• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.26 no.4
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• pp.378-386
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• 2017

Friction stir welding was performed using six welding conditions to evaluate the mechanical properties and microstructure of the welded zone based on its temperature change in the extruded plate of magnesium alloy AZ61. The welded zone temperature was measured using a thermocouple, and the maximum temperature ranges for the advancing and retreating sides were approximately $210-315^{\circ}C$ and $254-339^{\circ}C$, respectively. Depending on the welding conditions, a temperature difference of more than $100^{\circ}C$ was observed. In addition, the maximum yield strength and maximum tensile strength of the welded component was 84.4% and 96.9%, respectively, of those of the base material. For the temperatures exceeding $300^{\circ}C$, oxidation defects occurred in the weld zone, which decreased the mechanical strength of the weld zone. The microstructure and texture confirmed that fracture occurred because of the grain size deviation of the welding tool and the severe anisotropy of the texture of the welded joints.

• The Journal of the Petrological Society of Korea
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• v.23 no.4
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• pp.325-336
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• 2014

Even though Mesozoic Mudeungsan tuff, located within Neungju Basin, has been named several rock names, it should be named as Mudeungsan tuff due to several evidences, such as fiamme, welded texture and rock fragments in the Mudeungsan tuff. Volcanic eruption boundary between the Cheonwangbong and Anyangsan areas is not clear, but petrochemical and mineral chemical evidences with different ages indicate clear petrological boundary between Cheonwangbong and Anyangsan. The Mudeungsan tuffs from Cheonwangbong and Anyangsan is welded crystal tuff with dacitic composition and were generated from cogenetic calc-alkaline magma in the volcanic arc environment. Geochemical events indicate that magma beneath Cheonwangbong was seems to have been evolved from the magma beneath Anyangsan due to fractional crystallization dominated by plagioclase.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.3
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• pp.276-283
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• 2012

In this study, it was studies the utilization of LIT(lock-in infrared thermography) which can detect defects in welded parts of ship and offshore structures. Quantitative analysis was used through methods of filtering and texture measurement of image processing techniques to find the optimized experimental condition. We verified reliability in our methods by applying image processing techniques in order to normalize evaluations of comparative images that show phase difference. In addition, low to mid exposure showed good results whereas high exposure did not provide significant results in regards to intensity of light exposure on surface. Lock-in frequency was satisfactory around 0.1 Hz regardless of intensity of light source we had. In addition, having the integration time of thermography camera inversely proportional to intensity of exposed light source during the experiment allowed good outcome of results.

• Economic and Environmental Geology
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• v.55 no.3
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• pp.295-307
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• 2022

We studied the Cretaceous Jeonggaksan Formation to determine depositional processes of pyroclastic density currents entering into the lacustrine environments. This formation is composed largely of sandstone-mudstone couplets and (tuffaceous) normally graded sandstones deposited in lacustrine environments, interbedded with two pyroclastic beds: welded massive lapilli tuff and normally graded lapilli tuff. The welded massive lapilli tuff (10 m thick) is composed of poorly sorted, structureless lapilli supported by a welded ash matrix. The normally graded lapilli tuff (4 m thick) is characterized by moderately to well sorted natures and multiple normally graded divisions in the lower part of the bed with internal boundaries. The contrasting depositional features between these lapilli tuff are suggestive of different physical characteristics and depositional processes of pyroclastic density currents in the lake. Overall poorly sorted and massive natures of the thick, welded massive lapilli tuff are interpreted to have been formed by rapid settling of pyroclastic sediments from highly concentrated and sustained pyroclastic density currents. In this case, the pyroclastic density currents were able to displace lake water from shoreline and the pyrolclastic density currents preserved their own heat except for frontal parts of the currents. As a result, welded textures can be formed despite entrance of pyroclastic density currents into the lake. The internal boundaries of the normally graded lapilli tuff reflect unsteady natures of the pyroclastic density currents at the time of the deposition and the pyroclastic density currents can not provide sufficient pressure to displace lake water. As a consequence, the pyroclastic density currents transformed into water-saturated turbidity currents, forming relatively well sorted, normally graded lapilli tuff.

• The Journal of the Petrological Society of Korea
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• v.5 no.1
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• pp.108-120
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• 1996

This study reports petrography and geochemical characteristics of the Cretaceous volcanic rocks that are distributed in the vicinity of the Cheonsungsan area, Yangsan-Gun, Gyeongsangnam-Do. The Cretaceous volcanic rocks composed of andesitic rocks, Wonhyosan tuff, Cheonsungsan tuff in ascending order. Sedimentary rock is the basement in the study area cofered with volcanic rocks. These volcanic rocks are Wonhyosan tuff and Cheonsungsan tuff that represented the early phase of the Bulgugsa igneous activity. Wonhyosan tuff are classified into dacite tuff and dacite welded tuff based on the rock texture and their mineral composition. They are covered with Cheonsungsan tuff. Dacite tuff composed of lithic lapilli ash-flow tuff and vitric ash-flow tuff. Most dacite welded tuff are lapilli ash-flow tuff. Cheonsungsan tuff overlying the Wonhyosan tuff consists of rhyolite tuff and rhyolite welded tuff. Rhyolite tuff are lithic crystal ash-flow tuff and crystal vitric ash-flow tuff with somewhat accidental fragments of andesitic and sedimentary rocks. Rhyolite welded tuff is distinguishe from rhyolite tuff by is typical eelded fabrics and its rock color. According to petrochemical data, the volcanic rocks in study area belong to high-K orogenic suties. On the discriminant diagrams such as La/Yb versus Th/Yb, these rocks falls into the discriminant fields for the normal continental margin arc.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1996.03a
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• pp.73-80
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• 1996

Commerical purity aluminium , copper and STS 304 stainless steel sheets are welded by ultrasonic welding. The microstructures, x-ray diffraction profiles of planes , pole figures of the surface of original metal sheets are compared with those of the weld interface. The microstructures show disturbance and dark areas in the weld interface and grain refinement in the vicinity of the interface. The x-ray diffraction intensity of each plane in weld interface decreased in all metal sheets with exception of 9200) in steel sheet. The microstructure and x-ray diffraction intensity is affected by the mixture of deformation, heating and vibratin duringthe ultrasonic welding. Therefore, after the ultrasonic welding, the positions of the peak intensity in the pole figures are changed, the value of the maximum pole intensity is decreased in Al, is increased in copper and stainless steel. Very strong {100} <001> texture, strong {100} <001>,{123}<634> textures in original Al surface are transformed into weak, {100}<001>, {110}<112> and {112}<111> components in weld surface, weak (110) fiber is slightly changed to (110) fiber in copper, (100)and ${\gamma}$ fiber components are transformed into strong ${\gamma}$ fiber component in stainless steel.

• Journal of Magnetics
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• v.16 no.4
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• pp.427-430
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• 2011

The rolled steels for welded structure applied tensile stress have been examined by means of magnetic Barkhausen noise (MBN) method and of a physical parameter obtained from a hysteresis loop. The behaviors of MBN parameters and coercive force with tensile stress were discussed in relation to microstructure changes. There is no change in MBN parameters and coercive force below yield strength. The coercive force rises rapidly with tensile stress above yield strength. On the other hand, the rms voltage and the peak in averaged rms voltage take a maximum around yield strength and then decreases. The magnetomotive force at peak in the averaged rms voltage shows a minimum around yield strength. These phenomena are attributed to the combined effects of cell texture and dislocation density. In addition, the behaviors of MBN parameters around yield strength may be reflected by the localized changes in strain field due to the formation of dislocation tangles.

• Nuclear Engineering and Technology
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• v.55 no.11
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• pp.4066-4076
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• 2023

Pressure resistance welding is usually used to seal the connection between the cladding tube and the end plug made of zirconium alloy. The seal welded joint has a direct effect on the service performance of the fuel rod cladding structure. In this paper, the pressure resistance welded joints of zirconium alloy tube-plug structure were obtained by thermal-mechanical simulation experiments. The microstructure and microhardness of the joints were both analyzed. The effect of processing parameters on the microstructure was studied in detail. The results showed that there was no β-Zr phase observed in the joint, and no obvious element segregation. There were different types of Widmanstätten structure in the thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ) of the cladding tube and the end plug joint because of the low cooling rate. Some part of the grains in the joint grew up due to overheating. Its size was about 2.8 times that of the base metal grains. Due to the high dislocation density and texture evolution, the microhardnesses of TMAZ and HAZ were both significantly higher than that of the base metal, and the microhardness of the TMAZ was the highest. With the increasing of welding temperature, the proportion of recrystallization in TMAZ decreased, which was caused by the increasing of strain rate and dislocation annihilation.

• Journal of Ocean Engineering and Technology
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• v.26 no.5
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• pp.25-30
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• 2012

This study examined the use of LIT (lock-in infrared thermography) to detect defects in the welded parts of ships and offshore structures. A quantitative analysis was used with the filtering and texture measurement of image processing techniques to find the optimized experimental condition. We verified the reliability of our methods by applying image processing techniques in order to normalize the evaluations of comparative images that showed a phase difference. In addition, it was found that a low to mid-range intensity of light exposure on the surface showed good results, whereas high exposure did not provide significant results. A lock-in frequency of around 0.1 Hz was satisfactory regardless of the intensity of the light source. In addition, making the integration time of the thermography camera inversely proportional to the intensity of the exposed light source during the experiment provided good results.

• The Journal of the Petrological Society of Korea
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• v.25 no.1
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• pp.1-12
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• 2016

This study reports the results about the petrography of volcanic rocks in Namoo island and Namhyeongje island, off the southern coast of Busan City. The rocks in the Namhyeongje island composed of dacitic crystal-vitric welded tuff, showing phenocrysts of plagioclase, rock fragment with flow structure of elongated and flattened pumice fragments. In thin section it shows pyroclastic texture. The volcanic rocks in Namoo island are mainly dark grey-bluish dacite with phenocrysts of plagioclase and gradually changed to pink-greyish rhyodacite with auto-brecciated. In the northeastern part of the island, the volcanic rocks occurred as aggromerate with a poorly sorted mixture of blocks, lappili and ash and felsic feeder dike intrude the aggromerate. Major element composition of the volcanic rocks in Namhyeongje island and Namoo island are $SiO_2$ 73.6~74.4 wt.% and 65.5~68.3 wt.%, respectively. The volcanic rocks in these island are felsic volcanic rocks.