Papers by Author: Min Liu

Abstract: Ni8W alloy ingots were prepared by SPS technic, followed by homogenizing, cold rolling and recrystallization annealing. The influence of ball milling on cold rolling and cube texture formation of Ni8W alloy substrates was investigated during the course of preparation. Finally, high quality cube-textured Ni8W alloy substrates were successfully obtained using this powder metallurgy process, and characterized by electron backscatter diffraction technic. It indicated that the cube texture fraction was as high as 90% (<10^o) when it annealed at 1350°C for 2 h.

Abstract: High speed spindle is a multivariable and strong coupling complex system. In order to improve its dynamic response characteristics and control effectively, based on vector control, the high speed spindle needs to be decoupling first. Then neural network theory and BP algorithm are adopted to form a speed controller to adjust the rotational speed. In this controller, gradient searching technique is applied and the proportional and integral parameters are used as weight of neural network which is employed to adjust the corresponding control parameters. Therefore, a new model of high speed spindle is set up and simulated. The result of simulation indicates that the way combine the decoupling method and the speed controller based on neural network can track the rotational speed more accurate and promote the robustness of high speed spindle.

Abstract: Yb3+ and Ho3+ co-doped Lu2O3 nanocrystalline powders were synthesized by a reversestrike co-precipitation method. The as-prepared powders were examined by the X-ray diffraction and transmission electron microscopy. The phase composition of the powders was cubic and the particle size was in the range of 30~50 nm. Emission and excitation spectra of the powders were measured by a spectrofluorometer and the possible upconversion luminescence mechanism was also discussed.

Abstract: Y2.85Er0.15Al5O3 was prepared by combustion process. Phase evolution of the synthesized powders was determined by XRD. Single-phase cubic YAG: Er3+ crystalline powders were obtained by calcining the combusted product at 1000°C and no intermidiate phase was observed. SEM morphology showed that the resultant YAG: Er3+ powders were porous. Upconversion emission spectra were measured on the powder compact pumped by a 980nm continuous wave diode laser. The relationship between pump power and luminescence intensity suggested that a two-photon process is active in this sample. The upconversion machanism of YAG: Er3+ system was also discussed.

Abstract: Yb3+, Ho3+ co-doped Y2O3 nanocrystalline powders were synthesized via a reverse-strike co-precipitation method using nitrates and ammonia as raw materials. The as-prepared powders are cubic Y2O3 after fired at 7000C for 2 h. Field emission scanning electronic microscopy revealed that most of the particles are nearly spherical and the average diameter of the particles is in the range of 60-80 nm. Under the excitation with a 980 nm continuous wave diode laser, two main emission bands, i.e., green emission centered at 549 nm and red emission centered at 666 nm is observed, respectively. The green emission is attributed to the transition of (5S2, 5F4-5I8) levels of Ho3+; while for the red emission, the transition of 5F5-5I8 levels is suggested. In addition, near infrared emission centered at 755 nm is also detected, corresponding to the transition of (5S2, 5F4-5I7) levels. The dependence of the intensity of upconversion emissions upon the pump power of the diode laser suggests that two-photon absorption mechanism be involved in these processes.

Abstract: YBa2Cu3O7-δ(YBCO) films with highly biaxial textures were deposited on SrTiO3 single crystal, textured polycrystalline Ag and NiO/Ni substrates using pulsed laser deposition, metal-organic decomposition and ultrasonic spray pyrolysis method. The microstrains in different specimens with strong textures were measured using x-ray diffractometer and were compared each other.

Abstract: To increase the accuracy of R-F method, it is necessary to solve the problems of the linear expansion of failure function and non-normal variables. In this paper, the improved FOSM method was applied to calculate the failure probability of welded pipes with cracks. The examples show that this method is simple, efficient and accurate for reliability safety assessment of welded pipes with cracks. It can save more time than the Monte Carlo method does, so that the improved FOSM method is recommended for general engineering reliability safety assessment of welded pipes with cracks.