一种稳定的分形维数计算方法及其在孔结构分析中的应用（英文）

盒维法是最常用的图像分形维数测定方法之一,具有计算强度低、计算效率高、结算结果合理等优点。但是盒维法容易受噪声、图像尺寸、盒子初始尺寸等因素的影响。尤其当图像尺寸不能被盒子尺寸整除时,计算结果不稳定,这将影响分形维数的计算以及孔结构的准确分析。本研究在讨论盒维法稳定性的基础上,通过自适应地选取一个阈值,并规定当盒子中包含的目标像素点大于该阈值时才计数盒子,有效地降低了噪声、图像尺寸等因素的影响,提高了盒维法的稳定性。实验结果表明,与一般的盒维法相比,改进方法更准确可靠,该方法可用于多孔材料孔隙结构的表征。结合面积分形和曲线分形的参数CL可以更好地表征孔结构的不规则度。     

不锈钢纤维烧结多孔材料孔结构分形分析

借助分形几何理论研究了不锈钢纤维烧结多孔材料孔结构的分形特征.通过对不锈钢纤维烧结多孔材料的扫描图像进行数字化处理,并利用盒维法计算分形维数,研究了盒维法计算分形维数的影响因素.确定出分形维数与多孔材料孔隙度之间的定量关系,同时说明了分形维数的物理意义.     

多孔结构分形分析及其在材料性能预报中的应用

采用分形理论表征孔隙的结构特征,通过对烧结不锈钢纤维多孔材料的扫描电镜(SEM)照片进行图像处理和分形分析,详细研究图像分辨率、获取图像时的放大倍数、灰度图转化为二值图时阈值的大小等因素对孔结构分形分析结果的影响,并研究它们与分形维数的定性关系.结果表明,采用的烧结纤维多孔材料具有明显的分形特征,图像分辨率、放大倍数、阈值等因素对分形维数计算结果影响显著:与SEM图像的原始分辨率相比,分辨率变化越大则分形维数越大;分形维数随着放大倍数的增大而减小;灰度图转化为二值图时的阈值存在最佳值,且随着阈值的增大,分形维数先增大后减小.通过理论推导,建立了多孔材料孔隙度和渗透性能与孔结构分形维数之间的数学关系.可通过孔结构分形维数、面孔隙度、孔径等参数合理预测多孔材料的体孔隙度、渗透性能,预测结果与实测结果吻合良好.     

基于分形理论研究钢包底吹过程夹杂物的分形维数

依据相似理论,以LF精炼炉为研究对象,在不同时间节点拍照,采用图像分析软件(Iamge Pro-Plus)、Matlab软件和分形理论中计盒维数法,对液相中的不规则单颗粒及团聚体的分形维数进行计算,研究了不同流量下夹杂物粒子实际上浮速度与粒子边缘分形维数的关系。结果表明,盒维数求斜率法均可精确地求出夹杂物的分形维数,夹杂物的形貌越复杂,分形维数越大;增加吹气量,有利于夹杂物的碰撞团聚,使团聚体的分形维数变大;夹杂物的分形维数与实际上浮速度呈正相关,这与采用分形维数和动力直径计算的理论值基本一致,说明该方法是准确可行的。     

基于分形盒维数的双跨轴承转子系统故障诊断方法研究

以双跨轴承转子系统为研究对象,针对其状态监测与故障诊断中存在的问题,利用分形盒维数的方法对系统进行分析。通过提取试验台振动信号并计算其分形盒维数实现对系统的故障诊断。结果表明,不同工作状态下的盒维数各不相同,不平衡故障的盒维数最大,碰摩故障的盒维数次之,正常运转时的盒维数最小,盒维数随着计算网格数的增加而减小。该系统以分形盒维数为特征兆量,能够快速准确地对双跨轴承转子系统进行状态监测与故障诊断,具有一定的应用价值。     

充填体孔隙结构与中观参数跨尺度关联特征

充填体的孔隙结构特征对充填材料的力学性质直接产生影响,是充填体多尺度力学研究的基础。以体视学、分形理论为基础,利用充填体孔隙结构SEM图像,通过最大类间方差法、盒维数法计算其微观孔隙结构分形维数,获得充填材料孔隙结构定量表征,分析充填体分形维数与单轴抗压强度、含水率、孔隙度等中观参数的相关性,探究SEM像定量分析与充填体中观参数的跨尺度关联关系。结果表明:石粉水泥全尾胶结充填体微观孔隙结构分形维数可以表征孔隙结构的复杂程度;孔隙结构的分形维数与充填体的中观参数间具有一定的关系,其中与单轴抗压强度存在负相关性,与含水率存在正相关性;建立孔隙结构特征分形维数与单轴抗压强度、含水率的关联曲线,获得关联特征值的均方差,分形维数与单轴抗压强度和含水率的均方差值分别为R_r=-0.638和R_r=0.604。     

微间隙焊缝磁光成像分形维数识别方法

针对紧密对接、无坡口、肉眼难以分辨的微间隙焊缝,采用磁光成像方法获取焊缝位置信息,并运用分形维数方法解决焊缝磁光图像存在较多干扰的问题.根据图像大视野相关信息处理图像,避免受到图像微小细节干扰对焊缝位置识别精度的影响,较传统图像处理法具有显著的抗干扰性.对焊缝磁光图像进行滤波去噪,将图像细分成块并计算出每个图像块的分形维数,再选取合适阈值对图像进行分割,准确地提取出焊缝中心位置.试验结果表明,运用分形维数提取磁光图像焊缝边缘区域特征,能够获取较准确的焊缝位置信息,为焊缝跟踪控制提供重要基础.     

基于分块迭代函数系统的缸套表面织构的分形表征EI北大核心CSCD

表面织构的物理特征是影响活塞组件-缸套系统摩擦学特性和织构减摩效应的关键因素。为了准确有效地描述活塞组件-缸套系统减摩织构的物理特征,提出一种基于曲波变换和分块迭代函数系统(Partitioned iterated function system,PIFS)的减摩织构物理特征的定量表征方法。从活塞组件-缸套系统减摩织构表面的灰度图像出发,运用离散曲波变换方法对减摩织构表面的灰度图像在各个方向上进行多尺度分离。研究与减摩织构物理特征相关的灰度图像信息的分块迭代函数系统分形描述方法,通过计算减摩织构物理特征的分形维数,并与差分盒维数(differential box-counting,DBC)方法计算得到的分形维数进行对比,验证PIFS方法的有效性。结果表明,与差分盒维数方法计算得到的分形维数相比,针对不同网纹织构和不同形状组合、截面尺寸以及深度的凹坑织构,PIFS方法计算得到的分形维数能够更为敏感和有效地反映减摩织构物理特征的变化。     

材料断口分形维数测量方法研究进展

通过对材料断口定量研究重要性的描述引入分形理论。首先，从分形定义、分形特征图形和分形计算原理3个方面对分形理论进行阐述；其次，介绍小岛法、垂直截面法、计盒维数法等3种分形维数的基本测量方法及其改进方法；最后，对分形实验中可能出现的变量进行简要分析。本研究提出测量分形维数实验时优先考虑计盒维数法，以及在分形实验前需要控制断口参数、拍摄方案、拍摄数据处理方式等实验变量。     

赤泥的微结构及其分形维数的研究

赤泥微观性质的研究报道较少。本文通过氮气吸附-脱附试验研究,得到了赤泥孔结构参数,研究了四种不同的赤泥样品的孔径分布、比表面积和孔容等孔结构变化,并利用等温吸附数据计算赤泥颗粒的分形维数。结果表明:赤泥的颗粒是分形的,分形维数D在2.75～2.82之间,客观定量表征了赤泥粒度分布的结构特征。     

Effects of Post-weld Heat Treatment on Microstructure,Mechanical Properties and the Role of Weld Reinforcement in 2219 Aluminum Alloy TIG-Welded Joints

In as-welded state, each region of 2219 aluminum alloy TIG-welded joint shows diff erent microstructure and microhardness due to the diff erent welding heat cycles and the resulting evolution of second phases. After the post-weld heat treatment, both the amount and the size of the eutectic structure or θ phases decreased. Correspondingly, both the Cu content in α-Al matrix and the microhardness increased to a similar level in each region of the joint, and the tensile strength of the entire joint was greatly improved. Post-weld heat treatment played the role of solid solution strengthening and aging strengthening. After the post-weld heat treatment, the weld performance became similar to other regions, but weld reinforcements lost their reinforcing eff ect on the weld and their existence was more of an adverse eff ect. The joint without weld reinforcements after the post-weld heat treatment had the optimal tensile properties, and the specimens randomly crack in the weld zone.     

The First Phase of the SRIF Industrialized Base in ＂West Area＂ Has Been Put into Operation

After nearly two years＇ tense construction, the first phase of industrialized base of Shenyang Research Institute of Foundry （SRIF）, located at the Tiexi Casting and Forging Industrial Park in the west of Tiexi District, has now been completed and formally put into operation.     

Thermodynamics Study on the Decomposition of Chromite with KOH

Institute of Process Engineering, Chinese Academy of Sciences, China, has proposed a method for oxidative leaching of chromite with potassium hydroxide. Understanding the mechanism of chromite decomposition, especially in the potassium hydroxide fusion, is important for the optimization of the operating parameters of the oxidative leaching process. A traditional thermodynamic method is proposed and the thermal decomposition and the reaction decomposition during the oxidative leaching of chromite with KOH and oxygen is discussed, which suggests that chromite is mainly destroyed by reactions with KOH and oxygen. Meanwhile, equilibrium of the main reactions of the above process was calculated at different temperatures and oxygen partial pressures. The stable zones of productions, namely, K2CrO4 and Fe2O3, increase with the decrease of temperature, which indicates that higher temperature is not beneficial to thermodynamic reactions. In addition, a comparison of the general alkali methods is carried out, and it is concluded that the KOH leaching process is thermodynamically superior to the conventional chromate production process.     

Influence of Heat Treatment on Damping Behaviour of the Magnesium Wrought Alloy AZ61

The effect of isochronal heat treatments for 1h on variation of damping, hardness and microstructural change of the magnesium wrought alloy AZ61 was investigated. Damping and hardness behaviour could be attributed to the evolution of precipitation process. The influence of precipitation on damping behaviour was explained in the framework of the dislocation string model of Granato and Lücke.     

Effect of Rare Earth Doping on Impedance,Modulus and Conductivity Properties of Multiferroic Composites:0.5(BiLa_xFe_(1-x)O_3)–0.5(PbTiO_3)

The Lanthanum-doped bismuth ferrite–lead titanate compositions of 0.5(Bi LaxFe1-xO3)–0.5(Pb Ti O3)(x = 0.05,0.10,0.15,0.20)(BLxF1-x-PT) were prepared by mixed oxide method.Structural characterization was performed by X-ray diffraction and shows a tetragonal structure at room temperature.The lattice parameter c/a ratio decreases with increasing of La(x = 0.05–0.20) concentration of the composites.The effect of charge carrier/ion hopping mechanism,conductivity,relaxation process and impedance parameters was studied using an impedance analyzer in a wide frequency range(102–106Hz) at different temperatures.The nature of Nyquist plot confirms the presence of bulk effects only,and non-Debye type of relaxation processes occurs in the composites.The electrical modulus exhibits an important role of the hopping mechanism in the electrical transport process of the materials.The ac conductivity and dc conductivity of the materials were studied,and the activation energy found to be 0.81,0.77,0.76 and 0.74 e V for all compositions of x = 0.05–0.20 at different temperatures(200–300 °C).     

Quantitative Analysis of the Crystallographic Orientation Relationship Between the Martensite and Austenite in Quenching–Partitioning–Tempering Steels

The orientation relationships(ORs)between the martensite and the retained austenite in low-and medium-carbon steels after quenching–partitioning–tempering process were studied in this work.The ORs in the studied steels are identified by selected-area electron diffraction(SAED)as either K–S or N–W ORs.Meanwhile,the ORs were also studied based on numerical fitting of electron backscatter diffraction data method suggested by Miyamoto.The simulated K–S and N–W ORs in the low-index directions generally do not well coincide with the experimental pole figure,which may be attributed to both the orientation spread from the ideal variant orientations and high symmetry of the low-index directions.However,the simulated results coincide well with experimental pole figures in the high-index directions{123}_(bcc).A modified method with simplicity based on Miyamoto’s work was proposed.The results indicate that the ORs determined by modified method are similar to those determined by Miyamoto’method,that is,the OR is near K–S OR for the low-carbon Q–P–T steel,and with the increase of carbon content,the OR is closer to N–W OR in medium-carbon Q–P–T steel.     

Using Finite Element and Contour Method to Evaluate Residual Stress in Thick Ti-6Al-4V Alloy Welded by Electron Beam Welding

This work was to reveal the residual stress profile in electron beam welded Ti-6Al-4V alloy plates(50 mm thick) by using finite element and contour measurement methods.A three-dimensional finite element model of 50-mmthick titanium component was proposed,in which a column–cone combined heat source model was used to simulate the temperature field and a thermo-elastic–plastic model to analyze residual stress in a weld joint based on ABAQUS software.Considering the uncertainty of welding simulation,the computation was calibrated by experimental data of contour measurement method.Both test and simulated results show that residual stresses on the surface and inside the weld zone are significantly different and present a narrow and large gradient feature in the weld joint.The peak tensile stress exceeds the yield strength of base materials inside weld,which are distinctly different from residual stress of the thin Ti-6Al-4V alloy plates presented in references before.     

Microstructures and Tensile Properties of Ultrafine-Grained Ni–(1–3.5) wt% SiC_(NP) Composites Prepared by a Powder Metallurgy Route

Silicon carbide nanoparticle-reinforced nickel-based composites(Ni–Si CNP),with a Si CNPcontent ranged from1 to 3.5 wt%,were prepared using mechanical alloying and spark plasma sintering.In addition,unreinforced pure nickel samples were also prepared for comparative purposes.To characterize the microstructural properties of both the unreinforced pure nickel and the Ni–Si CNPcomposites transmission electron microscopy(TEM) was used,while their mechanical behavior was investigated using the Vickers pyramid method for hardness measurements and a universal tensile testing machine for tensile tests.TEM results showed an array of dislocation lines decorated in the sintered pure nickel sample,whereas,for the Ni–Si CNPcomposites,the presence of nano-dispersed Si CNPand twinning crystals was observed.These homogeneously distributed Si CNPwere found located either within the matrix,between twins or on grain boundaries.For the Ni–Si CNPcomposites,coerced coarsening of the Si CNPassembly occurred with increasing Si CNPcontent.Furthermore,the grain sizes of the Ni–Si CNPcomposites were much finer than that of the unreinforced pure nickel,which was considered to be due to the composite ball milling process.In all cases,the Ni–Si CNPcomposites showed higher strengths and hardness values than the unreinforced pure nickel,likely due to a combination of dispersion strengthening(Orowan effects) and particle strengthening(Hall–Petch effects).For the Ni–Si CNPcomposites,the strength increased initially and then decreased as a function of Si CNPcontent,whereas their elongation percentages decreased linearly.Compared to all materials tested,the Ni–Si CNPcomposite containing 1.5% Si C was found more superior considering both their strength and plastic properties.     

Directional Growth of Tin Crystals Controlled by Combined Solute Concentration Gradient Field and Static Magnetic Field

A new method was introduced to achieve directional growth of Sn crystals. Microstructures in liquid(Pb)/liquid(Sn) diffusion couples were investigated under various static magnetic fields. Results show that the β-Sn crystals mainly reveal an irregular dendritic morphology without or with a relatively low static magnetic field(B0.3 T). When the magnetic field is increased to 0.5 T, the β-Sn dendrites close to the final stage of growth begin to show some directional character. With a further increase in the magnetic field to a higher level(0.8–5 T), the β-Sn dendrites have an enhanced directional growth character, but the dendrites show a certain deflection. As the magnetic field is increased to 12 T, the directional growth of the β-Sn dendrites in the center of the couple is severely destroyed. The mechanism of the directional growth of the β-Sn crystals and the deflection of the β-Sn crystals with the application of static magnetic field was tentatively discussed.     

电化学噪声数据处理方法概述

综述了常见的电化学噪声数据处理方法,介绍了直流趋势剔除、统计分析、快速傅立叶变换(FFT)法计算功率谱密度(PSD)以及小波变换处理电化学噪声信号的基本过程,并阐释了各种数学处理及所得参数的物理意义。