Quasi-cube ZnFe2O4 nanocrystals: Hydrothermal synthesis and photocatalytic activity with TiO2 (Degussa P25) as nanocomposite

The fabrication and photocatalytic application of zinc ferrite nanocrystals were reported. Quasi-cube ZnFe₂O₄ nanocrystals with typical small sizes of 5-15 nm were successfully synthesized by a facile hydrothermal approach. ZnFe₂O₄/P25 nanocomposite was prepared by physically grinding the ZnFe₂O₄ nanocrystals with TiO₂ (commercial Degussa P25) at ambient temperature, and it exhibited excellent photocatalytic activity for the mineralization of Rhodamine B. UV-vis measurement and photocatalytic test results showed that ZnFe₂O₄ nanocrystals exhibited effective band-gap coupling to P25 nanopowders by simply physical grinding without any surface modification or high-energy balling, which is usually adopted in conventional mixture process. This phenomenon can be attributed to the high surface activities of the as-obtained tiny ZnFe₂O₄ nanocrystals and commercial P25 nanoparticles. It may imply that the mixing process of composite materials would be simplified by further lowering the grain sizes of their component particles.     

Essential parameter calibration for the 3D scanner with only single camera and projector

A calibration method for the five essential parameters is proposed. Using the calibration results, the three dimensional (3D) reconstruction can be performed directly. The five essential parameters include the distance between the camera and the projector, the distance between the reference plane and the camera, the fundamental frequency of the fringe pattern, the scale factor from the image coordinates to the world coordinate system in X axis direction and that in Y axis direction. The proposed calibration method is implemented and tested in our 3D reconstruction system. The mean calibration error is found to be 0.0215 mm over a volume of 400 mm (H)×300 mm (V)×500 mm (D). The proposed calibration method is accurate and useful for the 3D reconstruction system.     

非对称角根焊中焊枪偏移与熔透形态的关系

中厚板单侧开V形坡口角焊缝由于两侧结构不对称,根部焊接时散热差异大,易产生未熔合缺陷. 为保证根部打底焊良好熔透成形,提出根据正面熔池形貌变化实时调整焊枪角度的策略,提升焊接熔透质量. 结果表明,随着焊接角度变化,焊枪相对熔池发生了有规律位置偏移. 对采集到的正面熔池图像进行中值滤波等处理后获取焊枪中心的位置坐标,并研究了不同角度焊接的内部熔透形态,建立了熔池正面焊枪位置偏移量与内部熔透形态的定量关系,为利用正面熔池特征信息预测控制焊接内部熔透形态提供了一种新的方法.     

基于SPC与小波变换的光纤光栅型损伤识别

为了研究光纤光栅传感技术在振动型损伤识别技术中的优势,建立了基于非平衡M-Z干涉仪和PGC相位解调技术的光纤光栅结构损伤识别系统;构建了基于小波包节点能量相对变化率之和的结构损伤识别指标;介绍了统计过程控制原理,推导了均值-极差控制图进行结构连续损伤识别的过程;测试了结构处于健康状态和6种损伤状态下的振动信号并分析了损伤识别.试验结果表明,构建的损伤识别系统能判断损伤的存在,并且能对损伤的位置和损伤程度进行有效识别.     

低碳钢非对称角焊温度场有限元分析

针对单边开坡口的非对称角根焊中熔透不稳定、成形质量差的问题,对其温度场及熔池成形规律进行分析从而优化焊接参数的选取,改善成形质量.考虑温度、对流、辐射和相变潜热对材料物理性能的影响,利用有限元分析软件建立了低碳钢非对称角焊缝有限元模型,并进行仿真计算.对比讨论了不同结构情况下焊接电流对温度场的影响,重点分析了非对称角焊接参数对背部熔宽的影响.结果表明,非对称角焊缝温度分布不均匀,背部熔宽对电流的变化十分敏感,焊接电流大小对熔池形状影响较大.通过试验得到三组熔透情况不同的焊缝,其热影响区形状尺寸与仿真结果吻合良好,从而验证了理论分析的有效性.