Contact Friction Force Research Articles

Numerical simulation of friction characteristics of bionic flexible contact surface of front axle rocker arm sleeve of car

Based on the finite element software ABAQUS, the friction process of the flexible friction pair of the front axle rocker bushing of a car with a convex structure similar to the mantis head is established.The finite element model of the process is constructed and its friction characteristics are verified. By selecting a suitable hyperelastic constitutive model and changing the size of the convex structure on the surface of the sleeve,The simulation analysis of the mechanical characteristics of the flexible friction pair in radial and torsional directions shows that the bionic convex hull design changes the maximum stress of the bushing when it is subjected to force.The force and strain position are adjusted to reduce the possibility of cracking of the rubber bushing; the contact friction force and friction coefficient of the bionic bushing surface are significantly reduced, and the type 2 modelThe drag reduction and wear resistance of the profiled surface are the best.

Lubrication Characteristics of Dry-Gas Seals with Spiral Grooves

To obtain an optimal range of structural parameters for dry-gas seals with good performance, this study employed advanced sensing technology to monitor and analyze the internal flow characteristics of dry-gas seals in real time. Additionally, the validity of the calculation program was verified through experimentation. Using steady-state performance parameters as evaluation indices, a calculation model with lubrication characteristics was developed. The results indicate that when there are 12 grooves, the gas film pressure distribution is uniform and has a high value. At pressures greater than 2 MPa, the opening force, leakage, and gas film stiffness change significantly due to enhanced dynamic pressure effects with high-pressure differences, which reduces the local contact forces and frictional forces. At a constant speed, decreasing the gas film thickness increases the pressure difference while increasing both the opening force and film stiffness; however, at higher rotational speeds where the gas flow becomes non-uniform, the stability of the gas film is affected, leading to increased frictional forces. When there are between 10 and 16 grooves with depths ranging from 5.0 to 6.0 μm, dynamic pressure effects caused by pressure gradients become apparent, resulting in good dry-gas sealing performance being achieved. This research provides a theoretical reference for optimizing the design of dry-gas seals, as well as their steady-state seal performance.

A novel cohesive interlayer model considering friction

To understand the influence of friction on the shear-slip behavior of heterogeneous brittle composites, a novel cohesive interlayer model that can effectively capture the friction effect was proposed based on the classical Park-Paulino-Roesler model. Meanwhile, the unified potential energy function governing the interface tangential and normal behaviors was introduced to realize the mechanical interaction between Mode I fracture and Mode II fracture, and a smooth friction growth function was added in the elastic deformation stage for calculating the accurate contact pressure and friction force. Furthermore, the capability of the proposed model in addressing unloading and reloading was improved, and the fracture energy can vary accordingly during cyclic loading. To verify the effectiveness of the proposed model, it was examined by modelling the shear behavior of a masonry wallette. The results show that the relative error of the proposed model is 14.92% which is much lower than those of the other three pre-existing models when calculating the displacement corresponding to peak shear stress. Meanwhile, in terms of peak shear stress and initial displacement at residual stage, the relative errors of the proposed model are only 1.82% and 5.04%, respectively, indicating the high accuracy. Besides, the tangent stiffness determined by the second-order integration of the potential energy function is also continuous and smooth, which ensures the effective convergence of the proposed cohesive model.

Study on the Effect of Starved Lubrication on the Dynamic Characteristics of Locally Failed Roller Bearings

When the lubricant is not enough to maintain the ideal lubrication state of the bearing, the deep groove ball bearing will enter the starved lubrication state, which leads to the change of the vibration response of the deep groove ball bearing with localized defects. Previous bearing dynamics models mainly consider the lubrication state as an ideal lubrication condition, which may not reveal the effect of starved lubrication on the vibration characteristics of defective bearings. In this paper, the internal interaction of the system under starved condition is taken into account, and a dynamic model of defective deep groove ball bearings with insufficient lubricant is established to investigate the effects of different starved lubrication degrees on the contact force, friction force, cage speed, and system vibration characteristics. The results show that the lubricant insufficiency significantly changes the contact force inside the bearing, and the increase in friction caused by the increase in the degree of starved lubrication leads to the suppression of the degree of bearing slipping. The root mean square (RMS) value of the time-domain signal and the outer ring fault frequency both increase with the increase of the starved degree. The results of the study are helpful for fault diagnosis and condition monitoring of related equipment.

Heterogeneous solvent dissipation coupled with particle rearrangement in shear-thinning non-Brownian suspensions.

Dense non-Brownian suspensions exhibit significant shear thinning, although a comprehensive understanding of the full scope of this phenomenon remains elusive. This study numerically reveals intimate heterogenous coupled dynamics between many-body particle motions and solvent hydrodynamics in shear-thinning non-Brownian suspensions. In our simulation systems, we do not account for frictional contact forces, reflecting experimental conditions under low shear rates where shear thinning occurs, while hydrodynamic interactions are directly incorporated using the Smoothed Profile Method. We demonstrate the spatially correlated viscous dissipation and particle motions; they share the same characteristic length, which decreases with increasing shear rate. We further show that, at lower shear rates, significant particle density changes are induced against the incompressibility of the solvent, suggesting the cooperative creation and annihilation of gaps and flow channels. We discuss that hydrodynamic interactions may substantially restrict particle rearrangements even in highly dense suspensions, influencing the quantitative aspects of macroscopic rheology.

Numerical analysis of running resistance of a completion string with packers and sliding sleeves in horizontal wells

The installation of a completion string in small-diameter horizontal wells often presents challenges such as instability, bending, and high frictional resistance. To accurately estimate the running resistance during deployment and ensure safe descent to the bottom of the well, a three-dimensional numerical model has been developed incorporates real-time contact interaction between the completion string and the wellbore, while maintaining precision and field applicability. The analysis evaluates several factors, including buckling behavior, average and dynamics transient value of contact force, axial forces, and frictional forces. Results reveal that the upper pipe string exerting thrust on the lower pipe string causes bending and spiral buckling along with resulting contact with wellbore. Maximum hook load and maximum negative axial force occur at a inclination angle of 65°. Contact strength is more pronounced in inclined and horizontal section compared to vertical section. Leveraging extensive data, the study has yielded a quick prediction formula for quickly calculating the resistance experienced by a completion string of field area. The numerical results offer valuable insights into comprehending the resistance encountered during the descent of a completion string in horizontal wells, and provide robust theoretical support for predicting descent resistance.

Effects of liquid lubricants on the surface characteristics of 3D-printed polylactic acid

In this study, 3D-printed Polylactic acid (PLA) specimens were manufactured and polished using various lubricants to assess their surface, friction, and wear characteristics. After polishing, the surface roughness decreased by approximately 80% compared with that before polishing, except when acetone was used as the lubricant. In particular, under deionized (DI) water and acetone lubrication conditions, the friction coefficient decreased by 63% and 70%, respectively, whereas the specific wear rate decreased by 88% and 83%, respectively, compared with the unpolished specimens. In the case of dry polishing, adhesion, friction, and wear increase owing to surface damage. Ethanol and IPA polishing resulted in hydrolysis and increased friction, but slightly decreased wear rates. The surface of the specimen polished with acetone dissolved and became very rough. Only the surface polished with DI water exhibited hydrophobic properties. When acetone and DI water were used as lubricants, the surface adhesion force, adhesion energy, friction coefficient, and wear rate were lowest. The finite element analysis results showed that the polished surface exhibited stable contact pressure and friction force, while the unpolished surface showed large fluctuations in contact pressure and friction force owing to the laminated pattern. These results suggest that the polishing process is crucial for improving the surface characteristics and mechanical performance of 3D-printed PLA parts.

Nonlinear dynamics of planetary roller screw mechanism.

The synchronous meshing of the gear pair and the screw pair is a typical feature of the planetary roller screw mechanism. In order to fully derive and analyze the nonlinear dynamic characteristics of the system, this paper creatively incorporates the time-varying meshing stiffness of gear pair and the comprehensive transmission error into the research content. Combined with the thread contact force and friction force between the roller and the screw and between the roller and the nut, the nonlinear dynamic model of the planetary roller screw mechanism considering the meshing excitation of the gear pair is established. According to the time domain diagram, frequency domain diagram, phase plane diagram, Poincaré section diagram, three-dimensional spectrum diagram, and spatial phase diagram, the nonlinear behavior of the system is described in detail, and the bifurcation evolution process of the system under the excitation frequency parameters of the external load is revealed. In addition, based on the theory of multi-scale method and considering the variables such as meshing stiffness, meshing damping, and load fluctuation, the stability equation of the primary resonance of the system is derived. The analysis of the stability of the system under different working conditions shows that the parameters are selected within a reasonable range, which effectively reduces the primary common amplitude value and enhances the overall stability of the system. The research content improves the previous system dynamics modeling method and provides a theoretical basis for the nonlinear dynamics modeling method and parameter optimization design of the planetary roller screw mechanism.

Torque and Drag Analysis for Horizontal Extended Reach Coiled Tubing Drilling

One of the major elements faced in downhole drilling operations of oil and gas wells is the limited reach of coiled tubing (CT) in horizontal wellbores. To address this issue, this work creates an extended reach limit simulation of CT with starting bending curvature in a horizontal wellbore for an Iraqi well in the Ahdeb oil field. Using Drillbench software, a calculation approach is provided based on contact force and buckling models to determine the extended reach limit of CT. The findings of this study have significant implications for improving downhole drilling engineering design parameters and predicting the extended reach limit of CT. By considering factors such as friction resistance and contact force between the wellbore, a more accurate assessment of the CT’s abilities can be suggested based on well trajectory curvature and well devotion. To achieve this, a slim open hole with a diameter of 6 inches was drilled to a measured depth ranging from 3755 to 3986.5 m. The results showed that a consistent trend in azimuth and inclination in the completed section, with the hook load increasing by about 25 tons during pickup and decreasing by 11.4 tons during slack-off along the curved section due to friction effect. Additionally, elongation and relative stress showed slight increase during pickup in curved areas due to friction and temperature effect, while values decreased during slack-off due to drag action. Pressure loss in the curved section was found to be lower compared to the vertical section, primarily due to the bit nozzle discharge effect. Eventually, the friction coefficient values remained within acceptable industry limits. Ultimately, the study determined limited extended lengths for CT in this horizontal well.

The role of the damping component deformation in improving the tribological behavior at the high-speed train braking interface

Aiming to the issue of the unclear mechanism and lack of design basis for the influence of the deformation of the damping component installed in the brake pads of high-speed train, various perforated configurations were implemented on the damping component to obtain different typical deformation. The damping component was then installed on the back of the friction block and the tests on friction braking were performed using a test rig designed to assess high-speed train braking performance. A finite element model (FEM) was established for wear simulation to obtain block worn surfaces that closely matched the test results, succeeded by conducting both complex eigenvalue analysis (CEA) and implicit dynamic analysis (IDA). The findings indicate that the perforated configurations effectively provided damping components with different deformation capabilities, and increasing the deformation weakened its damping effect on vibration. The damping component deformation not only significantly affected the non-uniform wear on the block surface but also altered the wear patterns. Inappropriate deformation exacerbated the degree of non-uniform wear, leading to complex abrasive wear and adhesive wear, and added to the interface damage. Therefore, the damping component deformation significantly altered the friction-induced vibration and noise (FIVN) characteristics. Enhancing the deformation disrupted the continuity of FIVN but intensified its strength. The major reason is that the damping component deformation determined the time length of its compression and rebound, and inappropriate deformation significantly amplifying the oscillation intensity of contact area and friction force. This posed a challenge in establishing stable contact at the braking interface, ultimately leading to the generation of intense FIVN. Installation of damping components in brake pad to improve interface contact characteristics and suppress FIVN should carefully consider the structural of the braking system, and design damping components with appropriate deformation. Otherwise, it may lead to opposite effects.

A comprehensive review of experimental studies on shear behavior of bolted rock joints with varying rock joint and bolt parameters and normal stress

AbstractThe shear characteristics of bolted rock joints are crucial for the stability of tunneling and mining, particularly in deep underground engineering, where rock bolt materials are exposed to high stress, water pressure, and engineering disturbance. However, due to the complex interaction between bolted rock joints and various geological contexts, many challenges and unsolved problems arise. Therefore, more investigation is needed to understand the shear performance of bolted joints in the field of deep underground engineering. This study presents a comprehensive review of research findings on the responses of bolted joints subjected to shearing under different conditions. As is revealed, the average shear strength of bolted rock joints increases linearly with the normal stress and increases with the compressive strength of rock until it reaches a stable value. The joint roughness coefficient (JRC) affects the contact area, friction force, shear strength, bending angle, and axial force of bolted rock joints. A mathematical function is proposed to model the relationship between JRC, normal load, and shear strength. The normal stress level also influences the deformation model, load‐carrying capacity, and energy absorption ratio of bolts within bolted rock joints, and can be effectively characterized by a two‐phase exponential equation. Additionally, the angle of the bolts affects the ratio of tensile and shear strength of the bolts, as well as the mechanical behavior of both bolted rock joints and surrounding rock, which favors smaller angles. This comprehensive review of experimental data on the shear behavior of bolted rock joints offers valuable theoretical insights for the development of advanced shear devices and further pertinent investigations.

Application of Installations with Uniform-Strength Beams as Working Deformation Standards

A method for obtaining homogeneous deformation along the length of the measuring section of a uniform-strength beam and the possibility of its application as part of a working deformation standard are considered. The results of the analysis of the bending model and the design of a uniform-strength beam are presented. In the focus of attention are the parameters included in the measurement equation and related to methodological factors, as well as influencing the result of relative deformation measurements. The subjects of research are the presence of contact friction forces, heterogeneity of material properties, the special nature of the load application (bending, torsion, the presence of residual stresses in the body, geometrical parameters of the calibration beam, orientation of primary transducers on the beam, application of bending load, measurement of deflection and displacement of the neutral layer). The advantages and disadvantages of using a uniform-strength beam for determining the characteristics of primary strain transducers during testing, calibration, and verification were established. The deviation of signals of primary transducers located outside the axial cross-section when oriented along the beam axis and along the force lines converging at the point of load application was experimentally revealed. The error due to the orientation of the primary transducers on the beam depending on the angle between the lateral faces can range from 0.15 to 0.23 %. The study adds to the theoretical knowledge base on the possibility of using a cantilever uniform-strength beam as a load-bearing element in calibration installations. The conclusions may be useful for testing, calibrating, and verifying primary strain transducers.

Development of devices for measuring contact friction forces in the processes of volumetric plastic deformation

Development of devices for measuring contact friction forces in the processes of volumetric plastic deformation

Axisymmetric Pressing Problem of Discrete Metal Materials

The paper presents an analytically closed solution to the problem of axisymmetric pressing of discrete metal materials by the method of jointly solving the differential equations of equilibrium of the metal and the plasticity conditions of the porous body, taking into account all pressing factors without exception: the type and properties of the charge, loading conditions, porosity, temperature, friction, etc. The purpose of this work is to develop the foundations of the engineering theory of pressure processing of discrete materials using the example of solving the problem of axisymmetric pressing of structurally inhomogeneous metal chips in a movable closed matrix. The basis for constructing a physical and mathema-tical model of the process is the idealized case of uniform compaction of a porous body with the subsequent determination of the lateral pressure coefficient corresponding to the actual degree of compaction at various stages of loading. The resulting equation for the relationship between the stress tensor components and the yield stress and relative compaction density represents the cylindrical Mises plasticity condition, which in the limit at zero porosity transforms into the plasticity condition for compact metals. The boundary value problem is solved for tangential stresses, taking into account the magnitude and direction of action of contact friction forces, which in their physical nature do not differ from the friction forces in the depth of the pressed material. The physico-mathematical model makes it possible to calculate the stress fields and density of the body according to the coordinates of the deformation zone, as well as energy-power parameters (pressure, force, work of deformation) provided that three structural and rheological characteristics are determined: the yield strength, relative compression and the degree of deformation compaction. Due to the fact that the problem is solved in relation to bodies of rotation in a general form and in a general formulation, the solution itself should be considered as methodological for any axisymmetric loading scheme.

Enhanced modelling of planar radial-loaded deep groove ball bearings with smooth-contact formulation

AbstractBearings are mechanical components designed to restrict the relative rotary motion between moving parts and transmit loads with low friction. Their performance directly impacts the durability, efficiency and reliability of various machinery. Therefore, bearing failures can lead to economic costs, repair/stoppage times, accidents and regulatory compliance issues. In the context of Industry 4.0, the development of detailed and reliable computational models for simulating bearings’ dynamics plays a crucial role in establishing digital twins and implementing advanced predictive maintenance strategies.This work focuses on modelling radial-loaded deep groove ball bearings under the multibody systems dynamics framework and the components of the bearing (inner and outer rings, rolling elements, and cage) are treated as separate bodies. A smooth contact approach is utilised to characterise the contact/impact phenomena, providing flexibility and efficiency in monitoring the whole contact event. In this sense, suitable normal and friction contact force models are used to describe those interactions between the contacting bodies. The main contribution of this work relies on the modelling strategies to represent the cage/rolling element interaction.Having that in mind, several multibody models of radial-loaded deep groove ball bearings are developed considering different modelling assumptions, resulting in dynamic analyses with various levels of complexity. The underlying simplifications are described, and their main advantages and shortcomings are discussed. The simulation results demonstrated the significant impact of accurately selecting the modelling parameters. The promising results of this study pave the way for future investigations, extending to other geometries of rolling contact bearings and working conditions.

Stress-activated friction in sheared suspensions probed with piezoelectric nanoparticles.

A hallmark of concentrated suspensions is non-Newtonian behavior, whereby the viscosity increases dramatically once a characteristic shear rate or stress is exceeded. Such strong shear thickening is thought to originate from a network of frictional particle-particle contact forces, which forms under sufficiently large stress, evolves dynamically, and adapts to changing loads. While there is much evidence from simulations for the emergence of this network during shear thickening, experimental confirmation has been difficult. Here, we use suspensions of piezoelectric nanoparticles and exploit the strong local stress focusing within the network to activate charge generation. This charging can then be detected in the measured ac conductance and serve as a signature of frictional contact formation. The direct link between stress-activated frictional particle interactions and piezoelectric suspension response is further demonstrated by tracking the emergence of structural memory in the contact network under oscillatory shear and by showing how stress-activated friction can drive mechano-transduction of chemical reactions with nonlinear reaction kinetics. Taken together, this makes the ac conductance of piezoelectric suspensions a sensitive in-situ reporter of the micromechanics associated with frictional interactions.

Fluid effects in model granular flows

Pore fluid plays a crucial role in many granular flows, especially those in geophysical settings. However, the transition in behaviour between dry flows and fully saturated flows and the underlying physics that relate to this are poorly understood. In this paper, we report the results of small-scale flume experiments using monodisperse granular particles with varying water content and volume in which the basal pore pressure, total pressure, flow height and velocity profile were measured at a section. We compare the results with theoretical profiles for granular flow and with flow regimes based on dimensional analysis. The runout and the centre of mass were also calculated from the deposit surface profiles. As the initial water content by mass was increased from zero to around 10%, we first observed a drop in mobility by approximately 50%, as surface tension caused cohesive behaviour due to matric suction. As the water content was further increased up to 45%, the mobility also increased dramatically, with increased flow velocity up to 50%, increased runout distance up to 240% and reduced travel angle by up to 10° compared to the dry case. These effects can be directly related to the basal pore pressure, with both negative pressures and positive pore pressures being measured relative to atmospheric during the unsteady flow. We find that the initial flow volume plays a role in the development of relative pore pressure, such that, at a fixed relative water content, larger flows exhibit greater positive pore pressures, greater velocities and greater relative runout distances. This aligns with many other granular experiments and field observations. Our findings suggest that the fundamental role of the pore fluid is to reduce frictional contact forces between grains thus increasing flow velocity and bulk mobility. While this can occur by the development of excess pore pressure, it can also occur where the positive pore pressure is not in excess of hydrostatic, as shown here, since buoyancy and lubrication alone will reduce frictional forces.Graphical abstract

Numerical research on contact friction force with different structural brush seal hysteresis characteristics under differential pressure

The problems of leakage, frictional wear, and flow heat transfer caused by the hysteresis characteristics of brush seals are prominent, and existing models for solving the hysteresis characteristics of brush seals have convergence difficulties owing to the extreme degree of nonlinearity caused by additional contacts. In this study, numerical models based on the finite element software ABAQUS were proposed to address the hysteresis characteristics of brush seals with three different structures: basic, low-lag hysteresis, and low-wear high-pressure bearing. The models accounted for the contacts between: the brush, brush and the baffle, and brush and the rotor, while damping was introduced to improve the convergence of the models. The hysteresis of the three structures under differential pressure was investigated and compared with theoretical calculations and experimental test results. The hysteresis of the bristles was normalised by the contact force, the shift of the contact area, and the contact friction force when the hysteresis effect occurred in the brush seal. The results show that the basic model has the most obvious hysteresis characteristics in the presence of differential pressure. Although the low-lag hysteresis model and the low-wear high-pressure bearing model have the weakest hysteresis effect, the deformation variables of the last row of bristles of these two structures are larger than those of the basic model; therefore, the contact position is prone to fatigue fracture. Simultaneously, the hysteresis effect was verified by varying the contact area and contact friction force, and it was found that the larger the contact area and contact friction force, the larger the hysteresis.

A coupled isogeometric/multi-sphere discrete element approach for the contact interaction between irregular particles and structures

An isogeometric/multi-sphere discrete-element coupling method is presented to model the contact or impact between structures and particles with complex shape. This coupling method takes advantages of the multi-sphere discrete element method for particles to provide the high computational efficiency and excellent robustness of their contact modelling. The advantage of isogeometric analysis (IGA) for continuous solid material, e.g. the exact geometric description, is also taken to achieve a more accurate contact interaction with an excellent time continuity. In the coupling procedure, the CGRID method is used for the global searching. The exact contact situation of the discrete element and the IGA element surface is further determined in the local searching by solving non-linear equations numerically. Then, the normal contact force between a sphere and an IGA element is calculated using a penalty based Hertz-Mindlin contact model, and damping and friction forces are also considered. Both the accuracy and validity of the coupling method are examined by comparing the numerical results of an example with one particle impacting on a quarter of a cylinder, with those of the FEM model where the particle is modelled as a rigid body. Two additional examples involving particles impacting onto a corrugated plate and particles of different shapes impacting on a chute, are simulated to further assess the applicability and robustness of the proposed method.

Frictional resistance calculation and jacking force prediction of rectangular pipe jacking

In practical engineering, whilst estimating the jacking force of rectangular pipe jacking using an empirical formula, the results obtained from said formula deviate from reality and manifest inadequate engineering guidance. The equations governing the applied force during the installation of rectangular pipe jacking have been derived for various contact states involving the interaction between the pipe, slurry, and soil. The distinct stress conditions in the pipe jacking process as well as the shear-friction mechanism between the pipe and the surrounding soil have been taken into account. The displacement control method is introduced to simulate the pipe–slurry–soil contact friction during the pipe jacking process in FLAC3D. Additionally, the pipe jacking behavior, pipe–slurry–soil contact frictional force, and variation law of the jacking force are also simulated. Mutual verification was carried out using the results obtained from field monitoring, numerical and theoretical. The findings are as follows: the established equations for calculating pipe jacking force are highly applicable across various conditions of pipe–slurry–soil contact, and the outcomes derived from theoretical formulas align remarkably well with those obtained through field monitoring and numerical simulation. During the jacking process, the sidewalls exhibit initial partial sliding followed by a complete movement as the jacking force intensifies and subsequently diminishes, eventually attaining stability during the behavior adjustment phase. Moreover, the bottom pipe–soil contact is the most common situation in actual construction.