Effects of loading rate, notch geometry and loading mode on the local cleavage fracture stress of a C–Mn steel

Abstract

In this work, notched specimens with two notch geometries were tested in two loading modes (four-point bending (4PB) and three-point bending (3PB)) at various loading rates at a temperature of −110 • C for a C-Mn steel. An elastic-plastic finiteelement method (FEM) is used to determine the stress distributions ahead of notches. By accurately measuring the distances of the cleavage initiation sites from the notch roots, the local cleavage fracture stress σ f is measured. The results obtained and combining with previous studies by the authors show that the local cleavage fracture stress σ f is closely related to the cleavage fracture mechanism (critical events) in steels. The σ f values do not change with loading rate, notch geometry and loading mode, as long as the critical event of cleavage fracture does not change at various testing conditions. The σ f is mainly determined by the steel microstructure, and its scatter is mainly caused by the size distribution of the weakest constituent in steels (ferrite grain or pearlite colony with large sizes and large second phase particles) and the change of the critical events in cleavage process. The σ f can characterize the intrinsic toughness of steels and may be used in a "local approach" model for assessing integrity of flawed structures. The σ f values could be measured by both 4PB and 3PB tests.

Fracture behavior of S355J2W steel and weld at low temperature

“…As the controlling factor of cleavage rupture, the critical event is considered the most difficult stage for the initiation and propagation of cracks 19 . As stated in Wang et al, 24 when retained cracks are observed to be stopped at the grain boundary, the critical event is the expansion of the grain size crack into the adjacent grain. Figures 8 and 9 show the critical events of the retained cracks in S355J2W steel and WM TPB fracture specimens, respectively.…”

Influence of welding HAZ microstructure on low-temperature impact fracture behaviour in C–Mn shipbuilding steel

“…The approximate width of the active zone during blunt-notch testing is 300 µm [29, 30], much larger than the BF spacing. This implies that one or more banded structures can be sampled in the active zone.…”

Micromechanical Analysis of In-Plane Constraint Effect on Local Fracture Behavior of Cracks in the Weakest Locations of Dissimilar Metal Welded Joint

“…It can also be found that at the same J-integral, the TRIAX at crack tip increases with increasing in-plane constraint. For the high TRIAX can promote the initiation and propagation of brittle fracture or lower ductile fracture [31][32][33], the trend and percentage of brittle fracture will increase with increasing in-plane constraint, as described in Sect. 3.2.…”