• 한국재료학회지
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• 제10권2호
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• pp.128-137
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• 2000

가스터빈 블레이드 재료로 사용되는 IN738LC 니켈기 초합금 주조재에 대하여 고온등압압축(HIP) 공정에 의한 미세조직 변화와 고온 피로수명에 미치는 영향을 조사하였다. 세부적으로 HIP 처리에 따른 주조결함 제거와 피로변형 열화재의 물성재생효과 확인에 중점을 두었으며, 이를 위하여 회전굽힘 피로시험을 실시하고 변형전후의 미세조직을 광학 및 주사전자현미경으로 관찰하였다. HIP 처리 전후의 미세조직과 피로수명을 비교, 평가한 결과, 주조재와 열처리재의 피로수명 차는 크지 않았으나 HIP 처리재의 피로수명은 이들과 비교하여 평균 60배 이상 증가한 것으로 나타났다. 또한 인위적으로 고온 피로변형을 가한 열화재를 대상으로 반복 HIP 처리한 결과, 열화 변형조직이 신재 상태로 거의 완전히 재생될 뿐만 아니라, 재료내에 미세하게 잔존하던 주조결함까지 부가적으로 제거됨에 따라 반복 HIP 처리에 의한 피로수명 연장 효과가 크게 나타났다.

• 한국구조물진단유지관리공학회 논문집
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• 제14권6호
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• pp.117-123
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• 2010

일반적으로 고내구성 재료로 알려져 있는 FRP 재료가 유해한 환경요소에 노출될 경우 가수분해와 같은 화학적 반응으로 인하여 재료적 열화와 재료의 성질이 감소될 수 있다. 따라서, FRP 재료를 건설 주부재로 사용하기 위해서는 사용 환경에 따른 역학적 특성을 정확하게 파악하는 것이 중요하다. 이에 본 연구에서는 화학약품에 의한 급성 또는 만성적인 극심한 변화들을 가상적인 시뮬레이션을 실시하고자 강산과 강알칼리화합물 용액에 FRP 부재를 일정기간 보관한 후 압축강도, 인장강도, 전단강도 그리고 휨강도 실험을 실시하여 화학약품의 종류 및 보관일수에 따른 강도 변화를 분석하였다. 결론적으로 본 연구를 통하여 FRP 부재의 우수한 내화학약품성을 확인할 수 있었다.

• 대한치과보철학회지
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• 제44권3호
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• pp.333-342
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• 2006

Statement of problem. Although many studies have been carried out to investigate the correlation between the degree of conversion and the flexural strength of composite resins, there is minimal information in the literature attempting to compare degree of conversion, flexural strength and their correlation between restorative composite resins and flowable composite resins. Purpose. The purposes of this study were to measure the degree of conversion and flexural strength of composite resins with different rheological behavior and to correlate the two properties. Materials and methods. Four restorative (Vit-1-escence, Z-250, Tetric ceram, Esthet-X) and four flowable (Aeliteflo, Admiraflow, Permaflo, Revolution) light-curing composite resins were investigated. The degree of conversion(DC) was analyzed with Fourier transfer infra-red spectroscopy(FTIR) spectrum by a potassium bromide(KBr) pellet transmission method. The spectrum of the unpolymerized specimen had been measured before the specimen was irradiated for 60s with a visible light curing unit. The Poiymerized specimen was scanned for its in spectrum. The flexural strength(FS) was measured with 3-point bending test according to ISO 4049 after storage in water at $37^{\circ}C$ for 24 hours. The data were statistically analyzed by an independent sample t-test and one-way ANOVA at the significance level of 0.05. The dependence of flexural strength on the degree of conversion was also analyzed by regression analysis. Results. Mean DC and FS values ranged from 43% to 61% and from 84.7MPa to 156.7MPa respectively. DC values of the flowable composite resins were significantly higher than those of restorative composite resins (P < 0.05). The FS values of restorative composite resins were greater than those of flowable composite resins. No statistically significant correlation was observed between the DC and the FS tested in any of the composites. The dependence of FS on DC in restorative or flowable composite resins was not significant. Conclusion. It can be concluded that radical polymerization of the organic matrix is not a major factor in determining flexural strength of the commercially available composite resins.

• 대한치과보철학회지
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• 제34권4호
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• pp.823-832
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• 1996

The purpose of this study was to assess the effect of 1) the diameter(0.7,1.0,1.2mm) and number(1,2,3) of commonly available orthodontic metal wires embedded in self-curing orthodontic acrylic resin specimens($64{\times}10{\times}3mm$) and 2) the use of chemical adhesive system(Silicoater, Metalprimer) to prevent slipping at the interface between the resin and the metal wire on reinforcement by using three-point bending test. From this study, the following results were obtained. 1. No statistically significant difference was found among the transverse strengths for the control without reinforcement, one 0.7mm wire, two 0.7mm wires, three 0.7mm wires, and one 1.0mm wire groups(P>.05). 2. In the groups with 1.0 or 1.2mm wires, the transverse strength increased in proportion to the increase of number of wires(P<.05). 3. In the groups with 0.7 or 1.0mm wires, neither of Silicoater and Netalprimer increased the transverse strength significantly(P>.05). 4. No statistically significant difference was found in transverse strength between Silicoater groups and Metalprimer groups with same diameter of wires(P.>05). From these result, it is concluded that diameter of wires is a primary considering factor to reinforce the acrylic resin effectively and, when this requirement is satisfied, increased number of wires or chemical adhesive systems can be expected to produce the additional reinforcing effect.

• Geomechanics and Engineering
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• 제10권3호
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• pp.357-386
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• 2016

In this research work, an exact analytical solution for thermal stability of solar functionally graded rectangular plates subjected to uniform, linear and non-linear temperature rises across the thickness direction is developed. It is assumed that the plate rests on two-parameter elastic foundation and its material properties vary through the thickness of the plate as a power function. The neutral surface position for such plate is determined, and the efficient hyperbolic plate theory based on exact neutral surface position is employed to derive the governing stability equations. The displacement field is chosen based on assumptions that the in-plane and transverse displacements consist of bending and shear components, and the shear components of in-plane displacements give rise to the quadratic distribution of transverse shear stress through the thickness in such a way that shear stresses vanish on the plate surfaces. Therefore, there is no need to use shear correction factor. Just four unknown displacement functions are used in the present theory against five unknown displacement functions used in the corresponding ones. The non-linear strain-displacement relations are also taken into consideration. The influences of many plate parameters on buckling temperature difference will be investigated. Numerical results are presented for the present theory, demonstrating its importance and accuracy in comparison to other theories.

• 한국해양공학회지
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• 제29권2호
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• pp.120-127
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• 2015

When a deep-seabed lifting pump is kept this device has bending and deformation in the axis due to its long length(8m). These influences can be caused a breakdown. Therefore, a mounting must be developed to keep the lifting pump safe. This paper discusses the hydraulic cylinder design of the lifting pump and structural safety estimation of the mounting using SBD(simulation-based design). The multi-body dynamic simulation method is used, which has been used in the automotive, structural, ship building, and robotics industries. In this study, the position and diameter of the hydraulic cylinder were determined based on the results of the strokes and buckling loads for the design positions of the hydraulic cylinder. A structural dynamic model of the mounting system was constructed using the determined design values, and the structural safety was evaluated using this dynamic model. According to these results, this system has a sufficient safety factor to manufacture.

• 대한인간공학회지
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• 제30권3호
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• pp.419-426
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• 2011

Objective: The objective of this study was to evaluate a work of guards, using an ergonomic method(work analysis and posture analysis). Background: Most studies about guards were conducted in the field of medical, problems of shift, and the physical problems of old workers and social problems. But, guards consist of vulnerability group so it needs an ergonomic research in musculoskeletal disorders. Method: A head of an ergonomic estimation was work analysis(determination of combined task, work tool, work time and frequency of combined task) and posture analysis(upper body and lower body) of workers based on the video. Results: The result showed that combined task of guards was classification of patrolling, security, cleaning and waiting. The security indicated the highest ratio in the work time of combined tasks. The results of posture analysis for guards indicated high value in neutral. But, lower arm indicated high value in bending(left: 59%, right: 50%). Conclusion: The results of ergonomic methods indicated that guards' physical work load was not high during work, but comfortable work environment would be required for old guards. Application: If an ergonomic rule can be integrated into existing work environments, the risk of occupational injuries and stress will be reduced.

• 패션비즈니스
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• 제16권6호
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• pp.21-35
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• 2012

In consideration of the injuries and deaths occurring at manufacturing sites due to the use of inappropriate work clothes or safety devices, this study aims to categorize manufacturing work processes to develop functional work clothes for heavy industries including the automobile, machine and shipbuilding industries in South Korea. Defining the features of the work environments and work postures of these industries provided for a categorization of the work processes which would enable the development of suitable work clothes for each work process' category. The results of the study based on a questionnaire survey are as follows: Work process category 1, including steel panel pressing and auto body assembly, final inspection (in automobile) and inspection (in machine), requires work clothes with upper body and arm mobility and performance to protect from the toxic fume factor. Work process category 2, consisting of welding (in automobile), cutting-and-forming (in machine) and attachment-and-construction (in shipbuilding), requires clothing elasticity, durability and heat and fire resistance. Work process category 3 comprising welding and grinding in the machine and shipbuilding industries, requires work clothes' tear resistance and elasticity, particularly for lateral bending mobility, and work clothes' sleeves' and pants' hemlines with sealed designs to defend against iron filing penetration, as well as incombustible and heat-resistant material performance. Finally, work process category 4, including painting in machine and shipbuilding, requires work clothes with waterproofing, air permeability, thermal performance, elasticity, durability and abrasion resistance.

• 한국철도학회논문집
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• 제19권2호
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• pp.187-194
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• 2016

철도교량의 신뢰도 기반 한계상태설계법 도입 시 목표신뢰도지수 산정을 위하여 기존 철도교량의 신뢰도지수 산정이 선행되어야 한다. 대표적인 복선 철도교량 중 하나인 6주형 PSC-I형 거더교량에 대해 신뢰도지수를 산정하였다. 최외측 거더의 휨모멘트에 대한 신뢰도 해석을 수행하였다. 휨저항강도 및 고정하중효과는 도로교 한계상태설계법 도입 시 적용된 선행연구자들의 평균과 변동계수를 활용하였고, 열차의 활하중 효과는 여객/화물 혼용선 중 중량화차 통행이 빈번한 중앙선에서 현장계측 데이터를 활용하였다. 한계상태방정식에 대하여 개선된 일계이차 모멘트법(AFOSM)으로 신뢰도 분석을 수행하였으며, 하중효과와 저항효과의 각 요소가 신뢰도지수에 미치는 민감도를 분석하여 중요도를 검토하였다.

• 대한기계학회논문집A
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• 제41권10호
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• pp.997-1004
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• 2017

엘리베이터 와이어로프의 수명은 제품의 매우 중요한 특성 가운데 하나로서 사용자의 안전 및 장비의 정비 정책과 밀접한 관계가 있다. 엘리베이터 와이어로프의 수명을 사용조건에서 측정하는 것은 매우 비경제적이다. 이 연구에서는 엘리베이터 와이어로프 (8x19W-IWRC)의 가속열화시험 데이터를 활용하여 와이어로프의 수명을 추정하는 방법을 다루었다. 굽힘피로시험기를 이용하여 가속열화시험을 진행하였으며 가속변수로는 인장하중을 사용하였다. 와이어로프의 수명은 대수정규분포를 가정하였고, 선형회귀모형을 이용하여 가수명을 구한 후 가속수명모형을 이용하여 와이어로프의 수명을 추정하는 방법과 고장 확률에 대한 로지스틱 회귀모형을 이용하여 추정하는 방법을 제시하고 두 모형의 수명 추정결과를 비교하였다.