High Contact Forces Research Articles

Influence of the Fastening Modeling on the Vehicle-Track Interaction at Singular Rail Surface Defects

With up to 12 spring-damper groups distributed in the actual area of a rail pad, different fastening models are developed in this paper to include the nonuniform pressure distribution within a fastening system and model the constraints at the rail bottom more realistically for the purpose of high frequency dynamics between vehicle and track. Applied to a 3D transient FE model of the vehicle-track interaction, influence of the fastening modeling on the high frequency dynamic contact forces at singular rail surface defects (SRSDs) is examined. Two defect models, one is relatively large and the other is small, are employed. Such a work is of practical significance because squats, as a kind of SRSD, have become a wide spread problem. Results show that the fastening modeling plays an important role in the high frequency dynamic contact forces at SRSDs. Supports in the middle of the rail bottom, modeled as spring-damper groups located under rail web, are found to be most important. The less the rail bottom is constrained or supported, the more isolated the sleepers and substructure are from the wheel-rail interaction, and the more kinetic energy is kept in the rail after impact at a SRSD. Rolling speed is also varied to take into account its influence. Finally, based on the results of this work, influence of the service states of the fastening system on growth of relatively small SRSDs is discussed.

Novel Design Concepts for Piezoelectrically Driven Ohmic Switches

Abstract In this paper novel design concepts for ohmic RF-MEMS switches based on piezoelectric and electrostatic actuation are presented. In contrast to traditional cantilever designs the proposed concepts are based on circular and ring shaped piezo actuators offering significant advantages especially in providing high contact forces. As a result of a parametric study optimized designs have been developed which can deliver more than 2 mN force at small device sizes of less than 0.08 mm 2 . First actuator prototypes featuring 1 μm sputtered PZT films are currently being fabricated by means of MEMS technology.

Evaluation of Wear Behavior of Wheel Steel Using Twin-Disc Test

The wheel/rail contact is chracterized by high contact forces and small contact areas. Although the standard of railway wheel has sustained, the damages of railway wheel have been occurred in service running. The railway wheel damage can be divided into three types; wear, contact fatigue failure and thermal crack due to braking. In curves, especially, large sliding on the contact patch occurs at the wheel tread and flange. Due to this sliding, wear increases in the wheel/rail contact under the dry condition. To reduce wear, more durable wheel steels are required. In order to develop new materials and predict wear, It is important to understand the wear mechanism in wheel steels. In this study, we have investigated the wear characteriscs of RSW1 railway wheel steel using twin disc wear testing. Also the comparative wear behavior of RSW1 and R7 wheel steel under rolling-sliding contact was performed.

Sensitivity Analysis of Process Parameters in the Drawing and Ironing Processes

Deep drawing is one of the most important operations used in sheet metal forming. Within this, forming of cylindrical cup is one of the most widely studied deep drawing processes since it allows analysing the effect of different process parameters in phenomena such as earing, springback and ironing. In fact, during the deep drawing of a cylindrical cup the blank thickness gradually increases as the blank outer diameter is reduced to the die inner diameter, resulting in a thickness increase from a point near the bottom radius until the maximum value at the top of the cup. Therefore, if the gap between the punch and the die is not sufficiently large to allow the blank material to flow, ironing of the cup wall will occur. The ironing process typically imposes high contact forces, normal to the surface of the punch and the die, which can lead to the occurrence of galling, particularly for aluminium alloys. In this work an experimental device, adopted in previous studies, was used to analyse the influence of the lubricant conditions in the deep drawing of a cylindrical cup. The study considers an AA5754-O aluminium alloy blank with a diameter of 60 mm, which is fully deep drawn with a 33 mm diameter punch. Due to the forming conditions, the cup is deep drawn and ironing of the cup wall also occurs. The experimental tests were performed considering different amounts of lubricant in the blank surfaces in the contact with the die and with the blank-holder in order to better understand the influence of these tools on the process. The experimental study was complemented with numerical simulations, exploring the conditions induced by the ironing operation, quite challenging for the numerical simulation of the process using the finite element method. Besides the influence of the contact with friction conditions in the forming process (i.e. punch force evolution, thickness distribution along the cup wall and contact pressure), the influence of the die shoulder and inner radius were also analysed.

Active control strategy on a catenary–pantograph validated model

Dynamic simulation methods have become essential in the design process and control of the catenary–pantograph system, overall since high-speed trains and interoperability criteria are getting very trendy. This paper presents an original hardware-in-the-loop (HIL) strategy aimed at integrating a multicriteria active control within the catenary–pantograph dynamic interaction. The relevance of HIL control systems applied in the frame of the pantograph is undoubtedly increasing due to the recent and more demanding requirements for high-speed railway systems. Since the loss of contact between the catenary and the pantograph leads to arcing and electrical wear, and too high contact forces cause mechanical wear of both the catenary wires and the strips of the pantograph, not only prescribed but also economic and performance criteria ratify such a relevance. Different configurations of the proportional-integral-derivative (PID) controller are proposed and applied to two different plant systems. Since this paper is mainly focused on the control strategy, both plant systems are simulation models though the methodology is suitable for a laboratory bench. The strategy of control involves a multicriteria optimisation of the contact force and the consumption of the energy supplied by the control force, a genetic algorithm has been applied for this purpose. Thus, the PID controller is fitted according to these conflicting objectives and tested within a nonlinear lumped model and a nonlinear finite element model, being the last one validated against the European Standard EN 50318. Finally, certain tests have been accomplished in order to analyse the robustness of the control strategy. Particularly, the relevance or the plant simulation, the running speed and the instrumentation time delay are studied in this paper.

A wheel passing a crossing nose: Dynamic analysis under high axle loads using finite element modelling*

A finite element model for the process of a wheel passing a crossing is presented. In the dynamic model, one wheel, the wing rails and the crossing nose (frog) are modelled. The bogie, the complete wheel set and the support of the crossing are represented as a system consisting of masses, springs, dampers and friction-generating elements. The rolling/sliding behaviour between the wheel and crossing is studied using the proposed model. Due to the conical shape of the wheel tread and multiple contacts between the wheel and the crossing parts, sliding occurs during the transition of the wheel from the wing rail to the crossing nose or vice versa. At the same time, an impact occurs that produces high contact forces. The parameters of the model are the train speed and passing direction, the wheel and the crossing geometry, the axle load and the support of the crossing. In this paper, the crossover process is studied for high axle loads and compared with results of simulations using a normal axle load. Further parameters are three train velocities, both directions of passing and different crossing materials. The loading of the crossing nose is calculated for all cases (axle load, train speed and direction) and materials.

Subglacial clast/bed contact forces

AbstractA laboratory device was built to measure the forces that ice exerts on a 0.05 m diameter rigid plastic sphere in two different configurations: in contact with a flat bed or isolated from the bed. Measurements indicated that bed-normal contact forces were 1.8 times larger than drag forces due to creeping flow past a slippery sphere isolated from the bed. Measurements of forces as a function of the bed-normal ice velocity, estimations of the ice viscosity parameter and observations of markers in the ice indicate ice is Newtonian with a viscosity of ~1.3x 1011 Pas. Newtonian behavior is expected due to small and transient stresses. A model of regelation indicates that it had a negligible (<5%) influence on forces. Water pressure in the cavity beneath the sphere in contact with the bed had a likewise negligible influence on contact forces. When no cavity is present, drag forces can be correctly estimated using Stokes’s law (Newtonian viscosity) for a slippery sphere. The same law with a bed-enhancement factor of 1.8 is appropriate for estimating bed-normal contact forces. These results reinforce previous laboratory measurements and theories but provide no support for explanations of high debris/bed friction or rates of abrasion that depend on high contact forces.

Impact and Sliding Wear Resistance of Hadfield and Rail Steel

Railway networks are subjected to more and more severe loading conditions requiring the use of steels with a high resistance to wear and good fatigue behaviour. The surveys carried out on out of use equipment, such as rails or switches, show that these equipments fail by wear after quite a long period of use, but they can fail by fatigue in a substantially shorter time. In service, crossings are submitted to rolling, impact and sliding stresses. The impact-sliding is the result of the wheel transition from rail wing to crossing nose. Very high contact forces act on the crossing nose while such wheels are passing over it. These large contact forces between wheel and crossing can cause severe damage at crossing nose and wing rail. The influence of contact parameters on the damage of the crossing alloy (Hadfield steel GX120Mn13) in comparison with rail steel (R260) was investigated by impact and impact-sliding tests. The results are described and discussed using weight loss and microhardness measurements, optical and scanning electron microscopy observations of the contact surface. Examination of the results shows large plastic deformation in surface and subsurface of samples. In comparison with impact tests, sliding produces a change in size and shape of the contact area, a higher weight loss and lower hardening. A better impact–sliding wear resistance of Hadfield steel has been confirmed.

Prosthetic finger phalanges with lifelike skin compliance for low-force social touching interactions

BackgroundProsthetic arms and hands that can be controlled by the user's electromyography (EMG) signals are emerging. Eventually, these advanced prosthetic devices will be expected to touch and be touched by other people. As realistic as they may look, the currently available prosthetic hands have physical properties that are still far from the characteristics of human skins because they are much stiffer. In this paper, different configurations of synthetic finger phalanges have been investigated for their skin compliance behaviour and have been compared with the phalanges of the human fingers and a phalanx from a commercially available prosthetic hand.MethodsHandshake tests were performed to identify which areas on the human hand experience high contact forces. After these areas were determined, experiments were done on selected areas using an indenting probe to obtain the force-displacement curves. Finite element simulations were used to compare the force-displacement results of the synthetic finger phalanx designs with that of the experimental results from the human and prosthetic finger phalanges. The simulation models were used to investigate the effects of (a) varying the internal topology of the finger phalanx and (b) varying different materials for the internal and external layers.Results and ConclusionsDuring handshake, the high magnitudes of contact forces were observed at the areas where the full grasping enclosure of the other person's hand can be achieved. From these areas, the middle phalanges of the (a) little, (b) ring, and (c) middle fingers were selected. The indentation experiments on these areas showed that a 2 N force corresponds to skin tissue displacements of more than 2 mm. The results from the simulation model show that introducing an open pocket with 2 mm height on the internal structure of synthetic finger phalanges increased the skin compliance of the silicone material to 235% and the polyurethane material to 436%, as compared to a configuration with a solid internal geometry. In addition, the study shows that an indentation of 2 N force on the synthetic skin with an open pocket can also achieve a displacement of more than 2 mm, while the finger phalanx from a commercially available prosthetic hand can only achieve 0.2 mm.

Contributions of individual muscles to hip joint contact force in normal walking

The human hip joint withstands high contact forces during daily activity and is therefore susceptible to injury and structural deterioration over time. Knowledge of muscle-force contributions to hip joint loading may assist in the development of strategies to prevent and manage conditions such as osteoarthritis, femoro-acetabular impingement and fracture. The main aim of this study was to determine the contributions of individual muscles to hip contact force in normal walking. Muscle contributions to hip contact force were calculated based on a previously published dynamic optimization solution for normal walking, which provided the time histories of joint motion, ground reaction forces, and muscle forces during the stance and swing phases of gait. The force developed by each muscle plus its contribution to the ground reaction force were used to determine the muscle’s contribution to hip contact force. Muscles were the major contributors to hip contact force, with gravitational and centrifugal forces combined contributing less than 5% of the total contact force. Four muscles that span the hip – gluteus medius, gluteus maximus, iliopsoas, and hamstrings – contributed most significantly to the three components of the hip contact force and hip contact impulse (integral of hip contact force over time). Three muscles that do not span the hip – vasti, soleus, and gastrocnemius – also contributed substantially to hip joint loading. These results provide additional insight into lower-limb muscle function during walking and may also be relevant to studies of cartilage degeneration and bone remodelling at the hip.

Development of Strong Surfaces Using Functionally Graded Composites Inspired by Natural Teeth—A Theoretical Approach

In recent years functionally-graded composites have been proposed to develop strong surfaces that can withstand high contact and frictional forces. The present work presents a new graded composite that can be used for the development of surfaces with excellent strength properties. The composite is inspired by the human teeth, which nature builds as a hard and tough functionally-graded composite. The outer surface of teeth is of enamel, composed of prismatic hydroxyapatite crystallites, whereas the inner part of teeth is of dentine, composed collagen fibrils and hydroxyapatite. Enamel is hard, brittle, and wear resistant, while dentine is softer and flexible. The dentine-enamel junction is formed as a region at which enamel mixes with dentine in a continuous way. The nanomechanical properties of the transition zone have been recently revealed. Of particular interest in this investigation is the variation in the elastic modulus from the pure enamel to the pure dentine material, which leads to biomimetic graded composites that exhibit high surface strength. This work presents analytical solutions for the stress and displacement fields on an actual composite substrate, which is loaded by a line load. The elastic modulus of the substrate follows approximately the theoretical distribution.

Rotor—frame contact in a centrifuge installed on board a ship

The criticality of rotor and stator contact in a large-size marine separator is studied by numerical modelling. Two plausible mechanisms leading to such contact, namely rolling of a ship in steady-state motion and a suddenly occurring unbalance in the rotor, are considered. It is found that contact due to sea motion may be tolerable, while sudden development of unbalance at operating speed can lead to unacceptably high contact forces. This agrees with experience of centrifugal separators operating on board of ships.

Relative importance of gait vs. joint positioning on hip contact forces after total hip replacement

Implant loosening is a common indication for total hip replacement (THR) revision. High contact forces and implant twisting moments are thought to be associated with implant loosening. Relationships between joint positioning and hip forces, or outcomes, have been investigated through in vivo and in vitro modalities. Relationships between hip forces and gait are less understood, despite repeated findings that gait following a THR does not fully return to normal. We tested the hypothesis that gait parameters would be better predictors of implant force (peak contact forces and peak twisting moment during walking) than joint positioning parameters. Subjects underwent gait analysis, hip force modeling, and measurement of clinical radiographs 1 year after successful THR surgery. Gait parameters were consistently more influential in determining hip forces. Alone, gait explained as much as 67% of the variation in force, compared to a maximum of 33% by joint geometry. Combinations of gait and joint positioning parameters together explained up to 86% of the variation in hip force parameters. Results suggest that gait may provide a valuable postoperatively modifiable target to improve hip loads and potentially reduce the risk for implant loosening.

Technology Focus: Wellbore Tubulars (May 2009)

Technology Focus The subject of wellbore tubulars evolves continuously. The drilling of deeper and longer wells in more-inhospitable places, both geological and environmental, demands essential improvements of tubulars. Drilling, completion, and production of extended-reach, high-angle, short-radius, and multilateral wells require better modeling and design techniques. Over the last few years, many improvements have been achieved in modeling and design of 3D wells that find more applications in both offshore and onshore operations. Essential progress has been made in understanding the mechanics of tubulars better—in particular, buckling and axial-force transfer along the string to the drill bit. It also has been found that for accurate force and moment calculations, information about wellbore curvature and torsion are required. Only 2D wellbores have no torsion. For practical purposes, all wellbores are 3D in shape even if they are designed to be in a 2D plane. Good understanding of contact forces and their magnitude cannot be overestimated. High contact forces are responsible for grooves in casing, keyseats in uncased parts of wellbore, and frequent overheating of tool joints and components of the bottomhole assembly. Creative solutions have been applied successfully to overcome many organizational, economic, and technical challenges associated with drilling modern extended-reach (in the range of 40,000 ft), multilateral, and high-pressure/high-temperature wells. Ultrahigh-torque double-shoulder drillpipe connections, corrosion-resistant pipe coatings and alloys, and a 3D-rotary closed-loop steerable system with an integrated downhole motor are just a few examples of recent technology developments. It also is very important to mention the high-speed-telemetry-drillpipe (intelligent drillpipe) network that permits real-time monitoring of downhole conditions and drilling data. However, perhaps the most important advancement is in increased precision of well placement in 3D sections of wellbores. Taking this opportunity, I wish to encourage all readers to acquire a copy of the book Advanced Drilling and Well Technology that should be available from SPE by Fall 2009. This book covers many aspects of modern drilling including advances in mechanics of tubulars and design. I also hope that readers interested in tubulars and related technologies will take time to review the papers highlighted here. Wellbore Tubulars additional reading available at the SPE eLibrary: www.spe.org SPE 119552 • "Evaluating the Expandability and Collapse Resistance of Expandable Tubulars" by J. Agata, Nippon Steel Corporation, et al. SPE 115708 • "Titanium-Alloy Tubing for HP/HT Applications" by Manuel Gonzalez, SPE, Chevron, et al. SPE 115221 • "First Commercial Deployment of New Third-Generation Rotary-Shouldered Connections Demonstrates Cost Savings" by J.N. Brock, SPE, Grant Prideco, et al.

Robot based system for the automation of flow assembly lines

In this paper a promising approach to the automation of flow assembly lines is presented. The developed system uses a standard industrial robot and synchronizes it to the product in all degrees of freedom. The synchronization is enabled by dividing the assembly process in different phases and controlling the robot in each phase with an adequate sensor system. Besides that a compliance is integrated into the gripper system in order to reduce high contact forces and tolerate high frequent pose deviations. Main advantages of the synchronized assembly are the avoidance of buffers and the reduction of the throughput time.

Microfabricated diamond tip for nanoprobing

In nanoprobing experiments the tip should allow the manipulation and the probing of electrical, mechanical and other properties of nano-scale structures. In this work we present a novel approach for producing tips for nanoprobing using microfabrication technology. Conductive diamond was selected as a tip material to allow electrical measurements with high contact forces and to avoid tip wear during the probing. In-plane triangular shapes of the tip and the cantilever allow to position several nanoprobes in close proximity and to simultaneously observe the contact point in scanning electron microscopy (SEM). Atomic force microscopy (AFM) topography measurements and scanning spreading resistance measurements (SSRM) demonstrated nanometer-scale lateral resolution of the tips.

Fiber Assembly of MEMS Optical Switches With U-Groove Channels

A key process in assembly of microelectromechanical systems optical switches is of inserting fibers into U-grooves in silicon substrate. Due to positioning errors and dimensional tolerances in components, heavy collision occurs between fibers and the edges of U-grooves during insertion, throwing out fibers from the fiber holder or worse, damaging the components. Typical solutions to the problem involve determining errors using machine vision or force sensors, and then positioning fibers accurately by virtue of high precision multi-axis systems (with submicron repeatability). However, these approaches are costly and difficult to implement. In this paper, we present a low-cost passive assembly method to solve the problem. It utilizes a special flexure-based fixture to regulate high contact forces and accommodate assembly errors. Specifically, we model the problems happening in the process of fiber insertion and characterize the conditions of successful insertion. We then suggest how to design flexural fixtures so that the required insertion conditions can be met. Experimental results show that using such a fixture the fiber assembly can be successfully implemented even if the assembly system's accuracy is lower than 12 in and axes, and 0.07 in theta axis. These requirements are within the reach of most low-cost precision systems.

Effects of pre-impact pedestrian position and motion on kinematics and injuries from vehicle and ground contact

Pedestrian injuries from vehicle collisions arise from both the vehicle and the ground contact. Early work showed that above 7 m/s collision speed, the vehicle impact is responsible for higher severity injuries. There has now been considerable development of car design to reduce pedestrian injury severity and thus the role of the ground impact in causing severe head injury should be reexamined. A Madymo model is used to examine the relative severity of the road and vehicle impacts and the effect of pedestrian motion before impact. Results show head impact locations on the vehicle are predictable but their severity varies with pre-impact stance by up to 30%. In contrast, impacts between the body region and the ground are highly variable. The stiff ground results in high contact forces, but the ΔV for ground impact is less severe than the vehicle impacts, showing a higher momentum change in the latter. Evaluation of the HIC36 and 3 millisecond (ms) acceleration criteria for the head and the 3 ms for pelvis and chest also shows that the ground impact results in far more unpredictable injuries compared to the vehicle impact. However, at all speeds head 3 ms scores from the vehicle impact are higher than for the ground contact. Both the HIC36 and the 3 ms acceleration criteria for the head show that the relative importance of the ground impact compared to the vehicle impact reduces with vehicle impact speed. At low to medium speeds, the predicted chest 3 ms responses from the vehicle and ground impacts are similar on average, but at high speeds the vehicle impact is more severe. At low speeds, pelvis 3 ms accelerations from the ground impact are higher than for the vehicle impact, but this trend is reversed at higher speeds.

Dental Care with Manual Toothbrushes during Fixed Orthodontic Treatment—a New Testing Procedure

The aim of this investigation was to employ a new in-vitro testing system for manual toothbrushes in order to distinguish the more effective from those less so for dental care during fixed appliance treatment. The testing apparatus consisted of a sliding carriage able to execute a horizontal brushing movement, and a row of artificial teeth upon which the various toothbrushes were manipulated. The artificial row of teeth was fixed on a sensor that recorded in all three dimensions the forces and moments caused by the toothbrushes on the toothbrush field. All the tests were executed with a weight of 110 g on a tooth field with a multibracket appliance. Tests were also carried out with five toothbrushes having weights of 200 g, 250 g and 300 g. Here, the decisive target values were 1) the degree of exertion necessary in the brushing direction to move a brush over the artificial teeth, and 2) the maximum force occurring in the brushing direction. High target values indicated high interaction between toothbrush bristles and the surfaces being brushed. From testing five toothbrushes with four different weights, we have established profiles confirming the beneficial and less beneficial properties of certain toothbrushes involving various high contact forces.

Do sporting activities convey benefits to bone mass throughout the skeleton?

It is well known that sport and exercise play an important role in stimulating site-specific bone mineral density (BMD). However, what is less well understood is how these benefits dissipate throughout the body. Hence, the aim of the present study was to compare the BMD (recorded at nine sites throughout the skeleton) of 106 male athletes (from nine sports) with that of 15 male non-exercising age-matched controls. Given that BMD is known to increase with body mass and peak with age, multivariate and univariate analyses of covariance were performed to compare the BMD of the nine sports groups with controls (at all sites) using body mass and age as covariates. Our results confirmed a greater adjusted BMD in the arms of the upper-body athletes, the right arm of racket players and the legs of runners (compared with controls), supporting the site-specific nature (i.e. specific to the externally loaded site) of the bone remodelling response (all P <0.01). However, evidence that bone mass acquisition is not just site-specific comes from the results of the rugby players, strength athletes, triathletes and racket players. The rugby players' adjusted BMD was the greatest of all sports groups and greater than controls at all nine sites (all P <0.01), with differences ranging from 8% greater in the left arm to 21% in the lumbar spine. Similarly, the strength athletes' adjusted BMD was superior to that of controls at all sites (P <0.05) except the legs. The adjusted BMD of the triathletes was significantly greater than that of the controls in both the arms and the legs as well as the thoracic and lumbar spine. The racket players not only had significantly greater right arm BMD compared with the controls but also a greater BMD of the lumbar spine, the pelvis and legs. In contrast, the low-strain, low-impact activities of keep-fit, cycling and rowing failed to benefit BMD compared with the age-matched controls. These results suggest that sporting activities involving high impact, physical contact and/or rotational forces or strains are likely to convey significant benefits not only to the loaded sites, but also to other unloaded peripheral and axial sites throughout the skeleton.