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No description available.

No description available.

No description available.

The frictional behaviour of rubber is a topic of great interest and importance due to the invaluable uses of rubber in industry. The very particular behaviour of rubber also makes rubber friction a fascinating subject matter. Despite this it is still a topic not well understood. Previous studies have attempted to link the fracture mechanics of rubber crack propagation to the adhesive friction of rubber. The feasibility of such an approach to the adhesive friction of a rough rubber against a smooth surface, a configuration which can occur in various situations such as rubber seals or windscreen wipers, has been investigated. Rolling friction, described well by a fracture-like peeling process, is used to evaluate the viscoelastic dependence of sliding friction for various combinations of surfaces. A novel use of rubber is proposed as a material for particles to be used for jamming based soft robotics applications. This area of soft robotics is comparatively new and the materials that are being used at present are neither well established nor have been examined in great detail. Rubber would offer a material easily manufactured to desired shapes and dimensions with a wide range of moduli allowing modification to suit specific applications. The effect of jammed rubber particles on the response of a jammed packing to an externally applied load is examined. The evolution of inter-particle forces is studied using a rheometer configuration. Finite element techniques and modelling are employed to study the rubber in more detail.

Nearly five million Americans are living with heart failure and 550,000 new cases are diagnosed each year in the US. Amongst the new approaches to develop a better solution for Congestive Heart Failure, Ventricular Recovery (VR) holds the most promise. A team, under the guidance of Dr. Criscione in the Cardiac Mechanics Lab at Texas A&M University, is currently developing an investigative device which aims to assist in VR by restoration of physiological strain patterns in the myocardial cells. The contribution of this thesis has been towards the development of a molding apparatus that yields a polymeric membrane whose shape, when inflated, is similar to the shape of the human heart. This membrane would surround the epicardial surface of the heart, when used for the device being discussed and in particular for the prototypes being developed. Contribution also includes a testing apparatus that measures the inflation of a membrane and simulation to predict the behavior of isotropic ellipsoids upon inflation. After unsuccessful implementations of two processing techniques, the successful design, fabrication implementation and attachment method meets the design criteria and is based on a thermoforming technique. Inflation profiles for membranes developed using this technique were studied at different pressures, with the axis length as variable. At 1kpa, which is the normal coronary arterial pressure, the membrane with an axis length of 140mm was found to show a shape which is similar to the shape of the human heart. In order to better understand and predict the shape an isotropic ellipsoidal membrane would take upon inflation without experimentation, simulations were carried out. Successful conversion of ellipsoidal geometry, with a few degrees of freedom as parameters, aided in simulation.

<p> It is shown that the experimentally determined deflectional behavior of certain elastomer-lined sleeve bearings under static radial loads can be modeled to some extent by the compressive behavior of flat elastomeric slabs.</p> <p> An equation for the thermal bearing-bore change is developed using the conventional theory for the thermoelasticity of homogeneous cylinders. Some experimental results agree fairly well with this equation. An equation for the bore contraction due to liquid swell is developed in terms of thermoelasticity.</p> <p> Minimizing the lining thickness is recommended for minimizing both the radial deflections and the bore changes.</p> <p> An analysis is made of the frictional forces involved with the interference fit between the lining and its housing.</p> <p> Areas for further investigation are suggested.</p> / Thesis / Master of Engineering (MEngr)

Seismic isolation is a method of earthquake resistant design which has been proven to effectively reduce the damaging effects of earthquakes on buildings as well as the contents within them. However, traditional implementation of an isolation system tends to be expensive. For new construction, rigid diaphragms above and below the isolation layer and construction of a seismic gap contribute to expenses, while retrofit applications also require excavation beneath the building and may need extensive foundation work. To mitigate these major costs bearings may be placed on the tops of columns, forgoing the construction of a seismic gap, additional rigid diaphragm, and foundation work. However, columns under the isolation layer may be flexible, changing the bearing end conditions traditionally assumed. To investigate the effects of flexible end conditions on elastomeric bearings, an analytical model that accounts for translation and rotation of both endplates was developed based on Haringx's theory. The derivation accounts for compressibility of the rubber and results in a simple stiffness matrix. To evaluate the model, an experimental program testing column-bearing subassemblies under quasi-static cyclic conditions was conducted. Experimental findings show that flexible end conditions can significantly reduce the lateral stiffness of elastomeric bearings. Simulations with the theoretical model compare well under small deformations, but elastic softening of the moment-rotation relationship causes theoretical results to diverge from experimental with larger endplate rotations. The effectiveness of column-top isolation as a retrofit strategy was investigated through nonlinear time history analyses of a moment resisting frame designed to the 1965 National Building Code of Canada and retrofitted with column-top isolation. The frame was simulated under ground motions representative of current hazards and showed that the retrofit resulted in significant reductions in interstory drifts and floor accelerations. Yielding was observed throughout the original frame under maximum considered earthquakes, while the retrofit frame remained elastic. / Thesis / Master of Applied Science (MASc)

Proton Exchange Membrane (PEM) fuel cell stack requires gaskets and seals in each cell to keep the hydrogen and air/oxygen within their respective regions. The stability of the gaskets is critical to the operating life as well as the electrochemical performance of the fuel cell. Chemical degradation of five elastomeric gasket materials in a simulated and an aggressive accelerated fuel cell solution at PEM operating temperature for up to 63 weeks was investigated in this work. The five materials are Copolymeric Resin (CR), Liquid Silicone Rubber (LSR), Fluorosilicone Rubber (FSR), Ethylene Propylene Diene Monomer Rubber (EPDM), and Fluoroelastomer Copolymer (FKM). In order to assess the durability of the materials, observation of chemical degradation level, dynamic mechanical analysis, and micro-indentation test were adopted in this study. This experimental result showed that the influence of the chemical reaction could affect the material surface condition. Also, the chemical reaction could affect material¡¦s mechanical properties had been changed over the soaking time. By considering the level of chemical degradation and mechanical properties, the experimental results showed that EPDM is recommended as the best choice of sealing material for using in a PEMFC.

Within pressurised Metered Dose Inhalers (pMDIs) the contact between the valve components and elastomeric seals is of major significance, representing the main contributory factor to the overall system frictional characteristics. Therefore, the seal performance is extremely important and must be optimised to meet the contradictory requirements of preventing leakage and allowing smooth actuation. The environmentally driven trend to HFA formulations as opposed to CFC based ones has deteriorated this problem due to poor lubrication conditions and it has, consequently, increased the frictional losses during the pMDI actuation (hysteresis cycle). Research has been conducted into the key areas of the inhaler mechanism. As such, the contact pressure distribution and resulting reactions have been investigated, with emphasis on the correct treatment of the elastomer (seal) characteristics. The modelling of the device has been conducted within the environment of the multibody dynamics commercial software ADAMS, where a virtual prototype has been built using solid CAD geometries of the valve components. An equation was extrapolated to describe the relation between the characteristics of the ultra thin film contact conditions (sliding velocity, surface geometry, film thickness and reaction force) encountered within the inhaler valve and integrated into the virtual prototype allowing the calculation of friction within the conjuncture (due to viscous shear and adhesion). The latter allowed the analysis and optimisation of key device parameters, such as seal geometry, lubricant properties etc. It has been concluded that the dominant mechanism of friction is adhesion, while boundary lubrication is the prevailing lubrication regime due to the poor surface roughness to film thickness ratio. The multibody dynamics model represents a novel multi physics approach to study the behaviour of pMDIs, including rigid body inertial dynamics, general elasticity, surface interactions (such as adhesion), hydrodynamics and intermolecular surface interactions (such as Van der Waals forces). Good agreement has been obtained against experimental results at component and device level.