A new statistical local criterion for cleavage fracture in steel. Part I: model presentation

Bordet, S.R.

doi:10.1016/s0013-7944(04)00087-6

Cited by 9 publications

(14 citation statements)

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“…in a region of high strain and moderate stress. Initiation occurs in these regions when high strains 5,6,7 or strain energy densities 22 are required to crack the second phase particles, rendering particle cracking is the most difficult stage in fracture initiation. In these situations, the scatter in the K Jc data is dominated by the scatter in the locations at which the most-easily cracked particles are found 23 , and a correlation is observed between K Jc and X c .…”

Section: Discussionmentioning

confidence: 99%

The effect of a residual stress field on fracture initiation in RPV steel

Ortner

Lee

Sherry

2011

Fatigue &Amp; Fracture of Engineering Materials &Amp; Structures

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A B S T R A C T Whether flaws in structures containing residual (secondary) stresses will extend under particular operational (primary) loads depends on the extent to which the residual stress field affects: (a) the nature and distribution of initiators; (b) the combined (primary + secondary) stresses and strains experienced by potential initiators. This paper compares fractographic data from specimens loaded by only a primary stress with data from specimens also containing a tensile residual stress field. Three-dimensional elastic-plastic finite element calculations are used to characterize the stress-strain conditions at the initiation sites at the onset of brittle fracture. The introduction of a residual stress changes the dominant stage in fracture nucleation from microcrack extension to particle cracking. This offsets some of the decrease in fracture toughness expected when the residual stress field increases specimen constraint.CT = compact tension specimen E = Young's modulus EDX = energy-dispersive X-ray analysis of composition FE = finite element HT = heat treatment J = contour integral J c = value of J at cleavage K = stress intensity K Jc = stress intensity at specimen failure MVC = ductile microvoid coalescence PCT = pre-loaded compact tension specimen SEM = scanning electron microscope X c = separation of initiation site from pre-crack front (in direction of macroscopic crack growth) Z c = separation from initiation site from mid-line of specimen, in plane normal to loading direction ε 22elastic = elastic portion of ε 22,total ε 22,total = total (elastic+plastic) strain in loading direction, acting on plane normal to loading direction ν = Poisson's σ 22 = principal tensile stress, in loading direction, acting on plane normal to loading direction

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Section: Discussionmentioning

confidence: 99%

The effect of a residual stress field on fracture initiation in RPV steel

Ortner

Lee

Sherry

2011

Fatigue &Amp; Fracture of Engineering Materials &Amp; Structures

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“…This model has been recently amended by one of the authors to include the effect of plastic strain on the nucleation of microcracks and the deactivation of the latter if they are not immediately propagated. 27,35 It is worth mentioning that Beremin originally introduced a strain correction to Eq. (3) to account for the increase of the cleavage stress with strain observed in the steel that they investigated (A508 class 3): it amounted to increase σ u with strain while keeping all other assumptions unchanged, and it therefore differs from the new modifications presented here.…”

Section: Presentation Of the New Cleavage Modelmentioning

confidence: 99%

“…Hence the increment K = 10 MPa √ m is normally valid on the investigated range K wps = 60 to 100 MPa √ m. It is however argued that excessively raising K wps may induce alternative cleavage nucleation mechanisms and thus reduce the toughness benefits following WPS. The new cleavage model, proposed by one of the authors 27,35 , was calibrated from NT tests at −188 • C and toughness test results at −150 • C. In order to account for constraint effects on cleavage initiation, the reference strain ε p,0 was set to different values in the CT and NT geometries. Using local stress and strain measurements to set the values of the threshold cleavage stress σ th and ε p,0 enabled the calibrated model to satisfactorily describe all WPS cycles, although it remained slightly over-conservative.…”

Section: O N C L U S I O Nmentioning

confidence: 99%

Cleavage fracture of RPV steel following warm pre‐stressing: micromechanical analysis and interpretation through a new model

Bordet

Tanguy

Besson

et al. 2006

Fatigue Fract Eng Mat Struct

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A B S T R A C T In this paper, the warm pre-stress (WPS) effect on the cleavage fracture of an 18MND5 (A533B) RPV steel is investigated. This effect, which describes the effective enhancement of the cleavage fracture toughness at low temperature following a prior loading at high temperature, has received great interest in light of its significance in the integrity assessment of structures, such as nuclear pressure vessels, subjected to thermal transients. Several loading cycles between room temperature (RT) and −150 • C are considered: Load-Unload-Cool-Fracture (LUCF), Load-Cool-Fracture (LCF) and Load-Cool with Increasing K-Fracture (LCIKF). All experiments complied with the conservative principle, which states that no fracture will occur if the applied stress intensity factor (SIF) decreases (or is held constant) while the temperature at the crack-tip decreases, even if the fracture toughness of the virgin material is exceeded. The experimental results indicate that an effective WPS effect is present even at small pre-load (K wps = 40 MPa √ m), and that a minimum critical slope (− K / T) in the LCIKF cycle has to be exceeded to induce cleavage fracture between RT and −150 • C. Numerical modelling was performed using mixed isotropic and kinematic hardening laws identified on notched tensile (NT) specimens, tested in tension to large strains (up to 40%), followed by large compressive strains. Detailed microstructural investigations on compact tensile (CT) and NT fracture test specimens were performed so as to determine the nature of the cleavage initiation sites, as well as the local mechanical conditions at fracture. Based on this local information, a new cleavage model was calibrated and applied to predict the probability of cleavage fracture after WPS: it is shown that the predictions are in good agreement with the experimental results.a 0 = crack length in CT toughness specimen (mm) d = distance (mm) K = SIF increment between RT and −150 • C (MPa √ m) (− K/ T) = transient slope of the LICKF cycle between RT and −150 • C (MPa √ m· • C −1 ) K, K el = stress intensity factor (MPa √ m) K frac = stress intensity factor at fracture (MPa √ m) K Ic , K Jc = mode I fracture toughness for the virgin material (MPa √ m)K wps = stress intensity factor after warm pre-stressing (MPa √ m)

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“…The data seem to follow straight lines, but having temperature-dependent slopes. This led Bordet et al 16 to propose a strain correction to the classical local approach model. However, a different interpretation becomes obvious when the data are plotted against stress (Fig.…”

Section: F R a C T U R E O F G R A I N S ( S T E P 2 )mentioning

confidence: 99%

Aspects of cleavage fracture initiation – relative influence of stress and strain

Wallin¹,

Laukkanen²

2006

Fatigue Fract Eng Mat Struct

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A B S T R A C T Cleavage fracture initiation has generally been assumed to be controlled mainly by matrix stress. Recently, several different cleavage fracture models have been proposed, where also strain is included in the failure criterion. However, the proposals have been rather crude and unable to provide clearly improved fracture estimates. Here, the first two steps of cleavage fracture (particle failure and grain fracture) are examined in more detail. It is shown that both stress and strain are important for cleavage fracture initiation, but that strain mainly affects particle failure, whereas grain fracture is controlled by a pure Griffith criterion. The findings are important for the development of new cleavage fracture models and to the proper way of accounting for constraint. B = specimen thickness d = particle diameter d c = critical particle diameter d N = normalization diameter d = mean particle diameter d f = mean fractured particle diameter E = Young's modulus f = volume fraction of particles f (σ ) = stress function K I = stress intensity factor m = Weibull exponent N = number of initiators in volume element N V = average number of initiators in volume element V n = number of volume elements or strain hardening exponent P{d ≥ d 0 } = cumulative particle size distribution P {d /d } = particle size distribution P f = cumulative failure probability P{f} = proportion of fractured particles P{fd} = cumulative fracture probability of a spherical brittle particle of diameter d Pr{I} = cleavage initiation probability Pr{I/0} = conditional probability of cleavage initiation with no prior void initiation Pr{V/0} = probability of not having void initiation P{α} = crack plane angle distribution P{θ} = surface trace angle distribution

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A new statistical local criterion for cleavage fracture in steel. Part I: model presentation

Cited by 9 publications

References 0 publications

The effect of a residual stress field on fracture initiation in RPV steel

The effect of a residual stress field on fracture initiation in RPV steel

Cleavage fracture of RPV steel following warm pre‐stressing: micromechanical analysis and interpretation through a new model

Aspects of cleavage fracture initiation – relative influence of stress and strain

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