热焊工艺对2.25Cr1Mo钢焊接构件疲劳寿命影响

对2.25Cr1Mo试板分别在室温下进行焊接焊后自然冷却以及加热到600,700,800℃进行焊接焊后保温缓冷(即热焊工艺),采用小盲孔法测量焊接残余应力,以此为基础分析了热焊工艺对其疲劳寿命的影响。试验结果表明,采用热焊工艺进行焊接可以有效地提高焊接试件的疲劳寿命,并且加热温度越高,焊接试件的疲劳寿命越长。     

15MnVNR钢焊后热处理过程中应力松驰行为的热模拟研究

本文是在GLEEBLE—1500焊接热模拟试验机上,对15MnVNR压力容器钢接头热影响区的过热区在不同焊后热处理工艺条件下的应力松驰行为进行了研究。研究结果表明,焊后热处理过程中,焊接残余应力的消除效果主要决定于焊后处理工艺温度,而保温时间在超过30分钟后残余应力已趋稳定。试样经580～650℃焊后热处理,保温1小时,可消除焊接残余应力75～85％。     

再结晶退火工艺在硫化机上横梁焊后去应力上的应用及其效果初探

采用再结晶退火的热处理工艺方法消除大型重负荷焊件──１３１０（Ⅱ）型双模轮胎定型硫化机上焊梁的焊接应力，并用钻孔法测量再结晶退火前、后残余应力值的大小，摸清再结晶退火对该工件焊接应力消除的程度。     

大型储罐角焊缝焊趾表面裂纹应力强度因子数值计算

针对大型储罐典型失效模式——角焊缝开裂,利用ANSYS建立有限元模型求得角焊缝焊趾附近精确应力场;采用1/4节点奇异单元法和混合网格扩展法建立角焊缝焊趾表面半椭圆裂纹模型并求解应力强度因子;讨论了裂纹深度半长比a/c、裂纹深度板厚比a/t、焊脚尺寸板厚比Lw/t和焊趾角θ对应力强度因子数值分布的影响。计算结果表明:角焊缝焊趾表面裂纹应力强度因子沿裂纹前沿呈U形分布,在表面点取得最大;随着裂纹深度a的增加,表面点应力强度因子有增大趋势,而最深点的焊接放大效应则逐渐减小。     

对几种压力容器热处理的考虑

奥氏体不锈钢制压力容器是否需要焊后热处理 焊后热处理是利用金属材料在高温下屈服极限的降低,使应力高的地方产生塑性流变,从而达到消除焊接残余应力的目的。同时可以改善焊接接头及热影响区的塑性和韧性,提高抗应力腐蚀的能力。这种消除应力的方法在具有体心立方晶体结构的碳素钢、低合金钢制压力容器中被广泛采用。     

焊接电流对Q235钢焊接接头残余应力的影响

对12 mm厚Q235试板进行手工电弧焊试验研究。采用3种不同焊接电流参数对3组试板进行焊接,以研究不同焊接电流下焊接接头所产生的残余应力。3组试板均采用双面焊。分别对正面填充焊和盖面层焊采用155 A、165 A、175 A三种焊接电流。焊完后采用残余应力测试方法对焊接接头进行分析。研究结果表明,Q235钢在175 A电流下焊接接头残余应力比165 A电流下大,155 A电流下最小。随着焊接电流的增大,焊接残余应力升高。     

爆炸焊接钛/钢复合板残余应力分布状态研究

为研究爆炸焊接钛/钢复合板残余应力的分布状态以及热处理对钛/钢复合板应力状态的影响,本文采用爆炸焊接的方法实验制备了复层为5.5mm的钛/钢复合板试板,并使用钻孔法测量了爆炸态试板和热处理态试板(热处理制度为:随炉升温至540℃,保温2.5h,随炉冷却)复层残余应力的分布,实验表明:延爆轰传播方向钛/钢复合板残余应力无明显的分布规律;热处理对钛/钢复合板的残余应力有较大的影响,热处理后钛/钢复合板钛复层残余应力由爆炸态的拉应力状态转变为压应力状态,这有利于提高钛/钢复合板耐蚀性能。     

消除压力容器焊接残余应力技术探讨

焊后热处理是目前压力容器行业中被各方都能接受的消除焊接残余应力的方法,针对这一技术对奥氏体不锈钢制压力容器是否需要焊后热处理、爆炸复合材料的热处理、其他方式代替设备的整体热处理进行了阐述。     

加氢装置碳钢管道焊后热处理分析

加氢装置中,为防止焊接冷裂纹的产生和应力腐蚀开裂,需对碳钢管道进行焊后热处理以消除焊接残余应力。其中,应力腐蚀开裂仅在特定的腐蚀环境发生,焊后热处理是避免应力腐蚀开裂的主要措施之一。本文介绍了国内现行石化行业标准、国家标准和国外ASME标准等标准规范对碳钢管道进行焊后热处理的要求。加氢装置中应力腐蚀开裂主要表现为湿硫化氢应力腐蚀开裂,对于存在湿硫化氢应力腐蚀开裂的管道,应全部进行焊后热处理。同时,文中明确指出了加氢装置中应进行焊后热处理的碳钢管道。     

钻孔应力释放法应用于筒体校形后残余应力的测量

通过对产生较大椭圆度筒体的校形,运用钻孔应力释放法测量筒体中残余应力的大小,证明了筒节校形前后残余应力变化不大,附加残余应力只是筒体母材屈服强度的0.45%,从而确定筒体校形后不需要重新进行消应力的热处理。     

Laser transmission welding of PMMA to alumina ceramic

In this paper, a method of laser transmission welding on ceramic surface after pulse laser microtexture pretreatment was proposed to address the problem that welding ceramics with high transparency polymers is demanded but difficult to be performed. In this method, the polymer flows into the micro-texture of the blind hole on the surface to form mechanical riveting to enhance the welding strength. The formation characteristics and welding mechanism of PMMA welded joint with micro-texture alumina ceramics were studied experimentally and simulatively. The effects of blind hole microtexture size, continuous laser power and continuous laser scanning rate on solution flow and welding strength were studied. The results showed that the air bubbles formed in the welded seam by entering the micro-texture blind hole and trapped air in the blind hole were the key factors affecting the strength of the joint. A 3D finite element model of the transient temperature field and flow field of polymer during laser welding was established. The simulation results showed that the polymer on the left side of the blind hole melted first when heated and inflowed along the wall due to the effects of self-gravity and buoyancy caused by temperature differences. The gas expanded and extruded upward to the left, forming bubbles in the polymer melt pool and pushing the polymer melt into the blind pore microtexture. Finally, a complete molten pool was formed. The flow of polymer melt, the formation of bubbles and the formation of joint were revealed.     

Residual stresses in the quasi‐simultaneous laser transmission welding of amorphous thermoplastics

Laser transmission welding is frequently being used increasingly for joining complex, assembly‐oriented components, thanks to its small heat affected zone. As a result of the cooling processes, residual stresses can develop inside the components, potentially leading to stress cracking and premature component failure. One subgoal of process design should therefore be to reduce the level of residual stresses as far as possible when laser welding is employed. This work looks into experimental testing for residual stresses, as a factor for the weld parameters in quasi‐simultaneous laser transmission welding, with the objective of determining the optimum welding parameters. The ARAMIS optical measuring system for deformation analysis was used to this end, in conjunction with a modified hole‐drilling method. POLYM. ENG. SCI., 50:1520–1526, 2010. © 2010 Society of Plastics Engineers     

Micro-electrochemical characterization and Mott–Schottky analysis of corrosion of welded X70 pipeline steel in carbonate/bicarbonate solution

The electrochemical corrosion behavior of welded X70 pipeline steel in a bicarbonate/carbonate solution was studied by scanning vibrating electrode technique and localized electrochemical impedance spectroscopy as well as Mott–Schottky analysis. The effect of applied stress on corrosion of various zones in welded steel specimen was investigated. Results demonstrated that passivity can be established on various zones, i.e., weld metal, heat-affected zone (HAZ) and base steel, of welded X70 steel. There is a higher passive current density for the passivated HAZ than that for weld metal and base steel. Applied stress enhances the anodic dissolution of steel, as indicated by the decreasing charge-transfer resistance and increasing dissolution current density of steel with the increase of stress. A maximum current density is observed in HAZ at all stressing levels. With the positive shift of anodic potential, the stability of passive film is enhanced, and the dissolution current density decreases. When the applied potential approaches the water oxidation potential, the current density increased significantly again due to the oxidation of water. The passive film formed is an n-type semiconductor. There are higher donor density and thinner space-charge layer in passive film formed at HAZ than those formed on weld metal and base steel. Moreover, the donor densities in all zones increased significantly with the applied stresses. The metallurgical transformations and formation of low temperature hardening phase transformation products during welding result in the enhanced electrochemical activity in HAZ.     

压力容器筒体与平封头多级焊缝残余应力数值模拟

采用有限元软件ANSYS中生死单元技术对压力容器筒体与平封头单面焊焊接过程进行数值模拟,得出焊缝焊接残余应力、温度场及位移场的分布情况。经过分析可以得出：在焊缝区及熔合区温度极高;远离焊缝,温度峰值急剧下降。在熔舍区焊接残余应力达最大值;焊根处残余应力较小;在热影响区,沿焊缝方向多为拉应力,垂直焊缝方向多为压应力。     

Thermal Fracture Resistance of Ceramic Coatings Applied to Metal: I, Elastic Deformation

A study was made of the resistance to thermal fracture of four ceramic coatings of the cobalt-bearing ground-coat type applied to enameling-grade iron specimens. The study was made of coated-metal systems in the unsteady state, symmetrically cooled, and in the absence of viscous or plastic flow. Determinations were made of the elastic characteristics of the coating-metal composites, the effective coefficient of linear expansion, the temperature at which the coating and base metal were at dimensional equilibrium, and the temperature differential sufficient to induce coating fracture when water quenched. Coating-metal thickness ratios were correlated with the maximum specimen temperature withstood in water quenching without coating fracture. Studies indicated that ceramic coatings, after receiving a given thermal treatment, fracture when subjected to a thermal shock by a critical temperature differential. When no residual coating stress is present, thermal shock resistance is inversely related to the thermal expansion characteristics of the coating. The critical stress at which coating fracture occurs may be expressed as the sum of thermal and residual stresses developed in annealed systems in which viscous or plastic flow does not occur. Residual compressive stress in a coating is a major factor in improved thermal shock resistance. Increased thermal shock resistance is gained by decreased coating thickness.     

Effects of stress concentration and residual stress on vibration fatigue behavior of socket weld

The vibration fatigue behavior in socket weld of 304L stainless steel was investigated using experimental and numerical. The vibration fatigue test results indicate that original socket weld at a higher stress tend to occur toe failures while for the case of lower stress failures tend to originate at the root. In addition, the socket welded with groove can improve the fatigue property of weld root, but it has a bad influence on the weld toe. From the simulation results, the groove can decrease the stress concentration factor of weld root, and improve the fatigue property of root; whereas the groove can also increase the tensile residual stress of toe, resulting in having a detrimental effect on fatigue property of toe.     

粒子加速器筒体开方孔有限元分析

某粒子加速器筒体上开一方形孔,与方形法兰锻件焊接.常规设计方法没有对容器重要区域的应力进行严格而详细的应力分析计算,从而也就无法对由不同载荷引起的、对容器失效有不同影响的应力加以不同的限制.运用有限元分析软件ANSYS对某粒子加速器开方孔的应力进行模拟分析,采用JB 4732-1995对简体与方形锻件法兰焊接部分进行强度校核,结果表明,强度满足要求.     

Fire structural modelling and testing of welded aluminium plate

The structural response of welded aluminium in fire is computationally and experimentally analysed. A finite element (FE) model is developed to compute the deformation and failure of gas metal arc welded (GMAW) aluminium plate under combined loading and one‐sided unsteady‐state heating representative of fire. The FE model predicts the deformation of the weld, heat‐affected zone and parent plate based on the combined effects of elastic softening, plastic softening and creep. The effects of residual stresses in the weld and thermal expansion on the deformation response are also analysed. The numerical accuracy of the model is rigorously evaluated using a large amount of deformation and failure stress data obtained from fire structural tests performed with welded AA5083–AA5083, AA5083–AA6061 and AA6061–AA6061 plates. Good agreement is found between results computed with the FE model and experimental testing. The results reveal that GMAW welds do not reduce the structural performance of aluminium in fire unless the maximum temperature remains below the recrystallisation temperature. Copyright © 2014 John Wiley & Sons, Ltd.     

注塑工艺参数对制品残余应力和收缩的影响

注塑成型工艺参数对制品的最终残余应力和收缩有着直接的影响。基于线性黏弹性模型模拟计算了注塑成型过程中由温度和压力引起的残余应力和收缩。以无定型材料PS和ABS为例，系统地研究了不同成型工艺条件下平板制件的最终残余应力和收缩，并和实验结果进行对比验证。结果表明：在流动方向上无定型材料的收缩基本保持不变，残余应力沿壁厚分布的形状也基本相同，但流动末端处的应力值稍大于流动入口处；保压压力是影响制品收缩的关键因素，提高保压压力和注射温度可以降低制品的最终收缩，而模具温度对收缩的影响较小。     

Residual thermal stresses in injection molded products

Nonisothermal flow of a polymer melt in a cold mold cavity introduces stresses that are partly frozen-in during solidification. Flow-induced stresses cause anisotropy of mechanical, thermal, and optical properties, while the residual thermal stresses induce warpage and stress-cracking. In this study, the influence of the holding stage on the residual thermal stress distribution is investigated. Calculations with a linear viscoelastic constitutive law are compared with experimental results obtained with the layer removal method for specimens of polystyrene (PS) and acrylonitrile butadiene-styrene (ABS). In contrast to slabs cooled at ambient pressures, which show the well-known tensile stresses in the core and compressive stresses at the surfaces, during the holding stage in injection molding, when extra molten polymer is added to the mold to compensate for the shrinkage, tensile stresses may develop at the surface, induced by the pressure during solidification.