高体积含量颗粒增强复合材料的一个细观力学模型Ⅱ: 弹塑性与损伤分析

在高体积含量颗粒增强复合材料细观弹性分析的基础上, 引入了细观塑性和细观损伤模型: 基体用服从Von Mises 屈服准则的理想弹塑性材料模拟, 用沿圆柱形基体轴线方向的平均应力(即对称面上的应力) 来判断基体的屈服, 并将基体的塑性部分简化为圆柱状轴对称区域。建立了基体和颗粒/ 基体界面统一的损伤准则, 该准则同时考虑了最大应变和三轴应力的影响, 通过对细观塑性和细观损伤在空间取向上的平均, 建立了材料宏观模量的折减法则。用该细观力学模型, 数值模拟了一种实际金属基复合材料的强度实验, 理论模型与实验结果吻合。      

基于均匀化理论的三维编织复合材料细观应力数值模拟

从基于小参数渐近展开和摄动方法的均匀化理论出发,给出了求解细观应力的数学表达式。通过有限元方法对三维编织复合材料的细观应力场进行数值模拟,并结合适当的强度准则对拉伸极限强度下单元的失效情况进行判断,得出材料强度的一种细观失效判据。通过该方法得到的应力计算结果与实验结论基本相符。      

基于塑性理论的钢筋砼简支深梁的抗剪强度研究(一)

根据混凝土的塑性理论及极限分析的上限方法,探讨了求解钢筋混凝土简支深梁的抗剪强度的数值计算方法。材料性质采用理想的刚塑性模型,混凝土屈服准则采用不考虑混凝土拉应力的修正的库伦屈服准则。分析了钢筋混凝土简支深梁发生塑性剪切破坏时屈服线的形状以及屈服线上混凝土和钢筋的能量耗散情况。最后从能量守恒的原理出发,即屈服线上的混凝土和钢筋消耗能量等于外荷载所做的功,导出了深梁剪切破坏荷载比例因子的隐函数表达式,对此隐函数进行优化求解,得到了深梁发生塑性剪切破坏的极限荷载。     

复合材料多尺度分析方法与典型元件拉伸损伤模拟

复合材料具有多尺度特性,多尺度模拟方法能够考虑细观损伤、演变对宏观材料性能和力学行为的影响,是复合材料响应分析的一种重要方法和手段。基于多尺度渐进展开理论,对复合材料弹性问题控制方程进行尺度分解,推导了细观尺度与宏观尺度的控制方程,建立了复合材料宏观和细观尺度响应之间的关联。基于协同多尺度计算策略,利用通用有限元软件的用户子程序与脚本二次开发,在宏观模型计算中实时调用细观模型进行多尺度渐进损伤模拟,实现了宏观和细观尺度的信息传递与反馈。建立的复合材料多尺度数值模拟方法可以快速集成细观损伤模型以及宏观唯象强度理论,具有良好的通用性。碳/碳复合材料拉伸模拟算例结果与试验结果吻合较好。     

基于单胞(GMC)模型的韧性复合材料极限分析

本文将细观力学中的单胞(GMC)模型运用到塑性力学的静力极限分析中,研究韧性复合材料的塑性极限承载能力。从反映复合材料细观结构的代表性胞元入手,通过宏观强度域的概念建立了单胞极限载荷的计算格式,最终将上述问题归结为求解一组带约束的非线性数学规划问题,并采用序列二次规划法进行了求解。算例结果表明,本文方法为复合材料的强度分析提供了一个有效手段。     

反向法确定钨合金基体细观性能及其宏观验证

为了确定钨合金基体相的细观性能,采用纳米压痕实验测试了钨合金材料中基体相的细观硬度与弹性模量.利用反向确定法给出了钨合金材料中基体相的细观弹、塑性性质,根据纳米压痕实验中得到的载荷-位移关系,通过三维有限元计算给出了基体相的原位细观屈服强度和硬化模量.为探讨反向法确定钨合金基体细观性能的有效性,采用宏观实验给出了其宏观验证.宏观验证结果表明,用反向法确定钨合金基体材料的细观弹、塑性性质是可靠的.     

含相间损伤颗粒填充复合材料的塑性分析

基于多相固体本构等效理论及相间损伤细观模型,本文分析了颗粒填充复合材料的塑性行为.结合解析表达式和有限元解,给出了含相间损伤变量的宏观初始屈服函数,函数的构成反映了复合材料塑性行为对组分材料物理性质和几何参数的依赖关系,并包含了相间损伤的劣化影响.计算和试验结果的比较表明,本文的理论分析是可靠的.     

在复杂应力状态下厚壁圆筒的极限分析

应用双剪统一强度理论,考虑材料的拉压异性和同性,推导了在内压力和轴力联合作用下的厚壁圆筒的塑性极限载荷计算公式,并且绘制了其极限载荷线图。在这些计算公式中,当其系数取不同的值时,就能得到按Tresca屈服准则、线性逼近的Mises屈服准则和双剪应力屈服准则的计算结果。应用其极限载荷线图,根据其承受的载荷大小,就能判断厚壁圆筒是否达到了屈服极限状态。绘制了在不同屈服准则下的极限载荷线图,以便对其差异进行比较。     

计算加肋轴对称组合壳塑性极限载荷的缩减弹性模量有限元法

基于缩减弹性模量的理念,建立计算加肋轴对称组合壳塑性极限载荷的有限元方法。定义轴对称壳单元的"弹性状态"、"局部屈服状态"和"截面屈服状态",并提出判断条件。提出肋骨单元屈服的判断条件。外载荷分成若干载荷步,分步加载,通过缩减"局部屈服"壳单元和屈服的肋骨单元的弹性模量,模拟组合壳的弹塑性应力状态,直至组合壳达到"截面屈服"的塑性极限状态,从而得到组合壳的塑性极限载荷。编制了有限元计算程序,算例表明该方法计算速度快,计算精度较高,可用于工程计算。     

残余应力对复合材料弹2塑性变形的影响

从细观力学的角度给出了分析残余应力对一般复合材料塑性性能影响的一种解析方法, 该方法基于应力二阶矩的割线模量法及Ponte Castaneda 和W illis 给出的弹性细观模型。有残余应力时, 所提的细观解析模型能够同时考虑纤维形状, 体积百分比, 纤维取向及纤维的分布对复合材料变形的影响。计算结果表明, 残余应力的存在会引起复合材料拉压变形的不对称, 材料宏观的拉压硬化曲线又与复合材料的细观结构参数密切相关。对单向复合材料, 本文作者对其等效割线热膨胀系数, 拉压应力-应变曲线的有限元分析结果与给出的细观解析模型定量吻合。      

Limit analysis of composite materials with anisotropic microstructures: A homogenization approach

A nonlinear mathematical programming approach together with the finite element method and homogenization technique is developed to implement kinematic limit analysis for a microstructure and the macroscopic strength of a composite with anisotropic constituents can be directly calculated. By means of the homogenization theory, the classical kinematic theorem of limit analysis is generalized to incorporate the microstructure - Representative Volume Element (RVE) chosen from a periodic composite/heterogeneous material. Then, using an associated plastic flow rule, a general yield function is directly introduced into limit analysis and a purely-kinematic formulation is obtained. Based on the mathematical programming technique, the finite element model of microstructure is finally formulated as a nonlinear programming problem subject to only one equality constraint, which is solved by a direct iterative algorithm. The calculation is entirely based on a purely-kinematical velocity field without calculation of stress fields. Meanwhile, only one equality constraint is introduced into the nonlinear programming problem. So the computational cost is very modest. Both anisotropy and pressure-dependence of material yielding behavior are considered in the general form of kinematic limit analysis. The developed method provides a direct approach for determining the macroscopic strength domain of anisotropic composites and can serve as a powerful tool for microstructure design of composites.     

杨木纤维/聚乙烯复合材料拉伸性能微观力学模型

制备了不同杨木纤维含量的杨木纤维/聚乙烯复合材料,利用Hirsch模型、Kelly-Tyson模型和Bowyer-Bader模型对杨木纤维/聚乙烯复合材料的微观力学进行建模,通过对杨木纤维/聚乙烯复合材料及塑料基体的拉伸应力-应变曲线和杨木纤维长度分布的研究,计算得到杨木纤维在聚乙烯基体中的取向系数、界面剪切强度和本征...     

Stabilized shear banding of ZrCu-based metallic glass composites under tensile loading

The tensile plastic deformation behavior of ZrCu-based metallic glass composites with various crystalline volume fractions was investigated. A tensile plastic strain of more than 10 % was achieved in a metallic glass composite with a crystalline volume fraction of 32.6 %. It was found that the B2 phase can effectively activate the formation of multiple shear bands, which significantly stabilize the tensile plastic deformation of metallic glass composites. A critical volume fraction for stable tensile plastic deformation was determined. In addition to the volume fraction, the density of the stress concentration sites and the distribution of the B2 phase were also found to be key factors controlling the stable plastic deformation of ZrCu-based BMG composite.     

Asymptotic homogenization algorithm for reinforced metal-matrix elasto-plastic composites

The theory of the two-scale convergence was applied to homogenization of initial flow stresses and hardening constants in some exponential hardening laws for elasto-plastic composites with a periodic microstructure. The theory is based on the fact that both the elastic and the plastic part of the stress field two-scale converge to a limit, which can be factorized by parts, one of which depends only on the macroscopic, and the other one – only on the microscopic characteristics. The first factor is represented in terms of the homogenized stress tensor and the second factor – in terms of stress concentration tensor, that relates to the micro-geometry and elastic or plastic micro-properties of composite components. The theory was applied to a composite, that consists of the metallic elasto-plastic matrix with Ludwik and Hocket–Sherby hardening law and pure elastic silica inclusions. Results were compared with those of averaging based on the self-consistent methods.     

Pb-GF挤压包覆间隙的数值计算及实验研究

铅包覆玻璃纤维属于塑性材料包覆脆性材料,包覆条件是建立在玻璃纤维不发生变形的情况下,为此,入丝模芯顶端与挤压模口之间的间隙即包覆间隙的优化选择是成形工艺的关键问题.本文采用上限法对包覆挤压过程建立了数值模型,从能量的角度对包覆挤压过程进行了数值计算,将包覆间隙作为一变量引入功的表达武中,并通过数值计算软件给出了数值解,得出包覆间隙的最佳理论值.通过大量的实验证明了数值计算结果与实验结果基本吻合.运用本文结果可以确定不同规格的复合丝材成形时包覆间隙的大小,指导模具设计和工艺参数确定,具有工程意义.     

An empirical model for fatigue behavior prediction of glass fibre-reinforced plastic composites for various stress ratios and test frequencies

Current models used to predict the fatigue life of glass fibre-reinforced plastic composites do not accurately consider the effects of load stress ratios and load frequencies. These models usually require significant amount of experimental data to establish a set of characteristic fatigue curves for a given composite. This paper proposes a fatigue model for glass fibre-reinforced plastic composites that includes the non-linear effect of stress ratio and load frequency on the fatigue life. The model can be used to predict the fatigue behavior of a composite material using a well-defined minimum number of tests. Fatigue data from the literature and selected research laboratories were used to test the model. Predictions were found to be in good agreement with all experimental data adequately accounting for the influence of test frequency and stress ratio on the fatigue life of composites.     

Comparison of two micromechanical models for predicting elasto-plastic response of wood–plastic composites

The mechanical response of wood- and cellulose-filled polymers and its comparison to analytical models is studied in this article. To model the elasto-plastic response of the wood–plastic composite (WPC), two explicit semi-analytical micromechanical methods were used: Mori–Tanaka Method (MTM) and Generalised Method of Cells (GMC). For experimental purpose, several test specimens composed of matrix polypropylene (PP) or polystyrene (PS) and filled with wood or cellulose short fibres of different length to width aspect ratio and various volume fractions were injection moulded. Tensile testing was then used to gain experimental data, which were then compared to the calculated prediction of proposed micromechanical models to test their applicability. The comparison of results show that both methods can accurately predict the response of the composite in the elastic area; however Mori–Tanaka Method can achieve better results when forecasting plastic deformations of wood–plastic composites.     

废旧塑料在复合材料领域中回用技术的研究进展

介绍了国内外废旧塑料现状以及废旧塑料在复合材料领域利用新进展,综述了废旧塑料在植物纤维/废旧塑料复合材料、废纸/废塑料复合材料、木塑复合发泡材料、可生物降解塑料复合材料及其他复合材料领域的再利用技术新进展,并分析了废旧塑料在复合材料领域回收再利用技术的发展趋势,提出应进一步探讨不同种类废旧塑料对复合材料力学性能及植物纤维/废旧塑料界面相容性的影响。     

Fabrication and electromechanical characterization of near-field electrospun composite fibers

We report the use of near-field electrospinning (NFES) as a route to fabricate composite electrodes. Electrodes made of composite fibers of multi-walled carbon nanotubes in polyethylene oxide (PEO) are formed via liquid deposition, with precise control over their configuration. The electromechanical properties of free-standing fibers and fibers deposited on elastic substrates are studied in detail. In particular, we examine the elastic deformation limit of the resulting free-standing fibers and find, similarly to bulk PEO composites, that the plastic deformation onset is below 2% of tensile strain. In comparison, the apparent deformation limit is much improved when the fibers are integrated onto a stretchable, elastic substrate. It is hoped that the NFES fabrication protocol presented here can provide a platform to direct-write polymeric electrodes, and to integrate both stiff and soft electrodes onto a variety of polymeric substrates.