Dual-phase (DP) sheet steels have recently been used for automotive manufacturing to reduce vehicle weight and improve fuel economy. Dual-phase steels offer higher strength without reduced formability when compared to conventional high strength low alloy (HSLA) steels and so thinner gauge DP sheet steel can be used to meet the same design requirements. The DP steel microstructure is comprised of dual-phase mixture hard martensite particles, which provide strength, in a soft ferrite matrix, which provides ductility. Fusion welding processes, such as gas metal arc welding (GMAW), are used to join DP sheet steels; however, the heat input from fusion welding can cause the martensite islands to decompose into softer islands of tempered martensite. This can reduce the joint efficiency and cause premature localized necking in the region where tempered martensite forms. The weldability of coated 1.65 mm Cr Mo DP600 (dual-phase 600 MPa) sheet steel welded using the pulsed gas metal arc welding (GMAW-P) process was assessed. Processes with a range of GMAW P weld heat inputs were developed to make full penetration bead-on-plate welds that had similar bead geometry. The range of weld heat input was between 193 J/mm and 347 J/mm. Uniaxial transverse weld tensile tests of welds that were made at high heat input fractured in the heat affected zone (HAZ), welds that were made at low heat input fractured in the base metal (BM), which is most desirable, and at intermediate welding heat inputs, fracture locations were mixed. Heat input was compared to corresponding weld HAZ half-width measurements and it was shown that as heat input increased, HAZ half-width increased as well; this followed an expected linear trend. The ultimate tensile strength (UTS) was not diminished in specimens that exhibited BM fracture and 100% joint efficiency was achieved. Welded DP600 specimens that failed in the HAZ had minimal (< 5%) reduction of UTS. During the welding process development phase, the same range of heat input was used to make bead-on-plate full penetration welds onto coated 1.80 mm HSLA (high strength low alloy) sheet steel to assess its weldability. It was found that all of the welds fractured in the BM during uniaxial transverse weld tensile testing and, therefore, had achieved 100% joint efficiency. It was shown that by increasing the strength grade of DP sheet steel to DP780 and DP980, 100% joint efficiency was not retained. To better understand why high heat input welding caused HAZ fracture, low heat and high heat input welds that had consistently fractured in the BM and HAZ, respectively, were used to assess the differences between BM and HAZ fracture mechanisms. Fractographic analysis of BM and HAZ fracture surfaces of the dual-phase steels showed that fracture had occurred due to micro-void coalescence for both types of failure; however, the HAZ fracture had greater reduction of cross-sectional area and the surface had more numerous and smaller shear tearing ledges. Examination of the microstructure showed that there were decomposed martensite islands in the region the HAZ fracture; these likely increased ductility and led to a more significant tri-axial stress state. However, decomposed martensite was also found in the HAZ of welds that had BM fracture. The low and high heat input welds had similar reduction of martensite percentage (~3 – 4%) in the subcritical (SC) region of the HAZ; immediately below the Ac1 temperature where transformation from a BCC ferrite to FCC austenite occurs. Each weld HAZ was assessed with an average through-thickness microhardness (ATTH) profile. Four distinct regions of hardness were identified: hard intercritical (IC), which was formed by heating between Ac1 and Ac3 temperatures, soft subcritical (S SC), hard subcritical (H SC), and base-metal (BM). The width of the S-SC was slightly larger (~10%) for the HAZ fracture weld; however, the degree of softening (~8 – 11 VHNATTH/200g) compared to BM hardness was similar for both. It appeared that HAZ fracture could be shifted to the BM by reducing the width of the S SC so that the surrounding hard IC (+40 – 50 VHNATTH/200g) and H-SC (+5 – 10 VHNATTH/200g) could support the S SC and prevent a tri-axial stress state from developing; this is similar to increased strength of brazed joints caused by optimal gap width. Using this knowledge base, new welds were made onto different sheet thickness (1.20 mm and 1.80 mm) Cr-Mo DP600 sheet steels and onto higher strength grades of 1.20 mm Cr-Mo DP780 and 1.20 mm Mn –Si DP980 sheet steels. These were compared with the heavily studied 1.65 mm Cr Mo DP600 sheet steel described above. The 1.80 mm DP600 sheet steel (welded with the same range of heat input) fractured in the BM during all uniaxial transverse weld tensile tests; this was caused by a 4% increase in sheet thickness. The majority of thinner 1.20 mm welds fractured in the HAZ; there was one BM fracture for the DP600 sheet steel. Only the DP980 had a significant drop in UTS (~28%), and the DP600 and DP780 approached 100% joint efficiency (based on the UTS). The same distinct regions of hardness were observed for Cr Mo DP600 and Cr-Mo DP780. The Mn Si DP980 did not exhibit an H SC and had a significantly wider S SC (~80% wider) when compared to welds of similar heat input and sheet thickness. This suggested that the presence of an H SC region could improve joint efficiency. It also suggested that material chemistry played an important role in reducing the extent of softening during welding; however, the martensite percentage for the DP600, DP780, and DP980 were different (approximately 7.5%, 20%, and 46%, respectively) and this could also have affected the observed S SC widths. It was concluded that GMAW-P welded DP600 sheet steel shifted from a HAZ fracture to a more desirable BM fracture location during uniaxial transverse weld tensile testing as the S-SC region of hardness was narrowed. A narrow S-SC was supported by the adjacent hard IC and H-SC regions, which limited diffuse necking in the vicinity of the S-SC region. Diffuse necking continued to thin out material in the BM region, where there was a greater reduction in cross-sectional area prior to the onset of localized necking, and, therefore, the BM entered a state of higher stress than the S-SC and failed once it reached UTS. This was not observed for a higher strength grade of DP780 sheet steel, which had higher degree of softening, because, diffuse necking was not sufficient to reduce the BM cross-sectional area and hence the level of stress in the S-SC reached the UTS before the UTS was reached in the BM.

The Kuroshio, one of the most important western boundary currents of world, controls modern hydrology conditions of the East China Sea (ECS) and carries warm and saline water to high latitudes. Previous researches mentioned that the Kuroshio might change its flow path and volume in the ECS by East Asia monsoon (EAM), Equatorial climate conditions, or global sea level change during glacials. However, shifting or not of the Kuroshio out of the Okinawa Trough during Last Glacial Maximum (LGM) is still in debate. In this study, records derived from multi-proxies, include of Mg/Ca-based paleotemperatures and stable isotopes and foraminiferal census data, of core GH08-2004 was conducted for comparing with records derived from core MD012404 to understand the possible changes of the Kuroshio in the ESC since 26 ka. Our comparing results reveal that the surface hydrological environments have no obvious difference between eastern and western sides of the Ryukyu Arc and imply that the Kuroshio might not shifted outside of the OT during LGM. Otherwise, our reconstructed temperatures, oxygen isotopes and foraminiferal assemblages infer that the flowing volume of the Kuroshio was gradually increased since 19 ka associated with rising sea level. Thus we believe that emerged terrain caused by shallow sea level may be an important factor controlling the flowing path of the Kuroshio. In this study, differences of paleotemperatures and oxygen isotopes between G. ruber and N. dutertrei, surface and subsurface dweller, were decreased at the Holocene, whereas the delta values of carbon isotopes were larger meanwhile. This descrapncy implies that the East Asian winter and summer monsoons were enhanced synchronously.

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Diamond has superior characteristics, such as high hardness, high isolation, and high breakdown voltage, but it is also difficult to manufacture for industrial application. Because diamond is a nonconductor, the usual electrical discharge machining (EDM) method cannot be used. Hence, this study uses the plating nickel to keep the diamond powder as the composite electroplated layer of nickel-diamond powder. The variation of the composite layer and the diamond particle erosion characteristic after arc discharge can be realized by single-arc discharge. By the result of experiment, it can be known that the erosion area will be enlarged when the diamond particle is near to central erosion area, because the diamond that has good heat stability makes plasma to spread. The erosion area will be decreased when the diamond particle is near to edge of erosion area, because it stops the melted nickel to spread. The surface of diamond particle is broken slightly that the particle become more spherical and has some nickel remain on it when pulse voltage is less than 300 volt or the diamond particle is near to edge of erosion area. The surface of diamond particle is broken seriously that the particle is cracked to pieces when pulse voltage is more than 300 volt or the diamond particle is near to central erosion area.

The trends of present design in electronic systems are towards high speed, small size, and lower voltage levels. The noise immunity of high speed digital circuit decreases. ESD problem becomes more and more important for electric products because of the triboelectricity caused by human body with synthetic material. In this thesis we introduce the phenomenon in real life ESD caused by a charged human body source. Then we provide a good measurement method of ESD which enhances the repetition that gives a reliable and accurate result. Finally we try to build the numerical model for the air and contact discharge simulation by FDTD to provide a good measurement validation.

No description available.

This investigates the voltage flicker problem of a large steel plant and presents the mitigation strategy by applying the static var compensator (SVC) and cogenerator. The fluctuation of real power and reactive power consumption by an arc furnace has been measured and recorded during the steel production process. The dynamic load model of the A/C arc furnace is derived based on the actual field data and has been included in the computer simulation by the CYME software package for load flow analysis. The block diagrams of SVC controller and the excitation system of cogenerators are considered to solve the response of reactive power compensation according to the voltage fluctuation of the control bus. To maintain the electric service reliability of arc furnace when an external utility fault occurs, the tie line tripping and load shedding is implemented to prevent the tripping of cogenerator after system disturbance. It is found that the dynamic load behavior of arc furnace in the isolated industrial power system can be well compensated by the cogenerator with adaptive control of exciter and governor to generate proper reactive power and real power according to the fluctuation of bus voltage and system frequency respectively.

The bevel gears have been widely used for the intersected-axial transmission system for a long time. But mostly them are limited in the category of involute tooth profiles. It is believed that bevel gears with circular-arc tooth profile, similar to the Wildhaber-Novikov circular-arc helical gears, will improve the load capacity of the gear set. The bevel gears with circular-arc tooth profiles was firstly proposed by Kuo and Tsai in 2001. Although these new type of bevel gears can increase the load capacity of transmission, the expensive manufacturing process is still the problem. In this paper, the design parameters of bevel gear with circular-arc profiles developed by Kuo and Tsai are modified. Bevel gear set with spiral point contact path is developed. This improvement makes it possible to manufacturing the newly developed bevel gears in just a simple milling or/and grinding process with circular cutting edges. The manufacturing process is then cost down quit a lot. A method for checking the gear interference is also proposed. Finally, the 3D solid models of the bevel gear with circular-arc tooth profiles as well as the grinding wheel are constructed by using the computer software ¡§Pro/E¡¨. It is believed that the mathematical models and the design method developed in the thesis will provide a useful foundation for the further studies.

Abstract The arc behavior during the closing and opening of electrical contacts not only influences the surface morphology, but also causes the erosion of contact material. The mechanical stresses, the molten bridge, and the arc cause this erosion. Consequently, the erosion mechanism is very complex. Therefore, to avoid the influences of mechanical stresses and numerous arc striking, static-gap experiments with a single arc discharge are conducted to investigate the effects of pulse voltage, gap distance, and arc duration on the erosion characteristics and mechanism of silver based contact materials. Moreover, this experimental result is verified by the finding of the dynamic testing of electrical contacts. The results of the erosion characteristics show that the arcing and non-arcing regions have been distinguished at the supply voltage from 32 V to 500 V and the gap distance from 0.2 mm to 40 mm. The empirical formula for the minimum pulse voltage at arc initiation in terms of gap distance is established. When the pulse voltage is smaller than 200 V, the erosion area increases with increasing gap distance due to the action of the metallic-phase arc. However, when the pulse voltage is greater than 200 V, with increasing gap distance, the erosion area increases to a maxim, and finally diminishes due to the increase in the amount of gaseous-phase arc. The results of the erosion mechanism show that the arcing region is classified into three erosion patterns, namely, the molten metal bridge (B), metallic-phase arc (M), and gaseous-phase arc (G). At the gap distance of 0.2 mm, the erosion pattern of anode silver is varied from B, through B+M, and, M, to M+G. According to the electron transfer across triangular potential barrier, the thermionic emission causes the erosion patterns of B, B+M, and M, and mixed thermionic and field emission results in the erosion pattern of M+G. When the pulse voltage is 500 V, with increasing gap distance, the splashing of metallic particles around the anode crater becomes more dispersed, shorter with more silver powder, and finally disappeared with a little silver powder due to the influence of the gaseous-phase arc. The results of the anti-weld ability show that when the pulse voltage is 500 V and the arc energy is grater than 14 J at the static-gap experiments, the critical gap distance to produce welding for Ag-Ni, Ag-CdO, and Ag-SnO2 is 3 mm, 8 mm, and 15 mm, respectively. This indicates Ag-Ni contact possesses the best anti-weld ability. On the other hand, the results of dynamic testing of electrical contacts show that at the arc energy less than 10 J, the anti-erosion, anti-weld ability, and the welding area are seen to increase with contact materials in the following order: Ag-CdO > Ag-SnO2 > Ag-Ni. However, when the arc energy is greater than 10 J, the anti-erosion, anti-weld ability, and the erosion area are seen to increase in the reverse order: Ag-SnO2 < Ag-CdO < Ag-Ni, which are in very good agreement with the results of static-gap experiments. Furthermore, the erosion surface of the silver-based contact materials can be observed and analyzed by using the X-ray diffraction method (XRD), differential thermal analysis (DTA), and gravitation thermal analyzer (GTA). Results show that when the arc energy is greater than 14 J, Ag-CdO and Ag-SnO2 have been decomposed into Ag-Cd and Ag-Sn alloys, respectively, which reduce their anti-weld ability. On the other hand, the welding trend has been reduced due to the dispersion of NiO on the surface of Ag-Ni contact. Consequently, the anti-erosion and anti-weld ability for the Ag-Ni contacts are better than those of the other Ag-MeO contact materials.

Voltage flicker limitation of electric utilities has been discussed in the past three decades. Arc furnace is one of the most disturbing loads that cause flicker problems in the power network. If displeasing flicker levels are predictable, then corrective solution such as static var compensation or furnace controls could be developed in cooperation between the utility and the customer. In the past, the electric fluctuations in the arc furnace voltage have been proven to be chaotic in nature. This thesis proposes a phase space approach based on nonlinearity chaotic techniques to analyze and predict voltage flicker. The determination of the phase space dimension and the application of Lyapunov exponent for flicker prediction are described. Test results have shown that accurate prediction results are obtainable for short term flicker prediction based on chaos theory.