304不锈钢薄壁管件纵缝焊接接头残余应力数值模拟研究

目的 采用数值模拟方法代替传统测量方法,以准确模拟不锈钢薄壁管件焊接接头残余应力分布规律及预热温度对焊接残余应力的影响规律。方法 采用TIG焊接方法对304不锈钢进行圆管纵缝焊接试验,以最优焊接工艺参数为基础,基于ABAQUS有限元仿真软件,采用热力完全耦合模型,在DFLUX子程序中运用Fortran语言对模型进行汇编以完成ABAQUS的二次开发,模拟薄壁管件纵缝焊接热力耦合过程,并在模拟结果上添加预热温度为150 ℃的预热工艺。结果 304不锈钢薄壁管件焊接过程中会产生较大的残余应力,局部区域接近管材的屈服应力。纵向残余应力趋于焊缝中心方向由压应力转化为拉应力,焊缝中心横向应力承受压应力,并且随着向焊缝两侧移动,横向残余应力值逐渐趋近于0。焊缝厚度方向上的径向应力值变化幅度较小。预热可以有效降低不同方向上的焊接残余应力,其中对纵向残余应力的改善最为明显。结论 数值模拟方法能够准确计算出不锈钢薄壁管件焊接接头残余应力分布,预热处理能够有效降低接头残余应力。     

对接试板焊接残余应力实测与数值模拟

使用压痕法对两副对接试板进行了表面焊接残余应力测试，并通过焊接有限元仿真获得了对接试板焊接残余应力分布规律，对比分析了表面残余应力实测和数值模拟结果。分析结果表明，焊接残余应力数值仿真结果和压痕法实测结果趋势一致，数值相差不大，残余拉应力峰值实测为599 MPa,仿真结果为597 MPa,表明数值模拟方法可预测焊接残余应力；焊缝及热影响区最大纵向残余应力属于拉应力，而最大横向残余应力为压应力，横向残余应力峰值低于纵向残余应力峰值；等效应力(Mises应力)峰值792 MPa,高于试板材料在常温下的初始屈服强度，表明该材料具有明显的加工硬化现象。     

Q355钢板对接接头裂纹扩展所致焊接残余应力重分布研究

目的 定量研究裂纹扩展导致的焊接残余应力重分布效应,得到残余应力随裂纹扩展的变化规律。方法 首先采用盲孔法测试了Q355钢板对接接头的初始残余应力;其次利用线切割技术模拟了平行以及垂直于焊缝的裂纹扩展情况,并测试了裂纹扩展导致的残余应力变化量;最后根据测试数据提出了残余应力释放量Δσ与裂纹长度a之间的函数关系式,进一步得到了基于裂纹扩展的应力重分布计算公式。结果 Q355钢板对接焊的焊缝区纵向(沿焊缝方向)存在较大的残余拉应力,拉应力峰值出现在焊趾处,为屈服强度的1.13倍。焊缝区横向存在梯度较大、拉压交替变化的残余应力,压应力峰值出现在焊趾处,大小为52.6 MPa,拉应力峰值出现在距焊缝中心线17 mm处,大小为63.5 MPa。裂纹扩展能显著释放残余拉应力:裂纹沿焊缝中心扩展,横向残余拉应力峰值降低了45.8%;裂纹沿垂直于焊缝方向扩展,焊趾处的拉应力峰值降低了63.3%。结论 裂纹扩展会显著影响焊接构件的残余应力分布,根据实测数据提出的裂纹扩展应力重分布计算公式能够较好地反映残余应力重分布情况。     

铝合金T型接头激光+GMAW复合焊残余应力数值分析

目的 研究激光+GMAW复合焊中不同激光功率参数对铝合金T型接头残余应力的影响,从而提高焊接性能。方法 分别考虑了热弹塑性理论、传热学以及T型接头几何特性,建立了铝合金T型接头激光+电弧复合焊残余应力的数值分析模型。采用双椭球体热源模型表征电弧热输入与熔滴晗,采用锥体热源模型对激光深熔焊进行描述。基于所建立的T型接头模型,使用ANSYS有限元软件对12 mm厚铝合金激光+ GMAW焊T型接头残余应力进行模拟计算,并研究其分布特征;使用X射线衍射法对T型接头处的残余应力进行测量从而对所建模型的准确性进行验证。同时,对比了不同激光功率下铝合金T型接头对残余应力的影响规律。结果 当激光功率分别为2、3、4、5 kW时,铝合金T型接头路径L3上的纵向残余应力最大值分别为270、263、258、251 MPa,米塞斯-等效应力最大值分别为265、261、257、250 MPa。结论 后焊的焊缝A对焊缝B有明显的热处理作用,使应力明显降低;在T型接头焊缝及近缝区,横向残余应力和厚度方向残余应力峰值均比纵向残余应力峰值小,且随着激光功率的增大,焊缝及近缝区拉应力峰值不断减小。     

高强度船体钢环形拘束焊接接头残余应力的分布

本文采用数值模拟的方法,对船体结构的某一环形拘束焊缝进行焊接残余应力的模拟计算.同时采用压痕式应力测试仪,对实际船体结构进行测试,并与模拟结果相对比验证.结果表明,模拟结果与实测结果测得的焊接残余应力分布规律基本一致,环形拘束焊缝纵向残余应力大于横向残余应力,最大焊接残余应力位于靠近热影响区的直线段焊缝近表面处.     

焊接残余应力磁记忆信号特征的研究

针对焊接残余应力与金属磁记忆信号存在一定联系的现象,设计了Q345R焊接试件.以X射线法检测应力值为参考,研究焊接试件横向和纵向残余应力与试件焊接残余磁信号的对应关系.结果表明,焊接试件残余压应力和试件纵向残余拉应力与试件的磁信号梯度值,在数值和变化趋势上均无明显相关性;磁信号梯度值能用于较大横向拉应力的定位,且梯度最大值点与横向残余应力的最大值点存在一定的对应关系.     

低强匹配对接接头焊接残余应力的数值模拟分析

本文采用数值模拟方法,分析了低强匹配对接接头2种拘束条件、5种屈服强度匹配系数的焊接残余应力。结果表明,低强匹配接头焊根处的三向残余拉应力较小,对静载强度影响不大;焊趾处的三向残余拉应力较大,对疲劳强度和冷裂倾向有不利影响。自由状态的纵向残余应力和两端约束状态的横向残余应力,焊缝金属屈服强度每降低25MPa,其残余应力减少约11MPa。     

圆钢管加工方法诱导的残余应力分布检测与分析

为了研究圆钢管加工方法诱导的纵向残余应力分布规律,该文采用盲孔法对截面规格为 φ325×8的5组15个不同强度、不同加工方法的圆钢管试件进行了测量。基于测量数据,得到了试件截面残余应力分布和拉、压残余应力的数值大小,研究了埋弧焊、高频焊和热轧三种不同加工方法对残余应力分布的影响。试验结果表明,埋弧焊对圆钢管截面纵向残余应力的影响强于高频焊,高强度焊接圆钢管的残余应力分布比较均匀,且焊缝区最大残余拉应力分布在焊缝两侧各40 mm区域内;普通强度钢管截面的最大纵向残余压应力为0.35σ_y,而Q690高强钢焊接圆钢管截面的最大纵向残余压应力为0.21σ_y,同中点截面的纵向残余应力峰值相比,起焊点和落焊点截面处的纵向残余应力峰值偏小。不同于焊接圆钢管,热轧无缝圆钢管同一截面内外表面的最大纵向残余应力数值大小相同,符号相反,其最大值为0.15σ_y。     

轨道车辆型材结构搅拌摩擦焊残余状态研究

目的 研究轨道车辆中典型的箱型和V筋结构型材搅拌摩擦焊残余状态。方法 采用顺序热力耦合方法进行了搅拌摩擦焊残余应力及变形的仿真研究。结果 给出了上下壁板焊缝区域的残余应力大小及分布规律,阐述了两种结构的横向和纵向残余变形特征。对V筋结构型材,分析了不同筋板角度对焊接残余状态的影响。结论 残余应力方面,主要表现为纵向残余应力,上下壁板两条焊缝的残余应力峰值相近,高应力分布区域宽度差别较大。残余变形方面,箱型结构呈马鞍形,V筋型材呈下凹形。V筋型材筋板夹角的变化对残余应力没有显著影响。筋板角度增大,纵向残余变形减小而横向残余变形增大。     

小口径厚壁12Cr1MoVG钢管焊接残余应力的数值模拟

以小口径厚壁12Cr1MoVG珠光体耐热钢管多层多道焊接接头为对象,使用有限元模拟软件,采用生死单元法,计算焊接接头中的残余应力。计算结果表明:焊接接头外壁焊缝附近区域的残余应力为压应力,母材端的残余应力变化幅度要比焊缝区的小;焊接接头内壁焊缝及热影响区的残余应力为压应力,而母材承受拉应力。通过对比可知焊接接头内、外壁轴向残余应力分布的计算结果与实测结果高度吻合,说明数值模拟方法可以为管状接头的焊接工艺评定提供便利、可靠的技术支持。     

304不锈钢管TIG焊接头凝固行为及热力耦合研究

目的 对2mm厚不锈钢管的焊接工艺参数进行优化,并基于模拟仿真软件对接头的热应力场进行模拟,以解决薄壁管件接头应力测试不方便的问题。方法 以TIG焊对2 mm不锈钢管进行焊接,通过对接头宏观形貌、微观组织、显微硬度等结果进行优化进而得到最佳焊接工艺参数,采用双椭球热源和温度-位移耦合方法结合最优工艺参数进行数值模拟。结果 当焊接电流为150 A、焊接速度为66 cm/min时,焊接接头全部熔透,且正面及背面焊道均匀致密,成形良好。焊缝中心上部区域和下部区域均呈现等轴晶形貌,下部区域尺寸较上部区域尺寸略大,熔合线附近为柱状晶组织。焊接接头显微硬度整体分布呈现U形,其中热影响区显微硬度（197HV）大于焊缝区域硬度（162HV）,熔合线附近显微硬度达到最低值（145HV）。模拟结果显示,在焊接过程中,当纵向残余应力从母材向焊缝中心过渡时,由压应力逐步转化为拉应力;焊缝中心横向应力呈现为压应力,向两侧母材过渡时应力值逐渐趋近于0,径向应力值变化幅度较小,模拟数据变化趋势与实测数据变化趋势接近。     

Residual stress distribution and microstructure in the friction stir weld of 7075 aluminum alloy

In order to study the relationship between residual stress (RS) and the microstructure of friction stir weld (FSW), RS profiles through thickness in the un-welded aluminum alloy 7075 plate and in middle layer of its FSW joint were determined nondestructively by the short-wavelength X-ray diffraction (SWXRD) and neutron diffraction. Microstructure and mechanical properties of the FSW joint were also studied by optical microscopic analysis, and microhardness and tensile strength measurements. RS profiles measured by the two methods had the same distribution trend. The maximum tensile RS tested by SWXRD and neutron diffraction in transverse and longitudinal direction occurred in the weld nugget. Microhardness in the direction perpendicular to the weld line showed a “W” shape distribution. Position of the local maximal extremum of RS in thermo-mechanically affected zone corresponded to that of minimal microhardness. The grain-refined strengthening caused by the recrystallization in the weld nugget kept the joint from fracturing at this region notwithstanding the maximum tensile RS. And the tensile fracture occurred near the boundary of welding zone and thermo-mechanically affected zone where minimum of hardness and maximum of RS appear at the same position.     

Effects of mechanical heterogeneity on the tensile and fatigue behaviours in a laser-arc hybrid welded aluminium alloy joint

The effects of mechanical heterogeneity on the tensile and high cycle fatigue (10⁴–10⁷ cycles) properties were investigated for laser-arc hybrid welded aluminium alloy joints. Tensile–tensile cyclic loading with a stress ratio of 0.1 was applied in a direction perpendicular to the weld direction for up to 10⁷ cycles. The local mechanical properties in the tensile test and the accumulated plastic strain in the fatigue test throughout the weld’s different regions were characterized using a digital image correlation technique. The tensile results indicated heterogeneous tensile properties throughout the different regions of the aluminium welded joint, and the heat affected zone was the weakest region in which the strain localized. In the fatigue test, the accumulated plastic strain evolutions in different subzones of the weld were analyzed, and slip bands could be clearly observed in the heat affected zone. A transition of fatigue failure locations from the heat affected zone caused by accumulated plastic strain to the fusion zone induced by fatigue crack at pores could be observed under different cyclic stress levels. The welding porosity in the fusion zone significantly influences the high cycle fatigue behaviour.     

Microstructure and mechanical properties of spray formed 7055 aluminum alloy by underwater friction stir welding

Ultra-high strength spray formed 7055 aluminum alloy in which Zn is supersaturated solid solution requires strict control of heat input in welding process. In this paper, underwater friction stir welding is carried out in order to reduce heat input comparing with traditional friction stir welding and further improve the joint performances by varying welding temperature history. Through comparing the thermal cycle curves and distribution of residual stress of the plate welded in different media, the reason why the joint welded underwater shows a better performance is figured out. The result shows that tensile strength, hardness and plasticity of underwater welded joint are better than that welded in air. The underwater joint has a fine grained microstructure without “S line” defect, a typically distinct boundary between the weld nugget zone and the thermal mechanically affected zone and a narrow heat affected zone. The main strengthening phase in underwater joint is MgZn₂ .     

Ti75合金激光焊接接头的组织及力学性能

采用10 kW的连续光纤激光器对3 mm厚的Ti75合金板进行激光焊接,通过调整不同的激光功率来获得全熔透的焊接接头.同时,观察了不同热输入下焊接接头的宏观形貌、微观组织,测试了焊接接头的力学性能和显微硬度,对接头不同部位的组织特征及成形原因进行了分析.结果表明,随着焊接过程中激光功率的增加,焊缝的宽度逐渐变大,在不同...     

Local melting mechanism and its effects on mechanical properties of friction spot welded joint for Al-Zn-Mg-Cu alloy

Local melting and the eutectic film and liquation crack formation mechanisms during friction spot welding (FSpW) of Al-Zn-Mg-Cu alloy were studied by both experiment and finite element simulation. Their effects on mechanical properties of the joint were examined. When the welding heat input was high, the peak temperature in the stir zone was higher than the incipient melting temperature of the Al-Zn-Mg-Cu alloy. This resulted in local melting along the grain boundaries in this zone. In the retreating stage of the welding process, the formed liquid phase was driven by the flowing plastic material and redistributed as a “U-shaped” line in the stir zone. In the following cooling stage, this liquid phase transformed into eutectic films and liquation cracks. As a result, a new characteristic of “U” line that consisted of eutectic films and liquation cracks is formed in the FSpW join. This “U” line was located in the high stress region when the FSpW joint was loaded, thus it was adverse to the mechanical properties of the FSpW joint. During tensile shear tests, the “U” line became a preferred crack propagation path, resulting in the occurrence of brittle fracture.     

Influence of Heat Input on Microstructure and Mechanical Properties of Laser Welding GH4169 Bolt Assembly—Numerical and Experimental Analysis

By conducting the numerical and experimental analysis, the influence of heat input on the microstructures and mechanical properties of laser welding GH4169 bolt assembly is systematically investigated. The weld formation, temperature field, and residual stress distribution during laser welding by using the finite element modeling are consistent with experimental results. The numerical simulation results show that the increase of heat input imparts lower residual stresses and higher temperature gradient. During the process of laser welding, the steepest temperature gradient and the peak residual stress arise in the fusion zone (FZ). In addition, the dissolution of γ″ and γ′ toward the fusion line increases in heat affected zone (HAZ), but only Laves phase is observed in FZ. With increasing heat input from 24 to 48 J mm⁻¹, the ultimate tensile strength of welded joints decreases. Both the lowest microhardness values and tensile failure of GH4169 alloy laser welded joint are in FZ. Herein, it is that the relationship among the heat input, microstructures, and mechanical properties of GH4196 bolt assembly in laser welding is systematically established, which will be of guiding significance for the selection of welding parameters in aerospace.     

不同强度级别双相不锈钢激光焊接头的组织与力学性能

目的 为了合理制定不同强度等级DP钢同种和异种接头的激光焊接工艺,研究激光焊接工艺对接头组织性能的影响。方法 采用SEM、硬度试验、拉伸试验等手段,研究不同强度等级DP钢同种和异种激光焊接接头的微观组织和力学性能。结果 对于同种DP钢激光焊接,由于接头各个区域经历的热循环不同,因此其马氏体体积分数和形态、含碳量等存在明显差异。在焊缝熔合区,由于冷却速度较高,因此马氏体体积分数较高且为细条状,硬度高于母材硬度。在热影响区,由于马氏体发生了回火分解,因此其硬度值低于母材硬度,且软化的程度和范围大小与DP钢的强度级别相关。软化的热影响区成为接头的薄弱区域,降低了接头的拉伸性能。在异种DP钢激光焊接接头中,焊缝熔合区的硬度也明显高于母材硬度。靠近高强度级别母材侧的热影响区范围更大,软化程度更明显,接头硬度分布不再对称。接头的抗拉强度与低等级DP钢母材的抗拉强度基本一致。结论 激光焊接工艺对不同强度等级DP钢同种和异种接头组织性能的影响存在较大的差异,DP钢强度级别越高,接头或接头对应侧的热影响区软化程度越明显,这在制定焊接工艺以及焊后处理工艺过程中需要予以考虑。     

铝锂合金电子束焊接数值模拟分析及工艺优化

采用组合热源模型对Al-Li合金电子束焊接温度场分布进行数值模拟分析,通过热-力耦合,模拟计算得到接头区域的残余应力分布.结果表明,Al-Li合金电子束焊接温度场沿焊接方向呈椭圆形分布,电子束热源中心的温度最高,其附近区域的等温线分布密集,随着与热源中心的距离增大,等温线分布逐渐稀疏,焊缝区存在较大的温度梯度,较好地模拟出了电子束焊缝的钉形分布特征.接头的残余应力分布模拟结果显示,残余应力主要集中于焊缝区,由于修饰焊的热作用,焊缝上部具有相对较大的应力值.利用模拟计算得到的结果进行焊接工艺及参数优化,焊接工艺试验表明,试验焊缝形貌与模拟熔池形貌相吻合,进一步验证了模拟计算结果的可靠性.     

焊接工艺参数对Q345钢平板焊接残余应力的影响

为研究焊接工艺参数对Q345钢平板焊接残余应力的影响,对采用药芯焊丝半自动焊接后的8 mm厚平板焊缝结构进行仿真模拟,在经验数值范围内设置不同的焊接工艺参数值,分析平板在横向和厚度方向的焊接残余应力分布情况。研究结果表明:横向的最大焊接残余应力分布在热影响区,且随着焊接速度的增大和焊接层间温度的降低而降低;沿厚度方向的最大焊接残余应力为115.92 MPa,位于平板中间层,随着焊接速度的增大而先减小后增大;平板焊接在横向的残余应力远大于厚度方向的应力。根据焊接残余应力的变化情况,运用二元回归分析法对横向和厚度方向的最大焊接残余应力进行函数拟合与检验,并开展多因素拟合模型的分析,得到焊接速度和焊接层间温度对焊接残余应力的综合影响规律。通过研究残余应力的变化趋势可选定焊接残余应力最小时的工艺参数范围,实现焊接工艺参数优化。