Finite Element Analysis And Fatigue Study Of Ti-Ni Vascular Stent

As the development of industry and the change of the ecological environment, the incidence of vascular disease is increasing. Aortic dissection appears and expands, as a result, the false lumen emerges. It will make patients chest pain and even die, which affects people’s healthy seriously. Implanting the Ti-Ni shape memory alloy vascular stent into lesions part of body’s vascular has been an important treatment. The stent can support the cloth integrate closely with vascular intima to prevent the blood seep into the false lumen and guarantee the normal supply of the blood. The significant therapeutic effect makes its high needs, meanwhile how to improve the stents’performance attracts more attention gradually. Good fatigue resistance is required to endure the pulsating load. That the special structure of the stent makes it complicated to test its mechanical and fatigue property, as a result, using the finite element to analyze the stent has become the research hot spot.The research objective of this paper is analyzing the Ti-Ni thoracic aortic vascular stent produced by Grikin Advanced Material Co with the finite element analysis. In the research the Ansys software was used to simulate the mechanical compressing process and service condition of different size of stents. Then Goodman principal was utilized to appraise the fatigue lifetime, with doing a fatigue test in vitro to verify the theoretical analysis. It would guide the stent design and make research job of the stent more scientific.From the result of simulation we could find that the element type and the material parameters we chose in the analysis could accurately indicate the mechanical property of the alloy. By analyzing the stress nephogram, we could find the max von mises stress located in the internal surface of the stent’s bending part, which reveals that this part is the most dangerous and possible failure area.From the compressing simulation, it was found that the value of the max von mises stress increased with the out diameter expanding for the stents whose wire size was 0.40mm、0.45mm、0.45mm. Larger out diameter means the larger deformation of the stents with the same decrement, which goes against the fatigue property. Other structure parameter should be changed to control the deformation during the design.The mean stress and alternating stress of stents in service condition were put into Goodman diagram and found the points were under the fatigue curve, which illustrated that the stents were safe in theory.380 million pulse fatigue test was carried on the chosen stent by the fatigue machine. The result indicated that there was no fracture line in the stent and it was intact, which verified the simulation’s rationality.By contrasting the influence on the safety factor for different structure parameter, it was found that the safety factor was smaller with a larger out diameter by controlling the other two variable. While the wire diameter and the period number changed, the three factors may exist interactive influence.