Lentz, Charlotte
[UCL]
Jacques, Pascal
[UCL]
Abstract Metallic bioresorbable stents have gained attention in recent year. They are a good alternative to permanent metallic implants. In fact, the mechanical support of a stent is needed for about 6 to 12 months. After this period of time, the stent is no longer in use and its permanent presence in the body can cause medical complications. Those limitations are avoided when the stent degrades over time. However, the complex biological environment makes it difficult to predict the corrosion behaviour of such implants. Yet, there are several mechanical requirements that the stent must meet. The implant must provide radial strength to face the pressure of the vessel wall. It should also be easely deliverable. So, the stent must have good flexibility. In addition to that, the modification of the surface of a stent can induce a better control of the tissue compatibility, along with an improvement of the healing process the vessel. Some studies have demonstrated that grooved surfaces enhanced the migration of endothelial cells. Also, a microscopic pattern design on the surface of the stent could allow the control of the corrosion behavior of the metallic implant, avoiding premature loss in stent scaffolding support or too long and risky presence of the implant. Hence, trough this study, the impact of geometrical imperfections on the mechanical properties of specimens (stainless steel 316L) has been examined. To do so, uniaxial tensile tests have been performed using digital image correlation (DIC). Thereby, the standard mechanical properties from the stress-strain diagram and also the strain distribution along the specimens have been investigated. Various reduction of cross-sectional area in the central region of round specimens have been machined. Then, different groove depth on sheet specimen have also been tested. As a result, it appears that the mechanical properties of geometrically imperfect specimens decreases. Especially, the elongation at fracture of the specimen, so its ductility. In addition, greater imperfections lead to higher rate of concentration of strain in the imperfect region. The limiting strain outside of the imperfection also decreased with larger imperfection. Furthermore, the sheet metal stretching shows that a groove defect controls completely localized necking as the ratio of thickness at the groove and outside of it, is smaller than 95.90 %. However, a groove defined by an imperfection factor equal to 96.63 %, does not control localized necking anymore, as the most strained area is the uniform region of the specimen. Finally, in accordance with the theory of Chan & al [1], the imperfection initiates localized necking when it reduces the limiting strain below the value predicted by Hill’s theory.
Bibliographic reference |
Lentz, Charlotte. Analysis of the tensile properties of geometrically imperfect specimens of stainless steel 316L Context of bioresorbable stent applications. Ecole polytechnique de Louvain, Université catholique de Louvain, 2020. Prom. : Jacques, Pascal. |
Permanent URL |
http://hdl.handle.net/2078.1/thesis:26773 |