936 research outputs found

    Local delamination failure of thin material layers

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    Thin material layers have found various applications with various roles of functions, such as in fibre reinforced laminated composite materials, in integrated electronic circuits, in thermal barrier coating material system, and etc.. Interface delamination is a major failure mode due to either residual stress or applied load, or both. Over the past several decades, extensive research works have been done on this subject; however, there are still uncertainties and unsolved problems. This thesis presents the new developed analytical studies on local delamination failure of thin material layers. Firstly, the analytical theories are developed for post-local buckling-driven delamination in bilayer composite beams. The total energy release rate (ERR) is obtained more accurately by including the axial strain energy contribution from the intact part of the beam and by developing a more accurate expression for the post-buckling mode shape. The total ERR is partitioned by using partition theories based on the Euler beam, Timoshenko beam and 2D-elasticity theories. By comparing with independent test results, it has been found that for macroscopic thin material layers the analytical partitions based on the Euler beam theory predicts the propagation behaviour very well and much better than the others. Secondly, a hypothesis is made that delamination can be driven by pockets of energy concentration (PECs) in the form of pockets of tensile stress and shear stress on and around the interface between a microscopic thin film and a thick substrate. Both straight-edged and circular-edged spallation are considered. The three mechanical models are established using mixed-mode partition theories based on classical plate theory, first-order shear-deformable plate theory and full 2D elasticity theory. Experimental results show that all three of the models predict the initiation of unstable growth and the size of spallation very well; however, only the 2D elasticity-based model predicts final kinking off well. Based on PECs theory, the room temperature spallation of α-alumina oxidation film is explained very well. This solved the problem which can not be explained by conventional buckling theory. Finally, the analytical models are also developed to predict the adhesion energy between multilayer graphene membranes and thick substrates. Experimental results show that the model based on 2D elasticity partition theory gives excellent predictions. It has been found that the sliding effect in multilayered graphene membranes leads to a decrease in adhesion toughness measurements when using the circular blister test

    The mechanics of interface fracture in layered composite materials: (5) thin film spallation driven by pockets of energy concentration – microscopic interface fracture

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    A hypothesis is made that delamination can be driven by pockets of energy concentration (PECs) in the form of pockets of tensile stress and shear stress on and around the interface between a thin film and a thick substrate, where PECs can be caused by thermal, electrochemical or other processes. Based on this hypothesis, three analytical mechanical models are developed to predict several aspects of thinfilm spallation failure including nucleation, stable and unstable growth, size of spallation and final kinking off. The predictions from the developed models are compared against experimental results and excellent agreement is observed

    Neural network based models for efficiency frontier analysis: an application to East Asian economies' growth decomposition

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    There has been a long tradition in business and economics to use frontier analysis to assess a production unit’s performance. The first attempt utilized the data envelopment analysis (DEA) which is based on a piecewise linear and mathematical programming approach, whilst the other employed the parametric approach to estimate the stochastic frontier functions. Both approaches have their advantages as well as limitations. This paper sets out to use an alternative approach, i.e. artificial neural networks (ANNs) for measuring efficiency and productivity growth for seven East Asian economies at manufacturing level, for the period 1963 to 1998, and the relevant comparisons are carried out between DEA and ANN, and stochastic frontier analysis (SFA) and ANN in order to test the ANNs’ ability to assess the performance of production units. The results suggest that ANNs are a promising alternative to traditional approaches, to approximate production functions more accurately and measure efficiency and productivity under non-linear contexts, with minimum assumptions

    The mechanics of interface fracture: (4) room temperature spallation of α-alumina films grown by oxidation

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    An analytical mechanical model is developed to predict the room temperature spallation behavior, including the separation nucleation, stable and unstable growth, and final spallation and kinking off, of α-alumina films grown by oxidation on Fe-Cr-Al alloy. The predictions from the developed model are compared against experimental results and excellent agreement is observed. The work reveals a completely new failure mechanism of thin layer materials

    The mechanics of interface fracture in layered composite materials: (4) buckling driven delamination of thin layer materials

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    Analytical theories were developed for studying post-local buckling-driven delamination of thin layer materials under in-plane compressive stresses which can arise from externally applied mechanical loads, thermal stresses due to mismatch of coefficients of thermal expansion between the thin layer material and the thick substrates, the intercalation stresses due to electrochemical lithiation and delithiation, and etc. The development was based on three mixed mode partition theories. They are Euler beam or classical plate, Timoshenko beam or shear deformable plate [1-5] and 2D-elasticity [6-8] theories. Independent experimental tests [9] show that, in general, the analytical partitions based on the Euler beam or classical plate theory predicts the propagation behaviour very well and much better than the partitions based on the Timoshenko beam and 2D-elasticity theories

    Heavy the Sea

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    Solo Museum show Transformer Station Cleveland Jan - April 2017 Immersive installations take the audience into an alternate orphic world, moving from beds to swamps and caves, in search of a primordial return. Here, the photographic is loosened from its referent, slipping in and out of darkness, cloaked in dripping inks, bathed in subtle hues, evoking a liquid space of night. Narratives of loss and desire are entangled like the glistening tentacles wrapped around the artist’s body. Like the coral of the Red Sea said to be formed by Medusa’s blood spilled upon seaweed, Teichmann’s work transforms one thing into another, sliding between autobiography, fiction and myth, still and moving image, sculpture and painting. Esther Teichmann’s photographs, films and writings, picture mothers like caves, sisters like seashells, lovers like moons, tears like waterfalls. Entering the octopus darkness of Teichmann’s caverns we find ingestion and emission, mother and daughter, sister and sister, black and white, lover and lover, surrealism’s erotic jolt: the irritant that makes the pearl. Seashells with apertures like cameras. The womb as oceanic. Lovers as moons. Holding as withholding. Day as night. A zine published by Transformer Station, designed by the artist and Studio Hato, combines short stories and images by the artist with poems written in response to the work by artist-historian and writer Carol Mavor. Esther collaborated with the composer Deirdre Gribbin for Fulmine, a multi-screen film installation. Gribbin’s string quartet score will be performed live on certain days throughout the exhibition period. Founded in 2013, Transformer Station is a contemporary art museum located in Cleveland that presents the work of nationally and internationally recognized artists. It engages audiences with innovative experiences through its inspiring and thought provoking events and programming. Transformer Station alternates as a venue for exhibitions curated by the Bidwells from their renowned collection of contemporary art and exhibitions organized by the Cleveland Museum of Art. Fred Bidwell, Director of Transformer Station, is also founder and executive director of FRONT a new art triennial coming to Cleveland in the summer of 2018, under the artistic direction of Michelle Grabner and Jens Hoffman. Carol Mavor is an American writer, art historian, artist and a Professor of Art History at Manchester University. She has published five books. The first four were published by Duke University Press: Pleasures Taken: Performances of Sexuality and Loss in Victorian Photographs, Becoming: The Photographs of Clementina, Viscountess, Hawarden, Reading Boyishly: Roland Barthes, J. M. Barrie, Jacques Henri Lartigue, Marcel Proust, and D. W. Winnicott and Black and Blue: The Bruising Passion of Camera Lucida, La Jetée, Sans soleil and Hiroshima mon amour. The most recent monograph, Blue Mythologies: Reflections on a Colour, and her forthcoming book, Through the Eyes and Mouth of the Fairy Tale, are both published by Reaktion. Mavor has written extensively on Teichmann’s work in her books and for journals including Cabinet magazine and Frieze Masters. Deirdre Gribbin is a London based Irish composer Her music has been performed worldwide including The Lincoln Center for the Performing Arts, New York. Her orchestral work Empire States was an award winner in the 2003 UNESCO International Rostrum of Composers. Composed for feature films and theatre Gribbin is Senior Fellow in Composition at Trinity College of Music London, Fellow of the Royal Society of Arts. Cleveland based string quartet, OPUS 216, comprised of independent, classically trained musicians, will perform Gribbin’s work in costumes created by the artist, continuing their history of collaboration with other creative disciplines and institutions, including the Cleveland Museum of Art

    Application of a new Structural Joint Inversion Approach to Teleseismic and Gravity Data from Mt.Vesuvius, Italy

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    A 3-D joint inversion of seismic and gravimetric data is performed to re-investigate the subsurface structure of Mt. Vesuvius (Italy) utilizing an improved joint inversion method. The aim is to derive models of the 3D distribution of velocity and density perturbations that are consistent with both data sets and with local velocity models. Mt. Vesuvius is a strato volcano located within a graben (Campania Plain) formed in Plio-Pleistocene. Campania Plain is bordered by mostly Mesozoic carbonaceous rocks. Mt. Vesuvius is the southernmost and the youngest of a group of Pleistocene volcanoes, three of which (Ischia, Campi Flegrei and Mt. Vesuvius) have erupted in historical times. The most recent eruption of Mt. Vesuvius occurred in 1944 and since then the volcanic activity has been characterized by moderate low magnitude seismicity and low temperature fumaroles at the summit crater. We modified the coupling mechanism between velocity and density models in the JI-3D optimized joint inversion method (Jordan and Achauer, 1999). This method was designed to provide stable and high resolution results and involves iterative optimized parameterization, 3D ray tracing, and the incorporation of a priori information. The coupling of the velocity and density models, vital to the joint inversion, is based on a cross-gradient approach (e.g. Gallardo and Meju, 2004), which has been proven to work very well in a variety of cases involving seismic, magnetic, CSEM, MT and gravity data sets. We implemented the cross-gradient coupling for our 3-D irregular adaptive grid parameterization. In contrast to conventional joint inversion methods this approach encourages structural similarities in the models and does not rely on predefined relationships between velocity and density parameters. As a consequence, the resulting velocity-density relations are not contaminated by a priori assumptions and can be utilized to derive rock physical parameters. We apply this method to data from the TomoVes project (Gasparini et al. 1998), combining seismics and Bouguer gravity and local high resolution velocity models as a priori information. The starting models for the joint inversion are derived by separate inversions of the individual data sets. We show 3D distributions of velocity perturbations and density variations from the joint inversion of teleseismic relative traveltimes and Bouguer anomaly data with the aim of extracting further information about the physical status of the volcano- tectonic system

    SupplementaryVideo1_diffractionPatterns.avi

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    supplementary video showing diffraction patterns from highly periodic structures under Gaussian and OAM illuminations

    Rational Surface Modification of Two-Dimensional Layered Black Phosphorus: Insights from First-Principles Calculations

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    Surface modification of atomically thin semiconductors enables their electronic, optical, chemical, and mechanical properties to be tailored and allows these nanosheets to be processed in solutions. Here, we report first-principles density functional theory calculations, through which we show chemical functionalization of black phosphorus using phenyl, phenolate, and nitrene species, which were widely investigated for carbon-based materials. We find that covalent functionalization using nitrene-derived species introduces a strong P–N dative bond at the interface without perturbing its intrinsic electronic structure. The Lewis basic and nucleophilic P atom attacks, through a free pair of electrons, the Lewis acidic nitrene species. These results are further compared to other nitrene-derived functional groups on black phosphorus, including <i>N</i>-methylbenzene, <i>N</i>-aminobenzene, and <i>N</i>-nitrobenzene. We find that by tuning the charge redistribution at the interface, the work function of black phosphorus can be tuned by more than 2 eV. These results suggest valuable tunability of the electronic properties of two-dimensional layered black phosphorus by covalent functionalization for future device applications

    Effect of Functional Groups on the Sensing Properties of Silicon Nanowires toward Volatile Compounds

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    Molecular layers attached to a silicon nanowire field effect transistor (SiNW FET) can serve as antennas for signal transduction of volatile organic compounds (VOCs). Nevertheless, the mutual relationship between the molecular layers and VOCs is still a puzzle. In the present paper, we explore the effect of the molecular layer’s end (functional) groups on the sensing properties of VOCs. Toward this end, SiNW FETs were modified with tailor-made molecular layers that have the same backbone but differ in their end groups. Changes in the threshold voltage (Δ<i>V</i><sub>th</sub>) and changes in the mobility (Δμ<sub>h</sub>) were then recorded upon exposure to various VOCs. Model-based analysis indicates that the interaction between molecular layers and VOCs can be classified to three main scenarios: (a) dipole–dipole interaction between the molecular layer and the polar VOCs; (b) induced dipole–dipole interaction between the molecular layers and the nonpolar VOCs; and (c) molecular layer tilt as a result of VOCs diffusion. Based on these scenarios, it is likely that the electron-donating/withdrawing properties of the functional groups control the dipole moment orientation of the adsorbed VOCs and, as a result, determine the direction (or sign) of the ΔV<sub>th</sub>. Additionally, it is likely the diffusion of VOCs into the molecular layer, determined by the type of functional groups, is the main reason for the Δμ<sub>h</sub> responses. The reported findings are expected to provide an efficient way to design chemical sensors that are based on SiNW FETs to nonpolar VOCs, which do not exchange carriers with the molecular layers
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