3UPS-UP并联机构性能分析与优化北大核心

以三自由度并联机构3UPS-UP为研究对象,对机构进行运动学分析,建立机构模型和数学模型,求解完整的雅可比矩阵。建立工作空间、全域条件数和全域刚度三个性能指标,运用多岛遗传算法对该并联机构进行多目标优化,绘制设计变量和全域性能指标的关系图谱,并优化求解最优结构参数和最优Pareto解。借助散点矩阵分析设计变量和目标函数的变化趋势和相关性,结果表明,工作空间指标和全域条件性能指标是两个相互矛盾的指标;工作空间和全域刚度指标近似正相关。     

三自由度驱动冗余并联机器人刚度性能与尺寸关系研究

以平面三自由度驱动冗余并联机器人为研究对象,应用空间模型理论建立了机器人机构的空间模型,求解机器人机构的速度雅可比矩阵和柔度矩阵,进而得到全域刚度性能评价指标。在此基础上探讨了机器人机构刚度性能与运动学尺寸之间的关系,并绘制了刚度性能图谱。这些图谱将有助于该机器人机构的优化设计。     

三自由度平面驱动冗余并联机器人刚度性能与尺寸关系研究

以平面三自由度驱动冗余并联机器人为研究对象,应用空间模型理论建立了机器人机构的空间模型,求解机器人机构的速度雅可比矩阵和柔度矩阵,进而得到全域刚度性能评价指标。在此基础上探讨了机器人机构刚度性能与运动学尺寸之间的关系,并绘制了刚度性能图谱。这些图谱将有助于该机器人机构的优化设计。     

三自由度并联机构性能分析与优化

以含中间恰约束PU支链、能够实现三自由度的3UPS-PU、4UPS-PU并联机构为研究对象,对机构进行运动学分析,建立机构模型和位置数学模型,求解完整的雅可比矩阵。建立全域灵巧指标和全域刚度性能指标,基于粒子群优化算法对两种并联机构进行多目标优化,并进行比较分析。结果表明,4UPS-PU冗余并联机构比3UPS-PU并联机构具有更好的全域灵巧数和全域刚度数。     

三自由度并联机构的设计与运动学分析

设计了一种应用于各类表面加工的三自由度并联机构,充分研究了三自由度并联机构在空间的运行机理,使机构加工时,能够合理设置加工参数。首先,对三自由度并联机构进行了位置正逆解分析,并通过举例计算验证了其正确性,为机构的控制提供了理论参考。然后,对其进行了运动空间求解,研究了三自由度并联机构的工作空间,得出工作空间分布特点。最后,通过ADAMS仿真了并联机构的运动过程,验证了其运动学性能,对其移动平台的位移、速度、加速度进行了详细分析,说明了设计的机构能适应速度变化要求高的场合。     

薄壁高筋筒件的径向包络成形装备运动学分析

对径向包络成形装备的位置反解、奇异位形和工作空间等运动学进行分析。通过闭环矢量法建立六连杆三自由度并联机构的运动学模型,利用雅可比矩阵求解奇异位形,通过位置约束条件求解工作空间。揭示六连杆三自由度并联机构的运动学特性;建立驱动滑块位置和包络辊位姿之间的映射关系,得到驱动滑块的位移、速度和加速度表达式;得到并联机构的两种奇异位形;分析机构工作空间的影响因素和限制条件,求解了并联机构的工作空间。通过径向包络成形装备的运动学分析,表明了当前构型和运动参数的可行性,在运动平台转角γ最小时,并联机构可获得最大的移动工作空间。上述研究为径向包络成形装备运动控制提供了理论依据。     

空间三转动并联机构工作空间和刚度分析

针对数控回转台的实际运动需求,以三自由度并联构型3-PUS-RU为研究对象,利用封闭矢量法建立位置逆解方程和并联机构的雅可比矩阵。引入并联机构的工作空间和刚度性能指标,并绘制机构的工作空间和机构守恒协调刚度在工作空间中的分布图谱。结果表明,由于机构的对称性,使得工作空间和刚度性能仍出现对称分布,工作区域尽量选取刚度值大的位置。对该3-PUS-RU并联构型工作空间和守恒协调刚度性能进行研究,其研究结果对并联机构的设计具有一定的指导作用。     

3-UPU冗余驱动并联机构的冗余支链优选及仿真

由于当前3-UPU冗余驱动并联机构存在奇异缺陷,造成冗余支链选择方法可靠性低、刚度分布不均.提出一种新的3-UPU冗余驱动并联机构冗余支链优选方法.设计了3-UPU冗余驱动并联机构和自由度要求.将运动平台位姿参数看作变量,求出3-UPU冗余驱动并联机构的力矩阵和力矩矩阵.获取3-UPU冗余驱动并联机构输入,通过位置方程求出驱动螺旋参数和非冗余支链的驱动螺旋,提升可靠性.计算冗余驱动螺旋的参数,获取条件数机构的相关信息,确定刚度矩阵的力矩阵和力矩矩阵,利用灵巧度与刚度获取条件数和刚度最佳的冗余支链,解决刚度分布不均的问题.实验结果表明:所提方法可靠性高、刚度分布均匀.     

3-UPU冗余驱动并联机构的冗余支链优选及仿真（英文）

由于当前3-UPU冗余驱动并联机构存在奇异缺陷,造成冗余支链选择方法可靠性低、刚度分布不均。提出一种新的3-UPU冗余驱动并联机构冗余支链优选方法。设计了3-UPU冗余驱动并联机构和自由度要求。将运动平台位姿参数看作变量,求出3-UPU冗余驱动并联机构的力矩阵和力矩矩阵。获取3-UPU冗余驱动并联机构输入,通过位置方程求出驱动螺旋参数和非冗余支链的驱动螺旋,提升可靠性。计算冗余驱动螺旋的参数,获取条件数机构的相关信息,确定刚度矩阵的力矩阵和力矩矩阵,利用灵巧度与刚度获取条件数和刚度最佳的冗余支链,解决刚度分布不均的问题。实验结果表明:所提方法可靠性高、刚度分布均匀。     

3-SPT-S并联机构运动学性能指标分析

以3-SPT-S并联机构为研究对象,对机构进行位置分析,建立机构运动学模型和数学模型,推导出机构的雅可比矩阵和Hessian矩阵,并求解出局部速度灵巧度性能指标和加速度灵巧度性能指标。利用数学软件MATLAB绘制了局部性能指标的图谱,分析机构处于不同位姿下,性能指标的变化规律。     

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.     

Growth Kinetics of Single Inclusion Particle in Molten Melts

On the basis of the single-particle framework, a new theory on inclusion growth in metallurgical melts is developed to study the kinetics of inclusion growth on account of reaction and collision. The studies show that the early growth of inclusion depends on reaction growth and Brawnian motion collision, and where the former is decisive, the late growth depends on turbulence collision and Stokes＇ collision, and where the former is dominant; collision growth is very quick during the smelting process, lessened in the refining process, but nearly negligible in the continuous casting process.     

Theoretical Analysis for the Motion and Temperature of Melt Droplets in Spray Degassing Process

The motion of melt droplets in spray degassing process was analyzed theoretically. The height of the treatment tank in spray degassing process could be determined by the results of theoretical calculation of motion of melt droplets. To know whether the melt droplets would solidify during spraying process, the balance temperature of melt droplets was also theoretically analyzed. Then proof experiments for theoretical results about temperature of melt droplets were carried. In comparison, the experimental results were nearly similar to the calculation results.     

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.