Parametric identification of the mathematical model of the functioning of tribosystems in the conditions of boundary lubrication

The parametric identification of the tribosystem as an object of modeling the functioning of tribosystems in the conditions of boundary lubrication is performed in the work. Using the analysis of the dimensions of significant factors, expressions are obtained to calculate the gain and time constants. It is established that the coefficient takes into account the degree of influence of the load, sliding speed, tribological characteristics of the lubricating medium on the quality factor of the tribosystem. It is shown that the increase in the coefficient will have a positive effect on the processes inherent in tribosystems during operation. Coefficient – characterizes the magnitude of the change in volumetric wear rate and friction coefficient when changing the magnitude of the load, sliding speed, quality factor of the tribosystem. Coefficient – characterizes the ability of the tribosystem to self-organize when changing the values of the input parameters by rearranging the surface layers of materials from which the triboelements are made during secondary running-in. It is shown that the value of the coefficient is large will contribute to the rapid change in the roughness of the friction surfaces, the restructuring of the structure of the surface layers, the appearance of oxidizing films on the friction surfaces (secondary structures). It is proved that the time constant – this is the time required to change the roughness of the friction surfaces and rearrange the structure of the materials of the surface layers when changing external conditions. Time constant characterizes the time during which there is a stabilization of the temperature gradient by volume of triboelements, taking into account the thermal conductivity of materials when changing external conditions. Time constant characterizes the time during which the tribosystem returns to a steady state of operation after the cessation of the outrageous force, or the time to stabilize the parameters in the new mode of operation. It is proved that the value will be optimal for the process of self-organization. It is shown that one of the factors that can control the value , this is the sliding speed

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Structural identification of the mathematical model of the functioning of tribosystems under conditions of boundary lubrication

PROBLEMS OF TRIBOLOGY ◽

10.31891/2079-1372-2021-100-2-26-33 ◽

2021 ◽

Vol 100 (2) ◽

pp. 26-33

Author(s):

A. Voitov

Keyword(s):

Differential Equation ◽

Quality Factor ◽

Boundary Lubrication ◽

Input Signal ◽

Methodological Approach ◽

Structural Identification ◽

Material Structure ◽

Sliding Speed ◽

Time Constants ◽

Operating Modes

In the work, a methodological approach to obtaining mathematical models was further developed, which describe the functioning of tribosystems in stationary and transient modes under boundary lubrication conditions.The structural identification of the tribosystem as an object of modeling the functioning of tribosystems in the conditions of boundary lubrication is performed. It is established that the operation of tribosystems is described by a third-order differential equation and, in contrast to the known ones, takes into account the function of changing the quality factor of the tribosystem during running-in. It is shown that the nature of the functioning of tribosystems under conditions of ultimate lubrication depends on the gain and time constants included in the differential equation. It is shown that the coefficient К1 takes into account the degree of influence of the input signal (load, sliding speed, tribological characteristics of the lubricating medium), on the value of the output signal (quality factor of the tribosystem). Coefficient К2 takes into account the magnitude of the change of the output parameters (volumetric wear rate and friction coefficient) when changing the values of the input parameters (load, sliding speed, quality factor of the tribosystem. Coefficient К3 takes into account the degree of influence of the input signal on the restructuring of the material structure in the surface layers of the triboelements.The time constants of the tribosystem characterize the inertia of the processes occurring in the tribosystem, during running-in, or during changes in operating modes. Increasing the time constants makes the process less susceptible to changes in the input signal, the running-in process increases over time, and the tribosystem becomes insensitive to small changes in load and slip speed. Conversely, the reduction of time constants makes the tribosystem sensitive to any external changes.

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Assessment of the quality factor of tribosystems and relationship with tribological characteristics

PROBLEMS OF TRIBOLOGY ◽

10.31891/2079-1372-2020-98-4-20-26 ◽

2020 ◽

Vol 98 (4) ◽

pp. 20-26

Author(s):

V. Vojtov ◽

◽

A. Voitov ◽

Keyword(s):

Quality Factor ◽

Experimental Studies ◽

Propagation Rate ◽

Operating Conditions ◽

Maximum Effect ◽

Surface Layers ◽

Steady State Operation ◽

Definition Of ◽

Friction Surfaces ◽

The Relationship

The definition of the quality factor of the tribosystem has been further developed, which, unlike the known one, takes into account not only the geometric dimensions of the tribosystem, thermal diffusivity of triboelement materials, lubricating medium and deformation propagation rate in the surface layers of the material, but also the function of changing the rheological properties of the surface layers of materials during running-in and their increase during running-in. Theoretical studies have established that three parameters have the maximum effect on the quality factor: sliding speed, roughness of friction surfaces and lubricating medium. Experimental studies have established the relationship between the value of the quality factor, wear rate and coefficient of friction during steady-state operation of tribosystems. It has been shown that an increase in the figure of quality factor reduces the above parameters, and the criterion itself Qmax is a measure of the potential of the tribosystem adapt to the operating conditions.

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Chemical Modification of Friction Surfaces in Boundary Lubrication

A S L E Transactions ◽

10.1080/05698198208983117 ◽

1982 ◽

Vol 25 (4) ◽

pp. 483-488 ◽

Cited By ~ 14

Author(s):

R. M. Matveevsky

Keyword(s):

Chemical Modification ◽

Boundary Lubrication ◽

Friction Surfaces

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Experimental and Modeling Studies for Understanding Shoe-Floor-Contaminant Friction and Designing for Slip-Resistance

ASME/STLE 2012 International Joint Tribology Conference ◽

10.1115/ijtc2012-61191 ◽

2012 ◽

Author(s):

Kurt Beschorner

Keyword(s):

Experimental Data ◽

Finite Element ◽

Boundary Lubrication ◽

Viscous Fluids ◽

Finite Element Models ◽

Sliding Speed ◽

Friction Coefficients ◽

Real Area Of Contact ◽

Lubrication Regime ◽

Real Area

Insufficient friction at the shoe-floor interface causes a large number of slip and falling accidents each year. Developing solutions for enhancing shoe-floor-contaminant friction requires understanding the mechanisms that contribute to slippery surfaces. Over the past several years, our research group has conducted several experimental and modeling studies to reveal the critical tribological mechanisms contributing to shoe-floor-contaminant friction. This extended abstract will discuss the findings of these studies to: 1) determine the lubrication regime(s) that is/are most relevant to under-shoe conditions during slipping; 2) quantify how under-shoe conditions, shoes and flooring affect the two main contributions to boundary lubrication: adhesion and hysteresis; and 3) describe how this information can be used to design slip-resistant shoes and flooring. To identify the lubrication regime, interfacial pressures at the shoe-floor-contaminant interface were measured and coefficient of friction was monitored. Low viscous fluids and shoes with at least 2mm of tread were found to have negligible interfacial pressures and moderate friction coefficients (0.07–0.40). Untreaded shoes combined with high viscous fluids led to high interfacial pressures that supported up to 40% of the normal load and low friction coefficients (<0.01). These results suggest that mixed/elasto-hydrodynamic lubrication is relevant in some untreaded conditions but that boundary lubrication is relevant for most other conditions. In boundary lubrication, the primary factors contributing to friction are adhesion and hysteresis. Experimental data and finite element models demonstrate that hysteresis friction increases with floor roughness and the ratio of shoe to floor hardness. Adhesion friction is dependent on real area of contact and the shear stress required to break junctions. Experimental data suggests that adhesion is dependent on the fluid lubricant, sliding speed, floor roughness and shoe material. Finite element models confirm that a reduction in the real area of contact occurs with increasing floor roughness and sliding speed, consistent with the experimental adhesion effects. Ensuring that the shoe-floor-fluid interface is operating in the boundary lubrication regime requires establishing minimum tread threshold for fluid lubricants that are likely to be found in a given environment. Designing a high hysteresis shoe-floor combination is preferred because it is relatively unaffected by fluid contaminants or under-shoe conditions (i.e. sliding speed). Therefore, ensuring a minimum tread depth is used along with increasing floor roughness and shoe to floor hardness may be effective in addition to minimum tread thresholds.

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The role of palaeoclimate studies: modelling

Philosophical Transactions of the Royal Society B Biological Sciences ◽

10.1098/rstb.1993.0119 ◽

1993 ◽

Vol 341 (1297) ◽

pp. 341-342 ◽

Cited By ~ 1

Keyword(s):

Conceptual Framework ◽

Multiple Equilibria ◽

Rapid Change ◽

Atmospheric Composition ◽

Climate Modelling ◽

The Past ◽

External Conditions ◽

The Subject ◽

Almost All

Stepping back from the topic of the meeting, I should like to begin by addressing the role of palaeoclimate studies in the subject of climate and its prediction. I do not believe that it is only by looking at the past that one can see into the future. However, I do believe that studies of past climates have an important role to play. To perform climate modelling and to compare the data from models with observations, one must have a conceptual framework. Important elements in this framework are the roles of continents, mountains, solar input and atmospheric composition. It must include notions of rapid change. For example, the response to increasing atmospheric CO2 may be very slow until a certain critical point when it becomes very rapid: the ‘Joker in the pack’. The possibility of multiple equilibria, more than one possible climate for the same external conditions, must be recognized. The average situation is essentially irrelevant in a system that spends almost all of its time in either of two equilibra.

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Experimental Approach for Finding the Response Time of MR Dampers for Vehicle Applications

Volume 5: 19th Biennial Conference on Mechanical Vibration and Noise, Parts A, B, and C ◽

10.1115/detc2003/vib-48349 ◽

2003 ◽

Cited By ~ 6

Author(s):

Fernando D. Goncalves ◽

Jeong-Hoi Koo ◽

Mehdi Ahmadian

Keyword(s):

Response Time ◽

Time Constant ◽

Constant Velocity ◽

Mr Damper ◽

Initial State ◽

Final State ◽

Mr Dampers ◽

Automotive Suspension ◽

Magneto Rheological ◽

Time Required

This paper offers a method and an experimental example of determining the response time of Magneto-Rheological (MR) dampers. The response time of MR dampers for automotive suspension applications is valuable information because it is one of the key factors that determine the practical effectiveness of the use of MR dampers in vehicles. However, a detailed description of the response time of MR dampers is seldom given in the literature. Furthermore, the methods of computing the response time are not discussed in detail. Therefore, this study intends to develop a method for experimental determination of the response time of MR dampers for automotive suspensions. A triangle wave that maintains a constant velocity across the damper is proposed as the input to use in experiments. This triangle wave ensures a constant velocity across the damper in order to accurately evaluate the response time of the MR damper. The response time was defined as the time required to make the transition from the initial state to 63.2% of the final state, or one time constant. The time constant is a measure of how long it takes a system to respond to a given input. In other words, the response time is the time necessary for the damper to achieve the desired force upon activation. To demonstrate the method, the response time was found for an MR damper particularly designed and fabricated for vehicle applications. Two cases were considered: activation response time of the damper and deactivation response time of the damper. Both cases were studied during the rebound stroke of the damper. It was found that the response time of the MR damper under activation and deactivation was 15.4 ms and 13.9 ms respectively. The results are comparable to those found in the literature.

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A Proposed Model of Boundary Lubrication by Synovial Fluid: Structuring of Boundary Water

Journal of Biomechanical Engineering ◽

10.1115/1.3426243 ◽

1979 ◽

Vol 101 (3) ◽

pp. 185-192 ◽

Cited By ~ 54

Author(s):

W. H. Davis ◽

S. L. Lee ◽

L. Sokoloff

Keyword(s):

Synovial Fluid ◽

Boundary Lubrication ◽

Hydration Shell ◽

Check Valve ◽

Surface Layers ◽

Surface Shear ◽

Hydration Shells ◽

Proposed Model ◽

Artificial Surfaces

On the basis of data obtained from in-vitro friction tests using both cartilage and widely differing artificial surfaces, a general model for boundary lubrication of joint cartilage by synovial fluid is presented. It postulates that one portion of the synovial lubricating glycoprotein (LGP) is adsorbed to the surface. Reduction in surface shear is accomplished by formation of hydration shells about the polar portions of the adsorbed LGP creating a thin layer of viscous structured water at the surface. Mutual electrostatic repulsion between charged polysaccharide moieties aids in separation of the adsorbed surface layers. The hydration shell also serves as a check valve to control the movement of water out of and into the cartilage matrix during motion.

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Optimal Infeed Control for Accelerated Spark-Out in Plunge Grinding

Journal of Engineering for Industry ◽

10.1115/1.3185913 ◽

1984 ◽

Vol 106 (1) ◽

pp. 70-74 ◽

Cited By ~ 39

Author(s):

S. Malkin ◽

Y. Koren

Keyword(s):

Direct Measurement ◽

Time Constant ◽

Cycle Time ◽

Characteristic Time ◽

Control Policy ◽

Plunge Grinding ◽

Elastic Deflection ◽

Time Required

An optimal infeed control policy is proposed to minimize the cycle time in cylindrical plunge grinding. As compared with conventional infeed control consisting of roughing followed by spark-out, the proposed infeed control policy accelerates the spark-out by reducing the time required to recover the accumulated elastic deflection in the system and to reduce the infeed velocity to its final required value. This optimal infeed control policy is particularly advantageous for grinding systems having a long characteristic time constant. A practial method is described for implementing the optimal infeed control policy based upon direct measurement of the radial allowance remaining on the workpiece.

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