TiNi形状记忆合金变形特性实验研究

给出了一种ＴｉＮｉ形状记忆合金（多晶）的单轴拉压、循环拉伸加卸载、形状记忆效果、恢复力、相变塑性变形及拉压。扭转比例、非比例加卸载的实验结果，实验结果显示，其变形特性非常不同于普通的弹塑性材料：如Ｂａｕｓｃｈｉｎｇｅｒ效果提前，甚至于会出现于卸载阶段；低温下的残余变形会在加热后消失；恒载下冷却时产生相当大的塑性变形（相变塑性变形）且在加热时消失等等。多轴加载实验结果表明，比例加载时该材料的加载屈服面及卸载屈服面都基本满足Ｍｉｓｅｓ准则，但非比例加载时则不然。     

中厚板屈曲的加权残值方法

用加权残值方法分析了矩形中厚板的屈曲问题。试函数和权函数依据短梁函数进行构造。结果良好。     

Dynamics of Nonlinear Cyclic Systems with Structural Irregularity

The dynamics of weakly coupled, nonlinear cyclic assemblies are investigated in the presence of weak structural mistuning. The method of multiple scales is used to obtain a set of nonlinear algebraic equations which govern the steady-state, synchronous (modal-like) motions for the structures. Considering a degenerate assembly of uncoupled oscillators, spatially localized modes are computed corresponding to motions during which vibrational energy is spatially confined to one oscillator (strong localization) or a subset of oscillators (weak localization). In the limit of weak substructural coupling, asymptotic solutions are obtained which correspond to (i) spatially extended, (ii) strongly localized, and (iii) weakly localized modes for fully coupled systems. Throughout the analysis, the influence of structural mistunings on the resulting solutions are discussed. Additionally, numerical solutions (including linearized stability characteristics) are obtained for prototypical two- and three-degree-of-freedom (DoF) systems with various structural mistunings. The numerical results provide insight into the strong influence of structural irregularities on the dynamical behavior of nonlinear cyclic systems, and demonstrate that the combined influences of structural mistunings and nonlinearities do not lead to uniform improvement of motion confinement characteristics.     

Problem of Pulse Start-up of a Gas Bearing in a Generalized Formulation

The time-dependent motion in the lubricating layer of a gas bearing is analyzed on the basis of the compressible boundary layer equations with allowance for the inertial effects and the transverse temperature drop. After introducing certain assumptions concerning the order of the main dimensionless parameters, approximate expressions for the velocity and temperature are derived. As a result, the problem reduces to the determination of the pressure as a function of the space coordinate and time.     

CONTROLLABILITY OF A CLASS OF HYBRID DYNAMIC SYSTEMS (Ⅰ)—BASIC PROPERTIES AND PRELIMINARY RESULTS

The controllability for switched linear system with time-delay in controls was first investigated. The whole work contains three parts. This is the first part, including problem formulation and some preliminaries. Firstly, the mathematical model of switched linear systems with time-delay in control functions was presented. Secondly, the concept of column space, cyclic invariant subspace and generalized cyclic invariant subspace were introduced. And some basic properties, such as separation lemma, were presented. Finally, a basic lemma was given to reveal the relation between the solution set of a centain integral equations and the generalized cyclic invariant subspace. This lemma will play an important role in the determination of controllability. All these definitions and lemmas are necessary research tools for controllability analysis. Contributed by YE Qing-kai Foundation items: the National Natural Science Foundation of China (69925307, 60274001); the National Key Basic Reasearch and Development Program (2002CB312200); the Postdoctoral Program Foundation of China Biography: XIE Guang-ming (1972∼), Doctor (E-mail: xiegming@mech.pku.edu.cn)     

三维复合型断裂的试验方法探讨

探讨了一种能够揭示三维复合型断裂现象并能记录这些现象的三维复合型断裂研究的实验方法，用此方法完成了LC4－CS航空结构铝合金不同厚度紧凑拉伸试样的I＋Ⅱ复合型断裂试验。结果表明：此方法能够简便地确定出复合型裂纹的起裂载荷、破坏载荷、裂尖张开位移、滑移位移和起裂角，基本解决三维复合型断裂研究所需实验数据问题。同时发现此种材料试样的承载能力和超裂方向的确具有明显的厚度效应。     

复合材料层合板动态断裂韧性与损伤扩展的实验研究

研究了复合材料层合板在冲击载荷和不同温度条件下的力学行为及破坏机理。在不同温度环境下 ,利用MTS材料试验机 ,采用中等应变速率 (1/S) ,对玻璃布一环氧层板实施了冲击拉伸断裂实验 ,测试了该材料在不同温、不同应变速率下的断裂韧性值。分析了玻璃布 环氧层板材料的破坏过程及内部再伤情况     

Forced Nonstationary Vibrations of a Sandwich Cylindrical Shell with Cross-Ribbed Core

The equations of nonaxisymmetric vibrations of sandwich cylindrical shells with discrete core under nonstationary loading are presented. The components of the elastic structure are analyzed using a refined Timoshenko theory of shells and rods. The numerical method used to solve the dynamic equations is based on the integro-interpolation method of constructing finite-difference schemes for equations with discontinuous coefficients. The dynamic problem for a sandwich cylindrical shell under distributed nonstationary loading is solved with regard for the discreteness of the core__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 2, pp. 60–67, February 2005.     

随机振动载荷作用下结构Von Mises应力过程的研究

随机振动载荷作用下结构的多轴疲劳分析非常复杂，利用Von Mises应力准则将多轴应力响应转换为单轴应力是一条简单而有效的途径，其关键问题是Von Mises应力概率密度函数的确定。本文提出了Von Mises应力过程近似服从Weibull分布的假设，同时给出了确定Weibull参数的方法，为进一步直接利用Von Mises应力进行结构多轴疲劳分析创造了条件。     

岩石加卸荷破坏细观机理CT实时分析

利用与CT(computerizedtomography)机配套的专用岩石三轴加载试验设备 ,采用CT实时试验的手段对连续加载试验条件下和卸围压应力作用下砂岩破坏细观机理进行了对比研究。结果表明 ,岩石的卸荷损伤演化破坏具有突发性 ,卸围压破坏导致的扩容比连续加载破坏时大.