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1
Content available remote Climatic Response of Tracheid Features of Picea meyeri Along Altitude Gradient of Luyashan Mountains of North China
Wang M., Jiang Y., Zhang W., Dong M., Kang M., Xu H.
Polish Journal of Ecology
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2017
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Vol. 65, nr 4
345--358
EN
Changing localized environmental conditions along altitude gradients could modify the responses of tree xylem structures to climate variations. To explore how trees adapt to local environment and respond to climate variants, we analysed the variation of Picea meyeri xylem tracheid features and the relationships with climate variables along an altitude gradient (1970, 2240, 2490 and 2650 m above sea level) of the Luyashan Mountains in the North China. The results mainly indicated the following: (1) tracheid number and diameter of P. meyeri showed significant differences among the four sites along the altitude gradient; (2) trees at site 2 (2240 m) and site 3 (2490 m) are similar in age, but the xylem tracheid number and diameter of these trees were significantly different, which may indicate different functional adaptation; (3) the relationships between xylem features' residual chronologies and the monthly climate data were inconsistent along altitude gradients, which indicated that the limiting factor of P. meyeri growth along the altitude gradients, shifted from drought stress at lower altitudes to low-temperature stress at higher altitudes.
2
Content available remote Inverter DC resistance spot welding of magnesium alloy AZ31
Hwang I., Kim D., Kang M.
Archives of Materials Science and Engineering
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2011
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Vol. 48, nr 2
112-117
EN
The welding lobes of AC resistance spot welding and inverter DC resistance spot welding for the magnesium alloy sheet AZ31 were compared and analyzed.
3
Content available remote Inverter DC resistance spot weldability of 590 MPa galvannealed steel for automotive applications
Yoon H., Kim D., Kang M.
Archives of Materials Science and Engineering
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2011
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Vol. 49, nr 2
112-117
EN
Purpose: This study analyzes resistance spot weldability of coated and uncoated DP 590 steels. Design/methodology/approach: To compare the resistance spot weldability of coated (GAFC590, galvannealed) and uncoated (SPFC590) steels, tensile strength test and macro-section test were conducted for the resistance spot welds. Acceptable welding conditions were determined as a function of the resistance spot welding process parameters such as electrode force, welding time, and welding current. The lower limit of the welding lobe was the minimum shear tension strength for 590 MPa-grade steel while the upper limit was determined whether or not expulsion was detected. Findings: Galvannealed steel required more welding current than uncoated steel. Acceptable welding current condition and welding lobe were changed depending on whether steel is coated or not. Research limitations/implications: This study is forced on inverter DC resistance spot weldability of 590Mpa-grade steels for automotive application. Practical implications: This study confirms the weldability of galvannealed steel by comparing resistance spot weldability depending on whether or not the steels is coated. Originality/value: This study analysed resistance spot weldability depending on whether or not steel sheets are coated, where SPFC590 uncoated steel) and GAFC590 (galvannealed steel) were used. The required spot welding current for galvannealed steels was higher than the uncoated steel and welding lobes for coated and uncoated steels were determined.
4
Content available remote Weldability of pulse GMAW joints of 780 MPa dual-phase steel
So W., Kang M., Kim D.
Archives of Materials Science and Engineering
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2010
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Vol. 41, nr 1
53-60
EN
Purpose: This paper assesses the gap bridgeability of pulse GMAW joints of DP 780 for automobile body. Design/methodology/approach: Wire melting was analyzed using a high-speed camera. The impact of EN ratio on the shape of the bead section was examined after analyzing the macrosection of welding which was obtained on a bead-on-plate-welding experiment. Welding conditions that are robust to the gap were suggested through an analysis on tensile strength, macrosection of the weld and fracture appearance of tensile strength testing at the lap joint welding of DP 780. Findings: A relation among the welding current (welding process parameter of AC pulse GMAW), EN ratio, welding speed and bead shape parameters which include bead width, bead height and penetration were computed. Research limitations/implications: The suitable welding conditions proposed in this paper can change because of types of welding joints thickness of base metal and other reasons. Practical implications: In this study, the suitable welding conditions were presented for securing a good weld quality of DP 780 for the automobile body. Originality/value: Through this study, the correlation between the weld bead geometry and the EN ratio in the AC pulse GMAW was confirmed. Though the weld quality assessment, suitable pulse GMAW conditions of DP 780 were suggested.
5
Content available remote Weldability of 440 MPa galvanized steel with inverter DC resistance spot welding process
Hwang I., Yoon H., Kang M., Kim D.
Archives of Materials Science and Engineering
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2010
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Vol. 42, nr 1
37-44
EN
Purpose: This paper comparatively analyzes resistance spot weldability depending on whether or not 440 MPa-grade steel is galvanized at inverter DC spot welding. Design/methodology/approach: To compare the resistance spot weldability depending on whether or not the steel is galvanized, an inverter DC welding system was designed. Then, using this system, both tensile strength testing and macro-section testing were conducted on SPRC440 (uncoated steel) and SGARC440 (galvanized steel), and weldability was evaluated. Suitable welding conditions were calculated using the resistance spot welding variables such as electrode force, welding time and lobe diagram on the welding current. The low limit of the lobe diagram was set to the low limit of the tensile strength of 440 MPa-grade steel while the high limit was set depending on whether or not expulsion was detected. Findings: Compared to uncoated steel, galvanized steel had lower suitable welding current conditions and a narrower lobe diagram. Research limitations/implications: This paper compared resistance spot weldability and lobe diagram depending on whether or not 440 MPa-grade steel is galvanized. Practical implications: This paper confirms the weldability of galvanized steel by comparing resistance spot weldability depending on whether or not steel is galvanized. Originality/value: For analysis of resistance spot weldability depending on whether or not steel is galvanized, weldability was compared between SPRC440 (uncoated steel) and SGARC440 (galvanized steel) under the same welding conditions. As a result, compared to uncoated steel, galvanized steel had lower suitable welding current conditions and a narrower lobe diagram.
6
Content available remote Statistical analysis of welding industry of South Korea
Kim C., Kang M., Bae S.
Journal of Achievements in Materials and Manufacturing Engineering
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2009
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Vol. 36, nr 2
207-211
EN
Purpose: This paper represents the current status of welding industry of South Korea - how much the welding industry accounts for in monetary terms in the manufacturing industry of South Korea. Design/methodology/approach: We classify welding industry into welding equipment industry and materials & the welding engineering sub-industry. To decide the portion of the welding industry in other engineering industry, we adopt the Welding-Related Expenditures, Investments, and Productivity Measurement in U.S. Manufacturing, Construction, and Mining Industries, a report published by AWS in 2002. The statistical analysis was performed based on the NSO and KITA data. Findings: In South Korea, the welding-related portion in the engineering industry showed much higher figures - about 9 times higher in production amount and over 5 times in export amount - than the welding equipment and materials industry. In addition, the total production of the welding industry amounted to 2.6 billion $, indicating that the welding industry holds a very important place in the entire domestic industries. Research limitations/implications: The welding industry of South Korea was statistically analyzed using the welding related expenditure of the manufacturing industries. Research limitations/implications: This research quantitatively showed the relative importance of the welding industry in South Korea. Originality/value: Due to the nature of welding industry, it is difficult to identify the boundary of welding industry. In addition, monetary impact of welding industry was not revealed in practical manner. In this paper, we categorize the welding industry into two sub-industries and analyze the statistical data with our framework to reveal monetary impact of welding industry. With our results, it is possible to estimate the economical effects of welding industry in South Korea.
7
Content available remote Resistance spot welding of aluminium alloy sheet 5J32 using SCR type and inverter type power supplies
Kim D., Park H., Hwang I., Kang M.
Archives of Materials Science and Engineering
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2009
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Vol. 38, nr 1
55-59
EN
Purpose: A characteristic was compared and analyzed between the lobe diagram of SCR type resistance spot welding and that of inverter type resistance spot welding of the aluminum alloy sheet 5J32 for the car body. Design/methodology/approach: Using the lobe diagram on the electrode force, weld time, and weld current which are process variables of the resistance spot welding, the range of optimal welding condition was determined. The low limit of the range of the optimal welding condition was decided by the lower limit of the tensile strength of the aluminum alloy sheet 5J32, and the upper limit was decided by whether an expulsion occurs or not. Findings: It was found that the range of the optimal welding condition of the inverter type resistance spot welding was larger than the SCR type resistance welding and that the nugget size of inverter type resistance spot welding was larger in the same welding condition. Research limitations/implications: A comparison was between the lobe diagram at the SCR type on the aluminum alloy sheet 5J32 and the lobe diagram at the inverter type resistance spot welding. Practical implications: In this study, by comparing the range of the appropriate welding condition of the resistance spot welding between SCR type and inverter type power supplies, the characteristic of the appropriate welding range by the power supply characteristic could be confirmed. Originality/value: This study compared the characteristic of the resistance spot welding between the SCR type and inverter type power supply using lobe diagram. It was confirmed that the range of appropriate welding conditions of the inverter type resistance spot welding was large.
8
Content available remote Effect of flash butt welding parameters on weld quality of mooring chain
Kim D., So W., Kang M.
Archives of Materials Science and Engineering
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2009
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Vol. 38, nr 2
112-117
EN
Purpose: The effects of flash butt welding parameters on mechanical properties were explored for mooring chain for offshore structure. Design/methodology/approach: Through the tensile strength, impact energy, hardness of weld, macrosection, microstructure and waveform analysis of the flash butt weld, following the change of the flash mode, flash length, upset mode, and upset length which are the parameters of the flash butt welding, the weld quality has been assessed. Findings: It is confirmed that even if the mechanical properties of the weld are satisfied through experiments, a weld defect may exist, and in case of using force mode in upset process, the mechanical characteristics of the weld is superior to position mode. Research limitations/implications: The optimal welding condition presented in this study may be changed in accordance with the chemical composition of the material, size of mooring chain. Practical implications: In this study, the suitable welding conditions were presented for securing a good weld quality of the high strength steel mooring chain for the offshore structure. Originality/value: Through this study, the correlation between the weld parameters and the weld quality in the flash butt welding was confirmed. Though the weld quality assessment, flash butt welding condition of the ř84 mm mooring chain for the offshore structure was presented.
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