• Title, Summary, Keyword: 굽힘 피로강도

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Safety Assessment of Double Skin Hull Structure against Ultimate Bending and Fatigue Strength (이중선각구조 선박의 최종굽힘강도와 피로강도에 대한 안전성 평가)

  • P.D.C. Yang;Joo-Sung Lee
    • Journal of the Society of Naval Architects of Korea
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    • v.29 no.1
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    • pp.93-102
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    • 1992
  • In this paper presented is the reliability analysis of a double skinned hull structure against the ultimate bending moment and fatigue strength under longitudinal bending. The ultimate bending strength is obtained through the beam-column approach in which the load-end shortening curves(stress-strain curves) of stiffened plates under mini-axial compression are derived using the concept of plastic hinge collapse. The fatigue damage only is considered as fatigue failure for which the Miner's damage rule is employed. Assessed are fatigue reliability for the possible joint types found at deck structure. Also included is the reliability analysis of a series system of which elements are ultimate and fatigue failure.

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A Study on the Fatigue Strength Reduction Factor under the High Cycle Bending Fatigue (고사이클 굽힘 피로에서의 피로강도 감소계수에 관한 연구)

  • Pyo, Dong-Keun
    • Journal of Ocean Engineering and Technology
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    • v.6 no.2
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    • pp.71-75
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    • 1992
  • 기구나 구조물의 피로수명은 노치에서의 피로균열 방생수명에 의하여 지배되기때문에 노치로 인한 피로강도감소계수 $K_f$는 피로설계상 대단히 중요한 인자이다. 노치 선단(Notch root)에서의 피로균열발생명수 N$_c$를 기준으로하면 탄성응력집중계수 $K_t$가 10 정도까지 $K_f$$K_t$간에는 거의 직선적인 관계가 있음이 이다- 고에 의하여 명석해졌으나 이는 인장,압축의 축력이 작용하였을 때이며 따라서 기구나 구조부재는 축력외에도 굽힘 피로 하중이 작용하였을때도 많으므로 본 연구에서는 굽힘 피로 하중을 받았을때도 있다. -고의 결론이 적용되는지는 검시코져 본 연구를 실시하였다.

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A Study on the Optimum Shot Peening Condition for Al7075-T6 (AL7075-T6의 최적 쇼트피닝 조건에 관한 연구)

  • Jeong,Seong-Gyun;Kim,Tae-Hyeong
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.31 no.7
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    • pp.63-68
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    • 2003
  • Shot peening process is most often used to improve the fatigue properties of metal parts, In order to achieve an optimum, repeatable, and reliable fatigue enhancement from the shot peening process, the important shot peening parameters must be optimized, In this paper, the optimum peening intensity(Almen intensity) condition is investigated by experiment. Rotary bending fatigue test has been adopted to investigate the effects of optimum peening on the fatigue characteristics, Experimental results show that the fatigue strength and fatigue life has been tremendously increased by optimum-peening treatment. However, the fatigue strength and fatigue life has been decreased by under or over peening.

Effects of Postweld Aging Treatment on Rotary Bending Fatigue strength of Friction Welded Joints at Elevated Temperature (마찰 용접부의 고온 회전굽힘 피로 강도에 미치는 용접후 시효열처리의 영향에 관한 연구)

  • Oh, Sae Kyoo
    • Journal of the Korean Society of Marine Engineering
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    • v.7 no.2
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    • pp.36-49
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    • 1983
  • 최근 높은 경제성과 용접성의 우수성에 의한 마찰 용접의 응용에 있어서 내열.내식 재료가 개스터어빈, 기관, 핵 발전기등의 기계 부품 생산 공업에 널리 이용되고 있다. 따라서 이종내열 합금강의 마찰 용접된 부품을 이용함에 있어서 내식.내마모 및 용접성 뿐만 아니라 고온 피로 강도와 크리이프 강도 등의 복합 특성에 관한 연구가 요구되고 있다. 본 연구에서는 마르텐사이트계 실크롬 내열강과 오오스테나이트계 닉켈크롬 스테인레스강의 이종 내식.내열 합금강의 최적 용접조건하에서 마찰 용접된 후의 시효 열처리가 용접재의 700 .deg.C 고온 회전 굽힘 피로강도 특성에 미치는 영향에 관하여 실험과 강도해석에 의해 조사되었고 용접후의 용체화 처리와 시효 열처리법에 의한 내열강 마찰 용접강도 개선법을 개발코저한 것이다.

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A Study on Rotary Bending Fatigue Strength of the $CO_2$ Gas Welded Joint in Air and Sea Water ([$CO_2$] 용접이음재의 대기 및 해수중에서의 회전굽힘 피로강도에 관한 연구)

  • S.W. Kang;S.Y. Lee
    • Journal of the Society of Naval Architects of Korea
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    • v.37 no.2
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    • pp.118-126
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    • 2000
  • TMCP steel has been widely used to construct ships and offshore structures. When it comes to ship and offshore structures, corrosion fatigue damages caused by sea water and fatigue occurred by wave-induced forces usually go on occurring simultaneously. So the fatigue life in corrosion environment is decreased markedly in comparison with that in air. The fatigue crack in corrosion easily initiates on welded joints of structure like as the fatigue crack in air. Therefore it is very important to study the fatigue properties of those of their welded joints as well as steel plates. In this study, rotary bending fatigue tests have been performed to investigate fatigue crack initiation and behavior of fatigue crack growth on CO2 gas weld HAZ of TMCP steel. The fatigue test used the specimens with various stress concentration factors in air and 3% NaCl solution

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An experimental study of bending fatigue life (S-N curve) of the helical gear for the automotive transmission (자동차 Transimission용 Helical Gear의 굽힘 피로 수명 곡선(SS-N Curve)에 관한 실험적 고찰)

  • 이원희;허윤무
    • Journal of the korean Society of Automotive Engineers
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    • v.12 no.6
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    • pp.11-17
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    • 1990
  • 자동차용 변속기의 설계에 있어서 적용 Engine의 출력 및 차량 성능에 부합하는 동력전달 요소의 전달 용량 및 내구 수명을 고려해야 한다. 특히 자동차가 고속 경량화됨에 따라 변속기의 설계에 있어서도 동력전달 요소들의 소형 고용량화가 요구되며 이를 위해서는 설계시 동력전달 요소들의 정확한 강도 및 피로수명 예측이 필수적이다. 본 보고서에서는 Gear의 굽힘응력 계산식에 대한 고찰 및 Gear의 피로시험을 통하여 Helical 치차의 Bending stress에 대한 피로수명 곡선의 시험식을 도출하였다.

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Fatigue Strength of Fillet Weldment under Out-of-plane Bending Load (필릿 용접부의 면외굽힘하중에 대한 피로강도)

  • 강성원;한상혁;김화수;백영민
    • Journal of the Society of Naval Architects of Korea
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    • v.40 no.1
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    • pp.28-35
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    • 2003
  • Fatigue tests of transverse fillet weldment were performed under out-of-plane bending loads. Significant increase of the fatigue strength was observed under out-of-plane bending loads, compared to the one under in-plane loads (axial loads). Applicability of the crack propagation analysis using LEFM for the surface crack of fillet weldment were investigated as well, in parallel with the fatigue tests. For the rational assessment of the fatigue strength of welded ship structures where combined stresses of the in-plane axial stress and the out-of-plane bending stress are induced simultaneously due to complexity of applied load and structural geometry, further investigation is recommended for the effect of the out-of-plane bending stress on the fatigue strength of weldment.

Static and Fatigue Characteristics of Urethane Foam Cored Sandwich Structures (우레탄 폼 코아 샌드위치 구조물의 정적 및 피로 특성)

  • 김재훈;이영신;박병준;김덕회;김영기
    • Composites Research
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    • v.12 no.6
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    • pp.74-82
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    • 1999
  • The static and fatigue characteristics of polyurethane foam cored sandwich structures are investigated. Three types of the specimens with the glass fabric faces and the polyurethane foam core are used; non-stitched. stitched, and stiffened sandwich specimen. Especially additional structural reinforcements with the twisted polyester and glass fiber for thickness direction are made to stitched sandwich structure panel to minimize the delamination of structure which is stitched the upper and lower faces through the core and the resin is impregnated Into stitched fiber with the characteristics of low viscosity of resin at resin flow temperature and cured together with during the curing process. Bending strength of stitched specimen which is 50 mm $50{\times}50{\;}mm$ pitched is improved by 50 % as com-pared with non-stitched specimen and stiffened specimen is improved 10 times more than non-stitched structure. After fatigue testing of $10^6$cycles by 20% of ultimate load under monotonic load, the bending fatigue strength of non-stitched specimen is decreased by 27% of monotonic bending strength, 39% for stitched structure and 20% for stiffened specimen. To verify the aging effect of polyurethane form core, Ultrasonic C-scanning equipment is used to detect the damage of skin laminate alone after fatigue test. From results of UT C-scan images, there is no defect that can be damaged occurred during fatigue test. It is concluded that the decrease of bending strength for foam cored sandwich specimen is caused by the decrease of stiffness due to the aging of polyurethane foam core during fatigue cycles.

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High Temperature and Fatigue Strength of crack-healed Mullite/Silicon Carbide Ceramics (균열 치유된 Mullite/SiC 세라믹스의 고온강도와 피로강도)

  • Ando, K.;Chu, M.C.;Tsuji, K.;Sato, S.
    • Journal of the Korea Society For Power System Engineering
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    • v.6 no.1
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    • pp.88-95
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    • 2002
  • 본 연구에서는 균열 치유 거동을 가지는 소결된 Mullite/SiC의 모재, 열처리재, 균열재, 치유 균열재의 기계적 특성이 논의되었다. 반타원형 균열의 치수는 $100{\mu}m$$200{\mu}m$이다. 얻어진 결과는 다음과 같다. (a) Mullite/SiC 복합 세라믹스는 균열 치유 능력이 있었다. (b) 최적의 균열 치유 열처리 조건은 $1300^{\circ}C$, 1시간이었다. (c) 치유 가능한 최대 균열 길이는 직경 $100{\mu}m$의 반타원 균열이다. (d) 균열 치유부는 $1200^{\circ}C$이상에서 충분한 강도를 가졌고, 대부분의 시험편은 균열 치유부 이외의 영역에서 파단 하였다. (e) 공기중에서 예열처리는 본 재료의 피로강도 향상에 유용하였다.

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