Elastoplastic Axisymmetric Stress-Strain State of Laminated Shells Made of Isotropic and Transversely Isotropic Materials with Different Moduli

A method is developed for analysis of the elastoplastic stress-strain state of laminated shells of revolution under axisymmetric loading. The shells are made of isotropic and transversally isotropic materials with different moduli. The method is based on the Kirchhoff-Love hypotheses for the whole laminate, the theory of deformation along paths of small curvature (for isotropic materials), and the theory of elasticity with different tensile and compressive moduli (transversely isotropic materials). The problem is solved by the method of successive approximations. Numerical examples are given __________ Translated from Prikladnaya Mekhanika, Vol. 41, No. 8, pp. 88–96, August 2005.     

Axisymmetric free vibrations of infinite thermoelastic plate

The propagation of axisymmetric free vibrations in an infinite homogeneous isotropic micropolar thermoelastic plate without energy dissipation subjected to stress free and rigidly fixed boundary conditions is investigated. The secular equations for homogeneous isotropic micropolar thermoelastic plate without energy dissipation in closed form for symmetric and skew symmetric wave modes of propagation are derived. The different regions of secular equations are obtained. At short wavelength limits, the secular equations for symmetric and skew symmetric modes of wave propagation in a stress free insulated and isothermal plate reduce to Rayleigh surface wave frequency equation. The results for thermoelastic, micropolar elastic and elastic materials are obtained as particular cases from the derived secular equations. The amplitudes of displacement components, microrotation and temperature distribution are also computed during the symmetric and skew symmetric motion of the plate. The dispersion curves for symmetric and skew symmetric modes and amplitudes of displacement components, microrotation and temperature distribution in case of fundamental symmetric and skew symmetric modes are presented graphically. The analytical and numerical results are found to be in close agreement.     

NEW METHOD FOR LOW ORDER SPECTRAL MODEL AND ITS APPLICATION

In order to overcome the deficiency in classical method of low order spectral model, a new method for low order spectral model was advanced. Through calculating the multiple correlation coefficients between combinations of different functions and the recorded data under the least square criterion, the truncated functions which can mostly reflect the studied physical phenomenon were objectively distilled from these data. The new method overcomes the deficiency of artificially selecting the truncated functions in the classical low order spectral model. The new method being applied to study the inter-annual variation of summer atmospheric circulation over Northern Hemisphere, the truncated functions were obtained with the atmospheric circulation data of June 1994 and June 1998. The mechanisms for the two-summer atmospheric circulation variations over Northern Hemisphere were obtained with two-layer quasi-geostrophic baroclinic equation.     

Safety and comfort analysis of a 3-D vehicle model with optimal non-linear active seat suspension

A generalized nonlinear model is formulated for the dynamic analysis of suspension seats with passive, semi-active and active dampers. The model incorporates coulomb friction due to suspension linkages and bushings, forces arising from interactions with the elastic limit stops, a linear suspension spring and nonlinear damping force for passive, semi-active and active dampers, while the contribution due to biodynamics of the human operator is considered to be negligible. The semi-active and active dampers are characterized by force generators in accordance with the control laws based upon suspension mass velocity. Two different suspension seats are experimentally assessed in the laboratory under sinusoidal and random excitations arising from an urban bus, and the measured data is used to demonstrate the validity of the proposed generalized model. The results showed reasonably good agreement between the model results and the measured data. Optimal model parameters are selected using the sequential unconstrained minimization technique with an objective to minimize the acceleration due to vibration transmitted to the occupant mass. The comfort and safety performance characteristics of the optimal suspension seat with semi-active and active dampers are evaluated under both the sinusoidal and random excitations based on the guidelines provided by ISO-2631. From these results, it is concluded that the comfort performance of a suspension seat with semi-active and active dampers can be considerably enhanced by 20–30%.     

Mixed Formulations of Bending Problems for Homogeneous Elastic Plates and Beams

Mixed formulations of bending problems for homogeneous plates (beams) are proposed, whose essence is that the deformation of a plate (beam) near its fixed boundary is described by the threedimensional elasticity equations, and the remaining part by the conventional equations of plate (beam) bending. At the interface between these regions, the solutions of these equations are joined. The mixed formulation allows one to describe the threedimensional stress state in the neighborhood of the fixed boundaries of plates (beams) and take into account the complex nature of the fixing conditions. Finiteelement implementation is more efficient for the mixed formulations of plate (beam) bending problems than for the wellknown threedimensional formulations.     

Parametric excitation in non-linear dynamics

Consider a one-mass system with two degrees of freedom, non-linearly coupled, with parametric excitation in one direction. Assuming the internal resonance 1:2 and parametric resonance 1:2 we derive conditions for stability of the trivial solution by using both the harmonic balance method and the normal form method of averaging. If the trivial solution becomes unstable, a stable periodic solution may emerge, there are also cases where the trivial solution is stable and co-exists with a stable periodic solution; if both the trivial solution and the periodic solution(s) are unstable, we find an attracting torus with large amplitudes by a Neimark-Sacker bifurcation. The results of the harmonic balance method and averaging are compared, as well as the results on the Neimark-Sacker bifurcation obtained by the numerical software package CONTENT and by averaging. In all cases we have good agreement.     

爆炸荷载作用下钢筋混凝土梁的动力响应及破坏形态分析

对基于Timoshenko梁理论建立的非线性动力有限元法作了改进。根据压区理论得到混凝土的平均剪应力和平均剪应变关系,建立了能反映箍筋的抗剪作用的材料模型;此外,对结构在爆炸荷载作用下可能出现的各种响应现象进行了描述,以准确地预测梁破坏时不同位置截面上钢筋和混凝土的受力、变形及破坏情况。应用改进的材料模型,对爆炸荷载作用下的五个钢筋混凝土试验梁的动力响应和破坏形态进行了数值模拟,结果表明,该数值方法能较好地模拟钢筋混凝土梁的弯曲、弯剪和剪切等破坏形态。     

Rolling of a Rigid Cylinder over a Half-Plane with Initial Stresses (Harmonic and Bartenev–Khazanovich Potentials)

An asymmetric quasistationary problem for a prestressed half-plane with harmonic and Bartenev–Khazanovich potentials is solved based of the linearized theory of elasticity. The Mehler–Fock integral transform is used to solve the differential equations that describe the stress–strain state of the half-plane. The dependences of the normal and tangential stresses and stress intensity factors on the elongation are plotted     

热毛细对流温度场全息干涉检测研究

本文采用Ｈｅｌｅ－Ｓｈａｗ盒体,在地面上模拟二维热毛细对流,应用全息干涉技术对热毛细对流温度场进行了测试研究,为了获得感兴趣的热毛细对流温度增量分布,文中提出了将背景温度分布条纹与热毛细对流温度增量分布条纹相分离的方法。