Behavior of short fatigue crack at notch root

It has been recognized that the threshold stress intensity factor range AK_th of a short crack is lower than that of a long crack. The short crack behavior in plain specimen has been studied by many researchers. However, the behavior of a short crack at the root of a long notch is not yet clear. The crack closure behavior is considered to be affected by the constraint at notch root and it is dependent on the length and the root radius of notch. In this study, fatigue tests on specimens with short pre-crack at long notch were done and the difference in crack closure behavior was studied. As a result, short crack effect appeared in any notch root radius. In a sharp notch, the crack opening point easily reached its stable condition after a small amount of crack extension. On the contrary in a dull notch, the opening point was lower than the stable condition and consequently short crack effect lasted in relatively wide range of crack extension. The small crack effect of notched specimen was discussed based on crack closure behavior.