浅析焊接残余应力及其消除方法

简介了焊接残余应力危害的特点，影响因素、测量及消除残余应力的几种方法，重点论述爆炸法消除焊接残余应力的有关问题。     

爆炸法消除超厚板焊接残余应力的工艺研究

研究了炸药性能、药条尺寸、布药方式以及引爆方式对消除超厚钢板焊接残余应力效果的影响。在此基础上，提出了优化的工艺方案，为爆炸法消除焊接残余应力技术应用到大型或特大型焊接结构上提供了依据。     

爆炸处理消除焊接残余应力对奥氏体不锈钢焊接接头机械性能的影响

对爆炸处理消除奥氏体不锈钢焊接残余应力前后焊接接头常规机械性能进行对比试验研究，发现爆炸处理在显著消除焊接残余应力的同时，对材料机械性能影响不大。     

预热对铍环激光束钎焊过程的影响研究

研究预热对铍环激光束钎焊过程温度场和应力场分布的影响。采用轴对称模型和热力解耦的有限元方法，并假定沉积到钎缝表面的激光束能量为Gauss分布，预热通过在焊接加热前添加一个能量密度低、有效加热半径大的单独工况实现。结果表明，预热使镀环钎缝外表面焊接最高温度增加，温度梯度减小，但焊深明显增加；采用预热工况焊接后，钎缝附近塑性变形区焊接残余应力明显减小，而热影响区残余应力增大。从整体分布来看，预热使铍环外表面焊接残余应力分布均匀化。对铍环外表面钎缝附近焊接残余应力进行X射线应力测试，并与有限元分析结果对比，二者应力变化趋势基本一致。     

铁素体——马氏体双相钢焊接接头的应力腐蚀

在慢应变速率条件下，研究了Ｆｅ－Ｓｉ－Ｃ系铁素体－－马氏体双相钢焊接接头在人造海水中的应力腐蚀开裂行为，用单边预裂纹拉伸试样测定了焊接接头各部位的应力强度因子ＫＩ值。结果表明，焊接接头各部位在人造海水中的应力腐蚀开裂敏感性有很大差异，其中热影响区（ＨＡＺ）对ＳＣＣ最敏感，Ｋ１值最低；随着阴极电位朝负方向增加，ＳＣＣ敏感性增大；除氢处理可以改善焊接接头的ＳＣＣ抗力。     

焊接H型钢残余应力初步测定分析

通过用盲孔法对焊接H型钢的残余应力进行检测，并对检测结果进行分析，初步了解了焊接H型钢残余应力的状况。     

分段焊接对残余应力的影响

利用热弹性有元法对直通焊和分段焊两种焊接方法的温度场进行了分析，得出了分段焊接在减少焊接残余应力和焊接变形上都有显著的效果。     

超大型底座焊接变形控制

本文对焊接量大，焊后机械加工后要求不变形的大型底座的焊接变形问题进行了分析，制定了防止焊接变形的措施及焊接工艺以及消除焊接残余应力方法。     

钢结构焊接残余应力及焊接变形控制技术分析

焊接作业是钢结构施工的主要内容之一,而焊接时产生的焊接残余应力与焊接变形等,对钢结构的安全使用有非常大的影响。文章论述了焊接应力以及焊接变形的基本概念,分析了钢结构焊接参与应力产生的主要原因,进而探讨了钢结构焊接残余应力及焊接变形的控制技术,以供相关人员参考。     

转炉汽化冷却烟道制造焊接工艺方案及实施

根据汽化烟道的的结构特点，利用焊接的应力与变形，采用合理的焊接工艺，获得了满意的焊接质量，满足了设备的制造要求。     

蒸发器焊缝开裂的原因分析

系统分析蒸发器焊缝大面积开裂的原因 ,确定应力腐蚀—碱脆是焊缝开裂的主要原因 ,焊接残余应力是引起焊缝开裂的主要应力 ,并提出相应的防护措施     

Improving the Accuracy of Structural Hot‐spot Stress Approach

A method for extending the applicability of the structural hot‐spot stress method for fatigue assessment of welded structures is discussed. The structural hot‐spot stress method for plate structures, as currently presented in commonly used design guidance documents, cannot account for the effect of weld size, and load carrying fillet welds are assessed using a different S‐N curve as compared to non‐load carrying fillet welds. This paper presents a proposal to linearize the local stress distribution through the plate thickness in the plane of the weld toe. This proposal considers the forces transmitted by the weld itself. A bilinear stress distribution, which partially captures the local effect of the weld, is derived from the non‐linear stress distribution. The non‐linear distribution is based on equilibrium and the stress in the fillet weld. A simple procedure is presented to determine the bilinear curve from the nominal weld stress. This is a great advantage in finite element analysis when only nominal base plate stress and nominal weld stresses need to be determined. When compared to the more conventional structural stress approach, the new method also has the advantage that extrapolation is not required. The same weld stresses can also be used in the analysis of the root cracks. The proposed method was scaled to correspond to the traditional structural hot‐spot stress method using detailed linear elastic fracture mechanics simulations. The method is only applied to fully load‐carrying welds here but can also be used for partial load‐carrying welds. A symmetric splice plate having a fully loaded fillet weld is presented as an example case. The influence of base plate thickness is studied as well.     

大变形X80钢板制管前后性能分析

结合鞍钢供货实绩,分析了26.4 mm厚大变形X80钢板的组织,以及制管前后性能变化情况。分析结果表明:钢板组织为以铁素体、贝氏体为主的复合组织,低温韧性优良;制管后,材料的屈服强度、抗拉强度与屈强比升高,应力比与均匀延伸率降低;焊接接头处焊缝的韧性最差,热影响区的硬度最低。     

Microstructure and mechanical property correlations in AA 6061 aluminium alloy friction stir welds

The influence of friction stir welding on the microstructure development and its role on residual stress distribution in the weldment and mechanical properties has been investigated. The study also focused on the impact of post weld heat treatment on the microstructure and mechanical properties as well as on residual stress distribution. The weld nugget region contained fine equiaxed grains as a result of thermo-mechanical working. Hardness survey showed that nugget region is soft due to precipitates dissolution. Weld joint exhibited lower strength as compared to the parent metal. Post weld Solution Treatment and Aging (STA) of longitudinal welds resulted in strength and ductility equivalent to that of parent metal while transverse weld tensile strength and ductility were lower than that of parent metal even after post weld STA. Residual stress distribution profiles across the weld region are asymmetric with respect to weld centerline, with the largest residual; stress gradients occurring on the advancing side of the weld. Within the region inside the shoulder diameter, residual stress is entirely compressive. Welds exhibited tensile residual stresses in post weld STA condition     

Synchrotron X-ray measurement and finite element analysis of residual strain in tungsten inert gas welded aluminum alloy 2024

Residual strains have been measured in a tungsten inert gas (TIG) butt-welded 2024 aluminum alloy plate using synchrotron X-ray diffraction. Novel two-dimensional strain maps spanning the entire plate reveal steep gradients in residual stress and provide detailed validation data for finite element (FE) analysis. Two variants of a FE model have been used to predict the residual strain distributions, incorporating different levels of plate constraint. The model uses decoupled thermal and elastic-plastic mechanical analyses and successfully predicts the longitudinal and transverse residual strain field over the entire weld. For butt weld geometries, the degree of transverse constraint is shown to be a significant boundary condition, compared to simpler bead-on-plate analyses. The importance of transverse residual strains for detailed model validation is highlighted, together with the need for care in selecting the location for line scans. The residual stress is largest in the heat-affected zone (HAZ), being equal to the local postweld yield stress, though the strength increases subsequently by natural aging. In addition, a halving of the diffraction line width has been observed local to the weld, and this correlates with the microstructural changes in the region.     

The relaxation of residual stresses with postweld heat treatment in a high-performance weld measured with neutron diffraction

The residual stresses in a cylindrical weldment of HP-9-4-30 steel were measured with neutron diffraction in the as-welded (AW) state and after postweld heat treatment (PWHT). Large residual stresses are present in the interior of the material in the as-welded condition. The maximum principal stresses measured were found around the edges of the cap-pass heat-affected zone and reached up to 1045 MPa (76 pct of the base metal yield strength) in the as-welded condition. The principal stress directions for the residual stress tensors do not in general follow the hoop, axial, and radial axes of the weld and change from position to position within the weld, although the highest values are generally in the hoop direction. The postweld heat treatment relaxed the largest residual stresses, with the maximum value being 30 pct of the base metal yield stress. The need for position-dependent stress-free standards and the implications of stress gradients over the measurement volumes are discussed.     

Dynamic Wind Uplift Performance of Thermoplastic Roofing System with New Seaming Technology

Wind dynamics, on a conventional roofing system, lift the membrane and cause fluttering, introducing stresses at the attachment locations. To identify the component of the system that has the weakest resistance against wind uplift forces, a dynamic method of evaluating roofing systems is beneficial. A recent industry survey predicts significant growth for thermoplastic polyolefin (TPO) membranes. Among others, hot-air-weld ability is an advantage of the TPO. In mechanically attached TPO roofs, seams are formed by welding one side of the bottom sheet with the top sheet using hot-air machines. Advancements in welding technology have led to double-side weld procedures or encapsulated seams for the TPO membranes. Wind uplift evaluations are being carried out on the TPO systems with one-side weld and double-side weld. Experiments have been conducted at the dynamic roofing facility (DRF) of the National Research Council of Canada, using the SIGDERS (special interest group on dynamic evaluation of roofing systems) wind test protocol. Systems with double-side weld performed better than the systems with one-side weld. Use of double-side weld minimizes asymmetrical stress concentration and improves the wind rating of the mechanically attached TPO roofing systems.     

Characterization of Phase Transformations and Stresses During the Welding of a Ferritic Mild Steel

The transient stresses and phase evolution have been characterized in the quasi-steady state produced around a gas tungsten arc welding torch in a plain carbon (ASTM 1018) steel using in situ neutron diffraction. A novel method has been developed to isolate the deviatoric or plane stress state in the presence of isotropic contributions to the lattice parameter, such as thermal expansion and solute content. The stress state was found to evolve in the anticipated manner, with compressive stresses ahead of the weld and tensile stresses behind the weld, in the weld and heat-affected zone, and compression in the far field behind the weld. In particular, the region of compression in the heat-affected zone adjacent to and just behind the welding torch expected from weld models was observed. The evolution of phase fraction around the weld was also determined using the technique and the stresses obtained from the ferrite phase.     

Investigation of the conditions for weld metal hydrogen cracking of low carbon offshore steels by the IRC weldability test

Three low carbon structural steels of different plate thickness have been investigated for hydrogen assisted cold cracking by the IRC weldability test at different restraint intensities. At diffusible hydrogen levels of 10–15 N ml/100 g Fe (ISO 3690), cracking decreases at increasing heat inputs due to a drop in restraint stress and hardness as well as an increase in hydrogen diffusion times. Critical heat inputs for crack prevention range from 0.95 to 1.4 kJmm^?1. Higher restraints enforce higher cracking stresses as well as final stresses of uncracked test welds. Higher restraints and lower heat inputs also induce faster stress increase during cooling which, for the steels containing Ni and Cu, shift the location of cracking from the HAZ to the weld metal. The steel without Ni and lower maximum HAZ hardness reveals weld metal cracking only, regardless of welding conditions. It can be concluded that for weld metal cracking, the relation between stress increase- and hydrogen effusion rates but also the relation between weld metal and HAZ microstructure and mechanical properties are responsible.     

不锈钢焊接接头断裂原因分析

从钢材成分、焊接原理、焊接接头硬度及应力等方面分析了焊接接头断裂原因 ,为今后实施同类焊接提供依据