Elastomeric Pads Research Articles

Parametric Study of Suspension Elements for Ride Index Analysis of an Indian Railway Freight Vehicle

Approximately three hundred thousand three-piece bogie freight vehicles presently operate under Indian Railways. The dynamic behavior of a vehicle depends on primary and secondary suspension elements. In the present work, a parametric study of suspension elements has been performed at various operating speeds to analyze the ride index of vehicle. The freight vehicle model considered in the present work comprises 70 degrees of freedom (DOF). Spring indices of various springs used as suspension elements and damping coefficients of wedge block as well as elastomeric pad have been obtained experimentally. These values have been used along with actual recorded track irregularities data to solve a vehicle model using ADAMS/Rail. The behavior of vertical acceleration and ride index of the vehicle for different speeds limits have been observed. The parameters of suspensions elements have been sequentially varied and their effects on vertical acceleration and ride index have been studied for vehicle speeds up to 110 kmph. A new set of parameters for suspension elements which gives improved ride index has been suggested on the basis of results obtained.

Development of a Fiberoptic Distributive Shear/Pressure Sensor

An estimate of $6 billion is being spent annually to deal with diabetes-related health problems. In the United States, 6% of the population (about 18 million people) has diabetes, either diagnosed or undiagnosed. During their lifetimes, about 15% of diabetic patients will develop a foot ulcer. More than 60,000 of them will end up with amputations of lower extremities due to complications arising from diabetes mellitus, accounting for nearly two-thirds of the total number of nontraumatic amputations performed annually. Previous studies report that has indicated that both the vertical and shear components of ground reaction force play a role in the formation of plantar ulcers. However, the exact relationship between stresses and ulcer formation is still unclear. The reason for that is due to lack of a sensor that is currently available to be able to measure pressure and shear force on the plantar surface simultaneously. It is because of these inadequacies that have motivated the search for a new design to transduce pressure and shear stress based on a multi-layered optical bend loss sensor. We have recently developed a sensor that can be used to measure shear and pressure of an extended area using fiber optic technology. The fiber optic technique that we have developed has also been extended by utilizing an array of microfabricated waveguides made of polydimethylsiloxane (PDMS). For the fiberoptic technique, the pressure/shear sensor consisted of an array of optical fibers lying in perpendicular rows and columns separated by elastomeric pads. A map of pressure and shear stress was constructed based on observed macro bending through the intensity attenuation from the physical deformation of two adjacent perpendicular fibers. Each sensing layer consists of multiple fibers molded into a thin PDMS substrate. In this design, the top layer is composed of a 3 by 3 fiber mesh with 9 intersection points and the bottom layer is made of a 4 by 4 fiber mesh with 16 intersection points. The space between the adjacent fibers is 0.5 cm. The pressured points between the top and the bottom layer are offset by 0.25 cm which is used to increase the shear sensitivity. In the experiment, the sensor was tested with various loading condition. A force image algorithm using neural networks was developed to identify the loading pattern, magnitude and direction of loads that were applied at more than one pressure point. Here 3 loading patterns with 5 different loading directions and 3 different loading magnitudes were tested. The results show a >90% accuracy was obtained using an algorithm with 2 layered neural networks system.

Mechanical behaviour of a hyperelastic pad for an integrated cross-tie trackwork system

This paper presents the material characteristics and application of a hyperelastic pad used in an integrated cross-tie trackwork configuration, which is part of an advanced rapid transit (ART) system. The ART vehicle is powered by a linear induction motor (LIM); correspondingly, the steel cross-tie trackwork includes a LIM reaction rail as well as running rails to support the steel-wheeled vehicle. An elastomeric pad is placed under each end of the cross-tie to absorb the dynamic effects from the ART. The pad has been isolated from the integrated cross-tie system and tested to determine its material constants which are necessary for modeling of the cross-tie system. The pad is found to be nearly incompressible and demonstrates hyperelastic behaviour. The Mooney–Rivlin (three-term) model shows the best prediction of the pad behaviour among the five selected hyper-elasticity models and a simplified elastic foundation model also exhibits a reasonable engineering approximation. The contribution of variable pad stiffness values to the size of the required air gap between the LIM and the reaction rail, and to the fatigue life of welded connections in the cross-tie is studied.

Development of a numerical model for bridge–vehicle interaction and human response to traffic-induced vibration

The perceptible vibration of composite steel girder bridges under live loads is an important design consideration in today’s bridges, which have longer spans and lighter decks than older bridges, and have with limited damping. Although, in accordance with the bridge design codes, the strength design and the deflection control of these bridges are covered fairly well, vehicle movement on the bridge may still cause vibrations that are too strong from the viewpoint of pedestrians. This investigation presents a comprehensive numerical model for studying bridge–vehicle interaction and the resultant perceptible vibration. 3D finite element models are developed for trucks, road surface and the composite girder bridge itself. Truck parameters include the body, the suspension and the tires. The bridge is treated as a 3D composite steel girder bridge on a simply-supported span. A parametric study is performed to identify the effect of various parameters on the vibration of the bridge, such as vehicle speed, neoprene stiffness, the effect of the aspect ratio (ratio of height to length) of steel girders, vehicle type, continuity of the deck slab on top of the pier and the initial bounce of the vehicle due to road surface roughness. The results have been expressed in the form of human perceptibility curves (graphs of perceptible vibration acceleration versus vibration frequency). This study finds that the bridge response is significantly influenced by the vehicle speed, stiffness of the elastomeric pad, continuity of the RC deck slab at pier and the ratio of vehicle weight to total weight of the superstructure, especially for values greater than 10%. In order to validate the proposed interaction model, dynamic field tests were performed on a simple span composite steel girder bridge, located downstream of Karkheh River Dam in Iran, which has significant vibrations under moving truckloads. The results show that the inclusion of features such as increasing the aspect ratio of steel girders and decreasing the number of expansion joints of the RC slab in the design has major effects on the reduction of perceptible vibration.

The Effects of Interfacial Particles on the Contact of an Elastic Sphere With a Rigid Flat Surface

In chemical mechanical polishing (CMP), a rigid wafer is forced on a rough elastomeric polishing pad, while a slurry containing abrasive particles flows through the interface. One of the important factors that influence the material removal rate in CMP is the magnitude of contact force transmitted to the abrasive particles trapped at the contact interface. The total push-down force is distributed to the direct contact between the wafer and the pad, and to the three-body contact between the wafer, the pad, and the abrasive particles. The presence of the abrasive particles alters the asperity contact, which otherwise can be described by Hertz contact relationships. In this study, the effect of the interfacial particles on the single asperity contact is investigated. An approach used by Greenwood and Tripp (1967, “The Elastic Contact of Rough Spheres,” ASME J. Appl. Mech., 34, pp. 153–160) to study the contact of rough spheres is utilized since the presence of the particles provides a rough character to the contact. The results show that the contact behavior becomes non-Hertzian with decreasing contact force and increasing elastic modulus, particle size, and particle concentration. The role of the interfacial particles is to spread the contact over a larger area while lowering the maximum contact pressure at the center of contact predicted by Hertz contact. The conditions required to transfer the contact force on the particles effectively are also described.

Behavior of Integrated Crosstie Trackwork System

Light rail systems are an important transportation mode in urban centers. An advanced rail transit system has been developed that utilizes linear induction motors (LIM) for propulsion and braking of the vehicles. Due to the tight motor-to-rail air gap tolerances required for the efficient operation of the LIM system, the trackwork requires special consideration. An innovative crosstie trackwork system has been developed to address competing requirements for high stiffness to ensure efficient operation of the LIM, and low track stiffness for acceptable ride quality. The crosstie incorporates a hollow structural steel section welded at each end to formed steel base plates which are supported by elastomeric pads. The crosstie supports steel running rails. This paper describes a finite-element model developed to predict the response of a crosstie to loads that simulate the passage of a steel wheeled transit vehicle. The model uses tetrahedral elements for the hollow structural steel section and the base plates. The elastomeric pads are modeled using elastic foundation elements. The model predicts stresses and deflections in the crosstie. An experimental program that was carried out on the crosstie to investigate its fatigue performance and to obtain data to verify the finite-element model is also described. The model conservatively predicts crosstie deflections and stresses. The hot spot stress approach is used to provide a conservative fatigue life prediction of the crosstie.

Mechanical Gap Fillers: Concepts and Thermal Resistance Measurements

This paper discusses spring-loaded mechanical structures that can be used to make thermal connections between an object to be cooled, such as an integrated circuit, and a dissipative structure, like a cooling plate or heat sink. These metal structures are flexible and resilient, adapting to variations in position and orientation of the two objects to be coupled. Precision experiments demonstrate that they have much lower thermal resistance than elastomeric ldquogap-fillerrdquo pads that are usually used to perform this function.

Composite Optical Bend Loss Sensor for Pressure and Shear Measurement

A composite optical bend loss sensor for measuring 3-D forces has been developed. The sensor is composed of two optic fiber meshes which are embedded into a polydimethylsiloxane (PDMS) slab. The sensor consists of an array of optical fibers lying in perpendicular rows and columns sandwiched inside an elastomeric pad. A map of normal and shear stress is constructed based on observed macrobending through the intensity attenuation from physical deformation of two adjacent perpendicular fibers. Due to the new addition of the composite design and acrylic holder, the stability of the present sensor is found to be significantly better than our previously reported microfabricated optical bend loss sensor. In this paper, we will report the results of an optical bend loss simulation using the beam propagation method based on a series of images captured by a CCD camera on the fiber's bending curvatures. The result from the simulation will be compared with the results obtained from the experiment. Other results include vertical force and shear measurements at a single pressure point of the sensor. A force image algorithm is used to map the force distribution detected by the sensor. Here, we will present the results of six different shape patterns and two force magnitudes on each shape using a neural network system. We will also present a radio frequency sensor module, which we developed for the composite optical bend loss sensor for remote sensing.

A non‐linear optimisation technique based on the complex method

PurposeThe aim is to present findings of a theoretical analysis for optimal design of a concrete trough for a new lightweight low‐profile rail track system.Design/methodology/approachA non‐linear numerical optimisation technique is adopted to predict the minimum area of a pre‐tensioned pre‐stressed trough section satisfying the serviceability and ultimate limit states as per British Standard BS 8110 for critical loading and boundary conditions.FindingsAn optimum concrete trough section is calculated to carry all possible load combinations expected during the design life of the track. The performance of the rail, elastomeric pad and track base were found to be satisfactory under the same critical loading and boundary conditions.Originality/valueThe theoretical analysis gives a valuable insight into system parameter values that can optimise design performance and cost. However, these optimal design features now need to be tested experimentally.

Effect Of Types Of Bearing On The Load Distribution Among Girders Of The Bridge

The present paper involves three-dimensional nonlinear analysis for reinforced concrete bridge deck consisting of three main girders. Finite brick element is used to predict response of the bridge under monotonically increasing static loads up to failure. A main concern is given to the effects of boundary conditions at the supports, and their effects on the behaviour of the bridge. Three types of supports were considered, these are simple support, elastomeric pads and a simple springs. The study includes also the effect of boundary conditions on the failure load, the load distribution amongst the main girders, and variation of bearing reactions in both pre and post cracking phases. The study shows that the method of representing the supports significantly affects the distribution of the loads among the main girders of the bridge. Key Words : Bearings, Bridge, Finite Element, Load Distribution, Nonlinear Analysis, Reinforced Concrete.

Effect of the particle size of Al2O3 on the properties of filled heat‐conductive silicone rubber

AbstractAn elastomeric thermal pad with a thermal conductivity of 1.45 W/m K, needed for the heat dissipation of microelectronics, was obtained with hybrid alumina of different particle sizes as a filler and silicone rubber (vinyl‐end‐blocked polymethylsiloxane) as the matrix. The effects of the amount, particle size, and mixing mass ratio of the filler particles on the thermal conductivity and mechanical properties of silicone rubber were investigated. The results indicated that the thermal conductivity of the rubber filled with larger particles was superior to that of the rubber filled with the smaller grain size, and the rubber incorporated with a mixture of hybrid particles at a preferable mass ratio exhibited higher thermal conductivity than the rubber for which a filler with only a single particle size was used. In addition, the surface treatment of the hybrid filler with 3‐methacryloyloxypropyltrimethoxysilane could increase the thermal conductivity of the composite rubber. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1312–1318, 2007

Thermally conductive silicone rubber reinforced with boron nitride particle

AbstractThermally conductive silicone rubber used as elastomeric thermal pad is successfully developed with boron nitride powder as conductive filler. The effects of content and particle size of filler on the thermal conductivity and mechanical property of silicone rubber are investigated. The results indicate that the use of hybrid boron nitride with three different particle sizes at a preferable weight ratio gives silicone rubber better thermal conductivity compared with each boron nitride with single particle size at the same total filler content. Furthermore, scanning electron microscopy, differential scanning calorimeter, thermogravimetric, etc., are used to characterize the morphology, curing behavior, thermal stability, and coefficient of thermal expansion (CTE) of the silicone rubber composites. POLYM. COMPOS., 28:23–28, 2007. © 2007 Society of Plastics Engineers

Damage mitigation by innovative materials for Temple C at Selinunte

Greek temples are made of overlapped heavy stone blocks shaped to form columns and entablatures. Preservation of these constructions requires specific structural engineering effort. Present conditions of remains basically reflect centuries of loads and environmental actions, but also undesired effects of former restorations. The latter, if not properly designed, may affect the value and life expectation of these monuments. In the present paper, a novel interpretation of the jacketing technique for temporary interventions and the application to the Greek Temple C of the Selinunte’s (Sicily) archaeological site are presented. Purpose of jacketing is to avoid worsening of the crack pattern by light confinement of stone blocks. Titanium belts and elastomeric neoprene pads are combined to attain the above-mentioned performances. Simplified design model is proposed and a 3D finite elements analysis is performed to evaluate local effects of jacketing; finally information about in situ application are given.

Thermal characterization of Al 2O 3 and ZnO reinforced silicone rubber as thermal pads for heat dissipation purposes

Silicone rubber filled with thermally conductive, but electrically insulating Al 2O 3 or ZnO fillers were investigated to be used as elastomeric thermal pads, a class of thermal interface materials. The effect of Al 2O 3 or ZnO fillers on the thermal conductivity and coefficient of thermal expansion (CTE) of the silicone rubber were investigated, and it was found that with increasing Al 2O 3 or ZnO fillers, the thermal conductivity of the thermal pads increases, while the coefficient of thermal expansion (CTE) decreases. The thermal conductivity results obtained were also analyzed using the Agari model to explain the effect of Al 2O 3 or ZnO fillers on the formation of thermal conductive networks. Thermal gravimetry analysis (TGA) showed that the addition of either Al 2O 3 or ZnO fillers increases the thermal stability of the silicone rubber, while the scanning electron microscope (SEM) showed that at 10 vol.% filler loading percolation threshold has yet to be reached.

A shear and plantar pressure sensor based on fiber-optic bend loss

Lower-limb complications associated with diabetes include the development of plantar ulcers that can lead to infection and subsequent amputation. While we know from force-plate analyses that medial/lateral and anterior/posterior shear components of ground-reaction forces exist, little is known about the actual distribution of these stresses during daily activities or about the role that shear stresses play in causing plantar ulceration. Furthermore, one critical reason why these data have not been obtained previously is the lack of a validated, widely used, commercially available shear sensor, partly because of the various technical issues associated with measuring shear. In this study, we present a novel means of transducing plantar pressure and shear stress with a fiber-optic sensor. The pressure/shear sensor consists of an array of optical fibers lying in perpendicular rows and columns separated by elastomeric pads. We constructed a map of normal and shear stresses based on observed macrobending through the intensity attenuation from the physical deformation of two adjacent perpendicular fibers. Initial results show that this sensor exhibits low noise and responds to applied normal and shear loads with good repeatability.

On the behavior of sole plates in steel girders

Elastomeric bearing systems (elastomeric bearing pads or steel-reinforced elastomeric bearings) are used widely as a low cost option as well as for minimal maintenance. In elastomeric bearing components, the sole plates are important so as to resist not only compression but also flexural stresses due to bending of bridge girders and local stress concentration near the load-bearing diaphragm. In steel box and/or plate girders, the bottom flange and the sole plate may act together in dispersing concentrated stresses. In concrete girders, however, a major role of the sole plate is to spread the stresses into a finite area to make sure that the direct bearing stress acting on the concrete is within the allowable value specified. Although the sole plate is an important component of a bearing system, past studies have been focused on the elastomer or steel reinforcement in the elastomeric bearing system. No specific requirement is provided for the determination of the sole plate thickness in any standard specifications throughout the world. The behavior of the sole plates in the elastomeric bearing system has been investigated by a series of finite element analyses. Based on the analysis results, a simple design equation to determine the sole plate thickness is proposed. Finally, the reliability and rationality of the proposed equation is demonstrated through examples.

Fatigue crack growth behavior of NR and HNBR based vulcanizates with potential application to track pad for heavy weight vehicles

Generally, field performance of elastomeric track pad components has been poor, especially for the medium to heavy tonnage tracked vehicles, which are operated on the hilly cross-country course. The service life of these track pad, is affected not only by the terrain and environmental conditions but also by the speed, cornering, braking, weight of the vehicle, and the track tread design. In this research, modulus, tearing energy, and the rate of crack propagation of vulcanizates are evaluated by changing base materials to improve the service time of track pad. By increasing the contents of carbon black, modulus, tearing energy, and fatigue crack growth resistance of vulcanizates improved. Compared with the NR vulcanizate, the HNBR vulcanizate had a higher value of tearing energy. The rate of crack propagation of vulcanizates using smaller size carbon black was slower than that using larger size carbon black. When the HNBR was blended with the ZSC, the tearing energy of the vulcanizates was a little reduced because of the high modulus but the crack propagation rate was reduced significantly. In the relation between the crack propagation rate and the strain energy release rate, though up to 100% strain were applied to specimens, the slope on the log scale (β) varied between 1.72 and 2.3 with the kind of elastomer.

System for estimating bladder volume

A system for estimating the volume of fluid in the bladder sequentially scans the bladder with ultrasonic beams that section the bladder into a number of transverse planes. The system determines, from the scan lines associated with a given plane, a plurality of points on each of the front and back walls of the bladder. It then fits a curve to the set of front wall points and another curve to the set of back wall points, to determine an outline of the bladder in the plane. The system next calculates the cross sectional area of the bladder in the plane based on the two curves. After determining the area in each of the planes, the system determines the volume of the bladder by summing weighted version of the planar areas. The system includes a transducer that consists of a plurality of piezo-electric elements held in a relatively thin elastomeric pad and/or substrate that is acoustically impedance matched to skin. The elements are spaced and grouped such that the acoustic beams they produce lie on the plurality of planes, with the first and the last planes separated by approximately seventy degrees. The estimated volume may be compared with a predetermined overflow threshold, to determine if the user should then void. The system may include a timer that controls the times at which the system produces estimates. The time may decrease the time between estimate calculations if the estimated volume exceeds a predetermined percentage of the overflow threshold.

A numerical and experimental approach to optimise sheet stamping technologies: part II — aluminium alloys rubber-forming

The conventional way to develop press-formed metallic components requires a burdensome trial-and-error process for setting-up the technology, whose success chiefly depends on operator's skill and experience. In the aeronautical field, where sheet metal press-formed structures are produced in small series, a too lengthy and costly development phase cannot be accepted; the small number of components not allowing the investments depreciation. For these reasons, it is necessary that, during the conceptual design, possible technological troubles are preliminarily faced by means of numerical simulations. In the following report, the Guérin rubber-forming process of an aluminium alloy fuselage frame belonging to AerMacchi MB-339 trainer aircraft was optimised through this approach. Several effects, depending on stamping velocity, component geometry, sheet metal heat treatment, elastomeric rubber pad constitutive law and thickness are taken into account. It is shown how the preliminary tuning of these parameters allows us to minimise defects, increase component quality and reduce set-up times, complying at the same time to the demanding aeronautical requirements.

Two-layers Jacketing For Column Drums

Strengthening and repairing of archaeological handmade are very important issue for structural engineers, and require specific techniques h l l y consistent with needs of arts prevention. Interventions of rehabilitation are often invasive, they operate directly on the structure changing appearance, so they are not acceptable in application to relevant archaeological constructions. On the other hand, durability of materials used in restoration and preservation of archaeological arts is a very relevant aspect of the design process. In the present paper, a jacketing technique for multi-drum classical columns is presented. In particular, some aspects related to structural design of belts and to limitation of stresses on stone surfaces are discussed. The technique is based on utilisation of metallic belts and elastomeric pads, able to avoid direct contact between belt and stone, reduce localisation of stresses due to surface irregularities and ensure a full reversibility of the intervention.