一种预测颗粒增强复合材料界面力学性能的新方法

界面在颗粒增强复合材料中起到传递载荷的关键作用, 界面性能对复合材料整体力学行为产生重要影响. 然而由于复合材料内部结构较为复杂, 颗粒与基体间的界面强度和界面断裂韧性难以确定, 尤其是法向与切向界面强度的分别预测缺乏有效方法. 本文以氧化锆颗粒增强聚二甲基硅氧烷(PDMS)复合材料为研究对象, 提出一种预测颗粒增强复合材料界面力学性能的新方法. 首先, 实验获得纯PDMS基体材料及单颗粒填充PDMS试样的单轴拉伸应力$\!-\!$应变曲线, 标定出PDMS基体材料的单轴拉伸超弹性本构关系; 其次, 建立与单颗粒填充试样一致的有限元模型, 选择特定的黏结区模型描述界面力学行为, 通过样品不同阶段拉伸力学响应的实验与数值结果对比, 分别给出颗粒与基体界面的法向强度、切向强度及界面断裂韧性; 进一步应用标定的界面力学参数, 开展不同尺寸及不同数目颗粒填充试样的实验与数值结果比较, 验证界面性能预测结果的合理性. 本文提出的界面力学性能预测方法简便、易操作、精度高, 对定量预测颗粒增强复合材料的力学性能具有一定帮助, 亦对定量预测纤维增强复合材料的界面性能具有一定参考意义.      

碳纤维增强复合材料微观烧蚀行为数值模拟

碳纤维增强复合材料已广泛应用于烧蚀热防护系统中,其微观结构直接影响材料的烧蚀行为,因此材料微观烧蚀机制分析对材料设计和制备具有重要意义.本文采用有限体积法并引入固体相体积分数与界面重构技术,建立了碳纤维增强复合材料微观烧蚀数值模型.利用该微观烧蚀数值模型对碳基体包裹单根碳纤维进行烧蚀模拟,将数值模拟的烧蚀形貌与解析解结果进行对比,验证了数值求解方法的正确性.对单向碳纤维增强复合材料在不同碳纤维倾斜角下的微观烧蚀行为进行了模拟分析,得到了碳纤维倾斜角对微观烧蚀行为的影响规律.研究发现:对于碳纤维的抗氧化性能比基体强的情况,当氧扩散速率远远大于碳氧反应速率时,碳纤维将出现"笋尖"状的烧蚀形貌;当碳氧反应速率远远大于氧扩散速率时,纤维和基体将以相同速率烧蚀.当碳纤维的抗氧化性能比基体强时,纤维倾斜角会对材料微观烧蚀行为产生较大影响;相反,则影响不显著.     

陶瓷颗粒增强金属基复合材料的细观强度分析

陶瓷颗粒增强金属基复合材料的失效主要有界面脱粘、增强粒子开裂等新的细观结构损伤机制。为了减小这些不足并对细观失效过程有一个清晰的了解,近来人们对金属基复合材料进行了大量研究,在此基础上,本文用细观力学的方法和损伤模型研究了陶瓷颗粒增强金属基复合材料的强度和损伤失效。为了计算方便,陶瓷颗粒简化为在复合材料中随机分布的椭球形粒子,然后以二相胞元模型计算分析了金属基体、颗粒中的应力应变分布情况,结果表明,基体中应力极不均匀,界面区存在应力集中,并计算了界面弧形裂纹扩展时的能量。最后分别提出了基体,颗粒和界面的失效强度准则,本文结果对于颗粒增强金属基复合材料具有普遍的实用性。     

碳纤维增强复合材料微观烧蚀行为数值模拟

碳纤维增强复合材料已广泛应用于烧蚀热防护系统中,其微观结构直接影响材料的烧蚀行为,因此材料微观烧蚀机制分析对材料设计和制备具有重要意义.本文采用有限体积法并引入固体相体积分数与界面重构技术,建立了碳纤维增强复合材料微观烧蚀数值模型.利用该微观烧蚀数值模型对碳基体包裹单根碳纤维进行烧蚀模拟,将数值模拟的烧蚀形貌与解析解结果进行对比,验证了数值求解方法的正确性.对单向碳纤维增强复合材料在不同碳纤维倾斜角下的微观烧蚀行为进行了模拟分析,得到了碳纤维倾斜角对微观烧蚀行为的影响规律.研究发现:对于碳纤维的抗氧化性能比基体强的情况,当氧扩散速率远远大于碳氧反应速率时,碳纤维将出现"笋尖"状的烧蚀形貌;当碳氧反应速率远远大于氧扩散速率时,纤维和基体将以相同速率烧蚀.当碳纤维的抗氧化性能比基体强时,纤维倾斜角会对材料微观烧蚀行为产生较大影响;相反,则影响不显著.      

含旋转椭球形夹杂复合材料的弹塑性本构关系

在体胞模型的基础之上应用解析方法分析了颗粒或短纤维增强复合材料的本构行为，结合数值计算给出了表征材料本构关系的解析表达式，提出了一种新的正交椭球坐标变换以简化推导过程，在计算中，将真实位移场分为两部分：基本场的扰动场，然后通过摄动方法将原来的非线性问题转化为一组线性方程组的求解，计算了当基体材料和夹杂的特征参数取不同值时的应力应变曲线，并与已有的实验和分析结果进行了比较，符合得较好，通过对数值计算结果的拟合，提出了一个颗粒或短纤维增强复合材料的弹塑性本构关系的解析表达式。     

炭黑增强对橡胶复合材料温度相关力学行为的影响

利用含温度箱的自动网格法测试系统,对不同炭黑含量的橡胶复合材料开展不同温度下的超弹性性能试验,考察了炭黑增强对其温度相关力学行为的影响。结果表明,温升过程中炭黑颗粒对橡胶基体的增强作用在逐渐减弱,与之相关的内能弹性效应也逐渐减小,加上橡胶基体本身的熵弹性效应,这两者共同决定了炭黑增强胶料会随着温度的升高"先变软后变硬",而非如纯胶料般随着温度的升高直接变"硬"。换言之,温度变化对颗粒与基体间相互作用造成的影响,使得炭黑增强橡胶的温度相关力学行为比不含炭黑的纯橡胶更为复杂。另外,依据试验研究的结果,本文还推导了修正八链模型的温度相关显式表达式,它能较好地表征胶料超弹性力学行为与温度的相关性。     

SiCp/Al复合材料增强颗粒尺寸效应的细观分析

运用Voronoi方法建立了反映金属基颗粒增强复合材料(MMCp)微结构的多晶集合体代表性单元(RVE);采用Taylor关系推导了包含颗粒结构尺寸和体积分数参数的位错滑移硬化函数;建立了由300个平均粒度约为20μm的晶粒组成的多晶集合体代表性单元,并对MMCp3.5-5、MMCp3.5-10、MMCp10-5、MMCp10-10四种具有不同粒径和体积分数的铝基SiC颗粒增强复合材料在宏观均匀变形条件下的应力应变响应进行了数值模拟。计算结果表明:复合材料的应力应变模拟曲线与试验曲线吻合得较好,说明所推导的模型和硬化模式能够合理地描述颗粒增强尺度效应的变化趋势;多晶体模型也能够合理地表现复合材料内部应力应变在空间分布上的细观不均匀性。数值模拟结果反映了颗粒增强区承载着较大的载荷份额,而非颗粒存在区(基体)则承受着高达18%的应变,在两个区域的交界处出现了高达310MPa的应力集中,与已有文献试验观测的结果比较吻合。     

工字型加筋复合材料壁板的压缩屈曲行为实验研究

在复合材料结构整个屈曲承载过程中,从微观开始发生局部的纤维断裂、基体微裂纹等损伤,并随着屈曲程度的增加和屈曲模式的转化逐渐发生分层扩展。采用实验与数值计算相结合的方法,本文研究了工字型加筋壁板复合材料结构在压缩载荷作用下的屈曲行为。采用无损光学手段来非接触检测壁板表面的全场屈曲挠度,捕捉屈曲模态演化过程。基于有限元的数值模拟,预测了工字型加筋壁板复合材料结构的屈曲与后屈曲行为,用定量的实验数据来对比数值预测的壁板屈曲形态,表明实验和数值结果的离面挠度分布具有一致性。     

增强颗粒对铝基复合材料摩擦学性能的影响

采用自制的摩擦磨损试验机考察了增强颗粒对铝基复合材料摩擦磨损性能的影响。结果表明：在基体合金、陶瓷颗粒尺寸和体积分数相同的条件下,SiC增强铝基复合材料的摩擦磨损性能优于Al2O3增强铝基复合材料;增大颗粒尺寸或增加颗粒体积分数均使得SiC颗粒增强铝基复合材料的平均摩擦系数略有降低,耐磨性能提高;在与半金属摩擦材料配副时,颗粒增强铝基复合材料的摩擦系数与基体合金的相近,耐磨性能提高了3个数量级。     

2124 Al/SiC_p复合材料的动态变形行为及微结构效应

研究了在动态压缩时２１２４Ａｌ／ＳｉＣｐ复合材料的变形行为与微结构效应．分析结果表明，对于给定材料，复合材料的流动应力主要取决于微结构尺度效应．若增强相尺寸，基体晶粒尺寸以及增强相间距三者大小相当，则复合材料的流动应力取决于增强相的分散程度和位错密度；若增强相尺寸及其间距大小相当，但比基体晶粒大得多，那复合材料的流动应力主要取决于增强相的分散度．微观观测发现在同样加载条件下，变形局部化更容易在含较小碳化硅颗粒的复合材料内形成；变形区内的微损伤几乎都是基体与粒子界面脱粘和粒子角点邻近的微裂纹．对于所研究的这类复合材料，弹性模量及应变硬化几乎不受增强颗粒尺寸影响．     

Particulate size effects in the particle-reinforced metal-matrix composites

The influences of particle size on the mechanical properties of the particulate metal matrix composite are obviously displayed in the experimental observations. However, the phenomenon can not be predicted directly using the conventional elastic-plastic theory. It is because that no length scale parameters are involved in the conventional theory. In the present research, using the strain gradient plasticity theory, a systematic research of the particle size effect in the particulate metal matrix composite is carried out. The roles of many composite factors, such as: the particle size, the Young's modulus of the particle, the particle aspect ratio and volume fraction, as well as the plastic strain hardening exponent of the matrix material, are studied in detail. In order to obtain a general understanding for the composite behavior, two kinds of particle shapes, ellipsoid and cylinder, are considered to check the strength dependence of the smooth or non-smooth particle surface. Finally, the prediction results will be applied to the several experiments about the ceramic particle-reinforced metal-matrix composites. The material length scale parameter is predicted. The project supported by the National Natural Science Foundation of China (19891180, 19925211) and by the Chinese Academy of Sciences (KJ951-1-201) and “Bai Ren” plan     

具有界面相的球形粒子在无限大基体中的应力集中分析

研究了无限大基体内具有界面相的球形粒子在轴对称载荷作用下的应力场,并与线弹簧界面模型的情形进行了比较,对粒子／界面相以及界面相／基体两个界面的应力集中系数以及粒子内部的应力集中系数进行了分析．研究了应力二轴度、界面相厚度以及三相的模量对应力集中系数的影响．结果表明,对给定的模量和界面相厚度值,存在一个临界应力三轴度值．若应力二轴度小于此临界值,则界面相／基体界面的应力集中系数大于粒子／界面相界面的应力集中系数;否则,前者会小于后者．所做的应力分析可以为颗粒增强复合材料的强韧化设计提供一定参考．     

Thermo–elasto–plastic stresses in functionally graded materials under consideration of the fabrication process

Summary  The present study analyzes elasto–plastic thermal stresses in some particle-reinforced functionally graded material plates (FGP) by taking into consideration residual stresses of the fabrication process. For the FGP, the region near the cooling metal surface consists of distributed ceramic particles in a metal matrix, while the region near the heating ceramic surface contains distributed metal particles in a ceramic matrix. We use the thermo–elasto–plastic constitutive equation of a particle-reinforced composite, taking into consideration temperature changes and damage as well as the reinforcing effect of particles. Elasto–plastic thermal stresses are discussed here with the goal of reducing the thermal stresses. Two kinds of particle-reinforced FGP are considered: the first kind (FGP1) represents distributed ceramic particles in the metal matrix, and the second one (FGP2) represents distributed metal particles in the ceramic matrix. We modify the thermo–elasto–plastic constitutive equation of a particle-reinforced composite for the FGP2 by taking into consideration temperature changes and damage as well as the reinforcing effect of particles. Using the temperature-dependent material properties, three cases of temperature conditions are studied. The first one is the cooling from the fabrication temperature to the room temperature, the second one is the heating from the room temperature, and the last one is the heating after cooling from the fabrication temperature. The particle volume fraction is assumed to vary according to a power function in the thickness direction of the FGPs. Using the finite element method, the effects of the distribution parameter of the composition on the macroscopic stress, the stress in the matrix and the stress in the particle in the FGPs are discussed. Also, the effects of the particle volume fraction and the fabrication temperature on the maximum tensile matrix stress are discussed. Received 22 November 2000; accepted for publication 24 April 2001     

Particle fracture in high-volume-fraction ceramic-reinforced metals: Governing parameters and implications for composite failure

Weibull parameters of angular alumina particles are determined from experimental tensile test data on high-ceramic-content metal matrix composites using a micromechanical model that accounts for internal damage in the form of particle cracking, the dominant damage mode in these composites. The fraction of broken particles is assessed from the drop of Young's modulus and particle fracture is assumed to be stress controlled. Two extreme load-sharing modes, namely a purely local and a global load-sharing mode, are considered to account for the load redistribution due to particle fracture. Consistent powder strength parameters can be thus “back-calculated” for particles that are embedded in different Al-Cu matrices. On the other hand, this calculation fails for pure Al matrix composites, which exhibit a much larger strain to failure than Al-Cu matrix composites. It is shown that for Al matrix composites, the role of plastic (composite) strain on particle fracture constitutes a second parameter governing particle damage. This finding is rationalized by particle-particle interactions in these tightly packed ceramic particle-reinforced composites, and by the increase of matrix stress heterogeneity that is brought with increasing plastic strain. Failure of the alloyed matrix composites is well described by the (lower bound) local load-sharing micromechanical model, which predicts a catastrophic failure due to an avalanche of damage. The same model predicts failure of pure aluminium matrix composites to occur at the onset of tensile instability, also in agreement with experimental results once the role of plastic strain on damage accumulation is accounted for.     

弱界面复合材料的简化塑性模型

本文研究线弹簧型弱界面颗粒增强复合材料,在比例加载条件下的简化塑性模型。利用Ｍｏｒｉ－Ｔａｎａｋａ模型,得到弱界面复合材料的割线弹塑性模量和有效应力,进而通过算例讨论了界面柔度对复合材料宏观应力应变曲线的影响。     

Influences of reinforcing particle and interface bonding strength on material properties of Mg/nano-particle composites

In the present study, an effective model is proposed to predict the effective elastic behavior of the three-phase composite containing spherical inclusions, each of which is surrounded by an interphase layer. The constitutive equations are derived for the stress and strain of each phase of the composite subjected to a far-field tension. Based on these constitutive laws, the effective bulk, shear and Young’s modulus are obtained. A statistical debonding criterion is adopted to characterize the varying probability of the evolution of interphase debonding. Influences of debonding damage, particle volume fraction, interphase properties and bonding strength on overall mechanical behavior of composites are also discussed. Numerical analyses are carried out on particle-reinforced composites and the predictions have a good agreement with the experimental results.     

Material instability-induced extreme damping in composites: A computational study

We investigate the effective viscoelastic performance of particle-reinforced composite materials whose particulate phase undergoes a material instability resulting in temporarily non-positive-definite elastic moduli. Recent experiments have shown that phase transitions in geometrically-constrained composite phases (such as in particles embedded in a stiff matrix) can lead to stable non-positive-definite elastic moduli, and they hinted at strong damping increases that can be achieved from such metastable composite phases. All previous theoretical efforts to explain such phenomena have used simplistic one-dimensional models or they were based on composite bounds and specific two-phase solids. Here, we study particle–matrix composites with periodic randomized particle dispersion. A finite element discretization is used in combination with a sophisticated nonlinear solver in order to perform the numerous calculations in a feasible amount of computing time. Our computational analysis shows that stable non-positive-definite inclusion moduli can indeed lead to extreme damping increases (i.e. greatly exceeding the intrinsic damping of each composite phase) and that such extreme damping arises from a shift in microstructural mechanisms.     

Introducing Heterogeneity into the Micro-Scratch Test Fracture Toughness Relation for Brittle Particle Composites

Existing analysis methods of scratch test data are limited in their application to composite materials since they are built on the assumption of homogeneous material. In this study, the heterogeneity of the composite material is considered for analysis of scratch data on a resin and glass bead particle composite. Experiments are conducted using two approaches: macroscale three-point single edge notch and micro-scratch. An analysis method is presented which introduces a region in front of the crack tip to calculate the energy release rate during the fracture process which accounts for the heterogeneity of this region. By comparing with the experimental results, it is observed that this analysis method reduces the difference in fracture toughness derived from macroscale and microscale tests, and matches the trend of fracture toughness values as a function of particle volume fraction. This observation provides the insight that the local microstructure of the material needs to be considered in the scratch test analysis of particle composites.