Micromechanics of cleavage fracture initiation in ferritic steels by carbide cracking

Kroon, Martin; Faleskog, Jonas

doi:10.1016/j.jmps.2004.05.008

Cited by 67 publications

(33 citation statements)

References 39 publications

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“…It is now commonly accepted that, in ferritic steels, the origin of such micro-cracks is the rupturing of second-phase particles, predominantly carbides [1][2][3][4]. The particles present in steels differ in type, size and are distributed randomly in the volume [5]. These are typically elastic-brittle and, according to the current understanding, can rupture when overloaded by the plastically deforming matrix [1,2].…”

Section: Introductionmentioning

confidence: 99%

Cleavage Fracture Modelling for RPV Steels: Discrete Model for Collective Behaviour of Micro-Cracks

Abu-Muharib

Jivkov

James³

et al. 2013

Volume 6B: Materials and Fabrication

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The ability to predict variations in cleavage fracture toughness behaviour of ferritic RPV steels, accounting for the effects of irradiation and defect geometry, is vital to safety assessment and life extension decisions. Local approaches to cleavage fracture offer a promising methodology to accomplish such calculations. However, the limited progress achieved by improving the local failure probability expression suggests that the methodology for calculating global cleavage might not be adequately representing real material. The basis for the existing methodology is the weakest-link assumption that all individual failure events are independent and non-interacting. Here an approach is considered which utilises a microstructure-informed model incorporating the experimental knowledge needed to postulate deterministic criteria for particle rupture and micro-crack propagation, whilst accounting for the probabilistic distribution of particle sizes. This is then used in a lattice model that can help detail the evolution of the formation of micro-cracks on global failure, therefore inferring the suitability of the weakest-link assumption. Predicting the probability of cleavage fracture requires such models, as the macroscopic cleavage phenomenon is governed by a number of micro-structural features.The material microstructure is represented by a regular lattice of truncated octahedral cells forming a computational sitebond model, with sites located at the cell centres and connected by two distinct sets of bonds. These bonds are modelled with structural beam elements, which represent all the possible relative deformations between coordinated sites. Particles of various sizes are distributed in the bonds, based on an experimentally determined distribution of cleavage initiating particles in RPV steel (Euro Material A). Although only elastic deformations are considered here, the results demonstrate that the interactions between individual failure events could potentially have a strong effect on the way global failure is reached.Nucleation of micro-cracks by rupturing second-phase particles affects their subsequent formation. In particular, it was found that once formed there is a reduced probability of further development of micro-cracks at particles outside the crack planes and an enhanced probability of formation at particles along the crack planes. This will therefore influence the distribution of micro-crack sizes that could in principle be used to calculate the global probability of failure, and could lead to substantially different distributions of particle sizes, then used in the current local approach methods.

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Section: Introductionmentioning

confidence: 99%

Cleavage Fracture Modelling for RPV Steels: Discrete Model for Collective Behaviour of Micro-Cracks

Abu-Muharib

Jivkov

James³

et al. 2013

Volume 6B: Materials and Fabrication

View full text Add to dashboard Cite

show abstract

“…Therefore, cleavage fracture has been intensively investigated. Many researchers (1)- (6) discuss cleavage fracture from various aspects. Stroh (1), (2) proposed formation of a cleavage crack by coalescence of planar edge dislocations piled up by a barrier.…”

Section: Introductionmentioning

confidence: 99%

“…Chen and Wang (5) also observed the similar change in the critical event when the loading rate was increased. Recently, Kroon and Faleskog (6) carried out numerical analysis on cleavage fracture initiation from a carbide crack to examine plastic rate-sensitivity, carbide shape, and stress triaxiality. In this analysis, finite element method was used to simulate cleavage crack propagation.…”

Section: Introductionmentioning

confidence: 99%

Experimental and Discrete Dislocation Dynamics Approach to Initiation of Cleavage Fracture under Short Pulse Loads

Tran

Homma

2009

JMMP

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Mode I crack initiation properties under stress intensity pulses with durations of 25, 50 and 100 µs are investigated by experiment and discrete dislocation dynamics. The cleavage fracture initiation is examined under the consideration of the pile-up of dislocations against an obstacle ahead of the crack tip and the coalescence of piled-up dislocations. In the experiment, under very short pulse loads with the duration of less than 50 µs, the dynamic fracture toughness, K Id remarkably increases and the crack tip opening displacement is closely correlated with K Id . The numerical results are compared with the experimental ones in reasonable agreement.

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“…Finally, the microcrack must propagate into consecutive grains (iii) to link with or create a new macroscopic crack. Kroon and Faleskog (2005) examined step (ii) numerically and show that a microcrack can be arrested at or near the interface between the particle and the surrounding material, i.e. typically before a grain boundary is encountered.…”

Section: Introductionmentioning

confidence: 99%

“…Plastic rate sensitivity is such a material property, since it changes significantly in the DBT region (Campbell and Ferguson 1970;Klopp et al 1985). Kroon and Faleskog (2005) examine the influence of plastic rate sensitivity on step (ii) and show that the critical stress required to propagate a cleavage microcrack that nucleates from a cracking of a particle of a certain size, increases with temperature in the DBT region.…”

Section: Introductionmentioning

confidence: 99%

Influence of grain size on arrest of a dynamically propagating cleavage crack in ferritic steels—micromechanics

Stec

Faleskog

2009

Int J Fract

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Cleavage fracture in ferritic steels is controlled by several critical steps. First a microcrack must nucleate, grow and overcome barriers, such as grain boundaries. The latter is examined here by use of a periodic, axisymmetric model representing two grains. A microcrack nucleated at the center in one grain is driven by a constant remotely applied stress towards the second grain. The cleavage planes of the grain in which the microcrack is nucleated coincide with the principal loading direction. In the adjacent grain, due to misalignment in possible cleavage planes, the propagation direction changes and separation occurs in mixed mode, involving both normal and shear separations. The temperature dependence of the mechanical properties of the material is accounted for by use of a temperature dependent elasto viscoplastic material model. The largest grain size that can arrest a rapidly propagating microcrack is defined as the critical grain size. The effects of stress state and temperature on the critical grain size are examined. The influence of mismatch in lattice orientation between two adjacent grains in terms of a tilt angle is both qualitatively and quantitatively described. It is shown that the critical grain size is influenced by plastic geometry change and prestraining, which depend on the applied stress state. The results also show that a microcrack can be arrested in an adjacent grain under specific conditions. M. Stec · J. Faleskog (B) KTH Engineering Sciences, Solid Mechanics, Royal

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Micromechanics of cleavage fracture initiation in ferritic steels by carbide cracking

Cited by 67 publications

References 39 publications

Cleavage Fracture Modelling for RPV Steels: Discrete Model for Collective Behaviour of Micro-Cracks

Cleavage Fracture Modelling for RPV Steels: Discrete Model for Collective Behaviour of Micro-Cracks

Experimental and Discrete Dislocation Dynamics Approach to Initiation of Cleavage Fracture under Short Pulse Loads

Influence of grain size on arrest of a dynamically propagating cleavage crack in ferritic steels—micromechanics

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