Forces on high velocity dislocations

Hirth, J. P.; Zbib, Hussein M.; Lothe, J.

doi:10.1088/0965-0393/6/2/006

Cited by 105 publications

(69 citation statements)

References 9 publications

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“…When the dislocation is moving with a velocity v d , an apparent flow relative to the dislocation has to be added to the flux equation [24][25][26][27] and beyond a critical value of the dislocation velocity m c , defined by…”

Section: Macroscopic Mechanical Behavior and Viscous Dislocation Glidementioning

confidence: 99%

Deformation and reconstruction mechanisms in coarse-grained superplastic Al–Mg alloys

2006

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This paper concentrates on the superplastic response of fine-grained and coarse-grained Al-Mg alloys under uniaxial tension. To identify the main characteristics of superplastic deformation and to determine the optimum deformation parameters, the microstructure and dislocation substructure of the alloys are analyzed as a function of strain, strain rate and temperature using electron backscatter diffraction and transmission electron microscopy (TEM). Under optimum deformation conditions of temperature and strain rate, these Al-Mg alloys have an elongation to failure in excess of 300%. Dynamic recrystallization is dominant at strain rates in excess of 10 À1 s À1 and results in a strong coarsening of the microstructure and premature failure. Dynamic recovery prevails at a strain rate of around 10 À2 s À1 , leading to great enhancement of the plasticity of the coarse-grained materials. TEM observations show that subgrain formation proceeds slowly. During initial straining, subgrains are formed primarily along the original grain boundaries. This results in a ''core and mantle'' microstructure, with dynamic recovery mainly taking place in the mantle region. A uniform substructure is established at a strain of the order of 1.

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Section: Macroscopic Mechanical Behavior and Viscous Dislocation Glidementioning

confidence: 99%

Deformation and reconstruction mechanisms in coarse-grained superplastic Al–Mg alloys

2006

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“…Hirth et al [28] introduced a scheme to treat dislocation dynamics beyond the quasi-static approximation in the sense that the radiation of energy by an accelerating dislocation was considered to confer on the dislocation an effective mass and an inertial force. Zbib et al [29] incorporated the relativistic mass of Hirth et al [28] in their method of three-dimensional DDD, which was further expanded by Zbib & Diaz de la Rubia [30].…”

Section: Introduction (A) Plasticity and Dislocation Dynamicsmentioning

confidence: 99%

“…Zbib et al [29] incorporated the relativistic mass of Hirth et al [28] in their method of three-dimensional DDD, which was further expanded by Zbib & Diaz de la Rubia [30]. This method has been used in a number of studies of high strain rate and shock loading plasticity, such as those by Shehadeh et al [31] and Shehadeh [32], who have investigated the effects of strain rate, nucleation mechanisms and shock front rise times over different crystalline structures.…”

Section: Introduction (A) Plasticity and Dislocation Dynamicsmentioning

confidence: 99%

A dynamic discrete dislocation plasticity method for the simulation of plastic relaxation under shock loading

et al. 2013

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“…The mobility law of dislocations is adjusted to account for the likely presence of high speed dislocations [1,18,21,[23][24][25][26][27][28]; data about the mobility of dislocations is extracted from MD simulations of aluminum [22] (see Supplementary Materials).…”

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Attenuation of the Dynamic Yield Point of Shocked Aluminum Using Elastodynamic Simulations of Dislocation Dynamics

et al. 2015

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When a metal is subjected to extremely rapid compression, a shock wave is launched that generates dislocations as it propagates. The shock wave evolves into a characteristic two-wave structure, with an elastic wave preceding a plastic front. It has been known for more than six decades that the amplitude of the elastic wave decays the further it travels into the metal: this is known as "the decay of the elastic precursor". The amplitude of the elastic precursor is a dynamic yield point because it marks the transition from elastic to plastic behaviour. In this letter we provide a full explanation of this attenuation using the first method of dislocation dynamics to treat the time dependence of the elastic fields of dislocations explicitly. We show that the decay of the elastic precursor is a result of the interference of the elastic shock wave with elastic waves emanating from dislocations nucleated in the shock front. Our simulations reproduce quantitatively recent experiments on the decay of the elastic precursor in aluminum, and its dependence on strain rate.The dynamic behaviour of crystalline solids subjected to shock compression plays a central role in diverse applications, including bird strikes in aerospace [1], crashworthiness in the automobile industry [2], and manufacturing processes such as laser shock peening [3], amongst many others. Upon being shocked within a range of strain rates and pressures of typically 10 6 − 10 10 s −1 and 5 − 50GPa [1], the shock front in crystalline materials often displays a characteristic two-wave structure near the loading surface: the plastic wave front leading to the Hugoniot shocked state is preceded by an elastic precursor wave [1]. The amplitude of the elastic precursor wave decays as the wave front advances[1, 4]-a phenomenon known as the 'decay of the elastic precursor'. The amplitude of the elastic wave marks the onset of plasticity, i.e. it is the dynamic yield point. The subsequent plastic wave is commonly ascribed to the generation and motion of dislocations, the agents of plasticity in crystalline solids [9].The cause of its attenuation remains unclear after six decades [4][5][6][7][8]. Clifton and Markenscoff [4] calculated analytically the amplitude attenuation of a planar elastic shock wave caused by the destructive interference of elastic wavelets emanating from pre-existing dislocations set into motion by the passage of a shock wave of infinite strain rate; dislocation generation by the shock was neglected. Consequently, the elastic precursor decay was attributed to the density and initial velocity of pre-existing dislocations. Armstrong et al.[10] studied the dislocation relaxation mechanisms during high strain rate shock loading, concluding that dislocation generation dominates plastic relaxation under shock loading. This is because the number of pre-existing dislocations is about two to three orders of magnitude less than that generated during the shock [1,4,7].In this letter we show that we can account for the experimentally observed residual disloca...

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Forces on high velocity dislocations

Cited by 105 publications

References 9 publications

Deformation and reconstruction mechanisms in coarse-grained superplastic Al–Mg alloys

Deformation and reconstruction mechanisms in coarse-grained superplastic Al–Mg alloys

A dynamic discrete dislocation plasticity method for the simulation of plastic relaxation under shock loading

Attenuation of the Dynamic Yield Point of Shocked Aluminum Using Elastodynamic Simulations of Dislocation Dynamics

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