重力对全位置TIG焊熔池温度场与流场影响的有限元分析

建立了全位置TIG焊接中平焊、45°下向焊、立焊下向焊的熔池温度场、流场数值计算模型,计算了不同焊接位置以及不同重力加速度值情况下熔池的温度场和流场,分析了重力方向和大小对熔池内流场和温度场的影响规律;发现重力方向对熔池内液态金属的流场、温度场影响明显,液态金属的流动影响温度场分布明显,重力大小对熔池流场的分布形态没有影响,但是对流动速度影响明显. 得到的结论对于研究熔池失稳判定依据、指导设计全位置TIG焊乃至MAG焊工艺具有一定的参考价值.     

热处理工艺对高铬铸铁Cr20力学性能的影响

采用消失模熔铸法试制了亚共晶高铬铸铁Cr20,研究了淬火与回火加热温度和保温时间对其力学性能的影响。结果表明,高铬铸铁Cr20的淬火加热温度在1000～1050 ℃之间时,硬度较高,而且在1050 ℃时其冲击性能达到最高值。回火温度在300 ℃时出现一个拐点,其冲击性能出现较明显下降,而其硬度降低较小。在热处理试验工艺下,高铬铸铁的力学性能对热处理时的保温时间不敏感。高铬铸铁Cr20较佳的热处理工艺为1050 ℃´0.5 h淬火+300 ℃´2 h回火。     

Al-Nb含量对转子用GH706合金组织及力学性能的影响

研究了提Al降Nb对GH706合金经过高温长时时效处理前后的组织与力学性能的影响。结果表明,提Al降Nb的成分改进抑制了高温不稳定存在的γ′′相、η相及Laves相和δ相等TCP相的析出,同时,在经过750℃保温500h的处理后,只存在γ′和η相的轻微长大,力学性能下降幅度有限,仍保持在一个较高的水平,而未进行成分改进的合金(传统GH706)中的析出相等均发生明显长大,力学性能下降幅度较大,可见提Al降Nb的成分改进可使得合金在更高的温度服役。     

HPT不同压力下纯钼组织性能及热稳定性研究

通过高压扭转实验,在350℃条件下将难熔金属纯钼粉末制备成相对密度达0.98以上的金属钼坯,利用多种检测手段分析了高压扭转过程中钼粉颗粒孔隙演变及致密强化规律。通过改变预压钼坯压力参数,探讨了压力对压扭钼坯微观结构和力学性能及其热稳定性的影响。结果表明：压力由2.0GPa增大到3.0GPa,压扭钼坯致密度提升显著,其内部亚晶尺寸细化,微观应变增加,试样整体显微硬度值随压力增大而升高,边缘处略有降低。随压力增大,DSC后组织未发生显著长大,热稳定性较好。     

双丝三电弧焊中熔滴过渡及焊缝成形机理

为了验证双丝三电弧焊接过程中M弧不同的电流、脉冲频率对其熔滴过渡行为的影响;试验搭建了双丝三电弧焊的焊接系统以及高速摄像与波形同步采集系统.结果表明,熔滴过渡行为变化的主要原因是在M弧作用下熔滴的受力变化.其次,熔滴过渡行为和M弧电流的变化存在着对应关系:随着M弧电流增大,熔滴过渡行为依次为焊缝成形最佳的短路过渡+射流过渡、以及成形依次变差的大滴过渡、射滴过渡、射流过渡.随着M弧脉冲频率增加,熔滴过渡行为依次为一脉多滴、一脉一滴、多脉一滴三个阶段;其中焊接成形最理想的为一脉一滴的熔滴过渡阶段.     

Recent Research on the Deformation Behavior of Particle Reinforced Magnesium Matrix Composite: A Review

Particle reinforced magnesium matrix composite(PMMC) possesses the merits of high specific strength, high specific modulus, better dimensional stability, good wear resistance and lower production cost, which is thought as a promising material in the field of aerospace, automobile, electronic communication, etc. To eliminate the casting defect, the PMMC is usually experienced hot deformation process. The present paper mainly focuses on the deformation behavior of PMMCs. First, the development of PMMCs based on particle size is introduced. Then, the hot deformation technology and deformation mechanism of PMMCs at elevated temperature are given and analyzed, respectively. After reviewing the dynamic recrystallization and texture of PMMCs, its future development is suggested based on the current research progress.     

原子力显微镜在膜研究中的应用与展望

原子力显微镜(AFM)以其无可比拟的优势在膜科学领域中得到了广泛的应用。它不仅可以在空气,液体等不同环境中获得膜的表面三维形貌,同时还能定量地研究膜表面的粗糙度、膜孔结构,并且能用力曲线来评价膜污染机制。本文简介了原子力显微镜的的工作原理,并结合近年来原子力显微镜在膜研究中的发展,对其在膜表面表征、膜污染研究等重要方面进行了举例介绍。     

基于噪声拟合的核磁共振二维谱反演新方法

针对现有二维反演算法对噪声敏感或过度依赖于对噪声的估计的问题,提出了一种基于噪声拟合的核磁共振二维谱反演新方法.首先,使用小波滤波进行噪声提取;然后将噪声分布按照高斯白噪声的数学模型进行拟合,获取噪声方差;最后依据制定的新的停机准则和进化算法进行拟合,拟合残差与估计的噪声水平相当或最接近时,迭代停止并得到二维谱.通过使用该算法对不同信噪比的仿真数据和多组实验采集数据进行处理后发现,该算法具有很高的鲁棒性和准确性.这种新的反演算法能够满足不同应用领域、不同信噪比数据的反演要求,具有很高的实际应用价值.     

Optimal design of motion control for scan tracking measurement: A CMAC approach

This paper is concerned with the optimal design of motion control for scan tracking measurement using Cerebellar Model Articulation Controller (CMAC) neural networks in order to improve the measuring efficiency while maintaining the measurement accuracy, and to achieve friction compensation. Aiming at the effect of geometric shape and material friction of the model surface on the precision and efficiency of scan tracking measurement, technologies of model surface geometric and friction feature identification and quantification are researched. A novel optimal motion controller for scan tracking measurement is designed and realized, which automatically predicts the surface features (including geometric feature and friction feature) and adjusts the scan tracking velocity in advance. The approach to friction quantification and compensation in measuring process is given specifically. Finally, through Matlab simulation experiments, the realizability and application effect of the studied optimal motion control method for scan tracking measurement are verified, and the measuring efficiency is increased by 123.33%. Simulation results show that the proposed motion controller is an effective way to enhance the measurement efficiency remarkably compared with the traditional control strategy.