Stability and vibration of shear deformable plates––first order and higher order analyses

This work presents the highly accurate numerical calculation of the natural frequencies and buckling loads for thick elastic rectangular plates with various combinations of boundary conditions. The Reissener–Mindlin first order shear deformation plate theory and the higher order shear deformation plate theory of Reddy have been applied to the plate’s analysis. The governing equations and the boundary conditions are derived using the dynamic version of the principle of minimum of the total energy. The solution is obtained by the extended Kantorovich method. This approach is combined with the exact element method for the vibration and stability analysis of compressed members, which provides for the derivation of the exact dynamic stiffness matrix including the effect of in-plane and inertia forces. The large number of numerical examples demonstrates the applicability and versatility of the present method. The results obtained by both shear deformation theories are compared with those obtained by the classical thin plate’s theory and with published results. Many new results are given too.     

Dynamic behavior of long-span box girder bridges subjected to moving loads: Numerical analysis and experimental verification

In this study we conducted three-dimensional dynamic analyses of long-span box girder bridges subjected to moving loads, using four-node Lagrangian and Hermite finite elements. In finite element formulation, a 6 × 6 transformation matrix is derived to transform the system element matrices before assembly. The usual 5 degrees of freedom per node are appended with an additional drilling degree of freedom in order to fit the transformation. The numerical results show good agreement with the experimental data from an existing two-span prestressed concrete box girder bridge under travelling vehicles. Parametric studies are focused on the various effects of moving loads on the dynamic behavior for different locations on the cross-section of box girder bridges.     

Effects of electric field on crack growth for a penny-shaped dielectric crack in a piezoelectric layer

The assumptions of impermeable and permeable cracks give rise to significant errors in determining electro-elastic behavior of a cracked piezoelectric material. The former simply imposes that the permittivity or electric displacement of the crack interior vanishes, and the latter neglects also the effects of the dielectric of an opening crack interior. Considering the presence of the dielectric of an opening crack interior and the permeability of the crack surfaces for electric field, this paper analyzes electro-elastic behavior induced by a penny-shaped dielectric crack in a piezoelectric ceramic layer. In the cases of prescribed displacement or prescribed stress at the layer surfaces, the Hankel transform technique is employed to reduce the problem to Fredholm integral equations with a parameter dependent nonlinearly on the unknown functions. For an infinite piezoelectric space, a closed-form solution can be derived explicitly, while for a piezoelectric layer, an iterative technique is suggested to solve the resulting nonlinear equations. Field intensity factors are obtained in terms of the solution of the equations. Numerical results of the crack opening displacement intensity factors are presented for a cracked PZT-5H layer and the effect of applied electric field on crack growth are examined for both cases. The results indicate that the fracture toughness of a piezoelectric ceramic is affected by the direction of applied electric fields, dependent on the elastic boundary conditions.     

圆柱附加旋转整流罩表面压力分布及气动力特性

对圆柱附加固定整流罩的已有研究表明,它在降低升阻力和抑制涡激振动方面有优良的效果。但固定整流罩具有方向敏感性,当来流方向改变后效果会受到显著影响,甚至起到增加升阻力和加剧涡激振动的反作用。本文给圆柱附加了圆弧直径为40mm,形状夹角α分别为30°、45°、60°、75°和90°五种尺寸的旋转整流罩,并进行了风洞实验。其中整流罩可以自由地围绕圆柱轴线旋转。实验结果表明:旋转整流罩在流体力产生的力矩作用下,旋转至一个偏离尾流中心线固定角度的动态平衡位置,而平衡位置偏转角δ随着形状夹角α的增大而增大。附加旋转整流罩后,相对单圆柱能够提高尾迹区域压力,并能使时均阻力和脉动升力分别在α=30°和α=75°时获得最大43.5%和67.0%的降低。此外,对于小α(α≤60°)情况,漩涡脱落频率明显高于单圆柱情况,而对于大α(α≥75°)情况,则与单圆柱情况相接近。所有旋转整流罩升力主频的幅值较之单圆柱有了很大程度的降低,可见旋转整流罩在抑制漩涡脱落方面有很好的效果。     

PVC发泡板受力前后微观表面形貌变化规律的AFM实验研究

本文从微观角度对软质材料之一的PVC发泡板表面形貌与承受压载之间的关系进行实验研究.应用Veeco原子力显微镜(AFM),选取全新的1cm×1cm大小的PVC实验样品,轻轻地放置于AFM样品台上.先测试和记录一定范围内的没有压载作用时试件的微观表面形貌,然后依次测试和记录承受过一定数目压载情形下的表面形貌.其中,压载通过标准计量的砝码实现,重复多次实验,将实验数据进行统计分析.结果显示,经压载作用后,PVC的微观表面特性变化明显.随着压载荷的增加,样品微观表面的高度变化量、平均高度、粗糙度等明显增加,截面起伏度也越加明显.本实验结果对于PVC材料宏观承载应用及其微观结构变化机理等方面的研究将具有一定的参考意义.     

随机梁式结构静力损伤识别的一种改进方法

针对已有的损伤识别方法会出现损伤误识别的问题,本文在已有方法的基础上发展了一种随机梁式结构静力损伤识别的改进方法。假定静力荷载下梁式结构初始模型参数（如弹性模量和几何尺寸等）及测量误差为随机量,给出已有的基于随机有限元模型的梁式结构静力损伤识别方法,并进一步提出了一种改进方法。该方法通过设定损伤概率指标的阈值和反复迭代对结构损伤识别进行改进。数值算例和简支梁静力试验表明,考虑初始模型的不确定性以及静力响应测量误差,本文方法相较已有方法可以更有效地识别梁式结构的损伤。     

Finite element analysis for train–track–bridge interaction system

This article deals with the dynamic analysis of train–track–bridge interaction system using the finite element method. In this interaction system, each four-wheelset vehicle in the train is modeled by a mass–spring–damper system with 10 degrees of freedom; the rails and the bridge decks are modeled as a number of Bernoulli–Euler beam elements, while the elasticity and damping properties of the rail bed are represented by continuous springs and dampers. The equation of motion for the interaction system is presented in matrix form with time-dependent coefficients. The correctness of the proposed procedure is illustrated by a comparison with the numerical result from the existing literature. Several numerical examples are chosen to investigate the effect of two types of vehicle models, two types of bridge models and three damping values of bridge on the maximum dynamic responses of train, track and bridges.     

Propagation of slip pulse along frictionless contact interface with local separation between two piezoelectric solids

The Stroh formalism of piezoelectric materials,Fourier analysis and singular integral equation technique were used to investigate the existence of a pulse at the fric- tionless interface in presence of local separation between two contact piezoelectric solids. The two solids were combined together by uniaxial tractions and laid in the electric field. The problem was cast into a set of Cauchy singular integral equations,from which the closed-form solutions were derived.The numerical discussion on the existence of such a slip pulse was presented.The results show that such a slip pulse,which has square root singularities at both ends of the local separation zone,can propagate in most material combinations.And the existence of such a slip pulse will not be affected by the applied mechanical and electric fields in some special material combinations.     

三角形夹芯板夹心层的等效弹性常数

推导了三角形夹芯板夹心层的等效弹性常数,为验证所推导的弹性常数的合理性,用NASTRAN有限元计算程序对两种模型进行了静力计算比较,一种是用所推导的弹性常数将夹心等效后,以层合板的形式进行计算的模型,另一种是对整个结构直接采用板单元进行计算的模型.计算结果表明:两种模型结果吻合良好.