Evolution of the geometrical and morphological characteristics of splits during fracture toughness test

Abstract

Split is a brittle stochastic phenomenon sometimes observed in fracture toughness tests of hot rolled steels in T-L and L-T orientations. At present, there is no standard criteria to assess this event in R-curves due, among other things, to the lack of understanding of its characteristics and evolution during the test. This study analyzes the geometrical and morphological characteristics of splits as well as, their evolution and interaction during fracture toughness tests. The tests were performed according to ASTM E1820-20 in DH36 steel using SE(B) specimens in T-L orientation at −60 °C. Split's geometrical characteristics in the intermediate or final stages of the fracture toughness test were analyzed through Computed Tomography (CT). Also, Scatter Electron Microscopy and Optic Microscopy analysis were performed on the specimen fracture surfaces to study the split's morphological characteristics. The concomitant occurrence of two splits and micro-splits at the crack growth region are reported. The micro-splits did not cause measurables pop-ins in the load vs. displacement record. CT slices showed that some splits exhibit plane change, branching, and interaction with other splits. These phenomena are not necessarily noticeable on the fracture surface. Also, a split can grow after arrested and present distortion after their occurrence. The sequence of multiple split events can be determined by analyzing both the position on the fracture surface and the degree of distortion of the splits.