Finite element modelling of the expanson of small tubular parts by internal pressure
Chua Sing Ngie, David (2002) Finite element modelling of the expanson of small tubular parts by internal pressure. PhD thesis, Dublin City University.
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A stent is a device that is used to support arterial walls to alleviate the blockage of arteries by plaque. The slotted tube stent is one of the most common stent designs being widely used in many patients today. The amount of stent implantations is growing each year and for this it is becoming increasingly important in interventional cardiology. One of the reasons is that the use of stents has proved more effective in the therapy of coronary stenosis. However, it is evidenced that the success of the stent implantation is limited by re-stenosis, which is discussed almost entirely in terms of medical and biological reasons.
This work is concerned with investigating the deformation mechanism with variable conditions during slotted tube expansion processes using numerical simulation. The simulations were run and analysed using commercial finite element software. A nonlinear explicit solution method was used in each case. The processes chosen for simulation were: slotted tube expansion without balloon catheter, slotted tube expansion with balloon catheter, scaling the stent size, stent production defect and slotted tube expansion with the presence of artery and plaque. A number of process parameters were varied for balloon catheter (i.e. balloon length, thickness and friction factor) and the subsequent effects on the process were identified. Some trial experimental tests were carried out to verify the finite element results from the computer simulations.
From the results obtained it was concluded that higher rate of pressure increase results in higher stresses in stent for similar levels of expansion. Deployment of higher magnitude pressure might increase the expansion in radial direction but it does not necessarily increase the uniformity of the slotted tube. Appropriate balloon length has to be chosen to obtain a uniform expansion. Friction could reduce the foreshortening of the stent. When scaling down the stent, displacement deceases proportionally for similar deployment pressure and stent geometry. It was found from the simulations that the tubular stent is not very sensitive to imperfections. Altering sent strut configuration and number has practical effects on the clinical use of vascular stents, as the magnitude of expansion will change. The deformation characteristic of the slotted tube during deployment is affected by the presence of artery and plaque.
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