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Showing papers on "Indentation published in 2002"


Journal ArticleDOI
TL;DR: In this paper, the effects of the substrate on the determination of mechanical properties of thin films by nanoindentation were examined, and the properties of aluminum and tungsten films on the following substrates: aluminum, glass, silicon and sapphire.

1,410 citations


Journal ArticleDOI
TL;DR: In this article, the authors show that the indentation size effect for pyramidal and spherical indenters can be correlated, based on geometrically necessary dislocations and work-hardening.
Abstract: Experimental results are presented which show that the indentation size effect for pyramidal and spherical indenters can be correlated. For a pyramidal indenter, the hardness measured in crystalline materials usually increases with decreasing depth of penetration, which is known as the indentation size effect. Spherical indentation also shows an indentation size effect. However, for a spherical indenter, hardness is not affected by depth, but increases with decreasing sphere radius. The correlation for pyramidal and spherical indenter shapes is based on geometrically necessary dislocations and work-hardening. The Nix and Gao indentation size effect model (J. Mech. Phys. Solids 46 (1998) 411) for conical indenters is extended to indenters of various shapes and compared to the experimental results.

706 citations


Journal ArticleDOI
TL;DR: In this article, a simple model is developed based on observations from finite element simulations of indentation of elastic-plastic materials by a rigid cone that provides a physical explanation for the behavior.
Abstract: Experiments have shown that nanoindentation unloading curves obtained with Berkovich triangular pyramidal indenters are usually welldescribed by the power-law relation P = α(h − hf)m, where hf is the final depth after complete unloading and α and m are material constants. However, the power-law exponent is not fixed at an integral value, as would be the case for elastic contact by a conical indenter (m = 2) or a flat circular punch (m = 1), but varies from material to material in the range m = 1.2–1.6. A simple model is developed based on observations from finite element simulations of indentation of elastic–plastic materials by a rigid cone that provides a physical explanation for the behavior. The model, which is based on the concept of an indenter with an “effective shape” whose geometry is determined by the shape of the plastic hardness impression formed during indentation, provides a means by which the material constants in the power law relation can be related to more fundamental material properties such as the elastic modulus and hardness. Simple arguments are presented from which the effective indenter shape can be derived from the pressure distribution under the indenter.

439 citations


Journal ArticleDOI
TL;DR: Values of the elastic parameters of the cartilage are dependent on the measurement technique in use and may depend on the indenter size in use, as well as the equilibrium response of articular cartilage under unconfined and confined compression.

427 citations


Journal ArticleDOI
01 Jan 2002-Bone
TL;DR: The indentation modulus and hardness of bone ECM were investigated as a function of lamella type and indentation depth under wet and dry conditions and support compositional and/or ultrastructural differences between thick and thin lamellae.

336 citations


Journal ArticleDOI
TL;DR: In this article, the problem of indentation on a linear viscoelastic half-space is solved using the correspondence principle between elasticity and linear viscocelasticity, and the correction term due to creep in the apparent contact compliance is found to be equal to the ratio of the indenter displacement rate at the end of the load hold to the unloading rate.
Abstract: In modulus measurement by depth-sensing indentation, previous considerations assume elastic recovery to be the sole process during unloading, but in reality creep and thermal drift may also occur, causing serious errors in the measured modulus. In this work, the problem of indentation on a linear viscoelastic half-space is solved using the correspondence principle between elasticity and linear viscoelasticity. The correction term due to creep in the apparent contact compliance is found to be equal to the ratio of the indenter displacement rate at the end of the load hold to the unloading rate. A condition for nullifying the effect of thermal drift on modulus measurement is also proposed. With this condition satisfied, the effect of thermal drift on the calculated modulus is negligible irrespective of the magnitude of the drift rate.

313 citations


Journal ArticleDOI
TL;DR: In this paper, the authors link the indentation size effect (ISE) to a ratio between the energy of newly created surface and plastic strain energy dissipation, and propose an analytical model of hardness versus depth.
Abstract: For very shallow indentations in W, Al, Au, and Fe-3wt%Si single crystals, hardness decreased with increasing depth irrespective of increasing or decreasing strain gradients. As such, strain gradient theory appears insufficient to explain the indentation size effect (ISE) at depths less than several hundred nanometers. Present research links the ISE to a ratio between the energy of newly created surface and plastic strain energy dissipation. Also, the contact surface to plastic volume ratio was nearly constant for a range of shallow depths. Based on the above, an analytical model of hardness versus depth provides a satisfactory fit to the experimental data and correlates well with embedded atom simulations. ©2002 ASME

253 citations


Journal ArticleDOI
TL;DR: Results show that the effects of anisotropy on nanoindentation measurements can be quantitatively evaluated and are shown to exhibit the same trends as the corrected Mexp data.

242 citations


Journal ArticleDOI
TL;DR: In this paper, the authors present an attempt to explain in a simple way, understandable to a broad spectrum of readers, the unusual combination of the mechanical properties of the recently developed new class of superhard nanocomposites, such as high hardness which significantly exceeds that of the rule of mixtures, enhancement of the elastic modulus as measured by the indentation technique, very high elastic recovery which is observed upon the indentations and the absence of crack formation even under elastic deformation corresponding to a strain of more than 10%.
Abstract: This article presents an attempt to explain in a simple way, understandable to a broad spectrum of readers, the unusual combination of the mechanical properties of the recently developed new class of superhard nanocomposites, such as high hardness which significantly exceeds that of the rule of mixtures, enhancement of the elastic modulus as measured by the indentation technique, very high elastic recovery which is observed upon the indentation and the absence of crack formation even under elastic deformation corresponding to a strain of more than 10%. Future experimental work is suggested which should bring further progress towards the understanding of these materials.

235 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the low velocity impact response of a range of foam-based sandwich structures using an instrumented falling-weight impact tower and found that shear fracture was found in the PVC/PUR systems based on brittle core materials.
Abstract: The low velocity impact response of a range of foam-based sandwich structures has been investigated using an instrumented falling-weight impact tower. Initially, the rate-sensitivity of the skin and core materials was investigated through a series of flexure and indentation tests. Here, it was shown that the flexural modulus of the skins and all 11 foam materials did not exhibit any sensitivity to crosshead displacement rate over the conditions studied here. In addition, it was shown that the indentation response of the sandwich structures could be modelled using a simple indentation law, the parameters of which did not exhibit any sensitivity to loading rate. Low velocity impact tests on the sandwich structures resulted in a number of different failure modes. Here, shear fracture was found to occur in the PVC/PUR systems based on brittle core materials. In contrast, buckling failures in the uppermost composite skin were observed in the intermediate modulus systems, whereas initial damage in the higher modulus PVC/PUR systems took the form of delamination within the top surface skin. It has been shown that a simple energy-balance model based on the dissipation of energy during the impact event can be used to successfully model the elastic response of foam-based sandwich structures. The energy-balance model is particularly useful since it can be used to establish the partition of energy during the impact process.

231 citations


Journal ArticleDOI
TL;DR: In this article, the authors used a numerical method to simulate the fragmentation process induced by single and double indenters in a truncated indenter and showed that the simulated forcepenetration curve is an indication of the propagation of cracks, the crushing of microstructural grains and the formation of chips.

Journal ArticleDOI
TL;DR: Quantitative polarized light microscopy measurements from canine cartilage were utilized to characterize thickness and structure of the superficial, collageneous tissue layer as well as to reveal its relation to experimental indentation measurements, and FE results indicated effective stiffening of articular cartilage under indentation due to high transverse modulus of the deep tissue layer.

Journal ArticleDOI
TL;DR: In this article, the effect of specimen roughness on the accuracy of the indentation results is taken into account, and the results introduced show that the defined material elastoplastic deformation characteristics, based on the nanoindentation test results, are independent of the indenter type (Vickers or Berkovich) when deviations in the indent tip geometry from the ideal are considered.

Journal ArticleDOI
TL;DR: In this article, the authors studied the dependence of hardness on the loading time of the indentation process of a Chalcogenide glass, and showed that the penetration displacement is the sum of an elastic component which reaches values as high as 60% of the total displacement, and a creep one, which is strongly non-Newtonian (shear thinning), and leads to a significant decrease of hardness with an increase of loading time.
Abstract: Chalcogenide glasses from the Ge–Se system behave viscoelastically at room temperature. It follows that indentation measurements are time- or rate-dependent. The study of the dependence of hardness ( H ) on the loading duration for Ge x Se 1− x glasses with x between 0 and 0.4 shows that the penetration displacement is the sum of an elastic component which reaches values as high as 60% of the total displacement, and a creep one, which is strongly non-Newtonian (shear thinning), and leads to a significant decrease of H with an increase of the loading time. The apparent viscosity and activation energy for flow were derived from the H ( t ) data on the basis of a theoretical analysis of the indentation process, and the results are in good agreement with those obtained from conventional viscosity measurements.

Journal ArticleDOI
TL;DR: In this paper, the authors used rate effects to study low temperature deformation mechanisms using nanoindentation creep and load relaxation and found that the rate effects are conspicuous in terms of the rate sensitivity of the hardness, ∂H / ∂ ln e eff, and calculated the activation volume, V ∗, and compared data from indentation creep with data from uniaxial loading.

Journal ArticleDOI
TL;DR: The indentation method is not an adequate tool to exactly determine the fracture toughness of an unknown ceramic material and can only be used for a first rough K Ic estimation.

Journal Article
TL;DR: X-ray diffraction analysis showed that little phase transformation from tetragonal to monoclinic occurred when the specimens were fractured, supporting the existence of a modest difference of fracture toughness between the two ceramics.
Abstract: Purpose: This study compared the mechanical properties of In-Ceram Zirconia and InCeram Alumina. Materials and Methods: Ninety-four disks and six bars were prepared with the slip-casting technique. The disks were used to assess biaxial flexural strength (piston on three ball), Weibull modulus, hardness, and fracture toughness with two methods: indentation fracture and indentation strength. The bars were used to measure elastic moduli (Young’s modulus and Poisson’s ratio). X-ray diffraction analysis of the specimens was carried out upon every step of the specimen preparation and of the fractured surfaces. Results: Mean biaxial flexure strengths of In-Ceram Alumina and InCeram Zirconia were 600 MPa (SD 60) and 620 MPa (SD 61), respectively. Mean fracture toughness measured according to indentation strength was 3.2 MPa · m 1/2 (SD 0.34) for InCeram Alumina and 4.0 MPa · m 1/2 (SD 0.43) for In-Ceram Zirconia. Mean fracture toughnesses of In-Ceram Alumina and In-Ceram Zirconia measured according to indentation fracture were 2.7 MPa · m 1/2 (SD 0.34) and 3.0 MPa · m 1/2 (SD 0.48), respectively. X-ray diffraction analysis showed that little phase transformation from tetragonal to monoclinic occurred when the specimens were fractured, supporting the existence of a modest difference of fracture toughness between the two ceramics. Conclusion: No statistically significant difference was found in strength. In-Ceram Zirconia was tougher (P < .01) than In-Ceram Alumina when tested according to indentation strength. However, no significant difference was found in the fracture toughness when tested with the indentation fracture technique. Int J Prosthodont 2002;15:339‐346.

Journal ArticleDOI
TL;DR: In this article, a new high-temperature stage for small-scale mechanical property testing is described, which allows the determination of the load-penetration curve of a diamond tip in a temperature range extending from room temperature to 400°C.
Abstract: This paper describes a new high-temperature stage for small-scale mechanical property testing. This allows the determination of the load-penetration curve of a diamond tip in a temperature range extending from room temperature to 400°C. Both sample and indenter can be heated separately. Indentation curves show that very low thermal drift can be achieved. Nanoindentation results are presented for gold, soda—lime glass, fused silica and a polyimide and compared with existing microscale and bulk mechanical property data where available. Results from fused silica show that its mechanical properties exhibit a completely different temperature dependence from those of soda-lime glass, as expected since fused silica is an anomalous glass.

Journal ArticleDOI
TL;DR: In this article, the deformation of Pd−40Ni−20P bulk metallic glass (BMG) was investigated by instrumented nanoindentation experiments over a broad range of indentation strain rates.
Abstract: Plastic deformation of Pd–40Ni–20P bulk metallic glass (BMG) was investigated by instrumented nanoindentation experiments over a broad range of indentation strain rates. At low rates, the load–displacement curves during indentation exhibited numerous serrations or pop-ins, but these serrations became less prominent as the indentation rate was increased. Using the tip velocity during pop-in as a gauge of serration activity, we found that serrated flow is only significant at indentation strain rates below about 1–10/s. This result suggests a transition in plastic flow behavior at high strain rates, in agreement with prior studies of BMGs under different modes of loading.

Journal ArticleDOI
TL;DR: In this paper, several relationships that relate features of indentation loading and unloading curves to the hardness, the elastic modulus and the work of conical indentation in elastic-plastic solids with various angles are investigated.
Abstract: Using dimensional analysis and finite-element calculations, several relationships that relate features of indentation loading and unloading curves to the hardness, the elastic modulus and the work of indentation are extended to conical indentation in elastic-plastic solids with various angles. These relationships provide new insights into indentation measurements. They may also be useful to the interpretation of results obtained from instrumented indentation experiments.

Journal ArticleDOI
TL;DR: In this paper, the local elastic properties and the ferroelectric domain configuration of piezoelectric ceramics have been examined by atomic force acoustic microscopy and by ultrasonic PEM microscopy.
Abstract: The local elastic properties and the ferroelectric domain configuration of piezoelectric ceramics have been examined by atomic force acoustic microscopy and by ultrasonic piezoelectric force microscopy The contrast mechanisms of the two techniques are discussed From the local contact stiffness which is obtained by evaluation of the contact resonance spectra, the elastic constants of the sample surface can be calculated In the case of anisotropic materials these elastic constants correspond to the indentation moduli Indentation moduli for barium titanate and for a lead zirconate-titanate ceramics were calculated theoretically and are in reasonable agreement with experiments The non-linearity of the tip–sample interaction becomes noticeable at large vibration amplitudes or large mechanical tip loads

Journal ArticleDOI
TL;DR: In this article, a study concerning the hardness and the Young's modulus results determined by Vickers indentation on different materials was performed, and two methods were proposed for performing the indentation geometrical calibration of the contact area; these are compared with a former method proposed by Oliver and Pharr (OP).
Abstract: Depth-sensing indentation equipment is widely used for evaluation of the hardness and Young's modulus of materials. The depth resolution of this technique allows the use of ultra-low loads. However, aspects related to the determination of the contact area under indentation should be cautiously considered when using this equipment. These are related to the geometrical imperfections of the tip, the diamond pyramidal punch and the formation of pileup or the presence of sink-in, which alter the shape and size of the indent. These and other aspects, such as the thermal drift of the equipment and the scattering at the zero indentation depth position related to surface finishing, are discussed in this work. A study concerning the hardness and the Young's modulus results determined by Vickers indentation on different materials was performed. Samples of fused silica, BK7 glass, aluminium, copper and mild steel (for which the values of Young's modulus were previously known) were tested using indentation loads in the range 10–1000 mN. Moreover, two methods are proposed for performing the indentation geometrical calibration of the contact area; these are compared with a former method proposed by Oliver and Pharr (OP). The present methods are based on: (i) analysis of the punch profile using atomic force microscopy (AFM); and (ii) a linear penetration-depth function correction (LM), based on knowledge of the values of the Young's modulus of several materials. By applying these methods to the indentation load/indentation depth results, it was possible to draw some conclusions about the benefit of the AFM and LM methods now under proposal.

Journal ArticleDOI
TL;DR: In this paper, the apparent surface stress is defined as the energy dissipated per unit area of a solid surface in a nano-indentation test and a critical indentation depth is introduced.
Abstract: In this paper, we report on a study of the surface effect on nanoindentation and introduce the apparent surface stress that represents the energy dissipated per unit area of a solid surface in a nanoindentation test. The work done by an applied indentation load contains both bulk and surface work. Surface work, which is related to the apparent surface stress and the size and geometry of an indenter tip, is necessary in the deformation of a solid surface. Good agreement is found between theoretical first-order approximations and empirical data on depth-dependent hardness, indicating that the apparent surface stress plays an important role in depth-dependent hardness. In addition, we introduce a critical indentation depth. The surface deformation predominates if the indentation depth is shallower than the critical depth, while the bulk deformation predominates when the indentation depth is deeper than the critical depth.

Journal ArticleDOI
TL;DR: In this paper, a finite element method was used to study the initiation and advance of hard coatings during indentation, and the spacing between successive cracks was found to be of the order of the coating thickness.

Journal ArticleDOI
TL;DR: In this article, a new numerical and experimental approach for determining mechanical properties of steels is presented, based on the minimisation of error between the experimental curve (applied load-indenter displacement curve) and the theoretical curve which is a function of the studied materials.

Journal ArticleDOI
TL;DR: In this paper, the deformation of Zr-base and La-base metallic glass is investigated using instrumented nanoindentation experiments over a broad range of indentation strain rates.

Journal ArticleDOI
TL;DR: In this paper, the authors used the nano-indentation technique to measure hardness and elastic moduli profiles of AA6061 reinforced with Al2O3 particles, since it allows measurements of mechanical properties on a micrometer range.
Abstract: The nano-indentation technique is a suitable technique to measure hardness and elastic moduli profiles of AA6061 reinforced with Al2O3 particles, since it allows measurements of mechanical properties on a micrometer range. To investigate possible local variations in mechanical behaviour of the matrix material due to precipitation reactions being affected by the presence of ceramic reinforcements, nano-indentation tests were done on both metal matrix composite (MMC) as well as unreinforced reference material, in three different heat treatment conditions. Matrix response depends on heat treatment condition, but is approximately equal for the MMC and the base reference alloy. Due to the various imposed heat treatments, magnesium enrichment around the ceramic particles was observed, but hardness and elastic modulus of this interfacial layer could not be measured. To confirm the preferential segregation of Mg near the particle/matrix interface, linescans were made with a Scanning Electron Microscope (SEM) equipped with EDS (Energy Dispersive Spectrum) facilities. The limited width of the Mg rich zone explains the absence of typical 'interphase' indentations in this investigation. Hardly any differences in calculated elastic moduli and hardness values were found for the three heat treatment conditions investigated, when comparing results of AA6061 reference material with results of an AA6061 matrix in an MMC. This result is of great importance when modelling the mechanical behaviour of MMCs using the finite element method, since it permits the assumption that the MMC matrix material behaves similar to the same aluminium alloy without ceramic reinforcements.

Journal ArticleDOI
TL;DR: In this article, the authors developed an indentation model based on the theory of mechanism-based strain gradient plasticity to study the effect of the indenter tip radius on indentation hardness.
Abstract: The micro-indentation experiments have shown that the indentation hardness depends not only on the indentation depth hut also on the indenter tip radius. In fact, the indentation hardness displays opposite dependence on the indentation depth h for a sharp, conical indenter and for a spherical indenter, decreasing and increasing, respectively, with increasing h. We have developed an indentation model based on the theory of mechanism-based strain gradient plasticity to study the effect of indenter tip radius. The same indentation model captures this opposite depth dependence of indentation hardness, and shows the opposite depth dependence resulting from the different distributions of strain and strain gradient underneath a conical indenter and a spherical indenter. We have also used the finite element method to study the indentation hardness for a spherical indenter as well as for a conical indenter with a spherical tip. It is established that the effect of indenter tip radius disappears once the contact radius exceeds one half of the indenter tip radius.

Journal ArticleDOI
TL;DR: The mechanical deformation of wurtzite GaN epilayers grown on sapphire substrates is studied by spherical indentation, cross-sectional transmission electron microscopy (XTEM), and scanning cathodoluminescence (CL) monochromatic imaging as mentioned in this paper.
Abstract: The mechanical deformation of wurtzite GaN epilayers grown on sapphire substrates is studied by spherical indentation, cross-sectional transmission electron microscopy (XTEM), and scanning cathodoluminescence (CL) monochromatic imaging. CL imaging of indents which exhibit plastic deformation (based on indentation data) shows an observable “footprint” of deformation-produced defects that result in a strong reduction in the intensity of CL emission. Multiple discontinuities are observed during loading when the maximum load is above the elastic-plastic threshold, and such a behavior can be correlated with multiple slip bands revealed by XTEM. No evidence of pressure-induced phase transformations is found from within the mechanically damaged regions using selected-area diffraction patterns. The main deformation mechanism appears to be the nucleation of slip on the basal planes, with dislocations being nucleated on additional planes on further loading. XTEM reveals no cracking or delamination in any of the sam...

Journal ArticleDOI
TL;DR: In this article, the authors proposed a neural network-based method for the determination of the reduced modulus as well as the nonlinear hardening behavior of both the film and substrate materials.
Abstract: The indentation experiment is a popular method for the investigation of mechanical properties of thin films. By application of conventional methods, the hardness and the stiffness of the film material can be determined by limiting the indentation depth to well below the film thickness so that the substrate effects can be eliminated. In this work a new method is proposed, which allows for a determination of the reduced modulus as well as the nonlinear hardening behaviour of both the film and substrate materials. To this end, comparable deep indentations are made on the film/substrate composite to obtain sufficient information on the mechanical properties of both materials. The inverse problem is solved by training neural networks on the basis of finite–element simulations using only the easily measurable hardness and stiffness behaviour as input data. It is shown that the neural networks are very robust against noise in the load and depth. The identification of the material parameters of aluminium films on different substrates results in a significant increase in yield stress and initial work–hardening rate for a reduction of the film thickness from 1.5 to 0.5 µm, while the elastic modulus and the extent of work hardening remain constant.