Investigation on the process parameters of TIG-welded aluminum alloy through mechanical and microstructural characterization

Multi-pass TIG welding was conducted on plates (15×300×180 mm3) of aluminum alloy Al-5083 that usually serves as the component material in structural applications such as cryogenics and chemical processing industries. Porosity formation and solidification cracking are the most common defects when TIG welding Al-5083 alloy, which is sensitive to the welding heat input. In the experiment, the heat input was varied from 0.89 kJ/mm to 5 kJ/mm designed by the combination of welding torch travel speed and welding current. Tensile, micro-Vicker hardness and Charpy impact tests were executed to witness the impetus response of heat input on the mechanical properties of the joints. Radiographic inspection was performed to assess the joint's quality and welding defects. The results show that all the specimens displayed inferior mechanical properties as compared to the base alloy. It was established that porosity was progressively abridged by the increase of heat input. The results also clinched that the use of me-dium heat input (1-2 kJ/mm) offered the best mechanical properties by eradicating welding defects, in which only about 18.26% of strength was lost. The yield strength of all the welded specimens remained unaffected indicated no influence of heat input. Partially melted zone (PMZ) width also affected by heat input, which became widened with the increase of heat input. The grain size of PMZ was found to be coarser than the respective grain size in the fusion zone. Charpy impact testing revealed that the absorbed energy by low heat input specimen (welded at high speed) was greater than that of high heat input (welded at low speed) because of low porosity and the formation of equiaxed grains which induce better impact toughness. Cryogenic (-196 C) impact testing was also performed and the results corroborate that impact properties under the cryogenic environment revealed no appreciable change after welding at designated heat input. Finally, Macro and micro fractured surfaces of tensile and impact specimens were analyzed using Stereo and Scanning Electron Microscopy (SEM), which have supported the experimental findings.     

高温燃气与不同构型的再生冷却面板对流传热的数值模拟

对高温燃气与带有平行冷却通道的再生冷却面板之间的三维耦合传热开展了数值研究,其中冷却通道内冷却剂为超临界压力煤油,并结合理论分析探讨了冷却面板构型对耦合传热的影响。结果表明:随燃气侧壁厚以及冷却通道宽度和高度的增大,燃气侧壁面温度升高,热流密度降低。研究还发现:冷却通道不同壁面传递给煤油的热量占比几乎不随燃气侧壁厚变化,但随冷却通道宽度和高度的改变而变化。     

一起管道燃气火灾爆炸事故爆炸点形成原因探讨

通过对一起居民住宅管道燃气泄漏火灾爆炸事故现场破坏程度的勘查,分析了在管道燃气泄漏后,由于燃气化学组分和理化性质的不同,室内环境因素影响扩散条件的不同,不同浓度的爆炸性混合气体在不同的部位出现了不同的形成过程,从理论上论证了管道燃气的泄漏点不一定就是中心爆炸点的火灾现场现象。     

气体样品红外吸收系数测定方法研究

对气体样品红外光谱吸收系数的测定方法进行了探讨,包括气体样品的发生定量、浓度和吸收系数的测定与计算．对两类毒剂的模拟剂DMMP等样品的吸收系数进行了测定,并对测试结果进行了分析与讨论．     

Boltzmann 方程求解方法综述

本文论述了Ｂｏｌｔｚｍａｎｎ方程的求解方法，在分析了各类求解方法的优缺点之后指出目前Ｍｏｎｔｅ－Ｃａｒｌｏ直接模拟方法是解决稀薄气体动力学问题的最佳方法。     

逸出气体检测的程序升温气相色谱法

建立了一种利用程序升温气相色谱仪的逸出气体检测(EGD)系统,用于测量液薄膜、固薄膜、纤维,粉末等材料中微量的热挥发及(或)挥发性热分解组分。这类微量用常规热分析法(如热重法(TG)、微商热重(DTG)及差热分析(DTA)等)一般难以测出。用该法测量的GuSO_4·5H_2O粉末样品、端羟基聚丁二烯(HTPB)及邻苯二甲酸二丁酯(DBP)薄膜样品逸出气的EGD数据同TG-DTG-DTA联用技术所得结果作了比较。还用该系统检测了硼酸(槽浴)阳极氧化铝箔、碳纤维、碳化硅纤维的逸出气体。阐述了本法的优点及具体步骤。     

有限时间热力学研究的一些进展

介绍近年来在不可逆热机理论、回热式燃气轮机循环分析、类热机装置分析和广义热力学优化理论研究中的一些进展 ,并简要阐述其发展方向 .     

无铅汽油中烯烃、芳烃含量的分析

随着环境保护意识的加强,车用无铅汽油国家标准GB 17930-1999中对烯烃、芳烃含量提出了明确限值要求。相应分析方法是GB／T 11132-2002液体石油产品烃类测定法(荧光指示剂吸附法,FIA),该方法操作过程复杂,试验时间长,试验结果偏差大。为改进对汽油中烯烃、芳烃含量的测试方法,人们在这方面做了大量研究工作。对目前采用的快速、简便分析汽油中烯烃、芳烃含量的气相色谱和近红外光谱分析方法进行了评述。     

航天器推进系统气液路故障仿真

为了研究和分析航天器推进系统气液路故障的发展变化规律及对整个推进系统性能的影响,在某挤压式航天器推进系统仿真模型的基础上,分别采用Realizable k-ε湍流模型和一维可压缩流模型对气路泄漏和堵塞故障进行动态仿真,采用一维不可压瞬变管流模型与变流量系数模型对液路泄漏和堵塞故障进行仿真分析。仿真结果表明:推进系统增压气路堵塞和泄漏故障,会导致增压不足,使推进剂供应管路压强下降;推进剂供应管路堵塞故障和泄漏故障会导致混合比偏离设计值,使推进系统性能降低。两类故障都会引起推力不足,致使系统性能降低。两者的不同之处在于:堵塞故障下,故障组件上游压强高于额定工况,推进剂消耗低于额定工况;泄漏故障下,故障组件上游压强低于额定工况,推进剂消耗高于额定工况。     

大功率气体开关重复频率的理论分析

分析了影响气体开关重复频率的各因素,从理论上推导了开关耗能的恢复时间以及气体的冷却时间对重复频率的影响。提出了提高重复频率的方法。