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
Spherical nanoindentation of proton irradiated 304 stainless steel: A comparison of small scale mechanical test techniques for measuring irradiation hardening
Jordan S. Weaver,Siddhartha Pathak,Ashley Reichardt,H.T. Vo,Stuart A. Maloy,Peter Hosemann,Nathan A. Mara +6 more
TL;DR: In this article, the authors used spherical nanoindentation stress-strain curves on unirradiated and proton irradiated 304 stainless steel to quantify the mechanical effects of radiation damage.
Journal ArticleDOI
Extremely hard, damage-tolerant ceramic coatings with functionally graded, periodically varying architecture
P.C. Wo,P.C. Wo,Xiaoli Zhao,Paul Munroe,Zhifeng Zhou,Kwok Yan Li,Daryoush Habibi,Zonghan Xie +7 more
TL;DR: In this paper, a functional graded multilayer structure consisting of alternating TiN/TiSiN layers was synthesized in an attempt to overcome the innate brittleness of TiSiN nanocomposite coatings, whilst maintaining high hardness.
Journal ArticleDOI
Sudden stress-induced transformation events during nanoindentation of NiTi shape memory alloys
TL;DR: In this paper, the authors investigated the stress-induced formation of martensite during nanoindentation of an austenitic NiTi shape memory alloy, where stressinduced martensites is stable at room temperature.
Journal ArticleDOI
Evolution of plastic deformation in heavily deformed and recrystallized tungsten of ITER specification studied by TEM
TL;DR: In this paper, the deformation-induced microstructure was characterized and compared for the two grades in terms of the dislocation density, heterogeneity, observation of pile-ups and tangles specifically near high angle grain boundaries.
Journal ArticleDOI
Molecular dynamics study on compressive yield strength in Ni3Al micro-pillars
TL;DR: In this paper, molecular dynamics simulations are carried out to investigate the onset of yielding in Ni3Al nano-sized pillars, showing that dislocation generation is from the free surfaces of the micro-pillars, when thermal vibration induces too large a local interatomic displacement.
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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