基于自组装膜的光纤错位型氨气传感器

演示了一种基于单壁碳纳米管（SWCNTs）-聚合物自组装复合膜的光纤错位型氨气传感器。通过层层自组装技术在高Q谐振器上涂覆薄膜,薄膜上存在大量的游离羧基以及较大的比表面积,这提供了光与薄膜之间的强相互作用,以及对氨气的高吸附性和选择性。光谱随氨气浓度影响的有效折射率而变化。在(10～37) ×10⁻⁶的低浓度范围内,光谱变化与氨气浓度差之比即灵敏度为13.25 pm/10⁻⁶,检测极限为3.77 ×10⁻⁶并且具有良好的线性。这项工作研制为低浓度和高选择性氨气传感器提供了一种有效的方法。     

双金属爆炸焊接上限

本文根据热传导理论给出了爆炸焊接时双金属结合区附近的温度场解析解。并利用该解初步研究了双金属的爆炸焊接上限。     

Dual beam method for laser welding of galvanized steel: Experimentation and prospects

Laser welding of zinc-coated steel sheets in lap configuration poses a challenging problem, because of the zinc vapours spoiling the quality of the weld. In continuation to the earlier work, the novel solution of dual laser beam method for lap welding of galvanized steel sheets is discussed here in view of the recently obtained observations and ensuing concerns. In this method the precursor beam cuts a slot, thus making an exit path for the zinc vapours, while the second beam performs the needed welding. The metallurgical analysis of the welds is encouraging showing absence of zinc in the welded area. In the current work on this technique, new experimental results have been obtained verifying the earlier observations. Along with this, the possibility of using a transversely split-up beam for the welding purposes with this approach is discussed and analyzed in this paper. This new technique is expected to be very useful in prospective industrial applications requiring higher welding throughput along with the needed quality.     

Deposition of carbon nitride films for space application

Carbon nitride thin films were prepared by electron-beam evaporation assisted with nitrogen ion bombardment and TiN/CN_x composite films were by unbalanced dc magnetron sputtering, respectively. It was found that the sputtered films were better than the evaporated films in hardness and adhesion. The experiments of atomic oxygen action, cold welding, friction and wearing were emphasized, and the results proved that the sputtered TiN/CN_x composite films were suitable for space application.     

非晶合金条带的爆炸焊接

 报道了利用爆炸焊接技术对铁基、铁镍基非晶合金条带（厚度约25 μm）进行单层和多层爆炸焊接的结果。金相分析结果表明，条带间相互结合良好；X光衍射结果说明，焊接后的条带仍保持非晶态，即使采用表面已有部分晶化德条带进行焊接，焊接后仍转化为非晶态。这说明在焊接过程中条带表面已发生熔化，且冷却速度也可达10⁶ K/s量级。     

The Loewner differential equation and slit mappings

We show that the Loewner equation generates slits if the driving term is Hölder continuous with exponent 1/2 and small norm and that this is best possible.

     

Optical Measuring Method for Quality Monitoring Purpose in Laser Welding of Tin－plates

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A three-dimensional model of multiple reflections for high-speed deep penetration laser welding based on an actual keyhole

Keyhole shapes are observed experimentally by two high-speed cameras from two perpendicular directions in high-speed laser welding of glass. From the obtained keyhole pictures, it can be seen that in high-speed deep penetration laser welding, the keyhole is not only seriously bent in the direction opposite to that of welding speed, but also elongated along the direction of the welding speed. Based on the so-obtained keyhole photograph, the keyhole profiles in both the symmetric plane and its perpendicular plane (i.e., the cross-section plane) are determined by the method of polynomial fitting. Then, under the assumption of elliptical cross-section of the keyhole at each keyhole depth, a 3D bending keyhole is reconstructed, the behavior of focused Gaussian laser beam in the keyhole is analyzed by tracing a ray of light using geometrical optics theory. Fresnel absorption and multiple reflections in the keyhole are systematically studied, and the laser intensities absorbed on the keyhole walls are calculated. In determining the distribution of laser intensity on the keyhole wall, the bending of the keyhole plays the dominant role, elongation of the keyhole plays just a minor role. Because of the bending of the keyhole, not all the keyhole wall can be irradiated directly by laser beam. The absorbed laser intensity cannot be uniformly distributed on the keyhole wall even after multiple reflections. The keyhole wall absorbs laser intensity mainly on the small area near the front keyhole wall. Recoil pressure plays a dominant role in forming a keyhole and keeping it open.     

CP-MAS C NMR and FT-IR investigation of the degradation reactions of polymer constituents in wood welding

The essential chemical modifications involving the polymeric constituents of wood in friction welding occur in the first 5-6 s slowing down or even stopping afterwards. FT-IR and CP-MAS ¹³C NMR of the welded area of wood have shown dehydration and an apparent increase in the crystallinity of cellulose. A certain level of hemicelluloses degradation occurs, accompanied by the generation of some furfural. Cellulose degradation is instead very slight. Both analytical techniques show an increase in the proportion of lignin in the welding interphase. A proportion of methoxy groups of lignin is de-etherified to phenolic hydroxy groups. Self-condensation of lignin occurs by internal rearrangement with the formation of Ar-Ar and Ar-CH₂-Ar bridges. This progresses throughout the whole process of welding. The formation of C-O-C bridges, although stopping after 6 s welding, at the start of wood carbonisation, also appears to contribute to the increase in cross-linking of the lignin network.     

基于光谱分析的CO_2激光+脉冲GMAW复合焊峰值状态激光能量传输研究

在激光+脉冲GMAW复合焊接过程中,焊丝端部金属熔化产生大量的金属蒸汽,导致等离子体中电子、粒子的扩散现象加剧,使得激光的传输模式和工件对激光能量的吸收率和吸收模式发生变化。基于光谱分析的方法得到了复合焊接峰值状态的电子密度和温度分布,通过高速摄影分析了不同焊接模式下等离子体形态的变化,结合Beer-Lambert吸收定律计算了不同焊接模式下激光的吸收率。结果表明,在复合焊过程中,由于焊丝端部金属被熔化,焊丝的金属蒸汽进入激光等离子体内部,导致激光匙孔上方电子密度进一步提高,等离子体吸收激光能量能力增强,使得激光的传输效率从纯激光焊的94.16%降低到了CO_2激光+脉冲GMAW复合焊的85.84%。