• 한국산업융합학회 논문집
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• 제24권2_1호
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• pp.79-89
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• 2021

Poly(lactic acid) (PLA) is considered as one of the most promising bio-based polymers due to its high strength, high modulus, good processability, transparency after processing, and commercial availability. This study aimed to investigate the mechanical, thermal, and migration properties of poly(lactic acid)/zeolite (10 phr) composites prepared with various biocompatible plasticizers, such as triethyl citrate(TEC), tributyl citrate(TBC), and poly(ethylene glycol)(PEG400), through differential scanning calorimetry(DSC), thermo-gravimetric analysis(TGA) and standard tensile testing. The incorporation of PEG400 significantly increased the elongation at break, and DSC results showed that the addition of plasticizers drastically decreased the T_g of PLA/zeolite composites and improved the melt flow and processability. Besides, it was found from TGA results that PLA/zeolites composites plasticized by TEC and TBC were more easily to be thermally degraded than the composites plasticized by PEG400.

• 대한기계학회논문집
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• 제16권8호
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• pp.1566-1574
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• 1992

본 연구에서는 원형수직 충돌분류에 의한 가열평판의 전열특성을 해석하기 위 하여 최근 표면온도 측정에 많이 사용되고 있는 liquid crystal을 이용하였다. 즉 liquid crystal의 감온특성과 영상처리 기법을 이용하여 레이놀즈수 및 노즐과 충돌판 사이의 거리(L/D) 변화에 따른 전열면의 온도장 변화를 측정하였다.

• 한국레이저가공학회지
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• 제9권1호
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• pp.9-16
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• 2006

Glass is one of brittle materials. Generally, brittle material is weak for tensile stress but strong for compression stress. Laser breaking of glass used this brittle characteristics. Laser breaking of glass was simulated to optimize breaking condition by using commercial FEM code MARC which is applicable to thermo-mechanical coupling analysis. Various shapes of heat sources were applied to the analysis and the distance between heating and cooling source were varied for each simulation. The shapes of heat sources were circle, single and double ellipse and the distance was varied from 0mm to 30mm. Moving heat sources were designed on the basis of experimental condition. As a result, double elliptic shape of heat source was the most suitable among them in laser breaking of glass. And it should be useful to determine optimal condition of laser breaking for glass.

• 한국추진공학회지
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• 제21권1호
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• pp.17-25
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• 2017

초음파 진동자에 의해 미립화된 탄화수소계 액체연료를 태우는 버너의 연소특성을 고찰하기 위한 실험이 수행되었다. 고속카메라와 열화상 카메라를 이용하여 slit-jet 버너에서 생성된 화염의 이미지를 획득하였으며, 후처리를 통해 화염의 형상과 온도구배를 면밀히 분석하였다. 또한, 정밀유량 계측법을 이용하여 수송기체 실험조건 변화에 따른 연료소모량을 측정하였다. 그 결과, 수송기체 유량이 증가하면 무화된 연료의 분사량도 같이 증가한다는 사실을 확인하였으나, 낮은 유량 조건에서는 주변 장치의 진동에 의해 공연비(air/fuel ratio)와 수송기체 유량의 상관성이 관찰되지 않았다. 또한, 수송기체 유량과 초음파진동자의 소비전력이 증가하면 연소반응이 촉진되어 연소영역이 신장되고 화염온도가 증가하였다.

• 한국추진공학회지
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• 제22권6호
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• pp.1-10
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• 2018

초음파 진동자에 의해 미립화된 탄화수소계 액체연료를 분사하는 버너에서 생성되는 화염의 거동을 고찰하기 위한 실험이 수행되었다. 고속카메라와 열화상 카메라를 이용하여 slit-jet 버너에서 생성된 화염과 연소장 이미지를 획득하였으며, 후처리 과정을 통해 화염과 연소장의 구조변이를 면밀히 분석하였다. 그 결과, 수송기체 유량이 증가하면 연소반응이 촉진되어 연소반응영역이 신장되고, 반응온도가 증가하였다. 또한, 시간 변화에 따른 가시화염과 IR 연소장의 거동변화 비교를 통해 화염의 진동원인을 고찰하였으며, 화염면적의 FFT분석을 통해 생성화염의 진동주파수도 확인하였다.

• 한국공작기계학회논문집
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• 제14권2호
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• pp.42-47
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• 2005

Micro duplex stainless steel is used to denote a fine scale two-phase micro structure consisting austenite and firrite. The development of this structure was done by proper thermo-mechanical processing. The objective of present investigation is to study creep characteristics of this alloy. Since we have little design data about the W behaviors of the alloy. An apparatus has been designed and built fir conducting creep tests under constant load conditions. A series of creep tests on them have been performed to get the basic design data and life prediction of micro duplex stainless steel products and we have gotten the 1311owing results. First the stress exponents decrease as the test temperatures increase. Secondly, the creep activation energy Gradually decreases as the stresses become higher. Thirdly, the constant of Larson-Miller Parameters on this alloy is estimated as about 5. Last, the fiactographs at the creep rupture show both the ductile and brittle fracture modes according to the creep conditions.

• 소성∙가공
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• 제19권8호
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• pp.468-473
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• 2010

Shape memory alloys (SMAs) have the ability to recover their original shape upon thermo-mechanical loading even after large inelastic deformation. The unique feature is known as pseudoelasticity and shape memory effect caused by the crystalline structural transformation between two solid-state phases called austenite and martensite. To support the engineering application, a number of constitutive models, which can be formally classified into either micromechanics-based or phenomenological model, have been developed. Most of the constitutive models include a kinetic law governing the crystallographic transformation. The present work presents a one-dimensional, phenomenological constitutive model for SMAs in the context of the unified viscoplasticity theory. The proposed model does not incorporate the complex mechanisms of phase transformation. Instead, the effects induced by the transformation are depicted through the growth law for the back stress that is an internal state variable of the model.

• 소성∙가공
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• 제14권9호통권81호
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• pp.751-755
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• 2005

This paper is concerned with spring back after sheet forming of bulk amorphous alloys in the super cooled liquid state. The temperature-dependence and strain-rate dependence of Newtonian/non-Newtonian viscosities as well as the stress overshoot/undershoot behavior of amorphous alloys are reflected in the thermo-mechanical Finite Element simulations. Hemispherical deep drawing operations are simulated for various forming conditions such as punch velocity, die comer radius, friction, blank holder force, clearance and initial funning temperature. Here, spring back by an instantaneous elastic unloading was followed by thermal deformation during cooling, and two modes of spring back are examined in detail. It could be concluded that the superior sheet formability of an amorphous alloy can be obtained by taking the proper forming conditions for loading/unloading.

• 소성∙가공
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• 제21권6호
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• pp.378-383
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• 2012

Laser forming is an advanced process in sheet metal forming in which a laser heat source is used to shape the metal sheet. This is a new manufacturing technique that forms the metal sheet only by a thermal stress. Analyses of the temperature and stress fields are very important to identify the deformation mechanism in laser forming. In this paper, temperature distributions and deformation behaviors of DP980 steel sheets are investigated numerically and experimentally. FE simulations are first conducted to evaluate the response of a square sheet in bending. The effects of process parameters such as laser power and scanning speed are then analyzed numerically and experimentally. It is observed that experimental and numerical results are in good agreement. These results provide a relationship between the line energy and the angles for laser bending of DP980 steel sheets.

• Journal of Advanced Marine Engineering and Technology
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• 제28권2호
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• pp.277-284
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• 2004

This paper describes the influence of through-flow on the mixed convection in a parallel plates with the upper part is cooled and the lower part heated. When forced convection is imposed on natural convection, it is found that the flow pattern of mixed convection in the parallel plates can be classified into three patterns which were affected by Reynolds number. In such a mixed convection, the flow pattern plays an important role in the heat transfer process. In this study, thermo-sensitive liquid crystal suspension method is employed, then the visualization image acquired through the above method is processed by the color image processing technique and the two-dimensional velocity vector and temperature configuration are measured simultaneously.