柔性瓣架对生物心脏瓣膜应力的影响

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。     

界面裂纹问题中的弹性T项和应力强度因子

研究两相材料有限板含单边界面裂纹的断裂力学特性，对不同的材料组合用广义变分法分析了不同尺寸试件和裂纹长度下的应力强度因子和弹性T项，讨论了材料特性对应力强度因子和弹性T项的作用．分析了试件尺寸和裂纹长度对应力强度因子和弹性T项的影响．     

考虑损伤效应的双层结构界面蠕变应力分析

针对导致多层结构失效的界面应力问题,利用 ABAQUS 大型有限元程序,对比分析了线弹性、蠕变、蠕变-损伤条件下 Silicon/Epoxy 双层材料受到温度载荷作用时界面切应力和界面剥离应力的分布规律.分析结果表明:蠕变-损伤分析所得到界面切应力和界面剥离应力的结果要比线弹性有限元及蠕变有限元分析的结果小,其中线弹性分析得到的结果是三者中最大的;最大损伤出现在双层结构的界面边缘处,且损伤随着两种材料之间弹性模量差别的增大而增大;损伤沿界面的分布规律与界面剥离应力沿界面的分布规律类似.     

考虑应力波透反射作用的分层颗粒材料细观动力响应分析

为探究应力波界面透反射行为对分层黏弹性颗粒材料细观动力响应的影响规律，推导了界面透反射系数的理论表达，并建立了单频应力波入射和多频应力波入射两类条件下分层黏弹性颗粒材料的细观动力响应模型．典型算例分析结果表明：单频应力波入射时，上层颗粒动力响应形成“驻波”现象；双频应力波入射时，上下层颗粒动力响应均形成“行波”现象；两类条件下，分层界面处相邻颗粒的位移振幅均出现明显突变．以高速铁路无砟轨道路基基床为应用场景，分析基床填料刚度、阻尼系数及密度等参数对界面透反射特性的影响规律，探讨分层颗粒材料动力变形的调控思路，即增加基床表层填料的刚度、阻尼系数及密度，或减小基床底层填料的密度等措施可实现增益透射、抑制反射目标．此外，动力变形调控时还需控制路基颗粒材料固有频率远离动载激振特征频率．     

大瓣片高强钢球壳板冲压成形应力测试与分析

为对大瓣片高强钢球罐壳板成形过程进行应力测试与分析,在分析壳板成形工艺特点和力学特征的基础上,提出了在板材上附加随动测试架的测试方法,该测试架可随板材运动,实现对传感元件的保护,保证测试信号的输出,同时不干扰壳板的工艺条件,实现了准确测定冲压加工过程中特定状态下板壳内的应力分布及变化规律的目的。测试表明,压力加工过程中,当模具完全冲压到位时,在模具中心区域出现最大拉伸应变,应力值也最大,而卸载后该区反而出现了很小的压应力,这对容器的安全是有利的。因此在压制过程中只要控制冲压变形量,使得中间部位应力值小于材料的强度极限,就可保证板材不发生工艺性破裂,而且成形完成后该区也无不利的力学因素。     

考虑损伤的粘弹性梁的纯弯曲

根据粘弹性损伤理论,分析了带损伤粘弹性矩形梁在受纯弯曲时损伤对应力的影响,得到了在Laplace变换域内损伤场和应力场的分布．利用Laplace数值逆变换,分别得到了损伤弹性梁和损伤粘弹性梁的最大应力和最大损伤值,分析了材料的粘性对梁内应力和损伤的影响。     

正常及病态下静脉壁的力学特性分析

本文应用多束纤维加强超弹性复合材料应变能函数及厚壁圆筒模型,通过有限变形弹性理论研究了正常及病态下静脉壁在静脉压及轴向预拉伸作用下的变形和应力分布等力学特性,着重分析了静脉移植后自适应变化静脉壁在动脉压下的力学特性.首先利用超弹性材料厚壁圆筒模型得到了静脉壁在静脉压下的变形方程,给出了静脉压下静脉壁的变形和应力分布曲线,讨论了静脉壁的力学特性.给出了静脉移植后,正常和自适应变化静脉壁在动脉压下的变形和应力分布曲线,讨论了静脉移植后静脉壁的力学特性及其自适应性变化.然后给出了各种病态静脉壁的变形和应力分布曲线,讨论了材料参数的变化对静脉壁力学特性的影响规律.     

THERMAL BUCKLING ANALYSIS OF CIRCULAR PLATE EMBEDDED IN AN INFINITE ELASTIC PLATE 1)

分析了嵌入无限大弹性板中的圆板在变温时的热屈曲问题。由于圆板的热膨胀系数与无限大弹性板的热膨胀系数不同，温度变化时圆板中会产生压应力。当压应力达到其临界值时，圆板会发生热屈曲。首先，基于弹性力学平面应力问题的基本理论，得到圆板和无限大弹性板的应力和位移；然后建立圆板热屈曲的控制微分方程，求得临界屈曲温度的解析解和数值解，着重讨论圆板和无限大弹性板的材料物性参数的关系对圆板临界屈曲温度的影响。     

接合残余应力在界面端的应力奇异性

接合残余应力对异种接合材料强度的影响很大，正确地分析接合残余应力在界面端附近的分布及其奇异特性，是研究异材强度评价方法的关键问题之一，本文利用弹性学中的Ｇｏｕｒｓａｔ公式和有关微分方程解的理论，求得了平面近似下的界面端附近的残余应力场及其应力奇异性，与单纯的外力作用时的情况不同，残余应力在界面端有可能出现对数型的应力奇异性，并且不能仅用Ｄｕｎｄｅｒｓ的异材参数来描述。     

热超弹性材料中的空穴生成问题

研究热超弹性材料中的空穴生成问题,讨论了温度对空穴生成的影响．球体的材料为考虑温度影响的不可压Gent-Thomas材料,或者说是一种与不可压Gent—Thomas材料对应的热超弹性材料,得到了在表面死载荷作用下球体中空穴生成时的分叉曲线及临界载荷,给出了球体中的应力分布,讨论了温度对临界载荷、分叉曲线和应力分布的影响。     

采用瓣叶复合材料的生物心脏瓣膜的力学分析

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。     

Post-yield material nonlinearity: Optimal homogeneous shear-frame sections and hysteretic behavior

A nonlinear hardening rule that describes a general yield surface change for frame members is proposed. The rule is valid for homogeneous materials and is defined by a nonlinear constitutive model. The model is given as the stress–strain relationship through the section thickness. The post-yield behavior of shear frame members is assessed using a hardening index parameter, a plastic strain coefficient, and a smooth and optimal mathematical function to model the geometry of structural wide-flange and tube sections. This enables a continuous distribution of post-yield curvatures to exist along the member length and results in accurate finite-element member displacement predictions. Steady-state hysteresis responses are determined for frame sections using the model’s nonlinearly degrading stiffness. The hardening rule is used to model the detailed material behavior of shear frame members that are subjected to lateral loads. The results of the model are validated through experimental published literature.     

带边框承重墙板的应力分析

本文讨论周界用边框加固的承重墙板局部应力集中现象和整个应力分布情况.所用方法是以满足板的双调和方程为基础,运用最小余能原理,达到板与框架的位移协调一致.     

Numerical study of the plastic behaviour in tension of welds in high strength steels

The influence of the mismatch between material properties and constraint on the plastic deformation behaviour of the heat affected zone of welds in high strength steels is investigated in this study, using finite element simulations. An elastoplastic implicit three-dimensional finite element code (EPIM3D) was used in the analysis. The paper presents the mechanical model of the code and the methodology used for the numerical simulation of the tensile test of welded joints. Numerical results of the tensile test of welded samples with different hypothetical widths for the Heat Affected Zone and various material mismatch levels are shown. The analysis concerns the overall strength and ductility of the joint and in relation to the plastic behaviour of the heat affected zone. The influence of the yield stress, tensile strength and constraint on the stress and plastic strain distribution in the soft heat affected zone is also discussed.     

孔洞缺陷对3D打印Ti-6Al-4V合金疲劳试样应力分布的影响

3D打印金属技术因其个性化及可用于加工复杂零件等显著优点,在医用骨植入体领域得到了快速发展,但3D打印金属材料的孔洞缺陷所引起的应力集中现象严重降低了其疲劳强度,限制了3D打印生物金属材料的运用。本文针对3D打印Ti-6Al-4V合金超声疲劳试样,分析了Micro CT扫描试样得到的三维图像,获得了试样内孔洞缺陷的数量与体积;选择体积分数占比最大的孔洞,采用有限元方法分析了三种不同孔洞分布形式下的局部应力集中现象。研究发现,因空间位置的不同,独立的孔洞、接近自由表面的孔洞、相邻的孔洞三种不同孔洞的分布情况的应力集中系数差异显著。研究结果在一定程度上解释了目前EBM技术打印Ti-6Al-4V合金的孔洞缺陷如何对材料受力后的局部应力情况产生影响。     

Effect of phase interactions on crystal stress evolution over crystal orientation space under elastoplastic deformation of two-phase polycrystalline solids

It has been known for decades that crystal stress directions move toward the vertices of the single crystal yield surface (SCYS) during plastic flow of polycrystalline solids to satisfy the deformation compatibility among crystals. The alignment of crystal stress with a SCYS vertex is affected not only by plastic anisotropy, but also by other factors such as elastic anisotropy, loading direction, and grain interactions. Among the factors contributing to the degree of alignment, the effect of phase interactions on the crystal stress evolution during plastic flow has not been extensively investigated. In this research, the effect of phase interactions on the crystal stress direction evolution is investigated using simulations of an elastoplastically deforming two-phase (Cu/Fe) polycrystalline solid calibrated to a neutron diffraction experiment. By mapping the simulated crystal stresses over the crystal orientation space, crystal-orientation-dependent nonuniform partitioning of the crystal stress between phases can be observed. An analysis of the distribution of angles between the SCYS vertex and the crystal stress based on the simulation of the two-phase material shows that the crystal stress evolution pattern during plastic flow is strongly affected by phase interactions. These interactions result in low alignment and greater dispersion angles between the crystal stresses and SCYS vertices, particularly in the strong phase.     

Analysis of the stress singularity field at a vertex in 3D-bonded structures having a slanted side surface

The stress singularity that occurs at a vertex in a joint with a slanted side surface is investigated. The orders of stress singularity at a vertex and at a point on stress singularity lines for various material properties are determined using eigenanalysis. The stress distribution on an interface and the intensity of stress singularity at the vertex are investigated using BEM. It is shown that the order of stress singularity at the vertex in the joints can be reduced by slanting a side surface so as to decrease the angle between the interface and the side surface. The results of BEM analysis reveal that the distribution of stress on the interface is influenced by the slanted side surface. Finally, the 3D intensities of the singularity for stress components which are continuous at the interface are newly defined and determined for various material combinations.