抄録
A stretched zone is formed as a result of blunting and stretching at the tip of the crack during the fracture process. Consequently, the fracture surface becomes fine and smooth. Paying attention to this characteristic, the authors proposed a new method to evaluate the stretched zone width quantitatively, based on the difference in the fracture surface roughness.
To verify the validity of the proposed method, elastic-plastic fracture toughness tests were performed on compact tension specimens cut out of carbon steel pipes. After the fracture toughness tests, the stretched zone was observed with a high-resolution scanning electron microscope to measure the critical stretched zone width (SZWc) for stable crack initiation quantitatively. The critical stretched zone widths determined by the proposed method were compared with those reported in the references. The comparison led the conclusion that this method enabled us to measure SZWc quantitatively, which had been difficult to measure in the absence of skilled microscope operators. The method also showed the possibility to estimate the failure load from the fracture surface by using fracture mechanics parameters.
