Journal of Ocean Engineering and Technology (한국해양공학회지)

Korean Society of Ocean Engineers (한국해양공학회)
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Variation of Rotating Bending Fatigue Characteristics by UNSM on Ti-6Al-4V

Ti-6Al-4V재의 UNSM처리에 의한 회전굽힘피로특성변화

  • Suh, Chang-Min (School of Mechanical Engineering, Kyungpook National University) ;
  • Pyoun, Young-Sik (School of Mechanical Engineering, Sun MoonUniversity) ;
  • Suh, Min-Soo (School of Advanced Materials Engineering, Kookmin University)
  • 서창민 (경북대학교 공과대학 기계공학부) ;
  • 편영식 (선문대학교 공과대학 기계공학부) ;
  • 서민수 (국민대학교 공과대학 신소재공학부)
  • Received : 2011.08.18
  • Accepted : 2010.12.23
  • Published : 2011.12.31
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Abstract

In order to analyze feasibility of replacing a conventional 6-mm Ti bar with a 5-mm bar, a series of rotating bending fatigue tests were carried out on Ti-6Al-4V bars by strengthening the fatigue performance using a special technique called UNSM (Ultrasonic Nanocrystal Surface Modification). The results of S-N curves clearly showed that the performance of the 5-mm titanium specimen was similar to that of the 6-mm specimen when the UNSM treatment was applied. The 5-mm treated specimen converged with small scattering band into the linear line of the non-treated 6-mm one. Below the fatigue life of $10^5$ cycles, the UNSM treatment did not show any significant superiority in the bending stress and fatigue life. However, over the fatigue life of $10^5$ cycles, the effect of UNSM was superior for each fatigue life, and the bending stress became longer and higher than that of the untreated one. In the case of 6-mm Ti-bar with UNSM, the fatigue limit was about 592 MPa, and there was fatigue strength increase of about 30.7% at the fatigue life of $10^4$ cycles compared to the untreated 6-mm bar. Therefore, the compressive residual stress made by the UNSM in Ti-6Al-4V increased the fatigue strength by more than 30%.

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