Showing papers on "Indentation published in 2012"
TL;DR: In this paper, the authors used LS Dyna numerical simulation and test results for the through-thickness compression, hemispherical punch indentation and confined compression to develop a constitutive model for Li-ion batteries.
281 citations
TL;DR: In this article, a finite element model was developed, composed of shell elements representing outside casing, and solid elements for the active material with a binder lumped together with the current collectors and the separator.
249 citations
TL;DR: In this article, a numerical model has been elaborated in order to simulate the different impact damage types developing during low velocity/low energy impact, including matrix cracking, fiber failure and delamination.
197 citations
TL;DR: Analysis of the response of single 3T3 fibroblasts that were indented with a micrometer-sized bead attached to an AFM cantilever at forces from 30–600 pN found that at such small deformations, the elastic modulus of 100 Pa is largely determined by the presence of the actin cortex.
Abstract: The measurement of the elastic properties of cells is widely used as an indicator for cellular changes during differentiation, upon drug treatment, or resulting from the interaction with the supporting matrix. Elasticity is routinely quantified by indenting the cell with a probe of an AFM while applying nano-Newton forces. Because the resulting deformations are in the micrometer range, the measurements will be affected by the finite thickness of the cell, viscous effects and even cell damage induced by the experiment itself. Here, we have analyzed the response of single 3T3 fibroblasts that were indented with a micrometer-sized bead attached to an AFM cantilever at forces from 30-600 pN, resulting in indentations ranging from 0.2 to 1.2 micrometer. To investigate the cellular response at lower forces up to 10 pN, we developed an optical trap to indent the cell in vertical direction, normal to the plane of the coverslip. Deformations of up to two hundred nanometers achieved at forces of up to 30 pN showed a reversible, thus truly elastic response that was independent on the rate of deformation. We found that at such small deformations, the elastic modulus of 100 Pa is largely determined by the presence of the actin cortex. At higher indentations, viscous effects led to an increase of the apparent elastic modulus. This viscous contribution that followed a weak power law, increased at larger cell indentations. Both AFM and optical trapping indentation experiments give consistent results for the cell elasticity. Optical trapping has the benefit of a lower force noise, which allows a more accurate determination of the absolute indentation. The combination of both techniques allows the investigation of single cells at small and large indentations and enables the separation of their viscous and elastic components.
188 citations
TL;DR: In this article, the anisotropic indentation response of α-titanium was characterized by electron backscatter diffraction, which was performed for a number of different crystallographic orientations.
Abstract: This study reports on the anisotropic indentation response of α-titanium. Coarse-grained titanium was characterized by electron backscatter diffraction. Sphero-conical nanoindentation was performed for a number of different crystallographic orientations. The grain size was much larger than the size of the indents to ensure quasi-single-crystal indentation. The hexagonal c-axis was determined to be the hardest direction. Surface topographies of several indents were measured by atomic force microscopy. Analysis of the indent surfaces, following Zambaldi and Raabe (Acta Mater. 58(9), 3516–3530), revealed the orientation-dependent pileup behavior of α-titanium during axisymmetric indentation. Corresponding crystal plasticity finite element (CPFE) simulations predicted the pileup patterns with good accuracy. The constitutive parameters of the CPFE model were identified by a nonlinear optimization procedure, and reproducibly converged toward easy activation of prismatic glide systems. The calculated critical resolved shear stresses were 150 ± 4, 349 ± 10, and 1107 ± 39 MPa for prismatic and basal 〈a〉-glide and pyramidal〈c + a〉-glide, respectively.
163 citations
TL;DR: The results demonstrate the promise of contact-based load relaxation analysis toward rapid, robust characterization of mechanical and transport properties for poroelastic gels and tissues.
Abstract: Recent advances in contact mechanics have formalized approaches to distinguish between poroelastic and viscoelastic deformation regimes via load relaxation experiments, and to simultaneously extract the mechanical and transport properties of gels at the macroscale. As poroelastic relaxation times scale quadratically with contact diameter, contact radii and depths on the mm scale can require hours for a single load relaxation experiment to complete. For degradable materials such as biodegradable hydrogels and soft biological tissues, it is necessary to minimize the required experimental time. Here, we investigated the applicability of these methods at smaller (μm) length scales to shorten relaxation times. We conducted load relaxation experiments on hydrated polyacrylamide (PAAm) gels at the microscale via atomic force microscopy (AFM)-enabled indentation, as well as at the macroscale via instrumented indentation. We confirmed the approach as a reliable means to distinguish between viscoelastic and poroelastic relaxation regimes at the microscale: shear modulus G, drained Poisson's ratio νs, diffusivity D, and intrinsic permeability κ of the gels agreed well at the micro- and macroscale levels. Importantly, these properties were accessed accurately within seconds at the microscale, rather than within hours at the macroscale. Our results demonstrate the promise of contact-based load relaxation analysis toward rapid, robust characterization of mechanical and transport properties for poroelastic gels and tissues.
149 citations
TL;DR: In this paper, the authors used an instrumented nano-indenter to determine the number of layers of a single layer of graphene and the elastic modulus of the single layer.
144 citations
TL;DR: It is shown that, unlike unpressurized shells, the relationship between force and displacement demonstrates two linear regimes, and it is inferred that the internal osmotic pressure of yeast cells may be regulated in response to changes in the osmosis pressure of the external medium.
Abstract: Pressurized elastic capsules arise at scales ranging from the 10 m diameter pressure vessels used to store propane at oil refineries to the microscopic polymeric capsules that may be used in drug delivery. Nature also makes extensive use of pressurized elastic capsules: plant cells, bacteria and fungi have stiff walls, which are subject to an internal turgor pressure. Here, we present theoretical, numerical and experimental investigations of the indentation of a linearly elastic shell subject to a constant internal pressure. We show that, unlike unpressurized shells, the relationship between force and displacement demonstrates two linear regimes. We determine analytical expressions for the effective stiffness in each of these regimes in terms of the material properties of the shell and the pressure difference. As a consequence, a single indentation experiment over a range of displacements may be used as a simple assay to determine both the internal pressure and elastic properties of capsules. Our results are relevant for determining the internal pressure in bacterial, fungal or plant cells. As an illustration of this, we apply our results to recent measurements of the stiffness of baker's yeast and infer from these experiments that the internal osmotic pressure of yeast cells may be regulated in response to changes in the osmotic pressure of the external medium.
142 citations
TL;DR: In this paper, the authors measure the modulus of rigidity at small indentation depths for many systems, such as thin films, nanocomposites, biomaterials, etc.
Abstract: It is of interest to measure the modulus of rigidity at small indentation depths for many systems, such as thin films, nanocomposites, biomaterials, etc. Depth-dependence of the rigidity modulus of...
132 citations
TL;DR: The existence of an indentation size effect (ISE) in the onset of yield in a Zr-based bulk metallic glass (BMG) was investigated by employing spherical-tip nanoindentation experiments.
128 citations
TL;DR: In this article, the fracture toughness of thin coatings based on nano-indentation is analyzed and the mechanisms of various crack patterns and existing models used to determine fracture toughness have been discussed.
Abstract: There are many techniques to determine fracture toughness. Experimental simplicity and amenability to materials evaluation are features of general indentation testing. Sometimes indentation is the only practical means of obtaining fundamental information on critical lifetime-limiting damage modes in some ceramics and coatings. Fracture patterns are dependent on the indenter geometry and material properties. The analysis of interfacial toughness by indentation has been well documented. However, no such comprehensive review is available for the analysis of fracture toughness for thin coatings based on (nano)indentation. Therefore, this paper tends to fill this gap. The mechanisms of various crack patterns and existing models used to determine the fracture toughness have been discussed in this study.
TL;DR: In this paper, a finite element model of four-sided pyramidal indentation adopting cohesive interface elements is developed to study the effects of indenter geometry, load, cohesive interface parameters, and material properties on the initiation and propagation of the median/radial/half-penny crack systems.
TL;DR: The flexural strength of the best material (215 MPa) is significantly greater than that of cortical bone and comparable with that of apatite-wollastonite (A/W) bioglass ceramics, with the advantage that it shows a much lower elastic modulus.
TL;DR: The results of depth-sensing analysis of the mechanical properties of living fibroblasts measured under physiological conditions enable the non-homogeneity of the cell cytoskeleton, particularly, its contribution linked to actin filaments located beneath the cell membrane.
Abstract: Atomic force microscopy is a common technique used to determine the elastic properties of living cells. It furnishes the relative Young’s modulus, which is typically determined for indentation depths within the range 300–500 nm. Here, we present the results of depth-sensing analysis of the mechanical properties of living fibroblasts measured under physiological conditions. Distributions of the Young’s moduli were obtained for all studied cells and for every cell. The results show that for small indentation depths, histograms of the relative values of the Young’s modulus described the regions rich in the network of actin filaments. For large indentation depths, the overall stiffness of a whole cell was obtained, which was accompanied by a decrease of the modulus value. In conclusion, the results enable us to describe the non-homogeneity of the cell cytoskeleton, particularly, its contribution linked to actin filaments located beneath the cell membrane. Preliminary results showing a potential application to improve the detection of cancerous cells, have been presented for melanoma cell lines.
TL;DR: The Poroelastic relaxation relaxation Indentation (PRI) testing approach as discussed by the authors was proposed for quantifying the mechanical and transport properties of thin layers of poly(ethylene glycol) hydrogels with thickness on the order of 200 μm.
Abstract: In this work, we present the Poroelastic Relaxation Indentation (PRI) testing approach for quantifying the mechanical and transport properties of thin layers of poly(ethylene glycol) hydrogels with thicknesses on the order of 200 μm. Specifically, PRI characterizes poroelastic relaxation in hydrogels by indenting the material at fixed depth and measuring the contact area-dependent load relaxation process as a function of time. With the aid of a linear poroelastic theory developed for thin or geometrically confined swollen polymer networks, we demonstrate that PRI can quantify the water diffusion coefficient, shear modulus and average pore size of the hydrogel layer. This approach provides a simple methodology to quantify the material properties of thin swollen polymer networks relevant to transport phenomena.
TL;DR: In this article, the negative Poisson ratio with regard to the quasi-static and dynamic indentation compliances for isotropic homogeneous materials is considered and the effect of Poisson's ratio on these compliances is investigated.
TL;DR: In this article, the in situ effect of electrochemically charged hydrogen on the mechanical properties of austenitic stainless steel (ASS) was studied and a novel analysis method based on the Taylor assumption and the indentation size effect was used to calculate the effect of hydrogen on lattice friction.
TL;DR: In this article, the authors used the non-destructive optical technique of digital image correlation (DIC) to measure the force-penetration curve and the full-field displacements on the sandstones surfaces.
TL;DR: In this article, a simple model is proposed to predict the intrinsic hardness of thin films, which allows a more accurate fitting to empirical data and the estimation of ultimate film hardness, which can be used to interpret indentation data and extrapolate the indentation depth-hardness curve to an important region where indentation depths lie between 1% to 5 times of film thickness.
TL;DR: In this paper, the influence of nitrogen concentration on the local mechanical properties has been studied by repeating these indentation matrices in the same area after successive partial removals of the nitrided layer.
TL;DR: In this paper, the authors developed a methodology based on instrumented indentation to determine the mechanical properties of amorphous materials which present cohesive-frictional behaviour, based on the concept of a universal hardness equation, which results from the assumption of a characteristic indentation pressure proportional to the hardness.
Patent•
15 Nov 2012TL;DR: Alkali aluminosilicate glasses that are resistant to damage due to sharp impact and capable of fast ion exchange are provided in this article, where the glasses comprise at least 4 mol % P2O5 and, when ion exchanged, have a Vickers indentation crack initiation load of at least about 7 kgf.
Abstract: Alkali aluminosilicate glasses that are resistant to damage due to sharp impact and capable of fast ion exchange are provided. The glasses comprise at least 4 mol % P2O5 and, when ion exchanged, have a Vickers indentation crack initiation load of at least about 7 kgf.
Journal Article•
TL;DR: In this paper, a simple and easy indentation hardness test is proposed to predict the uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) of rock for designing surface and underground structures.
Abstract: Rock engineers have commonly used the uniaxial compressive strength (UCS) and Brazilian tensile strength (BTS) of rock for designing surface and underground structures. Determining these rock strengths is timeconsuming and expensive, particularly for the preliminary studies of projects. For this reason, indirect tests such as Schmidt rebound number and, ultrasonic test are often used for predicting rock strength. Since indirect tests require less or no sample preparation and the testing equipment is less sophisticated, these tests are very easy to carry out. In addition, these tests can usually be performed in the field. The indentation hardness test is a simple and easy test and can be conducted using a point load test apparatus. The test is of particular value when only a limited amount of rock material, e.g. a thin disc of core or a small lump sample, is available1. The UCS and BTS can easily be predicted from the indentation hardness index (IHI) for the preliminary investigations, if strong predictive correlations are established. Since rock indentation is the basic process in drilling and boring, numerous researchers2–16 have carried out indentation tests to understand the indentation phenomena or to develop prediction models for drilling or boring. Kahraman et al.15 also investigated the relationships between the slope of load-indentation curves and the rock properties. They found good correlations between the slope of load-indentation curves and the rock properties. Kahraman and Gunaydin17 investigated the sawability prediction of carbonate rocks from indentation hardness tests carried out by attaching a dial gauge to the point load apparatus for measuring penetration. They concluded that the indentation hardness test can be used for predicting the sawability of carbonate rocks. Recently, Yagiz18 suggested a new brittleness index and rock brittleness classification based on type, strength, and density of rock together with the results of punch penetration tests. A standard indentation test was recommended by ISRM1 and Equation [1] was suggested for the prediction of UCS from IHI
TL;DR: It is shown that the indentation stiffness of convex shells is dominated by either the mean or Gaussian curvature of the shell depending on the pressurization and indentation depth, revealing how geometry rules the rigidity of shells.
Abstract: Thin shells are found in nature at scales ranging from viruses to hens’ eggs; the stiffness of such shells is essential for their function. We present the results of numerical simulations and theoretical analyses for the indentation of ellipsoidal and cylindrical elastic shells, considering both pressurized and unpressurized shells. We provide a theoretical foundation for the experimental findings of Lazarus et al. [Phys. Rev. Lett. (submitted)] and for previous work inferring the turgor pressure of bacteria from measurements of their indentation stiffness; we also identify a new regime at large indentation. We show that the indentation stiffness of convex shells is dominated by either the mean or Gaussian curvature of the shell depending on the pressurization and indentation depth. Our results reveal how geometry rules the rigidity of shells.
TL;DR: In this article, the elastic modulus, micro-hardness and Vickers hardness of nanostructured thermal barrier coatings (TBCs) exhibit bimodal distribution while the conventional 8YSZ exhibit mono-modal distribution.
TL;DR: In this paper, the authors evaluate the validity of different definitions of both the indentation strain and the contact radius by applying the protocols on datasets generated from a finite element simulation of spherical indentation.
TL;DR: In this paper, the authors apply the Oliver-Pharr method to measure the elastic modulus of a particle embedded in a matrix and apply the real contact area value (not the one predicted from the indentation curve) with sufficient accuracy.
TL;DR: The hardness and Young's modulus of a highly porous metal-organic framework (MOF) using a standard nanoindentation technique was determined in this paper, demonstrating that this porous coordination polymer is substantially stiffer than normal polymers.
Abstract: We have determined the hardness and Young's modulus of a highly porous metal-organic framework (MOF) using a standard nanoindentation technique. Despite the very low density of these films, 1.22 g cm−3, Young's modulus reaches values of almost 10 GPa for HKUST-1, demonstrating that this porous coordination polymer is substantially stiffer than normal polymers. This progress in characterizing mechanical properties of MOFs has been made possible by the use of high quality, oriented thin films grown using liquid phase epitaxy on modified Au substrates.
TL;DR: In this article, the role of grain boundaries in the mechanical deformation of polycrystalline samples was investigated by systematically studying the changes in the indentation stress-strain curves as a function of the distance from the grain boundary.
Abstract: 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.
TL;DR: In this paper, a micromechanical-based model for temperature and rate Indentation Size Effects (TRISE) for body centered cubic (BCC) metals encountered in nanoindentation experiments is proposed.