Elastomer Layer Research Articles

The use of gas membranes for VOC-air separations

Abstract Industrial processes commonly emit organic components as dilute or concentrated streams. Environmental regulations impose stringent emission standards. Interest in membrane separation techniques has grown along with their acceptance for vapour recovery. They compete with absorption, adsorption, cryogenics and incineration. In research carried out in collaboration with GKSS, Geesthacht, Germany, the separation of gases and vapours was experimentally investigated for various thin film, composite membranes in a flat sheet configuration, with a dense elastomeric silicone film layer over a porous PEI or PVDF support. Available literature data were reviewed and assessed including the models to describe mass transfer through the membranes. Experimental results for pure substances and for binary mixtures were used to determine the permeability as a function of temperature and to calculate the selectivity toward N 2 . The free-volume model [1] approach was used to predict the permeabilities of hydrocarbons. The necessary surface area of the membrane separation module was determined for a given flow rate, concentration, operating temperature and pressure and from the characteristic selectivity of the membrane. The design is illustrated by the separation of butane from an air waste stream produced by polyethylene foaming and for the CH 4 -enrichment of a landfill biogas. A sensitivity analysis towards operating parameters illustrated the predicted effects. Finally, current industrial applications are briefly reviewed, e.g. enriching landfill gas, recovery of VC-monomer from PVC-process off gas, etc.

A two-dimensional shape memory alloy/elastomer actuator

This paper presents a theoretical model for the response of a two-dimensional, thermally driven, shape memory alloy (SMA)/elastomer actuator. The actuator is assumed to be constructed from a thin layer of SMA bonded to a layer of elastomer. The proposed device is considered to undergo small displacements and small strains. The governing equations are developed utilizing the classical laminated plate theory, energy balance equations, and a two-dimensional transition model of the SMA layer. A finite element model is developed to solve the nonlinear system of equations. Parametric studies are conducted to demonstrate the effects of the elastomer thickness, thermal conductivity, input energy, and heat sink strength on the overall time response of the SMA/elastomer actuator.

Bilayer nanocomposite molecular coatings from elastomeric/rigid polymers: fabrication, morphology, and micromechanical properties

We fabricated bilayered nanocomposite coatings composed of a hard polymer layer placed on top of an elastomeric layer. The primary layer of poly[styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) was attached to the surface by grafting to a chemically reactive silicon surface functionalized with epoxy-terminated SAM. The SEBS layer served as the compliant interlayer in the bilayered polymer coating. The topmost hard layer was a high performance polymer made of epoxy resin (EP) and an amino functionalized poly(paraphenylene) (PPP). We built the bilayered structure by spincoating the EP/PPP mixture on top of the grafted SEBS layer. The solidification of the topmost layer was initiated at low temperatures (40 - 50 °C) to avoid dewetting. The curing of the film was finished at 110 °C (15 hours) and the EP/PPP layer was strongly attached to the SEBS layer. It was found that the EP/PPP layer did not penetrate inside the elastic primary layer during the solidification. The elastic response of the hard polymer layer was affected significantly by the underlying elastomeric layer. The SEBS layer served as a compliant interlayer capable of dissipating the interfacial stresses originating from dissimilarities in the physical properties between the polymer coating and the inorganic substrate.

Nanocomposite polymer layers for molecular tribology

We discuss a novel strategy for the formation of elastomeric boundary lubrication coatings from block copolymers grafted to a reactive interface of a silicon substrate. We demonstrate molecularly thick thermoplastic elastomeric films with promising microtribological properties. These films are composed of an elastomeric rubber phase reinforced by the net of glassy nanodomains. These elastomeric layers are extremely wear resistant under shear stresses due to the unique combination of a chemically grafted elastic matrix capable of tremendous reversible deformation (500–1000%) stabilized by a chemically interconnected nanodomain net.

A three-dimensional shape memory alloy/elastomer actuator

This paper presents a mathematical model for analysis of a thermally-driven shape memory alloy (SMA)/elastomer actuator under arbitrary loading and boundary conditions. The actuator is a three-dimensional laminated composite box beam that consists of SMA and elastomer layers with a uniform rectangular cross section. The thermomechanical behavior of SMA layers is modeled utilizing Tanaka and Nagaki's constitutive equation and linear phase transformation kinetics. The behavior of the elastomer layers is assumed to be thermoelastic, in which the elastic modulus is considered to be temperature dependent. The classical laminated beam theory is employed to obtain the force-deformation relationships. The analysis provides explicit solutions to the structural response of the actuator, including strain and curvature of actuator's midplane. A numerical example for a cantilever box beam with uniform square cross-section subjected to a transverse concentrated load is presented. Results demonstrate that significant changes occur in the actuator's responses during phase transformation due to the strain recovery.

Analytical modelling of the elastomeric layer in soft layer hip replacements.

A mechanical analysis is carried out for a flat deformable layer, firmly anchored to a rigid substrate, and frictionlessly compressed by a rigid spherical indenter, with reference to the design of hip replacements whose cup is covered by an elastomeric layer. An available perturbation solution of differential character, developed for a layer subject to plane strain conditions, indented by a cylinder approximated as parabolic in shape and valid for high contact widths, is here extended to the axisymmetric problem of a layer compressed by a paraboloidal indenter. In addition to the paraboloidal idealization, an accurate mathematical description of the indenter spherical profile is incorporated into the modelling of this contact problem. Perturbed solutions up to the second order are developed for both compressible and incompressible layers. Selected numerical examples addressing actual joint geometries are included to assess the validity of the proposed analytical modelling, to explore the accuracy in describing the spherical profile and to compare the contact pressure profiles activated by paraboloidal and spherical indenters.

Pull-off behavior of epoxy bonded to silicone duplex coatings

Flat-head studs, 7.2 mm diameter, were epoxied to 0.1–0.9 mm thick silicone layers attached to a rigid substrate. Pull-off tests were performed at nominally 1.5 N/s to establish critical pull-off forces and detachment modes at the epoxy–silicone interface. Most tests were performed on a two-layer coating consisting of a silicone top coat and a stiffer silicone bond coat. A few tests were performed with a single layer of transparent silicone on a glass substrate, which allowed video analysis of the interface during pull-off. Critical pull-off force, P c, decreased as the thickness of the coated layers increased. The thickness dependence of P c was shown to be in good agreement with a model presented by Kendall for pulling a rigid cylinder from a elastomeric glue layer, but modified to account for a two-layer elastomeric coating; P c varied as t *1/2, where t * is an effective thickness, which depends on the bulk moduli of the coatings as well as their thicknesses. The observed pull-off mode was peeling, which occurred by nucleation, growth and coalescence of multiple voids initiated inside the contact area.

Three-Dimensional Stability Analysis of Free Surface Flows: Application to Forward Deformable Roll Coating

Coating flows, with a few exceptions, need to be steady and two-dimensional flows. Moreover, the flow states need to be stable at the operating conditions chosen. The goal of stability analysis of coating flows is to determine the region in the parameter space at which the flow is stable and therefore the coated layer uniform. To determine the stability of liquid flows, a generalized eigenvalue problem has to be solved. This paper describes a formulation for a linear, three-dimensional stability analysis of free surface flows that reduces the size of the eigenproblem, decreasing the computational cost, with no further simplification, when compared with the methods reported in the literature. This formulation is used to study the instability that arises in film-splitting flows between counter-rotating rolls in a deformable gap. This flow instability leads to nonuniform coating characterized by a wavy thickness profile in the transverse direction. This patterning is usually referred to as “ribs.” This type of instability has received a lot of attention in the literature. However, all previous work has addressed the flow between two rigid rolls. Often, in practice, one of the rolls of a pair is covered by a layer of elastomer. The deformation of the roll cover alters the conformation of the gap, the pressure gradient at the film-split meniscus, and, consequently, the critical parameters at the onset of ribbing change. The results indicate how a deformable cover can be used to delay the onset of ribbing in forward-roll coating.

Finite element analysis of fluid—solid interaction in the metering nip of a metering size press

In the metering section of a metering size press, the coat weight and film uniformity are mainly governed by the flow in the metering nip which is delimited by two rotating rolls, one of which (the soft roll) is covered with an elastomer layer. In this region, the shape of the soft layer and the hydrodynamics depend on each other; the soft roll may deform owing to the stresses imparted by the fluid flow which in turn may be altered by this deformation. In this article, a 2D model is proposed for the solution of this fluid—solid interaction problem in the case of the reverse roll coating process. The fluid flow between the two co-rotating rolls is obtained from the solution of the Navier—Stokes equations and the soft roll deformation is predicted from a static analysis under the assumptions that the elastomer is incompressible and Hookean. Both the flow and the elasticity problems are solved using finite element code POLY2D ™ from RheoTek. Finally, the model is tested against experimental data obtained from a laboratory coater.

Chemical Imaging of Thermoplastic Olefin (TPO) Surface Architecture

In the automotive industry, ethylene−propylene rubber (EPR) is mixed with polypropylene (PP) to form a thermoplastic olefin (TPO) for use as car bumpers and fascia. An adhesion promoting primer, chlorinated polyolefin (CPO), is spray coated onto the TPO surface to increase adhesion of the base and clear coat paints to the low surface free energy TPO substrate. The surface morphology of rubber domains within the CPO-coated TPO substrate contributes strongly to the material characteristics, including impact resistance and adhesion properties. However, elastomer-phase analysis is challenging using traditional microanalysis imaging techniques. We employ fluorescence and Raman chemical imaging to characterize the TPO architecture in order to better understand the surface properties of coated TPO. Fluorescence imaging makes use of Nile red (NR), a fluorescent solvatochromic dye, solvated in the primer, which is effective in differentiating rubber from polypropylene on the basis of large variations in the fluorescence quantum efficiency. Confocal fluorescence chemical imaging performed on TPO coated with NR-doped CPO shows a thin (2−3 μm) layer of elastomer that has migrated to the TPO surface. Raman chemical imaging is in direct agreement with the fluorescence experiments by measuring the intrinsic vibrational signatures of CPO, EPR, and PP without the need for dyes or stains. Raman contrast is enhanced using cosine correlation analysis, a novel multivariate processing technique that provides chemical contrast on the basis of differences in spectral shape.

Long-Term Performance of Elastomeric Bridge Bearings

The effects of long-term service on bridge bearings composed of steel plates laminated between elastomeric layers, as placed on twin structures carrying the Route 400 Aurora Expressway over Route 16 and Conrail tracks in New York’s Erie County, are summarized. Expansion-joint bearings replaced as part of a recent rehabilitation project were recovered for evaluation and were found to be in generally good condition. New York’s current accelerated aging test procedures were evaluated by comparing mean ratings for these bearings (after simulated aging in their original 1969 acceptance testing) with results of similar tests conducted from 1992 to 1995 (after their removal from these bridges). An analysis of mean ratings from other 1969 acceptance tests is included, with similar tests repeated to determine the effects of the years in service. As a final step, the recovered bearings underwent further testing for conformance with other current specifications. The bearings, as originally installed on these structures, had problematic design, construction, and material properties, but nevertheless performed very well in service and were insensitive to these deficiencies.

Behaviour of lead-rubber bearings

Experimental work undertaken to investigate the behaviour of lead-rubber bearings under compression and a combination of compression and shear or rotation has been reported on elsewhere. However, it is difficult to determine the state of stress within the bearings in terms of the applied forces and the interaction between the lead plug and the steel shims and elastomeric layers. In order to supply some of the missing information about the stress-strain state within the bearings, an analytical study using the finite element method was carried out. The available experimental results were used to validate the model and although agreement was not as good as expected (on account of difficulties in modelling the lead plug), the analyses did provide some information about the state of the stress within the bearing.

撚りコードの屈曲疲労特性における曲率の影響

Mechanics of cords under bending is important to understand the fatigue failure mechanism of synchronous belts, because the fatigue damage is usually accumulated in the cords when the belt works. In this paper, we discussed the mechanical meaning of curvature in cord-bending. At first, the distributions of stresses which were initiated in cords were discussed by using FEM analysis. The FEM model of cords was constructed from seven fibers and elastomer layer between the fibers. The results showed that the shearing stress along the fiber-axis was highest in the elastomer layer and had the maximum value when the layer turned to the vertical direction against the neutral a is of the cord-bending. These results suggested us that the shearing stress was the main stress component for the cord failure. We then discussed the relationship between the shearing stress and the curvature by using a simplified mechanical model. The analytical result reasonably explained the FEM results and showed that the shearing stress increased in exact proportion to the curvature.

Analysis of contact mechanics for composite cushion knee joint replacements.

Recent research in the area of cushion form bearings for total joint replacements has primarily used thin, soft, elastomeric layers with similar elastic modulus to articular cartilage, bonded to rigid substrates. These are designed to promote the body's natural lubricants to separate the articulating surfaces and prevent wear. Applications to joint replacements have revealed that the abrupt change in stiffness between the soft layer and the rigid substrate and the relatively low strength of the interface resulted in high shear stresses and debonding of the soft layer from the substrate. The approach adopted in this study is to use components with a graded modulus or composite construction. The composite construction consists of a soft compliant layer of polyurethane and a second stiffer polyurethane layer thought to be rigid enough to mechanically interlock to a metallic tibial tray. In this composite structure the deformation of the more rigid polyurethane underlay may generally influence the stress distribution and deformation in the softer upper layer and at the interface between the two materials. A simple analysis technique is presented in the present study where the composite double layer was approximated as an equivalent modulus single layer. Single layer theory, which is readily available in the literature, can then be used to determine the contact parameters, including the maximum contact pressure and the contact radius, for the composite structure. By varying the layer thicknesses and material properties of both the soft surface layer and the stiffer structural support layer, the magnitudes and locations of stresses can be controlled. Results of a parametric stress analysis are presented to assist in the selection of the most appropriate composite layers for cushion knee designs. A 4 mm thick surface layer with an elastic modulus of 20 MPa and a 4 mm thick structural support layer with an elastic modulus of 1000 MPa were considered suitable for this application.

Flows in Forward Deformable Roll Coating Gaps: Comparison between Spring and Plane-Strain Models of Roll Cover

Roll coating is distinguished by the use of one or more gaps between rotating cylinders to meter a continuous liquid layer and to apply it to a continuous flexible substrate. Of the two rolls that make a forward-roll coating gap, one is often covered by a layer of deformable elastomer. Thin films can be obtained without the risk of clashing two hard rolls. Liquid carried into the converging side of the gap can develop high enough pressure to deform the resilient cover, which changes the gap geometry and thus alters the velocity and pressure fields. The complete understanding of the flow in this situation is vital to the optimization of this widely used coating method; however, this elastohydrodynamic action is not well understood. The situation is similar to what is called the Soft-Elastohydrodynamic Lubrication regime (Soft EHL); however, the range of minimum distance between the rotating rolls, roll speed, and therefore flow rate through the gap in the roll coating process is one to three orders of magnitude larger than the typical values reported in previous work on Soft EHL. Earlier works on deformable roll coating analyzed the action with both the lubrication approximation and the full Navier–Stokes solution and different one-dimensional models of roll cover deformation. In order to test the accuracy of the past approaches, and to evaluate the relationship between the empirical constant used in the one-dimensional model to the relevant physical parameters, a complete, two-dimensional formulation has to be employed for both the liquid flow and the solid deformation. In this work, the flow between a rigid and a deformable rotating roll was examined by solving the complete Navier–Stokes system coupled with a non-linear plane-strain model of the roll cover deformation. The approximate and computationally cheaper approach is evaluated in which the compliant wall is represented by an array of radially-oriented Hookean springs. The equation system was solved by the Galerkin/finite element method; the resulting set of non-linear algebraic equations of the fully coupled problem was solved by Newton's method with initialization by pseudo-arc-length continuation as parameters were varied. Results show how roll deformation affects the total flow rate and forces on the rolls and illustrate how a deformable roll can be used to obtain thin coated layers with much less sensitivity to roll runout than those obtained with rigid rolls.

Turbulent flow noise estimate by use of a velocity sensor embedded in a three-layered composite structure

A theoretical model was developed to evaluate flow noise levels received by a velocity sensor that is embedded within an outer decoupler mounted on a low acoustic impedance surface. The model, a three-layer structure, consists of a layer of nonvoided elastomer (outer decoupler), which covers a layer of microvoided elastomer (inner decoupler) backed by an elastic plate. The rubberlike material of the outer decoupler is designed to reduce the flow noise generated by turbulent boundary layer pressure fluctuations, and the low acoustic impedance (soft) material of the inner decoupler is configured to reduce the flexural wave noise generated by the vibration of the elastic plate. The upper surface of the outer decoupler is in contact with turbulent flow (water) and the lower surface of the backing plate is in contact with semi-infinite space (air). This work uses the model of the three-layer composite structure for the analyses of both the flow noise and signal levels received by the embedded velocity sensor. The final noise levels are the equivalent plane-wave levels, which were obtained by subtracting the signal levels from the flow noise levels. [Work supported by the Office of Naval Research, Code 321SS.]

Reduction of structure-borne noise using an air-voided elastomer

A theoretical model was developed to evaluate the reduction of structure-borne noise that is generated by a line force applied on an infinite plate using an air-voided elastomeric baffle. The vibrating plate is covered with an elastomeric baffle layer to reduce the noise generated by the structural vibration. The vibrating plate is perfectly bonded to the elastomeric baffle layer. The outer surfaces of the vibrating plate and the elastomeric baffle are in contact with air and water, respectively. The analysis for modeling is based on the theory of elasticity and pertinent boundary conditions. Effects of various parameters such as baffle layer dimensions and material properties on the noise reduction are presented.

Deformable roll coating flows: steady state and linear perturbation analysis

Roll coating is distinguished by the use of one or more gaps between rotating cylinders to meter a continuous liquid layer and to apply it to a continuous flexible substrate. Of the two rolls that make a forward or reverse roll coating gap, one is often covered by a layer of more-or-less deformable elastomer. Liquid carried into the converging side of the nip can develop high enough pressure to deform the resilient cover, which changes the nip profile and thus alters the velocity and pressure field. This elastohydrodynamic coupled action is not yet well understood. Theoretical modelling has to take into account the viscous flow, the roll deformation and the free-surface effects in order to predict the flow behaviour.In this work the flow between a rigid and a deformable counter-rotating roll that shares the same angular speed is described by the lubrication approximation together with a viscocapillary model, based in the film-flow equation, for the film-split region. The deformation of the elastomer layer is modelled by Hookean springs oriented radially, which constitute a one-dimensional model. The stability of the system to transverse perturbation is analysed by examining the time-dependent response to infinitesimal disturbances in order to identify those that grow fastest.The corresponding system of equations is solved by Newton's method with first-order continuation. The relationship between coating thickness, operational parameters (loading force, gap setting, roll velocities, etc.), liquid properties and the properties of the cover is reported, as well as the critical capillary number for onset of ribbing and wavelengths of the ribbing pattern predicted by the mathematical model. The results indicate how a deformable cover may be used in order to delay the onset of ribbing for a desired coating thickness.In order to validate the theoretical predictions of the viscocapillary/Hookean spring model, the symmetric film-split flows between a pair of rigid rolls and a pair consisting of a deformable roll and a rigid one were also analysed experimentally.

Metallized polymer fibers as leadwires and intrafascicular microelectrodes

We have developed a process for producing fine, very flexible microwires suitable for use as small signal leadwires or nerve electrodes. The process incorporates metallization of high-performance monofilament polymer fibers to yield electrically conductive fibers with greatly improved flexibility over solid metal wires of similar strength. The metallization layers are produced by serial vacuum deposition of a 0.3 μm thick coating of three metals, titanium-tungsten (Ti/W), gold (Au), and platinum (Pt), onto monofilament, poly- p-phenyl-terephthalate aramid fibers (Kevlar ®). The metallized fibers are then insulated with an approx. 1 μm thick layer of silicone elastomer. The result is a microlead with high electrical conductivity (linear resistance = 30 Ω/cm), desirable interfacial properties, excellent mechanical stability and extremely high flexibility. These physical characteristics are appropriate for application as signal leadwires or recording/stimulating electrodes where small size and high flexibility are paramount. In this paper we report on the electrical and mechanical properties of these metallized fibers and demonstrate their use as intrafascicular electrodes for recording multi-unit neural activity in feline peripheral nerves.

Acoustic plane-wave reception by a single-axis velocity sensor aligned normally on an air-voided elastomer backed by an elastic plate

A theoretical model was developed to evaluate the acoustic plane-wave reception by a velocity sensor placed near an air-voided elastomer baffle layer backed by an elastic plate. The air-voided elastomeric baffle layer is designed to reduce the noise generated by the motion of the elastic plate and enhance the acoustic wave received by a velocity sensor with its axis perpendicular to the layer. The plate is perfectly bonded to the elastomeric baffle. The outer surfaces of the elastic plate and the elastomer baffle are in contact with air and water, respectively. The analysis for modeling is based on the theory of elasticity and pertinent boundary conditions. Computations were made using different properties for the elastomer. These computations show that by proper material and thickness selection the acoustic reception may be varied significantly as a function of frequency. [Work supported by the Office of Naval Research, Code 321SS.]