采用电子束焊和氩弧焊方法制备的TC4钛合金接头,在 4种温度条件下,测试了其焊缝、热影响区及母材的断裂韧性,并结合断口形貌、硬度分布及微观组织对比分析了断裂韧性测试结果.结果表明,TC4钛合金TIG焊接头焊缝及热影响区的断裂韧性优于钛合金母材,CTOD值随温度下降而降低;相较之下,EBW焊接头焊缝断裂韧性值较母材更低,热影响区断裂韧性与母材较接近,温度变化对其CTOD值无显著影响.钛合金TIG焊接头焊缝区域具有较低硬度值,其网篮状α相和较低比例的马氏体分布是其断裂韧性较高的根本原因;而钛合金EBW焊接头焊缝中针状马氏体的分布导致其局部硬度较高,并降低了断裂韧性.

The main S-N curve method is a new method for fatigue calculation,which is widely used in fatigue analysis of welded structures.In order to predict the fatigue life of welded structures under the test load,firstly,the bench model is taken as the boundary condition to make the test load become the input of simulation analysis,and the more accurate dynamic response of weld is obtained through steady-state dynamic calculation.Second,in the master S-N curve method of quasi static calculation process,based on the introduction of dynamic structural stress based on modal structural stress superposition calculation method,the method to obtain the modal coordinates and calculated by the dynamic welding structure modal stress superposition structure,structure dynamic stress and the equivalent stress calculation,the method adopts the Lord S-N curve forecasting life assessment.Finally,the fatigue evaluation software of welded structure modal structure stress method is developed.The software is used to carry out the fatigue evaluation and fatigue test comparison.The results show that:this method can effectively identify the fatigue failure parts of the car body under dynamic loading,which verifies the effectiveness and superiority of this method in fatigue evaluation of welded structures under dynamic loading,and provides a technical basis for the study of fatigue life evaluation of welded structures and the expansion of the main S-N curve method.

The influence of sensitization on the precipitation behaviour and environmentally assisted cracking (EAC) of AA5083 alloy with the –H128 temper have been investigated. 80 °C/500 h and 80 °C/1000 h sensitized specimens exhibit discontinuous Mg-rich precipitates along the grain boundaries, whereas almost continuous β′ phase is present along the grain boundaries in the 175 °C/100 h sensitized material. EAC susceptibility increases with increasing exposure time and elevated temperature. The relationship between nitric acid mass loss test (NAMLT) values and mechanical test results indicates that specimens with a NAMLT value greater than 25 mg/cm2 exhibit severe EAC. The test environment affects the degree of EAC due to the combined effects of anodic dissolution at the crack tip, hydrogen evolution, and hydrogen embrittlement. AA5083-H128 exhibits lower EAC susceptibility than AA5083-H131, likely due to its lower yield strength. High yield strength can produce more Mg-rich precipitates after sensitization, increase the constraint of the crack tip material and accelerate the diffusion rate of H atoms in the process zone of the crack tip.

In-situ heat treatment (IHT) was introduced in wire arc additive manufacturing (WAAM) process to fabricated Inconel625-high strength low alloy (HSLA) steel functionally graded material (FGM). The graded region with severe Laves phases precipitation was heat treated in 1080 degrees C/1h and 1080 degrees C/2h to alleviate the Laves phases adverse effects. Scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscope (TEM) were applied to analyze the microstructures of the FGMs. By using IHT, the Laves phases were dissolved, Nb-rich carbides packed with dislocation tangles and stacking faults generated, and the tensile strength along the building direction of the Inconel625-HSLA steel FGM has been improved from 512 +/- 15 MPa to 602 +/- 10 MPa.

Good root-pass welding is the basic guarantee for the formation of high-performance welded joints. In the 3G (vertical) position, the difference in the directions of gravity and arc force induces the issues of uneven weld shaping and discontinuous weld penetration more serious than those in the 1G (flat) position. In order to obtain a good weld penetration state for cold metal transfer (CMT) root-pass welding in the vertical-up position, the characteristic signals that could characterize the backside weld geometry were explored, and a prediction model for the backside weld width Wb was established. In this study, the topside weld pool images and the electrical signals were collected in real time. It was found that the two-dimensional topside weld pool geometrical parameters, such as weld pool area A, cannot accurately characterize the backside weld geometry. Due to the difference in arc force, the backside weld geometry with large differences can be obtained with a similar A. After the analysis of the electrical signals, the characteristic signals, namely welding heat input HI and the peak current time ratio PTR, which can represent the heat and force in the CMT welding process, respectively, were extracted, and the two were combined to establish a Wb prediction model, which had a good accuracy and laid the foundation for the weld penetration control after that.

In this study, the response of welding force characteristic to weld-forming process in friction stir welding (FSW) was systematically investigated. Assisted by machine learning technique, we found that both the force value and some detailed characteristics of force waveform are very important in reflecting the characteristics of weld formation. The mapping relations between force characteristics and weld/defect characteristics were compre-hensively summarized for the first time. The results show that the distortion of the force waveform signifies the formation of defect, and the distortion degree and deflection direction of the force waveform show high rele-vancy to the size and location of defect. Meanwhile, the force waveform is decomposed into three standard si-nusoidal waves with different frequencies, and the three sinusoidal waves correspond to the formation of the periodic weld microstructures in nugget zone. The causes of force fluctuations, with associated material defor-mation and flow behaviors during the FSW process, were also clarified to explain the above correspondences. The main reason is that force characteristics are closely related to the tool motion, probe geometric profile and welding parameter, which are key in heat generation and control the material flow in FSW. Therefore, it is concluded that the welding force characteristic is powerful in revealing some key information of the complicated weld-forming process, which can help us to make a deep understanding of FSW and develop intelligent FSW technologies.

In the study, a strain-based fracture assessment scheme with the Modified Mohr-Coulomb (MMC) model is established to numerically characterize the tensile strain capacity (TSC) of X80 steel pipe welded girth. The TSC at crack initiation and local instability are predicted based on a lode-dependent MMC model accounting for crack onset and propagation phases. The combined experimental-numerical calibration of the MMC criterion for crack onset is undertaken for X80 pipeline steel, where seven geometrical specimens are designated to represent various stress states from low to high triaxiality, and the parameter determination of the MMC criterion for crack growth is carried on by fitting the single-edge notched tension tests. Finally, the comparison between the present work and PRCI and ExxonMobil in terms of TSC is performed. A relatively good agreement can be achieved, whereas PRCI gives non-conservative predictions of TSC at crack initiation when crack depth a/t is longer than 0.4 and ExxonMobil gives conservative predictions of TSC at local instability when internal pressure is small.

The effect of welding constraint on nanoscale Cu-rich precipitation in welding heat affected zones (HAZs) of Cu -bearing steel was studied in this work. Due to the constraint tensile stress of 150 MPa, alpha-Fe transformation start temperature (Ts) of CGHAZ and FGHAZ increased by 55 degrees C and 42 degrees C, respectively. The volume fraction and average size of 9R-structural Cu-rich particles in FGHAZ increased from 0.3 % to 0.8 % and from 5 nm to 8 nm, respectively. Three-dimensional phase field simulation shows that the increment of Ts promoted the precipitation of Cu-rich particles in alpha-Fe matrix. However, the Ts of restrained CGHAZ was too low to favor the precipitation of Cu-rich particles. The tensile strength of FGHAZ increased from 970 MPa to 1032 MPa due to the nanoscale Cu -rich precipitation strengthening.

To clarify the effect of peak temperature on the Cu-rich nanoscale re-precipitation behavior and strength -toughness for welding heat affected zones (HAZs), Gleeble-3500 was utilized to simulate the HAZs for Cu -bearing high strength steel with the peak temperature of 780-1350 degrees C. 9R-Cu with the size of 5 nm precipi-tated in FGHAZ. Multi-structured Cu-rich particles precipitated in ICHAZ, including 9R-Cu with the size of 4 nm and 3R-Cu with the size of 12 nm. Phase field simulation showed that the re-precipitation behavior of Cu-rich particles was related to alpha-Fe transformation temperature. When the peak temperature was above Ac3, the increment of peak temperature decreased the alpha-Fe transformation temperature and inhibited the re-precipitation of Cu-rich particles. When the peak temperature was between Ac1 and Ac3, the increase of peak temperature promoted the re-precipitation of 9R-Cu and suppressed the coarsening of 3R-Cu in ICHAZ. Re-precipitation of Cu -rich particles provided precipitation strengthening of 132 MPa and 237 MPa for ICHAZ and FGHAZ, respectively. The high cooling rate during welding increased the grain boundary density of HAZs, which improved the strength of matrix and crack propagation energy. Therefore, the strength and toughness of HAZs for Cu-bearing steel were both higher than base metal.

In the study, the Chapetti cyclic resistance curve is modified by a R-dependence model based on the cyclic strain energy density to account for the mean stress effects on the long crack propagation threshold and fatigue limit. Accordingly, the crack growth model of the modified NASGRO with mechanically short crack extension and Kitagawa-Takahashi diagram are derived with mean stress sensitivity. Relatively good accuracy can be achieved in terms of the near-threshold propagation behaviors and SN curves at high cycle regime including engineering aluminum alloys and titanium alloys.

目的 验证超声冲击处理(UIT)对X80钢管环缝焊接接头疲劳性能的延寿效果.方法 分别开展X80管线钢GMAW自动焊环缝超声冲击前后的疲劳试验,根据国际焊接学会(ⅡW)的规范处理试验数据,并对结果进行对比.结果 稳定地控制管道内壁焊根区域的显微未熔合等焊接缺陷,是保证X80管线钢环焊缝具有优异抗疲劳性能的关键延寿途径之一.采用最大应力固定为屈服强度+全厚度小尺寸试件的焊接接头疲劳试验方法能够替代足尺寸或全尺寸焊接结构疲劳试验,也适用于评价超声冲击处理焊接接头的疲劳性能.在严格控制错边量的前提下,X80管线钢GMAW环缝可以达到BS7608 D级设计曲线要求.结论 超声冲击处理可以显著提高X80管线钢环缝接头的疲劳性能,大约延长疲劳寿命4～10倍左右.

The hydrogen-assisted fracture toughness degradation of X80 weld metal with different microstructure heterogeneity was investigated through a crack tip opening displacement (CTOD) test in air and an H2S-saturated solution combined with a microstructure-based simulation. Differences in microstructure heterogeneity do not lead to variations in corrosion resistance; thus, the degradation of fracture toughness associated with microstructure heterogeneity is mainly controlled by hydrogen embrittlement (HE). The combined effects of increased microstructure heterogeneity and hydrogen promote damage associated with enhanced plastic strain localization. Hydrogen-dislocation interactions make it easier for dislocations to follow the {110} slip plane, resulting in void formation and crack initiation.

The effects of different bonding temperatures on the microstructure and mechanical properties of TC11 alloy diffusion bonded joints were investigated and compared with the original base metal. The experimental results show that the optimal parameters for direct diffusion bonding of TC11 alloy are 900., 30 min, 60 min. There are no holes at the interface of the diffusion bonded joint, and the tensile strength of the joint is close to that of the original TC11 alloy base metal. In addition, the plasticity of TC11 alloy diffusion bonded joint is better than that of the original base metal. High cycle fatigue properties tests were performed at room temperature for the original TC11 alloy base metal and the diffusion bonded joints under optimal process parameters. Compared with the original TC11 alloy base metal, the fatigue property of the direct diffusion bonded TC11 alloy joint is reduced, and all the diffusion bonded joint fractures occur at the diffusion bonded interface. By observing the microstructural characteristics of the fatigue fracture and interface, it is concluded that the difference in the crystal orientation of the base metal on both sides of the interface of the diffusion joint causes fatigue crack initiation, which is the main reason for the reducing of the fatigue property of the diffusion bonded joint.

The deposited metals are prepared by flux cored arc welding used metal cored wire with Nb-V microalloying. The effects of Nb-V microalloying on microstructure, precipitate evolution, and mechanical properties of deposited metal as-welded and post-weld heat treatment (PWHT) are studied. The microstructure of deposited metals without Nb/V is bainite and massive martensite. The microstructure of deposited metals with 0.08

A steel catenary riser (SCR) is a flexible stand-up pipe that connects a subsea wellhead in the seabed (normally at a depth of more than 1500 m) to a floating platform. Waves, ocean currents, and winds apply substantial loads to SCRs that produce fatigue damage. Hence, the requirements for the appearance of SCR weld joints, particularly the weld root, are extremely strict. This paper proposes a new gas metal arc welding/pulse gas tungsten arc welding (GMAW/GTAW-P) double-sided root welding process for SCRs to obtain a nearly smooth root geometry. Test results show that the average values of root reinforcement, root transition angle, and transition radius achieved with this root welding process are only 169 mu m, 6.4 degrees, and 4055 mu m, respectively. These values are dramatically lower than those achievable with the best technologies available, such as the surface tension transfer (STT) root welding process and cold metal transfer (CMT) root welding process. The fatigue strength of the double-sided welding joints is improved by at least 45.8% because the root stress concentration is signifi-cantly reduced. However, incomplete penetration defects were found when the molten pool position was not appropriate. Solutions for this problem are discussed. The proposed process is believed to be a potential strategy for welding high fatigue life SCRs.

针对钢悬链立管单面焊双面成形过程,背部焊缝几何尺寸过大会极大降低立管疲劳寿命的问题,采用热输入小、电弧穿透力小的表面张力过渡焊接方法,研究小钝边(0～1 mm)、无间隙 V 型坡口全位置根焊缝背部成形工艺.对不同焊缝背部几何尺寸试样在 120 MPa、150 MPa、165 MPa、175 MPa 4 个应力范围下进行疲劳试验,研究不同焊缝背部几何尺寸、焊接位置对海洋立管疲劳寿命的影响.疲劳试验结果表明,该焊接工艺下管道具有良好的疲劳性能,试验数据均在DNV-RP-C203-2012 疲劳设计曲线F3 之上.将焊缝背面余高hb和焊缝背面宽度Wb控制在合理的范围内可极大提高海洋立管疲劳寿命.随着 hb/Wb或 hb的增加,焊缝应力集中系数增加,疲劳性能直线下降.不同焊接位置的疲劳寿命也有所不同.受重力影响,平焊位置焊缝背部几何尺寸较大,疲劳性能相对较差,立焊和仰焊位置焊缝背部几何尺寸较小,疲劳性能更好.

GI镀层热成形钢服役过程中具有阴极保护作用且生产成本低,具有较好的应用前景.然而GI镀层热成形钢在高温变形过程中存在"液化金属诱导脆性(LMIE)"开裂问题.通过研究GI镀层热成形钢在不同温度下的高温拉伸性能和U型零部件拐角处涂层微观组织演变和开裂行为,重点分析GI镀层热成形钢成形工艺窗口和"液化金属诱导脆性开裂"机理.实验结果将为GI镀层热成形钢开发和加热成形工艺的制定提供参考.

国际焊接学会（IIW）于2016年发布超声冲击改善焊接接头疲劳性能的推荐规范，该规范的制定主要基于轴向加载的小尺寸焊接接头的疲劳试验，没有充分考虑实际焊接结构中存在的高值焊接残余应力对疲劳延寿效果的影响。采用试验和有限元相结合的方法研究焊接残余应力对超声冲击处理焊接接头疲劳寿命的影响，结果表明，焊接残余拉应力的存在使超声冲击形成的有益残余压缩应力在疲劳服役过程中发生明显释放，进而降低超声冲击处理焊接接头的疲劳延寿效果；试件厚度方向的焊接残余应力平均值越大并且焊接残余应力在超声冲击形成的平衡拉应力区（表面向下1.5～4mm）的值越大，残余压缩应力越容易发生释放。研究充分证实焊接残余拉应力对超声冲击疲劳延寿效果产生不利影响，并揭示其影响因素，对超声冲击处理规范的制定和疲劳评估具有指导意义。

印刷电路板式换热器具有多层薄壁、微通道的结构,如何实现其高质量连接的问题亟待解决.316L不锈钢因其优异的力学性能、焊接性能与耐腐蚀性能,常用于印刷电路板式换热器的制造.文中采用真空扩散连接的方法实现了 316L奥氏体不锈钢的连接,并探究了最优工艺参数,建立了工艺参数—界面组织—力学性能之间的关系.结果表明,随焊接温度升高和保温时间的延长,接头焊合率、变形率上升,晶粒尺寸增长,硬度下降,抗拉伸剪切强度先升高后降低.1 000℃-60 min-10 MPa为最优参数,此时接头抗剪强度最高,为 626 MPa.该参数下的断裂方式为塑性断裂,断口呈典型的韧窝花样.