颗粒缺陷相互作用下复合材料的细观损伤模型

含尖角的非椭球颗粒附近应力集中较大,诱导缺陷形成裂纹是材料损伤的重要来源.对于强界面颗粒,大刚度颗粒诱导裂纹向基体中扩展形成近似平面片状裂纹,认为诱导裂纹受颗粒应力附近应力场控制,基于有效自洽理论建立了材料细观损伤模型,得到了单向拉伸下的损伤演化,并分析了颗粒形状、尺寸、颗粒性能以及颗粒与初始缺陷相对位置等因素对材料损伤的影响.结果表明,非椭球颗粒更易诱发裂纹,同样外载应力下,损伤程度更大,含非椭球颗粒材料强度更低;含扁平型的颗粒材料裂纹损伤过程更加明显并且材料强度更大;提高颗粒刚度和含量能够增大材料强度.材料中存在尺寸过大或过小的初始裂纹时材料损伤过程不明显.     

Two-Level Defect-Correction Method for Steady Navier-Stokes Problem with Friction Boundary Conditions

In this paper, we present two-level defect-correction finite element method for steady Navier-Stokes equations at high Reynolds number with the friction boundary conditions, which results in a variational inequality problem of the second kind. Based on Taylor-Hood element, we solve a variational inequality problem of Navier-Stokes type on the coarse mesh and solve a variational inequality problem of Navier-Stokes type corresponding to Newton linearization on the fine mesh. The error estimates for the velocity in the $H^1$ norm and the pressure in the $L^2$ norm are derived. Finally, the numerical results are provided to confirm our theoretical analysis.     

Characterization of the globular oxide inclusion ratings in steel using laser-induced breakdown spectroscopy

Grade assessment of steel is generally performed via the metallographic method, which is timeconsuming and is not able to provide the elemental distribution information. In this paper, we present a method to measure the globular oxide inclusion ratings in steel using laser-induced breakdown spectroscopy (LIBS). The measurement is performed in two basic steps: steel samples are polished using metallographic sand paper and the Al₂O₃ inclusion number and size distribution in a marked area are observed using scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDS) for further LIBS scanning analysis. The threshold intensity that distinguishes soluble aluminum and insoluble aluminum inclusions is determined using LIBS combined with the SEM/EDS statistical data. Carbon steel (the sample number is S9256) and bearing steel (the sample number is GCr15) are analyzed in scanning mode, and the number of Al₂O₃ inclusions in different size ranges is obtained from the statistical information derived from the Al₂O₃ size calibration curve. According to heavy and thin series for globular oxide inclusions grade assessment, the method we propose is comparable to the traditional metallographic method in terms of accuracy; however, the process is simplified and the measurement speed is significantly improved.     

A study of host-guest complexation between amodiaquine and native cyclodextrin. Characterization in solid state and its in-vitro anticancer activity

Amodiaquine (AQ) has been used widely as an antimalarial drug. Amodiaquine is a mannich base 4-amino quinolone with a mode of action similar to that of chloroquine. The inclusion complex of AQ with β-Cyclodextrin (β-CD) in solution phase is studied from the ground and excited state with UV-Visible and fluorescence spectroscopy, respectively. A binding constant and stoichiometric ratio between AQ and β-CD are calculated by BH equation. The solid complexes are prepared by physical method (PM), kneading method (KM) and co-precipitation method (CP). The solid complex is characterized by Fourier transform infrared spectroscopy, scanning electron microscopy and powder X-ray diffraction. The CP method gives the solid product with a better yield than that of physical mixture and KM products. The orientation and structure of the complex are proposed based on the analysis of Patch-Dock server. The anticancer activity also performed for pure AQ and their complex with β-CD. It is clearly shown that an improvement of anticancer activity of AQ while forming complex with β-CD. The solid inclusion complex behaves as the better anticancer ability than AQ alone.     

µ -symmetry and µ -conservation law for the extended mKdV equation

In this paper, we obtain µ -symmetry and µ -conservation law of the extended mKdV equation. The extended mKdV equation dose not admit a variational problem since it is of odd order. First we obtain µ -conservation law of the extended mKdV equation in potential form because it admits a variational problem, using it, we can obtain µ -conservation law of the extended mKdV equation.     

Green’s functions for multi-phase isotropic laminated plates

This work develops a series of Green’s functions for multi-phase Kirchhoff isotropic laminated plates. First, we derive the Green’s functions for a composite laminated plate composed of two bonded dissimilar isotropic laminated semi-infinite plates. Second, the obtained results for bimaterials are judiciously applied to obtain the Green’s function solution for a circular elastic inclusion embedded in an infinite isotropic laminated plate. Third, Green’s functions for a composite space composed of an arbitrary number of wedges of different isotropic laminated plates are derived. Finally, we derive Green’s functions for a laminated plate with an elliptical and a parabolic boundary, respectively.     

THE PARAMETRIC VARATIONAL PRINCIPLE AND NON-LINEAR FINITE ELEMENT METHOD FOR ANALYSIS OF ASTROMESH ANTENNA STRUCTURES

针对大型周边桁架式索网天线由拉索拉压模量不同引起的本构非线性和结构大变形引起的几何非线性问题,给出了基于参变量变分原理的几何非线性有限元方法. 首先针对含预应力索单元拉压模量不同分段描述的本构关系,通过引入参变量,导出了基于参变量及其互补方程的统一描述形式,避免了传统算法需要根据当前变形对索单元张紧/松弛状态的预测,提高了算法收敛性. 然后利用拉格朗日应变描述索网天线结构大变形问题,结合几何非线性有限元法,建立了基于参变量的非线性平衡方程和线性互补方程;并给出了牛顿-拉斐逊迭代法与莱姆算法相结合的求解算法. 数值算例验证了本文提出的算法比传统算法具有更稳定的收敛性和更高的求解精度,特别适合于大型索网天线结构的高精度变形分析和预测.     

ANALYTICAL SOLUTION FOR ROTATIONAL RUBBING PLATE UNDER THERMAL SHOCK

提出了热冲击和碰摩故障共同作用下的旋转悬臂板系统动力特性解析解法. 基于变分原理,推导出考虑碰摩力沿宽度方向差异性的薄板系统运动微分方程,将该方程的解分解为热冲击悬臂板准静态解和碰摩薄板热冲击动力解. 通过计算旋转悬臂板的模态特性和温度分布函数,获得了碰摩叶片旋转悬臂板模型的热冲击振动解析解,讨论分析得出热冲击和碰摩故障对薄板振动的影响规律. 研究表明:碰摩振动表现为复杂的多频率耦合振动,高频振动较为显著;热冲击振动表现为简单的低频振动形式,强烈的热冲击导致碰摩薄板趋于低频振动. 碰摩引起的振动形式较热冲击故障更加复杂,更容易引起叶片的破坏. 增大的摩擦系数加剧了碰摩引起的振动,利用减小表面粗糙程度等方法降低摩擦系数,可以达到减小碰摩破坏程度的目的.     

The principle of equivalent eigenstrain for inhomogeneous inclusion problems

In this paper, based on the principle of virtual work, we formulate the equivalent eigenstrain approach for inhomogeneous inclusions. It allows calculating the elastic deformation of an arbitrarily connected and shaped inhomogeneous inclusion, by replacing it with an equivalent homogeneous inclusion problem, whose eigenstrain distribution is determined by an integral equation. The equivalent homogeneous inclusion problem has an explicit solution in terms of a definite integral. The approach allows solving the problems about inclusions of arbitrary shape, multiple inclusion problems, and lends itself to residual stress analysis in non-uniform, heterogeneous media. The fundamental formulation introduced here will find application in the mechanics of composites, inclusions, phase transformation analysis, plasticity, fracture mechanics, etc.     

New nonconforming finite element method for solving transient Naiver-Stokes equations

For transient Naiver-Stokes problems, a stabilized nonconforming finite element method is presented, focusing on two pairs inf-sup unstable finite element spaces, i.e., pNC/pNC triangular and pNQ/pNQ quadrilateral finite element spaces. The semi- and full-discrete schemes of the stabilized method are studied based on the pressure projection and a variational multi-scale method. It has some attractive features： avoiding higher-order derivatives and edge-based data structures, adding a discrete velocity term only on the fine scale, being effective for high Reynolds number fluid flows, and avoiding increased computation cost. For the full-discrete scheme, it has second-order estimations of time and is unconditionally stable. The presented numerical results agree well with the theoretical results.