• 한국산학기술학회논문지
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• 제18권5호
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• pp.278-284
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• 2017

본 연구에서는 일정한 회전 속도에서 용접 속도를 제어하여 AZ61 마그네슘 합금에 적합한 입열량 조건을 도출하였다. 또한 산업적 측면에서는 더 빠른 용접 속도가 요구되기 때문에 용접 속도에 따른 효과를 연구하였다. 회전 속도 변수는 800rpm으로 일정하게 적용하였고, 용접 속도는 100 - 500mm/min 으로 변화시켜 용접부의 거동을 관찰 및 평가하였다. 기계적 물성 평가를 위하여 인장 및 경도 시험을 수행하였으며, 미세구조 관찰과 용접부의 건정성을 판단하기 위하여 광학현미경을 사용하였다. 용접 속도가 400mm/min 이상 적용되었을 때 용접부 내부에서 결함이 관찰되었다. 용접 속도가 증가할수록 교반부의 결정립 크기는 작아졌으며, 경도 또한 비례 증가하는 경향을 보였다. 회전속도 800rpm, 용접 속도 200mm/min과 300mm/min 일 때, 용접부 내 외부 적으로 결함이 없었으며, 우수한 기계적 물성이 기록되었다. 이때, 접합 효율은 각각 100.5%, 101.2%이었고, 최대인장강도가 모재의 강도와 유사하였다. 인장 시편의 파괴는 시편의 전진측과 교반부 사이에서 발생하였으며, 이는 횡단면부 경도 분포에서 경도가 일시적으로 감소하는 위치와 일치하였다.

• 한국표면공학회지
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• 제43권5호
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• pp.230-237
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• 2010

FTMP(friction thermo-mechanical process) is an adaptation of friction stir welding, and can be used as a generic process to modify the microstructure at selective locations. In this study, in order to analyze characteristics of surface modification of ACA4 castings by FTMP, change of rotating speed(R/S) and traveling speed(T/S) of tool were applied as conditional parameter. Analysis of microstructure, hardness, surface roughness and depth of modified zone(MZ) were searched. The best condition were obtained at R/S 600 rpm and T/S 100 mm/min. At this time, hardness was 82 HV, the surface roughness was 0.07 mm and the depth at MZ was 1.72 mm. Free defects microstructure and fine Si particles formation and strong forging effects were analyzed at MZ.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 추계학술발표대회 개요집
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• pp.135-137
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• 2005

The body of the work covers FSW welding of Al6061 and its thermal distribution based on an analytical model for the heat input at the probe/matrix boundary of Al plates and FSW tool due to the effect of combined translation and rotational motion of the tool pin and shoulder. Finally the 2D- finite element heat transfer analysis program has been used to plot the heat distribution at the Friction Stir Welded joint in Al 6061 plate. The work concludes that the heat distribution result obtained from FE analysis has a reasonable agreement with the experimentally measured values.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2007년 추계학술발표대회 개요집
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• pp.345-347
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• 2007

The microstructures and mechanical properties with the different Sc content of AA2519 FSW joint were investigated in this study. The sound FSW joints were obtained under applied all welding conditions such as the Sc content and the tool rotation speed. The grain size of the stir zone decreased slightly with increasing the Sc content. And the ultimate tensile strength increased and elongation decreased with increasing the Sc content. The intermetallic compound contained the Sc is considered to bring out the improvement of mechanical property in FSW joint.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2005년도 춘계학술발표대회 개요집
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• pp.223-225
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• 2005

In order to demonstrate the friction stir weldability of the Al 6061 T-6 unequal thickness joint and determine optimum welding parameters, the relations between welding parameters and properties of the joints have been studied in this paper. The experimental results showed that the tensile properties of the joints are affected by the welding heat inputs and tool shape. In this study, the maximum ultimate strength of the as-welded joint is equivalent to 78% and 18hour aged joint is equivalent to 93% that of the base metal. Though the voids-free joints are fractured at the thermally affected zone on the advancing side, the fracture occurs at the weld center when the void defects exist in the joints.

• Journal of Welding and Joining
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• 제28권6호
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• pp.70-75
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• 2010

This study intends to investigate the weldability and mechanical characteristics of butt weld joints by LAFSW for dissimilar materials (Al6061-T6 and SS400). At optimum welding conditions, the tensile strength of dissimilar materials joints made by FSW is found to be lower than that of LAFSW. Due to the increase in plastic flow and formation of finer recrystallized grains at the TMAZ and SZ by laser preheating in LAFSW, the hardness in LAFSW appeared to be higher than that of FSW. Compared with FSW, finer grain size is observed and elongated grains in parent metal are deformed in the same direction around the nugget zone in TMAZ of Al6061-T6 by LAFSW. Whereas, at weld nugget zone, coarse grain size is appeared in LAFSW compared to FSW, which is owing to more plastic flow due to laser preheating effect. In dissimilar materials joints by LAFSW, ductile mode of fracture is found to occur at Al6061 side with fewer brittle particles. Mixed mode of cleavage area and ductile fracture is observed at SS400 side.

• 소성∙가공
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• 제23권5호
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• pp.282-288
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• 2014

It is difficult to control welding variables during spot welding of non-ferrous metals like aluminum because of the low electrical resistance of the material. It has been suggested that a solid state welding process such as friction stir spot welding or extru-spot welding can be used to spot weld aluminum plates. In the extru-spot welding, there is a need to increase the weld strength by improving the shape of the welding die. The current study shows that the weld strength for an extru-spot welding can be increased by using a pin placed on the inside of the upper electrode in the welding die. In the current study, the deformed shape of the insert rivet and the stress distribution in the welding zone were analyzed by simulation. Extru-rivet spot welding experiments were performed by changing the height of pin on the inside of the upper electrode. From the experimental result, it is shown that the weld strength for an extru-rivet spot welding can be increased by adjusting the height of the pin. The optimal shape of the deformed rivet after the extru-rivet spot welding can be observed from the simulation results. The deformed shape of the insert rivet can also be controlled by the height of pin.

• 대한족부족관절학회지
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• 제10권2호
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• pp.117-124
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• 2006

Purpose: This study was aimed at elucidating the pathogenesis of talar osteochondral lesion by analyzing the histopathological findings. Materials and Methods: Twenty specimens from 20 patients who underwent surgical treatment for talus osteochondral lesions were studied. Preoperative MRI images including T1, T2, and stir images were taken and cases were classified according to modification of the Anderson's classification. There were 5 cases of MRI group 1, 6 cases of group 2, 7 cases of group 3 and 2 cases of group 4. A full thickness osteochondral plug including the osteochondral lesion of the talus was harvested from each patient and reviewed histopathologic changes of osteochondral fragment using H-E staining. Mean diameter of specimens was 8.5 mm and mean depth was 10.3 mm. Pathologic changes of articular cartilage and subchondral bone were observed. Subchondral bone was divided into superficial, middle and deep zones according to depth. Cartilage formation, trabecular thickening and marrow fibrosis were observed in each zone. Results: There were detachment of the joint cartilage at the tidemark in 16 cases of 20 cases and the separated cartilages were almost necrotic on the histopathologic findings. Cartilage formation within subchondral bone was discovered beneath the tidemark in 12 cases. Trabeculae were increased and thickened in 17 cases. These pathologic changes were similar to fracture healing process and these findings were more conspicuous near the tidemark and showed transition to normal bone marrow tissue with depth. No correlation between the pathological progression and MRI stages was found. A large cyst shown on MRI's was microscopically turned out to be multiple micro-cysts accompanied by fibrovascular structure and newly formed cartilage tissue. Conclusion: The histopathologic findings of osteochondral lesions are detachment of overlying cartilage at the tidemark and subsequent changes of subchondral bone. Subchondral bone changes are summarized as cartilage formation, marrow fibrosis and trabecular thickening that mean healing process following repeated micro fractures of trabecular. These osteochondral lesions should have differed from osteochondral fractures.

• 한국식품과학회지
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• 제40권3호
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• pp.337-342
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• 2008

'06년-'7년 시중 유통되는 가공식품과 단체급식의 메뉴를 대상으로 과잉 섭취 시 위해 가능한 영양성분의 하나인 당 함량 실태 조사를 한 결과 사탕류, 캐러멜류 및 젤리류에서 31.7-71.1%로 가장 높게 나타났고, 특히 학교주변 문방구등에서 판매되는 저가의 어린이 기호식품의 경우 대부분 당 함량이 높은 것으로 나타났다. 또한, 단체급식에서 제공되는 반찬 중 찜류 및 볶음류, 조림류에서 물엿이나 설탕을 첨가하는 경우 29.6-49.2%로 어린이 기호식품과 유사한 수준의 당을 함유하고 있었다. 가공식품 및 단체급식 메뉴를 통한 당 섭취를 줄이기 위해서는 산업체나 단체급식 시설에서의 설탕이나 물엿과 같은 단맛 성분의 사용을 최소화하고 급식에 대한 영양표시제 활성화가 필요하며, 소비자들은 제품을 선택할 때 영양성분표시를 확인하여 당 함량이 적은제품을 선택하고, 섭취 시에도 가급적 1회 제공량 범위를 넘지않도록 해야 할 것이다. 본 연구 결과를 기초로 지속적인 실태조사를 통하여 가공식품 및 음식의 당 함량 데이터베이스 및 원료성 식품에 대한 데이터베이스를 구축한다면 소비자들에게 올바른 영양정보를 제공하고 당 저감화를 추진하는 등 어린이 먹거리의 영양 안전성을 확보하게 될 것이다.