Evaluation of Pre-strain Effect on Abnormal Fracture Occurrence in Drop-Weight Tear Test for Linepipe Steel with High Charpy Energy

In this study, a compressive pre-straining at the impact hammer side in the DWTT specimen was evaluated under quasi-static load conditions. The specimen's surfaces were electrolytically-etched to print circle patterns with 5 mm in diameter in order to measure plastic strain. Charpy impact specimens were taken from the quasi-static loaded and unloaded DWTT specimen to measure the possible influence of pre-straining on toughness. The impact test results show that more than 2 % of the compressive pre-strain gave 7 to 10 % decrease of the Charpy upper-shelf energy. The effect of pre-straining on tensile property was also evaluated. These present experiments indicate that the occurrence of abnormal fracture near the hammer side can be attributed to the compressive pre-straining. Furthermore, the chevron-notched and the pre-cracked DWTTs and the partial gas burst test were conducted in order to compare the brittle-to-ductile transition temperature. Based on these experiments, the effect of notch configuration on the brittle-to-ductile transition temperature and the correlation between DWTTs and pipe test were discussed. In addition, the relationship between the pre-straining and the abnormal fracture appearance was considered.