含界面应力纳米尺度夹杂中刃型位错的稳定性分析

利用复变函数方法研究了刃型位错在含界面效应纳米尺寸夹杂中的稳定性问题.求解了作用在位错上的像力的精确表达式,给出了位错在纳米夹杂中稳定存在的夹杂临界半径条件.并且讨论了夹杂尺寸和界面效应等因素对夹杂临界半径的影响.研究表明:如果夹杂的半径保持不变,存在一个临界相对剪切模量或临界基体材料泊松比改变位错在夹杂中的稳定性.同...     

含双周期不等长刚性线材料有效反平面剪切模量研究

研究无限介质中含双周期刚性线夹杂复合材料的反平面问题,其基本胞元含有四条不同长度的刚性线夹杂。运用椭圆函数和保角变换理论,获得了该问题严格的闭合解。利用微结构的周期性和平均应力/应变定理得到了复合材料有效反平面剪切模量的精确公式。由结果的特殊情形可以得到一系列有意义的解答。数值结果给出了该类非均匀材料有效反平面剪切模量随微结构参数变化的规律。精确解可以为其它数值和近似方法提供有价值的参考。     

纳米尺度圆孔表面薄膜界面失配位错形核机理

研究了无限大基体内纳米尺度圆孔表面薄膜中界面螺型位错形核的临界条件,薄膜考虑了表/界面效应。运用弹性复势方法,获得了两个区域应力场的解析解答,并导出位错形核能公式,由此讨论了表/界面效应对薄膜界面位错形核的影响规律。算例结果表明,表/界面效应在纳米尺度下对位错形核的影响显著,不同表/界面效应下位错形核的临界薄膜厚度有很大差异,当基体与薄膜的相对剪切模量超过某一值后,只有考虑负的表/界面应力时位错才有可能形核;薄膜厚度在小于某一临界尺寸时负的表/界面应力更容易位错形核,薄膜厚度大于某一临界尺寸时正的表/界面应力更容易位错形核。     

复合材料中压电螺型位错与含刚性核夹杂的电弹干涉

为了研究压电复合材料中位于基体的压电螺型位错与含共焦椭圆导电刚性核椭圆夹杂的电弹相互作用, 基于复变函数方法, 获得了基体和夹杂区域的精确级数形式解析解。运用广义Peach-Koehler公式, 导出了作用在位错上像力的解析表达式。在此基础上讨论了椭圆刚性核和材料电弹特性对位错像力以及位错平衡位置的影响规律, 同时讨论了压电夹杂和弹性基体的复合情况。结果表明: 椭圆刚性核对位错有着明显的排斥作用, 可以增强硬夹杂对位错的排斥, 减弱软夹杂对位错的吸引; 对于软夹杂, 在界面附近位错存在一个不稳定的平衡位置; 在基体和夹杂的界面上, 像力迅速增大; 当夹杂的剪切模量远小于基体时, 界面附近不会出现位错的平衡位置。     

复合材料的椭圆夹杂模型线性温变问题的界面热应力分析

利用处理平面多连通域热弹性问题的一种有效方法,获得了椭圆夹杂模型线性温变问题的热弹性场解答,并讨论了夹杂和基体材料的热膨胀系数、热传导系数以及剪切模量对界面热应力的影响规律,所获得的结论为增强复合材料的设计与应用提供了有价值的参考依据.     

复合材料螺旋弹簧刚度及其影响因素分析

该研究制备了一种与中空圆截面簧丝轴线成±45°铺层的新型复合材料圆柱螺旋压缩弹簧,并对该弹簧进行准静态压缩试验。将纤维复合材料平板的剪切模量等效替代各向同性材料弹簧刚度表达式中的剪切模量,从而理论导出该类复合材料弹簧的刚度表达式。针对该表达式分析影响弹簧刚度的各种因素及其影响程度。结果表明:弹簧的刚度系数随着纤维弹性模量、纤维体积分数、簧丝外直径的增加而急剧增加,随它们的下降而显著下降;基体弹性模量与复合材料泊松比对弹簧刚度的影响十分微小;簧丝内直径在一定范围内变化时对弹簧刚度的影响几乎可以不计,但却能显著降低弹簧质量,超出该范围后,弹簧刚度随内直径增加而急剧下降;刚度系数随弹簧有效圈数和弹簧圈平均直径的增加而剧烈下降,随着它们的下降而急剧增加。     

增强相周期分布的多涂层纤维复合材料反平面问题的解析方法

采用增强纤维周期分布模型,通过引入非均匀的本征应变并结合双准周期Riemann边值问题理论,将非均匀介质问题转化为均匀介质的周期本征应变问题,获得了反平面载荷作用下多涂层纤维复合材料纤维、各涂层和基体中弹性场的解析解答。与有限元、广义自洽和渐进均匀化等方法的比较显示了该文方法的精度。讨论了涂层厚度和刚度等材料微结构参数对界面应力集中系数和有效反平面剪切模量的影响。该文为研究多涂层复合材料界面效应提供了一个有效的分析工具。     

一维六方准晶复合材料界面层中螺型位错分析

本文研究了一维六方准晶复合材料夹杂界面层中螺型位错与夹杂以及无限大基体的干涉效应。运用复变函数方法,得了该问题的解析解答,所得退化结果与已有文献结果一致,并得到了作用在圆环形界面层中螺型位错的位错力的精确表达式。讨论了一维六方准晶材料弹性常数对位错运动以及位错力的影响规律。结果表明,一维六方准晶中的材料弹性常数对位错力的变化影响是显著的。随着相位子场弹性常数或者声子场-相位子场耦合弹性常数的增大,其相应区域对位错的排斥或者吸引作用也分别增强。在夹杂界面或者基体界面附近,随着相位子场弹性常数和声子场-相位子场耦合弹性常数同时增大,夹杂或者基体对位错的吸引作用增强,但是并不改变位错平衡点的位置。     

纳米石墨/天然橡胶复合材料的应力软化与动态性能

以不同尺寸的纳米石墨为原料,制备了纳米石墨/天然橡胶(NR)复合材料.研究不同尺寸(30、80、150 nm)的纳米石墨对复合材料的应力软化效应(Mullins效应)、Payne效应、动态生热和损耗因子的影响.结果表明:随着纳米石墨尺寸的增大,纳米填料对纳米石墨/NR复合材料体系的补强作用明显,应力软化效应增大、动态损耗因子增加,但Payne效应降低;纳米石墨/NR复合材料动态损耗因子越大,其动态生热越高;动态生热还与填料粒子网络形成紧密相关.SEM观察及Payne效应分析结果表明:采用不同尺寸的纳米石墨材料填充天然橡胶,大尺寸石墨在橡胶基体中易于分散均匀,片层的聚集程度小,而小尺寸纳米片层表现出较明显的团聚.     

颗粒增强复合材料非理想界面刚度和有效模量的理论估计

采用内聚力模型(CZM)描述颗粒增强复合材料(PRCs)颗粒/基体非理想界面的力学行为,采用细观力学的Mori-Tanaka(M-T)方法和稀释解方法研究非理想界面刚度对该复合材料有效模量的影响。结果表明:复合材料某一体积含量下的有效模量和其颗粒/基体非理想界面刚度之间存在单调递增的关系曲线。同一复合材料不同体积含量的有效模量和非理想界面刚度关系曲线存在一个临界交点(CP),该点对应的临界界面刚度控制着颗粒体积分数对有效模量的影响。研究了基体和增强相的力学性能以及增强颗粒的尺寸对CP点临界界面刚度的影响。采用有效模量-界面刚度关系曲线,结合实验测得的有效模量,提出了估算PRCs的非理想界面刚度的方法,进而估计了复合材料的宏观有效模量。      

A generalized self-consistent method for nano composites accounting for fiber section shape under antiplane shear

A three-phase confocal elliptical cylinder model with interface stress is proposed. Based on the model, a generalized self-consistent method for the nano composites accounting for fiber section shape under antiplane shear is obtained. By applying the theory of Gurtin–Murdoch surface/interface and the conformal mapping technique, a closed-form solution of the effective antiplane shear modulus is obtained. Several existing solutions can be regarded as the degenerated cases. The major results are: (a) the effective antiplane shear modulus is size dependent when the size of the elliptical section fiber is on the order of nanometer, whereas the interface effect can be neglected when the fiber with large characteristic dimensions; (b) the interface effect of the nano fiber increases with the increase of the fiber section aspect ratio γ from 0 to 1; (c) the higher the fiber volume fraction is, the greater the interface effect is; (d) when the modulus of the fiber is small, the effective modulus of the nano composites depends strongly on the fiber interface effect, whereas when the modulus of the fiber is large, the fiber interface effect has little influence on the effective antiplane shear modulus.     

Contribution to critical shear stress of nanocomposites produced by interaction of screw dislocation with nanoscale inclusion

The contribution to the critical shear stress of nanocomposites caused by the interaction between screw dislocations and nanoscale circular cylindrical inclusions with interface stresses is derived by means of the Mott and Nabarro's model. The effect of the radius of the nanoscale inclusion and the volume fraction of inclusions as well as the interface stress on the critical shear stress is examined. The most important finding is that, when the negative interface stress is considered, a critical value of the radius of the nanoscale inclusion or the volume fraction of inclusions may exist to gain the best strengthening effects for the second-phase strengthened composites which differs from the classical solution without considering the interface stress under same external conditions.     

Dynamic Stress around Two Interacting Cylindrical Nano-Inhomogeneities with Surface/Interface Effects

On the basis of continuum surface elasticity, two interacting cylindrical nano-inhomogeneities with surface/interface effect in a small-sized solid under anti-plane shear waves are investigated, and the dynamic stress around the nano-inhomogeneities is analyzed. The wave function expansion method is used to expressed the wave field around the two nano-inhomogeneities. The total wave field is obtained by the addition theorem for cylindrical wave function. Through analysis, it is found that the distance between the two nano-inhomogeneities shows great effect on the dynamic stress in nano composites. The effect of the distance is also related to the properties of the nano-inhomogeneities and the interface, the wave frequency, and the incident angle of shear waves. To show the accuracy of the results for certain given parameters, comparison with the existing results is also given.     

分子模拟纳米ZnO/丁腈橡胶复合材料的摩擦学行为

采用分子模拟的方法研究了纳米ZnO/丁腈橡胶（NBR）复合材料的摩擦学行为,考察了纳米ZnO/NBR复合材料的回转半径、原子相对浓度和剪切行为,探讨了纳米ZnO/NBR复合材料摩擦学行为的微观机制。结果表明:与纯NBR材料相比,纳米ZnO/NBR复合材料具有更小的回转半径,橡胶分子链的柔顺性下降;与纳米ZnO/NBR复合材料相比,纯NBR材料摩擦界面具有更高的原子相对浓度,纯NBR材料上下摩擦表面的原子浓度峰值比纳米ZnO/NBR复合材料分别高了6.4%和4.3%。说明纳米ZnO的存在提高了纳米ZnO/NBR复合材料分子链的刚性,减小了能量耗散,从而改善了纳米ZnO/NBR复合材料的摩擦性能。      

Local Electroelastic Field and Effective Electroelastic Moduli of Piezoelectric Nanocomposites with Interface Effect

Due to the large ratio of surface area to volume in nanoscale objects, the property of surfaces and interfaces likely becomes a prominent factor in controlling the behavior of nano-heterogeneous materials. In this work, based on the Gurtin-Murdoch surface/interface elastic theory, a distinct expression is derived for embedded nano-inclusion in an infinite piezoelectric matrix coupled with interface effect. For the problem of a spherical inclusion in transversely isotropic piezoelectric medium, we reach a conclusion that the elastic and electric field are uniform when eigen-strain and eigen-electric field imposed on the inclusion are uniform even in the presence of the interface influence. The electroelastic fields in the inclusion are related to both interface electroelastic parameters and the radius of the inclusion. Then overall properties of the composites are estimated by using the dilute distribution model. Numerical results reveal that the effective electroelastic moduli are function of the interface parameters and the size of the nano-inhomogeneities.     

Dynamic stress in a semi-infinite solid with a cylindrical nano-inhomogeneity considering nanoscale microstructure

In this paper, the dynamic stress around a cylindrical nano-inhomogeneity embedded in a semi-infinite solid under anti-plane shear waves is investigated. The surface/interface stress effects around the nano-inhomogeneity and at the straight edge of the semi-infinite solid are both considered. The boundary condition at the straight edge of the semi-infinite solid with surface/interface effects is satisfied by the image method. The incident, scattered and refracted displacement fields in the nano-sized composites are expressed by employing the wave function expansion method. The addition theorem for a cylindrical wave function is applied to accomplish the superposition of wave fields in the two semi-infinite solids. Analyzes show that the effect of interface properties, especially that at the straight edge, on the dynamic stress is significant, and the effect increases noticeably due to the nanoscale of the structure. The incident frequency and angle of waves and the shear modulus ratio of the nano-inhomogeneity to matrix also show a pronounced effect on the dynamic stress distribution if the semi-infinite solid shrinks to nanoscale.     

Interface diffusion-induced creep and stress relaxation in unidirectional metal matrix composites under biaxial loading

Analytical solutions are developed for interface diffusion-induced creep and stress relaxation in unidirectional metal matrix composites under biaxial transverse loading. The driving force for the interface diffusion is the normal stress acting on the interface, which is obtained from rigorous Eshelby inclusion theory. The solutions are a function of the applied stress, volume fraction and radius of the reinforced-fiber, the modulus ratio between the fiber and the matrix, specially, exhibit a strong dependence of creep rate and stress relaxation behavior on the biaxial stress ratio. Moreover, the solution for the interface stress presented in this study also gives some insight into the relationship between the interface diffusion and interface slip. For the application of the solutions in the realistic composites, the scale effect is taken into account by detailed finite element analysis based on a unit cell model.     

Surface/interface Energy Effect on Electromechanical Responses Around a Nanosized Elliptical Inclusion under Far-field Loading at an Arbitrary Angle

Electro-elastic surface/interface around nano-sized piezoelectric inclusions shows great effect on the response of piezoelectric nano-structures. In this paper, a theoretical model is proposed to examine the surface/interface effect on the electromechanical responses around a nano-sized elliptical piezoelectric inclusion embedded in an infinite piezoelectric matrix under far-field loading with an arbitrary angle, and the effect of loading angle is considered Combining the conformal mapping technique and electro-elastic surface/interface theory, a closed form solution of this problem is obtained and the interactive effect between the surface/interface and the aspect ratio of the elliptical inclusion is examined.