Transactions of the Korean Society of Mechanical Engineers A (대한기계학회논문집A)

The Korean Society of Mechanical Engineers (대한기계학회)
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Evaluation of Variation in Residual Strength of Carbon Fiber Reinforced Plastic Plate with a Hole Subjected to Fatigue Load

피로하중에 의한 홀 노치 탄소섬유강화 복합재의 잔류강도변화 평가

  • 김상영 (성균관대학교 기계공학부) ;
  • 강민성 (성균관대학교 기계공학부) ;
  • 구재민 (성균관대학교 기계공학부) ;
  • 석창성 (성균관대학교 기계공학부)
  • Received : 2010.05.12
  • Accepted : 2010.08.12
  • Published : 2010.10.01
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Abstract

CFRP (Carbon Fiber Reinforced Plastic) has received considerable attention in various fields as a structural material, because of its high specific strength, high specific stiffness, excellent design flexibility, favorable chemical properties, etc. Most products consisting of several parts are generally assembled by mechanical joining methods (using rivets, bolts, pins, etc.). Holes must be drilled in the parts to be joined, and the strength of the components subjected to static and fatigue loads caused by stress concentration must be decreased. In this study, we experimentally evaluated the variation in the residual strength of a holenotched CFRP plate subjected to fatigue load. We repeatedly subjected the hole-notched specimen to fatigue load for a certain number of cycles, and then we investigated the residual strength of the hole-notched specimen by performing the fracture test. From the results of the test, we can observe the initiation of a directional crack caused by the applied fatigue load. Further, we observed that the residual strength increases with a decrease in the notch effect due to this crack. It was evaluated that the residual strength increases to a certain level and subsequently decreases. This variation in the residual strength was represented by a simple equation by using a model of the decrease in residual strength for plain plate, which was developed by Reifsnider and a stress redistribution model for hole-notched plate, which was developed by Yip.

탄소섬유강화 복합재료는 높은 비강도, 비강성, 설계유연성 및 우수한 화학적 특성 등으로 인하여 여러분야에서 각광받고 있는 구조재료이다. 대부분의 CFRP 복합재료 제품들은 여러 부품들을 주로 볼트, 핀 등의 기계적인 방법으로 조립하여 제작된다. 볼트나 핀에 의해 발생하는 hole 은 구조물 내에서 노치로 작용하여 부품의 강도저하의 원인으로 작용한다. 본 논문에서는 피로하중에 의한 CFRP 복합재료 홀 노치재의 잔류강도를 실험적으로 평가하였다. 이를 위하여, 시편에 일정 반복 수만큼 피로하중을 부여하였으며, 이후 파괴시험을 통하여 홀 노치재의 잔류강도를 측정하였다. 그 결과, 피로하중으로 인해 하중방향의 균열이 발생하는 것을 확인하였으며 이 균열이 홀의 노치효과를 감소시켜 잔류강도를 증가시키는 것으로 생각되었다. 시편의 잔류강도는 일정 수준까지 증가하다가 감소하는 것으로 평가되었으며, 이를 Reifsneider 등의 평활재 잔류강도 저하모델과 Yip 등의 홀 노치재 응력재분포 함수를 이용하여, 피로하중 하의 홀 노치재 잔류강도 변화를 수식으로 나타내었다.

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References

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