Electron beam Surfi-SculptTM is a novel surface treatment technique applied to produce high level performance Composite-Metal-Weld (ComeldTM) joints. Investigation on forming process during electron beam Surfi-SculptTM on Ti-6Al-4V alloy showed protrusions were formed via a layer-by-layer mode like additive manufacturing process. The near-surface region of electron beam Surfi-Sculpted Ti-6Al-4V alloy was occupied by fusion zone, heat-affected zone and base metal from the outermost surface to the underlying bulk alloy. The microstructure of fusion zone was characterized by a high density of fine acicular martensite phase, leading to a higher micro-hardness. A heat-affected zone was sandwiched between fusion zone and the underlying base metal, with different microstructural features compared to both fusion zone and the base metal.
This paper presents the defects existing in shaking table control including the overshoot of displacement under low-middle frequency input using three variable parameter controls, the narrow bandwidth resulting from the performance of servo-valve and low accuracy of seismic wave reproduction because of specimen and table interaction. The effects of these factors on the stability and control accuracy of shaking table are discussed, and then the reasons of these problems existing are analyzed. The aim of this paper is to improve the stability and control accuracy of shaking table, thus, some corresponding strategies for compensation control are proposed. And a series of shaking table tests with one-story frame and two-story frame for verifying the validity of compensation control algorithm are performed.
Compared with middle-span bridges, seismic response of long-span bridges is more complicated, and so is seismic design. For example, influence of high order modes is obvious, as well as multi-support excitation, all kinds of nonlinear factors and soil and structure interaction (SSI). It is necessary to study on seismic behavior of a long-span continuous girder bridge. With the help of shake table array and substructure test technology, study on seismic performance of a long-span continuous girder bridge has been done and some useful conclusions have been got.
Aiming at the microstructure difference of electron beam surfi-sculpt and base metal of 6063 aluminum alloy and its effect on corrosion resistance at different temperatures, the samples of electron beam surfi-scuplt were prepared and heat-treated. Then metallographic analysis, SEM analysis and soaking test in 3.5% NaCl solution were carried out. It was found that the microstructure of electron beam surfi-sculpt was typical cast structure, which was obviously different from that of the base metal. In different heat treatment process, the diameter of spherical β” phase in surfi-sculpt was 0.5-1μm which made the surfi-sculpt have better corrosion resistance. The β” phase in base metal was short rod-shaped which size was 3-10 μm. And with the change of heat treatment process, obvious changes in microstructure and corrosion resistance were found in base metal.
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