Adhesive and normal stress-dependent dynamic friction of a gelatin hydrogel

2021 ◽  
pp. 135065012110446
Author(s):  
Nitish Sinha ◽  
Arun Kumar Singh ◽  
Vinit Gupta ◽  
Jitendra Kumar Katiyar
Keyword(s):  
Experimental Data ◽  
Normal Stress ◽  
Scaling Law ◽  
Shear Velocity ◽  
Friction Model ◽  
Dynamic Friction ◽  
Practical Applications ◽  
Soft Solids ◽  
Gelatin Hydrogel ◽  
Stress Dependent

Adhesion and friction of soft solids on hard surfaces are the important properties for a variety of practical applications. In the present study, Coulomb's law of friction is used for characterizing adhesive friction as well as normal stress-dependent dynamic friction of a gelatin hydrogel on a fixed glass surface. The experimental data, concerning normal stress-dependent dynamic friction of different shear velocity, are obtained from literature. It is observed that both components of friction increase with shear velocity. More importantly, the scaling law shows that adhesive stress varies almost linearly with corresponding coefficient of friction of the hydrogel. A dynamic friction model is also used to analyze the same experimental data to predict a negative normal stress at which dynamic friction reduces to zero, and this result matches closely with the experimental value.

Scaling laws of gelatin hydrogels for steady dynamic friction

2016 ◽  
Vol 30 (26) ◽  
pp. 1650198 ◽  
Author(s):  
Vinit Gupta ◽  
Arun K. Singh
Keyword(s):  
Scaling Laws ◽  
Scaling Law ◽  
Mesh Size ◽  
Friction Model ◽  
Dynamic Friction ◽  
Sliding Velocity ◽  
Gelatin Hydrogel ◽  
Sliding Interface ◽  
Glass Interface ◽  
Frictional Behaviour

In this article, we use population balance based dynamic friction model for steady sliding to develop scaling laws in the terms of mesh size of gelatin hydrogels. First of all, it is observed in the sliding experiments that shear modulus of gelatin hydrogels depends on sliding velocity. This dependence is more evident in the case of low sliding velocity. Moreover, relaxation time constant of a dangling chain at the sliding interface scales with the same exponent as its stiffness. The scaling law is also developed for chain density and viscous retardation at the sliding interface. It is also established that the Hookean-based dynamic friction model is sufficient to study frictional behaviour of hydrogels. The reason for this observation is attributed to the weak bonding between a gelatin hydrogel and glass interface.

On the Modeling of Quasi-Steady and Unsteady Dynamic Friction in Sliding Lubricated Line Contact

2009 ◽  
Vol 132 (1) ◽  
Author(s):  
H. Sojoudi ◽  
M. M. Khonsari
Keyword(s):  
Experimental Data ◽  
Friction Coefficient ◽  
Reynolds Equation ◽  
Friction Model ◽  
Sliding Contact ◽  
Dynamic Friction ◽  
Line Contact ◽  
Sliding Velocity ◽  
Friction Behavior ◽  
Lubricated Sliding

A simple but realistic dynamic friction model for the lubricated sliding contact is developed based on decoupling the steady and unsteady terms in Reynolds equation. The model realistically captures the physics of friction behavior both when speed is increased unidirectionally or when operating under oscillating condition. The model can simulate the transition from boundary to mixed to full film regimes as the speed is increased. Two different classes of simulations are performed to show the utility of the model: the so-called quasisteady, where the sliding velocity is varied very slowly, and the oscillating sliding velocity, where the friction coefficient exhibits a hysteresis type behavior. Both categories of simulation are verified by comparing the results with published experimental data.

Diagnostics of metal samples using the results of experimental and theoretical study of positively charged microparticles formed upon sample destruction

2018 ◽  
Vol 84 (10) ◽  
pp. 23-28
Author(s):  
D. A. Golentsov ◽  
A. G. Gulin ◽  
Vladimir A. Likhter ◽  
K. E. Ulybyshev
Keyword(s):  
Experimental Data ◽  
Early Stage ◽  
Experimental Studies ◽  
Material Model ◽  
Total Charge ◽  
Cross Sectional ◽  
Practical Applications ◽  
Mechanical And Electrical Properties ◽  
Order Of Magnitude ◽  
Using Data

Destruction of bodies is accompanied by formation of both large and microscopic fragments. Numerous experiments on the rupture of different samples show that those fragments carry a positive electric charge. his phenomenon is of interest from the viewpoint of its potential application to contactless diagnostics of the early stage of destruction of the elements in various technical devices. However, the lack of understanding the nature of this phenomenon restricts the possibility of its practical applications. Experimental studies were carried out using an apparatus that allowed direct measurements of the total charge of the microparticles formed upon sample rupture and determination of their size and quantity. The results of rupture tests of duralumin and electrical steel showed that the size of microparticles is several tens of microns, the particle charge per particle is on the order of 10–14 C, and their amount can be estimated as the ratio of the cross-sectional area of the sample at the point of discontinuity to the square of the microparticle size. A model of charge formation on the microparticles is developed proceeding from the experimental data and current concept of the electron gas in metals. The model makes it possible to determine the charge of the microparticle using data on the particle size and mechanical and electrical properties of the material. Model estimates of the total charge of particles show order-of-magnitude agreement with the experimental data.

scholarly journals Study on Friction in Automotive Shock Absorbers Part 1: Friction Simulation Using a Dynamic Friction Model in the Contact Zone of an FEM Model

Vehicles ◽  
2021 ◽  
Vol 3 (2) ◽  
pp. 212-232
Author(s):  
Ludwig Herzog ◽  
Klaus Augsburg
Keyword(s):  
Ride Comfort ◽  
Viscous Friction ◽  
Simulation Method ◽  
Friction Model ◽  
Model Parameters ◽  
Dynamic Friction ◽  
Friction Modeling ◽  
Shock Absorbers ◽  
Operation Conditions ◽  
Wide Range

The important change in the transition from partial to high automation is that a vehicle can drive autonomously, without active human involvement. This fact increases the current requirements regarding ride comfort and dictates new challenges for automotive shock absorbers. There exist two common types of automotive shock absorber with two friction types: The intended viscous friction dissipates the chassis vibrations, while the unwanted solid body friction is generated by the rubbing of the damper’s seals and guides during actuation. The latter so-called static friction impairs ride comfort and demands appropriate friction modeling for the control of adaptive or active suspension systems. In this article, a simulation approach is introduced to model damper friction based on the most friction-relevant parameters. Since damper friction is highly dependent on geometry, which can vary widely, three-dimensional (3D) structural FEM is used to determine the deformations of the damper parts resulting from mounting and varying operation conditions. In the respective contact zones, a dynamic friction model is applied and parameterized based on the single friction point measurements. Subsequent to the parameterization of the overall friction model with geometry data, operation conditions, material properties and friction model parameters, single friction point simulations are performed, analyzed and validated against single friction point measurements. It is shown that this simulation method allows for friction prediction with high accuracy. Consequently, its application enables a wide range of parameters relevant to damper friction to be investigated with significantly increased development efficiency.

Boundary and Mixed Friction in the Presence of Dynamic Normal Loads: Part I—System Model

1995 ◽  
Vol 117 (2) ◽  
pp. 255-260 ◽  
Author(s):  
Andreas A. Polycarpou ◽  
Andres Soom
Keyword(s):  
Important Variable ◽  
Friction Model ◽  
System Model ◽  
Dynamic Friction ◽  
Discrete Elements ◽  
Friction Forces ◽  
Contact Compliance ◽  
Stiffness Characteristics ◽  
Nonlinear Normal ◽  
Linearized Model

The instantaneous normal motion between bodies in a sliding contact is an important variable in determining dynamic friction under unsteady sliding conditions. In order to model friction under dynamic conditions, it is therefore necessary to combine a dynamic model of the sliding system with an accurate model of the friction process. In the present work, the nonlinear normal dynamics of a friction test apparatus are described by a linearized model at a particular steady loading and sliding condition in a mixed or boundary-lubricated regime. The geometry is a line contact. The Hertzian bulk contact compliance and film and asperity damping and stiffness characteristics are included as discrete elements. In Part I of the paper, a fifth-order model is developed for the normal dynamics of the system, using both the Eigensystem Realization Algorithm (ERA) and classical experimental modal analysis techniques. In Part II, this system model is combined with a friction model, developed independently, to describe dynamic friction forces under both harmonic and impulsive applied normal loads.

Investigation on hydrodynamic forces leading to coarse particle entrainment using Large-Eddy Simulations

2021 ◽  
Author(s):  
Gaston Latessa ◽  
Angela Busse ◽  
Manousos Valyrakis
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Large Scale ◽  
Large Eddy Simulations ◽  
Flow Conditions ◽  
Mean Flow ◽  
Protection Measures ◽  
Practical Applications ◽  
Particle Entrainment ◽  
Large Eddy

<p>The prediction of particle motion in a fluid flow environment presents several challenges from the quantification of the forces exerted by the fluid onto the solids -normally with fluctuating behaviour due to turbulence- and the definition of the potential particle entrainment from these actions. An accurate description of these phenomena has many practical applications in local scour definition and to the design of protection measures.</p><p>In the present work, the actions of different flow conditions on sediment particles is investigated with the aim to translate these effects into particle entrainment identification through analytical solid dynamic equations.</p><p>Large Eddy Simulations (LES) are an increasingly practical tool that provide an accurate representation of both the mean flow field and the large-scale turbulent fluctuations. For the present case, the forces exerted by the flow are integrated over the surface of a stationary particle in the streamwise (drag) and vertical (lift) directions, together with the torques around the particle’s centre of mass. These forces are validated against experimental data under the same bed and flow conditions.</p><p>The forces are then compared against threshold values, obtained through theoretical equations of simple motions such as rolling without sliding. Thus, the frequency of entrainment is related to the different flow conditions in good agreement with results from experimental sediment entrainment research.</p><p>A thorough monitoring of the velocity flow field on several locations is carried out to determine the relationships between velocity time series at several locations around the particle and the forces acting on its surface. These results a relevant to determine ideal locations for flow investigation both in numerical and physical experiments.</p><p>Through numerical experiments, a large number of flow conditions were simulated obtaining a full set of actions over a fixed particle sitting on a smooth bed. These actions were translated into potential particle entrainment events and validated against experimental data. Future work will present the coupling of these LES models with Discrete Element Method (DEM) models to verify the entrainment phenomena entirely from a numerical perspective.</p>

Residual Strength: Does BS 5930 Help or Hinder?

1986 ◽  
Vol 2 (1) ◽  
pp. 279-282 ◽  
Author(s):  
A. B. Hawkins ◽  
K. D. Privett
Keyword(s):  
Stability Analysis ◽  
Normal Stress ◽  
Residual Strength ◽  
Clay Content ◽  
Failure Envelope ◽  
Strength Parameters ◽  
Effective Normal Stress ◽  
Ring Shear ◽  
Stress Dependent ◽  
Shear Box

AbstractBS 5930 offers little assistance to engineers wishing to use residual strength parameters in slope stability analysis. It wrongly suggests the ring shear gives lower parameters than the shear box.BS 5930 does not mention the fact that the residual strength is stress dependent, hence the failure envelope is curved and the parameters must be assessed using an appropriate effective normal stress. For this reason the correlation charts relating ϕ′R to plasticity index or clay content need replacing with a series of charts in which these properties are plotted against ϕ′R values obtained at a number of effective normal stress loadings. Even then such correlations should be treated with caution.

Pressure, Frictional Resistance, and Flow Characteristics of the Partially Wetted Rotating Disk

1968 ◽  
Vol 90 (2) ◽  
pp. 395-404 ◽  
Author(s):  
H. N. Ketola ◽  
J. M. McGrew
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Pressure Gradient ◽  
Flow Characteristics ◽  
Frictional Resistance ◽  
Rotating Disk ◽  
Practical Applications ◽  
Stationary Wall ◽  
Spacing Ratio ◽  
Analytical Expressions

A theory of the partially wetted rotating disk is described and experimental data presented which verify the application of this theory in practical applications. Four different flow regimes may be identified according to the value of the disk Reynolds number and the spacing ratio between the disk and stationary wall. The analytical expressions for prediction of the pressure gradient developed and the frictional resistance are uniquely determined by the disk Reynolds number, spacing ratio, and the degree of wetting of the disk.

scholarly journals Optimal Strategy to Certify Quantum Nonlocality

2021 ◽  
Author(s):  
S. Gómez ◽  
D. Uzcátegui ◽  
I. Machuca ◽  
E. S. Gómez ◽  
S. P. Walborn ◽  
...  
Keyword(s):  
Experimental Data ◽  
Random Number ◽  
Bell Inequality ◽  
Random Number Generation ◽  
Quantum Nonlocality ◽  
Entangled Photons ◽  
Challenging Problem ◽  
Practical Applications ◽  
Variable Limit ◽  
The One

Abstract Certification of quantum nonlocality plays a central role in practical applications like device-independent quantum cryptography and random number generation protocols. These applications entail the challenging problem of certifying quantum nonlocality, something that is hard to achieve when the target quantum state is only weakly entangled, or when the source of errors is high, e.g. when photons propagate through the atmosphere or a long optical fiber. Here we introduce a technique to find a Bell inequality with the largest possible gap between the quantum prediction and the classical local hidden variable limit for a given set of measurement frequencies. Our method represent an efficient strategy to certify quantum nonlocal correlations from experimental data without requiring extra measurements, in the sense that there is no Bell inequality with a larger gap than the one provided. Furthermore, we also reduce the photodetector efficiency required to close the detection loophole. We illustrate our technique by improving the detection of quantum nonlocality from experimental data obtained with weakly entangled photons.

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