安装角偏差引起的成形磨齿齿形误差分析

成形磨削加工中砂轮与齿轮相对位置的偏差会引起齿形误差。在研究成形磨齿机加工原理的基础上,通过VERICUT加工仿真分析了砂轮安装角偏差对加工后齿形精度的影响。首先,根据齿轮啮合原理,对安装角偏差引起的齿形误差进行了理论计算;其次,基于VERICUT软件平台,设计了完整的砂轮修整和磨齿加工仿真流程,并建立了精确的模型,得到齿形误差的仿真结果;最后,通过仿真结果与理论计算的对比,验证了齿形误差分析的合理性。     

基于ANSYS平面闸门的自振特性研究

以某水利工程平面闸门的动力学问题为背景,考虑流-固耦合[1]对闸门结构自振特性的影响,应用大型有限元分析软件ANSYS对平面闸门的自振特性进行分析研究.建立了该平面闸门的实体模型和有限元模型,分析了平面闸门在无水和有水状态下的振动特性,并计算出了闸门的自振频率和振型.结果表明:水体高度对平面闸门自振频率和振型有着显著影响,尤其是对低阶的振动频率更为显著.     

Effect of holding time on vacuum brazing for a stainless steel plate–fin structure

This paper presents a vacuum brazing of 304 stainless steel plate–fin structures with nickel-based BNi-2 filler metal. The effect of brazing holding time on tensile strength and microstructure has been investigated, aiming to obtain the optimal brazing holding time. The microstructure in brazing joint consists of diffusion-affected zone (DAZ), interface reaction zone (IRZ), isothermally solidified zone (ISZ) and athermally solidified zone (ASZ). The structure in the fillet is composed of solid solution, nickel silicon, nickel boron compound and a mixture with nickel silicon and nickel boron. The tensile strength increases along with the increase of holding time, but decreases when the holding time is over 25 min. A maximum tensile strength of 65.1 MPa is obtained with 25 min holding time. Too short holding time will make boron diffuse insufficiently and generate a great deal of brittle boride components, and too long holding time will make the base metal dissolve into the filler metal excessively and creates more corrosion voids.     

Intelligent control system of an industrial lime kiln process

In the face of strong competition, the pulp and paper industry is aiming at higher profitability through increased productivity and the reduction of costs. In addition, on the global scale the industry is facing increasing market demands for higher product quality, more specialty products and improved production flexibility and environmental protection. Consequently, extensive research is being conducted to improve existing processes. One alternative, which is gaining increasing attention within the industry, is the improved control of existing processes by means of intelligent systems. In this paper, an intelligent kiln control system is presented. In the system, neural network models are used in conjunction with advanced high-level controllers based on fuzzy logic principles and a novel linguistic equation approach. Finally, the testing results of the system are presented and discussed.     

Behavior of 3D orthogonal woven CFRP composites. Part II. FEA and analytical modeling approaches

In this paper, a 3D macro/micro finite element analysis (FEA) modeling approach and a 3D macro/micro analytical modeling approach are proposed for predicting the failure strengths of 3D orthogonal woven CFRP composites. These approaches include two different scale levels, macro- and micro-level. At the macro-level, a relatively coarse structural model is used to study the overall response of the structure. At the micro-level, the laminate block microstructure is modeled in detail for investigating the failure mechanisms of 3D orthogonal woven CFRP composites. The FEA and analytical models developed previously [Tan P, Tong L, Steven GP. Modeling approaches for 3D orthogonal woven composites, Journal of Reinforced Plastics and Composites, 1998:17;545–577] are employed to predict the mechanical properties of 3D orthogonal woven CFRP composites. All models presented in this paper are validated by comparing the relevant predictions with the experimental results, which were reported earlier in Part I of the paper [Tan P, Tong L, Steven GP. Behavior of 3D orthogonal woven CFRP composites. Part I. Experimental investigation, Composites, Part A: Applied Science and Manufacturing, 2000:31;259–71]. The comparison shows that there is a good agreement for the mechanical properties. An acceptable agreement exists for the failure strength in the x or stuffer yarn direction even though the FEA model gives a lower bound and the analytical model gives an upper bound. However, for the failure strength in the y or filler yarn direction, the difference between the predicted and experimental results is significant due to primarily ignoring of the waviness of filler yarn in the models. A curved beam model, which considers the waviness of the filler yarn, will be presented in Part III of the paper.     

基于分形理论的接触式机械密封泄漏模型

引言 机械密封基本性能主要包括密封特性(即泄漏率指标)和端面摩擦特性(即抵御摩擦磨损的能力).机械密封失效最重要和最直接的表现是在规定的工作条件下,机械密封在未达到规定的工作时间,就出现泄漏率超标现象.端面摩擦特性的好坏对机械密封的密封特性有着显著的影响.在摩擦副间建立流体摩擦工况、流体动压效应,可以改善端面摩擦特性,减小端面磨损.然而,改善端面摩擦特性所采取的措施,如减小端面比压,往往会给机械密封带来较大的泄漏损失,导致其泄漏率超标.为了减少物料流失、保护环境,以及防止因易燃易爆物料泄漏造成危害,充分考虑机械密封的密封特性,从理论上揭示运行过程中机械密封泄漏的影响因素,切实有效地控制机械密封泄漏率不仅是必要的而且是十分迫切的.     

Plasticity in multiphase intermetallics

We have studied the mechanical behavior of model NiAl-based eutectic composites to gain insight on micromechanisms of plasticity in multiphase intermetallics. We show that in composites where the NiAl matrix and the reinforcing ductile second phase can deform compatibly due to easy slip transfer across interfaces, high room temperature tensile ductility and fracture toughness are obtained. In composites where interfaces are strong barriers to slip transfer and the metallic second phase has high strength and limited ductility, incompatible deformation of the two phases results in negligible tensile ductility and limited toughness enhancement. Factors that affect ease of slip transfer across interfaces are discussed. Calculations of dislocation pile-up stresses are used to predict whether slip is activated prior to cleavage or vice-versa for a given set of respective yield strengths and crystallographic orientation relationships between the two phases.     

仿人机器人双足行走模型研究

针对仿人机器人双足行走的稳定性问题,引入零力矩点理论,根据稳定行走必须满足地面反作用力位于稳定区域内这个条件,推导出仿人机器人在行走过程中单双腿支撑期的稳定区域面积和稳定裕量。建立2种不同形状的仿人机器人双足模型,在足底和地面间创建一系列接触力,并通过机械系统动力学自动分析软件得到行走过程中足底各个点的受力曲线并进行受力分析,得出合理的双足形状。     

高压超临界萃取装置的模糊PID控制方法

高压超临界萃取控制参数具有时变、非线性的特点,对其进行精确控制具有很大难度.PID控制广泛应用于工业过程控制,但常规PID控制器参数对运行工况的适应性差.模糊控制具有不依赖系统数学模型、调节速度快、鲁棒性好等优点,但稳态精度欠佳.将PID控制与模糊控制相结合,设计了模糊PID反馈控制器,形成了模糊PID复合控制方法.以...     

Fabrication of Ce-doped(Gd_2Y)Al_5O_(12)/Y_3Al_5O_(12) composite-phase scintillation ceramic

In this paper, a novel Ce(Gd_2 Y)Al_5O_(12)/Ce:Y_3Al_5O_(12)(Ce:GYAG/Ce:YAG) composite scintillation ceramic was designed and fabricated by a solid-state reaction method. The phase, luminescence and scintillation properties were investigated. The Ce:GYAG/Ce:YAG composite ceramic consisting of two-phase has a broad emission band ranging from 500 to 750 nm. The total mass attenuation coefficient of Ce:GYAG/Ce:YAG is 0.3864 cm~(-1), in between those of Ce:YAG and Ce:GYAG ceramics. In addition, the composite ceramic had a high light yield of 20430 ph/MeV. By controlling the ratio of GYAG and YAG, the composite ceramic can realize a spectrum design and total mass attenuation coefficient control to meet the requirements for wide-X-ray-energy-range detectors.