Fabrication process of open surfaces by robotic fibre placement

Composite materials are being used extensively in many industrial sectors. They offer excellent material properties compared to other structural materials available. However, the traditional fabrication process using manual hand lay-up is time consuming and labour intensive. Therefore, robotic fibre placement has been introduced to overcome these drawbacks. This approach may greatly reduce cycle time and manufacturing costs. This paper describes the overall strategy for the establishment of a flexible robotic fibre placement technique. The fabrication process planning of this new technique is presented. Three different types of fibre placement for open surfaces are discussed. These include simulation-based fibre path generation, fibre steering, and sensory-based contour following methodologies. The system architecture for the process control is also presented.     

Diffuse transition and piezoelectric properties of Pb[(Zr1−xTix)0.74(Mg1/3Nb2/3)0.20(Zn1/3Nb2/3)0.06]O3 Ceramics

In this work, the piezoelectric ceramic system of Pb[(Zr_1−xTi_x)_0.74(Mg_1/3Nb_2/3)_0.20(Zn_1/3Nb_2/3)_0.06]O₃, 0.47≤x≤0.57, with composition close to the morphotropic phase boundary, was studied. From the results of X-ray diffraction and piezoelectric measurement, ceramics near x=0.51 were found at the morphotropic phase boundary (MPB) between the tetragonal and pseudocubic perovskite. The planar coupling factor (k_p=0.72) is high at compositions near the MPB, but the mechanical quality factor (Q_m=75) is low. The calculation of the diffuseness of phase transition shows that the region of phase coexistence of this system is broader than that of the ternary system.     

高压架空线路应力测试的光纤传感系统

近年来，光栅传感器的应用得到了很大的发展。本文主要论述了光栅传感系统在电力领域的应用，采用波分／时分复合技术同时检测应力等其他参数。     

Processing of alumina and zirconia nano-powders and compacts

Magnesia–doped alumina and yttria–doped zirconia nano-powders were synthesized using sucrose as a chelating agent and template material from the aqueous solutions of aluminium nitrate, magnesium nitrate, ytrrium nitrate and zirconyl nitrate, respectively. Synthesis parameters were optimized with varying sucrose to metal ion ratio, calcinations time, and temperature to produce these nano-powders. As-synthesized powders were characterized by room temperature X-ray diffraction, BET surface area analyzer and transmission electron microscopy. Y₂O₃–ZrO₂ nano-powders had particle size in the range of 80–200 nm with specific average surface area of 119 m²/g and for MgO–Al₂O₃ powders, particle sizes were 30–200 nm with the specific average surface area of 250 m²/g. Our results indicate that this synthesis method is a versatile one and can be applied to a variety of oxide-based materials to form nano-powders. Nano-powders were compacted uniaxially and densified in a muffle furnace. Sintered discs were used for hardness testing and density measurements, as well as for microstructural characterization.     

Modelling of Bird Strike on an Aircraft Wing Leading Edge Made from Fibre Metal Laminates – Part 2: Modelling of Impact with SPH Bird Model

Fibre Metal Laminates with layers of aluminium alloy and high strength glass fibre composite have been reported to possess excellent impact properties and be suitable for aircraft parts likely to be subjected to impacts such as runway debris or bird strikes. In a collaborative research project, aircraft wing leading edge structures with a glass-based FML skin have been designed, built, and subjected to bird strike tests that have been modelled with finite element analysis. In this second part of a two-part paper, a finite element model is developed for simulating the bird strike tests, using Smooth Particle Hydrodynamics (SPH) for modelling the bird and the material model developed in Part 1 of the paper for modelling the leading edge skin. The bird parameters are obtained from a system identification analysis of strikes on flat plates. Pre-test simulations correctly predicted that the bird did not penetrate the leading edge skin, and correctly forecast that one FML lay-up would deform more than the other. Post test simulations included a model of the structure supporting the test article, and the predicted loads transferred to the supporting structure were in good agreement with the experimental values. The SPH bird model showed no signs of instability and correctly modelled the break-up of the bird into particles. The rivets connecting the skin to the ribs were found to have a profound effect on the performance of the structure.     

微弯光纤传感器位移灵敏度研究

根据光纤模式耦合理论,光纤微弯时光纤中的传输光有光功率损耗,对微弯光纤传感器出射光强进行分析、测量,实验得出了位移灵敏度与微弯周期的关系,对应用微弯光纤组成分布式光纤测试系统的传感器具有重要意义。     

Photon scanning tunneling microscope,now and in the future

The concept of photon tunneling and the principle of the photon scanning tunneling microscope (PSTM) are described. The history of the PSTM and its development in China are reviewed. The principal problem in the recent development of the PSTM, together with its solution, is discussed. The distinguishing features and the future of the PSTM are described.     

磨料喷射喷嘴的应力分析及FGM模型设计

分析表明磨料喷射加工中喷嘴承受的应力在喷嘴入口最大、出口次之、中间区域相对较小。试验显示喷嘴的冲蚀磨损在喷嘴入口最严重、出口次之、中间区域相对较小。试验结果与应力分析结果一致,得出磨料喷射加工中喷嘴入口、出口处承受的高拉应力是造成其冲蚀磨损严重的主要原因的结论。针对提高均质陶瓷材料喷嘴抗冲蚀磨损能力的力度有限,提出运用梯度功能材料(Function gradient material,FGM)理论于喷嘴材料的设计和制造中,研发新型非均质的陶瓷喷嘴材料,将梯度功能陶瓷喷嘴制备中产生的残余压应力引入喷嘴入口、出口,使其减缓磨料喷射加工中喷嘴承受的拉应力,以提高喷嘴抗冲蚀磨损能力。结合喷嘴的冲蚀磨损特点、结构特点及陶瓷喷嘴材料制备工艺性等,建立了梯度陶瓷喷嘴物理模型和成分分布模型。根据本模型设计结果,研制出梯度 SiC／(W,Ti)C陶瓷喷嘴。结果表明,相同条件下制各的梯度SiC／(W,Ti)C陶瓷喷嘴的抗冲蚀磨损能力高于非梯度 SiC／(W,Ti)C陶瓷喷嘴。     

Fibre-top atomic force microscope probe with optical near-field detection capabilities

We present a fibre-top probe fabricated by carving a tipped cantilever on an optical fibre, with the tip machined in correspondence of the fibre core. When approached to an optical prism illuminated under total internal reflection conditions, the tip of the cantilever detects the optical tunnelling signal, while the light coupled from the opposite end of the fibre measures the deflection of the cantilever. Our results suggest that fibre-top technology can be used for the development of a new generation of hybrid probes that can combine atomic force microscopy with scanning near field optical microscopy.