熱処理により模擬した細粒HAZ組織を有する低炭素鋼の微小疲労き裂進展寿命評価方法

抄録

Small fatigue crack growth tests utilizing DIC technique are carried out for low carbon steel with two different heat treatment to establish the small fatigue crack growth evaluation method. As a result, small fatigue crack growth rate (FCGR) looked larger than that of large crack by evaluating with usual stress intensity factor range. The small fatigue crack opening stress, successfully measured by using DIC technique, were decreasing with loading stress was increasing. In addition, by using effective cyclic J integral range calculated with measured crack opening stress, even small fatigue crack growth rates were almost agreed with that of large crack data. Due to this evaluation, microstructural resistance, appeared in the region of crack length is 0.2 mm or less, is successfully visualized. Finally, estimated small fatigue crack growth life by using Paris’s law of large crack, effective cyclic J integral range and conventional approximation formula of crack opening stress was almost agreed with corresponding experimental data.