Journal ArticleDOI
Indentation size effects in crystalline materials: A law for strain gradient plasticity
William D. Nix,Huajian Gao +1 more
TLDR
In this article, the indentation size effect for crystalline materials can be accurately modeled using the concept of geometrically necessary dislocations, which leads to the following characteristic form for the depth dependence of the hardness: H H 0 1+ h ∗ h where H is the hardness for a given depth of indentation, h, H 0 is a characteristic length that depends on the shape of the indenter, the shear modulus and H 0.Abstract:
We show that the indentation size effect for crystalline materials can be accurately modeled using the concept of geometrically necessary dislocations. The model leads to the following characteristic form for the depth dependence of the hardness: H H 0 1+ h ∗ h where H is the hardness for a given depth of indentation, h, H0 is the hardness in the limit of infinite depth and h ∗ is a characteristic length that depends on the shape of the indenter, the shear modulus and H0. Indentation experiments on annealed (111) copper single crystals and cold worked polycrystalline copper show that this relation is well-obeyed. We also show that this relation describes the indentation size effect observed for single crystals of silver. We use this model to derive the following law for strain gradient plasticity: ( σ σ 0 ) 2 = 1 + l χ , where σ is the effective flow stress in the presence of a gradient, σ0 is the flow stress in the absence of a gradient, χ is the effective strain gradient and l a characteristic material length scale, which is, in turn, related to the flow stress of the material in the absence of a strain gradient, l ≈ b( μ σ 0 ) 2 . For materials characterized by the power law σ 0 = σ ref e 1 n , the above law can be recast in a form with a strain-independent material length scale l. ( builtσ σ ref ) 2 = e 2 n + l χ l = b( μ σ ref ) 2 = l ( σ 0 σ ref ) 2 . This law resembles the phenomenological law developed by Fleck and Hutchinson, with their phenomenological length scale interpreted in terms of measurable material parametersbl].read more
Citations
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Journal ArticleDOI
Microhardness anisotropy and the indentation size effect on the basal plane of single crystal hematite
TL;DR: The Knoop microhardness anisotropy of single crystal hematite, Fe 2 O 3, was investigated on the basal plane (0001) at indentation test loads from 50 to 1000 g as mentioned in this paper.
Journal ArticleDOI
Electronic-structure study of an edge dislocation in Aluminum and the role of macroscopic deformations on its energetics
TL;DR: In this article, the authors employed a real-space formulation of orbital-free density functional theory using finite-element basis to study the defect-core and energetics of an edge dislocation in Aluminum.
Journal ArticleDOI
Room temperature nanoindentation creep of nanocrystalline Cu and Cu alloys
TL;DR: In this paper, the authors conducted nanoindentation creep tests on nanocrystalline Cu, Cu 2.3Al and Cu 7.2Al alloys at room temperature and calculated the stress exponents from the loading curves.
Journal ArticleDOI
Microstructural evolution and hardening of GH3535 alloy under energetic Xe ion irradiation at room temperature and 650 °C
Hefei Huang,Jie Gao,Bertrand Radiguet,Renduo Liu,Jianjian Li,Guanhong Lei,Qing Huang,Min Liu,Ruobing Xie +8 more
TL;DR: In this article, the GH3535 alloy was irradiated with 7 MeV Xe26+ ions to a dose of 10 dpa at room temperature (RT) and 650°C, and subsequently examined using Transmission Electron Microscopy (TEM) and nanoindentation.
Journal ArticleDOI
A modified Johnson-Cook material model with strain gradient plasticity consideration for numerical simulation of cold spray process
Rohan Chakrabarty,Jun Song +1 more
TL;DR: In this article, a modified form of the Johnson-Cook model was developed to account for the viscous regimes experienced at high strain rates, which takes a simple mathematical form with less adjustable material parameters than previous modifications of the JC model.
References
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Journal ArticleDOI
The deformation of plastically non-homogeneous materials
TL;DR: The geometrically necessary dislocations as discussed by the authors were introduced to distinguish them from the statistically storages in pure crystals during straining and are responsible for the normal 3-stage hardening.
Journal ArticleDOI
Strain gradient plasticity: Theory and experiment
TL;DR: In this paper, a deformation theory of plasticity is introduced to represent in a phenomenological manner the relative roles of strain hardening and strain gradient hardening, which is a non-linear generalization of Cosserat couple stress theory.
Journal ArticleDOI
A phenomenological theory for strain gradient effects in plasticity
TL;DR: In this paper, a strain gradient theory of plasticity is introduced, based on the notion of statistically stored and geometrically necessary dislocations, which fits within the general framework of couple stress theory and involves a single material length scale l.
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