Fundamental aspects of dislocation theory

Simmons, John A.; Wit, R. de; Bullough, R.

doi:10.6028/nbs.sp.317v1

Cited by 117 publications

(45 citation statements)

References 12 publications

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“…Finally, we need to comment on earlier, similar works that have analyzed the stability of dislocations at high velocities: Our result disagrees with the earlier assessment of ref. [45] (see also [46]), whose author found that screw dislocations become unstable at high velocities whereas edge dislocations remain stable. On the other hand, our results are in perfect agreement with ref.…”

Section: Line Tension and Stabilitymentioning

confidence: 99%

Line tension of a dislocation moving through an anisotropic crystal

Blaschke

Szajewski

2018

Philosophical Magazine

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Plastic deformation, at all strain rates, is accommodated by the collective motion of crystalline defects known as dislocations. Here, we extend an analysis for the energetic stability of a straight dislocation, the so-called line tension (Γ), to steady-state moving dislocations within elastically anisotropic media.Upon simplification to isotropy, our model reduces to an explicit analytical form yielding insight into the behavior of Γ with increasing velocity. We find that at the first shear wave speed within an isotropic solid, the screw dislocation line tension diverges positively indicating infinite stability. The edge dislocation line tension, on the other hand, changes sign at approximately 80% of the first shear wave speed, and subsequently diverges negatively indicating that the straight configuration is energetically unstable.In anisotropic crystals, the dependence of Γ on the dislocation velocity is significantly more complex; At velocities approaching the first shear wave speed within the plane of the crystal defined by the dislocation line, Γ tends to diverge, with the sign of the divergence strongly dependent on both the elastic properties of the crystal, and the orientation of the dislocation line. We interpret our analyses within the context of recent molecular dynamics simulations (MD) of the motion of dislocations near the first shear wave speed. Both the simulations and our analyses are indicative of instabilities of nominally edge dislocations within fcc crystals approaching the first shear wave speed. We apply our analyses towards predicting the behavior of dislocations within bcc crystals in the vicinity of the first shear wave speed.

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Section: Line Tension and Stabilitymentioning

confidence: 99%

Line tension of a dislocation moving through an anisotropic crystal

Blaschke

Szajewski

2018

Philosophical Magazine

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“…The total stress field and the total distortion field can be decoupled according to [16] a (lid = Oij q-Old a B, = ~, + fi;;;…”

Section: 2)mentioning

confidence: 99%

Description of loadings and screenings of cracks with the aid of universal weight functions

Kirchner

1986

Int J Fract

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The stress intensity vector K i is defined as the limiting behaviour of the stress near the tip of a crack, the stress components being proportional to r-1/2 for any external loading. Internal stresses caused by dislocations show the same power dependence at the crack tip; the stress intensity associated with a loading can thus be screened (or amplified) by a plastic zone. Since for any particular specimen and crack geometry the stress intensity vector must be a functional of the loading and screening which are of vectorial character (lines of forces fi or dislocations with a Burgers vector bi) one can define two tensorial weight functions, one for screenings, Dsi(x, a), and one for forces, F~i(x, a), so that the stress intensity K s can be found by integration over the product of weight functions and dislocation or force density. In order to find the weight functions the displacement field and the Airy stress vector must be known for some, completely arbitrary, loading or screening.

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“…The dislocations must be extended into partials, more widely separated in this met~ than in Cu, and thus their climb is difficult, as postulated by Seeger [7,8]. [29] 14.17 -+ 2.13 Englert, Tompa and 70 BuUough (1970) [30] Stobb and Sworn (1971) [31] 41 These conclusions lead to two hypotheses about the mechanism of polygonization of the metals in study:…”

Section: Influence Of Impurities In Polygonization Of F C C Metals Of...mentioning

confidence: 91%