| Alexandrou, I., Scheibe, H. J., Kiely, C. J., Papworth, A. J., Amaratunga, G. A. J., and Schultrich, B. |
| Carbon films with an sp(2) network structure. |
| Physical Review B v.60, n.15, pp.10903-10907. (1999). |
| Abstract: Laser-arc evaporation of a graphite target has been used to deposit carbon films that exhibit high hardness (45 Cpa) and elastic recovery (85%). High-resolution electron microscopy (HREM) and electron energy loss spectroscopy (EELS) were subsequently used to study the microstructure and bonding of the resultant layers. The structure of the films from HREM is seen to consist of a dense array of parallel curved graphene sheet segments packed in various orientations. EELS reveals that the films are comprised of mainly sp(2)-bonded carbon. The results suggest that a form of carbon thin film with fullerenelike structure can be realized. In order to explain how a predominantly sp(2)-bonded material can exhibit such a high hardness, a simple model is proposed to correlate the excellent mechanical properties with the observed structure. [S0163-1829(99)00439-7] |
| Internal Reference: [ID: 1603]
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| Donadio, D., Colombo, L., and Benedek, G. |
| Elastic moduli of nanostructured carbon films. |
| Physical Review B (Condensed Matter and Materials Physics) v.70, n.19, pp.195419-195419-4. (2004). |
| Abstract: We have computed the elastic constants of nanostructured carbon films as obtained from classical molecular dynamics simulations of a cluster beam deposition process. The calculations show that the elastic constants of the deposited films are related to the average size of the clusters by a power law. This allows us to extrapolate the present theoretical data to the scale of the experimental results obtained by Brillouin scattering. |
| Internal Reference: [ID: 1804]
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| Field, J. S. and Swain, M. V. |
| The indentation characterisation of the mechanical properties of various carbon materials: Glassy carbon, coke and pyrolytic graphite. |
| Carbon v.34, n.11, pp.1357-1366. (1996). |
| Abstract: The force-displacement response of pyrolytic graphite, glassy carbon and coke with spherical tipped indenters is examined. The force-displacement behaviour for all these materials exhibits almost complete recovery with significant hysteresis between loading and unloading, the extent of which varies with material. Methods are discussed whereby the hysteretic indentation results may be interpreted to reveal evidence of deformation mechanisms. All three materials are shown to be elastic at very small strains with a secondary mechanism contributing to the inelastic displacement above a critical mean pressure. Indentation then proceeds with power law hardening. Unlike the behaviour of metals, which it resembles on loading, the secondary mechanism is reversible, with almost complete recovery on unloading. The secondary mechanism and hysteresis are discussed and rationalised in terms of the microstructure of the materials |
| Internal Reference: [ID: 1611]
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| Guo, W., Zhu, C. Z., Yu, T. X., Woo, C. H., Zhang, B., and Dai, Y. T. |
| Formation of sp3 Bonding in Nanoindented Carbon Nanotubes and Graphite. |
| Physical Review Letters v.93, n.24, pp.245502-245504. (2004). |
| Abstract: Nanoindentation-induced interlayer bond switching and phase transformation in carbon nanotubes (CNTs) and graphite are simulated by molecular dynamics. Both graphite and CNTs experience a soft-to-hard phase transformation at room temperature at compressive stresses of 12 and 16 GPa, respectively. Further penetration leads to the formation of interlayer sp3 bonds, which are reversible upon unloading if the compressive stress is under about 70 GPa, beyond which permanent interlayer sp3 bonds form. During nanoindentation, the maximum nanohardness of graphite can reach 109 GPa, and CNTs 120 GPa, which is comparable to that of diamond. |
| Internal Reference: [ID: 1617]
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| Iwamoto, C., Yang, H. S., Watanabe, S., and Yoshida, T. |
| Dynamic and atomistic deformation of sp(2)-bonded boron nitride nanoarrays. |
| Applied Physics Letters v.83, n.21, pp.4402-4404. (2003). |
| Abstract: With the aim of developing a nanostructure, we produced an sp(2)-bonded boron nitride nanoarray (BNNA), and observed its dynamic deformation behavior using high-resolution transmission electron microscopy with a piezoceramic tube for three-axis positioning of an indenter. The BNNA has remarkable flexibility and resiliency, such that no permanent deformation occurred when it was bent repeatedly to the minimum radius of curvature of about 4 nm. Even in repeated bends to the minimum radius of curvature of about 0.3 nm, the BNNA underwent no catastrophic failure. (C) 2003 American Institute of Physics |
| Internal Reference: [ID: 1619]
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| Iwashita, N., Field, J. S., and Swain, M. V. |
| Indentation hysteresis of glassy carbon materials. |
| Philosophical Magazine A: Physics of Condensed Matter, Structure, Defects and Mechanical Properties v.82, n.10, pp.1873-1881. (2002). |
| Abstract: Indentation hysteresis during both pointed and spherical indentation is a common feature of the observed force-displacement response of glassy carbon materials. Field and Swain proposed a method of analysis of this behaviour with spherical indenters in the form of classic indentation stress-strain curves. They also proposed that the response resulted from limited reversible slip of the graphite-like nanocrystalline structure of these so-called glassy carbon materials. The present work extends the previous study by investigating the influence of the nanocrystalline grain size and the hysteretic response with indenters of sharper apical angle. It is found that the extent of the hysteresis is dependent upon the grain size as is the contact stress for the initiation of yielding. The critical strain for the onset of non-recoverable hysteretic response is clearly identified with sharper-apical-angle indenters. This irreversibility of the hysteretic response is discussed in terms of an analysis proposed by Brown whereby the critical limit for the strain for reversible hysteretic behaviour was related to the percolation limit for plastic shear strain sites within a material. [12 Refs; In English] |
| Internal Reference: [ID: 1613]
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| Iwashita, N. and Swain, M. V. |
| Elasto-plastic deformation of glassy carbon by nano-indentation with spherical tipped indenters. |
| Molecular Crystals and Liquid Crystals v.386, pp.39-44. (2002). |
| Abstract: Nano-indentation of glassy carbons (GCs) heat-treated at different temperatures was carried out using spherical tipped indenters with different radii. Analysis of the force-displacement data enabled indentation stress-strain curves to be generated. It was found that the elastic modulus and the yield stress of GCs decreased with increasing the heat treatment temperature. It was also observed that the radius of spherical tipped indenters depended on the yield stress. From a simple the power law fitting of a non-linear elasto-plastic (contact stress-strain) deformation, beyond the initial elastic deformation, a better measure of hardness for brittle materials is proposed |
| Internal Reference: [ID: 1709]
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| Iwashita, N., Swain, M. V., Field, J. S., Ohta, N., and Bitoh, S. |
| Elasto-plastic deformation of glass-like carbons heat-treated at different temperatures. |
| Carbon v.39, n.10, pp.1525-1532. (2001). |
| Abstract: Nano-indentation of glass-like carbons (GCs) heat-treated at different temperatures was carried out with a 3 [mu]m radius spherical tipped indenter. The effect of crystal structure and micro-texture on elastic and elasto-plastic deformation resulting from the indentation was observed. The elastic modulus and yield stress of GCs was found to reduce with elevation of heat treatment temperature (HTT). The power law fitting constant k for the elasto-plastic deformation of the loading stress-strain curves by the indentation and the indentation elasticity index k/E* reduced with development of the graphitic structure of GC, so that 'elasticity' of GC decreased with the elevation of HTT of GCs. Hysteresis loops were observed on the indentation force-displacement curve during the loading-unloading cycle. Hysteresis energy loss, which corresponds to the area of the hysteresis loops, increased with the elevation of HTT for the same terminal load. The indentation ductility index D, the ratio of hysteresis energy loss to total indentation energy, was linearly dependent on indentation elasto-plastic deformation strain [epsiv]ep. The indentation elasto-plastic modulus m, which is obtained from the slope of the plots of D versus [epsiv]ep, reduced with the elevation of HTT of GCs. From the reduction of m, it was concluded that 'plasticity' (or 'ductility') of GC increased with the elevation of HTT of GCs |
| Internal Reference: [ID: 1612]
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| Kudin, K. N., Scuseria, G. E., and Yakobson, B. I. |
| C2F, BN, and C nanoshell elasticity from ab initio computations. |
| Physical Review B v.64, n.23, (2001). |
| Abstract: Two-dimensional lattices of carbon, boron-nitride, and fluorine-carbon compositions are treated with ab initio methods in order to evaluate and compare their mechanical properties in a uniform fashion. The demonstrated robustness of continuum elasticity up to very small length-scale allows one to define and compute the in-plane stiffness and flexural rigidity moduli of the representative nanoshells of C, BN, and CxF (x less than or equal to2). While only small deviations from linear elasticity are observed for C and BN, fluorination causes significant spontaneous shell folding. We discover that spontaneous curvature in fluorinated nanotubes shifts the energy minimum from a plane sheet towards the very small diameter tubes of (4,4) and even (3,3) indexes. Moreover, their equilibrium cross sections are distinctly polygonal, due to curvature self-localization, with an equilibrium angle of 71 degrees at each fluorine row attachment. Our analysis yields a simple physical model coupling the mechanical strain with chemical transformation energies |
| Internal Reference: [ID: 1658]
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| Michler, J. and Blank, E. |
| Analysis of coating fracture and substrate plasticity induced by spherical indentors: diamond and diamond-like carbon layers on steel substrates. |
| Thin Solid Films v.381, n.1, pp.119-134. (2001). |
| Abstract: Hard coatings as diamond or diamond-like carbon (DLC) layers are widely used as protective coatings on metal substrates, such as steel or hard metal. Failure mechanisms of the substrate/coating composite are studied in this paper through a parametric elastic-plastic finite element analysis, for the common load case of the indentation of spherical bodies into a layered surface considering a wide range of coating thicknesses. For the case of typical DLC layers on tool steel, the first damage of the layer/substrate composite is found to occur by substrate plasticity at or below the interface for most geometries. The fracture mode of the coating changes with varying ratio of layer thickness to indentor radius. If this ratio decreases from large to small values, radial and/or circumferential cracks are initiated first at the surface at the edge of the contact, then preferentially cracking occurrs at the interface on the symmetry axis or at the surface near to the contact edge, and finally again at the interface below the contact area, but without preference for the symmetry axis. Indentation experiments with DLC films on tool steel validate the fracture mechanisms deduced from calculations. For typical DLC layers on tool steel and diamond layers on tool steel, the critical forces for the onset of plastic deformation in the substrate and coating fracture are calculated by means of finite element analysis and analytical approximations of the contact problem. The results can be subsumed in normalised failure maps, from which the optimal coating thickness for the special load case of a spherical indentor can be estimated. Approximate analytical solutions to the results from finite element calculations are derived from simple mechanical analogues. They give more insight into the role of materials and geometry parameters and allow the extrapolation of the results to similar substrate coating systems. For instance, for coating thicknesses equal to or larger than the indentor radius, the load necessary to induce plasticity is shown to vary linearly with the substrate yield strength and the square of the layer thickness. Similarly, the load to initiate coating fracture varies with the square of the layer thickness and was linear with the coating fracture strength if the coating thickness is in the order of the indentor radius |
| Internal Reference: [ID: 1072]
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| Richter, A., Ries, R., Smith, R., Henkel, M., and Wolf, B. |
| Nanoindentation of diamond, graphite and fullerene films. |
| Diamond and Related Materials v.9, n.2, pp.170-184. (2000). |
| Abstract: The recently developed method of nanoindentation is applied to various forms of carbon materials with different mechanical properties, namely diamond, graphite and fullerite films. A diamond indenter was used and its actual shape determined by scanning force microscopy with a calibration grid. Nanoindentation performed on different surfaces of synthetic diamond turned out to be completely elastic with no plastic contributions. From the slope of the force-depth curve the Young's modulus as well as the hardness were obtained reflecting a very large hardness of 95 GPa and 117 GPa for the {100} and {111} crystal surfaces, respectively. Investigation of a layered material such as highly oriented pyrolytic graphite again showed elastic deformation for small indentation depths but as the load increased, the induced stress became sufficient to break the layers after which again an elastic deformation occurred. The Young's modulus was calculated to be 10.5 GPa for indentation in a direction perpendicular to the layers. Plastic deformation of a thin fullerite film during the indentation process takes place in the softer material of a molecular crystalline solid formed by C60 molecules. The hardness values of 0.24 GPa and 0.21 GPa for these films grown by layer epitaxy and island growth on mica and glass, respectively, vary with the morphology of the C60 films. In addition to the experimental work, molecular dynamics simulations of the indentation process have been performed to see how the tip-crystal interaction turns into an elastic deformation of atomic layers, the creation of defects and nanocracks. The simulations are performed for both graphite and diamond but, because of computing power limitations, for indentation depths an order of magnitude smaller than the experiment and over indentation times several orders of magnitude smaller. The simulations capture the main experimental features of the nanoindentation process showing the elastic deformation that takes place in both materials. However, if the speed of indentation is increased, the simulations indicate that permanent displacements of atoms are possible and permanent deformation of the material takes place |
| Internal Reference: [ID: 1602]
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|
| Robertson, J. |
| Mechanical-Properties and Coordinations of Amorphous Carbons. |
| Physical Review Letters v.68, n.2, pp.220-223. (1992). |
| Abstract: The elasticity and hardness of a-C and a-C:H are related to their mean network coordinations. It is shown that sp2 sites contribute no rigidity if they form graphitic clusters, as suggested by experiment and electronic structure calculations, despite having coordinations above the critical value 2.4. Hence both sp2 sites and polymeric = CH2 groups can severely lower the hardness of amorphous carbons |
| Internal Reference: [ID: 1149]
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| Sakai, M., Nakano, Y., and Shimizu, S. |
| Elastoplastic indentation on heat-treated carbons. |
| American Ceramic Society.Journal of the American Ceramic Society v.85, n.6, pp.1522-1528. (2002). |
| Abstract: A Vickers indenter, as an efficient mechanical microprobe, was applied to carbon materials heat-treated at temperatures in the range 880°-2600°C. The plasticity of the carbon materials, which was enhanced by increasing the heat-treatment temperature (HTT), was assessed from the relation between the indentation load, P, and the penetration depth, h. Using the concept of the true hardness, H, as a measure of plasticity and the experimental estimate of the H-value, the plasticity of the carbon materials was examined as a function of their crystallographic parameters. The residual impression of the carbons at HTT > 1800°C was hardly visible on the indented surface after unloading, because of the nearly complete elastic recovery of the indented surface, yielding a very unique indentation P-h hysteresis in the loading/unloading cycle. The microscopic processes associated with this unique elastic recovery during unloading are discussed here in relation to the reversible slip of the dislocation-network structures on the graphitic basal planes. [33 Refs; In English] |
| Internal Reference: [ID: 1608]
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Last modified: 21 July 2006