Tangential Force Research Articles

Investigation of Graphene Platelet-Based Dry Lubricating Film Formation in Tribological Contacts

Dry lubricants used in highly loaded rolling bearings are in the focus of current research. In previous studies, graphene platelets applied as dry lubricants on the surfaces of angular contact ball bearings demonstrated superior properties. These specific bearings, experiencing both rolling and spinning motion, create more severe conditions for dry lubricants. To gain deeper insights into the lubrication effects, micro-tribological studies were carried out on the respective film formation and running behavior effects. In the tests, a fixed steel ball slid against an oscillating counterpart under a defined load. During the measurements, the applied load and tangential forces on the ball were recorded to calculate the friction. Comparative investigations included nano-graphite particles and fullerene as dry lubricants, in addition to graphene platelets of various staple thicknesses. To increase the adhesion of the films to the surfaces, a pre-rolling process was implemented. Afterwards, the friction on the compressed films was measured. The results indicate that the pre-rolling process effectively reduces the friction of the system. After testing, the surfaces underwent analysis using laser scanning microscopy to assess the formed films, wear, and material transfer. It has been demonstrated that the pre-rolling process leads to the formation of a very thin compacted film with surface protective properties. With the ball as a counterpart, the graphene platelets generate a transfer film on the contacting surface.

Finite-time model-free robust synchronous control of multi-lift overhead cranes based on iterative learning

A model-free control method based on iterative learning law combined with adaptive super-twisting is proposed to realize the synchronous coordination control of multi-lift overhead crane system for the problems of inaccurate modeling, system parameter variation, and disturbance uncertainty that exist in multi-lift overhead crane system. First, a load-coupling model of the double-container overhead crane considering the deformation tangential force in the interlocking mode is established. Second, a time-varying sliding mode surface (TSMC) designed using nonlinear functions effectively improves the convergence speed of the system state. The method of iterative learning control is introduced to compensate the system dynamics to achieve model-free control, and the dynamic iterative learning control (DILC) is designed to improve the convergence speed of the error of the system and the steady-state performance. To suppress uncertainty disturbances and avoid control gain overestimation, an adaptive gain is added to the generalized super-twisting algorithm, which has the advantages of both finite-time convergence and chattering suppression, and improves the robustness and tracking performance of the multi-lift overhead crane system. The stability of the controlled system is analyzed using Lyapunov stability theory. The simulation experiments illustrate the effectiveness of the proposed synchronization control scheme.

Grindability Evaluation of Ultrasonic Assisted Grinding of Silicon Nitride Ceramic Using Minimum Quantity Lubrication Based SiO2 Nanofluid

Minimum quantity Lubrication (MQL) is a sustainable lubrication system that is famous in many machining systems. It involve the spray of an infinitesimal amount of mist-like lubricants during machining processes. The MQL system is affirmed to exhibit an excellent machining performance, and it is highly economical. The nanofluids are understood to exhibit excellent lubricity and heat evacuation capability, compared to pure oil-based MQL system. Studies have shown that the surface quality and amount of energy expended in the grinding operations can be reduced considerably due to the positive effect of these nanofluids. This work presents an experimental study on the tribological performance of SiO2 nanofluid during grinding of Si3N4 ceramic. The effect different grinding modes and lubrication systems during the grinding operation was also analyzed. Different concentrations of the SiO2 nanofluid was manufactured using canola, corn and sunflower oils. The quantitative evaluation of the grinding process was done based on the amount of grinding forces, specific grinding energy, frictional coefficient, and surface integrity. It was found that the canola oil exhibits optimal lubrication performance compared to corn oil, sunflower oil, and traditional lubrication systems. Additionally, the introduction of ultrasonic vibrations with the SiO2 nanofluid in MQL system was found to reduce the specific grinding energy, normal grinding forces, tangential grinding forces, and surface roughness by 65%, 57%, 65%, and 18% respectively. Finally, regression analysis was used to obtain an optimum parameter combinations. The observations from this work will aid the smooth transition towards ecofriendly and sustainable machining of engineering ceramics.

Hypergravity-exacerbated cracking in high-speed rotating 7075 aluminum blades

On Earth, high-speed rotating blades and rotors experience hypergravity, which is mainly derived from centrifugal force. Aluminum alloys are widely used in high-speed rotating machines. In particular, 7075 aluminum has excellent properties, providing it with great potential for application in high-temperature rotating parts. In this work, the cracking behavior and microstructural evolution characteristics of high-speed rotating blades under different stresses were studied. A specifically designed instrument and blades with multiple necks were assembled, and the stress was tuned by adding weight to the blade tip. Each rotating blade cracked on its root neck, indicating that the gradient hypergravitational force decreased from the root to the tip. The degree of high-temperature cracking obviously increased with a sawtooth-like tip, but the degree of low-temperature cracking did not obviously increase with a smooth tip. A comparison under a constant uniaxial force required a greatly increased ultimate cracking strength that was approximately 10–18 times greater than that under hypergravitational force at the same temperature. Force analysis indicated that the coupling of hypergravitational forces in the normal direction and torsional forces in the tangential direction accelerated cracking. A uniaxial force caused grains to extend along the blade direction. However, a tangential force cut these extended grains to accelerate cracking and grain refining. In this study, real-world simulated service conditions for commercial alloys rotating at high speeds and a new understanding of the mechanical properties of alloys under various severe conditions were provided.

Retinal detachment.

Retinal detachment (RD) occurs when the neurosensory retina, the neurovascular tissue responsible for phototransduction, is separated from the underlying retinal pigment epithelium (RPE). Given the importance of the RPE for optimal retinal function, RD invariably leads to decreased vision. There are three main types of RD: rhegmatogenous, tractional and exudative (also termed serous) RD. In rhegmatogenous RD, one or more retinal breaks enable vitreous fluid to enter the subretinal space and separate the neurosensory retina from the RPE. In tractional RD, preretinal, intraretinal or subretinal membranes contract and exert tangential forces and elevate the retina from the underlying RPE. Finally, in exudative RD, an underlying inflammatory condition, vascular abnormality or the presence of a tumour causes exudative fluid to accumulate in the subretinal space, exceeding the osmotic pump function of the RPE. The surgical management of RD usually involves pars plana vitrectomy, scleral buckling or pneumatic retinopexy. The approach taken often depends on patient characteristics as well as on practitioner experience and clinical judgement. Advances in surgical technology and continued innovation have improved outcomes for many patients. However, even if retinal re-attachment is achieved, some patients still experience decreased vision or other visual symptoms, such as metamorphopsia, that diminish their quality of life. Continued research in the areas of neuroprotection and retinal biology as well as continued surgical innovation are necessary to enhance therapeutic options and outcomes for these patients.

A GFDM based computational model for the analysis of tunnels under gravitational loadings

Based on an impedance relation, a new computational model is developed for the analysis of tunnels under gravitational loading. The shape of tunnel is arbitrary. The impedance matrix, representing the soil resistance, is evaluated through integration of the equations of elasticity by generalized finite difference method (GFDM). The rigidity matrix of tunnel ring is constructed by using two types of elements: plate and shell elements. The equations of these elements are evaluated through integration of the equations of higher order plate and shell theories again by GFDM. These element equations accommodate not only axial and bending deformations, but, also shear deformations in the ring. In the study, the rotational joint deformation is simulated through the use of rotational spring model and the slippage is considered by modifying the impedance matrix so that the tangential soil resistance force between the ring and soil medium vanishes. Some numerical results are presented, in nondimensional forms, for circular and square tunnels where the following three cases are considered for circular tunnels: a) the soil medium is infinite, the change in σv (vertical (in situ) compressional stress) in the vicinity of tunnel is disregarded b) the soil medium is infinite, the change in σv is taken into account c) the soil medium is halfspace (HS). In connection with the case of (a), a comparison is presented for the ring flexibility curves of radial displacement and section forces of circular ring with those reported in literature. In view of the interpretations of the results and comparisons, we think, the proposed model may be used reliably in the analysis of tunnels.

Kinematic analysis of an unrestrained passenger in an autonomous vehicle during emergency braking.

Analyzing human body movement is a critical aspect of biomechanical studies in road safety. While most studies have traditionally focused on assessing the head-neck system due to the restraint provided by seat belts, it is essential to examine the entire pelvis-thorax-head kinematic chain when these body regions are free to move. The absence of restraint systems is prevalent in public transport and is also being considered for future integration into autonomous vehicles operating at low speeds. This article presents an experimental study examining the movement of the pelvis, thorax and head of 18 passengers seated without seat belts during emergency braking in an autonomous bus. The movement was recorded using a video analysis system capturing 100 frames per second. Reflective markers were placed on the knee, pelvis, lumbar region, thorax, neck and head, enabling precise measurement of the movement of each body segment and the joints of the lumbar and cervical spine. Various kinematic variables, including angles, displacements, angular velocities and accelerations, were measured. The results delineate distinct phases of body movement during braking and elucidate the coordination and sequentiality of pelvis, thorax and head rotation. Additionally, the study reveals correlations between pelvic rotation, lumbar flexion, and vertical trunk movement, shedding light on their potential impact on neck compression. Notably, it is observed that the elevation of the C7 vertebra is more closely linked to pelvic tilt than lumbar flexion. Furthermore, the study identifies that the maximum angular acceleration of the head and the maximum tangential force occur during the trunk's rebound against the seatback once the vehicle comes to a complete stop. However, these forces are found to be insufficient to cause neck injury. While this study serves as a preliminary investigation, its findings underscore the need to incorporate complete trunk kinematics, particularly of the pelvis, into braking and impact studies, rather than solely focusing on the head-neck system, as is common in most research endeavors.

Development of a novel bulk metallic glass bonded single-layer diamond wheel

A novel manufacturing process was employed to develop a single-layer diamond wheel using bulk metallic glass (BMG) as the matrix and diamond particles as abrasives. BMG effectively prevented graphitisation and damage to the diamond abrasives because of its lower manufacturing temperature and avoidance of brazing flux. The Titanium (Ti) coating on the surface of diamond abrasives facilitated the formation of an interleaved dissolution-diffusion interface between the two constituents, creating mechanical occlusion at the BMG-diamond interface. The strong and tight bonding interface afforded a diamond abrasive joint strength of up to 112.59 N, with the main shear failure mode being transgranular fracture instead of pull-off failure. Furthermore, the manufactured BMG-bonded single-layer diamond wheel predominantly exhibited attritious wear instead of the exfoliation of abrasives when grinding Al2O3 ceramics. Compared with contemporary electroplated grinding wheels, the developed diamond wheel demonstrated a reduction in the normal and tangential grinding forces of 32.64% and 35.86%, respectively, and a 28.22% increase in the grinding ratio, making it an excellent candidate for grinding hard and brittle materials.

Investigation into the interface bond between polyurethane concrete and steel plate

PurposePolyurethane concrete (PUC), as a new type of steel bridge deck paving material, the bond-slip pattern at the interface with the steel plate is not yet clear. In this study, the mechanical properties of the PUC and steel plate interface under the coupled action of temperature, normal force and tangential force were explored through shear tests and numerical simulations. An analytical model for bond-slip at the PUC/steel plate interface and a predictive model for the shear strength of the PUC/steel plate interface were developed.Design/methodology/approachThe new shear test device designed in this paper overcomes the defect that the traditional oblique shear test cannot test the interface shear performance under the condition of fixed normal force. The universal testing machine (UTM) test machine was used to adjust the test temperature conditions. Combined with the results of the bond-slip test, the finite element simulation of the interface is completed by using the COHENSIVE unit to analyze the local stress distribution characteristics of the interface. The use of variance-based uncertainty analysis guaranteed the validity of the simulation.FindingsThe shear strength (τf) at the PUC-plate interface was negatively correlated with temperature while it was positively correlated with normal stress. The effect of temperature on the shear properties was more significant than that of normal stress. The slip corresponding to the maximum shear (D1) positively correlates with both temperature and normal stress. The interfacial shear ductility improves with increasing temperature.Originality/valueBased on the PUC bond-slip measured curves, the relationship between bond stress and slip at different stages was analyzed, and the bond-slip analytical model at different stages was established; the model was defined by key parameters such as elastic ultimate shear stress τ0, peak stress τf and interface fracture energy Gf.

Trade-off between torque ripple and vibration in an IPMSM by examining the temporal and spatial harmonics of flux density

Despite continuous effort to minimize torque ripple, the reduction of vibration has not been yet achieved due to the lack of link between these two performances. The difficulty of investigating the relationship stems from the fact that torque is solely influenced by tangential force whereas vibration is directly tied to radial force. In this paper, the correlation between torque ripple and vibration in an IPMSM (Interior Permanent Magnet Synchronous Motor) is established by examining the air-gap flux density in both radial and tangential directions. Its temporal and spatial harmonics are analyzed. A six-pole nine-slot IPMSM is used as a base configuration, and the air-gap flux density is varied by changing the height of a stator tooth tip. In the previous study, the same approach has been done to observe how to reduce torque ripple effectively. In this study, however, it is found that the trend of torque ripple is not the same as that of vibration with respect to the height of a pole tip, and the relation between the two is thoroughly observed and explained.

Forces on a singing wineglass rim

The characterization of friction is a multiscale problem involving a balance between asperity contacts and fluid film forces, most commonly modeled with a velocity-dependent coefficient of friction. Periodic stick–slip phenomena are often associated with the friction force that causes mechanical vibration. This type of vibration can cause noise to radiate via structural modes of a system. Notable examples include journal bearings, brake squeal, turkey calls, and wineglasses. Singing wineglasses have been used for centuries as musical instruments, so musical acousticians have studied the structural vibrations and acoustic output. However, the tri-axial force applied to the rim has not been measured. A test rig was designed to measure the vertical, tangential, and radial dynamic forces applied to the spinning glass rim and simultaneously capture the radiated noise. The sound radiated from the wineglass was observed to depend on the relative velocity at the rim and applied vertical load, so a stability region for a clear sound was determined. Additionally, the strongest radiating modes and harmonics in the pressure were found in the concurrently measured nonlinear force. This work may be extended to confirm the force measurement by existing friction models, a water medium, and more complicated systems.

Scratch hardness of diamond-like carbon (DLC) coatings deposited by closed-field unbalanced magnetron sputtering

Thin coatings are subject to scratch and wear damage in tribological applications. Scratch hardness numbers are used to evaluate scratch and abrasive wear resistance. Few studies have measured the scratch hardness of thin films, and a proper scratch hardness measurement method for thin coatings is still lacking. In this study, the scratch hardness of these DLC coatings was measured at both micro-scale and nano-scale, respectively. The micro-scratch test using a 200 µm tip is an inapplicable method because the substrate effect has dominated the scratch hardness measurement. On the other hand, a nano-scratch hardness test using a sharper tip is an effective method to measure the scratch hardness of thin coatings. Although the scratch hardness introduces a lateral force compared with the indentation hardness, it well correlates with the nano-indentation hardness. The ratio of the scratch hardness to the indentation hardness is close to 1 for DLC coatings due to the amorphous structure. It proves that the tangential force induced by scratching does not influence the hardness property. In addition, a simple approach is proposed to obtain the scratch hardness of DLC coatings qualitatively without width measurement.

Features of using the power skiving method for multi-pass cutting of internal gears

The paper presents the results of a simulation on a 3D model of undeformed chips and cutting forces during three-pass gear cutting using the power skiving method. At the level of individual blades and teeth in successive angular cutting positions, the main component of the cutting force and the tangential force on the cutter axis are shown. The analysis of the forces acting on a single gear tooth and the continuous cutting forces allowed the development of a methodology for the selection of rational cutting modes – the value of the axial feed, the number of passes with different cutting depths in order to ensure the minimum time consumption and to achieve the required accuracy of the gears in terms of the parameter of the permissible angular deviation of the profile of the cut gear. It is shown that, provided the required machining accuracy is ensured, higher productivity is achieved by increasing the axial feed at a lower depth of cut and increasing the number of passes, rather than by reducing the feed and increasing the depth of cut.

Laser-assisted surface grinding of innovative superhard SiC-bonded diamond (DSiC) materials

Silicon carbide (SiC)-bonded diamond materials, comprising approximately 50% diamond by volume, represent innovative composites with exceptional mechanical and thermal properties, including high hardness, wear and corrosion resistance, and elevated thermal conductivity. Despite these advantageous properties, the machining of these composites presents formidable challenges due to their extremely high hardness. Grinding with diamond tools is commonly employed among the limited viable machining methods. However, the efficiency of this process is hindered by high grinding forces, elevated temperatures, and significantly high tool wear. Additionally, the surface integrity, form, and dimensional accuracy of the workpiece are compromised by the effects of tool wear and high cutting forces. To address these technological constraints in the grinding of SiC-bonded diamond materials, a laser-assisted grinding process has been developed. Ultra-short pulsed laser radiations were effectively utilized to induce material ablation with controlled structural damages, enhancing the productivity and efficiency of the grinding process through reduced grinding forces, temperatures, and tool wear. Furthermore, this study investigated the influence of grinding tools' specifications, design variations, and parameters on key aspects such as grinding forces, surface quality, and tool wear. Substantial reductions of up to 70% in tangential grinding forces, 83% in normal grinding forces, and a modest improvement in surface roughness achieved. The surface integrity analysis revealed a damage-free ground surface when utilizing laser assistance. Furthermore, there was a substantial enhancement in the grinding ratio (G-ratio), achieving an increase of up to 247%, concurrently with a noteworthy improvement in the actual removal depth, reaching up to 99%, when compared to conventional grinding processes. Compared to the utilized segmented metal bonded diamond grinding wheel, the vitrified bonded diamond grinding wheel induced lower grinding forces and higher actual removal rates.

A CFD-DEM Simulation of Droplets in an Airless Spray Coating Process of a Square Duct

The purpose of this paper is to provide a numerical simulation, taking into account the collisional interactions of droplets in an airless rotary spray coating process. The hydrodynamics of gas and droplets are simulated using the CFD-discrete element method (DEM) with the JKR contact model in an airless rotary spray coating process of a horizontal square duct. The surface energy parameter used in the JKR model is calibrated using a virtual accumulation angle test in the funnel device. Based on the distribution of accumulation angles, a suitable surface energy for wall droplets is proposed. A rational gas RNG k-ε model is suggested in accordance with the comparisons of velocities, standard deviations, and the skewness of droplet number fractions from three turbulence models. The simulations of droplet film thicknesses agree with measurements from the literature regarding the film thickness along a vertical panel. The correlations of the exit gas and droplet velocities of sprayer holes are proposed with a discharge coefficient of 0.85 for gas and 5.87 for droplets. A number index of droplets is introduced in order to measure the uniformity of droplet distributions. A low droplet number index is found at low rotational speeds, representing a more uniform distribution of droplets as the rotation speeds reduce within the square duct. The normal force between the droplet and the wall is approximately an order of magnitude larger than the droplet–wall tangential force of collisions.

Scratch performance of natural rubber and natural rubber composites reinforced with nylon, kevlar, and carbon fabrics

The scratch performance of natural rubber (NR) and fibre-reinforced NR was investigated using a scratch test with acoustic emission (AE). Both maximum penetration depth and maximum tangential force were characterised by two procedures. Procedure 1 applied the corner of a steel cube at face leading orientation. Procedure 2 applied a steel pyramid indenter with a spherical tip at the edge leading orientation. AE was adopted in Procedure 2 for evaluation of cutting damage mode that varied from ploughing/tearing the matrix to cutting both the matrix and fabric. The scratched regions of all specimens were observed using an optical microscope to estimate the damage level and examine damage mechanisms. The results show that scratch resistance improved as fibre content and fibre stiffness increased. The maximum tangential force depended on the damage modes. Two or more fabric layers could further increase penetration resistance, but the damage level is more serious in most cases.

Discrete Element Simulation of Macro and Micro Mechanical Properties of Round Gravel Material under Triaxial Stress

In this study, the effects of relative density and confining pressure on the shear characteristics of round gravel are investigated using a large-scale triaxial apparatus and the discrete element method. A simple and efficient numerical method for simulating flexible membranes is introduced. The results show that the stress-strain curves develop from hardened to softened type with increasing relative density, while the stress-strain curves develop from softened to hardened type with increasing confining pressure. As the axial strain increases, the strong contact force chains are vertically distributed, and the larger the relative density and confining pressure, the greater the number and thickness of the strong contact force chains. In the shear process, the distribution of average normal and tangential contact forces show “peanut-shaped” and “petal-shaped”, respectively. The increase in relative density increases the anisotropy of the specimen, while the increase in confining pressure results in a decrease. A linear relationship exists between the macroscopic stress ratio and the anisotropy coefficient. The anisotropy coefficient of the normal contact force provides the greatest contribution to the macroscopic shear strength (about 55%), followed by the anisotropy coefficient of the contact normal (about 26%) and that of the tangential contact force (about 19%).

Analyzing cyclic shear behavior at the sand–rough concrete interface: An experimental and DEM study across varying displacement amplitudes

AbstractPile foundations frequently endure dynamic loads, necessitating an in‐depth examination of the cyclic shear properties at the pile–soil interface. This study involved a series of cyclic direct shear (CDS) tests conducted on sand and concrete with irregular surface, utilizing varying displacement amplitudes (1, 3, 6, and 10 mm) and joint roughness coefficients (0.4, 5.8, 9.5, 12.8, and 16.7). Discrete Element Method (DEM) models, informed by experimental data, facilitated mesoscopic mechanical response analyses. Findings indicate that the sand–concrete interface undergoes softening, with hysteresis loops' morphology dependent largely on displacement amplitude. A maximum ultimate shear stress corresponds to a specific critical surface roughness, while the initial tangent modulus escalates with increased concrete roughness. Volume variations of the specimen inversely correlate with displacement amplitude and directly with surface roughness. As displacement amplitude expands, there is a reduction in the maximum shear stiffness and an elevation in the maximum damping ratio. Empirical formulas for the surface roughness and normalized shear stiffness were proposed. Larger displacement amplitudes result in more substantial shear bands and heightened energy dissipation, yet the incremental energy ratio remains largely unaffected. Predominant energy dissipation mechanisms include both slip and rolling slip, with the former surpassing the latter in energy dissipation capacity. The anisotropy directions of contact normal, normal contact forces, and tangential contact forces consistently fluctuate with shear direction alterations.

Study on the atomic removal behavior and damage formation mechanism of nano cutting copper–nickel alloy with diamond tool

The effects of tool rake angle and cutting depth on cutting temperature, cutting force, friction coefficient of rake tool face, atomic accumulation of chip flow and removal, surface quality, sub-surface damage layer thickness, atomic stress, and dislocation evolution were studied by molecular dynamics simulations. The results showed that the cutting temperature was concentrated on the chip, and the chip was easy to flow out with the increase of the tool rake angle, which weakens the extrusion and shearing action of the workpiece, resulting in the gradual reduction of tangential force. The tool rake angle of 10° is beneficial to improve the surface/subsurface quality of the workpiece. The minimum root-mean-square roughness obtained was 0.73 Å. The atomic stress of the workpiece was mainly concentrated around the area of interaction with the tool, and the atoms on the finished surface underwent elastic recovery, so the atomic stress was not significant. The 1/6<112> (Shockley) dislocation density had always been in the leading position, and 1/6<112> (Shockley) dislocation was continuously synthesized and decomposed during the nano-cutting process. With the increase of cutting depth, the number of atoms removed increases rapidly, and the width of chip side flow increases, but the symmetry is weakened. The contour line map even shows deep wave valleys caused by the absence of atoms, which increases the surface roughness. Moreover, the area and depth of the atomic stress distribution in the subsurface layer increase, and the number of amorphous atoms and dislocation density increase.

Acceleration of shear flow ina viscoplastic half-plane with a depth-varying yield stress

The problem of acceleration from a state of rest of a shear flow in a viscoplastic half-plane is studied analytically when a tangential stress is specified at the boundary. It is assumed that the dynamic viscosity and density of the medium are constant, and the yield stress can change in a continuous or discontinuous manner depending on the depth. The entire half-plane at any moment of time consists of previously unknown layers where shear flow occurs and rigid zones. The latter can move as a rigid whole, or they can be motionless, such as, for example, a half-plane, to which disturbances caused by the action of tangential forces have not yet reached. To find the stress and velocity fields, a method is developed based on quasi-self-similar diffusion-vortex solutions of parabolic problems in areas with moving boundaries. The question of what conclusions about the depth distribution of the yield stress can be drawn from available measurements of the velocity of the half-plane boundary is discussed.