Sample records for tbc failure mechanisms

  1. Investigation by 3D FE simulations of delamination crack initiation in TBC caused by alumina growth

    Microsoft Academic Search

    M. Jinnestrand; S. Sjöström

    2001-01-01

    In gas turbines, thermal barrier coatings (TBCs) applied by air plasma spraying are widely used to reduce the temperature in hot components. The TBC allows higher gas temperature and\\/or reduces the need for internal cooling in the hot components, thus increasing the efficiency of the gas turbine. Spallation is a common failure mechanism of TBC and occurs after a critical

  2. Failure mechanisms in MEMS.

    SciTech Connect

    Walraven, Jeremy Allen

    2003-07-01

    MEMS components by their very nature have different and unique failure mechanisms than their macroscopic counterparts. This paper discusses failure mechanisms observed in various MEMS components and technologies. MEMS devices fabricated using bulk and surface micromachining process technologies are emphasized. MEMS devices offer uniqueness in their application, fabrication, and functionality. Their uniqueness creates various failure mechanisms not typically found in their bulk or IC counterparts. In ICs, electrical precautions are taken to mitigate failure. In MEMS, both electrical and mechanical precautions must be enacted to reduce the risk of failure and increased reliability. Unlike ICs, many MEMS components are designed to interact with their environment, making the fabrication, testing, and packaging processes critical for the success of the device.

  3. Oxidation-induced failure of EB-PVD thermal barrier coatings

    Microsoft Academic Search

    V. K Tolpygo; D. R Clarke; K. S Murphy

    2001-01-01

    Oxidation-induced failure of EB-PVD thermal barrier coatings (TBC) deposited on a single-crystal superalloy with a platinum aluminide bond coat has been studied in order to determine the specific mechanisms leading to TBC spallation. Cyclic oxidation tests performed at 1150°C show that failure of the TBC occurs when the alumina scale, growing at the bond coat–TBC interface, attains its critical thickness.

  4. Fracture Mechanics and Failure Analysis

    E-print Network

    New South Wales, University of

    Analysis (Weeks 7-12) Prof Alan Crosky 10 General practice in failure analysis 7 11 Ductile and brittle Final exam Course Outline Fracture mechanics, remnant life assessment, general practice in failure

  5. Mechanisms of thermal barrier coating degradation and failure

    NASA Technical Reports Server (NTRS)

    Demasi, J. T.; Sheffler, K. D.

    1985-01-01

    The objectives and initial results of a Thermal Barrier Coating (TBC) Life Prediction Model Development Program are described. The goals of this program are to: identify and understand TBC failure modes; generate quantitative TBC life data; and develop and verify a TBC life prediction model. The coating being studied is a two layer thermal barrier system incorporating a nominal ten mil outer layer of seven percent yttria partially stabilized zirconia plasma deposited over an inner layer of highly oxidation resistant low pressure plasma sprayed NiCrAlY bond coating. This coating currently is in flight service on turbine vane platforms in the JT-9D and PW2037 engines and is bill-of- material on turbine vane airfoils in the advanced PW4000 and IAE V2500 engines. Effort currently is in progress on the first task, which involves the identification and understanding of TBC failures. Five modes of coating damage were considered: thermomechanical ceramic failure; oxidative bond coat failure; hot corrosion; foreign object damage (FOD); and erosion.

  6. FAILURE MECHANISMS OF HENS' EGGS

    Microsoft Academic Search

    N. MacLeod?; M. M. Bain; S. E. Solomon; J. W. Hancock?

    The mechanics and mechanisms of failure of hens eggs have been examined experimentally under contact loading conditions. Eggs of known provenance were tested in compression between stiff platens, and the deformation modelled computationally as a Hertzian contact problem between a thin walled shell and a rigid plate. The associated contact damage was determined by scanning electron microscopy and by optical

  7. Ubiquitination and degradation of the hominoid-specific oncoprotein TBC1D3 is regulated by protein palmitoylation

    SciTech Connect

    Kong, Chen; Lange, Jeffrey J.; Samovski, Dmitri [Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 (United States)] [Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 (United States); Su, Xiong [Department of Internal Medicine, Center for Human Nutrition Washington University School of Medicine, St. Louis, MO 63110 (United States)] [Department of Internal Medicine, Center for Human Nutrition Washington University School of Medicine, St. Louis, MO 63110 (United States); Liu, Jialiu [Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 (United States)] [Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 (United States); Sundaresan, Sinju [Department of Internal Medicine, Center for Human Nutrition Washington University School of Medicine, St. Louis, MO 63110 (United States)] [Department of Internal Medicine, Center for Human Nutrition Washington University School of Medicine, St. Louis, MO 63110 (United States); Stahl, Philip D., E-mail: pstahl@wustl.edu [Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110 (United States)

    2013-05-03

    Highlights: •Hominoid-specific oncogene TBC1D3 is targeted to plasma membrane by palmitoylation. •TBC1D3 is palmitoylated on two cysteine residues: 318 and 325. •TBC1D3 palmitoylation governs growth factors-induced TBC1D3 degradation. •Post-translational modifications may regulate oncogenic properties of TBC1D3. -- Abstract: Expression of the hominoid-specific oncoprotein TBC1D3 promotes enhanced cell growth and proliferation by increased activation of signal transduction through several growth factors. Recently we documented the role of CUL7 E3 ligase in growth factors-induced ubiquitination and degradation of TBC1D3. Here we expanded our study to discover additional molecular mechanisms that control TBC1D3 protein turnover. We report that TBC1D3 is palmitoylated on two cysteine residues: 318 and 325. The expression of double palmitoylation mutant TBC1D3:C318/325S resulted in protein mislocalization and enhanced growth factors-induced TBC1D3 degradation. Moreover, ubiquitination of TBC1D3 via CUL7 E3 ligase complex was increased by mutating the palmitoylation sites, suggesting that depalmitoylation of TBC1D3 makes the protein more available for ubiquitination and degradation. The results reported here provide novel insights into the molecular mechanisms that govern TBC1D3 protein degradation. Dysregulation of these mechanisms in vivo could potentially result in aberrant TBC1D3 expression and promote oncogenesis.

  8. The lustering of TBC-2

    NASA Astrophysics Data System (ADS)

    Diver, Richard B.; Jones, Scott; Robb, Stacy; Mahoney, A. Rod

    1995-05-01

    Two test bed concentrators (TBC's) were designed to provide high-performance test beds for advanced solar receivers and converters. However, the second-surface silvered-glass mirror facets on the TBC's, which were originally manufactured by the Jet Propulsion Laboratory, have experienced severe silver corrosion. To restore reflectance, TBC-2 was refurbished with a lustering technique developed at Sandia National Laboratories. In the lustering technique, second-surface silvered thin-glass mirrors were applied over the corroded facets, thereby increasing the dish reflectivity and raising the available power of TBC-2 from approximately 70 to 78 kW(sub t). Degradation of the original optical accuracy of the TBC facets was determined to be minimal. Lustering was chosen over facet replacement because of the lower cost, the anticipated improvement in corrosion resistance, and the shorter project duration. This report includes background information, details of the lustering process, and test results from TBC-2 characterization, both before and after lustering.

  9. Failure of mechanical seals in centrifugal pumps

    Microsoft Academic Search

    Stan Shiels

    2002-01-01

    This fourth paper in the troubleshooting series deals with mechanical seals. Often a seal failure is diagnosed through visual inspection of the failed seal's components; this may yield the condition that existed in the seal cavity prior to, or at the time of, failure. The events that led to this condition are usually linked to the real cause of failure,

  10. Selected failure mechanisms of modern power modules

    Microsoft Academic Search

    Mauro Ciappa

    2002-01-01

    This paper reviews the main failure mechanisms occurring in modern power modules paying special attention to insulated gate bipolar transistor devices for high-power applications. This compendium provides the main failure modes, the physical or chemical processes that lead to the failure, and reports some major technological counter- measures, which are used for realizing the very stringent reliability requirements imposed in

  11. Compression-Failure Mechanisms in Composite Laminates

    NASA Technical Reports Server (NTRS)

    Shuart, M. J.; Williams, J. G.; Cooper, P. A.

    1986-01-01

    Failure mechanisms observed using transparent fiberglass/epoxy birefringent materials. Technique based on use of transparent fiberglass/epoxy birefringent material. Transparency allows visual observation of location of initial laminate failure and of subsequent failure propagation; birefringence allows laminate stress distribution to be observed during test and also after test if permanent residual stresses occur. Nondestructive technique developed to observe failure as it develops and as propagates within laminate.

  12. Oxidation-induced failure of thermal barrier coatings. Annual report, 1 October 1997--31 October 1998

    Microsoft Academic Search

    1998-01-01

    On prolonged high-temperature exposure in air, thermal barrier coatings (TBCs) on bond-coated superalloys fail by spalling. The author has focused on identifying the underlying mechanisms of failure and sought to establish whether it is a direct consequence of the failure of the underlying thermally grown oxide. He has discovered a new TBC failure mode, one in which failure is associated

  13. Degradation of TBC Systems in Environments Relevant to Advanced Gas Turbines for IGCC Systems

    SciTech Connect

    Gleeson, Brian [Univ. of Pittsburgh, PA (United States)

    2014-09-30

    Air plasma sprayed (APS) thermal barrier coatings (TBCs) are used to provide thermal insulation for the hottest components in gas turbines. Zirconia stabilized with 7wt% yttria (7YSZ) is the most common ceramic top coat used for turbine blades. The 7YSZ coating can be degraded from the buildup of fly-ash deposits created in the power-generation process. Fly ash from an integrated gasification combined cycle (IGCC) system can result from coal-based syngas. TBCs are also exposed to harsh gas environments containing CO2, SO2, and steam. Degradation from the combined effects of fly ash and harsh gas atmospheres has the potential to severely limit TBC lifetimes. The main objective of this study was to use lab-scale testing to systematically elucidate the interplay between prototypical deposit chemistries (i.e., ash and its constituents, K2SO4, and FeS) and environmental oxidants (i.e., O2, H2O and CO2) on the degradation behavior of advanced TBC systems. Several mechanisms of early TBC failure were identified, as were the specific fly-ash constituents responsible for degradation. The reactivity of MCrAlY bondcoats used in TBC systems was also investigated. The specific roles of oxide and sulfate components were assessed, together with the complex interplay between gas composition, deposit chemistry and alloy reactivity. Bondcoat composition design strategies to mitigate corrosion were established, particularly with regard to controlling phase constitution and the amount of reactive elements the bondcoat contains in order to achieve optimal corrosion resistance.

  14. 77 FR 34457 - Pipeline Safety: Mechanical Fitting Failure Reports

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-06-11

    ...PHMSA-2012-0079] Pipeline Safety: Mechanical Fitting Failure Reports AGENCY: Pipeline...pipeline facilities when completing the Mechanical Fitting Failure Report Form, PHMSA...facility to file a written report for any mechanical fitting failure that results in a...

  15. Sulfur and Moisture Effects on Alumina Scale and TBC Spallation

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    2007-01-01

    It has been well established that a few ppmw sulfur impurity may segregate to the interface of thermally grown alumina scales and the underlying substrate, resulting in bond degradation and premature spallation. This has been shown for NiAl and NiCrAl-based alloys, bare single crystal superalloys, or coated superalloys. The role of reactive elements (especially Y) has been to getter the sulfur in the bulk and preclude interfacial segregation. Pt additions are also very beneficial, however a similar thermodynamic explanation does not apply. The purpose of the present discussion is to highlight some observations of these effects on Rene'142, Rene'N5, PWA1480, and PWA1484. For PWA1480, we have mapped cyclic oxidation and spallation in terms of potential sulfur interfacial layers and found that a cumulative amount of about one monolayer is sufficient to degrade long term adhesion. Depending on substrate thickness, optimum performance occurs if sulfur is reduced below about 0.2-0.5 ppmw. This is accomplished in the laboratory by hydrogen annealing or commercially by melt-fluxing. Excellent 1150 C cyclic oxidation is thus demonstrated for desulfurized Rene'142, Rene'N5, and PWA1484. Alternatively, a series of N5 alloys provided by GE-AE have shown that as little as 15 ppmw of Y dopant was effective in providing remarkable scale adhesion. In support of a Y-S gettering mechanism, hydrogen annealing was unable to desulfurize these alloys from their initial level of 5 ppmw S. This impurity and critical doping level corresponds closely to YS or Y2S3 stoichiometry. In many cases, Y-doped alloys or alloys with marginal sulfur levels exhibit an oxidative sensitivity to the ambient humidity called Moisture-Induced Delayed Spallation (MIDS). After substantial scale growth, coupled with damage from repeated cycling, cold samples may spall after a period of time, breathing on them, or immersing them in water. While stress corrosion arguments may apply, we propose that the underlying cause is related to a hydrogen embrittlement reaction: Al alloy + 3 H2O = Al(OH)3 + 3H(+) + 3e(-). This mechanism is derived from an analogous moisture-induced hydrogen embrittlement mechanism originally shown for Ni3Al and FeAl intermetallics. Consequently, a cathodic hydrogen charging technique was used to demonstrate that electrolytic de-scaling occurs for these otherwise adherent alumina scales formed on Y-doped Rene'N5, in support of hydrogen effects. Finally, some TBC observations are discussed in light of all of the above. Plasma sprayed 8YSZ coatings, produced on PWA1484 without a bond coat, were found to survive more than 1000 1-hr cycles at 1100 C when desulfurized to below 0.1 ppmw. At higher sulfur (1.2 ppmw) levels, moisture sensitivity and delayed TBC failure, referred to as Desk Top Spallation, occurred at just 200 hr. Despite a large degree of scatter, a factor of 5 in life improvement is indicated for desulfurized samples in cyclic furnace tests, confirming the beneficial effect of low sulfur alloys on model TBC systems. (DTS and moisture effects are also observed on commercially applied PVD 7YSZ coatings on Rene'N5+Y with Pt-aluminide bond coats). These types of catastrophic failure were subverted on the model system by segmenting the substrate into a network of 0.010 high ribs, spaced in. apart, prior to plasma spraying. No failures occurred after 1000 cycles at 1150 C or after 2000 cycles at 1100 C, even after water immersion. The benefit is described in terms of elasticity models and a critical buckling stress.

  16. Ubiquitination and degradation of the hominoid-specific oncoprotein TBC1D3 is regulated by protein palmitoylation

    PubMed Central

    Kong, Chen; Lange, Jeffrey J.; Samovski, Dmitri; Su, Xiong; Liu, Jialiu; Sundaresan, Sinju; Stahl, Philip D.

    2013-01-01

    Expression of the hominoid-specific oncoprotein TBC1D3 promotes enhanced cell growth and proliferation by increased activation of signal transduction through several growth factors. Recently we documented the role of CUL7 E3 ligase in growth factors-induced ubiquitination and degradation of TBC1D3. Here we expanded our study to discover additional molecular mechanisms that control TBC1D3 protein turnover. We report that TBC1D3 is palmitoylated on two cysteine residues: 318 and 325. The expression of double palmitoylation mutant TBC1D3:C318/325S resulted in protein mislocalization and enhanced growth factors-induced TBC1D3 degradation. Moreover, ubiquitination of TBC1D3 via CUL7 E3 ligase complex was increased by mutating the palmitoylation sites, suggesting that depalmitoylation of TBC1D3 makes the protein more available for ubiquitination and degradation. The results reported here provide novel insights into the molecular mechanisms that govern TBC1D3 protein degradation. Dysregulation of these mechanisms in-vivo could potentially result in aberrant TBC1D3 expression and promote oncogenesis. PMID:23578663

  17. Failure mechanisms in wire ropes

    Microsoft Academic Search

    C. R. Chaplin

    1995-01-01

    The inevitable attrition of wire rope in service is discussed with an overview of the consequences in terms of inspection and replacement criteria. Details are presented of specific degradation mechanisms observed in three different applications: a mine hoist rope operating on a drum winder, a mooring rope for an offshore structure and a spin-resistant single-fall offshore crane rope. In each

  18. Enigmatic Moisture Effects on Al2O3 Scale and TBC Adhesion

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    2008-01-01

    Alumina scale adhesion to high temperature alloys is known to be affected primarily by sulfur segregation and reactive element additions. However adherent scales can become partially compromised by excessive strain energy and cyclic cracking. With time, exposure of such scales to moisture can lead to spontaneous interfacial decohesion, occurring while the samples are maintained at ambient conditions. Examples of this Moisture-Induced Delayed Spallation (MIDS) are presented for NiCrAl and single crystal superalloys, becoming more severe with sulfur level and cyclic exposure conditions. Similarly, delayed failure or Desk Top Spallation (DTS) results are reviewed for TBC s, culminating in the water drop failure test. Both phenomena are discussed in terms of moisture effects on bulk alumina and bulk aluminides. A mechanism is proposed based on hydrogen embrittlement and is supported by a cathodic hydrogen charging experiment. Hydroxylation of aluminum from the alloy interface appears to be the relevant basic reaction.

  19. FAILURE MECHANISMS OF SOLID PROPELLANT ROCKET NOZZLES

    Microsoft Academic Search

    Y. Baskin; T. A. Greening; M. J. Kemp

    1960-01-01

    Twenty-five refractory materials were evaluated as nozzle inserts in ; rocket motors using high-energy solid propellants. The motors, operated at ; various combinations of chamber pressure and burning time, yielded exhaust ; temperatures of about 4750 deg F. Although the degree of nozzle erosion varied ; considerably, all materials were attacked. Failure mechanisms, presented for the ; betterperforming materials, were

  20. Drop impact test - mechanics & physics of failure

    Microsoft Academic Search

    E. H. Wong; K. M. Lim; N. Lee; S. Seah; C. Hoe; J. Wang

    2002-01-01

    This paper deals with the mechanics and physics of board-level drop test with the intention of providing the fundamental understanding required to design and analyse the results of a drop test. Three finite element analyses were performed to understand the physics of failure in board-level drop impact: (i) velocity impact of a PCB - modeled as a beam; (ii) velocity

  1. 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.

  2. Analysis of possible failure mechanisms and root failure causes in power plant components using neural networks and structural failure database

    Microsoft Academic Search

    S. Yoshimura; A. S. Jovanovic

    1996-01-01

    This paper describes analyses of cast studies on failure of structural components in power plants using hierarchical (multilayer) neural networks. Using selected test data about case studies stored in the structural failure database of a knowledge-based system, the network is trained: either to predict possible failure mechanisms like creep, overheating (OH), or overstressing (OS)-induced failure (network of Type A), or

  3. The mechanics and mechanisms of failure of hens’ eggs

    Microsoft Academic Search

    Niall Macleod; Maureen M. Bain; John W. Hancock

    2006-01-01

    The mechanics and mechanisms of failure of hens’ eggs have been examined experimentally under contact loading conditions relevant\\u000a to industrial conditions by testing eggs of known provenance in compression between stiff platens. Deformation was modelled\\u000a computationally as a Hertzian contact problem between a thin walled elastic shell and a rigid plate. Contact damage was determined\\u000a by scanning electron microscopy and

  4. Failure mechanisms of legacy aircraft wiring and interconnects

    Microsoft Academic Search

    Brian G. Moffat; Eitan Abraham; Marc Desmulliez; Dennis Koltsov; Andrew Richardson

    2008-01-01

    This paper presents a comprehensive list of the causes and modes of failure and ageing in legacy aircraft wiring and interconnects. Taxonomies of the electrical, mechanical, chemical and thermal stresses that contribute to the various stages of ageing and\\/or failure are presented. A failure modes effects and analysis (FMEA) is conducted to categorize the most serious failures. The order of

  5. Mechanical failure of a lightweight polypropylene mesh.

    PubMed

    Lintin, L A D; Kingsnorth, A N

    2014-02-01

    We report the case of a 41-year-old male who underwent repair of a recurrent midline abdominal incisional hernia with components separation. The hernia defect was repaired with a 30 cm × 30 cm underlay biological (Strattice) mesh used to partially bridge a small residual gap between the rectus muscles and reinforced with a 30 cm × 30 cm lightweight polypropylene onlay mesh (BARD™ soft mesh). The patient later developed a large persistent seroma that was excised 18 weeks later. On exploration of the previous hernia repair, it was noted that the onlay polypropylene mesh had fractured leaving a 3 cm by 2 cm defect, but the underlying biological mesh was intact preventing a recurrence of the hernia (see Fig. 1). The fractured mesh was repaired with an additional onlay 10 cm × 10 cm polypropylene mesh, the seroma was de-roofed, and the patient was later discharged. This case highlights the early mechanical failure of a lightweight polypropylene mesh; the precise mechanism of failure in this case is unclear and, however, may be related to high intra-abdominal pressures postoperatively. Fig. 1 Photograph showing onlay polypropylene (BARD™ soft mesh) mesh superficial to a biological (Strattice) sublay mesh bridging the recti (on the left and right wound edges). Arrow indicates the 2 cm by 3 cm fracture. PMID:22824989

  6. Moisture-Induced TBC Spallation on Turbine Blade Samples

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    2011-01-01

    Delayed failure of TBCs is a widely observed laboratory phenomenon, although many of the early observations went unreported. "The weekend effect" or "DeskTop Spallation" (DTS) is characterized by initial survival of a TBC after accelerated laboratory thermal cycling, then failure by exposure to ambient humidity or water. Once initiated, failure can occur quite dramatically in less than a second. To this end, the water drop test and digital video recordings have become useful techniques in studies at NASA (Smialek, Zhu, Cuy), DECHMA (Rudolphi, Renusch, Schuetze), and CNRS Toulouse/SNECMA (Deneux, Cadoret, Hervier, Monceau). In the present study the results for a commercial turbine blade, with a standard EB-PVD 7YSZ TBC top coat and Pt-aluminide diffusion bond monitored by weight change and visual appearance. Failures were distributed widely over a 5-100 hr time range, depending on temperature. At some opportune times, failure was captured by video recording, documenting the appearance and speed of the moisture-induced spallation process. Failure interfaces exhibited alumina scale grains, decorated with Ta-rich oxide particles, and alumina inclusions as islands and streamers. The phenomenon is thus rooted in moisture-induced delayed spallation (MIDS) of the alumina scale formed on the bond coat. In that regard, many studies show the susceptibility of alumina scales to moisture, as long as high strain energy and a partially exposed interface exist. The latter conditions result from severe cyclic oxidation conditions, which produce a highly stressed and partially damaged scale. In one model, it has been proposed that moisture reacts with aluminum in the bond coat to release hydrogen atoms that 'embrittle' the interface. A negative synergistic effect with interfacial sulfur is also invoked.

  7. Moisture-Induced TBC Spallation on Turbine Blade Samples

    NASA Technical Reports Server (NTRS)

    Smialek, James

    2011-01-01

    Delayed failure of TBCs is a widely observed laboratory phenomenon, although many of the early observations went unreported. The weekend effect or DeskTop Spallation (DTS) is characterized by initial survival of a TBC after accelerated laboratory thermal cycling, then failure by exposure to ambient humidity or water. Once initiated, failure can occur quite dramatically in less than a second. To this end, the water drop test and digital video recordings have become useful techniques in studies at NASA (Smialek, Zhu, Cuy), DECHMA (Rudolphi, Renusch, Schuetze), and CNRS Toulouse/SNECMA (Deneux, Cadoret, Hervier, Monceau). In the present study the results for a commercial turbine blade, with a standard EB-PVD 7YSZ TBC top coat and Pt-aluminide diffusion bond coat are reported. Cut sections were intermittently oxidized at 1100, 1150, and 1200 C and monitored by weight change and visual appearance. Failures were distributed widely over a 5-100 hr time range, depending on temperature. At some opportune times, failure was captured by video recording, documenting the appearance and speed of the moisture-induced spallation process. Failure interfaces exhibited alumina scale grains, decorated with Ta-rich oxide particles, and alumina inclusions as islands and streamers. The phenomenon is thus rooted in moisture-induced delayed spallation (MIDS) of the alumina scale formed on the bond coat. In that regard, many studies show the susceptibility of alumina scales to moisture, as long as high strain energy and a partially exposed interface exist. The latter conditions result from severe cyclic oxidation conditions, which produce a highly stressed and partially damaged scale. In one model, it has been proposed that moisture reacts with aluminum in the bond coat to release hydrogen atoms that embrittle the interface. A negative synergistic effect with interfacial sulfur is also invoked.

  8. PVD TBC experience on GE aircraft engines

    NASA Astrophysics Data System (ADS)

    Maricocchi, A.; Bartz, A.; Wortman, D.

    1997-06-01

    The higher performance levels of modern gas turbine engines present significant challenges in the reli-ability of materials in the turbine. The increased engine temperatures required to achieve the higher per-formance levels reduce the strength of the materials used in the turbine sections of the engine. Various forms of thermal barrier coatings have been used for many years to increase the reliability of gas turbine engine components. Recent experience with the physical vapor deposition process using ceramic material has demonstrated success in extending the service life of turbine blades and nozzles. Engine test results of turbine components with a 125 ?m (0.005 in.) PVD TBC have demonstrated component operating tem-peratures of 56 to 83 °C (100 to 150 °F) lower than non-PVD TBC components. Engine testing has also revealed that TBCs are susceptible to high angle particle impact damage. Sand particles and other engine debris impact the TBC surface at the leading edge of airfoils and fracture the PVD columns. As the impacting continues, the TBC erodes in local areas. Analysis of the eroded areas has shown a slight increase in temperature over a fully coated area ; however, a significant temperature reduc-tion was realized over an airfoil without TBC.

  9. Heart failure and mechanical circulatory support.

    PubMed

    Esper, Stephen Andrew; Subramaniam, Kathirvel

    2012-06-01

    Cardiovascular disease (CVD) is defined as one of the following: hypertension, congestive heart failure (HF), stroke, coronary heart disease and congenital heart defects. CVD is the main cause of the disease burden (illness and death) in Europe (23% of all the disease burdens) and the second main cause of the disease burden in those European Union (EU) countries with very low child and adult mortality (17%).(1) Heart disease is a common health problem worldwide. According to the most recent Heart Disease and Stroke Statistics-2011 update,(2) greater than 82 000 000 adults living in the United States of America (USA) have one or more types of CVD. Many resources have been invested in attempting to understand and curtail the progression of congestive HF. This article attempts to address the growing concern over HF by looking at the epidemiology, pathophysiology and available therapies as anaesthesiologists encounter these patients more often nowadays in the operating room and intensive care units. Mechanical circulatory assistance and heart transplantation are two established treatment methods for end-stage HF. In this review, we also address the indications and contraindications for mechanical circulatory assistance, types and spectrum of available ventricular assist devices, efficacy, safety and cost analysis of circulatory support therapy. PMID:22910083

  10. MICRO-MECHANISMS OF COMPRESSION FAILURE Sia Nemat Nasser

    E-print Network

    Nemat-Nasser, Sia

    modes ranging from brittle to plastic failure depending on the deformation conditions. The under pinning confining pressures and at moderate deformation rates, brittle failure involves initiation of micro micro-mechanisms of dynamic brittle failure in compression are examined over a broad range

  11. Indentation Analysis of a Multi-Layered Hollow Cylinder for the Measurement of Interfacial Toughness in TBC Systems

    Microsoft Academic Search

    Q. Ma; J. L. Beuth; G. H. Meier; F. S. Pettit

    2008-01-01

    Summary This paper addresses the mechanics of indentation-induced delamination of a coating on a multi-layered hollow cylinder, for application to toughness testing of thermal barrier coating (TBC) systems. An electron-beam physical vapor depo- sition (EB-PVD) TBC system has been analyzed through a contact finite element model usingastandardconical indenterimpressed verticallyon thetop ofthecylin- der. Two cylinder sizes used in thermal-mechanical fatigue tests

  12. On the failure mechanism of metallized polypropylene pulse capacitors

    Microsoft Academic Search

    Lin Fuchang; Dai Xin; Li Jin; Yao Zonggan; Wang Nanyan

    2000-01-01

    Metallized pulse capacitors has gained wider and wider usage because of their unique “self-healing” character. Their failure mechanism has many differences from film\\/foil capacitors. Experiments were carried out on a number of metallized polypropylene pulse capacitors in order to understand their failure mechanism better. Using some model Metallized Polypropylene capacitors manufactured under different production parameters, it is observed that the

  13. Failure mechanisms in high performance materials

    SciTech Connect

    Early, J.G.; Shives, T.R.; Smith, J.H.

    1985-01-01

    This book presents papers on the identification and interpretation of degradation and failure modes in high-performance materials. The papers address a variety of materials, including structural ceramics, high-technology alloys, metal matrix composites, and polymer matrix composites.

  14. Metallurgical failure analysis of cold cracking in a structural steel weldment: Revisiting a classic failure mechanism

    Microsoft Academic Search

    M. E. Stevenson; S. L. Lowrie; R. D. Bowman; B. A. Bennett

    2002-01-01

    Cold cracking of structural steel weldments is a well-characterized, well-documented, and well-understood failure mechanism.\\u000a Extensive effort has been put forth to recognize the welding and materials selection parameters that are conducive to cold\\u000a cracking; however, these engineering efforts have not fully eliminated the occurrence of such failures. This article describes\\u000a cold cracking failure specifically related to the construction industry. This

  15. Corrosion of NiCoCrAlY Coatings and TBC Systems Subjected to Water Vapor and Sodium Sulfate

    NASA Astrophysics Data System (ADS)

    Eriksson, Robert; Yuan, Kang; Li, Xin-Hai; Lin Peng, Ru

    2015-05-01

    Thermal barrier coating (TBC) systems are commonly used in gas turbines for protection against high-temperature degradation. Penetration of the ceramic top coat by corrosive species may cause corrosion damage on the underlying NiCoCrAlY bond coat and cause failure of the TBC system. In the current study, four oxidation/corrosion conditions were tried: (i) lab air, (ii) water vapor, (iii) sodium sulfate deposited on the specimens, and (iv) water vapor + sodium sulfate. The test was done at 750 °C in a cyclic test rig with 48 h cycles. The corrosion damage was studied on NiCoCrAlY-coated specimens, thin APS TBC specimens, and thick APS TBC specimens. Water vapor was found to have very minor influence on the oxidation, while sodium sulfate increased the TGO thickness both for NiCoCrAlY specimens and TBC-coated specimens; the influence of the TBC thickness was found to be very small. Sodium sulfate promoted thicker TGO; more Cr-rich TGO; the formation of Y oxides, and internally, Y sulfides; pore formation in the coating as well as in the substrate; and the formation of a Cr-depleted zone in the substrate.

  16. 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.

  17. Some common corrosion mechanisms leading to boiler tube failure

    SciTech Connect

    Bain, D.I.; Haff, J.D.; Kelly, J.A.

    1996-10-01

    Corrosion mechanisms remain a major cause of tube failures in operating boiler units. Conditions resulting in caustic corrosion, acid corrosion, chelant corrosion and sulfate induced high temperature external corrosion of boiler tribes are reviewed. Three case histories are presented illustrating the impact of the conditions discussed on boiler tube failures.

  18. Failure mechanisms in composite panels subjected to underwater impulsive loads

    E-print Network

    Espinosa, Horacio D.

    Failure mechanisms in composite panels subjected to underwater impulsive loads Fe´lix Latourte a,1 Accepted 15 April 2011 Available online 21 April 2011 Keywords: Composite materials Fluid­structure interaction Dynamic failure Delamination Blast a b s t r a c t This work examines the performance of composite

  19. Some corrosion failure mechanisms of AMTEC cells

    Microsoft Academic Search

    Donald L. Alger

    1997-01-01

    Simulated models of four existing types of alkali metal thermoelectric converter (AMTEC) devices were chosen for this study. Each cell model was analyzed to determine whether metal is dissolved by sodium from cell materials and is deposited in regions that can degrade performance of the cell. Results of the study show that each cell model has at least one failure

  20. FAILURE MECHANISMS OF COMPOSITE SANDWICH STRUCTURES

    Microsoft Academic Search

    E. E Gdoutos

    Sandwich construction is of particular interest and widely used, because the concept is very suitable and amenable to the development of lightweight structures with high in-plane and flexural stiffness. Sandwich panels consist typically of two thin face sheets (or facings, or skins) and a lightweight thicker core. They display various failure modes under general bending, shear and in-plane loading. The

  1. 76 FR 5494 - Pipeline Safety: Mechanical Fitting Failure Reporting Requirements

    Federal Register 2010, 2011, 2012, 2013, 2014

    2011-02-01

    ...DEPARTMENT OF TRANSPORTATION Pipeline and Hazardous Materials Safety Administration...Amdt. 192-116] RIN 2137-AE60 Pipeline Safety: Mechanical Fitting Failure Reporting Requirements AGENCY: Pipeline and Hazardous Materials Safety...

  2. Prevent boiler tube failures -- Part 2: Waterside mechanisms

    Microsoft Academic Search

    Colannino

    1993-01-01

    Boiler tubes can fail due to problems on either the fire-side or the water-side of the tube. Part 1 of this article discussed fire-side failure mechanisms and measures for preventing failures. Here the author focuses on the tubes' water-side. The term water-side mechanisms'' refers to damage on the water side of the boiler tube (as opposed to the fire side).

  3. 49 CFR 191.12 - Distribution Systems: Mechanical Fitting Failure Reports

    Code of Federal Regulations, 2014 CFR

    2014-10-01

    ...2014-10-01 false Distribution Systems: Mechanical Fitting Failure Reports 191.12 Section...REPORTS § 191.12 Distribution Systems: Mechanical Fitting Failure Reports Each mechanical fitting failure, as required by §...

  4. 49 CFR 191.12 - Distribution Systems: Mechanical Fitting Failure Reports

    Code of Federal Regulations, 2012 CFR

    2012-10-01

    ...2012-10-01 false Distribution Systems: Mechanical Fitting Failure Reports 191.12 Section...REPORTS § 191.12 Distribution Systems: Mechanical Fitting Failure Reports Each mechanical fitting failure, as required by §...

  5. 49 CFR 191.12 - Distribution Systems: Mechanical Fitting Failure Reports

    Code of Federal Regulations, 2013 CFR

    2013-10-01

    ...2013-10-01 false Distribution Systems: Mechanical Fitting Failure Reports 191.12 Section...REPORTS § 191.12 Distribution Systems: Mechanical Fitting Failure Reports Each mechanical fitting failure, as required by §...

  6. 49 CFR 191.12 - Distribution Systems: Mechanical Fitting Failure Reports

    Code of Federal Regulations, 2011 CFR

    2011-10-01

    ...2011-10-01 false Distribution Systems: Mechanical Fitting Failure Reports 191.12 Section...REPORTS § 191.12 Distribution Systems: Mechanical Fitting Failure Reports Each mechanical fitting failure, as required by §...

  7. Some corrosion failure mechanisms of AMTEC cells

    SciTech Connect

    Alger, D.L. [Alger Stirling Co., Seville, OH (United States)

    1997-12-31

    Simulated models of four existing types of alkali metal thermoelectric converter (AMTEC) devices were chosen for this study. Each cell model was analyzed to determine whether metal is dissolved by sodium from cell materials and is deposited in regions that can degrade performance of the cell. Results of the study show that each cell model has at least one failure mode caused by dissolution of metal from the AMTEC surfaces.

  8. An autonomous distributed VQC method based on Q-TBC

    Microsoft Academic Search

    Masahiko Tanimoto; Yoshio Izui; Katsuhiko Matsuno; Naoto Fukuta; Kenichi Deno; T. Sasaki

    2000-01-01

    The authors propose a new method, the Q-TBC (Q tie-line bias control) method, for voltage and reactive power (Q) control (VQC). It is developed in the same way as TBC (tie-line bias control) to realize an autonomous and distributed balance of the supply and demand of reactive power in each divided power grid (block). The Q-TBC system in each block

  9. IMPERMEABLE THIN Al2O3 OVERLAY FOR TBC PROTECTION FROM SULFATE AND VANADATE ATTACK IN GAS TURBINES

    SciTech Connect

    Scott X. Mao

    2002-06-30

    In order to improve the hot corrosion resistance of conventional YSZ TBC system (YSZ/CoNiCrAlY/Inconel 601), an overlay Al{sub 2}O{sub 3} was sprayed on the surface of TBC samples by high velocity oxy-fuel (HVOF) spray techniques. The TBC preparation in Japan was based on our technical requirement by plasma spray. Bond coat CoNiCrAlY and the YSZ was produced by low-pressure plasma spray and air plasma spray respectively. Hot corrosion tests were carried out on the TBC with and without Al{sub 2}O{sub 3} coating in molten salts mixtures (Na{sub 2}SO{sub 4} + 5%V{sub 2}O{sub 5}) at 950 C for 10h. The microstructures of TBC and overlay before and after exposure were examined by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX) and X-ray diffraction (XRD). It has been found that TBC reacted with V{sub 2}O{sub 5} to form YVO{sub 4}. A substantial amount of M-phase was formed due to the leaching of Y{sub 2}O{sub 3} from YSZ. Al{sub 2}O{sub 3} overlay coating sprayed by HVOF was dense, continues and adherent to the TBC even after exposure to the molten salts. As a result, overlay Al{sub 2}O{sub 3} coating can prevent the YSZ from the attack by molten salts containing vanadium and arrest the penetration of salts into the YSZ along porous and cracks in the YSZ TBC. Accordingly, the amount of M-phase formed in TBC with Al{sub 2}O{sub 3} overlay was significantly lower than that in conventional YSZ TBC system. In the next period, the hot corrosion tests of TBC with EB-PVD Al{sub 2}O{sub 3} coating under Na{sub 2}SO{sub 4} + 5%V{sub 2}O{sub 5} will be again performed at 950 C. However before hot corrosion tests, the post-annealing will be carried at 1273K for 1h in order to transform the as-sputtered {gamma}-Al{sub 2}O{sub 3} overlay to crystalline {alpha}-Al{sub 2}O{sub 3} overlay. In addition, the effect of coating thickness on corrosion resistance and the mechanisms of cracking of EB-PVD alumina layer during hot corrosion will be also investigated.

  10. Renal dysfunction in acute heart failure: epidemiology, mechanisms and assessment

    Microsoft Academic Search

    Valentina Carubelli; Marco Metra; Carlo Lombardi; Luca Bettari; Silvia Bugatti; Valentina Lazzarini; Livio Dei Cas

    Renal dysfunction is often present and\\/or worsens in patients with heart failure and this is associated with increased costs\\u000a of care, complications and mortality. The cardiorenal syndrome can be defined as the presence or development of renal dysfunction\\u000a in patients with heart failure. Its mechanisms are likely related to low cardiac output, increased venous congestion and renal\\u000a venous pressure, neurohormonal

  11. Failure mechanism study of GaAs technology

    NASA Astrophysics Data System (ADS)

    Bowman, L. S.; Tarn, W.

    1981-07-01

    In this report we have discussed the characterization of the power FETs procured for this program and failure analysis of low noise devices, including wire bonding failures and environmental stress test failures. A method of etching gold while leaving the underlying refractory metals relatively unaffected was explained. An analysis of the Type A-6 low noise FET was given, in which a failure mode was discussed that involved possible channel doping compensation. Results were then presented on device failures from high and medium temperature stress tests on low noise FETs. A number of medium power devices were received from RADC for analysis. These were packaged FETs that had been subjected to various stresses at Texas Instruments on a RADC/TI reliability contract. Typically, the devices had failed during deliberate stressing to the maximum electrical limits or in temperature stress tests. Failure mechanism studies of two different ohmic contact metallizations showed that both fabrication procedures produced reliable contacts. Constant elevated temperature tests of gold-based gate diode FETs from two different manufacturers showed that one device type was considerably less prone to gate diode failure than the other, indicating the necessity of additional work on the gold gate versus aluminum gate reliability question. Failures were investigated that involve problems associated with gold contact pads overlaying aluminum gate pads with a refractory metal interface. Finally, temperature-accelerated studies of the resistance of aluminum gates were carried out.

  12. ESD Triggered Solar Array Failure Mechanism

    Microsoft Academic Search

    Ira Katz; V. A. Davis; David B. Snyder; Ernest A. Robertson

    1998-01-01

    A mechanism is presented which explains recent anomalies on geosynchronous (GEO) communications satellites. The symptoms of the anomalies are low impedance shorts between high and low voltage cells on a solar array string, and shorts between high voltage cells and the array ground. All of the anomalies occurred when other, instrumented, satellites measured a charging environment. In this paper we

  13. Applying the TBC Method in Introductory Programming Courses

    Microsoft Academic Search

    M. Rahman

    2007-01-01

    In our research, we have introduced and implemented a new software development method, Testing Before Coding (TBC), to bring in the benefits of using software development lifecycle in computer programming and improved students program quality. TBC follows the basic concept of Agile Method (such as Test-driven Development, TDD) and makes students a \\

  14. Applying the TBC method in introductory programming courses

    Microsoft Academic Search

    S. M. Rahman

    2007-01-01

    In our research, we have introduced and implemented a new software development method, testing before coding (TBC), to bring in the benefits of using software development lifecycle in computer programming and improved students program quality. TBC follows the basic concept of agile method (such as test-driven development, TDD) and makes students a \\

  15. Prevent boiler tube failures -- Part 2: Water-side mechanisms

    SciTech Connect

    Colannino, J. (Colannino Consultants, Oceanside, CA (United States))

    1993-11-01

    Boiler tubes can fail due to problems on either the fire-side or the water-side of the tube. Part 1 of this article discussed fire-side failure mechanisms and measures for preventing failures. Here the author focuses on the tubes' water-side. The term water-side mechanisms'' refers to damage on the water side of the boiler tube (as opposed to the fire side). However, the water itself is often not the culprit. Water-side corrosion mechanisms may be classified into two major categories: physical and chemical. Physical mechanisms include steam blanketing and overheating. Chemical mechanisms include: deposition; caustic, acidic, and chelant corrosion; oxidation; and hydrogen embrittlement.

  16. 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.

  17. Mechanical and electrical failures and reliability of Micro Scanning Mirrors

    Microsoft Academic Search

    E. Gaumont; Alexander Wolter; Harald Schenk; G. Georgelin; M. Schmoger

    2002-01-01

    We present results of failure and reliability investigations on silicon Micro Scanning Mirrors. The electrical insulation resistance, mechanical shock resistance and long-run stability were characterized. By design optimization including a combination of filled and open insulation trenches we achieve an average insulation resistance of more than 10 G? at 20 V. The experimental data from devices with an eigenfrequency between

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

    Microsoft Academic Search

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

    1997-01-01

    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

  19. Popcorning: a failure mechanism in plastic-encapsulated microcircuits

    Microsoft Academic Search

    Anthony A. Gallo; Ramesh Munamarty

    1995-01-01

    Popcorning is a failure mechanism in plastic-encapsulated microcircuits. It occurs when the inherently hygroscopic encapsulant is rapidly exposed to high temperatures during reflow solder assembly of the component to a printed circuit card. At these temperatures the moisture absorbed by the molding compound vaporizes and rapidly expands leading to the development of high stresses. When these stresses exceed both the

  20. Reliability and failure mechanism of isotropically conductive adhesives joints

    Microsoft Academic Search

    Li Li; J. E. Morris; Johan Liu; Zonghe Lai; L. Ljungkrona; Changhai Li

    1995-01-01

    Three recently developed silver filled isotropic electrically conductive adhesives from different manufacturers were selected for study. This work was focused on the use of isotropically conductive adhesives for joining surface mount devices (SMD) on printed circuit boards for potential solder replacement. The purpose of this study is to evaluate the reliability and failure mechanism of the adhesive joints in humid

  1. Migratory gold resistive shorts - Chemical aspects of a failure mechanism

    NASA Technical Reports Server (NTRS)

    Grunthaner, F. J.; Griswold, T. W.; Clendening, P. J.

    1975-01-01

    Integrated-circuit devices using the Ti/W/Au metal system are subject to failure mechanisms based on electrolytic corrosion. The migratory gold resistive short (MGRS) failure mode is one example of this mechanism and results in the formation of filamentary or dendritic deposits of gold between adjacent stripes on the IC chip. This reaction requires the presence of a sufficient amount of water, a bias voltage between adjacent stripes, and the activation of the cathodic (-) stripe. Gold ions are transported from anode to cathode through a film of moisture adsorbed on the surface of the chip; halide ions are probably involved in the transfer. Their presence is verified experimentally by X-ray photoelectron spectroscopy. Some of the chemical and electrostatic factors involved in the MGRS mechanism are discussed in this paper, including the questions of a threshold level of moisture and contamination.

  2. 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.

  3. Influence of EB-PVD TBC Microstructure on Thermal Barrier Coating System Performance Under Cyclic Conditions

    SciTech Connect

    Leyens, C.; Pint, B.A.; Schulz, U.; Wright, I.G.

    1999-04-12

    The lifetimes of electron beam physical vapor deposited (EB-PVD) thermal barrier coating systems (TBCs) with three different microstructures of the Y2O3-stabilized ZrO, YSZ) ceramic top layer were investigated in lh thermal cycles at 1100 and 1150°C in flowing oxygen. Single crystal alloys CMSX-4 and Rene N5 that had been coated with an EB-PVD NiCoCrAlY bond coat were chosen as substrate materials. At 1150°C all samples failed after 80-100, lh cycles, predominantly at the bond coat/alumina interface after cooling down from test temperature. The alumina scale remained adherent to the YSZ after spallation. Despite the different YSZ microstructures no clear tendency regarding differences in spallation behavior were observed at 1150°C. At 1100°C the minimum lifetime was 750 , lh cycles for CMSX-4, whereas the first Rene N5 specimen failed after 1750, lh cycles. The longest TBC lifetime on CMSX-4 substrates was 1250, lh cycles, whereas the respective Rene N5 specimens have not yet failed after 2300, lh cycles. The failure mode at 1100°C was identical to that at 115O?C, i.e. the TBC spalled off the surface exposing bare metal after cooling. Even though not all specimens have failed to date, the available results at 1100°C suggested that both, the substrate alloy chemistry and the YSZ microstructure significantly affect the spallation resistance of the TBC.

  4. Effect of Increased Water Vapor Levels on TBC Lifetime

    SciTech Connect

    Pint, Bruce A [ORNL; Garner, George Walter [ORNL; Lowe, Tracie M [ORNL; Haynes, James A [ORNL; Zhang, Ying [Tennessee Technological University

    2011-01-01

    To investigate the effect of increased water vapor levels on thermal barrier coating (TBC) lifetime, furnace cycle tests were performed at 1150 C in air with 10 vol.% water vapor (similar to natural gas combustion) and 90 vol.%. Either Pt diffusion or Pt-modified aluminide bond coatings were applied to specimens from the same batch of a commercial second-generation single-crystal superalloy and commercial vapor-deposited yttria-stabilized zirconia (YSZ) top coats were applied. Three coatings of each type were furnace cycled to failure to compare the average lifetimes obtained in dry O{sub 2}, using the same superalloy batch and coating types. Average lifetimes with Pt diffusion coatings were unaffected by the addition of water vapor. In contrast, the average lifetime of Pt-modified aluminide coatings was reduced by more than 50% with 10% water vapor but only slightly reduced by 90% water vapor. Based on roughness measurements from similar specimens without a YSZ coating, the addition of 10% water vapor increased the rate of coating roughening more than 90% water vapor. Qualitatively, the amount of {beta}-phase depletion in the coatings exposed in 10% water vapor did not appear to be accelerated.

  5. 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.

  6. IMPERMEABLE THIN AL2O3 OVERLAY FOR TBC PROTECTION FROM SULFATE AND VANADATE ATTACK IN GAS TURBINES

    SciTech Connect

    Scott X. Mao

    2002-01-31

    In order to improve the hot corrosion resistance of conventional YSZ TBC system, the overlay of Al{sub 2}O{sub 3} coating was deposited on the TBC by EB-PVD techniques. Hot corrosion tests were carried out on the TBC with and without Al{sub 2}O{sub 3} coating in molten salts mixtures (Na{sub 2}SO{sub 4} + 5%V{sub 2}O{sub 5}) at 950 C for 10h. The microstructures of TBC and overlay before and after exposure were examined by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX) and X-ray diffraction (XRD). It has been found that TBC will react with V{sub 2}O{sub 5} to form YVO{sub 4}. A substantial amount of M-phase was formed due to the leaching of Y{sub 2}O{sub 3} from YSZ. Al{sub 2}O{sub 3} overlay coating deposited by EB-PVD was dense, continues and adherent to the TBC. As a result, overlay Al{sub 2}O{sub 3} coating can prevent the YSZ from the attack by molten salts containing vanadium and arrest the penetration of salts into the YSZ along porous and cracks in the YSZ TBC, although there were some cracks in overlay Al{sub 2}O{sub 3} coating and at the interface between alumina and zirconia formed during hot corrosion tests due to the presence of tensile stress in the alumina coating. In the next reporting period, we will study the mechanisms of cracking of the overlay Al{sub 2}O{sub 3} layer and finish the hot corrosion tests of TBC with Al{sub 2}O{sub 3} coating deposited by high velocity oxy-fuel (HVOF) technique. The hot corrosion test of TBC with EB-PVD deposited Al{sub 2}O{sub 3} coating will be again performed. However before hot corrosion tests, a post-annealing will be carried out in vacuum (residual pressure 10{sup -3} Pa) at 1273K for 1h in order to transform the as-sputtered Al{sub 2}O{sub 3} overlay to crystalline {alpha}-Al{sub 2}O{sub 3} overlay.

  7. 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.

  8. 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.

  9. 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.

  10. Effect of higher water vapor content on TBC performance

    SciTech Connect

    Pint, Bruce A [ORNL; Haynes, James A [ORNL

    2012-01-01

    Coal gasification, or IGCC (integrated gasification combined cycle), is one pathway toward cleaner use of coal for power generation with lower emissions. However, when coal-derived synthesis gas (i.e., syngas) is burned in turbines designed for natural gas, turbine manufacturers recommend 'derating,' or lowering the maximum temperature, which lowers the efficiency of the turbine, making electricity from IGCC more expensive. One possible reason for the derating is the higher water vapor contents in the exhaust gas. Water vapor has a detrimental effect on many oxidation-resistant high-temperature materials. In a turbine hot section, Ni-base superalloys are coated with a thermal barrier coating (TBC) allowing the gas temperature to be higher than the superalloy solidus temperature. TBCs have a low thermal conductivity ceramic top coating (typically Y{sub 2}O{sub 3}-stabilized ZrO{sub 2}, or YSZ) and an oxidation-resistant metallic bond coating. For land-based gas turbines, the industry standard is air plasma sprayed (APS) YSZ and high velocity oxygen fuel (HVOF) sprayed NiCoCrAlY bond coatings. To investigate the role of higher water vapor content on TBC performance and possible mitigation strategies, furnace cycling experiments were conducted in dry O{sub 2} and air with 10% (typical with natural gas or jet fuel) or 50 vol% water vapor. Cycle frequency and temperature were accelerated to one hour at 1100 C (with 10 minute cooling to {approx}30 C between each thermal cycle) to induce early failures in coatings that are expected to operate for several years with a metal temperature of {approx}900 C. Coupons (16 mm diameter x 2 mm thick) of commercial second-generation single crystal superalloy CMSX4 were HVOF coated on both sides with {approx}125 {micro}m of Ni-22wt%Co-17Cr-12Al either with 0.7Y or 0.7Y-0.3Hf-0.4Si. One side was then coated with 190-240 {micro}m of APS YSZ. Coatings were cycled until the YSZ top coating spalled. Figure 2 shows the results of the initial phase of experiments. Compared to dry O{sub 2}, the addition of 10% water vapor decreased the lifetime of MCrAlY by {approx}30% for the conventional CMSX4 substrates. Higher average lifetimes were observed with Hf in the bond coating, but a similar decrease in lifetime was observed when water vapor was added. The addition of Y and La to the superalloy substrate did not change the YSZ lifetime with 10% water vapor. However, increasing water vapor content from 10 to 50% did not further decrease the lifetime of either bond coating with the doped superalloy substrate. Thus, these results suggest that higher water vapor contents cannot explain the derating of syngas-fired turbines, and other factors such as sulfur and ash from imperfect syngas cleanup (or upset conditions) need to be explored. Researchers continue to study effects of water vapor on thermally grown alumina scale adhesion and growth rate, and are looking for bond coating compositions more resistant to oxidation in the presence of water vapor.

  11. 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.

  12. IMPERMEABLE THIN AL2O3 OVERLAY FOR TBC PROTECTION FROM SULFATE AND VANADATE ATTACK IN GAS TURBINES

    SciTech Connect

    Scott X. Mao

    2002-01-31

    The project started on September 1, 2001. During last 4 months, one post-doctor has been hired for this project. We have received TBC samples (YSZ/CoNiCrAlY/ Inconel 601) from Tohoku University, Japan, while processing of the TBC samples was delayed in GE Corp. Research and Development. The TBC preparation in Japan was based on our technical requirement by plasma spray. Bond coat CoNiCrAlY and the YSZ was produced by low-pressure plasma spray and air plasma spray respectively. The morphology of the surface and the microstructure of cross-section of the sample was observed and analyzed by SEM and EDX. XRD was also used to detect the phases in the YSZ. Currently we are processing the overlay Al{sub 2}O{sub 3} on the TBC samples by EB-PVD and high velocity oxy-fuel (HVOF) spray techniques in collaboration with Penn State University and State University of New York at Stony Brook. We will finish comparing the hot corrosion behavior of the Al{sub 2}O{sub 3}/YSZ/CoNiCrAlY/superalloy system with the YSZ/CoNiCrAlY/superalloy system. The mechanism of hot corrosion will be investigated. The processing-structure-properties relationship of the overlays will be determined.

  13. Mechanical Measurement of Gels: Pre-stress and Failure

    NASA Astrophysics Data System (ADS)

    Fakhouri, Sami; Hutchens, Shelby; Crosby, Alfred

    2013-03-01

    A recently developed technique, Cavitation Rheology (CR), provides a means of measuring the mechanical properties of soft materials on length scales from ~ 0 . 1 ?m to mm at a specific location. CR involves inflation of a small bubble at the tip of a syringe needle which has been inserted into a material. After insertion, the pressure in the syringe is raised until a critical point where the material fails, resulting in rapid inflation of a cavity at the syringe tip. The critical pressure for failure can provide information about the materials properties of the system such as the elastic modulus, E, the critical strain energy release rate, Gc, and the surface energy, ?. Modulus measurements by CR have been made in many synthetic gels and biological tissues with similar accuracy to shear rheology. However, as CR requires insertion of a needle into the subject material, measurements are inherently made in a pre-stressed state. In this work, we have examined the pre-stress associated with needle insertion and the influence of this stress on failure in a synthetic gel of PMMA-PnBA-PMMA triblock copolymer in 2-ethylhexanol.

  14. On study of nonclassical problems of fracture and failure mechanics and related mechanisms

    Microsoft Academic Search

    Alexander N. Guz

    2009-01-01

    Nonclassical problems of fracture and failure mechanics that have been analyzed by the author and his collaborators at the\\u000a S. P. Timoshenko Institute of Mechanics (Kiev, National Academy of Sciences of Ukraine) during the past forty years are considered\\u000a in brief. The results of the analysis are presented in a form that would be quite informative for the majority of

  15. THEORETICAL & APPLIED MECHANICS LETTERS 1, 041002 (2011) Competing failure mechanisms of thin metal films on polymer substrates

    E-print Network

    Li, Teng

    2011-01-01

    failure mechanisms: metal film necking and grain boundary cracking. The quantitative results suggest potential applications including paper-like dis- plays, printable thin-film solar cells, and skin-like smartTHEORETICAL & APPLIED MECHANICS LETTERS 1, 041002 (2011) Competing failure mechanisms of thin metal

  16. A mixture Weibull proportional hazard model for mechanical system failure prediction utilising lifetime and monitoring data

    NASA Astrophysics Data System (ADS)

    Zhang, Qing; Hua, Cheng; Xu, Guanghua

    2014-02-01

    As mechanical systems increase in complexity, it is becoming more and more common to observe multiple failure modes. The system failure can be regarded as the result of interaction and competition between different failure modes. It is therefore necessary to combine multiple failure modes when analysing the failure of an overall system. In this paper, a mixture Weibull proportional hazard model (MWPHM) is proposed to predict the failure of a mechanical system with multiple failure modes. The mixed model parameters are estimated by combining historical lifetime and monitoring data of all failure modes. In addition, the system failure probability density is obtained by proportionally mixing the failure probability density of multiple failure modes. Monitoring data are input into the MWPHM to estimate the system reliability and predict the system failure time. A simulated sample set is used to verify the ability of the MWPHM to model multiple failure modes. Finally, the MWPHM and the traditional Weibull proportional hazard model (WPHM) are applied to a high-pressure water descaling pump, which has two failure modes: sealing ring wear and thrust bearing damage. Results show that the MWPHM is greatly superior in system failure prediction to the WPHM.

  17. E50K-OPTN-Induced Retinal Cell Death Involves the Rab GTPase-Activating Protein, TBC1D17 Mediated Block in Autophagy

    PubMed Central

    Chalasani, Madhavi Latha Somaraju; Kumari, Asha; Radha, Vegesna; Swarup, Ghanshyam

    2014-01-01

    The protein optineurin coded by OPTN gene is involved in several functions including regulation of endocytic trafficking, autophagy and signal transduction. Certain missense mutations in the gene OPTN cause normal tension glaucoma. A glaucoma-causing mutant of optineurin, E50K, induces death selectively in retinal cells. This mutant induces defective endocytic recycling of transferrin receptor by causing inactivation of Rab8 mediated by the GTPase-activating protein, TBC1D17. Here, we have explored the mechanism of E50K-induced cell death. E50K-OPTN-induced cell death was inhibited by co-expression of a catalytically inactive mutant of TBC1D17 and also by shRNA mediated knockdown of TBC1D17. Endogenous TBC1D17 colocalized with E50K-OPTN in vesicular structures. Co-expression of transferrin receptor partially protected against E50K-induced cell death. Overexpression of the E50K-OPTN but not WT-OPTN inhibited autophagy flux. Treatment of cells with rapamycin, an inducer of autophagy, reduced E50K-OPTN-induced cell death. An LC3-binding-defective mutant of E50K-OPTN showed reduced cell death, further suggesting the involvement of autophagy. TBC1D17 localized to autophagosomes and inhibited autophagy flux dependent on its catalytic activity. Knockdown of TBC1D17 rescued cells from E50K-mediated inhibition of autophagy flux. Overall, our results suggest that E50K mutant induced death of retinal cells involves impaired autophagy as well as impaired transferrin receptor function. TBC1D17, a GTPase-activating protein for Rab GTPases, plays a crucial role in E50K-induced impaired autophagy and cell death. PMID:24752605

  18. Brain edema in acute liver failure: mechanisms and concepts.

    PubMed

    Rama Rao, Kakulavarapu V; Jayakumar, Arumugam R; Norenberg, Michael D

    2014-12-01

    Brain edema and associated increase in intracranial pressure continue to be lethal complications of acute liver failure (ALF). Abundant evidence suggests that the edema in ALF is largely cytotoxic brought about by swelling of astrocytes. Elevated blood and brain ammonia levels have been strongly implicated in the development of the brain edema. Additionally, inflammation and sepsis have been shown to contribute to the astrocyte swelling/brain edema in the setting of ALF. We posit that ammonia initiates a number of signaling events, including oxidative/nitrative stress (ONS), the mitochondrial permeability transition (mPT), activation of the transcription factor (NF-?B) and signaling kinases, all of which have been shown to contribute to the mechanism of astrocyte swelling. All of these factors also impact ion-transporters, including Na(+), K(+), Cl(-) cotransporter and the sulfonylurea receptor 1, as well as the water channel protein aquaporin-4 resulting in a perturbation of cellular ion and water homeostasis, ultimately resulting in astrocyte swelling/brain edema. All of these events are also potentiated by inflammation. This article reviews contemporary knowledge regarding mechanisms of astrocyte swelling/brain edema formation which hopefully will facilitate the identification of therapeutic targets capable of mitigating the brain edema associated with ALF. PMID:24567229

  19. Redox-sensitive mechanisms underlying vascular dysfunction in heart failure.

    PubMed

    Konradi, J; Mollenhauer, M; Baldus, S; Klinke, A

    2015-06-01

    Regardless of the progress in therapeutic drugs and devices to treat heart failure (HF) during the last few years, the clinical outcome of this disease remains deleterious. Impaired left ventricular function leads to neurohumoral activation, altered local shear forces, and hypoxia, which might give rise to inflammatory processes within the vasculature. Among those, the imbalance of the redox equilibrium toward increased concentrations of reactive oxygen species (ROS) is particularly important, as it affects the integrity of vascular function. Apart from injured or dysfunctional cardiomyocytes, vascular dysfunction has been demonstrated to play a crucial role in the development and progression of HF, which makes it an interesting target for new HF therapies. The mechanisms that initiate vascular dysfunction in HF pathogenesis and the processes leading to oxidative stress are not yet fully elucidated. However, oxidative stress promotes a variety of redox-sensitive mechanisms contributing to vascular dysfunction in HF. Here, we will summarize the sources of ROS in the vasculature, elucidate the impact of oxidative stress on functional and structural vascular remodeling, and consider the link to vascular dysfunction. Furthermore, we will point out the importance of vascular dysfunction in HF and discuss therapeutic options. PMID:25788126

  20. Failure Mechanisms in Pipelines Bridging a Void J. G. Zornberg1

    E-print Network

    Zornberg, Jorge G.

    diameter. Failure patterns are observed along longitudinal and transverse cross-sections of the pipe. The mode of failure of flexible pipes involved buckling in the shoulder of the pipe and a reversal presents preliminary results of an experimental study aimed at identifying the failure mechanisms of pipes

  1. Analysis of failure of axle housing of crane truck with fracture mechanics

    Microsoft Academic Search

    Steven W. Bradley; Walter L. Bradley

    1995-01-01

    The failure of an axle housing in a crane truck has been successfully analyzed with the aid of fracture mechanics. The cause of failure was the field addition of stop blocks welded to the axle housing. The time from crack penetration of the axle housing to final failure was too short for the presence of such a crack to have

  2. IMPERMEABLE THIN AL2O3 OVERLAY FOR TBC PROTECTION FROM SULFATE AND VANADATE ATTACK IN GAS TURBINES

    SciTech Connect

    Scott X. Mao

    2002-08-31

    In order to improve the hot corrosion resistance of conventional YSZ TBC system, a dense and continues overlay of Al{sub 2}O{sub 3} coating of about 25 {micro}m thick was deposited on the surface of TBC by EB-PVD and high velocity oxy-fuel (HVOF) spray techniques. Hot corrosion tests were carried out on the TBC with and without Al{sub 2}O{sub 3} coating in molten salts mixtures (Na{sub 2}SO{sub 4} + 5% V{sub 2}O5) at 950 C for 10h. The microstructures of TBC and overlay before and after exposure were examined by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX), X-ray diffraction (XRD) and secondary ion mass spectrometry (SIMS). It has been found that TBC will react with V{sub 2}O{sub 5} to form YVO{sub 4}. A substantial amount of M-phase of ZrO{sub 2} was formed due to the leaching of Y{sub 2}O{sub 3} from YSZ. During hot corrosion test, there were no significant interactions between overlay Al{sub 2}O{sub 3} coating and molten salts. After exposure, the alumina coating, especially produced by HVOF, was still very dense and cover the surface of YSZ, although they had been translated to {alpha}-Al{sub 2}O{sub 3} from original {gamma}-Al{sub 2}O{sub 3}. As a result, Al{sub 2}O{sub 3} overlay coating decreased the penetration of salts into the YSZ and prevented the YSZ from the attack by molten salts containing vanadium. Accordingly, only a few M-phase was formed in YSZ TBC, compared with TBC without overlay coating. The penetration of salts into alumina coating was thought to be through microcracks formed in overlay Al{sub 2}O{sub 3} coating and at the interface between alumina and zirconia due to the presence of tensile stress in the alumina coating. In the next year, we will study the mechanisms of cracking of the overlay Al{sub 2}O{sub 3} layer. The hot corrosion test of TBC with EB-PVD deposited Al{sub 2}O{sub 3} coating will be again performed. However before hot corrosion tests, the post-annealing will be carried out in vacuum (residual pressure 10{sup -3} Pa) at 1273K for 1h in order to transform the as-sputtered Al{sub 2}O{sub 3} overlay to crystalline {alpha}-Al{sub 2}O{sub 3} overlay. The effect of thickness of Al{sub 2}O{sub 3} coating on hot corrosion resistance will also be investigated. We will prepare Al{sub 2}O{sub 3} coating by sol-gel method. The corrosion resistance of TBC with sol-gel Al{sub 2}O{sub 3} coating will be determined and discussed with the results of TBC with EB-PVD and HVOF Al{sub 2}O{sub 3} coating.

  3. Reduced synaptic vesicle protein degradation at lysosomes curbs TBC1D24/sky-induced neurodegeneration

    PubMed Central

    Fernandes, Ana Clara; Uytterhoeven, Valerie; Kuenen, Sabine; Wang, Yu-Chun; Slabbaert, Jan R.; Swerts, Jef; Kasprowicz, Jaroslaw; Aerts, Stein

    2014-01-01

    Synaptic demise and accumulation of dysfunctional proteins are thought of as common features in neurodegeneration. However, the mechanisms by which synaptic proteins turn over remain elusive. In this paper, we study Drosophila melanogaster lacking active TBC1D24/Skywalker (Sky), a protein that in humans causes severe neurodegeneration, epilepsy, and DOOR (deafness, onychdystrophy, osteodystrophy, and mental retardation) syndrome, and identify endosome-to-lysosome trafficking as a mechanism for degradation of synaptic vesicle-associated proteins. In fly sky mutants, synaptic vesicles traveled excessively to endosomes. Using chimeric fluorescent timers, we show that synaptic vesicle-associated proteins were younger on average, suggesting that older proteins are more efficiently degraded. Using a genetic screen, we find that reducing endosomal-to-lysosomal trafficking, controlled by the homotypic fusion and vacuole protein sorting (HOPS) complex, rescued the neurotransmission and neurodegeneration defects in sky mutants. Consistently, synaptic vesicle proteins were older in HOPS complex mutants, and these mutants also showed reduced neurotransmission. Our findings define a mechanism in which synaptic transmission is facilitated by efficient protein turnover at lysosomes and identify a potential strategy to suppress defects arising from TBC1D24 mutations in humans. PMID:25422373

  4. Reduced synaptic vesicle protein degradation at lysosomes curbs TBC1D24/sky-induced neurodegeneration.

    PubMed

    Fernandes, Ana Clara; Uytterhoeven, Valerie; Kuenen, Sabine; Wang, Yu-Chun; Slabbaert, Jan R; Swerts, Jef; Kasprowicz, Jaroslaw; Aerts, Stein; Verstreken, Patrik

    2014-11-24

    Synaptic demise and accumulation of dysfunctional proteins are thought of as common features in neurodegeneration. However, the mechanisms by which synaptic proteins turn over remain elusive. In this paper, we study Drosophila melanogaster lacking active TBC1D24/Skywalker (Sky), a protein that in humans causes severe neurodegeneration, epilepsy, and DOOR (deafness, onychdystrophy, osteodystrophy, and mental retardation) syndrome, and identify endosome-to-lysosome trafficking as a mechanism for degradation of synaptic vesicle-associated proteins. In fly sky mutants, synaptic vesicles traveled excessively to endosomes. Using chimeric fluorescent timers, we show that synaptic vesicle-associated proteins were younger on average, suggesting that older proteins are more efficiently degraded. Using a genetic screen, we find that reducing endosomal-to-lysosomal trafficking, controlled by the homotypic fusion and vacuole protein sorting (HOPS) complex, rescued the neurotransmission and neurodegeneration defects in sky mutants. Consistently, synaptic vesicle proteins were older in HOPS complex mutants, and these mutants also showed reduced neurotransmission. Our findings define a mechanism in which synaptic transmission is facilitated by efficient protein turnover at lysosomes and identify a potential strategy to suppress defects arising from TBC1D24 mutations in humans. PMID:25422373

  5. Gear Failure Modes—Importance of Lubrication and Mechanics

    Microsoft Academic Search

    P. M. Ku

    1976-01-01

    Any rational approach to gear design must consider, as a minimum, the impact of the various modes of gear-tooth failure on gear performance; operating life and reliability; and size, weight, and cost. Gear teeth may fail basically by either strength-related or lubrication-related causes. However, many strength-related failures are influenced by lubrication, or may be induced by lubrication-related failures. This paper

  6. 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

  7. Failure mechanisms in blends of linear low-density polyethylene and polystyrene

    SciTech Connect

    Li, T.; Topolkaraev, V.A.; Hiltner, A.; Baer, E. [Case Western Reserve Univ., Cleveland, OH (United States)

    1996-12-31

    Mechanical models which describe the deformation and failure mechanisms for uncompatibilized blends of linear low-density polyethylene and polystyrene are described. A ductile to brittle transition was observed.

  8. Mechanism of gas pipeline failures on Balboa Boulevard during the 1994 Northridge earthquake

    SciTech Connect

    Nishio, Nobuaki [Tokyo Gas Co., Ltd. (Japan)

    1995-12-31

    A possible mechanism of gas pipeline failures on Balboa Boulevard during the 1994 Northridge earthquake is proposed. This mechanism is the one that has been adopted by the Japan Gas Association in the Recommended Practice for the Earthquake-Resistant Design of Gas Pipelines. The possible mode of ground displacement that might have caused the above pipeline failures is also discussed.

  9. Properties and failure mechanisms of pinned composite lap joints in monotonic and cyclic tension

    Microsoft Academic Search

    P. Chang; A. P. Mouritz; B. N. Cox

    2006-01-01

    The effect of through-thickness reinforcement by fibrous pins on the static tensile strength, fatigue life and failure mechanisms of single lap joints made of carbon\\/epoxy composite is investigated. Pinning is highly effective in increasing the ultimate strength, elongation limit and fatigue life. Improvements to the monotonic and fatigue properties are attributed to transitions in the failure mechanisms, from unstable joint

  10. Contribution of Failure Mechanisms to Crush Energy Absorption in a Composite Tube

    Microsoft Academic Search

    Narasimhan Swaminathan; Ronald C. Averill

    2006-01-01

    The main energy absorbing mechanisms during quasi-static crush of a circular composite tube have been investigated using an axisymmetric finite element model. Failure mechanisms such as material failure, delamination, friction between plies and friction between a metallic initiator and the tube are explicitly represented in the model. A Design of Experiments (DOE) study is performed to estimate the contribution of

  11. Friction Stir Weld Failure Mechanisms in Aluminum-Armor Structures Under Ballistic

    E-print Network

    Grujicic, Mica

    Friction Stir Weld Failure Mechanisms in Aluminum-Armor Structures Under Ballistic Impact Loading and of the attendant ballistic-impact failure mechanisms in prototypical friction stir welding (FSW) joints found-armor weldments, the overall ballistic performance of the armor is controlled by the ballistic limits of its weld

  12. Failure mechanisms during melt injection along dykes in Iceland

    NASA Astrophysics Data System (ADS)

    White, Robert S.; Agustsdottir, Thorbjorg; Greenfield, Tim; Green, Robert; Brandsdottir, Bryndis; Woods, Jennifer; Pugh, David

    2015-04-01

    We show moment tensor solutions from seismicity produced during two extremely well monitored dyke injections in the mid-crust of Iceland. They demonstrate failure by double couple mechanisms with little or no volumetric component. The inferred failure planes are consistently orientated parallel to the dyke, from which we infer that the seismicity is produced primarily by breaking chilled magma emplaced during an earlier injection episode. The first dyke injection was at Upptyppingar in 2007 in the Northern Rift Zone of Iceland. Melt was injected in the mid-crust from 17.5 to 13.5 km depth over a 9 month period before freezing in situ. The dyke was inclined with a dip of approximately 50 degrees. The second dyke was injected sub-horizontally from Bárðarbunga at a depth of about 7 km over a two week period in late August 2014 until it erupted 45 km away in Holuhraun. The Holuhraun eruption precisely reoccupied old craters from a late eighteenth century (c. 1797) eruption. The petrology of the eighteenth century basalts suggests that the melt also came from Bárðarbunga. It is likely therefore that the 2014 dyke closely followed the earlier eighteenth century dyke path. Both dyke injections were monitored by a dense seismic network of broad-band three-component seismic stations deployed and operated from 2006 to the present by the University of Cambridge in collaboration with the Institute of Earth Sciences, University of Iceland. These enable well constrained hypocentral locations and moment tensor solutions to be made. At its present peak the network consists of over 75 broadband seismometers. Fifteen additional seismometers were deployed in the days immediately following the onset of the dyke injection, including four seismometers on the Vatnajökull ice cap beneath which the dyke propagated and the remainder on Holuhraun surrounding the eventual eruption site: indeed two of the seismometers had to be rescued shortly before they were encroached by the advancing lava in the days following the onset of the eruption. The opportunity to deploy seismometers directly above the dyke and around the dyke tip mean that the earthquake locations are unusually well constrained.

  13. Adriamycin-induced heart failure: mechanisms and modulation

    Microsoft Academic Search

    Pawan K. Singal; Timao Li; Dinender Kumar; Igor Danelisen; Natasha Iliskovic

    2000-01-01

    Adriamycin (doxorubicin) is one of the most effective chemotherapeutic agents against a variety of cancers, but its usefulness is seriously curtailed by the risk of developing heart failure. Available laboratory evidence suggests that an increase in oxidative stress, brought about by increased free radical production and decreased myocardial endogenous antioxidants, plays an important role in the pathogenesis of heart failure.

  14. Mechanisms by which exercise training benefits patients with heart failure

    Microsoft Academic Search

    Louis J. Ignarro; Francesco Cacciatore; Ettore Crimi; Claudio Napoli

    2009-01-01

    Clinical consequences of heart failure are fatigue, dyspnea, and progressive impairment of exercise tolerance. Regular exercise training is associated with health-improving effects. In patients with stable heart failure, exercise training can relieve symptoms, improve exercise capacity and quality of life, as well as reduce hospitalization and, to some extent, risk of mortality. Progressive exercise training is associated with pulmonary, cardiovascular,

  15. 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.

  16. Hydrodynamics of TBC with non-Newtonian liquids: Liquid holdup

    Microsoft Academic Search

    H. Abukhalifeh; M. E. Fayed; R. Dhib

    2009-01-01

    An experimental study was conducted to investigate the hydrodynamic characteristics of a turbulent bed contractor (TBC) with non-Newtonian liquids under different operating conditions. Hollow plastic spheres fluidized in an air stream countercurrently with an aqueous solution of carboxy methyl cellulose (CMC) of an apparent viscosity ranging from 5 to 25mPas. The first set of experiments confirmed the non-Newtonian behavior of

  17. Metallographic preparation of the conventional and new TBC layers

    Microsoft Academic Search

    G. Moskal; B. Witala

    Purpose: Verification of up-to-now used metallographic preparation of the TBC coating thermal barriers and adaptation of them to layers of new types, based on new ceramic compounds, sprayed on conventional high temperature creep resisting alloys by the APS method, is a purpose of this paper. New types of used ceramic powders are so called pyrochlores of a general formula RE2Zr2O7.

  18. Mechanisms of rock slope failure in conglomerates with variable lithification

    NASA Astrophysics Data System (ADS)

    Bundschuh, M.; Thuro, K.

    2012-04-01

    In conglomerates with variable lithification very special failure mechanisms my occur. On January 25th, 2010 at the village of Stein at the river Traun, at about 8 p.m. a 432 m3 large and 1,026 t heavy block was released from a conglomerate face obviously without warning, destroying the family home below. Only two of four inhabitants could be saved out of the debris by means of a spectacular rescue operation through the local fire brigade. After this event the question arised, if the rock fall could have been foreseen or if such spontaneous incidents are abrupt and unpredictable. In this paper the conducted studies to reconstruct the processes leading to this event will be presented. These investigations included field mapping, geodetic survey, laserscanning of the rupture face, mineralogical analysis of sinter crust thin sections, inventory of the block dimensions and reconstruction of the collapse kinematics, analysis of the weather data prior to the event and a 2D finite element calculation (Phase2, rocscience) using the geometry of the overhanging conglomerate strata. In this case, it seems like there was no clear triggering event prior to the wall collapse. Instead, it could be proved by engineering geology mapping, mineralogical analysis of the sinter crusts and numerical modelling, that the back scarp connected with a set of discontinuities started to propagate several years ago already. Also supported by early photographs of the cracks in the brick walls of the endangered house in 1993 and 2006 together with eye wittnesses, it could be shown, that the fracture propagation started tens of years beforehand and the rock topple - rock fall took place after the last rock bond bridges finally were sheared through. As a result of all field data and the numerical modeling, the causes of the event can be stated as: • caving in the rock mass of up to 9 m depth at the foot oft he wall; • the low strength values of the conglomerates; and • vertical joint sets caused by the geometrical constraints and the low rock strength properties. As trigger mechanism, the multiple freeze/thaw cycles and therefore the frequent contractions of the separated rock column are also responsible for fracture propagation. In fact, only the "last" freezing event can be identified as trigger, thus meaning that there was no "major" triggering event at all. The results of the numerical modeling also suggest, that shear cracks must have formed, subsequently generating a distinct crack pattern in the walls of the building. The results of the analyses of the thin sections of the sinter crusts derived from the back faces of the blocks suggest an increasing depth of the back joint with time and an age of at least 11 years or more. This means that the crack pattern must have been visible years before the event. Therefore it can be stated, that the rock fall of Stein could have been predicted, if the clear signs of damage would have been interpreted correctly and the failure process would have been fully understood.

  19. Dynamic failure mechanisms of ceramic bars : Experiments and numerical simulations

    NASA Astrophysics Data System (ADS)

    Espinosa, H. D.; Brar, N. S.

    1995-10-01

    Failure mechanisms in ceramics are investigated by means of bar impact experiments and numerical simulations of the wave propagation event. Stress histories are measured by embedding manganin stress gauges in the ceramic bars. The fracture event is examined by high speed photography. A violent radial expansion, in a region close to the impact surface, followed by a cloud of debris is observed. Numerical simulations of the inelastic wave propagation event are performed with a multiple-plane microcracking model. The simulations show that when the impact stress exceeds a material threshold, the stress wave in the bar has a relatively short duration which is controlled by the rate of unconfined compressive damage. A nonzero inelastic strain rate at the wave front is required in the simulations to properly capture the measured stress attenuation with propagation distance. This feature is related to a heterogeneous material microstructure which is a common occurrence in ceramics. Furthermore, the simulations predict a radial expansion of the bar as a result of not only compressive but also tensile damage. The radial velocity histories on the bar surface are functions of wave propagation distance and damage rate. Tensile damage is induced by stress release from the rod surface and is restricted to the bar core, due to wave focusing, and to the bar free end. In the latest case, reflection of the compressive pulse produces bar spallation. The two dimensional distribution of tensile and compressive damage is assessed by means of contour plots of volumetric strain and the second invariant of the inelastic strain tensor.

  20. Evaluation of the BD MGIT TBc Identification Test (TBc ID), a rapid chromatographic immunoassay for the detection of Mycobacterium tuberculosis complex from liquid culture

    Microsoft Academic Search

    Anandi Martin; Deirdre Bombeeck; Krista Fissette; Pim de Rijk; Ivan Hernández-Neuta; Patricia Del Portillo; Juan Carlos Palomino

    2011-01-01

    The BACTEC MGIT 960 system is increasingly used to culture Mycobacterium tuberculosis. We evaluated the performance of the new immunochromatographic assay BD MGIT TBc Identification Test (TBc ID) for the rapid identification of M. tuberculosis complex in clinical samples when performed directly from BACTEC MGIT 960 culture positive for acid-fast bacilli (AFB).Of 92 cultures evaluated, the sensitivity and specificity of

  1. Mechanisms of fatigue failure in thermal spray coatings

    Microsoft Academic Search

    R. Ahmed; M. Hadfield

    2002-01-01

    The aim of this experimental study was to ascertain the fatigue failure modes of thermal spray coatings in rolling\\/sliding\\u000a contact. These failure modes outline the design requirements of thermal spray coatings for high-stress tribological applications\\u000a including impact and point or line contact loading. Recently, a number of scientific studies have addressed the fatigue performance\\u000a and durability of thermal spray coatings

  2. Mechanical properties and failure mechanisms of graphene under a central load.

    PubMed

    Wang, Shuaiwei; Yang, Baocheng; Zhang, Shouren; Yuan, Jinyun; Si, Yubing; Chen, Houyang

    2014-09-15

    By employing molecular dynamics simulations, the evolution of deformation of a monolayer graphene sheet under a central transverse loading are investigated. Dependence of mechanical responses on the symmetry (shape) of the loading domain, on the size of the graphene sheet, and on temperature, is determined. It is found that the symmetry of the loading domain plays a central role in fracture strength and strain. By increasing the size of the graphene sheet or increasing temperature, the tensile strength and fracture strain decrease. The results have demonstrated that the breaking force and breaking displacement are sensitive to both temperature and the symmetry of the loading domain. In addition, we find that the intrinsic strength of graphene under a central load is much smaller than that of graphene under a uniaxial load. By examining the deformation processes, two failure mechanisms are identified namely, brittle bond breaking and plastic relaxation. In the second mechanism, the Stone-Wales transformation occurs. PMID:25044132

  3. Failure mechanisms of woven carbon and glass composites

    SciTech Connect

    Alif, N.; Carlsson, L.A. [Florida Atlantic Univ., Boca Raton, FL (United States). Dept. of Mechanical Engineering

    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.

  4. 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.

  5. Mechanism-Based Therapeutic Approaches to Rhabdomyolysis-Induced Renal Failure

    PubMed Central

    Boutaud, Olivier; Roberts, L. Jackson

    2010-01-01

    Rhabdomyolysis-induced renal failure represents up to 15% of all cases of acute renal failure. Many studies over the past four decades have demonstrated that accumulation of myoglobin in the kidney is central in the mechanism leading to kidney injury. However, some discussion exists regarding the mechanism mediating this oxidant injury. Although free iron-catalyzed fenton reaction has been proposed to explain the tissue injury, more recent evidence strongly suggests that the main cause of oxidant injury is myoglobin redox cycling and generation of oxidized lipids. These molecules can propagate tissue injury and cause renal vasoconstriction, two of the three main conditions associated with acute renal failure. This review presents the evidence supporting the two mechanisms of oxidative injury, describes the central role of myoglobin redox cycling in the pathology of renal failure associated with rhabdomyolysis, and discuss the value of therapeutic interventions aiming at inhibiting myoglobin redox cycling for the treatment of rhabdomyolysis-induced renal failure. PMID:21034813

  6. Failure modes and mechanisms in nickel alloys: Primarily austenitic stainless steel

    SciTech Connect

    Bush, S.H.

    1989-08-01

    Austenitic stainless steels and higher nickel alloys such as the Inconels are used extensively in the chemical and nuclear industries. This review will concentrate on their behavior in nuclear reactors because of the availability of information to the author. Emphasis is given to the failure modes and mechanisms occurring in the context of causal mechanisms and the implications of alloy composition. Major use is made of the austenitic steels both AISI 304 and 316 in United States nuclear plants. This is true for both boiling water reactors (BWRs) and pressurized water reactors (PWRs). Over the years there have been many failures in these materials where failure is defined as cracking, leaking, and, rarely, catastrophic breakage. This review will examine failure mechanisms such as stress corrosion cracking, both transgranular and intergranular, fatigue, including vibrational and thermal, and other corrosion-related failures. 16 refs., 12 figs.

  7. APPLICATION OF FAILURE EVENT DATA TO BENCHMARK PROBABILISTIC STRUCTURAL MECHANICS COMPUTER CODES

    SciTech Connect

    Simonen, Fredric A.; Gosselin, Stephen R.; Lydell, Bengt O.; Rudland, David L.; Wilkowski, Gery M.

    2007-07-22

    This paper describes an application of data on cracking, leak and rupture events from nuclear power plant operating experience to estimate failure frequencies for piping components that had been previously evaluated using the PROLOCA and PRAISE probabilistic fracture mechanics (PFM) computer codes. The calculations had addressed the failure mechanisms of stress corrosion cracking, intergranular stress corrosion cracking and fatigue for materials and operating conditions that were known to have failed components. The first objective was to benchmark the calculations against field experience. A second objective was a review of uncertainties in the treatments of the data from observed failures and in the structural mechanics models. The database PIPExp-2006 was applied to estimate failure frequencies. Because the number of reported failure events was small, there were also statistical uncertainties in the estimates of frequencies. Comparisons of predicted and observed failure frequencies showed that PFM codes correctly predicted relatively high failure probabilities for components that had experienced field failures. However, the predicted frequencies tended to be significantly greater than those estimated from plant operating experience. A review of the PFM models and inputs to the models showed that uncertainties in the calculations were sufficiently large to explain the differences between the predicted and observed failure frequencies.

  8. Failure modes and fracture mechanisms in flexure of Kevlar-epoxy composites

    Microsoft Academic Search

    M. Davidovitz; A. Mittelman; I. Roman; G. Marom

    1984-01-01

    The results of testing in three-point bending of aramid fibre-reinforced epoxy composites are described. This loading mode has been chosen in order to increase the variety of failure modes and of fracture mechanisms. The main failure modes observed are tensile and delamination, with a transition at a fibre volume fraction of about 46%. This mode transition is detectable by monitoring

  9. Safety impact of mechanical- and maintenance-induced seal failures of reactor coolant pumps

    Microsoft Academic Search

    M. A. Azarm; J. L. Boccio

    1985-01-01

    This paper presents an investigation of the safety impact resulting from mechanical- and maintenance-induced reactor coolant pump (RCP) seal failures in nuclear power plants. The intention of this study was to estimate the annual frequency for the spectrum of leak rates induced by RCP seal failures for the benefit of various pump designers and plant vendors; and to evaluate their

  10. Mechanical behavior and localized failure modes in a porous basalt from the Azores

    E-print Network

    Fortin, Jérôme

    Mechanical behavior and localized failure modes in a porous basalt from the Azores S. Loaiza,1 J September 2012; accepted 9 September 2012; published 11 October 2012. [1] Basaltic rocks are the main behavior and the failure modes of a porous basalt, with an initial connected porosity of 18%. Results were

  11. On-chip measurement to analyze failure mechanisms of ICs under System Level ESD stress

    E-print Network

    Paris-Sud XI, Université de

    On-chip measurement to analyze failure mechanisms of ICs under System Level ESD stress F. Caignet1 of electronic system failures. Reliability of ICs within the applications is strongly related to the on-chip measurement system providing more than 100GHz measurement bandwidth (BW). Some dedicated on-chip probes

  12. Incidence and causes of non-invasive mechanical ventilation failure after initial success

    Microsoft Academic Search

    Maurizio Moretti; Carmela Cilione; Auro Tampieri; Claudio Fracchia; Alessandro Marchioni; Stefano Nava

    2000-01-01

    BACKGROUNDThe rate of failure of non-invasive mechanical ventilation (NIMV) in patients with chronic obstructive pulmonary disease (COPD) with acute respiratory insufficiency ranges from 5% to 40%. Most of the studies report an incidence of “late failure” (after >48 hours of NIMV) of about 10–20%. The recognition of this subset of patients is critical because prolonged application of NIMV may unduly

  13. Power cycling simulation of an IC package: considering electromigration and thermal-mechanical failure

    Microsoft Academic Search

    Yong Liu; Scott Irving

    2003-01-01

    Power cycling is a critical reliability problem in package solder joint connection which may cause thermal-mechanical and electrical failures. Basically, power cycling has two fype of failures: the fatigue damage of solder joint due to the gradient of temperature distribution in the package by power cycle load, and the solder joint migration voids which is aggravated by the high current

  14. Failure mechanism of winding insulations in inverter-fed motors

    Microsoft Academic Search

    Weijun Yin

    1997-01-01

    The failure of magnet wires under repetitive pulses as seen in inverter-fed motors cannot be attributed to a single factor but is a result of the combined effects of partial discharge, dielectric heating, and space charge formation. Voltage overshoots produced by PWM drives may be above discharge inception voltage. Partial discharge may therefore be present in inverter-fed motors. In addition

  15. Failure mechanisms and design considerations for fault tolerant aerospace drives

    Microsoft Academic Search

    J. W. Bennett; B. C. Mecrow; D. J. Atkinson; G. J. Atkinson

    2010-01-01

    This paper considers existing More Electric technologies in commercial aircraft, observing recent technologies adopted by aerospace and discussing the reasons restricting the application of other designs. Fault tolerant drives are considered, assessing where reliability may affect application in aerospace. Failure conditions and design issues are proposed which will present challenges in the evolution of laboratory prototypes to actual aerospace hardware.

  16. 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...

  17. Fracture mechanics analysis of delamination failures in IC packages

    Microsoft Academic Search

    Andrew A. O. Tay

    2009-01-01

    This paper describes the application of fracture mechanics to the analysis of delamination in IC packages. An introduction to the fundamentals of interfacial fracture mechanics will first be given together with a description of some numerical methods for calculating fracture mechanics parameters such as strain energy release rate and mode mixity. Fracture mechanics methodology will then be applied to analyze

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

    SciTech Connect

    Grape, J.A.; Gupta, V. [Dartmouth College, Hanover, NH (United States). Thayer School of Engineering] [Dartmouth College, Hanover, NH (United States). Thayer School of Engineering

    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.

  19. Energy Emissions from Failure Phenomena: Mechanical, Electromagnetic, Nuclear

    Microsoft Academic Search

    A. Carpinteri; F. Cardone; G. Lacidogna

    2010-01-01

    Characterizing the nature of the different forms of energy emitted during compressive failure of brittle materials is an open\\u000a and debated argument in the scientific literature. Some research has been already conducted on this subject in the scientific\\u000a community based on the signals captured by the acoustic emission measurement systems. On the other hand, there are not many\\u000a studies yet

  20. Mechanism of failure of heat exchangers in cement furnaces

    Microsoft Academic Search

    M. A. Tylkin; B. N. Bogomolov; A. M. Sharkova

    1977-01-01

    Conclusions 1.Failure of heat exchangers made of steels Kh23N18 and Kh24N12SL results from carburizing and sulfur-alkali corrosion in the presence of compounds of vanadium forming a low-melting eutectic preferentially in austenite grain boundaries.2.The corrosion rate of heat exchangers in mazout furnaces is three times the corrosion rate of heat exchangers in gas furnaces.3.In heat exchangers that increase the gas flow

  1. Mechanical integrity of the IC device package-a key factor in achieving failure free product performance

    Microsoft Academic Search

    Sorin Witzman; Yves Giroux

    1991-01-01

    A methodology has been developed to maximize product hardware integrity and practically eliminate service affecting field failures. This methodology starts with the analysis of the field failures reported over a period of 5 to 10 years. Failed parts are analyzed and similar failures are reproduced in laboratory conditions. This procedure allows researchers to identify the failure mechanisms and the factors

  2. Deformation and failure mechanisms of graphite/epoxy composites under static loading

    NASA Technical Reports Server (NTRS)

    Clements, L. L.

    1981-01-01

    The mechanisms of deformation and failure of graphite epoxy composites under static loading were clarified. The influence of moisture and temperature upon these mechanisms were also investigated. Because the longitudinal tensile properties are the most critical to the performance of the composite, these properties were investigated in detail. Both ultimate and elastic mechanical properties were investigated, but the study of mechanisms emphasized those leading to failure of the composite. The graphite epoxy composite selected for study was the system being used in several NASA sponsored flight test programs.

  3. Mechanical properties, microscopy, and failure mechanisms of carbon fiber reinforced epoxy laminated composites

    SciTech Connect

    Thissell, W.R.; Zurek, A.K.; Addessio, F.

    1995-12-31

    The mechanical behavior of quasi-isotropic and unidirectional epoxy- matrix carbon-fiber laminated composites subjected to compressive loading at strain rates of 10{sup {minus}3} and 2000 s{sup {minus}1} are described. Failure in the studied composites was dominated by delamination which proceeded by brittle fracture of the epoxy matrix. The matrix-fiber bonding in these composites is very strong and prevented the occurrence of significant fiber-pullout. The mode I delamination strain energy release rate of the unidirectional composites was determined using the double cantilever beam and hole in plate compression methods. The DCB method indicated a significant R curve effect attributed to fiber bridging while the presently available hole in plate analytical methods show questionable validity for highly anisotropic materials.

  4. Mechanical properties and failure mechanisms of carbon fiber reinforced epoxy laminated composites

    SciTech Connect

    Thissell, W.R.; Zurek, A.K.; Addessio, F.

    1995-09-01

    The mechanical behavior of quasi-isotropic and unidirectional epoxy-matrix carbon-fiber laminated composites subjected compressive loading at strain rates of 10{sup {minus}3} and 2000 s{sup {minus}1} are described. Failure in the studied composites was dominated by delamination which proceeded by brittle fracture of the epoxy-matrix. The matrix-fiber bonding in these composites is very strong and prevented the occurrence of significant fiber-pullout. The mode I delamination strain energy release rate of the unidirectional composites was determined using the double cantilever beam and hole in plate compression method. The DCB method indicated a significant R curve effect attributed to fiber bridging while the presently available hole in plate analytical methods show questionable validity for highly anisotropic materials.

  5. 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.

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

    SciTech Connect

    Anoop Krishnan, N. M., E-mail: anoopnm@civil.iisc.ernet.in; Ghosh, Debraj [Indian Institute of Science, Bangalore 560012 (India)

    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.

  7. Failure mechanisms and pore water pressure conditions: analysis of a riverbank along the Arno River (Central Italy)

    Microsoft Academic Search

    Stefano Dapporto; Massimo Rinaldi; Nicola Casagli

    2001-01-01

    Mechanisms of failure occurring in two portions of a riverbank along the Arno River (Central Italy), are investigated in detail starting by a series of periodic field observations and bank profile measurements. Two dominant mechanisms involving the silty sand portion of the bank have been observed: (a) alcove-shaped failure in the middle portion of the bank; (b) slab failure involving

  8. Fractographic interpretation of failure mechanisms in titanium matrix composites

    Microsoft Academic Search

    W. S Johnson; J. L Miller; M Mirdamadi

    1995-01-01

    Titanium matrix composites (TMC) offer a combination of good mechanical properties and high temperature durability that make them attractive candidate materials for advanced engine components and high temperature structural applications. In such applications the material will be subjected to changing mechanical loads and temperature fluctuations, resulting in complex stress states within the constituents of the composite. This study examines how

  9. Failure mechanisms associated with the thermally grown oxide in plasma-sprayed thermal barrier coatings

    Microsoft Academic Search

    A Rabiei; A. G Evans

    2000-01-01

    The microstructure and durability of a thermal barrier coating (TBC) produced by the thermal spray method have been characterized. Upon exposure, the bond coat chemistry and microstructure change by inter-diffusion with the substrate and upon thickening of the thermally grown oxide (TGO). A wedge impression test, in conjunction with observations by scanning electron microscopy, has been used to probe the

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

    SciTech Connect

    Pan, Y.M. [Center for Nuclear Waste Regulatory Analyses, San Antonio, TX, 78238 (United States); Chan, K.S.; Riha, D.S. [Southwest Research Institute, San Antonio, TX, 78238 (United States)

    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)

  11. Failure mechanisms of a zirconia-8 wt% yttria thermal barrier coating

    Microsoft Academic Search

    Andrew H. Bartlett; Roberto Dal Maschio

    1995-01-01

    Isothermal and cyclic heat treatments of a plasma-sprayed zirconia-8 wt% yttria thermal barrier coating on a nickel superalloy substrate highlighted coating failure mechanisms. A reaction layer formed at the bond coat\\/ceramic interface, and failure of the coating initiated in the reaction layer due to opening thermal expansion mismatch stresses associated with a nonplanar interface. Crack propagation occurred in the ceramic

  12. Pathogenic mechanisms in early norepinephrine-induced acute renal failure: Functional and histological correlates of protection

    Microsoft Academic Search

    Robert E Cronin; Antoine de Torrente; Paul D Miller; Ruth Ellen Bulger; Thomas J Burke; Robert W Schrier

    1978-01-01

    Pathologic mechanisms in early norepinephrine-induced acute renal failure: Functional and histological correlates of protection. The present study investigated the protective effect of acute volume expansion (25%) with isotonic saline, isotonic mannitol, and hypertonic mannitol in a model of unilateral norepinephrine-induced acute renal failure (ARF). Three hours following a 40-min intrarenal infusion of norepinephrine (NE) (0.75 µg\\/kg\\/min), inulin clearance had fallen

  13. 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.

  14. Predictors of extubation failure and reintubation in newborn infants subjected to mechanical ventilation

    PubMed Central

    Costa, Ana Cristina de Oliveira; Schettino, Renata de Carvalho; Ferreira, Sandra Clecêncio

    2014-01-01

    Objective To identify risk factors for extubation failure and reintubation in newborn infants subjected to mechanical ventilation and to establish whether ventilation parameters and blood gas analysis behave as predictors of those outcomes. Methods Prospective study conducted at a neonatal intensive care unit from May to November 2011. A total of 176 infants of both genders subjected to mechanical ventilation were assessed after extubation. Extubation failure was defined as the need to resume mechanical ventilation within less than 72 hours. Reintubation was defined as the need to reintubate the infants any time after the first 72 hours. Results Based on the univariate analysis, the variables gestational age <28 weeks, birth weight <1,000g and low Apgar scores were associated with extubation failure and reintubation. Based on the multivariate analysis, the variables length of mechanical ventilation (days), potential of hydrogen (pH) and partial pressure of oxygen (pO2) remained associated with extubation failure, and the five-minute Apgar score and age at extubation were associated with reintubation. Conclusion Low five-minute Apgar scores, age at extubation, length of mechanical ventilation, acid-base disorders and hyperoxia exhibited associations with the investigated outcomes of extubation failure and reintubation. PMID:24770689

  15. 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.

  16. 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.

  17. Toward Optimum Scale and TBC Adhesion on Single Crystal Superalloys

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    1998-01-01

    Single crystal superalloys exhibit excellent cyclic oxidation resistance if their sulfur content is reduced from typical impurity levels of approximately 5 ppmw to below 0.5 ppmw. Excellent alumina scale adhesion was documented for PWA 1480 and PWA 1484 without yttrium additions. Hydrogen annealing produced effective desulfurization of PWA 1480 to less than 0.2 ppmw and was also used to achieve controlled intermediate levels. The direct relationship between cyclic oxidation behavior and sulfur content was shown. An adhesion criterion was proposed based on the total amount of sulfur available for interfacial segregation, e.g., less than or equal to 0.2 ppmw S will maximize adhesion for a 1 mm thick sample. PWA 1484, melt desulfurized to 0.3 ppmw S, also exhibited excellent cyclic oxidation resistance and encouraging TBC lives (10 mils of 8YSZ, plasma sprayed without a bond coat) in 1100 C cyclic oxidation tests.

  18. Product Reliability Trends, Derating Considerations and Failure Mechanisms with Scaled CMOS

    NASA Technical Reports Server (NTRS)

    White, Mark; Vu, Duc; Nguyen, Duc; Ruiz, Ron; Chen, Yuan; Bernstein, Joseph B.

    2006-01-01

    As microelectronics is scaled into the deep sub-micron regime, space and aerospace users of advanced technology CMOS are reassessing how scaling effects impact long-term product reliability. The effects of electromigration (EM), time-dependent-dielectric-breakdown (TDDB) and hot carrier degradation (HCI and NBTI) wearout mechanisms on scaled technologies and product reliability are investigated, accelerated stress testing across several technology nodes is performed, and FA is conducted to confirm the failure mechanism(s).

  19. Immune mechanisms in acetaminophen-induced acute liver failure

    PubMed Central

    Krenkel, Oliver; Mossanen, Jana C.

    2014-01-01

    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-? or IL-1?, 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 ?? 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

  20. 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-? or IL-1?, 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 ?? 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

  1. Failure of latch mechanism for motion control of safety rods

    SciTech Connect

    Yau, W.W.F.; Leader, D.R.

    1992-01-16

    During safety rod tests in K-reactor prior to startup, one safety rod could not be lifted because the ``button`` broke off and became lodged in the mechanism. Examination of the failed latch assembly along with other assemblies from both K-Area and L-Area revealed several missing buttons as well as severely deformed ``jaw hanger extensions.`` We participated in the investigation of the damage by request of the Reactor Restart Section. Based on our study of the latch mechanism, the modifications to the ``safety rod extension,`` and the operating history of the machine, this memorandum describes the causes of the observed damage with experimental evidence and calculations to support the findings. 3 refs.

  2. Failure of latch mechanism for motion control of safety rods

    SciTech Connect

    Yau, W.W.F.; Leader, D.R.

    1992-01-16

    During safety rod tests in K-reactor prior to startup, one safety rod could not be lifted because the button'' broke off and became lodged in the mechanism. Examination of the failed latch assembly along with other assemblies from both K-Area and L-Area revealed several missing buttons as well as severely deformed jaw hanger extensions.'' We participated in the investigation of the damage by request of the Reactor Restart Section. Based on our study of the latch mechanism, the modifications to the safety rod extension,'' and the operating history of the machine, this memorandum describes the causes of the observed damage with experimental evidence and calculations to support the findings. 3 refs.

  3. 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.

  4. Early laparotomy wound failure as the mechanism for incisional hernia formation

    PubMed Central

    Xing, Liyu; Culbertson, Eric J.; Wen, Yuan; Franz, Michael G.

    2015-01-01

    Background Incisional hernia is the most common complication of abdominal surgery leading to reoperation. In the United States, 200,000 incisional hernia repairs are performed annually, often with significant morbidity. Obesity is increasing the risk of laparotomy wound failure. Methods We used a validated animal model of incisional hernia formation. We intentionally induced laparotomy wound failure in otherwise normal adult, male Sprague-Dawley rats. Radio-opaque, metal surgical clips served as markers for the use of x-ray images to follow the progress of laparotomy wound failure. We confirmed radiographic findings of the time course for mechanical laparotomy wound failure by necropsy. Results Noninvasive radiographic imaging predicts early laparotomy wound failure and incisional hernia formation. We confirmed both transverse and craniocaudad migration of radio-opaque markers at necropsy after 28 d that was uniformly associated with the clinical development of incisional hernias. Conclusions Early laparotomy wound failure is a primary mechanism for incisional hernia formation. A noninvasive radiographic method for studying laparotomy wound healing may help design clinical trials to prevent and treat this common general surgical complication. PMID:23036516

  5. A Précis of Some Recent Developments in Computational Failure Mechanics

    E-print Network

    De Borst, R; Askes, Harm; Gutiérrez, Miguel A; Remmers, Joris J C; Wells, G N

    2002-01-01

    can become almost insensitive to the discretisa- tion. This is exemplified in Figures 1 and 2. Figure 1 shows the deformed mesh of a silicium-carbide specimen that is reinforced with carbon fibres (SiC/C composite). The dimensions of the specimen... . Mech., 7 (1962) 55-129. [5] A. Hillerborg, M. Modeer, P.E. Petersson, Analysis of crack formation and crack growth in concrete by means of fracture mechanics and finite elements, Cement Concrete Res., 6 (1976) 773-782. [6] J.C.J. Schellekens, R. de...

  6. Identification of fundamental deformation and failure mechanisms in armor ceramics

    NASA Astrophysics Data System (ADS)

    Muller, Andrea Marie

    Indentation of a surface with a hard sphere can be used to examine micromechanical response of a wide range of materials and has been shown to generate loading conditions resembling early stages of ballistic impact events. Cracking morphologies also show similarities, particularly with formation of cone cracks at the contact site. The approach in this thesis is to use this indentation technique to characterize contact damage and deformation processes in armor ceramics, as well as identify the role of cone cracking and inelastic behavior. To accomplish these objectives, an instrumented indentation system was designed and fabricated, extending depth-sensing capabilities originally developed for nano-indentation to higher forces. This system is also equipped with an acoustic emission system to detect onset of cone cracking and subsequent failure. Once calibrated and verified the system was used to evaluate elastic modulus and cone crack initiation forces of two commercial float glasses. As-received air and tin surfaces of soda-lime-silica and borosilicate float glass were tested to determine differences in elastic and fracture behavior. Information obtained from load--displacement curves and visual inspection of indentation sites were used to determine elastic modulus, and conditions for onset of cone cracking as a function of surface roughness. No difference in reduced modulus or cone cracking loads on as-received air and tin surfaces were observed. Abraded surfaces showed the tin surface to be slightly more resistant to cone cracking. A study focusing on the transition from elastic to inelastic deformation in two transparent fine-grained polycrystalline spinels with different grain sizes was then conducted. Congruent experiments included observations on evolution of damage, examinations of sub-surface damage and inspection of remnant surface profiles. Indentation stress--strain behavior obtained from load--displacement curves revealed a small difference in yielding and strain-hardening behavior given the significant grain size difference. Directly below the indentation sites, regions of grain boundary cracking, associated with the inelastic zone, were identified in both spinels. Comparison of Meyer hardness and in-situ hardness showed a discrepancy at low loads, a result of elastic recovery. Elastic-plastic indentation behavior of the two spinels was then compared to behavior of a transparent large-grained aluminum oxinitirde (AlON) and a small-grained sintered aluminum nitride (AlN). Subsurface indentation damage revealed transitions from intergranular to transgranular fracture in the two spinels, AlON showed a transition from multiple cleavage microcracks to transgranular fracture while AlN exhibited only intergranular fracture. Analysis of indentation stress-strain results showed a slight difference in yielding behaviors of the two spinels and AlON whereas AlN showed a much lower yield value comparatively. Slight differences in strain-hardening behavior were observed. When comparing indentation stress--strain energy density and work of indentation a linear correlation was observed and a clear distinction could be made between materials. Therefore, it is suggested by the work in this thesis that instrumented spherical indentation could serve as a useful method of evaluating armor materials, particularly when behavior is described using indentation stress and strain, as this is a useful way to evaluate onset and development of inelastic deformation under high contact pressures and self-confining stresses. Additionally, it proposes that comparison of the work of indentation and indentation strain energy density approaches provide a good foundation for evaluating and comparing a materials penetration resistance.

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

    SciTech Connect

    Zbib, Hussein M [Washington State University; Bahr, David F [Purdue University

    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 tri-layer composites. CINT formed nanolaminate composites were tested in tension, with bulge testing, using nanoindentation, and using micro-compression testing to demonstrate that the tri-layer films were indeed tougher and hardened more during deformation (they got stronger as we deformed them) than equivalent bi-layers. The seven graduate students, 4 post-docs and research faculty, and the two faculty co-PI’s were able to create a collaborated computational prediction and experimental validation team to demonstrate the benefits of this class of materials to the community. The computational work crossed from atomistic to bulk simulations, and the experiments coupled form nm-scale to the mm scale; closely matching the simulations. The simulations provided viable mechanisms that explained the observed results, and new experimental results were used to push the boundaries of the simulation tools. Over the life of the 7 years of this program we proved that tri-layer nanolaminate metallic composite systems exceeded the mechanical performance of bi-layer systems if the right materials were chosen, and that the mechanism responsible for this was tied to the cross slip of dislocations. With 30 journal publications resulting from this work we have broadly disseminated this family of results to the scientific community.

  8. Impact of mechanical- and maintenance-induced failures of main reactor coolant pump seals on plant safety

    Microsoft Academic Search

    M. A. Azarm; J. L. Boccio; S. Mitra

    1985-01-01

    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

  9. IMPERMEABLE THIN Al2O3 OVERLAY FOR TBC PROTECTION FROM SULFATE AND VANADATE ATTACK IN GAS TURBINES

    SciTech Connect

    Scott X. Mao

    2003-03-10

    In order to improve the hot corrosion resistance of conventional YSZ TBC system, a thin and dense {alpha}-Al{sub 2}O{sub 3} overlay has been deposited on the YSZ surface by the composite-sol-gel route (CSG). The YSZ substrates were dipped with boehmite sol containing calcined {alpha}-Al{sub 2}O{sub 3} particles, dried to form a gel film and calcined at 1200 C to form {alpha}-Al{sub 2}O{sub 3} overlay. Hot corrosion tests were carried out on the TBCs with and without Al{sub 2}O{sub 3} coating in molten salt mixtures (Na{sub 2}SO{sub 4} + 5% V{sub 2}O{sub 5}) at 950 C for 10 hours. The results showed that besides a thin and dense alumina overlay with the thickness of about 100-500 nm formed on the YSZ surface, the microcracks and porous near the surface in YSZ was also occupied by alumina because of penetration of the low viscosity precursor. As a result, the Al{sub 2}O{sub 3} overlay remarkably refrained the infiltration of the molten salt into the YSZ coating. The amount of M-phase in the TBC coating with Al{sub 2}O{sub 3} overlay was substantially reduced comparing to that without alumina overlay. In the next reporting period, we will prepare the alumina overlay by CSG route with different thickness and study the hot corrosion mechanism of YSZ TBC with thin Al{sub 2}O{sub 3} overlay coating produced by CSG.

  10. 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.

  11. 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 presentation. The model can be used to explain the Intel-reported reliability degradation in MLCCs with respect to the reduction of dielectric thickness. It can also be used to estimate the reliability of a MLCC based on its construction and microstructure parameters such as dielectric thickness, average grain size, and number of dielectric layers. Measures for preventing early failures are also discussed in this document.

  12. Properties of Plastic Materials and How They Relate to Device Failure Mechanisms

    Microsoft Academic Search

    S. M. Lee; J. J. Licari; A. Valles

    1965-01-01

    The investigation has been primarily concerned with a search for factors pertinent to mechanisms of failure in microdiode values which entailed design and screening evaluation of various experimental and analytical approaches. The data produced by this effort was reviewed for applicability to these components to verify postulated hypotheses. The interesting results of the program include: 1. The discovery of ammonia

  13. Mechanical behavior and failure of composite pyramidal truss core sandwich columns

    E-print Network

    Vaziri, Ashkan

    Mechanical behavior and failure of composite pyramidal truss core sandwich columns Jian Xiong a of pyramidal truss core sandwich panels made of carbon fiber composite under axial compression made of fiber reinforced composite. The response of the sandwich panels under axial compression

  14. The failure mechanisms of micro-scale cantilevers in shock and vibration stimuli

    Microsoft Academic Search

    Michael Sheehyl; Michael Reid; Jeff Punch; Suresh Goyal; Gerard Kelly

    2008-01-01

    Contemporary shock testing of micro-devices is carried out in controlled test environments where test parameters can be monitored with current metrology techniques. Due to demanding environments and limited scope of design rules, the reliability of micro devices has become a concern. A modified Hopkinson pressure bar (HPB) is used to investigate failure mechanisms of single crystal silicon (SCS) micro-cantilever devices

  15. Operating conditions and failure mechanisms in He-Ne hollow cathode glow discharge laser cavities

    Microsoft Academic Search

    V. K. Lakdawala; S. R. Hunter; J. A. Rees; J. L. Moruzzi

    1989-01-01

    A series of life test measurements has been performed in He-Ne gas laser discharges using several different types of laser discharge cells. These studies have explored the mechanisms that lead to the failure of the discharges in these cells. Specifically, the dependence of the life of the discharge on the operating parameters (discharge current, cell temperature, gas composition and total

  16. Failure of Mineralized Collagen Microfibrils Using Finite Element Simulation Coupled to Mechanical Quasi-brittle Damage

    E-print Network

    Paris-Sud XI, Université de

    Failure of Mineralized Collagen Microfibrils Using Finite Element Simulation Coupled to Mechanical law isotropic elasticity to investigate the fracture behaviour of composite materiel collagen- mineral (mineralized collagen microfibril). Fracture stress-number of cross-links and damping capacity-number of cross

  17. The application of fracture mechanics to failure analysis of photovoltaic solar modules

    Microsoft Academic Search

    C. P. Chen; M. H. Leipold

    1981-01-01

    Cracking of silicon solar cells and solar module transparent cover panels such as glass or polymethylmethacrylate (PMMA) is a major cause of photovoltaic solar module failure in field service. Silicon and cover materials are brittle, and cracking of these materials is expected to result from the extension of preexisting flaws under stress. Study of the cracking mechanisms is therefore an

  18. A Probabilistic Mechanical Model for Simulating the Fatigue Failure Process in Metals

    Microsoft Academic Search

    Sidney A. Guralnick; Jamshid Mohammadi; Amy M. Kephart

    2011-01-01

    A model for simulating fatigue damage accumulation and the fatigue failure process in metals is presented. The simulation is achieved by modeling material behavior with a series of nonlinear mechanical springs with randomized behavior. With each applied stress, a certain number of springs rupture. The damage accumulation process is modeled by the number of springs that have ruptured during the

  19. Surface characteristics, reliability, and failure mechanisms of tin\\/lead, copper, and gold metallizations

    Microsoft Academic Search

    Johan Liu; Katrin Gustafsson; Zonghe Lai; Changhai Li

    1997-01-01

    In this paper, surface characteristics, microstructure, reliability and failure mechanisms of tin\\/lead, copper and gold metallizations for conductive adhesive joining have been studied. Electron spectroscopy for chemical analysis (ESCA) and Auger electron spectroscopy (AES) have been used to analyze Sn37Pb, copper and gold metallizations. The analyzes show that copper and nickel may be present as impurities on the gold plated

  20. Mechanisms of Dynamic Deformation and Failure in Ultra-High Molecular Weight Polyethylene Fiber-Polymer

    E-print Network

    Wadley, Haydn

    in the fiber direction is ~25 times greater than that of conventional steels, weak (van der Waals) bonds direction. This weak intermolecular strength also leads to creep deformation under prolonged loading properties and dynamic deformation and failure mechanisms during the ballistic impact of these UHMWPE

  1. Metal-glass based composites for application in TBC-systems

    Microsoft Academic Search

    D. E. Mack; R. Vaßen; D. Stöver; S. M. Gross

    2006-01-01

    A new type of thermal barrier coating (TBC) based on metal-glass composite (MGC) consisting of an ordinary container glass and a NiCoCrAlY-alloy has been recently presented. This TBC material provides the possibility to easily adjust its thermal expansion coefficient to match the substrate by changing the metal to glass ratio of the composite. Vacuum plasma spraying (VPS) has been applied

  2. Metal-glass based composites for application in TBC-systems

    Microsoft Academic Search

    D. E. Mack; R. Vaßen; D. Stöver; S. M. Gross

    2006-01-01

    A new type of thermal barrier coating (TBC) based on metal-glass composite (MGC) consisting of an ordinary container glass\\u000a and a NiCoCrAlY-alloy has been recently presented. This TBC material provides the possibility to easily adjust its thermal\\u000a expansion coefficient to match the substrate by changing the metal to glass ratio of the composite. Vacuum plasma spraying\\u000a (VPS) has been applied

  3. Investigation of static and cyclic bearing failure mechanisms for GR/EP laminates

    NASA Technical Reports Server (NTRS)

    Walter, R. W.; Tuttle, M. M.

    1992-01-01

    Static, cyclic load (fatigue), and residual strength testing of graphite-epoxy (GR/EP) and aluminum pin bearing joints was completed to study bearing failure mechanisms. Parameters investigated included static strength, failure mode, fatigue life, hole growth, joint stiffness, and residual strength. Comparative evaluation of these results show that the MIL-HDBK-5 convention for the definition of bearing strength can be used for GR/EP materials while maintaining the same, or improved, level of structural integrity shown for metal joints.

  4. 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 ballistic efficiency was improved by nearly 20% for a mere 2% increase in areal density. High-speed photography, flash radiography, microscopy and numerical simulations provide insight into the failure mechanisms.

  5. Investigation of static and cyclic bearing failure mechanisms for GR/EP laminates

    SciTech Connect

    Walter, R.W.; Tuttle, M.M.

    1992-09-01

    Static, cyclic load (fatigue), and residual strength testing of graphite-epoxy (GR/EP) and aluminum pin bearing joints was completed to study bearing failure mechanisms. Parameters investigated included static strength, failure mode, fatigue life, hole growth, joint stiffness, and residual strength. Comparative evaluation of these results show that the MIL-HDBK-5 convention for the definition of bearing strength can be used for GR/EP materials while maintaining the same, or improved, level of structural integrity shown for metal joints.

  6. Mechanisms-based failure laws for AS4\\/3502 graphite\\/epoxy laminates under in-plane biaxial compression

    Microsoft Academic Search

    Daniel Potter; Vijay Gupta; Xu Chen; Jun Tian

    2005-01-01

    Failure mechanisms and stress–strain behaviors have been investigated for [±30]12s and [±45]12s graphite-epoxy (AS4\\/3502) laminates under in-plane biaxial compression by using a cruciform biaxial test frame and microscopy of load-interrupted samples. The loading confinement ratio R was varied from 0.24 to nearly 1.0 to measure the sensitivity of sample failure mechanisms and stress–strain behavior to different stress states. Failure modes

  7. Epigenetic activation of a cryptic TBC1D16 transcript enhances melanoma progression by targeting EGFR.

    PubMed

    Vizoso, Miguel; Ferreira, Humberto J; Lopez-Serra, Paula; Carmona, F Javier; Martínez-Cardús, Anna; Girotti, Maria Romina; Villanueva, Alberto; Guil, Sonia; Moutinho, Catia; Liz, Julia; Portela, Anna; Heyn, Holger; Moran, Sebastian; Vidal, August; Martinez-Iniesta, Maria; Manzano, Jose L; Fernandez-Figueras, Maria Teresa; Elez, Elena; Muñoz-Couselo, Eva; Botella-Estrada, Rafael; Berrocal, Alfonso; Pontén, Fredrik; Oord, Joost van den; Gallagher, William M; Frederick, Dennie T; Flaherty, Keith T; McDermott, Ultan; Lorigan, Paul; Marais, Richard; Esteller, Manel

    2015-07-01

    Metastasis is responsible for most cancer-related deaths, and, among common tumor types, melanoma is one with great potential to metastasize. Here we study the contribution of epigenetic changes to the dissemination process by analyzing the changes that occur at the DNA methylation level between primary cancer cells and metastases. We found a hypomethylation event that reactivates a cryptic transcript of the Rab GTPase activating protein TBC1D16 (TBC1D16-47 kDa; referred to hereafter as TBC1D16-47KD) to be a characteristic feature of the metastatic cascade. This short isoform of TBC1D16 exacerbates melanoma growth and metastasis both in vitro and in vivo. By combining immunoprecipitation and mass spectrometry, we identified RAB5C as a new TBC1D16 target and showed that it regulates EGFR in melanoma cells. We also found that epigenetic reactivation of TBC1D16-47KD is associated with poor clinical outcome in melanoma, while conferring greater sensitivity to BRAF and MEK inhibitors. PMID:26030178

  8. Direct evidence of electromigration failure mechanism in dual-damascene Cu interconnect tree structures

    NASA Astrophysics Data System (ADS)

    Vairagar, A. V.; Mhaisalkar, S. G.; Meyer, M. A.; Zschech, E.; Krishnamoorthy, Ahila; Tu, K. N.; Gusak, A. M.

    2005-08-01

    In situ secondary electron microscope (SEM) characterizations were carried out to study electromigration failure mechanism in dual-damascene Cu interconnect tree structures, which are important for reliability assessment as well as design optimizations of on-chip interconnects. Direct evidence of electromigration-induced degradation in interconnect tree structure consisting of void nucleation and void movement in opposite direction to electron flow along the Cu /SiNx interface was unraveled. The peculiar electromigration behavior of Cu interconnect tree structures can be clearly understood based on this mechanism. Dependence of electromigration mechanism of a segment in a Cu interconnect tree on current configuration in neighboring interconnect segment is discussed in detail.

  9. Failure modes of complex materials with spatially-correlated mechanical properties - the critical role of internal damage

    NASA Astrophysics Data System (ADS)

    Faillettaz, Jérome; Or, Dani

    2014-05-01

    The study reports a systematic evaluation of the role of spatially correlated mechanical elements on failure behavior of heterogeneous materials represented by fiber bundle models (FBM) with different load redistribution rules. Results indicate that FBM failure mode varies dramatically with increasing correlation length and localized load sharing rules. Systems with similar composition of mechanical elements exhibit a dramatic transition from ductile and diffuse damage for global load sharing to brittle single failure for correlated and local load sharing. These changes in mechanical responses also affect the statistical properties of fiber failure avalanches (micro-cracks) activity preceding rupture and sought after in various early warning scenarios. While diffuse damage behavior exhibits clear precursory signals (such as increased seismic activity prior to global failure), brittle failure occurs abruptly with only few precursors. Although increasing spatial correlations of mechanical properties promotes abrupt ruptures at lower external load, this study identified an "universal" global failure criterion based on macroscopic properties which is independent of the rupture mode, load redistribution rules, or the spatial organization of mechanical properties. This metric that considers the combined role of external load and cumulative damage provides a means for evaluating imminence of failure of heterogeneous materials without resolving details of the heterogeneity. This study also provides new insights that are potentially useful for understanding landslide (but also snow avalanche or rockfall) triggering and points out the importance of spatial organization of heterogeneities on the failure behavior of complex geomaterials.

  10. 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.

  11. TBC1D5 and the AP2 complex regulate ATG9 trafficking and initiation of autophagy.

    PubMed

    Popovic, Doris; Dikic, Ivan

    2014-04-01

    The RabGAP protein TBC1D5 controls cellular endomembrane trafficking processes and binds the retromer subunit VPS29 and the ubiquitin-like protein ATG8 (LC3). Here, we describe that TBC1D5 also associates with ATG9 and the active ULK1 complex during autophagy. Moreover, ATG9 and TBC1D5 interact with clathrin and the AP2 complex. Depletion of TBC1D5 leads to missorting of ATG9 to late endosomes upon activation of autophagy, whereas inhibition of clathrin-mediated endocytosis or AP2 depletion alters ATG9 trafficking and its association with TBC1D5. Taken together, our data show that TBC1D5 and the AP2 complex are important novel regulators of the rerouting of ATG9-containing vesicular carriers toward sites of autophagosome formation. PMID:24603492

  12. TBC1D5 and the AP2 complex regulate ATG9 trafficking and initiation of autophagy

    PubMed Central

    Popovic, Doris; Dikic, Ivan

    2014-01-01

    The RabGAP protein TBC1D5 controls cellular endomembrane trafficking processes and binds the retromer subunit VPS29 and the ubiquitin-like protein ATG8 (LC3). Here, we describe that TBC1D5 also associates with ATG9 and the active ULK1 complex during autophagy. Moreover, ATG9 and TBC1D5 interact with clathrin and the AP2 complex. Depletion of TBC1D5 leads to missorting of ATG9 to late endosomes upon activation of autophagy, whereas inhibition of clathrin-mediated endocytosis or AP2 depletion alters ATG9 trafficking and its association with TBC1D5. Taken together, our data show that TBC1D5 and the AP2 complex are important novel regulators of the rerouting of ATG9-containing vesicular carriers toward sites of autophagosome formation. PMID:24603492

  13. Identifying the failure mechanism in accelerated life tests by two-parameter lognormal distributions

    NASA Astrophysics Data System (ADS)

    Chunsheng, Guo; Yanfeng, Zhang; Ning, Wan; Hui, Zhu; Shiwei, Feng

    2014-08-01

    The failure mechanism stimulated by accelerated stress in the degradation may be different from that under normal conditions, which would lead to invalid accelerated life tests. To solve the problem, we study the relation between the Arrhenius equation and the lognormal distribution in the degradation process. Two relationships of the lognormal distribution parameters must be satisfied in the conclusion of the unaltered failure mechanism, the first is that the logarithmic standard deviations must be equivalent at different temperature levels, and the second is that the ratio of the differences between logarithmic means must be equal to the ratio of the differences between reciprocals of temperature. The logarithm of distribution lines must simultaneously have the same slope and regular interval lines. We studied the degradation of thick-film resistors in MCM by accelerated stress at four temperature levels (390, 400, 410 and 420 K), and the result agreed well with our method.

  14. Mechanical characterization of damage and failure in polymeric foams and glass/epoxy composites

    NASA Astrophysics Data System (ADS)

    Kidd, Theresa Hiromi

    The mechanical characterization including evolution of damage and failure of foams and composites are becoming increasingly important, as they form the basic components of sandwich structures. Sandwich structures consist of two faceplates that surround a core material. In many modern applications, faceplates and cores are typically comprised of composite materials and polymeric foam, respectively. Knowledge of the failure behavior of these individual components is necessary for understanding the failure behavior and design of sandwich structures. A systematic investigation of the damage evolution and failure behavior of foams and composites was conducted using a variety of experimental techniques.In-situ ultrasonic measurements were used to track the damage behavior in PVC polymeric foams with densities ranging from 130 to 250 kg/m3. The wave speeds were measured by two quartz piezoelectric shear transducers with a resonant frequency of 5 MHz in the transmission mode. A fixture was developed and constructed to protect the transducers during compression, while allowing them to take sound speed measurements of the sample along the axis of the load train. This fixture was placed in a servo-hydraulic MTS (Materials Testing System) machine, where the load-displacement response of the foam was recorded. A digital image correlation (DIC) method was used to capture the progression of failure under compression. Two dominant failure modes, elastic buckling and plastic collapse, were identified - and their onsets corresponded to the change in elastic wave speeds in the material, measured by the in-situ ultrasonic technique.The transverse response of S-Glass/Epoxy unidirectional composites was investigated under varying degrees of confinement and strain rates. The experimental setup utilizes a fixture that allowed for independent measurement of the three principal stresses in a confined specimen. A servo-hydraulic materials testing system and a Kolsky (split Hopkinson) pressure bar generated strain rates between 10-3 to 104 s-1. Post-test scanning electron microscopy (SEM) observations suggest that under transverse loading at low-strain rates, confinement contributes to localized band formation. In addition, micrographs indicated that macroscopic transverse failure is dominated by shear stress, and occurs within these localized bands. These shear dominated failure bands were found inclined in a direction approximately 35 degrees to the direction of loading. Implications of this orientation deviation of failure bands from maximum shear trajectories at 45 degrees are discussed in reference to the state of confinement.

  15. Sealing Mechanism and Failure Analysis of Automotive Engine Crankshaft Oil Seal

    Microsoft Academic Search

    Aifang Yan; Qingping Yan

    2012-01-01

    There are many factors that lead to the failure of automotive engine crankshaft back oil seal, these factors include seal working condition, seal`s material quality and seal`s technical parameters that directly affect the seal`s seal ability and service life. Aiming at the leakage problem of automotive engine crankshaft oil seal and basing on analysis of drain pump seal mechanism, I

  16. Failure mechanism in an extremely slow rock slide at Bitchu-Matsuyama castle site (Japan)

    Microsoft Academic Search

    Vladimir Greif; Kyoji Sassa; Hiroshi Fukuoka

    2006-01-01

    One of the specific problems related to historical structures is the fact that they are prone to damage caused by even very\\u000a small deformations acting over a long period of time, such as creep or extremely small rock displacements. If any damage has\\u000a already occurred, the determination of the rock slope failure mechanism is one of the prerequisites for successful

  17. Effect of load type on failure mechanisms of spruce in compression parallel to grain

    Microsoft Academic Search

    M. Gong; I. Smith

    2004-01-01

    Failure mechanisms of small clear specimens (6×6×24 mm) of air-dried black spruce ( Picea mariana) under parallel-to-grain compression were investigated by polarised-light microscopy. Fatigue load was used with a peak stress level of 90% static strength, a load frequency of 0.5 Hz, and a square waveform with a duty ratio of 0.50. Matched ‘pure’ creep and static load tests were carried out.

  18. IMPERMEABLE THIN AL2O3 OVERLAY FOR TBC PROTECTION FROM SULFATE AND VANADATE ATTACK IN GAS TURBINES

    Microsoft Academic Search

    Scott X. Mao

    2002-01-01

    The project started on September 1, 2001. During last 4 months, one post-doctor has been hired for this project. We have received TBC samples (YSZ\\/CoNiCrAlY\\/ Inconel 601) from Tohoku University, Japan, while processing of the TBC samples was delayed in GE Corp. Research and Development. The TBC preparation in Japan was based on our technical requirement by plasma spray. Bond

  19. Non-destructive thermal barrier coating (TBC) damage assessment using laser-induced luminescence and infrared radiometry

    Microsoft Academic Search

    B. Heeg; D. R. Clarke

    2005-01-01

    A new non-destructive evaluation (NDE) approach for assessing damage in thermal barrier coating (TBC) systems is described. It is based on a combined measurement of the optical and thermal response due to photo-excitation, through the TBC, of Cr3+ ions within the thermally grown oxide (TGO). This method has subsurface selectivity to the TBC\\/TGO interface, as it is based on using

  20. Effect of thermal aging on microstructure, shear and mechanical shock failures for solder ball bonding joint

    Microsoft Academic Search

    Dewen Tian; Hongtao Chen; Chunqing Wang

    2005-01-01

    The interfacial microstructure evolution between Sn-3.5Ag-0.75Cu solder ball and Au\\/Ni\\/Cu pad was investigated under as-bonded and thermal aging conditions. Moreover, the shear and mechanical shock tests were carried out to study the failure mechanisms. Results showed that only one intermetallic compound, fine needle-like AuSn4 was found at the solder\\/pad interface under as-bonded condition. After aging, Ag3Sn appeared in the solder

  1. 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.

  2. Cardiac arrhythmia mechanisms in rats with heart failure induced by pulmonary hypertension

    PubMed Central

    Benoist, David; Stones, Rachel; Drinkhill, Mark J.; Benson, Alan P.; Yang, Zhaokang; Cassan, Cecile; Gilbert, Stephen H.; Saint, David A.; Cazorla, Olivier; Steele, Derek S.; Bernus, Olivier

    2012-01-01

    Pulmonary hypertension provokes right heart failure and arrhythmias. Better understanding of the mechanisms underlying these arrhythmias is needed to facilitate new therapeutic approaches for the hypertensive, failing right ventricle (RV). The aim of our study was to identify the mechanisms generating arrhythmias in a model of RV failure induced by pulmonary hypertension. Rats were injected with monocrotaline to induce either RV hypertrophy or failure or with saline (control). ECGs were measured in conscious, unrestrained animals by telemetry. In isolated hearts, electrical activity was measured by optical mapping and myofiber orientation by diffusion tensor-MRI. Sarcoplasmic reticular Ca2+ handling was studied in single myocytes. Compared with control animals, the T-wave of the ECG was prolonged and in three of seven heart failure animals, prominent T-wave alternans occurred. Discordant action potential (AP) alternans occurred in isolated failing hearts and Ca2+ transient alternans in failing myocytes. In failing hearts, AP duration and dispersion were increased; conduction velocity and AP restitution were steeper. The latter was intrinsic to failing single myocytes. Failing hearts had greater fiber angle disarray; this correlated with AP duration. Failing myocytes had reduced sarco(endo)plasmic reticular Ca2+-ATPase activity, increased sarcoplasmic reticular Ca2+-release fraction, and increased Ca2+ spark leak. In hypertrophied hearts and myocytes, dysfunctional adaptation had begun, but alternans did not develop. We conclude that increased electrical and structural heterogeneity and dysfunctional sarcoplasmic reticular Ca2+ handling increased the probability of alternans, a proarrhythmic predictor of sudden cardiac death. These mechanisms are potential therapeutic targets for the correction of arrhythmias in hypertensive, failing RVs. PMID:22427523

  3. [Home mechanical ventilation : Invasive and noninvasive ventilation therapy for chronic respiratory failure].

    PubMed

    Huttmann, S E; Storre, J H; Windisch, W

    2015-06-01

    Home mechanical ventilation represents a valuable therapeutic option to improve alveolar ventilation in patients with chronic respiratory failure. For this purpose both invasive ventilation via tracheostomy and noninvasive ventilation via facemasks are available. The primary goal of home mechanical ventilation is a reduction of symptoms, improvement of quality of life and in many cases reduction of mortality. Elective establishment of home mechanical ventilation is typically provided for noninvasive ventilation in respect to clinical symptoms and partial pressure of carbon dioxide depending on the underlying disease. However, invasive mechanical ventilation is increasingly being used to continue ventilatory support in polymorbid patients following unsuccessful weaning. Recommendations and guidelines have been published by the German Respiratory Society (DGP). PMID:26065554

  4. Service failure of hot-stage turbine blades: The role and mechanisms of oxidation ratcheting

    SciTech Connect

    Oldfield, W.; Oldfield, F.M. (MRCS Corp., St. Augustine, FL (United States))

    1993-10-01

    Surface-connected porosity in current military aircraft hot-stage turbine engine blades is associated with blade failure. Oxidation ratcheting is suggested as the failure mechanism. Statistical comparison of new and used blade populations showed that for blades cast with an equiaxed structure, the porosity in new blades was associated with crack formation on the concave surface of the used blades. The pores did not tend to develop into cracks on the compressed (convex) surface of the blade. Insufficient suitable data on directionally solidified blades prevented similar statistical correlations. However, metallography of the directionally solidified blades showed that the in-service cracks were related to oxidation inside surface-connected pores and that the cracks were oriented in the same direction as the (axial) casting pores. Thus, the proposed failure mechanism through ratcheting is based on the following insights: (1) the blades are thermally cycled as a normal part of service; (2) the hot blades expand and the open pores are filled with oxide; (3) when the blade is cooled, thermal contraction of the metal is greater than the oxide, causing compressive stress and yield-, and (4) thermal expansion of the blades opens the pores again, since yield relaxed compressive stress at low temperature. These insights were supported by metallographic and computer-simulation studies which showed that the pores grow 20 to 50 pct in width per 100 missions (about 90 hours of operation) for a military aircraft on a typical mission profile.

  5. 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.

  6. Bench-to-bedside review: Weaning failure – should we rest the respiratory muscles with controlled mechanical ventilation?

    Microsoft Academic Search

    Theodoros Vassilakopoulos; Spyros Zakynthinos; Charis Roussos

    2005-01-01

    The use of controlled mechanical ventilation (CMV) in patients who experience weaning failure after a spontaneous breathing trial or after extubation is a strategy based on the premise that respiratory muscle fatigue (requiring rest to recover) is the cause of weaning failure. Recent evidence, however, does not support the existence of low frequency fatigue (the type of fatigue that is

  7. Research on the Deformation Mechanism and Failure Behavior of Punch Bonding Technology with Dissimilar Sheet Metals

    NASA Astrophysics Data System (ADS)

    Li, Feng; Li, Jian Hui; Li, Chao; Wang, L. L.

    2012-05-01

    This article presents a study of the deformation mechanisms and failure behavior of punch bonding technology for dissimilar sheet metals. Using theoretical and numerical methods, the simulation of the punch bonding process is presented and the results show that to realize effective punch bonding, the sheets with higher elastic modulus and yield strength should be located at the punch side. It is also shown that when the boss height of the female die ( X 1) is too small, it is liable to induce excessive stress concentration under the punch blade, whereas when X 1 is too large, the embedded depth of the sheets and the bonding reliability decrease significantly. Punch bonding experiments were performed and the results showed that for the configuration tested an X 1 value of 10 mm was optimal for connection strength. The failure behavior of the punch bonding joint was joint cracking with smaller female die boss height and joint pull-off with larger female die boss height.

  8. 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.

  9. TBC1D24 mutation causes autosomal-dominant nonsyndromic hearing loss.

    PubMed

    Azaiez, Hela; Booth, Kevin T; Bu, Fengxiao; Huygen, Patrick; Shibata, Seiji B; Shearer, A Eliot; Kolbe, Diana; Meyer, Nicole; Black-Ziegelbein, E Ann; Smith, Richard J H

    2014-07-01

    Hereditary hearing loss is extremely heterogeneous. Over 70 genes have been identified to date, and with the advent of massively parallel sequencing, the pace of novel gene discovery has accelerated. In a family segregating progressive autosomal-dominant nonsyndromic hearing loss (NSHL), we used OtoSCOPE® to exclude mutations in known deafness genes and then performed segregation mapping and whole-exome sequencing to identify a unique variant, p.Ser178Leu, in TBC1D24 that segregates with the hearing loss phenotype. TBC1D24 encodes a GTPase-activating protein expressed in the cochlea. Ser178 is highly conserved across vertebrates and its change is predicted to be damaging. Other variants in TBC1D24 have been associated with a panoply of clinical symptoms including autosomal recessive NSHL, syndromic hearing impairment associated with onychodystrophy, osteodystrophy, mental retardation, and seizures (DOORS syndrome), and a wide range of epileptic disorders. PMID:24729539

  10. Laboratory and 3-D distinct element analysis of the failure mechanism of a slope under external surcharge

    NASA Astrophysics Data System (ADS)

    Li, N.; Cheng, Y. M.

    2015-01-01

    Landslide is a major disaster resulting in considerable loss of human lives and property damages in hilly terrain in Hong Kong, China and many other countries. The factor of safety and the critical slip surface for slope stabilization are the main considerations for slope stability analysis in the past, while the detailed post-failure conditions of the slopes have not been considered in sufficient detail. There is however increasing interest in the consequences after the initiation of failure that includes the development and propagation of the failure surfaces, the amount of failed mass and runoff and the affected region. To assess the development of slope failure in more detail and to consider the potential danger of slopes after failure has initiated, the slope stability problem under external surcharge is analyzed by the distinct element method (DEM) and a laboratory model test in the present research. A more refined study about the development of failure, microcosmic failure mechanisms and the post-failure mechanisms of slopes will be carried out. The numerical modeling method and the various findings from the present work can provide an alternate method of analysis of slope failure, which can give additional information not available from the classical methods of analysis.

  11. The application of fracture mechanics to failure analysis of photovoltaic solar modules

    NASA Technical Reports Server (NTRS)

    Chen, C. P.; Leipold, M. H.

    1981-01-01

    Cracking of silicon solar cells and solar module transparent cover panels such as glass or polymethylmethacrylate (PMMA) is a major cause of photovoltaic solar module failure in field service. Silicon and cover materials are brittle, and cracking of these materials is expected to result from the extension of preexisting flaws under stress. Study of the cracking mechanisms is therefore an appropriate area for the application of fracture mechanics principles. In this study, fracture mechanics techniques were employed to identify the mode of crack propagation, to examine the fracture-initiating flaw, to estimate the nature and magnitude of fracture stress in the field, and to predict analytically the service lifetime. Recommendations for corrective actions are also made.

  12. Methods And Systms For Analyzing The Degradation And Failure Of Mechanical Systems

    DOEpatents

    Jarrell, Donald B. (Kennewick, WA); Sisk, Daniel R. (Richland, WA); Hatley, Darrel D. (Kennewick, WA); Kirihara, Leslie J. (Richland, WA); Peters, Timothy J. (Richland, WA)

    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.

  13. Non-invasive mechanical ventilation in acute respiratory failure due to chronic obstructive pulmonary disease: correlates for success

    Microsoft Academic Search

    N Ambrosino; K Foglio; F Rubini; E Clini; S Nava; M Vitacca

    1995-01-01

    BACKGROUND--Non-invasive mechanical ventilation is increasingly used in the treatment of acute respiratory failure in patients with chronic obstructive pulmonary disease (COPD). The aim of this study was to identify simple parameters to predict the success of this technique. METHODS--Fifty nine episodes of acute respiratory failure in 47 patients with COPD treated with non-invasive mechanical ventilation were analysed, considering each one

  14. Expression, phosphorylation and function of the Rab-GTPase activating protein TBC1D1 in pancreatic beta-cells.

    PubMed

    Rütti, Sabine; Arous, Caroline; Nica, Alexandra C; Kanzaki, Makoto; Halban, Philippe A; Bouzakri, Karim

    2014-01-01

    The Rab-GTPase activating protein TBC1D1 is a paralog of AS160/TBC1D4. AS160/TBC1D4, a downstream effector of Akt, has been shown to play a central role in beta-cell function and survival. The two proteins have overlapping function in insulin signalling in muscle cells. However, the expression and the potential role of TBC1D1 in beta-cells remain unknown. Therefore, the aim of this study is to investigate whether TBC1D1 is expressed in beta-cells and whether it plays, as AS160/TBC1D4, a role in beta-cell function and survival. Using human and rat beta-cells, this study shows for the first time that TBC1D1 is expressed and phosphorylated in response to glucose in these cells. Knockdown of TBC1D1 in beta-cells resulted in increased basal and glucose-stimulated insulin release, decreased proliferation but no change in apoptosis. PMID:24239544

  15. Modeling the Deformation-Failure Mechanisms of Thin Hollow Glass Microspheres

    NASA Astrophysics Data System (ADS)

    Garza-Cruz, Tryana V.; Nakagawa, Masami

    2009-06-01

    Thin Hollow Glass Microspheres (HGMs) are a potential candidate to insulate cryogenic tanks due to their high strength-to-weight ratio and thermal properties. In this study, HGMs were modeled using a Discrete Element Method (DEM) to simulate their deformation and fracture behavior. Due to lack of actual data, a chemical composition-based methodology was introduced to synthesize material properties that reproduce the mechanical properties of soda-lime-borosilicate glass. The modeled microsphere was subjected to a uniaxial compression test and failed due to buckling. This model captures some essential aspect of deformation-failure characteristics of a thin hollow glass microsphere.

  16. 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.

  17. Mechanical Consequences of Molecular Composition on Failure in Polyolefin Composites Containing Glassy, Elastomeric, and Semicrystalline Components

    SciTech Connect

    Mahanthappa, Mahesh K.; Hillmyer, Marc A.; Bates, Frank S. (UMM)

    2008-10-24

    In order to gain insights into the mechanisms of deformation and ultimate failure in a homologous series of lamellae-forming polyolefin block copolymers comprised of glassy poly(cyclohexylethylene) (C), elastomeric poly(ethylene-alt-propylene) (P), and semicrystalline poly(ethylene) (E), the anisotropic tensile properties of samples in which the microphase separate structure is oriented on a macroscopic length scale were probed. Reciprocating shear processing of monodisperse CPCPC and CPEPC-{xi} polymers having mass fraction w{sub c} 0.39--0.44 and 0 {<=} {xi} {<=} 1, where {xi} = w{sub E}/(w{sub E} + w{sub P}), produces 'single-grain' polymer samples with perpendicular-oriented lamellae. Tensile deformation studies in which the strain axis coincides with the lamellar normal direction yield varied mechanical responses ranging from brittle fracture for CEC ({xi} = 0) to ductile behavior for CPEPC ({xi} > 0) and CPCPC. Tandem small- and wide-angle X-ray scattering analysis of samples undergoing deformation shows that application of strain along the lamellar normal in the CPEPC materials results in formation of a folded lamellar structure or 'chevron' morpohology within which the E crystals cant relative to the strain direction. Since the ultimate failure mechanism for materials strained in this direction is chain pullout in the glassy domains, a simple mechanical model applied to the data enables quantitation of the stress required for chain pullout at {approx}4 MPa. Additionally, the mechanical properties of miscible blends of CEC and CPC polymers with matched segregation strengths are shown to mimic those of the covalently linked CPEPC pentablock copolymer.

  18. Manipulating failure mechanism of rapid prototyped scaffolds by changing nodal connectivity and geometry of the pores.

    PubMed

    Amirkhani, Soodeh; Bagheri, Reza; Zehtab Yazdi, Alireza

    2012-11-15

    The performance of cellular solids in biomedical applications relies strongly on a detailed understanding of the effects of pore topology on mechanical properties. This study aims at characterizing the failure mechanism of scaffolds based on nodal connectivity (number of struts that meet in joints) and geometry of the pores. Plastic models of scaffolds having the same relative density but different cubic and trigonal unit cells were designed and then fabricated via three dimensional (3-D) printing. Unit cells were repeated in different arrangements in 3-D space. An in-situ imaging technique was utilized to study the progressive deformation of the scaffold models. Different nodal connectivities resulted in a wide range of compressive behaviors in scaffold models, from elastic-plastic to fully brittle. The Maxwell necessary criterion for rigidity was used to explain mechanical behavior of the scaffolds. Nodal connectivity of 4 satisfied Maxwell's criterion for rigidity in the examined structures. In a stress-strain curve of scaffolds with cubic unit cells and nodal connectivities of 3 and 4, pore deformation was observed after yielding. On the other hand, scaffolds with trigonal unit cells and nodal connectivities of 4 and 6, exhibited brittle behavior in the absence of pore deformation. These results highlight the role of nodal connectivity on failure mechanism and subsequently mechanical performance of scaffolds. This study reveals that appropriate pore geometry can provide sufficient condition for rigidity when Maxwell's necessary condition is satisfied. In addition, this study demonstrates that Maxwell's criterion can be used in pre-designing of pore geometries for scaffolds with distinct nodal connectivities. PMID:22985476

  19. Reproduction of FRP Blade Failure for Wind Power Generators by Lightning and its Mechanism

    NASA Astrophysics Data System (ADS)

    Sakamoto, Haruo; Hanai, Masahiro

    In Japan, lightning damage to FRP blades for wind power generators is increasing, together with the increase in wind power generator installation in recent years. Lightning damage is a big issue in Japan since lightning in Japan seems to be severer than in Europe and the US. In Kochi, Shikoku, Japan, six 600-750kW grade generators have been installed, and some of them have been damaged by lightning several times. In order to solve this issue, the Kochi University of Technology received a research request of lightning protection, sponsored by the Kochi prefecture in 2002. After surveying the literature and questioning related organizations such as NREL (National Renewable Energy Laboratories) and Toray USA, experiments to reproduce lightning damage to FRP specimens were planned. The specimens prepared for this research are 1/2 size models and a 2/4 part of the full size blade. In the previous experiment, flat plate specimens of 450mm width × 2.5m length × 4mm thickness were used, and the experiments produced the damage by lightning. However, the damages were not exactly the same as the ones in the actual field. Therefore, this experiment aims to reproduce the blade failure in the actual field and to clarify the failure mechanism, using the 1/2 size blade model and full size blade specimens. The experiments were conducted mainly in the Toshiba Hamakawasaki High Voltage High Power Testing Laboratory as was made in the previous experiments. This Testing Laboratory is one of the biggest test laboratory for experiments involving high electric voltage and large current. The results showed the reproduction of the failed blades in fields, and clarified the failure mechanism.

  20. The progressive cardiorenal syndrome in heart failure: mechanisms and therapeutic insights.

    PubMed

    Brown, Jennifer R; Uber, Patricia A; Mehra, Mandeep R

    2008-08-01

    The cardiorenal syndrome refers to the interdependence of cardiocirculatory aberrations and renal dysfunction that signify a worsening in heart failure outcome. Biochemically, it appears covertly as an abnormality in renal function and when progressive, is manifested by symptom exacerbation and worsening renal impairment during application of therapy to ameliorate such symptoms. The pathways leading to these distinct impairments involve not only hemodynamic deterioration but also neurohormonal, inflammatory, and intrinsic renal mechanisms that produce this syndrome. Traditional therapy with diuretics typically worsens the cardiorenal syndrome, and vasodilator or inotropic therapy has not been shown to help either. New therapeutic avenues involving vasopressin antagonists, adenosine antagonists, and ultrafiltration are being investigated. In the absence of underlying primary renal parenchymal disease, mechanical ventricular assist devices or cardiac transplantation achieve reversal of the progressive cardiorenal syndrome, indicating the sentinel role of interrupting the cardiocirculatory aberrations that accompany this clinical manifestation. PMID:18647589

  1. 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.

  2. Blood markers of oxidative stress predict weaning failure from mechanical ventilation

    PubMed Central

    Verona, Cléber; Hackenhaar, Fernanda S; Teixeira, Cassiano; Medeiros, Tássia M; Alabarse, Paulo V; Salomon, Tiago B; Shüller, Ártur K; Maccari, Juçara G; Condessa, Robledo Leal; Oliveira, Roselaine P; Rios Vieira, Silvia R; Benfato, Mara S

    2015-01-01

    Patients undergoing mechanical ventilation (MV) often experience respiratory muscle dysfunction, which complicates the weaning process. There is no simple means to predict or diagnose respiratory muscle dysfunction because diagnosis depends on measurements in muscle diaphragmatic fibre. As oxidative stress is a key mechanism contributing to MV-induced respiratory muscle dysfunction, the aim of this study was to determine if differences in blood measures of oxidative stress in patients who had success and failure in a spontaneous breathing trial (SBT) could be used to predict the outcome of MV. This was a prospective analysis of MV-dependent patients (?72 hrs; n = 34) undergoing a standard weaning protocol. Clinical, laboratory and oxidative stress analyses were performed. Measurements were made on blood samples taken at three time-points: immediately before the trial, 30 min. into the trial in weaning success (WS) patients, or immediately before return to MV in weaning failure (WF) patients, and 6 hrs after the trial. We found that blood measures of oxidative stress distinguished patients who would experience WF from patients who would experience WS. Before SBT, WF patients presented higher oxidative damage in lipids and higher antioxidant levels and decreased nitric oxide concentrations. The observed differences in measures between WF and WS patients persisted throughout and after the weaning trial. In conclusion, WF may be predicted based on higher malondialdehyde, higher vitamin C and lower nitric oxide concentration in plasma. PMID:25854285

  3. Mechanical response and failure of High Performance Propellant (HPP) subject to uniaxial tension

    NASA Astrophysics Data System (ADS)

    Liu, C.; Thompson, D. G.

    2015-05-01

    As part of a program to characterize and understand the mechanical response and failure behavior of the High Performance Propellant (HPP), uniaxial tensile tests were conducted. The mechanical properties of the HPP solid propellant subject to tension are investigated as a function of both the loading (strain) rate and the temperature. The nominal strain rate varies from 10-6 to 10-2 s-1 and the temperature varies from -50 to 50 °C. Digital image correlation (DIC) technique was used to obtain the full field deformation measurement over the sample surface, from which both the axial strain and the circumferential strain were determined, and as a result, volume changes during the uniaxial tension were studied. Some of the material parameters, e.g., Young's modulus E, the tensile strength ? max, and uniaxial tensile strain at the maximum tensile stress ? max, were found to be extremely sensitive to both the strain rate and the temperature. It was also observed that during the linear portion of the uniaxial tension, the HPP is close to incompressible. But when deformation enters the nonlinear regime, volume change of the sample accelerates and such a significant volume increase during the nonlinear portion of the deformation can be attributed to the formation and extension of damage within the gage section, which lead to the macroscopic tearing failure of the material.

  4. Two-source jumping beam evaporation for advanced EB-PVD TBC systems

    Microsoft Academic Search

    U. Schulz; K. Fritscher; C. Leyens

    2000-01-01

    The continuous increase of the turbine inlet temperature in gas turbines necessitates new TBCs with a temperature capability beyond the current partially yttria stabilized material coatings. The present paper focuses on two-source jumping EB-PVD processed novel candidate layers for future TBC applications. It is shown that mixtures of oxides with widely different vapor pressures can be manufactured by this technique.

  5. The Oxidation Behavior of TBC with Cold Spray CoNiCrAlY Bond Coat

    Microsoft Academic Search

    W. R. Chen; E. Irissou; X. Wu; J.-G. Legoux; B. R. Marple

    2011-01-01

    Cold gas dynamic spray (CGDS) has been considered a potential technique to produce the metallic bond coat for TBC applications, because of its fast deposition rate and low deposition temperature. This article presents the influence of spray processes for bond coat, including air plasma spray, high velocity oxy-fuel, and in particular CGDS, on the oxidation performance of TBCs with a

  6. 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.

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

    PubMed

    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

  8. Crystal Structures of Human TBC1D1 and TBC1D4 (AS160) RabGTPase-activating Protein (RabGAP) Domains Reveal Critical Elements for GLUT4 Translocation

    SciTech Connect

    S Park; W Jin; S Shoelson

    2011-12-31

    We have solved the x-ray crystal structures of the RabGAP domains of human TBC1D1 and human TBC1D4 (AS160), at 2.2 and 3.5 {angstrom} resolution, respectively. Like the yeast Gyp1p RabGAP domain, whose structure was solved previously in complex with mouse Rab33B, the human TBC1D1 and TBC1D4 domains both have 16 {alpha}-helices and no {beta}-sheet elements. We expected the yeast Gyp1p RabGAP/mouse Rab33B structure to predict the corresponding interfaces between cognate mammalian RabGAPs and Rabs, but found that residues were poorly conserved. We further tested the relevance of this model by Ala-scanning mutagenesis, but only one of five substitutions within the inferred binding site of the TBC1D1 RabGAP significantly perturbed catalytic efficiency. In addition, substitution of TBC1D1 residues with corresponding residues from Gyp1p did not enhance catalytic efficiency. We hypothesized that biologically relevant RabGAP/Rab partners utilize additional contacts not described in the yeast Gyp1p/mouse Rab33B structure, which we predicted using our two new human TBC1D1 and TBC1D4 structures. Ala substitution of TBC1D1 Met{sup 930}, corresponding to a residue outside of the Gyp1p/Rab33B contact, substantially reduced catalytic activity. GLUT4 translocation assays confirmed the biological relevance of our findings. Substitutions with lowest RabGAP activity, including catalytically dead RK and Met{sup 930} and Leu{sup 1019} predicted to perturb Rab binding, confirmed that biological activity requires contacts between cognate RabGAPs and Rabs beyond those in the yeast Gyp1p RabGAP/mouse Rab33B structure.

  9. Compariso of two different modes for noninvasive mechanical ventilation in chronic respiratory failure: volume versus pressure controlled device

    Microsoft Academic Search

    B. Schönhofer; M. Sonneborn; P. Haidl; H. Böhrer; D. Köhler

    1997-01-01

    Comparison of two different modes for noninvasive mechanical ventilation in chronic respiratory failure: volume versus pressure controlled device. B. Schönhofer, M. Sonneborn, P. Haidl, H. Böhrer, D. Köhler. ©ERS Journals Ltd 1997. ABSTRACT: The most commonly used mode of noninvasive mechanical ventila- tion (NMV) is volume-controlled intermittent positive pressure ventilation (IPPV). Pressure support ventilation has recently become increasingly popular, but

  10. Finite element analysis of the failure mechanism of gentle slopes in weak disturbed clays

    NASA Astrophysics Data System (ADS)

    Lollino, Piernicola; Mezzina, Giuseppe; Cotecchia, Federica

    2014-05-01

    Italian south-eastern Apennines are affected by a large number of deep slow active landslide processes that interact with urban structures and infrastructures throughout the region, thus causing damages and economic losses. For most landslide processes in the region, the main predisposing factors for instability are represented by the piezometric regime and the extremely poor mechanical properties of the weak disturbed clays in the lower and central portions of the slopes that are overlaid in some cases by a stiffer cap layer, formed of rocky flysch, e.g. alternations of rock and soil strata. Based on phenomenological approaches, landslide processes are deemed to be triggered within the weaker clay layer and later on to develop upward to the stiffer cap, with the shear bands reaching also high depths. The paper presents the results of two-dimensional numerical analyses of the failure mechanisms developing in the unstable slopes of the region, carried out by means of the finite element method (Plaxis 2011) applied to slope conditions representative for the region. In particular, the effects of slope inclination, along with the thickness and the strength of the material forming the caprock at the top of the slope, on the depth of the sliding surface, the mobilised strengths, the evolution of the landslide process and the predisposing factors of landsliding have been explored by means of the finite element analysis of an ideal case study representative of the typical geomechanical context of the region. In particular, the increase of slope inclination is shown to raise the depth of the shear band as well as to extend landslide scarp upwards, in accordance with the field evidence. Moreover, the numerical results indicate how the increase of the caprock thickness tends to confine the development of the shear band to the underlying weaker clay layer, so that the depth of the shear band is also observed to reduce, and when the stiffer top stratum becomes involved in the retrogression of the failure process. The numerical results allow also for the investigation of the variation in seepage conditions that combine with the variations in litostratigraphy in determining the variations of the features of the failure mechanism.

  11. Mechanics-based statistics of failure risk of quasibrittle structures and size effect on safety factors.

    PubMed

    Bazant, Zden?k P; Pang, Sze-Dai

    2006-06-20

    In mechanical design as well as protection from various natural hazards, one must ensure an extremely low failure probability such as 10(-6). How to achieve that goal is adequately understood only for the limiting cases of brittle or ductile structures. Here we present a theory to do that for the transitional class of quasibrittle structures, having brittle constituents and characterized by nonnegligible size of material inhomogeneities. We show that the probability distribution of strength of the representative volume element of material is governed by the Maxwell-Boltzmann distribution of atomic energies and the stress dependence of activation energy barriers; that it is statistically modeled by a hierarchy of series and parallel couplings; and that it consists of a broad Gaussian core having a grafted far-left power-law tail with zero threshold and amplitude depending on temperature and load duration. With increasing structure size, the Gaussian core shrinks and Weibull tail expands according to the weakest-link model for a finite chain of representative volume elements. The model captures experimentally observed deviations of the strength distribution from Weibull distribution and of the mean strength scaling law from a power law. These deviations can be exploited for verification and calibration. The proposed theory will increase the safety of concrete structures, composite parts of aircraft or ships, microelectronic components, microelectromechanical systems, prosthetic devices, etc. It also will improve protection against hazards such as landslides, avalanches, ice breaks, and rock or soil failures. PMID:16769888

  12. CO boiler reliability: examination of failure mechanisms, root causes, corrective actions and monitoring required

    SciTech Connect

    Mort, T.; Rogers, M.E.; Skinner, B.; Parson, R. [Syncrude Canada Ltd., Fort McMurray, Alberta (Canada)

    1995-12-01

    The waste gas streams from upgrading processes pass as primary energy sources to two CO boilers. As Upgrading feed rates have increased, the volume flow rate, and properties of the streams have changed to such extent that the boilers have suffered severe reliability problems due to the new, and adverse fireside conditions. Heat flux rates have increased in critical sections of the boiler with consequent disruption in thermal hydraulic flow in water and steam circuits. Departure from nucleate boiling (DNB) and steam blanketing in generating bank tubes have resulted, causing treatment chemicals to precipitate, deposit, and react on the internal surfaces of the water wall tubes. This paper discusses the use of computational fluid dynamic simulation and other techniques to assess water and fireside conditions for the original, current, and future operating conditions (prior to and post boiler design modifications). The engineered changes required to correct the combustion and thermal hydraulic problems are described, as well as the rationale for introducing equilibrium phosphate treatment as the boiler water chemistry control corrective action. Micro-Raman spectroscopy was used for the first time to confirm the presence of maricite when investigating the root cause of generating bank tube failures. Maricite is one of the definitive corrosion products resulting from acid phosphate corrosion. The paper also discusses the use of the latest Electrical Power Research Institute guidelines for failure mechanism identification in boiler tubes and for monitoring cycle chemistry.

  13. TBC1D9B functions as a GTPase-activating protein for Rab11a in polarized MDCK cells

    PubMed Central

    Gallo, Luciana I.; Liao, Yong; Ruiz, Wily G.; Clayton, Dennis R.; Li, Min; Liu, Yong-Jian; Jiang, Yu; Fukuda, Mitsunori; Apodaca, Gerard; Yin, Xiao-Ming

    2014-01-01

    Rab11a is a key modulator of vesicular trafficking processes, but there is limited information about the guanine nucleotide-exchange factors and GTPase-activating proteins (GAPs) that regulate its GTP-GDP cycle. We observed that in the presence of Mg2+ (2.5 mM), TBC1D9B interacted via its Tre2-Bub2-Cdc16 (TBC) domain with Rab11a, Rab11b, and Rab4a in a nucleotide-dependent manner. However, only Rab11a was a substrate for TBC1D9B-stimulated GTP hydrolysis. At limiting Mg2+ concentrations (<0.5 mM), Rab8a was an additional substrate for this GAP. In polarized Madin–Darby canine kidney cells, endogenous TBC1D9B colocalized with Rab11a-positive recycling endosomes but less so with EEA1-positive early endosomes, transferrin-positive recycling endosomes, or late endosomes. Overexpression of TBC1D9B, but not an inactive mutant, decreased the rate of basolateral-to-apical IgA transcytosis—a Rab11a-dependent pathway—and shRNA-mediated depletion of TBC1D9B increased the rate of this process. In contrast, TBC1D9B had no effect on two Rab11a-independent pathways—basolateral recycling of the transferrin receptor or degradation of the epidermal growth factor receptor. Finally, expression of TBC1D9B decreased the amount of active Rab11a in the cell and concomitantly disrupted the interaction between Rab11a and its effector, Sec15A. We conclude that TBC1D9B is a Rab11a GAP that regulates basolateral-to-apical transcytosis in polarized MDCK cells. PMID:25232007

  14. Linking Seismicity at Depth to the Mechanics of a Lava Dome Failure - a Forecasting Approach

    NASA Astrophysics Data System (ADS)

    Salvage, R. O.; Neuberg, J. W.; Murphy, W.

    2014-12-01

    Soufriere Hills volcano (SHV), Montserrat has been in a state of ongoing unrest since 1995. Prior to eruptions, an increase in the number of seismic events has been observed. We use the Material Failure Law (MFL) (Voight, 1988) to investigate how an accelerating number of low frequency seismic events are related to the timing of a large scale dome collapse in June 1997. We show that although the forecasted timing of a dome collapse may coincide with the known timing, the accuracy of the application of the MFL to the data is poor. Using a cross correlation technique we show how characterising seismicity into similar waveform "families'' allows us to focus on a single process at depth and improve the reliability of our forecast. A number of families are investigated to assess their relative importance. We show that despite the timing of a forecasted dome collapse ranging between several hours of the known timing of collapse, each of the families produces a better forecast in terms of fit to the seismic acceleration data than when using all low frequency seismicity. In addition, we investigate the stability of such families between major dome collapses (1997 and 2003), assessing their potential for use in real-time forecasting. Initial application of Grey's Incidence Analysis suggests that a key parameter influencing the potential for a large scale slumping on the dome of SHV is the rate of low frequency seismicity associated with magma movement and dome growth. We undertook numerical modelling of an andesitic dome with a hydrothermally altered layer down to 800m. The geometry of the dome is based on SHV prior to the collapse of 2003. We show that a critical instability is reached once slope angles exceed 25°, corresponding to a summit height of just over 1100m a.s.l.. The geometry of failure is in close agreement with the identified failure plane suggesting that the input mechanical properties are broadly consistent with reality. We are therefore able to compare different failure geometries based on edifice geomorphology and determine a Factor of Safety associated with such scenarios. This modelling would be extremely useful in a holistic forecasting approach within a volcanic environment. Reference: Voight, B. (1988). A method for prediction of volcanic eruptions. Nature, 332: 125-130.

  15. Pressure-Sensitive Adhesives under the Influence of Relative Humidity: Inner Structure and Failure Mechanisms.

    PubMed

    Schindler, Markus; Koller, Manuel; Müller-Buschbaum, Peter

    2015-06-17

    Model pressure-sensitive adhesive (PSA) films of the statistical copolymer P(EHA-stat-20MMA), which comprises 80% ethylhexyl acrylate (EHA) and 20% methyl methacrylate (MMA), are studied. The PSA films are stored under different relative humidities from <2% to 96% for 24 h and subsequently investigated concerning the near-surface composition profile by measuring X-ray reflectivity (XRR) and tack performance. For both types of measurements, special custom-made sample environments are used, which ensure constant temperature and relative humidity during the XRR and tack measurements. Different failure mechanisms of the adhesive bond are found by adjusting the relative humidity. XRR measurements evidence enrichment layers in vicinity to and at the surface depending on the provided relative humidity during the postproduction treatment, which also influence the tack performance. This finding is supported by tack measurements using punches with different roughness. PMID:25396744

  16. Characterization of the fatigue failure mechanisms in austenitic and high nitrogen austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Roach, Michael David

    The aim of this study was to compare the properties of an implant grade 21Cr-23Mn-1N nitrogen-stabilized stainless (HNS) steel, to 316L and 22Cr-13Ni-5Mn stainless steels with a long history of implant use. The HNS steel showed excellent tensile, corrosion, and corrosion fatigue properties. However, the fracture surfaces of the notched tensile, notched stress corrosion cracking (SCC), smooth corrosion fatigue, and notched corrosion fatigue samples in the HNS steel showed a mixed-mode fracture consisting of areas of brittle facets intermingled with typical ductile features. Mixed-mode fractures were not exhibited in the other two nickel-stabilized stainless steel alloys. Since a substantial number of implant failures occur due to fatigue, the differences shown in fatigue fracture morphology for the HNS steel were of particular interest. It was hypothesized that the fatigue crack initiation and/or propagation mechanisms may be different for the HNS steel, and lead to the unusual fracture morphologies shown for the austenitic material. The current research set out to test this hypothesis, and compare the fatigue crack initiation and propagation mechanisms of 21Cr-23Mn-1N and 316L cold-worked implant grade steels. Electron backscattered diffraction (EBSD) techniques were used to analyze representative areas of the microstructure on the free surface of fatigue samples. Both low-cycle and high-cycle fatigue loading conditions were evaluated over a series of fatigue intervals for each alloy. Atomic Force Microscopy (AFM) was also employed in order to determine the surface topography on the nanometer scale associated with representative surface deformation features. In addition the fracture surfaces of selected fatigue samples were examined using scanning electron microscopy (SEM) failure analysis techniques. The EBSD crack initiation and propagation data were associated with fracture morphology features shown in the SEM analysis. Results from the EBSD analysis revealed former annealing twin boundaries to be a strongly preferred location for fatigue crack initiation in the 21Cr-23Mn-1N HNS alloy. Crack propagation was shown to typically follow a transcrystalline direction. Analysis of selected extended fatigue cracks suggested a mechanism involving preferential initiation along former annealing twin and grain boundaries followed by transcrystalline crack propagation to interconnect the previously initiated cracks. SEM failure analysis of the HNS alloy showed a large number of facets in the crack initiation regions of the fatigue fractures. The large number of brittle facets in the initiation region of the fatigue fracture surface agrees well with the preferential former annealing twin boundary crack initiation location shown in the EBSD analysis. In Contrast, EBSD analysis of the 316L alloy showed transgranular slip markings along {111} planes to be the strongly preferred location for fatigue crack initiation. Crack propagation was also shown to typically follow a transcrystalline direction in this alloy. Analysis of selected extended fatigue cracks suggested a mechanism of preferential initiation along slip markings followed by transcrystalline crack propagation to interconnect the previously initiated cracks. SEM failure analysis of the 316L alloy showed relatively few facets, which also supported the EBSD results showing a preference for transgranular slip marking crack initiation. AFM analysis revealed small extrusions due to dislocation pile-up along slip markings shown on the fatigue sample free surfaces of both alloys. The reduced heights of the extrusions compared to those shown previous studies on annealed alloys, was attributed to the degree of cold-working already present in the material prior to fatigue testing. In conclusion, EBSD analysis revealed the preferential location of fatigue crack initiation for the two alloys to be very different. These differences in fatigue crack initiation locations explain the differences shown in fracture morphologies in the two alloy systems. Also the addition of EBSD and AFM analys

  17. 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.

  18. Evaluation of SRV pipe-failure rates via probabilistic mechanical design

    Microsoft Academic Search

    J. R. Lehner; C. Economos

    1983-01-01

    For a risk assessment analysis of the postulated failure of the vapor suppression system in Mark I and Mark II containments during anticipated transients a pipe failure rate for safety relief valve (SRV) piping located in the wetwell air space of the containment was needed. The stress-strength overlap method was chosen to predict this failure rate. In this method the

  19. Failure of Mineralized Collagen Microfibrils Using Finite Element Simulation Coupled to Mechanical Quasi-brittle Damage

    E-print Network

    Barkaoui, Abdelwahed; Hambli, Ridha; 10.1016/j.proeng.2011.04.526

    2011-01-01

    Bone is a multiscale heterogeneous materiel of which principal function is to support the body structure and to resist mechanical loading and fractures. Bone strength does not depend only on the quantity and quality of bone which is characterized by the geometry and the shape of bones but also on the mechanical proprieties of its compounds, which have a significant influence on its deformation and failure. This work aim to use a 3D nano-scale finite element model coupled to the concept of quasi-brittle damage with the behaviour law isotropic elasticity to investigate the fracture behaviour of composite materiel collagen-mineral (mineralized collagen microfibril). Fracture stress-number of cross-links and damping capacity-number of cross-links curves were obtained under tensile loading conditions at different densities of the mineral phase. The obtained results show that number of cross-links as well as the density of mineral has an important influence on the strength of microfibrils which in turn clarify the ...

  20. 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 to coating better and a ductile and adhesive interface layer can delay the cracked coating from peeled-off.

  1. 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

  2. Mechanical Failure Begins Preferentially Near Resorption Cavities in Human Vertebral Cancellous Bone Under Compression

    PubMed Central

    Slyfield, C.R.; Tkachenko, E.V.; Fischer, S.E.; Ehlert, K.M.; Yi, I. H.; Jekir, M. G.; O’Brien, R. G.; Keaveny, T.M.; Hernandez, C.J.

    2012-01-01

    Summary The amount of bone turnover in the body has been implicated as a factor that can influence fracture risk and bone strength. Here we test the idea that remodeling cavities promote local tissue failure by determining if microscopic tissue damage (microdamage) caused by controlled loading in vitro is more likely to form near resorption cavities. Specimens of human vertebral cancellous bone (L4, 7 male and 2 female, age 70 ± 10, mean ± SD) were loaded in compression to the yield point, stained for microscopic tissue damage and submitted to three-dimensional fluorescent imaging using serial milling (image voxel size 0.7 × 0.7 × 5.0 µm). We found the resulting damage volume per bone volume (DV/BV) was correlated with percent eroded surface (p < 0.01, r2 = 0.65), demonstrating that whole specimen measures of resorption cavities and microdamage are related. Locations of microdamage were more than two times as likely to have a neighboring resorption cavity than randomly selected sites without microdamage (relative risk 2.39, 95% confidence interval of relative risk: 2.09 – 2.73), indicating a spatial association between resorption cavities and microdamage at the local level. Individual microdamage sites were 48,700 (40,100; 62,700) µm3 in size (median, 25th and 75th percentiles). That microdamage was associated with resorption cavities when measured at the whole specimen level as well as at the local level provides strong evidence that resorption cavities play a role in mechanical failure processes of cancellous bone and therefore have the potential to influence resistance to clinical fracture. PMID:22426306

  3. Characterization of rupture and fatigue resistance of TBC superalloy for combustion liners

    Microsoft Academic Search

    A. K. Ray; D. K. Das; B. Venkataraman; P. K. Roy; B. Goswami; N. Roy; S. K. Das; N. Parida; S. Tarafder; S. Chaudhuri; S. K. Sahay; R. N. Ghosh

    2005-01-01

    High-temperature, high-cycle fatigue and accelerated creep properties of thermal barrier coated (TBC) Superni C263 alloy used as a candidate material in combustor liners of aero engines are highlighted in this paper. An acoustic emission technique has been utilised to detect the ductile–brittle transition temperature of the bond coat. Results revealed that the ductile-to-brittle transition temperature (DBTT) of this bond coat

  4. TBC1D24, an ARF6-Interacting Protein, Is Mutated in Familial Infantile Myoclonic Epilepsy

    PubMed Central

    Falace, Antonio; Filipello, Fabia; La Padula, Veronica; Vanni, Nicola; Madia, Francesca; De Pietri Tonelli, Davide; de Falco, Fabrizio A.; Striano, Pasquale; Dagna Bricarelli, Franca; Minetti, Carlo; Benfenati, Fabio; Fassio, Anna; Zara, Federico

    2010-01-01

    Idiopathic epilepsies (IEs) are a group of disorders characterized by recurrent seizures in the absence of detectable brain lesions or metabolic abnormalities. IEs include common disorders with a complex mode of inheritance and rare Mendelian traits suggesting the occurrence of several alleles with variable penetrance. We previously described a large family with a recessive form of idiopathic epilepsy, named familial infantile myoclonic epilepsy (FIME), and mapped the disease locus on chromosome 16p13.3 by linkage analysis. In the present study, we found that two compound heterozygous missense mutations (D147H and A509V) in TBC1D24, a gene of unknown function, are responsible for FIME. In situ hybridization analysis revealed that Tbc1d24 is mainly expressed at the level of the cerebral cortex and the hippocampus. By coimmunoprecipitation assay we found that TBC1D24 binds ARF6, a Ras-related family of small GTPases regulating exo-endocytosis dynamics. The main recognized function of ARF6 in the nervous system is the regulation of dendritic branching, spine formation, and axonal extension. TBC1D24 overexpression resulted in a significant increase in neurite length and arborization and the FIME mutations significantly reverted this phenotype. In this study we identified a gene mutation involved in autosomal-recessive idiopathic epilepsy, unveiled the involvement of ARF6-dependent molecular pathway in brain hyperexcitability and seizures, and confirmed the emerging role of subtle cytoarchitectural alterations in the etiology of this group of common epileptic disorders. PMID:20727515

  5. Proto-TGO formation in TBC systems fabricated by spark plasma sintering

    Microsoft Academic Search

    Mathieu Boidot; Serge Selezneff; Daniel Monceau; Djar Oquab; Claude Estournès

    2010-01-01

    Thermal barrier coatings (TBC) are commonly used in modern gas turbines for aeronautic and energy production applications. The conventional methods to fabricate such TBCs are EB-PVD or plasma spray deposition. Recently, the spark plasma sintering (SPS) technique was used to prepare new multilayered coatings. In this study, complete thermal barrier systems were fabricated on single crystal Ni-based superalloy (AM1®) substrate

  6. Criteria of microstructural assessment of the conventional and new TBC layers

    Microsoft Academic Search

    G. Moskal

    Purpose: The purpose of this paper is to present principles and criteria of microstructural assessment of thermal barrier coatings (TBCs). The conventional layers are described in expert papers, whereas there is no literature on new type of thermal barrier coatings on the basis of RE2Zr2O7 compounds Design\\/methodology\\/approach: The study was carried out on the TBC layers, sprayed by using the

  7. The Oxidation Behavior of TBC with Cold Spray CoNiCrAlY Bond Coat

    Microsoft Academic Search

    W. R. Chen; E. Irissou; X. Wu; J.-G. Legoux; B. R. Marple

    2011-01-01

    Cold gas dynamic spray (CGDS) has been considered a potential technique to produce the metallic bond coat for TBC applications,\\u000a because of its fast deposition rate and low deposition temperature. This article presents the influence of spray processes\\u000a for bond coat, including air plasma spray, high velocity oxy-fuel, and in particular CGDS, on the oxidation performance of\\u000a TBCs with a

  8. The TBC/RabGAP Armus coordinates Rac1 and Rab7 functions during autophagy.

    PubMed

    Carroll, Bernadette; Mohd-Naim, Noor; Maximiano, Filipe; Frasa, Marieke A; McCormack, Jessica; Finelli, Mattea; Thoresen, Sigrid B; Perdios, Louis; Daigaku, Reiko; Francis, Richard E; Futter, Clare; Dikic, Ivan; Braga, Vania M M

    2013-04-15

    Autophagy is an evolutionarily conserved process that enables catabolic and degradative pathways. These pathways commonly depend on vesicular transport controlled by Rabs, small GTPases inactivated by TBC/RabGAPs. The Rac1 effector TBC/RabGAP Armus (TBC1D2A) is known to inhibit Rab7, a key regulator of lysosomal function. However, the precise coordination of signaling and intracellular trafficking that regulates autophagy is poorly understood. We find that overexpression of Armus induces the accumulation of enlarged autophagosomes, while Armus depletion significantly delays autophagic flux. Upon starvation-induced autophagy, Rab7 is transiently activated. This spatiotemporal regulation of Rab7 guanosine triphosphate/guanosine diphosphate cycling occurs by Armus recruitment to autophagosomes via interaction with LC3, a core autophagy regulator. Interestingly, autophagy potently inactivates Rac1. Active Rac1 competes with LC3 for interaction with Armus and thus prevents its appropriate recruitment to autophagosomes. The precise coordination between Rac1 and Rab7 activities during starvation suggests that Armus integrates autophagy with signaling and endocytic trafficking. PMID:23562278

  9. The Flimser Bergsturz - A new perspective on failure mechanisms and kinematics

    NASA Astrophysics Data System (ADS)

    Volken, Stefan; Wolter, Andrea; Loew, Simon

    2015-04-01

    The Flimser Bergsturz, which happened about 9000 years ago and involved a volume of 8-9 km3, is the largest rockslide event in the European Alpine belt and one of the largest in the world. The landslide deposit covers an area of around 52 km2 in the Vorderrhein valley. According to its characteristics, the Flimser Bergsturz can be termed a rockslide which transformed into a very rapid rock avalanche (Sturzstrom). Although a sliding plane is clearly visible close to the head scarp, there is no published work addressing the release mechanisms and the kinematics of the rockslide in detail. In the current work, extensive field and photogrammetric discontinuity surveys in the head scarp area and the first-time creation of 2D and 3D models of the release area give new insights on release mechanisms and kinematic processes. Detailed discontinuity surveys and mapping at the scarp provide information on persistent structures and consequently potential release mechanisms. In addition, existing descriptions of the landslide deposits, including locations and dimensions of intact rock slabs, suggest possible kinematic processes such as translational sliding. Distinct features such as the undulating sliding plane, which shows a mean dip of about 25° to the south, or the large step-forming features oblique to sliding direction, indicate the rupture surface geometry. The importance of persistent fracture sets can be seen in the morphology of the Flimserstein, which is controlled by these sets. A conceptual model of the evolution of the landscape in the failure area is developed using geomorphological maps and reconstructions of pre-event topography. With the aid of modeling programs, such as Phase2 and RS3 (RocScience 2014), 2D as well as 3D slope stability models are generated, and constrained by field observations and geomorphological mapping.

  10. Failure mechanism of the interturn insulation of low voltage electric machines fed by pulse-controlled inverters

    Microsoft Academic Search

    M. Kaufhold; G. Borner; M. Eberhardt; J. Speck

    1996-01-01

    Partial discharges (PDs) occur in the air-filled gaps of enameled wires that are touching. They erode the insulation and consequently lead to an interturn breakdown. This paper describes the failure mechanism of low voltage interturn insulation as a consequence of PDs and shows why and how it is influenced by the insulation design, temperature, and the applied voltage. Understanding the

  11. A New Member of the TBC1D15 Family from Chiloscyllium plagiosum: Rab GTPase-Activating Protein Based on Rab7 as a Substrate

    PubMed Central

    Li, Yuanyuan; Wang, Weidong; Cheng, Dandan; Wang, Tao; Lu, Conger; Chen, Jian; Nie, Zuoming; Zhang, Wenping; Lv, Zhengbing; Wu, Wutong; Shu, Jianhong

    2015-01-01

    APSL (active peptide from shark liver) is a hepatic stimulator cytokine from the liver of Chiloscyllium. It can effectively protect islet cells and improve complications in mice with alloxan-induced diabetes. Here, we demonstrate that the APSL sequence is present in the N-terminus of novel TBC (Tre-2, Bub2 and Cdc16) domain family, member 15 (TBC1D15) from Chiloscyllium plagiosum. This shark TBC1D15 gene, which contains an ORF of 2088 bp, was identified from a cDNA library of regenerating shark liver. Bioinformatic analysis showed that the gene is highly homologous to TBC1D15 genes from other species. Moreover, the N-terminus of shark TBC1D15 contains a motif of unknown function (DUF3548), which encompasses the APSL fragment. Rab-GAP activity analysis showed that shark TBC1D15 is a new member of the TBC1D15 family. These results demonstrated that shark TBC1D15 possesses Rab-GAP activity using Rab7 as a substrate, which is a common property of the TBC1D15 family. The involvement of APSL at the N-terminus of TBC1D15 also demonstrates that this protein might be involved in insulin signaling and may be associated with the development of type 2 diabetes. The current findings pave the way for further functional and clinical studies of these proteins from marine sources. PMID:25984991

  12. A New Member of the TBC1D15 Family from Chiloscyllium plagiosum: Rab GTPase-Activating Protein Based on Rab7 as a Substrate.

    PubMed

    Li, Yuanyuan; Wang, Weidong; Cheng, Dandan; Wang, Tao; Lu, Conger; Chen, Jian; Nie, Zuoming; Zhang, Wenping; Lv, Zhengbing; Wu, Wutong; Shu, Jianhong

    2015-01-01

    APSL (active peptide from shark liver) is a hepatic stimulator cytokine from the liver of Chiloscyllium. It can effectively protect islet cells and improve complications in mice with alloxan-induced diabetes. Here, we demonstrate that the APSL sequence is present in the N-terminus of novel TBC (Tre-2, Bub2 and Cdc16) domain family, member 15 (TBC1D15) from Chiloscyllium plagiosum. This shark TBC1D15 gene, which contains an ORF of 2088 bp, was identified from a cDNA library of regenerating shark liver. Bioinformatic analysis showed that the gene is highly homologous to TBC1D15 genes from other species. Moreover, the N-terminus of shark TBC1D15 contains a motif of unknown function (DUF3548), which encompasses the APSL fragment. Rab-GAP activity analysis showed that shark TBC1D15 is a new member of the TBC1D15 family. These results demonstrated that shark TBC1D15 possesses Rab-GAP activity using Rab7 as a substrate, which is a common property of the TBC1D15 family. The involvement of APSL at the N-terminus of TBC1D15 also demonstrates that this protein might be involved in insulin signaling and may be associated with the development of type 2 diabetes. The current findings pave the way for further functional and clinical studies of these proteins from marine sources. PMID:25984991

  13. Beneficial effects of yttrium on the mechanical failure and chemical stability of the passive film of 304 stainless steel

    Microsoft Academic Search

    X. Y. Wang; D. Y. Li

    2001-01-01

    Recent studies demonstrated that yttrium improved the resistance of stainless steel to corrosive wear. However, the mechanism responsible for the beneficial effect of yttrium was not well understood. In this work, the breakdown of passive films of Y-free and Y-containing 304 stainless steel specimens during indentation and scratch testing was studied using a micro-mechanical probe. The failure of the passive

  14. 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.

  15. 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.

  16. Perioperative risk factors for prolonged mechanical ventilation after liver transplantation due to acute liver failure

    PubMed Central

    Lee, Serin; Jung, Hyun Sik; Choi, Jong Ho; Lee, Jaemin; Hong, Sang Hyun; Lee, Sung Hyun

    2013-01-01

    Background Acute liver failure (ALF) is a rapidly progressing and fatal disease for which liver transplantation (LT) is the only treatment. Posttransplant mechanical ventilation tends to be more prolonged in patients with ALF than in other LT patients. The present study examined the clinical effects of prolonged posttransplant mechanical ventilation (PMV), and identified risk factors for PMV following LT for ALF. Methods We reviewed data of patients undergoing LT for ALF between January 2005 and June 2011. After grouping patients according to administration of PMV (? 24 h), donor and recipient perioperative variables were compared between the groups with and without PMV. Potentially significant factors (P < 0.1) from the univariate intergroup comparison were entered into a multivariate logistic regression to establish a predictive model for PMV. Results Twenty-four (25.3%) of 95 patients with ALF who received PMV had a higher mortality rate (29.2% vs 11.3%, P = 0.038) and longer intensive care unit stay (12.9 ± 10.4 vs 7.1 ± 2.7 days, P = 0.012) than patients without PMV. The intergroup comparisons revealed worse preoperative hepatic conditions, more supportive therapy, and more intraoperative fluctuations in vital signs and less urine output in the with- compared with the without-PMV group. The multivariate analysis revealed that preoperative hepatic encephalopathy (? grade III), intraoperative blood pressure fluctuation, and oliguria (< 0.5 ml/kg/h) were independent risk factors for PMV. Conclusions PMV was associated with deleterious outcomes. Besides care for known risk factors including hepatic encephalopathy, meticulous attention to managing intraoperative hemodynamic circulatory status is required to avoid PMV and improve the posttransplant prognosis in ALF patients. PMID:24101957

  17. 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 (V?CO2) 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

  18. Fatigue strength and failure mechanisms of wrought aluminium alloys in the VHCF-region considering material and component relevant influencing factors

    Microsoft Academic Search

    D. Schwerdt; B. Pyttel; C. Berger

    2011-01-01

    Investigations at room temperature were carried out with smooth specimens made of the aluminium alloys EN AW 6056 and EN AW 6082. Different failure mechanisms were investigated for instance according to material and number of cycles. The influence of mean stress on fatigue strength of smooth specimens made of EN AW 6056 and transition of failure mechanism from the high

  19. A study of failure mechanisms in CMOS & BJT ICs and their effect on device reliability

    Microsoft Academic Search

    M. G. Rajesh; G. Vinod; D. Das; P. V. Bhatnagar; C. K. Pithawa; A. Thaduri; A. K. Verma

    2010-01-01

    The reliability of electronic systems, used in nuclear power plants, is traditionally estimated with empirical databases such as MIL-HDBK-217, PRISM etc. These methods assign a constant failure rate to electronic devices, during their useful life. Currently, electronic reliability prediction is moving towards applying the Physics of Failure approach which considers information on process, technology, fabrication techniques, materials used, etc. The

  20. Mechanical behavior and failure of composite pyramidal truss core sandwich columns

    Microsoft Academic Search

    Jian Xiong; Li Ma; Linzhi Wu; Jiayi Liu; Ashkan Vaziri

    2011-01-01

    A series of analytical and experimental investigations is presented to study the response and failure of pyramidal truss core sandwich panels made of carbon fiber composite under axial compression. In the analytical part of the study, three failure modes: (i) Euler or core shear macro-buckling, (ii) face wrinkling, and (iii) face sheet crushing, were considered and theoretical relationships for predicting

  1. Mechanical Failure Mode of Metal Nanowires: Global Deformation versus Local Deformation

    PubMed Central

    Ho, Duc Tam; Im, Youngtae; Kwon, Soon-Yong; Earmme, Youn Young; Kim, Sung Youb

    2015-01-01

    It is believed that the failure mode of metal nanowires under tensile loading is the result of the nucleation and propagation of dislocations. Such failure modes can be slip, partial slip or twinning and therefore they are regarded as local deformation. Here we provide numerical and theoretical evidences to show that global deformation is another predominant failure mode of nanowires under tensile loading. At the global deformation mode, nanowires fail with a large contraction along a lateral direction and a large expansion along the other lateral direction. In addition, there is a competition between global and local deformations. Nanowires loaded at low temperature exhibit global failure mode first and then local deformation follows later. We show that the global deformation originates from the intrinsic instability of the nanowires and that temperature is a main parameter that decides the global or local deformation as the failure mode of nanowires. PMID:26087445

  2. Mutations in TBC1D24, a Gene Associated With Epilepsy, Also Cause Nonsyndromic Deafness DFNB86

    PubMed Central

    Rehman, Atteeq U.; Santos-Cortez, Regie Lyn P.; Morell, Robert J.; Drummond, Meghan C.; Ito, Taku; Lee, Kwanghyuk; Khan, Asma A.; Basra, Muhammad Asim R.; Wasif, Naveed; Ayub, Muhammad; Ali, Rana A.; Raza, Syed I.; Nickerson, Deborah A.; Shendure, Jay; Bamshad, Michael; Riazuddin, Saima; Billington, Neil; Khan, Shaheen N.; Friedman, Penelope L.; Griffith, Andrew J.; Ahmad, Wasim; Riazuddin, Sheikh; Leal, Suzanne M.; Friedman, Thomas B.

    2014-01-01

    Inherited deafness is clinically and genetically heterogeneous. We recently mapped DFNB86, a locus associated with nonsyndromic deafness, to chromosome 16p. In this study, whole-exome sequencing was performed with genomic DNA from affected individuals from three large consanguineous families in which markers linked to DFNB86 segregate with profound deafness. Analyses of these data revealed homozygous mutation c.208G>T (p.Asp70Tyr) or c.878G>C (p.Arg293Pro) in TBC1D24 as the underlying cause of deafness in the three families. Sanger sequence analysis of TBC1D24 in an additional large family in which deafness segregates with DFNB86 identified the c.208G>T (p.Asp70Tyr) substitution. These mutations affect TBC1D24 amino acid residues that are conserved in orthologs ranging from fruit fly to human. Neither variant was observed in databases of single-nucleotide variants or in 634 chromosomes from ethnically matched control subjects. TBC1D24 in the mouse inner ear was immunolocalized predominantly to spiral ganglion neurons, indicating that DFNB86 deafness might be an auditory neuropathy spectrum disorder. Previously, six recessive mutations in TBC1D24 were reported to cause seizures (hearing loss was not reported) ranging in severity from epilepsy with otherwise normal development to epileptic encephalopathy resulting in childhood death. Two of our four families in which deafness segregates with mutant alleles of TBC1D24 were available for neurological examination. Cosegregation of epilepsy and deafness was not observed in these two families. Although the causal relationship between genotype and phenotype is not presently understood, our findings, combined with published data, indicate that recessive alleles of TBC1D24 can cause either epilepsy or nonsyndromic deafness. PMID:24387994

  3. Mechanical assessment of local bone quality to predict failure of locked plating in a proximal humerus fracture model.

    PubMed

    Röderer, Götz; Brianza, Stefano; Schiuma, Damiano; Schwyn, Ronald; Scola, Alexander; Gueorguiev, Boyko; Gebhard, Florian; Tami, Andrea

    2013-09-01

    The importance of osteoporosis in proximal humerus fractures is well recognized. However, the local distribution of bone quality in the humeral head may also have a significant effect because it remains unclear in what quality of bone screws of standard implants purchase. The goal of this study was to investigate whether the failure of proximal humerus locked plating can be predicted by the DensiProbe (ARI, Davos, Switzerland). A 2-part fracture with metaphyseal impaction was simulated in 12 fresh-frozen human cadaveric humeri. Using the DensiProbe, local bone quality was determined in the humeral head in the course of 6 proximal screws of a standard locking plate (Philos; Synthes GmbH, Solothurn, Switzerland). Cyclic mechanical testing with increasing axial loading until failure was performed. Bone mineral density (BMD) significantly correlated with cycles until failure. Head migration significantly increased between 1000 and 2000 loading cycles and significantly correlated with BMD after 3000 cycles. DensiProbe peak torque in all screw positions and their respective mean torque correlated significantly with the BMD values. In 3 positions, the peak torque significantly correlated with cycles to failure; here BMD significantly influenced mechanical stability. The validity of the DensiProbe was proven by the correlation between its peak torque measurements and BMD. The correlation between the peak torque and cycles to failure revealed the potential of the DensiProbe to predict the failure of locked plating in vitro. This method provides information about local bone quality, potentially making it suitable for intraoperative use by allowing the surgeon to take measures to improve stability. PMID:24025003

  4. On the mechanism of impaired insulin secretion in chronic renal failure.

    PubMed Central

    Fadda, G Z; Hajjar, S M; Perna, A F; Zhou, X J; Lipson, L G; Massry, S G

    1991-01-01

    It has been suggested that a sustained rise in resting levels of cytosolic calcium [Ca2+]i of pancreatic islets is responsible for impaired insulin secretion in chronic renal failure (CRF). Evidence for such an event is lacking and the mechanisms through which it may affect insulin secretion are not known. Studies were conducted in normal, CRF, and normocalcemic, parathyroidectomized (PTX) CRF rats to answer these questions. Resting levels of [Ca2+]i of islets from CRF rats were higher (P less than 0.01) than in control of CRF-PTX rats. [3H]2-deoxyglucose uptake and cAMP production by islets were not different in the three groups. Insulin content of, and glucose-induced insulin secretion by islets from CRF rats was lower (P less than 0.01) than in control and CRF-PTX rats. In contrast, glyceraldehyde-induced insulin release by CRF islets was normal. Basal ATP content, both glucose-stimulated ATP content and ATP/ADP ratio, net lactic acid output, Vmax of phosphofructokinase-1, and Ca2+ ATPase of islets from CRF rats were lower (P less than 0.02-less than 0.01) than in normal or CRF-PTX animals. Data show that: (a) Glucose but not glyceraldehyde-induced insulin secretion is impaired in CRF; (b) the impairment in glucose-induced insulin release in CRF is due to a defect in the metabolism of glucose; (c) this latter defect is due to reduced ATP content induced partly by high [Ca2+]i of islets; and (d) the high [Ca2+]i in islets of CRF rats is due to augmented PTH-induced calcium entry into cells and decreased calcium extrusion from the islets secondary to reduced activity of the Ca2+ ATPase. Images PMID:1985099

  5. Probing the Failure Mechanism of SnO{sub 2} Nanowires for Sodium-Ion Batteries

    SciTech Connect

    Gu, Meng; Kushima, Akihiro; Shao, Yuyan; Zhang, Ji-Guang; Liu, Jun; Browning, Nigel D; Li, Ju; Wang, Chongmin

    2013-09-30

    Nonlithium metals such as sodium have attracted wide attention as a potential charge carrying ion for rechargeable batteries. Using in situ transmission electron microscopy in combination with density functional theory calculations, we probed the structural and chemical evolution of SnO{sub 2} nanowire anodes in Na-ion batteries and compared them quantitatively with results from Li-ion batteries (Huang, J. Y.; et al. Science 2010, 330, 1515-1520). Upon Na insertion into SnO{sub 2}, a displacement reaction occurs, leading to the formation of amorphous Na{sub x}Sn nanoparticles dispersed in Na{sub 2}O matrix. With further Na insertion, the Na{sub x}Sn crystallized into Na{sub 15}Sn{sub 4} (x = 3.75). Upon extraction of Na (desodiation), the Na{sub x}Sn transforms to Sn nanoparticles. Associated with the dealloying, pores are found to form, leading to a structure of Sn particles confined in a hollow matrix of Na{sub 2}O. These pores greatly increase electrical impedance, therefore accounting for the poor cyclability of SnO{sub 2}. DFT calculations indicate that Na{sup +} diffuses 30 times slower than Li{sup +} in SnO{sub 2}, in agreement with in situ TEM measurement. Insertion of Na can chemomechanically soften the reaction product to a greater extent than in lithiation. Therefore, in contrast to the lithiation of SnO{sub 2} significantly less 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.

  6. The impact of stylolites on brittle failure of carbonates: mechanical data and numerical simulations

    NASA Astrophysics Data System (ADS)

    Baud, Patrick; Heap, Michael; Xu, Tao; Rolland, Alexandra; Ferrand, Thomas; Nicolé, Marion; Reuschlé, Thierry; Conil, Nathalie

    2015-04-01

    Stylolites are complex column-and-socket interdigitation features that form as a result of intergranular pressure-solution. They are usually orientated perpendicular to the maximum principal stress (weight of the overburden or maximum tectonic stress). They typically form clay-enriched seams; and can sometimes reach a few hundred metres in length. While the impact of stylolites on fluid flow was recently quantified for several carbonate formations (Heap et al., 2012), there is however a paucity of data on their impact on the mechanical strength of carbonates. Observations in quarries suggest that the presence of stylolites is associated with significant mechanical weakening and anisotropy. The aim of this study was to quantify these effects based on laboratory experiments and numerical simulations. We used cores from limestone formations surrounding the ANDRA Underground Research Laboratory at Bure in the south of the Meuse district, France. Several different Oxfordian limestones were selected for this study and more than 50 samples were deformed under uniaxial conditions. The selected rocks are microporous and their average porosities range between 2 and 18%. The porosity of the samples with stylolites was found to be systematically larger than the stylolite-free samples. The stylolite-free rock is found to be mechanically isotropic, with comparable Uniaxial Compressive Strength (UCS) values in all tested orientations. We deformed samples with one stylolite in their central part oriented either horizontally (perpendicular to loading), vertically (parallel to loading) or oblique (30 degrees to loading). The samples with a stylolite were always significantly weaker than the stylolite-free samples but no systematic difference was observed in the different orientations. Visual inspection as well as microstructural analysis revealed some complex interactions between the stylolites and stress-induced microcracking. In particular, when the stylolite is oriented orthogonal to the loading, microcracks clearly appeared to nucleate from the stylolite. Whatever the stylolite orientation, the macroscopic fracture appeared to follow only small parts of the tortuous stylolite path. Numerical simulations were performed using stochastic modelling and the Failure and Process Analysis Code (RPFA). Two dimensional numerical samples (40 mm x 20 mm) consisted of 51200 (320 x 120) square elements were deformed uniaxially. To reflect material heterogeneity on the microscale, each square was assigned a value of strength (tensile and compressive) and Young's modulus using a Weibull probability density function. The model parameters were first set to reproduce the mechanical behavior of the stylolite-free material. Guided by our microstructural analysis we then introduced a weaker layer in several orientations in the numerical samples. The simulations showed good qualitative agreement with the experiments performed on samples with stylolites. Our study showed that stylolites have more impact of the mechanical properties than on fluid flow in the limestone from Bure.

  7. IMPERMEABLE THIN AL2O3 OVERLAY FOR TBC PROTECTION FROM SULFATE AND VANADATE ATTACK IN GAS TURBINES

    SciTech Connect

    Scott X. Mao

    2002-08-31

    In order to improve the hot corrosion resistance of conventional YSZ TBC system, the overlay of Al{sub 2}O{sub 3} coating was deposited on the TBC by EB-PVD techniques. Hot corrosion tests were carried out on the TBC with and without Al{sub 2}O{sub 3} coating in molten salts mixtures (Na{sub 2}SO{sub 4} + 5%V{sub 2}O{sub 5}) at 950 C for different time up to 100h. The microstructures of TBC and overlay before and after exposure were examined by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX) and X-ray diffraction (XRD). It has been found that TBC will react with V{sub 2}O{sub 5} to form YVO{sub 4}. The amount of M-phase, which was formed due to the leaching of Y{sub 2}O{sub 3} from YSZ, was increased with corrosion time. Al{sub 2}O{sub 3} overlay coating deposited by EB-PVD was dense, continues and adherent to the TBC. As a result, overlay Al{sub 2}O{sub 3} coating can prevent the YSZ from the attack by molten salts containing vanadium and decrease the penetration of salts into the YSZ along porous and cracks in the YSZ TBC. The amount of M-phase formed in YSZ covered with an overlay Al{sub 2}O{sub 3} is substantially lower than that formed in conventional YSZ TBC, even after 100h exposure to the molten salts. In the next reporting period, the hot corrosion test of TBC with EB-PVD deposited Al{sub 2}O{sub 3} coating will be again performed. However before hot corrosion tests, the post-annealing will be carried out in vacuum (residual pressure 10 -3 Pa) at 1273K for 1h in order to transform the as-sputtered Al{sub 2}O{sub 3} overlay to crystalline {alpha}-Al{sub 2}O{sub 3} overlay. In addition, the effect of the thickness of overlay Al{sub 2}O{sub 3} on corrosion resistance will also be investigated.

  8. Is remodeling the dominant compensatory mechanism in both chronic heart failure with preserved and reduced left ventricular ejection fraction?

    Microsoft Academic Search

    David H. MacIver

    2010-01-01

    The mechanisms of heart failure are ill understood with multiple, heterogeneous hypotheses proposed to describe the condition.\\u000a This study examines the individual effects of left ventricular hypertrophy, long-axis shortening and the effect of left ventricular\\u000a remodeling on ejection fraction, end-diastolic volume and stroke volume using a mathematical model of left ventricular contraction.\\u000a Reducing long-axis shortening caused a decline in stroke

  9. Failure of neural tube closure in the loop-tail ( Lp) mutant mouse: analysis of the embryonic mechanism

    Microsoft Academic Search

    Dianne Gerrelli; Andrew J Copp

    1997-01-01

    Loop-tail (Lp) is unique among mouse mutants in failing to initiate neural tube closure at the cervical\\/hindbrain boundary (so-called `Closure 1'), at the 5–7 somite stage. Lp\\/Lp embryos go on to develop a malformation that closely resembles cranio-rachischisis, the most severe neural tube defect found in humans. We investigated several possible embryological mechanisms that may underlie this failure of neural

  10. Investigation of the Failure Mechanism for an S-Band Pillbox Output Window Applied in High-Average-Power Klystrons

    Microsoft Academic Search

    Fang Zhu; Zhao-Chuan Zhang; Ji-Run Luo; Yu-Wen Zhang

    2010-01-01

    On the basis of the results of X-ray photoelectron spectroscopy, theoretical analyses, and numerical simulations, the failure mechanism of an S-band pillbox output window applied in a high-average-power klystron is discussed. The influence of the high-order cylindrical-guide modes on the microwave power loss, the direction of the power flow and the window disk cracking are investigated. The high-order cylindrical-guide TM11

  11. Negative pressure ventilation versus conventional mechanical ventilation in the treatment of acute respiratory failure in COPD patients

    Microsoft Academic Search

    A. Corrado; M. Gorini; R. Ginanni; C. Pelagatti; G. Villella; U. Buoncristiano; F. Guidi; E. Pagni; A. Peris; E. De Paola

    1998-01-01

    This case-control study was aimed to evaluate the effectiveness of nega- tive pressure ventilation (NPV) versus conventional mechanical ventilation (CMV) for the treatment of acute respiratory failure (ARF) in patients with chronic obstructive pulmonary disease (COPD) admitted to a respiratory intermediate intensive care unit (RIICU) and four general intensive care units (ICU). Twenty-six COPD patients in ARF admitted in 1994-95

  12. Influence of fibre weight fraction on failure mechanisms of poly(ethylene terephthalate) reinforced by short-glass-fibres

    Microsoft Academic Search

    Kiyoshi Takahashi; Nak-Sam Choi

    1991-01-01

    Failure mechanisms of short-glass-fibre reinforced poly(ethylene terephthalate) were investigated with particular attention\\u000a to the effects of fibre weight fraction (Wf=1 wt%, 30 wt% and 60 wt%). A fracture morphology study was carried out for the surface and for the interior of uniaxial tensile\\u000a specimens. On the surface, tensile cracks occurring mostly at the fibre ends seemed to be more influential

  13. Active wear and failure mechanisms of TiN-Coated high speed steel and tin-coated cemented carbide tools when machining powder metallurgically made stainless steels

    Microsoft Academic Search

    Laizhu Jiang; Hannu Hänninen; Jukka Paro; Veijo Kauppinen

    1996-01-01

    In this study, active wear and failure mechanisms of both TiN-coated high speed steel and TiN-coated cemented carbide tools\\u000a when machining stainless steels made by powder metallurgy in low and high cutting speed ranges, respectively, have been investigated.\\u000a Abrasive wear mechanisms, fatigue-induced failure, and adhesive and diffusion wear mechanisms mainly affected the tool life\\u000a of TiN-coated high speed steel tools

  14. Mechanisms of injury in porcine livers perfused with blood of patients with fulminant hepatic failure.

    PubMed

    Collins, B H; Chari, R S; Magee, J C; Harland, R C; Lindman, B J; Logan, J S; Bollinger, R R; Meyers, W C; Platt, J L

    1994-12-15

    Hyperacute rejection of renal and cardiac xenografts is initiated by the reaction of recipient natural antibodies and complement with endothelial cell antigens of the donor organ. The liver is thought to be less susceptible to this form of rejection; however, the mechanisms underlying its decreased susceptibility are not known. We investigated the organ injury occurring in porcine livers perfused with blood from 4 human subjects with fulminant hepatic failure. Nine porcine livers were perfused via an extracorporeal circuit in order to provide temporary metabolic support. Each porcine liver exhibited metabolic function, and the duration of xenoperfusion ranged from 2 to 5 hr. Histologic examination of the xenoperfused livers revealed focal hepatocellular necrosis, prominent infiltration of neutrophils, and, in 7 of 9 cases, periportal and centrilobular hemorrhage and thrombosis. Immunopathology demonstrated minimal or no human IgM and IgG along the small vessels and sinusoidal surfaces. Trace deposits of human IgM were observed along the luminal surfaces of large blood vessels in most cases. Trace deposits of C3 were noted in 2 of 9 livers; however, C4, iC3b, C5b, properdin, and the membrane attack complex were not detected. Human anti-porcine natural antibody titers decreased less than expected during the perfusions. Serum CH50, C3, and C4 levels were low before each procedure and decreased slightly with perfusion. One patient perfused 2 porcine livers and a human liver. The human liver had focal hepatocellular necrosis, trace deposits of IgM, no deposits of complement, and an infiltrate consisting of neutrophils; however, the neutrophil influx was less than that observed in the xenoperfused livers. To further evaluate the effects of alloperfusion, venovenous bypass was established in 2 pigs and the extracorporeal circuit was utilized to perfuse 2 porcine livers. The alloperfused porcine livers had focal hepatocellular necrosis and a minimal infiltrate of neutrophils. There were no deposits of porcine IgM, IgG, or complement components. In conclusion, although the porcine livers perfused by human blood sustained structural damage, the time course, the absence of immune deposits, and the findings of similar, albeit less severe, lesions in the alloperfused livers suggest that the pathogenesis of tissue injury in the xenoperfused livers differs from that of hyperacute rejection and may be related to the action of recipient neutrophils. PMID:7992356

  15. Enigmatic Moisture Effects on Al2O3 Scale and TBC Adhesion

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    2008-01-01

    Alumina scale adhesion to high temperature alloys is known to be affected primarily by sulfur segregation and reactive element additions. However, adherent scales can become partially compromised by excessive strain energy and cyclic cracking. With time, exposure of such scales to moisture can lead to spontaneous interfacial decohesion, occurring while the samples are maintained at ambient conditions. Examples of this Moisture-Induced Delayed Spallation (MIDS) are presented for NiCrAl and single crystal superalloys, becoming more severe with sulfur level and cyclic exposure conditions. Similarly, delayed failure or Desk Top Spallation (DTS) results are reviewed for thermal barrier coatings (TBCs), culminating in the water drop failure test. Both phenomena are discussed in terms of moisture effects on bulk alumina and bulk aluminides. A mechanism is proposed based on hydrogen embrittlement and is supported by a cathodic hydrogen charging experiment. Hydroxylation of aluminum from the alloy interface appears to be the relevant basic reaction.

  16. Mechanical Circulatory Support and the Role of LVADs in Heart Failure Therapy

    PubMed Central

    McLarty, Allison

    2015-01-01

    Heart failure is epidemic in the United States with a prevalence of over 5 million. The diagnosis carries a mortality risk of 50% at 5 years rivaling many diagnoses of cancer. Heart transplantation, long the “gold standard” treatment for end stage heart failure unresponsive to maximal medical therapy falls way short of meeting the need with only about 2,000 transplants performed annually in the United States due to donor limitation. Left ventricular devices have emerged as a viable option for patients as both a “bridge to transplantation” and as a final “destination therapy”. PMID:25983564

  17. On fibre debonding effects and the mechanism of transverse-ply failure in cross-ply laminates of glass fibre\\/thermoset composites

    Microsoft Academic Search

    J. E. Bailey; A. Parvizi

    1981-01-01

    The mechanism of transverse-ply failure in cross-ply laminates of glass fibre thermoset composites has been investigated. It is shown that fibre debonding initiates failure, the debonds subsequently joining up to form a transverse crack nucleus. In the epoxy system investigated fibre debonding causes an observable whitening effect and small modulus change; this effect is reversible in that rebonding can be

  18. 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 and experimental work.

  19. Mechanisms of slope failure in Valles Marineris, Mars D.P. Neuffer1,2

    E-print Network

    Geomechanics-Rock Fracture Group, Department of Geological Sciences and Engineering/172, Mackay School of Earth in the large relief exposures (up to 8 km) of basaltic wall rock and soft interior layered deposits (ILDs). Eleven landslides, including eight circular failures, were mapped in the ILDs. Two wall rock landslide

  20. A finite element analysis of dynamic fracture initiation by ductile failure mechanisms in a 4340 steel

    Microsoft Academic Search

    M. Jha; R. Narasimhan

    1992-01-01

    In some recent dropweight impact experiments [5] with pre-notched bend specimens of 4340 steel, it was observed that considerable crack tunneling occurred in the interior of the specimen prior to gross fracture initiation on the free surfaces. The final failure of the side ligaments happened because of shear lip formation. The tunneled region is characterized by a flat, fibrous fracture

  1. Failure Waves and Their Effects on Penetration Mechanics in Glass and Ceramics

    Microsoft Academic Search

    Stephan J. Bless; N. Singh Brar

    Penetration and impact failure of brittle materials is a subject of considerable practical importance. The high compressive strength of some ceramics has led to their use as armor against bullets and other kinetic energy penetrators. There are also many industrial applications of ceramics to prevent impact and penetration damage. Many geologic and structural materials also exhibit brittle behavior under impact

  2. Wavelet-based methods for the prognosis of mechanical and electrical failures in electric motors

    Microsoft Academic Search

    Wesley G. Zanardelli; Elias G. Strangas; Hassan K. Khalil; John M. Miller

    2005-01-01

    The ability to give a prognosis for failure of a system is a valuable tool and can be applied to electric motors. In this paper, three wavelet-based methods have been developed that achieve this goal. Wavelet and filter bank theory, the nearest-neighbour rule, and linear discriminant functions are reviewed. A framework for the development of a fault detection and classification

  3. Failure mechanism of pump chambers and their optimized design in deep mining at Qishan Coal Mine

    Microsoft Academic Search

    Xiaoming SUN; Chuangzhou WU; Feng CAI

    2010-01-01

    Pump chambers, normally used as dominant structures in mining engineering to insure the safety and production of underground coal mines, become generally deformed under conditions of deep mining. Given the geology and engineering condition of Qishan Coal Mine in Xuzhou, the failure characteristics of pump chambers at the ?1000 m level show that the main cause can be attributed to

  4. Failure mechanisms in wood joints bonded with urea-formaldehyde adhesives

    Microsoft Academic Search

    B. H. River; R. O. Ebewele; G. E. Myers

    1994-01-01

    Wood joints bonded with urea-formaldehyde (UF) are weakened by cyclic swelling and shrinking. To study the failure mecha- nisms in UF-bonded joints, specimens were bonded with unmod- ified, modified (amine), or phenol formaldehyde adhesive and subjected to accelerated aging. Modification of the adhesive properties increased the cleavage fracture toughness and shear strength of bonded joints and improved the resistance of

  5. An investigation of mechanical, acoustic and failure properties in unconsolidated sands

    Microsoft Academic Search

    Ali I. Mese; Azra N. Tutuncu

    1997-01-01

    Prediction of sand production and associated casing and tubing problems require a good understanding of failure behavior in unconsolidated and poorly consolidated sands. An experimental investigation was conducted on several fully saturated unconsolidated sand samples to determine stress states that cause sand production. Biaxial stress cycling measurements were performed at several confining pressures to demonstrate the effect of horizontal stress

  6. Embedded damage sensor using triboluminescence as a transduction mechanism for detecting failure of a material under load

    NASA Astrophysics Data System (ADS)

    Lesho, Jeffery Carl

    Damage sensors are devices that monitor the state of health of structures or materials and that provide a signal indication when external forces or other conditions have caused the structure to fail. Continuous monitoring of structures is vital for safety reasons as well as for reduction of maintenance costs. The present study investigated the use of triboluminescent materials as a transduction mechanism for the detection of failure, combined with development of an electronic system to telemeter the optical pulses to a remote receiver for analysis and classification. The goal of the latter work was to create a low cost system that was small enough to be implanted into a smart material with a useful life of one year. The investigation had four main parts. First a search for an intense triboluminescent radiative material was undertaken. When an appropriate material was identified, a new improved method was developed that yielded a more efficient approach to processing. Research into the mechanism for the chosen material was conducted to determine if a new material could be engineered to yield larger signals. Second, a very low power opto-electronics system was developed that included an electronic circuit designed to monitor the sensor, and when a triboluminescent optical pulse is detected, it activates a transmitter that telemeters the optical decay signal to an external receiver. The receiver captures the optical decay as sampled digital data and correlates the signal with the known optical decay of the triboluminescent radiation. Third, a 'smart material' was fabricated with the triboluminescent sensor embedded in a block of epoxy. This material was tested to failure and the failure event was captured and the data was classified. Lastly, a correlation procedure for classifying the optical decays was written to actively look for failure events and filter out noise. Positive correlation results indicate that fracture has actually occurred.

  7. Failure Morphologies of Cyclically Oxidized ZrO2-Based Thermal Barrier Coatings

    NASA Technical Reports Server (NTRS)

    Nesbitt, James A.; Zhu, Dongming; Miller, Robert A.; Barrett, Charles A.

    2002-01-01

    Advanced and baseline thermal barrier coatings (TBCs) were thermal cycle tested in air at 1163 C until delamination or spallation of the ceramic top coat. The top coat of the advanced TBC s consisted of ZrO2 with various amounts of Y2O3, Yb2O3, Gd2O3, or Nd2O3 dopants. The composition of the top coat of the baseline TBC was ZrO2-8wt.%Y2O3. All top coats were deposited by air plasma spraying. A NiCrAlY or NiCoCrAlY bond coat was deposited by low pressure plasma spraying onto a single-crystal, Ni-base superalloy. The TBC lifetime for the baseline coatings was approximately 190 cycles (45 minutes at 1163 C per cycle) while the lifetime for the advanced coatings was as high as 425 cycles. The fracture surfaces and sample cross sections were examined after TBC failure by SEM and optical microscopy, and the top coats were further examined by X-ray diffraction. These post-test studies revealed that the fracture path largely followed splat boundaries with some trans-splat fracture. However, there were no obvious distinguishing features which explained the difference in TBC lifetimes between some of the advanced and baseline coatings.

  8. fRcprioted froa thc Jourod ot tbc Aoclic.a CbGEicd Society,9l,3800 (1900).1 Copyrigbt 1969 bf tbe Aorericro Cbeo.icd Society rad regriated bt Deroirioo ol tbc copfrifht otocr.

    E-print Network

    Prentiss, Mara

    1900-01-01

    - t ' fRcprioted froa thc Jourod ot tbc Aoclic.a CbGEicd Society,9l,3800 (1900).1 Copyrigbt 1969 bf of many' of the individual steps in these trimerizations,thc elegant seriesof X-ray diffractionstudiesof

  9. Kinetics of Failure Rate Accumulation and TiNi Shape Memory Effect Alloy Fracture Under Mechanical Cycling

    NASA Astrophysics Data System (ADS)

    Bondarev, A. B.; Khusainov, M. A.; Plastilina, G. V.; Andreev, V. A.

    2010-06-01

    Wire specimens, d = 0.1 mm, made of Ti-(50.6-50.8)at.%-Ni alloy were exposed to thermo-mechanical treatment (TMT), thus making the samples straight and providing them with high superelasticity (?se). It was established that the most effective method of TMT is annealing with deformation at 500 and 300 °C. The optimum mode of treatment was used in the research of mechanical fatigue of alloys with high superelastic properties. Two stages characterizing the alloy behavior under mechanical cycling were found out: failure accumulation and fracture. It was shown that the duration of the cycles is determined by the value of the preset deformation (?set) in relation to the deformation on the plateau-shaped area. The results of low-cycle fatigue of the alloys under investigation were processed by means of the method of least squares. The equations of prognosis of longetivity at the preset level of deformation are presented.

  10. Heart failure with normal ejection fraction: Consideration of mechanisms other than diastolic dysfunction

    Microsoft Academic Search

    Travis Bench; Daniel Burkhoff; John B. O’Connell; Maria Rosa Costanzo; William T. Abraham; Martin St. John Sutton; Mathew S. Maurer

    2009-01-01

    More than half of patients with heart failure (HF) have a normal ejection fraction (EF). These patients are typically elderly,\\u000a are predominantly female, and have a high incidence of multiple comorbid conditions associated with development of ventricular\\u000a hypertrophy and\\/or interstitial fibrosis. Thus, the cause of HF has been attributed to diastolic dysfunction. However, the\\u000a same comorbidities may also impact myocardial

  11. Deformation and failure mechanism of dynamically loaded sandwich beams with aluminum-foam core

    Microsoft Academic Search

    J. L Yu; X Wang; Z. G Wei; E. H Wang

    2003-01-01

    In this paper the response and failure of dynamically loaded sandwich beams with an aluminum-foam core is investigated experimentally. The dynamic compressive stress–strain curves of the core material, an open-cell aluminum foam, are obtained by an SHPB technique. No strain-rate sensitivity is found. Quasi-static and dynamic bending tests are carried out for sandwich beams made of aluminum skins with an

  12. Role of folded anisotropic fabric in the failure mode of gneiss: new insights from mechanical, microseismic and microstructural laboratory data

    NASA Astrophysics Data System (ADS)

    Agliardi, Federico; Vinciguerra, Sergio; Dobbs, Marcus R.; Zanchetta, Stefano

    2015-04-01

    Fabric anisotropy is a key control of the mechanical behaviour of rocks in a variety of geological settings and on different timescales. However, the effects of inherited, tectonically folded anisotropic fabrics on the brittle strength and failure mode of foliated metamorphic rocks is yet to be fully understood. Data from laboratory uniaxial compression tests on folded gneiss (Agliardi et al., 2014, Tectonophysics) recently showed that the brittle failure mode of this rock type depends on the arrangement of two distinct anisotropies (i.e. foliation and fold axial plane anisotropy), and that rock strength correlates with failure mode. Here we investigate the effects of confining pressure on this behaviour by performing triaxial compression experiments with acoustic emission (AE) monitoring, and analyse resulting fracture mechanisms and their microfabric controls using high resolution microanalysis techniques. We tested the Monte Canale Gneiss (Austroalpine Bernina nappe, Central Italian Alps), characterized by low phyllosilicate content, compositional layering folded at the cm-scale, and absence of a well-developed axial plane foliation. We used a servo-controlled hydraulic loading system to test 19 air-dry cylindrical specimens (diameter: 54 mm) that were characterized both in terms of fold geometry and orientation of foliation and fold axial planes to the axial load direction. We instrumented the specimens with direct contact axial and circumferential strain gauges. We performed tests at confining pressures of 40 MPa and constant axial strain rates of 5*10-6 s-1, measuring acoustic emissions and P- and S-wave velocities by three wideband (350-1000 kHz) piezoelectric transceivers with 40 dB preamps, mounted in the compression platens. We carried out post-failure microscale observation of fracture mechanisms, microcrack patterns and related fabric controls on resin-impregnated samples, using X-ray MicroCT (resolution: 9 ?m), optical microscopy and SEM. Samples failed in three distinct brittle modes with different combinations of neat shear planes parallel to foliation, fractures parallel to fold axial planes, or less localized mm-scale brittle shear zones. The different failure modes, consistent with those previously described in uniaxial compression experiments, are associated with distinct stress-strain and acoustic emission signatures (i.e. overall activity, rate distribution, frequency and amplitude patterns). Failure modes involving the quartz-dominated axial plane anisotropy correspond to higher peak strength and axial strain, less brittle macroscopic behaviour with well-developed fracture process zones, and higher and more progressive acoustic emission activity than failure controlled by mica-dominated foliation anisotropy. Experimental and microstructural observations support a decisive control of folded microfabric on the overall behaviour of the same rock type, through the activation of Q-dominated vs. M-dominated crack nucleation / propagation mechanisms.

  13. Threshold of Breakout Formation: Stress Orientations and the Mechanics Borehole Failure

    NASA Astrophysics Data System (ADS)

    Moore, J. C.; Conin, M.; Flemings, P. B.; Urgeles, R.; Iturrino, G. J.

    2009-12-01

    Borehole breakouts in sedimentary sections at continental margins are common in ODP/IODP holes with resistivity imaging logs. Some examples show horizontally opposed low resistivity (conductive) zones that have been interpreted as breakouts and yield horizontal stress directions interpretable in terms of regional tectonics. Other examples show bilateral high resistivity anomalies that may represent incipient breakouts. These “resistive” breakouts show trends consistent with the more typical “conductive” breakouts. Resistive breakouts in the Gulf of Mexico show predicted hoop stresses around the borehole at well beyond failure, primarily because of the material is very weak and differential fluid pressure between the formation and the hole is high. Experiments on the sediments in this example indicate a relatively high strain before failure and a nearly perfectly plastic response after failure. Thus, the initial breakout process actually involves initial bulging into the borehole that extends the breakout towards the resistivity tool causing a high resistivity response. The small difference between initial and peak strength inhibits spallation into the borehole. “Resistive” breakouts occur in a number of ODP/IODP holes at circumPacific subduction zones and can we used to infer stress orientations along with the traditional “conductive” breakouts once the eye is tuned to their recognition. Overall in ODP/IODP holes breakouts, both incipient and evolved, comprise a reliable indicator of currently active horizontal stresses.

  14. Proportional and scale change models to project failures of mechanical components with applications to space station

    NASA Technical Reports Server (NTRS)

    Taneja, Vidya S.

    1996-01-01

    In this paper we develop the mathematical theory of proportional and scale change models to perform reliability analysis. The results obtained will be applied for the Reaction Control System (RCS) thruster valves on an orbiter. With the advent of extended EVA's associated with PROX OPS (ISSA & MIR), and docking, the loss of a thruster valve now takes on an expanded safety significance. Previous studies assume a homogeneous population of components with each component having the same failure rate. However, as various components experience different stresses and are exposed to different environments, their failure rates change with time. In this paper we model the reliability of a thruster valves by treating these valves as a censored repairable system. The model for each valve will take the form of a nonhomogeneous process with the intensity function that is either treated as a proportional hazard model, or a scale change random effects hazard model. Each component has an associated z, an independent realization of the random variable Z from a distribution G(z). This unobserved quantity z can be used to describe heterogeneity systematically. For various models methods for estimating the model parameters using censored data will be developed. Available field data (from previously flown flights) is from non-renewable systems. The estimated failure rate using such data will need to be modified for renewable systems such as thruster valve.

  15. Analyses of Failure Mechanisms and Residual Stresses in Graphite/Polyimide Composites Subjected to Shear Dominated Biaxial Loads

    NASA Technical Reports Server (NTRS)

    Kumosa, M.; Predecki, P. K.; Armentrout, D.; Benedikt, B.; Rupnowski, P.; Gentz, M.; Kumosa, L.; Sutter, J. K.

    2002-01-01

    This research contributes to the understanding of macro- and micro-failure mechanisms in woven fabric polyimide matrix composites based on medium and high modulus graphite fibers tested under biaxial, shear dominated stress conditions over a temperature range of -50 C to 315 C. The goal of this research is also to provide a testing methodology for determining residual stress distributions in unidirectional, cross/ply and fabric graphite/polyimide composites using the concept of embedded metallic inclusions and X-ray diffraction (XRD) measurements.

  16. Full-field Strain Methods for Investigating Failure Mechanisms in Triaxial Braided Composites

    NASA Technical Reports Server (NTRS)

    Littell, Justin D.; Binienda, Wieslaw K.; Goldberg, Robert K.; Roberts, Gary D.

    2008-01-01

    Composite materials made with triaxial braid architecture and large tow size carbon fibers are beginning to be used in many applications, including composite aircraft and engine structures. Recent advancements in braiding technology have led to commercially viable manufacturing approaches for making large structures with complex shape. Although the large unit cell size of these materials is an advantage for manufacturing efficiency, the fiber architecture presents some challenges for materials characterization, design, and analysis. In some cases, the static load capability of structures made using these materials has been higher than expected based on material strength properties measured using standard coupon tests. A potential problem with using standard tests methods for these materials is that the unit cell size can be an unacceptably large fraction of the specimen dimensions. More detailed investigation of deformation and failure processes in large unit cell size triaxial braid composites is needed to evaluate the applicability of standard test methods for these materials and to develop alternative testing approaches. In recent years, commercial equipment has become available that enables digital image correlation to be used on a more routine basis for investigation of full field 3D deformation in materials and structures. In this paper, some new techniques that have been developed to investigate local deformation and failure using digital image correlation techniques are presented. The methods were used to measure both local and global strains during standard straight-sided coupon tensile tests on composite materials made with 12 and 24 k yarns and a 0/+60/-60 triaxial braid architecture. Local deformation and failure within fiber bundles was observed, and this local failure had a significant effect on global stiffness and strength. The matrix material had a large effect on local damage initiation for the two matrix materials used in this investigation. Premature failure in regions of the unit cell near the edge of the straight-sided specimens was observed for transverse tensile tests in which the braid axial fibers were perpendicular to the specimen axis and the bias fibers terminated on the cut edges in the specimen gage section. This edge effect is one factor that could contribute to a measured strength that is lower than the actual material strength in a structure without edge effects.

  17. Mechanics of brittle deformation and slope failure at the North Menan Butte tuff cone, Eastern Snake River Plain, Idaho

    NASA Astrophysics Data System (ADS)

    Okubo, C. H.

    2013-12-01

    The Menan Volcanic Complex consists of phreatomagmatic tuff cones that were emplaced as part of the regional volcanic activity in the Snake River Plain during the late Pleistocene. These tuff cones, the ';Menan Buttes', resulted from the eruption of basaltic magma through water-saturated alluvium and older basalts along the Snake River. The tuffs are composed primarily of basaltic glass with occasional plagioclase and olivine phenocrysts. The tuff is hydrothermally altered to a massive palagonitic tuff at depth but is otherwise poorly welded. Mass movements along the flanks of the cones were contemporaneous with tuff deposition. These slope failures are manifest as cm- to meter-scale pure folds, faults and fault-related folds, as well as larger slumps that are tens to a few hundred meters wide. Previous investigations classified the structural discontinuities at North Menan Butte based on orientation and sense of displacement, and all were recognized as opening-mode or shear fractures (Russell and Brisbin, 1990). This earlier work also used a generalized model of static (i.e., aseismic) gravity-driven shear failure within cohesionless soils to infer a possible origin for these fractures through slope failure. Recent work at North Menan Butte has provided novel insight into the styles of brittle deformation present, the effect of this deformation on the circulation of subsurface fluids within the tuff cone, as well as the mechanisms of the observed slope failures. Field observations reveal that the brittle deformation, previously classified as fractures, is manifest as deformation bands within the non-altered, poorly welded portions of the tuff. Both dilational and compactional bands, with shear, are observed. Slumps are bounded by normal faults, which are found to have developed within clusters of deformation bands. Deformation bands along the down-slope ends of these failure surfaces are predominantly compactional in nature. These bands have a ~3800 millidarcy permeability, a decrease from the ~9400 millidarcy permeability typical of the non-deformed, poorly-welded tuff. As such, these bands would have acted to slow to the circulation of local fluids through the tuff cone, possibly reducing the slopes' stability further. Future work will employ slope stability models to investigate the tendency for slumping of these tuffs shortly after their emplacement, accounting for water-saturated conditions and the effects of eruption-related seismicity. These results will improve current understanding of the mechanics of fault growth within basaltic tuff and enable more rigorous assessments of the hazards posed by slope instability on active phreatomagmatic tuff cones.

  18. Applicability of failure criteria and empirical relations of mechanical rock properties from outcrop analogue samples for wellbore stability analyses

    NASA Astrophysics Data System (ADS)

    Reyer, D.; Philipp, S. L.

    2013-12-01

    Knowledge of failure criteria, Young's modulus and uniaxial and tensile strengths, are important to avoid borehole instabilities and adapt the drilling plan on rock mechanical conditions. By this means, a considerable reduction of the total drilling costs can be achieved. This is desirable to enlarge the profit margin of geothermal projects which is rather small compared with hydrocarbon projects. Because core material is rare we aim at predicting in situ rock properties from outcrop analogue samples which are easy and cheap to provide. The comparability of properties determined from analogue samples with samples from depths is analysed by performing conventional triaxial tests, uniaxial compressive strength tests and Brazilian tests of both quarry and equivalent core samples. Equivalent means that the quarry sample is of the same stratigraphic age and of comparable sedimentary facies and composition as the associated core sample. We determined the parameters uniaxial compressive strength (UCS), Young's modulus, and tensile strength for 35 rock samples from quarries and 14 equivalent core samples from the North German Basin. A subgroup of these samples, consisting of one volcanic rock sample, three sandstone and three carbonate samples, was used for triaxial tests. In all cases, comparability of core samples with quarry samples is evaluated using thin section analyses. For UCS versus Young's modulus and tensile strengths, linear- and non-linear regression analyses were performed. We repeat regression separately for clastic rock samples or carbonate rock samples only as well as for quarry samples or core samples only. Empirical relations have high statistical significance and properties of core samples lie within 90% prediction bands of developed regression functions of quarry samples. With triaxial tests we determined linearized Mohr-Coulomb failure criteria, expressed in both principal stresses and shear and normal stresses, for quarry samples. Comparison with samples from larger depths shows that it is possible to apply the obtained principal stress failure criteria on clastic and volcanic rocks, but less so for carbonates. Carbonate core samples have higher strengths and develop larger angles between fault normal and main principal stress than quarry samples. This considerably reduces the residuals between quarry failure criteria and core test results. Therefore, it is advised to use failure criteria, expressed in shear and normal stresses, for prediction of core sample failure conditions. We conclude that it is possible to apply failure criteria on samples from depth if the comparability, especially textural comparability and similar porosities, of chosen outcrop analogues samples is ensured. Applicability of empirical relations of UCS with Young's modulus and tensile strength to rocks at depths is expected. Presented results may help predict mechanical properties for in situ rocks, and thus develop suitable geomechanical models for the adaptation of the drilling strategy on rock mechanical conditions. The authors appreciate the support of 'Niedersächsisches Ministerium für Wissenschaft und Kultur' and 'Baker Hughes' within the gebo research project (http: www.gebo-nds.de).

  19. Spreading plastic failure as a mechanism for the shear modulus reduction in amorphous solids

    NASA Astrophysics Data System (ADS)

    Chikkadi, Vijayakumar; Gendelman, Oleg; Ilyin, Valery; Ashwin, J.; Procaccia, Itamar; Shor, Carmel A. B. Z.

    2015-05-01

    We focus on the observed reduction in shear modulus when the stress on an amorphous solid is increased beyond the initial linear region. Careful numerical quasi-static simulations reveal an intimate relation between plastic failure and the reduction in shear modulus. The attainment of the smallest value of the shear modulus is identified with spreading of the regions that underwent a plastic event. We present an elementary “two-state” model that interpolates between failed and virgin regions and provides a simple and effective characterization of the phenomenon.

  20. “Late sodium current: a mechanism for angina, heart failure, and arrhythmia”

    PubMed Central

    Makielski, Jonathan C.

    2015-01-01

    The peak sodium current underlies excitability and conduction in heart muscle, but a late sodium current flowing after the peak contributes to maintaining and prolonging the action potential plateau, and also to intracellular sodium loading, that in turn increases intracellular calcium with consequent effects on arrhythmia and diastolic function. Late sodium current is pathologically increased in both genetic and acquired heart disease, making it an attractive target for therapy to treat arrhythmia, heart failure, and angina. This review provides an overview of the underlying bases for the clinical implications of late sodium current block. PMID:19333133

  1. Exploring the temperature dependence of failure mechanisms in fragmenting metal cylinders

    NASA Astrophysics Data System (ADS)

    Jones, David; Chapman, David; Hazell, Paul; Bland, Simon; Eakins, Daniel

    2011-06-01

    We present current work to investigate the influence of temperature on the dynamic fragmentation of metals. Pre-heated/cooled cylinders of Ti-6Al-4V were subjected to rapid radial expansion up to and past the point of failure using a modified expanding insert method on a single stage gas gun. Additional experiments were performed using an electromagnetic drive system to produce uniform deformations on targets of differing dimensions (radius, wall thickness). Issues concerning the geometry of the experiments, methods of heating and cooling the sample and diagnostics are covered. Finally, the role of temperature on adiabatic shear banding and fragment distribution statistics is discussed.

  2. Acoustic emission and acousto-ultrasonic signature analysis of failure mechanisms in carbon fiber reinforced polymer materials

    NASA Astrophysics Data System (ADS)

    Carey, Shawn Allen

    Fiber reinforced polymer composite materials, particularly carbon (CFRPs), are being used for primary structural applications, particularly in the aerospace and naval industries. Advantages of CFRP materials, compared to traditional materials such as steel and aluminum, include: light weight, high strength to weight ratio, corrosion resistance, and long life expectancy. A concern with CFRPs is that despite quality control during fabrication, the material can contain many hidden internal flaws. These flaws in combination with unseen damage due to fatigue and low velocity impact have led to catastrophic failure of structures and components. Therefore a large amount of research has been conducted regarding nondestructive testing (NDT) and structural health monitoring (SHM) of CFRP materials. The principal objective of this research program was to develop methods to characterize failure mechanisms in CFRP materials used by the U.S. Army using acoustic emission (AE) and/or acousto-ultrasonic (AU) data. Failure mechanisms addressed include fiber breakage, matrix cracking, and delamination due to shear between layers. CFRP specimens were fabricated and tested in uniaxial tension to obtain AE and AU data. The specimens were designed with carbon fibers in different orientations to produce the different failure mechanisms. Some specimens were impacted with a blunt indenter prior to testing to simulate low-velocity impact. A signature analysis program was developed to characterize the AE data based on data examination using visual pattern recognition techniques. It was determined that it was important to characterize the AE event , using the location of the event as a parameter, rather than just the AE hit (signal recorded by an AE sensor). A back propagation neural network was also trained based on the results of the signature analysis program. Damage observed on the specimens visually with the aid of a scanning electron microscope agreed with the damage type assigned by the signature analysis program. The load level at which significant damage occurred in the specimens was evaluated using ASME Boiler and Pressure Vessel criteria. AU testing proved inconclusive for characterization of the damage due to common problems associated with AU testing such as: reproducibility difficulties due to degradation of the attachment of the sensors, damage not detected unless in the line of sight between sensors, and large intrinsic variation of the data.

  3. Investigations of micromechanical and failure mechanisms of toughened thermoplastics by electron microscopy

    SciTech Connect

    Michler, G.H.; Starke, J.U. [Martin-Luther-Univ. Halle-Wittenburg, Merseburg (Germany)

    1996-12-31

    The competitive influence of particle diameter and interparticle distance on the toughening mechanism was studied in various thermoplastics. The morphology, deformation, and fracture properties were also investigated.

  4. Distribution of coastal cliffs in Kerala, India: their mechanisms of failure and related human engineering response

    NASA Astrophysics Data System (ADS)

    Kumar, Avinash; Seralathan, P.; Jayappa, K. S.

    2009-08-01

    The 560-km-long Kerala coast is characterised by long barriers with narrow beaches and steep cliffs. Distribution of cliffs from nine sections measuring a cumulative length of 63.5 km is evaluated in ArcGIS Software using topomaps and field survey data. The cliff sections in the southern coast comprise both permeable and impermeable rocks, whereas those along northern coast are comprised of either Precambrian crystalline and/or Tertiary formations. Notches, caves and even small arches are developed in Cannanore, Dharmadam and Kadalundi cliffs, where only primary laterites are exposed to wave attack. Stacks composed of laterite and Precambrian crystallines found in nearshore of cliffed coast indicate recession of shoreline. Mass wasting, mudslide and mudflow type of cliff failures are common in permeable to semi-permeable rocks, whereas rotational sliding, rockfall and toppling failure are found in hard rock cliffs. Retreat of cliff sections are induced by natural or anthropogenic activities or both. Rate of recession vary from a few centimetres to one metre/year depending upon the nature of lithology, structures and recession agents acting upon the cliffs. Various methods of cliff protection for e.g. hard structures—revetments, groins, seawalls, breakwater and jetties—and soft measures—artificial reefs/marsh creation, floating breakwaters, beach nourishment, beach scraping and vegetation planting—are suggested.

  5. Mechanical failure of metal-polyethylene sandwich liner in metal-on-metal total hip replacement.

    PubMed

    Oshima, Yasushi; Fetto, Joseph F

    2015-01-01

    Metal-on-metal had been proposed as an optimal articulation in THRs, however, many monoblock prostheses have been recalled in the USA because of significant high rates of early failure. Metal-on-metal prostheses had been implanted in our institution, and this is a case history of a single patient, in whom metal-on-metal THRs with different femoral sizes of heads were implanted. A 57-year-old female patient underwent bilateral total hip replacements with metal-on-metal prostheses using metal-polyethylene "sandwich" liners 9 years ago on the right side and 7 years ago on the left side respectively. The only difference in both sides was the femoral head diameter of 28 mm in right and 34 mm in left. Seven years after the left surgery, the acetabular liner was dissociated, however, metallosis was not detected. Although the larger femoral head was thought to increase hip joint stability, it dictated a reduction in polyethylene thickness in this prosthesis design, and it was 4 mm in the left hip. Recently, metal-on-metal articulations are thought not to be optimal for hip joint bearing surface, however, this clinical failure was due to the polyethylene thickness and quality. PMID:25601670

  6. Knee Extensor Mechanism Reconstruction With Complete Extensor Allograft After Failure of Patellar Tendon Repair.

    PubMed

    Thakkar, Savyasachi C; Hsu, Nigel; Hasenboehler, Erik A

    2015-06-01

    Disruptions of the extensor mechanism of the knee may be bony or tendinous in nature. The consequences of such disruptions are not favorable because they prevent normal function of the knee, which is critical for independent ambulation. We report on a 30-year-old man who underwent a successful knee extensor mechanism reconstruction with allograft after his initial tendon repair failed. PMID:26047006

  7. Failure prediction analysis of an ACCC conductor subjected to thermal and mechanical stresses

    Microsoft Academic Search

    B. Burks; D. L. Armentrout; M. Kumosa

    2010-01-01

    In this work, the Aluminum Conductor Composite Core¿ (ACCC) was numerically investigated to evaluate stress distributions when subjected to thermal and mechanical loads. The thermal analysis was conducted to simulate the cooling cycle of the rod from 250°C to room temperature. Three types of mechanical loads were considered, namely axial tension, small bending, and large bending conditions. This was done

  8. Mechanisms of reduced contractility in an animal model of hypertensive heart failure.

    PubMed

    Ward, Marie-Louise; Crossman, David J; Cannell, Mark B

    2011-10-01

    1. Alterations in intracellular Ca(2+) homeostasis have frequently been implicated as underlying the contractile dysfunction of failing hearts. Contraction in cardiac muscle is due to a balance between sarcolemmal (SL) and sarcoplasmic reticulum (SR) Ca(2+) transport, which has been studied in single cells and small tissue samples. However, many studies have not used physiological temperatures and pacing rates, and this could be problematic given different temperature dependencies and kinetics for transport processes. 2. Spontaneously-hypertensive rats (SHR) and their age-matched Wistar Kyoto controls (WKY) provide an animal model of hypertensive failure with many features in common to heart failure in humans. Steady-state measurements of Ca(2+) and force showed that peak stress was reduced in trabeculae from failing SHR hearts in comparison to WKY, although the Ca(2+) transients were bigger and decayed more slowly. 3. Dynamic Ca(2+) cycling was investigated by determining the recirculation fraction (RF) of activator Ca(2+) through the SR between beats during recovery from experimental protocols that potentiated twitch force. No difference in RF between rat strains was found, although the RF was dependent on the potentiation protocol used. 4.?Superfusion with 10 mmol/L caffeine and 0 mmol/L [Ca(2+)](o) was used to measure SL Ca(2+) extrusion. The caffeine-induced [Ca(2+)](i) transient decayed more slowly in SHR trabeculae, suggesting that SL Ca(2+) extrusion was slower in SHR. 5. An ultrastructural immunohistochemical analysis of left ventricular free wall sections using confocal microscopy showed that t-tubule organization was disrupted in myocytes from SHR, with reduced labelling of the SR Ca(2+) -ATPase and Na(+) -Ca(2+) exchanger in comparison to WKY, with the latter possibly related to a lower fraction of t-tubules per unit cell volume. 6. We suggest that although Ca(2+) transport is altered in the progression to heart failure, force development is not limited by the amplitude of the Ca(2+) transient. Despite slower SR Ca(2+) transport, the recirculation fraction and dynamic response to a change of inotropic state minimally altered changes in the SHR model because there was a similar slowing in Ca(2+) extrusion across the surface membrane. PMID:21711381

  9. Impermeable thin AI2O3 overlay for TBC protection from sulfate and vanadate attack in gas turbines

    SciTech Connect

    Scott X. Mao

    2005-10-30

    In order to improve the hot corrosion resistance of conventional YSZ TBC system, a dense and continues overlay of Al{sub 2}O{sub 3} coating of about 0.1-25 {micro}m thick was deposited on the surface of TBC by EB-PVD, high velocity oxy-fuel (HVOF) spray and composite-sol-gel (CSG) techniques. Hot corrosion tests were carried out on the TBC with and without Al{sub 2}O{sub 3} coating in molten salts mixtures (Na{sub 2}SO{sub 4} + 5%V{sub 2}O{sub 5}) at 950 C for 10h. The microstructures of TBC and overlay before and after exposure were examined by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectrometer (EDX), X-ray diffraction (XRD) and secondary ion mass spectrometry (SIMS). In order to investigate the effect of Al{sub 2}O{sub 3} overlay on degradation and spalling of the TBC, indentation test has been employed to study spallation behaviors of YSZ coating with and without Al{sub 2}O{sub 3} overlay. It has been found that TBC will react with V{sub 2}O5 to form YVO{sub 4} in hot corrosion tests. A substantial amount of M-phase of ZrO{sub 2} was formed due to the leaching of Y{sub 2}O{sub 3} from YSZ. During hot corrosion test, there were no significant interactions between overlay Al{sub 2}O{sub 3} coating and molten salts. After exposure, the alumina coating, especially produced by HVOF, was still very dense and cover the surface of YSZ, although they had been translated to {alpha} - Al{sub 2}O{sub 3} from original {gamma} - Al{sub 2}O{sub 3}. As a result, Al{sub 2}O{sub 3} overlay coating decreased the penetration of salts into the YSZ and prevented the YSZ from the attack by molten salts containing vanadium. Accordingly, only a few M-phase was formed in YSZ TBC, compared with TBC without overlay coating. The penetration of salts into alumina coating was thought to be through microcracks formed in overlay Al{sub 2}O{sub 3} coating and at the interface between alumina and zirconia due to the presence of tensile stress in the alumina coating. Al{sub 2}O{sub 3} overlay acted as a barrier against the infiltration of the molten salt into the YSZ coating during exposure, thus significantly reduced the amount of M-phase of ZrO{sub 2} in YSZ coating. However, a thick Al{sub 2}O{sub 3} overlay was harmful for TBC by increasing compressive stress which causes crack and spalling of YSZ coating. As a result, a dense and thin Al{sub 2}O{sub 3} overlay is critical for simultaneously preventing YSZ from hot corrosion and spalling.

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

    NASA Technical Reports Server (NTRS)

    Lathrop, J. W.

    1984-01-01

    Research on the reliability of terrestrial solar cells was performed to identify failure/degradation modes affecting solar cells and to relate these to basic physical, chemical, and metallurgical phenomena. Particular concerns addressed were the reliability attributes of individual single crystalline, polycrystalline, and amorphous thin film silicon cells. Results of subjecting different types of crystalline cells to the Clemson accelerated test schedule are given. Preliminary step stress results on one type of thin film amorphous silicon (a:Si) cell indicated that extraneous degradation modes were introduced above 140 C. Also described is development of measurement procedures which are applicable to the reliability testing of a:Si solar cells as well as an approach to achieving the necessary repeatability of fabricating a simulated a:Si reference cell from crystalline silicon photodiodes.

  11. Mechanical analysis of congestive heart failure caused by bundle branch block based on an electromechanical canine heart model

    NASA Astrophysics Data System (ADS)

    Dou, Jianhong; Xia, Ling; Zhang, Yu; Shou, Guofa; Wei, Qing; Liu, Feng; Crozier, Stuart

    2009-01-01

    Asynchronous electrical activation, induced by bundle branch block (BBB), can cause reduced ventricular function. However, the effects of BBB on the mechanical function of heart are difficult to assess experimentally. Many heart models have been developed to investigate cardiac properties during BBB but have mainly focused on the electrophysiological properties. To date, the mechanical function of BBB has not been well investigated. Based on a three-dimensional electromechanical canine heart model, the mechanical properties of complete left and right bundle branch block (LBBB and RBBB) were simulated. The anatomical model as well as the fiber orientations of a dog heart was reconstructed from magnetic resonance imaging (MRI) and diffusion tensor MRI (DT-MRI). Using the solutions of reaction-diffusion equations and with a strategy of parallel computation, the asynchronous excitation propagation and intraventricular conduction in BBB was simulated. The mechanics of myocardial tissues were computed with time-, sarcomere length-dependent uniaxial active stress initiated at the time of depolarization. The quantification of mechanical intra- and interventricular asynchrony of BBB was then investigated using the finite-element method with an eight-node isoparametric element. The simulation results show that (1) there exists inter- and intraventricular systolic dyssynchrony during BBB; (2) RBBB may have more mechanical synchrony and better systolic function of the left ventricle (LV) than LBBB; (3) the ventricles always move toward the early-activated ventricle; and (4) the septum experiences higher stress than left and right ventricular free walls in BBB. The simulation results validate clinical and experimental recordings of heart deformation and provide regional quantitative estimates of ventricular wall strain and stress. The present work suggests that an electromechanical heart model, incorporating real geometry and fiber orientations, may be helpful for better understanding of the mechanical implications of congestive heart failure (CHF) caused by BBB.

  12. Noninvasive Mechanical Ventilation in the Weaning of Patients with Respiratory Failure Due to Chronic Obstructive Pulmonary Disease A Randomized, Controlled Trial

    Microsoft Academic Search

    Stefano Nava; Nicolino Ambrosino; Enrico Clini; Maurizio Prato; Giacomo Orlando; Michele Vitacca; Paolo Brigada; Claudio Fracchia; Fiorenzo Rubini

    Background: In patients with acute exacerbations of chronic obstructive pulmonary disease, mechanical venti­ lation is often needed. The rate of weaning failure is high in these patients, and prolonged mechanical ventilation increases intubation-associated complications. Objective: To determine whether noninvasive ventila­ tion improves the outcome of weaning from invasive me­ chanical ventilation. Design: Multicenter, randomized trial. Setting: Three respiratory intensive care

  13. Extensor mechanism reconstruction: a novel technique for bone patella allograft post partial patellectomy failure.

    PubMed

    Drexler, Michael; Blumberg, Nehemia; Haim, Amir; Arbel, Ron; Morag, Guy

    2011-06-01

    Extensor mechanism disruption, whether due to patella fracture or tendon rupture, generally occurs after low-energy trauma and frequently involves an indirect mechanism. When the fracture is comminuted and reconstruction is impossible, a partial or total patellectomy may be indicated. Although some authors advocate total patellectomy, partial patellectomy remains the standard treatment, especially for young and active patients. In the rare instance of a failed tendon repair after partial or total patellectomy, inadequate tissue is usually available for adequate restoration of the extensor mechanism. Extensor mechanism allograft, using the tibial tuberosity, patellar tendon, patella, and quadriceps tendon in continuity or the Achilles' tendon with calcaneal bone-block in continuity has been reported for extensor mechanism repair after total knee arthroplasty in patients who did not undergo patellectomy. We present a novel technique, using the bone patellar tendon bone allograft to reconstruct a posttraumatic defect of the extensor mechanism in a 28-year-old, active patient with a failed partial patellectomy following fracture of his patella. Union of the allograft was seen on x-ray after 4 months. After 6 months, the patient reached full range of motion and returned to his previous sporting activities. PMID:21874949

  14. On-Line Thermal Barrier Coating Monitoring for Real-Time Failure Protection and Life Maximization

    SciTech Connect

    Dennis H. LeMieux

    2004-10-01

    Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Westinghouse Power Corporation proposes a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization'', to develop, build and install the first generation of an on-line TBC monitoring system for use on land -based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability availability maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCs have been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can therefore accelerate the degradation of substrate components materials and eventually lead to a premature failure of critical component and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Westinghouse Power Corporation has teamed with Indigo Systems; a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization.

  15. On-Line Thermal Barrier Coating Monitoring for Real-Time Failure Protection and Life Maximization

    SciTech Connect

    Dennis H. LeMieux

    2005-04-01

    Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Westinghouse Power Corporation proposes a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization'', to develop, build and install the first generation of an on-line TBC monitoring system for use on land-based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability availability maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCs have been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can therefore accelerate the degradation of substrate components materials and eventually lead to a premature failure of critical component and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Westinghouse Power Corporation has teamed with Indigo Systems, a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization in the field of infrared non-destructive examination (NDE), to complete the program.

  16. ON-LINE THERMAL BARRIER COATING MONITORING FOR REAL-TIME FAILURE PROTECTION AND LIFE MAXIMIZATION

    SciTech Connect

    Dennis H. LeMieux

    2003-07-01

    Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Westinghouse Power Corporation proposes a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization,'' to develop, build and install the first generation of an on-line TBC monitoring system for use on land-based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability, availability, and maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCs have been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can, therefore, accelerate the degradation of substrate component materials and eventually lead to a premature failure of critical components and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Westinghouse Power Corporation has teamed with Indigo Systems, a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization in the field of infrared non-destructive examination (NDE), to complete the program.

  17. ON-LINE THERMAL BARRIER COATING MONITORING FOR REAL-TIME FAILURE PROTECTION AND LIFE MAXIMIZATION

    SciTech Connect

    Dennis H. LeMieux

    2003-10-01

    Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Westinghouse Power Corporation proposes a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization,'' to develop, build and install the first generation of an on-line TBC monitoring system for use on land-based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability, availability, and maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCs have been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can, therefore, accelerate the degradation of substrate component materials and eventually lead to a premature failure of critical components and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Westinghouse Power Corporation has teamed with Indigo Systems, a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization in the field of infrared non-destructive examination (NDE), to complete the program.

  18. ON-LINE THERMAL BARRIER COATING MONITORING FOR REAL-TIME FAILURE PROTECTION AND LIFE MAXIMIZATION

    SciTech Connect

    Dennis H. LeMieux

    2002-04-01

    Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Westinghouse Power Corporation proposes a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization,'' to develop, build and install the first generation of an on-line TBC monitoring system for use on land-based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability availability maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCs have been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can therefore accelerate the degradation of substrate components materials and eventually lead to a premature failure of critical component and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Westinghouse Power Corporation has teamed with Indigo Systems, a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization in the field of infrared non-destructive examination (NDE), to complete the program.

  19. On-Line Thermal Barrier Coating Monitoring for Real-Time Failure Protection and Life Maximization

    SciTech Connect

    Dennis H. LeMieux

    2005-10-01

    Under the sponsorship of the U. S. Department of Energy's National Energy Laboratory, Siemens Power Generation, Inc proposed a four year program titled, ''On-Line Thermal Barrier Coating (TBC) Monitor for Real-Time Failure Protection and Life Maximization'', to develop, build and install the first generation of an on-line TBC monitoring system for use on land-based advanced gas turbines (AGT). Federal deregulation in electric power generation has accelerated power plant owner's demand for improved reliability availability maintainability (RAM) of the land-based advanced gas turbines. As a result, firing temperatures have been increased substantially in the advanced turbine engines, and the TBCs have been developed for maximum protection and life of all critical engine components operating at these higher temperatures. Losing TBC protection can therefore accelerate the degradation of substrate components materials and eventually lead to a premature failure of critical component and costly unscheduled power outages. This program seeks to substantially improve the operating life of high cost gas turbine components using TBC; thereby, lowering the cost of maintenance leading to lower cost of electricity. Siemens Power Generation, Inc. has teamed with Indigo Systems, a supplier of state-of-the-art infrared camera systems, and Wayne State University, a leading research organization in the field of infrared non-destructive examination (NDE), to complete the program.

  20. Overall Quality of Life Improves to Similar Levels after Mechanical Circulatory Support Regardless of Severity of Heart Failure before Implantation

    PubMed Central

    Grady, Kathleen L; Naftel, David; Stevenson, Lynne; Dew, Mary Amanda; Weidner, Gerdi; Pagani, Francis D.; Kirklin, James K; Myers, Susan; Baldwin, Timothy; Young, James

    2014-01-01

    Background Pre implant heart failure severity may affect post implant health-related quality of life (HRQOL). The purpose of our study was to examine differences in HRQOL from before mechanical circulatory support (MCS) through 1 year after surgery, by INTERMACS patient profiles. Methods Data from adult patients with advanced heart failure who received primary continuous flow pumps between 6/23/06 – 3/31/10 and were enrolled in INTERMACS (n=1,559) were analyzed. HRQOL data were collected using the EQ-5D-3L survey pre implant and at 3, 6 and 12 months after implant. Statistical analyses included chi square and t-tests, using all available data for each time period. Paired ttests and sensitivity analyses were also conducted. Results Quality of life was poor before MCS implant among patients with INTERMACS profiles 1–7 and significantly improved after MCS for all profiles. Stratified by INTERMACS profile, problems within each of the five dimensions of HRQOL (i.e., mobility, self-care, usual activities, pain, and anxiety / depression) generally decreased from before to after implant. By six months after implant, patients with all INTERMACS profiles reported similar frequencies of problems for all HRQOL dimensions. Paired ttests and sensitivity analyses supported the vast majority of our findings. Conclusions HRQOL is poor among advanced heart failure patients with INTERMACS profiles 1–7 before MCS implantation and improves to similar levels for patients who remained on MCS 1 year after surgery. Patients have problems in HRQOL dimensions before and after MCS; the frequency of reporting problems decreases for all dimensions within most profiles across time. PMID:24360203

  1. Electronics reliability fracture mechanics. Volume 1: Causes of failures of shop replaceable units and hybrid microcircuits

    NASA Astrophysics Data System (ADS)

    Kallis, J.; Buechler, D.; Erickson, J.; Westerhuyzen, D. V.; Strokes, R.

    1992-05-01

    This is the first of two volumes. The other volume (WL-TR-91-3119) is 'Fracture Mechanics'. The objective of the Electronics Reliability Fracture Mechanics (ERFM) program was to develop and demonstrate a life prediction technique for electronic assemblies, when subjected to environmental stress of vibration and thermal cycling, based upon the mechanical properties of the materials and packaging configurations which make up an electronic system. A detailed investigation was performed of the following two shop replaceable units (SRUs): Timing and Control Module (P/N 3562102) and Linear Regulator Module (P/N 3569800). The SRUs are in the Programmable Signal Processor (3137042) Line Replaceable Unit (LRU) of the Hughes AN/APG-63 Radar for the F-15 Aircraft.

  2. Weld Growth Mechanisms and Failure Behavior of Three-Sheet Resistance Spot Welds Made of 5052 Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Li, Yang; Yan, Fuyu; Luo, Zhen; Chao, Y. J.; Ao, Sansan; Cui, Xuetuan

    2015-04-01

    This paper investigates the weld nugget formation in three-sheet aluminum alloy resistance spot welding. The nugget formation process in three equal thickness sheets and three unequal thickness sheets of 5052 aluminum alloy were studied. The results showed that the nugget was initially formed at the workpiece/workpiece interfaces (i.e., both upper interface and lower interface). The two small nuggets then grew along the radial direction and axial direction (welding direction) as the welding time increased. Eventually, the two nuggets fused into one large nugget. During the welding process, the Peltier effect between the Cu-Al caused the shift of the nugget in the welding direction. In addition, the mechanical strength and fracture mode of the weld nuggets at the upper and lower interfaces were also studied using tensile shear specimen configuration. Three failure modes were identified, namely interfacial, mixed, and pullout. The critical welding time and critical nugget diameter corresponding to the transitions of these modes were investigated. Finally, an empirical failure load formula for three-sheet weld similar to two-sheet spot weld was developed.

  3. Study of failure mechanisms for InGaN light-emitting diode chips with patterned sapphire substrates

    NASA Astrophysics Data System (ADS)

    Sun, Chia-Hung; Huang, Man-Fang; Yang, Hsu-Han; Chen, Fang-Ming; Chen, Tzung-Te

    2015-03-01

    In this paper, we investigated the failure mechanisms of blue InGaN LEDs grown on patterned sapphire substrates and demonstrated the influence of patterned sapphire substrates on the reliability of GaN LED by comparing with conventional LEDs grown on planar sapphire substrates. From experimental results, we found that InGaN LEDs grown on patterned substrates had a higher turn-on voltage but a smaller series resistance compared with conventional LEDs owing to rough inner patterns and small threading dislocation density. Both samples were then acceleratedly aged under a high DC current for two hours. Failure modes were studied with various measurements taken before and after aging. From the power evolution performance, we found that output power of LEDs with patterned substrates increased slightly due to fewer defects while output power of conventional LEDs decayed. This can be inferred from small reverse leakage currents and tunneling currents observed from Log I-V characteristics and EMMI measurement of P-LEDs. A slight redshift in emission wavelength was also found during aging because of possible leakage shunt paths caused by defect generation. Moreover, operation voltage increased slightly after aging which was caused by contact degradation induced by thermal annealing.

  4. Mechanism of decreased forward stroke volume in children and swine with ventricular septal defect and failure to thrive.

    PubMed Central

    Corin, W J; Swindle, M M; Spann, J F; Nakano, K; Frankis, M; Biederman, R W; Smith, A; Taylor, A; Carabello, B A

    1988-01-01

    Children with ventricular septal defect (VSD) often demonstrate failure to thrive (FTT). Such patients usually have reduced systemic cardiac output which has been postulated as a cause for their growth retardation. This study was conducted to ascertain the mechanism of the reduced cardiac output in children with VSD and FTT and also in a porcine model of VSD. Forward stroke volume was reduced in VSD-FTT children, 31 +/- 8 ml/m2, compared to normal children, 49 +/- 15 ml/m2 (P less than 0.05), but was not reduced in children with VSD and normal growth and development (41 +/- 16 ml/m2). Forward stroke volume was also reduced in swine with VSD compared to controls. Contractility assessed by mean velocity of circumferential shortening (Vcf) corrected for afterload was similar in normals and VSD-FTT children. Contractile performance was also similar in normal and VSD swine. Afterload assessed as systolic stress was similar in FTT-VSD children and normal subjects. Preload assessed as end-diastolic stress was increased in the VSD-FTT group. End-diastolic volume was not larger in the VSD-FTT group. We conclude that the reduced stroke volume seen in VSD-FTT children and VSD-swine was not due to reduced contractility, increased afterload or reduced preload. The reduced stroke volume may have been due to failure of end-diastolic volume to increase adequately. Images PMID:3403715

  5. Weld Growth Mechanisms and Failure Behavior of Three-Sheet Resistance Spot Welds Made of 5052 Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Li, Yang; Yan, Fuyu; Luo, Zhen; Chao, Y. J.; Ao, Sansan; Cui, Xuetuan

    2015-06-01

    This paper investigates the weld nugget formation in three-sheet aluminum alloy resistance spot welding. The nugget formation process in three equal thickness sheets and three unequal thickness sheets of 5052 aluminum alloy were studied. The results showed that the nugget was initially formed at the workpiece/workpiece interfaces (i.e., both upper interface and lower interface). The two small nuggets then grew along the radial direction and axial direction (welding direction) as the welding time increased. Eventually, the two nuggets fused into one large nugget. During the welding process, the Peltier effect between the Cu-Al caused the shift of the nugget in the welding direction. In addition, the mechanical strength and fracture mode of the weld nuggets at the upper and lower interfaces were also studied using tensile shear specimen configuration. Three failure modes were identified, namely interfacial, mixed, and pullout. The critical welding time and critical nugget diameter corresponding to the transitions of these modes were investigated. Finally, an empirical failure load formula for three-sheet weld similar to two-sheet spot weld was developed.

  6. Hygrothermal effects on mechanical behavior of graphite/epoxy laminates beyond initial failure

    NASA Technical Reports Server (NTRS)

    Ishai, O.; Garg, A.; Nelson, H. G.

    1984-01-01

    An investigation was conducted to determine the critical load levels and associated cracking beyond which a multidirectional laminate can be considered as structurally failed. Graphite/epoxy laminates were loaded to different strain levels up to ultimate failure. Transverse matrix cracking was monitored by acoustic and optical methods. Residual stiffness and strength that were parallel and perpendicular to the cracks were determined and related to the environmental/loading history. Results indicate that cracking density in the transverse layers has no major effect on laminate residual properties as long as the angle ply layers retain their structural integrity. Exposure to hot water revealed that cracking had only a small effect on absorption and reduced swelling when these specimens were compared with uncracked specimens. Cracked, moist specimens showed a moderate reduction in strength when compared with their uncracked counterparts. Within the range of environmental/loading conditions of the present study, it is concluded that the transverse cracking process is not crucial in its effect on the structural performance of multidirectional composite laminates.

  7. When Public Acts Like Private: The Failure of Estonia's School Choice Mechanism

    ERIC Educational Resources Information Center

    Poder, Kaire; Lauri, Triin

    2014-01-01

    This article aims to show the segregating effect of the market-like matching of students and schools at the basic school level. The natural experiment case is Tallinn, the capital of Estonia. The current school choice mechanism applied in this case is based on entrance tests. There are increasingly over-subscribed intra-catchment area public…

  8. Failure mechanisms of a notched CFRP laminate under multi-axial loading

    E-print Network

    Tan, J. L. Y.; Deshpande, V. S.; Fleck, N. A.

    2015-07-02

    ;42:874–84. doi:10.1016/j.compositesb.2011.01.011. [35] Freeman SM. Characterization of lamina and interlaminar damage in graphite/epoxy composite by the deply technique. ASTM STP 787 1982:50–62. [36] Spearing SM, Beaumont PWR. Fatigue damage mechanics...

  9. JAP-00590-2004 Mechanics, nonlinearity, and failure strength of lung tissue in a mouse

    E-print Network

    Lutchen, Kenneth

    of emphysema: possible role of collagen remodeling Satoru Ito, Edward P. Ingenito*, Kelly K. Brewer, Lauren D's Hospital, Harvard Medical School, Boston MA 02115 Running title: Respiratory mechanics of emphysema Address and re-organization of the connective tissue fiber network during the development of pulmonary emphysema

  10. A NEW FAILURE MECHANISM BY SCANNING ELECTRON MICROSCOPE INDUCED ELECTRICAL BREAKDOWN OF TUNGSTEN WINDOWS IN

    E-print Network

    Pearton, Stephen J.

    WINDOWS IN INTEGRATED CIRCUIT PROCESSING BY DAVID M. SHUTTLEWORTH A THESIS PRESENTED TO THE GRADUATE.............................................................................10 2.1.2 Mechanics of the Window Liner.4. THE PROCEDURE - EXPERIMENT ONE:WINDOW-1........ERROR! BOOKMARK NOT DEFINED. 3.5. THE PROCEDURE: EXPERIMENT 2

  11. Dynamic loading affects the mechanical properties and failure site of porcine spines

    Microsoft Academic Search

    Vanessa R Yingling; Jack P Callaghan; Stuart M McGill

    1997-01-01

    Objective. The purpose of this study was to investigate the effect of load rate on the mechanical characteristics of spinal motion segments under compressive loading.Design. An in vitro experiment using a porcine model which ensured a homogeneous population for age, weight, genetic background and physical activity.Background. Spinal motion segments comprise of viscoelastic materials, and as a result the rate of

  12. Mechanical property evaluation and failure analysis of cantilevered LIGA nickel microposts

    Microsoft Academic Search

    Lyndon S. Stephens; Kevin W. Kelly; Seshu Simhadri; Andy B. McCandless; E. I. Meletis

    2001-01-01

    An experimental apparatus has been built to measure the elastic modulus and bending strength (modulus of rupture) of LIGA nickel posts. The apparatus uses the static cantilever beam bending approach to measure mechanical properties in a direction parallel to the growth direction. Experimental results are presented for two sets of largely identical posts constructed using an overplating method. One set

  13. Successful allogeneic hematopoietic stem cell transplantation for acute myeloid leukemia during respiratory failure and invasive mechanical ventilation.

    PubMed

    Boehm, Alexandra; Rabitsch, Werner; Locker, Gottfried J; Worel, Nina; Robak, Oliver; Laczika, Klaus F; Staudinger, Thomas; Bojic, Andja; Siersch, Viktoria; Valent, Peter; Sperr, Wolfgang R

    2011-06-01

    Allogeneic hematopoietic stem cell transplantation (HSCT) is a curative treatment option for various hematologic disorders. However, life-threatening adverse events resulting from treatment-related toxicity, severe infections, and/or graft-versus-host disease (GvHD) can occur. We report on a 64-year-old patient suffering from secondary acute myeloid leukemia (AML) who underwent successful allogeneic HSCT while on invasive mandatory ventilation (IMV). The patient received reduced intensity conditioning (RIC) according to the FLAMSA-protocol. Acute respiratory failure occurred one day before scheduled HSCT. Following emergency endotracheal intubation the patient was transferred to the intensive care unit (ICU). Because of respiratory deterioration, stem cell infusion was postponed. After stabilization of respiratory parameters, HSCT was performed during IMV which was continued for seven days. Following hematopoietic regeneration the patient was discharged in good condition on day 35 after HSCT. This case illustrates that intubation and mechanical ventilation do not necessarily exclude leukemic patients from HSCT. PMID:21633813

  14. Strain shielding from mechanically activated covalent bond formation during nanoindentation of graphene delays the onset of failure.

    PubMed

    Kumar, Sandeep; Parks, David M

    2015-03-11

    Mechanical failure of an ideal crystal is dictated either by an elastic instability or a soft-mode instability. Previous interpretations of nanoindentation experiments on suspended graphene sheets,1,2 however, indicate an anomaly: the inferred strain in the graphene sheet directly beneath the diamond indenter at the measured failure load is anomalously large compared to the fracture strains predicted by both soft-mode and acoustic analyses. Through multiscale modeling combining the results of continuum, atomistic, and quantum calculations, and analysis of experiments, we identify a strain-shielding effect initiated by mechanochemical interactions at the graphene-indenter interface as the operative mechanism responsible for this anomaly. Transmission electron micrographs and a molecular model of the diamond indenter's tip suggest that the tip surface contains facets comprising crystallographic {111} and {100} planes. Ab initio and molecular dynamics (MD) simulations confirm that a covalent bond (weld) formation between graphene and the crystallographic {111} and {100} facets on the indenter's surface can be induced by compressive contact stresses of the order achieved in nanoindentation tests. Finite element analysis (FEA) and MD simulations of nanoindentation reveal that the shear stiction provided by the induced covalent bonding restricts relative slip of the graphene sheet at its contact with the indenter, thus initiating a local strain-shielding effect. As a result, subsequent to stress-induced bonding at the graphene-indenter interface, the spatial variation of continuing incremental strain is substantially redistributed, locally shielding the region directly beneath the indenter by limiting the buildup of strain while imparting deformation to the surrounding regions. The extent of strain shielding is governed by the strength of the shear stiction, which depends upon the level of hydrogen saturation at the indenter's surface. We show that at intermediate levels of hydrogen saturation the strain-shielding effect can enable the graphene to support experimentally determined fracture loads and displacements without prematurely reaching locally limiting states of stress and deformation. PMID:25554829

  15. Cytochrome c oxidase III as a mechanism for apoptosis in heart failure following myocardial infarction

    PubMed Central

    Wu, Changgong; Yan, Lin; Depre, Christophe; Dhar, Sunil K.; Shen, You-Tang; Sadoshima, Junichi; Vatner, Stephen F.

    2009-01-01

    Cytochrome c oxidase (COX) is composed of 13 subunits, of which COX I, II, and III are encoded by a mitochondrial gene. COX I and II function as the main catalytic components, but the function of COX III is unclear. Because myocardial ischemia affects mitochondrial oxidative metabolism, we hypothesized that COX activity and expression would be affected during postischemic cardiomyopathy. This hypothesis was tested in a monkey model following myocardial infarction (MI) and subsequent pacing-induced heart failure (HF). In this model, COX I protein expression was decreased threefold after MI and fourfold after HF (P < 0.05 vs. sham), whereas COX II expression remained unchanged. COX III protein expression increased 5-fold after MI and further increased 10-fold after HF compared with sham (P < 0.05 vs. sham). The physiological impact of COX III regulation was examined in vitro. Overexpression of COX III in mitochondria of HL-1 cells resulted in an 80% decrease in COX I, 60% decrease in global COX activity, 60% decrease in cell viability, and threefold increase in apoptosis (P < 0.05). Oxidative stress induced by H2O2 significantly (P < 0.05) increased COX III expression. H2O2 decreased cell viability by 47 ± 3% upon overexpression of COX III, but only by 12 ± 5% in control conditions (P < 0.05). We conclude that ischemic stress in vivo and oxidative stress in vitro lead to upregulation of COX III, followed by downregulation of COX I expression, impaired COX oxidative activity, and increased apoptosis. Therefore, upregulation of COX III may contribute to the increased susceptibility to apoptosis following MI and subsequent HF. PMID:19625613

  16. Application of EBSD method for the investigation of microstructure and crystallographic orientation in RE2Zr2O7 TBC

    Microsoft Academic Search

    B Chmiela; M Soza?ska; G Moskal

    2012-01-01

    Modern aero engine turbine blades made of nickel-based superalloys are covered by thermal barrier coatings (TBC) for thermal and oxidation protection. A new generation of TBCs consist of a bond coat (thin layer of MCrAlY, where M may be Ni, Co, Fe) followed by a ceramic top coat of RE2Zr2O7 (RE - rare earth element). In this paper we present

  17. Criteria of assessment of powders provided to spray by the APS method for new and conventional layers type TBC

    Microsoft Academic Search

    G. Moskal

    2009-01-01

    Purpose: Verification of up-to-now use of conventional powders, provided to spray by the APS method for layers type TBC and its possible adaptation to layers of new types, which are based on new ceramic compounds, sprayed on conventional high temperature creep resisting alloys. New types of used ceramic powders are so called pyrochlores of the RE2Zr2O7 general formula. Design\\/methodology\\/approach: A

  18. Screening for target Rabs of TBC (Tre-2/Bub2/Cdc16) domain-containing proteins based on their Rab-binding activity.

    PubMed

    Itoh, Takashi; Satoh, Megumi; Kanno, Eiko; Fukuda, Mitsunori

    2006-09-01

    It has recently been proposed that the TBC (Tre2/Bub2/Cdc16) domain functions as a GAP (GTPase-activating protein) domain for small GTPase Rab. Because of the large number of Rab proteins in mammals, however, most TBC domains have never been investigated for Rab-GAP activity. In this study we established panels of the GTP-fixed form of 60 different Rabs constructed in pGAD-C1, a yeast two-hybrid bait vector. We also constructed a yeast two-hybrid prey vector (pGBDU-C1) that harbors the cDNA of 40 distinct TBC proteins. Systematic investigation of 2400 combinations of 60 GTP-fixed Rabs and 40 TBC proteins by yeast two-hybrid screening revealed that seven TBC proteins specifically and differentially interact with specific Rabs (e.g. OATL1 interacts with Rab2A; FLJ12085 with Rab5A/B/C; and Evi5-like with Rab10). Measurement of in vitro Rab-GAP activity revealed that OATL1 and Evi5-like actually possess significant Rab2A- and Rab10-GAP activity, respectively, but that FLJ12085 do not display Rab5A-GAP activity at all. These results indicate that specific interaction between TBC protein and Rab would be a useful indicator for screening for the target Rabs of some TBC/Rab-GAP domains, but that there is little correlation between the Rab-binding activity and Rab-GAP activity of other TBC proteins. PMID:16923123

  19. Topical Report ''Corrosion Evaluation of LLW2 Skid-B Weld Failure Mechanisms (44139-92)

    SciTech Connect

    JI Young Chang

    2001-05-31

    An independent investigation of pipe welding leaks from the Low-Level Waste 2 (LLW2) Skid-B System for the possibilities of improper welding (IW), microbiologically influenced corrosion (MIC), sensitization, chloride pitting corrosion (CPC), and intergranular stress corrosion cracking (IGSCC) was conducted. The results show the prevailing mechanisms that caused the leaks are identified as IW, CPC, and the improper selection of weld filler material for the base metals in an environment of the North Plateau underground water. These is no evidence of MIC, sensitization, or IGSCC. The chloride pitting corrosion mechanism that took place at all the welds are also described. All the pipelines were replaced with polyvinyl chloride (PVC) for cost saving and the LLW2 Skid B System has been successfully operating since 1999. This report summarizes the findings and recommendations associated with preventive measures for future operations. The LLW2 Facility is a replacement for an existing waste treatment system. The Facility processes two different waste streams through two different ''skids.'' After seven months of operation, one of the two skids began to leak. Extensive evaluation of the corrosion mechanisms and the contributing factors are documented in this report. This report principally evaluates the physical and chemical configurations that led to the corrosion and leaks. Chloride pitting corrosion, exacerbated by weld defects, is the corrosion mechanism. The report also discusses fabrication and Quality Assurance (QA)/Quality Control (QC) actions that would have prevented their occurrence. It is believed that in the absence of either the defects or the chloride concentrations, corrosion would not have occurred. In developing the specification for processing skids to be used in the Facility, high chloride was not identified as a parameter of concern. As such, piping fabrication and inspection standards for the system did not identify more rigorous welding standards that could have prevented the corrosion and subsequent leaks.

  20. Mechanical behavior and dynamic failure of high-strength ultrafine grained tungsten under uniaxial compression

    E-print Network

    Wei, Qiuming

    compression Q. Wei a,*, T. Jiao b , K.T. Ramesh b , E. Ma b , L.J. Kecskes c , L. Magness c , R. Dowding c , V.U. Kazykhanov d , R.Z. Valiev d a Department of Mechanical Engineering, University of North Carolina.08.031 * Corresponding author. Tel.: +1 704 687 8213; fax: +1 704 687 8345. E-mail address: qwei@uncc.edu (Q. Wei). www.actamat-journals

  1. A coupled chemo-thermo-hygro-mechanical model of concrete at high temperature and failure analysis

    NASA Astrophysics Data System (ADS)

    Li, Xikui; Li, Rongtao; Schrefler, B. A.

    2006-06-01

    A hierarchical mathematical model for analyses of coupled chemo-thermo-hygro-mechanical behaviour in concretes at high temperature is presented. The concretes are modelled as unsaturated deforming reactive porous media filled with two immiscible pore fluids, i.e. the gas mixture and the liquid mixture, in immiscible-miscible levels. The thermo-induced desalination process is particularly integrated into the model. The chemical effects of both the desalination and the dehydration processes on the material damage and the degradation of the material strength are taken into account. The mathematical model consists of a set of coupled, partial differential equations governing the mass balance of the dry air, the mass balance of the water species, the mass balance of the matrix components dissolved in the liquid phases, the enthalpy (energy) balance and momentum balance of the whole medium mixture. The governing equations, the state equations for the model and the constitutive laws used in the model are given. A mixed weak form for the finite element solution procedure is formulated for the numerical simulation of chemo-thermo-hygro-mechanical behaviours. Special considerations are given to spatial discretization of hyperbolic equation with non-self-adjoint operator nature. Numerical results demonstrate the performance and the effectiveness of the proposed model and its numerical procedure in reproducing coupled chemo-thermo-hygro-mechanical behaviour in concretes subjected to fire and thermal radiation.

  2. Monitoring of Temperature Fatigue Failure Mechanism for Polyvinyl Alcohol Fiber Concrete Using Acoustic Emission Sensors

    PubMed Central

    Li, Dongsheng; Cao, Hai

    2012-01-01

    The applicability of acoustic emission (AE) techniques to monitor the mechanism of evolution of polyvinyl alcohol (PVA) fiber concrete damage under temperature fatigue loading is investigated. Using the temperature fatigue test, real-time AE monitoring data of PVA fiber concrete is achieved. Based on the AE signal characteristics of the whole test process and comparison of AE signals of PVA fiber concretes with different fiber contents, the damage evolution process of PVA fiber concrete is analyzed. Finally, a qualitative evaluation of the damage degree is obtained using the kurtosis index and b-value of AE characteristic parameters. The results obtained using both methods are discussed. PMID:23012555

  3. Decorrelated feature space and neural nets based framework for failure modes clustering in electronics subjected to mechanical-shock

    Microsoft Academic Search

    Pradeep Lall; Prashant Gupta; Kai Goebel

    2011-01-01

    Electronic systems under extreme shock and vibration environments including shock and vibration may sustain several failure modes simultaneously. Previous experience of the authors indicates that the dominant failure modes experienced by packages in a drop and shock frame work are in the solder interconnects including cracks at the package and the board interface, pad cratering, copper trace fatigue, and bulk-failure

  4. Evaluation of the onset of failure under mechanical and thermal stresses on luting agent for metal-ceramic and metal crowns by finite element analysis.

    PubMed

    Agnihotri, Hema; Bhatnagar, Naresh; Rao, G Venugopal; Jain, Veena; Parkash, Hari; Kar, Aswini Kumar

    2010-10-01

    Long-term clinical failures of cemented prosthesis depend, to a large extent, on the integrity of the luting agent. The causative factors that lead to microfracture and, hence, failure of the luting agents are the stresses acting inside the oral cavity. Therefore, the present study was designed to develop an understanding of the relationship between stresses in the tooth and the failure potential of the luting agent. Two-dimensional finite element stress analysis was performed on the mandibular second premolar. The behavior of zinc-phosphate and glass-ionomer were studied under different crowns (metal-ceramic and metal crown) and loading conditions (mechanical force of 450 N acting vertically over the occlusal surface, thermal loads of 60° and 0°C). It was observed from the study that failure threshold of the luting agent was influenced both by the elastic modulus of the luting agent and by the type of the crown. PMID:22114426

  5. Evaluation of the onset of failure under mechanical and thermal stresses on luting agent for metal–ceramic and metal crowns by finite element analysis

    PubMed Central

    Agnihotri, Hema; Bhatnagar, Naresh; Rao, G. Venugopal; Jain, Veena; Parkash, Hari; Kar, Aswini Kumar

    2010-01-01

    Long-term clinical failures of cemented prosthesis depend, to a large extent, on the integrity of the luting agent. The causative factors that lead to microfracture and, hence, failure of the luting agents are the stresses acting inside the oral cavity. Therefore, the present study was designed to develop an understanding of the relationship between stresses in the tooth and the failure potential of the luting agent. Two-dimensional finite element stress analysis was performed on the mandibular second premolar. The behavior of zinc-phosphate and glass-ionomer were studied under different crowns (metal–ceramic and metal crown) and loading conditions (mechanical force of 450 N acting vertically over the occlusal surface, thermal loads of 60° and 0°C). It was observed from the study that failure threshold of the luting agent was influenced both by the elastic modulus of the luting agent and by the type of the crown. PMID:22114426

  6. Noninvasive ventilation as a weaning strategy for mechanical ventilation in adults with respiratory failure: a Cochrane systematic review

    PubMed Central

    Burns, Karen E.A.; Meade, Maureen O.; Premji, Azra; Adhikari, Neill K.J.

    2014-01-01

    Background: Noninvasive ventilation has been studied as a means of reducing complications among patients being weaned from invasive mechanical ventilation. We sought to summarize evidence comparing noninvasive and invasive weaning and their effects on mortality. Methods: We identified relevant randomized and quasirandomized trials through searches of databases, conference proceedings and grey literature. We included trials comparing extubation and immediate application of noninvasive ventilation with continued invasive weaning in adults on mechanical ventilation. Two reviewers each independently screened citations, assessed trial quality and abstracted data. Our primary outcome was mortality. Results: We identified 16 trials involving 994 participants, most of whom had chronic obstructive pulmonary disease (COPD). Compared with invasive weaning, noninvasive weaning significantly reduced mortality (risk ratio [RR] 0.53, 95% confidence interval [CI] 0.36 to 0.80), weaning failures (RR 0.63, 95% CI 0.42 to 0.96), ventilator-associated pneumonia (RR 0.25, 95% CI 0.15 to 0.43), length of stay in the intensive care unit (mean difference [MD] ?5.59 d, 95% CI ?7.90 to ?3.28) and in hospital (MD ?6.04 d, 95% CI ?9.22 to ?2.87), and total duration of mechanical ventilation (MD ?5.64 d, 95% CI ?9.50 to ?1.77). Noninvasive weaning had no significant effect on the duration of ventilation related to weaning, but significantly reduced rates of tracheostomy (RR 0.19, 95% CI 0.08 to 0.47) and reintubation (RR 0.65, 95% CI 0.44 to 0.97). Mortality benefits were significantly greater in trials enrolling patients with COPD than in trials enrolling mixed patient populations (RR 0.36 [95% CI 0.24 to 0.56] v. RR 0.81 [95% CI 0.47 to 1.40]). Interpretation: Noninvasive weaning reduces rates of death and pneumonia without increasing the risk of weaning failure or reintubation. In subgroup analyses, mortality benefits were significantly greater in patients with COPD. PMID:24324020

  7. A preliminary analysis of failure mechanisms in karst and man-made underground caves in Southern Italy

    NASA Astrophysics Data System (ADS)

    Parise, M.; Lollino, P.

    2011-11-01

    Natural and anthropogenic caves may represent a potential hazard for the built environment, due to the occurrence of instability within caves, that may propagate upward and eventually reach the ground surface, inducing the occurrence of sinkholes. In particular, when caves are at shallow depth, the effects at the ground surface may be extremely severe. Apulia region (southern Italy) hosts many sites where hazard associated with sinkholes is very serious due to presence of both natural karst caves and anthropogenic cavities, the latter being mostly represented by underground quarries. The Pliocene-Pleistocene calcarenite (a typical soft rock) was extensively quarried underground, by digging long and complex networks of tunnels. With time, these underground activities have progressively been abandoned and their memory lost, so that many Apulian towns are nowadays located just above the caves, due to urban expansion in the last decades. Therefore, a remarkable risk exists for society, which should not be left uninvestigated. The present contribution deals with the analysis of the most representative failure mechanisms observed in the field for such underground instability processes and the factors that seem to influence the processes, as for example those causing weathering of the rock and the consequent degradation of its physical and mechanical properties. Aimed at exploring the progression of instability of the cavities, numerical analyses have been developed by using both the finite element method for geological settings represented by continuous soft rock mass, and the distinct element method for jointed rock mass conditions. Both the effects of local instability processes occurring underground and the effects of the progressive enlargement of the caves on the overall stability of the rock mass have been investigated, along with the consequent failure mechanisms. In particular, degradation processes of the rock mass, as a consequence of wetting and weathering phenomena in the areas surrounding the caves, have been simulated. The results obtained from the numerical simulations have then been compared with what has been observed during field surveys and a satisfactory agreement between the numerical simulations and the instability processes, as detected in situ, has been noticed.

  8. Compression strength failure mechanisms in unidirectional composite laminates containing a hole

    NASA Technical Reports Server (NTRS)

    Johnson, Eric R.

    1993-01-01

    Experiments on graphite-epoxy laminated plates containing unloaded small holes show that these laminates are notch insensitive. That is, the uniaxial strength of these laminates with small holes exceeds the strength predicted by a point stress criterion using the stress concentration factor for the in-plane stress field. Laminates containing large holes exhibit notch sensitive behavior and consequently their strength is reasonably well predicted by the stress concentration effect. This hole size effect is manifested both in tension and in compression. Apparently, some mechanism must cause in-plane stress relief for laminates containing small holes. The purpose of this research was to study the influence of geometric nonlinearity on the micromechanical response of a filamentary composite material in the presence of a strain gradient caused by a discontinuity such as a hole. A mathematical model was developed at the micromechanical level to investigate this geometrically nonlinear effect.

  9. Probing the failure mechanism of nanoscale LiFePO4 for Li-ion batteries

    NASA Astrophysics Data System (ADS)

    Gu, Meng; Shi, Wei; Zheng, Jianming; Yan, Pengfei; Zhang, Ji-guang; Wang, Chongmin

    2015-05-01

    LiFePO4 is a high power rate cathode material for lithium ion battery and shows remarkable capacity retention, featuring a 91% capacity retention after 3300 cycles. In this work, we use high-resolution transmission electron microscopy and electron energy loss spectroscopy to study the gradual capacity fading mechanism of LiFePO4 materials. We found that upon prolonged electrochemical cycling of the battery, the LiFePO4 cathode shows surface amorphization and loss of oxygen species, which directly contribute to the gradual capacity fading of the battery. The finding can guide the design and improvement of LiFePO4 cathode for high-energy and high-power rechargeable battery for electric transportation.

  10. Failure Mechanisms and Damage Model of Ductile Cast Iron Under Low-Cycle Fatigue Conditions

    NASA Astrophysics Data System (ADS)

    Wu, Xijia; Quan, Guangchun; MacNeil, Ryan; Zhang, Zhong; Sloss, Clayton

    2014-10-01

    Strain-controlled low-cycle fatigue (LCF) tests were conducted on ductile cast iron (DCI) at strain rates of 0.02, 0.002, and 0.0002/s in the temperature range from room temperature to 1073 K (800 °C). A constitutive-damage model was developed within the integrated creep-fatigue theory (ICFT) framework on the premise of strain decomposition into rate-independent plasticity and time-dependent creep. Four major damage mechanisms: (i) plasticity-induced fatigue, (ii) intergranular embrittlement (IE), (iii) creep, and (iv) oxidation were considered in a nonlinear creep-fatigue interaction model which represents the overall damage accumulation process consisting of oxidation-assisted fatigue crack nucleation and propagation in coalescence with internally distributed damage ( e.g., IE and creep), leading to final fracture. The model was found to agree with the experimental observations of the complex DCI-LCF phenomena, for which the linear damage summation rule would fail.

  11. Evaluation of seawater exposure on mechanical properties and failure behavior of E-Glass/BMI composite for marine use

    NASA Astrophysics Data System (ADS)

    Zhao, Yian; Wang, Zhiying; Seah, Leong Keey; Chai, Gin Boay

    2015-03-01

    Since composite material is playing an increasingly important role in the marine and offshore drilling industry, it is essential to have a good understanding on degradation of the material in the seawater environment. This study investigates the influence of seawater exposure on the mechanical and failure behavior of E-Glass/BMI composite. The water diffusion behavior in the composite has been studied through immersing the specimens in seawater under different conditions. The diffusion rate accelerates with increase of temperature, and the material shows irreversible damage due to seawater absorption at the temperature of 80°C. It is also found that external stress would significantly increase the water absorption. The water uptake in the specimen at 50°C showed a two stage behavior dominated by Fickian law and polymeric relaxation respectively, and saturation was not achieved in 8 months. After diffusion, the Tg of the material is considerably lowered due to plasticization effect. However the effect was found to be reversible after drying the specimen. Based on the testing results of tensile, flexure and fatigue properties of the composites, it is concluded that seawater exposure especially at elevated temperature leads to significant degradation on mechanical properties of the composite. However, the flexural strength of BMI composite with seawater absorption becomes less susceptible to temperature change. It is also found that the seawater absorption doesn't show significant effect on the stiffness of the material.

  12. Heart failure in 2010.

    PubMed

    El-Menyar, Ayman; AlMahmeed, Wael

    2010-09-01

    The Heart Failure Congress 2010 in Berlin presented the latest trials and trends in the medical and mechanical therapy of heart failure in the presence of impaired or preserved left ventricular ejection fraction. It covered all aspects of heart failure from epidemiology through basic and translational science to prevention. The congress highlighted new drugs, novel biomarkers, updated trials, the role of imaging in risk stratification and the importance of telecare in the reduction of heart failure readmission. PMID:20828344

  13. Impact of defects on the electrical transport, optical properties and failure mechanisms of GaN nanowires.

    SciTech Connect

    Armstrong, Andrew M.; Aubry, Sylvie; Shaner, Eric Arthur; Siegal, Michael P.; Li, Qiming; Jones, Reese E.; Westover, Tyler; Wang, George T.; Zhou, Xiao Wang; Talin, Albert Alec; Bogart, Katherine Huderle Andersen; Harris, C. Thomas; Huang, Jian Yu

    2010-09-01

    We present the results of a three year LDRD project that focused on understanding the impact of defects on the electrical, optical and thermal properties of GaN-based nanowires (NWs). We describe the development and application of a host of experimental techniques to quantify and understand the physics of defects and thermal transport in GaN NWs. We also present the development of analytical models and computational studies of thermal conductivity in GaN NWs. Finally, we present an atomistic model for GaN NW electrical breakdown supported with experimental evidence. GaN-based nanowires are attractive for applications requiring compact, high-current density devices such as ultraviolet laser arrays. Understanding GaN nanowire failure at high-current density is crucial to developing nanowire (NW) devices. Nanowire device failure is likely more complex than thin film due to the prominence of surface effects and enhanced interaction among point defects. Understanding the impact of surfaces and point defects on nanowire thermal and electrical transport is the first step toward rational control and mitigation of device failure mechanisms. However, investigating defects in GaN NWs is extremely challenging because conventional defect spectroscopy techniques are unsuitable for wide-bandgap nanostructures. To understand NW breakdown, the influence of pre-existing and emergent defects during high current stress on NW properties will be investigated. Acute sensitivity of NW thermal conductivity to point-defect density is expected due to the lack of threading dislocation (TD) gettering sites, and enhanced phonon-surface scattering further inhibits thermal transport. Excess defect creation during Joule heating could further degrade thermal conductivity, producing a viscous cycle culminating in catastrophic breakdown. To investigate these issues, a unique combination of electron microscopy, scanning luminescence and photoconductivity implemented at the nanoscale will be used in concert with sophisticated molecular-dynamics calculations of surface and defect-mediated NW thermal transport. This proposal seeks to elucidate long standing material science questions for GaN while addressing issues critical to realizing reliable GaN NW devices.

  14. TBCs for Gas Turbines under Thermomechanical Loadings: Failure Behaviour and Life Prediction

    NASA Astrophysics Data System (ADS)

    Beck, T.; Trunova, O.; Herzog, R.; Singheiser, L.

    2012-10-01

    The present contribution gives an overview about recent research on a thermal barrier coating (TBC) system consisted of (i) an intermetallic MCrAlY-alloy Bondcoat (BC) applied by vacuum plasma spraying (VPS) and (ii) an Yttria Stabilised Zirconia (YSZ) top coat air plasma sprayed (APS) at Forschungszentrum Juelich, Institute of Energy and Climate Research (IEK-1). The influence of high temperature dwell time, maximum and minimum temperature on crack growth kinetics during thermal cycling of such plasma sprayed TBCs is investigated using infrared pulse thermography (IT), acoustic emission (AE) analysis and scanning electron microscopy. Thermocyclic life in terms of accumulated time at maximum temperature decreases with increasing high temperature dwell time and increases with increasing minimum temperature. AE analysis proves that crack growth mainly occurs during cooling at temperatures below the ductile-to-brittle transition temperature of the BC. Superimposed mechanical load cycles accelerate delamination crack growth and, in case of sufficiently high mechanical loadings, result in premature fatigue failure of the substrate. A life prediction model based on TGO growth kinetics and a fracture mechanics approach has been developed which accounts for the influence of maximum and minimum temperature as well as of high temperature dwell time with good accuracy in an extremely wide parameter range.

  15. [Pharmacological and mechanical support of the myocardium in perioperative period in cardio-surgical patients with chronic heart failure].

    PubMed

    Babaev, M A; Eremenko, A A; Ziuliaeva, T P; Fedulova, S V; Molochnikov, I O; Fominykh, M V; Poliakova, P V; Dzemeshkevich, S L

    2014-01-01

    The article deals with a retrospective study devoted to the combined methods of myocardial support in cardiosurgical patients with chronic heart failure (III-IY FC according to NYHA) and low myocardial reserves capacity (LVEF 28.3 +/- 9.4%). This methods include pharmacologic (Levosimendan) and mechanical support (IABP). During the work we have analyzed data of 116 patients and measured pressure in the pulmonary artery (mmHg), end-systolic volume (ESV ml), end-diastolic volume (ED, ml), stroke volume output (SVO, ml), left ventricular ejection fraction (LVEF, %). We evaluated the level of valvular insufficiency and pulmonary hypertension (PH) and BNP concentration (pg/ml). The following indications for the usage of pharmacological and/or mechanical myocardial support were identified: I) Preventive usage of pharmacological and/or mechanical myocardial support is recommended for patients with CHF III-IY FC (NYHA) and low left ventricular EF(< or = 35%), significant valvular insufficiency, PH, PICS (postinfarction cardiosclerosis); 2) The certain method of the support can be chosen with the help of Levosimendan infusion testing; 3) In case one of the above mentioned indications (point 1) or in case of mild reaction to levosimendan infusion in patients with the lesions of more than 2 coronary arteries (including the trunk of the left coronary artery) the usage of combined support is recommended; 4) In case of < or = 6 scores according to EUROSCORE scale, lesions of 2 or more coronary arteries, tricuspid insufficiency (TriI), PH, and high pressure in pulmonary artery (higher than the 2nd degree), high end-diastolic volume, end-systolic volume of LV the isolated usage of levosimendan is recommended; 5) In case of significant ischemic heart disease, PICS, lesions of more than 2 coronary arteries, (including the trunk of the left coronary artery) but without significant decrease of pressure in the pulmonary artery, end-diastolic volume, end-systolic volume and TriI the isolated usage of IABP is recommended. PMID:25306682

  16. Failure Mechanism analysis of rainfall-induced landslide at Pingguang Stream in Taiwan: Mapping, Investigation, and Numerical Simulation

    NASA Astrophysics Data System (ADS)

    Huang, Wei-Kai; Lee, Ching-Fang; Lo, Chia-Ming; Chiu, Chun-Jung

    2015-04-01

    On September 15, 2012, torrential storm carried by the peripheral circulation of Typhoon Sanba and the northeast monsoon induced a translational landslide near Pingguang Road in Xindian District of New Taipei City, Taiwan. The total volume of the landslide was approximately 162,000 m^3. The sliding mass destroyed two houses across the stream and formed a landslide dam at the toe of the slope, constricting the stream. In this study, remote sensing images and LiDAR scanning were interpreted, and conducted onsite surveys to obtain material parameters, and performed simulations using the discrete element method to reconstruction the post event, in order to elucidate the mechanisms involved in the landslide process. Survey results revealed complex geological conditions with wide spreading tension cracks at source area. This facilitated the infiltration of surface runoff into weak surfaces and raised groundwater levels. Once the shear strength falls below a critical value, failure surface will occur along the stratum boundary. The results of numerical simulation reveal that at 80 sec after the Pingguang Stream landslide began, a maximum deposition depth of 20 m had been reached. The sliding mass cut off the stream and pushed the stream flow roughly 35 m to the southeast. Because the slope materials surrounding the study area and the landslide-inducing mechanisms are similar, the top of the slopes to the northwest of the study area require monitoring immediately. In addition to filling in the tension cracks, drainage facilities should be constructed to prevent further landslides. Keywords: translational landslide, onsite survey, discrete element method, mechanism, landslide process

  17. Mechanical properties and shear failure surfaces of two alumina powders in triaxial compression

    SciTech Connect

    ZEUCH,DAVID H.; GRAZIER,J. MARK; ARGUELLO JR.,JOSE G.; EWSUK,KEVIN G.

    2000-04-24

    In the manufacture of ceramic components, near-net-shape parts are commonly formed by uniaxially pressing granulated powders in rigid dies. Density gradients that are introduced into a powder compact during press-forming often increase the cost of manufacturing, and can degrade the performance and reliability of the finished part. Finite element method (FEM) modeling can be used to predict powder compaction response, and can provide insight into the causes of density gradients in green powder compacts; however, accurate numerical simulations require accurate material properties and realistic constitutive laws. To support an effort to implement an advanced cap plasticity model within the finite element framework to realistically simulate powder compaction, the authors have undertaken a project to directly measure as many of the requisite powder properties for modeling as possible. A soil mechanics approach has been refined and used to measure the pressure dependent properties of ceramic powders up to 68.9 MPa (10,000 psi). Due to the large strains associated with compacting low bulk density ceramic powders, a two-stage process was developed to accurately determine the pressure-density relationship of a ceramic powder in hydrostatic compression, and the properties of that same powder compact under deviatoric loading at the same specific pressures. Using this approach, the seven parameters that are required for application of a modified Drucker-Prager cap plasticity model were determined directly. The details of the experimental techniques used to obtain the modeling parameters and the results for two different granulated alumina powders are presented.

  18. Mechanisms of High-Temperature Fatigue Failure in Alloy 800H

    NASA Technical Reports Server (NTRS)

    BhanuSankaraRao, K.; Schuster, H.; Halford, G. R.

    1996-01-01

    The damage mechanisms influencing the axial strain-controlled Low-Cycle Fatigue (LCF) behavior of alloy 800H at 850 C have been evaluated under conditions of equal tension/compression ramp rates (Fast-Fast (F-F): 4 X 10(sup -3)/s and Slow-Slow (S-S): 4 X 10(sup -5)/s) and asymmetrical ramp rates (Fast-Slow (F-S): 4 x 10(sup -3)/s / 4 X 10(sup -5/s and Slow-Fast (S-F): 4 X 10(sup -5) / 4 X 10(sup -3)/s) in tension and compression. The fatigue life, cyclic stress response, and fracture modes were significantly influenced by the waveform shape. The fatigue lives displayed by different loading conditions were in the following order: F-F greater than S-S greater than F-S greater than S-F. The fracture mode was dictated by the ramp rate adopted in the tensile direction. The fast ramp rate in the tensile direction led to the occurrence of transgranular crack initiation and propagation, whereas the slow ramp rate caused intergranular initiation and propagation. The time-dependent processes and their synergistic interactions, which were at the basis of observed changes in cyclic stress response and fatigue life, were identified. Oxidation, creep damage, dynamic strain aging, massive carbide precipitation, time-dependent creep deformation, and deformation ratcheting were among the several factors influencing cyclic life. Irrespective of the loading condition, the largest effect on life was exerted by oxidation processes. Deformation ratcheting had its greatest influence on life under asymmetrical loading conditions. Creep damage accumulated the greatest amount during the slow tensile ramp under S-F conditions.

  19. Bhattacharya, S., Madabhushi, S. P. G. & Bolton, M. D. (2004). Geotechnique 54, No. 3, 203213 An alternative mechanism of pile failure in liquefiable deposits during

    E-print Network

    Bolton, Malcolm

    2004-01-01

    & Valsangkar (1970). The analysis shows that buckling will be confined to a critical length of the pile deposits during earthquakes. This failure mechanism, based on pile buckling, is formulated by back´sultats des essais centrifuges. INTRODUCTION Current understanding of buckling of piles Buckling of piles

  20. Active wear and failure mechanisms of TiN-coated high speed steel and TiN-coated cemented carbide tools when machining powder metallurgically made stainless steels

    SciTech Connect

    Jiang, L.; Haenninen, H.; Paro, J.; Kauppinen, V. [Helsinki Univ. of Technology, Espoo (Finland)

    1996-09-01

    In this study, active wear and failure mechanisms of both TiN-coated high speed steel and TiN-coated cemented carbide tools when machining stainless steels made by powder metallurgy in low and high cutting speed ranges, respectively, have been investigated. Abrasive wear mechanisms, fatigue-induced failure, and adhesive and diffusion wear mechanisms mainly affected the tool life of TiN-coated high speed steel tools at cutting speeds below 35 m/min, between 35 and 45 m/min, and over 45 m/min, respectively. Additionally, fatigue-induced failure was active at cutting speeds over 45 m/min in the low cutting speed range when machining powder metallurgically made duplex stainless steel 2205 and austenitic stainless steel 316L. In the high cutting speed range, from 100 to 250 m/min, fatigue-induced failure together with diffusion wear mechanism, affected the tool life of TiN-coated cemented carbide tools when machining both 316L and 2205 stainless steels. It was noticed that the tool life of TiN-coated high speed steel tools used in the low cutting speed range when machining 2205 steel was longer than that when machining 316L steel, whereas the tool life of TiN-coated cemented carbide tools used in the high cutting speed range when machining 316L steel was longer than that when machining 2205 steel.

  1. Up-regulation of hepatocyte growth factor receptor: An amplification and targeting mechanism for hepatocyte growth factor action in acute renal failure

    Microsoft Academic Search

    YOUHUA LIU; EVELYN M. TOLBERT; LIN LIN; MICHAEL A. THURSBY; ADAM M. SUN; TOSHIKAZU NAKAMURA; LANCE D. DWORKIN

    1999-01-01

    Up-regulation of hepatocyte growth factor receptor: An amplification and targeting mechanism for hepatocyte growth factor action in acute renal failure.BackgroundHepatocyte growth factor (HGF) and its c-met receptor comprise a signaling system that has been implicated in tissue repair and regeneration. HGF action is specifically targeted to the damaged organ following injury; however, the mechanism underlying this important targeting process remains

  2. Loss-of-Function Mutations in TBC1D20 Cause Cataracts and Male Infertility in blind sterile Mice and Warburg Micro Syndrome in Humans

    PubMed Central

    Liegel, Ryan P.; Handley, Mark T.; Ronchetti, Adam; Brown, Stephen; Langemeyer, Lars; Linford, Andrea; Chang, Bo; Morris-Rosendahl, Deborah J.; Carpanini, Sarah; Posmyk, Renata; Harthill, Verity; Sheridan, Eamonn; Abdel-Salam, Ghada M.H.; Terhal, Paulien A.; Faravelli, Francesca; Accorsi, Patrizia; Giordano, Lucio; Pinelli, Lorenzo; Hartmann, Britta; Ebert, Allison D.; Barr, Francis A.; Aligianis, Irene A.; Sidjanin, Duska J.

    2013-01-01

    blind sterile (bs) is a spontaneous autosomal-recessive mouse mutation discovered more than 30 years ago. Phenotypically, bs mice exhibit nuclear cataracts and male infertility; genetic analyses assigned the bs locus to mouse chromosome 2. In this study, we first positionally cloned the bs locus and identified a putative causative mutation in the Tbc1d20 gene. Functional analysis established the mouse TBC1D20 protein as a GTPase-activating protein (GAP) for RAB1 and RAB2, and bs as a TBC1D20 loss-of-function mutation. Evaluation of bs mouse embryonic fibroblasts (mEFs) identified enlarged Golgi morphology and aberrant lipid droplet (LD) formation. Based on the function of TBC1D20 as a RABGAP and the bs cataract and testicular phenotypes, we hypothesized that mutations in TBC1D20 may contribute to Warburg micro syndrome (WARBM); WARBM constitutes a spectrum of disorders characterized by eye, brain, and endocrine abnormalities caused by mutations in RAB3GAP1, RAB3GAP2, and RAB18. Sequence analysis of a cohort of 77 families affected by WARBM identified five distinct TBC1D20 loss-of-function mutations, thereby establishing these mutations as causative of WARBM. Evaluation of human fibroblasts deficient in TBC1D20 function identified aberrant LDs similar to those identified in the bs mEFs. Additionally, our results show that human fibroblasts deficient in RAB18 and RAB3GAP1 function also exhibit aberrant LD formation. These findings collectively indicate that a defect in LD formation/metabolism may be a common cellular abnormality associated with WARBM, although it remains unclear whether abnormalities in LD metabolism are contributing to WARBM disease pathology. PMID:24239381

  3. Modeling shear failure and permeability enhancement due to coupled Thermal-Hydrological-Mechanical processes in Enhanced Geothermal Reservoirs

    SciTech Connect

    Kelkar, Sharad [Los Alamos National Laboratory

    2011-01-01

    The connectivity and accessible surface area of flowing fractures, whether natural or man-made, is possibly the single most important factor, after temperature, which determines the feasibility of an Enhanced Geothermal System (EGS). Rock deformation and in-situ stress changes induced by injected fluids can lead to shear failure on preexisting fractures which can generate microseismic events, and also enhance the permeability and accessible surface area of the geothermal formation. Hence, the ability to accurately model the coupled thermal-hydrologic-mechanical (THM) processes in fractured geological formations is critical in effective EGS reservoir development and management strategies. The locations of the microseismic events can serve as indicators of the zones of enhanced permeability, thus providing vital information for verification of the coupled THM models. We will describe a general purpose computational code, FEHM, developed for this purpose, that models coupled THM processes during multiphase fluid flow and transport in fractured porous media. The code incorporates several models of fracture aperture and stress behavior combined with permeability relationships. We provide field scale examples of applications to geothermal systems to demonstrate the utility of the method.

  4. Study of the causes and identification of the dominant mechanisms of failure of bellows expansion joints used in district heating system pipelines at MOEK

    NASA Astrophysics Data System (ADS)

    Tomarov, G. V.; Nikolaev, A. E.; Semenov, V. N.; Shipkov, A. A.; Shepelev, S. V.

    2015-06-01

    The results of laboratory studies of material properties and of numerical and analytical investigations to assess the stress-strain state of the metal of the bellows expansion joints used in the district heating system pipelines at MOEK subjected to corrosion failure are presented. The main causes and the dominant mechanisms of failure of the expansion joints have been identified. The influence of the initial crevice defects and the operating conditions on the features and intensity of destruction processes in expansion joints used in the district heating system pipelines at MOEK has been established.

  5. Computational modeling of dynamic-failure mechanisms in armor/anti-armor materials. Final report, 1 Oct 88-30 Sep 91

    SciTech Connect

    Andrew, S.P.; Caligiuri, R.D.; Parnell, T.K.; Eiselstein, L.E.

    1991-02-01

    The purpose of this project was to develop improved dynamic failure models for brittle materials (primarily ceramics). The approach to developing these failure models was to establish a database (ACERAM) in which fundamental material properties and processing information could be directly correlated with ballistic performance data. Under this contract, a comprehensive literature search was conducted, many contacts were established in the armor/anti-armor research and development community, and database development was undertaken. A more limited project was also undertaken to assess and compare the effects of material properties and penetration mechanisms on the ballistic performance of depleted uranium and tungsten alloy penetrators.

  6. Detection, Diagnosis and Prognosis: Contribution to the energy challenge: Proceedings of the Meeting of the Mechanical Failures Prevention Group

    NASA Technical Reports Server (NTRS)

    Shives, T. R. (editor); Willard, W. A. (editor)

    1981-01-01

    The contribution of failure detection, diagnosis and prognosis to the energy challenge is discussed. Areas of special emphasis included energy management, techniques for failure detection in energy related systems, improved prognostic techniques for energy related systems and opportunities for detection, diagnosis and prognosis in the energy field.

  7. IMPERMEABLE THIN Al2O3 OVERLAY FOR TBC PROTECTION FROM SULFATE AND VANADATE ATTACK IN GAS TURBINES

    SciTech Connect

    Scott X. Mao

    2002-11-30

    In order to improve the hot corrosion resistance of conventional YSZ TBC system, the Al{sub 2}O{sub 3} overlay coating has been successfully produced on the surface of YSZ by the Sol-gel route. The YSZ substrates were coated with boehmite sol by dip coating process, dried to form a gel film and calcined at 1200 C to form {alpha}-Al{sub 2}O{sub 3} overlay. The microstructures of TBC and Al{sub 2}O{sub 3} overlay were examined by scanning electron microscopy (SEM). The results showed that micro-pores ranged from 3 {micro}m to 20 {micro}m and micro-cracks could be clearly seen on the surface of APS YSZ coating. The thickness of alumina overlay increased with increasing the number of dip coating circles. The small microcracks (0.5-1.0 {micro}m width) on the YSZ surface could be filled and blocked by calcined alumina particles, whereas large pores remained empty and the alumina overlay was un-continuous after one time dip coating circle. Alumina overlay thicker than 5 m m obtained by five times dip coating circles largely cracked after calcinations. As a result, multiple dip coatings up to three times were ideal for getting high quality, crack- free and continuous overlay. The optimal thickness of alumina overlay was in the range of 2.5-3.5 {micro}m. In the next reporting period, we will study the hot corrosion behaviors of YSZ TBC with Al{sub 2}O{sub 3} overlay coating produced by sol gel route by exposure the samples to molten salts mixtures (Na{sub 2}SO{sub 4} + 5%V{sub 2}O{sub 5}) at 950 C.

  8. The TBC (Tre-2/Bub2/Cdc16) Domain Protein TRE17 Regulates Plasma Membrane-Endosomal Trafficking through Activation of Arf6†

    PubMed Central

    Martinu, Lenka; Masuda-Robens, Jeffrey M.; Robertson, Sarah E.; Santy, Lorraine C.; Casanova, James E.; Chou, Margaret M.

    2004-01-01

    TBC (Tre-2/Bub2/Cdc16) domains are predicted to encode GTPase-activating proteins (GAPs) for Rab family G proteins. While approximately 50 TBC proteins are predicted to exist in humans, little is known about their substrate specificity. Here we show that TRE17 (also called Tre-2 and USP6), a founding member of the TBC family, targets the Arf family GTPase Arf6, which regulates plasma membrane-endosome trafficking. Surprisingly, TRE17 does not function as a GAP for Arf6 but rather promotes its activation in vivo. TRE17 associates directly with Arf6 in its GDP- but not GTP-bound state. Mapping experiments pinpoint the site of interaction to the TBC domain of TRE17. Forced expression of TRE17 promotes the localization of Arf6 to the plasma membrane, leading to Arf6 activation, presumably due to facilitated access to membrane-associated guanine nucleotide exchange factors (GEFs). Furthermore, TRE17 cooperates with Arf6 GEFs to induce GTP loading of Arf6 in vivo. Finally, short interfering RNA-mediated loss of TRE17 leads to attenuated Arf6 activation. These studies identify TRE17 as a novel regulator of the Arf6-regulated plasma membrane recycling system and reveal an unexpected function for TBC domains. PMID:15509780

  9. Cobalt-Alloy Implant Debris Induce HIF-1? Hypoxia Associated Responses: A Mechanism for Metal-Specific Orthopedic Implant Failure

    PubMed Central

    Samelko, Lauryn; Caicedo, Marco S.; Lim, Seung-Jae; Della-Valle, Craig; Jacobs, Joshua; Hallab, Nadim J.

    2013-01-01

    The historical success of orthopedic implants has been recently tempered by unexpected pathologies and early failures of some types of Cobalt-Chromium-Molybdenum alloy containing artificial hip implants. Hypoxia-associated responses to Cobalt-alloy metal debris were suspected as mediating this untoward reactivity at least in part. Hypoxia Inducible Factor-1? is a major transcription factor involved in hypoxia, and is a potent coping mechanism for cells to rapidly respond to changing metabolic demands. We measured signature hypoxia associated responses (i.e. HIF-1?, VEGF and TNF-?) to Cobalt-alloy implant debris both in vitro (using a human THP-1 macrophage cell line and primary human monocytes/macrophages) and in vivo. HIF-1? in peri-implant tissues of failed metal-on-metal implants were compared to similar tissues from people with metal-on-polymer hip arthroplasties, immunohistochemically. Increasing concentrations of cobalt ions significantly up-regulated HIF-1? with a maximal response at 0.3 mM. Cobalt-alloy particles (1 um-diameter, 10 particles/cell) induced significantly elevated HIF-1?, VEGF, TNF-? and ROS expression in human primary macrophages whereas Titanium-alloy particles did not. Elevated expression of HIF-1? was found in peri-implant tissues and synovial fluid of people with failing Metal-on-Metal hips (n?=?5) compared to failed Metal-on-Polymer articulating hip arthroplasties (n?=?10). This evidence suggests that Cobalt-alloy, more than other metal implant debris (e.g. Titanium alloy), can elicit hypoxia-like responses that if unchecked can lead to unusual peri-implant pathologies, such as lymphocyte infiltration, necrosis and excessive fibrous tissue growths. PMID:23840602

  10. Assessment of the BD MGIT TBc identification test for the detection of Mycobacterium tuberculosis complex in a network of mycobacteriology laboratories.

    PubMed

    Machado, Diana; Ramos, Jorge; Couto, Isabel; Cadir, Nureisha; Narciso, Inácio; Coelho, Elizabeth; Viegas, Sofia; Viveiros, Miguel

    2014-01-01

    We evaluate the performance of the TBcID assay in a panel of 100 acid-fast bacilli cultures. Sixty-four isolates were TBcID positive for Mycobacterium tuberculosis complex (MTBC), whereas 36 gave negative results. These included 28 nontuberculous mycobacteria, one nonmycobacterial isolate, one M. tuberculosis, and six M. bovis BCG strains. This corresponds to a sensitivity of 90.14%, specificity of 100%, and positive and negative predictive values of 100% and 80.55%, respectively. The test is rapid, easy to perform and interpret, and does not require sample preparation or instrumentation. However, a negative result does not exclude the presence of a strain belonging to MTBC, especially when mutations in mpb64 gene are present or some M. bovis BCG strains are isolated. The TBcID showed potential to assist in the identification of MTBC when the implementation and usage of molecular methods are often not possible, principally in resource-limited countries. PMID:24587985

  11. HPC failure prediction proficiency metrics

    Microsoft Academic Search

    Narate Taerat; Chokchai Leangsuksun

    2009-01-01

    Transient failures in large-scale HPC systems are significantly increasing due to the large number of components. Fault tolerance mechanisms exist, but they cost additional overhead per invocation to application. Thus, failure prediction is needed in order to gracefully mitigate such events and to minimize the usage of mechanism. However, the proficiency metrics for HPC failure prediction are borrowed from other

  12. Exercise Alleviates Lipid-Induced Insulin Resistance in Human Skeletal Muscle–Signaling Interaction at the Level of TBC1 Domain Family Member 4

    PubMed Central

    Pehmøller, Christian; Brandt, Nina; Birk, Jesper B.; Høeg, Louise D.; Sjøberg, Kim A.; Goodyear, Laurie J.; Kiens, Bente; Richter, Erik A.; Wojtaszewski, Jørgen F.P.

    2012-01-01

    Excess lipid availability causes insulin resistance. We examined the effect of acute exercise on lipid-induced insulin resistance and TBC1 domain family member 1/4 (TBCD1/4)-related signaling in skeletal muscle. In eight healthy young male subjects, 1 h of one-legged knee-extensor exercise was followed by 7 h of saline or intralipid infusion. During the last 2 h, a hyperinsulinemic-euglycemic clamp was performed. Femoral catheterization and analysis of biopsy specimens enabled measurements of leg substrate balance and muscle signaling. Each subject underwent two experimental trials, differing only by saline or intralipid infusion. Glucose infusion rate and leg glucose uptake was decreased by intralipid. Insulin-stimulated glucose uptake was higher in the prior exercised leg in the saline and the lipid trials. In the lipid trial, prior exercise normalized insulin-stimulated glucose uptake to the level observed in the resting control leg in the saline trial. Insulin increased phosphorylation of TBC1D1/4. Whereas prior exercise enhanced TBC1D4 phosphorylation on all investigated sites compared with the rested leg, intralipid impaired TBC1D4 S341 phosphorylation compared with the control trial. Intralipid enhanced pyruvate dehydrogenase (PDH) phosphorylation and lactate release. Prior exercise led to higher PDH phosphorylation and activation of glycogen synthase compared with resting control. In conclusion, lipid-induced insulin resistance in skeletal muscle was associated with impaired TBC1D4 S341 and elevated PDH phosphorylation. The prophylactic effect of exercise on lipid-induced insulin resistance may involve augmented TBC1D4 signaling and glycogen synthase activation. PMID:22851577

  13. Heart Failure

    MedlinePLUS

    ... version of this page please turn Javascript on. Heart Failure What is Heart Failure? In heart failure, the heart cannot pump ... the lungs, where it picks up oxygen. The Heart's Pumping Action In normal hearts, blood vessels called ...

  14. Identification of corrosion and damage mechanisms by using scanning electron microscopy and energy-dispersive X-ray microanalysis: contribution to failure analysis case histories

    NASA Astrophysics Data System (ADS)

    Pantazopoulos, G.; Vazdirvanidis, A.

    2014-03-01

    Emphasis is placed on the evaluation of corrosion failures of copper and machineable brass alloys during service. Typical corrosion failures of the presented case histories mainly focussed on stress corrosion cracking and dezincification that acted as the major degradation mechanisms in components used in piping and water supply systems. SEM assessment, coupled with EDS spectroscopy, revealed the main cracking modes together with the root-source(s) that are responsible for the damage initiation and evolution. In addition, fracture surface observations contributed to the identification of the incurred fracture mechanisms and potential environmental issues that stimulated crack initiation and propagation. Very frequently, the detection of chlorides among the corrosion products served as a suggestive evidence of the influence of working environment on passive layer destabilisation and metal dissolution.

  15. A reaction-layer mechanism for the delayed failure of micron-scale polycrystalline silicon structural films subjected to high-cycle fatigue loading

    Microsoft Academic Search

    C. L. Muhlstein; E. A. Stach; R. O. Ritchie

    2002-01-01

    A study has been made to discern the mechanisms for the delayed failure of 2-?m thick structural films of n+-type, polycrystalline silicon under high-cycle fatigue loading conditions. Such polycrystalline silicon films are used in small-scale structural applications including microelectromechanical systems (MEMS) and are known to display ‘metal-like’ stress-life (S\\/N) fatigue behavior in room temperature air environments. Previously, fatigue lives in

  16. Mechanical Strength and Failure Characteristics of Cast Mg-9 pctAl-1 pctZn Alloys Produced by a Heated-Mold Continuous Casting Process: Tensile Properties

    NASA Astrophysics Data System (ADS)

    Okayasu, Mitsuhiro; Takeuchi, Shuhei; Ohfuji, Hiroaki

    2014-11-01

    The mechanical properties and failure characteristics of a cast Mg alloy (AZ91: Mg-Al8.9-Zn0.6-Mn0.2) produced by a heated-mold continuous casting process (HMC) are investigated. In a modification of the original HMC process, the cooling of the liquid alloy by direct water spray is carried out in an atmosphere of high-purity argon gas. The HMC-AZ91 alloy exhibits excellent mechanical properties (high strength and high ductility) that are about twice as high as those for the same alloy produced by conventional gravity casting. The increased material strength and ductility of the HMC sample are attributed to nanoscale and microscale microstructural characteristics. The fine grains and tiny spherical eutectic structures ( e.g., Mg17Al12 and Al6Mn) distributed randomly in the matrix of the HMC alloy result in resistance to dislocation movement, leading to high tensile strength. Basal slip on (0001) planes in the relatively organized crystal orientation of the HMC alloy, as well as grain boundary sliding through tiny spherical eutectic structures, results in high ductility. Details of the failure mechanism under static loading in the HMC alloy are also discussed using failure models.

  17. The role of soil processes in determining mechanisms of slope failure and hillslope development in a humid-tropical forest eastern Puerto Rico

    NASA Astrophysics Data System (ADS)

    Simon, Andrew; Larsen, Matthew C.; Hupp, Cliff R.

    1990-09-01

    Translational failures, with associated downslope earthflow components and shallow slides, appear to be the primary mechanism of hillslope denudation in the humid tropical forests of the mountains of eastern Puerto Rico. In-situ weathering of quartz diorite and marine-deposited volcaniclastics produces residual soil (saprolite; up to 21 m deep) / weathered rock profiles. Discontinuous zones of contrasting density and permeability particularly in quartz-diorite slopes at 0.5 m, and between 3 and 7 m, create both pathways and impedances for water that can result in excess pore pressures and, ultimately, aid in determining the location of failure planes and magnitudes of slope failures. In combination with relict fractures which create planes of weakness within the saprolite, and the potential significance of tensile stresses in the upper zone of saprolite (hypothesized to be caused by subsurface soil creep), shear failure can then occur during or after periods of heavy rainfall. Results of in-situ shear-strength testing show negative y-intercepts on the derived Mohr-Coulomb failure envelopes (approximately 50% of all tests) that are interpreted as apparent tensile stresses. Observation of tension cracks 1-2 m deep support the test data. Subsurface soil creep can cause extension of the soil and the development of tensile stresses along upper-slope segments. Shear-strength data support this hypothesis for both geologic types. Apparent values of maximum and mean tensile stress are greatest along upper slopes (16.5 and 6.29 kPa). Previously documented maximum rates of downslope movement coincided with local minima of shear strength, and the shear-strength minimum for all tests was located near 0.5 m below land surface, the shallow zone of contrasting permeabilities. These results indicate that subsurface soil creep, a slow semi-continuous process, may exert a profound influence on rapid, shallow slope failures in saprolitic soils. Data indicate that cove slopes in quartz diorite tend to be the most unstable when saturation levels reach 75%. Deep failures (7 m deep) appear the most critical but not the most frequent because pore pressure build-up will occur more rapidly in the upper perched zone of translocated clays before reaching the lower zone between 3 and 7 m. Frequent shallow failures could reduce the probability of deeper failures by removing overburden and reducing shear stress at depth. Deep failures are more likely to result from storm events of great duration and intensity. Sixty-six 'naturally occurring' and more than 100 'road-related' landslides were mapped. Forest elevations exceed 1000 m, but the majority of these failures were found between 600 and 800 m in elevation. This appears to be the area where there is sufficient concentration of subsurface water to result in excess pore pressures. The high percentage of slope failures in the 600-800-m range, relative to the percentage at higher elevations, suggests that differences in soil-water processes are responsible for the form of these mountain slopes. Steep linear segments are maintained at higher elevations. Slope angles are reduced in the 600-800-m range by frequent shallow slides, creating a largely concave surface. In combination, slope segments above 800 m, and those between 600 and 800 m, produce the characteristic form of the mountains of eastern Puerto Rico.

  18. Eberhardt, E., Stead, D., Coggan, J.S., Willenberg, H., Hybrid finite-/discrete-element modelling of progressive failure in massive rock slopes. ISRM 2003Technology roadmap for rock mechanics, South African Institute of Mining and Metallurgy, 2003.

    E-print Network

    -/discrete-element modelling of progressive failure in massive rock slopes. ISRM 2003­Technology roadmap for rock mechanics of progressive failure in massive rock slopes E. Eberhardt* , D. Stead** , J.S. Coggan*** , H. Willenberg School of Mines, University of Exeter, UK ABSTRACT: Although individually both continuum and discontinuum

  19. IEEE TRANSACTIONS ON ELECTRON DEVICES, VOL. 57, NO. 11, NOVEMBER 2010 3163 Lifetime and Failure Mechanisms of an Arrayed

    E-print Network

    Walker, Mitchell

    propulsion, such as space tethers and spacecraft charge control [1], [4]. FE is the extraction of electrons flow to operate. To incorporate CNT emitters into propulsion systems, the cur- rent emission output. Resistive heating is believed to be the primary cause for failure in two thermally assisted modes: 1

  20. Modeling shear failure and permeability enhancement due to coupled Thermal-Hydrological-Mechanical processes in Enhanced Geothermal Reservoirs

    Microsoft Academic Search

    Kelkar; Sharad

    2011-01-01

    The connectivity and accessible surface area of flowing fractures, whether natural or man-made, is possibly the single most important factor, after temperature, which determines the feasibility of an Enhanced Geothermal System (EGS). Rock deformation and in-situ stress changes induced by injected fluids can lead to shear failure on preexisting fractures which can generate microseismic events, and also enhance the permeability

  1. Photovoltaic cell reliability research: Investigation of accelerated stress factors and failure-degradation mechanisms in terrestrial solar cells

    Microsoft Academic Search

    J. W. Lathrop

    1984-01-01

    Results of an ongoing research program into the reliability of terrestrial solar cells are presented. The main focus of the research is to identify failure\\/degradation modes affecting solar cells and to relate these to basic physical, chemical, and metallurgical phenomena. The program is concerned with the reliability attributes of individual single crystalline, polycrystalline, and amorphous thin film silicon cells. Results

  2. Autonomous Failure-handling mechanism for WF Long Running Transactions Manar S Ali and Stephan Reiff-Marganiec

    E-print Network

    Reiff-Marganiec, Stephan

    of an LRT, namely the normal execution mode and the compensation execution mode. During the normal execution handling, rule based reactive approach. I. INTRODUCTION Business processes naturally involve long running. In the absence of failure this should occur, but even if the LRT has not completed its normal path of execution

  3. Solder joint failure modes, mechanisms, and life prediction models of IC packages under board level drop impact

    Microsoft Academic Search

    Jing-en Luan; Tong Yan Tee; Xueren Zhang; E. Hussab

    2005-01-01

    Drop impact performance of solder joints of IC packages becomes a great concern for handheld products, such as mobile phones and PDA. Failure modes of solder joints under drop impact depend on solder alloys, interfacial strength, intermetallic formulation, and etc. Submodeling technique is applied to model detailed structure of critical solder joint. The stress and strain concentration at different locations

  4. Investigation of failure mechanisms in GFRP sandwich structures with face sheet wrinkle defects used for wind turbine blades

    Microsoft Academic Search

    Martin Leong; Lars C. T. Overgaard; Ole T. Thomsen; Erik Lund; Isaac M. Daniel

    Wrinkle defects can be formed during the production of wind turbine blades consisting of composite monolithic and sandwich laminates. Earlier studies have shown that the in-plane compressive strength of a sandwich panel with wrinkle defects may decrease dramatically. This study focuses on the failure modes of sandwich specimens consisting of thick GFRP face sheets with a wrinkle defect and a

  5. A three-dimensional numerical investigation of fracture initiation by ductile failure mechanisms in a 4340 steel

    Microsoft Academic Search

    R. Narasimhan; A. J. Rosakis; B. Moran

    1992-01-01

    Fracture initiation in ductile metal plates occurs due to substantial tunneling of the crack in the interior of the specimen followed by final failure of side ligaments by shear lip formation. The tunneled region is characterized by a flat, fibrous fracture surface. This phenomenon is clearly exhibited in a recent experimental investigation [8] performed on pre-notched plates of a ductile

  6. Characterization of commercial EB-PVD TBC systems with CVD (Ni,Pt)Al bond coatings

    Microsoft Academic Search

    J. A Haynes; M. J Lance; B. A Pint; I. G Wright

    2001-01-01

    Failure of electron-beam physical vapor deposition (EB-PVD) thermal barrier coatings (TBCs) with aluminide bond coats is strongly influenced by bond coat oxidation behavior. This study investigated oxide (Al2O3) formation during EB-PVD processing of TBCs with (Ni,Pt)Al bond coats. The effects of substrate composition, coating impurities and bond-coat grit-blasting on the oxide phases, residual stress and microstructure were evaluated. As-deposited, high-purity

  7. Myocardial Injury after Surgery Is a Risk Factor for Weaning Failure from Mechanical Ventilation in Critical Patients Undergoing Major Abdominal Surgery

    PubMed Central

    Li, Shu; An, You-zhong; Ren, Jing-yi; Zhu, Feng-xue; Chen, Hong

    2014-01-01

    Background Myocardial injury after noncardiac surgery (MINS) is a newly proposed concept that is common among adults undergoing noncardiac surgery and associated with substantial mortality. We analyzed whether MINS was a risk factor for weaning failure in critical patients who underwent major abdominal surgery. Methods This retrospective study was conducted in the Department of Critical Care Medicine of Peking University People's Hospital. The subjects were all critically ill patients who underwent major abdominal surgery between January 2011 and December 2013. Clinical and laboratory parameters during the perioperative period were investigated. Backward stepwise regression analysis was performed to evaluate MINS relative to the rate of weaning failure. Age, hypertension, chronic renal disease, left ventricular ejection fraction before surgery, Acute Physiologic and Chronic Health Evaluation II score, pleural effusion, pneumonia, acute kidney injury, duration of mechanical ventilation before weaning and the level of albumin after surgery were treated as independent variables. Results This study included 381 patients, of whom 274 were successfully weaned. MINS was observed in 42.0% of the patients. The MINS incidence was significantly higher in patients who failed to be weaned compared to patients who were successfully weaned (56.1% versus 36.5%; P<0.001). Independent predictive factors of weaning failure were MINS, age, lower left ventricular ejection fraction before surgery and lower serum albumin level after surgery. The MINS odds ratio was 4.098 (95% confidence interval, 1.07 to 15.6; P?=?0.04). The patients who were successfully weaned had shorter hospital stay lengths and a higher survival rate than those who failed to be weaned. Conclusion MINS is a risk factor for weaning failure from mechanical ventilation in critical patients who have undergone major abdominal surgery, independent of age, lower left ventricular ejection fraction before surgery and lower serum albumin levels after surgery. PMID:25409182

  8. Mechanical Properties and Tensile Failure Analysis of Novel Bio-absorbable Mg-Zn-Cu and Mg-Zn-Se Alloys for Endovascular Applications.

    PubMed

    Persaud-Sharma, Dharam; Budiansky, Noah; McGoron, Anthony J

    2013-03-01

    In this paper, the mechanical properties and tensile failure mechanism of two novel bio-absorbable as-cast Mg-Zn-Se and Mg-Zn-Cu alloys for endovascular medical applications are characterized. Alloys were manufactured using an ARC melting process and tested as-cast with compositions of Mg-Zn-Se and Mg-Zn-Cu, being 98/1/1 wt.% respectively. Nanoindentation testing conducted at room temperature was used to characterize the elastic modulus (E) and surface hardness (H) for both the bare alloys and the air formed oxide layer. As compared to currently available shape memory alloys and degradable as-cast alloys, these experimental alloys possess superior as-cast mechanical properties that can increase their biocompatibility, degradation kinetics, and the potential for medical device creation. PMID:23543822

  9. Mechanical Properties and Tensile Failure Analysis of Novel Bio-absorbable Mg-Zn-Cu and Mg-Zn-Se Alloys for Endovascular Applications

    PubMed Central

    Persaud-Sharma, Dharam; Budiansky, Noah; McGoron, Anthony J.

    2013-01-01

    In this paper, the mechanical properties and tensile failure mechanism of two novel bio-absorbable as-cast Mg-Zn-Se and Mg-Zn-Cu alloys for endovascular medical applications are characterized. Alloys were manufactured using an ARC melting process and tested as-cast with compositions of Mg-Zn-Se and Mg-Zn-Cu, being 98/1/1 wt.% respectively. Nanoindentation testing conducted at room temperature was used to characterize the elastic modulus (E) and surface hardness (H) for both the bare alloys and the air formed oxide layer. As compared to currently available shape memory alloys and degradable as-cast alloys, these experimental alloys possess superior as-cast mechanical properties that can increase their biocompatibility, degradation kinetics, and the potential for medical device creation. PMID:23543822

  10. Respiratory Failure

    MedlinePLUS

    Respiratory failure happens when not enough oxygen passes from your lungs into your blood. Your body's organs, such ... brain, need oxygen-rich blood to work well. Respiratory failure also can happen if your lungs can't ...

  11. Optimal elevation of ?-cell 11?-hydroxysteroid dehydrogenase type 1 is a compensatory mechanism that prevents high-fat diet-induced ?-cell failure.

    PubMed

    Turban, Sophie; Liu, Xiaoxia; Ramage, Lynne; Webster, Scott P; Walker, Brian R; Dunbar, Donald R; Mullins, John J; Seckl, Jonathan R; Morton, Nicholas M

    2012-03-01

    Type 2 diabetes ultimately results from pancreatic ?-cell failure. Abnormally elevated intracellular regeneration of glucocorticoids by the enzyme 11?-hydroxysteroid dehydrogenase type 1 (11?-HSD1) in fat or liver may underlie pathophysiological aspects of the metabolic syndrome. Elevated 11?-HSD1 is also found in pancreatic islets of obese/diabetic rodents and is hypothesized to suppress insulin secretion and promote diabetes. To define the direct impact of elevated pancreatic ?-cell 11?-HSD1 on insulin secretion, we generated ?-cell-specific, 11?-HSD1-overexpressing (MIP-HSD1) mice on a strain background prone to ?-cell failure. Unexpectedly, MIP-HSD1(tg/+) mice exhibited a reversal of high fat-induced ?-cell failure through augmentation of the number and intrinsic function of small islets in association with induction of heat shock, protein kinase A, and extracellular signal-related kinase and p21 signaling pathways. 11?-HSD1(-/-) mice showed mild ?-cell impairment that was offset by improved glucose tolerance. The benefit of higher ?-cell 11?-HSD1 exhibited a threshold because homozygous MIP-HSD1(tg/tg) mice and diabetic Lep(db/db) mice with markedly elevated ?-cell 11?-HSD1 levels had impaired basal ?-cell function. Optimal elevation of ?-cell 11?-HSD1 represents a novel biological mechanism supporting compensatory insulin hypersecretion rather than exacerbating metabolic disease. These findings have immediate significance for current therapeutic strategies for type 2 diabetes. PMID:22315313

  12. Heart Failure

    MedlinePLUS

    Heart failure is a condition in which the heart can't pump enough blood to meet the body's needs. Heart failure does not mean that your heart has stopped ... Tiredness and shortness of breath Common causes of heart failure are coronary artery disease, high blood pressure and ...

  13. The use of failure mode and effects analysis to construct an effective disposal and prevention mechanism for infectious hospital waste

    SciTech Connect

    Ho, Chao Chung, E-mail: ho919@pchome.com.tw [Department of Industrial Management, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China); Liao, Ching-Jong [Department of Industrial Management, National Taiwan University of Science and Technology, Taipei 106, Taiwan (China)

    2011-12-15

    Highlights: > This study is based on a real case in a regional teaching hospital in Taiwan. > We use Failure mode and effects analysis (FMEA) as the evaluation method. > We successfully identify the risk factors of infectious waste disposal. > We propose plans for the detection of exceptional cases of infectious waste. - Abstract: In recent times, the quality of medical care has been continuously improving in medical institutions wherein patient-centred care has been emphasized. Failure mode and effects analysis (FMEA) has also been promoted as a method of basic risk management and as part of total quality management (TQM) for improving the quality of medical care and preventing mistakes. Therefore, a study was conducted using FMEA to evaluate the potential risk causes in the process of infectious medical waste disposal, devise standard procedures concerning the waste, and propose feasible plans for facilitating the detection of exceptional cases of infectious waste. The analysis revealed the following results regarding medical institutions: (a) FMEA can be used to identify the risk factors of infectious waste disposal. (b) During the infectious waste disposal process, six items were scored over 100 in the assessment of uncontrolled risks: erroneous discarding of infectious waste by patients and their families, erroneous discarding by nursing staff, erroneous discarding by medical staff, cleaning drivers pierced by sharp articles, cleaning staff pierced by sharp articles, and unmarked output units. Therefore, the study concluded that it was necessary to (1) provide education and training about waste classification to the medical staff, patients and their families, nursing staff, and cleaning staff; (2) clarify the signs of caution; and (3) evaluate the failure mode and strengthen the effects.

  14. The use of failure mode and effects analysis to construct an effective disposal and prevention mechanism for infectious hospital waste.

    PubMed

    Ho, Chao Chung; Liao, Ching-Jong

    2011-12-01

    In recent times, the quality of medical care has been continuously improving in medical institutions wherein patient-centred care has been emphasized. Failure mode and effects analysis (FMEA) has also been promoted as a method of basic risk management and as part of total quality management (TQM) for improving the quality of medical care and preventing mistakes. Therefore, a study was conducted using FMEA to evaluate the potential risk causes in the process of infectious medical waste disposal, devise standard procedures concerning the waste, and propose feasible plans for facilitating the detection of exceptional cases of infectious waste. The analysis revealed the following results regarding medical institutions: (a) FMEA can be used to identify the risk factors of infectious waste disposal. (b) During the infectious waste disposal process, six items were scored over 100 in the assessment of uncontrolled risks: erroneous discarding of infectious waste by patients and their families, erroneous discarding by nursing staff, erroneous discarding by medical staff, cleaning drivers pierced by sharp articles, cleaning staff pierced by sharp articles, and unmarked output units. Therefore, the study concluded that it was necessary to (1) provide education and training about waste classification to the medical staff, patients and their families, nursing staff, and cleaning staff; (2) clarify the signs of caution; and (3) evaluate the failure mode and strengthen the effects. PMID:21807493

  15. Failure of Viral Shells

    NASA Astrophysics Data System (ADS)

    Klug, William S.; Bruinsma, Robijn F.; Michel, Jean-Philippe; Knobler, Charles M.; Ivanovska, Irena L.; Schmidt, Christoph F.; Wuite, Gijs J. L.

    2006-12-01

    We report a combined theoretical and experimental study of the structural failure of viral shells under mechanical stress. We find that discontinuities in the force-indentation curve associated with failure should appear when the so-called Föppl von Kármán (FvK) number exceeds a critical value. A nanoindentation study of a viral shell subject to a soft-mode instability, where the stiffness of the shell decreases with increasing pH, confirms the predicted onset of failure as a function of the FvK number.

  16. Investigation of deformation and failure mechanisms in woven and nonwoven fabrics under quasi-static loading conditions

    E-print Network

    Jearanaisilawong, Petch, 1979-

    2004-01-01

    The mechanical responses of high performance ballistic woven and nonwoven fabrics under in- plane quasi-static loading conditions have been investigated. The investigations focused on the responses of fabrics at the ...

  17. Saturn component failure rate and failure rate modifiers

    NASA Technical Reports Server (NTRS)

    1971-01-01

    Failure mode frequency ratios, environmental adjustment factors, and failure rates for mechanical and electromechanical component families are presented. The failure rates and failure rate modifiers resulted from a series of studies whose purpose was to provide design, tests, reliability, and systems engineers with accurate, up-to-date failure rate information. The results of the studies were achieved through an extensive engineering analysis of the Saturn Program test data and Unsatisfactory Condition Reports (UCR's) and the application of mathematical techniques developed for the studies.

  18. Pt-modified Ni aluminides, MCrAlY-base multilayer coatings and TBC systems fabricated by Spark Plasma Sintering for the protection of Ni-base superalloys

    Microsoft Academic Search

    Daniel Monceau; Djar Oquab; Claude Estournes; Mathieu Boidot; Serge Selezneff; Yannick Thebault; Yannick Cadoret

    2009-01-01

    Pt-modified Ni aluminides and MCrAlY coatings (where M=Ni and\\/or Co) are widely used on turbine blades and vanes for protection against oxidation and corrosion and as bond coatings in thermal barrier coating (TBC) systems. The present work shows the ability of a new fabrication technique, the Spark Plasma Sintering, to develop rapidly new coating compositions and microstructures. This technique allows

  19. Mechanism of flt3 ligand expression in bone marrow failure: translocation from intracellular stores to the surface of T lymphocytes after chemotherapy-induced suppression of hematopoiesis.

    PubMed

    Chklovskaia, E; Jansen, W; Nissen, C; Lyman, S D; Rahner, C; Landmann, L; Wodnar-Filipowicz, A

    1999-04-15

    The flt3 ligand (FL) is a growth factor for primitive hematopoietic cells. Serum levels of FL are inversely related to the number and proliferative capacity of early hematopoietic progenitors. We sought to elucidate the molecular mechanism underlying this regulation. Expression of FL was examined in peripheral blood (PB) and bone marrow (BM) cells under normal steady-state hematopoiesis and during transient BM failure induced by chemoradiotherapy in 16 patients with hematological malignancies. Using anti-FL antibodies in Western analysis, flow cytometry, and confocal microscopy, we detected high levels of preformed FL inside but not on the surface of T lymphocytes in steady-state hematopoiesis. Intracellular FL colocalized with giantin and ERGIC-53, indicating that it is stored within and close to the Golgi apparatus. After chemotherapy-induced hematopoietic failure, FL rapidly translocated to the surface of T lymphocytes and the levels of FL released to serum increased approximately 100-fold. Expression of FL mRNA was enhanced only about sevenfold; a similar, twofold to sixfold increase in mRNA was observed in the thymus and BM of mice with irradiation-induced aplasia. Upregulation of FL mRNA was delayed when compared with the appearance of cell surface-associated and soluble protein isoforms. The described changes in FL expression in response to chemotherapy-induced aplasia were observed in all patients, irrespective of the diagnosis and treatment regimen. Our data demonstrate that mobilization of preformed FL from intracellular stores rather than de novo synthesis is responsible for increased FL levels in BM failure. PMID:10194439

  20. Failure diagnosis of high speed gear

    Microsoft Academic Search

    Fang Wang; Shaoping Wang

    2011-01-01

    Directing to the failure of high speed gear pair, this paper investigates its failure mechanism. Based on the failure characteristics, this paper adopts the power spectrum and empirical mode decomposition to detect two types of gear tooth failures. Defects were intentionally seeded in two separate pinions to explore feasible approach to monitor the tooth condition in a high speed gear

  1. Electrophysiological Remodeling in Heart Failure

    PubMed Central

    Wang, Yanggan; Hill, Joseph A.

    2010-01-01

    Heart failure affects nearly 6 million Americans, with a half-million new cases emerging each year. Whereas up to 50% of heart failure patients die of arrhythmia, the diverse mechanisms underlying heart failure-associated arrhythmia are poorly understood. As a consequence, effectiveness of antiarrhythmic pharmacotherapy remains elusive. Here, we review recent advances in our understanding of heart failure-associated molecular events impacting the electrical function of the myocardium. We approach this from an anatomical standpoint, summarizing recent insights gleaned from pre-clinical models and discussing their relevance to human heart failure. PMID:20096285

  2. Failure mechanism analysis and process improvement on time-dependent dielectric breakdown of Cu/ultra-low-k dielectric based on complementary Raman and FTIR spectroscopy study

    NASA Astrophysics Data System (ADS)

    Wang, Dan Dan; Wang, Wei Lin; Huang, Maggie Yamin; Lek, Alan; Lam, Jeffrey; Mai, Zhi Hong

    2014-07-01

    Time-dependent dielectric breakdown (TDDB) is one of the most important reliability issues in Cu/low-k technology development. With continuous technology scalings to nanometer scales, TDDB issue is further exacerbated. In this paper, two failure mechanisms were investigated: the Ta ions migration model and the line-edge-roughness (LER) model, which is rendering the observed TDDB failure. Complimentary Raman and FTIR spectroscopy was applied to investigate the dielectric bonding characteristics. Our experimental results revealed the TDDB degradation behavior of Cu/ultra-low-k interconnects, suggesting the intrinsic degradation of the ultra-low-k dielectric. No out-diffusion of Cu ions was observed in Cu/Ta/TaN/SiCOH structures. Extensive TEM analysis further verified the migration of Ta ions from the Ta/TaN barrier bi-layer into the ultra-low-k dielectrics. Based on the LER model analysis, a comparative study in both passing and failing die elaborates that the sloped trench/via profile affected the TDDB performance.

  3. Exploratory Investigation of Failure Mechanisms in Transition Regions between Solid Laminates and X-cor(registered tm) Truss Sandwich

    NASA Technical Reports Server (NTRS)

    OBrien, T. Kevin; Paris, Isabelle L.

    2004-01-01

    Small sub-component specimens consisting of solid laminates at the ends that transition to X-cor(R) truss sandwich in the center, were tested in a combination of three point bending, uni-axial tension, and combined tension and bending. The failure process in the transition region was documented for each loading using digital video and high-resolution cameras. For the 3-point bending tests, most of the deformation occurred in the solid laminate regions on either end of the specimen. Some pin debonding from the skin of the X-cor(R) truss sandwich was observed in the transition region and was accompanied by audible "pings" throughout the loading. Tension loaded specimens failed in the sandwich skin in the middle of the gage length, accompanied by separation of the sandwich core from the back skin and by delamination between the top skin and bottom skin at the transition region. The pinging associated with pin debonding occurred as the load was increased. However, the frequency of the pinging exceeded any visual observations of pin debonding in the video of the transition region. For specimens tested in combined tension and bending, the greatest amount of pinging occurred during initial application of the axial load. High-resolution images in the transition region indicated that the pinging corresponded to pins debonding and buckling due to the through-thickness Poisson contraction of the specimen. This buckling continued to a much smaller extent as the transverse load was applied.

  4. Imposex and novel mechanisms of reproductive failure induced by tributyltin (TBT) in the freshwater snail Pomacea canaliculata.

    PubMed

    Giraud-Billoud, Maximiliano; Vega, Israel A; Wuilloud, Rodolfo G; Clément, María E; Castro-Vazquez, Alfredo

    2013-10-01

    The effects of tributyltin (TBT) on mortality and reproduction were studied in the invasive snail Pomacea canaliculata. The nominal median lethal concentration (LC50) was 9 µg TBT/L, after 28 d. The nominal no-observed effect on lethality concentration (NOECL) was 6 µg TBT/L after the same period. Male-female couples and females that had been group-mated but were isolated from males during the experiment (isolated females) were exposed (for 28 d) to either 0 µg/L or 6 µg/L of TBT (nominal NOECL-exposed). Copulation and oviposition frequencies, egg clutch mass, and percentage of egg fertility were recorded. Gonads (both sexes) and the seminal receptacle (females) were studied histologically at the end of the experiment. A significant decrease in copulation frequency was observed in mated-exposed females. Exposure also decreased oviposition frequency of mated-exposed and isolated-exposed females, but only the latter reached significance. No differences in either egg clutch mass or percentage of fertility were observed at first oviposition, but both parameters were drastically reduced in subsequent egg clutches of exposed females. No histological alterations were observed in gonads of TBT-exposed animals; however, sperm storage in the seminal receptacle was drastically decreased in exposed females. Imposex but no oviductal obstruction was observed in all exposed females. It is concluded that TBT induces reproductive failure in P. canaliculata by decreasing copulation frequency and by severely affecting sperm storage by the female. PMID:23775621

  5. Endoscopic Study of Mechanisms of Failure of Endotracheal Tube Advancement into the Trachea during Awake Fiberoptic Orotracheal Intubation

    Microsoft Academic Search

    Dana M. Johnson; Russell B. Smith; Mazen A. Maktabi

    2005-01-01

    Background: Advancing the endotracheal tube (ETT) over a flexible bronchoscope (FB) during awake fiberoptic orotra- cheal intubation is often impeded. The goal of this study was to identify the sites and mechanisms that inhibit the passing of the ETT into the trachea. Methods: Forty-five consenting patients underwent a clini- cally indicated awake fiberoptic orotracheal intubation. After topical anesthesia, nerve block,

  6. An electrostatic discharge failure mechanism in semiconductor devices, with applications to electrostatic discharge measurements using transmission line pulsing technique

    Microsoft Academic Search

    J. C Lee; A Hoque; G. D Croft; J. J Liou; R Young; J. C Bernier

    2000-01-01

    Electrostatic discharge (ESD) is responsible for more than 25% of semiconductor device and chip damage each year. This paper focuses on an ESD event resulting from the charge being transferred from a human body to an integrated circuit (called the human body model, HBM). In particular, the study provides simulation and experimental results to determine the main mechanism governing the

  7. Mechanisms of Ghrelin Anti-Heart Failure: Inhibition of Ang II-Induced Cardiomyocyte Apoptosis by Down-Regulating AT1R Expression

    PubMed Central

    Yang, Chunyan; Liu, Zhonghui; Liu, Kai; Yang, Ping

    2014-01-01

    Background Ghrelin is a novel growth hormone–releasing peptide administered to treat chronic heart failure (CHF). However, the underlying mechanism of its protective effects against heart failure (HF) remains unclear. Methods and Results A total of 68 patients with CHF and 20 healthy individuals were included. The serum levels of Angiotensin II (Ang II) and ghrelin were measured using ELISA. The results showed that Ang II and ghrelin were both significantly increased in CHF patients and that the ghrelin levels were significantly positively correlated with Ang II. The left anterior descending coronary artery was ligated to establish a rat model of CHF, and cultured cardiomyocytes from neonatal rats were stimulated with Ang II to explore the role of ghrelin in CHF. The results showed that ghrelin inhibited cardiomyocyte apoptosis both in vivo and in vitro. Furthermore, caspase-3 expression was examined, and the results revealed that Ang II induces cardiomyocyte apoptosis through the caspase-3 pathway, whereas ghrelin inhibits this action. Lastly, to further elucidate the mechanism by which ghrelin inhibits Ang II action, the expression of the AT1 and AT2 receptors was evaluated; the results showed that Ang II up-regulates the AT1 and AT2 receptors in cardiomyocytes, whereas ghrelin inhibits AT1 receptor up-regulation but does not affect AT2 receptor expression. Conclusions These data suggest that the serum levels of ghrelin are significantly positively correlated with Ang II in CHF patients and that ghrelin can inhibit Ang II-induced cardiomyocyte apoptosis by down-regulating AT1R, thereby playing a role in preventing HF. PMID:24465706

  8. Ballistic-Failure Mechanisms in Gas Metal Arc Welds of Mil A46100 Armor-Grade Steel: A Computational Investigation

    NASA Astrophysics Data System (ADS)

    Grujicic, M.; Snipes, J. S.; Galgalikar, R.; Ramaswami, S.; Yavari, R.; Yen, C.-F.; Cheeseman, B. A.

    2014-09-01

    In our recent work, a multi-physics computational model for the conventional gas metal arc welding (GMAW) joining process was introduced. The model is of a modular type and comprises five modules, each designed to handle a specific aspect of the GMAW process, i.e.: (i) electro-dynamics of the welding-gun; (ii) radiation-/convection-controlled heat transfer from the electric-arc to the workpiece and mass transfer from the filler-metal consumable electrode to the weld; (iii) prediction of the temporal evolution and the spatial distribution of thermal and mechanical fields within the weld region during the GMAW joining process; (iv) the resulting temporal evolution and spatial distribution of the material microstructure throughout the weld region; and (v) spatial distribution of the as-welded material mechanical properties. In the present work, the GMAW process model has been upgraded with respect to its predictive capabilities regarding the spatial distribution of the mechanical properties controlling the ballistic-limit (i.e., penetration-resistance) of the weld. The model is upgraded through the introduction of the sixth module in the present work in recognition of the fact that in thick steel GMAW weldments, the overall ballistic performance of the armor may become controlled by the (often inferior) ballistic limits of its weld (fusion and heat-affected) zones. To demonstrate the utility of the upgraded GMAW process model, it is next applied to the case of butt-welding of a prototypical high-hardness armor-grade martensitic steel, MIL A46100. The model predictions concerning the spatial distribution of the material microstructure and ballistic-limit-controlling mechanical properties within the MIL A46100 butt-weld are found to be consistent with prior observations and general expectations.

  9. Failure of anterior cruciate ligament reconstruction.

    PubMed

    Whitehead, Timothy S

    2013-01-01

    Failure after anterior cruciate ligament reconstruction is a potentially devastating event that affects a predominantly young and active population. This review article provides a comprehensive analysis of the potential causes of failure, including graft failure, loss of motion, extensor mechanism dysfunction, osteoarthritis, and infection. The etiology of graft failure is discussed in detail with a particular emphasis on failure after anatomic anterior cruciate ligament reconstruction. PMID:23177471

  10. Cliff Failure

    USGS Multimedia Gallery

    Cliff failure just south of San Gregorio Beach. Slide is 18.3 meters (60 ft) high and displaces approximately 6881 cubic meters (9,000 cubic yards) of material. Large boulders are 1 m (3 ft) across....

  11. Heart Failure

    MedlinePLUS

    ... this? Submit What's this? Submit Button Related CDC Web Sites Heart Disease Stroke High Blood Pressure Salt ... to Prevent and Control Chronic Diseases Million Hearts® Web Sites with More Information About Heart Failure For ...

  12. Combining mechanical and chemical effects in the deformation and failure of a cylindrical electrode particle in a Li-ion battery

    E-print Network

    Jeevanjyoti Chakraborty; Colin P. Please; Alain Goriely; S. Jonathan Chapman

    2014-07-31

    A general framework to study the mechanical behaviour of a cylindrical silicon anode particle in a lithium ion battery as it undergoes lithiation is presented. The two-way coupling between stress and concentration of lithium in silicon, including the possibility of plastic deformation, is taken into account and two particular cases are considered. First, the cylindrical particle is assumed to be free of surface traction and second, the axial deformation of the cylinder is prevented. In both cases plastic stretches develop through the entire cylinder and not just near the surface as is commonly found in spherical anode particles. It is shown that the stress evolution depends both on the lithiation rate and the external constraints. Furthermore, as the cylinder expands during lithiation it can develop a compressive axial stress large enough to induce buckling, which in turn may lead to mechanical failure. An explicit criterion for swelling-induced buckling obtained as a modification of the classical Euler buckling criterion shows the competition between the stabilising effect of radius increase and the destabilising effect of axial stress.

  13. [FeIV=O(TBC)(CH3CN)]2+: Comparative Reactivity of Iron(IV)-Oxo Species with Constrained Equatorial Cyclam Ligation

    PubMed Central

    Wilson, Samuel A.; Chen, Junying; Hong, Seungwoo; Lee, Yong-Min; Clémancey, Martin; Garcia-Serres, Ricardo; Nomura, Takashi; Ogura, Takashi; Latour, Jean-Marc; Hedman, Britt; Hodgson, Keith O.; Nam, Wonwoo; Solomon, Edward I.

    2012-01-01

    [FeIV=O(TBC)(CH3CN)]2+ (TBC = 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclotetradecane) is characterized and its reactivity differences relative to [FeIV=O(TMC)(CH3CN)]2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) are evaluated in hydrogen atom (H-atom) abstraction and oxo-transfer reactions. Structural differences are defined using X-ray absorption spectroscopy (XAS) and correlated to reactivities using density functional theory (DFT). The S = 1 ground states are highly similar and result in large activation barriers (~25 kcal/mol) due to steric interactions between the cyclam chelate and the substrate (e.g., ethylbenzene) associated with the equatorial ?-attack required by this spin state. Conversely, H-atom abstraction reactivity on an S = 2 surface allows for a ?-attack with an axial substrate approach. This results in decreased steric interactions with the cyclam and a lower barrier (~9 kcal/mol). For [FeIV=O(TBC)(CH3CN)]2+, the S = 2 excited state in the reactant is lower in energy and therefore more accessible at the transition state due to a weaker ligand field associated with the steric interactions of the benzyl substituents with the trans-axial ligand. This study is further extended to the oxo-transfer reaction, which is a two-electron process requiring both ? and ? electron transfer and thus a non-linear transition state. In oxo-transfer, the S = 2 has a lower barrier due to sequential vs. concerted (S = 1) two electron transfer which gives a high-spin ferric intermediate at the transition state. The [FeIV=O(TBC)(CH3CN)]2+ complex is more distorted at the transition state, with the iron farther out of the equatorial plane due to the steric interaction of the benzyl groups with the trans-axial ligand. This allows for better orbital overlap with the substrate, a lower barrier, and an increased rate of oxo-transfer. PMID:22708532

  14. Heart Failure Overview

    MedlinePLUS

    CHF; Congestive heart failure; Left-sided heart failure; Right-sided heart failure - Cor pulmonale; Cardiomyopathy - heart failure ... Heart failure is often a long-term (chronic) condition, but it may come on suddenly. It can ...

  15. [Obesity and cardiac failure].

    PubMed

    Galinier, M; Pathak, A; Roncalli, J; Massabuau, P

    2005-01-01

    Obesity alone is the cause of 11% of cases of cardiac failure in men and 14% of cases in women in the United States. The frequency of obesity continues to rise in our country, 41% of our compatriots being obese or overweight. It is expected that obesity will become an important cause of cardiac failure in the coming years. The Framingham study showed that, after correction for other risk factors, for every point increase in body mass index, the increase in risk of developing cardiac failure was 5% in men and 7% in women. There are three physiopathological mechanisms to explain the adverse effects of obesity on left ventricular function: an increase in ventricular preload secondary to increased plasma volume induced by the high fatty mass; an increase in left ventricular afterload due to the common association of hypertension generated by activation of the sympathetic nervous system by hyperinsulinism; and systolic and diastolic dysfunction due to changes in the myocardial genome and coronary artery disease induced by risk factors of atherosclerosis aggravated by obesity. The adipocyte also secretes a number of hormones which act directly or indirectly on the myocardium: angiotensin II, leptin, resistin, adrenomedulin, cytokines. These haemodynamic and hormonal changes profoundly modify the genetic expression of the myocardium in obesity, favourising hypertrophy of the myocyte and the development of interstitial fibrosis. Whether it be eccentric in the absence of hypertension or concentric when hypertension is associated with obesity, left ventricular hypertrophy, although normalising left ventricular wall stress, has adverse consequences causing abnormal relaxation and decreased left ventricular compliance. Therefore, in obese patients, two forms of cardiac failure may be observed. The more common is due to diastolic dysfunction, obesity being one of the principal causes of cardiac failure with preserved systolic function. Cardiac failure due to systolic dysfunction is less common and may be observed in cases with inappropriate left ventricular hypertrophy which does not normalise abnormal left ventricular wall stress leading to cardiomyopathy, and in cases with associated coronary artery disease. Whatever the underlying mechanism, the diagnosis of cardiac failure is made more difficult by obesity. From the prognostic point of view, in the global population of patients with cardiac failure, obesity improves survival because it counteracts the adverse effect of cachexia; however, obesity increases the risk of sudden death. In fact, obesity is associated with dynamic change in QT interval. In cases of cardiac failure secondary to obesity-related cardiomyopathy, loss of weight leads to an improved functional status and a reduction of left ventricular remodelling and an increase of the ejection fraction. PMID:15724418

  16. Mechanical dyssynchrony is additive to ECG criteria and independently associated with reverse remodelling and clinical response to cardiac resynchronisation therapy in patients with advanced heart failure

    PubMed Central

    Bank, Alan J; Gage, Ryan M; Marek, Josef J; Onishi, Toshinari; Burns, Kevin V; Schwartzman, David; Saba, Samir; Gorcsan, John

    2015-01-01

    Background QRS duration and morphology are known established predictors of cardiac resynchronisation therapy (CRT) response, whereas mechanical dyssynchrony is not. Our aim was to determine if mechanical dyssynchrony provides independent prognostic information on CRT response. Methods We studied 369 consecutive patients with heart failure (HF) with low ejection fraction (EF) and widened QRS receiving CRT. Radial dyssynchrony (septal-posterior radial peak strain delay ?130?ms by speckle tracking) assessment was possible in 318 patients (86%). Associations with left ventricular end-systolic volume (LVESV) changes were examined using linear regression, and clinical outcomes analysed using Cox regression adjusted for multiple established outcome correlates. Results Patients with radial dyssynchrony before CRT (64%) had greater improvements in EF (8.8±9.4 vs 6.1±9.7 units, p=0.04) and LVESV (?30±41 vs ?10±30?mL, p<0.01). Radial dyssynchrony was independently associated with reduction in LVESV (regression coefficient ?10.5?mL, 95% CI ?20.5 to ?0.5, p=0.040) as was left bundle-branch block (?17.7?mL, ?27.6 to ?7.7, p=0.001). Patients with radial dyssynchrony had a 46% lower incidence of death, transplant or implantation of a left ventricular assist device (adjusted HR 0.54, 95% CI 0.31 to 0.92, p=0.02) and a 39% lower incidence of death or HF hospitalisation (0.61, 0.40 to 0.93, p=0.02) over 2?years. Conclusions Radial dyssynchrony was associated with significant improvements in LVESV and clinical outcomes following CRT and is independent of QRS duration or morphology, and additive to current ECG selection criteria to predict response to CRT. PMID:25973213

  17. Heart Failure

    Microsoft Academic Search

    Susan Isakson BA; Alan Maisel

    Decompensated congestive heart failure (CHF) is a clinical syndrome often characterized by elevated left ventricular fi lling pressures (LVEDP). Therapy for decompensated CHF aims at normalizing fi lling pressures and thereby improves both symptoms and outcomes. However, therapy guided by direct measurements of fi lling pressure is not practical in most patients, focusing attention on non-invasive surrogate measures of LVEDP

  18. Failure Modes in Adhesively Bonded Carton Boards

    Microsoft Academic Search

    Christer Korin; Nils Hallbäck; Robert Junghans

    2008-01-01

    Carton board packages are often adhesively bonded. The adhesive joint may fail due to cohesive fracture in the adhesive, interfacial fracture between the adhesive and one of the carton board surfaces, or cohesive fracture in the carton board. The failure may also be a combination of these failure modes. From previous studies, it is well known that the failure mechanism

  19. Dependent failure analysis of NPP data bases

    SciTech Connect

    Cooper, S.E.; Lofgren, E.V. (Science Applications International Corp., San Diego, CA (USA)); Samanta, P.K.; Wong, See-Meng (Brookhaven National Lab., Upton, NY (USA))

    1990-01-01

    A technical approach for analyzing plant-specific data bases for vulnerabilities to dependent failures has been developed and applied. Since the main purpose of this work, to aid in the formulation of defenses to dependent failures, is different than that for other dependent failure analyses, the approach of this analysis is also critically different. For instance, component failures have been defined to include all types of component function loss (e.g., catastrophic, degraded, incipient). Also, the determination of component failure dependencies has been based upon identical failure mechanisms rather than failure modes. Consequently, in the context of this study, both the definition of component failure and a categorization scheme for component failure mechanisms are used to identify clusters of component failures which are termed common failure mechanism (CFM) events. Motor-operated valves (MOVs) in two nuclear power plant data bases have been analyzed with this approach. The analysis results include seven different failure mechanism categories; identified potential CFM events; and assessment of the risk-significance of the potential CFM events using existing probabilistic risk assessments (PRAs); and postulated defenses to the identified potential CFM events. 2 refs., 3 figs., 5 tabs.

  20. Modeling oxidation induced stresses in thermal barrier coatings

    Microsoft Academic Search

    A. M Freborg; B. L Ferguson; W. J Brindley; G. J Petrus

    1998-01-01

    Oxidation of the bond coat of a thermal barrier coating (TBC) is an important contributing factor to spallation of the ceramic top coat during service. However, the mechanisms by which oxidation facilitates TBC failure are poorly understood. It is also unclear how oxidation may interact with other potential degradation mechanisms. A finite element model was developed to evaluate stresses induced

  1. Failure analysis of wafer-level reliability testing failure

    NASA Astrophysics Data System (ADS)

    Oh, Chong K.; Neo, Soh P.; Bi, Jian H.; Wu, Zong M.; Goh, Lian C.; Redkar, Shailesh

    1999-08-01

    Wafer-level reliability (WLR) testing is an important tool that is used during the productization phase to investigate the reliability performance of devices and materials before full qualification cycle. The rapid nature of the WLR testing permits the process engineer to evaluate process variation and to obtain almost instantaneous feedback about its reliability impact. Fast reliability feedback is essential to help the process engineer build reliability into our product during the productization phase. Understand the root cause and failure mechanism after WLR testing, failure analysis plays a very important role. This paper describes the fundamental requirements for failure analysis equipment needed, the failure analysis and preparatory techniques used to locate the failure sites and cases study will be presented.

  2. Measurement of Trabecular Bone Microstructure Does Not Improve Prediction of Mechanical Failure Loads at the Distal Radius Compared with Bone Mass Alone

    Microsoft Academic Search

    E.-M. Lochmüller; J. Kristin; M. Matsuura; V. Kuhn; M. Hudelmaier; T. M. Link; F. Eckstein

    2008-01-01

    Bone mass predicts a high proportion of variability in bone failure strength but is known to overlap among subjects with and\\u000a without fractures. Here, we tested the hypothesis that trabecular bone microstructure, determined with micro-computed tomography\\u000a (?CT), can improve the prediction of experimental failure loads in the distal forearm compared with bone mass alone. The right\\u000a forearm and left distal

  3. Induction of autophagy markers is associated with attenuation of miR-133a in diabetic heart failure patients undergoing mechanical unloading

    PubMed Central

    Nandi, Shyam Sundar; Duryee, Michael J; Shahshahan, Hamid R; Thiele, Geoffrey M; Anderson, Daniel R; Mishra, Paras K

    2015-01-01

    Autophagy is ubiquitous in all forms of heart failure and cardioprotective miR-133a is attenuated in human heart failure. Previous reports from heart failure patients undergoing left ventricular assist device (LVAD) implantation demonstrated that autophagy is upregulated in the LV of the failing human heart. Studies in the murine model show that diabetes downregulates miR-133a. However, the role of miR-133a in the regulation of autophagy in diabetic hearts is unclear. We tested the hypothesis that diabetes exacerbates cardiac autophagy by inhibiting miR-133a in heart failure patients undergoing LVAD implantation. The miRNA assay was performed on the LV of 15 diabetic (D) and 6 non-diabetic (ND) heart failure patients undergoing LVAD implantation. Four ND with highly upregulated and 5 D with highly downregulated miR-133a were analyzed for autophagy markers (Beclin1, LC3B, ATG3) and their upstream regulators (mTOR and AMPK), and hypertrophy marker (beta-myosin heavy chain) by RT-qPCR, Western blotting and immunofluorescence. Our results demonstrate that attenuation of miR-133a in diabetic hearts is associated with the induction of autophagy and hypertrophy, and suppression of mTOR without appreciable difference in AMPK activity. In conclusion, attenuation of miR-133a contributes to the exacerbation of diabetes mediated cardiac autophagy and hypertrophy in heart failure patients undergoing LVAD implantation.

  4. Proficiency Metrics for Failure Prediction in High Performance Computing

    Microsoft Academic Search

    Narate Taerat; C. Leangsuksun; C. Chandler; N. Naksinehaboon

    2010-01-01

    The number of failures occurring in large-scale high performance computing (HPC) systems is significantly increasing due to the large number of physical components found on the system. Fault tolerance (FT) mechanisms help parallel applications mitigate the impact of failures. However, using such mechanisms requires additional overhead. As such, failure prediction is needed in order to smartly utilize FT mechanisms. Hence,

  5. 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.

  6. Invasive Ventilation and Acute Heart Failure Syndrome

    Microsoft Academic Search

    Jean-Damien Ricard; Damien Roux

    Because utilization of noninvasive ventilatory techniques considerably reduces the need for endotracheal intubation and invasive\\u000a mechanical ventilation during acute heart failure syndrome (AHFS) (1, 2), the recent guidelines issued by the European Society of Cardiology (3) recommend that invasive mechanical ventilation in the setting of acute heart failure (AHF) should be considered only after\\u000a failure of noninvasive methods, such as

  7. Failure studies on rubber and rubber composites

    Microsoft Academic Search

    Zhenghong Tao

    2005-01-01

    A research study has been conducted to investigate selected failure processes in rubber and rubbery composites. Specific failure modes and materials considered included mechanical tearing of rubber-coated fabrics and mechanical\\/thermal fatigue of carbon black-filled elastomers. Experimental efforts developed novel evaluation techniques that were used to access failure resistance of the materials, as well as to elucidate molecular structure\\/physical properties relationships.

  8. [Reprinted lrou thc Jourael of tbe Arnericeo Cbcaicrt Society,91,408O (1969).1 Copyright 1969 by tbc Araericeo Cbcmicd Socicty .!d repriqtcd by perrairsion of thc copyrigbt oracr.

    E-print Network

    Prentiss, Mara

    1969-01-01

    [Reprinted lrou thc Jourael of tbe Arnericeo Cbcaicrt Society,91,408O (1969).1 Copyright 1969 by tbc Araericeo Cbcmicd Socicty .!d repriqtcd by perrairsion of thc copyrigbt oracr. Hydrogen-Carbon,l3 of appropriatesymmetry,and single-crystalX-ray dif- (l) Supportedby thc NationalScienceFoundation,Grant GP-7266' (2

  9. Congestive heart failure. New frontiers.

    PubMed Central

    Parmley, W. W.; Chatterjee, K.; Francis, G. S.; Firth, B. G.; Kloner, R. A.

    1991-01-01

    Congestive heart failure is a common syndrome with high mortality in its advanced stages. Current therapy includes the use of vasodilator drugs, which have been shown to prolong life. Despite current therapy, mortality remains high in patients with severe heart failure. Potent new inotropic vasodilators have improved ventricular performance but have not prolonged life in patients with end-stage heart failure. Serious arrhythmias are implicated in the sudden deaths of 30% to 40% of patients with severe heart failure, but the benefits of antiarrhythmic therapy have not been established. Upcoming trials will address this question. Ventricular remodeling and progressive dilatation after myocardial infarction commonly lead to congestive heart failure; early unloading of the ventricle with an angiotensin-converting enzyme inhibitor may attenuate these events. These findings support the concept that angiotensin-converting enzyme inhibitors may be useful in managing heart failure of all degrees of severity, including left ventricular dysfunction and end-stage heart failure. Part of the damage that may occur with acute myocardial infarction, particularly in this era of thrombolysis therapy, is reperfusion injury, which may be mediated by oxygen-derived free radicals. Better knowledge of the mechanisms and treatment of myocardial infarction, the leading cause of congestive heart failure, may help prevent or attenuate the development of this syndrome. PMID:1678903

  10. Simulations of mechanical failure in ice: Implications of terrestrial fracture models as applied to they icy satellites of the outer solar system

    NASA Astrophysics Data System (ADS)

    Walker, C. C.; Bassis, J. N.

    2011-12-01

    At the South Pole of Enceladus, a small icy moon orbiting Saturn, is a heavily fractured ice plain surrounded by a nearly-circular mountain range. Remarkably, the Cassini orbiter detected jets of water emanating from the icy shell and into space, originating from 4 parallel "tiger stripe" rifts within the center of the ice plain. The tiger stripes imaged on Enceladus are morphologically similar to rifts observed to form under extensional stress regimes in terrestrial ice shelves; the putative subsurface ocean hypothesized beneath the icy shell strengthens the analogy that their formation may have similar mechanical origins. Past studies have also suggested that the tiger stripes are the result of a process similar to that of mid-ocean ridge spreading on the Earth, but it remains to be seen whether or not such motion is consistent with the mountainous features seen at the circular cliff-like boundary of the region. In an attempt to understand the formation of these tiger stripes and their relationship to the observed mountain chains, we apply a conceptual model in which the ice is considered to be less like a continuous fluid body and, instead, behaves like a granular material made up of discrete blocks of ice. The tidal forces on the small moon tug on the shell enough that it has been cracked many times over, motivating the assumption that the ice exists in a continuum between wholly intact ice and highly pre-fractured ice. We employ several experimental setups with the intention of mapping the deformation of the south polar segment of the shell, to determine the processes that may contribute to its observed morphological state. These setups range from large scale topographical models, e.g., simulating the build up of mountains and processes that lead to overall elevation differences in the region, to small-scale, and focus on the more detailed level of fracturing. We explore our ice-shelf rifting analogy by modeling both icy moon fracturing and ice shelf rifting to compare and contrast the failure modes that we observe, results that bolster both our comparative platform and, importantly, our understanding of fracture in ice shelves on the Earth as well. A similar approach could be applied to the chaos regions of Europa, where fractures are prevalent and whose underlying causes are not well understood.

  11. Progressive Failure Analysis Methodology for Laminated Composite Structures

    NASA Technical Reports Server (NTRS)

    Sleight, David W.

    1999-01-01

    A progressive failure analysis method has been developed for predicting the failure of laminated composite structures under geometrically nonlinear deformations. The progressive failure analysis uses C(exp 1) shell elements based on classical lamination theory to calculate the in-plane stresses. Several failure criteria, including the maximum strain criterion, Hashin's criterion, and Christensen's criterion, are used to predict the failure mechanisms and several options are available to degrade the material properties after failures. The progressive failure analysis method is implemented in the COMET finite element analysis code and can predict the damage and response of laminated composite structures from initial loading to final failure. The different failure criteria and material degradation methods are compared and assessed by performing analyses of several laminated composite structures. Results from the progressive failure method indicate good correlation with the existing test data except in structural applications where interlaminar stresses are important which may cause failure mechanisms such as debonding or delaminations.

  12. Light water reactor lower head failure analysis

    SciTech Connect

    Rempe, J.L.; Chavez, S.A.; Thinnes, G.L. [EG and G Idaho, Inc., Idaho Falls, ID (United States)] [and others

    1993-10-01

    This document presents the results from a US Nuclear Regulatory Commission-sponsored research program to investigate the mode and timing of vessel lower head failure. Major objectives of the analysis were to identify plausible failure mechanisms and to develop a method for determining which failure mode would occur first in different light water reactor designs and accident conditions. Failure mechanisms, such as tube ejection, tube rupture, global vessel failure, and localized vessel creep rupture, were studied. Newly developed models and existing models were applied to predict which failure mechanism would occur first in various severe accident scenarios. So that a broader range of conditions could be considered simultaneously, calculations relied heavily on models with closed-form or simplified numerical solution techniques. Finite element techniques-were employed for analytical model verification and examining more detailed phenomena. High-temperature creep and tensile data were obtained for predicting vessel and penetration structural response.

  13. SCC, bacteria top items in pipe service failures

    Microsoft Academic Search

    J. F. Kiefner; R. J. Eiber

    1987-01-01

    This conclusion of a three-part series updating causes of pipeline failures addresses failures due to stress-corrosion cracking (SCC), mechanical damage, and anaerobic bacterial corrosion. These causes, along with hydrogen effects comprise a shift in pipe service problems evident in failures reported since 1979. This shift was identified in a major study by Battelle Columbus Division laboratories. Several failures involving external

  14. Failure Assessment Robyn Lutz, Jet Propulsion Laboratory/Caltech and Iowa State University

    E-print Network

    Lutz, Robyn R.

    and characterization both of potential failure mechanisms in systems under development and of actual failure for failure assessment across the system lifecycle with an emphasis on the role of software. For each failure mechanisms in systems under development and of actual failure occurrences in operational systems

  15. Photovoltaic cell reliability research: investigation of accelerated stress factors and failure\\/degradation mechanisms in terrestrail solar cells. Fifth annual report

    Microsoft Academic Search

    Lathrop

    1984-01-01

    This annual report presents results of an ongoing research program into the reliability of terrestrial solar cells. The main focus of the research is to identify failure\\/degradation modes affecting solar cells and to relate these to basic physical, chemical, and metallurgical phenomena. The program is concerned with the reliability attributes of individual single crystalline, polycrystalline, and amorphous thin film silicon

  16. Amorphous silicon solar cell reliability research. Investigation of accelerated stress factors and failure\\/degradation mechanisms in terrestrial solar cells. Sixth annual report

    Microsoft Academic Search

    Lathrop

    1985-01-01

    This annual report presents the results of an ongoing research program into the reliability of terrestrial solar cells. The main focus of the research is to identify failure\\/degradation modes affecting solar cells through accelerated stress testing and to identify them to basic physical, chemical, and metallurgical phenomena. During the period covered in this report the program has concentrated on developing

  17. PNL-SA-22914 Presented at the 48th Meeting of the Mechanical Failures Prevention Group (MFPG 48) 19-21 April 1994 in Wakefield, MA

    E-print Network

    a real-time operational assessment, nor can it be readily modified to predict failures (perform and describe a prototype system that employs a real-time automated diagnostic paradigm. The prototype system maintenance practices is to automate diagnostics in a real- time system and to use prognostics to detect eq

  18. Respiratory muscle failure.

    PubMed

    Rochester, D F; Arora, N S

    1983-05-01

    The diseases which are commonly complicated by hypercapnic respiratory failure also compromise the respiratory muscles in several ways. Increased work of breathing, mechanical disadvantage, neuromuscular disease, impaired nutritional status, shock, hypoxemia, acidosis, and deficiency of potassium, magnesium, and inorganic phosphorus are the major non-neurologic factors which contribute to respiratory muscle fatigue and failure. Respiratory muscle fatigue has two components. High frequency fatigue occurs rapidly with intense contractile efforts but is usually not severe. It also recovers rapidly with rest. Low frequency fatigue develops more slowly but is severe and requires hours for recovery. Since the spontaneous rate of neural stimulation is predominantly in the low frequency range, this component of fatigue is of particular clinical importance. Fatigue of the inspiratory muscles leads to acute respiratory acidosis, but before carbon dioxide retention occurs, it can be recognized from characteristic symptoms and signs. These include dyspnea which responds to mechanical ventilation, rapid shallow breathing, and asynchronous movements of the chest and abdomen. Inspiratory muscle fatigue must be treated by putting these muscles to rest, by mechanically supporting ventilation. In addition, underlying metabolic nutritional and circulatory abnormalities must be corrected and infection treated. Aminophylline and isoproterenol can restore inspiratory muscle contractility, but controlled clinical trials remain to be done regarding their application in acute and chronic respiratory failure. Inspiratory muscle training improves strength and endurance in patients with obstructive lung disease, cystic fibrosis, and spinal cord injury, but does not always improve physical exercise performance. Again, more work is needed to develop the indications for inspiratory muscle training and to determine the optimum type and duration of the training regimen. PMID:6341727

  19. Review of failure modes in hot-water boilers

    SciTech Connect

    Herro, H.M.

    1999-07-01

    Hot-water boiler failures are commonly caused by oxygen corrosion, deposition, corrosion fatigue cracking and numerous other mechanisms. Each failure mode is discussed with regard to boiler location, boiler operation, boiler design, corrosion mechanisms, identification, elimination, special precautions and related problems. Almost all failures are preventable through careful chemical treatment and judicious boiler operation practices.

  20. Failure Analysis at the Kennedy Space Center

    NASA Technical Reports Server (NTRS)

    Salazar, Victoria L.; Wright, Clara

    2010-01-01

    History has shown that failures occur in every engineering endeavor, and what we learn from those failures contributes to the knowledge base to safely complete future missions. The necessity of failure analysis is at its apex at the end of one aged program (i.e. Shuttle) and at the beginning of a new and untested program (i.e. Constellation). The information that we gain through failure analysis corrects the deficiencies in the current vehicle to make the next generation of vehicles more efficient and safe. The Failure Analysis and Materials Evaluation section in the Materials Science Division at the Kennedy Space Center performs metallurgical, mechanical, electrical, and non-metallic failure analysis and accident investigations on both flight hardware and ground support equipment (GSE) for the Shuttle, International Space Station, Constellation, and Launch Services Programs. This presentation will explore a variety of failure case studies at KSC and the lessons learned that can be applied in future programs.

  1. Investigation of heat transfer in zirconium potassium perchlorate at low temperature: A study of the failure mechanism of the NASA standard initiator

    NASA Technical Reports Server (NTRS)

    Varghese, Philip L.

    1989-01-01

    The objective of this work was to study the reasons for the failure of pyrotechnic initiators at very low temperatures (10 to 100 K). A two-dimensional model of the NASA standard initiator was constructed to model heat transfer from the electrically heated stainless steel bridgewire to the zirconium potassium perchlorate explosive charge and the alumina charge cup. Temperature dependent properties were used in the model to simulate initiator performance over a wide range of initial temperatures (10 to 500 K). A search of the thermophysical property data base showed that pure alumina has a very high thermal conductivity at low temperatures. It had been assumed to act as a thermal insulator in all previous analyses. Rapid heat transfer from the bridgewire to the alumina at low initial temperatures was shown to cause failure of the initiators if the wire did not also make good contact with the zirconium potassium perchlorate charge. The mode is able to reproduce the results of the tests that had been conducted to investigate the cause for failure. It also provides an explanation for previously puzzling results and suggests simple design changes that will increase reliability at very low initial temperatures.

  2. 40 CFR 86.430-78 - Vehicle failure.

    Code of Federal Regulations, 2014 CFR

    2014-07-01

    ... CONTROL OF EMISSIONS FROM NEW AND IN-USE HIGHWAY VEHICLES AND ENGINES Emission Regulations for 1978 and Later New Motorcycles, General Provisions § 86.430-78 Vehicle failure. Any test vehicle which incurs major mechanical failure...

  3. Chemoreflex Function in Heart Failure

    Microsoft Academic Search

    Harold D. Schultz; Shu-Yu Sun

    2000-01-01

    Peripheral and central chemoreflexes are the dominant autonomic mechanisms regulating ventilatory patterns in response to changes in partial pressures of oxygen and carbon dioxide in arterial blood and exert powerful effects on neural circulatory control. Both reflex pathways are capable of eliciting increases in sympathetic nerve traffic and consequent increases in blood pressure. Chronic heart failure is accompanied by a

  4. Failure of the Intervertebral Disc

    Microsoft Academic Search

    Famke Kraaijeveld; Jacques M. Huyghe; Joris J. C. Remmers; Rene de Borst; Frank P. T. Baaijens

    2008-01-01

    In ionized porous media, such as shales, clays and biological tissues, localization or even crack forma- tion during swelling or shrinking can take place. This can lead to for example earthquakes, borehole instability and intervertebral disc (IVD) herniation. The goal is to study the effect of swelling on the failure mechanism. Currently, there is no numerical framework which includes osmotic

  5. A delamination mechanism for thermal barrier coatings subject to calcium–magnesium–alumino-silicate (CMAS) infiltration

    Microsoft Academic Search

    C. Mercer; S. Faulhaber; A. G. Evans; R. Darolia

    2005-01-01

    When a turbine airfoil attains temperatures that allow calcium–magnesium–alumino-silicate (CMAS) infiltration into the thermal barrier coating (TBC), a new mechanism of in-service spalling may be activated. The mechanism is associated with cold shock of the infiltrated layer during shut down. It has been identified by inspecting an airfoil removed from service. The identification has been based on observations of sub-surface

  6. Development of a ReaxFF reactive force field for ettringite and study of its mechanical failure modes from reactive dynamics simulations.

    PubMed

    Liu, Lianchi; Jaramillo-Botero, Andres; Goddard, William A; Sun, Huai

    2012-04-19

    Ettringite is a hexacalcium aluminate trisulfate hydrate mineral that forms during Portland cement hydration. Its presence plays an important role in controlling the setting rate of the highly reactive aluminate phases in cement paste and has also been associated with severe cracking in cured hardened cement. To understand how it forms and how its properties influence those of hardened cement and concrete, we have developed a first-principles-based ReaxFF reactive force field for Ca/Al/H/O/S. Here, we report on the development of this ReaxFF force field and on its validation and application using reactive molecular dynamics (RMD) simulations to characterize and understand the elastic, plastic, and failure response of ettringite at the atomic scale. The ReaxFF force field was validated by comparing the lattice parameters, pairwise distribution functions, and elastic constants of an ettringite crystal model obtained from RMD simulations with those from experiments. The predicted results are in close agreement with published experimental data. To characterize the atomistic failure modes of ettringite, we performed stress-strain simulations to find that Ca-O bonds are responsible for failure of the calcium sulfate and tricalcium aluminate (C3A) column in ettringite during uniaxial compression and tension and that hydrogen bond re-formation during compression induces an increase in plastic strain beyond the material's stress-strain proportionality limit. These results provide essential insight into understanding the mechanistic role of this mineral in cement and concrete degradation, and the ReaxFF potential developed in this work serves as a fundamental tool to further study the kinetics of hydration in cement and concrete. PMID:22413941

  7. FACTORS AFFECTING POWER TRANSFORMER FAILURE. A Bibliography

    Microsoft Academic Search

    1959-01-01

    After several costly transformer failures a bibliography was compiled ; with the hope that it would be helpful in seeking a solution to the problems. ; The bibliography is divided into four main sectionsi Transformers, Insulation ; Moisture, and Oil. Each section is subdivided for easy reference. Failures ; caused by mechanical defects or by lighting are not covered, since

  8. Analyses of Failure Mechanisms in Woven Graphite/Polyimide Composites with Medium and High Modulus Graphite Fibers Subjected to In-Plane Shear

    NASA Technical Reports Server (NTRS)

    Kumosa, M.; Armentrout, D.; Rupnowski, P.; Kumosa, L.; Shin, E.; Sutter, J. K.

    2003-01-01

    The application of the Iosipescu shear test for the room and high temperature failure analyses of the woven graphite/polyimide composites with the medium (T-650) and igh (M40J and M60J) modulus graphite fibers is discussed. The M40J/PMR-II-50 and M60J/PMR-II-50 composites were tested as supplied and after thermal conditioning. The effect of temperature and conditioning on the initiation of intralaminar damage and the shear strength of the composites was established.

  9. Bond Coat Engineering Influence on the Evolution of the Microstructure, Bond Strength, and Failure of TBCs Subjected to Thermal Cycling

    NASA Astrophysics Data System (ADS)

    Lima, R. S.; Nagy, D.; Marple, B. R.

    2015-01-01

    Different types of thermal spray systems, including HVOF (JP5000 and DJ2600-hybrid), APS (F4-MB and Axial III), and LPPS (Oerlikon Metco system) were employed to spray CoNiCrAlY bond coats (BCs) onto Inconel 625 substrates. The chemical composition of the BC powder was the same in all cases; however, the particle size distribution of the powder employed with each torch was that specifically recommended for the torch. For optimization purposes, these BCs were screened based on initial evaluations of roughness, porosity, residual stress, relative oxidation, and isothermal TGO growth. A single type of standard YSZ top coat was deposited via APS (F4MB) on all the optimized BCs. The TBCs were thermally cycled by employing a furnace cycle test (FCT) (1080 °C-1 h—followed by forced air cooling). Samples were submitted to 10, 100, 400, and 1400 cycles as well as being cycled to failure. The behavior of the microstructures, bond strength values (ASTM 633), and the TGO evolution of these TBCs, were investigated for the as-sprayed and thermally cycled samples. During FCT, the TBCs found to be both the best and poorest performing and had their BCs deposited via HVOF. The results showed that engineering low-oxidized BCs does not necessarily lead to an optimal TBC performance. Moreover, the bond strength values decrease significantly only when the TBC is about to fail (top coat spall off) and the as-sprayed bond strength values cannot be used as an indicator of TBC performance.

  10. On the oxidation of high-temperature alloys, and its role in failure of thermal barrier coatings

    E-print Network

    Loeffel, Kaspar Andreas

    2013-01-01

    Thermal barrier coating (TBC) systems are applied to superalloy turbine blades to provide thermal insulation and oxidation protection. A TBC system consists of (a) an outer oxide layer that imparts thermal insulation, and ...

  11. Steam generator tube failures

    SciTech Connect

    MacDonald, P.E.; Shah, V.N.; Ward, L.W.; Ellison, P.G.

    1996-04-01

    A review and summary of the available information on steam generator tubing failures and the impact of these failures on plant safety is presented. The following topics are covered: pressurized water reactor (PWR), Canadian deuterium uranium (CANDU) reactor, and Russian water moderated, water cooled energy reactor (VVER) steam generator degradation, PWR steam generator tube ruptures, the thermal-hydraulic response of a PWR plant with a faulted steam generator, the risk significance of steam generator tube rupture accidents, tubing inspection requirements and fitness-for-service criteria in various countries, and defect detection reliability and sizing accuracy. A significant number of steam generator tubes are defective and are removed from service or repaired each year. This wide spread damage has been caused by many diverse degradation mechanisms, some of which are difficult to detect and predict. In addition, spontaneous tube ruptures have occurred at the rate of about one every 2 years over the last 20 years, and incipient tube ruptures (tube failures usually identified with leak detection monitors just before rupture) have been occurring at the rate of about one per year. These ruptures have caused complex plant transients which have not always been easy for the reactor operators to control. Our analysis shows that if more than 15 tubes rupture during a main steam line break, the system response could lead to core melting. Although spontaneous and induced steam generator tube ruptures are small contributors to the total core damage frequency calculated in probabilistic risk assessments, they are risk significant because the radionuclides are likely to bypass the reactor containment building. The frequency of steam generator tube ruptures can be significantly reduced through appropriate and timely inspections and repairs or removal from service.

  12. Review of recent results using computational fluid dynamics simulations in patients receiving mechanical assist devices for end-stage heart failure.

    PubMed

    Farag, Mina Berty; Karmonik, Christof; Rengier, Fabian; Loebe, Matthias; Karck, Matthias; von Tengg-Kobligk, Hendrik; Ruhparwar, Arjang; Partovi, Sasan

    2014-01-01

    Many end-stage heart failure patients are not eligible to undergo heart transplantation due to organ shortage, and even those under consideration for transplantation might suffer long waiting periods. A better understanding of the hemodynamic impact of left ventricular assist devices (LVAD) on the cardiovascular system is therefore of great interest. Computational fluid dynamics (CFD) simulations give the opportunity to study the hemodynamics in this patient population using clinical imaging data such as computed tomographic angiography. This article reviews a recent study series involving patients with pulsatile and constant-flow LVAD devices in which CFD simulations were used to qualitatively and quantitatively assess blood flow dynamics in the thoracic aorta, demonstrating its potential to enhance the information available from medical imaging. PMID:25574347

  13. Fiber-optics cable failure analysis

    Microsoft Academic Search

    H. A. Scarton; W. R. Spillers

    1984-01-01

    The work reported is motivated by the mechanical failure of optical fibers in fiber optic cables used in underground testing at the Nevada Test Site. Focus is on basic mechanical tests, simulation of in-situ cable behavior, and proof tests. Preliminary flexure, creep, and tension test results are given together with both mechanical and optical instrumentation. (LEW)

  14. Postbuckling failure of composite plates with holes

    NASA Technical Reports Server (NTRS)

    Lee, H. H.; Hyer, M. W.

    1992-01-01

    This paper summarizes a study focused on understanding the failure mechanisms present in a plate with a centrally located circular hole loaded inplane into the postbuckling range of deflections. The study was numerical and experimental in nature and had as a goal the a priori prediction of failure using existing failure data from several sources, together with a stress analysis. The maximum stress failure criterion was used to predict failure and both intra- and interlaminar stresses were considered. Four laminates were considered. The phenomenon of modal interaction, or the jumping from one deformed configuration to another, is discussed. With this jumping, the plate configuration may change from one half-wave in the loading direction to two half-waves in the loading direction. The study concludes that the failure in (+/-45/0/90)2s and (+/-45/2(2))2s laminates is due to fiber compression failure and is predictable. The failure load is, for the most part, independent of response configuration. The (+/-45/0/(6))s laminate fails due to interlaminar shear along the simple support, while the response and failure of the (+/-45)4s laminate is governed to a large degree by material nonlinearities and progressive failure.

  15. Understanding Cytokinesis Failure

    PubMed Central

    Normand, Guillaume; King, Randall W.

    2011-01-01

    Cytokinesis is the final step in cell division. The process begins during chromosome segregation, when the ingressing cleavage furrow begins to partition the cytoplasm between the nascent daughter cells. The process is not completed until much later, however, when the final cytoplasmic bridge connecting the two daughter cells is severed. Cytokinesis is a highly ordered process, requiring an intricate interplay between cytoskeletal, chromosomal, and cell cycle regulatory pathways. A surprisingly broad range of additional cellular processes are also important for cytokinesis, including protein and membrane trafficking, lipid metabolism, protein synthesis and signaling pathways. As a highly regulated, complex process, it is not surprising that cytokinesis can sometimes fail. Cytokinesis failure leads to both centrosome amplification and production of tetraploid cells, which may set the stage for the development of tumor cells. However, tetraploid cells are abundant components of some normal tissues including liver and heart, indicating that cytokinesis is physiologically regulated. In this chapter, we summarize our current understanding of the mechanisms of cytokinesis, emphasizing steps in the pathway that may be regulated or prone to failure. Our discussion emphasizes findings in vertebrate cells although we have attempted to highlight important contributions from other model systems. PMID:20687468

  16. Failure models for textile composites

    NASA Technical Reports Server (NTRS)

    Cox, Brian

    1995-01-01

    The goals of this investigation were to: (1) identify mechanisms of failure and determine how the architecture of reinforcing fibers in 3D woven composites controlled stiffness, strength, strain to failure, work of fracture, notch sensitivity, and fatigue life; and (2) to model composite stiffness, strength, and fatigue life. A total of 11 different angle and orthogonal interlock woven composites were examined. Composite properties depended on the weave architecture, the tow size, and the spatial distributions and strength of geometrical flaws. Simple models were developed for elastic properties, strength, and fatigue life. A more complicated stochastic model, called the 'Binary Model,' was developed for damage tolerance and ultimate failure. These 3D woven composites possessed an extraordinary combination of strength, damage tolerance, and notch insensitivity.

  17. Valve system incorporating single failure protection logic

    DOEpatents

    Ryan, Rodger (San Jose, CA); Timmerman, Walter J. H. (Saratoga, CA)

    1980-01-01

    A valve system incorporating single failure protective logic. The system consists of a valve combination or composite valve which allows actuation or de-actuation of a device such as a hydraulic cylinder or other mechanism, integral with or separate from the valve assembly, by means of three independent input signals combined in a function commonly known as two-out-of-three logic. Using the input signals as independent and redundant actuation/de-actuation signals, a single signal failure, or failure of the corresponding valve or valve set, will neither prevent the desired action, nor cause the undesired action of the mechanism.

  18. Role of seepage forces on hydraulic fracturing and failure patterns

    E-print Network

    Paris-Sud XI, Université de

    Role of seepage forces on hydraulic fracturing and failure patterns Alexander Rozhko Thesis September 2007 #12;ii Role of seepage forces on hydraulic fracturing and failure patterns Abstract. The mechanical role of seepage forces on hydraulic fracturing and failure patterns was studied both

  19. Initial failure of cylindrical ribbed shells of reinforced materials

    Microsoft Academic Search

    B. S. Reznikov

    1980-01-01

    1.The calculations for cylindrical shells presented for various conditions of fixing show that the magnitude of the initial failure load and the type of initial failure depend both on the structure of reinforcement of the plating and the character of strengthening, and on the mechanical characteristics of the materials of the reinforcement and the bonding agent.2.The initial failure load will

  20. Strong exploration of a cast iron pipe failure model

    Microsoft Academic Search

    M. Moglia; P. Davis; S. Burn

    2008-01-01

    A physical probabilistic failure model for buried cast iron pipes is described, which is based on the fracture mechanics of the pipe failure process. Such a model is useful in the asset management of buried pipelines. The model is then applied within a Monte-Carlo simulation framework after adding stochasticity to input variables. Historical failure rates are calculated based on a

  1. Condition-based maintenance for systems under dependent competing failures

    Microsoft Academic Search

    L. P. Chen; Z. S. Ye; B. Huang

    2011-01-01

    Failures of complex systems may be various types. Natural failure due to degradation is one main mechanism. Other factors such as traumatic failure caused by random shocks from external environment are also critical to systems' operation. This paper proposes a new model to study complex systems that experience both degradation and shocks which are dependent. System reliability is analyzed and

  2. Understanding Protective Overcoat Damages: Failure Analysis to the Next Level

    Microsoft Academic Search

    F. V. Abitan; R. C. Angeles; M. G. Fabia; R. C. Flores; C. B. Gabunas

    2006-01-01

    Failure analysis (FA) is key in root cause identification for any problem solving journey. Diagnosis given provides insights on mechanisms by which failures occur. This helps in determining factors that lead to the failure and consequently the root cause, thus easier to provide corrective actions. In mid June 2004, a sudden increase in test fall-outs was encountered. Several devices from

  3. Preventing Spacecraft Failures Due to Tribological Problems

    NASA Technical Reports Server (NTRS)

    Fusaro, Robert L.

    2001-01-01

    Many mechanical failures that occur on spacecraft are caused by tribological problems. This publication presents a study that was conducted by the author on various preventatives, analyses, controls and tests (PACTs) that could be used to prevent spacecraft mechanical system failure. A matrix is presented in the paper that plots tribology failure modes versus various PACTs that should be performed before a spacecraft is launched in order to insure success. A strawman matrix was constructed by the author and then was sent out to industry and government spacecraft designers, scientists and builders of spacecraft for their input. The final matrix is the result of their input. In addition to the matrix, this publication describes the various PACTs that can be performed and some fundamental knowledge on the correct usage of lubricants for spacecraft applications. Even though the work was done specifically to prevent spacecraft failures the basic methodology can be applied to other mechanical system areas.

  4. P2X4 receptor–eNOS signaling pathway in cardiac myocytes as a novel protective mechanism in heart failure

    PubMed Central

    Yang, Ronghua; Beqiri, Dardan; Shen, Jian-Bing; Redden, John M.; Dodge-Kafka, Kimberly; Jacobson, Kenneth A.; Liang, Bruce T.

    2014-01-01

    We have demonstrated using immunoprecipitation and immunostaining a novel physical association of the P2X4 receptor (P2X4R), a ligand-gated ion channel, with the cardioprotective, calcium-dependent enzyme endothelial nitric oxide synthase (eNOS). Treatment of murine ventricular myocytes with the P2XR agonist 2-methylthioATP (2-meSATP) to induce a current (mainly Na+) increased the formation of nitric oxide (NO), as measured using a fluorescent probe. Possible candidates for downstream effectors mediating eNOS activity include cyclic GMP and PKG or cellular protein nitrosylation. A cardiac-specific P2X4R overexpressing mouse line was protected from heart failure (HF) with improved cardiac function and survival in post-infarct, pressure overload, and calsequestrin (CSQ) overexpression models of HF. Although the role of the P2X4R in other tissues such as the endothelium and monocytes awaits characterization in tissue-specific KO, cardiac-specific activation of eNOS may be more cardioprotective than an increased activity of global systemic eNOS. The intra-myocyte formation of NO may be more advantageous over NO derived externally from a donor. A small molecule drug stimulating this sarcolemmal pathway or gene therapy-mediated overexpression of the P2X4R in cardiac myocytes may represent a new therapy for both ischemic and pressure overloaded HF. PMID:25750695

  5. Candida albicans osteomyelitis of the zygomatic bone. A distinctive case with a possible peculiar mechanism of infection and therapeutic failure with fluconazole

    Microsoft Academic Search

    J. A. Arranz-Caso; V. M. Lopez-Pizarro; P. Gomez-Herruz; J. García-Altozano; J. Martinez-Martinez

    1996-01-01

    This report describes a distinctive case of zygomatic candidiasic osteomyelitis in a diabetic patient with oral candidiasis and malar ulceration secondary to topic 5-fluoroacil toxicity that eventually exposed part of the underlying bone. The mechanism of infection may have been self-inoculation of spores from muguet plaques on the oral mucosa to the exposed bone tissue by hand contact. Such a

  6. In Support of Failure

    ERIC Educational Resources Information Center

    Carr, Allison

    2013-01-01

    In this essay, I propose a concerted effort to begin devising a theory and pedagogy of failure. I review the discourse of failure in Western culture as well as in composition pedagogy, ultimately suggesting that failure is not simply a judgement or indication of rank but is a relational, affect-bearing concept with tremendous relevance to…

  7. The ? accrual failure detector

    Microsoft Academic Search

    Naohiro Hayashibara; X. Defago; R. Yared; T. Katayama

    2004-01-01

    The detection of failures is a fundamental issue for fault-tolerance in distributed systems. Recently, many people have come to realize that failure detection ought to be provided as some form of generic service, similar to IP address lookup or time synchronization. However, this has not been successful so far; one of the reasons being the fact that classical failure detectors

  8. Pipe failure prediction

    Microsoft Academic Search

    Chun hua Tian; Jing Xiao; Jin Huang; Felipe Albertao

    2011-01-01

    Preventa tive pipe maintenance is a key activity in pipe asset management. Central to such activity is a precise pipe failure (burstJIeakage) prediction. Here a statistical pipe failure prediction approach is proposed based on the massive data including pipe physical property, environmental factor, operational condition, historical failure records, and etc. Considering the biased training cases, survival analysis model is adopted

  9. Failures in military aircraft

    Microsoft Academic Search

    Graham Clark

    2005-01-01

    The severe operating conditions for components in military aircraft lead to a wide range of failure modes and introduce many factors which can influence those failures. As a result, the accident investigator or failure analyst may need to explore issues more widely than might be the case with systems operating in more benign or controlled environments. Complicating factors are the

  10. A signature analysis method for IC failure analysis

    SciTech Connect

    Henderson, C.L.; Soden, J.M.

    1996-10-01

    A new method of signature analysis is presented and explained. This method of signature analysis can be based on either experiential knowledge of failure analysis, observed data, or a combination of both. The method can also be used on low numbers of failures or even single failures. It uses the Dempster-Shafer theory to calculate failure mechanism confidence. The model is developed in the paper and an example is given for its use. 9 refs., 5 figs., 9 tabs.

  11. Failure Modes and Influence of the Quasi-static Deformation Rate on the Mechanical Behavior of Sandwich Panels with Aluminum Foam Cores

    Microsoft Academic Search

    Isabel Duarte; F. Teixeira-Dias; Ana Graça; António J. M. Ferreira

    2010-01-01

    The main purpose of this work is to study the bending behavior and deformation mechanisms of sandwich panels with AlSi7-alloy foam cores obtained by the powder metallurgy method. For this purpose, quasi-static three-point bending tests were performed on samples of AlSi7-alloy foam sandwich panels at different cross-head displacement rates: 1, 10, 20, 40 and 80 [mm\\/min]. Load-deflection values were registered

  12. The effect of time step, thermostat, and strain rate on ReaxFF simulations of mechanical failure in diamond, graphene, and carbon nanotube.

    PubMed

    Jensen, Benjamin D; Wise, Kristopher E; Odegard, Gregory M

    2015-08-01

    As the sophistication of reactive force fields for molecular modeling continues to increase, their use and applicability has also expanded, sometimes beyond the scope of their original development. Reax Force Field (ReaxFF), for example, was originally developed to model chemical reactions, but is a promising candidate for modeling fracture because of its ability to treat covalent bond cleavage. Performing reliable simulations of a complex process like fracture, however, requires an understanding of the effects that various modeling parameters have on the behavior of the system. This work assesses the effects of time step size, thermostat algorithm and coupling coefficient, and strain rate on the fracture behavior of three carbon-based materials: graphene, diamond, and a carbon nanotube. It is determined that the simulated stress-strain behavior is relatively independent of the thermostat algorithm, so long as coupling coefficients are kept above a certain threshold. Likewise, the stress-strain response of the materials was also independent of the strain rate, if it is kept below a maximum strain rate. Finally, the mechanical properties of the materials predicted by the Chenoweth C/H/O parameterization for ReaxFF are compared with literature values. Some deficiencies in the Chenoweth C/H/O parameterization for predicting mechanical properties of carbon materials are observed. © 2015 Wiley Periodicals, Inc. PMID:26096628

  13. A bulge-induced dehydration failure mode of nanocomposite hydrogel

    NASA Astrophysics Data System (ADS)

    Tang, Jingda; Yu, Zejun; Sun, Youyi; Pei, Yongmao; Fang, Daining

    2013-10-01

    Since hydrogels are very soft and usually weak in swollen state, they pose unique challenges to traditional mechanical experiments. The mechanical property of nanocomposite poly(N-isopropylacrylamide) hydrogel was characterized by the bulge test in this investigation. A dehydration failure phenomenon of the hydrogel was found and the failure mechanism was presented. A criterion is proposed that when strain reaches the threshold, water molecules migrate out of the polymer networks and the dehydration failure occurs. The critical strain keeps constant for orifices with different diameters. This failure mode can be applied in the controllable release of drugs.

  14. Molecular Dynamics Simulations of Interface Failure

    Microsoft Academic Search

    Martina E. Bachlechner; Deng Cao; Robert H. Leonard; Eli T. Owens; Wm. Trevor Swan III; Samuel C. Ducatman

    2007-01-01

    The mechanical integrity of silicon\\/silicon nitride interfaces is of great importance in their applications in micro electronics and solar cells. Large-scale molecular dynamics simulations are an excellent tool to study mechanical and structural failure of interfaces subjected to externally applied stresses and strains. When pulling the system parallel to the interface, cracks in silicon nitride and slip and pit formation

  15. Development of a Comprehensive Oxide Scale Failure Diagram

    Microsoft Academic Search

    M. SchutzeP; P. F. Tortorelli; I. G. Wright

    2010-01-01

    This paper describes a new approach towards the development of a comprehensive oxide scale failure diagram (OSFD) that delineates\\u000a the mechanical limits of scales for the different types of failure mechanisms. While former diagrams of a similar type were\\u000a based on relating the critical strain to scale failure to oxide scale thickness, the new approach replaces scale thickness\\u000a with a

  16. Micromechanics-Based Progressive Failure Analysis of Composite Laminates Using Different Constituent Failure Theories

    NASA Technical Reports Server (NTRS)

    Moncada, Albert M.; Chattopadhyay, Aditi; Bednarcyk, Brett A.; Arnold, Steven M.

    2008-01-01

    Predicting failure in a composite can be done with ply level mechanisms and/or micro level mechanisms. This paper uses the Generalized Method of Cells and High-Fidelity Generalized Method of Cells micromechanics theories, coupled with classical lamination theory, as implemented within NASA's Micromechanics Analysis Code with Generalized Method of Cells. The code is able to implement different failure theories on the level of both the fiber and the matrix constituents within a laminate. A comparison is made among maximum stress, maximum strain, Tsai-Hill, and Tsai-Wu failure theories. To verify the failure theories the Worldwide Failure Exercise (WWFE) experiments have been used. The WWFE is a comprehensive study that covers a wide range of polymer matrix composite laminates. The numerical results indicate good correlation with the experimental results for most of the composite layups, but also point to the need for more accurate resin damage progression models.

  17. Right heart failure: toward a common language

    PubMed Central

    2013-01-01

    Abstract In this guideline, the International Right Heart Foundation Working Group moves a step forward to develop a common language to describe the development and defects that exemplify the common syndrome of right heart failure. We first propose fundamental definitions of the distinctive components of the right heart circulation and provide consensus on a universal definition of right heart failure. These definitions will form the foundation for describing a uniform nomenclature for right heart circulatory failure with a view to foster collaborative research initiatives and conjoint education in an effort to provide insight into mechanisms of disease unique to the right heart. PMID:25006413

  18. Atrial Fibrillation in Congestive Heart Failure

    PubMed Central

    Lubitz, Steven A.; Benjamin, Emelia J.; Ellinor, Patrick T.

    2010-01-01

    Synopsis Atrial fibrillation and congestive heart failure are morbid conditions that share common risk factors and frequently coexist. Each condition predisposes to the other, and the concomitant presence of the two identifies individuals at increased risk for mortality. Recent data have emerged which help elucidate the complex genetic and non-genetic pathophysiological mechanisms that contribute to the development of atrial fibrillation in individuals with congestive heart failure. Clinical trial results offer insights into the noninvasive prevention and management of these conditions, though the emergence of newer technologies, such as catheter ablation for atrial fibrillation, have yet to be studied extensively in patients with congestive heart failure. PMID:20347787

  19. TUCOP failure threshold test CO6R

    Microsoft Academic Search

    G. E. Culley; P. C. Ferrell; R. Herbert; W. J. Woods

    1984-01-01

    The C06R test was the sixth single-pin test in the collaborative US\\/UK PFR\\/TREAT transient testing program. It was designed to study the mechanism, time and location of cladding failure and first fuel escape in an intermediate channel transient undercooling - overpower accident (TUCOP). It complements the LO5² and LO7³ tests which studied post failure fuel dispersal in a similar hypothetical

  20. Overwhelming respiratory failure associated with Legionella pneumophila.

    PubMed

    Dahmash, N S; Gad-El-Rab, M O; Al-Hajjaj, M S

    1994-05-01

    Four patients were admitted to the medical intensive care unit at King Khalid University Hospital (KKUH) with overwhelming respiratory failure. Extensive investigations revealed serological evidence of Legionella infection. Three patients required intubation and mechanical ventilation. All patients received erythromycin; rifampin was added to two patients. Two patients survived and two patients died. We report, for the first time in Saudi Arabia, four cases of Legionella pneumophila with severe respiratory failure. PMID:17586893

  1. Chronic inflammatory demyelinating polyneuropathy and respiratory failure.

    PubMed

    Henderson, Robert D; Sandroni, Paola; Wijdicks, Eelco F M

    2005-10-01

    Neuromuscular respiratory failure is not considered to be a clinical feature of chronic inflammatory demyelinating polyneuropathy (CIDP). We present 4 patients with CIDP who required respiratory assistance and mechanical ventilation. Two patients needed emergent intubation and one patient lapsed in a stupor from hypercapnia. Respiratory failure in CIDP should be considered exceptional, but more formal studies in CIDP may be needed to assess its prevalence. PMID:15940387

  2. Mechanism of spallation in platinum aluminide\\/electron beam physical vapor-deposited thermal barrier coatings

    Microsoft Academic Search

    Maurice Gell; Krishnakumar Vaidyanathan; Brent Barber; Eric Jordan; Jiangtian Cheng

    1999-01-01

    The spallation failure of a commercial thermal barrier coating (TBC), consisting of a single-crystal RENE N5 superalloy, a\\u000a platinum aluminide (Pt-Al) bond coat, and an electron beam-deposited 7 wt pct yttria-stabilized zirconia ceramic layer (7YSZ),\\u000a was studied following cyclic furnace testing. In the uncycled state and prior to deposition of the ceramic, the Pt-Al bond-coat\\u000a surface contains a cellular network

  3. A vision for reducing boiler tube failures. Part 2

    Microsoft Academic Search

    Dooley

    1992-01-01

    All of the currently occurring boiler tube failure (BTF) mechanisms in fossil fuel power plant are understood, and permanent solutions are available for all failures except corrosion fatigue. However, the state-of-the-art understanding of BTF mechanisms, root causes, maintenance, NDE and cycle chemistry are not, by themselves, sufficient to reduce the enormous availability loss due to BTF. This paper reports that

  4. Validating IC early-failure simulation

    NASA Astrophysics Data System (ADS)

    Moosa, Mohamod S.; Poole, Kelvin F.; Grams, Michael L.

    1995-09-01

    Early failures are the dominant concern as integrated circuit technology matures into consistently producing systems of high reliability. These failures are attributed to the presence of randomly occurring defects in elementary objects (contacts, vias, metal runs, gate oxides, bonds etc.) that result in extrinsic rather than intrinsic (wearout-related) mortality. A model relating system failure to failure at the elementary objective level has been developed. Reliability is modeled as a function of circuit architecture, mask layout, material properties, life-test data, worst-case use-conditions and the processing environment. The effects of competing failure mechanisms and the presence of redundant sub-systems are accounted for. Hierarchy is exploited in the analysis, allowing large scale designs to be simulated. Experimental validation of the modeling of oxide leakage related failure, based on correlation between actual failures reported for a production integrated circuit and Monte Carlo simulations that incorporate wafer-level test results and process defect monitor data, is presented. The state of the art in IC reliability simulation is advanced in that a methodology that provides the capability to design-in reliability while accounting for early failures has been developed; applications include process qualification, design assessment and fabrication monitoring.

  5. Multimodal Management of Mechanical Neck Pain Using a Treatment Based Classification System

    PubMed Central

    Heintz, Megan M.; Hegedus, Eric J.

    2008-01-01

    The purpose of this case study was twofold: 1) to illustrate the use of a treatment-based classification (TBC) system to direct the early intervention of a patient with mechanical neck pain, and 2) to show the progression of this patient with multimodal-modal intervention. The patient exhibited axial neck pain with referral into her upper extremity. Her pain peripheralized with cervical range of motion and centralized with joint mobilization placing her primarily in the centralization category. Her poor posture and associated muscle weakness along with the chronicity of symptoms placed her secondarily into the exercise and conditioning group resulting in a multi-modal treatment as the patient progressed. Although the design of this case report prevents wide applicability, this study does illustrate the effective use of the TBC system for the cervical spine as captured by accepted outcomes measures. PMID:19771194

  6. Understanding the nano- and macromechanical behaviour, the failure and fatigue mechanisms of advanced and natural polymer fibres by Raman/IR microspectrometry

    NASA Astrophysics Data System (ADS)

    Colomban, Philippe

    2013-03-01

    The coupled mechanical and Raman/infrared (IR) analysis of the (nano)structure and texture of synthetic and natural polymer fibres (polyamides (PA66), polyethylene terephthalate (PET), polypropylene (PP), poly(paraphenylene benzobisoxazole) (PBO), keratin/hair, Bombyx mori, Gonometa rufobrunea/postica Antheraea/Tussah silkworms and Nephila Madagascarensis spider silks) is applied so as to differentiate between crystalline and amorphous macromolecules. Bonding is very similar in the two cases but a broader distribution of conformations is observed for the amorphous macromolecules. These conclusions are then used to discuss the modifications induced by the application of a tensile or compressive stress, including the effects of fatigue. Detailed attention is paid to water and the inter-chain coupling for which the importance of hydrogen bonding is reconsidered. The significant role of the ‘amorphous’ bonds/domains in the process of fracture/fatigue is shown. Invited talk at the 6th International Workshop on Advanced Materials Science and Nanotechnology IWAMSN2012, 30 October–2 November 2012, Ha Long, Vietnam.

  7. Heart failure and depression.

    PubMed

    Newhouse, Amy; Jiang, Wei

    2014-04-01

    Depression frequently accompanies heart failure and has been linked with increased morbidity and mortality. Patients with heart failure who have depression have more somatic symptoms, hospitalizations, increased financial burden, and poorer quality of life. Furthermore, depression has been shown to be an independent predictor of future cardiac events in patients with heart failure, regardless of disease severity, making it worthwhile to consider among other cardiac risk factors, such as diabetes and smoking. This article summarizes the trials assessing the treatment of depression in heart failure and provides an algorithm for approaching these patients. PMID:24656106

  8. Failure analysis of woven kevlar fiber reinforced epoxy composites pinned joints

    Microsoft Academic Search

    Bülent Murat ?çten; Ramazan Karakuzu; M. Evren Toygar

    2006-01-01

    An investigation was performed to determine the failure mode and the failure load of mechanically fastened joints in woven kevlar epoxy composite plates. Two-dimensional finite element code is developed to predict damage initiation, progression and strength of joints. Hashin, Hoffman and Maximum Stress criteria were used in this failure analysis. Experiments were performed to find the failure load and to

  9. Optimal implementation of the weakest failure detector for solving consensus (brief announcement)

    Microsoft Academic Search

    Mikel Larrea; Antonio Fernández; Sergio Arévalo

    2000-01-01

    Unreliable failure detectors were introduced by Chandra and Toueg [2] as a mechanism that provides (possibly incorrect) information about process failures. They showed how unreliable failure detectors can be used to solve the Consensus problem in asynchronous systems. They also showed in [1] that one of the classes of failure detectors they defined, namely Eventually Strong (⋄S), is the weakest

  10. Brief Announcement: Optimal Implementation of the Weakest Failure Detector for Solving Consensus

    Microsoft Academic Search

    Mikel Larrea; Antonio Fernandez; Sergio Ardvalo

    Unreliable failure detectors were introduced by Chandra and Toueg (2) as a mechanism that provides (possibly incorrect) information about process failures. They showed how un- reliable failure detectors can be used to solve the Consen- sus problem in asynchronous systems. They also showed in (1) that one of the classes of failure detectors they de- fined, namely Eventually Strong (OS),

  11. ?-cell Failure as a Complication of Diabetes

    PubMed Central

    Chang-Chen, KJ; Mullur, R; Bernal-Mizrachi, E

    2015-01-01

    Type 2 diabetes mellitus is a complex disease characterized by ?-cell failure in the setting of insulin resistance. In early stages of the disease, pancreatic ?-cells adapt to insulin resistance by increasing mass and function. As nutrient excess persists, hyperglycemia and elevated free fatty acids negatively impact ?-cell function. This happens by numerous mechanisms, including the generation of reactive oxygen species, alterations in metabolic pathways, increases in intracellular calcium and the activation of endoplasmic reticulum stress. These processes adversely affect ?-cells by impairing insulin secretion, decreasing insulin gene expression and ultimately causing apoptosis. In this review, we will first discuss the regulation of ?-cell mass during normal conditions. Then, we will discuss the mechanisms of ?-cell failure, including glucotoxicity, lipotoxicity and endoplasmic reticulum stress. Further research into mechanisms will reveal the key modulators of ?-cell failure and thus identify possible novel therapeutic targets. PMID:18777097

  12. Learning from Failures: Archiving and Designing with Failure and Risk

    Microsoft Academic Search

    Michael Van Wie; Matt Bohm; Francesca Barrientos; Irem Tumer; Robert Stone

    The main goal of this work is to illustrate how past failures can be used for understanding failures, risks, and the processes used to elicit failures and risks during design. Through an examination of past failure data as well as observational studies of designers, this work shows how failures and risks can be archived and subsequently used during conceptual design.

  13. Steam generator tube failures

    Microsoft Academic Search

    P. E. MacDonald; V. N. Shah; L. W. Ward; P. G. Ellison

    1996-01-01

    A review and summary of the available information on steam generator tubing failures and the impact of these failures on plant safety is presented. The following topics are covered: pressurized water reactor (PWR), Canadian deuterium uranium (CANDU) reactor, and Russian water moderated, water cooled energy reactor (VVER) steam generator degradation, PWR steam generator tube ruptures, the thermal-hydraulic response of a

  14. Seawater refrigerating system failure

    Microsoft Academic Search

    S. Simison; F. Gomez; A. Steckinger; S. R. de Sanchez

    1995-01-01

    The cause of failures of copper-nickel pipes in the seawater refrigerating systems of two ships was analyzed. Failure is attributed to poor design of the weldments aggravated by seawater contamination. Welds placed too close to each other promoted sensitization of the material. The alloy had been heated to the precipitation range of an iron-rich second phase, and a pronounced root

  15. Reported tailings dam failures

    Microsoft Academic Search

    M. Rico; G. Benito; A. R. Salgueiro; A. D ´ õez-Herrero; H. G. Pereira

    2008-01-01

    A detailed search and re-evaluation of the known historical cases of tailings dam failure was carried out. A corpus of 147 cases of worldwide tailings dam disasters, from which 26 located in Europe, was compiled in a database. This contains six sections, including dam location, its physical and constructive characteristics, actual and putative failure cause, sludge hydrodynamics, socio-economical consequences and

  16. Workshop on systems failures

    Microsoft Academic Search

    John Donaldson; John Jenkins

    2001-01-01

    Systems failures cause havoc everywhere. Failures may be total, partial or temporary; and examination of the subject has to consider: implemented systems, systems being enhanced and totally new projects. When failing situations arise, the aftermath is highly complicated because there are so many possible contributing factors. For many years, students of Computer Science and Software Engineering - and indeed software

  17. A combined experimental and finite element study to predict the failure mechanisms in SiC coated carbon/carbon composites at room and elevated temperatures under flexural loading

    NASA Technical Reports Server (NTRS)

    Mahfuz, Hassan; Das, Partha S.; Xue, Dongwei; Krishnagopalan, Jaya; Jeelani, Shaik

    1993-01-01

    Response of quasi-isotropic laminates of SiC coated Carbon/Carbon (C/C) composites have been investigated under flexural loading at various temperatures. Variation of load-deflection behavior with temperatures are studied. Increase in flexural strength and stiffness are observed with the rise in temperature. Extensive analyses through Optical Microscope (OM) and Non-Destructive Evaluation (NDE) have been performed to understand the failure mechanisms. Damage zone is found only within the neighborhood of the loading plane. Isoparametric layered shell elements developed on the basis of the first order shear deformation theory have been used to model the thin laminates of C/C under flexural loading. Large deformation behavior has been considered in the finite element analysis to account for the non-linearities encountered during the actual test. Data generated using finite element analysis are presented to corroborate the experimental findings, and a comparison in respect of displacement and stress-strain behavior are given to check the accuracy of the finite element analysis. Reasonable correlation between the experimental and finite element results have been established.

  18. [Etiology and pathogenesis of acute respiratory failure].

    PubMed

    Ziliene, Violeta; Kondrotas, Anatolijus Juozas; Kevelaitis, Egidijus

    2004-01-01

    The aim of this study was to determine factors influencing acute respiratory failure and pathogenesis according to literature and clinical findings in critically ill patients. The term "respiratory failure" implies the inability to maintain either the normal delivery of oxygen to tissues and release or the normal removal of carbon dioxide from the tissues. There are many patients suffering from acute respiratory failure caused by nosocomial pneumonia, septic syndrome, aspiration, interstitial or alveolar lung edema, thromboembolism of a. pulmonalis, polytrauma and lung contusion, acute respiratory distress syndrome, long-term mechanical ventilation of the lungs, acute lung injury, status asthmaticus, rather massive transfusions of blood products, and lipid embolism in the intensive care unit. There are actually three processes involved: the transfer of oxygen across the alveolus, the transport to the tissues (by cardiac output), and the removal of carbon dioxide from blood into the alveolus with subsequent exhalation into the environment. Failure of any step in this process can lead to respiratory failure. Long-term hypoxia causes ischemic changes and dysfunction of brain, heart, kidney, lungs and can worsen the course of disease or cause higher mortality. It is important to determine the pathogenetic mechanisms of acute respiratory failure, estimate the main parameters and their interrelations and prescribe proper treatment. PMID:15064552

  19. Modelling early failures in Space Station Freedom

    NASA Technical Reports Server (NTRS)

    Navard, Sharon E.

    1993-01-01

    A major problem encountered in planning for Space Station Freedom is the amount of maintenance that will be required. To predict the failure rates of components and systems aboard Space Station Freedom, the logical approach is to use data obtained from previously flown spacecraft. In order to determine the mechanisms that are driving the failures, models can be proposed, and then checked to see if they adequately fit the observed failure data obtained from a large variety of satellites. For this particular study, failure data and truncation times were available for satellites launched between 1976 and 1984; no data past 1984 was available. The study was limited to electrical subsystems and assemblies, which were studied to determine if they followed a model resulting from a mixture of exponential distributions.

  20. Heart failure epidemiology: European perspective.

    PubMed

    Guha, K; McDonagh, T

    2013-05-01

    Heart failure poses an increasing problem for global healthcare systems. The epidemiological data which has been accrued over the last thirty years has predominantly been accumulated from experience within North America and Europe. Initial large cohort, prospective longitudinal studies produced the first publications; however latterly the focus has shifted onto epidemiological data governing hospitalisation and mortality. The emphasis behind this shift has been the resource implications with regards to repetitive, costly and prolonged hospitalisation. The European experience in heart failure, though similar to North America has recently demonstrated differences in hospitalisation which may underlie the differences between healthcare system configuration. Heart failure however remains an increasing global problem and the endpoint of a variety of cardiovascular diseases. Allied with the fact of increasingly elderly populations and prior data demonstrating a steep rise in prevalent cases within more elderly populations, it is likely that the increasing burden of disease will continue to pose challenges for modern healthcare. Despite the predicted increase in the number of patients affected by heart failure, over the last thirty years, a clear management algorithm has evolved for the use of pharmacotherapies (neuro-hormonal antagonists), device based therapies (Implantable Cardioverting Defibrillator (ICD) and Cardiac Resynchronisation Therapy (CRT)) and mechanical therapies including left ventricular assist devices and cardiac transplantation. Though the management of such patients has been clearly delineated in national and international guidelines, the underuse of all available and appropriate therapies remains a significant problem. When comparing various epidemiological studies from different settings and timepoints, it should be remembered that rates of prevalence and incidence may vary depending upon the definition used, methods of accumulating information (with the possibility of bias) and the chosen cut point of defining left ventricular systolic dysfunction (LVSD). PMID:23597298

  1. Ejection Fraction Heart Failure Measurement

    MedlinePLUS

    ... HF with preserved ejection fraction. Preserved ejection fraction (HFpEF) – also referred to as diastolic heart failure. The ... fraction reading and still have heart failure (called HFpEF or heart failure with preserved ejection fraction). If ...

  2. New diagnostic and therapeutic possibilities for diastolic heart failure

    PubMed Central

    Jeong, Euy-Myoung; Dudley, Samuel C.

    2014-01-01

    Despite the fact that up to half of all heart failure occurs in patients without evidence of systolic cardiac dysfunction, there are no universally accepted diagnostic markers and no approved therapies for heart failure with preserved ejection fraction (HFpEF). HFpEF, otherwise known as diastolic heart failure, has nearly the same grim prognosis as systolic heart failure, and diastolic heart failure is increasing in incidence and prevalence. Major trials have shown that many of the treatments that are salutary in systolic heart failure have no beneficial effects in diastolic heart failure, suggesting different underlying mechanisms for these two disorders. Even criteria for diagnosis of HFpEF are still debated, and there is still no gold standard marker to detect diastolic dysfunction. Here, we will review some promising new insights into the pathogenesis of diastolic dysfunction that may lead to new diagnostic and therapeutic tools. PMID:24494212

  3. Failure mechanism of recycled aggregate concrete

    Microsoft Academic Search

    M. Casuccio; M. C. Torrijos; G. Giaccio; R. Zerbino

    2008-01-01

    The use of recycled aggregate concrete (RAC) acquires particular interest in civil construction regarding sustainable development. Recycled aggregates usually present greater porosity and absorption, and lower density and strength than natural aggregates. Microstructural studies on RAC indicate differences in the characteristics of the interfacial transition zones between the cement paste and the aggregates. At the same time most experiences verify

  4. Modeling Different Failure Mechanisms in Metals

    E-print Network

    Zhang, Liang

    2012-02-14

    non-linear strain hardening/softening behavior and to obey the Hill-type Drucker-Prager yield criterion along with a non associated flow rule. The constitutive relations and the conditions for bifurcation in bulk and sheet metals are derived...

  5. Modeling Different Failure Mechanisms in Metals 

    E-print Network

    Zhang, Liang

    2012-02-14

    more elaborate considerations into the model. Several authors [55, 57, 58, 60] found that the constitutive relations for the material can significantly affect the onset of bifurcation. Specifically, plastic anisotropy, plastic non-normality...

  6. Respiratory failure in elderly patients.

    PubMed

    Sevransky, Jonathan E; Haponik, Edward F

    2003-02-01

    Elderly individuals comprise an increasing proportion of the population and represent a progressively expanding number of patients admitted to the ICU. Because of underlying pulmonary disease, loss of muscle mass, and other comorbid conditions, older persons are at increased risk of developing respiratory failure. Recognition of this vulnerability and the adoption of proactive measures to prevent decompensation requiring intrusive support are major priorities together with clear delineation of patients' wishes regarding the extent of support desired should clinical deterioration occur. Further, the development of coordinated approaches to identify patients at risk for respiratory failure and strategies to prevent the need for intubation, such as the use of NIV in appropriate patients, are crucial. As soon as endotracheal intubation and mechanical ventilation are implemented strategies that facilitate the liberation of elderly patients from the ventilator are especially important. The emphasis on a team approach, which characterizes geriatric medicine, is essential in coordinating the skills of multiple health care professionals in this setting. Respiratory failure can neither be effectively diagnosed nor managed in isolation. Integration with all other aspects of care is essential. Patient vulnerability to nosocomial complications and the "cascade effect" of these problems such as the effects of medications and invasive supportive procedures all impact on respiratory care of elderly patients. For example, prolonged mechanical ventilation may be required long after resolution of the underlying cause of respiratory failure because of unrecognized and untreated delirium or residual effects of small doses of sedative and/or analgesic agents or other medications in elderly patients with altered drug metabolism. The deleterious impact of the foreign and sometimes threatening ICU environment and/or sleep deprivation on the patient's course are too often overlooked because the physician focuses management on physiologic measurements, mechanical ventilator settings, and other technologic nuances of care [40]. Review of the literature suggests that the development of respiratory failure in patients with certain disease processes such as COPD, IPF, and ARDS in elderly patients may lead to worsened outcome but it appears that the disease process itself, rather than the age of the patient, is the major determinant of outcome. Additional studies suggest that other comorbid factors may be more important than age. Only when comorbid processes are taken into account should decisions be made about the efficacy of instituting mechanical ventilation. In addition, because outcome prediction appears to be more accurate for groups of patients rather than for individual patients a well-structured therapeutic trial of instituting mechanical ventilation, even if comorbidities are present, may be indicated in certain patients if appropriately informed patients wish to pursue this course. This approach requires careful and realistic definition of potential outcomes, focus on optimizing treatment of the reversible components of the illness, and continuous communication with the patient and family. Although many clinicians share a nihilistic view regarding the potential usefulness of mechanical ventilation in elderly patients few data warrant this negative prognostication and more outcome studies are needed to delineate the optimum application of this element of supportive care. As with other interventions individualization of the decision must take into account the patient's premorbid status, concomitant conditions, the nature of the precipitating illness and its prospects for improvement, and most important, patient preferences. In this determination pursuing the course most consistent with the patient's wishes is essential and it must be appreciated that caregivers' impressions regarding the vigor of support desired by the patient are often erroneous. The SUPPORT investigators observed that clinicians often underestimated the degree of i

  7. Failure of underground concrete structures subjected to blast loadings

    NASA Technical Reports Server (NTRS)

    Ross, C. A.; Nash, P. T.; Griner, G. R.

    1979-01-01

    The response and failure of two edges of free reinforced concrete slabs subjected to intermediate blast loadings are examined. The failure of the reinforced concrete structures is defined as a condition where actual separation or fracture of the reinforcing elements has occurred. Approximate theoretical methods using stationary and moving plastic hinge mechanisms with linearly varying and time dependent loadings are developed. Equations developed to predict deflection and failure of reinforced concrete beams are presented and compared with the experimental results.

  8. Landslide dam failure and flood hydraulics. Part I: experimental investigation

    Microsoft Academic Search

    Zhixian Cao; Zhiyuan Yue; Gareth Pender

    Landslide dam failure can trigger catastrophic flooding in the downstream. However, field observation of such flooding is\\u000a rarely available, while laboratory experimental studies are sparse. The mechanism of landslide dam failure and the flood has\\u000a so far remained insufficiently understood. Here, we present an experimental investigation of landslide dam failure and the\\u000a flood. A total of 28 runs of experiments

  9. Inverter ratio failure detector

    NASA Technical Reports Server (NTRS)

    Wagner, A. P.; Ebersole, T. J.; Andrews, R. E. (inventors)

    1974-01-01

    A failure detector which detects the failure of a dc to ac inverter is disclosed. The inverter under failureless conditions is characterized by a known linear relationship of its input and output voltages and by a known linear relationship of its input and output currents. The detector includes circuitry which is responsive to the detector's input and output voltages and which provides a failure-indicating signal only when the monitored output voltage is less by a selected factor, than the expected output voltage for the monitored input voltage, based on the known voltages' relationship. Similarly, the detector includes circuitry which is responsive to the input and output currents and provides a failure-indicating signal only when the input current exceeds by a selected factor the expected input current for the monitored output current based on the known currents' relationship.

  10. Triac failure detector

    NASA Technical Reports Server (NTRS)

    Nola, F. J. (inventor)

    1983-01-01

    A failure detector is provided for detecting unidirectional failures in triacs, particularly as used in power factor controllers for induction motors. In a first embodiment, the triac voltage waveform is sensed and upon detection of an unbalanced signal, corresponding to failure of the triac in either the positive or negative direction, the triac is turned full on in both directions. In a second embodiment, a pair of pulsed signals are derived, the pulse durations of which are proportional to the phase difference between the load current and voltage for each half cycle, and the triac is turned full on responsive to a difference in pulse duration between the half cycle signals. An unidirectional open circuit detector is adapted to use a signal from either of the first and second embodiment to turn the triac off in response to an open circuit failure in either direction.

  11. Analyzing Program "Failure."

    ERIC Educational Resources Information Center

    Decker, Daniel J.

    1990-01-01

    An analysis of apparent program failure should determine whether the fault lies with the program model, implementation strategy, expectations, or evaluation methods. The evaluation should be planned before completing and carrying out the program design. (SK)

  12. Genesis Failure Investigation Report

    NASA Technical Reports Server (NTRS)

    Klein, John

    2004-01-01

    The-Genesis mission to collect solar-wind samples and return them to Earth for detailed analysis proceeded successfully for 3.5 years. During reentry on September 8, 2004, a failure in the entry, descent and landing sequence resulted in a crash landing of the Genesis sample return capsule. This document describes the findings of the avionics sub-team that supported the accident investigation of the JPL Failure Review Board.

  13. Compression failure of angle-ply laminates

    NASA Technical Reports Server (NTRS)

    Peel, Larry D.; Hyer, Michael W.; Shuart, Mark J.

    1991-01-01

    The present work deals with modes and mechanisms of failure in compression of angle-ply laminates. Experimental results were obtained from 42 angle-ply IM7/8551-7a specimens with a lay-up of ((plus or minus theta)/(plus or minus theta)) sub 6s where theta, the off-axis angle, ranged from 0 degrees to 90 degrees. The results showed four failure modes, these modes being a function of off-axis angle. Failure modes include fiber compression, inplane transverse tension, inplane shear, and inplane transverse compression. Excessive interlaminar shear strain was also considered as an important mode of failure. At low off-axis angles, experimentally observed values were considerably lower than published strengths. It was determined that laminate imperfections in the form of layer waviness could be a major factor in reducing compression strength. Previously developed linear buckling and geometrically nonlinear theories were used, with modifications and enhancements, to examine the influence of layer waviness on compression response. The wavy layer is described by a wave amplitude and a wave length. Linear elastic stress-strain response is assumed. The geometrically nonlinear theory, in conjunction with the maximum stress failure criterion, was used to predict compression failure and failure modes for the angle-ply laminates. A range of wave length and amplitudes were used. It was found that for 0 less than or equal to theta less than or equal to 15 degrees failure was most likely due to fiber compression. For 15 degrees less than theta less than or equal to 35 degrees, failure was most likely due to inplane transverse tension. For 35 degrees less than theta less than or equal to 70 degrees, failure was most likely due to inplane shear. For theta less than 70 degrees, failure was most likely due to inplane transverse compression. The fiber compression and transverse tension failure modes depended more heavily on wave length than on wave amplitude. Thus using a single parameter, such as a ratio of wave amplitude to wave length, to describe waviness in a laminate would be inaccurate. Throughout, results for AS4/3502, studied previously, are included for comparison. At low off-axis angles, the AS4/3502 material system was found to be less sensitive to layer waviness than IM7/8551-7a. Analytical predictions were also obtained for laminates with waviness in only some of the layers. For this type of waviness, laminate compression strength could also be considered a function of which layers in the laminate were wavy, and where those wavy layers were. Overall, the geometrically nonlinear model correlates well with experimental results.

  14. Ventilatory failure, ventilator support, and ventilator weaning.

    PubMed

    Tobin, Martin J; Laghi, Franco; Jubran, Amal

    2012-10-01

    The development of acute ventilatory failure represents an inability of the respiratory control system to maintain a level of respiratory motor output to cope with the metabolic demands of the body. The level of respiratory motor output is also the main determinant of the degree of respiratory distress experienced by such patients. As ventilatory failure progresses and patient distress increases, mechanical ventilation is instituted to help the respiratory muscles cope with the heightened workload. While a patient is connected to a ventilator, a physician's ability to align the rhythm of the machine with the rhythm of the patient's respiratory centers becomes the primary determinant of the level of rest accorded to the respiratory muscles. Problems of alignment are manifested as failure to trigger, double triggering, an inflationary gas-flow that fails to match inspiratory demands, and an inflation phase that persists after a patient's respiratory centers have switched to expiration. With recovery from disorders that precipitated the initial bout of acute ventilatory failure, attempts are made to discontinue the ventilator (weaning). About 20% of weaning attempts fail, ultimately, because the respiratory controller is unable to sustain ventilation and this failure is signaled by development of rapid shallow breathing. Substantial advances in the medical management of acute ventilatory failure that requires ventilator assistance are most likely to result from research yielding novel insights into the operation of the respiratory control system. PMID:23720268

  15. Cardiac troponin levels in heart failure.

    PubMed

    Potluri, Srinivasa; Ventura, Hector O; Mulumudi, Mahesh; Mehra, Mandeep R

    2004-01-01

    Congestive heart failure (CHF) is a major cardiovascular disorder that is increasing in incidence, prevalence, and lethality. The prognostic significance of cardiac troponin levels among symptomatic and asymptomatic CHF has attracted recent interest. We sought to assess the significance of cardiac troponins in heart failure. These cardiac markers are associated with decreased left ventricular ejection fraction and poor prognosis in patients with CHF and are related to the severity of heart failure. The mechanism for the release of these markers seems to be from ventricular remodeling, ongoing myocyte degeneration, the presence of coronary artery disease, and reduced coronary reserve. In addition to B-type (brain) natriuretic peptide (BNP), cardiac troponin levels measured in patients admitted to the hospital could help risk-stratify patients and manage them effectively. BNP and cardiac troponins are easy to measure and can be repeated many times to follow patients, without interobserver variability. Theoretically, BNP is a marker of heart failure status and cardiac troponin is a marker of myocyte injury. The first therapeutic goal could be relief of circulatory congestion and lowering of BNP. The second goal could be attenuation of myocyte injury and lowering of cardiac troponins. Measuring and monitoring the levels of both could be highly effective means to reliably stratify the patients into low-, intermediate-, and high-risk groups for cardiac events and progression of heart failure. Furthermore, large-scale trials are necessary to establish them as noninvasive monitoring markers of heart failure and effectiveness of treatment. PMID:14667259

  16. An evaluation of mixed-mode delamination failure criteria

    NASA Technical Reports Server (NTRS)

    Reeder, J. R.

    1992-01-01

    Many different failure criteria have been suggested for mixed mode delamination toughness, but few sets of mixed mode data exist that are consistent over the full mode I opening to mode II shear load range. The mixed mode bending (MMB) test was used to measure the delamination toughness of a brittle epoxy composite, a state of the art toughened epoxy composite, and a tough thermoplastic composite over the full mixed mode range. To gain insight into the different failure responses of the different materials, the delamination fracture surfaces were also examined. An evaluation of several failure criteria which have been reported in the literature was performed, and the range of responses modeled by each criterion was analyzed. A new bilinear failure criterion was analyzed. A new bilinear failure criterion was developed based on a change in the failure mechanism observed from the delamination surfaces. The different criteria were compared to the failure criterion. The failure response of the tough thermoplastic composite could be modeled well with the bilinear criterion but could also be modeled with the more simple linear failure criterion. Since the materials differed in their mixed mode failure response, mixed mode delamination testing will be needed to characterize a composite material. A critical evaluation is provided of the mixed mode failure criteria and should provide general guidance for selecting an appropriate criterion for other materials.

  17. Failures analysis of compressor blades of aeroengines due to service

    Microsoft Academic Search

    V. Infante; J. M. Silva; M. de Freitas; L. Reis

    2009-01-01

    In spite of the high levels of reliability of modern aeroengine components resulting from rigid standards and practices, failures of compressor and turbine blades during normal operational environments are common situations which compromise the flight safety. The investigation of real failures affecting these components allows gaining a deeper knowledge concerning the mechanisms of crack initiation and propagation which, in turn,

  18. Correlation of electrical reactor cable failure with materials degradation

    Microsoft Academic Search

    Stuetzer

    1986-01-01

    Complete circuit failure (shortout) of electrical cables typically used in nuclear power plant containments is investigated. Failure modes are correlated with the mechanical deterioration of the elastomeric cable materials. It is found that for normal reactor operation, electrical cables are reliable and safe over very long periods. During high temperature excursions, however, cables pulled across corners under high stress may

  19. ASME code ductile failure criteria for impulsively loaded pressure vessels

    Microsoft Academic Search

    Robert E. Nickell; T. A. Duffey; E. A. Rodriguez

    2003-01-01

    Ductile failure criteria suitable for application to impulsively loaded high pressure vessels that are designed to the rules of the ASME Code Section VI11 Division 3 are described and justified. The criteria are based upon prevention of load instability and the associated global failure mechanisms, and on protection against progressive distortion for multiple-use vessels. The criteria are demonstrated by the

  20. Failure analysis of a 300M steel pressure vessel

    Microsoft Academic Search

    M. L. A. Graça; C. Y. Hoo; O. M. M. Silva; N. J. Lourenço

    2009-01-01

    A failure analysis was made in a 300M steel pressure vessel which has failed during hydrotest. The rupture occurred suddenly at a pressure level lower than what has been expected for the proof pressure. According to the results of various examinations it was concluded that hydrogen assisted stress corrosion cracking was the mechanism responsible for the failure. The root causes