A study on micro-mechanical deformation behaviour of heat-treated 20MnMoNi55 steel

Several heat treatment procedures are designed considering critical temperatures of phase transformation evaluated through dilatometric testing of 20MnMoNi55 steel to transform low carbon bainitic as-received material into ferrite-martensite dual-phase steels consisting of varied martensite fractions. A thorough metallographic study correlated with the micro-hardness of constituent phases ensures morphological characteristics along with its fractional variations in as-received and dual-phase steels. The impact of fractional variation in constituent phases on the uniaxial monotonic deformation characteristics of dual-phase steels has been observed with a correlation study between experimental tensile and finite element simulated results. Therefore, a physical-based model with a 2-dimensional representative volume element has been established, addressing actual morphological characteristics obtained from metallographic studies. Moreover, the constitutive flow behaviours of ferrite and martensite are also derived from the dislocation-based hardening model to address the actual deformation phenomenon. Finally, an inhomogeneous deformation behaviour among constituent phases and localization of plastic strain in ferrite matrix has been observed with von-Mises stress, and equivalent plastic strain distribution through finite element simulated results. This phenomenon is again confirmed with kernel average misorientation mapping and geometrically necessary dislocation density evaluation through electron backscattered diffraction of tensile samples subjected to different degrees of plastic strain.     

Holographic waveguide display with large field of view based on volume holographic grating

The field of view (FOV) of waveguide display systems based on volume holographic grating (VHG) is primarily constrained by the diffraction response bandwidth, which is currently insufficient to meet the need for AR immersive displays. Through the composite diffraction response bandwidths, red-responsive and green-responsive double-layer VHG structures are proposed to expand the FOV under varied image sources. The influence of several input spectral bandwidths on FOV improvement is also considered, and OLED micro-display and LCOS micro-display are selected as image sources. As a consequence, the horizontal FOV of the red-responsive double-layer VHG waveguide based on the LCOS micro-display is 19.5°, and that of the green-responsive double-layer VHG waveguide based on the OLED micro-display is 33.4°. Through the simulation and experiment, we effectively illustrate the effect of the double-layer VHG and the input spectral bandwidth on the FOV.     

一种高颗粒填充率丁羟推进剂二维细观模型生成方法

为了从机制上认识推进剂的宏观力学性能和试验现象,对推进剂开展细观力学研究十分必要,而代表体积单元（RVE）则是细观力学研究中的重要部分。在随机序列吸附（RSA）方法的基础上,提出将投递区域离散为背景网格,再进行二次随机投递,可以生成80vol%颗粒含量的细观模型,模型生成效率相较于传统RSA方法有所提高。采用Python语言编程,利用ABAQUS的二次开发接口,实现了推进剂RVE模型的快捷生成,并加载周期性边界条件。采用模型生成实例说明了本文方法的有效性,为开展推进剂的细观分析提供了参考依据。      

An exploration of the accuracy of an invasive method for measuring the volume of specimens of Amoeba proteus

A method is described for measuring the volume of individual specimens of Amoeba proteus which utilizes an easily constructed compressor to flatten the specimen to a known thickness. The microscopic image of the flattened specimen is captured on tape, digitized and analysed with the NIH Image software. The results from one specimen are given to illustrate the sources and magnitude of errors affecting these volume measurements.     

Entropy,Free Volume,and Cooperative Relaxation

The high frequency end of the relaxation spectrum for polymer molecules involves the rotation of the segmental bonds. This fast relaxation process, however, cannot take place easily in the condensed state crowded by the densely packed conformers, necessitating the slower cooperatively synchronous relaxation. As the temperature is lowered, the domain of cooperativity grows towards the infinite size at the Kauzmann zero entropy temperature, though actually the system deviates from the equilibrium as the glass transition intervenes typically at 50 K above that temperature. The excess enthalpy and entropy drop faster than predicted by the rotational isomeric states which would reach zero only at 0 K. The real ΔC_P is greater than that of the RIS value. The actual volume in excess of the crystalline lattice volume, however, points towards zero at 0 K. Thus, a polymer with higher T_g typically exhibits a lower density and modulus in the glassy state. Since the configurational entropy associated with the free volume is proportional to the logarithm of the latter, the Kauzmann temperature can be scaled by ln M, where M is the algebraic average of the conformer molecular weight. The temperature dependence of the most dominant, i.e., the largest equilibrium domain size will result in the Adam-Gibbs and Vogel equations for the characteristic relaxation time. The cooperative domain distribution leads to the relaxation spectrum that follows a power law. The relationship between the characteristic relaxation time and the rate of physical aging is derived.     

基于相邻层间相似性和空体素跳跃的体绘制加速算法研究

Splatting是经典的基于物序的直接体绘制方法,运算数据量的多少制约着算法绘制图像的速度。为了进一步提升绘制速度,采用基于相邻层间相似性和空体素跳跃相结合的方法进行加速,在读取数据过程中对图片中的三维纹理数据进行筛选,并使用足迹表对筛选后的三维纹理数据进行二维投影,利用相邻层间相似性计算每一个点的灰度值,并根据灰度值将数据分类,算出对成像没有影响的空体素,跳过其绘制过程从而加速算法。实验结果显示,该算法能够在保证绘制图像质量的基础上,在一定程度上解决和改善Splatting算法数据的空间相关性和运算效率的问题。     

高层建筑基础大体积混凝土抗裂措施分析

通过对混凝土水化热的分析,指出混凝土水化热是导致大体积混凝土裂缝的主要原因,给出了高层建筑基础大体积混凝土工程一般的抗裂构造措施。     

基于变权重组合模型的铁路客运量短期预测

科学、准确的铁路客运量短期预测是提高铁路客运系统竞争力与服务水平的关键。针对铁路短期客运量的特点,提出了一种基于灰色理论的变权重组合预测模型。为了获取不同模型在不同时刻的权重系数,采用广义回归神经网络对动态权重进行跟踪和预测。以2014年1~12月份的铁路客运量为研究对象,分别建立均值GM（1,1）模型、离散GM（1,1）模型、灰色Verhulst模型以及变权重组合预测模型。实例分析的结果表明,三个单一模型的平均相对误差分别为17.14%、16.99%和12.94%,而变权重组合模型为7.01%,变权重组合预测模型的预测精度明显高于单一模型。     

关于深基坑支护结构计算的增量法和总量法

简要论述了深基坑支护结构计算中的增量法与总量法的适用条件 ,指出对于线性受力继承性问题 ,两者的计算结果应是一致的