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Nanoindentation technology is an advanced method to explore the microscopic mechanical properties of layer or block materials. Grid nanoindentation coupled with statistical analysis is effective to give an insight into multiphase materials just like cement paste, mortar and concrete. However, traditional statistical methods, such as deconvolution analysis and Gaussian Mixture Model (GMM), are limited by the nondeterminacy of normal distribution assumption, computational instability due to random selection of initial values, and some problems induced by large amount of calculation. In this paper, clustering analysis, an advanced analysis method for mixed data and widely used in machine learning field, is developed to deal with grid nanoindentation test data. Calculation results suggested that K-medoid clustering is suitable and highly efficient to explain grid nanoindentation tests. Furtherly, clustering method is more robust than deconvolution analysis and GMM when data size is reduced. In addition, normal distribution assumption is not always available for the mechanical properties of some mineral phases in cement pastes. This work offers a new optional mathematical tool to interpret and understand the multiphase properties of cementitious materials probed by grid nanoindentation technology. [ABSTRACT FROM AUTHOR]

This paper presents a review of the mechanical characterisation of thin film and coated systems using indentation tests. The potential in assessing mechanical properties of films and coatings using indentation tests has received a great deal of attention since this knowledge is vital for predicting their performance. The relevant theoretical background is discussed. Experimental work, numerical studies and data interpretation techniques for indentation on single bulk materials and thin films are discussed. Surface conditions, indentation depths and indentation size effects for indentation tests on thin films and coated systems are discussed. Data interpretation methods for indentation on films and coated systems are reviewed with a discussion on their limitations. Other studies in this field concerning the substrate effects and critical indentation depth ratios are also discussed. Suggestions for future experimental work and data interpretation are provided. [ABSTRACT FROM AUTHOR]

This paper discusses the processing, characterization, and properties of aluminum-carbon nanotube (Al-CNT) open-cell foams. The effect of spark plasma sintering temperature on the developed internal surface macro/microstructure and local mechanical response is discussed. Grain size and amount of oxygen-rich internal scales increased with an increase in sintering temperature. Room temperature spherical indentation tests showed a general decline in load-bearing capacity of the foams with increase in sintering temperature. Cell-wall failure was found to be due to brittle fracture rather than plastic collapse. Analyses of the indentation unloading curves showed Al-CNT foams to be ~16% stiffer than Al foams processed at the same condition. [ABSTRACT FROM AUTHOR]

It is tempting to accept the predictions regarding indentation depth and radius of circle of contact between two elastic bodies in contact given by the well-known Hertz equations at face value. However, it is nevertheless of interest to examine these predictions either by experiment or by independent computation. Indentation depth may be readily compared using standard experimental apparatus but in this paper, attention is given to the radius of curvature of the indented surface for a condition of full load. The conclusion arising from the Hertz equations, that contact between a flat surface and a non-rigid indenter of radius R is equivalent to that between the flat surface and a perfectly rigid indenter of a larger radius, has not thus far been examined in detail in the literature, possibly because of the difficulty in measuring such a radius of curvature in situ while load is applied to the indenter. This feature of contact between two solids is of interest since it has been often used as the basis for various hardness theories which involve an elastic–plastic contact. This paper addresses the issue by utilizing the finite-element method to compute the radius of curvature of the contact surface for both elastic and elastic–plastic contacts. It is shown that indentations involving elastic–plastic deformations within either or both the specimen and the indenter are equivalent to indentations with a perfectly rigid spherical indenter whose radius is somewhat smaller than that calculated using the Hertz equations for elastic contact. An experimental compliance response is used to indirectly validate the finite-element results. [ABSTRACT FROM AUTHOR]

This paper presents the micro-shot peening of zirconia (ZrO)-advanced ceramics applicable for bio-medical, dental, automotive and aerospace sectors. A ZrO-advanced ceramic was micro-shot blasted with selected parameters as a first-step investigation focused on the topography, microstructure, surface hardness and the surface fracture toughness ( K) characteristics. A new technique of micro-blasting was conducted using a portable shot blaster. A white-light interferometer, scanning electron microscopy and Vickers indentation technique were employed for the analysis. This was followed by determining the K using an empirical equation. Surface roughness was improved by 34 % after micro-shot blasting treatment. No surface cracking was present which generally exists due to the brittle nature of the ceramic. The hardness, however, reduced by 5.6 % with a reduction in the Vickers crack length of 9 %. This improved the K by 3 % when comparing the micro-shot peened surface to the original, as-received surface. It is difficult to conclude if the ZrO-advanced ceramic has undergone plastic deformation and the movement of dislocations increased to strengthen the ZrO ceramic at this stage. However, based on the results, it can be predicted that a level of surface compression was induced beneath the micro-shot peened layer as indicated from the result of the surface topography and integrity. This would justify the hardness modification and the enhancement in K. [ABSTRACT FROM AUTHOR]

Severe plastic deformation (SPD) techniques have recently been developed for producing bulk ultrafine grained metallic materials. High pressure torsion (HPT) produces finer microstructures than those achieved by other SPD processes because of the higher imposed strain and hydrostatic pressure. It is known that HPT-processed metals show a highly heterogeneous microstructure not only along the radius due to the nature of torsional deformation but also through the thickness. Since the sample size for HPT is small, the local properties of HPT-processed specimens have not been investigated yet. In this paper, we propose a method to obtain stress-strain curves from nanoindenting curves by combining the finite element method and the recursion method. The nanoindentation technique was employed to elucidate the local mechanical properties, especially the stress-strain behavior. The method to extract the stress-strain curves from the load-displacement curves obtained by nanoindentation tests was applied to the edge region of the HPT-processed sample. The extracted properties correlated well with experimental results qualitatively.` [ABSTRACT FROM AUTHOR]

Indentation testing is a convenient means to study mechanical properties of thin coatings. We suggest a new method to identify the viscoplastic behavior of a polymer by using the force-penetration curves during nano-indentation testing performed with two indenter shapes. During loading, the load applied by the indenter and the penetration depth have been measured. These force-penetration curves have been compared to the load computed by using the finite element method with a two dimensional software. The viscoplastic behavior of the polymer is modeled with the G'sell-Jonas law. The main particularity of this law is the modeling of the large strain-hardening at large strains. The unknown parameters of this law have been obtained by fitting computed and experimental force-penetration curves. We have identified each parameter independently of the others by taking into account the indenter tip defect. The nano-indentation tests have been performed with three strain rates and with two indenter shapes: a Berkovich indenter and a cone with a semi angle of θ = 30° and a tip radius. In this paper, the polymer is a polycarbonate. Several authors have made rheological tests on this polymer. The true strain-true stress curve obtained with our method is in good agreement with the compression curve. [ABSTRACT FROM AUTHOR]

Indentation loading of thin, continuous silica coatings adhered to Bismaleimide (BMI) polymeric substrates induces a concentric array of cracks in the silica coating. For Vickers indentation, the array consists of diamond-shaped concentric cracks, while Hertzian indentation gives circular concentric cracks. This paper characterizes the indentation-induced crack damage in the coating in terms of: (1) fs, the area fraction of the coating (within the indentation-cracked region) that spalls off the substrate due to the indentation and (2) the spacing between the cracks in the crack array. For a given indentation crack field, the crack spacing was uniform as a function of radial distance outward from the center of the indentation. One of the key results of this study was that the curing temperature for the coating dramatically affected both the coating spalling area fraction, fS, and the manner in which the crack spacing changed as a function of the applied indentation load. [ABSTRACT FROM AUTHOR]

This paper describes methods of joining aluminium foams with mechanical fasteners and with adhesives, and characterises the mechanical properties of the resulting joints. Different techniques of joining were investigated under monotonic and cyclic pull-out and bearing loads. The effects of fastener geometry on pull-out and bearing-load failure are modelled. Cyclic loading reduces the maximum load a fastener can carry without failure to 0.35 of the static failure load. Epoxy adhesive joints are stronger than the foam itself in all modes of loading: failure always occurs remote from the joint. [ABSTRACT FROM AUTHOR]

Nanoindentation hardness tests are used to measure indentation hardness at the micro- and nanoscales and further to predict Vickers hardness on larger scales. Hence, the relationship between Vickers and nanoindentation hardness has gained considerable research interest. Here we introduce the concept of Meyer hardness as a mean contact pressure correctly into the two hardness in order to explain their linear correlation. The Vickers hardness is converted to the Vickers Meyer hardness (HVM) as defined by a load divided by the projected contact area; the Nix–Gao model is used to calculate the bulk-equivalent nanoindentation hardness (H0) from depth-dependent nanoindentation hardness. A linear relationship HVM = 0.86 × H0 is observed in the Fe–Cr alloys with a wide range of elastic modulus to hardness ratios and is suggested to be a universal relationship for various metallic materials. A tangent method can distinguish the indentation edge behaviors such as pile-up, sink-in, and the pseudo-pile-up phenomenon. A novel pile-up correction estimates the real contact area in nanoindentation tests, and actual residual contact area is measured to correct the pile-up around Vickers imprints. The corrected HVM and corrected H0 show almost same values after both pile-up corrections. [ABSTRACT FROM AUTHOR]

A simple model is proposed for the evaluation of crack-arrest fracture toughness KIc0 of thin films by Vickers indentation. This approach applies to films thinner than the penetration depth of the Vickers indenter. The model equations are provided in closed form, even though they are so complex that they must be integrated numerically in practical applications. The problem of the evaluation of KIc0 for thin films and substrates is derived in general form and applied to three cases: (i) evaluation of KIc0 for the film in the case that the depth of the crack in the film is smaller than the film thickness, (ii) evaluation of KIc0 for the film in the case that the crack emanating from the film either crosses the film/substrate interface or is stopped by it, (iii) evaluation of KIc0 for the substrate in the case that the crack emanating from the film crosses the film/substrate interface. The model was tested with original and literature experimental data: (i) revision KIc0 values of electroless Ni-P thin films were re-evaluated, (ii) KIc0 of electroless Ni-P thin films of various thickness with various loads were measured (original data) and computed, (iii) KIc0 of electroless Ni-P substrates coated with electrodeposited Au-Cu were measured (original data) and computed. [ABSTRACT FROM AUTHOR]

The onset of plasticity in a single crystal C60 fullerite was investigated by nanoindentation on the (111) crystallographic plane. The transition from elastic to plastic deformation in a contact was observed as pop-in events on loading curves. The respective resolved shear stresses were computed for the octahedral slip systems ⟨ 01 1 ¯ ⟩ 111 , supposing that their activation resulted in the onset of plasticity. A finite element analysis was applied, which reproduced the elastic loading until the first pop-in, using a realistic geometry of the Berkovich indenter blunt tip. The obtained estimate of the C60 theoretical shear strength was about 1 / 11 of the shear modulus on {111} planes. [ABSTRACT FROM AUTHOR]

Spherical indentations with deep penetration were conducted to single-crystal Cu along [001] direction. Zigzag slip bands induced by intersection of two groups of slip bands were found in the indentation pile-up region. On the material surface in the indentation pile-up region, micro-cracks were initiated along the slip bands radial to the indentation impression. The initiation of the micro-crack is affected by the indentation load and indenter radius. 3D crystal plasticity finite element simulation was applied to study the spherical indentation. Simulation results showed that the primary slip systems activated in indentation pile-up region were (1 ¯ 11) [ 0 1 ¯ 1 ] , (1 ¯ 11) [ 101 ] , (1 1 ¯ 1) [ 10 1 ¯ ] , and (1 1 ¯ 1) [ 011 ] , whose slip planes make intersection lines radial to indentation impression on the material surface. The secondary slip systems activated were (111) [ 0 1 ¯ 1 ] , (111) [ 10 1 ¯ ] , (11 1 ¯) [ 011 ] , and (11 1 ¯) [ 101 ] , whose slip planes make intersection lines tangent to indentation impression on the material surface. These two groups of slip bands, which both move outward the material surface, will intersect with each other and produce zigzag slip bands and jogs. The jogs would cause local stress concentration and thus provided the driving force to the initiation of micro-cracks. Meanwhile, simulation showed that the stress triaxiality in indentation pile-up region was around 0.6, which are closed to the stress state of plane strain tension and quite favorable to the initiation of cracks. Through simulations of spherical indentation along [ 110 ] and [ 111 ] , it illustrated that the initiation of cracks may be orientation dependent. [ABSTRACT FROM AUTHOR]

This work is focused on the mechanical characterization by multiscale indentation (nano and macro) of a brake pad material, with multiple phases and complex microstructure for applications in the railway industry. Grid nanoindentation tests allowed to identify the mechanical properties of the components in the formulation. The significant difference between constituent's properties gives a quickly composite response. In parallel, multicyclic macroindentation tests were performed to obtain a composite mechanical response. The properties change according to test locations and configurations of staking phases, due to the high heterogeneity of the brake pad material. The results demonstrated that multiscale indentation tests give a consistent response, which approximates the mechanical properties at different scales. Considering such a very heterogeneous material (broad distribution of properties and particle sizes), the used methodology is appropriate for other heterogeneous complex materials. A multiscale characterization of the mechanical properties is necessary to deal with the problematic of vibrations induced by friction, particularly for brake squeal prediction. [ABSTRACT FROM AUTHOR]

Using molecular dynamics simulation, we study the indentation of a metal-ceramics (Al/Si) composite and compare it to that of the pure elements. An Al/Si interface running perpendicular to the surface is indented centrally. We find that-due to its higher stiffness and yield strength-Si expands into the Al side. As a consequence, the plasticity on the Al side is enhanced, leading to the formation of complex dislocation networks. On the Si side, the phase transformation from cubic diamond to bct5 structure, and subsequent amorphization near the indenter are accelerated, while the number of dislocations formed in the surviving cubic diamond phase is reduced. In both materials, the mobility of the dislocations is enhanced, in particular because the dislocations glide easily on the interface; as a consequence the composite is softer than the average of its constituents. [ABSTRACT FROM AUTHOR]

Indentation-induced surface and subsurface deformation mechanisms in directionally solidified WC-WC eutectoids are investigated. The microstructures of the WC-WC composites consist of primary WC regions, WC-rich regions, and lamellar-type eutectoid regions, which form during the sequential phase transformations during laser processing. Indentation-induced surface crack profiles indicate little propensity for debonding at the WC-WC eutectoid interfaces, although some interactions with larger-scale microstructural features are observed. In the subsurface indentation regions, dislocation networks predominantly composed of partial dislocation pairs having Burgers vectors $$ b = \frac{1}{6}\left\langle {2\bar{1}\bar{1}3} \right\rangle $$ are observed in the primary WC regions, whereas shear banding and grain refinement are commonly observed in the micrometer-scale WC-rich regions. Deformation in the sub-micrometer eutectoid regions is distinct, with the dislocation activity primarily limited to the WC phase, with Burgers vectors of $$ b = \frac{1}{3}\left\langle {1\bar{2}13} \right\rangle $$ that terminate at the interfaces. [ABSTRACT FROM AUTHOR]

We have used high-resolution techniques (nanoindentation, atomic force microscopy) to further isolate and identify environmental effects previously reported as possibly affecting both the microindentation response of a range of ceramic materials and their tribological behaviour. In order to make meaningful comparisons, these new experiments have been conducted alongside conventional Knoop and Vickers microhardness experiments conducted under identical conditions on the same samples. A range of polycrystalline, single crystal and amorphous ceramic materials have been studied including some only available as coatings. Our results show that thin adsorbate-modified layers (of dimensions ~1 nm) are almost invariably present on all the materials studied but their presence is not directly identifiable even by nanoindentation in most cases even if it does affect friction response. However, in crystalline materials, [ $$ \left( {10\bar{1}2} \right) $$ sapphire and ZnO], we have been able to distinguish a further softening effect seen as a thicker layer (tens of nm) and believed associated with an adsorption-induced near-surface band-structure change affecting the motion of charged dislocations. This produces a measurable softening that is clearly evident in nanoindentation tests but less clear in microindentation tests. Finally, we present conclusions on the suitability of indentation testing for studying these phenomena, together with the implications of chemomechanical effects for influencing tribological performance and, thus, materials selection. [ABSTRACT FROM AUTHOR]

In this work, the influence of crack forms [radial crack (RC) and half-penny crack (HPC)] on indentation hardness test results of ceramic materials ( W/ W = 0.3-0.7) was studied by finite element analysis and verified by experiments. Excluding the influence of size effect, the values of HPC and RC indentation hardness from instrumented indentation tests on five ceramic materials (SiN, ZrO, ZTA, AlO, and silica) were compared with that of 'Non-Crack' indentation hardness. The results show that the influence of RC or HPC on indentation hardness test results of isotropic and homogeneous ceramic materials is verified to be negligible, both analytically and experimentally. But the 'Pop-in phenomenon' is found to have a great impact on indentation hardness test results for ceramic materials. Therefore, in the absence of 'Pop-in phenomenon,' the test results of indentation hardness of ceramic materials were practically reliable. This work provides a theoretical foundation for further study on instrumented indentation for determining the elastic-plastic properties and fracture toughness of ceramic materials. [ABSTRACT FROM AUTHOR]

Cubic 8 mol% YO-stabilised ZrO is well known for its good oxygen conductivity and therefore it is used in fuel cells, as oxygen sensor for liquid metals and as pH sensor in high temperature water. As a part of its fracture toughness assessment, the crack system caused by Vickers hardness indentations was examined by breaking specimens along an indentation diagonal. It was found that, although the normally observed fracture mode is transgranular, intergranular fracture occurred in the zone below an indentation. Annealing the specimen above 900 °C before breaking caused the disappearance of this effect. The intergranular fracture mode was explained by the combined effect of plastic deformation under the indentation and environmental humidity. Annealing is expected to cause restoration to the un-deformed structure. Observations on the intergranular and transgranular cracking pattern, slow crack growth occurrence and step formation at the fracture surface, are reported. [ABSTRACT FROM AUTHOR]

An elastic modulus mapping technique based on spatially continuous dynamic nanoindentation is applied to map microscale variations in a fine-grained, kerogen-rich shale consisting of inorganic minerals with an interpenetrating network of microscale pores filled with organic matter. Advantages and limitations of the application of this technique to shales are explored through varying sample preparation and scanning procedures. Filtering techniques are developed to remove data that are negatively impacted by topography and other issues inherent to the mapping technique. As a result, spatial variations of elastic modulus in kerogen-rich regions are seen at substantially higher resolution than has previously been reported. Spatial resolution and continuous mapping across high stiffness-contrast material boundaries are further improved with stringent sample preparation and the use of a sharp tip. Typical modulus values measured by this technique include approximately 10 GPa for kerogen, 15-45 GPa for clay depending on the morphology and orientation, and 50-70 GPa for quartz. [ABSTRACT FROM AUTHOR]

Enhancement of toughness is currently a critical engineering issue in tungsten metallurgy. The inherent toughness of tungsten single crystals is closely related to the capacity for local plastic slip. In this study we have investigated the plastic behavior of tungsten single crystals by means of micro-indentation experiments performed on specimens exposing (100), (110), and (111) surfaces. In parallel, FEM simulations were carried out with the Peirce-Asaro-Needleman crystal plasticity model considering both {110} 〈111〉 and {112} 〈111〉 slip systems. Plastic material parameters were identified by comparing the measured and predicted load-displacement curves as well as pile-up profiles. It is found that both measured and simulated plastic pile-up patterns on the indented surfaces exhibit significant anisotropy and orientation dependence, although the measured and simulated load-displacement curves manifest no such orientation dependence. The height and extension of pile-ups differ strongly as a function of surface orientation. The FEM simulations are able to reproduce the observed features of spherical indentation both qualitatively and quantitatively. [ABSTRACT FROM AUTHOR]

Porous gadolina-doped ceria (Ce0.9Gd0.1O1.95, GDC10) is commonly used as a functional electrode support in solid oxide fuel cells, gas sensors, and gas separators. In addition, dense GDC10 is commonly used as a solid oxide fuel cell electrolyte and a gas separation membrane. Although, porosity affects a wide range of electrical, thermal, and mechanical properties of solids, this study focuses on (i) the Vickers indentation hardness, H, as a function of volume fraction porosity, P, ranging from 0.08 to 0.60 and (ii) the load dependence of H for Vickers indentation loads of 0.98-9.8 N. For the 13 GDC10 included in this study, the decrease in H with increasing P is approximated by the empirical relationship H = H0 exp(− bHP), where H = 5.844 GPa and bH = 6.68. In addition, the H values were roughly independent of the applied load. [ABSTRACT FROM AUTHOR]

Mixed-mode fracture surfaces of an R-curve material were quantitatively assessed using fractography. The R-curve material chosen was a mica glass ceramic. Vickers indentation cracks of different sizes were introduced at the center of tensile surface of glass ceramic bars fractured in flexure. The bars were fractured in flexure by generating mixed-mode (I/II) loading conditions at crack tips by orienting indentation cracks at various angles with respect to the tensile axis. Quantitative fractography indicated that crack-to-mirror size ratios were a function of crack length and mode mixity. Stress intensity at branching for the mirror-hackle transition during mixed-mode (I/II) fracture condition was a constant and was less than the corresponding stress intensity at branching in mode I loading. An empirical relationship is derived for the effective geometric factors in mixed-mode fracture of ceramics from surface cracks in flexure. [ABSTRACT FROM AUTHOR]

The influence of the surface roughness on the indentation size effect in microindentation was examined using the proportional specimen resistance model. Stainless steel, aluminium, and copper surfaces were polished to different levels of roughness and subjected to microindentation. The results showed that the indentation size effect increases with increasing surface roughness, according to the proportional specimen resistance model. A normalized hardness equation H/ H = ( c + c R)/( a d) + 1 was established, and the value of c can be used to quantify the effect of surface roughness on the severity of the indentation size effect; this value was found to be highest for stainless steel, followed by copper and aluminium. [ABSTRACT FROM AUTHOR]

A commercial Al-7475 alloy with an initial grain size of ~40 μm was processed by high-pressure torsion (HPT) for up to 2 turns at room temperature under a pressure of 6.0 GPa. The mechanical properties of the processed materials were evaluated by the ball-indentation technique to give information on the yield strength and the ultimate tensile strength. Following HPT, microhardness measurements revealed a steady increase in the hardness values from the centers of the samples towards the edges. After 2 turns, the ultimate tensile strength was ~1050 MPa at the edge of the disk and the measured grain size was ~70 nm. The results demonstrate the potential for using HPT to achieve excellent grain refinement in the Al-7475 alloy. [ABSTRACT FROM AUTHOR]

A grade 2 pure Ti was processed by high-pressure torsion (HPT) under 3.0 GPa for 10 revolutions to achieve an improved strength. Wear tests revealed that HPT only slightly improved the wear resistance of pure Ti. Subsequently, a TiN coating with a thickness of 2.5 μm was deposited on different Ti substrates to improve the wear resistance. Both indentation and scratch testing demonstrated a much improved load-bearing capacity when ultrafine-grained Ti was chosen as the substrate compared with coarse-grained Ti. All results indicate that pure Ti processed by HPT, when combined with a subsequent coating, represents a good candidate material for bio-implant applications. [ABSTRACT FROM AUTHOR]

Mechanical properties of wet fiber surfaces of hardwood chemi-thermo-mechanical pulp and softwood kraft pulp were measured using an AFM as a nanoindetation device. Elastic modulus of wet fiber surfaces was observed in the range of 30 MPa to 1.6 GPa, which is significantly affected by chemical treatment of pulping and bleaching as well as mechanical refining. Plastic yield stress of wet fiber surfaces measured varies from a few MPa to about 100 MPa, and is also highly correlated to chemical and mechanical treatments of these fibers. Plasticity index shows no difference among once-dried hardwood and softwood pulp fibers, but it increases after refining. The dynamic responses of wet fiber surfaces to external loads were evaluated through creep analysis. Even creeps were observed on all wet fiber surfaces, deformation caused by creep is relatively small. The major portion of deformation still comes from instantaneous elastic and plastic deformations. Creep of wet fiber surfaces is a fast dynamic process when subjected to a load change, most of it occurs within several seconds after the initial contact. [ABSTRACT FROM AUTHOR]

We report on responses of hydrated and dehydrated cortical bone tissues to mechanical loading applied by a Vickers indenter. The Vickers indentations were imaged in two- and three-dimensions (2D and 3D) using confocal laser scanning microscopy (CLSM) to understand mechanical behavior of bone tissues. Serial optical sections of indentation patterns of dry and wet bones were collected using CLSM. The indention surface structures were mapped using topographical CLSM imaging. The observation of CLSM shows the fundamental indentation responses for both the hydrated and dehydrated bone tissues were plastic deformation. No visible fracture was observed in the Vickers indentation patterns in the wet bone tissue, while non-propagating lamellar microcracks occurred in the dry bone tissue. This indicates that drying resulted in increased brittleness of the bone tissue. The Vickers hardness values of dry bone tissue were significantly higher than those of wet bone tissue at any applied loads (analysis of variation, ANOVA, p < 0.05). The resolution limits of confocal microscopy were also discussed for bone tissue scanning. [ABSTRACT FROM AUTHOR]

An indentation-planarization method for NiTi shape memory alloys has been developed that produces a robust surface topographical memory effect that we call "surface form memory", or SFM. Surface form memory entails reversible transitions between one surface form (flat) and another (say, wavy) that occur on changing temperature. These transitions are cyclically stable and exhibit very high mechanical energy density. Our previous study has demonstrated SFM transitions in NiTi alloys derived from quasistatic (i.e., low strain rate) spherical indents, as well as other geometries. Here, we report on experiments using confined laser ablation to indent a similar martensitic NiTi substrate, but in the dynamical regime (very high strain rate). As in the quasistatic case, subsurface plastic strain gradients are created via martensite twinning reactions, and later by dislocation-mediated slip. The resulting defects and stress fields support the two-way shape memory effect underlying SFM. In the dynamical case however, relative cyclic two-way displacements are found to be significantly larger, when normalized to the initial indent depth, than is the case with quasistatic indentation. This confers certain processing and boundary condition advantages. Analysis of the shock dynamics is found to be consistent with the observed surface displacements. [ABSTRACT FROM AUTHOR]

For spot-welded joints, the resistance to mechanical stress depends on the local strength properties and gradients in the weld area. The commonly used methods for investigating the stress-strain behaviour across the weld area are connected with a high level of sample preparation and with considerable limitations in local resolution. A promising method for determining locally resolved stress-strain curves is the instrumented indentation test in connection with the method of representative stress and strain (RS) and the method of artificial neural networks (NNs). The stress-strain properties of the weld nugget and the base metal determined by these two methods are compared and discussed, additionally in relation to the stress-strain curves obtained from the tensile test. The measured Vickers hardness across the weld area is compared with the evaluated local stress-strain properties. Three steels used in automobile manufacturing are investigated: mild steel DC04 and two advanced high-strength steels (TRIP steel HCT690T and martensitic steel HDT 1200M). The results of the two methods (RS and NN) show good correspondence for the base metal area but some significant differences for the weld nugget. Comparing the data across the weld area, no evidence of the presence of residual stress (which would influence the results) was found. [ABSTRACT FROM AUTHOR]

In this article, we report on the application of our spherical nanoindentation data analysis protocols to study the mechanical response of grain boundary regions in as-cast and 30% deformed polycrystalline Fe-3%Si steel. In particular, we demonstrate that it is possible to investigate the role of grain boundaries in the mechanical deformation of polycrystalline samples by systematically studying the changes in the indentation stress-strain curves as a function of the distance from the grain boundary. Such datasets, when combined with the local crystal lattice orientation information obtained using orientation imaging microscopy, open new avenues for characterizing the mechanical behavior of grain boundaries based on their misorientation angle, dislocation density content near the boundary, and their propensity for dislocation source/sink behavior. [ABSTRACT FROM AUTHOR]

A retrospective on the use of sharp, fixed-profile indenters as materials probes is presented. Indentation is proposed as a simple but powerful methodology for evaluating basic mechanical properties-elastic modulus, hardness, toughness-in all classes of materials. Indentation also provides unique insight into fundamental deformation and fracture processes. Of particular interest is the existence of intrinsic size effects as characteristic contact dimensions pass from macro- to micro- to nano-scale dimensions. The utility of indentations as 'controlled flaws' in the context of strength of materials is outlined. The roles of two other important material factors-rate effects and microstructure-are considered. Examples of technological and biological applications are presented as illustrations of the widespread power of the technique. Strengths and limitations of the methodology as a routine testing protocol are discussed. [ABSTRACT FROM AUTHOR]

thick soda-lime glass plate was indented with a spherical indenter at high indentation forces up to 1.839 kN. A systematisation of the fracture figures showed a basic structure, consisting of four individual zones. The detailed characteristics of these zones depended on indentation force. Existing models for the assessment of contact diameter and radial and lateral vent cracks length were proven. The appearance of fracture lances was observed and discussed. It was found that these lances formed during the intersection of conchoidal (lateral) fractures, and that their formation was bound to the elastic-plastic period of the indentation process. Features of fracture lances, namely the formation of numerous symmetric lance fronts, periodically occurring lance fronts, lance front statistics, and lance dimensions were described and discussed in detail. It was also shown that the formation of fracture lances showed elements of self-similarity and fractal geometry. [ABSTRACT FROM AUTHOR]

In order to determine the influence of interlayers of ductile metals on the overall mechanical properties of the multilayer coatings, three-dimensional numerical simulations of depth-sensing indentation tests of titanium aluminium nitride (TiAlN) hard coatings with copper, silver, aluminium and titanium ductile interlayers were performed. The contribution of ductile interlayers to altering the hardness, the Young’s modulus and H/E and H2/ E ratios of the multilayer coating with respect to a monolithic TiAlN hard coating was established for the cases of composites with different number and thicknesses of interlayers. [ABSTRACT FROM AUTHOR]

The degradation of the mechanical properties of deformed PVDF during its mechanochemical ageing in sodium hydroxide (soda) was followed by microindentation measurements, especially the local reduction of the elastic modulus and the hardness. This allows measurements on a local scale of the mechanical properties on the surface and in-depth as a function of the strain level and the ageing time. Microindentation tests with Berkovich indenter have been performed with a Nanoindenter XP® (MTS). Measurements are made at penetration depth less than 2 μm for an applied load of 10 mN. During ageing in soda (Ph 14) at 90 °C up to 16 days, various deformations ε (0, 22 and 38%) are imposed on PVDF tensile specimen. For the first two imposed deformations (ε = 0 and ε = 22%), mechanical degradation is limited to some percent (less than 7%). For the greatest deformation (ε = 38%), mechanical degradation continues to decrease with ageing time (more than 21%). Microindentation tests show that a range of low deformations exists in which the mechanochemical degradation is limited and no limitation is observed for larger imposed deformation. [ABSTRACT FROM AUTHOR]

Elastic contact between a non-ideal Berkovich indenter and a half-space is investigated. The derived mathematical model of the contact allows for tangential displacements of the boundary points of the half-space. The tip of the blunted indenter is simulated as a smooth surface. The boundary element method is implemented in the model for numerical simulation of nanoindentation. The relative deviation function is introduced and calculated to quantify the influence of the tangential displacements on the load–displacement curves. A simple expression is derived for the impact of the tangential displacements on the values of the reduced Young’s modulus determined due to nanoindentation studies. The refined model was successfully applied to simulate the experimental load–displacement curves gained by elastic nanoindentations of flat LiF and KCl samples. Such values of the indenter bluntness (the varying parameter) were found that the simulated load–displacement curves coincided with those of the experimental data at displacements higher than 7.5 nm. The model neglecting tangential displacements gives slightly differing values for the parameter of the indenter bluntness. [ABSTRACT FROM AUTHOR]

A micro-scale analytical model for predicting size-dependent microhardness is presented. The indentation size effect is explained by dissipation energy associated with the contact surfaces. Micro-mechanics mechanism of this energy dissipation is studied via a plastic deformation analysis of micro-scale asperities on the contact surface under indentation. The analysis shows that the microhardness depends not only on the properties of the bulk material under test, but also the properties of the contact surface, such as the plastic behavior of the micro-asperities on contact surfaces. The dependence of microhardness on the roughness parameters of the contact surfaces is also revealed from the analysis. [ABSTRACT FROM AUTHOR]

Different microstructures of the 70%Si3N4-30%BAS self-reinforced composite, fine, coarse and bimodal, are obtained by pressureless sintering at 1920°C. Flexural strength, fracture toughness and crack-growth resistance ( R-Curve) behavior of each microstructure are characterized by three-point bending, indentation and modified compact tension methods respectively, at room temperature. The crack deflection, whisker bridging and pullout are considered as major toughening mechanisms in the composite. It is found that coarsening β-Si3N4 whiskers of this composite can improve the toughness/fracture resistance but deteriorate the strength. When limited large abnormally grown whiskers are introduced into the microstructure, the composite shows an improved toughness/fracture resistance behavior and concurrently sustains a high strength. [ABSTRACT FROM AUTHOR]

The static and dynamic fatigue properties of an Al2O3-10 composite were studied. The R-Curve behavior was determined using the indentation strength in bending (ISB) technique. Results indicated that both alumina and the Al2O3-Cr3C2 composite exhibit time-dependent slow crack growth under static fatigue test conditions. In addition, the resistance for slow crack growth in the Al2O3-Cr3C2 composite is higher than that in monolithic alumina. The toughness of alumina was substantially increased and R-curve behavior became evident after the incorporation of Cr3C2 particles. [ABSTRACT FROM AUTHOR]

A new methodology for the determination of the recrystallized volume fraction from anodically etched aluminium alloys using optical microscopy is described. The method involves the creation of a composite image from multiple micrographs taken at a series of orientations. The results of quantitative analysis of images obtained by this new method are compared with those obtained using the traditional single image optical microscopy technique, orientation imaging microscopy (OIM) and microhardness indentation. The multiple orientation image method is shown to consistently yield a recrystallized volume fraction which is significantly higher than that determined from a single image while multiple orientation imaging and OIM results are found to be in good agreement. Furthermore it is shown that, after the subtraction of the effect of concurrent recovery using the rule of mixtures, microhardness indentation can also be used to determine the recrystallized volume fraction. [ABSTRACT FROM AUTHOR]

A new pulse technique is proposed to investigate dynamics and micromechanisms of plastic deformations of materials underneath the indenter during microindentation. It is established that the process of indenter penetration under pulse loading conditions can be described by several distinct stages (as many as four in some cases) differing in kinetics and activation parameters. In each investigated material, the first stage was characterized by a high strain rate (≥103 s−1) and the high contact stresses (dynamic hardness), which exceeded static hardness by factor of 5–10. Typical values of activation volumes during the first stage were of the order of 10−30 m3, i.e. close to the volume occupied by an atom (ion) in a lattice. During the second and the subsequent stages, the activation volume in ionic crystals increased up to about 10−28 m3,( i.e. 10 b3, where b is Burger's vector of glide dislocations). Dynamics of initial stages of the indenter penetration was, therefore, determined by elastic and subsequently by plastic deformation, which is carried out by non-equilibrium point defects (most likely by interstitials or crowdions). A relative role of point defects in the process of mass transfer underneath the indenter and its contribution to microhardness is estimated. In soft materials (NaCl, LiF, Pb) during long indentation times (≥1 s) contribution of point defects can be estimated as more than 10%, and in the case of hard materials (Si, amorphous alloys) became closer to 100%. Dynamics of the final stages of the indenter penetration in soft crystals were governed by the dislocation creep. In all investigated materials for short indentation times (≪1 s) plastic deformation underneath the indenter occurred predominantly via generation and motion of interstitials and their clusters containing a few atoms. [ABSTRACT FROM AUTHOR]

The indentation toughness equation proposed by Anstis et al. was re-examined with a particular emphasis on the definition of the hardness parameter used. It was shown that, because of the existence of the well-known indentation size effect (ISE), the apparent hardness defined as the ratio of the applied load to the projected area of the resultant indentation usually varies with the applied load and seems not to be suitable for use in indentation toughness determination. A new equation for determining indentation toughness, in which a load-independent hardness number was incorporated, was proposed. [ABSTRACT FROM AUTHOR]

Indentation tests using a spherical indenter for split-type two half specimens, or the bonded-interface specimens, have been proposed as a means to evaluate the deformation behaviour or the internal damage of materials during indenting the conventional single piece specimen. The purpose of this study is to assess the validity of the split type technique and to better understand the mechanics during the indentation of the split type specimens with respect to the effect of the interface condition between the two split type half blocks. Indentation tests of Al 6065-T5 alloy specimens are chosen to study the whole elasto-plastic stress-strain behaviour. The finite element method was also employed to investigate the deformation behaviour of the two (single piece and split type) test systems loaded with a spherical indenter. The simulated geometry of the specimens and load-displacement curves during indentations are compared with the experimental data of the Al alloy specimens. The similarity and difference in deformation behaviour and stress distribution between the single piece specimen method and the split type specimen method are investigated. The effect of the friction between the two half blocks in the split type specimen test is discussed. [ABSTRACT FROM AUTHOR]

Mechanical and elastic properties of transparent TeO2-based glass-ceramics (15K2O · 15Nb2O5 · 70TeO2) consisting of nanocrystalline particles (each particle size: 40–50 nm) and showing optical second harmonic generation were evaluated by means of usual Vickers indentation and nanoindentation tests. The precursor glass has Vickers hardness Hv of 2.9 GPa, Young's modulus E of 54.7 GPa, the fracture toughness Kc of 0.25 MPam1/2 and Poisson's ratio of 0.24. The transparent nanocrystalline glass-ceramic heat-treated at 420°C for 1 h has Hv = 3.8 GPa, E = 75.9 GPa and Kc = 0.34 MPam1/2, and the opaque glass-ceramic heat-treated at 475°C for 1 h has Hv = 4.5 GPa, E = 82.9 GPa and Kc = 0.68 MPam1/2, demonstrating that poor mechanical and elastic properties of the precursor TeO2-based glass are improved through sufficient crystallization. The fracture surface energy, brittleness and elastic recoveries (about 44%) after unloading (the maximum load: 30 mN) of transparent nanocrystalline glass-ceramics are almost the same as those of the precursor glass, implying that the interaction among nanocrystalline particles is not so strong. [ABSTRACT FROM AUTHOR]

Many techniques have been used to measure the fractal dimension of brittle fracture surfaces. The purpose of this study was to create a protocol for obtaining the fractal dimension using a simplified optical technique for comparison to reported procedures. Four classes of ceramic materials were used in this study: baria silicate (a glass-ceramic), silicon nitride (a fine grain polycrystalline ceramic), zinc selenide (a large grain polycrystalline ceramic), and silicon (a single crystal ceramic). Contours were produced in perpendicular and parallel planes to the fracture surface using three techniques: slit-island (parallel), profile technique (perpendicular), and crack indentation technique (perpendicular). These contours were then analyzed using a method first introduced by Richardson. The slit-island technique produced statistically greater fractal dimensional increments, ranging from 0.08 to 0.28 for all the materials, than either the profile technique (0.01 to 0.03) or the indentation technique (0.02–0.05). This difference is due in part to the fact that many brittle fracture surfaces are self-affine objects and not self-similar objects. A list of recommendations for a protocol and sources of error for this technique are presented in the appendices. [ABSTRACT FROM AUTHOR]

The hardness and elastic properties of 20PbO · xBi2O3 · (80 − x)B2O3 glasses with x = 20–60 were evaluated through usual Vickers indentation and nanoindentation tests. The glass transition temperature ( Tg = 295–421°C), Vickers hardness ( Hv = 2.9–4.5 GPa), true hardness ( H = 1.5–3.8 GPa) and Young's modulus ( E = 24.4–72.6 GPa) decreased monotonously with increasing Bi2O3 content. This compositional trend demonstrates that the strength of Bi–O chemical bonds in these glasses is considerably weak compared with B–O bonds and plastic deformations under indentation loading occur easily. The elastic recovery after unloading was about 45% for the glasses with x = 20–50, and the Poisson's ratio was 0.27 for the glass with x = 20. The fracture toughness was evaluated to be 0.37–0.88 MPam1/2 from the values of Hv and E, and it was proposed that not only weak Bi–O bonds but also boron coordination polyhedra (BO3 or BO4) and their arrangements affect on crack formation. From the temperature dependence of Vickers hardness up to the glass transition region, it was suggested that the glasses with high Bi2O3 contents belong to the category to fragile glass-forming liquids. [ABSTRACT FROM AUTHOR]

Microstructures associated with room temperature indentation subsequently annealed at 450°C have been analyzed by TEM in Y and Nd based melt textured ceramic superconductors. It is shown that stress relaxation around indentations occurs by the nucleation of stacking faults with R = 1/6〈031〉 displacement vector in Y based material. Differently relaxation occurs in NdBaCuO by the nucleation of perfect dislocations with 〈100〉 Burgers vectors which can be locally dissociated. A model is proposed to explain these microstructures and is related to the difference in energies of stacking faults with R = 1/6〈031〉 displacement vector in these compounds. [ABSTRACT FROM AUTHOR]

Effect of YNbO4 addition on the fracture toughness and stress-strain characteristics of ZrO2(3Y) ceramics was investigated using micro-indentation, X-ray diffractometry and in-situ compression-diffraction techniques in the present work. X-ray diffraction patterns show that sintering of YNbO4 and ZrO2(3Y) mixture results in formation of a solid solution, and the tetragonality of ZrO2(3Y) ceramics increases with the content of YNbO4. The ratio of 002t to 200t peak intensity in X-ray diffraction spectra of the specimens changes significantly after a grinding process at low fractions of YNbO4 (less than 5 mol%) and approaches to a constant value as the content of YNbO4 is higher than 5 mol%, implying that the addition of YNbO4 reduces the domain switchability of the ZrO2(3Y) ceramics. Fracture toughness of modified-ZrO2(3Y) specimens with the same heat treatment conditions could be greatly enhanced by an appropriate addition of YNbO4. In addition, stress-strain curves of YNbO4-modified ZrO2(3Y) specimens exhibit an extraordinary elastic behavior. Data of in-situ loading-diffraction experiment show that an unidentified stress-induced transformation occurs and the peak intensity varies with the stress conditions. Analysis of the stress-strain characteristics and X-ray diffraction results suggest that the fracture toughness of the specimens cannot be simply attributed to the t-to-m phase transformation. [ABSTRACT FROM AUTHOR]

Vickers indentation of 6061-T6 aluminum was modeled using a three-dimensional finite element analysis (FEA) program. Two different work hardening behaviors were assumed. The results were compared with actual indentations using both a static microindenter and a load and depth recording microindenter. The hardness and plastic flow behavior showed excellent agreement, validating the FEA model, and implying that the work hardening of the aluminum decreases past a compressive strain of 0.09. The unloading results were analyzed using Sneddon's solution for the indentation of an elastic half-space by a rigid axisymmetric indenter. The results confirm the validity of applying Sneddon's solution in this case, implying that Bolshakov and Pharr's corrections of Sneddon's solution (which were determined for a conical indenter) are not directly applicable tothe Vickers indenter. [ABSTRACT FROM AUTHOR]