冠状动脉支架力学性能的理论和实验研究

冠状动脉支架必须具备的力学性能为:传送时的纵向柔软性,由球囊充压扩张时的动力大变形性能,在血管内支撑血管回缩压力的抗屈曲性能,以及术后金属支架留存在血管内的抗疲劳性能.本文内容分两部分:1、综述和评论支架的上述四种力学性能,2、重点论述金属支架纵向柔软性的最新研究结果.支架的结构刚度有离散性,介入治疗的要求和受力情况复杂,目前支架的力学性能质量标准尚未完善建立,支架结构设计中力学问题的处理仍存在盲目性.本文对于制定支架力学性能的质量标准以及改进和提高支架网架结构的力学性能设计都具有重要意义.     

深井软岩巷道U型钢支架壁后充填技术研究

为有效解决U型钢支架和围岩之间因为存在着空间而严重抑制着巷道支架支撑能力的发挥这一问题,基于围岩-充填体-支架的结构力学原理,研究分析了壁后充填技术及新的壁后充填材料的性能要求,并进行了充填材料的各种力学性能实验,结果表明填充材料的配比和力学性能符合充填材料的特性要求.工程应用效果表明U型钢支架壁后充填技术的效果较理想,支架受力均匀,巷道表面收敛量减少50%以上.     

血管支架撑开均匀性问题的随机模型研究

撑开均匀性是血管支架的一个重要力学性能,它对于筋的安全性有极大的影响作用.论文研究支架筋的宽度对于撑开均匀性影响规律.建立了基于串联模型的撑开均匀性力学模型;给出了激光切割过程中微管中心偏移量对于筋宽度的影响关系;建立了撑开均匀性随机分析的方法.论文组织了两个算例,详细说明了对该方法的应用,实现了激光偏心距发生随机变化时,对于血管支架撑开性能的随机分析.     

活性粉末混凝土抗多次侵彻实验研究及数值预测

活性粉末混凝土（reactive powder concrete,RPC）具有超高的强度和优异的阻裂性能。为了研究RPC在多次冲击荷载下的损伤规律,采用25 mm口径滑膛炮对直径为600 mm、高600 mm的RPC圆柱形靶体进行了多次侵彻实验,得到了每次侵彻后靶体的破坏数据,并根据实验数据确定了Forrestal经验公式中的相关系数。基于K&C本构模型和现有RPC基本力学性能的实验数据,修正了K&C模型的强度面参数、损伤参数、状态方程参数、损伤演化模型以及应变率效应相关参数,系统地确定了RPC的K&C模型参数。采用LS-DYNA软件中的重启动功能模拟了弹体多次侵彻RPC靶体的破坏结果,模拟结果与实验结果基本一致,验证了模拟方法的有效性。对长2 200 mm、宽2 200 mm、高1 260 mm的RPC靶体抗侵彻实验进行了数值预测,得到了侵彻深度与弹速之间的关系、弹体贯穿靶体时的极限速度以及弹体侵彻过程中的峰值加速度。     

柱壳在轴向冲击载荷作用下动态塑性屈曲的实验研究

圆柱壳的动态塑性屈曲问题的研究主要是集中在屈曲模态方面，至于屈曲的临介载荷与临介时时间则研究的较少，ＳＨＰＢ用于研究材料在高应变率下动态力学性能已为大家所熟悉，但用于研究结构的动态屈曲则未见报道，本文利用一装置对柱壳的动态塑性屈曲进行了实验研究，测出了壳体屈曲过程的载荷，轴向缩短量与时间的关系曲线，得到屈曲时的临介载荷与临介时间，同时发现壳体屈曲变形的一些规律并与静态实验的结果进行了比较，为理论分     

在役设备材料断裂力学参数测定方法综述--小冲杆实验力学研究进展之二

20多年以来, 用小型试件的小冲杆实验技术来测量在役设备材料的各种力学参数已经取得了很大进展. 小冲杆实验的试样虽然还没有标准, 但一般均采用直径为3～10mm,厚度为0.1～0.5mm的圆片试样.这个方法已经用来确定材料的弹性模量、屈服强度、塑性性能、抗拉强度、断裂形态转变温度、断裂韧性、蠕变性能以及表示塑性硬化和韧性损伤的微观力学参数和黏塑性性能等各种力学性能.该方法兼具取样方便和几乎无损的优点,非常适用于那些无法取出传统试样或取样不经济的场合,因此引起科技界和工业界的关注.本文综述了小冲杆试验的测量技术及从测量数据来确定材料断裂形态转变温度、断裂韧性和主曲线的移动温度的各种计算方法研究进展.     

不同标距及应变率下纤维丝间摩擦对Kevlar 49纤维束力学性能的影响

为了研究在不同标距和应变率下摩擦对Kevlar 49纤维束力学性能的影响,首先,利用MTI微型拉力试验机对不同标距(12.5mm,25.0mm,40.0mm)的Kevlar 49纤维丝力学性能进行拉伸测试。然后,利用MTS万能试验机对不同标距(25.0mm,50.0mm,100.0mm,200.0mm)的Kevlar 49纤维束在处理(涂油润滑)和未处理两种情况下进行静态拉伸测试。采用Instron落锤冲击系统对标距为25.0mm的纤维束(处理和未处理)进行动态拉伸测试(应变率为40s-1,80s-1,120s-1和160s-1)。最后,利用Weibull分布模型对实验数据进行统计分析,量化了纤维强度的离散性。结果表明:在一定范围内,Kevlar 49纤维丝的拉伸强度、韧性、峰值应变均随标距的增加而降低,弹性模量随标距的增加而增大。处理和未处理的纤维束静态拉伸强度、韧性、峰值应变及弹性模量相近,即在静态拉伸作用下减小纤维丝之间的摩擦对不同标距下的纤维束力学性能影响不大。随着应变率增大,相对于未处理的纤维束,经过处理的纤维束强度逐渐降低,降低幅度呈递增趋势,这表明在高应变率作用下纤维丝之间的摩擦对纤维束的力学性能影响显著。     

递进式凸轮加载的中等应变率实验技术

研制了一种可以实现多次加载的凸轮递进式中应变率压缩实验系统。该实验装置采用伺服电机驱动蓄能飞轮转动，后蓄能飞轮带动加载凸轮压缩加载杆的方法，实现对试样中应变率的压缩；同时在一级压缩即将结束时步进电机迅速推动蓄能飞轮贴近加载凸轮，实现多级压缩。试样的动态压缩载荷通过两侧杆上粘贴的应变片所记录的应变信号得到；试样变形过程通过激光干涉测速系统测得的试样两侧杆端的运动速度信号得到。以纸蜂窝试样为例，基于研制的中应变率实验系统，并结合高速摄影图片，研究了厚度10 mm、直径14.5 mm的纸蜂窝试样在应变率3.5 s^-1下的动态压缩力学性能，得到了单级压缩和两级压缩过程中纸蜂窝试样的应力-应变曲线和变形过程，并讨论了该实验系统的可靠性。此实验系统可以实现多级递进式中应变率加载；纸蜂窝试样在中等应变率下的峰值强度和平台应力对高应变率下的动态压缩实验数据和低应变率下的准静态实验数据进行了较好地衔接；试样的失效模式主要为准弹性变形后的外壁屈曲和面内剪切。     

空心玻璃微珠及玻璃纤维混合填充环氧树脂力学性能实验研究

制备了一种空心玻璃微珠质量比、四种玻璃纤维质量比的空心玻璃微珠及玻璃纤维混合填充环氧树脂复合泡沫材料。通过一系列准静态压缩、拉伸实验,研究了玻璃纤维填充量对复合材料的密度、强度、弹性模量等性能的影响,并分析了其影响原因。通过三点弯曲实验,研究了复合材料弯曲弹性模量、弯曲强度等力学性能与玻璃纤维填充量的关系。通过拉伸断口SEM照片分析了玻璃纤维增强复合材料力学性能的原因。研究表明:随着玻璃纤维填充量增加,复合材料的拉伸和弯曲强度、压缩屈服极限及弹性模量等力学性能都有较大的提高,且仍然保持了较好的弹性性能和塑性特征。     

Sm2O3增强聚四氟乙烯／混杂纤维复合材料的摩擦磨损性能研究

采用冷压烧结方法制备Sm2O3增强聚四氟乙烯／混杂纤维复合材料，用AG-1型电子万能试验机和MM-200型摩擦磨损试验机分别评价了Sm2O3增强聚四氟乙烯／混杂纤维复合材料的力学性能和摩擦磨损性能，采用扫描电子显微镜观察其磨损表面形貌．结果表明：添加少量Sm2O3可以提高炭纤维和玻璃纤维混杂填充PTFE复合材料的力学性能和摩擦磨损性能，尤其对改善减摩效果尤为显著；加入1％Sm2O3可以使PTFE／15％CF／10％GF复合材料的拉伸强度、弯曲强度和硬度分别提高9．0％、5．1％和49．1％，摩擦系数降低22％，磨痕宽度降低5．4％，得到性能较为优良的耐磨材料．这是由于Sm2O3起到了润滑及阻止纤维和基体磨损作用的缘故．     

弯曲动脉壁非线性弹性力学性质的理论分析

血管壁非线性力学特性是探索心血管中的血液流动规律及脉搏波传播现象的一个重要前提．在血管力学研究中,直管动脉壁的本构方程已有相当深人的研究,唯独象主动脉弓那样的弯管动脉壁本构方程;至今还没有建立一个理论模型．文中在已有的直管动脉壁本构方程研究基础上,提出一个理论方法来分析弯曲动脉壁的非线性弹性力学性质,在弯曲动脉壁被模拟为均质、正交各向异性、不可压缩材料的前提下,作者从理论上建立了一个表达弯管动脉壁非线性弹性性质的三维ｅ指数型本构方程文中还探讨了弯曲动脉壁内的残余应变分析．     

Mathematical modelling of couple stresses on fluid flow in constricted tapered artery in presence of slip velocity-effects of catheter

This paper explores the mathematical model for couple stress fluid flow through an annular region. The above model is used for studying the blood flow be-tween the clogged （stenotic） artery and the catheter. The asymmetric nature of the stenosis is considered. The closed form expressions for the physiological parameters such as impedance and shear stress at the wall are obtained. The effects of various geomet-ric parameters and the parameters arising out of the fluid considered are discussed by considering the slip velocity and tapering angle. The study of the above model is very significant as it has direct applications in the treatment of cardiovascular diseases.     

Dynamic principle for interaction between heart and arterial system

Various steady models for interaction between heart and arterial system have been given in literature. In our recent study, a dynamic principle, i.e. the principle of least cardiac work is proposed, and a dynamic model for interaction of heart and arterial system is established. Preliminary results of our experiments show that both the principle and the model are consistent with the physiological phenomena. It reveals that the present analysis may offer a new measure for the study of dynamic process of interaction between heart and arterial system.     

Numerical simulation of the haemodynamics in end‐to‐side anastomoses

In this paper, the commercial CFD package Ansys workbench 11 was used to analyse the three‐dimensional haemodynamics of a typical stenotic Coronary Artery Bypass Grafting (CABG). Two end‐to‐side CABG configurations with anastomosis angle of 20^° and 40^° and graft–artery diameter ratios of 1/0.6, 1/1 and 1/1.6 were examined. The flow measurements from in vitro Doppler guide wire technique acquired in left interior mammary artery (LIMA) and grafted to the left anterior descending artery (LAD) were used to impose the physiologically flow conditions at proximal and distal CABG inlet and outlet, respectively. The blood flow was considered to be incompressible, pulsatile, Newtonian, and laminar rheology. The main objective was to determine the effect of anastomosis angle and graft–artery diameter ratio on the flow patterns and the long‐term functionality of the graft. In analysing the results, the distributions of temporal and spatial wall shear stress (WSS) gradient and oscillating shear index (OSI) in the critical regions of CABG such as heel, toe and the centre of the junction were presented and the vortex motions and the occurrence of recirculation zones were examined. The findings showed asymmetrically disturbed flows in the localized regions of the proximal and distal host artery for all models considered and the movement of the recirculation zones from heel to toe was found to depend on the time at the cardiac cycle. These regions are known as susceptible sites to thrombosis and re‐stenosis due to their association with low values of WSS. Copyright © 2010 John Wiley & Sons, Ltd.     

Investigation of third-grade non-Newtonian blood flow in arteries under periodic body acceleration using multi-step differential transformation method

In this paper, a non-Newtonian third-grade blood in coronary and femoral arteries is simulated analytically and numerically. The blood is considered as the thirdgrade non-Newtonian fluid under the periodic body acceleration motion and the pulsatile pressure gradient. The hybrid multi-step differential transformation method (Hybrid-MsDTM) and the Crank-Nicholson method (CNM) are used to solve the partial differential equation (PDE), and a good agreement between them is observed in the results. The effects of the some physical parameters such as the amplitude, the lead angle, and the body acceleration frequency on the velocity and shear stress profiles are considered. The results show that increasing the amplitude, A_g, and reducing the lead angle of body acceleration, φ, make higher velocity profiles on the center line of both arteries. Also, the maximum wall shear stress increases when A_g increases.     

The effects of blood viscoelasticity on the pulse wave in arteries

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磁场和Hall电流对狭窄动脉中血液流动的影响

A micropolar model for blood simulating magnetohydrodynamic flow through a horizontally nonsymmetric but vertically symmetric artery with a mild stenosis is presented. To estimate the effect of the stenosis shape, a suitable geometry has been considered such that the horizontal shape of the stenosis can easily be changed just by varying a parameter referred to as the shape parameter. Flow parameters, such as velocity, the resistance to flow （the resistance impedance）, the wall shear stress distribution in the stenotic region, and its magnitude at the maximum height of the stenosis （stenosis throat）, have been computed for different shape parameters, the Hartmann number and the Hall parameter. This shows that the resistance to flow decreases with the increasing values of the parameter determining the stenosis shape and the Hail parameter, while it increases with the increasing Hartmann number. The wall shear stress and the shearing stress on the wall at the maximum height of the stenosis possess an inverse characteristic to the resistance to flow with respect to any given value of the Hartmann number and the Hall parameter. Finally, the effect of the Hartmann number and the Hall parameter on the horizontal velocity is examined.     

The micropolar fluid model for blood flow through a tapered artery with a stenosis

A micropolar model for axisymmetric blood flow through an axially nonsymmetreic but radially symmetric mild stenosis tapered artery is presented. To estimate the effect of the stenosis shape, a suitable geometry has been considered such that the axial shape of the stenosis can be changed easily just by varying a parameter （referred to as the shape parameter）. The model is also used to study the effect of the taper angle Ф. Flow parameters such as the velocity, the resistance to flow （the resistance impedance）, the wall shear stress distribution in the stenotic region and its magnitude at the maximum height of the stenosis （stenosis throat） have been computed for different values of the shape parameter n, the taper angle Ф, the coupling number N and the micropolar parameter m. It is shown that the resistance to flow decreases with increasing the shape parameter n and the micropolar parameter m while it increases with increasing the coupling number N. So, the magnitude of the resistance impedance is higher for a micropolar fluid than that for a Newtonian fluid model. Finally, the velocity profile, the wall shear stress distribution in the stenotic region and its magnitude at the maximum height of the stenosis are discussed for different values of the parameters involved on the problem.     

Oxygen transfer in human carotid artery bifurcation

Arterial bifurcations are places where blood flow may be disturbed and slow recirculation flow may occur. To reveal the correlation between local oxygen transfer and atherogenesis, a finite element method was employed to simulate the blood flow and the oxygen transfer in the human carotid artery bifurcation. Under steady-state flow conditions, the numerical simulation demonstrated a variation in local oxygen transfer at the bifurcation, showing that the convective condition in the disturbed flow region may produce uneven local oxygen transfer at the blood/wall interface. The disturbed blood flow with formation of slow eddies in the carotid sinus resulted in a depression in oxygen supply to the arterial wall at the entry of the sinus, which in turn may lead to an atherogenic response of the arterial wall, and contribute to the development of atherosclerotic stenosis there. The project supported by the National Natural Science Research Council of China (10632010, 10572017, 30670517).     

冠状动脉对称双路移植管中脉动血流的数值模拟

冠状动脉旁路移植管搭桥术后，常会产生血管再狭窄，导致手术失败，。这与移植管的几何结构及血流动力学是密切相关的。作为改进措施，作者提出了采用对称双路搭桥的设想。本文利用有限元分析方法，对冠状动脉搭桥术中对称双路移植管内的生理流动进行了数值仿真。计算了缝合区附近的流场、壁面切应力、压力等血流动力学因素在心动周期内的时空分布情况。计算结果表明，对称双路搭桥具有较好的血流动力学，可以改善血管流场状况和减轻再狭窄发生。这对临床手术计划是很有帮助和指导意义的。