• Journal of Welding and Joining
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• 제18권2호
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• pp.57-63
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• 2000

In this study, the lap welding between austenitic stainless steel and carbon steel was carried out using arc spot welding process and weldability of welded specimens was estimated. From the tensile-shear strength test, micro Vickers harness test, and microstructure observation, specimen of $psi6.5mm$(hole of upper plate) showed the best results in terms of tensile-shear strength and nugget shape. And there was an unmix zone in fusion boundary between the carbon steel base metal and bulk weld metal. This zone had very width with the hard microstructure. The shape of weld nugget in arc spot welding of dissimilar metal melds was predicted by searching thermal history of a weld joint through a three-dimensional finite element model. From the numerical analysis, predicted the shape of weld nugget showed good agreement with the experiment.

• 한국정밀공학회지
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• 제31권7호
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• pp.623-626
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• 2014

The LBB (Leak Before Break) concept is based on evaluating the fracture toughness. NUREG 1061, Vol.3 announced that the specimen for evaluating fracture resistance needs to have same thickness or thicker than pipe. Therefore, it is difficult to collect specimen from pipe which has same thickness as a pipe. So, ASTM standard suggested the use of standard specimen with 1 inch thickness. However, it has been known that an application of LBB by test results of standard specimen is conservative compare with that by real pipe. In this study, to supplement such conservatism, the evaluation of fracture resistance characteristics was performed with curved CT specimen, which has same thickness and curvature as a pipe. In addition, fracture resistance characteristics of curved CT specimen were compared with those of CT specimen. For this, shape factor F, hpl and g were obtained from FEM analysis using the limit load method.

• 대한치과기공학회지
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• 제23권1호
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• pp.65-73
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• 2001

The purpose of this study was to investigate the microstucture and hardness, corrosion of pure Ti alloy, which is widely used as partial denture frame work these days, depending on the cooling method, followed by casting. The first group was bench cooling at room temperature($18^{\circ}C$), the second group was slowly cooled in the furnace from $700^{\circ}C$ to room temperature, and third. rapidly cooled in $0^{\circ}C$ water. The microstructure of each specimen observed by means of photomicrograph taken by electron microscope, in add to the physical characteristics of each specimen were obtained using the rockwell Hardnest Number. the characteristics of corrosion. The results were obtained as follows: 1. From Potentiodynamic plot. we conclude furnace-cooled specimen had the best stabiltity of passive film and that air-cooled specimen showed similar characteristics. The density of electric current of quenched specimen was the highest, which formed kind of unstable passive film. 2. Specimen cooled at room temperature (air cooling) had the highest value of hardness of 81.26HRB, specimen cooled at ice-water, $0^{\circ}C$, had the value of 78.42HRB, and specimen furnace-cooled at $700^{\circ}C$ had lowest value of 77.1HRB. 3. Quenching treated micro-structure formed martensite structure by and large. In case of air cooling, we could see $\alpha$-structure widmanstatten formed overall. In furnace cooling, widmanstatten structure and various shape $\alpha$-structures forming colony with direction were detected.

• Composites Research
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• 제20권6호
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• pp.28-33
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• 2007

단섬유 강화고무의 관통 특성에 대해 섬유 종횡비(AR: 섬유 길이/섬유 직경), 섬유 함유량, 시편 크기 그리고 시험속도를 변수로 하여 연구하였다. 기지와 단섬유 강화고무의 관통 저항은 시편 크기의 증가에 따라 감소하였고, 동일한 시편 크기에서 시험 속도의 증가에 따라 관통 저항력은 증가하였다. 각각의 섬유 함유량에서 섬유 종횡비가 클수록 높은 관통응력 값을 보였다. 인장강도와 관통응력의 비교를 통해 시편 형상의 문제점에 대해 고찰하였다. 기지와 단섬유 강화고무의 막에 작용하는 힘은 시편의 크기에 관계없이 유사한 값을 보였고, 동일한 시편 크기에서 시험속도의 증가에 따라 증가하였다. 각각의 섬유함유량에서 섬유 종횡비가 클수록 막에 작용하는 힘은 크게 나타났다 전체적으로 시편 크기, 시험속도가 단섬유 강화고무의 관통 특성에 지대한 영향을 미침을 확인하였다.

• 폴리머
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• 제36권1호
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• pp.59-64
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• 2012

제품의 소형화와 경량화 추세에 따라 부품의 두께가 얇아지는 경향이 있다. 이러한 소형 및 경량 제품의 중요한 설계요소는 소재의 충격강도이다. 충격강도는 재료 고유의 물성값으로 기하학적 형상에 의존하지 않고 일정한 값을 가져야 한다. 그러나 충격강도 시험 시 시편의 두께에 따라 강도의 차이를 보이고 노치(notch)의 생성방법과 노치형상에 따라서도 민감도를 보인다. 본 연구에서는 시편의 두께와 노치형상 및 노치의 생성방법에 따른 충격강도를 알아보았다. 또한 노치의 각도와 노치에 대한 충격 방향에 따른 충격강도도 관찰하였다. 이를 위해 엔지니어링 플라스틱인 PC, ABS, 그리고 POM에 대하여 Izod 충격시험을 수행하였다. 그 결과 실험한 모든 수지에서 두께가 얇아질수록 충격강도가 높아지는 경향을 보였는데 PC수지가 가장 크게 증가하였다. PC수지는 두께가 두꺼울 때는 취성파괴를 보였는데 두께가 얇을 때는 연성파괴 양상을 보였다. 몰드노치 시편이 밀링노치 시편에 비해 충격강도가 높았고, 역방향 노치가 정방향 노치보다 충격강도가 높았다. 본 연구에서 실험한 수지 중에서 노치의 민감성은 PC가 가장 컸으며 다음이 POM, ABS순으로 나타났다.

• 소성∙가공
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• 제12권2호
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• pp.94-101
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• 2003

For the optimal net shape forging of S semi-solid materials (SSM), it is important to predict the deformation behavior and defects of materials. Among these defects, liquid segregation is detrimental to produce products with good mechanical properties. Moreover, to apply a numerical method to thixoforging, it is very important to prevent a liquid segregation during forming process. The liquid segregation phenomena in deformation behavior of semi-solid material with variation of test specimen size were studied. The SSM compression tests were performed by dynamic material test system with a furnace. Stress-strain curves and microstructures of SSM were investigated, and Porosities were analyzed to evaluate the effects of experiment parameters on liquid segregation.

• 한국공작기계학회논문집
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• 제16권2호
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• pp.37-43
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• 2007

In this paper, laser vision sensor is used to detect some defects any $co_{2}$ welded specimen in hardware. But, as the best expression of defects of welded specimen, the concept of segment splitting method and mean distance are introduced in software. The developed GUI software is used for deriding whether any welded specimen makes as proper shape or detects in real time. The criteria are based upon ISO 5817 as limits of imperfections in metallic fusion welds.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2000년도 특별강연 및 추계학술발표대회 개요집
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• pp.216-218
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• 2000

In case of hardfaced wrapping roll, beadmark shape appear at wrapping roll surface due to irregular wear between weld bead. Irregular wear of this is caused by difference of hardness between weld bead. This study aims at investigating which matrix is good for removing of beadmark at wrapping roll surface. So, we make specimen with martensitic matrix and austenitic matrix. The hardfacing alloys were deposited 4 times on a SS41 steel plate using self-shielding flux cored arc welding method. Difference of hardness between weld bead of specimen with matrix of martensite was higher than specimen with matrix of austenite both as-welded and after heat treatment. Therefore, austenitic matrix is better than martensitic matrix for removing of beadmark of wrapping roll surface.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계 학술발표회 논문집(II)
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• pp.537-540
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• 2006

In previous study, the effect of specimen sizes and shapes on the compressive strength of concrete specimens was experimentally investigated based on fracture mechanics. In this study, the relationship between the cube compressive strength and the cylinder strength for representative specimen sizes was investigated by linear regression analyses. And, by reanalyzing the compressive strength prediction equations with specimen size and shape obtained in previous studies, the compressive strength prediction equations were generalized. In addition, its verification was investigated by comparing with the results obtained from other researchers.

• International Journal of Precision Engineering and Manufacturing
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• 제9권2호
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• pp.28-33
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• 2008

In a scanning electron microscope (SEM), outside acoustic noise causes image noise that distorts observations of the specimen being examined. A SEM that is less sensitive to acoustic noise is highly desirable. This paper investigates the image noise problem by addressing the mode shapes of the base plate and the transmission path of the acoustic noise and vibration. By arranging the position of the rib, a new SEM base plate was developed that had twisting as the 1st and 2nd modes. In those two twisting modes, vibration nodes existed near the center of the base plate where the specimen chamber is placed. Less vibration was transmitted to the chamber and to the specimen by the twisting modes compared to bending ones, which are the 2nd and 3rd modes for a rectangular plain base plate. An SEM with the developed base plate installed exhibited a significant reduction of image noise when exposed to acoustic noises below 250 Hz.