An Elastic Contact Model for the Prediction of Workpiece-Fixture Contact Forces in Clamping

1999 ◽  
Vol 121 (3) ◽  
pp. 485-493 ◽  
Author(s):  
B. Li ◽  
S. N. Melkote
Keyword(s):  
Normal Force ◽  
Contact Region ◽  
Contact Forces ◽  
Contact Model ◽  
Quadratic Program ◽  
Elastic Contact ◽  
Complementary Energy ◽  
Elastic Bodies ◽  
Good Agreement ◽  
Tangential Friction

The design and evaluation of machining fixture performance requires accurate knowledge of workpiece-fixture contact forces since they strongly impact workpiece accuracy during clamping and machining. This paper presents an elastic contact model for the prediction of workpiece-fixture contact forces due to clamping. The fixture and workpiece are considered to be elastic bodies in the vicinity of the contact region. The model is formulated as a constrained quadratic program by applying the principle of minimum total complementary energy. The model predicts the normal force, and the magnitude and direction of the tangential (friction) force at each workpiece-fixture contact due to clamping forces. Experimental verification of the model under different clamping loads shows good agreement between predicted and measured normal and tangential contact forces. The model can be used to analyze fixture performance in terms of the contact forces and contact region deformation.

Wheel-Rail Multi-Point Contact Method for Railway Turnouts

2011 ◽  
Vol 97-98 ◽  
pp. 378-381
Author(s):  
Zhi Wei Chen ◽  
Linan Li ◽  
Shi Gang Sun ◽  
Jun Long Zhou
Keyword(s):  
Calculation Method ◽  
Normal Force ◽  
Contact Point ◽  
Point Contact ◽  
Contact Model ◽  
Contact Method ◽  
Elastic Contact ◽  
Simulation Calculation ◽  
Acute Change

A calculation method of wheel-rail multi-point contact based on the elastic contact model is introduced. Moreover, the simulation calculation of vehicles passing through branch lines of No.18 turnouts is carried out. The result showed that the acute change of wheel-rail normal force caused by the transfers of wheel-rail contact point between two rails can be avoid by wheel-rail multi-point contact method, and the transfers of wheel-rail normal force between two rails is smoother. The validity of wheel-rail multi-point contact method is verified.

On the prediction of passive contact forces of workpiece-fixture systems

2005 ◽  
Vol 219 (3) ◽  
pp. 309-324 ◽  
Author(s):  
Cai-Hua Xiong ◽  
Michael Yu Wang ◽  
Yong Tang ◽  
You-Lun Xiong
Keyword(s):  
Contact Point ◽  
Linear Equations ◽  
Contact Forces ◽  
Contact Model ◽  
Elastic Contact ◽  
Elastic Deformations ◽  
Non Linear ◽  
Determinate System ◽  
Fixture System ◽  
Non Linear Equations

The prediction of passive forces in a frictional workpiece-fixture system is an important problem, since the contact forces have a strong influence on clamp design and on workpiece accuracy during machining. This paper presents a general method for the computation of passive contact forces. Firstly, an indeterminate system of static equilibrium is defined, in which the passive, frictional contact forces cannot be determined arbitrarily as in an actively controlled robotic multifinger grasp. Then, a locally elastic contact model is used to describe the non-linear coupling between the contact forces and elastic deformations at the contact point. This model captures the essence of the passive contact. Further, a set of ‘compatibility’ equations is given so that the relationship can be developed between the elastic deformations at all contacts and the displacement of the workpiece. Finally, combining the force equilibrium, the locally elastic contact model and the ‘compatibility’ conditions, the passive force computation problem is transformed into a determinate system of non-linear equations governing all of the elastic deformations at all of the passive contacts. By solving the resulting non-linear equations, all passive contact forces can be accurately predicted in the frictional workpiece-fixture system. This method is illustrated with example cases. The method presented here may also have an application to other passive, indeterminate problems such as power grasps in robotics.

scholarly journals Application of Nadal Limit for the Prediction of Wheel Climb Derailment

2011 ◽  
Author(s):  
Brian Marquis ◽  
Robert Greif
Keyword(s):  
Alternative Explanation ◽  
Normal Force ◽  
Contact Point ◽  
Angle Of Attack ◽  
Steady Motion ◽  
Critical Value ◽  
Contact Forces ◽  
Creep Force ◽  
Rigid Body Mechanics ◽  
Tangential Friction

Application of the Nadal Limit to the prediction of wheel climb derailment is presented along with the effect of pertinent geometric and material parameters. Conditions which contribute to this climb include wheelset angle of attack, contact angle, friction and saturation surface properties, and lateral and vertical wheel loads. The Nadal limit is accurate for high angle of attack conditions, as the wheelset rolls forward in quasi-static steady motion leading to a flange climbing scenario. A detailed study is made of the effect of flange contact forces Ftan and N, the tangential friction force due to creep and the normal force, respectively. Both of these forces vary as a function of lateral load L. It is shown that until a critical value of L/V is reached, climb does not occur with increasing L since Ftan is saturated and the flange contact point slides down the rail. However, for a certain critical value of L/V (i.e. the Nadal limit) Ftan is about to drop below its saturated value and flange climb (rolling without sliding) up the rail occurs. Additionally, an alternative explanation of climb is given based on a comparison of force resultants in track and contact coordinates. The effects of longitudinal creep force Flong and angle of attack are also investigated. Using a saturated creep resultant based on both (Ftan, Flong) produces a climb prediction L/V larger (less conservative) than the Nadal limit. Additionally, for smaller angle of attack the standard Nadal assumption of Ftan = μN may lead to an overly conservative prediction for the onset of wheel climb. Finally, a useful analogy for investigating conditions for sliding and/or rolling of a wheelset is given from a study of a disk in rigid body mechanics.

Distributed Contact Model for Indeterminate Grasp Force Analysis towards Heavy-Duty Manipulation

2011 ◽  
Vol 383-390 ◽  
pp. 4837-4842
Author(s):  
Jin Cheng Mao ◽  
Wen Yu Yang
Keyword(s):  
Contact Forces ◽  
Contact Model ◽  
Elastic Contact ◽  
Three Dimension ◽  
Force Analysis ◽  
Heavy Duty ◽  
Linear Elastic ◽  
Grasp Force ◽  
The Relationship

This paper presents a new contact model to describe the contact constraints for heavy-duty manipulation. This contact model considers the contact area as a surface, which can translate three-dimension forces and torques. The contact deformations which are resulting from the large contact forces cannot be ignored. Distributed linear elastic contact model is adopted to describe the relationship between contact force and contact deformation. A case study is carried out in this paper based on this contact model for the grasp force analysis of heavy-duty manipulators.

The Mechanics of Adhesion: A Tutorial

2008 ◽  
Author(s):  
George G. Adams
Keyword(s):  
Contact Region ◽  
Adhesive Contact ◽  
Contact Model ◽  
Contact Theory ◽  
Asperity Contact ◽  
Spherical Contact ◽  
Elastic Bodies ◽  
Two Bodies

As the size of the contact region between two bodies decreases to the micro- and nano-scales, the effect of adhesion becomes increasingly important. In this tutorial, we review fundamental concepts of the mechanics of adhesion. Attention is placed on the contact of elastic bodies in which the shapes of the contacting bodies are locally spherical. We also discuss the use of spherical contact theory to model the adhesive contact of an asperity with a flat as part of a multi-asperity contact model.

On Prediction of Passive Contact Forces of Workpiece-Fixture Systems

2003 ◽  
Author(s):  
Cai-Hua Xiongand ◽  
You-Lun Xiong ◽  
Michael Yu Wang
Keyword(s):  
Rigid Body ◽  
Nonlinear Equations ◽  
Contact Point ◽  
Contact Forces ◽  
Contact Model ◽  
System Of Nonlinear Equations ◽  
Elastic Contact ◽  
Elastic Deformations ◽  
Determinate System ◽  
Fixture System

Prediction of passive forces in a frictional workpiece-fixture system is an important problem, since the contact forces have a strong influence on clamp design and on workpiece accuracy during machining. This paper presents a general method for the computation of the contact forces. First, based on the rigid-body kinematics, an indeterminate system of static equilibrium is defined, in which the passive, frictional contact forces cannot be determined arbitrarily as in an actively controlled robotic multi-finger grasp. Then, we define a locally elastic contact model to describe the nonlinear coupling between the contact forces and elastic deformations at the contact point. This model captures the essence of the passive contact. Further, a set of “compatibility” equations are given so that the elastic deformations among all passive contacts in the workpiece-fixture system result in a consistent set of rigid-body displacement of the workpiece in its global system. Finally, combining the locally elastic contact model and the “compatibility” conditions, we transform the force computation problem into a determinate system of nonlinear equations governing all of the elastic deformations at all of the passive contacts. By solving the resulting nonlinear equations with frictional constraints, we can accurately predict all contact forces in the frictional workpiece-fixtures system. This method is illustrated with example cases. The method presented here may also have an application to other passive, indeterminate problems such as power grasps in robotics.

Elastic Contact of Rough Surfaces Subject to Combined Force and Moment

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Ali Sepehri ◽  
Kambiz Farhang
Keyword(s):  
Half Plane ◽  
Normal Force ◽  
Rough Surfaces ◽  
Tangential Force ◽  
Contact Forces ◽  
Elastic Contact ◽  
Force Component ◽  
Angular Misalignment ◽  
Tangential Contact ◽  
Applied Forces

In this paper we consider the contact between two rectangular rough surfaces that provide normal and tangential contact forces, as well as contact moment, to counteract the net moment imposed by the applied forces. The surfaces are permitted to develop a slight angular misalignment, and thereby contact moment is derived. Through this scheme it is possible to also define elastic contribution to friction, since the half-plane tangential contact force on one side of an asperity is no longer balanced by the half-plane tangential force component on the opposite side. The elastic friction force, however, is shown to be of a much smaller order than the contact normal force.

Two-dimensional elastic contact analysis by coupling finite element and boundary element methods

1998 ◽  
Vol 33 (6) ◽  
pp. 459-468 ◽  
Author(s):  
C Oysu ◽  
R T Fenner
Keyword(s):  
Finite Element ◽  
Boundary Element ◽  
Flat Surface ◽  
Contact Region ◽  
Contact Problems ◽  
Boundary Element Methods ◽  
Elastic Contact ◽  
Two Dimensional ◽  
Cylindrical Punch ◽  
Good Agreement

A coupled finite element and boundary element method is introduced for the analysis of two-dimensional elastic contact problems without friction. The Lagrange multiplier method is used to apply the contact constraints. A computer program, which can analyse axisymmetric, plane strain and plane stress problems, has been developed and used to demonstrate the accuracy of the method. The program is applied to a sphere in contact with a flat surface, a rigid punch pressed on to an elastic foundation and an elastic cylindrical punch in contact with an elastic plate. In all cases good agreement is obtained with analytical solutions for stresses near the contact region.

Modeling of Tread Block Contact Mechanics Using Linear Viscoelastic Theory3

2008 ◽  
Vol 36 (3) ◽  
pp. 211-226 ◽  
Author(s):  
F. Liu ◽  
M. P. F. Sutcliffe ◽  
W. R. Graham
Keyword(s):  
High Speed ◽  
Slip Rate ◽  
Material Model ◽  
Contact Forces ◽  
Block Modeling ◽  
Rate Dependent ◽  
Linear Viscoelastic Material ◽  
Linear Viscoelastic ◽  
The Impact ◽  
Good Agreement

Abstract In an effort to understand the dynamic hub forces on road vehicles, an advanced free-rolling tire-model is being developed in which the tread blocks and tire belt are modeled separately. This paper presents the interim results for the tread block modeling. The finite element code ABAQUS/Explicit is used to predict the contact forces on the tread blocks based on a linear viscoelastic material model. Special attention is paid to investigating the forces on the tread blocks during the impact and release motions. A pressure and slip-rate-dependent frictional law is applied in the analysis. A simplified numerical model is also proposed where the tread blocks are discretized into linear viscoelastic spring elements. The results from both models are validated via experiments in a high-speed rolling test rig and found to be in good agreement.

Analysis of the Contact Deformation of a Radial Tire with Camber Angle

1995 ◽  
Vol 23 (1) ◽  
pp. 26-51 ◽  
Author(s):  
S. Kagami ◽  
T. Akasaka ◽  
H. Shiobara ◽  
A. Hasegawa
Keyword(s):  
Pressure Distribution ◽  
Contact Pressure ◽  
Contact Region ◽  
Contact Deformation ◽  
Contact Pressure Distribution ◽  
Radial Tire ◽  
Ring Model ◽  
Camber Angle ◽  
Contact Free ◽  
Good Agreement

Abstract The contact deformation of a radial tire with a camber angle, has been an important problem closely related to the cornering characteristics of radial tires. The analysis of this problem has been considered to be so difficult mathematically in describing the asymmetric deformation of a radial tire contacting with the roadway, that few papers have been published. In this paper, we present an analytical approach to this problem by using a spring bedded ring model consisting of sidewall spring systems in the radial, the lateral, and the circumferential directions and a spring bed of the tread rubber, together with a ring strip of the composite belt. Analytical solutions for each belt deformation in the contact and the contact-free regions are connected by appropriate boundary conditions at both ends. Galerkin's method is used for solving the additional deflection function defined in the contact region. This function plays an important role in determining the contact pressure distribution. Numerical calculations and experiments are conducted for a radial tire of 175SR14. Good agreement between the predicted and the measured results was obtained for two dimensional contact pressure distribution and the camber thrust characterized by the camber angle.

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