Crack Length Dependence of Threshold Stress Intensity Factor of Finite Plates with Semi-Elliptical Crack

In this study, the crack length dependence of the threshold stress intensity factor (△K_th) for semi-elliptical cracks in the finite plate subjected to bending stress was evaluated. (△K_th) of ultra high strength steel (UHS steel) increased sharply at short crack depth and length. Mild steel (M steel) showed a tendency to gently increase at short crack depth and length, compared to ultra high strength steel. That is, different characteristics were shown depending on the material strength. (△K_th) of UHS steel and M steel was constant regardless of the width and crack aspect ratio (As). Regardless of the steel grade and specimen size, (△K_th) of As=0.3 for the crack depth was slightly larger than 1.0. On the other hand, that of As=1.0 for the crack length was much larger than 0.3.