模糊随机荷载激励下模糊桁架结构的模糊随机动力响应的双因子分析方法

采用了一种新的双因子分析法研究了模糊参数桁架结构在模糊随机荷载激励下的动力响应问题.同时考虑结构参数模糊性和外载荷幅值的模糊随机性,利用模糊因子法和振型迭加法求出了动力响应模糊随机变量;进而基于随机因子法推导了动力响应的模糊数字特征.最后通过算例考察了结构参数和荷载的不确定性对动力响应的影响.     

截锥型薄壁结构声振耦合动力特性分析

采用大型通用软件ANSYS,建立截锥型薄壁结构的实体有限元动力学模型,通过与相关实验数据的对比验证了模型合理性。据此,利用无限元模拟自由声场边界,建立声场-截锥型薄壁结构的直接耦合有限元动力学模型。通过数值仿真分析研究了声场中截锥壳结构的振动特性,并讨论了声振动对结构动力特性的影响。研究结果表明:数值仿真结果和截锥壳声振实验数据比较一致。在考虑声场影响后发现:结构位移共振频率值大多有所降低,结构位移共振频率数量显著增多;在低频下,结构位移响应峰值在声场的影响下明显增大;在高频下则明显减小。     

A Method of Modeling the Interaction of Creep and High-Cycle Fatigue

The interaction of creep and fatigue in structural materials under high-cycle loading is modeled using isochronic limit stress diagrams. The hypothesis of a unified limit diagram invariant to the time to failure is used. The unified diagram is given by a cosine power function with the exponent describing creep-fatigue interaction and encompasses convex, concave, and S-like curves. The models build are tested for aluminum alloys, heat-resistant steels, creep-resistant steels and alloys, and laminates__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 1, pp. 25–36, January 2005.     

Postcritical deformation of steels in plane stress state

We study the laws determining the mechanical behavior of materials at the postcritical deformation stage. Proportional tension-torsion tests of thin-walled tubular specimens of structural steels were carried out for various deformation trajectories to obtain experimental data about the work softening of steels under plane stress state conditions. The obtained experimental data were analyzed to determine the instant of time in the deformation process at which the transition to the postcritical stage occurs.     

Loading rate spectra for fracture initiation in metals

In the first part of the paper a review of experimental results is presented on the effects of loading rate of the fracture initiation toughness of structural alloys. Recent progress in new experimental techniques enables for measuring the fracture initiation properties over ten orders of magnitude in , where loading rate for plane strain fracture toughness. The range covered in experiments is

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.Experimental results for aluminum and titanium alloys, as well as for some steels are discussed. Those results are shown as loading rate spectra where the fracture toughness K_Ic is plotted versus log at constant temperature. The patterns of the loading rate spectra demonstrate a negative role of the strain rate sensitivity in the process of fracture initiation, at least within a certain ranges of the loading rate .In the second part an attempt is presented to model the observed phenomena. Consequently, a new model has been proposed which combines an semi-empirical correlation between the critical fracture stress σ_F, yield stress σ_y from one side and a simple thermally activated potential of plastic flow from the other. It has been demonstrated that this simple approach can predict properly a fundamental changes in the loading rate spectra for steels.     

基于频率二阶摄动的结构损伤识别方法

结构损伤的定位和定量是结构健康监测的关键技术之一。本文将矩阵摄动理论、结构振动理论和有限元理论相结合推导出结构固有频率变化的二阶摄动公式,由此公式可以反演结构的损伤位置与损伤程度。该方法仅需要在役结构的固有频率测量值就能识别出结构的损伤位置和损伤程度,而且还可以识别出结构的老化程度。通过数值仿真算例证明了该方法的有效性和实用性。该方法可用于大型结构的损伤识别和健康监测。     

The dynamics of structural and functional complexity across the lifespan

The paper addresses the process of human physiological development and aging from the perspective complexity at the structural level and functional levels. The goal is to present a view of the human lifespan as a continuous increase in structural complexity of the human system, resulting in increased independence of the physiological subsystems. This brings about an increase in functional complexity early in the lifespan and an eventual loss of complexity during human aging (Lipsitz & Goldberger, 1995). Different nonlinear dynamics concepts are presented as a means of providing support for this theory of human aging and development.     

随机桁架结构的非平稳随机动力响应分析

本文研究了随机桁架结构在非平稳随机激励下的动力响应问题。在利用随机因子法分析随机结构动力特性的基础上，给出了一种分析随机结构非平稳随机响应的新方法。从结构非平稳随机响应的表达式出发，同时考虑桁架结构的物理参数、几何尺寸的随机性，利用求解随机变量函数矩的方法和求解随机变量数字特征的代数综合法，导出了随机桁架结构在非平稳随机激励下位移响应均方值和应力响应均方值的均值、方差和变异系数的计算表达式。通过算例，分析了结构物理参数和几何尺寸的随机性对结构位移响应均方值和应力响应均方值随机变量随机性的影响。本文方法具有对随机结构进行一次动力分析便可求得动力响应的数字特征，且可以考察结构任一参数的随机性对结构非平稳随机响应分析结果的影响之优点。     

弹性地基梁振动特性的近似分析方法

文中介绍了用模态摄动法分析复杂情况下弹性地基梁动力特性的近似方法。这一方法中可考虑纵向钢筋以及变地基弹性系数对弹性地基梁振动特性的影响，通过算例说明了这一方法的有效性。     

Finite element modified method of characteristics for the Navier–Stokes equations

An algorithm based on the finite element modified method of characteristics (FEMMC) is presented to solve convection–diffusion, Burgers and unsteady incompressible Navier–Stokes equations for laminar flow. Solutions for these progressively more involved problems are presented so as to give numerical evidence for the robustness, good error characteristics and accuracy of our method. To solve the Navier–Stokes equations, an approach that can be conceived as a fractional step method is used. The innovative first stage of our method is a backward search and interpolation at the foot of the characteristics, which we identify as the convective step. In this particular work, this step is followed by a conjugate gradient solution of the remaining Stokes problem. Numerical results are presented for:

• a Convection–diffusion equation. Gaussian hill in a uniform rotating field.
• b Burgers equations with viscosity.
• c Navier–Stokes solution of lid‐driven cavity flow at relatively high Reynolds numbers.
• d Navier–Stokes solution of flow around a circular cylinder at Re=100.

Copyright © 2000 John Wiley & Sons, Ltd.     

Phase composition and distribution of alloying elements in the transition layer

X-ray spectral and x-ray structural analyses and optical microscopy were used to study the chemical and phase compositions and the structure and morphology of alloying elements of the transition layer produced by gas-flame and plasma spraying on St. 3sp steels. It is shown that the structure and chemical and phase compositions of the transition layer depend significantly on the technological parameters, processing methods, and the chemical composition of the coating.     

Friction Correction of Austenite Flow Stress Curves Determined under Axisymmetric Compression Conditions

Experimental Mechanics - The experimental flow stress curves of structural steels obtained from axisymmetric compression tests conducted under hot-working conditions very often include the...     

碳含量对碳素钢磁场摩擦磨损性能的影响与作用机制研究

基于自制的HY-100销-盘式磁场摩擦磨损试验机，对比研究了有无外加磁场条件下，低碳钢、中碳钢和高碳钢的滑动干摩擦行为和其磨损特性，并使用扫描电子显微镜、金相显微镜等分析了摩擦微观表面与次表面，探讨了碳含量对碳素钢磁场摩擦的影响规律和作用机理. 试验结果显示:根据碳含量的不同，有无磁场条件下碳素钢摩擦系数的变化也不同，在外加磁场条件下，低碳钢摩擦系数降低，中碳、高碳钢摩擦系数升高；随着碳含量升高，磁场对其摩擦系数的影响越小. 外加磁场可以有效改善碳素钢的磨损性能，随着碳含量升高，磁场对其磨损率的改善程度越大. 分析其原因可能为铁碳竞争氧化，这既保证了铁氧化物的减磨效应，也减缓了铁氧化物积累后的剥落. EDS能谱分析结果表明高碳钢的氧铁比最低，和铁碳氧化竞争模型推论相一致.      

Physical aging and time–temperature behavior concerning fracture performance of polycarbonate

The effects of physical aging on fracture and yielding behavior are polycarbonate are considered. Two groups of Bisphenol A-based polycarbonate, consisted of extruded PC sheets (thickness of 0.25 mm) and injection molded PC bars (thickness of 3.18 mm) are used. These samples were annealed at various temperatures ranging from 60 to 120 °C, for different times varying up to 240 h. For PC sheets the essential work of fracture (EWF) method was used to analyze fracture behavior. The results are compared to the strain energy density with aging time and aging temperature in the ranges investigated. This effect is confirmed by the change in fracture toughness, as measured by three-point bending tests. The concept of fictive temperature (T_f) was used to characterize the degree of aging in the sample. T_f of a glass in an aged state at a time t is defined as the temperature at which the volume would be equal to the equilibrium volume at T_f if the sample were instantaneously removed to that temperature. Differential scanning calorimetry (DSC) was used to determine T_f. The variations of T_f with aging time and aging temperature are in agreement with both the strain energy density measurement and the three-point bending tests. These results contradict the effects of aging on fracture toughness observed by the essential work of fracture approach. The latter showed anomalous regions of increasing fracture toughness with aging, leading to spurious conclusions. The brittle–ductile transition in fracture behavior is analyzed by an activation energy approach. Aging increases the brittle–ductile transition temperature and the effect is more pronounced for the lower molecular-weight sample. Fracture tests also showed a decrease in the entropy with aging, confirming the results observed previously from tension and compression tests.     

大型上翻式拱形钢闸门流固耦合静动力特性分析研究

论文通过三维空间有限元数值计算模型研究大型上翻式拱形钢闸门的流固耦合动力特性,取得闸门结构流固耦合条件下的振动模态参数,为闸门结构共振分析和采取合理的控振措施提供了科学依据.此外对控制结构强度和刚度的门顶溢流工况进行了闸门位移和应力分布分析,指出了存在问题和修改方向.论文成果可供类似工程设计时参考.     

Analysis of the Vibrations of Flexible Discrete-Continuous One-Dimensional Systems with Nonpotential Deformation Characteristics

An approach is proposed to solve dynamic problems for discrete-continuous flexible one-dimensional systems with nonpotential deformation characteristics. The approach is based on a generalized stationarity principle. The solution algorithm employs cubic spline functions. A numerical example demonstrates the capabilities of this approach in determining the loads and displacements in such a system under external influence__________Translated from Prikladnaya Mekhanika, Vol. 41, No. 2, pp. 68–74, February 2005.     

Strain gradient plasticity analysis of transformation induced plasticity in multiphase steels

“To what extent do plastic strain gradients affect the strengthening resulting from the transformation of small metastable inclusions into hard inclusions within a plastically deforming matrix?” is the central question addressed here. Though general in the approach, the focus is on the behavior of TRIP-assisted multiphase steels. A two-dimensional embedded cell model of a simplified microstructure composed of a single metastable austenitic inclusion surrounded by a soft ferritic matrix is considered. The cell is inserted in a large homogenized medium. The transformation of a fraction of the austenite into a hard martensite plate is simulated, accounting for a transformation strain, and leading to complex elastic and plastic accommodation. The size of a transforming plate in real multiphase steels is typically between 0.1 and 2 μm, a range of size in which plastic strain gradient effects are expected to play a major role. The single parameter version of the Fleck–Hutchinson strain gradient plasticity theory is used to describe the plasticity in the austenite, ferrite and martensite phases. The higher order boundary conditions imposed on the plastic flow have a large impact on the predicted strengthening. Using realistic values of the intrinsic length parameter setting the scale at which the gradients effects have an influence leads to a noticeable increase of the strengthening on top of the increase due to the transformation of a volume fraction of the retained austenite. The geometrical parameters such as the volume fraction of retained austenite and of the transforming zone also bring significant strengthening. Strain gradient effects also significantly affect the stress state inside the martensite plate during and after transformation with a potential impact on the damage resistance of these steels.     

Influence of environmental factors on corrosion damage of aircraft structure

Corrosion is one of the important structural integrity concerns of aging aircraft, and it is estimated that a significant portion of airframe maintenance budgets is directed towards corrosion-related problems for both military and commercial aircraft. In order to better understand how environmental factors influence the corrosion damage initiation and propagation on aircraft structure and to predict pre-corrosion test pieces of fatigue life and structural integrity of an effective approach, this paper uses the cellular automaton (CA) method to character the effect of electrolyte concentrations, dissolution probabilities, and temperature on the corrosion damage of a metal structure exposed to an aggressive environment, and the procedure for applying the local rules between the cells of the CA to simulate the corrosion damage evolution is formulated. The simulation results show that the different electrolyte concentrations, dissolution probabilities and temperature, the laws of the dissolution current with time are investigated and they obey the time power function.     

测氡在滑坡研究中的应用

测氡是一种放射性地球物理方法,利用滑坡体与其周边岩土体的结构差异,应用测氡可对滑坡进行勘探,对滑坡的结构特征进行研究,达到节约投资,缩短勘探时间的目的,并可与地质分析相互验证,为工程应用提供依据。