Damage assessment for steel structures subjected to cyclic pre-strain Part2: SEM in-situ observations clarifying the effect of stress state on damage evolution during plastic deformation

Abstract

The authors conducted fracture toughness test results after the cyclic plastic strain and compared them with virgin steel in the previous report (Part 1 [1]). In this previous report, it was revealed that prestraining under high triaxiality stress state made more degradation of toughness. In this study, in order to deeply investigate the effect of triaxiality on material damage, tensile tests in a scanning electron microscope (SEM) were performed on two types of specimens with different triaxiality histories. First, material damage was evaluated by in-situ observation of the evolution of material damage under tensile loading using the EBSD (Electron Back Scattered Diffraction Pattern) method. As a result, it was confirmed that material damage tended to be more significant in the specimen with a higher triaxial field at the same equivalent plastic strain level and that material damage propagated more rapidly. The results of the slip evaluation based on the slip model for crystals in steel materials suggest that the ease of damage development associated with plastic deformation in a high triaxial field is due to the magnitude of movement of a particular slip plane.