The cutting quality of abrasive water jet cutting of aluminum alloy(Al-5083) for shipbuilding is affected by the surface roughness, cutting pressure, cutting speed, and the distance between nozzle and material. The cross-section of water jet cutting is formed a V-shape as the cutting speed increase. The upper width(kerf width) is wide and the lower surface is narrow. The width of cutting cross-sections are effected in the order of cutting speed, cutting pressure, and distance between nozzle and material. From the experimental results, to improve of cutting quality of abrasive water jet cutting of aluminum alloy(Al-5083) for shipbuilding, the optimal cutting conditions to improve the surface roughness and kef width are proposed and discussed.

Due to the strengthening of domestic and international environmental regulations, the replacement of FRP ships with aluminum ships for small ships is continuously in progress. Domestic aluminum ships are being applied to various types of ships, mainly special ships, passenger ships and fishing ships. Gas metal arc welding(GMAW) is used as a welding method when manufacturing ships using aluminum materials for ships with a thickness of 5mm or more. However, it is carried out manually by the workers in the shipyard, and there is a limit to relying on the skills of the workers. In this study, basic research on high-efficiency tandem welding was performed as a basic study for the application of high-quality automatic welding equipment when working on aluminum ships. In this study, welding deformation according to constraint conditions was comparatively analyzed using tandem welding equipment and cross-sections of welds were evaluated for each experiment.

최근 FRP 선박의 폐선 처리문제, 환경 규제의 강화, 자원 재활용 등의 관점에서 소형 알루미늄 합금 선박의 건조가 증가하는 추세이다. 그러나 알루미늄은 가볍기 때문에 해양에서 고속으로 운행 가능한 알루미늄 선박은 캐비테이션이 발생되어 기포붕괴에 따른 큰 충격압력에 의해 캐비테이션 침식이 일어남으로서 재료의 수명에 있어 문제점을 드러내고 있다. 따라서 본 연구에는 캐비테이션에 의한 손상을 방지하여 내구 수명을 연장시키기 위한 방법으로 워터 캐비테이션 피닝 기술을 선박용 알루미늄 합금에 적용하였다. 이를 위하여 워터 캐비테이션 피닝을 실시하여 내캐비테이션 특성이 가장 우수한 적용 시간을 규명하였다. 선박용 알루미늄 합금 5456-H116, 5083-H321 그리고 5052-O는 워터캐비테이션 피닝을 실시함으로써 내캐비테이션 특성이 워터 캐비테이션 피닝을 하지 않은 시편보다 무게감소량이 각각 42.11 %, 50.0 % 그리고 25.7 % 개선되었다.

본 논문의 1편에서는 레저선박의 실시간 선체구조모니터링시스템을 개발하기 위하여 도파로 어레이격자(AWG, Arrayed Waveguide Grating)와 광섬유 브래그격자센서(FBG, Fiber-optic Bragg Grating)를 이용한 선체구조모니터링시스템의 설계 및 적용 가능성을 검토하였다. 본 연구에서는 레저선박의 구조취약부의 실시간 모니터링을 위하여 광섬유센서 데이터의 측정 및 분석을 고속으로 처리할 수 있도록 시스템을 최적화하였으며, 레저선박의 선체구조안전모니터링을 위하여 레저선박의 선체 주재료인 FRP와 알루미늄 시편을 대상으로 재료 특성에 대한 기 초 데이터베이스를 구축하였다. 30feet 및 60feet급 세일요트의 알루미늄 마스트에 개발된 시스템을 적용하여 하중변화에 따른 변형률 특성 확인 및 레저선박의 선체구조안전성 평가를 위한 기초 연구를 수행하였다.

본 논문은 선박용 알루미늄 합금에 대하여 TIG, MIG 그리고 로봇을 이용한 용접 등과 같은 다양한 용접기술을 적용하여 기계적 특성을 평가하였다. TIG 용접을 실시하였을 경우는 항복강도, 인장강도 그리고 연신율은 모재에 비하여 각각 83.9%, 64.6% 그리고 21.9%를 나타냈다. MIG 용접은 ER5356 용접봉을 사용하여 용접한 경우 ER5183 용접봉을 사용한 경우에 비하여 기계적 특성이 대략 2-4% 정도 개선된 효과가 관찰되었다. 또한 로봇을 이용한 용접을 실시한 경우는 5456-H116 모재에 비하여 5083O 모재의 경우가 양호한 기계적 특성을 나타냈다.

Recently, with the tendency of more lightening, high-strength and high-speed in the marine industries such as marine structures, ships and chemical plants, the use of the aluminium Alloy is rapidly enlarge and there occurs much interest in the study of corrosion fatigue crack characteristics. In this paper, the initiation of surface crack and the propagation characteristics on the base metal and weld zone of 5086-H116 Aluminium Alloy Plate which is one of the Al-Mg serious alloy(A5000serious) used most when building the special vessels, were investigated by the plane bending corrosion fatigue under the environments of marine, air and applying cathodic protection. The effects of various specific resistances on the initiation, propagation behavior of corrosion fatigue crack and corrosion fatigue life in the base metal and heat affected zone were examined and its corrosion sensitivity was quantitatively obtained. The effects of corrosion on the crack depth in relation to the uniform surface crack length were also investigated. Also, the structural, mechanical and electro-chemical characteristics of the metal at the weld zone were inspected to verify the reasons of crack propagation behavior in the corrosion fatigue fracture. In addition, the effect of cathodic protection in the fracture surface of weld zone was examined fractographically by Scanning Electron Microscope(S.E.M.). The main results obtained are as follows; (1) The initial corrosion fatigue crack sensitibity under specific resistance of 25Ω.cm% show 2.22 in the base metal and 19.6 in the HEZ, and the sensitivity decreases as specific resistance increases (2) By removing reinforcement of weldment, the initiation and propagation of corrosion crack in the HAZ are delayed, and corrosion fatigue life increases. (3) As specific resistance decreases, the sensitivity difference of corrosion fatigue life in the base metal and HAZ is more susceptible than that of intial corrosion fatigue crack. (4) Experimental constant, m(Paris' rule) in the marine environment is in the range of about 3.69 to 4.26, and as specific resistance increases, thje magnitude of experimental constant, also increases and the effect by corrosion decreases. (5) Comparing surface crack length with crack depth, the crack depth toward the thickness of specimen in air is more deeply propagated than that in corrosion environment. (6) The propagation particulars of corrosion fatigue crack for HAZ under initial stress intensity factor range of δk sub(li) =27.2kgf.mm super(-3/2) and stress ratio of R=0 shows the retardative phenomenon of crack propagation by the plastic deformation at crack tip. (7) Number of stress cycles to corrosion fatigue crack initiation of the base metal and the welding heat affected zone are delayed by the cathodic protection under the natural sea water. The cathodic protection effect for corrosion fatigue crack initiation is eminent when the protection potential is -1100 mV(SCE). (8) When the protection potential E=-1100 mV(SCE), the corrosion fatigue crack propagation of welding heat affected zone is more rapid than that of the case without protection, because of the microfissure caused by welding heat cycle.

Recently with the rapid development in marine and shipbuilding industries such as marine structures, ships and chemical plants, it takes much interest in the study of corrosion fatigue characteristics that was close up an important role in mechanical design. In this study, characteristics of corner crack propagation on the base metal and heat affected zone of 5086 Al-Alloy was tested by using of a rotary bending fatigue tester and was investigated under the environments of specific resistance, σ=25Ω cm and air. The corrosion fatigue crack initiation and corrosion fatigue life sensitivity were quantitatively inspected for 5086 Al-Alloy in the specific resistance, σ=25Ω cm. Main results obtained are as follows: (1) The corrosion sensitivity of heat affected zone under specific resistance, σ=25Ωcm shows approximately 1.69~2.22 and corrosion sensitivity of base metal is more susceptible than that of heat affected zone. (2) The corrosion fatigue life sensitivity on heat affected zone decreases eminently than that of initial corrosion fatigue crack. (3) The characteristics of quarter elliptical corner crack propagation shows that depth crack is more grown than surface crack at crack initiation, but the surface crack is more propagated than depth crack as the crack propagation is increased. (4) The surface crack and depth crack growth on heat affected zone by softness show delayed phenomenon than that of base metal.

평면 굽힘부식피로 시험기를 사용하여 선박용 알루미늄합금재의 부식피로파양에 관한 연구를 한 결과 다음과 같은 결론을 얻었다. 1. 비저항이 증가함에 따라서 초기 부식피로균열발생까지의 반복회수는 지연되고, 그 부식감수성은 감소하는 양상을 나타낸다. 2. 비저항이 감소할수록 Paris rule의 실험상수 m 값은 작아지면서 응력강도 계수값에 비해 부식에 의한 영향이 더욱 민감해 진다. 3. 알루미늄 5086 합금의 부식피로균열은 입계균열파양의 양상을 보이고 있다. 4. 응력강도계수값이 증가함에 따라 부식감수성은 감소되어지고 응력강도계수값이 40kg.mm super(-3/2) 이상일 때 부식감수성은 거의 균일하게 된다.