| Project/Area Number |
60302039
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| Research Category |
Grant-in-Aid for Co-operative Research (A)
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| Allocation Type | Single-year Grants |
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| Research Field |
材料力学
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| Research Institution | Osaka University |
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Principal Investigator |
OHJI Kiyotsugu Faculty of Engineering, Osaka University, Professor, 工学部, 教授 (20028939)
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| Co-Investigator(Kenkyū-buntansha) |
TORII Tashiyuki Faculty of Engineering, Okayama University, Associate Professor, 工学部, 助教授 (80033249)
TANAKA Keisuke Faculty of Engineering, Kyoto University, Associate Professor, 工学部, 助教授 (80026244)
JONO Masahiro Faculty of Engineering, Osaka University, Professor, 工学部, 教授 (20029094)
MUKAI Yoshihiko Faculty of Engineering, Osaka University, Professor, 工学部, 教授 (20029044)
KOBAYASHI Hideo Faculty of Engineering, Tokyo Institute of Technology Associate Professor, 工学部, 助教授 (00016487)
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| Project Period (FY) |
1985 – 1986
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| Project Status |
Completed (Fiscal Year 1986)
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| Budget Amount *help |
¥8,400,000 (Direct Cost: ¥8,400,000)
Fiscal Year 1986: ¥3,100,000 (Direct Cost: ¥3,100,000)
Fiscal Year 1985: ¥5,300,000 (Direct Cost: ¥5,300,000)
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| Keywords | Fracture Mechanics / Strength of Materials / Fatigue Crack Growth / Life Estimation Metthod / Residual Stress / Crack Closure / 有効応力拡大係数繁囲 |
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| Research Abstract |
An engineering method for predicting fatigue lives of cracks growing in residual stress fields was proposed. In this method effective stress ratio R near crack tip in components containing residual stresses are determined by superposition of the stress intensity factor <K_r> due to the residual stresses and that for the applied stresses. The effective stress ratio R and stress intensity range <DELTA> K were used to estimate the effective crack opening ratio (U = <DELTA> <K_(eff)> / <DELTA> K) and crack growth rate, in terms of U-R and da/dN- <DELTA> <K_(eff)> relationships obtained experimentally with residual-stress-free specimens. Experiments and numerical calculations were conducted to examine the applicability of the proposed method and some extensions were made. Main results obtained are summarized as follows.
1. Experiments were conducted by using specimens with symmetric and asymmetric residual stresses. The predicted crack growth behavior agreed well with the experimental one. 2
… More
. An simulation method was proposed, in which the variations of R and <DELTA> K with crack growth in components containing residual stresses were simultaneously replicated using specimens free from residual stresses. It was found that this simulation method worked well, even when gradient of the residual stress was steep. 3. Crack growth path under fatigue conditions was almost perpendicular to cyclic tensioncompression load axis, irrespective of residual stress distribution. 4. The proposed method was successfully applied to crack growth under variable load conditions. 5. An inverse analysis scheme was proposed for determining initial residual stress distribution from redistributed residual stress due to crack initiation and growth. The usefulness of the method was numerically proved. 6. The effect of residual stress on growth of surface cracks under cyclic loads was evaluated. 7. The effects of plastic deformation, oxide and roughness of fractured surface were investigated in the near-threshold region of fatigue crack growth. Several models predicting crack closure and crack growth were proposed. Less
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