Friction Model Research Articles

Friction modelling and parameter estimation for heavy-duty robots

This article presents a dynamic model used in the modelling of heavy-duty robots that is associated with an estimation method to determine the dynamic parameters of the robot and the friction components. The dynamic model considers nonlinear friction effects localised on the motor and joint sides, since the proper operation of the gearbox depends on the friction effects occurring at the input and output of the bearings, as well as the friction in the gearbox due to the gear contact. In this study, two models are evaluated to determine the most effective friction and nonlinear model. First, static models, such as Coulomb friction on the motor and joint sides with 42 parameters, are evaluated. Second, a nonlinear reduction model is tested on the motor side while keeping the same Coulomb friction model on the joint side. Parameter identification is performed using the open-loop method based on the output error with a minimisation criterion in a quadratic form. The maximum number of parameters identified by the open-loop method for the six axes is 42 for the first model and 54 for the second model. To sum up, the second study revealed that embedding the nonlinear reduction model with Coulomb friction into the dynamic model yields better results.

Assessment of cutting force coefficient identification methods and force models for variable pitch and helix bull-nose tools

The mechanistic approach is commonly implemented to predict and optimise the cutting forces in milling processes to prevent tool breakages, reduce tool wear, reduce form error, and improve surface quality. To implement this method, the cutting force coefficients (CFCs), that characterise the mechanics of the process, must be calculated. This study compares the accuracy of the predicted cutting forces for variable pitch and helix bull-nose milling tools using a rapid testing (RT) optimisation-based mechanistic CFC identification method that only requires a single angular cut with increasing radial engagement to the traditional mechanistic approach that requires several straight cuts. Along with developing a hybrid technique that combines variation in feed rate and radial engagement. The traditional radial, tangential, and axial (RTA) force model is also compared with the frictional and normal rake face (UV) force model that is independent of the local tool rake and inclination angles which is a necessary for bull nose tools. The RT and the developed hybrid CFC identification method with the UV force model predicted the average Fx, Fy and Fz cutting forces to within 7.1 %, 4.3 %, and 3.8 % error, respectively. These methods were slightly less accurate than the traditional method, however they have significant industrial benefits because they have can be used to identify CFCs with either a single cut, or from any tool-path with chip-load variation, respectively. The RTA force model predicted the average cutting forces similarly to the UV force model, however, the UV force model had lower errors using the rapid RT testing method at the extreme corners of the experimental design space.

Implicit Frictional Dynamics With Soft Constraints.

Dynamics simulation with frictional contacts is important for a wide range of applications, from cloth simulation to object manipulation. Recent methods using smoothed lagged friction forces have enabled robust and differentiable simulation of elastodynamics with friction. However, the resulting frictional behavior can be inaccurate and may not converge to analytic solutions. Here we evaluate the accuracy of lagged friction models in comparison with implicit frictional contact systems. We show that major inaccuracies near the stick-slip threshold in such systems are caused by lagging of friction forces rather than by smoothing the Coulomb friction curve. Furthermore, we demonstrate how systems involving implicit or lagged friction can be correctly used with higher-order time integration and highlight limitations in earlier attempts. We demonstrate how to exploit forward-mode automatic differentiation to simplify and, in some cases, improve the performance of the inexact Newton method. Finally, we show that other complex phenomena can also be simulated effectively while maintaining smoothness of the entire system. We extend our method to exhibit stick-slip frictional behavior and preserve volume on compressible and nearly-incompressible media using soft constraints.

Optimized Modeling Strategies for the Parametrization of a Two-Parameter Friction Model Through Inverse Modeling of Conical Tube-Upsetting Tests

Friction is a critical influencing factor for a variety of forming processes, as it affects, for example, the required forming force. Complex models for the numerical description of friction often have two or more model parameters but lack appropriate calibration methods since calibration schemes developed for one-parameter models are not applicable. The objective of this work is to develop an evaluation method based on inverse modeling of the conical tube-upsetting test in order to allow for the parametrization of a two-parameter friction model, providing a unique solution for the model parameters. It is based on a comparison of the specimen’s outer contour for several points in time throughout the forming process according to the finite element model of the test. An optimization algorithm minimizes the deviation between the experimental and the simulated contour by adapting the friction model parameters. A two-parameter model is used that considers normal stress as well as relative velocity. First, purely numerical investigations show the necessity of a model adaption due to insufficient data. The modeling scheme is therefore adapted to consider data from two tests with different relative velocities. The results suggest a unique solution for the determination of the friction model parameters for purely numerical studies as well as for experimental conditions, comparing with the evolving contour of the conical tube-upsetting test specimen. Thus, this study presents a promising approach for the calibration of two-parameter friction models.

Interactive Friction Modelling and Digitally Enhanced Evaluation of Lubricant Performance During Aluminium Hot Stamping

Conventional lubricant testing methods focus on lab-scale constant contact conditions, which cannot represent the scenarios in actual hot-stamping processes. In recent studies, the concept of the ‘digital characteristics (DC)’ of metal forming has been proposed by unveiling the intrinsic nature of the specific forming, which presents a timely solution to address this challenge. In this work, the transient behaviours of three dedicated lubricants during the hot stamping of AA6111 material were investigated considering the effects of various contact conditions using an advanced friction testing system, and the interactive friction modelling was established accordingly. The lubricant limit diagram (LLD) of each lubricant was then generated to quantitatively evaluate the lubricant performance following the complex tool–workpiece interactions based on the tribological DCs, and a detailed investigation on the lubricant failure regions was conducted based on the interactive friction modelling. Finally, the industrial application index (IAI) was proposed and defined as a comprehensive evaluation of lubricant applications in the industry, and the most suitable lubricant was identified among the three candidates for mass production.

A robust 3D finite element framework for monolithically coupled thermo-hydro-mechanical analysis of fracture growth with frictional contact in porous media

This paper presents the formulation of a robust integrated framework for the coupled multiphysics and multiple fracture growth analysis in porous media. The finite element-based thermo-hydro-mechanical method for fracture growth with frictional contact (THMf-g) simultaneously solves monolithically coupled equations, incorporating contact and frictional constraints from fracture sliding. It also implements an adaptive process to update fields and geometries during fracture growth, effectively modeling emerging new surfaces. The thermo-hydro-mechanical fields are derived from fundamental principles of mass, momentum, and energy conservation and discretized numerically using the finite element method. Fractures are represented as sub-dimensional surfaces embedded within the volume of the porous medium. The growth of multiple fracture is modeled based on stress intensity factors at fracture tips, with fracture aperture and permeability emerging as dynamic properties of the system. The main novelty of this work lies in extending the implicitly solved monolithic coupling to include frictional and growth modeling for multiple non-planar fractures of emerging geometry in three dimensions. This includes the direct incorporation of cubic terms in the fracture flow equations and convection terms in the heat transfer equations, adopting an incremental method to solve these coupled, nonlinear equations. To ensure energy conservation, the heat equations are resolved using an implicit scheme, establishing a velocity dependency on pressure fields and introducing quadratic terms into the heat equation. Furthermore, the heat transfer equation has been revised to account for the work done on the fluid, enhancing the accuracy of thermal modeling. A contact mechanics leader–follower strategy tracks a conformal mesh split at each fracture, accounting explicitly for permeability changes during deformation and growth, effectively reducing computational complexity and cost. The iterative process for applying these constraints and the solution of the coupled THMf-g with friction and growth is described. The method does not require calibrated material properties or artificial length scale parameters, and relies on laboratory-measured properties with direct physical interpretation. A detailed algorithm is presented, including the updating of apertures and handling of new surfaces during the simulation, accounting for the variability of fracture permeability and its interplay with contact and friction during the non-linear solution. Several validating numerical experiments are benchmarked against analytical solutions, demonstrating the accuracy and reliability of the proposed framework in capturing complex fracture behavior and multiphysics interactions in porous media.

A quantitative characterization model for nonlinear dynamic parameters of O-rings

When the rubber O-ring follows the primary seal in the axial direction as a secondary seal, there is hysteresis behavior between the restoring force and displacement. However, the dynamic parameters of O-rings are mostly expressed as constants in dynamic analysis at present, which cannot accurately describe the dynamic behavior of sealing systems. In response to the problem of poor track performance of mechanical seals, based on the actual working conditions in nuclear reactor coolant pumps, vibration experiments with high pressure and water lubrication are carried out on ethylene-propylene-diene monomer (EPDM) rubber O-rings, which can reveal the laws in the actual situation. The experimental results confirm that there are nonlinear variations of O-ring dynamic parameters in vibration, which cannot be expressed by constants. In order to quantitatively characterize the nonlinear behavior, this study establishes a novel mathematical model and analyze the influence of working conditions. A method combining the nonlinear properties of both interfacial sliding and body viscoelasticity of O-rings is proposed. The nonlinear stiffness, damping and friction (NSDF) model is established based on the adjusted Iwan model and the trace method. The finite element analysis and vibration experiments are carried out to study the hysteretic behavior and determine the parameters of the model. Furthermore, the influence of medium pressure and vibration amplitude on interfacial stiffness and O-ring stiffness and damping are discussed. It is pointed out that O-ring stiffness and damping decrease with increasing amplitude and increase with increasing pressure. The comparative analysis of experiments and model shows that the proposed model can provide an accurate determination of the nonlinear behavior of O-rings in vibration. The results and the proposed model can provide a basis for the evaluation of the dynamic performance of mechanical seal systems.

VARIABLE FRICTION MODEL DEVELOPMENT AND IMPLEMENTATION TO THE PULLING FORCE PREDICTION OF THE SPLIT-SLEEVE COLD EXPANSION PROCESS FOR ALUMINUM 2024-T3

Abstract This study aims to improve the accuracy of the pulling force estimation by establishing the variable friction model of the dry-lubricated split sleeve when cold working an aluminum 2024-T3 hole. The variable friction model was empirically obtained from the friction experimental setup simplified from the split-sleeve cold expansion process. The contact-pressure-dependent variable friction model was derived through a systematic design of experiments approach with three different normal stress conditions, namely low normal stress (220 MPa), medium normal stress (440 MPa), and high normal stress (660 MPa), to cover the range of normal stresses occurred in the cold expansion process. A full quadratic response surface model was drawn for the friction coefficient's nonlinear relationship between the mandrel and the lubricated sleeve, depending on the normal stresses. The variable friction model was verified with 3-dimensional friction test finite-element (FE) simulations. This FE modeling validates the variable friction model to predict the pulling forces with a sound agreement between the estimated and experimentally obtained values. We conducted split-sleeve cold expansion experiments to obtain the pulling force profile. Two 3-dimensional (3D) FE numerical analyses of the same split-sleeve cold expansion process were conducted using the variable friction model and a constant frictional coefficient of 0.05. The pulling force profiles from the FE modeling with the variable friction model closely align with those from the experiments to show the four distinct regions.

Analysis of Tire-Road Interaction: A Literature Review

This paper presents a comprehensive literature review of the most popular and recent work on passenger and truck tires. Previous papers discuss a huge amount of work on the modeling of passenger car tires using finite element analysis. In addition, recent works on tire–road interaction and the validation of tires using experimental measurements have been described. Moreover, the history of the tire-road contact algorithms is explained. In addition, friction modeling that is implemented in tire–road interaction applications are discussed. Also, a summary of current state-of-the-art research work definitions and requirements of the tread rubber compound are covered from previous studies using various literature reviews and hyper-viscoelastic material models that are implemented for the tread top and the tread base rubber compound. Furthermore, the effect of tire temperature from previous works is presented here. Finally, this literature review also highlights the shortcomings of recent research work and describes the areas lacking in the literature.

Frictional Abrasion of Rubber: Transition from Sliding to Rolling

ABSTRACT To develop applicable friction and wear models on tire scale, reliable test data are required. Consequently, friction tests on block level are requested because the distribution of contact pressure as well as slip velocity is nearly homogeneous at the contact surface of the sliding rubber block. However, wear mechanism and energy intensity levels of sliding rubber blocks and rolling rubber wheels or tires differ significantly. Consequently, linking both sliding and rolling frictional abrasion is required; thus, a wear model for rubber material is introduced to consider both deformation slip and sliding. The model input for sliding friction and resulting wear rate is derived from linear friction test experiments using sliding rubber blocks at different loading. A unique and sophisticated re-mesh algorithm ensures proper mesh modification due to abrasion of the structure. A wear energy evolution approach is developed to consider low abrasion with small sliding distances to predict wear at rolling rubber wheels. The simulation framework of abrasion modeling is successfully validated using laboratory abrasion tests.

A novel friction coefficient model parameters identification method for needle-tissue insertion procedure

Abstract In endoscopic liver vascular insertion surgeries, during the process of angiographic operation, the success of vascular staining depends on precise needle insertion control which heavily relies on experienced surgeons. Endoscopic vascular insertion surgical navigation system shows the potential to improve position precision, however it relies on needle-tissue interaction model and parameter identification to provide essential information for improving needle insertion accuracy, in which the friction coefficient is important parameters but difficult to determine. In this paper, a novel needle-tissue friction coefficient identification method was proposed with unknown tissue Young's modulus under endoscopic liver surgery scenarios. A modified friction coefficient model was proposed including the adhesion and elastic friction component to describe needle-tissue dynamic interaction process which can predict the friction coefficient more precisely. The proposed parameter estimation method based on the modified friction model can simultaneously estimate friction coefficient and Young's modulus. The proposed method was demonstrated by the friction coefficient measurement experiment. The results showed that the friction coefficient model prediction results agreed well with expected value. The proposed method can be applied to provide essential tissue-needle interactive information to improve needle insertion precision in the endoscopic liver vascular insertion surgery scenarios.

An analysis and reliability-based optimization design method of trajectory accuracy for industrial robots considering parametric uncertainties

To address the challenges of poor trajectory accuracy in industrial robots, which has emerged as a technological bottleneck hindering further robots’ applications in high-precision manufacturing industries, this paper proposes a method for the analysis and reliability-based optimization design for industrial robots’ trajectory accuracy considering parametric uncertainties. Firstly, the dynamic equation of an articulated industrial robot with six degrees of freedom is derived, incorporating the Stribeck joint friction model, followed by the uncertain parameter identification of this dynamic model. Subsequently, an uncertainty simulation system for the robot is established based on the constructed dynamic model and the sensitivity of system uncertain parameters to the robot trajectory accuracy is analyzed, where 10 key parameters are obtained among 54 uncertain parameters. Finally, a reliability-based multi-objective optimization design methodology is proposed synthesizing the robot trajectory accuracy, manufacturing cost, and quality loss, to achieve tolerance design of the robot's parameters, and enables minimizing costs and quality losses while ensuring the robot's trajectory accuracy reliability. The performance and practicality of the proposed method were validated using a six-degree-of-freedom rotary joint serial industrial robot as an example.

A comprehensive investigation into the effect of vertical component of ground motion on response of sliding unanchored blocks

This study aims to quantify the effect of the vertical component of ground motion on the seismic response of sliding rigid blocks, in terms of maximum and residual displacements. A multi-stripe analysis approach is employed to examine the response with and without the vertical component under various levels of ground motion intensity. First, a parametric study is conducted using a Coulomb friction model with a constant coefficient of friction that does not account for any dependence of the friction coefficient on velocity or pressure. It is shown that the effect of the vertical component on maximum and residual displacement is more pronounced for ground motions that can barely initiate sliding. Moreover, the influence of the vertical component on the residual sliding displacement is higher than that on the maximum displacement. Subsequently, to account for the friction coefficient dependence on pressure and sliding velocity, two interface cases (steel-steel, and concrete-concrete) are analyzed. It is found that even when a variable coefficient of friction is used, the overall trends observed for a constant coefficient of friction do not change.

Dynamic Damping Control of High-Precision Servo System Based on Friction Model for Finite-Time Position Tracking With Deteriorating Friction

Dynamic Damping Control of High-Precision Servo System Based on Friction Model for Finite-Time Position Tracking With Deteriorating Friction

Effect of Pulse Current on Friction Coefficient of 7075-T6 Aluminum Alloy and Microstructure Analysis

Abstract A study on friction is necessary to improve the forming quality of stamped parts. It has been found that pulsed current can improve the forming properties of aluminum alloys, mainly in terms of Joule heat and electroplasticity. Thus, this article revolves around the effect of different current densities on the friction and wear of 7075-T6 aluminum alloy sheets. The change rule of friction coefficient under different current densities is derived through a friction test, and the variable friction simulation model is established. Scanning electron microscope (SEM) and X-ray diffraction (XRD) are used to analyze the micromorphology and elemental composition of the wear surface. The diffraction peaks of Al are analyzed by XRD, and grain size and dislocation density are calculated. Finally, the actual stamping results are compared with the simulation results. The results show that the friction coefficient decreases with the increase of current density when the current density is less than 10 A/mm2, and the wear mechanism is mainly abrasive wear. When the current density is greater than 10 A/mm2, the friction coefficient increases with the increase of current density and the wear mechanism is mainly adhesive and electrical wear. The grain size and dislocation density mainly depend on the electrical plasticity. The variable friction model's simulated thickness distribution and rebound results align more with the situation.

Simulation and experimental verification of the orthogonal friction continuous wear of PTFE-Kevlar fabric liner

Woven fabric liners, which are customizable and maintenance-free, have extensive applications in self-lubricating spherical bearings. However, owing to the orthogonal anisotropy and non-homogeneous characteristics, their frictional and wear behaviors are complex. Currently, average performance testing is primarily based on long-term macroscopic wear experiments. However, unobservable parameters such as mesoscopic stress and pressure distribution in liners are bottlenecks in the experimental exploration of wear sources and mechanisms. Therefore, an innovative strategy for modeling orthogonal friction and continuous wear in non-homogeneous liners is presented. This approach has the potential to overcome experimental limitations and significantly expedite liner design and cost-effective validation. The initial step involves establishing a mesoscopic voxel-based planar model of the liner that maintains the topological relationship during wear processes. This is achieved by introducing a circular voxel mesh and spatial transformation methods. Based on orthogonal friction and wear assumptions, separate constitutive models for orthogonal friction and wear are developed. Using the CETR UMT-3 friction and wear testing machine, GCr15 is selected as the counterface material, the pin disc wear method is adopted to conduct sliding test on PTFE and Kevlar fibers, and the required wear constitutive parameters are fitted. Furthermore, incremental equations for the total wear are derived. An element wear fusion strategy is introduced. This approach leads to the development of a continuous wear algorithm for liners and subsequently to the establishment of a voxel-based finite element model with continuous wear capability in the form of a circular voxel grid. This method transcends experimental methods and allows for the determination of the mesoscopic contact pressure, stress distribution, and variations in the contact material composition patterns of liner. The accuracy of the average macroscopic wear prediction is validated experimentally. This method has the potential for practical applications in bearing design.

Shear capacity prediction of carbon-fibre-reinforced polymer mesh fabric (CFRP-MF) stirrups reinforced concrete beams

Fibre-reinforced polymer mesh fabric (FRP-MF) is an effective substitute for normal steel stirrups in concrete to prevent steel corrosion in reinforced concrete (RC) structures. Nevertheless, methods for calculating the shear resistance of RC members rehabilitated in shear with FRP-MF configurations are lacking. Moreover, the methods for quantitative analysis of the shear contribution caused by the cracking control effect produced by CFRP-MF longitudinal FRP strips are unclear. In this paper, a mechanics-based segmental model is presented based on partial interaction analysis considering both transverse FRP strips and longitudinal reinforcements. By incorporating the carbon-fibre-reinforced polymer mesh fabric (CFRP-MF) stirrups into this model, a shear strength model was proposed and extended for design purposes in a closed form. In addition, the modified compression field theory (MCFT) model considering the shear strength of concrete in compression and the shear friction model (SFM) in the literature were appropriately modified and used for comparison with the segmental model. It should be noted that if the tensile strength of the longitudinal strips was added into the corresponding calculation formulas, it would cause the difference between the proposed novel models with the previous models. Finally, the shear strength of 14 CFRP-MF reinforced concrete beams were evaluated using these three models. The average ratios of the experimental values of the CFRP-MF RC beams to the shear capacity predicted by the modified segmental model, MCFT with the shear contribution of compressed concrete and SFM were 1.30, 1.19 and 1.19, respectively. It turns out that the modified mechanics-based segmental model yields the minimum discreteness based on the experiment results. This study can provide shear capacity calculation and design reference of RC beams with longitudinal FRP strip reinforcements for researchers and engineers.

Axial behavior variation of 72-story concrete-filled steel tubes with different joint connections due to interface debonding considering long-term deformation of concrete core

Long-term concrete deformation including shrinkage and creep occurring seriously threats the longevity, safety and serviceability of concrete-filled steel tube (CFST) structures. In this study, numerical simulation on the variation of axial behavior of 72-story CFST structures with different joint connection details due to interface debonding considering shrinkage and creep of concrete core is carried out. Three connection details including connections with inner horizonal diaphragms only, two-direction through-beams only, and inner horizontal diaphragms combined with two-direction through-beam, are considered, respectively. Vertical loading from floors is treated as centralized vertical force applied on steel tube directly. The shrinkage of concrete core is simulated by decreasing concrete temperature. A cohesive constitutive law and a Coulomb friction model are employed to describe the interface behavior in tangential direction before and after debonding, respectively. The interaction between concrete core and steel tube in normal direction is treated as a hard contact. The concrete plastic-damage (CPD) constitutive model is used for concrete core and a plastic constitutive law is employed for the steel tube. The initiation of the interface debonding between steel tube, H-shaped steel beam flanges, inner diaphragms and concrete, the variation of the force transfer path, stress redistribution, steel tube yielding and the final failure are described in detail. Results show that the axial load-carrying capacity of each CFST structure has a decrease of 26–28 % when compared with that determined by the current design code where the confinement effect is considered, and a decrease of 9–10 % when compared with that determined by the current design code where the confinement effect of steel tube is not considered. Moreover, the axial stiffness decreases to 76–78 % of their theoretical values when debonding is not considered. Numerical results show that the interface debonding negatively affects the long-term axial load-carrying capacity and stiffness obviously, which has not been considered in current design codes. Some comments on the design of CFST members are proposed based on the numerical simulation results.

Autofiction and the possibility of life in neoliberal ruins: reification, friction and the affective dominant in Weijers and Heti

ABSTRACT This essay analyses the intersection of the novel and neoliberalism as a relation of friction (Tsing). Whereas former studies of literature and neoliberalism imply models of resistance or complicity, the model of friction allows us to read novels as exploring possibilities of life and creativity within the worlds of neoliberal reification. We apply this model to contemporary autofiction: Kamers antikamers by Niña Weijers and How Should a Person Be? by Sheila Heti. Differing from idealist accounts of neoliberalism and a capitalist view of the subject as ‘entrepreneur of the self’, we engage a materialist approach that looks at the subject as a ‘gamer’ (Wark) whose affective and cognitive skills get reified into information. We conclude that both novels foreground the desire to find possibilities of life in affective attachments, which in their turn open up possibilities of difference and creativity in the context of neoliberal abstraction and alienation.

Lie-theory-based dynamic model identification of serial robots considering nonlinear friction and optimal excitation trajectory

Abstract Accurate dynamic model is essential for the model-based control of robotic systems. However, on the one hand, the nonlinearity of the friction is seldom treated in robot dynamics. On the other hand, few of the previous studies reasonably balance the calculation time-consuming and the quality for the excitation trajectory optimization. To address these challenges, this article gives a Lie-theory-based dynamic modeling scheme of multi-degree-of-freedom (DoF) serial robots involving nonlinear friction and excitation trajectory optimization. First, we introduce two coefficients to describe the Stribeck characteristics of Coulomb and static friction and consider the dependency of friction on load torque, so as to propose an improved Stribeck friction model. Whereafter, the improved friction model is simplified in a no-load scenario, a novel nonlinear dynamic model is linearized to capture the features of viscous friction across the entire velocity range. Additionally, a new optimization algorithm of excitation trajectories is presented considering the benefits of three different optimization criteria to design the optimal excitation trajectory. On the basis of the above, we retrieve a feasible dynamic parameter set of serial robots through the hybrid least square algorithm. Finally, our research is supported by simulation and experimental analyses of different combinations on the seven-DoF Franka Emika robot. The results show that the proposed friction has better accuracy performance, and the modified optimization algorithm can reduce the overall time required for the optimization process while maintaining the quality of the identification results.