血管内支架的疲劳强度的有限元模拟分析

为了揭示支架支撑体长度、宽度及圆弧曲率半径对其疲劳强度的影响规律,利用有限元法对不同结构参数的9种血管内支架进行动静态模拟分析,并用Goodman线图评价了支架的疲劳强度。结果显示,静态扩张过程中,随着支撑体长度或圆弧曲率半径的增加,支架所需的最大等效应力有减少的趋势,而随着支撑体宽度的增加,支架所需的最大等效应力有增加的趋势。动态加载过程中,支撑体长度、支撑体宽度及圆弧曲率半径均与疲劳安全系数成反比,其中支撑体宽度对疲劳安全系数的影响要比圆弧曲率半径和支撑体长度的影响较明显。关于支架疲劳强度的有限元分析结果,为支架的优化设计提供科学的理论依据。     

锡钴合金代铬镀层

铬镀层由于有光亮而美丽的色调和优良的耐蚀性,它作为防护装饰性高级镀层,在工业上被广泛应用。但镀铬废液污染环境,引起公害,长期以来,人们迫切希望开拓一种既保持镀铬层的优点,又不引起公害的代铬层的电镀新工艺。代铬镀层的新工艺,目前最有希望实现的是锡钴合金电镀。     

锡钴合金代铬镀层

“镀铬”是许多日常用品普遍采用的电镀层。它不仅由铬镀层组成,而且在很薄的铬层下面还有一层或多层镍镀层。镍层的厚度(5～50微米)比铬层(0.1～0.5微米)厚得多。因此,整个镀层的光亮性和整平性应归因于镍层,而最后的色泽则是取决于铬层。铬层除了有引人注目的色泽外,还有其它好的特     

用于快速制造装置的钴铬合金

美国Stratasys公司设计出一种ASTMF-75钴铬合金，其强度高、耐腐蚀而且耐磨。这种合金可用于Arcam EBM（电子束熔炼）工艺制造的零件。[第一段]     

药物洗脱支架可降解涂层的研究与制备

为研究制备方法对药物涂层的影响,分别采用超声喷涂法和喷墨打印法在药物洗脱支架表面制备以聚乳酸(PLA)为缓释物的雷帕霉素载药涂层。首先通过对PLA进行凝胶渗透色谱实验、差示扫描量热实验和拉伸试验,说明其物理化学性质能够用做药物支架的涂层材料。傅立叶红外光谱(FT-IR)结果显示药物雷帕霉素有效分布在聚合物PLA中。然后将两种方式制得的支架在扫描电子显微镜(SEM)下观察涂层的形貌;再利用球囊扩张法分析涂层与支架基体之间的结合力;最后在PBS(pH值=7.4)介质中模拟体液测试两种支架的药物释放动力学曲线。结果表明,两种方法制备的药物涂层在表面形貌、与支架基体之间的结合力方面均存在差异,药物释放曲线表明喷墨打印法制得的药物洗脱支架的整体释放趋势更为平缓。     

药物洗脱支架载体材料的选择与优化

对药物洗脱支架药物载体材料和支架涂层进行了综述,指出了药物载体材料的选择范围,提出了药物载体材料的优化原则、药物配合的条件以及药物载体材料的发展方向.     

不同铜含量钴铬合金的体外生物相容性

用CCK-8法和Annexin-V/PI双标记法研究了不同铜含量(质量分数,下同)的钴铬合金和钴铬合金的体外生物相容性(包括L929细胞增殖和凋亡)的影响。结果表明,4种合金的体外生物相容性按含1%铜的钴铬合金、含2%铜的钴铬合金、钴铬合金、含3%铜的钴铬合金的顺序递减;其细胞毒性等级都为1级,具有良好的体外生物相容性。     

钴铬钨合金耐高温冲蚀保护涂层的应用研究

长岭炼油厂新型催化裂化装置再生系统旋风分离器尺寸小，不能采用常规氧化铝内衬保护。为此，研制成钴铬钨耐高温冲蚀保护涂层，解决了该装置的技术难题。涂层采用氧－乙炔火焰喷焊工艺制成。     

选择性激光烧结工艺制备的钴铬合金的微观结构

对比选择性激光烧结工艺(SLM)和铸造工艺(cast)制备的Co-Cr合金的内部微观结构,分析产生不同微观结构的原因,并分析不同微观结构对Co-Cr合金性能可能造成的影响。选取组成接近的Co-Cr合金金属粉末和金属块,分别通过SLM工艺和cast工艺制作Co-Cr合金试样。利用场发射扫描电镜(SEM)观察样品内部的微观结构并采用X射线能谱(EDX)分析样品特征区域的化学成分。SLM工艺制备的样品的内部结构均匀,没有出现分相区,而离心cast工艺和真空cast工艺制备的样品内部均出现富含Mo元素的分相区。SLM工艺和cast工艺制备的样品的孔洞均较少。对于Co-Cr合金而言,SLM工艺的加工质量优于cast工艺。     

Fatigue crack closure determination by means of finite element analysis

Plasticity-induced crack closure is an observed phenomenon during fatigue crack growth. However, accurate determination of fatigue crack closure has been a complex task for years. It has been approached by means of experimental and numerical methods. The finite element method (FEM) has been the principal numerical tool employed. In this paper the results of a broad study of fatigue crack closure in plane stress and plane strain by means of FEM are presented. The effect of three principal factors has been analysed in depth, the maximum load, the crack length and the stress ratio. It has been found that the results are independent of maximum load and the crack length, and there exists a direct influence of the stress ratio. This relation has been numerically correlated and compared with experimental results. Differences have also been established between opening and closure points and between the different criteria employed to compute crack closure.     

Elastodynamic analysis of crack by finite element method using singular element

The finite element method using a singular element near the crack tip is extended to the elastodynamic problems of cracks where the displacement function of the singular element is taken from the solution of a propagating crack. The dynamic stress intensity factor for cracks of mode III or mode I deformations in a finite plate is determined.The results of computation for stationary cracks or propagating cracks under dynamic loadings are compared with the analytical solutions of other authors. It is shown that the present method satisfactorily describes the time variation of the stress intensity factor in dynamic crack problems.

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Résumé La méthode des éléments finis utilisant un élément singulier au voisinage de l'extrémité d'une fissure a été étendue aux problèmes élastodynamiques des fissures tels qu'ils se posent lorsque la fonction de déplacement d'un élément singulier est prise à partir de la solution d'une fissure en cours de propagation. Le facteur d'intensité des contraintes dynamiques correspondant à des fissures de mode III ou des déformations de mode I dans une plaque finie a été déterminé. Les résultats des calculs correspondant à des fissures stationnaires ou des fissures en cours de propagation sous des charges dynamiques sont comparées aux solutions analytiques obtenues par d'autres auteurs. On montre que la méthode présentée décrit de façon satisfaisante la variation en fonction du temps du facteur d'intensité des contraintes dans les problèmes de fissuration dynamique.

     

Time domain analysis by the point-matched finite element method

The solution of Maxwell's equations using the point-matched finite-element time-domain approach is presented. The solution scheme is explicit and does not require the solution of any matrix equations. The solution is carried out over a finite domain terminated using appropriate absorbing boundary conditions. Far-field quantities are obtained from the near-field solution by first computing the frequency-domain solutions from the time-domain solution using the fast Fourier transform and then using a near-field to far-field transformation algorithm.<>     

The analysis of dislocation systems by the finite element method

It is shown how the stress field due to any prescribed continuous distribution of dislocations can be determined. The finite element method is employed giving wide freedom with regard to boundary geometry and material properties. The presentation is limited to situations which conform to either the standard plane or anti-plane conditions. Some results are obtained for simple dislocation configurations and compared with theoretical expressions available. Solutions are then obtained to problems in which the material behaves elasto-plastically, a limiting shear stress criterion being employed. Finally the analysis of discrete edge dislocations by use of the slab analogy is presented.     

Tangential stress analysis of myocardial wall by finite element method

The stress and strain of heart are two important and effective parameters to describe the deformation of the myocardial wall to analysis the dynamic function of the heart, but which are difficult to be ascertained. In this paper, a novel method is presented to built the triangular surface model and calculate the tangential stress and strain of myocardial wall ,which can be further used to reflect the Left Ventricle Twisting(LVT)-a sensitive index to assess the systolic and diastolic function of heart. Firstly, Point Distribution Model (PDM) is used to obtain the feature points of the left ventricular (LV) surface in SPECT images. Secondly, the surface model of LV is constructed by triangular mesh, and then the subdivision strategy is introduced to refine the model. Thirdly, plane projection and FEM are applied to calculate the tangential stress and strain. Finally, the distribution of tangential modulus of elasticity is discussed. The stimulation results show the proposed method can be used to compute the tangential stress and strain of myocardial wall effectively and the computing result is consistent with the results mentioned in the literatures.     

Higher-order sensitivity analysis of finite element method by automatic differentiation

To design optimal mechanical structures, design sensitivity analysis technique using higher order derivatives are important. However, usual techniques for computing the derivatives, for example numerical differentiation methods, are hard to apply to real scale structures because of the large amount of computational time and the accumulation of computational errors.To overcome the problem, we have studied a new approach for higher order sensitivity analysis of the finite element method using automatic differentiation techniques. The method automatically transforms FORTRAN code to special purpose code which computes both the value of the given functional dependence and their derivatives. The algorithm used in the method automatically and efficiently computes accurate values of higher order partial derivatives of a given functional dependence on many variables.This paper reports the basic principles of the automatic differentiation method and some experiments on the sensitivity analysis of mechanical structures. The original program of structural analysis by the finite element method is implemented in FORTRAN, which is developed by the first author. Using the proposed method, we get more accurate sensitivity and prediction values compared with usual numerical differentiation. We also discuss the effectiveness of the proposed approach for the sensitivity analysis of the mechanical structures.     

冠脉支架对弯曲血管损伤机理的非线性有限元分析

针对支架植入术后的冠脉血管内支架再狭窄问题,通过非线性有限元法建立弯曲冠脉-支架介入系统生物力学模型及冠脉支架纵向柔顺性计算模型,开展了冠脉支架结构设计对血管壁面损伤与再狭窄的影响机理研究。数值分析结果表明,弯曲血管在支架端部存在高应力梯度,所产生的最大应力是直冠脉的4~6倍,易于损伤血管从而形成血管内支架再狭窄问题。冠脉支架结构的纵向柔顺性对弯曲血管的整体应力水平具有显著的影响,C型支架的纵向柔顺性远低于S型支架和N型支架,植入后所引起的血管整体应力水平最高;S型支架具有最好的纵向柔顺性,植入后所引起的血管整体应力水平最低。从支架与血管的相互作用以及支架纵向柔顺性的角度解释了临床中弯曲血管内支架再狭窄率较高的力学原因,为支架的临床选择及优化设计提供了重要指导作用。     

Three-dimensional compositional analysis of drug eluting stent coatings using cluster secondary ion mass spectrometry

Cluster secondary ion mass spectrometry (cluster SIMS) employing an SF5+ polyatomic primary ion sputter source in conjunction with a Bi3+ analysis source was used to obtain three-dimensional molecular information in polymeric-based drug-eluting stent coatings. The formulations of the coatings varied from 0% to 50% (w/w) sirolimus drug in poly(lactic-co-glycolic acid) and were prepared on both MP35N metal alloy coupons and bare metal stents. All cluster SIMS depth profiles obtained indicated a drug-enriched surface region, followed by a drug-depletion region, and finally a constant bulk composition region, similar to previous data obtained in polymeric blend systems. The drug overlayer thickness was determined to increase with increasing sirolimus content. Sample temperature was determined to play an important role in the resulting depth profiles, where it was shown that the best profiles were obtained at low temperatures (-100 degrees C). At these temperatures, molecular signals typically remained constant through the entire depth of the film (approximately 6.5 microm) in some cases, as opposed to the typical 1 microm-2 microm depth limit, which is achievable at room temperature. The 3-D imaging capabilities of cluster SIMS were successfully demonstrated and indicated a significant amount of subsurface domain formation in the 25% and 50% sirolimus samples, but not in the 5% sample, which was homogeneous. These results clearly illustrate the utility of cluster SIMS for probing the 3-D structure in polymeric-based drug delivery devices.     

Nonlinear hydrodynamic shock propagation analysis by the finite element method

The method of weighted residuals is used in conjunction with the finite element method to solve the nonlinear hydrodynamic field equations. The algebraic equations which result from the finite element approximations were solved using the Standard Newton-Raphson method, the Modified Newton-Raphson method, the Self-Correcting Incremental Method, and the Method of Successive Substitutions. Also, the Gear 2-Step and 3-Step temporal operators were employed along with the Park temporal operator and a first order backward difference method to obtain the transient response. Solutions for 1-dimensional shock and rarefaction waves obtained using the method agree with theoretically predicted values and with values obtained using a finite difference method. Of the four temporal operators investigated, none was determined to be superior. However, based upon computational cost and solution accuracy, the Self-Correcting Incremental Method and the Modified Newton-Raphson Method with Jacobian reformation after every three iterations both proved superior to the other methods studied for solution of the nonlinear equations.     

Fatigue failure prediction of a rear axle housing prototype by using finite element analysis

A premature failure that occurs prior to the expected load cycles during the vertical fatigue tests of a rear axle housing prototype is studied. In these tests, crack mainly originated from the same region on test samples. To determine the reason of the failure, a detailed CAD model of the housing was developed. Mechanical properties of the housing material were determined via tensile tests. Using these data, stress and fatigue analyses were performed by finite element method. Fatigue crack initiation locations and minimum number of load cycles before failure initiation were determined. Results provided from tests were compared with the analyses. Design enhancement solutions were proposed to increase the fatigue life of the housing.