A device for the production of anisotropic fibre reinforced tubes

Within the scope of the atherosclerosis project research is done on the genesis of this condition. The importance of hemodynamica1 factors on the development of atherosclerotic lesions is generally recognised. Also with respect to the diagnostics of atherosclerotic disease, it is of great clinical interest to gain insight in the complicated flow field in arteries and to investigate the influence of arterial mechanical properties on local flow phenomena. In this situation in vitro experiments can be very helpful. In this study a cylindrical-orthotropic tube showing nonlinear viscoelastic behaviour was developed. The model was made of EPDM K520 rubber reinforced with lycra fibres. The rubber was viscoelastic and the fibres introduced nonlinearity and anisotropy. Firstly an isotropic tube was made and in a second phase the lycra fibres were wound around it. The quality of the tube without fibres was very good and its thickness was quite homogeneous along its whole length. The quality of the anisotropic model was satisfactory, but a new winding machine shouid be designed to increase its homogeneity. The pitch and the number of fibres per unit of length were not constant and moreover their were wound with different pre-strains. In spite of these problems, the model showed nonlinear and viscoelastic behaviour. The stress-strain behaviour of the anisotropic tube was calculated by means of a mathematical model. The model underestimated the stress in the composite but it gave a good qualitative description of the stress-strain relation. No definitive conclusions can be drawn about the validity of the model until more information about the composite parameters will be known. This will be possible once a new machine that enables to control the pre-strain of the fibres will be made. The mechanical properties of the anisotropic model were confronted with those of the arterial wall. The model was too stiff both at lower and higher strains. The stiffness of the model can be correct by using another EPDM rubber (DSM, K320) which is less stiff. The use of 76 dtex lycra fibres, instead of the 78 dtex lycra fibres, will render the model less stiff too. Another advantage is that using this type of fibre more homogeneous tubes can be obtained.