Stress distribution in a glassfiber-reinforced plastic shell structure under impulsive transverse loading

The paper outlines a method and results of experimental determination of vibratory stresses in a shell structure contacting with a medium. The stresses peak at the junction between the shell and the branch pipe. It is established that when the shell is in contact with the medium, the vibratory stresses are much higher, while the vibratory accelerations are much lower     

Convective cooling/heating induced thermal stresses in a fluid saturated porous medium undergoing local thermal non-equilibrium

Local thermal non-equilibrium (LTNE) may have profound effects on the pore pressure and thermal stresses in fluid saturated porous media under transient thermal loads. This work investigates the temperature, pore pressure, and thermal stress distributions in a porous medium subjected to convective cooling/heating on its boundary. The LTNE thermo-poroelasticity equations are solved by means of Laplace transform for two fundamental problems in petroleum engineering and nuclear waste storage applications, i.e., an infinite porous medium containing a cylindrical hole or a spherical cavity subjected to symmetrical thermo-mechanical loads on the cavity boundary. Numerical examples are presented to examine the effects of LTNE under convective cooling/heating conditions on the temperature, pore pressure and thermal stresses around the cavities. The results show that the LTNE effects become more pronounced when the convective heat transfer boundary conditions are employed. For the cylindrical hole problem of a sandstone formation, the thermally induced pore pressure and the magnitude of thermal stresses are significantly higher than the corresponding values in the classical poroelasticity, which is particularly true under convective cooling with moderate Biot numbers. For the spherical cavity problem of a clay medium, the LTNE effect may become significant depending on the boundary conditions employed in the classical theory.     

A suppression method for thermomechanical stresses during the laser processing of structural elements

A method to reduce thermomechanical stresses during the laser processing of a beam-like specimen along its side surface and a thin disk along its central circular hole is considered. Some analytical temperature expressions are obtained in both these cases. The problems of determining thermal stresses during the heating of specimens with consideration of heat transfer on their surfaces are solved. The solutions obtained with heat transfer and without it are compared. It is shown that the side surface blowing can be used to suppress the fracture of heated specimens.     

Steady state responses of poroelastic half-space soil medium to a moving rectangular load

The dynamic steady state responses of a poroelastic half-space soil medium subjected to a moving rectangular load are investigated analytically/numerically. The full dynamic poroelastic theory of Biot is employed, under the assumption of an incompressible solid grain and neglecting the apparent mass density. Using the Fourier transform, the governing equations of motion are then reduced to a system of four coupled ordinary differential equations which are solved semi-analytically. Soil vertical displacements, accelerations and pore water pressures induced by moving load are calculated. Computed result shows that load velocity and intrinsic permeability of the soil medium shows an apparent effect on its dynamic responses and pore water pressures.     

Dynamic behavior of inelastic cylindrical shells at finite deformation

Numerical approaches based on a minimum principle in dynamic finite plasticity are developed to study the dynamic behavior of inelastic cylindrical thin shells and rectangular plates at finite deformation. The minimum principle, which is based on the concept of finite variations in accelerations, is expressed in terms of Lagrangian strains and Kirchhoff stresses. The responses of a clamped cylindrical shell panel and a clamped rectangular plate to impulsive loadings are analyzed by using an incremental finite-difference method. An incremental Kantorovich method is employed to study the dynamic behavior of a complete cylindrical shell of finite length and loaded impulsively on its inner surface. The motions are simulated through a timewise step-by-step integration scheme. The results obtained in this analysis compare favorably with the theoretical and experimental results available in the literature.     

Three-dimensional elastostatics of a layer and a layered medium

This paper is concerned with the determination of the distribution of stresses and displacements in an infinite three-dimensional, linear, elastic, isotropic, homogeneous layer subjected to concentrated body forces acting upon an arbitrary internal point.In §2 and §3 the governing partial differential field equations are reduced to a system or ordinary differential equations by the use of the two-dimensional Fourier transform, taken with respect to the two in-plane geometric variables (§4). Analytical expressions for the stresses and displacements are then obtained for the particular case of concentrated body forces, represented as Dirac delta functions (§5).The results are subsequently utilized to formulate the multilayered medium problem by means of transfer matrices. In §8 the typical problem of a non-adhesive layered medium is undertaken.     

饱和多孔介质化学-热-弹性模型及应用

本文基于热局部非平衡(LTNE)条件和加权平均温度概念,并假设孔隙流体由溶质和溶剂两组元组成,对页岩（饱和多孔介质）,推导给出了一种LTNE条件下的化学-热-弹性模型,同时讨论了耦合方程组的解耦求解问题．作为模型的应用,考虑无限大平面含一圆形孔的情况,研究了冷/热对流以及溶质摩尔分数突变边界条件下圆孔附近的孔隙压力和化-热应力问题,用Laplace变换得到了平面轴对称情况下有关力学变量的表达式．数值分析了圆孔边界上冷/热对流的Biot数和溶质摩尔分数改变量对圆孔附近孔隙压力和化-热应力的影响．结果表明：在Biot数为中等值(1~5)范围内,LTNE效应是非常明显的;化学作用对孔隙压力和固相应力的影响不可忽视．     

Comparison of near- and far-fault ground motion effect on the nonlinear response of dam–reservoir–foundation systems

In this paper, it is aimed to compare the near- and far-fault ground motion effects on the nonlinear dynamic response of dams including dam–reservoir–foundation interaction. Two different types of dams, which are concrete arch and concrete faced rockfill dams, are selected to investigate the near- and far-fault ground motion effects on the dam responses. The behavior of reservoir water is taken into account using Lagrangian approach. The Drucker–Prager material model is employed in nonlinear analyses. Near and far-fault strong ground motion records, which have approximately identical peak ground accelerations, of Loma Prieta (1989) earthquake are selected for the analyses. Displacements, maximum and minimum principal stresses are determined using the finite element method. The displacements and principal stresses obtained from the analyses of dams subjected to each fault effect are compared with each other. It is clearly seen that there is more seismic demand on displacements and stresses when the dam is subjected to near-fault ground motion.     

Symmetrical Representation of Stresses in the Stroh Formalism and its Application to a Dislocation and a Dislocation Dipole in an Anissotropic Elastic Medium

Symmetrical stress representation in the Stroh formalism for anisotropic elastic bodies is introduced and the range of its applicability is analysed. By making use of this stress representation new formulae for influence functions giving stresses in an infinite anisotropic medium subjected to a straight dislocation and a straight dislocation dipole are derived. The advantage of the new formulae is that they explicitly show the symmetrical structure of these influence functions not referred to previously. Relations of these influence functions to influence functions giving stresses and Airy stress function due to a straight wedge disclination, whose explicit expressions are also introduced, are derived. Application of these results in computation of stresses by the hypersingular and regularized Somigliana stress identities is discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

基座角振动对捷联惯导加速度测量所产生的影响及其误差补偿方法

在对捷联 子惯导进行空中传递对准时，针对基座的角振动而会给加速度的测量带来不可忽略的原理误差，从刚体运动学的角度出发，分析了此原理误差产生的机理和对传递对准所产生的影响的性质和程度，并给出根除此原理误差的各种有效的技术途径。     

Theoretical and experimental study of the isothermal mechanical behaviour of alloys in the semi-solid state

An isothermal constitutive model for semi-solid alloys based on the concepts of mechanics of continuous media and the theory of mixtures is presented. The model is applicable to semi-solid states obtained either by solidification from liquid state or partial remelting from solid state in which each of the solid and the liquid phases is contiguous. During deformation their behaviours are coupled: the densification of the solid matrix considered as a porous viscoplastic medium saturated with a liquid drives the fluid flow behaviour, and the resulting pressure distribution in the liquid affects in turn the stresses and the densification of the solid. The identification procedure of the model uses two types of mechanical tests: uniaxial compression and drained die pressing (filtration) carried out with A356 alloy. The identification results are then validated using drained triaxial compression.     

The Role of Effects Due to Nonlocality and Delay in Transfer Processes in Microstructured Media

The role of effects due to nonlocality and delay in irreversible transfer processes, which arise after taking into account nonequilibrium phenomena in the medium structure is studied. By an example of the isothermal response of the medium to an instantaneous perturbation of shear velocity, the evolution of stresstensor components is studied. It is shown that, in a medium of constant density, its strained state is determined by the tangent shear stress, by the first and second differences of normal stresses, and by the relaxation of these differences to their equilibrium values in an oscillatory process with a decaying amplitude. In this case, thermodynamic variables of state pressure tensor and internal energy are functions of shear velocity and time. It is found that the approximation of locally equilibrium thermodynamics is valid for microstructured media if their relaxation times are an order of magnitude shorter than the characteristic time of the problem.     

Defects in gradient micropolar elasticity—I: screw dislocation

A gradient micropolar elasticity is proposed based on first gradients of distortion and bend-twist tensors for an isotropic micropolar medium. This theory is an extension of the theory of micropolar elasticity with couple stresses together with gradient elasticity in a way that in addition to hyper stresses, hyper couple stresses also appear. In particular, the strain energy, besides its dependence upon the distortion and bend-twist terms of a micropolar medium (Cosserat continuum), depends also on distortion and bend-twist gradients. Using a simplified but rigorous version of this gradient theory, we can connect it to Eringen's nonlocal micropolar elasticity. In addition, it is used to study a screw dislocation in gradient micropolar elasticity. One important result is that we obtained nonsingular expressions for the force and couple stresses. The components of the force stress have maximum values near the dislocation line and those of the couple stress have maximum values at the dislocation line.     

Minimum principles in the dynamics of isotropic rigid-plastic and rigid-viscoplastic continuous media

Summary The paper discusses the incremental boundary value problem for rigid-viscoplastic isotropic continua subjected to dynamic actions. A pair of dual extremum theorems reduces the problem to the minimization of some functionals in a class of functions defined by appropriate constraints. The first theorem takes as variables stresses and accelerations, the latter only the accelerations. Some conclusions end the paper.

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Sommario Viene discussa la soluzione incrementale dei problemi al contorno per i mezzi continui rigido-viscoplastici isotropi soggetti ad azioni dinamiche. Si dimostrano due teoremi duali che riportano il problema alla minimizzazione di opportuni funzionali in una classe di funzioni definita attraverso vincoli appropriati. Il primo teorema concerne le tensioni e le accelerazioni, il secondo le sole accelerazioni. Alcune considerazioni conclusive chiudono il lavoro.

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The results presented in the paper form part of a Research supported by the National Research Council (C.N.R.).     

混凝土核安全壳干缩应力的计算

提出内约束干缩应力和外约束干缩应力的概念,利用混凝土的蠕变理论,建立了考虑施工过程的有限元计算模型,编制了电算程序,计算了秦山核安全壳在施工过程中的干缩应力。     

Mathematical modeling of transport-growth processes in multiphase biological continua

The model of a growing medium consisting of two phases, liquid and solid, is developed. Growth is treated as a combination of the irreversible deformation of the solid phase and its mass increment due to mass exchange with the liquid phase. The inelastic strain rate of the solid phase depends on the stresses in it, which are determined by the forces both external with respect to the medium and exerted by the liquid phase. In the liquid phase the pressure develops due to the presence of a chemical component whose displacement is hampered by its interaction with the solid phase. The approach developed makes it possible to waive many problems discussed in the theory of growing continua. Possible generalizations are considered.     

柔性轮对的离散时间传递矩阵法建模及垂向振动

针对铁道车辆轮对系统的弹性振动及台架高频激振试验仿真问题, 以离散时间传递矩阵法建立了柔性轮对振动模型. 基于Newmark-β隐式法积分格式推导了分布质量弹性轮轴、集总质量车轮及弹簧-阻尼单元的离散时间传递矩阵, 采用Riccati法、Newmark-β法实现轮对系统垂向振动加速度以及速度、位移的求解, 将轮对模型与采用新型显式积分法求解的构架、轨道轮组动力学模型集成, 完成机车车辆单轴滚振试验台的动力学建模, 提出了混合积分模式下动态仿真求解流程. 基于滚振试验台, 开展了轨道轮初始表面粗糙度、打磨多边形及局部凹陷状态下300 ~ 400 km/h高速运行试验, 同步开展了相应的动力学仿真, 通过在时域-频域对测试和计算结果的比较, 检验了理论模型. 结果表明, 在振动加速度的时域-频域特性和幅值分布上, 单轮对柔体模型总体能够较好反映500 Hz频率下系统的中高频振动规律, 有效捕捉车轮不圆、多边形磨耗、局部凹陷等动态激扰, 三种轨面状态下计算的轴箱加速度幅值误差总体低于9%, 模型具有较好的适应性和准确性. 但相关建模方法如何在复杂空间结构中应用需要进一步探索.      

Conditional Fluid-Particle Accelerations in Turbulence

Simple closures for average fluid-particle accelerations, conditional on fixed local fluid velocity, are considered in isotropic, homogeneous and stationary turbulence using exact probability density transport equations and are compared with direct numerical simulations (DNS). Such accelerations are common ingredients in Lagrangian stochastic models for fluid-particle trajectories in turbulence. One-particle accelerations are essentially trivial, so the focus is on two-particle relative accelerations, which are important in the relative dispersion process. The closure is simply a quadratic form in the velocity variable and this special form also defines the Eulerian velocity probability density function (pdf), and comparisons with DNS (for grids up to 512³) of both the acceleration closure and velocity pdf's are encouraging. Received 2 June 1997 and accepted 29 December 1997     

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针对回转窑运行轴线变化所引起筒体发生弯曲振动, 推导了托轮系统各向异性等效刚度计算方程，发展了传递矩阵法来建立回转窑的动力 学模型，并进行实例求解分析，从理论上阐明了常用的轴线检测方法存在动态误差的本质缺 陷，为计算筒体动应力和轴线检测动态误差提供了基础方程.     

FEA in elasticity of random structure composites reinforced by heterogeneities of non canonical shape

One considers linearly elastic composite media, which consist of a homogeneous matrix containing a statistically homogeneous random set of aligned homogeneous heterogeneities of non canonical shape. Effective elastic moduli as well as the first statistical moments of stresses in the phases are estimated. The explicit new representations of the effective moduli and stress concentration factors are expressed through some building block described by numerical solution for one heterogeneity inside the infinite medium subjected to homogeneous remote loading. The method uses as a background a new general integral equation proposed in Buryachenko, 2010a, Buryachenko, 2010b, which incorporates influence of stress inhomogeneity inside the inclusion on the effective field and makes it possible to reconsider basic concepts of micromechanics such as effective field hypothesis, quasi-crystalline approximation, and the hypothesis of “ellipsoidal symmetry”. The results of this reconsideration are quantitatively estimated for some modeled composite reinforced by aligned homogeneous heterogeneities of non canonical shape. Some new effects are detected that are impossible in the framework of a classical background of micromechanics.