Thesis

Compressive mechanical behaviour of nitinol wires used in aortic stent grafts

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Awarding institution
  • University of Strathclyde
Date of award
  • 2022
Thesis identifier
  • T16303
Person Identifier (Local)
  • 201753937
Qualification Level
Qualification Name
Department, School or Faculty
Abstract
  • The Anaconda endovascular stent graft is a medical device designed to treat abdominal aortic aneurysms, composed of a nitinol wire structure and a fabric graft. The graft is required to undergo significant deformations before and after the implementation of the device. This thesis addresses the material characterization of thin nitinol wire taking advantage of the test methods already established for tensile and compressive behaviour, mainly focussing on the compressive response. The tensile behaviour here presented consists of a preliminary study of the localised deformation on nitinol wire. The mechanical characterization of the wire under compression starts with the implementation of digital image correlation (DIC) technique to measure the sample strain field. The compressive test method was found to be unsuitable for compressive loading, where it was not possible to replicate the compressive tests, validate the DIC technique and does not hold the sample securely during the compressive test. This finding led to a complete change of the research goals and paved the way for the development of a test method for fine nitinol wire. A compressive test method is therefore proposed, which is shown to be valid under compressive loading and for obtaining the compressive material parameters as input to the numerical models. A parametric study was undertaken to understand the optimum ratio between the length and diameter of the sample. An attempt at using this method in a temperature-controlled environment is also presented. The application of the Auricchio constitutive model, implemented in the finite element software Abaqus, is considered. A comparison with an alternative non-commercial model is also studied and reported along with some suggested improvements. This results in better prediction of the asymmetric behaviour of nitinol wire under compressive and tensile loading and is shown to be very promising in physically representing the bending behaviour of nitinol wire.
Advisor / supervisor
  • Nash, David
  • Wheel, Marcus
Resource Type
DOI
Date Created
  • 2021

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