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A major impediment to the development of physics-based multi-scale homogenization (composite) theories is the lack of appropriate methods to characterize the local anisotropic elastic-plastic properties of microscale constituents and interfaces at various hierarchical length scales in composite material systems. This work aims to address this gap by combining the information obtained from spherical nanoindentation with different indenter sizes, structure characterization methods (e.g., Orientation Image Mapping in Scanning Electron Microscope, X-ray microtomography),and sophisticated finite element models to arrive at reliable estimates of the elusive local properties. The methods developed have been critically validated in a series of material systems with increasingly complex internal structures, starting with single-phase cubic and hexagonal metals and progressing to multi-phase metals, freeze-cast polymer-ceramic composite systems with novel but highly complex hierarchical internal structures, and various biomaterials. Using these novel approaches, we were able to quantify reliably for the first time the local mechanical properties exhibited by various microscale constituents and interfaces.

The ultimate goal of the research is to develop a fundamental understanding of crack growth near interfaces in optically transparent materials. Transparent magnesium aluminate spinel and a class of transparent glass ceramics were chosen because of their ability to allow systematic variation of the residual stress at interfaces. Once processing conditions are established, crack extension studies will be conducted to examine the crack path stability for cracks situated near interfaces and/or high residual stress gradients. Analytical modeling on the influence of higher order terms on the crack tip stress field has begun; results will be discussed at a later time.

Numerical simulations of compression Hopkinson bar tests on soft, nearly incompressible materials were performed in an effort to understand inertial effects in these tests. The specimen was modeled as either a linear elastic or a nonlinear elastic solid; the nonlinear model was calibrated to ballistic gelatin data. The simulations revealed a previously unreported phenomenon, namely, for sufficiently high strain rates in the specimen and sufficiently short rise times to the final strain rate, small gaps formed at both the specimen-incident bar and the specimen-transmission bar interfaces. The size of these gaps ranged from sub-micron to as large as 43 m. Gaps formed at small specimen strains but persisted out to large strains, closing and re-opening multiple times. At some instants the gaps extended over most of the face of the specimen. Unloading of the specimen and the pressure bars accompanied these gaps. In an effort to rule out numerical artifacts, the sensitivity of these results to mesh size and contact algorithm parameters was studied.

Bacterial communities living on surfaces are called biofilms. Microbial life on a surface has specific consequences for both the microbes (in terms of their physiology, metabolism, and gene expression), and for the substrate, as evidenced by the fouling and degradation of a wide array of materials from metals, to plastics, to medical implants. Understanding the molecular-scale and macroscale interactions between bacteria and surfaces is thus very important to a wide array of applications, from environmental ones such as subsurface soil remediation, microbial dissolution of minerals, microbial uptake of trace metals, drinking water quality, fate of pathogens in the subsurface, to biomedical applications such as cell-to-cell transfer of genetic material, and bacterial infections of implanted devices. This symposium will focus on understanding the interactions between bacteria and surfaces at the molecular and macroscale levels. In order to present a comprehensive set of symposium topics, both fundamental topics on bacterial adhesion measurements and modeling, as well as topics that focus on biofilm-materials interactions from the perspective of the industrially relevant, engineered material applications of bacterial adhesion, will be covered. This symposium will highlight research that brings new materials characterization tools to the discipline, both experimental and computational.

For multilayered materials, reflectivity depends on the complex dielectric function of all the constituent layers, and a detailed analysis is required to separate them. Furthermore, for some cases, new quantum states can occur at the interface which may change the optical properties of the material. In this paper, we discuss various aspects of such analysis, and present a self-consistent iteration procedure, a versatile method to extract and separate the complex dielectric function of each individual layer of a multilayered system. As a case study, we apply this method to LaAlO$_{3}$/SrTiO$_{3}$ heterostructure in which we are able to separate the effects of the interface from the LaAlO$_{3}$ film and the SrTiO$_{3}$ substrate. Our method can be applied to other complex multilayered systems with various numbers of layers.

The gap between imagining and imaging is getting ever smaller. Atomic-Scale Imaging of Surfaces and Interfaces, Symposium W at the 1992 MRS fall Meeting in Boston, Massachusetts, brought together researchers using most state-of-the-art imaging techniques capable of resolving atomic features. Methods represented were scanning tunneling microscopy (STM), atomic force microscopy (AFM), low energy electron microscopy (LEEM), transmission (TEM) and reflection (REM) electron microscopy, scanning electron microscopy (SEM), atom probe field ion microscopy (APFIM or POSAP), high and low energy external source electron holographies and internal source electron holographies. Some highlights from the STM papers included discussions of the limitations and future potential of STM as well as current findings. Several papers presented work with STM at elevated temperatures. Jene Golovchenko reviewed STM work showing cooperative diffusion events (Pb on Ge) involving many tens of substrate atoms. Don Eigler focused on atomic manipulation and some of its uses to enable fundamental studies of small atomic clusters.

Conference Was Held On The Following Area. In Situ Patterning: Selective Area Deposition and Etching, Properties of II-VI Semiconductors: Bulk Crystals, Expitaxial Films, Quantum Well Structures, and Dilute Magnetic Systems; Impurities, Defects and Diffusion in Semiconductors: Bulk and Layered Structures, Chemical Vapor Deposition of Refractory Metals and Ceramics, and Tailored Interfaces in Composite Materials.

Book Source: Digital Library of India Item 2015.199188 dc.contributor.author: Kumar, Santosh dc.date.accessioned: 2015-07-08T13:07:42Z dc.date.available: 2015-07-08T13:07:42Z dc.date.digitalpublicationdate: 2005-08-27 dc.identifier.barcode: 5990010101585 dc.identifier.origpath: /rawdataupload/upload/0101/587 dc.identifier.copyno: 1 dc.identifier.uri: http://www.new.dli.ernet.in/handle/2015/199188 dc.description.scannerno: 14 dc.description.scanningcentre: IIIT, Allahabad dc.description.main: 1 dc.description.tagged: 0 dc.description.totalpages: 154 dc.format.mimetype: application/pdf dc.language.iso: English dc.publisher: Indian Institute Of Technology Kanpur dc.rights: Out_of_copyright dc.source.library: Indian Institute Of Technology Kanpur dc.subject.classification: Technology dc.subject.classification: Engineering. Technology In General dc.title: Shape And Size Analysis Of Interfaces In Particulate Materials

This Symposium continues the ongoing MRS series devoted to the structure and dynamics of disordered materials. It includes sections dedicated to specific classes of disordered materials of particular current interest, including porous media, foams, colloids, and glasses. Also, the structures of chemically inhomogeneous systems in which chemical reactions are taking place, and pattern formation in solidifying alloys are each the subject of a section. Finally, a variety of disordered materials of interest to materials science are included. p10

The research focuses on establishing conditions when interfaces between interlayers are important in governing fracture processes in composites with graded compositions. A theoretical framework is sought that could ultimately quantify the role of interfaces when their presence dominates behavior. Initial work is driven towards establishing general trends. Experimentally, multilayer composites have been fabricated by several techniques that aim at modifying interface characteristics. The competition between fracture at notches of particular depth parallel to the interface and interface fracture is examined. A numerical model is being constructed to obtain crack tip and interface/free edge stress fields to better understand experimental trends. Also, models are being devised to examine how the presence of the interface modifies the stress field of an edge crack parallel to the interface. Experiments in which cracks are extended from notches placed near interfaces have been conducted utilizing optical moir interferometry (conducted at INEEL). The crack driving force and mode mixity as a function of type of interface and proximity to interface are being determined.

Our research and technology are focused on nonlinear issues in the aerothermochemistry of gases and materials and the associated physics and dynamics of interfaces. Our program is now organized to aggressively support the NASA Aeronautics Enterprise so as to: (a) develop a new generation of environmentally compatible, economic subsonic aircraft; (b) develop the technology base for an economically viable and environmentally compatible high-speed civil transport; (c) develop the technology options for new capabilities in high-performance aircraft; (d) develop hypersonic technologies for air-breathing flight; and (e) develop advanced concepts, understanding of physical phenomena, and theoretical, experimental, and computational tools for advanced aerospace systems. The implications from our research for aeronautical and aerospace technology have been both broad and deep. For example, using advanced computational techniques, we have determined exact solutions for the Schrodinger equation in electron-molecule scattering allowing us to evaluate atmospheric models important to reentry physics. We have also found a new class of exact solutions for the Navier Stokes equations. In experimental fluid dynamics, we have found explicit evidence of turbulence modification of droplet sizes in shock tube flow with condensation. We have developed a new diagnostic tool for the direct estimation of flow velocities at MHz sampling rates in quasi-one dimensional turbulent flow. This procedure suggests an unexpected confirmation of the possibility of 'natural' closure in Reynolds stresses with deep implications for the development of turbulent models. A transient increase is observed in both the spectral energy decay rate and the degree of chaotic complexity at the interface of a shock wave and a turbulent ionized gas. Even though the gas is apparently brought to rest by the shock wave, no evidence is found either of the expected relaminarization. A unique diamond-shaped nozzle has been designed for a detailed investigation of the effect of significant streamwise vorticity on the acoustic and IR characteristics of supersonic jets. Our results provide convincing evidence of the significant effect of vorticity on the far-field noise for the diamond jet as compared to the conventional round jets. We have found that the countercurrent shear layer mixes much more efficiently than conventional coflowing shear layers. We also developed the fluid thrust vectoring procedures which use counter flow to vector a jet. Our materials research has shown that the steep stress gradients at the fiber-matrix interface could be the primary cause of interface cracks after the processing of metallic and intermetallic matrix composites. New techniques have been evolved for: the microcharacterization of materials including microplastic strain and, point by point, the misorientation and plasticity for matrix composites; thermally induced stress measurements and load relaxation; the growth and characterization of metallic matrix composite interfaces; and for the growth of ferrite materials by pulsed laser deposition. The FAMU commitment to the HBCU Research Center also continues to be broad and deep.

This article is from Scientific Reports , volume 4 . Abstract Grain boundaries (GBs) are often the preferred sites for void nucleation in ductile metals. However, it has been observed that all boundaries do not contribute equally to this process. We present a mechanistic rationale for the role of GBs in damage nucleation in copper, along with a quantitative map for predicting preferred void nucleation at GBs based on molecular dynamics simulations in copper. Simulations show a direct correlation between the void nucleation stress and the ability of a grain boundary to plastically deform by emitting dislocations, during shock compression. Plastic response of a GB, affects the development of stress concentrations believed to be responsible for void nucleation by acting as a dissipation mechanism for the applied stress.

This article is from Scientific Reports , volume 4 . Abstract Grain boundaries (GBs) are often the preferred sites for void nucleation in ductile metals. However, it has been observed that all boundaries do not contribute equally to this process. We present a mechanistic rationale for the role of GBs in damage nucleation in copper, along with a quantitative map for predicting preferred void nucleation at GBs based on molecular dynamics simulations in copper. Simulations show a direct correlation between the void nucleation stress and the ability of a grain boundary to plastically deform by emitting dislocations, during shock compression. Plastic response of a GB, affects the development of stress concentrations believed to be responsible for void nucleation by acting as a dissipation mechanism for the applied stress.

This article is from Scientific Reports , volume 4 . Abstract Grain boundaries (GBs) are often the preferred sites for void nucleation in ductile metals. However, it has been observed that all boundaries do not contribute equally to this process. We present a mechanistic rationale for the role of GBs in damage nucleation in copper, along with a quantitative map for predicting preferred void nucleation at GBs based on molecular dynamics simulations in copper. Simulations show a direct correlation between the void nucleation stress and the ability of a grain boundary to plastically deform by emitting dislocations, during shock compression. Plastic response of a GB, affects the development of stress concentrations believed to be responsible for void nucleation by acting as a dissipation mechanism for the applied stress.

The Strategic Defense Initiative Organization has place d a great deal of emphasis on the development on new composite materials, specifically metal and ceramic matrix composites. These types of composite materials offer the advantages of being lighter, stiffer, stronger, and more resistant to creep and corrosion. However, because of physical and chemical differences of the matrix and reinforcing agents the interface is plagued by chemical reactions and a high level of residual stress. This impedes the ability of the interface to bear and transfer load and results in fracture upon subsequent loading. Thus, the need for nondestructive characterization of interfaces is critical to the development of these high technology composite materials. Feedback from a nondestructive interface characterization technique is also critical to the further development and refinement of the materials processing procedures. The goal of the Johns Hopkins University program was to study these characteristics and develop techniques which utilize interface waves for nondestructive evaluation of composite interfaces. This final report summarizes the results of two projects which examined the use of interface waves for nondestructive evaluation of composite interfaces. The first project focused on Stoneley waves and their sensitivity to interfacial bond quality and microstructural changes. The second project focused on the use of leaky waves for the nondestructive characterization of interfaces.

The Strategic Defense Initiative Organization has place d a great deal of emphasis on the development on new composite materials, specifically metal and ceramic matrix composites. These types of composite materials offer the advantages of being lighter, stiffer, stronger, and more resistant to creep and corrosion. However, because of physical and chemical differences of the matrix and reinforcing agents the interface is plagued by chemical reactions and a high level of residual stress. This impedes the ability of the interface to bear and transfer load and results in fracture upon subsequent loading. Thus, the need for nondestructive characterization of interfaces is critical to the development of these high technology composite materials. Feedback from a nondestructive interface characterization technique is also critical to the further development and refinement of the materials processing procedures. The goal of the Johns Hopkins University program was to study these characteristics and develop techniques which utilize interface waves for nondestructive evaluation of composite interfaces. This final report summarizes the results of two projects which examined the use of interface waves for nondestructive evaluation of composite interfaces. The first project focused on Stoneley waves and their sensitivity to interfacial bond quality and microstructural changes. The second project focused on the use of leaky waves for the nondestructive characterization of interfaces.

The objective of this project is to explore fundamental mechanisms through which interfaces (nanocrystalline grain boundaries or layer interface in multilayers) attract radiation induced point defects, expedite annihilation of vacancies and interstitials, and thus restore strong capability to absorb radiation induced point defects. The ultimate goal of this project is to construct unique interfaces to significantly enhance radiation tolerance of metallic materials.

Mechanical properties of metal-ceramic interfaces were measured at high temperatures. New methods were developed to measure the time and strain rate dependent properties of metal-ceramic interfaces under shear loading and under tensile loading. The shear experiment consisted of depositing a film of the ceramic on the metal and stretching the metal until periodic cracks developed in the ceramic film. Experiments on the copper/silica system demonstrated that these interfaces slide at high temperatures, with a linear relationship between sliding rate and the interfacial shear stress. In tensile experiments, bicrystals of copper and sapphire were loaded in tension.

Novel solar cell materials consisting of Si nanoparticles embedded in SiO2 layers have been studied using positron annihilation spectroscopy in Doppler broadening mode, and photoluminescence. Two positron-trapping interface states are observed after high temperature annealing at 1100{\deg}C. One of the states is attributed to the (SiO2/Si bulk) interface and the other to the interface between the Si nanoparticles and SiO2. A small reduction in positron trapping into these states is observed after annealing the samples in N2 atmosphere with 5% H2. Enhanced photoluminescence is also observed from the samples following this annealing step.

In this work we genetically programmed the M13 virus, so that the new clone expressed multifunctional coat protein sequences that selectively bind to designated surfaces and species. Using these new clones, composite network consisting of ironphosphate nanowire (a-FePO4) and single wall carbon nanotubes were self-assembled onto aluminum surfaces. Spectroscopic and electrochemical characterizations confirmed the 3D-structure as well as the electrochemical activity of such composite nanowires.