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Assessment for Propagation Behavior and Fracture Surface of Mixed-mode Fatigue Crack by Fracture Surface-Roughness Induced Crack Closure

파면거칠기 유도 균열닫힘에 의한 혼합모드 피로균열의 전파거동 및 파면에 대한 평가

  • 서기정 (한국기계연구원 마이크로응용역학팀) ;
  • 이정무 (LG화학 테크센타 응용기술팀)
  • Published : 2007.04.01

Abstract

In this study, we have investigated the closure behavior of fatigue cracks in SAPH440 steel plates under a mixed-mode I+II loading. A crack image capturing system as a direct measuring method was used to measure the closure levels at a crack tip. The crack closure levels in the fluctuation and stable sections were increased with the increase of the mode mixture ratio. The mode mixture ratio independent fatigue crack propagation rates equation was calculated by considering mixed-mode crack closure levels. The equation was examined according to the application method of crack opening ratio. The fracture surface analysis by C-scan method was also performed in order to investigate the closure mechanism and propagation mode of crack under the mixed-mode I+II loading. The crack closure under the mixed mode I+II is confirmed as a surface roughness closure by the quantitative analysis of fracture surface using the proposed surface roughness parameter.

Keywords

Mixed-mode I+II Loading;Mode Mixture Ratio;Surface-Roughness Induced Crack Closure;Crack Opening Ratio;Fracture Surface;Fracture Surface Roughness Parameter;Crack Propagaation Type

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