Multi-asperity contact: A comparison between discrete dislocation and crystal plasticity predictions

Nicola, Lucia; Bower, Allan F.; Kim, K.-S.; Needleman, A.; Giessen, van der Erik

doi:10.1080/14786430802566372

Cited by 24 publications

(20 citation statements)

References 34 publications

(46 reference statements)

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“…The roughness of the surface is strongly simplified to a sinusoidal wave function, but plasticity caused by dislocation glide is carefully computed by discrete dislocation simulations [9]. The numerical technique has so far proven successful to capture size dependent plastic behavior of isolated flat contacts [10] as well as interplay between plasticity underneath arrays of flat contacts [11,12].…”

Section: Introductionmentioning

confidence: 99%

Plastic flattening of a sinusoidal metal surface: A discrete dislocation plasticity study

Sun

Giessen

Nicola

2012

Wear

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a b s t r a c tThe plastic flattening of a sinusoidal metal surface is studied by performing plane strain dislocation dynamics simulations. Plasticity arises from the collective motion of discrete dislocations of edge character. Their dynamics is incorporated through constitutive rules for nucleation, glide, pinning and annihilation. By analyzing surfaces with constant amplitude we found that the mean contact pressure is inversely proportional to the wavelength. For small wavelengths, due to interaction between plastic zones of neighboring contacts, the mean contact pressure can reach values that are about 1/10 of the theoretical strength of the material, thus significantly higher than what is predicted by simulations that do not account for size dependent plasticity. Surfaces with the same amplitude to period ratio have a size dependent response, such that if we interpret each period of the sinusoidal wave as the asperity of a rough surface, smaller asperities are harder to be flattened than large ones. The difference between the limiting situations of sticking and frictionless contacts is found to be negligible.

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Section: Introductionmentioning

confidence: 99%

Plastic flattening of a sinusoidal metal surface: A discrete dislocation plasticity study

Sun

Giessen

Nicola

2012

Wear

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“…As deformation proceeds, the dislocations emanating from sources near neighboring contacts interact and this contributes to the increased mean contact pressure. A more detailed study of the role of contact size and contact fraction a=w will be reported in Nicola et al (2006b). In the remainder of this paper, unless stated otherwise, the contact size is a ¼ 1 mm and w ¼ 9 mm.…”

Section: Effect Of Contact Size and Friction Without Surface Sourcesmentioning

confidence: 99%

Surface versus bulk nucleation of dislocations during contact

Nicola

Bower

Kim

et al. 2007

Journal of the Mechanics and Physics of Solids

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The indentation of single crystals by a periodic array of flat rigid contacts is analyzed using discrete dislocation plasticity. Plane strain analyses are carried out with the dislocations all of edge character and modeled as line singularities in a linear elastic solid. The limiting cases of frictionless and perfectly sticking contacts are considered. The effects of contact size, dislocation source density, and dislocation obstacle density and strength on the evolution of the mean indentation pressure are explored, but the main focus is on contrasting the response of crystals having dislocation sources on the surface with that of crystals having dislocation sources in the bulk. When there are only bulk sources, the mean contact pressure for sufficiently large contacts is independent of the friction condition, whereas for sufficiently small contact sizes, there is a significant dependence on the friction condition. When there are only surface dislocation sources the mean contact pressure increases much more rapidly with indentation depth than when bulk sources are present and the mean contact pressure is very sensitive to the strength of the obstacles to dislocation glide. Also, on unloading a layer of tensile residual stress develops when surface dislocation sources dominate. r

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“…When the template contacts are closely spaced (small w) a larger force is required to imprint the films. This is partly due to the different elastic stress states developing during loading, but mainly to a different plastic behavior: the plastic zones underneath closely spaced contacts interact with each other and give rise to a harder response (see also [14,15]). Figures 3(a)-(c) show the stress σ 22 and dislocation distribution in the unit cells for w = 2, 5 and 10 µm at the maximum imprinting depth (u = 0.05 µm).…”

Section: Imprinting Simulationsmentioning

confidence: 99%

“…Once the stresses have been determined, the incremental change in position of each dislocation is calculated, and conditions are checked for nucleation, annihilation of dipoles and pinning at or release from obstacles. Details on the numerical procedure for solving the governing field equations and constitutive equations are presented in [14].…”

Section: Boundary Conditionsmentioning

confidence: 99%

Discrete dislocation simulations of the flattening of nanoimprinted surfaces

Zhang¹,

Giessen²,

Nicola³

2010

Modelling Simul. Mater. Sci. Eng.

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Simulations of rough surface flattening are performed on thin metal films whose roughness is created by nanoimprinting flat single crystals. The imprinting is carried out by means of a rigid template with equal flat contacts at varying spacing. The imprinted surfaces are subsequently flattened by a rigid platen, while the change of roughness and surface profile is computed. Attention is focused mainly on comparing the response of the film surfaces with those of identical films cleared of the dislocations and residual stresses left by the imprinting process. The aim of these studies is to understand to what extent the loading history affects deformation and roughness during flattening. The limiting cases of sticking and frictionless contact between rough surface and platen are analyzed. Results show that when the asperities are flattened such that the contact area is up to about one third of the surface area, the loading history strongly affects the flattening. Specifically, the presence of initial dislocations facilitates the squeezing of asperities independently of the friction conditions of the contact. For larger contact areas, the initial conditions affect only sticking contacts, while frictionless contacts lead to a homogeneous flattening of the asperities due to yield of the metal film. In all cases studied the final surface profile obtained after flattening has little to no resemblance to the original imprinted surface.

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Multi-asperity contact: A comparison between discrete dislocation and crystal plasticity predictions

Cited by 24 publications

References 34 publications

Plastic flattening of a sinusoidal metal surface: A discrete dislocation plasticity study

Plastic flattening of a sinusoidal metal surface: A discrete dislocation plasticity study

Surface versus bulk nucleation of dislocations during contact

Discrete dislocation simulations of the flattening of nanoimprinted surfaces

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