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Improvement of fatigue life evaluation methods based on advanced fracture mechanics approaches

ABSTRACT:
Our laboratory has been conducting the research related to fatigue life estimation based on the fracture mechanics approach; because this approach makes fatigue life estimation for large welded built-up structures more accurate. At present, two representative objectives for practical fatigue life estimation is carrying out: the establishment of a quantitative fatigue crack growth estimation procedure both for surface or embedded cracks, and for multiaxial working stress conditions in these structures. Fundamental research item, which is the improvement of fatigue crack growth simulation considering the work hardening effect of materials, is also executing.

This research fund is Grant-in-Aid for Young Scientists (S) (No. 21676007) by Japan Society for the Promotion of Science.

DETAILED:

photo

An example of fatigue crack growth estimation based
on improved fracture mechanics approachl

Many accidents are caused by fatigue in welded built-up steel structures, e.g. cars, ships, offshore structures, bridges, towers, railroad vehicle etc. As a result, it is important to estimate the fatigue lives of such structures quantitatively for safety reasons.

Fatigue accidents occur not only due to the carelessness of designers or manufactures in the production stages, but also to the insufficient ability of the conventional fatigue life estimation procedures based on the conventional S-N curves approach. The S-N curves approach is, however, powerless in the evaluation of fatigue integrity for new type structural designs. The only reliable enhanced method of fatigue lives is to reduce the working stress for structures through a trial and error process. A theoretical method to identify the amount of reduction of working stress has not been proposed yet.

Our research group has been conducting research based on the fracture mechanics approach; because this approach makes fatigue life estimation for large welded built-up structures more accurate.

In this research, two representative objectives for practical fatigue life estimation will be achieved: the establishment of a quantitative fatigue crack growth estimation procedure both for surface or embedded cracks, and for multiaxial working stress conditions in these structures. Fundamental research item, which is the improvement of fatigue crack growth simulation considering the work hardening effect of materials, is also executing.

This research fund is Grant-in-Aid for Young Scientists (S) (No. 21676007) by Japan Society for the Promotion of Science.

Fatigue and Fracture, Welding Mechanics and Production Systems Lab.,
Department. of Marine Systems Engineering, Faculty of Engineering, Kyushu University
Associate Professor Koji Gotoh
Assistant Professor Seiichiro Tsutsumi
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