Mechanical performance of Buckminster fullerene-reinforced composite with interface defects using finite element method through homogenization techniques

Several times, preferred properties are not accomplished when the fiber-reinforced composites are tested after they are prepared and the similar observations are also observed in the case of nanoparticle-reinforced composites. While the composites are manufactured under controlled conditions with stringent quality measures, it is complex to circumvent fiber-matrix interfacial debonding. The amount of debonding decides the final mechanical properties of composite material. In this study, an effort is made to quantify the debonding effect of nanoparticles on mechanical properties of nanoparticle-filled composites using finite element models with homogenization approach. Buckminster fullerene and conventional fiber T300 are selected as reinforcement medium. The predictions revealed that the longitudinal Young’s modulus is not affected by debonding.     

Grain- and macro-scale kinematics for granular micromechanics based small deformation micromorphic continuum model

Macro-scale deformation of granular solids comprising large number of grains (>10⁶) are most efficiently described within the framework of continuum mechanics. It is notable, however that the micro-scale deformations in these materials are concentrated at the grain-boundaries or grain-contacts. Thus, the deformation energies in these systems must be modeled by considering the deformations concentrated in the neighborhood of the grain-boundaries or grain-contacts. To address this issue, grain-interactions has been widely described in the Hertzian sense by considering the relative movement of points on either side of a grain boundary or contact treated as an imperfect interface. This communication introduces the relevant kinematic variables given in the terms of the grain displacements, spins and size that can be used to estimate the relative movement of a grain boundary or contact. The macro-scale kinematic variables useful for continuum modeling are then identified with the grain-scale kinematic variables. The deformation energy density of the granular solid can thus be expressed both in terms of the grain-scale as well as the macro-scale kinematic variables providing the necessary pathway for micro-macro identification which can lead to non-classical micromorphic continuum models that incorporate grain-scale representation.     

二维任意多边形有限单元

目前常用于单晶体材料的计算细观力学分析方法是将晶体细分成许多三角形或四边形有限元，对于多晶体材料，这方法的计算量之大将难于承受，实验观测表明，多晶体材料中除角点附近局部区域外每个晶体内部的变形、滑移基本上是绶慢变化的，因此可以将每个晶体简化为一个多边形有限单元，晶界简化为界面单元，使计算量大大减少，本文导出一类任意多边形等参有限元格式，并证明这类多边形单元中的任意两个都是相互协调的，无论其边数是否相等，算例表明任意多边形单元是有效可行的．     

松质骨的细观力学研究评述

用细观力学方法分析松质骨的力学性能，研究松质骨的弹性模量、压缩强度与其相对密度之间的关系，这是骨力学的一个重要研究方向．     

Micromechanics analyses of interface crack

A new mechanics model based on Peierls concept is presented in this paper, which can clearly characterize the intrinsic features near a tip of an interfacial crack. The stress and displacement fields are calculated under general combined tensile and shear loadings. The near tip stress fields show some oscillatory behaviors but without any singularity and the crack faces open completely without any overlapping when remote tensile loading is comparable with remote shear loading. A fracture criterion for predicting interface toughness has been also proposed, which takes into account for the shielding effects of emitted dislocations. The theoretical toughness curve gives excellent prediction, as compared with the existing experiment data. The project supported by the National Natural Science Foundation of China     

单晶铁电体的宏细观本构关系描述

以高技术电子材料－铁电单晶体为研究对象，在对铁电体中电畸内的细观力学耦合场分析的基础上，采用Ｍｏｒｉ－Ｔａｎａｋａ方法以自洽的方式导出了材料构元的Ｈｅｌｍｈｏｌｔｚ自由能及Ｇｉｂｂｓ自由能函数的解析表达式。并分析在广义应力空间和广义应变空间中，按Ｈｉｌｌ－Ｒｉｃｅ内变量本构理论框架，导出了铁电体畸变屈服面方程，增量型本构关系及内变量的演化方程。文末给出了对ＢａＴｉＯ３单晶材料力电行为的一维数值模拟     

金属基复合材料的蠕变与松弛

本文利用微观力学方法研究了金属基复合材料的常温蠕变和应力松弛,连续纤维在弹性粘塑性基体内单向铺设。本文的结果与实验结果符合较好。研究表明,纤维在轴向对基体的蠕变起到明显阻止作用,而在横向和剪切变形下的作用较小。在低应力水平下,复合材料的蠕变变形很小,在高应力水平时,蠕变变形明显甚至引起蠕变破坏。     

MICROMECHANICS ANALYSIS ON EVOLUTION OF CRACK IN VISCOELASTIC MATERIALS

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Cosserat modeling of cellular solidsModélisation des solides cellulaires selon Cosserat

Cellular solids inherit their macroscopic mechanical properties directly from the cellular microstructure. However, the characteristic material length scale is often not small compared to macroscopic dimensions, which limits the applicability of classical continuum-type constitutive models. Cosserat theory, however, offers a continuum framework that naturally features a length scale related to rotation gradients. In this paper a homogenization procedure is proposed that enables the derivation of macroscopic Cosserat constitutive equations based on the underlying microstructural morphology and material behavior. To cite this article: P.R. Onck, C. R. Mecanique 330 (2002) 717–722.     

有限元计算细观力学对复合材料力学行为的数值分析

有限元计算细观力学的发展是近十年来细观计算力学发展的主要特征和推动力．本文综述了有限元计算细观力学近十年来应用于复合材料力学行为分析研究方面的进展．介绍了基本的数值模型和计算方法，重点评述了强度和损伤等协同效应问题上的最新研究成果．最后对有限元计算细观力学应用于材料设计的前景做了展望