Geometrically necessary dislocation density measurements at a grain boundary due to wedge indentation into an aluminum bicrystal

Dahlberg, Carl F. O.; Saito, Yuki; Oztop, M.S.; Kysar, Jeffrey W.

doi:10.1016/j.jmps.2017.05.005

Cited by 35 publications

(18 citation statements)

References 65 publications

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“…To overcome this limitation, Aifantis (1984) has proposed in a pioneering work a strain gradient plasticity (SGP) model with a single internal length scale parameter embedded in the conventional plasticity theory. This model is capable of predicting plastic deformation gradients (plastic inhomogeneities), which correlate with size effects as experimentally observed and numerically predicted using dislocation mechanics (Zhou and Lesar, 2012;Dahlberg et al, 2017;Jiang et al, 2019). Plastic deformation gradients can physically be interpreted because they represent the geometrically necessary dislocations (GNDs; Ashby, 1970), which are associated with small scale crystalline incompatibilities (e.g., incompatibility of the mesoscopic plastic distortion).…”

Section: Introductionmentioning

confidence: 86%

“…In the size range between hundreds of nanometers and few tens of micrometers, the strength of materials is no longer scale-independent and the peculiar phenomenon "smaller is stronger" appears. This phenomenon has been revealed by several small scale experiments, such as micro-indentation (Ma et al, 2012;Sarac et al, 2016;Dahlberg et al, 2017), micro-bending of thin foils (Hayashi et al, 2011) and torsion of thin wires (Liu et al, 2013). Conventional plasticity theories cannot predict the size-dependent behavior of materials, due to lacking internal length scale(s).…”

Section: Introductionmentioning

confidence: 99%

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Strain gradient crystal plasticity model based on generalized non-quadratic defect energy and uncoupled dissipation

Jebahi

Cai

Abed‐Meraim

2020

International Journal of Plasticity

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The present paper proposes a flexible Gurtin-type strain gradient crystal plasticity (SGCP) model based on generalized non-quadratic defect energy and uncoupled constitutive assumption for dissipative processes. A power-law defect energy, with adjustable order-controlling index n, is proposed to provide a comprehensive investigation into the energetic length scale effects under proportional and non-proportional loading conditions. Results of this investigation reveal quite different effects of the energetic length scale, depending on the value of n and the type of loading. For n ≥ 2, regardless of the loading type, the energetic length scale has only influence on the rate of the classical kinematic hardening, as reported in several SGCP works. However, in the range of n < 2, this parameter leads to unusual nonlinear kinematic hardening effects with inflection points in the macroscopic mechanical response, resulting in an apparent increase of the yield strength under monotonic loading. More complex effects, with additional inflection points, are obtained under non-proportional loading conditions, revealing new loading history memory-like effects of the energetic length scale. Concerning dissipation, to make the dissipative effects more easily controllable, dissipative processes due to plastic strains and their gradients are assumed to be uncoupled. Separate formulations, expressed using different effective plastic strain measures, are proposed to describe such processes. Results obtained using these formulations show the great flexibility of the proposed model in controlling some major dissipative effects, such as elastic gaps. A simple way to remove these gaps under certain non-proportional loading conditions is provided. Application of the proposed uncoupled formulations to simulate the mechanical response of a sheared strip has led to accurate prediction of the plastic strain distributions, which compare very favorably with those predicted using discrete dislocation mechanics.

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Section: Introductionmentioning

confidence: 86%

Section: Introductionmentioning

confidence: 99%

Strain gradient crystal plasticity model based on generalized non-quadratic defect energy and uncoupled dissipation

Jebahi

Cai

Abed‐Meraim

2020

International Journal of Plasticity

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“…Kiener et al [119], McLaughlin and Clegg [95] and Demir et al [121] have reported anomalies regarding the description based on the forest hardening mechanism and strain gradient theory to capture the size effects during In order to unravel the hardening mechanism at small indentation depths, the dislocation microstructure should be monitored. Three experimental techniques of backscattered electron diffraction (EBSD) [22,43,45,49,50,96,[119][120][121], convergent beam electron diffraction (CBED) [95] and X-ray microdiffraction (µXRD) [122][123][124][125] have been used so far to observe the dislocation microstructure in metallic samples. These techniques can map the local lattice orientations with high spatial resolutions.…”

Section: Recent Experimental Observations and Theoretical Modelsmentioning

confidence: 99%

“…Besides the experimental observations, computer simulations have greatly contributed to the investigation of the response of materials during nanoindentation. The common modeling methods are finite element [24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41], crystal plasticity [42][43][44][45][46][47][48][49][50], discrete dislocation dynamics [51][52][53][54][55][56][57][58][59][60][61][62], the quasicontinuum method [63][64][65][66][67][68][69][70][71][72][73]…”

Section: Introductionmentioning

confidence: 99%

Review of Nanoindentation Size Effect: Experiments and Atomistic Simulation

2017

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Nanoindentation is a well-stablished experiment to study the mechanical properties of materials at the small length scales of micro and nano. Unlike the conventional indentation experiments, the nanoindentation response of the material depends on the corresponding length scales, such as indentation depth, which is commonly termed the size effect. In the current work, first, the conventional experimental observations and theoretical models of the size effect during nanoindentation are reviewed in the case of crystalline metals, which are the focus of the current work. Next, the recent advancements in the visualization of the dislocation structure during the nanoindentation experiment is discussed, and the observed underlying mechanisms of the size effect are addressed. Finally, the recent computer simulations using molecular dynamics are reviewed as a powerful tool to investigate the nanoindentation experiment and its governing mechanisms of the size effect.

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“…The deformation, within each sector, will be governed by either purely elastic or active plastic deformation on a number of slip systems. The fundamental properties of asymptotic fields, in relation to both fracture and wedge indentation in single crystals, have been investigated experimentally by a number of authors (Bastawros and Kim, 1998;Kysar, 2000;Crone and Shield, 2001; Kysar and Briant, 2002;Kysar et al, 2010;Saito and Kysar, 2011;Saito et al, 2012;Dahlberg et al, 2014;Sarac et al, 2016;Dahlberg et al, 2017;Juul et al, 2018;Sarac and Kysar, 2018). However, existing studies are limited to the three most common crystal structures being FCC, BCC, and HCP.…”

Section: Accepted Manuscriptmentioning

confidence: 99%

Wedge indentation of single crystalline monazite: A numerical investigation

Juul¹,

Nellemann²,

Nielsen

et al. 2019

International Journal of Plasticity

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Geometrically necessary dislocation density measurements at a grain boundary due to wedge indentation into an aluminum bicrystal

Cited by 35 publications

References 65 publications

Strain gradient crystal plasticity model based on generalized non-quadratic defect energy and uncoupled dissipation

Strain gradient crystal plasticity model based on generalized non-quadratic defect energy and uncoupled dissipation

Review of Nanoindentation Size Effect: Experiments and Atomistic Simulation

Wedge indentation of single crystalline monazite: A numerical investigation

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