Journal of the Korean Society for Precision Engineering (한국정밀공학회지)

Korean Society for Precision Engineering (한국정밀공학회)
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A Study on Physically small Surface Fatigue Crack Growth Behavior in 7075-T651 Aluminum Alloy

7075-T651 AI 합금에 있어서 물리적 미소 표면 피로균열 성장거동에 관한 연구

  • Sin, Yong-Seung (Dept.of Mechanical Engineering, Seoul National University of Technology) ;
  • Seo, Seong-Won (Dept.of Mechanical Engineering, Seoul National University of Technology) ;
  • Yu, Heon-Il (School of Mechanical Design engineering, Kookmin University)
  • 신용승 (서울산업대학 기계공학과) ;
  • 서성원 (서울산업대학 기계공학과) ;
  • 유헌일 (국민대학교 기계설계학과)
  • Published : 1992.03.01
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Abstract

In this study, the propagation behaviour and the closure phenomena of physically small surface cracks were investigated by the techinque of the Kikukawa-unloading elastic compliance method using a back face strain gage. The surface cracks initiated and propagated from notched specimens under constant amplitude bending load. The crack shape (aspect ratio) with approximately semi-circular at the early stage was changed to semi-elliptical as the cracks grew larger. The crack depth (a) could be expressed uniquenly by the crack length (c). The dependence of the crack propagation rate on the stress ratio R was strongly related in the lower ${\Delta}K$ range. The deceleration of the surface crack propagation rate was prominent in lower R during the crack length was small. When the propagation rate was rearranged with the effective stress intensity factor range ${\Delta}$K_{eff} the dependence of the crack propagation rate on the stress ratio R was found to be diminshed. These were caused by the crack closure phenomena that was most prominent at the lower propagation rate. The mechanism of crack closure phenomena was dominated by the plasticity-induced mechanism.

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