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      • KCI등재

        Thermal Analysis for Simulation of Metal Additive Manufacturing Process Considering Temperature- and History-Dependent Material Properties

        정선호,박은교,강재원,조진연,김정호,김기철 한국항공우주학회 2021 International Journal of Aeronautical and Space Sc Vol.22 No.1

        Additive manufacturing (AM) technology is increasingly being used in the aerospace industry due to its advantages for aerospace components such as reduction of weight. A deep understanding of the behavior and properties of additively manufactured materials or parts is required to effectively carry out the certification process which is inevitable for aerospace components. However, since AM has so many parameters that affect the performance of products, the help of high-fidelity process simulation techniques is essential to fully analyze and understand their effects. In this research, we propose a new method to effectively implement the thermal analysis for process simulations of laser powder-bed fusion technique, a representative AM technique for metal materials, using existing commercial finite element analysis software. Thermal analysis for simulations of AM process is performed and the melt pool size is compared with test results to verify the accuracy of the simulation. In AM process simulations, material properties may vary significantly with temperature, and they are also dependent on the temperature history of the material because whether the current state is a powder or solid state is determined by the maximum temperature value in the past temperature history. Therefore, in this paper, user-defined subroutines and field variables are implemented so that the temperature history of each integration point for the finite element analysis can be properly tracked and appropriate material properties can be assigned accordingly. Using the proposed methods, thermal analysis for AM process simulations can be performed successfully with good accuracy compared with the existing test results.

      • KCI등재

        그래핀 옥사이드/카르복실화한 스티렌-부타디엔 고무 나노 복합체에 관한 연구

        정선호,리시앙수,조을룡 한국반도체디스플레이기술학회 2017 반도체디스플레이기술학회지 Vol.16 No.1

        Graphene oxide (GO)/carboxylated styrene-butadiene rubber (XSBR) nanocomposites with various contents of GO were prepared by a latex compounding method. It has been confirmed that the functional groups of GO and the hydrogen bonds between GO and XSBR are existed. It can be seen that the scorch time (ts2), which is the measurement of incipient vulcanization of rubber, showed a delay after the addition of GO. Field emission scanning electron microscopy was employed to confirm the uniform dispersion of filler in the matrix. Indeed, with increasing fillers loading, the torque, tensile strength, thermal stability and crosslink density of obtained nanocomposites were improved. These results were correlated to the better dispersion of fillers through the rubber matrix.

      • Double-Acting Shock Absorber 내부 하중 예측을 위한 연구

        정선호,조진연,김정호,박찬익 한국항공우주학회 2015 한국항공우주학회 학술발표회 논문집 Vol.2015 No.4

        항공기 사고는 주로 이착륙시 발생하며 특히 착륙 시 경착륙과 같이 구조물에 영향을 미치는 경우가 간혹 발생한다. 따라서 착륙 시 항공기의 구조건전성을 확보하는 것이 필수적이며 이를 위해 착륙장치로부터 기체에 가해지는 하중을 파악하는 것이 필요하다. 착륙장치는 대표적으로 single-acting shock absorber와 double-acting shock absorber로 분류할 수 있는데 double-acting shock absorber가 상대적으로 무겁고 비싸지만 지상 주행 시 완충 특성이 증가하므로 전방착륙장치에 주로 이용되고 있다. 이에 따라 본 논문에서는 보다 실제적인 착륙 시뮬레이션 수행을 위해 double-acting shock absorber 내부하중을 계산하기 위한 수식을 유도하였으며 해석을 통해 그 특성을 확인하였다. Most of aircraft accidents occur during takeoff and landing, and those accidents such as hard-landing threaten the structural integrity of aircraft. Therefore, calculating forces from landing gear to aircraft is necessary for structural health monitoring. Landing gears can be typically classified into single-acting shock absorbers and double-acting shock absorbers. Double-acting shock absorbers are usually used in nose landing gears because they are more efficient during taxing on rough ground even if they are more expensive and heavy. In this paper, double-acting shock absorber equations are derived to calculate internal forces and the characteristics of double-acting shock absorbers are confirmed by multi-body dynamic analysis.

      • 혼성집적회로 기술에 의한 음악 전단증폭기의 설계와 제작

        정선호,정헌생 대한전자공학회 1971 전자공학회지 Vol.8 No.5

        음성 전단증폭기를 후막집적회로기술을 이용하여 집적회로화하는데에 파생되는 여러가지 기술적인 문제를 실제로 연구개발을 실시한 경험을 토대로 소개하였다. 특히 전자계산기를 이용한 회로해석을 통하여 전단증폭기의 성능을 가장 민감하게 좌우하는 저항소자를 찾아 내므로써 크기의 아루미나 기판상에 집적된 7개의 저항중에서 한개만을 조정하여도 원하는 주파수특성을 얻을 수 있음을 확인하였다. 이로써 7개의 저항을 설계치에 맞게 각각 조정하는 작업을 하지 않고 그 중 하나만을 원하는 특성이 나타날때까지 조정하는 기능조정방법을 찾아내어 조정작업에 소요되는 인건비를 1/7로 절감할 수 있도록 하였다. 이 외에도 저항체와 도체간의 접촉문제라든가, 크로쓰오바의 기생용량문계 또는 저항조정방법에 따르는 잡음도의 변화문제에 대해서도 상세히 다루었다. Problems and technologies involved in integrating an audio preamplifier in terms of thick film technology has been discussed in detail. In particular, an attempt has been made to find methods for functional trimming of the amplifer by employing computer analysis. Among seven resistors integrated on a alumina substrate, only one resistor was found to be very sensitive to over all performance of the preamplifier. By trimming this resistor to its freguency charcteristic reguirements, it was possible to cut down trimming labor by one seventh. Besides, problems concerning resistor conductor contacts, crossover parasitic capacitance and the relations between noise per(ormance and trimming method are discussed in detail.

      • 주요우울장애 환자에서 혈장 세로토닌치 변화와 임상호전도와의 관계

        정선호,이영식,박두병 중앙대학교 의과대학 의과학연구소 1996 中央醫大誌 Vol.21 No.1

        The purpose of this study was to compare plasma serotonin(5-HT) level in patients with major depressive disorder with in healthy normal control and investigate relationship between changes of plasma serotonin(5-HT) level and clinical improvement in patients with major depressive disorder. The subjects were thirty hospitalized patients with major depressive disorder who met DSM-Ⅳ(VPA 1994) diagnostic criteria and thirty healthy normal controls. Clinical evaluation with Hamilton Depression Rating Scale(HDRS) was done on admission and after 3 weeks of admission while the plasma serotonin(5-HT) level was checked at baseline, end of the 3rd weeks of treatment respectively. The results were as follows : 1) There was no significant sex differences in plasma 5-HT level in both patient and control group. 2) In the plasma 5-HT level, the mean was 0.016±01012 in the patient of major depressive disorder and 0.104±0.059 in the control group, showing significant differences. 3) There was significant differences between plasma 5-HT level in the patients group of major depressive disorder in pretreatment and after 3 weeks of treatment. 4) There was significant differences between plasma 5-HT level in the patients group of major depressive disorder after 3 weeks of treatment and control group. 5) Relationship between plasma 5-HT changes and clinical improvement during 3 weeks of treatment was significantly correlated. In summary, the present study was found significant differences in patients with major depressive disorder as compared with control group. And our results suggest that relationship between the changes of plasma 5-HT level and clinical improvement was significantly correlated in patients with major depressive disorder. Further studies are required to clarify the relationship between biochemical changes and clinical improvement.

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