Dependent Friction Model Research Articles

Experimental investigation of the effect of lubricant change on automotive component

Manufacturing problems resulting from lubricant supplier changes are relatively common in automotive press shops. Simulations using computer-aided design (process and tool) detect a significant proportion of manufacturing problems before tools are physically produced. In modern forming codes, an enhanced Coulomb model is used to numerically model the friction phenomena associated with lubrication. In the laboratory condition, determining model parameters through physical measurement is challenging. As a result, it became necessary to design a device that could be utilized in industrial environments. In this study, we present the prediction of a manufacturing problem resulting from a change in the lubricant of an industrial sheet metal part. The measuring device has been developed based on the parameters of the friction model of the lubricant materials. The developed measuring device may be used to determine the pressure and velocity dependent friction model parameters. The measuring device can only measure a limited range of pressures and velocities, so the results are extended to a wider range using a mathematical method. The results are used to demonstrate the effect of lubricant material changes on the forming process using the AutoForm code.

Performance Comparison Analysis of a Bridge Installed with Anti-seismic Devices using PVDF/MgO Friction Material According to Friction Analysis Models

In this study, structural analyses were conducted to analyze the performance of a bridge to which friction pendulum systems (FPSs) were applied using different friction models. A Coulomb friction model and a rate dependent friction model were constructed using the friction coefficient of a PVDF/MgO friction material to analyze the effect of different friction analysis models. The Coulomb friction model uses a single friction coefficient regardless of friction velocity, while the rate dependent friction model can reflect the change in the friction coefficient with friction velocity. Nonlinear time history and seismic fragility analyses were conducted to confirm responses of the bridge. The seismic responses of a deck and a column were used to evaluate the performance of the base isolated bridge, and a friction model that can effectively evaluate the performance of isolated bridges was analyzed.

Application of enhanced coulomb models and virtual tribology in a practical study

Abstract For the final quality of the part, metal forming trends are depending on improvements of friction and tribology. As a consequence, there is a trend in which tribology and friction are becoming increasingly important for correctly replicating the forming simulation of those parts. The objective of this work was to improve the forming simulation of an automotive shell part on AutoForm. The part was provided by a vehicle industry supplier. Enhanced Coulomb models consider a change on friction coefficient due to different factors, better approximating the description of friction to reality. For the current study, pressure and velocity dependent friction models were chosen as long as the combination of both. The virtual tribology was simulated using the software TriboForm. Velocity dependent friction model and the virtual tribology have shown similar results with expected lower coefficients of friction.

Influence of enhanced Coulomb’s model on the draw-in of the hood inner panel

A constant coefficient of friction (Coulomb) is commonly used as the current industry standard to describe friction on the sheet metal forming simulation software. The use of constant Coulomb’s friction may reduce precision and so the effectiveness of the simulation to represent real-world processes. This paper presents an approach using a physical measurement of friction combined with pressure dependent friction model as an input for the metal forming simulation of a hood inner part on AutoForm. The input variable parameters are the constant Coulomb and the enhanced pressure-dependent model. For the output this study analyses the Forming Limit Diagram (FLD) and blank’s draw-in in a real problem provided by a car manufacturer.

Effects of coefficient of friction coupled with a deformation dependent friction model in cutting simulations

A deformation dependent stick-slip based friction model is realised to better represent the contact stresses in the secondary shear zone. The instantaneous nodal limiting shear stress is implemented in a VFRIC friction model subroutine in ABAQUS\\Explicit in 2D ALE orthogonal cutting simulations to investigate effects on the accuracy of the simulations. This study highlights that the limiting shear stress varies along the rake face, as well as with the rake angle and uncut chip thickness. Lower coefficients of friction are necessary at lower rake angles and higher uncut chip thicknesses, although a variable coefficient of friction model is still necessary to predict both the cutting force and thrust force accurately together.

Application of an Inertia Dependent Flow Friction Model to Snow Avalanches: Exploration of the Model Using a Ping-Pong Ball Experiment

Snow avalanches are catastrophic phenomena because of their destructive power. Therefore, it is very important to forecast the affected area of snow avalanches using numerical simulations. In our study, we focus on applying a numerical model to snow avalanches. The inertia-dependent flow friction model, which we call the “I-dependent” model, is a promising numerical model based on granular flow experiments and includes the local inertial effect. This model was introduced in previous studies as it predicts the shape and velocity of the granular flow accurately. We numerically investigated the particle diameter effect of the I-dependent model, and found that the smaller the particle diameter is, the faster the flow front velocity becomes. The final flow shape is similar to a crescent shape when the particle diameter is small. We applied this model to the ping-pong ball flow experiment, which imitated a snow avalanche on a ski jump slope. Comparing between the experimental and simulated results, the flow shape is better reproduced when the particle diameter is small, while the numerical simulation using a real ping-pong ball diameter did not show the clear crescent shape. Moreover, the relative error analysis shows that the best fit between experimental and simulated flow front velocity occurs when the particle diameter is larger than the actual size of a ping-pong ball. We conjecture that this discrepancy is mainly caused by aerodynamic effects, which, in this case, are large due to the low density of ping-pong balls. Therefore, it is necessary to explore the granular features of ping-pong balls or snow avalanches by conducting experiments, as done in previous experimental studies. Through such efforts, it may be possible to apply this I-dependent model to snow avalanches in the future.

Experimental and numerical analyses of carbon steel sheet metal forming process using strain rate dependent friction model

Abstract The main objective of this study is to test experimentally and model numerically the forming process of a carbon steel cylinder including deep drawing, walls ironing, and annealing steps. The experimental tests were conducted using two drawing and ironing rings separated by a spacer ring. The geometric modeling of various stages of formation was conducted by applying the finite element method (FEM). The results obtained from the finite element model were compared and verified with the experimental tests. The output results showed a good agreement with the experimental tests. In addition, the effects of the forming parameters such as drawing speed on residual stresses and drawing force and cup height were investigated through FEM in two friction modes: strain rate-dependent coefficient of friction model and constant coefficient of friction. The results show that the coefficient of friction has a major effect on the drawing force and the wall thickness reduction.

Tribo-dynamic analysis and motion control of a rotating manipulator based on the load and temperature dependent friction model

Joint friction has a significant influence on the dynamics and motion control of manipulators. However, the friction effect is often omitted or simplified in previous studies. In this paper, we establish the dynamics model of a single joint in a rotating industrial manipulator taking detailed friction effects into consideration and propose a new control algorithm for the friction compensation purpose. Firstly, the manipulator dynamics modeling is carried out employing a recently-proposed extended static friction model, which depicts load and temperature influence on Coulomb, Stribeck and viscous terms. Moreover, based on the established dynamics model, the paper presents a new adaptive fast nonsingular terminal sliding mode (AFNTSM) controller. The proposed approach has the advantages of continuous control inputs, fast convergence rate, no singularity and great robustness against disturbances. Furthermore, its adaptive property does not require any prior knowledge of the upper bound of the uncertainties. Finally, the proposed controller is applied to the manipulator joint trajectory tracking problem with varying friction subject to load and temperature changes. The numerical simulation verifies the effectiveness of our proposed method and its advantages over other controllers.

Temperature and strain rate dependent friction model for hot forming of Ti-6Al-4V titanium alloy

Abstract Friction plays a significant role in hot deformation processes of metals. The effect of friction is especially important during hot deformation of titanium alloys. In this study friction factors in Levanov and shear laws during deformation of the Ti-6Al-4V titanium alloy at the temperature of 925 °C without lubrication, with lamellar graphite, tungsten disulfide and hexagonal boron nitride lubrication were studied. Effect of temperature in range of 825 °C–925 °C and strain rate in range of 0.01 s−1–1 s−1 on the friction factor with hexagonal boron nitride lubrication also was studied.

Temperature dependent micromechanics-based friction model for cold stamping processes

Temperature rise in cold stamping processes due to frictional heating and plastic deformation of sheet metal alters the tool-sheet metal tribosystem. This is more prominent in forming advanced high strength steels and multi-stage forming operations where the temperature on the tool surface can rise significantly. The rise in temperature directly affects the friction due to break down of lubricant, change in physical properties of tribolayers and material behavior. This can result in formability issues such as workpiece-splitting, etc. Therefore, it is important to account for temperature effects on friction in sheet metal forming analyses. In this study, the temperature effect was included in a micromechanics-based friction model which allows calculation of local friction coefficients as a function of contact pressure, bulk strain and relative sliding velocity. The temperature influence on friction was introduced through material behavior of sheet metal, viscosity of lubricant and shear strength of boundary layer in the micromechanics-based model. The model validation has been done by comparing the calculated fractional real contact area with the experimental results. The model can be used in formability analyses and to predict optimum stamping press parameters such as the blank holder force and the press speed.

Squeal simulation and analysis of brake system with pressure and speed dependent friction model and exerting process of pressure

In this paper, a complete finite element model of disc brake considering the ventilated brake disc, pads, back-plate, caliper, bracket, piston, rubber bushes and simplified fluid model driving piston is established. The pressure and speed dependent friction model and temperature field are considered. The results of complex eigenvalue analysis (CEA) show consistence with the existing achievements, thus the feasibility of the established model is verified. Subsequently, the transient dynamic analysis of the brake system is carried out for different exerting process of the pressure which represents the operation of different drivers. Besides, the vibration responses of different brake pressure and different speed are also investigated. The evolution process of the stability is studied by time-frequency analysis (STFT method). Both CEA and time-frequency analysis show the squeal tends to appear in the case of high friction coefficient, low speed and low brake pressure. It can also be found that the vibration frequency and its energy are not constant but fluctuate in a certain range. The results of different pressure exerting processes with simplified fluid model driving piston show that vibration response of disc brake not only depends on the value of brake pressure but also depends on the pressure exerting process. It is supposed that brake pressure and rotational speed determine the frequency of squeal while the process of exerting pressure determines the existing duration of brake squeal.

Influence of the pressure dependent coefficient of friction on deep drawing springback predictions

The aim of this work is to show the influence of defining a pressure dependent friction coefficient on numerical springback predictions of a DX54D mild steel, a HSLA380 and a DP780 high strength steel. The pressure dependent friction model of each material was fitted to the experimental data obtained by Strip Drawing tests and then implemented in the numerical simulation of an industrial automotive part drawing process. The results showed important differences between defining a pressure dependent or a constant friction coefficient. Finally, the experimental part was produced to compare the real geometry with the predictions obtained with the different simulation strategies. An improvement of 20–25% in springback prediction was achieved when using the pressure dependent friction model.

Stability of the rate, state and temperature dependent friction model and its applications

Stability of the rate, state and temperature dependent friction model and its applications

Evaluation of a Pipe–Flange Connection Method Based on Cold Work

The conventional joining method of a pipe and a flange uses welding. However, welded pipe–flange joints have the drawback with the inherent distortions and residual stresses resulting from the welding process, which can affect the mechanical integrity and performance of the flange significantly. In this study, a novel pipe–flange connection method based on cold work is evaluated using the finite element method. A weld neck flange is modified by manufacturing circumferential grooves at its internal surface and the pipe is cold worked into the grooves using a hydraulic expansion tool. The finite element model incorporates a pressure dependent friction model for the contact interaction between the tool–pipe–flange and a strain-based ductile failure locus for the pipe material accounting for ductile damage initiation during the cold work process utilizing a continuum damage mechanics approach. The finite element results show that a high load carrying capacity can be achieved for the cold work pipe–flange connection and has good potential for replacing the conventional welded joint.

Modeling of Kashmir Aftershock Decay Based on Static Coulomb Stress Changes and Laboratory-Derived Rate-and-State Dependent Friction Law

We model the spatial and temporal evolution of October 8, 2005 Kashmir earthquake’s aftershock activity using the rate-and-state dependent friction model incorporating uncertainties in computed coseismic stress perturbations. We estimated the best possible value for frictional resistance “Aσ n”, background seismicity rate “r” and coefficient of stress variation “CV” using maximum log-likelihood method. For the whole Kashmir earthquake sequence, we measure a frictional resistance Aσ n ~ 0.0185 MPa, r ~ 20 M3.7+ events/year and CV = 0.94 ± 0.01. The spatial and temporal forecasted seismicity rate of modeled aftershocks fits well with the spatial and temporal distribution of observed aftershocks that occurred in the regions with positive static stress changes as well as in the apparent stress shadow region. To quantify the effect of secondary aftershock triggering, we have re-run the estimations for 100 stochastically declustered catalogs showing that the effect of aftershock-induced secondary stress changes is obviously minor compared to the overall uncertainties, and that the stress variability related to uncertain slip model inversions and receiver mechanisms remains the major factor to provide a reasonable data fit.

Experimental and Numerical Investigation on a Pressure Dependent Friction Model

The objective of this paper is the investigation of the implemented pressure dependent friction model in the FE simulation program AutoForm. Since the values for the required parameters of this approach are not defined in the actual FE simulation program, this paper contributes to a first definition of these parameters. Therefore, experimental investigations with the cup drawing tests are carried out. With the support of the experimental results regarding the maximum stamping force, the model is calibrated and subsequently validated by the comparison of the sheet thicknesses of the experimental and numerical investigations. The results of this validation reveal a good accordance of simulation and reality in nearly all areas. However there are also areas in which the prediction accuracy decreases in comparison to the basic simulation. Therefore, additional investigations have to be carried out which concentrate on the modification of this pressure dependent approach towards a better universal prediction accuracy of the simulation.

Time-Dependent Earthquake Occurrence Rates along the Hellenic Arc

Seismicity rate changes in the Hellenic subduction zone (southern Aegean Sea) were studied by applying the Dieterich (1994) rate/state‐dependent friction model combined with static Coulomb stress changes (ΔCFF). The coseismic slip of the strongest earthquakes (with moment magnitude, M w≥6.0) was considered to contribute to the stress field evolution along with the continuous tectonic loading. Stress changes were calculated just after each strong event, and their influence was examined in connection with the smaller magnitude earthquake occurrence rates. Qualitative and quantitative comparison between the observed seismicity rates (smoothed by the means of a probability density function) and the expected ones, as they were forecasted by the rate/state model, were investigated for the interseismic periods (study periods) between subsequent strong earthquakes. The calculations aim to identify areas of expected increased seismicity rates as candidates to accommodate enhanced seismic activity. Results strongly depend on the determination (smoothing) of the unperturbed (reference) seismicity rates and data adequacy. Seismicity rate results were filtered by certain criteria and constraints, in an attempt to overcome model uncertainties (epicentral errors, rupture models, parameter values) and to provide reliable results for specific areas of major interest, that is, in areas with increased positive Coulomb stress changes values. The modeling approach resulted in satisfactory correlation between observed and synthetic seismicity rates and, in particular, the two strong ( M w≥6) earthquakes that occurred in 2013 are located in areas of increased expected seismicity rates.

Analysis of Ultralong Friction Pile Based on Gradient Dependent Nonlocal Friction Model

Based on the gradient theory, the gradient dependent nonlocal friction model is established. It is a new model which can describe the nonlocal friction effect. Based on Mindlin’s solution of displacement, an elastic solution of the lateral frictional resistance for ultralong friction pile is derived. The ultralong friction pile is analyzed by using the gradient dependent nonlocal friction model. Compared with the solution to the local friction law, the results shows that nonlocal friction law is feasible and reliable. The study is helpful for understanding the friction mechanism in geotechnical problems. It is a good attempt to set up the more actual and more accurate friction model.

Experimental investigation on friction under metal cutting conditions

This paper presents an experimental test to analyze friction phenomena within the tool–chip interface in metal cutting. Therefore, it is designed to obtain experimental data under conditions that are characterized by high contact temperatures, pressures and sliding velocities. The experimental approach is derived from an orthogonal cutting process, modified to a high speed forming and friction process by using an extremely negative rake angle. Such an angle suppresses the formation of chips and results in a smooth plastic flow of metal over the tool surface which generates very high contact temperatures and therefore approaches the conditions of metal cutting. Investigations were conducted for three workpiece materials AISI 1045, AISI 4140 and Inconel 718 in combination with uncoated WC-6Co cemented carbide tools. For these materials, the experimental analysis shows significant thermal softening within the contact interface caused by frictional heat generation and plastic deformation. To account for the observed phenomena, a temperature dependent friction model is proposed and evaluated by a finite element model.

Temperature dependent friction estimation: Application to lubricant health monitoring

In this work a method is presented to detect lubricant quality changes in mechanical transmissions. It is explored that the quality of the lubricant influences the friction parameters in fluid lubrication regime. An energy balance based fault detection method is proposed to detect slow changes in friction parameters. Since the properties of the lubricant depend on the temperature, the fault detector applies a temperature dependent friction model. A lubricant temperature estimator is also developed for the mechanical transmission, since in many applications the lubricant temperature is not measurable on-line. In the proposed approach the temperature of the lubricant is estimated based on the temperature of the housing, temperature of the environment, velocity and the identified parameters of the mechanical system. Experimental measurements are also presented to show the applicability of the proposed lubricant temperature observer and health monitoring algorithm.