Solid State Phenomena Vol. 295

Abstract: In order to improve the dynamic stability of precision micro slitting turn-milling machine tools, reduce or avoid the vibration problem during the cutting process, optimize the machine structure and processing parameters, the modal analysis of precision micro slitting turn-milling machine tool based on hammer experimental method was researched. In this paper, by analyzing the mechanism of precision micro slitting turn-milling machine tools, the multi degree-of-freedom mathematical vibration model of precision slitting turn-milling machine tools is constructed. The precision micro turn-milling machine tool is analyzed based on the hammer experiment analysis. The modal analysis obtained the first five natural frequencies and resonance speeds of the precision micro slitting turn-milling machine tool,including ST26, NN-25UB8K2 and NN-20UB87. The research results show that hammer experimental method can evaluate the vibration modal analysis of precision micro slitting turn-milling machine tools to some extent. The experimental modal analysis results guide and optimize the structural design and processing technology of precision micro slitting turn-milling machine tools.

Abstract: The deep holes cutting process by metal boring bar is usually limited due to the development of chatter vibration. This is because metal boring bar has not only low bending stiffness but also low structural damping. A chatter stability prediction of composite boring bar under regenerative cutting force is presented. Based on the theory of Euler-Bernoulli beam, the regenerative chatter dynamic model of composite boring bar is proposed, and the solution formula of the limited cutting depth and corresponding spindle speed is given. The dynamic stability lobes of the composite boring bar are obtained by numerical calculation. The results indicate that composite boring bar exhibits efficient chatter stability than metal boring bar. Chatter stability is closely related to fiber ply angle. It is demonstrated that when ply angle is 0o, carbon/ epoxy reaches its critical cutting depth, and for graphite/ epoxy boring bar about 25o of ply angle gives its critical cutting depth, It is also demonstrated that stability boundary decreases as the ratio length and diameter increases. Finally, the prediction results of stability are compared with those from the dynamic stiffness and time-domain response, agreement is found.

Abstract: This paper presents an efficient analytical method for design of streamline dies driven by fracture. The method is based on Bernoulli’s theorem relating pressure and velocity along any streamline extended to ideal flows in plasticity. The Cockroft-Latham criterion is adopted to predict the initiation of ductile fracture. In order to apply the method developed, it is not necessary to know the solution to the boundary value problem of plasticity. The final result is a simple relation between geometric parameters of the process and the constitutive parameter involved in the fracture criterion. Since the latter is supposed to be known for a given material, the relation determines a safe domain for drawing without fracture.

Abstract: This study prepared an SiC thin film by using the ratio frequency magnetron sputtering method, investigated the effects of different sputtering powers on the SiC material and analysed the changes in crystal morphology and photoluminescence characteristics caused by changes in the growth conditions used. It was considered that there was 6H-SiC crystal morphologies in the SiC thin film under the experimental conditions prevailing in this study. The SiC morphologies with small grain sizes intermingled and therefore formed anSiC thin film. The analyses of the photoluminescence spectra and Scanning Electron Microscope indicated that the SiC thin film materials with preferable crystal compositions could be prepared under appropriate power inputs.

Abstract: We performed an angle-resolved photoemission spectroscopy (ARPES) study of the Ni-based superconductors SrNi2P2. We observe both electron and hole Fermi surface pockets with different shapes and sizes which leads to very poor nesting conditions. Moreover, we observe a band structure reconstruction below the structural transition temperature (325 K), with bands shifting downwards and one extra hole-like band appearing around Г. These behaviors might be attributed to the length reduction of one third of P-P bonds between the adjacent NiP layers. The low temperature phase in SrNi2P2 can be regarded as a partially collapse phase. Our result may facilitate understanding the collapsed behavior which is important to unveil superconductivity mechanism in iron-based superconductors.

Abstract: Adiabatic foam was fabricated successfully using sodium silicate as the raw material with pre-sintered fly ash as additive. Fly ash was pre-sintered at 500 to 900 oC and the effect of the pre-sintering temperature on the performance, including the thermal conductivity, density, compressive strength and microstructure, was researched. The results show that the pre-sintering process effectively reduces the density of the samples while the thermal conductivity and compressive strength are higher than those of the samples fabricated by the fly ash without being pre-sintered. Moreover, the samples exhibit tri-modal spherical pore structure with macropores and mesopores. The pore size remains unchanged until the pre-sintering temperature exceeds 700 oC, and then starts to increase.