焊缝自动跟踪微机系统的数字控制器

对焊缝自动跟踪微机系统中的数字控制器进行了分析研究。在焊缝自动跟踪系统中,除了电弧传感器之外,大部分的传感器都有检测点超前于焊接点的情况。本文针对这种有普遍意义的传感器超前检测的自动控制系统的结构特点,分别设计了最少拍数字控制器、数字ＰＩＤ控制器以及一种实用型的数字控制器。这些数字控制器的仿真试验结果表明,本文提出的实用数字控制器具有跟踪结构精度高,结果简单、计算方便等优点,因而是这类传感器超前检     

一种基于积分反推原理的非线性伺服控制方法

针对机械伺服系统,提出了一种基于积分反推原理的新型的伺服控制器。该控制器对外部扰动及系统参数变化具有较强的鲁棒性。对直流电机伺服系统进行了数字仿真,结果表明了这种新型控制器的有效性。     

一种新型电阻焊机恒电压控制策略

针对电焊杌焊接时恒压控制的工艺要求,研制了一种基于恒压控制策略的DSP全数字控制器,详细介绍了数字控制器的控制原理、控制器结构以及控制程序设计.该数字控制器主要基于对阻焊变压器一次电压的监控以及负载特性的变化,当电网电压在一定范围内波动时,仍能保证一次电压恒定.其控制主电路通过双向晶闸管控制其触发导通角从而改变其输出电压,数字控制器采用TMS320F2812实现.实验表明该方法能有效地控制焊接时输出的恒电压.达到满意的效果.     

基于DSP的脉冲MIG焊数字控制系统的建模与仿真

为实现一脉一滴熔滴过渡,采用了双阶梯外特性和脉冲MIG焊电参数控制策略.构建了基于DSP(digital signal processor)的脉冲MIG焊数字控制系统模型.建立了控制系统的仿真模型.借助MATLAB对控制系统进行了仿真研究,得到了数字控制器的最佳参数范围.进行了脉冲MIG焊数字控制器的仿真试验.结果表明,所设计的数字控制器可以实现电弧电压、焊接电流的实时准确快速调节,能够实现脉冲MIG焊双阶梯形外特性和熔滴过渡的控制.     

数字电液比例位置控制系统

本文提出一种数字电液比例位置系统，研究采用状态反馈改善系统的动态性能，给出参数辨识和极点配置计算方法。此外，本文还提出电液比例专用数字控制器，简化了控制结构，使控制器成本低廉，可靠性高。     

电液数字阀的PLC直接控制及特性

采用可编程控制器(PLC)直接控制电液数字阀，可使液压系统的控制系统简洁、可靠、成本显著下降。介绍了PLC控制电液数字阀的方法，数字阀的伺服控制、驱动接日及PLC梯形图的控制逻辑。     

功率匹配泵的数字PID控制器的非线性控制寻优

本文把系统的动态性能指标转化为系统输出的约束条件,并以使约束的最大误差最小作为优化目标,从而使控制器的设计问题能够通过限定条件的非线性寻优算法得到解决。本文结合功率匹配泵,利用序列二次规划法对其数字PID控制器进行了非线性控制寻优,取得了很好的效果。     

步进式液压数字阀用永磁式步进电动机的非线性控制

通过现代非线性理论如混沌动力学理论研究了永磁式步进电动机的非线性动力学。本文的研究对象是三相步进电动机。研究表明在高频情况下系统会经历一个动态的分又(Hopf分叉)。由于步进电动机作为步进式液压数字阀的电气一机械转换元件被广泛地应用于液压数字压力阀、液压数字流量阀、液压数字方向阀。本文提出了对三相步进电动机的不稳定性的控制,设计了非线性鲁棒控制器,阐明了在一些电动机参数不确定的情况下,如何使系统稳定,并且具有令人满意的性能。     

基于模糊自调整PID控制的智能数字流量阀研究

针对PID控制数字流量阀的局限性,设计模糊自调整PID控制器,实现数字流量阀控制系统PID参数在线自整定的智能化.仿真结果表明:与常规PID控制的数字流量阀相比,智能数字流量阀具有更小超调量、更快动态响应及更强抗干扰特性,取得了优于传统PID控制的效果.     

高精度气动伺服阀的状态空间建模及数字化设计

伺服阀的性能是影响高精度气动精确定位系统性能的决定性因素.为了提高气动系统性能,改善伺服阀的性能至关重要.分析一种新型的高精度气动伺服阀的结构特点,建立其状态空间模型,设计数字控制器并进行仿真.仿真结果表明:该数字控制器是有效的,显著改善了气动伺服阀的动、静态性能.     

Influence of Fe on Microstructure and Mechanical Properties in Pdoped Ni–Cr–Fe Alloys

The influence of Fe on the microstructure and mechanical properties of P-doped Ni–Cr–Fe alloys has been investigated.Results showed that increasing Fe content refined the dendrite microstructure and enhanced the solubility of P in as-cast alloys. The change of microhardness in different dendrite regions was attributed to the segregation of P atoms in solid solution state, which had strengthening effects. Increasing Fe contents from 15.2 to 60.7 wt% reduced the yield strength and tensile strength but had little influence on the elongation of alloys. The stress rupture life of alloys after heat treatment decreased with the increment of Fe contents, and the failure fracture modes transferred from transgranular to intergranular fracture mode. The change of fracture modes was due to the weakness of grain boundaries caused by the increment of Fe.In addition, the precipitation of M_(23)C_6 was believed to be related to the segregation of P toward grain boundaries, which led to the fluctuation of carbon and chromium atoms near the grain boundaries in alloys with low Fe contents. Consequently, the increment of Fe decreased the strength of matrix and changed the existence of P atoms and the precipitates at grain boundaries.     

The structure of molten zones in explosion welding (aluminium–tantalum,copper–titanium)

Investigations were carried out into the relief of the flat- and wave-shaped interfaces for explosion-welded aluminium–tantalum and copper–titanium welded joints. For these systems, characterized by a relatively high mutual solubility of the initial elements, the results show a typical set of the structures of the interfaces replacing each other with the intensification of the welding conditions. The unusual shape of the projections on the flat interfaces was found. They are similar to splashes, which form on the surface of the liquid, although they are solid-phase splashes. The vortex structure of the zones of local melting was also detected. The unusual shape of the waves was found: in the presence of mutual solubility they consist of the specially ordered set of projections. It may be assumed that this is caused by the formation of intermetallic compounds on the surface of the projections. The processes of self-organization, ensuring the evolution of the relief of the interface in the intensification of the welding conditions, have been investigated. The role of intermetallic compounds in these self-organization processes is clarified.     

德育的现代转型刍议

我国改革开放的迅猛发展,要求德育实现从传统向现代的转型。这种转型因其受到国情,民情,社情,世情的制约,会很艰难,但当前大学生“三德”匮乏的现实增强了转型的紧迫感。改革传统的德育体制应首先从注重人格教育,公民教育,精英教育入手。     

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 Coupled FEM Analysis of the Transient Temperature Field During Inertia Friction Welding of GH4169 Alloy

The inertia friction welding process is a non-linear process because of the interaction between the temperature field and the material properties as well as the friction force. A thermo-mechanical coupled finite element model is established to simulate the temperature field of this process. The transient temperature distribution during the inertia friction welding process of two similar workpieces of GH4169 alloy is calculated. The region of the circular cross-section of the workpiece is divided into a number of four-nodded isoparametric elements. In this model, the temperature dependent thermal properties, time dependent heat inputs, contact condition of welding interface, and deformation of the flash were considered. At the same time, the convection and radiation heat losses at the surface of the workpieces were also considered. A temperature data acquisition system was developed. The temperature at some position near the welding interface was measured using this system. The calculated temperature agrees well with the experimental data. The deformation of the flash and the factor affecting the temperature distribution at the welding interface are also discussed.     

极地海洋环境服役材料的摩擦学研究进展

随着北极航行的发展及极地资源开发的需要，如何提高极地海洋环境服役材料的摩擦学性能愈发重要。在极地海洋环境中，碎冰、冰层和海水中的腐蚀性物质会使材料受到摩擦磨损、腐蚀及其耦合的影响;低温潮湿环境会增加材料的脆性、使材料表面覆冰、改变材料的摩擦磨损机理;强紫外线会加速涂层老化;这些因素都会降低材料的耐磨性能，最终导致材料失效。因此，极地海洋环境服役材料的摩擦学与材料的性能、服役寿命息息相关。本文介绍了极地探索所面临的摩擦磨损问题;阐述了极地温度、极地海洋大气及海水成分、海冰运动和极地微生物等极地海洋环境特点及其对材料摩擦学性能的影响;重点介绍了金属材料、无机非金属材料、高分子材料在极地海洋环境下的摩擦学进展;探讨了提升材料在极地海洋环境下的耐磨防腐技术，如改性、表面修饰等;最后，结合极地海洋环境服役材料摩擦磨损研究中所面临的问题及发展趋势，对未来极地海洋服役材料的摩擦学研究工作进行展望。     

微米尺寸不锈钢的形变与疲劳行为的尺寸效应

采用聚焦离子束溅射蚀刻加工了微米尺寸304不锈钢悬臂梁试样．利用静态及动态弯曲加载研究了微米尺寸材料的形变与疲劳开裂行为．结果表明：随薄膜厚度的减小,材料的屈服强度升高,塑性下降．屈服强度随悬壁梁厚度的变化关系与Hall—Perch晶粒强化关系相似．微小悬壁梁屈服强度的升高来源于小尺度材料在非均匀变形下引起的应变梯度贡献的增加;而塑性下降则归因于较薄薄膜的晶粒内较少的可动位错．疲劳裂纹从尖缺口处萌生的门槛值接近块体材料．     

集装箱底侧梁开裂原因分析

集装箱底侧梁在操作过程中发生开裂。通过化学分析、力学测试、金相检验以及断口分析等手段,对开裂的集装箱底侧梁进行综合分析。结果表明,集装箱底侧梁裂纹对应 R角处的板厚度减薄了近 50%,严重降低了该位置的承载能力;同时材料本身塑性较差,并且室温折弯过程很可能 R角处已经产生了裂纹,随后再对其进行焊接操作,使得该区域韧性进一步降低,在集装箱作业过程中箱内载荷作用下, R角处作为应力集中部位受拉应力而发生瞬间断裂。     

Corrosion‐erosion damage of heat exchanger tubes by desalted crude oil flowing at shell side

Heat exchanger tubes were locally heavily damaged by desalted crude forming a shell side stream under the pressure of 2.6 MPa and at the temperature of 385–395 K. Boiler steel tube temperature was 97 K higher compared to that of the crude oil at its inlet to the exchanger. Two types of segmental baffles effected cross vortex type flow that was lowered nearly to a standstill at locations where the highest damage occurred. Close to the baffles where the damage was the highest the flow was completely different from that of the window flow. These were found from analyses of the flow and of locations of perforations. Most of the tube surface was with no damage and was covered with protective organic‐inorganic deposit. Electrochemical investigation proved a cathodic character of the deposited film against bare steel. Metallography examination of the steel showed typical structures that could not affect much the damage. The crude with low water content was not found aggressive when a corrosion test was performed at elevated temperature. The tests excluded the possibility for high rate of electrochemical corrosion at the surfaces with removed protective layers. The only reason of the damage may be cavitation corrosion at the ways of crude slow vortex flow at which temperature was high enough to allow explosions of low volatile components [1].     

Simulation of 3-D Deformation and Material Flow During Roll Forging Process Using System of Oval-Round Groove

Basing on the analysis of the traits of the roll forging process, a system-model of computer simulation has been established. Three-dimensional rigid-plastic FEM has been used for the simulation of the deformation process in the oval and round pass rolling, including the entering, rolling, and separating stages. The analysis was conducted using the Deform-3D ver.5.0 code. The important information concerned with the deformation area characteristic, material flow, and velocity field has been presented. Otherwise,the location of the neutral plane in the deformation area was shown clearly.