Computational assessment of material structure weaknesses in polycrystalline materials

Summary By incorporating local grain orientation, grain geometry and macroscopic elastic properties, a numerical procedure has been developed for computational prediction of mesoscopic stress and strain distributions in simulated polycrystalline material samples. The numerical procedure is developed on the basis of the concept of grain-average fields, Kröner–Kneer model, Waldvogel-Rodin algorithm and a self-adaptive method. Repeated computer tests were performed to investigate mesoscopic stress variation in the samples, and find coherent interrelations of material structure weaknesses (MSWs) with local microstructure of the samples. It was found that the stronger the single crystal elastic anisotropy, the stronger the inhomogeneity of mesoscopic stress distribution. Not only the elastic anisotropy, but also the grain geometry, may produce significant local stress disturbances. It has been found that the defined orientation-geometry factor and correlation parameter are two adequate physical quantities which account for synergetic interactions due to grain-orientation geometry-induced anisotropy. By using the two quantities, MSWs can be well correlated with local microstructure. Computer tests also show that 250–400 conjoining grains are necessary to homogenize the mesoscopic stress distribution in the considered materials.     

A Chebyshev–Lagrangian method for acoustic analysis of a rectangular cavity with arbitrary impedance walls

A general Chebyshev–Lagrangian method is proposed to obtain the analytical solution for a rectangular acoustic cavity with arbitrary impedance boundary conditions. The originality of the present paper is the successful attempt of applying orthogonal polynomials, such as Chebyshev polynomials of the first kind, to the analysis of a rectangular sound field with general wall impedance. The sound pressure is uniformly expressed as triplicate Chebyshev polynomial series which is independent in each direction. The Chebyshev polynomial series solution is obtained using the Rayleigh–Ritz procedure after considering the influence of boundary impedance on the cavity as the work done by the impedance surfaces in the Lagrangian function. The accuracy and reliability of the proposed method are validated against the analytical solutions and some numerical results available in the literature. Excellent orthogonality and complete properties of the Chebyshev polynomials ensure the rapid convergence, numerical stability, high accuracy of the current solution. The simplicity and low computational cost of the present approach make it preferable to obtain the results of complex models even in the relative high frequency range by choosing enough truncated terms in the sound pressure expression. Numerous cases with various uniform or non-uniform impedance boundary conditions are analyzed numerically and some of the results can be used as benchmark. It is shown that the impedance boundary condition can effectively influence or modify the acoustic characteristics and response of a cavity.     

Motion blur parameters estimation for image restoration

This paper deals with estimation of parameters for motion blurred images. The objectives are to estimate the length (L) and the blur angle (θ) of the given degraded image as accurately as possible so that the restoration performance can be optimised. Gabor filter is utilized to estimate the blur angle whereas a trained radial basis function neural network (RBFNN) estimates the blur length. Once these parameters are estimated the conventional restoration is performed. To validate the proposed scheme, simulation has been carried out on standard images as well as in real images subjected to different blur angles and lengths. The robustness of the scheme is also validated in noise situations of different strengths. In all situations, the results have been compared with standard schemes. It is in general observed that the proposed scheme outperforms its counterparts in terms of restoration parameters and visual quality.     

基于流程的动车组制动系统试验方法

针对动车组制动系统试验自动化智能化的需求,提出了一种基于流程的动车组制动系统试验方法,将工艺流程编辑和调试运行分开,通过一个通用软件平台加载不同的调试工艺流程完成试验;该方法定义了一套指令信号描述规范,工艺人员按照规范以流程化的方式描述调试流程,在调试过程中采用通用软件平台依次执行调试步骤,驱动仪器完成相关动作;通过该方法固化了调试流程,提高了1倍的调试效率。     

航空相机动态调制传递函数分析与研究

影像位移是影响航空相机分辨率的主要因素。用MTF对动态成像质量做出评价,确立合理的稳定系统性能指标,是设计过程中常用的手段。为此研究了匀速运动,变速运动和正弦运动条件下的动态MTF,针对目前无法准确评价的低频正弦运动,提出了基于离散相位区间的动态MTF计算方法。分析结果表明,在像模糊斑大小相同的情况下,高频振动对像质的破坏最严重,直线运动次之,低频振动最轻。根据所作分析可以针对给定的影像位移计算出相应的动态MTF,为航空相机像质评价提供了准确定量的参考。     

腔镜失调对激光陀螺信号输出的影响

研究了不同腔镜结构不同失调情况对空间谐振式激光陀螺中光束空间位置的影响.利用Collins积分与Collins程函理论以及MATLAB软件工具,对腔镜失调前后激光陀螺中光束传输进行了仿真计算.结果表明,相同失调量的不同反射镜所产生的拍频频差是不同的,且分别从M1和M4镜探测到的拍信号频不相同|对于小增益激光器,使用球面镜的腔镜结构较平面镜的腔镜结构更易形成稳定光束空间位置分布|由所计算的空间坐标xn可以看出,双向行波光束的光斑中心发生了偏移,在一定的失调量下将会影响到激光陀螺的拍频输出.研究结果对激光陀螺的工程检测和腔镜调整有指导作用,有助于激光陀螺测量准确度的提高.     

Quantification of rubber in high impact polystyrene by Raman spectroscopy. Comparison of a band fitting method and chemometrics

An analytical method for the detection and the quantification of polybutadiene (rubber) in high impact polystyrene is described. The percentage of this product in high impact polystyrene pellets influences many of its properties, more the concentration is great, and more the mechanical resistance is high. The analytical method currently used to estimate the proportion of polybutadiene in high impact polystyrene pellets is nuclear magnetic resonance. Nevertheless, the application of Raman spectroscopy to polymers becomes more popular because of its sensitivity to the CC vinyl bond. This technique offers various advantages such as the absence of sample preparation. Raman spectroscopy is furthermore non destructive, and is a reproducible method. Information about conformations of polybutadiene can be easily accessible. Two different quantitative procedures were compared to evaluate which one is the best to estimate the percentage of polybutadiene in high impact polystyrene pellets. The first conventional method was based on the bands fitting of Raman spectra, and yielded a good prediction with a R² regression coefficient equal to 0.96. The second was based on chemometric techniques with a 0.98 − R². Consequently, others evaluation factors of the procedures such as the root-mean-square error, the bias, or the number of principal components must have some influence to select the most appropriate quantitative model.