1993 Fiscal Year Final Research Report Summary
High-Precision Determination of Fundamental Properties of Creep-Fatigue Crack Propagation
| Project/Area Number |
04452116
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
機械材料工学
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| Research Institution | Osaka University |
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Principal Investigator |
OHJI Kiyotsugu Osaka University, Faculty of Engineering, Professor, 工学部, 教授 (20028939)
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| Co-Investigator(Kenkyū-buntansha) |
TSUJI Masahiro Osaka University, Faculty of Engineering, Research Associate, 工学部, 助手 (10132630)
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| Project Period (FY) |
1992 – 1993
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| Keywords | Creep-Fatigue Crack Propagation / Creep Crack Propagation / Fatigue Crack Propagation / Fatigue Threshold / Crack Closure / Fracture Mechanics / Life Prediction / Laser-Based Interferometric Strain / Displacement Gage |
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| Research Abstract |
The safety assessment of high temperature equipment and strucures is indispensable for their effective use. In the present study prediction method of high temperature creep and fatigue crack propagation lives and fundamental crack propagation behavior were investigated for the assessment. The main conclusions obtained are summarized in the followings.
1.Using the laser-based interferometric strain/displacement gage system, crack closure in fatigue crack propagation tests was successfully measured at high temperatures. By using platinum plate for reflecting laser beam and filter for eliminating back-ground noise, the measurement was made up to 700'C.
2.The behaviors of crack propagation and crack closure were investigated under stress rations of R = -0., 0.1 and 0.5, at 450', 550', 650' and 700'C for type 304 stainless steel. The dependence of the crack propagation rate on R was reconsiled by DELTA K_<eff> which accounted for the effect of crack closure.
3.The effect of specimen geometry on the fatigue crack growth in type 304 stainless steel was studied at room and high temperatures. It was found that the near-threshold fatigue crack propagation behavior depended on specimen thickness.
4.Creep crack propagation in used 2 1/4 Cr 1Mo steel was studied. Creep crack propagation rate in the heat affected zone was higher than that in the base material. The crack propagation rate correlated well with the modified J integral.
5.The engineering approach was applied to predicting the creep crack propagation behavior. The predicted crack propagation in C(T) specimens agreed well with experimental one. The approach was then applied to the crack propagation of an inner longitudinal crack and an inner circumferential crack in pipes for the safety assessment of the pipe.
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