等离子接枝处理的CF/PAA复合材料层间剪切强度及其形貌研究

采用等离子技术对碳纤维(CF)进行接枝芳基乙炔(PAA)处理,研究了影响CF／PAA复合材料层间剪切强度(ILSS)的因素。结果表明,经等离子接枝PAA处理后,复合材料的ILSS有了很大提高。SEM显示经接枝处理后CF和PAA树脂之间的界面结合紧密,改善了复合材料的界面结合性能。     

循环接触下安定状态问题的研究

基于线性随动强化理论,运用算子分离技术,研究将弹塑性问题转换为弹性问题和残余问题的分析方法,且针对循环载荷接触安定状态,建立了计算机分析程序,该研究能够分析计算弹塑性接触载荷在安定状态下的应力、残余累积应变及残余应力,分析计算了不同载荷的安定状态,并探讨其残余应力场的分析方法。     

生长对超弹性球壳变形和稳定性的影响

应用连续介质力学有限变形理论建立受内压作用不可压超弹性球壳大变形问题的力学模型, 且运用基于变形梯度张量极分解的弹性体积生长理论分析生长对不可压超弹性球壳变形和稳定性的影响. 通过对球壳变形与内压关系式的数值计算得到不同生长条件下球壳的变形曲线和应力分布曲线及由生长引起的残余变形和残余应力分布. 计算结果表明生长对球壳变形特性有明显的影响, 生长影响球壳可产生不稳定变形的临界壁厚和临界内压, 且在某些情况下可改变球壳的稳定性. 生长在球壳中可产生一定的残余变形和残余应力, 对球壳中的应力分布有一定的影响. 另外当生长的程度足够大时, 即便没有外力作用,球壳仅在生长引起的残余应力作用下也可产生不稳定变形.      

Cohesive failure analysis of an array of IC chips bonded to a stretched substrate

The paper presents a mechanical model for predicting the cohesive failure of a periodic array of integrated circuit (IC) chips adhesively bonded to a stretched substrate. A unit cell of the layered structure consisting of the IC chips, adhesive layer, and substrate is modeled as an assembly of two elastic Timoshenko beams, representing the chip and substrate, connected by an elastic interface, representing the adhesive. Accordingly, the stresses and energy release rate (ERR) in the adhesive layer – responsible for the premature cracking of the adhesive and debonding of the IC chips – are identified with the corresponding quantities computed for the elastic interface. Expressions for the adhesive stresses and ERR are given in terms of geometrical dimensions and material properties, combined with integration constants obtained numerically via the multi-segment analysis method. For comparison, the stresses in the adhesive are also computed based on a finite element model, and the ERR is evaluated using the virtual crack-closure technique (VCCT). The analytical predictions and numerical results match fairly well, considering the effects of key factors, such as the distance between adjacent chips, the chip size, the material properties of adhesive and substrate. The interaction between the chips is shown to have relevant effects on the adhesive stresses. In particular, only the mode II contributes to the ERR which increases with the ratio of the chip size to the distance between the chips and with the compliance of the adhesive and substrate layers.     

各向同性钢材的断裂模型和屈服模型

基于钢材断裂前必先屈服的基本事实, 以钢材断裂面为屈服面后继扩大直至材料完整性(连续性）发生破坏为假设, 以已有的屈服模型的共同特征为切入点, 建议了各向同性钢材在主应力空间的二次函数型断裂模型和屈服模型. 根据不同钢材的特征应力值, 量化了各向同性钢材的二次函数型断裂模型和屈服模型. 依据不同钢材的特征应力值的相互关系, 建议的各向同性钢材的二次函数型断裂模型和屈服模型相应地描述为主应力空间的圆柱面、椭球面、抛物面和双曲面. 建议的各向同性钢材的二次函数型断裂模型和屈服模型较已有的强度模型更具一般性.     

Effect of electromechanical boundary conditions on the properties of epitaxial ferroelectric thin films

The effects of internal stresses and depolarization fields on the properties of epitaxial ferroelectric perovskite thin films are discussed by employing the dynamic Ginzburg-Landau equation (DGLE). The numerical solution for BaTiO₃ film shows that internal stress and the depolarization field have the most effects on ferroelectric properties such as polarization, Curie temperature and susceptibility. With the increase of the thickness of the film, the polarization of epitaxial ferroelectric thin film is enhanced rapidly under high internal compressively stress. With the thickness exceeding the critical thickness for dislocation formation, the polarization increases slowly and even weakens due to relaxed internal stresses and a weak electrical boundary condition. This indicates that the effects of mechanical and electrical boundary conditions both diminish for ferroelectric thick films. Consequently, our thermodynamic method is a full scale model that can predict the properties of ferroelectric perovskite films in a wide range of film thickness.     

A note on incremental equations for a new class of constitutive relations for elastic bodies

Some new classes of constitutive relations for elastic bodies have been proposed in the literature, wherein the stresses and strains are obtained from implicit constitutive relations. A special case of the above relations corresponds to a class of constitutive equations where the linearized strain tensor is given as a nonlinear function of the stresses. For such constitutive equations we consider the problem of decomposing the stresses into two parts: one corresponds to a time-independent solution of the boundary value problem, plus a small (in comparison with the above) time-dependent stress tensor. The effect of this initial time-independent stress in the propagation of a small wave motion is studied for an infinite medium.     

厚板的高阶剪切变形理论研究

已有多种厚板理论和高阶剪切变形模型,但仍需要进一步研究以更加完善.首先根据平均转角及上下表面剪应力自由这两个条件,提出了具有统一高阶剪切变形模型的中面位移模式,并将之表示为正交分解形式.根据正交特性,定义了板的广义应力;运用板问题应变能密度表示的等价性,提出了与广义应力功共轭的广义应变表示形式,建立了板的本构关系.证明了不同转角定义时虚功原理板理论表示的客观性,以及与三维弹性理论表示的等价性.运用虚功原理,建立了变分自洽的高阶厚板理论和变分渐近的低阶厚板理论,推导了相应的平衡方程及边界条件,分析了与已有板理论的异同.以广义应力形式建立了厚板理论的平衡方程,厘清了不同转角表示时板理论间的关系、低阶厚板理论与高阶厚板理论间的关系以及剪切系数计算等若干基本问题.对圣维南扭转问题的求解证明了该理论的正确性.      

Dependence of stresses on grain orientations in BCC polycrystalline films on substrates

Most thin films have different thermal expansion coefficients from their substrates, thus thermal stresses will be introduced into the films when the temperature is changed during annealing and service. Calculations of these stresses for grains in various crystallographic orientations have been made for seven BCC transition metals Cr, Fe, Mo, Nb, Ta, V and W. Neglecting W, which is isotropic and the stresses are equiaxial and without grain orientation （hkl） dependence, the BCC metals may be grouped into two classes. In the first class （Cr, Mo, Nb and V）, the （100）-oriented grains have the largest stresses, while the stresses σ1 and σ2 in other （hkl）-oriented grains decrease linearly with the increase of the angle between （hkl） and （100）, and with σ1 〈 σ2 except in （100）- and （lll）-oriented grains. In the second class （Fe and Ta）, on the contrary, the （100）-oriented grains have the lowest stresses, and the stresses σ1 and σ2 in other （hkl）-oriented grains increase linearly with the increase of the angle between （hkl） and （100）, and with σ1 〉 σ2 except in （100）- and （111）-oriented grains.