多向编织复合材料的力学性能研究

综述并评价了关于二维和三维编织复合材料的有效弹性模量研究的代表性工作,并从材料设计的思想出发,宏观与微观相结合,材料科学与力学相结合,对多向编织复合材料的宏观力学性能与细观织物结构、组分性能的关系及编织复合材料非线性行为进行了详细的理论分析和研究     

纤维搭桥技术在界面微观力学研究中的应用

界面在纤维增强复合材料中具有非常重要的作用,只有几十纳米到几十个微米的界面区域是复合材料的薄弱区域,严重影响复合材料的力学性能。通过微尺度实验力学研究微观结构与界面微观力学、宏观断裂性能之间的关系,有助于从微观角度解释复合材料界面应力传递和界面脱粘失效机理,从而为实际的纤维补强提供理论指导。显微共聚焦拉曼光谱是首选的界面微观力学研究方法。本文详细介绍了拉曼光谱在纤维搭桥技术中的应用,并重点从搭桥过程中纤维的架桥力、架桥纤维的止裂作用和界面应力传递三个方面综述了裂缝/架桥纤维的交互微力学。     

Nanoporous gold: 3D structural analyses of representative volumes and their implications on scaling relations of mechanical behaviour

We present a quantitative study of the salient structural parameters identified from so-called ‘representative volumes’ of the bicontinuous nanoporous gold (NPG) network, and examine the validity of self-similarity in describing its evolution. The approach is based on 3D-focused ion beam tomography applied to as-dealloyed and isothermally annealed NPG samples. After identifying sufficiently large representative volumes, we show that the ligament width distributions coarsen in a sufficiently self-similar, time-invariant manner, while the scaled connectivity density shows a self-similar ligament network topology. Using these critical parameters, namely mean ligament diameter and connectivity density, the Gibson–Ashby scaling laws for the mechanical response of cellular materials are revisited. The inappropriateness of directly applying the Gibson–Ashby model to NPG is demonstrated by comparing finite element method compression simulations of both the NPG reconstruction and that of the Gibson–Ashby solid model; rather than the solid volume fraction, we show that an effective load-bearing ring structure governs mechanical behaviour.     

Micromechanical analysis of transverse damage of fibre-reinforced composites

The mechanical behaviour of fibre-reinforced composites under transverse tension, compression and shear is studied using computational micromechanics. The representative volume element is constructed for fibre’s random distribution. The Drucker–Prager model and cohesive zone model are used to simulate the matrix damage and interfacial debonding, respectively. The stress distribution along the interface is studied using the model with only one fibre embedded in the matrix. It is found that the interface tensile failure at the equators of fibre firstly occurs under transverse tension; the interface shear failure firstly occurs under transverse compression; both the interface tensile failure and shear failure occur under transverse shear. The direction of fracture plane is perpendicular to the loading direction under transverse tension, 52.5° with the perpendicular direction under compression and 7.5° with the perpendicular or vertical direction under shear, respectively.     

水泥砂浆界面相弹性常数的反演计算

为了计算水泥砂浆界面过渡区的弹性常数,采用广义自洽方法(GSCM),根据水泥砂浆内部的微细观结构,建立了由水泥浆基体、岩石离散夹杂(骨料)、界面过渡区(ITZ)和有效弹性材料组成的四相复合材料模型.推导了界面相的体积模量和剪切模量方程.利用已知水泥砂浆材料的实验数据,计算了界面相的弹性常数.发现界面相剪切模量约为水泥浆基体剪切模量的50%.     

Dielectric elastomer composites: small-deformation theory and applications

Abstract

We provide estimates for the effective response of Electro-Active Polymer Composites (EAPCs) consisting of aligned ellipsoidal inclusions of a stiff dielectric material which are distributed randomly in an soft elastomeric matrix with “ellipsoidal” two-point statistics. The derivation of the results for the electro-mechanical response assumes linearized deformations, but includes non-linear (quadratic) terms in the electric fields. We investigate three different physical mechanisms contributing to the macroscopic electro-mechanical response of the composite: the intrinsic effect of the particles on the Maxwell stress, the inter-particle (dipole) interactions which are accounted for by evaluating the effect of changes in the “shape” of the two-point probability functions with the deformation, and the effect of particle rotations and torques when the geometric and/or anisotropy axis of the particles are not aligned with the applied electric field. Several illustrative examples are provided to emphasize the relative importance of the different effects on the overall electrostriction of the composites. In particular, for the “compliant electrode” boundary conditions that are widely used in applications, it is shown that inter-particle interactions are synergistic with the intrinsic effect of the particles on the Maxwell stress, leading to significant enhancements in the electro-mechanical coupling of the EAPCs, especially at high particle concentrations. On the other hand, the effect of electric torques on non-aligned particles is generally deleterious for electrostriction.     

Correlation of morphological parameters and mechanical performance of polyamide‐612/poly (ethylene–octene) elastomer blends

Blends of polyamide‐612 (PA‐612) and maleic anhydride grafted poly (ethylene–octene) elastomer (POE‐g‐MA) as an impact modifier have been prepared in the composition range of 0–35 wt. % of POE‐g‐MA and subsequently investigated for their structural, thermal, mechanical, dynamic mechanical properties and morphological attributes. X‐ray diffraction studies revealed a decrease in crystallinity whereas the thermal properties such as onset to degradation temperature and crystallization temperature remained broadly unaffected. Nearly three‐fold increase in the impact strength is registered accompanied by substantial increase in tensile failure strain, though tensile modulus (E) and tensile yield strength (σ _y) decreased with increase in impact modifier content. Dynamic mechanical analysis exhibited a singularity response in the loss factor in the temperature range of ~10°C–50°C. Micromechanical aspects were analyzed using conventional theoretical models for low strain mechanical response (E) such as rule of mixtures and foam model and for high strain mechanical response (σ _y) such as Nikolais–Narkis model and porosity model. Impact toughness and strain‐at‐break of the investigated composition were successfully correlated to the domain size (D_n) of the dispersed phase and their inter‐particle distances (τ). Scanning electron microscopy showed the coalescence of domains of the dispersed phase at higher POE content and thus reiterates the crucial role of inter‐particle distance in controlling the toughening mechanism of POE blended PA‐612. Copyright © 2013 John Wiley & Sons, Ltd.     

Investigation of the three-dimensional micromechanical behavior of woven-fabric composites

A three-dimensional representative volume-element model is presented to study the micromechanical behavior of woven-fabric composites. The effects of the fiber undulation zone and the fiber braid angle on the elastic modulus of the composites are taken into account in the unit cell. Based on isostrain and isostress assumptions, a standard homogenization procedure is used to calculate the effective elastic properties of woven-fabric composites, and all the final stiffness components are expressed in an explicit form. The results obtained by the model considered agree with published experimental results very well. The relationship between the geometric parameters, such as fiber width, thickness, volume fraction, etc., and the macromechanical behavior of the composites can be obtained by this model. Russian translation published in Mekhanika Kompozitnykh Materialov, Vol. 42, No. 2, pp. 209–220, April–May, 2006.     

The maximal advance path constraint for the homogenization of materials with random network microstructure

This paper presents a non-affine homogenization scheme for materials with a random network microstructure. It is based on a newly developed kinematic constraint that links the microscopic deformation of the network to the macroscopic strain of the material. This relation accounts for the network functionality and is established by means of maximal advance paths that are long enough to reach the macroscopic scales of the continuous body and deform accordingly but are also composed of the microscopic fibres that follow the network deformation. The exact distribution of the variable fibre stretch is determined by the principle of minimum averaged free energy, which ultimately allows one to derive the homogenized elastic response of the network at equilibrium. Besides the general formulation, the model is presented in detail for the case of tetrafunctional networks, for which the micro–macro relation and the expression for the homogenized elastic stress are derived in a compact and interpretable tensorial form. The performance of the model as well as the convexity and stability of the obtained homogenized response of the material is examined for networks composed of two different types of fibres, namely flexible chains and stiff filaments. The qualitative behaviour of the networks predicted for the two considered cases agrees with experimentally observed phenomena for soft materials. This includes a consistent explanation for the difference in the stiffness of elastomers at uniaxial and equibiaxial extension as well as a validation of recent experimental investigations of atypical normal stress amplitudes in biopolymer gels under shear loading.