含双尺度界面复相陶瓷的细观界面滑移应力

基于复相陶瓷显微特征和双尺度界面特性,分析含双尺度界面复相陶瓷内的细观界面滑移应力。首先,基于复相陶瓷宏观、细观和纳观弹性性能,计算双尺度界面复相陶瓷产生弹性变形时的细观平均应力场。然后,在纳观界面位移和应力连续基础上,提出了界面应变模型,确定了纳观界面附近纤维和基体内的位移函数,考虑界面应变的突变值与界面模量间的比例关系,根据纳观界面特性和纤维分布形式,确定出弹性变形条件下外载传递到细观界面上的切应力。最后,基于压痕实验测得复相陶瓷细观界面滑移的屈服切应力,得到细观界面滑移应力的理论计算公式并进行了定量分析。结果表明,复相陶瓷内纳观界面弹性模量越小或泊松比越小时,细观界面越易滑移,复相陶瓷越易产生塑性变形。     

非理想界面功能梯度压电/压磁双材料中的SH界面波

研究了非理想界面功能梯度压电/压磁双材料中SH界面波的传播特性,这里假定上、下半空间材料性能在垂直于界面的方向是按指数函数变化的。界面的机械条件由"弹簧"模型表征,即应力是连续的而位移是间断的;界面电磁学条件考虑电位移、电势、磁感、磁势连续和电学短路、磁学开路两种情况。推导了界面波显函形式的频散方程,通过数值计算表明了材料组合形式、界面非理想程度以及材料梯度变化对界面波相速度的影响。     

含非均匀界面相纤维增强复合材料热传导性能预测的递推公式

研究了含非均匀界面相纤维增强复合材料的宏观等效传热性能。将热导率沿径向连续变化的界面相离散为多个热导率均匀的同心圆柱层,采用广义自洽法和复变函数理论,推导了复合材料宏观等效热导率的解析递推公式,并由递推公式给出了均匀界面相和理想零厚度界面的封闭公式。理想零厚度界面复合材料的热导率与已有理论结果一致。理想零厚度界面和非均匀界面相模型的计算结果与实验数据比较表明,当纤维体积分数较小时,2种模型的预测结果与实验数据吻合均较好,当体积分数较大时,与实验数据相比,非均匀界面相模型的精度大大高于理想零厚度界面模型的精度。本文中给出的递推公式亦可用于计算多涂层纤维增强复合材料的热导率。     

弱粘接界面固-固界面波特性及与界面粘接性质关系数值研究

根据两固体粘接结构在不同粘接强度下的弹簧模型边界条件,通过傅里叶积分变换方法进行波动方程求解,理论分析和数值计算了相近横波速度的两种固体间界面波的频散及衰减特性.计算结果表明,当切向弹簧劲度系数从滑移粘接界面向完好粘接界面逐渐变化时,界面波的频散特性随之变化.在此基础上进一步计算了不同界面粘接条件下法向线源脉冲激发的界...     

含不完美界面的磁电复合材料倾斜裂纹问题

研究了含非完美界面的双层压电/压磁复合材料中压电相存在一个倾斜于界面的Ⅲ型裂纹问题。采用弹簧型耦合界面模型模拟非完美界面,运用Fourier积分变换法将裂纹面条件转化为奇异积分方程,并使用Lobatto-Chebyshev方法数值求解了裂纹尖端应力强度因子（SIF）。详细地研究了裂纹尖端SIF与界面参数、压电/压磁材料参数和材料的层厚、裂纹的倾斜角、裂纹与界面的距离等几何参数的关系。结果表明：力学不完美性可以独立地增大SIF,而磁学、电学不完美性只有与力学不完美性耦合时才会减小SIF;力学-电学、力学-磁学不完美性的耦合会减小SIF,而磁学-电学不完美性的耦合不会影响SIF;磁场作用下,增大压磁层弹性模量会减小SIF,而增大压电层压电系数,减小压电层弹性模量和介电常数,均会减小SIF;界面不完美性会影响SIF随裂纹倾斜角度或裂纹与界面之间距离的变化规律;在一定范围内增加压电层或压磁层厚度可以减小SIF。     

脆性及准脆性开裂界面的剪胀内聚力模型

根据界面剪胀与Ⅱ型断裂能间的关系,给出构造含剪胀效应张力-位移关系的新途径,该方法先假定Ⅱ型张力-位移关系,再计算界面剪胀函数,从而更易于应用。通过定义基于能量和界面不连续位移的4个损伤变量,给出含剪胀效应的损伤张力-位移关系表示形式,使模型不仅能模拟单调加载问题,而且可模拟反复加载问题。对界面在受压状态下的切向粘结强度、法向位移和摩擦作用分别进行了讨论,给出了相应的计算方法或取值建议。最后通过一个张力-位移关系的实例讨论了界面压力作用、复合模式开裂、卸载-再加载行为和接触罚刚度对法向位移的影响等模型性质。     

三维四向编织复合材料界面损伤机理数值分析

考虑界面脱粘表面压应力下摩擦力对材料界面力学性能的影响,建立损伤-摩擦相结合的界面本构模型,编写用户材料子程序VUMAT,实现其在有限元软件ABAQUS中的嵌入。基于周期性胞元分析思想,在单胞模型中纤维束/基体、纤维束/纤维束分界面引入界面单元,结合损伤-摩擦相结合的界面本构模型,建立含界面相三维四向编织复合材料的细观有限元模型。模拟典型载荷下界面损伤的起始和扩展过程,分析界面应力传递和界面破坏机理,研究界面性能对复合材料宏细观力学性能的影响规律,为实现三维四向编织复合材料界面性能优化设计和控制提供参考。      

接触界面对拉杆组合柔性转子轴承系统的非线性动力特性影响

对于拉杆柔性组合转子轴承系统,其接触界面类型复杂、数量众多,是影响其动力特性的众多因素之一。以拉杆柔性组合转子轴承系统各轮盘间的接触界面为考察对象,根据接触界面压力结合微观模型有限元分析,得到其宏观尺寸下的界面接触刚度。采用无质量无长度的均质面弹簧对接触界面进行等效,推导了接触界面作为附加弹簧单元对系统产生附加刚度矩阵的一般形式,并完成了计及接触界面效应的系统动力学建模。结合应用计及轴向力的铁木辛格梁轴单元的整体转轴建立的有限元模型,得到系统的动力学方程。而后采用打靶法和Floquet稳定性判别理论对系统进行分析求解,得到了计入接触界面影响后系统的稳定性边界和分叉形式,数值结果表明接触界面对不平衡组合转子的动力特性影响不可忽略。     

固体粘接界面的非线性共振特性研究

研究考虑粘接界面非线性的条件下,双层固体粘接薄板的振动特性。将双层板间的振动耦合看作一组非线性弹簧,理论上运用分离变量等数学方法,求解得到粘接层的应力应变关系为线性条件下的解析解,以及考虑非线性参量时系统共振的数值解。通过对双层铝板的环氧树脂粘接模型进行仿真研究分析,发现界面的共振频率随着界面粘接强度非线性参量的增加呈现先增大后减小的趋势,当界面强度弹性参量为300GN/m3时,共振频率的最大偏移量达到10%。在粘接强度退化早期,利用界面的非线性共振特性可以更好地检测粘接质量。     

短纤维增强橡胶密封复合材料界面疲劳损伤行为

依据广义自洽方法,建立了包含芳纶纤维、界面相、橡胶基体和等效介质的代表性体积单元(RVE)模型。采用自定义材料子程序对内聚力疲劳累积损伤模型进行编译,分别在基体/界面相的界面和纤维/界面相的界面设置内聚力单元,研究界面相性能参数对纤维增强橡胶密封复合材料(SFRC)界面疲劳损伤行为的影响。探讨了界面相厚度和模量的确定方法,获得了不同界面相厚度和模量下SFRC界面脱粘起始位置以及脱粘起始疲劳次数。结果表明,较低的界面相模量能够抑制界面脱粘的产生;随着界面相厚度的增加,界面脱粘的起始疲劳次数增加,SFRC抗疲劳损伤能力得到提高。     

Three‐dimensional numerical modelling by XFEM of spring‐layer imperfect curved interfaces with applications to linearly elastic composite materials

The spring‐layer interface model is widely used in describing some imperfect interfaces frequently involved in materials and structures. Typically, it is appropriate for modelling a thin soft interphase layer between two relatively stiff bulk media. According to the spring‐layer interface model, the displacement vector suffers a jump across an interface whereas the traction vector is continuous across the same interface and is, in the linear case, proportional to the displacement vector jump. In the present work, an efficient three‐dimensional numerical approach based on the extended finite element method is first proposed to model linear spring‐layer curved imperfect interfaces and then applied to predict the effective elastic moduli of composites in which such imperfect interfaces intervene. In particular, a rigorous derivation of the linear spring‐layer interface model is provided to clarify its domain of validity. The accuracy and convergence rate of the elaborated numerical approach are assessed via benchmark tests for which exact analytical solutions are available. The computated effective elastic moduli of composites are compared with the relevant analytical lower and upper bounds. Copyright © 2011 John Wiley & Sons, Ltd.     

Asymptotic analysis of a thin interface: The case involving similar rigidity

This study deals with a linear elastic body consisting of two solids connected by a thin adhesive interphase with a small thickness ε. The three parts have similar elastic moduli. It is proposed to model the limit behavior of the interphase when ε→0. It has been established [1], using matched asymptotic expansions, that at order zero, the interphase reduces to a perfect interface, while at order one, the interphase behaves like an imperfect interface, with a transmission condition involving the displacement and the traction vectors at order zero. The perfect interface model is exactly recovered using a Γ-convergence argument. At a higher order, a new model of imperfect interface is obtained by studying the properties of a suitable (weakly converging) sequence of equilibrium solutions. Some analytical examples are given to illustrate the results obtained.     

Interfacial models in viscoplastic composites materials

The aim of the present work is to extend the concept of interphase and equivalent imperfect interface in the context of viscoplasticity. The interphase takes the form of a thin curved layer of constant thickness, made up of a rigid viscoplastic material located between two other surrounding materials. We aim at representing this interphase by an interface with appropriately devised interface conditions. To reach this objective, a Taylor expansion of the relevant physical fields in the thin region is used. It is shown that, depending of the degree of stiffness of the layer with respect to the neighboring media, this interphase can be replaced by an idealized imperfect interface involving the jump of the velocity field or the traction vector. The first kind of interface model, applicable to soft interphases, is the “spring-type” interface across which the traction are continuous but the velocity field exhibits a discontinuity which is given in term of the traction by a power-law type relation. Moreover, it is shown that the constant of the model can be expressed in terms of the material parameters of the interphase. When the interphase is stiffer than the two surrounding media, it can be replaced by an imperfect interface described by a generalization of the so-called Young Laplace model to viscoplastic solids.     

Torsion of compound cross-sections with imperfect interface

Summary The Saint-Venant torsion problem of compound sections with imperfect interfaces is studied. Two kinds of an imperfect interface are considered: an imperfect interface which models a thin interphase of low shear modulus and an interface which models a thin interphase of high shear modulus. At the former kind, the tractions are continuous but the warping displacement undergoes a discontinuity; at the latter kind the warping displacement is continuous but the shear traction undergoes a discontinuity. These imperfect interface conditions have been derived in a companion study [1]. The present paper is concerned with deriving benchmark solutions for the Saint-Venant torsion problem of compound sections with imperfect interfaces. Specifically, analytical solutions are given for a) a two-phase rectangular section, b) a two-phase section in the shape of a circular sector with an imperfect interface located along a circular arc, c) a two-phase circular sector with an imperfect interface along a radial line. The effect of imperfect bonding on the torsional rigidity of the compound bar is examined.     

Thermoelastic properties of fiber composites with imperfect interface

Imperfect interface conditions are defined in terms of linear relations between interface tractions and displacement jumps. All of the thermoelastic properties of unidirectional fiber composites with such interface conditions are evaluated on the basis of the generalized self consistent scheme (GSCS) model. Results for elastic interphase are obtained as a special case by evaluation of interface parameters in terms of interphase characteristics. Numerical evaluation has shown that imperfect interface may have a significant effect on transverse thermal expansion coefficient, transverse shear and Young's moduli and axial shear modulus, a moderate effect on axial Poisson's ratio, small effect on axial thermal expansion coefficient and an insignificant effect on axial Young's modulus.     

Interface waves along an anisotropic imperfect interface between anisotropic solids

First and second order asymptotic boundary conditions are introduced to model a thin anisotropic layer between two generally anisotropic solids. Such boundary conditions can be used to describe wave interaction with a solid-solid imperfect anisotropic interface. The wave solutions for the second order boundary conditions satisfy energy balance and give zero scattering from a homogeneous substrate/layer/substrate system. They couple the in-plane and out-of-plane stresses and displacements on the interface even for isotropic substrates. Interface imperfections are modeled by an interfacial multiphase orthotropic layer with effective elastic properties. This model determines the transfer matrix which includes interfacial stiffness and inertial and coupling terms. The present results are a generalization of previous work valid for either an isotropic viscoelastic layer or an orthotropic layer with a plane of symmetry coinciding with the wave incident plane. The problem of localization of interface waves is considered. It is shown that the conditions for the existence of such interface waves are less restrictive than those for Stoneley waves. The results are illustrated by calculation of the interface wave velocity as a function of normalized layer thickness and angle of propagation. The applicability of the asymptotic boundary conditions is analyzed by comparison with an exact solution for an interfacial anisotropic layer. It is shown that the asymptotic boundary conditions are applicable not only for small thickness-to-wavelength ratios, but for much broader frequency ranges than one might expect. The existence of symmetric and SH-type interface waves is also discussed.     

A three-phase circular inhomogeneity with imperfect interface under thermomechanical loadings in plane elasticity

Summary The solution for a homogeneous circular inhomogeneity embedded in an infinite elastic matrix with a single interphase layer plays a fundamental role in many practical and theoretical applications. In particular, it serves as the basis for the solution of the generalized self-consistent method in the mechanics of composite materials. Thus, the study of three-phase problems is of great interest.A general method is presented for the rigorous solution of a three-phase circular inhomogeneity under thermomechanical loadings in plane elasticity. The bonding at the inhomogeneity-interphase interface is considered to be inperfect with the assumption that the interface imperfections are constant. On the remaining boundary, that being the interphase-matrix interface, the bonding is considered to be perfect. Although the problem of a three-phase circular inhomogeneity with imperfect bonding has previously been studied, it seems that the explicit expressions for the complete solutions cannot be located in the literature. In this paper, it is found that stress field within the inhomogeneity is determined by three, in general, complex coefficients while the stress field in the matrix is controlled by three other, in general, complex coefficients. The role of the interphase layer as well as the influence of the imperfect bonding condition, on the stress fields, is manifested by their effect on the six, in general, complex coefficients.The exact closed-form solutions are applied to the design of a three-phase circular inhomogeneity. In particular, for specific thermomechanical loadings, it is shown that a uniform stress state within the inhomogeneity can be achieved with the imperfect interface model provided the imperfect interface parameters are suitably chosen.     

Variational bounds for the effective electroelastic moduli of piezoelectric composites with electromechanical coupling spring-type interfaces

The present work focuses on variational bounds for the effective electroelastic moduli of multiphase piezoelectric composites with thin piezoelectric interphase. Both the inhomogeneities and the matrix are assumed to be piezoelectric and transversely isotropic. The piezoelectric interphase is modeled as the spring-type interface with electromechanical coupling. The inhomogeneities are assumed to be spheroidal so that the reinforcement geometry is able to range from thin flake to continuous fiber. The effective properties of the piezoelectric composite with interfacial imperfection are defined and the principles of minimum internal energy and enthalpy are derived. These principles are applied to analytically obtain the upper and lower bounds for the effective electroelastic moduli. Unlike the Voigt–Reuss-type bounds for perfect interface, the present bounds depend not only on the material properties and volume fraction, but also on the interface parameters, inhomogeneity shape and orientation. An example of a two-phase composite is given for detailed discussion, where dependence of the electroelastic moduli and their bounds on the inhomogeneity shapes and orientations as well as the interface properties is provided and discussed. To qualitatively account for the dependence, analysis based on two possible mechanisms, i.e., the simple mixture rule of composite and the weakening effect by imperfect interface, are also provided.     

Ultrasonic scattering from imperfect interfaces: A quasi-static model

A quasi-static model for the ultrasonic transmission and reflection at imperfect interfaces is developed. The interface is represented by a distributed spring, determined by the change in static compliance of the medium with respect to one with a perfect interface, and a distributed mass, representing excess mass at the interface. Comparison of the model predictions to exact solutions for two simple cases illustrates its accuracy at low frequencies. The spring stiffnesses can be derived from existing solutions for the elastic displacement of materials containing cracks and inclusions under static load. Results for a variety of cases are reviewed. Applications of the model to study the characteristics of partially contacting surfaces in several problem areas of current interest are discussed.