Study on Fatigue life priduction of microstructural short crack region

1998 Fiscal Year Final Research Report Summary

• Project/Area Number: 09555312
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 展開研究
• Research Field: 海洋工学
• Research Institution: KYUSHU UNIVERSITY
• Principal Investigator: TOYOSADA Masahiro Kyushu university, Faculty of engineering, Professor, 工学部, 教授 (30188817)
• Co-Investigator(Kenkyū-buntansha): ONO Hideo Kawasaki heavy industries, LTD., Akashi research center, Manager, 明石技術研究所強度研究部, 研究員 ; YAMAGUCHI Kikuji Kyushu university, Faculty of engineering, Research Associate, 工学部, 助手 (70037943) ; NIWA Toshio Kyushu university, Faculty of engineering, Assistant Professor, 工学部, 講師 (10208267) ; GOTOH Koji Kyushu university, Faculty of engineering, Associate Professor, 工学部, 助教授 (60274487)
• Project Period (FY): 1997 – 1998
• Keywords: fatigue life priduction / fatigue surface crack / crack closure / coalescence of surface crack / DELTAK_<RP> / fatigue damage region size

Research Abstract

It is that a purpose of this study establishes algorithm to estimate crack growth curve without initiation life. Fatigue life of microstructural short crack region must estimate it as follows. When a notch is deep, fatigue life must be evaluated using yield stress under static condition. When a notch is slight, effect of cyclic loading needs to be considered and fatigue life must be evaluated using yield stress under cyclic condition. Fatigue life of physically small crack region and a long crack region must be calculated using the logarithmic curve of da/dN-DELTAK_<RP>. Therefore, Crack growth curves are calculated for a crack emanating from a notch root. without distinguishing between crack initiation and propagation. This result can be considered in establishing a unified fatigue life assessment theory to replace the combined S-Ncurve and crack propagation curve of linear fracture mechanics.