双模数复合材料层板分析中的一种新方法——有限层元素法

一种分析双模数复合材料层板的新方法——有限层元素法在本文中提出,与文献[1]提出的有限层法相比,精度有明显提高。与其它文献中的已有解比较,吻合较好。      

Stochastic finite element method applied to non-linear analysis of embankments

The deterministic Finite Element Method (FEM) is a valuable tool for understanding and predicting the mechanical behaviour of earth structures. The main difficulty in the application of this technique generally arises from the large uncertainties affecting the mechanical properties of materials to be introduced in the analysis. In many instances, these parameters should actually be considered as random variables or random fields. The Stochastic Finite Element Method (SFEM) should then be used to assess the results of the analyses in probabilistic terms.In this paper, the usefulness of the SFEM approach for engineering purposes is discussed and illustrated by analyses of embankments constructed by placing successive lifts of compacted soil. Construction materials are assumed to follow a simple non-linear constitutive law (Duncan JM, Chang CY. Non-linear analysis of stress and strain in soils, Journal of the Soils Mechanics and Foundation Division, ASCE 1970;96(5):1629–1653). Stochastic finite element analyses are performed using both the First Order-Second Moment method (FOSM) and Monte Carlo simulations (MC). A simple example shows that SFEM analyses can be useful to evaluate the relative influence of each of the parameters of the constitutive model on the results. Uncertainties affecting displacements, strains and stresses predictions for a large earth dam are also presented.     

Damage evolution in ductile materials: from micro- to macro-damage

This research presents a new simulation concept of damage evolution for metallic materials under large displacements and deformations. The complete damage range is subdivided into both the micro-damage and the macro-damage range. The micro-damage phase is described by the Cocks/Ashby void-growth model for isotropic, ductile materials under isothermal conditions. After having reached a critical void-volume fraction, a macro-crack is introduced into the model. With such a concept the damage evolution from nucleation and growth of first micro-voids to initiation of macro-cracks and complete failure of the material can be simulated. Applying the Finite Element Method for the numerical formulation, at every incremental macro-crack step the Finite Element mesh is adapted such that the crack path remains independent of the initial mesh.     

隔振胶块材料对车门NVH性能的影响

基于有限元理论建立完整的车门子系统NVH性能仿真模型。开发出一套材料试验方法以获得在复杂工艺环境下隔振胶块的真实力学属性,将不同材料的参数带入仿真模型中,通过结果对比了解不同隔振胶块材料对车门子系统NVH性能的影响,从而帮助设计人员制定隔振胶块材料的选取准则并为材料配方的改进提供指导。     

拆除爆破研究中数值分析方法的比较与选择

概述了数值分析法的分类。介绍了平面杆系有限元法、离散元法、数值流形法和不连续变形分析等几种数值分析方法。简单地讨论了平面杆系有限元法的分析步骤以及在拆除爆破中适于解决的问题 ;同时叙述了流形分析中采用的有限覆盖技术。通过分析和比较这几种方法在拆除爆破研究中的应用 ,作者认为 ,当前应用传统的有限元法进行爆破理论研究或拆除爆破模拟存在一些困难 ;离散元法用于拆除爆破理论的研究是可行的 ;不连续变形分析法对于拆除爆破模拟研究是一种具有良好前景的数值方法     

拆除爆破研究中数值分析方法的比较与选择

概述了数值分析法的分类。介绍了平面杆系有限元法、离散元法、数值流形法和不连续变形分析等几种数值分析方法。简单地讨论了平面杆系有限元法的分析步骤以及在拆除爆破中适于解决的问题 ;同时叙述了流形分析中采用的有限覆盖技术。通过分析和比较这几种方法在拆除爆破研究中的应用 ,作者认为 ,当前应用传统的有限元法进行爆破理论研究或拆除爆破模拟存在一些困难 ;离散元法用于拆除爆破理论的研究是可行的 ;不连续变形分析法对于拆除爆破模拟研究是一种具有良好前景的数值方法     

Combination of finite and boundary elements for magnetic field analysis

A procedure is proposed which utilizes combined Finite Elements Method and Boundary Elements Method for magnetic field analysis. Given a region constituted by sub-regions, some of which require a dense discretization, the field analysis is carried out by using the Finite Elements Method, and the Boundary Elements Method is used for the other sub-regions which require a large discretization. The procedure is applied for studying the magnetic field due to a coil and the obtained results are compared with the values given by formulas known in the scientific literature[5].     

Daubechies条件小波混合有限元法在梁计算中的应用

常规的Daubechies小波有限元法是以挠度为基本未知量的单变量有限元法,其弯矩函数需要通过挠度函数的二阶求导间接求解,故弯矩的计算精度一般比挠度低。此外,目前常用的Daubechies小波有限元法需要借助于转换矩阵引入位移边界条件,大大影响了计算精度。结合广义变分原理,将边界条件作为附加条件构造修正泛函,以该修正泛...     

塑料包装材料迁移物在食品内不稳定性的数值模拟

塑料包装材料化学迁移物(添加剂、单体、低聚体、分解产物等)在食品(模拟物)内存在不稳定现象。文中介绍了迁移物不稳定性相关研究进展,分析了迁移物的不稳定机理,基于有限差分方法和MATLAB平台开发了迁移预测软件MigraSoft 2006,数值模拟了食品(模拟物)内化学物的不稳定性。     

Discrete Element Method for the thermal field: Proof of concept and determination of the material parameters

The physical behaviour of materials and complicated components is nowadays numerically predicted by using the Finite Element Method (FEM). Another method, older than the finite element idea, is the Discrete Element Method (DEM), with which it is possible to make continuum-based calculations not only in the mechanical field but also in the thermal field, as will be shown in this paper.One major drawback of the FEM is that continuum-based methods are unable to include the stochastically distributed microscopic effects in the macroscopically oriented calculations. The Discrete Element Method is one method with which these effects can be considered.For making realistic fracture and life time predictions for components at high temperatures, it is important to adapt the DEM for the thermal field. This paper describes the mathematical proof of the 2D Discrete Element Method (or Lattice Model) for the thermal field. It will specifically be shown that the heat flux inside the framework can be transferred to the heat conduction equation. Furthermore, some examples demonstrate how the heat flux can be calculated with this method and how the corresponding material parameters are found and implemented. Also, as will be shown in this paper, anisotropic or orthotropic heat flux effects can be integrated in the DEM model.     

The Determination of Stress Distribution and Elastic Properties for Heterogeneous Materials with Hybrid Finite Element

This paper describes a numerical method for evaluating the micro and macromechanical response of two-dimensional heterogeneous materials with both periodic and random distribution of the second phase. The proposed method uses two different numerical programs, based on the Voronoi Cell Finite Element Method, developed by the authors. Various numerical examples are executed for validating the effectiveness of the proposed method in evaluating the overall elastic constants of heterogeneous materials, and different comparison with analytical models and experimental results are shown. In order to validate the accuracy of the programs for predicting the stress micro-fields around the inclusion, some comparisons with a FEM commercial numerical code are performed.     

RTM加工工艺充模过程的计算机模拟

RTM加工工艺是一种先进复合材料加工的方法。但这种加工工艺技术含量高,设计不当非常容易出次品,尤其注射口和溢料口的设计。因此相当多的科技工作者对RTM加工工艺进行了计算机模拟研究,并已得到很大的发展,其计算方法和实验手段已获得广泛认可。由于有限元控制体积法不需要对变界面进行网格的重新划分而获得广泛采用。但是在众多的文献中,绝大多数使用的是三角形有限元网格,对于更加有效的四边形有限元网格没有提及或仅仅一笔带过。本文作者比较详细地阐述三角形和四边形有限元控制体积法的使用和实施,通过例子分析了三角形单元、四边形单元及其混合使用的情况下的计算结果。分析表明,四边形单元计算精度高、速度快,与三角形混合使用情况良好。     

Elastic solution of a two-dimensional functionally graded thick truncated cone with finite length under hydrostatic combined loads

In this paper, a thick truncated hollow cone with finite length made of two-dimensional functionally graded materials (2D-FGM) subjected to combined loads as internal, external and axial pressure is considered. The volume fraction distribution of materials and geometry are assumed to be axisymmetric but not uniform along the axial direction. The Finite Element Method based on the Rayliegh-Ritz energy formulation is applied to obtain the elastic behavior of the functionally graded thick truncated cone. By using this method, the effects of semi-vertex angle of the cone and the power law exponents on the distribution of different types of displacements and stresses are considered. The results show that using 2D-FGM leads to a more flexible design so that both the maximum stresses and stress distribution can be controlled by the material distribution.     

Finite difference energy techniques for arbitrary meshes applied to linear plate problems

A new energy based finite difference analytical technique is introduced. The method incorporates certain energy concepts and the ability to use arbitrary, irregular meshes within the framework of the Finite Difference Method. This formulation reduces any governing partial differential equations to a set of difference equations containing partial derivatives up to and including the second order. Further, certain strong similarities with the popular Finite Element Method are shown and the ability to solve problems with irregular boundaries is discussed. To demonstrate the Finite Difference Energy Method several plate bending problems are solved.     

Nodal sensitivities as error estimates in computational mechanics

Summary This paper proposes the use of special sensitivities, called nodal sensitivities, as error indicators and estimators for numerical analysis in mechanics. Nodal sensitivities are defined as rates of change of response quantities with respect to nodal positions. Direct analytical differentiation is used to obtain the sensitivities, and the infinitesimal perturbations of the nodes are forced to lie along the elements. The idea proposed here can be used in conjunction with general purpose computational methods such as the Finite Element Method (FEM), the Boundary Element Method (BEM) or the Finite Difference Method (FDM); however, the BEM is the method of choice in this paper. The performance of the error indicators is evaluated through two numerical examples in linear elasticity.     

Influence of corrugation geometry on the substitute stiffness matrix of corrugated laminates

This work investigates the influence of the cross-section geometry of corrugated laminates on the stiffnesses of a substitute plate model and on the anisotropy. A corresponding geometry parameterization is presented which allows several cross-sections to be analyzed. The studies are conducted with the help of the Finite Element Method using a unit-cell approach and a linear generalized plane-strain Finite Element (FE) formulation. The investigations show the design freedom that can be used for tailoring of initial stiffnesses by changing the corrugation geometry.     

On probabilistic fatigue models for composite materials

The general purpose of this article is to review the main ideas in fatigue analysis of composites in the context of the application of probabilistic methods, both theoretical and computational. That is why most deterministic concepts of composite materials fatigue are summarized together with stochastic approaches. The application of the perturbation based Stochastic Finite Element Method (SFEM) to fatigue analysis of homogeneous and heterogeneous media is shown. Further, homogenization method in its effective modules approach is proposed below for application in fatigue processes modeling of linear elastic periodic random composites. Considering stochastic character of the analysis, the reliability tools appropriate to multicomponent materials are presented together with the specially adopted brittle and ductile fracture criteria.     

The finite element method vs the edge function method for linear fracture analysis

An investigation was performed to compare the Finite Element Method and the Edge Function Method for the solution of two dimensional linear elastic fracture problems. The comparison was made to determine whether one of the procedures had a distinct advantage over the other for fracture analysis. Although each method has minor advantages for the computation of specific quantities or the analysis of specific types of problems, there is no major advantage for either procedure which is immediately apparent. Because of the considerable investment which many organizations have already expended on developing a Finite Element capability, and the additional investment which would be required to implement the Edge Function Method the application of the Edge Function Method will probably be very limited.     

地下室钢筋混凝土墙板裂缝控制的材料参数设计

本文通过有限元计算和非线性回归,建立了地下室钢筋混凝土墙板沿高度方向上的约束系数计算式.在此基础上,建立了混凝土在温度变形和收缩变形共同作用下的应力计算模型.并根据常用材料特性和气象资料确立了几何参数、材料参数及温度参数,并通过工程实型试验,验证了理论计算结果与实测结果的一致性,进一步提出了不同几何参数条件下,允许的最大温度变形、有效补偿量与裂缝控制的定量关系.     

A novel methodology for the rapid identification of the water diffusion coefficients of composite materials

The paper presents a novel methodology for the rapid identification of the water diffusion coefficients of composite materials. The methodology consists in employing a numerical parametric Proper Generalized Decomposition (PGD) method allowing incorporating the diffusion coefficients among the number of degrees of freedom. Compared to classical identification schemes, often based on Finite Element Method (FEM) iterations, the proposed method allows achieving consistent CPU time gain. The method is general and can be applied when diffusion anomalies take place or when diffusion–reaction coupling must be taken into account, moreover can deal with anisotropic materials. However, for the scope of illustration, in the present case, it is applied to the simple case of “classical diffusion” (Fick’s model with constant boundary conditions) and concerns isotropic materials.