基于BP神经网络L-M优化算法的Ti-6Al-4V电火花线切割工艺参数优化

针对机械切削性能差、难加工的Ti-6Al-4V合金,运用正交试验法进行了电火花线切割加工工艺试验研究。探讨了电火花线切割加工的规律和特性,分析了脉冲宽度、脉冲间隔、功放管数和运丝速度等工艺参数对Ti-6Al-4V加工质量的影响,得到了线切割加工最优化参数组合。借助L-M优化算法的BP神经网络搭建了线切割加工工艺网络预测模型,该模型预测精度较高,可为钛合金高质量切割提供可靠的工艺参数预测,对Ti-6Al-4V的实际生产加工具有一定的参考作用。     

Effect of nozzle angle and depth of cut on grinding titanium under cryogenic CO2

Grinding force and grinding energy are the significant factors associated with the grinding process. The higher heat at the contact zone leads to dulling grits and frequent breakage of grit particle resulting in increase of the grinding force. This problem can be met by bringing down the temperature at the contact zone. The oil-based coolant fails to eliminate the heat at the grinding zone. Hence, the approach of cryogenic coolant is required for this problem. In the present study, an experimental work has been made on the grinding Ti-6Al-4V under cryogenic carbon dioxide (CO₂) and conventional coolant condition. Grinding experiments were performed with an electroplated cubic boron nitride (CBN) wheel, with two factors such as nozzle inclination angle and depth of cut (DOC). The output response parameters considered were surface roughness (R_a), tangential force (F_t), normal force (F_n) grinding zone temperature (GT), and specific energy. The effect of CO₂ and wet coolant on the chip morphology and surface modification in grinding Ti-6Al-4V was analyzed. The experimental result indicates when cryogenic CO₂ was used as a coolant the F_t is reduced from 3 to 21% and 2 to 99% in F_n. The R_a was reduced by 333% and GT by 48% over conventional grinding.     

Empirical approach to develop a multilayer icebonded abrasive polishing tool for ultrafine finishing of Ti-6Al-4V alloy

This paper covers the development of a multilayer icebonded abrasive polishing (IBAP) tool for multistage polishing of Ti-6Al-4V alloy specimens based on a systematic study that determined the number of layers, thickness of each layer, and the type, size and concentration of abrasives in each layer. Based on this study, a three-layered IBAP tool with the bottom layer consisting of soft aluminum oxide abrasives of 3?µm size with 5% concentration, the middle layer with moderately hard silicon carbide abrasives of 8?µm size with 10% concentration and the top layer with hard boron carbide abrasives of 15?µm size with 30% concentration was formulated for ultrafine finishing of Ti-6Al-4V alloy specimen in a single setup. The performance of the three-layered IBAP tool assessed in terms of finish and morphology over the work surface showed 81% improvement in surface finish, showing its effectiveness over a single-layered IBAP tool. Polishing studies have clearly demonstrated the generation of ultrafine surfaces, yielding a finish of 37?nm while the morphological studies on the polished surface have shown a nearly scratch-free surface on the Ti-6Al-4V alloy.     

Threshold Fluence Measurement for Laser Liftoff of InP Thin Films by Selective Absorption

We explore conditions for achieving laser liftoff in epitaxially grown heterojunctions, in which single crystal thin films can be separated from their growth substrates using a selectively absorbing buried intermediate layer. Because this highly non‐linear process is subject to a variety of process instabilities, it is essential to accurately characterize the parameters resulting in liftoff. Here, we present an InP/InGaAs/InP heterojunction as a model system for such characterization. We show separation of InP thin films from single crystal InP growth substrates, wherein a ≈10 ns, Nd:YAG laser pulse selectively heats a coherently strained, buried InGaAs layer. We develop a technique to measure liftoff threshold fluences within an inhomogeneous laser spatial profile, and apply this technique to determine threshold fluences of the order 0.5 J cm^?2 for our specimens. We find that the fluence at the InGaAs layer is limited by non‐linear absorption and InP surface damage at high powers, and measure the energy transmission in an InP substrate from 0 to 8 J cm^?2. Characterization of the ejected thin films shows crack‐free, single crystal InP. Finally, we present evidence that the hot InGaAs initiates a liquid phase front that travels into the InP substrate during liftoff.

     

Impact of arteriovenous fistula cannulation on the quality of dialysis

Introduction: Adequate hemodialysis directly improves health. Puncturing an arteriovenous fistula (AVF) and the amount of blood recirculation greatly affect the quality of dialysis. Few studies have assessed the method to cannulate a fistula and its influence on efficiency of hemodialysis. Methods: This prospective pilot study included 14 patients with end‐stage renal failure receiving regular intermittent hemodialysis. Patients received three consecutive treatments with both needles directed upstream then three consecutive treatments with the venous needle directed upstream and the arterial needle directed downstream. With both techniques, the distance between the needles was kept constant at 2.5 cm. Recirculation rate and Kt/V ratio were measured during each treatment using thermodilution and a diascan Fresenius generator. Findings: The 14 patients received 84 hemodialysis sessions: i.e., 8 (57.1%) males and 6 (42.8%) females, mean age 62.3 ± 15.57 years. Results showed that mean recirculation rates and Kt/V did not significantly differ between the two techniques. Discussion: Because no significant difference was found between the two techniques, the direction of insertion of needles should be decided upon on a case‐by‐case basis depending on the anatomy of the AVF and the feasibility of the puncture.     

Temperature-gradient induced microstructure evolution in heat-affected zone of electron beam welded Ti-6Al-4V titanium alloy

The heat-affected zone (HAZ) of electron beam welded (EBW) joint normally undergoes a unique heat-treating process consisting of rapid temperature rising and dropping stages, resulting in temperature-gradient in HAZ as a function of the distance to fusion zone (FZ). In the current work, microstructure, elements distribution and crystallographic orientation of three parts (near base material (BM) zone, mid-HAZ and near-FZ) in the HAZ of Ti-6Al-4V alloy were systematically investigated. The microstructure observation revealed that the microstructural variation from near-BM to near-FZ included the reduction of primary α (α_p) grains, the increase of transformed β structure (β_t) and the formation of various α structures. The rim-α, dendritic α and abnormal secondary α (α_s) colonies formed in the mid-HAZ, while the “ghost” structures grew in the near-FZ respectively. The electron probe microanalyzer (EPMA) and electron back-scattered diffraction (EBSD) technologies were employed to evaluate the elements diffusion and texture evolution during the unique thermal process of welding. The formation of the various α structures in the HAZ were discussed based on the EPMA and EBSD results. Finally, the nanoindentation hardness of “ghost” structures was presented and compared with nearby β_t regions.     

Improved Tribocorrosion Properties of Ti6Al4V Alloy by Anodic Plasma Electrolytic Oxidation

Ti6Al4V alloy has good corrosion resistance due to the formation of the passive oxide films on the surface of Ti6Al4V alloy. However, Ti6Al4V alloy has poor tribocorrosion resistance in the seawater environment. Herein the present work, plasma electrolytic oxidation (PEO) with the electrolyte of glycerol and sodium borate is used to generate PEO coatings on the surface of Ti6Al4V alloy to improve its tribocorrosion properties. The microstructure and tribocorrosion properties of PEO coatings are investigated by using scanning electron microscopy, X-ray diffraction, and tribometer, respectively. The growth kinetics and the tribocorrosion mechanisms of PEO coatings are discussed in detail. It is shown in the results that PEO coatings deposited on the surface of Ti6Al4V alloy are composed of rutile and anatase phases. The surface hardness and thickness of PEO coatings are enhanced with the increase of the voltage and time. The wear rate of Ti6Al4V alloy with PEO coatings is significantly reduced in artificial seawater.     

25Cr_2Mo_1V钢螺栓在长期高温高压下脆化机理的研究

通过对已脆化的２５Ｃｒ２Ｍｏ１Ｖ钢螺栓及经恢复热处理后的螺栓的金相及电子显微分析,阐述了２５Ｃｒ２Ｍｏ１Ｖ钢在长期高温高压下工作发生脆化的原因,讨论了恢复热处理对脆化螺栓恢复性能的作用     

Control allocation for a V/STOL aircraft based on robust fuzzy control

This study addresses the design of an output-feedback H-infinity and fuzzy mixed controller for an advanced vertical and/or short take-off and landing aircraft that exhibits satisfactory global stability criteria. A fuzzy logic based optimization approach is employed to solve autonomously the constrained control allocation problem by suitably adjusting the components of the output vector and finding a proper vector in the attainable moment set. Simulations show that the designed fuzzy controller is better s...     

SDH专网的接入网网络管理系统设计

接入网是通信发展演变的主要方向之一,从网络管理的角度来看,接入网也是最复杂,最难管理的网络之一。由于光通信技术已经基本成熟,光纤接入网已成为当前接入网市场的主流。在本文SDH光纤接入网中,为了适应用户网络多种业务接入的需要,采用V5这一国际标准的数字接口作为接入网连接公共电信网的纽带。同时接入网中必须提供Q3接口,以实现电信管理网对接入网侧V5接口的管理。首先研究SDH光同步数字传输网络与专网通信。对基于本项目2.5G光纤接入平台的V5接入网,分析其V5接口结构、功能、相关协议以及V5接口系统的实现方案。在此基础上,探讨了电信管理网(TMN)的体系结构,相关协议与管理信息库。提出一种基于TMNQ3代理(Agent)的方案——管理者-代理-后台的设计方案,分析此方案的信息模型、通信协议栈及模块划分。接着,根据迈力特2.5G光纤综合业务传输网络的实际情况,在不更改此方案信息模型的基础上,用SNMP实现SDH接入网的管理并阐述其具体实现。在此之后,通过一致性测试和功能行测试,对该软件测试行进说明。