Structure Design Of Stainless Steel Coronary Stent And Dynamic Stress Numerical Simulation

Coronary stents as important medical devices are used in treating occlusive cardiovasculardiseases. It is expanded in the atherosclerotic blood vessel and keeps blood flow. Ideal stentdesign has attracted a lot of attention all over the world at the present. Based on the fundamentaltheory of finite element analysis method, in this thesis, the geometrical configuration of coronarystent were designed and optimized, the fatigue performance of stent were analyzed and evaluated,and the influences of stent planting on haemodynamics in coronary artery was investigated.This thesis focused on the numerical simulation about the mechanical process behavior ofstent expansion. First, it described the basic theory of finite element method and the applicationof nonlinear finite element method in stent design. Then the three-dimensional solid modelingsoftware of Pro/Engineer with the finite element analysis (FEA) software of ANSYS were usedto construct three-dimensional coronary stent models with “peanut” units. The stress-strain,recoil of radial diameter and length, percentage of metal coverage and flexibility performance ofthe stents were calculated and analyzed. The result shows that designed stent has a better recoilrate performance of radial diameter and length. Maximum residual stress occurs at the locationsof the connection between single unit and circumferential link struts after unloading. Theresidual stress can reduce the value of a small amount by extending the unloading timeappropriately.As an implantable medical device, coronary stent should have enough life longer than10years. In human bodies, the stent bears high-cycle stress, which is long-term blood flow incoronary artery to withstand the impact of more than400million cycles of the radial pulsesystolic and diastolic pressure. The stent should have a certain anti-fatigue properties in order toensure safe and reliable work in their lifetime. The thesis used ANSYS/Fe-safe software toestablish a complete research system of the fatigue analysis for a coronary stent in stent structure,material property, processing characteristics work environment and other aspects. The fatiguelife distribution and safety factor are obtained through the fatigue calculation under thesuperimposed load of all stress loadings. The result shows the part near the connection betweenstent unit and circumference strut has a lower fatigue life value which agrees with the actualsituation, and the locations is the stress concentration area during expanding. In addition, thereliability analysis of the fatigue life is completed after the reliability calculation of fatigue performance provided atheoretical basis for fatigue design of a stent.Computational fluid dynamics (CFD) is an effective method to predict fluid motion. Basedon the fundamental fluid mechanics theory, a vascular haemodynamics model in the stentedvessel was created in this thesis. The effect of stent design parameters on the haemodynamicswere studied by means of CFD technology. Fluent software was used to calculate the coronaryartery blood flow in three-dimensional computational simulation. And the analysis was carriedout under both steady and transient conditions. During the simulation a number of assumptionsabout the blood flow characteristics, such as the vessel was assumed to be a rigid wall and theblood was regarded as Newtonian fluid were used. The effects of stent structure parameters onhemodynamics were obtained during the steady calculation. The stent implantation has someinfluence on the wall shear stress, the velocity of blood flow and the flow pattern. The bloodvessels proximal to stent have low value of wall shear stress and there were flow stagnationphenomenon here. Vortex phenomenon could be observerd in this location. Low wall shearstress is more likely to cause restenosis and other arterial lesions, so the stent should be designedto minimize the low shear stress zone produced by stent struts. In the transient simulation, theblood inlet flow was defined as pulsatile flow, and the simulation results could illustrate the realdynamics of intravascular blood flow. The wall shear stress of the stent vessel changedperiodically with the inlet velocity.