首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到18条相似文献,搜索用时 109 毫秒
1.
生物瓣膜应力的数值模拟   总被引:2,自引:0,他引:2  
应用有限元方法分析了瓣架的材料特性、瓣叶的材料特性和瓣叶的钙化等因素对瓣叶的应力分布的影响。分析结果表明:采用全弹性材料的瓣架将改善瓣叶的应力分布,最大应力区域将远离接缝部位;将生物瓣瓣叶材料简化为拟线弹性材料时,对瓣叶最大主应力等值线的分布影响不大,计算结果在一定范围内存在差异;当瓣叶出现钙化时,钙化点及其周围产生应力集中,促进钙化的进一步加剧。  相似文献   

2.
双材料间界面断裂分析的广义界面层模型   总被引:1,自引:0,他引:1  
王旭跃  邹振祝  王铎 《力学学报》1997,29(4):486-490
给出了双材料间界面层区域的广义模型,并对承受扭转载荷的界面间硬币形裂纹进行了分析与计算.通过处理奇异积分方程得到了应力强度因子,数值结果给出了材料特性、界面层厚度、尤其是分布特征参数k对应力强度因子的影响.与Erdogan界面层模型的结果比较表明,本文的模型更具有一般性.  相似文献   

3.
丰王健  李欣 《力学季刊》2020,41(1):59-68
模拟绝缘栅双极型晶体管(IGBT)模块中用烧结银对直接覆铜(DBC)基板与铜底板进行大面积连接的过程,发现大面积基板连接会产生很大的翘曲与严重的残余应力.增加铜底板厚度使其刚度增大,能有效改善基板连接的翘曲问题.基板连接的最大残余应力产生于DBC上铜层与陶瓷层连接的角点处,随DBC铜层厚度的增加而增加,随陶瓷层厚度的增加而减小,与焊层厚度关系不大.其主要原因是各层材料厚度变化对结构整体热膨胀系数的改变程度不同,而DBC铜层与陶瓷层之间热失配程度最严重.结构厚度改变对连接层应力大小影响不大,但增加底板厚度会恶化连接层的应力分布,不利于模块长期可靠性.采用DBC下沉法和反向预翘曲法可以在控制连接层残余应力的条件下有效降低IGBT模块因烧结引起的翘曲,不会降低模块的可靠性.  相似文献   

4.
Q235A钢用新型耐磨覆层材料的残余应力计算   总被引:1,自引:0,他引:1  
计算了Q2 35A钢用新型耐磨金属陶瓷覆层材料的残余应力分布 ,通过对残余应力的计算发现覆层材料中的残余应力随覆层与基体厚度比的变化而变化。由于此种新型覆层材料的覆层厚度可不受限制 ,据此本文提出了可以对覆层材料的厚度进行优化 ,从而得到有利的残余应力分布的设计方案  相似文献   

5.
李珏  匡震邦 《力学学报》2000,32(3):343-354
采用微观组织结构分析及宏观复合材料分析结合的方法,分析了猪主动脉瓣的非线性复合材料性质,提出了一种适用于猪主动脉瓣的非线性复合材料本构模型,用提出的非线性复合材料本构模型,对闭合承载状态下的等厚度与变厚度几何模型的猪主动脉瓣的应力分布及变形进行了有限元数值模拟,发现:与各向同性瓣叶相比,单向增强复合材料的瓣叶不但具有较强的承载能力,而且具有较大的柔软性。  相似文献   

6.
田桥  徐耀玲  肖俊华 《力学季刊》2019,40(3):488-497
利用复变函数方法并结合双准周期Riemann边值问题理论,获得了含双周期分布非均匀相(夹杂/界面层)的复合材料在远场均匀反平面应力下弹性场的全场解答.该解答可用于对纳米夹杂复合材料的应力进行分析,结合平均场理论也用于预测纳米夹杂复合材料的有效性能.计算结果表明:当夹杂尺度在纳米量级时,应力和有效反平面剪切模量具有明显的尺度依赖性,并且随着夹杂尺寸的增加,趋近于不考虑界面效应时的结果;界面层厚度和性能对应力和有效反平面剪切模量明显变化时所对应的夹杂尺度范围和趋近于无界面效应结果的快慢有显著影响;当界面厚度足够薄时,界面层模型可用于模拟零厚度界面情况.  相似文献   

7.
采用零厚度界面模型和界面层模型研究了无限介质中单个纳米涂层圆柱形夹杂的反平面问题,利用复变函数方法获得了两种模型夹杂、涂层和基体内应力场的封闭解析解.研究表明,当界面层模型中的界面相厚度趋于零时,界面层模型可以解析地退化为零厚度界面模型.数值算例分析了界面模量不同取值时应力场的分布和应力的尺度依赖性.本文结果丰富了对纳米夹杂力学行为的认识,并可为直接采用零厚度界面模型有困难的纳米夹杂问题的研究提供有价值的参考.  相似文献   

8.
本文采用切割法测定了沿焊缝横向残余应力的分布规律.由于切割试样可以近似地模拟疲劳裂纹扩展,通过测量释放的应力,计算出残余应力的分布,可发现残余应力对疲劳裂纹扩展速率的影响规律.  相似文献   

9.
V型缺口裂端的三维应力状态及约束分析   总被引:1,自引:0,他引:1  
利用三维有限元方法,研究了有限厚度板中V型缺口根部穿透裂纹前沿的三维弹性应力场。对不同厚度、不同缺口张开角和裂纹长度对应力强度因子及裂尖附近的三维约束程度的影响进行了分析,同时还讨论了三维约束区的大小。研究结果显示:当缺口张开角小于60度时,不同缺口的应力强度因子和离面约束因子的分布基本一致,角度的影响不明显。应力强度因子是厚度的函数,板中面的应力强度因子随厚度的增加逐渐减小趋近干平面值,最大为1.08倍的平面值。当板厚超过15倍的缺口深度时,应力强度因子最大值将从中面转移至接近自由表面位置,距中面约0.4倍板厚。三维约束非常明显的区域在裂尖前沿约0.45倍厚度的范围内.二维到三维的过渡区在裂尖前沿1.5倍厚度的区域内;在中面上三维效应影响区最大,随着离中面距离的增加逐渐减小,在自由表面上降为0。  相似文献   

10.
活塞环组摩擦及润滑特性的综合分析   总被引:9,自引:2,他引:7  
基于二维平均流量模型和微凸体接触模型,提出了一种分析内燃机活塞环组润滑的模型,同时还对油膜厚度进行了实测,理论值与实测值具有良好的一致性,并且运用这种模型求出了活塞环-缸套之间油膜厚度的三维分布,发现油膜厚度沿圆周方向存在不均匀性.在分析中还考虑了贫油的影响,而且首次探讨了活塞系统的二阶运动对活塞环组润滑特性的影响,给出了不同结构下活塞系统的摩擦力和摩擦功耗.  相似文献   

11.
Elastic solutions for axisymmetric rotating disks made of functionally graded material with variable thickness are presented. The material properties and disk thickness profile are assumed to be represented by two power-law distributions. In the case of hollow disk, based on the form of the power-law distribution for the mechanical properties of the constituent components and the thickness profile function, both analytical and semi-analytical solutions are given under free–free and fixed-free boundary conditions. For the solid disk, only semi-analytical solution is presented. The effects of the material grading index and the geometry of the disk on the stresses and displacements are investigated. It is found that a functionally graded rotating disk with parabolic or hyperbolic convergent thickness profile has smaller stresses and displacements compared with that of uniform thickness. It is seen that the maximum radial stress for the solid functionally graded disk with parabolic thickness profile is not at the centre like uniform thickness disk. Results of this paper suggest that a rotating functionally graded disk with parabolic concave or hyperbolic convergent thickness profile can be more efficient than the one with uniform thickness.  相似文献   

12.
柔性瓣架对生物心脏瓣膜应力的影响   总被引:3,自引:0,他引:3  
采用非线性大变形超参数八结点板壳元,针对用猪主动脉瓣制成的人工心瓣所用的瓣架材料,形状,侧边高度等对其应力的影响进行数值模拟分析,其中瓣叶的几何形式保持不变。结果表明:弹性瓣架存在一个合适的弹性模量范围,能使瓣叶的最大应力降低较明显;对同一种瓣叶和具有相同弹性模量的瓣架而言、使瓣架立柱顶端产生位移最大的瓣架形状,往往亦是使瓣叶最大应力降低2的最明显的瓣架形状。  相似文献   

13.
For bonded dissimilar materials, the free-edge stress singularity usually prevails near the intersection of the free-surface and the interface. When two materials are bonded by using an adhesive, an interlayer develops between the two bonded materials. When a ceramic and a metal are bonded, the residual stress develops because of difference in the coefficient of thermal expansion. An interlayer may be inserted between the two materials to defuse the residual stress. Stress field near the intersection of the interface and free-surface in the presence of the interlayer is then very important for evaluating the strength of bonded dissimilar materials.In this study, stress distributions on the interface of bonded dissimilar materials with an interlayer were calculated by using the boundary element method to investigate the effect of the interlayer on the stress distribution. The relation between the free-edge singular stress fields of bonded dissimilar materials with and without an interlayer was investigated numerically. It was found that the influence of the interlayer on the stress distributions was confined within a small area of the order of interlayer thickness around the intersection of the interface and the free-surface when the interlayer was very thin. The stress distribution near the intersection of the interface and the free-surface was controlled by the free-edge stress singularity of the bonded dissimilar materials without the interlayer. In this case, the interlayer can be called free-edge singularity-controlled interlayer. If a stress distribution on the interface is known for one thickness of an interlayer h, stress distributions on the interface for other values of h can be estimated.  相似文献   

14.
In this paper transient thermal stresses in a thick hollow cylinder with finite length made of two-dimensional functionally graded material (2D-FGM) based on classical theory of thermoelasticity are considered. The volume fraction distribution of materials, geometry and thermal load are assumed to be axisymmetric but not uniform along the axial direction. The finite element method with graded material properties within each element is used to model the structure. Temperature, displacements and stress distributions through the cylinder at different times are investigated. Also the effects of variation of material distribution in two radial and axial directions on the thermal stress distribution and time responses are studied. The achieved results show that using 2D-FGM leads to a more flexible design so that time responses of structure, maximum amplitude of stresses and uniformity of stress distributions can be modified to a required manner by selecting suitable material distribution profiles in two directions.  相似文献   

15.
A finite-difference analysis of the state of stress in a double-notch interlaminar shear strength specimen is developed. The effects of geometry and material parameters on the stress distributions are investigated. It has been found that, in agreement with previous determinations,1–7 a uniform distribution of shear stress on the fracture plane does not exist. The shear stress distribution becomes more uniform for increased material anisotropy and for small (L/T) ratios, whereL is the distance between the notches andT is the specimen thickness. Also, it has been determined that the notch size (W) and the distance from the notches to the loaded ends of the specimen (h) do not influence the stress distributions significantly. The effects of variations in the (L/T) ratio, the notch size (W), and the length (h) were investigated experimentally. For a graphite/epoxy laminate of 0/90-deg square wave it has been found that the apparent shear strength determined by double-notch shear tests decreases significantly with an increase in (L/T) ratio. The decrease in the apparent shear strength with an increase inh, however, is very small. Also, the apparent shear strength is not affected significantly by increasing the notch sizeW.  相似文献   

16.
Flow physics of transvalvular flows in the aorta with bioprosthetic valves are investigated using computational modelling. For the efficient simulations of flow-structure-interaction in transvalvular flows, a simplified, reduced degree of freedom valve model is employed with a sharp interface immersed boundary based incompressible flow solver. Simulations are performed for normal as well as abnormal valves with reduced leaflet motion that models the effect of early leaflet thrombosis. The structure of the aortic jet and the hemodynamic stresses on the aortic wall are analysed to understand the hemodynamic impacts and possible long-term clinical implications of sub-clinical, reduced leaflet motion. The simulation results have shown that the reduced leaflet motion tilts the direction of aortic jet and generates stronger flow separation and re-attachment on the aortic wall downstream from the reduced motion leaflets. The modified flow pattern increases the wall pressure fluctuation and average wall shear stress on the downstream aortic wall, and results in the asymmetric oscillatory shear index distributions, which may have long-term clinical implications such as aortic wall damage and remodelling.  相似文献   

17.
以能量密度为参量的管中导波无损检测参数选择   总被引:2,自引:0,他引:2  
一般情况下,检测管状结构时采用位移分布或应力分布来选择超声无损检测的导波模式及其频厚积,这在有些情况下是不合适的。本文用总能量密度来选择检测管状结构的最佳导波模式及其频厚积,并用位移分布进行了比较,最后用混合边界元法进行了数值模拟,对其结果的有效性进行了验证。结果表明,总能量密度能有效的选择检测管材的最佳导波模式及其频厚积范围的检测的最佳位置。  相似文献   

18.
研究反对称斜交叠层板的双向弯曲问题。根据横向基理论,在厚度方向,给出了三个方向位移沿厚度的分布规律;在面内方向,采用升阶谱位移函数;然后,应用最小势能原理导出叠层板的静力控制方程。通过对多种层数和铺层角的层板力学响应计算分析表明:在典型位置的应力分布,本文解与三维弹性解符合很好,并有较好的收敛性。  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号