Showing papers on "Indentation published in 1992"
TL;DR: In this paper, the authors used a Berkovich indenter to determine hardness and elastic modulus from indentation load-displacement data, and showed that the curve of the curve is not linear, even in the initial stages of the unloading process.
Abstract: The indentation load-displacement behavior of six materials tested with a Berkovich indenter has been carefully documented to establish an improved method for determining hardness and elastic modulus from indentation load-displacement data. The materials included fused silica, soda–lime glass, and single crystals of aluminum, tungsten, quartz, and sapphire. It is shown that the load–displacement curves during unloading in these materials are not linear, even in the initial stages, thereby suggesting that the flat punch approximation used so often in the analysis of unloading data is not entirely adequate. An analysis technique is presented that accounts for the curvature in the unloading data and provides a physically justifiable procedure for determining the depth which should be used in conjunction with the indenter shape function to establish the contact area at peak load. The hardnesses and elastic moduli of the six materials are computed using the analysis procedure and compared with values determined by independent means to assess the accuracy of the method. The results show that with good technique, moduli can be measured to within 5%.
22,557 citations
TL;DR: In this paper, Sneddon's analysis for the elastic contact between a rigid, axisymmetric punch and an elastic half space is used to show that a simple relationship exists between the contact stiffness, the contact area, and the elastic modulus that is not dependent on the geometry of the punch.
Abstract: Results of Sneddon's analysis for the elastic contact between a rigid, axisymmetric punch and an elastic half space are used to show that a simple relationship exists between the contact stiffness, the contact area, and the elastic modulus that is not dependent on the geometry of the punch. The generality of the relationship has important implications for the measurement of mechanical properties using load and depth sensing indentation techniques and in the measurement of small contact areas such as those encountered in atomic force microscopy.
1,363 citations
TL;DR: In this article, a software-controlled hardness tester (Nanoindenter) operating in the load range 2-60 mN was used to characterize the deformation structures associated with these very small-scale hardness impressions.
Abstract: The ultra-low load indentation response of ceramic single crystal surfaces (Al2O3, SiC, Si) has been studied with a software-controlled hardness tester (Nanoindenter) operating in the load range 2–60 mN. In all cases, scanning and transmission electron microscopy have been used to characterize the deformation structures associated with these very small-scale hardness impressions. Emphasis has been placed on correlating the deformation behavior observed for particular indentations with irregularities in recorded load-displacement curves. For carefully annealed sapphire, a threshold load (for a given indenter) was observed below which the only surface response was elastic flexure and beyond which dislocation loop nucleation occurred at, or near, the theoretical shear strength to create the indentation. This onset of plasticity was seen as a sudden displacement discontinuity in the load-displacement response. At higher loads, indentations appeared to be accommodated predominantly by dislocation activity, though microcracks were observed to form at contact loads of only tens of milliNewtons. Possibly such cracks are the incipient slip-induced nuclei for the much larger, indentation-induced cracks usually apparent only on the surface at much higher loads and often used for estimating indentation toughness. By contrast, silicon did not show this behavior but exhibited unusually large amounts of depth recovery within indentations, resulting in a characteristic reverse thrust on the indenter during unloading. TEM studies of indentations in silicon revealed less evidence of obvious dislocation activity than in sapphire (particularly at the lowest loads used) but did show residual highly imperfect–and often amorphous–structures within the indentations, consistent with a densification transformation occurring at the very high hydrostatic stresses produced under the indenter. The reverse thrust is caused by the relaxation of densified material during unloading. Thus, it appears that the low-load hardness response of silicon is controlled by a pressure-sensitive phase transformation. Though SiC has been predicted to undergo a densification transformation similar to silicon, its load-displacement behavior was found to be similar to Al2O3 suggesting that, for these contact experiments at least, the critical resolved shear stress for dislocation nucleation is exceeded before the critical hydrostatic pressure for densification is reached. In all cases, residual, plastically formed indentations were measured to be smaller than the fully loaded indentation depths would suggest, confirming that a significant portion of the deformation is elastic surface flexure. However, there is some doubt as to whether silicon displays elastic-only deformation even at very small penetration depths. The use of microstructural studies to complement nanoindentation experiments is shown to be a key route not only to interpreting the recorded load-displacement responses, but also to examining the deformation mechanisms controlling the mechanical behavior of ceramics to surface contacts at these small spatial scales.
509 citations
TL;DR: In this paper, the elastic contact problem of a rigid cylindrical punch indenting a multi-layered linear elastic half space is studied and then used to model the unloading phase of a microindentation test of thin fims deposited on a substrate.
438 citations
TL;DR: In this article, the effect of surface friction characteristics of aramid fabrics with respect to their static deformation behavior and their ballistic capture performance was investigated, and a simulation of the ballistic deformation process in fabrics was devised on the basis of this first-order model of the quasi static indentation process.
226 citations
TL;DR: The nanoindentation technique for submicrohardness measurement described elsewhere in this issue by Pharr and Oliver is a recent example of such an approach as mentioned in this paper, but it is difficult to separate the influence of the substrate properties from the film properties, and the indentation process is inherently too complex to determine fundamental materials parameters.
Abstract: Evaluating the mechanical properties of thin films on thick substrates is tricky. Some useful techniques for mechanical property measurements on macroscopic film specimens exist, e.g., internal stress measurements by x-ray diffraction or by wafer buckling. Many conventional techniques, however, such as indentation for hardness measurement or scratch testing for evaluation of adhesion or wear resistance, yield results that are difficult or impossible to evaluate in terms of more fundamental film properties. In fact, these techniques are more practical engineering tools than tools for scientific study.One solution is to miniaturize the test probe to dimensions approaching the film thickness. The nanoindentation technique for submicrohardness measurement described elsewhere in this issue by Pharr and Oliver is a recent example of such an approach. Still, for very thin films it is difficult to separate the influence of the substrate properties from the film properties, and the indentation process is inherently too complex to be well suited for determining fundamental materials parameters.The rapidly evolving field of micromechanics offers some new possibilities in thin film characterization. Important film properties such as internal stress, elastic moduli, plastic yield limit, and fracture data can be extracted from experiments with micromachined test structures in the 10–1,000 μm size range.
164 citations
TL;DR: The short-time stress-relaxation responses of the tissue demonstrate the essential role of the fluid phase in supporting the load applied to the tissue, and by extrapolation to shorter times characteristics of normal joint motion, suggest the essential roles of a biphasic model in representing soft tissue behavior in joint response.
Abstract: The indentation problem of a thin layer of hydrated soft tissue such as cartilage or meniscus by a circular plane-ended indenter is investigated. The tissue is represented by a biphasic continuum model consisting of a solid phase (collagen and proteoglycan) and a fluid phase (interstitial water). A finite element formulation of the linear biphasic continuum equations is used to solve an axisymmetric approximation of the indentation problem. We consider stress-relaxation problems for which analytic solution is intractable; where the indenter is impermeable (solid) and/or when the interface between the indenter and tissue is perfectly adhesive. Thicknesses corresponding to a thin and thick specimen are considered to examine the effects of tissue thickness. The different flow, pressure, stress and strain fields which are predicted within the tissue, over time periods typically used in the mechanical testing of soft tissues, will be presented. Results are compared with the case of a porous free-draining indenter with a perfectly lubricated tissue-indenter interface, for which an analytic solution is available, to show the effects of friction at the tissue-indenter interface, and the effects of an impermeable indenter. While these effects are present for both thin and thick tissues, they are shown to be more significant for the thin tissue. We also examine the effects of the stiffness of the subchondral bone on the response of the soft tissue and demonstrate that the subchondral bone substrate can be modeled as a rigid, impermeable boundary. The effects of a curved tissue-subchondral bone interface, and the early time response are also studied. For physiologically reasonable levels of curvature, we will show that the curved tissue-subchrondral bone interface has negligible influence on the tissue response away from the interface. In addition, the short-time stress-relaxation responses of the tissue (e.g., at times less than 1s) demonstrate the essential role of the fluid phase in supporting the load applied to the tissue, and by extrapolation to shorter times characteristics of normal joint motion, suggest the essential role of a biphasic model in representing soft tissue behavior in joint response.
152 citations
TL;DR: In this article, an objective methodology is developed for evaluating toughness curves (T-curves) of ceramics using indentation flaws, using data on an appropriate base material with single-valued toughness.
Abstract: An objective methodology is developed for evaluating toughness curves (T-curves) of ceramics using indentation flaws. Two experimental routes are considered: (i) conventional measurement of inert strength as a function of indentation load; (ii) in situ measurement of crack size as a function of applied stress. Central to the procedure is a proper calibration of the indentation coefficients that determine the K-field of indentation cracks in combined residual-contact and applied-stress loading, using data on an appropriate base material with single-valued toughness. Tests on a fine-grain alumina serve to demonstrate the approach. A key constraint in the coefficient evaluation is an observed satisfaction of the classical indentation strength–(load)−1/3 relation for such materials, implying an essential geometrical similarity in the crack configurations at failure. T-curves for any alumina-based ceramic without single-valued toughness can then be generated objectively from inert-strength or in situ crack-size data. The methodology thereby circumvents the need for any preconceived model of toughening, or for any prescribed analytical representation of the T-curve function. Data on coarse-grained aluminas and alumina-matrix material with aluminum titanate second-phase particles are used in an illustrative case study.
138 citations
TL;DR: In this paper, the effects of indentation on the electrical resistance of rectifying gold-chromium contacts on silicon and germanium have been studied using nanoindentation techniques, and it was shown that a large portion of the resistance drop is due to decreases in the resistance of the metal-to-semiconductor interface rather than the bulk semiconductor.
Abstract: The effects of indentation on the electrical resistance of rectifying gold-chromium contacts on silicon and germanium have been studied using nanoindentation techniques. The DC resistance of circuits consisting of positively and negatively biased contacts with silicon and germanium in the intervening gap was measured while indenting either directly in the gap or on the contacts. Previous experiments showed that a large decrease in resistance occurs when an indentation bridges a gap, which was used to support the notion that a transformation from the semiconducting to the metallic state occurs beneath the indenter. The experimental results reported here, however, show that a large portion of the resistance drop is due to decreases in the resistance of the metal-to-semiconductor interface rather than the bulk semiconductor. Experimental evidence supporting this is presented, and a simple explanation for the physical processes involved is developed which still relies on the concept of an indentation-induced, semiconducting-to-metallic phase transformation.
120 citations
TL;DR: In this paper, a depth-sensing indentation instrument with indentation depths in the submicron range was used for constant load creep experiments on polycrystalline Sn and sputtered Al films on Si substrates.
Abstract: Constant load creep experiments were conducted using a depth-sensing indentation instrument with indentation depths in the submicron range. Experiments were conducted on polycrystalline Sn and sputtered Al films on Si substrates. The results show that the plastic depth versus time curves and the strain rate versus stress plots from these experiments are analogous to those obtained from conventional creep experiments using bulk specimens. The value of the stress exponent for Sn is close to the reported values from uniaxial creep tests. Tests on Al films showed that the stress exponent is dependent on the indentation depth and is governed by the proximity to the film/substrate interface. Load change experiments were also performed and the data from these tests were analyzed. It is concluded that indentation creep experiments may be useful in elucidating the deformation properties of materials and in identifying deformation mechanisms.
119 citations
TL;DR: In this paper, the authors used alumina + 20 vol% aluminum titanate (AAT20) for both the surface layer and the bulk material for a laminated composite construction of a high-toughness body.
Abstract: Adding aluminum titanate to alumina can result in dramatic improvements in toughness and R-curve properties. However, the improved toughness is offset by a significant reduction in strength at small flaw sizes. This problem can be overcome through the use of a laminated composite construction. By placing a thin layer of high-strength material on the surface of a high-toughness body, the toughness and flaw tolerance of the body material can be maintained without sacrificing small flaw strength. In this study, alumina + 20 vol% aluminum titanate (AAT20) was used for both the surface layer and the bulk material. The surface material was a homogeneous, fine-grained mixture of the two phases, while the bulk was an inhomogeneous mixture having a bimodal grain structure. In monolithic form, the homogeneous AAT20 displays a nearly P−1/3 indentation strength response, and the inhomogeneous material displays a flat strength response, indicative of R-curve behavior. The trilayer material shows a composite indentation strength response, with high strength throughout the entire range of starting flaw sizes. A method for predetermining the optimum surface layer thickness is presented. The processing and mechanical properties of these materials will be discussed.
TL;DR: In this article, the Griffith equation and indentation fracture mechanics were used to characterize the R-curve behavior of two in-situ reinforced silicon nitrides, and the effects of these properties on design were discussed.
Abstract: R-curves for two in-situ reinforced silicon nitrides A and B of nominally the same composition are characterized using the Griffith equation and indentation fracture mechanics. These R-curves are calibrated against fine-grained silicon nitrides which have a known chevron-notch (long-crack) toughness and with a nearly flat R-curve behavior. Silicon nitride A, with its coarser microstructure and higher chevron-notch toughness, shows lower resitance to crack growth than silicon nitride B if the crack size is less than ∼200 μm. These results are consistent with the indentation–Strength measurements which show a crossover of strength between the two materials at an indentation load between 49 and 98 N, and below the crossover A has a lower strength. The toughening behavior is explained using an elastic-bridging model for the short crack, and a pullout model for the long crack. The effects of R-curve properties on design are discussed.
TL;DR: In this paper, the indentation load/size effect (ISE) for the Knoop microhardness measurement of vitreous silica is considered for indentation in different test environments, through the application of Meyer's Law, the Hays/Kendall approach of a critical load for the initiation of flow and the proportional specimen resistance (PSR) model.
Abstract: The indentation load/size effect (ISE) for the Knoop microhardness measurement of vitreous silica is considered for indentation in different test environments. Analysis was through the application of Meyer's Law, the Hays/Kendall approach of a critical load for the initiation of flow and the proportional specimen resistance (PSR) model proposed by Li and Bradt. The PSR model in combination with a normalized form of Meyer's Law was found to describe consistently the measurements and to yield a load-independent Knoop microhardness for fused silica of 540 kg/mm2. The model also explains the effects of different indentation test environments, suggesting the effect is a result of their lubricating effects at the indenter facet/specimen interface.
TL;DR: This report presents the results obtained by the five U.S. participating laboratories in the VAMAS round-robin for fracture toughness of advanced ceramics, which found interpretation of fracture toughness in the zirconia alumina composite was complicated by R-curve and environmentally-assisted crack growth phenomena.
Abstract: Results of round-robin fracture toughness tests on advanced ceramics are reported. A gas-pressure silicon nitride and a zirconia-toughened alumina were tested using three test methods: indentation fracture, indentation strength, and single-edge precracked beam. The latter two methods have produced consistent results. The interpretation of fracture toughness test results for the zirconia alumina composite is shown to be complicated by R-curve and environmentally assisted crack growth phenomena.
TL;DR: In this article, the effect of porosity upon indentation resistance is explored for a sticking conical indenter, and two material models are used: the Gurson model which is appropriate for lower porosities, where there are well separated voids that are roughly spherical in shape, and the particle yield model of Fleck et al.
TL;DR: In this paper, a relation between the fractal dimension of a surface and its statistical properties was found between the power index and fractal dimensions of the surface and the print, and asymptotic power laws were obtained to associate the force operating on the punched and the depth of indentation.
TL;DR: In this paper, the authors used molecular dynamics simulations to model the dynamics of indentation and the resulting damage for a (111) surface of a (1 × 1) hydrogen terminated diamond tip interacting with the surface of both a ( 1 × 1)-terminated diamond crystal and a non-hydrogen terminated diamond crystal.
TL;DR: In this article, the authors compared various methods to measure fracture toughness using indentation precracks using soda-lime glass as a test material and found that stress intensity factors based on classical half-penny crack shapes overestimate toughness values and produce an apparent R-curve effect.
Abstract: Various methods to measure fracture toughness using indentation precracks were compared using soda-lime glass as a test material. In situ measurements of crack size as a function of applied stress allow both the toughness K[sub c] and the residual-stress factor [chi] to be independently determined. Analysis of the data showed that stress intensity factors based on classical half-penny crack shapes overestimate toughness values and produce an apparent R-curve effect. This is due to a constraint on crack shape imposed by primary lateral cracks in soda-lime glass. Models based on elliptical cracks were developed to account for the crack-shape effects.
TL;DR: A finite element method has been used to investigate the contract stresses due to elastic indentation of coating/substrate systems consisting of a high modulus surface coating on a low modulus substrate as discussed by the authors.
TL;DR: The microhardness of Si (MP 1688 K), GaP (1623 K), and GaAs (1510 K) single crystals was determined by indentation (Vicker's hardness, VHN) of low-index facets at loads of 5-100g at 296-673 K, complementing earlier work on Ge and InSb as discussed by the authors.
Abstract: The microhardness of Si (MP 1688 K), GaP (1623 K), GaAs (1510 K) and InP (1327 K) single crystals was determined by indentation (Vicker's hardness, VHN) of low-index facets at loads of 5–100g at 296–673 K, complementing earlier work on Ge and InSb. In the brittle range, extending up to about 0.35 T
melt (K), cracking occurred preferentially along the diagonals of the indentations, and was observed at all loads, with the possible exception of the lowest (5 g) in the case of InP at 289 K. At higher temperatures the relative orientations of crack and slip traces on the crystal surface, as observed by SEM, suggested that cracks nucleated preferentially at the slip-band intersection, as was also noted by Hirsch et al. (Phil. Mag.3 (1985) 759) in GaAs above 600 K. As earlier in Ge, the VHN was found to depend on the load, L, as L
p, and on the indentation diameter, d, as dn, with p = 1/2 and n = 2, as required by the model of indentation plasticity of Banerjee and Feltham [4, 5], but higher p and n values were found if chipping at the indentation edges was evident. The effect was related to the resulting decrease in indentation diameter due to the work lost, through chipping, by the indenter. Above about 0.35 T
melt (K), relaxation of the dislocation structures entails a decrease of p and n; both parameters tend to zero as T → T
melt. Shear and tensile stresses seem to co-operate in the process of plastic deformation, the role of normal stresses, acting across slip planes, predominating in the ‘brittle’ range.
TL;DR: In this paper, the room-temperature fracture behavior of polycrystalline MoSi2 was characterized using Vickers indentation fracture, aided by the optically active grain structure revealed under polarized light.
Abstract: The room-temperature fracture behavior of polycrystalline MoSi2 was characterized using Vickers indentation fracture. Fracture analysis was aided by the optically active grain structure of MoSi2 revealed under polarized light. Radial crack propagation from indentations was found to be predominantly transgranular. The approximate indentation fracture toughness of MoSi2 was 3 MPa.m1/2, while the measured hardness was 8.7 GPa. Fracture behavior is believed to be controlled by anisotropy and cleavage energy of the tetragonal MoSi2 crystal structure.
TL;DR: In this article, the results of ultralow load indentation (nanoindentation) tests carried out on a range of thin film coated systems are reported. And the authors explore the extent to which it is possible to generalize the nanoindentations response of the various systems in terms of the relative mechanical properties of the coating and the substrate.
TL;DR: In this paper, the general theory of axisymmetric hardness tests on nonlinear media is approached from the standpoint of similarity transformations, and it is shown how an entire process of indentation can be made to depend on the solution of just one boundary-value problem in scaled variables and with a fixed geometry.
Abstract: The general theory of axisymmetric hardness tests on nonlinear media is approached from the standpoint of similarity transformations. It is shown how an entire process of indentation can be made to depend on the solution of just one boundary-value problem in scaled variables and with a fixed geometry. Once this single auxiliary solution has been obtained, the values of all physical quantities in the original problem can be generated readily at any stage without further numerical error. Even by themselves the similarity relations provide valuable information about (for example) an invariant connection between the depth of penetration and the radius of contact, or about the variation of penetration with time in a creep test under dead load. Two kinds of material behaviour are considered: (a) nonlinear elastic (modelling strain-hardening plasticity) and (b) nonlinear viscous (modelling secondary creep). In either category the constitutive specification is sufficiently flexible to represent a wide range of actual responses in the context of hardness testing. The analysis for case (a) extends a theory of ball indentation by Hill et al. to a class of indenters with shapes varying from flat to conical. It also prepares the ground for case (b) which is more difficult and calls for a quite different auxiliary problem.
TL;DR: A method for determining the fracture toughness by Hertzian indentation has been developed in this article, where three materials, a ceramic matrix composite, a fine grained Al2O3 and glass, were indented by a spherical WC/Co indenter at various loads.
Abstract: A method for determining the fracture toughness by Hertzian indentation has been developed. Three materials, a ceramic matrix composite, a fine grained Al2O3 and glass, were indented by a spherical WC/Co indenter at various loads. The samples were then sectioned and polished and the length of the Hertzian cone cracks were measured. The fracture toughness was found to be independent of cone crack length and indentation load. Values of fracture toughness for the ceramic composite, the fine grained Al2O3 and soda-lime glass were 6.7, 3.77 and 0.8 MPa m 1 2 respectively.
TL;DR: In this article, the fracture toughness of aligned YBa2Cu3O7−δ obtained by melt processing was found to be highly anisotropic, i.e., the critical stress intensity factor for propagating a crack on the (001) basal plane is the lowest.
Abstract: The hardness and fracture toughness of aligned YBa2Cu3O7−δ obtained by melt processing was found to be highly anisotropic. Indentation measurements show that the (001), (100), and (010) planes are the preferred fracture planes in this material and that the critical stress intensity factor for propagating a crack on the (001) basal plane is the lowest, i.e., Kc001
TL;DR: In this paper, the authors used spherically tipped indenters of known tip radius and followed the transition from elastic to plastic deformation to determine the variation in the mean indentation pressure with depth of penetration and construct an equivalent stress-strain response of a material.
TL;DR: In this article, a point contact microscope with a very sharp diamond tip was used to perform indentation, scratch and wear mark tests on polycarbonate and epoxy surfaces using loads ranging from submicronwtons to micronewtons.
Abstract: A point-contact microscope (PCM) with a very sharp diamond tip works with loads as light as 10 nN, which allows high-resolution topographies to be obtained. This PCM can also be used to perform indentation, scratch and wear mark tests. Nanometre-level wear mark tests were performed on polycarbonate and epoxy surfaces using loads ranging from submicronewtons to micronewtons. During these tests, the scanning-scratched surfaces of polycarbonate formed projections, and no depressions or wear particles were observed. This phenomenon is novel compared with the depressed wear marks formed on the scratched surfaces of ordinary materials such as metals or ceramics. The projections on the surface involve an increase in volume and they are softer than the non-scratched surface. It seems that this distortion was caused by the frictional force. In contrast, an epoxy surface did not show any growth of projections, and wear particles were produced from the surface.
30 Jun 1992-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, single crystals of MoSi 2 have been grown by the Czochralski method and characterized by X-ray and transmission electron microscopy (TEM) methods.
Abstract: Single crystals of MoSi 2 have been grown by the Czochralski method and characterized by X-ray and transmission electron microscopy (TEM) methods. The mechanical properties have been studied at room temperature using indentation testing coupled with TEM methods which investigate the region below the indentation. The plastic zone below the indentation as been characterized in terms of the distribution of two different types of dislocations. In addition the fracture of MoSi 2 has been studied as a function of indentation size.
TL;DR: In this article, the authors obtained information such as the surface profile around a residual indentation, the lengths of its diagonals, its depth, the angles between its face/pyramid edge and the undisturbed indented surface, and the volume of material within the pile-up region.
Abstract: Scanning tunnelling microscope (STM) images of low-load (15-50 gf) Vickers diamond pyramid indentations in a (111) surface of a p-doped single crystal of silicon have been obtained. From these, information such as the surface profile around a residual indentation, the lengths of its diagonals, its depth, the angles between its face/pyramid edge and the undisturbed indented surface, and the volume of material within the pile-up region (i.e. above the original indented surface), has been obtained. In some cases, the volume of the piled-up material has been found to be over 80% of the residual indentation. The experimental findings have been discussed in the light of the existing theories of indentation and the process of elastic recovery.