초기 균열길이 및 섬유방향이 CFRP/GFRP 하이브리드 적층재의 층간 파괴에 미치는 영향

권우덕 부경대학교 2013 국내석사

Renewable energy resources, of which wind energy is prominent, are part of the solution to the global energy problem. Considering the wind power system and the rotor blades which are composed of much technology, the wind power blade would be the most dangerous part because it revolves at high speed and weighs about dozens of tons, if the accident happens. Therefore, the light weight composite materials have been replacing as substitutional materials. The object of this study is to examine the delamination and damage for CFRP/GFRP hybrid laminate composite that is used for strength improvement of a wind power blade. The influence of the initial crack length and fiber orientation for the interlaminar delamination was estimated for the safety of blade. Plain woven CFRP instead of GFRP material was inserted into the layer of the box spar for the improvement of strength and blade life. Fracture toughness and damage examination of interlaminar delamination were evaluated by using DCB(Double Cantilever Beam) specimen. The materials used in the experiments are a commercial material known as CF 3327 EPC (Hankuk Carbon Co.) in plain woven carbon prepreg and UD glass fiber prepreg (Hyundai Fiber Co.). The 5kN universal testing machine and a traveling microscope connected to a PC were used for the experiments. From the results, crack growth rate have not so different according to the initial crack length. ModeⅠ interlamainar fracture toughness of fiber direction 0° is higher than those of 45° . Interlaminar fracture have an effect on fiber orientation and K decreased with lower value according to the increasing initial crack length. Also energy release rate fracture toughness was evaluated because CFRP/GFRP hybrid composite with a different thickness in each layer is under the mixed mode condition. The interlaminar fracture was almost governed by mode I fracture even though the mixed mode condition. After crack advanced along the interface of CFRP and GFRP layers, growing crack stops and restart at the GFRP layer. After that, crack grew toward the interface again. GFRP fiber strands were pulled-out and show the bridging effect which connecting the CFRP and GFRP layers. And other fiber of GFRP were shown as truncated form. The crack initiates from 5mm and 3mm displacement for a= 0.42 and 0.375, respectively regardless of CFRP fiber orientation. The crack growth rate for the load displacement at the 45° case is lower than 0° case. According to the initial crack length, the crack growth rate was not much different. The total energy release rate G is 0.67kJ/m and the mode I contribution G is 0.664kJ/m for the fiber orientation 0° and a=0.42. Therefor, the interlaminar fracture is governed by the mode I. In other cases, similar results are obtained. The mode mixity angle is obtained as = 6.61°.

노사정위원회의 권력작용에 관한 연구

권우덕 서울시립대학교 대학원 2001 국내석사

노사정위원회의 권력작용에 관한 연구

권우덕 서울시립대학교 대학원 2001 국내석사

능직 탄소/아라미드 복합재료의 환경변화에 따른 파괴인성 및 파손특성에 관한 연구

권우덕 부경대학교 2023 국내박사

Since the industrial revolution, renewable energy and eco-friendly materials have been required worldwide due to global warming and depletion of fossil fuels. Composite materials are materials that overcome the disadvantages of existing metal materials such as strength, stiffness, corrosion resistance, and heat resistance. A hybrid fiber composite is manufactured using two or more fibers such as carbon fiber, aramid fiber, and glass fiber. The aramid fiber has high toughness and heat resistance and high elasticity, and is used in various fields such as industrial protective materials, bulletproof helmets and vests. However carbon fiber composites are somewhat vulnerable to the impact of external objects even though it has excellent specific properties. On the other hand, the aramid fiber tends to decrease in elastic modulus and strength when applied to the epoxy matrix and if the aramid fiber is exposed to water or heat, its mechanical properties are often deteriorated. Thus, the carbon and aramid fiber are selected to hybrid for the complementary relationship. In this study, the tensile and flexural test were accomplished on the twill woven carbon/aramid fiber hybrid composites to investigate the effects of high temperature and water absorption. And a delamination fracture toughness was investigated under mode I loading by 2 kinds of MBT and MCC deduction. An acoustic emission (AE) evaluation was conducted for the carbon fiber/aramid fiber hybrid composites degraded and damaged by high-temperature seawater environments. The test specimen was molded using an autoclave. The flexural test specimen was fabricated as non treated (N), high temperature (H), impacted (I), water absorption (W). And mode Ⅰ test specimen was fabricated with 20 hybrid fabric plies. The initial crack was made by inserting the teflon tape in the center plane with a0/W=0.5 length. The test specimen was immersed in 70°C seawater for 224 days. In order to imitate the damage, a hole was machined with a diameter of 3 mm using a diamond drill. And the specimen with a hole was repaired by patch attachment processing. The flexural experiment was implemented by a three-point bending and an AE sensor with a resonance frequency of 150 kHz was attached to evaluate the damage and the effect of patch attachment. From the tensile test of the twill carbon fiber/aramid fiber hybrid composite, the elastic modulus was 23.4 GPa, the poisson's ratio was 0.032, and the tensile strength was 539 MPa. On the flexural test, the impact damage with absorbing moisture showed the largest a reduction rate of flexural strength among the IW, H300, I specimen. And from the results of the MBT and MCC evaluation methods for the energy release rate, the MCC evaluation showed a difference of about 4 to 12% in the two evaluation values according to on the crack growth length, and the fracture toughness value was 0.1849 kJ/m2 and 0.1916 kJ/m2 in MBT and MCC, respectively. With resin impregnation and patch fiber lamination in the hole damage area of the SWH specimen, the maximum load was recovered up to 99% of SW specimen. AE accumulative counts obtained at the maximum load were 69.2, 67.1, and 91.2 for SW, SHH, SWR. AE maximum amplitude was detected as almost same with low values. The results obtained in this study are expected to be useful for designing safety and health structures and mechanical facilities composed of twill weave carbon fiber/aramid fiber hybrid composites.

서번트 리더십이 조직시민행동에 미치는 영향에 관한 연구

권우덕 서울시립대학원 2010 국내박사

국문초록 세계화와 무한 경쟁 속에서 조직연구의 화두는 조직생산성을 향상시킬 수 있는 방법을 모색하는 것이다. 조직생산성을 향상시키기 위한 다양한 요인들 가운데서 최근에 주목을 받고 있는 것이 구성원들의 역할외 행동(extra-role behavior)이다. 역할외 행동은 순수하게 조직을 관리하는데 투입될 자원을 보다 생산적인 분야에 투자할 수 있도록 하고, 구성원들 사이의 협력이 원활히 이루어질 수 있는 분위기를 만들기 때문에 전체적으로 조직이 효과적으로 기능하고, 기대 이상의 성과를 올리는 것이 가능하도록 한다. 이와 같은 역할외 행동의 대표적인 유형이 조직시민행동이다. 우리나라 공공조직은 고도경제성장의 시기를 지나면서 재정확대가 어렵게 되었지만, 지방자치제도의 실시 이후 시민들의 행정서비스에 대한 수요는 증가하는 어려움에 직면하게 되었다. 그래서 공공조직도 자원의 효율적 이용과 생산성 증대가 중요한 화두가 되었다. 이러한 환경변화는 공공조직에서도 조직시민행동에 관심을 기울이도록 하였다. 본 논문은 조직시민행동을 제고하기 위한 영향요인으로 서번트 리더십과 직무만족, 그리고 상사몰입을 선정하였으며, 공공조직인 서울시 공무원들을 대상으로 설문조사를 실시하였다. 설문분석 결과를 요약하면 다음과 같다. 첫째, 서번트 리더십의 하위요인 가운데서 지혜는 조직시민행동에 긍정적인 영향을 미치며, 이타적 소명과 감성적 치유는 직무만족을 매개로 조직시민행동에 유의미한 영향을 미치는 것으로 나타났다. 반면에 상사몰입의 매개효과는 없는 것으로 나타났다. 둘째, 서번트 리더십은 상사몰입과 직무만족에 유의미한 정의 영향을 미치는 것으로 나타났다. 서번트 리더십의 하위요인들은 설득, 감성적 치유, 이타적 소명의 순으로 상사몰입에 유의미한 정의 영향을 미치는 것으로 나타났다. 그리고 서번트 리더십의 하위요소들 가운데 치유와 지혜가 직무만족에 유의미한 정의 영향을 미치며, 설득은 유의미한 부(-)의 영향을 미치는 것으로 나타났다. 설득이 부의 영향을 미치는 것은 직무와 관련해서 상사가 업무의 중요성 등을 강조하는 것은 오히려 직무를 수행하는 직원에게는 부담으로 작용해서 직무스트레스로 연결될 수 있다는 것을 암시한다. 셋째, 직무만족의 하위요인 가운데 직무자체만족과 동료만족은 조직시민행동에 유의미한 정의 영향을 미치는 것으로 나타났다. 하지만 승진은 조직시민행동에 유의미한 부(-)의 영향을 미치는 것으로 나타났다. 승진이 조직시민행동에 부의 영향을 미치는 이유는 공무원들이 공직생활에서 중요하게 여기는 승진이 임박할수록 근무평가 등에 유리한 주어진 역할에 따른 직무성과를 올리는데 집중하고, 성과평가 등에 실질적으로 어떤 영향을 미칠 것인지 알 수 없는 조직시민행동과 같은 역할외 성과에는 노력을 기울이지 않기 때문으로 판단되었다. 넷째, 상사몰입에 영향을 미치는 요인을 분석하기 위한 위계적 회귀분석 결과에 따르면, 직무만족의 하위 요소 가운데는 승진이, 서번트 리더십의 하위 요소 중에서는 지혜를 제외한 모든 요인이 긍정적인 영향을 미치는 것으로 나타났다. 다섯째, 상사몰입의 하위요소 가운데 감성몰입만이 조직시민행동에 유의미한 영향을 미치는 것으로 나타났다. 여섯째, 서번트 리더십은 직무만족을 매개로 조직시민행동에 긍정적인 영향을 미치는 것으로 나타났다. 본 논문의 연구결과가 가지는 이론적․정책적 함의는 다음과 같다. 첫째, 서번트 리더십이 공공조직에서도 유용하다는 것을 실증적으로 확인하였으며, 둘째, 상사몰입과 조직시민행동의 영향관계에 대한 검증결과 상사몰입은 조직시민행동과 같은 역할외 행동보다는 직무성과와 보다 연관이 있을 것이라는 것을 추론할 수 있었다. 셋째, 직무만족이 조직시민행동을 설명하는 중요한 변수라는 것을 확인하였다. 넷째, 정책적으로 서울시의 인사제도 개혁이 성공을 거두기 위해서는 객관성과 합리성을 확보할 방안을 모색해야 한다. 마지막으로 중간관리자들의 리더십 행위가 구성원들의 행태에 긍정적인 영향을 미치기 때문에 중간관리자들에 대한 교육에서 리더십에 대한 교육이 필요하다는 시사점을 얻을 수 있었다. 검색어 : 조직시민행동, 서번트 리더십, 직무만족, 상사몰입 Abstract A Study on the Effect of Servant Leadership on Organizational Citizenship Behavior Kwon Woodeok Department of Public Administration Graduate School of the University of Seoul Improving organizational productivity has been a main topic of organizational research with ongoing competitive globalization. A factor that recently draws attention among various factors for improving organizational productivity is related to extra-role behavior of organizational members. Extra-role behavior may reduce the need for devoting scarce resources to maintain functioning of the organization. It can make resources use more productive and allow organizations to be more effective. Organizational Citizenship Behavior(OCB) is a representative type as extra-role behavior. Passing by a period of rapid economic growth, it is hard to increase finance scale for public organizations in Korea, but because of increased citizens' demands for public service, local governments have faced with difficulty. It is reason why the efficient use of resources and improving productivity are being emphasized. So public organizations should give attention to OCB. This paper selected servant leadership, job satisfaction, and commitment to supervisor as influencing variables for improving OCB. Survey to public servants in Seoul Metropolitan Government was conducted. A Survey results can be summarized as following. First, wisdom, subfactor of servant leadership, influences positively OCB. Altruistic calling and emotional healing affected significantly OCB through job satisfaction, mediation factor. In contrast, the commitment to supervisor as a mediating variable did not influence to OCB. Second, the servant leadership influence positively on commitment to supervisor and job satisfaction. Persuasion among subfactors of servant leadership has the highest and most positive influence on commitment to supervisor. The next positive factors are emotional healing and altruistic calling in order. Emotional healing and wisdom have not significant influence on job satisfaction. Persuasion has a significant and negative influence on job satisfaction, because organizational members recognize persuasion add more work to them. Third, nature of job itself and coworker satisfaction among subfactors of job satisfaction influence OCB positively. In contrast, promotion has significantly negative affect on OCB, because members think that extra-role behavior is not helpful to promotion. Forth, according to hierarchical regression analysis, promotion is the only positive factor among subfactor of jab satisfaction to commitment to supervisor . In subfactor of servant readership, all factors except wisdom have positive effect on commitment to supervisor. Fifth, only affective commitment among subfactors of commitment to supervisor has significant influence on OCB. Sixth, servant leadership positively affect OCB through job satisfaction as a mediating variable. Key Word : Organizational Citizenship Behavior , Servant Leadership, Job Satisfaction, Commitment to Supervisor.