An Elastomeric Energy Storage System to Improve Vehicle Efficiency.

Most regenerative braking systems studied hitherto have made use of batteries, tlywheels and hydraulic accumulators. The present study has investigated the use of elastomers for such systems. The ability of elastomers to store large amounts of energy, together with the fact that this energy can be recovered quickly, makes them attractive materials for propulsion devices and inherently simple to engineer. Theoretical and experimental research has shown that the development of an elastomeric regenerative braking system does appear to be technically feasible. The predicted rubber characteristics have been compared with the known characteristics of a conventional engine. The results show that the tractive effort produced by the elastomer is capable of matching the characteristics of the engine considered in this work. Rates of input and output energy have also been calculated to determine the process of energy storage and retrieval throughout a typical driving cycle. The energy store appears to be capable of reproducing many stages of the three driving cycles considered. When there is insufticient energy in the system, power boosts from the conventional engine are required. In order to increase the overall savings achieved by the system, the engine was 'replaced' by one which had force (and therefore power) characteristics of one half of the conventional engine initially considered. It was found that the reduced power engine was sufficient to supply the extra power boosts as required. In addition to reduced engine and brake wear, fuel consumption and emissions have been shown to be drastically reduced. If these values could be achieved in practice, the benefits of such a system are immediately apparent. The potential financial savings available to the car user corresponding to the decrease in fuel consumption would provide a strong incentive. Environmentally the benefits are two fold, firstly the reduction in pollution emissions means cleaner air and has an impact on global warming, and secondly reduced fuel consumption means that fossil fuel reserves may last considerably longer than currently predicted thus reducing the immediate need for alternatives sources

Application of activated barrier hopping theory to viscoplastic modeling of glassy polymers

YesAn established statistical mechanical theory of amorphous polymer deformation has been incorporated as a plastic mechanism into a constitutive model and applied to a range of polymer mechanical deformations. The temperature and rate dependence of the tensile yield of PVC, as reported in early studies, has been modeled to high levels of accuracy. Tensile experiments on PET reported here are analyzed similarly and good accuracy is also achieved. The frequently observed increase in the gradient of the plot of yield stress against logarithm of strain rate is an inherent feature of the constitutive model. The form of temperature dependence of the yield that is predicted by the model is found to give an accurate representation. The constitutive model is developed in two-dimensional form and implemented as a user-defined subroutine in the finite element package ABAQUS. This analysis is applied to the tensile experiments on PET, in some of which strain is localized in the form of shear bands and necks. These deformations are modeled with partial success, though adiabatic heating of the instability causes inaccuracies for this isothermal implementation of the model. The plastic mechanism has advantages over the Eyring process, is equally tractable,and presents no particular difficulties in implementation with finite elements.F. Boutenel acknowledges an Erasmus Programme Scholarshi

Analytically Solvable Asymptotic Model of Atrial Excitability

We report a three-variable simplified model of excitation fronts in human atrial tissue. The model is derived by novel asymptotic techniques \new{from the biophysically realistic model of Courtemanche et al (1998) in extension of our previous similar models. An iterative analytical solution of the model is presented which is in excellent quantitative agreement with the realistic model. It opens new possibilities for analytical studies as well as for efficient numerical simulation of this and other cardiac models of similar structure

Theoretical and finite-element investigation of the mechanical response of spinodal structures

noIn recent years there have been major advances in our understanding of the mechanisms of phase separation in polymer and copolymer blends, to the extent that good control of phase-separated morphology is a real possibility. Many groups are studying the computational simulation of polymer phase separation. In the light of this, we are exploring methods which will give insight into the mechanical response of multiphase polymers. We present preliminary results from a process which allows the production of a two-dimensional finite-element mesh from the contouring of simulated composition data. We examine the stretching of two-phase structures obtained from a simulation of linear Cahn-Hilliard spinodal phase separation. In the simulations, we assume one phase to be hard, and the other soft, such that the shear modulus ratio ... is large (... ). We indicate the effect of varying composition on the material modulus and on the distribution of strains through the stretched material. We also examine in some detail the symmetric structures obtained at 50% composition, in which both phases are at a percolation threshold. Inspired by simulation results for the deformation of these structures, we construct a "scaling" theory, which reproduces the main features of the deformation. Of particular interest is the emergence of a lengthscale, below which the deformation is non-affine. This length is proportional to ... , and hence is still quite small for all reasonable values of this ratio. The same theory predicts that the effective composite modulus scales also as ..., which is supported by the simulations

Fibre orientation

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Fibre orientation structures and their effects on crack resistance of injection moulded transverse ribbed plate

NoAn extensive study of the fibre orientation structures developed in a transverse ribbed plate during injection moulding, and the use of these structures to investigate the effect of local fibre orientation state on crack initiation resistance, is reported. The fibre orientation results for the ribbed plate, measured using large area image analysis system developed at Leeds University, showed that after an initial settling down period, the central core region, where the fibres are aligned perpendicular to the flow direction, decreased in size monotonically, with an associated monotonic increase in the outer shell regions, where the fibres are aligned preferentially along the injection direction. Interestingly, the level of orientation in the two regions remained almost constant: only the proportions of the two regions were found to change with flow length. Across the plate, close to the gate, the central core region was found to have a lens-like shape, while at the other end of the plate the core was thinner and also consistent in thickness across the sample width. The transverse rib was found to cause little disturbance to the fibre orientation of the base plate. The different proportions of the shell and core regions at different locations over the ribbed plate provided an ideal case to test the proposition of Friedrich that the crack resistance of a short fibre reinforced material depends on the number of fibres that are perpendicular to the crack tip. The impact test results gathered in this way confirmed this hypothesis of Friedrich