ADB610钢焊接接头疲劳裂纹扩展机理分析

采用焊条电弧焊方法对ADB610钢进行焊接,对焊接接头进行了疲劳裂纹扩展试验和金相试验,从微观机理上分析三区域疲劳裂纹扩展差异。采用两步七点拟合法计算焊缝区、热影响区以及母材区在一系列相同裂纹长度下的对数裂纹扩展速率均值和方差,发现:总体上焊缝区裂纹扩展分散性最大,母材区的最小;焊缝区裂纹扩展最慢,母材区的最快;裂纹扩展末期,三区域裂纹扩展差异不大。对金相组织研究结果表明:焊缝和热影响区的金相组织差异稍大,母材区金相组织差异较小,而且焊缝区晶粒较细,热影响区有网状组织结构,热影响区和母材区晶粒较粗大。这导致疲劳裂纹扩展性能方面焊缝和热影响区的分散性较大,母材区和热影响区裂纹扩展抗力低于焊缝区,母材区的低于热影响区。     

高强度桥梁钢焊接接头疲劳裂纹扩展速率的研究

利用高频疲劳试验机对高强度桥梁钢的母材、热影响区和焊缝的疲劳裂纹扩展速率进行了测定,并结合疲劳扩展断口分析各部位疲劳裂纹扩展快慢的原因。结果表明,高强度桥梁钢焊接接头中焊缝裂纹扩展速率最低,抗疲劳裂纹扩展能力最高;母材疲劳裂纹扩展速率最高,抗疲劳裂纹扩展能力最差;热影响区介于二者之间。焊缝的疲劳断裂模式是以穿晶断裂为主,母材是以沿Z字形路径扩展的沿晶断裂为主,热影响区则介于两者之间。     

基于两步七点拟合ADB610钢焊接接头疲劳裂纹扩展

在应力比为0.1、恒幅加载载荷下,对低碳贝氏体ADB610钢手工电弧焊焊接接头母材区、热影响区和焊缝区采用CT(紧凑拉伸)试样进行疲劳裂纹扩展试验研究。采用两步七点递增多项式拟合方法计算疲劳裂纹扩展速率(da/dN),并计算应力强度因子范围(ΔK),分别将母材区、热影响区和焊缝区每个试样的(da/dN)和(ΔK)数据进行了回归拟合,得到了以Paris公式表达的ADB610钢母材区、热影响区、焊缝区(da/dN)与(ΔK)的关系式。并将这三区域中多个试样Paris公式中的参数取均值,得到三区域均值裂纹扩展速率表达式。结果表明,在裂纹扩展的初期和中期,母材区的裂纹扩展速率最快,焊缝区的裂纹扩展速率最慢;在裂纹扩展末期,三区域的裂纹扩展快慢相当。     

GH625和GH536变形高温合金焊接的疲劳裂纹扩展速率分析

测定GH625和GH536变形高温合金在室温下的疲劳裂纹扩展速率,分析合金疲劳裂纹扩展速率与断口特征以及微观组织的关系。结果表明:应力强度因子幅ΔK较小时GH625合金焊缝处的疲劳裂纹扩展速率小于母材,ΔK较大时焊缝处的疲劳裂纹扩展速率较快;在裂纹稳定扩展阶段,GH536合金热影响区的疲劳裂纹扩展速率大于母材;GH625和GH536合金母材断口裂纹扩展区可见明显的疲劳条带特征,而焊缝中心裂纹扩展区以类解理特征为主;GH625和GH536合金焊接部位的疲劳裂纹扩展速率的快慢受焊缝或热影响区内部的析出物影响较大。     

基于原位SEM的激光-MIG复合焊接7075-T6铝合金疲劳裂纹扩展行为

通过扫描电镜原位观察激光复合焊接头各区裂纹的扩展行为. 结果表明,焊缝各区组织的不同使得疲劳裂纹扩展行为发生明显改变,疲劳裂纹位于焊缝中心时,裂纹总体沿着垂直于载荷主轴的方向扩展;疲劳裂纹位于热影响区时,裂纹大致成"Z"字型路径进行扩展;疲劳裂纹在焊缝中心和热影响区扩展时都存在二次裂纹;疲劳裂纹在母材区扩展时,呈现出单一和典型的裂纹扩展模式. 此外,通过原位SEM观察获得不同循环周期下的裂纹扩展长度,进而推算得到7075-T6铝合金接头各区内疲劳裂纹扩展速率的Paris公式.     

6N01铝合金MIG焊接头疲劳裂纹扩展性能研究

研究了6N01铝合金MIG焊接头不同区域的疲劳裂纹扩展速率,对接头的宏观形貌、显微组织、显微硬度和疲劳断口进行了分析。结果表明,焊缝区为等轴树枝晶,接头热影响区主要由淬火区和过时效软化区组成。疲劳裂纹在焊缝中的扩展速率最高;热影响区内,应力值范围较低时,疲劳裂纹扩展速率低于母材,随着应力值范围的增加,其扩展速率高于母材。疲劳断口分析表明,裂纹在焊缝中以不规则和粗糙的脆性疲劳条纹形式扩展,而在热影响区则以塑性的疲劳条纹扩展,扩展抗力较高。     

E36海洋平台用钢焊接接头疲劳裂纹扩展行为研究

针对海洋平台用钢E36-Z35钢的焊接特点,开发了一种药芯焊丝焊接工艺,并对焊接接头的母材、焊缝、热影响区和熔合线进行了疲劳裂纹扩展速率试验.结果表明:由于焊材及工艺选择合理,焊缝、热影响区及熔合线处的疲劳裂纹扩展速率低于母材.     

考虑焊缝和母材不同材料特性的焊接平板疲劳裂纹扩展行为模拟

为准确描述焊接结构的疲劳裂纹扩展行为，基于Abaqus、Zencrack及相应子程序建立了考虑材料不连续的疲劳裂纹扩展模拟方法.对于初始埋藏裂纹位于焊缝区的平板焊接结构，考虑焊缝和母材不同强度匹配，进行疲劳裂纹扩展模拟，研究了不同强度匹配对焊接结构疲劳裂纹扩展寿命和扩展特性的影响.研究结果表明，当裂纹前缘由焊缝跨越至母材区域时，焊缝和母材区域的应力强度因子计算结果出现明显变化，并随着裂纹尺寸的逐渐加大，两者差异越大.随着焊缝材料裂纹扩展参数逐渐增大，母材区域的裂纹扩展相对速率逐渐变慢，裂纹形状逐渐由圆形向扁平状椭圆形过渡；相反地，母材区域的裂纹扩展相对速率逐渐变快，裂纹形状逐渐由圆形向椭圆形过渡.文中的模拟方法有望为准确预测焊接结构的跨材料裂纹扩展行为提供有效途径.     

TC4钛合金微束等离子弧焊接接头疲劳性能研究

运用微束等离子弧焊接方法对TC4钛合金薄板进行堆焊,通过测试母材及焊接接头在振动载荷下的疲劳裂纹扩展速率发现,焊接接头的抗裂纹扩展能力比母材强。观察并分析母材及焊接接头的金相组织及疲劳断口可知,焊缝区的网篮组织中存在许多细长α′针状马氏体,会阻碍裂纹的扩展,提高焊缝抗裂纹扩展能力;热影响区组织中的α′针状马氏体比焊缝区数量更多,形态更加短小,是其拥有比焊缝区更好的抗裂纹扩展性能的原因。     

A6N01-T5合金FSW和MIG焊接头疲劳裂纹扩展行为的对比

研究了6N01-T5铝合金搅拌摩擦焊(FSW)和氩弧焊(MIG)接头不同部位的疲劳裂纹扩展性能, 并对疲劳断口和接头组织进行了分析. 结果表明,对于FSW和MIG焊接头, 其裂纹扩展速率从高到低的部位依次为焊缝(核)区、热影响区和母材. 裂纹在FSW和MIG焊接头相同区域的扩展速率无明显差别, 然而裂纹在FSW接头细晶组织中开始扩展所需的门槛值ΔK要比对应的MIG焊接头高, 总体上其裂纹在FSW焊核区的抗疲劳裂纹扩展性能要优于对应的MIG焊缝区. 裂纹在FSW和MIG焊接头焊核(缝)区扩展的疲劳断口表现为脆性断裂, 而在热影响区则以规则和光滑的疲劳条纹形式扩展.     

Fatigue properties of ferrite/bainite dual-phase X80 pipeline steel welded joints

Fatigue properties are important parameters for the safety design and security evaluation of pipelines. In this work, fatigue life and fatigue crack propagation of full-thickness X80 pipeline steel joints compared with the base metal (BM) was investigated. Full-thickness BM specimens showed superior fatigue life compared with that of welded joints. The fatigue crack initiation of full-thickness X80 welded joint specimens occurred at the outside weld toe and then grew inward until a fracture was formed. During fatigue crack growth in the heat-affected zone (HAZ), crack growth rate linearly increased with increased ΔK in each HAZ subregion. However, the change rate of fatigue crack growth rate (da/dN) differed among HAZ subregions. This difference was related to the variation in crack path and fracture mode because of the possible microstructural sensitivity of fatigue crack propagation behaviour.     

A7N01P-T4铝合金激光-MIG复合焊接头微区性能

以高速列车用14 mm A7N01P-T4铝合金为研究对象,对其激光-MIG复合焊接头的焊缝（WM）、热影响区（HAZ）两个微区以及母材（BM）进行微区拉伸、断裂韧度等性能测试,并结合金相、断口扫描等分析该种接头各区及母材的性能差异.结果表明,A7N01P-T4铝合金母材的抗拉强度最高,其次为激光-MIG复合焊接头热影响区,焊缝最差;接头热影响区的断裂韧度J_m（14）值最高,约为119.580 kJ/mm2,其抵抗裂纹扩展的能力是3个区域中最强的;Shapiro-Wilk正态性检验表明,A7N01P-T4铝合金激光-MIG复合焊接头的断裂韧度测试结果具有较高的可靠性.     

Effect of notch location on fatigue crack growth behavior of strength-mismatched high-strength low-alloy steel weldments

Welding of high-strength low-alloy (HSLA) steels involves the use of low-strength, equal-strength, and high-strength filler materials (electrodes) compared with the parent material, depending on the application of the welded structures and the availability of filler material. In the present investigation, the fatigue crack growth behavior of weld metal (WM) and the heat-affected zone (HAZ) of undermatched (UM), equally matched (EM), and overmatched (OM) joints has been studied. The base material used in this investigation is HSLA-80 steel of weldable grade. Shielded metal arc welding (SMAW) has been used to fabricate the butt joints. A center-cracked tension (CCT) specimen has been used to evaluate the fatigue crack growth behavior of welded joints, utilizing a servo-hydraulic-controlled fatigue-testing machine at constant amplitude loading (R=0). The effect of notch location on the fatigue crack growth behavior of strength mismatched HSLA steel weldments also has been analyzed.     

16Mn钢埋弧焊接头疲劳裂纹扩展速率的研究

对16Mn钢双面埋弧焊CT试样的焊缝、热影响区、母材及垂直焊缝方向的疲劳裂纹扩展速率进行了研究。结果表明,焊接接头的不同部位疲劳裂纹扩展速率不同,平均应力、焊接残余应力、金相组织对疲劳裂纹的扩展速率都有一定的影响。     

焊接接头热影响区裂纹启裂行为的探讨

针对结构完整性评定中焊接接头难以评估问题，文中通过非匹配焊接接头“三材料”结构模型，建立热影响区中心裂纹启裂临界应力的失效评定图预测方法. 基于有限元ABAQUS软件分析，研究焊接接头热影响区裂纹启裂. 结果表明，高匹配焊缝促进热影响区裂纹启裂，软化的热影响区促进热影响区裂纹启裂，低匹配焊接接头，热影响区软化时，增加热影响区宽度促进热影响区裂纹启裂；热影响区硬化时，减小热影响区宽度促进热影响区裂纹启裂. 高匹配焊接接头，热影响区无论软化、硬化，增加热影响区宽度均促进热影响区裂纹启裂.     

Study on microtexture of laser welded 5A90 aluminium–lithium alloys using electron backscattered diffraction

Abstract

The microtexture features of Nd:YAG laser welded joints in 5A90 aluminium–lithium (Al–Li) alloys were examined using electron back scattered diffraction (EBSD). Microtexture was determined by means of the grain orientation image maps (OIM), pole figures (PF), misorientation angles and orientation distribution function (ODF) of the weld metal (WM), heat affected zone (HAZ) and unaffected base metal (BM) of the welded joint. The results show that there is a change of microtexture in the WM and HAZ of the welded joint in terms of the component and intensity of the texture. The HAZ of the welded joint inherits the texture characteristics of the BM, whereas the welding heat input has an important influence on the component C {112}<111>. The WM of the welded joint is composed of predominantly equiaxed grains with a random microtexture.     

X80管线钢焊接热模拟热影响区疲劳裂纹扩展行为的分析及预测

通过焊接热模拟方法对X80双相管线钢不同焊接热影响区疲劳裂纹扩展行为进行了研究,并分析实际焊接试样与焊接热模拟试样的热影响区疲劳裂纹扩展行为的差异,讨论了焊接热模拟技术应用于疲劳裂纹扩展寿命预测的可行性。结果表明,当裂纹在粗晶热影响区(CGHAZ)和临界热影响区(ICHAZ)上扩展时,由实际焊接试样与焊接热模拟试样热影响区所测得的疲劳裂纹扩展速率曲线(da/dN-DK曲线)存在明显差异,其原因与显微组织变化引起的裂纹扩展阻力大小不同有关。因此,建议采用实际焊接试样完整的热影响区所测得的da/dN-DK曲线来评估疲劳裂纹扩展寿命。     

Integrated fracture mechanics approach to analyse fatigue behaviour of welded joints

Abstract

Current fracture mechanics methods for fatigue assessment, including those that consider thresholds for crack propagation, are based on long crack behaviour. The present work is concerned with an attempt to predict the fatigue strength of welded joints using a fracture mechanics approach that takes into account the fatigue behaviour of short cracks. The methodology estimates the fatigue crack propagation rate as a function of the difference between the applied driving force and the material threshold for crack propagation, which is a function of crack length. The fatigue strength of butt welded specimens stressed transversely was analysed. Experimental results from the literature were used for comparison. Estimations are obtained by using only the fatigue limit and the fatigue propagation threshold for long cracks, and the applied stress distribution along the crack path obtained from simple finite element models. The influence of plate thickness, initial crack length, and reinforcement angle on fatigue strength of butt welded joints was analysed. Results show good agreement with experimental trends.     

Influence of HAZ cracks on fatigue resistance of resistance spot welded joints made of advanced high strength steels

Abstract

A method is reported with which heat affected zone (HAZ) cracks in a specific region of spot welded joints, made of advanced high strength steels, could be realised. The influence of HAZ cracks on the fatigue behaviour, which is the focus of the contribution, was studied by evaluating the stiffness characteristics as a function of the number of cycles N in comparison with crack-free specimens, i.e. by analysing HAZ and fatigue cracks on the specimen surface and the surface of fatigue fractures containing beach marks. It was found that the fatigue cracks are not initiated at the HAZ cracks. The number of cycles to failure N_f is not significantly reduced for specimens with HAZ cracks. Overall, the examinations did not reveal any influence of HAZ cracks on the fatigue strength of resistance spot welded joints.