bluuebunny/crossref_metadata_2025_split huggingface dataset:
Experimental Investigation of Rate-Dependent Inner Hysteresis Loops in PZT
Authors: York Alexander , Seelecke Stefan 
Published: June 2019

AbstractThe rate-dependence of piezoelectric materials resulting from the kinetics of domain switching is an important factor that needs to be included in realistic modeling attempts. This paper provides a systematic study of the rate-dependent hysteresis behavior of a commercially available PZT stack actuator. Experiments covering full as well as minor loops are conducted at different loading rates with polarization and strain recorded. In addition, the creep behavior at different constant levels of the electric field is observed. This provides evidence of kinetics being characterized by strongly varying relaxation times that can be associated with different switching mechanisms.
Effective Medium Approach For Calculation of Linear and Nonlinear Properties of Porous Semiconductor Composites.
Authors: Kochergin Vladimir , Föll Helmut 
Published: June 2019

AbstractThe general methodology of calculating linear and nonlinear properties of nanoporous and nanostructured semiconductor materials and composites is presented. A Maxwell-Garnett approach is generalized for the case of porous semiconductor materials composed of a number of differently oriented pore lattices. Specifically, the cases of electrochemically etched mesoporous silicon on (110)-oriented substrate and electrochemically-etched porous InP and GaAs materials on (100) substrates are considered. The observed optical anisotropy of mesoporous Si is explained. A biaxial anisotropy of the porous InP or GaAs material with crystallographic pores is predicted.
Finite Element Analysis of the non Linear Behavior of a Multilayer Piezoelectric Actuator
Authors: Elhadrouz M. , Zineb T. Ben , Patoor E. 
Published: June 2019

AbstractA constitutive law for ferroelectric and ferroelastic piezoceramics is implemented in ABAQUS Standard using the subroutine user element. A linear solid element is defined: it is an eight-node hexahedron having the mechanical displacement components and the electric potential as degrees of freedom for each node. The element is formulated for static analysis and it needs the definition of the contribution of this element to the Jacobian (stiffness) and the definition of an array containing the contributions of this element to the right-hand-side vectors of the overall system of equations The subroutine is called for each element that is of a user-defined element type each time element calculations are required. As an example, the element is used for the simulation of a multilayer actuator made of piezoceramics. In this case, the piezoelectric equations are not valid since the electric loading induces non linear phenomena, which are captured through the constitutive law implemented in the user element.
Micromechanical Modelling of Ferroelectric Films
Authors: Huber J. E. 
Published: June 2019

AbstractFerroelectric films are growing in significance as non-volatile memory devices, sensors and microactuators. The stress state of the film, induced by processing or constraints such as the substrate, strongly affects device behaviour. Thus it is important to be able to model the coupled and constrained behaviour of film material. This work presents a preliminary study of the application of micromechanical modelling to ferroelectric films. A self-consistent micromechanics model developed for bulk ferroelectrics is adapted for thin film behaviour by incorporating features such as grain structure, mechanical clamping by the substrate, residual stresses, and crystallographic orientation of the film.
Practical Sorption Kinetics of TiCl3 Catalyzed NaAlH4
Authors: Tang Xia , Mosher Daniel A , Anton Donald L 
Published: June 2019

AbstractSodium alanate has been studied as a promising candidate material for reversible hydrogen storage due to its intermediate temperature range and relatively high storage capacity. Its rates of desorption and absorption of hydrogen have been shown to be enhanced by the addition of Ti in various compounds. To date, the sorption kinetics, especially absorption kinetics, is not well understood. In this study, a practical sorption kinetics model for TiCl3 catalyzed NaAlH4 has been developed to assist in the engineering design and evaluation of a prototype hydrogen storage system.
Entropic Elasticity Controls Nanomechanics of Single Tropocollagen Molecules
Authors: Buehler Markus J. , Wong Sophie 
Published: June 2019

ABSTRACTWe report molecular modeling of stretching single molecules of tropocollagen, the building block of collagen fibrils and fibers that provide mechanical support in connective tissues. For small deformation, we observe a dominance of entropic elasticity. At larger deformation, we find a transition to energetic elasticity, which is characterized by first stretching and breaking of hydrogen bonds, followed by deformation of covalent bonds in the protein backbone, eventually leading to molecular fracture. Our force-displacement curves show excellent quantitative agreement with optical tweezer experiments, suggesting a persistence length of approximately 16 nm. We demonstrate that assembly of single TC molecules into fibrils significantly decreases their flexibility, leading to decreased contributions of entropic effects during deformation. We develop a simple continuum model capable of describing entire deformation range of TC molecules.
Time Dependent Nanomechanical Response of Nacre
Authors: Mohanty Bedabibhas , Verma Devendra , Katti Kalpana S , Katti Dinesh R 
Published: June 2019

ABSTRACTNacre, the shiny inner layer of seashells is a model biomimetic system composed of 95% of inorganic (aragonite) phase and 5% of organic phase (mainly proteins and polysaccharides). Nacre exhibits an interlocked layered “brick and mortar” structure where the bricks are made up of aragonite and mortar is the organic phase. We have performed nanoindentation and dynamic nanoindentation tests to study the nanomechanical and dynamic nanomechanical response of nacre. The indentation experiments performed at low loads indicate an elastic modulus of about 15 GPa for the organic phase. The low load, low penetration experiments appear to be better indicators of nanomechanical behavior. Dynamic nanomechanical response of nacre was studied using dynamic nanoindentation (nano-DMA). Significant increase in the values of tan δ was observed with increase in frequency. Also the dynamic nanoindentation experiments indicate that nacre exhibits viscoelastic behavior. Further, fourier transform spectroscopy experiments of nacre in innate and undisturbed state indicate the presence of water in nacre. The nanograin structure of nacre platelets, as well as the entrapped and adsorbed water, is two important contributors to the viscoelastic response of nacre. Atomic force microscopy experiments also indicate a very high force to remove organic from the aragonite in nacre. These experiments provide important insight into nanomechanical response of nacre, its constituents and also interfaces.
Ultrastructural Mechanical and Material Characterization of Fossilized Bone
Authors: Olesiak Sara Elizabeth , Oyen Michelle , Sponheimer Matthew , Eberle Jaelyn J. , Ferguson Virginia L. 
Published: June 2019

ABSTRACTBone plays a key role in the paleontological and archeological records and can provide insight into the biology, ecology and the environment of ancient vertebrates. Examination of bone at the tissue level reveals a definitive relationship between nanomechanical properties and the local organic content, mineral content, and microstructural organization. However, it is unclear as to how these properties change following fossilization, or diagenesis, where the organic phase is rapidly removed and the remaining mineral phase is reinforced by the deposition of apatites, calcites, and other minerals. While the process of diagenesis is poorly understood, its outcome clearly results in the potential for dramatic alteration of the mechanical response of biological tissues. In this study, fossilized specimens of mammalian long bones, collected from Colorado and Wyoming, were studied for mechanical variations. Nanoindentation performed in both longitudinal and transverse directions revealed preservation of bone's natural anisotropy as transverse modulus values were consistently smaller than longitudinal values. Additionally modulus values of fossilized bone from 35.0 to 89.1 GPa increased linearly with logarithm of the sample's age. Future studies will aim to clarify what mechanical and material elements of bone are retained during diagenesis as bone becomes part of the geologic milieu.
Mechanical Properties and Microarchitecture of Nanoporous Hydroxyapatite Bioceramic Nanoparticle Coatings on Ti and TiN
Authors: Stanishevsky Andrei , Chowdhury Shafiul , Greenstein Nathaniel , Yockell-Lelievre Helene , Koskinen Jari 
Published: June 2019

ABSTRACTThe hydroxyapatite (HA) based bioceramic materials are usually prepared at high sintering temperatures to attain suitable mechanical properties. The sintering process usually results in a material which is compositionally and morphologically different from nonstoichiometric nano-crystalline HA phase of hard tissue. At the same time, HA particulates used as precursors in ceramic manufacturing are often very similar to the natural HA nanocrystals. It has been shown that synthetic nanoparticle HA (nanoHA) based materials improve the biological response in vitro and in vivo, but the information on mechanical properties of these materials is scarce.In this work we studied the HA nanoparticle (10 – 80 nm mean size) coatings with 30 – 70% porosity prepared by a dip-coating technique on Ti and TiN substrates. It has been found that the mechanical properties of HA nanoparticle coatings are strongly influenced by the initial size, morphology, and surface treatment of nanoparticles. The nanoindentation Young's modulus and hardness of as–deposited nanoHA coatings were in the range of 2.5 – 6.9 GPa and 80 – 230 MPa, respectively. The coatings were stable after annealing up to at least 600 °C, reaching the Young's modulus up to 23 GPa and hardness up to 540 MPa, as well as in simulated body fluids.
How Baby Plants Avoid Getting Hurt and Blossom into Adulthood: The Story of a Tropical Seed
Authors: Lucas Peter W. , Cook Robert , Lowrey Timothy K. 
Published: June 2019

ABSTRACTThe seed shell of Mezzettia parviflora (Annonaceae), an understory tree from the lowland tropical rain forest of Malaysia, has an extraordinarily sophisticated structure. The shell is entirely made of sclerenchyma (mechanical support tissue) that is in all parts equally dense (about 95% of volume occupied by cell wall). Yet, differences in cell shape and orientation have a strong influence on fracture resistance. The structure appears designed to allow the seed to open for germination, but to limit predation by large animals.
Universal Microstructural Patterns in Bone: Micromechanics-Based Prediction of Anisotropic Material Behavior
Authors: Fritsch Andreas , Hellmich Christian 
Published: June 2019

ABSTRACTBone materials are characterized by an astonishing variability and diversity. Still, because of ‘architectural constraints’, their fundamental hierarchical organization or basic building plans remain largely unchanged during biological evolution. These building plans govern the mechanical interaction of the elementary components of bone (hydroxyapatite, collagen, water; with directly measurable tissue-independent elastic properties), which are here quantified through a multiscale homogenization scheme delivering effective elastic properties of bone materials: At a scale of 10 nm, long cylindrical collagen molecules, attached to each other at their ends by ∼1.5 nm long crosslinks and hosting intermolecular water inbetween, form a contiguous matrix called wet collagen. At a scale of several hundred nanometers, wet collagen and mineral crystal agglomerations interpenetrate each other, forming the mineralized fibril. At a scale of 5 microns, the solid bone matrix is represented as collagen fibril inclusions embedded in a foam of largely disordered (extrafibrillar) mineral crystals. Remarkably, needle and sphere type representations of disordered minerals deliver quasi-identical mechanical behavior of such extrafibrillar porous polycrystals. At a scale above the ultrastructure lacunae are embedded in extracellular bone matrix, forming the extravascular bone material. Model estimates predicted from tissue-specific composition data agree remarkably well with corresponding stiffness experiments across cortical and trabecular materials, which opens new possibilities in the exploitation of computer tomographic data for nano-to-macro mechanics of bone organs, especially in combination with currently investigated extensions towards damage and failure.
Modeling Receptor-Ligand Mediated Adhesion in Nanoindentation of Cells
Authors: Chunyu Zhang , Yongwei Zhang 
Published: June 2019

ABSTRACTThe specific adhesion mediated by receptor-ligand binding in the nanoindentation of cells was studied by using a continuum-kinetics approach. It was found that the adhesion force only causes a shift to the indentation loading curve whereas the unloading curve is tilted downward by the adhesion force, resulting in a hysteresis. Parametric studies were conducted to investigate how experimental conditions influence the adhesion force. It was found that the maximum adhesion force is sensitive to the geometry of the indenter but insensitive to the indentation depth and the mechanical properties of cells. It was also shown that the dependence of the adhesion force on the loading and unloading rates is controlled by the association rate of the receptor-ligand binding, leading to three well-defined regimes.
Equilibrium and Dynamic Properties of Dislocation Dipoles
Authors: Veyssiere Patrick 
Published: June 2019

AbstractThis paper embraces several aspects related to dislocation self-organization in single slip. The formation of prismatic loops, seminal to the nucleation and growth of dislocation braids, is a dynamical process involving elastic dipolar interactions. Preliminary simulations of the concerted process of loop generation are presented. Elastic properties of dislocation dipoles are analysed as a function of dipole character. Equilibrium properties are investigated under the isotropic and anisotropic elastic approximations. The orientation dependence of the so-called dipole passing stress is examined, and its implication in the elementary mechanisms that take place under constrained deformation conditions, such as fatigue cycling, are discussed.
Effects of Sample Size on the Fracture Behavior in Fe-3%Si Alloy Single Crystals
Authors: Takashima Kazuki , Taki Eiji , Kawakami Yuji , Otsu Masaaki 
Published: June 2019

AbstractFracture tests have been performed for both macro- and micro-sized specimens prepared from an Fe-3%Si alloy single crystal, and the effects of length scale on fracture behavior have been investigated. Micro-sized cantilever beam specimens with dimensions of 10 × 10 × 50 μm3 were prepared by focused ion beam machining. Notches with a depth of 5 μm were introduced into the micro-sized specimens and fatigue pre-crack was also introduced ahead of the notch. Macro-sized three-point bending specimens with dimensions of 2 × 2 × 10 mm3 were also cut from the same Fe-3%Si alloy single crystal. Notches with a depth of 1mm were introduced into the macro-sized specimens, and fatigue pre-crack was also introduced. Notch plane was set to be (100), which is a cleavage plane of this material, and notch direction was set to be [010] for both size of specimens. For macro-sized specimens, cleavage fracture occurred during introducing fatigue pre-crack. In contrast, the micro-sized specimens were fractured by ductile manner. A plastic zone was clearly observed on the specimen surface near the crack tip and dimples were found on the fracture surface. The plastic zone size of this material is calculated to be 90 μm. This size is small enough to satisfy small scale yielding for macro-sized specimens, although this size corresponds to large scale yielding in micro-sized specimens. This may cause the size effect on the fracture behavior of this material.
Study of the Effects of Si Addition on the Properties of Hard Nanocomposite Thin Films
Authors: Endrino Jose Luis , Palacin Sergio , Gutierrez Alejandro , Aguirre Myriam , Schäfers Franz 
Published: June 2019

AbstractIn the present study, hard TiSiN coating compounds with different Si content have been deposited by the magnetron sputtering technique. X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) have been employed to investigate the effects of Si addition on the composition, structure and phase development of the cubic NaCl-type structure. To get some insight on these changes, X-ray absorption spectra have been measured at the Ti and Si K-edges in fluorescence yield mode. The collected data showed that the interaction between Ti and Si was weak and the formation of a-Si3N4 can be assumed. Hardness measurements were also consistent with the formation of hard nanocomposite films. A maximum hardness of about 36 GPa was obtained for the sample with 11 at. % Si.
The Identation Size Effect and Hall-Petch Behaviour of Annealed Polycrystalline Copper
Authors: Hou XiaoDong , Zhu T.T. , Jennett N. M. , Bushby A. J. 
Published: June 2019

AbstractMethods to obtain tensile stress-strain properties of materials from a practically non-destructive indentation test are of great industrial interest. However, to do this successfully, indentation size effects must be accounted for. Many indentation size effects, such as strain gradient plasticity and micro-pillar experiments [1], show a size dependence proportional to the inverse square root of a length scale, in common with Hall-Petch behavior. Recently, however, the indentation size effect from small radius spherical indenters has been shown, for a range of fcc metals, not to follow a Hall-Petch-like relationship but to be proportional to the inverse cube root of indenter radius [2]. Here, we investigate these differences further and present results for the indentation size effect with spherical indenters on Cu samples that have been engineered to have different grain sizes. The important experimental control parameter of the relative size of the indentation compared to the grain size is also explored since the cross over from grains significantly smaller than the contact radius to grains significantly larger than the contact radius occurs at different length scales in each sample. A thorough understanding of the various length-scale effects in the different test methods (e.g. the indentation size effect and grain size effect in indentation), is essential if a relationship, robust enough for industrial application, is to be defined to obtain tensile properties from an essentially non-destructive indentation test.
Two-way Shape Memory Surfaces
Authors: Zhang Yijun , Cheng Yang-Tse , Grummon David S 
Published: June 2019

AbstractRecently, we discovered that a two-way shape memory effect can be realized on NiTi shape memory alloy surfaces by spherical indentation. Either thermomechanical cycling or slip-plastic deformation under contact loading conditions is effective in inducing reversible indent depth changes: deeper indents in the low temperature martensitic phase and shallower indents in the high temperature austenitic phase [1, 2]. By planarization of these spherical indents to restore a flat surface, circular reversible surface protrusions appear upon heating and disappear upon cooling. Nano-protrusions are also realized in sputter deposited NiTi thin films. Furthermore, two-way reversible line protrusions are made by planarizing scratch tracks on a NiTi shape memory alloy. Shape memory surfaces can be exploited for a wide range of potential applications, including information storage, optical devices, and smart tribological surfaces.
Phase Transformations in Non-stoichiometric GaAs with Sb and P Doping
Authors: Chaldyshev Vladimir , Bert Nikolay A. , Boitsov Anton V. , Musikhin Yurii G. , Yagovkina Maria A. , Preobrazhenskii Valerii V. , Putyato Mikhail A. , Semyagin Boris R. 
Published: June 2019

AbstractWe investigate the phase transformation in non-stoichiometric GaAs films, which are doped with group V isovalent impurities, namely Sb and P. In contrast to Al and In atoms of group III, group V atoms may not only form substitutional alloys with the GaAs matrix, but also can be dissolved in As precipitates. Our experimental study based on transmission electron microscopy, x-ray diffraction and optical characterizations revealed an opposite impact of the P and Sb alloying on the nucleation, growth and coarsening of the second phase. While Sb enhances the precipitation rate, P retards it. Delta-doping with Sb causes two-dimensional precipitation, whereas such doping with P does not result in heterogeneous nucleation. The microstructure and strains have been found to be different around nanoinclusions in the Sb-doped and P-doped materials, indicating different thermodynamics and kinetics of segregation of the two isovalent impurities in As nanoclusters. We analyze the observed phenomena in terms of thermodynamic and kinetic models taking into account the underlying phase equilibriums and diffusion mechanisms.
Analysis of Split Patterns in ?-?' Ni Alloys
Authors: Calderon Hector A. , Kisielowski Christian , Mori Tsutomu 
Published: June 2019

AbstractPairs of ?' particles in different Ni base alloys are investigated in order to determine the mechanism responsible for the formation of several particle arrays. Special attention is given to symmetrically arranged particles or the split patterns i.e., they have been believed to result from the splitting of large particles. High resolution electron microscopy is used to determine the translation domains of coherent ?' particles. The [001] zone axis allows determination of all possible translations due to differently nucleated domains. About 72 % of particle pairs forming splitting configurations are in the out-of-phase relationship (different translation order domains), indicating that most adjacent pairs are not formed by the splitting of a large particle. On the other hand, particles in symmetrical array (quartets) always have at least one particle with a different translation order domain. Additionally, the frequency of out-of-phase pairs is 78 % in quartet configurations. Calculation of probabilities shows that the quartet split patterns are not formed by splitting but most likely by means of migration due to diffusion.
Phase Stability of Carbides and Nitrides in Steel
Authors: Sluiter Marcel 
Published: June 2019

AbstractCarbides, nitrides, and carbonitrides have great influence on the properties of steel but are relatively little studied at a fundamental level: experimentally because of small dimensions of the precipitates and other difficulties, theoretically because of complex structures and poorly defined compositions. Modern density functional calculations reveal significant trends that can be partially summarized in terms of atomic size, carbon affinity, and hybridization de-magnetization concepts. Phase stability and order-disorder phenomena in widely occurring Cr-based M23C6 carbides and Mo-based M6C carbides are used to illustrate predictions relevant to low alloyed steel.