In this study, the fundamental mechanism of friction stir welding was investigated to establish the relationship among the three components of the forces acting on the work pieces, the variation of the stirring energy, and the joint characteristics of the materials. A dynamometer designed by Chiou et al., was used to measure the axial force (z-direction), the feed force (x-direction), and the clamping force (y-direction). The output energy of servo motor was monitored by power meter. Experimental results show that with increasing welding speed, the feed force increases obviously, the axial force increases slightly, and the energy almost remains constant for the fixed rotation speed of the spindle. At the rotation speed of spindle of 800 rpm, the spindle angle of 1¢X, the pre-clamping force of 2kN and the welding speed of 60 mm/min, results show that the feed force is about 1kN when the probe is plunged into the specimens but the shoulder does not be in contact with the surface of the specimen. However, when the probe is plunges into the specimens entirely and the shoulder is in contact with the surface slightly, the feed force is reduced to 0.48kN. Moreover, when the shoulder is in contact with the surface heavily, the feed force is reduced to 0.2kN. This result indicates that the contact force between the shoulder and the specimen causes the material to become soft and to backfill into the weld, and then decreases the feed force. After the specimen of the 6061-T6 aluminum has been welding, the micro hardness measurements are made. Results show that the distribution of the hardness is quite consistent along the welding as the feed force approaches to 0.2kN. Furthermore, the appearance on the surface of the weld is quite fine, and thereby it is able to get the high and uniform quality. The spacing distance of the weld surface can be theoretically analyzed. It is found that the spacing distance increases with welding speed and decreases with rotation speed of spindle. The theoretical predictions are in very good agreement with the experimental measurements.

In the friction stir welding (FSW) process, a high-speed rotating tool, which consists of the probe and the shoulder, are employed to plunge into the faying surfaces. By using the friction heating and the stirring action of the material, the solid-state welding is accomplished to joint two pieces of metal by material diffusion to form a densification structure in the weld. According to the experimental results, the mechanism of friction stir welding is as follows: the probe plunge into the sample and the shoulder is in contact with the sample to generate a large amount of friction heat, which causes the materials soft. When the probe moves forward, the soft materials in front of the probe are scratched. The scratched materials are subjected to the rotational and squeeze actions of the shoulder so that they are refilled into the welded surface behind the probe. For the dissimilar metals joint (6061-T6 aluminum and C1100 copper plates), results show that when C1100 copper is located at the advancing side, the measured feed force appears drastic changes and it is also seen that the components of the force for the friction-stir welding of dissimilar metals become more unstable than those for the same metals joint, so that the structure which has been observed by optical microscopy appears to be open with pores and defects so that the welded quality becomes poor. According to the three components of the measured force during FSW process, the friction between the probe and the work piece can be computed. By using the friction theory, the hardness and the yield strength of the materials in front of the probe can be calculated, and then the faying surface temperature is approximately predicted to be 565.5 oC.

中文摘要 對於資本市場來說是外國公司的買賣價差的三個成分：逆選擇成分、交易成本成分及存貨成本成分相對於本國公司的買賣價差三成分構成有可能不同。 此篇論文中比較相同股票在不同市場所發行股票，其買賣價差三成分。根據本篇實證結果，相同一支股票在美國NYSE或是NASDAQ的逆選擇成分顯著的高於在TSEC發行的逆選擇成分，這暗指著資本市場中有很多不一樣的地方值得探討，像是流通貨幣的不同、或是法規治令的不同以及取得非公開資訊的難易程度也不同。另外，根據之前的研究的顯示，買單接著買單、賣單接著賣單的機率趨勢也很強，我們也發現了這種現象在TSEC很明顯，根據此篇論文的結論，這大部分的原因很可能是因為TSEC有「限價」規定的緣故。 / Abstract The three components, adverse selection component, order processing component and inventory holding cost, of companies which regarded as foreign companies in terms of the capital market are different from those in domestic capital market. In this paper, the adverse selection components of the stocks we choose in NYSE or NASDAQ are significant higher than those in TSEC. It implies the differences of capital markets, such as currency ,regulation and easy or not obtaining the private information of the company. Furthermore, similar to previous studies, there are strong tendencies for buys follow buys and sells follow sells. We find that the most part of proportion of order persistence derives from price limit in TSEC.