非完美界面多边形夹杂复合材料弹性场研究

导出了在非完美界面下，具有均匀本征应变的多边形夹杂复合材料位移场的计算公式，利用边界单元法求解了均匀剪切本征应变下多边形夹杂内应变场的分布。数值结果表明界面连结的完好与否对夹杂内部应变分布有比较明显的影响；随着界面缺陷程度的加剧，多边形内的应变偏离完好界面情形的相应应变就越大，这与实际情况相符。     

非完美界面复合材料的损伤界面能研究

根据能量法求出的非完美界面复合材料应变能表达式,定义了损伤界面能。分别计算了体变所引起的损伤界面能密度与夹杂内应变能密度的比值和畸变引起的两者比值．发现这两个比值正是文献[8]中所定义的两个无量纲因子αt和αG。这就为αk和αG赋与了新的物理含义,从而揭示了非完美界面复合材料定规模量随αk、αG增大而减小的物理本质,即损伤界面能越大刚度越小。文未给出了常见夹杂形状的αk、αG因子公式。     

非完美界面复合材料刚度下限相关式

通过构造以夹杂纵横比为交量的函数,导出了计算非完美界面复合材料有效模量中,将任意夹杂形状转化为球形夹杂计算的普遍公式。进而得到了纤维夹杂和圆盘夹杂非完美界面复合材料有效模量4个下限之间的相关公式。     

非完美界面复合材料的驻值原理与相应变分方程等价的充分 …

当界面非完美时,复合材料的能量泛函必须计入非完美界面效应,该效应界面积分形式出现,与完美界面不同的是,由于这个积分项的引入,非完美界面复合材料的驻值原理不再与相应的变分方程等价。这在理论上是不完整的。本文基于驻值地界面积分项作出整体假定,由此得到了非完美界面复合材料驻值原理与相应变分方程等价的充分条件,指出了实现这种假设所必须的界面几何形状性质 。     

有限变形下含非完美椭圆界面复合材料刚度的限界

应用文献（１３）中有限变形下非界面弹性复合材料有效模量的近似公式和微分几何方法，计算了含一般旋转椭球体夹杂弹性复合材料有效体积模量和有效剪切模量的上下限界，所得结果为研究大变形下实际弹性复合材料的刚度估值提供了定量判据。     

聚合物基复合材料界面剪切强度的测试

本文在亚太地区首次用声发射(AE)技术确定纤维断裂的位置,从而决定纤维断裂段的长度分布。这里采用了含有单纤维丝聚的聚合物基复合材料试件。应用细观力学的模型,根据纤维断裂段的长度,可确是纤维和基体之间的界面剪切强度。这种方法适用于不透明的复合材料基体,因而有可能用它来测定金属基和陶瓷基复合材料的界面剪切强度。     

非完美界面复合材料的驻值原理与相应变分方程等价的充分条件

当界面非完美时,复合材料的能量泛函必须计入非完美界面效应,该效应以界面积分项形式出现。与完美界面不同的是,由于这个积分项的引入,非完美界面复合材料的驻值原理不再与相应的变分方程等价。这在理论上是不完整的。本文基于驻值原理对界面积分项作出整体假定,由此得到了非完美界面复合材料驻值原理与相应变分方程等价的充分条件,指出了实现这种假设所必须的界面几何形状性质。     

有限变形下含非完美椭圆界面复合材料刚度的限界

应用文献［１３］中有限变形下非完美界面弹性复合材料有效模量的近似公式和微分几何方法，计算了含一般旋转椭球体夹杂弹性复合材料有效体积模量和有效剪切模量的上下限界。所得结果为研究大变形下实际弹性复合材料的刚度估值提供了定量判据。     

动荷载作用下纤维沥青路面的黏弹性响应

目的为了分析动荷载作用下纤维的加入对路面黏弹性响应的影响.方法以Burgers模型模拟纤维沥青混凝土的黏弹性性质,基于黏弹性理论,应用有限元方法分析单周期动荷载作用下,不同荷载作用时间对不同纤维沥青路面的路表各点最大竖向位移和卸载后加载中心点竖向位移的影响规律.结果纤维加入到沥青路面后,减小了路面的竖向位移;对于不同纤维沥青路面结构,在荷载作用时间较短时,路面结构的流变性质不显著;荷载作用时间较长时,卸载后还有部分残余变形不能恢复,但路面响应规律基本相同.结论纤维的加入提高了路面的整体变形能力,但没有明显改变沥青混凝土的黏弹性性质;在单周期动荷载作用下,若荷载作用时间很短时,可以忽略纤维沥青混凝土的黏弹性特征.     

Elastic Properties of Particulate Composites with Imperfect Interface

An effective analytical approach is developed for the problem of particulate composites containing spherical inclusion with imperfect iraerface between the matrix and spherical inclusions. In this paper, a general interface model for a variety of interracial defects has been presented, in which both displacement discontinuity across the interface and the elastic moduli varing with radius outside of the inclusion are considered. The imperfect interface conditions are appropriate in the case of thin coatings on the inclusion. Furthermore, in the ease of thin elastic interphase , the displacement field and the stress field in the inclusion and matrix are exactly solved for the boundary problem of hydrostatic compression of an infinite spherical symmetrical body by Frobenius series, and the erpression of the normal interface parameter, Dr, is derived. In addition, it has been proved that two previous results derived in some literatures by considering the interface to be a thin iruetptmse with displacement jump or with some variance in its moduli can be reverted from the present formula, respectively. Numerical results are given to demonstrate the significance of the general imperfect interface effects.     

Damping behaviors of metal matrix composites with interface layer

A novel technique of designing the interface layer in metal matrix composites of high damping capacity was developed via different CVD coatings on carbon fibers in Cc/AI composites. It was shown that the interface layer improved the tensile strength, elastic modulus and damping capacity of the Cf/AI composites. A carbon layer showed the highest improvement and a silicon layer the lowest, while a mixed carbon and silicon layer exhibited an intermediate effect. Moreover, the thickness of interface layer also influences the damping capacity. A thicker carbon layer produced a better damping capacity because the dependence of damping capacity on strain amplitude was increased. It is suggested that a micro-sliding action occurring in the interface layer is the main mechanism responsible for the high damping capacity of the composites.     

A macro-meso constitutive law for concrete having imperfect interface and nonlinear matrix

The overall behavior of concrete depends on its meso structures such as aggregate shape, interface status, and mortar matrix property. The two key meso structure characters of concrete, bond status of interface and nonlinear property of matrix, are considered in focus. The variational structure principle is adopted to establish the macro-meso constitutive law of concrete. Specially, a linear reference composite material is selected to make its effective behavior approach the nonlinear overall behavior of concrete. And the overall property of linear reference composite can be estimated by classical estimation method such as self-consistent estimates method and Mori-Tanaka method. This variational structure method involves an optimum problem ultimately. Finally, the macro-meso constitutive law of concrete is established by optimizing the shear modulus of matrix of the linear reference composite. By analyzing the constitutive relation of concrete established, we find that the brittleness of concrete stems from the imperfect interface and the shear dilation property of concrete comes from the micro holes contained in concrete. Supported by the National Natural Science Foundation of China (Grant Nos. 50679022, 90510017, 50539090) and National Basic Research Program of China (Grant No. 2007CB714104)     

短纤维增强金属基复合材料弹性模量临界值计算预测

基于短纤维增强金属基复合材料弹性模量理论模型,提出了弹性模量临界值的定义,并建立了可用于预测计算的纤维临界长径比和材料参数之间的解析函数。将与曲线拐点切线和最大值水平直线交点相对应的长径比值定义为纤维临界长径比,将与此相对应的函数值定义为弹性模量临界值。计算结果表明,纤维临界长径比随纤维弹性模量的增加而增加,随基体弹性模量和纤维体积分数的增加而降低。     

预应力CFRP板加固钢-混凝土组合梁受弯性能试验

为研究钢-混凝土组合梁经预应力碳纤维板加固后的受弯性能,设计4根预应力碳纤维板加固试件和1根不加固的对比试件. 5根试件均为工字形钢-混凝土组合简支梁,采用四点弯曲静力加载.锚固装置为自主研发的装配式预应力碳纤维板锚固系统,碳纤维板与钢梁之间的锚固主要依靠端部锚具,并辅之以专用环氧胶的黏结作用.试验中考虑碳纤维板的加固量和预应力水平两种因素对加固效果的影响.结果表明:加载全过程截面应变基本符合平截面假定;增大碳纤维板的加固量能提高钢-混凝土组合梁的抗弯极限承载力;增大碳纤维板的预应力有助于提高钢-混凝土组合梁的屈服承载力,对结构抗弯刚度贡献有限;破坏阶段碳纤维板有断裂和剥离两种形式,其强度利用率可达到80%以上.所采用的锚固系统锚固力大、可靠度高,工程实用价值大;预应力碳纤维板加固钢-混凝土组合梁,能有效提高结构的抗弯承载力,是一种补强效果很好的主动加固技术.     

碳纳米管增强钛基复合材料的界面应力分布

为了了解工业领域中综合性能优异的金属基复合材料,采用结构分析软件ANSYS建立了有限元模型,研究了复合材料界面应力场的分布情况.结果表明,在受压载荷作用下,钛基复合材料发生屈服现象的可能性较小,但碳纳米管的顶部界面边缘处出现了明显的应力集中现象,导致此处发生断裂破坏的可能性相对较大.在拉伸载荷作用下,钛基复合材料的应力分布比较均匀,且未出现明显的应力集中现象,因而复合材料发生屈服、断裂破坏的可能性较小.当碳纳米管的相位角为15°时,复合材料发生界面脱离和基体开裂的可能性相对较小.     

纤维增强复合材料桥联增韧模型

提出一个纤维增韧模型和一个桥联本构函数，考虑到界面滑移和分离特性，运用建立在纤维强度
基础上的韦布尔分布来模拟有效的桥联裂纹长度.当桥联载荷、总体外载荷、桥联应力和桥联应力强度因
子之间的关系联合求解时，描述了一个完全的桥联轮廓.对纤维增强复合材料作数值计算，结果表明，计
算值和现有实验值吻合得较好.建立在数值结果基础上，提出一个有限元法，通过比较半裂纹展开位移，
证实提出的模型和函数对模拟桥联律是有效的.     

复合材料桥联问题中的半桥问题

针对纤维增强复合材料的半桥问题，即部分桥联增韧的问题，给出了数值计算结果。由此得到了一个近似解析解--应力强度因子线性模型。利用这一模型，根据纤维基体界面强弱的不同情况，分别给出了III型裂纹的若干强度条件。     

Wear behavior of Cu matrix composites reinforced with mixture of carbon and carbon nanotubes

In order to improve wear resistance and decrease the cost, carbon and carbon nanotubes reinforced copper matrix composites were fabricated by the power metallurgy method. The effects of carbon (carbon and carbon nanotubes) volume fraction and applied load on the friction coefficient and wear rate under dry sliding of the composites were investigated at room temperature. By scanning electron microscopy (SEM), the worn surfaces and debris were observed, and wear mechanism was also analyzed and discussed. The experimental wear process consists of the run-in, steady wear and severe wear process with the increasing of sliding distance. Both the friction coefficient and wear rate of the composites first decrease and then increase with the increasing of carbon volume fraction. The minimum friction coefficient and wear rate are obtained when carbon is 4.0vol%. The wear mechanisms of the composites change from the adhesive wear and delamination wear to abrasive wear with the increasing of carbon volume fraction. Funded by the National Natural Science Foundation of China (50873047) and the Natural Science Foundation of Gansu Province (3ZS061-A25-039)     

Lagged strain of laminates in RC beams strengthened with fiber-reinforced polymer

Based on the theory of concrete structure, a new expression was derived for lagged strain of fiber-reinforced polymer （FLIP） laminates in reinforced concrete （RC） beams strengthened with FRP. The influence of different preloaded states and nonlinear stress-strain relationship of compressed concrete were both taken into account in this approach. Then a simplified expression was given by ignoring tensile resistance of concrete. Comparison of analytical predictions with experimental results indicates satisfactory accuracy of the procedures. The errors are less than 8% and 10% respectively when the tensile resistance of concrete is or not considered. While the maximum error of existing procedures is up to 60%.