bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multi-Scale Modeling of Human Cortical Bone: Aging and Failure Studies
Authors: Budyn Elisa , Hoc Thierry 
Published: June 2019

ABSTRACTA multi-scale analysis for unit cells of human cortical bone is presented. Two studies are conducted: the first study concerns the effect of aging over the structural and mechanical properties of human cortical bone; the second study is devoted to the failure mechanism and the development of cracks in cortical bone under various loading conditions. Experiments are conducted on human specimen of different ages in order to measure relevant geometrical and mechanical parameters and obtain microscopic data that will be injected into finite element models. First a continuum FEM model will compute macroscopic information that will be validated through comparison with the experimental measurements. For the failure mechanism study, an XFEM model will be developed in order to allow the growth of multiple cracks until complete failure of the cell. An elastic-damage criterion will be used in order to place the initial cracks in maximum strain locations. To follow the global response of the cell, the stress intensity factors are computed at each crack tip and a load parameter is adjusted so that the stress intensity factors remain at the critical value. In the case of competitive crack tips, a stability analysis is performed by computing the second derivative of the potential energy for each crack. Fatigue loading will be also investigated. The discretization utilizes the eXtended Finite Element Method and requires no remeshing as the cracks grow. The crack geometries are arbitrary with respect to the mesh, and are described by a vector level set. Special boundary conditions and the algorithm for detecting crack bridging and crack entering Haversian canals which allows the cracks to grow until maximum failure and/or percolation is presented.
Directed Mineralization on Polyelectrolyte Multilayer Films
Authors: Advincula Maria C. , Patel Pritesh A. , Mather Patrick T. , Underhill Daniel , Huey Bryan D. , Goldberg A. Jon 
Published: June 2019

ABSTRACTSilica formation aided by polypeptides is being actively investigated for a wide range of applications including biomaterials synthesis, ceramics and controlled release systems. We envision that biocatalyzed mineralization could have application as a dental material where in situ formation of mineral layers could provide needed wear-resistance or sealing capability. The approach would be more clinically relevant, if a polymer host could be used to carry and specifically position the biocatalyst on a surface and additionally maintain the catalyst activity.Accordingly, we studied the influence of simple catalytic polypeptides on silica formation from prehydrolyzed alkoxide precursor solutions onto a surface. The polypeptides were localized on to the surface as multilayered thin films using the layer-by-layer (LbL) assembly of polyelectrolytes. Polylysine (PLL) or another biocatalytic polycation, poly(ethyleneimine) (PEI), was adsorbed layer-by-layer up to 10 bilayers on silicon wafers in combination with a negatively charged polyelectrolyte polymer host, poly(sodium-4-styrene sulfonate) (PSS) to prepare PEI-(PLL/PSS)10, PEI-(PEI/PSS)10 and PEI-(PEI/PSS/PLL/PSS)10 multilayer films. Pre-hydrolyzed alkoxysilane solutions were placed dropwise on the catalytic films for silicification. Additionally, the effects of precursor concentration, solvent and drying were evaluated. The morphology, roughness and contact mechanical stiffness of the formed silica were investigated using optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM).The resulting silica morphology was plate-like or spherical, and porous with average particle size depending on the catalyst and its positions on the surface. Without a catalyst the silica formed over longer times with a fine, gel-like appearance. The morphology of silica produced on the substrate was different from that of particles catalyzed in solution with the same polypeptide catalyst. Additionally, it was found that the homogeneity of PEI-(PLL/PSS)10 films increased with drying temperature, silica precursor concentration and the presence of ethanol. The contact mechanical stiffness of the silica particles (40 N/m) catalyzed from PEI-(PLL/PSS)10 films was lower than the non-silicified areas (48 N/m) suggesting that regions of the silica were amorphous and hydrated. These results show that a polypeptide applied to a surface as a multiple layer with an oppositely charged polymer host (PSS) maintains its activity for silicification. The generally coherent nature of the mineral coating suggests its potential for enhancing critical restorative dental interfaces; however properties like porosity, hydration and their effect on hardness and permeability will need further study.
Effects of Volume Fraction and Composition on the Rheological Properties of Polyacrylic Acid/Polyacrylamide Hydrogels
Authors: Baker Bryan , Murff Rebecca , Milam Valeria T. 
Published: June 2019

ABSTRACTPolyacrylamide-based hydrogels are popular materials that have been extensively studied for their applications in the field of biomaterials due to their permeability and biological compatibility. A major limitation of this polymeric material, however, in biological applications stems from their limited mechanical stiffness. The current study examines the mechanical properties of polyacrylamide-polyacrylic acid-based hydrogels at varying volume fractions and compositions using oscillatory rheology. For a fixed chemical cross-linker concentration, an increase in the volume fraction of hydrogel resulted in an increase in the shear elastic modulus of the hydrogel. Additionally, varying the relative ratio of polyacrylamide to polyacrylic acid resulted in modest changes in the shear elastic modulus.
Mechanical Properties Evolution of Polydimethylsiloxane During Crosslinking Process
Authors: Zhao Yi , Zhang Xin 
Published: June 2019

ABSTRACTThis paper reports mechanical properties evolution of polydimethylsiloxane (PDMS) during the crosslinking process. In this work, PDMS crosslinking was induced by mixing base prepolymer and curing agent at certain ratios. The liquid prepolymer was spun coated on a silicon wafer, and the curvature change of the wafer was measured continuously using a curvature measurement system. The relationship between the curvature change and typical mechanical properties was investigated using a bilayer model; and the evolution of the properties was derived, as a function of operational parameters. This work is expected to help better understanding of the crosslinking process and provide practical strategies for controlling the mechanical behavior of the resulting polymer structures, especially those for mechanical sensing applications.
Structural Evolution and Mechanical Behavior of Bio-inspired Oxide Films on Self-Assembled Organic Layers
Authors: Zhang Guangneng , Cho Junghyun 
Published: June 2019

ABSTRACTA bio-inspired approach is employed to deposit the oxide films on the substrates coated with self-assembled organic layers. Particularly, titania and zirconia films are grown in aqueous precursor solutions at near room temperatures. This process, directed by the nanoscale organic template, mimics the controlled nucleation and growth of the biominerals such as bones and teeth. Multiscale structural evolution resulting from initial bulk nucleation, nanoparticle aggregation, and ultimate film formation are systematically studied by adjusting the precursor solution conditions. Dynamic light scattering (DLS) is utilized to characterize initial nanoparticles and their associated aggregates/clusters formed in situ in solution. Corresponding nano- and microstructure developments of the oxide films are investigated through high-resolution transmission electron microscope (TEM) and scanning electron microscope (SEM). In addition, mechanical performance is evaluated with the aid of a dynamic nanoindentation testing to establish the structure-property relationships of the bio-inspired oxide films. The goal of this study is to have a capability to tailor microstructures and mechanical behaviors by identifying the controlling mechanisms responsible for nucleation and growth of such oxide films.
Strength of Calcium Phosphate Cements
Authors: Veresov Alexander , Stepuk Alexander , Kuznetsov Alexander , Putlayev Valery , Kuznetsov Vladimir 
Published: June 2019

ABSTRACTCalcium phosphates materials are widely used to treat the bones defects. HA bioceramics traditionally used in medicine has some serious disadvantage – week resorbility properties. Calcium phosphate cements seems to be promising compounds to replace conventional ceramics. High macroporosity of hardened materials leads to low mechanical strength. The main objective of present work was a development of new chemically bonded materials based on α-tricalcium phosphate (α-TCP) and hydroxylapatite phase. The main idea was to combine the benefit of ceramics technology (compacting of powders to reduce the starting macroporosity) to improve the materials strength with advantages of cement product (small resorbable calcium phosphate particles). α-Ca3(PO4)2-based biocements were synthesized with initial composition of HA, α- and β-TCP containing 80% wt. of TCP phase. The rate of α-TCP transformation to apatite phase during setting reaction was about 20% wt. in case of cylindrical samples (8mm × 8 mm) at 60°C for 50 hours. The fabricated TCP – bio-composites demonstrated high mechanical strength and stiffness characteristic. Most efficient results were achieved with chitosan biopolymer containing samples (σc = 120 MPa).
What is Behind the Inverse Hall-Petch Behavior in Nanocrystalline Materials?
Authors: Carlton Christopher , Ferreira P. J. 
Published: June 2019

AbstractAn inverse Hall-Petch effect has been observed for nanocrystalline materials by a large number of researchers. This result implies that nanocrystalline materials get softer as grain size is reduced below a critical value. Postulated explanations for this behavior include dislocation based mechanisms and diffusion based mechanisms. In this paper, we report an explanation for the inverse Hall-Petch effect based on the statistical absorption of dislocations by grain boundaries, showing that the yield strength is both dependent on strain rate and temperature, and that it deviates from the Hall-Petch relationship at a critical grain size.
Atomic Events at the Onset of Plasticity in the Au(001) Surface
Authors: Carrasco Esther , Rodríguez de la Fuente Oscar , Rojo Juan Manuel 
Published: June 2019

AbstractAtomic defects, in the form of dislocation configurations, are identified following nanoindentation of Au(001) surfaces. Combined STM, dislocation theory and atomistic simulations fully characterise these defects and describe their motion. By comparing with AFM data the emission of those defects are correlated with the incipient stages of plasticity, the latter recognised from force vs penetration curves. The size distribution, the spatial pattern and the motion of these dislocations under stress have also been investigated and explained in terms of the theory of dislocations in a continuum.
Thermo-Mechanical and Size-Dependent Behavior of Freestanding AuAg and Nanoporous-Au Beams
Authors: Seker Erkin , Zhu Jianzhong , Bart-Smith Hilary , Begley Matthew , Kelly Robert , Zangari Giovanni , Reed Michael L. 
Published: June 2019

AbstractNanoporous gold (np-Au), produced by selectively removing silver from an AuAg alloy, has recently gained considerable attention from the scientific community. Biocompatibility, chemical inertness, increased surface area, relatively low elastic modulus, and ease of synthesis make np-Au an important candidate for biomedical, catalytic, and MEMS applications. Np-Au films also offer substantial ground for theoretical and empirical research, including mechanical characterization, fracture mechanics, and porosity evolution. Even though a significant effort has been directed towards exploring blanket np-Au films (i.e., foils, strips), to our knowledge no work has been done on fabricating or investigating freestanding np-Au structures (i.e., micro-beams, cantilevers). Recently we have developed techniques to create freestanding clamped np-Au beams with widths from 5 to 40 microns and lengths from 20 to 500 microns. The percentage yield was more than 97% for 2880 beams on a 2-inch wafer. A critical step in the fabrication process, necessary to prevent tensile failure of the beams during dealloying, is a thermal heat treatment prior to dealloying. The study of thermal treatment of beams at temperatures between 100°C and 600°C prior to dealloying revealed three distinct beam behavior regimes, namely quasi-elastic buckling, plastic buckling, and material interdiffusion. This paper will present the preliminary results from thermal treatment experiments particularly focusing on how beam dimensions affect percentage yield and beam fracture.
Investigation of the Bi-linear Behavior of the Indentation Size Effects in Single and Polycrystalline Ni Thin Films/MEMS Thin Films
Authors: Elmustafa Abdelmageed A. , Lou J. , Zong Z. , Soboyejo W. O. 
Published: June 2019

AbstractThis paper presents the results of an experimental study of the indentation size effects at the nano, sub-micron, and micron-scales. The size dependence of the indentation hardness in these regimes is shown to exhibit a bi-linear behavior when the data are fitted to Taylor Dislocation Hardening (TDH) model. The deformation in indent sizes corresponding to the onset of the transition from micro and deep nano indents to shallow nano indents represent dislocation substructures at the sub-micron and micron scales whereas the deformation at the nano-scale represents dislocation source-limited behavior.
Size Effects in LiF Micron-Scale Single Crystals of Low Dislocation Density
Authors: Nadgorny Edward M. , Dimiduk Dennis M. , Uchic Michael D. 
Published: June 2019

AbstractThis study examines the deformation response of 20, 5, and 1 micron diameter samples fabricated by FIB-milling from bulk ultrapure LiF single crystals. The bulk crystals have a very low initial dislocation density as revealed by an etch-pit technique. Two types of <001> microsamples were deformed preferentially by single slip when compressed inside a nanoindentation system. Similar to previously studied FCC-derivative metals, LiF microsamples demonstrate dramatic strengthening achieving the engineering flow stress σ ≈ 650 MPa in 1-μm samples. The stress-diameter dependence obeys a power law, σ ∼ D−m, where m ≈ 0.8. Stochastic variation of flow stress, fast intermittent deformation events (“avalanches”) and highly localized slip bands after avalanches - all characteristic of size effects in metals, are also observed in LiF. Possible dislocation mechanisms of the observed size effects are discussed.
Size Effects on Yield Instabilities in Nickel
Authors: Cordill Megan J , Moody Neville R , Gerberich William W 
Published: June 2019

AbstractDislocation events are seen as excursions, or pop-in events, in the load-displacement trace of nanoindentation experiments. When indenting single crystal metals these events occur frequently during quasi-static and dynamic loading. A single crystal of Ni (111) has been indented quasi-statically using three different loading rates (10, 100, and 1000 μN/s) as well as with three different radii diamond indenter tips (1000 nm cone, 300 nm Berkovich, and 50 nm cube corner) to examine the occurrences of excursions. As expected, excursions at higher loads have larger displacements, and that initial loading follows Hertzian behavior up to the point of yield. Also, as the tip size is reduced the excursion loads are reduced. The excursion events depend mostly on the statistical distribution of surface sources and substructure dislocation arrangements.
Mechanical Behavior of Nanocrystalline Cu Alloy Thin Film on Elastomer Substrates Under Constant Uniaxial Tensile Strain
Authors: Inoue Junya , Fujii Yousuke , Koseki Toshihiko 
Published: June 2019

AbstractIn this study, mechanical behavior of nanocrystalline Cu alloy thin films under constant tensile strain is studied, by taking advantage of the enhanced resistance to strain localization of a thin metal film on a thick elastomer with appropriate Young's modulus. Cu and Cu alloy thin films with a thickness of 100nm were deposited on heat-resistant polyimide substrates. On the top of the Cu alloy layer, Ta thin film was further deposited to suppress the surface diffusion of Cu alloy. A uniform uniaxial tensile strain was induced to the films by applying a constant radius of curvature to the polyimide substrate. Isothermal deformation and rupture modes of the films were studied by keeping the samples at various elevated temperatures. Microstructural observation was carried out using SEM, TEM, STEM, and confocal violet laser microscope at several stages of deformation. From the observation, the evolution of damage in the sub-critical strain level and the effect of alloying elements are discussed.
Phase Transformations Induced by Grinding: What is Revealed by Molecular Materials
Authors: Descamps Marc , Willart Jean François , DUDOGNON Emeline , LEFORT Ronan , DESPREZ Sylvain , CARON Vincent 
Published: June 2019

AbstractThe purpose of this paper is to show some examples of phase transformations induced by grinding molecular materials. These materials are considered because they are extremely sensitive to external disturbances and are generally very good glass formers. This allows investigating more easily a broad range of the parameters which are open to influence the nature of the end product namely the temperature and intensity of grinding. Such an investigation has also a practical interest in pharmaceutical science. It is shown that the position of the grinding temperature with regard to the glass transition temperature of the compound is a key parameter. Comparison of the effects of temperature and intensity of grinding demonstrates that the driven material concept offers a framework to rationalize all the observed transformations.
Precipitation Sequence in Mg-Zn-Sn Based Alloys
Authors: Gorny Anton , Katsman Alexander , Shepelev Dmitry , Bamberger Menahem 
Published: June 2019

AbstractExtensive experimental research work has been carried out in order to develop an Mg-Zn-Sn based creep resistant alloy. It was found that the addition of Y improves the structural stability of this alloy. The main goal of this work was to investigate precipitation sequence in Mg-Zn-Sn-Y alloys during aging at different temperatures. In order to elucidate the sequence of phase formation, XRD, TEM, SEM and EDS analyses were applied. It was found that, firstly, an hcp-MgZn2 phase nucleates homogeneously, and grows in the form of needles having coherent interphase boundaries with Mg-matrix. High-resolution TEM images in combination with Fourier transformed images reveal a topotaxial orientation relationship which is given by {110}MgZn2 <100>MgZn2∥(002)α-Mg<110>α-Mg. The cubic fcc Mg2Sn-phase nucleates heterogeneously, mainly at the tips of MgZn2-needles when the needle's width reaches a certain critical value. The orientation of Mg2Sn-precipitates is usually perpendicular to the one of MgZn2-needles. Two-phase T-like particles are very typical of alloys aged for 1-16 days at 175-225C. The width/length ratio of MgZn2-needles inside T-like particles differs substantially from the one found in single needles. The elastic/surface energy balance of needles and its influence on the morphology and coarsening behaviour has been analyzed.
Texture Evolution of Lithium Fluoride Thin Films by Nucleation
Authors: Kim Hakkwan , King Alexander H. 
Published: June 2019

AbstractWe have used a transmission electron microscope (TEM)-based method to extract grain size information for 〈111〉 surface normal grains in lithium fluoride (LiF) thin films, and applied this to analyze textures as a function of substrate temperature and annealing time. The size distributions of grains diffracting into the (111)+(200) and (220) rings were measured separately using dark field (DF) TEM images. From these data, we deduce the distribution of 〈111〉 surface normal grain sizes based on the assumption that only 3 principal textures (100), (110) and (111) exist in films. The (111) texture formation was also observed by x-ray diffraction (XRD). For all deposition and annealing conditions, the grain size data can be matched to lognormal distributions within an acceptable error, but at longer annealing times the distribution becomes bimodal. A novel feature of the LiF films is that the (111) texture component strengthens with annealing and substrate temperature, through the nucleation of new grains rather than the growth of existing ones.
Precipitation of Zr2Cu Stable Crystalline Phase from Zr70Cu27.5Rh2.5 Amorphous Alloy
Authors: Cushman David , Saida Junji , Li Chunfei 
Published: June 2019

AbstractThe crystallization process of Zr70Cu27.5Rh2.5 metallic glass was studied with Transmission Electron Microscopy (TEM). In contrast to previous studies where the precipitation of metastable icosahedral quasicrystalline (IQC) particles is of the interest, we designed the present work to focus on the nucleation process of the stable Zr2Cu crystalline phase. It has been found that the alloy consists of IQC particles distributed in amorphous matrix prior to the precipitation of the Zr2Cu stable crystalline phase and Zr2Cu nucleates from the amorphous matrix. The encounter of the IQC phase with Zr2Cu transforms the former into the latter so quickly that no interface between them was found in the present experiment. These insights provide the basis for a discussion of the stability of metallic glasses and the IQC particles.
Strengthening Mechanisms for Fe-Al-based Alloys with Increased Creep Resistance at High Temperatures
Authors: Palm Martin , Krein Ronny , Milenkovic Srdjan , Sauthoff Gerhard , Risanti Doty , Stallybrass Charles , Schneider André 
Published: June 2019

AbstractLack of strength, in particular creep resistance, has been considered as the principal shortcoming of Fe-Al-based alloys for long which prevented their use for structural applications at high temperatures. Only recently it has been realized that various strengthening mechanisms are available by which Fe-Al-based alloys can be sufficiently strengthened for applications at high temperatures. From the recent studies at the Max-Planck-Institut für Eisenforschung GmbH (MPIE) examples of applying different strengthening mechanisms are presented by which Fe-Al-based alloys with considerable creep resistance have been obtained.
Strengthening at High Temperatures in an Iron-Aluminium Alloy by the Precipitation of Stable and Coherent Intermetallic Particles
Authors: Morris David G. , Muñoz-Morris Maria A. , Requejo Luis M. 
Published: June 2019

AbstractDespite decades of intensive research iron aluminides remain characterised by relatively poor ductility at room temperature and low strength at high temperatures, especially under slow strain rate or creep conditions. A variety of strengthening particles has been tested for improving high temperature strength, but each has serious limitations: typical carbide precipitates are unable to resist dissolution or coarsening at high temperatures; as-solidified iron aluminides with sufficient amounts of transition elements such as Nb or Mo show heavy solidification segregation and are embrittled by a network of Laves phase; mechanical milling with stable oxides appears an excessively expensive processing route. A new iron-aluminium alloy has been developed with Zr and Cr additions that forms fine coherent precipitates even after extended annealing at temperatures as high as 900ºC. These precipitates have a complex Fe3Zr structure and form in a cube-on-cube orientation relationship in the bcc matrix. The low solubility and diffusivity of the solute, as well as the low energy, near-coherent interface ensures excellent stability of these intermetallic precipitates. Interesting strengthening is possible for this material under the relevant high temperature creep conditions.