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Fatigue Crack Initiation Analysis in 1060 Steel
並列摘要
This study investigates initiation of small cracks on dumble-shaped plate type specimens of 1060 steel at the load ratio of R=0 under varied cyclic stress amplitudes between 0.6 and 1.0 of yield stress using the Instron machine (model: 8501). Sinusoidal wave of a frequency of 10 Hz was used in the experiment. The experiment was conducted at a room temperature of 23℃. Each test for different applied stress ranges was carried out for 2×10^4 cycles. Microstructure and fractography of the fractured specimen were also analyzed. Nucleations of cracks were observed at Ferrite-Ferrite G rain Boundary (FFGB) as well as inside Ferrite Grain Body (FGB), but the FFGB location was preferred. Results show that the average length of FFGB cracks is found larger than that of the average length of cracks initiated inside FGB at the same cyclic loading conditions. The formation of slip band inside grain body, slip band impingement at grain boundary and elastic-plastic incompatibility synergistically have significant influence on fatigue crack initiation in 1060 steel. Additionally, the formation of irregular voids inside slip bands, initiation and growth of small voids at grain boundary and the subsequent joining of these with other voids were seen as specific characteristics of 1060 steel. It was also established that cracks nucleate both at grain boundary and inside grain body in 1060 steel in the investigated domain of 0.6 to 1.0σ(subscript y).It was further established that the orientation of the grain body cracks at low stress level is greater than 45° and the average angle of orientation of these cracks increases like that of grain boundary cracks with increased magnitude of stress range.
並列關鍵字
Crack initiation ； cyclic loading ； fatigue ； ferrite grain body ； ferrite grain boundary ； fractography ； growth ； small crack ； 1060 steel延伸閱讀
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