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Sample records for adhesive failure mechanisms

  1. Statistical failure analysis of adhesive resin cement bonded dental ceramics

    PubMed Central

    Wang, Yaou; Katsube, Noriko; Seghi, Robert R; Rokhlin, Stanislav I.

    2007-01-01

    The goal of this work is to quantitatively examine the effect of adhesive resin cement on the probability of crack initiation from the internal surface of ceramic dental restorations. The possible crack bridging mechanism and residual stress effect of the resin cement on the ceramic surface are examined. Based on the fracture-mechanics-based failure probability model, we predict the failure probability of glass-ceramic disks bonded to simulated dentin subjected to indentation loads. The theoretical predictions match experimental data suggesting that both resin bridging and shrinkage plays an important role and need to be considered for accurate prognostics to occur. PMID:18670583

  2. Fracto-emission accompanying adhesive failure

    NASA Technical Reports Server (NTRS)

    Dickinson, J. T.

    1984-01-01

    The fractoemission characteristics of various material interfaces have been investigated experimentally. The interfaces studied include brittle materials/epoxy, glass/elastomers and brittle materials/pressure sensitive adhesives. Results are presented for both large (1 sq cm) planar surfaces together with a few small microns fibers (E-glass, S-glass, Kevlar, and graphite), and a small (10-500 micron) particles in polymer matrices. The composition and energies of the particles emitted during adhesive failure were measured over a wide range of time scales by means of conventional particle counting techniques and photon imaging. Measurements of the time dependence, energy distribution, crack velocity dependence, and spatial distribution of fractoemissive particles are also presented. Some correlations between the various fractoemission components are described in detail.

  3. Wear mechanism based on adhesion

    NASA Technical Reports Server (NTRS)

    Yamamoto, T.; Buckley, D. H.

    1982-01-01

    Various concepts concerning wear mechanisms and deformation behavior observed in the sliding wear track are surveyed. The mechanisms for wear fragment formation is discussed on the basis of adhesion. The wear process under unlubricated sliding conditions is explained in relation to the concept of adhesion at the interface during the sliding process. The mechanism for tearing away the surface layer from the contact area and forming the sliding track contour is explained by assuming the simplified process of material removal based on the adhesion theory.

  4. Failure strength prediction for adhesively bonded single lap joints

    NASA Astrophysics Data System (ADS)

    Rahman, Niat Mahmud

    For adhesively bonded joint, failure strength depends on many factors such as material properties (both adhesive and adherend), specimen geometries, test environments, surface preparation procedures, etc. Failure occurs inside constitutive materials or along joint interfaces. Based on location, adhesively bonded failure mode can be classified as adhesive failure mode, cohesive failure mode and adherend failure mode. Failure mode directly affects the failure strength of joint. For last eight decades, researchers have developed analytical, empirical or semi-empirical methods capable of predicting failure strength for adhesively bonded joints generating either cohesive failure or adherend failure. Applicability of most of the methods is limited to particular cases. In this research, different failure modes for single lap joints (SLJs) were generated experimentally using epoxy based paste adhesive. Based on experimental data and analytical study, simplified failure prediction methods were developed for each failure mode. For adhesive failure mode, it is observed that peel stress distributions concur along interface near crack initiation points. All SLJs for this test endured consistent surface treatments. Geometric parameters of the joints were varied to study their effect on failure strength. Peel stress distributions were calculated using finite analysis (FEA). Based on peel stress distribution near crack initiation point, a failure model is proposed. Numerous analytical, empirical and semi-empirical models are available for predicting failure strengths of SLJs generating cohesive failures. However, most of the methods in the literature failed to capture failure behavior of SLJs having thickness of adhesive layer as variable. Cohesive failure mode was generated experimentally using aluminum as adherend and epoxy adhesive considering thickness of adhesive layers as variable within SLJs. Comparative study was performed among various methods. It was observed that

  5. Adhesive fracture mechanics. [stress analysis for bond line interface

    NASA Technical Reports Server (NTRS)

    Bennett, S. J.; Devries, K. L.; Williams, M. L.

    1974-01-01

    In studies of fracture mechanics the adhesive fracture energy is regarded as a fundamental property of the adhesive system. It is pointed out that the value of the adhesive fracture energy depends on surface preparation, curing conditions, and absorbed monolayers. A test method reported makes use of a disk whose peripheral part is bonded to a substrate material. Pressure is injected into the unbonded central part of the disk. At a certain critical pressure value adhesive failure can be observed. A numerical stress analysis involving arbitrary geometries is conducted.

  6. An insect trap as habitat: cohesion-failure mechanism prevents adhesion of Pameridea roridulae bugs to the sticky surface of the plant Roridula gorgonias.

    PubMed

    Voigt, Dagmar; Gorb, Stanislav

    2008-08-01

    The glandular trichomes of the plant Roridula gorgonias release an extremely adhesive, visco-elastic, resinous secretion that traps a variety of insects, including those having a considerable body size. However, the specialized mutualistic mirid bug Pameridea roridulae lives and walks on this sticky plant surface without being trapped. We have sought to reveal the mechanism underlying the apparent non-sticky nature of the cuticle of this bug. In this study, we have visualized intact plant and insect surfaces using cryo-scanning electron microscopy and measured the adhesive properties of the plant secretion on different surfaces. We present a combination of structural and experimental results that suggest that a thick and cohesively weak film of an outermost, epicuticular greasy secretion acts as a ;sloughing-off' layer, preventing the formation of contacts between the sticky plant secretion and the solid insect cuticle. In a comparative study of fresh cuticle fractures of flies representing a typical prey of R. gorgonias, a thin, fragmentary layer of epicuticular grease was revealed. These results indicate that, when trapping prey, the plant adhesive might form proper contact with solid islands of the insect cuticle that are free of epicuticular grease. PMID:18689418

  7. Characterization of mode I and mixed-mode failure of adhesive bonds between composite adherends

    NASA Technical Reports Server (NTRS)

    Mall, S.; Johnson, W. S.

    1986-01-01

    A combined experimental and analytical investigation of an adhesively bonded composite joint was conducted to characterize both the static and fatigue beyond growth mechanism under mode 1 and mixed-mode 1 and 2 loadings. Two bonded systems were studied: graphite/epoxy adherends bonded with EC 3445 and FM-300 adhesives. For each bonded system, two specimen types were tested: a double-cantilever-beam specimen for mode 1 loading and a cracked-lapshear specimen for mixed-mode 1 and 2 loading. In all specimens tested, failure occurred in the form of debond growth. Debonding always occurred in a cohesive manner with EC 3445 adhesive. The FM-300 adhesive debonded in a cohesive manner under mixed-mode 1 and 2 loading, but in a cohesive, adhesive, or combined cohesive and adhesive manner under mode 1 loading. Total strain-energy release rate appeared to be the driving parameter for debond growth under static and fatigue loadings.

  8. Characterization of mode 1 and mixed-mode failure of adhesive bonds between composite adherends

    NASA Technical Reports Server (NTRS)

    Mall, S.; Johnson, W. S.

    1985-01-01

    A combined experimental and analytical investigation of an adhesively bonded composite joint was conducted to characterize both the static and fatigue beyond growth mechanism under mode 1 and mixed-mode 1 and 2 loadings. Two bonded systems were studied: graphite/epoxy adherends bonded with EC 3445 and FM-300 adhesives. For each bonded system, two specimen types were tested: a double-cantilever-beam specimen for mode 1 loading and a cracked-lapshear specimen for mixed-mode 1 and 2 loading. In all specimens tested, failure occurred in the form of debond growth. Debonding always occurred in a cohesive manner with EC 3445 adhesive. The FM-300 adhesive debonded in a cohesive manner under mixed-mode 1 and 2 loading, but in a cohesive, adhesive, or combined cohesive and adhesive manner under mode 1 loading. Total strain-energy release rate appeared to be the driving parameter for debond growth under static and fatigue loadings.

  9. Adhesive mechanisms in cephalopods: a review.

    PubMed

    von Byern, Janek; Klepal, Waltraud

    2006-01-01

    Several genera of cephalopods (Nautilus, Sepia, Euprymna and Idiosepius) produce adhesive secretions, which are used for attachment to the substratum, for mating and to capture prey. These adhesive structures are located in different parts of the body, viz. in the digital tentacles (Nautilus), in the ventral surface of the mantle and fourth arm pair (Sepia), in the dorsal epidermis (Euprymna), or in the dorsal mantle side and partly on the fins (Idiosepius). Adhesion in Sepia is induced by suction of dermal structures on the mantle, while for Nautilus, Euprymna and Idiosepius adhesion is probably achieved by chemical substances. Histochemical studies indicate that in Nautilus and Idiosepius secretory cells that appear to be involved in adhesion stain for carbohydrates and protein, whilst in Euprymna only carbohydrates are detectable. De-adhesion is either achieved by muscle contraction of the tentacles and mantle (Nautilus and Sepia) or by secretion of substances (Euprymna). The de-adhesive mechanism used by Idiosepius remains unknown. PMID:17110356

  10. Damage mechanics - failure modes

    SciTech Connect

    Krajcinovic, D.; Vujosevic, M.

    1996-12-31

    The present study summarizes the results of the DOE sponsored research program focused on the brittle failure of solids with disordered microstructure. The failure is related to the stochastic processes on the microstructural scale; namely, the nucleation and growth of microcracks. The intrinsic failure modes, such as the percolation, localization and creep rupture, are studied by emphasizing the effect of the micro-structural disorder. A rich spectrum of physical phenomena and new concepts that emerges from this research demonstrates the reasons behind the limitations of traditional, deterministic, and local continuum models.

  11. Critical length scale controls adhesive wear mechanisms

    PubMed Central

    Aghababaei, Ramin; Warner, Derek H.; Molinari, Jean-Francois

    2016-01-01

    The adhesive wear process remains one of the least understood areas of mechanics. While it has long been established that adhesive wear is a direct result of contacting surface asperities, an agreed upon understanding of how contacting asperities lead to wear debris particle has remained elusive. This has restricted adhesive wear prediction to empirical models with limited transferability. Here we show that discrepant observations and predictions of two distinct adhesive wear mechanisms can be reconciled into a unified framework. Using atomistic simulations with model interatomic potentials, we reveal a transition in the asperity wear mechanism when contact junctions fall below a critical length scale. A simple analytic model is formulated to predict the transition in both the simulation results and experiments. This new understanding may help expand use of computer modelling to explore adhesive wear processes and to advance physics-based wear laws without empirical coefficients. PMID:27264270

  12. Critical length scale controls adhesive wear mechanisms.

    PubMed

    Aghababaei, Ramin; Warner, Derek H; Molinari, Jean-Francois

    2016-01-01

    The adhesive wear process remains one of the least understood areas of mechanics. While it has long been established that adhesive wear is a direct result of contacting surface asperities, an agreed upon understanding of how contacting asperities lead to wear debris particle has remained elusive. This has restricted adhesive wear prediction to empirical models with limited transferability. Here we show that discrepant observations and predictions of two distinct adhesive wear mechanisms can be reconciled into a unified framework. Using atomistic simulations with model interatomic potentials, we reveal a transition in the asperity wear mechanism when contact junctions fall below a critical length scale. A simple analytic model is formulated to predict the transition in both the simulation results and experiments. This new understanding may help expand use of computer modelling to explore adhesive wear processes and to advance physics-based wear laws without empirical coefficients. PMID:27264270

  13. Critical length scale controls adhesive wear mechanisms

    NASA Astrophysics Data System (ADS)

    Aghababaei, Ramin; Warner, Derek H.; Molinari, Jean-Francois

    2016-06-01

    The adhesive wear process remains one of the least understood areas of mechanics. While it has long been established that adhesive wear is a direct result of contacting surface asperities, an agreed upon understanding of how contacting asperities lead to wear debris particle has remained elusive. This has restricted adhesive wear prediction to empirical models with limited transferability. Here we show that discrepant observations and predictions of two distinct adhesive wear mechanisms can be reconciled into a unified framework. Using atomistic simulations with model interatomic potentials, we reveal a transition in the asperity wear mechanism when contact junctions fall below a critical length scale. A simple analytic model is formulated to predict the transition in both the simulation results and experiments. This new understanding may help expand use of computer modelling to explore adhesive wear processes and to advance physics-based wear laws without empirical coefficients.

  14. Tissue Mechanics and Adhesion during Embryo Development

    PubMed Central

    Shawky, Joseph H.; Davidson, Lance A.

    2014-01-01

    During development cells interact mechanically with their microenvironment through cell-cell and cell-matrix adhesions. Many proteins involved in these adhesions serve both mechanical and signaling roles. In this review we will focus on the mechanical roles of these proteins and their complexes in transmitting force or stress from cell to cell or from cell to the extracellular matrix. As forces operate against tissues they establish tissue architecture, extracellular matrix assembly, and pattern cell shapes. As tissues become more established, adhesions play a major role integrating cells with the mechanics of their local environment. Adhesions may serve as both a molecular-specific glue, holding defined populations of cells together, and as a lubricant, allowing tissues to slide past one another. We review the biophysical principles and experimental tools used to study adhesion so that we may aid efforts to understand how adhesions guide these movements and integrate their signaling functions with mechanical function. As we conclude we review efforts to develop predictive models of adhesion that can be used to interpret experiments and guide future efforts to control and direct the process of tissue self-assembly during development. PMID:25512299

  15. Failure Surface Analysis of Polyimide/Titanium Notched Coating Adhesion Specimens

    SciTech Connect

    GIUNTA,RACHEL K.; KANDER,RONALD G.

    2000-12-18

    Adhesively bonded joints of LaRC{trademark} PETI-5, a phenylethynyl-terminated polyimide, with chromic acid anodized titanium were fabricated and debonded interfacially. The adhesive-substrate failure surfaces were investigated using several surface analysis techniques. From Auger spectroscopy, field emission scanning electron microscopy, and atomic force microscopy studies, polymer appears to be penetrating the pores of the anodized substrate to a depth of approximately 100 nm. From x-ray photoelectron spectroscopy data, the polymer penetrating the pores appears to be in electrical contact with the titanium substrate, leading to differential charging. These analyses confirm that the polymer is becoming mechanically interlocked within the substrate surface.

  16. Molecular mechanics of mussel adhesion proteins

    NASA Astrophysics Data System (ADS)

    Qin, Zhao; Buehler, Markus J.

    2014-01-01

    Mussel foot protein (mfp), a natural glue produced by marine mussel, is an intriguing material because of its superior ability for adhesion in various environments. For example, a very small amount of this material is sufficient to affix a mussel to a substrate in water, providing structural support under extreme forces caused by the dynamic effects of waves. Towards a more complete understanding of its strength and underwater workability, it is necessary to understand the microscropic mechanisms by which the protein structure interacts with various substrates. However, none of the mussel proteins' structure is known, preventing us from directly using atomistic modeling to probe their structural and mechanical properties. Here we use an advanced molecular sampling technique to identify the molecular structures of two mussel foot proteins (mfp-3 and mfp-5) and use those structures to study their mechanics of adhesion, which is then incorporated into a continuum model. We calculate the adhesion energy of the mussel foot protein on a silica substrate, compute the adhesion strength based on results obtained from molecular modeling, and compare with experimental data. Our results show good agreement with experimental measurements, which validates the multiscale model. We find that the molecular structure of the folded mussel foot protein (ultimately defined by its genetic sequence) favors strong adhesion to substrates, where L-3,4-dihydroxyphenylalanine (or DOPA) protein subunits work in a cooperative manner to enhance adhesion. Our experimental data suggests a peak attachment force of 0.4±0.1 N, which compares favorably with the prediction from the multiscale model of Fc=0.21-0.33 N. The principles learnt from those results could guide the fabrication of new interfacial materials (e.g. composites) to integrate organic with inorganic surfaces in an effective manner.

  17. Adhesive bond failure monitoring with triboluminescent optical fiber sensor

    NASA Astrophysics Data System (ADS)

    Shohag, Md Abu S.; Hammel, Emily C.; Olawale, David O.; Okoli, Okenwa O.

    2016-04-01

    One of the most severe damage modes in modern wind turbines is the failure of the adhesive joints in the trailing edge of the large composite blades. The geometrical shape of the blade and current manufacturing techniques make the trailing edge of the wind turbine blade more sensitive to damage. Failure to timely detect this damage type may result in catastrophic failures, expensive system downtime, and high repair costs. A novel sensing system called the In-situ Triboluminescent Optical Fiber (ITOF) sensor has been proposed for monitoring the initiation and propagation of disbonds in composite adhesive joints. The ITOF sensor combines the triboluminescent property of ZnS:Mn with the many desirable features of optical fiber to provide in-situ and distributed damage sensing in large composite structures like the wind blades. Unlike other sensor systems, the ITOF sensor does not require a power source at the sensing location or for transmitting damage-induced signals to the hub of the wind turbine. Composite parts will be fabricated and the ITOF integrated within the bondline to provide in-situ and real time damage sensing. Samples of the fabricated composite parts with integrated ITOF will be subjected to tensile and flexural loads, and the response from the integrated sensors will be monitored and analyzed to characterize the performance of the ITOF sensor as a debonding damage monitoring system. In addition, C-scan and optical microscopy will be employed to gain greater insights into the damage propagation behavior and the signals received from the ITOF sensors.

  18. Experimental methods for identifying failure mechanisms

    NASA Technical Reports Server (NTRS)

    Daniel, I. M.

    1983-01-01

    Experimental methods for identifying failure mechanisms in fibrous composites are studied. Methods to identify failure in composite materials includes interferometry, holography, fractography and ultrasonics.

  19. Mechanical Failure in Colloidal Gels

    NASA Astrophysics Data System (ADS)

    Kodger, Thomas Edward

    When colloidal particles in a dispersion are made attractive, they aggregate into fractal clusters which grow to form a space-spanning network, or gel, even at low volume fractions. These gels are crucial to the rheological behavior of many personal care, food products and dispersion-based paints. The mechanical stability of these products relies on the stability of the colloidal gel network which acts as a scaffold to provide these products with desired mechanical properties and to prevent gravitational sedimentation of the dispersed components. Understanding the mechanical stability of such colloidal gels is thus of crucial importance to predict and control the properties of many soft solids. Once a colloidal gel forms, the heterogeneous structure bonded through weak physical interactions, is immediately subject to body forces, such as gravity, surface forces, such as adhesion to a container walls and shear forces; the interplay of these forces acting on the gel determines its stability. Even in the absence of external stresses, colloidal gels undergo internal rearrangements within the network that may cause the network structure to evolve gradually, in processes known as aging or coarsening or fail catastrophically, in a mechanical instability known as syneresis. Studying gel stability in the laboratory requires model colloidal system which may be tuned to eliminate these body or endogenous forces systematically. Using existing chemistry, I developed several systems to study delayed yielding by eliminating gravitational stresses through density matching and cyclic heating to induce attraction; and to study syneresis by eliminating adhesion to the container walls, altering the contact forces between colloids, and again, inducing gelation through heating. These results elucidate the varied yet concomitant mechanisms by which colloidal gels may locally or globally yield, but then reform due to the nature of the physical, or non-covalent, interactions which form

  20. Focal adhesions, stress fibers and mechanical tension

    PubMed Central

    Burridge, Keith; Guilluy, Christophe

    2016-01-01

    Stress fibers and focal adhesions are complex protein arrays that produce, transmit and sense mechanical tension. Evidence accumulated over many years led to the conclusion that mechanical tension generated within stress fibers contributes to the assembly of both stress fibers themselves and their associated focal adhesions. However, several lines of evidence have recently been presented against this model. Here we discuss the evidence for and against the role of mechanical tension in driving the assembly of these structures. We also consider how their assembly is influenced by the rigidity of the substratum to which cells are adhering. Finally, we discuss the recently identified connections between stress fibers and the nucleus, and the roles that these may play, both in cell migration and regulating nuclear function. PMID:26519907

  1. The Effect of Composite Patches on the Failure of Adhesively-Bonded Joints Under Bending Moment

    NASA Astrophysics Data System (ADS)

    Akpinar, Salih

    2013-12-01

    In this study, it was aimed to compare mechanical behavior of double-strap joints with aluminum (AA2024-T3) or 16-ply laminate of carbon/epoxy composite (T300/934) patches of different orientation angles at their overlap area subjected to bending moment. For this purpose, AA2024-T3 aluminum was used as adherend, while the adhesive was a two-part paste (DP 460). Six different types of joint samples were subjected to bending moment. The effect of patch material on failure load and stress distribution was examined experimentally and numerically. In the numerical analysis, the composite patches were assumed to behave linearly elastic, while adherend and adhesive layers were assumed to be nonlinear. It was found that the data obtained from 3-D finite element analysis were coherent with experimental results. Meanwhile, experiments showed that fiber orientation angles of the patches markedly affected the failure load of joints, failure mode and stress distributions appeared in adhesive and composite.

  2. Rate and time dependent failure of structural adhesives

    NASA Technical Reports Server (NTRS)

    Brinson, H. F.; Renieri, M. P.; Herakovich, C. T.

    1975-01-01

    Studies on two adhesives (Metlbond 1113 and 1113-2) identified as having important applications in the bonding of composite materials are presented. A testing program to ascertain stress-strain, strain-rate, time, yield, and/or failure behavior of these materials in bulk form using uniaxial tensile constant strain-rate, creep, and relaxation tests is described. The stress-strain behavior of each material is shown to be significantly rate dependent. A rate dependent stress whitening (crazing) phenomenon occurs prior to either yield or fracture. A region of linear elasticity, a region of viscoelasticity, and the onset of yielding are identified in the stress-strain behavior. The linear elastic limit and the yield point are shown to be rate dependent and agree well with an empirical equation proposed by Ludwik. A creep to failure phenomenon is shown to exist and is correlated with a delayed yield equation proposed by Crochet. Analytical predictions based on a modified Bingham model are shown to agree well with experimental stress-strain strain-rate data. Analytical predictions based on a modified Ramberg-Osgood equation are also shown for comparison purposes.

  3. Failure mechanisms of DC and capacitive RF MEMS switches

    NASA Astrophysics Data System (ADS)

    Patton, Steven T.; Zabinski, Jeffrey S.

    2006-01-01

    Microelectromechanical systems (MEMS) radio frequency (RF) switches hold great promise in a myriad of commercial, aerospace, and military applications including cellular phones and phased array antennas. However, there is limited understanding of the factors determining the performance and reliability of these devices. Fundamental studies of hot-switched DC (gold versus gold) and capacitive (gold versus silicon nitride) MEMS RF switch contacts were conducted in a controlled air environment at MEMS-scale forces using a micro/nanoadhesion apparatus as a switch simulator. This paper reviews key experimental results from the switch simulator and how they relate to failure mechanisms of MEMS switches. For DC switch contacts, electric current had a profound effect on deformation mechanisms, adhesion, contact resistance (R), and reliability/durability. At low current (1-10 μA), junction growth/force relaxation, slightly higher R, and switching induced adhesion growth were prominent. At high current (1-10 mA), asperity melting, slightly lower R, and shorting were present. Adhesion increased during cycling at low current and was linked to the creation of smooth contact surfaces, increased van der Waals interaction, and chemical bonding. Surface roughening by nanowire formation (which also caused shorting) prevented adhesion at high current. Aging of the contacts in air led to hydrocarbon adsorption and less adhesion. Studies of capacitive switches demonstrated that excessive adhesion was the primary failure mechanism and that both mechanical and electrical effects were contributing factors. The mechanical effect is adhesion growth with cycling due to surface smoothening, which allows increased van der Waals interaction and chemical bonding. The electrical effect on adhesion is due to electrostatic force associated with trapped parasitic charge in the dielectric, and was only observed after operating the switch at 40 V bias and above. The two effects are additive; however

  4. Evaluation of a Linear Cumulative Damage Failure Model for Epoxy Adhesive

    NASA Technical Reports Server (NTRS)

    Richardson, David E.; Batista-Rodriquez, Alicia; Macon, David; Totman, Peter; McCool, Alex (Technical Monitor)

    2001-01-01

    Recently a significant amount of work has been conducted to provide more complex and accurate material models for use in the evaluation of adhesive bondlines. Some of this has been prompted by recent studies into the effects of residual stresses on the integrity of bondlines. Several techniques have been developed for the analysis of bondline residual stresses. Key to these analyses is the criterion that is used for predicting failure. Residual stress loading of an adhesive bondline can occur over the life of the component. For many bonded systems, this can be several years. It is impractical to directly characterize failure of adhesive bondlines under a constant load for several years. Therefore, alternative approaches for predictions of bondline failures are required. In the past, cumulative damage failure models have been developed. These models have ranged from very simple to very complex. This paper documents the generation and evaluation of some of the most simple linear damage accumulation tensile failure models for an epoxy adhesive. This paper shows how several variations on the failure model were generated and presents an evaluation of the accuracy of these failure models in predicting creep failure of the adhesive. The paper shows that a simple failure model can be generated from short-term failure data for accurate predictions of long-term adhesive performance.

  5. Physics of Cell Adhesion Failure and Human Diseases

    NASA Astrophysics Data System (ADS)

    Family, Fereydoon

    Emergent phenomena in living systems, including your ability to read these lines, do not obviously follow as a consequence of the fundamental laws of physics. Understanding the physics of living systems clearly falls outside the conventional boundaries of scientific disciplines and requires a collaborative, multidisciplinary approach. Here I will discuss how theoretical and computational techniques from statistical physics can be used to make progress in explaining the physical mechanisms that underlie complex biological phenomena, including major diseases. In the specific cases of macular degeneration and cancer that we have studied recently, we find that the breakdown of the mechanical stability in the local tissue structure caused by weakening of the cell-cell adhesion plays a key role in the initiation and progression of the disease. This finding can help in the development of new therapies that would prevent or halt the initiation and progression of these diseases.

  6. Mechanism of Focal Adhesion Kinase Mechanosensing.

    PubMed

    Zhou, Jing; Aponte-Santamaría, Camilo; Sturm, Sebastian; Bullerjahn, Jakob Tómas; Bronowska, Agnieszka; Gräter, Frauke

    2015-11-01

    Mechanosensing at focal adhesions regulates vital cellular processes. Here, we present results from molecular dynamics (MD) and mechano-biochemical network simulations that suggest a direct role of Focal Adhesion Kinase (FAK) as a mechano-sensor. Tensile forces, propagating from the membrane through the PIP2 binding site of the FERM domain and from the cytoskeleton-anchored FAT domain, activate FAK by unlocking its central phosphorylation site (Tyr576/577) from the autoinhibitory FERM domain. Varying loading rates, pulling directions, and membrane PIP2 concentrations corroborate the specific opening of the FERM-kinase domain interface, due to its remarkably lower mechanical stability compared to the individual alpha-helical domains and the PIP2-FERM link. Analyzing downstream signaling networks provides further evidence for an intrinsic mechano-signaling role of FAK in broadcasting force signals through Ras to the nucleus. This distinguishes FAK from hitherto identified focal adhesion mechano-responsive molecules, allowing a new interpretation of cell stretching experiments. PMID:26544178

  7. Mechanism of Focal Adhesion Kinase Mechanosensing

    PubMed Central

    Sturm, Sebastian; Bullerjahn, Jakob Tómas; Bronowska, Agnieszka; Gräter, Frauke

    2015-01-01

    Mechanosensing at focal adhesions regulates vital cellular processes. Here, we present results from molecular dynamics (MD) and mechano-biochemical network simulations that suggest a direct role of Focal Adhesion Kinase (FAK) as a mechano-sensor. Tensile forces, propagating from the membrane through the PIP2 binding site of the FERM domain and from the cytoskeleton-anchored FAT domain, activate FAK by unlocking its central phosphorylation site (Tyr576/577) from the autoinhibitory FERM domain. Varying loading rates, pulling directions, and membrane PIP2 concentrations corroborate the specific opening of the FERM-kinase domain interface, due to its remarkably lower mechanical stability compared to the individual alpha-helical domains and the PIP2-FERM link. Analyzing downstream signaling networks provides further evidence for an intrinsic mechano-signaling role of FAK in broadcasting force signals through Ras to the nucleus. This distinguishes FAK from hitherto identified focal adhesion mechano-responsive molecules, allowing a new interpretation of cell stretching experiments. PMID:26544178

  8. Mechanical properties of methacrylate-based model dentin adhesives: effect of loading rate and moisture exposure.

    PubMed

    Singh, Viraj; Misra, Anil; Parthasarathy, Ranganathan; Ye, Qiang; Park, Jonggu; Spencer, Paulette

    2013-11-01

    The aim of this study is to investigate the mechanical behavior of model methacrylate-based dentin adhesives under conditions that simulate the wet oral environment. A series of monotonic and creep experiments were performed on rectangular beam samples of dentin adhesive in three-point bending configuration under different moisture conditions. The monotonic test results show a significant effect of loading rate on the failure strength and the linear limit (yield point) of the stress-strain response. In addition, these tests show that the failure strength is low, and the failure occurs at a smaller deformation when the test is performed under continuously changing moisture conditions. The creep test results show that under constant moisture conditions, the model dentin adhesives can have a viscoelastic response under certain low loading levels. However, when the moisture conditions vary under the same low loading levels, the dentin adhesives have an anomalous creep response accompanied by large secondary creep and high strain accumulation. PMID:23744598

  9. ADHESION OF AMORPHOUS CALCIUM PHOSPHATE COMPOSITES BONDED TO DENTIN: A STUDY IN FAILURE MODALITY

    PubMed Central

    O’Donnell, J.N.R.; Schumacher, G.E.; Antonucci, J.M.; Skrtic, D.

    2009-01-01

    Aims As a bioactive filler capable of remineralizing tooth structures, the main disadvantage of as-made amorphous calcium phosphate (am-ACP) are its large agglomerates. The objective of this study was to mill ACP, and compare the adhesive strength to dentin, work to fracture, and failure modes of both groups to glass-filled composites and one commercial compomer after 24 h, 1 week, 1, 3 and 6 months of exposure to simulated saliva solution (SLS). Flat dentin surfaces were acid-etched, primed, and photopolymerized. Composites were applied, photo-cured, and debonded in shear. The resin used in each composite was identical: ethoxylated bisphenol A dimethacrylate, triethylene glycol dimethacrylate, 2-hydroxyethyl methacrylate and methacryloxyethyl phthalate. Fillers consisted of am-ACP and milled ACP (m-ACP), and a strontium-containing glass (Sr-glass) at respective mass fractions of (40, 60, and 75) %. Findings 90 % of the fracture surfaces in this study showed adhesive failure, with most of these occurring at the dentin/primer interface. 52 % of failures after 24 h immersion occurred at the primer/composite interface. After six months of SLS exposure, 80 % of specimens failed at the dentin/primer interface, with a 42 % overall reduction in bond strength. Conclusions Milled ACP composites showed initial mechanical advantages over am-ACP composites and the compomer, and produced a higher incidence of a failure mode consistent with stronger adhesion. Evidence is provided which suggests that milled ACP composites may offer enhanced potential in clinical bonding applications. PMID:19107798

  10. Adhesion mechanism of a gecko-inspired oblique structure with an adhesive tip for asymmetric detachment

    NASA Astrophysics Data System (ADS)

    Sekiguchi, Yu; Takahashi, Kunio; Sato, Chiaki

    2015-12-01

    An adhesion model of an oblique structure with an adhesive tip is proposed by considering a limiting stress for adhesion to describe the detachment mechanism of gecko foot hairs. When a force is applied to the root of the oblique structure, normal and shear stresses are generated at contact and the adhesive tip is detached from the surface when reaching the limiting stress. An adhesion criterion that considers both the normal and shear stresses is introduced, and the asymmetric detachment of the oblique structure is theoretically investigated. In addition, oblique beam array structures are manufactured, and an inclination effect of the structure on the asymmetric detachment is experimentally verified.

  11. Probabilistic assessment of failure in adhesively bonded composite laminates

    SciTech Connect

    Minnetyan, L.; Chamis, C.C.

    1997-07-01

    Damage initiation and progressive fracture of adhesively bonded graphite/epoxy composites is investigated under tensile loading. A computer code is utilized for the simulation of composite structural damage and fracture. Structural response is assessed probabilistically during degradation. The effects of design variable uncertainties on structural damage progression are quantified. The Fast Probability Integrator is used to assess the response scatter in the composite structure at damage initiation. Sensitivity of the damage response to design variables is computed. Methods are general purpose in nature and are applicable to all types of laminated composite structures and joints, starting from damage initiation to unstable damage propagation and collapse. Results indicate that composite constituent and adhesive properties have a significant effect on structural durability. Damage initiation/progression does not necessarily begin in the adhesive bond. Design implications with regard to damage tolerance of adhesively bonded joints are examined.

  12. The effects of inherent flaws on the time and rate dependent failure of adhesively bonded joints

    NASA Technical Reports Server (NTRS)

    Sancaktar, E.; Padgilwar, S.

    1982-01-01

    Inherent flaws, as well as the effects of rate and time, are shown by tests on viscoelastic adhesive-bonded single lap joints to be as critical in joint failure as environmental and stress concentration effects, with random inherent flaws and loading rate changes resulting in an up to 40% reduction in joint strength. It is also found that the asymptotic creep stress, below which no delayed failure may occur, may under creep loading be as much as 45% less than maximum adhesive strength. Attention is given to test results for the case of titanium-LARC-3 adhesive single-lap specimens.

  13. On the mechanical properties of bovine serum albumin (BSA) adhesives.

    PubMed

    Berchane, N S; Andrews, M J; Kerr, S; Slater, N K H; Jebrail, F F

    2008-04-01

    Biological adhesives, natural and synthetic, are of current active interest. These adhesives offer significant advantages over traditional sealant techniques, in particular, they are easier to use, and can play an integral part in the healing mechanism of tissue. Thus, biological adhesives can play a major role in medical applications if they possess adequate mechanical behavior and stability over time. In this work, we report on the method of preparation of bovine serum albumin (BSA) into a biological adhesive. We present quantitative measurements that show the effect of BSA concentration and cross-linker content on the bonding strength of BSA adhesive to wood. A comparison is then made with synthetic poly(glycidyl methacrylate) (PGMA) adhesive, and a commercial cyanoacrylate glue, which was used as a control adhesive. In addition, BSA samples were prepared and characterized for their water content, tensile strength, and elasticity. We show that on dry surface, BSA adhesive exhibits a high bonding strength that is comparable with non-biological commercial cyanoacrylate glues, and synthetic PGMA adhesive. Tensile testing on wet wood showed a slight increase in the bonding strength of BSA adhesive, a considerable decrease in the bonding strength of cyanoacrylate glue, and negligible adhesion of PGMA. Tests performed on BSA samples demonstrate that initial BSA concentration and final water content have a significant effect on the stress-strain behavior of the samples. PMID:18197367

  14. Mechanical principle of enhancing cell-substrate adhesion via pre-tension in the cytoskeleton.

    PubMed

    Chen, Bin; Gao, Huajian

    2010-05-19

    Motivated by our earlier study on the effect of pre-tension in gecko adhesion, here we investigate whether and how pre-tension in cytoskeleton influences cell adhesion by developing a stochastic-elasticity model of a stress fiber attached on a rigid substrate via molecular bonds. By comparing the variations in adhesion lifetime and observing the sequences of bond breaking with and without pre-tension in the stress fiber under the same applied force, we demonstrate that the effect of pre-tension is to shift the interfacial failure mode from cracklike propagation toward uniform bond failure within the contact region, thereby greatly increasing the adhesion lifetime. Since stress fibers are the primary load-bearing components of cells, as well as the basic functional units of cytoskeleton that facilitate cell adhesion, this study suggests a feasible mechanism by which cell adhesion could be actively controlled via cytoskeletal contractility and proposes that pre-tension may be a general principle in biological adhesion. PMID:20483323

  15. Mechanical behavior of adhesive joints subjected to cyclic thermal loading

    SciTech Connect

    Humfeld, G.R.; Dillard, D.A.

    1996-12-31

    Stresses induced in bimaterial systems due to changing temperature has been the subject of much study since the publication of Timoshenko`s classic paper of 1925. An adhesive bond is one example of a bimaterial system in which thermal stress can play an important role. However, adhesives are viscoelastic in nature, and their mechanical behavior is dictated by the temperature- and time-dependence of their material properties; analytical solutions for elastic materials do not adequately describe their true behavior. The effect of the adhesive`s viscoelasticity on stress in an adhesive bond subjected to changing temperature is therefore of compelling interest and importance for the adhesives industry. The objective of this research is to develop an understanding of the viscoelastic effect in an adhesive bond subjected to cycling temperature, particularly when the temperature range spans a transition temperature of the adhesive. Numerical modeling of a simplified geometry was first undertaken to isolate the influence of viscoelasticity on the stress state from any particular specimen geometry effect. Finite element modeling was then undertaken to examine the mechanical behavior of the adhesive in a layered geometry. Both solution methods predicted development of residual tensile stresses in the adhesive. For the layered geometry this was found to correspond with residual tensile peel stresses, which are thought to be the cause of interfacial debonding.

  16. Fiber optics - Failure modes and mechanisms

    NASA Astrophysics Data System (ADS)

    Hyle, Richard A., Jr.

    A study was conducted to investigate the frequency and cause of failures of fiber-optic transmitters, waveguides, receivers, connectors, and splices. To accomplish this, quantitative and qualitative data were collected and evaluated to determine why and when failures occurred and to identify design options which can be made to avoid these failure conditions. An understanding of fiber-optic device failure modes and mechanisms is critical to insuring unit reliability, improving the manufacturing process, and allowing design flexibility of the overall fiber-optic system. The author summarizes the specific failure modes uncovered for typical items such as transmitters, receivers, fiber, cable, connectors, and splices. He also discusses fiber-optic performance criteria, design considerations, failure rate data, and failure mode information.

  17. Mechanically robust, negative-swelling, mussel-inspired tissue adhesives.

    PubMed

    Barrett, Devin G; Bushnell, Grace G; Messersmith, Phillip B

    2013-05-01

    Most synthetic polymer hydrogel tissue adhesives and sealants swell considerably in physiologic conditions, which can result in mechanical weakening and adverse medical complications. This paper describes the synthesis and characterization of mechanically tough zero- or negative-swelling mussel-inspired surgical adhesives based on catechol-modified amphiphilic poly(propylene oxide)-poly(ethylene oxide) block copolymers. The formation, swelling, bulk mechanical, and tissue adhesive properties of the resulting thermosensitive gels were characterized. Catechol oxidation at or below room temperature rapidly resulted in a chemically cross-linked network, with subsequent warming to physiological temperature inducing a thermal hydrophobic transition in the PPO domains and providing a mechanism for volumetric reduction and mechanical toughening. The described approach can be easily adapted for other thermally sensitive block copolymers and cross-linking strategies, representing a general approach that can be employed to control swelling and enhance mechanical properties of polymer hydrogels used in a medical context. PMID:23184616

  18. Sticky Matrix: Adhesion Mechanism of the Staphylococcal Polysaccharide Intercellular Adhesin.

    PubMed

    Formosa-Dague, Cécile; Feuillie, Cécile; Beaussart, Audrey; Derclaye, Sylvie; Kucharíková, Soňa; Lasa, Iñigo; Van Dijck, Patrick; Dufrêne, Yves F

    2016-03-22

    The development of bacterial biofilms on surfaces leads to hospital-acquired infections that are difficult to fight. In Staphylococci, the cationic polysaccharide intercellular adhesin (PIA) forms an extracellular matrix that connects the cells together during biofilm formation, but the molecular forces involved are unknown. Here, we use advanced force nanoscopy techniques to unravel the mechanism of PIA-mediated adhesion in a clinically relevant methicillin-resistant Staphylococcus aureus (MRSA) strain. Nanoscale multiparametric imaging of the structure, adhesion, and elasticity of bacteria expressing PIA shows that the cells are surrounded by a soft and adhesive matrix of extracellular polymers. Cell surface softness and adhesion are dramatically reduced in mutant cells deficient for the synthesis of PIA or under unfavorable growth conditions. Single-cell force spectroscopy demonstrates that PIA promotes cell-cell adhesion via the multivalent electrostatic interaction with polyanionic teichoic acids on the S. aureus cell surface. This binding mechanism rationalizes, at the nanoscale, the well-known ability of PIA to strengthen intercellular adhesion in staphylococcal biofilms. Force nanoscopy offers promising prospects for understanding the fundamental forces in antibiotic-resistant biofilms and for designing anti-adhesion compounds targeting matrix polymers. PMID:26908275

  19. The Morphology and Adhesion Mechanism of Octopus vulgaris Suckers

    PubMed Central

    Tramacere, Francesca; Beccai, Lucia; Kuba, Michael; Gozzi, Alessandro; Bifone, Angelo; Mazzolai, Barbara

    2013-01-01

    The octopus sucker represents a fascinating natural system performing adhesion on different terrains and substrates. Octopuses use suckers to anchor the body to the substrate or to grasp, investigate and manipulate objects, just to mention a few of their functions. Our study focuses on the morphology and adhesion mechanism of suckers in Octopus vulgaris. We use three different techniques (MRI, ultrasonography, and histology) and a 3D reconstruction approach to contribute knowledge on both morphology and functionality of the sucker structure in O. vulgaris. The results of our investigation are two-fold. First, we observe some morphological differences with respect to the octopus species previously studied (i.e., Octopus joubini, Octopus maya, Octopus bimaculoides/bimaculatus and Eledone cirrosa). In particular, in O. vulgaris the acetabular chamber, that is a hollow spherical cavity in other octopuses, shows an ellipsoidal cavity which roof has an important protuberance with surface roughness. Second, based on our findings, we propose a hypothesis on the sucker adhesion mechanism in O. vulgaris. We hypothesize that the process of continuous adhesion is achieved by sealing the orifice between acetabulum and infundibulum portions via the acetabular protuberance. We suggest this to take place while the infundibular part achieves a completely flat shape; and, by sustaining adhesion through preservation of sucker configuration. In vivo ultrasonographic recordings support our proposed adhesion model by showing the sucker in action. Such an underlying physical mechanism offers innovative potential cues for developing bioinspired artificial adhesion systems. Furthermore, we think that it could possibly represent a useful approach in order to investigate any potential difference in the ecology and in the performance of adhesion by different species. PMID:23750233

  20. The morphology and adhesion mechanism of Octopus vulgaris suckers.

    PubMed

    Tramacere, Francesca; Beccai, Lucia; Kuba, Michael; Gozzi, Alessandro; Bifone, Angelo; Mazzolai, Barbara

    2013-01-01

    The octopus sucker represents a fascinating natural system performing adhesion on different terrains and substrates. Octopuses use suckers to anchor the body to the substrate or to grasp, investigate and manipulate objects, just to mention a few of their functions. Our study focuses on the morphology and adhesion mechanism of suckers in Octopus vulgaris. We use three different techniques (MRI, ultrasonography, and histology) and a 3D reconstruction approach to contribute knowledge on both morphology and functionality of the sucker structure in O. vulgaris. The results of our investigation are two-fold. First, we observe some morphological differences with respect to the octopus species previously studied (i.e., Octopus joubini, Octopus maya, Octopus bimaculoides/bimaculatus and Eledone cirrosa). In particular, in O. vulgaris the acetabular chamber, that is a hollow spherical cavity in other octopuses, shows an ellipsoidal cavity which roof has an important protuberance with surface roughness. Second, based on our findings, we propose a hypothesis on the sucker adhesion mechanism in O. vulgaris. We hypothesize that the process of continuous adhesion is achieved by sealing the orifice between acetabulum and infundibulum portions via the acetabular protuberance. We suggest this to take place while the infundibular part achieves a completely flat shape; and, by sustaining adhesion through preservation of sucker configuration. In vivo ultrasonographic recordings support our proposed adhesion model by showing the sucker in action. Such an underlying physical mechanism offers innovative potential cues for developing bioinspired artificial adhesion systems. Furthermore, we think that it could possibly represent a useful approach in order to investigate any potential difference in the ecology and in the performance of adhesion by different species. PMID:23750233

  1. Force nanoscopy of cell mechanics and cell adhesion

    NASA Astrophysics Data System (ADS)

    Dufrêne, Yves F.; Pelling, Andrew E.

    2013-05-01

    Cells are constantly exposed to mechanical stimuli in their environment and have several evolved mechanisms to sense and respond to these cues. It is becoming increasingly recognized that many cell types, from bacteria to mammalian cells, possess a diverse set of proteins to translate mechanical cues into biochemical signalling and to mediate cell surface interactions such as cell adhesion. Moreover, the mechanical properties of cells are involved in regulating cell function as well as serving as indicators of disease states. Importantly, the recent development of biophysical tools and nanoscale methods has facilitated a deeper understanding of the role that physical forces play in modulating cell mechanics and cell adhesion. Here, we discuss how atomic force microscopy (AFM) has recently been used to investigate cell mechanics and cell adhesion at the single-cell and single-molecule levels. This knowledge is critical to our understanding of the molecular mechanisms that govern mechanosensing, mechanotransduction, and mechanoresponse in living cells. While pushing living cells with the AFM tip provides a means to quantify their mechanical properties and examine their response to nanoscale forces, pulling single surface proteins with a functionalized tip allows one to understand their role in sensing and adhesion. The combination of these nanoscale techniques with modern molecular biology approaches, genetic engineering and optical microscopies provides a powerful platform for understanding the sophisticated functions of the cell surface machinery, and its role in the onset and progression of complex diseases.

  2. Basic failure mechanisms in advanced composites

    NASA Technical Reports Server (NTRS)

    Mullin, J. V.; Mazzio, V. F.; Mehan, R. L.

    1972-01-01

    Failure mechanisms in carbon-epoxy composites are identified as a basis for more reliable prediction of the performance of these materials. The approach involves both the study of local fracture events in model specimens containing small groups of filaments and fractographic examination of high fiber content engineering composites. Emphasis is placed on the correlation of model specimen observations with gross fracture modes. The effects of fiber surface treatment, resin modification and fiber content are studied and acoustic emission methods are applied. Some effort is devoted to analysis of the failure process in composite/metal specimens.

  3. Mechanical circulatory support in heart failure

    PubMed Central

    Szczurek, Wioletta; Suliga, Kamil; Rempega, Grzegorz; Rajwa, Paweł

    2016-01-01

    The increasing number of end-stage heart failure patients eligible for heart transplant and the disproportionately low number of donor hearts have led to increased interest in ventricular assist devices (VAD). These devices can be used as a bridge to decision, bridge to recovery, or bridge to candidacy. The main advantage of mechanical circulatory support (MCS) is the improvement of organ perfusion and function, which leads to better quality of life and survival. The MCS can also be used as a destination therapy in end-stage heart failure patients who are not eligible for heart transplant. It should be remembered that, despite the tangible benefits, VAD implantation may also be associated with the risk of serious complications, such as bleeding, infection, arrhythmias, blood clots, right ventricular failure, and cardiovascular events. This study presents an up-to-date overview of the current knowledge on the role of MCS in modern medicine. PMID:27516785

  4. Basic failure mechanisms in advanced composites

    NASA Technical Reports Server (NTRS)

    Mullin, J. V.; Mazzio, V. F.; Mehan, R. L.

    1971-01-01

    Fundamental failure mechanisms in carbon-epoxy composites were studied for more reliable prediction of the performance of these materials. Single and multiple fiber specimens were tested under tensile loads, and the sequence of failure events was observed. Parameters such as resin crack sensitivity, fiber surface treatment and variations in fibers from batch to batch are being evaluated. The analysis of bulk composite fracture processes using acoustic emission techniques is being studied in order to correlate microscopic observations with bulk composite behavior. Control of the fracture process through matrix and interface modification is being attempted, and study of failure processes in composite/metal specimens is being conducted. Most of the studies involved DEN 438 epoxy novolac as the matrix, but some experiments are now underway using the higher temperature resin ERLA 4617.

  5. Coating of carbon nanotube fibers: variation of tensile properties, failure behavior and adhesion strength

    NASA Astrophysics Data System (ADS)

    Mäder, Edith; Liu, Jian-Wen; Hiller, Janett; Lu, Weibang; Li, Qingwen; Zhandarov, Serge; Chou, Tsu-Wei

    2015-07-01

    An experimental study of the tensile properties of CNT fibers and their interphasial behavior in epoxy matrices is reported. One of the most promising applications of CNT fibers is their use as reinforcement in multifunctional composites. For this purpose, an increase of the tensile strength of the CNT fibers in unidirectional composites as well as strong interfacial adhesion strength is desirable. However, the mechanical performance of the CNT fiber composites manufactured so far is comparable to that of commercial fiber composites. The interfacial properties of CNT fiber/polymer composites have rarely been investigated and provided CNT fiber/epoxy interfacial shear strength of 14.4 MPa studied by the microbond test. In order to improve the mechanical performance of the CNT fibers, an epoxy compatible coating with nano-dispersed aqueous based polymeric film formers and low viscous epoxy resin, respectively, was applied. For impregnation of high homogeneity, low molecular weight epoxy film formers and polyurethane film formers were used. The aqueous based epoxy film formers were not crosslinked and able to interdiffuse with the matrix resin after impregnation. Due to good wetting of the individual CNT fibers by the film formers, the degree of activation of the fibers was improved leading to increased tensile strength and Young’s modulus. Cyclic tensile loading and simultaneous determination of electric resistance enabled to characterize the fiber’s durability in terms of elastic recovery and hysteresis. The pull-out tests and SEM study reveal different interfacial failure mechanisms in CNT fiber/epoxy systems for untreated and film former treated fibers, on the one hand, and epoxy resin treated ones, on the other hand. The epoxy resin penetrated between the CNT bundles in the reference or film former coated fiber, forming a relatively thick CNT/epoxy composite layer and thus shifting the fracture zone within the fiber. In contrast to this, shear sliding along

  6. Possible mechanism of adhesion in a mica supported phospholipid bilayer

    SciTech Connect

    Pertsin, Alexander; Grunze, Michael

    2014-05-14

    Phospholipid bilayers supported on hydrophilic solids like silica and mica play a substantial role in fundamental studies and technological applications of phospholipid membranes. In both cases the molecular mechanism of adhesion between the bilayer and the support is of primary interest. Since the possibilities of experimental methods in this specific area are rather limited, the methods of computer simulation acquire great importance. In this paper we use the grand canonical Monte Carlo technique and an atomistic force field to simulate the behavior of a mica supported phospholipid bilayer in pure water as a function of the distance between the bilayer and the support. The simulation reveals a possible adhesion mechanism, where the adhesion is due to individual lipid molecules that protrude from the bilayer and form widely spaced links with the support. Simultaneously, the bilayer remains separated from the bilayer by a thin water interlayer which maintains the bilayer fluidity.

  7. Effect of adhesive interleaving and discontinuous plies on failure of composite laminates subject to transverse normal loads

    NASA Technical Reports Server (NTRS)

    Jegley, Dawn C.

    1989-01-01

    Results of a series of tests to determine the effects of adhesive interleaving and discontinuous plies (plies with end-to-end gaps) on the displacements, failure loads and failure modes of graphite-epoxy laminates subjected to transverse normal loads are presented. Adhesive interleaving can be used to contain local damage within a group of plies, i.e., to arrest crack propagation on the interlaminate level, and it can increase the amount of normal displacement the laminate can withstand before failure. However, the addition of adhesive interleaving to a laminate does not significantly increase its load carrying capability. A few discontinuous plies in a laminate can reduce the normal displacement and load at failure by 10 to 40 percent compared to a laminate with no discontinuous plies, but the presence of the ply discontinuities does not generally change the failure location or the failure mode of the laminate.

  8. Compression failure mechanisms of composite structures

    NASA Technical Reports Server (NTRS)

    Hahn, H. T.; Sohi, M.; Moon, S.

    1986-01-01

    An experimental and analytical study was conducted to delineate the compression failure mechanisms of composite structures. The present report summarizes further results on kink band formation in unidirectional composites. In order to assess the compressive strengths and failure modes of fibers them selves, a fiber bundle was embedded in epoxy casting and tested in compression. A total of six different fibers were used together with two resins of different stiffnesses. The failure of highly anisotropic fibers such as Kevlar 49 and P-75 graphite was due to kinking of fibrils. However, the remaining fibers--T300 and T700 graphite, E-glass, and alumina--failed by localized microbuckling. Compressive strengths of the latter group of fibers were not fully utilized in their respective composite. In addition, acoustic emission monitoring revealed that fiber-matrix debonding did not occur gradually but suddenly at final failure. The kink band formation in unidirectional composites under compression was studied analytically and through microscopy. The material combinations selected include seven graphite/epoxy composites, two graphite/thermoplastic resin composites, one Kevlar 49/epoxy composite and one S-glass/epoxy composite.

  9. Adhesion

    MedlinePlus

    ... adhesions Ovarian cyst References Munireddy S, Kavalukas SL, Barbul A. Intra-abdominal healing: gastrointestinal tract and adhesions. Surg Clin N Am Kulaylat MN, Dayton, MT. Surgical complications. In: Townsend CM Jr, Beauchamp RD, Evers BM, Mattox KL, ...

  10. Role of failure-mechanism identification in accelerated testing

    NASA Technical Reports Server (NTRS)

    Hu, J. M.; Barker, D.; Dasgupta, A.; Arora, A.

    1993-01-01

    Accelerated life testing techniques provide a short-cut method to investigate the reliability of electronic devices with respect to certain dominant failure mechanisms that occur under normal operating conditions. However, accelerated tests have often been conducted without knowledge of the failure mechanisms and without ensuring that the test accelerated the same mechanism as that observed under normal operating conditions. This paper summarizes common failure mechanisms in electronic devices and packages and investigates possible failure mechanism shifting during accelerated testing.

  11. Fatigue of the Resin-Enamel Bonded Interface and the Mechanisms of Failure

    PubMed Central

    Yahyazadehfar, Mobin; Mutluay, Mustafa Murat; Majd, Hessam; Ryou, Heonjune; Arola, Dwayne

    2013-01-01

    The durability of adhesive bonds to enamel and dentin and the mechanisms of degradation caused by cyclic loading are important to the survival of composite restorations. In this study a novel method of evaluation was used to determine the strength of resin-enamel bonded interfaces under both static and cyclic loading, and to identify the mechanisms of failure. Specimens with twin interfaces of enamel bonded to commercial resin composite were loaded in monotonic and cyclic 4-point flexure to failure within a hydrated environment. Results for the resin-enamel interface were compared with those for the resin composite (control) and values reported for resin-dentin adhesive bonds. Under both modes of loading the strength of the resin-enamel interface was significantly (p≤0.0001) lower than that of the resin composite and the resin-dentin bonded interface. Fatigue failure of the interface occurred predominately by fracture of enamel, adjacent to the interface, and not due to adhesive failures. In the absence of water aging or acid production of biofilms, the durability of adhesive bonds to enamel is lower than that achieved in dentin bonding. PMID:23571321

  12. Failure mechanisms of thermal barrier systems

    NASA Astrophysics Data System (ADS)

    Xu, Tao

    Thermal barrier coatings (TBCs) are widely used in turbines for propulsion and power generation. The benefit results from their ability to sustain high thermal gradients in the presence of adequate backside cooling. Lowering the temperature of the metal substrate prolongs the life of the component: whether from environmental attack, creep rupture, or fatigue. Thermal barrier systems exhibit multiple failure mechanisms, depends on the deposition methods of the TBCs, chemical composition of the bond coats, and their working environments. Some of the most prevalent are studied in this thesis. There are two types of thermal barrier systems based on the chemical composition of the bond coats: Pt-aluminide and NiCoCrAlY bond coats. Ratcheting happens the most in the systems with Pt-aluminide bond coats; while edge delamination is considered a possible failure mechanism for the systems with NiCoCrAlY bond coats. Ratcheting is motivated by displacement instability in the thermally grown oxide (TGO). Interactions between cracks induced in TBCs upon thermal cycling have been calculated. Cracks that converge from neighboring imperfections exhibit a minimum energy release rate prior to coalescence. Equating this minimum to the toughness of the TBC provides a criterion for coalescence and failure. Imposing this criterion allows the change in crack length upon cycling and the number of cycles to failure to be ascertained. This simulation capability is used to explore various influences on durability. Samples with NiCoCrAlY bond coat are studied after subjected to thermal cycling in a burner rig. In each case, a dominant delamination has been identified, that extends primarily along the interface between the TGO and the bond coat. Calculations of the delamination energy release rate, upon comparison with the interface toughness, reveals a critical TGO thickness, (h tgo)c ≈ 3mum, comparable to that found experimentally.

  13. Probing the intrinsic failure mechanism of fluorinated amorphous carbon film based on the first-principles calculations

    PubMed Central

    Zhang, Ren-hui; Wang, Li-ping; Lu, Zhi-bin

    2015-01-01

    Fluorinated amorphous carbon films exhibit superlow friction under vacuum, but are prone to catastrophic failure. Thus far, the intrinsic failure mechanism remains unclear. A prevailing view is that the failure of amorphous carbon film results from the plastic deformation of substrates or strong adhesion between two contacted surfaces. In this paper, using first-principles and molecular dynamics methodology, combining with compressive stress-strain relation, we firstly demonstrate that the plastic deformation induces graphitization resulting in strong adhesion between two contacted surfaces under vacuum, which directly corresponds to the cause of the failure of the films. In addition, sliding contact experiments are conducted to study tribological properties of iron and fluorinated amorphous carbon surfaces under vacuum. The results show that the failure of the film is directly attributed to strong adhesion resulting from high degree of graphitization of the film, which are consistent with the calculated results. PMID:25803202

  14. Neuroimmune mechanisms of depression in heart failure.

    PubMed

    Jiménez, Jessica A; Mills, Paul J

    2012-01-01

    Heart failure (HF) is a major and costly public health concern, and its prognosis is grim-with high hospitalization and mortality rates. It is well documented that HF patients experience disproportionately high rates of depression and that depressed HF patients have worse clinical outcomes than their non-depressed counterparts. The purpose of this chapter is to introduce the reader to the study of depression in HF, and how psychoneuroimmunologic principals have been applied to further elucidate the mechanisms (i.e., neurohormonal and cytokine activation) linking these co-morbid disorders. PMID:22933146

  15. Failure Analysis and Mechanisms of Failure of Fibrous Composite Structures

    NASA Technical Reports Server (NTRS)

    Noor, A. K. (Compiler); Shuart, M. J. (Compiler); Starnes, J. H., Jr. (Compiler); Williams, J. G. (Compiler)

    1983-01-01

    The state of the art of failure analysis and current design practices, especially as applied to the use of fibrous composite materials in aircraft structures is discussed. Deficiencies in these technologies are identified, as are directions for future research.

  16. Mechanotransduction at focal adhesions: integrating cytoskeletal mechanics in migrating cells

    PubMed Central

    Kuo, Jean-Cheng

    2013-01-01

    Focal adhesions (FAs) are complex plasma membrane-associated macromolecular assemblies that serve to physically connect the actin cytoskeleton to integrins that engage with the surrounding extracellular matrix (ECM). FAs undergo maturation wherein they grow and change composition differentially to provide traction and to transduce the signals that drive cell migration, which is crucial to various biological processes, including development, wound healing and cancer metastasis. FA-related signalling networks dynamically modulate the strength of the linkage between integrin and actin and control the organization of the actin cytoskeleton. In this review, we have summarized a number of recent investigations exploring how FA composition is affected by the mechanical forces that transduce signalling networks to modulate cellular function and drive cell migration. Understanding the fundamental mechanisms of how force governs adhesion signalling provides insights that will allow the manipulation of cell migration and help to control migration-related human diseases. PMID:23551528

  17. Insulin Resistance and Heart Failure: Molecular Mechanisms

    PubMed Central

    Aroor, Annayya R.; Mandavia, Chirag H.; Sowers, James R.

    2012-01-01

    Insulin resistance and associated reductions in cardiac insulin metabolic signaling is emerging as a major factor for the development of heart failure and assumes more importance because of an epidemic increase in obesity and the cardiorenal metabolic syndrome and our aging population. Major factors contributing to the development of cardiac insulin resistance are oxidative stress, hyperglycemia, hyperlipidemia, dysregulated secretion of adipokines/cytokines and inappropriate activation of renin-angiotensin II-aldosterone system (RAAS) and the sympathetic nervous system. The effects of cardiac insulin resistance are exacerbated by metabolic, endocrine and cytokine alterations associated with systemic insulin resistance. The aggregate of these various alterations leads to an insulin resistant phenotype with metabolic inflexibility, impaired calcium handling, mitochondrial dysfunction and oxidative stress, dysregulated myocardial-endothelial interactions resulting in energy deficiency, impaired diastolic dysfunction, myocardial cell death and cardiac fibrosis. Therefore, understanding the molecular mechanisms linking insulin resistance and heart failure may help to design new and more effective mechanism-based drugs to improve myocardial and systemic insulin resistance. PMID:22999243

  18. Effects of mechanical properties of adhesive resin cements on stress distribution in fiber-reinforced composite adhesive fixed partial dentures.

    PubMed

    Yokoyama, Daiichiro; Shinya, Akikazu; Gomi, Harunori; Vallittu, Pekka K; Shinya, Akiyoshi

    2012-01-01

    Using finite element analysis (FEA), this study investigated the effects of the mechanical properties of adhesive resin cements on stress distributions in fiber-reinforced resin composite (FRC) adhesive fixed partial dentures (AFPDs). Two adhesive resin cements were compared: Super-Bond C&B and Panavia Fluoro Cement. The AFPD consisted of a pontic to replace a maxillary right lateral incisor and retainers on a maxillary central incisor and canine. FRC framework was made of isotropic, continuous, unidirectional E-glass fibers. Maximum principal stresses were calculated using finite element method (FEM). Test results revealed that differences in the mechanical properties of adhesive resin cements led to different stress distributions at the cement interfaces between AFPD and abutment teeth. Clinical implication of these findings suggested that the safety and longevity of an AFPD depended on choosing an adhesive resin cement with the appropriate mechanical properties. PMID:22447051

  19. Clays causing adhesion with tool surfaces during mechanical tunnel driving

    NASA Astrophysics Data System (ADS)

    Spagnoli, G.; Fernández-Steeger, T.; Stanjek, H.; Feinendegen, M.; Post, C.; Azzam, R.

    2009-04-01

    During mechanical excavation with a tunnel boring machine (TBM) it is possible that clays stick to the cutting wheel and to other metal parts. The resulting delays in the progress of construction work, cause great economic damage and often disputes between the public awarding authorities and executing companies. One of the most important factors to reduce successfully the clay adhesion is the use of special polymers and foams. But why does the clay stick to the metal parts? A first step is to recognize which kind of clay mineralogy shows serious adhesion problems. The mechanical properties of clay and clay suspensions are primarily determined by surface chemistry and charge distribution at the interfaces, which in turn affect the arrangement of the clay structure. As we know, clay is a multi-phase material and its behaviour depends on numerous parameters such as: clay mineralogy, clay fraction, silt fraction, sand fraction, water content, water saturation, Atterberg limits, sticky limit, activity, cation exchange capacity, degree of consolidation and stress state. It is therefore likely that adhesion of clay on steel is also affected by these clay parameters. Samples of clay formations, which caused problems during tunnel driving, will be analyzed in laboratory. Mineralogical analyses (diffractometry, etc.) will be carried out to observe which minerals are responsible for adherence problems. To manipulate the physical properties, batch tests will be carried out in order to eliminate or reduce the adhesion on tool surfaces through variation of the zeta potential. Second step is the performance of vane shear tests on clay samples. Different pore fluid (distilled water, pure NaCl solution, ethanol and methanol) will be used to study the variation of the mechanical behaviour of clay depending on the dielectric constant of the fluids. This project is funded by the German Federal Ministry of Education and Research (BMBF) and the DFG (German Research Foundation) in the

  20. Adhesion mechanisms of bituminous crack sealant to aggregate and laboratory test development

    NASA Astrophysics Data System (ADS)

    Hajialiakbari Fini, Elham

    Crack sealing is a common pavement maintenance treatment because it extends pavement service life. However, crack sealant often fails prematurely due to a loss of adhesion. Since current test methods are mostly empirical and only provide a qualitative measure of bond strength, they cannot predict sealant adhesive failure accurately. Hence, there is an urgent need for test methods based on bituminous sealant rheology that can better predict sealant field performance. This study introduces three laboratory tests aimed to assess the bond property of hot-poured crack sealant to pavement crack walls. The three tests are designed to serve the respective needs of producers, engineers, and researchers. The first test implements the principle of surface energy to measure the thermodynamic work of adhesion, which is the energy spent in separating the two materials at the interface. The work of adhesion is reported as a measure of material compatibility at an interface. The second test is a direct adhesion test, a mechanical test which is designed to closely resemble both the installation process and the crack expansion due to thermal loading. This test uses the Direct Tension Test (DTT) device. The principle of the test is to apply a tensile force to detach the sealant from its aggregate counterpart. The maximum load, Pmax, and the energy to separation, E, are calculated and reported to indicate interface bonding. The third test implements the principles of fracture mechanics in a pressurized circular blister test. The apparatus is specifically designed to conduct the test for bituminous crack sealant, asphalt binder, or other bitumen-based materials. In this test, a fluid is injected at a constant rate at the interface between the substrate (aggregate or a standard material) and the adhesive (crack sealant) to create a blister. The fluid pressure and blister height are measured as functions of time; the data is used to calculate Interfacial Fracture Energy (IFE), which is a

  1. Wear and Adhesive Failure of Al2O3 Powder Coating Sprayed onto AISI H13 Tool Steel Substrate

    NASA Astrophysics Data System (ADS)

    Amanov, Auezhan; Pyun, Young-Sik

    2016-04-01

    In this study, an alumina (Al2O3) ceramic powder was sprayed onto an AISI H13 hot-work tool steel substrate that was subjected to sanding and ultrasonic nanocrystalline surface modification (UNSM) treatment processes. The significance of the UNSM technique on the adhesive failure of the Al2O3 coating and on the hardness of the substrate was investigated. The adhesive failure of the coating sprayed onto sanded and UNSM-treated substrates was investigated by a micro-scratch tester at an incremental load. It was found, based on the obtained results, that the coating sprayed onto the UNSM-treated substrate exhibited a better resistance to adhesive failure in comparison with that of the coating sprayed onto the sanded substrate. Dry friction and wear property of the coatings sprayed onto the sanded and UNSM-treated substrates were assessed by means of a ball-on-disk tribometer against an AISI 52100 steel ball. It was demonstrated that the UNSM technique controllably improved the adhesive failure of the Al2O3 coating, where the critical load was improved by about 31%. Thus, it is expected that the application of the UNSM technique to an AISI H13 tool steel substrate prior to coating may delay the adhesive failure and improve the sticking between the coating and the substrate thanks to the modified and hardened surface.

  2. Wear and Adhesive Failure of Al2O3 Powder Coating Sprayed onto AISI H13 Tool Steel Substrate

    NASA Astrophysics Data System (ADS)

    Amanov, Auezhan; Pyun, Young-Sik

    2016-07-01

    In this study, an alumina (Al2O3) ceramic powder was sprayed onto an AISI H13 hot-work tool steel substrate that was subjected to sanding and ultrasonic nanocrystalline surface modification (UNSM) treatment processes. The significance of the UNSM technique on the adhesive failure of the Al2O3 coating and on the hardness of the substrate was investigated. The adhesive failure of the coating sprayed onto sanded and UNSM-treated substrates was investigated by a micro-scratch tester at an incremental load. It was found, based on the obtained results, that the coating sprayed onto the UNSM-treated substrate exhibited a better resistance to adhesive failure in comparison with that of the coating sprayed onto the sanded substrate. Dry friction and wear property of the coatings sprayed onto the sanded and UNSM-treated substrates were assessed by means of a ball-on-disk tribometer against an AISI 52100 steel ball. It was demonstrated that the UNSM technique controllably improved the adhesive failure of the Al2O3 coating, where the critical load was improved by about 31%. Thus, it is expected that the application of the UNSM technique to an AISI H13 tool steel substrate prior to coating may delay the adhesive failure and improve the sticking between the coating and the substrate thanks to the modified and hardened surface.

  3. Mechanical Properties and Failure Mechanisms in Polycrystalline Graphene

    NASA Astrophysics Data System (ADS)

    Gonzalez, Joseph; Perriot, Romain; Oleynik, Ivan

    Large-scale growth of graphene using chemical vapor deposition produces polycrystalline material containing grain boundaries. Recent experiments demonstrate that polycrystalline graphene is nearly as strong as pristine. In this work, the mechanical properties of bi-crystal and polycrystalline graphene samples are investigated by simulating nano-indentation of a circular membrane using classical molecular dynamics and a novel Screened Environment Dependent Reactive Bond Order (SED-REBO) potential. The failure mechanisms and crack propagation in graphene samples containing grain boundaries are also discussed.

  4. Effects of Constituent Properties on Compression Failure Mechanisms

    NASA Technical Reports Server (NTRS)

    Hahn, H. T.

    1984-01-01

    Compression failure mechanisms were investigated through the analysis of matrix-embedded fiber bundles. The use of fiber bundle specimens can provide much needed information on compression failure mechanisms because failure of the bundle is well contained and can be monitored during testing. The method can clearly distinguish between buckling-induced failure and shear-induced failure. The results indicate that WY and T300 graphite fibers and E-glass fiber fail in buckling while the high-modulus P75S graphite fiber fails in shear. Buckling-induced failure becomes more evident with low-modulus fiber in softer epoxy.

  5. Collective cell migration induced by mechanical stress and substrate adhesiveness

    NASA Astrophysics Data System (ADS)

    Köpf, Michael H.

    2015-01-01

    Mechanical stress normal to the boundary of a tissue sheet can arise in both constrained as well as unconstrained epithelial layers through pushing and pulling of surrounding tissue and substrate adhesiveness, respectively. A continuum model is used to investigate how such stress influences the epithelial dynamics. Four types of spreading and motility can be identified: a uniformly stretched stationary state, uniform sheet migration, active stress compensation by polarization close to the boundary, and a wormlike progression by deformation waves. Analytical and numerical solutions are presented along with bifurcation diagrams using normal stress and active force as control parameters.

  6. Facile fabrication of superhydrophobic film with high adhesion and the adhesive mechanism

    NASA Astrophysics Data System (ADS)

    Guo, Yonggang; Wang, Zhongying; Wu, Haihong

    2015-11-01

    In this paper, rod-like basic cupric carbonate grew into bundles on the copper substrate by a simple direct oxidation process of copper in the weak alkaline solution of sodium bicarbonate. After surface chemical modification with fluoro-alkyl silane, the corresponding wettability of the as-prepared film changed from superhydrophilicity to superhydrophobicity with the contact angle larger than 150°. However, water droplets attached to the film even when the surface was upside down, showing a large adhesion between water droplets and the resulting film. The X-ray photoelectron spectroscopy results indicated the change of the surface chemical compositions before and after the modification with fluoro-alkyl silane. The surface microstructure was characterized by field-emission scanning electron microscopy. The adhesive mechanism was analyzed by the schematic diagram of the surface microstructure and the corresponding action model between the film and water droplet. The unique surface structure can make water droplets partially penetrate into the large pores, leading to the capillary effect and the near-Wenzel state.

  7. Failure stress criterion for adhesively bonded joint at different strain rates by using dynamic Arcan test device

    NASA Astrophysics Data System (ADS)

    Dufour, Ludovic; Bourel, Benjamin; Lauro, Franck; Haugou, Gregory; Leconte, Nicolas; Carrere, Nicolas

    2015-09-01

    The purpose of this work is to determine the failure criterion evolution of assembly bonded with a strain rate dependent adhesive. A new modified ARCAN device is then designed to obtain the average stress at failure under different loading angles and for strain up to 350 s-1. Tests are performed on a hydraulic jack machine and a Digital Image Correlation measurement is used to control the opening and the sliding displacements of the two substrates.

  8. Polyampholyte- and nanosilicate-based soft bionanocomposites with tailorable mechanical and cell adhesion properties.

    PubMed

    Jain, Minkle; Matsumura, Kazuaki

    2016-06-01

    Engineered tissues are excellent substitutes for treating organ failure associated with disease, injury, and degeneration. Designing new biomaterials with controlled release profiles, good mechanical properties, and cell adhesion characteristics can be useful for the formation of specific functional tissues. Here, we report the formulation of nanocomposite hydrogels based on carboxylated poly-l-lysine and synthetic clay laponite XLG in which four-arm polyethylene glycol with N-hydroxy succinimide ester (PEG-NHS) was used as the chemical crosslinker. Interestingly, the degradation of this gel could be adjusted from a few days to a few months. Incorporation of laponite XLG resulted in the formation of mechanically tough hydrogels and conferred cytocompatibility. The mechanical properties of the nanocomposite could be modulated by changing the crosslinking density and laponite concentration. The feasibility of using this system for cellular therapies was investigated by evaluating cell adhesion on the nanocomposite surface. Thus, these nanocomposites can serve as scaffolds with tunable mechanical and degradation properties that also provide structural integrity to tissue constructs. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 1379-1386, 2016. PMID:26833827

  9. On the mechanism of adhesion in biological systems

    NASA Astrophysics Data System (ADS)

    Persson, B. N. J.

    2003-04-01

    I study adhesion relevant to biological systems, e.g., flies, crickets and lizards, where the adhesive microstructures consist of arrays of thin fibers. The effective elastic modulus of the fiber arrays can be very small which is of fundamental importance for adhesion on smooth and rough substrates. I study how the adhesion depend on the substrate roughness amplitude and apply the theoretical results to lizards.

  10. A role for leukocyte-endothelial adhesion mechanisms in epilepsy

    PubMed Central

    Fabene, Paolo F.; Mora, Graciela Navarro; Martinello, Marianna; Rossi, Barbara; Merigo, Flavia; Ottoboni, Linda; Bach, Simona; Angiari, Stefano; Benati, Donatella; Chakir, Asmaa; Zanetti, Lara; Schio, Federica; Osculati, Antonio; Marzola, Pasquina; Nicolato, Elena; Homeister, Jonathon W.; Xia, Lijun; Lowe, John B.; McEver, Rodger P.; Osculati, Francesco; Sbarbati, Andrea; Butcher, Eugene C.; Constantin, Gabriela

    2009-01-01

    The mechanisms involved in the pathogenesis of epilepsy, a chronic neurological disorder that affects approximately 1 percent of the world population, are not well understood1–3. Using a mouse model of epilepsy, we show that seizures induce elevated expression of vascular cell adhesion molecules and enhanced leukocyte rolling and arrest in brain vessels mediated by the leukocyte mucin P-selectin glycoprotein ligand-1 (PSGL-1) and leukocyte integrins α4β1 and αLβ2. Inhibition of leukocyte-vascular interactions either with blocking antibodies, or in mice genetically deficient in functional PSGL-1, dramatically reduced seizures. Treatment with blocking antibodies following acute seizures prevented the development of epilepsy. Neutrophil depletion also inhibited acute seizure induction and chronic spontaneous recurrent seizures. Blood-brain barrier (BBB) leakage, which is known to enhance neuronal excitability, was induced by acute seizure activity but was prevented by blockade of leukocyte-vascular adhesion, suggesting a pathogenetic link between leukocyte-vascular interactions, BBB damage and seizure generation. Consistent with potential leukocyte involvement in the human, leukocytes were more abundant in brains of epileptics than of controls. Our results suggest leukocyte-endothelial interaction as a potential target for the prevention and treatment of epilepsy. PMID:19029985

  11. Peptides@mica: from affinity to adhesion mechanism.

    PubMed

    Gladytz, A; John, T; Gladytz, T; Hassert, R; Pagel, M; Risselada, H J; Naumov, S; Beck-Sickinger, A G; Abel, B

    2016-09-14

    Investigating the adsorption of peptides on inorganic surfaces, on the molecular level, is fundamental for medicinal and analytical applications. Peptides can be potent as linkers between surfaces and living cells in biochips or in implantation medicine. Here, we studied the adsorption process of the positively charged pentapeptide RTHRK, a recently identified binding sequence for surface oxidized silicon, and novel analogues thereof to negatively charged mica surfaces. Homogeneous formation of monolayers in the nano- and low micromolar peptide concentration range was observed. We propose an alternative and efficient method to both quantify binding affinity and follow adhesion behavior. This method makes use of the thermodynamic relationship between surface coverage, measured by atomic force microscopy (AFM), and the concomitant free energy of adhesion. A knowledge-based fit to the autocorrelation of the AFM images was used to correct for a biased surface coverage introduced by the finite lateral resolution of the AFM. Binding affinities and mechanisms were further explored by large scale molecular dynamics (MD) simulations. The combination of well validated MD simulations with topological data from AFM revealed a better understanding of peptide adsorption processes on the atomistic scale. We demonstrate that binding affinity is strongly determined by a peptide's ability to form salt bridges and hydrogen bonds with the surface lattice. Consequently, differences in hydrogen bond formation lead to substantial differences in binding affinity despite conservation of the peptide's overall charge. Further, MD simulations give access to relative changes in binding energy of peptide variations in comparison to a lead compound. PMID:27491508

  12. Neutrophil adhesion and chemotaxis depend on substrate mechanics

    NASA Astrophysics Data System (ADS)

    Jannat, Risat A.; Robbins, Gregory P.; Ricart, Brendon G.; Dembo, Micah; Hammer, Daniel A.

    2010-05-01

    Neutrophil adhesion to the vasculature and chemotaxis within tissues play critical roles in the inflammatory response to injury and pathogens. Unregulated neutrophil activity has been implicated in the progression of numerous chronic and acute diseases such as rheumatoid arthritis, asthma and sepsis. Cell migration of anchorage-dependent cells is known to depend on both chemical and mechanical interactions. Although neutrophil responses to chemical cues have been well characterized, little is known about the effect of underlying tissue mechanics on neutrophil adhesion and migration. To address this question, we quantified neutrophil migration and traction stresses on compliant hydrogel substrates with varying elasticity in a micromachined gradient chamber in which we could apply either a uniform concentration or a precise gradient of the bacterial chemoattractant fMLP. Neutrophils spread more extensively on substrates of greater stiffness. In addition, increasing the stiffness of the substrate leads to a significant increase in the chemotactic index for each fMLP gradient tested. As the substrate becomes stiffer, neutrophils generate higher traction forces without significant changes in cell speed. These forces are often displayed in pairs and focused in the uropod. Increases in the mean fMLP concentration beyond the KD of the receptor lead to a decrease in chemotactic index on all surfaces. Blocking with an antibody against β2-integrins leads to a significant reduction, but not an elimination, of directed motility on stiff materials, but no change in motility on soft materials, suggesting neutrophils can display both integrin-dependent and integrin-independent motility. These findings are critical for understanding how neutrophil migration may change in different mechanical environments in vivo and can be used to guide the design of migration inhibitors that more efficiently target inflammation.

  13. Quantifying adhesion energy of mechanical coatings at atomistic scale

    NASA Astrophysics Data System (ADS)

    Yin, Deqiang; Peng, Xianghe; Qin, Yi; Feng, Jiling; Wang, Zhongchang

    2011-12-01

    Coatings of transition metal compounds find widespread technological applications where adhesion is known to influence or control functionality. Here, we, by first-principles calculations, propose a new way to assess adhesion in coatings and apply it to analyze the TiN coating. We find that the calculated adhesion energies of both the (1 1 1) and (0 0 1) orientations are small under no residual stress, yet increase linearly once the stress is imposed, suggesting that the residual stress is key to affecting adhesion. The strengthened adhesion is found to be attributed to the stress-induced shrinkage of neighbouring bonds, which results in stronger interactions between bonds in TiN coatings. Further finite elements simulation (FEM) based on calculated adhesion energy reproduces well the initial cracking process observed in nano-indentation experiments, thereby validating the application of this approach in quantifying adhesion energy of surface coating systems.

  14. Failure and fatigue mechanisms in composite materials

    NASA Technical Reports Server (NTRS)

    Rosen, B. W.; Kulkarni, S. V.; Mclaughlin, P. V., Jr.

    1975-01-01

    A phenomenological description of microfailure under monotonic and cyclic loading is presented, emphasizing the significance of material inhomogeneity for the analysis. Failure in unnotched unidirectional laminates is reviewed for the cases of tension, compression, shear, transverse normal, and combined loads. The failure of notched composite laminates is then studied, with particular attention paid to the effect of material heterogeneity on load concentration factors in circular holes in such laminates, and a 'materials engineering' shear-lay type model is presented. The fatigue of notched composites is discussed with the application of 'mechanistic wearout' model for determining crack propagation as a function of the number of fatigue cycles.-

  15. Failure mechanism characterization of platinum alloy

    NASA Technical Reports Server (NTRS)

    Rosen, J. M.; Mcfarlen, W. T.

    1986-01-01

    This article describes procedures and results of testing performed on a platinum/10-percent rhodium, thin-wall tubular product. The purpose of the testing was to develop exemplar SEM fractographs to be used to characterize failures under various environmental conditions. Conditions evaluated for the platinum alloys included high temperature, hydrogen environment, braze metal contamination, and cyclic loading.

  16. Cell-adhesive and mechanically tunable glucose-based biodegradable hydrogels

    PubMed Central

    Shin, Hyeongho; Nichol, Jason W.; Khademhosseini, Ali

    2010-01-01

    The development of materials with biomimetic mechanical and biological properties is of great interest for regenerative medicine applications. In particular, hydrogels are a promising class of biomaterials due to their high water content, which mimic that of natural tissues. We have synthesized a hydrophilic biodegradable polymer, designated poly(glucose malate)methacrylate (PGMma), that is composed of glucose and malic acid which are commonly found in the human metabolic system. This polymer is made photocrosslinkable by the incorporation of methacrylate groups. The resulting properties of the hydrogels can be tuned by altering the reacting ratio of the starting materials, the degree of methacrylation, and the polymer concentration of the resultant hydrogel. Hydrogels exhibited compressive moduli ranging from 1.8 ± 0.4kPa to 172.7 ± 36kPa with compressive strain at failure from 37.5 ± 0.9% to 61.2 ± 1.1%, and hydration by mass ranging from 18.7 ± 0.5% to 114.1 ± 1.3%. PGMma hydrogels also showed a broad range of degradation rates and were cell-adhesive, enabling the spreading of adherent cells. Overall, this work introduces a class of cell adhesive, mechanically tunable and biodegradable glucose-based hydrogels that may be useful for various tissue engineering and cell culture applications. PMID:20647064

  17. The peel test in experimental adhesive fracture mechanics

    NASA Technical Reports Server (NTRS)

    Anderson, G. P.; Devries, K. L.; Williams, M. L.

    1974-01-01

    Several testing methods have been proposed for obtaining critical energy release rate or adhesive fracture energy in bond systems. These tests include blister, cone, lap shear, and peel tests. Peel tests have been used for many years to compare relative strengths of different adhesives, different surface preparation techniques, etc. The present work demonstrates the potential use of the peel test for obtaining adhesive fracture energy values.

  18. Investigation of accelerated stress factors and failure/degradation mechanisms in terrestrial solar cells

    NASA Technical Reports Server (NTRS)

    Lathrop, J. W.

    1983-01-01

    Results of an ongoing research program into the reliability of terrestrial solar cells are presented. Laboratory accelerated testing procedures are used to identify failure/degradation modes which are then related to basic physical, chemical, and metallurgical phenomena. In the most recent tests, ten different types of production cells, both with and without encapsulation, from eight different manufacturers were subjected to a variety of accelerated tests. Results indicated the presence of a number of hitherto undetected failure mechanisms, including Schottky barrier formation at back contacts and loss of adhesion of grid metallization. The mechanism of Schottky barrier formation is explained by hydrogen, formed by the dissociation of water molecules at the contact surface, diffusing to the metal semiconductor interface. This same mechanism accounts for the surprising increase in sensitivity to accelerated stress conditions that was observed in some cells when encapsulated.

  19. Thesaurus of terms for information on mechanics of structural failure

    NASA Technical Reports Server (NTRS)

    Carpenter, J. L., Jr.; Moya, N.

    1973-01-01

    A Thesaurus of approximately 700 subject terms used to describe the six problem areas in the mechanics of structural failure is presented. The initial criteria for the selection of terms are their significance and frequency of use in the literature describing the mechanics of structural failure. The purpose of the Thesaurus is to provide the Aerospace Safety Research and Data Institute a list of key works and identifiers that afford effective retrieval of information regarding failure modes and mechanisms for aerospace structures. The Thesaurus includes both a conventional listing of subject terms and a Key Words In Context (KWIC) listing.

  20. Mechanical switching and coupling between two dissociation pathways in a P-selectin adhesion bond

    NASA Astrophysics Data System (ADS)

    Evans, Evan; Leung, Andrew; Heinrich, Volkmar; Zhu, Cheng

    2004-08-01

    Many biomolecular bonds exhibit a mechanical strength that increases in proportion to the logarithm of the rate of force application. Consistent with exponential decrease in bond lifetime under rising force, this kinetically limited failure reflects dissociation along a single thermodynamic pathway impeded by a sharp free energy barrier. Using a sensitive force probe to test the leukocyte adhesion bond P-selectin glycoprotein ligand 1 (PSGL-1)-P-selectin, we observed a linear increase of bond strength with each 10-fold increase in the rate of force application from 300 to 30,000 pN/sec, implying a single pathway for failure. However, the strength and lifetime of PSGL-1-P-selectin bonds dropped anomalously when loaded below 300 pN/sec, demonstrating unexpectedly faster dissociation and a possible second pathway for failure. Remarkably, if first loaded by a "jump" in force to 20-30 pN, the bonds became strong when subjected to a force ramp as slow as 30 pN/sec and exhibited the same single-pathway kinetics under all force rates. Applied in this way, a new "jump/ramp" mode of force spectroscopy was used to show that the PSGL-1-P-selectin bond behaves as a mechanochemical switch where force history selects between two dissociation pathways with markedly different properties. Furthermore, replacing PSGL-1 by variants of its 19-aa N terminus and by the crucial tetrasaccharide sialyl LewisX produces dramatic changes in the failure kinetics, suggesting a structural basis for the two pathways. The two-pathway switch seems to provide a mechanism for the "catch bond" response observed recently with PSGL-1-P-selectin bonds subjected to small-constant forces.

  1. The mechanism of binding of neural cell adhesion molecules.

    PubMed

    Hoffman, S; Edelman, G M

    1984-01-01

    The experimental results reviewed in this paper strongly suggest that the molecular mechanism of N-CAM-mediated cell adhesion involves the direct interaction of N-CAM molecules on one cell with N-CAM molecules on a second cell. The rate of this aggregation has a high-order dependence on the local N-CAM concentration, and is inversely related to the sialic acid content of the N-CAM molecules involved. In accordance with their relative sialic acid concentrations, the relative rates of aggregation mediated by E and A forms of N-CAM are A-A greater than A-E greater than E-E. Further removal of sialic acid from N-CAM below the level found in the A form gives little further enhancement of aggregation. These results provide one basis upon which to interpret the modulation hypothesis (Edelman, 1983) for control of N-CAM function, i.e. the adhesive strength of N-CAM bonds in an in vitro system can be altered in a graded manner over a wide range by variations in the local surface density of N-CAM or by chemical modification of N-CAM (differential sialylation). It is important to stress that these results do not preclude the possibility of other forms of modulation of N-CAM function or the function of other molecules in cell-cell interactions. It will be much more difficult to assess the role of N-CAM and the modulation of its function on pattern formation in vivo. It is pertinent to mention, however, that recent experiments on transformed neural cells (Greenberg et al., 1984) show loss of N-CAM following transformation with accompanying loss of aggregation and increased motility of the transformed cells. Aside from the possible implications for metastasis (transformation has for the first time been shown to affect a defined CAM and alter cellular sociology), these findings are consonant with the notion that alteration of surface N-CAM affects expression of other cellular processes. Clearly additional experiments are required to define the mechanisms by which this occurs. In

  2. Instantly switchable adhesion of bridged fibrillar adhesive via gecko-inspired detachment mechanism and its application to a transportation system

    NASA Astrophysics Data System (ADS)

    Bae, Won-Gyu; Kim, Doogon; Suh, Kahp-Yang

    2013-11-01

    Inspired by the exceptional climbing ability of gecko lizards, artificial fibrillar adhesives have been extensively studied over the last decade both experimentally and theoretically. Therefore, a new leap towards practical uses beyond the academic horizon is timely and highly anticipated. To this end, we present a fibrillar adhesive in the form of bridged micropillars and its application to a transportation system with the detachment mechanism inspired by the climbing behaviour of gecko lizards. The adhesive shows strong normal attachment (~30 N cm-2) as well as easy and fast detachment within 0.5 s without involving complex dynamic mechanisms or specific stimulus-responsive materials. The fabrication of the bridged micropillars consists of replica moulding of polydimethylsiloxane (PDMS) micropillars, transfer of the PDMS precursor to the heads of the micropillars, and inverse placement on an inert Teflon-coated surface. Owing to the spontaneous interconnections of low viscosity PDMS precursor, bridged micropillars with a uniform capping nanomembrane (~800 nm thickness) are formed over a large area. Interestingly, macroscopic adhesion in the normal direction can be immediately switched between on and off states by changing the two detachment modes of pulling and peeling, respectively. To prove the potential of the fibrillar adhesive for practical use, an automated transportation system is demonstrated for lifting and releasing a mass of stacked glass slides over 1000 cycles of attachment and detachment.Inspired by the exceptional climbing ability of gecko lizards, artificial fibrillar adhesives have been extensively studied over the last decade both experimentally and theoretically. Therefore, a new leap towards practical uses beyond the academic horizon is timely and highly anticipated. To this end, we present a fibrillar adhesive in the form of bridged micropillars and its application to a transportation system with the detachment mechanism inspired by the

  3. Mechanical failure and glass transition in metallic glasses

    SciTech Connect

    Egami, Takeshi

    2011-01-01

    The current majority view on the phenomenon of mechanical failure in metallic glasses appears to be that it is caused by the activity of some structural defects, such as free-volumes or shear transformation zones, and the concentration of such defects is small, only of the order of 1%. However, the recent results compel us to revise this view. Through molecular dynamics simulation it has been shown that mechanical failure is the stress-induced glass transition. According to our theory the concentration of the liquid-like sites (defects) is well over 20% at the glass transition. We suggest that the defect concentration in metallic glasses is actually very high, and percolation of such defects causes atomic avalanche and mechanical failure. In this article we discuss the glass transition, mechanical failure and viscosity from such a point of view.

  4. Ionizing radiation increases adhesiveness of human aortic endothelial cells via a chemokine-dependent mechanism.

    PubMed

    Khaled, Saman; Gupta, Kiran B; Kucik, Dennis F

    2012-05-01

    Exposure to radiation from a variety of sources is associated with increased risk of heart disease and stroke. Since radiation also induces inflammation, a possible mechanism is a change in the adhesiveness of vascular endothelial cells, triggering pro-atherogenic accumulation of leukocytes. To investigate this mechanism at the cellular level, the effect of X rays on adhesiveness of cultured human aortic endothelial cells (HAECs) was determined. HAECs were grown as monolayers and exposed to 0 to 30 Gy X rays, followed by measurement of adhesiveness under physiological shear stress using a flow chamber adhesion assay. Twenty-four hours after irradiation, HAEC adhesiveness was increased, with a peak effect at 15 Gy. Radiation had no significant effect on surface expression of the endothelial adhesion molecules ICAM-1 and VCAM-1. Antibody blockade of the leukocyte integrin receptors for ICAM-1 and VCAM-1, however, abolished the radiation-induced adhesiveness. Since these leukocyte integrins can be activated by chemokines presented on the endothelial cell surface, the effect of pertussis toxin (PTX), an inhibitor of chemokine-mediated integrin activation, was tested. PTX specifically inhibited radiation-induced adhesiveness, with no significant effect on nonirradiated cells. Therefore, radiation induces increased adhesiveness of aortic endothelial cells through chemokine-dependent signaling from endothelial cells to leukocytes, even in the absence of increased expression of the adhesion molecules involved. PMID:22087741

  5. Mechanical properties of adhesive systems at cryogenic and other temperatures

    NASA Technical Reports Server (NTRS)

    Staton, W. L.; Klich, P. J.; Cockrell, C. E.

    1982-01-01

    This paper presents a summary of the National Transonic Facility (NTF) fan blade adhesive characterization tests. Data was obtained at -300 F, room temperature (RT) and 200 F. The adhesive characterization data was acquired using specimens fabricated from materials orientated to simulate the lay up of the fan blades. Specimen fabrication, characterization tests, test equipment, test data, results and concluding remarks are reported. Adhesive test results are presented for specimens of the following types: lap shear, double lap shear, butt, short beam shear, flexure, and differential strain.

  6. Mechanism of tantalum adhesion on SiLK{sup TM}

    SciTech Connect

    Hu Yue; Yang Shuowang; Chen Xiantong; Lu Dong; Feng Yuanping; Wu Ping

    2005-09-19

    Tantalum adhesion on SiLK{sup TM} was investigated using first-principles method based on density functional theory. Phenylene groups were found to play a major role and the adjacent semi-benzene rings also contribute significantly to Ta adhesion on SiLK{sup TM}. In addition, the degradation effects of H{sub 2}/He reactive plasma clean on Ta adhesion on SiLK{sup TM} was investigated. Based on our findings, argon plasma treatment was suggested and implemented after reactive plasma cleaning process, which resulted in integration of SiLK{sup TM} with Cu up to seven metal layers.

  7. The effect of adhesive layer elasticity on the fracture mechanics of a blister test specimen

    NASA Technical Reports Server (NTRS)

    Updike, D. P.

    1975-01-01

    An analytical model of a blister type specimen for evaluating adhesive bond strength was developed. Plate theory with shear deformation was used to model the deformation of the plate, and elastic deformation of the adhesive layer is taken into account. It is shown that the inclusion of the elastic deformation of the adhesive layer can have a significant influence in the energy balance calculations of fracture mechanics.

  8. T-cadherin structures reveal a novel adhesive binding mechanism

    SciTech Connect

    Ciatto, Carlo; Bahna, Fabiana; Zampieri, Niccolò; VanSteenhouse, Harper C.; Katsamba, Phini S; Ahlsen, Goran; Harrison, Oliver J.; Brasch, Julia; Jin, Xiangshu; Posy, Shoshana; Vendome, Jeremie; Ranscht, Barbara; Jessell, Thomas M.; Honig, Barry; Shapiro, Lawrence

    2010-03-30

    Vertebrate genomes encode 19 classical cadherins and about 100 nonclassical cadherins. Adhesion by classical cadherins depends on binding interactions in their N-terminal EC1 domains, which swap N-terminal {beta}-strands between partner molecules from apposing cells. However, strand-swapping sequence signatures are absent from nonclassical cadherins, raising the question of how these proteins function in adhesion. Here, we show that T-cadherin, a glycosylphosphatidylinositol (GPI)-anchored cadherin, forms dimers through an alternative nonswapped interface near the EC1-EC2 calcium-binding sites. Mutations within this interface ablate the adhesive capacity of T-cadherin. These nonadhesive T-cadherin mutants also lose the ability to regulate neurite outgrowth from T-cadherin-expressing neurons. Our findings reveal the likely molecular architecture of the T-cadherin homophilic interface and its requirement for axon outgrowth regulation. The adhesive binding mode used by T-cadherin may also be used by other nonclassical cadherins

  9. Effect of surface treatment of brackets and mechanical cycling on adhesion to enamel.

    PubMed

    Arrais, Fabiola Rossato; Degrazia, Felipe; Peres, Bernardo Urbanetto; Ferrazzo, Vilmar Antonio; Grehs, Renesio Armindo; Valandro, Luiz Felipe

    2014-01-01

    This in vitro study sought to evaluate how surface conditioning from bracket and mechanical cycling aging affected the bond strength between metallic brackets and bovine enamel, and to determine the adhesive remnant index. Eighty bovine incisors were embedded in acrylic resin using polyvinyl chloride rings and divided into 4 groups based on surface treatment (n = 20). Group 1 (control) received no surface treatment, Group 2 specimens were sandblasted with aluminum oxide particles, Group 3 specimens were sandblasted with silicon oxide and treated with a tribochemichemical silica coupling agent, and Group 4 specimens were primed with a multidomain protein-based agent. Half of the specimens were submitted to shear bond testing, while the others were subjected to mechanical cycling. ANOVA showed that mechanical cycling did not have a significant influence on bond strength (P = 0.9244), while surface conditioning of the brackets did (P = 0.0001). Tukey's test results were similar for mechanical cycling, and indicated that only Group 3 significantly improved the resin bond to the brackets; however, this group also demonstrated the highest percentage of enamel failure. PMID:24784526

  10. Evaluation of the mechanical properties of dental adhesives and glass-ionomer cements.

    PubMed

    Magni, Elisa; Ferrari, Marco; Hickel, Reinhard; Ilie, Nicoleta

    2010-02-01

    Adhesives and lining/base materials should relieve the stresses concentrated at the tooth/restoration interface. The study aimed at comparing the mechanical properties of eight adhesives and six glass-ionomer cements (GICs). The adhesives were applied on dentin disks, whereas 2 mm x 3 mm x 2 mm GICs specimens were prepared in a teflon mold. Vicker's hardness (VH), elastic modulus (E), creep (Cr) and elastic work (We/Wtot) were measured with a micro hardness indenter. One-way ANOVA and Tukey's test were used to compare the mechanical properties within each materials' type and among the materials' classes. Enamel and dentin were used as references. Significant differences were detected within each materials' type and among the materials' classes and enamel and dentin. GICs were superior to adhesives in VH and E and showed a VH similar to dentin. GICs presented mechanical properties more similar to enamel and dentin than adhesives. PMID:19241096

  11. An Adhesion-Dependent Switch between Mechanisms That Determine Motile Cell Shape

    PubMed Central

    Barnhart, Erin L.; Lee, Kun-Chun; Keren, Kinneret; Mogilner, Alex; Theriot, Julie A.

    2011-01-01

    Keratocytes are fast-moving cells in which adhesion dynamics are tightly coupled to the actin polymerization motor that drives migration, resulting in highly coordinated cell movement. We have found that modifying the adhesive properties of the underlying substrate has a dramatic effect on keratocyte morphology. Cells crawling at intermediate adhesion strengths resembled stereotypical keratocytes, characterized by a broad, fan-shaped lamellipodium, clearly defined leading and trailing edges, and persistent rates of protrusion and retraction. Cells at low adhesion strength were small and round with highly variable protrusion and retraction rates, and cells at high adhesion strength were large and asymmetrical and, strikingly, exhibited traveling waves of protrusion. To elucidate the mechanisms by which adhesion strength determines cell behavior, we examined the organization of adhesions, myosin II, and the actin network in keratocytes migrating on substrates with different adhesion strengths. On the whole, our results are consistent with a quantitative physical model in which keratocyte shape and migratory behavior emerge from the self-organization of actin, adhesions, and myosin, and quantitative changes in either adhesion strength or myosin contraction can switch keratocytes among qualitatively distinct migration regimes. PMID:21559321

  12. Nano-mechanics of Tunable Adhesion using Non Covalent Forces

    SciTech Connect

    Kenneth Liechti

    2012-09-08

    The objective of this program was to examine, via experiment and atomistic and continuum analysis, coordinated noncovalent bonding over a range of length scales with a view to obtaining modulated, patterned and reversible bonding at the molecular level. The first step in this project was to develop processes for depositing self-assembled monolayers (SAMs) bearing carboxylic acid and amine moieties on Si (111) surfaces and probe tips of an interfacial force microscope (IFM). This allowed the adhesive portion of the interactions between functionalized surfaces to be fully captured in the force-displacement response (force profiles) that are measured by the IFM. The interactionswere extracted in the form of traction-separation laws using combined molecular and continuum stress analyses. In this approach, the results of molecular dynamics analyses of SAMs subjected to simple stress states are used to inform continuum models of their stress-strain behavior. Continuum analyses of the IFM experiment were then conducted, which incorporate the stress-strain behavior of the SAMs and traction-separation relations that represent the interactions between the tip and functionalized Si surface. Agreement between predicted and measured force profiles was taken to imply that the traction-separation relations have been properly extracted. Scale up to larger contact areas was considered by forming Si/SAM/Si sandwiches and then separating them via fracture experiments. The mode 1 traction-separation relations have been extracted using fracture mechanics concepts under mode 1 and mixed-mode conditions. Interesting differences were noted between the three sets of traction-separation relations.

  13. Chemical adhesion rather than mechanical retention enhances resin bond durability of a dental glass-ceramic with leucite crystallites.

    PubMed

    Meng, X F; Yoshida, K; Gu, N

    2010-08-01

    This study aims to evaluate the effect of chemical adhesion by a silane coupler and mechanical retention by hydrofluoric acid (HFA) etching on the bond durability of resin to a dental glass ceramic with leucite crystallites. Half of the ceramic plates were etched with 4.8% HFA (HFA group) for 60 s, and the other half were not treated (NoHFA group). The scale of their surface roughness and rough area was measured by a 3D laser scanning microscope. These plates then received one of the following two bond procedures to form four bond test groups: HFA/cement, NoHFA/cement, HFA/silane/cement and NoHFA/silane/cement. The associated micro-shear bond strength and bond failure modes were tested after 0 and 30 000 thermal water bath cycles. Four different silane/cement systems (Monobond S/Variolink II, GC Ceramic Primer/Linkmax HV, Clearfil Ceramic Primer/Clearfil Esthetic Cement and Porcelain Liner M/SuperBond C&B) were used. The data for each silane/cement system were analyzed by three-way ANOVA. HFA treatment significantly increased the surface R(a) and R(y) values and the rough area of the ceramic plates compared with NoHFA treatment. After 30 000 thermal water bath cycles, the bond strength of all the test groups except the HFA/Linkmax HV group was significantly reduced, while the HFA/Linkmax HV group showed only adhesive interface failure. The other HFA/cement groups and all NoHFA/cement groups lost bond strength completely, and all NoHFA/silane/cement groups with chemical adhesion had significantly higher bond strength and more ceramic cohesive failures than the respective HFA/cement groups with mechanical retention. The result of the HFA/silane/cement groups with both chemical adhesion and mechanical retention revealed that HFA treatment could enhance the bond durability of resin/silanized glass ceramics, which might result from the increase of the chemical adhesion area on the ceramic rough surface and subsequently reduced degradation speed of the silane coupler

  14. A fracture mechanics approach for designing adhesively bonded joints

    NASA Technical Reports Server (NTRS)

    Johnson, W. S.; Mall, S.

    1983-01-01

    An analytical and experimental investigation was undertaken to determine if the adhesive debond initiation stress could be predicted for arbitrary joint geometries. The analysis was based upon a threshold total strain-energy-release rate (Gth) concept. Two bonded systems were tested: T300/5208 graphite/epoxy adherends bonded with either EC-3445 or FM-300 adhesive. The Gth for each adhesive was determined from cracked-lap-shear (CLS) specimens by initiation tests. Finite-element analyses of various tapered CLS specimen geometries predicted the specimen stress at which the total strain-energy-release rate (GT) equaled Gth at the joint tip. Experiments verified the predictions. The approach described herein predicts the maximum stress at which an adhesive joint can be cycled yet not debond. Furthermore, total strain-energy-release rate appeared to be the driving parameter for cyclic debonding and debond initiation in structural adhesives. In addition, debond initiation and growth were found to occur with virtually no peel stress present.

  15. AFM probing of polymer/nanofiller interfacial adhesion and its correlation with bulk mechanical properties in a poly(ethylene terephthalate) nanocomposite.

    PubMed

    Aoyama, Shigeru; Park, Yong Tae; Macosko, Christopher W; Ougizawa, Toshiaki; Haugstad, Greg

    2014-11-01

    The interfacial adhesion between polymer and nanofiller plays an important role in affecting the properties of nanocomposites. The detailed relationship between interfacial adhesion and bulk properties, however, is unclear. In this work, we developed an atomic force microscopy (AFM)-based abrasive scanning methodology, as applied to model laminate systems, to probe the strength of interfacial adhesion relevant to poly(ethylene terephthalate) (PET)/graphene or clay nanocomposites. Graphite and mica substrates covered with ∼2 nm thick PET films were abrasively sheared by an AFM tip as a model measurement of interfacial strength between matrix PET and dispersed graphene and clay, respectively. During several abrasive raster-scan cycles, PET was shear-displaced from the scanned region. At temperatures below the PET glass transition, PET on graphite exhibited abrupt delamination (i.e., full adhesive failure), whereas PET on mica did not; rather, it exhibited a degree of cohesive failure within the shear-displaced layer. Moreover, 100-fold higher force scanning procedures were required to abrade through an ultimate "precursor" layer of PET only ∼0.2-0.5 nm thick, which must be largely disentangled from the matrix polymer. Thus, the adhesive interface of relevance to the strength of clay-filler nanocomposites is between matrix polymer and strongly bound polymer. At 90 °C, above the bulk PET glass transition temperature, the PET film exhibited cohesive failure on both graphite and mica. Our results suggest that there is little difference in the strength of the relevant interfacial adhesion in the two nanocomposites within the rubbery dynamic regime. Further, the bulk mechanical properties of melt mixed PET/graphene and PET/clay nanocomposites were evaluated by dynamic mechanical analysis. The glassy dynamic storage modulus of the PET/clay nanocomposite was higher than that of PET/graphene, correlating with the differences in interfacial adhesion probed by AFM. PMID

  16. Adhesion Failures Determine the Pattern of Choroidal Neovascularization in the Eye: A Computer Simulation Study

    PubMed Central

    Shirinifard, Abbas; Glazier, James Alexander; Swat, Maciej; Gens, J. Scott; Family, Fereydoon; Jiang, Yi; Grossniklaus, Hans E.

    2012-01-01

    Choroidal neovascularization (CNV) of the macular area of the retina is the major cause of severe vision loss in adults. In CNV, after choriocapillaries initially penetrate Bruch's membrane (BrM), invading vessels may regress or expand (CNV initiation). Next, during Early and Late CNV, the expanding vasculature usually spreads in one of three distinct patterns: in a layer between BrM and the retinal pigment epithelium (sub-RPE or Type 1 CNV), in a layer between the RPE and the photoreceptors (sub-retinal or Type 2 CNV) or in both loci simultaneously (combined pattern or Type 3 CNV). While most studies hypothesize that CNV primarily results from growth-factor effects or holes in BrM, our three-dimensional simulations of multi-cell model of the normal and pathological maculae recapitulate the three growth patterns, under the hypothesis that CNV results from combinations of impairment of: 1) RPE-RPE epithelial junctional adhesion, 2) Adhesion of the RPE basement membrane complex to BrM (RPE-BrM adhesion), and 3) Adhesion of the RPE to the photoreceptor outer segments (RPE-POS adhesion). Our key findings are that when an endothelial tip cell penetrates BrM: 1) RPE with normal epithelial junctions, basal attachment to BrM and apical attachment to POS resists CNV. 2) Small holes in BrM do not, by themselves, initiate CNV. 3) RPE with normal epithelial junctions and normal apical RPE-POS adhesion, but weak adhesion to BrM (e.g. due to lipid accumulation in BrM) results in Early sub-RPE CNV. 4) Normal adhesion of RBaM to BrM, but reduced apical RPE-POS or epithelial RPE-RPE adhesion (e.g. due to inflammation) results in Early sub-retinal CNV. 5) Simultaneous reduction in RPE-RPE epithelial binding and RPE-BrM adhesion results in either sub-RPE or sub-retinal CNV which often progresses to combined pattern CNV. These findings suggest that defects in adhesion dominate CNV initiation and progression. PMID:22570603

  17. Mechanisms of platelet adhesion to the basal lamina.

    PubMed Central

    Huang, T. W.; Benditt, E. P.

    1978-01-01

    The human glomerular basal lamina (HGBL) is composed of collagenous and noncollagenous glycoproteins. We assessed the role played by each costituent in platelet-basal-lamina interaction by selective cleavage and removal of each component by clostridial collagenase or by pepsin. When noncollagenous proteins are removed from HGBL, human platelets exhibit littel reactivity toward the residual collagen framework of the isolated basal lamina. With the noncollagen matrix of basal lamina, after removal of the bulk of the collagen, platelet adhesion and spreading proceed normally in the presence of divalent cations, similar to what occurs on intact basal lamina. No platelet degranulation or aggregation is observed. The results indicate that the basal lamina collagen, even in its native packing arrangement, lacks affinity for platelet adhesion and is incapable of triggering platelet release reactions. Platelet adhesion and spreading on the basal lamina appears to depend primarily on the presence of the noncollagen components and to require divalent cations. The data suggest the presence on platelets of receptors for basal lamina distinct from those for interstitial collagens. These receptors activate a unique modulation of platelet behavior, ie, adhesion and spreading without degranulation. A difference in biologic function of the basal lamina and interstitial collagens is apparent in these experiments. Images Figure 4 Figure 5 Figure 6 Figure 1 Figure 2 Figure 3 PMID:210672

  18. Mechanisms of fluid production in smooth adhesive pads of insects.

    PubMed

    Dirks, Jan-Henning; Federle, Walter

    2011-07-01

    Insect adhesion is mediated by thin fluid films secreted into the contact zone. As the amount of fluid affects adhesive forces, a control of secretion appears probable. Here, we quantify for the first time the rate of fluid secretion in adhesive pads of cockroaches and stick insects. The volume of footprints deposited during consecutive press-downs decreased exponentially and approached a non-zero steady state, demonstrating the presence of a storage volume. We estimated its size and the influx rate into it from a simple compartmental model. Influx was independent of step frequency. Fluid-depleted pads recovered maximal footprint volumes within 15 min. Pads in stationary contact accumulated fluid along the perimeter of the contact zone. The initial fluid build-up slowed down, suggesting that flow is driven by negative Laplace pressure. Freely climbing stick insects left hardly any traceable footprints, suggesting that they save secretion by minimizing contact area or by recovering fluid during detachment. However, even the highest fluid production rates observed incur only small biosynthesis costs, representing less than 1 per cent of the resting metabolic rate. Our results show that fluid secretion in insect wet adhesive systems relies on simple physical principles, allowing for passive control of fluid volume within the contact zone. PMID:21208970

  19. A novel composite-to-composite adhesive bond mechanism.

    PubMed

    Akimoto, Naotake; Sakamoto, Tominori; Kubota, Yuya; Kondo, Yoshie; Momoi, Yasuko

    2011-01-01

    The purpose of this study was to determine if adhesion between various resin composites can occur by a chelation reaction of elemental ions. The surface composition of four commercially available resin composites (Beautifil II, Clearfil AP-X, Estelite Σ Quick and Solare) were measured by X-ray fluorescence analysis. Composite-to-composite adhesion with conventional silane coupling treatment was compared to self-etching primer treatment and evaluated by conventional shear bond strength testing. Our results detected Strontium and Barium (alkaline metallic earth ions) on the surface of Beautifil II and Clearfil AP-X resins. The shear bond strength values of self-etching primer treatments of Beautifil II and Clearfil AP-X was significantly higher than Estelite Σ Quick and Solare. Our data suggest that self-etching primer treatment is effective for adhesion of resin composites, depending on their filler composition, due to the chelation adhesion reaction between the acidic monomer and incorporated alkaline metal ions. PMID:21778602

  20. The distinct element analysis of toppling failure mechanisms

    NASA Astrophysics Data System (ADS)

    Özge Dinç, Şaziye; Sinan Işık, Nihat; Karaca, Zeki

    2016-04-01

    This project investigates the toppling failure mechanisms of rock masses having different rock materials and discontinuity properties in slopes that are designed in different heights. For this purpose, PFC2D as a distinct element code was used to anticipate the post failure behaviors of rock masses. After the simulation of laboratory tests on the samples in 2 (width) *4 (height) m, macro mechanical properties of rock masses were determined to be assigned the slopes. The properties of discontinuities were set up based on the smooth-joint method in PFC. The movements in the slopes -equipped with persistent and non-persistent discontinuities- were analyzed by using gravity increase method. The results show that the post failure behaviors of all rock samples have been controlled primarily by joint location and joint length. In addition to this, an increase on the slope height has an influence on the failure mechanism such that triggers the materials to transit from the toppling to circular yielding manner in some models. It has been also worth note that all models begin to fail as soon as the wing cracks develop by tension stresses, thus the tensile strength of the relevant rock material is the most critical mechanic parameter on the failure.

  1. Rockfall failure mechanisms in Yosemite Valley, California (USA)

    NASA Astrophysics Data System (ADS)

    Matasci, Battista; Guerin, Antoine; Carrea, Dario; Stock, Greg M.; Jaboyedoff, Michel; Collins, Brian

    2014-05-01

    Rockfall hazard is especially high in Yosemite Valley, with tens of rockfalls inventoried every year. A rockfall on 5 October 2013 from Ahwiyah Point consisted of a volume of 740 cubic meters and occurred within the perimeter of a larger event on 28 March 2009 that released 25'400 cubic meters of rock (Zimmer et al., 2012). In both events (2009 and 2013), the initial rockfall volumes dislodged a second one approximately equivalent in size by impacting the cliff below the source area during the fall. Rock fragments of up to several cubic meters were deposited on the talus slope, damaging a heavily used and recently reconstructed hiking path. We performed extensive mapping of structural features for several cliffs of Yosemite Valley to improve the assessment of the most susceptible rockfall areas. In particular we mapped and characterized the main brittle structures, the exfoliation joints and the failure mechanisms of the past rockfalls. Several failure mechanisms exist in Yosemite including the propagation of brittle structures that may lead to tensile, planar sliding, wedge sliding or toppling failures. Frequently, topographically-parallel exfoliation joints and topographically-oblique discontinuities coexist, resulting in complex failures. We also developed a methodology to examine how the distribution of joints within the cliff faces of Yosemite Valley affects overall stability with respect to the identified failure mechanisms. For these analyses, we used terrestrial laser scanning (TLS) to collect high resolution point clouds of the vertical and overhanging rock faces throughout the Valley. This provided the necessary 3D data to identify the main joint sets, perform spacing and trace length measurements, and calculate volumes of previous and potential rockfalls. We integrated this information with stability calculations to identify the likely failure mechanisms for each area of cliff and to obtain the number of potential failures per square meter of cliff face

  2. Dynamic mechanical analysis and esterase degradation of dentin adhesives containing a branched methacrylate

    PubMed Central

    Park, Jong-Gu; Ye, Qiang; Topp, Elizabeth M.; Lee, Chi H.; Kostoryz, Elisabet L.; Misra, Anil; Spencer, Paulette

    2010-01-01

    A study of the dynamic mechanical properties and the enzymatic degradation of new dentin adhesives containing a multifunctional methacrylate are described. Adhesives contained 2-hydroxyethyl methacrylate (HEMA), 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy) phenyl]-propane (BisGMA), and a new multifunctional methacrylate with a branched side chain-trimethylolpropane mono allyl ether dimethacrylate (TMPEDMA). Adhesives were photopolymerized in the presence of 0, 8 and 16 wt% water to simulate wet bonding conditions in the mouth and compared to control adhesives. The degree of conversion as a function of irradiation time was comparable for experimental and control adhesives. In dynamic mechanical analysis (DMA), broad tan δ peaks were obtained for all samples, indicating that the polymerized networks are heterogeneous; comparison of the full-width-at-half-maximum values obtained from the tan δ curves indicated increased heterogeneity for samples cured in the presence of water and/or containing TMPEDMA. The experimental adhesive showed higher Tg and higher rubbery modulus indicating increased crosslink density as compared to the control. The improvement in esterase resistance afforded by adhesives containing the TMPEDMA is greater when this material is photopolymerized in the presence of water, suggesting better performance in the moist environment of the mouth. The improved esterase resistance of the new adhesive could be explained in terms of the densely crosslinked network structure and/or the steric hindrance of branched alkyl side chains. PMID:19358261

  3. Failure mechanisms in energy-absorbing composite structures

    NASA Astrophysics Data System (ADS)

    Johnson, Alastair F.; David, Matthew

    2010-11-01

    Quasi-static tests are described for determination of the energy-absorption properties of composite crash energy-absorbing segment elements under axial loads. Detailed computer tomography scans of failed specimens were used to identify local compression crush failure mechanisms at the crush front. These mechanisms are important for selecting composite materials for energy-absorbing structures, such as helicopter and aircraft sub-floors. Finite element models of the failure processes are described that could be the basis for materials selection and future design procedures for crashworthy structures.

  4. Application of the time-temperature superposition principle to the mechanical characterization of elastomeric adhesives for crash simulation purposes

    NASA Astrophysics Data System (ADS)

    Rauh, A.; Hinterhölzl, R.; Drechsler, K.

    2012-05-01

    In the automotive industry, finite element simulation is widely used to ensure crashworthiness. Mechanical material data over wide strain rate and temperature ranges are required as a basis. This work proposes a method reducing the cost of mechanical material characterization by using the time-temperature superposition principle on elastomeric adhesives. The method is based on the time and temperature interdependence which is characteristic for mechanical properties of polymers. Based on the assumption that polymers behave similarly at high strain rates and at low temperatures, a temperature-dominated test program is suggested, which can be used to deduce strain rate dependent material behavior at different reference temperatures. The temperature shift factor is found by means of dynamic mechanical analysis according to the WLF-equation, named after Williams, Landel and Ferry. The principle is applied to the viscoelastic properties as well as to the failure properties of the polymer. The applicability is validated with high strain rate tests.

  5. Geckos as Springs: Mechanics Explain Across-Species Scaling of Adhesion

    PubMed Central

    Gilman, Casey A.; Imburgia, Michael J.; Bartlett, Michael D.; King, Daniel R.; Crosby, Alfred J.; Irschick, Duncan J.

    2015-01-01

    One of the central controversies regarding the evolution of adhesion concerns how adhesive force scales as animals change in size, either among or within species. A widely held view is that as animals become larger, the primary mechanism that enables them to climb is increasing pad area. However, prior studies show that much of the variation in maximum adhesive force remains unexplained, even when area is accounted for. We tested the hypothesis that maximum adhesive force among pad-bearing gecko species is not solely dictated by toepad area, but also depends on the ratio of toepad area to gecko adhesive system compliance in the loading direction, where compliance (C) is the change in extension (Δ) relative to a change in force (F) while loading a gecko’s adhesive system (C = dΔ/dF). Geckos are well-known for their ability to climb on a range of vertical and overhanging surfaces, and range in mass from several grams to over 300 grams, yet little is understood of the factors that enable adhesion to scale with body size. We examined the maximum adhesive force of six gecko species that vary in body size (~2–100 g). We also examined changes between juveniles and adults within a single species (Phelsuma grandis). We found that maximum adhesive force and toepad area increased with increasing gecko size, and that as gecko species become larger, their adhesive systems become significantly less compliant. Additionally, our hypothesis was supported, as the best predictor of maximum adhesive force was not toepad area or compliance alone, but the ratio of toepad area to compliance. We verified this result using a synthetic “model gecko” system comprised of synthetic adhesive pads attached to a glass substrate and a synthetic tendon (mechanical spring) of finite stiffness. Our data indicate that increases in toepad area as geckos become larger cannot fully account for increased adhesive abilities, and decreased compliance must be included to explain the scaling of

  6. Mechanical failure probability of glasses in Earth orbit

    NASA Technical Reports Server (NTRS)

    Kinser, Donald L.; Wiedlocher, David E.

    1992-01-01

    Results of five years of earth-orbital exposure on mechanical properties of glasses indicate that radiation effects on mechanical properties of glasses, for the glasses examined, are less than the probable error of measurement. During the 5 year exposure, seven micrometeorite or space debris impacts occurred on the samples examined. These impacts were located in locations which were not subjected to effective mechanical testing, hence limited information on their influence upon mechanical strength was obtained. Combination of these results with micrometeorite and space debris impact frequency obtained by other experiments permits estimates of the failure probability of glasses exposed to mechanical loading under earth-orbit conditions. This probabilistic failure prediction is described and illustrated with examples.

  7. Testing within the continuum of multiple lubrication and failure mechanisms

    SciTech Connect

    Wedeven, L.D.; Totten, G.E.; Bishop, R.J. Jr.

    1997-12-31

    The inherent difficulty of bench testing for the tribological performance of hydraulic fluids is the interaction of multiple lubrication and failure mechanisms. The engineer judges the performance limits in descriptive terms relating to what the load bearing surfaces have experienced. The lubrication and failure pathway that leads to the final surface condition is at the mercy of what lubrication and failure mechanisms have been invoked. Lubrication mechanisms, such as hydrodynamic, elastohydrodynamic, and boundary can be isolated with specialized testing, along with failure mechanisms, such as those described in general terms of wear, scuffing, and pitting. The interaction and competitive nature of these mechanisms, which exist in hardware, makes bench testing a nightmare. A rational approach using a highly flexible and computerized test machine, WAM3, is described. The approach demonstrates how performance attributes of fluids and materials can be evaluated as they are made to travel through multiple lubrication and failure pathways. The testing protocol is terminated with the test specimen`s surface reaches the same failure condition the engineer uses to judge performance limits of component hardware. Testing pathways are demonstrated that lead to wear, scuffing and micro-pitting. Along the testing pathway, viscous film-forming attributes and chemical boundary lubrication attributes of the fluid are characterized. Tests conducted with a range of fluid types, including two hydraulic fluids, demonstrate a wide range of traction, viscous film-forming and boundary film attributes. The continuum approach, which maps out performance in terms of hardware relevant criteria, provides a means to determine the impact of development strategies based on fluid and material technologies.

  8. Adaptive Shape Functions and Internal Mesh Adaptation for Modelling Progressive Failure in Adhesively Bonded Joints

    NASA Technical Reports Server (NTRS)

    Stapleton, Scott; Gries, Thomas; Waas, Anthony M.; Pineda, Evan J.

    2014-01-01

    Enhanced finite elements are elements with an embedded analytical solution that can capture detailed local fields, enabling more efficient, mesh independent finite element analysis. The shape functions are determined based on the analytical model rather than prescribed. This method was applied to adhesively bonded joints to model joint behavior with one element through the thickness. This study demonstrates two methods of maintaining the fidelity of such elements during adhesive non-linearity and cracking without increasing the mesh needed for an accurate solution. The first method uses adaptive shape functions, where the shape functions are recalculated at each load step based on the softening of the adhesive. The second method is internal mesh adaption, where cracking of the adhesive within an element is captured by further discretizing the element internally to represent the partially cracked geometry. By keeping mesh adaptations within an element, a finer mesh can be used during the analysis without affecting the global finite element model mesh. Examples are shown which highlight when each method is most effective in reducing the number of elements needed to capture adhesive nonlinearity and cracking. These methods are validated against analogous finite element models utilizing cohesive zone elements.

  9. Veneer vs. core failure in adhesively bonded all-ceramic crown layers.

    PubMed

    Lee, J J-W; Kwon, J-Y; Bhowmick, S; Lloyd, I K; Rekow, E D; Lawn, B R

    2008-04-01

    Joining a brittle veneer to a strong ceramic core with an adhesive offers potential benefits over current fabrication methods for all-ceramic crowns. We tested the hypothesis that such joining can withstand subsurface radial cracking in the veneer, from enhanced flexure in occlusal loading, as well as in the core. Critical conditions to initiate fractures were investigated in model crown-like layer structures consisting of glass veneers epoxy-joined onto alumina or zirconia cores, all bonded to a dentin-like polymer base. The results showed a competition between critical loads for radial crack initiation in the veneers and cores. Core radial cracking was relatively independent of adhesive thickness. Zirconia cores were much less susceptible to fracture than alumina, attributable to a relatively high strength and low modulus. Veneer cracking did depend on adhesive thickness. However, no significant differences in critical loads for veneer cracking were observed for specimens containing alumina or zirconia cores. PMID:18362320

  10. 77 FR 34457 - Pipeline Safety: Mechanical Fitting Failure Reports

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-06-11

    ...,'' ``Material or Welds/Fusions,'' ``Equipment,'' ``Incorrect Operation,'' and ``Other.'' These apparent cause... the mechanical fitting. One option is ``Material or Welds/Fusions'' with a subcategory of... is PHMSA's intent to capture failure data under the ``Material or Welds/Fusions'' leak cause...

  11. Experimental Investigation on the Morphology and Adhesion Mechanism of Leech Posterior Suckers

    PubMed Central

    Dong, Wenhao

    2015-01-01

    The posterior sucker of a leech represents a fascinating natural system that allows the leech to adhere to different terrains and substrates. However, the mechanism of adhesion and desorption has not yet to be elucidated. In order to better understand how the adhesion is performed, we analyzed the surface structure, adsorption movements, the muscles’ distribution, physical characteristics, and the adsorption force of the leech posterior suckers by experimental investigation. Three conclusions can be drawn based on the obtained experimental results. First, the adhesion by the posterior sucker is wet adhesion, because the surface of the posterior sucker is smooth and the sealing can only be achieved on wet surfaces. Second, the deformation texture, consisting of soft collagen tissues and highly ductile epidermal tissues, plays a key role in adhering to rough surfaces. Finally, the adhesion and desorption is achieved by the synergetic operation of six muscle fibers working in different directions. Concrete saying, directional deformation of the collagen/epithermal interface driven by spatially-distributed muscle fibers facilitates the excretion of fluids in the sucker venter, thus allowing liquid sealing. Furthermore, we found that the adhesion strength is directly related to the size of the contact surface which is generated and affected by the sucker deformation. Such an underlying physical mechanism offers potential cues for developing innovative bio-inspired artificial adhesion systems. PMID:26536352

  12. Experimental Investigation on the Morphology and Adhesion Mechanism of Leech Posterior Suckers.

    PubMed

    Feng, Huashan; Chai, Ningli; Dong, Wenhao

    2015-01-01

    The posterior sucker of a leech represents a fascinating natural system that allows the leech to adhere to different terrains and substrates. However, the mechanism of adhesion and desorption has not yet to be elucidated. In order to better understand how the adhesion is performed, we analyzed the surface structure, adsorption movements, the muscles' distribution, physical characteristics, and the adsorption force of the leech posterior suckers by experimental investigation. Three conclusions can be drawn based on the obtained experimental results. First, the adhesion by the posterior sucker is wet adhesion, because the surface of the posterior sucker is smooth and the sealing can only be achieved on wet surfaces. Second, the deformation texture, consisting of soft collagen tissues and highly ductile epidermal tissues, plays a key role in adhering to rough surfaces. Finally, the adhesion and desorption is achieved by the synergetic operation of six muscle fibers working in different directions. Concrete saying, directional deformation of the collagen/epithermal interface driven by spatially-distributed muscle fibers facilitates the excretion of fluids in the sucker venter, thus allowing liquid sealing. Furthermore, we found that the adhesion strength is directly related to the size of the contact surface which is generated and affected by the sucker deformation. Such an underlying physical mechanism offers potential cues for developing innovative bio-inspired artificial adhesion systems. PMID:26536352

  13. Influence of thermal and mechanical load cycling on microtensile bond strengths of total and self-etching adhesive systems.

    PubMed

    Mitsui, Fabio Hiroyuki Ogata; Peris, Alessandra Rezende; Cavalcanti, Andrea Nóbrega; Marchi, Giselle Maria; Pimenta, Luiz André Freire

    2006-01-01

    This study evaluated the influence of different thermal (TC) and mechanical (MC) cycling protocols on microtensile bond strength (muTBS) to cervical dentin margins of Class II restorations using two total-etch (TE) adhesives and one self-etching (SE) primer. Class II slot cavities were prepared on the mesial surfaces of 168 bovine incisors and were divided into three groups according to the bonding system used: Single Bond, OptiBond Solo Plus and Clearfil SE Bond. All cavities were restored with Filtek Z250 composite. Following restorative procedures, the restored teeth were allocated to seven subgroups (n = 8) according to the thermal/mechanical protocol performed: G1-control (no cycling), G2-100,000 MC, G3-200,000 MC, G4-500,000 MC, G5-100,000 MC+1,000 TC, G6-200,000 MC+1,000 TC, G7-500,000 MC+1,000 TC. TC was performed using 5 +/- 2 degrees C and 55 +/- 2 degrees C baths, with a dwell time of 60 seconds in each bath. MC was achieved with an axial force of 80 N at 2 cycles/second. The restorations were sectioned perpendicular to the cervical bonded interface into two 0.8-1-mm thick slabs. The slabs were trimmed at the interface to obtain a cross-sectional surface area of 0.8-1 mm2. All specimens were then subjected to muTBS (v = 0.5 mm/minute). Fracture mode analysis was performed using SEM. Bond strength mean values (MPa) were analyzed with ANOVA 3-way and Tukey's test (alpha = 5%). Dunnett's test was used to compare tested groups against Control groups of each adhesive system (alpha = 56%). SE primer presented lower mean bond strength values when compared to TE adhesives (p = 0.05). In addition, specimens restored with the SE primer did not resist to the 200,000 and 500,000 MC associated with TC. The application of 100,000 MC did not present a significant decrease in bond strength when compared to the control. Mixed failures were predominant for all groups. The higher the amount of thermal/mechanical cycles, the greater the number of mixed failures and the

  14. Cellular and molecular investigations of the adhesion and mechanics of Listeria monocytogenes

    NASA Astrophysics Data System (ADS)

    Eskhan, Asma Omar

    Atomic force microscopy has been used to quantify the adherence and mechanical properties of an array of L. monocytogenes strains and their surface biopolymers. First, eight L. monocytogenes strains that represented the two major lineages of the species were compared for their adherence and mechanics at cellular and molecular levels. Our results indicated that strains of lineage' II were characterized by higher adhesion and Young's moduli, longer and more rigid surface biopolymers and lower specific and nonspecific forces when compared to lineage' I strains. Additionally, adherence and mechanical properties of eight L. monocytogenes epidemic and environmental strains were probed. Our results pointed to that environmental and epidemic strains representative of a given lineage were similar in their adherence and mechanical properties when investigated at a cellular level. However, when the molecular properties of the strains were considered, epidemic strains were characterized by higher specific and nonspecific forces, shorter, denser and more flexible biopolymers compared to environmental strains. Second, the role of environmental pH conditions of growth on the adhesion and mechanics of a pathogenic L. monocytogenes EGDe was investigated. Our results pointed to a transition in the adhesion energies for cells cultured at pH 7. In addition, when the types of molecular forces that govern the adhesion were quantified using Poisson statistical approach and using a new proposed method, specific hydrogen-bond energies dominated the bacterial adhesion process. Such a finding is instrumental to researchers designing methods to control bacterial adhesion. Similarly, bacterial cells underwent a transition in their mechanical properties. We have shown that cells cultured at pH 7 were the most rigid compared to those cultured in lower or higher pH conditions of growth. Due to transitions observed in adherence and mechanics when cells were cultured at pH 7, we hypothesized that

  15. Failure Mechanisms for Ceramic Matrix Textile Composites at High Temperature

    SciTech Connect

    Cox, Brian

    1999-03-01

    OAK B188 Failure Mechanisms for Ceramic Matrix Textile Composites at High Temperature. This summary refers to work done in approximately the twelve months to the present in our contract ''Failure Mechanisms for Ceramic Matrix Textile Composites at High Temperature,'' which commenced in August, 1997. Our activities have consisted mainly of measurements of creep-controlled crack growth in ceramic matrix composites (CMCS) at high temperature; imaging of deformation fields in textile CMCS; the assessment of mechanisms of damage in textile composites, especially those with through-thickness reinforcement; the formulation of models of delamination crack growth under fatigue in textile composites; analytical models of the bridging traction law for creeping fibers in a CMC at high temperature; and an analytical model of a bridging fiber tow in a textile composite.

  16. Register of experts for information on mechanics of structural failure

    NASA Technical Reports Server (NTRS)

    Carpenter, J. L., Jr.; Stuhrke, W. F.

    1975-01-01

    This register is comprised of a list of approximately 300 experts from approximately 90 organizations who have published results of theoretical and/or experimental research related to six problem areas in the mechanics of structural failure: (1) life prediction for structural materials, (2) fracture toughness testing, (3) fracture mechanics analysis; (4) hydrogen embrittlement; (5) protective coatings; and (6) composite materials. The criteria for the selection of names for the register are recent contributions to the literature, participation in or support of relevant research programs, and referral by peers. Each author included is listed by organizational affiliation, address, and principal field of expertise. The purpose of the register is to present, in easy reference form, sources for dependable information regarding failure modes and mechanisms of aerospace structures. The register includes two indexes; an alphabetical listing of the experts and an alphabetical listing of the organizations with whom they are affiliated.

  17. Deformation and failure mechanisms in metal matrix composites

    NASA Technical Reports Server (NTRS)

    Newaz, G.; Majumdar, B. S.

    1991-01-01

    An investigation was undertaken to determine the key deformation mechanisms and their interaction leading to failure of both 0 degree and 90 degree Ti 15-3/SCS-6 laminae under monotonic loading. The experimental results suggest that inelastic deformation in the 0-degree lamina is dominated by plastic deformation and that in the 90-degree lamina is dominated by both fiber-matrix debonding and plasticity. The loading-unloading response, monitoring of Poisson's ratio and microscopy were utilized to identify the key deformation mechanisms. The sequence of deformation mechanisms leading to failure are identified for both the 0 and the 90-degree specimens. The threshold strains for plasticity or damage which are referred to as 'microdeformation' in the 0 deg and 90 deg laminae are approximately 0.004 and 0.002, respectively, at room temperature. These strain levels may be considered critical in initiation based structural design with these composites.

  18. Retrograde Fluxes of Focal Adhesion Proteins in Response to Cell Migration and Mechanical Signals

    PubMed Central

    Guo, Wei-hui

    2007-01-01

    Recent studies suggest that mechanical signals mediated by the extracellular matrix play an essential role in various physiological and pathological processes; yet, how cells respond to mechanical stimuli remains elusive. Using live cell fluorescence imaging, we found that actin filaments, in association with a number of focal adhesion proteins, including zyxin and vasodilator-stimulated phosphoprotein, undergo retrograde fluxes at focal adhesions in the lamella region. This flux is inversely related to cell migration, such that it is amplified in fibroblasts immobilized on micropatterned islands. In addition, the flux is regulated by mechanical signals, including stretching forces applied to flexible substrates and substrate stiffness. Conditions favoring the flux share the common feature of causing large retrograde displacements of the interior actin cytoskeleton relative to the substrate anchorage site, which may function as a switch translating mechanical input into chemical signals, such as tyrosine phosphorylation. In turn, the stimulation of actin flux at focal adhesions may function as part of a feedback mechanism, regulating structural assembly and force production in relation to cell migration and mechanical load. The retrograde transport of associated focal adhesion proteins may play additional roles in delivering signals from focal adhesions to the interior of the cell. PMID:17804814

  19. Novel molecular mechanisms and regeneration therapy for heart failure.

    PubMed

    Oka, Toru; Morita, Hiroyuki; Komuro, Issei

    2016-03-01

    Heart failure (HF) is one of the leading causes of mortality in the world. Various molecular mechanisms have been proposed for HF, but its precise mechanisms are still largely unknown. In this review, summarizing the "President's Distinguished Lecture Award" of XX World Congress of International Society for Heart Research 2010 in Kyoto, Japan, we introduce recent our studies on HF, including 1) p53-induced suppression of Hif-1-induced angiogenesis as a novel mechanism of HF, 2) angiogenesis as a potential therapeutic strategy for HF, and 3) IGFBP-4 as a novel factor for cardiomyogenesis by inhibiting canonical Wnt signaling. PMID:26829118

  20. Assessing mechanical vulnerability in water distribution networks under multiple failures

    NASA Astrophysics Data System (ADS)

    Berardi, Luigi; Ugarelli, Rita; Røstum, Jon; Giustolisi, Orazio

    2014-03-01

    Understanding mechanical vulnerability of water distribution networks (WDN) is of direct relevance for water utilities since it entails two different purposes. On the one hand, it might support the identification of severe failure scenarios due to external causes (e.g., natural or intentional events) which result into the most critical consequences on WDN supply capacity. On the other hand, it aims at figure out the WDN portions which are more prone to be affected by asset disruptions. The complexity of such analysis stems from the number of possible scenarios with single and multiple simultaneous shutdowns of asset elements leading to modifications of network topology and insufficient water supply to customers. In this work, the search for the most disruptive combinations of multiple asset failure events is formulated and solved as a multiobjective optimization problem. The higher vulnerability failure scenarios are detected as those causing the lower supplied demand due to the lower number of simultaneous failures. The automatic detection of WDN topology, subsequent to the detachments of failed elements, is combined with pressure-driven analysis. The methodology is demonstrated on a real water distribution network. Results show that, besides the failures causing the detachment of reservoirs, tanks, or pumps, there are other different topological modifications which may cause severe WDN service disruptions. Such information is of direct relevance to support planning asset enhancement works and improve the preparedness to extreme events.

  1. Delayed mechanical failure of silver-interlayer diffusion bonds

    SciTech Connect

    Kassner, M.E. ); Rosen, R.S.; Henshall, G.A. . Physical Metallurgy and Joining Section)

    1990-12-01

    Silver-interlayer diffusion bonds were fabricated using planar-magnetron sputtering (PMS). The bonds exhibit very high tensile strengths, despite the soft interlayer, because of the constraint by the base metal. However, these joints undergo delayed failure at relatively low tensile stresses at ambient temperatures, apparently by a ductile microvoid coalescence mechanism at the bond interfaces. Two classes of delayed tensile failure were investigated. In the first case, the applied stress does not produced any plastic deformation in the base metal, and failure appears to be controlled by time-dependent plasticity within the silver interlayer as a result of the effective stress in the interlayer. The plasticity causes cavity nucleation and, eventually, interlinkage and failure. In the second case, time-dependent plasticity is observed in base metals, and concomitant shear occurs within the softer silver under a high triaxial stress state. Here, the time-dependent plasticity of the base metal accelerates plasticity and failure in the interlayer. These models were substantiated by careful analysis of the stress and temperature dependence of the rupture times, finite element analysis of the stress state within the interlayer, and microscopy of the fracture surfaces and interfaces loaded to various fractions of the expected rupture times. These findings are applicable to bonds in which the interlayers are prepared by processes other than physical vapor deposition.

  2. Mathematical model for the effects of adhesion and mechanics on cell migration speed.

    PubMed Central

    DiMilla, P A; Barbee, K; Lauffenburger, D A

    1991-01-01

    Migration of mammalian blood and tissue cells over adhesive surfaces is apparently mediated by specific reversible reactions between cell membrane adhesion receptors and complementary ligands attached to the substratum. Although in a number of systems these receptors and ligand molecules have been isolated and identified, a theory capable of predicting the effects of their properties on cell migration behavior currently does not exist. We present a simple mathematical model for elucidating the dependence of cell speed on adhesion-receptor/ligand binding and cell mechanical properties. Our model can be applied to propose answers to questions such as: does an optimal adhesiveness exist for cell movement? How might changes in receptor and ligand density and/or affinity affect the rate of migration? Can cell rheological properties influence movement speed? This model incorporates cytoskeletal force generation, cell polarization, and dynamic adhesion as requirements for persistent cell movement. A critical feature is the proposed existence of an asymmetry in some cell adhesion-receptor property, correlated with cell polarity. We consider two major alternative mechanisms underlying this asymmetry: (a) a spatial distribution of adhesion-receptor number due to polarized endocytic trafficking and (b) a spatial variation in adhesion-receptor/ligand bond strength. Applying a viscoelastic-solid model for cell mechanics allows us to represent one-dimensional locomotion with a system of differential equations describing cell deformation and displacement along with adhesion-receptor dynamics. In this paper, we solve these equations under the simplifying assumption that receptor dynamics are at a quasi-steady state relative to cell locomotion. Thus, our results are strictly valid for sufficiently slow cell movement, as typically observed for tissue cells such as fibroblasts. Numerical examples relevant to experimental systems are provided. Our results predict how cell speed might

  3. Adhesion mechanism in a DOPA-deficient foot protein from green mussels†

    PubMed Central

    Hwang, Dong Soo; Zeng, Hongbo; Lu, Qingye; Israelachvili, Jacob; Waite, J. Herbert

    2012-01-01

    The holdfast or byssus of Asian green mussels, Perna viridis, contains a foot protein, pvfp-1, that differs in two respects from all other known adhesive mussel foot proteins (mfp): (1) instead of the hallmark L-3,4-dihydroxyphenylalanine (DOPA) residues in mfp-1, for example, pvfp-1 contains C2-mannosyl-7-hydroxytryptophan (Man7OHTrp). (2) In addition, pvfp-1 chains are not monomeric like mfp-1 but trimerized by collagen and coiled-coil domains near the carboxy terminus after a typical domain of tandemly repeated decapeptides. Here, the contribution of these peculiarities to adhesion was examined using a surface forces apparatus (SFA). Unlike previously studied mfp-1s, pvfp-1 showed significant adhesion to mica and, in symmetric pvfp-1 films, substantial cohesive interactions were present at pH 5.5. The role of Man7OHTrp in adhesion is not clear, and a DOPA-like role for Man7OHTrp in metal complexation (e.g., Cu2+, Fe3+) was not observed. Instead, cation–π interactions with low desolvation penalty between Man7OHTrp and lysyl side chains and conformational changes (raveling and unraveling of collagen helix and coiled-coil domains) are the best explanations for the strong adhesion between pvfp-1 monomolecular films. The strong adhesion mechanism induced by cation–π interactions and conformational changes in pvfp-1 provides new insights for the development of biomimetic underwater adhesives. PMID:23105946

  4. Old and sticky—adhesive mechanisms in the living fossil Nautilus pompilius (Mollusca, Cephalopoda)

    PubMed Central

    von Byern, Janek; Wani, Ryoji; Schwaha, Thomas; Grunwald, Ingo; Cyran, Norbert

    2012-01-01

    Nautiloidea is the oldest group within the cephalopoda, and modern Nautilus differs much in its outer morphology from all other recent species; its external shell and pinhole camera eye are the most prominent distinguishing characters. A further unique feature of Nautilus within the cephalopods is the lack of suckers or hooks on the tentacles. Instead, the animals use adhesive structures present on the digital tentacles. Earlier studies focused on the general tentacle morphology and put little attention on the adhesive gland system. Our results show that the epithelial parts on the oral adhesive ridge contain three secretory cell types (columnar, goblet, and cell type 1) that differ in shape and granule size. In the non-adhesive aboral epithelium, two glandular cell types (cell types 2 and 3) are present; these were not mentioned in any earlier study and differ from the cells in the adhesive area. The secretory material of all glandular cell types consists mainly of neutral mucopolysaccharide units, whereas one cell type in the non-adhesive epithelium also reacts positive for acidic mucopolysaccharides. The present data indicate that the glue in Nautilus consists mainly of neutral mucopolysaccharides. The glue seems to be a viscous carbohydrate gel, as known from another cephalopod species. De-attachment is apparently effectuated mechanically, i.e., by muscle contraction of the adhesive ridges and tentacle retraction. PMID:22221553

  5. Mechanisms of endothelial cell-dependent leukocyte adhesion stimulated by platelet-activating factor.

    PubMed

    Ding, Z; Li, S; Wu, Z

    1992-04-01

    Platelet-activating factor (PAF) stimulates leukocyte-endothelial cell (EC) adhesion through its effects either on leukocytes or on ECs. ECs may be injured, synthesize, or express new adhesive proteins to increase leukocyte adhesion. Intermediary mediators produced by activated ECs are also likely involved in promoting leukocyte adhesion. Our experiments demonstrated that PAF induced no obvious damage to bovine pulmonary artery ECs evaluated by lactic dehydrogenase release rate, angiotensin-converting enzyme activity, and cellular malondialdehyde content. Treatment of EC monolayers with 10(-9) M PAF increased polymorphonuclear leukocyte (PMN) adhesion. Increasing PAF concentration did not induce more PMN adherence. PAF elicited both a rapid and prolonged increment of PMN adherence to EC monolayers. The rapid adherence was greatly attenuated by pretreatment of ECs with PAF receptor antagonist SRI 63-441 but was not affected by pretreatment of PMNs with SRI 63-441, suggesting that PAF increases PMN adherence rapidly through its effects on specific receptors on ECs. Increased PMN adherence lasted if PAF treatment of ECs was sustained for 3 or 6 h. Pretreatment of ECs with actinomycin D, a protein synthesis inhibitor, significantly decreased PAF-induced sustained PMN adherence, but the inhibition is incomplete, suggesting that other mechanisms than protein synthesis also participated in the prolonged PMN adherence. We concluded from the results that PAF may induce both rapid and prolonged PMN adhesion to ECs. The effects are receptor mediated. The prolonged PMN adhesion is partly the result of protein synthesis. PMID:1592489

  6. Analysis of Mechanical Failure of Polymer Microneedles by Axial Force

    PubMed Central

    Park, Jung-Hwan; Prausnitz, Mark R.

    2010-01-01

    A polymeric microneedle has been developed for drug delivery applications. The ultimate goal of the polymeric microneedle is insertion into the specified region without failure for effective transdermal drug delivery. Mechanical failure of various geometries of microneedles by axial load was modeled using the Euler formula and the Johnson formula to predict the failure force of tapered-column microneedles. These formulas were compared with measured data to identify the mechanical behavior of microneedles by determining the critical factors including the actual length and end-fixed factor. The comparison of the two formulas with the data showed good agreement at the end-fixity (K) of 0.7. This value means that a microneedle column has one fixed end and one pinned end, and that part of the microneedle was overloaded by axial load. When the aspect ratio of length to equivalent diameter is 12:1 at 3 GPa of Young’s modulus, there is a transition from the Euler region to the Johnson region by the decreased length and increased base diameter of the microneedle. A polymer having less than 3 GPa of stiffness would follow the Euler formula. A 12:1 aspect ratio of length to equivalent diameter of the microneedle was the mechanical indicator determining the failure mode between elastic buckling and inelastic buckling at less than 3 GPa of Young’s modulus of polymer. Microneedles with below a 12:1 aspect ratio of length-to-equivalent diameter and more than 3 GPa of Young’s were recommended for reducing sudden failure by buckling and for successfully inserting the microneedle into the skin. PMID:21218133

  7. Register of experts for information on mechanics of structural failure

    NASA Technical Reports Server (NTRS)

    Carpenter, J. L., Jr.; Moya, N.

    1973-01-01

    A list of approximately 150 experts from approximately 60 organizations who have published results of theoretical and/or experimental research related to six problem areas in the mechanics of structural failure is presented. Each author included is listed by organizational affiliation, address and principal field of expertise. The initial criteria for the selection of names for the register are recent contributions to the literature, participation in or support of relevant research programs, and referral by peers. The purpose of the register is to present, in easy reference form, sources for dependable information regarding failure modes and mechanisms of aerospace structures. The Register includes two indexes: an alphabetical listing of the experts and an alphabetical listing of the organizations with whom they are affiliated.

  8. Lamellipodial actin mechanically links myosin activity with adhesion-site formation.

    PubMed

    Giannone, Grégory; Dubin-Thaler, Benjamin J; Rossier, Olivier; Cai, Yunfei; Chaga, Oleg; Jiang, Guoying; Beaver, William; Döbereiner, Hans-Günther; Freund, Yoav; Borisy, Gary; Sheetz, Michael P

    2007-02-01

    Cell motility proceeds by cycles of edge protrusion, adhesion, and retraction. Whether these functions are coordinated by biochemical or biomechanical processes is unknown. We find that myosin II pulls the rear of the lamellipodial actin network, causing upward bending, edge retraction, and initiation of new adhesion sites. The network then separates from the edge and condenses over the myosin. Protrusion resumes as lamellipodial actin regenerates from the front and extends rearward until it reaches newly assembled myosin, initiating the next cycle. Upward bending, observed by evanescence and electron microscopy, results in ruffle formation when adhesion strength is low. Correlative fluorescence and electron microscopy shows that the regenerating lamellipodium forms a cohesive, separable layer of actin above the lamellum. Thus, actin polymerization periodically builds a mechanical link, the lamellipodium, connecting myosin motors with the initiation of adhesion sites, suggesting that the major functions driving motility are coordinated by a biomechanical process. PMID:17289574

  9. Acoustic emission spectral analysis of fiber composite failure mechanisms

    NASA Technical Reports Server (NTRS)

    Egan, D. M.; Williams, J. H., Jr.

    1978-01-01

    The acoustic emission of graphite fiber polyimide composite failure mechanisms was investigated with emphasis on frequency spectrum analysis. Although visual examination of spectral densities could not distinguish among fracture sources, a paired-sample t statistical analysis of mean normalized spectral densities did provide quantitative discrimination among acoustic emissions from 10 deg, 90 deg, and plus or minus 45 deg, plus or minus 45 deg sub s specimens. Comparable discrimination was not obtained for 0 deg specimens.

  10. Effect of Heat Treatment on Some Mechanical Properties of Laminated Window Profiles Manufactured Using Two Types of Adhesives

    PubMed Central

    Korkut, Derya Sevim; Korkutand, Suleyman; Dilik, Tuncer

    2008-01-01

    The mechanical properties of laminated window profiles manufactured using two types of adhesives were determined. The objective of this study is to evaluate the effects of heat treatment on some mechanical properties of laminated window profiles that manufactured from Kosipo (Entandrophragma candollei Harms.) using differenet type adhesives. Commercially produced polyurethane based Macroplast UR 7221 and polyvinyl acetate (PVAc) adhesive were used for experiments. The overall test results were found to be comparable to those obtained in the previous studies. Both types of adhesives resulted in significant differences in their strength characteristics at 95% confidence level. Adhesive UR 7221 improved the overall properties of the samples in contrast to PVAc. PMID:19325761

  11. Effect of new adhesion promoter and mechanical interlocking on bonding strength in metal-polymer composites

    NASA Astrophysics Data System (ADS)

    Schuberth, A.; Göring, M.; Lindner, T.; Töberling, G.; Puschmann, M.; Riedel, F.; Scharf, I.; Schreiter, K.; Spange, S.; Lampke, T.

    2016-03-01

    There are various opportunities to improve the adhesion between polymer and metal in metal-plastic composites. The addition of a bonding agent which reacts with both joining components at the interfaces of the composite can enhance the bonding strength. An alternative method for the adjustment of interfaces in metal-plastic composites is the specific surface structuring of the joining partners in order to exploit the mechanical interlock effect. In this study the potential of using an adhesion promoter based on twin polymerization for metal-plastic composites in combination with different methods of mechanical surface treatment is evaluated by using the tensile shear test. It is shown that the new adhesion promoter has a major effect when applied on smooth metal surfaces. A combination of both mechanical and chemical surface treatment of the metal part is mostly just as effective as the application of only one of these surface treatment methods.

  12. Bibliography of information on mechanics of structural failure

    NASA Technical Reports Server (NTRS)

    Carpenter, J. L., Jr.; Moya, N.; Shaffer, R. A.; Smith, D. M.

    1973-01-01

    A bibliography of approximately 1500 reference citations related to six problem areas in the mechanics of failure in aerospace structures is presented. The bibliography represents a search of the literature published in the ten year period 1962-1972 and is largely limited to documents published in the United States. Listings are subdivided into the six problem areas: (1) life prediction of structural materials; (2) fracture toughness data; (3) fracture mechanics analysis; (4) hydrogen embrittlement; (5) protective coatings; and (6) composite materials. An author index is included.

  13. Methods of failure and reliability assessment for mechanical heart pumps.

    PubMed

    Patel, Sonna M; Allaire, Paul E; Wood, Houston G; Throckmorton, Amy L; Tribble, Curt G; Olsen, Don B

    2005-01-01

    Medical Instrumentation (AAMI), and the Bethesda Conference. It further discusses studies that evaluate the failure, reliability, and safety of artificial blood pumps including in vitro and in vivo testing. A descriptive summary of mechanical and human error studies and methods of artificial blood pumps is detailed. PMID:15644079

  14. Failure Mechanisms and Life Prediction of Thermal and Environmental Barrier Coatings under Thermal Gradients

    NASA Technical Reports Server (NTRS)

    Zju, Dongming; Ghosn, Louis J.; Miller, Robert A.

    2008-01-01

    Ceramic thermal and environmental barrier coatings (TEBCs) will play an increasingly important role in gas turbine engines because of their ability to further raise engine temperatures. However, the issue of coating durability is of major concern under high-heat-flux conditions. In particular, the accelerated coating delamination crack growth under the engine high heat-flux conditions is not well understood. In this paper, a laser heat flux technique is used to investigate the coating delamination crack propagation under realistic temperature-stress gradients and thermal cyclic conditions. The coating delamination mechanisms are investigated under various thermal loading conditions, and are correlated with coating dynamic fatigue, sintering and interfacial adhesion test results. A coating life prediction framework may be realized by examining the crack initiation and propagation driving forces for coating failure under high-heat-flux test conditions.

  15. The Evolutionary Origin of Epithelial Cell-Cell Adhesion Mechanisms

    PubMed Central

    Miller, Phillip W.; Clarke, Donald N.; Weis, William I.; Lowe, Christopher J.; Nelson, W. James

    2014-01-01

    SUMMARY A simple epithelium forms a barrier between the outside and the inside of an organism, and is the first organized multicellular tissue found in evolution. We examine the relationship between the evolution of epithelia and specialized cell-cell adhesion proteins comprising the classical cadherin/β-catenin/α-catenin complex (CCC). A review of the divergent functional properties of the CCC in metazoans and non-metazoans, and an updated phylogenetic coverage of the CCC using recent genomic data reveal: 1) The core CCC likely originated before the last common ancestor of unikonts and their closest bikont sister taxa. 2) Formation of the CCC may have constrained sequence evolution of the classical cadherin cytoplasmic domain and β-catenin in metazoa. 3) The α-catenin binding domain in β-catenin appears to be the favored mutation site for disrupting β-catenin function in the CCC. 4) The ancestral function of the α/β-catenin heterodimer appears to be an actin-binding module. In some metazoan groups, more complex functions of α-catenin were gained by sequence divergence in the non-actin binding (N-, M-) domains. 5) Allosteric regulation of α-catenin, rather than loss of function mutations, may have evolved for more complex regulation of the actin cytoskeleton. PMID:24210433

  16. A numerical study on intended and unintended failure mechanisms in blanking of sandwich plates

    NASA Astrophysics Data System (ADS)

    Chen, L.; Soyarslan, C.; Tekkaya, A. E.

    2013-05-01

    Metal-polymer-metal sandwich plates are widely used in the automotive and aerospace industry. As for different applications the sandwich plates can be divided into two types. They are sound-damping laminates with a polymer core much thinner than the metallic faces and low-density laminates with a core thickness of approximately 40-60% of the total thickness. One frequent process step in production of parts made of these plates is the blanking process whose hereditary effects draw the limits of further forming stages or service performance and life; e.g. the failure of the adhesive in the thermoplastic polymer interface affects the sound-damping efficiency intensively. With this motivation, we present FE simulation of an axi-symmetric blanking process of steel/polyethylene/steel sound-damping laminates. The mechanical behavior of the metallic layers was characterized by finite strain rate independent elasto-plasticity where progressive material deterioration and fracture are given account for using continuum damage mechanics (CDM). This material model is made accessible via implementations as VUMAT subroutines for ABAQUS/Explicit. Possible failure of the thermoplastic polymer which may lead to delamination of the metallic layers is modeled using ABAQUS built-in cohesive zone elements. The results show that existing intended and unintended failure modes, e.g. blanking of the metallic and thermoplastic polymer constituents as well as failure of polymer layer under shear and compression, can be effectively studied with the proposed framework for process enhancement. As a future work, a damage coupled nonlinear visco-elastic constitutive model will be devised for the simulation of the thermoplastic layer in low-density laminates.

  17. Failure analysis for micro-electrical-mechanical systems (MEMS)

    SciTech Connect

    Peterson, K.A.; Tangyunyong, P.; Barton, D.L.

    1997-10-01

    Micro-Electrical Mechanical Systems (MEMS) is an emerging technology with demonstrated potential for a wide range of applications including sensors and actuators for medical, industrial, consumer, military, automotive and instrumentation products. Failure analysis (FA) of MEMS is critically needed for the successful design, fabrication, performance analysis and reliability assurance of this new technology. Many devices have been examined using techniques developed for integrated circuit analysis, including optical inspection, scanning laser microscopy (SLM), scanning electron microscopy (SEM), focused ion beam (FIB) techniques, atomic force microscopy (AFM), infrared (IR) microscopy, light emission (LE) microscopy, acoustic microscopy and acoustic emission analysis. For example, the FIB was used to microsection microengines that developed poor performance characteristics. Subsequent SEM analysis clearly demonstrated the absence of wear on gear, hub, and pin joint bearing surfaces, contrary to expectations. Another example involved the use of infrared microscopy for thermal analysis of operating microengines. Hot spots were located, which did not involve the gear or hub, but indicated contact between comb structures which drive microengines. Voltage contrast imaging proved useful on static and operating MEMS in both the SEM and the FIB and identified electrostatic clamping as a potentially significant contributor to failure mechanisms in microengines. This work describes MEMS devices, FA techniques, failure modes, and examples of FA of MEMS.

  18. Arsenic Exposure Increases Monocyte Adhesion to the Vascular Endothelium, a Pro-Atherogenic Mechanism.

    PubMed

    Lemaire, Maryse; Negro Silva, Luis Fernando; Lemarié, Catherine A; Bolt, Alicia M; Flores Molina, Manuel; Krohn, Regina M; Smits, Judit E; Lehoux, Stéphanie; Mann, Koren K

    2015-01-01

    Epidemiological studies have shown that arsenic exposure increases atherosclerosis, but the mechanisms underlying this relationship are unknown. Monocytes, macrophages and platelets play an important role in the initiation of atherosclerosis. Circulating monocytes and macrophages bind to the activated vascular endothelium and migrate into the sub-endothelium, where they become lipid-laden foam cells. This process can be facilitated by platelets, which favour monocyte recruitment to the lesion. Thus, we assessed the effects of low-to-moderate arsenic exposure on monocyte adhesion to endothelial cells, platelet activation and platelet-monocyte interactions. We observed that arsenic induces human monocyte adhesion to endothelial cells in vitro. These findings were confirmed ex vivo using a murine organ culture system at concentrations as low as 10 ppb. We found that both cell types need to be exposed to arsenic to maximize monocyte adhesion to the endothelium. This adhesion process is specific to monocyte/endothelium interactions. Hence, no effect of arsenic on platelet activation or platelet/leukocyte interaction was observed. We found that arsenic increases adhesion of mononuclear cells via increased CD29 binding to VCAM-1, an adhesion molecule found on activated endothelial cells. Similar results were observed in vivo, where arsenic-exposed mice exhibit increased VCAM-1 expression on endothelial cells and increased CD29 on circulating monocytes. Interestingly, expression of adhesion molecules and increased binding can be inhibited by antioxidants in vitro and in vivo. Together, these data suggest that arsenic might enhance atherosclerosis by increasing monocyte adhesion to endothelial cells, a process that is inhibited by antioxidants. PMID:26332580

  19. Damage and failure mechanisms associated with photoablation of biological tissues

    SciTech Connect

    Antoun, T.; Seaman, L.; Curran, D.; Glinsky, M.

    1996-05-01

    This paper aims to examine the processes associated with failure of the cornea and other collagenous tissues during photoablation. Two different constitutive models are applied to simulate a series of laser deposition experiments into porcine reticular dermis (1), a biological tissue similar to the cornea in composition and photoablation characteristics. The first of our constitutive models, DFRACT, is a physically motivated, micromechanical model based on the nucleation and growth of spherical voids (2). The second is a relatively simple model that allows the material to vaporize and thermally soften. The simulation results reproduce the prominent features observed experimentally thereby shedding a new light on the operative mechanisms during photoablation. The good qualitative agreement between the simulated stress histories and the stress histories measured during the experiments also demonstrates the effectiveness of micromechanical damage and failure modeling as a viable tool for optimizing existing laser surgery procedures and designing new ones. {copyright} {ital 1996 American Institute of Physics.}

  20. Mechanics of load-drag-unload contact cleaning of gecko-inspired fibrillar adhesives.

    PubMed

    Abusomwan, Uyiosa A; Sitti, Metin

    2014-10-14

    Contact self-cleaning of gecko-inspired synthetic adhesives with mushroom-shaped tips has been demonstrated recently using load-drag-unload cleaning procedures similar to that of the natural animal. However, the underlying mechanics of contact cleaning has yet to be fully understood. In this work, we present a detailed experiment of contact self-cleaning that shows that rolling is the dominant mechanism of cleaning for spherical microparticle contaminants, during the load-drag-unload procedure. We also study the effect of dragging rate and normal load on the particle rolling friction. A model of spherical particle rolling on an elastomer fibrillar adhesive interface is developed and agrees well with the experimental results. This study takes us closer to determining design parameters for achieving self-cleaning fibrillar adhesives. PMID:25244526

  1. Tearing as a test for mechanical characterization of thin adhesive films

    NASA Astrophysics Data System (ADS)

    Hamm, Eugenio; Reis, Pedro; Leblanc, Michael; Roman, Benoit; Cerda, Enrique

    2008-05-01

    Thin adhesive films have become increasingly important in applications involving packaging, coating or for advertising. Once a film is adhered to a substrate, flaps can be detached by tearing and peeling, but they narrow and collapse in pointy shapes. Similar geometries are observed when peeling ultrathin films grown or deposited on a solid substrate, or skinning the natural protective cover of a ripe fruit. Here, we show that the detached flaps have perfect triangular shapes with a well-defined vertex angle; this is a signature of the conversion of bending energy into surface energy of fracture and adhesion. In particular, this triangular shape of the tear encodes the mechanical parameters related to these three forms of energy and could form the basis of a quantitative assay for the mechanical characterization of thin adhesive films, nanofilms deposited on substrates or fruit skin.

  2. Correlation Between Thermal Interface Conductance and Mechanical Adhesion Strength in Cu-Coated Glassy Carbon

    NASA Astrophysics Data System (ADS)

    Pelzl, J.; Kijamnajsuk, P.; Chirtoc, M.; Horny, N.; Eisenmenger-Sittner, C.

    2015-09-01

    The influence of defective areas in the interface on the correlation between the thermal interface conductance and the mechanical adhesion strength was investigated on as-prepared and heat-treated samples of copper-coated carbon flat specimens with different bonding layers between the copper film and the substrate. The thermal interface conductance was determined by frequency-domain photothermal radiometry. The mechanical adhesion strength of the film coating was deduced from pull-off experiments. The imperfect interfaces were modeled by two different values for the thermal interface conductance, G1 and G2, which co-exist at different areas on the interface and are weighted according to their areas, A1 and A2. The model parameters were determined by adjusting the frequency dependence of the normalized phases and phase differences of the PTR signals from as-prepared and heat-treated samples. The total thermal conductance of the interface was found to exhibit a correlation with the adhesion strength for most of the heat-treated samples whereas, among the as-prepared samples, considerable deviations from such a trend exist. The observations are explained by the impact of supplementary stress on the adhesion strength measurements which are due to the strain developed during the preparation process at the interface. The interfacial stress and strain are mostly released during thermal annealing. A semi-empirical formula was developed that describes the impact of the defective areas on the adhesion strength using the experimentally determined thermal model parameters.

  3. Mechanisms of Staphylococcus epidermidis adhesion to model biomaterial surfaces: Establising a link between thrombosis and infection

    NASA Astrophysics Data System (ADS)

    Higashi, Julie Miyo

    Infections involving Staphylococcus epidermidis remain a life threatening complication associated with the use of polymer based cardiovascular devices. One of the critical steps in infection pathogenesis is the adhesion of the bacteria to the device surface. Currently, mechanisms of S. epidermidis adhesion are incompletely understood, but are thought to involve interactions between bacteria, device surface, and host blood elements in the form of adsorbed plasma proteins and surface adherent platelets. Our central hypothesis is that elements participating in thrombosis also promote S. epidermidis adhesion by specifically binding to the bacterial surface. The adhesion kinetics of S. epidermidis RP62A to host modified model biomaterial surface octadecyltrichlorosilane (OTS) under hydrodynamic shear conditions were characterized. Steady state adhesion to adsorbed proteins and surface adherent platelets was achieved at 90-120 minutes and 60-90 minutes, respectively. A dose response curve of S. epidermidis adhesion in the concentration range of 10sp7{-}10sp9 bac/mL resembled a multilayer adsorption isotherm. Increasing shear stress was found to LTA, and other LTA blocking agents significantly decreased S. epidermidis adhesion to the fibrin-platelet clots, suggesting that this interaction between S. epidermidis and fibrin-platelet clots is specific. Studies evaluated the adhesion of S. epidermidis to polymer immobilized heparin report conflicting results. Paulsson et al., showed that coagulase negative staphylococci adhered in comparable numbers to both immobilized heparin and nonheparinized surfaces, while exhibiting significantly greater adhesion to both surfaces than S. aureus. Preadsorption of the surfaces with specific heparin binding plasma proteins vitronectin, fibronectin, laminin, and collagen significantly increased adhesion. It was postulated that immobilized heparin contained binding sites for the plasma proteins, exposing bacteria binding domains of the

  4. Adhesion-delamination mechanics of a prestressed rectangular film adhered onto a rigid substrate

    NASA Astrophysics Data System (ADS)

    Wong, Ming-Fung; Duan, Gang; Wan, Kai-Tak

    2007-01-01

    A prestressed rectangular film clamped at both ends delaminates from a rigid punch. Based on a thermodynamic energy balance, the delamination mechanics is derived to relate the simultaneous external tensile force applied to the punch, punch displacement, and contact area. Effects of the coupled tensile residual membrane stress and adhesion energy at the punch-film interface are investigated. A "pinch off" (stable shrinking of the contact area to a line) is predicted, contrasting the nonzero "pull-off" radius in a clamped circular film. The model is useful in understanding the behavior of various adhesion-delamination phenomena, especially in one dimensional capacitive microelectromechanical systems radio frequency switches, microstructure network, and nanostructures.

  5. Scale Adhesion, Sulfur Content, and TBC Failure on Single Crystal Superalloys

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    2002-01-01

    This paper summarizes the main effects of sulfur impurity content on the cyclic oxidation resistance of single crystal superalloys, with emphasis on scale and TBC adhesion. Eleven hundred degrees C cyclic oxidation of PWA 1480 produces scale spallation leading to a weight loss of more than 30 Mg/sq cm after 500 one-hr cycles for a sulfur content of 6 ppmw. The sulfur content was reduced to levels below 0.1 ppmw by hydrogen annealing, resulting in weight gains of only 0.5 to 1.0 Mg/sq cm after 1000 one-hr cycles. Samples were produced with various sulfur contents by adjusting the annealing temperature, time, and sample thickness (i.e., diffusion product Dt/L(exp 2)). The subsequent cyclic oxidation behavior, mapped over a sulfur content/thickness diagram, shows a transition to adherent behavior at sulfur levels equivalent to 1 monolayer of total segregation. Additional information is contained in the original extended abstract.

  6. Mechanical and water soaking properties of medium density fiberboard with wood fiber and soybean protein adhesive.

    PubMed

    Li, Xin; Li, Yonghui; Zhong, Zhikai; Wang, Donghai; Ratto, Jo A; Sheng, Kuichuan; Sun, Xiuzhi Susan

    2009-07-01

    Soybean protein is a renewable and abundant material that offers an alternative to formaldehyde-based resins. In this study, soybean protein was modified with sodium dodecyl sulfate (SDS) as an adhesive for wood fiber medium density fiberboard (MDF) preparation. Second-order response surface regression models were used to study the effects and interactions of initial moisture content (IMC) of coated wood fiber, press time (PT) and temperature on mechanical and water soaking properties of MDF. Results showed that IMC of coated fiber was the dominant influencing factor. Mechanical and soaking properties improved as IMC increased and reached their highest point at an IMC of 35%. Press time and temperature also had a significant effect on mechanical and water soaking properties of MDF. Second-order regression results showed that there were strong relationships between mechanical and soaking properties of MDF and processing parameters. Properties of MDF made using soybean protein adhesive are similar to those of commercial board. PMID:19329303

  7. Mechanics in Mechanosensitivity of Cell Adhesion and its Roles in Cell Migration

    NASA Astrophysics Data System (ADS)

    Zhong, Yuan; He, Shijie; Ji, Baohua

    2012-12-01

    Cells sense and respond to external stimuli and properties of their environment through focal adhesion complexes (FACs) to regulate a broad range of physiological and pathological processes, including cell migration. Currently, the basic principles in mechanics of the mechanosensitivity of cell adhesion and migration have not been fully understood. In this paper, an FEM-based mechano-chemical coupling model is proposed for studying the cell migration behaviors in which the dynamics of stability of FACs and the effect of cell shape on cell traction force distribution are considered. We find that the driving force of cell migration is produced by the competition of stability of cell adhesion between the cell front and cell rear, which consequently controls the speed of cell migration. We show that the rigidity gradient of matrix can bias this competition which allows cell to exhibit a durotaxis behavior, i.e. the larger the gradient, the higher the cell speed.

  8. Small-scale mechanical characterization of viscoelastic adhesive systems

    NASA Astrophysics Data System (ADS)

    Shean, T. A. V.

    Aero engine hot end components are often covered with ceramic Thermal Barrier Coatings (TBCs). Laser drilling in the TBC coated components can be a source of service life TBC degradation and spallation. The present study aims to understand the mechanisms of TBC delamination and develop techniques to drill holes without damaging the TBC, Nimonic 263 workpieces coated with TBC are used in the experiments. Microwave non-destructive testing (NDT) is employed to monitor the integrity of the coating /substrate interfaces of the post-laser drilled materials. A numerical modelling technique is used to investigate the role of melt ejection on TBC delamination. The model accounts for the vapour and the assist gas flow effects in the process. Broadly, melt ejection induced mechanical stresses for the TBC coating / bond coating and thermal effects for the bond coating / substrate interfaces are found the key delamination mechanisms. Experiments are carried out to validate the findings from the model. Various techniques that enable laser drilling without damaging the TBC are demonstrated. Twin jet assisted acute angle laser drilling is one successful technique that has been analysed using the melt ejection simulation. Optimisation of the twin jet assisted acute angle laser drilling process parameters is carried out using Design of Experiments (DoE) and statistical modelling approaches. Finally, an industrial case study to develop a high speed, high quality laser drilling system for combustor cans is described. Holes are drilled by percussion and trepan drilling in TBC coated and uncoated Haynes 230 workpieces. The production rate of percussion drilling is significantly higher than the trepan drilling, however metallurgical hole quality and reproducibility is poor. A number of process parameters are investigated to improve these characteristics. Gas type and gas pressure effects on various characteristics of the inclined laser drilled holes are investigated through theoretical

  9. Mussel Adhesion is Significantly Enhanced Due to the Shape and Mechanics of Its Holdfast

    NASA Astrophysics Data System (ADS)

    Desmond, Kenneth; Zacchia, Nicholas; Waite, Herbert; Valentine, Megan

    2014-03-01

    Mussels permanently adhere to surfaces through a circular plaque that is attached to the animal body via a long thin thread; forming a mushroom-shaped geometry. A plaque just a few millimeters in diameter with a 250-micron diameter thread can withstand large pull forces of a several Newtons without debonding. While the strength of individual chemical bonds plays a role in determining the adhesive strength, the contact mechanics associated with the mushroom shape is also critically important. In fact, numerous other organisms also use mushroom-shaped holdfasts to create strong bonds, suggesting the mushroom geometry is particularly effective for adhesion. To better understand the role of contact mechanics on the adhesive strength of mussels, we study mussel detachment using a custom built load frame capable of pulling on samples along any orientation and measuring the resulting force, while simultaneously imaging the plaque deformation and the glass-plaque interface. We will show that the holdfast shape improves bond strength by an order of magnitude compared to other simple geometries and that force-induced yielding of the mussel plaque improves the bond strength by another two orders of magnitude. These results show that by optimizing for contact mechanics, adhesive strength can be finely tuned for a particular application without changing the interface chemistry.

  10. Photocrosslinked nanocomposite hydrogels from PEG and silica nanospheres: structural, mechanical and cell adhesion characteristics.

    PubMed

    Gaharwar, Akhilesh K; Rivera, Christian; Wu, Chia-Jung; Chan, Burke K; Schmidt, Gudrun

    2013-04-01

    Photopolymerized hydrogels are extensively investigated for various tissue engineering applications, primarily due to their ability to form hydrogels in a minimally invasive manner. Although photocrosslinkable hydrogels provide necessary biological and chemical characteristics to mimic cellular microenvironments, they often lack sufficient mechanical properties. Recently, nanocomposite approaches have demonstrated potential to overcome these deficits by reinforcing the hydrogel network with. In this study, we investigate some physical, chemical, and biological properties of photocrosslinked poly(ethylene glycol) (PEG)-silica hydrogels. The addition of silica nanospheres significantly suppresses the hydration degree of the PEG hydrogels, indicating surface interactions between the silica nanospheres and the polymer chains. No significant change in hydrogel microstructure or average pore size due to the addition of silica nanospheres was observed. However, addition of silica nanospheres significantly increases both the mechanical strength and the toughness of the hydrogel networks. The biological properties of these nanocomposite hydrogels were evaluated by seeding fibroblast cells on the hydrogel surface. While the PEG hydrogels showed minimum cell adhesion, spreading and proliferation, the addition of silica nanospheres enhanced initial cell adhesion, promoted cell spreading and increased the metabolic activity of the cells. Overall, results indicate that the addition of silica nanospheres improves the mechanical stiffness and cell adhesion properties of PEG hydrogels and can be used for biomedical applications that required controlled cell adhesion. PMID:23827639

  11. Strength and failure mechanisms of polyimide-coated optical fibers

    NASA Astrophysics Data System (ADS)

    Skontorp, Arne

    2000-06-01

    Embedded optical fibers and sensors must survive and remain functional for the lifetime of the structure being monitored, as repairs are generally impossible. Thus, the feasibility of an embedded optical fiber monitoring concept depends heavily on the durability of the optical fiber. Processes that degrade the mechanical properties of these fibers are therefore of great concern. During the process of writing a Bragg grating sensor in a fiber, the polyimide coating is damaged locally by ablation, making the fiber vulnerable to moisture degradation. To rectify this situation, the coating in the area around the grating is commonly removed and the fiber is recoated. However, this procedure itself makes the fiber susceptible to degradation by moisture and handling. Tensile experiments were conducted on both virgin fiber and on fibers that had been recoated to study deterioration related to the recoating process. Weibull theory was used to model the strength distributions and a fracture mechanics approach was used in conjunction with microscopy to study failure initiation and to evaluate the relative significance of coating defects. The results indicated that two independent flaw populations existed in the fibers, one associated with manufacturing defects and the other with inherent flaws on the surface of the glass fiber. The failure was always initiated on the glass surface, not in the coating, and the condition of the coating did not effect the failure location. The recoated fibers always failed in the recoated section at a significantly reduced load, due to degradation after exposure of the glass to the environment. This suggested that the recoating process might actually worsen the situation.

  12. Theory of the mechanical response of focal adhesions to shear flow

    NASA Astrophysics Data System (ADS)

    Biton, Y. Y.; Safran, S. A.

    2010-05-01

    The response of cells to shear flow is primarily determined by the asymmetry of the external forces and moments that are sensed by each member of a focal adhesion pair connected by a contractile stress fiber. In the theory presented here, we suggest a physical model in which each member of such a pair of focal adhesions is treated as an elastic body subject to both a myosin-activated contractile force and the shear stress induced by the external flow. The elastic response of a focal adhesion complex is much faster than the active cellular processes that determine the size of the associated focal adhesions and the direction of the complex relative to the imposed flow. Therefore, the complex attains its mechanical equilibrium configuration which may change because of the cellular activity. Our theory is based on the experimental observation that focal adhesions modulate their cross-sectional area in order to attain an optimal shear. Using this assumption, our elastic model shows that such a complex can passively change its orientation to align parallel to the direction of the flow.

  13. Knowledge Discovery Process for Characterization of Materials Failure Mechanism

    NASA Technical Reports Server (NTRS)

    Cios, Krzysztof J.

    1999-01-01

    It is the intent of this project to provide a platform to visualize the various data collected from stress-strain testing of composite ceramic matrix materials. The data collected from the stress-strain tests are acoustic emissions (AE). As a material is subjected to a stress-strain test, various failure mechanisms occur in the material. The recorded sounds emitted during the test may correspond to various failure mechanisms. This project, thus, will give a possible way to visualize the data and data derived from the recorded AE. The stress-strain testing was performed on several composite matrix material combinations. Each of these tests produced anywhere from 1000 to 10,000+ AE events. For each AE event recorded, several characteristics in both the time and frequency domains are created. This project has two goals. First, this project will provide a summation page for a selected waveform. This page will include all of the characteristics determined from the AE event waveform along with graphs of the AE event waveform and its corresponding Power Spectrum. The other function of this project is to retrieve and display selected AE event waveforms for comparison.

  14. Experimental Investigations Of Failure Mechanisms Associated With Slow Slip Events

    NASA Astrophysics Data System (ADS)

    Zhu, W.; Tamarkin, T.

    2010-12-01

    Slow slip events such as very low frequency earthquakes (VLFEs) are detected in the Nankai accretionary prism [Ito and Obara, 2006]. It is proposed that high pore fluid pressure weakens the out-of-sequence-thrusts and mega-splay faults by reducing effective normal stress on the fault plane and consequently generates slip instability producing low stress drop VLFEs. However, the frictional behaviors and failure mechanisms associated with reduction of effective normal stress are not well understood. In this study, we conducted frictional experiments on porous sedimentary rocks with a saw-cut. Sediments with different clay content from NantroSEIZE drilling project ODP Legs 315, 316, and 322 are used as fault gouge. A new triaxial loading configuration was designed to investigate the effect of high pore pressure on frictional instability and failure modes. During the deformation experiments, samples were subjected to constant axial stress and decreasing radial stresses. Distinguishing from the conventional loading configuration in which mean stress increases during deformation, with the alternative loading path, mean stress decreases during deformation. Under fully drained conditions where pore pressure remains constant, the effective stress decreases in these experiments, analoguous to increasing pore pressure. Our preliminary results indicate that: 1) frictional strength is comparable to that observed under conventional loading; 2) the rate of fracture energy release is considerably slower, which bears similar characteristics with observed slow slip events. Microstructural analyses on the deformed samples provide experimental constraints on deformation mechanisms associated with slow slip events.

  15. Interfaces and failure mechanisms in Al-SiC composites

    NASA Technical Reports Server (NTRS)

    Nutt, S. R.

    1986-01-01

    Aluminum alloys reinforced with silicon carbide whiskers exhibit significantly higher strength and modulus than the unreinforced alloys. However, the composites also exhibit low ductility and poor fracture toughness for reasons which are not well-understood. In this study, high resolution and conventional TEM techniques are used to analyze interface microstructure and failure mechanisms in P/M 2124 and 6061 aluminum alloys reinforced with silicon carbide whiskers. Interfacial oxides are typical of both composite materials, often distributed in clusters or in a discrete layer 2-5 nm thick along the whisker-matrix interface. Highly deformed regions beneath bulk tensile fracture surfaces reveal possible fracture nucleation centers as well as sites of stress concentration where intense plastic strain has occurred. Observations of such highly deformed regions include (1) void initiation at whisker ends, (2) interface decohesion involving the thin oxide layer, (3) transverse cracks in whiskers, and (4) cracks in large constituent particles. TEM results are presented and discussed in relation to mechanisms of composite failure.

  16. Dynamic transcription factor activity networks in response to independently altered mechanical and adhesive microenvironmental cues.

    PubMed

    Peñalver Bernabé, Beatriz; Shin, Seungjin; Rios, Peter D; Broadbelt, Linda J; Shea, Lonnie D; Seidlits, Stephanie K

    2016-08-01

    Multiple aspects of the local extracellular environment profoundly affect cell phenotype and function. Physical and chemical cues in the environment trigger intracellular signaling cascades that ultimately activate transcription factors (TFs) - powerful regulators of the cell phenotype. TRACER (TRanscriptional Activity CEll aRrays) was employed for large-scale, dynamic quantification of TF activity in human fibroblasts cultured on hydrogels with a controlled elastic modulus and integrin ligand density. We identified three groups of TFs: responders to alterations in ligand density alone, substrate stiffness or both. Dynamic networks of regulatory TFs were constructed computationally and revealed distinct TF activity levels, directionality (i.e., activation or inhibition), and dynamics for adhesive and mechanical cues. Moreover, TRACER networks predicted conserved hubs of TF activity across multiple cell types, which are significantly altered in clinical fibrotic tissues. Our approach captures the distinct and overlapping effects of adhesive and mechanical stimuli, identifying conserved signaling mechanisms in normal and disease states. PMID:27470442

  17. Joining technologies for the 1990s: Welding, brazing, soldering, mechanical, explosive, solid-state, adhesive

    NASA Technical Reports Server (NTRS)

    Buckley, John D. (Editor); Stein, Bland A. (Editor)

    1986-01-01

    A compilation of papers presented in a joint NASA, American Society for Metals, The George Washington University, American Welding Society, and Society of Manufacturing Engineers Conference on Welding, Bonding, and Fastening at Langley Research Center, Hampton, VA, on October 23 to 25, 1984 is given. Papers were presented on technology developed in current research programs relevant to welding, bonding, and fastening of structural materials required in fabricating structures and mechanical systems used in the aerospace, hydrospace, and automotive industries. Topics covered in the conference included equipment, hardware and materials used when welding, brazing, and soldering, mechanical fastening, explosive welding, use of unique selected joining techniques, adhesives bonding, and nondestructive evaluation. A concept of the factory of the future was presented, followed by advanced welding techniques, automated equipment for welding, welding in a cryogenic atmosphere, blind fastening, stress corrosion resistant fasteners, fastening equipment, explosive welding of different configurations and materials, solid-state bonding, electron beam welding, new adhesives, effects of cryogenics on adhesives, and new techniques and equipment for adhesive bonding.

  18. Failure Mechanisms in High Chrome Oxide Gasifier Refractories

    NASA Astrophysics Data System (ADS)

    Bennett, James P.; Kwong, Kyei-Sing

    2011-04-01

    Gasification is a high-temperature, high-pressure chemical process used to convert a carbon feedstock into CO and H2 (syngas) for use in power generation and the production of chemicals. It is also a leading candidate as a source of hydrogen in a hydrogen economy and is one of several technologies expected to see increased use in advanced fossil fuel power systems in the future. Gasification is being evaluated because of its high efficiency, its ability to capture CO2 for sequestration or reuse in other applications, and its potential for carbon feedstock fuel flexibility. At the heart of the gasification process is a gasifier, a high pressure chemical reaction vessel used to contain the interactions between carbon and water in a shortage of oxygen, producing syngas. The gasifier is lined with high chrome oxide materials to protect the containment vessel. Gasifiers are complex systems, and failure of the refractories used to line them was identified by industry as a limitation to their reliability and availability and to their increased use. NETL researchers have examined spent high-Cr2O3 (over 90 pct Cr2O3) refractories from numerous gasifiers to determine in-service failure mechanisms. This analysis revealed that premature failure of the high chrome oxide refractories was related to ash in the carbon feedstock, which liquefies during gasification and interacts with the refractories, leading to wear by chemical dissolution or spalling (structural and chemical). A discussion of this postmortem wear of spent refractory materials and of thermodynamic modeling used to explain microstructural changes leading to wear are explained in this article. This information will serve the basis to develop improved performance refractory materials.

  19. Mechanical characterization of a bifunctional Tetronic hydrogel adhesive for soft tissues.

    PubMed

    Sanders, Lindsey; Stone, Roland; Webb, Kenneth; Mefford, Thompson; Nagatomi, Jiro

    2015-03-01

    Although a number of tissue adhesives and sealants for surgical use are currently available, attaining a useful balance in high strength, high compliance, and low swelling has proven difficult. Recent studies have demonstrated that a four-arm poly(propylene oxide)-poly(ethylene oxide) block copolymer, Tetronic, can be chemically modified to form a hydrogel tissue adhesive (Cho et al., Acta Biomater 2012;8:2223-2232; Barrett et al., Adv Health Mater 2012;1-11; Balakrishnan, Evaluating mechanical performance of hydrogel-based adhesives for soft tissue applications. Clemson University, All Theses, Paper 1574: Tiger Prints; 2013). Building on the success of these studies, this study explored bifunctionalization of Tetronic with acrylates for chemical crosslinking of the hydrogel and N-hydroxysuccinimide (NHS) for reaction with tissue amines. The adhesive bond strengths of various uni and bifunctional Tetronic blends (T1107 ACR: T1107 ACR/NHS) determined by lap shear testing ranged between 8 and 74 kPa, with the 75:25 (T1107 ACR: T1107 ACR/NHS) blend displaying the highest value. These results indicated that addition of NHS led to improvement of tissue bond strength over acrylation alone. Furthermore, ex vivo pressure tests using the rat bladder demonstrated that the bifunctional Tetronic adhesive exhibited high compliance and maintained pressures under hundreds of filling and emptying cycles. Together, the results of this study provided evidence that the bifunctional Tetronic adhesive with a proper blend ratio may be used to achieve an accurate balance in bulk and tissue bond strengths, as well as the compliance and durability for soft tissue such as the bladder. PMID:25111445

  20. Mechanisms of compressive failure in woven composites and stitched laminates

    NASA Technical Reports Server (NTRS)

    Cox, B. N.; Dadkhah, M. S.; Inman, R. V.; Morris, W. L.; Schroeder, S.

    1992-01-01

    Stitched laminates and angle interlock woven composites have been studied in uniaxial, in-plane, monotonic compression. Failure mechanisms have been found to depend strongly on both the reinforcement architecture and the degree of constraint imposed by the loading grips. Stitched laminates show higher compressive strength, but are brittle, possessing no load bearing capacity beyond the strain for peak load. Post-mortem inspection shows a localized shear band of buckled and broken fibers, which is evidently the product of an unstably propagating kink band. Similar shear bands are found in the woven composites if the constraint of lateral displacements is weak; but, under strong constraint, damage is not localized but distributed throughout the gauge section. While the woven composites tested are weaker than the stitched laminates, they continue to bear significant loads to compressive strains of approx. 15 percent, even when most damage is confined to a shear band.

  1. Failure Mechanism for Thermal Fatigue of Thermal Barrier Coating Systems

    NASA Astrophysics Data System (ADS)

    Giolli, C.; Scrivani, A.; Rizzi, G.; Borgioli, F.; Bolelli, G.; Lusvarghi, L.

    2009-06-01

    Thick thermal barrier coatings (TBCs), consisting of a CoNiCrAlY bond coat and yttria-partially stabilized zirconia top coat with different porosity values, were produced by air plasma spray (APS). The thermal fatigue resistance limit of the TBCs was tested by furnace cycling tests (FCT) according to the specifications of an original equipment manufacturer (OEM). The morphology, residual stresses, and micromechanical properties (microhardness, indentation fracture toughness) of the TBC systems before and after FCT were analyzed. The thermal fatigue resistance increases with the amount of porosity in the top coat. The compressive in-plane stresses increase in the TBC systems after thermal cycling; nevertheless the increasing rate has a trend contrary to the porosity level of top coat. The data suggest that the spallation happens at the TGO/top coat interface. The failure mechanism of thick TBCs was found to be similar to that of conventional thin TBC systems made by APS.

  2. A failure modes, mechanisms, and effects analysis (FMMEA) of lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Hendricks, Christopher; Williard, Nick; Mathew, Sony; Pecht, Michael

    2015-11-01

    Lithium-ion batteries are popular energy storage devices for a wide variety of applications. As batteries have transitioned from being used in portable electronics to being used in longer lifetime and more safety-critical applications, such as electric vehicles (EVs) and aircraft, the cost of failure has become more significant both in terms of liability as well as the cost of replacement. Failure modes, mechanisms, and effects analysis (FMMEA) provides a rigorous framework to define the ways in which lithium-ion batteries can fail, how failures can be detected, what processes cause the failures, and how to model failures for failure prediction. This enables a physics-of-failure (PoF) approach to battery life prediction that takes into account life cycle conditions, multiple failure mechanisms, and their effects on battery health and safety. This paper presents an FMMEA of battery failure and describes how this process enables improved battery failure mitigation control strategies.

  3. Nature's Mechanisms for Tough, Self-healing Polymers and Polymer Adhesives

    NASA Astrophysics Data System (ADS)

    Hansma, Paul

    2007-03-01

    Spider silk^2 and the natural polymer adhesives in abalone shells^3 and bone^4,5 can give us insights into nature's mechanisms for tough, self-healing polymers and polymer adhesives. The natural polymer adhesives in biomaterials have been optimized by evolution. An optimized polymer adhesive has five characteristics. 1) It holds together the strong elements of the composite. 2) It yields just before the strong elements would otherwise break. 3) It dissipates large amounts of energy as it yields. 4) It self heals after it yields. 5) It takes just a few percent by weight. Both natural polymer adhesives and silk rely on sacrificial bonds and hidden length for toughness and self-healing.^6 A relatively large energy, of order 100eV, is required to stretch a polymer molecule after a weak bond, a sacrificial bond, breaks and liberates hidden length, which was previously hidden, typically in a loop or folded domain, from whatever was stretching the polymer. The bond is called sacrificial if it breaks at forces well below the forces that could otherwise break the polymer backbone, typically greater than 1nN. In many biological cases, the breaking of sacrificial bonds has been found to be reversible, thereby also providing a ``self-healing'' property to the material.^2-4 Individual polymer adhesive molecules based on sacrificial bonds and hidden length can supply forces of order 300pN over distances of 100s of nanometers. Model calculations show that a few percent by weight of adhesives based on these principles could be optimized adhesives for high performance composite materials including nanotube and graphene sheet composites. ^2N. Becker, E. Oroudjev, S. Mutz et al., Nature Materials 2 (4), 278 (2003). ^3B. L. Smith, T. E. Schaffer, M. Viani et al., Nature 399 (6738), 761 (1999). ^4J. B. Thompson, J. H. Kindt, B. Drake et al., Nature 414 (6865), 773 (2001). ^5G. E. Fantner, T. Hassenkam, J. H. Kindt et al., Nature Materials 4, 612 (2005). ^6G. E. Fantner, E. Oroudjev, G

  4. Mechanical Properties and Sliding-impact Wear Resistance of Self-adhesive Resin Cements.

    PubMed

    Furuichi, T; Takamizawa, T; Tsujimoto, A; Miyazaki, M; Barkmeier, W W; Latta, M A

    2016-01-01

    The present study determined the mechanical properties and impact-sliding wear characteristics of self-adhesive resin cements. Five self-adhesive resin cements were used: G-CEM LinkAce, BeautiCem SA, Maxcem Elite, Clearfil SA Automix, and RelyX Unicem 2. Clearfil Esthetic Cement was employed as a control material. Six specimens for each resin cement were used to determine flexural strength, elastic modulus, and resilience according to ISO specification #4049. Ten specimens for each resin cement were used to determine the wear characteristics using an impact-sliding wear testing apparatus. Wear was generated using a stainless-steel ball bearing mounted inside a collet assembly. The maximum facet depth and volume loss were determined using a noncontact profilometer in combination with confocal laser scanning microscopy. Data were evaluated using analysis of variance followed by the Tukey honestly significantly different test (α=0.05). The flexural strength of the resin cements ranged from 68.4 to 144.2 MPa; the elastic modulus ranged from 4.4 to 10.6 GPa; and the resilience ranged from 4.5 to 12.0 MJ/m(3). The results for the maximum facet depth ranged from 25.2 to 235.9 μm, and volume loss ranged from 0.0107 to 0.5258 mm(3). The flexural properties and wear resistance were found to vary depending upon the self-adhesive resin cement tested. The self-adhesive cements tended to have lower mechanical properties than the conventional resin cement. All self-adhesive resin cements, apart from G-CEM LinkAce, demonstrated significantly poorer wear resistance than did the conventional resin cement. PMID:26918929

  5. Doxorubicin induced heart failure: Phenotype and molecular mechanisms

    PubMed Central

    Mitry, Maria A.; Edwards, John G.

    2016-01-01

    Long term survival of childhood cancers is now more than 70%. Anthracyclines, including doxorubicin, are some of the most efficacious anticancer drugs available. However, its use as a chemotherapeutic agent is severely hindered by its dose-limiting toxicities. Most notably observed is cardiotoxicity, but other organ systems are also degraded by doxorubicin use. Despite the years of its use and the amount of information written about this drug, an understanding of its cellular mechanisms is not fully appreciated. The mechanisms by which doxorubicin induces cytotoxicity in target cancer cells have given insight about how the drug damages cardiomyocytes. The major mechanisms of doxorubicin actions are thought to be as an oxidant generator and as an inhibitor of topoisomerase 2. However, other signaling pathways are also invoked with significant consequences for the cardiomyocyte. Further the interaction between oxidant generation and topoisomerase function has only recently been appreciated and the consequences of this interaction are still not fully understood. The unfortunate consequences of doxorubicin within cardiomyocytes have promoted the search for new drugs and methods that can prevent or reverse the damage caused to the heart after treatment in cancer patients. Alternative protocols have lessened the impact on newly diagnosed cancer patients. However the years of doxorubicin use have generated a need for monitoring the onset of cardiotoxicity as well as understanding its potential long-term consequences. Although a fairly clear understanding of the short-term pathologic mechanisms of doxorubicin actions has been achieved, the long-term mechanisms of doxorubicin induced heart failure remain to be carefully delineated. PMID:27213178

  6. Computational and numerical aspects of using the integral equation method for adhesive layer fracture mechanics analysis

    SciTech Connect

    Giurgiutiu, V.; Ionita, A.; Dillard, D.A.; Graffeo, J.K.

    1996-12-31

    Fracture mechanics analysis of adhesively bonded joints has attracted considerable attention in recent years. A possible approach to the analysis of adhesive layer cracks is to study a brittle adhesive between 2 elastic half-planes representing the substrates. A 2-material 3-region elasticity problem is set up and has to be solved. A modeling technique based on the work of Fleck, Hutchinson, and Suo is used. Two complex potential problems using Muskelishvili`s formulation are set up for the 3-region, 2-material model: (a) a distribution of edge dislocations is employed to simulate the crack and its near field; and (b) a crack-free problem is used to simulate the effect of the external loading applied in the far field. Superposition of the two problems is followed by matching tractions and displacements at the bimaterial boundaries. The Cauchy principal value integral is used to treat the singularities. Imposing the traction-free boundary conditions over the entire crack length yielded a linear system of two integral equations. The parameters of the problem are Dundurs` elastic mismatch coefficients, {alpha} and {beta}, and the ratio c/H representing the geometric position of the crack in the adhesive layer.

  7. Comparing the mechanical influence of vinculin, focal adhesion kinase and p53 in mouse embryonic fibroblasts

    SciTech Connect

    Klemm, Anna H.; Diez, Gerold; Alonso, Jose-Luis

    2009-02-13

    Cytoskeletal reorganization is an ongoing process when cells adhere, move or invade extracellular substrates. The cellular force generation and transmission are determined by the intactness of the actomyosin-(focal adhesion complex)-integrin connection. We investigated the intracellular course of action in mouse embryonic fibroblasts deficient in the focal adhesion proteins vinculin and focal adhesion kinase (FAK) and the nuclear matrix protein p53 using magnetic tweezer and nanoparticle tracking techniques. Results show that the lack of these proteins decrease cellular stiffness and affect cell rheological behavior. The decrease in cellular binding strength was higher in FAK- to vinculin-deficient cells, whilst p53-deficient cells showed no effect compared to wildtype cells. The intracellular cytoskeletal activity was lowest in wildtype cells, but increased in the following order when cells lacked FAK+p53 > p53 > vinculin. In summary, cell mechanical processes are differently affected by the focal adhesion proteins vinculin and FAK than by the nuclear matrix protein, p53.

  8. Homophilic Adhesion Mechanism of Neurofascin, a Member of the L1 Family of Neural Cell Adhesion Molecules

    SciTech Connect

    Liu, Heli; Focia, Pamela J.; He, Xiaolin

    2012-02-13

    The L1 family neural cell adhesion molecules play key roles in specifying the formation and remodeling of the neural network, but their homophilic interaction that mediates adhesion is not well understood. We report two crystal structures of a dimeric form of the headpiece of neurofascin, an L1 family member. The four N-terminal Ig-like domains of neurofascin form a horseshoe shape, akin to several other immunoglobulin superfamily cell adhesion molecules such as hemolin, axonin, and Dscam. The neurofascin dimer, captured in two crystal forms with independent packing patterns, reveals a pair of horseshoes in trans-synaptic adhesion mode. The adhesion interaction is mediated mostly by the second Ig-like domain, which features an intermolecular {beta}-sheet formed by the joining of two individual GFC {beta}-sheets and a large but loosely packed hydrophobic cluster. Mutagenesis combined with gel filtration assays suggested that the side chain hydrogen bonds at the intermolecular {beta}-sheet are essential for the homophilic interaction and that the residues at the hydrophobic cluster play supplementary roles. Our structures reveal a conserved homophilic adhesion mode for the L1 family and also shed light on how the pathological mutations of L1 affect its structure and function.

  9. Severe inflammatory reaction induced by peritoneal trauma is the key driving mechanism of postoperative adhesion formation

    PubMed Central

    2011-01-01

    Background Many factors have been put forward as a driving mechanism of surgery-triggered adhesion formation (AF). In this study, we underline the key role of specific surgical trauma related with open surgery (OS) and laparoscopic (LS) conditions in postoperative AF and we aimed to study peritoneal tissue inflammatory reaction (TIR), remodelling specific complications of open surgery (OS) versus LS and subsequently evaluating AF induced by these conditions. Methods A prospective randomized study was done in 80 anaesthetised female Wistar rats divided equally into 2 groups. Specific traumatic OS conditions were induced by midline incision line (MIL) extension and tissue drying and specific LS conditions were remodelled by intraperitoneal CO2 insufflation at the 10 cm of water. TIR was evaluated at the 24th, 72nd, 120th and 168th hour by scoring scale. Statistical analysis was performed by the non-parametric t test and two-way ANOVA using Bonferroni post-tests. Results More pronounced residual TIR was registered after OS than after LS. There were no significant TIR interactions though highly significant differences were observed between the OS and LS groups (p < 0.0001) with regard to surgical and time factors. The TIR change differences between the OS and LS groups were pronounced with postoperative time p < 0.05 at the 24th and 72nd; p < 0.01 - 120th and p < 0.001 - 168th hrs. Adhesion free wounds were observed in 20.0 and 31.0% of cases after creation of OS and LS conditions respectively; with no significant differences between these values (p > 0.05). However larger adhesion size (41.67 ± 33.63) was observed after OS in comparison with LS (20.31 ± 16.38). The upper-lower 95% confidential limits ranged from 60.29 to 23.04 and from 29.04 to 11.59 respectively after OS and LS groups with significant differences (p = 0.03). Analogous changes were observed in adhesion severity values. Subsequently, severe TIR parameters were followed by larger sizes of severe

  10. The role of focal adhesion kinase in the regulation of cellular mechanical properties

    NASA Astrophysics Data System (ADS)

    Mierke, Claudia Tanja

    2013-12-01

    The regulation of mechanical properties is necessary for cell invasion into connective tissue or intra- and extravasation through the endothelium of blood or lymph vessels. Cell invasion is important for the regulation of many healthy processes such as immune response reactions and wound healing. In addition, cell invasion plays a role in disease-related processes such as tumor metastasis and autoimmune responses. Until now the role of focal adhesion kinase (FAK) in regulating mechanical properties of cells and its impact on cell invasion efficiency is still not well known. Thus, this review focuses on mechanical properties regulated by FAK in comparison to the mechano-regulating protein vinculin. Moreover, it points out the connection between cancer cell invasion and metastasis and FAK by showing that FAK regulates cellular mechanical properties required for cellular motility. Furthermore, it sheds light on the indirect interaction of FAK with vinculin by binding to paxillin, which then impairs the binding of paxillin to vinculin. In addition, this review emphasizes whether FAK fulfills regulatory functions similar to vinculin. In particular, it discusses the differences and the similarities between FAK and vinculin in regulating the biomechanical properties of cells. Finally, this paper highlights that both focal adhesion proteins, vinculin and FAK, synergize their functions to regulate the mechanical properties of cells such as stiffness and contractile forces. Subsequently, these mechanical properties determine cellular invasiveness into tissues and provide a source sink for future drug developments to inhibit excessive cell invasion and hence, metastases formation.

  11. Deformation and Failure Mechanisms of Shape Memory Alloys

    SciTech Connect

    Daly, Samantha Hayes

    2015-04-15

    The goal of this research was to understand the fundamental mechanics that drive the deformation and failure of shape memory alloys (SMAs). SMAs are difficult materials to characterize because of the complex phase transformations that give rise to their unique properties, including shape memory and superelasticity. These phase transformations occur across multiple length scales (one example being the martensite-austenite twinning that underlies macroscopic strain localization) and result in a large hysteresis. In order to optimize the use of this hysteretic behavior in energy storage and damping applications, we must first have a quantitative understanding of this transformation behavior. Prior results on shape memory alloys have been largely qualitative (i.e., mapping phase transformations through cracked oxide coatings or surface morphology). The PI developed and utilized new approaches to provide a quantitative, full-field characterization of phase transformation, conducting a comprehensive suite of experiments across multiple length scales and tying these results to theoretical and computational analysis. The research funded by this award utilized new combinations of scanning electron microscopy, diffraction, digital image correlation, and custom testing equipment and procedures to study phase transformation processes at a wide range of length scales, with a focus at small length scales with spatial resolution on the order of 1 nanometer. These experiments probe the basic connections between length scales during phase transformation. In addition to the insights gained on the fundamental mechanisms driving transformations in shape memory alloys, the unique experimental methodologies developed under this award are applicable to a wide range of solid-to-solid phase transformations and other strain localization mechanisms.

  12. Effect of the regional variability of dentinal substrate and modes of application of adhesive systems on the mechanical properties of the adhesive layer

    PubMed Central

    Pupo, Yasmine Mendes; Michél, Milton Domingos; Gomes, Osnara Maria Mongruel; Lepienski, Carlos Maurício; Gomes, João Carlos

    2012-01-01

    Aim: This study assessed the effect of the dentin depth and the application mode on the hardness and elastic modulus of the adhesive layer. Materials and Methods: Occlusal surfaces of 48 caries-free human third molars were removed, at two levels: Superficial and deep dentin. For each type of surface, the test specimens were randomly divided into groups which underwent the application: A conventional two-step adhesive system (Adper™ Single Bond [SB]) and self-etch adhesives system (Adper™ SE Plus [SE] and AdheSE® [AD]). The adhesives applied were active or passive. Composite build-ups were constructed incrementally. The teeth were sectioned, embedded, and polished. The nanoindentation test was performed in the adhesive layer. The results were analyzed by ANOVA and Tukey tests. Results: In the adhesive layer, the higher hardness (0.307 ± 0.006 GPa) and elastic modulus (4.796 ± 0.165 GPa) of SE were obtained in superficial dentin in passive application. The elastic modulus of SE (4.115 ± 0.098 GPa) was lowest in active application in superficial dentin. The active application significantly increased the hardness of the SB in the deep dentin (0.011 ± 0.314 GPa) compared the superficial dentin (0.280 ± 0.010 GPa). For the AD, only the mode of application was statistically significant (P=0.0041) for the hardness, active application (0.289 ± 0.015 GPa) being higher than passive application (0.261 ± 0.013 GPa) (P=0.0042) in deep dentin. Conclusion: The experimental results reveal that the mechanical properties were influenced for the application mode of adhesive systems and dentin depth. PMID:22557810

  13. Ultrasensitivity of Cell Adhesion to the Presence of Mechanically Strong Ligands

    NASA Astrophysics Data System (ADS)

    Roein-Peikar, Mehdi; Xu, Qian; Wang, Xuefeng; Ha, Taekjip

    2016-01-01

    Integrins, a class of membrane proteins involved in cell adhesion, participate in the cell's sensing of the mechanical environments. We previously showed that, for the initial cell adhesion to occur, single integrins need to experience a threshold force of 40 pico-Newton (pN) through their bond with surface-bound ligands. This force requirement was determined using a series of double-stranded DNA tethers called tension gauge tethers (TGTs), each with a different rupture force, linked to the ligand. Here, we performed cell-adhesion experiments using surfaces coated with two different TGTs, one of a strong rupture force (around 54 pN) and the other of a weak rupture force (around 12 pN). When presented with one type of TGT only, cells adhered to the strong TGT-coated surface but not to the weak TGT-coated surface. However, when presented with both, the presence of the strong TGTs transforms the way cells respond to the weak TGTs such that cells treat both TGTs the same, as if the weak TGTs were strong. Furthermore, a subpopulation of cells can adhere to and spread on a surface displaying just a few molecules of the strong TGTs per cell if, and only if, they are presented along with many weak TGTs. This ultrasensitivity to just a few tethers that can withstand strong forces raises a question of how the cells can achieve such remarkable sensitivity to their mechanical environment without amplifying noise.

  14. A bio-inspired attachment mechanism for long-term adhesion to the small intestine.

    PubMed

    Xie, Wanchuan; Kothari, Vishal; Terry, Benjamin S

    2015-08-01

    To achieve long-term attachment of capsule endoscopes (CEs) and miniature biosensors in the human gastrointestinal (GI) tract, a tissue attachment mechanism (TAM) was designed, optimized and tested for safety and adhesive capabilities on excised tissue in vitro and in vivo on a live pig model. Six TAMs were tested for their attachment strength in an in vitro attachment tensile experiment in which each TAM was tested on three different proximal intestine tissue samples. The maximum strength and average value are 8.09 N and 4.54 N respectively. The initial attachment damage was tested for 10 min using a sine wave pull force on the TAM with a 0.4 N peak value and 6 s period, which represents typical human intestinal traction force from peristalsis. The in vitro attachment tensile test verified that the tissue was not visually damaged nor perforated by the attachment process. In the in vivo experiment, four TAMs were placed in the intestine of a pig through individual longitudinal enterotomies. X-ray images were taken each hour after the surgery and showed zero migration of the TAMs after 24 h of adhesion. X-ray images taken each day indicated the attachment duration of this mechanism lasted up to 6 days. Post experiment inspection confirmed the attachment did not cause visible damage to tissue. These results confirmed the reliability of the TAM in vivo and demonstrated preliminary feasibility of long-term sensor adhesion to the GI tract. PMID:26044204

  15. Investigation of Interface States and Failure Mechanisms in Mnos Devices

    NASA Astrophysics Data System (ADS)

    Lu, Hsing-Liang

    The objective of this dissertation is to conduct a quantitative study of the interface state characteristics at Si-SiO(,2) interface and the failure mechanisms in the silicon MNOS nonvolatile memory devices under different write/erase (W/E) cycling conditions. The main thrust of this research is to quantitatively characterize the interface states in MNOS devices and to correlate the results of the measurements to the failure mechanisms in the exercised MNOS devices for W/E cycles up to 1 x 10('11) cycles. The Constant-Capacitance Deep Level Transient Spectroscopy (CC-DLTS) technique is employed for the first time to characterize the interface states in the MNOS device. The existing theory for the CC-DLTS technique is modified to analyze the interface state density and electron capture cross sections of the trap states at Si-SiO(,2) interface. An exact equivalent circuit model for the p('+)-gridded MNOS capacitors is developed to predict the high frequency C -V behavior in the exercised MNOS devices. The results show little change in the interface state density was observed for W/E cycles less than 1 x 10('7) and increased rapidly for W/E cycles greater than 1 x 10('7). For W/E cycles greater than 5 x 10('9), a gradual increase in interface state density with W/E cyclings was observed. The negative shift of threshold voltage in the exercised MNOS devices can be attributed to the creation of interface states for W/E cycles less than 10('9) and primarily due to the generation of interface states for W/E cycles exceeding 1 x 10('9). The increase in interface state densities and the degradation of the thin oxide layer after prolonged W/E cycling increase the back tunneling current which results in the increase of retention decay rate. Furthermore, mobility degradation in the inversion layer was observed in the MNOS transistors for W/E cycling exceeds 10('9). This is attributed to the generation of surface state densities. Improvement in retention and endurance of the

  16. Mechanisms relating to reducing stress in curing thick sections of UV adhesives

    NASA Astrophysics Data System (ADS)

    Norland, Eric A.; Martin, Frank S.

    1993-09-01

    Ultraviolet curing adhesives are widely used in optical lamination of precision optical lenses, safety windows, holographic displays, and flat panel displays. In most of these applications they are being used in relatively thin films from 3 microns to 40 mils, because most formulations will only allow uv light to penetrate to a certain depth. If the formulation does cure in thicker sections, the stress due to shrinkage typically becomes a problem. U.V. adhesives have been developed which can be cured in relatively thick sections with minimum stress. In this paper, a number of formulations are compared for variations in stress when cured in thick sections and the conditions and mechanism to minimize stress are characterized.

  17. Functional properties of adhesive ankle taping: neuromuscular and mechanical effects before and after exercise.

    PubMed

    Alt, W; Lohrer, H; Gollhofer, A

    1999-04-01

    The purpose of the study was to investigate effects of adhesive ankle taping. Using electromyographic, goniometric, and thermologic methods, different ankle tapes were tested before and after athletic exercise in simulated inversion trauma. Twelve subjects with stable ankle joints performed five trials: with two different materials, with two taping techniques, and one trial without tape as control. After the simulated inversion trauma, approximately 35% of the initial maximum inversion amplitude was decreased by ankle taping. Depending on the technique, there was a loss of tape stability < or =14% after 30 min of athletic exercise. Thermologic analysis revealed a postexercise 6 degrees C temperature increase in the foot, especially under the tape. Initially, interpreted as the primary effect, the improved joint stabilization is based on mechanical stiffness caused by the adhesive tape. Joint stability was influenced positively by neuromuscular proprioceptive and physiological processes, characterized by relatively increased electromyographic activation. PMID:10229280

  18. The Effect of Surface Contamination on Adhesive Forces as Measured by Contact Mechanics

    SciTech Connect

    EMERSON,JOHN A.; GIUNTA,RACHEL K.; MILLER,GREGORY V.; SORENSEN,CHRISTOPHER R.; PEARSON,RAYMOND A.

    2000-12-18

    The contact adhesive forces between two surfaces, one being a soft hemisphere and the other being a hard plate, can readily be determined by applying an external compressive load to mate the two surfaces and subsequently applying a tensile load to peel the surfaces apart. The contact region is assumed the superposition of elastic Hertzian pressure and of the attractive surface forces that act only over the contact area. What are the effects of the degree of surface contamination on adhesive forces? Clean aluminum surfaces were coated with hexadecane as a controlled contaminant. The force required to pull an elastomeric hemisphere from a surface was determined by contact mechanics, via the JKR model, using a model siloxane network for the elastomeric contact sphere. Due to the dispersive nature of the elastomer surface, larger forces were required to pull the sphere from a contaminated surface than a clean aluminum oxide surface.

  19. Gigaseal Mechanics: Creep of the Gigaseal under the Action of Pressure, Adhesion, and Voltage

    PubMed Central

    2015-01-01

    Patch clamping depends on a tight seal between the cell membrane and the glass of the pipet. Why does the seal have such high electric resistance? Why does the patch adhere so strongly to the glass? Even under the action of strong hydrostatic, adhesion, and electrical forces, it creeps at a very low velocity. To explore possible explanations, we examined two physical models for the structure of the seal zone and the adhesion forces and two respective mechanisms of patch creep and electric conductivity. There is saline between the membrane and glass in the seal, and the flow of this solution under hydrostatic pressure or electroosmosis should drag a patch. There is a second possibility: the lipid core of the membrane is liquid and should be able to flow, with the inner monolayer slipping over the outer one. Both mechanisms predict the creep velocity as a function of the properties of the seal and the membrane, the pipet geometry, and the driving force. These model predictions are compared with experimental data for azolectin liposomes with added cholesterol or proteins. It turns out that to obtain experimentally observed creep velocities, a simple viscous flow in the seal zone requires ∼10 Pa·s viscosity; it is unclear what structure might provide that because that viscosity alone severely constrains the electric resistance of the gigaseal. Possibly, it is the fluid bilayer that allows the motion. The two models provide an estimate of the adhesion energy of the membrane to the glass and membrane’s electric characteristics through the comparison between the velocities of pressure-, adhesion-, and voltage-driven creep. PMID:25295693

  20. Gigaseal mechanics: creep of the gigaseal under the action of pressure, adhesion, and voltage.

    PubMed

    Slavchov, Radomir I; Nomura, Takeshi; Martinac, Boris; Sokabe, Masahiro; Sachs, Frederick

    2014-11-01

    Patch clamping depends on a tight seal between the cell membrane and the glass of the pipet. Why does the seal have such high electric resistance? Why does the patch adhere so strongly to the glass? Even under the action of strong hydrostatic, adhesion, and electrical forces, it creeps at a very low velocity. To explore possible explanations, we examined two physical models for the structure of the seal zone and the adhesion forces and two respective mechanisms of patch creep and electric conductivity. There is saline between the membrane and glass in the seal, and the flow of this solution under hydrostatic pressure or electroosmosis should drag a patch. There is a second possibility: the lipid core of the membrane is liquid and should be able to flow, with the inner monolayer slipping over the outer one. Both mechanisms predict the creep velocity as a function of the properties of the seal and the membrane, the pipet geometry, and the driving force. These model predictions are compared with experimental data for azolectin liposomes with added cholesterol or proteins. It turns out that to obtain experimentally observed creep velocities, a simple viscous flow in the seal zone requires ~10 Pa·s viscosity; it is unclear what structure might provide that because that viscosity alone severely constrains the electric resistance of the gigaseal. Possibly, it is the fluid bilayer that allows the motion. The two models provide an estimate of the adhesion energy of the membrane to the glass and membrane's electric characteristics through the comparison between the velocities of pressure-, adhesion-, and voltage-driven creep. PMID:25295693

  1. Oxide film microstructure: the link between surface preparation processes and strength/durability of adhesively bonded aluminum. Final report

    SciTech Connect

    Hsia, K. Jimmy; Pearlstein, Arne J.; Scheeline, Alexander; Shang, Jian Ku

    2000-11-30

    Strength and durability of adhesive bonding of aluminum alloys structures are intrinsically determined by the surface microstructures and interfacial failure micromechanisms. The current project presents a multidisciplinary approach to addressing critical issues controlling the strength and durability of adhesive bonds of aluminum alloys. Three main thrust areas have been pursued: surface treatment technology development to achieve desirable surface microstructures; relationship between surface structure and properties of adhesive bonds; and failure mechanisms of adhesively bonded components.

  2. Failure Criterion for Brick Masonry: A Micro-Mechanics Approach

    NASA Astrophysics Data System (ADS)

    Kawa, Marek

    2015-02-01

    The paper deals with the formulation of failure criterion for an in-plane loaded masonry. Using micro-mechanics approach the strength estimation for masonry microstructure with constituents obeying the Drucker-Prager criterion is determined numerically. The procedure invokes lower bound analysis: for assumed stress fields constructed within masonry periodic cell critical load is obtained as a solution of constrained optimization problem. The analysis is carried out for many different loading conditions at different orientations of bed joints. The performance of the approach is verified against solutions obtained for corresponding layered and block microstructures, which provides the upper and lower strength bounds for masonry microstructure, respectively. Subsequently, a phenomenological anisotropic strength criterion for masonry microstructure is proposed. The criterion has a form of conjunction of Jaeger critical plane condition and Tsai-Wu criterion. The model proposed is identified based on the fitting of numerical results obtained from the microstructural analysis. Identified criterion is then verified against results obtained for different loading orientations. It appears that strength of masonry microstructure can be satisfactorily described by the criterion proposed.

  3. Mechanism of low-temperature-induced pollen failure in rice.

    PubMed

    Al Mamun, Ezaz; Cantrill, Laurence C; Overall, Robyn L; Sutton, Bruce G

    2010-05-01

    Low-temperature stress during microspore development alters cellular organization in rice anthers. The major cellular damage includes unusual starch accumulation in the plastids of the endothecium in postmeiotic anthers, abnormal vacuolation and hypertrophy of the tapetum, premature callose (1,3-beta-glucan) breakdown and lack of normal pollen wall formation. These cellular lesions arise from damage to critical biochemical processes that include sugar metabolism in the anthers and its use by the microspores. Failure of utilization of the callose breakdown product and other microspore wall components like sporopollenin can also be considered as critical. In recent years, considerable progress has been made in the understanding of major biochemical processes including the expression of critical genes that are sensitive to low temperature in rice and cause male sterility. This paper combines a discussion of cellular organization and associated biochemical processes that are sensitive to low temperatures and provides an overview of the potential mechanisms of low-temperature-induced male sterility in rice. PMID:20100170

  4. Mechanical Unloading Promotes Myocardial Energy Recovery in Human Heart Failure

    PubMed Central

    Gupte, Anisha A.; Hamilton, Dale J.; Cordero-Reyes, Andrea M.; Youker, Keith A.; Yin, Zheng; Estep, Jerry D.; Stevens, Robert D.; Wenner, Brett; Ilkayeva, Olga; Loebe, Matthias; Peterson, Leif E.; Lyon, Christopher J.; Wong, Stephen T.C.; Newgard, Christopher B.; Torre-Amione, Guillermo; Taegtmeyer, Heinrich; Hsueh, Willa A.

    2015-01-01

    Background Impaired bioenergetics is a prominent feature of the failing heart, but the underlying metabolic perturbations are poorly understood. Methods and Results We compared metabolomic, gene transcript, and protein data from six paired failing human left ventricular (LV) tissue samples obtained during left ventricular assist device (LVAD) insertion (heart failure (HF) samples) and at heart transplant (post-LVAD samples). Non-failing left ventricular (NFLV) wall samples procured from explanted hearts of patients with right HF served as novel comparison samples. Metabolomic analyses uncovered a distinct pattern in HF tissue: 2.6 fold increased pyruvate concentrations coupled with reduced Krebs cycle intermediates and short-chain acylcarnitines, suggesting a global reduction in substrate oxidation. These findings were associated with decreased transcript levels for enzymes that catalyze fatty acid oxidation and pyruvate metabolism and for key transcriptional regulators of mitochondrial metabolism and biogenesis, peroxisome proliferator-activated receptor gamma co-activator1α (PGC1A, 1.3 fold) and estrogen-related receptor α (ERRA, 1.2 fold) and γ (ERRG, 2.2 fold). Thus, parallel decreases in key transcription factors and their target metabolic enzyme genes can explain the decreases in associated metabolic intermediates. Mechanical support with LVAD improved all of these metabolic and transcriptional defects. Conclusions These observations underscore an important pathophysiologic role for severely defective metabolism in HF, while the reversibility of these defects by LVAD suggests metabolic resilience of the human heart. PMID:24825877

  5. Mechanisms of renal hyporesponsiveness to BNP in heart failure.

    PubMed

    Egom, Emmanuel E; Feridooni, Tiam; Hotchkiss, Adam; Kruzliak, Peter; Pasumarthi, Kishore B S

    2015-06-01

    The B-type natriuretic peptide (BNP), a member of the family of vasoactive peptides, is a potent natriuretic, diuretic, and vasodilatory peptide that contributes to blood pressure and volume homeostasis. These attributes make BNP an ideal drug that could aid in diuresing a fluid-overloaded patient who had poor or worsening renal function. Despite the potential benefits of BNP, accumulating evidence suggests that simply increasing the amount of circulating BNP does not necessarily increase natriuresis in patients with heart failure (HF). Moreover, despite high BNP levels, natriuresis falls when HF progresses from a compensated to a decompensated state, suggesting the emergence of renal resistance to BNP. Although likely multifactorial, several mechanisms have been proposed to explain renal hyporesponsiveness in HF, including, but not limited to, decreased renal BNP availability, down-regulation of natriuretic peptide receptors, and altered BNP intracellular signal transduction pathways. Thus, a better understanding of renal hyporesponsiveness in HF is required to devise strategies to develop novel agents and technologies that directly restore renal BNP efficiency. It is hoped that development of these new therapeutic approaches will serve to limit sodium retention in patients with HF, which may ultimately delay the progression to overt HF. PMID:25881664

  6. Fatigue failure mechanisms of single-walled carbon nanotube ropes embedded in epoxy

    NASA Astrophysics Data System (ADS)

    Ren, Y.; Fu, Y. Q.; Liao, K.; Li, F.; Cheng, H. M.

    2004-04-01

    In this work, fatigue failure mechanisms of single-walled carbon nanotube (SWCNT) bundles embedded in epoxy matrix under repeated tensile load were studied. Observed damage and failure modes include: (1) splitting of SWCNT bundles, (2) kink formation and subsequent failure in SWCNTs, and (3) fracture of SWCNT bundles. Patterns of crack propagation under tension in SWCNTs were studied by molecular mechanics simulations, where defect-free SWCNTs and SWCNTs with two different modes of Stone-Wales defects were studied. It is demonstrated by the results of molecular mechanics simulation that the observed fracture surfaces of SWCNT can be reproduced reasonably well, suggesting possible fatigue failure mechanisms of SWCNT in the composite.

  7. Flexible polyacrylamide substrata for the analysis of mechanical interactions at cell-substratum adhesions

    NASA Technical Reports Server (NTRS)

    Beningo, Karen A.; Lo, Chun-Min; Wang, Yu-Li

    2002-01-01

    We have described a powerful tool for the study of mechanical interactions between cells and their physical environment. Although the approach has already been used in a variety of ways to measure traction forces and to characterize active and passive responses of cultured cells to mechanical stimulation, it can be extended easily and combined with other microscopic approaches, including fluorescent analog imaging (Beningo et al., 2001), photobleaching, calcium imaging, micromanipulation, and electrophysiology. This method will be particularly useful for studying the functions of various components at focal adhesions, and the effects of mechanical forces on focal adhesion-mediated signal transduction. In addition, the method can be extended to a 3D setting, e.g., by sandwiching cultured cells between two layers of polyacrylamide to create an environment mimicking that in the tissue of a multicellular organism. Whereas chemical interactions between cells and the environment have been investigated extensively, many important questions remain as to the role of physical forces in cellular functions and the interplay between chemical and physical mechanisms of communication. The present approach, as well as other approaches capable of probing physical interactions, should fill in this important gap in the near future.

  8. Effects of Gravitational Mechanical Unloading in Endothelial Cells: Association between Caveolins, Inflammation and Adhesion Molecules

    PubMed Central

    Grenon, S. Marlene; Jeanne, Marion; Aguado-Zuniga, Jesus; Conte, Michael S.; Hughes-Fulford, Millie

    2013-01-01

    Mechanical forces including gravity affect endothelial cell (ECs) function, and have been implicated in vascular disease as well as physiologic changes associated with low gravity environments. The goal of this study was to investigate the impact of gravitational mechanical unloading on ECs phenotype as determined by patterns of gene expression. Human umbilical vascular endothelial cells were exposed to 1-gravity environment or mechanical unloading (MU) for 24 hours, with or without periods of mechanical loading (ML). MU led to a significant decrease in gene expression of several adhesion molecules and pro-inflammatory cytokines. On the contrary, eNOS, Caveolin-1 and -2 expression were significantly increased with MU. There was a decrease in the length and width of the cells with MU. Addition of ML during the MU period was sufficient to reverse the changes triggered by MU. Our results suggest that gravitational loading could dramatically affect vascular endothelial cell function. PMID:23511048

  9. Mechanisms of failure of coatings used in flue gas desulfurization systems

    SciTech Connect

    Leidheiser, H. Jr.; White, M.L.; Granata, R.D.; Vedage, H.L.

    1986-05-01

    Coating resins were evaluated for their ability to protect steel against corrosion in acid environments. Four types of resins (vinylester, fluoropolymers, epoxies, and a polyester) were applied to sandblasted steel surfaces and exposed to either 0.1M H/sub 2/SO/sub 4/ or a solution containing MgCl/sub 2/ and NaF that was about 1M in H/sub 2/SO/sub 4/. Measurements were made of cathodic delamination rates, corrosion potential, AC coating conductance, tensile adhesion, weight gain and the visual appearance of the coating and substrate. A failure mechanism was developed: acid diffuses through the coating, reacts with the underlying steel to oxidize it, with attendant reduction of the hydrogen ion to hydrogen gas. Debonding of the coating results. If the hydrogen gas is formed at a greater rate than it diffuses out through the coating, a blister is formed. If swelling of the polymer coating occurs in the environment, the blistering rate is increased by the concurrent effects of swelling and hydrogen generation. Different physical and chemical pretreatments of the steel had some effect on the initial values of some of the coating parameters, but after several hundred hours of acid exposure, these differences disappeared. Coating resins were evaluated for their ability to provide corrosion protection. A vinyl ester and a fluoropolymer were the most effective. A polyester and an epoxy hardened with a polyamideamine were the least effective.

  10. Mechanism of platelet adhesion to von Willebrand factor and microparticle formation under high shear stress

    PubMed Central

    Reininger, Armin J.; Heijnen, Harry F. G.; Schumann, Hannah; Specht, Hanno M.; Schramm, Wolfgang; Ruggeri, Zaverio M.

    2006-01-01

    We describe here the mechanism of platelet adhesion to immobilized von Willebrand factor (VWF) and subsequent formation of platelet-derived microparticles mediated by glycoprotein Ibα (GPIbα) under high shear stress. As visualized in whole blood perfused in a flow chamber, platelet attachment to VWF involved one or few membrane areas of 0.05 to 0.1 μm2 that formed discrete adhesion points (DAPs) capable of resisting force in excess of 160 pN. Under the influence of hydrodynamic drag, membrane tethers developed between the moving platelet body and DAPs firmly adherent to immobilized VWF. Continued stretching eventually caused the separation of many such tethers, leaving on the surface tube-shaped or spherical microparticles with a diameter as low as 50 to 100 nm. Adhesion receptors (GPIbα, αIIbβ3) and phosphatidylserine were expressed on the surface of these microparticles, which were procoagulant. Shearing platelet-rich plasma at the rate of 10 000 s–1 in a cone-and-plate viscosimeter increased microparticle counts up to 55-fold above baseline. Blocking the GPIb-VWF interaction abolished microparticle generation in both experimental conditions. Thus, a biomechanical process mediated by GPIbα-VWF bonds in rapidly flowing blood may not only initiate platelet arrest onto reactive vascular surfaces but also generate procoagulant microparticles that further enhance thrombus formation. PMID:16449527

  11. Mechanisms of degradation in adhesive joint strength: Glassy polymer thermoset bond in a humid environment

    SciTech Connect

    Kropka, Jamie Michael; Adolf, Douglas Brian; Spangler, Scott Wilmer; Austin, Kevin N.; Chambers, Robert S.

    2015-08-06

    The degradation in the strength of napkin-ring (NR) joints bonded with an epoxy thermoset is evaluated in a humid environment. While adherend composition (stainless steel and aluminum) and surface preparation (polished, grit blasted, primed, coupling agent coated) do not affect virgin (time=0) joint strength, they can significantly affect the role of moisture on the strength of the joint. Adherend surface abrasion and corrosion processes are found to be key factors in determining the reliability of joint strength in humid environments. In cases where surface specific joint strength degradation processes are not active, decreases in joint strength can be accounted for by the glass transition temperature, Tg, depression of the adhesive associated with water sorption. Under these conditions, joint strength can be rejuvenated to virgin strength by drying. In addition, the decrease in joint strength associated with water sorption can be predicted by the Simplified Potential Energy Clock (SPEC) model by shifting the adhesive reference temperature, Tref, by the same amount as the Tg depression. When surface specific degradation mechanisms are active, they can reduce joint strength below that associated with adhesive Tg depression, and joint strength is not recoverable by drying. Furthermore, a critical relative humidity (or, potentially, critical water sorption concentration), below which the surface specific degradation does not occur, appears to exist for the polished stainless steel joints.

  12. Mechanisms of degradation in adhesive joint strength: Glassy polymer thermoset bond in a humid environment

    DOE PAGESBeta

    Kropka, Jamie Michael; Adolf, Douglas Brian; Spangler, Scott Wilmer; Austin, Kevin N.; Chambers, Robert S.

    2015-08-06

    The degradation in the strength of napkin-ring (NR) joints bonded with an epoxy thermoset is evaluated in a humid environment. While adherend composition (stainless steel and aluminum) and surface preparation (polished, grit blasted, primed, coupling agent coated) do not affect virgin (time=0) joint strength, they can significantly affect the role of moisture on the strength of the joint. Adherend surface abrasion and corrosion processes are found to be key factors in determining the reliability of joint strength in humid environments. In cases where surface specific joint strength degradation processes are not active, decreases in joint strength can be accounted formore » by the glass transition temperature, Tg, depression of the adhesive associated with water sorption. Under these conditions, joint strength can be rejuvenated to virgin strength by drying. In addition, the decrease in joint strength associated with water sorption can be predicted by the Simplified Potential Energy Clock (SPEC) model by shifting the adhesive reference temperature, Tref, by the same amount as the Tg depression. When surface specific degradation mechanisms are active, they can reduce joint strength below that associated with adhesive Tg depression, and joint strength is not recoverable by drying. Furthermore, a critical relative humidity (or, potentially, critical water sorption concentration), below which the surface specific degradation does not occur, appears to exist for the polished stainless steel joints.« less

  13. Transcriptional mechanisms link epithelial plasticity to adhesion and differentiation of epidermal progenitor cells

    PubMed Central

    Lee, Briana; Villarreal-Ponce, Alvaro; Fallahi, Magid; Ovadia, Jeremy; Sun, Peng; Yu, Qian-Chun; Ito, Seiji; Sinha, Satrajit; Nie, Qing; Dai, Xing

    2014-01-01

    During epithelial tissue morphogenesis, developmental progenitor cells undergo dynamic adhesive and cytoskeletal remodeling to trigger proliferation and migration. Transcriptional mechanisms that restrict such mild form of epithelial plasticity to maintain lineage-restricted differentiation in committed epithelial tissues are poorly understood. Here we report that simultaneous ablation of transcriptional repressor-encoding Ovol1 and Ovol2 results in expansion and blocked terminal differentiation of embryonic epidermal progenitor cells. Conversely, mice overexpressing Ovol2 in their skin epithelia exhibit precocious differentiation accompanied by smaller progenitor cell compartments. We show that Ovol1/2-deficient epidermal cells fail to undertake α-catenin–driven actin cytoskeletal reorganization and adhesive maturation, and exhibit changes that resemble epithelial-to-mesenchymal transition (EMT). Remarkably, these alterations as well as defective terminal differentiation are reversed upon depletion of EMT-promoting transcriptional factor Zeb1. Collectively, our findings reveal Ovol-Zeb1-α-catenin sequential repression and highlight functions of Ovol as gatekeepers of epithelial adhesion and differentiation by inhibiting progenitor-like traits and epithelial plasticity. PMID:24735878

  14. Mechanism for interfacial adhesion strength of an ion beam mixed Cu/polyimide with a thin buffer layer

    NASA Astrophysics Data System (ADS)

    Chang, G. S.; Chae, K. H.; Whang, C. N.; Kurmaev, E. Z.; Zatsepin, D. A.; Winarski, R. P.; Ederer, D. L.; Moewes, A.; Lee, Y. P.

    1999-01-01

    A Cu (400 Å)/Al (50 Å)/polyimide system showed larger adhesion strength than that of Cu (400 Å)/polyimide after N2+ ion beam mixing. X-ray emission spectroscopy was performed to elucidate the mechanism of adhesion enhancement of the ion beam mixed Cu (400 Å)/polyimide with a thin Al buffer layer. Cu L2,3 x-ray emission spectra showed the formation of a CuAl2O4 layer which is strongly correlated with the large adhesion strength of a Cu/Al/polyimide. A decrease in adhesion strength at an ion dose higher than 5×1015cm-2 was also explained by the formation of an amorphous carbon. This was understood by investigating C Kα x-ray emission spectra. The overall spectroscopic results were in accordance with the behavior of quantitative adhesion strength.

  15. Mechanisms of Cardiotoxicity and the Development of Heart Failure.

    PubMed

    Lee, Christopher S

    2015-12-01

    Cardiotoxicity is a broad term that refers to the negative effects of toxic substances on the heart. Cancer drugs can cause cardiotoxicity by effects on heart cells, thromboembolic events, and/or hypertension that can lead to heart failure. Rheumatoid arthritis biologics may interfere with ischemic preconditioning and cause/worsen heart failure. Long-term and heavy alcohol use can result in oxidative stress, apoptosis, and decreased contractile protein function. Cocaine use results in sympathetic nervous system stimulation of heart and smooth muscle cells and leads to cardiotoxicity and evolution of heart failure. The definition of cardiotoxicity is likely to evolve along with knowledge about detecting subclinical myocardial injury. PMID:26567492

  16. Failure Mechanisms and Color Stability in Light-Emitting Diodes during Operation in High- Temperature Environments in Presence of Contamination

    SciTech Connect

    Lall, Pradeep; Zhang, Hao; Davis, J Lynn

    2015-05-26

    The energy efficiency of light-emitting diode (LED) technology compared to incandescent light bulbs has triggered an increased focus on solid state luminaries for a variety of lighting applications. Solid-state lighting (SSL) utilizes LEDs, for illumination through the process of electroluminescence instead of heating a wire filament as seen with traditional lighting. The fundamental differences in the construction of LED and the incandescent lamp results in different failure modes including lumen degradation, chromaticity shift and drift in the correlated color temperature. The use of LED-based products for safety-critical and harsh environment applications necessitates the characterization of the failure mechanisms and modes. In this paper, failure mechanisms and color stability has been studied for commercially available vertical structured thin film LED (VLED) under harsh environment conditions with and without the presence of contaminants. The VLED used for the study was mounted on a ceramic starboard in order to connect it to the current source. Contamination sources studied include operation in the vicinity of vulcanized rubber and adhesive epoxies in the presence of temperature and humidity. Performance of the VLEDs has been quantified using the measured luminous flux and color shift of the VLEDs subjected to both thermal and humidity stresses under a forward current bias of 350 mA. Results indicate that contamination can result in pre-mature luminous flux degradation and color shift in LEDs.

  17. Integrin binding and mechanical tension induce movement of mRNA and ribosomes to focal adhesions

    NASA Technical Reports Server (NTRS)

    Chicurel, M. E.; Singer, R. H.; Meyer, C. J.; Ingber, D. E.

    1998-01-01

    The extracellular matrix (ECM) activates signalling pathways that control cell behaviour by binding to cell-surface integrin receptors and inducing the formation of focal adhesion complexes (FACs). In addition to clustered integrins, FACs contain proteins that mechanically couple the integrins to the cytoskeleton and to immobilized signal-transducing molecules. Cell adhesion to the ECM also induces a rapid increase in the translation of preexisting messenger RNAs. Gene expression can be controlled locally by targeting mRNAs to specialized cytoskeletal domains. Here we investigate whether cell binding to the ECM promotes formation of a cytoskeletal microcompartment specialized for translational control at the site of integrin binding. High-resolution in situ hybridization revealed that mRNA and ribosomes rapidly and specifically localized to FACs that form when cells bind to ECM-coated microbeads. Relocation of these protein synthesis components to the FAC depended on the ability of integrins to mechanically couple the ECM to the contractile cytoskeleton and on associated tension-moulding of the actin lattice. Our results suggest a new type of gene regulation by integrins and by mechanical stress which may involve translation of mRNAs into proteins near the sites of signal reception.

  18. Failure mechanisms of thermal barrier coatings exposed to elevated temperatures

    NASA Technical Reports Server (NTRS)

    Miller, R. A.; Lowell, C. E.

    1982-01-01

    The failure of a ZrO2-8%Y2O3/Ni-14% Al-0.1% Zr coating system on Rene 41 in Mach 0.3 burner rig tests was characterized. High flame and metal temperatures were employed in order to accelerate coating failure. Failure by delamination was shown to precede surface cracking or spalling. This type of failure could be duplicated by cooling down the specimen after a single long duration isothermal high temperature cycle in a burner rig or a furnace, but only if the atmosphere was oxidizing. Stresses due to thermal expansion mismatch on cooling coupled with the effects of plastic deformation of the bond coat and oxidation of the irregular bond coat are the probable life limiting factors. Heat up stresses alone could not fail the coating in the burner rig tests. Spalling eventually occurs on heat up but only after the coating has already failed through delamination.

  19. Central Mechanisms of Abnormal Sympathoexcitation in Chronic Heart Failure

    PubMed Central

    Kishi, Takuya; Hirooka, Yoshitaka

    2012-01-01

    It has been recognized that the sympathetic nervous system is abnormally activated in chronic heart failure, and leads to further worsening chronic heart failure. In the treatment of chronic heart failure many clinical studies have already suggested that the inhibition of the abnormal sympathetic hyperactivity by beta blockers is beneficial. It has been classically considered that abnormal sympathetic hyperactivity in chronic heart failure is caused by the enhancement of excitatory inputs including changes in peripheral baroreceptor and chemoreceptor reflexes and chemical mediators that control sympathetic outflow. Recently, the abnormalities in the central regulation of sympathetic nerve activity mediated by brain renin angiotensin system-oxidative stress axis and/or proinflammatory cytokines have been focused. Central renin angiotensin system, proinflammatory cytokines, and the interaction between them have been determined as the target of the sympathoinhibitory treatment in experimental animal models with chronic heart failure. In conclusion, we must recognize that chronic heart failure is a syndrome with an abnormal sympathoexcitation, which is caused by the abnormalities in the central regulation of sympathetic nerve activity. PMID:22919539

  20. Human climbing with efficiently scaled gecko-inspired dry adhesives

    PubMed Central

    Hawkes, Elliot W.; Eason, Eric V.; Christensen, David L.; Cutkosky, Mark R.

    2015-01-01

    Since the discovery of the mechanism of adhesion in geckos, many synthetic dry adhesives have been developed with desirable gecko-like properties such as reusability, directionality, self-cleaning ability, rough surface adhesion and high adhesive stress. However, fully exploiting these adhesives in practical applications at different length scales requires efficient scaling (i.e. with little loss in adhesion as area grows). Just as natural gecko adhesives have been used as a benchmark for synthetic materials, so can gecko adhesion systems provide a baseline for scaling efficiency. In the tokay gecko (Gekko gecko), a scaling power law has been reported relating the maximum shear stress σmax to the area A: σmax ∝ A−1/4. We present a mechanical concept which improves upon the gecko's non-uniform load-sharing and results in a nearly even load distribution over multiple patches of gecko-inspired adhesive. We created a synthetic adhesion system incorporating this concept which shows efficient scaling across four orders of magnitude of area, yielding an improved scaling power law: σmax ∝ A−1/50. Furthermore, we found that the synthetic adhesion system does not fail catastrophically when a simulated failure is induced on a portion of the adhesive. In a practical demonstration, the synthetic adhesion system enabled a 70 kg human to climb vertical glass with 140 cm2 of adhesive per hand. PMID:25411404

  1. Burn prevention mechanisms and outcomes: pitfalls, failures and successes.

    PubMed

    Atiyeh, Bishara S; Costagliola, Michel; Hayek, Shady N

    2009-03-01

    Burns are responsible for significant mortality and morbidity worldwide and are among the most devastating of all injuries, with outcomes spanning the spectrum from physical impairments and disabilities to emotional and mental consequences. Management of burns and their sequelae even in well-equipped, modern burn units of advanced affluent societies remains demanding and extremely costly. Undoubtedly, in most low and middle income countries (LMICs) with limited resources and inaccessibility to sophisticated skills and technologies, the same standard of care is obviously not possible. Unfortunately, over 90% of fatal fire-related burns occur in developing or LMICs with South-East Asia alone accounting for over half of these fire-related deaths. If burn prevention is an essential part of any integrated burn management protocol anywhere, focusing on burn prevention in LMICs rather than treatment cannot be over-emphasized where it remains the major and probably the only available way of reducing the current state of morbidity and mortality. Like other injury mechanisms, the prevention of burns requires adequate knowledge of the epidemiological characteristics and associated risk factors, it is hence important to define clearly, the social, cultural and economic factors, which contribute to burn causation. While much has been accomplished in the areas of primary and secondary prevention of fires and burns in many developed or high-income countries (HICs) such as the United States due to sustained research on the epidemiology and risk factors, the same cannot be said for many LMICs. Many health authorities, agencies, corporations and even medical personnel in LMICs consider injury prevention to have a much lower priority than disease prevention for understandable reasons. Consequently, burns prevention programmes fail to receive the government funding that they deserve. Prevention programmes need to be executed with patience, persistence, and precision, targeting high

  2. Mechanism maps for electromigration-induced failure of metal and alloy interconnects

    NASA Astrophysics Data System (ADS)

    Andleigh, Vaibhav K.; Srikar, V. T.; Park, Young-Joon; Thompson, Carl V.

    1999-12-01

    Numerical simulation of electromigration-induced stress evolution provides a versatile technique for analyzing the reliability of interconnects under a wide range of conditions. We study the evolution of stress in confined, layered, stud-terminated, pure metal, and alloy interconnects. Failure times are estimated using different failure criteria associated with different failure modes for broad ranges of line lengths and current densities. The simulation results can be conveniently catalogued through construction of failure mechanism maps that display domains of dominance of different failure modes. Failure mechanism maps are constructed for several different failure criteria, illustrating regimes of line immortality, void-nucleation-limited failure, void-growth-limited failure, and compressive failure as a function of line length and current density. The effects of changes in failure criteria, geometry, and composition are studied for representative interconnect stacks at accelerated and service temperatures. Failure maps may be used to: (i) provide an overview of predicted reliability behavior, (ii) assess how data from accelerated tests can be accurately scaled to service conditions, and (iii) predict the effects of changes in interconnect and shunt-layer materials and dimensions on interconnect reliability.

  3. Nondestructive Characterization of Adhesive Bonds from Guided Wave Data

    NASA Technical Reports Server (NTRS)

    Mal, A. K.; Lih, S-S.; Bar-Cohen, Y.

    1994-01-01

    The critical role played by adhesive bonds in the fracture and failure of composites and other bonded materials is well known. A good knowledge of the mechanical properties of these adhesion joints is a prerequisite to reliable design and reliable prediction of the performance of these bonded structures.

  4. Automated failure mode effects and criticality analyses for reliability prediction of multibody mechanical systems

    NASA Astrophysics Data System (ADS)

    Chiang, Alex Chih-Chien

    Reliability is important to ensure both serviceability and safety of a mechanical system. A method for simulation-based Failure Mode Effects and Criticality Analysis (FMECA) for reliability prediction of mechanical systems is presented. This approach integrates recursive formulation for dynamic analysis, failure criteria for failure determination, graphics techniques for collision detection, and new techniques for modifying dynamics model during the simulation. The automated FMECA method developed consists of three libraries and a graphics collision detection technique. First, a library of mechanical failure modes is created using cause-effect relationships for mechanical failure modes. Second, a library of component failure criteria is constructed by collecting different material test data. Third, a library of simulation algorithms and supporting techniques is built by developing simulation technologies to perform FMECA for mechanical failure modes. In addition, the automated FMECA method uses the developed graphics software VDS for collision detection. Finally, this approach is used to investigate the consequences of four failure modes of a vehicle system. The difficulty in formulating mathematical expressions for a damaged mechanical system is resolved by manipulating the number of cut joint constraints and generalized coordinates to implicitly update the original system topology. Formulations for virtual joints are derived, as well as other new techniques to permit multiple failures during a dynamic simulation. A near-minimum set of generalized coordinates is thus retained throughout the dynamic simulation. Four general-purpose dynamics codes are implemented and effects of four mechanical failure modes of a mechanical system are investigated; suspension failure, joint degradation and breakage, joint stiction, and component yielding and breakage. Failure histories as well as Mean Time Between Failure (MTBF) and Mean Time To Failure (MTTF) are obtained. The

  5. Failure mechanisms of woven carbon and glass composites

    SciTech Connect

    Alif, N.; Carlsson, L.A.

    1997-12-31

    Stress-strain responses in tension, compression, and shear of a five-harness satin-weave carbon/epoxy composite and a four-harness satin-weave glass/epoxy composite have been examined. Damage progression under tension was examined by optical microscopic inspection of the polished edges of the specimens. Models for elastic property and failure predictions of woven-fabric composites were examined and correlated with the experimental data. Damage inspection of the carbon/epoxy composite under tension revealed that the initial failure was cracking of pure matrix regions followed by transverse bundle cracking. Fill/weft debonding and longitudinal splits of the fill bundles occurred close to ultimate failure of the composite. The glass/epoxy composite displayed damage in the form of fill/weft debonding and longitudinal splits, but no transverse yarn cracking. The damage observed in both composites was confined to the region where ultimate failure occurred. Elastic properties of the composites were overall in good agreement with micromechanical predictions based on uniform strain, but failure stress predictions were less accurate.

  6. Failure mechanism of coated biomaterials under high impact-sliding contact stresses

    NASA Astrophysics Data System (ADS)

    Chen, Ying

    This study uses a newly developed testing method--- inclined cyclic impact-sliding test to investigate the failure behaviors of different types of biomaterials, (SS316L, Ti6Al4V and CoCr) coated by different coatings (TiN, DLC and PEO), under extremely high dynamic contact stress conditions. This test method can simulate the combined impact and sliding/rolling loading conditions, which is very practical in many aspects of commercial usages. During the tests, fatigue cracking, chipping, peeling and material transferring were observed in damaged area. This research is mainly focused on the failure behaviors of load-bearing materials which cyclic impacting and sliding are always involved. This purpose was accomplished in the three stages: First, impact-sliding test was carried out on TiN coated unhardened M2. It was found that soft substrate can cause early failure of coating due to the considerable plastic deformation in the substrate. In this case, stronger substrate is required to support coating better when tested under high contact stresses. Second, PEO coated Ti-6Al-4V was tested under pure sliding and impact-sliding wear conditions. PEO coating was found not strong enough to afford the high contact pressure under cyclic impact-sliding wear test due to its porous surface structure. However, the wear performance of PEO coating was enhanced due to the sub-stoichiometric oxide. To sum up, for load-bearing biomedical implants involved in high impacting movement, PEO coating may not be a promising surface protection. Third, the dense, smooth PVD/CVD bio-inert coatings were reconsidered. DLC and TiN coatings, combined by different substrates together with different interface materials were tested under the cyclic impact-sliding test using a set of proper loading. The results show that to choose a proper combination of coating, interface and substrate based on their mechanical properties is of great importance under the test condition. Hard substrates provide support

  7. Epigenetic mechanisms of cell adhesion-mediated drug resistance in multiple myeloma.

    PubMed

    Furukawa, Yusuke; Kikuchi, Jiro

    2016-09-01

    Multiple myeloma cells acquire the resistance to anti-cancer drugs through physical and functional interactions with the bone marrow microenvironment via two overlapping mechanisms. First, bone marrow stromal cells (BMSCs) produce soluble factors, such as interleukin-6 and insulin-like growth factor-1, to activate signal transduction pathways leading to drug resistance (soluble factor-mediated drug resistance). Second, BMSCs up-regulate the expression of cell cycle inhibitors, anti-apoptotic members of the Bcl-2 family and ABC drug transporters in myeloma cells upon direct adhesion [cell adhesion-mediated drug resistance (CAM-DR)]. Elucidation of the mechanisms underlying drug resistance may greatly contribute to the advancement of cancer therapies. Recent investigations, including ours, have revealed the involvement of epigenetic alterations in drug resistance especially CAM-DR. For example, we found that class I histone deacetylases (HDACs) determine the sensitivity of proteasome inhibitors and the histone methyltransferase EZH2 regulates the transcription of anti-apoptotic genes during the acquisition of CAM-DR by myeloma cells. In addition, another histone methyltransferase MMSET was shown to confer drug resistance to myeloma cells by facilitating DNA repair. These findings provide a rationale for the inclusion of epigenetic drugs, such as HDAC inhibitors and histone methylation modifiers, in combination chemotherapy for MM patients to increase the therapeutic index. PMID:27411688

  8. Macrophages Mediate the Repair of Brain Vascular Rupture through Direct Physical Adhesion and Mechanical Traction.

    PubMed

    Liu, Chi; Wu, Chuan; Yang, Qifen; Gao, Jing; Li, Li; Yang, Deqin; Luo, Lingfei

    2016-05-17

    Hemorrhagic stroke and brain microbleeds are caused by cerebrovascular ruptures. Fast repair of such ruptures is the most promising therapeutic approach. Due to a lack of high-resolution in vivo real-time studies, the dynamic cellular events involved in cerebrovascular repair remain unknown. Here, we have developed a cerebrovascular rupture system in zebrafish by using multi-photon laser, which generates a lesion with two endothelial ends. In vivo time-lapse imaging showed that a macrophage arrived at the lesion and extended filopodia or lamellipodia to physically adhere to both endothelial ends. This macrophage generated mechanical traction forces to pull the endothelial ends and facilitate their ligation, thus mediating the repair of the rupture. Both depolymerization of microfilaments and inhibition of phosphatidylinositide 3-kinase or Rac1 activity disrupted macrophage-endothelial adhesion and impaired cerebrovascular repair. Our study reveals a hitherto unexpected role for macrophages in mediating repair of cerebrovascular ruptures through direct physical adhesion and mechanical traction. PMID:27156384

  9. Micro-measurements of mechanical properties for adhesives and composites using digital imaging technology

    NASA Technical Reports Server (NTRS)

    Brinson, Hal F.

    1994-01-01

    The need for a constituent based durability or accelerated life prediction procedure to be used for the engineering design of polymer matrix composites is discussed in the light of current plans for the High Speed Civil Transport (HSCT) concerns about the U.S. infrastructure (bridges, pipelines, etc.) and other technological considerations of national concern. It is pointed out that good measurement procedures for insitu resin properties are needed for both adhesives and composites. A double cantilever beam (DCB) specimen which shows promise for the easy determination of adhesive shear properties is presented and compared with measurements of strains within the bondline using a new optical digital imaging micro-measurement system (DIMMS). The DCB specimen is also used to assess damage in a bonded joint using a dynamic mechanical thermal analysis system (DMTA). The possible utilization of the same DIMMS and DMTA procedures to determine the insitu properties of the resin in a composite specimen are discussed as well as the use of the procedures to evaluate long term mechanical and physical aging. Finally, a discussion on the state-of-the art of the measurement of strains in micron and sub-micron domains is given.

  10. The role of penetrant structure in the transport and mechanical properties of a thermoset adhesive

    NASA Astrophysics Data System (ADS)

    Kwan, Kermit S.

    In this work the relationships between penetrant structure, its transport properties, and its effects on the mechanical properties of a polymer matrix were investigated. Although there is a vast amount of data on the diffusion of low molecular weight molecules into polymeric materials and on the mechanical properties of various polymer-penetrant systems, no attempts have been made to inter-relate the two properties with respect to the chemical structure of the diffusant. Therefore, two series of penetrants---n-alkanes and esters---were examined in this context, with the goal of correlating molecular size, shape, and chemical nature of the penetrant to its final transport and matrix mechanical properties. These correlations have been demonstrated to allow quantitative prediction of one property, given a reasonable set of data on the other parameters. A series of n-alkanes (C6--C17) and esters (C5--C17) have been used to separate the effects of penetrant size and shape, from those due to polymer-penetrant interactions, in the diffusion through a polyamide polymeric adhesive. These effects have been taken into account in order to yield a qualitative relationship that allows for prediction of diffusivity based upon penetrant structural information. Transport properties have been analyzed using mass uptake experiments as well as an in-situ FTIR-ATR technique to provide detailed kinetic as well as thermodynamic information on this process. The phenomenon of diffusion and its effects on the resulting dynamic mechanical response of a matrix polymeric adhesive have been studied in great detail using the method of reduced variables. The concept of a diffusion-time shift factor (log aDt) has been introduced to create doubly-reduced master curves, taking into account the effects of temperature and the variations in the polymer mechanical response due to the existence of a low molecular weight penetrant.

  11. Failure mechanisms of notched laminated composites under compressive loading at room and elevated temperature

    NASA Astrophysics Data System (ADS)

    Ahn, Jung Hyun

    1999-10-01

    Understanding the mechanisms of failure of composite structures and developing mechanism based failure criteria are important considerations in designing structures made of composite materials. The compressive response of composite materials and structures has received considerable attention due to their significance in the aerospace industry and the complexity associated with compressive failure. Several competing failure mechanisms such as fiber instability, fiber/matrix interfacial failure, fiber microbuckling/kinking, delamination initiation and delamination buckling may become active in compressive loading. Environmental effect such as an elevated temperature can alter and affect these failure mechanisms. In this thesis, a micromechanics based finite element predictive model for notched strength of multidirectional laminates is presented. The in-situ shear response of the matrix, the fiber mechanical properties, the lay-up (stacking sequence) and fiber volume fraction serve as input to the model. The prediction of the model is found to match favorably with experimental data. The effect of ply angle and its influence on the failure mechanism are quantified and compared with a set of available experimental data. The present work is the first development of a non-empirical mechanics based failure prediction methodology for notched compressive strength of composite laminates. Both an experimental and an analytical study are presented herein.

  12. Role of focal adhesions and mechanical stresses in the formation and progression of the lamellipodium-lamellum interface [corrected].

    PubMed

    Shemesh, Tom; Verkhovsky, Alexander B; Svitkina, Tatyana M; Bershadsky, Alexander D; Kozlov, Michael M

    2009-09-01

    Actin network in the front part of a moving cell is organized into a lamellipodium and a lamellum. A distinct lamellipodium-lamellum interface is associated with focal adhesions and consists of a series of arclike segments linking neighboring focal adhesions in the front row. The interface advances by leaping onto new rows of focal adhesions maturating underneath the lamellipodium. We propose a mechanism of the lamellipodium-lamellum boundary generation, shape formation, and progression based on the elastic stresses generated in the lamellipodial actin gel by its friction against the focal adhesions. The crucial assumption of the model is that stretching stresses trigger actin gel disintegration. We compute the stress distribution throughout the actin gel and show that the gel-disintegrating stresses drive formation of a gel boundary passing through the row of focal adhesions. Our computations recover the lamellipodium-lamellum boundary shapes detected in cells and predict the mode of the boundary transition to the row of the newly maturing focal adhesions in agreement with the experimental observations. The model fully accounts for the current phenomenology of the lamellipodium-lamellum interface formation and advancing, and makes experimentally testable predictions on the dependence of these phenomena on the sizes of the focal adhesions, the character of the focal adhesion distribution on the substrate, and the velocity of the actin retrograde flow with respect to the focal adhesions. The phase diagram resulting from the model provides a background for quantitative classification of different cell types with respect to their ability to form a lamellipodium-lamellum interface. In addition, the model suggests a mechanism of nucleation of the dorsal and arclike actin bundles found in the lamellum. PMID:19720013

  13. Failure Mechanisms of Hollow Fiber Supported Ionic Liquid Membranes.

    PubMed

    Zeh, Matthew; Wickramanayake, Shan; Hopkinson, David

    2016-01-01

    Hollow fiber supported ionic liquid membranes (SILMs) were tested using the bubble point method to investigate potential failure modes, including the maximum transmembrane pressure before loss of the ionic liquid from the support. Porous hollow fiber supports were fabricated with different pore morphologies using Matrimid(®) and Torlon(®) as the polymeric material and 1-hexyl-3-methylimidalzolium bis(trifluoromethylsulfonyl)imide ([C₆mim][Tf₂N]) as the ionic liquid (IL) component. Hollow fiber SILMs were tested for their maximum pressure before failure, with pressure applied either from the bore side or shell side. It was found that the membranes exhibited one or more of three different modes of failure when pressurized: liquid loss (occurring at the bubble point), rupture, and collapse. PMID:27023620

  14. Failure Mechanisms of Hollow Fiber Supported Ionic Liquid Membranes

    PubMed Central

    Zeh, Matthew; Wickramanayake, Shan; Hopkinson, David

    2016-01-01

    Hollow fiber supported ionic liquid membranes (SILMs) were tested using the bubble point method to investigate potential failure modes, including the maximum transmembrane pressure before loss of the ionic liquid from the support. Porous hollow fiber supports were fabricated with different pore morphologies using Matrimid® and Torlon® as the polymeric material and 1-hexyl-3-methylimidalzolium bis(trifluoromethylsulfonyl)imide ([C6mim][Tf2N]) as the ionic liquid (IL) component. Hollow fiber SILMs were tested for their maximum pressure before failure, with pressure applied either from the bore side or shell side. It was found that the membranes exhibited one or more of three different modes of failure when pressurized: liquid loss (occurring at the bubble point), rupture, and collapse. PMID:27023620

  15. Adhesion/decalcification mechanisms of acid interactions with human hard tissues.

    PubMed

    Yoshioka, M; Yoshida, Y; Inoue, S; Lambrechts, P; Vanherle, G; Nomura, Y; Okazaki, M; Shintani, H; Van Meerbeek, B

    2002-01-01

    In order to study adhesion/decalcification mechanisms of acid interactions with human hard tissues such as bones and teeth, the chemical interaction of five carboxylic acids (acetic, citric, lactic, maleic, and oxalic) and two inorganic acids (hydrochloric and nitric) with enamel and two synthetic hydroxyapatite (HAp) powders with, respectively, a high and a low crystallinity were analyzed using X-ray photoelectron spectroscopy (XPS), atomic absorption spectrophotometry (AAS), and spectrophotometry (S). X-ray diffraction revealed that the crystallinity of the highly crystallized HAp was considerably higher than that of enamel while the crystallinity of the poorly crystallized HAp was similar to that of dentin and bone. XPS of acid-treated enamel demonstrated for all carboxylic acids ionic bonding to calcium of HAp. AAS and S showed for both HAps that all carboxylic and inorganic acids except oxalic acid extracted Ca significantly more than P, leading to a Ca/P ratio close to that of synthetic HAp (2.16 w/w). Oxalic acid extracted hardly any Ca, but substantially more P, leading to a significantly smaller Ca/P ratio than that of HAp. AAS showed that the calcium salt of oxalic acid hardly could be dissolved, whereas the calcium salts of all the other acids were very soluble in their respective acid solution. These results confirm the adhesion/decalcification concept (AD-concept) previously advanced. Depending on the dissolution rate of the respective calcium salts, acids either adhere to or decalcify apatitic substrates. It is concluded that the AD-concept that originally dictated the interaction of carboxylic acids with human hard tissues can be extended to inorganic acids, such as hydrochloric and nitric acid. Furthermore, HAp crystallinity was found not to affect the adhesion/decalcification behavior of acids when interacting with apatitic substrates, so that the AD-concept can be applied to all human hard tissues with varying HAp crystallinity. PMID:11745537

  16. 76 FR 5494 - Pipeline Safety: Mechanical Fitting Failure Reporting Requirements

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-01

    ... INFORMATION: I. Background The DIMP Notice of Proposed Rulemaking (NPRM) published on June 25, 2008, (73 FR... 4, 2009, (74 FR 63906) PHMSA deleted the proposed requirement to report plastic pipe failures but..., 2009, (74 FR 69286) PHMSA extended the comment period to February 4, 2010, as requested by the...

  17. Groundwater seepage mechanisms of streambank erosion and failure

    Technology Transfer Automated Retrieval System (TEKTRAN)

    The importance of groundwater seepage and pipeflow is unknown with respect to other fundamental processes of streambank erosion and failure, although seepage and pipeflow features are observed on streambanks throughout the world that span a range of geomorphologic conditions. Previous field and labo...

  18. Role of seta angle and flexibility in the gecko adhesion mechanism

    NASA Astrophysics Data System (ADS)

    Hu, Congcong; Alex Greaney, P.

    2014-08-01

    A model is developed to describe the reversible nature of gecko dry adhesion. The central aspect of this model is that the seta can be easily peeled away from the contacting surface by a small moment at the contact tip. It is shown that this contact condition is very sensitive, but can result in robust adhesion if individual setae are canted and highly flexible. In analogy to the "cone of friction," we consider the "adhesion region"—the domain of normal and tangential forces that maintain adhesion. Results demonstrate that this adhesion region is highly asymmetric enabling the gecko to adhere under a variety of loading conditions associated with scuttling horizontally, vertically, and inverted. Moreover, under each of these conditions, there is a low energy path to de-adhesion. In this model, obliquely canted seta (as possessed by geckos) rather than vertically aligned fibers (common in synthetic dry adhesive) provides the most robust adhesion.

  19. α-Catenin phosphorylation promotes intercellular adhesion through a dual-kinase mechanism.

    PubMed

    Escobar, David J; Desai, Ridhdhi; Ishiyama, Noboru; Folmsbee, Stephen S; Novak, Megan N; Flozak, Annette S; Daugherty, Rebecca L; Mo, Rigen; Nanavati, Dhaval; Sarpal, Ritu; Leckband, Deborah; Ikura, Mitsu; Tepass, Ulrich; Gottardi, Cara J

    2015-03-15

    The cadherin-catenin adhesion complex is a key contributor to epithelial tissue stability and dynamic cell movements during development and tissue renewal. How this complex is regulated to accomplish these functions is not fully understood. We identified several phosphorylation sites in mammalian αE-catenin (also known as catenin α-1) and Drosophila α-Catenin within a flexible linker located between the middle (M)-region and the carboxy-terminal actin-binding domain. We show that this phospho-linker (P-linker) is the main phosphorylated region of α-catenin in cells and is sequentially modified at casein kinase 2 and 1 consensus sites. In Drosophila, the P-linker is required for normal α-catenin function during development and collective cell migration, although no obvious defects were found in cadherin-catenin complex assembly or adherens junction formation. In mammalian cells, non-phosphorylatable forms of α-catenin showed defects in intercellular adhesion using a mechanical dispersion assay. Epithelial sheets expressing phosphomimetic forms of α-catenin showed faster and more coordinated migrations after scratch wounding. These findings suggest that phosphorylation and dephosphorylation of the α-catenin P-linker are required for normal cadherin-catenin complex function in Drosophila and mammalian cells. PMID:25653389

  20. Semaphorin signals in cell adhesion and cell migration: functional role and molecular mechanisms.

    PubMed

    Casazza, Andrea; Fazzari, Pietro; Tamagnone, Luca

    2007-01-01

    Cell migration is pivotal in embryo development and in the adult. During development a wide range of progenitor cells travel over long distances before undergoing terminal differentiation. Moreover, the morphogenesis of epithelial tissues and of the cardiovascular system involves remodelling compact cell layers and sprouting of new tubular branches. In the adult, cell migration is essential for leucocytes involved in immune response. Furthermore, invasive and metastatic cancer cells have the distinctive ability to overcome normal tissue boundaries, travel in and out of blood vessels, and settle down in heterologous tissues. Cell migration normally follows strict guidance cues, either attractive, or inhibitory and repulsive. Semaphorins are a wide family of signals guiding cell migration during development and in the adult. Recent findings have established that semaphorin receptors, the plexins, govern cell migration by regulating integrin-based cell substrate adhesion and actin cytoskeleton dynamics, via specific monomeric GTPases. Plexins furthermore recruit tyrosine kinases in receptor complexes, which allows switching between multiple signaling pathways and functional outcomes. In this article, we will review the functional role of semaphorins in cell migration and the implicated molecular mechanisms controlling cell adhesion. PMID:17607949

  1. Molecular mechanism of vinculin activation and nano-scale spatial organization in focal adhesions

    PubMed Central

    Case, Lindsay B.; Baird, Michelle A.; Shtengel, Gleb; Campbell, Sharon L.; Hess, Harald F.; Davidson, Michael W.; Waterman, Clare M.

    2015-01-01

    Focal adhesions (FAs) link the extracellular matrix (ECM) to the actin cytoskeleton to mediate cell adhesion, migration, mechanosensing and signaling. FAs have conserved nanoscale protein organization, suggesting that the position of proteins within FAs regulates their activity and function. Vinculin binds different FA proteins to mediate distinct cellular functions, but how vinculin’s interactions are spatiotemporally organized within FA is unknown. Using interferometric photo-activation localization (iPALM) super-resolution microscopy to assay vinculin nanoscale localization and a FRET biosensor to assay vinculin conformation, we found that upward repositioning within the FA during FA maturation facilitates vinculin activation and mechanical reinforcement of FA. Inactive vinculin localizes to the lower integrin signaling layer in FA by binding to phospho-paxillin. Talin binding activates vinculin and targets active vinculin higher in FA where vinculin can engage retrograde actin flow. Thus, specific protein interactions are spatially segregated within FA at the nano-scale to regulate vinculin activation and function. PMID:26053221

  2. Isocyanate emission from PUR adhesives: influence of temperature, monomer content, and curing mechanism.

    PubMed

    Wirts, Martin; Salthammer, Tunga

    2002-04-15

    The isocyanate emission potential of polyurethane (PUR) adhesives was evaluated by measuring the area-specific emission rate (SERa;microg m(-2) h(-1)) in a laboratory emission test chamber. The chamber was constructed for the analysis of reactive substances allowing quantitative trapping of all isocyanate monomers emitted from the substrate. Isocyanates were analyzed as their 1-(2-pyridyl)piperazine derivatives by HPLC with fluorescence and UV detection. The influence of temperature, the content of the diisocyanate in the resin, and the system pressure were investigated. These parameter studies gave evidence thatthe diisocyanate emission from the resins is a gas-phase-limited mass transfer. The overall mass-transfer coefficient (beta = Ddelta(-1)) was calculated for HDI and MDI. From the temperature dependence of emission rates, the enthalpies of evaporation for 2,4'-MDI, 4,4'-MDI, and HDI from their resins were determined. The influence of monomer content on SERa followed Henry's and Raoult's laws in the cases of HDI and MDI, respectively, allowing the prediction of emission rates proportional to diisocyanate content. Therefore, from simple parameters such as application temperature and monomer content, isocyanate emission rates can be predicted. Additionally, MDI emission from curing PUR adhesives was studied. These results elucidate the influence of monomer reactivity and curing mechanism on the decrease of MDI emission with time. PMID:11993883

  3. Stem cell differentiation increases membrane-actin adhesion regulating cell blebability, migration and mechanics

    PubMed Central

    Sliogeryte, Kristina; Thorpe, Stephen D.; Lee, David A.; Botto, Lorenzo; Knight, Martin M.

    2014-01-01

    This study examines how differentiation of human mesenchymal stem cells regulates the interaction between the cell membrane and the actin cortex controlling cell behavior. Micropipette aspiration was used to measure the pressure required for membrane-cortex detachment which increased from 0.15 kPa in stem cells to 0.71 kPa following chondrogenic differentiation. This effect was associated with reduced susceptibility to mechanical and osmotic bleb formation, reduced migration and an increase in cell modulus. Theoretical modelling of bleb formation demonstrated that the increased stiffness of differentiated cells was due to the increased membrane-cortex adhesion. Differentiated cells exhibited greater F-actin density and slower actin remodelling. Differentiated cells also expressed greater levels of the membrane-cortex ezrin, radixin, moeisin (ERM) linker proteins which was responsible for the reduced blebability, as confirmed by transfection of stem cells with dominant active ezrin-T567D-GFP. This study demonstrates that stem cells have an inherently weak membrane-cortex adhesion which increases blebability thereby regulating cell migration and stiffness. PMID:25471686

  4. The failure mechanism of a nickel electrode in a nickel-hydrogen cell

    NASA Technical Reports Server (NTRS)

    Lim, H. S.; Verzwyvelt, S. A.

    1985-01-01

    Studies on a number of types of nickel electrodes after cycle failure in a Ni/H2 cell showed that the failure is due to the loss of high rate discharge capability rather than an absolute capacity loss. The failure mechanism is speculated to be a combination of migration of the active material away from the current collecting nickel sinter, increased porosity of the active material caused by cycling, and an electrical isolation process of the active material during discharge.

  5. Failure criteria used in a probabilistic fracture mechanics code

    SciTech Connect

    Lo, T.Y.

    1985-01-01

    Two criteria are implemented in a piping reliability analysis code to assess the stability of crack growth in pipes. One is the critical net section stress criterion. It is simple and convenient but its application is limited to very ductile materials. The other is the tearing modulus stability criterion. This criterion has a solid technical base. However, calculating the J-integral, J, and the associated tearing modulus, T, usually requires a complicated finite element method (FEM). In this piping reliability code, existing J and T solutions in tabular or formula form instead of the FEM are used for computational efficiency. These two failure criteria are discussed and compared in terms of their effects on the estimation of pipe failure probability. 5 refs., 9 figs.

  6. Method of Testing and Predicting Failures of Electronic Mechanical Systems

    NASA Technical Reports Server (NTRS)

    Iverson, David L.; Patterson-Hine, Frances A.

    1996-01-01

    A method employing a knowledge base of human expertise comprising a reliability model analysis implemented for diagnostic routines is disclosed. The reliability analysis comprises digraph models that determine target events created by hardware failures human actions, and other factors affecting the system operation. The reliability analysis contains a wealth of human expertise information that is used to build automatic diagnostic routines and which provides a knowledge base that can be used to solve other artificial intelligence problems.

  7. Register of specialized sources for information on mechanics of structural failure

    NASA Technical Reports Server (NTRS)

    Carpenter, J. L., Jr.; Denny, F. J.

    1973-01-01

    Specialized information sources that generate information relative to six problem areas in aerospace mechanics of structural failure are identified. Selection for inclusion was based upon information obtained from the individual knowledge and professional contacts of Martin Marietta Aerospace staff members and the information uncovered by the staff of technical reviewers. Activities listed perform basic or applied research related to the mechanics of structural failure and publish the results of such research. The purpose of the register is to present, in easy reference form, original sources for dependable information regarding failure modes and mechanisms of aerospace structures.

  8. Probing mechanical principles of focal contacts in cell–matrix adhesion with a coupled stochastic–elastic modelling framework

    PubMed Central

    Gao, Huajian; Qian, Jin; Chen, Bin

    2011-01-01

    Cell–matrix adhesion depends on the collective behaviours of clusters of receptor–ligand bonds called focal contacts between cell and extracellular matrix. While the behaviour of a single molecular bond is governed by statistical mechanics at the molecular scale, continuum mechanics should be valid at a larger scale. This paper presents an overview of a series of recent theoretical studies aimed at probing the basic mechanical principles of focal contacts in cell–matrix adhesion via stochastic–elastic models in which stochastic descriptions of molecular bonds and elastic descriptions of interfacial traction–separation are unified in a single modelling framework. The intention here is to illustrate these principles using simple analytical and numerical models. The aim of the discussions is to provide possible clues to the following questions: why does the size of focal adhesions (FAs) fall into a narrow range around the micrometre scale? How can cells sense and respond to substrates of varied stiffness via FAs? How do the magnitude and orientation of mechanical forces affect the binding dynamics of FAs? The effects of cluster size, cell–matrix elastic modulus, loading direction and cytoskeletal pretension on the lifetime of FA clusters have been investigated by theoretical arguments as well as Monte Carlo numerical simulations, with results showing that intermediate adhesion size, stiff substrate, cytoskeleton stiffening, low-angle pulling and moderate cytoskeletal pretension are factors that contribute to stable FAs. From a mechanistic point of view, these results provide possible explanations for a wide range of experimental observations and suggest multiple mechanisms by which cells can actively control adhesion and de-adhesion via cytoskeletal contractile machinery in response to mechanical properties of their surroundings. PMID:21632610

  9. Mechanically Induced Focal Adhesion Assembly Amplifies Anti-Adipogenic Pathways in Mesenchymal Stem Cells

    PubMed Central

    Sen, Buer; Guilluy, Christophe; Xie, Zhihui; Case, Natasha; Styner, Maya; Thomas, Jacob; Oguz, Ipek; Rubin, Clinton; Burridge, Keith; Rubin, Janet

    2013-01-01

    The fate of pluripotent mesenchymal stem cells (MSC) is determined through integration of chemical, spatial, and physical signals. The suppression of MSC adipogenesis by mechanical stimuli, which requires Akt-induced inhibition of glycogen synthase kinase 3β (GSK3β) with β-catenin activation, can be enhanced by repetitive dosing within a single day. Here, we demonstrate that reapplication of cyclic strain within a 24-hour period leads to amplification of both Akt activation and its subsequent inhibition of GSK3β, such that total cycle number can be reduced while still inhibiting adipogenesis. Amplification of Akt signaling is facilitated by a dynamic restructuring of the cell in response to mechanical signals, as evidenced by a transient increase in focal adhesion (FA) number and increased RhoA activity. Preventing FA assembly or development of tension blocks activation of Akt by mechanical signals, but not by insulin. This indicates that the FA infrastructure is essential to the physical, but not necessarily the chemical, sensitivity, and responsiveness of the cell. Exploiting the transient nature of cytoskeletal remodeling may represent a process to enhance cell responsiveness to mechanical input and ultimately define the fate of MSCs with a minimal input. PMID:21898699

  10. Failure modes in surface micromachined microelectromechanical actuators

    SciTech Connect

    Miller, S.L.; Rodgers, M.S.; LaVigne, G.; Sniegowski, J.J.; Clews, P.; Tanner, D.M.; Peterson, K.A.

    1998-03-01

    In order for the rapidly emerging field of MicroElectroMechanical Systems (MEMS) to meet its extraordinary expectations regarding commercial impact, issues pertaining to how they fail must be understood. The authors identify failure modes common to a broad range of MEMS actuators, including adhesion (stiction) and friction induced failures caused by improper operational methods, mechanical instabilities, and electrical instabilities. Demonstrated methods to mitigate these failure modes include implementing optimized designs, model based operational methods, and chemical surface treatments.

  11. Mono- and multiple TiN(/Ti) coating adhesion mechanism on a Ti-13Nb-13Zr alloy

    NASA Astrophysics Data System (ADS)

    Li, Jianzhong; Zheng, Hua; Sinkovits, Theo; Hee, Ay Ching; Zhao, Yue

    2015-11-01

    Mono- and multiple TiN(/Ti) coatings deposited on Ti-13Nb-13Zr alloy substrates by the filtered arc deposition system were examined using scratch testing and depth-sensing indentation in terms of the relationship between the coating adhesion, deformation mechanism, and microstructure, and mechanical properties at the film/substrate interface. The results show that multilayer TiN/Ti coatings offer a greater resistance to cracking and delamination than monolithic TiN coatings under the same conditions on the Ti-13Nb-13Zr alloys substrates. And increasing the number of layers for TiN multilayer coating improves the coatings adhesion. In contrast, for the coatings on the Ti-13Nb-13Zr alloys substrates that were heat-treated to a higher hardness, the limited deformation in the substrates improved remarkably the coating adhesion indiscriminately. The substrate mechanical properties play the major roles in controlling the coating adhesion, and increasing thickness and layers of the TiN multilayer have a limited improvement to the adhesion of coating.

  12. Mechanism of TMI-1 steam-generator failures

    SciTech Connect

    Newman, R.C.; Bandy, R.; Roberge, R.

    1983-01-01

    The low-temperature stress-corrosion cracking (SCC) of sensitized Inconel 600 was studied using various borated solutions of sulfur compounds. Sodium thiosulfate and sodium tetrathionate were equally aggressive provided that the alloy was sufficiently severely sensitized. Tetrathionate was more effective on marginally sensitized material. The threshold concentration of thiosulfate was below 10/sup -6/ M. LiOH additions inhibited SCC. Oxygen is necessary for SCC in these solutions. The relevance of the laboratory tests to the steam generator failures is discussed.

  13. The N terminus of SKAP55 enables T cell adhesion to TCR and integrin ligands via distinct mechanisms

    PubMed Central

    Ophir, Michael J.; Liu, Beiyun C.

    2013-01-01

    The T cell receptor (TCR) triggers the assembly of “SLP-76 microclusters,” which mediate signals required for T cell activation. In addition to regulating integrin activation, we show that Src kinase–associated phosphoprotein of 55 kD (SKAP55) is required for microcluster persistence and movement, junctional stabilization, and integrin-independent adhesion via the TCR. These functions require the dimerization of SKAP55 and its interaction with the adaptor adhesion and degranulation-promoting adaptor protein (ADAP). A “tandem dimer” containing two ADAP-binding SKAP55 Src homology 3 (SH3) domains stabilized SLP-76 microclusters and promoted T cell adhesion via the TCR, but could not support adhesion to integrin ligands. Finally, the SKAP55 dimerization motif (DM) enabled the coimmunoprecipitation of the Rap1-dependent integrin regulator Rap1-GTP–interacting adaptor molecule (RIAM), the recruitment of talin into TCR-induced adhesive junctions, and “inside-out” signaling to β1 integrins. Our data indicate that SKAP55 dimers stabilize SLP-76 microclusters, couple SLP-76 to the force-generating systems responsible for microcluster movement, and enable adhesion via the TCR by mechanisms independent of RIAM, talin, and β1 integrins. PMID:24368808

  14. Agent autonomy approach to probabilistic physics-of-failure modeling of complex dynamic systems with interacting failure mechanisms

    NASA Astrophysics Data System (ADS)

    Gromek, Katherine Emily

    A novel computational and inference framework of the physics-of-failure (PoF) reliability modeling for complex dynamic systems has been established in this research. The PoF-based reliability models are used to perform a real time simulation of system failure processes, so that the system level reliability modeling would constitute inferences from checking the status of component level reliability at any given time. The "agent autonomy" concept is applied as a solution method for the system-level probabilistic PoF-based (i.e. PPoF-based) modeling. This concept originated from artificial intelligence (AI) as a leading intelligent computational inference in modeling of multi agents systems (MAS). The concept of agent autonomy in the context of reliability modeling was first proposed by M. Azarkhail [1], where a fundamentally new idea of system representation by autonomous intelligent agents for the purpose of reliability modeling was introduced. Contribution of the current work lies in the further development of the agent anatomy concept, particularly the refined agent classification within the scope of the PoF-based system reliability modeling, new approaches to the learning and the autonomy properties of the intelligent agents, and modeling interacting failure mechanisms within the dynamic engineering system. The autonomous property of intelligent agents is defined as agent's ability to self-activate, deactivate or completely redefine their role in the analysis. This property of agents and the ability to model interacting failure mechanisms of the system elements makes the agent autonomy fundamentally different from all existing methods of probabilistic PoF-based reliability modeling. 1. Azarkhail, M., "Agent Autonomy Approach to Physics-Based Reliability Modeling of Structures and Mechanical Systems", PhD thesis, University of Maryland, College Park, 2007.

  15. Mechanisms of lymphocyte adhesion to endothelial cells: studies using a LFA-1-deficient cell line.

    PubMed Central

    Haskard, D O; Strobel, S; Thornhill, M; Pitzalis, C; Levinsky, R J

    1989-01-01

    In order to investigate the role of lymphocyte function-associated antigen 1 (LFA-1) in lymphocyte adhesion to endothelial cells (EC), we have studied the adhesion of a LFA-1-deficient lymphoblastoid cell line, ICH-KM, which has < 10% of the cell surface LFA-1 expressed on a normal lymphoblastoid cell line, ICH-BJ. The adhesion of ICH-KM cells to unstimulated EC was 49.9 +/- 8.6% (mean +/- SD) that of ICH-BJ cells. Moreover, phorbol ester-stimulated ICH-KM cells showed a considerably weaker increase in adhesion to unstimulated EC compared with ICH-BJ cells (mean +/- SD increase in percentage adhesion, 3.8 +/- 2.3 compared with 18.5 +/- 8.0; P<0.025). In contrast, there was no significant difference between the enhanced adhesion of ICH-KM cells and ICH-BJ cells to interleukin-1 (IL-1)-stimulated EC. Thus ICH-KM cells showed a 22.7 +/- 11.0 (mean +/- SD) increase in percentage adhesion to IL-1-stimulated EC compared with the 24.8 +/- 8.5 increase in percentage adhesion of ICH-BJ cells. Anti-LFA-1 monoclonal antibodies had no effect on the enhanced adhesion of ICH-KM and ICH-BJ cells to IL-1-stimulated EC but abolished the differences in adhesion between the two cell lines. The study therefore indicates that although a major part of unstimulated and phorbol ester-stimulated lymphocyte-EC adhesion is dependent upon LFA-1, the enhanced adhesion due to stimulation of EC with IL-1 is not dependent upon this molecule. The data therefore supports the existence of cytokine-inducible LFA-1-independent adhesion molecules for lymphocytes on EC. PMID:15493272

  16. Electrochemical evaluation of a corrosion fatigue failure mechanism in a duplex stainless steel

    NASA Astrophysics Data System (ADS)

    Stoudt, M. R.; Ricker, R. E.

    2004-08-01

    Laboratory corrosion fatigue studies on smooth and precracked samples indicated that two duplex stainless steels would have similar service lives in a paper-processing environment; but, in service, one of these alloys has exhibited premature failures. Since corrosion fatigue experiments had proven unable to detect this failure mechanism, electrochemical measurements and slow strain rate tensile tests were used to evaluate four alloy composition-dependent failure mechanism hypotheses. No significant differences were found in the dissolution rates or hydrogen fugacities produced when mechanical processes expose bare surface, and slow strain rate tensile tests found no indication of a difference in cracking susceptibility for the same hydrogen fugacity. Electrochemical experiments found that pits nucleate in one phase of the duplex microstructure at lower potentials in the failure prone alloy, but do not propagate beyond the microscopic dimensions of this phase. These microstructurally limited “micropits” were found to nucleate fracture in slow strain rate tensile tests, and examination of a service failure confirmed the presence of microscopic pits at crack initiation sites. The premature failures are attributed to the lower pitting resistance of the failure prone alloy, and the failure of laboratory experiments to predict this behavior is attributed to the slow kinetics of pit nucleation in these experiments. A laboratory testing methodology is suggested that will ensure detection of similar susceptibilities in future corrosion fatigue testing programs.

  17. Failure mechanisms in laminated carbon/carbon composites under biaxial compression

    SciTech Connect

    Grape, J.A.; Gupta, V.

    1995-07-01

    The failure mechanisms of 2D carbon/carbon (C/C) woven laminates have been determined under inplane biaxial compression loads, and the associated failure envelopes that account for the effect of matrix-type and loading directions were also obtained. The failure was in the form of micro-kinking of fiber bundles, interspersed with localized interply delaminations to form an overall shear fault. The shear fault was aligned with the major axis of loading except at above 75% of balanced biaxial compressive stress where failure occurred along both axes. Although the biaxial strength varied significantly with the ratio of in-plane principal stresses, R, there was no variation in the local failure mechanisms. Accordingly, it was found that the samples fail upon achieving a critical strain along the primary axis of loading.

  18. Accelerated Thermal Cycling and Failure Mechanisms for BGA and CSP Assemblies

    NASA Technical Reports Server (NTRS)

    Ghaffarian, Reza

    2000-01-01

    This paper reviews the accelerated thermal cycling test methods that are currently used by industry to characterize the interconnect reliability of commercial-off-the-shelf (COTS) ball grid array (BGA) and chip scale package (CSP) assemblies. Acceleration induced failure mechanisms varied from conventional surface mount (SM) failures for CSPs. Examples of unrealistic life projections for other CSPs are also presented. The cumulative cycles to failure for ceramic BGA assemblies performed under different conditions, including plots of their two Weibull parameters, are presented. The results are for cycles in the range of -30 C to 100 C, -55 C to 100 C, and -55 C to 125 C. Failure mechanisms as well as cycles to failure for thermal shock and thermal cycling conditions in the range of -55 C to 125 C were compared. Projection to other temperature cycling ranges using a modified Coffin-Manson relationship is also presented.

  19. Molecular dynamics investigation of the adhesion mechanism acting between dopamine and the surface of dopamine-processed aramid fibers.

    PubMed

    Chai, Dongliang; Xie, Zhimin; Wang, Youshan; Liu, Li; Yum, Young-Jin

    2014-10-22

    Dopamine, as a universal material for surface treatment, can effectively improve the surface performance of aramid fibers. However, directly processing the surface of aramid fibers using dopamine currently incurs a high cost. To seek dopamine substitutes, one must first explore the adhesion mechanism responsible for binding the dopamine to the surface of the fiber. In this study, we construct an all-atomic molecular dynamics model of an aramid fiber before and after surface modification using dopamine. A force field based on condensed-phase optimized molecular potentials for atomistic simulation studies (COMPASS) is used. Using it, we analyze the surface adhesion mechanism of polydopamines aggregated by 21 kinds of molecular structures typically found on the surface of aramid fibers. The results show that a clear and smooth interface is formed between the polydopamine nanofilm layer and the surface of the aramid fiber. The high atomic density of the polydopamine in the small interface region is found to be conducive to noncovalent bonds of polydopamines with the surface of the aramid fiber. In addition, we investigate the works of adhesion of the 21 molecular structures typically found on the surface of aramid fibers. The results suggest that the work of adhesion of 5,6-indolequinone is the highest, followed by annular eumelanin molecules with annular planar structure. Straight-chain shaped dimers proved to be the molecules with the highest adhesion ability of the dihydroxyindole chain oligomers. Therefore, there is reason to suppose that more molecular structures (as above) can be formed by processing the surface of aramid fibers using dopamine by controlling the processing conditions. These molecular structures help improve the adhesion ability of the dopamine on the surface of the aramid fiber. Additionally, if these polydopamine molecules with high adhesion ability can be synthesized on a large scale, then new surface-processing materials are possible. PMID

  20. Failure mechanics of fiber composite notched charpy specimens. [stress analysis

    NASA Technical Reports Server (NTRS)

    Chamis, C. C.

    1976-01-01

    A finite element stress analysis was performed to determine the stress variation in the vicinity of the notch and far field of fiber composites Charpy specimens (ASTM Standard). NASTRAN was used for the finite element analysis assuming linear behavior and equivalent static load. The unidirectional composites investigated ranged from Thornel 75 Epoxy to S-Glass/Epoxy with the fiber direction parallel to the long dimension of the specimen. The results indicate a biaxial stress state exists in (1) the notch vicinity which is dominated by transverse tensile and interlaminar shear and (2) near the load application point which is dominated by transverse compression and interlaminar shear. The results also lead to the postulation of hypotheses for the predominant failure modes, the fracture initiation, and the fracture process. Finally, the results indicate that the notched Charpy test specimen is not suitable for assessing the impact resistance of nonmetallic fiber composites directly.

  1. Lubrication and failure mechanisms of graphite fluoride films

    NASA Technical Reports Server (NTRS)

    Fusaro, R. L.

    1978-01-01

    An optical microscope, equipped with a vertical illuminator and two polaroid filters (one rotatable), was used to visually study 440C HT steel surfaces lubricated with rubbed graphite fluoride films. Friction and wear results were compared to visual observations as a function of sliding distance for films applied to three surface finishes - polished, sanded, and sand-blasted. In general, the lubricating process was one of initial deformation or wear of metallic asperities into flat plateaus and then the formation of thin, layer-like, dynamic films which sheared between the flats and eventually flowed through the contact area. Failure was due to depletion of the graphite fluoride with the subsequent formation of excessive powdery metallic debris that formed a heavy, powdery film on both the rider and disk surfaces.

  2. Wellbore failure mechanisms in shales: Prediction and prevention

    SciTech Connect

    Gazaniol, D.; Forsans, T.; Boisson, M.J.F.; Piau, J.M.

    1994-12-31

    Shales stability is still one of the most important problems faced during drilling. Until recently, stability problems were attributed, most often to the swelling of shales. Recent research work performed by Elf and others shows that several mechanisms are involved, and that their relative importance can be estimated. A review of these mechanisms is presented here. More precisely, pore pressure diffusion, plasticity, anisotropy, capillary effects, osmosis, and physicochemical alteration are discussed. Considering all these phenomena, the way of acting of different kinds of muds is discussed. The practical use of rock mechanics models is also addressed.

  3. A fundamental approach to adhesion: Synthesis, surface analysis, thermodynamics and mechanics

    NASA Technical Reports Server (NTRS)

    Dwight, D. W.; Wightman, J. P.

    1977-01-01

    The effects of composites as adherends was studied. Several other variables were studied by fractography: aluminum powder adhesive filler, fiber glass cloth scrim or adhesive carrier, new adhesives PPQ-413 and LARC-13, and strength-test temperature. When the new results were juxtaposed with previous work, it appeared that complex interactions between adhesive, adherend, bonding, and testing conditions govern the observed strength and fracture-surface features. The design parameters likely to have a significant effect upon strength-test results are listed.

  4. Creasable Batteries: Understanding Failure Modes through Dynamic Electrochemical Mechanical Testing.

    PubMed

    Blake, Aaron J; Kohlmeyer, Ryan R; Drummy, Lawrence F; Gutiérrez-Kolar, Jacob S; Carpena-Núñez, Jennifer; Maruyama, Benji; Shahbazian-Yassar, Reza; Huang, Hong; Durstock, Michael F

    2016-03-01

    Thin-film batteries that can be folded, bent, and even repeatedly creased with minimal or no loss in electrochemical performance have been demonstrated and systematically evaluated using two dynamic mechanical testing approaches for either controlled bending or creasing of flexible devices. The results show that mechanically robust and flexible Li-ion batteries (Li4Ti5O12//LiFePO4) based on the use of a nonwoven multiwalled carbon nanotube (MWNT) mat as a current collector (CC) exhibited a 14-fold decrease in voltage fluctuation at a bending strain of 4.2%, as compared to cells using traditional metal foil CCs. More importantly, MWNT-based full-cells exhibited excellent mechanical integrity through 288 crease cycles, whereas the foil full-cell exhibited continuously degraded performance with each fold and catastrophic fracture after only 94 folds. The enhancements due to MWNT CCs can be attributed to excellent interfacial properties as well as high mechanical strength coupled with compliancy, which allow the batteries to easily conform during mechanical abuse. These results quantitatively demonstrate the substantial enhancement offered in both mechanical and electrochemical stability which can be realized with traditional processing approaches when an appropriate choice of a flexible and robust CC is utilized. PMID:26741734

  5. Fundamental study of failure mechanisms of pressure vessels under thermo-mechanical cycling in multiphase environments

    NASA Astrophysics Data System (ADS)

    Penso Mula, Jorge Antonio

    Cracking and bulging in welded and internally lined pressure vessels that work in thermal-mechanical cycling services have been well known problems in the petrochemical, power and nuclear industries. Published literature and industry surveys show that similar problems have been occurring during the last 50 years. Understanding the causes of cracking and bulging would lead to improvements in the reliability of these pressure vessels. This study attempts to add information required for improving the knowledge and fundamental understanding of these problems. Cracking and bulging, most often in the weld areas, commonly experienced in delayed coking units (e.g. coke drums) in oil refineries are typical examples. The coke drum was selected for this study because of the existing field experience and past industrial investigation results that were available to serve as the baseline references for the analytical studies performed for this dissertation. Another reason for selecting the delayed coking units for this study was due to their high economical yields. Shutting down these units would cause a high negative economic impact on the refinery operations. Several failure mechanisms were hypothesized. The finite element method was used to analyze these significant variables and to verify the hypotheses. In conclusion, a fundamental explanation of the occurrence of bulging and cracking in pressure vessels in multiphase environments has been developed. Several important factors have been identified, including the high convection coefficient of the boiling layer during filling and quenching, the mismatch in physical, thermal and mechanical properties in the dissimilar weld of the clad plates and process conditions such as heating and quenching rate and warming time. Material selection for coke drums should consider not only fatigue strength but also corrosion resistance at high temperatures and low temperatures. Cracking occurs due to low cycle fatigue and corrosion. The FEA

  6. Directing epithelial to mesenchymal transition through engineered microenvironments displaying orthogonal adhesive and mechanical cues.

    PubMed

    Markowski, Marilyn C; Brown, Ashley C; Barker, Thomas H

    2012-08-01

    Cell interactions with their extracellular matrix (ECM) microenvironments play a major role in directing cellular processes that can drive wound healing and tissue regeneration but, if uncontrolled, lead to pathological progression. One such process, epithelial to mesenchymal transition (EMT), if finely controlled could have significant potential in regenerative medicine approaches. Despite recent findings that highlight the influence of biochemical and mechanical properties of the ECM on EMT, it is still unclear how these two orthogonal cues act synergistically to control epithelial cell phenotype. Here, we cultured lung epithelial cells on combinations of different mutants of fibronectin's cell binding domain that preferentially engage specific integrins and substrates of varying stiffness. Our results suggest that while stiff substrates induce spontaneous EMT, this response can be overcome by with fragments of fibronectin that support α3 and α5 integrin engagement. Furthermore, we found that substrate-induced EMT correlates with transforming growth factor beta activation by resident epithelial cells and is dependent on Rho/ROCK signaling. Suppressing cell-contractility was sufficient to maintain an epithelial phenotype. Our results suggest that integrin-specific engagement of fibronectin adhesive domains and the mechanics of the ECM act synergistically to direct EMT. PMID:22615133

  7. Mechanical Properties of Anisotropic Conductive Adhesive Film Under Hygrothermal Aging and Thermal Cycling

    NASA Astrophysics Data System (ADS)

    Gao, Li-Lan; Chen, Xu; Gao, Hong

    2012-07-01

    Mechanical properties of anisotropic conductive adhesive film (ACF) were investigated experimentally under various environmental conditions. The temperature sweep test was conducted to investigate the effects of temperature on dynamical mechanical properties of the ACF. The ACF exhibited transitions to the glass state, viscoelastic state, and rubber state with increasing temperature, and its glass-transition temperature ( T g) was determined to be 149°C. The creep-recovery behaviors of the ACF were investigated, and it was found that the initial strains, instantaneous strains, and creep or recovery rates increased with increasing temperature. No obvious creep phenomenon was observed at low temperatures (≤0°C). The creep strain and creep rates at any time decreased with increasing hygrothermal aging time. The uniaxial tensile behaviors of the ACF were also investigated under hygrothermal aging and thermal cycling. The results show that the Young's modulus and tensile strength of the ACF decrease with increasing hygrothermal aging time; however, they increase at first and then decrease with increasing thermal cycling time. T g decreases slightly for the ACF after hygrothermal aging; however, it increases after thermal cycling.

  8. Investigation of failure mechanisms in integrated vacuum circuits

    NASA Technical Reports Server (NTRS)

    Rosengreen, A.

    1972-01-01

    The fabrication techniques of integrated vacuum circuits are described in detail. Data obtained from a specially designed test circuit are presented. The data show that the emission observed in reverse biased devices is due to cross-talk between the devices and can be eliminated by electrostatic shielding. The lifetime of the cathodes has been improved by proper activation techniques. None of the cathodes on life test has shown any sign of failure after more than 3500 hours. Life tests of triodes show a decline of anode current by a factor of two to three after a few days. The current recovers when the large positive anode voltage (100 V) has been removed for a few hours. It is suggested that this is due to trapped charges in the sapphire substrate. Evidence of the presence of such charges is given, and a model of the charge distribution is presented consistent with the measurements. Solution of the problem associated with the decay of triode current may require proper treatment of the sapphire surface and/or changes in the deposition technique of the thin metal films.

  9. Mechanical properties and failure behavior of unidirectional porous ceramics

    PubMed Central

    Seuba, Jordi; Deville, Sylvain; Guizard, Christian; Stevenson, Adam J.

    2016-01-01

    We show that the honeycomb out-of-plane model derived by Gibson and Ashby can be applied to describe the compressive behavior of unidirectional porous materials. Ice-templating allowed us to process samples with accurate control over pore volume, size, and morphology. These samples allowed us to evaluate the effect of this microstructural variations on the compressive strength in a porosity range of 45–80%. The maximum strength of 286 MPa was achieved in the least porous ice-templated sample (P(%) = 49.9), with the smallest pore size (3 μm). We found that the out-of-plane model only holds when buckling is the dominant failure mode, as should be expected. Furthermore, we controlled total pore volume by adjusting solids loading and sintering temperature. This strategy allows us to independently control macroporosity and densification of walls, and the compressive strength of ice-templated materials is exclusively dependent on total pore volume. PMID:27075397

  10. Sarcopenia in heart failure: mechanisms and therapeutic strategies

    PubMed Central

    Collamati, Agnese; Marzetti, Emanuele; Calvani, Riccardo; Tosato, Matteo; D'Angelo, Emanuela; Sisto, Alex N; Landi, Francesco

    2016-01-01

    Chronic heart failure (CHF) is a highly prevalent condition among the elderly and is associated with considerable morbidity, institutionalization and mortality. In its advanced stages, CHF is often accompanied by the loss of muscle mass and strength. Sarcopenia is a geriatric syndrome that has been actively studied in recent years due to its association with a wide range of adverse health outcomes. The goal of this review is to discuss the relationship between CHF and sarcopenia, with a focus on shared pathophysiological pathways and treatments. Malnutrition, systemic inflammation, endocrine imbalances, and oxidative stress appear to connect sarcopenia and CHF. At the muscular level, alterations of the ubiquitin proteasome system, myostatin signaling, and apoptosis have been described in both sarcopenia and CHF and could play a role in the loss of muscle mass and function. Possible therapeutic strategies to impede the progression of muscle wasting in CHF patients include protein and vitamin D supplementation, structured physical exercise, and the administration of angiotensin-converting enzyme inhibitors and β-blockers. Hormonal supplementation with growth hormone, testosterone, and ghrelin is also discussed as a potential treatment. PMID:27605943

  11. Mechanical properties and failure behavior of unidirectional porous ceramics

    NASA Astrophysics Data System (ADS)

    Seuba, Jordi; Deville, Sylvain; Guizard, Christian; Stevenson, Adam J.

    2016-04-01

    We show that the honeycomb out-of-plane model derived by Gibson and Ashby can be applied to describe the compressive behavior of unidirectional porous materials. Ice-templating allowed us to process samples with accurate control over pore volume, size, and morphology. These samples allowed us to evaluate the effect of this microstructural variations on the compressive strength in a porosity range of 45–80%. The maximum strength of 286 MPa was achieved in the least porous ice-templated sample (P(%) = 49.9), with the smallest pore size (3 μm). We found that the out-of-plane model only holds when buckling is the dominant failure mode, as should be expected. Furthermore, we controlled total pore volume by adjusting solids loading and sintering temperature. This strategy allows us to independently control macroporosity and densification of walls, and the compressive strength of ice-templated materials is exclusively dependent on total pore volume.

  12. Sarcopenia in heart failure: mechanisms and therapeutic strategies.

    PubMed

    Collamati, Agnese; Marzetti, Emanuele; Calvani, Riccardo; Tosato, Matteo; D'Angelo, Emanuela; Sisto, Alex N; Landi, Francesco

    2016-07-01

    Chronic heart failure (CHF) is a highly prevalent condition among the elderly and is associated with considerable morbidity, institutionalization and mortality. In its advanced stages, CHF is often accompanied by the loss of muscle mass and strength. Sarcopenia is a geriatric syndrome that has been actively studied in recent years due to its association with a wide range of adverse health outcomes. The goal of this review is to discuss the relationship between CHF and sarcopenia, with a focus on shared pathophysiological pathways and treatments. Malnutrition, systemic inflammation, endocrine imbalances, and oxidative stress appear to connect sarcopenia and CHF. At the muscular level, alterations of the ubiquitin proteasome system, myostatin signaling, and apoptosis have been described in both sarcopenia and CHF and could play a role in the loss of muscle mass and function. Possible therapeutic strategies to impede the progression of muscle wasting in CHF patients include protein and vitamin D supplementation, structured physical exercise, and the administration of angiotensin-converting enzyme inhibitors and β-blockers. Hormonal supplementation with growth hormone, testosterone, and ghrelin is also discussed as a potential treatment. PMID:27605943

  13. Wellbore failure mechanisms in shales: Prediction and prevention

    SciTech Connect

    Gazaniol, D.; Forsans, T.; Boisson, M.J.F.; Piau, J.M.

    1995-07-01

    Shale stability is still one of the most important problems faced during drilling. Until recently, stability problems were most often attributed to shale swelling; however, recent research shows that several mechanisms are involved and that their relative importance can be estimated. This paper presents a review of these mechanisms, including pore-pressure diffusion, plasticity, anisotropy, capillary effects, osmosis, and physicochemical alteration. Pore-pressure diffusion into the rock in the vicinity of the wellbore (transition from undrained to drained behavior) appears to be of major importance in these very-low-permeability rocks. Plasticity is discussed in terms of modeling. Compared with simple elastic models, modeling of plasticity can simulate the actual behavior of wellbore better. The behavior of different types of muds is discussed while taking these phenomena into consideration, and the practical use of rock-mechanics models is also addressed.

  14. Defect induced plasticity and failure mechanism of boron nitride nanotubes under tension

    SciTech Connect

    Anoop Krishnan, N. M. Ghosh, Debraj

    2014-07-28

    The effects of Stone-Wales (SW) and vacancy defects on the failure behavior of boron nitride nanotubes (BNNTs) under tension are investigated using molecular dynamics simulations. The Tersoff-Brenner potential is used to model the atomic interaction and the temperature is maintained close to 300 K. The effect of a SW defect is studied by determining the failure strength and failure mechanism of nanotubes with different radii. In the case of a vacancy defect, the effect of an N-vacancy and a B-vacancy is studied separately. Nanotubes with different chiralities but similar diameter is considered first to evaluate the chirality dependence. The variation of failure strength with the radius is then studied by considering nanotubes of different diameters but same chirality. It is observed that the armchair BNNTs are extremely sensitive to defects, whereas the zigzag configurations are the least sensitive. In the case of pristine BNNTs, both armchair and zigzag nanotubes undergo brittle failure, whereas in the case of defective BNNTs, only the zigzag ones undergo brittle failure. An interesting defect induced plastic behavior is observed in defective armchair BNNTs. For this nanotube, the presence of a defect triggers mechanical relaxation by bond breaking along the closest zigzag helical path, with the defect as the nucleus. This mechanism results in a plastic failure.

  15. [AMP-activated protein kinase activation regulates adhesion of monocytes to vascular endothelial cells and the underlying mechanism].

    PubMed

    Bai, Hong-Bo; Wang, Yun; Zhang, Yu-Hua; Zhang, Yuan

    2016-02-25

    The present study was aimed to explore the effect of AMP-activated protein kinase (AMPK) on monocyte adhesion to vascular endothelial cells and underlying molecular mechanism. Tumor necrosis factor α (TNFα)-activated human aortic endothelial cells (HAECs) were treated with different concentrations of AMPK agonist 5-Aminoimidazole-4-carboxamide-1-β-D-ribonucleotide (AICAR) or AMPK inhibitor compound C. And other HAECs were overexpressed with constitutive active or dominant negative AMPK protein and then treated with TNFα. The rates of monocytes adhering to endothelial cells were detected by fluorescent staining. Intercellular cell adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) mRNA levels and protein secretions were detected by quantitative PCR and ELISA, respectively. Acetylation of NF-κB p65 at lysine 221 site was assessed by Western blot. NF-κB p65 DNA binding activity was analyzed by an ELISA-based method. By using small interfering RNA based strategy, p300 expression in HAECs was down-regulated and then cells were incubated with TNFα. NF-κB p65 DNA binding activity, ICAM-1 and VCAM-1 expressions and adhesion rates were detected, respectively. The activity of p300 was also detected by ELISA. The results showed that AICAR treatment significantly reduced monocyte-endothelial adhesion rate, as well as ICAM-1 and VCAM-1 mRNA levels and protein secretions, in TNFα-activated HAECs. Moreover, transfection of constitutive active AMPKα but not dominant negative AMPKα strongly diminished TNFα-induced upregulation of ICAM-1 and VCAM-1 mRNA expressions and secretions, as well as monocyte-endothelial adhesion. Furthermore, AMPK activation decreased TNFα-mediated acetylation of NF-κB p65 at Lys221 site and reduced NF-κB p65 DNA binding activity. Silencing p300 by siRNA significantly abolished the effect of TNFα- induced adhesion molecules expression and monocyte-endothelial adhesion. Blocking AMPK activation by compound C almost

  16. Degradation mechanisms and stability forecasting and adhesion contacts of metal films with binary dielectric substrates

    SciTech Connect

    Stolyarova, S.; Nemirovsky, Y.; Simanovskis, A.

    1996-12-31

    In this paper the authors present their conception of degradation and stability on the adhesion contacts of metal films with binary nonmetallic crystals. There are numerous works devoted to the atomic scale determination of adhesion forces and development of adhesion interaction laws. But in the real life the kinetic processes, taking place on the adhesion contact, can lead to such dramatic changes in adhesion strength values that the initial adhesion characteristics do not worth much for practice. Sometimes, adhesion contact with a metal which supposed to be highly adhesive failes in a short period of aging time. What the authors have learned from their studies of the contact processes is that in many cases the aging could not be separately addressed to the individual properties of film metal or to those of the substrate material. It depends mainly on the relationships between the parameters of interacting pair. The question is: what parameters should be taken into account to explain degradation phenomena and to predict them? The purpose of the present work is to show how the relative chemical activity of film metal and substrate cation affects the contact degradation in a vacuum and in different environmental conditions.

  17. Immune mechanisms in acetaminophen-induced acute liver failure.

    PubMed

    Krenkel, Oliver; Mossanen, Jana C; Tacke, Frank

    2014-12-01

    An overdose of acetaminophen (N-acetyl-p-aminophenol, APAP), also termed paracetamol, can cause severe liver damage, ultimately leading to acute liver failure (ALF) with the need of liver transplantation. APAP is rapidly taken up from the intestine and metabolized in hepatocytes. A small fraction of the metabolized APAP forms cytotoxic mitochondrial protein adducts, leading to hepatocyte necrosis. The course of disease is not only critically influenced by dose of APAP and the initial hepatocyte damage, but also by the inflammatory response following acetaminophen-induced liver injury (AILI). As revealed by mouse models of AILI and corresponding translational studies in ALF patients, necrotic hepatocytes release danger-associated-molecular patterns (DAMPs), which are recognized by resident hepatic macrophages, Kupffer cell (KC), and neutrophils, leading to the activation of these cells. Activated hepatic macrophages release various proinflammatory cytokines, such as TNF-α or IL-1β, as well as chemokines (e.g., CCL2) thereby further enhancing inflammation and increasing the influx of immune cells, like bone-marrow derived monocytes and neutrophils. Monocytes are mainly recruited via their receptor CCR2 and aggravate inflammation. Infiltrating monocytes, however, can mature into monocyte-derived macrophages (MoMF), which are, in cooperation with neutrophils, also involved in the resolution of inflammation. Besides macrophages and neutrophils, distinct lymphocyte populations, especially γδ T cells, are also linked to the inflammatory response following an APAP overdose. Natural killer (NK), natural killer T (NKT) and T cells possibly further perpetuate inflammation in AILI. Understanding the complex interplay of immune cell subsets in experimental models and defining their functional involvement in disease progression is essential to identify novel therapeutic targets for human disease. PMID:25568858

  18. Glioblastoma expression of vitronectin and the alpha v beta 3 integrin. Adhesion mechanism for transformed glial cells.

    PubMed Central

    Gladson, C L; Cheresh, D A

    1991-01-01

    Glioblastoma multiforme, the most malignant astroglial-derived tumor, grows as an adherent mass and locally invades normal brain. An examination of adult cerebral glioblastoma biopsy material for the expression of adhesive proteins that might potentiate adhesion and invasion demonstrated tumor cell-associated vitronectin (5/5). In contrast, vitronectin was not detected associated with glial cells in low grade astroglial tumors (0/4), reactive astrogliosis (0/4), or in normal adult cortex and cerebral white matter (0/5). Also, a wide variety of other adhesive ligands were absent from the glioblastoma tumor parenchyma. The alpha v beta 3 integrin was the only vitronectin receptor identified in glioblastoma tumors in situ, and was also not expressed on low grade astroglial-derived tumors, reactive astrogliosis, or on glia or neurons in normal adult cortex and cerebral white matter. In a cell attachment assay, cultured glioblastoma cells attached to the parenchyma of glioblastoma tumor cryostat sections at the sites of vitronectin expression, but failed to attach to normal brain. This adhesion was inhibited by antibodies directed against vitronectin, the alpha v beta 3 integrin, and with an Arg-Gly-Asp-containing peptide. These data provide evidence for a cell adhesion mechanism in glioblastoma tumors that might potentiate glioblastoma cell invasion of normal brain. Images PMID:1721625

  19. Mechanical Performance and Failure Mechanism of Thick-walled Composite Connecting Rods Fabricated by Resin Transfer Molding Technique

    NASA Astrophysics Data System (ADS)

    Liu, Gang; Luo, Chuyang; Zhang, Daijun; Li, Xueqin; Qu, Peng; Sun, Xiaochen; Jia, Yuxi; Yi, Xiaosu

    2015-08-01

    A resin transfer molding technique was used to fabricate thick-walled composite connecting rods, and then the mechanical performance of the connecting rod was studied experimentally, at the same time the stress and failure index distributions were simulated numerically. The experimental results show that under a tensile load, the connecting rod first cracks near the vertex of the triangle areas at the two ends, and then the damage propagates along the interface between the main bearing beam and the triangle area as well as along the round angle of the triangle area. Whereas under a compressive load, the delamination primarily occurs at the corner of the U-shaped flange, and the final destruction is caused by the fracture of fibers in the main bearing beam. The simulated results reveal that the tensile failure is originated from the delamination at the round angle transition areas of the T-joints, and the failure strength is determined by the interlaminar strength. Whereas the compressive failure is caused by the fracture of fibers in the main bearing beam, and the failure strength of the structure is determined by the longitudinal compressive strength of the composite material. The simulated results are basically consistent with the experimental results. Hence the mechanical performance and failure mechanism of the complicated composite structure are revealed in great detail through the coupling of the two kinds of research methods, which is helpful for the optimal design of composite structures.

  20. Hydrophobic recovery of UV/ozone treated poly(dimethylsiloxane): adhesion studies by contact mechanics and mechanism of surface modification

    NASA Astrophysics Data System (ADS)

    Oláh, Attila; Hillborg, Henrik; Vancso, G. Julius

    2005-01-01

    Silicone elastomers (Sylgard 184 and 170), based on poly(dimethylsiloxane) (PDMS), were surface treated by a combined exposure to UV and ozone. The effects of the treatments were analyzed as a function of time elapsed after stopping the treatments using different standard surface characterization techniques, such as water contact angle measurements, XPS and atomic force microscopy (AFM). However, the primary focus of this study was to apply the Johnson-Kendall-Roberts (JKR) contact mechanics approach to investigate PDMS samples prior to and following UV/ozone surface treatment. A gradual formation of a hydrophilic, silica-like surface layer with increasing modulus was observed with increasing UV/ozone exposure. A subsequent hydrophobic recovery after UV/ozone exposure was observed, as indicated by increasing contact angles. This supports the hypothesis that the hydrophobic recovery is mainly caused by the gradual coverage of a permanent silica-like structure with free siloxanes and/or reorientation of polar groups. PDMS containing a homogenously dispersed filler (Sylgard 184), exhibited a decreasing surface roughness (by AFM) when the oxidized surface region "collapsed" into a smooth SiO x layer (final surface roughness <2 nm). PDMS containing heterogeneously distributed, aggregated filler particles (Sylgard 170), exhibited an increasing surface roughness with treatment dose, which was attributed to the "collapse" of the oxidized surface region thus exposing the contours of the underlying filler aggregates (final surface roughness ˜140 nm). A dedicated device was designed and built to study the contact mechanics behavior of PDMS prior to, and following surface treatment. The value of the combined elastic modulus obtained for PDMS lens and semi-infinite flat surface system showed an increase in full agreement with the formation of a silica-like layer exhibiting a high elastic modulus (compared with untreated PDMS). The work of adhesion observed in JKR experiments

  1. A mathematical model of the coupled mechanisms of cell adhesion, contraction and spreading.

    PubMed

    Vernerey, Franck J; Farsad, Mehdi

    2014-03-01

    Recent research has shown that cell spreading is highly dependent on the contractility of its cytoskeleton and the mechanical properties of the environment it is located in. The dynamics of such process is critical for the development of tissue engineering strategy but is also a key player in wound contraction, tissue maintenance and angiogenesis. To better understand the underlying physics of such phenomena, the paper describes a mathematical formulation of cell spreading and contraction that couples the processes of stress fiber formation, protrusion growth through actin polymerization at the cell edge and dynamics of cross-membrane protein (integrins) enabling cell-substrate attachment. The evolving cell's cytoskeleton is modeled as a mixture of fluid, proteins and filaments that can exchange mass and generate contraction. In particular, besides self-assembling into stress fibers, actin monomers able to polymerize into an actin meshwork at the cell's boundary in order to push the membrane forward and generate protrusion. These processes are possible via the development of cell-substrate attachment complexes that arise from the mechano-sensitive equilibrium of membrane proteins, known as integrins. After deriving the governing equation driving the dynamics of cell evolution and spreading, we introduce a numerical solution based on the extended finite element method, combined with a level set formulation. Numerical simulations show that the proposed model is able to capture the dependency of cell spreading and contraction on substrate stiffness and chemistry. The very good agreement between model predictions and experimental observations suggests that mechanics plays a strong role into the coupled mechanisms of contraction, adhesion and spreading of adherent cells. PMID:23463540

  2. A mathematical model of the coupled mechanisms of cell adhesion, contraction and spreading

    PubMed Central

    Vernerey, Franck J.; Farsad, Mehdi

    2013-01-01

    Recent research has shown that cell spreading is highly dependent on the contractililty of its cytoskeleton and the mechanical properties of the environment it is located in. The dynamics of such process is critical for the development of tissue engineering strategy but is also a key player in wound contraction, tissue maintenance and angiogenesis. To better understand the underlying physics of such phenomena, the paper describes a mathematical formulation of cell spreading and contraction that couples the processes of stress fiber formation, protrusion growth through actin polymerization at the cell edge and dynamics of cross-membrane protein (integrins) enabling cell-substrate attachment. The evolving cell’s cytoskeleton is modeled as a mixture of fluid, proteins and filaments that can exchange mass and generate contraction. In particular, besides self-assembling into stress fibers, actin monomers able to polymerize into an actin meshwork at the cell’s boundary in order to push the membrane forward and generate protrusion. These processes are possible via the development of cell-substrate attachment complexes that arise from the mechano-sensitive equilibrium of membrane proteins, known as integrins. After deriving the governing equation driving the dynamics of cell evolution and spreading, we introduce a numerical solution based on the extended finite element method, combined with a level set formulation. Numerical simulations show that the proposed model is able to capture the dependency of cell spreading and contraction on substrate stiffness and chemistry. The very good agreement between model predictions and experimental observations suggests that mechanics plays a strong role into the coupled mechanisms of contraction, adhesion and spreading of adherent cells. PMID:23463540

  3. On mechanics and material length scales of failure in heterogeneous interfaces using a finite strain high performance solver

    NASA Astrophysics Data System (ADS)

    Mosby, Matthew; Matouš, Karel

    2015-12-01

    Three-dimensional simulations capable of resolving the large range of spatial scales, from the failure-zone thickness up to the size of the representative unit cell, in damage mechanics problems of particle reinforced adhesives are presented. We show that resolving this wide range of scales in complex three-dimensional heterogeneous morphologies is essential in order to apprehend fracture characteristics, such as strength, fracture toughness and shape of the softening profile. Moreover, we show that computations that resolve essential physical length scales capture the particle size-effect in fracture toughness, for example. In the vein of image-based computational materials science, we construct statistically optimal unit cells containing hundreds to thousands of particles. We show that these statistically representative unit cells are capable of capturing the first- and second-order probability functions of a given data-source with better accuracy than traditional inclusion packing techniques. In order to accomplish these large computations, we use a parallel multiscale cohesive formulation and extend it to finite strains including damage mechanics. The high-performance parallel computational framework is executed on up to 1024 processing cores. A mesh convergence and a representative unit cell study are performed. Quantifying the complex damage patterns in simulations consisting of tens of millions of computational cells and millions of highly nonlinear equations requires data-mining the parallel simulations, and we propose two damage metrics to quantify the damage patterns. A detailed study of volume fraction and filler size on the macroscopic traction-separation response of heterogeneous adhesives is presented.

  4. A Probabilistic-Micro-mechanical Methodology for Assessing Zirconium Alloy Cladding Failure

    SciTech Connect

    Pan, Y.M.; Chan, K.S.; Riha, D.S.

    2007-07-01

    Cladding failure of fuel rods caused by hydride-induced embrittlement is a reliability concern for spent nuclear fuel after extended burnup. Uncertainties in the cladding temperature, cladding stress, oxide layer thickness, and the critical stress value for hydride reorientation preclude an assessment of the cladding failure risk. A set of micro-mechanical models for treating oxide cracking, blister cracking, delayed hydride cracking, and cladding fracture was developed and incorporated in a computer model. Results obtained from the preliminary model calculations indicate that at temperatures below a critical temperature of 318.5 deg. C [605.3 deg. F], the time to failure by delayed hydride cracking in Zr-2.5%Nb decreased with increasing cladding temperature. The overall goal of this project is to develop a probabilistic-micro-mechanical methodology for assessing the probability of hydride-induced failure in Zircaloy cladding and thereby establish performance criteria. (authors)

  5. Fibrillar Adhesive for Climbing Robots

    NASA Technical Reports Server (NTRS)

    Pamess, Aaron; White, Victor E.

    2013-01-01

    A climbing robot needs to use its adhesive patches over and over again as it scales a slope. Replacing the adhesive at each step is generally impractical. If the adhesive or attachment mechanism cannot be used repeatedly, then the robot must carry an extra load of this adhesive to apply a fresh layer with each move. Common failure modes include tearing, contamination by dirt, plastic deformation of fibers, and damage from loading/ unloading. A gecko-like fibrillar adhesive has been developed that has been shown useful for climbing robots, and may later prove useful for grasping, anchoring, and medical applications. The material consists of a hierarchical fibrillar structure that currently contains two levels, but may be extended to three or four levels in continuing work. The contacting level has tens of thousands of microscopic fibers made from a rubberlike material that bend over and create intimate contact with a surface to achieve maximum van der Waals forces. By maximizing the real area of contact that these fibers make and minimizing the bending energy necessary to achieve that contact, the net amount of adhesion has been improved dramatically.

  6. Interface failure modes explain non-monotonic size-dependent mechanical properties in bioinspired nanolaminates.

    PubMed

    Song, Z Q; Ni, Y; Peng, L M; Liang, H Y; He, L H

    2016-01-01

    Bioinspired discontinuous nanolaminate design becomes an efficient way to mitigate the strength-ductility tradeoff in brittle materials via arresting the crack at the interface followed by controllable interface failure. The analytical solution and numerical simulation based on the nonlinear shear-lag model indicates that propagation of the interface failure can be unstable or stable when the interfacial shear stress between laminae is uniform or highly localized, respectively. A dimensionless key parameter defined by the ratio of two characteristic lengths governs the transition between the two interface-failure modes, which can explain the non-monotonic size-dependent mechanical properties observed in various laminate composites. PMID:27029955

  7. Interface failure modes explain non-monotonic size-dependent mechanical properties in bioinspired nanolaminates

    NASA Astrophysics Data System (ADS)

    Song, Z. Q.; Ni, Y.; Peng, L. M.; Liang, H. Y.; He, L. H.

    2016-03-01

    Bioinspired discontinuous nanolaminate design becomes an efficient way to mitigate the strength-ductility tradeoff in brittle materials via arresting the crack at the interface followed by controllable interface failure. The analytical solution and numerical simulation based on the nonlinear shear-lag model indicates that propagation of the interface failure can be unstable or stable when the interfacial shear stress between laminae is uniform or highly localized, respectively. A dimensionless key parameter defined by the ratio of two characteristic lengths governs the transition between the two interface-failure modes, which can explain the non-monotonic size-dependent mechanical properties observed in various laminate composites.

  8. Development Testing and Subsequent Failure Investigation of a Spring Strut Mechanism

    NASA Technical Reports Server (NTRS)

    Dervan, Jared; Robertson, Brandan; Staab, Lucas; Culberson, Michael; Pellicciotti, Joseph

    2014-01-01

    The NASA Engineering and Safety Center (NESC) and Lockheed Martin (LM) performed random vibration testing on a single spring strut development unit to assess its ability to withstand qualification level random vibration environments. Failure of the strut while exposed to random vibration resulted in a follow-on failure investigation, design changes, and additional development tests. This paper focuses on the results of the failure investigations referenced in detail in the NESC final report [1] including identified lessons learned to aid in future design iterations of the spring strut and to help other mechanism developers avoid similar pitfalls.

  9. Development Testing and Subsequent Failure Investigation of a Spring Strut Mechanism

    NASA Technical Reports Server (NTRS)

    Dervan, Jared; Robertson, Brandon; Staab, Lucas; Culberson, Michael; Pellicciotti, Joseph

    2014-01-01

    The NASA Engineering and Safety Center (NESC) and Lockheed Martin (LM) performed random vibration testing on a single spring strut development unit to assess its ability to withstand qualification level random vibration environments. Failure of the strut while exposed to random vibration resulted in a follow-on failure investigation, design changes, and additional development tests. This paper focuses on the results of the failure investigations referenced in detail in the NESC final report including identified lessons learned to aid in future design iterations of the spring strut and to help other mechanism developers avoid similar pitfalls.

  10. Interface failure modes explain non-monotonic size-dependent mechanical properties in bioinspired nanolaminates

    PubMed Central

    Song, Z. Q.; Ni, Y.; Peng, L. M.; Liang, H. Y.; He, L. H.

    2016-01-01

    Bioinspired discontinuous nanolaminate design becomes an efficient way to mitigate the strength-ductility tradeoff in brittle materials via arresting the crack at the interface followed by controllable interface failure. The analytical solution and numerical simulation based on the nonlinear shear-lag model indicates that propagation of the interface failure can be unstable or stable when the interfacial shear stress between laminae is uniform or highly localized, respectively. A dimensionless key parameter defined by the ratio of two characteristic lengths governs the transition between the two interface-failure modes, which can explain the non-monotonic size-dependent mechanical properties observed in various laminate composites. PMID:27029955

  11. An adhesive contact mechanics formulation based on atomistically induced surface traction

    NASA Astrophysics Data System (ADS)

    Fan, Houfu; Ren, Bo; Li, Shaofan

    2015-12-01

    In this work, we have developed a novel multiscale computational contact formulation based on the generalized Derjuguin approximation for continua that are characterized by atomistically enriched constitutive relations in order to study macroscopic interaction between arbitrarily shaped deformable continua. The proposed adhesive contact formulation makes use of the microscopic interaction forces between individual particles in the interacting bodies. In particular, the double-layer volume integral describing the contact interaction (energy, force vector, matrix) is converted into a double-layer surface integral through a mathematically consistent approach that employs the divergence theorem and a special partitioning technique. The proposed contact model is formulated in the nonlinear continuum mechanics framework and implemented using the standard finite element method. With no large penalty constant, the stiffness matrix of the system will in general be well-conditioned, which is of great significance for quasi-static analysis. Three numerical examples are presented to illustrate the capability of the proposed method. Results indicate that with the same mesh configuration, the finite element computation based on the surface integral approach is faster and more accurate than the volume integral based approach. In addition, the proposed approach is energy preserving even in a very long dynamic simulation.

  12. Personal electronics printing via tapping mode composite liquid metal ink delivery and adhesion mechanism.

    PubMed

    Zheng, Yi; He, Zhi-Zhu; Yang, Jun; Liu, Jing

    2014-01-01

    Printed electronics is becoming increasingly important in a variety of newly emerging areas. However, restricted to the rather limited conductive inks and available printing strategies, the current electronics manufacture is usually confined to industry level. Here, we show a highly cost-effective and entirely automatic printing way towards personal electronics making, through introducing a tapping-mode composite fluid delivery system. Fundamental mechanisms regarding the reliable printing, transfer and adhesion of the liquid metal inks on the substrate were disclosed through systematic theoretical interpretation and experimental measurements. With this liquid metal printer, a series of representative electronic patterns spanning from single wires to desired complex configurations such as integrated circuit (IC), printed-circuits-on-board (PCB), electronic paintings, or more do-it-yourself (DIY) devices, were demonstrated to be printed out with high precision in a moment. And the total machine cost already reached personally affordable price. This is hard to achieve by a conventional PCB technology which generally takes long time and is material, water and energy consuming, while the existing printed electronics is still far away from the real direct printing goal. The present work opens the way for large scale personal electronics manufacture and is expected to generate important value for the coming society. PMID:24699375

  13. Personal electronics printing via tapping mode composite liquid metal ink delivery and adhesion mechanism

    NASA Astrophysics Data System (ADS)

    Zheng, Yi; He, Zhi-Zhu; Yang, Jun; Liu, Jing

    2014-04-01

    Printed electronics is becoming increasingly important in a variety of newly emerging areas. However, restricted to the rather limited conductive inks and available printing strategies, the current electronics manufacture is usually confined to industry level. Here, we show a highly cost-effective and entirely automatic printing way towards personal electronics making, through introducing a tapping-mode composite fluid delivery system. Fundamental mechanisms regarding the reliable printing, transfer and adhesion of the liquid metal inks on the substrate were disclosed through systematic theoretical interpretation and experimental measurements. With this liquid metal printer, a series of representative electronic patterns spanning from single wires to desired complex configurations such as integrated circuit (IC), printed-circuits-on-board (PCB), electronic paintings, or more do-it-yourself (DIY) devices, were demonstrated to be printed out with high precision in a moment. And the total machine cost already reached personally affordable price. This is hard to achieve by a conventional PCB technology which generally takes long time and is material, water and energy consuming, while the existing printed electronics is still far away from the real direct printing goal. The present work opens the way for large scale personal electronics manufacture and is expected to generate important value for the coming society.

  14. Personal electronics printing via tapping mode composite liquid metal ink delivery and adhesion mechanism

    PubMed Central

    Zheng, Yi; He, Zhi-Zhu; Yang, Jun; Liu, Jing

    2014-01-01

    Printed electronics is becoming increasingly important in a variety of newly emerging areas. However, restricted to the rather limited conductive inks and available printing strategies, the current electronics manufacture is usually confined to industry level. Here, we show a highly cost-effective and entirely automatic printing way towards personal electronics making, through introducing a tapping-mode composite fluid delivery system. Fundamental mechanisms regarding the reliable printing, transfer and adhesion of the liquid metal inks on the substrate were disclosed through systematic theoretical interpretation and experimental measurements. With this liquid metal printer, a series of representative electronic patterns spanning from single wires to desired complex configurations such as integrated circuit (IC), printed-circuits-on-board (PCB), electronic paintings, or more do-it-yourself (DIY) devices, were demonstrated to be printed out with high precision in a moment. And the total machine cost already reached personally affordable price. This is hard to achieve by a conventional PCB technology which generally takes long time and is material, water and energy consuming, while the existing printed electronics is still far away from the real direct printing goal. The present work opens the way for large scale personal electronics manufacture and is expected to generate important value for the coming society. PMID:24699375

  15. New functions and signaling mechanisms for the class of adhesion G protein–coupled receptors

    PubMed Central

    Liebscher, Ines; Ackley, Brian; Araç, Demet; Ariestanti, Donna M.; Aust, Gabriela; Bae, Byoung-il; Bista, Bigyan R.; Bridges, James P.; Duman, Joseph G.; Engel, Felix B.; Giera, Stefanie; Goffinet, André M.; Hall, Randy A.; Hamann, Jörg; Hartmann, Nicole; Lin, Hsi-Hsien; Liu, Mingyao; Luo, Rong; Mogha, Amit; Monk, Kelly R.; Peeters, Miriam C.; Prömel, Simone; Ressl, Susanne; Schiöth, Helgi B.; Sigoillot, Séverine M.; Song, Helen; Talbot, William S.; Tall, Gregory G.; White, James P.; Wolfrum, Uwe; Xu, Lei; Piao, Xianhua

    2014-01-01

    The class of adhesion G protein–coupled receptors (aGPCRs), with 33 human homologs, is the second largest family of GPCRs. In addition to a seven-transmembrane α-helix—a structural feature of all GPCRs—the class of aGPCRs is characterized by the presence of a large N-terminal extracellular region. In addition, all aGPCRs but one (GPR123) contain a GPCR autoproteolysis–inducing (GAIN) domain that mediates autoproteolytic cleavage at the GPCR autoproteolysis site (GPS) motif to generate N- and a C-terminal fragments (NTF and CTF, respectively) during protein maturation. Subsequently, the NTF and CTF are associated non-covalently as a heterodimer at the plasma membrane. While the biological function of the GAIN domain–mediated autocleavage is not fully understood, mounting evidence suggests that the NTF and CTF possess distinct biological activities in addition to their function as a receptor unit. We discuss recent advances in understanding the biological functions, signaling mechanisms, and disease associations of the aGPCRs. PMID:25424900

  16. An autonomous recovery mechanism against optical distribution network failures in EPON

    NASA Astrophysics Data System (ADS)

    Liem, Andrew Tanny; Hwang, I.-Shyan; Nikoukar, AliAkbar

    2014-10-01

    Ethernet Passive Optical Network (EPON) is chosen for servicing diverse applications with higher bandwidth and Quality-of-Service (QoS), starting from Fiber-To-The-Home (FTTH), FTTB (business/building) and FTTO (office). Typically, a single OLT can provide services to both residential and business customers on the same Optical Line Terminal (OLT) port; thus, any failures in the system will cause a great loss for both network operators and customers. Network operators are looking for low-cost and high service availability mechanisms that focus on the failures that occur within the drop fiber section because the majority of faults are in this particular section. Therefore, in this paper, we propose an autonomous recovery mechanism that provides protection and recovery against Drop Distribution Fiber (DDF) link faults or transceiver failure at the ONU(s) in EPON systems. In the proposed mechanism, the ONU can automatically detect any signal anomalies in the physical layer or transceiver failure, switching the working line to the protection line and sending the critical event alarm to OLT via its neighbor. Each ONU has a protection line, which is connected to the nearest neighbor ONU, and therefore, when failure occurs, the ONU can still transmit and receive data via the neighbor ONU. Lastly, the Fault Dynamic Bandwidth Allocation for recovery mechanism is presented. Simulation results show that our proposed autonomous recovery mechanism is able to maintain the overall QoS performance in terms of mean packet delay, system throughput, packet loss and EF jitter.

  17. Exertional dyspnoea in chronic heart failure: the role of the lung and respiratory mechanical factors.

    PubMed

    Dubé, Bruno-Pierre; Agostoni, Piergiuseppe; Laveneziana, Pierantonio

    2016-09-01

    Exertional dyspnoea is among the dominant symptoms in patients with chronic heart failure and progresses relentlessly as the disease advances, leading to reduced ability to function and engage in activities of daily living. Effective management of this disabling symptom awaits a better understanding of its underlying physiology.Cardiovascular factors are believed to play a major role in dyspnoea in heart failure patients. However, despite pharmacological interventions, such as vasodilators or inotropes that improve central haemodynamics, patients with heart failure still complain of exertional dyspnoea. Clearly, dyspnoea is not determined by cardiac factors alone, but likely depends on complex, integrated cardio-pulmonary interactions.A growing body of evidence suggests that excessively increased ventilatory demand and abnormal "restrictive" constraints on tidal volume expansion with development of critical mechanical limitation of ventilation, contribute to exertional dyspnoea in heart failure. This article will offer new insights into the pathophysiological mechanisms of exertional dyspnoea in patients with chronic heart failure by exploring the potential role of the various constituents of the physiological response to exercise and particularly the role of abnormal ventilatory and respiratory mechanics responses to exercise in the perception of dyspnoea in patients with heart failure. PMID:27581831

  18. Evidence of an emerging levee failure mechanism causing disastrous floods in Italy

    NASA Astrophysics Data System (ADS)

    Orlandini, Stefano; Moretti, Giovanni; Albertson, John D.

    2015-10-01

    A levee failure occurred along the Secchia River, Northern Italy, on 19 January 2014, resulting in flood damage in excess of $500 million. In response to this failure, immediate surveillance of other levees in the region led to the identification of a second breach developing on the neighboring Panaro River, where rapid mitigation efforts were successful in averting a full levee failure. The paired breach events that occurred along the Secchia and Panaro Rivers provided an excellent window on an emerging levee failure mechanism. In the Secchia River, by combining the information content of photographs taken from helicopters in the early stage of breach development and 10 cm resolution aerial photographs taken in 2010 and 2012, animal burrows were found to exist in the precise levee location where the breach originated. In the Panaro River, internal erosion was observed to occur at a location where a crested porcupine den was known to exist and this erosion led to the collapse of the levee top. This paper uses detailed numerical modeling of rainfall, river flow, and variably saturated flow in the levee to explore the hydraulic and geotechnical mechanisms that were triggered along the Secchia and Panaro Rivers by activities of burrowing animals leading to levee failures. As habitats become more fragmented and constrained along river corridors, it is possible that this failure mechanism could become more prevalent and, therefore, will demand greater attention in both the design and maintenance of earthen hydraulic structures as well as in wildlife management.

  19. Influence of Martensite Mechanical Properties on Failure Mode and Ductility of Dual Phase Steels

    SciTech Connect

    Choi, Kyoo Sil; Liu, Wenning N.; Sun, Xin; Khaleel, Mohammad A.

    2009-04-01

    In this paper, the effects of the mechanical properties of the martensite phase on the failure mode and ductility of dual phase (DP) steels are investigated using a micromechanics-based finite element method. Actual microstructures of DP sheet steels obtained from scanning electron microscopy are used as representative volume element (RVE) in two-dimensional plane-stress finite element calculations. Failure is predicted as plastic strain localization in the RVE during deformation. The mechanical properties of the ferrite and martensite phases in a commercial DP 980 steel are obtained based on the in-situ X-ray diffraction measurements of a uniaxial tensile test. Computations are then conducted on the RVE in order to investigate the influence of the martensite mechanical properties and volume fraction on the macroscopic behavior and failure mode of DP steels. The computations show that, as the strength and volume fraction of the martensite phase increase, the ultimate tensile strength (UTS) of DP steels increases but the UTS strain and failure strain decrease. These results agree well with the general experimental observations on DP steels. Additionally, shear dominant failure modes usually develop for DP steels with lower martensite strengths, whereas split failure modes typically develop for DP steels with higher martensite strengths.

  20. Molecular mechanisms underlying the force-dependent regulation of actin-to-ECM linkage at the focal adhesions.

    PubMed

    Hirata, Hiroaki; Sokabe, Masahiro; Lim, Chwee Teck

    2014-01-01

    The linkage of the actin cytoskeleton to extracellular matrices (ECMs) at focal adhesions provides a physical path for cells to exert traction forces on substrates during cellular processes such as migration and morphogenesis. Mechanical strength of the actin-to-ECM linkage increases in response to forces loaded at this linkage. This is achieved by local accumulations of actin filaments, as well as linker proteins connecting actins to integrins, at force-bearing adhesion sites, which leads to an increase in the number of molecular bonds between the actin cytoskeleton- and ECM-bound integrins. Zyxin-dependent actin polymerization and filamin-mediated actin bundling are seemingly involved in the force-dependent actin accumulation. Each actin-integrin link is primarily mediated by the linker protein talin, which is strengthened by another linker protein vinculin connecting the actin filaments to talin in a force-dependent manner. This eliminates slippage between the actin cytoskeleton and talin (clutch mechanism), thus playing a crucial role in creating cell membrane protrusions mediated by actin polymerization. Finally, each integrin-ECM bond is also strengthened when a force is loaded on it, which ensures force transmission at focal adhesions, contributing to stable cell-substrate adhesion in cell migration. PMID:25081617

  1. Hic-5 mediates TGFβ-induced adhesion in vascular smooth muscle cells by a Nox4-dependent mechanism

    PubMed Central

    Fernandez, Isabel; Martin-Garrido, Abel; Zhou, Dennis W.; Clempus, Roza E.; Seidel-Rogol, Bonnie; Valdivia, Alejandra; Lassègue, Bernard; García, Andrés J.; Griendling, Kathy K.; Martin, Alejandra San

    2015-01-01

    Objective Focal adhesions (FAs) link the cytoskeleton to the extracellular matrix and as such play important roles in growth, migration and contractile properties of vascular smooth muscle cells (VSMCs). Recently, it has been shown that downregulation of Nox4, a transforming growth factor beta (TGFβ)-inducible, H2O2-producing enzyme, affects the number of FAs. However, the effectors downstream of Nox4 that mediate FA regulation are unknown. The FA resident protein hydrogen peroxide-inducible clone-5 (Hic-5) is H2O2- and TGFβ-inducible, and a binding partner of the heat shock protein (Hsp)27. The objective of this study was to elucidate the mechanism by which Hic-5 and Hsp27 participate in TGFβ-induced, Nox4-mediated VSMC adhesion and migration. Approach and Results Through a combination of molecular biology and biochemistry techniques, we found that TGFβ, by a Nox4-dependent mechanism, induces the expression and interaction of Hic-5 and Hsp27, which is essential for Hic-5 localization to FAs. Importantly, we found that Hic-5 expression is required for the TGFβ-mediated increase in FA number, and adhesive forces and migration. Mechanistically, Nox4 downregulation impedes Smad signaling by TGFβ, and Hsp27 and Hic-5 upregulation by TGFβ is blocked in Smad4-deficient cells. Conclusions Hic-5 and Hsp27 are effectors of Nox4 required for TGFβ-stimulated FA formation and adhesion strength and migration in VSMC. PMID:25814672

  2. Investigating Deformation and Failure Mechanisms in Nanoscale Multilayer Metallic Composites

    SciTech Connect

    Zbib, Hussein M; Bahr, David F

    2014-10-22

    Over the history of materials science there are many examples of materials discoveries that have made superlative materials; the strongest, lightest, or toughest material is almost always a goal when we invent new materials. However, often these have been a result of enormous trial and error approaches. A new methodology, one in which researchers design, from the atoms up, new ultra-strong materials for use in energy applications, is taking hold within the science and engineering community. This project focused on one particular new classification of materials; nanolaminate metallic composites. These materials, where two metallic materials are intimately bonded and layered over and over to form sheets or coatings, have been shown over the past decade to reach strengths over 10 times that of their constituents. However, they are not yet widely used in part because while extremely strong (they don’t permanently bend), they are also not particularly tough (they break relatively easily when notched). Our program took a coupled approach to investigating new materials systems within the laminate field. We used computational materials science to explore ways to institute new deformation mechanisms that occurred when a tri-layer, rather than the more common bi-layer system was created. Our predictions suggested that copper-nickel or copper-niobium composites (two very common bi-layer systems) with layer thicknesses on the order of 20 nm and then layered 100’s of times, would be less tough than a copper-nickel-niobium metallic composite of similar thicknesses. In particular, a particular mode of permanent deformation, cross-slip, could be activated only in the tri-layer system; the crystal structure of the other bi-layers would prohibit this particular mode of deformation. We then experimentally validated this predication using a wide range of tools. We utilized a DOE user facility, the Center for Integrated Nanotechnology (CINT), to fabricate, for the first time, these

  3. Internal instability as a possible failure mechanism for layered composites.

    PubMed

    Guz, I A; Menshykova, M; Soutis, C

    2016-07-13

    This paper revisits a three-dimensional analytical approach to study internal instability in layered composites, when the behaviour of each component of the material is described by the three-dimensional equations of solid mechanics. It shows the development of a unified computational procedure for numerical realization of the three-dimensional analytical method as applied to various constitutive equations of the layers and fibres, and different loading schemes (uniaxial or biaxial loading). The paper also contains many examples of calculation of critical controlled parameters for particular composites as well as analysis of different buckling modes. The results of this method can be used as a benchmark for simplified models. This article is part of the themed issue 'Multiscale modelling of the structural integrity of composite materials'. PMID:27242292

  4. Acoustic emission classification for failure prediction due to mechanical fatigue

    NASA Astrophysics Data System (ADS)

    Emamian, Vahid; Kaveh, Mostafa; Tewfik, Ahmed H.

    2000-06-01

    Acoustic Emission signals (AE), generated by the formation and growth of micro-cracks in metal components, have the potential for use in mechanical fault detection in monitoring complex- shaped components in machinery including helicopters and aircraft. A major challenge for an AE-based fault detection algorithm is to distinguish crack-related AE signals from other interfering transient signals, such as fretting-related AE signals and electromagnetic transients. Although under a controlled laboratory environment we have fewer interference sources, there are other undesired sources which have to be considered. In this paper, we present some methods, which make their decision based on the features extracted from time-delay and joint time-frequency components by means of a Self- Organizing Map (SOM) neural network using experimental data collected in a laboratory by colleagues at the Georgia Institute of Technology.

  5. Regulation of T-lymphocyte motility, adhesion and de-adhesion by a cell surface mechanism directed by low density lipoprotein receptor-related protein 1 and endogenous thrombospondin-1

    PubMed Central

    Talme, Toomas; Bergdahl, Eva; Sundqvist, Karl-Gösta

    2014-01-01

    T lymphocytes are highly motile and constantly reposition themselves between a free-floating vascular state, transient adhesion and migration in tissues. The regulation behind this unique dynamic behaviour remains unclear. Here we show that T cells have a cell surface mechanism for integrated regulation of motility and adhesion and that integrin ligands and CXCL12/SDF-1 influence motility and adhesion through this mechanism. Targeting cell surface-expressed low-density lipoprotein receptor-related protein 1 (LRP1) with an antibody, or blocking transport of LRP1 to the cell surface, perturbed the cell surface distribution of endogenous thrombospondin-1 (TSP-1) while inhibiting motility and potentiating cytoplasmic spreading on intercellular adhesion molecule 1 (ICAM-1) and fibronectin. Integrin ligands and CXCL12 stimulated motility and enhanced cell surface expression of LRP1, intact TSP-1 and a 130 000 MW TSP-1 fragment while preventing formation of a de-adhesion-coupled 110 000 MW TSP-1 fragment. The appearance of the 130 000 MW TSP-1 fragment was inhibited by the antibody that targeted LRP1 expression, inhibited motility and enhanced spreading. The TSP-1 binding site in the LRP1-associated protein, calreticulin, stimulated adhesion to ICAM-1 through intact TSP-1 and CD47. Shear flow enhanced cell surface expression of intact TSP-1. Hence, chemokines and integrin ligands up-regulate a dominant motogenic pathway through LRP1 and TSP-1 cleavage and activate an associated adhesion pathway through the LRP1–calreticulin complex, intact TSP-1 and CD47. This regulation of T-cell motility and adhesion makes pro-adhesive stimuli favour motile responses, which may explain why T cells prioritize movement before permanent adhesion. PMID:24877199

  6. Influence of metabolic dysfunction on cardiac mechanics in decompensated hypertrophy and heart failure.

    PubMed

    Tewari, Shivendra G; Bugenhagen, Scott M; Vinnakota, Kalyan C; Rice, J Jeremy; Janssen, Paul M L; Beard, Daniel A

    2016-05-01

    Alterations in energetic state of the myocardium are associated with decompensated heart failure in humans and in animal models. However, the functional consequences of the observed changes in energetic state on mechanical function are not known. The primary aim of the study was to quantify mechanical/energetic coupling in the heart and to determine if energetic dysfunction can contribute to mechanical failure. A secondary aim was to apply a quantitative systems pharmacology analysis to investigate the effects of drugs that target cross-bridge cycling kinetics in heart failure-associated energetic dysfunction. Herein, a model of metabolite- and calcium-dependent myocardial mechanics was developed from calcium concentration and tension time courses in rat cardiac muscle obtained at different lengths and stimulation frequencies. The muscle dynamics model accounting for the effect of metabolites was integrated into a model of the cardiac ventricles to simulate pressure-volume dynamics in the heart. This cardiac model was integrated into a simple model of the circulation to investigate the effects of metabolic state on whole-body function. Simulations predict that reductions in metabolite pools observed in canine models of heart failure can cause systolic dysfunction, blood volume expansion, venous congestion, and ventricular dilation. Simulations also predict that myosin-activating drugs may partially counteract the effects of energetic state on cross-bridge mechanics in heart failure while increasing myocardial oxygen consumption. Our model analysis demonstrates how metabolic changes observed in heart failure are alone sufficient to cause systolic dysfunction and whole-body heart failure symptoms. PMID:27085901

  7. Conditions and possible mechanisms of VCD-induced ovarian failure.

    PubMed

    Liu, Wei; Wang, Ling-Yan; Xing, Xiao-Xue; Fan, Guan-Wei

    2015-12-01

    Perimenopause is an important period in women's lives, in which they experience a series of physiological changes. Current animal models of perimenopause fail to adequately replicate this particular stage in female life, while current in vitro models are too simplistic and cannot account for systemic effects. Neither the naturally-ageing animal model, nor the ovariectomised animal model, mimic the natural transitional process that is the menopause. In vivo and in vitro studies have confirmed that the occupational chemical, 4-vinylcyclohexene diepoxide (VCD), can cause selective destruction of the ovarian primordial and primary follicles of rats and mice by accelerating the apoptotic process, which successfully mimics the perimenopausal state in women. However, it is the in vivo VCD-induced rodent perimenopausal models that are currently the most widely used in research, rather than any of the available in vitro models. Studies on the mechanisms involved have found that VCD induces ovotoxicity via interference with the c-kit/kit ligand and apoptotic signalling pathways, among others. Overall, the VCD-induced perimenopausal animal models have provided some insight into female perimenopause, but they are far from ideal models of the human situation. PMID:26753941

  8. Molecular mechanisms of deformation and failure in glassy materials

    NASA Astrophysics Data System (ADS)

    Rottler, Joerg

    2004-03-01

    Understanding the molecular origins of macroscopic mechanical properties is a fundamental scientific challenge. Fracture of both amorphous and crystalline materials involves many length scales reaching from the continuum to atomic level processes near a crack tip. Using molecular simulations of simple models for amorphous glassy materials, we first study elastoplastic deformation and discuss the nature of the shear yield stress and its dependence on loading conditions, strain rate and temperature. We then focus on the deformation of glassy polymeric systems into crazes at large strains. In the craze, polymers ( 0.5 nm diameter) are bundled into an intricate network of 10 nm diameter fibrils that extends 10 micrometers on either side of a mm crack tip. Analysis of local geometry and stresses provide insight into the real-space nature of the entanglements that control craze formation as well as melt dynamics. Crazes are also shown to share many features with jammed systems such as granular media and foams, but are unique in jamming under a tensile load. This allows explanations for the exponential force distribution in jammed systems to be tested. The force distribution strongly influences the ultimate breakdown of the craze fibrils either through disentanglement or chain scission. We conclude by quantifying the contribution of crazing to the unusually large fracture energy of glassy polymers.

  9. A fundamental approach to adhesion: Synthesis, surface analysis, thermodynamics and mechanics

    NASA Technical Reports Server (NTRS)

    Chen, W.; Wightman, J. P.

    1979-01-01

    Adherend surfaces and fractography were studied using electron spectroscopy for chemical analysis and scanning electron microscopy/energy dispersive analysis of X-rays. In addition, Auger Electron Spectroscopy with depth profiling capability was used. It is shown that contamination of adhesion systems plays an important role not only in determining initial bond strengths but also in the durability of adhesive bonds. It is concluded that the analytical techniques used to characterize and monitor such contamination.

  10. Experimental and computational models to investigate the effect of adhesion on the mechanical properties of bone-cement composites.

    PubMed

    Helgason, B; Stirnimann, P; Widmer, R; Ferguson, S J

    2011-10-01

    A generic finite element approach was developed to study the effect of adhesion on the mechanical response of bone cement composites and validated against literature data. The results showed that a zero friction bone-cement (PMMA) interface conditions captured the results of the experimental testing better than assuming a fully bonded interface. An experimental model for studying the effect of interface adhesion in a bone-cement like composite was also developed in the present study. The results using this model indicate that the difference in Young's modulus and ultimate strength between a fully bonded interface and unbonded interface is approximately 30% for bone volume fraction similar to what can be found in osteoporotic vertebrae. Apart from concluding that bone to cement adhesion is a major contributor to the mechanical response of bone-cement composites, our studies based on the generic FE approach also indicate that the mechanical properties of the cement is the most important contributor to the resulting mechanical properties of the composite at bone volume fraction relevant in terms of vertebroplasty treatment. PMID:21714083

  11. Mechanical failure modes of chronically implanted planar silicon-based neural probes for laminar recording

    PubMed Central

    Kozai, Takashi D. Y.; Catt, Kasey; Li, Xia; Gugel, Zhannetta V.; Olafsson, Valur T.; Vazquez, Alberto L.; Cui, X. Tracy

    2014-01-01

    Penetrating intracortical electrode arrays that record brain activity longitudinally are powerful tools for basic neuroscience research and emerging clinical applications. However, regardless of the technology used, signals recorded by these electrodes degrade over time. The failure mechanisms of these electrodes are understood to be a complex combination of the biological reactive tissue response and material failure of the device over time. While mechanical mismatch between the brain tissue and implanted neural electrodes have been studied as a source of chronic inflammation and performance degradation, the electrode failure caused by mechanical mismatch between different material properties and different structural components within a device have remained poorly characterized. Using Finite Element Model (FEM) we simulate the mechanical strain on a planar silicon electrode. The results presented here demonstrate that mechanical mismatch between iridium and silicon leads to concentrated strain along the border of the two materials. This strain is further focused on small protrusions such as the electrical traces in planar silicon electrodes. These findings are confirmed with chronic in vivo data (133–189 days) in mice by correlating a combination of single-unit electrophysiology, evoked multi-unit recordings, electrochemical impedance spectroscopy, and scanning electron microscopy from traces and electrode sites with our modeling data. Several modes of mechanical failure of chronically implanted planar silicon electrodes are found that result in degradation and/or loss of recording. These findings highlight the importance of strains and material properties of various subcomponents within an electrode array. PMID:25453935

  12. Nitric oxide regulates human eosinophil adhesion mechanisms in vitro by changing integrin expression and activity on the eosinophil cell surface

    PubMed Central

    Conran, N; Ferreira, H H A; Lorand-Metze, I; Thomazzi, S M; Antunes, E; de Nucci, G

    2001-01-01

    The nitric oxide synthase (NOS) inhibitor, Nω-nitro-L-arginine methyl ester (L-NAME), inhibits both rat and human eosinophil chemotaxis in vitro. Here, the role of nitric oxide (NO) in human eosinophil cell surface integrin expression and function was investigated. Human peripheral blood eosinophils were treated with L-NAME (0.01 – 1.0 mM) and their adhesion to human fibronectin and serum observed. Adhesion of cells to fibronectin and serum increased by 24.0±4.6 and 43.8±4.7%, respectively, when eosinophils were treated with 1.0 mM L-NAME. Increased adhesion by L-NAME could be abolished when cells were co-incubated with VLA-4- and Mac-1-specific monoclonal antibodies (mAbs). The NO donor, sodium nitroprusside (2.5 mM), significantly inhibited eosinophil adhesion to fibronectin and serum by 34.3±4.5 and 45.2±5.6%, respectively. This inhibition was accompanied by a 4 fold increase in the levels of intracellular cyclic GMP. Flow cytometrical analysis demonstrated that L-NAME induced an increased expression of CD11b (Mac-1) on the eosinophil cell surface of 36.3±7.4%. L-NAME had no effect upon CD49d (VLA-4) expression. Treatment of human eosinophils, in vitro, with H-[1,2,4] oxadiazolo quinoxalin-1-one (ODQ) (0.1 mM), an inhibitor of soluble guanylate cyclase, also significantly increased eosinophil adhesion to fibronectin and serum by 73.5±17.9 and 91.7±12.9%, respectively. This increase in adhesion could also be inhibited by co-incubation with the Mac-1 and VLA-4-specific mAbs. In conclusion, results indicate that NO, via a cyclic GMP-dependent mechanism, inhibits the adhesion of human eosinophils to the extracellular matrix (ECM). This inhibition is accompanied by a decrease in the expression and function of the eosinophil's adhesion molecules, in particular, the expression of the Mac-1 integrin and the function of the VLA-4 integrin. PMID:11588118

  13. Effect of current reversal on the failure mechanism of Al-Cu-Si narrow interconnects

    NASA Astrophysics Data System (ADS)

    Kim, Choong-Un; Kang, S. H.; Morris, J. W.

    1996-02-01

    The work reported here concerns the effect of a brief exposure to a reversed current on the electromigration failure of narrow Al-Cu thin-film conducting lines. While the precise mechanism by which Cu retards electromigration in AlCu alloys is not fully understood, the consistent observation that electromigration failure is preceded by the sweeping of Cu from the failure site can be used to improve electromigration resistance by stabilizing the distribution of Cu. One way of doing this is to expose the Al-Cu line to a reverse current for some period of time. The present work shows that this method is particularly effective in thin lines with “quasi-bamboo” microstructures. It has the effect of building a reservoir of Cu at the upstream ends of the polygranular segments that are the preferred failure sites, and significantly increases both the mean time to failure, and the time to first failure of a distribution of lines. It can be inferred from these results that Al-Cu lines that conduct alternating current should be exceptionally resistant to electromigration failure.

  14. Modeling the Progressive Failure of Jointed Rock Slope Using Fracture Mechanics and the Strength Reduction Method

    NASA Astrophysics Data System (ADS)

    Zhang, Ke; Cao, Ping; Meng, Jingjing; Li, Kaihui; Fan, Wenchen

    2015-03-01

    The fracturing process during the progressive failure of a jointed rock slope is numerically investigated by using fracture mechanics and the strength reduction method (SRM). A displacement discontinuity method containing frictional elements is developed for the calculation of the stress intensity factor (SIF). The failure initiation of the jointed rock slope is analyzed by evaluating the SIF. A new joint model is proposed by combining solid elements with interface elements in the commercial software FLAC3D. These represent the discontinuous planes in a rock mass on which sliding or separation can occur. The progressive failure process is simulated by reducing the shear strength of the rock mass, which includes the process of stress concentration, crack initiation, crack propagation, slip weakening, and coalescence of failure surfaces. The factor of safety (FS) and location of the critical failure surface are determined by the SRM. The influence of the joint inclination is investigated using the FS and the SIF. Laboratory experiments on specimens containing an inclined flaw under compression-shear stress are also conducted to investigate the effect of the angle between the shear direction and the flaw inclination, which provides an experimental explanation for the shear behavior of jointed rock. The results show that the joint inclination dominates the failure behavior of jointed rock slope, and two failure patterns have been classified.

  15. Li-ion Battery Separators, Mechanical Integrity and Failure Mechanisms Leading to Soft and Hard Internal Shorts.

    PubMed

    Zhang, Xiaowei; Sahraei, Elham; Wang, Kai

    2016-01-01

    Separator integrity is an important factor in preventing internal short circuit in lithium-ion batteries. Local penetration tests (nail or conical punch) often produce presumably sporadic results, where in exactly similar cell and test set-ups one cell goes to thermal runaway while the other shows minimal reactions. We conducted an experimental study of the separators under mechanical loading, and discovered two distinct deformation and failure mechanisms, which could explain the difference in short circuit characteristics of otherwise similar tests. Additionally, by investigation of failure modes, we provided a hypothesis about the process of formation of local "soft short circuits" in cells with undetectable failure. Finally, we proposed a criterion for predicting onset of soft short from experimental data. PMID:27581185

  16. Li-ion Battery Separators, Mechanical Integrity and Failure Mechanisms Leading to Soft and Hard Internal Shorts

    PubMed Central

    Zhang, Xiaowei; Sahraei, Elham; Wang, Kai

    2016-01-01

    Separator integrity is an important factor in preventing internal short circuit in lithium-ion batteries. Local penetration tests (nail or conical punch) often produce presumably sporadic results, where in exactly similar cell and test set-ups one cell goes to thermal runaway while the other shows minimal reactions. We conducted an experimental study of the separators under mechanical loading, and discovered two distinct deformation and failure mechanisms, which could explain the difference in short circuit characteristics of otherwise similar tests. Additionally, by investigation of failure modes, we provided a hypothesis about the process of formation of local “soft short circuits” in cells with undetectable failure. Finally, we proposed a criterion for predicting onset of soft short from experimental data. PMID:27581185

  17. Failure mechanisms of concrete slab-soil double-layer structure subjected to underground explosion

    NASA Astrophysics Data System (ADS)

    Tan, Z.; Zhang, W.; Cho, C.; Han, X.

    2014-09-01

    The failure mechanism of a concrete slab-soil double-layer structure subjected to an underground explosion was investigated by experimental and numerical methods in this paper. Two underground explosion depths of 150 and 350 mm were tested. The typical failure modes such as the conoid spall of concrete, the bulge of the concrete slab and the cavity in the soil were obtained experimentally. Numerical simulations of the experiments were performed using a hydrodynamic code to analyze the effects of both the stress wave and the expansion of the blast products. Based on the experimental and numerical results, the effects of explosive depth, blast wave front and expansion of the blast products on the failure modes and failure mechanisms were discussed. The underground explosion process at different explosion depths was also analyzed. The results show that attenuation of the stress wave in the soil is significant. The blast wave front and the expansion of the blast products play different roles at different explosion depths. At the explosion depth of 150 mm, the failure mode is mainly caused by a point load induced by the blast wave front, whereas at the depth of 350 mm a sphere-shaped load resulting from the expansion of the blast products is a key factor for failure.

  18. Modelling the failure precursor mechanism of lamellar fibrous tissues, example of the annulus fibrosus.

    PubMed

    Mengoni, Marlène; Jones, Alison C; Wilcox, Ruth K

    2016-10-01

    The aims of this study were to assess the damage and failure strengths of lamellar fibrous tissues, such as the anterior annulus fibrosus (AF), and to develop a mathematical model of damage propagation of the lamellae and inter-lamellar connections. This level of modelling is needed to accurately predict the effect of damage and failure induced by trauma or clinical interventions. 26 ovine anterior AF cuboid specimens from 11 lumbar intervertebral discs were tested in radial tension and mechanical parameters defining damage and failure were extracted from the in-vitro data. Equivalent 1D analytical models were developed to represent the specimen strength and the damage propagation, accounting for the specimen dimensions and number of lamellae. Model parameters were calibrated on the in-vitro data. Similar to stiffness values reported for other orientations, the outer annulus was found stronger than the inner annulus in the radial direction, with failure at higher stress values. The inner annulus failed more progressively, showing macroscopic failure at a higher strain value. The 1D analytical model of damage showed that lamellar damage is predominant in the failure mechanism of the AF. The analytical model of the connections between lamellae allowed us to represent separately damage processes in the lamellae and the inter-lamellar connections, which cannot be experimentally tested individually. PMID:27442918

  19. Failure mechanisms and structural optimization of shredder hammer for metal scraps

    NASA Astrophysics Data System (ADS)

    Zhou, Xianyan; Hu, Zhili; Tao, Yijun; Qin, Xunpeng; Hua, Lin

    2016-06-01

    Recycling retired cars can relieve the environmental pollution and resource waste efficiently. However, a few publications can be found on the failure mechanisms and optimization method of recycling equipment, shredders. Thus, the failure mechanisms and structural optimization of shredder hammers for retired cars are studied aiming improving shredding efficiency and reducing cost. Failure types of shredder hammer are studied theoretically, and it is found that wear failure and fatigue failure are the two main failure types of shredder hammer. The shredding process of metal scraps is analyzed by finite element method, and it can be divided into four stages based on the stress states: initial stage, collision stage, grinding stage and separation stage. It is proved that the shredding efficiency can be improved by increasing cutouts on the hammer head. Finally, it is determined that the hammer with two cutouts is the optimal structure for metal scraps, which can improve the shredding efficiency by 20% and lengthen the hammer life by 15%. This study provides scientific basis for the industry application and theoretical foundation for further research.

  20. Unsmooth cuticles of soil animals and theoretical analysis of their hydrophobicity and anti-soil-adhesion mechanism.

    PubMed

    Jia, Xian

    2006-03-15

    Soil adhesion is a natural phenomenon, and it is harmful to terrain machines and tillage equipment that have soil as their work medium, such as automobiles, tractors, earth-moving machines, spades, hoes, and plows. Soil adhesion increases motion resistance and energy consumption, quickens damage to the soil-engaging components, and lowers work quality. The biomimetic research has provided a promising method to solve the soil adhesion problem. In this work, the cuticles of typical soil animals were observed by scanning electron microscopy (SEM) and their wettability and mechanism of antiadhesion were analyzed in theory. The results of experimental observation have shown that the cuticles of soil animals have different unsmooth appearances, such as pimple-shaped, pit-like, and undee structures. But for the cross sections of the unsmooth cuticles, their common character is undee. Theoretical analysis has indicated that the larger the ratio of the amplitude of the wave to the period of the wave, the stronger the hydrophobicity, the more easily the composite interface between the liquid and the unsmooth cuticles forms, and the function of reducing soil adhesion of the unsmooth cuticles will be better. PMID:16298383

  1. Effect of Fluoride-Releasing Adhesive Systems on the Mechanical Properties of Eroded Dentin.

    PubMed

    Guedes, Ana Paula Albuquerque; Moda, Mariana Dias; Suzuki, Thaís Yumi Umeda; Godas, André Gustavo de Lima; Sundfeld, Renato Herman; Briso, André Luiz Fraga; Santos, Paulo Henrique dos

    2016-01-01

    The aim of the study was to evaluate the effect of erosive pH cycling with solutions that simulate dental erosion on Martens hardness (HMV) and elastic modulus (Eit) of dentin restored with fluoride-releasing adhesive systems. Twenty-seven bovine dentin slabs were restored with three adhesive systems: Adper Single Bond 2 total-etch adhesive system, One Up Bond F and Clearfil SE Protect fluoride-containing self-etching adhesive systems. The restorations were made with Filtek Z250. The HMV and Eit values at distances of 10, 30, 50 and 70 µm from the interface were evaluated using a dynamic ultra microhardness tester before and after immersion in deionized water, citric acid and hydrochloric acid (n=9). Data were submitted to repeated-measures ANOVA and Fisher's PLSD tests (=0.05). After erosive cycling, HMV values of dentin decreased in all groups. For dentin restored with Adper Single Bond 2, the lowest values were found closer to the hybrid layer, while for One Up Bond F and Clearfil SE Protect, the values remained unaltered at all distances. For dentin restored with fluoride-releasing adhesive systems, a decrease in Eit was found, but after 30 µm this difference was not significant. The acid substances were able to alter HMV and Eit of the underlying dentin. For fluoride-releasing adhesives, the greater the distance from bonded interface, the lower the Eit values. The fluoride in One Up Bond F and Clearfil SE Protect was able to protect the underlying dentin closer to the materials. In this way, the fluoride from adhesive systems could have some positive effect in the early stages of erosive lesions. PMID:27058377

  2. Reliability characterization of UV-curable adhesives used in optical devices

    NASA Astrophysics Data System (ADS)

    Plitz, Irene M.; Gebizlioglu, Osman S.; Dugan, Michael P.

    1994-09-01

    UV (ultra-violet)-curable adhesives were identified as the underlying cause for failure of devices subjected to accelerated aging conditions. These adhesives must be resistant to degradation and dimensional/mechanical instabilities such as creep. We examined two UV-curable adhesives and found that thermal post-curing caused some shrinkage and degradation. However, post-curing also raised the adhesive glass transition temperature, thereby reducing the reliability risk associated with mechanical instability. We investigated the dimensional/mechanical stability of UV adhesives by measuring thermal expansion/contraction and creep compliance. We found that the adhesive thermal expansion and creep compliance are large enough to pose device reliability risk. Raising the glass transition temperature of UV-curable adhesives by thermal post-cure can improve optical device reliability by lowering the creep compliance.

  3. Mechanical Characterization of a Bi-functional Tetronic Hydrogel Adhesive for Soft Tissues

    PubMed Central

    Sanders, Lindsey; Stone, Roland; Webb, C. Kenneth; Mefford, O. Thompson; Nagatomi, Jiro

    2014-01-01

    Although a number of tissue adhesives and sealants for surgical use are currently available, attaining a useful balance in high strength, high compliance, and low swelling has proven difficult. Recent studies have demonstrated that a 4-arm poly(propylene oxide)-poly(ethylene oxide) (PPO-PEO) block copolymer, Tetronic, can be chemically modified to form a hydrogel tissue adhesive21–23. Building on the success of these studies, the present study explored bi-functionalization of Tetronic with acrylates for chemical crosslinking of the hydrogel and N-hydroxysuccinimide (NHS) for reaction with tissue amines. The adhesive bond strengths of various uni- and bi-functional Tetronic blends (T1107 ACR: T1107 ACR/NHS) determined by lap shear testing ranged between 8 and 74 kPa, with the 75:25 (T1107 ACR: T1107 ACR/NHS) blend displaying the highest value. These results indicated that addition of NHS led to improvement of tissue bond strength over acrylation alone Furthermore, ex vivo pressure tests using the rat bladder demonstrated that the bi-functional Tetronic adhesive exhibited high compliance and maintained pressures under hundreds of filling and emptying cycles. Together, the results of the present study provided evidence that the bi-functional Tetronic adhesive with a proper blend ratio may be used to achieve an accurate balance in bulk and tissue bond strengths, as well as the compliance and durability for soft tissue such as the bladder. PMID:25111445

  4. Advanced research on the microRNA mechanism in heart failure.

    PubMed

    Deng, Jianying; Zhong, Qianjin

    2016-10-01

    Heart failure is the end stage of most cardiac diseases and also an important cardiovascular disease. Ventricular remodeling, a complicated pathophysiological process involving multiple molecular pathways, is a crucial mechanism for the occurrence and development of heart failure. A microRNA (miRNA) is a highly conservative noncoding molecule containing 18-25 nucleotides. miRNA is different from other RNAs. It mainly serves as an endogenous gene-regulating factor, and is a member of the complex regulatory network. It induces gene repression of target transcripts by affecting mRNA at the post-transcriptional level Vasudevan et al. (2007) . This study aimed at determining the mechanism of miRNA action in heart failure. PMID:27372044

  5. Degradation and corresponding failure mechanism for GaN-based LEDs

    NASA Astrophysics Data System (ADS)

    Fu, Jiajia; Zhao, Lixia; Cao, Haicheng; Sun, Xuejiao; Sun, Baojuan; Wang, Junxi; Li, Jinmin

    2016-05-01

    The degradation behaviors of high power GaN-based vertical blue LEDs on Si substrates were measured using in-situ accelerated life test. The results show that the dominant failure mechanism would be different during the operation. Besides that, the corresponding associated failure mechanisms were investigated systematically by using different analysis technologies, such as Scan Electron Microscopy, Reflectivity spectroscopy, Transient Thermal Analysis, Raman Spectra, etc. It is shown that initially, the failure modes were mainly originated from the semiconductor die and interconnect, while afterwards, the following serious deterioration of the radiant fluxes was attributed to the package. The interface material and quality, such as die attach and frame, play an important role in determining the thermal performance and reliability. In addition, the heating effect during the operation will also release the compressive strain in the chip. These findings will help to improve the reliability of GaN-based LEDs, especially for the LEDs with vertical structure.

  6. The microstructural mechanism of electromigration failure in narrow interconnects of Al alloys

    SciTech Connect

    Kim, Choongun

    1993-04-01

    This thesis reports a study of the mechanism of electromigration failure in Al-2Cu-1Si thin-film conducting lines on Si. Samples were patterned from 0.5 {mu}m thick vapor-deposited films with various mean grain sizes (G), and had lines widths (W) of 1.3, 2, 4 and 6 {mu}m. The lines were aged at various conditions to change the Cu-precipitate distribution and were tested to failure at T = 225{degrees}C and j = 2.5 {times} 10{sup 6} A/cm{sup 2}. Some samples were tested over a range of substrate temperatures, current densities and current reversal times. Aging produces an initially dense distribution of metastable {Theta}{prime} (Al{sub 2}Cu; coherent) in the grain interiors, with stable {Theta} (Al{sub 2}Cu; incoherent) at the grain boundaries. The intragranular {theta}{prime} is gradually absorbed into the grain boundary precipitates. In the wide lines the mean time to failure increases slowly and monotonically with pre-aging time and current reversal time. The failure mode is the formation and coalescence of voids that form on grain boundaries with an apparent activation energy of 0.65 eV. In the narrow lines, the lines failed by a transgranular-slit mechanism with an activation energy near 0.93 eV. The distribution of the polygranular segments and the kinetics of failure varies with the linewidths. Failure occurs after Cu has been swept from the grains that fail. Pre-aging the line to create a more stable distribution of Cu significantly increases the time to failure. When the density of intragranular {Theta}-phase precipitates is maximized, the transgranular-slit failure mechanism is suppressed, and the bamboo grain fails by diffuse thinning to rupture. The results from the current reversal test indicate that the time to sweep Cu in the polygranular segments is longer for longer polygranular segments. Thus the time to first failure in an array of lines is much longer than predicted by a log-normal fit to the distribution of failure times.

  7. The mechanism of electromigration failure of narrow Al-2Cu-1Si thin-film interconnects

    NASA Astrophysics Data System (ADS)

    Kim, Choongun; Morris, J. W., Jr.

    1993-05-01

    This work is principally concerned with the microstructure of electromigration failure in narrow Al-2Cu-1Si conducting lines on Si. Samples were patterned from 0.5-μm-thick vapor-deposited films with mean grain size of 2.4 μm, and had linewidths of 1.3 μm (W/G≊0.5), 2 μm (W/G≊0.8), and 6 μm (W/G≊2.5). The lines were tested to failure at T=226 °C and j=2.5×106 A/cm2. Other samples were tested over a range of substrate temperatures and current densities to test the effect of these variables, and 1.3 μm lines were tested after preaging at 226 °C for various times to change the Cu-precipitate distribution prior to testing. Three failure modes were observed: The 6 μm specimens failed by separation along grain boundaries with an apparent activation energy of 0.65 eV; the 1.3 μm specimens that were preaged for 24 h failed after very long times by gradual thinning to rupture; all other narrow lines failed by the transgranular-slit mechanism with an activation energy near 0.93 eV. Microstructural studies suggest that the transgranular-slit failure mechanism is due to the accumulation of a supersaturation of vacancies in the bamboo grains that terminate polygranular segments in the line. Failure occurs after Cu has been swept from the grain that fails. Failure happens first at the end of the longest polygranular segment of the line, at a time that decreases exponentially with the polygranular segment length. Preaging the line to create a more stable distribution of Cu lengthens the time required to sweep Cu from the longest polygranular segment, and significantly increases the time to failure. In the optimal case the transgranular-slit failure mechanism is suppressed, and the bamboo grain fails by diffuse thinning to rupture. Preaging is particularly effective in increasing the lifetimes of lines that contain very long polygranular segments, and has the consequence that the time to first failure in an array of lines is much longer than predicted by a log

  8. Mechanics of rainfall-induced flow failure in unsaturated shallow slopes (Invited)

    NASA Astrophysics Data System (ADS)

    Buscarnera, G.

    2013-12-01

    The increase in pore water pressure due to rain infiltration can be a dominant component in the activation of slope instabilities. This work shows an application of the theory of material stability to the triggering analysis of this important class of natural hazards. The goal is to identify the mechanisms through which the process of rain infiltration promotes instabilities of the flow-type in the soil covers. The interplay between increase in pore water pressure and failure mechanisms is investigated at material point level. To account for multiple failure mechanisms, the second-order energy input is linked to the controllability theory and used to define different types of stability indices, each associated with a specific mode of slope failure. It is shown that the theory can be used to assess both shear failure and static liquefaction in saturated and unsaturated soil covers. In particular, it is shown that these instability modes are regulated by the hydro-mechanical characteristics of the soil covers, as well as by their mutual coupling. This finding discloses the importance of the constitutive functions that simulate the interaction between the response of the solid skeleton and the fluid-retention characteristics of the soil. As a consequence, they suggest that even material properties that are not be to directly associated with the shearing resistance (e.g., the potential for wetting compaction) may play a role in the initiation of catastrophic slope failures. According to the proposed interpretation, the process of pore pressure increase can be seen as the trigger of uncontrolled strains, which can anticipate the onset of frictional failure and promote a solid-to-fluid transition.

  9. Some Aspects of the Failure Mechanisms in BaTiO3-Based Multilayer Ceramic Capacitors

    NASA Technical Reports Server (NTRS)

    Liu, David Donhang; Sampson, Michael J.

    2012-01-01

    The objective of this presentation is to gain insight into possible failure mechanisms in BaTiO3-based ceramic capacitors that may be associated with the reliability degradation that accompanies a reduction in dielectric thickness, as reported by Intel Corporation in 2010. The volumetric efficiency (microF/cm3) of a multilayer ceramic capacitor (MLCC) has been shown to not increase limitlessly due to the grain size effect on the dielectric constant of ferroelectric ceramic BaTiO3 material. The reliability of an MLCC has been discussed with respect to its structure. The MLCCs with higher numbers of dielectric layers will pose more challenges for the reliability of dielectric material, which is the case for most base-metal-electrode (BME) capacitors. A number of MLCCs manufactured using both precious-metal-electrode (PME) and BME technology, with 25 V rating and various chip sizes and capacitances, were tested at accelerated stress levels. Most of these MLCCs had a failure behavior with two mixed failure modes: the well-known rapid dielectric wearout, and so-called 'early failures." The two failure modes can be distinguished when the testing data were presented and normalized at use-level using a 2-parameter Weibull plot. The early failures had a slope parameter of Beta >1, indicating that the early failures are not infant mortalities. Early failures are triggered due to external electrical overstress and become dominant as dielectric layer thickness decreases, accompanied by a dramatic reduction in reliability. This indicates that early failures are the main cause of the reliability degradation in MLCCs as dielectric layer thickness decreases. All of the early failures are characterized by an avalanche-like breakdown leakage current. The failures have been attributed to the extrinsic minor construction defects introduced during fabrication of the capacitors. A reliability model including dielectric thickness and extrinsic defect feature size is proposed in this

  10. Supramolecular Cross-Links in Poly(alkyl methacrylate) Copolymers and Their Impact on the Mechanical and Reversible Adhesive Properties.

    PubMed

    Heinzmann, Christian; Salz, Ulrich; Moszner, Norbert; Fiore, Gina L; Weder, Christoph

    2015-06-24

    Hydrogen-bonded, side-chain-functionalized supramolecular poly(alkyl methacrylate)s were investigated as light- and temperature-responsive reversible adhesives that are useful for bonding and debonding on demand applications. Here, 2-hydroxyethyl methacrylate (HEMA) was functionalized with 2-ureido-4[1H]pyrimidinone (UPy) via a hexamethylenediisocyanate (HMDI) linker, to create a monomer (UPy-HMDI-HEMA) that serves to form supramolecular cross-links by way of forming quadruple hydrogen bonded dimers. UPy-HMDI-HEMA was copolymerized with either hexyl methacrylate or butyl methacrylate to create copolymers comprising 2.5, 5, or 10 mol % of the cross-linker. The mechanical properties of all (co)polymers were investigated with stress-strain experiments and dynamic mechanical analysis. Furthermore, the adhesive properties were studied at temperatures between 20 and 60 °C by testing single lap joints formed with stainless steel substrates. It was found that increasing the concentration of the UPy-HMDI-HEMA cross-linker leads to improved mechanical and adhesive properties at elevated temperatures. Concurrently, the reversibility of the bond formation remained unaffected, where rebonded samples displayed the same adhesive strength as regularly bonded samples. Debonding on demand abilities were also tested exemplarily for one copolymer, which for light-induced debonding experiments was blended with a UV-absorber that served as light-heat converter. Single lap joints were subjected to a constant force and heated or irradiated with UV light until debonding occurred. The necessary debonding temperature was comparable for direct heating and UV irradiation and varied between 28 and 82 °C, depending on the applied force. The latter also influenced the debonding time, which under the chosen conditions ranged from 30 s to 12 min. PMID:26043809

  11. Mechanical properties and failure analysis of visible light crosslinked alginate-based tissue sealants.

    PubMed

    Charron, Patrick N; Fenn, Spencer L; Poniz, Alex; Oldinski, Rachael A

    2016-06-01

    Moderate to weak mechanical properties limit the use of naturally-derived tissue sealants for dynamic medical applications, e.g., sealing a lung leak. To overcome these limitations, we developed visible-light crosslinked alginate-based hydrogels, as either non-adhesive methacrylated alginate (Alg-MA) hydrogel controls, or oxidized Alg-MA (Alg-MA-Ox) tissue adhesive tissue sealants, which form covalent bonds with extracellular matrix (ECM) proteins. Our study investigated the potential for visible-light crosslinked Alg-MA-Ox hydrogels to serve as effective surgical tissue sealants for dynamic in vivo systems. The Alg-MA-Ox hydrogels were designed to be an injectable system, curable in situ. Burst pressure experiments were conducted on a custom-fabricated burst pressure device using constant air flow; burst pressure properties and adhesion characteristics correlated with the degrees of methacrylation and oxidation. In summary, visible light crosslinked Alg-MA-Ox hydrogel tissue sealants form effective seals over critically-sized defects, and maintain pressures up to 50mm Hg. PMID:26897093

  12. Acute dissection of a Contegra conduit: a rare mechanism of failure.

    PubMed

    Kavarana, Minoo N; Dorfman, Adam L; Agarwal, Prachi P; Bove, Edward L

    2010-09-01

    The Contegra (Medtronic Inc, Minneapolis, MN) bovine jugular vein conduit has been used with increasing frequency in congenital heart disease for the reconstruction of the right ventricular outflow tract. In this report, we describe a mechanism for conduit failure secondary to an acute dissection of the inner neointimal peel from the conduit wall. PMID:20732536

  13. [The effect of non-invasive mechanical ventilation in postoperative respiratory failure].

    PubMed

    Ozyılmaz, Ezgi; Kaya, Akın

    2012-01-01

    Postoperative respiratory failure is related with the highest mortality and morbidity among all perioperative complications. The most common underlying mechanism of postoperative respiratory failure is the development of atelectasis. Anaesthesia, medications which cause respiratory depression, high FiO2 use, postoperative pain and disruption of muscle forces due to surgery leads to decrease in functional residual capacity and results in atelectasis formation. Atelectasis causes severe hypoxemia due to ventilation, perfusion mismatch, shunt and increased peripheral vascular resistance. Intrathoracic positive pressure is an effective therapeutic option in both prevention and treatment of atelectasis. Non-invasive mechanical ventilation is related with a lower mortality and morbidity rate due to lack of any potential complication risks of endotracheal intubation. Non-invasive mechanical ventilation can be applied as prophylactic or curative. Both of these techniques are related with lower reintubation rates, nosocomial infections, duration of hospitalization and mortality in patients with postoperative respiratory failure. The differences of this therapy from standard application and potential complications should be well known in order to improve prognosis in these group of patients. The primary aim of this review is to underline the pathogenesis of postoperative respiratory failure. The secondary aim is to clarify the optimum method, effect and complications of non-invasive mechanical ventilation therapy under the light of the studies which was performed in specific patient groups. PMID:22779943

  14. Lubrication and failure mechanisms of molybdenum disulfide films. 2: Effect of substrate roughness

    NASA Technical Reports Server (NTRS)

    Fusaro, R. L.

    1978-01-01

    An optical microscope was used to study the lubrication and failure mechanisms of rubbed MoS2 films applied to three substrate surface finishes; polished, sanded, and sandblasted as a function of sliding distance. The lubrication mechanism was the plastic flow of thin films of MoS2 between flat plateaus on the rider and on the metallic substrate. If the substrate was rough, flat plateaus were created during run-in and the MoS2 flowed across them. Wear life was extended by increasing surface roughness since valleys in the roughened substrate served as reservoirs for MoS2 and as deposit sites for wear debris. In moist air the failure mechanism was the transformation of metallic colored MoS2 films to a black, powdery material that was found by X-ray diffraction to be alpha iron, MoO3, and possibly FeMoO3. In dry argon the failure mechanism was the gradual depletion of MoS2 from the contact region by transverse flow, and the wear debris on the track at failure was alpha iron, residual MoS2, and possibly FeS.

  15. Effect of substrate surface finish on the lubrication and failure mechanisms of molybdenum disulfide films

    NASA Technical Reports Server (NTRS)

    Fusaro, R. L.

    1981-01-01

    An optical microscope was used to study the lubrication and failure mechanisms of rubbed (burnished) MoS2 films applied to three substrate surface finishes - polished, sanded, and sandblasted - as a function of sliding distance. The lubrication mechanism was the plastic flow of thin films of MoS2 between flat plateaus on the rider and on the metallic substrate. If the substrate was rough, flat plateaus were created during 'run-in' and the MoS2 flowed across them. Wear life was extended by increasing surface roughness since valleys in the roughened substrate served as reservoirs for MoS2 and a deposit site for wear debris. In moist air, the failure mechanism was the transformation of metallic-colored MoS2 films to a black, powdery material that was found by X-ray diffraction to consist primarily of alpha-iron and MoO3 powders. In dry argon, the failure mechanism was the gradual depletion of the MoS2 film from the contact region by transverse flow. Analysis of the wear debris on the wear track at failure showed it consisted mainly of alpha-iron and some residual MoS2. No molybdenum oxides were found.

  16. Effect of Substrate Surface Finish on the Lubrication and Failure Mechanisms of Molybdenum Disulfide Films

    NASA Technical Reports Server (NTRS)

    Fusaro, R. L.

    1980-01-01

    An optical microscope was used to study the lubrication and failure mechanisms of rubbed (burnished) MoS2 films applied to three substrate surface finishes - polished, sanded, and sandblasted - as a function of sliding distance. The lubrication mechanism was the plastic flow of thin films of MoS2 between flat plateaus on the rider and on the metallic substrate. If the substrates were rough, flat plateaus were created during 'run in' and the MoS2 flowed across them. Wear life was extended by increasing surface roughness since valleys in the roughened substrate served as reservoirs for MoS2 and a deposit site for wear debris. In moist air, the failure mechanism was the transformation of metallic colored MoS2 films to a black, powdery material that was found by X ray diffraction to consist primarily of alpha iron and MoO3 powders. In dry argon, the failure mechanism was the gradual depletion of the MoS2 film from the contact region by transverse flow. Analysis of the wear debris on the wear track at failure showed it consisted mainly of alpha iron and some residual MoS2. No molybdenum oxides were found.

  17. A method to define degradation mechanisms and failure rates for piping

    SciTech Connect

    Gamble, R.M.; Gosselin, S.R.

    1996-12-01

    This paper describes a process currently being employed to develop an easy to use procedure for identifying degradation mechanisms and computing failure rates for piping. The procedure includes guidelines to identify degradation mechanisms that may be present in piping systems. The identified mechanisms along with other system or segment specific features of the piping determine the piping failure rate. Implementation of this procedure requires a data or knowledge base that reflects the service and operational conditions that affect piping reliability and availability. This procedure is being developed for use by plant engineers, and will not require expertise in probability, stress, or fracture mechanics analyses. The method can be used to provide input for performing plant safety assessments and defining risk based inspection programs.

  18. Basic failure mechanisms in advanced composites. [composed of epoxy resins reinforced with carbon fibers

    NASA Technical Reports Server (NTRS)

    Mazzio, V. F.; Mehan, R. L.; Mullin, J. V.

    1973-01-01

    The fundamental failure mechanisms which result from the interaction of thermal cycling and mechanical loading of carbon-epoxy composites were studied. This work was confined to epoxy resin uniderictionally reinforced with HTS carbon fibers, and consists of first identifying local fiber, matrix and interface failure mechanisms using the model composite specimen containing a small number of fibers so that optical techniques can be used for characterization. After the local fracture process has been established for both mechanical loading and thermal cycling, engineering composite properties and gross fracture modes are then examined to determine how the local events contribute to real composite performance. Flexural strength in high fiber content specimens shows an increase in strength with increased thermal cycling. Similar behavior is noted for 25 v/o material up to 200 cycles; however, there is a drastic reduction after 200 cycles indicating a major loss of integrity probably through the accumulation of local cleavage cracks in the tensile region.

  19. Primary cilia utilize glycoprotein-dependent adhesion mechanisms to stabilize long-lasting cilia-cilia contacts

    PubMed Central

    2012-01-01

    Background The central tenet of cilia function is sensing and transmitting information. The capacity to directly contact extracellular surfaces would empower primary cilia to probe the environment for information about the nature and location of nearby surfaces. It has been well established that flagella and other motile cilia perform diverse cellular functions through adhesion. We hypothesized that mammalian primary cilia also interact with the extracellular environment through direct physical contact. Methods We identified cilia in rod photoreceptors and cholangiocytes in fixed mouse tissues and examined the structures that these cilia contact in vivo. We then utilized an MDCK cell culture model to characterize the nature of the contacts we observed. Results In retina and liver tissue, we observed that cilia from nearby cells touch one another. Using MDCK cells, we found compelling evidence that these contacts are stable adhesions that form bridges between two cells, or networks between many cells. We examined the nature and duration of the cilia-cilia contacts and discovered primary cilia movements that facilitate cilia-cilia encounters. Stable adhesions form as the area of contact expands from a single point to a stretch of tightly bound, adjacent cilia membranes. The cilia-cilia contacts persisted for hours and were resistant to several harsh treatments such as proteases and DTT. Unlike many other cell adhesion mechanisms, calcium was not required for the formation or maintenance of cilia adhesion. However, swainsonine, which blocks maturation of N-linked glycoproteins, reduced contact formation. We propose that cellular control of adhesion maintenance is active because cilia adhesion did not prevent cell division; rather, contacts dissolved during mitosis as cilia were resorbed. Conclusions The demonstration that mammalian primary cilia formed prolonged, direct, physical contacts supports a novel paradigm: that mammalian primary cilia detect features of the

  20. Dynamic tensile failure mechanics of the musculoskeletal neck using a cadaver model.

    PubMed

    Yliniemi, Eno M; Pellettiere, Joseph A; Doczy, Erica J; Nuckley, David J; Perry, Chris E; Ching, Randal P

    2009-05-01

    Although the catapult phase of pilot ejections has been well characterized in terms of human response to compressive forces, the effect of the forces on the human body during the ensuing ejection phases (including windblast and parachute opening shock) has not been thoroughly investigated. Both windblast and parachute opening shock have been shown to induce dynamic tensile forces in the human cervical spine. However, the human tolerance to such loading is not well known. Therefore, the main objective of this research project was to measure human tensile neck failure mechanics to provide data for computational modeling, anthropometric test device development, and improved tensile injury criteria. Twelve human cadaver specimens, including four females and eight males with a mean age of 50.1+/-9 years, were subjected to dynamic tensile loading through the musculoskeletal neck until failure occurred. Failure load, failure strain, and tensile stiffness were measured and correlated with injury type and location. The mean failure load for the 12 specimens was 3100+/-645 N, mean failure strain was 16.7+/-5.4%, and mean tensile stiffness was 172+/-54.5 N/mm. The majority of injuries (8) occurred in the upper cervical spine (Oc-C3), and none took place in the midcervical region (C3-C5). The results of this study assist in filling the existing void in dynamic tensile injury data and will aid in developing improved neck injury prevention strategies. PMID:19388771

  1. Relaxin for the Treatment of Acute Decompensated Heart Failure: Pharmacology, Mechanisms of Action, and Clinical Evidence.

    PubMed

    Ng, Tien M H; Goland, Sorel; Elkayam, Uri

    2016-01-01

    Acute heart failure remains a major cause of morbidity, and its treatment requires an increasing investment of the health care system. Whereas success in treating chronic heart failure has been achieved over the last decades, several pharmacological approaches for acute heart failure have been introduced but have failed to demonstrate any clinical benefit. Serelaxin is a recombinant human relaxin-2 vasoactive peptide that causes systemic and renal vasodilation. Data suggest that the clinical benefits may be attributable to a potential combination of multiple actions of serelaxin, including improving systemic, cardiac, and renal hemodynamics, and protecting cells and organs from damage via neurohormonal, anti-inflammatory, antiremodeling, antifibrotic, anti-ischemic, and proangiogenic effects. Recently, a number of clinical trials have demonstrated that serelaxin infusion over 48 hours improved dyspnea with more rapid relief of congestion during the first days after admission for heart failure. In addition, administration of serelaxin diminished cardiac, renal, and hepatic damage, which were associated with improved long-term mortality. Available data support substantial clinical benefits and significant promise for serelaxin as a treatment option for patients with acute heart failure. This review focuses on the pharmacology and mechanisms of action of serelaxin and provides a detailed discussion of the clinical evidence for this novel therapy in acute heart failure. PMID:26331289

  2. A fundamental approach to adhesion: Synthesis, surface analysis, thermodynamics and mechanics. [titanium alloys

    NASA Technical Reports Server (NTRS)

    Chen, W.; Dwight, D. W.; Wightman, J. P.

    1978-01-01

    Various surface preparations for titanium 6-4 alloy were studied. An anodizing method was investigated, and compared with the results of other chemical treatments, namely, phosphate/fluoride, Pasa-Jell and Turco. The relative durability of the different surface treatments was assessed by monitoring changes in surface chemistry and morphology occasioned by aging at 505 K (450 F). Basic electron spectroscopic data were collected for polyimide and polyphenylquinoxaline adhesives and synthetic precursors. Fractographic studies were completed for several combinations of adherend, adhesive, and testing conditions.

  3. Mechanical failure (leaflet disruption) of a porcine aortic heterograft: rare cause of acute aortic insufficiency.

    PubMed

    Housman, L B; Pitt, W A; Mazur, J H; Litchford, B; Gross, S A

    1978-08-01

    Use of the Hancock, glutaraldehyde-preserved, stented heterograft for aortic valve replacement has gained wide acceptance in the past 7 years. Nevertheless, very little is known about the long-term mechanical and pathological characteristics following implantation. A rare case is presented in which mechanical valve failure occurred secondary to leaflet disruption in the absence of infection 23 months after implantation. The literature is reviewed and the implications of this unusual complication are discussed. PMID:567263

  4. Modeling and characterization of interfacial adhesion and fracture

    NASA Astrophysics Data System (ADS)

    Yao, Qizhou

    2000-09-01

    The loss of interfacial adhesion is mostly seen in the failure of polymer adhesive joints. In addition to the intrinsic physical attraction across the interface, the interfacial adhesion strength is believed to highly depend on a number of factors, such as adhesive chemistry/structure, surface topology, fracture pattern, thermal and elastic mismatch across the interface. The fracture failure of an adhesive joint involves basically three aspects, namely, the intrinsic interfacial strength, the driving force for fracture and other energy dissipation. One may define the intrinsic interfacial strength as the maximum value of the intrinsic interfacial adhesion. The total work done by external forces to the component that contains the interface is partitioned into two parts. The first part is consumed by all other energy dissipation mechanisms (plasticity, heat generation, viscosity, etc.). The second part is used to debond the interface. This amount should equal to the intrinsic adhesion of the interface according to the laws of conservation of energy. It is clear that in order to understand the fundamental physics of adhesive joint failure, one must be able to characterize the intrinsic interfacial adhesion and be able to identify all the major energy dissipation mechanisms involved in the debonding process. In this study, both physical and chemical adhesion mechanisms were investigated for an aluminum-epoxy interface. The physical bonding energy was estimated by computing the Van de Waals forces across the interface. A hydration model was proposed and the associated chemical bonding energy was calculated through molecular simulations. Other energy dissipation mechanisms such as plasticity and thermal residual stresses were also identified and investigated for several four-point bend specimens. In particular, a micromechanics based model was developed to estimate the adhesion enhancement due to surface roughness. It is found that for this Al-epoxy system the major

  5. Investigation of the design and static behavior of cylindrical tubular composite adhesive joints utilizing the finite element method and stress-based failure theories

    NASA Astrophysics Data System (ADS)

    Lambert, Michael D.

    2011-12-01

    The stress and strength behavior of cylindrical tubular adhesive joints composed of dissimilar materials was explored. This was accomplished with the finite element method (FEM) and stress-based failure theories. Also, it was shown how a design of experiments (DOE) based method can be used to objectively organize the process of optimizing joint strength by using stress-based failure criteria. The finite element program used in this work was written in-house from scratch to implement the FEM for the purpose of solving both axisymmetric and three-dimensional linear elastic governing equations of static equilibrium. The formulation of the three-dimensional model is presented, and the required operations to arrive to the axisymmetric model are also presented. The axisymmetric model is two dimensional, capable of using four and eight node quadrilateral elements. However, only four node elements are used because a mesh of eight node elements requires more memory and increased mesh refinement. The three-dimensional model is capable of using eight and twenty node brick elements, but only eight node brick elements are used for the same reason. Both of the axisymmetric and three-dimensional models calculate the nodal displacements, strains, stress values for each material, and strength values for each material. The external static loads can be individually applied, or coupled together. The outputs seem to be most useful for interpretation when plotted through-the-thickness (TTT) and along-the-length (ATL) of the joint or tube. Outputs are valid only for materials that behave linearly elastic up to (or near) failure, and the stress-based failure criteria are used to define that limit. A small laboratory-sized joint was modeled to look at the theoretical stress and strength distributions plotted along-the-length of the joint at different radial locations. These stress and strength distributions can be correlated to the type of load being applied because of unique or prominent

  6. Failure Mechanisms During Isothermal Fatigue of SiC/Ti-24Al-11Nb Composites

    NASA Technical Reports Server (NTRS)

    Brindley, P. K.; Bartolotta, P. A.

    1995-01-01

    Failure mechanisms during isothermal fatigue of unidirectional SiC/Ti-24Al-11Nb (at.%) composites have been determined by microstructural analysis of samples from tests interrupted prior to the end of life and from tests conducted to failure. Specimens from three regions of life were examined based on the maximum strain from a fatigue life diagram: Region 1 (high strain), Region 2 (mid-strain) and Region 3 (low strain). Crack lengths were also measured from interrupted samples and compared based on temperature (23-815 C), region of life and numbers of cycles. Region 1 was controlled by fiber-dominated failure. A transition zone was observed between Regions 1 and 2 due to competition between failure mechanisms. Failure in Region 2 was generally described as surface-initiated cracking with varying amounts of fiber bridging. However, the specific descriptions of crack propagation through the fibers and matrix varied with strain and temperature over this broad region. Region 3 exhibited endurance behaviour at 23 C with no cracking after lO(exp 6) cycles. However at 425 C, surface-initiated cracking was observed after 10(exp 6) cycles with fractured fibers in the crack wake. If endurance behaviour exists for conditions of isothermal fatigue in air at temperatures of greater than or equal to 425 C, it may only be found at very low strains and at greater than 10(exp 6) cycles.

  7. High performance Cu adhesion coating

    SciTech Connect

    Lee, K.W.; Viehbeck, A.; Chen, W.R.; Ree, M.

    1996-12-31

    Poly(arylene ether benzimidazole) (PAEBI) is a high performance thermoplastic polymer with imidazole functional groups forming the polymer backbone structure. It is proposed that upon coating PAEBI onto a copper surface the imidazole groups of PAEBI form a bond with or chelate to the copper surface resulting in strong adhesion between the copper and polymer. Adhesion of PAEBI to other polymers such as poly(biphenyl dianhydride-p-phenylene diamine) (BPDA-PDA) polyimide is also quite good and stable. The resulting locus of failure as studied by XPS and IR indicates that PAEBI gives strong cohesive adhesion to copper. Due to its good adhesion and mechanical properties, PAEBI can be used in fabricating thin film semiconductor packages such as multichip module dielectric (MCM-D) structures. In these applications, a thin PAEBI coating is applied directly to a wiring layer for enhancing adhesion to both the copper wiring and the polymer dielectric surface. In addition, a thin layer of PAEBI can also function as a protection layer for the copper wiring, eliminating the need for Cr or Ni barrier metallurgies and thus significantly reducing the number of process steps.

  8. Cellular and Molecular Investigations of the Adhesion and Mechanics of Listeria monocytogenes Lineages’ I and II Environmental and Epidemic Strains

    PubMed Central

    Eskhan, Asma O.; Abu-Lail, Nehal I.

    2013-01-01

    Atomic force microscopy (AFM) was used to probe the mechanical and adherence properties of eight L. monocytogenes’ strains representative of the species’ two phylogenetic lineages I and II. From a functional perspective, lineage’ I strains were characterized by lower overall adhesion forces and higher specific and nonspecific forces compared to lineage’ II strains. From a structural perspective, lineage’ II strains were characterized by higher Young’s moduli and longer and stiffer biopolymers compared to lineage’ I strains. Both lineages’ I and II strains were similar in their grafting densities. Finally, our results indicated that epidemic and environmental strains of L. monocytogenes and irrespective of their lineage group were characterized by similar Young’s moduli of elasticties and adhesion forces at the cellular level. However, at the molecular level, epidemic strains were characterized by higher specific and nonspecific forces, shorter, denser and more flexible biopolymers compared to environmental strains. PMID:23261349

  9. Cellular and molecular investigations of the adhesion and mechanics of Listeria monocytogenes lineages' I and II environmental and epidemic strains.

    PubMed

    Eskhan, Asma O; Abu-Lail, Nehal I

    2013-03-15

    Atomic force microscopy (AFM) was used to probe the mechanical and adherence properties of eight Listeria monocytogenes' strains representative of the species' two phylogenetic lineages I and II. From a functional perspective, lineage' I strains were characterized by lower overall adhesion forces and higher specific and nonspecific forces compared to lineage' II strains. From a structural perspective, lineage' II strains were characterized by higher Young's moduli and longer and stiffer biopolymers compared to lineage' I strains. Both lineages' I and II strains were similar in their grafting densities. Finally, our results indicated that epidemic and environmental strains of L. monocytogenes and irrespective of their lineage group were characterized by similar Young's moduli of elasticities and adhesion forces at the cellular level. However, at the molecular level, epidemic strains were characterized by higher specific and nonspecific forces, shorter, denser, and more flexible biopolymers compared to environmental strains. PMID:23261349

  10. Dynamic failure mechanisms in armor grade ceramics (the effect of lateral confinement and membrane restraint)

    NASA Astrophysics Data System (ADS)

    Sarva, Sai Sushilkumar

    Light weight ceramics such as SiC and Al2O3, have been used in impact related applications such as integrated armor for more than a decade and are an excellent prospect for the next-generation multi-functional armor systems. It is known that ceramics fail under a wide variety of failure modes ranging from brittle to ductile depending on the deformation conditions, such as the strain rate and the state of stress. The dynamic properties are dependent on the underlying failure mechanisms. The underpinning mechanisms of compression failure and their effect on the mechanical properties have been examined over a range of deformation rates from quasi-static to ballistic strain rates. Under moderate confining pressures [˜350 MPa] and at moderate deformation rates [strain-rates up to a few thousand per second], occurring during quasi-static and Hopkinson bar experiments, brittle failure involves initiation of micro-cracks at dominant micro-flaws and pre-existing micro-cracks and their subsequent interactive growth leading to axial splitting, faulting or a mixture of brittle-ductile failure. Experimental results relating to SiC have been compared to a wing-crack array model, developed by Nemat-Nasser and Deng, which describes the influence of microstructure on the dynamic behavior of materials. Under extreme conditions of stress, attained during shock impact, ceramics pulverize into fine powder. Classical crack-growth models seem inadequate for representing the actual failure initiation and evolution. Experiments have also been conducted to study the ballistic performance and failure of ceramic tiles. It has been observed that the defeat capability can be vastly improved by restraining the impact-face of ceramic tiles with a membrane of suitable tensile strength. The comparative effect of restraint by materials such as E-glass/epoxy pre-preg, carbon-fiber/epoxy pre-preg and Ti-3%Al-2.5%V alloy has been studied. Tungsten heavy alloy was used as the projectile material. The

  11. Continuum Damage Mechanics Models for the Analysis of Progressive Failure in Open-Hole Tension Laminates

    NASA Technical Reports Server (NTRS)

    Song, Kyonchan; Li, Yingyong; Rose, Cheryl A.

    2011-01-01

    The performance of a state-of-the-art continuum damage mechanics model for interlaminar damage, coupled with a cohesive zone model for delamination is examined for failure prediction of quasi-isotropic open-hole tension laminates. Limitations of continuum representations of intra-ply damage and the effect of mesh orientation on the analysis predictions are discussed. It is shown that accurate prediction of matrix crack paths and stress redistribution after cracking requires a mesh aligned with the fiber orientation. Based on these results, an aligned mesh is proposed for analysis of the open-hole tension specimens consisting of different meshes within the individual plies, such that the element edges are aligned with the ply fiber direction. The modeling approach is assessed by comparison of analysis predictions to experimental data for specimen configurations in which failure is dominated by complex interactions between matrix cracks and delaminations. It is shown that the different failure mechanisms observed in the tests are well predicted. In addition, the modeling approach is demonstrated to predict proper trends in the effect of scaling on strength and failure mechanisms of quasi-isotropic open-hole tension laminates.

  12. Compression failure mechanisms of single-ply, unidirectional, carbon-fiber composites

    NASA Technical Reports Server (NTRS)

    Ha, Jong-Bae; Nairn, John A.

    1992-01-01

    A single-ply composite compression test was used to study compression failure mechanisms as a function of fiber type, matrix type, and interfacial strength. Composites made with low- and intermediate-modulus fibers (Hercules AS4 and IM7) in either an epoxy (Hercules 3501-6) or a thermoplastic (ULTEM and LARC-TPI) matrix failed by kink banding and out-of-plane slip. The failures proceeded by rapid and catastrophic damage propagation across the specimen width. Composites made with high-modulus fibers (Hercules HMS4/3501-6) had a much lower compression strength. Their failures were characterized by kink banding and longitudinal splitting. The damage propagated slowly across the specimen width. Composites made with fibers treated to give low interfacial strength had low compression strength. These composites typically failed near the specimen ends and had long kink bands.

  13. Failure mechanisms of polyester fiber anterior cruciate ligament implants: A human retrieval and laboratory study.

    PubMed

    Amis, A A; Kempson, S A

    1999-01-01

    It has been hypothesized that ACL implant failure is often caused by bone impingement in knee extension following malplacement of the tibial tunnel. This study examined polyethylene terephtalate fiber ACL implants retrieved from a clinical study, and, to confirm the hypothesis, also set up a laboratory study intended to duplicate the failure mechanism. SEM and TEM examination of 25 ruptured implants gave details of fiber failure morphology, with shearing into longitudinal fibrils, followed by rupture, when the fibrils burst apart. Cadaver joints were run in a knee simulator, with deliberately impinging ACL implants. SEM examination of implants abraded in the knee in vitro showed identical fiber damage patterns, thus confirming the impingement hypothesis. PMID:10421698

  14. Mechanical behaviour and failure modes in the Whakaari (White Island volcano) hydrothermal system, New Zealand

    NASA Astrophysics Data System (ADS)

    Heap, Michael J.; Kennedy, Ben M.; Pernin, Noémie; Jacquemard, Laura; Baud, Patrick; Farquharson, Jamie I.; Scheu, Bettina; Lavallée, Yan; Gilg, H. Albert; Letham-Brake, Mark; Mayer, Klaus; Jolly, Arthur D.; Reuschlé, Thierry; Dingwell, Donald B.

    2015-03-01

    Volcanic hydrothermal systems host a prodigious variety of physico-chemical conditions. The physico-chemical state and mechanical behaviour of rocks within is correspondingly complex and often characterised by vast heterogeneity. Here, we present uniaxial and triaxial compression experiments designed to investigate the breadth of mechanical behaviour and failure modes (dilatant or compactant) for hydrothermally-altered lava and ash tuff deposits from Whakaari (White Island volcano) in New Zealand, a volcano with a well-documented and very active hydrothermal system. Our deformation experiments show that the failure mode of low porosity lava remains dilatant over a range of depths (up to pressures corresponding to depths of about 2 km). Upon failure, shear fractures, the result of the coalescence of dilatational microcracks, are universally present. The high porosity ash tuffs switch however from a dilatant to a compactant failure mode (driven by progressive distributed pore collapse) at relatively low pressure (corresponding to a depth of about 250 m). We capture the salient features of the dynamic conditions (e.g., differential stress, effective pressure) in a schematic cross section for the Whakaari hydrothermal system and map, for the different lithologies, areas susceptible to either dilatant vs. compactive modes of failure. The failure mode will impact, for example, the evolution of rock physical properties (e.g., porosity, permeability, and elastic wave velocity) and the nature of the seismicity accompanying periods of unrest. We outline accordingly the potential implications for the interpretation of seismic signals, outgassing, ground deformation, and the volcanic structural stability for Whakaari and similar hydrothermally-active volcanoes worldwide.

  15. Atomistic simulations to micro-mechanisms of adhesion in automotive applications

    NASA Astrophysics Data System (ADS)

    Sen, Fatih Gurcag

    This study aimed at depicting atomistic and microstructural aspects of adhesion and friction that appear in different automotive applications and manufacturing processes using atomistic simulations coupled with tribological tests and surface characterization experiments. Thin films that form at the contact interfaces due to chemical reactions and coatings that are developed to mitigate or enhance adhesion were studied in detail. The adhesion and friction experiments conducted on diamond-like carbon (DLC) coatings against Al indicated that F incorporation into DLC decreased the coefficient of friction (COF) by 30% -with respect to H-DLC that is known to have low COF and anti-adhesion properties against Al- to 0.14 owing to formation of repulsive F-F interactions at the sliding interface as shown by density functional theory (DFT) calculations. F atoms transferred to the Al surface with an increase in the contact pressure, and this F transfer led to the formation of a stable AlF3 compound at the Al surface as confirmed by XPS and cross-sectional FIB-TEM. The incorporation of Si and O in a F-containing DLC resulted in humidity independent low COF of 0.08 due to the hydration effect of the Si-O-Si chains in the carbonaceous tribolayers that resulted in repulsive OH-OH interactions at the contact interface. At high temperatures, adhesion of Al was found to be enhanced as a result of superplastic oxide fibers on the Al surface. Molecular dynamics (MD) simulations of tensile deformation of Al nanowires in oxygen carried out with ReaxFF showed that native oxide of Al has an oxygen deficient, low density structure and in O2, the oxygen diffusion in amorphous oxide healed the broken Al-O bonds during applied strain and resulted in the superplasticity. The oxide shell also provided nucleation sites for dislocations in Al crystal. In fuel cell applications, where low Pt/carbon adhesion is causing durability problems, spin-polarized DFT showed that metals with unfilled d

  16. Hydrological Effects on Failure Mechanism of the Shiaolin Landslide, Taiwan Induced by Typhoon Morakot

    NASA Astrophysics Data System (ADS)

    Lin, Meei-Ling; Chou, Li-Sheng

    2016-04-01

    In 2009 Typhoon Morakot struck southern Taiwan and induced a catastrophic landslide in Shiaolin Village, Kaoshiung City, and more than 400 people were killed. This research focused on the hydrological condition and its effect on the failure mechanism of the catastrophic Shiaolin Landslide. The topographic analysis was conducted using the DEM before and LiDAR derived DEM after the landslide. Based on results of the topographic analysis, a wedge type failure mode was deduced. In order to determine the critical sliding condition and geometry of the failure wedge, the PIV analysis, slope & aspect analysis and attitude analysis were conducted, and comparisons of results were made to finalize the geometry and attitude of the critical sliding condition of the Shiaolin Landslide. The stability analysis was conducted accordingly using material properties from laboratory test and estimation from the similar formation. The effects of ground water variation, possible effect of fault gouge on seepage water table, and the strength reduction of rock mass material were considered in the detailed analysis. The results suggested that the Shiaolin Landslide has a wedge type failure mode, and the ground water variation played an important role of the landslide, and the existence of fault gouge affected the ground hydrology significantly, which could lead to the critical failure of the Shiaolin Landslide.

  17. Kinetic Mechanism and Rate-Limiting Steps of Focal Adhesion Kinase-1

    SciTech Connect

    Schneck, Jessica L.; Briand, Jacques; Chen, Stephanie; Lehr, Ruth; McDevitt, Patrick; Zhao, Baoguang; Smallwood, Angela; Concha, Nestor; Oza, Khyati; Kirkpatrick, Robert; Yan, Kang; Villa, James P.; Meek, Thomas D.; Thrall, Sara H.

    2010-12-07

    Steady-state kinetic analysis of focal adhesion kinase-1 (FAK1) was performed using radiometric measurement of phosphorylation of a synthetic peptide substrate (Ac-RRRRRRSETDDYAEIID-NH{sub 2}, FAK-tide) which corresponds to the sequence of an autophosphorylation site in FAK1. Initial velocity studies were consistent with a sequential kinetic mechanism, for which apparent kinetic values k{sub cat} (0.052 {+-} 0.001 s{sup -1}), K{sub MgATP} (1.2 {+-} 0.1 {micro}M), K{sub iMgATP} (1.3 {+-} 0.2 {micro}M), K{sub FAK-tide} (5.6 {+-} 0.4 {micro}M), and K{sub iFAK-tide} (6.1 {+-} 1.1 {micro}M) were obtained. Product and dead-end inhibition data indicated that enzymatic phosphorylation of FAK-tide by FAK1 was best described by a random bi bi kinetic mechanism, for which both E-MgADP-FAK-tide and E-MgATP-P-FAK-tide dead-end complexes form. FAK1 catalyzed the {beta}{gamma}-bridge:{beta}-nonbridge positional oxygen exchange of [{gamma}-{sup 18}O{sub 4}]ATP in the presence of 1 mM [{gamma}-{sup 18}O{sub 4}]ATP and 1.5 mM FAK-tide with a progressive time course which was commensurate with catalysis, resulting in a rate of exchange to catalysis of k{sub x}/k{sub cat} = 0.14 {+-} 0.01. These results indicate that phosphoryl transfer is reversible and that a slow kinetic step follows formation of the E-MgADP-P-FAK-tide complex. Further kinetic studies performed in the presence of the microscopic viscosogen sucrose revealed that solvent viscosity had no effect on k{sub cat}/K{sub FAK-tide}, while k{sub cat} and k{sub cat}/K{sub MgATP} were both decreased linearly at increasing solvent viscosity. Crystallographic characterization of inactive versus AMP-PNP-liganded structures of FAK1 showed that a large conformational motion of the activation loop upon ATP binding may be an essential step during catalysis and would explain the viscosity effect observed on k{sub cat}/K{sub m} for MgATP but not on k{sub cat}/K{sub m} for FAK-tide. From the positional isotope exchange, viscosity, and

  18. Splat Formation and Adhesion Mechanisms of Cold Gas-Sprayed Al Coatings on Al2O3 Substrates

    NASA Astrophysics Data System (ADS)

    Drehmann, R.; Grund, T.; Lampke, T.; Wielage, B.; Manygoats, K.; Schucknecht, T.; Rafaja, D.

    2014-01-01

    The metallization of ceramics by means of cold gas spraying (CGS) has been in the focus of numerous publications in the recent past. However, the bonding mechanism of metallic coatings on non-ductile substrates is still not fully understood. Former investigations of titanium coatings deposited on corundum revealed that a combination of recrystallization induced by adiabatic shear processes and hetero-epitaxial growth might be responsible for the high adhesion strengths of coatings applied on smooth ceramic surfaces. In the present work, the interface formation between CGS aluminum and alumina substrates is examined for different particle sizes and substrate temperatures. Furthermore, the influence of subsequent heat treatment on tensile strength and hardness is investigated. The splat formation of single particles is examined by means of scanning electron microscopy, while a high resolution transmission electron microscope is used to study the Al/Al2O3 interface. First results suggest that mechanical interlocking is the primary adhesion mechanism on polycrystalline substrates having the roughness in sub-micrometer range, while the heteroepitaxy between Al and Al2O3 can be considered as the main bonding mechanism for single-crystalline sapphire (α-Al2O3) substrates with the surface roughness in nanometer range. The heteroepitaxial growth is facilitated by deformation-induced recrystallisation of CGS aluminum.

  19. The effect of ionic strength on oil adhesion in sandstone – the search for the low salinity mechanism

    PubMed Central

    Hilner, E.; Andersson, M. P.; Hassenkam, T.; Matthiesen, J.; Salino, P. A.; Stipp, S. L. S.

    2015-01-01

    Core flood and field tests have demonstrated that decreasing injection water salinity increases oil recovery from sandstone reservoirs. However, the microscopic mechanism behind the effect is still under debate. One hypothesis is that as salinity decreases, expansion of the electrical double layer decreases attraction between organic molecules and pore surfaces. We have developed a method that uses atomic force microscopy (AFM) in chemical force mapping (CFM) mode to explore the relationship between wettability and salinity. We functionalised AFM tips with alkanes and used them to represent tiny nonpolar oil droplets. In repeated measurements, we brought our “oil” close to the surface of sand grains taken from core plugs and we measured the adhesion between the tip and sample. Adhesion was constant in high salinity solutions but below a threshold of 5,000 to 8,000 ppm, adhesion decreased as salinity decreased, rendering the surface less oil wet. The effect was consistent, reproducible and reversible. The threshold for the onset of low salinity response fits remarkably well with observations from core plug experiments and field tests. The results demonstrate that the electric double layer force always contributes at least in part to the low salinity effect, decreasing oil wettability when salinity is low. PMID:25899050

  20. Therapeutic effects of tyroservatide on metastasis of lung cancer and its mechanism affecting integrin–focal adhesion kinase signal transduction

    PubMed Central

    Huang, Yu-ting; Zhao, Lan; Fu, Zheng; Zhao, Meng; Song, Xiao-meng; Jia, Jing; Wang, Song; Li, Jin-ping; Zhu, Zhi-feng; Lin, Gang; Lu, Rong; Yao, Zhi

    2016-01-01

    Tyroservatide (YSV) can inhibit the growth and metastasis of mouse lung cancer significantly. This study investigated the therapeutic effects of tripeptide YSV on metastasis of human lung cancer cells and explored its possible mechanism that affects integrin–focal adhesion kinase (FAK) signal transduction in tumor cells. YSV significantly inhibited the adhesion and the invasion of highly metastatic human lung cancer cell lines 95D, A549, and NCI-H1299. In addition, YSV significantly inhibited phosphorylation of FAK Tyr397 and FAK Tyr576/577 in the 95D, A549, and NCI-H1299 human lung cancer cells in vitro. And the mRNA level and protein expression of FAK in these human lung cancer cells decreased at the same time. YSV also significantly inhibited mRNA and protein levels of integrin β1 and integrin β3 in the 95D, A549, and NCI-H1299 human lung cancer cells. Our research showed that YSV inhibited adhesion and invasion of human lung cancer cells and exhibited therapeutic effects on metastasis of lung cancer. PMID:27041993

  1. The effect of ionic strength on oil adhesion in sandstone--the search for the low salinity mechanism.

    PubMed

    Hilner, E; Andersson, M P; Hassenkam, T; Matthiesen, J; Salino, P A; Stipp, S L S

    2015-01-01

    Core flood and field tests have demonstrated that decreasing injection water salinity increases oil recovery from sandstone reservoirs. However, the microscopic mechanism behind the effect is still under debate. One hypothesis is that as salinity decreases, expansion of the electrical double layer decreases attraction between organic molecules and pore surfaces. We have developed a method that uses atomic force microscopy (AFM) in chemical force mapping (CFM) mode to explore the relationship between wettability and salinity. We functionalised AFM tips with alkanes and used them to represent tiny nonpolar oil droplets. In repeated measurements, we brought our "oil" close to the surface of sand grains taken from core plugs and we measured the adhesion between the tip and sample. Adhesion was constant in high salinity solutions but below a threshold of 5,000 to 8,000 ppm, adhesion decreased as salinity decreased, rendering the surface less oil wet. The effect was consistent, reproducible and reversible. The threshold for the onset of low salinity response fits remarkably well with observations from core plug experiments and field tests. The results demonstrate that the electric double layer force always contributes at least in part to the low salinity effect, decreasing oil wettability when salinity is low. PMID:25899050

  2. Ly6Chigh Monocytes Protect against Kidney Damage during Sepsis via a CX3CR1-Dependent Adhesion Mechanism.

    PubMed

    Chousterman, Benjamin G; Boissonnas, Alexandre; Poupel, Lucie; Baudesson de Chanville, Camille; Adam, Julien; Tabibzadeh, Nahid; Licata, Fabrice; Lukaszewicz, Anne-Claire; Lombès, Amélie; Deterre, Philippe; Payen, Didier; Combadière, Christophe

    2016-03-01

    Monocytes have a crucial role in both proinflammatory and anti-inflammatory phenomena occurring during sepsis. Monocyte recruitment and activation are orchestrated by the chemokine receptors CX3CR1 and CCR2 and their cognate ligands. However, little is known about the roles of these cells and chemokines during the acute phase of inflammation in sepsis. Using intravital microscopy in a murine model of polymicrobial sepsis, we showed that inflammatory Ly6C(high) monocytes infiltrated kidneys, exhibited altered motility, and adhered strongly to the renal vascular wall in a chemokine receptor CX3CR1-dependent manner. Adoptive transfer of Cx3cr1-proficient monocyte-enriched bone marrow cells into septic Cx3cr1-depleted mice prevented kidney damage and promoted mouse survival. Modulation of CX3CR1 activation in septic mice controlled monocyte adhesion, regulated proinflammatory and anti-inflammatory cytokine expression, and was associated with the extent of kidney lesions such that the number of lesions decreased when CX3CR1 activity increased. Consistent with these results, the pro-adhesive I249 CX3CR1 allele in humans was associated with a lower incidence of AKI in patients with sepsis. These data show that inflammatory monocytes have a protective effect during sepsis via a CX3CR1-dependent adhesion mechanism. This receptor might be a new therapeutic target for kidney injury during sepsis. PMID:26160897

  3. Examination of cadmium safety rod thermal test specimens and failure mechanism evaluation

    SciTech Connect

    Thomas, J.K.; Peacock, H.B.; Iyer, N.C.

    1992-01-01

    The reactor safety rods may be subjected to high temperatures due to gamma heating after the core coolant level has dropped during the ECS phase of a hypothetical LOCA event. Accordingly, an experimental cadmium safety rod testing subtask was established as part of a task to address the response of reactor core components to this accident. Companion reports describe the experiments and a structural evaluation (finite element analysis) of the safety rod. This report deals primarily with the examination of the test specimens, evaluation of possible failure mechanisms, and confirmatory separate effects experiments. It is concluded that the failures observed in the cadmium safety rod thermal tests which occurred at low temperature (T < 600{degrees}C) with slow thermal ramp rates (slow cladding strain rates) resulted from localized dissolution of the stainless steel cladding by the cadmium/aluminum solution and subsequent ductility exhaustion and rupture. The slow thermal ramp rate is believed to be the root cause for the failures; specifically, the slow ramp rate led to localized cladding shear deformation which ruptured the protective oxide film on the cladding inner surface and allowed dissolution to initiate. The test results and proposed failure mechanism support the conclusion that the rods would not fail below 500{degrees}C even at slow ramp rates. The safety rod thermal test specimen failures which occurred at high temperature (T > 800{degrees}C) with fast thermal ramp rates are concluded to be mechanical in nature without significant environmental degradation. Based on these tests, tasks were initiated to design and manufacture B{sub 4}C safety rods to replace the cadmium safety rods. The B{sub 4}C safety rods have been manufactured at this time and it is currently planned to charge them to the reactor in the near future. 60 refs.

  4. Application of dynamic fracture mechanics to the investigation of catastrophic failure in aircraft structures

    NASA Astrophysics Data System (ADS)

    Chow, Benjamin Bin

    A dynamic fracture mechanics approach to the estimation of the residual strength of aircraft structures is presented. The dependence of the dynamic crack initiation toughness of aluminum 2024-T3 on loading rate is first studied experimentally. Based on the experimental results and on established dynamic fracture mechanic concepts, a fracture mechanics based failure model is established and is used to estimate the residual strength of aircraft structures. A methodology to determine residual strength of dynamically loaded structures based on global structural analysis coupled with local finite element analysis is introduced. Local finite element calculations were performed for different loading rates to simulate the conditions encountered in an explosively loaded aircraft fuselage. The results from the analyses were then used in conjunction with the experimental results for the dynamic fracture toughness of a 2024-T3 aluminum alloy as a function of loading rate, KdIC vs. K˙d(t), to determine the time to failure, tf, for a given loading rate. A failure envelope, sf vs. ṡ , based on the failure model and finite element analysis, is presented for the different cases and the implications for the residual strength of aircraft structures is discussed. Mixed mode dynamic crack initiation in aluminum 2024-T3 alloy is investigated by combining experiments with numerical simulations. The optical technique of coherent gradient sensing (CGS) and a strain gage method are employed to study the evolution of the mixed mode stress intensity factors. The dynamic mixed mode failure envelope is obtained using the crack initiation data from the experiments at a nominal loading rate of 7 x 105 MPam/s . Numerical simulations of the experiments are conducted to both help in designing the experiments and to validate the results of the experiments. The numerical simulations show good correlation with the experimental results.

  5. Friction Stir Weld Failure Mechanisms in Aluminum-Armor Structures Under Ballistic Impact Loading Conditions

    NASA Astrophysics Data System (ADS)

    Grujicic, M.; Pandurangan, B.; Arakere, A.; Yen, C.-F.; Cheeseman, B. A.

    2013-01-01

    A critical assessment is carried out of the microstructural changes in respect of the associated reductions in material mechanical properties and of the attendant ballistic-impact failure mechanisms in prototypical friction stir welding (FSW) joints found in armor structures made of high-performance aluminum alloys (including solution-strengthened and age-hardenable aluminum alloy grades). It is argued that due to the large width of FSW joints found in thick aluminum-armor weldments, the overall ballistic performance of the armor is controlled by the ballistic limits of its weld zones (e.g., heat-affected zone, the thermomechanically affected zone, the nugget, etc.). Thus, in order to assess the overall ballistic survivability of an armor weldment, one must predict/identify welding-induced changes in the material microstructure and properties, and the operative failure mechanisms in different regions of the weld. Toward this end, a procedure is proposed in the present study which combines the results of the FSW process modeling, basic physical-metallurgy principles concerning microstructure/property relations, and the fracture mechanics concepts related to the key blast/ballistic-impact failure modes. The utility of this procedure is demonstrated using the case of a solid-solution strengthened and cold-worked aluminum alloy armor FSW-weld test structure.

  6. Tension and twist of chiral nanotubes: torsional buckling, mechanical response and indicators of failure

    NASA Astrophysics Data System (ADS)

    Aghaei, Amin; Dayal, Kaushik

    2012-12-01

    We report on molecular dynamic calculations of combined tension-torsion of chiral single-wall nanotubes. We work within the framework of objective structures that exploits symmetry groups to enable torsion of chiral nanotubes, in addition to non-equilibrium extension. We apply the method to study the mechanical response and failure of nanotubes of various chiralities. We find that three distinct regimes exist for nanotubes under twist: distorted but unbuckled, reversible torsional buckling and irreversible torsional buckling. When twisted but unbuckled nanotubes are subject to tension, there is minimal change in failure strain, whereas reversibly buckled nanotubes have substantially reduced failure strain and load. We also observe the evolution of the twisting moment during the elongation process while keeping the twist angle fixed. This evolution has two interesting and potentially useful features: first, some nanotubes ‘unbuckle’ in the process of extension, and second, there is a clear correlation between extrema in the evolution of the twisting moment and impending nanotube failure. Given the sensitivity of electrical properties in carbon nanotubes to torsion, and the recent demonstrations of measuring torsion-induced changes, the latter feature suggests the possibility of real-time diagnostics to detect critical mechanical events.

  7. A fundamental approach to adhesion: Synthesis, surface analysis, thermodynamics and mechanics

    NASA Technical Reports Server (NTRS)

    Dwight, D. W.; Wightman, J. P.

    1977-01-01

    The ability of SEM/EDAX to determine the physical and chemical composition of very small areas was used to study several diverse types of samples representative of NASA-LaRC technology. More systematic investigation was carried out on differences in the results of grit-blasting Ti 6-4 adherends and the presence of extraneous elements, primarily silicon, in some polymer/HT-S fiber composites. Initial results were obtained from a fractured (ILS) short-beam shear specimen, and from Ti 6-4 alloy, before and after a proprietary Boeing anodizing surface preparation for adhesive bonding. Photomicrographs and EDAX spectra were also obtained from new, fractured lap shear strength specimens that employed PPQ and LARC-13 adhesives.

  8. Arginine stimulates intestinal cell migration through a focal adhesion kinase dependent mechanism

    PubMed Central

    Rhoads, J M; Chen, W; Gookin, J; Wu, G Y; Fu, Q; Blikslager, A T; Rippe, R A; Argenzio, R A; Cance, W G; Weaver, E M; Romer, L H

    2004-01-01

    Background: l-Arginine is a nutritional supplement that may be useful for promoting intestinal repair. Arginine is metabolised by the oxidative deiminase pathway to form nitric oxide (NO) and by the arginase pathway to yield ornithine and polyamines. Aims: To determine if arginine stimulates restitution via activation of NO synthesis and/or polyamine synthesis. Methods: We determined the effects of arginine on cultured intestinal cell migration, NO production, polyamine levels, and activation of focal adhesion kinase, a key mediator of cell migration. Results: Arginine increased the rate of cell migration in a dose dependent biphasic manner, and was additive with bovine serum concentrate (BSC). Arginine and an NO donor activated focal adhesion kinase (a tyrosine kinase which localises to cell matrix contacts and mediates β1 integrin signalling) after wounding. Arginine stimulated cell migration was dependent on focal adhesion kinase (FAK) signalling, as demonstrated using adenovirus mediated transfection with a kinase negative mutant of FAK. Arginine stimulated migration was dependent on NO production and was blocked by NO synthase inhibitors. Arginine dependent migration required synthesis of polyamines but elevating extracellular arginine concentration above 0.4 mM did not enhance cellular polyamine levels. Conclusions: These results showed that l-arginine stimulates cell migration through NO and FAK dependent pathways and that combination therapy with arginine and BSC may enhance intestinal restitution via separate and convergent pathways. PMID:15016745

  9. Multiscale treatment of theoretical mechanisms for the protection of hydrogel surfaces from adhesive forces

    NASA Astrophysics Data System (ADS)

    Sokoloff, J. B.

    2014-09-01

    One role of a lubricant is to prevent wear of two surfaces in contact, which is likely to be the result of adhesive forces that cause a pair of asperities belonging to two surfaces in contact to stick together. Such adhesive sticking of asperities can occur both for sliding surfaces and for surfaces which are pressed together and then pulled apart. The latter situation, for example, is important for contact lenses, as prevention of sticking reduces possible damage to the cornea as the lenses are inserted and removed from the eye. Contact lenses are made from both neutral and polyelectrolyte hydrogels. It is demonstrated here that sticking of neutral hydrogels can be prevented by repulsive forces between asperities in contact, resulting from polymers attached to the gel surface but not linked with each other. For polyelectrolyte hydrogels, it is shown that osmotic pressure due to counterions, held at the interface between asperities in contact by the electrostatic attraction between the ions and the fixed charges in the gel, can provide a sufficiently strong repulsive force to prevent adhesive sticking of small-length-scale asperities.

  10. Mechanisms Regulating the Degradation of Dentin Matrices by Endogenous Dentin Proteases and their Role in Dental Adhesion. A Review

    PubMed Central

    Sabatini, Camila; Pashley, David H.

    2015-01-01

    Purpose This systematic review provides an overview of the different mechanisms proposed to regulate the degradation of dentin matrices bye host-derived dentin proteases, particularly as it relates to their role in dental adhesion. Methods Significant developments have taken place over the last few years that have contributed to a better understanding of all the factors affecting the durability of adhesive resin restorations. The complexity of dentin-resin interfaces mandates a thorough understanding of all the mechanical, physical and biochemical aspects that play a role in the formation of hybrid layers. The ionic and hydrophilic nature of current dental adhesives yields permeable, unstable hybrid layers susceptible to water sorption, hydrolytic degradation and resin leaching. The hydrolytic activity of host-derived proteases also contributes to the degradation of the resin-dentin bonds. Preservation of the collagen matrix is critical to the improvement of resin-dentin bond durability. Approaches to regulate collagenolytic activity of dentin proteases have been the subject of extensive research in the last few years. A shift has occurred from the use of proteases inhibitors to the use of collagen cross-linking agents. Data provided by fifty-one studies published in peer-reviewed journals between January 1999 and December 2013 was compiled in this systematic review. Results Appraisal of the data provided by the studies included in the present review yielded a summary of the mechanisms which have already proven to be clinically successful and those which need further investigation before new clinical protocols can be adopted. PMID:25831604

  11. Mechanical properties and platelet adhesion behavior of diamond-like carbon films synthesized by pulsed vacuum arc plasma deposition

    NASA Astrophysics Data System (ADS)

    Leng, Y. X.; Chen, J. Y.; Yang, P.; Sun, H.; Wan, G. J.; Huang, N.

    2003-05-01

    Diamond-like carbon (DLC) is an attractive biomedical material due to its high inertness and excellent mechanical properties. In this study, DLC films were fabricated on Ti6Al4V and Si(1 0 0) substrates at room temperature by pulsed vacuum arc plasma deposition. By changing the argon flow from 0 to 13 sccm during deposition, the effects of argon flow on the characteristics of the DLC films were systematically examined to correlate to the blood compatibility. The microstructure and mechanical properties of the films were investigated using Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) surface analysis, a nano-indenter and pin-on-disk tribometer. The blood compatibility of the films was evaluated using in vitro platelet adhesion investigation, and the quantity and morphology of the adherent platelets was investigated employing optical microscopy and scanning electron microscopy. The Raman spectroscopy results showed a decreasing sp 3 fraction (an increasing trend in ID/ IG ratio) with increasing argon flow from 0 to 13 sccm. The sp 3:sp 2 ratio of the films was evaluated from the deconvoluted XPS spectra. We found that the sp 3 fraction decreased as the argon flow was increased from 0 to 13 sccm, which is consistent with the results of the Raman spectra. The mechanical properties results confirmed the decreasing sp 3 content with increasing argon flow. The Raman D-band to G-band intensity ratio increased and the platelet adhesion behavior became better with higher flow. This implies that the blood compatibility of the DLC films is influenced by the sp 3:sp 2 ratio. DLC films deposited on titanium alloys have high wear resistance, low friction and good adhesion.

  12. Deformation and failure of single- and multi-phase silicate liquids: seismic precursors and mechanical work

    NASA Astrophysics Data System (ADS)

    Vasseur, Jeremie; Lavallée, Yan; Hess, Kai-Uwe; Wassermann, Joachim; Dingwell, Donald B.

    2013-04-01

    Along with many others, volcanic unrest is regarded as a catastrophic material failure phenomenon and is often preceded by diverse precursory signals. Although a volcanic system intrinsically behave in a non-linear and stochastic way, these precursors display systematic evolutionary trends to upcoming eruptions. Seismic signals in particular are in general dramatically increasing prior to an eruption and have been extensively reported to show accelerating rates through time, as well as in the laboratory before failure of rock samples. At the lab-scale, acoustic emissions (AE) are high frequency transient stress waves used to track fracture initiation and propagation inside a rock sample. Synthesized glass samples featuring a range of porosities (0 - 30%) and natural rock samples from volcán de Colima, Mexico, have been failed under high temperature uniaxial compression experiments at constant stresses and strain rates. Using the monitored AEs and the generated mechanical work during deformation, we investigated the evolutionary trends of energy patterns associated to different degrees of heterogeneity. We observed that the failure of dense, poorly porous glasses is achieved by exceeding elevated strength and thus requires a significant accumulation of strain, meaning only pervasive small-scale cracking is occurring. More porous glasses as well as volcanic samples need much lower applied stress and deformation to fail, as fractures are nucleating, propagating and coalescing into localized large-scale cracks, taking the advantage of the existence of numerous defects (voids for glasses, voids and crystals for volcanic rocks). These observations demonstrate that the mechanical work generated through cracking is efficiently distributed inside denser and more homogeneous samples, as underlined by the overall lower AE energy released during experiments. In contrast, the quicker and larger AE energy released during the loading of heterogeneous samples shows that the

  13. Parametric Studies Of Failure Mechanisms In Thermal Barrier Coatings During Thermal Cycling Using FEM

    NASA Astrophysics Data System (ADS)

    Srivathsa, B.; Das, D. K.

    2015-12-01

    Thermal barrier coatings (TBCs) are widely used on different hot components of gas turbine engines such as blades and vanes. Although, several mechanisms for the failure of the TBCs have been suggested, it is largely accepted that the durability of these coatings is primarily determined by the residual stresses that are developed during the thermal cycling. In the present study, the residual stress build-up in an electron beam physical vapour deposition (EB-PVD) based TBCs on a coupon during thermal cycling has been studied by varying three parameters such as the cooling rate, TBC thickness and substrate thickness. A two-dimensional thermomechanical generalized plane strain finite element simulations have been performed for thousand cycles. It was observed that these variations change the stress profile significantly and the stress severity factor increases non-linearly. Overall, the predictions of the model agree with reported experimental results and help in predicting the failure mechanisms.

  14. Electrochemical corrosion failure mechanism of M152 steel under a salt-spray environment

    NASA Astrophysics Data System (ADS)

    Yi, Pan; Xiao, Kui; Ding, Kang-kang; Wang, Xu; Yan, Li-dan; Mao, Cheng-liang; Dong, Chao-fang; Li, Xiao-gang

    2015-11-01

    The corrosion failure mechanism of M152 was studied using the neutral salt-spray test to better understand the corrosion behavior of 1Cr12Ni3Mo2VN (M152), provide a basis for the optimization of material selection, and prevent the occurrence of failure. Moreover, the mechanism was investigated using the mass loss method, polarization curves, electrochemical impedance spectroscopy (EIS), stereology microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy (EDS). The results show that M152 steel suffers severe corrosion, especially pitting corrosion, in a high-salt-spray environment. In the early stage of the experiment, the color of the corrosion products was mainly orange. The products then gradually evolved into a dense, brown substance, which coincided with a decrease of corrosion rate. Correspondingly, the EIS spectrum of M152 in the late test also exhibited three time constants and presented Warburg impedance at low frequencies.

  15. Failure mechanisms of additively manufactured porous biomaterials: Effects of porosity and type of unit cell.

    PubMed

    Kadkhodapour, J; Montazerian, H; Darabi, A Ch; Anaraki, A P; Ahmadi, S M; Zadpoor, A A; Schmauder, S

    2015-10-01

    Since the advent of additive manufacturing techniques, regular porous biomaterials have emerged as promising candidates for tissue engineering scaffolds owing to their controllable pore architecture and feasibility in producing scaffolds from a variety of biomaterials. The architecture of scaffolds could be designed to achieve similar mechanical properties as in the host bone tissue, thereby avoiding issues such as stress shielding in bone replacement procedure. In this paper, the deformation and failure mechanisms of porous titanium (Ti6Al4V) biomaterials manufactured by selective laser melting from two different types of repeating unit cells, namely cubic and diamond lattice structures, with four different porosities are studied. The mechanical behavior of the above-mentioned porous biomaterials was studied using finite element models. The computational results were compared with the experimental findings from a previous study of ours. The Johnson-Cook plasticity and damage model was implemented in the finite element models to simulate the failure of the additively manufactured scaffolds under compression. The computationally predicted stress-strain curves were compared with the experimental ones. The computational models incorporating the Johnson-Cook damage model could predict the plateau stress and maximum stress at the first peak with less than 18% error. Moreover, the computationally predicted deformation modes were in good agreement with the results of scaling law analysis. A layer-by-layer failure mechanism was found for the stretch-dominated structures, i.e. structures made from the cubic unit cell, while the failure of the bending-dominated structures, i.e. structures made from the diamond unit cells, was accompanied by the shearing bands of 45°. PMID:26143351

  16. Bibliography of information on mechanics of structural failure (hydrogen embrittlement, protective coatings, composite materials, NDE)

    NASA Technical Reports Server (NTRS)

    Carpenter, J. L., Jr.

    1976-01-01

    This bibliography is comprised of approximately 1,600 reference citations related to four problem areas in the mechanics of failure in aerospace structures. The bibliography represents a search of the literature published in the period 1962-1976, the effort being largely limited to documents published in the United States. Listings are subdivided into the four problem areas: Hydrogen Embrittlement; Protective Coatings; Composite Materials; and Nondestructive Evaluation. An author index is included.

  17. Vimentin contributes to epithelial-mesenchymal transition cancer cell mechanics by mediating cytoskeletal organization and focal adhesion maturation

    PubMed Central

    Liu, Ching-Yi; Lin, Hsi-Hui; Tang, Ming-Jer; Wang, Yang-Kao

    2015-01-01

    Modulations of cytoskeletal organization and focal adhesion turnover correlate to tumorigenesis and epithelial-mesenchymal transition (EMT), the latter process accompanied by the loss of epithelial markers and the gain of mesenchymal markers (e.g., vimentin). Clinical microarray results demonstrated that increased levels of vimentin mRNA after chemotherapy correlated to a poor prognosis of breast cancer patients. We hypothesized that vimentin mediated the reorganization of cytoskeletons to maintain the mechanical integrity in EMT cancer cells. By using knockdown strategy, the results showed reduced cell proliferation, impaired wound healing, loss of directional migration, and increased large membrane extension in MDA-MB 231 cells. Vimentin depletion also induced reorganization of cytoskeletons and reduced focal adhesions, which resulted in impaired mechanical strength because of reduced cell stiffness and contractile force. In addition, overexpressing vimentin in MCF7 cells increased cell stiffness, elevated cell motility and directional migration, reoriented microtubule polarity, and increased EMT phenotypes due to the increased β1-integrin and the loss of junction protein E-cadherin. The EMT-related transcription factor slug was also mediated by vimentin. The current study demonstrated that vimentin serves as a regulator to maintain intracellular mechanical homeostasis by mediating cytoskeleton architecture and the balance of cell force generation in EMT cancer cells. PMID:25965826

  18. Improving the fatigue resistance of adhesive joints in laminated wood structures

    NASA Technical Reports Server (NTRS)

    Laufenberg, Theodore L.; River, Bryan H.; Murmanis, Lidija L.; Christiansen, Alfred W.

    1988-01-01

    The premature fatigue failure of a laminated wood/epoxy test beam containing a cross section finger joint was the subject of a multi-disciplinary investigation. The primary objectives were to identify the failure mechanisms which occurred during the finger joint test and to provide avenues for general improvements in the design and fabrication of adhesive joints in laminated wood structures.

  19. Investigation into the Formation and Adhesion of Cyclopentane Hydrates on Mechanically Robust Vapor-Deposited Polymeric Coatings.

    PubMed

    Sojoudi, Hossein; Walsh, Matthew R; Gleason, Karen K; McKinley, Gareth H

    2015-06-01

    Blockage of pipelines by formation and accumulation of clathrate hydrates of natural gases (also called gas hydrates) can compromise project safety and economics in oil and gas operations, particularly at high pressures and low temperatures such as those found in subsea or arctic environments. Cyclopentane (CyC5) hydrate has attracted interest as a model system for studying natural gas hydrates, because CyC5, like typical natural gas hydrate formers, is almost fully immiscible in water; and thus CyC5 hydrate formation is governed not only by thermodynamic phase considerations but also kinetic factors such as the hydrocarbon/water interfacial area, as well as mass and heat transfer constraints, as for natural gas hydrates. We present a macroscale investigation of the formation and adhesion strength of CyC5 hydrate deposits on bilayer polymer coatings with a range of wettabilities. The polymeric bilayer coatings are developed using initiated chemical vapor deposition (iCVD) of a mechanically robust and densely cross-linked polymeric base layer (polydivinylbenzene or pDVB) that is capped with a covalently attached thin hydrate-phobic fluorine-rich top layer (poly(perfluorodecyl acrylate) or pPFDA). The CyC5 hydrates are formed from CyC5-in-water emulsions, and differential scanning calorimetry (DSC) is used to confirm the thermal dissociation properties of the solid hydrate deposits. We also investigate the adhesion of the CyC5 hydrate deposits on bare and bilayer polymer-coated silicon and steel substrates. Goniometric measurements with drops of CyC5-in-water emulsions on the coated steel substrates exhibit advancing contact angles of 148.3 ± 4.5° and receding contact angles of 142.5 ± 9.8°, indicating the strongly emulsion-repelling nature of the iCVD coatings. The adhesion strength of the CyC5 hydrate deposits is reduced from 220 ± 45 kPa on rough steel substrates to 20 ± 17 kPa on the polymer-coated steel substrates. The measured strength of CyC5 hydrate

  20. Failure mechanisms of polycrystalline diamond compact drill bits in geothermal environments

    SciTech Connect

    Hoover, E.R.; Pope, L.E.

    1981-09-01

    Over the past few years the interest in polycrystalline diamond compact (PDC) drill bits has grown proportionately with their successful use in drilling oil and gas wells in the North Sea and the United States. This keen interest led to a research program at Sandia to develop PDC drill bits suitable for the severe drilling conditions encountered in geothermal fields. Recently, three different PDC drill bits were tested using either air or mud drilling fluids: one in the laboratory with hot air, one in the Geysers field with air, and one in the Geysers field with mud. All three tests were unsuccessful due to failure of the braze joint used to attach the PDC drill blanks to the tungsten carbide studs. A post-mortem failure analysis of the defective cutters identified three major failure mechanisms: peripheral nonbonding caused by braze oxidation during the brazing step, nonbonding between PDC drill blanks and the braze due to contamination prior to brazing, and hot shortness. No evidence was found to suggest that the braze failures in the Geysers field tests were caused by frictional heating. In addition, inspection of the PDC/stud cutter assemblies using ultrasonic techniques was found to be ineffective for detecting the presence of hot shortness in the braze joint.

  1. How heterogeneity in the shear dilation of a deposit controls the mechanics of breaching slope failure

    NASA Astrophysics Data System (ADS)

    You, Yao; Flemings, Peter; Mohrig, David; Germaine, John

    2014-11-01

    Breaching is a type of retrogressive submarine slope failure associated with pore pressure drops in both space and time, and this drop strengthens the failing deposit. Breaching is characterized by a near-vertical failure surface that retreats with a relatively constant velocity, on the order of a millimeter per second. Breaching is controlled by interactions between shear-dilation-generated pore pressure drops and pore pressure dissipation through intergranular fluid flow. Laboratory measurements show that shear dilation in a deposit increases with increasing effective stress ratio between the major principal effective stress and the minor principal effective stress as well as decreasing confining stress. We present a two-dimensional numerical model that indicates how effective stress ratio and confining stress produce spatially varying dilation, affecting the mechanics of breaching. Experimental results show that dilation in a breaching deposit increases with proximity to the failure surface. As a result, the maximum magnitude of pore pressure drop is very close to the failure surface. The numerical model confirms that the sediment release is dominated by pore pressure dissipation through intergranular fluid flow in the horizontal direction. This allows the erosion rate to be treated as a constant in the vertical direction. Numerical model results also show that because dilation decreases with increasing vertical depth, the deposit becomes less stable with depth, suggesting a potential upper limit for the thickness of the deposit undergoing breaching.

  2. MUC16 contributes to the metastasis of pancreatic ductal adenocarcinoma through focal adhesion mediated signaling mechanism

    PubMed Central

    Chugh, Seema; Rachagani, Satyanarayana; Lakshmanan, Imayavaramban; Gupta, Suprit; Seshacharyulu, Parthasarathy; Smith, Lynette M.; Ponnusamy, Moorthy P.; Batra, Surinder K.

    2016-01-01

    MUC16, a heavily glycosylated type-I transmembrane mucin is overexpressed in several cancers including pancreatic ductal adenocarcinoma (PDAC). Previously, we have shown that MUC16 is significantly overexpressed in human PDAC tissues. However, the functional consequences and its role in PDAC is poorly understood. Here, we show that MUC16 knockdown decreases PDAC cell proliferation, colony formation and migration in vitro. Also, MUC16 knockdown decreases the tumor formation and metastasis in orthotopic xenograft mouse model. Mechanistically, immunoprecipitation and immunofluorescence analyses confirms MUC16 interaction with galectin-3 and mesothelin in PDAC cells. Adhesion assay displayed decreased cell attachment of MUC16 knockdown cells with recombinant galectin-1 and galectin-3 protein. Further, CRISPR/Cas9-mediated MUC16 knockout cells show decreased tumor-associated carbohydrate antigens (T and Tn) in PDAC cells. Importantly, carbohydrate antigens were decreased in the region that corresponds to MUC16 and suggests for the decreased MUC16-galectin interactions. Co-immunoprecipitation also revealed a novel interaction between MUC16 and FAK in PDAC cells. Interestingly, we observed decreased expression of mesenchymal and increased expression of epithelial markers in MUC16-silenced cells. Additionally, MUC16 loss showed a decreased FAK-mediated Akt and ERK/MAPK activation. Altogether, these findings suggest that MUC16-focal adhesion signaling may play a critical role in facilitating PDAC growth and metastasis. PMID:27382435

  3. Failure and deformation mechanisms at macro- and nano-scales of alkali activated clay

    NASA Astrophysics Data System (ADS)

    Sekhar Das, Pradip; Bhattacharya, Manjima; Chanda, Dipak Kr; Dalui, Srikanta; Acharya, Saikat; Ghosh, Swapankumar; Mukhopadhyay, Anoop Kumar

    2016-06-01

    Here we report two qualitative models on failure and deformation mechanisms at macro- and nano-scales of alkali activated clay (AACL), a material of extraordinary importance as a low cost building material. The models were based on experimental data of compressive failure and nanoindentation response of the AACL materials. A 420% improvement in compressive strength (σ c) of the AACL was achieved after 28 days (d) of curing at room temperature and it correlated well with the decrements in the residual alkali and pH concentrations with the increase in curing time. Based on extensive post-mortem FE-SEM examinations, a schematic model for the compressive failure mechanism of AACL was proposed. In addition, the nanoindentation results of AACL provided the first ever experimental evidence of the presence of nano-scale plasticity and a nano-scale contact deformation resistance that increased with the applied load. These results meant the development of a unique strain tolerant microstructure in the AACL of Indian origin. The implications of these new observations were discussed in terms of a qualitative model based on the deformation of layered clay structure.

  4. Tension Strength, Failure Prediction and Damage Mechanisms in 2D Triaxial Braided Composites with Notch

    NASA Technical Reports Server (NTRS)

    Norman, Timothy L.; Anglin, Colin

    1995-01-01

    The unnotched and notched (open hole) tensile strength and failure mechanisms of two-dimensional (2D) triaxial braided composites were examined. The effect of notch size and notch position were investigated. Damage initiation and propagation in notched and unnotched coupons were also examined. Theory developed to predict the normal stress distribution near an open hole and failure for tape laminated composites was evaluated for its applicability to 2D triaxial braided textile composite materials. Four different fiber architectures were considered; braid angle, yarn and braider size, percentage of longitudinal yarns and braider angle varied. Tape laminates equivalent to textile composites were also constructed for comparison. Unnotched tape equivalents were stronger than braided textiles but exhibited greater notch sensitivity. Notched textiles and tape equivalents have roughly the same strength at large notch sizes. Two common damage mechanisms were found: braider yarn cracking and near notch longitudinal yarn splitting. Cracking was found to initiate in braider yarns in unnotched and notched coupons, and propagate in the direction of the braider yarns until failure. Damage initiation stress decreased with increasing braid angle. No significant differences in prediction of near notch strain between textile and tape equivalents could be detected for small braid angle, but the correlations were weak for textiles with large braid angle. Notch strength could not be predicted using existing anisotropic theory for braided textiles due to their insensitivity to notch.

  5. Failure Mechanism of Fast-Charged Lithium Metal Batteries in Liquid Electrolyte

    SciTech Connect

    Lu, Dongping; Shao, Yuyan; Lozano, Terence J.; Bennett, Wendy D.; Graff, Gordon L.; Polzin, Bryant; Zhang, Jiguang; Engelhard, Mark H.; Saenz, Natalio T.; Henderson, Wesley A.; Bhattacharya, Priyanka; Liu, Jun; Xiao, Jie

    2015-02-01

    In recent years, lithium anode has re-attracted broad interest because of the necessity of employing lithium metal in the next-generation battery technologies such as lithium sulfur (Li-S) and lithium oxygen (Li-O2) batteries. Fast capacity degradation and safety issue associated with rechargeable lithium metal batteries have been reported, although the fundamental understanding on the failure mechanism of lithium metal at high charge rate is still under debate due to the complicated interfacial chemistry between lithium metal and electrolyte. Herein, we demonstrate that, at high current density, the quick growth of porous solid electrolyte interphase towards bulk lithium, instead of towards the separator, dramatically builds up the cell impedance that directly leads to the cell failure. Understanding the lithium metal failure mechanism is very critical to gauge the various approaches used to address the stability and safety issues associated with lithium metal anode. Otherwise, all cells will fail quickly at high rates before the observation of any positive effects that might be brought from adopting the new strategies to protect lithium.

  6. Failure mechanism of shear-wall dominant multi-story buildings

    USGS Publications Warehouse

    Yuksel, S.B.; Kalkan, E.

    2008-01-01

    The recent trend in the building industry of Turkey as well as in many European countries is towards utilizing the tunnel form (shear-wall dominant) construction system for development of multi-story residential units. The tunnel form buildings diverge from other conventional reinforced concrete (RC) buildings due to the lack of beams and columns in their structural integrity. The vertical load-carrying members of these buildings are the structural-walls only, and the floor system is a flat plate. Besides the constructive advantages, tunnel form buildings provide superior seismic performance compared to conventional RC frame and dual systems as observed during the recent devastating earthquakes in Turkey (1999 Mw 7.4 Kocaeli, Mw 7.2 Duzce, and 2004 Mw 6.5 Bingol). With its proven earthquake performance, the tunnel form system is becoming the primary construction technique in many seismically active regions. In this study, a series of nonlinear analyses were conducted using finite element (FE) models to augment our understanding on their failure mechanism under lateral forces. In order to represent the nonlinear behavior adequately, The FE models were verified with the results of experimental studies performed on three dimensional (3D) scaled tunnel form building specimens. The results of this study indicate that the structural walls of tunnel form buildings may exhibit brittle flexural failure under lateral loading, if they are not properly reinforced. The global tension/compression couple triggers this failure mechanism by creating pure axial tension in the outermost shear-walls.

  7. Lubrication and failure mechanisms of molybdenum disulfide films. 1: Effect of atmosphere

    NASA Technical Reports Server (NTRS)

    Fusaro, R. L.

    1978-01-01

    Friction, wear, and wear lives of rubbed molybdenum disulfide (MoS2 films applied to sanded 440C HT steel surfaces were evaluated in moist air, dry air, and dry argon. Optical microscope observations were made as a function of sliding distance to determine the effect of moisture and oxygen on the lubricating and failure mechanisms of MoS2 films. In general, the lubrication process consisted of the formation of a thin, metallic colored, coalesced film of MoS2 that flowed between the surfaces in relative motion. In air, failure was due to the transformation of the metallic colored, coalesced films to a black, powdery material. Water in the air appeared to accelerate the transformation rate. In argon, no transformation of MoS2 was observed with the microscope, but cracking and spalling of the coalesced film occurred and resulted in the gradual depletion of the film.

  8. Mechanisms of epoxyeicosatrienoic acids to improve cardiac remodeling in chronic renal failure disease.

    PubMed

    Zhang, Kun; Wang, Ju; Zhang, Huanji; Chen, Jie; Zuo, Zhiyi; Wang, Jingfeng; Huang, Hui

    2013-02-15

    Both clinical and basic science studies have demonstrated that cardiac remodeling in patients with chronic renal failure (CRF) is very common. It is a key feature during the course of heart failure and an important risk factor for subsequent cardiac mortality. Traditional drugs or therapies rarely have effects on cardiac regression of CRF and cardiovascular events are still the first cause of death. Epoxyeicosatrienoic acids (EETs) are the products of arachidonic acids metabolized by cytochrome P450 epoxygenases. It has been found that EETs have important biological effects including anti-hypertension and anti-inflammation. Recent data suggest that EETs are involved in regulating cardiomyocyte injury, renal dysfunction, chronic kidney disease (CKD)-related risk factors and signaling pathways, all of which play key roles in cardiac remodeling induced by CRF. This review analyzes the literature to identify the possible mechanisms for EETs to improve cardiac remodeling induced by CRF and indicates the therapeutic potential of EETs in it. PMID:23313758

  9. Study on the Effects of Adipic Acid on Properties of Dicyandiamide-Cured Electrically Conductive Adhesive and the Interaction Mechanism

    NASA Astrophysics Data System (ADS)

    Wang, Ling; Wan, Chao; Fu, Yonggao; Chen, Hongtao; Liu, Xiaojian; Li, Mingyu

    2014-01-01

    A small quantity of adipic acid was found to improve the performance of dicyandiamide-cured electrically conductive adhesive (ECA) by enhancing its electrical conductivity and mechanical properties. The mechanism of action of the adipic acid and its effects on the ECA were examined. The results indicated that adipic acid replaced the electrically insulating lubricant on the surface of the silver flakes, which significantly improved the electrical conductivity. Specifically, one of the acidic functional groups in adipic acid reacted with the silver flakes, and an amidation reaction occurred between the other acidic functional group in adipic acid and the dicyandiamide, which participated in the curing reaction. Therefore, adipic acid may act as a coupling agent to improve the overall ECA performance.

  10. Failure mechanisms and lifetime prediction methodology for polybutylene pipe in water distribution system

    NASA Astrophysics Data System (ADS)

    Niu, Xiqun

    Polybutylene (PB) is a semicrystalline thermoplastics. It has been widely used in potable water distribution piping system. However, field practice shows that failure occurs much earlier than the expected service lifetime. What are the causes and how to appropriately evaluate its lifetime motivate this study. In this thesis, three parts of work have been done. First is the understanding of PB, which includes material thermo and mechanical characterization, aging phenomena and notch sensitivity. The second part analyzes the applicability of the existing lifetime testing method for PB. It is shown that PB is an anomaly in terms of the temperature-lifetime relation because of the fracture mechanism transition across the testing temperature range. The third part is the development of the methodology of lifetime prediction for PB pipe. The fracture process of PB pipe consists of three stages, i.e., crack initiation, slow crack growth (SCG) and crack instability. The practical lifetime of PB pipe is primarily determined by the duration of the first two stages. The mechanism of crack initiation and the quantitative estimation of the time to crack initiation are studied by employing environment stress cracking technique. A fatigue slow crack growth testing method has been developed and applied in the study of SCG. By using Paris-Erdogan equation, a model is constructed to evaluate the time for SCG. As a result, the total lifetime is determined. Through this work, the failure mechanisms of PB pipe has been analyzed and the lifetime prediction methodology has been developed.

  11. The mysterious nature of bacterial surface (gliding) motility: A focal adhesion-based mechanism in Myxococcus xanthus.

    PubMed

    Islam, Salim T; Mignot, Tâm

    2015-10-01

    Motility of bacterial cells promotes a range of important physiological phenomena such as nutrient detection, harm avoidance, biofilm formation, and pathogenesis. While much research has been devoted to the mechanism of bacterial swimming in liquid via rotation of flagellar filaments, the mechanisms of bacterial translocation across solid surfaces are poorly understood, particularly when cells lack external appendages such as rotary flagella and/or retractile type IV pili. Under such limitations, diverse bacteria at the single-cell level are still able to "glide" across solid surfaces, exhibiting smooth translocation of the cell along its long axis. Though multiple gliding mechanisms have evolved in different bacterial classes, most remain poorly characterized. One exception is the gliding motility mechanism used by the Gram-negative social predatory bacterium Myxococcus xanthus. The available body of research suggests that M. xanthus gliding motility is mediated by trafficked multi-protein (Glt) cell envelope complexes, powered by proton-driven flagellar stator homologues (Agl). Through coupling to the substratum via polysaccharide slime, Agl-Glt assemblies can become fixed relative to the substratum, forming a focal adhesion site. Continued directional transport of slime-associated substratum-fixed Agl-Glt complexes would result in smooth forward movement of the cell. In this review, we have provided a comprehensive synthesis of the latest mechanistic and structural data for focal adhesion-mediated gliding motility in M. xanthus, with emphasis on the role of each Agl and Glt protein. Finally, we have also highlighted the possible connection between the motility complex and a new type of spore coat assembly system, suggesting that gliding and cell envelope synthetic complexes are evolutionarily linked. PMID:26520023

  12. Mechanical characteristics of antibacterial epoxy resin adhesive wood biocomposites against skin disease

    PubMed Central

    Chen, Zi-xiang; Zhang, Zhong-feng; Aqma, Wan Syaidatul

    2015-01-01

    Moldy wood can cause some skin disease. However epoxy resin adhesive (EP) can inhibit mold growth. Therefore, antibacterial EP/wood biocomposites were reinforced and analyzed by the nonlinear finite element. Results show that glass fiber cloth and aluminum foil have the obvious reinforced effect under flat pressure, but this was not the case under side pressure. And when the assemble pattern was presented in 5A way, the strengthening effect was better. The nonlinear finite element showed that the aluminum foil and glass fiber cloth have the obvious reinforced effect. The mutual influence and effect of span, thickness and length on the ultimate bearing capacity of specimen were studied. And the simulation results agreed with the test. It provided a theoretical basis on the preparation of antibacterial EP/wood biocomposites against skin disease. PMID:26858557

  13. Ibuprofen inhibits adhesion-dependent neutrophil response by a glycoprotein-unrelated mechanism.

    PubMed

    Ottonello, L; Pastorino, G; Dapino, P; Beretta, A; Dallegri, F

    1992-01-01

    The anti-inflammatory drug ibuprofen was found to inhibit neutrophil aggregation and chemotaxis, triggered by the chemotactic factor N-formyl-methionyl-leucyl-phenylalanine (FMLP). The drug did not modify the surface expression of the glycoprotein CD11b-CD18, required for both aggregation and chemotaxis. Consistent with this finding, ibuprofen did not affect the release of lactoferrin from secondary granules which contain CD11b-CD18 molecules in their membranes. As the drug failed to interfere with the neutrophil oxidant production and primary granule release, the results suggest that it acts primarily at the initial steps of the neutrophil response during inflammation, i.e. the cell recruitment at inflamed tissue sites. Moreover, the data prove that adhesion-dependent neutrophil responses required cell processes independent of CD11b-CD18 but controlled, at least in part, by ibuprofen-inhibitable pathways. PMID:1350975

  14. Mechanical characteristics of antibacterial epoxy resin adhesive wood biocomposites against skin disease.

    PubMed

    Chen, Zi-Xiang; Zhang, Zhong-Feng; Aqma, Wan Syaidatul

    2016-01-01

    Moldy wood can cause some skin disease. However epoxy resin adhesive (EP) can inhibit mold growth. Therefore, antibacterial EP/wood biocomposites were reinforced and analyzed by the nonlinear finite element. Results show that glass fiber cloth and aluminum foil have the obvious reinforced effect under flat pressure, but this was not the case under side pressure. And when the assemble pattern was presented in 5A way, the strengthening effect was better. The nonlinear finite element showed that the aluminum foil and glass fiber cloth have the obvious reinforced effect. The mutual influence and effect of span, thickness and length on the ultimate bearing capacity of specimen were studied. And the simulation results agreed with the test. It provided a theoretical basis on the preparation of antibacterial EP/wood biocomposites against skin disease. PMID:26858557

  15. Antiviral adhesion molecular mechanisms for influenza: W. G. Laver's lifetime obsession

    PubMed Central

    Garman, Elspeth F.

    2015-01-01

    Infection by the influenza virus depends firstly on cell adhesion via the sialic-acid-binding viral surface protein, haemagglutinin, and secondly on the successful escape of progeny viruses from the host cell to enable the virus to spread to other cells. To achieve the latter, influenza uses another glycoprotein, the enzyme neuraminidase (NA), to cleave the sialic acid receptors from the surface of the original host cell. This paper traces the development of anti-influenza drugs, from the initial suggestion by MacFarlane Burnet in 1948 that an effective ‘competitive poison’ of the virus' NA might be useful in controlling infection by the virus, through to the determination of the structure of NA by X-ray crystallography and the realization of Burnet's idea with the design of NA inhibitors. A focus is the contribution of the late William Graeme Laver, FRS, to this research. PMID:25533092

  16. A mechanism based modeling approach to failure in fiber reinforced composites

    NASA Astrophysics Data System (ADS)

    Yerramalli, Chandra Sekher

    The increasing use of fiber reinforced polymer composites (FRPC) in civil and military applications has made it imperative that the behavior of FRPC be understood under a variety of loading conditions. It is known that the compressive load carrying capacity of FRPC is low compared to its tensile load carrying capacity. Thus, the compressive behavior of FRPC has been a limiting factor in the design of FRPC structures. In the current work, the compressive behavior of FRPC has been studied with an aim to identify and understand the important parameters affecting the compressive strength and failure mechanisms in FRPC, particularly under combined stress states. The purpose is to establish compressive strength degradation (or enhancement) in the presence of combined stress states. Results from experiments have led to the development of a mechanism based failure model, based on the principles of fracture mechanics for the splitting failure of FRPC. A mechanics model has been developed for both pure compression and combined compression-torsion loading. The predictions of the model were found to compare favorably with experimental data obtained from glass and carbon FRPC under pure compression and combined compression-torsion loading. A 3D finite element simulation of a representative cylindrical section of the composite was performed. The results indicated the importance of fiber diameter on the predicted compressive response of the composite. It also indicated the possibilities of fiber breakage under axial loading as a cause for the initiation of kinking in case of small diameter fiber reinforced composites. Pure compression tests were also conducted on hybrid (glass/carbon) composites under static and dynamic loading conditions. The static compressive strength of hybrid composites shows a non-monotonic behavior with respect to the hybrid ratio. The compressive strength first decreases and then increases as we approach either pure carbon or pure glass composites. The

  17. Methods And Systms For Analyzing The Degradation And Failure Of Mechanical Systems

    DOEpatents

    Jarrell, Donald B.; Sisk, Daniel R.; Hatley, Darrel D.; Kirihara, Leslie J.; Peters, Timothy J.

    2005-02-08

    Methods and systems for identifying, understanding, and predicting the degradation and failure of mechanical systems are disclosed. The methods include measuring and quantifying stressors that are responsible for the activation of degradation mechanisms in the machine component of interest. The intensity of the stressor may be correlated with the rate of physical degradation according to some determinable function such that a derivative relationship exists between the machine performance, degradation, and the underlying stressor. The derivative relationship may be used to make diagnostic and prognostic calculations concerning the performance and projected life of the machine. These calculations may be performed in real time to allow the machine operator to quickly adjust the operational parameters of the machinery in order to help minimize or eliminate the effects of the degradation mechanism, thereby prolonging the life of the machine. Various systems implementing the methods are also disclosed.

  18. Mechanical properties of {beta}-SiAlON ceramics joined using composite {beta}-SiAlON-glass adhesives

    SciTech Connect

    Walls, P.A.; Ueki, Masanori

    1995-04-01

    The mechanical properties of {beta}-SiAlON ceramics joined using {beta}-SiAlON-glass-forming adhesives consisting of mixed Si{sub 3}N{sub 4}, Y{sub 2}O{sub 3}, Al{sub 2}O{sub 3}, and SiO{sub 2} powders are described. Use of adhesives with a {beta}-SiAlON:glass ratio of 60:40 gave an optimum joint strength of 650 MPa in four-point bending mode, i.e., 85% of that of unbonded material, when joining was carried out at 1,600-C for 10 min, under an applied uniaxial pressure of 2 MPa. Bonding pressures in excess of 2 MPa caused excessive compressive creep distortion during the joining operation. The strengths of postjoined HIPed material and HIPed, unbonded material, differed by only 4%, i.e., 975 and 1,010 MPa, respectively, which indicates that HIPing reduces the size of critical defects in the joint. Fracture toughness of the joint also improved upon HIPing.

  19. Failure Predictions for VHTR Core Components using a Probabilistic Contiuum Damage Mechanics Model

    SciTech Connect

    Fok, Alex

    2013-10-30

    The proposed work addresses the key research need for the development of constitutive models and overall failure models for graphite and high temperature structural materials, with the long-term goal being to maximize the design life of the Next Generation Nuclear Plant (NGNP). To this end, the capability of a Continuum Damage Mechanics (CDM) model, which has been used successfully for modeling fracture of virgin graphite, will be extended as a predictive and design tool for the core components of the very high- temperature reactor (VHTR). Specifically, irradiation and environmental effects pertinent to the VHTR will be incorporated into the model to allow fracture of graphite and ceramic components under in-reactor conditions to be modeled explicitly using the finite element method. The model uses a combined stress-based and fracture mechanics-based failure criterion, so it can simulate both the initiation and propagation of cracks. Modern imaging techniques, such as x-ray computed tomography and digital image correlation, will be used during material testing to help define the baseline material damage parameters. Monte Carlo analysis will be performed to address inherent variations in material properties, the aim being to reduce the arbitrariness and uncertainties associated with the current statistical approach. The results can potentially contribute to the current development of American Society of Mechanical Engineers (ASME) codes for the design and construction of VHTR core components.

  20. Failure analysis of radio frequency (rf) micro-electro-mechanical systems (MEMS)

    NASA Astrophysics Data System (ADS)

    Walraven, Jeremy A.; Cole, Edward I., Jr.; Sloan, Lynn R.; Hietala, Susan L.; Tigges, Chris P.; Dyck, Christopher W.

    2001-10-01

    MEMS are rapidly emerging as critical components in the telecommunications industry. This enabling technology is currently being implemented in a variety of product and engineering applications. MEMS are currently being used as optical switches to reroute light, tunable filters, and mechanical resonators. Radio frequency (RF) MEMS must be compatible with current Gallium Arsenide (GaAs) microwave integrated circuit (MMIC) processing technologies for maximum integration levels. The RF MEMS switch discussed in this paper was fabricated using various layers of polyimide, silicon oxynitride (SiON), gold, and aluminum monolithically fabricated on a GaAs substrate. Fig. 1 shows a metal contacting series switch. This switch consists of gold signal lines (transmission lines), and contact metallization. SiON was deposited to form the fixed-fixed beam, and aluminum was deposited to form the top actuation electrode. To ensure product performance and reliability, RF MEMS switches are tested at both the wafer and package levels. Various processing irregularities may pass the visual inspection but fail electrical testing. This paper will focus on the failure mechanisms found in the first generation of RF MEMS developed at Sandia National Laboratories. Various tools and techniques such as scanning electron microscopy (SEM), resistive contrast imaging (RCI), focused ion beam (FIB), and thermally-induced voltage alteration (TIVA) have been employed to diagnose the failure mechanisms. The analysis performed using these tools and techniques led to corrective actions implemented in the next generation of RF MEMS metal contacting series switches.

  1. Spironolactone promotes autophagy via inhibiting PI3K/AKT/mTOR signalling pathway and reduce adhesive capacity damage in podocytes under mechanical stress

    PubMed Central

    Li, Dong; Lu, Zhenyu; Xu, Zhongwei; Ji, Junya; Zheng, Zhenfeng; Lin, Shan; Yan, Tiekun

    2016-01-01

    Mechanical stress which would cause deleterious adhesive effects on podocytes is considered a major contributor to the early progress of diabetic nephropathy (DN). Our previous study has shown that spironolactone could ameliorate podocytic adhesive capacity in diabetic rats. Autophagy has been reported to have a protective role against renal injury. The present study investigated the underlying mechanisms by which spironolactone reduced adhesive capacity damage in podocytes under mechanical stress, focusing on the involvement of autophagy. Human conditional immortalized podocytes exposed to mechanical stress were treated with spironolactone, LY294002 or rapamycin for 48 h. The accumulation of LC3 puncta was detected by immunofluorescence staining. Podocyte expression of mineralocorticoid receptor (MR), integrin β1, LC3, Atg5, p85-PI3K, p-Akt, p-mTOR were detected by Western blotting. Podocyte adhesion to collagen type IV was also performed with spectrophotometry. Immunofluorescence staining showed that the normal level of autophagy was reduced in podocytes under mechanical stress. Decreased integrin β1, LC3, Atg5 and abnormal activation of the PI3K/Akt/mTOR pathway were also detected in podocytes under mechanical stress. Spironolactone up-regulated integrin β1, LC3, Atg5 expression, down-regulated p85-PI3K, p-Akt, p-mTOR expression and reduced podocytic adhesive capacity damage. Our data demonstrated that spironolactone inhibited mechanical-stress-induced podocytic adhesive capacity damage through blocking PI3K/Akt/mTOR pathway and restoring autophagy activity. PMID:27129295

  2. Spironolactone promotes autophagy via inhibiting PI3K/AKT/mTOR signalling pathway and reduce adhesive capacity damage in podocytes under mechanical stress.

    PubMed

    Li, Dong; Lu, Zhenyu; Xu, Zhongwei; Ji, Junya; Zheng, Zhenfeng; Lin, Shan; Yan, Tiekun

    2016-08-01

    Mechanical stress which would cause deleterious adhesive effects on podocytes is considered a major contributor to the early progress of diabetic nephropathy (DN). Our previous study has shown that spironolactone could ameliorate podocytic adhesive capacity in diabetic rats. Autophagy has been reported to have a protective role against renal injury. The present study investigated the underlying mechanisms by which spironolactone reduced adhesive capacity damage in podocytes under mechanical stress, focusing on the involvement of autophagy. Human conditional immortalized podocytes exposed to mechanical stress were treated with spironolactone, LY294002 or rapamycin for 48 h. The accumulation of LC3 puncta was detected by immunofluorescence staining. Podocyte expression of mineralocorticoid receptor (MR), integrin β1, LC3, Atg5, p85-PI3K, p-Akt, p-mTOR were detected by Western blotting. Podocyte adhesion to collagen type IV was also performed with spectrophotometry. Immunofluorescence staining showed that the normal level of autophagy was reduced in podocytes under mechanical stress. Decreased integrin β1, LC3, Atg5 and abnormal activation of the PI3K/Akt/mTOR pathway were also detected in podocytes under mechanical stress. Spironolactone up-regulated integrin β1, LC3, Atg5 expression, down-regulated p85-PI3K, p-Akt, p-mTOR expression and reduced podocytic adhesive capacity damage. Our data demonstrated that spironolactone inhibited mechanical-stress-induced podocytic adhesive capacity damage through blocking PI3K/Akt/mTOR pathway and restoring autophagy activity. PMID:27129295

  3. Cyclic GMP-independent mechanisms contribute to the inhibition of platelet adhesion by nitric oxide donor: A role for α-actinin nitration

    PubMed Central

    Marcondes, Sisi; Cardoso, Marcia H. M.; Morganti, Rafael P.; Thomazzi, Sara M.; Lilla, Sergio; Murad, Ferid; De Nucci, Gilberto; Antunes, Edson

    2006-01-01

    The nitric oxide-mediated actions are mostly due to cyclic GMP (cGMP) formation, but cGMP-independent mechanisms, such as tyrosine nitration, have been suggested as potential signaling pathways modulating the NO-induced responses. However, the mechanisms that lead to tyrosine nitration in platelets are poorly studied, and the protein targets of nitration have not been identified in these cells. Therefore, we have used the model of platelet adhesion to fibrinogen-coated plates to investigate the cGMP-independent mechanisms of the NO-donor sodium nitroprusside (SNP) that leads to inhibition of platelet adhesion. SNP concentration-dependently inhibited platelet adhesion, as observed at 15-min and 60-min adhesion. Additionally, SNP markedly increased the cGMP levels, and the soluble guanylate inhibitor ODQ nearly abolished the SNP-mediated cGMP elevations in all experimental conditions used. Nevertheless, ODQ failed to affect the adhesion inhibition obtained with 1.0 mM SNP at 15 min. On the other hand, superoxide dismutase or peroxynitrite (ONOO−) scavenger epigallocatechin gallate significantly reversed the inhibition of platelet adhesion by SNP (1 mM, 15 min). Western blot analysis in SNP (1 mM, 15 min)-treated platelets showed a single tyrosine-nitrated protein with an apparent mass of ≈105 kDa. Nanospray LC-MS/MS identified the human α-actinin 1 cytoskeletal isoform (P12814) as the protein contained in the nitrated SDS gel band. Thus, tyrosine nitration of α-actinin, through ONOO− formation, may be a key modulatory mechanism to control platelet adhesion. PMID:16492779

  4. [Chronic cervical vagal stimulation. Mechanisms of action and clinical relevance for heart failure].

    PubMed

    Kuschyk, J; Doesch, C; Akin, I; Borggrefe, M; Roeger, S

    2015-11-01

    Increased sympathetic nerve activity and reduced vagal activity are associated with increased mortality in patients after myocardial infarction and patients with chronic heart failure; furthermore, vagal withdrawal has been documented to precede acute decompensation. Experimental studies have indicated that increased parasympathetic activity by means of vagal stimulation may reduce mortality in animal models of postinfarction sudden cardiac death and of chronic heart failure. First clinical results have demonstrated that chronic vagus nerve stimulation in heart failure patients with severe systolic dysfunction appears to be safe and tolerable and may improve the quality of life and left ventricular (LV) function. Vagus nerve stimulation gives rise to these potential clinical benefits by multiple mechanisms of action, including reduced heart rate, restoration of heart rate variability and baroreflex sensitivity, suppression of proinflammatory cytokines and antiarrhythmic effects. First clinical results suggest that vagal nerve stimulation is safe and tolerable and could lead to a marked clinical improvement but discrepancies in the findings due to different study designs warrant further discussion. PMID:26555481

  5. Development Testing and Subsequent Failure Investigation of a Spring Strut Mechanism

    NASA Technical Reports Server (NTRS)

    Dervan, Jared; Robertson, Brandon; Staab, Lucas; Culberson, Michael

    2014-01-01

    Commodities are transferred between the Multi-Purpose Crew Vehicle (MPCV) crew module (CM) and service module (SM) via an external umbilical that is driven apart with spring-loaded struts after the structural connection is severed. The spring struts must operate correctly for the modules to separate safely. There was no vibration testing of strut development units scoped in the MPCV Program Plan; therefore, any design problems discovered as a result of vibration testing would not have been found until the component qualification. The NASA Engineering and Safety Center (NESC) and Lockheed Martin (LM) performed random vibration testing on a single spring strut development unit to assess its ability to withstand qualification level random vibration environments. Failure of the strut while exposed to random vibration resulted in a follow-on failure investigation, design changes, and additional development tests. This paper focuses on the results of the failure investigations including identified lessons learned and best practices to aid in future design iterations of the spring strut and to help other mechanism developers avoid similar pitfalls.

  6. [Non-invasive mechanical ventilation therapy in patients with heart failure].

    PubMed

    Dursunoğlu, Dursun; Dursunoğlu, Neşe

    2012-05-01

    Non-invasive mechanical ventilation (NIMV) therapy in patients with acute heart failure (HF) improves left ventricular functions via decreasing left ventricular afterload and reduces intubation rate and short-term mortality. In patients with chronic HF, NIMV therapy eliminates central and obstructive apneas and Cheyne-Stokes respiration, and improves morbidity. There are essentially three modes of NIMV that are used in the treatment of HF: Continuous positive airway pressure (CPAP), bilevel positive airway pressure (BIPAP) and adaptive servo-ventilation (ASV). Hereby, NIMV therapy in patients with acute and chronic HF is reviewed as well as methods, indications, effectiveness and complications. PMID:22381927

  7. User-defined Material Model for Thermo-mechanical Progressive Failure Analysis

    NASA Technical Reports Server (NTRS)

    Knight, Norman F., Jr.

    2008-01-01

    Previously a user-defined material model for orthotropic bimodulus materials was developed for linear and nonlinear stress analysis of composite structures using either shell or solid finite elements within a nonlinear finite element analysis tool. Extensions of this user-defined material model to thermo-mechanical progressive failure analysis are described, and the required input data are documented. The extensions include providing for temperature-dependent material properties, archival of the elastic strains, and a thermal strain calculation for materials exhibiting a stress-free temperature.

  8. Analysis of electrolyte abnormalities and the mechanisms leading to arrhythmias in heart failure. A literature review.

    PubMed

    Urso, C; Canino, B; Brucculeri, S; Firenze, A; Caimi, G

    2016-01-01

    About 50% of deaths from heart failure (HF) are sudden, presumably referable to arrhythmias. Electrolyte and acid-base abnormalities are a frequent and potentially dangerous complication in HF patients. Their incidence is almost always correlated with the severity of cardiac dysfunction; furthermore leading to arrhythmias, these imbalances are associated with a poor prognosis. The frequency of ventricular ectopic beats and sudden cardiac death correlate with both plasma and whole body levels of potassium, especially in alkalemia. The early recognition of these alterations and the knowledge of the pathophysiological mechanisms are useful for the management of these HF patients. PMID:27598028

  9. The Effect of Defects on Mechanical Properties and Failure Mechanisms of Graphene

    NASA Astrophysics Data System (ADS)

    Willman, Jonathan; Gonzalez, Joseph; Perriot, Romain; Oleynik, Ivan

    Recent experiments involving nanoindentation of graphene have demonstrated counterintuitive increasing of Young's modulus with increasing concentrations of point defects in graphene. To fully resolve this controversy we perform large-scale molecular dynamics simulations of graphene nanoindentation. The relaible description of interatomic interactions is achieved by using recently developed screened environment-dependent bond order (SED-REBO) potential. The elastic properties of the defective graphene, the breaking strength and the mechanisms of fracture under indenter are investigated as a function of defect concentration and other factors specific to Atomic Force Microscopy (AFM) nanoindentation experiments.

  10. Physical Mechanisms of Failure, Ultralow Partial Pressure Lubrication, and the Reservoir Effect in MEMS

    NASA Astrophysics Data System (ADS)

    Hook, David Adam

    The aim of this work is to examine the effectiveness of self-assembled monolayer (SAM) coatings as long term lubrication coatings in microsystems, to examine the failure regimes of SAM coated devices, to examine the role of mobility in adsorbed lubricating films, and to examine evolution of the coefficient of friction of devices surrounded by ultralow partial pressures of alcohols up to saturation. Finally the role of self assembled monlayers in vapor phase lubrication is examined. Self-assembled monolayers are ubiquitous in fabrication of free-standing microdevices because of their ability to prevent release related and dormancy related stiction. However their ability to lubricate under sliding and normal contact conditions is not well documented. It can be shown that the energy dissipated per unit area in one sliding cycle due to friction is significant under general loading conditions. Therefore from an energy dissipated standpoint the bond energies of the silane molecules should not be enough to withstand even a short number of cycles. An extension of this is the energy imparted to the surface through a normal loading cycle through a loss of kinetic energy. It can also be shown that this is enough to break the silicon oxygen bonds however this is over a longer time scale than in sliding. Also there is an open question on the role of mobile and non-mobile adsorbed species on friction. Is the mobility of a molecule/layer on a surface an indicator of the effectiveness of the lubrication potential of the layer? Do submonolayer coverages of alcohols "lock-up" to contacting surfaces by disrupting non-corrogated potentials? Is there a distinct lowering of frictional forces at the formation of a monolayer? Controlled adsorption of mobile and non-mobile species on rubbing contacts is necessary to elucidate this physical relationship. To accomplish this one must take into account that friction measurements are highly scale dependant. Therefore to ensure the accuracy of

  11. A damage mechanics approach for quantifying stress changes due to brittle failure of porous rocks

    NASA Astrophysics Data System (ADS)

    Jacquey, Antoine B.; Cacace, Mauro; Blöcher, Guido; Milsch, Harald; Scheck-Wenderoth, Magdalena

    2016-04-01

    Natural fault zones or man-made injection or production of fluid impact the regional stress distribution in Earth's crust and can be responsible for localized stress discontinuities. Understanding the processes controlling fracturing of the porous rocks and mechanical behaviour of fault zones is therefore of interest for several applications including geothermal energy production. In this contribution, we will present a thermodynamically consistent visco-poroelastic damage model which can deal with the multi-scale and multi-physics nature of the physical processes controlling the deformation of porous rocks during and after brittle failure. Deformation of a porous medium is crucially influenced by the changes in the effective stress. Considering a strain-formulated yield cap and the compaction-dilation transition, three different regimes can be identified: quasi-elastic deformation, cataclastic compaction with microcracking (damage accumulation) and macroscopic brittle failure with dilation. The governing equations for deformation, damage accumulation/healing and fluid flow have been implemented in a fully-coupled finite-element-method based framework (MOOSE). The MOOSE framework provides a powerful and flexible platform to solve multiphysics problems implicitly and in a tightly coupled manner on unstructured meshes which is of interest for such non-linear context. To illustrate the model, simulation of a compaction experiment of a sandstone leading to shear failure will be presented which allows to quantify the stress drop accompanying the failure. Finally, we will demonstrate that this approach can also be used at the field scale to simulate hydraulic fracturing and assess the resulting changes in the stress field.

  12. DEFORMATION AND FRACTURE OF POORLY CONSOLIDATED MEDIA - Borehole Failure Mechanisms in High-Porosity Sandstone

    SciTech Connect

    Bezalel c. Haimson

    2005-06-10

    We investigated failure mechanisms around boreholes and the formation of borehole breakouts in high-porosity sandstone, with particular interest to grain-scale micromechanics of failure leading to the hitherto unrecognized fracture-like borehole breakouts and apparent compaction band formation in poorly consolidated granular materials. We also looked at a variety of drilling-related factors that contribute to the type, size and shape of borehole breakouts. The objective was to assess their effect on the ability to establish correlations between breakout geometry and in situ stress magnitudes, as well as on borehole stability prediction, and hydrocarbon/water extraction in general. We identified two classes of medium to high porosity (12-30%) sandstones, arkosic, consisting of 50-70% quartz and 15 to 50% feldspar, and quartz-rich sandstones, in which quartz grain contents varied from 90 to 100%. In arkose sandstones critical far-field stress magnitudes induced compressive failure around boreholes in the form of V-shaped (dog-eared) breakouts, the result of dilatant intra-and trans-granular microcracking subparallel to both the maximum horizontal far-field stress and to the borehole wall. On the other hand, boreholes in quartz-rich sandstones failed by developing fracture-like breakouts. These are long and very narrow (several grain diameters) tabular failure zones perpendicular to the maximum stress. Evidence provided mainly by SEM observations suggests a failure process initiated by localized grain-bond loosening along the least horizontal far-field stress springline, the packing of these grains into a lower porosity compaction band resembling those discovered in Navajo and Aztec sandstones, and the emptying of the loosened grains by the circulating drilling fluid starting from the borehole wall. Although the immediate several grain layers at the breakout tip often contain some cracked or even crushed grains, the failure mechanism enabled by the formation of the

  13. Effect of viscous macromolecules on peritoneal plasminogen activator activity: a potential mechanism for their ability to reduce postoperative adhesion formation.

    PubMed

    Mayer, M; Yedgar, S; Hurwitz, A; Palti, Z; Finzi, Z; Milwidsky, A

    1988-10-01

    Activity of peritoneal plasminogen activator and its regulation by dextran and other macromolecules that clinically suppress postoperative adhesions was studied. Plasminogen activator activity was assayed by a two-stage globinolytic assay that monitors formation of plasmin, as well as by cleavage of a chromogenic peptide substrate (S-2444) in the presence of aprotinin (Trasylol). Plasminogen activator activity was located on the outer surface of human peritoneum. Incubation of peritoneal tissue with buffer in vitro (conditioning) prompted release of plasminogen activator into the conditioning medium. The released plasminogen activator formed a single band on sodium dodecyl sulfate-gel electrophoresis at an apparent molecular weight of 174,000 and was markedly suppressed by antiserum raised against human melanoma tissue-type plasminogen activator. Nonspecific proteolytic activity did not accumulate in the medium during conditioning. The presence of dextran 80 during conditioning of peritoneum reversibly suppressed tissue-bound plasminogen activator activity and reduced plasminogen activator activity in the spent medium. A similar inhibition of peritoneal plasminogen activator was induced by dextran 500, methyl cellulose, and polyvinylpyrrolidone. Dextran, when added to the medium after conditioning, had no direct inhibitory effect on plasminogen activator activity. Dextran did not induce peritoneal production of inhibitor(s) of trypsin, chymotrypsin, or urokinase. On the basis of these findings, two possible mechanisms for the effect of viscous polymers in the reduction of adhesion formation are proposed. These mechanisms consider the importance of peritoneal tissue-type plasminogen activator for removal of fibrin clots and suggest that polymer coating either prevents the shedding of plasminogen activator into the abdominal cavity or reduces the access of fibrin clots to the serosal surfaces. PMID:2459968

  14. Loss-of-Function Mutations in SERPINB8 Linked to Exfoliative Ichthyosis with Impaired Mechanical Stability of Intercellular Adhesions.

    PubMed

    Pigors, Manuela; Sarig, Ofer; Heinz, Lisa; Plagnol, Vincent; Fischer, Judith; Mohamad, Janan; Malchin, Natalia; Rajpopat, Shefali; Kharfi, Monia; Lestringant, Giles G; Sprecher, Eli; Kelsell, David P; Blaydon, Diana C

    2016-08-01

    SERPINS comprise a large and functionally diverse family of serine protease inhibitors. Here, we report three unrelated families with loss-of-function mutations in SERPINB8 in association with an autosomal-recessive form of exfoliative ichthyosis. Whole-exome sequencing of affected individuals from a consanguineous Tunisian family and a large Israeli family revealed a homozygous frameshift mutation, c.947delA (p.Lys316Serfs(∗)90), and a nonsense mutation, c.850C>T (p.Arg284(∗)), respectively. These two mutations are located in the last exon of SERPINB8 and, hence, would not be expected to lead to nonsense-mediated decay of the mRNA; nonetheless, both mutations are predicted to lead to loss of the reactive site loop of SERPINB8, which is crucial for forming the SERPINB8-protease complex. Using Sanger sequencing, a homozygous missense mutation, c.2T>C (p.Met1?), predicted to result in an N-terminal truncated protein, was identified in an additional family from UAE. Histological analysis of a skin biopsy from an individual homozygous for the variant p.Arg284(∗) showed disadhesion of keratinocytes in the lower epidermal layers plus decreased SERPINB8 levels compared to control. In vitro studies utilizing siRNA-mediated knockdown of SERPINB8 in keratinocytes demonstrated that in the absence of the protein, there is a cell-cell adhesion defect, particularly when cells are subjected to mechanical stress. In addition, immunoblotting and immunostaining revealed an upregulation of desmosomal proteins. In conclusion, we report mutations in SERPINB8 that are associated with exfoliative ichthyosis and provide evidence that SERPINB8 contributes to the mechanical stability of intercellular adhesions in the epidermis. PMID:27476651

  15. Testing and Failure Mechanisms of Ice Phase Change Material Heat Exchangers

    NASA Technical Reports Server (NTRS)

    Leimkuehler, Thomas O.; Stephan, Ryan A.; Hawkins-Reynolds, Ebony

    2011-01-01

    Phase change materials (PCM) may be useful for thermal control systems that involve cyclical heat loads or cyclical thermal environments such as specific spacecraft orientations in Low Earth Orbit (LEO) and low beta angle Low Lunar Orbit (LLO). Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. One advantage that PCM s have over evaporators in this scenario is that they do not use a consumable. The use of water as a PCM rather than the more traditional paraffin wax has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. A number of ice PCM heat exchangers were fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion were investigated. This paper presents the results of testing that occurred from March through September of 2010 and builds on testing that occurred during the previous year.

  16. Biological mechanisms of premature ovarian failure caused by psychological stress based on support vector regression

    PubMed Central

    Wang, Xiu-Feng; Zhang, Lei; Wu, Qing-Hua; Min, Jian-Xin; Ma, Na; Luo, Lai-Cheng

    2015-01-01

    Psychological stress has become a common and important cause of premature ovarian failure (POF). Therefore, it is very important to explore the mechanisms of POF resulting from psychological stress. Sixty SD rats were randomly divided into control and model groups. Biomolecules associated with POF (β-EP, IL-1, NOS, NO, GnRH, CRH, FSH, LH, E2, P, ACTH, and CORT) were measured in the control and psychologically stressed rats. The regulation relationships of the biomolecules were explored in the psychologically stressed state using support vector regression (SVR). The values of β-EP, IL-1, NOS, and GnRH in the hypothalamus decreased significantly, and the value of NO changed slightly, when the values of 3 biomolecules in the hypothalamic-pituitary-adrenal axis decreased. The values of E2 and P in the hypothalamic-pituitary-ovarian axis decreased significantly, while the values of FSH and LH changed slightly, when the values of the biomolecules in the hypothalamus decreased. The values of FSH and LH in the pituitary layer of the hypothalamic-pituitary-ovarian axis changed slightly when the values of E2 and P in the target gland layer of the hypothalamic-pituitary-ovarian axis decreased. An Imbalance in the neuroendocrine-immune bimolecular network, particularly the failure of the feedback action of the target gland layer to pituitary layer in the pituitary-ovarian axis, is possibly one of the pathogenic mechanisms of POF. PMID:26885082

  17. Reasons of PEG failure to eliminate gastroesophageal reflux in mechanically ventilated patients

    PubMed Central

    Douzinas, Emmanuel E; Andrianakis, Ilias; Livaditi, Olga; Bakos, Dimitrios; Flevari, Katerina; Goutas, Nikos; Vlachodimitropoulos, Dimitrios; Tasoulis, Marios-Konstantinos; Betrosian, Alex P

    2009-01-01

    AIM: To investigate factors predicting failure of percutaneous endoscopic gastrostomy (PEG) to eliminate gastroesophageal reflux (GER). METHODS: Twenty-nine consecutive mechanically ventilated patients were investigated. Patients were evaluated for GER by pH-metry pre-PEG and on the 7th post-PEG day. Endoscopic and histologic evidence of reflux esophagitis was also carried out. A beneficial response to PEG was considered when pH-metry on the 7th post-PEG day showed that GER was below 4%. RESULTS: Seventeen patients responded (RESP group) and 12 did not respond (N-RESP) to PEG. The mean age, sex, weight and APACHE II score were similar in both groups. GER (%) values were similar in both groups at baseline, but were significantly reduced in the RESP group compared with the N-RESP group on the 7th post-PEG day [2.5 (0.6-3.8) vs 8.1 (7.4-9.2, P < 0.001)]. Reflux esophagitis and the gastroesophageal flap valve (GEFV) grading differed significantly between the two groups (P = 0.031 and P = 0.020, respectively). Histology revealed no significant differences between the two groups. CONCLUSION: Endoscopic grading of GEFV and the presence of severe reflux esophagitis are predisposing factors for failure of PEG to reduce GER in mechanically ventilated patients. PMID:19916176

  18. Pathophysiological Basis of Acute Respiratory Failure on Non-Invasive Mechanical Ventilation

    PubMed Central

    Romero-Dapueto, C; Budini, H; Cerpa, F; Caceres, D; Hidalgo, V; Gutiérrez, T; Keymer, J; Pérez, R; Molina, J; Giugliano-Jaramillo, C

    2015-01-01

    Noninvasive mechanical ventilation (NIMV) was created for patients who needed noninvasive ventilator support, this procedure decreases the complications associated with the use of endotracheal intubation (ETT). The application of NIMV has acquired major relevance in the last few years in the management of acute respiratory failure (ARF), in patients with hypoxemic and hypercapnic failure. The main advantage of NIMV as compared to invasive mechanical ventilation (IMV) is that it can be used earlier outside intensive care units (ICUs). The evidence strongly supports its use in patients with COPD exacerbation, support in weaning process in chronic obstructive pulmonary disease (COPD) patients, patients with acute cardiogenic pulmonary edema (ACPE), and Immunosuppressed patients. On the other hand, there is poor evidence that supports the use of NIMV in other pathologies such as pneumonia, acute respiratory distress syndrome (ARDS), and during procedures as bronchoscopy, where its use is still controversial because the results of these studies are inconclusive against the decrease in the rate of intubation or mortality. PMID:26312101

  19. Development, Testing, and Failure Mechanisms of a Replicative Ice Phase Change Material Heat Exchanger

    NASA Technical Reports Server (NTRS)

    Leimkuehler, Thomas O.; Hansen, Scott; Stephan, Ryan A.

    2009-01-01

    Phase change materials (PCM) may be useful for thermal control systems that involve cyclical heat loads or cyclical thermal environments such as Low Earth Orbit (LEO) and Low Lunar Orbit (LLO). Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. One advantage that PCM s have over evaporators in this scenario is that they do not use a consumable. Wax PCM units have been baselined for the Orion thermal control system and also provide risk mitigation for the Altair Lander. However, the use of water as a PCM has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. An ice PCM heat exchanger that replicates the thermal energy storage capacity of an existing wax PCM unit was fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion are investigated. This paper presents the results to date of this investigation.

  20. Testing and Failure Mechanisms of Ice Phase Change Material Heat Exchangers

    NASA Technical Reports Server (NTRS)

    Leimkuehler, Thomas O.; Stephan, Ryan A.; Hawkins-Reynolds, Ebony

    2010-01-01

    Phase change materials (PCM) may be useful for thermal control systems that involve cyclical heat loads or cyclical thermal environments such as Low Earth Orbit (LEO) and Low Lunar Orbit (LLO). Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. One advantage that PCM s have over evaporators in this scenario is that they do not use a consumable. The use of water as a PCM rather than the more traditional paraffin wax has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. A number of ice PCM heat exchangers were fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion were investigated. This paper presents the results of testing that occurred from March through September of 2010 and builds on testing that occurred during the previous year.

  1. Thermo-mechanical Fatigue Failure of Thermal Barrier Coated Superalloy Specimen

    NASA Astrophysics Data System (ADS)

    Subramanian, Rajivgandhi; Mori, Yuzuru; Yamagishi, Satoshi; Okazaki, Masakazu

    2015-09-01

    Failure behavior of thermal barrier coated (TBC) Ni-based superalloy specimens were studied from the aspect of the effect of bond coat material behavior on low cycle fatigue (LCF) and thermo-mechanical fatigue (TMF) at various temperatures and under various loading conditions. Initially, monotonic tensile tests were carried out on a MCrAlY alloy bond coat material in the temperature range of 298 K to 1273 K (25 °C to 1000 °C). Special attention was paid to understand the ductile to brittle transition temperature (DBTT). Next, LCF and TMF tests were carried out on the thermal barrier coated Ni-based alloy IN738 specimen. After these tests, the specimens were sectioned to understand their failure mechanisms on the basis of DBTT of the bond coat material. Experimental results demonstrated that the LCF and TMF lives of the TBC specimen were closely related to the DBTT of the bond coat material, and also the TMF lives were different from those of LCF tests. It has also been observed that the crack density in the bond coat in the TBC specimen was significantly dependent on the test conditions. More importantly, not only the number of cracks but also the crack penetration probability into substrate were shown to be sensitive to the DBTT.

  2. Failure Mechanism for Fast-Charged Lithium Metal Batteries with Liquid Electrolytes

    SciTech Connect

    Lv, DP; Shao, YY; Lozano, T; Bennett, WD; Graff, GL; Polzin, B; Zhang, JG; Engelhard, MH; Saenz, NT; Henderson, WA; Bhattacharya, P; Liu, J; Xiao, J

    2014-09-11

    In recent years, the Li metal anode has regained a position of paramount research interest because of the necessity for employing Li metal in next-generation battery technologies such as Li-S and Li-O-2. Severely limiting this utilization, however, are the rapid capacity degradation and safety issues associated with rechargeable Li metal anodes. A fundamental understanding of the failure mechanism of Li metal at high charge rates has remained elusive due to the complicated interfacial chemistry that occurs between Li metal and liquid electrolytes. Here, it is demonstrated that at high current density the quick formation of a highly resistive solid electrolyte interphase (SEI) entangled with Li metal, which grows towards the bulk Li, dramatically increases up the cell impedance and this is the actual origin of the onset of cell degradation and failure. This is instead of dendritic or mossy Li growing outwards from the metal surface towards/through the separator and/or the consumption of the Li and electrolyte through side reactions. Interphase, in this context, refers to a substantive layer rather than a thin interfacial layer. Discerning the mechanisms and consequences for this interphase formation is crucial for resolving the stability and safety issues associated with Li metal anodes.

  3. Development, Testing, and Failure Mechanisms of a Replicative Ice Phase Change Material Heat Exchanger

    NASA Technical Reports Server (NTRS)

    Leimkuehler, Thomas O.; Hansen, Scott; Stephan, Ryan A.

    2010-01-01

    Phase change materials (PCM) may be useful for thermal control systems that involve cyclical heat loads or cyclical thermal environments such as Low Earth Orbit (LEO) and Low Lunar Orbit (LLO). Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. One advantage that PCM's have over evaporators in this scenario is that they do not use a consumable. Wax PCM units have been baselined for the Orion thermal control system and also provide risk mitigation for the Altair Lander. However, the use of water as a PCM has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. An ice PCM heat exchanger that replicates the thermal energy storage capacity of an existing wax PCM unit was fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion are investigated. This paper presents the results to date of this investigation. Nomenclature

  4. Analyzing failure modes of rock mass based on statistical mechanics of rock mass

    NASA Astrophysics Data System (ADS)

    Bao, H.; Wu, F.

    2015-12-01

    Joints influence mechanical properties of rock mass. Based on the strength criterion of statistical mechanics of rock mass, we analyzed the four different failure modes of rock mass with a group of joints by combining with Mohr-Coulomb strength criterion. We also deduced an expression of the critical confining pressure for explaining the transformation from structure control to stress control of rock mass strength. On this basis, rock mass with a group of joints were divided into four classes according to the relations between rock mass and joints parameters. Then, the possible failure modes and their corresponding conditions were discussed. At last, the strength characteristics of diorite with a group of joints were analyzed. The results showed that the diorite belonged to class rock mass and performed significant anisotropy in compressive strength. At the condition of vertical pressure, the rock start failing after joints at the critical confining pressure of 9.12MPa. However, with the confining pressure increasing, the anisotropy of strength became weak, and the strength of diorite would convert from structure control to stress control under some particular loading directions.

  5. Stickiness--some fundamentals of adhesion.

    PubMed

    Gay, Cyprien

    2002-12-01

    We review some adhesion mechanisms that have been understood in the field of synthetic adhesives, and more precisely for adhesives that adhere instantaneously (a property named tackiness) and whose adhesive strength usually depends on the applied pressure (pressure-sensitive adhesives). The discussion includes effects of surface roughness, elasticity, cavitation, viscous and elastic fingering, substrate flexibility. PMID:21680396

  6. Mechanisms and Clinical Consequences of Untreated Central Sleep Apnea in Heart Failure

    PubMed Central

    Costanzo, Maria Rosa; Khayat, Rami; Ponikowski, Piotr; Augostini, Ralph; Stellbrink, Christoph; Mianulli, Marcus; Abraham, William T.

    2015-01-01

    Central sleep apnea (CSA) is a highly prevalent, though often unrecognized, comorbidity in patients with heart failure (HF). Data from HF population studies suggest that it may present in 30% to 50% of HF patients. CSA is recognized as an important contributor to the progression of HF and to HF-related morbidity and mortality. Over the past 2 decades, an expanding body of research has begun to shed light on the pathophysiologic mechanisms of CSA. Armed with this growing knowledge base, the sleep, respiratory, and cardiovascular research communities have been working to identify ways to treat CSA in HF with the ultimate goal of improving patient quality of life and clinical outcomes. In this paper, we examine the current state of knowledge about the mechanisms of CSA in HF and review emerging therapies for this disorder. PMID:25572513

  7. Mechanisms and clinical consequences of untreated central sleep apnea in heart failure.

    PubMed

    Costanzo, Maria Rosa; Khayat, Rami; Ponikowski, Piotr; Augostini, Ralph; Stellbrink, Christoph; Mianulli, Marcus; Abraham, William T

    2015-01-01

    Central sleep apnea (CSA) is a highly prevalent, though often unrecognized, comorbidity in patients with heart failure (HF). Data from HF population studies suggest that it may present in 30% to 50% of HF patients. CSA is recognized as an important contributor to the progression of HF and to HF-related morbidity and mortality. Over the past 2 decades, an expanding body of research has begun to shed light on the pathophysiologic mechanisms of CSA. Armed with this growing knowledge base, the sleep, respiratory, and cardiovascular research communities have been working to identify ways to treat CSA in HF with the ultimate goal of improving patient quality of life and clinical outcomes. In this paper, we examine the current state of knowledge about the mechanisms of CSA in HF and review emerging therapies for this disorder. PMID:25572513

  8. A procedure for combining acoustically induced and mechanically induced loads (first passage failure design criterion)

    NASA Technical Reports Server (NTRS)

    Crowe, D. R.; Henricks, W.

    1983-01-01

    The combined load statistics are developed by taking the acoustically induced load to be a random population, assumed to be stationary. Each element of this ensemble of acoustically induced loads is assumed to have the same power spectral density (PSD), obtained previously from a random response analysis employing the given acoustic field in the STS cargo bay as a stationary random excitation. The mechanically induced load is treated as either (1) a known deterministic transient, or (2) a nonstationary random variable of known first and second statistical moments which vary with time. A method is then shown for determining the probability that the combined load would, at any time, have a value equal to or less than a certain level. Having obtained a statistical representation of how the acoustic and mechanical loads are expected to combine, an analytical approximation for defining design levels for these loads is presented using the First Passage failure criterion.

  9. Effect of cathodic polarization on failure and degradation of mechanical properties of some aluminum alloys

    SciTech Connect

    Czechowski, M.; Zielinski, A.

    1994-01-15

    The effect of hydrogen on failure and mechanical properties has thus far been investigated for pure aluminum and Al-Mg, Al-Zn-Mg, Al-Zn-Mg-Cu, Al-Mg-Cu, and Al-Li alloys. Up to now investigations have usually been made by a non-time-consuming test. In such experiment, total exposure is relatively short and the long-term effect of environment, e.g. build-up of hydrogen microbubbles within a thin surface layer, or a film of corrosion products, may be underestimated. Therefore, the authors decided to study the influence of hydrogen on mechanical properties and microstructure by prolonged testing under constant sustained load.

  10. Mechanics-Based Definition of Safety Factors Against Flow Failure in Unsaturated Shallow Slopes

    NASA Astrophysics Data System (ADS)

    Buscarnera, G.; Lizarraga-Barrera, J.

    2014-12-01

    Physical models for landslide forecasting rely on the combination of hydrologic models for water infiltration and stability criteria based on infinite slope mechanics. Such concepts can be used to derive safety factors for shallow landsliding, in which the mobilization of the soil cover is associated with the attainment of critical values of pore water pressures expressed as a function of the frictional strength. While such models capture the role of important geomorphic features and geotechnical properties, their performance depends on the validity of the postulate of frictional failure. As a result, the safety factors do not to consider a broader range of solid-fluid interactions promoting different slope failure mechanisms, such as flow slides. This work combines principles of soil stability, unsaturated soil mechanics and plasticity theory to derive an alternative set of safety factors. While frictional slips are included in the study as a particular case, the proposed analytical methodology can also be applied to cases in which an increase in degree of saturation promotes liquefaction instabilities, i.e. possible transitions from solid- to fluid-like response. The study shows that the incorporation of principles of unsaturated soil mechanics into slope stability analyses generates suction-dependent coefficients that alter the value of the safety factors. As a result, while the proposed approach can still be combined with standard hydrologic models simulating the evolution of pore pressures in the near-surface, it can also provide a spatially distributed assessment of evolving safety conditions in landscapes susceptible to landslides of the flow type.

  11. Congestive heart failure with preserved ejection fraction is associated with severely impaired dynamic Starling mechanism

    PubMed Central

    Shibata, Shigeki; Hastings, Jeff L.; Prasad, Anand; Fu, Qi; Bhella, Paul S.; Pacini, Eric; Krainski, Felix; Palmer, M. Dean; Zhang, Rong

    2011-01-01

    Sedentary aging leads to increased cardiovascular stiffening, which can be ameliorated by sufficient amounts of lifelong exercise training. An even more extreme form of cardiovascular stiffening can be seen in heart failure with preserved ejection fraction (HFpEF), which comprises ∼40∼50% of elderly patients diagnosed with congestive heart failure. There are two major interrelated hypotheses proposed to explain heart failure in these patients: 1) increased left ventricular (LV) diastolic stiffness and 2) increased arterial stiffening. The beat-to-beat dynamic Starling mechanism, which is impaired with healthy human aging, reflects the interaction between ventricular and arterial stiffness and thus may provide a link between these two mechanisms underlying HFpEF. Spectral transfer function analysis was applied between beat-to-beat changes in LV end-diastolic pressure (LVEDP; estimated from pulmonary artery diastolic pressure with a right heart catheter) and stroke volume (SV) index. The dynamic Starling mechanism (transfer function gain between LVEDP and the SV index) was impaired in HFpEF patients (n = 10) compared with healthy age-matched controls (n = 12) (HFpEF: 0.23 ± 0.10 ml·m−2·mmHg−1 and control: 0.37 ± 0.11 ml·m−2·mmHg−1, means ± SD, P = 0.008). There was also a markedly increased (3-fold) fluctuation of LV filling pressures (power spectral density of LVEDP) in HFpEF patients, which may predispose to pulmonary edema due to intermittent exposure to higher pulmonary capillary pressure (HFpEF: 12.2 ± 10.4 mmHg2 and control: 3.8 ± 2.9 mmHg2, P = 0.014). An impaired dynamic Starling mechanism, even more extreme than that observed with healthy aging, is associated with marked breath-by-breath LVEDP variability and may reflect advanced ventricular and arterial stiffness in HFpEF, possibly contributing to reduced forward output and pulmonary congestion. PMID:21310890

  12. Shear lag sutures: Improved suture repair through the use of adhesives.

    PubMed

    Linderman, Stephen W; Kormpakis, Ioannis; Gelberman, Richard H; Birman, Victor; Wegst, Ulrike G K; Genin, Guy M; Thomopoulos, Stavros

    2015-09-01

    Suture materials and surgical knot tying techniques have improved dramatically since their first use over five millennia ago. However, the approach remains limited by the ability of the suture to transfer load to tissue at suture anchor points. Here, we predict that adhesive-coated sutures can improve mechanical load transfer beyond the range of performance of existing suture methods, thereby strengthening repairs and decreasing the risk of failure. The mechanical properties of suitable adhesives were identified using a shear lag model. Examination of the design space for an optimal adhesive demonstrated requirements for strong adhesion and low stiffness to maximize the strength of the adhesive-coated suture repair construct. To experimentally assess the model, we evaluated single strands of sutures coated with highly flexible cyanoacrylates (Loctite 4903 and 4902), cyanoacrylate (Loctite QuickTite Instant Adhesive Gel), rubber cement, rubber/gasket adhesive (1300 Scotch-Weld Neoprene High Performance Rubber & Gasket Adhesive), an albumin-glutaraldehyde adhesive (BioGlue), or poly(dopamine). As a clinically relevant proof-of-concept, cyanoacrylate-coated sutures were then used to perform a clinically relevant flexor digitorum tendon repair in cadaver tissue. The repair performed with adhesive-coated suture had significantly higher strength compared to the standard repair without adhesive. Notably, cyanoacrylate provides strong adhesion with high stiffness and brittle behavior, and is therefore not an ideal adhesive for enhancing suture repair. Nevertheless, the improvement in repair properties in a clinically relevant setting, even using a non-ideal adhesive, demonstrates the potential for the proposed approach to improve outcomes for treatments requiring suture fixation. Further study is necessary to develop a strongly adherent, compliant adhesive within the optimal design space described by the model. PMID:26022966

  13. Mechanical Failure of Revision Knee Prosthesis at both Femoral and Tibial Modular Metaphyseal Stem Junctions

    PubMed Central

    Woodgate, Ian G; Rooney, John; Mulford, Johnathan S; Gillies, R Mark

    2016-01-01

    Introduction: This is a report of a mechanical failure of an S-ROM revision total knee prosthesis. The prosthesis was used as a revision implant following deep peri-prosthetic infection in a morbidly obese male. The prosthesis failed on both the femoral and tibial sides at the modular metaphyseal stem junctions and required a further revision using the same type of implant after infection was excluded. Case Presentation: A 57 year old male had previously undergone a left total knee arthroplasty in 1999 for osteoarthritis. He acquired a late deep peri-prosthetic infection with a multi-resistant Staphylococcus epidermidis. The organism was sensitive to vancomycin and rifampicin. A two stage revision was undertaken after clinical signs of infection had resolved and blood parameters had normalized. Intra-operative gram stain was negative for micro-organisms and frozen section of deep tissue was less than five polymorphs per high power field. A cemented S-ROM prosthesis was implanted using a coronal tibial osteotomy and a lateral release for exposure. After three years of the second stage of revision, the patient again presented to the orthopaedic department after reportedly falling on a wet floor six weeks ago. Conclusion: Radiographically, there was a broken tibial wire, osteolysis and pedestal formation around both the femoral and distal tibial stem extensions. The prosthesis was bent at the proximal tibial sleeve and stem junction. The prosthesis was considered loose with mechanical failure. At implant removal, it was noted that the femoral and tibial components at the modular metaphyseal sleeve-stem junction were fractured. Surgeons should be cautious in the use of these implants in morbidly obese patients where the stresses generated maybe above the yield stress of the material and the frictional forces that may overcome the modular taper junction’s locking mechanism. PMID:27299124

  14. How can health literacy influence outcomes in heart failure patients? Mechanisms and interventions.

    PubMed

    Westlake, Cheryl; Sethares, Kristen; Davidson, Patricia

    2013-09-01

    Health literacy is discussed in papers from 25 countries where findings suggest that approximately a third up to one half of the people in developed countries have low health literacy. Specifically, health literacy is the mechanism by which individuals obtain and use health information to make health decisions about individual treatments in the home, access care in the community, promote provider-patient interactions, structure self-care, and navigate health care programs both locally and nationally. Further, health literacy is a key determinant of health and a critical dimension for assessing individuals' needs, and, importantly, their capacity for self-care. Poorer health knowledge/status, more medication errors, costs, and higher rates of morbidity, readmissions, emergency room visits, and mortality among patients with health illiteracy have been demonstrated. Individuals at high risk for low health literacy include the elderly, disabled, Blacks, those with a poverty-level income, some or less high school education, either no insurance or Medicare or Medicaid, and those for whom English is a second language. As a consequence, health literacy is a complex, multifaceted, and evolving construct including aspects of social, psychological, cultural and economic circumstances. The purpose of this paper is to describe the mechanisms and consequences of health illiteracy. Specifically, the prevalence, associated demographics, and models of health literacy are described. The mechanism of health illiteracy's influence on outcomes in heart failure is proposed. Tools for health literacy assessment are described and compared. Finally, the health outcomes and general interventions to enhance the health outcomes in heart failure are discussed. PMID:23873404

  15. Failure analysis of porcupine quills under axial compression reveals their mechanical response during buckling.

    PubMed

    Torres, Fernando G; Troncoso, Omar P; Diaz, John; Arce, Diego

    2014-11-01

    Porcupine quills are natural structures formed by a thin walled conical shell and an inner foam core. Axial compression tests, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR) were all used to compare the characteristics and mechanical properties of porcupine quills with and without core. The failure mechanisms that occur during buckling were analyzed by scanning electron microscopy (SEM), and it was found that delamination buckling is mostly responsible for the decrease in the measured buckling stress of the quills with regard to predicted theoretical values. Our analysis also confirmed that the foam core works as an energy dissipater improving the mechanical response of an empty cylindrical shell, retarding the onset of buckling as well as producing a step wise decrease in force after buckling, instead of an instantaneous decrease in force typical for specimens without core. Cell collapse and cell densification in the inner foam core were identified as the key mechanisms that allow for energy absorption during buckling. PMID:25123434

  16. Impact of mechanical- and maintenance-induced failures of main reactor coolant pump seals on plant safety

    SciTech Connect

    Azarm, M A; Boccio, J L; Mitra, S

    1985-12-01

    This document presents an investigation of the safety impact resulting from mechanical- and maintenance-induced reactor coolant pump (RCP) seal failures in nuclear power plants. A data survey of the pump seal failures for existing nuclear power plants in the US from several available sources was performed. The annual frequency of pump seal failures in a nuclear power plant was estimated based on the concept of hazard rate and dependency evaluation. The conditional probability of various sizes of leak rates given seal failures was then evaluated. The safety impact of RCP seal failures, in terms of contribution to plant core-melt frequency, was also evaluated for three nuclear power plants. For leak rates below the normal makeup capacity and the impact of plant safety were discussed qualitatively, whereas for leak rates beyond the normal make up capacity, formal PRA methodologies were applied. 22 refs., 17 figs., 19 tabs.

  17. Biophysically inspired model for functionalized nanocarrier adhesion to cell surface: roles of protein expression and mechanical factors

    PubMed Central

    Ramakrishnan, N.; Tourdot, Richard W.; Eckmann, David M.; Ayyaswamy, Portonovo S.; Muzykantov, Vladimir R.; Radhakrishnan, Ravi

    2016-01-01

    In order to achieve selective targeting of affinity–ligand coated nanoparticles to the target tissue, it is essential to understand the key mechanisms that govern their capture by the target cell. Next-generation pharmacokinetic (PK) models that systematically account for proteomic and mechanical factors can accelerate the design, validation and translation of targeted nanocarriers (NCs) in the clinic. Towards this objective, we have developed a computational model to delineate the roles played by target protein expression and mechanical factors of the target cell membrane in determining the avidity of functionalized NCs to live cells. Model results show quantitative agreement with in vivo experiments when specific and non-specific contributions to NC binding are taken into account. The specific contributions are accounted for through extensive simulations of multivalent receptor–ligand interactions, membrane mechanics and entropic factors such as membrane undulations and receptor translation. The computed NC avidity is strongly dependent on ligand density, receptor expression, bending mechanics of the target cell membrane, as well as entropic factors associated with the membrane and the receptor motion. Our computational model can predict the in vivo targeting levels of the intracellular adhesion molecule-1 (ICAM1)-coated NCs targeted to the lung, heart, kidney, liver and spleen of mouse, when the contributions due to endothelial capture are accounted for. The effect of other cells (such as monocytes, etc.) do not improve the model predictions at steady state. We demonstrate the predictive utility of our model by predicting partitioning coefficients of functionalized NCs in mice and human tissues and report the statistical accuracy of our model predictions under different scenarios. PMID:27429783

  18. A new failure mechanism in thin film by collaborative fracture and delamination: Interacting duos of cracks

    NASA Astrophysics Data System (ADS)

    Marthelot, Joël; Bico, José; Melo, Francisco; Roman, Benoît

    2015-11-01

    When a thin film moderately adherent to a substrate is subjected to residual stress, the cooperation between fracture and delamination leads to unusual fracture patterns, such as spirals, alleys of crescents and various types of strips, all characterized by a robust characteristic length scale. We focus on the propagation of a duo of cracks: two fractures in the film connected by a delamination front and progressively detaching a strip. We show experimentally that the system selects an equilibrium width on the order of 25 times the thickness of the coating and independent of both fracture and adhesion energies. We investigate numerically the selection of the width and the condition for propagation by considering Griffith's criterion and the principle of local symmetry. In addition, we propose a simplified model based on the criterion of maximum of energy release rate, which provides insights of the physical mechanisms leading to these regular patterns, and predicts the effect of material properties on the selected width of the detaching strip.

  19. Cyclic Failure Mechanisms of Thermal and Environmental Barrier Coating Systems Under Thermal Gradient Test Conditions

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Lee, Kang N.; Miller, Robert A.

    2002-01-01

    Plasma-sprayed ZrO2-8wt%Y2O3 and mullite+BSAS/Si multilayer thermal and environmental barrier coating (TBC-EBC) systems on SiC/SiC ceramic matrix composite (CMC) substrates were thermally cyclic tested under high thermal gradients using a laser high-heat-flux rig in conjunction with furnace exposure in water-vapor environments. Coating sintering and interface damage were assessed by monitoring the real-time thermal conductivity changes during the laser heat-flux tests and by examining the microstructural changes after exposure. Sintering kinetics of the coating systems were also independently characterized using a dilatometer. It was found that the coating failure involved both the time-temperature dependent sintering and the cycle frequency dependent cyclic fatigue processes. The water vapor environments not only facilitated the initial coating conductivity increases due to enhanced sintering and interface reaction, but also promoted later conductivity reductions due to the accelerated coating cracking and delamination. The failure mechanisms of the coating systems are also discussed based on the cyclic test results and are correlated to the sintering and thermal stress behavior under the thermal gradient test conditions.

  20. Failure of fluid-saturated granular materials: a unified approach to capture diffuse and localized instability mechanisms

    NASA Astrophysics Data System (ADS)

    Mihalache, Constance; Buscarnera, Giuseppe

    2013-04-01

    Granular materials are susceptible to a wide variety of failure and deformation mechanisms, especially because of their interaction with the pore fluids and the surrounding environment. An adequate modeling of their mechanical response is therefore essential for understanding a number of geological processes, such as the onset of rapid landslides, hillslope denudation and sediment transport, or even the mechanics of fault gauges. Depending on the type of material, the groundwater conditions and the surrounding kinematic constraints, both diffuse and localized mechanisms are possible, and these may occur under either drained or undrained conditions. In the geomechanics literature, failure modes are usually explained and modeled with the tools of continuum mechanics, such as the mathematical theory of plasticity. Due to the complexity of granular material behavior, however, most classical models for frictional strength are unable to capture the variety of instability mechanisms observed for such class of geomaterials (e.g., liquefaction, shear banding, etc.). Sophisticated strain-hardening plasticity models are therefore required for numerical modeling purposes, thus making the evaluation of critical failure conditions less straightforward than in perfect plasticity theories. Here we propose a mathematical strategy that can be adapted to any elastoplastic model and allows the onset of failure in elastoplastic geomaterials to be expressed in a more general manner. More specifically, our theory expresses the failure conditions as a function of local kinematics and solid-fluid interactions. The stability criterion used in this study is based on the so-called stability modulus, a scalar index of failure that was formulated by linking the physical concept controllability to the mathematical notion of plastic admissibility upon an incremental loading path [Buscarnera et al, 2011]. In this contribution, different loading constraints are considered, accounting for the

  1. Cognitive Mechanisms in Chronic Tinnitus: Psychological Markers of a Failure to Switch Attention

    PubMed Central

    Trevis, Krysta J.; McLachlan, Neil M.; Wilson, Sarah J.

    2016-01-01

    The cognitive mechanisms underpinning chronic tinnitus (CT; phantom auditory perceptions) are underexplored but may reflect a failure to switch attention away from a tinnitus sound. Here, we investigated a range of components that influence the ability to switch attention, including cognitive control, inhibition, working memory and mood, on the presence and severity of CT. Our participants with tinnitus showed significant impairments in cognitive control and inhibition as well as lower levels of emotional well-being, compared to healthy-hearing participants. Moreover, the subjective cognitive complaints of tinnitus participants correlated with their emotional well-being whereas complaints in healthy participants correlated with objective cognitive functioning. Combined, cognitive control and depressive symptoms correctly classified 67% of participants. These results demonstrate the core role of cognition in CT. They also provide the foundations for a neurocognitive account of the maintenance of tinnitus, involving impaired interactions between the neurocognitive networks underpinning attention-switching and mood. PMID:27605920

  2. Durable mechanical circulatory support in advanced heart failure: a critical care cardiology perspective.

    PubMed

    Lala, Anuradha; Mehra, Mandeep R

    2013-11-01

    Though cardiac transplantation for advanced heart disease patients remains definitive therapy for patients with advanced heart failure, it is challenged by inadequate donor supply, causing durable mechanical circulatory support (MCS) to slowly become a new primary standard. Selecting appropriate patients for MCS involves meeting a number of prespecifications as is required in evaluation for cardiac transplant candidacy. As technology evolves to bring forth more durable smaller devices, selection criteria for appropriate MCS recipients will likely expand to encompass a broader, less sick population. The "Holy Grail" for MCS will be a focus on clinical recovery and explantation of devices rather than the currently more narrowly defined indications of bridge to transplantation or lifetime device therapy. PMID:24188222

  3. Cognitive Mechanisms in Chronic Tinnitus: Psychological Markers of a Failure to Switch Attention.

    PubMed

    Trevis, Krysta J; McLachlan, Neil M; Wilson, Sarah J

    2016-01-01

    The cognitive mechanisms underpinning chronic tinnitus (CT; phantom auditory perceptions) are underexplored but may reflect a failure to switch attention away from a tinnitus sound. Here, we investigated a range of components that influence the ability to switch attention, including cognitive control, inhibition, working memory and mood, on the presence and severity of CT. Our participants with tinnitus showed significant impairments in cognitive control and inhibition as well as lower levels of emotional well-being, compared to healthy-hearing participants. Moreover, the subjective cognitive complaints of tinnitus participants correlated with their emotional well-being whereas complaints in healthy participants correlated with objective cognitive functioning. Combined, cognitive control and depressive symptoms correctly classified 67% of participants. These results demonstrate the core role of cognition in CT. They also provide the foundations for a neurocognitive account of the maintenance of tinnitus, involving impaired interactions between the neurocognitive networks underpinning attention-switching and mood. PMID:27605920

  4. [Non-invasive mechanical ventilation in the treatment of acute heart failure].

    PubMed

    Alfonso Megido, Joaquín; González Franco, Alvaro

    2014-03-01

    When acute heart failure progresses and there is acute cardiogenic pulmonary edema, routine therapeutic measures should be accompanied by other measures that help to correct oxygenation of the patient. The final and most drastic step is mechanical ventilation. Non-invasive ventilation has been developed in the last few years as a method that attempts to improve oxygenation without the need for intubation, thus, in theory, reducing morbidity and mortality in these patients. The present article describes the controversies surrounding the results of this technique and discusses its indications. The article also discusses how to start non-invasive ventilation in patients with acute pulmonary edema from a practical point of view. PMID:24930085

  5. A mechanics framework for a progressive failure methodology for laminated composites

    NASA Technical Reports Server (NTRS)

    Harris, Charles E.; Allen, David H.; Lo, David C.

    1989-01-01

    A laminate strength and life prediction methodology has been postulated for laminated composites which accounts for the progressive development of microstructural damage to structural failure. A damage dependent constitutive model predicts the stress redistribution in an average sense that accompanies damage development in laminates. Each mode of microstructural damage is represented by a second-order tensor valued internal state variable which is a strain like quantity. The mechanics framework together with the global-local strategy for predicting laminate strength and life is presented in the paper. The kinematic effects of damage are represented by effective engineering moduli in the global analysis and the results of the global analysis provide the boundary conditions for the local ply level stress analysis. Damage evolution laws are based on experimental results.

  6. Finite Element Modeling of the Different Failure Mechanisms of a Plasma Sprayed Thermal Barrier Coatings System

    NASA Astrophysics Data System (ADS)

    Ranjbar-Far, M.; Absi, J.; Mariaux, G.

    2012-12-01

    A new finite element model is used to investigate catastrophic failures of a thermal barrier coatings system due to crack propagation along the interfaces between the ceramic top-coat, thermally grown oxide, and bond-coat layers, as well as between the lamellas structure of the ceramic layer. The thermo-mechanical model is designed to take into account a non-homogenous temperature distribution and the effects of the residual stresses generated during the coating process. Crack propagation is simulated using the contact tool "Debond" present in the ABAQUS finite element code. Simulations are performed with a geometry corresponding to similar or dissimilar amplitudes of asperity, and for different thicknesses of the oxide layer. The numerical results have shown that crack evolution depends crucially on the ratio of the loading rate caused by growth and swelling of the oxide layer and also on the interface roughness obtained during the spraying of coatings.

  7. An experimental study of the mechanism of failure of rocks under borehole jack loading

    NASA Technical Reports Server (NTRS)

    Van, T. K.; Goodman, R. E.

    1971-01-01

    Laboratory and field tests with an experimental jack and an NX-borehole jack are reported. The following conclusions were made: Under borehole jack loading, a circular opening in a brittle solid fails by tensile fracturing when the bearing plate width is not too small. Two proposed contact stress distributions can explain the mechanism of tensile fracturing. The contact stress distribution factor is a material property which can be determined experimentally. The borehole tensile strength is larger than the rupture flexural strength. Knowing the magnitude and orientation of the in situ stress field, borehole jack test results can be used to determine the borehole tensile strength. Knowing the orientation of the in situ stress field and the flexural strength of the rock substance, the magnitude of the in situ stress components can be calculated. The detection of very small cracks is essential for the accurate determination of the failure loads which are used in the calculation of strengths and stress components.

  8. Initiation of vacuum breakdown and failure mechanism of the carbon nanotube during thermal field emission

    NASA Astrophysics Data System (ADS)

    Dan, Cai; Lie, Liu; Jin-Chuan, Ju; Xue-Long, Zhao; Hong-Yu, Zhou; Xiao, Wang

    2016-04-01

    The carbon nanotube (CNT)-based materials can be used as vacuum device cathodes. Owing to the excellent field emission properties of CNT, it has great potentials in the applications of an explosive field emission cathode. The falling off of CNT from the substrate, which frequently appears in experiments, restricts its application. In addition, the onset time of vacuum breakdown limits the performance of the high-power explosive-emission-cathode-based diode. In this paper, the characteristics of the CNT, electric field strength, contact resistance and the kind of substrate material are varied to study the parameter effects on the onset time of vacuum breakdown and failure mechanism of the CNT by using the finite element method. Project supported by the National Natural Science Foundation of China (Grant Nos. 11305263 and 61401484).

  9. A novel COX-independent mechanism of sulindac sulfide involves cleavage of epithelial cell adhesion molecule protein.

    PubMed

    Liggett, Jason L; Min, Kyung-Won; Smolensky, Dmitriy; Baek, Seung Joon

    2014-08-01

    Non-steroidal anti-inflammatory drugs (NSAIDs) are extensively used over the counter to treat headaches and inflammation as well as clinically to prevent cancer among high-risk groups. The inhibition of cyclooxygenase (COX) activity by NSAIDs plays a role in their anti-tumorigenic properties. NSAIDs also have COX-independent activity which is not fully understood. In this study, we report a novel COX-independent mechanism of sulindac sulfide (SS), which facilitates a previously uncharacterized cleavage of epithelial cell adhesion molecule (EpCAM) protein. EpCAM is a type I transmembrane glycoprotein that has been implemented as an over-expressed oncogene in many cancers including colon, breast, pancreas, and prostate. We found EpCAM to be down-regulated by SS in a manner that is independent of COX activity, transcription regulation, de novo protein synthesis, and proteasomal degradation pathway. Our findings clearly demonstrate that SS drives cleavage of the extracellular portion of EpCAM near the N-terminus. This SS driven cleavage is blocked by a deleting amino acids 55-81 as well as simply mutating arginine residues at positions 80 and 81 to alanine of EpCAM. Proteolysis of EpCAM by SS may provide a novel mechanism by which NSAIDs affect anti-tumorigenesis at the post-translational level. PMID:24859349

  10. Deglacial temperature patterns in the Arabian Sea and mechanisms for Indian monsoon failure

    NASA Astrophysics Data System (ADS)

    Tierney, J. E.; Pausata, F. S. R.; deMenocal, P. B.

    2015-12-01

    Both paleoclimate data and climate model simulations demonstrate that the Indian monsoon system responds to remote coolings in the North Atlantic. The textbook examples are the stadial events associated with the last deglaciation — the Younger Dryas and Heinrich Stadial 1 — when the monsoon weakened dramatically and caused drying throughout the Indian Ocean rim. The mechanism by which the North Atlantic influences the monsoon system is not completely clear: locally cool SSTs, increases in continental albedo, and southward migration of the intertropical convergence zone have all been raised as possibilities. Here we synthesize biomarker and foraminiferal estimates of temperature to study the evolution of the Arabian Sea water column during the deglaciation and test hypotheses of monsoon failure during stadials. Alkenone and Mg/Ca data clearly indicate that the Arabian Sea cools during the YD and H1, although H1 cooling is partly obscured by the overall warming trend associated with orbital forcing and rising greenhouse gases. In contrast, TEX86 data record warmings during the YD and H1. The stark difference between the TEX86 response and the alkenone and foraminiferal data, as well as comparison with climate model simulations, indicates that TEX86 is most likely acting as a subsurface temperature proxy in the Arabian Sea over these timescales. Taken together, the paleoclimate data describe a pattern of surface cooling and subsurface warming in response to North Atlantic cooling. This oceanographic response is in excellent agreement with both timeslice and transient model simulations spanning the last deglaciation, and strongly supports the hypothesis that locally cool SSTs are a requisite for monsoon failure. Furthermore, subsurface warming causes a destratification of the Arabian Sea water column and provides a mechanism for previously observed reductions in productivity during stadial events.

  11. Mechanisms of improvement of respiratory failure in patients with COPD treated with NIV

    PubMed Central

    Nickol, Annabel H; Hart, Nicholas; Hopkinson, Nicholas S; Hamnegård, Carl-Hugo; Moxham, John; Simonds, Anita; Polkey, Michael I

    2008-01-01

    Background Noninvasive ventilation (NIV) improves gas-exchange and symptoms in selected chronic obstructive pulmonary disease (COPD) patients with hypercapnic respiratory failure. We hypothesized NIV reverses respiratory failure by one or all of increased ventilatory response to carbon-dioxide, reduced respiratory muscle fatigue, or improved pulmonary mechanics. Methods Nineteen stable COPD patients (forced expiratory volume in one second 35% predicted) were studied at baseline (D0), 5–8 days (D5) and 3 months (3M) after starting NIV. Results Ventilator use was 6.2 (3.7) hours per night at D5 and 3.4 (1.6) at 3M (p = 0.12). Mean (SD) daytime arterial carbon-dioxide tension (PaCO2) was reduced from 7.4 (1.2) kPa to 7.0 (1.1) kPa at D5 and 6.5 (1.1) kPa at 3M (p = 0.001). Total lung capacity decreased from 107 (28) % predicted to 103 (28) at D5 and 103 (27) % predicted at 3M (p = 0.035). At D5 there was an increase in the hypercapnic ventilatory response and some volitional measures of inspiratory and expiratory muscle strength, but not isolated diaphragmatic strength whether assessed by volitional or nonvolitional methods. Conclusion These findings suggest decreased gas trapping and increased ventilatory sensitivity to CO2 are the principal mechanism underlying improvements in gas-exchange in patients with COPD following NIV. Changes in some volitional but not nonvolitional muscle strength measures may reflect improved patient effort. PMID:18990974

  12. Thermal Cycling Reliability of Sn-Ag-Cu Solder Interconnections—Part 2: Failure Mechanisms

    NASA Astrophysics Data System (ADS)

    Hokka, Jussi; Mattila, Toni T.; Xu, Hongbo; Paulasto-Kröckel, Mervi

    2013-06-01

    Part 1 of this study focused on identifying the effects of (i) temperature difference (Δ T), (ii) lower dwell temperature and shorter dwell time, (iii) mean temperature, (iv) dwell time, and (v) ramp rate on the lifetime of ball grid array (with 144 solder balls) component boards. Based on the characteristic lifetime, the studied thermal cycling profiles were categorized into three groups: (i) highly accelerated conditions, (ii) moderately accelerated conditions, and (iii) mildly/nonaccelerated conditions. In this work, the observed differences in component board lifetime are explained by studying the failure mechanisms and microstructural changes that take place in the three groups of loading conditions. It was observed that, under the standardized thermal cycling conditions (highly accelerated conditions), the networks of grain boundaries formed by recrystallization provided favorable paths for cracks to propagate intergranularly. It is noteworthy that the coarsening of intermetallic particles was strong in the recrystallized regions (the cellular structure had disappeared completely in the crack region). However, under real-use conditions (mildly/nonaccelerated conditions), recrystallization was not observed in the solder interconnections and cracks had propagated transgranularly in the bulk solder or between the intermetallic compound (IMC) layer and the bulk solder. The real-use conditions showed slight coarsening of the microstructure close to the crack region, but the solder bulk still included finer IMC particles and β-Sn cells characteristic of the as-solidified microstructures. These findings suggest that standardized thermal cycling tests used to assess the solder interconnection reliability of BGA144 component boards create failure mechanisms that differ from those seen in conditions representing real-use operation.

  13. Comparative role of disc degeneration and ligament failure on functional mechanics of the lumbar spine.

    PubMed

    Ellingson, Arin M; Shaw, Miranda N; Giambini, Hugo; An, Kai-Nan

    2016-07-01

    Understanding spinal kinematics is essential for distinguishing between pathological conditions of spine disorders, which ultimately lead to low back pain. It is of high importance to understand how changes in mechanical properties affect the response of the lumbar spine, specifically in an effort to differentiate those associated with disc degeneration from ligamentous changes, allowing for more precise treatment strategies. To do this, the goals of this study were twofold: (1) develop and validate a finite element (FE) model of the lumbar spine and (2) systematically alter the properties of the intervertebral disc and ligaments to define respective roles in functional mechanics. A three-dimensional non-linear FE model of the lumbar spine (L3-sacrum) was developed and validated for pure moment bending. Disc degeneration and sequential ligament failure were modelled. Intersegmental range of motion (ROM) and bending stiffness were measured. The prediction of the FE model to moment loading in all three planes of bending showed very good agreement, where global and intersegmental ROM and bending stiffness of the model fell within one standard deviation of the in vitro results. Degeneration decreased ROM for all directions. Stiffness increased for all directions except axial rotation, where it initially increased then decreased for moderate and severe degeneration, respectively. Incremental ligament failure produced increased ROM and decreased stiffness. This effect was much more pronounced for all directions except lateral bending, which is minimally impacted by ligaments. These results indicate that lateral bending may be more apt to detect the subtle changes associated with degeneration, without being masked by associated changes of surrounding stabilizing structures. PMID:26404463

  14. Mechanical properties and failure behaviors of the interface of hybrid graphene/hexagonal boron nitride sheets

    PubMed Central

    Ding, Ning; Chen, Xiangfeng; Wu, Chi-Man Lawrence

    2016-01-01

    Hybrid graphene/h-BN sheet has been fabricated recently and verified to possess unusual physical properties. During the growth process, defects such as vacancies are unavoidably present at the interface between graphene and h-BN. In the present work, typical vacancy defects, which were located at the interface between graphene and h-BN, were studied by density functional theory. The interface structure, mechanical and electronic properties, and failure behavior of the hybrid graphene/h-BN sheet were investigated and compared. The results showed that the formation energy of the defective graphene/h-BN interface basically increased with increasing inflection angles. However, Young’s modulus for all graphene/h-BN systems studied decreased with the increase in inflection angles. The intrinsic strength of the hybrid graphene/h-BN sheets was affected not only by the inflection angles, but also by the type of interface connection and the type of defects. The energy band structure of the hybrid interface could be tuned by applying mechanical strain to the systems. These results demonstrated that vacancies introduced significant effects on the mechanical and electronic properties of the hybrid graphene/h-BN sheet. PMID:27527371

  15. Failure mechanisms of single-crystal silicon electrodes in lithium-ion batteries

    PubMed Central

    Shi, Feifei; Song, Zhichao; Ross, Philip N.; Somorjai, Gabor A.; Ritchie, Robert O.; Komvopoulos, Kyriakos

    2016-01-01

    Long-term durability is a major obstacle limiting the widespread use of lithium-ion batteries in heavy-duty applications and others demanding extended lifetime. As one of the root causes of the degradation of battery performance, the electrode failure mechanisms are still unknown. In this paper, we reveal the fundamental fracture mechanisms of single-crystal silicon electrodes over extended lithiation/delithiation cycles, using electrochemical testing, microstructure characterization, fracture mechanics and finite element analysis. Anisotropic lithium invasion causes crack initiation perpendicular to the electrode surface, followed by growth through the electrode thickness. The low fracture energy of the lithiated/unlithiated silicon interface provides a weak microstructural path for crack deflection, accounting for the crack patterns and delamination observed after repeated cycling. On the basis of this physical understanding, we demonstrate how electrolyte additives can heal electrode cracks and provide strategies to enhance the fracture resistance in future lithium-ion batteries from surface chemical, electrochemical and material science perspectives. PMID:27297565

  16. Failure mechanism of monolayer graphene under hypervelocity impact of spherical projectile.

    PubMed

    Xia, Kang; Zhan, Haifei; Hu, De'an; Gu, Yuantong

    2016-01-01

    The excellent mechanical properties of graphene have enabled it as appealing candidate in the field of impact protection or protective shield. By considering a monolayer graphene membrane, in this work, we assessed its deformation mechanisms under hypervelocity impact (from 2 to 6 km/s), based on a serial of in silico studies. It is found that the cracks are formed preferentially in the zigzag directions which are consistent with that observed from tensile deformation. Specifically, the boundary condition is found to exert an obvious influence on the stress distribution and transmission during the impact process, which eventually influences the penetration energy and crack growth. For similar sample size, the circular shape graphene possesses the best impact resistance, followed by hexagonal graphene membrane. Moreover, it is found the failure shape of graphene membrane has a strong relationship with the initial kinetic energy of the projectile. The higher kinetic energy, the more number the cracks. This study provides a fundamental understanding of the deformation mechanisms of monolayer graphene under impact, which is crucial in order to facilitate their emerging future applications for impact protection, such as protective shield from orbital debris for spacecraft. PMID:27618989

  17. Failure mechanisms of single-crystal silicon electrodes in lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Shi, Feifei; Song, Zhichao; Ross, Philip N.; Somorjai, Gabor A.; Ritchie, Robert O.; Komvopoulos, Kyriakos

    2016-06-01

    Long-term durability is a major obstacle limiting the widespread use of lithium-ion batteries in heavy-duty applications and others demanding extended lifetime. As one of the root causes of the degradation of battery performance, the electrode failure mechanisms are still unknown. In this paper, we reveal the fundamental fracture mechanisms of single-crystal silicon electrodes over extended lithiation/delithiation cycles, using electrochemical testing, microstructure characterization, fracture mechanics and finite element analysis. Anisotropic lithium invasion causes crack initiation perpendicular to the electrode surface, followed by growth through the electrode thickness. The low fracture energy of the lithiated/unlithiated silicon interface provides a weak microstructural path for crack deflection, accounting for the crack patterns and delamination observed after repeated cycling. On the basis of this physical understanding, we demonstrate how electrolyte additives can heal electrode cracks and provide strategies to enhance the fracture resistance in future lithium-ion batteries from surface chemical, electrochemical and material science perspectives.

  18. Mechanical properties and failure behaviors of the interface of hybrid graphene/hexagonal boron nitride sheets.

    PubMed

    Ding, Ning; Chen, Xiangfeng; Wu, Chi-Man Lawrence

    2016-01-01

    Hybrid graphene/h-BN sheet has been fabricated recently and verified to possess unusual physical properties. During the growth process, defects such as vacancies are unavoidably present at the interface between graphene and h-BN. In the present work, typical vacancy defects, which were located at the interface between graphene and h-BN, were studied by density functional theory. The interface structure, mechanical and electronic properties, and failure behavior of the hybrid graphene/h-BN sheet were investigated and compared. The results showed that the formation energy of the defective graphene/h-BN interface basically increased with increasing inflection angles. However, Young's modulus for all graphene/h-BN systems studied decreased with the increase in inflection angles. The intrinsic strength of the hybrid graphene/h-BN sheets was affected not only by the inflection angles, but also by the type of interface connection and the type of defects. The energy band structure of the hybrid interface could be tuned by applying mechanical strain to the systems. These results demonstrated that vacancies introduced significant effects on the mechanical and electronic properties of the hybrid graphene/h-BN sheet. PMID:27527371

  19. Failure mechanisms of single-crystal silicon electrodes in lithium-ion batteries.

    PubMed

    Shi, Feifei; Song, Zhichao; Ross, Philip N; Somorjai, Gabor A; Ritchie, Robert O; Komvopoulos, Kyriakos

    2016-01-01

    Long-term durability is a major obstacle limiting the widespread use of lithium-ion batteries in heavy-duty applications and others demanding extended lifetime. As one of the root causes of the degradation of battery performance, the electrode failure mechanisms are still unknown. In this paper, we reveal the fundamental fracture mechanisms of single-crystal silicon electrodes over extended lithiation/delithiation cycles, using electrochemical testing, microstructure characterization, fracture mechanics and finite element analysis. Anisotropic lithium invasion causes crack initiation perpendicular to the electrode surface, followed by growth through the electrode thickness. The low fracture energy of the lithiated/unlithiated silicon interface provides a weak microstructural path for crack deflection, accounting for the crack patterns and delamination observed after repeated cycling. On the basis of this physical understanding, we demonstrate how electrolyte additives can heal electrode cracks and provide strategies to enhance the fracture resistance in future lithium-ion batteries from surface chemical, electrochemical and material science perspectives. PMID:27297565

  20. Nonlinear elastic behavior and failure mechanism of polyhedral graphite particles undergoing uniaxial compression

    NASA Astrophysics Data System (ADS)

    Li, B.; Zhang, P.; Fu, Q. Q.; Li, X. F.; Zhao, X.; Song, X. L.

    2014-08-01

    Load-displacement responses and ultimate strength of polyhedral graphite particles (PGPs) undergoing in situ nano-compression at ambient temperature have been studied. The dynamic responses of PGPs to uniaxial loads exhibit a typical nonlinear elastic behavior for graphitic nanomaterials. Based on the analysis of stress-strain relationship, the intrinsic strength is slightly larger than actual ultimate strength, indicating the mechanical properties influenced by the initial defects in PGPs. For a given case, compressive Young's modulus E and third-order elastic modulus D achieve to 12.8 GPa and -13.9 GPa, respectively. Weibull probability analysis confirmed its broad range of structural defects inside PGPs and mechanical properties are sensitive to initial defects. The values of ultimate strength of tested PGPs with diameter of 150-400 nm fall within 2-4.5 GPa, which are in the range between shear elastic modulus C44 of turbo-g (minimum) and C44 of hex-g (maximum) in the literature. The deformation and failure mechanisms are discussed and rationalized in terms of structural factors and elastic moduli of perfect graphite crystals.

  1. Development of a shock wave adhesion test for composite bonds by laser pulsed and mechanical impacts

    NASA Astrophysics Data System (ADS)

    Ecault, Romain; Boustie, Michel; Touchard, Fabienne; Arrigoni, Michel; Berthe, Laurent; CNRS Collaboration

    2013-06-01

    Evaluating the bonding quality of composite material is becoming one of the main challenges faced by aeronautic industries. This work aims the development of a technique using shock wave, which would enable to quantify the bonding mechanical quality. Laser shock experiments were carried out. This technique enables high tensile stress generation in the thickness of composite bond without any mechanical contact. The resulting damage has been quantified using different method such as confocal microscopy, ultrasound and cross section observation. The discrimination between a correct bond and a weak bond was possible thanks to these experiments. Nevertheless, laser sources are not well adapted for optimization of such a test since it has often fixed parameters. That is why mechanical impacts bonded composites were also performed in this work. By changing the thickness of aluminum projectiles, the tensile stresses generated by the shock wave propagation were moved toward the composite/bond interface. The observations made prove that the optimization of the technique is possible. The key parameters for the development of a bonding test using shock wave have been identified.

  2. Atomic force microscopy, lateral force microscopy, and transmission electron microscopy investigations and adhesion force measurements for elucidation of tungsten removal mechanisms

    SciTech Connect

    Stein, D.J.; Cecchi, J.L.; Hetherington, D.L.

    1999-09-01

    We investigated various interactions between alumina and tungsten films that occur during chemical mechanical polishing (CMP). Atomic force microscopy surface topography measurements of post-CMP tungsten indicate that the roughness of the tungsten is independent of polish pressure and rotation rate. Pure mechanical abrasion is therefore an unlikely mechanism of material removal during CMP. Transmission electron microscopy images corroborate these results. The adhesion force between alumina and tungsten was measured in solution. The adhesive force increased with KIO{sub 3} concentration. Friction forces were measured in solution using lateral force microscopy. The friction force in buffered solutions was independent of KIO{sub 3} concentration. These results indicate that interactions other than purely mechanical interactions exist during CMP. {copyright} {ital 1999 Materials Research Society.}

  3. Development of a shock wave adhesion test for composite bonds by pulsed laser and mechanical impacts

    NASA Astrophysics Data System (ADS)

    Ecault, R.; Boustie, M.; Touchard, F.; Arrigoni, M.; Berthe, L.

    2014-05-01

    Evaluating the bonding quality of composite material is becoming one of the main challenges faced by aeronautic industries. This work aims to the development of a technique using shock wave, which would enable to quantify the bonding mechanical quality. Laser shock experiments were carried out. This technique enables high tensile stress generation in the thickness of composite bonds. The resulting damage has been quantified using different methods such as confocal microscopy, ultrasound and cross section observation. The discrimination between a correct bond and a weak bond was possible thanks to these experiments. Nevertheless, laser sources are not well adapted for optimization of such a test because of often fixed settings. That is why mechanical impacts on bonded composites were also performed in this work. By changing the thickness of aluminum projectiles, the generated tensile stresses by the shock wave propagation were moved toward the composite/bond interface. The made observations prove that the technique optimization is possible. The key parameters for the development of a bonding test using shock waves have been identified.

  4. Shale Failure Mechanics and Intervention Measures in Underground Coal Mines: Results From 50 Years of Ground Control Safety Research

    PubMed Central

    2015-01-01

    Ground control research in underground coal mines has been ongoing for over 50 years. One of the most problematic issues in underground coal mines is roof failures associated with weak shale. This paper will present a historical narrative on the research the National Institute for Occupational Safety and Health has conducted in relation to rock mechanics and shale. This paper begins by first discussing how shale is classified in relation to coal mining. Characterizing and planning for weak roof sequences is an important step in developing an engineering solution to prevent roof failures. Next, the failure mechanics associated with the weak characteristics of shale will be discussed. Understanding these failure mechanics also aids in applying the correct engineering solutions. The various solutions that have been implemented in the underground coal mining industry to control the different modes of failure will be summarized. Finally, a discussion on current and future research relating to rock mechanics and shale is presented. The overall goal of the paper is to share the collective ground control experience of controlling roof structures dominated by shale rock in underground coal mining. PMID:26549926

  5. Shale Failure Mechanics and Intervention Measures in Underground Coal Mines: Results From 50 Years of Ground Control Safety Research

    NASA Astrophysics Data System (ADS)

    Murphy, M. M.

    2016-02-01

    Ground control research in underground coal mines has been ongoing for over 50 years. One of the most problematic issues in underground coal mines is roof failures associated with weak shale. This paper will present a historical narrative on the research the National Institute for Occupational Safety and Health has conducted in relation to rock mechanics and shale. This paper begins by first discussing how shale is classified in relation to coal mining. Characterizing and planning for weak roof sequences is an important step in developing an engineering solution to prevent roof failures. Next, the failure mechanics associated with the weak characteristics of shale will be discussed. Understanding these failure mechanics also aids in applying the correct engineering solutions. The various solutions that have been implemented in the underground coal mining industry to control the different modes of failure will be summarized. Finally, a discussion on current and future research relating to rock mechanics and shale is presented. The overall goal of the paper is to share the collective ground control experience of controlling roof structures dominated by shale rock in underground coal mining.

  6. Structural integrity and failure mechanisms of a smart piezoelectric actuator under a cyclic bending mode

    NASA Astrophysics Data System (ADS)

    Woo, Sung-Choong; Goo, Nam Seo

    2008-08-01

    Information on the onset and evolution of damage within materials is essential for guaranteeing the integrity of actuator systems. The authors have evaluated the structural integrity and the failure mechanisms of smart composite actuators with a PZT ceramic plate under electric cyclic loading. For this, two kinds of actuators, actuator 1 and actuator 2, were manufactured. Prior to the main testing, performance testing was performed on the actuators to determine their resonant frequencies. Electric cyclic tests were conducted up to twenty million cycles. An acoustic emission technique was used for monitoring the damage evolution in real time. We observed the extent of the damage after testing using scanning electron microscopy and reflected optical microscopy to support characteristics in the acoustic emission behavior that corresponded to specific types of damage mechanisms. It was shown that the initial damage mechanism of the smart composite actuator under electric cyclic loading originated from the transgranular micro-fatigue damage in the PZT ceramic layer. With increasing cycles, a local intergranular crack initiated and developed onto the surface of the PZT ceramic layer or propagated into the internal layer. Finally, short-circuiting led to the electric breakdown of the actuator. These results were different depending on the drive frequencies and the configuration of the actuators. Moreover, we differentiated between the aforementioned damage mechanisms via AE signal pattern analyses based on the primary frequency and the waveform. From our results, we conclude that the drive frequency and the existence of a protecting layer are dominant factors in the structural integrity of the smart composite actuator.

  7. Reliability characterizations and failure mechanism of ultra-thin oxides for MOS devices

    NASA Astrophysics Data System (ADS)

    Wang, Bin

    The aggressive scaling of smaller/faster logic and memory devices demands accurate reliability characterization and knowledge of the failure mechanisms of ultra-thin (<30 A) silicon dioxide (SiO 2) layers in the gates of metal-oxide semiconductor (MOS) structures. The increased occurrence of soft breakdown in ultra-thin oxide films necessitates the development of more sophisticated techniques to detect breakdown. One such technique is by interrupting stress and monitoring stress-induced leakage current (SILC) or interface state density (Dit). The effect of interrupting stress was carefully studied and determined not to affect device lifetime. A comprehensive time-dependent dielectric breakdown (TDDB) study was conducted on ultra-thin oxide over a temperature ranging from 220°C to 350°C to study temperature acceleration. The results of the study showed that both hard and soft breakdown modes exhibit the same temperature dependence. The choice of a failure model for time/charge to breakdown (tBD /QBD) is critical for accurate reliability extrapolation. In this work, two more experiments were carried out to clarify the current physical mechanisms responsible to dielectric wear-out. The first experiment investigated the effects of pulsed biased stress on device lifetime. A lifetime enhancement under bipolar pulse stress was observed. The results suggest that previously proposed mechanism of hole de-trapping in thick oxide may not be responsible for the lifetime increase observed here for ultra-thin oxides. The second experiment studied the effects of heavy ion on the reliability of ultra-thin SiO2. Annealing and electron injection experiments on irradiated devices with heavy ion implied that holes were significantly created and trapped inside SiO2 without causing the SiO2 to breakdown. The results from these two studies suggest that breakdown of ultra-thin oxides is not caused by holes and that the anode hole injection (AHI) model for constant voltage stress (CVS) is

  8. Constructing an effective prevention mechanism for MSW lifecycle using failure mode and effects analysis.

    PubMed

    Chen, Ying-Chu; Wu, Wen-Fang

    2015-12-01

    Municipal solid waste in Taiwan is a valuable source of renewable energy. Phases of municipal solid waste lifecycle (classification, disposal, storage, collection and transportation) before incineration or landfilled face various potential failures. Applying a proper technique to eliminate or decrease potential failures is desirable and needed. Failure Modes and Effects Analysis to municipal solid waste lifecycle was found in literature. This study utilized the Failure Modes and Effects Analysis as a convenient technique for determining, classifying and analyzing common failures in the municipal solid waste lifecycle. As a result, an appropriate risk scoring of severity, occurrence, and detection of failure modes and computing the Risk Priority Number for identifying the high potential failure modes were made. Nineteen failure modes were identified, and nine of them were ranked as the priority items for improvement. Recommended actions for all failure modes were suggested. Occurrences of failures were remarkably reduced after implementing the procedure for six months. The results of this study have minimized potential failures and brought continuous improvement, thus achieving a better protection of the environment. PMID:26372404

  9. Enhanced dielectric standoff and mechanical failure in field-structured composites

    NASA Astrophysics Data System (ADS)

    Martin, James E.; Tigges, Chris P.; Anderson, Robert A.; Odinek, Judy

    1999-09-01

    We report dielectric breakdown experiments on electric-field-structured composites of high-dielectric-constant BaTiO3 particles in an epoxy resin. These experiments show a significant increase in the dielectric standoff strength perpendicular to the field structuring direction, relative to control samples consisting of randomly dispersed particles. To understand the relation of this observation to microstructure, we apply a simple resistor-short breakdown model to three-dimensional composite structures generated from a dynamical simulation. In this breakdown model the composite material is assumed to conduct primarily through particle contacts, so the simulated structures are mapped onto a resistor network where the center of mass of each particle is a node that is connected to neighboring nodes by resistors of fixed resistance that irreversibly short to perfect conductors when the current reaches a threshold value. This model gives relative breakdown voltages that are in good agreement with experimental results. Finally, we consider a primitive model of the mechanical strength of a field-structured composite material, which is a current-driven, conductor-insulator fuse model. This model leads to a macroscopic fusing behavior and can be related to mechanical failure of the composite.

  10. Modeling Structure Property Relations and Failure Mechanisms of PPTA Fibers using Reactive Molecular Dynamics

    NASA Astrophysics Data System (ADS)

    Yilmaz, Dundar

    Failure mechanisms of poly(p-phenylene terephthalamide (PPTA) under extreme tensile deformation has been studied using reactive potentials with molecular dynamics simulations. Amorphous PPTA systems with different molecular weights generated using an in-house developed amorphous builder. Tensile modulus of amorphous PPTA has been calculated as up to 6.7 GPa. Nitrogen and carbon vacancy defects were introduced to both crystalline and amorphous systems. The tensile modulus of defects-free crystalline PPTA calculated as 350 GPa. Introduction of 5% nitrogen vacancy defects reduced the tensile modulus to 197 GPa. PPTA fibers generated with skin core structure where skin region composed of PPTA chains in crystalline order and core region was composed of unordered PPTA chains vice versa. Relation between ratios of skin and core regions and mechanical properties of the fiber studied. Tensile load was mostly accommodated through stretching of bonds between amide group and phenyl groups. Under extreme tensile deformation PPTA chains failed at these C-N bonds. TUBITAK Grant No: 113F358.

  11. Numerical modeling of the failure mechanisms in silicon thin film anode for lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Patel, Siddharth H.

    2011-12-01

    In recent times, the demand for the storage of electrical energy has grown rapidly for both static applications and the portable electronics enforcing the substantial improvement in battery systems, and Li-ion batteries have been proven to have maximum energy storage density in all rechargeable batteries. However, major breakthroughs are required to consummate the requirement of higher energy density with lower cost to penetrate new markets. Graphite anode having limited capacity has become a bottle neck in the process of developing next generation batteries and can be replaced by higher capacity metals such as Silicon. In the present study we are focusing on the mechanical behavior of the Si-thin film anode under various operating conditions. A numerical model is developed to simulate the intercalation induced stress and the failure mechanism of the complex anode structure. Effect of the various physical phenomena such as diffusion induced stress, plasticity and the crack propagation are investigated to predict better performance parameters for improved design.

  12. Effect and mechanism of Bushen Huoxue recipe on ovarian reserve in mice with premature ovarian failure.

    PubMed

    Song, Kun-Kun; Ma, Wen-Wen; Huang, Cong; Ding, Jia-Hui; Cui, Dan-Dan; Tan, Xiu-Juan; Xiao, Jing; Zhang, Ming-Min

    2016-08-01

    The aim of the present study was to explore the effect and mechanism of Bushen Huoxue recipe (BHR) on ovarian reserve in mice with premature ovarian failure (POF). Mice were divided into 3 groups: normal group, model group and BHR group. Intraperitoneal injection of cyclophosphamide was performed to create the POF model. Primordial follicular (PDF) number, ovarian wet weight, ovarian index, and estrous cycle were analyzed to evaluate the effect of BHR on POF. Meanwhile, the mRNA and protein level of Mouse Vasa Homologue (MVH) in the bone marrow, peripheral blood and ovary were detected, to explore the underlying mechanism of the treatment efficacy of BHR on ovarian reserve. By the time of BHR treatment for 28 days, BHR increased the PDF number and shortened the estrous cycle of POF mice. BHR also decreased the mRNA level of MVH in the bone marrow, and increased mRNA and protein level of MVH in the ovary of POF mice. Our results demonstrated a treatment efficacy of BHR on POF mice, and revealed that BHR might repair the dysfunction of germline stem cells in the bone marrow, and thus to improve the ovarian reserve and enhance the ovarian function of POF mice through neo-oogenesis. PMID:27465335

  13. Unraveling new mechanisms of exercise intolerance in chronic heart failure: role of exercise training.

    PubMed

    Conraads, Viviane M; Van Craenenbroeck, Emeline M; De Maeyer, Catherine; Van Berendoncks, An M; Beckers, Paul J; Vrints, Christiaan J

    2013-01-01

    Despite remarkable progress in the therapeutic approach of patients with chronic heart failure (CHF), exercise intolerance remains one of the hallmarks of the disease. During the past two decades, evidence has accumulated to underscore the key role of both endothelial dysfunction and skeletal muscle wasting in the process that gradually leads to physical incapacity. Whereas reverse ventricular remodeling has been attributed to aerobic exercise training, the vast majority of studies conducted in this specific patient population emphasize the reversal of peripheral abnormalities. In this review, we provide a general overview on underlying pathophysiological mechanisms. In addition, emphasis is put on recently identified pathways, which contribute to a deeper understanding of the main causes of exercise tolerance and the potential for reversal through exercise training. Recently, deficient bone marrow-related endothelial repair mechanisms have received considerable attention. Both acute exercise bouts, as well as exercise training, affect the mobilization of endothelial progenitor cells and their function. The observed changes following exercise training are believed to significantly contribute to improvement of peripheral endothelial function, as well as exercise capacity. With regard to skeletal muscle dysfunction and energy deprivation, adiponectin has been suggested to play a significant role. The demonstration of local skeletal muscle adiponectin resistance may provide an interesting and new link between the insulin resistant state and skeletal muscle wasting in CHF patients. PMID:22684340

  14. Investigation of failure mechanisms in high-power microwave transmission windows

    NASA Astrophysics Data System (ADS)

    Bosman, Herman L.

    Thermal runaway and window failure restrict the power output of high power (˜1 MW), long pulse length (˜10 sec) gyrotrons used for plasma heating in magnetic confinement fusion experiments. Chemical vapor deposition diamond is used as window material due to its low loss tangent and high thermal conductivity, but still suffers from occasional, unpredictable failure. With the use of a simple model, it is shown that a uniform thin film of contaminant on a microwave window may absorb up to 50 percent of the incident power, even if the film thickness is only a small fraction of its resistive skin depth. The fraction of power absorbed by thin films on diamond gyrotron windows is estimated by comparison with published data obtained via two different experimental routes. Typically about a fraction of one percent of the incident power is absorbed by the thin films. Discontinuous surface films, where the surface contaminants have a patchy or island structure, are modeled with an equivalent transmission line circuit. Patchy surface contaminants on diamond gyrotron windows do not contribute significantly to the overall power absorbed on the window surface. An unexpected result is that most of the power is absorbed on the 'clean' window surface. The uniform thin film model is therefore adequate to describe surface power losses for diamond windows. The discontinuous film model, applied to alumina windows with TIN coatings, shows power absorption values of approximately 0.1--0.3%. Graphitic contaminants embedded in the CVD diamond absorb RE power from both the RE electric and magnetic field components. The absorbed power is insufficient to cause significant heating or cause graphitization in the diamond. The power absorbed in a diamond gyrotron window causes thermal gradient stresses in the window, with the maximum tensile stress occurring close to the window edge. For power absorption values up to 2000 W, the tensile stresses alone are insufficient to cause mechanical failure

  15. Three Potential Mechanisms for Failure of HIFU Ablation in Cardiac Tissue

    PubMed Central

    Laughner, Jacob I.; Sulkin, Matthew S.; Wu, Ziqi; Deng, Cheri X.; Efimov, Igor R.

    2012-01-01

    Background High Intensity Focused Ultrasound (HIFU) has been introduced for treatment of cardiac arrhythmias, because it offers the ability to create rapid tissue modification in confined volumes without directly contacting the myocardium. In spite of the benefits of HIFU, a number of limitations have been reported, which hindered its clinical adoption. Methods and Results In this study, we used a multimodal approach to evaluate thermal and non-thermal effects of HIFU in cardiac ablation. We designed a computer-controlled system capable of simultaneous fluorescence mapping and HIFU ablation. Using this system, linear lesions were created in isolated rabbit atria (n = 6) and point lesions were created in the ventricles of whole-heart (n = 6) preparations by applying HIFU at clinical doses (4–16W). Additionally, we evaluate the gap size in ablation lines necessary for conduction in atrial preparations (n = 4). The voltage sensitive dye di-4-ANEPPS was used to assess functional damage produced by HIFU. Optical coherence tomography and general histology were used to evaluate lesion extent. Conduction block was achieved in 1 (17%) of 6 atrial preparations with a single ablation line. Following 10 minutes of rest, 0 (0%) of 6 atrial preparations demonstrated sustained conduction block from a single ablation line. Tissue displacement of 1–3mm was observed during HIFU application due to acoustic radiation force along the lesion line. Additionally, excessive acoustic pressure and high temperature from HIFU generated cavitation causing macroscopic tissue damage. A minimum gap size of 1.5mm was found to conduct electrical activity. Conclusions This study identified three potential mechanisms responsible for the failure of HIFU ablation in cardiac tissues. Both acoustic radiation force and acoustic cavitation in conjunction with inconsistent thermal deposition can increase the risk of lesion discontinuity and result in gap sizes that promote ablation failure. PMID:22322367

  16. Abdominal Adhesions

    MedlinePlus

    ... Abdominal Adhesions 1 Ward BC, Panitch A. Abdominal adhesions: current and novel therapies. Journal of Surgical Research. 2011;165(1):91– ... are abdominal adhesions and intestinal obstructions ... generally do not require treatment. Surgery is the only way to treat abdominal ...

  17. Control of adhesion force between ceria particles and polishing pad in shallow trench isolation chemical mechanical planarization.

    PubMed

    Seo, Jihoon; Moon, Jinok; Bae, Jae-Young; Yoon, Kwang Seob; Sigmund, Wolfgang; Paik, Ungyu

    2014-06-01

    The adhesion force between ceria and polyurethane (PU) pad was controlled to remove the step height from cell region to peripheral region during Shallow Trench Isolation Chemical Mechanical Planarization (STI-CMP) for NAND flash. Picolinic acid was found to be adsorbed on ceria particles at pH 4.5 following a Langmuir isotherm with the maximum adsorbed amount of 0.36 mg/m2. The ceria suspension with full surface coverage of picolinic acid showed a threefold increase in the number of adhered ceria particles on the PU pad over non-coated ceria particles. It was shown that the coverage percent of picolinic acid on ceria corresponds well with the amount percent of adsorbed ceria on PU pad. The change in adsorbed particles was directly reflected in the CMP polishing process where significant improvements were achieved. Particularly, convex areas on the chip experienced higher friction force from the attached abrasives on the PU pad than concave areas. As a result, the convex areas have increased removal rate of step height compared to the ceria suspension without picolinic acid. The changing profiles of convex areas are reported during the step height reduction as a function of polishing time. PMID:24738395

  18. The role of growth temperature in the adhesion and mechanics of pathogenic L. monocytogenes: an AFM study.

    PubMed

    Gordesli, Fatma Pinar; Abu-Lail, Nehal I

    2012-01-17

    The adhesion strengths of pathogenic L. monocytogenes EGDe to a model surface of silicon nitride were quantified using atomic force microscopy (AFM) in water for cells grown under five different temperatures (10, 20, 30, 37, and 40 °C). The temperature range investigated was chosen to bracket the thermal conditions in which L. monocytogenes survive in the environment. Our results indicated that adhesion force and energy quantified were at their maximum when the bacteria were grown at 30 °C. The higher adhesion observed at 30 °C compared to the adhesion quantified for bacterial cells grown at 37, 40, 20, and 10 °C was associated with longer and denser bacterial surface biopolymer brushes as predicted from fitting a model of steric repulsion to the approach distance-force data as well from the results of protein colorimetric assays. Theoretically predicted adhesion energies based on soft-particle DLVO theory agreed well with the adhesion energies computed from AFM force-distance retraction data (r(2) = 0.94); showing a minimum energy barrier to adhesion at 30 °C. PMID:22133148

  19. Unbinding and unfolding of adhesion protein complexes through stretching: interplay between shear and tensile mechanical clamps.

    PubMed

    Różycki, Bartosz; Mioduszewski, Łukasz; Cieplak, Marek

    2014-11-01

    Using coarse-grained molecular dynamics simulations, we analyze mechanically induced dissociation and unfolding of the protein complex CD48-2B4. This heterodimer is an indispensable component of the immunological system: 2B4 is a receptor on natural killer cells whereas CD48 is expressed on surfaces of various immune cells. So far, its mechanostability has not been assessed either experimentally or theoretically. We find that the dissociation processes strongly depend on the direction of pulling and may take place in several pathways. Interestingly, the CD48-2B4 interface can be divided into three distinct patches that act as units when resisting the pulling forces. At experimentally accessible pulling speeds, the characteristic mechanostability forces are in the range between 100 and 200 pN, depending on the pulling direction. These characteristic forces need not be associated with tensile forces involved in the act of separation of the complex because prior shear-involving unraveling within individual proteins may give rise to a higher force peak. PMID:25142868

  20. Mechanism of a cytosolic O-glycosyltransferase essential for the synthesis of a bacterial adhesion protein

    PubMed Central

    Chen, Yu; Seepersaud, Ravin; Bensing, Barbara A.; Sullam, Paul M.; Rapoport, Tom A.

    2016-01-01

    O-glycosylation of Ser and Thr residues is an important process in all organisms, which is only poorly understood. Such modification is required for the export and function of adhesin proteins that mediate the attachment of pathogenic Gram-positive bacteria to host cells. Here, we have analyzed the mechanism by which the cytosolic O-glycosyltransferase GtfA/B of Streptococcus gordonii modifies the Ser/Thr-rich repeats of adhesin. The enzyme is a tetramer containing two molecules each of GtfA and GtfB. The two subunits have the same fold, but only GtfA contains an active site, whereas GtfB provides the primary binding site for adhesin. During a first phase of glycosylation, the conformation of GtfB is restrained by GtfA to bind substrate with unmodified Ser/Thr residues. In a slow second phase, GtfB recognizes residues that are already modified with N-acetylglucosamine, likely by converting into a relaxed conformation in which one interface with GtfA is broken. These results explain how the glycosyltransferase modifies a progressively changing substrate molecule. PMID:26884191

  1. SLOPE FAILURE MECHANISMS IN COHESIVE SOILS: INSIGHTS FROM THEORETICAL AND NUMERICAL ANALYSES OF FIELD AND LABORATORY-TRIGGERED EVENTS

    NASA Astrophysics Data System (ADS)

    Malet, J.; Spickermann, A.; van Asch, T.

    2009-12-01

    A landslide can show a variety of failure modes which depends on the given conditions of the slope such as geometry, material characteristics and presence of discontinuities. Besides the gravity as main loading factor, it is assumed that slope failures are often caused by hydrological processes. The identification and modelling of failure modes and triggering mechanisms are essential requirements in landslide forecasting and in the design of reliable early warning systems. This work is an attempt to get a better understanding of the mode of failure and possible failure mechanisms taking place in cohesive slopes. Theoretical analysis has been carried out on the basis of (1) field observations of two failure events of the clay-rich Super-Sauze mudslide (Southeast France) and (2) small-scale landslides triggered in a flume using clay from Zoelen (Netherlands) and reworked black marls from Super-Sauze. To investigate the failure behaviour numerically a simple analytical model, named 2LM (Landslide Liquefaction Model) (van Asch et al. 2006; van Asch & Malet, in press) is used. The model assumes that liquefaction is related to previous development of slip surfaces, i.e. deformation of the landslide body (sliding blocks, slumps) during motion leading to the generation of excess pore water pressure and thus to fluidization. The model is based on the theory of limiting equilibrium dividing the area above an estimated slip surface into slices of constant width. Immediately after failure, the difference in movement for each slice is calculated assuming a viscous shear band and using the Coulomb-viscous model. The differential movements conduct to differential strains which are transferred to excess pore water pressures. The potential fluidization is then evaluated for each slice in relation to the displacements. Results from an application of this model on the two slump-type failures that occurred in the Super-Sauze mudslide are presented. Then the model is applied to the

  2. Switchable bio-inspired adhesives

    NASA Astrophysics Data System (ADS)

    Kroner, Elmar

    2015-03-01

    Geckos have astonishing climbing abilities. They can adhere to almost any surface and can run on walls and even stick to ceilings. The extraordinary adhesion performance is caused by a combination of a complex surface pattern on their toes and the biomechanics of its movement. These biological dry adhesives have been intensely investigated during recent years because of the unique combination of adhesive properties. They provide high adhesion, allow for easy detachment, can be removed residue-free, and have self-cleaning properties. Many aspects have been successfully mimicked, leading to artificial, bio-inspired, patterned dry adhesives, and were addressed and in some aspects they even outperform the adhesion capabilities of geckos. However, designing artificial patterned adhesion systems with switchable adhesion remains a big challenge; the gecko's adhesion system is based on a complex hierarchical surface structure and on advanced biomechanics, which are both difficult to mimic. In this paper, two approaches are presented to achieve switchable adhesion. The first approach is based on a patterned polydimethylsiloxane (PDMS) polymer, where adhesion can be switched on and off by applying a low and a high compressive preload. The switch in adhesion is caused by a reversible mechanical instability of the adhesive silicone structures. The second approach is based on a composite material consisting of a Nickel- Titanium (NiTi) shape memory alloy and a patterned adhesive PDMS layer. The NiTi alloy is trained to change its surface topography as a function of temperature, which results in a change of the contact area and of alignment of the adhesive pattern towards a substrate, leading to switchable adhesion. These examples show that the unique properties of bio-inspired adhesives can be greatly improved by new concepts such as mechanical instability or by the use of active materials which react to external stimuli.

  3. Systems Biology Reveals Cigarette Smoke-Induced Concentration-Dependent Direct and Indirect Mechanisms That Promote Monocyte-Endothelial Cell Adhesion.

    PubMed

    Poussin, Carine; Laurent, Alexandra; Peitsch, Manuel C; Hoeng, Julia; De Leon, Hector

    2015-10-01

    Cigarette smoke (CS) affects the adhesion of monocytes to endothelial cells, a critical step in atherogenesis. Using an in vitro adhesion assay together with innovative computational systems biology approaches to analyze omics data, our study aimed at investigating CS-induced mechanisms by which monocyte-endothelial cell adhesion is promoted. Primary human coronary artery endothelial cells (HCAECs) were treated for 4 h with (1) conditioned media of human monocytic Mono Mac-6 (MM6) cells preincubated with low or high concentrations of aqueous CS extract (sbPBS) from reference cigarette 3R4F for 2 h (indirect treatment, I), (2) unconditioned media similarly prepared without MM6 cells (direct treatment, D), or (3) freshly generated sbPBS (fresh direct treatment, FD). sbPBS promoted MM6 cells-HCAECs adhesion following I and FD, but not D. In I, the effect was mediated at a low concentration through activation of vascular inflammation processes promoted in HCAECs by a paracrine effect of the soluble mediators secreted by sbPBS-treated MM6 cells. Tumor necrosis factor α (TNFα), a major inducer, was actually shed by unstable CS compound-activated TNFα-converting enzyme. In FD, the effect was triggered at a high concentration that also induced some toxicity. This effect was mediated through an yet unknown mechanism associated with a stress damage response promoted in HCAECs by unstable CS compounds present in freshly generated sbPBS, which had decayed in D unconditioned media. Aqueous CS extract directly and indirectly promotes monocytic cell-endothelial cell adhesion in vitro via distinct concentration-dependent mechanisms. PMID:26141392

  4. Electrochemical layer-by-layer approach to fabricate mechanically stable platinum black microelectrodes using a mussel-inspired polydopamine adhesive

    NASA Astrophysics Data System (ADS)

    Kim, Raeyoung; Nam, Yoonkey

    2015-04-01

    Objective. Platinum black (PtBK) has long been used for microelectrode fabrication owing to its high recording performance of neural signals. The porous structure of PtBK enlarges the surface area and lowers the impedance, which results in background noise reduction. However, the brittleness of PtBK has been a problem in practice. In this work, we report mechanically stable PtBK microelectrodes using a bioinspired adhesive film, polydopamine (pDA), while maintaining the low impedance of PtBK. Approach. The pDA layer was incorporated into the PtBK structure through electrochemical layer-by-layer deposition. Varying the number of layers and the order of materials, multi-layered pDA-PtBK hybrids were fabricated and the electrical properties, both impedance and charge injection limit, were evaluated. Main results. Multilayered pDA-PtBK hybrids had electrical impedances as low as PtBK controls and charge injection limit twice larger than controls. For the 30 min-ultrasonication agitation test, impedance levels rarely changed for some of the pDA-PtBK hybrids indicating that the pDA improved the mechanical property of the PtBK structures. The pDA-PtBK hybrid microelectrodes readily recorded neural signals of cultured hippocampal neurons, where background noise levels and signal-to-noise were 2.43 ∼ 3.23 μVrms and 28.4 ∼ 69.1, respectively. Significance. The developed pDA-PtBK hybrid microelectrodes are expected to be applicable to neural sensors for neural prosthetic studies.

  5. Development of a new code to solve hydro-mechanical coupling, shear failure and tensile failure due to hydraulic fracturing operations.

    NASA Astrophysics Data System (ADS)

    María Gómez Castro, Berta; De Simone, Silvia; Carrera, Jesús

    2016-04-01

    Nowadays, there are still some unsolved relevant questions which must be faced if we want to proceed to the hydraulic fracturing in a safe way. How much will the fracture propagate? This is one of the most important questions that have to be solved in order to avoid the formation of pathways leading to aquifer targets and atmospheric release. Will the fracture failure provoke a microseismic event? Probably this is the biggest fear that people have in fracking. The aim of this work (developed as a part of the EU - FracRisk project) is to understand the hydro-mechanical coupling that controls the shear of existing fractures and their propagation during a hydraulic fracturing operation, in order to identify the key parameters that dominate these processes and answer the mentioned questions. This investigation focuses on the development of a new C++ code which simulates hydro-mechanical coupling, shear movement and propagation of a fracture. The framework employed, called Kratos, uses the Finite Element Method and the fractures are represented with an interface element which is zero thickness. This means that both sides of the element lie together in the initial configuration (it seems a 1D element in a 2D domain, and a 2D element in a 3D domain) and separate as the adjacent matrix elements deform. Since we are working in hard, fragile rocks, we can assume an elastic matrix and impose irreversible displacements in fractures when rock failure occurs. The formulation used to simulate shear and tensile failures is based on the analytical solution proposed by Okada, 1992 and it is part of an iterative process. In conclusion, the objective of this work is to employ the new code developed to analyze the main uncertainties related with the hydro-mechanical behavior of fractures derived from the hydraulic fracturing operations.

  6. Study the mechanical pulmonary changes in patients with congestive heart failure (CHF) by impulse oscillometry

    PubMed Central

    Nourizadeh, Mohammad; Ghelich, Yunose; Amin, Ahmad; Eidani, Esmaeel; Gholampoor, Yousef; Asadmoghadam, Mahsa; Asadinia, Najme

    2013-01-01

    Background Heart failure is one of the most leading cause of death worldwide, but the mechanical characteristics of the pulmonary system in these patients have not been studied enough. The aim of this study was to measure mechanical pulmonary changes in patients with congestive heart failure (CHF) by using impulse oscillometry (IOS), which can obtain data by simpler means and independently from respiratory muscle strength. Materials and methods We assessed 24 CHF patients and 24 controls by spirometry and IOS using the Jaeger IOS system. IOS measures central and peripheral airway resistances (R20, R5) and central and peripheral reactances (X20, X5) using sound waves with different frequencies, which superimposed on the patients respiratory tidal volume and then records reflects. P value < 0.05 was taken to be significant. Results The mean age of patients and controls was 61 ± 10 and 57 ± 7 years, respectively. The mean ejection fraction (EF) was 37 ± 17% for patients and 55 ± 7% for controls. Patients had a lower X5 (−0.20 ± 0.13 vs −0.13 ± 0.07; P < 0.05), forced expiratory volume in 1 second (FEV1; 2.26 ± 0.68 vs 3.09 ± 0.82: P < 0.01 L/min), and forced vital capacity (FVC; 2.55 ± 0.86 vs 3.32 ± 0.87; P < 0.05) compared to the controls. They also had elevated R5: 0.37 ± 0.21 vs 0.27 ± 0.09; P < 0.06). X5 was correlated with spirometric abnormalities (P < 0.05) and was lower in patients than in controls. Conclusion X5 was lower and R5 was higher in patients than in controls. CHF patients can be assessed by IOS more comfortable than by spirometry. IOS can reliably measure peripheral airway resistance in this group of patients. PMID:24027371

  7. Atrial Fibrillation on Intensive Care Unit Admission Independently Increases the Risk of Weaning Failure in Nonheart Failure Mechanically Ventilated Patients in a Medical Intensive Care Unit

    PubMed Central

    Tseng, Yen-Han; Ko, Hsin-Kuo; Tseng, Yen-Chiang; Lin, Yi-Hsuan; Kou, Yu Ru

    2016-01-01

    Abstract Atrial fibrillation (AF) is one of the most frequent arrhythmias in clinical practice. Previous studies have reported the influence of AF on patients with heart failure (HF). The effect of AF on the non-HF critically ill patients in a medical intensive care unit (ICU) remains largely unclear. The study aimed to investigate the impact of AF presenting on ICU admission on the weaning outcome of non-HF mechanically ventilated patients in a medical ICU. A retrospective observational case–control study was conducted over a 1-year period in a medical ICU at Taipei Veterans General Hospital, a tertiary medical center in north Taiwan. Non-HF mechanically ventilated patients who were successful in their spontaneous breathing trial and underwent ventilator discontinuation were enrolled. The primary outcome measure was the ventilator status after the first episode of ventilator discontinuation. A total of 285 non-HF patients enrolled were divided into AF (n = 62) and non-AF (n = 223) groups. Compared with the non-AF patients, the AF patients were significantly associated with old age (P = 0.002), a higher rate of acute respiratory distress syndrome causing respiratory failure (P = 0.015), a higher percentage of sepsis before liberation from mechanical ventilation (MV) (P = 0.004), and a higher serum level of blood urea nitrogen on the day of liberation from MV (P = 0.003). Multivariate logistic regression analysis demonstrated that AF independently increased the risk of weaning failure [adjusted odds ratio (AOR), 3.268; 95% confidence interval (CI), 1.254–8.517; P = 0.015]. Furthermore, the AF patients were found to be independently associated with a high rate of ventilator dependence (log rank test, P = 0.026), prolonged total ventilator use (AOR, 1.979; 95% CI, 1.032–3.794; P = 0.040), increased length of ICU stay (AOR, 2.256; 95% CI, 1.049–4.849; P = 0.037), increased length of hospital stay (AOR, 2.921; 95% CI, 1

  8. Investigating compression failure mechanisms in composite laminates with a transparent fiberglass-epoxy birefringent materials

    NASA Technical Reports Server (NTRS)

    Shuart, M. J.; Williams, J. G.

    1984-01-01

    The response and failure of a + or - 45s class laminate was studied by transparent fiberglass epoxy composite birefringent material. The birefringency property allows the laminate stress distribution to be observed during the test and also after the test if permanent residual stresses occur. The location of initial laminate failure and of the subsequent failure propagation are observed through its transparency characteristics. Experimental results are presented.

  9. The effect of pretreatment on adhesive strength of Cu-plated liquid crystal polymer (LCP)

    NASA Astrophysics Data System (ADS)

    Zhou, Meisheng; Zhang, Wenlong; Ding, Dongyan; Li, Ming

    2012-01-01

    Copper metallization on LCP was carried out by means of electroless plating followed by electroplating and the effect of pretreatment on the adhesive strength of the Cu-plated LCP was investigated in detail. Compared with the other etching agents used here, potassium permanganate was found to be the most effective and the optimum etching time is 20 min. With potassium permanganate as the etching agent, the adhesive strength could reach 12.08 MPa, which is much higher than the reported maximum adhesive strength (lower than 8.0 MPa). XPS spectra of LCP film indicated that hydrophilic groups were introduced into the LCP surface by etching, creating a nanometer-scale surface roughness and improving the wettability between copper and LCP. SEM and AFM observations revealed that the distinctly increased adhesive strength could be attributed to the improved wetting and the mechanical interlocking effect. The failure mode of Cu-plated LCP film was found to be dependent on the etching time. When the etching time was short, the failure mode of Cu-plated LCP film was mainly adhesive. As the etching time increased, cohesive failure gradually occurred, causing an adhesive/cohesive mixed failure mode.

  10. Advanced composites: Design and application. Proceedings of the meeting of the Mechanical Failures Prevention Group

    NASA Technical Reports Server (NTRS)

    Shives, T. R.; Willard, W. A.

    1979-01-01

    The design and application of advanced composites is discussed with emphasis on aerospace, aircraft, automotive, marine, and industrial applications. Failure modes in advanced composites are also discussed.

  11. Determination of adhesion between thermoplastic and liquid silicone rubbers in hard-soft-combinations via mechanical peeling test

    NASA Astrophysics Data System (ADS)

    Kühr, C.; Spörrer, A.; Altstädt, V.

    2014-05-01

    The production of hard-soft-combinations via multi injection molding gained more and more importance in the last years. This is attributed to different factors. One principle reason is that the use of two-component injection molding technique has many advantages such as cancelling subsequent and complex steps and shortening the process chain. Furthermore this technique allows the combination of the properties of the single components like the high stiffness of the hard component and the elastic properties of the soft component. Because of the incompatibility of some polymers the adhesion on the interface has to be determined. Thereby adhesion is not only influenced by the applied polymers, but also by the injection molding parameters and the characteristics of the mold. Besides already known combinations of thermoplastics with thermoplastic elastomers (TPE), there consists the possibility to apply liquid silicone rubber (LSR) as soft component. A thermoplastic/LSR combination gains in importance due to the specific advantages of LSR to TPE. The faintly adhesion between LSR and thermoplastics is currently one of the key challenges when dealing with those combinations. So it is coercively necessary to improve adhesion between the two components by adding an adhesion promoter. To determine the promoters influence, it is necessary to develop a suitable testing method to investigate e.g. the peel resistance. The current German standard "VDI Richtlinie 2019', which is actually only employed for thermoplastic/TPE combinations, can serve as a model to determine the adhesion of thermoplastic/LSR combinations.

  12. Postoperative Peritoneal Adhesions

    PubMed Central

    Ryan, Graeme B.; Grobéty, Jocelyne; Majno, Guido

    1971-01-01

    This paper describes an experimental model of peritoneal adhesions, in the rat, based on two relatively minor accidents that may occur during abdominal surgery in man: drying of the serosa, and bleeding. Drying alone had little effect; drying plus bleeding consistently produced adhesions to the dried area. Fresh blood alone produced adhesions between the three membranous structures [omentum and pelvic fat bodies (PFBs)]. The formation of persistent adhesions required whole blood. Preformed clots above a critical size induced adhesions even without previous serosal injury; they were usually captured by the omentum and PFBs. If all three membranous structures were excised, the clots caused visceral adhesions. The protective role of the omentum, its structure, and the mechanism of omental adhesions, are discussed. These findings are relevant to the pathogenesis of post-operative adhesions in man. ImagesFig 3Fig 4Fig 5Fig 6Fig 7Fig 12Fig 13Fig 1Fig 2Fig 14Fig 15Fig 8Fig 9Fig 10Fig 11 PMID:5315369

  13. Embryo malposition as a potential mechanism for mercury-induced hatching failure in bird eggs

    USGS Publications Warehouse

    Herring, G.; Ackerman, J.T.; Eagles-Smith, C. A.

    2010-01-01

    We examined the prevalence of embryo malpositions and deformities in relation to total mercury (THg) and selenium (Se) concentrations in American avocet (Recurvirostra americana), black-necked stilt (Himantopus mexicanus), and Forster's tern (Sterna forsteri) eggs in San Francisco Bay (CA, USA) during 2005 to 2007. Overall, 11% of embryos were malpositioned in eggs ???18 d of age (n=282) and 2% of embryos were deformed in eggs ???13 d of age (n=470). Considering only those eggs that failed to hatch (n=62), malpositions occurred in 24% of eggs ???18 d of age and deformities occurred in 7% of eggs ???13 d of age. The probability of an embryo being malpositioned increased with egg THg concentrations in Forster's terns, but not in avocets or stilts. The probability of embryo deformity was not related to egg THg concentrations in any species. Using a reduced dataset with both Se and THg concentrations measured in eggs (n=87), we found no interaction between Se and THg on the probability of an embryo being malpositioned or deformed. Results of the present study indicate that embryo malpositions were prevalent in waterbird eggs that failed to hatch and the likelihood of an embryo being malpositioned increased with egg THg concentrations in Forster's terns. We hypothesize that malpositioning of avian embryos may be one reason for mercury-related hatching failure that occurs late in incubation, but further research is needed to elucidate this potential mechanism. ?? 2010 SETAC.

  14. Mechanisms of habitual approach: Failure to suppress irrelevant responses evoked by previously reward-associated stimuli.

    PubMed

    Anderson, Brian A; Folk, Charles L; Garrison, Rebecca; Rogers, Leeland

    2016-06-01

    Reward learning has a powerful influence on the attention system, causing previously reward-associated stimuli to automatically capture attention. Difficulty ignoring stimuli associated with drug reward has been linked to addiction relapse, and the attention system of drug-dependent patients seems especially influenced by reward history. This and other evidence suggests that value-driven attention has consequences for behavior and decision-making, facilitating a bias to approach and consume the previously reward-associated stimulus even when doing so runs counter to current goals and priorities. Yet, a mechanism linking value-driven attention to behavioral responding and a general approach bias is lacking. Here we show that previously reward-associated stimuli escape inhibitory processing in a go/no-go task. Control experiments confirmed that this value-dependent failure of goal-directed inhibition could not be explained by search history or residual motivation, but depended specifically on the learned association between particular stimuli and reward outcome. When a previously high-value stimulus is encountered, the response codes generated by that stimulus are automatically afforded high priority, bypassing goal-directed cognitive processes involved in suppressing task-irrelevant behavior. (PsycINFO Database Record PMID:27054684

  15. Ultimate tensile strength of dentin: Evidence for a damage mechanics approach to dentin failure.

    PubMed

    Staninec, Michal; Marshall, Grayson W; Hilton, Joan F; Pashley, David H; Gansky, Stuart A; Marshall, Sally J; Kinney, John H

    2002-01-01

    Dentin structure and properties are known to vary with orientation and location. The present study explored the variation in the ultimate tensile strength (UTS) of dentin with location in the tooth. Hourglass specimens were prepared from dentin located in the center, under cusps, and in the cervical regions of human molar teeth. These were tested in tension at various distances from the pulp. Median tensile strengths ranged from 44.4 MPa in the inner dentin near the pulp, to 97.8 MPa near the dentino-enamel junction (DEJ). This increase in the median UTS with distance from the pulp to the DEJ was statistically significant (P <.001). Of particular importance was the observation that the UTS measurements followed a Weibull probability distribution, with a Weibull modulus of about 4.5. The Weibull behavior of the UTS data strongly suggests that the large variances in fracture strength data result from a distribution of preexisting defects in the dentin. These findings justify a damage-mechanics approach to studies of dentin failure. PMID:12115767

  16. Embryo malposition as a potential mechanism for mercury-induced hatching failure in bird eggs.

    PubMed

    Herring, Garth; Ackerman, Joshua T; Eagles-Smith, Collin A

    2010-08-01

    We examined the prevalence of embryo malpositions and deformities in relation to total mercury (THg) and selenium (Se) concentrations in American avocet (Recurvirostra americana), black-necked stilt (Himantopus mexicanus), and Forster's tern (Sterna forsteri) eggs in San Francisco Bay (CA, USA) during 2005 to 2007. Overall, 11% of embryos were malpositioned in eggs > or =18 d of age (n = 282) and 2% of embryos were deformed in eggs > or =13 d of age (n = 470). Considering only those eggs that failed to hatch (n = 62), malpositions occurred in 24% of eggs > or =18 d of age and deformities occurred in 7% of eggs > or =13 d of age. The probability of an embryo being malpositioned increased with egg THg concentrations in Forster's terns, but not in avocets or stilts. The probability of embryo deformity was not related to egg THg concentrations in any species. Using a reduced dataset with both Se and THg concentrations measured in eggs (n = 87), we found no interaction between Se and THg on the probability of an embryo being malpositioned or deformed. Results of the present study indicate that embryo malpositions were prevalent in waterbird eggs that failed to hatch and the likelihood of an embryo being malpositioned increased with egg THg concentrations in Forster's terns. We hypothesize that malpositioning of avian embryos may be one reason for mercury-related hatching failure that occurs late in incubation, but further research is needed to elucidate this potential mechanism. PMID:20821633

  17. Mechanistic study of the rubber-brass adhesion interphase

    NASA Astrophysics Data System (ADS)

    Ashirgade, Akshay

    Brass-plated steel tire cords form an essential strengthening component of a radial automobile tire. Adhesion between rubber compound and brass-plated steel tire cord is crucial in governing the overall performance of tires. The rubber-brass interfacial adhesion is influenced by the chemical composition and thickness of the interfacial layer. It has been shown that the interfacial layer consists mainly of sulfides and oxides of copper and zinc. This thesis discusses the effect of changes in the chemical composition and the structure of the interfacial layers due to addition of adhesion promoter resins. Grazing incidence X-Ray Diffraction (GIXRD) experiments were run on sulfidized polished brass coupons previously bonded to six experimental rubber compounds. It was confirmed that heat and humidity conditions lead to physical and chemical changes of the rubber-steel tire cord interfacial layer, closely related to the degree of rubber-brass adhesion. Morphological transformation of the interfacial layer led to loss of adhesion after aging. The adhesion promoter resins inhibit unfavorable morphological changes in the interfacial layer thus stabilizing it during aging and prolonging failure. Tire cord adhesion tests illustrated that the one-component resins improved adhesion after aging using a rubber compound with lower cobalt loading. Based on the acquired diffraction profiles, these resins were also found to impede crystallization of the sulfide layer after aging leading to improved adhesion. Secondary Ion Mass Spectrometry (SIMS) depth profiles, SEM micrographs and AFM images strongly corroborated the findings from GIXRD. FTIR was utilized in a novel way to understand the degradation mechanism due to aging. A model for rubber and interfacial layer degradation is proposed to illustrate the effect of aging and the one-component resins. This interfacial analysis adds valuable new information to our understanding of the complex nature of the rubber-brass bonding

  18. Microscale failure mechanisms leading to internal short circuit in Li-ion batteries under complex loading scenarios

    NASA Astrophysics Data System (ADS)

    Sahraei, Elham; Bosco, Emanuela; Dixon, Brandy; Lai, Benjamin

    2016-07-01

    One of the least understood mechanisms of Li-ion batteries is the development of internal short circuits under mechanical loads. In this study, a micro mechanical model is developed and subjected to various loading scenarios to understand the sequence of failure in the multi-layer, multi-material structure of a Li-ion battery jellyroll. The constitutive response of each component of the electrode stack is obtained by comprehensive experimental tests using uniaxial and biaxial tensile and compressive loads. The homogenized response of the model is recovered through the computational homogenization theory. The model is validated by comparing the results of a macroscale simulation against experimental data. The study focuses next on the development of a failure criterion for the electrode stack based on the microstructural observations. Results show distinct failure mechanisms when the loading is predominantly tensile versus when it is compressive or combined tensile/compressive. A failure locus is plotted from the results of the simulations as a criterion to detect the onset of short circuit under complex multi-axial loading scenarios.

  19. Mechanism of augmented exercise hyperpnea in chronic heart failure and dead space loading

    PubMed Central

    Poon, Chi-Sang; Tin, Chung

    2013-01-01

    Patients with chronic heart failure (CHF) suffer increased alveolar VD/VT (dead-space-to-tidal-volume ratio), yet they demonstrate augmented pulmonary ventilation such that arterial PCO2 (PaCO2) remains remarkably normal from rest to moderate exercise. This paradoxical effect suggests that the control law governing exercise hyperpnea is not merely determined by metabolic CO2 production (V̇CO2) per se but is responsive to an apparent (real-feel) metabolic CO2 load (V˙CO2o) that also incorporates the adverse effect of physiological VD/VT on pulmonary CO2 elimination. By contrast, healthy individuals subjected to dead space loading also experience augmented ventilation at rest and during exercise as with increased alveolar VD/VT in CHF, but the resultant response is hypercapnic instead of eucapnic, as with CO2 breathing. The ventilatory effects of dead space loading are therefore similar to those of increased alveolar VD/VT and CO2 breathing combined. These observations are consistent with the hypothesis that the increased series VD/VT in dead space loading adds to V˙CO2o as with increased alveolar VD/VT in CHF, but this is through rebreathing of CO2 in dead space gas thus creating a virtual (illusory) airway CO2 load within each inspiration, as opposed to a true airway CO2 load during CO2 breathing that clogs the mechanism for CO2 elimination through pulmonary ventilation. Thus, the chemosensing mechanism at the respiratory controller may be responsive to putative drive signals mediated by within-breath PaCO2 oscillations independent of breath-to-breath fluctuations of the mean PaCO2 level. Skeletal muscle afferents feedback, while important for early-phase exercise cardioventilatory dynamics, appears inconsequential for late-phase exercise hyperpnea. PMID:23274121

  20. Probing the Failure Mechanism of SnO2 Nanowires for Sodium-ion Batteries

    SciTech Connect

    Gu, Meng; Kushima, Akihiro; Shao, Yuyan; Zhang, Jiguang; Liu, Jun; Browning, Nigel D.; Li, Ju; Wang, Chong M.

    2013-09-30

    Non-lithium metals such as sodium have attracted wide attention as a potential charge carrying ion for rechargeable batteries, performing the same role as lithium in lithium- ion batteries. As sodium and lithium have the same +1 charge, it is assumed that what has been learnt about the operation of lithium ion batteries can be transferred directly to sodium batteries. Using in-situ TEM, in combination with DFT calculations, we probed the structural and chemical evolution of SnO2 nanowire anodes in Na-ion batteries and compared them quantitatively with results from Li-ion batteries [Science 330 (2010) 1515]. Upon Na insertion into SnO2, a displacement reaction occurs, leading to the formation of amorphous NaxSn nanoparticles covered by crystalline Na2O shell. With further Na insertion, the NaxSn core crystallized into Na15Sn4 (x=3.75). Upon extraction of Na (desodiation), the NaxSn core transforms to Sn nanoparticles. Associated with a volume shrinkage, nanopores appear and metallic Sn particles are confined in hollow shells of Na2O, mimicking a peapod structure. These pores greatly increase electrical impedance, therefore naturally accounting for the poor cyclability of SnO2. DFT calculations indicate that Na+ diffuses 30 times slower than Li+ in SnO2, in agreement with in-situ TEM measurement. Insertion of Na can chemo-mechanically soften the reaction product to greater extent than in lithiation. Therefore, in contrast to the lithiation of SnO2, no dislocation plasticity was seen ahead of the sodiation front. This direct comparison of the results from Na and Li highlights the critical role of ionic size and electronic structure of different ionic species on the charge/discharge rate and failure mechanisms in these batteries.

  1. Mechanism of augmented exercise hyperpnea in chronic heart failure and dead space loading.

    PubMed

    Poon, Chi-Sang; Tin, Chung

    2013-03-01

    Patients with chronic heart failure (CHF) suffer increased alveolar VD/VT (dead-space-to-tidal-volume ratio), yet they demonstrate augmented pulmonary ventilation such that arterial [Formula: see text] ( [Formula: see text] ) remains remarkably normal from rest to moderate exercise. This paradoxical effect suggests that the control law governing exercise hyperpnea is not merely determined by metabolic CO2 production ( [Formula: see text] ) per se but is responsive to an apparent (real-feel) metabolic CO2 load ( [Formula: see text] ) that also incorporates the adverse effect of physiological VD/VT on pulmonary CO2 elimination. By contrast, healthy individuals subjected to dead space loading also experience augmented ventilation at rest and during exercise as with increased alveolar VD/VT in CHF, but the resultant response is hypercapnic instead of eucapnic, as with CO2 breathing. The ventilatory effects of dead space loading are therefore similar to those of increased alveolar VD/VT and CO2 breathing combined. These observations are consistent with the hypothesis that the increased series VD/VT in dead space loading adds to [Formula: see text] as with increased alveolar VD/VT in CHF, but this is through rebreathing of CO2 in dead space gas thus creating a virtual (illusory) airway CO2 load within each inspiration, as opposed to a true airway CO2 load during CO2 breathing that clogs the mechanism for CO2 elimination through pulmonary ventilation. Thus, the chemosensing mechanism at the respiratory controller may be responsive to putative drive signals mediated by within-breath [Formula: see text] oscillations independent of breath-to-breath fluctuations of the mean [Formula: see text] level. Skeletal muscle afferents feedback, while important for early-phase exercise cardioventilatory dynamics, appears inconsequential for late-phase exercise hyperpnea. PMID:23274121

  2. Advances in Quantification of Meniscus Tensile Mechanics Including Nonlinearity, Yield, and Failure.

    PubMed

    Peloquin, John M; Santare, Michael H; Elliott, Dawn M

    2016-02-01

    The meniscus provides crucial knee function and damage to it leads to osteoarthritis of the articular cartilage. Accurate measurement of its mechanical properties is therefore important, but there is uncertainty about how the test procedure affects the results, and some key mechanical properties are reported using ad hoc criteria (modulus) or not reported at all (yield). This study quantifies the meniscus' stress-strain curve in circumferential and radial uniaxial tension. A fiber recruitment model was used to represent the toe region of the stress-strain curve, and new reproducible and objective procedures were implemented for identifying the yield point and measuring the elastic modulus. Patterns of strain heterogeneity were identified using strain field measurements. To resolve uncertainty regarding whether rupture location (i.e., midsubstance rupture versus at-grip rupture) influences the measured mechanical properties, types of rupture were classified in detail and compared. Dogbone (DB)-shaped specimens are often used to promote midsubstance rupture; to determine if this is effective, we compared DB and rectangle (R) specimens in both the radial and circumferential directions. In circumferential testing, we also compared expanded tab (ET) specimens under the hypothesis that this shape would more effectively secure the meniscus' curved fibers and thus produce a stiffer response. The fiber recruitment model produced excellent fits to the data. Full fiber recruitment occurred approximately at the yield point, strongly supporting the model's physical interpretation. The strain fields, especially shear and transverse strain, were extremely heterogeneous. The shear strain field was arranged in pronounced bands of alternating positive and negative strain in a pattern similar to the fascicle structure. The site and extent of failure showed great variation, but did not affect the measured mechanical properties. In circumferential tension, ET specimens underwent

  3. A Study of the Failure Mechanism of Planar Non-Persistent Open Joints Using PFC2D

    NASA Astrophysics Data System (ADS)

    Ghazvinian, A.; Sarfarazi, V.; Schubert, W.; Blumel, M.

    2012-09-01

    Particle flow code 2D (PFC2D) was adopted to simulate the shear behavior of rocklike material samples containing planar non-persistent joints. Direct shear loading was conducted to investigate the effect of joint separation on the failure behavior of rock bridges. Initially calibration of PFC was undertaken with respect to the data obtained from experimental laboratory tests to ensure the conformity of the simulated numerical models response. Furthermore, validation of the simulated models were cross checked with the results of direct shear tests performed on non-persistent jointed physical models. Through numerical direct shear tests, the failure process was visually observed, and the failure patterns were found reasonably similar to the experimentally observed trends. The discrete element simulations demonstrated that the macro-scale shear zone resulted from the progressive failure of the tension-induced micro-cracks. The failure pattern was mostly influenced by joint separation, while the shear strength was linked to the failure pattern and failure mechanism. Furthermore, it was observed that the failure zone is relatively narrow and has a symmetrical pattern when rock bridges occupy a low percentage of the total shear surface. This may be due to the high stress interactions between the subsequent joints separated by a rock bridge. In contrast, when rock bridges are occupying sufficient area prohibiting the stress interactions to occur then the rupture of surface is more complex and turns into a shear zone. This zone was observed to be relatively thick with an unsymmetrical pattern. The shear strength of rock bridges is reduced by increasing the joint length as a result of increasing both the stress concentration at tip of the joints and the stress interaction between the joints.

  4. Mechanical properties of a waterborne pressure-sensitive adhesive with a percolating poly(acrylic acid)-based diblock copolymer network: effect of pH.

    PubMed

    Gurney, Robert S; Morse, Andrew; Siband, Elodie; Dupin, Damien; Armes, Steven P; Keddie, Joseph L

    2015-06-15

    Copolymerizing an acrylic acid comonomer is often beneficial for the adhesive properties of