Friction Coeffi Research Articles

Using a two circuit negative feedback in adaptive friction clutches

It is shown that the introduction of the concept of adaptive friction clutches of the dual negative feedback with time sharing of the action of the circuits and shutting down one of the paths in the interval of values of the friction coeffi cient allows to increase the rated torque while maintaining the accuracy of clutch operation. It is proved that the accuracy of clutch operation is higher in the case where the value of the maximum torque under the action of the second feedback loop is greater than the maximum torque under the action of the fi rst feedback loop, and minimum torques are the same.

Modernization of the adaptive friction clutch with variable gain (second option)

The dependences of the spacer force and feedback gain on the current value of the friction coeffi cient are found, for which an adaptive friction coupling with a variable gain value has a theoretically ideal load characteristic. It is proved that the real way to increase the coeffi cient of multiplicity of increasing the rated load capacity of the coupling is to increase the number of friction pairs of the friction group.

Simulation of the Extruder Screw Parameters

Extrusion of feed ensures a high quality of the fi nished product.(Research purpose) To increase structural elements durability of the press extruder by optimizing their strength characteristics.(Materials and methods) The authors studied the technological principle of extrusion. The experiment planning method was applied. They examined the process of press extruder operation with a variable pitch screw during the lentils processing. The strength characteristics of the press-extruder elements were checked during design or strength calculations.(Results and discussion) The authors showed the role of the main geometrical parameters of the extruder screw – the slope of the turn and the cutting step – in the preparation of high-quality grain feed. It was found that the turn pitch should be calculated depending on the friction coeffi cient of the starting material against the press-extruder body, the type and properties of the supplied material. The auger fatigue stresses were determined as a result of constant sign shear load and temperature eff ects. The drive power, the extruder productivity were calculated to clarify the screw characteristics, as well as the hydraulic resistance of the matrix output head, the distance of the technological zones. It was confi rmed that the prefabricated screw structure, consisting of sections with diff erent pitch, gave the press extruder versatility.(Conclusions) The authors found that the key was one of the most loaded structural elements of the press-extruder screw. The maximum calculated voltage from a constant load was calculated – 26.98 megapascals. It was determined that the stress in the cross-section of the key under temperature action was 591 megapascals, which exceeded the yield stress for the selected material, equal to 360 megapascals for steel 45. In the course of experimental studies, a value of impact strength was obtained that corresponded to the standard value of the initially selected steel grade (38 kilojoules per cubic meter), but didn’t meet the requirements for this structural element (at least 50 kilojoules per cubic meter).

Influence of the characteristics surface layer of the tool and composition technological lubricant on the coefficient of friction in methods combined mandreling of holes

The influence of the nature and parameters microgeometry of the surface layer tool on the sliding friction coeffi cient in the combined methods opening under the conditions of using metal-coating lubricants, which implement the effect of wear-free friction of Garkunov—Kragelsky, is studied comparatively using the theoretical provisions of the adhesivedeformation theory of friction

Results for calculation of optimal delta-criteria for deformation zone shape in drawing of round solid profi le

Formulas for calculating of the optimal delta-criterion are proposed, which, in contrast to the two similar formulas of foreign researchers considered, take into account the back-pull stress and the hardening model. The optimal delta-criterion depends on the deformation parameters and the hardening model. Approximate equalities are proposed that refl ect the relationship between the criteria of the deformation zone and the indicators of the strain state. The values of the criteria for the deformation zone and the strain state for the drawing angles is 4 and 9° and the optimal drawing angle are given. According to two formulas of foreign researchers and the proposed formula, dependencies for the optimal delta-criterion on the drawing and friction coeffi cients are constructed. The criteria values for these formulas do not differ signifi cantly. Taking into account the nature of the relationship for the criteria of the deformation zone shape and the strain state contributes to rational choice of drawing modes.

Study of variation patterns in sliding friction coeffi cient in innovative methods of combined hole mandrelling

The variation patterns of sliding friction coefficient in innovative methods of hole mandrelling by regular microrelief tool of the working surfaces under the conditions of using modern metal plaque lubricants, which implement the fundamental scientific discovery "Garkunov—Kragelsky frictionlessness effect", are studied using the theoretical foundations of the adhesion-deformation friction theory.

Numerical Treatment of MHD Flow of Casson Nanofluid via Convectively Heated Non-Linear Extending Surface with Viscous Dissipation and Suction/Injection Effects

This paper introduces the effect of heat absorption (generation) and suction (injection) on magnetohydrodynamic (MHD) boundary-layer flow of Casson nanofluid (CNF) via a non-linear stretching surface with the viscous dissipation in two dimensions. By utilizing the similarity transformations, the leading PDEs are transformed into a set of ODEs with adequate boundary conditions and then resolved numerically by (4–5)th-order Runge-Kutta Fehlberg procedure based on the shooting technique. Numerical computations are carried out by Maple 15 software. With the support of graphs, the impact of dimensionless control parameters on the nanoparticle concentration profiles, the temperature, and the flow velocity are studied. Other parameters of interest, such as the skin friction coeffi- cient, heat, and mass transport at the diverse situation and dependency of various parameters are inspected through tables and graphs. Additionally, it is verified that the numerical computations with the reported earlier studies are in an excellent approval. It is found that the heat and mass transmit rates are enhanced with the increasing values of the power-index and the suction (blowing) parameter, whilst are reduced with the boosting Casson and the heat absorption (generation) parameters. Also, the drag force coefficient is an increasing function of the powerindex and a reduction function of Casson parameter.

Influence of Conditions Employed in Application of Ti–Zr–Si–N Nanostructured Coatings on their Composition, Structure, and Tribomechanical Properties

Nanostructured coatings of thickness from 1.5 to 2 μm are applied to Ar+ ions-prepurifi ed stainless steel substrates by means of reactive magnetron sputtering of composite targets with the content of Ti–Zr–Si components 56, 36, 8 at.% and 36, 56, 8 at.%, respectively. Using the methods of Rutherford back scattering and transmission electron microscopy, we studied the structure of the coatings obtained, their phase composition, and the distribution of components over the depth of coatings. The microhardness of coatings was measured and their basic tribomechanical characteristics were investigated. The dependence of the composition and properties of coatings on the conditions of their application has been examined. The optimum regimes of application of coatings with high tribomechanical properties that ensure microhardness of coating of 31 GPa and double decrease in the friction coeffi cient have been determined.

Performance of WC- inserts coated with nanometric [TiN/TiAlN]n- multilayer for the cutting processing of hardened AISI 4340 steel

In the present work wear resistance of 4 μm uncoated tungsten carbide inserts (WC) and coated with [TiN/TiAlN]n multinanolayered or with commercial TiCN-Al2O3-TiN monolayers (TINAL) are examined. Life tests, cutting area temperature analysis, surface roughness measurements on work pieces, roughness measurements on the attacked surface, contact track analysis between chip-insert and chemical composition analysis (EDS) were carried out. Mechanical tests were conducted on AISI 4340 steel parts using cutting regime and applying high speed cutting (HSC). Machining results showed that for a distance of 8,000 m the inserts coated with 300 bilayers exhibited wear values of 0.117 mm, inserts coated with 200 bilayers showed values of 0.138 mm and those coated with TINAL presented wear values of 0.174 mm. Moreover, the temperature values for cutting speed at 176.6 m/mim for 300 bilayers was 522.6 oC, for 200 bilayers was 721.4 oC and 1,327.6 oC for inserts coated with TINAL. Lower temperatures, caused by a lower friction coeffi cient and cutting force, contribute to life-time increasing at WC inserts.

An iterative numerical method for determination of temperature-dependent friction coefficients in thermomechanical model analysis of cold bolt forging

A set of temperature-dependent friction coeffi- cients was developed to increase the accuracy of finite element (FE) simulations of cold bolt forging. The initially attained friction coefficients at different temperatures were calibrated with the iterations between the experimental and thermomechanical model extrusion test loads. The constant friction coefficient and the determined set of friction coef- ficients as function of temperature were then implemented to the simulations of the cold bolt-forging processes. Further calibrations and model validations were made based on the temperature measurements of the workpiece in the actual bolt-forging processes. To show the advantages of devel- oped temperature-dependent friction coefficients, the loads of four different bolt-forging processes were compared with the thermomechanical model loads calculated using the constant friction and temperature-dependent friction coeffi- cients. The modeling results indicated that the use of temperature-dependent friction coefficients in the FE simu- lations resulted in nearer temperature distributions and the loads of the workpiece during forging as compared with the use of a constant friction coefficient.

Fluctuation theorem for an optically trapped tracer in dense colloids. A simulation study

The work supplied by an external parabolic potential that traps one tracer in a colloidal system is studied in this work by computer simulations. The density of the bath is changed from zero up to values close to the glass transition, and the velocity varies over several decades from the linear behaviour in the low Peclet limit to the high Peclet limit. The work distributions are analyzed using the model for the isolated Brownian particle, where the friction coeffi cient and temperature of the medium have been fitted to reproduce the position distribution of the tracer in the trap. The overall agreement is good but not perfect. The region of negative works is studied in more detail using the predictions of the fluctuation theorem, finding good qualitative agreement with the model of the isolated Brownian particle. The present results indicate that the fluctuation theorem is of application in cases where the tracer dynamics is complex, as predicted by theoretical works.

Novel estimation of tyre-road friction coefficient and slip ratio using electrical parameters of traction motor for electric vehicles

The estimation of the friction coeffi cient and the slip ratio is crucial for advanced traction control or anti-brake control of electric vehicles. In this paper, dynamic behaviours of electrical parameters of the traction motor under road change are modelled and analysed. Novel estimation only using the measurements of the armature voltage and the current is proposed. The proposed method is much quicker than traditional methods, contributing to adjust the vehicle’s motion state more quickly and precisely. Further, it can eliminate the speed measuring devices of the wheel speed and the vehicle speed. Simulations verify the effectiveness.

A simplified approach for modelling airborne nanoparticules transport and diffusion

A simplifi ed approach is proposed and used to study the TiO 2 nanoparticle transport and diffusion in an exposure chamber. This exposure chamber is used to assess lung toxicity in rats resulting from the inhalation of airborne nanoparticles. The simplifi ed approach uses computational fl uid dynamics (CFD) commercial software. The mathematical model for airfl ow is based on the three-dimensional Reynoldsaveraged Navier–Stokes equations with turbulence modeling. The mathematical model for airborne nanoparticles transport is based on assumptions such that their motions are similar to those of a singlesized diameter distribution of a passive contaminant. This model is valid as long as the nanoparticle concentration is low and the particle diameter is small enough that settling is negligible, which is the case for the exposure chamber studied. With this model, the diffusion coeffi cient is a property that plays a signifi cant role in the transport of airborne nanoparticles. The particle diffusion coeffi cient can be expressed in terms of a friction coeffi cient, and three possible relationships to model particle diffusion are presented. Their infl uences on the friction and diffusion coeffi cients are considered for the particular case of TiO 2 nanoparticles. Although all the models studied here predict a decrease in the value of the diffusion coeffi cient with increasing particle diameter, some signifi cant variations can be observed between the models. A specifi c diffusion model is selected and then used with the simplifi ed approach. The simplifi ed approach is fivalidated against available correlations for particle deposition on walls. Correlation for deposition loss rate in the case of a room agrees with numerical prediction for particle diameter between 10 and 200 nm. Particle mass concentration distribution inside the exposure chamber is also studied. The computed concentration distribution is quite uniform inside the exposure chamber and corresponds to single point measurements.

Determination of plant characteristics used in discharge capacity assessment of Turkey Creek watershed on South Carolina coastal plain, USA

Determination of plant characteristics used in discharge capacity assessment of Turkey Creek watershed on South Carolina coastal plain, USA. Riparian vegetation type, composition, structure, and its abundance on fl oodplains exert a strong infl uence on riparian surface and subsurface hydrology and discharges of rivers and streams. The conditions of fl ood waters fl ow in such valley types are shaped by the existing vegetation cover. In this study, on the basis of vegetation inventory in four selected and representative basins, the substitute geometrical parameters of the medium and tall vegetation were determined and friction coeffi cients for low vegetation. These parameters were determined for 72 km2 forested watershed draining a 3rd order stream as affected by fl oodplain riparian vegetation on the Atlantic Coastal Plain in South Carolina, USA. The vegetation parameters, determined directly from the measurements, were verifi ed against the rating curve, that was achieved from discharge measurements as well as from discharge capacity calculations of the valley cross-section. In discharge capacity calculation, the Pasche method was used to calculate the total Darcy-Weisbach friction factor for each cross section according to the type of vegetation and fl ow interaction between the main channel and vegetated areas. In this approach friction caused by interaction between the main channel and vegetated areas are taken into account. The calculations performed on the basis of determined geometrical parameters of tall vegetation, show good agreement between the model and the measurements.

Influence of sliding contact local dynamics on macroscopic friction coefficient variation

The aim of this paper is to present a means of analysing “friction instabilities”. The explicit dynamic finite element software PLAST3 in 3D is used to simulate the behaviour of the two bodies (pin and disk) of a tribometer during frictional contact. Coulomb's friction law is used at the contact surface. The phenomenon of relay between the instantaneous contact zone, the contact stresses distribution and the kinematics of the contact surfaces are presented. As the friction coefficient and velocity of the disk are considered constants in the simulations, the contact zone (stick, slip) and separation depend on a “dynamic effect”. This generates wave propagation in the interface and involves a variation of normal contact stress. Definitions of macroscopic and local friction coefficients are given. The interfacial instabilities due to the dynamic effect produce a macroscopic friction coefficient that is less than the local friction coefficient. The influence of disk velocity on the macroscopic friction coeffi...

Bed-Load Transport Equation for Sheet Flow

When open-channel flows become sufficiently powerful, the mode of bed-load transport changes from saltation to sheet flow. Where there is no suspended sediment, sheet flow consists of a layer of colliding grains whose basal concentration approaches that of the stationary bed. These collisions give rise to a dispersive stress that acts normal to the bed and supports the bed load. An equation for predicting the rate of bed-load transport in sheet flow is developed from an analysis of 55 flume and closed conduit experiments. The equation is i b5v where i b5immersed bed-load transport rate; and v5flow power. That i b5v implies that e b5tan a5ub /u, where e b 5Bagnold's bed-load transport efficiency; ub5mean grain velocity in the sheet-flow layer; and tan a5dynamic internal friction coeffi- cient. Given that tan a'0.6 for natural sand, ub'0.6u, and e b'0.6. This finding is confirmed by an independent analysis of the experimental data. The value of 0.60 for e b is much larger than the value of 0.12 calculated by Bagnold, indicating that sheet flow is a much more efficient mode of bed-load transport than previously thought.