Presence Of Friction Research Articles

Adaptive motion control using neural network approximations

In this paper, we present a new adaptive technique for tracking control of mechanical systems in the presence of friction and periodic disturbances. Radial Basis Functions (RBFs) are used to compensate for the effects of nonlinearly occurring parameters in the friction and periodic disturbance model. Theoretical analysis, such as stability and transient performance, is provided. Furthermore, the performance of the adaptive RBF controller and its non-adaptive counterpart are compared.

A Class of Novel Space Platform-Based Manipulators With Slewing and Deployable Links: Analyses and Experiments

This paper studies dynamics of a space platform—based mobile two-module manipulator with each module consisting of two links, one free to slew (revolute joint) and the other permitted to deploy and retrieve (prismatic joint). Both the platform and the manipulator are considered flexible. Using the computation ally efficient order-N Lagrangian formulation of the system, the paper presents results of a comprehensive parametric study aimed at assessing effects of initial conditions, system variables, and manipulator maneu vers on the uncontrolled response. In general, the mass of payload, speed of maneuver, and joint flexibility represent three important parameters governing the system dynamics. Results suggest significant coupling between the platform, link, and joint vibrations as well as the system libration. The system exhibited unac ceptable response under critical combinations of parameters, thus indicating a need for active control. Next, effectiveness of a composite control strategy, involving the feedback linearization technique (FLT) applied to the rigid degrees of freedom with flexible generalized coordinates regulated through the linear quadratic regulator, is assessed. The control procedure proves to be remarkably successful in damping even relatively large disturbances in a robust fashion. Finally, the numerical simulation results are complemented with the prescribed trajectory tracking data, obtained using a two-module (four links) ground-based prototype manip ulator in conjunction with the FLT and proportional integral derivative control. Considering the presence of friction and backlash at the joints, the tracking results may be considered satisfactory. The comprehensive study lays a sound foundation for the design of this class of novel manipulators.

Work and energy in the presence of friction: the need for amesoscopic analysis

This paper deals with some of the difficulties involved in correctlylinking the mechanical and thermodynamic descriptions of situationswhere there are bodies in motion and changes in temperature and/orheat exchanges. It proposes and discusses a definition of internalenergy and shows that the total work of the non-conservative forces,such as frictional forces, always equals zero. The energy balances oftwo bodies in motion in the presence of sliding friction are analysedin this way; the calculation of the work of frictional forces isdiscussed, taking into account the mesoscopic level.

Fatiga oligocíclica de la aleación Ti<sub>6</sub>Al<sub>4</sub>V nitrurada termoquímicamente

The use of titanium and its alloys in applications with the presence of friction is limited, due to low hardness and reduced tribological properties. Some surface treatments are available in order to correct these problems, like the thermal surface treatment by means of nitrogen gaseous diffusion at high temperature. Nitrogen enters into the material by diffusion, creating a surface layer of increased hardness. Oligocyclic fatigue behaviour in air of Ti6Al4V alloy has been studied. Results show a reduction of oligocyclic fatigue loads up to 10 % compared to the not-treated material. Studies suggest it is not related to the titanium nitride surface layer, but to microstructural changes caused by the high temperature treatment.

Experimental investigation of the forming parameters of the rotational upset forging process

In a conventional upset forging, the presence of friction at the tool–workpiece interface not only increases the forging pressure and force, but also leads to non-homogeneity of deformation. In this study, to solve the above problems, a parametric study is presented on a new rotational upset forging process. Twisting torque can change the harmful effect of friction into a useful effect. Experiments were carried out to generate data of forming parameters, which are the friction factor, the sliding factor, the punch velocity and the geometry of the billets, on the rotational upset forging process. Comparing with the conventional upset forging process, the rotational upset forging process reduces both the forming load and bulging. The deformation of rotational upset forging is more uniformly distributed and its total deformation is greater than that of conventional upset forging for the same reduction of height.

Finite Element Analysis of Non-Laminated Composite Pin-Loaded Straps for Civil Engineering

Presented is a finite element analysis for carbon fiber reinforced plastic pin-loaded straps of non-laminated form. TheMARCK6.2 code was used. The goal was the determination of tensile strength from a knowledge of the peak stresses in the region where a (multi-layer) strap makes contact with the two steel circular pins. The paper illustrates difficulties other researchers and analysts may encounter if they are to analyze similar composite material problems. Numerical problems were found because of computing resource limitations, the highly orthotropic elastic constants, the geometric non-linearity, the geometric and material discontinuities, and the presence of friction and sliding contact. Their influence on stresses is illustrated by way of a simplified model for a single-layer strap. Peak stresses are shown to change significantly on varying a finite element model parameter that is not physical. Acceptable finite element stresses, away from the region with the peak stresses, are found on comparing them with a classical stress solution and experimental measurement.

Modeling the failure of hoisting load chain

Electric chain hoists are often called upon to operate at or near their rated capacities at high duty cycles. A critical hoist component is its load chain, which is frequently manufactured from a carburizing, or case hardening, grade of nickel alloy steel. After thermal treatment, a chain link possesses a thin hard outer case and a tough inner core. Failure of load chain is frequently associated with pitting of the link surfaces that contact other links. Nonlinear finite element analysis of the stresses and deformations due to the contact of two chain links with each other are conducted. Results indicate that shakedown occurs after one or two load cycles and that the presence of friction alters the stress field so as to encourage pitting.

Stress intensity factors for a surface‐breaking crack in a half‐plane subject to contact loading

Modes I and II stress intensity factors are derived for a crack breaking the surface of a half‐plane which is subject to various forms of contact loading. The method used is that of replacing the crack by a continuous distribution of edge dislocations and assume the crack to be traction‐free over its entire length. A traction free crack is achieved by cancelling the tractions along the crack site that would be present if the half‐plane was uncracked. The stress distribution for an elastic uncracked half‐plane subject to an indenter of arbitrary profile in the presence of friction is derived in terms of a single Muskhelishvili complex stress function from which the stresses and displacements in either the half‐plane or indenter can be determined. The problem of a cracked half‐plane reduces to the numerical solution of a singular integral equation for the determination of the dislocation density distribution from which the modes I and II stress intensity factors can be obtained. Although the method of representing a crack by a continuous distribution of edge dislocations is now a well established procedure, the application of this method to fracture mechanics problems involving contact loading is relatively new. This paper demonstrates that the method of distributed dislocations is well suited to surface‐breaking cracks subject to contact loading and presents new stress intensity factor results for a variety of loading and crack configurations.

A Theoretical Approach of an Intelligent Robot Gripper to Grasp Polygon Shaped Objects

This paper presents an approach for grasp planning and grasp forces optimization of polygon shaped objects. The proposed approach is an intelligent rule-based method that figures out the minimal number of fingers and minimal values of contact forces. These fingers are required to securely grasp a rigid body in the presence of friction and under the action of some external force. This is accomplished by finding optimal contact points on the object boundary along with minimal number of fingers required for achieving the aforementioned goal. Our system handles every object case independently. It generates a rule base for each object based on adequate values of external forces. The system uses the genetic algorithm as its search mechanism, and a rule evaluation mechanism called bucket brigade for the reinforcement learning of the rules. The process mainly consists of two stages; learning then retrieval. Retrievals act on line utilizing previous knowledge and experience embedded in a rule base. If retrievals fail in some cases, learning is presumed until that case is resolved. The algorithm is very general and can be adapted for interface with any object shape. The resulting rule base varies in size according to the degree of difficulty and dimensionality of the grasping problem.

Finite Element Analysis of Non-Laminated Composite Pin-Loaded Straps for Civil Engineering

Presented is a finite element analysis for carbon fiber reinforced plastic pin-loaded straps of non-laminated form. TheMARCK6.2 code was used. The goal was the determination of tensile strength from a knowledge of the peak stresses in the region where a (multi-layer) strap makes contact with the two steel circular pins. The paper illustrates difficulties other researchers and analysts may encounter if they are to analyze similar composite material problems. Numerical problems were found because of computing resource limitations, the highly orthotropic elastic constants, the geometric non-linearity, the geometric and material discontinuities, and the presence of friction and sliding contact. Their influence on stresses is illustrated by way of a simplified model for a single-layer strap. Peak stresses are shown to change significantly on varying a finite element model parameter that is not physical. Acceptable finite element stresses, away from the region with the peak stresses, are found on comparing them with a classical stress solution and experimental measurement.

Wear of an Elastic Block

The classical theory of wearing, proposed by Reye 140 years ago and universally accepted for predicting the life of a component of a machine, can be rendered more precise by considering the effective stresses causing the smoothing of two surfaces mutually sliding in the presence of friction.

An experimental study of the tribological behaviour of the brass/steel pair

This paper presents a study of the behaviour of the brass/steel pair in the presence of friction and wear. A plan of experiments, based on the techniques of Taguchi, was performed on a pin-on-disc machine. The objective was to establish a correlation between load, sliding velocity and temperature in contact with the wear and coefficient of friction. These correlations were obtained by multiple linear regression. Finally, confirmation tests were performed to make a comparison between the foreseen results from the mentioned correlations and the experimental results.

Non–continuation of the periodic oscillations of a forced pendulum in the presence of friction

A well known theorem says that the forced pendulum equation has periodic solutions if there is no friction and the external force has mean value zero. In this paper we show that this result cannot be extended to the case of linear friction.

Stable computed-torque control of robot manipulators via fuzzy self-tuning

Computed-torque control is a well-known motion control strategy for manipulators which ensures global asymptotic stability for fixed symmetric positive definite (proportional and derivative) gain matrices. In this paper, we show that global asymptotic stability also holds for a class of gain matrices depending on the manipulator state. This feature increases the potential of the computed-torque control scheme to handle practical constraint in actual robots such as presence of friction in the joints and actuators with limited torque capabilities. We illustrate this potential by means of a fuzzy self-tuning algorithm to select the proportional and derivative gains according to the actual tracking position error. Experiments on a two degrees of freedom robot arm show the usefulness of the proposed approach.

Numerical study of initial pulsed motion of a powder layer in a duct under the action of a compressed gas

One-dimensional plane pulsed joint motion of a gas phase and a disperse phase in the presence of friction of the latter against the duct walls are studied numerically using the model of a heterogeneous medium. It is established that two qualitatively different regimes of motion are possible, depending on the initial conditions in a high-pressure chamber and the value of the friction factor. It is found that the powder exit velocity is self-similar with respect to friction.

Contact mechanics

Contact problems are central to Solid Mechanics, because contact is the principal method of applying loads to a deformable body and the resulting stress concentration is often the most critical point in the body. Contact is characterized by unilateral inequalities, describing the physical impossibility of tensile contact tractions (except under special circumstances) and of material interpenetration. Additional inequalities and/or non-linearities are introduced when friction laws are taken into account. These complex boundary conditions can lead to problems with existence and uniqueness of quasi-static solution and to lack of convergence of numerical algorithms. In frictional problems, there can also be lack of stability, leading to stick–slip motion and frictional vibrations. If the material is non-linear, the solution of contact problems is greatly complicated, but recent work has shown that indentation of a power-law material by a power law punch is self-similar, even in the presence of friction, so that the complete history of loading in such cases can be described by the (usually numerical) solution of a single problem. Real contacting surfaces are rough, leading to the concentration of contact in a cluster of microscopic actual contact areas. This affects the conduction of heat and electricity across the interface as well as the mechanical contact process. Adequate description of such systems requires a random process or statistical treatment and recent results suggest that surfaces possess fractal properties that can be used to obtain a more efficient mathematical characterization. Contact problems are very sensitive to minor profile changes in the contacting bodies and hence are also affected by thermoelastic distortion. Important applications include cases where non-uniform temperatures are associated with frictional heating or the conduction of heat across a non-uniform interface. The resulting coupled thermomechanical problem can be unstable, leading to a rich range of physical phenomena. Other recent developments are also briefly surveyed, including examples of anisotropic materials, elastodynamic problems and fretting fatigue.

Force fluctuations in a vertically pushed granular column

We present series of experiments on the resistance force encountered by a bottom piston pushing a vertical granular column confined in a two-dimensional cell. We show that, due to the presence of friction at the boundaries and between the grains, the signal shows many complex features. At slow driving velocities, we observe a transition to a stick-slip dynamic instability. Depending on the granular material used, the elementary stick-slip events may either be well characterized or largely distributed. We present a statistical study on the waiting time between events and the distribution of energy release as a function of the spring stiffness and the driving velocity.

On the Nonuniform Deformation of the Cylinder Compression Test

A theoretical model based on Hill’s general method is developed in the present study to calculate the flow stress in a cylindrical specimen under axial compression in the presence of friction at the die-specimen interface. Unlike most of the published methods which studied the incipient barreling only, the proposed theoretical model takes the barreled shape of the deforming specimen into account. In order to construct the stress-strain curve, the mean effective strain of the barreled specimen was also calculated on the basis of an assumed velocity field. As the present study shows, the proposed theoretical model provides good results, both in magnitude and in trend, for the prediction of flow stresses in the barreled specimen during the compression test. [S0094-4289(00)00602-2]

Influence of contact interaction between the sides of crack on characteristics of failure mechanics in action ofP- andSV-waves

The effect of contact between the sides of a rectilinear crack in the planeR 2={x: x3=0} on the characteristics of the fallure mechanics is studied for the case in which the crack is affected by harmonic tensile-compression waves and shifts. The surfaces of the crack may assume any orientation relative to the direction of propagation of the waves. The presence of friction in the zone of contact of the sides of the crack is taken into account. The method of solving the problem stated is iterative in nature and is based on the solution of a sequence of boundary integral equations for the Fourier coefficients of the displacement discontinuity vector and the contact force vector. It is also corrected at each step of the solution so as to satisfy one-sided restrictions in the zone of contact.

Substantiation of the Darcy law for a porous medium with condition of partial adhesion

A study is made of a stationary Stokes's system in a periodically perforated domain with boundary conditions of mixed type, which describes the motion of a viscous incompressible fluid in a porous medium in the presence of friction between the fluid and the walls of the pores. The relation between the leading terms of the asymptotic expansions with respect to for the fluid velocity and the pressure is obtained, where is the parameter characterizing the fineness of the porous structure.