Cleavage Fracture of Ultra-High-Strength Steels. Microscopic Observations. Numerical Analysis. Local Fracture Criterion

Abstract

In the paper the fracture mechanisms in ultra-high-strength steel are examined. However, the emphasis is on cleavage fracture, which was observed in the whole temperature range tested. The extent of cleavage depends on the specimen thickness and temperature. The experimental program consisted of tensile and fracture tests and was followed by scanning microscope observations of the fracture surfaces. Then, a full 3D elastic-plastic finite element analysis was carried out assuming finite strains. The numerical results support the postulate that the onset of cleavage jump is observed when the maximum opening stresses become higher than the critical value (the material property at a given temperature) over a distance greater than the critical value (material property independent of temperature). A discussion of so-called 3D stress parameters is presented.

The influence of the out-of- and in-plane constraint on fracture toughness of high strength steel in the ductile to brittle transition temperature range

“…The model was proposed (Eq. 4) for cleavage fracture and was based on the results of earlier studies [14], [15], [16]. Furthermore, an empirical formula was proposed (Eq.…”

“…2) for this purpose. The physical reason for this selection was a criterion of cleavage fracture proposed in [14] and experimentally verified in [15] and [16]. The criterion was based on two quantities: the critical stress and the critical length.…”

“…The parameter φ denotes the normalised by J/σ 0 distance from the crack tip, and σ C is the critical stress (see Table 1). The values for the critical stresses were computed in [16]. Coefficient β establishes the value of the σ 22 stress at the crack tip, which was computed numerically.…”

Analysis of Stress and Strain Fields in and around Inclusions of Various Shapes in a Cylindrical Specimen Loaded in Tension

“…In another report [20], the critical stress for Hardox-400 steel was estimated to be 3200 MPa. This level of stress was never reached in our numerical analysis.…”

Application of modified Ritchie-Knott-Rice criterion to cellular automata

“…The main idea of this criterion is that the opening stress (assuming finite strain) should exceed the critical value on a sufficiently large area (or length for two-dimensional cases) in front of a crack to initiate cleavage fracture. In previous analyses (Neimitz et al, 2014), the critical length, where stresses reached the required level, was determined as well as the critical stress values for each analysed temperature. However, the critical stress values were estimated for plane strain conditions; therefore, for a three-dimensional analysis they should be adjusted because in this case, the stress must exceed the critical value within the surface (Fig.…”