Contact Force Variation Research Articles

Elastic-Plastic Finite Element Analysis of Nonsteady State Partial Slip Wheel-Rail Rolling Contact

A finite element analysis with the implementation of an advanced cyclic plasticity theory was conducted to study the elastic-plastic deformation under the nonsteady state rolling contact between a wheel and a rail. The consideration of nonsteady state rolling contact was restricted to a harmonic variation of the wheel-rail normal contact force. The normal contact pressure was idealized as the Hertzian distribution, and the tangential force presented by Carter was used. Detailed rolling contact stresses and strains were obtained for repeated rolling contact. The harmonic variation of the normal (vertical) contact force results in a wavy rolling contact surface profile. The results can help understand the influence of plastic deformation on the rail corrugation initiation and growth. The creepage or stick-slip condition greatly influences the residual stresses and strains. While the residual strains and surface displacements increased at a reduced rate with increasing rolling passes, the residual stresses stabilize after a limited number of rolling passes. The residual stresses and strains near the wave trough of the residual wavy deformation are higher than those near the wave crest.

Initiation and propagation of damage in laminated composite shells due to low velocity impact

A finite element analysis procedure is developed to investigate the initiation and propagation of damage in laminated composite shells, using a Continuum Damage Mechanics (CDM) model. A phenomenological damage model assuming the effective stress concept is introduced with a fourth order damage tensor to model the damage in a lamina. A nine nodded isoparametric shell element based on the first order shear deformation theory is used to develop the finite element analysis procedure. The initiation and progress of damage, variation of contact force and displacement in a spherical shell due to low velocity impact are studied for different impactor velocities.

EXPLICIT FINITE ELEMENT ANALYSIS OF TRACKING CAPABILITY OF ROTARY FACE SEAL FOR INDUSTRIAL FLUID POWER APPLICATIONS

Seals are generally inexpensive machine elements, but in industrial fluid power systems the costs of sealing failure can be much higher than the cost of replacing the damaged seal due to, e.g., costs related to process downtime. Consequently, careful design evaluation is needed. In this study, the capability of a large diameter rotary face seal of spring-loaded type to respond to unwanted axial motion between the sealing surfaces caused by sudden changes in loading of components of the process machinery was evaluated.Explicit fmite element analysis, well suited for highly non-linear problems involving frictional contact, was used to compute the response of the seal to forced relative axial motion of the sealing surfaces. For condition monitoring, temporal variation of the total contact force exerted on the counterface, i.e., the sealing force during excitations was recorded, representing simple virtual sensor output describing the relation between axial motion and contact situation.

Sand-Production Simulation in Heavy-Oil Reservoirs

Summary A new sand-production model is developed based on interparticle contact-force variations at the discrete micromechanical level, scaled up to the macroscopic level. Two mechanisms for sand production are expected in the field: dynamic detachment (plucking of particles) and equilibrium yield (shear dilation followed by liquefaction at ~50% porosity). The model discussed in this paper describes the sand-production mechanism in the dynamic detachment process. Within the new model formulation, sand production arises because of either a large porosity gradient or a large pressure gradient. The 1D steady-state solution of the new model is also presented; it may be used for simple sensitivity analysis for parameters such as field stress and pressure-depletion effect.

Hardware in the Loop Test‐Rig for Identification and Control Application on High Speed Pantographs

Trains current collection for traction motors is obtained by means of a sliding contact between the overhead line (OHL) and the collector strips mounted on the pantograph head. The normal force by which the collector presses against the contact wire ensures the contact pressure for the electrical contact. As the train speed increases, the variation of contact force between pantograph and catenary increases, and the pantograph‐OHL dynamic interaction becomes greater. This condition causes excessive mechanical wear and contact wire uplift (for high values of contact forces), and leads to high percentage of contact loss, arcing and electrically related wear.The topic of actively controlled pantograph is gaining more interest as a tool to increase the performance of the current collection at high speed. In the last few years, it appears possible to transfer the knowledge based on numerical experiments, to the real operating condition. An important step in this direction is the set up of a laboratory hardware in the loop test‐rig in which the control strategies and the actuation can be tested, before tests performing in real life conditions, in order to demonstrate their actual feasibility. The present paper describes an hardware in the loop (HIL) test‐rig developed by the authors, which allows to reproduce the dynamical interaction between overhead lines and pantograph in high speed railways. Using the described laboratory set‐up, experimental investigation on the problems related with pantograph‐OHL interaction can be performed, very similarly to the real life operating conditions, with the advantage of varying test parameters and conditions easily.

Squeal noise of rail-bound vehicles influenced by lateral contact position

A frequency domain model has been developed to describe squeal noise of rail-bound vehicles generated by unstable lateral creepage between wheel and rail. The model is based on a combination of existing models for contact mechanics, contact dynamics, wheel dynamics and rail dynamics, which are transformed into the frequency domain. The relation between friction coefficient and lateral creepage is linearized to allow frequency domain calculations. This enables fast calculations and enhances insight into frequency-dependent phenomena relating to squeal. In addition to existing models, the variation of the normal contact force is implemented in the model. This addition to the model is essential to explain several effects. One of these effects is the influence of the lateral contact position on the wheel tread on squeal noise; squeal noise by lateral creepage only occurs for a certain contact position interval. A laboratory test rig (scale 1:3) was designed to validate the model. Two measurements will be presented in this paper. The friction coefficient of the rolling contact is measured as a function of lateral creepage, for cases with and without squeal (but with the similar contact surface conditions), giving different results. The required wheel damping to prevent squeal noise is measured as a function of the lateral contact position. The test rig has been used for model validation and will be used to evaluate and optimize particular measures against squeal noise. The model can be used as a design tool for measures against squeal noise by lateral creepage.

Finite element modelling of frictional instability between deformable rocks

AbstractEarthquakes are recognized as resulting from a stick–slip frictional instability along faults. Based on the node‐to‐point contact element strategy (an arbitrarily shaped contact element strategy applied with the static‐explicit algorithm for modelling non‐linear frictional contact problems proposed by authors), a finite element code for modelling the 3‐D non‐linear friction contact between deformable bodies has been developed and extended here to analyse the non‐linear stick–slip frictional instability between deformable rocks with a rate‐ and state‐dependent friction law. A typical fault bend model is taken as an application example to be analysed here. The variations of the normal contact force, the frictional force, the transition of stick–slip instable state and the related relative slip velocity along the fault between the deformable rocks and the stress evolution in the total bodies during the different stages are investigated, respectively. The calculated results demonstrate the usefulness of this code for simulating the non‐linear frictional instability between deformable rocks. Copyright © 2003 John Wiley & Sons, Ltd.

Ultrasonic testing of adhesive bonds of thin metal sheets

This article discusses the use of pulse-echo ultrasonic testing for the inspection of adhesive bonds between thin metal sheets (0.8 mm). The method is based on the measurement of the reflection coefficient at the metal/adhesive interface. After describing briefly the physical aspects of the phenomenon, an index is defined to detect defective zones of the joint (both for the lack of adhesive and for insufficient adhesion); the influence of the experimental variables (transducer frequency, coupling medium and contact force) on the measurement is discussed. The analysis shows that coupling medium and transducer frequency do not influence the results and that the method is robust with respect to the variation of contact force. By means of a control experiment it is shown that the statistical distribution of the index corresponding to good and defective adhesion zones are sufficiently separate to be distinguished. Finally, a procedure based on the statistical theory of decisions is proposed to evaluate the integrity of the joint under test.

Active Control of a High-Speed Pantograph

The design and performance of an active controller for a pantograph which collects current for a high-speed train are considered. A dynamic model of the pantograph/catenary system is described and control objectives are established. A design which incorporates a frame-actuated controller and requires only a single measurement is described. Over an array of train speeds, the contact force variation with the actively controlled pantograph is 50 percent less than for the equivalent passive pantograph system.

Development of Low-Noise Current Collector with Contact Force H.INF. Controller for High-Speed Railways.

To reduce noise caused by a current collector for the high-speed railways, a diamond shaped lownoise current collector has been developed. But it becomes difficult for this current collector to maintain the predetermined contact force between the contact strip and the trolley-wire, since its mass is three times as heavy as the conventional one and it suffers from ten times the lift force compared to the donventional one. So the vertical height of those apparatus should be controlled by using an active control system. The upper part of the insulator is located in high voltage which prevents us from using sensors. When using sensors only under the insulator, it is difficult to distinguish wire disturbance from lift one. In this study, the difficulty is solved by the H∞ controller which separates those disturbances in the frequency range. In the numerical calculation and experiment using a prototype experimental equipment, it is confirmed that the contact force variation corresponding to the roughness of the trolley-wire at 2 Hz, 20 mm is reduced by about 70% compared with a passive model, and the contact force against the lift force at the ramp is reduced by about 30%.

Running Test on Current Collector with Contact Force Controller for High-Speed Railways.

To reduce noise caused by current collectors on high-speed railways, a wing-Shaped low-noise current collector has been developed. This collector head is directly supported by a composite insulator. However, it becomes difficult to maintain the predetermined contact force of the contact strip against the trolley wire. Therefore, the vertical height of those apparatus should be controlled actively. The upper part of the composite insulator is under high voltage. When using sensors only under the insulator, it is difficult to distinguish wire disturbance from lift disturbance. In this study, the difficulty is solved by using H∞ controller to estimate those disturbances in each frequency range. In traveling experiments using full-size prototype equipment on the running vehicle, it was confirmed that the contact force variation due to lift of 68 N at the speed of 112km / h was reduced by about 33% compared with active control without lift compensation, and the wire push-up variation was reduced by about 67%.

Measurements of human force control during a constrained arm motion using a force-actuated joystick

1. When interacting with the environment, human arm movements may be prevented in certain directions (i.e., when sliding the hand along a surface) resulting in what is called a "constrained motion." In the directions that the movement is restricted, the subject is instead free to control the forces against the constraint. 2. Control strategies for constrained motion may be characterized by two extreme models. Under the active compliance model, an essentially feedback-based approach, measurements of contact force may be used in real time to modify the motor command and precisely control the forces generated against the constraint. Under the passive compliance model the motion would be executed in a feedforward manner, using an internal model of the constraint geometry. The feedforward model relies on the compliant behavior of the passive mechanical system to maintain contact while avoiding excessive contact forces. 3. Subjects performed a task in which they were required to slide the hand along a rigid surface. This task was performed in a virtual force environment in which contact forces were simulated by a two-dimensional force-actuated joystick. Unknown to the subject, the orientation of the surface constraint was varied from trial to trial, and contact force changes induced by these perturbations were measured. 4. Subjects showed variations in contact force correlated with the direction of the orientation perturbation. "Upward" tilts resulted in higher contact forces, whereas "downward" tilts resulted in lower contact forces. This result is consistent with a feedforward-based control of a passively compliant system. 5. Subject responses did not, however, correspond exactly to the predictions of a static analysis of a passive, feedforward-controlled system. A dynamic analysis reveals a much closer resemblance between a passive, feedforward model and the observed data. Numerical simulations demonstrate that a passive, dynamic system model of the movement captures many more of the salient features observed in the measured human data. 6. We conclude that human subjects execute surface-following motions in a largely feedforward manner, using an a priori model of the surface geometry. The evidence does not suggest that active, real time use of force feedback is used to guide the movement or to control limb impedance. We do not exclude, however, the possibility that the internal model of the constraint is updated at somewhat longer latencies on the basis of proprioceptive information.

Development of an Adaptive Force/Position Controller for Robot-Automated Composite Tape-Layering

The quality of parts produced by a composite tape-laying process is sensitive to the contact force exerted and the abutment of adjacent tape courses kept when the tapes are laid. Thus, a prerequisite for a high performance laying process automated by means of industrial manipulators is the ability to regulate laying force and position precisely in the presence of robot motion inaccuracies and laying contour variations. An on-line adaptive force/position controller for robot-automated laying processes was presented. The contact force error normal to a laying surface is measured by a wrist sensor in real time, while the position error tangent to the surface is measured by sensors found in manipulator joints. Both are modeled as autoregressive (AR) processes, on the basis of which future errors in Cartesian coordinates are forecasted. Via a compliance selection matrix, both predicted errors are fed to joint actuators in a similar manner for taking compensatory actions. In view of the similarity, the force control portion of the scheme was implemented in an experiment using a three degree-of-freedom manipulator and the results indicated a 40 percent average reduction in contact force variations.

Responses of human mechanoreceptive afferents to embossed dot arrays scanned across fingerpad skin

The spatial resolving capacities of the four classes of mechanoreceptive afferents innervating human fingerpad skin were investigated to determine which class sets the limit of tactile spatial resolution for scanning stimuli. The stimulus consisted of an array of embossed dots (0.7 mm diameter, 0.5 mm high) arranged in a tetragonal pattern with dot spacing decreasing linearly from 6.4 mm at one end of the array to 0.87 mm at the other. The pattern was wrapped around a drum and repeatedly scanned across the receptive field of single afferents by continuously rotating the drum. Responses to many closely spaced scans were obtained by imposing a lateral shift of the pattern between each revolution. Impulses were recorded microneurographically. Responses were plotted in raster form to produce a neural image of the pattern. Responses of rapidly and slowly adapting type I (FAI and SAI) afferents resolved dots down to a spacing of about 1.5 mm. Responses of type II (FAII and SAII) afferents resolved dots down to a spacing of about 3.5 mm. Variation in scanning speed (range, 20-90 mm/sec) and contact force (range, 0.4-1.0 N) had minimal effects on spatial resolution of all afferents. The response clusters associated with individual widely spaced dots were used to investigate receptive field structure. FAI and SAI fields (mean areas, 6.1 and 4.8 mm2, respectively) each contained several zones of maximal sensitivity. FAI fields had five to eight such zones, whereas SAI fields had three to five such zones. As dot spacing decreased, neighboring dots interacted to affect the responses associated with the individual zones within a field. Initially, one or more zones were deactivated, effectively reducing receptive field size and allowing representation of finer spatial detail than would be predicted from the overall area of the receptive field. At very close dot spacings responses were only obtained when more than one sensitive zone within a field were simultaneously activated by different dots.

Performance Sensitivity of an Actively Damped Vehicle Suspension to Feedback Variation

A two degree of freedom vehicle model is analyzed for its performance sensitivity as a function of the system’s feedback gains. Three measures of performance, namely, sprung mass isolation, suspension travel, and tire contact force variation are examined. The varied feedback gains are the spring stiffness, the passive damping coefficient, and the active damping coefficient. Both frequency response and RMS response of the performance variables are considered and surfaces are formed to examine output sensitivity to suspension feedback. The results show that RMS vehicle isolation is increased by both softening the suspension and adding active damping. RMS tire contact force is influenced mostly by passive damping and only marginally affected by active damping. Suspension stiffness is shown to have no influence suspension travel for the passive suspension modeled.

Analytical and Experimental Investigations of Reed Contact Bouncing

Studies of variations of the reed bounce-dynamics during operation are reported. The influence of such factors as temperature, contact current, gap discharge, as well as the energizing MMF value are investigated. Simplified mathematical models of the reed switch with one and two degrees of freedom, which take into account the magnetic effect of the current flow through the contact and the contact force variation with the gap length, are developed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Analytical and experimental investigations of reed contact bouncing

Studies of variations of the reed bounce-dynamics during operation are reported. The influence of such factors as temperature, contact current, gap discharge, as well as the energizing MMF value are investigated. Simplified mathematical models of the reed switch with one and two degrees of freedom, which take into account the magnetic effect of the current flow through the contact and the contact force variation with the gap length, are developed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Two Contrasting Versions of the Optimal Active Vehicle Suspension

It is generally agreed that vehicle suspensions should isolate the body from roadway unevenness inputs but it is less clear on which other functions are most important. Some studies focus on keeping the wheel-road contact force excursions as small as possible for safety reasons and others focus on limiting the main suspension deflection for good rigid body motion control. In this paper, two performance indices are used which lead to optimal state variable feedback laws for the suspension force. Body isolation is traded off in one case against contact force variation and in the other against suspension deflection. The use of symmetric root locus sketches shows the types of system that result in both cases. It is shown that optimal active suspensions designed according to different criteria are not necessarily comparable and it may not be fair to compare an optimal suspension with a conventional one, unless all aspects of suspension performance are considered simultaneously.

An analytical and experimental study of impulsive stresses in a glass plate subjected to the transverse impact of steel balls.

In this paper, an attempt is made to analyze the impulsive stresses in a glass plate subjected to the transverse impact of steel balls. For the case of a mass striking an infinite glass plate, the contact force variation is obtained by solving a nonlinear integral equation given by the use of Lagrange's classical plate theory and Hertz's law of contact. By regarding this force as an impact load for the case of the central impact of a steel ball on a supported circular glass plate, the impulsive stresses in a glass plate are analyzed using the three-dimensional dynamic theory of elasticity. Finally, it is shown that these analytical results are in good agreement with the experimental results.

Computer Evaluation of Controlled Pantographs for Current Collection From Simple Catenary Overhead Equipment at High Speed

A digital computer simulation technique is used to study the effects of changing pantograph characteristics upon the quality of current collection from simple catenary overhead equipment at high speed. In particular, the likely benefits to be derived by the use of controlled pantographs are assessed. Pantograph performance is judged on the basis of contact force variation and displacement responses of pantograph and contact wire. These studies have shown that the dynamic displacements of the combined system are determined primarily by the overhead line parameters rather than by the pantograph. At higher speeds droppers in the vicinity of the pantograph slacken and this is seen to influence significantly the contact force profile. On a “constant height” overhead line, the proposed “frame compensated” and “panhead inertia compensated” pantographs do not show any marked improvement in the quality of current collection.