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
Static and dynamic analysis of the postbuckling of bi-directional functionally graded material microbeams
TL;DR: In this paper, the static and dynamic responses of bi-directional functionally graded (BDFG) microbeams are investigated using von-Karman geometric nonlinearity and third-order shear deformation beam theory.
Journal ArticleDOI
Evaluation of length-scale effects for mechanical behaviour of micro- and nanocantilevers: I. Experimental determination of length-scale factors
Chenzhi Tang,Gursel Alici +1 more
TL;DR: In this paper, the length-scale factors for micro-and nano-sized silicon cantilevers are estimated using experimental data collected from nanoindentation and microindention experiments.
Journal ArticleDOI
Microstructure evolution and deformation mechanisms during high rate and cryogenic sliding of copper
TL;DR: In this paper, the authors investigated the deformation mechanism of a sliding surface during reciprocating sliding of copper and found that an increase in strain rate and a decrease in temperature each result in a transition from dislocation slip to twinning-mediated plasticity at the very beginning of sliding.
Journal ArticleDOI
Size-dependent plasticity and fracture of a metallic glass in compression
Sujing Xie,Easo P. George +1 more
TL;DR: In this paper, the deformation and fracture behavior of bulk metallic glass (BMG) is investigated and the authors demonstrate that it is important to take specimen size into account when interpreting plasticity and fracture of BMGs.
Journal ArticleDOI
Investigation of slip transmission behavior across grain boundaries in polycrystalline Ni3Al using?nanoindentation
TL;DR: In this paper, the influence of grain boundaries on material deformation in Ni3Al was investigated by relating the material pile-up at grain boundaries and the propagation of slip across grain boundaries to the misorientation between the corresponding grains.
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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An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments
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