Aspect ratio and stochastic effects in the plasticity of uniformly loaded micrometer-sized specimens

Senger, J.; Weygand, D.; Motz, Christian; Gumbsch, Peter; Kraft, O.

doi:10.1016/j.actamat.2011.01.034

Cited by 38 publications

(38 citation statements)

References 58 publications

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“…Table 1 gives an overview of the data base for the evaluation. The number of configurations per size is chosen according to the outer dimension: The smaller the outer dimension, the more samples were simulated, since smaller samples are subjected to a higher statistical variation [13,27,28]. All reported samples are loaded to a total strain of e tot ¼ 0:5% and all values of d ffiffiffi ffi q p are measured at this point.…”

Section: Resultsmentioning

confidence: 99%

“…Therefore preexisting FR sources are activated more easily, due to their persistent nature, and contribute more to the overall plastic slip. The first type of initial configuration (i) has been included since it is a known way of initializing DDD samples [27][28][29][30][31].…”

Section: Discussionmentioning

confidence: 99%

“…All micropillars have an aspect ratio of 3 and a square cross-section of side length d with the long axis along the tensile direction to reduce the influence of the displacement controlled boundaries at the top and bottom [27]. The chosen side lengths d are 0:5; 1:0; 1:5 and 2:0 lm.…”

Section: Method/setupmentioning

confidence: 99%

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Dislocation multiplication mechanisms – Glissile junctions and their role on the plastic deformation at the microscale

Stricker

Weygand

2015

Acta Materialia

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Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

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Dislocation multiplication mechanisms – Glissile junctions and their role on the plastic deformation at the microscale

Stricker

Weygand

2015

Acta Materialia

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“…3 In general, a conventional nanoindenter with a flat-end tip is used to compress the pillar samples and facilitates the measurement of the load-displacement and hence the stress-strain curves of materials for pillar sizes ranging from several micrometers to sizes as small as 300 nm in diameter. 4,5 Indeed, it was demonstrated in several experimental 6 and computational [7][8][9][10] studies that the mechanical strength of single crystalline metallic pillars is directly related to the pillar diameter and the initial dislocation structures.…”

Section: Introductionmentioning

confidence: 99%

Mechanical assessment of ultrafine-grained nickel by microcompression experiment and finite element simulation

et al. 2011

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Over the past two decades, nanoindentation has been the most versatile method for mechanical testing at small length scales. Because of large strain gradients, it does not allow for a straightforward identification of material parameters such as yield and tensile strength, though. This represents a major drawback and has led to the development of alternative microscale testing techniques with microcompression as one of the most popular ones today. In this research, the influence of the realistic sample configuration and unavoidable variations in the experimental conditions is studied systematically by combing in-situ microcompression experiments on ultrafine-grained nickel and finite element simulations. It will be demonstrated that neither qualitative let alone quantitative analyses are as straightforward as they may appear, which diminishes the apparent advantages of microcompression testing.

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“…One approach to model the rather complex phenomena caused by the collective motion of dislocations is the numerical solution of the equation of motion of individual dislocations called discrete dislocation dynamics (DDD). During the past decades numerous DDD simulation algorithms have been developed both in 2 [7][8][9][10][11][12][13][14][15][16][17] and 3 [18][19][20][21][22] dimensions, allowing to study problems like hardening [14,18,20], size effect [15,[21][22][23][24], jamming-flowing transition [10,25], relaxation [17] dislocation avalanches [9,16,26], etc.…”

mentioning

confidence: 99%

Scale-Free Phase Field Theory of Dislocations

2015

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According to recent experimental and numerical investigations if the characteristic size of a specimen is in the submicron size regime several new interesting phenomena emerge during the deformation of the samples. Since in such a systems the boundaries play a crucial role, to model the plastic response of submicron sized crystals it is crucial to determine the dislocation distribution near the boundaries. In this paper a phase field type of continuum theory of the time evolution of an ensemble of parallel edge dislocations with identical Burgers vectors, corresponding to the dislocation geometry near boundaries, is presented. Since the dislocation-dislocation interaction is scale free (1/r), apart from the average dislocation spacing the theory cannot contain any length scale parameter. As shown, the continuum theory suggested is able to recover the dislocation distribution near boundaries obtained by discrete dislocation dynamics simulations. One may expect, however, that for a large number of problems not all the details accounted by DDD simulations are important, the response of the dislocation network can be well described on a continuum level. Although several such continuum theories of dislocations have been developed, [27-37] most of them correspond either to mean field approximation or are based on completely phenomenological grounds. However, the role of dislocation-dislocation correlation, crucial because of the long range nature of dislocation-dislocation interaction, is far from understood. Correlation effects are taken into account in a systematic manner only in the limit when the signed dislocation density κ (geometrically necessary dislocation (GND) density) is much smaller than the stored density ρ. [38][39][40][41][42].With the advance of nanotechnology the characteristic size of the microstructure of crystalline materials reduced to the submicron level. As a consequence, the role of boundaries (sample surface, grain boundary, etc.) has become even more important than earlier. So, to model the plastic response of samples with features on the submicron scale it is crucial to determine the dislocation distribution near the boundaries. Close to a boundary the GND density is often comparable to the stored one, so the assumption |κ| ρ is not valid. The dislocation distribution near a boundary is traditionally described by the 1D pile-up of the dislocations [43]. For many real dislocation configurations, however, the interaction between dislocations in different slip planes is important requiring to go up to modeling in minimum of 2D. In this paper a phase field type theory is suggested for the simplest possible 2D dislocation arrangement consisting of straight parallel dislocations with single slip. The evolution equations of the dislocation densities are obtained from a functional of the dislocation densities and the stress potential. In contrast to other approaches suggested recently, where a set of walls of dislocations with equidistant slip distances is considered to model the dislocation config...

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Aspect ratio and stochastic effects in the plasticity of uniformly loaded micrometer-sized specimens

Cited by 38 publications

References 58 publications

Dislocation multiplication mechanisms – Glissile junctions and their role on the plastic deformation at the microscale

Dislocation multiplication mechanisms – Glissile junctions and their role on the plastic deformation at the microscale

Mechanical assessment of ultrafine-grained nickel by microcompression experiment and finite element simulation

Scale-Free Phase Field Theory of Dislocations

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