电弧填丝增材制造高强度低合金钢的组织和力学性能

A high-building multi-directional pipe joint (HBMDPJ) was fabricated by wire and arc additive manufacturing using high-strength low-alloy (HSLA) steel. The microstructure characteristics and transformation were observed and analyzed. The results show that the forming part includes four regions. The solidification zone solidifies as typical columnar crystals from a molten pool. The complete austenitizing zone forms from the solidification zone heated to a temperature greater than 1100°C, and the typical columnar crystals in this zone are difficult to observe. The partial austenitizing zone forms from the completely austenite zone heated between Ac1 (austenite transition temperature) and 1100°C, which is mainly equiaxed grains. After several thermal cycles, the partial austenitizing zone transforms to the tempering zone, which consistes of fully equiaxed grains. From the solidification zone to the tempering zone, the average grain size decreases from 75 to 20 μm. The mechanical properties of HBMDPJ satisfies the requirement for the intended application.     

基于EBSD数据，采用考虑各向异性效应的改进蒙特卡罗模型对冷轧超薄晶粒取向硅钢的再结晶过程进行了模拟

A Monte Carlo Potts model was developed to simulate the recrystallization process of a cold-rolled ultra-thin grain-oriented silicon steel. The orientation and image quality data from electron backscatter diffraction measurements were used as input information for simulation. Three types of nucleation mechanisms, namely, random nucleation, high-stored-energy site nucleation (HSEN), and high-angle boundary nucleation (HABN), were considered for simulation. In particular, the nucleation and growth behaviors of Goss-oriented ({011}<100>) grains were investigated. Results showed that Goss grains had a nucleation advantage in HSEN and HABN. The amount of Goss grains was the highest according to HABN, and it matched the experimental measurement. However, Goss grains lacked a size advantage across all mechanisms during the recrystallization process.     

烧结温度对纳米石墨烯增强ZA27基复合材料孔隙比和力学性能的影响

Nano graphene platelet (Gr) reinforced nano composites with a zinc–aluminum alloy (ZA27) matrix were produced by powder metallurgy at four different mass ratios (0.5wt%, 1.0wt%, 2.0wt% and 4.0wt%) and three different sintering temperatures (425, 450, and 475°C). In order to investigate the effect of sintering temperatures and nano graphene reinforcement materials on the composite structure, the microstructures of the composite samples were investigated and their densities were determined with a scanning electron microscope. Hardness, transverse rupture, and abrasion wear tests were performed to determine the mechanical properties. According to the test results, the porosity increased and the mechanical strength of the nano composites decreased as the amount of nano graphene reinforcement in ZA27 increased. However, when the composites produced in different reinforcement ratios were evaluated, the increase in sintering temperature increased the mechanical structure by positively affecting the composite structure.     

煤田火灾的形成机理及其探测和控制技术

Coalfield fires are considered a global crisis that contributes significantly to environmental destruction and loss of coal resources and poses a serious threat to human safety and health. In this paper, research related to the initiation, development, and evolution of coalfield fires is reviewed. The existing detection and control techniques of coalfield fires are also reviewed. Traditional firefighting is associated with waste of resources, potential risks of recrudescence, potential safety hazards, extensive and expensive engineering works, and power shortages. Recently, coalfield fires have been recognized as having significant potential for energy conservation and heat energy recovery. Thermoelectric power generation is regarded as a suitable technology for the utilization of heat from coalfield fires. The extraction of heat from coalfield fires can also control coalfield fires and prevent reignition leading to combustion. Technologies for absorbing heat from burning coal and overlying rocks are also analyzed. In addition, the control mode of “three-region linkage” is proposed to improve firefighting efficiency. Integrating heat energy recovery with firefighting is an innovative method to control coalfield fires.     

焊接速度对自适应双轴肩搅拌摩擦焊接Al–Mg合金接头微观组织和机械性能的影响

The butt welds of 4-mm thick 5A06 aluminum alloy plates were produced by adjustable-gap bobbin-tool friction stir travel with travel speeds of 200, 300, and 400 mm/min in this study. The microstructure was studied using optical microscopy and electron backscatter diffraction (EBSD). Tensile tests and microhardness measurements were performed to identify the effect of the travel speed on the joint mechanical properties. Sound joints were obtained at 200 mm/min while voids were present at different positions of the joints as the travel speed increased. The EBSD results show that the grain size, high angle grain boundaries, and density of geometrically necessary dislocations in different regions of the joint vary depending on the recovery and recrystallization behavior. Specific attention was given to the relationship between the local microstructure and mechanical properties. Microhardness measurements show that the average hardness of the stir zone (SZ) was greater than that of the base material, which was only affected slightly by the travel speed. The tensile strength of the joint decreased with increasing travel speed and the maximal strength efficiency reached 99%.     

增材制造镍基高温合金IN718的热处理优化

Additive manufacturing (AM) of Ni-base superalloy components can lead to a significant reduction of weight in aerospace applications. AM of IN718 by selective laser melting results in a very fine dendritic microstructure with a high dislocation density due to the fast solidification process. The complex phase composition of this alloy, with three different types of precipitates and high residual stresses, necessitates adjustment of the conventional heat treatment for AM parts. To find an optimized heat treatment, the microstructures and mechanical properties of differently solution heat-treated samples were investigated by transmission and scanning electron microscopy, including electron backscatter diffraction, and compression tests. After a solution heat treatment (SHT), the Nb-rich Laves phase dissolves and the dislocation density is reduced, which eliminates the dendritic substructure. SHT at 930 or 954°C leads to the precipitation of the δ-phase, which reduces the volume fraction of the strengthening γ′- and γ′′-phases formed during the subsequent two stage aging treatment. With a higher SHT temperature of 1000°C, where no δ-phase is precipitated, higher γ′ and γ′′ volume fractions are achieved, which results in the optimum strength of all of the solution heat treated conditions.     

搅拌摩擦法和搅拌摩擦振动法制备镁表面纳米复合材料的对比研究

Friction stir processing (FSP) can be used to improve surface composites. In this study, a modified method of FSP called friction stir vibration processing (FSVP) was applied to develop a surface composite on AZ91 magnesium alloy. In this technique, the workpiece is vibrated normal to the processing direction. The results illustrated that compared with the FSP method, the FSVP caused a better homogeneous distribution of SiC particles in the microstructure. The results also showed that matrix grains of friction stir vibration processed (FSV-processed) samples ((26.43 ± 2.00) μm) were finer than those of friction stir processed (FS-processed) specimens ((39.43 ± 2.00) μm). The results indicated that the ultimate tensile strength (UTS) of FSV-processed specimens (361.82 MPa) was higher than that of FS-processed specimens (324.97 MPa). The higher plastic strain in the material during FSVP, due to workpiece vibration, resulted in higher dynamic recrystallization, and consequently, finer grains were developed. The elongation and formability index of the FSV-processed specimen (16.88% and 6107.52 MPa·%, respectively) were higher than those of the FS-processed sample (15.24% and 4952.54 MPa·%, respectively). Moreover, the effects of FSVP were also found to intensify as the vibration frequency increased.     

结晶器内电磁搅拌对结晶器表面负偏析影响的模型预测

Aiming at the problem of negative segregation under a bloom surface, a coupling macrosegregation model considering electromagnetic field, flow, heat, and solute transport was established based on the volume average method to study the effect of in-mold electromagnetic stirring (M-EMS) on the negative segregation under the bloom surface. In the model, the influence of dendrite structure on the flow and solute transport was described by the change of permeability. The model was validated by the magnetic induction intensity of M-EMS and carbon segregation experiment. The results show that the solute C in the solidified shell in the turbulent zone of the bloom undergoes two negative segregations, whereby the first is caused by nozzle jet, and the second by the M-EMS. The severities of the negative segregation caused by M-EMS at different currents and frequencies are also different, and the larger the current is, or the smaller the frequency is, the more serious will be the negative segregation. With the M-EMS, the solute C distribution in the liquid phase of the bloom is more uniform, but the mass fraction of C in the liquid phase is higher than that without M-EMS.     

通过高温预处理高磷鲕状赤铁矿实现铁富集和脱磷

The efficient development and utilization of high-phosphorus oolitic hematite is of great strategic significance for the sustainable supply of iron-ore resources in China. In this paper, the mechanism of high-temperature pretreatment for enhancing the effect of iron enrichment and dephosphorization in the magnetization roasting–leaching process was studied by X-ray diffraction (XRD), vibration sample magnetometer (VSM), scanning electron microscopy and energy dispersive spectrometry (SEM–EDS). Compared with the process without high-temperature pretreatment, the iron grade of the magnetic separation concentrate after high-temperature pretreatment had increased by 0.98%, iron recovery rate had increased by 1.33%, and the phosphorus content in the leached residue had decreased by 0.12%. High-temperature pretreatment resulted in the dehydration and decomposition of hydroxyapatite, the dehydration of limonite and the thermal decomposition of siderite, which can produce pores and cracks and weaken the compactness of the ore, improve the magnetization characteristics of roasted ore, and strengthen the iron enrichment and dephosphorization during the magnetization roasting and leaching process.     

初始ECAP道次对5083铝合金晶织构和残余应力的影响

To produce a highly refined microstructure, several metals or alloys have been processed via equal-channel angular pressing (ECAP). In this work, the mechanical and microstructural changes of the 5083 aluminum alloy in H11 condition after processed by two ECAP passes were investigated. An ECAP H13 steel die with an inner angle (α) of 120° and outer curvature (β) of 20° was used. The microstructural changes were associated with the loss of texture symmetry. The morphologies of the Mg₂Si and α-Al(Mn,Fe)Si precipitates for the sample at the initial condition were similar to those subjected to two ECAP passes. The peak broadening measured by X-ray diffraction revealed an increment of both grain refinement and microstrain. After the second extrusion pass, the hardness increased by 62% compared with the initial condition. Moreover, the heterogeneous hardness behavior was compatible with a highly localized dislocation density. After two ECAP passes, shear parallel bands were observed to be at nearly 45° to the extrusion direction. The evaluation of first-order residual stress as a function of the depth of the analyzed sample displayed compressive or tensile values, depending on the measured face. With the plastic deformation applied, the first and second-order residual stresses exhibited significant increment. Williamson-Hall plots showed positive slopes, indicating an increment in the microstrain.     

Software framework for off-road autonomous robot navigation system

This paper presents a software framework for off-road autonomous robot navigation system.With the requirements of accurate terrain perception and instantaneous obstacles detection,one navigation software framework was advanced based on the principles of "three layer architecture" of intelligence system.Utilized the technologies of distributed system,machine learning and multiple sensor fusion,individual functional module was discussed.This paper aims to provide a framework reference for autonomous robot nav...     

无人作战平台认知导航及其类脑实现思想

无人作战平台将是未来空天战场的主要作战力量,认知导航正是应无人化平台智能自主运行控制的需要而提出的新型导航技术。通过对认知导航进行了深入剖析,给出了认知导航的基本内涵,以及在这一内涵下的认知导航框架结构和导航信息处理流程,并分析了认知导航所具备的新质导航能力,探讨了采用"类脑"技术实现认知导航的新途径,最后提出了实现认知导航需要解决的关键技术。为实现无人化作战平台智能自主能力提供了理论框架,具有较强的指导意义。     

卫星导航系统自主导航技术研究与验证

本文结合全球卫星导航系统自主导航技术发展现状,介绍了自主导航能力的发展特点及重要作用,分析设计了卫星导航系统自主导航体系架构,并对自主导航关键的时空基准保持技术进行了分析,提出了基于星间观测的完全自主导航的滤波算法、滤波状态噪声协方差信息选择方法及自主导航星载数据处理方法.论证了基于地面观测数据(锚固站)的半自主导航方法,比较了不同锚固站分布、数量及观测周期对自主导航性能的影响,并利用一套地面仿真试验系统验证了自主和半自主模式下的精密定轨和时间同步精度,可为卫星导航系统自主导航设计提供参考.     

基于VxWorks的水下机器人嵌入式导航系统的研究

构建了基于VxWorks嵌入式操作系统的智能水下机器人组合导航系统,详细阐述了水下机器人导航系统软、硬件体系结构.硬件采用基于PC104总线的多板卡嵌入式系统,导航系统核心处理器采用Intel公司的PIIX-4芯片处理器以及VxWorks实时嵌入式操作系统.文中还详细阐述了导航系统软件信息流程、数据处理及基于强跟踪卡尔曼滤波的船位推算算法.最后通过自主目标搜索、长距离航行试验等海试验证了该导航系统的可行性与可靠性.     

一种自主移动机器人智能导航控制系统设计

提出一种实用的自主移动机器人智能导航控制方案,以研制的模型样机HN-9为例,阐述了其具体实现技术.机器人采用扫描式超声波实现作业环境的探测,基于码盘和电子罗盘的组合导航子系统实现定位估计,利用模糊决策子系统产生反应式智能导航控制行为.仿真实验及模型样机的实际运行效果验证了该系统构成的可行性.这种模块化的低成本设计方案便于在移动机器人的嵌入式控制系统上实现,便于对已有移动机器人系统进行改造以实现自主导航功能,用以提高操作机动性与可靠性.     

基于多代理的制造系统建模框架和实现方法

介绍了基于功能建模和基于过程建模两种制造系统建模框架与方法,分析了软件对象技术、组件技术和代理技术的不同特点·提出了基于多代理的制造系统建模框架,它由对象自治性层次维、软件生命周期维和多视图模型维组成·采用基于多代理的软件工程实现方法,开发了基于多代理的制造系统软件·与软件对象和组件相比,智能代理具有更强的自治性和智能性,能够满足复杂制造系统对分布式数据和分散控制的要求,为制造系统过程集成提供了新的途径·     

基于自适应动态规划算法的小车自主导航控制策略设计

小车自主导航系统是路径规划领域研究的难点问题。本文利用自适应动态规划算法对小车自主寻路、避障的控制策略进行了设计。介绍了仿真过程中小车检测环境状态量的方法,提出了小车通过连续型奖励/惩罚信号自主学习寻路、避障的控制策略,并结合虚拟现实技术创建了不同路径和不同障碍物状态的仿真环境。通过不同路径状态的仿真实验,验证了自适应动态规划算法在解决小车自主导航避障控制策略问题上的可靠性和稳定性。     

基于视觉的缩微智能车车道检测与控制

针对智能车辆自主驾驶行为研究,提出并实现了一种基于视觉导航的缩微智能车系统.从软硬件架构、数据通信方式上介绍了缩微智能车系统的整体设计,并针对缩微道路交通环境中传统车道线检测技术易受光照变化影响的问题,提出一种灰度形态学Top-Hat变换与亮度轮廓扫描方法相结合的车道线检测算法.为分析智能车在缩微交通环境下的自主驾驶表现,设计了一种模拟驾驶员转向行为的舵机模糊控制算法.实验结果表明,该方法可以有效模拟车辆在真实道路交通环境中的自主驾驶行为,为智能交通系统研究提供了一种新思路.     

多智能体自主车辆导航技术研究

将基于GPS／GIS的导航技术与基于视觉的导航技术进行集成,提出了基于信息融合技术的多智能体自主车辆导航系统的概念,为提高基于视觉的导航控制系统的鲁棒性进行了有益的尝试,这一研究将为自主车辆导航控制创造一个更加实用化的平台．     

一种基于星敏感器的自主导航方法

由于惯性器件存在漂移,很难进一步提高采用惯性设备提供水平基准来实现星敏感器自主导航精度;而由于大气模型不精确,很难进一步提高利用星光折射来实现星敏感器自主导航的精度。为此,本文提出根据星敏感器的识别结果以及激光水平测量部件分别测量星敏感器的两个像平面轴来实现星敏感器自主导航。外场实验结果表明:采用本文的方法来实现星敏感器自主导航不仅能为载体提供角秒级精度的三轴姿态,而且能为载体提供角秒级的载体经度和纬度,所以该系统为载体提供了高精度的导航信息。