| Project/Area Number |
63470053
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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 |
金属材料(含表面処理・腐食防食)
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| Research Institution | OSAKA UNIVERSITY |
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Principal Investigator |
SHIBATA Toshio FACULTY OF ENGINEERING PROFESSOR, 工学部, 教授 (90001205)
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| Co-Investigator(Kenkyū-buntansha) |
FUJIMOTO Hhinji FACULTY OF ENGINEERING RESEARCH ASSOCIATE, 工学部, 助手 (70199371)
TANIGUCH Shigeji FACULTY OF ENGINEERING ASSOCIATE PROFESSOR, 工学部, 助教授 (50029196)
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| Project Period (FY) |
1988 – 1989
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| Project Status |
Completed (Fiscal Year 1989)
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| Budget Amount *help |
¥5,100,000 (Direct Cost: ¥5,100,000)
Fiscal Year 1989: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1988: ¥4,400,000 (Direct Cost: ¥4,400,000)
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| Keywords | Pitting corrosion / Statistical and probabilistic properties / Birth and death stochastic model / Monte Carlo simulation / モンテカルロシミュレ-ション / 局部腐食 / 孔食発生誘導時間分布 / 孔食電位分布 / モンテカルロシシュレーション / 出生死滅確率モデル |
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| Research Abstract |
For corrosion resistant materials such as stainless steels, more than half cases of corrosion failure had been known to be caused by localized corrosion. It is well known that data of localized corrosion show wide scatter in space or in time, namely statistical and probabilistic variations. For this reason, statistical and probabilistic nature of localized corrosion shckild be studied in more detail in order to evaluate failure life of materials for various structures with more confidence.
This study aims to refine the birth and death stochastic model of pitting corrosion which had been proposed previously and to simulate the actual pit foreation process by using Monte Carlo similation based on the proposed model. Simulated distributions of pitting potential and induction time for pit generation were compared with the observed distributions by the experiments in order to establish the confidence of the proposed model. The basic assumptions for the birth and death stochastic model are as
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follows: 1) Pit generation obeys a Posson stochastic process, so that the distribution of pit senation time follows exponential probability distribution.
Transition probability corresponding to the pit generation rate is given by a function of potential. 2) The size of pit nucleus increases with time and the proportional constant of the rate law is expressed as an exponential function of potential. 3) Below a critical size, the growth of pit nucleus will stop due to repassivation. Death process of pit nucleus obeys also Poisson process, so that the distribution law for life time until death follows also exponential probability law. 4) Large pit which grows over a critical size will not die and continue to grow.
Based on the above model and assumptions, Monte Carlo simulation provided the following results: 1) The distribution of pitting potential obeys normal probability distribution as a first approximation. 2) Median of pitting potential is proportional to the square root of potential sweep velocity. 3) The probability distribution of induction time for pit generation obeys distorted distribution. The above results were found to simulate the results observed in the experiments with a high confidence. Increase in heterogenuity due to recrystalization of amorphous alloys by heat treatment was analyzed based on the model. Less
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