Browsing by Author "Liu, TT"

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A study on the hardness variation of alpha- and beta-pure titanium with different grain sizes
(2005-05-25)
Kao, YL
;
Tu, GC
;
Huang, CA
;
Liu, TT
;
材料科學與工程學系
In this study, the hardness and the microstructure of alpha and beta-pure Ti treated with different grain sizes were investigated. The alpha-Ti specimens were obtained by heating pure Ti at 750 degrees C for various periods and then quenched in water, while the beta-Ti specimens by heating at 1000 degrees C for various periods and then quenched in water. Experimental results show that the hardness of a-Ti decreased with increasing the grain size; whereas, the hardness of beta-Ti tends to increase with increasing grain size. From the microstructures examined with transmission electron microscope, it can be realized that the strengthening mechanisms of alpha- and beta-Ti are quite different. Grain boundary could be the main strengthening microstructure of alpha-Ti and the smaller grain size the higher hardness. The major strengthening microstructure of beta-Ti was martensitic twin with a very high dislocation density. The amount of martensitic twin increased with increasing the grain size of beta-Ti and, therefore, the larger grain size the higher hardness. (c) 2005 Elsevier B.V. All rights reserved.
The application of laser metrology and resonant optical cavity techniques to the measurement of G
(1999-06-01)
Ni, WT
;
Liu, DK
;
Liu, TT
;
Mei, HH
;
Pan, SS
Our goal is to measure the gravitational constant G to within 1-10 ppm using a high-finesse Fabry-Perot optical cavity. The two high-reflectivity mirrors of the Fabry-Perot cavity will be suspended separately by two nearly identical simple pendulums of length about 1 m. For the source of attraction, we have built a rotating mass source with 12 lead bricks (each brick is of mass 11.5 kg) on each of two opposite sides of a rotating table. The period of rotation can be adjusted. We normally use a rotation period of 200 s. For this rotating mass, the relative equilibrium displacement of the two mirrors is over 10 nm and we are working for a preliminary measurement of this distance to one part in 10(4). Auxiliary quantities such as the positions of the test mass and the positions of Fabry-Perot cavity mirrors can be monitored using real-time laser metrology. The stability and real-time monitoring of the pendulums, building stability, and the compensation or averaging of mass inhomogeneity need special considerations.