Study on crack opening/closing behavior of fatigue surface crack and fatigue life priduction

1998 Fiscal Year Final Research Report Summary

• Project/Area Number: 08455478
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• 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): 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): 1996 – 1998
• Keywords: fatigue life / fatigue surface crack / crack opening / closing behavior / interference effect / laser interference displacement indicator

Research Abstract

It is that a purpose of this study establishes fatigue life assessment method of surface crack emanated from weld toe. The life during plural surface crack usually occupies the major portion of total fatigue life. Therefore it is necessary to establish the estimation method of fatigue propagation life before completion of crack coalescence. A supposed surface crack which exist alone at the notch root and of which K value is the same as K value with considering interference effect from near crack is considered. Then it becames clear that thereis a important law about the change of ratio for the supposed crack with respect to K value which may represent indirectly crack propagation behavior for multiple surface cracks emanated from notch root with welding tensile residual stress field.
The measuring system using laser interference displacement indicator was developed for the purpose of obtaining the crack opening/closing behavior. Then problems of this system were investigated and some improved points were indicated.