1996 Fiscal Year Final Research Report Summary
Fatigue crack propagation under various kind of loading
| Project/Area Number |
06555302
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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| Allocation Type | Single-year Grants |
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| Section | 試験 |
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| Research Field |
船舶工学
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
TOYOSADA Masahiro Faculty of Engineering, KYUSHU UNIVERSITY Professor, 工学部, 教授 (30188817)
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| Co-Investigator(Kenkyū-buntansha) |
ISHIKAWA Kuniteru NKK corporation Engineering Research Center, General Manager of Ship & Marine St, エンジニアリング研究所, 構造研究室室長
NIWA Toshio Faculty of Engineering, KYUSHU UNIVERSITY Research Associate, 工学部, 助手 (10208267)
YAMAGUCHI Kikuji Faculty of Engineering, KYUSHU UNIVERSITY Research Associate, 工学部, 助手 (70037943)
GOTOH Koji Faculty of Engineering, KYUSHU UNIVERSITY Assistant Professor, 工学部, 講師 (60274487)
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| Project Period (FY) |
1994 – 1996
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| Keywords | crack opening and closure / random load / DELTAKAPPA_<RP> / plastic zone size received fatigue damage / inherent stress / cohesive force model |
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| Research Abstract |
A Simulation model of fatigue crack opening and closing phenomena is introduced by developing Dugdale model.It is confirmed that the simulated RPG load (Re-tensile plastic zone Generated load) is in good agreement with experimental one.It becomes clear that a delayd retardation effect on fatigue crack propagation just after decreased maximum load can be also quantitatively assessed by effective stress intensity factor range DELTAKAPPA_<RP> corresponding to the period in which the re-tensile plastic zone appears, and stopping condition of a fatigue crack propagation is that DELTAKAPPA_<RP>*0.
It is also confirmed from the model that plastic zone size omega received fatigue damage is proportional to a two power of DELTAKAPPA_<RP>. It is reported that a fatigue crack propagation curve in residual stress distribution field and under "storm model" loading with changing mean load can be quantitatively assessed by using omega. However a problem occures in case of receiving very large spike load, which is assessed to unsafe side.
In the early stage of fatigue initiation, small surface cracks emanate and repeat coalescence one after another. Therefore aspect ratio of each surface crack has a large scatter. However the aspect ratio of a flctitious representative surface crack of which K value at the deepest point is the same as an increased K value due to interference effect of vicinity surface cracks and the depth is the same of the same of the deepest surface crack among surface cracks changes to be linear to the depth before the completion of coalesence. Moreover the method of a surface crack to be modeled into two dimensional problem by series springs model is also introduced.
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Research Products
(14 results)
