Practicability and Limitations of Finite Element Simulation of the Dilation Behaviour of Coronary Stents

After first implantation of a metallic stent into cardiac vessels in 1986 stent implantation has become a standard technique for treatment of coronary heart disease. During implantation of balloon‐expandable stents, the structure of the stent undergoes high plastic deformation. Despite the fact, that stents are used for more than 15 years nearly no information about the mechanical and micro structural process during dilation are known. The present paper presents a detailed study and comparison of the experimental and the simulated expansion behaviour of metallic stents. Used material models are discussed and crystallographic details are presented. Dilation curves describe the behaviour of balloon‐expandable coronary stents. The dilation behaviour depends on both the materials properties and the design of the stent. A numerical simulation of the dilation process by means of FE is suitable. A comparison of the experimental measurement and the numerical simulation demonstrates, that a Cauchy stress‐strain material model should be used for numerical simulations. A local failure criterion is introduced, which considers void initiation as a criterion for mechanical failure.     

Numerical Simulation of Elastic Behaviour and Failure Processes in Heterogeneous Material

A general numerical approach is developed to model the elastic behaviours and failure processes of heterogeneous materials. The heterogeneous material body is assumed composed of a large number of convex polygon lattices with different phases. These phases are locally isotropic and elastic-brittle with the different lattices displaying variable material parameters and a Weibull-type statistical distribution. When the effective strain exceeds a local fracture criterion, the full lattice exhibits failure uniformly, and this is modelled by assuming a very small Young modulus value. An auto-select loading method is employed to model the failure process. The proposed hybrid approach is applied to plane stress problems with fracture patterns and effective load-displacement curves presented to illustrate the full failure process.     

导热系数测量系统的数值模拟

对中国计量科学研究院的稳态保护热平板导热系数测量系统的温度场分布进行数值计算,并在此基础上对实验材料内测温点的选择进行了分析.结果表明,测温点复盖了实验材料内温度的最低和最高点,且呈线性分布,满足实验材料导热系数测量所需温度梯度测量的要求.此外,对热流密度测量的探讨发现,热流密度测量范围的确定是实现精密测量导热系数的关键.     

血管支架输送性的体外测试装置及实验研究

依托自主设计的血管支架力学输送性能测试平台,对316L不锈钢材料的微管雕刻冠脉支架及其输送系统进行了体外输送性实验研究．该测试平台集成了基于PC的数据采集和机器视觉系统,较准确地模拟了体内状况．经重复性实验的验证,实验平台具有很好的精度和数据可重复性（6次重复性实验的标准偏差达0．03N）．实验分别测试了不同输送速度下和不同转弯半径下的输送力的大小,结果表明：支架球囊系统在模拟冠状动脉血管的160mm输送行程中,输送力呈逐渐增大的趋势,最高处达到了1．2N;而在通过弯段血管时,输送力出现显著的上升,随后减小,在圆弧的中点附近存在一个输送力的峰值;输送力随输送速度的增大而增大,随管道的转弯半径的增大而增大,此结果可对临床上心脏介入手术提供一定的参考价值．     

Evaluation of Coronary Stents in the Animal Model: A Review

Metallic vascular endoprotheses (stents) have been introduced clinically to help to retain or to restore a patent vascular lumen after balloon angioplasty and to improve long-term patency of vessels. Despite the widespread use of intracoronary stents, instent restenosis remains a major clinical problem. During the last years considerable research effort had been spent on the understanding of the pathophysiology of restenosis and developing strategies to prevent this major shortcoming of PTCA and stent implantation. The current review focuses in its first part on basic pathophysiological mechanisms, which are involved in the formation of restenosis after ballon angioplasty and stent implantation. In the second part different animal models are presented, which serve as experimental models for examining these processes and testing strategies for the prevention of restenosis. Advantages and disadvantages of each model will be discussed, which are important when transferring results from animal models to clinical practice.     

真空炉温度均匀性测量的数值模拟研究

热电偶是检测真空炉温度均匀性的常用计量器具,但目前热电偶的几何特性及发射率对炉温均匀性检测影响方面的研究较少.本文利用数值模拟方法研究了热电偶发射率和直径对真空炉温度均匀性检测的影响,结果表明直径和发射率对常用规格热电偶稳态温度影响量级相当.开展零维模型分析,结果表明热电偶温度对直径和发射率相对变化率的敏感性相等,验证...     

冠状动脉支架纵向拉伸变形行为有限元分析

纵向强度是冠状动脉支架的一项重要力学性能,因强度不足而导致的支架纵向变形行为已成为经皮冠状动脉支架介入术最严重的并发症之一。运用有限元方法系统地分析了支架的扩张尺度、拉伸力的作用点位置和支撑单元之间的周向连接单元数量与形状对支架纵向拉伸变形行为的影响。结果显示,在支架结构设计参数中,连接单元的数量对支架纵向拉伸变形行为影响最大,增加连接单元的数量可以提高支架抵抗变形能力。连接单元形状对支架纵向拉伸变形行为影响次之,当支架的纵向变形位移为0.5mm且将连接单元形状由S型转换为L型时支架纵向强度可以提高50%。对于同一种连接单元类型的支架,扩张尺度越大的支架越容易发生纵向变形。同时,结果显示支架远端与近端端部比支架中部更容易发生纵向变形。合理调整支架的设计参数可以有效改善支架的纵向拉伸变形行为,所得结论有助于支架设计师优化支架的结构设计以降低支架纵向变形程度。     

烤燃试验温度压力数值模拟技术研究

针对快速烤燃和慢速烤燃试验过程,本文结合两种烤燃条件和升温速率下密闭容器的试验环境,建立了温度和热应力的有限元模型,利用Ansys软件分别模拟了密闭容器在快速烤燃和慢速烤燃过程中的热传递,研究了烤燃过程中内部各区域温度和热应力的变化情况,得出密闭容器热反应过程中的热传递规律.     

对接试板焊接残余应力实测与数值模拟

使用压痕法对两副对接试板进行了表面焊接残余应力测试,并通过焊接有限元仿真获得了对接试板焊接残余应力分布规律,对比分析了表面残余应力实测和数值模拟结果。分析结果表明,焊接残余应力数值仿真结果和压痕法实测结果趋势一致,数值相差不大,残余拉应力峰值实测为599 MPa,仿真结果为597 MPa,表明数值模拟方法可预测焊接残余应力;焊缝及热影响区最大纵向残余应力属于拉应力,而最大横向残余应力为压应力,横向残余应力峰值低于纵向残余应力峰值;等效应力(Mises应力)峰值792 MPa,高于试板材料在常温下的初始屈服强度,表明该材料具有明显的加工硬化现象。     

室内航空发动机进气流场流量测量数值模拟研究

通过对某航空发动机试车间的进气流场特性进行数值模拟研究,得出发动机试车间的进气流场流动特性,分析了流量测量误差随测量截面及探针深入位置的变化规律,并针对特定截面和深入位置,研究了边界层厚度随不同马赫数和不同雷诺数的变化规律,最后对工程中的流量系数测量方法做了系统性分析。结果表明,随测量截面向发动机进气口的推移,附面层越来越薄,压力测点越向中心区分布,测量速度越来越接近截面的平均速度;马赫数对流量系数的影响很小,流量系数随着雷诺数的增大而增大。     

Theoretical and Numerical Aspects in the Thermo-Viscoelastic Material Behaviour of Rubber-Like Polymers

Most current models for finite deformation thermo-viscoelasticity are restricted to linear evolution laws for the viscous behaviour and to thermorheologically simple materials. In this paper, we extend a model for finite deformation viscoelasticity that utilizes a nonlinear evolution law to include thermal effects. In particular, we present a thermodynamically consistent framework for the model and give a detailed form for then on-equilibrium Helmholtz free energy of the material in terms of the isothermal free energy function. The use of the model in a computational setting is addressed and it is shown that an efficient predictor-correct oralgorithm can be used to integrate the evolution equation of the proposed constitutive model. The integration algorithm makes crucial use of the exponential map as has been done previously in elastoplasticity. Numerical examples are presented to show some interesting features of the new model. This revised version was published online in July 2006 with corrections to the Cover Date.     

Numerical Differentiation in the Measurement Model

Measurement Techniques - The problems of increasing the accuracy of numerical differentiation in the measurement model are investigated. We consider the measurements of target characteristics of an...     

室内气流组织数值模拟及仿真软件

不同的气流组织形式对室内空气品质会产生影响,用CFD技术模拟气流组织具体影响,将室内空气品质的研究体现在工程设计上是必要的。本文就数值方法和相关的气流组织模拟软件作了分析和介绍,并说明了在应用过程中的步骤。     

Efficient Permeability Measurement and Numerical Simulation of the Resin Flow in Low Permeability Preform Fabricated by Automated Dry Fiber Placement

We propose a new experimental method using a Hassler cell and air injection to measure the permeability of fiber preform while avoiding a race tracking effect. This method was proven to be particularly efficient to measure very low through-thickness permeability of preform fabricated by automated dry fiber placement. To validate the reliability of the permeability measurement, the experiments of viscous liquid infusion into the preform with or without a distribution medium were performed. The experimental data of flow front advancement was compared with the numerical simulation result using the permeability values obtained by the Hassler cell permeability measurement set-up as well as by the liquid infusion experiments. To address the computational cost issue, the model for the equivalent permeability of distribution medium was employed in the numerical simulation of liquid flow. The new concept using air injection and Hassler cell for the fiber preform permeability measurement was shown to be reliable and efficient.     

Numerical Analysis of Thermodynamic Behaviour of Through-Thickness Stitched Sandwich Laminate

Effects of stitching angle on mechanical properties, thermal protection capability and induced thermal stress of stitched sandwich laminate (SSL) are numerically analyzed by ABAQUS codes. Interest centers on the potential for microcracking in the vicinity of the through-thickness stitches and the skins/foam interfaces. Two numerical models, in-depth heat transfer and thermoelastic deformation, are coupled to yield the transient response of the SSL. Six different stitching angles are considered and the simulation results showed that: the heat conductivity ability of the SSL is improved as the stitching angle increasing, which alters the mechanical behaviour and the thermal stress state of the SSL.     

带材边界位置的在线测量与计算方法

介绍了带材边界位置测量传感器的原理,并根据传感器的输入-输出特性,提出用最佳一次逼近多项式或近似最佳三次逼近多项式逼近输出函数,从而方便地计算出带材边界的位置。     

充型过程的数值模拟技术

铸造充型过程的数值模拟技术是铸造领域的前沿技术.采用这些技术进行充型过程的数值模拟可以帮助人们更清楚地了解充型过程中金属液流动的自由表面和速度分布.介绍了充型过程数值模拟的发展过程、数学模型,探讨了充型过程的计算方法以及自由表面的处理,并指出了当前研究中存在的问题.     

聚乙烯热裂解行为的分子动力学模拟

基于AMBER力场,采用周期性边界条件对聚乙烯模化物的热解过程进行了分子动力学模拟,模拟温度为300～1200 K.模拟结果表明,当温度高于600K时,C-C键开始发生断裂,整个分子链发生解聚,形成各种大分子碎片,随着温度的进一步升高,大分子碎片进一步分解成小分子碎片.聚乙烯的热解是典型的无规裂解,运用自由基链反应理论分析了各种热解主要产物的形成机理.     

Numerical Simulation of Polymolecular Adsorption

A model of the polymolecular adsorption on homogeneous and inhomogeneous surfaces in the absence of lateral interactions and also with their allowance for the case of the homogeneous surface is presented. A procedure to calculate isotherms on the basis of statistical data on the substance distribution over the surface is suggested. The calculated dependences of the differential adsorption energy on the degree of filling and the isotherms are compared with the experimental data for the system benzene vapor–graphitized soot.