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Baloon_Elasticity_Analysis_Experiment_2007 - E P2 IA Mats...

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EP2 IA Mats. & Min. Sci. - E: Mech. Behaviour of Solids - Practicals Guide EPG13 TWC - Lent 2007 Rubber Elasticity 1. Background There are two parts to this practical, which can be carried out in either order. Both involve experimental study of the equations of rubber elasticity. In the first part, the relationship between the size of a spherical balloon and the pressure within it is explored using a simple manometer arrangement. The results allow an estimate to be made of the cross-link density within the rubber of the balloon. In the second part, a long cylindrical balloon made of a similar rubber is subjected to uniaxial tension and is then heated. This allows both the cross-link density to be measured and the observed dependence of stiffness on temperature to be compared with theory. 2. Experimental Procedures 2.1 Inflation of a Spherical Balloon Firstly, the balloon is completely inflated, using a bicycle pump. This must be done while the bung is placed in the end of the U-tube, in order to ensure that the manometer fluid (coloured water) is not ejected by the pressure pulses associated with operation of the pump. Once the balloon is fully inflated, the tap is closed, so that air cannot escape from the balloon, and the bung is removed in order to allow the trapped air out and the internal pressures to equalise. Fig.1 Photograph of the apparatus for studying the pressure-size relationship in a spherical balloon.
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