旁路耦合电弧焊温度场模拟及验证

针对旁路耦合电弧焊的特点, 建立了一种适于用旁路耦合电弧焊的复合热源模型. 利用该热源模型对不同焊接参数下的旁路耦合电弧焊温度场进行了数值分析, 得到了总电流相同时不同旁路电流下的焊缝熔深、母材温度和特征点焊接热循环曲线的模拟结果, 分析了旁路耦合电弧焊焊接参数对母材热输入的影响, 并将特征点热循环曲线的模拟结果与相同条件下的试验结果进行了比较. 结果表明, 焊接总电流相同时母材热输入随着旁路电流的增加而降低, 且越靠近焊缝母材热输入的降幅越大, 特征点焊接热循环曲线的模拟结果与试验结果基本一致, 旁路耦合电弧焊温度场模型是合理的, 所建立的热源模型能够正确反映焊接参数与母材热输入之间的关系.     

爆炸焊接斜碰撞过程的数值模拟

 借助动力学分析软件ANSYS/LS-DYNA 11.0,建立了考虑材料强度的流体弹塑性力学模型,运用光滑粒子流体动力学（SPH）方法,对爆炸焊接斜碰撞过程进行了数值模拟。界面波和射流的模拟结果与爆炸焊接生产实际中的现象较为吻合,说明采用SPH方法对爆炸焊接斜碰撞过程进行模拟研究是有科学价值的。     

双丝脉冲MIG焊接电弧光谱诊断及热源耦合机理分析

搭建了双丝脉冲MIG焊接试验系统,为了分析研究双丝脉冲MIG焊接的热源耦合机理以及电弧温度场,采用光谱技术对其电弧进行了诊断分析,采用中空探针法进行等离子体的辐射采集,得到电弧等离子体的光信号,利用Boltzmann图法计算了双丝脉冲MIG焊接电弧等离子体的电子温度,得出了电弧等离子体的电子温度分布规律,并结合电信号采集和高速摄像技术对电弧进行了综合分析。研究创新之处在于结合了电弧的高速摄像图片信息和电弧等离子体的光信号对双电弧耦合机理进行分析,对电弧温度场进行了较为直观的分析研究。试验结果表明,在本试验条件下焊接过程实现了推挽式输出,实现了一脉一滴的过渡方式;两个电弧在焊接过程中在磁场的作用下相互吸引,向中心发生了偏移,在双电弧的几何中心形成了新的热源中心,并且电弧发生上飘现象;双电弧电子温度整体呈倒V型分布,在双电弧几何中心位置,距工件表面3 mm的位置电弧电子温度最高,为16 887.66 K,比最低温度11 963.63 K高大约4 900 K。     

Microstructural evolution of pure copper during friction-stir welding

The microstructural evolution of pure copper during friction-stir welding was found to be principally influenced by welding temperature. At temperatures below ~0.5 T_m (where T_m is melting point), the microstructure was shown to be essentially determined by continuous recrystallization, leading to significant grain refinement and related material strengthening in the stir zone. In contrast, grain structure development at temperatures above ~0.5 T_m was dominated by discontinuous recrystallization producing a relatively coarse grain structure in the stir zone and giving rise to material softening.     

万瓦级光纤激光焊接过程中小孔内外等离子体研究

为了进一步深入了解超高功率光纤激光深熔焊接过程中等离子体特征,试验拍摄了深熔小孔内外等离子体形态,并采用光谱仪检测分析了光纤激光致等离子体光谱信号.利用检测得到的等离子体光谱信号,计算研究了等离子体的电子温度、电子密度、电离度以及等离子体压力特征,并分析了在小孔内不同深度处及孔外等离子体的变化规律.结果表明,孔内等离子体呈现不均匀分布特征,孔外金属蒸气远多于等离子体.等离子体光谱分析显示,光纤激光致等离子体辐射出的谱线较少,即电离程度较低.进一步的计算结果同样证实了光纤激光致等离子体处于弱电离状态,但等离子体电子密度仍然处于较高水平,且等离子体瞬态压力可达到数百个大气压.     

过渡层对锆/钢爆炸复合板剪切强度的影响

为了考察钛作为过渡层提高锆/钢复合板结合强度的有效性,同时给出合理的爆炸焊接碰撞参数,对双层锆/钢和三层锆/钛/钢进行了小倾角法爆炸焊接实验研究。借助金相显微技术测量了复合板结合界面的波形参数,采用光滑粒子动力学法模拟得到了不同位置的碰撞速度和碰撞角,并按照国家标准(GB/T 6396-2008)测量了复合板结合界面的爆炸态及退火态的剪切强度。结果表明:钛作为过渡层能够显著提高锆/钢界面的剪切强度;退火消除加工应力后,锆/钢及钛/钢结合面的剪切强度会有所降低;当锆/钛界面的碰撞速度为734~805 m/s,碰撞角为19.8°~20.8°,钛/钢界面的碰撞速度为803~904m/s,碰撞角为19.5°~20.5°时,锆/钛/钢三层复合板的锆/钛和钛/钢界面的剪切强度都能高于140 MPa。     

Laser welding of polymers using unsymmetrical squaraine dyes

Transmission laser welding of plastic is typically achieved by incorporating a laser absorbing dye into one of the two pieces of plastic one wishes to weld together and mediating the welding process using a laser emitting light at a suitable wavelength. Desirable properties of laser absorbing dyes include: (1) the dye is colorless in the visible region but absorbs strongly in the region at the wavelength where the laser emits, (2) the dye has a good conversion of the energy from the laser to heat, (3) the dye is stable enough to be incorporated into the molten plastic, (4) the dye is soluble in the plastic of choice to give an even distribution in the plastic, and (5) the dye is nontoxic. Here, we explore an alternative approach to achieve laser welding of colorless plastics using a laser dye that is colored, but that can be bleached after the welding process. Nonsymmetrical squaraine dyes were prepared by condensation of squaric acid and two equivalents of various 3,5-dimethoxy-N,N-dialkylanilines. After the incorporation into polyethylene and laser welding, the plastic was bleached either by heat treatment or by irradiation with a high pressure Xe-lamp giving colorless polyethylene. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2245–2254     

爆炸焊接与相图

在爆炸焊接的过程中,结合区一薄层基体金属,在高温下将发生熔化、熔解或化合。大量的检验结果表明,这种熔体内的化学和物理组成,与对应组元的一般相图内的物理和化学组成相似。这种相似性便为相图在爆炸焊接中的如下应用打下了基础:可以根据相图来估计对应的复合材料中的熔体的组成,估计金属材料之间的爆炸焊接性,估计它们的结合强度,估计后续热加工或热处理对结合性能的影响,从而为爆炸焊接工艺参数和热加工及热处理工艺参数的制订提供理论依据。     

Fatigue life prediction of welded cruciform joints using strain energy density factor approach

The influences of two welding processes, namely, shielded metal arc welding (SMAW) and flux cored arc welding (FCAW), on fatigue life of cruciform joints containing lack of penetration (LOP) defects have been analyzed by using the strain energy density factor (SEDF) approach. Load carrying cruciform joints were fabricated from ASTM 517 ‘F’ grade steel. Fatigue crack growth experiments were carried out in a mechanical resonance vertical pulsator (SCHENCK 200 kN capacity) with a frequency of 30 Hz under constant amplitude loading (R=0). It was found that the fatigue lives of the cruciform joints fabricated by SMAW process were relatively higher than the FCAW counterpart. Moreover, fracture mechanics equations have been developed to predict the fatigue life of the cruciform joints fabricated by the above-mentioned two processes.     

金属管线高温环境下的断裂失效分析

超燃冲压发动机燃烧室试验台配置了大量金属管线,煤油作为燃料和冷却介质在其中输运,在实验过程中发生管线早期断裂失效,对此开展了分析。首先利用三维体视显微镜与扫描电镜进行了断口观察与分析,表明管线的开裂起源于焊缝根部,具有典型的多源起源特征;裂纹源区具有蓝色半圆形特征,表明存在焊接裂纹。同时,断口呈现明显的疲劳辉纹,间距为亚微米量级。根据辉纹间距与管材壁厚以及使用寿命分析,确定了疲劳载荷的频率范围;根据理论公式与有限元模态分析对管线的自振频率进行了估算,其结果与断口分析的结果吻合良好。以上研究结果表明管线断裂是典型的振动疲劳失效导致的。为此,建议在管线中部增加固定点约束,改变管线的自振频率以降低振幅,并改进焊接工艺,提高管线焊接质量。基于以上措施,有效解决了管线的早期断裂失效问题。