Variation Of Friction Coefficient Research Articles

Design and Implementation of an Electromechanical Brake System

Nowadays, hydraulic brakes are already being replaced by electromechanical brakes (EMB) to improve quick-response brakes, efficient fuel consumption, environmentally sound, simple maintenance, and enhanced safety design. It is suggested that the electromechanical brake will be one of the most important brake systems in the future. This study focuses on designing and implementing an electromechanical brake based on a brushless DC (BLDC) motor and position controller to generate and control the required braking force at a variable friction coefficient between disc and pad. A feedback controller equipped with a measuring sensor is usually utilized to control this type of brake. Thus, three controllers for current, speed, and position were implemented in successive loops to control the motor movement. This system has current, speed, and force sensors. Due to implementation difficulties and cost issues of braking, the clamping sensor should be replaced with a position sensor with some modification where a position controller has been designed and implemented. The results showed that the clamping force of the brake system can follow the target accurately and it has good performance. Also, it is shown that this system can adjust the brake force more accurately and quickly compared with the traditional.

Stress-based topology optimization of continuum structures for the elastic contact problems with friction.

Structural problems have various nonlinearities in the real world and these nonlinearities should be accommodated in structural topology optimization. This work proposes a topology optimization method for minimizing the maximum von Mises stress of elastic continuum structures with frictional contact under material usage constraint, using an extended Bi-directional Evolutionary Structural Optimization (BESO) method. Stresses are treated as global performance (objective) function, the global von Mises stress is measured by the p-norm stress aggregation approach, and the friction behavior is governed by the Coulomb friction law regularized in analogy with the perfect elasto-plastic theory. BESO method based on discrete variables which can avoid the well-known stress singularity and the numerical instability issue in frictional contact problems. The adjoint sensitivity analysis method is adopted to derive the sensitivity numbers. The effectiveness of the proposed method is validated through a series of comparison studies including elastic-rigid and elastic-elastic contact problems. The influence of varying friction coefficient on the optimized results and the stress distributions are investigated in comparison with the maximum stiffness design. The effect of different parameters including p-norm, volume fraction and mesh density on the optimized results are discussed. The optimized results, for elastic-rigid contact, indicate that the maximum stress can be reduced compared with elastic-elastic contact. The optimized stress decreases as the friction coefficient increases because the friction behavior resists the tangential deformation at the contact interface. The results also show that the proposed approach can achieve a reasonable design that effectively controls the stress level and reduces the stress concentration effect at the critical stress areas.

Assessment of the tribolological behavior of a metallic tribopair: LM25 alloy-Si3N4 composites against EN 31 steel

In the present research work, tribological behavior of hard ceramic silicon nitride (Si3N4) reinforced aluminium alloy LM 25 based composites against EN 31 steel in ambient conditions at various loads (19.60–58.86 N) and sliding distances (1200–2400 m) on pin-on-disk test rig was investigated for commercial purpose of machine components. Three sets of composites were fabricated with 4–12 % of silicon nitride by stir casting technique. SEM Micrographs revealed formation of a homogeneous α-aluminum dendrites network structure developed due to the super-cooling of casting during solidification. EDS showed increased content of hard silicon and nitrogen from 29.04 to 73.96 % and 6.68–14.54 % respectively with 4–12 % reinforcement addition which led to high hardness. Increase in hardness from 58.02 to 63.70 BHN is observed with increase in reinforcement which led to reduction in wear by reducing the actual contact area during sliding whereas strength is reduced on addition of Si3N4. The wear resistance of composite is found greater with 12 % Si3N4 reinforced composite with reduced wear at low sliding distance. Due to continuous sliding, wear debris embedded with the surface forming a layer which resulted in variation in coefficient of friction (COF). COF increased at a high rate up to 1800 m followed at a slow rate up to 2400 m sliding distance with increase of normal load. SEM analysis of worn surfaces revealed removal of surface layer with generation of micro cracks with subsequent sliding in composites reinforced with 4 % and 8 % silicon nitride whereas ploughing mechanism is observed in composite with addition of 12 % Si3N4. The linear increasing trend was observed in wear loss against the dissipated energy for the investigated composites.

Development and analysis of friction characteristics of coir fiber added organic brake pad composite

Automobile brake pads are built of composite materials that contain greater than six different elements. In the current scenario, research into new materials to substitute asbestos is being investigated. The friction material chosen has a significant effect on a vehicle's braking attainment. Drivers anticipate the brake system to bring the vehicle to a complete stop in any situation. Dried coir fibre is employed as a new material in brake pads in this research. In the mix of other standard materials in brake pads, different amounts of coir fibre are employed. A recently developed brake pad material including six distinct constituents was put to the test in the Pin on Disc Test (Sliding Wear), as well as the Sand Wear Test (Abrasion Wear). The variations in friction coefficient, the pressure on the friction surface, and the quantity of wear are all documented in this research. Furthermore, scanning electron microscopy is used to characterize the microstructure of brake pads (SEM).

An experimental analysis on nanoparticles role in drilling fluids

The study around nanotechnology has increased in the last decade or so, with rise in applications in many industries. There are now many nanotechnology-based products available like in healthcare, defense, coating industries etc. It has seen rise in usage in oil and gas industry as well. Application of nano particles in water based muds results in reduction of fluid loss and hence increases the wellbore stability and drilling efficiency. In this study, we have examined the fluid loss on water-based mud by adding graphene nanoparticles as additive and estimated the optimum value of nanoparticle composition for having less fluid loss. The results of experimental analysis for filtration loss from water-based mud with addition of graphite nanoparticles was studied and effect of friction factor was analyzed. The nanoparticles concentration added in fluid ranges from 1 to 5 lb/bbl and the size of the particles was observed to be 30–80 nm. Variation of fluid loss volume and friction coefficient under different nanoparticle composition was established.

Modeling and Analysis of Runway Friction Coefficient Prediction Methods Based on Multivariable Coupling

Friction, generated in the contact patch between tires and runway, has long been recognized as a key issue to a safe landing. Moreover, soft sensing technology is also considered to be one of the effective means to improve measurement accuracy and reduce measurement cost of friction coefficient. This article presents a study on the prediction methods of runway friction coefficient based on multivariable coupling. Firstly, the relationships between friction coefficient and tread frictional stress under different working conditions are investigated using finite element analysis; meanwhile, the modeling dataset and test datasets for multivariate coupling are established. Secondly, regression analysis and BP neural network (BPNN) are used to develop prediction models between independent variables (inflation pressure, load, velocity, slip, and frictional stress) and dependent variable (friction coefficient). Finally, the prediction models are evaluated based on internal and external verification. The results demonstrate the superior performance of both prediction models. After further comparison, it is concluded that the performance of BPNN is even better combining the error range and model evaluation indicators including MAE, RMSE, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}^{2}$ </tex-math></inline-formula> .

Tribological Analysis of a Radial Plain Bearing

The paper presents experimental determination of the friction coefficient variation at a radial plain bearing, depending on the values of the radial force R and the angular speed ω of the spindle at a constant lubricant temperature value.

Study and comparison of wear behaviour of Ni-Al2O3 coatings deposited by hot and cold spray

The sliding wear of hot and cold spray nickel-alumina coatings on SA 213-T 91 boiler steel has been evaluated and compared. The investigation was conducted with pin-on-disc apparatus. The wear testing was done by varying normal loads of 30, 40, and 50 N at a constant sliding velocity of 1 ms−1. Then another set of experimentation was done at different sliding velocities of 0.5, 1, and 2 ms−1 at a constant normal load of 30 N. This experimentation was designed to study the effect of varying normal loads and sliding velocities on the wear performance of coatings developed with hot and cold spray techniques. The variation of friction coefficient and wear rate with variation in normal loads and sliding velocities were plotted and analyzed. The evaluation of wear mechanisms and characteristics of Ni-Al2O3 coatings is done with the help of weight change measurements and FE-SEM analysis. The wear resistance of hot spray coatings was found better at high normal loads and sliding velocities in comparison to cold sprayed coatings.

Assisting and opposing flow of a MHD hybrid nanofluid flow past a permeable moving surface with heat source/sink and thermal radiation

The aim of the current investigation is to study the assisting and opposing flow effects on hybrid nanofluid ( SiO 2 - MoS 2 /water) flow past a moving surface under the impact of heat source/sink, thermal radiation and velocity slip. Also, the moving surface is exposed to convective heating and surface is assumed to be permeable in an attempt to achieve the suction/injection of hybrid nanofluid boundary layer through the surface. As a novelty, we have presented a comparative analysis of all the results for assisting and opposing flow cases. Similarity transformations are utilized to transcribe the momentum and thermal equations in non-dimensional form. The “bvp4c” solver is used to solve the hybrid nanofluid flow problem numerically. Effects of the assisting and opposing flow with nanoparticles volume fraction, heat source/sink, Biot number, thermal radiation parameter, velocity slip parameter and suction/injection parameter on the temperature and velocity profiles are studied. The variations in skin friction and heat transfer coefficient are discussed through tables outlined and three-dimensional figures. Results reveals that hybrid nanofluid velocity is higher in case of assisting flow in comparison to opposing flow. The role of increasing values of Biot number and thermal radiation parameter is to surge the temperature of the hybrid nanofluid ( SiO 2 - MoS 2 /water) flow as well as rate of heat transfer at the surface. The nanoparticles volume fraction (of MoS 2 and SiO 2 ) also enhances the temperature at the wall. It is revealed that slip parameter has contrary effects on both heat transfer and skin friction coefficient for assisting and opposing flow.

Experimental and Numerical investigation of implementing a novel vortex generator: A Perforated Delta Wing Vortex Generator (PDWVG) on the performance of Solar Air Collector

Experiments were carried out for the numerical investigation of heat transfer enhancement in a solar air collector using different types of baffles and vortex generators. In this study, the vortex generator was implemented to increase the efficiency of the solar air collector. The variations in Nusselt number, pressure drop, friction coefficient, thermal and exergy efficiency in four collectors with different baffles arrangement (type A, B, C, D) were investigated. Type A was chosen as the optimum collector for implementing the vortex generator on the absorber surface. In the solar air collector the effects of using a novel vortex generator - the Perforated Delta Wing Vortex Generator (PDWVG), in comparison with a flat one - the Flat Delta Wing Vortex Generator (FDWVG), were considered. In order to determine the maximum efficiency of the solar air collector, four different pitch ratios of vortex generators were studied. The Nusselt number and pressure drop increased with Reynolds number but the friction coefficient decreased with Reynolds; the experimental and numerical results revealed that the thermal and exergy efficiency decreased from a specific range. The comparison of PDWVG and FDWVG showed that presence of holes on the novel vortex generator, led to reduced pressure drop and increased the heat transfer between the air flow and the absorber surface. Increasing the number of vortex generator rows had a slight effect on increasing the studied parameters. The results showed that collector type A with ep=0.55 of PDWVG improves the energy and exergy efficiency 4.43% and 5.29% respectively.

Straight-line path-following control for roll-out phase of the equipped-skid aircraft

The paper deals with straight-line path-following control design for the aircraft equipped with skid landing gears. First, a simple yet accurate on-ground aircraft model is established, which takes into account the effects of the aerodynamic and ground forces. To improve the directional stability of the aircraft during the roll-out phase, a novel skid with variable friction coefficients is proposed. Second, the path-following problem is converted to the attitude control problem by constructing a guiding vector field that generates the commanded course, and then an improved error function is proposed to manage the trade-off between the convergence rate and the strong lateral maneuvers. To achieve a good performance in path following, the incremental nonlinear control allocation is applied to make full use of three available actuators (nose wheel, variable friction skid, and rudder). The expected path here is the runway centerline so as to avoid runway excursions. Finally, the effectiveness and robustness of the path-following control are validated on different initial conditions. Results show that the proposed skid structure and control scheme are propitious to enhancing the resistance to crosswind. Moreover, the maximum lateral displacement during the path-following process decreases, especially in the low-speed region.

Finite element modeling of tessellated beams

Tessellated Structural-Architectural (TeSA) systems are composed of repeated tiles that can interconnect, be designed to have load carrying capacity, and are aesthetically pleasing. TeSA systems may localize damage to few tiles when subjected to extreme loads, may facilitate easier or faster reparability, and contribute to resilience. This research investigates numerical modeling of simply supported TeSA beams. Finite Element (FE) analysis was performed and the results were validated using experiments of TeSA beams made of Medium Density Fiberboard (MDF). The FE analysis incorporated gaps and interaction between tiles. The results showed that contact properties and gap size between tiles affected the calculated load-displacement relationship and strain of the TeSA beam. Contact properties were captured by a pressure-overclosure relationship, which required calibration using the global load-displacement response obtained from testing. Incorporation of geometric nonlinearity did not affect the results significantly. Beams with varying friction coefficient between tiles, load and support bearing width, Poisson's ratio and aspect ratios were analyzed. The results showed that TeSA beams had smaller stiffness than solid beams with similar dimensions. The outcomes of this research provide insights on the behavior and modeling of TeSA structures.

Duality Solutions in Hydromagnetic Flow of SWCNT-MWCNT/Water Hybrid Nanofluid over Vertical Moving Slender Needle

Recently, the topic of convection of heat transfer has created an interest among researchers because of its numerous applications in the daily life. The objective of this paper was to study theoretically the problem of mixed convection boundary layer flow and heat transfer of single-wall carbon nanotube (SWCNT) and multi-wall carbon nanotube (MWCNT) in presence of hydromagnetic effects. The problem was initiated by formulating a mathematical model in partial differential equation (PDE) for the hybrid nanofluid flow with appropriate boundary conditions. The similarity equation was used to transform the PDE into an ordinary differential equation (ODE) and solved using bvp4c in MATLAB. The graphical results on variation of skin friction coefficient, Cf, local Nusselt number, Nux, shear stress, f″c and local heat flux, −θ′c with the effects of magnetic, M, size of needle, c, mixed convection parameter, λ and volume fraction of nanoparticles, φ were presented and discussed in detail. The study revealed that duality of solutions appears when the buoyance force is in opposing flow of the fluid motion, λ&lt;0. The presence of M in hybrid nanofluid reduced the skin friction coefficient and heat transfer. On the other hand, the Cf and Nux increased as different concentrations of φ1 and c were added. It gives an insight into the medical field, especially in treating cancer cells. By means, it reveals that CNTs hybrid nanofluid shows high potential in reaching the site of tumors faster compared with nanofluid. A stability analysis has to be carried out. It is noticed that the first solution was stable and physically realizable.

Robust fuzzy sliding mode controller for a skid-steered vehicle subjected to friction variations.

Skid-steered vehicles (SSV) are gaining huge importance in the market due to their applications like construction, agricultural work, material handling etc. The accuracy of performing such tasks require a robust control algorithm. The design of such controller is very challenging task due to external disturbances caused by wheel-ground interaction and aerodynamic effects. This paper proposes robust fractional and integral order fuzzy sliding mode controllers (FSMC, FFSMC) for a skid-steered vehicles with varying coefficient of friction and a displaced center of gravity (CG). FFSMC controller reduces the outcome of forces generated as a result of ground tire interaction during skidding and friction variations. The proposed controllers are implemented for a four-wheel SSV under high-speed turning motion. A simulation environment is constructed by implementing the SSV dynamics with wheel-road model and the performance of the proposed algorithms is tested. The simulation test is conducted for a Pioneer-3AT (P-3AT) robot SSV vehicle with displaced CG and variable coefficient of tires friction. Simulation results demonstrate the efficiency of the proposed FFSMC algorithm in term of reduced state errors and minimum chattering. The proposed controller compensates the effect of different responses of the wheels generated as a result of variable CG. The chattering phenomenon generated by conventional SMCs is also minimized by fuzzy tuning approach.

Rheology of two-dimensional granular chute flows at high inertial numbers

Contrary to the popular inertial number-based rheology of dense granular flows, recent studies suggest a non-monotonic variation of the effective friction coefficient μ(I) with the inertial number I in plane shear flows. While the popular rheology assuming monotonic variation of μ(I) with I suggests existence of an upper limit of inclination angle for steady chute flows, the non-monotonic variation suggests the possibility of two different flow states for chute flows at a given inclination angle. In this work, we perform DEM simulations of chute flow of frictional inelastic disks and show that steady, fully developed flows are possible at inclinations much higher than those predicted from the monotonic μ−I rheology. We observe steady flows up to inertial number I≈2 and find non-monotonic variation of the effective friction at high inertial numbers for chute flow of disks. The flows at high inertial numbers exhibit a constant density bulk region supported on top of a very dilute energetic basal layer of particles. We show that, in addition to a modified effective friction law that accounts for the non-monotonic variation of μ(I) and the dilatancy law relating the solids fraction ϕ with I, the rheological description also needs to account for the stress anisotropy by means of a normal stress difference law. By accounting for the presence of the normal stress difference, we also establish that only a single flow state is possible at any given inclination angle despite the non-monotonic variation of the effective friction coefficient.

Multiple slips and heat source effects on MHD stagnation point flow of casson fluid over a stretching sheet in the presence of chemical reaction

The numerical analysis of the steady MHD stagnation point flow of a Casson fluid flow over a stretching sheet in the presence of a heat source and the first-order chemical reaction with multiple slip boundary conditions taking into account viscous dissolution, Joule warming, and the first-order chemical response with multiple slip boundary conditions is performed. The governing flow equations are interpreted with the assistance of identity transmutations, and the condensed nonlinear coupled ordinary differential equalisations are determined applying the shooting approach. With the use of graphs, the impacts of several factors on the dimensionless velocity, temperature, and concentration profiles are demonstrated. In addition, graphical representations of the variation in skin friction coefficient for different values of the Casson fluid parameter against the Eckert number, the variation in the rate of heat transfer coefficients for various values of the Radiation specification against the Schmidt number, and the variation in the rate of mass transfer for different values of the chemical reaction specification against the Schmidt number are provided. Our findings indicate that when there is an increase in Heat source and Chemical reaction parameter always leads to degeneration in temperature profile and Chemical reaction. The Chemical reaction parameter was found to enhance the Sherwood number.

Development of wear resistant Cu-12Sn-1.5Ni alloy via minor addition of Fe during casting process

The evolution of microstructure and mechanical properties in as-cast Cu-12Sn-1.5Ni-(0–1.5)Fe (wt. %) alloys was investigated in the previous work. Herein, the effect of minor Fe (0, 0.053, 0.63 wt%) addition on wear behavior of the alloy surface was explored. The coefficient of friction (COF) (0.61 to 0.51 at load of 10 N, 0.67 to 0.42 at 5 N) and wear rate (42.0 × 10−5 to 23.1 × 10−5 mm3/(N·m) at 10 N, 18.7 × 10−5 to 3.6 × 10−5 mm3/(N·m) at 5 N) decreased with addition of Fe. A transition in wear mechanisms was noticed with applied load. Abrasion wear was the dominant mechanism at 10 N together with slight oxidative wear, while adhesion and tribo-oxidation mechanisms controlled the wear at 5 N. The delamination and wear debris on worn surfaces lessened with increasing Fe both at 10 and 5 N, in line with the variation in COF and wear rate. The mechanisms underlying the improved wear behavior were evaluated in terms of microstructural optimization, densification and enhancement in mechanical properties. This work indicates the advantage of minor amount of Fe addition to achieve better wear resistance of nickel bronze alloys.

An improved mesh stiffness model of helical gear pair considering axial mesh force and friction force influenced by surface roughness under EHL condition

An improved mesh stiffness calculation model of helical gear pair is proposed, in which the transverse gear tooth stiffness, transverse gear foundation stiffness, in addition to axial gear tooth stiffness, axial gear foundation stiffness, that influenced by surface roughness under elastohydrodynamic lubrication (EHL) condition are fully considered. The time varying friction coefficients are obtained by elastoplastic model under varying surface roughness, and then the influence of friction force on mesh stiffness calculation are investigated. The results show that the improved mesh stiffness calculation model could obtain the mesh stiffness under actual lubrication condition compared with conventional method, in which the axial mesh forces and friction forces acting on the gear tooth and gear foundation are always ignored in the mesh stiffness calculation for helical gear pair.

Numerical simulation of the frictional heat problem of subway brake discs considering variable friction coefficient and slope track

Friction heating during braking may causes premature wear, thermal cracks and other damages which could weak the braking performance of subway vehicles. It is therefore important to determine the temperature field of the brake disc. The purpose of this paper is to propose a one-dimensional brake disc model and apply a new solution algorithm to obtain the temperature field of the brake disc, which is validated by the Renk Dynamometer test bench. The advantage of this numerical model is that the variable friction coefficient and slope are taken into account. The experimental dependency of the coefficient of friction on the velocity is approximated by interpolation and applied to the numerical model. The calculation is based on two cases of constant and velocity-dependent friction coefficient (COF) by using the method of lines (MOL), which has the advantage of shorter computation time and improved accuracy. The numerical results agree well with the experimental data. It was proved that disregarding the velocity dependence of the coefficient of friction, the maximum temperature during the entire braking process was underestimated by 15%. In addition, the subway vehicle braking on slope should decrease the speed limit appropriately to reduce the maximum temperature of the brake disc. This study can provide a theoretical basis for further fatigue study of brake discs.

Effect of processing speed on wear and corrosion behavior of novel MoS2 and CeO2 reinforced hybrid aluminum matrix composites fabricated by friction stir processing

The extensive use of aluminum matrix composites as structural material urges it to possess good surface properties such as wear and corrosion resistance. To achieve that, mixture of MoS 2 and CeO 2 powder was reinforced in Al7075 alloy through friction stir processing with different processing speed and multi-pass approach. The microstructural image analysis by optical microscope and scanning electron microscope revealed reduction of matrix grain size and improvement of particle distribution for lower processing speed and multi-pass processing. The elemental analysis indicated well dispersion of reinforcement particles in matrix along with the presence of compounds of aluminum alloy. The microhardness and tensile strength were increased with reduction of processing speed and increase of number of pass. The friction coefficient and the wear loss were also low for composites produced with low processing speed and multi-pass. A combined abrasive and adhesive wear was observed in all the processed composites. With increase of processing speed and number of pass, the corrosion behavior of the composites in 3.5% NaCl solution deteriorated. The composite produced with 30 mm/min and 2 pass exhibited best particle distribution, microhardness and wear resistance. However, the composite fabricated with 30 mm/min and 1 pass yielded best corrosion resistance. • Novel hybrid aluminum matrix composites developed by friction stir processing • Microstructure of the fabricated composites analyzed • Microhardness distribution measured • Wear mechanism and friction coefficient variation analyzed and effect of processing speed on wear loss discussed • Corrosion behavior and effect of process parameters on corrosion parameters discussed