EVALUATION FOR ABNORMAL FRACTURE APPEARANCE IN DROP WEIGHT TEAR TEST WITH HIGH TOUGHNESS LINEPIPE

摘要

The West-Jefferson type full scale partial gas burst test was earried out in order to investigate appropriate evaluation method for resistance to brittle fracture propagation in high toughness line-pipe materials that exhibits abnormal fracture appearance by the Drop Weight Tear Test (DWTT). Shear area fraction (SA%) of the DWTT that had been derived from the way regarding or disregarding the abnormal fracture appearance was compared with the shear area fraction obtained from the fracture surface by the full scale burst test. It was shown that SA% obtained by the burst tests corresponded well with that by the pressed notch DWTT for the cases of disregarding abnormal fracture appearance. On the other hand, SA% in the DWTT was lower than that in the burst test when the abnormal fracture appearance was treated in the same manner as the brittle fracture that occurs at the notch tip of the specimen. Therefore, it can be stated that the evaluation by regarding the abnormal fracture surface can be conservative and much relevant evaluation can be possible by disregarding the abnormal fracture appearance. SA% of the fracture surface in the Chevron notch DWTT showed slightly lower value than that in the burst test, regardless of whether abnormal fracture appearances was regarded or disregarded. This means the Chevron notch DWTT is also severe testing method, as well as the pressed notch DWTT with regarding the abnormal fracture surface.