A7N01铝合金焊接接头的不均匀特性

以A7N01铝合金焊接接头为分析对象,通过金相试验、显微硬度试验、拉伸试验和缺口疲劳试验分析了焊接接头微区的不均匀性．结果表明,A7N01铝合金焊接接头母材、焊缝、热影响区内的组织和硬度差别较大,焊缝硬度最低约为HV75,母材焊缝最高约为HVI10,热影响区内硬度变化较大．母材的屈服强度和抗拉强度高于焊缝和热影响区．而热影响区的断后伸长率最高．三个区域内疲劳裂纹萌生寿命差异较小,裂纹萌生寿命与总寿命之比近似为常数,疲劳总寿命差别明显,母材的疲劳总寿命最长,焊缝疲劳总寿命最短．     

7075-T6铝合金激光-MIG复合焊焊接接头疲劳寿命原位研究

本文对7075-T6铝合金激光复合焊焊接接头的疲劳寿命进行了探究。结果表明：疲劳裂纹萌生寿命与疲劳寿命之间存在着一定的比例关系。对于母材试样,该比值为64.5%;而对于焊接接头试样,该比值为20.2%。疲劳断口表面观察发现,母材试样的疲劳断口上存在大量韧窝,而焊接接头试样疲劳断口上存在许多气孔。这些气孔被认为是引起焊接接头疲劳裂纹萌生寿命急剧下降的主要原因。     

X80大应变钢管焊接接头的疲劳性能北大核心CSCD

采用MTS landmark 370型液压伺服动静疲劳拉伸试验机研究了应力比(R=σmin/σmax)为0.1时X80大应变管线钢焊接接头的拉拉疲劳寿命;并采用显微硬度计和扫描电镜对焊接接头的硬度及疲劳断口进行了分析。结果表明:焊接接头的疲劳寿命显著低于母材;疲劳裂纹均萌生在焊缝熔合线处;裂纹沿热影响区向内扩展,当裂纹扩展到一定程度时,裂纹沿热影响区快速开裂。焊缝金属咬边所形成的夹杂物、焊缝的应力集中及热影响区性能恶化是疲劳裂纹萌生及快速扩展的原因。     

TA15钛合金电子束焊焊接接头力学性能

钛合金材料以及相关制造技术是实现飞机先进性的重要基础之一,电子束焊接是钛合金板材一种先进的焊接形式.对TA15钛合金板材电子束焊接试样进行了金相分析和静力试验、疲劳试验和扫描电镜(SEM)分析.结果表明,TA15板材电子束焊焊接接头的焊缝、热影响区和母材的微观组织差别明显;焊缝韧性降低,抗拉强度高于母材;热影响区尺寸较小,在1～2 mm左右,是焊接接头的薄弱部位;疲劳裂纹大多萌生于焊接热影响区区域,疲劳破坏试样断口的SEM分析表明,疲劳裂纹大多起源于焊接热影响区的气孔处.     

X80大应变钢管焊接接头的疲劳性能

采用MTS landmark 370型液压伺服动静疲劳拉伸试验机研究了应力比(R=σmin/σmax)为0.1时X80大应变管线钢焊接接头的拉拉疲劳寿命;并采用显微硬度计和扫描电镜对焊接接头的硬度及疲劳断口进行了分析。结果表明:焊接接头的疲劳寿命显著低于母材;疲劳裂纹均萌生在焊缝熔合线处;裂纹沿热影响区向内扩展,当裂纹扩展到一定程度时,裂纹沿热影响区快速开裂。焊缝金属咬边所形成的夹杂物、焊缝的应力集中及热影响区性能恶化是疲劳裂纹萌生及快速扩展的原因。     

TC17钛合金电子束焊接接头的疲劳裂纹扩展规律及疲劳剩余寿命

首先通过试验取得母材及焊接接头的疲劳裂纹扩展速率,然后结合TC17钛合金电子束焊接接头CTOD试验结果及裂纹容限计算值,以估算其疲劳剩余寿命.结果表明:在低应力水平或低△K下,TC17电子束焊缝的da/dN数据与母材的基本相当;然而随着应力水平的增加,焊缝的da/dN值越来越大.在初始裂纹尺寸相同的情况下,TC17合金电子束焊缝与母材疲劳裂纹扩展寿命曲线存在交叉点.当应力幅大于交叉点应力幅时,TC17母材疲劳裂纹扩展到临界裂纹尺寸的剩余寿命要高于相应焊缝的剩余寿命;当应力幅小于交叉点应力幅时,TC17母材扩展到临界裂纹尺寸的剩余寿命要低于相应焊缝的剩余寿命.     

6N01铝合金MIG焊接头疲劳裂纹扩展性能研究

研究了6N01铝合金MIG焊接头不同区域的疲劳裂纹扩展速率,对接头的宏观形貌、显微组织、显微硬度和疲劳断口进行了分析。结果表明,焊缝区为等轴树枝晶,接头热影响区主要由淬火区和过时效软化区组成。疲劳裂纹在焊缝中的扩展速率最高;热影响区内,应力值范围较低时,疲劳裂纹扩展速率低于母材,随着应力值范围的增加,其扩展速率高于母材。疲劳断口分析表明,裂纹在焊缝中以不规则和粗糙的脆性疲劳条纹形式扩展,而在热影响区则以塑性的疲劳条纹扩展,扩展抗力较高。     

载荷方向对TC4钛合金激光焊缝疲劳性能的影响

针对不同载荷方向对TC4钛合金激光焊缝的疲劳性能的影响展开对比试验分析,对激光直、斜焊缝的疲劳寿命和疲劳断口进行了对比计算与分析.结果表明,直焊缝试件的疲劳寿命相比斜焊缝的分散性小,斜焊缝试件的中值疲劳寿命是直焊缝的1.98倍;直、斜焊缝试件疲劳裂纹均起始于显微硬度最低的热影响区表面,直焊试件裂纹在焊缝区扩展至断裂,疲劳裂纹扩展区有脆性解理特征,而斜焊试件裂纹穿过焊缝进入母材扩展至断裂,扩展区有典型韧性扩展特征;在瞬断区,斜焊缝试件比直焊缝表现出更好的韧性.     

ADB610钢焊接接头概率疲劳裂纹扩展分析

采用焊条电弧焊方法对ADB610钢进行焊接,对焊接接头进行疲劳裂纹扩展试验,研究其概率疲劳裂纹扩展规律.采用两步七点递增多项式拟合方法,计算了一系列相同裂纹长度下母材区、热影响区和焊缝区的对数裂纹扩展速率方差和存活率分别为50%,90%,95%,99%,99.9%的裂纹扩展速率.结果表明,总体上母材区的裂纹扩展分散性最小,热影响区其次,焊缝区分散性最大;而且总体上存活率相同时,在裂纹扩展的初期,母材区的裂纹扩展速率最快,焊缝区的裂纹扩展速率最慢;在裂纹扩展末期,三区域的裂纹扩展快慢相当;随着存活率增大,三区域裂纹扩展快慢差别不大时所对应的裂纹长度减小.     

TC4-DT钛合金电子束焊接接头疲劳断裂过程的原位观测

通过对TC4-DT钛合金焊接接头显微组织的观察和疲劳断裂过程的原位观测,分析了焊接接头的显微组织特征,研究了焊接接头的疲劳裂纹萌生与扩展行为.结果表明:TC4-DT焊接接头疲劳断裂于母材区,疲劳裂纹萌生于试样的边缘,裂纹既可以沿着初生α相扩展又能直接切过初生α相扩展,裂纹的萌生寿命占整个疲劳寿命的比例较大,裂纹的扩展寿命很短.     

Fatigue crack initiation for Al-Zn-Mg alloy welded joint

To investigate fatigue crack initiation characteristics of Al-Zn-Mg alloy welded joint, notched specimens were used in fatigue test for the base metal, welding bead and heat affected zone (HAZ). The fatigue fracture surface near the fatigue crack initiation site was observed by scanning electron microscope (SEM). The results show that the differences of fatigue crack initiation life among base metal, welding bead and HAZ are not obvious. Inhomogeneity in microstructure and mechanical performance of HAZ influences the fatigue crack initiation life. The ratio of fatigue crack initiation life (Ni) to fatigue failure life (Nf) for the base metal, welding bead and HAZ of A7N01 aluminium alloy welded joint are 26.32%, 40.21% and 60.67%, respectively. Fatigue crack initiation life can be predicted using a uniform model. Observation of fatigue fracture surfaces shows that for the welding bead a fatigue crack initiates from the smooth surface due to the welding process, the blowhole in HAZ causes fatigue crack and the crushed second phase particles play an important role in fatigue crack initiation for the base metal.     

TC11钛合金电子束焊接接头超高周疲劳性能

采用天津大学自行研制的TJU-HJ-I型超声疲劳试验系统研究了TC11钛合金电子束焊焊接接头的超高周疲劳性能. 试验结果表明,TC11钛合金电子束焊接接头在107周次以上仍然会发生疲劳失效,S-N曲线呈现连续下降的趋势,没有明显的转折. 试件的断裂位置大多数为母材处,焊缝和热影响区的疲劳性能要比母材好,这与焊接接头的微观组织有关. 通过SEM对超声疲劳断口形貌进行观察发现,断裂试件的疲劳裂纹大部分在表面萌生,然而在应力范围较低时,疲劳裂纹的萌生位置有从表面转向次表面的趋势.     

Computer-aided experiment on arc welding

Fatigue properties of cast aluminium welded joints by friction stir welding (FSW) and MIG welding were investigated, comparing with that of the base plate. Fatigue crack propagation tests for the da/dN ? ΔK relation and bending fatigue tests for the S–N relation were carried out. Fatigue cracks in both FSW and MIG specimens were accelerated, when the fatigue crack tip reached the stir zone or the weld metal. This behaviour was discussed based on the crack closure induced by the crack surface roughness and the residual stress. In the S–N properties, the influence of specimen surface finishing on fatigue life was also examined. Fatigue lives of the FSW and MIG specimens in the ‘as weld’ condition were in the range of the largely scattered base plate fatigue lives, in spite of the different fatigue crack initiation sites in each specimen such as the porosity in the base plate, the tool mark bottom in the FSW and the weld toe in the MIG. The FSW specimens with the polished surface showed the particular improvement in fatigue strength for finite fatigue life.     

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.     

TC4钛合金薄板激光焊接接头的疲劳寿命及断口分析

研究了TC4钛合金薄板激光焊接接头及母材的疲劳性能,并对其疲劳断口进行了观察.结果表明,接头的疲劳寿命在低应力水平时高于母材,在高应力水平时低于母材.母材疲劳裂纹萌生于试样表面;在裂纹扩展区有平行排列的弯曲的二次裂纹和期间更细的疲劳辉纹,瞬断区为细小的等轴韧窝.焊缝疲劳裂纹起源于表面的气孔,源区有笔直且平行排列的二次裂纹;在裂纹扩展区,断口形貌与组织有关,细晶区为韧窝,在细晶与柱状晶交界处为敞口浅韧窝,柱状晶和粗晶区为晶粒大小的刻面,上有大量的微剪切滑移带,断裂机理为滑移带形成及开裂.     

Fatigue properties of ferrite/bainite dual-phase X80 pipeline steel welded joints

Fatigue properties are important parameters for the safety design and security evaluation of pipelines. In this work, fatigue life and fatigue crack propagation of full-thickness X80 pipeline steel joints compared with the base metal (BM) was investigated. Full-thickness BM specimens showed superior fatigue life compared with that of welded joints. The fatigue crack initiation of full-thickness X80 welded joint specimens occurred at the outside weld toe and then grew inward until a fracture was formed. During fatigue crack growth in the heat-affected zone (HAZ), crack growth rate linearly increased with increased ΔK in each HAZ subregion. However, the change rate of fatigue crack growth rate (da/dN) differed among HAZ subregions. This difference was related to the variation in crack path and fracture mode because of the possible microstructural sensitivity of fatigue crack propagation behaviour.     

A6N01-T5合金FSW和MIG焊接头疲劳裂纹扩展行为的对比

研究了6N01-T5铝合金搅拌摩擦焊(FSW)和氩弧焊(MIG)接头不同部位的疲劳裂纹扩展性能, 并对疲劳断口和接头组织进行了分析. 结果表明,对于FSW和MIG焊接头, 其裂纹扩展速率从高到低的部位依次为焊缝(核)区、热影响区和母材. 裂纹在FSW和MIG焊接头相同区域的扩展速率无明显差别, 然而裂纹在FSW接头细晶组织中开始扩展所需的门槛值ΔK要比对应的MIG焊接头高, 总体上其裂纹在FSW焊核区的抗疲劳裂纹扩展性能要优于对应的MIG焊缝区. 裂纹在FSW和MIG焊接头焊核(缝)区扩展的疲劳断口表现为脆性断裂, 而在热影响区则以规则和光滑的疲劳条纹形式扩展.