• Advanced Composite Materials
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• 제17권3호
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• pp.259-275
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• 2008

This study aims to optimize the mechanical and electrical properties of electrically conductive polymer composites (CPCs) for use as a material of bipolar plates for PEM fuel cells. The thin CPCs consisting of conductive fillers and polymer resin were fabricated by a preform molding technique. Expanded graphite (EG), flake-type graphite (FG) and carbon fiber (CF) were used as conductive fillers. This study tested two types of CPCs, EG/FG filled CPCs and EG/CF filled CPCs, to optimize the material properties. First, the characteristics of EG/FG filled CPCs were investigated according to the FG ratio for 7 and $100{\mu}m$ sized FG. CPCs using $100{\mu}m$ FG showed optimal material properties at 60 wt% FG ratio, which were an electrical conductivity of 390 S/cm and flexural strength of 51 MPa. The particle size was an important parameter to change the mechanical and electrical behaviors. The flexural strength was sensitive to the particle size due to the different levels of densification. The electrical conductivity also showed size-dependent behavior because of the different contributions to the conductive network. Meanwhile, the material properties of EG/CF filled CPCs was also optimized according to the CF ratio, and the optimized electrical conductivity and flexural strength were 290 S/cm and 58 MPa, respectively. The electrical conductivity of this case decreased similarly to the EG/FG filled case. On the other hand, the behavior of the flexural strength was more complicated than the EG/FG filled case, and the reason was attributed to the interaction between the strengthening effect of CF and the deterioration of voids.

• STI Policy Review
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• 제3권2호
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• pp.111-129
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• 2012

The integration of products and services is being expanded in both manufacturing and service companies such as in Apple's iPod & iTunes, Amazon's Kindle, and Hyundai Motor Company's Mozen. This phenomenon has recently accelerated due to multiple factors including market change, lessening of differences in quality of products or services, the paradigm of participation and sharing, and deindustrialization and evolution toward becoming a service economy. The objective of this paper is to investigate and analyze the status and characteristics of integration of products and services in Korean firms and to suggest policy directions promoting this integration. Towards this purpose, income statements from the Korea Listed Companies Association (KLCA) database of companies listed on the Korea Stock Exchange are analyzed regarding the servitization of manufacturing firms as well as the productization of service firms. In addition, this research investigates the Korean Innovation Survey 2011 database for the service sector and 2010 database for the manufacturing sector in order to evaluate R&D activity in each. In the manufacturing sector, the average ratio of service sales (servitization) was low at 0.208, with bias in the level and distribution of ratios associated with the manufacturing sector. 18 out of a total of 23 sectors (78%) have low servitization, showing there's a long way to go for servitization in the Korean manufacturing sector. In the service sector, the average ratio of product sales (productization) was 9.53%, which is relatively high compared to that of the manufacturing sector. However, the distribution of ratios is also biased, as with the manufacturing sector. Based on this analysis, policy directions are proposed in terms of 1) R&D, 2) concept boost, 3) R&D result spread, 4) statistics, 5) infrastructure and 6) green growth.

• 한국자동차공학회논문집
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• 제13권6호
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• pp.105-112
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• 2005

This study aims at evaluating the environmental impacts stemmed from the End-of-Life Vehicle(ELV) treatment systems in Korea, using Life Cycle Assessment(LCA) method. In this study, both environmental burden from the ELV dismantling process & recycling processes and environmental benefit which were derived from the avoided environmental impacts by substituting recycled materials for virgin materials were considered. First of all, the key issues which were defined as the environmental aspects that account for more than $1\%$ out of the total environmental impacts were identified from the Life Cycle Impact Assessment(LCIA). $CO_2$, crude oil, natural gas, coal, etc. were found out to be the key issue parameters. From the LCI Analysis and LCIA studies, it was shown that the significant environmental aspects were related with the recycling process of ferro scrap, the shredding process of compressed car bodies and the dismantling process of end-of-life engines. In particular, the recycling process of ferro scrap has the most significant effects on the environmental impacts of the ELV treatment systems. Based on these results, it is recommended to improve the recycling process of ferro scrap in order to make the ELV treatment systems more environmentally sound.

• 한국재료학회지
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• 제25권1호
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• pp.54-59
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• 2015

Glancing angle deposition (GLAD) is a powerful technique to control the morphology and microstructure of thin film prepared by physical vapor deposition. Chromium (Cr) thin films were deposited on a polymer substrate by a sputtering technique using GLAD. The change in thickness and Vickers microhardness for the samples was observed with a change in the glancing angle. The adhesion properties of the critical load (Lc) by a scratch tester for the samples were also measured with varying the glancing angle. The critical load, thickness and Vickers microhardness for the samples decreased with an increase in the glancing angle. However, the thickness of the Cr thin film prepared at a $90^{\circ}$ glancing angle showed a relatively large value of 50 % compared to that of the sample prepared at $0^{\circ}$. The results of X-ray diffraction and scanning electron microscopy demonstrated that the effect of GLAD on the microstructure of samples prepared by sputter technique was not as remarkable as the samples prepared by evaporation technique. The relatively small change in thickness and microstructure of the Cr thin film is due to the superior step-coverage properties of the sputter technique.

• Journal of Mechanical Science and Technology
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• 제20권10호
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• pp.1638-1645
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• 2006

This paper proposes a modeling technique which is able to not only reliably and easily represent the hysteretic characteristics but also analyze the dynamic stress of a taper leaf spring. The flexible multi-body dynamic model of the taper leaf spring is developed by interfacing the finite element model and computation model of the taper leaf spring. Rigid dummy parts are attached at the places where a finite element leaf model is in contact with an adjacent one in order to apply contact model. Friction is defined in the contact model to represent the hysteretic phenomenon of the taper leaf spring. The test of the taper leaf spring is conducted for the validation of the reliability of the flexible multi-body dynamic model of the taper leaf spring developed in this paper. The test is started at an unloaded state with the excitation amplitude of $1{\sim}2mm/sec$ and frequency of 132 mm. First, the simulation is conducted with the same condition as the test. Then, the simulations are conducted with various amplitudes in a loaded state. The hysteretic diagram from the test is compared with the ones from the simulation for the validation of the reliability of the model. The dynamic stress analysis of the taper leaf spring is also conducted with the developed flexible multi-body dynamic model under a dynamic loading condition.

• 한국자동차공학회논문집
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• 제23권1호
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• pp.65-73
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• 2015

The ride quality has become a key component of not only design but car selling as the technology developed and the requirement of passengers grew up. Thus car industry invests lots of time and cost for the higher ride quality. The evaluation of the ride quality mainly is expressed by subjective element that drivers felt. In this paper, instead of the original transfer path analysis method, relatively new methods such as OPAX(Operational path analysis with eXogeneous inputs) and OTPA(operational transfer path analysis) are used for analyzing the main hindrance element of ride quality. With those new method, contribution rate of all paths that the vibration propagate along analyzed after driving test on the roads having different characteristic. The comprehensive hindrance elements of ride quality are deduced from the contribution rate and the improve experiment by changing one of hindrance elements for higher ride quality.

• 한국정보통신학회논문지
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• 제22권3호
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• pp.434-442
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• 2018

본 논문에서는 주행하는 차량에 탑재된 카메라에서 획득한 도로 영상에서 차선의 색상을 판별하는 방법을 제안하였다. 자동차의 자율주행기술에 있어 차선 정보는 차선이탈방지(ldws), 능동적 차선유지(lkas), 고속도로주행보조(hda) 등의 자율주행의 레벨(level)이 올라갈수록 중요하다. 특히 차선의 색상, 특히 흰색 및 황색 차선의 구별은 교통사고와 직접적인 관련이 있는 정보이기에 더욱 필요한 기술이다. 본 논문에서는 주행 차선 검출 결과를 기반으로 차선 및 도로의 관심 영역을 추출하고 각 영역의 컬러 정보를 2차원 S-색상 공간으로 투영하였다. S-공간에 투영된 색상의 특징 분포에서 개선된 mean-shift 알고리즘을 이용하여 특징의 무게중심을 구하였다. 좌, 우 차선과 도로영역의 색상특징의 중심점들 사이의 거리 정보를 이용하여 차선의 색상을 판별하였다. 다양한 조명환경에서 약 97%의 색상 인식 성공률을 보였다.

• 한국가스학회지
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• 제20권1호
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• pp.52-61
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• 2016

액화석유가스는 환경 친화적이며 에너지 효율성과 출력성능이 뛰어나 실용성이 높고, 경쟁연료에 비해 가격 경쟁력이 우수하기 때문에 촉망받는 대체연료 중 하나로 간주된다. 스파크점화 엔진에서 직분식 기술은 엔진 체적효율을 눈에 띄게 증가시키며, 상대적으로 더 높은 연소효율이 가능한 성층급기를 이용해 엔진을 작동시킨다. 본 연구에서는 가솔린직접분사 엔진의 원리를 적용하여 가시화 시스템을 장착한 연소실을 설계하였다. 이를 통해 스파크점화직분식 LPG의 점화성과 화염전파 과정을 디지털 방식으로 기록하고 분석하였다. 이러한 연구의 결과는 스파크점화직분식 LPG 엔진의 설계 및 최적화를 위한 광범위한 기초 자료로서 기여하고자 한다.

• Journal of Mechanical Science and Technology
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• 제19권6호
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• pp.1229-1242
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• 2005

When natural rubber is used for a long period of time, it becomes aged; it usually becomes hardened and loses its damping capability. This aging process affects not only the material property but also the (fatigue) life of natural rubber. In this paper the aging effects on the material property and the fatigue life were experimentally investigated. In addition, several fatigue life prediction equations for natural rubber were proposed. In order to investigate the aging effects on the material property, the load-stretch ratio curves were plotted from the results of the tensile test, the compression test and the simple shear test for virgin and heat-aged rubber specimens. Rubber specimens were heat-aged in an oven at a temperature ranging from $50^{\circ}C$ to $90^{\circ}C$ for a period ranging from 2 days to 16 days. In order to investigate the aging effects on the fatigue life, fatigue tests were conducted for differently heat-aged hourglass-shaped and simple shear specimens. Moreover, finite element simulations were conducted for the specimens to calculate physical quantities occurring in the specimens such as the maximum value of the effective stress, the strain energy density, the first invariant of the Cauchy-Green deformation tensor and the maximum principal nominal strain. Then, four fatigue life prediction equations based on one of the physical quantities could be obtained by fitting the equations to the test data. Finally, the fatigue life of a rubber bush used in an automobile was predicted by using the prediction equations, and it was compared with the test data of the bush to evaluate the reliability of those equations.

• 한국항공우주학회지
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• 제49권8호
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• pp.661-669
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• 2021

종래 우주용 전장품 개발과정에서는 발사진동환경에 대한 탑재 전자소자 솔더 접합부의 피로수명 보장을 위해 기판 상에 보강재를 적용하여 강성을 증가시킴으로써 기판의 동적거동을 최소화하였다. 그러나 종래의 설계는 전장품의 부피 및 무게의 증가를 야기하여 소형/경량화 설계에 한계를 갖는다. 선행 연구에서 제안된 점탄성 테이프 기반 고댐핑 적층형 전자기판은 굽힘변위 저감을 통한 소자의 피로수명 연장에 효과적임을 입증하였으나 고댐핑 부여를 위한 적층구조가 기판에 직접 장착되는 관계로 소자 실장 공간의 효율이 저하되는 한계를 지닌다. 본 연구에서는 전장품 소형/경량/고집적화 설계 구현을 위해 일반 금속 대비 높은 댐핑과 복원 특성을 갖는 초탄성 형상기억합금에 점탄성 테이프를 적용한 적층구조의 초탄성 형상기억합금 보강재 기반 고댐핑 전자기판을 제안하였다. 제안 기판의 기본특성 파악을 위해 정하중시험 및 자유진동시험을 수행하였으며, 랜덤진동시험을 통해 진동환경 하 고댐핑 특성 및 설계 유효성을 입증하였다.