“Internal Variables” Effects in Punch Friction Characterization

1998 ◽  
Vol 120 (3) ◽  
pp. 510-516
Author(s):  
Tze-Chi Hsu ◽  
Chi-Chia Liu
Keyword(s):  
Metal Forming ◽  
Initial Boundary ◽  
Friction Model ◽  
Internal Variables ◽  
Friction Modeling ◽  
Lubrication Regimes ◽  
Mixed Regime ◽  
Constant Friction ◽  
Tensile Strip ◽  
Friction Models

Despite the complexity and importance of friction, most current simulations of metal-forming processes use relatively simple friction models such as the Amontons-Coulomb constant friction coefficient. It has been pointed out that simple models are not capable of capturing the influence of process variables such as geometry, speed, and surface topography on friction. A realistic friction model should include the internal variables such as lubricant film thickness, tooling roughness, and workpiece roughness. In the present research, the punch friction tests which use a tensile strip experiment to simulate the stretching of sheet over a punch corner radius in a typical draw die are used to measure the effects of internal variables on friction in various stretching conditions. The measured friction coefficients increase with lower stretching speed and decrease if lubricant is applied at the interface between workpiece and cylindrical pin. Theoretical friction modeling, which includes the different lubrication regimes range from thick film, thin film, mixed regime and boundary regime, are presented. Numerical methods have been used to solve the governing differential equations with the known initial boundary conditions obtained from the experiments. The theoretical prediction shows the same trend as the experimental measurements.

A Realistic Friction Model for Computer Simulation of Sheet Metal Forming Processes

1995 ◽  
Vol 117 (2) ◽  
pp. 202-209 ◽  
Author(s):  
W. R. D. Wilson ◽  
T-C. Hsu ◽  
X-B. Huang
Keyword(s):  
Sheet Metal ◽  
Sheet Metal Forming ◽  
Metal Forming ◽  
Realistic Model ◽  
Friction Model ◽  
Operating Conditions ◽  
Lubrication Regimes ◽  
Constant Friction ◽  
Coupled Codes ◽  
Measured Strain

A realistic model for friction in lubricated sheet-metal forming which takes account of the different lubrication regimes which may occur at the sheet/tooling interface is developed. Friction is expressed in terms of internal interface variables (mean lubricant film thickness, sheet roughness and tooling roughness) in addition to the more traditional external variables (interface pressure, sliding speed and strain rate). The new model has been coupled to an existing finite element membrane analysis of axisymmetric stretch forming. Numerical results using the coupled codes showed excellent agreement with measured strain distributions over a range of operating conditions. Computational times with the refined friction model were typically increased by about 10 percent compared to those with a simple Amontons-Coulomb constant friction coefficient model.

Comparison of numerical simulation results of sheet metal parts’ production for AutoForm and TriboForm friction models

2020 ◽  
pp. 359-372
Author(s):  
M.A. Petrov
Keyword(s):  
Sheet Metal ◽  
Metal Forming ◽  
Coulomb Friction ◽  
Friction Model ◽  
Metal Parts ◽  
Sheet Metal Parts ◽  
Friction Models ◽  
The Difference ◽  
Coulomb Friction Model

The results of numerical simulations with two friction models are studied. The fi rst model corresponded the Coulomb friction model and used in AutoForm on default. The second friction model took into account the quality of surface treatment, its roughness and amount of the lubricant and the effect of the asperities’ height evolution. It is used in TriboForm. The results obtained for the second friction model are used to simulate sheet metal forming processes in AutoForm. It is found that the TriboForm friction model affected the results of the drawing operation. The difference in the results increased due to bigger deformation values of the technological operation.

A Physics-Based Friction Model and Integration to a Simple Dynamical System

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
M. Eriten ◽  
A. A. Polycarpou ◽  
L. A. Bergman
Keyword(s):  
Friction Model ◽  
Lap Joints ◽  
Dynamical Response ◽  
Friction Modeling ◽  
Roughness Effects ◽  
Contact Conditions ◽  
Reduced Order ◽  
Interface Contact ◽  
Friction Models ◽  
Simple Dynamical System

Dynamical modeling and simulation of mechanical structures containing jointed interfaces require reduced-order fretting models for efficiency. The reduced-order models in the literature compromise both accuracy and the physical basis of the modeling procedure, especially with regard to interface contact and friction modeling. Recently, physics-based fretting models for nominally flat-on-flat contacts, including roughness effects, have been developed and validated on individual (isolated) mechanical lap joints (Eriten et al., 2011, “Physics-Based Modeling for Fretting Behavior of Nominally Flat Rough Surfaces,” Int. J. Solids Struct., 48(10), pp. 1436-1450). These models follow a “bottom up” modeling approach; utilizing the micromechanics of sphere-on-flat fretting contact (asperity scale), and statistical summation to model flat-on-flat contacts at the macroscale. Since these models are physical, the effects of surface roughness, contact conditions, and material properties on fretting and dynamical response of the jointed interfaces can be studied. The present work illustrates an example of how the physics-based models can be incorporated into studies of the dynamics of jointed structures. A comparison with friction models existing in the literature is also provided.

An Investigation of New Tribological Variables in Friction Modeling of Bulk Metal Forming

1998 ◽  
Vol 120 (3) ◽  
pp. 528-535
Author(s):  
Sy-Wei Lo ◽  
Tzu-Chern Horng
Keyword(s):  
Metal Forming ◽  
Orange Peel ◽  
Hot Extrusion ◽  
Friction Model ◽  
Surface Roughening ◽  
Rolled Sheet ◽  
Friction Modeling ◽  
Related Factors ◽  
Bulk Metal ◽  
Bulk Metal Forming

The present “realistic” friction model is examined by a series of upsetting tests. Specimens made of different aluminum alloys and prepared by various processes display diverse results. Severe surface roughening takes place in some cases using A6061T4 bar manufactured by hot extrusion. It results in a lubrication condition which is very different from the theoretical prediction. From hardness tests and microstructure observations, it is found that there is no obvious correlation between the hardness and the roughening process for A6061T4 alloy. The severe roughening is attributed to the distortion of the coarse grains recrystallized during the preprocess, that is, the hot extrusion. This is rare in sheet metal forming where most workpieces are prepared from cold rolled sheet metals. The orange peel appearance not only changes the lubrication mechanics, but also makes the surface finish of the product unacceptable. Since the existing friction model fails to predict such phenomena, surface roughening and all its related factors must be considered as new, important tribological variables in the friction modeling of bulk metal forming.

A Finite Element Study on Contact Pressure Distribution in Draw-Bend Friction Test and Its Effect on Friction Measurement

2005 ◽  
Author(s):  
Young Suk Kim ◽  
Don R. Metzger ◽  
Mukesh K. Jain
Keyword(s):  
Finite Element ◽  
Coulomb Friction ◽  
Friction Model ◽  
Friction Test ◽  
Friction Measurement ◽  
Explicit Finite Element ◽  
Constant Friction ◽  
Friction Models ◽  
Bend Tests ◽  
Coulomb Friction Model

Various experimental and numerical works have shown the existence of pressure peaks at the contact interface of draw-bend tests. From this observation, a need has been raised for the re-examination of the methodology to calculate the friction coefficient from the draw-bend friction test. In this paper, the draw-bend friction tests have been simulated by the explicit finite element method. By using 3D finite element models and local axis system, the existence of pressure peaks was confirmed. A non-constant friction model (Stribeck friction model), which is more realistic for sheet metal forming than a constant friction model (Coulomb friction model), was implemented into the finite element code. Simulations were performed with constant and non-constant friction models. From the comparisons, the effect of existence of pressure peaks on the friction measurement was evaluated.

Refined Friction Modeling for Simple Upsetting

1997 ◽  
Vol 119 (4A) ◽  
pp. 563-570 ◽  
Author(s):  
Tze-Chi Hsu ◽  
Chung-Hung Lee
Keyword(s):  
Friction Stress ◽  
Normal Pressure ◽  
Friction Model ◽  
Lubricant Film ◽  
Asperity Contact ◽  
Friction Modeling ◽  
Lubrication Regimes ◽  
Mixed Lubrication Regime ◽  
Boundary Model ◽  
Semi Empirical

A refined model for friction in lubricated simple upsetting processes which takes account of the different lubrication regimes which may occur at the workpiece/tooling interface is developed. The refined friction model considers not only the full film situation but also the mixed and boundary lubrication condition. The load carrying capacity of the lubricant in the mixed lubrication regime is evaluated by using the average flow model to treat the influence of surface roughness on lubricant flow. The mechanics of asperity contact is governed by a semi-empirical boundary model in which the plastic deformation of the workpiece is considered. The lubricant film thickness is then determined by using a shooting method to ensure that the interface pressure is partially supported by the asperity contact and partially supported by the lubricant film. The refined friction model is then combined with a rigid-plasticity finite element code to analyze the simple upsetting processes. Numerical results using the coupled codes such as the distribution of the friction stress and normal pressure, the geometry and surface topography of the deformed workpiece are compared with previous numerical and experimental investigation under different lubrication conditions. The simulation results are in good agreement with the experimental data.

scholarly journals Study on Friction in Automotive Shock Absorbers Part 1: Friction Simulation Using a Dynamic Friction Model in the Contact Zone of an FEM Model

Vehicles ◽  
2021 ◽  
Vol 3 (2) ◽  
pp. 212-232
Author(s):  
Ludwig Herzog ◽  
Klaus Augsburg
Keyword(s):  
Ride Comfort ◽  
Viscous Friction ◽  
Simulation Method ◽  
Friction Model ◽  
Model Parameters ◽  
Dynamic Friction ◽  
Friction Modeling ◽  
Shock Absorbers ◽  
Operation Conditions ◽  
Wide Range

The important change in the transition from partial to high automation is that a vehicle can drive autonomously, without active human involvement. This fact increases the current requirements regarding ride comfort and dictates new challenges for automotive shock absorbers. There exist two common types of automotive shock absorber with two friction types: The intended viscous friction dissipates the chassis vibrations, while the unwanted solid body friction is generated by the rubbing of the damper’s seals and guides during actuation. The latter so-called static friction impairs ride comfort and demands appropriate friction modeling for the control of adaptive or active suspension systems. In this article, a simulation approach is introduced to model damper friction based on the most friction-relevant parameters. Since damper friction is highly dependent on geometry, which can vary widely, three-dimensional (3D) structural FEM is used to determine the deformations of the damper parts resulting from mounting and varying operation conditions. In the respective contact zones, a dynamic friction model is applied and parameterized based on the single friction point measurements. Subsequent to the parameterization of the overall friction model with geometry data, operation conditions, material properties and friction model parameters, single friction point simulations are performed, analyzed and validated against single friction point measurements. It is shown that this simulation method allows for friction prediction with high accuracy. Consequently, its application enables a wide range of parameters relevant to damper friction to be investigated with significantly increased development efficiency.

scholarly journals An extension of Gronwall inequality in the theory of bodies with voids

Open Physics ◽  
2020 ◽  
Vol 18 (1) ◽  
pp. 1161-1167
Author(s):  
Marin Marin ◽  
Praveen Ailawalia ◽  
Ioan Tuns
Keyword(s):  
Boundary Value Problem ◽  
Internal State ◽  
Boundary Value ◽  
Initial Boundary ◽  
Initial Boundary Value Problem ◽  
Uniqueness Result ◽  
Internal Variables ◽  
State Variables ◽  
Gronwall’S Inequality ◽  
Initial Boundary Value

Abstract In this paper, we obtain a generalization of the Gronwall’s inequality to cover the study of porous elastic media considering their internal state variables. Based on some estimations obtained in three auxiliary results, we use this form of the Gronwall’s inequality to prove the uniqueness of solution for the mixed initial-boundary value problem considered in this context. Thus, we can conclude that even if we take into account the internal variables, this fact does not affect the uniqueness result regarding the solution of the mixed initial-boundary value problem in this context.

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