DUCTILE CRACK GROWTH BEHAVIOUR OF COMPRESSIVELY PRESTRAINED STEELS

摘要

In the case of considering the fracture behaviour of actual structures, ductile crack could grow through prestrained zone generated by load histories and then final fracture could occur. Therefore, it is important to figure out ductile crack growth property of prestrained steels. In this study, using compressively prestrained SM400B and HT780, ductile crack growth properties were discussed experimentally and analytically. As a result, it was found that the resistance to ductile crack growth of SM400B was different depending on prestrain levels and brittle fractures occurred for most -10 % prestrained SM400B. On the other hand, the resistance of HT780 was independent of prestrain levels. From SEM observations, micro crack was observed in fracture surface for which brittle fracture occurred. The difference in the resistance to ductile crack growth due to compressive prestrain could be understandable from stress distributions and stress triaxiality factor at crack tip obtained from FE-analyses. In the case that stress triaxiality factor, which is dependent on each stress component, increases due to compressive prestrain, resistance to ductile crack growth could become lower.