GTAW焊接工艺对船用Ti-Al-Mo-Ni-Zr钛合金焊接接头性能影响

本文对船用Ti-Al-Mo-Ni-Zr合金GTAW焊接工艺验证试验进行了总结。制作了GTAW不同焊接状态下焊接试板并进行性能对比,着重分析了保护情况、返修及线能量对焊缝、熔合线及热影响区各性能的影响,总结了GTAW焊Ti-Al-Mo-Ni-Zr合金焊缝的性能特点,为产品建造提供技术参考。     

GTAW焊接过程声音信号的分析

研究分析钨极氩弧焊（GTAW）时焊接气流,焊接速度,电弧长度和声音信号采集角度对采集到的声压信号的影响。结果表明：速度对声压影响最小;焊接声音随气体流增加而增加,当流量大于15L／min,声压信号趋于恒定;电弧长度在3．5—5mm之间时,声压随弧长变化显著,当超过5mm时变化不明显;声压随麦克风采集角的增加而增加,当大于60°时声压值变化不大,焊接声压强度在空间的分布近似于声源模型中的偶极子模型。     

Dissimilar welding of carbon steel to 5754 aluminum alloy by Nd:YAG pulsed laser

Laser welding of low carbon steel to 5754 aluminum alloy was studied in keyhole welding mode in steel-on-aluminum overlap configuration. In order to decrease formation of intermetallic components during laser welding, effect of laser power, pulse duration and overlapping factor was investigated. Tensile test was performed to identify the effect of each parameter on the weld. The phase composition was characterized by energy dispersive spectrometry and Vickers microhardness test and microstructure by optical and scanning electronic microscopes. Results obtained show that increasing peak power (in constant pulse energy), pulse duration (in constant peak power) and overlapping factor (in constant pulse energy and peak power) will increase percentage of intermetallic components (PIC). On the other hand, decreasing the mentioned parameters will cause destructive effects such as inadequate penetration depth, spattering and cavity formation. Improvement in the tensile strength was attributed to low values of intermetallic components in weld metal. Finally, an optimized peak power, pulse duration and overlapping factor were reported.     

Neural networks prediction of different frequencies effects on corrosion resistance obtained from pulsed nanocrystalline plasma electrolytic carburizing

This paper deals with the surface modification of commercially pure titanium by using pulsed nanocrystalline plasma electrolytic carburizing. In order to fully characterize the complex underlying mechanism of this process and evaluate the effects of a thorough range of frequencies, a prediction model is developed using a hybrid of Neural Networks and Genetic Algorithms (GA). Process variables, i.e. time, frequency and corrosion resistance of nanocrystalline carbides, have been experimentally studied. Corrosion resistances were measured by PDS technique for different coated samples. A portion of this dataset is used to train the prediction model, while the rest is set aside to test its predictive performance. This hybrid Neural Networks model uses GA to achieve its optimal architecture for prediction. Finally, it is concluded that the proposed model has an excellent prediction capability of final corrosion resistance of nanocrystalline carbides in the various range of frequencies by comparing the results with the experimental data.     

焊前热处理对压铸镁合金GTAW焊气孔的影响

在不同温度下对压铸AM60B母材进行焊前热处理,待冷至室温后对其实施不填丝GTAW重熔焊接。焊后用扫描电镜对焊缝截面的气孔分布及形貌进行观察,并用粒径分析软件Nano measurer 1.2测量焊缝中气孔尺寸,用基于Matlab二次开发的图像分析程序识别和计算焊缝气孔率。结果表明:焊缝气孔主要分布在焊缝熔融区及熔合线附近;与未经焊前热处理母材对应的焊缝相比,经焊前热处理后所得焊缝中的气孔率及气孔尺寸均降低;随着焊前热处理温度升高,焊后气孔率及气孔尺寸均逐渐增加。     

城市隧道爆破振动速度峰值预测神经网络法应用

结合南京机场线地铁项目,进行了邻近隧道爆破开挖作用下既有隧道的爆破振动速度现场监测试验,应用BP神经网络,建立了既有隧道爆破振动速度的预测模型,并与多种经验公式预测进行了比较分析.结果表明:BP神经网络爆破振动速度预测数据与试验监测数据拟合较好,相比于经验公式预测,具有误差小、精度高的特点.研究成果可为邻近隧道爆破开挖作用下既有隧道爆破振动控制和新建隧道爆破开挖方案完善提供理论参考.     

城市隧道爆破振动速度峰值预测神经网络法应用

结合南京机场线地铁项目,进行了邻近隧道爆破开挖作用下既有隧道的爆破振动速度现场监测试验,应用BP神经网络,建立了既有隧道爆破振动速度的预测模型,并与多种经验公式预测进行了比较分析。结果表明:BP神经网络爆破振动速度预测数据与试验监测数据拟合较好,相比于经验公式预测,具有误差小、精度高的特点。研究成果可为邻近隧道爆破开挖作用下既有隧道爆破振动控制和新建隧道爆破开挖方案完善提供理论参考。     

A neuro-fuzzy identification of non-linear transient systems: Application to a pilot refrigeration plant

This study proposes to determine empirical models that represent the non-linear dynamics of a pilot refrigeration system (chiller), by using identification techniques of neuro-fuzzy systems (ANFIS). A detailed experimental study of a pilot refrigeration process using compression was conducted. Non-linearities were detected in the experimental data obtained from the system. Neuro-fuzzy models were developed for the prediction of the following process temperatures: condensation; evaporation; and refrigerated fluid (propylene glycol aqueous solution). The validation of the models was successfully conducted offline and online. The values obtained for VAF (“variance accounted for”) performance index and the dispersion plots showed the high performance of the models. These empirical models will be especially useful in the development of different non-linear control strategies, such as: fuzzy, neuro-fuzzy and model predictive control.     

TA16换热管5G位置脉冲GTAW机动焊工艺研究

研究了TA16换热管5G位置脉冲GTAW机动焊工艺,研究了脉冲频率、脉宽比、起弧位置、装配要求及增加熔化环对焊缝成型及内部质量的影响。结果表明,优化工艺参数下制备的焊接接头各项指标均可满足相关规范要求,研究结果为TA16钛合金换热管在蒸汽发生器上的应用提供一定试验研究依据。     

不同焊接条件下TIG焊接紫铜厚板的热效应研究

为改善紫铜厚板的焊接性,采用商业有限元软件Marc对钨极气体保护焊接紫铜厚板的温度场进行模拟,并详细讨论了焊接电流以及预热温度对熔池和热影响区的影响.结果表明,熔池和热影响区均随着预热温度和焊接电流的增加而增加,因此,在采用不同的预热温度和焊接电流的组合可以得到相同尺寸的熔池,但热影响区尺寸差别很大;在20℃时采用He或N2气保护焊得到的熔池尺寸与Ar气保护预热400℃时得到的熔池尺寸基本一致,但热影响区的尺寸窄于Ar气保护预热400℃时得到的热影响区尺寸.     

薄膜热电偶的动态特性及动态补偿研究

针对用于瞬态高温测量薄膜热电偶的动态特性研究问题,本提出了为展宽其工作频带,以此来减小动态误差的方法。采用了一种脉冲激光法对薄膜热电偶进行了动态校准实验;利用基于沃尔什函数的建模方法建立了较好的薄膜热电偶动态模型;比一般的最小二乘法具有更高的拟合程度;通过地模型的极点和工作频带的分析,设计了动态补偿数字滤波器,改善薄膜热电偶的动态特性。     

Dynamic simulations for preparing the acceptance test of JT-60SA cryogenic system

Power generation in the future could be provided by thermo-nuclear fusion reactors like tokamaks. There inside, the fusion reaction takes place thanks to the generation of plasmas at hundreds of millions of degrees that must be confined magnetically with superconductive coils, cooled down to around 4.5 K. Within this frame, an experimental tokamak device, JT-60SA is currently under construction in Naka (Japan).The plasma works cyclically and the coil system is subject to pulsed heat loads. In order to size the refrigerator close to the average power and hence optimizing investment and operational costs, measures have to be taken to smooth the heat load.Here we present a dynamic model of the JT-60SA’s Auxiliary Cold box (ACB) for preparing the acceptance tests of the refrigeration system planned in 2016 in Naka. The aim of this study is to simulate the pulsed load scenarios using different process controls. All the simulations have been performed with EcosimPro® and the associated cryogenic library: CRYOLIB.     

包装过程的故障检测与诊断

对于控制复杂、难以精确描述数学模型的包装过程,提出了基于小波变换的故障检测方法,故障诊断能过神经网络来实现。     

传感器动态非线性分析及在动态建模中的应用

利用非线性系统的Volterra级数展开方法,并针对实际传感器中二次非线性影响较大的情况,利用一维和二维频谱分析方法,着重研究了二次非线性对传感器动态测试及动态建模的影响,最后针对具体传感器给出了应用实例。     

浅谈压力容器焊接质量控制

焊接质量对压力容器的寿命和安全运行起着关键作用,对其应加以控制,主要从焊接工艺、焊接材料和焊接检验方面阐述怎样控制。     

基于参数估计的动态称重新方法

提出了一种新的动态称重法。首先导出了二阶称重系统的自回归滑动平均模型(ARMA);借助这一模型和递推最小二乘法(RLS),可以由极短的称重阶跃响应估计出模型参数和被称质量。数字仿真研究表明:在称重信号含有输入端白噪声污染的情况下,这一方法具有良好的准确度。     

Pulsed MIG welding of AZ31B magnesium alloy

Abstract

Pulsed metal inert gas welding of AZ31B magnesium alloy is carried out, and continuous butt joints of high quality are obtained at optimised parameters. The effects of parameters on weld formation and welding stability are studied. The microstructure, mechanical properties and fracture of weld beads with different filler wires are investigated. The results show that it is a stable drop transition process with optimised parameters, which belongs to globular transfer. The precipitates in fusion zone and heat affected zone (HAZ) are uniform, dispersive and almost granular. The grain size in fusion zone is fine, and the grain size does not grow too large in HAZ compared with the base metal. The ultimate tensile strength of weld beads can be 94% of base metal, and the average elongation is 11%. Dimples and coarse tearing ridges can be observed on the fracture of the weld bead.     

Comparison of Laser and Gas Tungsten Arc Weldments of Stabilized 17wt% Cr Ferritic Stainless Steel

One of the major factors influencing weldability of stabilized 17 wt% Cr ferritic stainless steels is extensive grain coarsening in the fusion zone (FZ) and in the heat affected zone (HAZ). This study aimed at exploiting low heat input characteristics of laser welding to effectively control grain coarsening in the FZ and HAZ of 1.2-mm thick stabilized 17 wt% Cr ferritic stainless steel weldment. The study demonstrated that as compared with gas tungsten arc welding (GTAW), laser welding brought about significant grain refinement in the FZ and HAZ. Laser weldments exhibited superior ductility over their GTA counterparts. An important observation of the study was that, in contrast to GTA weldment, laser weldment was associated with weaker interfaces along columnar grain boundaries in the FZ that served to arrest crack propagation normal to them.     

Analyses of cleavage crack arrest experiments: influence of specimen vibration

The crack propagation resistance of a low alloy bainitic steel used for nuclear pressure vessels was studied. Thermal shock experiments were carried out on pre-cracked discs. These tests were analyzed using the finite element method according to various assumptions, from elastic-static to full transient elastic-viscoplastic analysis. The crack propagation was modeled using node release technique. It was shown that crack deceleration at the end of the propagation greatly modifies the stress field at crack tip, due to interactions with structural vibrations. Therefore, it may be inaccurate to transfer the arrest toughness obtained from specimens under static analysis to components.