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Sample records for based indentation technique

  1. A Load-Based Multiple-Partial Unloading Micro-Indentation Technique for Mechanical Property Evaluation

    SciTech Connect

    C. Feng; J.M. Tannenbaum; B.S. Kang; M.A. Alvin

    2009-07-23

    A load-based multiple-partial unloading microindentation technique has been developed for evaluating mechanical properties of materials. Comparing to the current prevailing nano/micro-indentation methods, which require precise measurements of the indentation depth and load, the proposed technique only measures indentation load and the overall indentation displacement (i.e. including displacement of the loading apparatus). Coupled with a multiple-partial unloading procedure during the indentation process, this technique results in a load-depth sensing indentation system capable of determining Young’s modulus of metallic alloys with flat, tubular, or curved architectures. Test results show consistent and correct elastic modulus values when performing indentation tests on standard alloys such as steel, aluminum, bronze, and single crystal superalloys. The proposed micro-indentation technique has led to the development of a portable loaddepth sensing indentation system capable of on-site, in-situ material property measurement.

  2. Viscoelastic properties of healthy human artery measured in saline solution by AFM based indentation technique

    SciTech Connect

    Lundkvist, A.; Lilleodden, E.; Sickhaus, W.; Kinney, J.; Pruitt, L.; Balooch, M.

    1998-02-09

    Using an Atomic Force Microscope with an attachment for indentation, we have measured local, in vitro mechanical properties of healthy femoral artery tissue held in saline solution. The elastic modulus (34. 3 kPa) and viscoelastic response ({tau}sub{epsilon} {equals} 16.9 s and {tau}sub{sigma} {equals} 29.3 s) of the unstretched,intimal vessel wall have been determined using Sneddon theory and a three element model(standard linear solid) for viscoelastic materials. The procedures necessary to employ the indenting attachment to detect elastic moduli in the kPa range in liquid are described.

  3. Mechanical Characterization of Mesoscale Interfaces Using Indentation Techniques

    NASA Astrophysics Data System (ADS)

    Kalidindi, Surya R.; Mohan, Soumya; Rossi, Alicia

    2017-01-01

    Mesoscale interfaces and interphases play a central role in controlling the many macroscale mechanical properties and performance characteristics of structural materials. Modern instrumented indenters present an unprecedented opportunity to measure, reliably and consistently, the local mechanical responses at a multitude of length scales ranging from tens of nanometers to hundreds of microns. When these high-fidelity measurements are combined with rigorous data analyses protocols, it is possible to systematically study the mechanical role of individual mesoscale interfaces and quantify their contributions to the overall mechanical response of the material system . The advantages of these new measurement and analyses protocols as well as the potential for development and implementation of novel high-throughput assays is discussed.

  4. Shear band evolution in zirconium/hafnium-based bulk metallic glasses under static and dynamic indentations

    NASA Astrophysics Data System (ADS)

    Zhang, Hongwen

    In this thesis, a detailed investigation of thermal stability and mechanical deformation behavior of Zr/Hf-based Bulk Metallic Glasses is conducted. First, systematic studies had been implemented to understand the influence of relative compositions of Zr and Hf on thermal stability and mechanical property evolution. Second, shear band evolution under indentations were investigated experimentally and theoretically. It was found in the present work that gradually replacing Zr by Hf remarkably increases the density and improves the mechanical properties. However, a slight decrease in glass forming ability with increasing Hf content has also been identified through thermodynamic analysis although all the materials in the current study were still found to be amorphous. Many indentation studies have revealed only a few shear bands surrounding the indent on the top surface of the specimen. This small number of shear bands cannot account for the large plastic deformation beneath the indentations. Therefore, a bonded interface technique has been used to observe the slip-steps due to shear band evolution. Vickers indentations were performed along the interface of the bonded split specimen at increasing loads. At small indentation loads, the plastic deformation was primarily accommodated by semi-circular primary shear bands surrounding the indentation. At higher loads, secondary and tertiary shear bands were formed inside this plastic zone. A modified expanding cavity model was then used to predict the plastic zone size characterized by the shear bands and to identify the stress components responsible for the evolution of the various types of shear bands. The applicability of various hardness - yield-strength (H-sigma y) relationships currently available in the literature for bulk metallic glasses (BMGs) is also investigated. Experimental data generated on ZrHf-based BMGs in the current study and those available elsewhere on other BMG compositions were used to validate the

  5. Experimental pressure solution creep of quartz by indenter technique

    NASA Astrophysics Data System (ADS)

    Gratier, J.; Guiguet, R.; Renard, F.; Jenatton, L.

    2006-12-01

    The principle of the experiment is to measure the displacement-rate of indenter that dissolve mineral under stress in order to establish creep laws. A stainless steel cylindrical indenter (200 microns diameter) mounted under a free-moving piston is put in contact with a crystal of quartz in presence of its saturated solution. A dead weigh put on the piston sets the stress. The device is maintained within pressure vessel during several weeks or months at constant temperature and fluid pressure. The depths of the dissolution holes are measured at the end of the experiments. Various types of experimental protocols have been used with difference (i) about quartz (synthetic or natural), (ii) about the nature of the solution (Na0H N, H20, dry), (iii) about the way the contact solid/solution/solid is filled (iv) about the relation between stress and optical quartz axis. Results are shown as displacement-rate versus stress relations for the 4 configurations, with always the same temperature (350°C), solution (NaOH N) and fluid pressure (200 MPa) and with several weeks or months of duration. When using dry contact or water no significant hole may be seen. Short durations (days) never allowed measurable hole to develop. The results show a large scattering of displacement-rates for same stress values, even for the same protocol. From observations under microscope two explanations are possible either a strong effect of the roughening of the dissolution interface that evolve with time and that seems to play a crucial role in the displacement-rate versus stress relation or some effects of temporary undersaturating during the experiment due to experimental perturbations. The results also show a large overlapping between the displacement-rates obtained with the 4 protocols. Plotting all the results on the same log-log diagram shows a displacement-rate versus stress relation that fit a power law with a stress exponent of 1.75. Due to the relatively high stress values this is not

  6. Measuring Depth-dependent Dislocation Densities and Elastic Strains in an Indented Ni-based Superalloy

    SciTech Connect

    Barabash, O.M.; Santella, M.; Barabash, R.I.; Ice, G.E.; Tischler, J.

    2011-12-14

    The indentation-induced elastic-plastic zone in an IN 740 Ni-based superalloy was studied by three-dimensional (3-D) x-ray microdiffraction and electron back scattering diffraction (EBSD). Large lattice reorientations and the formation of geometrically necessary dislocations are observed in the area with a radius of {approx}75 {mu}m. A residual compression zone is found close to the indent edge. An elastic-plastic transition is observed at {approx}20 {mu}m from the indent edge. Depth dependent dislocation densities are determined at different distances from the indent edge.

  7. Evaluation of Mechanical Properties of Nuclear Materials Using Non-Destructive Ball Indentation Technique

    SciTech Connect

    Mathew, M.D.; Linga Murty, K.

    2002-07-01

    Integrity of structural components depends on the deformation and fracture behavior of materials. For evaluating the material condition in-service, it is generally not feasible or practical or advisable to cut samples from operating structures. Non-destructive testing (NDT) techniques are required to evaluate the mechanical properties. Although several NDT techniques such as ultrasound, magnetic strength, Barkhausen noise, microhardness etc., are employed for estimating the mechanical property degradation, these methodologies are generally empirical and indirect. Automated Ball Indentation (ABI) is a non-destructive testing technique for direct measurement of mechanical and fracture properties of metallic engineering materials. Because of the small area over which the test is carried out, it is possible to determine point to point variations in the mechanical and fracture properties, such as those that exist in weldments. Although ABI technique is non-intrusive, it is a state-of-the-art mechanical test that measures directly the current/local deformation behavior of the material. In this paper, we present results from studies on the application of ABI technique to determine tensile and fracture properties of ferritic steels, an austenitic stainless steel, a nickel base superalloy and Zircaloy in different thermo-mechanical conditions. The effects of aging and cold work on these properties were determined from the ABI tests. Gradients in mechanical properties of ferritic steel welds, particularly in the narrow heat-affected zone, were clearly established. ABI technique was found to be useful in determining the anisotropy in the tensile properties of Zircaloy cladding tubes. The technique has potential as a non-destructive method for assessing structural integrity of aged components. (authors)

  8. NON-DESTRUCTIVE THERMAL BARRIER COATING SPALLATION PREDICTION BY A LOADBASED MICRO-INDENTATION TECHNIQUE

    SciTech Connect

    J. M. Tannenbaum; K. Lee; B. S.-J. Kang; M.A. Alvin

    2010-11-18

    Currently, the durability and life cycle of thermal barrier coatings (TBC) applied to gas turbine blades and combustor components are limiting the maximum temperature and subsequent efficiency at which gas turbine engines operate. The development of new materials, coating technologies and evaluation techniques is required if enhanced efficiency is to be achieved. Of the current ceramic coating materials used in gas turbine engines, yttria stabilized zirconia (YSZ) is most prevalent, its low thermal conductivity, high thermal expansion coefficient and outstanding mechanical strength make it ideal for use in TBC systems. However, residual stresses caused by coefficients of thermal expansion mismatches within the TBC system and unstable thermally grown oxides are considered the primary causes for its premature and erratic spallation failure. Through finite element simulations, it is shown that the residual stresses generated within the thermally grown oxide (TGO), bond coat (BC), YSZ and their interfaces create slight variations in indentation unloading surface stiffness response prior to spallation failure. In this research, seven air plasma sprayed and one electron beam physical vapor deposition yttria partially stabilized zirconia TBCs were subjected to isothermal and cyclic loadings at 1100°C. The associated coating degradation was evaluated using a non-destructive multiple partial unloading micro-indentation procedure. The results show that the proposed non-destructive micro-indentation evaluation technique can be an effective and specimenindependent TBC failure prediction tool capable of determining the location of initial spallation failure prior to its actual occurrence.

  9. Critical aspects of nano-indentation technique in application to hardened cement paste

    SciTech Connect

    Davydov, D. Jirasek, M.; Kopecky, L.

    2011-01-15

    Several open questions related to the experimental protocol and processing of data acquired by the nano-indentation (NI) technique are investigated. The volume fractions of mechanically different phases obtained from statistical NI (SNI) analysis are shown to be different from those obtained by back-scattered electron (BSE) image analysis and X-ray diffraction (XRD) method on the same paste. Judging from transmission electron microscope (TEM) images, the representative volume element of low-density calcium-silicate hydrates (C-S-H) can be considered to be around 500 nm, whereas for high-density C-S-H it is about 100 nm. This raises the question how the appropriate penetration depth for NI experiments should be selected. Changing the maximum load from 1 mN to 5 mN, the effect of penetration depth on the experimental results is studied. As an alternative to the SNI method, a 'manual' indentation method is proposed, which combines information from BSE and atomic-force microscopy (AFM), coupled to the NI machine. The AFM allows to precisely indent a high-density C-S-H rim around unhydrated clinkers in cement paste. Yet the results from that technique still show a big scatter.

  10. Indentation and tribological behavior of nickel titanium alloys and study of instrumented spherical indentation

    NASA Astrophysics Data System (ADS)

    Ni, Wangyang

    In this work, microscopic shape memory (SME) and superelastic (SE) effects in martensitic and austenitic NiTi alloys were probed by instrumented indentation techniques. Both pyramidal and spherical indenters were used to study the mechanical response of the NiTi alloys. It was found that deformation due to indentation was recoverable by the shape memory or superelastic effect and that the magnitude of indent recovery can be rationalized using the concept of the representative strain and maximum strain. Instrumented indentation techniques, especially using spherical indenters, are shown to be useful in quantifying shape memory and superelastic effects at micron and nanometer length scales. Novel tribological applications of superelastic NiTi thin films suggested by these results were also studied. A novel composite coating, with a superelastic NiTi interlayer between soft aluminum substrate and hard CrN coating, was studied using instrumented indentation, scratch, and pin-on-disk wear tests. It was found that a superelastic NiTi interlayer can dramatically improve hard-coating adhesion and wear resistance. The improved coating performance is attributed to the large elastic recovery ratio and strain tolerance of the superelastic NiTi interlayer. It was demonstrated that spherical indentation is very useful in the characterization of the mechanical properties of NiTi shape memory alloys. To further understand the spherical indentation process, a general study of spherical indentation in elastic-plastic materials was carried out. Two previously unknown relationships between hardness, reduced modulus, indentation depth, indenter radius, and work of indentation were found. Based on these relationships a novel energy-based method for determining contact area, reduced modulus, and hardness of materials from instrumented spherical indentation measurements was proposed. This method also provides a new way of calibrating the effective radius of imperfectly shaped spherical

  11. A Nano-indentation Identification Technique for Viscoelastic Constitutive Characteristics of Periodontal Ligaments

    PubMed Central

    Ashrafi, H.; Shariyat, M.

    2016-01-01

    Introduction Nano-indentation has recently been employed as a powerful tool for determining the mechanical properties of biological tissues on nano and micro scales. A majority of soft biological tissues such as ligaments and tendons exhibit viscoelastic or time-dependent behaviors. The constitutive characterization of soft tissues is among very important subjects in clinical medicine and especially, biomechanics fields. Periodontal ligament plays an important role in initiating tooth movement when loads are applied to teeth with orthodontic appliances. It is also the most accessible ligament in human body as it can be directly manipulated without any surgical intervention. From a mechanical point of view, this ligament can be considered as a thin interface made by a solid phase, consisting mainly of collagen fibers, which is immersed into a so-called ground substance. However, the viscoelastic constitutive effects of biological tissues are seldom considered rigorous during Nano-indentation tests. Methods In the present paper, a mathematical contact approach is developed to enable determining creep compliance and relaxation modulus of distinct periodontal ligaments, using constant–rate indentation and loading time histories, respectively. An adequate curve-fitting method is presented to determine these characteristics based on the Nano-indentation of rigid Berkovich tips. Generalized Voigt-Kelvin and Wiechert models are used to model constitutive equations of periodontal ligaments, in which the relaxation and creep functions are represented by series of decaying exponential functions of time. Results Time-dependent creep compliance and relaxation function have been obtained for tissue specimens of periodontal ligaments. Conclusion To improve accuracy, relaxation and creep moduli are measured from two tests separately. Stress relaxation effects appear more rapidly than creep in the periodontal ligaments. PMID:27672630

  12. On the determination of elastic moduli of cells by AFM based indentation

    NASA Astrophysics Data System (ADS)

    Ding, Yue; Xu, Guang-Kui; Wang, Gang-Feng

    2017-04-01

    The atomic force microscopy (AFM) has been widely used to measure the mechanical properties of biological cells through indentations. In most of existing studies, the cell is supposed to be linear elastic within the small strain regime when analyzing the AFM indentation data. However, in experimental situations, the roles of large deformation and surface tension of cells should be taken into consideration. Here, we use the neo-Hookean model to describe the hyperelastic behavior of cells and investigate the influence of surface tension through finite element simulations. At large deformation, a correction factor, depending on the geometric ratio of indenter radius to cell radius, is introduced to modify the force-indent depth relation of classical Hertzian model. Moreover, when the indent depth is comparable with an intrinsic length defined as the ratio of surface tension to elastic modulus, the surface tension evidently affects the indentation response, indicating an overestimation of elastic modulus by the Hertzian model. The dimensionless-analysis-based theoretical predictions, which include both large deformation and surface tension, are in good agreement with our finite element simulation data. This study provides a novel method to more accurately measure the mechanical properties of biological cells and soft materials in AFM indentation experiments.

  13. On the determination of elastic moduli of cells by AFM based indentation

    PubMed Central

    Ding, Yue; Xu, Guang-Kui; Wang, Gang-Feng

    2017-01-01

    The atomic force microscopy (AFM) has been widely used to measure the mechanical properties of biological cells through indentations. In most of existing studies, the cell is supposed to be linear elastic within the small strain regime when analyzing the AFM indentation data. However, in experimental situations, the roles of large deformation and surface tension of cells should be taken into consideration. Here, we use the neo-Hookean model to describe the hyperelastic behavior of cells and investigate the influence of surface tension through finite element simulations. At large deformation, a correction factor, depending on the geometric ratio of indenter radius to cell radius, is introduced to modify the force-indent depth relation of classical Hertzian model. Moreover, when the indent depth is comparable with an intrinsic length defined as the ratio of surface tension to elastic modulus, the surface tension evidently affects the indentation response, indicating an overestimation of elastic modulus by the Hertzian model. The dimensionless-analysis-based theoretical predictions, which include both large deformation and surface tension, are in good agreement with our finite element simulation data. This study provides a novel method to more accurately measure the mechanical properties of biological cells and soft materials in AFM indentation experiments. PMID:28368053

  14. On the determination of elastic moduli of cells by AFM based indentation.

    PubMed

    Ding, Yue; Xu, Guang-Kui; Wang, Gang-Feng

    2017-04-03

    The atomic force microscopy (AFM) has been widely used to measure the mechanical properties of biological cells through indentations. In most of existing studies, the cell is supposed to be linear elastic within the small strain regime when analyzing the AFM indentation data. However, in experimental situations, the roles of large deformation and surface tension of cells should be taken into consideration. Here, we use the neo-Hookean model to describe the hyperelastic behavior of cells and investigate the influence of surface tension through finite element simulations. At large deformation, a correction factor, depending on the geometric ratio of indenter radius to cell radius, is introduced to modify the force-indent depth relation of classical Hertzian model. Moreover, when the indent depth is comparable with an intrinsic length defined as the ratio of surface tension to elastic modulus, the surface tension evidently affects the indentation response, indicating an overestimation of elastic modulus by the Hertzian model. The dimensionless-analysis-based theoretical predictions, which include both large deformation and surface tension, are in good agreement with our finite element simulation data. This study provides a novel method to more accurately measure the mechanical properties of biological cells and soft materials in AFM indentation experiments.

  15. Evaluation of the Fracture Toughness of Nb-40Al-8Cr-1W-1Y-0.05B Intermetallic Material by Indentation Techniques

    NASA Technical Reports Server (NTRS)

    Choi, S. R.; Salem, J. A.; Hebsur, M. G.

    1993-01-01

    The fracture toughness of an Nb-40Al-8Cr - 1W-1Y-0.05B intermetallic material was evaluated by indentation techniques at room temperature. Two widely used indentation methods, crack size measurement and indent strength, yielded excellent agreement with a conventional fracture toughness technique using straight-through precracked specimens, despite the occasional formation of poorly configured cracks. However, the modified indentation technique, using dummy indent flaws, resulted in a low fracture toughness compared to that evaluated by the other methods. The material did not exhibit rising R-curve behavior, as evaluated from the indentation strength data. These results indicate that indentation fracture principles are applicable to this brittle intermetallic material without modification of the residual contact stress term originally calibrated for ceramic materials.

  16. Indentation size effects in the nano- and micro-hardness of a Fe-based bulk metallic glass

    NASA Astrophysics Data System (ADS)

    Xu, F.; Ding, Y. H.; Deng, X. H.; Zhang, P.; Long, Z. L.

    2014-10-01

    Hardness of a Fe-based bulk metallic glass (BMG) was evaluated by both atomic force microscopy (AFM) nanoindentation (nano-hardness) and instrumented indentation with a traditional indenter setup (micro-hardness) under different maximum loads at room temperature. The nano-hardness and the micro-hardness were found to be comparable. For both of the indentation methods, indentation size effect (ISE) is detected as increase in hardness with decrease in indentation peak load. It is proposed that strain rate dependent softening, loading history and the lag between free volume creation and mechanical softening should be responsible for the ISE in this BMG. Furthermore, ISE is found to be more significant in AFM nanoindentation than in instrumented indentation. This can be explained by taking into account the effect of exerted peak load and the face angle of the indenter in a qualitative manner.

  17. Optical coherence tomography-based contact indentation for diaphragm mechanics in a mouse model of transforming growth factor alpha induced lung disease.

    PubMed

    Wang, Kimberley C W; Astell, Chrissie J; Wijesinghe, Philip; Larcombe, Alexander N; Pinniger, Gavin J; Zosky, Graeme R; Kennedy, Brendan F; Berry, Luke J; Sampson, David D; James, Alan L; Le Cras, Timothy D; Noble, Peter B

    2017-05-04

    This study tested the utility of optical coherence tomography (OCT)-based indentation to assess mechanical properties of respiratory tissues in disease. Using OCT-based indentation, the elastic modulus of mouse diaphragm was measured from changes in diaphragm thickness in response to an applied force provided by an indenter. We used a transgenic mouse model of chronic lung disease induced by the overexpression of transforming growth factor-alpha (TGF-α), established by the presence of pleural and peribronchial fibrosis and impaired lung mechanics determined by the forced oscillation technique and plethysmography. Diaphragm elastic modulus assessed by OCT-based indentation was reduced by TGF-α at both left and right lateral locations (p < 0.05). Diaphragm elastic modulus at left and right lateral locations were correlated within mice (r = 0.67, p < 0.01) suggesting that measurements were representative of tissue beyond the indenter field. Co-localised images of diaphragm after TGF-α overexpression revealed a layered fibrotic appearance. Maximum diaphragm force in conventional organ bath studies was also reduced by TGF-α overexpression (p < 0.01). Results show that OCT-based indentation provided clear delineation of diseased diaphragm, and together with organ bath assessment, provides new evidence suggesting that TGF-α overexpression produces impairment in diaphragm function and, therefore, an increase in the work of breathing in chronic lung disease.

  18. Indentation Analysis of Biphasic Viscoelastic Hydrogels

    PubMed Central

    Toohey, K.S.; Kalyanam, S.; Palaniappan, J.; Insana, M.F.

    2015-01-01

    Mechanical properties of soft biological materials are dependent on the responses of the two phases of which they are comprised: the solid matrix and interstitial fluid. Indentation techniques are commonly used to measure properties of such materials, but comparisons between different experimental and analytical techniques can be difficult. Most models relating load and time during spherical indentation are based on Hertzian contact theory, but the exact limitation of this theory for soft materials are unclear. Here, we examine the response of gelatin hydrogels to shear and indentation loading to quantify combined effects of the solid and fluid phases. The instantaneous behavior of the hydrogels is different for each test geometry and loading rate, but the relaxed response, measured by the relaxed modulus, is the same for all tests, within 17%. Additionally, indentation depths from 15–25% of the radius of the spherical indenter are found to minimize error in the estimate of relaxed modulus. PMID:26568646

  19. Nano-indentation study on the (001) face of KDP crystal based on SPH method

    NASA Astrophysics Data System (ADS)

    Xiaoguang, Guo; Ziyuan, Liu; Hang, Gao; Dongming, Guo

    2015-08-01

    In order to avoid the defects of mesh distortion when dealing with large deformation problems through using the finite element method, a mess-free simulation method—smooth particle hydrodynamics (SPH) has been introduced. The material constitutive model of KDP crystal has been established based on the elastic-plastic theory. Then the nano-indentation on the (001) face of KDP crystal has been carried out using SPH method. Simulation results show that the maximum equivalent stress and the maximum plastic strain concentrate on the area that located near the tip of the indenter during the loading process. The distribution shape of Von Mises stress is similar to concentric circles. During the unloading process, no obvious variation of plastic strain distribution exists. The maximum Von Mises stress is mainly located at the indentation and its edge at the end of the unloading process. The approximate direct proportion relationship between the maximum indentation depth and the depth of the maximum Von Mises stress distribution has been discovered when the maximum load is lower than 8 mN. In addition, the nano-indentation experiments on KDP crystal's (001) face have been carried out. Both the material parameters and the adjusted stress-strain curve have been verified. The hindering role of the affected layer has been found and analyzed. Project supported by the National Basic Research Program of China (No. 51135002), and the Science Fund for Creative Research Groups (No. 51321004).

  20. Characterization of Corneal Indentation Hysteresis.

    PubMed

    Ko, Match W L; Dongming Wei; Leung, Christopher K S

    2015-01-01

    Corneal indentation is adapted for the design and development of a characterization method for corneal hysteresis behavior - Corneal Indentation Hysteresis (CIH). Fourteen porcine eyes were tested using the corneal indentation method. The CIH measured in enucleated porcine eyes showed indentation rate and intraocular pressure (IOP) dependences. The CIH increased with indentation rate at lower IOP (<; 25 mmHg) and decreased with indentation rate at higher IOP (> 25 mmHg). The CIH was linear proportional to the IOP within an individual eye. The CIH was positively correlated with the IOP, corneal in-plane tensile stress and corneal tangent modulus (E). A new method based on corneal indentation for the measurement of Corneal Indentation Hysteresis in vivo is developed. To our knowledge, this is the first study to introduce the corneal indentation hysteresis and correlate the corneal indentation hysteresis and corneal tangent modulus.

  1. Evaluation of flow properties in the weldments of vanadium alloys using a novel indentation technique

    SciTech Connect

    Gubbi, A.N.; Rowcliffe, A.F.; Lee, E.H.; King, J.F.; Goodwin, G.M.

    1996-10-01

    Automated Ball Indentation (ABI) testing, was successfully employed to determine the flow properties of the fusion zone, heat affected zone (HAZ), and base metal of the gas tungsten arc (GTA) and electron beam (EB) welds of the V-4Cr-4Ti (large heat no. 832665) and the V-5Cr-5Ti (heat 832394) alloys. ABI test results showed a clear distinction among the properties of the fusion zone, HAZ, and base metal in both GTA and EB welds of the two alloys. GTA and EB welds of both V-4Cr-4Ti and V-5Cr-5Ti alloys show strengthening of both the fusion zone and the HAZ (compared to base metal) with the fusion zone having higher strength than the HAZ. These data correlate well with the Brinell hardness. On the other hand, GTA welds of both alloys, after a post-weld heat treatment of 950{degrees}C for 2 h, show a recovery of the properties to base metal values with V-5Cr-5Ti showing a higher degree of recovery compared to V-4Cr-4Ti. These measurements correlate with the reported recovery of the Charpy impact properties.

  2. Electromechanical probe and automated indentation maps are sensitive techniques in assessing early degenerated human articular cartilage.

    PubMed

    Sim, Sotcheadt; Chevrier, Anik; Garon, Martin; Quenneville, Eric; Lavigne, Patrick; Yaroshinsky, Alex; Hoemann, Caroline D; Buschmann, Michael D

    2016-06-09

    Recent advances in the development of new drugs to halt or even reverse the progression of Osteoarthritis at an early-stage requires new tools to detect early degeneration of articular cartilage. We investigated the ability of an electromechanical probe and an automated indentation technique to characterize entire human articular surfaces for rapid non-destructive discrimination between early degenerated and healthy articular cartilage. Human cadaveric asymptomatic articular surfaces (4 pairs of distal femurs and 4 pairs of tibial plateaus) were used. They were assessed ex vivo: macroscopically, electromechanically (maps of the electromechanical quantitative parameter, QP, reflecting streaming potentials), mechanically (maps of the instantaneous modulus, IM) and through cartilage thickness. Osteochondral cores were also harvested from healthy and degenerated regions for histological assessment, biochemical analyses and unconfined compression tests. The macroscopic visual assessment delimited three distinct regions on each articular surface: region I was macroscopically degenerated, region II was macroscopically normal but adjacent to region I and region III was the remaining normal articular surface. Thus, each extracted core was assigned to one of the three regions. A mixed effect model revealed that only the QP (p < 0.0001) and IM (p < 0.0001) were able to statistically discriminate the three regions. Effect size was higher for QP and IM than other assessments, indicating greater sensitivity to distinguish early degeneration of cartilage. When considering the mapping feature of the QP and IM techniques, it also revealed bilateral symmetry in a moderately similar distribution pattern between bilateral joints. This article is protected by copyright. All rights reserved.

  3. Inference of the phase-to-mechanical property link via coupled X-ray spectrometry and indentation analysis: Application to cement-based materials

    SciTech Connect

    Krakowiak, Konrad J.; Wilson, William; James, Simon; Musso, Simone; Ulm, Franz-Josef

    2015-01-15

    A novel approach for the chemo-mechanical characterization of cement-based materials is presented, which combines the classical grid indentation technique with elemental mapping by scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDS). It is illustrated through application to an oil-well cement system with siliceous filler. The characteristic X-rays of major elements (silicon, calcium and aluminum) are measured over the indentation region and mapped back on the indentation points. Measured intensities together with indentation hardness and modulus are considered in a clustering analysis within the framework of Finite Mixture Models with Gaussian component density function. The method is able to successfully isolate the calcium-silica-hydrate gel at the indentation scale from its mixtures with other products of cement hydration and anhydrous phases; thus providing a convenient means to link mechanical response to the calcium-to-silicon ratio quantified independently via X-ray wavelength dispersive spectroscopy. A discussion of uncertainty quantification of the estimated chemo-mechanical properties and phase volume fractions, as well as the effect of chemical observables on phase assessment is also included.

  4. Experimental layering development by indenter technique and application to fault rheology differentiation

    NASA Astrophysics Data System (ADS)

    Gratier, J. P.; Noiriel, C. N.; Renard, F.

    2014-12-01

    Natural deformation of rocks is often associated with differentiation processes leading to irreversible transformations of their microstructural thus leading in turn to modifications of their rheological properties. The mechanisms of development of such processes at work during diagenesis, metamorphism or fault differentiation are poorly known as they are not easy to reproduce in the laboratory due to the long duration required for most of chemically controlled differentiation processes. Here we show that experimental compaction with layering development, similar to what happens in natural deformation, can be obtained in the laboratory by indenter techniques. Samples of plaster mixed with clay and samples of diatomite loosely interbedded with clays were loaded during several months at 40°C (plaster) and 150°C (diatomite) in presence of their saturated solutions. High-resolution X-ray tomography and SEM studies show that the layering development is a self-organized process. Stress driven dissolution of the soluble minerals (gypsum in plaster, silica in diatomite) is initiated in the zones initially richer in clays because the kinetics of diffusive mass transfer along the clay/soluble mineral interfaces is much faster than along the healed boundaries of the soluble minerals. The passive concentration of the clay minerals amplifies the localization of the dissolution along some layers oriented perpendicular to the maximum compressive stress component. Conversely, in the areas with initial low content in clay and clustered soluble minerals, dissolution is more difficult as the grain boundaries of the soluble species are healed together. These areas are less deformed and they act as rigid objects that concentrate the dissolution near their boundaries thus amplifying the differentiation. Applications to fault processes are discussed: i) localized pressure solution and sealing processes may lead to fault rheology differentiation with a partition between two end

  5. Review of Instrumented Indentation

    PubMed Central

    VanLandingham, Mark R.

    2003-01-01

    Instrumented indentation, also known as depth-sensing indentation or nanoindentation, is increasingly being used to probe the mechanical response of materials from metals and ceramics to polymeric and biological materials. The additional levels of control, sensitivity, and data acquisition offered by instrumented indentation systems have resulted in numerous advances in materials science, particularly regarding fundamental mechanisms of mechanical behavior at micrometer and even sub-micrometer length scales. Continued improvements of instrumented indentation testing towards absolute quantification of a wide range of material properties and behavior will require advances in instrument calibration, measurement protocols, and analysis tools and techniques. In this paper, an overview of instrumented indentation is given with regard to current instrument technology and analysis methods. Research efforts at the National Institute of Standards and Technology (NIST) aimed at improving the related measurement science are discussed. PMID:27413609

  6. Indentation of Transversely Isotropic Materials

    NASA Astrophysics Data System (ADS)

    Bhat, Talapady Srivatsa

    Instrumented indentation, as a tool for characterization of mechanical properties, has well been established in the past decades. Studies have been conducted to understand the behavior of isotropic materials under indentation and techniques to accurately predict isotropic material properties have also been reported. Further, within the isotropic regime, work has been done to predict the indentation hardness without having to investigate the area of contact during indentation. Studies have also reported the prospect of utilizing indentation to predict the fatigue behavior of isotropic materials. This dissertation is made with the intent of extending the use of indentation, as a characterization tool, to the anisotropic regime. The effect of transverse isotropy on the indentation response of materials is systematically studied here. Extensive computational analysis is performed to elucidate the underlying deformation mechanics of indentation of transversely isotropic materials. Owing to the anisotropy, indentation may be performed parallel or perpendicular to the plane of isotropy of the specimen. It is observed that the indentation response varies significantly for each of these cases. The two cases are treated as unique and an identical systematic analysis is carried for both. The indentation orientations shall henceforth be referred to as transverse and longitudinal indentation for indentation parallel and perpendicular to the plane of isotropy respectively. A technique is developed capable of extracting the elastic-plastic properties of transversely isotropic materials from interpretation of indentation response in either direction. The technique is rigorously tested for its robustness, accuracy and uniqueness of results. A sensitivity analysis is performed to determine how sensitive the technique is to errors in experimental results. Rigorous studies are performed to understand the variation in pile-up or sink-in during indentation with varying anisotropy in the

  7. Comparison of cyclic and impact-based reference point indentation measurements in human cadaveric tibia.

    PubMed

    Karim, Lamya; Van Vliet, Miranda; Bouxsein, Mary L

    2015-04-07

    Although low bone mineral density (BMD) is strongly associated with increased fracture risk, up to 50% of those who suffer fractures are not detected as high-risk patients by BMD testing. Thus, new approaches may improve identification of those at increased risk for fracture by in vivo assessment of altered bone tissue properties, which may contribute to skeletal fragility. Recently developed reference point indentation (RPI) allows for the assessment of cortical bone indentation properties in vivo using devices that apply cyclic loading or impact loading, but there is little information available to assist with the interpretation of RPI measurements. Our goals were to use human cadaveric tibia to determine: 1) the associations between RPI variables, cortical bone density, and morphology; 2) the association between variables obtained from RPI systems using cyclic, slow loading versus a single impact load; and 3) the age-related differences in RPI variables. We obtained 20 human tibia and femur pairs from female donors (53-97years), measured total hip BMD using dual-energy X-ray absorptiometry, assessed tibial cortical microarchitecture using high-resolution peripheral quantitative computed tomography (HR-pQCT), and assessed cortical bone indentation properties at the mid-tibial diaphysis using both the cyclic and impact-based RPI systems (Biodent and Osteoprobe, respectively, Active Life Scientific, Santa Barbara, CA). We found a few weak associations between RPI variables, BMD, and cortical geometry; a few weak associations between measurements obtained by the two RPI systems; and no age-related differences in RPI variables. Our findings indicate that in cadaveric tibia from older women RPI measurements are largely independent of age, femoral BMD, and cortical geometry. Furthermore, measurements from the cyclic and impact loading RPI devices are weakly related to each other, indicating that each device reflects different aspects of cortical bone indentation

  8. Quantification of stiffness change in degenerated articular cartilage using optical coherence tomography-based air-jet indentation.

    PubMed

    Huang, Yan-Ping; Wang, Shu-Zhe; Saarakkala, Simo; Zheng, Yong-Ping

    2011-10-01

    Articular cartilage is a thin complex tissue that covers the bony ends of joints. Changes in the composition and structure of articular cartilage will cause degeneration, which may further lead to osteoarthritis. Decreased stiffness is one of the earliest symptoms of cartilage degeneration and also represents the imperfect quality of repaired cartilage. An optical coherence tomography (OCT)-based air-jet indentation system was recently developed in our group to measure the mechanical properties of soft tissues. In this study, this system was applied to quantify the change of mechanical properties of articular cartilage after degeneration induced by enzymatic digestions. Forty osteochondral disks (n = 20 × 2) were prepared from bovine patellae and treated with collagenase and trypsin digestions, respectively. The apparent stiffness of the cartilage was measured by the OCT-based air-jet indentation system before and after the degeneration. The results were also compared with those from a rigid contact mechanical indentation and an ultrasound water-jet indentation. Through the air-jet indentation, it was found that the articular cartilage stiffness dropped significantly by 84% (p < 0.001) and 63% (p < 0.001) on average after collagenase and trypsin digestions, respectively. The stiffness measured by the air-jet indentation system was highly correlated (R > 0.8, p < 0.001) with that from the other two indentation methods. This study demonstrated that the OCT-based air-jet indentation can be a useful tool to quantitatively assess the mechanical properties of articular cartilage, and this encourages us to further develop a miniaturized probe suitable for arthroscopic applications.

  9. Pyrolytic carbon indentation crack morphology.

    PubMed

    Ely, J L; Stupka, J; Haubold, A D

    1996-06-01

    In studying fatigue and fracture behavior of brittle materials, Vickers diamond indentation cracks are often used. Many of the studies of indentation cracks use crack system models such as the radial-median crack or Palmqvist crack. These systems are also used to study small crack growth in brittle materials, and have been studied for pyrolytic carbon. However, the true morphology of these cracks in pyrolytic carbon coatings on graphite substrates have not been described. This study examined Vickers diamond and spherical ball indentation cracks in pyrolytic carbon coatings using several techniques, including serial metallographic cross sections, indentation fracture in bending, acoustic emission, and residual surface indentation scanning. The crack systems developed using these techniques were not typical of either radial median or Palmqvist systems. The morphology is unique to this material, possibly because of the coating thickness limitations. Given the difference in crack system, the application of standard indentation crack equations in studying fracture mechanics, especially for small cracks, must be questioned.

  10. Single fiber push-out characterization of interfacial mechanical properties in unidirectional CVI-C/SiC composites by the nano-indentation technique

    NASA Astrophysics Data System (ADS)

    Zhang, Lifeng; Ren, Chengzu; Zhou, Changling; Xu, Hongzhao; Jin, Xinmin

    2015-12-01

    The characterization of interfaces in woven ceramic matrix composites is one of the most challenging problems in composite application. In this investigation, a new model material consisting of the chemical vapor infiltration unidirectional C/SiC composites with PyC fiber coating were prepared and evaluated to predict the interfacial mechanic properties of woven composites. Single fiber push-out/push-back tests with the Berkovich indenter were conducted on the thin sliced specimens using nano-indentation technique. To give a detailed illustration of the interfacial crack propagation and failure mechanism, each sector during the push-out process was analyzed at length. The test results show that there is no detectable difference between testing a fiber in a direct vicinity to an already tested fiber and testing a fiber in vicinity to not-pushed fibers. Moreover, the interface debonding and fiber sliding mainly occur at the PyC coating, and both the fiber and surrounding matrix have no plastic deformation throughout the process. Obtained from the load-displacement curve, the interfacial debonding strength (IDS) and friction stress (IFS) amount to, respectively, 35 ± 5 MPa and 10 ± 1 MPa. Based on the findings, the interfacial properties with PyC fiber coating can be predicted. Furthermore, it is expected to provide a useful guideline for the design, evaluation and optimal application of CVI-C/SiC.

  11. An indentation fatigue strength law

    NASA Astrophysics Data System (ADS)

    Xu, Baoxing; Yonezu, Akio; Chen, Xi

    2010-05-01

    Indentation fatigue, where a cyclic load is applied on the sample via an indenter, emerges as an alternative approach for measuring the fatigue properties of materials. We have carried out indentation fatigue tests on a poly(vinyl chloride) (PVC) bulk material, as well as on TiN and NiP films/coatings deposited on SUS304 steel substrates, and demonstrate that a simple power-law relationship can be established between the indentation load amplitude and number of cycles to failure. Such a law is very similar to the conventional fatigue strength law obtained from uniaxial tests. The agreement between the fatigue stress exponents obtained by uniaxial and indentation fatigue tests suggests the potential applicability of the indentation fatigue technique for extracting the fatigue properties of materials.

  12. Indentation of a stretched elastomer

    NASA Astrophysics Data System (ADS)

    Zheng, Yue; Crosby, Alfred J.; Cai, Shengqiang

    2017-10-01

    Indentation has been intensively used to characterize mechanical properties of soft materials such as elastomers, gels, and soft biological tissues. In most indentation measurements, residual stress or stretch which can be commonly found in soft materials is ignored. In this article, we aim to quantitatively understand the effects of prestretches of an elastomer on its indentation measurement. Based on surface Green's function, we analytically derive the relationship between indentation force and indentation depth for a prestretched Neo-Hookean solid with a flat-ended cylindrical indenter as well as a spherical indenter. In addition, for a non-equal biaxially stretched elastomer, we obtain the equation determining the eccentricity of the elliptical contacting area between a spherical indenter and the elastomer. Our results clearly demonstrate that the effects of prestretches of an elastomer on its indentation measurement can be significant. To validate our analytical results, we further conduct correspondent finite element simulations of indentation of prestretched elastomers. The numerical results agree well with our analytical predictions.

  13. Temperature-dependent indentation behavior of transformation-toughened zirconia-based ceramics

    NASA Technical Reports Server (NTRS)

    Tikare, Veena; Heuer, Arthur H.

    1991-01-01

    Indentation behavior of Ce-TZP, Y-TZP, and Mg-PSZ between room temperature and 1300 C was investigated. Hardness decreased with increasing temperature for all three materials, but indentation cracking increased with increasing temperature. The opposing temperature dependences are discussed in terms of dislocation and transformation plasticity.

  14. Temperature-dependent indentation behavior of transformation-toughened zirconia-based ceramics

    NASA Technical Reports Server (NTRS)

    Tikare, Veena; Heuer, Arthur H.

    1991-01-01

    Indentation behavior of Ce-TZP, Y-TZP, and Mg-PSZ between room temperature and 1300 C was investigated. Hardness decreased with increasing temperature for all three materials, but indentation cracking increased with increasing temperature. The opposing temperature dependences are discussed in terms of dislocation and transformation plasticity.

  15. Evaluation of the mechanical properties of conventionally-cast Al matrix composites reinforced by quasicrystalline Al-Cu-Fe particles using continuous ball indentation technique

    NASA Astrophysics Data System (ADS)

    Fleury, E.; Lee, S. M.; Kim, W. T.; Kim, D. H.

    2000-10-01

    Room temperature mechanical properties of the Al/(AlCuFe)p and Al96Cu4/(AlCuFe)p cast composites were estimated from uniaxial compressive test and continuous ball indentation technique. Values of the Young's modulus and yield stress determined from continuous ball indentation tests were slightly overestimated, suggesting a surface effect on the mechanical properties. However, it was shown that the Al-Cu-Fe particles provided a significant increase of the elastic modulus, yield stress, and strain hardening, especially in the range up to 10% volume fraction of reinforcements. Also, determination of the hardness by continuous-ball-indentation tests revealed a strong influence of the matrix strength on the mechanical properties of the conventionally cast composites.

  16. Measurement of diabetic wounds with optical coherence tomography-based air-jet indentation system and a material testing system.

    PubMed

    Choi, M-C; Cheung, K-K; Ng, G Y-F; Zheng, Y-P; Cheing, G L-Y

    2015-11-01

    Material testing system is a conventional but destructive method for measuring the biomechanical properties of wound tissues in basic research. The recently developed optical coherence tomography-based air-jet indentation system is a non-destructive method for measuring these properties of soft tissues in a non-contact manner. The aim of the study was to examine the correlation between the biomechanical properties of wound tissues measured by the two systems. Young male Sprague-Dawley rats with streptozotocin-induced diabetic were wounded by a 6 mm biopsy punch on their hind limbs. The biomechanical properties of wound tissues were assessed with the two systems on post-wounding days 3, 7, 10, 14, and 21. Wound sections were stained with picro-sirius red for analysis on the collagen fibres. Data obtained on the different days were charted to obtain the change in biomechanical properties across the time points, and then pooled to examine the correlation between measurements made by the two devices. Qualitative analysis to determine any correlation between indentation stiffness measured by the air-jet indentation system and the orientation of collagen fibres. The indentation stiffness is significantly negatively correlated to the maximum load, maximum tensile stress, and Young's modulus by the material testing system (all p<0.05). The orientation of collagen changes with the indentation stiffness over time. Our findings support the use of optical coherence tomography-based air-jet indentation system to evaluate the biomechanical properties of wounds in a non-contact manner. It is a potential clinical device to examine the biomechanical properties of chronic wounds in vivo in a repeatable manner.

  17. A biphasic model for micro-indentation of a hydrogel-based contact lens.

    PubMed

    Chen, Xiaoming; Dunn, Alison C; Sawyer, W Gregory; Sarntinoranont, Malisa

    2007-04-01

    The stiffness and hydraulic permeability of soft contact lenses may influence its clinical performance, e.g., on-eye movement, fitting, and wettability, and may be related to the occurrence of complications; e.g., lesions. It is therefore important to determine these properties in the design of comfortable contact lenses. Micro-indentation provides a nondestructive means of measuring mechanical properties of soft, hydrated contact lenses. However, certain geometrical and material considerations must be taken into account when analyzing output force-displacement (F-D) data. Rather than solely having a solid response, mechanical behavior of hydrogel contact lenses can be described as the coupled interaction between fluid transport through pores and solid matrix deformation. In addition, indentation of thin membranes ( approximately 100 microm) requires special consideration of boundary conditions at lens surfaces and at the indenter contact region. In this study, a biphasic finite element model was developed to simulate the micro-indentation of a hydrogel contact lens. The model accounts for a curved, thin hydrogel membrane supported on an impermeable mold. A time-varying boundary condition was implemented to model the contact interface between the impermeable spherical indenter and the lens. Parametric studies varying the indentation velocities and hydraulic permeability show F-D curves have a sensitive region outside of which the force response reaches asymptotic limits governed by either the solid matrix (slow indentation velocity, large permeability) or the fluid transport (high indentation velocity, low permeability). Using these results, biphasic properties (Young's modulus and hydraulic permeability) were estimated by fitting model results to F-D curves obtained at multiple indentation velocities (1.2 and 20 microm/s). Fitting to micro-indentation tests of Etafilcon A resulted in an estimated permeability range of 1.0 x 10(-15) to 5.0 x 10(-15) m(4)N s and

  18. Residual stress in glass: indentation crack and fractography approaches.

    PubMed

    Anunmana, Chuchai; Anusavice, Kenneth J; Mecholsky, John J

    2009-11-01

    To test the hypothesis that the indentation crack technique can determine surface residual stresses that are not statistically significantly different from those determined from the analytical procedure using surface cracks, the four-point flexure test, and fracture surface analysis. Soda-lime-silica glass bar specimens (4 mm x 2.3 mm x 28 mm) were prepared and annealed at 650 degrees C for 30 min before testing. The fracture toughness values of the glass bars were determined from 12 specimens based on induced surface cracks, four-point flexure, and fractographic analysis. To determine the residual stress from the indentation technique, 18 specimens were indented under 19.6N load using a Vickers microhardness indenter. Crack lengths were measured within 1 min and 24h after indentation, and the measured crack lengths were compared with the mean crack lengths of annealed specimens. Residual stress was calculated from an equation developed for the indentation technique. All specimens were fractured in a four-point flexure fixture and the residual stress was calculated from the strength and measured crack sizes on the fracture surfaces. The results show that there was no significant difference between the residual stresses calculated from the two techniques. However, the differences in mean residual stresses calculated within 1 min compared with those calculated after 24h were statistically significant (p=0.003). This study compared the indentation technique with the fractographic analysis method for determining the residual stress in the surface of soda-lime-silica glass. The indentation method may be useful for estimating residual stress in glass.

  19. Residual stress in glass: indentation crack and fractography approaches

    PubMed Central

    Anunmana, Chuchai; Anusavice, Kenneth J.; Mecholsky, John J.

    2009-01-01

    Objective To test the hypothesis that the indentation crack technique can determine surface residual stresses that are not statistically significantly different from those determined from the analytical procedure using surface cracks, the four-point flexure test, and fracture surface analysis. Methods Soda-lime-silica glass bar specimens (4 mm × 2.3 mm × 28 mm) were prepared and annealed at 650 °C for 30 min before testing. The fracture toughness values of the glass bars were determined from 12 specimens based on induced surface cracks, four-point flexure, and fractographic analysis. To determine the residual stress from the indentation technique, 18 specimens were indented under 19.6 N load using a Vickers microhardness indenter. Crack lengths were measured within 1 min and 24 h after indentation, and the measured crack lengths were compared with the mean crack lengths of annealed specimens. Residual stress was calculated from an equation developed for the indentation technique. All specimens were fractured in a four-point flexure fixture and the residual stress was calculated from the strength and measured crack sizes on the fracture surfaces. Results The results show that there was no significant difference between the residual stresses calculated from the two techniques. However, the differences in mean residual stresses calculated within 1 min compared with those calculated after 24 h were statistically significant (p=0.003). Significance This study compared the indentation technique with the fractographic analysis method for determining the residual stress in the surface of soda-lime silica glass. The indentation method may be useful for estimating residual stress in glass. PMID:19671475

  20. Indentation of Foam-Based Polymer Composite Sandwich Beams and Panels Under Static Loading

    NASA Astrophysics Data System (ADS)

    Rizov, V.

    2009-06-01

    Foam core composite sandwich structures are highly susceptible to damage when subjected to localized loading. Therefore, thorough study of the role of factors such as face sheet thickness, indentor diameter value, and crosshead displacement rate in indentation events is important. The objective of the present work is to investigate experimentally and numerically the influence of these factors on the nonlinear static indentation behavior of sandwich beams and panels consisting of glass fiber/resin face sheets and PVC (polyvinylchloride) foam core. Static indentation tests are carried out on sandwich composite beam and panel specimens using steel cylindrical and spherical indentors, respectively. Numerical models are developed for simulating the mechanical response of sandwich structures subjected to localized indentation beyond the limit of elastic deformation in the foam core. In this relation, the *CRUSHABLE FOAM and the *CRUSHABLE FOAM HARDENING options in the ABAQUS finite element program system are used. The numerical analysis results demonstrate good agreement with experimental data. It is found that increasing the face sheet thickness and indentor diameter value leads to increase in the load (for a given displacement). It is shown also that the indentation behavior does not exhibit sensitivity to crosshead displacement rate over the conditions considered in the present work.

  1. An examination of the indentation size effect in FCC metals and alloys from a kinetics based perspective using nanoindentation

    NASA Astrophysics Data System (ADS)

    Stegall, David Earl

    The indentation size effect (ISE) in metals is described as the rise in hardness with decreasing depth of indentation and contradicts conventional plasticity behavior. The goal of this dissertation is to further examine the fundamental dislocation mechanisms that may be contributing to the so-called indentation size effect. In this work, we examined several metals and alloys including 99.999% Aluminum, 99.95% Nickel, 99.95% Silver, and three alloys, alpha brass 70/30, 70/30 nickel copper, and 7075 AlZn to study the effect of stacking fault energy on the ISE. The current work sought to address several objectives including; 1) Verify the existence of an ISE and the bilinear behavior of various FCC metals using single indentation test platform and the same tip for various stress decades: 2) Examine the thermally activated mechanisms that could contribute to the ISE via the kinetics of plastic deformation based on indentation experiments for constant load creep and load relaxation as well as classical uniaxial testing to study the coupled relationship between strain rate, dislocation density, and dislocation velocity: 3) Examine the possible contribution of stacking fault energy (SFE) on the ISE by comparing pure metals over a wide SFE range as well as the effect of alloying. We demonstrate that all the metals tested exhibit a clear ISE using a new approach that included the use of a single machine and using a single tip capable of reaching depths of 30 microm. This eliminated any uncertainty in measurements when comparing data for any metal across the nano to micro-range (from 0.07 mN to 10 N). It was found that the pure metals should be examine separately from the alloys when examining any dependency on SFE. Activation volume analysis, based on indentation creep experiments, was used to examine the stress dependency of the activation volume for each metal. We verified through various experiments across a wide stress range that the ISE has a kinetic signature similar

  2. Interaction of Cracks Between Two Adjacent Indents in Glass

    NASA Technical Reports Server (NTRS)

    Choi, S. R.; Salem, J. A.

    1993-01-01

    Experimental observations of the interaction behavior of cracks between two adjacent indents were made using an indentation technique in soda-lime glass. It was specifically demonstrated how one indent crack initiates and propagates in the vicinity of another indent crack. Several types of crack interactions were examined by changing the orientation and distance of one indent relative to the other. It was found that the residual stress field produced by elastic/plastic indentation has a significant influence on controlling the mode of crack interaction. The interaction of an indent crack with a free surface was also investigated for glass and ceramic specimens.

  3. Interaction of Cracks Between Two Adjacent Indents in Glass

    NASA Technical Reports Server (NTRS)

    Choi, S. R.; Salem, J. A.

    1993-01-01

    Experimental observations of the interaction behavior of cracks between two adjacent indents were made using an indentation technique in soda-lime glass. It was specifically demonstrated how one indent crack initiates and propagates in the vicinity of another indent crack. Several types of crack interactions were examined by changing the orientation and distance of one indent relative to the other. It was found that the residual stress field produced by elastic/plastic indentation has a significant influence on controlling the mode of crack interaction. The interaction of an indent crack with a free surface was also investigated for glass and ceramic specimens.

  4. Determination of the mechanical and physical properties of cartilage by coupling poroelastic-based finite element models of indentation with artificial neural networks.

    PubMed

    Arbabi, Vahid; Pouran, Behdad; Campoli, Gianni; Weinans, Harrie; Zadpoor, Amir A

    2016-03-21

    One of the most widely used techniques to determine the mechanical properties of cartilage is based on indentation tests and interpretation of the obtained force-time or displacement-time data. In the current computational approaches, one needs to simulate the indentation test with finite element models and use an optimization algorithm to estimate the mechanical properties of cartilage. The modeling procedure is cumbersome, and the simulations need to be repeated for every new experiment. For the first time, we propose a method for fast and accurate estimation of the mechanical and physical properties of cartilage as a poroelastic material with the aid of artificial neural networks. In our study, we used finite element models to simulate the indentation for poroelastic materials with wide combinations of mechanical and physical properties. The obtained force-time curves are then divided into three parts: the first two parts of the data is used for training and validation of an artificial neural network, while the third part is used for testing the trained network. The trained neural network receives the force-time curves as the input and provides the properties of cartilage as the output. We observed that the trained network could accurately predict the properties of cartilage within the range of properties for which it was trained. The mechanical and physical properties of cartilage could therefore be estimated very fast, since no additional finite element modeling is required once the neural network is trained. The robustness of the trained artificial neural network in determining the properties of cartilage based on noisy force-time data was assessed by introducing noise to the simulated force-time data. We found that the training procedure could be optimized so as to maximize the robustness of the neural network against noisy force-time data. Copyright © 2016 Elsevier Ltd. All rights reserved.

  5. Effects of elastic indenter deformation on spherical instrumented indentation tests: the reduced elastic modulus

    NASA Astrophysics Data System (ADS)

    Aida Rodríguez, Sara; Alcalá, Jorge; Martins Souza, Roberto

    2011-03-01

    Although the Hertz theory is not applicable in the analysis of the indentation of elastic-plastic materials, it is common practice to incorporate the concept of indenter/specimen combined modulus to consider indenter deformation. The appropriateness was assessed of the use of reduced modulus to incorporate the effect of indenter deformation in the analysis of the indentation with spherical indenters. The analysis based on finite element simulations considered four values of the ratio of the indented material elastic modulus to that of the diamond indenter, E/Ei (0, 0.04, 0.19, 0.39), four values of the ratio of the elastic reduced modulus to the initial yield strength, Er/Y (0, 10, 20, 100), and two values of the ratio of the indenter radius to maximum total displacement, R/δmax (3, 10). Indenter deformation effects are better accounted for by the reduced modulus if the indented material behaves entirely elastically. In this case, identical load-displacement (P - δ) curves are obtained with rigid and elastic spherical indenters for the same elastic reduced modulus. Changes in the ratio E/Ei , from 0 to 0.39, resulted in variations lower than 5% for the load dimensionless functions, lower than 3% in the contact area, Ac , and lower than 5% in the ratio H/Er . However, deformations of the elastic indenter made the actual radius of contact change, even in the indentation of elastic materials. Even though the load dimensionless functions showed only a little increase with the ratio E/Ei , the hardening coefficient and the yield strength could be slightly overestimated when algorithms based on rigid indenters are used. For the unloading curves, the ratio δe/δmax , where δe is the point corresponding to zero load of a straight line with slope S from the point (Pmax, δmax ), varied less than 5% with the ratio E/Ei . Similarly, the relationship between reduced modulus and the unloading indentation curve, expressed by Sneddon's equation, did not reveal the necessity

  6. Reference point indentation is not indicative of whole mouse bone measures of stress intensity fracture toughness

    PubMed Central

    Carriero, Alessandra; Bruse, Jan L.; Oldknow, Karla J.; Millán, José Luis; Farquharson, Colin; Shefelbine, Sandra J.

    2014-01-01

    Bone fragility is a concern for aged and diseased bone. Measuring bone toughness and understanding fracture properties of the bone are critical for predicting fracture risk associated with age and disease and for preclinical testing of therapies. A reference point indentation technique (BioDent) has recently been developed to determine bone's resistance to fracture in a minimally invasive way by measuring the indentation distance increase (IDI) between the first and last indentations over cyclic indentations in the same position. In this study, we investigate the relationship between fracture toughness KC and reference point indentation parameters (i.e. IDI, total indentation distance (TID) and creep indentation distance (CID)) in bones from 38 mice from six types (C57Bl/6, Balb, oim/oim, oim/+, Phospho1−/− and Phospho1 wild type counterpart). These mice bone are models of healthy and diseased bone spanning a range of fracture toughness from very brittle (oim/oim) to ductile (Phospho1−/−). Left femora were dissected, notched and tested in 3-point bending until complete failure. Contralateral femora were dissected and indented in 10 sites of their anterior and posterior shaft surface over 10 indentation cycles. IDI, TID and CID were measured. Results from this study suggest that reference point indentation parameters are not indicative of stress intensity fracture toughness in mouse bone. In particular, the IDI values at the anterior mid-diaphysis across mouse types overlapped, making it difficult to discern differences between mouse types, despite having extreme differences in stress intensity based toughness measures. When more locations of indentation were considered, the normalised IDIs could distinguish between mouse types. Future studies should investigate the relationship of the reference point indentation parameters for mouse bone in other material properties of the bone tissue in order to determine their use for measuring bone quality. PMID:25280470

  7. Reference point indentation is not indicative of whole mouse bone measures of stress intensity fracture toughness.

    PubMed

    Carriero, Alessandra; Bruse, Jan L; Oldknow, Karla J; Millán, José Luis; Farquharson, Colin; Shefelbine, Sandra J

    2014-12-01

    Bone fragility is a concern for aged and diseased bone. Measuring bone toughness and understanding fracture properties of the bone are critical for predicting fracture risk associated with age and disease and for preclinical testing of therapies. A reference point indentation technique (BioDent) has recently been developed to determine bone's resistance to fracture in a minimally invasive way by measuring the indentation distance increase (IDI) between the first and last indentations over cyclic indentations in the same position. In this study, we investigate the relationship between fracture toughness KC and reference point indentation parameters (i.e. IDI, total indentation distance (TID) and creep indentation distance (CID)) in bones from 38 mice from six types (C57Bl/6, Balb, oim/oim, oim/+, Phospho1(-/-) and Phospho1 wild type counterpart). These mice bone are models of healthy and diseased bone spanning a range of fracture toughness from very brittle (oim/oim) to ductile (Phospho1(-/-)). Left femora were dissected, notched and tested in 3-point bending until complete failure. Contralateral femora were dissected and indented in 10 sites of their anterior and posterior shaft surface over 10 indentation cycles. IDI, TID and CID were measured. Results from this study suggest that reference point indentation parameters are not indicative of stress intensity fracture toughness in mouse bone. In particular, the IDI values at the anterior mid-diaphysis across mouse types overlapped, making it difficult to discern differences between mouse types, despite having extreme differences in stress intensity based toughness measures. When more locations of indentation were considered, the normalised IDIs could distinguish between mouse types. Future studies should investigate the relationship of the reference point indentation parameters for mouse bone in other material properties of the bone tissue in order to determine their use for measuring bone quality.

  8. Effect of storage methods on indentation-based material properties of abdominal organs.

    PubMed

    Lu, Yuan-Chiao; Untaroiu, Costin D

    2013-03-01

    To investigate the possible changes in material properties of cadaveric abdominal organs due to the preservation methods, the indentation data obtained from porcine abdominal organs (kidney, liver, and spleen) preserved by cooling and freezing are analyzed statistically in this study. Indentation tests were first conducted on fresh specimens. One half of the specimens of each organ were then frozen (preserved at - 12 degrees C), and the other half of the specimens were cooled (preserved at 4 degrees C). All preserved specimens were retested after 20 days. Force and displacement data recorded during indentation were analyzed using a quasi-linear viscoelastic model. The results show that both cooling and freezing storage increased the kidney stiffness. In contrast, both storage methods decreased the stiffness of the spleen specimens. While cooling increased the liver stiffness, no significant changes of the instantaneous elastic response were observed in the liver specimens preserved by freezing. The liver and spleen's reduced relaxation responses and the liver's instantaneous elastic response were significantly different when comparing between cooling and freezing effects after 20 days of preservation. This study showed that both cooling and freezing storage methods significantly changed the material properties of abdominal organs, especially the instantaneous elastic response. More research is needed in investigating the effect of preservation on failure properties and mechanical properties under large deformation.

  9. Determination of fracture toughness of calcium phosphate coatings deposited onto Ti6Al4V substrate by using indentation technique

    NASA Astrophysics Data System (ADS)

    Aydin, Ibrahim; Cetinel, Hakan; Pasinli, Ahmet

    2012-09-01

    In this study, fracture toughness values of calcium phosphate (CaP) coatings deposited onto Ti6Al4V substrate were determined by using Vickers indentation method. In this new patent holding method, the activation processes were performed with NaOH and NaOH+H2O2 on the Ti6Al4V material surface. Thicknesses of CaP coatings were measured from cross-sections of the samples by using optical microscopy. Vickers indentation tests were performed by using microhardness tester. Young's modulus values of the coatings were determined by using ultra microhardness tester. As a result, fracture toughness (K1C) values of the CaP coatings produced by using two different activation processes, were calculated by using experimental study results. These were found to be 0.43 MPa m1/2 and 0.39 MPa m1/2, respectively. It was determined that the CaP coating on Ti6Al4V activated by NaOH+H2O2 had higher fracture toughness than the CaP coating on Ti6Al4V activated by NaOH.

  10. Change detection technique for muscle tone during static stretching by continuous muscle viscoelasticity monitoring using wearable indentation tester.

    PubMed

    Okamura, Naomi; Kobayashi, Yo; Sugano, Shigeki; Fujie, Masakatsu G

    2017-07-01

    Static stretching is widely performed to decrease muscle tone as a part of rehabilitation protocols. Finding out the optimal duration of static stretching is important to minimize the time required for rehabilitation therapy and it would be helpful for maintaining the patient's motivation towards daily rehabilitation tasks. Several studies have been conducted for the evaluation of static stretching; however, the recommended duration of static stretching varies widely between 15-30 s in general, because the traditional methods for the assessment of muscle tone do not monitor the continuous change in the target muscle's state. We have developed a method to monitor the viscoelasticity of one muscle continuously during static stretching, using a wearable indentation tester. In this study, we investigated a suitable signal processing method to detect the time required to change the muscle tone, utilizing the data collected using a wearable indentation tester. By calculating a viscoelastic index with a certain time window, we confirmed that the stretching duration required to bring about a decrease in muscle tone could be obtained with an accuracy in the order of 1 s.

  11. Molecular dynamics of silicon indentation

    NASA Astrophysics Data System (ADS)

    Kallman, J. S.; Hoover, W. G.; Hoover, C. G.; de Groot, A. J.; Lee, S. M.; Wooten, F.

    1993-04-01

    We use nonequilibrium molecular dynamics to simulate the elastic-plastic deformation of silicon under tetrahedral nanometer-sized indentors. The results are described in terms of a rate-dependent and temperature-dependent phenomenological yield strength. We follow the structural change during indentation with a computer technique that allows us to model the dynamic simulation of diffraction patterns.

  12. Parameter identification of hyperelastic material properties of the heel pad based on an analytical contact mechanics model of a spherical indentation.

    PubMed

    Suzuki, Ryo; Ito, Kohta; Lee, Taeyong; Ogihara, Naomichi

    2017-01-01

    Accurate identification of the material properties of the plantar soft tissue is important for computer-aided analysis of foot pathologies and design of therapeutic footwear interventions based on subject-specific models of the foot. However, parameter identification of the hyperelastic material properties of plantar soft tissues usually requires an inverse finite element analysis due to the lack of a practical contact model of the indentation test. In the present study, we derive an analytical contact model of a spherical indentation test in order to directly estimate the material properties of the plantar soft tissue. Force-displacement curves of the heel pads are obtained through an indentation experiment. The experimental data are fit to the analytical stress-strain solution of the spherical indentation in order to obtain the parameters. A spherical indentation approach successfully predicted the non-linear material properties of the heel pad without iterative finite element calculation. The force-displacement curve obtained in the present study was found to be situated lower than those identified in previous studies. The proposed framework for identifying the hyperelastic material parameters may facilitate the development of subject-specific FE modeling of the foot for possible clinical and ergonomic applications. Copyright © 2016 Elsevier Ltd. All rights reserved.

  13. The relationship between indentation and uniaxial creep in amorphous selenium

    SciTech Connect

    Poisl, W.H.; Oliver, W.C.; Fabes, B.D.

    1995-08-01

    Ultralow load indentation techniques can be used to obtain time-dependent mechanical properties, termed indentation creep, of materials. However, the comparison of indentation creep data to that obtained during conventional creep testing is difficult, mainly due to the determination of the strain rate experienced by the material during indentation. Using the power-law creep equation and the equation for Newtonian viscosity as a function of stress and strain rate, a relationship between indentation strain rate,{center_dot}{epsilon}{sub {ital l}}={ital @};Dh/{ital h}, and the effective strain rate occurring during the indentation creep process is obtained. Indentation creep measurements on amorphous selenium in the Newtonian viscous flow regime above the glass transition temperature were obtained. The data was then used to determine that the coefficient relating indentation strain rate to the effective strain rate is equal to 0.09, or{center_dot}{epsilon}=0.0{center_dot}{epsilon}{sub {ital l}}.

  14. Further Insight into the Depth-Dependent Microstructural Response of Cartilage to Compression Using a Channel Indentation Technique

    PubMed Central

    Thambyah, Ashvin; Broom, Neil D.

    2013-01-01

    Stress relaxation and structural analysis were used to investigate the zonally differentiated microstructural response to compression of the integrated cartilage-on-bone tissue system. Fifteen cartilage-on-bone samples were divided into three equal groups and their stress relaxation responses obtained at three different levels of axial compressive strain defined as low (~20%), medium (~40%) and high (~60%). All tests were performed using a channel indenter which included a central relief space designed to capture the response of the matrix adjacent to the directly loaded regions. On completion of each stress relaxation test and while maintaining the imposed axial strain, the samples were formalin fixed, decalcified, and then sectioned for microstructural analysis. Chondron aspect ratios were used to determine the extent of relative strain at different zonal depths. The stress relaxation response of cartilage to all three defined levels of axial strain displayed an initial highly viscous response followed by a significant elastic response. Chondron aspect ratio measurements showed that at the lowest level of compression, axial deformation was confined to the superficial cartilage layer, while in the medium and high axial strain samples the deformation extended into the midzone. The cells in the deep zone remained undeformed for all compression levels. PMID:24023589

  15. Deformation field heterogeneity in punch indentation

    PubMed Central

    Murthy, Tejas G.; Saldana, Christopher; Hudspeth, Matthew; M'Saoubi, Rachid

    2014-01-01

    Plastic heterogeneity in indentation is fundamental for understanding mechanics of hardness testing and impression-based deformation processing methods. The heterogeneous deformation underlying plane-strain indentation was investigated in plastic loading of copper by a flat punch. Deformation parameters were measured, in situ, by tracking the motion of asperities in high-speed optical imaging. These measurements were coupled with multi-scale analyses of strength, microstructure and crystallographic texture in the vicinity of the indentation. Self-consistency is demonstrated in description of the deformation field using the in situ mechanics-based measurements and post-mortem materials characterization. Salient features of the punch indentation process elucidated include, among others, the presence of a dead-metal zone underneath the indenter, regions of intense strain rate (e.g. slip lines) and extent of the plastic flow field. Perhaps more intriguing are the transitions between shear-type and compression-type deformation modes over the indentation region that were quantified by the high-resolution crystallographic texture measurements. The evolution of the field concomitant to the progress of indentation is discussed and primary differences between the mechanics of indentation for a rigid perfectly plastic material and a strain-hardening material are described. PMID:24910521

  16. An optical coherence tomography (OCT)-based air jet indentation system for measuring the mechanical properties of soft tissues

    NASA Astrophysics Data System (ADS)

    Huang, Yan-Ping; Zheng, Yong-Ping; Wang, Shu-Zhe; Chen, Zhong-Ping; Huang, Qing-Hua; He, Yong-Hong

    2009-01-01

    A novel noncontact indentation system with the combination of an air jet and optical coherence tomography (OCT) was presented in this paper for the quantitative measurement of the mechanical properties of soft tissues. The key idea of this method is to use a pressure-controlled air jet as an indenter to compress the soft tissue in a noncontact way and utilize the OCT signals to extract the deformation induced. This indentation system provides measurement and mapping of tissue elasticity for small specimens with high scanning speed. Experiments were performed on 27 silicone tissue-mimicking phantoms with different Young's moduli, which were also measured by uniaxial compression tests. The regression coefficient of the indentation force to the indentation depth (N mm-1) was used as an indicator of the stiffness of tissue under air jet indentation. Results showed that the stiffness coefficients measured by the current system correlated well with the corresponding Young's moduli obtained by conventional mechanical testing (r = 0.89, p < 0.001). Preliminary in vivo tests also showed that the change of soft tissue stiffness with and without the contraction of the underlying muscles in the hand could be differentiated by the current measurement. This system may have broad applications in tissue assessment and characterization where alterations of mechanical properties are involved, in particular with the potential of noncontact micro-indentation for tissues.

  17. Investigation of Quasi-Static Indentation Response of Inkjet Printed Sandwich Structures under Various Indenter Geometries

    PubMed Central

    Dikshit, Vishwesh; Nagalingam, Arun Prasanth; Yap, Yee Ling; Sing, Swee Leong; Yeong, Wai Yee; Wei, Jun

    2017-01-01

    The objective of this investigation was to determine the quasi-static indentation response and failure mode in three-dimensional (3D) printed trapezoidal core structures, and to characterize the energy absorbed by the structures. In this work, the trapezoidal sandwich structure was designed in the following two ways. Firstly, the trapezoidal core along with its facesheet was 3D printed as a single element comprising a single material for both core and facesheet (type A); Secondly, the trapezoidal core along with facesheet was 3D printed, but with variation in facesheet materials (type B). Quasi-static indentation was carried out using three different indenters, namely standard hemispherical, conical, and flat indenters. Acoustic emission (AE) technique was used to capture brittle cracking in the specimens during indentation. The major failure modes were found to be brittle failure and quasi-brittle fractures. The measured indentation energy was at a maximum when using a conical indenter at 9.40 J and 9.66 J and was at a minimum when using a hemispherical indenter at 6.87 J and 8.82 J for type A and type B series specimens respectively. The observed maximum indenter displacements at failure were the effect of material variations and composite configurations in the facesheet. PMID:28772649

  18. Indentation-induced structural phase transformations of semiconductor materials and applications

    NASA Astrophysics Data System (ADS)

    Khayyat, Maha; Sosa, Norma; Chaudhri, M. Munawar; Cavendish laboratory, University of Cambridge Team; T. J. Watson Research Center, IBM Collaboration

    During hardness indentation materials are subjected to highly localized pressures. These pressures may cause a complete change of the crystal structure of the material within the indented zone. Such structural phase transformations were observed within Vickers indentations made at room temperature in single crystals and amorphous films of Si and Ge. However, when indentations were made at 77 K in Si and Ge, no phase transitions were observed in either. Measurements were also taken from indentations made in silicon single crystals at different temperatures namely 263, 243, 235 and 206 K, and they showed a strong correlation of phase transformation with temperature. It was suggested that during room temperature indentations there is a significant temperature rise approximately to 760 K, which may assist phase transformation. Raman spectroscopy was used as an ex-situ tool monitoring phase transformations in semiconductor materials. In-situ electrical characterizations of indentation-induced metallization in single crystals of silicon were performed using two- and four-contact measurements. The previous work has led to a technique relates to semiconductor device manufacturing, including solar cells, which is a method for controlling the removal of a surface layer from a base substrate utilizing low-temperature. KACST is acknowledged for support.

  19. Dynamic indentation hardness of materials

    NASA Astrophysics Data System (ADS)

    Koeppel, Brian James

    Indentation hardness is one of the simplest and most commonly used measures for quickly characterizing material response under static loads. Hardness may mean resistance to cutting to a machinist, resistance to wear to a tribologist, or a measure of flow stress to a design engineer. In this simple technique, a predetermined force is applied to an indenter for 5-30 seconds causing it to penetrate a specimen. By measuring the load and the indentation size, a hardness value is determined. However, the rate of deformation during indenter penetration is of the order of 10sp{-4}\\ ssp{-1}. In most practical applications, such as high speed machining or impact, material deforms at strain rates in excess of 10sp3{-}10sp5\\ ssp{-1}. At such high rates, it is well established that the plastic behavior of materials is considerably different from their static counterpart. For example, materials exhibit an increase in their yield stress, flow stress, fracture stress, and fracture toughness at high strain rates. Hence, the use of static hardness as an indicator of material response under dynamic loads may not be appropriate. Accordingly, a simple dynamic indentation hardness tester is developed for characterizing materials at strain rates similar to those encountered in realistic situations. The experimental technique uses elastic stress wave propagation phenomena in a slender rod. The technique is designed to deliver a single indentation load of 100-200 mus duration. Similar to static measurements, the dynamic hardness is determined from the measured load and indentation size. Hardness measurements on a range of metals have revealed that the dynamic hardness is consistently greater than the static hardness. The increase in hardness is strongly dependent on the crystal structure of the material. The observed trends in hardness are also found to be consistent with the yield and flow stresses of these materials under uniaxial compression. Therefore, it is suggested that the

  20. Influence of surface stresses on indentation response.

    PubMed

    Buchwald, J; Mayr, S G

    2015-03-27

    Surface stresses lead to an effective change in the elastic constants of thin films and at surfaces. The development of modern scanning probe techniques like contact resonance atomic force microscopy empowers the experimenter to measure at scales where these effects become increasingly relevant. In this paper we employ a computational multiscale approach where we compare density functional theory (DFT) and molecular dynamics simulations as tools to calculate the thin-film/surface elastic behavior for silicon and strontiumtitanate. From the surface elastic constants gained by DFT calculations we develop a continuum finite-element multilayer model to study the impact of surface stresses on indentation experiments. In general the stress field of an indenter and thus the impact of surface stresses on the indentation modulus depends on its contact radius and on its particular shape. We propose an analytical model that describes the behavior of the indentation modulus as a function of the contact radius. We show that this model fits well to simulation results gained for a spherical and a flat punch indenter. Our results demonstrate a surface-stress-induced reduction of the indentation modulus of about 5% for strontiumtitanate and 6% for silicon for a contact radius of [Formula: see text], irrespective of the indenter shape.

  1. Influence of surface stresses on indentation response

    NASA Astrophysics Data System (ADS)

    Buchwald, J.; Mayr, S. G.

    2015-03-01

    Surface stresses lead to an effective change in the elastic constants of thin films and at surfaces. The development of modern scanning probe techniques like contact resonance atomic force microscopy empowers the experimenter to measure at scales where these effects become increasingly relevant. In this paper we employ a computational multiscale approach where we compare density functional theory (DFT) and molecular dynamics simulations as tools to calculate the thin-film/surface elastic behavior for silicon and strontiumtitanate. From the surface elastic constants gained by DFT calculations we develop a continuum finite-element multilayer model to study the impact of surface stresses on indentation experiments. In general the stress field of an indenter and thus the impact of surface stresses on the indentation modulus depends on its contact radius and on its particular shape. We propose an analytical model that describes the behavior of the indentation modulus as a function of the contact radius. We show that this model fits well to simulation results gained for a spherical and a flat punch indenter. Our results demonstrate a surface-stress-induced reduction of the indentation modulus of about 5% for strontiumtitanate and 6% for silicon for a contact radius of {{r}c}=5 \\text{nm}, irrespective of the indenter shape.

  2. Directionality of residual stress evaluated by instrumented indentation testing using wedge indenter

    NASA Astrophysics Data System (ADS)

    Ahn, Hee-Jun; Kim, Jong-hyoung; Xu, Huiwen; Lee, Junsang; Kim, Ju-Young; Kim, Young-Cheon; Kwon, Dongil

    2017-05-01

    In instrumented indentation testing (IIT), residual stress can be evaluated by shift in indentation load-depth curves for stress-free and stressed states. Although the average surface residual stress is able to be evaluated with Vickers indenter, in order to know stress directionality, another indentation tests with two-fold symmetric indenter, for example, Knoop indenter, are needed. As some necessities for evaluating nonequibiaxial residual stress within small indent area, we suggest a novel way to evaluate directionality of residual stress, p, using wedge indenter characterized by two parameters, edge length and inclined angle. We develop wedge-indentation-mechanics model based on predetermined conversion factors which are determined by IITs for various uniaxial stressed states combining with finite element analysis simulations. By utilizing the developed model, directionality of residual stress is evaluated through two serial wedge IITs with respect to principal directions. We find good agreements between applied residual stress and residual stress evaluated by the developed model for biaxial tensile stress states.

  3. Microhardness and fracture toughness of dental materials by indentation method.

    PubMed

    Sakar-Deliormanli, Aylin; Güden, Mustafa

    2006-02-01

    The main objective of this study was to measure the fracture toughness of the human teeth enamel using the microindentation technique and to compare the results calculated from the equations developed for Palmqvist and radial-median cracks. Vickers microhardness measurements of dental ceramic (alumina) and human teeth were performed using indentation fracture method. The fracture toughness of enamel was calculated using different equations reported in the literature. Vickers microhardness of the sintered alumina specimen (98.8% theoretical density) was measured to be 14.92 GPa under 9.8 N indentation load. Three equations based on the radial-median cracks were found to be applicable for the fracture toughness determination of the enamel. Results show that indentation fracture method is adequate to measure microhardness and fracture toughness of dental materials. However the calculation of fracture toughness depended on the nature of the cracks and also on the location of the indentation. Therefore, it is necessary to identify the crack profile and to select the appropriate equation for accurate fracture toughness values. Copyright 2005 Wiley Periodicals, Inc.

  4. Measurement of Young's modulus of vocal folds by indentation.

    PubMed

    Chhetri, Dinesh K; Zhang, Zhaoyan; Neubauer, Juergen

    2011-01-01

    To assess the accuracy of the indentation method for stiffness measurements and to estimate the Young's modulus of the vocal fold using this technique. Basic science. Indentation tests were performed using a range of indenter diameters and indentation depths on single- and double-layer silicone rubber models with various cover-layer thicknesses with known geometry and Young's moduli. Measurements were repeated on intact vocal folds and isolated muscle and cover-layer samples from three cadaveric human larynges. Indentation on single-layer rubber models yielded Young's moduli with acceptable accuracy when the indentation depth was equal to or smaller than the indenter diameter, and both were smaller than the physical dimensions of the material sample. On two-layer models, the stiffness estimation was similarly influenced by indenter diameter and indentation depth, and acceptable accuracy was reached when indentation depth was much smaller than the height of the top cover layer. Measurements on midmembranous vocal fold tissue revealed location-dependent Young's moduli (in kPa) as follows: intact hemilarynx, 8.6 (range=5.3-13.1); isolated inferior medial surface cover, 7.5 (range=7-7.9); isolated medial surface cover, 4.8 (range=3.9-5.7); isolated superior surface cover, 2.9 (range=2.7-3.2); and isolated thyroarytenoid muscle, 2.0 (range=1.3-2.7). Indenter diameter, indentation depth, and material thickness are important parameters in the measurement of vocal fold stiffness using the indentation technique. Measurements on human larynges showed location-dependent differences in stiffness. The stiffness of the vocal folds was also found to be higher when the vocal fold structure was still attached to the laryngeal framework compared with that when the vocal fold was separated from the framework. Copyright © 2011 The Voice Foundation. Published by Mosby, Inc. All rights reserved.

  5. Indentation methods for adhesion measurement in thermal barrier coating systems

    NASA Astrophysics Data System (ADS)

    Ma, Qin

    This thesis investigates the fundamentals of indentation-induced delamination of electron beam physical vapor deposition thermal barrier coatings (EB-PVD TBCs). Thermal barrier coatings are thin ceramic coatings used to insulate gas turbine components. In the as-processed state, TBCs are well-bonded to the metallic substrate they are deposited upon. However, as these coatings are exposed to high temperatures during turbine operation, they lose their adhesion. The goal of this thesis is to determine how to use indentation testing techniques, coupled with fracture mechanics principles, to track this loss of adhesion and to identify mechanisms causing it. This thesis addresses four primary topics. First, a detailed fracture mechanics analysis of indentation-induced delamination is made, including the quantification of energy release rates, interfacial toughnesses and mode mix. The second topic addressed is application of the indentation test to track toughness losses in TBC systems subjected to a variety of thermal exposures. Three subtopics are included: (1) mechanism-based tests for the isothermal dry air exposures; (2) mechanism-based tests for exposures with water vapor and (3) mechanism-based tests for cyclic thermal exposures. In the first subtopic, TGO thickening and TBC sintering are modeled. Various mechanisms that lead to toughness degradation are discussed and analyzed quantitatively. An Arrhenius analysis has been performed to understand accelerated testing methods. The second subtopic presents the results of toughness degradation and the evolution of microstructures due to isothermal exposure with water vapor. The third subtopic investigates the toughness degradation for cyclic thermal exposures in dry air. Piezospectroscopy method has been applied to track the evolution of residual stresses in the TGO layer with thermal cycles. Quantitative analysis has been provided to give insights into the effects of oxide damage during thermal cycling. The final two

  6. Characterizing white matter tissue in large strain via asymmetric indentation and inverse finite element modeling.

    PubMed

    Feng, Yuan; Lee, Chung-Hao; Sun, Lining; Ji, Songbai; Zhao, Xuefeng

    2017-01-01

    Characterizing the mechanical properties of white matter is important to understand and model brain development and injury. With embedded aligned axonal fibers, white matter is typically modeled as a transversely isotropic material. However, most studies characterize the white matter tissue using models with a single anisotropic invariant or in a small-strain regime. In this study, we combined a single experimental procedure - asymmetric indentation - with inverse finite element (FE) modeling to estimate the nearly incompressible transversely isotropic material parameters of white matter. A minimal form comprising three parameters was employed to simulate indentation responses in the large-strain regime. The parameters were estimated using a global optimization procedure based on a genetic algorithm (GA). Experimental data from two indentation configurations of porcine white matter, parallel and perpendicular to the axonal fiber direction, were utilized to estimate model parameters. Results in this study confirmed a strong mechanical anisotropy of white matter in large strain. Further, our results suggested that both indentation configurations are needed to estimate the parameters with sufficient accuracy, and that the indenter-sample friction is important. Finally, we also showed that the estimated parameters were consistent with those previously obtained via a trial-and-error forward FE method in the small-strain regime. These findings are useful in modeling and parameterization of white matter, especially under large deformation, and demonstrate the potential of the proposed asymmetric indentation technique to characterize other soft biological tissues with transversely isotropic properties.

  7. Identification and design of novel polymer-based mechanical transducers: A nano-structural model for thin film indentation

    SciTech Connect

    Villanueva, Joshua; Huang, Qian; Sirbuly, Donald J.

    2014-09-14

    Mechanical characterization is important for understanding small-scale systems and developing devices, particularly at the interface of biology, medicine, and nanotechnology. Yet, monitoring sub-surface forces is challenging with current technologies like atomic force microscopes (AFMs) or optical tweezers due to their probe sizes and sophisticated feedback mechanisms. An alternative transducer design relying on the indentation mechanics of a compressible thin polymer would be an ideal system for more compact and versatile probes, facilitating measurements in situ or in vivo. However, application-specific tuning of a polymer's mechanical properties can be burdensome via experimental optimization. Therefore, efficient transducer design requires a fundamental understanding of how synthetic parameters such as the molecular weight and grafting density influence the bulk material properties that determine the force response. In this work, we apply molecular-level polymer scaling laws to a first order elastic foundation model, relating the conformational state of individual polymer chains to the macroscopic compression of thin film systems. A parameter sweep analysis was conducted to observe predicted model trends under various system conditions and to understand how nano-structural elements influence the material stiffness. We validate the model by comparing predicted force profiles to experimental AFM curves for a real polymer system and show that it has reasonable predictive power for initial estimates of the force response, displaying excellent agreement with experimental force curves. We also present an analysis of the force sensitivity of an example transducer system to demonstrate identification of synthetic protocols based on desired mechanical properties. These results highlight the usefulness of this simple model as an aid for the design of a new class of compact and tunable nanomechanical force transducers.

  8. Identification and design of novel polymer-based mechanical transducers: A nano-structural model for thin film indentation

    NASA Astrophysics Data System (ADS)

    Villanueva, Joshua; Huang, Qian; Sirbuly, Donald J.

    2014-09-01

    Mechanical characterization is important for understanding small-scale systems and developing devices, particularly at the interface of biology, medicine, and nanotechnology. Yet, monitoring sub-surface forces is challenging with current technologies like atomic force microscopes (AFMs) or optical tweezers due to their probe sizes and sophisticated feedback mechanisms. An alternative transducer design relying on the indentation mechanics of a compressible thin polymer would be an ideal system for more compact and versatile probes, facilitating measurements in situ or in vivo. However, application-specific tuning of a polymer's mechanical properties can be burdensome via experimental optimization. Therefore, efficient transducer design requires a fundamental understanding of how synthetic parameters such as the molecular weight and grafting density influence the bulk material properties that determine the force response. In this work, we apply molecular-level polymer scaling laws to a first order elastic foundation model, relating the conformational state of individual polymer chains to the macroscopic compression of thin film systems. A parameter sweep analysis was conducted to observe predicted model trends under various system conditions and to understand how nano-structural elements influence the material stiffness. We validate the model by comparing predicted force profiles to experimental AFM curves for a real polymer system and show that it has reasonable predictive power for initial estimates of the force response, displaying excellent agreement with experimental force curves. We also present an analysis of the force sensitivity of an example transducer system to demonstrate identification of synthetic protocols based on desired mechanical properties. These results highlight the usefulness of this simple model as an aid for the design of a new class of compact and tunable nanomechanical force transducers.

  9. Indentation Methods in Advanced Materials Research Introduction

    SciTech Connect

    Pharr, George Mathews; Cheng, Yang-Tse; Hutchings, Ian; Sakai, Mototsugu; Moody, Neville; Sundararajan, G.; Swain, Michael V.

    2009-01-01

    Since its commercialization early in the 20th century, indentation testing has played a key role in the development of new materials and understanding their mechanical behavior. Progr3ess in the field has relied on a close marriage between research in the mechanical behavior of materials and contact mechanics. The seminal work of Hertz laid the foundations for bringing these two together, with his contributions still widely utilized today in examining elastic behavior and the physics of fracture. Later, the pioneering work of Tabor, as published in his classic text 'The Hardness of Metals', exapdned this understanding to address the complexities of plasticity. Enormous progress in the field has been achieved in the last decade, made possible both by advances in instrumentation, for example, load and depth-sensing indentation and scanning electron microscopy (SEM) and transmission electron microscopy (TEM) based in situ testing, as well as improved modeling capabilities that use computationally intensive techniques such as finite element analysis and molecular dynamics simulation. The purpose of this special focus issue is to present recent state of the art developments in the field.

  10. Analysis of indentation creep

    Treesearch

    Don S. Stone; Joseph E. Jakes; Jonathan Puthoff; Abdelmageed A. Elmustafa

    2010-01-01

    Finite element analysis is used to simulate cone indentation creep in materials across a wide range of hardness, strain rate sensitivity, and work-hardening exponent. Modeling reveals that the commonly held assumption of the hardness strain rate sensitivity (mΗ) equaling the flow stress strain rate sensitivity (mσ...

  11. Shear-banding Induced Indentation Size Effect in Metallic Glasses

    PubMed Central

    Lu, Y. M.; Sun, B. A.; Zhao, L. Z.; Wang, W. H.; Pan, M. X.; Liu, C. T.; Yang, Y.

    2016-01-01

    Shear-banding is commonly regarded as the “plasticity carrier” of metallic glasses (MGs), which usually causes severe strain localization and catastrophic failure if unhindered. However, through the use of the high-throughput dynamic nanoindentation technique, here we reveal that nano-scale shear-banding in different MGs evolves from a “distributed” fashion to a “localized” mode when the resultant plastic flow extends over a critical length scale. Consequently, a pronounced indentation size effect arises from the distributed shear-banding but vanishes when shear-banding becomes localized. Based on the critical length scales obtained for a variety of MGs, we unveil an intrinsic interplay between elasticity and fragility that governs the nanoscale plasticity transition in MGs. Our current findings provide a quantitative insight into the indentation size effect and transition mechanisms of nano-scale plasticity in MGs. PMID:27324835

  12. Full-Field Indentation Damage Measurement Using Digital Image Correlation.

    PubMed

    López-Alba, Elías; Díaz-Garrido, Francisco A

    2017-07-10

    A novel approach based on full-field indentation measurements to characterize and quantify the effect of contact in thin plates is presented. The proposed method has been employed to evaluate the indentation damage generated in the presence of bending deformation, resulting from the contact between a thin plate and a rigid sphere. For this purpose, the 3D Digital Image Correlation (3D-DIC) technique has been adopted to quantify the out of plane displacements at the back face of the plate. Tests were conducted using aluminum thin plates and a rigid bearing sphere to evaluate the influence of the thickness and the material behavior during contact. Information provided by the 3D-DIC technique has been employed to perform an indirect measurement of the contact area during the loading and unloading path of the test. A symmetrical distribution in the contact damage region due to the symmetry of the indenter was always observed. In the case of aluminum plates, the presence of a high level of plasticity caused shearing deformation as the load increased. Results show the full-field contact damage area for different plates' thicknesses at different loads. The contact damage region was bigger when the thickness of the specimen increased, and therefore, bending deformation was reduced. With the proposed approach, the elastic recovery at the contact location was quantified during the unloading, as well as the remaining permanent indentation damage after releasing the load. Results show the information obtained by full-field measurements at the contact location during the test, which implies a substantial improvement compared with pointwise techniques.

  13. Discrete dislocation plasticity analysis of the wedge indentation of films

    NASA Astrophysics Data System (ADS)

    Balint, D. S.; Deshpande, V. S.; Needleman, A.; Van der Giessen, E.

    2006-11-01

    The plane strain indentation of single crystal films on a rigid substrate by a rigid wedge indenter is analyzed using discrete dislocation plasticity. The crystals have three slip systems at ±35.3∘ and 90∘ with respect to the indentation direction. The analyses are carried out for three values of the film thickness, 2, 10 and 50 μm, and with the dislocations all of edge character modeled as line singularities in a linear elastic material. The lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation are incorporated through a set of constitutive rules. Over the range of indentation depths considered, the indentation pressure for the 10 and 50 μm thick films decreases with increasing contact size and attains a contact size-independent value for contact lengths A>4 μm. On the other hand, for the 2 μm films, the indentation pressure first decreases with increasing contact size and subsequently increases as the plastic zone reaches the rigid substrate. For the 10 and 50 μm thick films sink-in occurs around the indenter, while pile-up occurs in the 2 μm film when the plastic zone reaches the substrate. Comparisons are made with predictions obtained from other formulations: (i) the contact size-independent indentation pressure is compared with that given by continuum crystal plasticity; (ii) the scaling of the indentation pressure with indentation depth is compared with the relation proposed by Nix and Gao [1998. Indentation size effects in crystalline materials: a law for strain gradient plasticity. J. Mech. Phys. Solids 43, 411-423]; and (iii) the computed contact area is compared with that obtained from the estimation procedure of Oliver and Pharr [1992. An improved technique for determining hardness and elastic-modulus using load and displacement sensing indentation experiments, J. Mater. Res. 7, 1564-1583].

  14. The topography of a continental indenter: The interplay between crustal deformation, erosion, and base level changes in the eastern Southern Alps

    PubMed Central

    Heberer, B.; Prasicek, G.; Neubauer, F.; Hergarten, S.

    2017-01-01

    Abstract The topography of the eastern Southern Alps (ESA) reflects indenter tectonics causing crustal shortening, surface uplift, and erosional response. Fluvial drainages were perturbed by Pleistocene glaciations that locally excavated alpine valleys. The Late Miocene desiccation of the Mediterranean Sea and the uplift of the northern Molasse Basin led to significant base level changes in the far field of the ESA and the Eastern Alps (EA), respectively. Among this multitude of mechanisms, the processes that dominate the current topographic evolution of the ESA and the ESA‐EA drainage divide have not been identified. We demonstrate the expected topographic effects of each mechanism in a one‐dimensional model and compare them with observed channel metrics. We find that the normalized steepness index increases with uplift rate and declines from the indenter tip in the northwest to the foreland basin in the southeast. The number and amplitude of knickpoints and the distortion in longitudinal channel profiles similarly decrease toward the east. Changes in slope of χ‐transformed channel profiles coincide spatially with the Valsugana‐Fella fault linking crustal stacking and uplift induced by indenter tectonics with topographic evolution. Gradients in χ across the ESA‐EA drainage divide imply an ongoing, north directed shift of the Danube‐ESA watershed that is most likely driven by a base level rise in the northern Molasse basin. We conclude that the regional uplift pattern controls the geometry of ESA‐EA channels, while base level changes in the far field control the overall architecture of the orogen by drainage divide migration. PMID:28344912

  15. The topography of a continental indenter: The interplay between crustal deformation, erosion, and base level changes in the eastern Southern Alps

    NASA Astrophysics Data System (ADS)

    Robl, J.; Heberer, B.; Prasicek, G.; Neubauer, F.; Hergarten, S.

    2017-01-01

    The topography of the eastern Southern Alps (ESA) reflects indenter tectonics causing crustal shortening, surface uplift, and erosional response. Fluvial drainages were perturbed by Pleistocene glaciations that locally excavated alpine valleys. The Late Miocene desiccation of the Mediterranean Sea and the uplift of the northern Molasse Basin led to significant base level changes in the far field of the ESA and the Eastern Alps (EA), respectively. Among this multitude of mechanisms, the processes that dominate the current topographic evolution of the ESA and the ESA-EA drainage divide have not been identified. We demonstrate the expected topographic effects of each mechanism in a one-dimensional model and compare them with observed channel metrics. We find that the normalized steepness index increases with uplift rate and declines from the indenter tip in the northwest to the foreland basin in the southeast. The number and amplitude of knickpoints and the distortion in longitudinal channel profiles similarly decrease toward the east. Changes in slope of χ-transformed channel profiles coincide spatially with the Valsugana-Fella fault linking crustal stacking and uplift induced by indenter tectonics with topographic evolution. Gradients in χ across the ESA-EA drainage divide imply an ongoing, north directed shift of the Danube-ESA watershed that is most likely driven by a base level rise in the northern Molasse basin. We conclude that the regional uplift pattern controls the geometry of ESA-EA channels, while base level changes in the far field control the overall architecture of the orogen by drainage divide migration.

  16. Crystalline cellulose elastic modulus predicted by atomistic models of uniform deformation and nanoscale indentation

    Treesearch

    Xiawa Wu; Robert J. Moon; Ashlie Martini

    2013-01-01

    The elastic modulus of cellulose Iß 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...

  17. Non-linear elastic properties of the lingual and facial tissues assessed by indentation technique. Application to the biomechanics of speech production.

    PubMed

    Gerard, J M; Ohayon, J; Luboz, V; Perrier, P; Payan, Y

    2005-12-01

    This paper aims at characterizing the mechanical behavior of two human anatomical structures, namely the tongue and the cheek. For this, an indentation experiment was provided, by measuring the mechanical response of tongue and cheek tissues removed from the fresh cadaver of a 74 year old woman. Non-linear relationships were observed between the force applied to the tissues and the corresponding displacements. To infer the mechanical constitutive laws from these measurements, a finite element (FE) analysis was provided. This analysis aimed at simulating the indentation experiment. An optimization process was used to determine the FE constitutive laws that provided the non-linear force/displacements observed during the indentation experiments. The tongue constitutive law was used for simulations provided by a 3D FE biomechanical model of the human tongue. This dynamical model was designed to study speech production. Given a set of tongue muscular commands, which levels correspond to the force classically measured during speech production, the FE model successfully simulated the main tongue movements observed during speech data.

  18. Electron channeling contrast imaging of plastic deformation induced by indentation in polycrystalline nickel.

    PubMed

    Kaboli, Shirin; Goldbaum, Dina; Chromik, Richard R; Gauvin, Raynald

    2013-12-01

    Vickers microindentation and Berkovich nanoindentation tests were carried out on a polycrystalline nickel (Ni) bulk specimen. Electron channeling contrast imaging (ECCI) in conjunction with electron backscattered diffraction was used to image and characterize plastic deformation inside and around the indents using a field emission scanning electron microscope. The ECCI was performed with a 5 keV beam energy and 0° tilt specimen position. The strain field distribution, slip lines, and Taylor lattices were imaged on an indented surface. Orientation mapping was used to investigate the local crystallographic misorientation and identify specific ⟨110⟩ slip systems. An ion milling surface preparation technique was used to remove materials from the surface which permitted the study of deformed microstructure below the indent. A dislocation density of 1011 cm-2 was calculated based on the curvature of bend contours observed in the ECCI micrographs obtained from the Vickers indents. A yield strength of 500 MPa was calculated based on the size of the strain field measured from the ECCI micrographs of the nanoindents. The combination of ion milling, ECCI, and electron backscattered diffraction was shown to be beneficial to investigate the indentation-induced plastic deformation in a polycrystalline Ni bulk specimen.

  19. Application of reference point indentation for micro-mechanical surface characterization of calcium silicate based dental materials.

    PubMed

    Antonijević, Djordje; Milovanović, Petar; Riedel, Christoph; Hahn, Michael; Amling, Michael; Busse, Björn; Djurić, Marija

    2016-04-01

    The objective of this study was to elucidate micromechanical properties of Biodentine and two experimental calcium silicate cements (CSCs) using Reference Point Indentation (RPI). Biomechanical characteristics of the cement type and the effects of a radiopacifier, liquid components, acid etching treatment and bioactivation in simulated body fluid (SBF) were investigated by measuring the microhardness, average unloading slope (Avg US) and indentation distance increase (IDI). Biodentine had a greater microhardness than the experimental CSCs, while the Avg US and IDI values were not significantly different among investigated materials. There was a statistically significant difference in microhardness and IDI values between pure CSCs and radiopacified cements (p < 0.05). Micromechanical properties were not affected by different liquid components used. Acid-etching treatment reduced Biodentine's microhardness while cements' immersion in SBF resulted in greater microhardness and higher IDI values compared to the control group. Clearly, the physiological environment and the cements' composition affect their surface micromechanical properties. The addition of calcium chloride and CSCs' immersion in SBF are beneficial for CSCs' micromechanical performance, while the addition of radiopacifiers and acid etching treatment weaken the CSCs' surface. Application of RPI aids with the characterization of micromechanical properties of synthetic materials' surfaces.

  20. Assessing mechanical properties from cone indentation hardness

    NASA Astrophysics Data System (ADS)

    Dicarlo, Anthony Albert

    This dissertation investigates methods for assessing the mechanical properties of materials using hardness values obtained from cone indentations. A broad range of isotropic metallic materials was simulated using finite element analysis. In particular, the elastic and plastic bulk properties, which define the stress-strain behavior of materials that exhibit power law hardening, are studied. Other investigators have found that the Young's modulus, E, can be determined from the unloading data of a cone indentation. Therefore, the remaining properties of interest, in this study, are the yield strength, Y, and the work hardening exponent, n. Atkins and Tabor have conducted pioneering work in the area of determining the stress-strain behavior of a metallic material from cone indentation experiments. This work has been re-visited in this study using computational models implementing an expanded range of mechanical properties. Consequently, discrepancies in this prediction method were uncovered when the mechanical properties were outside of the original range studied. As a result, two new prediction methods have been developed using the data collected from the finite element simulations in conjunction with a regression technique. The first method correlates the non-dimensional hardness values, H/E, collected from five cone indentations to the non-dimensional mechanical properties, Y/E and n. The second method is similar in principle, but uses two hardness values as opposed to five. The yield strength can be estimated with a priori knowledge of E. Both of these methods are compared to the method developed by Atkins and Tabor. Although the majority of the work mentioned is focused on the macro-scale, bulk mechanical properties, there is some investigation of meso-scale cone indentations. At the meso-scale, the number of geometric dislocations is significant enough to noticeably increase the strength of a material. This length scale effect is studied for various angled cone

  1. Extraction of mechanical properties of foot plantar tissues using ultrasound indentation associated with genetic algorithm.

    PubMed

    Ling, Hang-Yin; Choi, Pong-Chi; Zheng, Yong-ping; Lau, Kin-Tak

    2007-08-01

    This paper demonstrates the use of ultrasound indentation technique for estimating the mechanical properties of foot plantar tissues in virtue of the reconstruction of the force response using genetic algorithm (GA) from an indentation test based on a quasi-linear viscoelastic (QLV) model. The indentation test on the plantar tissues covering the right first metatarsal head of a normal subject was carried out to verify the feasibility of the GA for the extraction of the tissue properties. The QLV properties of the plantar tissues were determined by the GA with a fixed Poisson's ratio. Such results were then compared with those obtained using a classical optimization method. Moreover, the GA was further employed to simultaneously determine the QLV properties as well as the Poisson's ratio of the plantar tissues. The correlations between the QLV properties and the Poisson's ratio are discussed.

  2. Evaluation of the degradation of plasma sprayed thermal barrier coatings using nano-indentation.

    PubMed

    Kim, Dae-Jin; Cho, Sung-Keun; Choi, Jung-Hun; Koo, Jae-Mean; Seok, Chang-Sung; Kim, Moon-Young

    2009-12-01

    In this study, the disk type of a thermal barrier coating (TBC) system for a gas turbine blade was isothermally aged at 1100 degrees C for various times up to 400 hours. For each aging condition, the thickness of the thermally grown oxide (TGO) was measured by optical microscope and mechanical properties such as the elastic modulus and hardness were measured by micro-indentation and nano-indentation on the cross-section of a coating specimen. In the case of micro-indentation, the mechanical properties of a Ni-base superalloy substrate and MCrAlY bond coat material did not significantly change with an increase in exposure time. In the case of nano-indentation, the gamma-Ni phase and beta-NiAl phase in the bond coat and top coat material show no significant change in their properties. However, the elastic modulus and the hardness of TGO show a remarkable decrease from 100 h to 200 h then remain nearly constant after 200 h due to the internal delamination of TBC. It has been confirmed that the nano-indentation technique is a very effective way to evaluate the degradation of a thermal barrier coating system.

  3. Plastically deformed region around indentations on Si angle crystal

    NASA Astrophysics Data System (ADS)

    Yoshioka, M.

    1994-12-01

    Expansion of a hemispherical shell by inner pressure has been widely applied for the model of the deformation by an indentation on a flat surface; however, the deformed region is not necessarily spherically symmetric, especially in anisotropic materials such as single crystals. Therefore, whether the spherical model is applicable in an indentation process for objective materials must always be kept in mind. Indentations have been made on the (111) surface of silicon crystal at various temperatures. The three-dimensional shape of the plastically deformed region was experimentally measured by means of an etching technique and its difference from the hemisphere was observed. It was never spherical but much more complicated, similar to a bottle gourd. The slip mechanism, which resulted in the observed shape of the plastic region, is discussed further. The plastic region was analytically obtained also on the assumption that the stress distribution was spherically symmetrical. The result is approximately in accordance with the observed shape. It is therefore concluded that the stress distribution is nearly spherical although the plastic region is far from it. The yield strength of silicon crystals and their temperature dependence were obtained based on the spherical model.

  4. Non-contact, Ultrasound-based Indentation Method for Measuring Elastic Properties of Biological Tissues Using Harmonic Motion Imaging (HMI)

    PubMed Central

    Vappou, Jonathan; Hou, Gary Y.; Marquet, Fabrice; Shahmirzadi, Danial; Grondin, Julien; Konofagou, Elisa E.

    2015-01-01

    Noninvasive measurement of mechanical properties of biological tissues in vivo could play a significant role in improving the current understanding of tissue biomechanics. In this study, we propose a method for measuring elastic properties non-invasively by using internal indentation as generated by Harmonic Motion Imaging (HMI). In HMI, an oscillating acoustic radiation force is produced by a focused ultrasound transducer at the focal region, and the resulting displacements are estimated by tracking RF signals acquired by an imaging transducer. In this study, the focal spot region was modeled as a rigid cylindrical piston that exerts an oscillatory, uniform internal force to the underlying tissue. The HMI elastic modulus EHMI was defined as the ratio of the applied force to the axial strain measured by 1D ultrasound imaging. The accuracy and the precision of the EHMI estimate were assessed both numerically and experimentally in polyacrylamide tissue-mimicking phantoms. Initial feasibility of this method in soft tissues was also shown in canine liver specimens in vitro. Very good correlation and agreement was found between the actual Young’s modulus and the HMI modulus in the numerical study (r2>0.99, relative error <10%) and on polyacrylamide gels (r2=0.95, relative error <24%). The average HMI modulus on five liver samples was found to EHMI=2.62±0.41 kPa, compared to EMechTesting=4.2±2.58 kPa measured by rheometry. This study has demonstrated for the first time the initial feasibility of a non-invasive, model-independent method to estimate local elastic properties of biological tissues at a submillimeter scale using an internal indentation-like approach. Ongoing studies include in vitro experiments in a larger number of samples and feasibility testing in in vivo models as well as pathological human specimens. PMID:25776065

  5. Non-contact, ultrasound-based indentation method for measuring elastic properties of biological tissues using Harmonic Motion Imaging (HMI)

    NASA Astrophysics Data System (ADS)

    Vappou, Jonathan; Hou, Gary Y.; Marquet, Fabrice; Shahmirzadi, Danial; Grondin, Julien; Konofagou, Elisa E.

    2015-04-01

    Noninvasive measurement of mechanical properties of biological tissues in vivo could play a significant role in improving the current understanding of tissue biomechanics. In this study, we propose a method for measuring elastic properties non-invasively by using internal indentation as generated by harmonic motion imaging (HMI). In HMI, an oscillating acoustic radiation force is produced by a focused ultrasound transducer at the focal region, and the resulting displacements are estimated by tracking radiofrequency signals acquired by an imaging transducer. In this study, the focal spot region was modeled as a rigid cylindrical piston that exerts an oscillatory, uniform internal force to the underlying tissue. The HMI elastic modulus EHMI was defined as the ratio of the applied force to the axial strain measured by 1D ultrasound imaging. The accuracy and the precision of the EHMI estimate were assessed both numerically and experimentally in polyacrylamide tissue-mimicking phantoms. Initial feasibility of this method in soft tissues was also shown in canine liver specimens in vitro. Very good correlation and agreement was found between the measured Young’s modulus and the HMI modulus in the numerical study (r2 > 0.99, relative error <10%) and on polyacrylamide gels (r2 = 0.95, relative error <24%). The average HMI modulus on five liver samples was found to EHMI = 2.62  ±  0.41 kPa, compared to EMechTesting = 4.2  ±  2.58 kPa measured by rheometry. This study has demonstrated for the first time the initial feasibility of a non-invasive, model-independent method to estimate local elastic properties of biological tissues at a submillimeter scale using an internal indentation-like approach. Ongoing studies include in vitro experiments in a larger number of samples and feasibility testing in in vivo models as well as pathological human specimens.

  6. Non-contact, ultrasound-based indentation method for measuring elastic properties of biological tissues using harmonic motion imaging (HMI).

    PubMed

    Vappou, Jonathan; Hou, Gary Y; Marquet, Fabrice; Shahmirzadi, Danial; Grondin, Julien; Konofagou, Elisa E

    2015-04-07

    Noninvasive measurement of mechanical properties of biological tissues in vivo could play a significant role in improving the current understanding of tissue biomechanics. In this study, we propose a method for measuring elastic properties non-invasively by using internal indentation as generated by harmonic motion imaging (HMI). In HMI, an oscillating acoustic radiation force is produced by a focused ultrasound transducer at the focal region, and the resulting displacements are estimated by tracking radiofrequency signals acquired by an imaging transducer. In this study, the focal spot region was modeled as a rigid cylindrical piston that exerts an oscillatory, uniform internal force to the underlying tissue. The HMI elastic modulus EHMI was defined as the ratio of the applied force to the axial strain measured by 1D ultrasound imaging. The accuracy and the precision of the EHMI estimate were assessed both numerically and experimentally in polyacrylamide tissue-mimicking phantoms. Initial feasibility of this method in soft tissues was also shown in canine liver specimens in vitro. Very good correlation and agreement was found between the measured Young's modulus and the HMI modulus in the numerical study (r(2) > 0.99, relative error <10%) and on polyacrylamide gels (r(2) = 0.95, relative error <24%). The average HMI modulus on five liver samples was found to EHMI = 2.62  ±  0.41 kPa, compared to EMechTesting = 4.2  ±  2.58 kPa measured by rheometry. This study has demonstrated for the first time the initial feasibility of a non-invasive, model-independent method to estimate local elastic properties of biological tissues at a submillimeter scale using an internal indentation-like approach. Ongoing studies include in vitro experiments in a larger number of samples and feasibility testing in in vivo models as well as pathological human specimens.

  7. Low-energy dynamic indentation method for analysis of ophthalmic materials.

    PubMed

    Artús, Pau; Dürsteler, Juan C; Martínez, Antonio B

    2008-01-01

    The purpose of the present work is to understand and study the mechanical behavior and critical parameters of ophthalmic polymers. The article introduces a novel low-energy indentation method that can be used to study and optimize the mechanical properties of ophthalmic materials. The technique has been developed in the frame of a larger study on the impact resistance of materials. The low-energy dynamic indentation method is based on a lumped mass-spring model solved by a 4th-order Runge-Kutta numerical method. The model can be used to predict the material response to the indentation of a hemi-spherical tip and calculate the elasticity modulus of materials, dissipated energy during impact, residual deformation after impact, indentation depth and their conservative and nonconservative components. As an example, two ophthalmic polymers were compared: CR-39 as the universal ophthalmic standard, and Superfin as Indo Lens U.S., standard. Results showed the model is in good agreement with experimental data and allowed to obtain elasticity moduli for both materials, which showed similar values. A larger conservative component of the displacement for Superfin was also obtained and a smaller calculated residual displacement, which is indicative of less deformed material after low energy impacts. The model can satisfactorily predict the behavior of materials under low energy indentation situations. In addition, it can be used to distinguish two apparently similar materials, such as CR-39 and Superfin, and classify them according to their response to these kind of indentations. The technique could be used as a very powerful tool to improve ophthalmic materials.

  8. Cable indenter aging monitor

    SciTech Connect

    Shook, T.A.; Gardner, J.B.

    1988-07-01

    This project was undertaken to develop a hand-held, nondestructive test device to assess the aged condition of electrical cable by in situ measurement of mechanical properties of polymeric jackets and insulations. The device is an indenter similar to those used to make hardness measurements. Comparison of measurements made on installed cables with previous measurements serving as baseline aging/mechanical property data will determine the state of aging of the field cables. Such a device will be valuable in nuclear and fossil plant life extension programs. Preliminary laboratory tests on cables covered with ethylene propylene rubber (EPR) and chlorosulfated polyethylene (CSPE) point to the measurement of the rate of force increase resulting from constant rate deformation as having the best correlation with progressive thermal aging. This first phase of the work has demonstrated the technical feasibility of the method. A second phase will include the generation of additional groundwork data and the design of the portable indenter for in situ plant measurements.

  9. Johnson-Kendall-Roberts adhesive contact for a toroidal indenter

    NASA Astrophysics Data System (ADS)

    Argatov, Ivan; Li, Qiang; Pohrt, Roman; Popov, Valentin L.

    2016-07-01

    The unilateral axisymmetric frictionless adhesive contact problem for a toroidal indenter and an elastic half-space is considered in the framework of the Johnson-Kendall-Roberts theory. In the case of a semi-fixed annular contact area, when one of the contact radii is fixed, while the other varies during indentation, we obtain the asymptotic solution of the adhesive contact problem based on the solution of the corresponding unilateral non-adhesive contact problem. In particular, the adhesive contact problem for Barber's concave indenter is considered in detail. In the case when both contact radii are variable, we construct the leading-order asymptotic solution for a narrow annular contact area. It is found that for a v-shaped generalized toroidal indenter, the pull-off force is independent of the elastic properties of the indented solid.

  10. Validation of cartilage thickness calculations using indentation analysis.

    PubMed

    Koff, Matthew F; Chong, Le Roy; Virtue, Patrick; Chen, Dan; Wang, Xioanan; Wright, Timothy; Potter, Hollis G

    2010-04-01

    Different methods have been used to cross-validate cartilage thickness measurements from magnetic resonance images (MRIs); however, a majority of these methods rely on interpolated data points, regional mean and/or maximal thickness, or surface mean thickness for data analysis. Furthermore, the accuracy of MRI cartilage thickness measurements from commercially available software packages has not necessarily been validated and may lead to an under- or overestimation of cartilage thickness. The goal of this study was to perform a matching point-to-point validation of indirect cartilage thickness calculations using a magnetic resonance (MR) image data set with direct cartilage thickness measurements using biomechanical indentation testing at the same anatomical locations. Seven bovine distal femoral condyles were prepared and a novel phantom filled with dilute gadolinium solution was rigidly attached to each specimen. High resolution MR images were acquired, and thickness indentation analysis of the cartilage was performed immediately after scanning. Segmentation of the MR data and cartilage thickness calculation was performed using semi-automated software. Registration of MR and indentation data was performed using the fluid filled phantom. The inter- and intra-examiner differences of the measurements were also determined. A total of 105 paired MRI-indentation thickness data points were analyzed, and a significant correlation between them was found (r=0.88, p<0.0001). The mean difference (+/-std. dev.) between measurement techniques was 0.00+/-0.23 mm, with Bland-Altman limits of agreement of 0.45 mm and -0.46 mm. The intra- and inter-examiner measurement differences were 0.03+/-0.22 mm and 0.05+/-0.24 mm, respectively. This study validated cartilage thickness measurements from MR images with thickness measurements from indentation by using a novel phantom to register the image-based and laboratory-based data sets. The accuracy of the measurements was comparable to

  11. Estimation of Musculotendon Kinematics under Controlled Tendon Indentation

    PubMed Central

    Chardon, Matthieu K.; Dhaher, Yasin Y.; Suresh, Nina I.; Jaramillo, Giselle; Rymer, W. Zev

    2015-01-01

    The effects of tendon indentation on musculotendon unit mechanics have been left largely unexplored. Tendon indentation is however routinely used in the tendon reflex exam to diagnose the state of reflex pathways. Because muscle mechanoreceptors are sensitive to mechanical changes of the musculotendon unit, this gap in knowledge could potentially impact our understanding of these neurological exams. Accordingly, we have used ultrasound (US) imaging to compare the effects of tendon indentation with the effects angular rotation of the elbow in six neurologically intact individuals. We used sagittal ultrasound movies of the biceps brachii to compare length changes induced by each of these perturbations. Length changes were quantified using a pixel-tracking protocol. Our results show that a 20 mm indentation of the distal tendon is broadly equivalent to a 15° elbow rotation. We also show that within the imaging window the strain differences between the two stretching protocols are statistically insignificant. Finally, we show that there exists a significant linear relationship between the two stretching techniques and that this relationship spans a large rotational angle to indentation depth. We have used a novel tendon probe to administer controlled tendon indentations as a way to characterize musculotendon kinematics. Using this probe, we confirm that tendon indentation can be physiologically equated with joint rotation, and can thus be used as an input for muscle stretching protocols. Furthermore, this is potentially a simpler and more practical alternative to externally imposed angular joint motion. PMID:26321363

  12. Finite element simulation of Reference Point Indentation on bone.

    PubMed

    Idkaidek, Ashraf; Agarwal, Vineet; Jasiuk, Iwona

    2017-01-01

    Reference Point Indentation (RPI) is a novel technique aimed to assess bone quality. Measurements are recorded by the BioDent instrument that applies multiple indents to the same location of cortical bone. Ten RPI parameters are obtained from the resulting force-displacement curves. Using the commercial finite element analysis software Abaqus, we assess the significance of the RPI parameters. We create an axisymmetric model and employ an isotropic viscoelastic-plastic constitutive relation with damage to simulate indentations on a human cortical bone. Fracture of bone tissue is not simulated for simplicity. The RPI outputs are computed for different simulated test cases and then compared with experimental results, measured using the BioDent, found in literature. The number of cycles, maximum indentation load, indenter tip radius, and the mechanical properties of bone: Young׳s modulus, compressive yield stress, and viscosity and damage constants, are varied. The trends in the RPI parameters are then investigated. We find that the RPI parameters are sensitive to the mechanical properties of bone. An increase in Young׳s modulus of bone causes the force-displacement loading and unloading slopes to increase and the total indentation distance (TID) to decrease. The compressive yield stress is inversely proportional to a creep indentation distance (CID1) and the TID. The viscosity constant is proportional to the CID1 and an average of the energy dissipated (AvED). The maximum indentation load is proportional to the TID, CID1, loading and unloading slopes, and AvED. The damage parameter is proportional to the TID, but it is inversely proportional to both the loading and unloading slopes and the AvED. The value of an indenter tip radius is proportional to the CID1 and inversely proportional to the TID. The number of load cycles is inversely proportional to an average of a creep indentation depth (AvCID) and the AvED. The indentation distance increase (IDI) is strongly

  13. Aerodynamic measurement techniques. [laser based diagnostic techniques

    NASA Technical Reports Server (NTRS)

    Hunter, W. W., Jr.

    1976-01-01

    Laser characteristics of intensity, monochromatic, spatial coherence, and temporal coherence were developed to advance laser based diagnostic techniques for aerodynamic related research. Two broad categories of visualization and optical measurements were considered, and three techniques received significant attention. These are holography, laser velocimetry, and Raman scattering. Examples of the quantitative laser velocimeter and Raman scattering measurements of velocity, temperature, and density indicated the potential of these nonintrusive techniques.

  14. Improved Indentation Test for Measuring Nonlinear Elasticity

    NASA Technical Reports Server (NTRS)

    Eldridge, Jeffrey I.

    2004-01-01

    A cylindrical-punch indentation technique has been developed as a means of measuring the nonlinear elastic responses of materials -- more specifically, for measuring the moduli of elasticity of materials in cases in which these moduli vary with applied loads. This technique offers no advantage for characterizing materials that exhibit purely linear elastic responses (constant moduli of elasticity, independent of applied loads). However, the technique offers a significant advantage for characterizing such important materials as plasma-sprayed thermal-barrier coatings, which, in cyclic loading, exhibit nonlinear elasticity with hysteresis related to compaction and sliding within their microstructures.

  15. PMMA microlens array fabricated by indentation process

    NASA Astrophysics Data System (ADS)

    Cirino, Giuseppe A.; Jasinevicius, Renato G.

    2017-02-01

    This work reports the fabrication of a PMMA-based spherical microlens array (MLA), targeting application of Shack-Hartmann wavefront sensor for lens characterization. The array present 10 by 10 elements, with f-number f/# = f/10 (1 mm diameter, 10 mm focal length). The fabrication method employs a computer-controlled mechanical indentation for the fabrication of an insert mold, and subsequent replication by injection molding on PMMA. After replication and de-molding, the PMMA surface containing the negative of the phase profile of the lens array was evaluated by optical profilometry technique, in terms of the surface quality as well as the replication fidelity. The RMS surface roughness level of approximately (λ/10) was found, considering operation in the visible range of spectrum. Optical characterization was based on the evaluation of the sharpness, FWHM, and maximum intensity, IMAX, values associated to the profiles of each of the 100 generated light spots, obtained in the back focal plane of the MLA. An average sharpness of FWHMAVG = 13.9 +/- 8% μm, and average maximum intensity of IMAX AVG = 0.72 +/- 7% a.u. was obtained.

  16. Occurrence of spherical ceramic debris in indentation and sliding contact

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1982-01-01

    Indenting experiments were conducted with the silicon carbide (0001) surface in contact with a spherical diamond indenter in air. Sliding friction experiments were also conducted with silicon carbide in contact with iron and iron-based binary alloys at room temperature and 800 C. Fracture pits with a spherical particle and spherical wear debris were observed as a result of indenting and sliding. Spherical debris may be produced by a mechanism that involves a spherical-shaped fracture along the circular or spherical stress trajectories under the inelastic deformation zone.

  17. Fatigue Life of Postbuckled Structures with Indentation Damages

    NASA Technical Reports Server (NTRS)

    Davila, Carlos G.; Bisagni, Chiara

    2016-01-01

    The fatigue life of composite stiffened panels with indentation damage was investigated experimentally using single stringer compression specimens. Indentation damage was induced on one of the two flanges of each stringer. The experiments were conducted using advanced instrumentation, including digital image correlation, passive thermography, and in-situ ultrasonic scanning. Specimens with initial indentation damage lengths of 32 millimeters to 56 millimeters were tested quasi-statically and in fatigue, and the effects of cyclic load amplitude and damage size were studied. A means of comparison of the damage propagation rates and collapse loads based on a stress intensity measure and the Paris law is proposed.

  18. Fatigue Life of Postbuckled Structures with Indentation Damage

    NASA Technical Reports Server (NTRS)

    Davila, Carlos G.; Bisagni, Chiara

    2016-01-01

    The fatigue life of composite stiffened panels with indentation damage was investigated experimentally using single stringer compression specimens. Indentation damage was induced on one of the two flanges of the stringer. The experiments were conducted using advanced instrumentation, including digital image correlation, passive thermography, and in-situ ultrasonic scanning. Specimens with initial indentation damage lengths of 37 millimeters to 56 millimeters were tested in fatigue and the effects of cyclic load amplitude and damage size were studied. A means of comparison of the damage propagation rates and collapse loads based on a stress intensity measure and the Paris law is proposed.

  19. Elastic response of thermal spray deposits under indentation tests

    SciTech Connect

    Leigh, S.H.; Lin, C.K.; Berndt, C.C.

    1997-08-01

    The elastic response behavior of thermal spray deposits at Knoop indentations has been investigated using indentation techniques. The ration of hardness to elastic modulus, which is an important prerequisite for the evaluation of indentation fracture toughness, is determined by measuring the elastic recovery of the in-surface dimensions of Knoop indentations. The elastic moduli of thermal spray deposits are in the range of 12%--78% of the comparable bulk materials and reveal the anisotropic behavior of thermal spray deposits. A variety of thermal spray deposits has been examined, including Al{sub 2}O{sub 3}, yttria-stabilized ZrO{sub 2} (YSZ), and NiAl. Statistical tools have been used to evaluate the error estimates of the data.

  20. Effects of water molecules on tribological behavior and property measurements in nano-indentation processes - a numerical analysis

    PubMed Central

    2013-01-01

    Nano/micro-manufacturing under wet condition is an important consideration for various tool-based processes such as indentation, scratching, and machining. The existence of liquids adds complexity to the system, changes the tool/work interfacial condition, and affects material behaviors. For indentation, it may also affect material property measurements. However, little effort has been made to study this challenging issue at nano- or atomistic scale. In this study, we tackle this challenge by investigating nano-indentation processes submerged in water using the molecular dynamics (MD) simulation approach. Compared with dry indentation in which no water molecules are present, the existence of water molecules causes the increase of indentation force in initial penetration, but the decrease of indentation force in full penetration. It also reduces the sticking phenomenon between the work and tool atoms during indenter retraction, such that the indentation geometry can be better retained. Meanwhile, nano-indentation under wet condition exhibits the indentation size effect, while dry nano-indentation exhibits the reverse indentation size effect. The existence of water leads to higher computed hardness values at low indentation loads and a smaller value of Young's modulus. In addition, the friction along the tool/work interface is significantly reduced under wet indentation. PMID:24044504

  1. Effects of water molecules on tribological behavior and property measurements in nano-indentation processes - a numerical analysis.

    PubMed

    Wang, Yachao; Shi, Jing

    2013-09-17

    Nano/micro-manufacturing under wet condition is an important consideration for various tool-based processes such as indentation, scratching, and machining. The existence of liquids adds complexity to the system, changes the tool/work interfacial condition, and affects material behaviors. For indentation, it may also affect material property measurements. However, little effort has been made to study this challenging issue at nano- or atomistic scale. In this study, we tackle this challenge by investigating nano-indentation processes submerged in water using the molecular dynamics (MD) simulation approach. Compared with dry indentation in which no water molecules are present, the existence of water molecules causes the increase of indentation force in initial penetration, but the decrease of indentation force in full penetration. It also reduces the sticking phenomenon between the work and tool atoms during indenter retraction, such that the indentation geometry can be better retained. Meanwhile, nano-indentation under wet condition exhibits the indentation size effect, while dry nano-indentation exhibits the reverse indentation size effect. The existence of water leads to higher computed hardness values at low indentation loads and a smaller value of Young's modulus. In addition, the friction along the tool/work interface is significantly reduced under wet indentation.

  2. Determining Tension-Compression Nonlinear Mechanical Properties of Articular Cartilage from Indentation Testing.

    PubMed

    Chen, Xingyu; Zhou, Yilu; Wang, Liyun; Santare, Michael H; Wan, Leo Q; Lu, X Lucas

    2016-04-01

    The indentation test is widely used to determine the in situ biomechanical properties of articular cartilage. The mechanical parameters estimated from the test depend on the constitutive model adopted to analyze the data. Similar to most connective tissues, the solid matrix of cartilage displays different mechanical properties under tension and compression, termed tension-compression nonlinearity (TCN). In this study, cartilage was modeled as a porous elastic material with either a conewise linear elastic matrix with cubic symmetry or a solid matrix reinforced by a continuous fiber distribution. Both models are commonly used to describe the TCN of cartilage. The roles of each mechanical property in determining the indentation response of cartilage were identified by finite element simulation. Under constant loading, the equilibrium deformation of cartilage is mainly dependent on the compressive modulus, while the initial transient creep behavior is largely regulated by the tensile stiffness. More importantly, altering the permeability does not change the shape of the indentation creep curves, but introduces a parallel shift along the horizontal direction on a logarithmic time scale. Based on these findings, a highly efficient curve-fitting algorithm was designed, which can uniquely determine the three major mechanical properties of cartilage (compressive modulus, tensile modulus, and permeability) from a single indentation test. The new technique was tested on adult bovine knee cartilage and compared with results from the classic biphasic linear elastic curve-fitting program.

  3. The compelling case for indentation as a functional exploratory and characterization tool

    DOE PAGES

    Tandon, Rajan; Marshall, David B.; Cook, Robert F.; ...

    2015-07-30

    The utility of indentation testing for characterizing a wide range of mechanical properties of brittle materials is highlighted in light of recent articles questioning its validity, specifically in relation to the measurement of toughness. Contrary to assertion by some critics, indentation fracture theory is fundamentally founded in Griffith–Irwin fracture mechanics, based on model crack systems evolving within inhomogeneous but well-documented elastic and elastic–plastic contact stress fields. Notwithstanding some numerical uncertainty in associated stress intensity factor relations, the technique remains an unrivalled quick, convenient and economical means for comparative, site-specific toughness evaluation. Most importantly, indentation patterns are unique fingerprints of mechanicalmore » behavior and thereby afford a powerful functional tool for exploring the richness of material diversity. At the same time, it is cautioned that unconditional usage without due attention to the conformation of the indentation patterns can lead to overstated toughness values. Limitations of an alternative, more engineering approach to fracture evaluation, that of propagating a precrack through a “standard” machined specimen, are also outlined. Thus misconceptions in the critical literature concerning the fundamental nature of crack equilibrium and stability within contact and other inhomogeneous stress fields are discussed.« less

  4. The compelling case for indentation as a functional exploratory and characterization tool

    SciTech Connect

    Tandon, Rajan; Marshall, David B.; Cook, Robert F.; Padture, Nitin P.; Oyen, Michelle L.; Pajares, Antonia; Bradby, Jodie E.; Reimanis, Ivar E.; Page, Trevor F.; Pharr, George M.; Lawn, Brian R.

    2015-07-30

    The utility of indentation testing for characterizing a wide range of mechanical properties of brittle materials is highlighted in light of recent articles questioning its validity, specifically in relation to the measurement of toughness. Contrary to assertion by some critics, indentation fracture theory is fundamentally founded in Griffith–Irwin fracture mechanics, based on model crack systems evolving within inhomogeneous but well-documented elastic and elastic–plastic contact stress fields. Notwithstanding some numerical uncertainty in associated stress intensity factor relations, the technique remains an unrivalled quick, convenient and economical means for comparative, site-specific toughness evaluation. Most importantly, indentation patterns are unique fingerprints of mechanical behavior and thereby afford a powerful functional tool for exploring the richness of material diversity. At the same time, it is cautioned that unconditional usage without due attention to the conformation of the indentation patterns can lead to overstated toughness values. Limitations of an alternative, more engineering approach to fracture evaluation, that of propagating a precrack through a “standard” machined specimen, are also outlined. Thus misconceptions in the critical literature concerning the fundamental nature of crack equilibrium and stability within contact and other inhomogeneous stress fields are discussed.

  5. Measuring soft tissue material properties using stereovision and indentation: a proof-of-concept study

    NASA Astrophysics Data System (ADS)

    Ji, Songbai; Fan, Xiaoyao; Hartov, Alex; Roberts, David W.; Paulsen, Keith D.

    2013-03-01

    Accurate measurement of soft tissue material properties is critical for characterizing its biomechanical behaviors but can be challenging especially for the human brain. Recently, we have applied stereovision to track motion of the exposed cortical surface noninvasively for patients undergoing open skull neurosurgical operations. In this paper, we conduct a proof-of-concept study to evaluate the feasibility of the technique in measuring material properties of soft tissue in vivo using a tofu phantom. A block of soft tofu was prepared with black pepper randomly sprinkled on the top surface to provide texture to facilitate image-based displacement mapping. A disk-shaped indenter made of high-density tungsten was placed on the top surface to induce deformation through its weight. Stereoscopic images were acquired before and after indentation using a pair of stereovision cameras mounted on a surgical microscope with its optical path perpendicular to the imaging surface. Rectified left camera images obtained from stereovision reconstructions were then co-registered using optical flow motion tracking from which a 2D surface displacement field around the indenter disk was derived. A corresponding finite element model of the tofu was created subjected to the indenter weight and a hyperelastic material model was chosen to account for large deformation around the intender edges. By successively assigning different shear stiffness constant, computed tofu surface deformation was obtained, and an optimal shear stiffness was obtained that matched the model-derived surface displacements with those measured from the images. The resulting quasi-static, long-term shear stiffness for the tofu was 1.04 k Pa, similar to that reported in the literature. We show that the stereovision and free-weight indentation techniques coupled with an FE model are feasible for in vivo measurement of the human brain material properties, and it may also be feasible for other soft tissues.

  6. Indentation plasticity and fracture in silicon

    NASA Technical Reports Server (NTRS)

    Rybicki, George C.; Pirouz, P.

    1988-01-01

    Measurements of the ductile-brittle transition temperature of heavily doped silicon were carried out using indentation techniques. Diamond pyramid hardness tests were performed on the (100) face of heavily doped N-type and P-type and intrinsic silicon single crystals. Tests were performed over the range 200 C to 850 C and loads of 100 to 500 g were used. Samples were subsequently etched to reveal dislocation rosettes produced by indentation. Intrinsic silicon underwent a ductile-brittle transition at 660 C, P-type at 645 C and N-type at 625 C. Hardness values varied from 1.1 GPa at 700 C to 11.7 GPa at 200 C. Significant effects of hardness on doping were present only at the highest temperatures. Lower loads generally produced higher hardness but load did not affect the Ductile-Brittle Transition Temperature (DBTT). Fracture toughness values ranged from 0.9 MPa m(1/2) at 200 C to 2.75 MPa m(1/2) near the DBTT. Doping did not affect the fracture toughness of silicon. P-type doping increased the size of dislocation rosettes observed after indentation, but N-type did not, in contradiction of the expected results. Results are discussed in terms of the effect of doping on the dislocation mobility in silicon.

  7. MEASUREMENT OF YOUNG’S MODULUS OF VOCAL FOLDS BY INDENTATION

    PubMed Central

    Chhetri, Dinesh K.; Zhang, Zhaoyan; Neubauer, Juergen

    2009-01-01

    Objectives To assess accuracy of the indentation method for stiffness measurements and to estimate the Young’s modulus of the vocal fold using this technique. Study Design Basic science. Methods Indentation tests were performed using a range of indenter diameters and indentation depths on single and double layer silicone rubber models with a range of cover layer thicknesses with known geometry and Young’s moduli. Measurements were repeated on intact vocal folds and isolated muscle and cover layer samples from three cadaveric human larynges. Results Indentation on single-layer rubber models yielded Young’s moduli with acceptable accuracy when the indentation depth was equal to or smaller than the indenter diameter, and both were smaller than the physical dimensions of the material sample. On two-layer models the stiffness estimation was similarly influenced by indenter diameter and indentation depth, and acceptable accuracy was reached when indentation depth was much smaller than the height of the top cover layer. Measurements on mid-membranous vocal fold tissue revealed location-dependent Young’s moduli (in kPa) as follows: intact hemilarynx 8.6 (range 5.3 – 13.1), isolated inferior medial surface cover 7.5 (range 7 – 7.9), isolated medial surface cover 4.8 (range 3.9–5.7), isolated superior surface cover 2.9 (range 2.7 – 3.2), and isolated thyroarytenoid muscle 2.0 (range 1.3 – 2.7). Conclusions Indenter diameter, indentation depth, and material thickness are important parameters in measurement of vocal fold stiffness using the indentation technique. Measurements on human larynges showed location-dependent differences in stiffness. The stiffness of the vocal folds was also found to be higher when the vocal fold structure was still attached to the laryngeal framework as compared to when the vocal fold was separated from the framework. PMID:20171829

  8. Robust strategies for automated AFM force curve analysis--I. Non-adhesive indentation of soft, inhomogeneous materials.

    PubMed

    Lin, David C; Dimitriadis, Emilios K; Horkay, Ferenc

    2007-06-01

    The atomic force microscope (AFM) has found wide applicability as a nanoindentation tool to measure local elastic properties of soft materials. An automated approach to the processing of AFM indentation data, namely, the extraction of Young's modulus, is essential to realizing the high-throughput potential of the instrument as an elasticity probe for typical soft materials that exhibit inhomogeneity at microscopic scales. This paper focuses on Hertzian analysis techniques, which are applicable to linear elastic indentation. We compiled a series of synergistic strategies into an algorithm that overcomes many of the complications that have previously impeded efforts to automate the fitting of contact mechanics models to indentation data. AFM raster data sets containing up to 1024 individual force-displacement curves and macroscopic compression data were obtained from testing polyvinyl alcohol gels of known composition. Local elastic properties of tissue-engineered cartilage were also measured by the AFM. All AFM data sets were processed using customized software based on the algorithm, and the extracted values of Young's modulus were compared to those obtained by macroscopic testing. Accuracy of the technique was verified by the good agreement between values of Young's modulus obtained by AFM and by direct compression of the synthetic gels. Validation of robustness was achieved by successfully fitting the vastly different types of force curves generated from the indentation of tissue-engineered cartilage. For AFM indentation data that are amenable to Hertzian analysis, the method presented here minimizes subjectivity in preprocessing and allows for improved consistency and minimized user intervention. Automated, large-scale analysis of indentation data holds tremendous potential in bioengineering applications, such as high-resolution elasticity mapping of natural and artificial tissues.

  9. Modeling of indentation into inhomogeneous soft tissues

    NASA Astrophysics Data System (ADS)

    Lyubicheva, A. N.; Goryacheva, I. G.; Dosaev, M. Z.; Su, F.-Ch.

    2017-01-01

    A simulation of a contact interaction of the indenter and inhomogeneous soft biological tissues is carried out. The soft tissue is modeled by the incompressible elastic body which contains structural inhomogeneities (spherical or longitudinal inclusions). The elastic moduli of inclusions are higher than the bulk soft tissue modulus. These inclusions may be considered, in particular, as the models of the pathological growths. The indenter has the form of a hollow hemisphere (shell). It is the model of the mechanoreceptor developed in [1] to study the mechanical properties of soft tissues. The hydrostatic pressure can be applied inside the shell. Based on the numerical analysis, the dependences of the contact area size, and contact pressure on penetration of the indenter into the sample for several values of the inclusion size, depth, its location, the ratio of the elastic moduli of inclusion and the surrounding material, but also for various values of hydrostatic pressure inside the shell were obtained. The possibility of an inverse problem solution for determining the mechanical properties of the inclusion, and its size by measuring the contact characteristics is discussed.

  10. Indentation law for composite laminates

    NASA Technical Reports Server (NTRS)

    Yang, S. H.

    1981-01-01

    Static indentation tests are described for glass/epoxy and graphite/epoxy composite laminates with steel balls as the indentor. Beam specimens clamped at various spans were used for the tests. Loading, unloading, and reloading data were obtained and fitted into power laws. Results show that: (1) contact behavior is not appreciably affected by the span; (2) loading and reloading curves seem to follow the 1.5 power law; and (3) unloading curves are described quite well by a 2.5 power law. In addition, values were determined for the critical indentation, alpha sub cr which can be used to predict permanent indentations in unloading. Since alpha sub cr only depends on composite material properties, only the loading and an unloading curve are needed to establish the complete loading-unloading-reloading behavior.

  11. In situ spectroscopic study of the plastic deformation of amorphous silicon under nonhydrostatic conditions induced by indentation

    DOE PAGES

    Gerbig, Yvonne B.; Michaels, C. A.; Bradby, Jodie E.; ...

    2015-12-17

    Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique (IIT). The occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were observed. Furthermore, the obtained experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a model for the deformation behavior of a-Si under indentation loading.

  12. Residual stress and plastic anisotropy in indented 2024-T351 aluminum disks

    SciTech Connect

    Clausen, Bjorn; Prime, Michael B; Saurabh, Kabra; Brown, Donald W; Pagliaro, Pierluigi; Backlund, Peter; Shaw, Sanjiv; Criss, Everett

    2009-01-01

    Recent studies have proven that generating a well defined residual stress state using the indented disk approach is an excellent way to validate experimental and modeling techniques for measuring and predicting residual stresses. The previous studies dealt with indented stainless steel disks, and included experimental determination of residual stresses using the Contour Method and neutron diffraction measurements. The measured residual stress states showed good agreement between the techniques, and a Finite Element Model predicted residual stress state based upon material properties determined form standard tension and compression/tension tests was also in good agreement with the measurements. In the present work, disks of 2024-T351 Aluminum were investigated. As before, the residual stress profile was measured using neutron diffraction and the Contour Method and Finite Element Modeling was employed to predict the residual stress profile. Analysis and comparison of the three techniques were complicated by the fact that the experimental data shows evidence of plastic anisotropy and strong Bauschinger effect within the indented disks.

  13. Inducing phase transformations using depth-sensing indentation

    NASA Astrophysics Data System (ADS)

    Juliano, Thomas Frank

    Phase transformations in solids occur during a number of common contact loading situations including polishing, cutting, and grinding. To understand and optimize material response to such processes or to engineer a surface with specific properties (i.e. electrical, optical, mechanical) at a micro-scale, depth-sensing indentation is used to study point loading situations and simulate dynamic processes. Sometimes, evidence of phase transformation can be found from load-displacement curves. Raman spectroscopy or other techniques (i.e. transmission electron microscopy, atomic force microscopy, or x-ray diffraction) on residual impressions often provides useful information to characterize transformations which take place during indentation. In this work, depth-sensing indentation and Raman spectroscopy are used as the primary techniques to identify phase transformations under different maximum applied loads, loading rates and unloading rates. Single-crystal silicon and lead zirconate titanate modified by niobium (PNZT) are used as exemplary materials for study because of their widespread industrial importance. A general technique for studying phase transformations induced by indentation is developed. Silicon undergoes a transformation from the cubic-diamond (Si-I) to beta-tin phase (Si-II) on loading around 12 GPa, and from Si-II to the r8 (Si-XII), bc8 (Si-III) or amorphous silicon on unloading. Using a number of different loading conditions, the stability of Si-II was found to range between 4 and 12 GPa, depending on maximum applied load, unloading rate and indenter tool geometry. 95/5 PNZT undergoes a ferroelectric to antiferroelectric phase change around 300 MPa of contact pressure. Both sharp (Berkovich) and spherical indentation are used to study different stress states for each material, and its influence on phase changes. On silicon, over 4500 indentations are made to determine the statistical nature of phase changes. Differentiation of load-displacement curves

  14. Determining the Elastic Modulus of Compliant Thin Films Supported on Substrates from Flat Punch Indentation Measurements

    Treesearch

    M.J. Wald; J.M. Considine; K.T. Turner

    2013-01-01

    Instrumented indentation is a technique that can be used to measure the elastic properties of soft thin films supported on stiffer substrates, including polymer films, cellulosic sheets, and thin layers of biological materials. When measuring thin film properties using indentation, the effect of the substrate must be considered. Most existing models for determining the...

  15. Review of fracture properties of nuclear materials determined by Hertzian indentation

    SciTech Connect

    Routbort, J.; Matzke, H.

    1985-01-01

    A brief description of the determination of the surface fracture energy and the fracture toughness from a Hertzian indentation test is given. A number of theoretical and experimental problems are discussed. Results obtained on a variety of nuclear fuels and nuclear-waste-containment materials are reviewed and compared with values measured by other techniques. The Hertzian indentation test yields reliable fracture parameters.

  16. On the relationship between indentation hardness and modulus, and the damage resistance of biological materials.

    PubMed

    Labonte, David; Lenz, Anne-Kristin; Oyen, Michelle L

    2017-07-15

    The remarkable mechanical performance of biological materials is based on intricate structure-function relationships. Nanoindentation has become the primary tool for characterising biological materials, as it allows to relate structural changes to variations in mechanical properties on small scales. However, the respective theoretical background and associated interpretation of the parameters measured via indentation derives largely from research on 'traditional' engineering materials such as metals or ceramics. Here, we discuss the functional relevance of indentation hardness in biological materials by presenting a meta-analysis of its relationship with indentation modulus. Across seven orders of magnitude, indentation hardness was directly proportional to indentation modulus. Using a lumped parameter model to deconvolute indentation hardness into components arising from reversible and irreversible deformation, we establish criteria which allow to interpret differences in indentation hardness across or within biological materials. The ratio between hardness and modulus arises as a key parameter, which is related to the ratio between irreversible and reversible deformation during indentation, the material's yield strength, and the resistance to irreversible deformation, a material property which represents the energy required to create a unit volume of purely irreversible deformation. Indentation hardness generally increases upon material dehydration, however to a larger extent than expected from accompanying changes in indentation modulus, indicating that water acts as a 'plasticiser'. A detailed discussion of the role of indentation hardness, modulus and toughness in damage control during sharp or blunt indentation yields comprehensive guidelines for a performance-based ranking of biological materials, and suggests that quasi-plastic deformation is a frequent yet poorly understood damage mode, highlighting an important area of future research. Instrumented

  17. Indentation across interfaces between stiff and compliant tissues.

    PubMed

    Armitage, Oliver E; Oyen, Michelle L

    2017-01-04

    Bone-tendon, bone-ligament and bone-cartilage junctions are multi-tissue interfaces that connect materials that differ by two orders of magnitude in mechanical properties, via gradual variations in mineral content and matrix composition. These sites mediate load transfer between highly dissimilar materials and are consequently a primary site of injury during orthopedic failure. Given the large incidence rate and the lack of suitable surgical solutions for their regeneration or repair, characterization of their natural structure and subsequent replication through tissue engineering is important. Here, we evaluate the ability and accuracy of instrumented indentation to characterize the mechanical properties of both biological tissues and engineered scaffolds with interfaces between materials that contain significant changes in mechanical properties. In this study, finite element simulations and reference samples are developed that characterize how accurately indentation measures the modulus of a material as it varies with distance across a continuous interface between dissimilar tissues with multiple orders of magnitude difference in properties. Finite element simulations accurately predicted discrepancies between the modulus function across an interface observed by indentation and the true modulus function of the material and hence allow us to understand the limits of instrumented indentation as a technique for quantifying gradual changes in material properties. It was found that in order to accurately investigate mechanical property variations in tissues with significant modulus heterogeneity the indenter size should be less than 10 percent of the expected length scale of the modulus variations.

  18. Characterizing Multiscale Mechanical Properties of Brain Tissue Using Atomic Force Microscopy, Impact Indentation, and Rheometry.

    PubMed

    Canovic, Elizabeth Peruski; Qing, Bo; Mijailovic, Aleksandar S; Jagielska, Anna; Whitfield, Matthew J; Kelly, Elyza; Turner, Daria; Sahin, Mustafa; Van Vliet, Krystyn J

    2016-09-06

    To design and engineer materials inspired by the properties of the brain, whether for mechanical simulants or for tissue regeneration studies, the brain tissue itself must be well characterized at various length and time scales. Like many biological tissues, brain tissue exhibits a complex, hierarchical structure. However, in contrast to most other tissues, brain is of very low mechanical stiffness, with Young's elastic moduli E on the order of 100s of Pa. This low stiffness can present challenges to experimental characterization of key mechanical properties. Here, we demonstrate several mechanical characterization techniques that have been adapted to measure the elastic and viscoelastic properties of hydrated, compliant biological materials such as brain tissue, at different length scales and loading rates. At the microscale, we conduct creep-compliance and force relaxation experiments using atomic force microscope-enabled indentation. At the mesoscale, we perform impact indentation experiments using a pendulum-based instrumented indenter. At the macroscale, we conduct parallel plate rheometry to quantify the frequency dependent shear elastic moduli. We also discuss the challenges and limitations associated with each method. Together these techniques enable an in-depth mechanical characterization of brain tissue that can be used to better understand the structure of brain and to engineer bio-inspired materials.

  19. A Micro-Indentation Method for Assessment of TBC Bond Coat Systems

    SciTech Connect

    Feng, C.; Alvin, M.A.; Kang, B.S.

    2007-09-01

    Under elevated temperatures, the presence of high thermal stresses along or within thermal barrier coatings (TBCs) can lead to the development of creep cavities and wedge cracks which can ultimately form microcracks and result in interfacial debonding in the TBC bond coat region. Defects detection on the subsurface TBC layers has shown some progress by using laser scattering and other non-destructive testing (NDT) methods. However, the difficulty of determining interfacial debonding and degradation assessment of the TBC remains a significant hurdle to overcome due to the TBC’s complex multi-layer structure, and frequently rough surface morphology. The TBC has high attenuation, high porosity, and many interfaces of different materials, which are the challenges that need to be overcome by the NDT techniques. Based on our recent research development of a Transparent Indenter Measurement (TIM) method, we have further developed a simplified micro-indentation technique for mechanical property degradation measurement and debonding/spallation detection of TBC bond coat in this research effort. NETL bond-coated coupons were subjected to cumulative rapid thermal cycling, and after every 100 high temperature thermal cycles, micro-indentation tests were conducted on bond-coat superalloy and single crystal coupons. Preliminary test results showed that the measured surface stiffness responses of the NETL bond coat decreased with exposure to continued thermal cycling. Currently these data are being correlated with microstructural analyses to address potential degradation and/or spalling of the applied NETL bond coat.

  20. A multi-sphere indentation method to determine Young's modulus of soft polymeric materials based on the Johnson-Kendall-Roberts contact model

    NASA Astrophysics Data System (ADS)

    Peng, Xiaoling; Huang, Jianyong; Deng, Hao; Xiong, Chunyang; Fang, Jing

    2011-02-01

    Tissue cells can sense mechanical properties of their surroundings, which, in vitro, generally refer to substrates coated with proteins. The elastic moduli of soft polymers used as substrates have been proved to affect many cellular processes, such as migration, development, and even differentiation. In this note, we present a cost-effective experimental design by using multi-sphere indentations to find the relation between indentation depth and sphere radius, and then apply the Johnson-Kendall-Roberts (JKR) contact theory with consideration of adhesive work to fit the experimental results so as to assess the value of Young's modulus. Two compliant polymeric materials, polyacrylamide gels and polydimethylsiloxane elastomers, are tested with this method. The results are in good agreement with those reported by previous experiments. Comparisons between JKR and traditional Hertz fittings highlight the demand for taking adhesive forces into account to measure Young's modulus of soft sticky polymeric substrates in cell-substrate interaction studies.

  1. Variability of in vivo reference point indentation in skeletally mature inbred rats.

    PubMed

    Allen, Matthew R; Newman, Christopher L; Smith, Eric; Brown, Drew M; Organ, Jason M

    2014-07-18

    Reference point indentation (RPI) has emerged as a novel tool to measure material-level biomechanical properties in vivo. Human studies have been able to differentiate fracture versus non-fracture patients while a dog study has shown the technique can differentiate drug treatment effects. The goal of this study was to extend this technology to the in vivo measurement of rats, one of the most common animal models used to study bone, with assessment of intra- and inter-animal variability. Seventy-two skeletally mature male Sprague-Dawley rats were subjected to in vivo RPI on the region between the tibial diaphysis and proximal metaphysis. RPI data were assessed using a custom MATLAB program to determine several outcome parameters, including first cycle indentation distance (ID-1st), indentation distance increase (IDI), total indentation distance (TID), first cycle unloading slope (US-1st), and first cycle energy dissipation (ED-1st). Intra-animal variability ranged from 13% to 21% with US-1st and Tot Ed 1st-L being the least variable properties and IDI the most highly variable. Inter-animal variability ranged from 16% (US-1st) to 25% (ED-1st and IDI). Based on these data, group size estimates would need to range from 9 to 18/group to achieve sufficient power for detecting a 25% difference in a two-group experiment. Repeat tests on the contralateral limb of a small cohort of animals (n=17) showed non-significant differences over 28 days ranging from -6% to -18%. These results provide important data on RPI variability (intra- and inter-animal) in rats that can be used to properly power future experiments using this technique.

  2. Deciphering indented impressions on plastic.

    PubMed

    Brown, Sharon; Klein, Asne; Chaikovsky, Alan

    2003-07-01

    The questioned document laboratory is often called upon to decipher writing that has been erased, obliterated, or that has faded. In cases like these, the original writing is no longer legible to the naked eye, but may be enhanced using various light sources. Certain remnants of the ink's components absorb into the substrate's fibers and can be visualized, usually as luminescence or absorbance. A case is described here that involved the theft of a credit card. An empty plastic credit card holder was found in the possession of a suspect, and as submitted for examination. Indented impressions could be discerned on its clear plastic window and presumably originated from the credit card that had been held in the envelope. These indented impressions were deciphered in the hope that they would reveal enough details from the credit card to establish a connection between the plastic envelope and the stolen credit card. With methods generally utilized in the toolmarks and materials laboratory and the photography laboratory of the Israel Police, most of the indented impressions on the plastic were deciphered and a connection between the plastic envelope and the stolen credit card was demonstrated.

  3. Indenter geometry effects on the measurements of mechanical properties by nanoindentation with sharp indenters

    SciTech Connect

    Tsui, T.Y.; Pharr, G.M.; Oliver, W.C.

    1996-05-01

    The measurement of mechanical properties by nanoindentation methods is most often conducted using indenters with the Berkovich geometry (a triangular pyramid) or with a sphere. These indenters provide a wealth of information, but there are certain circumstances in which it would be useful to make measurements with indenters of other geometries. We have recently explored how the measurement of hardness and elastic modulus can be achieved using sharp indenters other than the Berkovich. Systematic studies in several materials were conducted with a Vickers indenter, a conical indenter with a half-included tip angle of 70.3{degrees}, and the standard Berkovich indenter. All three indenters are geometrically similar and have nominally the same area-to-depth relationship, but there are distinct differences in the behavior of each. Here, we report on the application of these indenters in the measurement of hardness and elastic modulus by nanoindentation methods and some of the difficulties that occur.

  4. Traceable Micro-Force Sensor for Instrumented Indentation Calibration

    SciTech Connect

    Smith, D T; Shaw, G A; Seugling, R M; Xiang, D; Pratt, J R

    2007-04-02

    Instrumented indentation testing (IIT), commonly referred to as nanoindentation when small forces are used, is a popular technique for determining the mechanical properties of small volumes of material. Sample preparation is relatively easy, usually requiring only that a smooth surface of the material to be tested be accessible to a contact probe, and instruments that combine sophisticated automation with straightforward user interfaces are available commercially from several manufacturers. In addition, documentary standards are now becoming available from both the International Standards Organization (ISO 14577) and ASTM International (E28 WK382) that define test methods and standard practices for IIT, and will allow the technique to be used to produce material property data that can be used in product specifications. These standards also define the required level of accuracy of the force data produced by IIT instruments, as well as methods to verify that accuracy. For forces below 10 mN, these requirements can be difficult to meet, particularly for instrument owners who need to verify the performance of their instrument as it is installed at their site. In this paper, we describe the development, performance and application of an SI-traceable force sensor system for potential use in the field calibration of commercial IIT instruments. The force sensor itself, based on an elastically deforming capacitance gauge, is small enough to mount in a commercial instrument as if it were a test specimen, and is used in conjunction with an ultra-high accuracy capacitance bridge. The sensor system is calibrated with NIST-traceable masses over the range 5.0 {micro}N through 5.0 mN. We will present data on its accuracy and precision, as well its potential application to the verification of force in commercial instrumented indentation instruments.

  5. Indentation of an osteochondral repair: sensitivity to experimental variables and boundary conditions.

    PubMed

    Smith, C L; Mansour, J M

    2000-11-01

    The sensitivity of the affects of indenter radius, defect depth, cartilage permeability and flow boundary conditions, on the indentation testing of a repairing osteochondral defect was investigated. Since the boundary condition on the flow across the cartilage repair-subchondral bone interface is not known, the effects of two different conditions were investigated: free-flow and no-flow. A poroelastic finite element model of an osteochondral defect at different stages of the repair process was developed using dimensions typical of the rabbit knee. Results showed when the radius of the indenter was much less than the thickness of the cartilage the sensitivity of the indentation displacement to flow boundary conditions decreased. Simulated indentation displacement was insensitive to bone regeneration up to 50% of the initial defect depth, which suggests that only the properties of the material in the upper-half of the defect are being evaluated. Small variations in permeability had little affect on the simulated indentation. In a fully repaired defect, the simulated indentation is independent of the boundary condition. However, while the defect is in the process of repair and the regenerated cartilage is deeper than the host, indentation is sensitive to the flow boundary condition. Based on these results, and feasible experimental conditions, we conclude that the boundary condition on the repair-subchondral bone interface must be known in all cases except when the defect approaches full repair, if accurate estimates of material properties are to be obtained from indentation.

  6. Characterization of Local Mechanical Properties of Polymer Thin Films and Polymer Nanocomposites via AFM indentations

    NASA Astrophysics Data System (ADS)

    Cheng, Xu

    AFM indentation has become a tool with great potential in the characterization of nano-mechanical properties of materials. Thanks to the nanometer sized probes, AFM indentation is capable of capturing the changes of multiple properties within the range of tens of nanometers, such task would otherwise be difficult by using other experiment instruments. Despite the great potentials of AFM indentation, it operates based on a simple mechanism: driving the delicate AFM probe to indent the sample surface, and recording the force-displacement response. With limited information provided by AFM indentation, efforts are still required for any practice to successfully extract the desired nano-scale properties from specific materials. In this thesis, we focus on the mechanical properties of interphase between polymer and inorganic materials. It is known that in nanocomposites, a region of polymer exist around nanoparticles with altered molecular structures and improved properties, which is named as interphase polymer. The system with polymer thin films and inorganic material substrates is widely used to simulate the interphase effect in nanocomposites. In this thesis, we developed an efficient and reliable method to process film/substrate samples and characterize the changes of local mechanical properties inside the interphase region with ultra-high resolution AFM mechanical mapping technique. Applying this newly developed method, the interphase of several film/substrate pairs were examined and compared. The local mechanical properties on the other side of the polymer thin film, the free surface side, was also investigated using AFM indentation equipped with surface modified probes. In order to extract the full spectrum of local elastic modulus inside the surface region in the range of only tens of nanometers, the different contact mechanics models were studied and compared, and a Finite Element model was also established. Though the film/substrate system has been wide used as

  7. In search of validated measurements of the properties of viscoelastic materials by indentation with sharp indenters

    NASA Astrophysics Data System (ADS)

    Monclus, M. A.; Jennett, N. M.

    2011-03-01

    Industry requires validated high-resolution methods for the characterisation viscoelastic materials to obtain local (or small volume) polymer properties for input to part design (e.g. micro-mouldings, packaging, coatings, composite interfaces, etc.). This paper examines the capability of dynamic (oscillatory) indentation (DI) and simple force-controlled "force-increase ramp and hold" indentation creep methods to deliver equivalent results compatible with those obtained on the same materials by dynamic mechanical analysis (DMA) and uniaxial tensile testing. We test three commercial polymers (two photo stress materials and polyoxymethylene (POM)). A creep analysis based on conical-pyramidal elastic-viscoelastic correspondence 1 and a three-element standard linear solid (SLS) model is used to give an output of two elastic moduli (E 1 and E 2) and a viscosity (η). Mathematically, E 1, E 2 and η can be used to calculate loss and storage modulus values at any frequency without further measurement. Indentation creep results obtained using various maximum forces (P max) and two indenter geometries (pyramidal (Berkovich) and conical (0.6 µm tip radius)) are compared with DI and DMA measurements at 40 Hz on the same materials and with tensile data from the POM sample fitted using the same SLS creep model. Between-method agreement of storage modulus values for all materials is sufficient to suggest that a route to validated measurement methods is available. However, simple models (as commonly used in DI and DMA) are inadequate to generate reproducible quantitative values for viscosity parameters. We show that more complex models are necessary to successfully produce loss/viscosity parameters that are equivalent.

  8. Stress measurement with non-indentation

    SciTech Connect

    Jakus, K.; Evans, N.D.; Hay, J.C.

    1998-11-01

    The feasibility of using nano-indentation to measure residual stress in glasses was studied. Indents were placed on the side of flexure specimens at four different distances from the neutral axis while the specimens were under load in four-point-bending. Three different glasses (soda-lime, boro-silicate, and fused silica) were indented with a cube-corner indenter using 2 to 30 mN indentation loads. A high resolution scanning electron microscope was used to measure the length of the cracks emanating from the corners of the indents while the specimen remained under load. The measured crack lengths were correlated to the local stress using indentation theory. For the correlation, elastic beam theory was used to calculate the magnitude of the local stress at the indentation sites. Results derived from crack lengths were in good agreement with local stress within experimental scatter. However, this scatter was found to be rather large as a result of the stochastic nature of crack formation. It can be concluded from this study that nano-indentation can be used to measure residual surface stresses with high spatial resolution provided that a sufficient number of indents are used to assure good statistical accuracy.

  9. Using residual indent morphology to measure the tilt between the triangular pyramid indenter and the sample surface

    NASA Astrophysics Data System (ADS)

    Huang, Hu; Zhao, Hongwei; Shi, Chengli; Zhang, Lin

    2013-10-01

    The tilt between the indenter and the sample surface will affect the measuring results and the accuracy of nanoindentation and scratches. In this paper, the potential factors leading to the tilt are firstly discussed. Then, based on the Cartesian coordinate system at the tip of the triangular pyramid indenter established by Kashani and Madhavan, a theoretical approach is proposed to measure the tilt angle η and the rotation angle ξ of the surface normal \\hat n using the residual indent morphology. In order to reduce the input parameters for solving the equations and also make the equations dimensionless, two coefficients m and n are defined. One practical application is given to verify the feasibility of the theoretical approach. The theoretical approach is simplified and unified by analyzing the calculation results. The presented theoretical approach can be used to measure the tilt between the indenter and the sample surface indirectly, which is the premise for the adjustment of indentation instruments or the practical correction of the tilt.

  10. Reference point indentation study of age-related changes in porcine femoral cortical bone.

    PubMed

    Rasoulian, Ramin; Raeisi Najafi, Ahmad; Chittenden, Michael; Jasiuk, Iwona

    2013-06-21

    The reference point indentation (RPI) method is a microindentation technique involving successive indentation cycles. We employed RPI to measure average stiffness (Ave US), indentation distance increase (IDI), total indentation distance (TID), average energy dissipated (Ave ED), and creep indentation distance (CID) of swine femoral cortical bone (mid-diaphysis) as a function of age (1, 3.5, 6, 14.5, 24, and 48 months) and loading directions (longitudinal and transverse). The Ave US increases with animal age, while the IDI, TID, Ave ED, and CID decrease with age, for both longitudinal (transverse surface) and transverse (periosteal surface) loading directions. Longitudinal measurements generally give higher Ave US and lower IDI and TID values compared to transverse measurements. The RPI measurements show similar trends to those obtained using nanoindentation test, and ash and water content tests.

  11. Competing indentation deformation mechanisms in glass using different strengthening methods

    NASA Astrophysics Data System (ADS)

    Luo, Jian; Lezzi, Peter; Vargheese, K. Deenamma; Tandia, Adama; Harris, Jason; Mauro, John

    2016-11-01

    Chemical strengthening via ion exchange, thermal tempering, and lamination are proven techniques for strengthening of oxide glasses. For each of these techniques, the strengthening mechanism is conventionally ascribed to the linear superposition of the compressive stress profile on the glass surface. However, in this work we use molecular dynamics simulations to reveal the underlying indentation deformation mechanism beyond the simple linear superposition of compressive and indentation stresses. In particular, the plastic zone can be dramatically different from the commonly assumed hemispherical shape, which leads to a completely different stress field and resulting crack system. We show that the indentation-induced fracture is controlled by two competing mechanisms: the compressive stress itself and a potential reduction in free volume that can increase the driving force for crack formation. Chemical strengthening via ion exchange tends to escalate the competition between these two effects, while thermal tempering tends to reduce it. Lamination of glasses with differential thermal expansion falls in between. The crack system also depends on the indenter geometry and the loading stage, i.e., loading vs. after unloading. It is observed that combining thermal tempering or high free volume content with ion exchange or lamination can impart a relatively high compressive stress and reduce the driving force for crack formation. Therefore, such a combined approach might offer the best overall crack resistance for oxide glasses.

  12. Monitoring and control of electrode indentation

    SciTech Connect

    Killian, M.L.; Hutchenreuther, A.J.

    1994-12-31

    Unregulated electrode indentation, the dent caused by electrodes pushing into the material surface during resistance welding, is undesirable. However, indentation correlates to high weld strength. Working with Atek, Eaton engineers added a point sensor to a resistance welder equipped with a modified Atek Truamp III controller. During a weld the sensor acquires displacement information. Processed displacement data provides feedback for monitoring the weld and for controlling the current and/or time required to reach the desired indentation. Welds characterized by dynamically measured indentations were tested for shear strength. This new approach to resistance weld monitoring and control uses an off-axis sensor to measure indentation and to provide feedback for adjusting current or time dynamically. A point sensor directed at an area nearby the welding electrode continually measures distance and supplies this data to the controller. The controller adjusts welding current or number of cycles to keep the real time identification tracking to the target amount of indentation. This approach represents a technical departure from previous work that relies on expansion data for feedback. An off-axis point sensor providing feedback for dynamically varying current or time offers a viable method to obtain specific amounts of electrode indentation. Electrode indentation, not expansion, correlates directly to weld strength. Controlling electrode indentation is a robust method to assure the quality and strength of production resistance welds.

  13. Measurement of corneal tangent modulus using ultrasound indentation.

    PubMed

    Wang, Li-Ke; Huang, Yan-Ping; Tian, Lei; Kee, Chea-Su; Zheng, Yong-Ping

    2016-09-01

    Biomechanical properties are potential information for the diagnosis of corneal pathologies. An ultrasound indentation probe consisting of a load cell and a miniature ultrasound transducer as indenter was developed to detect the force-indentation relationship of the cornea. The key idea was to utilize the ultrasound transducer to compress the cornea and to ultrasonically measure the corneal deformation with the eyeball overall displacement compensated. Twelve corneal silicone phantoms were fabricated with different stiffness for the validation of measurement with reference to an extension test. In addition, fifteen fresh porcine eyes were measured by the developed system in vitro. The tangent moduli of the corneal phantoms calculated using the ultrasound indentation data agreed well with the results from the tensile test of the corresponding phantom strips (R(2)=0.96). The mean tangent moduli of the porcine corneas measured by the proposed method were 0.089±0.026MPa at intraocular pressure (IOP) of 15mmHg and 0.220±0.053MPa at IOP of 30mmHg, respectively. The coefficient of variation (CV) and intraclass correlation coefficient (ICC) of tangent modulus were 14.4% and 0.765 at 15mmHg, and 8.6% and 0.870 at 30mmHg, respectively. The preliminary study showed that ultrasound indentation could be applied to the measurement of corneal tangent modulus with good repeatability and improved measurement accuracy compared to conventional surface displacement-based measurement method. The ultrasound indentation can be a potential tool for the corneal biomechanical properties measurement in vivo.

  14. An Improved Approach to Fracture Toughness Assessment of Brittle Coating on Ductile Substrate Systems under Indentation

    NASA Astrophysics Data System (ADS)

    Demidova, Natalia V.

    Fracture toughness is an important material property that determines the structural integrity of a component with pre-existing or service-generated flaws. In the present research, an indentation-based method and the associated fracture mechanics model are proposed for fracture toughness assessment of brittle coating/ductile substrate systems. The proposed models consider well-developed radial/median cracks generated under sharp indentation, despite that the crack formation process may have gone through crack initiation and propagation phases. For generality, the geometry of a well-developed crack is assumed to be semi-elliptical in shape. The driving force of the crack is considered to stem from the residual plastic zone expansion under the indenter, as well as the far-field Boussinesq (elastic) stress. Three well-defined configurations are studied. For the first configuration, a crack with a depth of less than 7% of the coating thickness is considered. In this case, the problem is treated as the one for the monolithic material with the coating material properties. For the second configuration, a crack that runs deeper than 7% of the coating thickness but is still within the coating layer is analyzed. In this case, the composite hardness is introduced into the analysis to account for the influence of the substrate material properties; and furthermore, an interface correction factor is proposed to take into account the presence of the coating/substrate interface and its influence on the stress intensity factor of the well-developed elliptical cracks. For the third configuration, a crack penetrating into the substrate is considered. In this case, based on the condition of deformation compatibility across the coating/substrate interface, the bulk modulus for the coating/substrate system is introduced into the analysis. A series of indentation tests are conducted on a WC/10Co/4Cr coating/1080 low carbon steel substrate specimen, which is a brittle coating on a ductile

  15. Indentation analysis of nano-particle using nano-contact mechanics models during nano-manipulation based on atomic force microscopy

    NASA Astrophysics Data System (ADS)

    Daeinabi, Khadijeh; Korayem, Moharam Habibnejad

    2011-03-01

    Atomic force microscopy is applied to measure intermolecular forces and mechanical properties of materials, nano-particle manipulation, surface scanning and imaging with atomic accuracy in the nano-world. During nano-manipulation process, contact forces cause indentation in contact area between nano-particle and tip/substrate which is considerable at nano-scale and affects the nano-manipulation process. Several nano-contact mechanics models such as Hertz, Derjaguin-Muller-Toporov (DMT), Johnson-Kendall-Roberts-Sperling (JKRS), Burnham-Colton-Pollock (BCP), Maugis-Dugdale (MD), Carpick-Ogletree-Salmeron (COS), Pietrement-Troyon (PT), and Sun et al. have been applied as the continuum mechanics approaches at nano-scale. In this article, indentation depth and contact radius between tip and substrate with nano-particle for both spherical and conical tip shape during nano-manipulation process are analyzed and compared by applying theoretical, semiempirical, and empirical nano-contact mechanics models. The effects of adhesion force, as the main contrast point in different nano-contact mechanics models, on nano-manipulation analysis is investigated for different contact radius, and the critical point is discussed for mentioned models.

  16. Prediction of Indentation Behavior of Superelastic TiNi

    NASA Astrophysics Data System (ADS)

    Neupane, Rabin; Farhat, Zoheir

    2014-09-01

    Superelastic TiNi shape memory alloys have been extensively used in various applications. The great interest in TiNi alloys is due to its unique shape memory and superelastic effects, along with its superior wear and dent resistance. Assessment of mechanical properties and dent resistance of superelastic TiNi is commonly performed using indentation techniques. However, the coupling of deformation and reversible martensitic transformation of TiNi under indentation conditions makes the interpretation of results challenging. An attempt is made to enhance current interpretation of indentation data. A load-depth curve is predicted that takes into consideration the reversible martensitic transformation. The predicted curve is in good agreement with experimental results. It is found in this study that the elastic modulus is a function of indentation depth. At shallow depths, the elastic modulus is high due to austenite dominance, while at high depths, the elastic modulus drops as the depth increases due to austenite to martensite transition, i.e., martensite dominance. It is also found that TiNi exhibits superior dent resistance compared to AISI 304 steel. There is two orders of magnitude improvement in dent resistance of TiNi in comparison to AISI 304 steel.

  17. Indentation analysis of biphasic articular cartilage: nonlinear phenomena under finite deformation.

    PubMed

    Suh, J K; Spilker, R L

    1994-02-01

    The nonlinear indentation response of hydrated articular cartilage at physiologically relevant rates of mechanical loading is studied using a two-phase continuum model of the tissue based on the theory of mixtures under finite deformation. The matrix equations corresponding to the governing mixture equations for this nonlinear problem are derived using a total Lagrangian penalty finite element method, and solved using a predictor-corrector iteration within a modified Newton-Raphson scheme. The stress relaxation indentation problem is examined using either a porous (free draining) indenter or solid (impermeable) indenter under fast and slow compression rates. The creep indentation problem is studied using a porous indenter. We examine the finite deformation response and compare with the response obtained using the linear infinitesimal response. Differences between the finite deformation response and the linear response are shown to be significant when the compression rate is fast or when the indenter is impermeable. The finite deformation model has a larger ratio of peak-to-equilibrium reaction force, and higher relaxation rate than the linear model during the early relaxation period, but a similar relaxation time. The finite deformation model predicts a slower creep rate than the linear model, as well as a smaller equilibrium creep displacement. The pressure distribution below the indenter, particularly near the loaded surface is also larger with the finite deformation model.

  18. Hybrid method for determining material properties from instrumented micro-indentation experiments

    NASA Astrophysics Data System (ADS)

    Chen, Y.-M.; Ruff, A. W.; Dally, J. W.

    1994-05-01

    The impact code EPIC was employed to study the relationship between the applied force and the penetration depth in a micrometer-scale indentation experiment with oxygen free high conductivity (OFHC) copper. EPIC is an elastic-plastic finite element code that uses a Lagrangian formulation and triangular mesh, which can accommodate large deformation without the need to remesh during the computation process. By fitting the force-penetration curves for a triangular indenter with second degree polynomials, it was demonstrated that the fit changed with two material constants in the constitutive equation. A systematic procedure for determining the material constants is described that is based on matching either the slope or the curvature of the force penetration depth curves from numerical simulation and experiments. It is concluded that material constants can be determined from indentation data obtained using pyramidal or spherical indenters as well as a flat-ended indenter.

  19. In situ spectroscopic study of the plastic deformation of amorphous silicon under nonhydrostatic conditions induced by indentation

    SciTech Connect

    Gerbig, Yvonne B.; Michaels, C. A.; Bradby, Jodie E.; Haberl, Bianca; Cook, Robert F.

    2015-12-17

    Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique (IIT). The occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were observed. Furthermore, the obtained experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a model for the deformation behavior of a-Si under indentation loading.

  20. Deducing the stress-strain response of anisotropic Zr-2.5%Nb pressure tubing by spherical indentation testing

    NASA Astrophysics Data System (ADS)

    Oviasuyi, R. O.; Klassen, R. J.

    2013-01-01

    In this paper we developed a method of analysis by which the average stress-plastic strain flow curve of mechanically anisotropic materials can be deduced from spherical indentation test data. Our analysis is based upon spherical indentation tests performed on the extruded and cold-drawn Zr-2.5%Nb CANDU pressure tube material over the range of temperature from 25 °C to 300 °C. The indentation force and depth data were analyzed and σavg and ɛavg were calculated using previously reported equations developed for spherical indentation of isotropic material which were then modified, by incorporating the appropriate Hill's anisotropy coefficients, to characterize the anisotropic yield stress of the indented material. The resulting flow curves were dependent on indentation direction and correspond closely with flow curves obtained from previously reported conventional uniaxial stress tests performed on the Zr-2.5%Nb material. Indentation tests performed with large, 200 μm, and small, 40 μm, diameter spheres indicate that for small diameter indentations, when the indentation depth is less than several micrometers, the calculated σavg is heavily influenced by the depth dependence of the yield strength of the indented material.

  1. Modeling of Weak Fused Optical Fibers Using Vickers Indentations

    NASA Astrophysics Data System (ADS)

    Lin, Bochien

    This thesis addresses issues of modeling mechanical behavior of flaw containing weak silica fibers. Vickers indentation is used to model "nature" flaws present on fiber surface, especially for the contact damages. Novel and reliable experimental techniques have been developed that permit the inert (liquid nitrogen) strength of air -indented fiber to be determined across a broad range of values which encompasses the threshold region for radial crack formation. Inert strength of subthreshold indents can be simply modeled by a Griffith flaw of a size equal the indent size and the residual stresses have negligible influence, except for the long term behavior under low applied stress in a fatiguing environment where the strength is comparable to the magnitude of the residual stresses. A low n-value of ~11 is observed in the pH 7 buffer, extended from the subthreshold to the threshold regions. Neglecting this fact will introduce substantial error for lifetime predictions. The behavior of fatigue strength in alkali-hydroxides solutions suggests that subthreshold flaws degrade by surface mechanisms, rather than mechanisms occurring around the crack tip and further implies that subthreshold indents, at least in this regime, act simply as surface shape discontinuities. Fatigue strength exhibits an asymptotic curve-down behavior at the threshold in the alkali-hydroxides that implies the existence of propagation controlled subthreshold behavior. Long term aging improves mechanical properties, i.e., increase in strength and n, except for near threshold right in the region of interest. Residual stress release and crack tip blunting take place concurrently during zero -stress aging and crack tip blunting is dominant for the increase of strength and n-value. Several fracture models have been fit with experimental data for their validity for both sub- and postthreshold flaws.

  2. Morphometric Analysis of Major Catchments Draining the Adriatic Indenter

    NASA Astrophysics Data System (ADS)

    Robl, Jörg; Heberer, Bianca; Neubauer, Franz; Prasicek, Günther; Hergarten, Stefan

    2016-04-01

    Topography and relief in collisional orogens such as the European Alps result from the interplay of uplift driven by plate convergence and crustal shortening, and erosional surface processes that act along evolving topographic gradients and counteract topography formation. Due to ongoing indentation of the Adriatic indenter into the Eastern Alps, the eastern segment of the Adriatic indenter is one of the tectonically most active zones of the Central Mediterranean region. The region is characterized by numerous earthquakes, distinct spatial gradients in recent uplift rates and exhumation level, and active faulting. However, the predominance of carbonaceous lithology hindered low-temperature thermochronology and cosmogenic nuclide dating, so that timing, rates and drivers of south-alpine topography development are still not well constrained. Further on, a systematic morphometric analysis of rivers draining the south-alpine indenter is still missing. In this study we fill this gap and investigate the interplay of tectonics and climate by a morphometric analysis of drainage systems of the eastern segment of the Adriatic indenter. We systematically extract a variety of characteristic channel metrics of four major drainage systems (Adige, Brenta, Piave, and Tagliamento) of this domain and interpret the morphometric results in terms of (a) lithological effects such as erodibility contrasts and karstification, (b) spatially variable uplift rates, (c) base level lowering caused by glacial erosion and possible Messinian preconditioning, and (d) the migration of drainage divides. We find a clear correlation between the normalized steepness index (ksn) and bedrock type. ksn - values are systematically increased whenever rivers incise into the basement of the south-alpine indenter. However, the outcrop of the basement indicates a high level of exhumation and thus the highest overall uplift of the domain such that both increased uplift rates and low rock erodibility may be

  3. Water jet indentation for local elasticity measurements of soft materials.

    PubMed

    Chevalier, N R; Dantan, Ph; Gazquez, E; Cornelissen, A J M; Fleury, V

    2016-01-01

    We present a novel elastography method for soft materials (100Pa-100kPa) based on indentation by a μm-sized water jet. We show that the jet creates a localized deformation ("cavity") of the material that can be easily visualized. We study experimentally how cavity width and depth depend on jet speed, height, incidence angle and sample elasticity. We describe how to calibrate the indenter using gels of known stiffness. We then demonstrate that the indenter yields quantitative elasticity values within 10% of those measured by shear rheometry. We corroborate our experimental findings with fluid-solid finite-element simulations that quantitatively predict the cavity profile and fluid flow lines. The water jet indenter permits in situ local stiffness measurements of 2D or 3D gels used for cell culture in physiological buffer, is able to assess stiffness heterogeneities with a lateral resolution in the range 50-500μm (at the tissue scale) and can be assembled at low cost with standard material from a biology laboratory. We therefore believe it will become a valuable method to measure the stiffness of a wide range of soft, synthetic or biological materials.

  4. Evaluation of Fracture Toughness of Tantalum Carbide Ceramic Layer: A Vickers Indentation Method

    NASA Astrophysics Data System (ADS)

    Song, Ke; Xu, Yunhua; Zhao, Nana; Zhong, Lisheng; Shang, Zhao; Shen, Liuliu; Wang, Juan

    2016-07-01

    A tantalum carbide (TaC) ceramic layer was produced on gray cast iron matrix by in situ technique comprising a casting process and a subsequent heat treatment at 1135 °C for 45 min. Indentation fracture toughness in TaC ceramic layer was determined by the Vickers indentation test for various loads. A Niihara approach was chosen to assess the fracture toughness of TaC ceramic layer under condition of the Palmqvist mode in the experiment. The results reveal that K IC evaluation of TaC ceramic layer by the Vickers indentation method strongly depends on the selection of crack system and K IC equations. The critical indentation load for Vickers crack initiation in TaC ceramic layer lies between 1 and 2 N and the cracks show typical intergranular fracture characteristics. Indentation fracture toughness calculated by the indentation method is independent of the indentation load on the specimen. The fracture toughness of TaC ceramic layer is 6.63 ± 0.34 MPa m1/2, and the toughening mechanism is mainly crack deflection.

  5. Measuring the mechanical properties of plant cells by combining micro-indentation with osmotic treatments.

    PubMed

    Weber, Alain; Braybrook, Siobhan; Huflejt, Michal; Mosca, Gabriella; Routier-Kierzkowska, Anne-Lise; Smith, Richard S

    2015-06-01

    Growth in plants results from the interaction between genetic and signalling networks and the mechanical properties of cells and tissues. There has been a recent resurgence in research directed at understanding the mechanical aspects of growth, and their feedback on genetic regulation. This has been driven in part by the development of new micro-indentation techniques to measure the mechanical properties of plant cells in vivo. However, the interpretation of indentation experiments remains a challenge, since the force measures results from a combination of turgor pressure, cell wall stiffness, and cell and indenter geometry. In order to interpret the measurements, an accurate mechanical model of the experiment is required. Here, we used a plant cell system with a simple geometry, Nicotiana tabacum Bright Yellow-2 (BY-2) cells, to examine the sensitivity of micro-indentation to a variety of mechanical and experimental parameters. Using a finite-element mechanical model, we found that, for indentations of a few microns on turgid cells, the measurements were mostly sensitive to turgor pressure and the radius of the cell, and not to the exact indenter shape or elastic properties of the cell wall. By complementing indentation experiments with osmotic experiments to measure the elastic strain in turgid cells, we could fit the model to both turgor pressure and cell wall elasticity. This allowed us to interpret apparent stiffness values in terms of meaningful physical parameters that are relevant for morphogenesis.

  6. Ceramic wear in indentation and sliding

    NASA Technical Reports Server (NTRS)

    Miyoshi, K.; Buckley, D. H.

    1984-01-01

    The various wear mechanisms involved with single-crystal ceramic materials in indentation and in sliding contacts. Experiments simulating interfacial events have been conducted with hemispherical, conical and pyramidal indenters (riders). With spherical riders, under either abrasive or adhesive conditions, two types of fracture pits have been observed. First, spherical-shaped fracture pits and wear particles are found as a result of either indenting or sliding. These are shown to be due to a spherical-shaped fracture along the circular or spherical stress trajectories. Second, polyhedral fracture pits and debris, produced by anisotropic fracture, and also found both during indenting and sliding. These are primarily controlled by surface and subsurface cracking along cleavage planes. Several quantitative results have also been obtained from this work. For example, using a pyramidal diamond, crack length of Mn-Zn ferrite in the indentation process grows linearly with increasing normal load. Moreover, the critical load to fracture both in indentation and sliding is essentially isotropic and is found to be directly proportional to the indenter radius.

  7. [Evidence-based TEP technique].

    PubMed

    Köckerling, F

    2017-01-13

    The guidelines of all international hernia societies recommend as procedures of choice the laparoendoscopic techniques total extraperitoneal patch plasty (TEP) and transabdominal preperitoneal patch plasty (TAPP) as well as the open Lichtenstein operation for elective inguinal hernia repair. The learning curve associated with the laparoendoscopic techniques, in particular TEP, is longer than that for the open Lichtenstein technique due to the complexity of the procedures. Accordingly, for laparoendoscopic techniques it is particularly important that the operations are conducted in a standardized manner in compliance with the evidence-based recommendations given for the technical details. When procedures are carried out in strict compliance with the guidelines of the international hernia societies, low rates of perioperative complications, complication-related reoperations, recurrences and chronic pain can be expected for TEP. Compliance with the guidelines can also positively impact mastery of the learning curve for TEP. The technical guidelines on TEP are based on study results and on the experiences of numerous experts; therefore, it is imperative that they are implemented in routine surgical practice.

  8. Full-surface deformation measurement of anisotropic tissues under indentation.

    PubMed

    Genovese, Katia; Montes, Areli; Martínez, Amalia; Evans, Sam L

    2015-05-01

    Inverse finite element-based analysis of soft biological tissues is an important tool to investigate their complex mechanical behavior and to develop physical models for medical simulations. Although there have recently been advances in dealing with the computational complexities of modeling biological materials, the collection of a sufficiently dense set of experimental data to properly capture their typically regionally varying properties still remains a critical issue. The aim of this work was to develop and test an optical system that combines 2D-Digital Image Correlation (DIC) and a novel Fringe Projection method with radial sensitivity (RFP) to test soft biological tissues under in vitro indentation. This system has the distinctive capability of using a single camera to retrieve the shape and 3D deformation of the whole upper surface of the indented sample without any blind measurement areas (with exception of the area under the indenter), with nominal depth and in-plane resolution of 0.05 mm and 0.004 mm, respectively. To test and illustrate the capabilities of the developed DIC/RFP system, the in vitro response to indentation of a homogeneous and isotropic latex foam is presented against the response of a slab of porcine ventricular myocardium, a highly in-homogeneous and anisotropic tissue. Our results illustrate the enhanced capabilities of the developed method to capture asymmetry in deformation with respect to standard indentation tests. This feature, together with the possibility of miniaturizing the system into a hand-held probe, makes this method potentially extendable to in vivo settings, alone or in combination with ultrasound measurements.

  9. A novel pillar indentation splitting test for measuring fracture toughness of thin ceramic coatings

    NASA Astrophysics Data System (ADS)

    Sebastiani, M.; Johanns, K. E.; Herbert, E. G.; Carassiti, F.; Pharr, G. M.

    2015-06-01

    The fracture toughness of thin ceramic films is an important material property that plays a role in determining the in-service mechanical performance and adhesion of this important class of engineering materials. Unfortunately, measurement of thin film fracture toughness is affected by influences from the substrate and the large residual stresses that can exist in the films. In this paper, we explore a promising new technique that potentially overcomes these issues based on nanoindentation testing of micro-pillars produced by focused ion beam milling of the films. By making the pillar diameter approximately equal to its length, the residual stress in the upper portion of the pillar is almost fully relaxed, and when indented with a sharp Berkovich indenter, the pillars fracture by splitting at reproducible loads that are readily quantified by a sudden displacement excursion in the load displacement behaviour. Cohesive finite element simulations are used for analysis and development of a simple relationship between the critical load at failure, pillar radius and fracture toughness for a given material. The main novel aspect of this work is that neither crack geometries nor crack sizes need to be measured post test. In addition, the residual stress can be measured at the same time with toughness, by comparison of the indentation results obtained on the stress-free pillars and the as-deposited film. The method is tested on three different hard coatings created by physical vapour deposition, namely titanium nitride, chromium nitride and a CrAlN/Si3N4 nanocomposite. Results compare well to independently measured values of fracture toughness for the three brittle films. The technique offers several benefits over existing methods.

  10. A novel pillar indentation splitting test for measuring fracture toughness of thin ceramic coatings

    DOE PAGES

    Sebastiani, Marco; Johanns, K. E.; Herbert, Erik G.; ...

    2014-05-16

    Fracture toughness is an important material property that plays a role in determining the in-service mechanical performance and adhesion of thin ceramic films. Unfortunately, measuring thin film fracture toughness is affected by influences from the substrate and the large residual stresses that can exist in the films. In this paper, we explore a promising new technique that potentially overcomes these problems based on nanoindentation testing of micro-pillars produced by focused ion beam milling of the films. By making the pillar diameter approximately equal to its length, the residual stress in the pillar’s upper portion is almost fully relaxed, and whenmore » indented with a sharp Berkovich indenter, the pillars fracture by splitting at reproducible loads that are readily quantified by a sudden displacement excursion in the load displacement behavior. Cohesive finite element simulations are used to analyze and develop, for a given material, a simple relation between the critical load at failure, pillar radius, and fracture toughness. The main novel aspect of this work is that neither crack geometries nor crack sizes need to be measured post test. Furthermore, the residual stress can be measured at the same time with toughness, by comparing the indentation results from the stress-free pillars and the as-deposited film. The method is tested on three different hard coatings formed by physical vapor deposition: titanium nitride, chromium nitride, and a CrAlN/Si3N4 nanocomposite. Results compare well to independently measured values of fracture toughness for the three brittle films. The technique offers several benefits over existing methods.« less

  11. A novel pillar indentation splitting test for measuring fracture toughness of thin ceramic coatings

    SciTech Connect

    Sebastiani, Marco; Johanns, K. E.; Herbert, Erik G.; Carassiti, Fabio; Pharr, George Mathews

    2014-05-16

    Fracture toughness is an important material property that plays a role in determining the in-service mechanical performance and adhesion of thin ceramic films. Unfortunately, measuring thin film fracture toughness is affected by influences from the substrate and the large residual stresses that can exist in the films. In this paper, we explore a promising new technique that potentially overcomes these problems based on nanoindentation testing of micro-pillars produced by focused ion beam milling of the films. By making the pillar diameter approximately equal to its length, the residual stress in the pillar’s upper portion is almost fully relaxed, and when indented with a sharp Berkovich indenter, the pillars fracture by splitting at reproducible loads that are readily quantified by a sudden displacement excursion in the load displacement behavior. Cohesive finite element simulations are used to analyze and develop, for a given material, a simple relation between the critical load at failure, pillar radius, and fracture toughness. The main novel aspect of this work is that neither crack geometries nor crack sizes need to be measured post test. Furthermore, the residual stress can be measured at the same time with toughness, by comparing the indentation results from the stress-free pillars and the as-deposited film. The method is tested on three different hard coatings formed by physical vapor deposition: titanium nitride, chromium nitride, and a CrAlN/Si3N4 nanocomposite. Results compare well to independently measured values of fracture toughness for the three brittle films. The technique offers several benefits over existing methods.

  12. From elasticity to capillarity in soft materials indentation

    NASA Astrophysics Data System (ADS)

    Pham, Jonathan T.; Schellenberger, Frank; Kappl, Michael; Butt, Hans-Jürgen

    2017-06-01

    For soft materials with Young's moduli below 100 kPa, quantifying mechanical and interfacial properties by small scale indentation is challenging because in addition to adhesion and elasticity, surface tension plays a critical role. Until now, microscale contact of very soft materials has only been studied by static experiments under zero external loading. Here we introduce a combination of the colloidal probe technique and confocal microscopy to characterize the force-indentation and force-contact radius relationships during microindentation of soft silicones. We confirm that the widespread Johnson-Kendall-Roberts theory must be extended to predict the mechanical contact for soft materials. Typically a liquid component is found within very soft materials. With a simple analytical model, we illustrate that accounting for this liquid surface tension can capture the contact behavior. Our results highlight the importance of considering liquid that is often associated with soft materials during small scale contact.

  13. Indentation of pressurized viscoplastic polymer spherical shells

    NASA Astrophysics Data System (ADS)

    Tvergaard, V.; Needleman, A.

    2016-08-01

    The indentation response of polymer spherical shells is investigated. Finite deformation analyses are carried out with the polymer characterized as a viscoelastic/viscoplastic solid. Both pressurized and unpressurized shells are considered. Attention is restricted to axisymmetric deformations with a conical indenter. The response is analyzed for various values of the shell thickness to radius ratio and various values of the internal pressure. Two sets of material parameters are considered: one set having network stiffening at a moderate strain and the other having no network stiffening until very large strains are attained. The transition from an indentation type mode of deformation to a structural mode of deformation involving bending that occurs as the indentation depth increases is studied. The results show the effects of shell thickness, internal pressure and polymer constitutive characterization on this transition and on the deformation modes in each of these regimes.

  14. Controlled crack shapes for indentation fracture of soda-lime glass

    SciTech Connect

    Smith, S.M.; Scattergood, R.O. . Dept. of Materials Science and Engineering)

    1992-01-01

    Radial cracks for indented soda-lime glass aged in distilled water were highly elliptical because of truncation by lateral cracks. Indentation in silicone oil minimized radial/lateral crack interaction but still produced cracks having nominally constant ellipticity during bend testing. Analysis of applied stress/indentation crack length data using stress intensity factors based on half-penny crack shape resulted in apparent R-curve behavior and/or overestimation of the fracture toughness. Incorporation of elliptical shape factors eliminated the R-curve behavior and reduced measured toughness to near the accepted value for soda-lime glass.

  15. Evaluation of eyes with relative pupillary block by indentation ultrasound biomicroscopy gonioscopy.

    PubMed

    Matsunaga, Koichi; Ito, Kunio; Esaki, Koji; Sugimoto, Kota; Sano, Toru; Miura, Katsuya; Sasoh, Mikio; Uji, Yukitaka

    2004-03-01

    To investigate changes in anterior chamber angle configuration with indentation ultrasound biomicroscopy gonioscopy of relative pupillary block (RPB). Cross-sectional study. This study included 26 eyes of 26 patients with RPB. We determined angle opening distance 500 and angle recess area using indentation ultrasound biomicroscopy gonioscopy and compared a small-sized standard eye cup with a new eye cup with an area for inducing pressure. Indentation ultrasound biomicroscopy images documented concavity of the iris in eyes with RPB. Both the new and the small standard eye cups widened the anterior chamber angle significantly (P <.0001) without causing corneal damage. Angle changes were significantly greater for the new eye cup design. Indentation ultrasound biomicroscopy gonioscopy is a useful technique for observation and diagnosis of RPB. Using a small standard or the newly designed eye cup, the procedure can be performed easily and without causing corneal damage.

  16. On the micro-indentation of plant cells in a tissue context.

    PubMed

    Mosca, Gabriella; Sapala, Aleksandra; Strauss, Soeren; Routier-Kierzkowska, Anne-Lise; Smith, Richard S

    2017-02-09

    The effect of geometry on cell stiffness measured with micro-indentation techniques has been explored in single cells, however it is unclear if results on single cells can be readily transferred to indentation experiments performed on a tissue in vivo. Here we explored this question by using simulation models of osmotic treatments and micro-indentation experiments on 3D multicellular tissues with the finite element method. We found that the cellular context does affect measured cell stiffness, and that several cells of context in each direction are required for optimal results. We applied the model to micro-indentation data obtained with cellular force microscopy on the sepal of A. thaliana, and found that differences in measured stiffness could be explained by cellular geometry, and do not necessarily indicate differences in cell wall material properties or turgor pressure.

  17. On the micro-indentation of plant cells in a tissue context

    NASA Astrophysics Data System (ADS)

    Mosca, Gabriella; Sapala, Aleksandra; Strauss, Soeren; Routier-Kierzkowska, Anne-Lise; Smith, Richard S.

    2017-02-01

    The effect of geometry on cell stiffness measured with micro-indentation techniques has been explored in single cells, however it is unclear if results on single cells can be readily transferred to indentation experiments performed on a tissue in vivo. Here we explored this question by using simulation models of osmotic treatments and micro-indentation experiments on 3D multicellular tissues with the finite element method. We found that the cellular context does affect measured cell stiffness, and that several cells of context in each direction are required for optimal results. We applied the model to micro-indentation data obtained with cellular force microscopy on the sepal of A. thaliana, and found that differences in measured stiffness could be explained by cellular geometry, and do not necessarily indicate differences in cell wall material properties or turgor pressure.

  18. Spherical indentation of a freestanding circular membrane revisited: Analytical solutions and experiments

    NASA Astrophysics Data System (ADS)

    Jin, Congrui; Davoodabadi, Ali; Li, Jianlin; Wang, Yanli; Singler, Timothy

    2017-03-01

    Due to the development of novel micro-fabrication techniques to produce ultra-thin materials and increasing interest in thin biological membranes, in recent years, the mechanical characterization of thin films has received a significant amount of attention. To provide a more accurate solution for the relationship among contact radius, load and deflection, the fundamental and widely applicable problem of spherical indentation of a freestanding circular membrane have been revisited. The work presented here significantly extends the previous contributions by providing an exact analytical solution to the governing equations of Föppl-Hecky membrane indented by a frictionless spherical indenter. In this study, experiments of spherical indentation has been performed, and the exact analytical solution presented in this paper is compared against experimental data from existing literature as well as our own experimental results.

  19. Spherical indentation of a freestanding circular membrane revisited: Analytical solutions and experiments

    DOE PAGES

    Jin, Congrui; Davoodabadi, Ali; Li, Jianlin; ...

    2017-01-11

    Because of the development of novel micro-fabrication techniques to produce ultra-thin materials and increasing interest in thin biological membranes, in recent years, the mechanical characterization of thin films has received a significant amount of attention. To provide a more accurate solution for the relationship among contact radius, load and deflection, the fundamental and widely applicable problem of spherical indentation of a freestanding circular membrane have been revisited. The work presented here significantly extends the previous contributions by providing an exact analytical solution to the governing equations of Föppl–Hecky membrane indented by a frictionless spherical indenter. In this study, experiments ofmore » spherical indentation has been performed, and the exact analytical solution presented in this article is compared against experimental data from existing literature as well as our own experimental results.« less

  20. Measurement of the microstructural fracture toughness of cortical bone using indentation fracture.

    PubMed

    Mullins, L P; Bruzzi, M S; McHugh, P E

    2007-01-01

    The purpose of this work is to investigate the use of indentation fracture as a method of measuring toughness at the microscale in cortical bone. Indentation fracture employs sharp indenters to initiate cracks, whose length can be used to calculate the toughness of the material. Only a cube corner indenter tip is found to initiate cracks at a suitable size scale for microstructural measurement. Cracks from 7 to 56 microm in length are produced using loads from 0.05 to 3N. Preliminary data predicts rising toughness with increasing crack length (rising R-curve behaviour) at the microscale. This technique provides a new insight into fracture in cortical bone since it allows the investigator to observe mechanisms and measure toughness at a size scale at which in vivo damage is known to exist.

  1. Quantifying the deep tendon reflex using varying tendon indentation depths: applications to spasticity.

    PubMed

    Chardon, Matthieu K; Rymer, W Zev; Suresh, Nina L

    2014-03-01

    The deep tendon reflex (DTR) is often utilized to characterize the neuromuscular health of individuals because it is cheap, quick to implement, and requires limited equipment. However, DTR assessment is unreliable and assessor-dependent improve the reliability of the DTR assessment, we devised a novel standardization procedure. Our approach is based on the hypothesis that the neuromuscular state of a muscle changes systematically with respect to the indentation depth of its tendon. We tested the hypothesis by progressively indenting the biceps tendons on each side of nine hemiplegic stroke survivors to different depths, and then superimposing a series of brief controlled taps at each indentation depth to elicit a reflex response. Our results show that there exists a unique indentation depth at which reflex responses are consistently recorded (termed the Reflex Threshold) with increasing amplitude along increasing indentation depth. We further show that the reflex threshold depth is systematically smaller on the affected side of stroke survivors and that it is negatively correlated with the Modified Ashworth Score (VAF 70%). Our procedure also enables measurement of passive mechanical properties at the indentation location. In conclusion, our study shows that controlling for the indentation depth of the tendon of a muscle alters its reflex response predictably. Our novel device and method could be used to estimate neuromuscular changes in muscle (e.g., spasticity). Although some refinement is needed, this method opens the door to more reliable quantification of the DTR.

  2. Role of indenter material and size in veneer failure of brittle layer structures.

    PubMed

    Bhowmick, Sanjit; Meléndez-Martínez, Juan José; Hermann, Ilja; Zhang, Yu; Lawn, Brian R

    2007-07-01

    The roles of indenter material and size in the failure of brittle veneer layers in all-ceramic crown-like structures are studied. Glass veneer layers 1 mm thick bonded to alumina layers 0.5 mm thick on polycarbonate bases (representative of porcelain/ceramic-core/dentin) are subject to cyclic contact loading with spherical indenters in water (representative of occlusal biting environment). Two indenter materials-glass and tungsten carbide-and three indenter radii-1.6, 5.0, and 12.5 mm-are investigated in the tests. A video camera is used to follow the near-contact initiation and subsequent downward propagation of cone cracks through the veneer layer to the core interface, at which point the specimen is considered to have failed. Both indenter material and indenter radius have some effect on the critical loads to initiate cracks within the local Hertzian contact field, but the influence of modulus is weaker. The critical loads to take the veneer to failure are relatively insensitive to either of these indenter variables, since the bulk of the cone crack propagation takes place in the contact far field. Clinical implications of the results are considered, including the issue of single-cycle overload versus low-load cyclic fatigue and changes in fracture mode with loading conditions.

  3. Analysis of the equivalent indenter concept used to extract Young’s modulus from a nano-indentation test: some new insights into the Oliver-Pharr method

    NASA Astrophysics Data System (ADS)

    Andriollo, Tito; Thorborg, Jesper; Hattel, Jesper

    2017-06-01

    In this paper a thorough analysis of the equivalent indenter concept applied to nano-indentation is carried out, motivated by the fact that previous works in the field have not considered the requirement of a consistent relation between contact depth and projected contact area. Dimensional analysis is initially used to prove that the shape of the axisymmetric equivalent indenter can be regarded as a material property, provided that size-effects are negligible. Subsequently, it is shown that such shape can effectively be employed to describe the nano-indentation unloading stage by means of Sneddon's elastic solution which is formally valid only for indentation into a flat surface. This allows for formulating the problem of extracting Young's modulus from the unloading curve as an optimization problem. However, it is proved that the latter does not have a unique solution, due to the particular mathematical structure of the underlying equations; hence, additional constraints are needed to set restrictions on the admissible equivalent indenter shapes. An example of such constraint is hidden in some apparent inconsistencies of the well-known Oliver-Pharr method, which is demonstrated to be based on an equivalent conical indenter whose semi-apical angle depends on the ratio between residual and total penetration. Specifically, this angle tends to 90° when the material exhibits extensive inelastic deformation, whereas it reduces to the one characteristic of the real indenter for a perfectly elastic material. This provides a new physical explanation for the relatively good accuracy of the method even in presence of a non-negligible residual contact impression on the sample.

  4. Simultaneous estimation of Poisson's ratio and Young's modulus using a single indentation: a finite element study

    NASA Astrophysics Data System (ADS)

    Zheng, Y. P.; Choi, A. P. C.; Ling, H. Y.; Huang, Y. P.

    2009-04-01

    Indentation is commonly used to determine the mechanical properties of different kinds of biological tissues and engineering materials. With the force-deformation data obtained from an indentation test, Young's modulus of the tissue can be calculated using a linear elastic indentation model with a known Poisson's ratio. A novel method for simultaneous estimation of Young's modulus and Poisson's ratio of the tissue using a single indentation was proposed in this study. Finite element (FE) analysis using 3D models was first used to establish the relationship between Poisson's ratio and the deformation-dependent indentation stiffness for different aspect ratios (indentor radius/tissue original thickness) in the indentation test. From the FE results, it was found that the deformation-dependent indentation stiffness linearly increased with the deformation. Poisson's ratio could be extracted based on the deformation-dependent indentation stiffness obtained from the force-deformation data. Young's modulus was then further calculated with the estimated Poisson's ratio. The feasibility of this method was demonstrated in virtue of using the indentation models with different material properties in the FE analysis. The numerical results showed that the percentage errors of the estimated Poisson's ratios and the corresponding Young's moduli ranged from -1.7% to -3.2% and 3.0% to 7.2%, respectively, with the aspect ratio (indentor radius/tissue thickness) larger than 1. It is expected that this novel method can be potentially used for quantitative assessment of various kinds of engineering materials and biological tissues, such as articular cartilage.

  5. Finite-element analysis of micro-indentation on pollen tubes

    NASA Astrophysics Data System (ADS)

    Bolduc, Jean-Francois; Geitmann, Anja; Lewis, Laurent J.; Groupe de Recherche en Biomecanique et Biomateriaux

    2004-03-01

    Pollen tubes are plant cells that exhibit extremely rapid tip growth with the purpose of delivering the male gametes to the egg apparatus of a receptive flower. On their way to the ovule, pollen tubes have to penetrate the transmitting tissue and to resist lateral deformation forces to allow for the passage of the gametes. We investigate the mechanical properties of pollen tubes experimentally with the help of micro-indentation techniques. This technique is based on the application of local deformations with the purpose to assess local cellular stiffness and visco-elasticity. The results are compared to a computer model created using finite-element analysis (FEA). Our objective is to characterize and quantify the influence of different structural molecules present in the cell wall and the cytoplasm on the pollen tube's resistance to deformation. The FEA model represents a simulation of the micro-indentation experiment. Starting from a simple model for the pollen tube assuming a solid homogeneous elastic body we attempt to refine it by adding structural cellular elements.

  6. Quantitative Measurements of Elastic Properties with Ultrasonic-Based AFM and Conventional Techniques

    NASA Astrophysics Data System (ADS)

    Hurley, D. C.

    A prime motivation for the original development of ultrasonic-based AFM methods was to enable measurements of elastic properties with nanoscale spatial resolution. In this chapter, we discuss the quantitative measurement of elastic modulus with ultrasonic-based AFM methods and compare it to measurement by more conventional or established techniques. First, we present the basic principles of modulus measurement with methods that involve contact resonance spectroscopy, such as atomic force acoustic microscopy (AFAM) and ultrasonic AFM (U-AFM). Fundamental concepts of modulus measurement with more established approaches, especially instrumented (nano-) indentation (NI) and surface acoustic wave spectroscopy (SAWS), are then discussed. We consider the relative strengths and limitations of various approaches, for example measurement accuracy, spatial resolution, and applicability to different materials. Example results for specific material systems are given with an emphasis on studies involving direct intercomparison of different techniques. Finally, current research in this area and opportunities for future work are described.

  7. Experimental Validation of the New Modular Application of the Upper Bound Theorem in Indentation

    PubMed Central

    Bermudo, Carolina; Martín, Francisco; Martín, María Jesús; Sevilla, Lorenzo

    2015-01-01

    Nowadays, thanks to the new manufacturing processes, indentation is becoming an essential part of the new arising processes such as the Incremental Forming Processes. This work presents the experimental validation of the analytical model developed for an indentation-based process. The analytical model is originated from the Upper Bound Theorem application by means of its new modular distribution. The modules considered are composed of two Triangular Rigid Zones each. The experimental validation is performed through a series of indentation tests with work-pieces of annealed aluminium EN AW-2030 and punches of steel AISI 304, under plane strain conditions. The results are compared with the ones obtained from the application of this new modular distribution of the Upper Bound Theorem, showing a good approximation and suitability of the model developed for an indentation-based process. PMID:25826738

  8. Indentation-induced plasticity of thin metal films

    NASA Astrophysics Data System (ADS)

    Lilleodden, Erica Thea

    In this dissertation, the results from an experimental and computational study of the nanoindentation response of various metal systems is presented, relating microstructural length-scale to anomalous behavior associated with the initiation and evolution of plasticity. In the cases of coarse-grained structures and epitaxial films, a discrete transition from Hertzian elastic load-displacement behavior is observed at near-theoretical shear stresses, implying that plasticity is initiated by dislocation nucleation. Discrete load-displacement response is also observed during quasi-constant stress experiments and is discussed in terms of "jerky" dislocation motion. At larger displacements the hardness is observed to decrease with increasing displacement. This widely observed indentation size effect is explained, in part, by a strain gradient plasticity law developed by Nix and Gao; at shallow depths an increased dislocation density can lead to an increase in the flow resistance of a material, as described by the Taylor relation. However, such a strain-gradient model maintains a continuum framework and cannot be expected to explain discrete load-displacement behavior observed at the nanometer scale. Furthermore, when the indentation is confined to very small displacements the dependence on dislocation density can be the opposite; an elevated density of dislocation sources can provide an easy mechanism for plasticity at relatively small loads. In contrast to the behavior observed in coarse-grained structures and epitaxial films, indentation into fine-grained films result in initially soft behavior followed by immediate hardening. Rationale for such behavior has been based on the availability of dislocation sources at the grain boundary for initiating plasticity, followed by a Hall-Petch type strengthening mechanism that overwhelms the strain gradient effects. It is also shown that the competition between dislocation nucleation and activation of pre-existing dislocations is

  9. Unified solution for poroelastic oscillation indentation on gels for spherical, conical and cylindrical indenters.

    PubMed

    Lai, Yang; Hu, Yuhang

    2017-01-25

    An oscillation indentation method is developed for characterizing the local poroelastic properties of soft and hydrated materials such as hydrogels and biological tissues. In the dynamic oscillation indentation measurement, an indenter is pressed into the material to a certain depth and held for a period of time. After a plateau of force is reached, an oscillation of small depth is superimposed sweeping through a range of frequencies. The shift between the force and displacement spectra is denoted as the phase lag that characterizes the energy dissipative behavior of the soft hydrated materials due to solvent migration. A unified solution is obtained for the three widely used shapes of indenters for soft materials: cylindrical punch, spherical indenter and conical indenter. The solutions are summarized in remarkably simple forms allowing for easy extraction of material parameters including shear modulus, Poisson's ratio and diffusivity from the oscillation indentation measurements. The oscillation indentation measurement was demonstrated on a polyacrylamide (PAAm) gel using an atomic force microscope. It is shown that the time-dependent behavior of the PAAm gel at the micron scale is dominated by poroelasticity and the properties can be accurately extracted from the explicit expressions derived in this work. This method has great potential to be applied on heterogeneous biological tissues where local properties are of interest.

  10. Forward Analysis of Transversely Isotropic Thin Film by Indentation Method

    NASA Astrophysics Data System (ADS)

    Zhi, Zheng

    Instrument indentation based methods for determining elasto-plastic properties of bulk specimen or thin film have received considerable and continue growing attention for recent decades, due to its simplicity, operability, and potential applications. However, the researches of transversely isotropic thin film are still at the beginning stage. In order to obtain a deeper understand of the relationship between P -- h curve and thin film properties, both dimensional analysis method and finite element method were applied in the present work. Extensive computational analysis of 630 sets of materials properties was carried out here. Through systematical studies, a more reasonable and intrinsic relationship, between indenter displacement h and the force P on it, was revealed. Also, an effect of materials transverse isotropic properties was summarized. Moreover, accurate and powerful forward analysis functions were established at the end of this thesis. These functions were, then, tested and mismatches were studied.

  11. Evaluation of barely visible indentation damage (BVID) in CF/EP sandwich composites using guided wave signals

    NASA Astrophysics Data System (ADS)

    Mustapha, Samir; Ye, Lin; Dong, Xingjian; Alamdari, Mehrisadat Makki

    2016-08-01

    Barely visible indentation damage after quasi-static indentation in sandwich CF/EP composites was assessed using ultrasonic guided wave signals. Finite element analyses were conducted to investigate the interaction between guided waves and damage, further to assist in the selection process of the Lamb wave sensitive modes for debonding identification. Composite sandwich beams and panels structures were investigated. Using the beam structure, a damage index was defined based on the change in the peak magnitude of the captured wave signals before and after the indentation, and the damage index was correlated with the residual deformation (defined as the depth of the dent), that was further correlated with the amount of crushing within the core. Both A0 and S0 Lamb wave modes showed high sensitivity to the presence of barely visible indentation damage with residual deformation of 0.2 mm. Furthermore, barely visible indentation damage was assessed in composite sandwich panels after indenting to 3 and 5 mm, and the damage index was defined, based on (a) the peak magnitude of the wave signals before and after indentation or (b) the mismatch between the original and reconstructed wave signals based on a time-reversal algorithm, and was subsequently applied to locate the position of indentation.

  12. Dent Resistance and Effect of Indentation Loading Rate on Superelastic TiNi Alloy

    NASA Astrophysics Data System (ADS)

    Farhat, Zoheir; Jarjoura, George; Shahirnia, Meisam

    2013-08-01

    The large recoverable deformation associated with reversible stress-induced martensitic transformation for superelastic TiNi alloys has been widely exploited in many applications. However, to employ superelastic TiNi in applications where high impact loading is expected, as in bearings, the effect of loading rate on superelasticity needs to be understood. In the current article, the effect of indentation loading rate on dent resistance and superelasticity of TiNi is studied. Indentation tests are performed, at different loading rates on superelastic TiNi alloy and correlated to tensile stress-strain data. It is found that the reversible deformation drops as loading rate is increased and superelasticity diminishes. Based on data collected and results analysis it is proposed that the loss in superelastic behavior under high indentation loading rate is related to retardation of the stress-induced martensitic transformation. Furthermore, a simple heat model was proposed and showed that the temperature rise during indentation is not significant.

  13. Estimating the elastic properties of few-layer graphene from the free-standing indentation response.

    PubMed

    Zhou, Lixin; Wang, Yugang; Cao, Guoxin

    2013-11-27

    Using molecular mechanics simulations, the elastic properties of multi-layer graphene (MLG) are investigated; this includes both the linear analysis based on the indentation load-displacement relationship and the nonlinear analysis based on the strain energy. The elastic properties of graphene layers in MLG are similar to each other and also quite close to those of monolayer graphene. The van der Waals (VDW) interaction between graphene layers (interlayer interaction) will create a difference between the indenter tip displacement and the deviation of MLG in indentation, which will cause an overestimation of the elastic modulus of MLG based on classic indentation analysis. This overestimation can be as high as 20%. In addition, the interlayer interaction will significantly affect the nonlinear elastic behavior of MLG in free-standing indentation. With an increase in the number of layers of MLG, the second-order elastic stiffness of MLG is very sensitive to the indentation loading range, and the third-order nonlinear elastic constant is significantly increased.

  14. Localization in thin shells under indentation

    NASA Astrophysics Data System (ADS)

    Nasto, Alice; Adjari, Amin; Lazarus, Arnaud; Vaziri, Ashkan; Reis, Pedro

    2013-03-01

    We perform a hybrid experimental and numerical investigation of deformation in thin spherical elastic shells under indentation. Past the initial linear response, an inverted cap develops as a Pegorelov circular ridge. For further indentation, this ridge loses axis-symmetry and sharp points of localized curvature form, which we refer to as 's-cones' (for shell-cones), in contrast with their developable cousins in plates, 'd-cones'. We quantify how the formation and evolution of s-cones is affected by systematically varying the indenter's curvature. In our precision model experiments, rapid prototyping is used to fabricate elastomeric shells and rigid indenters of various shapes. The mechanical response is quantified through load-displacement comparison tests and the deformation process is further characterized through digital imaging. In parallel, the experimental results are contrasted against nonlinear Finite Element simulations, which enable us to explore the role of friction at the shell-indenter contacts and characterize the relative strain energy focusing properties at different loci of localization. Our combined experimental and computational approach allows us to gain invaluable physical insight towards rationalizing this geometrically nonlinear process.

  15. Indentation of aluminium foam at low velocity

    NASA Astrophysics Data System (ADS)

    Shi, Xiaopeng; Miao, Yinggang; Liu, Shuangyan; Li, Yulong; Lu, Guoxing

    2015-09-01

    The indentation behaviour of aluminium foams at low velocity (10 m/s ˜ 30 m/s) was investigated both in experiments and numerical simulation in this paper. A flat-ended indenter was used and the force-displacement history was recorded. The Split Hopkinson Pressure bar was used to obtain the indentation velocity and forces in the dynamic experiments. Because of the low strength of the aluminium foam, PMMA bar was used, and the experimental data were corrected using Bacon's method. The energy absorption characteristics varying with impact velocity were then obtained. It was found that the energy absorption ability of aluminium foam gradually increases in the quasi-static regime and shows a significant increase at ˜10 m/s velocity. Numerical simulation was also conducted to investigate this process. A 3D Voronoi model was used and models with different relative densities were investigated as well as those with different failure strain. The indentation energy increases with both the relative density and failure strain. The analysis of the FE model implies that the significant change in energy absorption ability of aluminium foam in indentation at ˜10 m/s velocity may be caused by plastic wave effect.

  16. An Investigation of the Influence of Body Size and Indentation Asymmetry of the Effectiveness of Body Indentation in Combination with a Cambered Wing

    NASA Technical Reports Server (NTRS)

    Patterson, James C., Jr.; Loving, Donald L.

    1961-01-01

    An investigation has been made of a 450 sweptback cambered wing in combination with an unindented body and a body symmetrically indented with respect to its axes designed for a Mach number of 1.2. The ratio of body frontal area to wing planform area was 0.08 for these wing-body combinations. In order to determine the influence of body size on the effectiveness of indentation, the test data have been compared with previously obtained data for similar configurations having a ratio of body frontal area to wing planform area of 0.04. Also, in order to investigate the relative effectiveness of indentation asymmetry, a specially indented body designed to account for the wing camber and also designed for a Mach number of 1.2 has been included in these tests. The investigation was conducted in the Langley 8-Foot Tunnels Branch at Mach numbers from 0.80 to 1.43 and a Reynolds number of approximately 1.85 x 10(exp 6), based on a mean aerodynamic chord length of 5.955 inches. The data indicate that the configurations with larger ratio of body frontal area to wing planform area had smaller reductions in zero-lift wave drag associated with body indentation than the configurations with smaller ratio of body frontal area to wing planform area. The 0.08-area-ratio configurations also had correspondingly smaller increases in the values of maximum lift-drag ratio than the 0.04-area-ratio configurations. The consideration of wing camber in the body indentation design resulted in a 35.5-percent reduction in zero-lift wave drag, compared with a 21.5-percent reduction associated with the symmetrical indentation, but had a negligible effect on the values of maximum lift-drag ratio.

  17. Indentation Size Effects in Single Crystal Copper as Revealed by Synchrotron X-ray Microdiffraction

    SciTech Connect

    Feng, G.; Budiman, A. S.; Nix, W. D.; Tamura, N.; Patel, J. R.

    2007-11-19

    The indentation size effect (ISE) has been observed in numerous nanoindentation studies on crystalline materials; it is found that the hardness increases dramatically with decreasing indentation size - a 'smaller is stronger' phenomenon. Some have attributed the ISE to the existence of strain gradients and the geometrically necessary dislocations (GNDs). Since the GND density is directly related to the local lattice curvature, the Scanning X-ray Microdiffraction ({mu}SXRD) technique, which can quantitatively measure relative lattice rotations through the streaking of Laue diffractions, can used to study the strain gradients. The synchrotron {mu}SXRD technique we use - which was developed at the Advanced Light Source (ALS), Berkeley Lab - allows for probing the local plastic behavior of crystals with sub-micrometer resolution. Using this technique, we studied the local plasticity for indentations of different depths in a Cu single crystal. Broadening of Laue diffractions (streaking) was observed, showing local crystal lattice rotation due to the indentation-induced plastic deformation. A quantitative analysis of the streaking allows us to estimate the average GND density in the indentation plastic zones. The size dependence of the hardness, as found by nanoindentation, will be described, and its correlation to the observed lattice rotations will be discussed.

  18. Defect formation by pristine indenter at the initial stage of nanoindentation

    SciTech Connect

    Chen, I-Hsien; Hsiao, Chun-I; Behera, Rakesh K.; Hsu, Wen-Dung

    2013-12-07

    Nano-indentation is a sophisticated method to characterize mechanical properties of materials. This method samples a very small amount of material during each indentation. Therefore, this method is extremely useful to measure mechanical properties of nano-materials. The measurements using nanoindentation is very sensitive to the surface topology of the indenter and the indenting surfaces. The mechanisms involved in the entire process of nanoindentation require an atomic level understanding of the interplay between the indenter and the substrate. In this paper, we have used atomistic simulation methods with empirical potentials to investigate the effect of various types of pristine indenter on the defect nucleation and growth. Using molecular dynamics simulations, we have predicted the load-depth curve for conical, vickers, and sperical tip. The results are analyzed based on the coherency between the indenter tip and substrate surface for a fixed depth of 20 Å. The depth of defect nucleation and growth is observed to be dependent on the tip geometry. A tip with larger apex angle nucleates defects at a shallower depth. However, the type of defect generated is dependent on the crystalline orientation of the tip and substrate. For coherent systems, prismatic loops were generated, which released into the substrate along the close-packed directions with continued indentation. For incoherent systems, pyramidal shaped dislocation junctions formed in the FCC systems and disordered atomic clusters formed in the BCC systems. These defect nucleation and growth process provide the atomistic mechanisms responsible for the observed load-depth response during nanoindentation.

  19. Optimal interaction of indenter with inhomogeneous plate

    NASA Technical Reports Server (NTRS)

    Aptukov, Valery N.

    1991-01-01

    Consideration is given to a new class of problems dealing with an optimal design of an inhomogeneous plate during dynamic penetration of the rigid indenter. The quality criterion of the process is defined by the specific mass of the target, which absorbs the given kinetic mass of the indenter. Parameters of control are expressed in terms of mechanical characteristics, i.e., distribution of density and the related hardness across the plate thickness. The maximum principle of Pontryagin is used to search for the piecewise continuous control function. With consideration of impact conditions and characteristics for a given class of material, an optimal target structure criterion was estimated for engineering applications.

  20. Mechanical response of adherent giant liposomes to indentation with a conical AFM-tip.

    PubMed

    Schäfer, Edith; Vache, Marian; Kliesch, Torben-Tobias; Janshoff, Andreas

    2015-06-14

    Indentation of giant liposomes with a conical indenter is described by means of a tension-based membrane model. We found that nonlinear membrane theory neglecting the impact of bending sufficiently describes the mechanical response of liposomes to indentation as measured by atomic force microscopy. Giant vesicles are gently adsorbed on glassy surfaces via avidin-biotin linkages and indented centrally using an atomic force microscope equipped with conventional sharp tips mounted on top of an inverted microscope. Force indentation curves display a nonlinear response that allows to extract pre-stress of the bilayer T0 and the area compressibility modulus KA by computing the contour of the vesicle at a given force. The values for KA of fluid membranes correspond well to what is known from micropipet suction experiments and inferred from membrane undulation monitoring. Assembly of actin shells inside the liposome considerably stiffens the vesicles resulting in significantly larger area compressibility modules. The analysis can be easily extended to different indenter geometries with rotational symmetry.

  1. Semianalytical Solution for the Deformation of an Elastic Layer under an Axisymmetrically Distributed Power-Form Load: Application to Fluid-Jet-Induced Indentation of Biological Soft Tissues

    PubMed Central

    Lu, Minhua; Huang, Shuai; Yang, Lei; Mao, Rui

    2017-01-01

    Fluid-jet-based indentation is used as a noncontact excitation technique by systems measuring the mechanical properties of soft tissues. However, the application of these devices has been hindered by the lack of theoretical solutions. This study developed a mathematical model for testing the indentation induced by a fluid jet and determined a semianalytical solution. The soft tissue was modeled as an elastic layer bonded to a rigid base. The pressure of the fluid jet impinging on the soft tissue was assumed to have a power-form function. The semianalytical solution was verified in detail using finite-element modeling, with excellent agreement being achieved. The effects of several parameters on the solution behaviors are reported, and a method for applying the solution to determine the mechanical properties of soft tissues is suggested. PMID:28373991

  2. Semianalytical Solution for the Deformation of an Elastic Layer under an Axisymmetrically Distributed Power-Form Load: Application to Fluid-Jet-Induced Indentation of Biological Soft Tissues.

    PubMed

    Lu, Minhua; Huang, Shuai; Yang, Xianglong; Yang, Lei; Mao, Rui

    2017-01-01

    Fluid-jet-based indentation is used as a noncontact excitation technique by systems measuring the mechanical properties of soft tissues. However, the application of these devices has been hindered by the lack of theoretical solutions. This study developed a mathematical model for testing the indentation induced by a fluid jet and determined a semianalytical solution. The soft tissue was modeled as an elastic layer bonded to a rigid base. The pressure of the fluid jet impinging on the soft tissue was assumed to have a power-form function. The semianalytical solution was verified in detail using finite-element modeling, with excellent agreement being achieved. The effects of several parameters on the solution behaviors are reported, and a method for applying the solution to determine the mechanical properties of soft tissues is suggested.

  3. Mechanical evaluation of five flowable resin composites by the dynamic micro-indentation method

    PubMed Central

    Hirayama, Satoshi; Iwai, Hirotoshi

    2014-01-01

    Measurement of the strength of brittle materials, such as resin composites, is extremely difficult. Micro-indentation hardness testing is a convenient way of investigating the mechanical properties of a small volume of material. In this study, the mechanical properties of five commercially available flowable resin composites were investigated by the dynamic micro-indentation method. Additionally, the effects of inorganic-filler content on the dynamic hardness and elastic modulus of flowable composites obtained by this method were investigated. The weight percentages of the inorganic fillers in the resin composites were determined by the ashing technique. The results indicate that the mechanical properties of flowable composites are affected by not only the filler content but also the properties of the resin matrix. In conclusion, the dynamic micro-indentation method is a useful technique for determining the mechanical behavior of dental resin composites as brittle material. PMID:25342983

  4. Towards a standardized reference point indentation testing procedure.

    PubMed

    Setters, Alexander; Jasiuk, Iwona

    2014-06-01

    We study the reference point indentation (RPI) technique which has a potential to directly measure mechanical properties of bone in patients. More specifically, we tested 6 month swine femoral cortical bone at mid-diaphysis region to investigate the effect of several testing variables on the RPI outputs. They include the force magnitude, preconditioning, variation within a sample and between samples, number of cycles, indentation surface (transverse versus longitudinal, polished versus unpolished), and micro-computed tomography radiation exposure. The force magnitude variation test shows that all RPI parameters increase linearly with the increasing force magnitude except the indentation distance increase which shows a cubic trend with a plateau for force magnitudes between 4N and 8N. Preconditioning does not affect the trends for a force magnitude variation test. The cycle variation test shows that most RPI parameters reach either a maximum or minimum at 15-20 cycles. Transverse surface measurements are more consistent than the longitudinal surface measurements, but a rough surface and periosteum on the longitudinal surface could account for this difference. Exposure to the micro-computed tomography radiation in general does not have effect on the RPI measurements. For the 6 month swine femoral cortical bone, testing using 6N force and 20 cycles with preconditioning on an unpolished longitudinal surface is recommended. This study advances our knowledge on how the RPI testing variables influence the RPI outputs and provides guidance on the RPI measurements. It may also serve as a framework for developing a standardized testing procedure for the RPI technique.

  5. Axisymmetric indentation of curved elastic membranes by a convex rigid indenter

    PubMed Central

    Pearce, S.P.; King, J.R.; Holdsworth, M.J.

    2011-01-01

    Motivated by applications to seed germination, we consider the transverse deflection that results from the axisymmetric indentation of an elastic membrane by a rigid body. The elastic membrane is fixed around its boundary, with or without an initial pre-stretch, and may be initially curved prior to indentation. General indenter shapes are considered, and the load–indentation curves that result for a range of spheroidal tips are obtained for both flat and curved membranes. Wrinkling may occur when the membrane is initially curved, and a relaxed strain-energy function is used to calculate the deformed profile in this case. Applications to experiments designed to measure the mechanical properties of seed endosperms are discussed. PMID:22298913

  6. Strength determination of rocks by using indentation tests with a spherical indenter

    NASA Astrophysics Data System (ADS)

    Kitamura, Manami; Hirose, Takehiro

    2017-05-01

    We conducted spherical indentation and uniaxial compression tests on four rock types of various porosities (<20%). For both methods, the compressive strength increased with decreasing porosity, but the strength obtained by the uniaxial compression test (Co) was lower than that obtained by the indentation test (Ci). We established a linear relationship between Co and Ci, expressed by Co = 0.513 × Ci. The difference in strength obtained by the two methods might reflect a considerable amount of inelastic deformation due to pore collapse under the indenter, and the lack during indentation testing of the lateral deformation characteristic of uniaxial compression. The empirical relationship between the two methods will allow conversion of the results of indentation tests to values equivalent to those obtained from uniaxial compression tests. We applied the method to drill-cuttings retrieved from the Nankai accretionary prism during Integrated Ocean Drilling Program Expedition 348. The Co-porosity relationship of the cuttings determined by the indentation tests was consistent with the previously reported relationships obtained from cylindrical specimens by using conventional compression experiments. The method can be used to characterize the mechanical behavior of rocks by obtaining data from smaller specimens than those required for conventional rock deformation experiments.

  7. Crack-shape effects for indentation fracture toughness measurements

    SciTech Connect

    Smith, S.M.; Scattergood, R.O. . Dept. of Materials Science and Engineering)

    1992-02-01

    Various methods to measure fracture toughness using indentation precracks were compared using soda-lime glass as a test material. In situ measurements of crack size as a function of applied stress allow both the toughness K[sub c] and the residual-stress factor [chi] to be independently determined. Analysis of the data showed that stress intensity factors based on classical half-penny crack shapes overestimate toughness values and produce an apparent R-curve effect. This is due to a constraint on crack shape imposed by primary lateral cracks in soda-lime glass. Models based on elliptical cracks were developed to account for the crack-shape effects.

  8. Substrate-dependent cell elasticity measured by optical tweezers indentation

    NASA Astrophysics Data System (ADS)

    Yousafzai, Muhammad S.; Ndoye, Fatou; Coceano, Giovanna; Niemela, Joseph; Bonin, Serena; Scoles, Giacinto; Cojoc, Dan

    2016-01-01

    In the last decade, cell elasticity has been widely investigated as a potential label free indicator for cellular alteration in different diseases, cancer included. Cell elasticity can be locally measured by pulling membrane tethers, stretching or indenting the cell using optical tweezers. In this paper, we propose a simple approach to perform cell indentation at pN forces by axially moving the cell against a trapped microbead. The elastic modulus is calculated using the Hertz-model. Besides the axial component, the setup also allows us to examine the lateral cell-bead interaction. This technique has been applied to measure the local elasticity of HBL-100 cells, an immortalized human cell line, originally derived from the milk of a woman with no evidence of breast cancer lesions. In addition, we have studied the influence of substrate stiffness on cell elasticity by performing experiments on cells cultured on two substrates, bare and collagen-coated, having different stiffness. The mean value of the cell elastic modulus measured during indentation was 26±9 Pa for the bare substrate, while for the collagen-coated substrate it diminished to 19±7 Pa. The same trend was obtained for the elastic modulus measured during the retraction of the cell: 23±10 Pa and 13±7 Pa, respectively. These results show the cells adapt their stiffness to that of the substrate and demonstrate the potential of this setup for low-force probing of modifications to cell mechanics induced by the surrounding environment (e.g. extracellular matrix or other cells).

  9. A numerical investigation on mechanical property improvement of styrene butadine rubber by static straight blade indentation

    NASA Astrophysics Data System (ADS)

    Setiyana, B.; Ismail, R.; Jamari, J.; Schipper, D. J.

    2016-04-01

    Mechanical property improvement of rubber is widely carried out by adding carbon black or silica as a filler in rubber. In general, this improvement aims on the increase of stiffness and abrasion resistance. By means of the static straight blade indentation technique, this paper studies the mechanical properties of Unfilled Styrene Butadiene Rubber (SBR-0) and Filled Styrene Butadiene Rubber that is compounded with carbon black (SBR-25). The numerical method applied was Finite Element Analysis (FEA) in which the rubber was modeled as a hyper-elastic material and indented by a blade indenter with various wedge angles i.e. 30, 45 and 60 degrees. At the same depth of indentation, the results showed that there was an increase in both rubber stiffness and maximum stress if the rubber was compounded. However, it is found that the rubber stiffness showed a regular slight increase, while the maximum stress experienced an irregularly significant increase. Especially for the 30 degree wedge angle, the maximum stress extremely increased at a certain depth of indentation.

  10. In situ spectroscopic study of the plastic deformation of amorphous silicon under nonhydrostatic conditions induced by indentation

    NASA Astrophysics Data System (ADS)

    Gerbig, Y. B.; Michaels, C. A.; Bradby, J. E.; Haberl, B.; Cook, R. F.

    2015-12-01

    Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generated in situ Raman maps provide unique insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published papers on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately fivefold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of sixfold coordinated atomic arrangements. These sixfold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystalline

  11. In situ spectroscopic study of the plastic deformation of amorphous silicon under non-hydrostatic conditions induced by indentation

    PubMed Central

    Gerbig, Y.B; Michaels, C.A.; Bradby, J.E.; Haberl, B.; Cook, R.F.

    2016-01-01

    Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generated in situ Raman maps provide unique, new insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately five-fold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of six-fold coordinated atomic arrangements. These six-fold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystalline

  12. In situ spectroscopic study of the plastic deformation of amorphous silicon under non-hydrostatic conditions induced by indentation.

    PubMed

    Gerbig, Y B; Michaels, C A; Bradby, J E; Haberl, B; Cook, R F

    2015-12-01

    Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generated in situ Raman maps provide unique, new insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately five-fold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of six-fold coordinated atomic arrangements. These six-fold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystalline

  13. Possibilities of tribospectroscopy using two indenters for identifying defects in the surface layer

    NASA Astrophysics Data System (ADS)

    Eremina, Galina M.; Smolin, Alexey Yu.

    2016-11-01

    Currently, for the study of the topography of material surface with nanoscale roughness tribospectroscopy is used as a method based on the analysis of the forces acting between two loading indenters and the sample surface. Recently, it has been shown theoretically that it is possible to determine nanodefects in the surface layer based on the analysis of the frictional force during sliding of one indenter. In this article, based on computer simulation by the method of movable cellular automata, we investigated the possibility of the tribospectroscopic method to identify nanodefects in the surface layer using a system of two indenters. For this purpose, we compared Fourier spectra for the normal and tangential components of the forces of interaction of both indenters for the cases of a defect-free sample and a sample with nanoscale plane cracks perpendicular to the studied surface. The data obtained from the numerical simulation showed that the presence of the second indenter provides additional useful information about the state of the sample surface, which is reflected in the estimates of the spectral density of the time history of the corresponding forces.

  14. Evaluating the nucleus effect on the dynamic indentation behavior of cells.

    PubMed

    Cao, Guoxin; Sui, Jie; Sun, Shuli

    2013-01-01

    The effect of the nucleus on the cell mechanical behavior was investigated based on the dynamic indentation response of cells under a spherical tip. A "two-component" cell model (including cytoplasm and nucleus) is used, and the dynamic indentation behavior is studied by a semiempirical method, which is established based on fitting the numerical simulation results of the quasi-static indentation response of cells. We found that the "routine analysis" (based on the Hertz's contact solution of homogeneous model) significantly overestimated the nucleus effect on the overall cell indentation response due to the effects of the Hertz contact radius and the substrate stiffening. These effects are significantly stronger in the "two-component" cell model than in the homogeneous model. The inaccuracy created by the "routine analysis" slightly increases with the modulus ratio of nucleus to cytoplasm and the volume fraction of nucleus. Finally, the error sensitivity to the geometrical parameters used in the model is discussed, which shows the indentation analysis is not very sensitive to these parameters, and the reasonable assumptions for these parameters are effective. This systematic analysis can provide a useful guideline to understanding the mechanical behavior of cells and nuclei.

  15. All optical indentation probe for endoscopic diagnosis of ostheoarthritis

    NASA Astrophysics Data System (ADS)

    Marchi, G.; Jost, M.; Steinkopff, A.; Prein, C.; Aszodi, A.; Clausen-Schaumann, H.; Roths, J.

    2015-05-01

    A novel kind of miniaturized, all optical probe concept to measure the elasticity of biological tissues is here presented. The probe is based on fibre Bragg grating sensors (FBG) inscribed in optical fibres. The measurement procedure exploits the high strain sensitivity of Bragg gratings. A study on the reproducibility, reliability, and resolution of the sensor is presented and a first measurement on bovine cartilage tissue is reported. A linear elastic model of the cartilage has been used to analyse the data. The results indicate a good agreement with previous values given in the literature for micro-indentation.

  16. Balloon-based interferometric techniques

    NASA Technical Reports Server (NTRS)

    Rees, David

    1985-01-01

    A balloon-borne triple-etalon Fabry-Perot Interferometer, observing the Doppler shifts of absorption lines caused by molecular oxygen and water vapor in the far red/near infrared spectrum of backscattered sunlight, has been used to evaluate a passive spaceborne remote sensing technique for measuring winds in the troposphere and stratosphere. There have been two successful high altitude balloon flights of the prototype UCL instrument from the National Scientific Balloon Facility at Palestine, TE (May 80, Oct. 83). The results from these flights have demonstrated that an interferometer with adequate resolution, stability and sensitivity can be built. The wind data are of comparable quality to those obtained from operational techniques (balloon and rocket sonde, cloud-top drift analysis, and from the gradient wind analysis of satellite radiance measurements). However, the interferometric data can provide a regular global grid, over a height range from 5 to 50 km in regions of clear air. Between the middle troposphere (5 km) and the upper stratosphere (40 to 50 km), an optimized instrument can make wind measurements over the daylit hemisphere with an accuracy of about 3 to 5 m/sec (2 sigma). It is possible to obtain full height profiles between altitudes of 5 and 50 km, with 4 km height resolution, and a spatial resolution of about 200 km, along the orbit track. Below an altitude of about 10 km, Fraunhofer lines of solar origin are possible targets of the Doppler wind analysis. Above an altitude of 50 km, the weakness of the backscattered solar spectrum (decreasing air density) is coupled with the low absorption crosssection of all atmospheric species in the spectral region up to 800 nm (where imaging photon detectors can be used), causing the along-the-track resolution (or error) to increase beyond values useful for operational purposes. Within the region of optimum performance (5 to 50 km), however, the technique is a valuable potential complement to existing wind

  17. Study of indentation of a sample equine bone using finite element simulation and single cycle reference point indentation.

    PubMed

    Hoffseth, Kevin; Randall, Connor; Hansma, Paul; Yang, Henry T Y

    2015-02-01

    In an attempt to study the mechanical behavior of bone under indentation, methods of analyses and experimental validations have been developed, with a selected test material. The test material chosen is from an equine cortical bone. Stress-strain relationships are first obtained from conventional mechanical property tests. A finite element simulation procedure is developed for indentation analyses. The simulation results are experimentally validated by determining (1) the maximum depth of indentation with a single cycle type of reference point indentation, and (2) the profile and depth of the unloaded, permanent indentation with atomic force microscopy. The advantage of incorporating in the simulation a yield criterion calibrated by tested mechanical properties, with different values in tension and compression, is demonstrated. In addition, the benefit of including damage through a reduction in Young's modulus is shown in predicting the permanent indentation after unloading and recovery. The expected differences in response between two indenter tips with different sharpness are predicted and experimentally observed. Results show predicted indentation depths agree with experimental data. Thus, finite element simulation methods with experimental validation, and with damage approximation by a reduction of Young's modulus, may provide a good approach for analysis of indentation of cortical bone. These methods reveal that multiple factors affect measured indentation depth and that the shape of the permanent indentation contains useful information about bone material properties. Only further work can determine if these methods or extensions to these methods can give useful insights into bone pathology, for example the bone fragility of thoroughbred racehorses.

  18. Atomistic simulation on indented defects in silicon.

    PubMed

    Trandinh, Long; Cheon, Seong Sik; Kang, Woojong

    2013-12-01

    Silicon is known as one of the widely used materials in electronic fields for its excellent semiconductive characteristics. However, these characteristics are vulnerable to internal defects, which randomly exist in any materials. In the present study, defects in single crystalline silicon thin film were investigated by atomistic simulation of nano-indentation at zero temperature. The Tersoff potential and the spherical indenter were applied to the model of silicon. The symmetric axis parameter method is novelly proposed to identify defects in the diamond cubic structure. Under the nanoindentation condition, the ring slip appears close to the indentation region on the free surface and propagates along with [110]/(111). The dislocation is initiated closely to the ring slip and emitted on the (111) plane by the dissociation into two partial dislocations. It was found that the symmetric axis parameter method successfully separated the perfect dislocations, the partial dislocations and the stacking fault from perfect structure, i.e., diamond cubic structure, even though it was not able to distinguish between glide set and shuffle set dislocations.

  19. A Comparison of Quasi-Static Indentation to Low-Velocity Impact

    NASA Technical Reports Server (NTRS)

    Nettles, A. T.; Douglas, M. J.

    2000-01-01

    A static test method for modeling low-velocity foreign object impact events to composites would prove to be very beneficial to researchers since much more data can be obtained from a static test than from an impact test. In order to examine if this is feasible, a series of static indentation and low-velocity impact tests were carried out and compared. Square specimens of many sizes and thicknesses were utilized to cover the array of types of low velocity impact events. Laminates with a pi/4 stacking sequence were employed since this is by far the most common type of engineering laminate. Three distinct flexural rigidities -under two different boundary conditions were tested in order to obtain damage ranging from that due to large deflection to contact stresses and levels in-between to examine if the static indentation-impact comparisons are valid under the spectrum of damage modes that can be experienced. Comparisons between static indentation and low-velocity impact tests were based on the maximum applied transverse load. The dependent parameters examined included dent depth, back surface crack length, delamination area, and to a limited extent, load-deflection behavior. Results showed that no distinct differences could be seen between the static indentation tests and the low-velocity impact tests, indicating that static indentation can be used to represent a low-velocity impact event.

  20. Spherical indentation method for determining the constitutive parameters of hyperelastic soft materials.

    PubMed

    Zhang, Man-Gong; Cao, Yan-Ping; Li, Guo-Yang; Feng, Xi-Qiao

    2014-01-01

    A comprehensive study on the spherical indentation of hyperelastic soft materials is carried out through combined theoretical, computational, and experimental efforts. Four widely used hyperelastic constitutive models are studied, including neo-Hookean, Mooney-Rivlin, Fung, and Arruda-Boyce models. Through dimensional analysis and finite element simulations, we establish the explicit relations between the indentation loads at given indentation depths and the constitutive parameters of materials. Based on the obtained results, the applicability of Hertzian solution to the measurement of the initial shear modulus of hyperelastic materials is examined. Furthermore, from the viewpoint of inverse problems, the possibility to measure some other properties of a hyperelastic material using spherical indentation tests, e.g., locking stretch, is addressed by considering the existence, uniqueness, and stability of the solution. Experiments have been performed on polydimethylsiloxane to validate the conclusions drawn from our theoretical analysis. The results reported in this study should help identify the extent to which the mechanical properties of hyperelastic materials could be measured from spherical indentation tests.

  1. Spherical indentation of soft matter beyond the Hertzian regime: numerical and experimental validation of hyperelastic models

    PubMed Central

    Shreiber, David I.; Dimitriadis, Emilios K.; Horkay, Ferenc

    2012-01-01

    The lack of practicable nonlinear elastic contact models frequently compels the inappropriate use of Hertzian models in analyzing indentation data and likely contributes to inconsistencies associated with the results of biological atomic force microscopy measurements. We derived and validated with the aid of the finite element method force-indentation relations based on a number of hyperelastic strain energy functions. The models were applied to existing data from indentation, using microspheres as indenters, of synthetic rubber-like gels, native mouse cartilage tissue, and engineered cartilage. For the biological tissues, the Fung and single-term Ogden models achieved the best fits of the data while all tested hyperelastic models produced good fits for the synthetic gels. The Hertz model proved to be acceptable for the synthetic gels at small deformations (strain < 0.05 for the samples tested), but not for the biological tissues. Although this finding supports the generally accepted view that many soft materials can be assumed to be linear elastic at small deformations, the nonlinear models facilitate analysis of intrinsically nonlinear tissues and large-strain indentation behavior. PMID:18979205

  2. Mapping Viscoelastic and Plastic Properties of Polymers and Polymer-Nanotube Composites using Instrumented Indentation.

    PubMed

    Gayle, Andrew J; Cook, Robert F

    An instrumented indentation method is developed for generating maps of time-dependent viscoelastic and time-independent plastic properties of polymeric materials. The method is based on a pyramidal indentation model consisting of two quadratic viscoelastic Kelvin-like elements and a quadratic plastic element in series. Closed-form solutions for indentation displacement under constant load and constant loading-rate are developed and used to determine and validate material properties. Model parameters are determined by point measurements on common monolithic polymers. Mapping is demonstrated on an epoxy-ceramic interface and on two composite materials consisting of epoxy matrices containing multi-wall carbon nanotubes. A fast viscoelastic deformation process in the epoxy was unaffected by the inclusion of the nanotubes, whereas a slow viscoelastic process was significantly impeded, as was the plastic deformation. Mapping revealed considerable spatial heterogeneity in the slow viscoelastic and plastic responses in the composites, particularly in the material with a greater fraction of nanotubes.

  3. An elastic failure model of indentation damage. [of brittle structural ceramics

    NASA Technical Reports Server (NTRS)

    Liaw, B. M.; Kobayashi, A. S.; Emery, A. F.

    1984-01-01

    A mechanistically consistent model for indentation damage based on elastic failure at tensile or shear overloads, is proposed. The model accommodates arbitrary crack orientation, stress relaxation, reduction and recovery of stiffness due to crack opening and closure, and interfacial friction due to backward sliding of closed cracks. This elastic failure model was implemented by an axisymmetric finite element program which was used to simulate progressive damage in a silicon nitride plate indented by a tungsten carbide sphere. The predicted damage patterns and the permanent impression matched those observed experimentally. The validation of this elastic failure model shows that the plastic deformation postulated by others is not necessary to replicate the indentation damage of brittle structural ceramics.

  4. An elastic failure model of indentation damage. [of brittle structural ceramics

    NASA Technical Reports Server (NTRS)

    Liaw, B. M.; Kobayashi, A. S.; Emery, A. F.

    1984-01-01

    A mechanistically consistent model for indentation damage based on elastic failure at tensile or shear overloads, is proposed. The model accommodates arbitrary crack orientation, stress relaxation, reduction and recovery of stiffness due to crack opening and closure, and interfacial friction due to backward sliding of closed cracks. This elastic failure model was implemented by an axisymmetric finite element program which was used to simulate progressive damage in a silicon nitride plate indented by a tungsten carbide sphere. The predicted damage patterns and the permanent impression matched those observed experimentally. The validation of this elastic failure model shows that the plastic deformation postulated by others is not necessary to replicate the indentation damage of brittle structural ceramics.

  5. Simulation of indentation fracture in crystalline materials using mesoscale self-assembly.

    PubMed

    Thalladi, Venkat R; Schwartz, Alexander; Phend, Jennifer N; Hutchinson, John W; Whitesides, George M

    2002-08-21

    A new physical model based on mesoscale self-assembly is developed to simulate indentation fracture in crystalline materials. Millimeter-scale hexagonal objects exhibiting atom-like potential functions were designed and allowed to self-assemble into two-dimensional (2D) aggregates at the interface between water and perfluorodecalin. Indentation experiments were performed on these aggregates, and the stresses and strains involved in these processes were evaluated. The stress field in the aggregates was analyzed theoretically using the 2D elastic Hertz solution. Comparison of the experimental results with theoretical analysis revealed that fracture develops in regions subjected to high shear stress and some, albeit low, tensile stress. The potential for the broader application of the model is illustrated using indentation of assemblies with point defects and adatoms introduced at predetermined locations, and using a two-phase aggregate simulating a compliant film on a stiff substrate.

  6. Indentation quantification for in-liquid nanomechanical measurement of soft material using an atomic force microscope: Rate-dependent elastic modulus of live cells

    PubMed Central

    Ren, Juan; Yu, Shiyan; Gao, Nan; Zou, Qingze

    2014-01-01

    In this paper, a control-based approach to replace the conventional method to achieve accurate indentation quantification is proposed for nanomechanical measurement of live cells using atomic force microscope. Accurate indentation quantification is central to probe-based nanomechanical property measurement. The conventional method for in-liquid nanomechanical measurement of live cells, however, fails to accurately quantify the indentation as effects of the relative probe acceleration and the hydrodynamic force are not addressed. As a result, significant errors and uncertainties are induced in the nanomechanical properties measured. In this paper, a control-based approach is proposed to account for these adverse effects by tracking the same excitation force profile on both a live cell and a hard reference sample through the use of an advanced control technique, and by quantifying the indentation from the difference of the cantilever base displacement in these two measurements. The proposed control-based approach not only eliminates the relative probe acceleration effect with no need to calibrate the parameters involved, but it also reduces the hydrodynamic force effect significantly when the force load rate becomes high. We further hypothesize that, by using the proposed control-based approach, the rate-dependent elastic modulus of live human epithelial cells under different stress conditions can be reliably quantified to predict the elasticity evolution of cell membranes, and hence can be used to predict cellular behaviors. By implementing the proposed approach, the elastic modulus of HeLa cells before and after the stress process were quantified as the force load rate was changed over three orders of magnitude from 0.1 to 100 Hz, where the amplitude of the applied force and the indentation were at 0.4–2 nN and 250–450 nm, respectively. The measured elastic modulus of HeLa cells showed a clear power-law dependence on the load rate, both before and after the

  7. Indentation testing and optimized property identification for viscoelastic materials using the finite element method

    NASA Astrophysics Data System (ADS)

    Resapu, Rajeswara Reddy

    tested in a Dynamic Mechanical Analyzer (DMA) via indentation. Two dimensional finite element models are developed to characterize the optimal material properties of PVC film and wire from the experimental load-displacement data. The aging of the PVC film is studied by characterizing the optimal material properties at different aging times; it is demonstrated that the thermally aged film and wires show degradation effects in terms of increased modulus with aging (i.e. increasingly brittle response). This indentation-finite element analysis approach has also been used to characterize the properties of pristine high and low density polyethylene (PE) films using both sharp (Vickers) and spherical indenters; the comparison of the results from both the indenters is performed. The mechanical properties of lamb and cow liver tissue have also been investigated by indentation. Specifically, tests using a spherical indenter is carried out on liver using both DMA (displacement controlled) and dead-weight loading (force controlled) in a Micro Computed Tomography (Micro-CT) chamber. Material properties are initially calculated using the 2D model from the DMA tests. The material properties are later validated by a 3D finite element model generated by image reconstruction through the X-Ray images of the specimen taken by the Micro-CT. These studies used a hyperelastic (Neo-Hookean) viscoelasticity material model to account for large strain effects. The approach used in this study successfully characterizes mechanical properties of polymers and tissues using non-destructive test methods. The properties obtained are validated by predicting the response of the material under other loading conditions. Good correlation between the experimental and finite element results has been obtained. The study also provides ideas for future work which can lead to improvements to this new technique.

  8. Techniques for Enhancing Web-Based Education.

    ERIC Educational Resources Information Center

    Barbieri, Kathy; Mehringer, Susan

    The Virtual Workshop is a World Wide Web-based set of modules on high performance computing developed at the Cornell Theory Center (CTC) (New York). This approach reaches a large audience, leverages staff effort, and poses challenges for developing interesting presentation techniques. This paper describes the following techniques with their…

  9. Photoacoustic Microscopy of Vickers Indentations in Metals with Piezoelectric Detection

    NASA Astrophysics Data System (ADS)

    Glazov, A. L.; Morozov, N. F.; Muratikov, K. L.

    2017-07-01

    The effect of mechanical stress influence on the thermoelastic photoacoustic signals inside Vickers indents in steel and nanonickel has been experimentally demonstrated. It has been shown that photoacoustic signal changes due to external stresses can be reversible or irreversible, depending on the indent orientation and the stress applied to the sample. Reversible changes in the photoacoustic signal can reach significant values at the level of tens percent of the average signal amplitude from the sample. Relative changes in the photoacoustic signal amplitudes have been theoretically evaluated for Vickers-indented and non-indented areas, taking into account the dependence of the elastic modulus of metals on temperature. It has been shown that this theoretical consideration provides qualitative explanation of differences in the behavior of photoacoustic signals under stress in indented and non-indented areas in metals.

  10. Material Flow Analysis in Indentation by Two-Dimensional Digital Image Correlation and Finite Elements Method

    PubMed Central

    Bermudo, Carolina; Sevilla, Lorenzo; Castillo López, Germán

    2017-01-01

    The present work shows the material flow analysis in indentation by the numerical two dimensional Finite Elements (FEM) method and the experimental two-dimensional Digital Image Correlation (DIC) method. To achieve deep indentation without cracking, a ductile material, 99% tin, is used. The results obtained from the DIC technique depend predominantly on the pattern conferred to the samples. Due to the absence of a natural pattern, black and white spray painting is used for greater contrast. The stress-strain curve of the material has been obtained and introduced in the Finite Element simulation code used, DEFORM™, allowing for accurate simulations. Two different 2D models have been used: a plain strain model to obtain the load curve and a plain stress model to evaluate the strain maps on the workpiece surface. The indentation displacement load curve has been compared between the FEM and the experimental results, showing a good correlation. Additionally, the strain maps obtained from the material surface with FEM and DIC are compared in order to validate the numerical model. The Von Mises strain results between both of them present a 10–20% difference. The results show that FEM is a good tool for simulating indentation processes, allowing for the evaluation of the maximum forces and deformations involved in the forming process. Additionally, the non-contact DIC technique shows its potential by measuring the superficial strain maps, validating the FEM results. PMID:28773038

  11. Material Flow Analysis in Indentation by Two-Dimensional Digital Image Correlation and Finite Elements Method.

    PubMed

    Bermudo, Carolina; Sevilla, Lorenzo; Castillo López, Germán

    2017-06-21

    The present work shows the material flow analysis in indentation by the numerical two dimensional Finite Elements (FEM) method and the experimental two-dimensional Digital Image Correlation (DIC) method. To achieve deep indentation without cracking, a ductile material, 99% tin, is used. The results obtained from the DIC technique depend predominantly on the pattern conferred to the samples. Due to the absence of a natural pattern, black and white spray painting is used for greater contrast. The stress-strain curve of the material has been obtained and introduced in the Finite Element simulation code used, DEFORM™, allowing for accurate simulations. Two different 2D models have been used: a plain strain model to obtain the load curve and a plain stress model to evaluate the strain maps on the workpiece surface. The indentation displacement load curve has been compared between the FEM and the experimental results, showing a good correlation. Additionally, the strain maps obtained from the material surface with FEM and DIC are compared in order to validate the numerical model. The Von Mises strain results between both of them present a 10-20% difference. The results show that FEM is a good tool for simulating indentation processes, allowing for the evaluation of the maximum forces and deformations involved in the forming process. Additionally, the non-contact DIC technique shows its potential by measuring the superficial strain maps, validating the FEM results.

  12. Mechanical indentation improves cerebral blood oxygenation signal quality of functional near-infrared spectroscopy (fNIRS) during breath holding

    NASA Astrophysics Data System (ADS)

    Vogt, William C.; Romero, Edwin; LaConte, Stephen M.; Rylander, Christopher G.

    2013-03-01

    Functional near-infrared spectroscopy (fNIRS) is a well-known technique for non-invasively measuring cerebral blood oxygenation, and many studies have demonstrated that fNIRS signals can be related to cognitive function. However, the fNIRS signal is attenuated by the skin, while scalp blood content has been reported to influence cerebral oxygenation measurements. Mechanical indentation has been shown to increase light transmission through soft tissues by causing interstitial water and blood flow away from the compressed region. To study the effects of indentation on fNIRS, a commercial fNIRS system with 16 emitter/detector pairs was used to measure cerebral blood oxygenation at 2 Hz. This device used diffuse reflectance at 730 nm and 850 nm to calculate deoxy- and oxy-hemoglobin concentrations. A borosilicate glass hemisphere was epoxied over each sensor to function as both an indenter and a lens. After placing the indenter/sensor assembly on the forehead, a pair of plastic bands was placed on top of the fNIRS headband and strapped to the head to provide uniform pressure and tightened to approx. 15 N per strap. Cerebral blood oxygenation was recorded during a breath holding regime (15 second hold, 15 second rest, 6 cycles) in 4 human subjects both with and without the indenter array. Results showed that indentation increased raw signal intensity by 85 +/- 35%, and that indentation increased amplitude of hemoglobin changes during breath cycles by 313% +/- 105%. These results suggest that indentation improves sensing of cerebral blood oxygenation, and may potentially enable sensing of deeper brain tissues.

  13. The effect of friction on indenter force and pile-up in numerical simulations of bone nanoindentation.

    PubMed

    Adam, C J; Swain, M V

    2011-10-01

    Nanoindentation is a useful technique for probing the mechanical properties of bone, and finite element (FE) modeling of the indentation allows inverse determination of elastoplastic constitutive properties. However, all but one FE study to date have assumed frictionless contact between indenter and bone. The aim of this study was to explore the effect of friction in simulations of bone nanoindentation. Two-dimensional axisymmetric FE simulations were performed using a spheroconical indenter of tip radius 0.6 μm and angle 90°. The coefficient of friction between indenter and bone was varied between 0.0 (frictionless) and 0.3. Isotropic linear elasticity was used in all simulations, with bone elastic modulus E = 13.56 GPa and Poisson's ratio of 0.3. Plasticity was incorporated using both Drucker-Prager and von Mises yield surfaces. Friction had a modest effect on the predicted force-indentation curve for both von Mises and Drucker-Prager plasticity, reducing maximum indenter displacement by 10% and 20% respectively as friction coefficient was increased from zero to 0.3 (at a maximum indenter force of 5 mN). However, friction has a much greater effect on predicted pile-up after indentation, reducing predicted pile-up from 0.27 to 0.11 μm with a von Mises model, and from 0.09 to 0.02 μm with Drucker-Prager plasticity. We conclude that it is potentially important to include friction in nanoindentation simulations of bone if pile-up is used to compare simulation results with experiment. Copyright © 2011 Elsevier Ltd. All rights reserved.

  14. Quantitative Imaging of Young's Modulus of Soft Tissues from Ultrasound Water Jet Indentation: A Finite Element Study

    PubMed Central

    Lu, Min-Hua; Mao, Rui; Lu, Yin; Liu, Zheng; Wang, Tian-Fu; Chen, Si-Ping

    2012-01-01

    Indentation testing is a widely used approach to evaluate mechanical characteristics of soft tissues quantitatively. Young's modulus of soft tissue can be calculated from the force-deformation data with known tissue thickness and Poisson's ratio using Hayes' equation. Our group previously developed a noncontact indentation system using a water jet as a soft indenter as well as the coupling medium for the propagation of high-frequency ultrasound. The novel system has shown its ability to detect the early degeneration of articular cartilage. However, there is still lack of a quantitative method to extract the intrinsic mechanical properties of soft tissue from water jet indentation. The purpose of this study is to investigate the relationship between the loading-unloading curves and the mechanical properties of soft tissues to provide an imaging technique of tissue mechanical properties. A 3D finite element model of water jet indentation was developed with consideration of finite deformation effect. An improved Hayes' equation has been derived by introducing a new scaling factor which is dependent on Poisson's ratios v, aspect ratio a/h (the radius of the indenter/the thickness of the test tissue), and deformation ratio d/h. With this model, the Young's modulus of soft tissue can be quantitatively evaluated and imaged with the error no more than 2%. PMID:22927890

  15. Quantitative imaging of young's modulus of soft tissues from ultrasound water jet indentation: a finite element study.

    PubMed

    Lu, Min-Hua; Mao, Rui; Lu, Yin; Liu, Zheng; Wang, Tian-Fu; Chen, Si-Ping

    2012-01-01

    Indentation testing is a widely used approach to evaluate mechanical characteristics of soft tissues quantitatively. Young's modulus of soft tissue can be calculated from the force-deformation data with known tissue thickness and Poisson's ratio using Hayes' equation. Our group previously developed a noncontact indentation system using a water jet as a soft indenter as well as the coupling medium for the propagation of high-frequency ultrasound. The novel system has shown its ability to detect the early degeneration of articular cartilage. However, there is still lack of a quantitative method to extract the intrinsic mechanical properties of soft tissue from water jet indentation. The purpose of this study is to investigate the relationship between the loading-unloading curves and the mechanical properties of soft tissues to provide an imaging technique of tissue mechanical properties. A 3D finite element model of water jet indentation was developed with consideration of finite deformation effect. An improved Hayes' equation has been derived by introducing a new scaling factor which is dependent on Poisson's ratios v, aspect ratio a/h (the radius of the indenter/the thickness of the test tissue), and deformation ratio d/h. With this model, the Young's modulus of soft tissue can be quantitatively evaluated and imaged with the error no more than 2%.

  16. Confocal microscopy indentation system for studying in situ chondrocyte mechanics.

    PubMed

    Han, Sang-Kuy; Colarusso, Pina; Herzog, Walter

    2009-10-01

    Chondrocytes synthesize extracellular matrix molecules, thus they are essential for the development, adaptation and maintenance of articular cartilage. Furthermore, it is well accepted that the biosynthetic activity of chondrocytes is influenced by the mechanical environment. Therefore, their response to mechanical stimuli has been studied extensively. Much of the knowledge in this area of research has been derived from testing of isolated cells, cartilage explants, and fixed cartilage specimens: systems that differ in important aspects from chondrocytes embedded in articular cartilage and observed during loading conditions. In this study, current model systems have been improved by working with the intact cartilage in real time. An indentation system was designed on a confocal microscope that allows for simultaneous loading and observation of chondrocytes in their native environment. Cell mechanics were then measured under precisely controlled loading conditions. The indentation system is based on a light transmissible cylindrical glass indentor of 0.17 mm thickness and 1.64 mm diameter that is aligned along the focal axis of the microscope and allows for real time observation of live cells in their native environment. The system can be used to study cell deformation and biological responses, such as calcium sparks, while applying prescribed loads on the cartilage surface. It can also provide novel information on the relationship between cell loading and cartilage adaptive/degenerative processes in the intact tissue.

  17. On the determination of elastic coefficients from indentation experiments

    NASA Astrophysics Data System (ADS)

    Tardieu, N.; Constantinescu, A.

    2000-06-01

    The main result of this paper is the extension of the adjoint state method to variational inequalities. This is done for the Signorini contact problem (Kikuchi N and Oden J T 1988 Contact Problems in Elasticity: a Study of Variational Inequalities and Finite Element Methods (Philadelphia: SIAM)) and used for the identification of elastic coefficients from an indentation test. The result is obtained by two independent approaches based on the penalized and respectively, mixed formulations of the direct problem, a Signorini contact problem. An important and astonishing result is that the obtained adjoint problem is a linear problem with Dirichlet boundary conditions. This is expected for problems described with variational equalities (Bui H D 1993 Introduction Aux Problèmes Inverses en Mécanique des Matériaux (Paris: Eyrolles) (Engl. Transl. (Boca Raton, FL: CRC Press)), Lions J L 1968 Contrôle Optimal des Systèmes Gouvernés par des Équations aux Dérivées Partielles (Dunod)), but is a new result for problems described with variational inequalities. As an application, the elastic coefficients of an isotropic body have been identified from the knowledge of a displacement-force curve measured during an indentation test. The efficiency of the method is illustrated on numerical examples for the identification of a bimaterial and a functional gradient material.

  18. Scleral indentation height after laser scleral buckling

    NASA Astrophysics Data System (ADS)

    Kang, Se W.; Parel, Jean-Marie A.; Manns, Fabrice; Lee, Jawheung; Smiddy, William E.

    1998-06-01

    Laser scleral buckling (LSB) and scleral buckling are methods of inducing scleral indentation, a necessary objective in standard retinal reattachment surgery. The purpose of this study was to compare the height of scleral indentation produced by both modalities. Twenty (4 columns, 5 rows) overlapping spots of pulsed Holmium:YAG or Thulium:YAG laser were applied at the equatorial sclera in 20 human cadaver eyes (LSB group). The diameter of each laser spot was set to 2.5 mm using a custom-made laser probe. Total energy of Holmium:YAG and Thulium:YAG applied to each laser spot were 1285 mJ and 815 mJ, respectively. Scleral shrinkage and change in scleral thickness were measured. A radially oriented 5 mm silicone band was placed at the equator in 10 human cadaver eyes (explant group). The intraocular pressure (IOP) was adjusted to 4 mm Hg preoperatively, and to 16 mm Hg postoperatively in all eyes and monitored during the procedure. Scleral indentation height, assessed in frozen sections made along the eyeball equator, produced by Holmium:YAG (1.07 mm) and Thulium:YAG (1.30 mm) was less than that of explant group (3.12 mm) (p less than 0.05). Each application of a laser spot elevated the IOP by 4.9 mm Hg and the IOP decreased into a quarter of its elevation after 3.64 seconds. LSB with Thulium:YAG laser is potentially useful in retinal detachments when combined with vitrectomy for creating a shallow and broad buckling effect (i.e. in proliferative vitreoretinopathy cases).

  19. Estimation of local anisotropy of plexiform bone: Comparison between depth sensing micro-indentation and Reference Point Indentation.

    PubMed

    Dall'Ara, E; Grabowski, P; Zioupos, P; Viceconti, M

    2015-11-26

    The recently developed Reference Point Indentation (RPI) allows the measurements of bone properties at the tissue level in vivo. The goal of this study was to compare the local anisotropic behaviour of bovine plexiform bone measured with depth sensing micro-indentation tests and with RPI. Fifteen plexiform bone specimens were extracted from a bovine femur and polished down to 0.05µm alumina paste for indentations along the axial, radial and circumferential directions (N=5 per group). Twenty-four micro-indentations (2.5µm in depth, 10% of them were excluded for testing problems) and four RPI-indentations (~50µm in depth) were performed on each sample. The local indentation modulus Eind was found to be highest for the axial direction (24.3±2.5GPa) compared to the one for the circumferential indentations (19% less stiff) and for the radial direction (30% less stiff). RPI measurements were also found to be dependent on indentation direction (p<0.001) with the exception of the Indentation Distance Increase (IDI) (p=0.173). In particular, the unloading slope US1 followed similar trends compared to the Eind: 0.47±0.03N/µm for axial, 11% lower for circumferential and 17% lower for radial. Significant correlations were found between US1 and Eind (p=0.001; R(2)=0.58), while no significant relationship was found between IDI and any of the micro-indentation measurements (p>0.157). In conclusion some of the RPI measurements can provide information about local anisotropy but IDI cannot. Moreover, there is a linear relationship between most local mechanical properties measured with RPI and with micro-indentations, but IDI does not correlate with any micro-indentation measurements.

  20. Bone Tissue Properties Measurement by Reference Point Indentation in Glucocorticoid-Induced Osteoporosis.

    PubMed

    Mellibovsky, Leonardo; Prieto-Alhambra, Daniel; Mellibovsky, Fernando; Güerri-Fernández, Roberto; Nogués, Xavier; Randall, Connor; Hansma, Paul K; Díez-Perez, Adolfo

    2015-09-01

    Glucocorticoids, widely used in inflammatory disorders, rapidly increase bone fragility and, therefore, fracture risk. However, common bone densitometry measurements are not sensitive enough to detect these changes. Moreover, densitometry only partially recognizes treatment-induced fracture reductions in osteoporosis. Here, we tested whether the reference point indentation technique could detect bone tissue property changes early after glucocorticoid treatment initiation. After initial laboratory and bone density measurements, patients were allocated into groups receiving calcium + vitamin D (Ca+D) supplements or anti-osteoporotic drugs (risedronate, denosumab, teriparatide). Reference point indentation was performed on the cortical bone layer of the tibia by a handheld device measuring bone material strength index (BMSi). Bone mineral density was measured by dual-energy X-ray absorptiometry (DXA). Although Ca+D-treated patients exhibited substantial and significant deterioration, risedronate-treated patients exhibited no significant change, and both denosumab- and teriparatide-treated participants exhibited significantly improved BMSi 7 weeks after initial treatment compared with baseline; these trends remained stable for 20 weeks. In contrast, no densitometry changes were observed during this study period. In conclusion, our study is the first to our knowledge to demonstrate that reference point indentation is sensitive enough to reflect changes in cortical bone indentation after treatment with osteoporosis therapies in patients newly exposed to glucocorticoids.

  1. Grid indentation analysis of mechanical properties of composite electrodes in Li-ion batteries

    SciTech Connect

    Vasconcelos, Luize Scalco de; Xu, Rong; Li, Jianlin; Zhao, Kejie

    2016-03-09

    We report that electrodes in commercial rechargeable batteries are microscopically heterogeneous materials. The constituent components, including active materials, polymeric binders, and porous conductive matrix, often have large variation in their mechanical properties, making the mechanical characterization of composite electrodes a challenging task. In a model system of LiNi0.5Mn0.3Co0.2O2 cathode, we employ the instrumented grid indentation to determine the elastic modulus and hardness of the constituent phases. The approach relies on a large array of nanoindentation experiments and statistical analysis of the resulting data provided that the maximum indentation depth is carefully chosen. The statistically extracted properties of the active particles and the surrounding medium are in good agreement with the tests of targeted indentation at selected sites. Lastly, the combinatory technique of grid indentation and statistical deconvolution represents a fast and reliable route to quantify the mechanical properties of composite electrodes that feed the parametric input for the mechanics models.

  2. Grid indentation analysis of mechanical properties of composite electrodes in Li-ion batteries

    DOE PAGES

    Vasconcelos, Luize Scalco de; Xu, Rong; Li, Jianlin; ...

    2016-03-09

    We report that electrodes in commercial rechargeable batteries are microscopically heterogeneous materials. The constituent components, including active materials, polymeric binders, and porous conductive matrix, often have large variation in their mechanical properties, making the mechanical characterization of composite electrodes a challenging task. In a model system of LiNi0.5Mn0.3Co0.2O2 cathode, we employ the instrumented grid indentation to determine the elastic modulus and hardness of the constituent phases. The approach relies on a large array of nanoindentation experiments and statistical analysis of the resulting data provided that the maximum indentation depth is carefully chosen. The statistically extracted properties of the active particlesmore » and the surrounding medium are in good agreement with the tests of targeted indentation at selected sites. Lastly, the combinatory technique of grid indentation and statistical deconvolution represents a fast and reliable route to quantify the mechanical properties of composite electrodes that feed the parametric input for the mechanics models.« less

  3. Intraoperative measurement of indenter-induced brain deformation: a feasibility study

    NASA Astrophysics Data System (ADS)

    Ji, Songbai; Fan, Xiaoyao; Roberts, David W.; Paulsen, Keith D.

    2014-03-01

    Accurate measurement of soft tissue material properties is critical for characterizing its biomechanical behaviors but can be challenging especially for the human brain in vivo. In this study, we investigated the feasibility of inducing and detecting cortical surface deformation intraoperatively for patients undergoing open skull neurosurgeries. A custom diskshaped indenter made of high-density tungsten (diameter of 15 mm with a thickness of 6 mm) was used to induce deformation on the brain cortical surface immediately after dural opening. Before and after placing the indenter, sequences (typically 250 frames at 15 frames-per-second, or ~17 seconds) of high-resolution stereo image pairs were acquired to capture the harmonic motion of the exposed cortical surface as due to blood pressure pulsation and respiration. For each sequence with the first left image serving as a baseline, an optical-flow motion-tracking algorithm was used to detect in-sequence cortical surface deformation. The resulting displacements of the exposed features within the craniotomy were spatially averaged to identify the temporal frames corresponding to motion peak magnitudes. Corresponding image pairs were then selected to reconstruct full-field three-dimensional (3D) cortical surfaces before and after indentation, respectively, from which full 3D displacement fields were obtained by registering their projection images. With one clinical patient case, we illustrate the feasibility of the technique in detecting indenter-induced cortical surface deformation in order to allow subsequent processing to determine material properties of the brain in vivo.

  4. Investigation of inhomogeneous and anisotropic material behavior of porcine thoracic aorta using nano-indentation tests.

    PubMed

    Kermani, Golriz; Hemmasizadeh, Ali; Assari, Soroush; Autieri, Michael; Darvish, Kurosh

    2017-05-01

    This study investigates the inhomogeneity and anisotropy of porcine descending thoracic aorta in three dimensions using a custom-made nano-indentation technique and a quasi-linear viscoelastic modeling approach. The indentation tests were conducted in axial, circumferential, and radial orientations with about 100 μm spatial resolution. The ratio of the elastic moduli obtained in different orientations was used to quantify the tissue local anisotropy. The distal sections were generally stiffer than the proximal ones in both axial and circumferential indentations. Four distinct layers were identified across the thickness with significantly different mechanical properties. The stiffness of the medial quadrant was significantly lower than all other quadrants in axial indentation. The anisotropic behavior of the tissue was more pronounced in the lateral quadrant of the distal sections. The results of this study can be used to better understand the mechanisms of aorta deformation and improve the spatial accuracy of computational models of aorta. Copyright © 2016 Elsevier Ltd. All rights reserved.

  5. Computational and experimental methodology for site-matched investigations of the influence of mineral mass fraction and collagen orientation on the axial indentation modulus of lamellar bone☆

    PubMed Central

    Spiesz, Ewa M.; Reisinger, Andreas G.; Kaminsky, Werner; Roschger, Paul; Pahr, Dieter H.; Zysset, Philippe K.

    2013-01-01

    Relationships between mineralization, collagen orientation and indentation modulus were investigated in bone structural units from the mid-shaft of human femora using a site-matched design. Mineral mass fraction, collagen fibril angle and indentation moduli were measured in registered anatomical sites using backscattered electron imaging, polarized light microscopy and nano-indentation, respectively. Theoretical indentation moduli were calculated with a homogenization model from the quantified mineral densities and mean collagen fibril orientations. The average indentation moduli predicted based on local mineralization and collagen fibers arrangement were not significantly different from the average measured experimentally with nanoindentation (p=0.9). Surprisingly, no substantial correlation of the measured indentation moduli with tissue mineralization and/or collagen fiber arrangement was found. Nano-porosity, micro-damage, collagen cross-links, non-collagenous proteins or other parameters affect the indentation measurements. Additional testing/simulation methods need to be considered to properly understand the variability of indentation moduli, beyond the mineralization and collagen arrangement in bone structural units. PMID:23994944

  6. The nano-epsilon dot method for strain rate viscoelastic characterisation of soft biomaterials by spherical nano-indentation.

    PubMed

    Mattei, G; Gruca, G; Rijnveld, N; Ahluwalia, A

    2015-10-01

    Nano-indentation is widely used for probing the micromechanical properties of materials. Based on the indentation of surfaces using probes with a well-defined geometry, the elastic and viscoelastic constants of materials can be determined by relating indenter geometry and measured load and displacement to parameters which represent stress and deformation. Here we describe a method to derive the viscoelastic properties of soft hydrated materials at the micro-scale using constant strain rates and stress-free initial conditions. Using a new self-consistent definition of indentation stress and strain and corresponding unique depth-independent expression for indentation strain rate, the epsilon dot method, which is suitable for bulk compression testing, is transformed to nano-indentation. We demonstrate how two materials can be tested with a displacement controlled commercial nano-indentor using the nano-espilon dot method (nano-ε̇M) to give values of instantaneous and equilibrium elastic moduli and time constants with high precision. As samples are tested in stress-free initial conditions, the nano-ε̇M could be useful for characterising the micro-mechanical behaviour of soft materials such as hydrogels and biological tissues at cell length scales.

  7. Indentability of conventional and negative Poisson's ratio foams

    NASA Technical Reports Server (NTRS)

    Lakes, R. S.; Elms, K.

    1992-01-01

    The indentation resistance of foams, both of conventional structure and of reentrant structure giving rise to negative Poisson's ratio, is studied using holographic interferometry. In holographic indentation tests, reentrant foams had higher yield strength and lower stiffness than conventional foams of the same original relative density. Calculated energy absorption for dynamic impact is considerably higher for reentrant foam than conventional foam.

  8. Nanoscale Etching and Indentation of Silicon Surfaces with Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Dzegilenko, Fedor N.; Srivastava, Deepak; Saini, Subhash

    1998-01-01

    The possibility of nanolithography of silicon and germanium surfaces with bare carbon nanotube tips of scanning probe microscopy devices is considered with large scale classical molecular dynamics (MD) simulations employing Tersoff's reactive many-body potential for heteroatomic C/Si/Ge system. Lithography plays a key role in semiconductor manufacturing, and it is expected that future molecular and quantum electronic devices will be fabricated with nanolithographic and nanodeposition techniques. Carbon nanotubes, rolled up sheets of graphene made of carbon, are excellent candidates for use in nanolithography because they are extremely strong along axial direction and yet extremely elastic along radial direction. In the simulations, the interaction of a carbon nanotube tip with silicon surfaces is explored in two regimes. In the first scenario, the nanotubes barely touch the surface, while in the second they are pushed into the surface to make "nano holes". The first - gentle scenario mimics the nanotube-surface chemical reaction induced by the vertical mechanical manipulation of the nanotube. The second -digging - scenario intends to study the indentation profiles. The following results are reported in the two cases. In the first regime, depending on the surface impact site, two major outcomes outcomes are the selective removal of either a single surface atom or a surface dimer off the silicon surface. In the second regime, the indentation of a silicon substrate by the nanotube is observed. Upon the nanotube withdrawal, several surface silicon atoms are adsorbed at the tip of the nanotube causing significant rearrangements of atoms comprising the surface layer of the silicon substrate. The results are explained in terms of relative strength of C-C, C-Si, and Si-Si bonds. The proposed method is very robust and does not require applied voltage between the nanotube tips and the surface. The implications of the reported controllable etching and hole-creating for

  9. Nanoscale Etching and Indentation of Silicon Surfaces with Carbon Nanotubes

    NASA Technical Reports Server (NTRS)

    Dzegilenko, Fedor N.; Srivastava, Deepak; Saini, Subhash

    1998-01-01

    The possibility of nanolithography of silicon and germanium surfaces with bare carbon nanotube tips of scanning probe microscopy devices is considered with large scale classical molecular dynamics (MD) simulations employing Tersoff's reactive many-body potential for heteroatomic C/Si/Ge system. Lithography plays a key role in semiconductor manufacturing, and it is expected that future molecular and quantum electronic devices will be fabricated with nanolithographic and nanodeposition techniques. Carbon nanotubes, rolled up sheets of graphene made of carbon, are excellent candidates for use in nanolithography because they are extremely strong along axial direction and yet extremely elastic along radial direction. In the simulations, the interaction of a carbon nanotube tip with silicon surfaces is explored in two regimes. In the first scenario, the nanotubes barely touch the surface, while in the second they are pushed into the surface to make "nano holes". The first - gentle scenario mimics the nanotube-surface chemical reaction induced by the vertical mechanical manipulation of the nanotube. The second -digging - scenario intends to study the indentation profiles. The following results are reported in the two cases. In the first regime, depending on the surface impact site, two major outcomes outcomes are the selective removal of either a single surface atom or a surface dimer off the silicon surface. In the second regime, the indentation of a silicon substrate by the nanotube is observed. Upon the nanotube withdrawal, several surface silicon atoms are adsorbed at the tip of the nanotube causing significant rearrangements of atoms comprising the surface layer of the silicon substrate. The results are explained in terms of relative strength of C-C, C-Si, and Si-Si bonds. The proposed method is very robust and does not require applied voltage between the nanotube tips and the surface. The implications of the reported controllable etching and hole-creating for

  10. The bone diagnostic instrument II: indentation distance increase.

    PubMed

    Hansma, Paul; Turner, Patricia; Drake, Barney; Yurtsev, Eugene; Proctor, Alexander; Mathews, Phillip; Lulejian, Jason; Lelujian, Jason; Randall, Connor; Adams, Jonathan; Jungmann, Ralf; Garza-de-Leon, Federico; Fantner, Georg; Mkrtchyan, Haykaz; Pontin, Michael; Weaver, Aaron; Brown, Morton B; Sahar, Nadder; Rossello, Ricardo; Kohn, David

    2008-06-01

    The bone diagnostic instrument (BDI) is being developed with the long-term goal of providing a way for researchers and clinicians to measure bone material properties of human bone in vivo. Such measurements could contribute to the overall assessment of bone fragility in the future. Here, we describe an improved BDI, the Osteoprobe IItrade mark. In the Osteoprobe IItrade mark, the probe assembly, which is designed to penetrate soft tissue, consists of a reference probe (a 22 gauge hypodermic needle) and a test probe (a small diameter, sharpened rod) which slides through the inside of the reference probe. The probe assembly is inserted through the skin to rest on the bone. The distance that the test probe is indented into the bone can be measured relative to the position of the reference probe. At this stage of development, the indentation distance increase (IDI) with repeated cycling to a fixed force appears to best distinguish bone that is more easily fractured from bone that is less easily fractured. Specifically, in three model systems, in which previous mechanical testing and/or tests reported here found degraded mechanical properties such as toughness and postyield strain, the BDI found increased IDI. However, it must be emphasized that, at this time, neither the IDI nor any other mechanical measurement by any technique has been shown clinically to correlate with fracture risk. Further, we do not yet understand the mechanism responsible for determining IDI beyond noting that it is a measure of the continuing damage that results from repeated loading. As such, it is more a measure of plasticity than elasticity in the bone.

  11. Invited Article: Indenter materials for high temperature nanoindentation

    NASA Astrophysics Data System (ADS)

    Wheeler, J. M.; Michler, J.

    2013-10-01

    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.

  12. A novel collagen gel-based measurement technique for quantitation of cell contraction force

    PubMed Central

    Jin, Tianrong; Li, Li; Siow, Richard C. M.; Liu, Kuo-Kang

    2015-01-01

    Cell contraction force plays an important role in wound healing, inflammation, angiogenesis and metastasis. This study describes a novel method to quantify single cell contraction force in vitro using human aortic adventitial fibroblasts embedded in a collagen gel. The technique is based on a depth sensing nano-indentation tester to measure the thickness and elasticity of collagen gels containing stimulated fibroblasts and a microscopy imaging system to estimate the gel area. In parallel, a simple theoretical model has been developed to calculate cell contraction force based on the measured parameters. Histamine (100 µM) was used to stimulate fibroblast contraction while the myosin light chain kinase inhibitor ML-7 (25 µM) was used to inhibit cell contraction. The collagen matrix used in the model provides a physiological environment for fibroblast contraction studies. Measurement of changes in collagen gel elasticity and thickness arising from histamine treatments provides a novel convenient technique to measure cell contraction force within a collagen matrix. This study demonstrates that histamine can elicit a significant increase in contraction force of fibroblasts embedded in collagen, while the Young's modulus of the gel decreases due to the gel degradation. PMID:25977960

  13. A novel collagen gel-based measurement technique for quantitation of cell contraction force.

    PubMed

    Jin, Tianrong; Li, Li; Siow, Richard C M; Liu, Kuo-Kang

    2015-05-06

    Cell contraction force plays an important role in wound healing, inflammation,angiogenesis and metastasis. This study describes a novel method to quantify single cell contraction force in vitro using human aortic adventitial fibroblasts embedded in a collagen gel. The technique is based on a depth sensing nano-indentation tester to measure the thickness and elasticity of collagen gels containing stimulated fibroblasts and a microscopy imaging system to estimate the gel area. In parallel, a simple theoretical model has been developed to calculate cell contraction force based on the measured parameters. Histamine (100 mM) was used to stimulate fibroblast contraction while the myosin light chain kinase inhibitor ML-7 (25 mM) was used to inhibit cell contraction. The collagen matrix used in the model provides a physiological environment for fibroblast contraction studies. Measurement of changes in collagen gel elasticity and thickness arising from histamine treatments provides a novel convenient technique to measure cell contraction force within a collagen matrix. This study demonstrates that histamine can elicit a significant increase in contraction force of fibroblasts embedded in collagen,while the Young's modulus of the gel decreases due to the gel degradation.

  14. On the Influence of Elastic Deformation for Residual Stress Determination by Sharp Indentation Testing

    NASA Astrophysics Data System (ADS)

    Larsson, Per-Lennart

    2017-08-01

    The determination of residual stresses in engineering materials using sharp indentation testing is studied analytically and numerically. The numerical part of the investigation is based on the finite element method. In particular, the effect from elastic deformations on global indentation properties is discussed in detail. This effect is essential when residual stresses are to be determined based on the change of the contact area due to such stresses. However, standard relations for this purpose are founded on the fact that the material hardness is invariant as regards residual (applied) stresses. Presently, this assumption is scrutinized and it is shown that it is only valid at dominating plastic deformation around the contact region. The hardness dependence of residual stresses can, however, be correlated in the same way as in the case of stress-free materials, indicating that the wealth of characterization formulas pertinent to indentation hardness is available also for the purpose of residual field determination. Only cone indentation of elastic-perfectly plastic materials is considered, but the generality of the results is discussed in some detail.

  15. On the Influence of Elastic Deformation for Residual Stress Determination by Sharp Indentation Testing

    NASA Astrophysics Data System (ADS)

    Larsson, Per-Lennart

    2017-07-01

    The determination of residual stresses in engineering materials using sharp indentation testing is studied analytically and numerically. The numerical part of the investigation is based on the finite element method. In particular, the effect from elastic deformations on global indentation properties is discussed in detail. This effect is essential when residual stresses are to be determined based on the change of the contact area due to such stresses. However, standard relations for this purpose are founded on the fact that the material hardness is invariant as regards residual (applied) stresses. Presently, this assumption is scrutinized and it is shown that it is only valid at dominating plastic deformation around the contact region. The hardness dependence of residual stresses can, however, be correlated in the same way as in the case of stress-free materials, indicating that the wealth of characterization formulas pertinent to indentation hardness is available also for the purpose of residual field determination. Only cone indentation of elastic-perfectly plastic materials is considered, but the generality of the results is discussed in some detail.

  16. Insights into reference point indentation involving human cortical bone: sensitivity to tissue anisotropy and mechanical behavior.

    PubMed

    Granke, Mathilde; Coulmier, Aurélie; Uppuganti, Sasidhar; Gaddy, Jennifer A; Does, Mark D; Nyman, Jeffry S

    2014-09-01

    Reference point indentation (RPI) is a microindentation technique involving 20 cycles of loading in "force-control" that can directly assess a patient׳s bone tissue properties. Even though preliminary clinical studies indicate a capability for fracture discrimination, little is known about what mechanical behavior the various RPI properties characterize and how these properties relate to traditional mechanical properties of bone. To address this, the present study investigated the sensitivity of RPI properties to anatomical location and tissue organization as well as examined to what extent RPI measurements explain the intrinsic mechanical properties of human cortical bone. Multiple indents with a target force of 10N were done in 2 orthogonal directions (longitudinal and transverse) per quadrant (anterior, medial, posterior, and lateral) of the femoral mid-shaft acquired from 26 donors (25-101 years old). Additional RPI measurements were acquired for 3 orthogonal directions (medial only). Independent of age, most RPI properties did not vary among these locations, but they did exhibit transverse isotropy such that resistance to indentation is greater in the longitudinal (axial) direction than in the transverse direction (radial or circumferential). Next, beam specimens (~2mm×5mm×40mm) were extracted from the medial cortex of femoral mid-shafts, acquired from 34 donors (21-99 years old). After monotonically loading the specimens in three-point bending to failure, RPI properties were acquired from an adjacent region outside the span. Indent direction was orthogonal to the bending axis. A significant inverse relationship was found between resistance to indentation and the apparent-level mechanical properties. Indentation distance increase (IDI) and a linear combination of IDI and the loading slope, averaged over cycles 3 through 20, provided the best explanation of the variance in ultimate stress (r(2)=0.25, p=0.003) and toughness (r(2)=0.35, p=0.004), respectively

  17. Adhesion between dental ceramic and bonding resin: quantitative evaluation by Vickers indenter methodology.

    PubMed

    Doucet, Sylvie; Tavernier, Bruno; Colon, Pierre; Picard, Bernard

    2008-01-01

    The purpose of this study was to evaluate the adhesion to dental ceramic by Vickers indenter methodology. This technique allows the creation of adhesive fractures and determines the influence of the surface treatment on adhesive capacities. A single bond adhesive system (One Step Bisco) was applied to ceramic Vitapan 3D Master CE 0124 samples. Ceramic samples were polished with 500 or 4000-grit paper, sandblasted or not (Sa/NSa), treated with fluorhydric acid or not (A/NA) and silane or not (Si/NSi). The experimental groups (Gr) were: (Gr 1) 4000; (Gr 2) 4000+Si; (Gr 3) 4000+Sa+A; (Gr 4) 4000+Sa+A+Si; (Gr 5) 500+Sa+A+Si. Each sample was indented with the diamond Vickers indenter Leitz Durimet 2 (Wetzlar, Germany) using a load of 20N for 30s. The surfaces of the debonded areas were observed in an optical microscope providing a digital image of the debonded surface. The adhesion bond strength was calculated according to the formula of Engel and Roshon [Engel PA, Roshon DD. Indentation-debonding of an adhered surface layer. J Adhesion 1979;10(33): 237-53]. The statistical analysis was conducted using Student's t test (p<0.05). The values obtained for each group were: (Gr 1) 32MPa; (Gr 2) 52MPa; (Gr 3) 112MPa; (Gr 4) 131MPa; (Gr 5) 265MPa. There is a significant improvement in bond strength with the silane application on the 4000 polished surface (Gr 2). However, there is no significant difference when silane is applied or not on a sanded and etched ceramic (Gr 4). Bond strengths were higher with 500 grit polished, sanded, etched with silane application on the surface (Gr 5). The Vickers indenter methodology is able to discriminate between the influences of different surface treatments on the adhesion of an adhesive layer on a feldspathic ceramic.

  18. Indentation creep behavior of a direct-filling silver alternative to amalgam.

    PubMed

    Xu, H H; Liao, H; Eichmiller, F C

    1998-12-01

    Amalgam creep has been identified as a key parameter associated with marginal breakdown and corrosion. The aim of this study was to evaluate the time-dependent deformation (creep) of a novel silver filling material as an alternative to amalgam. We made the silver specimens by pressing a precipitated powder at room temperature to a density that can be achieved in clinical hand consolidation. The surface of the silver was either polished or burnished. To examine local contact creep and the effect of surface finishing, we used an indentation creep method in which a Vickers indenter was loaded on the specimen surface at a load of 10 N with dwell times of 5 sec to 6x10(4) sec. We used a bonded-interface technique to examine subsurface creep mechanisms. The flexural strength (mean+/-SD; n = 10) was 86+/-20 MPa for amalgam, 180+/-21 MPa for polished silver, and 209+/-19 MPa for burnished silver-values which are significantly different from each other (family confidence coefficient = 0.95; Tukey's multiple-comparison test). Indentation creep manifested as hardness number decreasing with increased dwell time. With dwell time increasing from 5 sec to 6x10(4) sec, the hardness number of amalgam was reduced by approximately 80%; that of the polished silver and the burnished silver was reduced by only 40%. Subsurface creep in amalgam consisted of the shape change of the alloy particles from spherical to elongated shapes, and the separation of matrix grains from each other, possibly due to grain-boundary sliding. Creep of the polished silver occurred by densification reducing porosity and increasing hardness; that of the burnished silver occurred by the displacement of the burnished layer. These results suggest that, due to creep-induced subsurface work-hardening and densification, the consolidated silver exhibits a higher resistance to indentation creep than does amalgam. The hardness number of silver approaches that of amalgam after prolonged indentation loading.

  19. Compression of nanowires using a flat indenter: diametrical elasticity measurement.

    PubMed

    Wang, Zhao; Mook, William M; Niederberger, Christoph; Ghisleni, Rudy; Philippe, Laetitia; Michler, Johann

    2012-05-09

    A new experimental approach for the characterization of the diametrical elastic modulus of individual nanowires is proposed by implementing a micro/nanoscale diametrical compression test geometry, using a flat punch indenter. A 250 nm diameter single crystal silicon nanowire is compressed inside of a scanning electron microscope. Since silicon is highly anisotropic, the wire crystal orientation in the compression axis is determined by electron backscatter diffraction. In order to analyze the load-displacement compression data, a two-dimensional analytical closed-form solution based on a classical contact model is proposed. The results of the analytical model are compared with those of finite element simulations and to the experimental diametrical compression results and show good agreement.

  20. Topographic evolution of a continental indenter: The eastern Southern Alps

    NASA Astrophysics Data System (ADS)

    Robl, Jörg; Heberer, Bianca; Prasicek, Günther; Neubauer, Franz; Hergarten, Stefan

    2017-04-01

    The topographic evolution of the eastern Southern Alps (ESA) is controlled by the Late Oligocene - Early Miocene indentation of the Adriatic microplate into an overthickened orogenic wedge emplaced on top of the European plate. Rivers follow topographic gradients that evolve during continental collision and in turn incise into bedrock counteracting the formation of topography. In principle, erosional surface processes tend to establish a topographic steady state so that an interpretation of topographic metrics in terms of the latest tectonic history should be straightforward. However, a series of complications impede deciphering the topographic record of the ESA. The Pleistocene glaciations locally excavated alpine valleys and perturbed fluvial drainages. The Late Miocene desiccation of the Mediterranean Sea and the uplift of the northern Molasse Basin led to significant base level changes in the far field of the ESA and the Eastern Alps (EA), respectively. Among this multitude of mechanisms, the processes that dominate the current topographic evolution of the ESA and the ESA-EA drainage divide have not been identified and a number of questions regarding the interaction of crustal deformation, erosion and climate in shaping the present-day topography remain. We demonstrate the expected topographic effects of each mechanism in a 1-dimensional model and compare them with observed channel metrics. Modern uplift rates are largely consistent with long-term exhumation in the ESA and with variations in the normalized steepness index (ksn) indicating a stable uplift and erosion pattern since Miocene times. We find that ksn increases with uplift rate and declines from the indenter tip in the northwest to the foreland basin in the southeast. The number and magnitude of knickpoints and the distortion in longitudinal channel profiles similarly decrease towards the east. Most knickpoints probably evolved during Pleistocene glaciation cycles, but may represent the incrementally

  1. Influence of Penetration Rate and Indenter Diameter in Strength Measurement by Indentation Testing on Small Rock Specimens

    NASA Astrophysics Data System (ADS)

    Haftani, Mohammad; Bohloli, Bahman; Nouri, Alireza; Javan, Mohammad Reza Maleki; Moosavi, Mahdi; Moradi, Majid

    2015-03-01

    Indentation testing has been developed as an unconventional method to determine intact rock strength using small rock specimens within the size of drill cuttings. In previous investigations involving indentation testing, researchers have used different indenter stylus geometries, penetration rate (PR) and specimen sizes. These dissimilarities can restrict applications of this method for strength measurement and lead to non-comparable results. This paper investigates the influence of indenter diameter (ID) and PR on indentation indices for carbonate rocks to provide objective comparison and application of the existing correlations. As part of this research, several indentation tests were conducted using different IDs and PRs. The laboratory test results showed that indentation indices can be affected by ID while PR has only minor effect on the indentation indices. Thus, a normalizing function was presented to reduce the dependency of test results to ID. Verification of the findings with independent data confirms the suitability of the suggested normalizing function in determining the rock uniaxial compressive strength using testing data obtained from various IDs and PRs.

  2. Viscosity of solids determined by shock wave action on hemispherical indentations

    SciTech Connect

    Maiden, D.; Mitchell, A.; Wilkins, M.

    1989-01-31

    An experimental technique for determining the viscosity of solids is investigated. The technique was developed by Mali from the Institute of Hydrodynamics at Novosibirsk. It involves determining the jet-no-jet condition from a shock wave impacting a plate with hemispherical indentations. The indentation radius when a jet does not form identifies a critical Reynolds number. Numerical simulations of the experiment are performed using a viscoplastic constitutive model. The viscosity is determined by adjusting it until the speed of the jet and the critical Reynolds number match experiment. Results show that the viscosity of copper is two orders of magnitude lower than Mali's, but are in agreement with data derived from shock wave profiles by USA authors. 10 refs., 12 figs., 3 tabs.

  3. Indentation Load Effect on Young's Modulus and Hardness of Porous Sialon Ceramic by Depth Sensing Indentation Tests

    NASA Astrophysics Data System (ADS)

    Osman, Sahin

    2007-11-01

    Depth sensing indentation (DSI) tests at the range of 200-1800 mN are performed on porous sialon ceramic to determine the indentation load on Young's modulus and hardness values. The Young modulus and hardness (Dynamic and Martens) values are deduced by analysing the unloading segments of the DSI test load-displacement curves using the Oliver-Pharr method. It is found that Young's modulus Er, the dynamic hardness HD and the Martens hardness HM exhibit significant indentation load dependences. The values of Young's modulus and hardness decrease with the increasing indentation load, as a result of indentation load effect. The experimental hf/hm ratios lower than the critical value 0.7, with hm being the maximum penetration depth during loading and hf the final unloading depth, indicate that our sample shows the work hardening behaviour.

  4. A Progressive Damage Model for Predicting Permanent Indentation and Impact Damage in Composite Laminates

    NASA Astrophysics Data System (ADS)

    Ji, Zhaojie; Guan, Zhidong; Li, Zengshan

    2016-12-01

    In this paper, a progressive damage model was established on the basis of ABAQUS software for predicting permanent indentation and impact damage in composite laminates. Intralaminar and interlaminar damage was modelled based on the continuum damage mechanics (CDM) in the finite element model. For the verification of the model, low-velocity impact tests of quasi-isotropic laminates with material system of T300/5228A were conducted. Permanent indentation and impact damage of the laminates were simulated and the numerical results agree well with the experiments. It can be concluded that an obvious knee point can be identified on the curve of the indentation depth versus impact energy. Matrix cracking and delamination develops rapidly with the increasing impact energy, while considerable amount of fiber breakage only occurs when the impact energy exceeds the energy corresponding to the knee point. Predicted indentation depth after the knee point is very sensitive to the parameter μ which is proposed in this paper, and the acceptable value of this parameter is in range from 0.9 to 1.0.

  5. Indentation of a rigid sphere into an elastic substrate with surface tension and adhesion

    PubMed Central

    Hui, Chung-Yuen; Liu, Tianshu; Salez, Thomas; Raphael, Elie; Jagota, Anand

    2015-01-01

    The surface tension of compliant materials such as gels provides resistance to deformation in addition to and sometimes surpassing that owing to elasticity. This paper studies how surface tension changes the contact mechanics of a small hard sphere indenting a soft elastic substrate. Previous studies have examined the special case where the external load is zero, so contact is driven by adhesion alone. Here, we tackle the much more complicated problem where, in addition to adhesion, deformation is driven by an indentation force. We present an exact solution based on small strain theory. The relation between indentation force (displacement) and contact radius is found to depend on a single dimensionless parameter: ω=σ(μR)−2/3((9π/4)Wad)−1/3, where σ and μ are the surface tension and shear modulus of the substrate, R is the sphere radius and Wad is the interfacial work of adhesion. Our theory reduces to the Johnson–Kendall–Roberts (JKR) theory and Young–Dupre equation in the limits of small and large ω, respectively, and compares well with existing experimental data. Our results show that, although surface tension can significantly affect the indentation force, the magnitude of the pull-off load in the partial wetting liquid-like limit is reduced only by one-third compared with the JKR limit and the pull-off behaviour is completely determined by ω. PMID:25792953

  6. Wavelet-based technique for target segmentation

    NASA Astrophysics Data System (ADS)

    Sadjadi, Firooz A.

    1995-07-01

    Segmentation of targets embedded in clutter obtained by IR imaging sensors is one of the challenging problems in automatic target recognition (ATR). In this paper a new texture-based segmentation technique is presented that uses the statistics of 2D wavelet decomposition components of the lcoal sections of the image. A measure of statistical similarity is then used to segment the image and separate the target from the background. This technique is applied on a set of real sequential IR imagery and has shown to produce a high degree of segmentation accuracy across varying ranges.

  7. Effects of Gel Thickness on Microscopic Indentation Measurements of Gel Modulus

    PubMed Central

    Long, Rong; Hall, Matthew S.; Wu, Mingming; Hui, Chung-Yuen

    2011-01-01

    In vitro, animal cells are mostly cultured on a gel substrate. It was recently shown that substrate stiffness affects cellular behaviors in a significant way, including adhesion, differentiation, and migration. Therefore, an accurate method is needed to characterize the modulus of the substrate. In situ microscopic measurements of the gel substrate modulus are based on Hertz contact mechanics, where Young's modulus is derived from the indentation force and displacement measurements. In Hertz theory, the substrate is modeled as a linear elastic half-space with an infinite depth, whereas in practice, the thickness of the substrate, h, can be comparable to the contact radius and other relevant dimensions such as the radius of the indenter or steel ball, R. As a result, measurements based on Hertz theory overestimate the Young's modulus. In this work, we discuss the limitations of Hertz theory and then modify it, taking into consideration the nonlinearity of the material and large deformation using a finite-element method. We present our results in a simple correction factor, ψ, the ratio of the corrected Young's modulus and the Hertz modulus in the parameter regime of δ/h ≤ min (0.6, R/h) and 0.3 ≤ R/h ≤ 12.7. The ψ factor depends on two dimensionless parameters, R/h and δ/h (where δ is the indentation depth), both of which are easily accessible to experiments. This correction factor agrees with experimental observations obtained with the use of polyacrylamide gel and a microsphere indentation method in the parameter range of 0.1 ≤ δ/h ≤ 0.4 and 0.3 ≤ R/h ≤ 6.2. The effect of adhesion on the use of Hertz theory for small indentation depth is also discussed. PMID:21806932

  8. The Instrumented Indentation Study of HVOF-Sprayed Hardmetal Coatings

    NASA Astrophysics Data System (ADS)

    Houdková, Šárka; Bláhová, Olga; Zahálka, František; Kašparová, Michaela

    2012-01-01

    Elastic-plastic properties, namely, hardness and Young's modulus, of four HVOF-sprayed hardmetal coatings were measured by instrumented indentation using Oliver-Pharr method Nanoindenter XP MTS with a continuous stiffness measurement (CSM) module. The results show that with sufficient number of CSM measurements, one can distinguish between indents made in the hard particles and indents made in the binder material. This can be accomplished by analyzing the plots of hardness and Young's modulus versus load (or versus indentation depth). Further development of the dependence curves enables the load (or indentation depth) to be set to correspond to the point of transition from a single structure component to the composite material and to determine the properties of both. Comparison of results of CSM measurement with the results of single indentation measurement at a defined load reveals a new perspective on the origin of the indentation size effect in hardmetal coatings. The measurements show that the increase in both the hardness and Young's modulus with decreasing load is caused mainly by the predominant influence of hard particles in the coatings.

  9. Finite Element Analysis of Deformation Due to Ball Indentation and Evaluation of Tensile Properties of Tempered P92 Steel

    NASA Astrophysics Data System (ADS)

    Barbadikar, Dipika R.; Ballal, A. R.; Peshwe, D. R.; Mathew, M. D.

    2015-08-01

    Ball indentation (BI) technique has been effectively used to evaluate the tensile properties with minimal volume of material. In the present investigation, BI test carried out on P92 steel (9Cr-0.5Mo-1.8W), using 0.76 mm diameter silicon nitride ball indenter was modeled using finite element (FE) method and analyzed. The effect of test temperature [300 K and 923 K (27 °C and 650 °C)], tempering temperature [1013 K, 1033 K, and 1053 K (740 °C, 760 °C, and 780 °C)], and coefficient of friction of steel (0.0 to 0.5) on the tensile strength and material pile-up was investigated. The stress and strain distributions underneath the indenter and along the top elements of the model have been studied to understand the deformation behavior. The tensile strength was found to decrease with increase in tempering and test temperatures. The increased pile-up around the indentation was attributed to the decrease in strain hardening exponent ( n) with increase in the test temperature. The pile-up height determined from profilometry studies and FE analysis as well as the load depth curve from BI and FE analysis was in agreement. The maximum strain location below the indentation changes with the test temperature. Stress-strain curves obtained by conventional tensile, BI test, and representative stress-strain concepts of FE model were found exactly matching.

  10. Nano-scale elastic-plastic properties and indentation-induced deformation of single crystal 4H-SiC.

    PubMed

    Nawaz, A; Mao, W G; Lu, C; Shen, Y G

    2017-02-01

    The nanoscale elastic-plastic response of single crystal 4H-SiC has been investigated by nanoindentationwith a Berkovich tip. The hardness (H) and elastic modulus (E) determined in the load-independent region were 36±2GPa and 413±8GPa, respectively. The indentation size effect (ISE) of hardness within an indentation depth of 60nm was systematically analyzed by the Nix-Gao model. Pop-in events occurring at a depth of ~23nm with indentation loads of 0.60-0.65mN were confirmed to indicate the elastic-plastic transition of the crystal, on the basis of the Hertzian contact theory and Johnson's cavity model. Theoritically calculated maximum tensile strength (13.5GPa) and cleavage strength (33GPa) also affirms the deformation due to the first pop-in rather than tensile stresses. Further analyses of deformation behavior across the indent was done in 4H-SiC by a combined technique of focused ion beam and transmission electron microscope, revealing that slippage occurred in the (0001) plane after indentation. Copyright © 2016 Elsevier Ltd. All rights reserved.

  11. Improving lithographic masks with the assistance of indentations

    NASA Astrophysics Data System (ADS)

    Guo, Ying-Nan; Li, Xu-Feng; Pan, Shi; Wang, Qiao; Wang, Shuo; Wu, Yong-Kuan

    2012-05-01

    Indentations etched on the output surface of a metallic mask are proposed to produce fine lithographic patterns with a resolution of 500 nm using the finite-difference time domain (FDTD) method. Such a designed mask is capable of enhancing near field lithography (NFL) resolution more than three times compared with the structure without indentations. The simulation results show that the interference disturbance between the adjacent lithographic channels can be eliminated efficiently by employing the indentations. As a straightforward consequence, the channel-to-channel interspaces can be shortened significantly, maintaining a uniform field distribution and high contrast.

  12. Elastic characterization of transversely isotropic soft materials by dynamic shear and asymmetric indentation.

    PubMed

    Namani, R; Feng, Y; Okamoto, R J; Jesuraj, N; Sakiyama-Elbert, S E; Genin, G M; Bayly, P V

    2012-06-01

    The mechanical characterization of soft anisotropic materials is a fundamental challenge because of difficulties in applying mechanical loads to soft matter and the need to combine information from multiple tests. A method to characterize the linear elastic properties of transversely isotropic soft materials is proposed, based on the combination of dynamic shear testing (DST) and asymmetric indentation. The procedure was demonstrated by characterizing a nearly incompressible transversely isotropic soft material. A soft gel with controlled anisotropy was obtained by polymerizing a mixture of fibrinogen and thrombin solutions in a high field magnet (B = 11.7 T); fibrils in the resulting gel were predominantly aligned parallel to the magnetic field. Aligned fibrin gels were subject to dynamic (20-40 Hz) shear deformation in two orthogonal directions. The shear storage modulus was 1.08 ± 0. 42 kPa (mean ± std. dev.) for shear in a plane parallel to the dominant fiber direction, and 0.58 ± 0.21 kPa for shear in the plane of isotropy. Gels were indented by a rectangular tip of a large aspect ratio, aligned either parallel or perpendicular to the normal to the plane of transverse isotropy. Aligned fibrin gels appeared stiffer when indented with the long axis of a rectangular tip perpendicular to the dominant fiber direction. Three-dimensional numerical simulations of asymmetric indentation were used to determine the relationship between direction-dependent differences in indentation stiffness and material parameters. This approach enables the estimation of a complete set of parameters for an incompressible, transversely isotropic, linear elastic material.

  13. Multiview video codec based on KTA techniques

    NASA Astrophysics Data System (ADS)

    Seo, Jungdong; Kim, Donghyun; Ryu, Seungchul; Sohn, Kwanghoon

    2011-03-01

    Multi-view video coding (MVC) is a video coding standard developed by MPEG and VCEG for multi-view video. It showed average PSNR gain of 1.5dB compared with view-independent coding by H.264/AVC. However, because resolutions of multi-view video are getting higher for more realistic 3D effect, high performance video codec is needed. MVC adopted hierarchical B-picture structure and inter-view prediction as core techniques. The hierarchical B-picture structure removes the temporal redundancy, and the inter-view prediction reduces the inter-view redundancy by compensated prediction from the reconstructed neighboring views. Nevertheless, MVC has inherent limitation in coding efficiency, because it is based on H.264/AVC. To overcome the limit, an enhanced video codec for multi-view video based on Key Technology Area (KTA) is proposed. KTA is a high efficiency video codec by Video Coding Expert Group (VCEG), and it was carried out for coding efficiency beyond H.264/AVC. The KTA software showed better coding gain than H.264/AVC by using additional coding techniques. The techniques and the inter-view prediction are implemented into the proposed codec, which showed high coding gain compared with the view-independent coding result by KTA. The results presents that the inter-view prediction can achieve higher efficiency in a multi-view video codec based on a high performance video codec such as HEVC.

  14. Simulation and Experiment on Surface Morphology and Mechanical Properties Response in Nano-Indentation of 6H-SiC

    NASA Astrophysics Data System (ADS)

    Li, Chen; Zhang, Feihu; Meng, Binbin; Ma, Zhaokai

    2017-03-01

    The nano-indentation test for 6H-SiC is carried out with a Berkovich indenter. The indentation surface morphology is analyzed by SEM, which show that when the maximum load P max is 8 mN, there is only plastic deformation and no cracks on the surface of workpiece after unloading process, and when P max is 10 mN, there is the initiation of crack occurring on the surface of workpiece after unloading process. Based on the strain hardening model, the three-dimensional finite element method of nano-indentation for 6H-SiC is carried out. Simulation results show that in the unloading process the maximum stress and the maximum strain occur in the contact area between the workpiece with the indenter edges, which is consistent with the experimental results. When propagate to the surface from the subsurface, the cracks are subjected to the type I stress and the type II stress due to elastic recovery. After propagating to surface of workpiece, the cracks propagate along a fixed direction because the proportion of type I stress is much larger than that of type II stress. The influence of the cleavage plane on the propagation direction of cracks is obvious. The cracks propagate more easily when the indenter edges are along cleavage plane. The indentation depth and residual depth increase with the increase of P max. While, the elastic recovery rate gradually decreases and tends to be stable with the increase of P max. When P max is <10 mN, the micro-hardness and the elastic modulus increase linearly with the increase of P max. When P max exceeds 10 mN, the micro-hardness decreases with the increase of P max and then gradually tends to be stable, and the elastic modulus increases by power function with the increase of P max and then gradually tends to be stable.

  15. Simulation and Experiment on Surface Morphology and Mechanical Properties Response in Nano-Indentation of 6H-SiC

    NASA Astrophysics Data System (ADS)

    Li, Chen; Zhang, Feihu; Meng, Binbin; Ma, Zhaokai

    2017-02-01

    The nano-indentation test for 6H-SiC is carried out with a Berkovich indenter. The indentation surface morphology is analyzed by SEM, which show that when the maximum load P max is 8 mN, there is only plastic deformation and no cracks on the surface of workpiece after unloading process, and when P max is 10 mN, there is the initiation of crack occurring on the surface of workpiece after unloading process. Based on the strain hardening model, the three-dimensional finite element method of nano-indentation for 6H-SiC is carried out. Simulation results show that in the unloading process the maximum stress and the maximum strain occur in the contact area between the workpiece with the indenter edges, which is consistent with the experimental results. When propagate to the surface from the subsurface, the cracks are subjected to the type I stress and the type II stress due to elastic recovery. After propagating to surface of workpiece, the cracks propagate along a fixed direction because the proportion of type I stress is much larger than that of type II stress. The influence of the cleavage plane on the propagation direction of cracks is obvious. The cracks propagate more easily when the indenter edges are along cleavage plane. The indentation depth and residual depth increase with the increase of P max. While, the elastic recovery rate gradually decreases and tends to be stable with the increase of P max. When P max is <10 mN, the micro-hardness and the elastic modulus increase linearly with the increase of P max. When P max exceeds 10 mN, the micro-hardness decreases with the increase of P max and then gradually tends to be stable, and the elastic modulus increases by power function with the increase of P max and then gradually tends to be stable.

  16. Crack initiation and growth characteristics in SiC/SiC under indentation test

    NASA Astrophysics Data System (ADS)

    Zhang, W.; Hinoki, T.; Katoh, Y.; Kohyama, A.; Noda, T.; Muroga, T.; Yu, J.

    1998-10-01

    The mechanical behavior of ceramic matrix composites (CMC) is known to be strongly influenced by fiber-matrix interfacial properties and there have been many efforts to clarify the interfacial characteristics. To understand the fracture mechanism of the materials it is necessary to clarify how the cracks initiate and propagate among fibers, interphase (coating) and matrix. The objective of this study is to investigate crack initiation and growth characteristics in SiC/SiC composites with variations in coating thickness and coating methods by means of micro-indentation technique. Micro-indentation tests and hardness tests were carried out on SiC/SiC composites produced by the chemical vapour infiltration (CVI) process. The intrinsic catastrophic mode of failure of the brittle composite was prevented by application of single carbon and multiple coatings on fibers. Thinner coatings are sensitive to make fibers debonded and may improve the toughness of the composites.

  17. In situ SEM micro-indentation of single wood pulp fibres in transverse direction.

    PubMed

    Adusumalli, Ramesh-Babu; Raghavan, Rejin; Schwaller, Patrick; Zimmermann, Tanja; Michler, Johann

    2010-01-01

    Fibre deformations such as kinks and micro-compressions are significant parameters in determining the quality of industrial pulps. Undoubtedly, very little information has been obtained so far on fibre deformation because it is very tedious to handle the specimens. In this study, a novel in situ scanning electron microscope (SEM) micro-indentation technique was adopted for the first time to study the deformation of single industrial pulp fibres in the transverse direction. A one-to-one correspondence between load drops in load-displacement curve and cell wall deformation was obtained by using the SEM video sequence recorded during micro-indentation. The cell wall deformation occurred by 'elastic' sinking-in and lateral bulging of the microfibrils. Finally, the critical load (stress) required to initiate a crack in the cell wall was measured for different unbleached pulp fibres.

  18. Indentation-flexure and low-velocity impact damage in graphite/epoxy laminates

    NASA Technical Reports Server (NTRS)

    Kwon, Young S.; Sankar, Bhavani V.

    1992-01-01

    Static indentation and low velocity impact tests were performed on quasi-isotropic and cross ply graphite/epoxy composite laminates. The load deflection relations in static tests and impact force history in the impact tests were recorded. The damage was assessed by using ultrasonic C-scanning and photomicrographic techniques. The static behavior of the laminates and damage progression during loading, unloading, and reloading were explained by a simple plate delamination model. A good correlation existed between the static and impact responses. It was found that results from a few static indentation-flexture tests can be used to predict the response and damage in composite laminates due to a class of low velocity impact events.

  19. Indentation of zirconia thermal barrier coatings

    NASA Astrophysics Data System (ADS)

    Kernan, Brian Daniel

    Zirconia Thermal Barrier Coatings (TBCs) are widely used in gas turbine engines to protect metal parts from both heat and oxidation. However, TBCs fail after some time due to build up of stresses caused by microstructural changes, or by damage due to particle ingestion and impact commonly referred to as Foreign Object Damage (FOD). TBC mechanical properties are needed to be able to model stress development and the predication of cracking, particularly at high temperature. A TBC made by Electron Beam Physical Vapor Deposition (EBPVD) was found to be very strain rate sensitive in its hardness response in both the as-deposited and aged conditions from room temperature to 1200°C. The through-thickness hardness of the as-deposited TBC was measured from room temperature to 500°C. A high temperature vacuum displacement sensitive indenter was developed to measure both elastic modulus and hardness, as well as provide simulation of FOD under fast loading conditions. Some solutions to current performance problems of the machine are given.

  20. Surface effects on nanoindentation of soft solids by different indenters

    NASA Astrophysics Data System (ADS)

    Ding, Yue; Niu, Xin-Rui; Wang, Gang-Feng; Feng, Xi-Qiao; Yu, Shou-Wen

    2016-11-01

    For soft materials like biological tissues and gels, surface energy and hyperelasticity have significant influences on their mechanical response to external load. In this paper, we investigate the effects of surface energy on nanoindentation of hyperelastic solids by using conical, flat and spherical indenters. The hyperelastic behavior of soft solids is characterized by the neo-Hookean model, and the influence of surface energy is analyzed through finite element simulations. For the three typical indenters, the explicit relations between compressive load and indent depth are obtained considering both finite deformation and surface energy. When the contact radius is comparable with the ratio of surface energy density to elastic modulus, surface energy will evidently alter the contact pressure, surface profile, and overall response. Compared to the linear elastic predictions, the neo-Hookean hyperelasticity tends to increase the indent depth, while surface energy has a reverse effect. The obtained results are helpful to accurately characterize the mechanical response of soft solids via nanoindentation tests.

  1. Estimation of capping incidence by indentation fracture tests.

    PubMed

    Kuppuswamy, R; Anderson, S R; Augsburger, L L; Hoag, S W

    2001-01-01

    The purpose of this study was to predict the capping tendencies of pharmaceutical powders by creating indentation fracture on compacts. Three sets of binary mixtures containing different concentrations of each ingredient were used in the study. The binary mixtures were chosen to represent plastic-plastic, plastic-brittle, and brittle-brittle combination of materials. The mixtures were tableted at different pressures and speeds on Prester, a tablet press simulator. These mixtures were also compacted on the Instron Universal Testing Machine 4502. Static indentation tests were done on these compacts at different depths until surface cracking and chipping were observed. The extent of surface cracking and chipping was observed from light microscope and scanning electron microscope images. A rank order correlation was observed between lamination susceptibility and the depth at which indentation failure occurred. It was concluded that indentation fracture tests could provide a useful estimate of lamination properties of pharmaceutical powders.

  2. Compressive Microfracture and Indentation Damage in Al2O3.

    DTIC Science & Technology

    1977-08-30

    lateral cracks produced during indentation loading is characterized in terms of microplasticity , and the particle velocity range over which the mechanism is expected to be operative is computed. (Author)

  3. A 200 W Hall thruster with hollow indented anode

    NASA Astrophysics Data System (ADS)

    Ding, Yongjie; Sun, Hezhi; Wei, Liqiu; Li, Peng; Su, Hongbo; Peng, Wuji; Yu, Daren

    2017-10-01

    A hollow indented anode is proposed for increasing the neutral gas density in a discharge channel, in order to improve the performance of the thruster. The experimental results show that a hollow indented anode structure can effectively improve the performance, compared to a hollow straight anode under similar operating conditions, in terms of thrust, propellant utilization, ionization rate, and anode efficiency. Furthermore, simulations show that the indented anode can effectively increase the neutral gas density in a discharge channel and on the centerline of the channel, compared to a hollow straight anode. In addition, it can increase the ionization rate in the channel and the pre-ionization in the anode. Therefore, the hollow indented anode could be considered as an important design idea for improving thruster performance.

  4. 5. Top surface of dock showing indented section (bay) on ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. Top surface of dock showing indented section (bay) on SW side; looking NW. Ferry in background is at Winslow ferry dock. - Pacific Creosoting Plant, West Dock, 5350 Creosote Place, Northeast, Bremerton, Kitsap County, WA

  5. Instrumented Indentation of M855 Cartridge, Core, and Jacket Materials

    DTIC Science & Technology

    2005-08-01

    Instrumented indentation was used to estimate the mechanical properties of as-processed materials used in 5.56-mm M855 projectiles . Three indentation tip...determined experimentally from the as- processed materials. For 5.56-mm M855 projectiles , thin-walled copper and brass are used for the bullet...nylon and a tungsten- tin metal blend. Measuring mechanical performance of M855 projectile components, however, is difficult using traditional

  6. Indentability of conventional and negative Poisson's ratio foams

    NASA Technical Reports Server (NTRS)

    Lakes, R. S.; Elms, K.

    1992-01-01

    The indentation resistance of foams, both of conventional structure and of re-entrant structure giving rise to negative Poisson's ratio, is studied using holographic interferometry. In holographic indentation tests, re-entrant foams had higher yield strengths sigma(sub y) and lower stiffness E than conventional foams of the same original relative density. Calculated energy absorption for dynamic impact is considerably higher for re-entrant foam than conventional foam.

  7. Elastic response, buckling, and instability of microtubules under radial indentation.

    PubMed

    Schaap, Iwan A T; Carrasco, Carolina; de Pablo, Pedro J; MacKintosh, Frederick C; Schmidt, Christoph F

    2006-08-15

    We tested the mechanical properties of single microtubules by lateral indentation with the tip of an atomic force microscope. Indentations up to approximately 3.6 nm, i.e., 15% of the microtubule diameter, resulted in an approximately linear elastic response, and indentations were reversible without hysteresis. At an indentation force of around 0.3 nN we observed an instability corresponding to an approximately 1-nm indentation step in the taxol-stabilized microtubules, which could be due to partial or complete rupture of a relatively small number of lateral or axial tubulin-tubulin bonds. These indentations were reversible with hysteresis when the tip was retracted and no trace of damage was observed in subsequent high-resolution images. Higher forces caused substantial damage to the microtubules, which either led to depolymerization or, occasionally, to slowly reannealing holes in the microtubule wall. We modeled the experimental results using finite-element methods and find that the simple assumption of a homogeneous isotropic material, albeit structured with the characteristic protofilament corrugations, is sufficient to explain the linear elastic response of microtubules.

  8. Elastic Response, Buckling, and Instability of Microtubules under Radial Indentation

    PubMed Central

    Schaap, Iwan A. T.; Carrasco, Carolina; de Pablo, Pedro J.; MacKintosh, Frederick C.; Schmidt, Christoph F.

    2006-01-01

    We tested the mechanical properties of single microtubules by lateral indentation with the tip of an atomic force microscope. Indentations up to ∼3.6 nm, i.e., 15% of the microtubule diameter, resulted in an approximately linear elastic response, and indentations were reversible without hysteresis. At an indentation force of around 0.3 nN we observed an instability corresponding to an ∼1-nm indentation step in the taxol-stabilized microtubules, which could be due to partial or complete rupture of a relatively small number of lateral or axial tubulin-tubulin bonds. These indentations were reversible with hysteresis when the tip was retracted and no trace of damage was observed in subsequent high-resolution images. Higher forces caused substantial damage to the microtubules, which either led to depolymerization or, occasionally, to slowly reannealing holes in the microtubule wall. We modeled the experimental results using finite-element methods and find that the simple assumption of a homogeneous isotropic material, albeit structured with the characteristic protofilament corrugations, is sufficient to explain the linear elastic response of microtubules. PMID:16731557

  9. A Comparison of Quasi-Static Indentation and Drop-Weight Impact Testing on Carbon/Epoxy Laminates

    NASA Technical Reports Server (NTRS)

    Prabhakaran, R.; Douglas, Michael J.

    2000-01-01

    This project was initiated to investigate the damage tolerance of polymer matrix composites (PMC). After a low velocity impact-such as the ones that can occur during manufacturing or service there is usually very little visual damage. There are two possible methods to simulate foreign object impact on PMC: static indentation and drop weight impact. A static method for modeling low velocity foreign object impact events for composites can prove to be very beneficial to researchers since much more data can be obtained from a static test than from an impact test. In order to examine if this is feasible, a series of static indentation and low velocity impact tests were performed and compared. Square specimens of different sizes and thicknesses were tested to cover a wide array of low velocity impact events. Laminates with a 45 degree stacking sequence were used since this is a common type of engineering laminate. Three distinct flexural rigidities under two different boundary conditions were tested in order to obtain damage due to large deflections. Comparisons between static indentation and low velocity impact tests were based on the maximum applied transverse load. The dependent parameters examined were dent depth, back surface crack length, delamination area, and load-deflection behavior. Results showed that no distinct differences could be seen between the static indentation tests and the low velocity impact tests, indicating that static indentation tests can be used to simulate low velocity impact events.

  10. Chipping fracture resistance of dental CAD/CAM restorative materials: Part 2. Phenomenological model and the effect of indenter type

    PubMed Central

    Quinn, G.D.; Giuseppetti, A.A.; Hoffman, K.H.

    2014-01-01

    The edge chipping resistances of six CAD/CAM dental restoration materials are analyzed and correlated to other mechanical properties. A new quadratic relationship that is based on a phenomenological model is presented. Objective The purpose of this study was to further analyze the edge chipping resistance of the brittle materials evaluated in Part 1. One objective was to determine why some force-distance trends were linear and others were nonlinear. A second objective was to account for differences in chipping resistance with indenter type. Methods Edge chipping experiments were conducted with different indenters, including some custom-made sharp conical indenters. A new force – distance quadratic expression was correlated to the data and compared to the linear and power law trends. Results The new quadratic function was an excellent fit in every instance. It can account for why some materials can be fit by a linear trend, while others can be fit by the power law trend. The effects of indenter type are accounted for variations in crack initiation and by the wedging stresses once an indentation hole is created. Significance The new quadratic force – edge distance function can be used with edge chipping data for all brittle materials, not just those evaluated in this study. The data trends vary from linear to nonlinear depending upon the material’s hardness, fracture toughness, and elastic modulus. PMID:24685179

  11. Variable temperature thin film indentation with a flat punch

    NASA Astrophysics Data System (ADS)

    Cross, Graham L. W.; O; ²Connell, Barry S.; Pethica, John B.; Rowland, Harry; King, William P.

    2008-01-01

    We present modifications to conventional nanoindentation that realize variable temperature, flat punch indentation of ultrathin films. The technique provides generation of large strain, thin film extrusion of precise geometries that idealize the essential flows of nanoimprint lithography, and approximate constant area squeeze flow rheometry performed on thin, macroscopic soft matter samples. Punch radii as small as 185nm have been realized in ten-to-one confinement ratio testing of 36nm thick polymer films controllably squeezed in the melt state to a gap width of a few nanometers. Self-consistent, compressive stress versus strain measurements of a wide variety of mechanical testing conditions are provided by using a single die-sample system with temperatures ranging from 20to125°C and loading rates spanning two decades. Low roughness, well aligned flat punch dies with large contact areas provide precise detection of soft surfaces with standard nanoindenter stiffness sensitivity. Independent heating and thermometry with heaters and thermocouples attached to the die and sample allow introduction of a novel directional heat flux measurement method to ensure isothermal contact conditions. This is a crucial requirement for interpreting the mechanical response in temperature sensitive soft matter systems. Instrumented imprint is a new nanomechanics material testing platform that enables measurements of polymer and soft matter properties during large strains in confined, thin film geometries and extends materials testing capabilities of nanoindentation into low modulus, low strength glassy, and viscoelastic materials.

  12. Variable temperature thin film indentation with a flat punch.

    PubMed

    Cross, Graham L W; O'Connell, Barry S; Pethica, John B; Rowland, Harry; King, William P

    2008-01-01

    We present modifications to conventional nanoindentation that realize variable temperature, flat punch indentation of ultrathin films. The technique provides generation of large strain, thin film extrusion of precise geometries that idealize the essential flows of nanoimprint lithography, and approximate constant area squeeze flow rheometry performed on thin, macroscopic soft matter samples. Punch radii as small as 185 nm have been realized in ten-to-one confinement ratio testing of 36 nm thick polymer films controllably squeezed in the melt state to a gap width of a few nanometers. Self-consistent, compressive stress versus strain measurements of a wide variety of mechanical testing conditions are provided by using a single die-sample system with temperatures ranging from 20 to 125 degrees C and loading rates spanning two decades. Low roughness, well aligned flat punch dies with large contact areas provide precise detection of soft surfaces with standard nanoindenter stiffness sensitivity. Independent heating and thermometry with heaters and thermocouples attached to the die and sample allow introduction of a novel directional heat flux measurement method to ensure isothermal contact conditions. This is a crucial requirement for interpreting the mechanical response in temperature sensitive soft matter systems. Instrumented imprint is a new nanomechanics material testing platform that enables measurements of polymer and soft matter properties during large strains in confined, thin film geometries and extends materials testing capabilities of nanoindentation into low modulus, low strength glassy, and viscoelastic materials.

  13. Artificial Intelligence based technique for BTS placement

    NASA Astrophysics Data System (ADS)

    Alenoghena, C. O.; Emagbetere, J. O.; Aibinu, A. M.

    2013-12-01

    The increase of the base transceiver station (BTS) in most urban areas can be traced to the drive by network providers to meet demand for coverage and capacity. In traditional network planning, the final decision of BTS placement is taken by a team of radio planners, this decision is not fool proof against regulatory requirements. In this paper, an intelligent based algorithm for optimal BTS site placement has been proposed. The proposed technique takes into consideration neighbour and regulation considerations objectively while determining cell site. The application will lead to a quantitatively unbiased evaluated decision making process in BTS placement. An experimental data of a 2km by 3km territory was simulated for testing the new algorithm, results obtained show a 100% performance of the neighbour constrained algorithm in BTS placement optimization. Results on the application of GA with neighbourhood constraint indicate that the choices of location can be unbiased and optimization of facility placement for network design can be carried out.

  14. RAPID COMMUNICATION: Measurement of residual stresses around Vickers indentations in a ruby crystal using a Raman luminescence microscope

    NASA Astrophysics Data System (ADS)

    Banini, G. K.; Chaudhri, M. M.; Smith, T.; Hayward, I. P.

    2001-11-01

    A Raman luminescence microscope has been used to determine the residual stresses around Vickers diamond indentations in a relatively large, well-polished, R-cut (10 bar 1 2) ruby single crystal. The principle of the method is based on the fact that the frequencies of the luminescence R lines of the ruby shift in a systematic manner with applied stress. It is shown that the hydrostatic component of the residual stress around a 25 N Vickers indentation can be as high as about 2 GPa, and that its magnitude decreases as A/r3, where r is the distance from the centre of indentation and A is a constant. These measurements are shown to be in qualitative agreement with the predictions of the current analytical models, although the magnitudes of the measured residual stresses are an order of magnitude smaller than those predicted by theory. Possible reasons for these differences are discussed.

  15. Estimation of the quasi-static Young's modulus of the eardrum using a pressurization technique.

    PubMed

    Ghadarghadar, Nastaran; Agrawal, Sumit K; Samani, Abbas; Ladak, Hanif M

    2013-06-01

    The quasi-static Young's modulus of the eardrum's pars tensa is an important modeling parameter in computer simulations. Recent developments in indentation testing and inverse modeling allow estimation of this parameter with the eardrum in situ. These approaches are challenging because of the curved shape of the pars tensa which requires special care during experimentation to keep the indenter perpendicular to the local surface at the point of contact. Moreover, they involve complicated contact modeling. An alternative computer-based method is presented here in which pressurization is used instead of indentation. The Young's modulus of a thin-shell model of the eardrum with subject-specific geometry is numerically optimized such that simulated pressurized shapes match measured counterparts. The technique was evaluated on six healthy rat eardrums, resulting in a Young's modulus estimate of 22.8±1.5MPa. This is comparable to values estimated using indentation testing. The new pressurization-based approach is simpler to use than the indentation-based method for the two reasons noted above. Copyright © 2012 Elsevier Ireland Ltd. All rights reserved.

  16. Intraoperative electrophysiological evaluations of macular function during peripheral scleral indentation

    PubMed Central

    Akiyama, Goichi; Matsumoto, Celso Soiti; Shinoda, Kei; Terauchi, Gaku; Matsumoto, Harue; Watanabe, Emiko; Iwata, Takeshi; Mizota, Atsushi; Miyake, Yozo

    2016-01-01

    Scleral indentation is widely used to examine the peripheral fundus, however it can increase the intraocular pressure (IOP) to high levels which can then affect retinal function. We evaluated the effects of scleral indentation on the macular function electrophysiologically. Intraoperative focal macular electroretinograms (iFMERGs) were recorded with and without controlling the IOP in 7 eyes. Without IOP control, the IOP increased from 21.7 ± 4.9 to 92.7 ± 20.2 mmHg significantly (P = 0.020) and the amplitudes of the b-wave (from 6.29 ± 1.160 to 3.71 ± 1.98 uV, P = 0.007), on-photopic negative response (from 2.29 ± 0.99 to 0.72 ± 0.47 uV, on-PhNR, P = 0.005), and d-wave (from 2.57 ± 0.41 to 1.64 ± 0.69 uV, P = 0.007) decreased significantly soon after beginning the indentation. All values returned to the baseline levels after releasing the indentation. In the eyes with IOP controlled, the IOP and the amplitude of all components did not change significantly during and after the indentation except the on-PhNR amplitude which was significantly reduced during the indentation. The changes in the iFMERGs and macular function caused by scleral indentation were transient and reversible. The changes can be minimized by controlling the IOP. PMID:27762313

  17. Mechanophore activation in a crosslinked polymer matrix via instrumented indentation

    NASA Astrophysics Data System (ADS)

    Davis, Chelsea; Forster, Aaron; Woodcock, Jeremiah; Wang, Muzhou; Gilman, Jeffrey; Material Measurement Laboratory Team

    Recent advances in mechanically-activated fluorophores will enable a host of unique scientific challenges and opportunities to be addressed. Several mechanophores (MPs) in polymers have been reported, yet the specific deformation required to activate these molecules in a bulk polymer network has not been sufficiently specified. In an effort to develop the mechano-activation/deformation relationship of a spirolactam-based MP, scratches were applied to a MP-functionalized glassy crosslinked material at varying normal loads and lateral displacement rates. This experimental design allowed strain and strain rate effects to be decoupled. The fluorescence activation was then observed with a laser scanning confocal microscope. Areas of elastic and plastic deformation as well as brittle fracture were observed within each scratch as the normal loading of the indenter increased. The fluorescence intensity increased with increasing strain. Contact mechanics models are employed to demonstrate that relatively high degrees of strain are required to initiate the ring-opening activation transition within the spirolactam-based MP. These self-reporting damage sensors can be incorporated within polymeric coatings to allow real time structural health monitoring for a myriad of applications.

  18. Single Cell Wall Nonlinear Mechanics Revealed by a Multiscale Analysis of AFM Force-Indentation Curves.

    PubMed

    Digiuni, Simona; Berne-Dedieu, Annik; Martinez-Torres, Cristina; Szecsi, Judit; Bendahmane, Mohammed; Arneodo, Alain; Argoul, Françoise

    2015-05-05

    Individual plant cells are rather complex mechanical objects. Despite the fact that their wall mechanical strength may be weakened by comparison with their original tissue template, they nevertheless retain some generic properties of the mother tissue, namely the viscoelasticity and the shape of their walls, which are driven by their internal hydrostatic turgor pressure. This viscoelastic behavior, which affects the power-law response of these cells when indented by an atomic force cantilever with a pyramidal tip, is also very sensitive to the culture media. To our knowledge, we develop here an original analyzing method, based on a multiscale decomposition of force-indentation curves, that reveals and quantifies for the first time the nonlinearity of the mechanical response of living single plant cells upon mechanical deformation. Further comparing the nonlinear strain responses of these isolated cells in three different media, we reveal an alteration of their linear bending elastic regime in both hyper- and hypotonic conditions.

  19. Contribution to the Determination of In Vivo Mechanical Characteristics of Human Skin by Indentation Test

    PubMed Central

    Zahouani, Hassan

    2013-01-01

    This paper proposes a triphasic model of intact skin in vivo based on a general phenomenological thermohydromechanical and physicochemical (THMPC) approach of heterogeneous media. The skin is seen here as a deforming stratified medium composed of four layers and made out of different fluid-saturated materials which contain also an ionic component. All the layers are treated as linear, isotropic materials described by their own behaviour law. The numerical simulations of in vivo indentation test performed on human skin are given. The numerical results correlate reasonably well with the typical observations of indented human skin. The discussion shows the versatility of this approach to obtain a better understanding on the mechanical behaviour of human skin layers separately. PMID:24324525

  20. Monsoon Forecasting based on Imbalanced Classification Techniques

    NASA Astrophysics Data System (ADS)

    Ribera, Pedro; Troncoso, Alicia; Asencio-Cortes, Gualberto; Vega, Inmaculada; Gallego, David

    2017-04-01

    Monsoonal systems are quasiperiodic processes of the climatic system that control seasonal precipitation over different regions of the world. The Western North Pacific Summer Monsoon (WNPSM) is one of those monsoons and it is known to have a great impact both over the global climate and over the total precipitation of very densely populated areas. The interannual variability of the WNPSM along the last 50-60 years has been related to different climatic indices such as El Niño, El Niño Modoki, the Indian Ocean Dipole or the Pacific Decadal Oscillation. Recently, a new and longer series characterizing the monthly evolution of the WNPSM, the WNP Directional Index (WNPDI), has been developed, extending its previous length from about 50 years to more than 100 years (1900-2007). Imbalanced classification techniques have been applied to the WNPDI in order to check the capability of traditional climate indices to capture and forecast the evolution of the WNPSM. The problem of forecasting has been transformed into a binary classification problem, in which the positive class represents the occurrence of an extreme monsoon event. Given that the number of extreme monsoons is much lower than the number of non-extreme monsoons, the resultant classification problem is highly imbalanced. The complete dataset is composed of 1296 instances, where only 71 (5.47%) samples correspond to extreme monsoons. Twenty predictor variables based on the cited climatic indices have been proposed, and namely, models based on trees, black box models such as neural networks, support vector machines and nearest neighbors, and finally ensemble-based techniques as random forests have been used in order to forecast the occurrence of extreme monsoons. It can be concluded that the methodology proposed here reports promising results according to the quality parameters evaluated and predicts extreme monsoons for a temporal horizon of a month with a high accuracy. From a climatological point of view

  1. A robotic indenter for minimally invasive measurement and characterization of soft tissue response.

    PubMed

    Samur, Evren; Sedef, Mert; Basdogan, Cagatay; Avtan, Levent; Duzgun, Oktay

    2007-08-01

    The lack of experimental data in current literature on material properties of soft tissues in living condition has been a significant obstacle in the development of realistic soft tissue models for virtual reality based surgical simulators used in medical training. A robotic indenter was developed for minimally invasive measurement of soft tissue properties in abdominal region during a laparoscopic surgery. Using the robotic indenter, force versus displacement and force versus time responses of pig liver under static and dynamic loading conditions were successfully measured to characterize its material properties in three consecutive steps. First, the effective elastic modulus of pig liver was estimated as 10-15 kPa from the force versus displacement data of static indentations based on the small deformation assumption. Then, the stress relaxation function, relating the variation of stress with respect to time, was determined from the force versus time response data via curve fitting. Finally, an inverse finite element solution was developed using ANSYS finite element package to estimate the optimum values of viscoelastic and nonlinear hyperelastic material properties of pig liver through iterations. The initial estimates of the material properties for the iterations were extracted from the experimental data for faster convergence of the solutions.

  2. Hardness variation with indenter sharpness in an Au thin-film.

    PubMed

    Lee, Yun-Hee; Kim, Yong-Il; Hahn, Jun-Hee

    2012-07-01

    The effects of the indenter shape on hardness were studied from thin-film nanoindentations. Two Berkovich indenters with different operating histories were prepared and their morphologies were measured with an atomic force microscope. The curvature radii of both indenters that were measured through an image analysis were 58.8 nm and 732.2 nm, respectively. The nanoindentations were carried out on a 1.2 microm-thick Au thin-film with a Nanoindenter XP system with both indenters. Various nanoindentation data with indenter exchanges were surveyed, and they showed that the peak indentation loads under the blunter indenter were higher than those of the sharper indenter at the same indentation depths. The indenter sharpness parameter was used to correct the raw nanoindentation curves. The corrected curves overlapped well and the resulting hardness values were consistent regardless of the indenter sharpness. The intrinsic hardness values of the Au thin-film from both indenters agreed with each other, with only a 0.6% difference. This means the indenter sharpness was properly corrected and that the sharpness must be considered when the contact properties are measured at shallow indentations.

  3. Micro-indentation fracture behavior of human enamel.

    PubMed

    Padmanabhan, Sanosh Kunjalukkal; Balakrishnan, Avinash; Chu, Min-Cheol; Kim, Taik Nam; Cho, Seong Jai

    2010-01-01

    The purpose of this study was to determine the crack resistance behavior (K(R)) of human enamel in relation to its microstructure. Human molar teeth were precision cut, polished and tested using Vickers micro-indentation at different loads ranging from 0.98 to 9.8 N. Five indentation load levels were considered, 20 indentation cracks for each load level were introduced on the surface of the test specimen (10 indentations per tooth) and their variability was evaluated using Weibull statistics and an empirical model. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) were used to analyze the crack morphology and propagation mechanisms involved. The results showed that enamel exhibited increasing cracking resistance (K(R)) with increasing load. It was found that the crack propagation mainly depended on the location and the microstructure it encountered. SEM showed the formation of crack bridges and crack deflection near the indentation crack tip. The crack mode was of Palmqvist type even at larger loads of 9.8 N. This was mainly attributed to the large process zone created by the interwoven lamellar rod like microstructure exhibited by the enamel surface. This study shows that there are still considerable prospects for improving dental ceramics and for mimicking the enamel structure developed by nature.

  4. Reference-point indentation correlates with bone toughness assessed using whole-bone traditional mechanical testing.

    PubMed

    Gallant, Maxime A; Brown, Drew M; Organ, Jason M; Allen, Matthew R; Burr, David B

    2013-03-01

    Traditional bone mechanical testing techniques require excised bone and destructive sample preparation. Recently, a cyclic-microindentation technique, reference-point indentation (RPI), was described that allows bone to be tested in a clinical setting, permitting the analysis of changes to bone material properties over time. Because this is a new technique, it has not been clear how the measurements generated by RPI are related to the material properties of bone measured by standard techniques. In this paper, we describe our experience with the RPI technique, and correlate the results obtained by RPI with those of traditional mechanical testing, namely 3-point bending and axial compression. Using different animal models, we report that apparent bone material toughness obtained from 3-point bending and axial compression is inversely correlated with the indentation distance increase (IDI) obtained from RPI with r(2) values ranging from 0.50 to 0.57. We also show that conditions or treatments previously shown to cause differences in toughness, including diabetes and bisphosphonate treatment, had significantly different IDI values compared to controls. Collectively these results provide a starting point for understanding how RPI relates to traditional mechanical testing results.

  5. Correlating confocal microscopy and atomic force indentation reveals metastatic cancer cells stiffen during invasion into collagen I matrices

    NASA Astrophysics Data System (ADS)

    Staunton, Jack R.; Doss, Bryant L.; Lindsay, Stuart; Ros, Robert

    2016-01-01

    Mechanical interactions between cells and their microenvironment dictate cell phenotype and behavior, calling for cell mechanics measurements in three-dimensional (3D) extracellular matrices (ECM). Here we describe a novel technique for quantitative mechanical characterization of soft, heterogeneous samples in 3D. The technique is based on the integration of atomic force microscopy (AFM) based deep indentation, confocal fluorescence microscopy, finite element (FE) simulations and analytical modeling. With this method, the force response of a cell embedded in 3D ECM can be decoupled from that of its surroundings, enabling quantitative determination of the elastic properties of both the cell and the matrix. We applied the technique to the quantification of the elastic properties of metastatic breast adenocarcinoma cells invading into collagen hydrogels. We found that actively invading and fully embedded cells are significantly stiffer than cells remaining on top of the collagen, a clear example of phenotypical change in response to the 3D environment. Treatment with Rho-associated protein kinase (ROCK) inhibitor significantly reduces this stiffening, indicating that actomyosin contractility plays a major role in the initial steps of metastatic invasion.

  6. Correlating confocal microscopy and atomic force indentation reveals metastatic cancer cells stiffen during invasion into collagen I matrices

    PubMed Central

    Staunton, Jack R.; Doss, Bryant L.; Lindsay, Stuart; Ros, Robert

    2016-01-01

    Mechanical interactions between cells and their microenvironment dictate cell phenotype and behavior, calling for cell mechanics measurements in three-dimensional (3D) extracellular matrices (ECM). Here we describe a novel technique for quantitative mechanical characterization of soft, heterogeneous samples in 3D. The technique is based on the integration of atomic force microscopy (AFM) based deep indentation, confocal fluorescence microscopy, finite element (FE) simulations and analytical modeling. With this method, the force response of a cell embedded in 3D ECM can be decoupled from that of its surroundings, enabling quantitative determination of the elastic properties of both the cell and the matrix. We applied the technique to the quantification of the elastic properties of metastatic breast adenocarcinoma cells invading into collagen hydrogels. We found that actively invading and fully embedded cells are significantly stiffer than cells remaining on top of the collagen, a clear example of phenotypical change in response to the 3D environment. Treatment with Rho-associated protein kinase (ROCK) inhibitor significantly reduces this stiffening, indicating that actomyosin contractility plays a major role in the initial steps of metastatic invasion. PMID:26813872

  7. The response of solids to elastic/plastic indentation. I. Stresses and residual stresses

    SciTech Connect

    Chiang, S. S.; Marshall, D. B.; Evans, A. G.

    1982-01-01

    We present a new approach for analyzing indentation plasticity and for determining indentation stress fields. The analysis permits relations to be established between material properties (notably hardness, yield strength, and elastic modulus) and the dimensions of the indentation and plastic zone. The predictions are demonstrated to correlate with observations performed on a wide range of materials. The indentation stress fields are computed along trajectories pertinent to three dominant indentation crack systems: radial, median, and lateral cracks. Lastly, the peak load and residual tensile stresses are shown to be consistent with observed trends in indentation fracture.

  8. Mapping Viscoelastic and Plastic Properties of Polymers and Polymer-Nanotube Composites using Instrumented Indentation

    PubMed Central

    Gayle, Andrew J.; Cook, Robert F.

    2016-01-01

    An instrumented indentation method is developed for generating maps of time-dependent viscoelastic and time-independent plastic properties of polymeric materials. The method is based on a pyramidal indentation model consisting of two quadratic viscoelastic Kelvin-like elements and a quadratic plastic element in series. Closed-form solutions for indentation displacement under constant load and constant loading-rate are developed and used to determine and validate material properties. Model parameters are determined by point measurements on common monolithic polymers. Mapping is demonstrated on an epoxy-ceramic interface and on two composite materials consisting of epoxy matrices containing multi-wall carbon nanotubes. A fast viscoelastic deformation process in the epoxy was unaffected by the inclusion of the nanotubes, whereas a slow viscoelastic process was significantly impeded, as was the plastic deformation. Mapping revealed considerable spatial heterogeneity in the slow viscoelastic and plastic responses in the composites, particularly in the material with a greater fraction of nanotubes. PMID:27563168

  9. Establishing isothermal contact at a known temperature under thermal equilibrium in elevated temperature instrumented indentation testing

    NASA Astrophysics Data System (ADS)

    Hou, X. D.; Alvarez, C. L. M.; Jennett, N. M.

    2017-02-01

    Instrumented indentation testing (IIT) at elevated temperatures has proved to be a useful tool to study plastic and elastic deformation and understand the performance of material components at (or nearer to) the actual temperatures experienced in-service. The value of elevated temperature IIT data, however, depends on the ability not only to achieve a stable, isothermal indentation contact at thermal equilibrium when taking data, but to be able to assign a valid temperature to that contact (and so to the data). The most common method found in the current literature is to use the calculated thermal drift rate as an indicator, but this approach has never been properly validated. This study proves that using the thermal drift rate to determine isothermal contact may lead to large errors in the determination of the real contact temperature. Instead, a more sensitive and validated method is demonstrated, based upon using the indenter tip and the tip heater control thermocouple as a reproducible and calibrated contact temperature sensor. A simple calibration procedure is described, along with step by step guidance to establish an isothermal contact at a known temperature under thermal equilibrium when conducting elevated temperature IIT experiments.

  10. Indentation size effect and the plastic compressibility of glass

    SciTech Connect

    Smedskjaer, Morten M.

    2014-06-23

    Oxide glasses exhibit significant densification under an applied isostatic pressure at the glass transition temperature. The glass compressibility is correlated with the chemical composition and atomic packing density, e.g., borate glasses with planar triangular BO{sub 3} units are more disposed for densification than silicate glasses with tetrahedral units. We here show that there is a direct relation between the plastic compressibility following hot isostatic compression and the extent of the indentation size effect (ISE), which is the decrease of hardness with indentation load exhibited by most materials. This could suggest that the ISE is correlated with indentation-induced shear bands, which should form in greater density when the glass network is more adaptable to volume changes through structural and topological rearrangements under an applied pressure.

  11. Master-slave robotic system for needle indentation and insertion.

    PubMed

    Shin, Jaehyun; Zhong, Yongmin; Gu, Chengfan

    2017-09-22

    Bilateral control of a master-slave robotic system is a challenging issue in robotic-assisted minimally invasive surgery. It requires the knowledge on contact interaction between a surgical (slave) robot and soft tissues. This paper presents a master-slave robotic system for needle indentation and insertion. This master-slave robotic system is able to characterize the contact interaction between the robotic needle and soft tissues. A bilateral controller is implemented using a linear motor for robotic needle indentation and insertion. A new nonlinear state observer is developed to online monitor the contact interaction with soft tissues. Experimental results demonstrate the efficacy of the proposed master-slave robotic system for robotic needle indentation and needle insertion.

  12. Indentation size effect and the plastic compressibility of glass

    NASA Astrophysics Data System (ADS)

    Smedskjaer, Morten M.

    2014-06-01

    Oxide glasses exhibit significant densification under an applied isostatic pressure at the glass transition temperature. The glass compressibility is correlated with the chemical composition and atomic packing density, e.g., borate glasses with planar triangular BO3 units are more disposed for densification than silicate glasses with tetrahedral units. We here show that there is a direct relation between the plastic compressibility following hot isostatic compression and the extent of the indentation size effect (ISE), which is the decrease of hardness with indentation load exhibited by most materials. This could suggest that the ISE is correlated with indentation-induced shear bands, which should form in greater density when the glass network is more adaptable to volume changes through structural and topological rearrangements under an applied pressure.

  13. Influence of Indenter Tip Geometry on Elastic Deformation during Nanoindentation

    NASA Astrophysics Data System (ADS)

    Bei, H.; George, E. P.; Hay, J. L.; Pharr, G. M.

    2005-07-01

    Nanoindentation with a Berkovich indenter is commonly used to investigate the mechanical behavior of small volumes of materials. To date, most investigators have made the simplifying assumption that the tip is spherical. In reality, indenter tips are much more complex. Here, we develop a new method to describe the tip shape using the experimentally determined area function of the indenter at small depths (0 100 nm). Our analysis accurately predicts the elastic load-displacement curve and allows the theoretical strength of a material to be determined from pop-in data. Application of our new method to single crystal Cr3Si shows that the predicted theoretical strengths are within 12% of the ideal strength G/2π, where G is the shear modulus.

  14. Elastic anisotropy of uniaxial mineralized collagen fibers measured using two-directional indentation. Effects of hydration state and indentation depth

    PubMed Central

    Spiesz, Ewa M.; Roschger, Paul; Zysset, Philippe K.

    2012-01-01

    Mineralized turkey leg tendon (MTLT) is an attractive model of mineralized collagen fibers, which are also present in bone. Its longitudinal structure is advantageous for the relative simplicity in modeling, yet its anisotropic elastic properties remain unknown. The aim of this study was to quantify the extent of elastic anisotropy of mineralized collagen fibers by using nano- and microindentation to probe a number on MTLT samples in two orthogonal directions. The large dataset allowed the quantification of the extent of anisotropy, depending on the final indentation depth and on the hydration state of the sample. Anisotropy was observed to increase with the sample re-hydration process. Artifacts of indentation in a transverse direction to the main axis of the mineralized tendons in re-hydrated condition were observed. The indentation size effect, that is, the increase of the measured elastic properties with decreasing sampling volume, reported previously on variety of materials, was also observed in MTLT. Indentation work was quantified for both directions of indentation in dried and re-hydrated conditions. As hypothesized, MTLT showed a higher extent of anisotropy compared to cortical and trabecular bone, presumably due to the alignment of mineralized collagen fibers in this tissue. PMID:22664658

  15. Protection of cortex by overlying meninges tissue during dynamic indentation of the adolescent brain.

    PubMed

    MacManus, David B; Pierrat, Baptiste; Murphy, Jeremiah G; Gilchrist, Michael D

    2017-07-15

    Traumatic brain injury (TBI) has become a recent focus of biomedical research with a growing international effort targeting material characterization of brain tissue and simulations of trauma using computer models of the head and brain to try to elucidate the mechanisms and pathogenesis of TBI. The meninges, a collagenous protective tri-layer, which encloses the entire brain and spinal cord has been largely overlooked in these material characterization studies. This has resulted in a lack of accurate constitutive data for the cranial meninges, particularly under dynamic conditions such as those experienced during head impacts. The work presented here addresses this lack of data by providing for the first time, in situ large deformation material properties of the porcine dura-arachnoid mater composite under dynamic indentation. It is demonstrated that this tissue is substantially stiffer (shear modulus, μ=19.10±8.55kPa) and relaxes at a slower rate (τ1=0.034±0.008s, τ2=0.336±0.077s) than the underlying brain tissue (μ=6.97±2.26kPa, τ1=0.021±0.007s, τ2=0.199±0.036s), reducing the magnitudes of stress by 250% and 65% for strains that arise during indentation-type deformations in adolescent brains. We present the first mechanical analysis of the protective capacity of the cranial meninges using in situ micro-indentation techniques. Force-relaxation tests are performed on in situ meninges and cortex tissue, under large strain dynamic micro-indentation. A quasi-linear viscoelastic model is used subsequently, providing time-dependent mechanical properties of these neural tissues under loading conditions comparable to what is experienced in TBI. The reported data highlights the large differences in mechanical properties between these two tissues. Finite element simulations of the indentation experiments are also performed to investigate the protective capacity of the meninges. These simulations show that the meninges protect the underlying brain tissue by

  16. Micro-indentation relaxation measurements in polymer thin films

    NASA Astrophysics Data System (ADS)

    Shinozaki, D. M.; Lu, Y.

    1997-07-01

    A micro-indenter consisting of a piezo-electric driven flat cylindrical punch has been used to measure the dynamic mechanical properties of polystyrene films as thin as 50 μm. The measured viscoelastic response was sensitive to the bonding of the polystyrene to an underlying silicon substrate for films which were thinner than one indenter diameter. The instrument therefore was shown to have practical use in measuring the dynamic mechanical response of polymer films, and the strength of bonding between disparate materials.

  17. A New Tissue Resonator Indenter Device and Reliability Study

    PubMed Central

    Jia, Ming; Zu, Jean W.; Hariri, Alireza

    2011-01-01

    Knowledge of tissue mechanical properties is widely required by medical applications, such as disease diagnostics, surgery operation, simulation, planning, and training. A new portable device, called Tissue Resonator Indenter Device (TRID), has been developed for measurement of regional viscoelastic properties of soft tissues at the Bio-instrument and Biomechanics Lab of the University of Toronto. As a device for soft tissue properties in-vivo measurements, the reliability of TRID is crucial. This paper presents TRID’s working principle and the experimental study of TRID’s reliability with respect to inter-reliability, intra-reliability, and the indenter misalignment effect as well. PMID:22346623

  18. Nuclear based techniques for detection of contraband

    SciTech Connect

    Gozani, T.

    1993-12-31

    The detection of contraband such as explosives and drugs concealed in luggage or other container can be quite difficult. Nuclear techniques offer capabilities which are essential to having effective detection devices. This report describes the features of various nuclear techniques and instrumentation.

  19. The Ufa indenter: stratigraphic and geophysic evidences for an actual indentation of the Southern Urals by the East European craton

    NASA Astrophysics Data System (ADS)

    Lefort, Jean-Pierre; Danukalova, Guzel

    2014-07-01

    Study of the altitudes of the lowest part of the Upper Cretaceous-Eocene and Aktschagylian-Quaternary stratigraphic ensembles known on the western slope of the Southern Urals evidences the existence of an East-West elongated dome which follows the N53° latitude. This ridge is superimposed at depth with the remnants of the Sernovodsk-Abdulino Aulacogen and with the Belaya tear fault, which support the existence of a recent rejuvenation of these old structures. North of these disruptions the Southern Urals display a clear bent towards the East. Detailed microstructural studies show that this curvature is associated with a typical stress pattern which suggests the existence of an indentation of the fold belt by the East European craton. The hypothesis of an Ufa indenter is not supported by an equivalent East-West deep fault north of the bend. However, a long N100° magnetic anomaly, interpreted as a shear zone, suggests that the indenter is a reality. Quaternary uplift and crustal thickening at its front as well as seismological data support our interpretation. It is not stressed that the curvature of the Urals observed at 56° latitude results solely from this recent indentation. It is only assumed that the actual indentation is rejuvenating a former unevenness which existed before in the East European craton. Study of the inner part of the indenter shows that this type of structure is not necessarily rigid and undeformed. Some of the structures described on the URSEIS deep seismic line could be much younger than previously expected.

  20. DCT-based cyber defense techniques

    NASA Astrophysics Data System (ADS)

    Amsalem, Yaron; Puzanov, Anton; Bedinerman, Anton; Kutcher, Maxim; Hadar, Ofer

    2015-09-01

    With the increasing popularity of video streaming services and multimedia sharing via social networks, there is a need to protect the multimedia from malicious use. An attacker may use steganography and watermarking techniques to embed malicious content, in order to attack the end user. Most of the attack algorithms are robust to basic image processing techniques such as filtering, compression, noise addition, etc. Hence, in this article two novel, real-time, defense techniques are proposed: Smart threshold and anomaly correction. Both techniques operate at the DCT domain, and are applicable for JPEG images and H.264 I-Frames. The defense performance was evaluated against a highly robust attack, and the perceptual quality degradation was measured by the well-known PSNR and SSIM quality assessment metrics. A set of defense techniques is suggested for improving the defense efficiency. For the most aggressive attack configuration, the combination of all the defense techniques results in 80% protection against cyber-attacks with PSNR of 25.74 db.

  1. Indentation and needle insertion properties of the human eye

    PubMed Central

    Matthews, A; Hutnik, C; Hill, K; Newson, T; Chan, T; Campbell, G

    2014-01-01

    Purpose Characterization of the biomechanical properties of the human eye has a number of potential utilities. One novel purpose is to provide the basis for development of suitable tissue-mimicking material. The purpose of this study was to determine the indentation and needle insertion characteristics on human eye globes and tissue strips. Methods An indenter assessed the elastic response of human eye globes and tissue strips under increasing compressive loads. Needle insertion determined the force (N) needed to penetrate various areas of the eye wall. Results The results demonstrated that globes underwent slightly greater indentation at the midline than at the central cornea, and corneal strips indented twofold more than scleral strips, although neither difference was significant (P=0.400 and P=0.100, respectively). Significant differences were observed among various areas of needle insertion (P<0.001). Needle insertion through the anterior sclera (adjacent to the limbus) and posterior sclera (adjacent to the optic nerve) required the greatest amount of force (0.954 and 1.005 N, respectively). The force required to penetrate the central cornea (0.518 N) was significantly lower than all other areas except the midline sclera (0.700 N) Conclusion These data form the basis for further research into the development of a tissue-mimicking human eye construct with potential utility as a model for use in ophthalmology research and surgical teaching. PMID:24810571

  2. S-cones in thin shells under indentation

    NASA Astrophysics Data System (ADS)

    Nasto, Alice; Ajdari, Amin; Lazarus, Arnaud; Vaziri, Ashkan; Reis, Pedro

    2012-02-01

    We perform a hybrid experimental and numerical investigation of the localization of deformation in indented thin spherical elastic shells. Past the initial linear response, an inverted cap develops as a Pogorelov circular ridge. For further indentation, this ridge looses axis-symmetry and sharp points of localized curvature form. We refer to these localized objects as s-cones (for shell-cones), in contrast with their developable cousins in plates (d-cones). We quantify the effect of systematically varying the indenter's radius of curvature (from point to plate load) on the formation and evolution of s-cones. In our precision desktop-scale experiments we use rapid prototyped elastomeric shells and rigid indenters of various shape. The mechanical response is measured through load-displacement compression tests and the deformation process is further characterized through digital imaging. In parallel, the experimental results are contrasted against nonlinear Finite Element simulations. Merging these two complementary approaches allows us to gain further physical insight towards rationalizing this geometrically nonlinear process.

  3. Rigid indented cylindrical cathode for X-ray tube

    DOEpatents

    Hudgens, Claude R.

    1985-01-01

    A cathode assembly for a vacuum tube includes a wire filament, a straight bular anode parallel to and surrounding the wire filament, and insulating spacers for rigidly fastening the filament with respect to the anode, and with one side of the anode indented or flattened such that only one portion of the anode is heated to emitting temperatures by the filament.

  4. Membrane indentation triggers clathrin lattice reorganization and fluidization.

    PubMed

    Cordella, Nicholas; Lampo, Thomas J; Melosh, Nicholas; Spakowitz, Andrew J

    2015-01-21

    Clathrin-mediated endocytosis involves the coordinated assembly of clathrin cages around membrane indentations, necessitating fluid-like reorganization followed by solid-like stabilization. This apparent duality in clathrin's in vivo behavior provides some indication that the physical interactions between clathrin triskelia and the membrane effect a local response that triggers fluid-solid transformations within the clathrin lattice. We develop a computational model to study the response of clathrin protein lattices to spherical deformations of the underlying flexible membrane. These deformations are similar to the shapes assumed during intracellular trafficking of nanoparticles. Through Monte Carlo simulations of clathrin-on-membrane systems, we observe that these membrane indentations give rise to a greater than normal defect density within the overlaid clathrin lattice. In many cases, the bulk surrounding lattice remains in a crystalline phase, and the extra defects are localized to the regions of large curvature. This can be explained by the fact that the in-plane elastic stress in the clathrin lattice are reduced by coupling defects to highly curved regions. The presence of defects brought about by indentation can result in the fluidization of a lattice that would otherwise be crystalline, resulting in an indentation-driven, defect-mediated phase transition. Altering subunit elasticity or membrane properties is shown to drive a similar transition, and we present phase diagrams that map out the combined effects of these parameters on clathrin lattice properties.

  5. Multi-Indenter Device for in Vivo Biomechanical Tissue Measurement.

    PubMed

    Petron, Arthur; Duval, Jean-Francois; Herr, Hugh

    2017-05-01

    Biomechanical tissue properties have been hypothesized to play a critical role in the quantification of prosthetic socket production for individuals with limb amputation. In this investigation, a novel indenter platform is presented and its performance evaluated for the purposes of residual-limb tissue characterization. The indenter comprised 14 position- and force-controllable actuators that circumferentially surround a biological residuum to form an actuator ring. Each indenter actuator was individually controllable in position ( [Formula: see text] accuracy) and force (330 mN accuracy) at a PC controller feedback rate of 500 Hz, allowing for a range of measurement across a residual stump. Data were collected from 162 sensors over an EtherCAT fieldbus to characterize the mechanical hyperviscoelastic tissue response of two transtibial residual-limbs from a study participant with bilateral amputations. At five distinct anatomical locations across the residual-limb, force versus deflection data-including hyperviscoelastic tissue properties-are presented, demonstrating the accuracy and versatility of the multi-indenter platform for residual-limb tissue characterization.

  6. A simple measuring device for laboratory indentation tests on cartilage.

    PubMed

    Koeller, Wolfgang; Kunow, Julius; Ostermeyer, Oliver; Stomberg, Peter; Boos, Carsten; Russlies, Martin

    2008-04-01

    Mechanical testing of articular cartilage and repair tissue enables judgment of their capacity in withstanding mechanical loading. In the past, different methods have been developed requiring a complex technical setup and extensive data analysis. Therefore, the aim of the present project was to build up a simple measuring apparatus for laboratory indentation tests. The device consists of an incremental optical displacement transducer with a sleeve bearing guided plunger and a spherical tip made of polished steel (radius: 0.75 or 1.5 mm), a sensitive load cell and a stiff frame. The indentation force results from the plunger's gravity plus the force of the spring inside the displacement transducer and levels at 0.170 N or 0.765 N. The displacement transducer is fixed to the frame via the load cell that enables one to detect the initial contact of the tip with the tissue. The load cell has a standard uncertainty of 2 mN and the displacement transducer of 1 microm. From indentation-creep tests, a "0.25-s elastic modulus" is calculated. Measurements on thin rubber sheets were carried out to determine the quality of the measuring device. Compression tests on cylinders made of these rubber sheets yielded control data, and a good agreement with the "0.25-s elastic modulus" was found. Indentation tests on cartilage at different sites of sheep femoral condyles yielded a very good repeatability of the measurement results (+/-7.5%).

  7. Nasal base narrowing: the combined alar base excision technique.

    PubMed

    Foda, Hossam M T

    2007-01-01

    To evaluate the role of the combined alar base excision technique in narrowing the nasal base and correcting excessive alar flare. The study included 60 cases presenting with a wide nasal base and excessive alar flaring. The surgical procedure combined an external alar wedge resection with an internal vestibular floor excision. All cases were followed up for a mean of 32 (range, 12-144) months. Nasal tip modification and correction of any preexisting caudal septal deformities were always completed before the nasal base narrowing. The mean width of the external alar wedge excised was 7.2 (range, 4-11) mm, whereas the mean width of the sill excision was 3.1 (range, 2-7) mm. Completing the internal excision first resulted in a more conservative external resection, thus avoiding any blunting of the alar-facial crease. No cases of postoperative bleeding, infection, or keloid formation were encountered, and the external alar wedge excision healed with an inconspicuous scar that was well hidden in the depth of the alar-facial crease. Finally, the risk of notching of the alar rim, which can occur at the junction of the external and internal excisions, was significantly reduced by adopting a 2-layered closure of the vestibular floor (P = .01). The combined alar base excision resulted in effective narrowing of the nasal base with elimination of excessive alar flare. Commonly feared complications, such as blunting of the alar-facial crease or notching of the alar rim, were avoided by using simple modifications in the technique of excision and closure.

  8. Low Temperature Plasticity of Olivine Determined by Nano-indentation

    NASA Astrophysics Data System (ADS)

    Skemer, P. A.; Kranjc, K.; Rouse, Z.; Flores, K.

    2015-12-01

    Earth's upper mantle is thought to deform mainly by dislocation creep, during which strain-rate and stress are related by a simple power law equation. However at much higher stresses there is a break-down in the power law relationship and strain-rate depends exponentially on stress. This phenomenon, known as low temperature plasticity, may be important in the shallow ductile or semi-brittle regions of the lithosphere, at the tips of cracks, or during high-stress laboratory experiments. Several studies have attempted to constrain the low-temperature rheology of olivine using micro-indentation or high pressure experiments. In this study we provide the first measurements of olivine rheology at low temperature using instrumented nano-indention. Although nano-indentation has been widely used in the materials sciences, its application in the Earth sciences has been very limited. Nano-indentation methods provide rheological measurements that are significantly more precise than other mechanical tests at high pressure and temperature. Moreover, experiments are rapid and largely non-destructive, so many tests can be conducted in a short amount of time. In this study, olivine single crystal and polycrystalline samples were tested using a Hysitron TI950 TriboIndenter. Temperature was varied using a cooling/heating stage from 0-175°C. Experiments were conducted under quasi-static and constant strain-rate conditions. Indentation hardness measurements were converted to uniaxial rheological properties to facilitate direct comparison with previous studies. Yield strengths for olivine range from 4.19 GPa at 175°C to 4.60 GPa at 0°C. Using various models for obstacles to dislocation motion, data are extrapolated to 0 Kelvin to extract a Peierls stress for olivine (5.32-6.45 GPa), which is at the lower end of the range of values determined in previous studies. This study demonstrates the efficacy of the nano-indentation method for the study of mineral rheology, and opens a

  9. Applying knowledge compilation techniques to model-based reasoning

    NASA Technical Reports Server (NTRS)

    Keller, Richard M.

    1991-01-01

    Researchers in the area of knowledge compilation are developing general purpose techniques for improving the efficiency of knowledge-based systems. In this article, an attempt is made to define knowledge compilation, to characterize several classes of knowledge compilation techniques, and to illustrate how some of these techniques can be applied to improve the performance of model-based reasoning systems.

  10. Flood alert system based on bayesian techniques

    NASA Astrophysics Data System (ADS)

    Gulliver, Z.; Herrero, J.; Viesca, C.; Polo, M. J.

    2012-04-01

    The problem of floods in the Mediterranean regions is closely linked to the occurrence of torrential storms in dry regions, where even the water supply relies on adequate water management. Like other Mediterranean basins in Southern Spain, the Guadalhorce River Basin is a medium sized watershed (3856 km2) where recurrent yearly floods occur , mainly in autumn and spring periods, driven by cold front phenomena. The torrential character of the precipitation in such small basins, with a concentration time of less than 12 hours, produces flash flood events with catastrophic effects over the city of Malaga (600000 inhabitants). From this fact arises the need for specific alert tools which can forecast these kinds of phenomena. Bayesian networks (BN) have been emerging in the last decade as a very useful and reliable computational tool for water resources and for the decision making process. The joint use of Artificial Neural Networks (ANN) and BN have served us to recognize and simulate the two different types of hydrological behaviour in the basin: natural and regulated. This led to the establishment of causal relationships between precipitation, discharge from upstream reservoirs, and water levels at a gauging station. It was seen that a recurrent ANN model working at an hourly scale, considering daily precipitation and the two previous hourly values of reservoir discharge and water level, could provide R2 values of 0.86. BN's results slightly improve this fit, but contribute with uncertainty to the prediction. In our current work to Design a Weather Warning Service based on Bayesian techniques the first steps were carried out through an analysis of the correlations between the water level and rainfall at certain representative points in the basin, along with the upstream reservoir discharge. The lower correlation found between precipitation and water level emphasizes the highly regulated condition of the stream. The autocorrelations of the variables were also

  11. A novel method to obtain modulus image of soft tissues using ultrasound water jet indentation: a phantom study.

    PubMed

    Lu, Min-Hua; Zheng, Yong-Ping; Huang, Qing-Hua

    2007-01-01

    The alteration of tissue stiffness is generally known to be associated with pathological changes. Ultrasound indentation is one of the methods that can be used to assess the mechanical properties of the soft tissues. It uses a flat-ended ultrasound transducer to directly contact the tissue to sense tissue deformation under an applied load. This paper introduced a novel noncontact ultrasound indentation system using water jet compression. The key idea was to utilize a water jet as the indenter as well as the coupling medium for propagation of the ultrasound beam. High frequency focused ultrasound (20 MHz) was used to measure the indentation deformation at a microscopic level. It has been demonstrated that the system could effectively assess the tissue-mimic phantoms with different stiffness. Water jet coupling allows the system to conduct C-scan on soft tissues rapidly and conveniently. By applying different pressures while taking C-scan sequences, the modulus images of the phantoms could be obtained based on the applied pressure and the phantom deformation and thickness. This paper presented the preliminary results on gel phantoms. The spatial resolution, the contrast resolution of the measurements and the reproducibility of the results were also discussed.

  12. Long base line interferometry: a new technique.

    PubMed

    Broten, N W; Legg, T H; Locke, J L; McLeish, C W; Richards, R S; Chisholm, R M; Gush, H P; Yen, J L; Galt, J A

    1967-06-23

    The technique of using magnetic-tape recorders and atomic frequency standards to operate two widely separated radio telescopes as a phase-coherent interferometer when the stations have no radio-frequency connecting link has been successfully tested at the National Research Council of Canada's Algonquin Radio Observatory.

  13. A new device for assessing changes in skin viscoelasticity using indentation and optical measurement.

    PubMed

    Clancy, Neil T; Nilsson, Gert E; Anderson, Chris D; Leahy, Martin J

    2010-05-01

    Skin is a viscoelastic material, comprised of fluidic and fibrous components. Changes in viscoelasticity can arise due to a number of conditions including dehydration, swelling (associated with injury or disease), impaired heart function, rehydration therapy, ageing, scarring, sun exposure and genetic conditions affecting connective tissue. Quantification of changes in skin viscoelasticity due to these processes is of great clinical interest in the fields of therapy monitoring, wound healing and disease screening. However, devices currently available to measure aspects of the mechanical properties of skin have limitations in ease-of-use, accessibility, and depth of measurement. This paper describes a new technique to follow changes in the viscoelasticity of the skin, using a novel approach to an indentation manoeuvre. The device is portable, low-cost and easy to use while at the same time providing rich information on the mechanical response of the skin. The method proposed optically tracks the skin's recovery from an initial strain, made with a novel linear indentor, using diffuse side-lighting and a CCD video camera. Upon indentation, the skin's elastin fibres are stretched and fluid is displaced from the compressed region. When the indentor is removed, the rate of recovery of the skin from this imprint is therefore principally dependent on its hydration and elasticity. Using the blue colour plane of the image and polarisation filtering, it is possible to examine the surface topography only, and track the decay of the imprint over time. The decrease in size of the imprint over time (decay curve) recorded by the device is shown to agree with the theoretical predictions of an appropriate viscoelastic model of skin mechanical behaviour. The contributors to the response measured using the indentation device are fully characterised and evaluated using separate measurement techniques including high-frequency ultrasound, polarisation spectroscopy and optical coherence

  14. Investigation into local cell mechanics by atomic force microscopy mapping and optical tweezer vertical indentation

    NASA Astrophysics Data System (ADS)

    Coceano, G.; Yousafzai, M. S.; Ma, W.; Ndoye, F.; Venturelli, L.; Hussain, I.; Bonin, S.; Niemela, J.; Scoles, G.; Cojoc, D.; Ferrari, E.

    2016-02-01

    Investigating the mechanical properties of cells could reveal a potential source of label-free markers of cancer progression, based on measurable viscoelastic parameters. The Young’s modulus has proved to be the most thoroughly studied so far, however, even for the same cell type, the elastic modulus reported in different studies spans a wide range of values, mainly due to the application of different experimental conditions. This complicates the reliable use of elasticity for the mechanical phenotyping of cells. Here we combine two complementary techniques, atomic force microscopy (AFM) and optical tweezer microscopy (OTM), providing a comprehensive mechanical comparison of three human breast cell lines: normal myoepithelial (HBL-100), luminal breast cancer (MCF-7) and basal breast cancer (MDA-MB-231) cells. The elastic modulus was measured locally by AFM and OTM on single cells, using similar indentation approaches but different measurement parameters. Peak force tapping AFM was employed at nanonewton forces and high loading rates to draw a viscoelastic map of each cell and the results indicated that the region on top of the nucleus provided the most meaningful results. OTM was employed at those locations at piconewton forces and low loading rates, to measure the elastic modulus in a real elastic regime and rule out the contribution of viscous forces typical of AFM. When measured by either AFM or OTM, the cell lines’ elasticity trend was similar for the aggressive MDA-MB-231 cells, which were found to be significantly softer than the other two cell types in both measurements. However, when comparing HBL-100 and MCF-7 cells, we found significant differences only when using OTM.

  15. On Bitstream Based Edge Detection Techniques

    DTIC Science & Technology

    2009-01-01

    IEEE Transactions on, vol. 38, no. 1, pp. xviii– iv, Feb 1992. [5] Rafael C. Gonzalez and Richard E. Woods, Digital Image Processing, Addison-Wesley...Carmona-Poyato, R. Medina- Carnicer, and F. J. Madrid- Cuevas , “Automatic genera- tion of consensus ground truth for the comparison of edge detection techniques,” Image Vision Comput., vol. 26, no. 4, pp. 496–511, 2008.

  16. Nano-indentation testing of new and fractured nickel-titanium endodontic instruments.

    PubMed

    Jamleh, A; Sadr, A; Nomura, N; Yahata, Y; Ebihara, A; Hanawa, T; Tagami, J; Suda, H

    2012-05-01

    To investigate the effect of cyclic fatigue on nickel-titanium (NiTi) endodontic instruments using a nano-indentation test. Eight ProFile NiTi rotary instruments (size 30, taper 0.06; Dentsply Maillefer, Ballaigues, Switzerland) were tested using a cyclic fatigue set-up until fracture. The fractured instruments and eight new NiTi instruments of the same size and taper were used for a nano-indentation test on the internal surfaces of a NiTi instruments in the region just adjacent to their fractured edge (group I) and in the same region of the new group (group II), and the cutting part beside the shaft for both instruments [group III (fractured) and group IV (new)]. Data were statistically analyzed using one-way analysis of variance and Games-Howell post hoc test. The alpha-type error was set at 0.05. Significant differences in terms of hardness and elastic modulus for each group (P < 0.05) were found, with group I having the lowest mean values followed by group III. Additionally, standard deviations increased remarkably after failure, as represented by groups I and III. The nano-indentation technique can be applied to determine the performance and the failure mechanism of NiTi instruments. The fatigue process revealed a significant decrease in the hardness and elastic modulus of the NiTi instrument. As indicated by the low hardness, the fatigue process did not result in work hardening but rather work softening. © 2011 International Endodontic Journal.

  17. Finite-element modeling of soft tissue rolling indentation.

    PubMed

    Sangpradit, Kiattisak; Liu, Hongbin; Dasgupta, Prokar; Althoefer, Kaspar; Seneviratne, Lakmal D

    2011-12-01

    We describe a finite-element (FE) model for simulating wheel-rolling tissue deformations using a rolling FE model (RFEM). A wheeled probe performing rolling tissue indentation has proven to be a promising approach for compensating for the loss of haptic and tactile feedback experienced during robotic-assisted minimally invasive surgery (H. Liu, D. P. Noonan, B. J. Challacombe, P. Dasgupta, L. D. Seneviratne, and K. Althoefer, "Rolling mechanical imaging for tissue abnormality localization during minimally invasive surgery, " IEEE Trans. Biomed. Eng., vol. 57, no. 2, pp. 404-414, Feb. 2010; K. Sangpradit, H. Liu, L. Seneviratne, and K. Althoefer, "Tissue identification using inverse finite element analysis of rolling indentation," in Proc. IEEE Int. Conf. Robot. Autom. , Kobe, Japan, 2009, pp. 1250-1255; H. Liu, D. Noonan, K. Althoefer, and L. Seneviratne, "The rolling approach for soft tissue modeling and mechanical imaging during robot-assisted minimally invasive surgery," in Proc. IEEE Int. Conf. Robot. Autom., May 2008, pp. 845-850; H. Liu, P. Puangmali, D. Zbyszewski, O. Elhage, P. Dasgupta, J. S. Dai, L. Seneviratne, and K. Althoefer, "An indentation depth-force sensing wheeled probe for abnormality identification during minimally invasive surgery," Proc. Inst. Mech. Eng., H, vol. 224, no. 6, pp. 751-63, 2010; D. Noonan, H. Liu, Y. Zweiri, K. Althoefer, and L. Seneviratne, "A dual-function wheeled probe for tissue viscoelastic property identification during minimally invasive surgery," in Proc. IEEE Int. Conf. Robot. Autom. , 2008, pp. 2629-2634; H. Liu, J. Li, Q. I. Poon, L. D. Seneviratne, and K. Althoefer, "Miniaturized force indentation-depth sensor for tissue abnormality identification," IEEE Int. Conf. Robot. Autom., May 2010, pp. 3654-3659). A sound understanding of wheel-tissue rolling interaction dynamics will facilitate the evaluation of signals from rolling indentation. In this paper, we model the dynamic interactions between a wheeled probe and a

  18. Liquid Tunable Microlenses based on MEMS techniques

    PubMed Central

    Zeng, Xuefeng; Jiang, Hongrui

    2013-01-01

    The recent rapid development in microlens technology has provided many opportunities for miniaturized optical systems, and has found a wide range of applications. Of these microlenses, tunable-focus microlenses are of special interest as their focal lengths can be tuned using micro-scale actuators integrated with the lens structure. Realization of such tunable microlens generally relies on the microelectromechanical system (MEMS) technologies. Here, we review the recent progress in tunable liquid microlenses. The underlying physics relevant to these microlenses are first discussed, followed by description of three main categories of tunable microlenses involving MEMS techniques, mechanically driven, electrically driven, and those integrated within microfluidic systems. PMID:24163480

  19. PIE: A Dynamic Failure-Based Technique

    NASA Technical Reports Server (NTRS)

    Voas, Jeffrey M.

    1990-01-01

    This paper presents a dynamic technique for statistically estimating three program characteristics that affect a program's computational behavior: (1) the probability that a particular section of a program is executed, (2) the probability that the particular section affects the data state, and (3) the probability that a data state produced by that section has an effect on program output. These three characteristics can be used to predict whether faults are likely to be uncovered by software testing. Index Terms: Software testing, data state, fault, failure, testability. 1 Introduction

  20. Two-way indent depth recovery in a NiTi shape memory alloy

    NASA Astrophysics Data System (ADS)

    Zhang, Yijun; Cheng, Yang-Tse; Grummon, David S.

    2006-03-01

    Controlled reversible changes in surface texture and topography are of interest to many applications, including information storage, optical communication devices, micro-fluidic instruments for drug delivery, and smart tribological surfaces for friction and wear control. Here, we demonstrate a method of inducing two-way reversible changes in an indentation made on the surface of a shape memory NiTi alloy. The two-way indent shape change is accomplished by thermomechanical training of spherical indents in NiTi shape memory alloy. After training, spherical indents exhibit two-way depth recovery: Shallow indent depth at high temperature and deep indent depth at low temperature. The reversible depth change is about 45% of the total indent depth and is stable over many cycles. The reversible depth change can have a wide range of engineering applications.

  1. Apprenticeship Learning Techniques for Knowledge Based Systems

    DTIC Science & Technology

    1988-12-01

    domain, such as medicine. The Odysseus explanation-based learning program constructs explanations of problem-solving actions in the domain of medical...theories and empirical methods so as to allow construction of an explanation. The Odysseus learning program provides the first demonstration of using the... Odysseus explanation-based learning program is presfuted, which constructs explanations of human problem-solving actions in the domain of medical di

  2. Hertzian indentation of colloidally processed titanium carbide-nickel aluminide composites

    NASA Astrophysics Data System (ADS)

    Collier, R. Bradley

    Advanced cermets based on titanium carbide (TiC), with a ductile nickel aluminide (Ni3Al) binder, have shown significant promise for use in a variety of demanding wear environments, due to a combination of high strength and good corrosion behaviour. A unique feature of TiC-Ni3Al cermets is that they show increasing strength from room temperature up to ˜1,000°C, while current materials such as tungsten carbide/cobalt (WC/Co) show significant strength degradation above ˜500°C. In this thesis, aqueous colloidal forming methods have been applied to process TiC preforms. The mechanisms and effectiveness of suspension stabilization were examined using methods such as zeta potential analysis, rheological measurements, and sedimentation trials for two common dispersants; an ammonium salt of polymethacrylate (PMA-NH 4) and two molecular weights (l,800 and 10,000) of polyethylenimine (PEI). TiC preforms were prepared by slip casting suspensions of up to 50 vol. % solids content. After drying, the TiC-based cermets were processed by melt infiltration with the Ni3Al alloy (IC-50) at 1475°C.Ni 3Al content was varied between 20 and 50 vol. % using this approach, resulting in final densities that exceeded 98% of theoretical. These samples were subjected to Hertzian indentation testing with loads ranging from 250 -- 2000 N, using WC-Co spheres with sizes ranging from 1.191 to 2.38 mm. Indentation stress-strain curves were produced from the indentation data and compared to the calculated elastic Hertzian response. The bonded interface method was used to examine the subsurface deformation of the material under load. Significant deformation of the binder and the eventual fracture of the TiC grains were observed. The nature of the quasi-plasticity of TiC-Ni 3Al and the effects of binder content on surface and subsurface deformation is examined.

  3. Trends and Techniques for Space Base Electronics

    NASA Technical Reports Server (NTRS)

    Trotter, J. D.; Wade, T. E.; Gassaway, J. D.

    1979-01-01

    Simulations of various phosphorus and boron diffusions in SOS were completed and a sputtering system, furnaces, and photolithography related equipment were set up. Double layer metal experiments initially utilized wet chemistry techniques. By incorporating ultrasonic etching of the vias, premetal cleaning a modified buffered HF, phosphorus doped vapox, and extended sintering, yields of 98% were obtained using the standard test pattern. A two dimensional modeling program was written for simulating short channel MOSFETs with nonuniform substrate doping. A key simplifying assumption used is that the majority carriers can be represented by a sheet charge at the silicon dioxide silicon interface. Although the program is incomplete, the two dimensional Poisson equation for the potential distribution was achieved. The status of other Z-D MOSFET simulation programs is summarized.

  4. Acoustic emission analysis of Vickers indentation fracture of cermet and ceramic coatings

    NASA Astrophysics Data System (ADS)

    Faisal, N. H.; Ahmed, R.

    2011-12-01

    The aim of this work was to develop an instrumented experimental methodology of quantitative material evaluation based on the acoustic emission (AE) monitoring of a dead-weight Vickers indentation. This was to assess the degree of cracking and hence the toughness of thermally sprayed coatings. AE data were acquired during indentation tests on samples of coatings of nominal thickness 250-325 µm at a variety of indentation loads ranging from 49 to 490 N. Measurements were carried out on five different carbide and ceramic coatings (HVOF as-sprayed WC-12%Co (JP5000 and JetKote), HIPed WC-12%Co (JetKote) and as-sprayed Al2O3 (APS/Metco and HVOF/theta-gun)). The raw AE signals recorded during indentation were analysed and the total surface crack length around the indent determined. The results showed that the total surface crack length measured gave fracture toughness (K1c) values which were consistent with the published literature for similar coatings but evaluated using the classical approach (Palmqvist/half-penny model). Hence, the total surface crack length criteria can be applied to ceramic and cermet coatings which may or may not exhibit fracture via radial cracks. The values of K1c measured were 3.4 ± 0.1 MPa m1/2 for high-velocity oxygen fuel (HVOF) (theta-gun) Al2O3, 4.6 ± 0.3 MPa m1/2 for as-sprayed HVOF (JetKote) WC-12%Co, 7.1±0.1 MPa m1/2 for as-sprayed HVOF (JP5000) WC-12%Co and 7.4 ± 0.2 MPa m1/2 for HIPed HVOF (JetKote) WC-12%Co coatings. The crack lengths were then calibrated against the AE response and correlation coefficients evaluated. The values of K1c measured using AE correlations were 3.3 MPa m1/2 for HVOF (theta-gun) Al2O3, 2.6 MPa m1/2 for APS (Metco) Al2O3, 2.5 MPa m1/2 for as-sprayed HVOF (JetKote) WC-12%Co, 6.3 MPa m1/2 for as-sprayed HVOF (JP5000) WC-12%Co and 8.6 MPa m1/2 for HIPed HVOF (JetKote) WC-12%Co coatings. It is concluded that within each category of coating type, AE can be used as a suitable surrogate for crack length

  5. A Validation Approach for Quasistatic Numerical/Experimental Indentation Analysis in Soft Materials Using 3D Digital Image Correlation.

    PubMed

    Felipe-Sesé, Luis; López-Alba, Elías; Hannemann, Benedikt; Schmeer, Sebastian; Diaz, Francisco A

    2017-06-28

    A quasistatic indentation numerical analysis in a round section specimen made of soft material has been performed and validated with a full field experimental technique, i.e., Digital Image Correlation 3D. The contact experiment specifically consisted of loading a 25 mm diameter rubber cylinder of up to a 5 mm indentation and then unloading. Experimental strains fields measured at the surface of the specimen during the experiment were compared with those obtained by performing two numerical analyses employing two different hyperplastic material models. The comparison was performed using an Image Decomposition new methodology that makes a direct comparison of full-field data independently of their scale or orientation possible. Numerical results show a good level of agreement with those measured during the experiments. However, since image decomposition allows for the differences to be quantified, it was observed that one of the adopted material models reproduces lower differences compared to experimental results.

  6. A Validation Approach for Quasistatic Numerical/Experimental Indentation Analysis in Soft Materials Using 3D Digital Image Correlation

    PubMed Central

    Felipe-Sesé, Luis; López-Alba, Elías; Hannemann, Benedikt; Schmeer, Sebastian; Diaz, Francisco A.

    2017-01-01

    A quasistatic indentation numerical analysis in a round section specimen made of soft material has been performed and validated with a full field experimental technique, i.e., Digital Image Correlation 3D. The contact experiment specifically consisted of loading a 25 mm diameter rubber cylinder of up to a 5 mm indentation and then unloading. Experimental strains fields measured at the surface of the specimen during the experiment were compared with those obtained by performing two numerical analyses employing two different hyperplastic material models. The comparison was performed using an Image Decomposition new methodology that makes a direct comparison of full-field data independently of their scale or orientation possible. Numerical results show a good level of agreement with those measured during the experiments. However, since image decomposition allows for the differences to be quantified, it was observed that one of the adopted material models reproduces lower differences compared to experimental results. PMID:28773081

  7. The characterization of Vicker`s microhardness indentations and pile-up profiles as a strain-hardening microprobe

    SciTech Connect

    Santos, C. Jr.; Odette, G.R.; Lucas, G.E.; Schroeter, B.; Klinginsmith, D.; Yamamoto, T.

    1998-04-01

    Microhardness measurements have long been used to examine strength properties and changes in strength properties in metals, for example, as induced by irradiation. Microhardness affords a relatively simple test that can be applied to very small volumes of material. Microhardness is nominally related to the flow stress of the material at a fixed level of plastic strain. Further, the geometry of the pile-up of material around the indentation is related to the strain-hardening behavior of a material; steeper pile-ups correspond to smaller strain-hardening rates. In this study the relationship between pile-up profiles and strain hardening is examined using both experimental and analytical methods. Vickers microhardness tests have been performed on a variety of metal alloys including low alloy, high Cr and austenitic stainless steels. The pile-up topology around the indentations has been quantified using confocal microscopy techniques. In addition, the indentation and pile-up geometry has been simulated using finite element method techniques. These results have been used to develop an improved quantification of the relationship between the pile-up geometry and the strain-hardening constitutive behavior of the test material.

  8. A skin indentation system using a pneumatic bellows.

    PubMed

    Ferguson-Pell, M; Hagisawa, S; Masiello, R D

    1994-01-01

    A pneumatic indentation system using a copper bellows has been developed for physiological studies where a controlled uniaxial compressive force is required to be applied to the surface of the skin. Such a system is useful for studies where the physiological response of the tissues is to be monitored following a known loading history. The indentation system is driven by a vacuum/compression pneumatic pump through solenoid valves under closed-loop computer control. A load cell placed between the indentor and bellows monitors the applied force providing a feedback signal to the computer. The signal from the computer activates the valves supplying air pressure to the bellows, and the applied force is controlled using a digital closed-loop protocol. This system can be used to provide a controlled loading sequence to the skin without utilizing gravitational forces, which allows the subject to keep a more natural position during the experiment.

  9. Impact strength and indentation hardness of high-strength ceramics

    SciTech Connect

    Grady, D.E.

    1993-08-01

    Hugoniot elastic limit and indentation hardness data are provided for selected high-strength ceramics AlN, Al{sub 2}O{sub 3}, B{sub 4}C, SiC, TiB, Zr{sub 2}. Degree of correlation of the strength data by the two test methods is examined. Influence of reformation mechanism on strength measurement, including rate sensitivity, size scale and confining pressure, is discussed.

  10. Information fusion based techniques for HEVC

    NASA Astrophysics Data System (ADS)

    Fernández, D. G.; Del Barrio, A. A.; Botella, Guillermo; Meyer-Baese, Uwe; Meyer-Baese, Anke; Grecos, Christos

    2017-05-01

    Aiming at the conflict circumstances of multi-parameter H.265/HEVC encoder system, the present paper introduces the analysis of many optimizations' set in order to improve the trade-off between quality, performance and power consumption for different reliable and accurate applications. This method is based on the Pareto optimization and has been tested with different resolutions on real-time encoders.

  11. Extraordinary Indentation Strain Stiffening Produces Superhard Tungsten Nitrides

    NASA Astrophysics Data System (ADS)

    Lu, Cheng; Li, Quan; Ma, Yanming; Chen, Changfeng

    2017-09-01

    Transition-metal light-element compounds are a class of designer materials tailored to be a new generation of superhard solids, but indentation strain softening has hitherto limited their intrinsic load-invariant hardness to well below the 40 GPa threshold commonly set for superhard materials. Here we report findings from first-principles calculations that two tungsten nitrides, hP4-WN and hP 6 -WN2 , exhibit extraordinary strain stiffening that produces remarkably enhanced indentation strengths exceeding 40 GPa, raising exciting prospects of realizing the long-sought nontraditional superhard solids. Calculations show that hP4-WN is metallic both at equilibrium and under indentation, marking it as the first known intrinsic superhard metal. An x-ray diffraction pattern analysis indicates the presence of hP4-WN in a recently synthesized specimen. We elucidate the intricate bonding and stress response mechanisms for the identified structural strengthening, and the insights may help advance rational design and discovery of additional novel superhard materials.

  12. Accelerator based techniques for contraband detection

    NASA Astrophysics Data System (ADS)

    Vourvopoulos, George

    1994-05-01

    It has been shown that narcotics, explosives, and other contraband materials, contain various chemical elements such as H, C, N, O, P, S, and Cl in quantities and ratios that differentiate them from each other and from other innocuous substances. Neutrons and γ-rays have the ability to penetrate through various materials at large depths. They are thus able, in a non-intrusive way, to interrogate volumes ranging from suitcases to Sea-Land containers, and have the ability to image the object with an appreciable degree of reliability. Neutron induced reactions such as (n, γ), (n, n') (n, p) or proton induced γ-resonance absorption are some of the reactions currently investigated for the identification of the chemical elements mentioned above. Various DC and pulsed techniques are discussed and their advantages, characteristics, and current progress are shown. Areas where use of these methods is currently under evaluation are detection of hidden explosives, illicit drug interdiction, chemical war agents identification, nuclear waste assay, nuclear weapons destruction and others.

  13. SI traceable calibration of an instrumented indentation sensor spring constant using electrostatic force.

    PubMed

    Chung, Koo-Hyun; Scholz, Stefan; Shaw, Gordon A; Kramar, John A; Pratt, Jon R

    2008-09-01

    We present a measurement scheme for creating reference electrostatic forces that are traceable to the International System of Units. This scheme yields reference forces suitable for calibrating the force sensitivity of instrumented indentation machines and atomic force microscopes. Forces between 10 and 200 muN were created and expressed in terms of the voltage, length, and capacitance between a pair of interacting electrodes. The electrodes comprised an electrically conductive sphere mounted as a tip on an instrumented indentation sensor, and a planar counterelectrode fixed to a sample stage in close proximity to the sphere. For comparison, we applied mechanical forces of similar magnitudes, first using deadweights and then using a reference force sensor. The deflection of the sensor due to the various applied forces was measured using an interferometer. A spring constant for the sensor was computed from the observed records of force versus displacement. Each procedure yielded a relative standard uncertainty of approximately 1%; however, the electrostatic technique is scalable and could provide traceable reference forces as small as a few hundred piconewtons, a range far below anything yet achieved using deadweights.

  14. SI traceable calibration of an instrumented indentation sensor spring constant using electrostatic force

    SciTech Connect

    Chung, Koo-Hyun; Scholz, Stefan; Shaw, Gordon A.; Kramar, John A.; Pratt, Jon R.

    2008-09-15

    We present a measurement scheme for creating reference electrostatic forces that are traceable to the International System of Units. This scheme yields reference forces suitable for calibrating the force sensitivity of instrumented indentation machines and atomic force microscopes. Forces between 10 and 200 {mu}N were created and expressed in terms of the voltage, length, and capacitance between a pair of interacting electrodes. The electrodes comprised an electrically conductive sphere mounted as a tip on an instrumented indentation sensor, and a planar counterelectrode fixed to a sample stage in close proximity to the sphere. For comparison, we applied mechanical forces of similar magnitudes, first using deadweights and then using a reference force sensor. The deflection of the sensor due to the various applied forces was measured using an interferometer. A spring constant for the sensor was computed from the observed records of force versus displacement. Each procedure yielded a relative standard uncertainty of approximately 1%; however, the electrostatic technique is scalable and could provide traceable reference forces as small as a few hundred piconewtons, a range far below anything yet achieved using deadweights.

  15. Using Indentation to Characterize Water Transport and Structure in Nafion Thin Films

    NASA Astrophysics Data System (ADS)

    Davis, Eric; Nadermann, Nichole; Page, Kirt; Stafford, Christopher; Chan, Edwin

    Perfluorinated ionomers, specifically Nafion, are the state-of-the-art polymer used in fuel cells. For this application, Nafion is utilized in both a bulk (hundreds of microns) and confined (tens of nanometers) state. For Nafion thin films in a confined state, i.e., Nafion as thin film coatings on catalyst particles, in-plane transport may play a critical role in the movement of water and protons through this catalysis layer. In this study, water transport was measured for a series of Nafion thin film thicknesses using poroelastic relaxation indentation (PRI). Unlike traditional through-thickness diffusion measurement techniques for thin polymer films (e.g., quartz crystal microbalance), PRI can be used to probe the in-plane water transport behavior. Relative to bulk Nafion, reduced in-plane water diffusion was observed in thin film Nafion, and below approximately 1 micron, water diffusivity and Nafion film thickness exhibited a logarithmic relationship. Equilibrium swelling measurements of water saturated Nafion thin films were used in conjunction with pore network theory to develop a picture of how the molecular-scale structure of Nafion changes with confinement to nanoscale film thicknesses. Using Indentation to Characterize Water Transport and Structure in Nafion Thin Films.

  16. Atomic force microscopy indentation and inverse analysis for non-linear viscoelastic identification of breast cancer cells.

    PubMed

    Nguyen, Nhung; Shao, Yue; Wineman, Alan; Fu, Jianping; Waas, Anthony

    2016-07-01

    Breast cancer cells (MCF-7 and MCF-10A) are studied through indentation with spherical borosilicate glass particles in atomic force microscopy (AFM) contact mode in fluid. Their mechanical properties are obtained by analyzing the recorded reaction force-time response. The analysis is based on comparing experimental data with predictions from finite element (FE) simulation. Here, FE modeling is employed to simulate the AFM indentation experiment which is neither a displacement nor a force controlled test. This approach is expected to overcome many underlying problems of the widely used models such as Hertz contact model due to its capability to capture the contact behaviors between the spherical indentor and the cell, account for cell geometry, and incorporate with large strain theory. In this work, a non-linear viscoelastic (NLV) model in which the viscoelastic part is described by Prony series terms is used for the constitutive model of the cells. The time-dependent material parameters are extracted through an inverse analysis with the use of a surrogate model based on a Kriging estimator. The purpose is to automatically extract the NLV properties of the cells with a more efficient process compared to the iterative inverse technique that has been mostly applied in the literature. The method also allows the use of FE modeling in the analysis of a large amount of experimental data. The NLV parameters are compared between MCF-7 and MCF-10A and MCF-10A treated and untreated with the drug Cytochalasin D to examine the possibility of using relaxation properties as biomarkers for distinguishing these types of breast cancer cells. The comparisons indicate that malignant cells (MCF-7) are softer and exhibit more relaxation than benign cells (MCF-10A). Disrupting the cytoskeleton using the drug Cytochalasin D also results in a larger amount of relaxation in the cell's response. In addition, relaxation properties indicate larger differences as compared to the elastic moduli

  17. FDI and Accommodation Using NN Based Techniques

    NASA Astrophysics Data System (ADS)

    Garcia, Ramon Ferreiro; de Miguel Catoira, Alberto; Sanz, Beatriz Ferreiro

    Massive application of dynamic backpropagation neural networks is used on closed loop control FDI (fault detection and isolation) tasks. The process dynamics is mapped by means of a trained backpropagation NN to be applied on residual generation. Process supervision is then applied to discriminate faults on process sensors, and process plant parameters. A rule based expert system is used to implement the decision making task and the corresponding solution in terms of faults accommodation and/or reconfiguration. Results show an efficient and robust FDI system which could be used as the core of an SCADA or alternatively as a complement supervision tool operating in parallel with the SCADA when applied on a heat exchanger.

  18. Limit case analysis of the "stable indenter velocity" method for obtaining creep stress exponents from constant load indentation creep tests

    NASA Astrophysics Data System (ADS)

    Campbell, J.; Dean, J.; Clyne, T. W.

    2017-02-01

    This study concerns a commonly-used procedure for evaluating the steady state creep stress exponent, n, from indentation data. The procedure involves monitoring the indenter displacement history under constant load and making the assumption that, once its velocity has stabilised, the system is in a quasi-steady state, with stage II creep dominating the behaviour. The stress and strain fields under the indenter are represented by "equivalent stress" and "equivalent strain rate" values. The estimate of n is then obtained as the gradient of a plot of the logarithm of the equivalent strain rate against the logarithm of the equivalent stress. Concerns have, however, been expressed about the reliability of this procedure, and indeed it has already been shown to be fundamentally flawed. In the present paper, it is demonstrated, using a very simple analysis, that, for a genuinely stable velocity, the procedure always leads to the same, constant value for n (either 1.0 or 0.5, depending on whether the tip shape is spherical or self-similar). This occurs irrespective of the value of the measured velocity, or indeed of any creep characteristic of the material. It is now clear that previously-measured values of n, obtained using this procedure, have varied in a more or less random fashion, depending on the functional form chosen to represent the displacement-time history and the experimental variables (tip shape and size, penetration depth, etc.), with little or no sensitivity to the true value of n.

  19. Arts-based data collection techniques used in child research.

    PubMed

    Driessnack, Martha; Furukawa, Ryoko

    2012-01-01

    The purpose of this study was to identify the different arts-based techniques being used in health-related research with children. A systematic survey of literature was conducted. Two hundred and ten articles were initially identified and reviewed. Of these, 116 met inclusion criteria of arts-based techniques in research with children 7-12 years of age. The different categories of techniques identified included (a) drawings, (b) photographs, (c) graphics, and (d) artifacts. Only 19% of the studies were health related. Further, 79% were conducted outside the United States, revealing that arts-based techniques appear to be underused by nurses and other healthcare researchers, especially in the United States. To ensure that children actively engage in research involving them, nurses can familiarize themselves with and advocate for the use of arts-based techniques. © 2011, Wiley Periodicals, Inc.

  20. Flexible control techniques for a lunar base

    NASA Technical Reports Server (NTRS)

    Kraus, Thomas W.

    1992-01-01

    applications with little or no customization. This means that lunar process control projects will not be delayed by unforeseen problems or last minute process modifications. The software will include all of the tools needed to adapt to virtually any changes. In contrast to other space programs which required the development of tremendous amounts of custom software, lunar-based processing facilities will benefit from the use of existing software technology which is being proven in commercial applications on Earth.

  1. Nano-mechanical characterization of plasma surface tungstenized layer by depth-sensing nano-indentation measurement

    NASA Astrophysics Data System (ADS)

    Wu, Hongyan; Li, Yin; Tang, Xiao; Hussain, G.; Zhao, Haofeng; Li, Qingfang; Adedotun, Adetunla

    2015-01-01

    Plasma surface tungstenizing was performed on Ti-Al-Nb substrate using the double-glow plasma surface alloying technique. The microstructure and composition of the tungstenized layer were determined by scanning electron microscope, X-ray diffraction and X-ray photoelectron spectroscopy. The mechanical properties of the substrate and the tungstenized layer were characterized by the dynamic micro-hardness and the elastic modulus. The results showed that the tungstenized layer was comprised of three distinct sub-layers namely sediment layer, transition layer and diffusion layer, with a total layer thickness of over 25 μm. The concentration of the tungsten decreased gradually as the layer depth increased and the continuous change in the tungsten content affects the mechanical properties of the alloyed layer. The dynamic micro-hardness and elastic modulus of the tungstenized layer and substrate were investigated by the depth-sensing nano-indentation measurement under different conditions. According to the findings, the values of dynamic micro-hardness exhibited no significant dependence on the indentation load. However, the elastic modulus of the tungstenized layer tended to decrease as the indentation load was increased. Furthermore, the dynamic micro-hardness and elastic modulus curves of the tungstenized layer revealed a pattern similar to the concentration distribution of the tungsten. Both surface micro-hardness and elastic modulus of plasma alloyed surface gradually decreased with the increase of indentation depth, most probably because of the three different regions in the alloyed layer. As for the mechanical properties, the tungstenized layer exhibited significantly higher dynamic micro-hardness and elastic modulus than the substrate. As the cyclic loading-unloading curves of the substrate and the tungstenized layer showed, the elastic recovery and uniform plastic deformation decrease and the fatigue damage of the tungstenized layer is lower than that of the

  2. Comparison and improvement of color-based image retrieval techniques

    NASA Astrophysics Data System (ADS)

    Zhang, Yujin; Liu, Zhong W.; He, Yun

    1997-12-01

    With the increasing popularity of image manipulation with contents, many color-based image retrieval techniques have been proposed in the literature. A systematic and comparative study of 8 representative techniques is first presented in this paper, which uses a database of 200 images of flags and trademarks. These techniques are determined to cover the variations of the color models used, of the characteristic color features employed and of the distance measures calculated for judging the similarity of color images. The results of this comparative study are presented both by the list of retrieved images for subjective visual inspection and by the retrieving ratios computed for objective judgement. All of them show that the cumulative histogram based techniques using Euclidean distance measures in two perception related color spaces give best results among the 8 techniques under consideration. Started from the best performed techniques, works toward further improving their retrieving capability are then carried on and this has resulted 2 new techniques which use local cumulative histograms. The new techniques have been tested by using a database of 400 images of real flowers which are quite complicated in color contents. Some satisfactory results, compared to that obtained by using existing cumulative histogram based techniques are obtained and presented.

  3. Fictive temperature-independent density and minimum indentation size effect in calcium aluminosilicate glass

    SciTech Connect

    Gross, T. M.; Tomozawa, M.

    2008-09-15

    Using the calcium aluminosilicate system a glass was developed that exhibits fictive temperature-independent density by creating an intermediate glass between normal and anomalous glasses. Normal glass, such as soda-lime silicate glass, exhibits decreasing density with increasing fictive temperature while anomalous glass, such as silica glass, exhibits increasing density with increasing fictive temperature. This intermediate glass composition was found to exhibit the minimum indentation size effect during indentation hardness testing. It appears that the indentation size effect is correlated with a deformation-induced fictive temperature increase, which is accompanied by a density change and hardness change in the vicinity of the indentation. It is suggested from these observations that indentation size effect originates from the energy required to create interfaces and defects such as shear bands, subsurface cracks, and point defects near the indenter-specimen boundary, which accompany the volume change.

  4. A Word-Based Compression Technique for Text Files.

    ERIC Educational Resources Information Center

    Vernor, Russel L., III; Weiss, Stephen F.

    1978-01-01

    Presents a word-based technique for storing natural language text in compact form. The compressed text consists of a dictionary and a text that is a combination of actual running text and pointers to the dictionary. This technique has shown itself to be effective for both text storage and retrieval. (VT)

  5. Nano-indentation of single-layer optical oxide thin films grown by electron-beam deposition

    SciTech Connect

    Mehrotra, K.; Oliver, J. B.; Lambropoulos, J. C.

    2015-01-01

    Mechanical characterization of optical oxide thin films is performed using nano-indentation, and the results are explained based on the deposition conditions used. These oxide films are generally deposited to have a porous microstructure that optimizes laser induced damage thresholds, but changes in deposition conditions lead to varying degrees of porosity, density, and possibly the microstructure of the thin film. This can directly explain the differences in the mechanical properties of the film studied here and those reported in literature. Of the four single-layer thin films tested, alumina was observed to demonstrate the highest values of nano-indentation hardness and elastic modulus. This is likely a result of the dense microstructure of the thin film arising from the particular deposition conditions used.

  6. Method for quantitative measurements of the elastic modulus of biological cells in AFM indentation experiments.

    PubMed

    Sokolov, Igor; Dokukin, Maxim E; Guz, Nataliia V

    2013-04-01

    Here we overview and further develop a quantitative method to measure mechanics of biological cells in indentation experiments, which is based on the use of atomic force microscopy (AFM). We demonstrate how the elastic modulus of the cell body should be measured when the cellular brush is taken into account. The brush is an essential inelastic part of the cell, which surrounds all eukaryotic (the brush is mostly microvilli and glycocalyx) and gram-negative prokaryotic cells (the brush is polysaccharides). The other main feature of the described method is the use of a relatively dull AFM probe to stay in the linear stress-strain regime. In particular, we show 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. Besides the elastic modulus, the method presented allows obtaining the parameters of cellular brush, such as the effective length and grafting density of the brush. Although the method is demonstrated on eukaryotic cells, it is directly applicable for all types of cells, and even non-biological soft materials surrounded by either a brush or any field of long-range forces. Copyright © 2013 Elsevier Inc. All rights reserved.

  7. Discrete element modeling of indentation tests to investigate mechanisms of CO2-related chemomechanical rock alteration

    NASA Astrophysics Data System (ADS)

    Sun, Zhuang; Espinoza, D. Nicolas; Balhoff, Matthew T.

    2016-11-01

    During CO2 injection into geological formations, petrophysical and geomechanical properties of host formations can be altered due to mineral dissolution and precipitation. Field and laboratory results have shown that sandstone and siltstone can be altered by CO2-water mixtures, but few quantitative studies have been performed to fully investigate underlying mechanisms. Based on the hypothesis that CO2-water mixtures alter the integrity of rock structure by attacking cements rather than grains, we attempt to explain the degradation of cementation due to long-term contact with CO2 and water and mechanisms for changes in rock mechanical properties. Many sandstones, including calcite-cemented quartzitic sandstone, chlorite-cemented quartzitic sandstone, and hematite-cemented quartzitic sandstone, contain interparticle cements that are more readily affected by CO2-water mixtures than grains. A model that couples the discrete element method and the bonded-particle model is used to perform simulations of indentation tests on synthetic rocks with crystal and random packings. The model is verified against the analytical cavity expansion model and validated against laboratory indentation tests on Entrada sandstone with and without CO2 alteration. Sensitivity analysis is performed for cementation microscopic parameters including stiffness, size, axial, and shear strength. The simulation results indicate that the CO2-related degradation of mechanical properties in bleached Entrada sandstone can be attributed to the reduction of cement size rather than cement strength. Our study indicates that it is possible to describe the CO2-related rock alteration through particle-scale mechanisms.

  8. Deformation mechanisms in advanced structural ceramics due to indentation and scratch processes

    NASA Astrophysics Data System (ADS)

    Ghosh, Dipankar

    Plasma pressure compaction technique was used to develop boron carbide (B4C) and zirconium diboride-silicon carbide (ZrB2-SiC) composite. B4C ceramics are extensively used as body armor in military and civilian applications, and ZrB2-SiC composite has been recognized as a potential candidate for high-temperature aerospace applications. In this dissertation, processing parameters, quasistatic and high-strain rate mechanical response, and fundamental deformation mechanisms of these materials have been investigated. In the case of B4C, the rate sensitivity of indentation hardness was determined using a dynamic indentation hardness tester that can deliver loads in 100 micros. By comparing dynamic hardness with the static hardness, it was found that B4C exhibits a lower hardness at high-strain rate, contrary to known behavior in many structural ceramics. However, these results are consistent with the ballistic testing of B4C armors as reported in recent literature. This behavior was further investigated using a series of spectroscopic techniques such as visible and UV micro-Raman, photoluminescence and infrared. These studies not only confirmed that structural transformation occurred during indentation experiments similar to that in ballistic testing of B4C but also suggested a greater degree of structural changes under dynamic loading compared to static loading. Due to the potential application as external heat shields in supersonic vehicles, scratch studies were conducted on the ZrB2-SiC composite. These studies revealed metal-like slip-line patterns which are indeed an unusual in brittle solids at room-temperature. Utilizing classical stress field solutions under combined normal and tangential loads, a rationale was developed for understanding the formation of scratch-induced deformation features. Also, an analytical framework was developed, combining the concept of 'blister field' and the 'secular equation' relating Raman peaks to strain, to measure scratch

  9. Exploiting interactions between structure size and indentation size effects to determine the characteristic dimension of nano-structured materials by indentation

    NASA Astrophysics Data System (ADS)

    Hou, Xiaodong; Jennett, Nigel M.; Parlinska-Wojtan, Magdalena

    2013-07-01

    It was shown that yield (or flow) stress is determined by a critical dimension and the reciprocal sum of component critical dimensions (such as indentation size, structure size and dislocation density) combine into a single critical dimension as predicted by slip distance theory (Hou et al 2012 Acta. Mater. 60 4128). This suggests that ‘length determines strength’ and all lengths contribute at all times to the critical value. We have already shown that Cu hardness increases when grain size falls below six times the indentation contact radius (Hou et al 2008 J. Phys. D: Appl. Phys. 41 074006). In this paper, we test the inverse case (indent size greater than grain size), by indenting two different metallic glasses (NiAl and ZrTiAlCuBe). We show that the indentation size effect (ISE) does indeed become observable even when the indent size is larger than the grain size by up to an order of magnitude. The indentation depth (size) at onset of the ISE is proportional to the characteristic structure size of these nano-structured materials and suggests a novel use of ISE as a determinant of structure size. These findings have implications for the design of hardness reference blocks and the use of hardness mapping to determine materials property variations.

  10. The detection of bulk explosives using nuclear-based techniques

    SciTech Connect

    Morgado, R.E.; Gozani, T.; Seher, C.C.

    1988-01-01

    In 1986 we presented a rationale for the detection of bulk explosives based on nuclear techniques that addressed the requirements of civil aviation security in the airport environment. Since then, efforts have intensified to implement a system based on thermal neutron activation (TNA), with new work developing in fast neutron and energetic photon reactions. In this paper we will describe these techniques and present new results from laboratory and airport testing. Based on preliminary results, we contended in our earlier paper that nuclear-based techniques did provide sufficiently penetrating probes and distinguishable detectable reaction products to achieve the FAA operational goals; new data have supported this contention. The status of nuclear-based techniques for the detection of bulk explosives presently under investigation by the US Federal Aviation Administration (FAA) is reviewed. These include thermal neutron activation (TNA), fast neutron activation (FNA), the associated particle technique, nuclear resonance absorption, and photoneutron activation. The results of comprehensive airport testing of the TNA system performed during 1987-88 are summarized. From a technical point of view, nuclear-based techniques now represent the most comprehensive and feasible approach for meeting the operational criteria of detection, false alarms, and throughput. 9 refs., 5 figs., 2 tabs.

  11. Slab pull and indentation tectonics: insights from 3D laboratory experiments

    NASA Astrophysics Data System (ADS)

    Regard, Vincent; Faccenna, Claudio; Martinod, Joseph; Bellier, Olivier

    2005-03-01

    We investigate, using 3D laboratory experiments, how the dynamics of indentation process are affected by the evolution at depth of the oceanic and continental subductions. Lithospheric plates are modelled by sand-silicone plates floating on glucose syrup, and the density contrast between oceanic and continental lithospheric plates and asthenosphere is reproduced. Analogue experiments model the convergence between two lithospheric plates, a small continent indenting a large continental plate. We show that the surface deformation in front of the indenter and above the oceanic subduction zone depends on the behaviour of the slab below the collision zone. Slab break-off following the subduction of the small continent favours the indentation process, because it results in an increasing compression in front of the indenter, and extension above the neighbouring oceanic subduction, both of them being responsible for the appearance of the indenter-like geometry of the plate boundary. When the slab does not deform significantly at depth, in contrast, the closure of the oceanic domain in front of the indenter is followed by a longer period of continental subduction, during which the tectonic regime within the wide continent remains quite homogeneous. Comparing the presented analogue experiments with the subductions both part of the Arabian indenter within Eurasia, our results suggest that the different tectonic regime on both sides of the Arabia indenter may partly result from the probable occurrence of a detachment at depth under eastern Anatolia.

  12. An evaluation of the advantages and limitations in simulating indentation cracking with cohesive zone finite elements

    NASA Astrophysics Data System (ADS)

    Johanns, K. E.; Lee, J. H.; Gao, Y. F.; Pharr, G. M.

    2014-01-01

    A cohesive zone model is applied to a finite element (FE) scheme to simulate indentation cracking in brittle materials. Limitations of using the cohesive zone model to study indentation cracking are determined from simulations of a standard fracture toughness specimen and a two-dimensional indentation cracking problem wherein the morphology of the crack and the geometry of the indenter are simplified. It is found that the principles of linear-elastic fracture mechanics can be applied when indentation cracks are long in comparison to the size of the cohesive zone. Vickers and Berkovich pyramidal indentation crack morphologies (3D) are also investigated and found to be controlled by the ratio of elastic modulus to yield strength (E/Y), with median type cracking dominating at low ratios (e.g. E/Y = 10) and Palmqvist type cracking at higher ratios (e.g. E/Y = 100). The results show that cohesive FE simulations of indentation cracking can indeed be used to critically examine the complex relationships between crack morphology, material properties, indenter geometry, and indentation test measurements, provided the crack length is long in comparison to the cohesive zone size.

  13. Boundary condition and pre-strain effects on the free standing indentation response of graphene monolayer.

    PubMed

    Zhou, Lixin; Wang, Yugang; Cao, Guoxin

    2013-11-27

    Using molecular mechanics simulations, we investigated the true pre-stress/pre-strain state of graphene in free standing indentation and the effect of the pre-strain (ε0) on the free standing indentation response of graphene is also considered. We found that there is essentially no effective pre-tension in graphene during free standing indentation and the reported pre-tensile stress determined from the indentation tests does not show the true pre-stress state of graphene, which is a 'fake stress' caused by the assumption (the indenter tip displacement is equal to the displacement of graphene) typically used in the classic indentation analysis. A negative ε0 will increase the van der Waals (VDW) interaction between the indenter tip and graphene to cause a larger overestimation of both values of the elastic modulus (E) and the nonlinear elastic constant (c) of graphene from the classic indentation analysis. However, applying a positive ε0 in graphene, the VDW effect will be significantly decreased, and a more accurate value of E can be obtained, but the value of c will decrease to zero, which may become an effective way to more accurately obtain the elastic stiffness of graphene from indentation tests.

  14. Detection of indentation induced Fe-to-Afe phase transformation in lead zirconate titanate.

    SciTech Connect

    Baddorf, Arthur P.; Shin, Junsoo; Gogotsi, Yury G.; Buchheit, Thomas Edward; Watson, Chad Samuel; Kalinin, Sergei; Juliano, Thomas F.

    2005-08-01

    Instrumented indentation was combined with microscopy and spectroscopy analysis to investigate the local mechanically induced ferroelectric to anti-ferroelectric phase transformation of niobium-modified lead zirconate titanate 95/5. Indentation experiments to a depth of 2 {micro}m were performed using a Berkovich pyramidal three-sided diamond tip. Subsequent Raman spectroscopy and piezoelectric force microscopy revealed that indentation locally induced the ferroelectric to antiferroelectric phase transformation. Piezoelectric force microscopy demonstrated the ability to map the individual phases within and near indented regions on the niobium-modified lead zirconate titanate ceramics.

  15. Micro- and nanopatterning of inorganic and polymeric substrates by indentation lithography.

    PubMed

    Gong, Jinlong; Lipomi, Darren J; Deng, Jiangdong; Nie, Zhihong; Chen, Xin; Randall, Nicholas X; Nair, Rahul; Whitesides, George M

    2010-07-14

    This paper describes the use of a nanoindenter, equipped with a diamond tip, to form patterns of indentations on planar substrates (epoxy, silicon, and SiO(2)). The process is called "Indentation Lithography" (IndL). The indentations have the form of pits and furrows, whose cross-sectional profiles are determined by the shapes of the diamond indenters, and whose dimensions are determined by the applied load and hardness of the substrate. IndL makes it possible to indent hard materials, to produce patterns with multiple levels of relief by changing the loading force, and to control the profiles of the indentations by using indenters with different shapes. This paper also demonstrates the transfer of indented patterns to elastomeric PDMS stamps for soft lithography, and to thin films of evaporated gold or silver. Stripping an evaporated film from an indented template produces patterns of gold or silver pyramids, whose tips concentrate electric fields. Patterns produced by IndL can thus be used as substrates for surface-enhanced Raman scattering (SERS) and for other plasmonic applications.

  16. A novel noncontact ultrasound indentation system for measurement of tissue material properties using water jet compression.

    PubMed

    Lu, M H; Zheng, Y P; Huang, Q H

    2005-06-01

    This study is aimed to develop a novel noncontact ultrasonic indentation system for measuring quantitative mechanical properties of soft tissues, which are increasingly important for tissue assessment and characterization. The key idea of this method is to use a water jet as an indenter to compress the soft tissue while at the same time as a medium for an ultrasound beam to propagate through. The use of water jet indentation does not require a rigid compressor in front of the focused high frequency ultrasound transducer to compress the tissue, so that the additional attenuation caused by the rigid compressor and the strong echoes reflected from its surfaces can be avoided. The indentation deformation was estimated from the ultrasound echoes using a cross-correlation algorithm and the indentation force was calculated from the water pressure measured inside the water pipe. Experiments were performed on uniform tissue-mimicking phantoms with different stiffness. The Young's moduli and Poisson's ratios of these phantoms were measured using a uniaxial ultrasound compression system. The ratio of the indentation pressure to the tissue relative deformation was obtained from the water indentation. This ratio was well correlated with the Young's modulus (r = 0.87). The results also demonstrated that the water indentation approach could differentiate materials with different stiffness in a combined phantom (288 kPa and 433 kPa). This novel noncontact water indentation approach could be potentially used for the measurement of the elasticity of small samples and with a fast scanning speed.

  17. The Effect of Indenter Ball Radius on the Static Load Capacity of the Superelastic 60NiTi for Rolling Element Bearings

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher; Moore, Lewis E.; Clifton, Joshua S.

    2014-01-01

    Static load capacity is a critical design parameter for rolling element bearings used in space mechanisms because of the potential for Brinell (surface dent) damage due to shock and vibration loading events during rocket launch. Brinell damage to bearing raceways can lead to torque variations (noise) and reduced bearing life. The growing use of ceramic rolling elements with high stiffness in hybrid bearings exacerbates the situation. A new family of hard yet resilient materials based upon nickel-titanium is emerging to address such bearing challenges. 60NiTi is a superelastic material that simultaneously exhibits high hardness and a relatively low elastic modulus (100GPa) and has been shown to endure higher indentation loads than conventional and high performance steel. Indentation load capacity has been reported for relatively large (12.7mm diameter) ceramic (Si3N4) indenter balls pressed against flat plates of 60NiTi. In order to develop damage load threshold criteria applicable to a wide range of bearing designs and sizes, the effects of indenter ball radius and the accuracy of interpolation of the Hertz contact stress relations for 60NiTi must be ascertained. In this paper, results of indentation tests involving ceramic balls ranging from 6.4 to 12.7mm in diameter and highly polished 60NiTi flat plates are presented. When the resulting dent depth data for all the indenter ball sizes are normalized using the Hertz equations, the data (dent depth vs. stress) are comparable. Thus when designing bearings made from 60NiTi, the Hertz stress relations can be applied with relative confidence over a range of rolling element sizes and internal geometries.

  18. The Effect of Indenter Ball Radius on the Static Load Capacity of the Superelastic 60NiTi for Rolling Element Bearings

    NASA Technical Reports Server (NTRS)

    Dellacorte, Christopher; Moore, Lewis E.

    2014-01-01

    Static load capacity is a critical design parameter for rolling element bearings used in space mechanisms because of the potential for Brinell (surface dent) damage due to shock and vibration loading events during rocket launch. Brinell damage to bearing raceways can lead to torque variations (noise) and reduced bearing life. The growing use of ceramic rolling elements with high stiffness in hybrid bearings exacerbates the situation. A new family of hard yet resilient materials based upon nickel-titanium is emerging to address such bearing challenges. 60NiTi is a superelastic material that simultaneously exhibits high hardness and a relatively low elastic modulus (approx. 100 GPa) and has been shown to endure higher indentation loads than conventional and high performance steel. Indentation load capacity has been reported for relatively large (12.7 mm diameter) ceramic (Si3N4) indenter balls pressed against flat plates of 60NiTi. In order to develop damage load threshold criteria applicable to a wide range of bearing designs and sizes, the effects of indenter ball radius and the accuracy of interpolation of the Hertz contact stress relations for 60NiTi must be ascertained. In this paper, results of indentation tests involving ceramic balls ranging from 6.4 to 12.7 mm in diameter and highly polished 60NiTi flat plates are presented. When the resulting dent depth data for all the indenter ball sizes are normalized using the Hertz equations, the data (dent depth versus stress) are comparable. Thus when designing bearings made from 60NiTi, the Hertz stress relations can be applied with relative confidence over a range of rolling element sizes and internal geometries.

  19. The Effect of Indenter Ball Radius on the Static Load Capacity of the Superelastic 60NiTi for Rolling Element Bearings

    NASA Technical Reports Server (NTRS)

    DellaCorte, Christopher; Moore, Lewis E., III; Clifton, Joshua S.

    2014-01-01

    Static load capacity is a critical design parameter for rolling element bearings used in space mechanisms because of the potential for Brinell (surface dent) damage due to shock and vibration loading events during rocket launch. Brinell damage to bearing raceways can lead to torque variations (noise) and reduced bearing life. The growing use of ceramic rolling elements with high stiffness in hybrid bearings exacerbates the situation. A new family of hard yet resilient materials based upon nickel-titanium is emerging to address such bearing challenges. 60NiTi is a superelastic material that simultaneously exhibits high hardness and a relatively low elastic modulus (approx. 100 GigaPascals) and has been shown to endure higher indentation loads than conventional and high performance steel. Indentation load capacity has been reported for relatively large (12.7 millimeters diameter) ceramic (Si3N4) indenter balls pressed against flat plates of 60NiTi. In order to develop damage load threshold criteria applicable to a wide range of bearing designs and sizes, the effects of indenter ball radius and the accuracy of interpolation of the Hertz contact stress relations for 60NiTi must be ascertained. In this paper, results of indentation tests involving ceramic balls ranging from 6.4 to 12.7 mm in diameter and highly polished 60NiTi flat plates are presented. When the resulting dent depth data for all the indenter ball sizes are normalized using the Hertz equations, the data (dent depth versus stress) are comparable. Thus when designing bearings made from 60NiTi, the Hertz stress relations can be applied with relative confidence over a range of rolling element sizes and internal geometries.

  20. An investigation of the physico-mechanical properties of pharmaceutical compounds by compaction simulator and nano-indentation

    NASA Astrophysics Data System (ADS)

    Bordawekar, Mangesh

    In early development, pharmaceutical formulation scientists are often faced with challenges of developing robust and scalable formulations in extremely stringent timelines based on limited API quantities. Hence, tablet formulation development would benefit significantly from tools that enable predictive analysis based on limited quantities of API to enable selection of excipients with appropriate physico-mechanical properties that would result in robust and scalable formulations. With the recent technological advances, especially in sensor technologies, tools such as the compaction simulator, and instrumented nanoindentation offer hitherto unavailable means of assessing material properties with limited quantities. The goal of this work was to evaluate the physico-mechanical properties of selected pharmaceutical excipients and active pharmaceutical ingredients using a macro-scale analysis technique (compaction simulator), and a micro-scale analysis technique (nanoindentation tester) and compare the results obtained from these techniques in order to determine whether a rank order correlation exists between the two. Excipients representing diverse physic-mechanical properties, and a group of APIs were selected for the study. For the compaction simulator studies, tablets were uniaxially compressed using a flat faced 11.28mm round tooling on the STYLCAM® 200R compaction simulator, to a target final porosity at two different cam speeds (5 rpm and 25 rpm). The force displacement profiles, plastic, elastic, and total compression energies, plasticity index, energy density and the Heckel plots were determined for each compact. These compacts were further analyzed with a Berkovich geometry indenter. The plasticity index, hardness, elastic modulus, as well as creep and relaxation were determined from the force-displacement profiles. The nature of force-displacement curves was studied to differentiate compounds based on predominant mechanisms of deformation. Compaction

  1. Latent practice profiles of substance abuse treatment counselors: do evidence-based techniques displace traditional techniques?

    PubMed

    Smith, Brenda D; Liu, Junqing

    2014-04-01

    As more substance abuse treatment counselors begin to use evidence-based treatment techniques, questions arise regarding the continued use of traditional techniques. This study aims to (1) assess whether there are meaningful practice profiles among practitioners reflecting distinct combinations of cognitive-behavioral and traditional treatment techniques; and (2) if so, identify practitioner characteristics associated with the distinct practice profiles. Survey data from 278 frontline counselors working in community substance abuse treatment organizations were used to conduct latent profile analysis. The emergent practice profiles illustrate that practitioners vary most in the use of traditional techniques. Multinomial regression models suggest that practitioners with less experience, more education, and less traditional beliefs about treatment and substance abuse are least likely to mix traditional techniques with cognitive-behavioral techniques. Findings add to the understanding of how evidence-based practices are implemented in routine settings and have implications for training and support of substance abuse treatment counselors. Copyright © 2014 Elsevier Inc. All rights reserved.

  2. Sample-free control of the mechanical properties of aluminum-based alloys with rare-earth metal additions

    NASA Astrophysics Data System (ADS)

    Matyunin, V. M.; Agafonov, R. Yu.; Zarubin, A. L.; Danilin, V. V.; Popkova, O. G.

    2015-12-01

    A technique is developed for sample-free control of the 0.2 offset yield strength and the ultimate tensile strength of aluminum alloys with rare-earth metal additions using indentation with a spherical indenter.

  3. Nano-indentation of Polycarbonate and Diamine Blends

    NASA Astrophysics Data System (ADS)

    Ahuja, Suresh

    2012-02-01

    Nanoindentation of complex surfaces is of great interest from academic and industrial point of view. There are unique properties such as indentation effects resulting in strain softening and strain hardening. There is a differentiation in structure with the depth exhibited with variation of Tg. Hertzian and non-linear deformation models including usage of FEM offer opportunity in analyzing nano-indentation. In polycarbonate, the effective elastic modulus and the hardness decreases as the applied load is increased. As the hold time was increased, the effective elastic modulus and the hardness also decreased. The contact stress increases as the contact strain rate is increased. Presence of diamine(MTBD) in polycarbonate results in making the surface and bulk brittle and acts as an anti-plasticizer by increasing it modulus and reducing yield stress (hardness) and strain to break. Data on modulus and hardness of polycarbonate and blends of diamine as function of depth (strain) and strain rate are presented and compared with those of composites with silica.

  4. Quantitative Hardness Measurement by Instrumented AFM-indentation.

    PubMed

    Caron, Arnaud

    2016-11-22

    In this work, a combination of amplitude-modulated non-contact atomic force microscopy and atomic force spectroscopy is applied for instrumented hardness measurements on an Au(111) surface with atomistic resolution of single plasticity events. A careful experimental procedure is described that includes the force sensor selection, its calibration, the calibration of the cantilever deflection detection system, and the minimization of instrumental drift for accurate and reproducible force-distance measurements. Also, a method for the data analysis is presented that allows the extraction of force-penetration curves from recorded force-distance curves. A typical curve displays a clear elastic deformation regime up to the first plasticity event, or pop-in, with a length in the range of one to two Burger's vectors. Later plasticity events exhibit the same magnitude. The work of plasticity is further extracted from the measurements. Finally, the hardness is determined in combination with the indentation curve using non-contact atomic force microscopy images of the remaining indents.

  5. Quasi-Static Indentation Analysis of Carbon-Fiber Laminates.

    SciTech Connect

    Briggs, Timothy; English, Shawn Allen; Nelson, Stacy Michelle

    2015-12-01

    A series of quasi - static indentation experiments are conducted on carbon fiber reinforced polymer laminates with a systematic variation of thicknesses and fixture boundary conditions. Different deformation mechanisms and their resulting damage mechanisms are activated b y changing the thickn ess and boundary conditions. The quasi - static indentation experiments have been shown to achieve damage mechanisms similar to impact and penetration, however without strain rate effects. The low rate allows for the detailed analysis on the load response. Moreover, interrupted tests allow for the incremental analysis of various damage mechanisms and pr ogressions. The experimentally tested specimens are non - destructively evaluated (NDE) with optical imaging, ultrasonics and computed tomography. The load displacement responses and the NDE are then utilized in numerical simulations for the purpose of model validation and vetting. The accompanying numerical simulation work serves two purposes. First, the results further reveal the time sequence of events and the meaning behind load dro ps not clear from NDE . Second, the simulations demonstrate insufficiencies in the code and can then direct future efforts for development.

  6. Single cell metastatic phenotyping using pulsed nanomechanical indentations

    NASA Astrophysics Data System (ADS)

    Babahosseini, Hesam; Strobl, Jeannine S.; Agah, Masoud

    2015-09-01

    The existing approach to characterize cell biomechanical properties typically utilizes switch-like models of mechanotransduction in which cell responses are analyzed in response to a single nanomechanical indentation or a transient pulsed stress. Although this approach provides effective descriptors at population-level, at a single-cell-level, there are significant overlaps in the biomechanical descriptors of non-metastatic and metastatic cells which precludes the use of biomechanical markers for single cell metastatic phenotyping. This study presents a new promising marker for biosensing metastatic and non-metastatic cells at a single-cell-level using the effects of a dynamic microenvironment on the biomechanical properties of cells. Two non-metastatic and two metastatic epithelial breast cell lines are subjected to a pulsed stresses regimen exerted by atomic force microscopy. The force-time data obtained for the cells revealed that the non-metastatic cells increase their resistance against deformation and become more stiffened when subjected to a series of nanomechanical indentations. On the other hand, metastatic cells become slightly softened when their mechanical microenvironment is subjected to a similar dynamical changes. This distinct behavior of the non-metastatic and metastatic cells to the pulsed stresses paradigm provided a signature for single-cell-level metastatic phenotyping with a high confidence level of ∼95%.

  7. Stress Imaging in Indented Si Wafers by Confocal Raman Microscopy

    NASA Astrophysics Data System (ADS)

    Schoenmaker, Jeroen; Cook, Robert F.; Novotny, Lukas; Stranick, Stephan J.

    2007-03-01

    Controlling stress and strain, and consequently, carrier mobility in semiconductor devices is one of the main goals of recent electronic industry. On the other hand, fracture propagation is commonly related to performance degradation in microelectronic and microelectromechanical (MEMS) devices. As miniaturization reaches submicron scales, characterization tools with improved resolution and capable to detect buried surfaces is required. In this work we present confocal Raman imaging in Si wafers to analyze stress and fracture by means of hyperspectral measurements (typically 128x128 spectra). We analyzed indented Si wafers presenting wide range of plastic deformation and fractures. Wide scans (up to 150x150 μm^2) as well as high-resolution scans depict the stress distribution around indented regions and side fractures. Some of the samples were covered with 8 nm of Ti deposited in LN2 temperature. In these samples we acquired hyperspectral images in subsurface conditions and detected possible influences of thermal budged in the stress distribution. We also demonstrate depth sensitivity in a vertical scan. Images suggest 0.3 μm resolution.

  8. Surface form memory by indentation-planarization training of nickel titanium shape memory alloys

    NASA Astrophysics Data System (ADS)

    Fei, Xueling

    Shape memory alloys respond to deformation by indentation with strong two-way cyclic displacements on heating and cooling. Shallow indents can vanish on heating, and deeper indents will change depth when thermally cycled. In the present work, following indentation by an added step of surface planarization can furthermore produce what has been termed "Surface Form Memory" or SFM. The term SFM describes an effect that causes one surface form to reversibly transform to another, under thermal excitation. The term surface form is meant to distinguish between say, flat and "bumpy" surfaces, on a scale much larger than the intrinsic surface roughness. Surface protrusions, or 'exdents' may reach an amplitude near 20% of the initial indent depth, and may be created on nano to macroscopic size scales. The surface form memory effect may have special applications into novel optical, microelectromechanical, and tribological systems. Surface deformation of a NiTi shape memory alloy (SMA) was accomplished using spherical, cylindrical, pyramidal, and flat punch indenters. Single indents and indent arrays have been made. The amplitude of SFM after planarization was found to be related to the size of the subsurface deformation zone and can be maximized by thermal cycling, multiple indentations, by changing indent depth and spacing, and by varying indentation temperature parameters. The spatial extent of the subsurface deformation zone was studied by both experimental methods and finite element modeling. Methods such as successive front and back thinning probed the size of the deformation zone directly, while finite element modeling provided stress-strain information supporting the conclusion that the deformation zone responsible for the two-way effect was a slip zone that had plastic strains larger than 7%. NiTi SFM, when studied in constrained recovery experiments, showed an energy density up to 10 MJ/m3, which is about the same as that of a conventional NiTi actuator. This proves

  9. Efficient Plant Supervision Strategy Using NN Based Techniques

    NASA Astrophysics Data System (ADS)

    Garcia, Ramon Ferreiro; Rolle, Jose Luis Calvo; Castelo, Francisco Javier Perez

    Most of non-linear type one and type two control systems suffers from lack of detectability when model based techniques are applied on FDI (fault detection and isolation) tasks. In general, all types of processes suffer from lack of detectability also due to the ambiguity to discriminate the process, sensors and actuators in order to isolate any given fault. This work deals with a strategy to detect and isolate faults which include massive neural networks based functional approximation procedures associated to recursive rule based techniques applied to a parity space approach.

  10. Diode laser based water vapor DIAL using modulated pulse technique

    NASA Astrophysics Data System (ADS)

    Pham, Phong Le Hoai; Abo, Makoto

    2014-11-01

    In this paper, we propose a diode laser based differential absorption lidar (DIAL) for measuring lower-tropospheric water vapor profile using the modulated pulse technique. The transmitter is based on single-mode diode laser and tapered semiconductor optical amplifier with a peak power of 10W around 800nm absorption band, and the receiver telescope diameter is 35cm. The selected wavelengths are compared to referenced wavelengths in terms of random error and systematic errors. The key component of modulated pulse technique, a macropulse, is generated with a repetition rate of 10 kHz, and the modulation within the macropulse is coded according to a pseudorandom sequence with 100ns chip width. As a result, we evaluate both single pulse modulation and pseudorandom coded pulse modulation technique. The water vapor profiles conducted from these modulation techniques are compared to the real observation data in summer in Japan.

  11. Impact of Knowledge-Based Techniques on Emerging Technologies

    DTIC Science & Technology

    2006-09-01

    coherent location (PCL), tracking in multistatic radar, and ‘spatial denial’ as a waveform diversity technique to prevent the exploitation by an enemy...performing a variety of surveillance and tracking tasks. Knowledge-based processing may be used to control the scheduling of tasks in such a radar, showing...techniques to bistatic and multistatic radar, including the use of information on waveform properties in passive coherent location (PCL), tracking

  12. Bond strength with custom base indirect bonding techniques.

    PubMed

    Klocke, Arndt; Shi, Jianmin; Kahl-Nieke, Bärbel; Bismayer, Ulrich

    2003-04-01

    Different types of adhesives for indirect bonding techniques have been introduced recently. But there is limited information regarding bond strength with these new materials. In this in vitro investigation, stainless steel brackets were bonded to 100 permanent bovine incisors using the Thomas technique, the modified Thomas technique, and light-cured direct bonding for a control group. The following five groups of 20 teeth each were formed: (1) modified Thomas technique with thermally cured base composite (Therma Cure) and chemically cured sealant (Maximum Cure), (2) Thomas technique with thermally cured base composite (Therma Cure) and chemically cured sealant (Custom I Q), (3) Thomas technique with light-cured base composite (Transbond XT) and chemically cured sealant (Sondhi Rapid Set), (4) modified Thomas technique with chemically cured base adhesive (Phase II) and chemically cured sealant (Maximum Cure), and (5) control group directly bonded with light-cured adhesive (Transbond XT). Mean bond strengths in groups 3, 4, and 5 were 14.99 +/- 2.85, 15.41 +/- 3.21, and 13.88 +/- 2.33 MPa, respectively, and these groups were not significantly different from each other. Groups 1 (mean bond strength 7.28 +/- 4.88 MPa) and 2 (mean bond strength 7.07 +/- 4.11 MPa) showed significantly lower bond strengths than groups 3, 4, and 5 and a higher probability of bond failure. Both the original (group 2) and the modified (group 1) Thomas technique were able to achieve bond strengths comparable to the light-cured direct bonded control group.

  13. Dissociation techniques in mass spectrometry-based proteomics.

    PubMed

    Jones, Andrew W; Cooper, Helen J

    2011-09-07

    The field of proteomics, the large-scale analysis of proteins, has undergone a huge expansion over the past decade. Mass spectrometry-based proteomics relies on the dissociation of peptide and/or protein ions to provide information on primary sequence and sites of post-translational modifications. Fragmentation techniques include collision-induced dissociation, electron capture dissociation and electron transfer dissociation. Here, we describe each of these techniques and their use in proteomics. The principles, advantages, limitations, and applications are discussed.

  14. Review of surface profile measurement techniques based on optical interferometry

    NASA Astrophysics Data System (ADS)

    Wang, Yunzhi; Xie, Fang; Ma, Sen; Dong, Lianlian

    2017-06-01

    With the fast development of modern science and technology, two or three-dimensional surface profile measurement techniques with high resolution and large dynamic range are urgently required. Among them, the techniques based on optical interferometry have been widely used for their good properties of non-contact, high resolution, large dynamic measurement range and well-defined traceability route to the definition of meter. A review focused on surface profile measurement techniques of optical interferometry is introduced in this paper with a detailed classification sorted by operating principles. Examples in each category are discussed and analyzed for better understanding.

  15. Image analysis techniques associated with automatic data base generation.

    NASA Technical Reports Server (NTRS)

    Bond, A. D.; Ramapriyan, H. K.; Atkinson, R. J.; Hodges, B. C.; Thomas, D. T.

    1973-01-01

    This paper considers some basic problems relating to automatic data base generation from imagery, the primary emphasis being on fast and efficient automatic extraction of relevant pictorial information. Among the techniques discussed are recursive implementations of some particular types of filters which are much faster than FFT implementations, a 'sequential similarity detection' technique of implementing matched filters, and sequential linear classification of multispectral imagery. Several applications of the above techniques are presented including enhancement of underwater, aerial and radiographic imagery, detection and reconstruction of particular types of features in images, automatic picture registration and classification of multiband aerial photographs to generate thematic land use maps.

  16. Toner and paper-based fabrication techniques for microfluidic applications.

    PubMed

    Coltro, Wendell Karlos Tomazelli; de Jesus, Dosil Pereira; da Silva, José Alberto Fracassi; do Lago, Claudimir Lucio; Carrilho, Emanuel

    2010-08-01

    The interest in low-cost microfluidic platforms as well as emerging microfabrication techniques has increased considerably over the last years. Toner- and paper-based techniques have appeared as two of the most promising platforms for the production of disposable devices for on-chip applications. This review focuses on recent advances in the fabrication techniques and in the analytical/bioanalytical applications of toner and paper-based devices. The discussion is divided in two parts dealing with (i) toner and (ii) paper devices. Examples of miniaturized devices fabricated by using direct-printing or toner transfer masking in polyester-toner, glass, PDMS as well as conductive platforms as recordable compact disks and printed circuit board are presented. The construction and the use of paper-based devices for off-site diagnosis and bioassays are also described to cover this emerging platform for low-cost diagnostics.

  17. Investigation on hardening behavior of metallic glass under cyclic indentation loading via molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Zhao, Dan; Zhao, Hongwei; Zhu, Bo; Wang, Shunbo

    2017-09-01

    Mechanical behavior of a Cu-Zr metallic glass (MG) under cyclic indentation loading is investigated via molecular dynamics simulation. A large-depth indentation after cycling is conducted, and the indentation curves show that hardening behavior occurs with cyclic indentation amplitudes exceeding elastic range. The atomic Von Mises shear strain distributions during the large-depth indentation are investigated, and the pre-existing plastic deformation induced by cyclic indentation is found to be the main contributor to the hardening behavior. By monitoring the atom trajectories and Voronoi atom volume, structure densification and free volume reduction phenomenon are found in the area beneath indenter after cycles. The accumulations of irreversible shear strain during cycling induce the area beneath indenter experience atom structure transition and become densified, thus the sample becomes more resistant to further deformation. In addition, the effects of temperatures and loading rates on the hardening behavior are studied. With higher temperature, more homogenous deformation and plasticity are produced, and then inducing more severe hardening in the MG. While with lower loading rate, the hardening phenomenon is found to be less severe because of the localization of shear strain during cycling.

  18. Indentation-induced solid-state dewetting of thin Au(Fe) films

    NASA Astrophysics Data System (ADS)

    Kosinova, Anna; Schwaiger, Ruth; Klinger, Leonid; Rabkin, Eugen

    2017-07-01

    We studied the effect of local plastic deformation on the thermal stability and solid-state dewetting of thin homogeneous Au(Fe) films deposited on sapphire substrates. The films with ordered square arrays of indents produced by nanoindentation were annealed at the temperature of 700 °C in a forming gas atmosphere. The behavior of the film in the region of shallow indents (reaching a depth up to one half of the film thickness) was very different from the one in the region of deep indents (with depths greater than one half of the film thickness). In the first case, the grain growth in indented and unperturbed regions of the film proceeded quite similarly, and nearly complete healing of the indents was observed. In the latter case, a recrystallization process in the vicinity of the indents resulted in the formation of small new grains with misorientation angles that were not present in the as-deposited film. The thermal grooving along the corresponding new high-energy grain boundaries caused an increase of the depth of the indents and the formation of the dewetting holes. The morphology of these holes and their size were different compared to the holes formed randomly in the unperturbed regions of the same films. In particular, the interaction between the individual indents of an array led to the preferential formation of holes at the periphery of the arrays. These findings shed a new light on the process of nucleation of the solid-state dewetting in thin films.

  19. A novel sample preparation method to avoid influence of embedding medium during nano-indentation

    Treesearch

    Yujie Meng; Siqun Wang; Zhiyong Cai; Timothy M. Young; Guanben Du; Yanjun Li

    2012-01-01

    The effect of the embedding medium on the nano-indentation measurements of lignocellulosic materials was investigated experimentally using nano-indentation. Both the reduced elastic modulus and the hardness of nonembedded cell walls were found to be lower than those of the embedded samples, proving that the embedding medium used for specimen preparation on cellulosic...

  20. Indentations and Starting Points in Traveling Sales Tour Problems: Implications for Theory

    ERIC Educational Resources Information Center

    MacGregor, James N.

    2012-01-01

    A complete, non-trivial, traveling sales tour problem contains at least one "indentation", where nodes in the interior of the point set are connected between two adjacent nodes on the boundary. Early research reported that human tours exhibited fewer such indentations than expected. A subsequent explanation proposed that this was because…

  1. Laser-based direct-write techniques for cell printing

    PubMed Central

    Schiele, Nathan R; Corr, David T; Huang, Yong; Raof, Nurazhani Abdul; Xie, Yubing; Chrisey, Douglas B

    2016-01-01

    Fabrication of cellular constructs with spatial control of cell location (±5 μm) is essential to the advancement of a wide range of applications including tissue engineering, stem cell and cancer research. Precise cell placement, especially of multiple cell types in co- or multi-cultures and in three dimensions, can enable research possibilities otherwise impossible, such as the cell-by-cell assembly of complex cellular constructs. Laser-based direct writing, a printing technique first utilized in electronics applications, has been adapted to transfer living cells and other biological materials (e.g., enzymes, proteins and bioceramics). Many different cell types have been printed using laser-based direct writing, and this technique offers significant improvements when compared to conventional cell patterning techniques. The predominance of work to date has not been in application of the technique, but rather focused on demonstrating the ability of direct writing to pattern living cells, in a spatially precise manner, while maintaining cellular viability. This paper reviews laser-based additive direct-write techniques for cell printing, and the various cell types successfully laser direct-written that have applications in tissue engineering, stem cell and cancer research are highlighted. A particular focus is paid to process dynamics modeling and process-induced cell injury during laser-based cell direct writing. PMID:20814088

  2. Laser-based direct-write techniques for cell printing.

    PubMed

    Schiele, Nathan R; Corr, David T; Huang, Yong; Raof, Nurazhani Abdul; Xie, Yubing; Chrisey, Douglas B

    2010-09-01

    Fabrication of cellular constructs with spatial control of cell location (+/-5 microm) is essential to the advancement of a wide range of applications including tissue engineering, stem cell and cancer research. Precise cell placement, especially of multiple cell types in co- or multi-cultures and in three dimensions, can enable research possibilities otherwise impossible, such as the cell-by-cell assembly of complex cellular constructs. Laser-based direct writing, a printing technique first utilized in electronics applications, has been adapted to transfer living cells and other biological materials (e.g., enzymes, proteins and bioceramics). Many different cell types have been printed using laser-based direct writing, and this technique offers significant improvements when compared to conventional cell patterning techniques. The predominance of work to date has not been in application of the technique, but rather focused on demonstrating the ability of direct writing to pattern living cells, in a spatially precise manner, while maintaining cellular viability. This paper reviews laser-based additive direct-write techniques for cell printing, and the various cell types successfully laser direct-written that have applications in tissue engineering, stem cell and cancer research are highlighted. A particular focus is paid to process dynamics modeling and process-induced cell injury during laser-based cell direct writing.

  3. Deformation analysis of micro/nano indentation and diamond grinding on optical glasses

    NASA Astrophysics Data System (ADS)

    Zhao, Qingliang; Zhao, Lingling; Guo, Bing; Stephensin, David; Corbett, John

    2012-05-01

    The previous research of precision grinding optical glasses with electrolytic in process dressing (ELID) technology mainly concentrated on the action of ELID and machining parameters when grinding, which aim at generating very "smoothed" surfaces and reducing the subsurface damage. However, when grinding spectrosil 2000 and BK7 glass assisted with ELID technology, a deeply comparative study on material removal mechanism and the wheel wear behaviors have not been given yet. In this paper, the micro/nano indentation technique is initially applied for investigating the mechanical properties of optical glasses, whose results are then refereed to evaluate the machinability. In single grit diamond scratching on glasses, the scratching traces display four kinds of scratch characteristics according to different material removal modes. In normal grinding experiments, the result shows BK7 glass has a better machinability than that of spectrosil 2000, corresponding to what the micro/nano indentation vent revealed. Under the same grinding depth parameters, the smaller amplitude of acoustic emission (AE) raw signals, grinding force and grinding force ratio correspond to a better surface quality. While for these two kinds of glasses, with the increasing of grinding depth, the variation trends of the surface roughness, the force ratio, and the AE raw signals are contrary, which should be attributed to different material removal modes. Moreover, the SEM micrographs of used wheels surface indicate that diamond grains on the wheel surface after grinding BK7 glass are worn more severely than that of spectrosil 2000. The proposed research analyzes what happened in the grinding process with different material removal patterns, which can provide a basis for producing high-quality optical glasses and comprehensively evaluate the surface and subsurface integrity of optical glasses.

  4. Determination of the shape of indenters for nanohardness testers via interferometry

    NASA Astrophysics Data System (ADS)

    Kazieva, T. V.; Kuznetsov, A. P.; Gubskii, K. L.; Ponarina, M. V.; Reshetov, V. N.

    2017-02-01

    A method for determination of the contact-area functions for diamond indenters of nanohardness testers using a metrological atomic-force microscope with three-coordinate laser interferometer is proposed. Face shapes of a number of indenters of Berkovich pyramid type are measured. The precision of the indenter surface coordinates measurement is 1 nm. It is demonstrated that the indenter tip shape changes in the course of its use; in particular, for the first 100 nm the deviation from the ideal pyramid can exceed 30 nm. Thus, one of the methods for verification of the contact-area function for an indenter is its periodic calibration using a metrological atomic-force microscope.

  5. Indentation of Ultrathin Elastic Films and the Emergence of Asymptotic Isometry

    NASA Astrophysics Data System (ADS)

    Vella, Dominic; Huang, Jiangshui; Menon, Narayanan; Russell, Thomas P.; Davidovitch, Benny

    2015-01-01

    We study the indentation of a thin elastic film floating at the surface of a liquid. We focus on the onset of radial wrinkles at a threshold indentation depth and the evolution of the wrinkle pattern as indentation progresses far beyond this threshold. Comparison between experiments on thin polymer films and theoretical calculations shows that the system very quickly reaches the far from threshold regime, in which wrinkles lead to the relaxation of azimuthal compression. Furthermore, when the indentation depth is sufficiently large that the wrinkles cover most of the film, we recognize a novel mechanical response in which the work of indentation is transmitted almost solely to the liquid, rather than to the floating film. We attribute this unique response to a nontrivial isometry attained by the deformed film, and we discuss the scaling laws and the relevance of similar isometries to other systems in which a confined sheet is subjected to weak tensile loads.

  6. Rate-dependent indentation hardness of a power-law creep solder alloy

    NASA Astrophysics Data System (ADS)

    Ma, Xin; Yoshida, Fusahito

    2003-01-01

    Berkovich depth-sensing indentation tests with different loading rates have been performed on a creep material, Sn-3.5Ag-0.75Cu solder alloy. The resulting indentation load-depth curves are rate dependent and have varying creep penetration depths during the same hold time. Creep indentation hardness H, defined from the concept of "work of indentation," varies with the volume strain occurring during the creep hold time, which is a measure of creep strain rate ɛ˙cr. Thus, rate sensitivity m of the indented material can be determined from the ln H vs ln ɛ˙cr curve. The derived value of m is consistent with the results from conventional uniaxial tensile and compression experiments of bulk solder alloy.

  7. A combination of concave/convex surfaces for field-enhancement optimization: the indented nanocone.

    PubMed

    García-Etxarri, Aitzol; Apell, Peter; Käll, Mikael; Aizpurua, Javier

    2012-11-05

    We introduce a design strategy to maximize the Near Field (NF) enhancement near plasmonic antennas. We start by identifying and studying the basic electromagnetic effects that contribute to the electric near field enhancement. Next, we show how the concatenation of a convex and a concave surface allows merging all the effects on a single, continuous nanoantenna. As an example of this NF maximization strategy, we engineer a nanostructure, the indented nanocone. This structure, combines all the studied NF maximization effects with a synergistic boost provided by a Fano-like interference effect activated by the presence of the concave surface. As a result, the antenna exhibits a NF amplitude enhancement of ~ 800, which transforms into ~1600 when coupled to a perfect metallic surface. This strong enhancement makes the proposed structure a robust candidate to be used in field enhancement based technologies. Further elaborations of the concept may produce even larger and more effective enhancements.

  8. A Novel Nanofabrication Technique of Silicon-Based Nanostructures

    NASA Astrophysics Data System (ADS)

    Meng, Lingkuan; He, Xiaobin; Gao, Jianfeng; Li, Junjie; Wei, Yayi; Yan, Jiang

    2016-11-01

    A novel nanofabrication technique which can produce highly controlled silicon-based nanostructures in wafer scale has been proposed using a simple amorphous silicon (α-Si) material as an etch mask. SiO2 nanostructures directly fabricated can serve as nanotemplates to transfer into the underlying substrates such as silicon, germanium, transistor gate, or other dielectric materials to form electrically functional nanostructures and devices. In this paper, two typical silicon-based nanostructures such as nanoline and nanofin have been successfully fabricated by this technique, demonstrating excellent etch performance. In addition, silicon nanostructures fabricated above can be further trimmed to less than 10 nm by combing with assisted post-treatment methods. The novel nanofabrication technique will be expected a new emerging technology with low process complexity and good compatibility with existing silicon integrated circuit and is an important step towards the easy fabrication of a wide variety of nanoelectronics, biosensors, and optoelectronic devices.

  9. Membrane-based microextraction techniques in analytical chemistry: A review.

    PubMed

    Carasek, Eduardo; Merib, Josias

    2015-06-23

    The use of membrane-based sample preparation techniques in analytical chemistry has gained growing attention from the scientific community since the development of miniaturized sample preparation procedures in the 1990s. The use of membranes makes the microextraction procedures more stable, allowing the determination of analytes in complex and "dirty" samples. This review describes some characteristics of classical membrane-based microextraction techniques (membrane-protected solid-phase microextraction, hollow-fiber liquid-phase microextraction and hollow-fiber renewal liquid membrane) as well as some alternative configurations (thin film and electromembrane extraction) used successfully for the determination of different analytes in a large variety of matrices, some critical points regarding each technique are highlighted.

  10. A Novel Nanofabrication Technique of Silicon-Based Nanostructures.

    PubMed

    Meng, Lingkuan; He, Xiaobin; Gao, Jianfeng; Li, Junjie; Wei, Yayi; Yan, Jiang

    2016-12-01

    A novel nanofabrication technique which can produce highly controlled silicon-based nanostructures in wafer scale has been proposed using a simple amorphous silicon (α-Si) material as an etch mask. SiO2 nanostructures directly fabricated can serve as nanotemplates to transfer into the underlying substrates such as silicon, germanium, transistor gate, or other dielectric materials to form electrically functional nanostructures and devices. In this paper, two typical silicon-based nanostructures such as nanoline and nanofin have been successfully fabricated by this technique, demonstrating excellent etch performance. In addition, silicon nanostructures fabricated above can be further trimmed to less than 10 nm by combing with assisted post-treatment methods. The novel nanofabrication technique will be expected a new emerging technology with low process complexity and good compatibility with existing silicon integrated circuit and is an important step towards the easy fabrication of a wide variety of nanoelectronics, biosensors, and optoelectronic devices.

  11. Chemiresistors based on conducting polymers: a review on measurement techniques.

    PubMed

    Lange, Ulrich; Mirsky, Vladimir M

    2011-02-21

    This review covers the development of measurement configurations for chemiresistors based on conducting polymers. The simplest chemiresistors are based on application of a two-electrode technique. Artifacts caused by contact resistance can be overcome by application of a four-electrode technique. Simultaneous application of the two- and four-electrode measurement configurations provides an internal control of sensor integrity. An incorporation of two additional electrodes controlling the redox state of chemosensitive polymers and connecting to the measurement electrodes through liquid or (quasi)solid electrolyte results in a six-electrode technique; an electrically driven regeneration of such sensors allows one to perform fast and completely reversible measurements. Copyright © 2010 Elsevier B.V. All rights reserved.

  12. Quantifying Local Stiffness Variations in Radiofrequency Ablations with Dynamic Indentation

    PubMed Central

    DeWall, Ryan J.; Varghese, Tomy; Brace, Christopher L.

    2012-01-01

    Elastographic imaging can be used to monitor ablation procedures, however confident and clear determination of the ablation boundary is essential to ensure complete treatment of the pathological target. To investigate the potential for ablation boundary representation on elastographic images, local variations in the viscoelastic properties in radiofrequency ablated regions that were formed in vivo in porcine liver tissue were quantified using dynamic indentation. Spatial stiffness maps were then correlated to stained histology, the gold standard for determination of the ablation periphery or boundary. Regions of interest in eleven radiofrequency ablation samples were indented at 18–24 locations each, including the central zone of complete necrosis and more peripheral transition zones including normal tissue. Storage modulus and rate of stiffening were both greatest in the central ablation zone and decreased with radial distance away from the center. The storage modulus and modulus contrast at the ablation outer transition zone boundary were 3.1 ± 1.0 kPa and 1.6 ± 0.4, respectively, and 36.2 ± 9.1 kPa and 18.3 ± 5.5 at the condensation boundary within the ablation zone. Elastographic imaging modalities were then compared to gross pathology in ex vivo bovine liver tissue. Area estimated from strain, shear wave velocity, and gross pathology images were 470 mm2, 560 mm2, and 574 mm2, respectively, and ablation widths were 19.4 mm, 20.7 mm, and 23.0 mm. This study has provided insights into spatial stiffness distributions within radiofrequency ablations and suggests that low stiffness contrast on the ablation periphery leads to the observed underestimation of ablation extent on elastographic images. PMID:22167553

  13. On the mechanical properties of tooth enamel under spherical indentation.

    PubMed

    Chai, Herzl

    2014-11-01

    The mechanical properties of tooth enamel generally exhibit large variations, which reflect its structural and material complexity. Some key properties were evaluated under localized contact, simulating actual functioning conditions. Prominent cusps of extracted human molar teeth were polished down ~0.7 mm below the cusp tip and indented by tungsten carbide balls. The internal damage was assessed after unloading from longitudinal or transverse sections. The ultimate tensile stress (UTS) was determined using a novel bilayer specimen. The damage is characterized by penny-like radial cracks driven by hoop stresses and cylindrical cracks driven along protein-rich interrod materials by shear stresses. Shallow cone cracks typical of homogeneous materials which may cause rapid tooth wear under repeat contact are thus avoided. The mean stress vs. indentation strain curve is highly nonlinear, attributable to plastic shearing of protein between and within enamel rods. This curve is also affected by damage, especially radial cracks, the onset of which depends on ball radius. Several material properties were extracted from the tests, including shear strain at the onset of ring cracks γ(F) (=0.14), UTS (=119 MPa), toughness K(C) (=0.94 MPa m(1/2)), a crack propagation law and a constitutive response determined by trial and error with the aid of a finite-element analysis. These quantities, which are only slightly sensitive to anatomical location within the enamel region tested, facilitate a quantitative assessment of crown failure. Causes for variations in published UTS and K(C) values are discussed.

  14. Mapping the climate: guidance on appropriate techniques to map climate variables and their uncertainty

    NASA Astrophysics Data System (ADS)

    Kaye, N. R.; Hartley, A.; Hemming, D.

    2012-02-01

    Maps are a crucial asset in communicating climate science to a diverse audience, and there is a wealth of software available to analyse and visualise climate information. However, this availability makes it easy to create poor maps as users often lack an underlying cartographic knowledge. Unlike traditional cartography, where many known standards allow maps to be interpreted easily, there is no standard mapping approach used to represent uncertainty (in climate or other information). Consequently, a wide range of techniques have been applied for this purpose, and users may spend unnecessary time trying to understand the mapping approach rather than interpreting the information presented. Furthermore, communicating and visualising uncertainties in climate data and climate change projections, using for example ensemble based approaches, presents additional challenges for mapping that require careful consideration. The aim of this paper is to provide background information and guidance on suitable techniques for mapping climate variables, including uncertainty. We assess a range of existing and novel techniques for mapping variables and uncertainties, comparing "intrinsic" approaches that use colour in much the same way as conventional thematic maps with "extrinsic" approaches that incorporate additional geometry such as points or features. Using cartographic knowledge and lessons learned from mapping in different disciplines we propose the following 6 general mapping guidelines to develop a suitable mapping technique that represents both magnitude and uncertainty in climate data:

    indent:1em;">- use a sensible sequential or diverging colour scheme;

    indent:1em;">- use appropriate colour symbolism if it is applicable;

    indent:1em;">- ensure the map is usable by colour blind people;

    indent:1em;">- use a data classification scheme that does not misrepresent the data;

    indent:1em;">- use a map

  15. Advanced alloy design technique: High temperature cobalt base superalloy

    NASA Technical Reports Server (NTRS)

    Dreshfield, R. L.; Freche, J. C.; Sandrock, G. D.

    1972-01-01

    Advanced alloy design technique was developed for treating alloys that will have extended life in service at high temperature and intermediate temperatures. Process stabilizes microstructure of the alloy by designing it so that compound identified with embrittlement is eliminated or minimized. Design process is being used to develop both nickel and cobalt-base superalloys.

  16. Image encryption techniques based on the fractional Fourier transform

    NASA Astrophysics Data System (ADS)

    Hennelly, B. M.; Sheridan, J. T.

    2003-11-01

    The fractional Fourier transform, (FRT), is a generalisation of the Fourier transform which allows domains of mixed spatial frequency and spatial information to be examined. A number of method have recently been proposed in the literature for the encryption of two dimensional information using optical systems based on the FRT. Typically, these methods require random phase screen keys to decrypt the data, which must be stored at the receiver and must be carefully aligned with the received encrypted data. We have proposed a new technique based on a random shifting or Jigsaw transformation. This method does not require the use of phase keys. The image is encrypted by juxtaposition of sections of the image in various FRT domains. The new method has been compared numerically with existing methods and shows comparable or superior robustness to blind decryption. An optical implementation is also proposed and the sensitivity of the various encryption keys to blind decryption is quantified. We also present a second image encryption technique, which is based on a recently proposed method of optical phase retrieval using the optical FRT and one of its discrete counterparts. Numerical simulations of the new algorithm indicates that the sensitivity of the keys is much greater than any of the techniques currently available. In fact the sensitivity appears to be so high that optical implementation, based on existing optical signal processing technology, may be impossible. However, the technique has been shown to be a powerful method of 2-D image data encryption.

  17. Video Multiple Watermarking Technique Based on Image Interlacing Using DWT

    PubMed Central

    Ibrahim, Mohamed M.; Abdel Kader, Neamat S.; Zorkany, M.

    2014-01-01

    Digital watermarking is one of the important techniques to secure digital media files in the domains of data authentication and copyright protection. In the nonblind watermarking systems, the need of the original host file in the watermark recovery operation makes an overhead over the system resources, doubles memory capacity, and doubles communications bandwidth. In this paper, a robust video multiple watermarking technique is proposed to solve this problem. This technique is based on image interlacing. In this technique, three-level discrete wavelet transform (DWT) is used as a watermark embedding/extracting domain, Arnold transform is used as a watermark encryption/decryption method, and different types of media (gray image, color image, and video) are used as watermarks. The robustness of this technique is tested by applying different types of attacks such as: geometric, noising, format-compression, and image-processing attacks. The simulation results show the effectiveness and good performance of the proposed technique in saving system resources, memory capacity, and communications bandwidth. PMID:25587570

  18. Video multiple watermarking technique based on image interlacing using DWT.

    PubMed

    Ibrahim, Mohamed M; Abdel Kader, Neamat S; Zorkany, M

    2014-01-01

    Digital watermarking is one of the important techniques to secure digital media files in the domains of data authentication and copyright protection. In the nonblind watermarking systems, the need of the original host file in the watermark recovery operation makes an overhead over the system resources, doubles memory capacity, and doubles communications bandwidth. In this paper, a robust video multiple watermarking technique is proposed to solve this problem. This technique is based on image interlacing. In this technique, three-level discrete wavelet transform (DWT) is used as a watermark embedding/extracting domain, Arnold transform is used as a watermark encryption/decryption method, and different types of media (gray image, color image, and video) are used as watermarks. The robustness of this technique is tested by applying different types of attacks such as: geometric, noising, format-compression, and image-processing attacks. The simulation results show the effectiveness and good performance of the proposed technique in saving system resources, memory capacity, and communications bandwidth.

  19. Optical supervised filtering technique based on Hopfield neural network

    NASA Astrophysics Data System (ADS)

    Bal, Abdullah

    2004-11-01

    Hopfield neural network is commonly preferred for optimization problems. In image segmentation, conventional Hopfield neural networks (HNN) are formulated as a cost-function-minimization problem to perform gray level thresholding on the image histogram or the pixels' gray levels arranged in a one-dimensional array [R. Sammouda, N. Niki, H. Nishitani, Pattern Rec. 30 (1997) 921-927; K.S. Cheng, J.S. Lin, C.W. Mao, IEEE Trans. Med. Imag. 15 (1996) 560-567; C. Chang, P. Chung, Image and Vision comp. 19 (2001) 669-678]. In this paper, a new high speed supervised filtering technique is proposed for image feature extraction and enhancement problems by modifying the conventional HNN. The essential improvement in this technique is to use 2D convolution operation instead of weight-matrix multiplication. Thereby, neural network based a new filtering technique has been obtained that is required just 3 × 3 sized filter mask matrix instead of large size weight coefficient matrix. Optical implementation of the proposed filtering technique is executed easily using the joint transform correlator. The requirement of non-negative data for optical implementation is provided by bias technique to convert the bipolar data to non-negative data. Simulation results of the proposed optical supervised filtering technique are reported for various feature extraction problems such as edge detection, corner detection, horizontal and vertical line extraction, and fingerprint enhancement.

  20. Manual, In situ, Real-Time Nanofabrication using Cracking through Indentation

    PubMed Central

    Nam, Koo Hyun; Suh, Young D.; Yeo, Junyeob; Woo, Deokha

    2016-01-01

    Nanofabrication has seen an increasing demand for applications in many fields of science and technology, but its production still requires relatively difficult, time-consuming, and expensive processes. Here we report a simple but very effective one dimensional (1D) nano-patterning technology that suggests a new nanofabrication method. This new technique involves the control of naturally propagating cracks initiated through simple, manually generated indentation, obviating the necessity of complicated equipment and elaborate experimental environments such as those that employ clean rooms, high vacuums, and the fastidious maintenance of processing temperatures. The channel fabricated with this technique can be as narrow as 10 nm with unlimited length and very high cross-sectional aspect ratio, an accomplishment difficult even for a state-of-the-art technology such as e-beam lithography. More interestingly, the fabrication speed can be controlled and achieved to as little as several hundred micrometers per second. Along with the simplicity and real-time fabrication capability of the technique, this tunable fabrication speed makes the method introduced here the authentic nanofabrication for in situ experiments. PMID:26725520

  1. Manual, In situ, Real-Time Nanofabrication using Cracking through Indentation

    NASA Astrophysics Data System (ADS)

    Nam, Koo Hyun; Suh, Young D.; Yeo, Junyeob; Woo, Deokha

    2016-01-01

    Nanofabrication has seen an increasing demand for applications in many fields of science and technology, but its production still requires relatively difficult, time-consuming, and expensive processes. Here we report a simple but very effective one dimensional (1D) nano-patterning technology that suggests a new nanofabrication method. This new technique involves the control of naturally propagating cracks initiated through simple, manually generated indentation, obviating the necessity of complicated equipment and elaborate experimental environments such as those that employ clean rooms, high vacuums, and the fastidious maintenance of processing temperatures. The channel fabricated with this technique can be as narrow as 10 nm with unlimited length and very high cross-sectional aspect ratio, an accomplishment difficult even for a state-of-the-art technology such as e-beam lithography. More interestingly, the fabrication speed can be controlled and achieved to as little as several hundred micrometers per second. Along with the simplicity and real-time fabrication capability of the technique, this tunable fabrication speed makes the method introduced here the authentic nanofabrication for in situ experiments.

  2. Comparison of laser-based rapid prototyping techniques

    NASA Astrophysics Data System (ADS)

    Humphreys, Hugh; Wimpenny, David

    2002-04-01

    A diverse range of Rapid Prototyping, or layer manufacturing techniques have evolved since the introduction of the first process in the late 1980s. Many, although not all, rapid prototyping processes rely on lasers to provide a localised and controllable source of light for curing a liquid photopolymer or heat to fuse thermoplastic powders to form objects. This paper will provide an overview of laser based rapid prototyping methods and discuss the future direction of this technology in light of the threats posed by low cost 3D printing techniques and the opportunity for the direct manufacture of metal components.

  3. Graphene-based terahertz photodetector by noise thermometry technique

    SciTech Connect

    Wang, Ming-Jye; Wang, Ji-Wun; Wang, Chun-Lun; Chiang, Yen-Yu; Chang, Hsian-Hong

    2014-01-20

    We report the characteristics of graphene-based terahertz (THz) photodetector based on noise thermometry technique by measuring its noise power at frequency from 4 to 6 GHz. Hot electron system in graphene microbridge is generated after THz photon pumping and creates extra noise power. The equivalent noise temperature and electron temperature increase rapidly in low THz pumping regime and saturate gradually in high THz power regime which is attributed to a faster energy relaxation process involved by stronger electron-phonon interaction. Based on this detector, a conversion efficiency around 0.15 from THz power to noise power in 4–6 GHz span has been achieved.

  4. Dynamic impact indentation of hydrated biological tissues and tissue surrogate gels

    NASA Astrophysics Data System (ADS)

    Ilke Kalcioglu, Z.; Qu, Meng; Strawhecker, Kenneth E.; Shazly, Tarek; Edelman, Elazer; VanLandingham, Mark R.; Smith, James F.; Van Vliet, Krystyn J.

    2011-03-01

    For both materials engineering research and applied biomedicine, a growing need exists to quantify mechanical behaviour of tissues under defined hydration and loading conditions. In particular, characterisation under dynamic contact-loading conditions can enable quantitative predictions of deformation due to high rate 'impact' events typical of industrial accidents and ballistic insults. The impact indentation responses were examined of both hydrated tissues and candidate tissue surrogate materials. The goals of this work were to determine the mechanical response of fully hydrated soft tissues under defined dynamic loading conditions, and to identify design principles by which synthetic, air-stable polymers could mimic those responses. Soft tissues from two organs (liver and heart), a commercially available tissue surrogate gel (Perma-Gel™) and three styrenic block copolymer gels were investigated. Impact indentation enabled quantification of resistance to penetration and energy dissipative constants under the rates and energy densities of interest for tissue surrogate applications. These analyses indicated that the energy dissipation capacity under dynamic impact increased with increasing diblock concentration in the styrenic gels. Under the impact rates employed (2 mm/s to 20 mm/s, corresponding to approximate strain energy densities from 0.4 kJ/m3 to 20 kJ/m3), the energy dissipation capacities of fully hydrated soft tissues were ultimately well matched by a 50/50 triblock/diblock composition that is stable in ambient environments. More generally, the methodologies detailed here facilitate further optimisation of impact energy dissipation capacity of polymer-based tissue surrogate materials, either in air or in fluids.

  5. Quantitative Study of the Elastic Modulus of Loosely Attached Cells in AFM Indentation Experiments

    PubMed Central

    Dokukin, Maxim E.; Guz, Nataliia V.; Sokolov, Igor

    2013-01-01

    When measuring the elastic (Young’s) modulus of cells using AFM, good attachment of cells to a substrate is paramount. However, many cells cannot be firmly attached to many substrates. A loosely attached cell is more compliant under indenting. It may result in artificially low elastic modulus when analyzed with the elasticity models assuming firm attachment. Here we suggest an AFM-based method/model that can be applied to extract the correct Young’s modulus of cells loosely attached to a substrate. The method is verified by using primary breast epithelial cancer cells (MCF-7) at passage 4. At this passage, approximately one-half of cells develop enough adhesion with the substrate to be firmly attached to the substrate. These cells look well spread. The other one-half of cells do not develop sufficient adhesion, and are loosely attached to the substrate. These cells look spherical. When processing the AFM indentation data, a straightforward use of the Hertz model results in a substantial difference of the Young’s modulus between these two types of cells. If we use the model presented here, we see no statistical difference between the values of the Young’s modulus of both poorly attached (round) and firmly attached (close to flat) cells. In addition, the presented model allows obtaining parameters of the brush surrounding the cells. The cellular brush observed is also statistically identical for both types of cells. The method described here can be applied to study mechanics of many other types of cells loosely attached to substrates, e.g., blood cells, some stem cells, cancerous cells, etc. PMID:23708352

  6. An evaluation of indentation and finishing properties of bearing grade silicon nitrides

    SciTech Connect

    Dill, J.F.; Gardos, M.N.; Hardisty, R.G.

    1997-01-01

    This paper describes the results of studies of the machining performance and the indentation hardness and fracture toughness of different silicon nitride materials as part of an effort to better define the optimum machining conditions for bearing components. This work builds on prior efforts by two of the authors, Gardos and Hardisty (1993) who formulated a simple relationship between diamond grinding performance of silicon nitride bearing balls and a wear equation first detailed by Evans and Wilshaw (1976). The goal of this present work was to determine the general applicability of such a relationship, i.e., could simple indentation studies be used to define finishing conditions for different silicon nitride materials? The availability of such a simple test would reduce the time required for developing an acceptable process when a supplier changes his formulation, or when a new material becomes available. Quicker development of optimum finishing conditions would eventually result in a lower-cost product for users. The initial study by Gardos and Hardisty (1993) was based on limited data taken at a fixed set of conditions. This study expanded the range of conditions evaluated and the number of ceramic materials studied in an effort to define the universality of the relationship between grinding wear, hardness, and toughness. This study has shown that no simple relationship like that first envisioned by the authors exists. The results showed that the grinding wear of the individual silicon nitride materials increased at different rates as a function of load. Because of the differences found in the load dependence of grinding rates, no simple relationship between hardness, fracture toughness, and grinding rate could be found that fit the data over the range of conditions studied.

  7. Quantitative study of the elastic modulus of loosely attached cells in AFM indentation experiments.

    PubMed

    Dokukin, Maxim E; Guz, Nataliia V; Sokolov, Igor

    2013-05-21

    When measuring the elastic (Young's) modulus of cells using AFM, good attachment of cells to a substrate is paramount. However, many cells cannot be firmly attached to many substrates. A loosely attached cell is more compliant under indenting. It may result in artificially low elastic modulus when analyzed with the elasticity models assuming firm attachment. Here we suggest an AFM-based method/model that can be applied to extract the correct Young's modulus of cells loosely attached to a substrate. The method is verified by using primary breast epithelial cancer cells (MCF-7) at passage 4. At this passage, approximately one-half of cells develop enough adhesion with the substrate to be firmly attached to the substrate. These cells look well spread. The other one-half of cells do not develop sufficient adhesion, and are loosely attached to the substrate. These cells look spherical. When processing the AFM indentation data, a straightforward use of the Hertz model results in a substantial difference of the Young's modulus between these two types of cells. If we use the model presented here, we see no statistical difference between the values of the Young's modulus of both poorly attached (round) and firmly attached (close to flat) cells. In addition, the presented model allows obtaining parameters of the brush surrounding the cells. The cellular brush observed is also statistically identical for both types of cells. The method described here can be applied to study mechanics of many other types of cells loosely attached to substrates, e.g., blood cells, some stem cells, cancerous cells, etc. Copyright © 2013 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  8. Size effects in the conical indentation of an elasto-plastic solid

    NASA Astrophysics Data System (ADS)

    Danas, K.; Deshpande, V. S.; Fleck, N. A.

    2012-09-01

    The size effect in conical indentation of an elasto-plastic solid is predicted via the Fleck and Willis formulation of strain gradient plasticity (Fleck, N.A. and Willis, J.R., 2009, A mathematical basis for strain gradient plasticity theory. Part II: tensorial plastic multiplier, J. Mech. Phys. Solids, 57, 1045-1057). The rate-dependent formulation is implemented numerically and the full-field indentation problem is analyzed via finite element calculations, for both ideally plastic behavior and dissipative hardening. The isotropic strain-gradient theory involves three material length scales, and the relative significance of these length scales upon the degree of size effect is assessed. Indentation maps are generated to summarize the sensitivity of indentation hardness to indent size, indenter geometry and material properties (such as yield strain and strain hardening index). The finite element model is also used to evaluate the pertinence of the Johnson cavity expansion model and of the Nix-Gao model, which have been extensively used to predict size effects in indentation hardness.

  9. Elastic modulus and stress-strain response of human enamel by nano-indentation.

    PubMed

    He, Li Hong; Fujisawa, Naoki; Swain, Michael V

    2006-08-01

    Nano-indentation with a sharp (Berkovich) and two spherical indenters with nominal tip radii of 5 and 20 microm was used to determine the elastic modulus and stress-strain response of human enamel. Indentation tests were made over a wide range of peak loads from 1 to 450 mN in two orthogonal directions, i.e., parallel and perpendicular to enamel prisms. The elastic modulus and hardness (mean contact pressure) versus depth of penetration were determined for the three indenters. From the spherical indentation data, stress-strain curves (H-tantheta curve) of enamel were determined in the two orthogonal directions and were found to be different. The elastic modulus showed load dependence for both orientations of the enamel rod structure that depended on the indenter. However, these differences could be normalized upon considering the contact diameter. The indented sample was imaged with an SEM to investigate the near surface damage. In conclusion, prism-sheath structure played an important role in determining the mechanical properties as well as the localized fracture of enamel.

  10. Further damage induced by water in micro-indentations in phosphate laser glass

    NASA Astrophysics Data System (ADS)

    Yu, Jiaxin; Jian, Qingyun; Yuan, Weifeng; Gu, Bin; Ji, Fang; Huang, Wen

    2014-02-01

    Using a microhardness tester, artificial flaws were made by micro-indentation in N31 Nd-doped phosphate laser glass. Indentation fracture toughness, KIC, was estimated as 0.45-0.53 MPa m1/2 from these indentations. The glasses with indentations were then immersed in ultrapure water to investigate further water-induced damage of these indentations. Stress-enhanced hydrolysis leads to the propagations of radial crack, lateral cracks and microcracks in the subsurface. These crack propagations therefore cause deformation in subsurface to form annular reflections regions around the indentations and further material collapse within imprints. After the residual stresses are exhausted, the leaching plays a more dominated role in glass corrosion in the further immersion. After immersion, the material structure slackens around micro-indentation, which decreases the contact stiffness and results in a lower nano-hardness. For the surface far away from flaws, water immersion presents a weak effect on the near-surface mechanical since the matrix leaching in phosphate glass restricts the formation of hydration layer. During first 20 min immersion, due to higher chemical activity and lower fracture toughness, the radial cracks show a faster propagation in phosphate glass compared with that in K9 silicate glass. For further immersion, crack healing occurs in silicate glass but not in phosphate glass. Analysis shows that the formation of hydration layer on crack walls plays an important role in crack healing in glasses.

  11. The Jugaad Technique for Jaw Reconstruction: Denture Based Inverse Planning.

    PubMed

    Kumar, Vinay V; Jacob, P C; Kekatpure, Vikram; Hedne, Naveen; Koch, Felix P; Kuriakose, Moni A

    2016-09-01

    The aim of this clinical paper is to introduce a technique to plan for functional maxillofacial reconstructions. Preoperative dental casts were made of the patient and mock surgery performed on the casts. A fibula analogue was then placed in an ideal functional reconstruction position. New dentures were fabricated on the fibula analogue and drill holes for the placement of implants were placed through the denture. This denture formed as a guide to position the fibula transplant during surgery. This technique was useful in producing functional and rehabilitative outcomes in cases of both maxillary and mandibular reconstructive surgeries. The Jugaad technique-denture based inverse planning-is a cost effective method for planning and executing maxillofacial reconstructions using mock surgery on casts and interim dentures.

  12. Optical center alignment technique based on inner profile measurement method

    NASA Astrophysics Data System (ADS)

    Wakayama, Toshitaka; Yoshizawa, Toru

    2014-05-01

    Center alignment is important technique to tune up the spindle of various precision machines in manufacturing industry. Conventionally such a tool as a dial indicator has been used to adjust and to position the axis by manual operations of a technical worker. However, it is not easy to precisely control its axis. In this paper, we developed the optical center alignment technique based on inner profile measurement using a ring beam device. In this case, the center position of the cylinder hole can be determined from circular profile detected by optical sectioning method using a ring beam device. In our trials, the resolution of the center position is proved less than 10 micrometers in extreme cases. This technique is available for practical applications in machine tool industry.

  13. Telematics techniques for image based diagnosis, therapy planning and monitoring.

    PubMed

    Bidaut, L M; Scherrer, J R

    1998-01-01

    This paper is intended to describe and illustrate some of the actual use of telematics related techniques together with modern biomedical imaging capabilities for helping in diagnosis, as well as for the planning and monitoring of therapy. To this end, most current imaging modalities are initially introduced. Then it is shown how telematics related techniques are necessary to improve the outcome of current image-based protocols. Such techniques allow data, means, or competencies--which may intrinsically be of a complementary nature or distributed at many different locations--to be integrated together and transcend the simple sum of individual expectations. Examples of actual implementations are given in the fields of radio-oncology, neurosurgery and orthopedics. To conclude, the papers and posters presented in the corresponding session of the MIE'97 symposium are summarized to provide further telematics references for the reader.

  14. A technique based on droplet evaporation to recognize alcoholic drinks

    NASA Astrophysics Data System (ADS)

    González-Gutiérrez, Jorge; Pérez-Isidoro, Rosendo; Ruiz-Suárez, J. C.

    2017-07-01

    Chromatography is, at present, the most used technique to determine the purity of alcoholic drinks. This involves a careful separation of the components of the liquid elements. However, since this technique requires sophisticated instrumentation, there are alternative techniques such as conductivity measurements and UV-Vis and infrared spectrometries. We report here a method based on salt-induced crystallization patterns formed during the evaporation of alcoholic drops. We found that droplets of different samples form different structures upon drying, which we characterize by their radial density profiles. We prove that using the dried deposit of a spirit as a control sample, our method allows us to differentiate between pure and adulterated drinks. As a proof of concept, we study tequila.

  15. A technique based on droplet evaporation to recognize alcoholic drinks.

    PubMed

    González-Gutiérrez, Jorge; Pérez-Isidoro, Rosendo; Ruiz-Suárez, J C

    2017-07-01

    Chromatography is, at present, the most used technique to determine the purity of alcoholic drinks. This involves a careful separation of the components of the liquid elements. However, since this technique requires sophisticated instrumentation, there are alternative techniques such as conductivity measurements and UV-Vis and infrared spectrometries. We report here a method based on salt-induced crystallization patterns formed during the evaporation of alcoholic drops. We found that droplets of different samples form different structures upon drying, which we characterize by their radial density profiles. We prove that using the dried deposit of a spirit as a control sample, our method allows us to differentiate between pure and adulterated drinks. As a proof of concept, we study tequila.

  16. Copyright protection scheme based on chaos and secret sharing techniques

    NASA Astrophysics Data System (ADS)

    Lou, Der-Chyuan; Shieh, Jieh-Ming; Tso, Hao-Kuan

    2005-11-01

    A copyright protection scheme based on chaos and secret sharing techniques is proposed. Instead of modifying the original image to embed a watermark in it, the proposed scheme extracts a feature from the image first. Then, the extracted feature and the watermark are scrambled by a chaos technique. Finally, the secret sharing technique is used to construct a shadow image. The watermark can be retrieved by performing an XOR operation between the shadow images. The proposed scheme has the following advantages. Firstly, the watermark retrieval does not need the original image. Secondly, the scheme does not need to modify the original image for embedding the watermark. Thirdly, compared with several schemes, the scheme is secure and robust in resisting various attacks.

  17. MEMS-based power generation techniques for implantable biosensing applications.

    PubMed

    Lueke, Jonathan; Moussa, Walied A

    2011-01-01

    Implantable biosensing is attractive for both medical monitoring and diagnostic applications. It is possible to monitor phenomena such as physical loads on joints or implants, vital signs, or osseointegration in vivo and in real time. Microelectromechanical (MEMS)-based generation techniques can allow for the autonomous operation of implantable biosensors by generating electrical power to replace or supplement existing battery-based power systems. By supplementing existing battery-based power systems for implantable biosensors, the operational lifetime of the sensor is increased. In addition, the potential for a greater amount of available power allows additional components to be added to the biosensing module, such as computational and wireless and components, improving functionality and performance of the biosensor. Photovoltaic, thermovoltaic, micro fuel cell, electrostatic, electromagnetic, and piezoelectric based generation schemes are evaluated in this paper for applicability for implantable biosensing. MEMS-based generation techniques that harvest ambient energy, such as vibration, are much better suited for implantable biosensing applications than fuel-based approaches, producing up to milliwatts of electrical power. High power density MEMS-based approaches, such as piezoelectric and electromagnetic schemes, allow for supplemental and replacement power schemes for biosensing applications to improve device capabilities and performance. In addition, this may allow for the biosensor to be further miniaturized, reducing the need for relatively large batteries with respect to device size. This would cause the implanted biosensor to be less invasive, increasing the quality of care received by the patient.

  18. MEMS-Based Power Generation Techniques for Implantable Biosensing Applications

    PubMed Central

    Lueke, Jonathan; Moussa, Walied A.

    2011-01-01

    Implantable biosensing is attractive for both medical monitoring and diagnostic applications. It is possible to monitor phenomena such as physical loads on joints or implants, vital signs, or osseointegration in vivo and in real time. Microelectromechanical (MEMS)-based generation techniques can allow for the autonomous operation of implantable biosensors by generating electrical power to replace or supplement existing battery-based power systems. By supplementing existing battery-based power systems for implantable biosensors, the operational lifetime of the sensor is increased. In addition, the potential for a greater amount of available power allows additional components to be added to the biosensing module, such as computational and wireless and components, improving functionality and performance of the biosensor. Photovoltaic, thermovoltaic, micro fuel cell, electrostatic, electromagnetic, and piezoelectric based generation schemes are evaluated in this paper for applicability for implantable biosensing. MEMS-based generation techniques that harvest ambient energy, such as vibration, are much better suited for implantable biosensing applications than fuel-based approaches, producing up to milliwatts of electrical power. High power density MEMS-based approaches, such as piezoelectric and electromagnetic schemes, allow for supplemental and replacement power schemes for biosensing applications to improve device capabilities and performance. In addition, this may allow for the biosensor to be further miniaturized, reducing the need for relatively large batteries with respect to device size. This would cause the implanted biosensor to be less invasive, increasing the quality of care received by the patient. PMID:22319362

  19. New Flutter Analysis Technique for CFD-based Unsteady Aeroelasticity

    NASA Technical Reports Server (NTRS)

    Pak, Chan-gi; Jutte, Christine V.

    2009-01-01

    This paper presents a flutter analysis technique for the transonic flight regime. The technique uses an iterative approach to determine the critical dynamic pressure for a given mach number. Unlike other CFD-based flutter analysis methods, each iteration solves for the critical dynamic pressure and uses this value in subsequent iterations until the value converges. This process reduces the iterations required to determine the critical dynamic pressure. To improve the accuracy of the analysis, the technique employs a known structural model, leaving only the aerodynamic model as the unknown. The aerodynamic model is estimated using unsteady aeroelastic CFD analysis combined with a parameter estimation routine. The technique executes as follows. The known structural model is represented as a finite element model. Modal analysis determines the frequencies and mode shapes for the structural model. At a given mach number and dynamic pressure, the unsteady CFD analysis is performed. The output time history of the surface pressure is converted to a nodal aerodynamic force vector. The forces are then normalized by the given dynamic pressure. A multi-input multi-output parameter estimation software, ERA, estimates the aerodynamic model through the use of time histories of nodal aerodynamic forces and structural deformations. The critical dynamic pressure is then calculated using the known structural model and the estimated aerodynamic model. This output is used as the dynamic pressure in subsequent iterations until the critical dynamic pressure is determined. This technique is demonstrated on the Aerostructures Test Wing-2 model at NASA's Dryden Flight Research Center.

  20. New Flutter Analysis Technique for CFD-based Unsteady Aeroelasticity

    NASA Technical Reports Server (NTRS)

    Pak, Chan-gi; Jutte, Christine V.

    2009-01-01

    This paper presents a flutter analysis technique for the transonic flight regime. The technique uses an iterative approach to determine the critical dynamic pressure for a given mach number. Unlike other CFD-based flutter analysis methods, each iteration solves for the critical dynamic pressure and uses this value in subsequent iterations until the value converges. This process reduces the iterations required to determine the critical dynamic pressure. To improve the accuracy of the analysis, the technique employs a known structural model, leaving only the aerodynamic model as the unknown. The aerodynamic model is estimated using unsteady aeroelastic CFD analysis combined with a parameter estimation routine. The technique executes as follows. The known structural model is represented as a finite element model. Modal analysis determines the frequencies and mode shapes for the structural model. At a given mach number and dynamic pressure, the unsteady CFD analysis is performed. The output time history of the surface pressure is converted to a nodal aerodynamic force vector. The forces are then normalized by the given dynamic pressure. A multi-input multi-output parameter estimation software, ERA, estimates the aerodynamic model through the use of time histories of nodal aerodynamic forces and structural deformations. The critical dynamic pressure is then calculated using the known structural model and the estimated aerodynamic model. This output is used as the dynamic pressure in subsequent iterations until the critical dynamic pressure is determined. This technique is demonstrated on the Aerostructures Test Wing-2 model at NASA's Dryden Flight Research Center.

  1. Effect of grain orientation on mechanical properties and thermomechanical response of Sn-based solder interconnects

    SciTech Connect

    Chen, Hongtao; Yan, Bingbing; Yang, Ming; Ma, Xin; Li, Mingyu

    2013-11-15

    The thermomechanical response of Sn-based solder interconnects with differently oriented grains was investigated by electron backscattered diffraction technique under thermal cycling and thermal shock testing in this study. The results showed that deformation and cracking of solder interconnects have a close relationship with the unique characteristics of grain orientation and boundaries in each solder interconnect, and deformation was frequently confined within the high-angle grain boundaries. The micro Vickers hardness testing results showed that the hardness varied significantly depending on the grain orientation and structure, and deformation twins can be induced around the indents by the indentation testing. - Highlights: • Thermomechanical response shows a close relationship with the grain structure. • Deformation was frequently confined within the high-angle grain boundaries. • Different grain orientations exhibit different hardness. • Deformation twins can be induced around the indents in SAC105 solder interconnects.

  2. A new index for the prediction of the indentation of composites under low velocity impact loads

    NASA Astrophysics Data System (ADS)

    Lopresto, V.; Caprino, G.; Leone, C.

    2012-07-01

    The effectiveness of a new empirical model for the prediction of the indentation depth resulting in a glass fibre laminates subjected to a low velocity impact, was verified. CFRP indentation data, drawn from a database, were considered to validate the new model. The advantage of the new model is that the effect of the tup diameter is explicitly accounted for. Furthermore, a single material constant has to be experimentally determined and it can be assumed as an index for the indentation sensitivity. The constant was found similar for GFRP and CFRP laminates denoting independence of constraint conditions, laminate type or laminae orientation and stacking sequence.

  3. Indentation Size Effect (ISE) of Transparent AION and MgAl2O4

    DTIC Science & Technology

    2006-07-01

    Indentation Size Effect (ISE) of Transparent AlON and MgAl2O4 by Parimal J. Patel, Jeffrey J. Swab, Mark Staley, and George D. Quinn ARL...3852 July 2006 Indentation Size Effect (ISE) of Transparent AlON and MgAl2O4 Parimal J. Patel and Jeffrey J. Swab Weapons and Materials...CONTRACT NUMBER 5b. GRANT NUMBER 4. TITLE AND SUBTITLE Indentation Size Effect (ISE) of Transparent AlON and MgAl2O4 5c. PROGRAM ELEMENT NUMBER 5d

  4. Gabor-based fusion technique for Optical Coherence Microscopy.

    PubMed

    Rolland, Jannick P; Meemon, Panomsak; Murali, Supraja; Thompson, Kevin P; Lee, Kye-sung

    2010-02-15

    We recently reported on an Optical Coherence Microscopy technique, whose innovation intrinsically builds on a recently reported - 2 microm invariant lateral resolution by design throughout a 2 mm cubic full-field of view - liquid-lens-based dynamic focusing optical probe [Murali et al., Optics Letters 34, 145-147, 2009]. We shall report in this paper on the image acquisition enabled by this optical probe when combined with an automatic data fusion method developed and described here to produce an in-focus high resolution image throughout the imaging depth of the sample. An African frog tadpole (Xenopus laevis) was imaged with the novel probe and the Gabor-based fusion technique, demonstrating subcellular resolution in a 0.5 mm (lateral) x 0.5 mm (axial) without the need, for the first time, for x-y translation stages, depth scanning, high-cost adaptive optics, or manual intervention. In vivo images of human skin are also presented.

  5. Comparative analysis of affinity-based 5-hydroxymethylation enrichment techniques

    PubMed Central

    Thomson, John P.; Hunter, Jennifer M.; Nestor, Colm E.; Dunican, Donncha S.; Terranova, Rémi; Moggs, Jonathan G.; Meehan, Richard R.

    2013-01-01

    The epigenetic modification of 5-hydroxymethylcytosine (5hmC) is receiving great attention due to its potential role in DNA methylation reprogramming and as a cell state identifier. Given this interest, it is important to identify reliable and cost-effective methods for the enrichment of 5hmC marked DNA for downstream analysis. We tested three commonly used affinity-based enrichment techniques; (i) antibody, (ii) chemical capture and (iii) protein affinity enrichment and assessed their ability to accurately and reproducibly report 5hmC profiles in mouse tissues containing high (brain) and lower (liver) levels of 5hmC. The protein-affinity technique is a poor reporter of 5hmC profiles, delivering 5hmC patterns that are incompatible with other methods. Both antibody and chemical capture-based techniques generate highly similar genome-wide patterns for 5hmC, which are independently validated by standard quantitative PCR (qPCR) and glucosyl-sensitive restriction enzyme digestion (gRES-qPCR). Both antibody and chemical capture generated profiles reproducibly link to unique chromatin modification profiles associated with 5hmC. However, there appears to be a slight bias of the antibody to bind to regions of DNA rich in simple repeats. Ultimately, the increased specificity observed with chemical capture-based approaches makes this an attractive method for the analysis of locus-specific or genome-wide patterns of 5hmC. PMID:24214958

  6. Simple Electrical Logging Technique for Base Metal Exploration

    NASA Astrophysics Data System (ADS)

    Pant, P. R.; Gupta, D.

    It is well known that electrical logs of boreholes can play a signi|fi|cant role in base metal exploration in identifying mineralised zones, especially when there is core loss or the borehole diameter is small or if drilling is by percussion. However, electrical logging is not widely utilised because of the additional burden on finances and time.A simple electrical logging technique, based on a pole-pole (hole-to-surface) configuration with one borehole electrode and nearly akin to the single point method, for S.P., resistivity and I.P. parameters, is presented. It is shown that it has the resolution of the single point method and the penetration of a very long normal sonde which is helpful for detection. Besides these features, the main advantage of this technique is that it can be easily carried out using ground I.P. (time domain) equipment.The electrical logs obtained in different base metal belts in Rajasthan, India, employing this technique and using ground I.P. equipment in connection with mise-à-la-masse surveys, illustrate the above features. A comparison with logs recorded by means of multi-electrode drill hole I.P. equipment of Scintrex, Canada, substantiates the same.

  7. Ball Indentation Studies on the Effect of Nitrogen on the Tensile Properties of 316LN SS

    NASA Astrophysics Data System (ADS)

    Mathew, M. D.; Ganesh Kumar, J.; Ganesan, V.; Laha, K.

    2015-12-01

    Type 316L(N) stainless steel (SS) containing 0.02-0.03 wt% carbon and 0.06-0.08 wt% nitrogen is used as the major structural material for the components of fast reactors. Research is underway to improve the high-temperature mechanical properties of 316LN SS by increasing the nitrogen content in the steel above the level of 0.08 wt%. In this investigation, ball indentation (BI) technique was used to evaluate the effect of nitrogen content on the tensile properties of 316LN SS. BI tests were conducted on four different heats of 316LN SS containing 0.07, 0.11, 0.14 and 0.22 wt% nitrogen in the temperature range 300-923 K. The tensile properties such as yield strength and ultimate tensile strength increased with increase in nitrogen content at all the investigated temperatures. These results were consistent with the corresponding uniaxial tensile test results. These studies showed that BI technique can be used to optimize the chemical composition during alloy development by evaluating tensile properties with minimum volume of material.

  8. An image morphing technique based on optimal mass preserving mapping.

    PubMed

    Zhu, Lei; Yang, Yan; Haker, Steven; Tannenbaum, Allen

    2007-06-01

    Image morphing, or image interpolation in the time domain, deals with the metamorphosis of one image into another. In this paper, a new class of image morphing algorithms is proposed based on the theory of optimal mass transport. The L(2) mass moving energy functional is modified by adding an intensity penalizing term, in order to reduce the undesired double exposure effect. It is an intensity-based approach and, thus, is parameter free. The optimal warping function is computed using an iterative gradient descent approach. This proposed morphing method is also extended to doubly connected domains using a harmonic parameterization technique, along with finite-element methods.

  9. An Image Morphing Technique Based on Optimal Mass Preserving Mapping

    PubMed Central

    Zhu, Lei; Yang, Yan; Haker, Steven; Tannenbaum, Allen

    2013-01-01

    Image morphing, or image interpolation in the time domain, deals with the metamorphosis of one image into another. In this paper, a new class of image morphing algorithms is proposed based on the theory of optimal mass transport. The L2 mass moving energy functional is modified by adding an intensity penalizing term, in order to reduce the undesired double exposure effect. It is an intensity-based approach and, thus, is parameter free. The optimal warping function is computed using an iterative gradient descent approach. This proposed morphing method is also extended to doubly connected domains using a harmonic parameterization technique, along with finite-element methods. PMID:17547128

  10. Indentation Pileup Behavior of Ti-6Al-4V Alloy: Experiments and Nonlocal Crystal Plasticity Finite Element Simulations

    NASA Astrophysics Data System (ADS)

    Han, Fengbo; Tang, Bin; Yan, Xu; Peng, Yifei; Kou, Hongchao; Li, Jinshan; Deng, Ying; Feng, Yong

    2017-01-01

    This study reports on the indentation pileup behavior of Ti-6Al-4V alloy. Berkovich nanoindentation was performed on a specimen with equiaxed microstructure. The indented area was characterized by electron backscattered diffraction (EBSD) to obtain the indented grain orientations. Surface topographies of several indents were measured by atomic force microscopy (AFM). The pileup patterns on the indented surfaces show significant orientation dependence. Corresponding nonlocal crystal plasticity finite element (CPFE) simulations were carried out to predict the pileup patterns. Analysis of the cumulative shear strain distributions and evolutions for different slip systems around the indents found that the pileups are mainly caused by prismatic slip. The pileup patterns evolve with the loading and unloading process, and the change in pileup height due to the elastic recovery at unloading stage is significant. The density distributions of geometrically necessary dislocations (GNDs) around the indent were predicted. Simulation of nanoindentation on a tricrystal model was performed.

  11. Indentation Pileup Behavior of Ti-6Al-4V Alloy: Experiments and Nonlocal Crystal Plasticity Finite Element Simulations

    NASA Astrophysics Data System (ADS)

    Han, Fengbo; Tang, Bin; Yan, Xu; Peng, Yifei; Kou, Hongchao; Li, Jinshan; Deng, Ying; Feng, Yong

    2017-04-01

    This study reports on the indentation pileup behavior of Ti-6Al-4V alloy. Berkovich nanoindentation was performed on a specimen with equiaxed microstructure. The indented area was characterized by electron backscattered diffraction (EBSD) to obtain the indented grain orientations. Surface topographies of several indents were measured by atomic force microscopy (AFM). The pileup patterns on the indented surfaces show significant orientation dependence. Corresponding nonlocal crystal plasticity finite element (CPFE) simulations were carried out to predict the pileup patterns. Analysis of the cumulative shear strain distributions and evolutions for different slip systems around the indents found that the pileups are mainly caused by prismatic slip. The pileup patterns evolve with the loading and unloading process, and the change in pileup height due to the elastic recovery at unloading stage is significant. The density distributions of geometrically necessary dislocations (GNDs) around the indent were predicted. Simulation of nanoindentation on a tricrystal model was performed.

  12. Surgical technique for repair of complex anterior skull base defects.

    PubMed

    Reinard, Kevin; Basheer, Azam; Jones, Lamont; Standring, Robert; Lee, Ian; Rock, Jack

    2015-01-01

    Modern microsurgical techniques enable en bloc resection of complex skull base tumors. Anterior cranial base surgery, particularly, has been associated with a high rate of postoperative cerebrospinal fluid (CSF) leak, meningitis, intracranial abscess, and pneumocephalus. We introduce simple modifications to already existing surgical strategies designed to minimize the incidence of postoperative CSF leak and associated morbidity and mortality. Medical records from 1995 to 2013 were reviewed in accordance with the Institutional Review Board. We identified 21 patients who underwent operations for repair of large anterior skull base defects following removal of sinonasal or intracranial pathology using standard craniofacial procedures. Patient charts were screened for CSF leak, meningitis, or intracranial abscess formation. A total of 15 male and 6 female patients with an age range of 26-89 years were included. All patients were managed with the same operative technique for reconstruction of the frontal dura and skull base defect. Spinal drainage was used intraoperatively in all cases but the lumbar drain was removed at the end of each case in all patients. Only one patient required re-operation for repair of persistent CSF leak. None of the patients developed meningitis or intracranial abscess. There were no perioperative mortalities. Median follow-up was 10 months. The layered reconstruction of large anterior cranial fossa defects resulted in postoperative CSF leak in only 5% of the patients and represents a simple and effective closure option for skull base surgeons.

  13. Surgical technique for repair of complex anterior skull base defects

    PubMed Central

    Reinard, Kevin; Basheer, Azam; Jones, Lamont; Standring, Robert; Lee, Ian; Rock, Jack

    2015-01-01

    Background: Modern microsurgical techniques enable en bloc resection of complex skull base tumors. Anterior cranial base surgery, particularly, has been associated with a high rate of postoperative cerebrospinal fluid (CSF) leak, meningitis, intracranial abscess, and pneumocephalus. We introduce simple modifications to already existing surgical strategies designed to minimize the incidence of postoperative CSF leak and associated morbidity and mortality. Methods: Medical records from 1995 to 2013 were reviewed in accordance with the Institutional Review Board. We identified 21 patients who underwent operations for repair of large anterior skull base defects following removal of sinonasal or intracranial pathology using standard craniofacial procedures. Patient charts were screened for CSF leak, meningitis, or intracranial abscess formation. Results: A total of 15 male and 6 female patients with an age range of 26–89 years were included. All patients were managed with the same operative technique for reconstruction of the frontal dura and skull base defect. Spinal drainage was used intraoperatively in all cases but the lumbar drain was removed at the end of each case in all patients. Only one patient required re-operation for repair of persistent CSF leak. None of the patients developed meningitis or intracranial abscess. There were no perioperative mortalities. Median follow-up was 10 months. Conclusion: The layered reconstruction of large anterior cranial fossa defects resulted in postoperative CSF leak in only 5% of the patients and represents a simple and effective closure option for skull base surgeons. PMID:25722926

  14. A Different Web-Based Geocoding Service Using Fuzzy Techniques

    NASA Astrophysics Data System (ADS)

    Pahlavani, P.; Abbaspour, R. A.; Zare Zadiny, A.

    2015-12-01

    Geocoding - the process of finding position based on descriptive data such as address or postal code - is considered as one of the most commonly used spatial analyses. Many online map providers such as Google Maps, Bing Maps and Yahoo Maps present geocoding as one of their basic capabilities. Despite the diversity of geocoding services, users usually face some limitations when they use available online geocoding services. In existing geocoding services, proximity and nearness concept is not modelled appropriately as well as these services search address only by address matching based on descriptive data. In addition there are also some limitations in display searching results. Resolving these limitations can enhance efficiency of the existing geocoding services. This paper proposes the idea of integrating fuzzy technique with geocoding process to resolve these limitations. In order to implement the proposed method, a web-based system is designed. In proposed method, nearness to places is defined by fuzzy membership functions and multiple fuzzy distance maps are created. Then these fuzzy distance maps are integrated using fuzzy overlay technique for obtain the results. Proposed methods provides different capabilities for users such as ability to search multi-part addresses, searching places based on their location, non-point representation of results as well as displaying search results based on their priority.

  15. Benchmarking time-of-flight based depth measurement techniques

    NASA Astrophysics Data System (ADS)

    Süss, Andreas; Rochus, Veronique; Rosmeulen, Maarten; Rottenberg, Xavier

    2016-03-01

    In the last decade significant progress has been made on optical non-contact time-of-flight (ToF) based ranging techniques. Direct implementations based on time-correlated single photon counting (TCSPC-dToF), coincidence detection (CD-TCSPC-dToF) as well as multiple indirect realizations based on e.g. single-photon synchronous detection (SPSD-iToF), continuous-wave modulation (CW-iToF) or pulse modulation (PM-iToF) have been presented. All those modulation/demodulation techniques can be employed in scanning (scanning LIDAR) as well as non-scanning (Flash-LIDAR) schemes. Many parameters impact key performance metrics such as depth measurement precision or angular resolution. Unfortunately, publications or datasheets rarely quote all relevant parameters. Thus, benchmarking between different approaches based on published metrics is cumbersome. The authors believe that such a benchmark would have to be founded on modeling in order to ensure fair comparison. This work presents an overview over the most common ToF based depth measurement approaches, how these can be modeled and how they compare.

  16. Nasal base narrowing: the alar flap advancement technique.

    PubMed

    Ismail, Ahmed Soliman

    2011-01-01

    To evaluate the role of creating an alar-based advancement flap in narrowing the nasal base and correcting excessive alar flare. Case series with chart review. This is a retrospective record review study. The study included 35 cases presenting with a wide nasal base and excessive alar flaring. The surgical procedure combined the alar base reduction with alar flare excision by creating a single laterally based alar flap. Any caudal septal deformities and any nasal tip modification procedures were corrected before the nasal base narrowing. The mean follow-up period was 23 months. The mean alar flap narrowing was 6.3 mm, whereas the mean width of sill narrowing was 2.9 mm. This single laterally based advancement alar flap resulted in a more conservative external resection, thus avoiding alar wedge overresection or blunting of the alar-facial crease. No cases of postoperative bleeding, infection, or keloid were encountered, and the external alar wedge excision healed with no apparent scar that was hidden in the depth of the alar-facial crease. The risk of notching of the alar rim at the sill incision is reduced by adopting a 2-layer closure of the vestibular floor. The alar base advancement flap is an effective technique in narrowing both the nasal base and excessive alar flare. It adopts a single skin excision to correct the 2 deformities while commonly feared complications were avoided.

  17. GIS Based Stereoscopic Visualization Technique for Weather Radar Data

    NASA Astrophysics Data System (ADS)

    Lim, S.; Jang, B. J.; Lee, K. H.; Lee, C.; Kim, W.

    2014-12-01

    As rainfall characteristic is more quixotic and localized, it is important to provide a prompt and accurate warning for public. To monitor localized heavy rainfall, a reliable disaster monitoring system with advanced remote observation technology and high-precision display system is needed. To advance even more accurate weather monitoring using weather radar, there have been growing concerns regarding the real-time changes of mapping radar observations on geographical coordinate systems along with the visualization and display methods of radar data based on spatial interpolation techniques and geographical information system (GIS). Currently, the method of simultaneously displaying GIS and radar data is widely used to synchronize the radar and ground systems accurately, and the method of displaying radar data in the 2D GIS coordinate system has been extensively used as the display method for providing weather information from weather radar. This paper proposes a realistic 3D weather radar data display technique with higher spatiotemporal resolution, which is based on the integration of 3D image processing and GIS interaction. This method is focused on stereoscopic visualization, while conventional radar image display works are based on flat or two-dimensional interpretation. Furthermore, using the proposed technique, the atmospheric change at each moment can be observed three-dimensionally at various geological locations simultaneously. Simulation results indicate that 3D display of weather radar data can be performed in real time. One merit of the proposed technique is that it can provide intuitive understanding of the influence of beam blockage by topography. Through an exact matching each 3D modeled radar beam with 3D GIS map, we can find out the terrain masked areas and accordingly it facilitates the precipitation correction from QPE underestimation caused by ground clutter filtering. It can also be expected that more accurate short-term forecasting will be

  18. Laser image denoising technique based on multi-fractal theory

    NASA Astrophysics Data System (ADS)

    Du, Lin; Sun, Huayan; Tian, Weiqing; Wang, Shuai

    2014-02-01

    The noise of laser images is complex, which includes additive noise and multiplicative noise. Considering the features of laser images, the basic processing capacity and defects of the common algorithm, this paper introduces the fractal theory into the research of laser image denoising. The research of laser image denoising is implemented mainly through the analysis of the singularity exponent of each pixel in fractal space and the feature of multi-fractal spectrum. According to the quantitative and qualitative evaluation of the processed image, the laser image processing technique based on fractal theory not only effectively removes the complicated noise of the laser images obtained by range-gated laser active imaging system, but can also maintains the detail information when implementing the image denoising processing. For different laser images, multi-fractal denoising technique can increase SNR of the laser image at least 1~2dB compared with other denoising techniques, which basically meet the needs of the laser image denoising technique.

  19. X-Ray microanalytical techniques based on synchrotron radiation.

    PubMed

    Snigireva, Irina; Snigirev, Anatoly

    2006-01-01

    The development of 3rd generation synchrotron radiation sources like European Synchrotron Radiation Facility (ESRF) in parallel with recent advances in the technology of X-ray microfocusing elements like Kirkpatrick-Baez (KB) mirrors, diffractive (Fresnel zone plates, FZP) and refractive (compound refractive lenses, CRL) optics, makes it possible to use X-ray microscopy techniques with high energy X-rays (energy superior to 4 keV). Spectroscopy, imaging, tomography and diffraction studies of samples with hard X-rays at micrometre and sub-micrometre spatial resolutions are now possible. The concept of combining these techniques as a high-energy microscopy has been proposed and successfully realized at the ESRF beamlines. Therefore a short summary of X-ray microscopy techniques is presented first. The main emphasis will be put on those methods which aim to produce sub-micron and nanometre resolution. These methods fall into three broad categories: reflective, refractive and diffractive optics. The basic principles and recent achievements will be discussed for all optical devices. Recent applications of synchrotron based microanalytical techniques to characterise radioactive fuel particles (UO(2)) released from the Chernobyl reactor are reported.

  20. Hypergraph Based Feature Selection Technique for Medical Diagnosis.

    PubMed

    Somu, Nivethitha; Raman, M R Gauthama; Kirthivasan, Kannan; Sriram, V S Shankar

    2016-11-01

    The impact of internet and information systems across various domains have resulted in substantial generation of multidimensional datasets. The use of data mining and knowledge discovery techniques to extract the original information contained in the multidimensional datasets play a significant role in the exploitation of complete benefit provided by them. The presence of large number of features in the high dimensional datasets incurs high computational cost in terms of computing power and time. Hence, feature selection technique has been commonly used to build robust machine learning models to select a subset of relevant features which projects the maximal information content of the original dataset. In this paper, a novel Rough Set based K - Helly feature selection technique (RSKHT) which hybridize Rough Set Theory (RST) and K - Helly property of hypergraph representation had been designed to identify the optimal feature subset or reduct for medical diagnostic applications. Experiments carried out using the medical datasets from the UCI repository proves the dominance of the RSKHT over other feature selection techniques with respect to the reduct size, classification accuracy and time complexity. The performance of the RSKHT had been validated using WEKA tool, which shows that RSKHT had been computationally attractive and flexible over massive datasets.

  1. Noninvasive in vivo glucose sensing using an iris based technique

    NASA Astrophysics Data System (ADS)

    Webb, Anthony J.; Cameron, Brent D.

    2011-03-01

    Physiological glucose monitoring is important aspect in the treatment of individuals afflicted with diabetes mellitus. Although invasive techniques for glucose monitoring are widely available, it would be very beneficial to make such measurements in a noninvasive manner. In this study, a New Zealand White (NZW) rabbit animal model was utilized to evaluate a developed iris-based imaging technique for the in vivo measurement of physiological glucose concentration. The animals were anesthetized with isoflurane and an insulin/dextrose protocol was used to control blood glucose concentration. To further help restrict eye movement, a developed ocular fixation device was used. During the experimental time frame, near infrared illuminated iris images were acquired along with corresponding discrete blood glucose measurements taken with a handheld glucometer. Calibration was performed using an image based Partial Least Squares (PLS) technique. Independent validation was also performed to assess model performance along with Clarke Error Grid Analysis (CEGA). Initial validation results were promising and show that a high percentage of the predicted glucose concentrations are within 20% of the reference values.

  2. Apprenticeship learning techniques for knowledge-based systems

    SciTech Connect

    Wilkins, D.C.

    1987-01-01

    This thesis describes apprenticeship learning techniques for automation of the transfer of expertise. Apprenticeship learning is a form of learning by watching, in which learning occurs as a byproduct of building explanations of human problem-solving actions. As apprenticeship is the most-powerful method that human experts use to refine and debug their expertise in knowledge-intensive domains such as medicine; this motivates giving such capabilities to an expert system. The major accomplishment in this thesis is showing how an explicit representation of the strategy knowledge to solve a general problem class, such as diagnosis, can provide a basis for learning the knowledge that is specific to a particular domain, such as medicine. The Odysseus learning program provides the first demonstration of using the same technique to transfer of expertise to and from an expert system knowledge base. Another major focus of this thesis is limitations of apprenticeship learning. It is shown that extant techniques for reasoning under uncertainty for expert systems lead to a sociopathic knowledge base.

  3. Bone indentation recovery time correlates with bond reforming time

    NASA Astrophysics Data System (ADS)

    Thompson, James B.; Kindt, Johannes H.; Drake, Barney; Hansma, Helen G.; Morse, Daniel E.; Hansma, Paul K.

    2001-12-01

    Despite centuries of work, dating back to Galileo, the molecular basis of bone's toughness and strength remains largely a mystery. A great deal is known about bone microsctructure and the microcracks that are precursors to its fracture, but little is known about the basic mechanism for dissipating the energy of an impact to keep the bone from fracturing. Bone is a nanocomposite of hydroxyapatite crystals and an organic matrix. Because rigid crystals such as the hydroxyapatite crystals cannot dissipate much energy, the organic matrix, which is mainly collagen, must be involved. A reduction in the number of collagen cross links has been associated with reduced bone strength and collagen is molecularly elongated (`pulled') when bovine tendon is strained. Using an atomic force microscope, a molecular mechanistic origin for the remarkable toughness of another biocomposite material, abalone nacre, has been found. Here we report that bone, like abalone nacre, contains polymers with `sacrificial bonds' that both protect the polymer backbone and dissipate energy. The time needed for these sacrificial bonds to reform after pulling correlates with the time needed for bone to recover its toughness as measured by atomic force microscope indentation testing. We suggest that the sacrificial bonds found within or between collagen molecules may be partially responsible for the toughness of bone.

  4. Indentation metrology of clamped, ultra-thin elastic sheets.

    PubMed

    Vella, Dominic; Davidovitch, Benny

    2017-03-06

    We study the indentation of ultrathin elastic sheets clamped to the edge of a circular hole. This classical setup has received considerable attention lately, being used by various experimental groups as a probe to measure the surface properties and stretching modulus of thin solid films. Despite the apparent simplicity of this method, the geometric nonlinearity inherent in the mechanical response of thin solid objects renders the analysis of the resulting data a nontrivial task. Importantly, the essence of this difficulty is in the geometric coupling between in-plane stress and out-of-plane deformations, and hence is present in the behaviour of Hookean solids even when the slope of the deformed membrane remains small. Here we take a systematic approach to address this problem, using the membrane limit of the Föppl-von-Kármán equations. This approach highlights some of the dangers in the use of approximate formulae in the metrology of solid films, which can introduce large errors; we suggest how such errors may be avoided in performing experiments and analyzing the resulting data.

  5. Cell poking: quantitative analysis of indentation of thick viscoelastic layers.

    PubMed

    Duszyk, M; Schwab, B; Zahalak, G I; Qian, H; Elson, E L

    1989-04-01

    A recently introduced device, the cell poker, measures the force required to indent the exposed surface of a cell adherent to a rigid substratum. The cell poker has provided phenomenological information about the viscoelastic properties of several different types of cells, about mechanical changes triggered by external stimuli, and about the role of the cytoskeleton in these mechanical functions. Except in special cases, however, it has not been possible to extract quantitative estimates of viscosity and elasticity moduli from cell poker measurements. This paper presents cell poker measurements of well characterized viscoelastic polymeric materials, polydimethylsiloxanes of different degrees of polymerization, in a simple shape, a flat, thick layer, which for our purposes can be treated as a half space. Analysis of the measurements in terms of a linear viscoelasticity theory yields viscosity values for three polymer samples in agreement with those determined by measurements on a macroscopic scale. Theoretical analysis further indicates that the measured limiting static elasticity of the layers may result from the tension generated at the interface between the polymer and water. This work demonstrates the possibility of obtaining quantitative viscoelastic material properties from cell poker measurements and represents the first step in extending these quantitative studies to more complicated structures including cells.

  6. Cell poking: quantitative analysis of indentation of thick viscoelastic layers.

    PubMed Central

    Duszyk, M; Schwab, B; Zahalak, G I; Qian, H; Elson, E L

    1989-01-01

    A recently introduced device, the cell poker, measures the force required to indent the exposed surface of a cell adherent to a rigid substratum. The cell poker has provided phenomenological information about the viscoelastic properties of several different types of cells, about mechanical changes triggered by external stimuli, and about the role of the cytoskeleton in these mechanical functions. Except in special cases, however, it has not been possible to extract quantitative estimates of viscosity and elasticity moduli from cell poker measurements. This paper presents cell poker measurements of well characterized viscoelastic polymeric materials, polydimethylsiloxanes of different degrees of polymerization, in a simple shape, a flat, thick layer, which for our purposes can be treated as a half space. Analysis of the measurements in terms of a linear viscoelasticity theory yields viscosity values for three polymer samples in agreement with those determined by measurements on a macroscopic scale. Theoretical analysis further indicates that the measured limiting static elasticity of the layers may result from the tension generated at the interface between the polymer and water. This work demonstrates the possibility of obtaining quantitative viscoelastic material properties from cell poker measurements and represents the first step in extending these quantitative studies to more complicated structures including cells. PMID:2720066

  7. Indentation Damage and Crack Repair in Human Enamel*

    PubMed Central

    Rivera, C.; Arola, D.; Ossa, A.

    2013-01-01

    Tooth enamel is the hardest and most highly mineralized tissue in the human body. While there have been a number of studies aimed at understanding the hardness and crack growth resistance behavior of this tissue, no study has evaluated if cracks in this tissue undergo repair. In this investigation the crack repair characteristics of young human enamel were evaluated as a function of patient gender and as a function of the distance from the Dentin Enamel Junction (DEJ). Cracks were introduced via microindentation along the prism direction and evaluated as a function of time after the indentation. Microscopic observations indicated that the repair of cracks began immediately after crack initiation and reaches saturation after approximately 48 hours. During this process he crack length decreased up to 10% of the initial length, and the largest degree of reduction occurred in the deep enamel, nearest the DEJ. In addition, it was found that the degree of repair was significantly greater in the enamel of female patients. PMID:23541701

  8. On the Measurement of Power Law Creep Parameters from Instrumented Indentation

    NASA Astrophysics Data System (ADS)

    Sudharshan Phani, P.; Oliver, W. C.; Pharr, G. M.

    2017-08-01

    Recently the measurement of the creep response of materials at small scales has received renewed interest largely because the equipment required to perform high-temperature nanomechanical testing has become available to an increasing number of researchers. Despite that increased access, there remain several significant experimental and modeling challenges in small-scale mechanical testing at elevated temperatures that are as yet unresolved. In this regard, relating the creep response observed with high-temperature instrumented indentation experiments to macroscopic uniaxial creep response is of great practical value. In this review, we present an overview of various methods currently being used to measure creep with instrumented indentation, with a focus on geometrically self-similar indenters, and their relative merits and demerits from an experimental perspective. A comparison of the various methods to use those instrumented indentation results to predict the uniaxial power law creep response of a wide range of materials will be presented to assess their validity.

  9. Scanning electron acoustic microscopy of indentation-induced cracks and residual stresses in ceramics

    NASA Technical Reports Server (NTRS)

    Cantrell, John H.; Qian, Menglu; Ravichandran, M. V.; Knowles, K. M.

    1990-01-01

    The ability of scanning electron acoustic microscopy (SEAM) to characterize ceramic materials is assessed. SEAM images of Vickers indentations in SiC whisker-reinforced alumina clearly reveal not only the radial cracks, the length of which can be used to estimate the fracture toughness of the material, but also reveal strong contrast, interpreted as arising from the combined effects of lateral cracks and the residual stress field left in the SiC whisker-reinforced alumina by the indenter. The strong contrast is removed after the material is heat treated at 1000 C to relieve the residual stresses around the indentations. A comparison of these observations with SEAM and reflected polarized light observations of Vickers indentations in soda-lime glass both before and after heat treatment confirms the interpretation of the strong contrast.

  10. Aqueous humour dynamics in anterior chamber under influence of cornea indentation

    NASA Astrophysics Data System (ADS)

    Zuhaila, I.; Jiann, L. Y.; Sharidan, S.; Fitt, A.

    2017-04-01

    The existing temperature different between the cornea and the pupil induces the aqueous humour (AH) to circulate in the anterior chamber (AC). The buoyancy forces produced by the temperature gradient has driven the AH to flow. Previous studies have shown that cornea indentation changes the structure of the AC. This imply that the cornea indentation may change the fluid flow behaviour in the AC. A mathematical model of AH flow has been developed in order to analyse the fluid mechanics concerning the indentation of the cornea. Naiver-Stokes equations is used to describe the flow of AH in the AC. The governing equations have been solved numerically using finite element method. The results show that the cornea indentation has slow down the circulation the AH in the AC.

  11. Development of an ultra-low-load microhardness indentation test machine

    NASA Astrophysics Data System (ADS)

    Schmale, D. T.; Bourcier, R. J.; Martinez, E.

    1986-04-01

    As part of a program to characterize the mechanical response of surface modified materials, a microhardness indentation test machine has been developed. An electromagnetic drive system controls a diamond indenter which is suspended on a low friction ball slide. The test specimen is mounted on a cantilevered arm in a vertical plane perpendicular to the indentation direction on an X-Y micrometer translation system. Tests are controlled with a 16-bit A/D closed loop digital controller/function generator designed for this system. Load is monitored with a strain gage load cell while displacement is measured with a set of capacitance probes. Load/depth/time data are stored on a digital oscilloscope which is linked to a DEC LSI 11/23 for subsequent processing. The system allows indentation loading up to 1 kg with load resolutions of 5 mg and a depth resolution of 10 nm.

  12. Scanning electron acoustic microscopy of indentation-induced cracks and residual stresses in ceramics

    NASA Technical Reports Server (NTRS)

    Cantrell, John H.; Qian, Menglu; Ravichandran, M. V.; Knowles, K. M.

    1990-01-01

    The ability of scanning electron acoustic microscopy (SEAM) to characterize ceramic materials is assessed. SEAM images of Vickers indentations in SiC whisker-reinforced alumina clearly reveal not only the radial cracks, the length of which can be used to estimate the fracture toughness of the material, but also reveal strong contrast, interpreted as arising from the combined effects of lateral cracks and the residual stress field left in the SiC whisker-reinforced alumina by the indenter. The strong contrast is removed after the material is heat treated at 1000 C to relieve the residual stresses around the indentations. A comparison of these observations with SEAM and reflected polarized light observations of Vickers indentations in soda-lime glass both before and after heat treatment confirms the interpretation of the strong contrast.

  13. Adaptive differential correspondence imaging based on sorting technique

    NASA Astrophysics Data System (ADS)

    Wu, Heng; Zhang, Xianmin; Shan, Yilin; He, Zhenya; Li, Hai; Luo, Chunling

    2017-04-01

    We develop an adaptive differential correspondence imaging (CI) method using a sorting technique. Different from the conventional CI schemes, the bucket detector signals (BDS) are first processed by a differential technique, and then sorted in a descending (or ascending) order. Subsequently, according to the front and last several frames of the sorted BDS, the positive and negative subsets (PNS) are created by selecting the relative frames from the reference detector signals. Finally, the object image is recovered from the PNS. Besides, an adaptive method based on two-step iteration is designed to select the optimum number of frames. To verify the proposed method, a single-detector computational ghost imaging (GI) setup is constructed. We experimentally and numerically compare the performance of the proposed method with different GI algorithms. The results show that our method can improve the reconstruction quality and reduce the computation cost by using fewer measurement data.

  14. An osmolyte-based micro-volume ultrafiltration technique.

    PubMed

    Ghosh, Raja

    2014-12-07

    This paper discusses a novel, simple, and inexpensive micro-volume ultrafiltration technique for protein concentration, desalting, buffer exchange, and size-based protein purification. The technique is suitable for processing protein samples in a high-throughput mode. It utilizes a combination of capillary action, and osmosis for drawing water and other permeable species from a micro-volume sample droplet applied on the surface of an ultrafiltration membrane. A macromolecule coated on the permeate side of the membrane functions as the osmolyte. The action of the osmolyte could, if required, be augmented by adding a supersorbent polymer layer over the osmolyte. The mildly hydrophobic surface of the polymeric ultrafiltration membrane used in this study minimized sample droplet spreading, thus making it easy to recover the retained material after separation, without sample interference and cross-contamination. High protein recoveries were observed in the micro-volume ultrafiltration experiments described in the paper.

  15. New MPLS network management techniques based on adaptive learning.

    PubMed

    Anjali, Tricha; Scoglio, Caterina; de Oliveira, Jaudelice Cavalcante

    2005-09-01

    The combined use of the differentiated services (DiffServ) and multiprotocol label switching (MPLS) technologies is envisioned to provide guaranteed quality of service (QoS) for multimedia traffic in IP networks, while effectively using network resources. These networks need to be managed adaptively to cope with the changing network conditions and provide satisfactory QoS. An efficient strategy is to map the traffic from different DiffServ classes of service on separate label switched paths (LSPs), which leads to distinct layers of MPLS networks corresponding to each DiffServ class. In this paper, three aspects of the management of such a layered MPLS network are discussed. In particular, an optimal technique for the setup of LSPs, capacity allocation of the LSPs and LSP routing are presented. The presented techniques are based on measurement of the network state to adapt the network configuration to changing traffic conditions.

  16. New modulation-based watermarking technique for video

    NASA Astrophysics Data System (ADS)

    Lemma, Aweke; van der Veen, Michiel; Celik, Mehmet

    2006-02-01

    Successful watermarking algorithms have already been developed for various applications ranging from meta-data tagging to forensic tracking. Nevertheless, it is commendable to develop alternative watermarking techniques that provide a broader basis for meeting emerging services, usage models and security threats. To this end, we propose a new multiplicative watermarking technique for video, which is based on the principles of our successful MASK audio watermark. Audio-MASK has embedded the watermark by modulating the short-time envelope of the audio signal and performed detection using a simple envelope detector followed by a SPOMF (symmetrical phase-only matched filter). Video-MASK takes a similar approach and modulates the image luminance envelope. In addition, it incorporates a simple model to account for the luminance sensitivity of the HVS (human visual system). Preliminary tests show algorithms transparency and robustness to lossy compression.

  17. A VIKOR Technique with Applications Based on DEMATEL and ANP

    NASA Astrophysics Data System (ADS)

    Ou Yang, Yu-Ping; Shieh, How-Ming; Tzeng, Gwo-Hshiung

    In multiple criteria decision making (MCDM) methods, the compromise ranking method (named VIKOR) was introduced as one applicable technique to implement within MCDM. It was developed for multicriteria optimization of complex systems. However, few papers discuss conflicting (competing) criteria with dependence and feedback in the compromise solution method. Therefore, this study proposes and provides applications for a novel model using the VIKOR technique based on DEMATEL and the ANP to solve the problem of conflicting criteria with dependence and feedback. In addition, this research also uses DEMATEL to normalize the unweighted supermatrix of the ANP to suit the real world. An example is also presented to illustrate the proposed method with applications thereof. The results show the proposed method is suitable and effective in real-world applications.

  18. Cyclic Fatigue of Brittle Materials with an Indentation-Induced Flaw System

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Salem, Jonathan A.

    1996-01-01

    The ratio of static to cyclic fatigue life, or 'h ratio', was obtained numerically for an indentation flaw system subjected to sinusoidal loading conditions. Emphasis was placed on developing a simple, quick lifetime prediction tool. The solution for the h ratio was compared with experimental static and cyclic fatigue data obtained from as-indented 96 wt.% alumina specimens tested in room-temperature distilled water.

  19. Corneal perforation during scleral indentation in a patient with pellucid marginal degeneration

    PubMed Central

    Mercieca, Karl; Dharmasena, Aruna; Hopley, Charles

    2016-01-01

    An observational case report of corneal perforation following scleral indentation in a patient with previously undiagnosed pellucid marginal degeneration is presented. Clinical examination, investigations, and subsequent management of this unwarranted and rare complication are described and discussed. The case highlights the need for thorough anterior segment examination before indirect ophthalmoscopy particularly in the presence of ectatic corneal pathology in which case scleral indentation should be avoided. PMID:27146937

  20. Indentation Versus Tensile Measurements of Young's Modulus for Soft Biological Tissues

    PubMed Central

    McKee, Clayton T.; Last, Julie A.

    2011-01-01

    In this review, we compare the reported values of Young's modulus (YM) obtained from indentation and tensile deformations of soft biological tissues. When the method of deformation is ignored, YM values for any given tissue typically span several orders of magnitude. If the method of deformation is considered, then a consistent and less ambiguous result emerges. On average, YM values for soft tissues are consistently lower when obtained by indentation deformations. We discuss the implications and potential impact of this finding. PMID:21303220

  1. Determination of the elastic modulus of native collagen fibrils via radial indentation

    NASA Astrophysics Data System (ADS)

    Heim, August J.; Matthews, William G.; Koob, Thomas J.

    2006-10-01

    The authors studied the elastic response of single, native collagen fibrils extracted from tissues of the inner dermis of the sea cucumber, Cucumaria frondosa, via local nanoscale indentation with an atomic force microscope (AFM). AFM imaging of fibrils under ambient conditions are presented, demonstrating a peak-to-peak periodicity, the d band, of dehydrated, unfixed fibrils to be ˜64.5nm. Radial indentation experiments were performed, and the measured value for the reduced modulus is 1-2GPa.

  2. Characterization and Evaluation of Micro-mechanical Properties of Ultra High Strength Concrete by using Micro-indentation Test

    NASA Astrophysics Data System (ADS)

    Murthy, A. Ramachandra; Iyer, Nagesh R.; Raghu Prasad, B. K.

    2016-09-01

    This work presents the details of characterization and micro-mechanical properties of ultra high strength concrete. Characterization was carried out for High Strength Concrete (HSC, HSC1) and Ultra High Strength Concrete (UHSC). Various mechanical properties, namely, compressive strength, split tensile strength and modulus of elasticity have been estimated for HSC, HSC1 and UHSC. It was observed from characterization studies that the split tensile strength is high in the case of UHSC compared to HSC and HSC1. X-ray diffraction analysis has been performed for cement, silica fume and quartz powder to know the chemical composition. The amount of quantified phases has been estimated. Micro indentation technique has been employed to evaluate the micromechanical properties such as modulus of elasticity and hardness. Oliver and Pharr method has been used to compute modulus of elasticity and hardness. It is observed that the value of modulus of elasticity obtained from the micro indentation test is in very good agreement with that of the value obtained from uniaxial compression test data of a cylindrical specimen. Finally micro-structure of the specimen has been obtained for various magnifications to examine the voids/pores in the UHSC matrix.

  3. Vision based techniques for rotorcraft low altitude flight

    NASA Technical Reports Server (NTRS)

    Sridhar, Banavar; Suorsa, Ray; Smith, Philip

    1991-01-01

    An overview of research in obstacle detection at NASA Ames Research Center is presented. The research applies techniques from computer vision to automation of rotorcraft navigation. The development of a methodology for detecting the range to obstacles based on the maximum utilization of passive sensors is emphasized. The development of a flight and image data base for verification of vision-based algorithms, and a passive ranging methodology tailored to the needs of helicopter flight are discussed. Preliminary results indicate that it is possible to obtain adequate range estimates except at regions close to the FOE. Closer to the FOE, the error in range increases since the magnitude of the disparity gets smaller, resulting in a low SNR.

  4. Vision based techniques for rotorcraft low altitude flight

    NASA Technical Reports Server (NTRS)

    Sridhar, Banavar; Suorsa, Ray; Smith, Philip

    1991-01-01

    An overview of research in obstacle detection at NASA Ames Research Center is presented. The research applies techniques from computer vision to automation of rotorcraft navigation. The development of a methodology for detecting the range to obstacles based on the maximum utilization of passive sensors is emphasized. The development of a flight and image data base for verification of vision-based algorithms, and a passive ranging methodology tailored to the needs of helicopter flight are discussed. Preliminary results indicate that it is possible to obtain adequate range estimates except at regions close to the FOE. Closer to the FOE, the error in range increases since the magnitude of the disparity gets smaller, resulting in a low SNR.

  5. Annealing-induced recovery of indents in thin Au(Fe) bilayer films

    PubMed Central

    Kosinova, Anna; Schwaiger, Ruth; Klinger, Leonid

    2016-01-01

    We employed depth-sensing nanoindentation to produce ordered arrays of indents on the surface of 50 nm-thick Au(Fe) films deposited on sapphire substrates. The maximum depth of the indents was approximately one-half of the film thickness. The indented films were annealed at a temperature of 700 °C in a forming gas atmosphere. While the onset of solid-state dewetting was observed in the unperturbed regions of the film, no holes to the substrate were observed in the indented regions. Instead, the film annealing resulted in the formation of hillocks at the indent locations, followed by their dissipation and the formation of shallow depressions nearby after subsequent annealing treatments. This annealing-induced evolution of nanoindents was interpreted in terms of annihilation of dislocation loops generated during indentation, accompanied by the formation of nanopores at the grain boundaries and their subsequent dissolution. The application of the processes uncovered in this work show great potential for the patterning of thin films. PMID:28144556

  6. Antimisting kerosene: Base fuel effects, blending and quality control techniques

    NASA Technical Reports Server (NTRS)

    Yavrouian, A. H.; Ernest, J.; Sarohia, V.

    1984-01-01

    The problems associated with blending of the AMK additive with Jet A, and the base fuel effects on AMK properties are addressed. The results from the evaluation of some of the quality control techniques for AMK are presented. The principal conclusions of this investigation are: significant compositional differences for base fuel (Jet A) within the ASTM specification DI655; higher aromatic content of the base fuel was found to be beneficial for the polymer dissolution at ambient (20 C) temperature; using static mixer technology, the antimisting additive (FM-9) is in-line blended with Jet A, producing AMK which has adequate fire-protection properties 15 to 20 minutes after blending; degradability of freshly blended and equilibrated AMK indicated that maximum degradability is reached after adequate fire protection is obtained; the results of AMK degradability as measured by filter ratio, confirmed previous RAE data that power requirements to decade freshly blended AMK are significantly higher than equilibrated AMK; blending of the additive by using FM-9 concentrate in Jet A produces equilibrated AMK almost instantly; nephelometry offers a simple continuous monitoring capability and is used as a real time quality control device for AMK; and trajectory (jet thurst) and pressure drop tests are useful laboratory techniques for evaluating AMK quality.

  7. Color demosaicking using deinterlacing and median-based filtering techniques

    NASA Astrophysics Data System (ADS)

    Huang, Wen-Tsung; Chen, Wen-Jan; Tai, Shen-Chuan

    2010-10-01

    Color demosaicking is critical to the image quality of single-sensor-based imaging devices. Caused by the sampling pattern of color filter array (CFA), the demosaicked images typically suffer from visual color artifacts in regions of high frequency and sharp edge structures, degrading the quality of camera output. We present a new high-quality demosaicking algorithm by taking advantage of deinterlacing and median-based filtering techniques. We treat the sampled green data of Bayer CFA as a form of diagonal interlaced green planes and make use of some key concepts about spatial deinterlacing to help the edge estimation in terms of both various directions and accuracy. In addition, a specific edge feature, sharp line edge of width 1 pixel, can also be handed well by the proposed method. The median-based filtering techniques are developed for suppressing most visual demosaicking artifacts, such as zipper effect, false color artifact, and interpolation artifact. Experimental results show that our algorithm is effective in suppressing visual artifacts, preserving the edges of image with sharpness and satisfying visual inspection, while keeping computational efficiency.

  8. Gearbox diagnostics using wavelet-based windowing technique

    NASA Astrophysics Data System (ADS)

    Omar, F. K.; Gaouda, A. M.

    2009-08-01

    In extracting gear box acoustic signals embedded in excessive noise, the need for an online and automated tool becomes a crucial necessity. One of the recent approaches that have gained some acceptance within the research arena is the Wavelet multi-resolution analysis (WMRA). However selecting an accurate mother wavelet, defining dynamic threshold values and identifying the resolution levels to be considered in gearboxes fault detection and diagnosis are still challenging tasks. This paper proposes a novel wavelet-based technique for detecting, locating and estimating the severity of defects in gear tooth fracture. The proposed technique enhances the WMRA by decomposing the noisy data into different resolution levels while data sliding it into Kaiser's window. Only the maximum expansion coefficients at each resolution level are used in de-noising, detecting and measuring the severity of the defects. A small set of coefficients is used in the monitoring process without assigning threshold values or performing signal reconstruction. The proposed monitoring technique has been applied to a laboratory data corrupted with high noise level.

  9. Radiation-Based Medical Imaging Techniques: An Overview

    NASA Astrophysics Data System (ADS)

    Prior, John O.; Lecoq, Paul

    This chapter will present an overview of two radiation-based medical imaging techniques using radiopharmaceuticals used in nuclear medicine/molecular imaging, namely, single-photon emission computed tomography (SPECT) and positron emission tomography (PET). The relative merits in terms of radiation sensitivity and image resolution of SPECT and PET will be compared to the main conventional radiologic modalities that are computed tomography (CT) and magnetic resonance (MR) imaging. Differences in terms of temporal resolution will also be outlined, as well as the other similarities and dissimilarities of these two techniques, including their latest and upcoming multimodality combination. The main clinical applications are briefly described and examples of specific SPECT and PET radiopharmaceuticals are listed. SPECT and PET imaging will be then further detailed in the two subsequent chapters describing in greater depth the basics and future trends of each technique (see Chaps. 37, "SPECT Imaging: Basics and New Trends" 10.1007/978-3-642-13271-1_37 and 38, "PET Imaging: Basics and New Trends" 10.1007/978-3-642-13271-1_38.

  10. Evaluation of sinking-in and cracking behavior of soda-lime glass under varying angle of trigonal pyramid indenter

    NASA Astrophysics Data System (ADS)

    Yoshida, Satoshi; Wada, Ken; Fujimura, Takahiro; Yamada, Akihiro; Kato, Mitsuo; Matsuoka, Jun; Soga, Naohiro

    2016-12-01

    It is well known that glass undergoes elastic and inelastic deformation under a sharp diamond indenter. Although brittle or less-brittle behavior of glass must be connected with such mechanical responses of glass under the indenter, there has been limited research on in-situ deformation behavior of glass during the loading and unloading indentation cycle. This is because most indentation tests were conducted using a commercial hardness tester for which this information is not available. In this study, the in-situ sinking-in region of glass during indentation test is determined using a custom-designed indentation microscope with trigonal pyramid indenters having different tip angles. It is found that both the shape of contact region and the amount of sinking-in are affected by indenter geometries, and that the projected contact region of the glass sample under Berkovich indenter is not a regular triangle, but a concave triangle with bowed-in edges. This is due to the larger amount of sinking-in under the face than under the ridge of indenter. It is also found that these deformation behaviors of glass are inseparably linked with contact damage or cracking in glass.

  11. Influence of cooling rate on cracking and plastic deformation during impact and indentation of borosilicate glasses.

    NASA Astrophysics Data System (ADS)

    Zehnder, Christoffer; Bruns, Sebastian; Peltzer, Jan-Niklas; Durst, Karsten; Korte-Kerzel, Sandra; Möncke, Doris

    2017-03-01

    The influence of a changing glass topology on local mechanical properties was studied in a multi-technique nanomechanical approach. The glass response against sharp contacts can result in structural densification, plastic flow or crack initiation. Using instrumented indentation testing, the mechanical response was studied in different strain rate regimes for a sodium-boro-silicate glass (NBS) exhibiting altering structures due to varying processing conditions. Comparison with data from former studies as well as with literature data on other glass structures helped to elucidate the role of the borate and silicate sub-networks and to understand the overall mechanical properties of the mixed glass systems. A peculiarity of some of the NBS glasses tested in this study is the fact that the connectivity of the borate and silicate entities depends on the sample’s thermal history. While the influence on macroscopic material properties such as E and H is minor, the onset of cracking indeed is influenced by those structural changes within the glass. Rapidly quenched glass shows an improved crack resistance, which is even more pronounced at high strain rates. Studies on various processing conditions further indicate that this transition is closely related to the cooling rate around Tg. The strain rate dependence of cracking is discussed in terms of the occurrence of shear deformation and densification.

  12. Evolutionary Based Techniques for Fault Tolerant Field Programmable Gate Arrays

    NASA Technical Reports Server (NTRS)

    Larchev, Gregory V.; Lohn, Jason D.

    2006-01-01

    The use of SRAM-based Field Programmable Gate Arrays (FPGAs) is becoming more and more prevalent in space applications. Commercial-grade FPGAs are potentially susceptible to permanently debilitating Single-Event Latchups (SELs). Repair methods based on Evolutionary Algorithms may be applied to FPGA circuits to enable successful fault recovery. This paper presents the experimental results of applying such methods to repair four commonly used circuits (quadrature decoder, 3-by-3-bit multiplier, 3-by-3-bit adder, 440-7 decoder) into which a number of simulated faults have been introduced. The results suggest that evolutionary repair techniques can improve the process of fault recovery when used instead of or as a supplement to Triple Modular Redundancy (TMR), which is currently the predominant method for mitigating FPGA faults.

  13. Thiophene-based monolayer OFETs prepared by Langmuir techniques

    NASA Astrophysics Data System (ADS)

    Agina, Elena V.; Sizov, Alexey S.; Anisimov, Daniil S.; Trul, Askold A.; Borshchev, Oleg V.; Paraschuk, Dmitry Y.; Shcherbina, Maxim A.; Chvalun, Sergey N.; Ponomarenko, Sergey A.

    2015-08-01

    A novel fast, easily processible and highly reproducible approach to thiophene-based monolayer OFETs fabrication by Langmuir-Blodgett or Langmuir-Schaefer techniques was developed and successfully applied. It is based on selfassembly of organosilicon derivatives of oligothiophenes or benzothienobenzothiophene on the water-air interface. Influence of the conjugation length and the anchor group chemistry of the self-assembling molecules on the monolayer structure and electric performance of monolayer OFETs was systematically investigated. The efficient monolayer OFETs with the charge carrier mobilities up to 0.01 cm2/Vs and on/off ratio up to 106 were fabricated, and their functionality in integrated circuits under normal air conditions was demonstrated.

  14. RBF-based technique for statistical demodulation of pathological tremor.

    PubMed

    Gianfelici, Francesco

    2013-10-01

    This paper presents an innovative technique based on the joint approximation capabilities of radial basis function (RBF) networks and the estimation capability of the multivariate iterated Hilbert transform (IHT) for the statistical demodulation of pathological tremor from electromyography (EMG) signals in patients with Parkinson's disease. We define a stochastic model of the multichannel high-density surface EMG by means of the RBF networks applied to the reconstruction of the stochastic process (characterizing the disease) modeled by the multivariate relationships generated by the Karhunen-Loéve transform in Hilbert spaces. Next, we perform a demodulation of the entire random field by means of the estimation capability of the multivariate IHT in a statistical setting. The proposed method is applied to both simulated signals and data recorded from three Parkinsonian patients and the results show that the amplitude modulation components of the tremor oscillation can be estimated with signal-to-noise ratio close to 30 dB with root-mean-square error for the estimates of the tremor instantaneous frequency. Additionally, the comparisons with a large number of techniques based on all the combinations of the RBF, extreme learning machine, backpropagation, support vector machine used in the first step of the algorithm; and IHT, empirical mode decomposition, multiband energy separation algorithm, periodic algebraic separation and energy demodulation used in the second step of the algorithm, clearly show the effectiveness of our technique. These results show that the proposed approach is a potential useful tool for advanced neurorehabilitation technologies that aim at tremor characterization and suppression.

  15. Risk-based maintenance--techniques and applications.

    PubMed

    Arunraj, N S; Maiti, J

    2007-04-11

    Plant and equipment, however well designed, will not remain safe or reliable if it is not maintained. The general objective of the maintenance process is to make use of the knowledge of failures and accidents to achieve the possible safety with the lowest possible cost. The concept of risk-based maintenance was developed to inspect the high-risk components usually with greater frequency and thoroughness and to maintain in a greater manner, to achieve tolerable risk criteria. Risk-based maintenance methodology provides a tool for maintenance planning and decision making to reduce the probability of failure of equipment and the consequences of failure. In this paper, the risk analysis and risk-based maintenance methodologies were identified and classified into suitable classes. The factors affecting the quality of risk analysis were identified and analyzed. The applications, input data and output data were studied to understand their functioning and efficiency. The review showed that there is no unique way to perform risk analysis and risk-based maintenance. The use of suitable techniques and methodologies, careful investigation during the risk analysis phase, and its detailed and structured results are necessary to make proper risk-based maintenance decisions.

  16. Modern Micro and Nanoparticle-Based Imaging Techniques

    PubMed Central

    Ryvolova, Marketa; Chomoucka, Jana; Drbohlavova, Jana; Kopel, Pavel; Babula, Petr; Hynek, David; Adam, Vojtech; Eckschlager, Tomas; Hubalek, Jaromir; Stiborova, Marie; Kaiser, Jozef; Kizek, Rene

    2012-01-01

    The requirements for early diagnostics as well as effective treatment of insidious diseases such as cancer constantly increase the pressure on development of efficient and reliable methods for targeted drug/gene delivery as well as imaging of the treatment success/failure. One of the most recent approaches covering both the drug delivery as well as the imaging aspects is benefitting from the unique properties of nanomaterials. Therefore a new field called nanomedicine is attracting continuously growing attention. Nanoparticles, including fluorescent semiconductor nanocrystals (quantum dots) and magnetic nanoparticles, have proven their excellent properties for in vivo imaging techniques in a number of modalities such as magnetic resonance and fluorescence imaging, respectively. In this article, we review the main properties and applications of nanoparticles in various in vitro imaging techniques, including microscopy and/or laser breakdown spectroscopy and in vivo methods such as magnetic resonance imaging and/or fluorescence-based imaging. Moreover the advantages of the drug delivery performed by nanocarriers such as iron oxides, gold, biodegradable polymers, dendrimers, lipid based carriers such as liposomes or micelles are also highlighted. PMID:23202187

  17. A polarization-based Thomson scattering technique for burning plasmas

    NASA Astrophysics Data System (ADS)

    Parke, E.; Mirnov, V. V.; Den Hartog, D. J.

    2014-02-01

    The traditional Thomson scattering diagnostic is based on measurement of the wavelength spectrum of scattered light, where electron temperature measurements are inferred from thermal broadening of the spectrum. At sufficiently high temperatures, especially those predicted for ITER and other burning plasmas, relativistic effects cause a change in the degree of polarization (P) of the scattered light; for fully polarized incident laser light, the scattered light becomes partially polarized. The resulting reduction of polarization is temperature dependent and has been proposed by other authors as a potential alternative to the traditional spectral decomposition technique. Following the previously developed Stokes vector approach, we analytically calculate the degree of polarization for incoherent Thomson scattering. For the first time, we obtain exact results valid for the full range of incident laser polarization states, scattering angles, and electron temperatures. While previous work focused only on linear polarization, we show that circularly polarized incident light optimizes the degree of depolarization for a wide range of temperatures relevant to burning plasmas. We discuss the feasibility of a polarization based Thomson scattering diagnostic for ITER-like plasmas with both linearly and circularly polarized light and compare to the traditional technique.

  18. Robust 3D ATR techniques based on geometric invariants

    NASA Astrophysics Data System (ADS)

    Jeffris, M. A.

    2005-05-01

    Automatic target classification in general is complicated owing to the influence of pose, articulation, and overall viewing geometry on two dimensional SAR data. Three dimensional (3D) data, however, affords the opportunity to develop robust classification techniques independent of those issues. Based on geometric invariants, discriminants can be obtained assuming the target or its phase center lattice can be well modelled by 3D geometries subject to independent rigid body motions, (i.e. reflection, rotation, and translation). Toward this end, we present recent results in the development of a unique 3D classification algorithm. The concepts herein are developed for the full 3D observation space. In particular, we discuss several discrimination metrics based on a target's geometry. As such, they are necessarily invariant to pose and articulation and consequently provide robust classification performance. These geometric-invariant discriminants are concisely expressed as equations unique to a single target structure, or to the spatial interrelationships of multiple structures (this addresses the articulation problem). Once established, these equations can subsequently be used to properly classify the structure or structures at a later time without the need for explicit knowledge of the 3D orientation of the structures within the field of view. We present the mathematical basis behind these classification schemes, discuss implementation concepts, and finish by demonstrating these techniques on synthetic data.

  19. Towards Optical Coherence Tomography-based elastographic evaluation of human cartilage.

    PubMed

    Nebelung, Sven; Brill, Nicolai; Müller, Felix; Tingart, Markus; Pufe, Thomas; Merhof, Dorit; Schmitt, Robert; Jahr, Holger; Truhn, Daniel

    2016-03-01

    Optical Coherence Tomography (OCT) is an imaging technique that allows the surface and subsurface evaluation of semitransparent tissues by generating microscopic cross-sectional images in real time, to millimetre depths and at micrometre resolutions. As the differentiation of cartilage degeneration remains diagnostically challenging to standard imaging modalities, an OCT- and MRI-compatible indentation device for the assessment of cartilage functional properties was developed and validated in the present study. After describing the system design and performing its comprehensive validation, macroscopically intact human cartilage samples (n=5) were indented under control of displacement (δ1=202µm; δ2=405µm; δ3=607µm; δ4=810µm) and simultaneous OCT imaging through a transparent indenter piston in direct contact with the sample; thus, 3-D OCT datasets from surface and subsurface areas were obtained. OCT-based evaluation of loading-induced changes included qualitative assessment of image morphology and signal characteristics. For inter-method cross referencing, the device׳s compatibility with MRI as well as qualitative morphology changes under analogous indentation loading conditions were evaluated by a series of T2 weighted gradient echo sequences. Cartilage thickness measurements were performed using the needle-probe technique prior to OCT and MRI imaging, and subsequently referenced to sample thickness as determined by MRI and histology. Dynamic indentation testing was performed to determine Young׳s modulus for biomechanical reference purposes. Distinct differences in sample thickness as well as corresponding strains were found; however, no significant differences in cartilage thickness were found between the used techniques. Qualitative assessment of OCT and MRI images revealed either distinct or absent sample-specific patterns of morphological changes in relation to indentation loading. For OCT, the tissue area underneath the indenter piston could be

  20. Enhancing the effectiveness of IST through risk-based techniques

    SciTech Connect

    Floyd, S.D.

    1996-12-01

    Current IST requirements were developed mainly through deterministic-based methods. While this approach has resulted in an adequate level of safety and reliability for pumps and valves, insights from probabilistic safety assessments suggest a better safety focus can be achieved at lower costs. That is, some high safety impact pumps and valves are currently not tested under the IST program and should be added, while low safety impact valves could be tested at significantly greater intervals than allowed by the current IST program. The nuclear utility industry, through the Nuclear Energy Institute (NEI), has developed a draft guideline for applying risk-based techniques to focus testing on those pumps and valves with a high safety impact while reducing test frequencies on low safety impact pumps and valves. The guideline is being validated through an industry pilot application program that is being reviewed by the U.S. Nuclear Regulatory Commission. NEI and the ASME maintain a dialogue on the two groups` activities related to risk-based IST. The presenter will provide an overview of the NEI guideline, discuss the methodological approach for applying risk-based technology to IST and provide the status of the industry pilot plant effort.

  1. Characterization of Indentation Response and Stiffness Reduction of Bone using a Continuum Damage Model

    PubMed Central

    Zhang, Jingzhou; Michalenko, Michelle M.; Kuhl, Ellen; Ovaert, Timothy C.

    2009-01-01

    Indentation tests can be used to characterize the mechanical properties of bone at small load/length scales offering the possibility of utilizing very small test specimens, which can be excised using minimally-invasive procedures. In addition, the need for mechanical property data from bone may be a requirement for fundamental multi-scale experiments, changes in nano- and micro-mechanical properties (e.g., as affected by changes in bone mineral density) due to drug therapies, and/or the development of computational models. Load vs. indentation depth data, however, is more complex than those obtained from typical macro-scale experiments, primarily due to the mixed state of stress, and thus interpretation of the data and extraction of mechanical properties is more challenging. Previous studies have shown that cortical bone exhibits a visco-elastic response combined with permanent deformation during indentation tests, and that the load vs. indentation depth response can be simulated using a visco-elastic/plastic material model. The model successfully captures the loading and creep displacement behavior, however, it does not adequately reproduce the unloading response near the end of the unloading cycle, where a pronounced decrease in contact stiffness is observed. It is proposed that the stiffness reduction observed in bone results from an increase in damage; therefore, a plastic-damage model was investigated and shown capable of simulating a typical bone indentation response through an axisymmetric finite element simulation. The plastic-damage model was able to reproduce the full indentation response, especially the reduced stiffness behavior exhibited during the latter stages of unloading. The results suggest that the plastic-damage model is suitable for describing the complex indentation response of bone and may provide further insight into the relationship between model parameters and mechanical/physical properties. PMID:20129418

  2. Carpal tunnel and transverse carpal ligament stiffness with changes in wrist posture and indenter size.

    PubMed

    Holmes, Michael W R; Howarth, Samuel J; Callaghan, Jack P; Keir, Peter J

    2011-11-01

    This study investigated the effects of loading and posture on mechanical properties of the transverse carpal ligament (TCL). Ten fresh-frozen cadaver arms were dissected to expose the TCL and positioned in the load frame of a servo-hydraulic testing machine, equipped with a load cell and custom made indenters. Four cylindrical indenters (5, 10, 20, and 35 mm) loaded the TCL in three wrist postures (30° extension, neutral and 30° flexion). Three loading cycles with a peak force of 50 N were applied at 5 N/s for each condition. The flexed wrist posture had significantly greater TCL stiffness (40.0 ± 3.3 N/mm) than the neutral (35.9 ± 3.5 N/mm, p = 0.045) and extended postures (34.9 ± 2.8 N/mm, p = 0.025). TCL stiffness using the 10 and 20 mm indenters was larger than the 5 mm indenter. Stiffness was greatest with the 20 mm indenter, which had the greatest indenter contact area on the TCL. The 35 mm indenter covered the carpal bones, compressed the carpal tunnel and produced the lowest stiffness. The complexity of the TCL makes it an important part of the carpal tunnel and the mechanical properties found are essential to understanding mechanisms of carpal tunnel syndrome.  Copyright © 2011 Orthopaedic Research Society.

  3. Indentation property and corrosion resistance of electroless nickel-phosphorus coatings deposited on austenitic high-Mn TWIP steel

    NASA Astrophysics Data System (ADS)

    Hamada, A. S.; Sahu, P.; Porter, D. A.

    2015-11-01

    A multilayer coating using electroless nickel-phosphorus (Ni-P) was applied on a twinning-induced plasticity (TWIP) steel containing nominally 25 wt.% Mn and 3 wt.% Al to improve the indentation hardness and corrosion properties. Microindentation tests with two different indenters, namely, a three-sided pyramidal Berkovich indenter and a ball indenter were performed to study the mechanical response, the indentation hardness and elastic modulus of the coatings in conditions: as-plated, and post treated (PT) at 350 °C and 700 °C for 1 h. The deformation morphology underneath the indenters was examined using a scanning laser microscope. The results showed that Ni-P coatings could significantly enhance the surface hardness of the TWIP steel. Significant improvement in the corrosion resistance could be observed in a sulfuric acid solution for the Ni-P coated steel compared to the uncoated substrate TWIP steel.

  4. A New MRI-Based Pediatric Subcortical Segmentation Technique (PSST).

    PubMed

    Loh, Wai Yen; Connelly, Alan; Cheong, Jeanie L Y; Spittle, Alicia J; Chen, Jian; Adamson, Christopher; Ahmadzai, Zohra M; Fam, Lillian Gabra; Rees, Sandra; Lee, Katherine J; Doyle, Lex W; Anderson, Peter J; Thompson, Deanne K

    2016-01-01

    Volumetric and morphometric neuroimaging studies of the basal ganglia and thalamus in pediatric populations have utilized existing automated segmentation tools including FIRST (Functional Magnetic Resonance Imaging of the Brain's Integrated Registration and Segmentation Tool) and FreeSurfer. These segmentation packages, however, are mostly based on adult training data. Given that there are marked differences between the pediatric and adult brain, it is likely an age-specific segmentation technique will produce more accurate segmentation results. In this study, we describe a new automated segmentation technique for analysis of 7-year-old basal ganglia and thalamus, called Pediatric Subcortical Segmentation Technique (PSST). PSST consists of a probabilistic 7-year-old subcortical gray matter atlas (accumbens, caudate, pallidum, putamen and thalamus) combined with a customized segmentation pipeline using existing tools: ANTs (Advanced Normalization Tools) and SPM (Statistical Parametric Mapping). The segmentation accuracy of PSST in 7-year-old data was compared against FIRST and FreeSurfer, relative to manual segmentation as the ground truth, utilizing spatial overlap (Dice's coefficient), volume correlation (intraclass correlation coefficient, ICC) and limits of agreement (Bland-Altman plots). PSST achieved spatial overlap scores ≥90% and ICC scores ≥0.77 when compared with manual segmentation, for all structures except the accumbens. Compared with FIRST and FreeSurfer, PSST showed higher spatial overlap (p FDR  < 0.05) and ICC scores, with less volumetric bias according to Bland-Altman plots. PSST is a customized segmentation pipeline with an age-specific atlas that accurately segments typical and atypical basal ganglia and thalami at age 7 years, and has the potential to be applied to other pediatric datasets.