不确定非线性结构动力响应的区间分析方法

研究多自由度非线性不确定参数系统的动力响应问题. 以区间数学为基础，将不确定 性参数用区间进行定量化，借助一阶Taylor级数，给出了近似估计非线性振动系统动力响 应范围的区间分析方法. 从数学证明和数值算例两方面，将其与概率摄动有限元法进行了比 较，结果显示区间分析方法对不确定参数先验信息具有要求较少、精度较高的优点.     

大挠度弯曲直梁混合变量最小势能原理的应用

应用大挠度弯曲直梁混合变量最小势能原理,求解均载两端固定大挠度柱面弯曲板条的轴向挠度分布和轴向弯矩分布．实例计算表明:该方法简单实用、精度高,是一种计算大挠度柱面弯曲板条变形的有效方法．     

定量开采条件下径向渗流的液固耦合问题

考虑到多孔介质渗透率随孔隙度变化的特点，建立了力学模型，研究定量抽放问题；对于广义平面应力状态下的非线性渗流耦合问题，提出了解的构造方法和解耦方法；求出了耦合条件下的孔隙压力，多孔介质总应力、总应变和总位移的解析解；进行了实例计算，并与Biot理论进行了对比，结果表明两种理论的差别很大。因此在渗透系数有较明显变化的场舍下不能采用Biot理论进行分析。     

Regime diagram of the development of long-wave near-wall disturbances in a hypersonic boundary layer

A regime diagram of the development of slow near-wall disturbances induced by an unsteady self-induced pressure perturbation in a hypersonic boundary layer is constructed for a disturbance wavelength greater than the boundary layer thickness. It is shown that the main factors shaping the perturbed flow are the gas enthalpy near the body surface, the intensity of the viscous-inviscid interaction, and the nature (sub- or supersonic) of the main part of the boundary layer. Nonlinear boundary-value problems are formulated for regimes in which the near-wall boundary layer region plays a decisive role. Numerical and analytical solutions are obtained in the linear approximation. It is shown that intensification of the viscous-inviscid interaction or an increase in the role of the supersonic main region of the boundary layer impart generally supersonic properties to the main part of the boundary layer, i.e. the upstream propagation of the disturbances is damped and the disturbance growth downstream becomes more intense. Damping of the viscous-inviscid interaction and an increase in the role of the subsonic main part of the boundary layer have the opposite effect. Surface cooling increases the effect of the main part of the boundary layer on the formation of pressure disturbances and surface heating leads to an increase in the effect of the near-wall boundary layer region. It is also shown that for the regimes considered disturbances propagate in a direction opposite to that of the free stream from the turbulent flow region located downstream of the local disturbance development region.Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, 2004, pp. 59–71. Original Russian Text Copyright © 2004 by Bogolepov and Neiland.     

浅埋的圆柱形孔洞对SH波的散射与地震动

研究了浅埋的圆柱形孔洞对以任意方向入射的平面SH波的散射与地震动问题。利用复变函数和多极坐标方法构造了问题的位移解。当入射波的波长与圆孔的半径相比较小时,地震动将受到较大的影响。影响地震动有三个主要参数:(1)SH波的入射角0;(2)入射波波数,即圆柱形孔洞的半径与入射波半波长之比;(3)h/R,即圆柱形孔洞至表面的距离与圆孔半径之比。当较大时,地震动幅值变化激烈,位移幅值可出现跳动和放大的现象。当h/R增大至10～12时,位移幅值变化恢复至半空间的情况,表明圆柱形孔洞的影响可被忽略。     

Processing and characterization of epoxy/clay nanocomposites

Nanocomposite materials consisting of an epoxy matrix and silicate clay particles have been processed and characterized mechanically. The clay material used was a modified natural montmorillonite. The clay particles consisted of 1 nm thick layers with aspect ratios in the range of 100–1000. The clay particles were mixed with acetone and sonicated, then mixed with the polymer, deaerated and cured. The ultimate objective of processing was to produce a polymer/clay nanocomposite with separated (exfoliated) platelets, dispersed as uniformly as possible. Samples were prepared with clay concentrations of up to 10 wt%. The process used resulted in limited exfoliation but mostly intercalation, i.e., infusion of polymer between the silicate layers and increase of interlayer spacing. The characteristics of the nanocomposite were assessed by transmission electron microscopy and x-ray diffraction. Results from these observations show that the basal spacing of clay platelets increased from an initial pre-processing value of 1.85 nm to 4.5 nm. Enhancement of mechanical properties was measured by tensile testing of coupons. Stiffness increases of up to 50% over that of the unfilled epoxy were measured for clay concentrations of 5 wt%. Strength increases were also measured for low clay concentrations and low strain rate loading. Micromechanics modeling of mechanical behavior is discussed as a function of clay platelet dispersion.     

A thermodynamic approach with internal variables using Lagrange formalism. Part II. Continuous symmetries in the case of the time–temperature equivalence

In the first part of this contribution, the Lie-symmetries of the principle of least action associated to the constitutive equations of the DNLR formalism of relaxation have been presented. We examine in this second part the continuous symmetries corresponding to the simple case of stress relaxation under isothermal conditions. The well-known principle of time/temperature equivalence is discussed in terms of variational symmetry for the Jacobi’s action functional, and connected to the Onsager’s relation near the thermodynamic equilibrium.     

Ultrasonic sizing of embedded vertical cracks in ferritic steel welds

Embedded vertical cracks are very often encountered in structural components necessitating reliable procedure for determining their size. Specialized ultrasonic techniques are required for estimation of through thickness height of these cracks [Mater. Eval. (1970) 28; J. NDI 26 (1977) 320; NND (1975) 146]. The conventional pulse-echo technique has serious limitations for quantitative estimation of vertical cracks because it is subject to variations due to reflectivity, coupling factors etc. The present study aims to improve the accuracy of embedded crack height measurement based on transit time rather than the reflected amplitude [NDT Int. (1982) 315; J. JSNDT 27 (1978) 118]. A unique method has been developed for generating known sizes of fatigue cracks ranging from 2.5 to 18 mm in height and 15 mm in length. These cracks were generated in rectangular steel specimens and subsequently embedded at predetermined locations using welding. These welded specimens containing the embedded vertical cracks were examined using ultrasonic techniques based on transit time like (a) flaw tip echo method and (b) mode conversion method. Using both the techniques excellent agreement was obtained between the estimated crack height and actual crack height with an accuracy of ±1 mm.     

开区注氮采空区自燃温度场的数值模拟研究

为了研究开区注氮采空区遗煤自燃和被抑制的力学过程，用非均质多孔介质中的渗流连续性方程、气体弥散方程和综合传热方程的联立，建立了采空区注氮非定常数值模型．结合实例，用迎风格式有限元方法求解．给出了采空区的漏风流态、氮气流态，描绘了采空区自燃过程中氧、CO浓度和温度分布的变化过程．计算考虑了瓦斯涌出和工作面推进的影响．得到注氮条件下采空区高温区形状变窄；随着注氮量的提高，使自然发火期逐渐变长，直至不自燃．理论计算与实际情况吻合．     

Drained and Undrained Poroelastic Properties of Healthy and Pathological Bone: A Poro-Micromechanical Investigation

Poro-micromechanics allows for the quantification of poroelastic properties such as the Biot and Skempton coefficients, once a continuum micromechanics model for the material under consideration has been developed and validated. Employing such a model for the transversely isotropic elasticity of cortical and trabecular bone, we determine the tensors of Biot and Skempton coefficients as functions of the volume fractions of mineral, collagen, and the micropore space (Haversian and Volkmann canals, and the inter-trabecular space). Increase of microporosity, as experienced in osteoporosis, as well as decrease of mineral content, as experienced in osteomalacia, lead to an increase of Biot and Skempton coefficients, i. e. to magnification of the mechanical role of the marrow filling the micropore space. For quantification of the marrow pressure rise upon downfall, undrained conditions are appropriate, as can be shown by model predictions of non-destructive impact experiments.