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Applied mechanics, Materials engineering, Medical engineering
Flexible polyurethane foam is an open-celled polymeric material that exhibits strain rate and temperature effects. It has found various applications in areas including the packaging, medical, sports, aerospace and aeronautical industries. Polyurethane foam is ubiquitous in seating applications and finds particular use in specialised wheelchair seating where customised seating solutions are required which can provide proper comfort and support without the risk of developing pressure ulcers. Proper seating design is critical for users if this problem is to be avoided, but a lack of quantitative knowledge of this material’s behaviour has limited its effectiveness. The objectives of the work presented here are twofold. Firstly to characterise the behaviour of the materials and secondly to develop a validated numerical model which can be used to increase understanding of in-service behaviour. Three commonly used foams having different densities and viscoelastic properties were subjected to compression in a uni-axial test machine fitted with a custom-built temperature chamber. The results of these tests were analysed and are presented to aid in the characterisation of these materials. The effects on the stiffness of foam of different additives, densities, strain rates and temperatures were noted. A material model was developed to simulate indentation, in which compression and shear were the predominant modes of deformation. The results from the uni-axial characterisation tests were employed to determine material constants for Ogden’s constitutive model for compressible materials. Simple shear tests were also conducted with a custom-built dual lap shear tester and material constants were then determined for this mode of deformation. A curve-fit was developed which was a compromise between both modes of deformation to provide increased material model robustness. To validate the accuracy of the developed model, uni-axial indentation of standard polyurethane seating foam was then modelled using Finite Element (FE) code. Results show a high degree of accuracy.
Briody, C., Duignan, B., Jerrams, S.: Characterisation, material modelling and simulation of flexible polyurethane foam. Proceedings of the International conference on Materials, Tribology and Recycling (MATRIB). Vela Luka, Croatia, 29 June – 01 July, 2011.