Microstructure and mechanical properties of dissimilar pure copper/1350 aluminum alloy butt joints by friction stir welding

The dissimilar friction stir welding of pure copper/1350 aluminum alloy sheet with a thickness of 3 mm was investigated. Most of the rotating pin was inserted into the aluminum alloy side through a pin-off technique, and sound welds were obtained at a rotation speed of 1000 r/min and a welding speed of 80 mm/min. Complicated microstructure was formed in the nugget, in which vortex-like pattern and lamella structure could be found. No intermetallic compounds were found in the nugget. The hardness distribution indicates that the hardness at the copper side of the nugget is higher than that at the aluminum alloy side, and the hardness at the bottom of the nugget is generally higher than that in other regions. The ultimate tensile strength and elongation of the dissimilar welds are 152 MPa and 6.3%, respectively. The fracture surface observation shows that the dissimilar joints fail with a ductile-brittle mixed fracture mode durin~ tensile test.

Wettability, microstructure and properties of 6061 aluminum alloy/304 stainless steel butt joint achieved by laser-metal inert-gas hybrid welding-brazing

Laser-metal inert-gas(MIG)hybrid welding-brazing was applied to the butt joint of 6061-T6 aluminum alloy and 304 stainless steel.The microstructure and mechanical properties of the joint were studied.An excellent joint-section shape was achieved from good wettability on both sides of the stainless steel.Scanning electron microscopy,energy-dispersive spectroscopy and X-ray diffractometry indicated an intermetallic compound(IMC)layer at the 6061-T6/304 interface.The IMC thickness was controlled to be^2μm,which was attributed to the advantage of the laser-MIG hybrid method.Fe3Al dominated in the IMC layer at the interface between the stainless steel and the back reinforcement.The IMC layer in the remaining regions consisted mainly of Fe4Al13.A thinner IMC layer and better wettability on both sides of the stainless steel were obtained,because of the optimized energy distribution from a combination of a laser beam with a MIG arc.The average tensile strength of the joint with reinforcement using laser-MIG hybrid process was improved to be 174 MPa(60%of the 6061-T6 tensile strength),which was significantly higher than that of the joint by traditional MIG process.

Fatigue life analysis of SMA490BW steel welded butt joint for train bogie based on ABAQUS/FE-SAFE

Stress concentration has a significant effect on fatigue properties of welded butt joint of bogie.The influences of joint geometric parameters {weld edge transition arc radius r,weld toe inclination angle θ） on stress concentration coefficient Kt at weld toe and fatigue life N were studied based on the finite element software ABAQUS/FE-SAFE,and the parametric equations were founded based on regression analysis of Origin software.The results show that weld edge transition arc radius r plays the most important role in stress concentration coefficient Kt as well as weld toe inclination angle 0.For the same inclination angle θ,stress concentration coefficient Kt decreases gradually with transition arc radius r increasing.With inclination angle θ increases,the effect of transition arc radius r on stress concentration factor Kt is increasing continuously,also the effect of change in stress concentration coefficient Kt caused by r on fatigue life N is increasing continuously.While in the case of same weld edge transition arc radius r,stress concentration coefficient Kt increases with inclination angle θincreasing.With transition arc radius r increases,the effect of inclination angle θ on stress concentration factor Kt is decreasing constantly,the effect of change in stress concentration coefficient Kt caused by θ on fatigue life N is decreasing constantly.The associated parametric equations have important instructive significance for the improvement of stress concentration degree and fatigue life of welded butt joint for train bogie.

Fatigue properties of friction stir welded butt joint and base metal of MB8 magnesium alloy

The fatigue properties of friction stir welded （FSW） butt joint and base metal of MB8 magnesium alloy were investigated. The comparative fatigue tests were carried out using EHF-EM2OOK2-070-IA fatigue testing machine for both FSW butt joint and base metal specimens. The fatigue fractures were observed and analyzed using a scanning electron microscope of JSM-6063LA type. The experimental results show that the fatigue performance of the FSW butt joint of MB8 magnesium alloy is sharply decreased. The conditional fatigue limit （2 x 106） of base metal and welded butt joint is about 77.44 MPa and 49. 91 MPa, respectively. The conditional fatigue limit （2 x 106 ） of the welded butt joint is 64.45% of that of base metal. The main reasons are that the welding can lead to stress concentration in the flash area, tensile welding residual stress in the welded joint（ The residual stress value was 30. 5 MPa）, as well as the grain size is not uniform in the heat-affected zone. The cleavage steps or quasi-cleavage patterns present on the fatigue fracture surface, the fracture type of the FSW butt joint belongs to a brittle fracture.

Influence of geometric parameters on stress concentration factors of undermatched butt joint with single V-groove under three-point bending load

In order to improve the bending load-carrying capacity （BLCC） of undermatched butt joint under three-point bending load, the influence of joint geometric parameters on stress concentration factors （SCF） at the weld bottom center and the weld toe of uudermatched butt joint with single V-groove are studied respectively based on the finite element method in this paper. Results show that the reinforcement height and the cover pass width play decisive role in the BLCC for undermatched butt joint. BLCC of undermatched butt joint can be improved by choosing the appropriate joint geometric parameters.

Experimental Study on the Bending Properties of Grouting Butt Joints Reinforced by Steel Plate Embedded in Bamboo Tube

The construction of grouting butt joints of bamboo tubes is simple and efficient.However,when the joint is bent,the low tensile strength of the mortar easily leads to cracking of the mortar prior to the failure of the bamboo tube.In this paper,a comparative test of the bending capacity was performed on grouting butt joints reinforced by nonperforated,fully perforated,and semiperforated steel plates embedded in bamboo tubes to obtain the loaddisplacement curves and ultimate bearing capacity of various specimens.The strengthening effect of CFRP pasted on bamboo tubes was also studied.The results show that the opening at the end of the steel plate is beneficial to resist the slip between the mortar and steel plate,while the complete section in the middle of the steel plate is conducive to making full use of the tensile strength of the steel plate.Therefore,it is best to insert the semiperforated steel plate with openings in the end and without openings in the middle into the mortar to enhance the bending properties of the grouting butt joint,which can make the failure mode of the joint change from brittle failure of mortar to ductile compression failure of bamboo tube.In addition,pasting CFRP sheets on the external wall of the bamboo tube helps to reduce the tensile stress of the mortar,while increasing the width of the steel plate can increase the bending moment of inertia of the mixture of the steel plate and mortar.These two complementary measures are very effective in delaying the cracking of the bamboo tube and improving the bending capacity of the joint.

The influence of joint geometric parameters on shape factor of butt joint with center through crack

In this research, the influence of such joint geometric parameters as weld width and reinforcement on shape ~actor of butt joint with center crack subjected to static loading was investigated by finite element analyses method. According to the analytical resuhs, a well fracture resistant joint shape of butt joint with center crack has been approved.

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 reinforcement of steel structure post fire.

Experimental Investigation of Laser Welding Process in Butt-Joint Configurations

This paper presents an experimental investigation of laser welding low carbon galvanized steel in butt-joint configurations. The experimental work is focused on the effects of various laser welding parameters on the welds quality. The investigations are based on a structured experimental design using the Taguchi method. Welding experiments are conducted using a 3 kW Nd:YAG laser source. The selected laser welding parameters (laser power, welding speed, laser fiber diameter, gap between sheets and sheet thickness) are combined and used to evaluate the variation of four weld quality attributes (bead width, penetration depth, underfill and hardness) and to identify the possible relationship between welding parameters and weld physical and geometrical attributes. The effects of these parameters are studied using ANOVA to find their contributions to the variation of different weld characteristics. Plots of the main effects and the interaction effects are also used to understand the influence of the welding parameters. The results reveal that all welding parameters are relevant to bead width (BDW) and depth of penetration (DOP) with a relative predominance of laser power and welding speed. The effect of laser fiber diameter on penetration depth is insignificant. Typical gap-dependent weld shapes show that a small gap results in a narrower and deeper weld. Due to the standard sheared edge, an underfill between 5% and 10% occurs for no-gap experiments. The resulting hardness values are relatively similar for all the experimental tests.

黏接结构在扭转循环载荷下力学行为的试验与理论研究

在应变控制的试验条件下,对圆柱形中空对接试件进行了扭转循环加载的试验,分析了平均剪应变和剪应变幅值对黏接结构的扭转循环应力松弛和软化的影响.试验结果表明:在扭转循环载荷作用下,黏接结构的应力-应变响应曲线形状为下凹形,说明该黏接结构在扭转循环载荷下黏接界面的变形较小,且黏接结构出现了扭转循环应力松弛和循环软化情况.松弛应力在初始阶段下降较快,但随着循环次数的增加逐渐稳定.循环软化在循环加载的初始几圈较为严重,随着循环圈数的增加而减弱.平均剪应变与剪应变幅值的增大都会导致黏接结构的扭转应力松弛与循环软化加剧.此外,通过此黏接结构在扭转循环载荷作用下的力学行为试验分析,本文提出了一个可描述黏接结构在扭转循环载荷下力学响应的非线性黏-弹性循环模型,考虑了扭转循环应力松弛及循环软化的变化规律,以及平均剪应变与剪应变幅值对其力学响应的影响.通过模型计算结果与试验曲线对比,可以看出模型计算的应力-应变响应循环曲线与试验曲线重合度较好,证明该模型可以较好地描述黏接结构在不同循环载荷条件下的力学行为.此研究结果可为黏接结构及相关复合材料疲劳损伤的预测与评价提供试验和理论支持.

无缝隙对接护理在急性消化内镜护理中的效果及对身心应激反应的影响分析

目的 评估无缝隙对接护理应用在急性消化内镜护理中的效果及对身心应激反应的影响。方法 随机选取2022年12月—2023年10月广西医科大学第一附属医院接受急性消化内镜诊疗的100例患者为研究对象,按照随机数字表法分组,对照组(纳入50例,给予常规护理)、观察组(纳入50例,给予无缝隙对接护理),比较两组生理应激[舒张压(Diastolic Blood Pressure,DBP)、收缩压(Systolic Blood Pressure,SBP)、心率(Heart Rate,HR)]、心理应激[焦虑(Self-rating Anxiety Scale,SAS)及抑郁(Self-rating Depression Scale,SDS)自评量表、自我效能感量表(General Self-efficacy Scale,GSES)]、护理满意度、配合度。结果 护理后,相比于对照组,观察组DBP、SBP、HR、SAS、SDS均更低,GSES、护理总满意度更高,差异有统计学意义(P均<0.05)。观察组总配合率(98.00%)高于对照组(84.00%),差异有统计学意义(χ^(2)=5.983,P<0.05)。结论 在急性消化内镜护理中实施无缝隙对接护理,可以减轻身心应激反应,提高满意度及配合度。

气孔缺陷对Q355B对接接头疲劳行为的影响

通过疲劳试验、硬度测试、显微组织观察,对焊缝宽度为20,25,30mm的含气孔缺陷Q355B对接接头单轴应力状态下的疲劳性能进行研究。研究结果表明,随着应力水平由220MPa降至160MPa,对接接头疲劳寿命离散性增加,微观破坏形式由穿晶破坏变为沿晶破坏;对接接头疲劳断裂均由多个疲劳源共同作用,约41%的对接接头因表面缺陷断裂于母材;当气孔缺陷位置相同时,焊缝宽度越小,对接接头疲劳寿命越短;当气孔缺陷位置不同时,缺陷越靠近底面,对接接头疲劳寿命越短;在相似的应力水平和缺陷尺寸下,焊缝中心气孔缺陷对焊缝影响更大,处于边缘的气孔缺陷对母材影响更大。

分体式全灌浆套筒连接在装配式框架结构梁柱节点中的应用

装配式框架结构是国际上公认的最适合装配的结构形式之一,但由于传统的梁柱节点内梁筋连接方法存在诸多难点,一定程度上限制了装配式框架结构在国内的发展。介绍了一种适用于小空间梁柱节点内钢筋对接连接的新型分体式全灌浆套筒,并在装配式框架结构项目中进行了应用实践,总结了分体式全灌浆套筒连接应用过程中节点深化设计、构件生产及安装施工的要点等。项目实施结果表明,分体式全灌浆套筒连接可有效缩短所需的安装操作空间,可以实现构件标准化设计、方便构件生产、加快现场安装速度。

10mm厚Q1100E超高强钢板对接焊残余应力演变研究

为研究10mm厚Q1100E超高强钢板对接焊焊接时的残余应力及演变,利用有限元模拟软件进行焊接残余应力变化规律的模拟。同时,结合对接接头形式,根据GMAW焊接过程中Q1100E钢板焊接残余应力的变化趋势,进行模拟结果的验证,两者相互印证,以获得可靠的焊接接头残余应力分布。试验结果表明:多道焊时的焊缝往往会经历多次焊接热循环;每道的焊缝中心受热源影响较大,温度冷却快,焊缝收缩剧烈,残余应力较大,部分位置可以达到屈服强度,远离焊缝处受热源影响较小,残余应力相对较小。

焊趾工艺优化对压力管道对接接头残余应力的影响

为探讨焊趾工艺优化方案对压力管道对接接头残余应力分布的影响,以提高管道的疲劳寿命和整体性能。通过设计三种不同的焊趾工艺优化方案,利用有限元分析模拟了三种方案对X70管线钢对接接头周向和轴向残余应力的影响,并采用盲孔法对仿真结果进行了验证。仿真和试验结果表明,三种优化方案的周向和轴向残余应力变化趋势基本一致;焊趾位置凹形过渡(方案2)在减少应力峰值和平均应力方面表现最佳,其周向残余应力峰值为539.22 MPa,轴向应力峰值为204.57 MPa;盲孔法测量结果显示,残余应力仿真与试验结果趋势一致,误差控制在8.5%以内,该结果验证了仿真模型的可靠性。焊趾位置的凹形过渡设计能有效降低残余应力,提高压力管道的安全性和耐用性。

模拟海水环境下G20Mn5QT/Q355异种钢对接焊接接头腐蚀疲劳性能试验研究

金属材料焊接接头的腐蚀疲劳失效往往会引发严重的工程事故。本工作对G20Mn5QT/Q355异种钢对接焊接接头在模拟海水环境下的腐蚀疲劳性能进行了研究,开展了其在3.5%NaCl溶液中的腐蚀疲劳试验,并对腐蚀疲劳断口进行了扫描电子显微镜试验,分析了其腐蚀疲劳的失效机理。揭示了在较大应力水平(>220 MPa)下,母材缺陷及焊接缺陷是导致裂纹形核的主要原因;而在较小应力水平(≤220 MPa)下,表面蚀坑是导致裂纹形核的主要原因。分别采用Stromeyer公式与基于三参数威布尔分布的模型建立了对接焊接接头的腐蚀疲劳寿命预测方法,结果表明三参数威布尔分布的腐蚀疲劳S-N曲线拟合精度更高,对实际工程疲劳设计具有指导意义。

不锈钢钎焊接头残余应力数值分析

钎焊接头的残余应力对接头的静力学强度、疲劳强度有着重要的影响。为了获得铜基不锈钢钎焊对接接头的残余应力场信息,采用有限元方法对钎焊过程进行分析,获得在不同焊缝宽度和不同钎焊温度条件下,钎焊接头的残余应力分布情况。结果显示,随着钎焊间隙增大,纵向残余应力减小,而钎焊温度升高则提高了纵向残余应力峰值;考虑钎焊接头产生裂纹的情况,计算残余应力强度因子Kres来表征残余应力二次变化对接头疲劳强度的影响。随着裂纹扩展,残余应力强度因子变大,钎焊接头削弱显著。

基于内聚力模型的气波机振荡管304对接钎焊接头拉伸强度研究

气波机核心部件振荡管采用钎焊连接,钎焊接头拉伸性能对气波机结构强度具有重要影响。为了对钎焊接头界面裂纹扩展过程进行探究,笔者针对气波机振荡管钎焊结构,制备304对接钎焊接头试样进行拉伸试验,并对拉伸断口进行形貌分析,断口处表现为韧性断裂;基于内聚力模型,开发了VUMAT子程序,进行了有限元模拟分析。模拟断裂载荷为5 039 N,试验值为5 242 N,2者误差为3.9%,验证了模拟的准确性,结果表明内聚力模型可以较好地模拟气波机振荡管钎焊接头的裂纹萌生与扩展过程。在此基础上研究焊缝缺陷对钎焊接头断裂载荷的影响,发现缺陷处内聚力单元损伤速率加快,引起断裂载荷显著下降。

Texture and mechanical properties of metal inert gas welded 6082-T651 aluminum alloy joints

Metal inert gas(MIG)welding was conducted with 12 mm thick 6082-T651 aluminum alloy plate to investigate the microstructure and mechanical properties of welded joint.The microstructure and element distribution of weld seam were characterized by electron backscattered diffraction(EBSD)and electron probe microanalysis(EPMA).The weld seam has typical cube texture({001}<100>)characteristics.The closer to the center of weld seam,the weaker the texture feature,the higher the proportion of high-angle grain boundaries.The average tensile strength of joint was 232 MPa which is up to 72%of 6082 aluminum alloy base metal,and the bending angle for the root bend test sample reached 90°without cracks.The lack of strengthening phase and the existence of welding pores and inclusions in the weld seam caused the degradation of mechanical properties of resultant joint.The microhardness increased from the weld center to the base metal,but the overaging zone caused by welding thermal cycle was softening part of the joint,which had lower hardness than the weld seam.

Improving fatigue performance of welded joints of X65 pipeline steel by UIT

Treating weld toes properly can improve the fatigue performance. Ultrasonic impact treatment （UIT） is a more effective and convenient method to enhance the fatigue strength of welded joints and suchlike structures. Fatigue tests were conducted on the specimens made of X65 pipeline steel. The test specimens were investigated on the fatigue strength and the fatigue life at the same stress range level by comparing the ones peened by UIT with the others without the treatment： the fatigue strength of the specimens as UIT, 90% of the fatigue strength of the base mental, is increased by 38% compared with that of as welded only; the fatigue life of the ones as UIT is prolonged by 11 multiples of the ones as welded only.