热-机荷载作用的P-FGM扁球壳跳跃屈曲分析

基于经典壳体理论和Sanders非线性应变-位移关系,导出了幂律型功能梯度材料(P-FGM)扁球壳在热-机械荷载作用下的几何非线性常微分控制方程。推导过程考虑了沿厚度存在一维热传导温度场和法向均布荷载作用。采用打靶法求解了由控制方程和固定夹紧边界条件构成的两点边值问题。得到了FGM扁球壳的一些典型的屈曲平衡路径和双稳态构形。对热-机械荷载作用的FGM扁球壳的跳跃屈曲行为进行了参数影响分析。结果表明：温度上升时,球壳上临界荷载显著增加、下临界荷载变化不明显。梯度指数增加时,球壳上、下临界荷载均显著减小。组分材料模量增加时,球壳上、下临界荷载均显著增加。当底圆半径和厚度给定时,随壳体中面曲率半径增加,球壳上、下临界荷载均显著增加。当中面曲率半径和厚度给定时,随底圆半径增加,球壳下临界荷载显著减小,上临界荷载几乎不变。     

PUBLICATIONS ON THERMAL STRESSES

The study of the nonlinear response of sandwich flat panels exposed to thermomechanical loading systems is the topic of this article. The sandwich structure considered in this article consists of a thick core layer bonded by the face layers, which are assumed to be symmetrically located with respect to the midplane of the overall structure. The loads involved in this analysis consist of biaxial compressive edge loads, a lateral pressure, and a nonuniform temperature field. The effects of the unavoidable initial geometric imperfections and the character of tangential boundary conditions are incorporated, and their implications upon the structural response are explored. In short, the results of this study are intended to provide pertinent information on the thermomechanical load-carrying capacity of flat sandwich structures.     

局部加强体对预压双稳态结构跳转力学特征的影响分析

基于轴向挤压后屈曲模态的双稳态结构,其跳转力、保持力和跳转行程等双稳态特征与预应力分布和后屈曲模态密切相关,使得难以通过仅调整预压缩量来实现特定双稳态指标的设计。本文提出引入局部加强体调控预压双稳态梁临界屈曲载荷、应力分布及跳转特征的方法,建立了具有对称局部加强体的预压双稳态梁跳转分析模型,分析了预应力、加强体尺寸参数和位置对屈曲临界载荷、跳转力和行程的影响规律。结果表明:局部加强体不影响原结构跳转力和保持力相等的特征;与尺寸参数相比加强体位置参数对跳转力有较大影响,随着位置的变化,跳转力存在由大变小再变大的变化过程,且调控同行程双稳态梁跳转力的幅度可达17.04%;跳转行程主要依赖于局部加强体的刚度和所承受的预应力。     

钢结构失稳监测方法和失稳监控部件研究

为了预防钢结构发生灾难性失稳破坏,根据结构失稳与结构响应或特征参数之间的关系,将目前应用于结构健康监测和损伤诊断的方法扩展到钢结构失稳监测领域;评述并归纳了基于应变和位移变化趋势、基于振动-失稳相关性、基于薄壳体积改变率、基于失稳先兆的钢结构失稳监测方法;进一步对3种钢结构失稳监控部件进行了概念设计,包括钢套管压力监控、节点塌陷监控、坦拱和扁壳跃越失稳监控;总结了各种监测方法的特点和存在的问题。     

基于突变理论的扁拱跳跃屈曲分析

分析了扁拱在静载荷或动载荷作用下发生跳跃屈曲的原因。采用尖点突变理论建立悬链线形拱的跳跃屈曲模型，推导临界荷载公式，并采用Matlab工具计算及Ansys验算模型理论正确性，最后对上述两种方法所得值进行比较。     

Radiolysis of Hydrogen Cyanide in an Aqueous System, (III)

Dependence of radiolysis on pH in deaerated aqueous HCN (6 mM) has been investigated. The radiolytic yield of HCN decomposed, G(— HCN), decreases to a limiting value of 2.9 in the pH range while G(— HCN) at pH 5–8 is observed to be 5.8. The radiolytic yields of ammonia (G = 1.9), formaldehyde (G = l.l) and carbon dioxide (G = 0.6–0.8) are little affected by changes in pH. The formation of polymeric HCN is inhibited by decreasing pH. This can be explained as the result of the degradation from dimeric to monomeric form undergone by HCN, which is known to be an intermediate compound.

Based on experiments on the effect of adding Cl as OH radical scavenger, it is considered that formaldehyde and a part of ammonia are produced through methylenimine as intermediate.

The radiolysis of aqueous KCN is also studied for making a comparison of the radiolysis behavior between cyanide ions and undissociated HCN.     

弧长法中初始荷载增量参数符号确定准则的改进

在结构非线性全过程跟踪分析中,弧长控制类方法由于其概念简单明了、计算方便可靠,目前已成为一种最主要的跟踪技术。在该方法的使用过程中,初始荷载增量参数符号的确定非常重要,它决定了当前跟踪分析是向前还是返回(Tracing-back)。本文在比较现有准则的基础上,提出了一种依据当前刚度参数进行判定的新准则,并以两个经典算例为例进行考证,其中一个算例同时存在跳跃(Snap-Through)及跳回(Snap-Back)现象且具有分枝路径。分析结果表明,该准则简单实用,在跟踪复杂失稳过程中是非常有效的,具有很好的适用性。     

In-plane elastic stability of fixed parabolic shallow arches

The nonlinear behavior of fixed parabolic shallow arches subjected to a vertical uniform load is inves- tigated to evaluate the in-plane buckling load. The virtual work principle method is used to establish the non-linear equilibrium and buckling equations. Analytical solutions for the non-linear in-plane sym- metric snap-through and antisymmetric bifurcation buckling loads are obtained. Based on the least square method, an approximation for the symmetric buckling load of fixed parabolic arch is proposed to...     

Numerical evaluation of buckling behavior in space structure considering geometrical parameters with joint rigidity简

The buckling behavior of single layer space structure is very sensitive. The joint rigidity, moreover, is one of the main factors of stability which may determine the entire failure behavior. Thus, the reasonable stiffness of joint system, which is neither total pin assumption nor perfect fix condition, is very important to apply to the real single layer space one. Therefore, the purpose of this work was to investigate the buckling behavior of single layer space structure, using the development of the upgraded stiffness matrix for the joint rigidity. To derive tangential stiffness matrix, a displacement function was assumed using translational and rotational displacement at the node. The geometrical nonlinear analysis was simulated not only with perfect model but also with imperfect one. As a result, the one and two free nodal numerical models were investigated using derived stiffness matrix. It was figured out that the buckling load increases in proportion to joint rigidity with rise-span ratio. The stability of numerical model is very sensitive with the initial imperfection, responding of bifurcation in the structure.     

Non-linear coupled multi-field mechanics and finite element for active multi-stable thermal piezoelectric shells

In this paper, a coupled multi-field mechanics framework is presented for analyzing the non-linear response of shallow doubly curved adaptive laminated piezoelectric shells undergoing large displacements and rotations in thermal environments. The mechanics incorporate coupling between mechanical, electric and thermal fields and encompass geometric non-linearity effects due to large displacements and rotations. The governing equations are formulated explicitly in orthogonal curvilinear coordinates and are combined with the kinematic assumptions of a mixed-field shear-layerwise shell laminate theory. A finite element methodology and an eight-node coupled non-linear shell element are developed. The discrete coupled non-linear equations of motion are linearized and solved, using an extended cylindrical arc-length method together with a Newton–Raphson technique, to enable robust numerical predictions of non-linear active shells transitioning between multiple stable equilibrium paths. Validation and evaluation cases on laminated cylindrical strips and cylindrical panels demonstrate the accuracy of the method and its robust capability to predict non-linear response under thermal and piezoelectric actuator loads. Moreover, the results illustrate the capability of the method to model piezoelectric shells undergoing large shape changes by actively jumping between stable equilibrium states and quantify the strong relationship between shell curvature, applied electric potential, applied temperature differential and induced shape change. Copyright © 2008 John Wiley & Sons, Ltd.