Showing papers on "Indentation published in 2000"
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01 Jan 2000
TL;DR: In this article, the authors present a depth-sensing Indentation Testing (DSIT) test for brittle fracture in brittle solids, which is based on the Hertzian Fracture.
Abstract: Mechanical Properties of Materials.- Linear Elastic Fracture Mechanics.- Delayed Fracture in Brittle Solids.- Statistics of Brittle Fracture.- Elastic Indentation Stress Fields.- Elastic Contact.- Hertzian Fracture.- Elastic-Plastic Indentation Stress Fields.- Hardness.- Elastic and Elastic-Plastic Contact.- Depth-Sensing Indentation Testing.- Indentation Test Methods.
577 citations
TL;DR: In this paper, Suresh et al. described nanoindentation experiments on thin films of polycrystalline Al of known texture and different thicknesses, and of single crystal Al of different crystallographic orientations.
494 citations
TL;DR: In this article, the reverse type of indentation size effect (ISE), where the apparent microhardness increases with increasing applied test load, was critically examined for the experimentally reported data for a number of single crystals differing in crystal structure and chemical bond, using the theoretical models reported in the literature.
412 citations
TL;DR: In this article, the phase transformation of diamond cubic silicon under nano-indentation with the aid of molecular dynamics analysis using the Tersoff potential was discussed. But, the authors did not consider the effect of nanoindentations on the transition from a tetrahedron structure to an amorphous phase.
Abstract: This paper discusses the phase transformation of diamond cubic silicon under nano-indentation with the aid of molecular dynamics analysis using the Tersoff potential. By monitoring the positions of atoms within the model, the microstructural changes as silicon transforms from its diamond cubic structure to other phases were identified. The simulation showed that diamond cubic silicon transforms into a body-centred tetragonal form (β-silicon) upon loading of the indentor. The change of structure is accomplished by the flattening of the tetrahedron structure in diamond cubic silicon. Upon unloading, the body-centred tetragonal form transforms into an amorphous phase accompanied by the loss of long-range order of the silicon atoms. By performing a second indentation on the amorphous zone, it was found that the body-centred-tetragonal-to-amorphous phase transformation could be a reversible process.
307 citations
TL;DR: In this paper, the methods of analysis of data obtained from sub-micron indentation testing such as that performed on thin-film systems are discussed and the underlying theory behind the extraction of elastic modulus and hardness from the unloading load-displacement data obtained with spherical indenter and Berkovich pyramidal indenters is given in some detail.
294 citations
TL;DR: In this article, the authors derived the solutions of the equations of viscoelastic deformation under the boundary conditions of flat-punch indentation of a viscous half-space.
Abstract: The indentation of standard viscoelastic solids, that is, the three-element viscoelastic material, by an axisymmetric, flat-ended indenter has been investigated theoretically. Under the boundary conditions of flat-punch indentation of a viscoelastic half-space, the solutions of the equations of viscoelastic deformation are derived for the standard viscoelastic material. Their generality resides in their inclusion of compressible as well as incompressible solids. They cover the two transient situations: flat-punch creep test and load-relaxation test. In experimental tests of their applicability, nanoindentation and microindentation probes under creep and relaxation conditions yielded a modulus from 0.1 to 1.1 GPa and viscosity from 1 to 37 Gpa · s for a crosslinked glassy polyurethane coatings. For bulk polystyrene, the values vary from 1 to 2 GPa and from 20 to 40 Gpa · s, respectively. The analysis here provides a fundamental basis for probing elastic and viscous properties of coatings with nanoindentation or microindentation tests. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 10–22, 2000
241 citations
01 Jan 2000
TL;DR: Instrumented indentation testing (IIT) as mentioned in this paper is a relatively new form of mechanical testing that significantly expands on the capabilities of traditional hardness testing and has been widely used in the literature.
Abstract: INSTRUMENTED INDENTATION TESTING (IIT), also known as depth-sensing indentation, continuous-recording indentation, ultra-low-load indentation, and nanoindentation, is a relatively new form of mechanical testing that significantly expands on the capabilities of traditional hardness testing. Developed largely over the past two decades, IIT employs high-resolution instrumentation to continuously control and monitor the loads and displacements of an indenter as it is driven into and withdrawn from a material (Ref 1–13). Depending on the details of the specific testing system, loads as small as 1 nN can be applied, and displacements of 0.1 nm (1 A) can be measured. Mechanical properties are derived from the indentation load-displacement data obtained in simple tests. The advantages of IIT are numerous, as indentation load-displacement data contain a wealth of information, and techniques have been developed for characterizing a variety of mechanical properties. The technique most frequently employed measures the hardness, but it also gives the elastic modulus (Young’s modulus) from the same data (Ref 8, 11). Although not as well-developed, methods have also been devised for evaluating the yield stress and strain-hardening characteristic of metals (Ref 14–16); parameters characteristic of damping and internal friction in polymers, such as the storage and loss modulus (Ref 17, 18); and the activation energy and stress exponent for creep (Ref 19–25). IIT has even been used to estimate the fracture toughness of brittle materials using optical measurement of the lengths of cracks that have formed at the corners of hardness impressions made with special sharp indenters (Ref 13, 26, 27). In fact, almost any material property that can be measured in a uniaxial tension or compression test can conceivably be measured, or at least estimated, using IIT. An equally important advantage of IIT results because load-displacement data can be used to determine mechanical properties without having to image the hardness impressions. This facilitates property measurement at very small scales. Mechanical properties are routinely measured from submicron indentations, and with careful technique, properties have even been determined from indentations only a few nanometers deep. Because of this, IIT has become a primary tool for examining thin films, coatings, and materials with surfaces modified by techniques such as ion implantation and laser heat treatment. Many IIT testing systems are equipped with automated specimen manipulation stages. In these systems, the spatial distribution of the near-surface mechanical properties can be mapped on a point-to-point basis along the surface in a fully automated way. Lateral spatial resolutions of about a micron have been achieved. An example of small indentations located at specific points in an electronic microcircuit is shown in Fig. 1. The purpose of this article is to provide a practical reference guide for instrumented indentation testing. Emphasis is placed on the better-developed measurement techniques and the procedures and calibrations required to obtain accurate and meaningful measurements.
229 citations
TL;DR: In this article, a theoretical framework for instrumented sharp indentation and a general methodology that enables determination of the elasto-plastic properties of (and residual stresses in) materials through an analysis of the force-depth (P-h) relationship was presented.
220 citations
TL;DR: In this paper, a yield surface is proposed to describe cellular solids, including foamed metals, and designed to be fitted to three experimental results: (1) the compressive stress-strain response (including densification), (2) the difference between the tensile and compressive yield points and (3) the degree of compressibility of the foam, as measured by the lateral expansion during a uniaxial stress compression test.
215 citations
TL;DR: Tapping-mode atomic force microscopy was used to study the radial deformability of a multiwalled carbon nanotube (MWCNT) and demonstrate its remarkable reversible radial deformable and reveal internal discontinuities along its length.
Abstract: Tapping-mode atomic force microscopy was used to study the radial deformability of a multiwalled carbon nanotube (MWCNT). By imaging the MWCNT under different tapping forces, we were able to demonstrate its remarkable reversible radial deformability (up to $\ensuremath{\sim}40%$) and reveal internal discontinuities along its length. The values of the effective elastic modulus of several sections of the MWCNT in the radial direction were estimated with the Hertz model.
199 citations
TL;DR: In this article, the surface displacement at the contact boundary under applied load and in the unloaded state is correlated with the uniaxial strain hardening exponent, n, and it is found that sinking-in predominates in materials where n > 0.2.
TL;DR: In this article, the authors used cross-sectional transmission electron microscopy (XTEM) to study spherical indentation of crystalline silicon and found that a thin layer of polycrystalline material has been identified on the low-load indentation.
Abstract: Spherical indentation of crystalline silicon has been studied using cross-sectional transmission electron microscopy (XTEM). Indentation loads were chosen below and above the yield point for silicon to investigate the modes of plastic deformation. Slip planes are visible in the XTEM micrographs in both indentation loads studied. A thin layer of polycrystalline material has been identified (indexed as Si-XII from diffraction patterns) on the low-load indentation. The higher-load indentation revealed a large region of amorphous silicon. The sequence of structural deformation by indentation in silicon has been observed with the initial deformation mechanism being slip until phase transformations can take place.
TL;DR: In this article, the authors present the results of an experimental investigation concerning the low-velocity impact response of sandwich composites with graphite/epoxy face sheets and foam or honeycomb cores.
TL;DR: The hypothesis under examination in this paper is that the lifetimes of dental restorations are limited by the accumulation of contact damage during oral function; and, moreover, that strengths of dental ceramics are significantly lower after multi- cycle loading than after single-cycle loading.
Abstract: The hypothesis under examination in this paper is that the lifetimes of dental restorations are limited by the accumulation of contact damage during oral function; and, moreover, that strengths of dental ceramics are significantly lower after multi-cycle loading than after single-cycle loading. Accordingly, indentation damage and associated strength degradation from multi-cycle contacts with spherical indenters in water are evaluated in four dental ceramics: "aesthetic" ceramics-porcelain and micaceous glass-ceramic (MGC), and "structural" ceramics-glass-infiltrated alumina and yttria-stabilized tetragonal zirconia polycrystal (Y-TZP). At large numbers of contact cycles, all materials show an abrupt transition in damage mode, consisting of strongly enhanced damage inside the contact area and attendant initiation of radial cracks outside. This transition in damage mode is not observed in comparative static loading tests, attesting to a strong mechanical component in the fatigue mechanism. Radial cracks, once formed, lead to rapid degradation in strength properties, signaling the end of the useful lifetime of the material. Strength degradation from multi-cycle contacts is examined in the test materials, after indentation at loads from 200 to 3000 N up to 10(6) cycles. Degradation occurs in the porcelain and MGC after approximately 10(4) cycles at loads as low as 200 N; comparable degradation in the alumina and Y-TZP requires loads higher than 500 N, well above the clinically significant range.
TL;DR: In this article, the geometry of the grooves left on the surface of a viscoelastic viscoplastic body by a moving cone-shaped diamond tip having a radius of about 40 μm was analyzed.
Abstract: Most existing models describing the scratch properties of materials take into account forces acting at the interface between the material and a grooving tip, but do not consider the stress and strain properties of the material far beneath or ahead of the tip. In the case of polymer scratches, there are no models at all which take into account the viscoelastic viscoplastic behaviour of the material. In standard indentation tests with a non moving tip, the elastic plastic boundary and the limits of the region subjected to hydrostatic pressure beneath the tip are known. These models were used to analyse the geometry of the grooves left on the surface of a viscoelastic viscoplastic body by a moving cone-shaped diamond tip having a radius of about 40 μm. A new apparatus was built to control the velocity of the tip over the range 1 to 104 μm/s, at several different temperatures from −10°C to 100°C. The material was a commercial grade of cast poly(methylmethacrylate) (PMMA). The normal and tangential loads and groove size were used to evaluate the dynamic hardness, which behaved like a stress and temperature activated process. Values of the activation energy and volume of the dynamic hardness and of the interfacial shear stress were in good agreement with those usually attributed to the mechanical properties of PMMA.
TL;DR: Komanduri et al. as discussed by the authors investigated the anisotropy in hardness and friction coefficient of single crystal aluminum in various crystal orientations and directions of scratching, and found that the hardness is increased significantly as the indentation depth is reduced to atomic dimensions.
TL;DR: In this article, the authors presented a new interpretation of nanoindentation data for silicon, germanium, and gallium arsenide based on Raman microanalysis of indentations.
Abstract: This paper supplies new interpretation of nanoindentation data for silicon, germanium, and gallium arsenide based on Raman microanalysis of indentations. For the first time, Raman microspectroscopy analysis of semiconductors within nanoindentations is reported. The given analysis of the load-displacement curves shows that depth-sensing indentation can be used as a tool for identification of pressure-induced phase transformations. Volume change upon reverse phase transformation of metallic phases results either in a pop-out (or a kink-back) or in a slope change (elbow) of the unloading part of the load-displacement curve. Broad and asymmetric hysteresis loops of changing width, as well as changing slope of the elastic part of the loading curve in cyclic indentation can be used for confirmation of a phase transformation during indentation. Metallization pressure can be determined as average contact pressure (Meyer’s hardness) for the yield point on the loading part of the load-displacement curve. The pressure of the reverse transformation of the metallic phase can be measured from pop-out or elbow on the unloading part of the diagram. For materials with phase transformations less pronounced than in Si, replotting of the loaddisplacement curves as average contact pressure versus relative indentation depth is required to determine the transformation pressures and/or improve the accuracy of data interpretation.
TL;DR: In this article, the authors derived simple scaling relationships for loading and unloading curve, contact depth, and hardness, and derived a scaling theory for indentation in power-law creep solids using self-similar indenters.
Abstract: Using dimensional analysis and finite element calculations, we derive simple scaling relationships for loading and unloading curve, contact depth, and hardness. The relationship between hardness and the basic mechanical properties of solids, such as Young's modulus, initial yield strength, and work-hardening exponent, is then obtained. The conditions for 'piling-up' and 'sinking-in' of surface profiles during indentation are determined. A method for estimating contact depth from initial unloading slope is examined. The work done during indentation is also studied. A relationship between the ratio of hardness to elastic modulus and the ratio of irreversible work to total work is discovered. This relationship offers a new method for obtaining hardness and elastic modulus. Finally, a scaling theory for indentation in power-law creep solids using self-similar indenters is developed. A connection between creep and 'indentation size effect' is established.
TL;DR: In this paper, the authors used a scanning force microscope (SFM) scanner with three laser interferometers fitted in the co-ordinate axes x, y and z to measure the area function near the indenter tip.
TL;DR: A series of tests have been conducted on (i) auxetic, (ii) compression moulded and (iii) sintered ultra high molecular weight polyethylene as discussed by the authors, and it was found that the auxetic material was both more difficult to indent than the other materials at low loads (from 10-100 N) and was the least plastic with the most rapid viscoelastic creep recovery of any residual deformation.
Abstract: A series of tests have been conducted on (i) auxetic, (ii) compression moulded and (iii) sintered ultra high molecular weight polyethylene. The auxetic material possesses a negative Poisson's ratio, ν, due to its complex porous microstructure which consists of nodules interconnected by fibrils and the sintered material has a positive ν and is microporous but does not contain fibrils. It was found that the auxetic material was both more difficult to indent than the other materials at low loads (from 10–100 N) and was the least plastic with the most rapid viscoelastic creep recovery of any residual deformation. Indeed, at low loads, where the resistance to local indentation is most elastic, the hardness increased by up to a factor of 8 on changing the Poisson's ratio from ν ≈ 0 to ν ≈ −0.8. A mechanism is proposed based on local densification under the indentor of the nodules and fibrils which explains how the microstructural response of an auxetic polymer can be used to interpret the results.
TL;DR: In this article, the authors used the indentation quench method to explore susceptibility to thermal fracture in a range of brittle materials on condition that it is possible to insert an indentation precrack.
TL;DR: In this paper, both static and dynamic Vickers indentations were performed on brittle materials to investigate the rate effects in hardness, induced crack morphologies, and fracture toughness on material removal mechanisms.
TL;DR: In this article, a diamond indenter was used and its actual shape determined by scanning force microscopy with a calibration grid, 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.
TL;DR: In this paper, it is shown that a separation of the elastic film properties is possible by using a novel analytical solution for the elastic deformation of a film on a flat substrate can be used to simulate the load-depth data.
Abstract: Indentation is an important method for the determination of mechanical properties of surfaces and thin films. It is well known that the measurement results from thin layers are strongly influenced by the substrate properties. For hardness measurements it is frequently quoted that the indentation depth should be less than one-tenth of the film thickness (1/10th rule). This rule is often not practicable for thickness values below 1 μm. Therefore a correction method is required that allows the separation of substrate and film properties from the load-depth data. Moreover, the calculation is complicated if plastic deformation occurs. The use of a spherical indenter allows one to remain completely within the elastic range if the indenter radius is large enough and the load is low enough. In this case a novel analytical solution for the elastic deformation of a film on a flat substrate can be used to simulate the load-depth data. With this solution the determination of Young’s modulus of thin layers is possible independent of indentation depth and film thickness. Measurement data from a UMIS-2000 indentation system for different film substrate combinations are compared with theoretical results. It is shown, that a separation of the elastic film properties is possible. For metal films on Si the load-depth data did not differ from that of uncoated substrates. This can be explained mainly by delamination.
TL;DR: In this paper, the energy dissipated during normal indentation of coated materials is analyzed and related to the coating and interfacial fracture toughness, and the relationship between irreversibly dissipated energy and the ratio of the hardness to elastic modulus is analyzed in detail and it is shown that this relationship is similar as for monolithic materials, although various fracture events occurred.
Abstract: The energy dissipated during normal indentation of coated materials is analyzed and related to the coating and interfacial fracture toughness. Hybrid organic–inorganic coatings, which were prepared using a sol–gel process, were used as model materials. The loading and unloading curves are integrated and the differences in irreversibly dissipated energy after delamination and chipping are used to calculate the energy release rates. The calculated energy release rates are inversely proportional to the coating thickness and a factor of up two tens larger than previous results. Furthermore, it is shown that the energy dissipated during indentation is a measure of the system's response and that the system's response is altered by the fracture events. Extrapolation to infinite coating thickness leads to values that are in agreement with previously published results. The relationship between irreversibly dissipated energy and the ratio of the hardness to elastic modulus is analyzed in detail and it is shown that this relationship is similar as for monolithic materials, although various fracture events occurred, thus suggesting that the underlying relationship is independent of the history of the coating–substrate system.
TL;DR: In this article, a relative method for measuring the Young's modulus E of a polymer surface by AFM indentation, involving a calibration step obtained from a set of standards constituted by pure polymers with known modulus, was proposed.
Abstract: Atomic force microscopy (AFM) is currently used to investigate polymer surface morphology, to obtain roughness parameters or to map the qualitative differences of surface properties. Some previous studies have attempted to determine quantitatively the elastic surface properties, but the difficulty with AFM is that the contact geometry is not very well known, due to the complexity of the mechanical system composed of the cantilever-tip set and the solid surface. We propose here a relative method for measuring the Young's modulus E of a polymer surface by AFM indentation, involving a calibration step obtained from a set of standards constituted by pure polymers with known modulus. Contact stiffness, indentation at peak load and shape of unloading curve are obtained for each reference polymer, leading to a linear relationship between E and a function of these parameters. This calibration curve allows the unknown Young's modulus values of the different phases at the surface of a biphase polymer system to be determined. The force volume mode was used to record force curves. Compared to classical indentation techniques, the force volume mode gives the advantage of imaging surface domains exhibiting elasticity differences. Thus, the elastic modulus can be quantified with a spatial resolution on a nanometric scale.
TL;DR: In this paper, the radial compressive elastic modulus at different compression levels and the compressive strength to be well beyond 5.3 GPa have been determined using a scanning probe microscope with an indentation/scratch function.
Abstract: Efforts have been made to characterize the mechanical properties of carbon nanotubes. Previous work has concentrated on the tubes' longitudinal properties, and studies of their radial properties have lagged behind. We have used a scanning probe microscope with an indentation/scratch function to investigate the radial compression of multiwalled carbon nanotubes under an asymmetric stress. In particular, we have determined the radial compressive elastic modulus at different compression levels and have estimated the compressive strength to be well beyond 5.3 GPa.
01 Jun 2000
TL;DR: A generalized equation between elastic indentation depth and load is proposed that approximates Maugis' solution very closely and can be easily fit to experimental data.
Abstract: Continuum mechanics models describing the contact between two adhesive elastic spheres, such as the JKR and DMT models, provide a relationship between the elastic indentation depth and the normal load, but the general intermediate case between these two limiting cases requires a more complex analysis. The Maugis–Dugdale theory gives analytical solutions, but they are difficult to use when comparing to experimental data such as those obtained by scanning force microscopy. In this paper we propose a generalized equation between elastic indentation depth and load that approximates Maugis' solution very closely. If the normal contact stiffness can be described as the force gradient, that is the case of the force modulation microcopy, then a generalized equation between normal contact stiffness and load can be deduced. Both general equations can be easily fit to experimental data, and then interfacial energy and elastic modulus of the contact can be determined if the radius of the indenting sphere is known.
TL;DR: In this article, the indentation load-displacement behavior of an organic-inorganic hybrid coating was tested using a Berkovich indenter in an attempt to offer a simple and fast method to analyze the mechanical properties of a coating.