剪弯梁宏细观多尺度非线性有限元分析

为深入研究细观粗骨料粒径对混凝土宏观构件非线性力学性能的影响,通过生成满足Fuller级配的骨料粒径,以放置区域像素的RGB(红绿蓝)值判断骨料重叠情况,实现骨料在混凝土内部的随机分布.在此基础上,运用均匀化方法求解二维细观随机多边形骨料模型的等效弹性模量及刚度矩阵,并引入混凝土材料损伤因子模拟剪弯梁裂缝展开,由此构建...     

三维取向短纤维增强复合材料弹性模量的计算

基于单取向纤维增强复合材料的力学性能计算模型,借助于纤维取向分布函数及坐标转换,建立了三维取向短纤维增强复合材料弹性模量的数值计算模型。按该模型对短纤维增强树脂基复合材料的弹性模量进行计算,将其结果与同类材料的实验结果比较验证。结果表明,该模型的预测具有较好的准确性。     

孔隙率对复合材料单向板横向力学性能的影响

在考虑纤维和孔隙随机分布的情况下,通过随机算法生成包含孔隙的代表性体积单元Representative Volume Element(RVE)。对生成的RVE建立有限元模型,引入基体的塑性本构模型和界面的双线性本构模型,采用有限元方法研究了孔隙率对碳纤维/环氧树脂复合材料单向板横向力学性能的影响。研究显示,孔隙随机分布对横向力学性能的影响不是很大;当孔隙率不超过临界值时,孔隙对横向力学性能的影响相对较小;当孔隙率超过临界值后,材料横向弹性模量、横向拉伸强度和横向压缩强度都会有较大的下降。     

基于均匀化理论的混凝土等效弹性模量预测

在细观层次上,将混凝土视为由骨料、水泥砂浆及骨料-水泥砂浆间界面过渡区构成的三相复合材料,基于Python语言,运用蒙特卡罗方法建立具有周期性的混凝土单胞模型,结合均匀化理论和周期性边界条件,提出了考虑界面层作用的混凝土等效弹性模量预测方法。采用已有文献结果验证了模型预测值的有效性,在此基础上,进一步研究单胞尺寸、界面层厚度、骨料体积率及骨料最大粒径对混凝土等效弹性模量的影响规律。结果表明,混凝土单胞模型可有效预测混凝土复合材料的弹性性能,与已有方法预测结果的误差范围为1.87%～4.97%,混凝土单胞模型的尺寸建议以150 mm为宜,20%～40%内的骨料体积率对混凝土等效弹性模量的影响最为明显,而界面层厚度与骨料最大粒径对混凝土弹性模量的影响较小,呈单调递减或单调递增的影响规律。     

含粗骨料超高性能混凝土的力学性能EI北大核心CSCD

采用河砂替代石英砂并添加粗骨料的方式制备含粗骨料的超高性能混凝土(UHPC),研究不同粗骨料掺量和粒径对UHPC力学性能的影响。结果表明:粗骨料掺量的增加对UHPC基体新拌混合物的流动性具有降低作用,粗骨料粒径对新拌混凝土的流动性具有不规则增强效应;当粗骨料掺量不大于400kg/m3时,UHPC基体立方体抗压强度和轴心抗压强度呈现不同程度的增长,当粗骨料掺量继续增加,UHPC基体立方体抗压强度和轴心抗压强度出现下降;粗骨料粒径的增加对UHPC基体的立方体抗压强度和轴心抗压强度具有增强效应,而对UHPC抗折及劈裂抗拉强度影响不大。骨料掺量对UHPC基体的弹性模量具有增强效应,骨料粒径越小,弹性模量越大;UHPC初裂强度、峰值强度、初裂挠度、峰值挠度以及各阶段耗能均随粗骨料掺量的增加缓慢降低;初裂强度、峰值强度、各阶段耗能均随粗骨料粒径的增大而降低,初裂挠度与峰值挠度随粗骨料粒径的增加呈现缓慢上升的趋势;韧性指数I5、I10、I20均随骨料掺量和粒径的增加而逐渐减小。     

颗粒形状对陶瓷基复合材料有效力学性能的影响分析

在ANSYS平台上建立不同形状随机颗粒增强陶瓷基复合材料的有限元模型,以二维和三维模型为例,利用不同的方法对复合材料的有效弹性模量和有效热膨胀系数进行预测,并比较各方法的异同。结果表明:有效弹性模量随颗粒体积比的增加而增加,有效热膨胀系数随颗粒体积比的增加而减小;不同形状之间有效力学性能存在一定差别:均质化法能较准确地预测复合材料的有效力学性能。     

骨料对氯离子在水泥基复合材料中扩散系数的影响

为了确定骨料对氯离子在水泥基复合材料中扩散系数的影响,利用压汞技术和稳态电迁移法分别对含不同类型、不同粒径分布、不同体积分数骨料的砂浆和混凝土试样,进行了孔结构和氯离子扩散系数的测试,并根据试样配合比、骨料的粒径分布以及界面过渡区(简称界面区)厚度进行了界面区体积分数计算,最后提出了界面区有效扩散系数的预测模型。结果表明:氯离子在水泥基复合材料中的扩散系数由基体扩散系数、界面区扩散系数、骨料以及界面区的体积决定,而界面区的体积分数主要取决于骨料的粒径分布、骨料体积和界面区厚度;骨料改变了水泥基复合材料中浆体的孔结构,其稀释效应和曲折效应降低了氯离子的传输性能;界面区特殊的微观结构增加了传输性能,其中,界面区效应要大于其曲折和稀释效应。根据试验结果采用回归分析法,得到氯离子在砂浆和混凝土界面区的扩散系数分别是基体的13.26倍和18.45倍。     

基体中含有随机分布裂纹的纤维增强复合材料的总体弹性常数

本文应用自洽方法计算了含随机分布裂纹的基体的等效弹性常数,然后利用GMC方法计算了复合材料的总体弹性常数.结果表明,随着裂纹密度的增加,基体的等效弹性模量和泊松比会降为零;而同时,复合材料的纤维方向的弹性模量的下降,但是仍然能达到没有裂纹时的90%.这表明当基体完全破坏的时候,纤维仍能够在纵向承受载荷.另外,当基体的等效弹性模量和泊松比会降为零时,复合材料的横向弹性模量和剪切模量都接近为零,表明这时复合材料无法承受横向的拉压力和剪切力.     

基于MATLAB程序语言建立再生混凝土随机骨料几何模型分析

学习认识再生混凝土细观组成，建立其细观模型。根据富勒级配理论，利用瓦拉文级配公式，分别求得试件在二维、三维层次上各种骨料粒径的颗粒数，然后应用蒙特卡罗方法，基于MATLAB程序语言研究出圆形普通混凝土放置编程，实现其二维、三维随机骨料几何模型的生成。最后依照再生混凝土组成，对几何模型进行改进，提出再生骨料的简化模型，并在ANSYS中建立再生混凝土二维、三维随机骨料几何模型图。     

注射成型短玻纤增强PP微观结构及力学性能研究

测定了注射成型短玻璃纤维增强聚丙烯的微观结构及有效拉伸弹性模量,定量分析了微观结构对材料力学性能的影响,测定了纤维长度分布及取向分布.采用Mori-Tanaka模型计算了单取向短纤维增强复合材料的拉伸弹性模量,采用取向平均法计算了具有任意平面取向的单层板材料弹性常数,运用层合板理论计算了短纤维增强复合材料的整体有效拉伸弹性模量,实验对比证明,这种方法是有效的.     

Characterizing elastic properties of carbon nanotube‐based composites by using an equivalent fiber

Effective elastic properties for carbon nanotube (CNT)‐reinforced composites are obtained through a variety of micromechanics techniques. An embedded CNT in a polymer matrix and its surrounding interphase is replaced with an equivalent fiber for predicting the mechanical properties of the CNT/polymer composite. Formulas to extract the effective material constants from solutions for the representative volume element under three loading cases are derived based on the elasticity theory. The effects of an interphase layer between the nanotubes and the polymer matrix as result of effective interphase layer are also investigated. Furthermore, this research is aimed at characterizing the elastic properties of CNTs‐reinforced composites using Eshelby–Mori–Tanaka approach based on an equivalent fiber. The variations of mechanical properties with tube radius, interphase thickness, and degree of aggregation are investigated. It is shown that the presence of aggregates has stronger impact than the interphase thickness on the effective modulus of the composite. This is because aggregates have significantly lower modulus than individual CNTs. POLYM. COMPOS., 2013 © 2013 Society of Plastics Engineers     

A theoretical study of the effect of an interfacial layer on the properties of composites

A theoretical analysis using finite element methods has been applied to oriented short-fiber composites and spherical particle composites in order to predict the influence of a finite layer at the interface on mechanical properties. In this study the interfacial layer has been modeled by assuming that a layer surrounds the interface and that this layer has a modulus of elasticity different than both the fiber and the matrix. The stress distribution near the interface has been determined as a function of the elastic constants of the interface layer and the interface layer volume fraction. This analysis has also been performed for two volume fractions of fibers and two fiber length to diameter ratios. From this stress distribution, the composite modulus and toughness have been determined as a function of interface modulus. It is theoretically shown that the toughness, measured by amount of strain energy absorbed, can be maximized by controlling the interface modulus. Furthermore, recent experimental results appear to verify the theory.     

三维编织复合材料力学性能研究现状

对三维编织复合材料的力学性能研究现状进行了综述,研究内容大致归纳为细观结构特征研究、有限元仿真研究及实验研究。细观结构研究主要是研究单胞几何模型的建立和编织工艺与单胞结构模型的关系。有限元研究主要集中在利用有限元软件对细观结构模型进行力学分析、刚度强度性能预测。实验研究是运用实验的方法对材料的拉伸性能、弯曲性能及疲劳性能进行研究,并分析编织工艺参数和温度对其力学性能的影响。最后,对目前研究中存在的问题和今后的发展趋势进行了展望。     

An efficient nanoscale representative volume element simulation including graded interphase for tensile behavior of epoxy/silica nanocomposites

The behavior of interphase-particle adhesion and interphase region around the nanoparticles can significantly affect the stress distribution and mechanical properties of polymeric nanocomposites. In this study, the elastic modulus of epoxy/silica nanocomposites is analyzed using the finite element method and different mathematical models. A nanoscale representative volume element including graded interphase, homogenous interphase, and no interphase model is implemented. Furthermore, the effect of interfacial adhesion is also considered. The final elastic modulus was clearly affected by the interphase modulus, especially at higher nanoparticle content. Under imperfect interfacial bonding, the existence of an interphase region leads to a slight increase in modulus, and in the absence of that area, the elastic modulus decreases to 3.28 GPa. In perfect bonding models, stress transferred from the matrix to interphase and, then, to nanoparticle, which led to a significant increase in elastic modulus. Unlike the imperfect bonding, the maximum stress was located in the elements along to the loading direction. A maximum 26% increase in elastic modulus for perfect bonding/graded interphase model with 6.54 vol% of nanosilica particles compared to bulk epoxy was achieved. Finally, on comparing the FEM analysis and theoretical results with the experimental data, good agreement between obtained results was found.     

Stress distribution in and around a spherically ended fiber embedded in a polymer matrix

The effect of fiber end geometry, especially one with an enlarged spherical end, on the stress distribution in a polycarbonate/short glass-fiber reinforced model composite was studied using photoelasticity and finite element analysis (FEA). The role played by the fiber/matrix interfacial strength was also investigated. The photoelastic method was applied to examine the stress distribution in the vicinity of a single fiber embedded in a thermoplastic polycarbonate matrix. Linear elastic, axisymmetric FEA was carried out to investigate the fibers effectiveness as a load bearing constituent, the effect of interfacial debonding, and stress concentration near the fiber ends. Both photoelastic analysis and FEA demonstrated the efficiency of the spherical enlarged fiber end in load transfer ability and in delayed debonding, which may be important in enhancing strength and modulus of thermoplastic matrices.     

Finite element analysis and experiment study on the elastic properties of randomly and controllably distributed carbon fiber-reinforced hydroxyapatite composites

Randomly distributed carbon fiber-reinforced hydroxyapatite (RCF/HA) and controllably distributed carbon fiber-reinforced hydroxyapatite (CCF/HA) composites were firstly studied to design and prepare different required composite artificial bones with satisfying mechanical properties by combining experiment approach, theoretical prediction and finite element analysis (FEA). A plug-in was obtained by secondary development of ABAQUS for the FEA. A 3D representative volume element (RVE) for RCF/HA and CCF/HA can be easily generated using this tool. Stress and strain analyses of three directions of RVE were performed by ABAQUS with different fiber mass fractions and distributions. The elastic modulus of CF/HA composites were obtained. With 0.2 wt% fiber, the elastic modulus of RCF/HA and CCF/HA composites increased by 6.31% and 54.4% compared with that of HA, respectively. For CCF/HA composites, the elastic modulus increased significantly with the increasing fiber mass fraction in the E₁₁ of the fiber. The results of experiment study and theoretical prediction were consistent with that of FEA. The maximum error between the FEA and experiment study was 2.84%, which confirmed that the RVE model was rational and accurate. The results indicated the fiber distribution can greatly affect the elastic modulus of the composites. In the future study, the controllably distributed fiber–reinforced composites would be a good choice because they can improve the mechanical properties as required. This study would endow possibility of designing and preparing the CF/HA bio-ceramics with satisfied mechanical properties by FEA and proper preparation parameter. It would also speed up application of clinical practice for CF/HA composites.     

Mechanical properties of cellular materials. I. Linear analysis of hexagonal honeycombs

The purpose of this series of studies is to develop finite element computer models of the mechanical properties of cellular polymers, especially open cell foams. Using finite element methods, both the properties of the material making up the struts, as well as the geometrical structure of the cell, can be readily varied. The series of studies begins with two-dimensional hexagonal honeycombs because of their ease of analysis and comparison with previous works. Comparison of the present solutions and analytic ones have been conducted, and excellent agreement is obtained. The effects of cell dimensions, such as strut length, strut depth, and cell height, of irregular hexagons on the effective Young's modulus of foams were studied in the low strain and elastic regime. Load direction and cell geometry anisotropy effects are also investigated. In addition, the effects of friction model and the specimen size on the effective Young's modulus of the foam are studied. Nonuniform strut thickness was also a variable. The modulus effects of these variations in geometry ranged from minimal to highly significant and provide an understanding of geometry effects on foam performance. © 1997 John Wiley & Sons, Inc.     

Effect of porosity on the elastic properties of porcelainized stoneware tiles by a multi-layered model

Porcelainized stoneware represents a leading product in the world market of ceramic tiles, thanks to its relevant bending strength (with respect to other classes of tiles) and extremely low water absorption: these properties derive from its really low content of residual porosity. Nevertheless, an accurate investigation of the cross section of a porcelainized stoneware tile reveals a non-uniform distribution of the residual pores through the thickness, which results in a spatial gradient of properties. Porcelainized stoneware, therefore, may be looked at as a functionally graded material. In the present research, commercial porcelainized stonewares were analysed in order to define the effect of the residual porosity and its spatial distribution on the mechanical properties of tiles. Polished cross sections of porcelainized stoneware tiles were investigated by optical and scanning electron microscopy in order to define the content and distribution of residual pores as a function of distance from the working surface. For each porcelainized stoneware, the local elastic properties of the ceramic matrix were measured by a depth-sensing Vickers micro-indentation technique, then the so-obtained microstructural images and elastic properties were used to model the stoneware tile mechanical properties. In particular, the cross section of each tile was described as a multi-layered system, each layer of which was considered as a composite material formed by a ceramic matrix and residual pores. The elastic properties of each layer were predicted by applying analytical equations derived from the theory of composite materials and, as a new approach, by performing microstructure-based finite element simulations. In order to validate the proposed multi-layered model and identify the most reliable predictive technique, the numerical results were compared with experimental data obtained by a resonance-based method.     

Predicting the mechanical properties of Cu–Al2O3 nanocomposites using machine learning and finite element simulation of indentation experiments

Micromechanics model, finite element (FE) simulation of microindentation and machine learning were deployed to predict the mechanical properties of Cu–Al₂O₃ nanocomposites. The micromechanical model was developed based on the rule of mixture and grain and grain boundary sizes evolution to predict the elastic modulus of the produced nanocomposites. Then, a FE model was developed to simulate the microindentation test. The input for the FE model was the elastic modulus that was computed using the micromechanics model and wide range of yield and tangent stresses values. Finally, the output load-displacement response from the FE model, the elastic modulus, the yield and tangent strengths used for the FE simulations, and the residual indentation depth were used to train the machine learning model (Random vector functional link network) for the prediction of the yield and tangent stresses of the produced nanocomposites. Cu–Al₂O₃ nanocomposites with different Al₂O₃ concentration were manufactured using insitu chemical method to validate the proposed model. After training the model, the microindentation experimental load-displacement curve for Cu–Al₂O₃ nanocomposites was fed to the machine learning model and the mechanical properties were obtained. The obtained mechanical properties were in very good agreement with the experimental ones achieving 0.99 coefficient of determination R2 for the yield strength.     

纺织陶瓷基复合材料力学性能研究进展

纺织陶瓷基复合材料在航空航天器的热端部件有着广阔的应用前景.对近年来关于纺织陶瓷基复合材料力学性能的研究方法和内容进行了综述,归纳出3类主要研究方法:试验研究、力学模型研究、数值仿真研究.试验研究集中于测试各种参数对其力学性能指标的影响并探索其损伤破坏规律.力学模型研究主要有连续损伤力学和细观力学两种方法.数值仿真研究是基于材料的线弹性力学,利用有限元分析法对其力学性能进行数值仿真.提出了当前研究存在的问题和今后研究的发展方向.