FMC仿真软件中几何造型技术

本文从ＦＭＣ仿真的需要探讨了几何造型技术，主要讨论了几何造型与仿真软件的关系，造型数据结构及型体的拓扑运算方法。     

模具CAD中的几何模拟研究

在模具ＣＡＤ系统中，描述被加零件的几何特征是最重要的方面之一，故本文对几何模拟过程中的几个主要问题进行了探讨，如几何形体的描述、数据结构的建立及基本构造方法等。     

模具CAD中的几何模拟研究

在模具ＣＡＤ系统中，描述被加工零件的几何特征是最重要的方面之一，故本文对几何模拟过程中的几个主要问题进行了探讨，如几何形体的描述、数据结构的建立及基本构造方法等。     

三维形体CAD/CAM系统中的形体表示方式及其数据结构的设计与实现

本文以实体造型和曲面造型为基础,采用CSG和B—Dep综合表示形式,设计了一个适用于三维形体CAD/CAM一体化系统之数据结构。     

基于海量点云的曲面增量扩展重建算法

针对现有的曲面重建算法难以兼顾海量点云数据重建效率与重建结果拓扑正确性的问题,提出一种基于局部样本扩展重建的曲面重建算法。采用二维Delaunay网格剖分与三维Delaunay网格过滤相结合的方法重建曲面局部样本;通过鉴别新生成面片相关样点Cocone近邻点的完整性,删除局部重建网格中重建不准确的边缘面片;基于波前环的扩张、分裂将上述局部重建过程传播至整个采样点集,获得插值于整体采样点集的二维定向流形网格曲面。实验表明,该算法能够在保证重建结果的拓扑正确性的基础上,显著提高海量点云的重建效率,适用于重建封闭和非封闭曲面。     

一种自重构机器人及其重构策略研究

设计了新型均一性可移动空间多角度自重构机器人单元模块MSMAbot,由于其丰富的连接面与自由度,可在平面与空间组成多种不同构型。结合该模块的结构特点与图论理论,建立双模块动态连接边信息规则,提出了基于空间连接信息矩阵组的拓扑描述方法;利用有界深度优先搜索算法对构型进行识别,实现了任意构型的空间信息表达。通过对不同构型间的连接信息进行分层并行比对,得到构型最优公共拓扑匹配与最优模块匹配映射,并对非公共拓扑部分模块进行重构,有效减少了重构模块与步数,缩短了重构时间。最后,在ADAMS环境下对两种构型的重构进行了仿真实验,验证了分层并行重构策略的有效性。     

复杂曲面边界线自动提取技术研究

复杂曲面零件的几何模型重构是逆向工程的研究重点之一,由零件表面的数字化数据提取边界线是构造几何模型的重要步骤。针对由CMM获取的三维数据“点云”,提出了经纬线扫描算法自动提取单值曲面边界线,提出了基于局部增量网格扩张的三维散乱数据三角剖分算法,实现了任意非封闭曲面边界线的自动提取。实践证明,通过该算法得到的复杂曲面的边界线能够满足模型重建的工程需求。     

基于SOFM和NURBS的散乱数据点自由曲面重构

提出了利用NURBS实现曲面散乱点数据几何建模的方法。首先利用Unigraphics软件设计原始曲面,在所设计的原始曲面上划分若干条曲线,并在曲线上随机设置大量的散乱点数据;然后用自组织神经网络SOFM对原始曲面上的散乱数据点进行聚类,构建NURBS曲线并完成曲面重构。最后通过仿真实验分析了重构曲面相对原始曲面的误差,实验表明所提出的几何建模方法是有效的,并能较精确拟合原始曲面。     

板料成形FE中网格节点重构参数曲面的方法研究

有限元模拟成形仿真的结果,可以帮助设计开发者正确选择冲压工艺参数和模具形状及材料特性等。在对模拟进行后处理过程中,往往必须了解由有限元节点构成的参数曲面的性质,为后续回弹分析及毛坯设计提供重要支持。如何应用变形后的节点阵构成光顺的几何曲面是问题的关键。文章给出了由节点序列散点构成非均匀B样条光顺曲面的实际算法,并开发了应用程序。对散乱点数据构成曲面进行了系统的阐述,所开发的方法已经用于板料成形仿真中FE网格节点重构曲面。     

基于三维CAD的工艺尺寸链计算系统的关键技术研究

针对基于三维CAD可视化的工艺尺寸链计算系统的关键技术进行了研究。首先介绍系统的体系结构,然后提出利用三维CAD中存储的几何拓扑信息来解决尺寸信息输入的问题,并介绍了具体的操作,接着利用面向对象的技术,设计一种新的数据结构通过人机交互的方式存储尺寸信息,最后用方程迭代求解工序尺寸。     

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。