伴随变阻尼作用的干摩擦下的车辆系统非线性动力学分析

对分段线性阻尼和干摩擦共同作用下的车辆悬挂系统进行了非线性动力学分析研究，阐述了判定系统周期运动稳定性的理论方法；利用数值模拟方法分析了具有不同阻尼参数组合的系统对简谐激励的振动响应，并分析了由干摩擦引起的粘-滑振动行为．结果表明：提高摩擦力对抑制响应有利，但车辆系统在低速下运行时会出现复杂的粘-滑振动，轮轨之间产生较大的瞬时刚性冲击；而通过增加轮对与侧架的弹性悬挂可以有效减弱这种瞬时刚性冲击．     

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。     

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。     

平地机牵引架等效加载分析

为研究平地机牵引架的作业负载,分析了平地机最大牵引力及平地机铲刀作用阻力．通过研究工作装置各部件间的运动幅关系,构建了工作装置机构运动简图,建立了工作装置运动坐标系．利用空间坐标系变换理论,将等效铲刀工作负载施加于牵引架上．基于Mechanical APDL及有限元分析理论,对牵引架的Pro/E实体模型进行网格划分．以平地机受最大牵引力作用时的铲刀斜向刮土为例,进行了牵引架静力强度分析．结果表明,牵引架强度在许用强度范围内,经等效加载后的牵引架应力分布与工程实际相符．该工作负载等效方法有效并可简化复杂工况的牵引架受载分析．     

15万立米气柜残余应力及工作应力测试分析

报导了１５万立米大型煤气气柜挂圈走台的残余应力及气柜升降时工作应力的测试结果。该气柜服役十余年后发生煤气泄漏，为分析其原因，进行了残余应力及气柜修复前后的工作应力测试，结果表明：修复前残余应力及工作应力均达到很高水平，气柜升起时伴有严重侧偏现象，修复后应力状态有明显好转。     

双向应力状态下三维球形空穴应力集中的实验研究

用光弹三维应力冻结切片法研究了双向应力状态下球穴附近应力分布和集中问题，介绍了含球穴的三维光弹性模型的尺寸确定、浇注工艺和实现双向应力状态及大面积均匀拉伸加载的方法，分析了在特定平面上的正应力σ，剪应力τ沿球穴边缘的分布及衰减规律。文中对实验数据进行了统计分析处理，证明了实验与理论结果符合一致     

关于孔隙压力系数

在提出剪缩系数概念和修正体积压缩系数概念的基础上,导出了两种轴对称应力状态和一般三向应力状态下孔隙 压力增量与主应力增量关系的理论公式,给出了这三种应力状态下孔隙压力系数的表达式,对这三种应力状态下孔隙压力系 数的关系和变化规律进行了分析,提出了孔隙压力增量与主应力增量关系表达形式的建议。     

正常与钙化变厚度生物心瓣应力分布的数值模拟

采用八结点超参数板壳元，对猪主动脉瓣在闭合承载状态下的应力分布进行了非线性有限元数值模拟．分析了变厚度瓣膜和等厚度瓣膜应力分布的差别，发现厚度对应力分布具有较大影响．进一步分析了正常及具有几个散布钙化点的瓣膜的应力分布，发现钙化区域应力显著增大．本文结果与临床病变瓣膜的观察结果较为符合     

射电偏振仪PПy—1的结构及其工作原理

本文介绍了射电偏振仪ＰПｙ—１的结构及其工作原理。该仪器是利用发射偏振的超高频无线电磁波透射复合材料构件，对接收到的信号进行分析来确定构件在工作状态下的应力应变值。本文还通过测试实例说明了仪器的使用及各种参数的确定方法。     

乏燃料贮存格架跌落事故冲击分析和试验验证

乏燃料贮存格架是核电厂贮存乏燃料的重要设备，在满载条件下和地震/跌落事故中，都应保持稳定和安全状态．本文基于LS-DYNA对乏燃料贮存格架进行了跌落事故冲击分析，考虑了最重重物从可能最高处意外跌落的情况．分析时考虑了碰撞、几何大变形、材料非线性等非线性因素．分析发现，浅跌落情况下贮存格架变形较大，但为局部变形，冲击载荷不影响贮存格架的安全功能．深跌落情况下，组件跌落在支座上方时支座承受的载荷最大，并在许用载荷范围内．为确保核电厂安全性和可靠性，基于分析得到的现象，设计和开展了乏燃料贮存格架浅跌落和深跌落试验．试验采用了等比例贮存腔和真实燃料组件的管座．同时对试验件进行了跌落分析，并与试验结果进行了对比，验证了分析技术的保守性和准确性．掌握的分析技术可应用于所有压水堆核电站乏燃料贮存格架的跌落事故分析．     

三向应力Mohr圆的真实构成及剪应力作用方向的确定

三向应力Mohr圆的构成在传统上是借助公式推证而得，并以平面图形来表示，缺乏三维的真实感和直观性。在应力应变分析中，对于平面应力问题，可以通过平面应力摩尔圆确定过一点不同斜面上的应力分量及其作用方向。对于三维问题，利用摩尔圆图解法可以确定某一斜面上的正应力和剪应力的数值，但不能表示剪应力的作用方向。剪应力的作用方向需要通过另外的图解方法来确定。本文分别从坐标系旋转和数值计算的角度解释了三向应力Mohr圆的构成过程，形象地说明了Mohr圆的物理本质。针对三向应力Mohr圆不能表示剪应力作用方向的问题，通过矢量运算，给出了剪应力作用方向的确定公式。     

The solid phase stress tensor in porous media mechanics and the Hill-Mandel condition

An assessment of the stress tensors used currently for the modeling of partially saturated porous media is made which includes concepts like total stress, solid phase stress, and solid pressure. Thermodynamically constrained averaging theory is used to derive the solid phase stress tensor. It is shown that in the upscaling procedure the Hill conditions are satisfied, which is not trivial. The stress tensor is then compared to traditional stress measures. The physical meaning of two forms of solid pressure and of the Biot coefficient is clarified. Finally, a Bishop-Skempton like form of the stress tensor is obtained and a form of the total stress tensor that does not make use of the effective stress concept.     

Convergence of local atomistic stress based on periodic lattice

Local stress in an atomic system, which provides an average stress measurement within a spatial volume containing a collection of atoms, is essential for determining the mechanical properties of a nanoscale structure as well as developing a proper multiscale modeling technique. Theoretically, the smaller averaging volume where a local stress can converge, the closer this atomistic stress definition can approach the ideal continuum stress. As a result, the more accurate stress concentration can be evaluated for the inhomogeneous case. With reference to the previous studies focusing on the spherical averaging volume, dependent on the type of crystals, the convergent radius of the virial stress or Hardy stress usually spans the size of several lattice constants. In this paper, we find that, once the averaging volume is periodic, the convergence of the virial stress and Hardy stress can be accomplished within one single lattice, which is much smaller than what is required by other non-periodic volumes such as a sphere. In the final section, a cracked sodium chloride crystal is considered to demonstrate that the crack opening stress described by the periodic lattices captures the stress concentration near the crack tip.     

CONDITIONS FOR THE APPLICATION OF THE STRESS TRANSFORMATION FORMULA 1)

斜面应力公式,即一点应力的坐标旋转变换公式,是材料力学和弹性力学里最常用的公式之一,并广泛用于固体力学和工程设计中。一个让学生感觉例外的典型例子是含V 形切口的薄板在切口尖端的应力情况,如果利用斜面应力公式和切口面的自由面条件,就会得出切口尖点处于零应力状态的结果,而这与线弹性断裂力学给出切口处应力趋于无限大的结果不符。为消除这一疑虑,考察了尖端应力的特性,指出：只有在过一点的各个斜面上的应力是单值连续的情况下,斜面应力公式才能适用,此时,该点的全部应力分量组成应力张量。在V形切口的尖端、裂纹尖端,自由面与顺其延伸至介质内侧的面上的应力不同,应力在该面上就不是单值连续的,该点的应力状态就不能用张量表示,斜面应力公式在切口或裂纹尖端就不适用了。     

一种新的应力率定义

本文研究客观应力率的定义及表示,在放弃了客观应力率形式上的对称性以后定义了一类广义的非对称的客观应力率。从Cauchy应力原理出发,通过构造应力向量形式上和变形及变形率无关的客观导数,得到两种形式的应力率;它们表示作用在参考构形中单位物质面元应力向量的真实变化,这样就消除了应力率定义中的不确定性。用新应力率对次弹性体简单剪切进行了计算,得到的应力不振荡,且满足超弹性正应力-剪应力普适关系。     

新的一个求解带孔薄板弹性问题的二维杂交应力单元

建立了一个新的求解带圆孔薄板弹性问题的二维杂交应力单元,该单元为四节点四边形平面单元,名为P-HS4-8β。由极坐标系下的物理方程和几何方程求解出了一个极坐标方向的应力,通过将这个应力带入由Hellinger-Reissner原理推导的极坐标系下平面应力问题的能量方程中,得到了消除了该应力的能量方程,基于这个能量方程建立了杂交应力单元列式。根据圆孔边无外力条件和相容方程,推导了适用于求解带圆孔薄板问题的极坐标系下的二应力插值矩阵,并将此矩阵应用于新的有限单元列式中。数值算例表明新单元在求解孔边附近的应力时具有较高的精度。     

The effect of biaxial loading on the critical resolved shear stress of zinc single crystals

This paper reports an experimental investigation to test the hypothesis that the critical resolved shear stress is independent of the resolved normal stress on the active slip system plane. The resolved normal stress is varied independently for crystals of constant orientation by applying a uniform biaxial tension stress through slitted rubber strips glued to a flat tension sample. It is found that the critical resolved shear stress is constant until the resolved normal stress on the active slip system becomes twice the resolved shear stress; and then, for further increases in the resolved normal stress, the critical resolved shear stress begins to decrease.     

Magneto-elastic stress in a thin infinite plate with an elliptical hole under uniform magnetic field

Two-dimensional magnetic field and magneto-elastic stress solutions are presented for a magnetic material of a thin infinite plate with an elliptical hole under uniform magnetic field. The linear constitutive equation is used for the magnetic field and the stress analyses. The magneto-elastic stress is analyzed using Maxwell stress since only Maxwell stress is caused as a body force according to the electro magneto theory. Except the approximation of the plane stress state in which the plate is thin, no further assumption is made for the stress analysis, though Maxwell stress components are expressed by nonlinear terms. The rigorous boundary condition expressed by Maxwell stress is completely satisfied without any linear assumptions on the boundary. First, magnetic field and stress for soft ferromagnetic material is analyzed and then those for paramagnetic and diamagnetic materials are analyzed. It is stated that the stress components are the same expressions for those materials and the difference is only the magnitude of the permeability, though the magnetic fields are different each other in the plates. If the analysis of magnetic field of paramagnetic materials is easier than that of soft ferromagnetic material, the stress analysis may be carried out using the magnetic field for paramagnetic material. Shear deflection as well as stress in the direction of the plate thickness arises and the solutions are also obtained. Figures of the magnetic field and stress distribution are shown. Stress intensity factors are also derived.     

Three-dimensional local stress analysis on grain boundaries in polycrystalline material

In order to understand the initiation behavior of microstructurally small cracks in a stress corrosion cracking condition, it is important to know the tensile normal stress acting on the grain boundary (normal GB stress). The local stress in a polycrystalline body is enhanced by the inhomogeneity which stems from the shape and orientation of each grain. The stress in a three-dimensional polycrystalline body consisting of 100 grains with random orientation, under a remote uniform tensile stress condition, is evaluated by the finite element method. It was revealed that the local stress on the polycrystalline body is inhomogeneous under uniform applied stress and becomes large at those grain boundaries that are perpendicular to the load axis, though there is large fluctuation. It was also shown that the normal GB stress tends to be large near the triple points due to the deformation constraint caused by adjacent grains. Finally, the maximum stress on the surface of a large component caused by the inhomogeneity was evaluated by using Gumbel statistics.     

Global material constraints and their associated reactive stresses

The stress field in a material subject to a global material constraint is composed of a reactive stress and an active stress. The active stress is determined by the deformation while the reactive stress arises because of the constraint. The static equilibrium equations can be reduced to equations involving only the active stress. The resulting equations may then be solved to determine the deformation. Although the reactive stress is not needed in order to find the deformation, it is needed to satisfy traction boundary conditions. Rod, shell, and finite element theories can therefore be developed in an unambiguous way. As an example, one can calculate explicitly a reactive stress in a rod-like body subjected to a compressive end load.