焊缝匹配对力学性能影响的综合研究

对几种钢在静载、动载和疲劳载荷条件下的焊缝强度匹配分别进行了研究,并对有关接头进行了残余应力的测试。得出的结论是恰当地提高焊缝金属强度无论是对抗开裂性能还是止裂性能均是有利的;采用同种焊条LB52NS施焊A131和A537所构成的两种接头其强度匹配系数的差别对ΔK (th)无影响,对da/dN无论是在常规疲劳还是海水腐蚀疲劳也均无显著影响;强度匹配系数较高A131接头焊缝残余应力略低于强度匹配系数较低的A537接头焊缝的残余应力。     

非均质焊接接头裂纹尖端塑性区

采用平面应力弹塑性大应变有限元法分析了非均质焊接接头裂纹尖端塑性区的扩展规律，指出在非均质焊接接头中存在着塑性变形的不同时性与不均匀性，且焊缝金属强度匹配、材料本构关系以及裂纹长度（韧带长度）对塑性区的发生发展均有重要影响。     

力学不均匀性对含横向裂纹焊接接头J积分的影响

采用 MARC有限元程序提供的 Delorenzi虚拟裂纹扩展方法计算了平面应力条件下不同强度匹配的焊缝纵向受载的含横向裂纹的焊接接头在不同载荷的广义 J积分。计算结果表明 :力学不均匀性对含横向裂纹焊接接头的 J积分有重要影响 ,低匹配焊接接头中积分路径穿越焊缝与母材界面的 J积分值高于积分路径在焊缝内的 J积分值 ,高匹配焊接接头中积分路径穿越焊缝与母材界面的 J积分值低于积分路径在焊缝内的 J积分值 ;载荷越大 ,焊缝与母材的强度差别越大 ;积分路径中包含的焊缝与母材界面长度越大 ,J积分的差值越大。力学不均匀性对焊缝纵向受载的含横向裂纹的焊接接头 J积分的影响是由焊缝与母材的强度差别及积分路径中包含的焊缝与母材界面长度的不同造成的     

低强匹配焊接接头特征及界定方法

焊接接头的强度匹配方式对接头的设计、制造工艺、裂纹敏感性以及破坏行为有重要影响，焊缝金属、母材、焊接接头的强度分布以及焊接接头强度匹配系数的分布是焊接结构强度、寿命和可靠性计算的基础。通过对12Ni3CrMoV钢焊接接头强度匹配系数分布的研究，提出低强匹配焊接接头的界定方法，强度匹配系数的均值小于95％、强度匹配系数的均值加上其标准差应小于100％，并且强度匹配系数大于105％的概率应小于3％。计算结果表明，12Ni3CrMoV钢焊接接头低强、等强、超强匹配概率分别为85．44％、11．85％和3．35％，低强匹配特征明显，强度匹配系数的均值位置非常合理。但由于母材强度的标准差较大，约为焊缝金属强度标准差的1．56倍，是造成强度匹配系数低于低强匹配下限值86％的概率高达7．79％和强度匹配系数高于105％的概率超过3％的主要原因。此外，这也是低强匹配焊接接头中出现冷裂纹的主要原因之一。     

焊接接头中不均匀性因素与裂端拘束强度

采用有限元方法研究了平面应变条件下焊接接头中不均匀性因素对裂端拘束强度－应力三轴性的影响。结果表明焊接接头裂端应力三轴性焊缝和母材匹配性质及裂纹几何不同而变化。与均匀材料相比，高匹配接头裂端应力三轴性降低，低匹配接头裂端应力三轴性升高。裂纹变浅后，应力三轴性降低，屈服强度匹配的影响也更为显著。焊缝宽度变化时，裂端应力三轴性也有改变。这些对了解不同接头断裂行为，以改进焊接结构设计具有重要意义。     

不同强韧性组配的16Mn钢焊接接头的断裂性能和裂行为

对16Mn钢不同组配焊接接头的断裂性能和断裂行为进行了试验研究。认为在高应力塑性断裂和高应力脆性断裂状态下,16Mn钢接头的断裂强度为焊缝强度和接头各部分塑性变形能力所决定,提高焊缝强度以及提高焊缝和母材的塑性均有利于提高接头的抗断裂能力;在低应力脆性断裂状态下,接头的抗断裂性能是可以根据焊缝的低温冲击韧度进行评价的。焊接接头各部分塑性变形能力及其相互关系对焊接接头的断裂行为具有不可忽视的影响,是评价接头断裂性能的重要依据。     

2219铝合金VPTIG焊接接头的断裂韧性

对2219铝合金变极性钨极惰性气体保护(VPTIG)焊接接头进行了拉伸、冲击和三点弯曲试验,对比研究了接头与母材的拉伸性能、冲击性能、断裂韧性及裂纹扩展行为。结果表明:焊接接头的抗拉强度为266~282 MPa,强度系数为0.6,接头强度远低于母材的;焊缝的冲击功为7~8 J,热影响区的冲击功为6~11 J,均高于母材的;当裂纹扩展量在0.14~0.35 mm时,焊缝裂纹尖端张开位移(CTOD)为0.056~0.124 mm,CTOD随裂纹扩展而增大;焊缝金属表现出比母材更好的断裂韧性,焊缝断口为弹塑性断裂,裂纹扩展区呈韧窝形貌,韧窝内存在第二相质点,使裂纹失稳扩展所消耗的能量增大。     

低热裂纹敏感性纯镍铸铁焊条的研究

研究了纯镍铸铁焊条冷焊时，稀土金属镧、铈、镨、钇及钕对焊缝热裂纹敏感性的影响规律，并分析了铈对焊接接头力学性能和加工性能的影响。结果表明：稀土镧、铈、钇和镨能在一定范围内提高焊缝临界变形速度υBL，改善纯镍铸铁焊缝抗热裂性。适量的铈能提高接头力学性能，稀土钕会增加焊缝热裂纹敏感性。在此基础上，研制了具有较低热裂纹敏感性、良好的加工性能，能满足高强度灰口铸铁力学性能要求的纯镍铸铁冷焊焊条。     

下压量对7N01铝合金搅拌摩擦焊接头性能的影响

在不同下压量(0.3,0.7,1.0 mm)下对7N01铝合金进行搅拌摩擦焊，研究了下压量对接头截面形貌、拉伸性能、抗撕裂性能及疲劳性能的影响。结果表明：下压量对7N01铝合金搅拌摩擦焊接头的拉伸性能影响不大；当下压量为0.7,1.0 mm时，接头的启裂能、裂纹扩展能及撕裂强度均相近，但当下压量为0.3 mm时，接头焊缝区域的启裂能、裂纹扩展能及撕裂强度均显著降低；随着下压量的增加，焊接接头疲劳强度增大；当下压量为1.0 mm时焊接接头的疲劳性能及抗裂纹扩展性能最优。     

几何和材料拘束与高匹配焊接接头断裂韧性的统一关联

采用数值计算方法研究了拘束参数A_p对高匹配窄间隙焊接接头面内/面外几何拘束和材料拘束的统一表征能力,以及参数A_p与接头不同位置裂纹断裂韧性的可关联性。结果表明,几何和材料拘束对高匹配窄间隙焊接接头的J-R阻力曲线和断裂韧性J_C具有显著的影响。参数A_p可以统一地表征该种接头不同位置裂纹的面内/面外几何拘束及由材料强度失配引起的材料拘束,基于A_p可建立统一拘束与接头断裂韧性的关联。计算得到了不同位置裂纹的标称断裂韧性J_C/Jref与A_p的关联式。     

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     

Limit load solution for electron beam welded joints with single edge weld center crack in tension

Limit loads are widely studied and several limit load solutions are proposed to some typical geometry of weldments.However,there are no limit load solutions exist for the single edge crack weldments in tension(SEC(T)),which is also a typical geometry in fracture analysis.The mis-matching limit load for thick plate with SEC(T) are investigated and the special limit load solutions are proposed based on the available mis-matching limit load solutions and systematic finite element analyses.The real weld configurations are simplified as a strip,and different weld strength mis-matching ratio M,crack depth/width ratio a/W and weld width 2H are in consideration.As a result,it is found that there exists excellent agreement between the limit load solutions and the FE results for almost all the mis-matching ration M,a/W and ligament-to-weld width ratio(W-a)/H.Moreover,useful recommendations are given for evaluating the limit loads of the EBW structure with SEC(T).For the EBW joints with SEC(T),the mis-matching limit loads can be obtained assuming that the components are wholly made of base metal,when M changing from 1.6 to 0.6.When M decreasing to 0.4,the mis-matching limit loads can be obtained assuming that the components are wholly made of base metal only for large value of(W-a)/H.The recommendations may be useful for evaluating the limit loads of the EBW structures with SEC(T).The engineering simplifications are given for assessing the limit loads of electron beam welded structure with SEC(T).     

Effect of post weld aging treatment on tensile properties of electron beam welded AA2219 aluminum alloy

Aluminum alloy 2219 (Al-6.5%Cu) is a favourite age hardenable alloy for aerospace applications because of its excellent welding characteristics. Though AA2219 has got an edge over its 6000 and 7000 series counterparts in terms of weldability, it also suffers from poor joint strength when welded. In this investigation an attempt has been made to improve the welded joint strength through post weld aging treatment. This paper presents the effect of post-weld aging treatment on tensile properties of electron beam welded AA2219 aluminum alloy. Square butt joints were fabricated using an electron beam welding (EBW) machine of 100 kV capacity. The joints were given post-weld artificial aging treatment. Tensile tests were carried out using 100 kN, electro-mechanical controlled universal testing machine. It is found that the post-weld aging treatment is beneficial for improving weld metal hardness and tensile properties. This is mainly due to the uniform distribution of CuAl₂ precipitates in the weld metal region in post-weld aged joints compared to as welded joints as evident from weld metal microstructure.     

Domex700MC低合金高强钢药芯焊丝CO2气体保护焊焊接接头的组织与性能

用药芯焊丝CO2气体保护焊焊接Domex700MC低合金高强钢,用光学显微镜、硬度计和冲击试验机等对焊接接头的显微组织和力学性能进行了分析。结果表明：焊缝金属晶粒细小且分布均匀,有较多针状铁素体,但熔合区组织比较粗大,使熔合区附近塑性降低,为焊接接头的薄弱部位;焊缝金属显微硬度较高,为315HV,而在热影响区为225HV,出现软化现象;焊接接头力学性能优良,具有较高的抗拉强度（630．94MPa）和冲击功（135．34J）。     

25 Cr2 Ni2 MoV 钢焊接接头低周疲劳性能研究

对新型汽轮机焊接转子材料25Cr2Ni2MoV焊接接头及其母材进行应变控制的低周疲劳试验,并进行了相应的断裂位置统计和循环变形特征分析。试验结果表明,焊接削弱了焊接接头的疲劳强度,受到结构非均匀性和各部分力学性能的相对不匹配等因素的影响,焊接接头的断裂位置体现出明显的应变水平依赖性;焊接接头和母材在循环变形过程中均表现出循环软化特性,且存在明显的拉压不对称性,拉压不对称程度随应变水平的增加而增加;与母材相比,焊接接头表现出更加明显的平均应力松弛现象,且平均应力绝对值随着循环周次不断减小最后趋于常值。     

激光焊接对镀锌平板力学性能及拉伸断口影响研究

采用光纤激光对海工装备中的镀锌平板进行焊接,对镀锌平板焊接接头母材区、热影响区、焊缝区的微观硬度进行测量,研究了焊接试样的拉伸性能和断口形貌。结果表明,激光焊接接头的强度和硬度均高于母材。焊缝区接头组织获得了低碳马氏体,因而接头硬度不及热影响区高。     

激光焊接对镀锌平板力学性能及拉伸断口影响研究

采用光纤激光对海工装备中的镀锌平板进行焊接,对镀锌平板焊接接头母材区、热影响区、焊缝区的微观硬度进行测量,研究了焊接试样的拉伸性能和断口形貌。结果表明,激光焊接接头的强度和硬度均高于母材。焊缝区接头组织获得了低碳马氏体,因而接头硬度不及热影响区高。     

TC17-TC11异种钛合金线性摩擦焊接头弯曲性能分析与改善

分析了TC11和TC17异种钛合金线性摩擦焊接接头的弯曲性能,探寻了焊缝区弯曲塑性的薄弱区。通过测试焊接接头的硬度、分析焊缝区组织、断口形貌,特别是弯曲试样表面滑移线形态,研究了弯曲断裂机制。通过焊后超声冲击以及高温固溶+时效热处理,探索了改善焊接接头弯曲塑性的工艺方法。研究结果表明,采用接头弯曲性能试验,可以更好地表征TC11和TC17异种钛合金线性摩擦焊接接头焊缝区的宏观性能;经焊后时效热处理的线性焊接头的弯曲角度只有TC17母材的38%,TC11母材的30%。弯曲塑性是其力学性能的薄弱环节;焊合区及TC17侧变形区是接头弯曲塑性的薄弱区,弯曲断口均呈脆性断裂特征。焊合区断口为细小等轴晶粒的晶间断裂,焊接界面对TC17侧的滑移有明显的阻碍作用,容易在焊合区TC17侧形成微观裂纹;TC17变形区的弯曲起裂断口是大面积滑移剪切所形成的剪切韧窝,而TC17侧变形区晶粒大而长,有利于形成更长的滑移线和更集中的位错聚集,所以弯曲试验时TC17侧变形区最容易开裂。焊后进行超声冲击处理,在试件表面形成了约20 μm厚度的变形层,接头的弯曲角度相对提高34%;接头进行高温固溶+时效处理后,接头的弯曲塑性提高,最高平均弯曲角度达到31.2°,相对提高82%。为钛合金线性摩擦焊接接头的宏观塑性性能分析与改善提出了一个有意义的研究方向。     

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.