• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 1994년도 춘계학술대회 논문집
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• pp.92-100
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• 1994

Forming limit diagrams for three different galvanized deep drawing quality steel sheets have been measured by hemispherical punch stretching. The experimental forming limit diagrams have been compared with results calculated using the shear instability criterion and the M-K model which takes into account a strain gradient effect resulting from bending (curvature) of a flat sheet by punch stretching. The measured data were in good agreement with the results calculated using exponent M value of 8 in Hosford's yield criterion for the M-K model and M= 6 for the shear instability model.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.120-123
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• 2007

The effects of annealing condition on the occurrence of the delamination in cold drawn hyper-eutectoid steel wires, were investigated. Annealing treatment was performed on cold drawn steel wires for temperature range of $425^{\circ}C\sim500^{\circ}C$ with the variation of annealing time from 30sec to 15min. The increase of annealing temperature and time would cause the decrease of tensile strength and the increase of ductility. However, the occurrence of the delamination, representing torsional ductility, showed the different way from the variation of ductility.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2007년도 추계학술대회 논문집
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• pp.124-127
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• 2007

In this study, we focused on investigation of governing parameters affected on the fatigue properties in the hyper-eutectoid steel wires used for TBR tires. Steel wires are fabricated under different drawing strain from 3.36 to 3.80. Their diameters are 0.21 mm and 0.185mm, respectively. The fatigue properties was measured by hunter rotating beam tester, specially designed thin-sized steel wires. The results showed that the fatigue properites of steel wire, marked as A-1, were greater than the others, due to the low value of residual stress. In order to elucidate the variations of fatigue properties, the microstructure, surface defect and residual stress were observed and measured by useful analysis technique, such as TEM, 3D profiler and FIB.

• 산업기술연구
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• 제30권A호
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• pp.49-57
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• 2010

A forming limit diagram (FLD) defines the extent to which specific sheet material can be deformed by drawing, stretching or any combination of those two. To determine the forming limit curve (FLC) accurately, it is necessary to perform the tests under well-organized conditions. In this study, the influence of several geometric or process parameters such as the blank shape and dimensions, strain measuring equipments, test termination time, forming speed and lubricants on the FLC is investigated.

• 한국정밀공학회지
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• 제13권3호
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• pp.80-93
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• 1996

A 2-dimensional FEM/GEM program was developed under the plane strain assumption using linear line elements for analyzing stretch/draw forming operations of an arbitrarily shaped draw-die. FEM formulation adopted a new algorithm for solving force equilibrium as well as non-penetration condition simultaneously. Also, a rigid-viscoplastic material model with Hill's normal anisotropic yield condition and rate-sensitive hardening law is assumed, along with the Coulomb friction law in the contact regions. For the case of numerical divergence at nearly final forming stages, geometric force equilibrium method(GEM) is also introduced. The developed program was tested by simulating the forming processes of cylindrical punch/open die, and the drawing processes of automotive oilpan and hood inner panel in order to verify the usefulness and validity of FEM/GEM formulation. The numerical simulation verified the validity and robustness of developed program.

• 대한지구과학교육학회지
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• 제2권1호
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• pp.80-90
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• 2009

The purpose of this study is to investigate the characteristics of the mind maps which were drawn with pencil or color pens by elementary students. For this study, 31 students of the 6th grade were selected and trained mind mapping. After training, the subjects had drawn mind maps with color pens about the ROCK for 15minutes and drew mind maps with pencil after 2days of mind mapping using color pens. In addition to activities of mind mapping, the students handed in their papers which were written one's impression of drawing two kinds of mind mapping. The results were follows: First, in central circle which was linked words connected firstly with ROCK as key word, the difference of 2kinds mind maps were little showed in the quantity and quality of the words, branches and their adequacy. Second, the mind maps using pencils had more words, branches and images than mind maps of using color pens in the whole assessment. Third, the most students suggested that the mind mapping using pencil were advantage to economy of time, retouching words and branches, also the mind mapping using pencil made the students relax the strain for drawing it because of retouching possibility. Consequently, the results of this study suggest the mind mapping using pencil has advantage effect on the purpose of gaining students' thinking abundantly and economy of time in elementary science classes.

• 접착 및 계면
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• 제12권4호
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• pp.105-110
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• 2011

폴리에스터/멜라민 경화형 도료는 기계적 물성, 내화학성 및 내마모성 등이 우수하여 pre-primed 도료 및 pre-coated metal에 널리 사용되고 있다. 그러나, 폴리에스터 수지 도료의 경화 도막은 강인하지만 유연성과 성형성이 낮은 문제점을 갖고 있다. 본 연구에서는 polycarbonate diol의 long alkyl chain을 폴리에스터 분자 구조 내에 연결시켜 경화 도막의 성형성을 개선하고자 하였으며, 성형성이 개선된 폴리에스터 도료의 선도장 강판용 도료의 적용 가능성을 확인하였다. 또한, 폴리카보네이트디올 분자량이 경화 도막 물성에 미치는 영향을 평가하고자 인장강도와 점탄성을 측정하였으며, 성형성을 확인하고자 drawing test를 실시하였다.

• 한국정밀공학회지
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• 제11권4호
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• pp.77-87
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• 1994

This paper deals with an automated forming sequence design system by which designers can determine desirable operation sequences even if they have little experience in the design of cold forging process. The forming sequence design in the cold forging is very important and requires many kinds of technical and empirical knowledge. They system isproposed, which generates forming sequence plans for the multistage cold forging of axisymmtrical solid products. Since the process of metal forming can be considered as a transformation of geometry, treatment of the geometry of the product is a key in planning process. To recognize the geometry of the product section, section entity representation and primitive geometries were used. Section entity representation can be used for the calculation of maximum diameter, maximum height, and volume. Forming sequence for the part can be determined by means of primitive geometries such as cylinder, cone, convex, and concave. By utilizing this geometrical characteristics (diameter, height, and radius), the product geometry is expressed by a list of the priitive geometries. Accordingly the forming sequence design is formulated as the search problem which starts with a billet geometry and finishes with a given product one. Using the developed system, the sequence drawing with all dimensions, which includes the proper sequence of operations for the part, is generated under the environment of AutoCAD. Based on the results of forming sequence, process variables(strain, punch pressure, die inner pressure, and forming load) are determined.

• 감성과학
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• 제25권4호
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• pp.45-52
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• 2022

최근 신체활동에 대해 인식하는 센서와 그 제품군에 대한 관심 및 수요가 증가하고 있다. 특히 유연하고 연신이 가능하며 사용자의 생체신호를 감지할 수 있는 웨어러블 소재에 대한 개발이 주목받고 있다. 본 연구에서는 소수성 소재에 Micro Needle을 통해 미세 구멍을 형성한 후 SWCNT 분산용액에 대한 함침 효율을 향상시키는 실험을 수행하였다. 본 연구에서는 구멍을 뚫지 않은 소재를 대조(control) 군으로 함침을 진행, 비교 분석하였다. 센서의 전기전도도를 평가하기 위해 Strain UTM (Universal Testing Machine, UTM, Dacell)과 저항을 측정하는 멀티미터(Keysight)를 이용해 센서를 인장했을 때의 센서의 전기전도도를 측정하였다. 또한 센서의 내구성을 평가하기 위해 시료별로 500회 인장을 진행한 후에 센서의 전기전도도를 평가하였다. 그 결과 Needling을 한 센서의 전기전도성이 Needling을 하지 않은 센서에 비해 최소 16배 이상 뛰어남을 알 수 있었다. 또한 센서의 초기 저항에 비해 게이지 팩터도 우수해 센서로서 좋은 성능을 확인할 수 있었다. 이를 통해 친수성 소재에 비해 물성이 뛰어나지만, 높은 표면장력 때문에 함침 효율이 좋지 않았던 소수성 소재의 함침 효율을 높여 신체의 움직임을 더 효과적으로 감지하고 내구성과 활용 가능성이 뛰어난 센서를 제작했다.

• 화약ㆍ발파
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• 제26권2호
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• pp.20-28
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• 2008

터널설계 시 내공변위 예측은 흔히 탄소성 해석을 통하여 수행되므로, 탄소성 해석법은 많은 연구자들의 관심을 끌고 있는 연구 주제이다. 그러나 일반화된 Hoek-Broun 암반에 굴착된 원형터널의 탄소성 거동은 그 중요성에도 불구하고 아직까지 연구가 미진한 실정이다. 이 연구에서는 Lee & Pietruszczak (2008)의 연구를 응용하여 주변이 환형으로 보강된 원형터널의 탄소성 해석을 위한 간단한 수치 해석법을 제안하였다. 터널은 일반화된 Hoek-Brown 파괴조건을 따르는 변형률연화 암반에 굴착되는 것으로 가정하였다. 제안된 방법의 검증을 위해 상업코드인 FLAC이 이용되었다. 예제 해석을 통해 Hoek-Brown 강도정수 a와 보강대의 두께가 터널 주변의 탄소성 거동에 미치는 영향을 검토하였다. 해석결과 이 두 변수가 터널주변의 응력 및 변위 분포에 미치는 영향은 상당히 큰 것으로 나타났다.