General higher-order layer-wise theory for free vibrations of doubly-curved laminated composite shells and panels

ABSTRACT

The present article illustrates a general formulation for a higher-order layer-wise theory related to the analysis of the free vibrations of thick doubly-curved laminated composite shells and panels. The theoretical framework relates to the dynamic analysis of shell structures by using a general displacement field based on the Carrera Unified Formulation (CUF), including the stretching effect for each layer. The order of the expansion along the thickness direction is taken as a free parameter. The starting point of the present general higher-order layer-wise formulation is to propose a kinematic assumption, with an arbitrary number of degrees of freedom. The main aim of this work is to determine the explicit fundamental operators that can be used for the layer-wise (LW) approach. These fundamental operators are obtained for the first time by the author and are related to motion equations of doubly-curved shells described in an orthogonal curvilinear co-ordinate system. The free vibration shell and panel problems are computationally solved using the generalized differential quadrature (GDQ) and generalized integral quadrature (GIQ) techniques. The numerical results are compared with recent papers in the literature and commercial finite element codes.     

条形基础下地基非线性沉降的改进计算方法

 针对地基土体孔隙压缩性导致其变形力学参数变化的特征,对条形基础下地基的非线性沉降计算方法进行改进。首先,通过深入探讨附加应力和应力历史对地基土体模量影响的力学机制,分别建立地基土体变形力学参数随附加应力和应力历史变化的分析模型;然后,利用地基沉降计算的传统分层总和法,考虑地基沉降计算的非线性特征,并引入分级加载的思想,提出条形基础非线性沉降的新型计算方法,该方法不仅反映地基土体变形力学参数随附加荷载变化的特征,也反映地基土体由于初始应力水平或应力历史不同而引起的土体模量不同对地基沉降计算的影响,而且可有效地避免地基沉降计算中压缩试验曲线的使用;最后,通过工程实例计算与分析,并与实测沉降值和其他方法计算结果进行比较,表明方法的合理性与可行性。     

Progressive delamination growth analysis using discontinuous layered element

In this paper, a fracture mechanic approach is used to analyze delamination propagation between layers of composite laminates. A finite element method based on layer-wise theory is extended for the analysis of delamination growth. In this approach, delamination is modeled by jump discontinuity conditions at the interfaces. The layer-wise finite element is developed to calculate the strain energy release rates based on the virtual crack closure technique (VCCT). A procedure is proposed to handle the progressive delamination of laminates. Finally, analyses of the edge delamination propagation for several composite laminates are performed and the corresponding failure stresses are calculated. The predicted results are compared with the available experimental and numerical results. It is shown that the predicted failure stresses using this method are comparable with those obtained using interface elements.     

浅基础底面形状对基础沉降的影响

分析了不同形状基础底面浅基础的沉降问题，并用VB6．0编制浅基础沉降计算程序，通过对各种底面形状的对比，得到沉降量与基础底面形状的关系，为广大设计人员提供参考。     

分层总和法计算地基沉降浅析

分析了现行国家规范法计算地基沉降与弹性理论解在理论上的差异以及与工程实测沉降产生偏差的根本原因,阐明了基础宽度、基础埋深、土的泊松比等因素对地基沉降的影响,并提出程序计算方法和修正的计算公式,以期指导工程设计。