stimulation/suppression of the open–close RyR tunneling probability can be considered as a main contributor to temperature effects on the RyR gating. Results of the computer modeling allowed us to successfully reproduce all the temperature effects observed for an isolated RyR gating in vitro under reducing the temperature: increase in Popen and mean open time without any significant effect on mean closed

A molecular dynamics analysis of internal friction effects on the plasticity of Zr65Cu35 metallic glass

Abstract The effects of internal friction (IF) on Zr 65 Cu 35 metallic glass plasticity are investigated through molecular dynamics simulations. Results show that the Voronoi polyhedron 〈0, 3, 6, 3〉 increases as IF increases, thereby effectively inhibiting localized deformation and improving metallic glass plasticity. The simulations allow reproduction of images of IF evolution in metallic glasses subjected to isothermal annealing at 730 K and 850 K respectively, which can help explain the experimental observations. IF could be adjusted by selecting suitable annealing temperatures and cooling rates. The results of this work provide a strong foundation for future metallic glass designs.

Kinetics of the chemical reaction front in spherically symmetric problems of mechanochemistry

The establishment of relations between chemicalreactions and processes of deformation and destruction is of importance from the viewpoint of both fundamental science and engineering applications. Theeffect of mechanical stresses on the reaction rate isconventionally taken into account heuristically—bypostulating the dependences of the diffusion processand the reaction constant on certain characteristics ofthe stressed state. At the same time, Gibbs [1] and DeDonder [2] laid the foundation for the theory of chemical reactions based on the concept of chemical affinity, which is a linear combination of the chemicalpotentials of substances participating in the reaction.In the classical physical chemistry dealing with gasesand ideal liquids, the chemical potential and, consequently, the chemical affinity are scalar values dependent, in particular, on pressure. However, in studiesdevoted to investigation of phase transformations indeformable materials, it was shown that the chemicalpotential should be a tensor (see, for example, [3–7]).Recently in [8, 9] for the case of a reaction between gasand deformable solid components, the expression forthe chemicalaffinity tensor was obtained as a result ofthe analysis of balances of mass, momentum, energy,and the second principle of thermodynamics. In turn,this has made it possible to obtain in a natural way thedependence of the reaction rate on stresses.Previously, we investigated the propagation of reaction fronts in the axisymmetrical problems [10] and fora plane front [11]. In this study, we investigated thekinetics of the reaction front in spherically symmetricproblems for linearly elastic solid components of thereaction.BASIC RELATIONSWe consider the chemical reaction of the type ofwhere , and are the chemical formulas ofmaterials of reacting components, and are thesolid elastic components, and is the gas component. We assume that the reaction is localized at thefront separating the regions occupied with materials and and supported by the diffusion of the component through the formed material . We assumealso that the all the gas that came to the reaction frontis spent for the reaction. An example of such a reactionis the oxidation of silicon .We consider the solid component as a solidsceleton for the diffusing gas component assumingthat the gas component causes additional deformations of the frame. Also we disregard the effects ofinternal friction related to the relative motion of thegas and solid components, the thermal effect of thereaction considering the temperature

Dependence of internal friction on folding mechanism.

An outstanding challenge in protein folding is understanding the origin of “internal friction” in folding dynamics, experimentally identified from the dependence of folding rates on solvent viscosity. A possible origin suggested by simulation is the crossing of local torsion barriers. However, it was unclear why internal friction varied from protein to protein or for different folding barriers of the same protein. Using all-atom simulations with variable solvent viscosity, in conjunction with transition-path sampling to obtain reaction rates and analysis via Markov state models, we are able to determine the internal friction in the folding of several peptides and miniproteins. In agreement with experiment, we find that the folding events with greatest internal friction are those that mainly involve helix formation, while hairpin formation exhibits little or no evidence of friction. Via a careful analysis of folding transition paths, we show that internal friction arises when torsion angle changes are an important part of the folding mechanism near the folding free energy barrier. These results suggest an explanation for the variation of internal friction effects from protein to protein and across the energy landscape of the same protein.

Differential settlements in foundations under embankment load: Theoretical model and experimental verification

To research and analyze the differential settlements of foundations specifically, site investigations of existing railways and metro were firstly carried out. Then, the centrifugal test was used to observe differential settlements in different position between foundations on the basis of investigation. The theoretical model was established according to the stress diffusion method and Fourier method to establish an analytical solution of embankment differential settlement between different foundations. Finally, theoretical values and experimental values were analyzed comparatively. The research results show that both in horizontal and vertical directions, evident differential settlement exists in a limited area on both sides of the vertical interface between different foundations. The foundation with larger elastic modulus can transfer more additional stress and cause relatively less settlement. Differential settlement value decreases as the distance to vertical interface decreases. In the vertical direction of foundation, mass differential settlement also exists on both sides of the vertical interface and foundation with larger elastic modulus can transfer more additional stress. With the increase of relative modulus of different foundations, foundation with lower elastic modulus has larger settlement. Meanwhile, differential settlement is more obvious. The main error sources in theoretical and experimental values include: (a) different load form; (b) foundation characteristics differences; (c) modulus conversion; (d) effect of soil internal friction.

Influence of composition and heat treatment on damping and magnetostrictive properties of Fe–18%(Ga + Al) alloys

The structure, magnetostriction and damping properties of Fe82Ga(18−x)Alx (x=0, 5, 8, 12) alloys were analyzed. The anelastic response of Fe–18(Ga+Al) alloys was studied as a function of temperature (from 0 to 600°C), frequency (from 0.01 to 200Hz) and amplitude (from 0.0004% to 0.2%) of forced vibrations. The origin of the relatively high damping capacity of Fe–Ga–Al alloy at room temperature was determined by applying a magnetic field and different heat treatment regimes. The substitution of Ga by Al in Fe–18% Ga alloys was found to decrease magnetostriction and damping. The heat treatment of alloys influences the damping capacity of alloys more than variations of their chemical compositions. Thermally activated frequency and temperature-dependent anelastic effects in Fe–Ga–Al alloys were analyzed and the corresponding activation parameters for relaxation processes were evaluated. Internal friction effects caused by structural transformations were recorded and were found to be consistent with the A2→D03→L12 reaction. The physical mechanisms for all anelastic effects are discussed.

Molecular origins of internal friction effects on protein-folding rates.

Recent experiments on protein folding dynamics have revealed strong evidence for internal friction effects. That is, observed relaxation times are not simply proportional to the solvent viscosity as might be expected if the solvent were the only source of friction. However, a molecular interpretation of this remarkable phenomenon is currently lacking. Here, we use all-atom simulations of peptide and protein folding in explicit solvent, to probe the origin of the unusual viscosity dependence. We find that an important contribution to this effect, explaining the viscosity dependence of helix formation and the folding of a helix-containing protein, is the insensitivity of torsion angle isomerization to solvent friction. The influence of this landscape roughness can, in turn, be quantitatively explained by a rate theory including memory friction. This insensitivity of local barrier crossing to solvent friction is expected to contribute to the viscosity dependence of folding rates in larger proteins.

Acoustic waves in media with hysteretic nonlinearity and linear dispersion

A hysteresis equation of state is proposed for polycrystalline solids with saturation of nonlinear losses. Effects of amplitude-dependent internal friction and higher harmonic generation that result from propagation of harmonic acoustic waves in rods made of such materials are theoretically and numerically studied.

Optimal performance of a spin quantum Carnot heat engine with multi-irreversibilities

By using quantum master equation, semi-group approach and finite time thermodynamics (FTT), this paper derives the expressions of cycle period, power and efficiency of an irreversible quantum Carnot heat engine with irreversibilities of heat resistance, internal friction and bypass heat leakage, and provides detailed numerical examples. The irreversible quantum Carnot heat engine uses working medium consisting of many non-interacting spin-1/2 systems and its cycle is composed of two isothermal processes and two irreversible adiabatic processes. The optimal performance of the quantum heat engine at high temperature limit is deduced and analyzed by numerical examples. Effects of internal friction and bypass heat leakage on the optimal performance are discussed. The endoreversible case, frictionless case and the case without bypass heat leakage are also briefly discussed.

A modeling approach for robotic catheters: effects of nonlinear internal device friction

Recently, robotic surgery systems using passive flexible catheters have been developed for minimally invasive surgical applications – such as in the treatment of atrial fibrillation – where catheter control in the open chamber of the heart is required. The soft, atraumatic construction of these devices help reduce injury to delicate cardiac structures while providing a means of tool placement and control. To provide kinematic and control relationships, various models of continuous catheters have been developed. However, these approaches cannot explain the nonlinear behavior of the catheter when the effect of internal friction is considered. In this paper, we describe a lumped-parameter modeling approach which directly accounts for the effects of internal device friction. The nonlinear model is validated against experimental results from a prototype robotic catheter and is shown to correctly predict the variations in curvature and path-dependent instantaneous behavior observed. Finally, the validated model is used to investigate and describe a set of non-ideal catheter motions observed in practice.

Structure-mechanical model for plasto-elastic behavior of soft magnetic elastomers

The effect of field-induced plasticity (magnetic shape memory) displayed by polymer composites filled with multi-domain ferromagnetic microparticles is discussed. Such a soft magnetic elastomer (SME) magnetizes, that is, the filler particles acquire magnetic moments only upon application of an external magnetic field. ‘Switching-on’ of interparticle magnetic interactions essentially affects the internal structure of SMEs since the magnetic forces by far exceed the high-elasticity ones due to attachment of the particles to the polymer matrix. According to the hypothesis, in a SME there self-organizes a network of clusters that gives birth to the effect of internal dry friction and by that imparts plasticity to the composite. Field-induced structuring, together with plasticity, disappears as soon as the external field is turned off. Under these conditions, elastic forces no longer experience any resistance and move the particles back to their initial spatial positions: the sample ‘recalls’ its initial shape. To account for the above-described plasto-elastic behavior of a magnetized SME, a structure-mechanical model (scheme) is proposed, which comprises the elastic elements (springs) and the entities (Saint-Venant elements) mimicking the dry-friction effect. The elements of the model are heuristically identified with two networks. One of them is related to the polymer matrix as itself, while another resembles the particle clusters formed due to the field-induced magnetic interactions. Both networks are interwoven and may deform only affinely. On the basis of the model, the tensile deformation cycles obtained in experiments on the two types of SMEs made of weakly-linked silicone rubber filled with carbonyl iron microparticles are interpreted. The tested SMEs differ by the dispersity of the filler. The samples of the first type contain only ‘fine’ iron particles with the size of 2-5 microns, while in the SME of the second type the filler consists of equal (by weight) amounts of ‘fine’ and ‘coarse’ (~70 microns) particles. The cycles measured under a number of external fields are presented. By fitting experimental data, the parameters of the theoretical scheme are evaluated, and their dependence on the applied field strength is determined. For the field dependencies of the scheme parameters of the isotropic SMEs examined here, the expressions borrowed from the phenomenology of textured SMEs are taken and tested, proving their applicability for this case.

Combined effects of internal friction and bed height on the Brazil-nut problem in a shaker

We experimentally studied the influence of an intruder's friction coefficient and bed-filling height on the Brazil-nut effect in a quasi-2D vertical vibration granular bed. The motion of intruder was successfully measured using a high-speed camera and the rising time of intruder was determined by using a particle tracking method with the help of image processing technology. The results show that an intruder's friction coefficient and filling bed height play significant roles in the rise dynamics. The results also show that the rise time increases when the intruder's friction coefficient increases, which is reduced when the filling bed height decreases. Penetration length and friction drag force were also determined in this study. The penetration length was reduced and the friction drag force was enhanced with the increase of an intruder's friction coefficient and bed height. Additionally, the variation between the rise times of the smooth and rough intruders was not significant with the lower bed-filling heights.

Assessment of Local Friction in Protein Folding Dynamics Using a Helix Cross-Linker

Internal friction arising from local steric hindrance and/or the excluded volume effect plays an important role in controlling not only the dynamics of protein folding but also conformational transitions occurring within the native state potential well. However, experimental assessment of such local friction is difficult because it does not manifest itself as an independent experimental observable. Herein, we demonstrate, using the miniprotein trp-cage as a testbed, that it is possible to selectively increase the local mass density in a protein and hence the magnitude of local friction, thus making its effect directly measurable via folding kinetic studies. Specifically, we show that when a helix cross-linker, m-xylene, is placed near the most congested region of the trp-cage it leads to a significant decrease in both the folding rate (by a factor of 3.8) and unfolding rate (by a factor of 2.5 at 35 °C) but has little effect on protein stability. Thus, these results, in conjunction with those obtained with another cross-linked trp-cage and two uncross-linked variants, demonstrate the feasibility of using a nonperturbing cross-linker to help quantify the effect of internal friction. In addition, we estimate that a m-xylene cross-linker could lead to an increase in the roughness of the folding energy landscape by as much as 0.4-1.0k(B)T.

SH-waves in viscoelastic heterogeneous layer over half-space with self-weight

The effect of gravity, heterogeneity and internal friction on propagation of SH-waves (horizontally polarised shear waves) in viscoelastic layer over a half-space has been studied. Using the method of separation of variables, dispersion equation has been obtained and used to recover the damped velocity of SH-waves. Both the real and imaginary parts of dispersion equation are in well agreement with the classical Love wave equation. It has been observed that heterogeneity of the medium affects the velocity profile of SH-wave significantly. Some other peculiarities have been observed and discussed in our study.

Exploring the role of internal friction in the dynamics of unfolded proteins using simple polymer models

Recent experiments showed that the reconfiguration dynamics of unfolded proteins are often adequately described by simple polymer models. In particular, the Rouse model with internal friction (RIF) captures internal friction effects as observed in single-molecule fluorescence correlation spectroscopy (FCS) studies of a number of proteins. Here we use RIF, and its non-free draining analog, Zimm model with internal friction, to explore the effect of internal friction on the rate with which intramolecular contacts can be formed within the unfolded chain. Unlike the reconfiguration times inferred from FCS experiments, which depend linearly on the solvent viscosity, the first passage times to form intramolecular contacts are shown to display a more complex viscosity dependence. We further describe scaling relationships obeyed by contact formation times in the limits of high and low internal friction. Our findings provide experimentally testable predictions that can serve as a framework for the analysis of future studies of contact formation in proteins.

Model for Elastic Modulus of Multi-Constituent Particulate Composites

In this paper, a methodology has been developed to accurately predict the elastic properties of multi-constituent particulate composites by accounting for irreversible effects, such as energy loss that arises due to internal friction. The complex dependence on loading density and particle properties (i.e., size, shape, morphology, etc.) is investigated in terms of their effects on the effective elastic modulus of the composite. Confirmed by experimental data from the compression loading of individual Ni and Al particles dispersed in an epoxy matrix, it is believed that this approach captures the effects of internal friction, consequently providing a more accurate and comprehensive representation for predicting and understanding the material behavior of multi-constituent particulate reinforced composites. The present methodology provides a model to directly compare the elastic modulus from an uncomplicated test, such as dual-cantilever beam loading in dynamic mechanical analysis (DMA), to the modulus obtained by other more complex experimental methods such as quasi-static compression. The model illustrates an efficient method to incorporate input data from DMA to represent realistic elastic moduli, hence promising for the characterization and design of particulate composites.

Interplay of non-Markov and internal friction effects in the barrier crossing kinetics of biopolymers: Insights from an analytically solvable model

Conformational rearrangements in biomolecules (such as protein folding or enzyme-ligand binding) are often interpreted in terms of low-dimensional models of barrier crossing such as Kramers' theory. Dimensionality reduction, however, entails memory effects; as a result, the effective frictional drag force along the reaction coordinate nontrivially depends on the time scale of the transition. Moreover, when both solvent and "internal" friction effects are important, their interplay results in a highly nonlinear dependence of the effective friction on solvent viscosity that is not captured by common phenomenological models of barrier crossing. Here, these effects are illustrated using an analytically solvable toy model of an unstructured polymer chain involved in an inter- or intramolecular transition. The transition rate is calculated using the Grote-Hynes and Langer theories, which--unlike Kramers' theory--account for memory. The resulting effective frictional force exerted by the polymer along the reaction coordinate can be rationalized in terms of the effective number of monomers engaged in the transition. Faster transitions (relative to the polymer reconfiguration time scale) involve fewer monomers and, correspondingly, lower friction forces, because the polymer chain does not have enough time to reconfigure in response to the transition.