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Nanoindentation of functionally graded hybrid polymer/metal thin films

Nunes, J.; Piedade, A. P.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
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Hybrid functionally graded coatings (2D-FGC) were deposited by magnetron co-sputtering from poly(tetrafluoroethylene) (PTFE) and AISI 316L stainless steel (316L) targets. The carbon and fluorine content varied from 7.3 to 23.7 at.% and from 0 to 57 at.%, respectively. The surface modification was developed to change the surface of 316L vascular stents in order to improve the biocompatibility of the outmost layer of the metallic biomaterial. In-depth XPS analysis revealed the presence of a graded chemical composition accompanied by the variation of the film structure. These results were complemented by those of transmission electron microscopy (TEM) analysis that highlighted the nanocomposite nature of the coatings. The nanomechanical characterization of 2D-FGC was performed by nanoindentation at several loads on the thin films deposited onto two different steel substrates: 316L and AISI M2. The study allowed establishing 0.7 mN as the load that characterized the coatings without substrate influence. Both hardness and Young modulus decrease with the increase of fluorine content due to the evolution in chemical composition, chemical bonds and structure.

Estudos de dinâmica molecular aplicados ao crescimento epitaxial e nanoindexação; Studie pf molecular dynamics applied to the epitaxial growth and nanoindentation

Zenner Silva Pereira
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 06/03/2009 PT
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Nós apresentamos nesse trabalho dois assuntos relevantes na atualidade:Crescimento de filmes finos metálicos e nanoindentação.Estudamos esses sistemas utilizando dinâmica molecular com potenciais empíricos. Nós mostramos que é possível modelar o crescimento epitaxial utilizando potenciais adequados e uma específica metodologia de deposição. No crescimento de filmes finos estudamos três sistemas utilizando o potencial EAM:Cu/Ag(001),Cu/Au(001) e Pd/Au(001). Para Cu sobre Au e Cu sobre Ag obtivemos resultados de acordo com experimentos anteriores. Enfatizamos que a temperatura e a espessura do filme depositado estão relacionadas com as estruturas apresentadas durante o crescimento. Mostramos que a princípio o filme cresce sob stress numa fase instável bcc, porém ao atingir uma espessura crítica relaxa numa estrutura bct. Então, após a relaxação o filme apresenta um padrão de deformação (stripes). A Relação entre temperatura espessura e porcentagem de átomos nucleados bcc foi quantificada num gráfico. Para o caso Pd sobre Au mostramos que o crescimento resultou num padrão de deformação após atingir 11 camadas. Analisamos as estruturas e indentificamos defeitos tipo "falhas de empilhamento ". Para a modelagem de sistemas semicondutores nós utilizamos o potencial de Terso ..Com um indentador esférico de diamante indentamos uma superfície de silício.Um gráfico de deslocamento do indentador em função da pressão é apresentado. Analisamos o número de coordenação dos átomos de silício quando o indentador atingiu certos valores de pressão.; In this work we present two important and current subjects:Metalic thin .lms and nanoindentation. We studied these systems using molecular dynamics with empirical potentials. We showed that it is possible to model the epitaxial growth using a suitable potential and a specific methodology for deposition.Concerning the growth of thin films...

Desenvolvimento da técnica de identificação de fases por metalografia óptica com nanoindentação em liga inoxidável com efeito de memória de forma; Development of phase identification technique by optic metallography with nanoindentation in stainless alloys with shape memory effect

Juliana Cristina Bueno
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 05/12/2005 PT
Relevância na Pesquisa
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Neste trabalho foi estudada uma liga inoxidável Fe-Mn-Si-Cr-Ni-Co com efeito de memória de forma (EMF) e os objetivos principais foram otimizar a técnica de coloração por ataque químico (color etching) para identificação e análise das fases presentes na microestrutura, o que permitiu a determinação da dureza da martensita-? e da austenita-? através da técnica de nanoindentação. O desenvolvimento deste processo também permitiu a quantificação das fases e e g por microscopia óptica. A técnica de coloração por ataque químico consiste na utilização de reagentes específicos que resultam em uma microestrutura composta por várias colorações, o que permite identificar fases por microscopia óptica. Os resultados de dureza obtidos por nanoindentação foram de 7,0 GPa para a martensita-? e de 3,0 GPa para a austenita-?. Já para a fração volumétrica da martensita-?, os resultados obtidos por microscopia óptica variaram de 33 a 40 % para amostras no estado deformado. Para amostras de tamanho de grão 123 ?m e 3º ciclo de treinamento, os resultados foram coerentes com os obtidos por difração de raios X de trabalhos anteriores para a mesma liga; In this work a Fe-Mn-Si-Cr-Ni-Co stainless alloy with shape memory effect (SME) was studied and the main objectives were to optimize the technique of coloration by chemical attack (color etching) for identification and analysis of the phases in the microstructure...

Nanotechnology and construction: use of nanoindentation measurements to predict macroscale elastic properties of high strength cementitious composites

Silva,W. R. L. da; Němeček,J.; Štemberk,P.
Fonte: IBRACON - Instituto Brasileiro do Concreto Publicador: IBRACON - Instituto Brasileiro do Concreto
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/2012 EN
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This paper aims to present the experimental results involving the use of nanoindentation measurements and prediction of macroscale elastic properties of high performance cementitious composites (HPCC). The elastic properties of HPCC mixture were evaluated at different length scales by nanoindentation (microscale), and elastic moduli and compressive strength tests (macroscale). The nanoindentation results, obtained by grid indentation with subsequent phase deconvolution, were complemented by an independent porosimetry test and inserted into a two-step analytical homogenization scheme to predict the overall macroscale properties. The final results show that the presented method allows a reliable advanced prediction of HPCC elastic properties indicating, thus, that inserting nanotechnology in the concrete industry can be promising, since it would allow the production of a more predictable composite in an easier and less expensive way.

Time-dependent mechanical characterization of poly(2-hydroxyethyl methacrylate) hydrogels using nanoindentation and unconfined compression

Kaufman, Jessica D.; Miller, Gregory J.; Morgan, Elise F.; Klapperich, Catherine M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /05/2008 EN
Relevância na Pesquisa
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Hydrogels pose unique challenges to nanoindentation including sample preparation, control of experimental parameters, and limitations imposed by mechanical testing instruments and data analysis originally intended for harder materials. The artifacts that occur during nanoindentation of hydrated samples have been described, but the material properties obtained from hydrated nanoindentation have not yet been related to the material properties obtained from macroscale testing. To evaluate the best method for correlating results from microscale and macroscale tests of soft materials, nanoindentation and unconfined compression stress-relaxation tests were performed on poly-2-hydroxyethyl methacrylate (pHEMA) hydrogels with a range of cross-linker concentrations. The nanoindentation data were analyzed with the Oliver–Pharr elastic model and the Maxwell–Wiechert (j = 2) viscoelastic model. The unconfined compression data were analyzed with the Maxwell–Wiechert model. This viscoelastic model provided an excellent fit for the stress-relaxation curves from both tests. The time constants from nanoindentation and unconfined compression were significantly different, and we propose that these differences are due to differences in equilibration time between the microscale and macroscale experiments and in sample geometry. The Maxwell–Wiechert equilibrium modulus provided the best agreement between nanoindentation and unconfined compression. Also...

Direct comparison of nanoindentation and macroscopic measurements of bone viscoelasticity

Shepherd, Tara N.; Zhang, Jingzhou; Ovaert, Timothy C.; Roeder, Ryan K.; Niebur, Glen L.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
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Nanoindentation has become a standard method for measuring mechanical properties of bone, especially within microstructural units such as individual osteons or trabeculae. The use of nanoindentation to measure elastic properties has been thoroughly studied and validated. However, it is also possible to assess time dependent properties of bone by nanoindentation. The goal of this study was to compare time dependent mechanical properties of bone measured at the macroscopic level with those measured by nanoindentation. Twelve samples were prepared from the posterior distal femoral cortex of young cows. Initially, dogbone samples were prepared and subjected to torsional stress relaxation in a saline bath at 37 C. A 5 mm thick disk was subsequently sectioned from the gage length, and subjected to nanoindentation. Nanoindentation was performed on hydrated samples using a standard protocol with 20 indents performed in 20 different osteons in each sample. Creep and stress relaxation data were fit to a Burgers four parameter rheological model, a five parameter generalized Maxwell model, and a three parameter standard linear solid. For Burgers viscoelastic model, the time constants measured by nanoindentation and torsion were weakly negatively correlated...

The Use of Polyacrylamide Gels for Mechanical Calibration of Cartilage – A Combined Nanoindentation and Unconfined Compression Study

Li, Cheng; Allen, Jessica; Alliston, Tamara; Pruitt, Lisa A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
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This study investigates polyacrylamide (PA) gel as a calibration material to measure the nanomechanical compressive modulus of cartilage using nanoindentation. Both nanoindentation and unconfined compression testing were performed on PA gel and porcine rib cartilage. The equilibrium moduli measured by the two methods were discernable. Nanoindentation has the advantage of distinguishing between spatially dependent constituent properties that affect tissue mechanical function in heterogeneous and hierarchically structured tissues such as cartilage. Both sets of measurements exhibited similar positive correlation with increasing gel crosslinker concentration. The compressive modulus measurements from compression in the PA gels ranged from 300 kPa—1.4 MPa, whereas those from nanoindentation ranged from 100 kPa—1.1MPa. Using this data, a method for relating nanoindentation measurements to conventional mechanical property measurements is presented for porcine rib cartilage. It is shown that based on this relationship, the local tissue modulus as measured from nanoindentation (1.1—1.4 MPa) was able to predict the overall global modulus of the same sample of rib cartilage (2.2 MPa), as confirmed by experimental measurements from unconfined compression. This study supports the use of nanoindentation for the local characterization of cartilage tissues and may be applied to other soft tissues and constructs.

Mechanical Characterization of the Heat Affected Zone of Gold Wirebonds Using Nanoindentation

Shah, M.; Zeng, K.; Tay, A.A.O.; Suresh, Subra
Fonte: MIT - Massachusetts Institute of Technology Publicador: MIT - Massachusetts Institute of Technology
Tipo: Artigo de Revista Científica Formato: 818000 bytes; application/pdf
EN_US
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With increasing miniaturization in microelectronics the wirebonds used in IC packages are witnessing a thrust towards fine pitch wirebonding. To have a precise control over loop height of the wirebond for fine pitch wirebonding, it is imperative to do mechanical characterization of the wirebond. The present work studies the mechanical properties of gold wire and wirebond using nanoindentation. The wirebond specimen surface was planarized using mechanical polishing. The loop height of the gold wirebond is directly proportional to the length of the heat affected zone (HAZ) above the ball of gold wirebond. Metallographic preparation of gold wirebond cross section reveals the presence of undesirable coarse grain structure in HAZ due to recrystallization and grain growth in the gold wire adjacent to the ball. The recrystallization temperature of our gold wire was found using D.S.C. to be 340.66°C. The doping elements present in the gold wire used, were identified using TOF-SIMS. Nanoindentation of the gold wire was done at different maximum loads to observe the hardness variation with load. The nanoindentation of gold wirebond has confirmed a v-shaped hardness profile in the HAZ. The hardness minima for the particular gold wire used with a ball size ratio of 2.4 was observed at distance of 160-170 µm from the neck of the ball. The elastic modulus was found to vary randomly and to be independent of the microstructure in the wirebond. A yield stress profile based on empirical hardness-yield strength correlation has been predicted for the gold wirebond.; Singapore-MIT Alliance (SMA)

Nanoindentation of Silicon and Germanium

Kiran, M.S.R.N.; Haberl, B.; Bradby, J.E.; Williams, J.S.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Nanoindentation of silicon and germanium is of interest not only for the measurement of their mechanical properties but more importantly for the fact that they undergo a series of phase transformations under applied pressure. Indeed, after complete pressure release, the material does not return to the starting diamond cubic phase, but several metastable phases are possible, depending on the indentation conditions. In silicon, both crystalline (diamond cubic) and amorphous phases undergo a phase transformation to a dense metallic phase at around 11 GPa, a deformation process that defines the hardness of these materials. On pressure release, either a mixture of a rhombohedral (r8) phase and a body-centered cubic (bc8) phase or a pressure-induced amorphous silicon structure results. The mixed r8/bc8 phase is stable to 200 °C and has been shown to have properties of a narrow bandgap semiconductor and can be doped both n- and p-type. In germanium, the deformation processes under indentation are more complex with both plastic deformation by slip and twinning as well as phase transformation observed for diamond cubic germanium, depending on the indentation conditions. Amorphous germanium is easier to phase transform since slip-induced processes are avoided. Both crystalline and amorphous forms of germanium can be transformed to a high-density metallic phase under pressure...

Micromechanical properties of human trabecular bone: A hierarchical investigation using nanoindentation

Norman, J.; Shapter, J.; Short, K.; Smith, L.; Fazzalari, N.
Fonte: John Wiley & Sons, Inc. Publicador: John Wiley & Sons, Inc.
Tipo: Artigo de Revista Científica
Publicado em //2008 EN
Relevância na Pesquisa
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The ability to assess the risk of fracture, evaluate new therapies, predict implant success and assess the influence of bone remodeling disorders requires specific measurement of local bone micromechanical properties. Nanoindentation is an established tool for assessing the micromechanical properties of hard biological tissues. In this study, elastic modulus and hardness were quantified using nanoindentation for human trabecular bone from the intertrochanteric region of the proximal femur. These properties were demonstrated to be heterogeneous and highly correlated at the intraspicule, interspicule, and interspecimen levels. The results of this study have important implications for current understanding of structure-function relationships throughout the trabecular bone structural hierarchy.; Jonathan Norman, Joe G. Shapter, Ken Short, Lachlan J. Smith and Nicola L. Fazzalari; Copyright © 2008 Wiley Periodicals, Inc., A Wiley Company

Finite element studies of mechanical property testing by nanoindentation methods

Bolshakov, Alexei
Fonte: Universidade Rice Publicador: Universidade Rice
Tipo: Thesis; Text Formato: 134 p.; application/pdf
ENG
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Nanoindentation is a widely recognized method for characterizing the mechanical properties of thin films and small volumes. This dissertation reports the results of finite element analyses of elastic and elastic-plastic indentation by a rigid cone aimed at improving methods for measuring of contact area, hardness and elastic modulus by nanoindentation methods. Analytical and finite element results are presented which show that corrections to Sneddon's solution are needed to properly describe elastic indentation by a cone. Since most nanoindentation methods are based on Sneddon's solution, these corrections have important consequences for making accurate mechanical property measurements. Elastic-plastic finite element simulations are presented which show that pile-up can significantly affect the accuracy of nanoindentation measurements. It is shown that an experimentally measurable parameter, the ratio of the final depth to the total depth of indentation, is useful in determining the amount of pile-up in the material. An investigation of plastic zones and stresses in indented materials reveals important correlations between them and the nanoindentation behavior of the material. Implications of these results for indentation cracking are also discussed. A long standing problem in nanoindentation is why load-displacement data obtained during unloading fit well to a power relation with a power law exponents in the range 1.25-1.50. Finite element simulations combined with elastic contact analyses are presented which provide a simple explanation for this behavior. General recommendations are made for improving of nanoindentation methods for measuring mechanical properties.

Annealing of nanoindentation-induced high pressure crystalline phases created in crystalline and amorphous silicon

Ruffell, Simon; Haberl, Bianca; Koenig, S; Bradby, Jodie; Williams, James S
Fonte: American Institute of Physics Publicador: American Institute of Physics
Tipo: Artigo de Revista Científica Formato: 8 pages
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Thermally induced phase transformation of Si-III/Si-XII zones formed by nanoindentation has been studied during low temperature (200

Nanoindentation-induced deformation mechanisms in germanium

Oliver, David John
Fonte: Universidade Nacional da Austrália Publicador: Universidade Nacional da Austrália
Tipo: Thesis (PhD); Doctor of Philosophy (PhD)
EN
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Germanium (Ge), a Group IV elemental semiconductor, is an important electronic material used in many technological applications. Although it is frequently considered to be a classic brittle material, deforming elastically under mechanical stress up to the point of fracture, in practise this is not the case. Instead, under indentation with a sharp tip, plastic deformation plays a dominant role and other deformation mechanisms may be activated. In the literature there is some controversy as to what is the dominant indentation response of Ge at room temperature, shear-induced plasticity or high-pressure phase transformation. This thesis addresses that controversy by investigating the indentation response of germanium over a range of loading regimes and sample preparation conditions. A diverse range of responses is observed, shedding light on the behaviour of Ge at nano- and microscale contact events. A wide range of techniques has been employed in this work to investigate the sharp contact response of Ge. Instrumented nanoindentation with a sharp diamond tip has been used to introduce mechanical damage at small scales. Features of the indentation forcedisplacement(P-h) curve can be linked to changes induced in the material. A number of techniques have been applied to characterise the damage produced...

A contact area function for Berkovich nanoindentation : Application to hardness determination of a TiHfCN thin film

CHICOT, D.; YETNA N'JOCK, M.; PUCHI-CABRERA, E.S.; IOST, Alain; STAIA, M.H.; LOUIS, G.; BOUSCARRAT, G.; AUMAITRE, R.
Fonte: Elsevier Publicador: Elsevier
EN
Relevância na Pesquisa
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In nanoindentation, especially at very low indenter displacements, the indenter/material contact area must be defined in the best possible way in order to accurately determine the mechanical properties of the material. One of the best methodologies for the computation of the contact area has been proposed by Oliver and Pharr [W.C.Oliver, G.M.Pharr, J.Mater. Res. 7 (1992) 1564], which involves a complex phenomenological area function. Unfortunately, this formulation is only valid when the continuous stiffness measurement mode is employed. For other conditions of indentation, different contact area functions, which take into account the effective truncation length or the radius of the rounded indentertip, as well as some fitting parameters, have been proposed. However, most of these functions require a calibration procedure due to the presence of such parameters. To avoid such a calibration, in the present communication a contact area function only related to the truncation length representative of the indenter tip defect, which can be previously estimated with high resolution microscopy, has been proposed. This model allows the determination of consistent indentation data from indenter displacements of only few nanometers indepth. When this proposed contact area function is applied to the mechanical characterization of a TiHfCN film of 2.6 μm in thickness deposited onto a tool steel substrate...

The effect of laser excitation on the Raman microspectroscopy of nanoindentation-induced silicon phase transformation

Mahon, Denise C; Mahon, Peter; Creagh, Dudley C
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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It is well established that silicon undergoes a series of phase transformations when subjected to the pressure of nanoindentation. Phase transformations in silicon are studied using diamond anvil apparatus. The effect of the high pressure is an increase i

Nanoindentation-induced phase transformation in crystalline silicon and relaxed amorphous silicon

Rao, Rui; Bradby, Jodie; Ruffell, Simon; Williams, James
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
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Nanoindentation-induced phase transformation in both crystalline silicon (c-Si) and relaxed amorphous silicon (a-Si) have been studied. A series of nanoindentations were made with a sharp diamond Berkovich tip. During nanoindentations, maximum loads were

Nanoindentation of Si Nanocrystals in SiO2

Pok, W; Bradby, Jodie; Elliman, Robert
Fonte: Institute of Electrical and Electronics Engineers (IEEE Inc) Publicador: Institute of Electrical and Electronics Engineers (IEEE Inc)
Tipo: Conference paper
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Nanoindentation is used to investigate the effects of mechanical deformation on systems of silicon nanocrystals (Sinc) embedded in SiO 2. The process is found to introduce non-radiative defects to the crystals which quench their luminescence in the locali

The characterisation of ferroelectric thin films using nanoindentation; Caracterización de láminas delgadas ferroeléctricas por nanoidentación

Algueró, M.; Calzada, M. L.; Pardo, Lorena; Bushby, A. J.; Cheng, B. L.; Guiu, F.; Reece, M. J.
Fonte: Sociedad Española de Cerámica y Vidrio Publicador: Sociedad Española de Cerámica y Vidrio
Tipo: Artículo Formato: 343463 bytes; application/pdf
ENG
Relevância na Pesquisa
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[EN] Nanoindentation techniques have been used to determine the mechanical properties of two well characterised Pb0.88La0.08TiO3 ferroelectric thin films which have been shown to be promising for MEMs applications. Aceramic with the same nominal composition and the substrate material were also tested as an aid in the interpretation of results. Test routines have been developed using the spherical indentation geometry to distinguish the elastic and permanent deformation of the materials. Mechanical data for different layers in the heterostructure could be determined by using indenters with different radii. The technique provides information on the elastic modulus of the film, the onset and nature of permanent deformation, film delamination and the effects of porosity and residual stress. These techniques open the possibility to characterise fully the mechanical response of a microdevice.; [ES] Se han usado técnicas de nanoindentación para determinar las propiedades mecánicas de dos láminas delgadas ferroeléctricas de Pb0.88La0.08TiO3 bien caracterizadas y que se han considerado prometedoras para aplicaciones MEMs. También se han realizado medidas en una cerámica con la misma composición nominal y en el sustrato de las láminas como ayuda para la interpretación de los resultados. Se han desarrollado rutinas usando la geometría de indentación con esfera para distinguir las deformaciones elástica y permanente del material. Podría ser posible obtener parámetros mecánicos de las distintas capas de la heteroestructura lámina sustrato mediante el uso de indentadores con radio distinto. La técnica proporciona información sobre el modulo elástico de la lámina...

Nanoindentation Under Dynamic Conditions

Wheeler, Jeffrey M
Fonte: University of Cambridge; Department of Materials Science and Metallurgy Publicador: University of Cambridge; Department of Materials Science and Metallurgy
Tipo: Thesis; doctoral; PhD
EN
Relevância na Pesquisa
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Nanoindentation has emerged as a leading technique for the investigation of mechanical properties on small volumes of material. Extensive progress has been made in the last 20 years in refining the nstrumentation of nanoindentation systems and in analysis of the resulting data. Recent development has enabled investigation of materials under several dynamic conditions. The palladium-hydrogen system has a large miscibility gap, where the palladium lattice rapidly expands to form a hydrogen-rich ? phase upon hydrogenation. Nanoindentation was used to investigate the mechanical effects of these transformations on foils of palladium. Study of palladium foils, which had been cycled through hydrogenation and dehydrogenation, allowed the extent of the transformed region to be determined. Unstable palladium foils, which had been hydrogenated and were subject to dynamic hydrogen loss, displayed significant hardening in the regions which were not expected to have transformed. The reason for this remains unclear. Impact indentation, where the indenter encounters the sample at relatively high speeds, can be used to probe the strain rate dependence of materials. By combining impact indentation and elevated temperature indentation, the strain rate dependence of the superelasticity of nickel-titanium was probed over a range of temperatures. Similar trends in elastic energy ratios with temperature were observed with the largest elastic proportions occurring at the Austenite finish transformation temperature. Multiple impact and scratch indentation are two modes of indentation which are thought to approximate erosive and abrasive wear mechanisms...

Molecular dynamics simulation of nanoindentation in Cr, Al layers and Al/Cr bilayers, using a hard spherical nanoindenter

Amaya-Roncancio,Sebastián; Restrepo-Parra,Elisabeth; Devia-Narvaez,Diana Marcela; Arias- Mateus,Diego Fernando; Gómez-Hermida,Mónica María
Fonte: DYNA Publicador: DYNA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2014 EN
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Three-dimensional molecular dynamics (MD) simulations of a nanoindentation technique using the hard sphere method for Cr (bcc) and Al (fcc) thin films and (Cr/Al)n (n=1,2) systems were carried out. For the model implementation, Morse interatomic potential was used for describing the single crystal interaction and the contact between Cr and Al structures. On the other hand, fixed boundary conditions were used and the repulsive radial potential was employed for modeling the spherical tip, and ideal mechanical properties at 0 K were obtained by simulating load-unload curves. Bilayers presented higher hardness and Young's modulus than Cr and Al layers. Moreover, the region of atoms movement after the unload process shows a continuous parabolic boundary for Al and Cr layers and a discontinuous boundary for the bilayers caused by the interfaces.