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Showing papers on "Indentation published in 2013"


Journal ArticleDOI
TL;DR: In this paper, three-dimensional digital image correlation (digital volume correlation) is applied to study deformation beneath indentations, mapping the relative displacements between high-resolution synchrotron X-ray computed tomographs (0.9 μm voxel size).
Abstract: Hardness testing obtains material properties from small specimens via measurement of load-displacement response to an imposed indentation; it is a surface characterisation technique so, except in optically transparent materials, there is no direct observation of the assumed damage and deformation processes within the material. Three-dimensional digital image correlation (digital volume correlation) is applied to study deformation beneath indentations, mapping the relative displacements between high-resolution synchrotron X-ray computed tomographs (0.9 μm voxel size). Two classes of material are examined: ductile aluminium-silicon carbide composite (Al-SiC) and brittle alumina (Al2O3). The measured displacements for Hertzian indentation in Al-SiC are in good agreement with an elastic-plastic finite element simulation. In alumina, radial cracking is observed beneath a Vickers indentation and the crack opening displacements are measured, in situ under load, for the first time. Potential applications are discussed of this characterization technique, which does not require resolution of microstructural features.

493 citations


Journal ArticleDOI
TL;DR: SEM observations of the indentation induced cracks indicate that the polymer network causes greater crack deflection than the dense ceramic material, pointing out the correlation between ceramic network density, elastic modulus and hardness of PICNs.

400 citations


Journal ArticleDOI
TL;DR: In this paper, the creep properties of calcium silicate hydrates (C-S-H) are assessed by means of nanoindentation creep experiments on a wide range of substoichiometric cement pastes.

231 citations


Journal ArticleDOI
01 Apr 2013-Methods
TL;DR: It is shown that the elastic modulus (aka the Young's modulus) of cells is independent of the indentation depth up to 10-20% deformation for the eukaryotic cells studied here.

145 citations


Journal ArticleDOI
TL;DR: A general nano-mechanical test platform capable of performing variable temperature and variable strain rate testing in situ in the scanning electron microscope is described, and the effects of indenter geometry and of radiation on imaging conditions are discussed.
Abstract: A general nano-mechanical test platform capable of performing variable temperature and variable strain rate testing in situ in the scanning electron microscope is described. A variety of test geometries are possible in combination with focused ion beam machining or other fabrication techniques: indentation, micro-compression, cantilever bending, and scratch testing. The system is intrinsically displacement-controlled, which allows it to function directly as a micro-scale thermomechanical test frame. Stable, elevated temperature indentation/micro-compression requires the indenter tip and the sample to be in thermal equilibrium to prevent thermal displacement drift due to thermal expansion. This is achieved through independent heating and temperature monitoring of both the indenter tip and sample. Furthermore, the apex temperature of the indenter tip is calibrated, which allows it to act as a referenced surface temperature probe during contact. A full description of the system is provided, and the effects of indenter geometry and of radiation on imaging conditions are discussed. The stabilization time and temperature distribution throughout the system as a function of temperature is characterized. The advantages of temperature monitoring and thermal calibration of the indenter tip are illustrated, which include the possibility of local thermal conductivity measurement. Finally, validation results using nanoindentation on fused silica and micro-compression of ⟨100⟩ silicon micro-pillars as a function of temperature up to 500 °C are presented, and procedures and considerations taken for these measurements are discussed. A brittle to ductile transition from fracture to splitting then plastic deformation is directly observed in the SEM for silicon as a function of temperature.

141 citations


Journal ArticleDOI
TL;DR: In this paper, the Vickers indentation test was used to study the crack initiation and deformation behaviors of oxide glasses belonging to different chemical systems, and the glass types were compared according to their resistance to the formation of corner cracks.

137 citations


Journal ArticleDOI
TL;DR: In this article, three auxetic periodic microstructures based on 2D geometries are considered for being used as sandwich-core materials, and elastic moduli are computed for each microstructure by using finite elements combined with periodic homogenization technique.
Abstract: Materials presenting a negative Poisson’s ratio (auxetics) have drawn attention for the past two decades, especially in the field of lightweight composite structures and cellular media. Studies have shown that auxeticity may result in higher shear modulus, indentation toughness and acoustic damping. In this work, three auxetic periodic microstructures based on 2D geometries are considered for being used as sandwich-core materials. Elastic moduli are computed for each microstructure by using finite elements combined with periodic homogenization technique. Anisotropy of elastic properties is investigated in and out-of-plane. Comparison is made between auxetics and the classical honeycomb cell. A new 3D auxetic lattice is proposed for volumic applications. Cylindrical and spherical elastic indentation tests are simulated in order to conclude on the applicability of such materials to structures. Proof is made that under certain conditions, auxetics can be competitive with honeycomb cells in terms of indentation strength. Their relatively soft response in tension can be compensated, in some situations, by high shear moduli.

130 citations


Journal ArticleDOI
TL;DR: In this article, the authors studied the strain-rate sensitivity of ultrafine-grained aluminum (Al) and nanocrystalline nickel (Ni) with an improved nanoindentation creep method.
Abstract: The strain-rate sensitivity of ultrafine-grained aluminum (Al) and nanocrystalline nickel (Ni) is studied with an improved nanoindentation creep method. Using the dynamic contact stiffness thermal drift influences can be minimized and reliable creep data can be obtained from nanoindentation creep experiments even at enhanced temperatures and up to 10 h. For face-centered cubic (fcc) metals it was found that the creep behavior is strongly influenced by the microstructure, as nanocrystalline (nc) as well as ultrafine-grained (ufg) samples show lower stress exponents when compared with their coarse-grained (cg) counterparts. The indentation creep behavior resembles a power-law behavior with stress exponents n being ∼ 20 at room temperature. For higher temperatures the stress exponents of ufg-Al and nc-Ni decrease down to n ∼ 5. These locally determined stress exponents are similar to the macroscopic exponents, indicating that similar deformation mechanisms are acting during indentation and macroscopic deformation. Grain boundary sliding found around the residual indentations is related to the motion of unconstrained surface grains.

126 citations


Journal ArticleDOI
TL;DR: This study aims to indicate the likely clinical behavior by evaluating the damage tolerance and R-curve behavior of dental ceramics by in-vitro strength degradation and fracture toughness measurements.
Abstract: Objectives To determine the flexural strength and subsequent strength degradation of a range of dental CAD/CAM ceramic materials and novel PICN (Polymer-Infiltrated-Ceramic-Network) materials by means of pre-damaging with Vickers indentations at various loads. Methods The materials tested included (Mark II, PICN test material 1 and 2, In-Ceram Alumina, VM 9, In-Ceram YZ; Vita Zahnfabrik, Bad Saeckingen, Germany) and (IPS e.max CAD, Ivoclar Vivadent, Schaan, Liechtenstein). Bending bars were cut and lapped with 15 µm diamond suspension. Initial flexural strength (n=10) was determined in three-point-bending. To evaluate the damage tolerance, Vickers indentations were placed on the bending bars (n=35) with varying loads (1.96–98.07 N). The indented bending bars were subsequently loaded to fracture in three-point-bending. In addition, the fracture toughness was determined by the indentation strength (IS) and the SEVNB technique (n=5). Results With increasing indentation loads the fracture strength of all materials tested decreased. The material with the highest fracture resistance to indentation induced damage, was the PICN test material 1 with an indentation load-flexural strength curve slope of 0.21. In-Ceram YZ exhibited the highest damage susceptibility with a slope of 0.4. The fracture toughness varied with the measurement technique and material in the range of 0.82 (VM 9) to 4.94 (In-Ceram YZ) MPa√m for the SEVNB method and 0.96 (VM 9) to 4.97 (In-Ceram YZ) MPa√m for the IS method respectively. Significance This study aims to indicate the likely clinical behavior by evaluating the damage tolerance and R-curve behavior of dental ceramics by in-vitro strength degradation and fracture toughness measurements.

121 citations


Journal ArticleDOI
TL;DR: In this paper, Bower et al. used finite element simulations to establish the influences of finite indenter geometry and transients caused by elasticity, and explored experimentally using amorphous selenium as a model material.
Abstract: New experimental methods are developed to measure the uniaxial power-law creep parameters α and n in the relation e = α σ n ( e is the creep strain rate and σ is the creep stress) from indentation data obtained with a conical or pyramidal indenter. The methods are based on an analysis of Bower et al., which relates the indentation creep rate to the uniaxial creep parameters based on simple assumptions about the constitutive behavior ( Bower et al., 1993 ). Using finite element simulations to establish the influences of finite indenter geometry and transients caused by elasticity, the proposed methods are explored experimentally using amorphous selenium as a model material. This material is well suited for the study because it creeps at temperatures slightly above ambient in a load-history independent fashion with a stress exponent close to unity. Indentation creep tests were conducted with a Berkovich indenter using three different loading methods. With a few notable exceptions, the values of both α and n derived from the indentation data are generally in good agreement with those measured in uniaxial compression tests, thus demonstrating the validity of the approach.

113 citations


Journal ArticleDOI
TL;DR: In this article, the authors used the finite element method combined with dimensional analysis to simulate a series of spherical indentation tests on shape memory alloys (SMAs) and found that the measured indentation modulus strongly depends on the elastic moduli of the two phases, the indentation depth, the forward transformation stress, the transformation hardening coefficient and the maximum transformation strain.
Abstract: Instrumented indentation test has been extensively applied to study the mechanical properties such as elastic modulus of different materials. The Oliver–Pharr method to measure the elastic modulus from an indentation test was originally developed for single phase materials. During a spherical indentation test on shape memory alloys (SMAs), both austenite and martensite phases exist and evolve in the specimen due to stress-induced phase transformation. The question, “What is the measured indentation modulus by using the Oliver–Pharr method from a spherical indentation test on SMAs?” is answered in this paper. The finite element method, combined with dimensional analysis, was applied to simulate a series of spherical indentation tests on SMAs. Our numerical results indicate that the measured indentation modulus strongly depends on the elastic moduli of the two phases, the indentation depth, the forward transformation stress, the transformation hardening coefficient and the maximum transformation strain. Furthermore, a method based on theoretical analysis and numerical simulation was established to determine the elastic moduli of austenite and martensite by using the spherical indentation test and the Oliver–Pharr method. Our numerical experiments confirmed that the proposed method can be applied in practice with satisfactory accuracy. The research approach and findings can also be applied to the indentation of other types of phase transformable materials.

Journal ArticleDOI
TL;DR: In this article, the elastic modulus of cellulose Iβ in the axial and transverse directions was obtained from atomistic simulations using both the standard uniform deformation approach and a complementary approach based on nanoscale indentation.
Abstract: The elastic modulus of cellulose Iβ in the axial and transverse directions was obtained from atomistic simulations using both the standard uniform deformation approach and a complementary approach based on nanoscale indentation. This allowed comparisons between the methods and closer connectivity to experimental measurement techniques. A reactive force field was used that explicitly describes hydrogen bond, coulombic and van der Waals interactions, allowing each contribution to the inter- and intra-molecular forces to be analyzed as a function of crystallographic direction. The uniform deformation studies showed that the forces dominating elastic behavior differed in the axial and transverse directions because of the relationship between the direction of the applied strain and the hydrogen bonding planes. Simulations of nanoscale indentation were then introduced to model the interaction between a hemispherical indenter with the \((1\bar{1}0)\) surface of a cellulose Iβ rod. The role of indenter size, loading force and indentation speed on the transverse elastic modulus was studied and, for optimized parameters, the results found to be in good agreement with experimentally-measured transverse elastic modulus for individual cellulose crystals.

Journal ArticleDOI
TL;DR: A review of indenter materials for usage at high temperatures is instructive for identifying appropriate indenter-sample materials combinations to prevent indenter loss or failure due to chemical reactions or wear during indentation.
Abstract: As nanoindentation at high temperatures becomes increasingly popular, a review of indenter materials for usage at high temperatures is instructive for identifying appropriate indenter-sample materials combinations to prevent indenter loss or failure due to chemical reactions or wear during indentation. This is an important consideration for nanoindentation as extremely small volumes of reacted indenter material will have a significant effect on measurements. The high temperature hardness, elastic modulus, thermal properties, and chemical reactivities of diamond, boron carbide, silicon carbide, tungsten carbide, cubic boron nitride, and sapphire are discussed. Diamond and boron carbide show the best elevated temperature hardness, while tungsten carbide demonstrates the lowest chemical reactivity with the widest array of elements.

Journal ArticleDOI
TL;DR: In this paper, the authors used a discrete element model based on interaction given by 3D beam model to simulate the elastic properties at the macroscopic scale of brittle cracks, which is achieved by computing a failure criterion based on an equivalent hydrostatic stress.

Journal ArticleDOI
TL;DR: In this paper, the role of intermetallic compounds on mechanical and creep behavior of Bi-Sn-based alloys has been investigated by dynamic resonance technique and Vickers indentation testing at room temperature and compared to the traditional Pb-Sn eutectic alloy.
Abstract: Mechanical properties and indentation creep of the melt-spun process Bi–42 wt%Sn, Bi–40 wt%Sn–2 wt%In, Bi–40 wt%Sn–2 wt%Ag and Bi–38 wt%Sn–2 wt%In–2 wt%Ag were studied by dynamic resonance technique and Vickers indentation testing at room temperature and compared to that of the traditional Sn–37 wt%Pb eutectic alloy. The results show that the structure of Bi–42 wt%Sn alloy is characterized by the presence of rhombohedral Bi and body centered tetragonal β-Sn. The two ternary alloys exhibit additional constituent phases of intermetallic compounds SnIn19 for Bi–40 wt%Sn–2 wt%In and e-Ag3Sn for Bi–40 wt%Sn–2 wt%Ag alloys. Attention has been paid to the role of intermetallic compounds on mechanical and creep behavior. The In and Ag containing solder alloy exhibited a good combination of higher creep resistance, good mechanical properties and lower melting temperature as compared with Pb–Sn eutectic solder alloy. This was attributed to the strengthening effect of Bi as a strong solid solution element in the Sn matrix and formation of intermetallic compounds β-SnBi, e-Ag3Sn and InSn19 which act as both strengthening agent and grain refiner in the matrix of the material. Addition of In and Ag decreased the melting temperature of Bi–Sn lead-free solder from 143 °C to 133 °C which was possible mainly due to the existence of InSn19 and Ag3Sn intermetallic compounds. Elastic constants, internal friction and thermal properties of Bi–Sn based alloys have been studied and analyzed.

Journal ArticleDOI
TL;DR: In this paper, the authors present a mechanics model that predicts the cutting forces in feed ( x ), normal ( y ) and axial ( z ) directions by modeling the chip thickness distribution, and cutting and indentation mechanics.
Abstract: Simulation of multi-axis ball-end milling of dies, molds and aerospace parts with free-form surfaces is highly desirable in order to optimize the machining processes in virtual environment ahead of costly trials. This paper presents a mechanics model that predicts the cutting forces in feed ( x ), normal ( y ) and axial ( z ) directions by modeling the chip thickness distribution, and cutting and indentation mechanics. The shearing forces are based on commonly known cutting mechanics models. The indentation of the cutting edge into the work material is modeled analytically by considering elasto-plastic deformation of the work material pressed by a rigid cutting tool edge with a positive or negative rake angle. The distribution of chip thickness and geometry of indentation zone are evaluated by considering five-axis motion of the tool along the toolpath. The proposed model has been experimentally validated in plunge indentation, as well as in three and five-axis ball-end milling of free-form surfaces. The prediction of axial ( z ) cutting forces is shown to be improved significantly when the proposed indentation model is integrated into the mechanics of ball-end milling.

Journal ArticleDOI
TL;DR: In this paper, the pop-ins generated during spherical nanoindentation on (0, 0,0,1), (1, 0,−1,2) and (1, 0,−1,0) surfaces were examined by transmission electron microscopy (TEM) to identify the deformation mechanisms.

Journal ArticleDOI
TL;DR: In this paper, the fracture toughness of polycrystalline Li 7 La 3 Zr 2 O 12 was measured using an indentation technique and subsurface crack propagation was analyzed using a focused ion beam/scanning electron microscope (FIB-SEM) technique.

Journal ArticleDOI
TL;DR: In this article, a complex procedure of indentation result analysis, based on the transformation of load-penetration depth curves into stress-strain curves, was presented for 0.7-2.4-μm thick titanium nitride (TiN) coatings deposited by the Pulsed Laser Deposition (PLD) technique on steel substrates.

Journal ArticleDOI
TL;DR: In this paper, the hardness and strain rate sensitivity of ultrafine-grained (UFG) aluminium were examined as a function of temperature using in situ strain rate jump indentation in a SEM at temperatures up to 250 °C.
Abstract: The hardness and strain rate sensitivity of ultrafine-grained (UFG) aluminium was examined as a function of temperature using in situ strain rate jump indentation in a SEM at temperatures up to 250 °C. Measured strain rate sensitivities were in good agreement with earlier bulk compression measurements. Activation energies and volumes for deformation were extracted and discussed. Transitions in the deformation mechanism are observed at lower temperatures for smaller grain sizes.

Journal ArticleDOI
TL;DR: In this paper, the microstructure, indentation toughness, room and high temperature tribological properties of alumina-carbon nanotubes nanocomposites with various contents of carbon carbon sintering are described.

Journal ArticleDOI
TL;DR: In this paper, the hardness measured by the nanosize indenter under atomic indentation is examined for the cases of nanocrystalline nickel by means of molecular dynamics simulations.

Journal ArticleDOI
TL;DR: In this paper, Vickers hardness, indentation and E -modulus are determined by micro-indentation tests on undried, polished concrete samples taken from a structure damaged by ASR.

Journal ArticleDOI
TL;DR: In this paper, the authors studied the nanoindentation of monolayer graphene by molecular dynamics simulations and found that the response of graphene to indentation is deflection dependent.
Abstract: We studied the nanoindentation of monolayer graphene by molecular dynamics simulations. It is found that the response of graphene to indentation is deflection dependent. In small deflection range, the response obeys point load model, while large-deflection indentation follows the sphere load model. Hence, we proposed to make sectional fittings and use different response models in different deflection ranges. In this way, a consistent Young's modulus is obtained that is almost independent of the size ratio of intender to graphene and the pretensions of graphene. The calculated Young's modulus is about 1.00 TPa, in good agreement with the experiments.

Journal ArticleDOI
TL;DR: In this article, an extended expanding cavity model (ECM) was proposed to evaluate flow properties measured in uniaxial mechanical testing, and the mean pressure of the projected surface from radial stress at the hemispherical core boundary with a scaling factor for strain-hardening metals.

Journal ArticleDOI
TL;DR: In this paper, the deformation of an elastic-plastic half-space by a rigid spherical indenter was examined with the finite element method, and the authors derived constitutive relations of the dimensionless mean contact pressure and contact area from finite element simulation results.


Journal ArticleDOI
TL;DR: In this paper, the authors measured the crystallographic dependence of the mechanical responses of an α-Ti-7-wt.% Alloy by nanoindentation using spherical and Berkovich indenters, and the dislocation structures resulting from indentation were characterized by electron microscopy.

Journal ArticleDOI
TL;DR: In this paper, crystal plasticity simulations and experiments of cylindrical indentation on Nickel base single crystal superalloy specimens are presented and discussed and the subsurface stress and strain fields presented are similar to those observed in meso-scale dovetail joints in single crystal turbine blades.

Journal ArticleDOI
TL;DR: In this paper, the authors used a nanoindenter with a Berkovich tip to study local mechanical properties of two polycrystalline intermetallics with a B2 crystal structure, NiAl and NiTi.