Source: https://nuclear-power-engineering.ru/en/article/2017/04/10/
Timestamp: 2019-04-22 00:11:23+00:00

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Konobeev Yu.V. Pechenkin V.A. Garner F.A.
A conventional approach for estimating the yield strength consists in calculation of a critical shear stress for bowing out of gliding dislocation segments between barriers. According to Orovan theory, the critical shear stress τk is determined by the average distance l between obstacles: τk = αGb / l, where α is the constant; G is the shear module; b is the Burgers vector.The superposition of various barriers is taken into account as additive of different contributions τk = τ1 + τ2 + τ3 + …, or as τk2= τ12+ τ22+ τ32+ … . Both procedures have yet no theoretical ground. On the basis of the maximum shear stress concept, the critical shear stress τk in polycrystals is related to the tensile yield strength σy as follows: σy = 2τk (Tresca criterion). On the basis of the effective stress concept this relationship has well known form: σy = (√3)τk (Mises criterion). Sometimes the Taylor criterion is used, according to which σy = 3.06τk. In the present paper an another method of calculating the yield strength of metals and alloys is proposed. The energy condition of plasticity (Mises criterion) is used. According to this condition the plastic flow of a material occurs when the deformation potential energy which is proportional to the square of the effective stress σeff , reaches a certain limiting value proportional to the square of the yield stress σy under uniaxial tension.
In this paper, it is assumed that for the onset of plastic flow the specific potential energy of deformation caused by external forces should exceed the limiting value equal to the potential energy of deformation created by all microstructure defects (dislocations, dislocation loops, voids, precipitates, etc.). Such an approach allows to calculate barrier strengthening coefficients α. Also, according to this approach the total yield stress is equal to the square root of the sum of yield stress squares for different types of crystal defects («geometric superposition of strengthening barriers contributions»).
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