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Copper, permalloy, cobalt, and silicon are the materials that have been widely utilised in magnetic devices. When the size of interest is down to the nanoscale, the inter-diffusion between certain materials becomes influential. This paper studies the nanoscale friction characteristics between frictional pairs with and without inter-diffusion properties through the atomic force microscope. The distinct evolution features of nanoscale friction force when inter-diffusion is involved are discovered experimentally, which is also confirmed through theoretical analysis. Firstly, through the thin film deposition method, four pairs of contact materials (Cu–Ni81Fe19, Si–Ni81Fe19, Cu–Co, Cu–Si) are designed for friction tests, in which diffusion occurs at the interface of Cu–Ni81Fe19 pair. Then, the effects of sliding velocity and loading force on the nano friction of each pair are measured. It is found that regardless of the diffusion phenomenon: (1) the adhesion force values exhibit a notable correlation to the values of the friction force; (2) the friction force in all four material pairs consistently increases with the growth of the normal loading force, although the growth rate may differ. In terms of the sliding velocity effect, the friction forces of immiscible materials (Si–Ni81Fe19, Cu–Co, and Cu–Si) are found to increase with the increasing sliding velocity. However, the friction force of Cu–Ni81Fe19, decreases with the increasing sliding velocity. Furthermore, a compositive friction model considering both the velocity and the normal force effect was proposed, which shows good agreement with the experimental results and explains the nano friction behaviour of both miscible and immiscible metals. [ABSTRACT FROM AUTHOR]

Graphene on a stainless steel substrate will appear as localized bulges, and these bulges will lead to large fluctuations in friction force, which is the key to influencing the lubrication efficiency of graphene. Here, the effect of normal load on the nanofriction behavior of the bulged graphene on a stainless steel substrate is investigated. In the normal load study interval from 20 to 110 nN, an increment of 10 nN of normal load can increase friction force the more the normal load increases, and the two are not linearly correlated. The friction force in the graphene bulge region consists of two parts: the first part originates from the interaction of the graphene material itself in contact with the tip, and the second part originates from the resistance due to the pile-up of graphene deformation in front of the tip. The nonlinear correlation between the normal load and friction force is mainly related to the pile-up effect of bulged graphene. In addition, the friction force increase due to the graphene bulge region needs to go through a process, which is divided into two stages. The first stage is the increase in friction force due to the tip starting to contact the bulged graphene and the contact area increasing. The second stage is the increase in friction force due to the graphene regulating its configuration and repeatedly interacting with the tip. The normal load is linearly related to the first stage but not linearly related to the second stage. The nonlinear correlation between the normal load and friction force is mainly related to the second stage of friction force rise. Therefore, the change of normal load affects the stacking effect and the ability to regulate the configuration of bulged graphene, which leads to a nonlinear increase of friction force. This contributes to the application of graphene for nanolubrication of stainless-steel components in MEMS. [ABSTRACT FROM AUTHOR]

It is of great significance to deeply understand the stress damage mechanism of the pile–soil interface under cyclic loading for the safety control of engineering entities. Large-scale self-developed shear equipment was used to conduct cyclic shear tests of the interface between steel and siliceous sand, and the macroscopic shear characteristics and particle crushing characteristics were analyzed. Finally, the interface micro characteristics were analyzed through numerical simulation. The results indicate that the interface peak shear stress under constant stress conditions mainly exhibits strengthening characteristics, while under constant stiffness conditions it exhibits weakening characteristics. The position of the relationship curve between shear stress and normal stress gradually moves towards the direction of low normal stress as the experiment progresses, and the distance between the curves gradually decreases. The degree of particle breakage increases with the number of cycles but is mainly concentrated in the first few cycles. The principal stress is proportional to the normal stress, and its rotation degree gradually weakens with the normal stress. The contact number of particles at any angle increases with the normal stress. [ABSTRACT FROM AUTHOR]

Background: Worm gear sets are used in many applications of the transmission field. These mechanisms have interesting advantages. Despite this, its modelization is still challenging. This is due to its complex geometry. The goal behind this is to have an accurate model that allows improvement of the design of worm gear sets. Purpose: In this context, the paper presents a new mathematical model of a worm gear drive under rotational external excitations. Methods: Dynamic model is defined by fourteen degrees of freedom describing all rotations and translations of worm gear set, AQ1 bearings, a motor and a receiver connected together. First, equations of motion are developed to describe the dynamic behavior. Lagrange formula is, thus, employed. Elastic deformations of meshed teeth are considered. The normal load associated with the meshing is established as function of the model degrees of freedom through the elastic deflection. Second, a numerical simulation is carried out. Newmark Beta method is used to solve equations. Results: Numerical results are presented to discuss the model accuracy. The impact of the variation of friction coefficient and the stiffness of the worm gear is finally studied to discuss the consistency of the new formulation developed through this work. [ABSTRACT FROM AUTHOR]

In the field of aerospace, weapons and other complex assembly, there are more than 50 factors affecting the performance degradation of joint structures, among which the friction coefficient is the main factor. Nickel steel is widely used in large complex equipment due to its advantages of high strength. Therefore, this paper first establishes a theoretical model of friction coefficient based on fractal theory. Secondly, the friction coefficient experiment was carried out to measure the friction coefficient of nickel steel plates with different roughness under different normal loads. Finally, the experimental results are compared with the theoretical results, and the accuracy and error analysis of the model is carried out. The results show that the friction coefficient increases with the increase in roughness. When the normal load is greater than 50 kg, the friction coefficient gradually tends to be stable. The error of identification results of correction factor a was all within 5%. The error between theoretical model prediction and experimental data is 6%–15%, which indicates that the calculation of the friction coefficient has high accuracy. The results of this study can provide data and theoretical support for the friction coefficient evaluation of nickel steel plate joint structures, and contribute to the health detection and reliability evaluation of nickel steel plate joint structures. [ABSTRACT FROM AUTHOR]

A micro-arc oxidation (MAO) coating was in–situ grew on Ti6Al4V alloy to improve the friction-wear performance, and the morphologies, chemical compositions and phases of obtained coating were analyzed using a scanning electron microscope, energy dispersive spectroscopy, and X–ray diffraction, respectively. The effect of normal load on the tribological performance of MAO coating at 400 °C was investigated on a ball–on–disc wear tester. The results show that the MAO coating exhibits irregular–pore structure, which is mainly composed of TiO2 phase. The coefficient of friction (COF) and wear rate of MAO coating under the normal load of 2 N are 0.32 and of 0.84 × 10–5 mm3 N−1 m−1, respectively, showing the best friction reduction and wear resistance among the three kinds of loads. The wear mechanism of MAO coating under the normal load of 2 N is abrasive wear; while those under the normal loads of 4 and 6 N are adhesion wear fatigue wear, respectively, in which the MAO coating has the tendency of plastic deformation with the increase of normal load. [ABSTRACT FROM AUTHOR]

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The friction behavior of clay particles plays an essential role in controlling its mechanical properties, but remains unclear in microscale. As one of the major clay particles, the nanoscale friction properties of hydrated montmorillonite have been studied using steered molecular dynamics (SMD) simulation method, considering the coupling effect of water content of 0 ∼ 30 % and normal load of 1 atm ∼ 10 GPa. The SMD friction along the y -direction has been performed to investigate the frictional mechanism of hydrated montmorillonite and its structural properties of interlayer water. The evolution of average friction load with water content, friction coefficients, and the distribution of interlayer water molecules were obtained. Furthermore, the SMD pulling along the z -direction was conducted to study the effect of interlayer water molecules on the interaction between montmorillonite layers. All simulation results showed that more energy and a higher friction load were required to slide at a higher normal load. The friction coefficient of 0.058 ∼ 0.17 and internal friction angle of 3.3°∼9.6° for hydrated montmorillonite agreed well with previous studies in microscale, showing the weak friction properties. The evolution of friction coefficient with water content was different at different normal loads, where the friction coefficient of 5 % hydrated montmorillonite was the highest at 3 ∼ 10 GPa. Moreover, the increasing normal load could change the distribution of interlayer water molecules. [ABSTRACT FROM AUTHOR]

It is of great significance to deeply understand the stress damage mechanism of the pile–soil interface under cyclic loading for the safety control of engineering entities. Large-scale self-developed shear equipment was used to conduct cyclic shear tests of the interface between steel and siliceous sand, and the macroscopic shear characteristics and particle crushing characteristics were analyzed. Finally, the interface micro characteristics were analyzed through numerical simulation. The results indicate that the interface peak shear stress under constant stress conditions mainly exhibits strengthening characteristics, while under constant stiffness conditions it exhibits weakening characteristics. The position of the relationship curve between shear stress and normal stress gradually moves towards the direction of low normal stress as the experiment progresses, and the distance between the curves gradually decreases. The degree of particle breakage increases with the number of cycles but is mainly concentrated in the first few cycles. The principal stress is proportional to the normal stress, and its rotation degree gradually weakens with the normal stress. The contact number of particles at any angle increases with the normal stress.

The experiment was carried out in a reciprocating lubricated conformal sliding contact between steel discs of the same hardness. The effects of disc surface texturing on the friction coefficient at various operating conditions (temperature, normal load, and frequency of oscillations) were studied. Under various conditions, surface texturing caused friction reductions of sliding pairs. The largest reduction was 4.6 times at a lower temperature and 2.5 times at a higher temperature. The effect of the pit area ratio on the friction reduction was visible at a higher temperature. The highest dimple density of 25% corresponded to a lower coefficient of friction than the smallest density of 9%. The sliding pair with a dimple density of 17% led to large variation of the friction force. At lower temperatures, the coefficients of friction were lower compared to tests at higher temperatures. [ABSTRACT FROM AUTHOR]

Fretting wear phenomenon has a non-negligible impact on the reliability of the contact parts of mechanical power systems. The impact of temperature increases in actual working conditions is taken into consideration in order to increase the accuracy of fretting wear prediction. Temperature-dependent wear coefficients were added to the energy dissipation wear model, and the UMESHMOTION subroutine was created. A temperature-displacement-coupled finite element model of fretting wear is established based on a cylinder/plane fretting test of Ti-6Al-4V alloy materials. The model takes into account the interaction between temperature, stress, and wear. The effects of the plastic deformation of materials, temperature, number of cycles, fretting velocity, and variable normal load on wear and temperature rise are explored. The results show that the wear amount is small when the temperature rises, and the plastic deformation of materials is not considered. The wear profile is no longer a smooth Hertzian shape when the plastic deformation of materials is considered. The amount of wear increases with the fretting speed and the number of cycles. Meanwhile, the temperature of the contact area and the surface near the contact area increases with the increase in fretting speed. Peak temperature rise of the contact surface increases with the number of cycles, and its horizontal position moves with the cylinder specimen. Furthermore, the wear profile is less smooth under the variable normal load, but the two variable normal loads in the same phase have similar wear profiles and temperature rise distributions. The theoretical resources provided by the research work can be used to design control strategies and optimize mechanical power systems. [ABSTRACT FROM AUTHOR]

Surface texturing plays an increasingly important role as it can directly influence the tribological behaviors of contact surfaces in many ways. In texturing, tribological performance depends upon the types of design texture used and methods of fabricating texture on the surface. In this research work, friction and wear behaviors of surface textured EN-31 alloy steel have been investigated under wet condition by using DUCOM linear reciprocating tribometer. The textured dimples are fabricated by micro-EDM and micro-drilling CNC machining processes. Initially un-textured surfaces of EN-31 alloy steel with EN-8 steel pin are experimented for friction and wear under ISO-68 and ISO-220 lubricant oil. Under the different normal load conditions, it has been observed that the ISO 68 oil gives better friction-wear characteristics with respect to ISO-220 oil. Then after textured surfaces were investigated by using optimized ISO-68 lubricant. Experimental results on micro-EDM provide better friction and wear properties with respect to micro-drilling CNC. Surface texturing may act as wear debris trapper, lubricant reservoirs, hydrodynamic lift, and retarding the lubricant molecules flow in a particular path where potential exists. In this work, it has observed that texturing by micro-EDM enhanced mixed lubrication and minimum friction in mixed lubrication leads to decrement of wear loss

Analysis of non-local, phase-lag, and temperature-dependent properties of modified couple stress thermoelastic diffusive medium is examined in conditions of exciting by thermomechanical sources. The governing equations are framed involving non-local, phase-lag, and temperature-dependent properties. These equations are simplified by using the potential functions and employing the Laplace and Fourier transforms for further study. The problem is solved by deploying suitable thermomechanical loads. A specific type of normal and thermal loading of the ramp-type is considered. The transformed components of the physical field like the displacements, stresses, temperature change, and chemical potential are derived. A numerical analysis is performed for these quantities using the numerical technique. The graphs of the resulting quantities are shown to analyze the impact of non-local, phase-lag, and temperature-dependent properties. The specific cases are also mentioned. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to compare the influence of the normal load on the friction and wear behaviour of nickel-based alloys, which is use communally in the industry. We chose two samples of nickel-based alloys (NI-Cr-B-Si-C-W) elaborated by isostatic compression with a difference in their microstructure composition and quantity of micro constituent. The friction coefficient, the wear loss and the wear rate are evaluated using a tribometer (pin on disc) and a test bench created to reproduce the same industrial environment. Experiments showed that the applied normal load affects differently on the behaviour of the samples. The results conclude that the friction and wear resistance of the alloy do not just depend on the increase of the normal load but also on the distribution, the location and the morphology of the hard compounds formed in the alloys.

Multiple passage of power machinery system particularly heavy machines with high wheel loads creates sub-soil compaction which results into increasing in soil bulk density & penetration resistance and reduction in crop germination, growth as well as yield. This study was conducted to determine the wheat crop growth and yield models could be developed to predict growth as well as yield of crop considering normal load and number of passes of tractor. A 36-plot experiment consisting of 12 treatments with three replications were set up using a randomized block design in a uniform field of Division of Agricultural Engineering, IARI, New Delhi. Prediction models were developed between compaction parameters (normal loads and number of passes) and crop parameters like (a) plant height, (b) number of plants per meter, and (c) yield. Further, another relationship between crop yield and sub-soil bulk density and penetration resistance were established and their sensitivity analysis was done. The best fit model for plant height and number of plants per meter row was quadratic. However, the best fit models between yield vs soil bulk density and yield vs penetration resistance for critical layer and whole soil were exponential and quadratic, respectively. The developed model is not more sensitive for number of plants per meter row and yield vs soil bulk density. However, model was more sensitive to plant height model as well as yield vs soil penetration resistance. [ABSTRACT FROM AUTHOR]

The friction behavior of high-purity titanium in microscale was experimentally investigated by using atomic force microscopy to scan two neighboring grains with different crystalline orientations across the grain boundary. The results indicated that there were obvious friction contrast (FG1/FG2) between the two neighboring grains. The friction contrast became more obvious when higher normal load was applied, and this trend could be well reproduced by using the DMT model. Based on this, the interfacial shear strength was identified as the main factor causing the friction contrast. Higher scan velocity reduced the friction, which was regarded as the result of the decreased ability to maintain a stable capillary bridge in ambient atmosphere. However, the scan velocity had no significant effect on the friction contrast. [ABSTRACT FROM AUTHOR]

The pin-on-disc test model system was used to simulate contact wear between wheel flange and rail gauge corner. Pins were extracted from a class C cast steel wheel and discs were extracted from premium and intermediate steel grades rail, both hypereutectoid and with hardness between 321 and 392 HB. Rails are pearlitic and the bainitic wheel is in its first life. Dry and lubricated tests were performed with normal load variation (40, 80 and 120 N). Under dry condition, there was no influence of the pair hardness to mass loss of the tribosystem studied, contrary to what is stated by literature. For the lubricated tests, mass loss was significantly lower and regardless of both, hardness ratio and normal load, than in the other tests. This shows the technological importance of: (i) implementing wheel flange lubrication (locomotive embedded process); (ii) improving rail lubrication techniques (mobile or way side process) and/or friction coefficient measurement techniques and (iii) need for revision of wheel standards and/or specifications.

In the present study, experiments have been carried out by sliding hard elastic material on ductile flat surface. The different state of stress has been achieved by changing the geometry of hard material and different orientation of changed geometry with respect to sliding direction. Experiments have been carried out using pin on disc wear test rig. The tests were conducted with Al6061 alloy disc and EN8 alloy steel pin with different tip geometries and orientations. The obtained results revealed that coefficient of friction was higher at lower loads compared to higher loads in hemisphere pin geometry. An exception has been found at 90° orientation at low loads. It has been attributed to adhesive effect. The state of stress and its configuration with respect to direction of sliding was found to influence the sliding phenomenon. Micrograph studies revealed damages due to adhesion, abrasion and extrusion.

Structural superlubricity (SSL), a state of ultra-low friction between two solid contacts, is a fascinating phenomenon in modern tribology. With extensive molecular dynamics simulations, for systems showing SSL, here we discover two different dependences between friction and normal load by varying the size of the loading area. The essence behind the observations stems from the coupling between the normal load and the edge effect of SSL systems. Keeping normal load constant, we find that by reducing the loading area, the friction can be reduced by more than 65% compared to the large loading area cases. Based on the discoveries, a theoretical model is proposed to describe the correlation between the size of the loading area and friction. Our results reveal the importance of loading conditions in the friction of systems showing SSL, and provide an effective way to reduce and control friction.

The experiment was carried out in a reciprocating lubricated conformal sliding contact between steel discs of the same hardness. The effects of disc surface texturing on the friction coefficient at various operating conditions (temperature, normal load, and frequency of oscillations) were studied. Under various conditions, surface texturing caused friction reductions of sliding pairs. The largest reduction was 4.6 times at a lower temperature and 2.5 times at a higher temperature. The effect of the pit area ratio on the friction reduction was visible at a higher temperature. The highest dimple density of 25% corresponded to a lower coefficient of friction than the smallest density of 9%. The sliding pair with a dimple density of 17% led to large variation of the friction force. At lower temperatures, the coefficients of friction were lower compared to tests at higher temperatures.

Surface texturing plays a significant role on the tribological performance of contact surfaces. The tribological characteristics are mostly dependent upon the different pattern and methods of surface texturing. This research works investigates lubricated wear behaviour on circular dimples textured EN-31 alloy steel materials using DUCOM linear reciprocating tribometer. The surface dimples are fabricated by micro-EDM and micro-drilling CNC methods. Initially plane surfaces are tested under different lubricants ISO-68 and ISO-220 oil on a couple of EN31 plates with EN8 steel pin. At loading conditions the results clearly shows that the ISO 68 oil gives better performance than ISO-220 oil in terms of frictional force and COF. The operation during test under ISO-220 oil observed is very noisy and wear rate is also more. Then after experiments under different load conditions on textured surfaces were investigated using optimized ISO-68 oil. An experimental results on m-EDM provides superior frictional characteristics with respect to m-CNC. Surface texturing may act as wear debris trapper, lubricant reservoirs, hydrodynamic lift, and retarding the lubricant molecules flow in a particular path where potential exists. Here micro-dimples EDM surface textures can enhance mixed lubrication and in mixed lubrication the friction is least and this may leads to decrement of wear loss.

Surface texturing plays an increasingly important role as it can directly influence the tribological behaviors of contact surfaces in many ways. In texturing, tribological performance depends upon the types of design texture used and methods of fabricating texture on the surface. In this research work, friction and wear behaviors of surface textured EN-31 alloy steel have been investigated under wet condition by using DUCOM linear reciprocating tribometer. The textured dimples are fabricated by micro-EDM and micro-drilling CNC machining processes. Initially un-textured surfaces of EN-31 alloy steel with EN-8 steel pin are experimented for friction and wear under ISO-68 and ISO-220 lubricant oil. Under the different normal load conditions, it has been observed that the ISO 68 oil gives better friction-wear characteristics with respect to ISO-220 oil. Then after textured surfaces were investigated by using optimized ISO-68 lubricant. Experimental results on micro-EDM provide better friction and wear properties with respect to micro-drilling CNC. Surface texturing may act as wear debris trapper, lubricant reservoirs, hydrodynamic lift, and retarding the lubricant molecules flow in a particular path where potential exists. In this work, it has observed that texturing by micro-EDM enhanced mixed lubrication and minimum friction in mixed lubrication leads to decrement of wear loss. [ABSTRACT FROM AUTHOR]

Tribological performances are significantly affected by the tribo-chemical reaction of the mating materials, while the effect on the B₄C film under high relative humidity conditions are poorly investigated. Therefore, fiction tests of three tribo-pairs (B₄C/WC, B₄C/steel and B₄C/Al₂O₃) under 85% RH with various normal loads and sliding frequencies were performed. The results show that the B₄C/WC tribo-pair exhibits excellent tribological properties, including very stable friction curves, minimum friction coefficients & wear rates, maximum carrying-load capacity and the smallest fluctuations with the change of the normal load. Similar results have been obtained for the B₄C/WC tribo-pair with the increase in the sliding frequency. This is mainly attributed to the oxidation of WC to form WO₃ that is conducive in enhancing the tribological performances. Therefore, the sliding contact of B4₄C/WC is the desirable design for engineering applications under high relative humidity.

Fretting wear phenomenon has a non-negligible impact on the reliability of the contact parts of mechanical power systems. The impact of temperature increases in actual working conditions is taken into consideration in order to increase the accuracy of fretting wear prediction. Temperature-dependent wear coefficients were added to the energy dissipation wear model, and the UMESHMOTION subroutine was created. A temperature-displacement-coupled finite element model of fretting wear is established based on a cylinder/plane fretting test of Ti-6Al-4V alloy materials. The model takes into account the interaction between temperature, stress, and wear. The effects of the plastic deformation of materials, temperature, number of cycles, fretting velocity, and variable normal load on wear and temperature rise are explored. The results show that the wear amount is small when the temperature rises, and the plastic deformation of materials is not considered. The wear profile is no longer a smooth Hertzian shape when the plastic deformation of materials is considered. The amount of wear increases with the fretting speed and the number of cycles. Meanwhile, the temperature of the contact area and the surface near the contact area increases with the increase in fretting speed. Peak temperature rise of the contact surface increases with the number of cycles, and its horizontal position moves with the cylinder specimen. Furthermore, the wear profile is less smooth under the variable normal load, but the two variable normal loads in the same phase have similar wear profiles and temperature rise distributions. The theoretical resources provided by the research work can be used to design control strategies and optimize mechanical power systems.

The effect of waste carbonized eggshell and silicon carbide (SiC) wt.% on the dry sliding wear behavior of AA2014 alloy green composites produced by electromagnetic stir casting method was investigated. The percentage of waste carbonized eggshell particles and SiC particles varied from 2.5% to 12.5%. The tribological behavior of AA2014/waste carbonized eggshell/SiC hybrid green metal matrix composites (MMCs) was investigated on a pin-on-disc apparatus. The weight percentages of waste carbonized eggshell and of SiC, normal load, and sliding speed and distance were taken as input process parameters, and wear rate was taken as a response. Response surface methodology was used to plan and analyze the experiment. Minimum wear rate was found to be 8.89×10−5 mm3/m with desirability one at optimum parameters of 1.75 m/s (sliding velocity), 6.5 (carbonized eggshell wt.%), 34.24 N (normal load), 1219.63 m (sliding distance), and 11 wt.% (SiC wt.%). In the confirmation experiment, the experimental wear rate of the hybrid green MMC at optimum parameters was found to be 9.5×10−5. Results showed that the experimental wear rate and density of the hybrid green MMC were reduced by about 36.66% and 0.35%, respectively, compared with the matrix.

The present study consists in analyzing the friction coefficient as a variable of the normal load and slip speed for 5% Cr steel, by applying the Block-on-Disk method according to ASTM D2714. The friction coefficient increases linearly 23,25 % from 0,214 to 0,266 when the load is increased from 196 N to 392 N; the same phenomenon is observed when the friction coefficient increases 47,82 % from 0,23 to 0,34 when the slip speed increases from 0,18 m/sec to 0,54 m/sec. The friction coefficient increased by 23,25 % for an increase in the load from 196 N to 392 N, which corresponds to 100 %, while an increase of the friction coefficient of 47,82 % occurred by increasing the speed from 0,18 m/sec to 0,54 m/sec which corresponds to 200 %.

The purpose of this paper is to compare the influence of the normal load on the friction and wear behaviour of nickel-based alloys, which is use communally in the industry. We chose two samples of nickel-based alloys (NI-Cr-B-Si-C-W) elaborated by isostatic compression with a difference in their microstructure composition and quantity of micro constituent. The friction coefficient, the wear loss and the wear rate are evaluated using a tribometer (pin on disc) and a test bench created to reproduce the same industrial environment. Experiments showed that the applied normal load affects differently on the behaviour of the samples. The results conclude that the friction and wear resistance of the alloy do not just depend on the increase of the normal load but also on the distribution, the location and the morphology of the hard compounds formed in the alloys. [ABSTRACT FROM AUTHOR]

The pin-on-disc test model system was used to simulate contact wear between wheel flange and rail gauge corner. Pins were extracted from a class C cast steel wheel and discs were extracted from premium and intermediate steel grades rail, both hypereutectoid and with hardness between 321 and 392 HB. Rails are pearlitic and the bainitic wheel is in its first life. Dry and lubricated tests were performed with normal load variation (40, 80 and 120 N). Under dry condition, there was no influence of the pair hardness to mass loss of the tribosystem studied, contrary to what is stated by literature. For the lubricated tests, mass loss was significantly lower and regardless of both, hardness ratio and normal load, than in the other tests. This shows the technological importance of: (i) implementing wheel flange lubrication (locomotive embedded process); (ii) improving rail lubrication techniques (mobile or way side process) and/or friction coefficient measurement techniques and (iii) need for revision of wheel standards and/or specifications. [ABSTRACT FROM AUTHOR]

Applying accurate normal load to a specimen in direct shear tests under constant normal stiffness (CNS) is of importance for the quality of the resulting data, which in turn influences the conclusions. However, deficiencies in the test system give rise to a normal stiffness, here designated as system normal stiffness, which results in deviations between the intended and actual applied normal loads. Aiming to reduce these deviations, this paper presents the effective normal stiffness approach applicable to closed-loop control systems. Validation through direct shear tests indicates a clear influence of the system normal stiffness on the applied normal load (13% for the test system used in this work). The ability of the approach to compensate for this influence is confirmed herein. Moreover, it is demonstrated that the differences between the measured and the nominal normal displacements are established by the normal load increment divided by the system normal stiffness. This further demonstrates the existence of the system normal stiffness. To employ the effective normal stiffness approach, the intended normal stiffness (user defined) and the system normal stiffness must be known. The latter is determined from a calibration curve based on normal loading tests using a stiff test dummy. Finally, a procedure is presented to estimate errors originating from the application of an approximate representation of the system normal stiffness. The approach is shown to effectively reduce the deviations between intended normal loads and the actual applied normal loads. [ABSTRACT FROM AUTHOR]

To clarify the unconscious response actions to a friction stimulus applied to a finger, ten participants performed a friction test using their right index finger and a specimen on which a self-assembled monolayer was striped to intentionally change the shear strength. Drastic changes were observed in both normal load and shear strength when a finger slid across the striped surface. Because the rate of change under normal load was negligible as the sliding speed increased, the response action to the friction stimulus appeared to depend on sliding speed. • A self-assembled monolayer was striped to change the shear strength. • A negative correlation between the differences in normal load and shear strength. • The shear strength remained constant as the sliding speed increased. • The change rate of the normal load approached zero as the sliding speed increased. • The response to the stimulus depended on the speed at which the finger slid. [ABSTRACT FROM AUTHOR]

The paper deals with the plane problem of normal and tangential load for microperiodic composite with slant lamination. The boundary condition was considered as a normal and tangential load given on the surface of the composite half-plane. Microperiodic composite consisted of two components, differing in their Young's modules. The homogenized model with microlocal parameters, which is presented by Woźniak (Int J Eng Sci 25:483–498, 1987. 10.1016/0020-7225(87)90102-9), Jędrysiak (Compos Struct 202:1253–1262, 2018. 10.1016/J.COMPSTRUCT.2018.05.155) was used to solve the considered problem. The problem was formulated and solved using the averaged boundary condition given by Perkowski et al. (Compos Sci Technol 67:2683–2690, 2007. 10.1016/J.COMPSCITECH.2007.02.013). The considered boundary value problem will be solved using the Fourier transform method. An analytical solution was obtained in a general form for any form of the function describing normal and tangential loads on the surface of a half-plane. An analytical solution was determined for the special cases of an elliptical, normal and tangential loads and for the special case of the concentrated force. The results are shown in the form of figures. [ABSTRACT FROM AUTHOR]

The rail transit system is a large electric vehicle system that is strongly dependent on the energy technologies of the power system. The use of new energy-saving amorphous alloy transformers can not only reduce the loss of rail transit power, but also help alleviate the power shortage situation and electromagnetic emissions. The application of the transformer in the field of rail transit is limited by the problem that amorphous alloy is prone to debris. this paper studied the stress conditions of amorphous alloy transformer cores under different working conditions and determined that the location where the core is prone to fragmentation, which is the key problem of smoothly integrating amorphous alloy distribution transformers on rail transit power supply systems. In this study, we investigate the changes in the electromagnetic field and stress of the amorphous alloy transformer core under different operating conditions. The finite element model of an amorphous alloy transformer is established and verified. The simulation results of the magnetic field and stress of the core under different working conditions are given. The no-load current and no-load loss are simulated and compared with the actual experimental data to verify practicability of amorphous alloy transformers. The biggest influence on the iron core is the overload state and the maximum value is higher than the core stress during short circuit. The core strain caused by the side-phase short circuit is larger than the middle-phase short circuit.

Amorphous carbon–containing CrAlCN coating was deposited on Cr12MoV steel by cathodic arc ion plating. The effect of amorphous carbon on the tribological performance of obtained coating under the different normal loads was investigated using a ball–on–disc tester, and the lubrication and wear mechanisms of amorphous carbon were discussed in detail. The results show that the CrAlCN coating is composed of AlN, CrN and CrC phases with the amorphous carbon. The average coefficient of friction of CrAlCN coatings under the normal loads of 2, 4 and 6 N are 0.458, 0.586, and 0.666, respectively, where the amorphous carbon plays a self–lubrication role in the friction process. The wear degree is deteriorated with the increase of normal load, and the wear mechanism is changed from abrasive wear to adhesive wear. • The amorphous carbon–containing CrAlCN coating presents the high nanohardness and elastic modulus • The CrAlCN coating improves the friction reduction and wear resistance performances. • The amorphous C in the CrAlCN coating plays the roles of friction reduction and wear resistance. • The wear mechanism of CrAlCN coating is changed with the increase of normal load. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Relationship between material removal mode and scratching direction is investigated. • A theoretical model is developed to relate machining depth with normal load. • An optimal machining direction is selected based on the quality of the grooves. Abstract The material removal state, which is closely related to machining quality, is an important factor in any machining process. During the machining using a non-rotational symmetric cutting tool, scratching direction manifests significant influence on the material removal state. In the present study, the relationship between material removal mode and scratching direction was investigated during the nanoscratching process on single crystal copper using an atomic force microscopy (AFM) tip. Considering the installation angle of the cantilever and the height of pile-up, a theoretical model was developed to relate machining depth with normal load for the machining of a single groove. Experimental results revealed that the theoretical normal load model was more suitable when materials were expelled in constant chip formation with small pile-ups. In addition, based on the scratching tests in different directions, the critical included cutting angle determined whether materials were expelled in chip formation or not. The height of pile-up was also influenced by the included cutting angle during the scratching in face-forward direction; however, during the machining in edge-forward direction, the distance between the cutting swept faces formed by the lateral and front edges determined the height of pile-up. Finally, an optimal machining direction is selected based on the quality of the machined grooves, which can be used in the potential application. [ABSTRACT FROM AUTHOR]

Composite materials are wildly applied in the engineering and a lot of them behave as orthotropic. An accurate and efficient method for the orthotropic plate will contribute to the accurate design and quality promotion of this kind of structure. In this paper, the 2D Green's function for the orthotropic plate loaded by a normal line force is derived at first. By virtue of the 2D general solution of orthotropic material, a series of new harmonic functions which contain undetermined constants are constructed. Inserting the harmonic function into the general solution, the corresponding elastic fields in the orthotropic plate are obtained. These undetermined constants can be determined by the boundary conditions and the equilibrium equations. Then, based on the superposition principle and the obtained Green's function, the solutions for the arbitrary distributed normal loads can be obtained. At last, numerical analysis is presented to discuss the accuracy and efficiency of this method and the stress distribution in an orthotropic plate loaded by the normal loads are studied. [ABSTRACT FROM AUTHOR]

Electrostatic charging resulted by sliding contacts of particles and wall is ubiquitous in gas-solid systems. However, the mechanism of sliding electrification involved the initial charge is still unclear. In the current paper, to accurately obtain triboelectric charge, the initial charge and the final charge were measured. A quantitative comparison of the experimental results and the value of theoretical model based on the condenser model is provided. And the results suggest the final charge of the grain is linear with the initial charge for a short sliding distance, whereas the experimental data become scattered for a long sliding length. The longer sliding length generation was found to generate more triboelectric charge, and the influences of the normal load on the triboelectric charge density were analyzed by considering the contact area. It provides a comprehensive perspective that the triboelectrification is fundamentally described as a synergistic effect of the sliding contact area and the real contact area. [ABSTRACT FROM AUTHOR]

The present study consists in analyzing the friction coefficient as a variable of the normal load and slip speed for 5 % Cr steel, by applying the Block-on-Disk method according to ASTM D2714. The friction coefficient increases linearly 23,25 % from 0,214 to 0,266 when the load is increased from 196 N to 392 N; the same phenomenon is observed when the friction coefficient increases 47,82 % from 0,23 to 0,34 when the slip speed increases from 0,18 m/sec to 0,54 m/sec. The friction coefficient increased by 23,25 % for an increase in the load from 196 N to 392 N, which corresponds to 100 %, while an increase of the friction coefficient of 47,82 % occurred by increasing the speed from 0,18 m/sec to 0,54 m/sec which corresponds to 200 %. [ABSTRACT FROM AUTHOR]

In this study, an in-situ Single Wheel Tester (iSWT) was used to investigate the effect of the most important independent variables on the lateral force of a high lug agricultural tire. The variables include some soil parameters and tire characteristics. Response Surface Methodology (RSM) also was used to construct a design of experiment and propose the lateral force model as a function of seven variables (various combination treatments of soil characteristics and tire parameters). A total of 152 experimental tests were conducted to find the appropriate model. Reduced form of a quadratic model was selected to predict the tire lateral force (R2>0.9). The results showed that the side slip angle and the moisture content had major and minimal effect on tire lateral force respectively. When all other variables were in their middle points, the 95% increase of the normal load would cause the 112% increment in the lateral force. Also, the difference between the lateral force when the moisture content is at minimum and maximum levels, is about 4%. Noteworthily, increasing the tire normal load, not only increases the maximum value of tire lateral force attainment, but also pushes the peak value of the lateral force to higher slip angles. [ABSTRACT FROM AUTHOR]

The friction of hydrogenated diamond-like carbon (H-DLC) films was evaluated under the controlled environments of humid air and vacuum by varying the applied load. In humid air, there is a threshold applied load below which no obvious friction drop occurs and above which the friction decreases to a relatively low level following the running-in process. By contrast, superlubricity can be realized at low applied loads but easily fails at high applied loads under vacuum conditions. Further analysis indicates that the graphitization of the sliding H-DLC surface has a negligible contribution to the sharp drop of friction during the running-in process under both humid air and vacuum conditions. The low friction in humid air and the superlow friction in vacuum are mainly attributed to the formation and stability of the transfer layer on the counterface, which depend on the load and surrounding environment. These results can help us understand the low-friction mechanism of H-DLC film and define optimized working conditions in practical applications, in which the transfer layer can be maintained for a long time under low applied load conditions in vacuum, whereas a high load can benefit the formation of the transfer layer in humid air.

In the present study, friction coefficient and wear rate of gear fiber reinforced plastic (gear fiber) and glass fiber reinforced plastic (glass fiber) sliding against mild steel are investigated experimentally. In order to do so, a pin on disc apparatus is designed and fabricated. Experiments are carried out when smooth or rough mild steel pin slides on gear fiber and glass fiber disc. Experiments are conducted at normal load 10, 15 and 20 N, sliding velocity 1, 1.5 and 2 m/s and relative humidity 70%. Variations of friction coefficient with the duration of rubbing at different normal loads and sliding velocities are investigated. Results show that friction coefficient is influenced by duration of rubbing, normal load and sliding velocity. In general, friction coefficient increases for a certain duration of rubbing and after that it remains constant for the rest of the experimental time. The obtained results reveal that friction coefficient decreases with the increase in normal load for gear fiber and glass fiber mating with smooth or rough mild steel counterface. On the other hand, it is also found that friction coefficient increases with the increase in sliding velocity for both of the tested materials. Moreover, wear rate increases with the increase in normal load and sliding velocity. The magnitudes of friction coefficient and wear rate are different depending on sliding velocity and normal load for both smooth and rough counterface pin materials.

The subject of the paper includes theoretical considerations, the conducting of experimental tests, and the analysis of exposed test results related to determination of the coefficient of static friction of previously heat-treated contact pairs. One contact element is previously, before the procedure of determining the coefficient of static friction, heated at temperatures in the range of ambient temperature to 280°C and then cooled down to ambient temperature. The results of experimental tests of five different materials show that depending on the heat treatment of one contact element, there is a significant decrease in the coefficient of static friction. The authors of the paper consider that the reasons for the decreasing coefficient of static friction are related to oxide formation and changes in the surface layer of the contact element which is previously heat-treated.