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

The Korean Society of Mechanical Engineers (대한기계학회)
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Fatigue Crack Propagation and Fatigue Life Evaluation of High-Performance Steel using Modified Forman Model

수정 Forman 모델을 이용한 고성능 강재의 피로균열전파와 피로수명평가

  • Choi, Sung-Won (Dept. of Automotive Engineering, Hanyang Univ.) ;
  • Kang, Dong-Hwan (Dept. of Automotive Engineering, Hanyang Univ.) ;
  • Lee, Jong-Kwan (Steel Structure Research Laboratory, Research Institute of Industrial Science & Technology) ;
  • Kim, Tae-Won (School of Mechanical Engineering, Hanyang Univ.)
  • 최성원 (한양대학교 자동차공학과) ;
  • 강동환 (한양대학교 자동차공학과) ;
  • 이종관 (포항산업과학연구원 강구조연구소) ;
  • 김태원 (한양대학교 기계공학부)
  • Received : 2010.12.13
  • Accepted : 2011.09.07
  • Published : 2011.11.01
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Abstract

Fatigue crack propagation behavior and the fatigue life in-high performance steel were investigated by means of fatigue crack propagation tests under constant loading conditions of 'R=0.1 and f=0.1 Hz', 'R=0.3 and f=0.3 Hz', and 'R=0.5 and f=0.5 Hz' for the load ratio and frequency, respectively. A modified Forman model was developed to describe the fatigue crack propagation behavior for the conditions. The modified Forman model is applicable to all fatigue crack propagation regions I, II, and III by implementing the threshold stress intensity factor range and the effective stress intensity factor range caused by crack closure. The results show that predicted fatigue lives of Forman and modified Forman models were 8,814 and 12,292 cycles, respectively when the crack propagated approximately 5.0 mm and the load ratio and frequency were both 0.1. Comparison of the test results indicates that the modified Forman model showed much more effective fatigue crack propagation behavior in high-performance steel.

응력확대계수비와 하중 주파수가 각각 'R=0.1, f=0.1 Hz', 'R=0.3, f=0.3 Hz' 및 'R=0.5, f=0.5 Hz'인 세가지 하중 조건에서 피로균열전파 실험을 하였으며 이를 바탕으로 고성능 강재의 피로균열전파거동 분석과 피로수명평가를 수행하였다. 하중 조건에 따른 피로균열전파거동을 모사하기 위해 수정된 Forman 모델을 제안하였으며 제안된 모델은 하한 응력확대계수폭과 균열 닫힘 현상에 의한 유효 응력확대계수폭을 고려함으로써 거동의 전 영역을 모사할 수 있었다. 응력확대계수비와 하중 주파수가 0.1 인 경우, 균열이 약 5.0 mm 전파될 때 피로수명을 평가한 결과, Forman 모델은 8,814 cycles, 수정된 모델은 12,292 cycles 의 계산결과를 얻었으며, 이를 12,774 cycles 의 실제 실험결과와 비교할 때 수정된 Forman 모델이 실제 피로균열전파거동을 보다 효과적으로 모사하고 있음을 확인할 수 있었다.

Keywords

References

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