A concept of mechanical stability of structural steels

Котречко, С. А.; Meshkov, Yu. Ya.

doi:10.1007/s11223-009-9117-4

Cited by 4 publications

(5 citation statements)

References 21 publications

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“…Therefore a degree of excess of the parameter P ms over a unity specifies a stability level of the metal plastic state in PZ at the given loading conditions (load, temperature, fluence etc.) [9][10][11]. Higher the value of P ms in comparison to a unity, higher the level of stability of plastic state, and, respectively, higher the allowable radiation hardening value for the RPV metal.…”

Section: Theoretical Basicmentioning

confidence: 99%

“…In criterion (3) the local characteristics σ f and σ 11 are used. A transition from local to global parameters was realized in [9][10][11]. Therefore the criterion of fracture initiation may be presented as follows:…”

Section: Theoretical Basicmentioning

confidence: 99%

“…Equation (11) determines the key factors which specify the RPV radiation life time, however, for the engineering application it is reasonable to simplify this criterion by eliminating R MC . As it was shown in [9,10] for the specimen with a crack the value q σ numerically equal to K ms at the critical temperature, T c , when fracture occurs at the specified stress K I .…”

Section: Theoretical Basicmentioning

confidence: 99%

“…Substituting ( 12) to (11) with account of the invariance of R MC to irradiation dose and equation (9) gives:…”

Section: Theoretical Basicmentioning

confidence: 99%

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Mechanical stability paradigm for prediction of rpv service life

Kotrechko,

Meshkov,

Nekludov

et al. 2012

Preprint

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In the framework of the engineering version of a Local approach to fracture the criterion of a fracture limit of RPV with crack-like flaw is derived. It has been shown that the level of ductile state stability (mechanical stability) of metal ahead of a crack governs the value of critical fluence. On this basis, the new paradigm of life-time prediction using the condition of exhaustion of mechanical stability of irradiated PV metal has been proposed. The technique of an end-of-life fluence assessment is developed, and predictive capabilities of this approach are demonstrated by the example of WWER-1000 pressure vessels.

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Section: Theoretical Basicmentioning

confidence: 99%

Section: Theoretical Basicmentioning

confidence: 99%

Section: Theoretical Basicmentioning

confidence: 99%

“…Substituting ( 12) to (11) with account of the invariance of R MC to irradiation dose and equation (9) gives:…”

Section: Theoretical Basicmentioning

confidence: 99%

See 2 more Smart Citations

Mechanical stability paradigm for prediction of rpv service life

Kotrechko,

Meshkov,

Nekludov

et al. 2012

Preprint

View full text Add to dashboard Cite

show abstract

“…References [3,4] present in detail the physical fundamentals of the mechanical stability concept. However, to get the substance of this concept clear, it is sufficient to analyze the simplified tensile strain hardening diagram for metal (Fig.…”

Section: Mechanical Stability -A Measure Of the Resistance Of Metal Tmentioning

confidence: 99%

Ductility and cold resistance of structural steels

2010

Self Cite

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and A. V. ShiyanThe interrelation between ductility and cold resistance characteristics is considered, as which can be established by using a special characteristic, mechanical stability coefficient (a universal measure of the resistance of metal to ductile-brittle transition). It has been found that ductility cannot ensure the required brittle fracture resistance of metal, but only creates prerequisites for the attainment of the required mechanical stability. A condition for high mechanical stability is a wide stress range between the current strength of metal and brittle rupture strength.1. Formulation of the Problem. Strength and ductility are primary mechanical properties of metal alloys, ductility (in combination with strength) giving the metal one more property, toughness, which provides for it brittle fracture resistance under the action of such embrittlement factors as notches, cracks, dynamic loading and operating temperature decrease. In the last case, the low-temperature embrittlement resistance of alloy characterizes its cold resistance. However, in the modern science of the mechanical properties of structural alloys there is no clear under-standing of how ductility (ψ is reduction of area at fracture) affects cold resistance, i.e., how the required toughness can be retained at extreme climatic temperatures, i.e., at temperatures that are lower by 100°C than room temperatures (T r ) (ΔT T T r c = − , where T c is the critical ductile-brittle transition temperature of metal according to the accepted brittleness criterion). Thus the object is to find out in what measure ductility ψ affects in rupture tests cold resistance ΔT c , which is determined, e.g., in serial Charpy impact tests according to the existing brittleness criteria. To achieve the object in view, a special characteristic must be introduced into consideration, which combines two properties: strength and ductility, i.e., just the properties which actually determine unit rupture work or impact toughness. This characteristic is mechanical stability coefficient K ms , proposed in [1-4]. Mechanical Stability -a Measure of the Resistance of Metal to Ductile-Brittle Transition.References [3,4] present in detail the physical fundamentals of the mechanical stability concept. However, to get the substance of this concept clear, it is sufficient to analyze the simplified tensile strain hardening diagram for metal (Fig. 1).The reserve of metal ductility under uniaxial tension is described not only by the characteristic ψ, but also (with allowance for strain-hardening exponent n) by the ratio of two force characteristics of the diagram: S k σ 0 2 . . Although this correlation between the strength ratio S k σ 0 2 . and ductility ψ (via the exponent n), which is obvious for uniaxial tension, is not of great interest, the above idea proves to be useful for the analysis of more complex fracture conditions in a local region (notch apex or crack tip).In the ductile zone under the notch, the smallest value of the brittle strength of metal R mc [5, 6], but no...

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Modeling of the phenomenon of brittle-plastic transition by the method of dislocation dynamics

Borysovska¹

2022

Usp. materiаlozn.

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Computer modeling by the DD method is based on the Rice and Thompson model, according to which the force reliefnear the crack tip is created by three forces: an external load, an image force acting on dislocations from the free surfaces, and a resistance force from the crystal lattice. The interaction between dislocations in the plastic zone is calculated step by step. At each step, the stress is calculated for all dislocations in the ensemble and the velocities and corresponding new positions are calculated. Computer calculations make it possible to predict the impact of dislocation ensemble shielding on the current value of the stress intensity factor. The calculated value of crack resistance was determined under the condition of reaching the critical value of the stress intensity coefficient of the brittle material at the crack head. The effect of temperature and strain rate on the viscous-brittle transition in polycrystalline molybdenum was modeled using the dislocation dynamics method. From the results of the calculations, it follows that when the test temperature changes, the size of the plastic zone increases by more than an order of magnitude. As the loading rate decreases, the abnormal increase in crack resistance shifts to smaller grain sizes. This effect is significantly smaller than the effect of temperature. Changing the parameters of the model does not change the general mechanism of the viscous-brittle transition, which is associated with the peculiarities of the interaction of dislocations in the plastic zone with grain boundaries in polycrystalline molybdenum. Regardless of the speed of loading and the temperature of the tests, three characteristic ranges of grain sizes can be distinguished: With large grains, the fracture toughness remains unchanged because the size of the plastic zone is much smaller than the grain size. With the average grain size, a dislocation cluster is formed near the boundary, grain boundary sources begin to work in the neighboring grain, forming a small number of dislocations there, which contributes to a slight increase in crack resistance. With a small grain size, the fracture toughness begins to increase rapidly, since the plastic zone covers several grains. The dislocation cluster moves to the top of the crack and screens its propagation. Keywords: phenomenon of brittle-plastic transition, dislocation clustering, dislocation dynamics.

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A concept of mechanical stability of structural steels

Cited by 4 publications

References 21 publications

Mechanical stability paradigm for prediction of rpv service life

Mechanical stability paradigm for prediction of rpv service life

Ductility and cold resistance of structural steels

Modeling of the phenomenon of brittle-plastic transition by the method of dislocation dynamics

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