Effect of relative grain size on the flow stress of polycrystalline FCC sheets

A dynamic explicit finite element code and rate-dependent elastic-viscoplastic polycrystalline model were used to simulate the simple tension test of annealing FCC polycrystal and 6111-T4 aluminum alloy sheet metal. The variability of flow stress was investigated, which was induced by various grain boundary constraints when the ratio of thickness-to-grain size was changed. The simulated results show that, when the relative grain size increases, the constraint of grain boundary will increase accordingly, which results in the increase of the flow stress of polycrystal. The results agree with experiments.     

Reanalysis of the 3D quasi-stationary grain size distribution based on Hillert's grain growth rate equation

Based on Hillert's 3D grain growth rate equation, the grain growth continuity equation was solved. The results show that there are an infinite number of 3D quasi-stationary grain size distributions. This conclusion has gained strong supports from results of different computer simulations reported in the literature.     

基于仿真切割的晶粒三维尺寸分布评价系统

以Mendelson在评价三维尺寸时所描述的陶瓷结构特征为基础,对不同σ,μ值的等轴晶粒三维尺寸对数正态分布进行等区间数据处理.利用仿真切割方法得到随机截面,并进行随机截线长度、概率的计算,得到随机截线分布并以此建立尺寸分布数据库.在实际应用时,通过测量材料切面上晶粒的随机截线,可绘制出随机截线分布曲线,再通过对尺寸分布数据库的检索,找出与实测随机截线分布相吻合的随机截线分布,得到所对应的三维尺寸分布的σ,μ值,从而得到材料内部晶粒的三维尺寸分布.     

Influence of grain size on distribution of temperature and thermal stress in ZnO varistor ceramics

The nonuniformity of temperature distribution within ZnO varistor ceramics would decrease its energy absorption capability. In this paper, the distributions of current, temperature and thermal stress within the microstructures of ZnO varistor ceramics are simulated using Voronoi diagram models. The results show that the current concentrates through a few paths in ZnO varistor due to the nonuniformity of ZnO grain size and the variety of electrical characteristics of grain boundaries, which induces local high temperature and great thermal stress when injecting impulse current into ZnO varistor, and leads to melting puncture or cracking failure. The influence of the ZnO grain size on the distributions of temperature and thermal stress within ZnO varistor ceramics is analyzed in detail. The energy absorption capability of ZnO varistor ceramics can be greatly improved by increasing the uniformity of ZnO grain size or decreasing the average size of ZnO grains.     

沙土孔隙内水分形态及分布

通过CCD结合显微镜实验观察研究了沙土孔隙内水分分布形态。通过研究分析认为,除了传统上认为沙土中水分有吸附水、结合水和容积水等形态之外,相对粗糙的骨架表面还存在表面毛细水。低含湿率时,孔隙内水分形态有吸附水、结合水、表面毛细水和液桥(容积水);高含湿率时,孔隙中的水分并不是按孔隙均匀分布,而是出现大团水体中夹杂气团。对于气团中的孔隙,水分形态仍然有吸附水、结合水、表面毛细水和液桥。     

沙土孔隙内水分形态及分布

通过CCD结合显微镜实验观察研究了沙土孔隙内水分分布形态。通过研究分析认为,除了传统上认为沙土中水分有吸附水、结合水和容积水等形态之外,相对粗糙的骨架表面还存在表面毛细水。低含湿率时,孔隙内水分形态有吸附水、结合水、表面毛细水和液桥（容积水）;高含湿率时,孔隙中的水分并不是按孔隙均匀分布,而是出现大团水体中夹杂气团。对于气团中的孔隙,水分形态仍然有吸附水、结合水、表面毛细水和液桥。     

Controlled size and density distribution of nanoparticles by thermal ammonia etching method

Nickel nanometer catalyst thin films were prepared on SiO₂/Si substrates using sputtering coater. The effects of ammonia pretreatment on the catalyst films from continuous film to the nanoparticles were investigated. The nanostructures of the Ni thin films as a function of the catalyst film original thickness, the pretreatment time and temperature were discussed. The optimum parameters of etching process were obtained, and the functional mechanism of ammonia was primarily analyzed. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to evaluate the obtained nanoparticles. It is demonstrated that the controlled size and density distribution of the nanoparticles can be achieved by employing ammonia etching method.     

Grain size distribution and topology in 3D grain growth simulation with large-scale Monte Carlo method

Three-dimensional normal grain growth was appropriately simulated using a Potts model Monte Carlo algorithm. The quasi-stationary grain size distribution obtained from simulation agreed well with the experimental result of pure iron. The Weibull function with a parameter β=2.77 and the Yu-Liu function with a parameter ν =2.71 fit the quasi-stationary grain size distribution well. The grain volume distribution is a function that decreased exponentially with increasing grain volume. The distribution of bounda...     

最佳晶粒尺寸和介观效应

理论研究表明：存在最佳晶粒尺寸是一种新的介观效应,它来自当晶粒尺寸缩小到一定程度时反映吸附氧负离子的Fermi统计失效;根据当晶粒尺寸缩小到特征长度rm时晶粒将保持电中性的Kubo理论,对Fermi统计公式进行修改,从而给出了最佳晶粒尺寸最佳晶粒尺寸等于2rm的理论结果.用Kubo理论电子逸出功公式估算了rm与最佳晶粒尺寸r*0的数值,其结果与实验一致.     

最佳晶粒尺寸和介观效应

理论研究表明：存在最佳晶粒尺寸是一种新的介观效应，它来自当晶粒尺寸缩小到一定程度时反映吸附氧负离子的Fermi统计失效；根据当晶粒尺寸缩小到特征长度rm时晶粒将保持电中性的Kubo理论，对Fermi统计公式进行修改，从而给出了最佳晶粒尺寸最佳晶粒尺寸等于2rm的理论结果．用Kubo理论电子逸出功公式估算了rm用与最佳晶粒尺寸r0^＊的数值，其结果与实验一致。     

考虑泥沙分选及床沙级配调整的二维数值模拟研究

在正交曲线坐标系下建立平面2维河流数学模型,包括水流模型、泥沙模型。在前人研究成果的基础上,通过修正泥沙模型中非均匀沙挟沙力公式以考虑泥沙分选影响;并根据近底床沙质量守恒方程计算床沙级配调整。利用seal水槽下游细化试验资料,对模型进行了验证,结果表明,本模型能够合理模拟水槽地形及其床面泥沙分布变化,反映试验水槽沿程细化的趋势,具有研究实际河道河床变形及床沙分布变化的潜力。     

节理长度分布形式对迹长测量误差的影响

在分析导致节理迹和测量误差诸因素的基础上，用计算机对线测量的实施过程进行了模拟研究，结果表明，除了从所周知的导致节理工测量误差的因素外，节理长度概率密度分布形式对节理迷长测量误差也有影响。     

深度还原工艺对铁颗粒粒度影响规律研究

采用深度还原技术处理浸染微细粒度的复杂难选铁矿石,控制铁颗粒粒度是分选出合格产品的关键.根据深度还原物料中铁颗粒的球形特征,通过测量铁颗粒二维截面参数,求取了其累计粒度特性曲线,定性地描述了不同深度还原工艺对铁颗粒粒度的影响规律.结果表明:适当的提高还原温度、延长还原时间、增大配碳系数,都有利于铁颗粒的长大,但还原温度过高、配碳系数过大将阻碍铁颗粒长大;适宜的工艺条件为:还原温度1 225℃,还原时间30min,配碳系数2.0,获得铁颗粒的d50为278.88μm.     

Characteristic grain size: Part I description and definition

Characteristic grain size, G _c, is defined in the present paper. It indicates an intrinsic size of grain for a given system, and has the following advantages over the average grain size which is based on a statistical mean value of the linear intercept length of grains: (1) The characteristic grain size G _c has clear and determined geometric meaning, i. e. G _c refers to two times of the area-weighted average height of the surface elements to the centroid of grain or the average length of the chord through the centroid of grain; (2) The value of G _c can be directly obtained without introducing any correcting factors such as grain shape or grain size distribution factors. Generally, G _c is larger than the average grain size G when the Heyn intercept method is adopted for the grain size measurement. Project supported by the British Council Academic Link Scheme Synopsis of the first author Cao Shunhua, lecturer, born in Jan. 1965, strong interest in the following research areas: ceramic composites, FGMs, prototype design of WC-Co alloys, and preparation of β-SiC and sialon powders.     

Derivation of Hillert-type 3D grain growth rate model with topological considerations and discussion on its grain size parameter

A Hillert-type three-dimensional grain growth rate model was derived through the grain topology-size correlation model, combined with a topology-dependent grain growth rate equation in three dimensions. It shows clearly that the Hillert-type 3D grain growth rate model may also be described with topology considerations of microstructure. The size parameter bearing in the model is further discussed both according to the derived model and in another approach with the aid of quantitative relationship between the grain size and the integral mean curvature over grain surface. Both approaches successfully demonstrate that, if the concerned grains can be well approximated by a space-filling convex polyhedra in shape, the grain size parameter bearing in the Hillert-type 3D grain growth model should be a parameter proportional to the mean grain tangent radius.     

面粉车间储粮害虫的种类和分布研究

为研究面粉车间储粮害虫的种群动态、发生规律,利用瓦楞纸板诱捕器跟踪诱捕2017年3月-2018年3月的储粮害虫,并采用地质统计学等高线绘图技术结合面粉车间内温度、湿度的变化,分析面粉车间储粮害虫的种类、分布以及影响储粮害虫种群数量的各种因素.沿着面粉车间(长84 m,宽42 m)建筑物内墙和柱子设置60个瓦楞纸板诱捕器...     

The Influence of Grain Size on Decomposition Reaction of Limestone in Dispersing State

The thermal behavior and kinetic parameters of decomposition reaction of limestone in a temperature-programmde mode were investigated by means of TG,The experumental results shour that the kinetic model functions in different forms for the theermal decomposition rdactions of different limestone grain sizes in dispersing state under the almosphere of static air are 4(1-a)^3/4 for small size limestone and (1-a) for large size limestone.Information was obtained on the relationship among the decomposition temperature.decomposition time.decomposition fraction.decomposition reaction rate constant and grain grain size of limestone.     

脉冲电流对30钢奥氏体化晶粒大小的影响

研究了经脉冲电流和常规电阻炉奥氏体化热处理后30钢晶粒大小的变化,结果表明在同等的奥氏体化加热温度和加热时间及冷却速度的实验条件下,经电阻炉处理后试样的金相组织与原始组织相同即仍为先共析铁素体加珠光体组织,而经脉冲电流处理后的试样其金相组织则为魏氏组织.经过深入分析魏氏体组织的形成条件及对晶粒尺寸的比对,可知经脉冲电流...     

晶粒尺寸对ZnO纳米粒子光催化活性的影响

采用水热合成法制备纳米ZnO材料,并用所制备的纳米材料光催化降解罗丹明B溶液,以罗丹明B的降解率作为评价方式,考察了不同浓度的氧化锌对光催化性能的影响.运用XRD对制备的样品进行了表征.结果表明:随着水热溶液中原料配比的浓度增大,氧化锌晶粒尺寸逐渐减小,光催化的活性增强.当氧化锌样品的浓度为150m M时,10mg/40ml的罗丹明B在紫外灯下降解率达93%.     

高纯铝晶粒尺寸与晶粒拓扑学参数定量关系研究

本文采用晶界渗镓剥离晶粒技术实现了三维晶粒尺寸及其拓扑学参数（晶粒界面数N2）的直接实验测量,利用回归分析,得出了晶粒尺寸与晶粒拓扑学参数定量关系;晶粒界面数N2与晶粒尺寸R^-间存在线性对应关系。