基体特性对δ-Al2O3/Al合金复合材料力学行为的影响

基体行为是短纤维增强金属基复合材料中一个重要的因素.本文将通过实验分析方法和在一定的理论分析模型上,借助于弹塑性有限元分析方法,对基体特性的变化对δ-Al2O3/Al合金复合材料力学行为的影响作较为详细的研究,其中包括基体性能对应力传递、抗拉强度以及断裂机理的影响.研究表明,基体性能的变化显著影响基体与纤维间的应力传递,从而对复合材料的抗拉强度和断裂机理产生较大的影响.     

基体特性对D-Al2O3/Al 合金复合材料力学行为的影响

基体行为是短纤维增强金属基复合材料中一个重要的因素。本文将通过实验分析方法和在一定的理论分析模型上, 借助于弹塑性有限元分析方法, 对基体特性的变化对D-Al₂O₃/Al 合金复合材料力学行为的影响作较为详细的研究, 其中包括基体性能对应力传递、抗拉强度以及断裂机理的影响。研究表明, 基体性能的变化显著影响基体与纤维间的应力传递, 从而对复合材料的抗拉强度和断裂机理产生较大的影响。     

三维机织陶瓷基复合材料的面内剪切性能及损伤研究

采用IOSIPESCU纯剪切试件, 考虑纤维的编织结构和失效机理, 研究了三维机织碳/碳化硅(C/SiC)复合材料在面内剪切载荷作用下的力学性能和损伤过程. 材料具有明显的非线性应力-应变行为和残余变形等特性. 材料主要的损伤机制为基体微裂纹开裂, 界面脱粘和纤维断裂, 其中界面裂纹是材料应力-应变等力学行为的主要影响因素. 基于连续介质损伤力学分析方法, 提出了简单的损伤演化模型并对损伤演化过程进行了描述.     

形状记忆合金的力学及界面参数和体积分数对大块金属玻璃基复合材料增韧的影响

采用考虑塑性的超弹性材料模型和基于损伤塑性的准脆性材料模型,建立了三维单胞有限元模型,模拟了形状记忆合金颗粒增韧大块金属玻璃基复合材料的单调拉伸行为。讨论了形状记忆合金的力学参数、体积分数、界面厚度和界面材料参数对金属玻璃增韧效果的影响。结果表明:提高形状记忆合金的相变应变和马氏体塑性屈服应力将显著提高形状记忆合金颗粒增韧大块金属玻璃基复合材料的拉伸失效应变;形状记忆合金弹性模量超过50.0GPa、马氏体塑性屈服应力超过1.8GPa后,复合材料的拉伸失效应变变化不大。能同时兼顾失效应变和失效应力的形状记忆合金体积分数为15%左右。复合材料界面弹性模量和界面屈服应力的增加将提高复合材料的失效应力,但对失效应变影响不大;复合材料界面厚度的增加在提高失效应变的同时,也降低了复合材料的失效应力。     

铝基复合材料应力传递的有限元分析

本文使用大型有限元分析软件Ansys建立了短纤维增强铝基复合材料的有限元模型,模拟复合材料界面上的应力应变分布,进一步详细分析了纤维的不同参数对纤维使用效率的影响,以及不同纤维弹性模量的匹配对应力传递的影响。     

考虑界面时细观几何结构对复合材料力学性能的影响

基于应力为未知量的通用单胞模型改进算法在保证计算精度的前提下,可以提高计算效率,本文利用该方法计算了考虑界面时细观结构对纤维增强复合材料力学性能的影响.计算结果表明,当界面结合较差时,必须考虑界面性能对复合材料的影响;当界面模量接近或等于基体的模量时,已满足界面结合完好的条件,因此可不考虑界面对复合材料的影响;界面对复合材料的弹性模量、泊松比以及应力-应变曲线的影响较大,因此,界面是复合材料力学性能预测中不可忽略的重要环节.同时,纤维截面形状及排列方式对复合材料宏观的力学性能影响较大.     

偶联剂处理对碳纤维/竹展平板复合材料界面结合强度的影响

碳纤维/竹展平板是提高竹材在工程产品中应用的一种新型复合材料。胶合界面是复合材料传递力的桥梁,胶合界面的胶合性能是影响复合材料整体力学性能的关键。研究了羟甲基化间苯二酚(Hydroxymethylated resorcinol,HMR)偶联剂处理竹展平板表面对碳纤维/竹展平板复合材料的胶合性能的影响,按照不同的组坯方式和竹展平板表面处理方式将测试的试件分为4组。从碳纤维/竹展平板复合材料胶合界面的端面密度分布梯度、应变分布和应力传递及微观形貌3个角度进行测试分析。结果表明：HMR偶联剂处理后,碳纤维/竹展平板复合材料的胶合强度相较于未处理组提高了42.7%;碳纤维/竹展平板复合材料胶合界面密度明显增大,胶层厚度变宽,胶层应变分布和应力传递更加均匀,HMR偶联剂起到了良好的桥接作用;HMR偶联剂与碳纤维协同作用,使胶合界面的应力传递更连续,提高了碳纤维/竹展平板复合材料的胶合性能。     

-Al_2O_3/Al合金基复合材料拉伸行为的分析和模拟

本文以-Al2O3Al合金基复合材料为研究对象,在细观层次上建立分析模型,采用三维弹塑性有限元分析方法,对它的拉伸行为进行了较为详细的描述。研究涉及该类复合材料加载初期的应力-应变曲线的模拟和各种微结构特征的变化对应力应变行为的影响。同时考虑了纤维位向变化的影响,并引入了实际测得的短纤维位向分布规律,对随机分布短纤维复合材料的力学行为进行了模拟。研究表明,基体性能、纤维长径比和体积分数、纤维位向以及界面结合对-Al2O3Al合金基复合材料的拉伸行为均有较大的影响;本文所采用的有限元分析方法对该类复合材料加载初期的应力-应变曲线的预测也是较为准确的。     

δ-Al2O3/Al合金基复合材料拉伸行为的分析和模拟

本文以δ-Al2O3/Al合金基复合材料为研究对象,在细观层次上建立分析模型,采用三维弹塑性有限元分析方法,对它的拉伸行为进行了较为详细的描述。研究涉及该类复合材料加载初期的应力-应变曲线的模拟和各种微结构特征的变化对应力应变行为的影响。同时考虑了纤维位向变化的影响,并引入了实际测得的短纤维位向分布规律,对随机分布短纤维复合材料的力学行为进行了模拟。研究表明,基体性能、纤维长径比和体积分数、纤维位向以及界面结合对δ-Al2O3/Al合金基复合材料的拉伸行为均有较大的影响;本文所采用的有限元分析方法对该类复合材料加载初期的应力-应变曲线的预测也是较为准确的。     

界面过渡层对SiC/Al双连续相复合材料性能的影响

研究了界面过渡层对SiC/Al双连续相复合材料性能的影响.结果表明,界面过渡层降低了复合材料中的残余应力,改善了界面的结合,提高了复合材料的压缩性能.当界面过渡层中SiC的体积分数接近50%时,复合材料的压缩强度最高,塑性最好,但弹性模量较低.界面过渡层的存在改变了复合材料的弯曲断裂机制.SiC原始泡沫增强的复合材料在断裂时,增强体SiC泡沫先断裂,基体后破坏,断裂表面凹凸不平;含界面过渡层的复合材料断裂时,过渡层的外侧界面先被撕开,内侧界面结合良好,基体与增强体同时断裂,断口平整.     

Inherent sensing and interfacial evaluation of carbon nanofiber and nanotube/epoxy composites using electrical resistance measurement and micromechanical technique

Inherent sensing of load, micro-damage and stress transferring effects were evaluated for carbon nanotube (CNT) and carbon nanofiber (CNF)/epoxy composites (with various added contents) by an electro-micromechanical technique, using the four-point probe method. Carbon black (CB)/epoxy composites, with conventional nanosize material added, were used for the comparison with CNT and CNF composites. Subsequent fracture of the carbon fiber in the dual matrix composites (DMC) was detected by acoustic emission (AE) and by the change in electrical resistance, ΔR due to electrical contacts of neighboring CNMs. Stress/strain sensing of the nanocomposites was detected by an electro-pullout test under uniform cyclic loading/subsequent unloading. CNT/epoxy composites showed the best sensitivity to fiber fracture, matrix deformation and stress/strain sensing, whereas CB/epoxy composite exhibited poorer sensitivity. From the apparent modulus (as a result of matrix modulus and interfacial adhesion), the stress transferring effects reinforced by CNT was highest among three CNMs. The thermodynamic work of adhesion, W_a as found by dynamic contact angle measurements of the CNT/epoxy composite as a function of added CNT content was correlated and found to be consistent with the apparent mechanical modulus. Uniform dispersion and interfacial adhesion appear to be key factors for improving both sensing and mechanical performance of nanocomposite. Thermally treated-CNF composites exhibited a slightly higher apparent modulus, whereas higher testing temperatures appeared to lower the apparent modulus.     

Numerical analysis of the stress–strain distributions in the particle reinforced metal matrix composite SiC/6064Al

The axisymmetric cell model consisting of interface, matrix and reinforced particle is used to simulate the tensile test of particle reinforced metal matrix composite for predicting the micro stress/strain field and macro tensile stress/strain curve. In simulation of the tensile test, the cohesive element model is selected to model interfacial crack growth. It mainly analyzed the effects of interfacial properties, reinforcement volume fractions and aspect ratios on the stress–strain states of particle reinforced metal matrix composite. The results show that the peak micro stress and plastic strain occur at the interface in which it is a certain angle from the tensile stress direction; with the interfacial fracture toughness and reinforcement volume fraction increasing, the flow stress increases firstly and then decreases. The tensile stress–strain properties of SiC/6064Al are good when the interfacial fracture toughness is equal to 60 J/m and the reinforcement fraction volume is equal to 20%. Smaller reinforcement aspect ratio leads to smaller micro stress in composites.     

Effects of particle plasticity characteristics on local interface stress in particle reinforced composite during uniaxial tension

For elastoplastic particle reinforced metal matrix composites, failure may originate from interface debonding between the particles and the matrix, both elastoplastic and matrix fracture near the interface. To calculate the stress and strain distribution in these regions, a single reinforcing particle axisymmetric unit cell model is used in this article. The nodes at the interface of the particle and the matrix are tied. The development of interfacial decohesion is not modelled. Finite element modelling is used, to reveal the effects of particle strain hardening rate, yield stress and elastic modulus on the interfacial traction vector (or stress vector), interface deformation and the stress distribution within the unit cell, when the composite is under uniaxial tension. The results show that the stress distribution and the interface deformation are sensitive to the strain hardening rate and the yield stress of the particle. With increasing particle strain hardening rate and yield stress, the interfacial traction vector and internal stress distribution vary in larger ranges, the maximum interfacial traction vector and the maximum internal stress both increase, while the interface deformation decreases. In contrast, the particle elastic modulus has little effect on the interfacial traction vector, internal stress and interface deformation.     

On the elastic stress transfer and longitudinal modulus of unidirectional multi-short-fiber composites

An analysis is presented on the elastic stress transfer and longitudinal modulus of unidirectional multi-short-fiber composites. The analysis involves a three-cylinder model consisting of fiber, matrix and composite medium. The fiber axial stress and the interface shear stress are derived as functions of the fiber axial position. The effects of fiber-aspect ratio, fiber-volume fraction, fiber-to-matrix modulus ratio and inter-fiber separation (or fiber end gap) on stress transfer are studied in detail. The influence of neighbouring fibers on stress transfer is considered in a global manner by including the effect of the composite medium. The significance of the influence is clearly shown by comparing the stress transfer in multi-short-fiber composites with that in single-short-fiber composites. The composite modulus can be expressed by a modified rule of mixtures equation by introducing a fiber-length factor. Then, the effects of fiber-aspect ratio, fiber-volume fraction, fiber-to-matrix modulus ratio and inter-fiber separation (or fiber end gap) on the fiber-length factor are investigated. Some interesting findings are obtained. Finally, the present theory is compared with several existing theories.     

Tensile properties of randomly oriented short δ-Al2O3 fiber reinforced aluminum alloy composites: II. Finite element analysis for stress transfer,elastic modulus and stress–strain curve

The tensile properties of aluminum alloy matrix composites containing randomly oriented short δ-Al₂O₃ fibers were simulated numerically and compared to experimental results. A three-dimensional finite element model based on a representative volume, containing a single fiber was constructed and used for elastic–plastic analysis. Both aligned and tilted fibers were considered in the model. Using this model, the stress transfer between short fiber and matrix was studied. Based on the theory of effective performance, the tensile elastic modulus and initial stress–strain curves of δ-Al₂O₃/Al–5.5Zn, δ-Al₂O₃/Al–5.5Mg and δ-Al₂O₃/Al–12Si alloy composites were analyzed in detail. The effects of microstructural features such as fiber's orientation, interfacial bond and matrix performance on the elastic modulus and the initial stress–strain curve of the composite were also taken into account. On comparison with the measured results, it was concluded that the predicted results agreed well with the measured ones, especially for elastic modulus.     

A study of mechanisms of stress transfer in continuous- and discontinuous-fibre model composites by laser Raman spectroscopy

The micromechanics of stress transfer in single-fibre/epoxy-resin model composites has been investigated. Two specimen geometries are examined incorporating both continuous and discontinuous fibres in epoxy resin blocks. In both cases, the point-by-point strain in the fibre is measured from the fibre Raman spectrum and its strain dependence. The continuous-fibre model composites (CFMC) are subjected to incremental tensile loading and the fibre fragmentation process is continuously monitored. The short-fibre model composites (SFMC) are loaded incrementally to levels of stress of sufficient magnitude to cause interfacial failure and the fibre strain profiles are obtained at each level of applied stress.

In addition to fibre strain measurements, the interfacial shear stress distribution is derived at each increment of applied stress by means of a balance-of-forces argument. The effects of fibre surface treatment and fibre modulus on the strain transfer profile and the distribution of the interfacial shear stress along the fibre are examined. The importance of parameters such as fibre/matrix debonding and interphase yielding in the vicinity of fibre breaks or fibre ends is discussed.     

正交铺设陶瓷基复合材料单轴拉伸行为

采用细观力学方法对正交铺设陶瓷基复合材料单轴拉伸应力-应变行为进行了研究。采用剪滞模型分析了复合材料出现损伤时的细观应力场。采用断裂力学方法、 临界基体应变能准则、 应变能释放率准则及Curtin统计模型4种单一失效模型确定了90°铺层横向裂纹间距、 0°铺层基体裂纹间距、 纤维/基体界面脱粘长度和纤维失效体积分数。将剪滞模型与4种单一损伤模型结合, 对各损伤阶段应力-应变曲线进行了模拟, 建立了复合材料强韧性预测模型。与室温下正交铺设陶瓷基复合材料单轴拉伸应力-应变曲线进行了对比, 各个损伤阶段的应力-应变、 失效强度及应变与试验数据吻合较好。分析了90°铺层横向断裂能、 0°铺层纤维/基体界面剪应力、 界面脱粘能、 纤维Weibull模量对复合材料损伤及拉伸应力-应变曲线的影响。