Abstract
In order to investigate the ultimate strength of structures and components under the unexpected huge earth quake, it is necessary to understand the final fracture condition under static and cyclic loading conditions. This study compared the crack growth behavior under monotonic and cyclic loading conditions for carbon steel SGV410 used for pipes of nuclear power plants. Crack lengths were measured by unloading elastic compliance method. Fatigue tests were carried out by two kinds of methods, which are constant load amplitude and increasing load line displacement tests. With the increase in the number of cycles, the crack accelerated and then fractured. of fatigue crack growth characteristics coincide under the present test conditions regardless of specimen thickness. However, with increasing the J-integral range, ΔJI, crack growth rate accelerated and then unstable fracture occurred. Upper bound of the fatigue crack growth rate was the blunting line. Finally, the monotonic R curve becomes the upper bound characteristics of fatigue crack growth under the unstable fracture conditions. In fact, critical characteristics of fatigue crack growth are monotonic R curve.
