Brittle fracture in structural steels: perspectives at different size-scales

Abstract

This paper describes characteristics of transgranular cleavage fracture in structural steel, viewed at different size-scales. Initially, consideration is given to structures and the service duty to which they are exposed at the macroscale, highlighting failure by plastic collapse and failure by brittle fracture. This is followed by sections describing the use of fracture mechanics and materials testing in carryingout assessments of structural integrity. Attention then focuses on the microscale, explaining how values of the local fracture stress in notched bars or of fracture toughness in pre-cracked test-pieces are related to features of the microstructure: carbide thicknesses in wrought material; the sizes of oxide/silicate inclusions in weld metals. Effects of a microstructure that is 'heterogeneous' at the mesoscale are treated briefly, with respect to the extraction of test-pieces from thick sections and to extrapolations of data to low failure probabilities. The values of local fracture stress may be used to infer a local 'work-of-fracture' that is found experimentally to be a few times greater than that of two free surfaces. Reasons for this are discussed in the conclusion section on nano-scale events. It is suggested that, ahead of a sharp crack, it is necessary to increase the compliance by a cooperative movement of atoms (involving extra work) to allow the crack-tip bond to displace sufficiently for the energy of attraction between the atoms to reduce to zero.

A review of probabilistic structural integrity assessment in the nuclear sector and possible future directions

“…The potential modes of failure can be divided into those which cause failure on the net cross section such as plastic collapse, bending, buckling, torsion, and shear as well as those which cause failure by progressive growth of a crack, that is, creep, fatigue, environmental effects (e.g., oxidation, carburization, irradiation, and hydrogen embrittlement), and fracture. 18,19 Probabilistic structural analysis, also referred to as structural reliability analysis, can be categorized into three levels 20 ; see below and Table 1. These levels may be used in general cases where the limit state function is more complex than the simple linear form in Equation 1.…”

Investigation of the size of the fracture process zone and the cleavage stress in cracked steel parts

“…However, the problem is still current today in many facilities operating under severe climatic conditions. [1][2][3] The study and prediction of the strength of solids with cracks are performed using the methods of fracture mechanics. Nonlinear fracture mechanics deals with the effects of plastic material properties on the fracture toughness of parts and structures.…”

“…Improvements in steel quality and the development of structural technologies alleviated the severity of the situation. However, the problem is still current today in many facilities operating under severe climatic conditions 1–3 …”

Increasing Low-Temperature Toughness of 09Mn2Si Steel through Lamellar Structuring by Helical Rolling

“…Aspects related to the possibility of strength increasing with toughness retention (strength vs. toughness or hardness vs. ductility) for materials of various classes are discussed in a large number of papers (for example [21,22]) using the concepts of fracture mechanics. In [23], transcrystalline fracture patterns are shown from the perspective of various scale levels as applied to structural steels. At the micro-level, it is proposed to use local fracture stress values to assess the local "work-of-fracture" parameter.…”