PERFORMANCE ANALYSIS AND KINEMATIC DESIGN OF PURE TRANSLATIONAL PARALLEL MECHANISM WITH VERTICAL GUIDE-WAYS

Performance analysis and kinematic design of the 3-PUU pure translational parallel mechanism with vertical guide-ways are investigated. Two novel performance indices, the critical slider stroke and the main section area of workspace, are defined; The expressions of two other indices, i.e. the global dexterity and global force transfer ratio are revised based on the main section of workspace. Using these indices, performance changes versus the varieties of dimensional parameters of mechanism are investigated in detail and the graphic descriptions of change tendencies of the performance indices are illustrated. By means of these obtained graphic descriptions, kinematic parameters for the 3-PUU pure translational parallel mechanism with better characteristics can be directly acquired.

Slab breakoff： a causal mechanism or pure convenience？

The idea of lithosphere delamination has long been conceived as a mechanism to cause tectonic uplift,metamorphism and magmatism in active orogenic belts[1–3].Since the publication of the two seminal papers by Davies and von Blanckenburg[4,5],the idea of slab breakoff has been more widely accepted over the last$20 years as the favored mechanism to cause collision zone mag-

Influence of Surface Nanocrystallization on Ti Ion Implantation of Pure Iron

In order to increase the depth or concentration of Ti ion implantation of pure iron, the surface mechanical attrition treatment(SMAT), which can fabricate a nanometer-grained surface layer without porosity and contamination in a pure iron plate, was used before ion implantation. Ti ion was implanted into the SMA treated sample and coarse-grained counterpart by using a metal vapor vacuum arc source implanter. The changing of depth and concentration of Ti was studied in a function of implantation time.By optical microscopy, transmission electron microscopy and X-ray diffraction, the grain size of the nano structured surface was studied. Micro-hardness, friction and wear behavior of nano surface layers were studied. By energy dispersive X-ray spectroscopy and Auger electron spectroscopy, the chemical composition and concentration of Ti ion in the surface implantation layer were studied. Experimental results showed that the concentration of Ti increased dramatically compared with untreated coarsegrained samples, which is attributed to the existence of higher density of defects(supersaturated vacancies, dislocations, non-equilibrium grain boundaries etc.) and compression stress field in the SMA treated nanocrystallined surface layer. The interaction between the defects and the implanted solute atoms leads to the increment of solid solubility. But the implantation depth showed inconspicuous change. It is shown that the ion range is just relevant to the energy and mass of the ion, dose of injection,the mass and density of target material.