韧-脆转变温度区间内焊接接头断裂韧度预测

首先对采用同种焊接材料施焊的X80及X65管线用钢焊接接头,在韧脆转变温度区间测试了其断裂韧度,试验研究了强度匹配、试样几何形式对接头断裂行为的影响。然后根据局部法由标准三点弯曲试样的断裂韧度值,得出反映材料的脆性断裂控制参量m、σu,再根据该参量对同种接头及不同强度匹配接头双边裂纹拉伸试样的断裂行为进行了定量预测,当考虑韧脆转变温度区间内的延性裂纹扩展后,预测结果与试验结果相当吻合。表明,局部法能很好地描述材料的断裂行为。     

基于微观损伤机理的延性裂纹扩展行为分析

在考虑材料内部塑性损伤的基础上,通过有限元数值方法(特殊单元模型法),编制了求解韧性断裂特征参量的程序,模拟材料的韧性断裂过程.通过单轴拉伸试验的模拟结果,得出反映材料微观损伤的控制参量,再根据该参量对同种材料的标准三点弯曲试验进行定量预测,即实现从一种试验结果预测同种材料的其它试验结果.结果表明,在韧性裂纹扩展时,考虑塑性损伤的特殊单元模型能够很好地描述材料的韧性断裂过程,可以实现同种材料不同试验间相互预测的目的.     

1Cr18Ni9Ti/20G双金属爆炸焊接界面裂纹的扩展行为

利用奥氏体不锈钢／低碳锅炉钢（1Cr18Ni9Ti/20G）爆炸焊接复合板，通过电子束焊接得到带有界面裂纹的三点弯曲J积分裂纹扩展阻力试样和四点弯曲疲劳试样。分别进行了带界面裂纹材料和相应单一材料试样的裂纹扩展阻力曲线及其疲劳扩展行为的实验研究。结果表明：双材料界面裂纹的静态和动态扩展阻力均低于裂纹在相应单一材料中的扩展阻力。     

焊接接头延性裂纹扩展的数值模拟

用GTN损伤模型对30Cr2Ni4MoV转子钢焊接接头延性裂纹的扩展进行了有限元模拟.模拟得到的焊缝、母材和热影响区断裂韧性试样的载荷—位移曲线和J-△a阻力曲线与试验曲线吻合良好,以此确定了GTN模型中的材料损伤参数.结果表明,焊缝的裂纹扩展阻力最低,热影响区最高,母材居中;当初始裂纹位于母材和热影响区界面时,裂纹偏向强度和扩展阻力较低的母材一侧扩展,其阻力曲线和母材相似;当初始裂纹位于热影响区和焊缝界面时,裂纹向焊缝一侧偏离且沿着界面扩展,阻力曲线较焊缝稍有降低.     

宏观力学不均匀性对焊接接头动态J积分的影响

焊接接头是一个宏观力学不均匀体，力学不均匀性对焊接接头的动态断裂行为有重要的影响。采用MARC有限元程序，对含焊缝中心裂纹的低匹配焊接接头三点弯曲试样的动态断裂响应进行了计算模拟，并采用虚拟裂纹扩展方法计算了动态J积分断裂参量。作为比较，计算了相同条件下全母材及全焊缝三点弯曲试样的动态响应。由于惯性效应的作用，动态载荷响应曲线周期振动，焊接接头试样的动态载荷响应值介于全母材与全焊缝之间。用虚拟裂纹扩展方法计算的动态J积分与路径无关，惯性效应对动态J积分基本没有影响。低匹配焊接接头的动态J积分低于全母材而高于全焊缝。研究结果为承受动载的焊接结构安全评定奠定了基础。     

残余应力对管线钢韧性断裂的影响

以弹塑性断裂力学理论为基础,应用ABAQUS有限元软件,采用固有应变法引入残余应力,并基于细观塑性损伤模型研究了残余应力对管线钢韧性裂纹扩展阻力曲线的影响.模型中选择了具有不同深浅裂纹的单边缺口弯曲（SENB）试样和DNV推荐准则中用于管线钢断裂评估的单边缺口拉伸（SENT）试样,并对这两种断裂力学试样在大范围屈服条件下的裂纹扩展阻力曲线（CTOD-R曲线）行为进行了对比分析.结果表明,对于深裂纹试样,残余应力降低了韧性裂纹扩展阻力曲线,而浅裂纹试样受残余应力的影响可忽略不计.     

裂纹深度和强度组配对焊接接头断裂性能的影响

利用弹塑性有限元计算和三点弯曲试验对不同裂纹深度，不同强度组配焊接接头试样的断裂性能进行了研究，着重讨论了裂纹深度和组配的不同对焊接接头试样加载过程中塑性区形状及大小，深浅裂纹分界点，抗断性能，裂纹尖端张开位移ＣＴＯＤ，Ｊ积分的影响。结果表明，裂纹越浅。加载时塑性区域大，断裂韧性值越高，高组配焊接接头试样加载时由于塑性区扩展到母材而具有较大的塑性区，低组配焊接接头试样加载时塑性区被抑制在焊缝中，尺     

断裂应变对含损伤焊接接头裂纹扩展驱动力影响的数值

利用弹塑性损伤-应变耦合有限元方法，对含有损伤的焊接接头三点弯曲裂纹试样进行了模拟计算，讨论了母材区的断裂应变εfB的变化对焊缝区裂纹的扩展驱动力J积分的影响规律。结果表明，焊缝中裂纹的断裂行为受到焊缝两侧母材断裂应变的明显影响。对于无论何种强度匹配的接头，在焊缝区各项力学性能参数保持不变的条件下，随着母材区断裂应变的减小，损伤率的增加，损伤区的扩大，焊缝中裂纹韧带区塑性应变及裂纹扩展驱动力J积分均有明显的提高；随着接头强度匹配比M的降低(即母材屈服强度的升高)，母材区断裂应变的变化对J积分的影响作用逐渐减弱；随着焊缝宽度的逐渐增加，母材断裂应变的变化对J积分的影响作用逐渐减弱，焊接接头试样的计算J积分值逐渐趋向于全焊缝材料试样计算得到的J积分值；当焊缝宽度增加到2H／a约为0．6时，母材断裂应变的变化对焊缝区裂纹扩展驱动力J积分的影响作用完全消失。     

疲劳损伤对核电汽轮机焊接转子接头应力腐蚀开裂敏感性的影响

采用慢应变速率拉伸试验(SSRT)研究了不同程度疲劳损伤对核电汽轮机焊接转子接头应力腐蚀开裂敏感性的影响,利用扫描电子显微镜等观察手段讨论了疲劳损伤对汽轮机焊接接头应力腐蚀开裂敏感性和二次裂纹的作用机理. 结果表明,疲劳损伤增强了核电汽轮机焊接转子接头应力腐蚀开裂敏感性. 此外,疲劳损伤的作用使空气中试样的塑性提高而在腐蚀溶液中塑性降低,也影响了试样内部二次裂纹的产生和扩展.     

T2紫铜-45钢电子束焊双材料界面性能与裂纹偏转

焊接接头性能与缺陷一直是焊接材料相关课题的重要方面,大量的研究描述了焊接材料的接头性能与特征,但异种焊接材料的界面与开裂问题研究并不充分. 文中对T2紫铜-C45钢电子束焊接双材料界面强度和裂纹开裂的问题,首先采用标准拉伸和三点弯曲试验,得到该材料焊缝区抗拉强度、屈服强度、弹性模量参数,并依此计算判断出断裂韧性值;其次对拉伸和三点弯曲试验试样的宏观和微观断口分析,表征其断口形貌特征,得出断口断裂类型为准解理和沿晶脆性复合断裂模式;基于试验分析结果对裂纹开裂偏转路径进行讨论,得出裂纹沿焊缝区扩展并偏向T2紫铜端;最后以实测参数为基准,基于ABAQUS有限元分析得出三点弯曲试验下焊缝区的裂纹扩展和偏转方向结果,为该种异种金属焊接材料接头性能的提升提供了依据.     

NUMERICAL MODELING OF DUCTILE CRACK EXTENSION USING COMPUTATIONAL CELL ELEMENTS FOR WELDED JOINTS

1.IntroductionConstrainteffectsonfracturetoughnessofferritesteelsremainakeyissueforthesafetyaJssessmentofstructures.Strllcturalandpressurevesselsteelsgenerallyexhibitincreaseinfracturetoughnessoverthefirstfewdistance0fstablecrackgr0wth.Laborat0rytestingoffracturespecimenstomeasureresistancecurves(R-curves)c0nsistentlyrevealsamarkedeffect0fabsolutespecimensize,ge0metry,andloadingmode0nRcurvesI1-3].Forthesamematerial,deep-notchbendspecimensyieldl0wRcurvewhiletheshallow-notchbendspecimenortensi…     

Study on ductile crack initiation limit from notch root of pipeline girth welded joints with strength mismatch

This study investigated ductile crack initiation limit of pipeline girth welded joints with different strength mismatches. The ductile crack initiation limit for the girth welded joints was evaluated by conducting three-point bending fracture toughness tests and wide plate tensile tests with a surface notch. In addition, effect of heat input on the ductile crack initiation limit of weld metal (WM) was evaluated on the assumption that a welding condition would be varied in the field in the actual pipeline construction. As the results, the equivalent plastic strain at the notch tip for the ductile crack initiation of the three-point bending tests was consistent with those of the wide plate tests, and the heat input hardly affected the ductile crack initiation limit within the range of this study. This meant that the ductile crack initiation limit of the pipeline girth welded joints with strength mis-match was able to be estimated using the equivalent plastic strain obtained from the three-point bending tests. Based on these results, we proposed a procedure to determine the rational fracture toughness requirements which took into account the difference in the plastic constraint between standard fracture toughness test and pipeline girth welded joints. This procedure was also possible to determine the required strength matching level for a strain-based design for girth welded joint containing surface notch in the centre of the WM in terms of preventing the ductile crack initiation.     

Study on the J-Integral and Failure Assessment Line of Electron Beam Welded Thick TC4-DT Alloy Joints

The effects of strength mis-matching on J-integral and failure assessment line (FAL) of electron beam welded thick TC4-DT titanium alloy joints have been investigated.Elastic and elastic-plastic finite elements (FE) calculations on centre crack tensile (CCT) specimens were made,and the condition of 20% strength mis-matching was considered.The results indicate that the limit load of the joint can be substituted by that of the base metal.The error of substitution is less than 5%.The failure assessment lines for both over-matching and under-matching joints are increasingly close to that of the base metal,with the ratio of weld width to specimen width (H/W) decreasing.Moreover,the failure assessment lines of the joints can be devised using the stress-strain curves of the base metal,which will be convenient for the practical application of engineering structures     

Experimental investigation on tensile strength of butt welded joint post high temperatures

In order to investigate the laws of variation on tensile strength of butt welded joint post high temperatures, the wide plate tension tests for butt welded joint were conducted after cooling down from different high temperatures. The tests indicate that specimens appear ductile fracture at the steel plate during the tension tests after cooling down. The maximum temperatures undergone and the cooling pattern are major factors influencing tensile strength of butt welded joint post high temperatures. The tensile strength mostly reduces by 8% within 900℃. Based on the experimental results, the paper proposes the calculation formulas of tensile strength of butt welded joint post high temperatures. The conclusions of the paper supply references for evaluation damage and feinforcement of steel structure post fire.     

焊接接头高应变速率条件下的冲击韧度测试技术

为满足焊接接头在冲击载荷作用下的冲击韧度研究要求 ,结合气炮加载式Hopkinson装置与Charpy冲击三点弯曲试样测试技术 ,建立了一套在气炮式Hopkinson压杆装置上进行高应变速率条件下的冲击韧度测试系统 ,较好地解决了测试中所遇到的加载、记录、数据处理以及动态效应等技术难题 ,并就相关影响因素进行了讨论。通过对E5 0 15焊接接头V形缺口试样及带预制裂纹的V形缺口试样在此系统上进行冲击韧度测试 ,取得了较理想的结果 ,表明该系统设计思想正确 ,测试结果可靠。     

焊接接头高应变率下的动态断裂韧度分析

对采用Hopkinson气炮加载－Charpy V形冲击试样试验方法对焊接接头高应变率下的动态断裂韧度数据进行了分析研究，通过对试样断口形貌、冲击吸收功、断裂韧度及其影响因素进行分析，表明在高应变率加载条件下，焊接接头冲击试样断口形貌有特殊的表现，延伸带或钝化区的尺寸大小反映了裂纹萌生前的塑性变形大小，也反映了裂纹萌生功的变化趋势。同时说明焊接接头在高速动态冲击载荷作用下，其断裂韧度参量受组配强度、冲击速度及环境温度等因素影响显著，焊接热影响区的断裂韧度值关系到焊接接头断裂韧度的好坏。