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
Incompressibility and Hardness of Solid Solution Transition Metal Diborides: Os1−xRuxB2
Michelle B. Weinberger,Jonathan B. Levine,Hsiu-Ying Chung,Robert W. Cumberland,Haider I. Rasool,Jenn-Ming Yang,Richard B. Kaner,Sarah H. Tolbert +7 more
TL;DR: In this paper, the authors synthesize pure RuB2 and solid solutions of Os1−xRuxB2 using in situ high-pressure X-ray diffraction and Vickers hardness testing techniques and provide a refinement of the rules previously reported for the design of new superhard materials.
Journal ArticleDOI
Post heat treatment of additive manufactured AlSi10Mg: On silicon morphology, texture and small-scale properties
F. Alghamdi,X. Song,Amir Hadadzadeh,Amir Hadadzadeh,Amir Hadadzadeh,Babak Shalchi-Amirkhiz,Babak Shalchi-Amirkhiz,Mohsen Mohammadi,Meysam Haghshenas +8 more
TL;DR: In this paper, the effect of various cooling rates on the microstructure (specifically eutectic-Si morphology) and small-scale mechanical properties, measured by employing a depth-sensing nanoindentation platform, of the selective laser melted AlSi10Mg alloy.
Journal ArticleDOI
Mechanical Stability of Surface Architecture-Consequences for Superhydrophobicity
TL;DR: The delicate interplay between chemistry and physical structure has been highlighted through theory and characterization of porous and rough interfaces within and outside the framework of superhydrophobics, and insights can be drawn from biology.
Journal ArticleDOI
Work of indentation methods for determining copper film hardness
TL;DR: In this paper, the authors investigated the indentation hardness of sputter deposited copper films on oxidised silicon substrates and compared the results obtained by the Oliver and Pharr method and the work of indentation methods.
Journal ArticleDOI
Effects of rare-earth element, Y, additions on the microstructure and mechanical properties of CoCrFeNi high entropy alloy
Long Zhang,Mengdi Zhang,Ze-an Zhou,Jiantao Fan,Peng Cui,Pengfei Yu,Jing Qin,Mingzhen Ma,Peter K. Liaw,Guoliang Li,Guoliang Li,R.P. Liu +11 more
TL;DR: In this paper, the effects of rare-earth element, Y, additions on the microstructures and mechanical properties of CoCrFeNi alloy have been investigated by the means of X-ray diffraction, scanning electron microscope, and transmission electron microscope.
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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