Marangoni convection in weld pools with a free surface

A steady-state two-dimensional model of heat transfer and fluid flow was developed to describe Marangoni convection in the weld pool. Both the pool surface and the fusion boundary were calculated. The validity of the model was verified against an asymptotic solution for Marangoni-convection-induced free surface geometry. Two different cases were studied, i.e. a negative surface tension temperature coefficient ?γ/?T a positive one, and the resultant shapes of the weld pool surface were compared.     

基于多重动态共价键的环氧类玻璃网络的制备与性能

以三羟甲基丙烷三缩水甘油醚(TTE)为基体, 2,2′-(1,4-亚苯基)-双[4-硫醇1,3,2-二氧杂戊烷](BDB)和3,3-二硫代二丙酸(DTDPA)为交联剂, 通过环氧-巯基“点击”反应和环氧-羧酸酯化反应, 制备了基于多重动态共价键(硼酸酯键、 二硫键和酯键)的环氧类玻璃网络. 利用红外光谱和拉曼光谱对其结构进行了表征, 结果表明, 环氧类玻璃中不仅存在硼酸酯键、 二硫键和酯键, 还存在可逆氢键, 并且大量氢键的存在能提高环氧类玻璃的交联度. 对所得环氧网络的热稳定性、 热机械性能和力学性能进行了测试, 并对基于多重动态共价键环氧网络进行了自修复、 焊接、 形状记忆和再加工能力测试. 结果表明, 在80 ℃下可实现网络的完全自修复、 再加工与焊接, 且焊接后样品的力学性能(拉伸强度)恢复率在80%以上, 具有优异的功能性.     

Pseudolinear equivalent constant rigidity concept for analyzing welding residual deformation

To ascertain the extent of deformation due to the thermal cycles caused by welding it calls for solving a complex thermal elasto-plastic problem, which is non-linear and involves plastic deformation of the medium at high temperature varying in both time and space. Analytical solutions turned out to be inadequate. At the same time conventional numerical techniques proved to be highly time consuming and thereby prohibitively expensive in real life situations. The concept of pseudolinear equivalent constant rigidity system was developed in this investigation for thermo-mechanical analysis of plates undergoing variation of rigidity due to a continuously changing temperature profile as is encountered in welding situations. The initial non-linear problem with modulus varying with temperature was transformed into a pseudolinear equivalent system of constant rigidity that was solved by applying linear analysis.     

Numerical simulation of welding induced damage and residual stress of martensitic steel 15-5PH

This paper is about the modeling of damage and residual stresses induced by a complex history of thermo-elasto-plastic multiphase in welding heat affected zone (HAZ). A two-scale model for elasto-plastic damaged multiphase is developed. The constitutive equations of the model are coupling ductile damage, elasto-plastic strains, phase transformation and transformation plasticity. In this study, an equation of damage evolution is proposed based on the continuum damage mechanics. In order to validate the proposed damage evolution, a set of flat notched bars with various notches are to simulated and then compared to experimental results. An example of laser heated disk is simulated to elaborate the two-scale model and the simulated results of the two-scale model in CAST3M^® is compared the results calculated by a homogenized macroscopic model in SYSWELD^®. The study shows the two-scale model provides valuable freedom to choose the material or mechanical law for each phase. The proposed damage equation extends the application of existing ductile damage models. In the calculation of residual stresses, damage decreases the residual stresses in HAZ by a small amount.     

SAF2205双相不锈钢焊接工艺及耐蚀性的研究

本试验以获得合理的奥氏体/铁素体两相比例为指导原则,采用6组焊接工艺参数对2205双相不锈钢板材进行对接。首先对各个焊接接头进行定量金相计算及分析,然后通过拉伸、弯曲试验选取力学性能优良的焊接接头进行腐蚀试验。焊缝的耐蚀性因其焊缝中奥氏体含量区别不大而无太大差异,腐蚀介质浓度较高时,在保护气中加入2%的氮气,试样耐蚀性较强,但3组试样的焊接接头焊缝的耐蚀性均小于母材。     

超大焊接厂房自然通风方式模拟与对比研究

针对超大焊接厂房通风防尘风流路线长易导致焊接烟气滞留,严重威胁作业者职业健康的问题,研究最不利自然通风条件下保障厂房环境的通风方式。基于焊接烟羽热扩散机理,建立将超大焊接厂房分为上、中、下三层的模型框架,确定下层通风、中层通风、上层通风、下进上出通风四种通风方式。采用k-ε两方程湍流模型对四种通风方式下厂房焊接烟尘流动进行了三维模拟实验,得到了四种通风方式下焊接烟尘扩散随风量变化的空间分布规律。通过对比研究,得出下进上出通风方式能够在焊接烟尘最高允许浓度下获得最大纵向防尘深度,适合超大厂房焊接烟尘防治。     

现代焊接技术的新发展

随着社会的进步,时代的前进和发展,焊接在生产的各个领域起到了举足轻重的作用。针对焊接工艺的工作特点,简介现代焊接技术的若干新发展及应用。     

Observation of the mechanisms causing two kinds of undercut during laser hybrid arc welding

Two different kinds of undercut were identified when laser hybrid welding hot rolled HSLA-steel in either the as-rolled condition or with the top surface mill scale removed. The presence of mill scale on the steel surface was found to give a sharp angled undercut combined with a sharp oxide inclusion at the edge of the weld which would have the same mechanical effect as a crack in this position. Removal of the surface oxides before welding resulted in the elimination of the oxide inclusions and a more rounded undercut geometry indicative of superior mechanical properties, particularly fatigue life. The mechanisms of the formation of both types of undercut have been analysed by high speed photography and SEM.     

Structural Analysis of Steel to Aluminum Welded Overlap Joint by Digital Image Correlation

In this paper, the structural analysis of steel to aluminum overlap joint is performed with digital image correlation. For this, it is necessary (i) to find the mechanical response in the two sheets after welding and (ii) to find some structural information in order to assess modeling. Because the overlap joint is a peculiar structure with non uniform stress distribution, finite element seems to impose itself in order to assess failure. Thus, local mechanical behavior must be identified. Digital image correlation is an accurate method of identifying material behavior after welding. Once identified, the mechanical response is introduced in a model. Structural finite element model is then compared with some structural experimental measurements (strain field and out of plane displacement field).     

大型不锈钢复合板容器的焊接工艺

结合设备制造实际 ,针对目前奥氏体不锈钢和碳素钢构成的复合钢板在焊接工艺方面存在的缺陷 ,提出有效的改进措施 ,确定了新的焊接工艺 ,消除缺陷 ,使其更有利于实际操作。经过设备运行检验 ,本文的焊接工艺合理 ,焊接质量满足设计要求 ,可用于同类材料进行制造时参考