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。     

焊接接头损伤条件下的断裂力学参量数值模拟

利用弹塑性损伤-应变耦合有限元方法研究了不同强度匹配焊接接头中母材区断裂应变的变化对焊缝区裂纹断裂力学参量J积分的影响规律.结果表明,对于强度高匹配、等匹配和低匹配的焊接接头,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,焊缝区的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(母材屈服强度的升高),母材区断裂应变的变化对J积分值的影响作用减小.     

焊缝的非匹配对含表面裂纹管道接头J积分的影响研究

采用有限元方法对几种匹配情况下管道接头表面裂纹的J积分值进行了计算,结果表明焊缝强度匹配以及应变硬化参数匹配的影响随载荷加大而加大,但应变参数匹配影响比强度匹配影响小。对强度匹配对J积分值的影响进行了详细讨论,其结果表明对于高匹配接头来说,J焊缝金属相似文献   

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。     

裂纹长度、焊缝宽度及强度组配对焊接接头J积分的影响

采用虚拟裂纹扩展法对焊接接头力学不均匀体的断裂参量J积分进行了数值模拟分析，考察了焊接接头J积分的守恒性以及不同的裂纹长度（a/W=0.1-0.5)，焊缝宽度（H／c=0.1-0.5)和强度组配（M＝0.6-1.4)在加载过程中对J积分的影响，计算结果表明：焊接接头裂纹尖端近场的J积分具有路径依赖性，而在远离裂尖的J积分表现出路径无关性。强度组配因子M对J积分值有很大的影响，焊缝宽度，裂纹长度对J积分值也有影响。     

强度失配焊接接头的裂纹尖端张开位移数值分析

采用有限元方法对平面应变条件下含裂纹不同强度失配的平板拉伸焊接接头进行了弹塑性分析,研究了焊缝与母材强度失配、裂纹长度、母材应力应变曲线类型等因素对焊接接头裂纹尖端张开位移的影响.结果表明,强度失配系数增大,焊接接头裂纹尖端张开位移值降低,裂纹长度越短,强度失配的影响越显著.母材无屈服平台时,裂纹尖端张开位移随外加应变的增大呈单调上升趋势,母材有屈服平台时,在高匹配或者裂纹长度较短时,裂纹尖端张开位移曲线会出现阶段性变化,这主要是由于母材形变硬化滞后焊缝变形所产生的.     

高匹配焊接接头裂纹的J积分研究

本文研究了含有纵向裂纹或缺陷的高匹配焊接接头材料不均匀性和焊缝宽度对弹塑性断裂表征参量J积分的影响规律.高匹配焊缝被理想化为含有一平行裂纹的一个硬夹层,其屈服应力高于母材.在平面应力条件下利用弹塑性有限元计算得到数值解.研究结果表明,材料不均匀性和焊缝宽度对J积分值有显著影响,特别当名义应力或名义应变较高时影响更大.因此,估算高匹配接头的裂纹推力时必须对此加以考虑.     

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     

力学失配对电子束焊接接头疲劳裂纹扩展行为的影响

研究了高温合金电子束焊接接头区的疲劳裂纹扩展行为,深入分析了接头区力学失配对疲劳裂纹扩展方向及疲劳裂纹扩展速率的影响规律。结果表明,由于力学不均匀性的影响,电子束焊接接头的疲劳裂纹扩展具有不稳定性,位于高匹配焊接区的疲劳裂纹偏离原裂纹扩展方向,跨越焊接区与母材,呈复合型扩展;焊接区疲劳裂纹的集团使得裂纹尖端有效应力强度因子减小,因而焊缝区裂尖局部有效裂纹扩展驱动力下降,导致接头的疲劳裂纹扩展速率下     

热轧态镍基高温合金电子束焊接接头裂纹容限

对GH4169合金电子束焊接接头进行了裂纹尖端张开位移(CTOD)试验分析,试验温度为20℃和650℃,评价GH4169合金接头的抗断裂性能.在CTOD试验的基础上,开展GH4169合金电子束焊接接头裂纹容限评定.试验结果表明,不论是在常温下(20℃)还是在高温下(650℃),母材的CTOD值高于其焊缝值,即母材的抗断裂能力优于焊缝值,并且焊缝的CTOD值较低,易发生脆性断裂.裂纹容限的计算结果表明,在同一应力水平下,母材的裂纹容限比焊缝值高,但母材与焊缝的裂纹容限差值随着应力水平的升高而减小.     

裂纹位置对强度失配焊接接头极限载荷的影响

采用有限元方法对平面应变条件下含裂纹的强度失配焊接接头极限载荷进行了计算,研究了裂纹位于焊缝不同位置时对接头极限载荷的影响.结果表明,裂纹尺寸和焊缝宽度增大时,接头极限载荷接近均质焊缝的极限载荷,此时失配系数的影响很大;裂纹尺寸和焊缝宽度减小,不同失配系数接头的极限载荷逐渐趋于一致.当焊缝强度失配程度一定时,裂纹偏置量在裂纹尺寸较大且焊缝较宽时对接头极限载荷的影响较大,裂纹偏置量增大可使低匹配接头极限载荷提高,对高匹配接头则相反,随着裂纹尺寸和焊缝宽度的减小,裂纹偏置量对接头极限载荷的影响程度减弱.     

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.     

微合金化灰铸铁气焊丝焊接接头组织与性能

以弱碳化焰熔化微合金化灰铸铁焊丝,并充填灰铸铁棒材U型坡口,通过金相观察接头微观组织,发现铸铁同质焊缝微观组织对微合金化元素含量十分敏感,微合金化处理能够实现焊缝金属与基体金属的高强度冶金结合,微合金元素促进焊缝石墨化,并有效避免白口组织及焊接裂纹形成.焊接接头抗拉强度高于基体且硬度接近基体金属,机械加工性能良好.微合金化气焊丝成分可调,可满足各种牌号灰铸铁件的气焊需要.     

STUDY ON DYNAMIC J-INTEGRAL OF MECHANICAL HETEROGENEOUS WELDED JOINT

Welded joint is a mechanical heterogeneous body, and mechanical heterogeneity has great effect on dynamic fracture behaviour of welded joints. In the present investigation, dynamic response curve and dynamic J-integral of practical undermatched welded joint and whole base and whole weld three-point-bend (TPB) models containing longitudinal crack are computed. Dynamic J-integral is evaluated using virtual crack extension (VCE) method and the computation is performed using MARC finite element code. Because of the effect of inertia,dynamic load response curve of computed model waves periodically. Dynamic J-integral evaluated by VCE method is path independent. The effect of inertia has little influence on dynamic J-integral curve. The value of dynamic J-integral of undermatched welded joint is lower than that of whole base metal and higher than that of whole weld metal. The results establish the foundation of safety evaluation for dynamic loaded welded structures.     

转向架用SMA490BW钢焊接接头超高周疲劳性能

采用超声疲劳试验方法对SMA490BW钢焊接接头的超高周疲劳性能进行研究,通过X射线应力仪对焊接试样残余应力进行测试,采用扫描电镜对疲劳裂纹的萌生、扩展及疲劳断裂机理进行观察和分析. 结果表明,SMA490BW钢母材的疲劳性能远高于焊接接头,在1 × 108循环周次条件下,接头的疲劳强度为141 MPa,仅为母材的44.2%. 接头裂纹主要萌生于焊趾表面缺陷处,疲劳断裂机理表现为准解理断裂, 并伴有塑性变形痕迹. 焊趾处几何不连续造成的应力集中和焊缝及其附近区域一定的残余拉应力,以及接头各微区组织和性能的不均匀性,是导致焊接接头疲劳性能偏低的主要原因.     

ON FATIGUE CRACK PATH DEVIATION AT ELEVATED TEMPERATURE IN ELECTRON BEAM REPAIRED WELDMENTS OF TURBINE DISK

Fatigue crack growth behaviors in electron beam weldments of a nickel-base superalloy are. studied. The objective of this paper is to discuss effects of the inhomogeneity of mechanical performance on fatigue crack growth (FCG) rate and crack path deviation (CPD). The base metal served in a turbine disk of aerospace engine was selected to fabricate bead-on-plate weldments by using electron beam welding. Some wedge-type opening loading specimens, notched in three different zone of weld metal, HAZ and base metal, were employed and performed fatigue crack growth tests at 650℃. The results show that the fatigue crack growth of electron beam welded joints is instable due to the influence of mechanical heterogeneities. Owing to the crack deviation at the weld metal and heat-affected-zone (HAZ), the effective growth driving force at the tip of fatigue crack was reduced with the reduction of the effective stress intensity factor (SIF) which finally causes fatigue crack rate decrease. Fatigue crack was strongly affected by size and the symmetrical characteristics of the plastic zone at the crack tip, which means that the integrity of the welded structure containing the fatigue crack mainly depended on the toughness of the low strenqth zone.     

Effects of strength matching and crack depth on the fracture parameters for welded joints

ＥｆｆｅｃｔｓｏｆｓｔｒｅｎｇｔｈｍａｔｃｈｉｎｇａｎｄｃｒａｃｋｄｅｐｔｈｏｎｔｈｅｆｒａｃｔｕｒｅｐａｒａｍｅｔｅｒｓｆｏｒｗｅｌｄｅｄｊｏｉｎｔｓＴａｎｇＷｅｉａｎｄＳｈｉＹａｏｗｕ（Ｘｉ＇ａｎＪｉａｏｔｏｎｇＵｎｉｖｅｒｓｉｔｙ）Ａｂｓｔｒａ...