马氏体不锈钢大拘束度结构焊接裂纹及防止措施

马氏体不锈钢常温组织为硬脆的马氏体组织,它的导热性较碳钢差,焊接残余应力较大,使得在焊后冷却时容易产生裂纹。从力学、金属学两方面分析了产生裂纹的原因,并通过更改焊接材料、优化焊接参数等解决了约束型马氏体不锈钢产生焊接裂纹的问题。     

Statistical aspects of fatigue crack growth life of base metal,weld metal and heat affected zone in FSWed 7075-T651 aluminum alloy

The statistical aspects of fatigue crack growth life of base metal (BM), weld metal (WM) and heat affected zone (HAZ) in friction stir welded (FSWed) 7075-T651 aluminum alloy has been studied by Weibull statistical analysis. The fatigue crack growth tests were performed at room temperature on ASTM standard CT specimens under three different constant stress intensity factor range controls. The main objective of this paper is to investigate the effects of statistical aspects of fatigue crack growth life on stress intensity factor ranges and material properties, namely BM, WM and HAZ specimens. In this work, the Weibull distribution was employed to estimate the statistical aspects of fatigue crack growth life. The shape parameter of Weibull distribution for fatigue crack growth life was significantly affected by material properties and the stress intensity factor range. The scale parameter of WM specimen exhibited the lowest value at all stress intensity factor ranges.     

16Mn钢焊接件疲劳裂纹扩展的微观特征研究

研究了在循环载荷作用下,16Mn钢焊接件疲劳裂纹的扩展情况.通过光学显微镜观察了裂纹扩展的微观特征,发现了裂纹在焊接结构不同部位的扩展路径方式并分析了显微组织对裂纹扩展的影响.裂纹在母材处为穿晶扩展,在热影响区和焊缝金属中的扩展为穿晶和沿晶混合型.     

LZ92镁锂合金激光焊接接头的显微组织与力学性能

采用CO2激光焊接厚度为2 mm的LZ92镁锂合金板,研究了焊接接头的显微组织、物相组成、显微硬度与拉伸性能.结果表明:LZ92镁锂合金焊接接头成形良好,焊缝中无明显气孔、裂纹等缺陷;母材与焊缝的物相组成相同,由α相、β相和中间相Mg7Zn3组成;母材由等轴状β相和枝晶状与颗粒状α相组成,热影响区由粗大的β相和少量细小...     

Experimental and numerical study of the temperature field during creep feed grinding

In this study, commercially pure titanium sheets (American Society for Testing and Materials grade?2) were welded by resistance spot welding at various welding parameters. The welded joints were subjected to tensile-shearing tests in order to determine the strength values. In addition, the hardness and microstructural examinations were carried out in order to examine the influence of welding parameters on the welded joints. The experimental results showed that increasing electrode force, welding current and welding time increased the tensile-shearing strength of the welded specimens. Hardness measurement results indicated that welding nugget had the highest hardness and this was followed by the heat-affected zone and the base metal. Microstructural examinations showed the growth of the weld nugget grains with increasing heat input. Besides, due to plastic deformation during the welding process, twins were formed and at the same time twins increased with increasing electrode force, welding current and welding time.     

Influences of post weld heat treatment on fatigue crack growth behavior of TIG welding of 6013 T4 aluminum alloy joint (Part 1. Fatigue crack growth across the weld metal)

The present study evaluates the influences of PWHT on FCG behavior and tensile properties of TIG butt welded Al 6013-T4 sheets. Crack propagation tests were carried out on compact tension (CT) specimens. The T82 heat treatment was varied in three artificial aging times (soaking) of 6, 18 and 24 hours. The results of T82 heat treatment with artificial aging variations were tested for their fatigue crack growth rates at the main metal zone, the heat-affected zone (HAZ), and the welded metal zone. It has been observed that the various agings in heat treatment T82 are sensitive to the mechanical properties (fatigue crack growth rate test, tensile test). The results show that PWHT-T82 for 18 hours aging is the highest fatigue resistance, while the aging 18 hours provided the highest tensile test result.     

低碳钢焊缝金属强度组配对焊接残余应力分布的影响规律

采用热弹塑性有限元方法,对平板对接接头中焊缝金属强度组配对焊接残余应力分布的影响进行了研究。结果表明,对于高组配接头,纵向残余应力的峰值接近焊缝金属的屈服极限,出现在焊缝中心。对于低组配接头,纵向残余应力的峰值接近母材的屈服极限,并发生在焊缝附近。随着对含有残余应力的接头施加外载,焊缝金属强度组配对纵向应力分布的影响依然存在,但残余应力的影响在减小。对承受外载的焊接接头,逐步卸除外载后,焊缝横截面     

核电汽轮机转子焊缝金属原奥氏体尺寸对疲劳裂纹稳定扩展区和近门槛区临界点的影响规律研究

研究了25Cr2Ni2MoV核电汽轮机低压焊接转子模拟件埋弧焊焊缝金属疲劳裂纹扩展速率和应力强度因子幅关系曲线,发现了不同试样疲劳裂纹稳定扩展区和近门槛区临界点对应的应力强度因子幅不同的现象。使用逆推法在金相中确定了临界点位置,并进一步研究了临界点处的原奥氏体晶粒尺寸,发现其与裂纹尖端单向塑性区最大尺寸有较好的对应关系。而模拟件多层多道焊焊缝金属组织不均匀性带来的临界点位置的差异是造成门槛值测试结果分散的重要原因之一。     

用弹塑性有限元法对焊接接头裂尖场J积分的研究

采用平面应力弹塑性有限元法研究了中心裂纹板焊接接头裂尖场J积分参量及其应用的可行性，数值分析采用MARC软件的二维弹塑性分析模型，探讨了不同强度匹配（高，等，低匹配）的焊接接头试样在加载过程中裂尖场J积分的变化情况，计算结果表明，靠近焊接接头裂纹尖端的J积分回路明显的路径相关性，而远离裂尖的J积分回路表现出路径无关性，焊接接头强度匹配因子M对裂纹尖端的J积分值有很大的影响，对应于每一个载荷P／P0，J积分的值随M的增大而减小，特别是当P／P0＞1．0时这种情况更明显。     

Effects of weld cross-section profiles and microstructure on properties of pulsed Nd:YAG laser welding of Ti6Al4V sheet

In this study, the influence of weld cross-sectional profiles and microstructure, under different welding conditions, was investigated on the mechanical properties of pulsed Nd:YAG laser-welded joint of Ti6A14V alloy. The V- and H-shaped weld cross-section profiles were obtained under low and high heat input, respectively. The microstructure in the fusion zone (FZ) of V- and H-shaped welded joint consisted of a fine acicular martensitic α′ solidification structure within the prior-β grains, responsible for the maximum hardness in the FZ. Tensile tests revealed that the V-shaped welded joint fractured at the near heat-affected zone (HAZ)/base metal (BM) interface, but the H-shaped welded joint fractured in the BM. Furthermore, the tensile strength of the V-shaped welded joint was lower than that of the H-shaped welded joint. This was attributed to the fact that the heterogeneity of strain distribution at the interface of HAZ and BM of the V-shaped welded joint was greater than that of the H-shaped welded joint during tensile process.     

高压气瓶母材、焊缝和热影响区的疲劳裂纹扩展速率实验研究

通过高压气瓶母材、焊缝和热影响区的疲劳裂纹扩展实验 ,研究了高压气瓶的断裂薄弱环节以及薄弱环节的疲劳裂纹扩展速率 ,并用蒙特卡罗法模拟疲劳裂纹扩展速率的分散性 ,给出了疲劳裂纹扩展速率及其分布区间。     

基于ANSYS的裂纹尖端应力强度因子研究

通过ANSYS建立焊接接头三区域模型。分别定义了不同的力学性能参数来模拟焊接接头各个区域力学性能的不均匀性,分别计算裂纹处在焊接接头各个区域的应力强度因子。计算结果表明：焊缝应力强度因子最低,母材次之,热影响区最高。说明材料的屈服强度与裂纹尖端的应力强度因子有密切的关系。屈服强度越高,应力强度因子越低。     

力学性能不均匀性对焊接接头三点弯曲试样塑性区发展规律的影响

利用弹塑性有限元方法对焊接接头试样在三点弯曲试验中塑性区的发展情况进行了计算。分析了不同的裂纹深度、强度组配，焊缝宽度以及不同位置裂纹的焊接接头试样对塑性区形状发展的影响规律。分析结果显示，不同强度组配和几何特征的焊接接头试样对裂纹尖端塑性区的发展规律有较大的影响，由于裂纹尖端拘束程度的不同会造成塑性区的形状和尺寸的改变，因此在做焊接接头试样三点弯曲试验时，可能会得出与均质材料试样不同的驱动力曲线     

基于汽车驱动桥壳再制造的堆焊可靠性研究

为了研究汽车驱动桥壳表面损伤后的堆焊修复层能否满足再制造的要求,选用H13CrMoA和ER50-6焊丝并采用亚激光瞬间熔工艺,在汽车驱动桥壳片表面制备不同厚度的堆焊层。利用金属磁记忆检测仪和扫描电镜分析堆焊试样的应力分布和断面组织特征,同时测试堆焊试样的硬度并进行渗透、磁粉和X射线三种无损检测。结果表明：ER50-6堆焊试样的堆焊层与母材硬度相近,母材热影响区未发生局部软化,堆焊层与母材结合良好,不存在焊接缺陷和应力集中区,应力分布不均匀程度低于H13CrMoA堆焊试样。
     

点焊搭接接头中的应力分布及接头疲劳行为研究

基于实际点焊接头硬度分布的分析,建立了包括熔核,热影响区和母材的单点点焊搭接接头计算模型。用三维弹塑性有限元分析方法,全面分析了点焊搭接头的应力分布情况。分析结果表明：接头搭接区内表面上焊点边缘处的应力集中是接头高周疲劳裂纹起裂和扩展的决定因素。焊点边缘附近区域中的存在的高应力,导致高周疲劳裂纹由强度较低的母材起裂并扩展。     

X80管线钢焊接接头TEM观察下的断裂行为对比

对X80管线钢焊接接头3个区域的试样在透射电子显微镜（TEM）下进行原位拉伸试验,通过观察各个区域裂纹的萌生与扩展过程,对其微观断裂行为进行了研究和分析。结果表明：母材区中,裂纹萌生扩展主要以多裂纹起裂为主,表现为沿晶扩展的断裂形式,最后造成在切应力作用下的剪切脆性断裂;热影响区内,主裂纹首先在切应力作用下以45°方向起裂,整个扩展过程是主裂纹钝化、位错发射、主裂纹前方无位错区形成、微裂纹形核、主裂纹与微裂纹连接扩展这一多尺度过程不断重复的过程,最后导致准解理穿晶断裂;焊缝区中,从主裂纹分支出多条裂纹,裂纹均以与拉伸轴成45°的方向起裂,表现为沿晶与穿晶混合的断裂模式,最后造成穿晶脆性解理断裂。     

Characterisation of joint properties through spatial mapping of cracks in fatigue specimens,extracted from the linearly friction welded steel coupon

Linear friction welding (LFW) is widely used for the fabrication of high-value components in the aero-industry. The versatility of use and high integrity of joints produced by LFW, suggest that this technology could contribute greatly to sustainable engineering of the future. For example, in near-net-shape manufacturing, LFW is predicted to offer a substantial reduction in material waste and processing time, in addition to offering the capability of bonding material pairs currently difficult to fusion weld. LFW of steel components is seldom researched in published literature, with little information available on fatigue strength and fracture behaviour of such joints. This may hamper the confidence needed to popularise LFW in wider industry. Thusly, authors conducted a discovery-oriented fatigue study, followed by metallography and micro-hardness tests, conducted on a 100Cr steel LFW coupon and corresponding batch of parent material. The weld coupon was dissected into a set of fatigue specimens, to allow mapping of the joint's internal properties through individual fatigue estimates and fracture morphology of each specimen in the set. A prototype fatigue machine was constructed, designed to deliver independent displacement and force controlled bending or torsional loadings, representing complex real-world conditions more accurately than common, uniaxial tests. The hour-glass shape of fatigue specimens allowed for targeting strictly the weld region, inducing fracture at the weakest material section, which was found to lay far outside the immediate contact interface. Referencing distances from fracture points to the theoretical weld interface plane in each fatigue trial, resulted in discovery of a macroscopic pattern. Interpolated to a crack initiation plane, this pattern is proposed to reflect the heat-affected zone, across the greater LFW coupon. Authors also studied crack paths and suggest a link between fracture direction, residual stresses in joint and angular orientation of the crack initiation plane in respect to the theoretical weld interface.     

压力容器焊接基本现象模拟与仿真研究现状及展望

综述了近年来国内外在焊接基本现象模拟与仿真方面的研究现状及发展趋势,对焊接过程中的熔池流场、焊接温度场与力学场、焊接变形和残余应力、氢扩散分析、异种钢焊接接头碳迁移、特种焊接过程、焊接接头微观组织、焊接热影响区晶粒长大过程等的仿真模拟,以及焊接模拟计算机软件等进行了较全面的介绍和分析。     

裂纹位置对焊接接头断裂参量的影响

结合焊接结构的工程安全评定,针对焊接接头熔合线上容易出现缺陷的问题,本文利用有限元计算方法,编写了断裂参量J积分计算的有限元程序,并对裂纹位置不同时的焊接接头进行了有限元计算。结果表明,无论是平面应变还是平面应力条件下,焊接接头J积分值都与全母材和全焊缝材料不同;与此同时,裂纹位于熔合线上和裂纹处于焊缝中,焊接接头的J积分值也是有所差异的,并且,这种差异在平面应变状态下表现得更加明显。在实际工作中,对焊接接头的断裂参量的计算必须考虑裂纹所处位置的影响。     

蒸汽发生器管子管板内角环焊残余应力数值模拟研究

应用ANSYS有限元软件,对核电蒸汽发生器管子管板内角环焊残余应力进行数值模拟研究。在研究中,建立三维有限元模型,基于ANSYS参数化设计语言实现带状温度热源的逐步加载和计算,得到焊接接头处残余应力分布规律,分析相邻管子先后焊接对焊接区残余应力的影响,并模拟出不同热处理温度下的残余应力。研究结果表明,管子管板焊接最大径向和环向残余应力出现在焊缝熔合区,最大轴向残余应力出现在管子内表面热影响区。相邻管子先后进行焊接时,后焊管子温度场的作用会使先焊管子焊接区域的残余应力减小。当热处理温度为600℃时,可以有效减小焊接区的残余应力。