薄板的初应力辨识

由于工程结构和构件无初应力的小变形运动与附加于初应力位形的小变形运动有不同的支配方程。因此，总可以根据初应力构件表现的力学行为来识别应力。本文提出了描写薄板初应力的数值特征，讨论用附加于初应力位形的小变形识别初应力数值特征的原理和途径，给出了常见情况下初应力数值特征的识别方案。     

初应力拱侧向振动的固有频率

在初应力位形上附加变形场论的框架下,引入自然坐标系,采用平截面假设,建立对数值方法和解析方法十分有用的、初应力曲拱位移变分方程。给出了平面曲拱在平面初始变形状态下附加变形变分方程,将拱的初始内力嵌入其中。根据所得的方程,讨论了面内载荷对圆截面初应力圆弧形拱侧向振动固有频率的影响,给出了侧向振动固有频率与初载荷的解析关系。结果表明,面内初始载荷的存在减小了侧向挠曲的固有频率;减少的数值与用频率方法诊断构件缺陷通常可得到的灵敏度属同量级。     

初应力位形上小的变形问题

论文研究初应力杆的小变形问题。用初应力作为参数,提出初应力位形上小变形问题的位移变分原理;针对直杆的几何特点,提出了用数值参数描写直杆初应力,用所提出的变分原理建立了初应力杆的小变形位移分量的定解问题。所得的方程中包含了初应力的数值参数。分析表明,初应力的不同的数值参数可以对相关的刚度、压杆的临界力以及基本变形的耦合与固有频率产生显著的影响。     

圆弧拱平面内弯曲失稳一般理论

现有的拱的平面内稳定理论有很大分歧。本文采用平截面假定,未作任何近似地采用了有限变形理论中的应变位移关系,完整地考虑了横向应力和剪应力的二阶效应,用虚功原理推导了拱的平面内非线性分析的平衡方程。之所以引入横向应力的非线性效应,是因为保持平衡所需的各应力分量的二阶效应会部分相互抵消,忽略其中任何一个都可能导致不正确的结果。文中还给出了内力采用线性分析结果的近似非线性分析方程,可以用于绝大多数工程问题的求解。对拱的内力和位移的线性问题进行了精确求解,代入非线性方程后得到了圆弧拱屈曲分析的平衡微分方程。用Galerkin法求得了考虑/不考虑拱内弯矩和剪力影响、考虑/不考虑屈曲前变形影响的临界荷载,并讨论了拱轴不可伸长假定的影响。系统地与前人的研究进行了比较。     

体外预应力钢筋极限应力的理论分析

本文研究体外预应力混凝土梁的本外力筋极限应力的计算问题，它是研究结构抗弯承载力的关键。根据结构破坏时的变形几何关系，提出了一个计入二次影响问题的理论方程，用这个方程分析一组实验梁，结果与实验值符合良好。     

基于MATLAB的应力环校准方程线性回归分析

工程实践中通过测量应力环的变形量来完成硫化物应力腐蚀开裂试验.本文用软件实现应力环校准方程的最小二乘法线性回归分析,并给出了直观的曲线拟合界面.该法用于计量校准,使计量中线性回归分析更加简单易行、直观明了.     

反拱曲面X形异形桩产生附加应力计算方法研究

X形桩是一种具有反拱曲面的新型异形桩,该文以半无限体内受竖向集中力作用的Mindlin应力解为依据,通过沿X形桩桩周8个积分区间线积分,再沿桩长进行积分,得到了X形桩侧摩阻力沿桩身线性增长、沿桩周均匀分布、沿桩身矩形分布、沿桩周均匀分布侧摩阻力产生竖向附加应力系数的数值计算方法。通过沿X形桩截面3个积分区间面积积分,得到了X形桩均布端阻力在地基内产生竖向附加应力系数的数值计算方法。X形桩侧摩阻力和端阻力产生附加应力系数均随着外包方形截面边长和开弧间距增大而减小,随弧度数增大而增大。同周长X形桩侧摩阻力产生附加应力系数大于圆形桩,周长越大差别越大;同面积X形桩端阻力产生附加应力系数小于圆形桩,面积越大差别越大。     

具有初应力的多层空心圆柱体中的导波

基于“增量变形力学”理论,研究了轴向初应力和径向初应力对多层空心圆柱体中导波传播特性的影响,应用Legendre多项式方法求解了耦合波动方程,并通过数值算例讨论了该方法的收敛性,分析了初应力对纵向波和扭转波的影响,数值分析结果表明初应力对两者的影响是非常不同的。此外,轴向初应力对频散曲线的影响与径向初应力的影响也非常不同。     

直埋敷设热力管道强度设计理论及方法

描述了直埋敷设热力管道上的作用以及相应的变形，将作用产生的应力分为一次应力、二次应力和峰值应力，提出了直埋敷设热力管道强度设计的应力分类法。分析了直埋敷设热力管道的破坏方式，直管的破坏方式包括循环塑性变形的整体失稳，而疲劳破坏是管件的主要破坏方式，针对不同的破坏方式，讨论了强度设计方法。     

载流悬臂柱壳的非线性数值分析

针对在电磁场和机械场耦合作用下的载流柱壳的非线性变形问题的数值解法进行了研究。给出了载流柱壳在耦合场作用下的几何方程、物理方程、二维电动力学方程、磁弹性非线性运动方程和洛仑兹力表达式,建立了差分格式和线性化迭代方程,给出了这些方程的数值解系统,并以悬臂柱壳为例,计算了该壳在电磁场和机械载荷耦合作用下的应力及变形;讨论了其应力及变形与外加电磁参量之间的关系;证明了变化电磁参量可以对壳的工作状态实施控制。     

满足板面载荷和横向剪应力连续的层板理论

本文提出了一种简单高阶剪切变形层板理论.其位移场满足层间位移和横向剪应力的连续性,τ_xx、τ_yx在板面等于与板面平行的载荷.位移场的变量与一阶剪切变形理论一样只有五个,但无论厚薄板均逼近精确解.文中合理考虑了层板板面上与板面平行的载荷对层板的作用,大大改善了这类问题解的精度.      

Stable linear traction‐based equilibrium elements for elastostatics: Direct access to linear statically admissible stresses and quadratic kinematically admissible displacements for dual analysis

This paper establishes the basic framework for the traction‐based equilibrium finite element method (traction‐based EFEM). Stable linear traction‐based equilibrium elements are formulated using the macro‐element technique. An arbitrary internal macro‐point renders a linear triangular element stable, while a stable linear quadrilateral element requires the macro‐point to locate at the intersection of diagonals. Then, a Lagrangian formulation is utilized to minimize the complementary energy under equilibrium constraints, and consequently, tractions as well as additional Lagrange multipliers are obtained. Linear statically admissible (SA) stresses are thereafter acquired from tractions. As for Lagrange multipliers, they turn out to coincide well with rigid‐body displacements in each element after simple modifications. With rigid‐body displacements and linear tractions known, quadratic displacements and the kinematically admissible (KA) counterpart thereof by recovery are obtainable. The knowledge of both SA stresses and KA displacements renders dual analysis directly applicable. That is to say, the traction‐based EFEM is featured with direct access to strict upper and lower bounds of strain energy and other quantities of interest. Copyright © 2014 John Wiley & Sons, Ltd.     

High-order free vibrations of doubly-curved sandwich panels with flexible core based on a refined three-layered theory

There are few reports on the free vibration of soft core doubly-curved sandwich shells. Previous studies are largely based on the equivalent single layer theories in which the natural frequencies are grossly overestimated. This study deals with the analytical free vibrations of doubly curved sandwich shell with flexible core based on a refined general-purpose sandwich panel theory. In this theory, equations of motion are formulated based on displacements and transverse stresses at the interfaces of the core. The first order shear deformation theory and assumptions of linear distribution of transverse normal stress and uniform shear stresses over the thickness of core (based on 3D-elasticity solution of weak core) are used in the present theory. In this model, the in-plane displacements take cubic polynomial distributions and the transverse displacement has a quadratic one thorough the core thickness. Hamilton’s principle is used to obtain the equations of motion. The obtained results are validated by the analytical and numerical results published in the literatures. Parametric study is also included to investigate the effects of radius of curvature, thickness and flexibility of core.     

单向复合材料弹塑性变形行为的研究

本文利用微观力学方法研究了单向连续纤维增强的金属基复合材料的弹塑性变形行为。纤维是线弹性材料,基体是弹性一粘塑性各向同性材料。在复合材料的纵向拉伸、横向拉伸和纵向剪切变形状态下,预测了复合材料的弹性模量和初始屈服应力值,并考虑了应变率对弹塑性变形行为的影响。以硼/铝复合材料为例,进行了数值分析,预测结果与实验值符合较好。      

EXPONENTIAL MAP ALGORITHM FOR STRESS UPDATES IN ANISOTROPIC MULTIPLICATIVE ELASTOPLASTICITY FOR SINGLE CRYSTALS

This paper presents a new stress update algorithm for large-strain rate-independent single-crystal plasticity. The theoretical frame is the well-established continuum slip theory based on the multiplicative decomposition of the deformation gradient into elastic and plastic parts. A distinct feature of the present formulation is the introduction and computational exploitation of a particularly simple hyperelastic stress response function based on a further multiplicative decomposition of the elastic deformation gradient into spherical and unimodular parts, resulting in a very convenient representation of the Schmid resolved shear stresses on the crystallographic slip systems in terms of a simple inner product of Eulerian vectors. The key contribution of this paper is an algorithmic formulation of the exponential map exp: sl(3) → SL(3) for updating the special linear group SL(3) of unimodular plastic deformation maps. This update preserves exactly the plastic incompressibility condition of the anisotropic plasticity model under consideration. The resulting fully implicit stress update algorithm treats the possibly redundant constraints of single-crystal plasticity by means of an active set search. It exploits intrinsically the simple representation of the Schmid stresses by formulating the return algorithm and the associated consistent elastoplastic moduli in terms of Eulerian vectors updates. The performance of the proposed algorithm is demonstrated by means of a representative numerical example.     

INTERLAMINAR STRESSES IN SHELLS OF REVOLUTION

SUMMARY

A comparative study of the interlaminar stresses in shells of revolution has been made between first order shear deformation theory (FSDT), higher order shear deformation theory with thickness stretch (HSDT7), higher order shear deformation theory with higher order inplane displacement terms (HSDT9) and three-dimensional finite element (3D) models. A semi-analytical approach is used for all the models. Interlaminar stresses are evaluated using equilibrium equations in the cases of FSDT, HSDT7 and HSDT9 models as interlaminar stresses obtained from constitutive equations are not correct. For the 3D model an eight-noded quadratic quadrilateral semi-analytic solid element is used whereas for equivalent single layer (ESL) theories a three-noded isoparametric curved element is used. Crossply parabolic and hyperbolic caps subjected to uniform external pressure and a simply supported cylindrical shell subjected to an internal sinusoidal pressure are considered in the present study.     

非线性隔振理论初探

本文以线必阻尼，立方刚度非线性系统为例，对非线性隔振理论进行了初步探讨，导出了系统的无量纲运动响应和传递率，并与线性隔振系统进行了比较，着重讨论了非线性对它们的影响，获得了一些有用的结论。     

隔膜压缩机膜片破裂理论分析

隔膜压缩机膜片裂纹通常产生在支板最外圈环槽边沿及中间处,且裂纹呈周向分布,因此径向应力过大是导致膜片破裂的主要原因。隔膜压缩机中柱塞泵不稳定工作会导致油缸内油量不足,在此情况下当活塞运动到下止点时膜片会紧贴支板,环槽处膜片承受贴合支板引起的大挠度变形径向应力及环槽处附加变形引起的小挠度变形径向应力。该文利用薄板大挠度及小挠度理论对两种应力进行了求解,计算结果表明:当进气压力为1.7MPa,最外圈环槽两边沿处及中间处膜片总径向应力为272.6MPa、275.7MPa、220.4MPa,大于膜片许用径向应力170MPa,其中小挠度变形径向应力为140.1MPa、138.2MPa、107.4MPa,因此附加变形对膜片寿命影响很大。     

基于整体-局部位移假设的高阶理论及其三角形板单元

本文推导一种基于整体-局部位移假设的高阶理论, 该理论满足层间位移、应力连续条件, 满足上、下自由表面条件。建立基于此高阶理论的三节点三角形层合板单元。数值计算结果表明此高阶理论能很好地描述剪切变形效应, 该位移单元不仅能很好地计算整体位移参数, 而且能很好地计算横向剪切应力。