Contact Spots Research Articles

Dispersion forces and equilibrium distance between deposited rough films in contact

The average distance ${h}_{0}$ separating two contacting bodies is a critical parameter for many problems, for example, for control of unwanted stiction in micro/nanoelectromechanical systems. Here this problem is analyzed in relation to precise determination of the dispersion forces in a difficult for measurement range of $5\ensuremath{-}30\phantom{\rule{0.222222em}{0ex}}\mathrm{nm}$. The unloaded contact between two deposited rough films characterized by a relatively large number of high asperities is considered. The equilibrium distance ${h}_{0}$ can be found from the balance of attractive dispersion forces and repulsive forces acting in the spots of real contact. A simple columnar model associated with AFM images of rough surfaces is used to describe the balance. The numerical analysis, which treats the high asperities as elastoplastic semispheroids, demonstrates that the columnar model describes the contact adequately. It is shown that in contrast with the value of ${h}_{0}$ the adhesion energy between the surfaces is nearly entirely defined by the dispersion interaction, but the effects of contact interaction and plastic deformations can be neglected. This property is proposed to use for more precise determination of the equilibrium distance.

Relative Slippage During the Modulation of Interaction of a Pneumatic Tire with a Bearing Surface

In design problems for new vehicles and modernization of existing ones mathematical models are required. Such models must represent the main features of the automobile as a manipulation object and allow to predict the reaction and behavior of the car to the impact both of the external environment and driver. Deep theoretical research is important for the adjustment of the vehicle design at all stages of modelling and construction and implementation of necessary changes in technical decisions previously taken. During creation of an imitational mathematical model of movement of the vehicle the most important problem is to credibly describe the physics of interaction between pneumatic tire and bearing surface in order to determine the forces acting in the contact spot. Initial parameters for the calculations of a single wheel are: the coefficients of relative slippage, the coefficients of adhesion and the angle of withdrawal.

Method for estimating the initial welding current of closed high-current contacts under pulsed heating

A study of the softening process of contact spots of closed high-current copper contacts caused by recrystallization of the material during short-circuit shock currents has been carried out. An original method has been developed for calculating the magnitude of the pulse current, which initiates the welding of contacts, which does not require preliminary experimental measurements. Keywords: Electrical contact, pulse heating, numerical calculation, welding.

Метод оценки тока начального сваривания замкнутых сильноточных контактов при импульсном нагреве

A study of the softening process of contact spots of closed high-current copper contacts caused by recrystallization of the material during short-circuit shock currents has been carried out. An original method has been developed for calculating the magnitude of the pulse current, which initiates the welding of contacts, which does not require preliminary experimental measurements.

Method for the influence design assessment of a wheeled agricultural vehicle on the soil

The impact of a wheeled agricultural vehicle on the deformable support surface determines the vehicle's ability to move, as well as soil compaction, which is not desirable in agriculture. The agricultural machine must not cause more pressure on the ground than is permissible. Therefore, in the tasks of design numerical modelling of the agricultural vehicle movement or trailer, it is required to calculate the specified parameter. It is impossible to calculate without knowledge of the geometric characteristics of the contact spot associated with the normal deformation of the tire under normal load. To calculate these characteristics, it is necessary to have universal dependencies for determining the normal stiffness of the tire. These are available for tires of various purposes. The elastic properties of ultra-low pressure tires are insufficiently studied. Experimental studies of the elastic properties of these tires have been carried out with the authors participation. However, there are currently no dependencies to describe them. This does not provide the possibility of a correct design calculation of the influence of such tires on the soil. The purpose of the work: to develop a universal method for calculating the influence on the soil of agricultural vehicle. A universal method for calculating the impact of a wheeled agricultural machine on the ground has been developed. Universal design-experimental dependence for determining the normal stiffness of ultra-low pressure tires is obtained. It takes into account tire pressure, normal load under specific conditions and geometric characteristics.

The role of contact spots of friction pairs of microprotrusions in the energy loading of braking devices

The role of contact spots of friction pairs of microprotrusions in the energy loading of braking devices

NUMERCNAL ANALYSIS OF CONTACT INTERACTION OF BODIES WITH NEARLY FORM SURFACES

Contact interaction of structural elements has been studied in the case of nominally close (nearly matching) surfaces. A non uniform gap is present between the contacting parts. Contact pressure and contact spot depend on the shape of this gap. Correspondingly so does the stress-strain state of the contacting bodies too. Since the problem is essentially nonlinear, the contact pressure distribution and the contact zones change with the growing loads. The solution is qualitatively different to the case of perfectly matching bodies. For the latter case, the contact pressure is linearly proportional to the load and the contact zone is predefined. Hence for the real structures for which the deviation from the nominal shape is unavoidable the impact of these inaccuracies on the contact pressure distribution and the stress-strain state need to be taken into account. This problem is addressed in the paper by example of elements of stamping dies. Keywords: element of stamping dies, stress-strain state, contact pressure, contact interaction, variational inequalities, Kalker’s variational principle, finite element method, boundary element method

Microanalysis of Worn Surfaces of Selected Rotating Parts of an Internal Combustion Engine.

The present paper analyzes the damage of surfaces at spots of frictional contact, namely, the friction nodes on a camshaft and the connecting rod pins of a crankshaft. The resulting wear of the monitored friction nodes reduces the technical life of the machines, which can lead to the decommissioning of the machine. Wear was assessed by measuring roughness and microhardness and by observing the microstructures of the materials. The results of the experiments show that the rotating parts displayed visible wear on the cams, as well as on the connecting rod pins. The experiments revealed that wear was caused by the heating of the material to a high temperature during the operation of the machine and that there was a gradual cooling and tempering of the material, which led to a reduction in the microhardness of the monitored object. Lower microhardness values can be a cause of greater wear of the monitored objects. When comparing the microhardness of the used and the new camshaft, the hardened layer of the new camshaft from secondary production has a significantly smaller thickness compared to worn cams, which leads to the finding of a different material quality compared to the original parts from primary production. This fact indicates that the wear of a new camshaft as a spare part can contribute to the shortening of the technical life of friction nodes.

Influence of Different Modified Gears on the Vibration and Noise of Electric Vehicle Reducer

The tooth profile crowning modification was applied onto paired gears for reducing the noise of an electric vehicle reducer. The simulated gear contact spots are compared before and after modification, and are validated by a contact spot experiment. Based on the rigid-flexible coupling model of the gear transmission system, the time-varying meshing stiffness, time-varying meshing force, and the vibration and noise of the gear pairs with different modified gears obtained by simulating calculation are analyzed. The results showed that the selection of modified gear has a great influence on the modification effect. In the way of tooth profile crowning, it is not advisable to modify the pinion independently, as it may increase the frequency and degree of meshing impact between the helical gear pair, making the transmission become less smooth; while modifying the wheel and pinion at the same time can effectively reduce the time-varying meshing stiffness and force, and the vibration and noise. Also, the optimized gear modification scheme is verified by the noise test.

Analysis of the influence of design parameters on the agro-ecological qualities of tractor tires

Experimental studies of the impact of agricultural mobile machinery movers on the soil are seasonal in nature and require complex experimental equipment. The complexity of the physical processes occurring in the elastic wheel-ground system requires the introduction of many assumptions and limitations that reduce the accuracy of the results, according to the design of simulation models performed in the software environment. The aim of the research was to study the influence of the design parameters of the tire on the efficiency of the normal deflection along the contact spot zone X. Studies have shown that 65% to 77% of the normal deflection of the tire is used when passing the contact spot. The reinforcement parameters of the tire frame have the greatest impact on the efficiency of the normal deflection along the contact spot zone. With an increase in the number of layers of the frame cord from 2 to 8, the coefficient of usability of the normal deviation for the stroke of the contact spot decreases from 0.761 to 0.689, with an increase in the angle of inclination of the frame cords - decreases from 0.755 to 0.693.

Increasing the load capacity of a gear transmission under skew conditions by reducing contact stresses by means of longitudinal modification of the teeth

A method was developed and dependencies were obtained for determining the parameters of the longitudinal modification of the gear wheels teeth. Longitudinal modification is an effective way to reduce contact stresses in case of misalignment of axes in gear mechanisms, increases the load capacity of the gear transmission. Examples of calculation are given. Keywords: gear transmission, contact spot, axle misalignment, uneven load distribution, longitudinal modification, barrel shape. filnahat7@mail.ru

Wheel drive with integrated differential

The performance indicators of wheeled arable machine-tractor units, which are accelerated on the working gear, depend on the operating modes of the wheels during this period. When the wheel is skidding, soil lumps break down in the contact spot, the soil structure is destroyed. Based on the system analysis of the wheels operation, the method of their improvement is justified by continuous control of the eccentric point of application of the driving torque and external load. As a result of the analysis for the first time, a soil-sparing wheel mover with the properties of a differential, a tangential force regulator and clearance regulator was developed. In the case of an eccentric application of a vertical load and a longitudinal pushing force, one of the satellites of the wheeled planetary gearbox is the leading and bearing one. The purpose of the article is to analyze the factors influencing the automatic adaptation of the wheel drive to changing operating conditions. It is established the relationship between the driving moment and the rolling resistance moment, the moments of inertia of the wheel and the drive gear of the integrated differential.

Modeling of Frictional Stick-Slip of Contact Interfaces Considering Normal Fractal Contact

Abstract In this paper, a new modeling approach is proposed to represent the tangential frictional stick-slip behaviors of contact interfaces in mechanical systems considering the surface fractal feature and normal loading conditions. Initially, surrogate asperities are defined to express the fractal feature of contact surface topography and the normal load of interface, and Jenkins elements are used to describe the tangential stick-slip motions between surrogate contact asperities. Then, a geometric series distribution principle of the normal loads at contact asperities is proposed to determine the yield forces of the Jenkins elements. The criterion for identifying the micro- and macro-slips of the contact interfaces is proposed, which are determined by the stick and slip conditions of the largest contact spot. An experimental setup for measuring the frictional stick-slip of contact interfaces is constructed, upon which tangential quasi-static experiments are conducted. Satisfactory agreements between the theoretical and experimental results indicate that the proposed modeling approach can perfectly predict the stick-slip behavior of contact interfaces. Finally, mechanical characteristics of the contact interfaces are investigated in detail by employing the validated modeling approach. Owing to the definite physical significance of the proposed modeling approach, the mechanism of the tangential stick-slip behavior of contact interfaces is partially demonstrated.

Erosion potential of ultrasonic food processing

Introduction. Cavitation is the most significant factor that affects liquid food products during ultrasound treatment. Ultrasonic treatment intensifies diffusion, dissolution, and chemical interactions. However, no physical model has yet been developed to unambiguously define the interaction between ultrasonic cavities and structural particles of liquid food media. Physical models used to describe ultrasonic interactions in liquid food media are diverse and, sometimes, contradictory. The research objective was to study ultrasonic devices in order to improve their operating modes and increase reliability.
 Study objects and methods. The present research featured ultrasonic field generated in water by the cylindrical emitter, the intensity of flexural ultrasonic waves and their damping rate at various distances from the emitter.
 Results and discussion. The paper offers a review of available publications on the theory of acoustic cavitation in various media. The experimental studies featured the distribution of cavities in the ultrasound field of rod vibrating systems in water. The research revealed the erosion capacity of ultrasonic waves generated by the cylindrical emitter. The article also contains a theoretical analysis of the cavitation damage to aluminum foil in water and the erosive effect of cavitation on highly rigid materials of ultrasonic vibration systems. The obtained results were illustrated by semi-graphical dependences. 
 Conclusion. The present research made it possible to assess the energy capabilities of cavities generated by ultrasonic field at different distances from the ultrasonic emitter. The size of the contact spot and the penetration depth can serve as a criterion for the erosion of the surface of the ultrasonic emitter.

Simulation and experimental investigation of contact spot temperature for electrical contact components

The contact spot temperature of electrical contact components substantially affects the reliability and electrical life of any electrical connections within the electrical engineering. In this paper, finite element model of typical spring structure components is built by using COMSOL Multiphysics software. Furthermore, the transient process of contact temperature is simulated by taking account of film resistance on the contact surface. Moreover, a test rig is introduced that makes it possible to measure the electrical contact resistance and temperature within the electrical contact components simultaneously. Finally, correlation between contact resistance and contact spot temperature with different contact force and current levels are investigated explicitly.

Development of a device for determining the coefficient of adhesion of a tire simulator with a flat support surface

To ensure optimal braking performance, i.e. minimum braking distance while maintaining the stability of the car at the limit of controllability, anti-lock systems are currently installed on cars. The relative fraction of the rest friction in the contact spot, which is used to form the longitudinal reaction of the support surface at the appropriate value of the slip coefficient, in relation to the total fraction of the rest friction in the contact spot is a constant value for any type and condition of the road surface. The coefficient of adhesion in physical essence is the coefficient of friction at rest. The proposed device for determining the coefficient of adhesion of a tire simulator with a flat horizontal support surface will simplify the design and increase the measurement accuracy. Keywords: coefficient of adhesion, a device for determining the coefficient of adhesion, a device

Influence of Stress Intensity Factor on Rail Fatigue Crack Propagation by Finite Element Method.

Wheel rail rolling contact fatigue is a very common form of damage, which can lead to uneven rail treads, railhead nuclear damage, etc. Therefore, ANSYS software was used to establish a three-dimensional wheel–rail contact model and analyze the effects of several main characteristics, such as the rail crack length and crack propagation angle, on the fatigue crack intensity factor during crack propagation. The main findings were as follows: (1) With the rail crack length increasing, the position where the crack propagated by mode I moved from the inner edge of the wheel–rail contact spot to the outer edge. When the crack propagated to 0.3–0.5 mm, it propagated to the rail surface, causing the rail material to peel or fall off and other damage. (2) When the crack propagation angle was less than 30°, the cracks were mainly mode II cracks. When the angle was between 30 and 70°, the cracks were mode I–II cracks. When the angle was more than 70°, the cracks were mainly mode I cracks. When the crack propagation angle was 60°, the equivalent stress intensity factor reached the maximum, and the rail cracks propagated the fastest.

Snow Temperature Behind Sliding Skis as an Indicator for Frictional Meltwater

For many years, a frictional meltwater film has been assumed to be the reason for the low friction between skis and snow, but experimental studies have been inconclusive. Therefore, the aim of our study was to find indications or evidence for the presence of frictional meltwater. The friction between snow at −4°C and an XC ski as well as a flat ski was measured on a large-scale linear snow tribometer at realistic skiing speeds from 5 to 25 m/s. We used an infrared camera to analyze the snow temperature behind the skis. From the maximum snow surface temperature, we estimated the temperature at the spots where ski and snow contacted. Assuming that the contact spot temperature does not notably exceed 0°C, we calculated the relative contact area between ski and snow. Maximum snow surface temperatures were very close to 0°C. Given that not the entire snow surface is in contact with the ski, this finding is a strong indication for snow melting. Heat flow considerations led to the conclusion that there must be energy dissipation beyond the heat flow into ski and snow. The most obvious mechanism for the additional energy dissipation is snow melting. Presuming that the contact spot temperatures are at most slightly above 0°C, we calculated relative contact areas of 21–98%. Previous research has reported much lower values; however, most studies were conducted under conditions that are not realistic for skiing.

Basic Theory and Design Method of Variable Shaft Angle Line Gear Mechanism

In this paper, a novel line gear mechanism is proposed; it is called the variable shaft angle line gear mechanism (VSALGM). VSALGM has two rotational degrees of freedom, one is the rotation of the two gears with a constant transmission ratio, and the other is the relative swing of the two gears shafts. First, a novel contact model of VSALGM composed of one driven contact curve and one driving line teeth working surface (DLTWS) was proposed. With the concept, the basic design equations for VSALGM were derived on the basis of the space curve meshing theory of line gear. Moreover, the design criterion of pressure angle for VSALGM was analysed and proposed on the basis of the contact model. A basic design method for VSALGM was thus developed. A design example was given, and prototypes were manufactured using three-dimensional (3D) printing. Kinematic experiments and gear contact spot testing were carried out on a self-made kinematic test rig by the prototypes. The results show that the VSALGM designed in this paper can achieve a continuous, smooth and stable meshing transmission while the shaft angle is continuously changed within its setting range.

Research on the centre distance separability of parallel shaft line gear pair

For gear pairs with centre-distance separability, transmission ratios are not affected by centre distance error. Based on space curve meshing theory, the centre distance separability of a line gear pair was studied. A novel line gear pair called the separable and pure rolling parallel shaft line gear pair (SPRPSLG) was proposed, which has centre-distance separability characteristics and pure rolling transmission. The basic design theory of the SPRPSLG pair was established. A design method of the SPRPSLG pair with an eccentric arc tooth profile was given. An SPRPSLG pair example was designed and manufactured using the form milling method. Kinematic experiments and meshing efficiency experiments were conducted. Gear contact spot testing and gear contact simulation analysis were carried out. The SPRPSLG pair was shown to have centre distance separability, which provides a further theoretical basis for the popularization and application of line gears.