Showing papers on "Indentation published in 1993"
TL;DR: In this paper, a simple model is described with which the entire force versus penetration behavior of indentation with a sphere, during loading and unloading, may be simulated from knowledge of the four test material parameters, Young's modulus, Poisson's ratio, flow stress at the onset of full plastic flow and strain hardening index, and the elastic properties of the indenter.
Abstract: A simple model is described with which the entire force versus penetration behavior of indentation with a sphere, during loading and unloading, may be simulated from knowledge of the four test material parameters, Young's modulus, Poisson's ratio, flow stress at the onset of full plastic flow and strain hardening index, and the elastic properties of the indenter. The underlying mechanisms are discussed and the predictions of the model are compared with data produced by an ultra low load, penetration measuring instrument.
641 citations
TL;DR: In this paper, a proportional specimen resistance (PSR) model has been proposed that consists of the elastic resistance of the test specimen and frictional effects at the indentor facet/specimen interface during microindentation.
Abstract: The microhardness indentation load/size effect (ISE) on the Knoop microhardness of single crystals of TiO2 and SnO2 has been investigated. Experimental results have been analysed using the classical power law approach and from an effective indentation test load viewpoint. The Hays/Kendall concept of a critical applied test load for the initiation of plastic deformation was considered, but rejected to explain the ISE. A proportional specimen resistance (PSR) model has been proposed that consists of the elastic resistance of the test specimen and frictional effects at the indentor facet/specimen interface during microindentation. The microhardness test load, P, and the resulting indentation size, d, have been found to follow the relationship
$$P = a_1 d + a_2 d^2 = a_1 d + (P_c /d_0^2 ) d^2$$
The ISE is a consequence of the indentation-size proportional resistance of the test specimen as described by a
1. a
2 is found to be related to the load-independent indentation hardness. It consists of the critical indentation load, P
c, and the characteristic indentation size, d
o.
388 citations
TL;DR: In this article, the authors studied the indentation resistance of foams, both of conventional structure and of a novel reentrant structure giving rise to negative Poisson's ratio, using holo graphic interferometry.
Abstract: The indentation resistance of foams, both of conventional structure and of a novel re-entrant structure giving rise to negative Poisson's ratio, was studied using holo graphic interferometry. In holographic indentation tests, re-entrant foams had higher yield strengths σy and lower stiffness E than conventional foams of the same original relative density. Damage in both kinds of foam occurred primarily directly under the indenter. Calculated energy absorption for dynamic impact is considerably higher for re-entrant foam than conventional foam
371 citations
TL;DR: In this article, the deformation of a creeping half-space with uniaxial stress-strain behavior is investigated, where the shape of the punch is described by most indenter profiles of practical importance.
Abstract: The aim of this paper is to establish a rigorous theoretical basis for interpreting the results of hardness tests on creeping specimens. We investigate the deformation of a creeping half-space with uniaxial stress-strain behaviour ⋵ = ⋵ 0 (σ/σ 0 ) m , which is indented by a rigid punch. Both axisymmetric and plane indenters are considered. The shape of the punch is described by a general expression which includes most indenter profiles of practical importance. Two methods are used to solve the problem. The main results are found using a transformation method suggested by R. Hill. It is shown that the creep indentation problem may be reduced to a form which is independent of the geometry of the punch, and depends only on the material properties through m . The reduced problem consists of a nonlinear elastic half-space, which is indented to a unit depth by a rigid flat punch of unit radius (in the axisymmetric case), or unit semi-width (in the plane case). Exact solutions are given for m = 1 and m = ∞. For m between these two limits, the reduced problem has been solved using the finite element method. The results enable the load on the indenter and the contact radius to be calculated in terms of the indentation depth and rate of penetration. The stress, strain and displacement fields in the half-space may also be deduced. The accuracy of the solution is demonstrated by comparing the results with full-field finite element calculations. The predictions of the theory are shown to be consistent with experimental observations of hardness tests on creeping materials reported in the literature.
308 citations
TL;DR: The unloading process in an indentation experiment is often modelled as a contact problem of a rigid punch on an elastically isotropic half space as discussed by the authors, which allows one to derive simple formulae to determine the indentation modulus from experimental data.
Abstract: The unloading process in an indentation experiment is often modelled as a contact problem of a rigid punch on an elastically isotropic half space. This allows one to derive simple formulae to determine the indentation modulus from experimental data. We have studied the contact problem of a flat circular punch and a paraboloid on an elastically anisotropic half space and have shown that the formulae used for isotropic materials can be used for anisotropic materials as long as the half space has three or fourfold rotational symmetry. In the case of lower symmetry, the indentation modulus depends on the shape of the indenter. We have calculated the indentation modulus of {100}, {111} and {110} surfaces of cubic crystals for a wide range of elastic constants. The {110} indentation modulus was calculated for the case of a flat circular punch. The single-crystal indentation moduli differ substantially from the isotropic polycrystalline indentation moduli and the differences increase with increasing anisotropy f...
275 citations
TL;DR: In this article, energy-based considerations on the inelastic surface deformation of brittle materials are conducted, where the hysteresis loop energy Ur which is dissipated during the indentation loading-unloading cycle is related to the true hardness H, apparent hardness H, and the work-of-indentation Γ 1.
Abstract: Energy-based considerations on the inelastic surface deformation of brittle materials are conducted. The hysteresis loop energy Ur which is dissipated during the indentation loading-unloading cycle is related to the true hardness H, apparent hardness H , and the work-of-indentation Γ1. The true hardness has its energy-derived meaning of the irreversible energy consumption to create a unit volume of the indentation impression of ideally plastic materials. The relationships between Ur and the three-half power of indentation load P 3 2 , and between Ur and the volume of the indentation impression V1 are used to separate the plastic contribution from the complicated plastic/elastic surface deformation processes in indentation hardness tests. The linear relationship of Ur vs P 3 2 provides an important experimental technique for determining the true hardness H of brittle materials. The linear relationship of Ur vs V1 is available to the experimental determination of Γ1. The mechanical and physical meanings of the conventional Vickers indentation hardness of brittle materials are also addressed in relation to H, H and Γ1.
239 citations
TL;DR: In this article, a simple model of the dislocation densities produced under the indenter tip describes the data well, based on the fact that the high density of dislocations expected under a shallow indentation would cause an increase in measured hardness.
Abstract: Ultra micro-indentation tests on Ni and Cu samples showed increasing hardness with decreasing penetration depth over a range from 200 to 2000 nm. The results suggest increased strain hardening with decreased indentation depth. To establish that this is a real material effect, a series of tests were conducted on amorphous materials, for which strain hardening is not expected. The hardness of Metglas® was found to be independent of depth. A simple model of the dislocation densities produced under the indenter tip describes the data well. The model is based on the fact that the high density of dislocations expected under a shallow indentation would cause an increase in measured hardness. At large depths, the density of geometrically necessary dislocations is sufficiently small to have little effect on hardness, and the measured hardness approaches the intrinsic hardness of the material.
234 citations
TL;DR: The role of friction between the microhardness indenter and the test specimen is addressed through the analysis of dry (unlubricated) and lubricated tests on iron by Atkinson and Shi as discussed by the authors.
Abstract: The role of friction between the microhardness indenter and the test specimen is addressed through the analysis of dry (unlubricated) and lubricated tests on iron by Atkinson and Shi. Quantitative evaluation through a proportional specimen resistance model accurately describes the results. It suggests that friction is a major portion of the observed hardness increase at low test loads, the indentation size effect. The ISE is related to the surface-area-to-volume ratio of the indentation, which is inversely related to the indentation dimension.
194 citations
TL;DR: In this article, the authors assess the current possibilities for, and limitations of, nanoindentation for assessing the properties of thin-film-coated systems, and further demonstrate the difficulty of assessing properties as a function of the depth into the coated system.
Abstract: Ultralow load indentation testing, or nanoindentation, has considerable potential for studying the near-surface mechanical properties of solids and seems especially suited to the mechanical characterization of thin-film-coated systems where both low contact loads and high spatial precision can be advantageous. This paper assesses the current possibilities for, and limitations of, nanoindentation for assessing the properties of coated systems. In particular, the pursuit of hardness values alone is questioned, especially when the continuous load and depth data from the indentation cycle provide a far more complete mechanical “fingerprint” from which a number of important parameters describing the system behaviour can be calculated. The further difficulty of assessing the properties as a function of the depth into the coated system is also demonstrated. The additional information accessible through post facto microstructural characterization of the indentations themselves, the possible use of various indenter geometries and the need for parallel computer modelling to predict response are also discussed.
161 citations
TL;DR: In this paper, the authors investigated the hysteretic behavior of silicon under indentation using an ultra-micro-indentation system with an 8.5 μm spherical-tipped indenter.
Abstract: The recently reported hysteretic behavior of silicon under indentation (Clarke et al.1 and Pharret al.2-5) is investigated using an ultra-micro-indentation system with an 8.5 μm spherical-tipped indenter. The onset of “plastic” behavior during loading and hysteresis during unloading was readily observed at loads in excess of 70 mN. Cracking about the residual impression was observed only at loads of 350 mN and higher. An analysis of the data is presented that estimates the following: (1) the initial onset of deformation occurs at a mean pressure of 11.8 ± 0.6 GPa, (2) the mean pressure at higher loads is 11.3 ± 1.3 GPa, and (3) the hysteretic transition on unloading occurs at mean pressures between 7.5 and 9.1 GPa. These values are in good agreement with the accepted literature values for the known silicon transformation pressures. A simulation of the force-displacement data based on the analysis and model is presented and is found to fit the observations very well.
155 citations
Journal Article•
TL;DR: In this article, a simple Hertzian contact procedure for investigating cyclic fatigue damage in brittle polycrystalline ceramics is described, and the mode of damage is one of deformation-induced intergranular microfracture, leading ultimately at large numbers of cycles and high contact pressures to severe grain dislodgement.
Abstract: A simple Hertzian contact procedure for investigating cyclic fatigue damage in brittle polycrystalline ceramics is described. Repeat loading of a spherical indenter on a coarse alumina ceramic produces cumulative mechanical damage. The mode of damage is one of deformation-induced intergranular microfracture, leading ultimately at large numbers of cycles and high contact pressures to severe grain dislodgement. In contrast to the classical Hertzian cone cracks that form in more homogeneous materials in the regions of tensile stress outside the contact circle, the damage in the coarse-grain alumina develops in a zone of high shear stress and hydrostatic compression beneath the contact circle
TL;DR: In this paper, an elastic-plastic indentation into an Fe−3 wt. % Si single crystal was measured and the volume displaced to the surface is nearly equal to the volume of the cavity.
Abstract: Atomic force microscope measurements of elastic-plastic indentation into an Fe−3 wt. % Si single crystal showed that the volume displaced to the surface is nearly equal to the volume of the cavity. The surface displacement profiles and plastic zone size caused by a 69 nm penetration of a Vickers diamond tip are reasonably represented by an elastic-plastic continuum model. Invoking conservation of volume, estimates of the number of dislocations emanating from the free surface are reasonably consistent with the number of dislocations that have formed in the plastic zone to represent an average calculated plastic strain of 0.044.
TL;DR: In this article, the authors present an experimental analysis for contact and low-velocity impact re sponses of composite laminates by rigid spheres and find that the contact force corresponding to the onset of laminate damage is independent of the indentor size.
Abstract: Experimental results are presented for contact and low-velocity-impact re sponses of composite laminates by rigid spheres. The contact phenomenon is different in small and large indentation stages, which is due to occurrence of laminate damage. The contact force corresponding to the onset of laminate damage is found to be independent of the indentor size. In the small indentation stage where the plate is intact, the change of laminate stacking sequence has an insignificant effect on the force-indentation relation ship. However, the force-indentor size relationship does not follow the modified contact law for thin laminates indented by large indentors. Beyond the small indentation stage, damage occurs. The size of the delamination area is proportional to the applied loads and the number of repeated loading cycles. The passage of the delamination crack front can be detected using strain gauges. Also, the indentation spring becomes stiffer under repeated loading. Finally, the delamination damage and the stra...
IBM1
TL;DR: In this paper, the authors measured the propagation of indentation radial cracks in soda-lime silicate glass and showed distinct threshold, reaction-limited and transport-limited behavior in the crack velocity responses, in agreement with measurements made using macroscopic crack geometries.
Abstract: The propagation of indentation radial cracks in soda—lime silicate glass is measured as a function of time after indentation. Rapid lift-off of the indenter from the specimen surface causes a step-function perturbation in the radial crack mechanical energy release rate, thus providing access to a large range of observable crack velocities in the indentation stress field. Analysis of the data shows distinct threshold, reaction-limited, and transport-limited behavior in the crack velocity responses, in agreement with measurements made using macroscopic crack geometries. Atomistic models of fracture kinetics in reactive environments are fit to the data and are deconvoluted to yield the underlying atomic-scale, bond-rupture parameters. These latter are used to calculate potential functions for activated fracture and predict crack velocity responses as a function of temperature and pressure.
TL;DR: In this article, a depth-sensing low-load indentation technique was used to measure the hardness of polyimide Kapton and spin-cast polyamic acid on sapphire.
Abstract: Polyimide Kapton and spin-cast polyamic acid (PAA) on sapphire have been implanted with 1 MeV Ar ions to a dose of 4.7 × 1015 cm−2 at ambient temperature. The properties of both pristine and implanted surfaces were characterized by a depth-sensing low-load indentation technique. Experiments were carried out to investigate the effects of substrate, indentation rate, relaxation, and indentation technique. The results showed that (1) hardness was depth-dependent and decreased with increasing indentation depth, (2) measurements of the ion beam hardened surface with the untreated material as a substrate underestimated the hardness while measurements over the sapphire substrate overestimated it, (3) the effects of loading/unloading rates were apparent in the load displacement results, and (4) hardness values measured using the force modulation technique showed very little depth dependence. The hardness value at 100 nm depth is used for comparison purposes since the hardness value at this depth was almost independent of substrate, indentation rate, and indentation method. The hardness of Kapton, which was measured using the techniques described herein, was increased by over 30 times after Ar implantation, from 0.43 to 13 GPa at 100 nm indentation depth. A similar increase in hardness was also observed for polyamic acid. This result suggests that spin-cast PAA film may have potential technological applications for protective coatings where hardness and wear resistance are required.
TL;DR: In this paper, a simple model of free abrasive machining is developed which is based on indentation fracture and takes into account the abrasive particle distribution in the slurry, which is used to predict the number of particles actually involved in the machining process, the distribution of load among these particles, and the depth of the plastically deformed layer on the workpiece surface.
TL;DR: This work uses nonequilibrium molecular dynamics to simulate the elastic-plastic deformation of silicon under tetrahedral nanometer-sized indentors and follows the structural change during indentation with a computer technique that allows the dynamic simulation of diffraction patterns.
Abstract: We use nonequilibrium molecular dynamics to simulate the elastic-plastic deformation of silicon under tetrahedral nanometer-sized indentors. The results are described in terms of a rate-dependent and temperature-dependent phenomenological yield strength. We follow the structural change during indentation with a computer technique that allows us to model the dynamic simulation of diffraction patterns.
TL;DR: In this article, the elastic contact theories of Hertz and Love reproduced the elastic portion of the load-displacement curves of a single crystal Fe (3 wt.% Si) with a thin passivation film.
Abstract: Continuous microindentation tests performed on the electropolished surfaces of single crystal Fe (3 wt.% Si), known to have a thin passivation film, show a sharp discontinuity at a load of 1.8 mN. To this point, there was no apparent plastic deformation in the metal in that the loading and unloading curves exactly overlay each other. Stresses at the discontinuity were close to the theoretical strength of the metal. Elastic contact theories of Hertz and Love reproduced the elastic portion of the load-displacement curves. On removing the passivation film with a HCl solution, indentation tests yielded strengths nearly two orders of magnitude smaller. The strength recovered to near its initial value after the liquid evaporated and the passivation film re-formed.
TL;DR: In this paper, dislocation arrangements about a range of microindentations into the face of an Fe−3 wt. % Si single crystal have been accomplished, with the experimental observations being reasonably consistent with continuum models.
Abstract: Direct observations of dislocation arrangements about a range of microindentations into the [100] face of an Fe−3 wt. % Si single crystal have been accomplished. Dislocations of both large loop character initiated from the indenter and small loop character initiated as secondary reactions are found. Analysis of these allows the various contributions to the plastic strain gradient around the indentation to be assessed, with the experimental observations being reasonably consistent with continuum models.
TL;DR: A fundamental understanding of basic tribological processes such as surface indentation and scraping was provided by Gane and Bowden as mentioned in this paper, who related this critical yielding to the theoretical shear strength in the metal, the strength required to create dislocations.
Abstract: The precision machining of metal surfaces and the ductile-regime grinding of ceramic surfaces are examples of fundamental cutting processes used in fabricating high-tolerance parts. Components with dimensional tolerances of a few tens of nanometers are currently being produced by direct machining with single-point diamond tools. Despite the ability to fabricate these parts, little is understood of the basic deformation mechanisms that determine how material is removed and deformed, how a tool-tip interacts with a workpiece, how induced surface and subsurface damage occurs, and how cutting tools wear.The key to solving these problems is a fundamental understanding of basic tribological processes such as surface indentation and scraping. Indentation experiments measure the mechanical response of a surface, the onset of plastic deformation, and material hardness. Macroscopic hardness measurements have been shown to correlate well with observed tensile yield strengths. Microscopic indentation studies, where the indentation size is smaller than the material grain size, show new and interesting phenomena. In the pioneering work of Gane and Bowden, no permanent penetration occurred until a critical load was achieved. They related this critical yielding to the theoretical shear strength in the metal, the strength required to create dislocations. Yielding of this sort has since been observed by many investigators.
TL;DR: In this article, the authors present the results of a detailed study on different kinds of reinforced polymer composites (carbon and glass fibres embedded in thermoplastic and thermoset matrices).
TL;DR: In this paper, the indentation technique for determining material toughness is applied to spinel and yttria-stabilized zirconia plasma-sprayed coatings in an investigation.
Abstract: The indentation technique for determining material toughness is applied to spinel and yttria-stabilized zirconia plasma-sprayed coatings in this investigation. Fracture toughness of the coatings ranged from 1.9 to 3.4 MPa√m for spinel and 2.0 to 3.3 MPa√m for yttria-stabilized zirconia. These results are in good agreement with those obtained by other experimenters for bulk materials.
15 Dec 1993
TL;DR: In this article, several hydrogenated amorphous carbon (a-C:H) coated systems have been investigated with systematic variations in coating thickness and substrate characteristics, and the resultant data have been analyzed in terms of load-displacement curves and various comparative parameters (e.g. hardness, total displacements and elastic recovery) derived from them.
Abstract: In order to further our interpretation of nanoindentation data from coated systems, and to learn more about the systems themselves, several hydrogenated amorphous carbon (a-C:H) coated systems have been investigated with systematic variations in coating thickness and substrate characteristics. Three different substrates have been used: a tool steel (M42), a semi-plastic ceramic single crystal (MgO) and a polymer (polytetrafluorethylene (PTFE)), each with chemically vapour-deposited a-C:H coatings of thickness 0.1–1 microm. Low load indentation experiments were performed with a Nano Indenter TM II with indenter displacements typically less than, or of the order of, the nominal coating thicknesses. The resultant data have been analysed in terms of load-displacement curves and various comparative parameters ( e.g. hardness, total displacements and elastic recovery) derived from them. High resolution scanning electron microscopy has also been used to examine the deformation structures at the indention sites, the occurrence of various crack types in the coating being of particular interest. Our results clearly show how the change in near-surface elastic and plastic properties conferred by the coating can be characterized for a given system. Generally, the coatings were found to support part of the load and to delay the elastic-plastic transition in surface deformation behaviour to higher loads. The MgO studies clearly demonstrate that “pop-ins” in the load-displacement curves can arise from dislocation generation in the substrate as well as crack propagation in the coatings. The PTFE studies demonstrate how the viscoelastic response of the substrate can be modified by the coating.
TL;DR: A new model is developed to describe that stage of nano-intentation creep prior to `pop-in', i.e. when the indentation load induces purely elastic stresses within the sample.
Abstract: A new model is developed to describe that stage of nano-intentation creep prior to `pop-in', i.e. when the indentation load induces purely elastic stresses within the sample. Expressions for the st ...
TL;DR: In this paper, a finite element model was used to analyze indentation of hard-face materials, where the materials (substrate and coating) are supposed elastoplastic, the spherical indenter is elastic.
Abstract: A finite element model previously described is used to analyze indentation of hard - face materials. The materials (substrate and coating) are supposed elastoplastic, the spherical indenter is elastic. The state of stress during indentation (including unloading) of hard-face materials (chromium layer on steel) is investigated in details. The tensile stresses which might lead to failure are especially discussed, and related with experiments showing fracture or delamination of the coating. The model also shows the influence of film thickness on surface and interface stresses
TL;DR: In this paper, a low-velocity impact testing was conducted to determine the failure modes due to impact, and the results showed that the strength degradation in ARALL laminates resulting from impact depends on the fiber orientation.
01 Jan 1993
TL;DR: In this article, a simple Hertzian contact procedure for investigating cyclic fatigue damage in brittle polycrystalline ceramics is described, and the mode of damage is one of deformation-induced intergranular microfracture, leading ultimately at large numbers of cycles and high contact pressures to severe grain dislodgement.
Abstract: A simple Hertzian contact procedure for investigating cyclic fatigue damage in brittle polycrystalline ceramics is described. Repeat loading of a spherical indenter on a coarse alumina ceramic produces cumulative mechanical damage. The mode of damage is one of deformation-induced intergranular microfracture, leading ultimately at large numbers of cycles and high contact pressures to severe grain dislodgement. In contrast to the classical Hertzian cone cracks that form in more homogeneous materials in the regions of tensile stress outside the contact circle, the damage in the coarse-grain alumina develops in a zone of high shear stress and hydrostatic compression beneath the contact circle
01 May 1993-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a three-dimensional finite element simulation is applied to investigate the general behavior of coated samples subjected to an indentation test, which provides the deformation characteristics and material displacements under or after local load as well as the stress distribution inside the coating and across the interface into the substrate.
Abstract: Three-dimensional finite element simulation is applied to investigate the general behavior of coated samples subjected to an indentation test. MARC®, a commercially available finite element software package, was used to study the Vickers indentation process on the following two representative systems: copper-coated high-speed steel as an example for a soft layer on a hard substrate and titanium nitride-coated high-speed steel as the reverse situation. The calculation provides the deformation characteristics and material displacements under or after local load as well as the stress distribution inside the coating and across the interface into the substrate. The results are given in two different cross-sectional planes, i.e., along the plane through one pair of the opposite pyramidal edges and along the plane perpendicular to one pair of the opposite pyramidal side faces. Distinct differences are obtained with respect to the material deformation, extension and shape of the stress fields and the plastically deformed zone. The indenter load vs. indentation depth relationship during loading and unloading as well as the hardnesses at peak load are also calculated for both examples. The hardness determination is based either on the diagonal of the residual permanent imprint (Vickers definition) or on the contact depth when loaded (similar to the plastic depth in the depth-sensing instrument) or on the real loaded contact area as provided by the finite element simulation.
TL;DR: In this paper, the authors applied the energy principle of indentation mechanics to the continuous indentation test performed on pure sapphire and found that the indentation hysteresis loop energy and the related true hardness parameter have been determined for various crystallographic orientations, as well as for two different orientations of the indenter.
Abstract: The recently developed energy principle of indentation mechanics was applied to the continuous indentation test performed on pure sapphire. Three crystallographic planes, M = (10$\overline 1$0), A = (1$\overline 1$10), and C = (0001), have been indented by a symmetrical triangular pyramid (Berkovich). The distinct anisotropic behavior of the indented crystal has been observed for the maximum indentation loads of 1.961 N, 0.686 N, and 0.392 N. The indentation hysteresis loop energy and the related “true hardness parameter” have been determined for various crystallographic orientations, as well as for two different orientations of the indenter. The observed effects have been discussed in terms of the energy principle of indentation with crystallographic considerations. The effective resolved shear stresses for the slip and twinning systems were calculated and applied to the anisotropic indentation behavior. It was concluded that the energy principle is highly recommended for analyzing the data of continuous indentation tests.