繰返し大変形下の疲労き裂進展評価法に関する研究

概要

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In this study, evaluation method for fatigue crack growth rate under large scale yielding condition was investigated based on J integral range, ΔJ. Low cycle fatigue crack growth tests were conducted using compact tension (CT) specimens of SM400B steel with some sizes of plate thickness. As the results, thickness effect appears in the relationships between fatigue crack growth rate and ΔJ calculated by Merkle and Corten's conventional equation. Moreover, ΔJ and P-V (load versus load line displacement) curves were analytically calculated using cyclic stress-strain curves based on 2σ_y concept as the FEM constitutive equation. 2σ_y concept is that yield stress is approximately set to about double magnitude of yield stress obtained from tensile test. It was found that P-V curves using in calculating ΔJ were approximately coincident by taking account of stress triaxiality factor at the crack tip obtained from above FEM analysis in addition to thickness. Therefore, conventional equation of ΔJ was modified by the stress triaxiality factor. Fatigue crack growth rates could be predicted by the modified ΔJ without depending on the size of thickness.
社団法人日本機械学会の論文
2008-09-25