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A Study on Non-propagating Crack in Fatigue Behavior of Pure Titanium

공업용 순 티타늄의 피로거동에서 정류균열에 관한 연구

  • Published : 2000.04.01

Abstract

To verify the existing theory, non-propagating crack(NPC) does not exist in Ti which fulfills the good conditions for being of NPC, NPC detection in Ti was tried out. Also, the conception of fatigue limit in Ti and a main cause for NPC being were inquired. NPC was detected in both sharp notch root ( $\rho$=0.02mm) and micro pit (diameter = 0.25mm) which held fast to the end under stressing of fatigue limit. Therefore, the existing theory was identified as mistake. But, NPC can not be detected in smooth specimen. This fact would be due to the presumption that NPC is very small or crack does not initiate in smooth specimen. Anyway, the fatigue limit of Ti does not correspond to critical stress of crack initiation but correspond to critical stress of NPC growth. Measurement on the COD of NPC in Ti showed that the crack tip was closed even under the peak stress level at fatigue limit. But, after stress relieving annealing crack tip was opened. Consequently, compressive residual stress which is induced around the crack tip is considered to be the factor causing the NPC being.

Keywords

Titanium;Crack Closure;Fatigue Limit;Fatigue;Non-propagating Crack;Coaxing Effect

References

  1. Frost, N.E., 1959, 'A Relation Between the Critical Alternating Propagation Stress and Crack Length for Mild Steel,' Proc. Inst. Mech. Engrs., 173-35, pp. 811-827
  2. 北川, 西谷, 松本, 1973, '病勞き裂成長の下限界應力大係數 ${\Delta}K_{th}$とき裂材$\cdot$切欠材の病勞限度との關係について,' 日本機械學會論文集, 42-356, pp. 996-1000
  3. Elber, W., 1971, 'The Significance of Fatigue Crack Closure,' ASTM STP 486, pp. 230-242
  4. 西谷, 高尾, 1974, '1應力サイクル間における停留き裂先端部の擧動,' 日本機械學會論文集, 40-338, pp. 2725-2733
  5. 김민건, 1991, '구조용 강재에 발생하는 미소 피로크랙의 정류요인,' 대한기계학회논문집, 15-3, pp. 880-886
  6. 石橋 正, 1967, '金屬の病勞と破壤の防止,' 養賢堂
  7. 西谷, 田中, 戶高, 1980, 'S15C低溫燒入れ時效材のコ一キシソグ效果と效視的き裂の關係,' 材科, 29-317, pp. 143-149
  8. 西谷, 田中, 山田, 寺西, 1987, 'S10C豫ひずみ材のコ一キシソグ效果と微視的き裂の關係,' 日本機械學會論文集, 54-498, pp. 190-195
  9. 김민건, 지정근, 1998, '유동상로를 이용한 질화처리 티타늄의 피로강도 특성,' 대한기계학회논문집, A권, 22-1, pp. 142-147
  10. 西谷, 1976, '停留き裂(切欠き),' 材科, 26-282, pp. 98-108
  11. Takao, K., Nishitani, H., 1984, 'Notch Sensitivity and Behavior of Small Fatigue Crack of Commercial Purity Titanium,' FATIGUE 84, Vol. II, pp. 827-834
  12. 高尾, 松本, 西谷, 1985, '工業用純チタソにおける病勞き裂の開閉口擧動,' 日本機械學會論文集, 51-462, pp. 450-454
  13. 森田, 淸水, 千葉, 1990, '室化處理を施したTi-6Al-4V合金の病勞擧動,' 日本機械學會論文集, 56-529, pp. 1915-1921
  14. 高尾, 西谷, 1984, '工業用純チタソの病勞き裂發生過程と切欠き感度,' 日本機械學會論文集, 50-453, pp. 1049-1053