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1

FEM simulation of TBC failure in a model system  

NASA Astrophysics Data System (ADS)

In order to study the behavior of the complex failure mechanisms in thermal barrier coatings on turbine blades, a simplified model system is used to reduce the number of system parameters. The artificial system consists of a bond-coat material (fast creeping Fecralloy or slow creeping MA956) as the substrate with a Y2O3 partially stabilized plasma sprayed zircon oxide TBC on top and a TGO between the two layers. A 2-dimensional FEM simulation was developed to calculate the growth stress inside the simplified coating system. The simulation permits the study of failure mechanisms by identifying compression and tension areas which are established by the growth of the oxide layer. This provides an insight into the possible crack paths in the coating and it allows to draw conclusions for optimizing real thermal barrier coating systems.

Seiler, P.; Bäker, M.; Beck, T.; Schweda, M.; Rösier, J.

2010-07-01

2

Effect of bond coat creep and oxidation on TBC integrity  

NASA Technical Reports Server (NTRS)

The potential of thermal barrier coatings (TBCs) on high-pressure turbine (HPT) nozzles and blades is limited at present by the inability to quantitatively predict TBC life for these components. The goal is to isolate the major TBC failure mechanisms, which is part of the larger program aimed at developing TBC life prediction models. Based on the results of experiments to isolate TBC failure mechanisms, the effects of bond coat oxidation and bond coat creep on TBC integrity is discussed. In bond coat oxidation experiments, Rene prime 80 specimens coated with a NiCrAlY/ZrO2-8 percent Y2O3 TBC received isothermal pre-exposures at 2000 F in static argon, static air, or received no pre-exposure. The effects of oxidation due to the pre-exposures were determined by thermal cycle tests in both static air and static argon at 2000 F. To study the effect of bond coat creep on TBS behavior, four bond coats with different creep properties were evaluated by thermal cycle tests in air at 2000 F. The test results, the relative importance of these two failure mechanisms, and how their effects may be quantified will also be discussed.

Duderstadt, E. C.; Pilsner, B. H.

1985-01-01

3

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

NASA Technical Reports Server (NTRS)

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

Smialek, James L.

2002-01-01

4

Fatigue Testing of TBC on Structural Steel by Cyclic Bending  

NASA Astrophysics Data System (ADS)

For applications with variable loading, fatigue performance of coated parts is of utmost importance. In this study, fatigue performance of conventional structural steel coated with thermal barrier coating (TBC) was evaluated in cyclic bending mode by "SF-Test" device. Testing was carried out at each stage of the TBC preparation process, i.e., for as-received and grit-blasted substrates, as well as for samples with Ni-based bond-coat and complete TBC: bond-coat with YSZ-based top-coat. Comparison of results obtained for different loading amplitudes supplemented by fractographic analysis enabled identification of dominating failure mechanisms and demonstrated applicability of the high-frequency resonant bending test for evaluation of fatigue resistance alteration at each stage of the TBC deposition process.

Musalek, Radek; Kovarik, Ondrej; Medricky, Jan; Curry, Nicholas; Bjorklund, Stefan; Nylen, Per

2015-01-01

5

TBC experience in land based gas turbines  

NASA Technical Reports Server (NTRS)

Prior and on-going machine evaluations of TBC coatings for power generation applications are summarized. Rainbow testing of various TBC's on turbine nozzles, shrouds and buckets are described along with one test on combustor liners. GEPG has conducted over 15 machine tests with TBC coated turbine nozzles of various coatings. Rainbow test times generally range between 10,000 to 24,000 hours. TBC performance has been quite good and additional testing, including TBC's on shrouds and buckets is continuing. The results show that TBC's have the capability of surviving in power generation machines for the times required. The earlier rainbow tests which evaluated various top coat compositions resulted in confirmation of the superiority of YSZ and especially the 6-8 YSZ composition. On-going tests are more focused on TBC process and property variations. The prevalent failure modes seen thus far in the various rainbow tests are erosion, foreign object damage and buildup of deposits. Additional post test analysis is required to investigate bond coat oxidation and other time/temperature dependent changes to the system.

Nelson, W. A.; Orenstein, R. M.

1995-01-01

6

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

SciTech Connect

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.

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

7

FEM simulation of oxidation induced stresses with a coupled crack propagation in a TBC model system  

NASA Astrophysics Data System (ADS)

Plasma sprayed thermal barrier coating systems are used on top of highly stressed components, e.g. on gas turbine blades, to protect the underlying substrate from the high surrounding temperatures. A typical coating system consists of the bond-coat (BC), the thermal barrier coating (TBC), and the thermally grown oxide (TGO) between the BC and the TBC. This study examines the failure mechanisms which are caused by the diffusion of oxygen through the TBC and the resulting growth of the TGO. To study the behaviour of the complex failure mechanisms in thermal barrier coatings, a simplified model system is used to reduce the number of system parameters. The model system consists of a bond-coat material (fast creeping Fecralloy or slow creeping MA956) as the substrate with a Y2O3 partially stabilised plasma sprayed zircon oxide TBC on top and a TGO between the two layers. Alongside the experimental studies a FEM simulation was developed to calculate the stress distribution inside the simplified coating system [1]. The simulation permits the identification of compression and tension areas which are established by the growth of the oxide layer. Furthermore a 2-dimensional finite element model of crack propagation was developed in which the crack direction is calculated by using short trial cracks in different directions. The direction of the crack in the model system is defined as the crack direction with the maximum energy release rate [2,3]. The simulated stress distributions and the obtained crack path provide an insight into the possible failure mechanisms in the coating and allow to draw conclusions for optimising real thermal barrier coating systems. The simulated growth stresses of the TGO show that a slow creeping BC may reduce lifetime. This is caused by stress concentration and cracks under the TGO. A slow creeping BC on the other hand reduces the stresses in the TBC. The different failure mechanisms emphasise the existence of a lifetime optimum which depends on the creep properties of the used bond-coat material. Experimental results show a good agreement with the predicted failure mechanisms.

Seiler, P.; Bäker, M.; Rösier, J.

2010-06-01

8

TBC experience in land based gas turbines  

NASA Technical Reports Server (NTRS)

This paper summarizes prior and on-going machine evaluations of TBC coatings for power generation applications. Rainbow testing of TBC's on turbine nozzles, shrouds, and buckets are described along with a test on combustor liners. GEPG has conducted over 15 machine tests with TBC coated turbine nozzles of various coatings. TBC performance has been quite good and additional testing, including TBC's on shrouds and buckets, is continuing. Included is a brief comparison of TBC requirements for power generation and aircraft turbines.

Nelson, Warren A.; Orenstein, Robert M.

1995-01-01

9

The lustering of TBC-2  

SciTech Connect

Two test bed concentrators (TBCs) were designed to provide high-performance test beds for advanced solar receivers and converters. However, the second-surface silvered-glass mirror facets on the TBCs, 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.

Diver, R.B.; Jones, S.; Robb, S.; Mahoney, A.R.

1995-05-01

10

Mechanisms of heart failure in obesity.  

PubMed

Heart failure is a leading cause of morbidity and mortality and its prevalence continues to rise. Because obesity has been linked with heart failure, the increasing prevalence of obesity may presage further rise in heart failure in the future. Obesity-related factors are estimated to cause 11% of heart failure cases in men and 14% in women. Obesity may result in heart failure by inducing haemodynamic and myocardial changes that lead to cardiac dysfunction, or due to an increased predisposition to other heart failure risk factors. Direct cardiac lipotoxicity has been described where lipid accumulation in the heart results in cardiac dysfunction inexplicable of other heart failure risk factors. In this overview, we discussed various pathophysiological mechanisms that could lead to heart failure in obesity, including the molecular mechanisms underlying cardiac lipotoxicity. We defined the obesity paradox and enumerated various premises for the paradoxical associations observed in the relationship between obesity and heart failure. PMID:25434909

Ebong, Imo A; Goff, David C; Rodriguez, Carlos J; Chen, Haiying; Bertoni, Alain G

2014-01-01

11

Failure mechanism models for cyclic fatigue  

NASA Astrophysics Data System (ADS)

This tutorial illustrates design situations where mechanical fatigue under cyclic loading, of one or more components, can compromise system performance. In this failure mechanism, damage accumulates with each load cycle, thereby causing a physical wearout failure mechanism. Phenomenological continuum length-scale models, based on micromechanical considerations, are presented to predict the onset (or initiation) of fatigue cracking in ductile materials. Fatigue-crack propagation is modeled with continuum fracture-mechanics principles. The number of load cycles required to cause failure is predicted based on these models. Approaches for modeling creep-fatigue interactions are briefly discussed. Analytic physics-of-failure methods and examples are presented for designing against wearout failure due to cyclic fatigue. These models can be implemented in an engineering design environment. The associated stress analysis requires numerical finite-element techniques in many cases. The associated material property characterization techniques have matured since the 1950s and are specified in engineering handbooks.

Dasgupta, Abhijit

1993-12-01

12

Mechanisms of failure in nanoscale metallic glass.  

PubMed

The emergence of size-dependent mechanical strength in nanosized materials is now well-established, but no fundamental understanding of fracture toughness or flaw sensitivity in nanostructures exists. We report the fabrication and in situ fracture testing of ?70 nm diameter Ni-P metallic glass samples with a structural flaw. Failure occurs at the structural flaw in all cases, and the failure strength of flawed samples was reduced by 40% compared to unflawed samples. We explore deformation and failure mechanisms in a similar nanometallic glass via molecular dynamics simulations, which corroborate sensitivity to flaws and reveal that the structural flaw shifts the failure mechanism from shear banding to cavitation. We find that failure strength and deformation in amorphous nanosolids depend critically on the presence of flaws. PMID:25198652

Gu, X Wendy; Jafary-Zadeh, Mehdi; Chen, David Z; Wu, Zhaoxuan; Zhang, Yong-Wei; Srolovitz, David J; Greer, Julia R

2014-10-01

13

Sulfur and Moisture Effects on Alumina Scale and TBC Spallation  

NASA Technical Reports Server (NTRS)

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.

Smialek, James L.

2007-01-01

14

Enigmatic Moisture Effects on Al2O3 Scale and TBC Adhesion  

NASA Technical Reports Server (NTRS)

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.

Smialek, James L.

2008-01-01

15

Failure mechanisms and mechanisms-based life predictions for electron beam physical vapor deposition thermal barrier coatings  

NASA Astrophysics Data System (ADS)

This research is designed to define failure mechanisms and to develop and experimentally validate non-destructive life prediction methodologies for electron beam physical vapor deposition (EB-PVD) thermal barrier coatings (TBCs). It is shown that for the two TBCs of this study ((Ni,Pt)Al and NiCoCrAlY bond coated TBCs) different failure mechanisms are exhibited, and therefore, the selected life prediction methodologies are accordingly different. For the (Ni,Pt)Al bond coated TBC tested at three temperatures, progressive rumpling of the thermally grown oxide (TGO) and bond coat interface is responsible for the failure at a critical rumpling value. Rumpling is a single value function of TGO thickness, suggesting that TGO growth strains are critical to rumpling, and the TGO growth controls rumpling, which in turn controls spallation life. Associated with rumpling, the TGO stress, as measured by the Photoluminescence Piezospectroscopy (PLPS) technique, decreases linearly with thermal cycles. Longer life specimens exhibit shallower slopes. The relationships among rumpling rate, stress relaxation rate and spallation life are defined: as temperature increases, rumpling and stress relaxation rates increase, and spallation life decreases. The rumpling of the TGO provides a physical basis for use of TGO stress measurements as a non-destructive method for TBC damage initiation, progression and life prediction. Temperature-blind remaining life predictions were made successfully using regression and neural network methods based on only TGO stress measurements at three temperatures. The lowest root mean square error for the prediction using neural networks and regression methods was 6.6% and 14.7%, respectively. Bimodal luminescence spectra, obtained using PLPS, are shown to be related to TGO cracking. The degree of cracking increases initially as theta- transforms to alpha-Al2O3, then decreases as the cracks heal, and then increases again prior to spallation. Area stress maps, based on the bimodal luminescence and average fraction of bimodal spectra with cycles, show damage progression and have the potential for non-destructive prediction of spallation failure. For NiCoCrAlY bond coated TBCs, damage initiates at localized debonds at the TGO/bond coat interface due to an increasing out-of-plane tensile stress. The spallation of the coating is driven by the strain energy stored in the TGO. (Abstract shortened by UMI.)

Wen, Mei

16

Basic failure mechanisms in advanced composites  

NASA Technical Reports Server (NTRS)

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.

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

1972-01-01

17

Basic failure mechanisms in advanced composites  

NASA Technical Reports Server (NTRS)

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

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

1971-01-01

18

A Critical Review of Landslide Failure Mechanisms  

NASA Astrophysics Data System (ADS)

During the last ten years several comprehensive geotechnical studies have been completed on major historic landslides including Randa in Switzerland, Frank in Canada, Aknes in Norway, La Clapiere in France and Vaiont in Italy. In addition, numerous researchers have documented deep-seated gravitational deformations and a wide variety of large prehistoric rock slope failures. The information provided by these studies is evidence of the significant advances made in our ability to map, monitor and model landslides. Over the same period, the mining industry has developed large open pits with slope heights exceeding 1000 m that provide important analogues to high mountain slopes. In this paper we analyse data from the literature to illustrate the importance of brittle fracture, 3D controls, anisotropy, overburden stress, geomorphic processes, groundwater and temperature in major landslides and provide some indicators as to the research required to further understand the complexity of rock slope failure mechanisms. The nature of the landslide failure surface has received inadequate attention in the past, with failure surfaces typically considered in 2D and simulated as discrete, smooth and often planar features. Current work shows that failure surfaces are inherently three-dimensional and have much structural variability across the area of the landslide scarp, reflecting complex structural histories. Such anisotropy and variations may result in multiple events or distinct blocks that move at different rates. Just as most failure surfaces vary spatially, they may also change with depth and thus should more realistically be considered failure zones rather than discrete surfaces. The increasing recognition of the importance of step-path failures, internal dilation and brittle fracture are indicative of the complexity in slope failure surfaces. Related to the variation in failure surface characteristics is the importance of 3D rotational displacements and both the availability and orientation of lateral and rear release surfaces. Accompanying the large increase in the application of numerical models, more consideration needs to be given to both the 3D shape and thickness of major landslides in order to address such questions as: are major landslides symmetric or asymmetric, of limited thickness or deep seated, brittle or ductile?

Stead, D.; Wolter, A.; Clague, J. J.

2011-12-01

19

Compression failure mechanisms of composite structures  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

20

Failure Analysis and Mechanisms of Failure of Fibrous Composite Structures  

NASA Technical Reports Server (NTRS)

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

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

1983-01-01

21

NON-DESTRUCTIVE TBC SPALLATION DETECTION BY A MICRO-INDENTATION METHOD  

SciTech Connect

In this research, a load-based depth-sensing micro-indentation method for spallation detection and damage assessment of thermal barrier coating (TBC) materials is presented. A non-destructive multiple loading/partial unloading testing methodology was developed where in stiffness responses of TBC coupons subjected to various thermal cyclic loading conditions were analyzed to predict the spallation site and assess TBC degradation state. The measured stiffness responses at various thermal loading cycles were used to generate time-series color maps for correlation with accumulation of TBC residual stress states. The regions with higher stiffness responses can be linked to a rise in out-of-plane residual stress located near or at the yttria stabilized zirconia (YSZ)/thermally grown oxide (TGO) interface, which is ultimately responsible for initiating TBC spallation failure. A TBC thermal exposure testing plan was carried out where time-series cross-sectional microstructural analyses of damage accumulation and spallation failure associated with the evolution of bond coat/TGO/top coat composite (e.g. thickness, ratcheting, localized oxidations, etc.) of air plasma sprayed (APS) TBCs were evaluated and correlated to the measured stiffness responses at various thermal cycles. The results show that the load-based micro-indentation test methodology is capable of identifying the spallation site(s) before actual occurrence. This micro-indentation technique can be viewed as a viable non-destructive evaluation (NDE) technique for determining as-manufactured and process-exposed TBCs. This technique also shows promise for the development of a portable instrument for on-line, in-situ spallation detection/prediction of industrial-size TBC turbine components.

J. M. Tannenbaum; B.S.-J. Kang; M.A. Alvin

2010-06-18

22

Mechanics of failure of composite materials  

NASA Technical Reports Server (NTRS)

Composite materials are both inhomogeneous and anisotropic. Both of these characteristics affect the internal stress distributions since inhomogeneity involves variations in both strength and stiffness. The fracture mechanics of nonuniform materials are considered, taking into account the effect of nonuniformity on stress distributions near the crack tip, predicted yield zones in nonuniform and uniform materials, and the fracture of a center-notched unidirectional specimen. The mechanics of failure of laminated materials is discussed. It is found that the development of damage in a laminate with increasing load and, possibly, increasing numbers of cycles of loading is peculiar to the laminate in question, i.e., the material system, the stacking sequence, and the geometry. Approaches for monitoring damage development are also described.

Reifsnider, K. L.

1978-01-01

23

Effect of Residual Stresses and Prediction of Possible Failure Mechanisms on Thermal Barrier Coating System by Finite Element Method  

NASA Astrophysics Data System (ADS)

This work is focused on the effect of the residual stresses resulting from the coating process and thermal cycling on the failure mechanisms within the thermal barrier coating (TBC) system. To reach this objective, we studied the effect of the substrate preheating and cooling rate on the coating process conditions. A new thermomechanical finite element model (FEM) considering a nonhomogeneous temperature distribution has been developed. In the results, we observed a critical stress corresponding to a low substrate temperature and high cooling rate during spraying of the top-coat material. Moreover, the analysis of the stress distribution after service shows that more critical stresses are obtained in the case where residual stresses are taken into account.

Ranjbar-Far, M.; Absi, J.; Mariaux, G.; Shahidi, S.

2010-09-01

24

Mechanical failure of a lightweight polypropylene mesh.  

PubMed

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

Lintin, L A D; Kingsnorth, A N

2014-02-01

25

Moisture-Induced TBC Spallation on Turbine Blade Samples  

NASA Technical Reports Server (NTRS)

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.

Smialek, James

2011-01-01

26

Moisture-Induced TBC Spallation on Turbine Blade Samples  

NASA Technical Reports Server (NTRS)

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.

Smialek, James L.

2011-01-01

27

In Situ Observation of Creep and Fatigue Failure Behavior for Plasma-Sprayed Thermal Barrier Coating Systems  

NASA Astrophysics Data System (ADS)

In order to investigate crack initiation sites and the crack propagation behavior in connection with the microstructure of thermal barrier coating (TBC) systems under creep and fatigue loadings, the failure behavior was observed in situ for plasma-sprayed TBC systems by optical microscopy, as a first step for elucidating the thermo-mechanical failure mechanism. Two types of TBC systems with differing top-coat (TC) microstructures were prepared by changing the processing conditions. The mechanical failure behavior of TBC system was found to depend strongly on the loading conditions. Under static creep loading, many segmentation cracks in the TC widened with increasing creep strain in the substrate. However, the propagation of these cracks into the bond-coat (BC) and alloy substrate was prevented due to the stress relief induced by plastic flow in the BC layer at elevated temperatures. As a result, the TBC system exhibited typical creep rupture behavior with nucleation and coalescence of microcracks in the alloy substrate interior regardless of the TC microstructure. Under dynamic fatigue loading, on the other hand, many fatigue cracks initiated not only from the tips of segmentation cracks in the TC layer but also from the TC/BC interface. Furthermore, it was found that the fatigue cracks propagated into the BC and alloy substrate even at elevated temperatures above the ductile-brittle transition temperature of the BC; the fatigue failure behavior under dynamic fatigue loading was dependent on the TC microstructure and the properties of the TC/BC interface.

Takahashi, Satoru; Harada, Yoshio

28

A Micro-Indentation Method for Assessment of TBC Bond Coat Systems  

SciTech Connect

Under elevated temperatures, the presence of high thermal stresses along or within thermal barrier coatings (TBCs) can lead to the development of creep cavities and wedge cracks which can ultimately form microcracks and result in interfacial debonding in the TBC bond coat region. Defects detection on the subsurface TBC layers has shown some progress by using laser scattering and other non-destructive testing (NDT) methods. However, the difficulty of determining interfacial debonding and degradation assessment of the TBC remains a significant hurdle to overcome due to the TBC’s complex multi-layer structure, and frequently rough surface morphology. The TBC has high attenuation, high porosity, and many interfaces of different materials, which are the challenges that need to be overcome by the NDT techniques. Based on our recent research development of a Transparent Indenter Measurement (TIM) method, we have further developed a simplified micro-indentation technique for mechanical property degradation measurement and debonding/spallation detection of TBC bond coat in this research effort. NETL bond-coated coupons were subjected to cumulative rapid thermal cycling, and after every 100 high temperature thermal cycles, micro-indentation tests were conducted on bond-coat superalloy and single crystal coupons. Preliminary test results showed that the measured surface stiffness responses of the NETL bond coat decreased with exposure to continued thermal cycling. Currently these data are being correlated with microstructural analyses to address potential degradation and/or spalling of the applied NETL bond coat.

Feng, C.; Alvin, M.A.; Kang, B.S.

2007-09-01

29

Mechanisms of failure for shallow foundations under earthquake loading  

Microsoft Academic Search

It is widely known that the bearing capacity of a shallow foundation is reduced when the foundation is subjected to rocking moments and horizontal loads during an earthquake event. Analytical solutions generally require an assumption to be made of the kinematic failure mechanism in the soil, when the true failure mechanism is unknown. This paper discusses a series of experiments

J. A. Knappett; S. K. Haigh; S. P. G. Madabhushi

2006-01-01

30

Failure criterion for materials with spatially correlated mechanical properties  

NASA Astrophysics Data System (ADS)

The role of spatially correlated mechanical elements in the failure behavior of heterogeneous materials represented by fiber bundle models (FBMs) was evaluated systematically for different load redistribution rules. Increasing the range of spatial correlation for FBMs with local load sharing is marked by a transition from ductilelike failure characteristics into brittlelike failure. The study identified a global failure criterion based on macroscopic properties (external load and cumulative damage) that is independent of spatial correlation or load redistribution rules. This general metric could be applied to assess the mechanical stability of complex and heterogeneous systems and thus provide an important component for early warning of a class of geophysical ruptures.

Faillettaz, J.; Or, D.

2015-03-01

31

Failure and fatigue mechanisms in composite materials  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

32

Failure mechanism characterization of platinum alloy  

NASA Technical Reports Server (NTRS)

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

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

1986-01-01

33

Failure mechanisms in lithium-ion batteries  

NASA Astrophysics Data System (ADS)

Lithium-ion batteries have become one of the leading candidates for energy storage in electric and hybrid-electric vehicles due to their high energy and power densities. However, the life of this class of rechargeable cells is limited, and is usually considerably shorter than the requirement for an economically feasible alternative to the internal combustion engine. The goal of this research is to explore specific mechanisms for cell failure via mathematical modeling of phenomena that occur in a broad assortment of lithium-ion cells. The theoretical framework of the models presented here is general enough to be applicable to most lithium-ion cells and even electrochemical cells that fall outside the realm of lithium-ion technology, but the properties and parameters that are used are specific enough that quantitative predictions can be made. Specifically, models for passive-film growth at the electrode/electrolyte interface and for particle fracture are presented. In addition, we discuss a framework for describing and understanding various types of capacity fade. Finally, we optimize the design of a lithium-titanate based cell using an existing full-cell model and compare its performance to that of a graphite based cell. The passive-film model indicates that the extent of film growth and impedance rise in a cell should depend strongly upon the state of charge (SOC) at which a battery is stored. We further show that current efficiency increases with the rate at which a cell is charged, although the cycling range of the cell decreases as the current is raised due to the impedance of the film. The particle-fracture model elucidates the conditions under which both graphitic and lithium-manganese-oxide particles surpass their yield strength, at which point cracking is initiated and particle fragmentation may occur. Higher rates of charge and larger particle size generally lead to a higher likelihood of fracture, although this dependence is absent in materials that undergo a two-phase transition. Pressure diffusion and nonidealities embodied in solid-state diffusion and the kinetics of lithium insertion are included in the model, and are shown to have significant impact on the results. Variations in the thermodynamic factor with lithium content result in local SOCs at which the stress in the material is much higher than would be predicted for an ideal solution. The implications of these variations, including the possibility of selecting SOC windows for battery operation that minimize stress, are examined in detail. The high-rate performance of cells with lithium-titanate negative electrodes can be enhanced, relative to cells with graphitic negative electrodes, through the selection of active material of small particle size. The high potential of the lithium-titanate electrode prevents many of the undesirable side reactions that occur in graphitic electrodes, including passive-film formation and lithium deposition. We conclude that the lithium-titanate electrode is probably the more attractive candidate for hybrid-electric-vehicle and other high-power applications.

Christensen, John Francis

34

Software Tools for Lifetime Assessment of Thermal Barrier Coatings Part II — Bond Coat Aluminum Depletion Failure  

NASA Astrophysics Data System (ADS)

The use of thermal barrier coatings (TBCs) made from yttria stabilized zirconia (YSZ) on superalloy base materials has been a significant step to a new level of operational limits in high temperature applications. By the application of a TBC in conjunction with cooling of the component material the operating temperature can be raised and higher efficiencies are achieved. As a consequence of the raised temperature failure of a TBC leads to an increased oxidative attack of the underlying bond coat material and therefore needs to be avoided. The lifetime prediction of thermal barrier coatings is therefore of interest to ensure safe operation within the inspection intervals. Several mechanisms have been identified to play a critical role in the degradation of TBC systems. Here we discuss failure of TBC systems due to bond coat aluminum depletion. This type of chemical failure may occur when the bond coat material is critically depleted of aluminum and instead of a dense slow growing ?-alumina the formation of voluminous and fast growing spinels is promoted. Lifetime prediction for this failure mode requires a fundamental understanding of diffusion mechanisms and in particular the interaction of different diffusion rates in the bond coat and substrate material. Aim of this work was therefore to develop software tools that allow user friendly analysis of measured Al profiles for the assessment of diffusion rates and consequently for lifetime prediction.

Renusch, Daniel; Rudolphi, Mario; Schütze, Michael

35

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

SciTech Connect

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.

Scott X. Mao

2002-06-30

36

Failure analysis of an MVR (mechanical vapor recompressor) Impeller  

Microsoft Academic Search

This article describes the root cause failure analysis of a mechanical vapor recompressor (MVR) impeller used in a dairy processing plant. An impeller blade was thrown during commissioning after approximately 150h of service. Visual examination of the blade’s fracture surface indicated that the crack growth mechanism was fatigue and this was confirmed by scanning electron microscope (SEM) examinations. A detailed

Keith Alexander; Brian Donohue; Troy Feese; Gordon Vanderlinden; Milo Kral

2010-01-01

37

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

Microsoft Academic Search

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

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

38

Mechanics concepts for failure in ferroelectric ceramics  

NASA Astrophysics Data System (ADS)

The article reviews mechanics concepts suitable for analyzing defects (cracks, domain walls, etc.) in ferroelectric ceramics. Constitutive laws are summarized for dielectric, electrostrictive and piezoelectric ceramics. The formulation is based on an energy function of strain and induction, and a few experimental facts. Also summarized are the differential equations that govern stress and electric fields. Griffith's energy release rate is examined for a body containing a defect under applied force and voltage, followed by applications to multilayer capacitors, conducting cracks, impermeable cracks and domain bands. A generalized Irwin-Kies relation is presented, explaining the peculiar results that the energy release rates are negative for non-conducting cracks but positive for conducting cracks. Singular fields around impermeable and conducting cracks axe contrasted. The possibility of using the energy release rate to correlate breakdown resistance of a ceramic is considered.

Suo, Z.

39

Testing within the continuum of multiple lubrication and failure mechanisms  

SciTech Connect

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

Wedeven, L.D. [Wedeven Associates Inc., Edgement, PA (United States); Totten, G.E.; Bishop, R.J. Jr. [Union Carbide Corp., Tarrytown, NY (United States)

1997-12-31

40

Failure mechanisms of ventricular tissue due to deep penetration.  

PubMed

Lead perforation is a rare but serious complication of pacemaker implantations, and in the present study the associated tissue failure was investigated by means of in-vitro penetration of porcine and bovine ventricular tissue. Rectangular patches from the right ventricular free wall and the interventricular septum were separated, bi-axially stretched and immersed in physiological salt solution at 37( composite function)C before load displacement curves of in total 891 penetrations were recorded. To this end flat-bottomed cylindrical punches of different diameters were used, and following mechanical testing the penetration sites were histological analyzed using light and electron microscopes. Penetration pressure, i.e. penetration force divided by punch cross-sectional area decreased slightly from 2.27(SD 0.66) to 1.76(SD0.46)N/mm(2) for punches of 1.32 to 2.30 mm in diameter, respectively. Deep penetration formed cleavages aligned with the local fiber orientation of the tissue, and hence, a mode-I crack developed, where the crack faces were wedged open by the advancing punch. The performed study derived novel failure data from ventricular tissue due to deep penetration and uncovered associated failure mechanisms. This provides information to derive mechanical failure models, which are essential to enrich our current understanding of failure of soft biological tissues and to guide medical device development. PMID:19200998

Gasser, T Christian; Gudmundson, Peter; Dohr, Gottfried

2009-03-26

41

Methodology to Analyze Failure Mechanisms of Ohmic Contacts on MEMS Switches IRPS_ABroue_2009_final_NON corrumpu.doc Methodology to Analyze Failure Mechanisms of  

E-print Network

of micro-scale contact physics especially failure mechanisms due to the heating of the contact on MEMS switches. Keywords-electrical contacts; contact heating; failure mechanisms; switches-standing element and the increase of the electrical contact resistance (Rc). The mechanisms leading to failure

Paris-Sud XI, Université de

42

Reliability and failure mechanism of isotropically conductive adhesives joints  

Microsoft Academic Search

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

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

1995-01-01

43

Simulation of the failure mechanisms of quasi-brittle materials  

Microsoft Academic Search

One of the major technical interests for quasi-brittle materials is the failure mechanism under uniaxial or triaxial loading, or under some other standard tests such as beam bending specimen and compact specimen. Recent research has led to development of formal procedures for predicting damage behavior of quasi-brittle material using computational simulation in the tests mentioned above. These procedures have subsequently

M. L Wang; Z. L Chen

1999-01-01

44

Norepinephrine-related mechanism in hypertension accompanying renal failure  

Microsoft Academic Search

Norepinephrine-related mechanism in hypertension accompanying renal failure. Various blood pressure (BP)-regulating factors were assessed before and after 4 weeks of selective norepinephrine (NE) inhibition with the sympathetic neurone blocker, debrisoquine, in nine hypertensive, nine normotensive hemodialysis patients (HDP), and 11 normal subjects. On placebo, hypertensive HDP had an increased total blood volume (P < 0.05) and exchangeable sodium (P <

Dominique Schohn; Peter Weidmann; Henri Jahn; Carlo Beretta-Piccoli

1985-01-01

45

Mechanical and electrical failures and reliability of Micro Scanning Mirrors  

Microsoft Academic Search

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

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

2002-01-01

46

Failure Mechanisms for Ceramic Matrix Textile Composites at High Temperature  

SciTech Connect

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

Cox, Brian

1999-03-01

47

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

SciTech Connect

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.

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

1999-04-12

48

Effect of Increased Water Vapor Levels on TBC Lifetime  

SciTech Connect

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.

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

2011-01-01

49

Delayed mechanical failure of silver-interlayer diffusion bonds  

SciTech Connect

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

Kassner, M.E. (Oregon State Univ., Corvallis, OR (United States)); Rosen, R.S.; Henshall, G.A. (Lawrence Livermore National Lab., CA (United States). Physical Metallurgy and Joining Section)

1990-12-01

50

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

SciTech Connect

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.

Scott X. Mao

2002-01-31

51

Acoustic emission spectral analysis of fiber composite failure mechanisms  

NASA Technical Reports Server (NTRS)

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.

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

1978-01-01

52

[Immune mechanisms in pathogenesis of chronic heart failure].  

PubMed

In the review the new information about a participation of immune mechanisms in a pathogenesis of a chronic heart failure (CHF) is presented. Significance of a bacterial endotoxin, as inductor of activation of immune system at CHF, and factors of a system inflammation in a pathogenesis of the disease, breaking balance of matrix metalloproteinases and tissue inhibitors of metalloproteinases system, leading to change of structure of an extracellular matrix of a myocardium, are discussed. PMID:22708411

Egorova, E N; Kalinkin, M N; Mazur, E S

2012-01-01

53

Mechanisms of Carvedilol Action in Human Congestive Heart Failure  

Microsoft Academic Search

The precise mechanism by which b-adrenoceptor blockers exert their beneficial actions in patients with heart failure remains unclear. Several possibilities have been proposed, including heart rate reduction, b2-adrenoceptor- mediated modulation of catecholamine release, antagonism of the receptor-mediated toxic actions of norepinephrine on the myocardium, and favorable effects on myocardial energetics. In the present study we evaluated the effect of 3

David M. Kaye; Leonie Johnston; Gautam Vaddadi; Hanspeter Brunner-LaRocca; Garry L. Jennings; Murray D. Esler

2010-01-01

54

Emerging therapies for heart failure: renal mechanisms and effects  

Microsoft Academic Search

Improved understanding of the pathophysiology of salt and water homeostasis has provided a foundation for explaining the renal\\u000a mechanisms of emerging therapies for heart failure, as well as why renal function might potentially be improved or harmed.\\u000a These aspects are reviewed in this article for a number of newer therapies including adenosine, endothelin, and vasopressin\\u000a receptor antagonists, as well as

Amir KazoryEdward; Edward A. Ross

55

Failure mechanism of epoxy polymer: transition from ductile to brittle failure  

NASA Astrophysics Data System (ADS)

The failure processes of an epoxy polymer (Epicote 21506) were studied by using a high speed camera evolving over a range of strain rates from 0.0001s-1 to 668s-1. The front surface of the specimen was monitored by the high speed camera to capture the deformation and cracking processes. A split Hopkinson pressure bar (SHPB) was utilized to examine the dynamic response of the material, and the uniaxial compression test was applied for its quasi-static behavior. The microstructure of the specimen fracture surface after quasi-static and dynamic compression was also investigated by using a Scanning Electron Microscope (SEM) to look insight into the failure mechanism of the material. With the coupled analysis of stress-strain curves and captured images, the behaviors of the specimen under static and dynamic loading can be determined precisely with sufficient details. The specimen under static loading displayed ductile failure, while that under dynamic loading revealed different brittle damage behaviors.

Wu, Wei; Ma, Guowei

2010-03-01

56

Failure mechanism of epoxy polymer: transition from ductile to brittle failure  

NASA Astrophysics Data System (ADS)

The failure processes of an epoxy polymer (Epicote 21506) were studied by using a high speed camera evolving over a range of strain rates from 0.0001s-1 to 668s-1. The front surface of the specimen was monitored by the high speed camera to capture the deformation and cracking processes. A split Hopkinson pressure bar (SHPB) was utilized to examine the dynamic response of the material, and the uniaxial compression test was applied for its quasi-static behavior. The microstructure of the specimen fracture surface after quasi-static and dynamic compression was also investigated by using a Scanning Electron Microscope (SEM) to look insight into the failure mechanism of the material. With the coupled analysis of stress-strain curves and captured images, the behaviors of the specimen under static and dynamic loading can be determined precisely with sufficient details. The specimen under static loading displayed ductile failure, while that under dynamic loading revealed different brittle damage behaviors.

Wu, Wei; Ma, Guowei

2009-12-01

57

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

E-print Network

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 limit, failure mechanisms, friction stir welding 1. Introduction In the context of military tactical

Grujicic, Mica

58

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

E-print Network

A NEW FAILURE MECHANISM BY SCANNING ELECTRON MICROSCOPE INDUCED ELECTRICAL BREAKDOWN OF TUNGSTEN..................................................................15 2.1.3 Mechanics of CVD Tungsten 2.2.2 Tungsten Corrosion

Pearton, Stephen J.

59

Failure mechanisms of DC and capacitive RF MEMS switches  

NASA Astrophysics Data System (ADS)

Microelectromechanical systems (MEMS) radio frequency (RF) switches hold great promise in a myriad of commercial, aerospace, and military applications including cellular phones and phased array antennas. However, there is limited understanding of the factors determining the performance and reliability of these devices. Fundamental studies of hot-switched DC (gold versus gold) and capacitive (gold versus silicon nitride) MEMS RF switch contacts were conducted in a controlled air environment at MEMS-scale forces using a micro/nanoadhesion apparatus as a switch simulator. This paper reviews key experimental results from the switch simulator and how they relate to failure mechanisms of MEMS switches. For DC switch contacts, electric current had a profound effect on deformation mechanisms, adhesion, contact resistance (R), and reliability/durability. At low current (1-10 ?A), junction growth/force relaxation, slightly higher R, and switching induced adhesion growth were prominent. At high current (1-10 mA), asperity melting, slightly lower R, and shorting were present. Adhesion increased during cycling at low current and was linked to the creation of smooth contact surfaces, increased van der Waals interaction, and chemical bonding. Surface roughening by nanowire formation (which also caused shorting) prevented adhesion at high current. Aging of the contacts in air led to hydrocarbon adsorption and less adhesion. Studies of capacitive switches demonstrated that excessive adhesion was the primary failure mechanism and that both mechanical and electrical effects were contributing factors. The mechanical effect is adhesion growth with cycling due to surface smoothening, which allows increased van der Waals interaction and chemical bonding. The electrical effect on adhesion is due to electrostatic force associated with trapped parasitic charge in the dielectric, and was only observed after operating the switch at 40 V bias and above. The two effects are additive; however, the electrical effect was not present until the surfaces were worn smooth by cycling. Surface smoothening increases the electric field in the dielectric, which results in trapped charges, alterations in electrostatic force, and higher adhesion. Excessive adhesion can explain decreased lifetime at high bias voltage previously reported with actual capacitive MEMS switches. Switch sticking, self actuation, failure to actuate, and self release can all be explained by the experimental results.

Patton, Steven T.; Zabinski, Jeffrey S.

2006-01-01

60

Interfaces and failure mechanisms in Al-SiC composites  

NASA Technical Reports Server (NTRS)

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

Nutt, S. R.

1986-01-01

61

An investigation of fatigue failures of turbine blades in a gas turbine engine by mechanical analysis  

Microsoft Academic Search

Blade failures in gas turbine engines often lead to loss of all downstream stages and can have a dramatic effect on the availability of the turbine engines. Thorough failure investigation is essential for the effective management of engine airworthiness. In this paper blade fatigue failures are investigated by mechanical analyses and by examination of failed blades. A series of mechanical

Jianfu Hou; Bryon J Wicks; Ross A Antoniou

2002-01-01

62

Thermal fatigue failure induced by delamination in thermal barrier coating  

Microsoft Academic Search

The paper presents the experimental and theoretical investigation on the thermal fatigue failure induced by delamination in thermal barrier coating system. Laser heating method was used to simulate the operating state of TBC (thermal barrier coating) system. The non-destructive evaluation such as acoustic emission (AE) detect was used to study the evolution of TBC system damage. Micro-observation and AE detect

Y. C. Zhou; T. Hashida

2002-01-01

63

Effect of higher water vapor content on TBC performance  

SciTech Connect

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.

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

2012-01-01

64

Failure mechanisms of particulate two-phase composites  

SciTech Connect

In many composites consisting of hard and brittle inclusions embedded in a ductile matrix failure can be attributed to particle cleavage followed by ductile crack growth in the matrix. Both mechanisms are significantly sensitive towards the presence of residual stresses. On the one hand particle failure depends on the stress distribution inside the inclusion, which, in turn, is a function of various geometrical parameters such as the aspect ratio and the position relative to adjacent particles as well as the external load. On the other hand it has been observed that the absolute size of each particle plays a role as well and will, therefore, be taken into account in this work by means of the Weibull theory. Unit cells containing a number of quasi-randomly oriented elliptical inclusions serve as the basis for the finite element calculations. The numerical results are then correlated to the geometrical parameters defining the inclusions. The probability of fracture has been evaluated for a large number of inclusions and plotted versus the particle size. The parameters of the fitting curves to the resulting data points depend on the choice of the Weibull parameters. A crack tip opening angle criterion (CTOA) is used to describe crack growth in the matrix emanating from a broken particle. It turns out that the crack resistance of the matrix largely depends on the distance from an adjacent particle. Residual stresses due to quenching of the material tend to reduce the risk of particle cleavage but promote crack propagation in the matrix.

Antretter, T.; Fischer, F.D. [Montanuniversitaet Leoben (Austria). Inst. of Mechanics

1998-12-31

65

Failure mechanisms and surface roughness statistics of fractured Fontainebleau sandstone.  

PubMed

In an effort to investigate the link between failure mechanisms and the geometry of fractures of compacted grains materials, a detailed statistical analysis of the surfaces of fractured Fontainebleau sandstones has been achieved. The roughness of samples of different widths W is shown to be self-affine with an exponent zeta=0.46+/-0.05 over a range of length scales ranging from the grain size d up to an upper cutoff length xi approximately =0.15 W. This low zeta value is in agreement with measurements on other sandstones and on sintered materials. The probability distributions pi delta z(delta h) of the variations of height over different distances delta z>d can be collapsed onto a single Gaussian distribution with a suitable normalization and do not display multiscaling features. The roughness amplitude, as characterized by the height-height correlation over fixed distances delta z, does not depend on the sample width, implying that no anomalous scaling of the type reported for other materials is present. It is suggested, in agreement with recent theoretical work, to explain these results by the occurrence of brittle fracture (instead of damage failure in materials displaying a higher value of zeta approximately =0.8 ). PMID:17930307

Ponson, L; Auradou, H; Pessel, M; Lazarus, V; Hulin, J P

2007-09-01

66

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

SciTech Connect

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.

Scott X. Mao

2002-01-31

67

Mechanisms of compressive failure in woven composites and stitched laminates  

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

68

Evolution of Tre-2/Bub2/Cdc16 (TBC) Rab GTPase-activating proteins  

PubMed Central

Rab GTPases serve as major control elements in the coordination and definition of specific trafficking steps and intracellular compartments. Rab activity is modulated in part by GTPase-activating proteins (GAPs), and many RabGAPs share a Tre-2/Bub2/Cdc16 (TBC)–domain architecture, although the majority of TBC proteins are poorly characterized. We reconstruct the evolutionary history of the TBC family using ScrollSaw, a method for the phylogenetic analysis of pan-eukaryotic data sets, and find a sophisticated, ancient TBC complement of at least 10 members. Significantly, the TBC complement is nearly always smaller than the Rab cohort in any individual genome but also suggests Rab/TBC coevolution. Further, TBC-domain architecture has been well conserved in modern eukaryotes. The reconstruction also shows conservation of ancestral TBC subfamilies, continuing evolution of new TBCs, and frequent secondary losses. These patterns give additional insights into the sculpting of the endomembrane system. PMID:23485563

Gabernet-Castello, Carme; O'Reilly, Amanda J.; Dacks, Joel B.; Field, Mark C.

2013-01-01

69

ACBD3 Interaction with TBC1 Domain 22 Protein Is Differentially Affected by Enteroviral and Kobuviral 3A Protein Binding  

PubMed Central

ABSTRACT Despite wide sequence divergence, multiple picornaviruses use the Golgi adaptor acyl coenzyme A (acyl-CoA) binding domain protein 3 (ACBD3/GCP60) to recruit phosphatidylinositol 4-kinase class III beta (PI4KIII?/PI4KB), a factor required for viral replication. The molecular basis of this convergent interaction and the cellular function of ACBD3 are not fully understood. Using affinity purification-mass spectrometry, we identified the putative Rab33 GTPase-activating proteins TBC1D22A and TBC1D22B as ACBD3-interacting factors. Fine-scale mapping of binding determinants within ACBD3 revealed that the interaction domains for TBC1D22A/B and PI4KB are identical. Affinity purification confirmed that PI4KB and TBC1D22A/B interactions with ACBD3 are mutually exclusive, suggesting a possible regulatory mechanism for recruitment of PI4KB. The C-terminal Golgi dynamics (GOLD) domain of ACBD3 has been previously shown to bind the 3A replication protein from Aichi virus. We find that the 3A proteins from several additional picornaviruses, including hepatitis A virus, human parechovirus 1, and human klassevirus, demonstrate an interaction with ACBD3 by mammalian two-hybrid assay; however, we also find that the enterovirus and kobuvirus 3A interactions with ACBD3 are functionally distinct with respect to TBC1D22A/B and PI4KB recruitment. These data reinforce the notion that ACBD3 organizes numerous cellular functionalities and that RNA virus replication proteins likely modulate these interactions by more than one mechanism. PMID:23572552

Greninger, Alexander L.; Knudsen, Giselle M.; Betegon, Miguel; Burlingame, Alma L.; DeRisi, Joseph L.

2013-01-01

70

Simulated Hail Ice Mechanical Properties and Failure Mechanism at Quasi-Static Strain Rates  

NASA Astrophysics Data System (ADS)

Hail is a significant threat to aircraft both on the ground and in the air. Aeronautical engineers are interested in better understanding the properties of hail to improve the safety of new aircraft. However, the failure mechanism and mechanical properties of hail, as opposed to clear ice, are not well understood. A literature review identifies basic mechanical properties of ice and a failure mechanism based upon the state of stress within an ice sphere is proposed. To better understand the properties of Simulated Hail Ice (SHI), several tests were conducted using both clear and cotton fiber reinforced ice. Pictures were taken to show the internal crystal structure of SHI. SHI crush tests were conducted to identify the overall force-displacement trends at various quasi-static strain rates. High speed photography was also used to visually track the failure mechanism of spherical SHI. Compression tests were done to measure the compression strength of SHI and results were compared to literature data. Fracture toughness tests were conducted to identify the crack resistance of SHI. Results from testing clear ice samples were successfully compared to previously published literature data to instill confidence in the testing methods. The methods were subsequently used to test and characterize the cotton fiber reinforced ice.

Swift, Jonathan M.

71

Mechanisms of Cell Death in Acute Liver Failure  

PubMed Central

Acute liver failure (ALF) can be the consequence of various etiologies, that might vary between different geographic regions. Most frequent are intoxications with acetaminophen, viral hepatitis, or liver damage of unknown origin. ALF occurs when the extent of hepatocyte death exceeds the regenerative capacity of the liver. The mode of liver cell death that is predominantly induced in ALF, i.e., apoptosis or necrosis, is still controversial and presumably determined by the etiology, duration, and magnitude of liver injury. Severe liver damage involves oxidative stress and depletion of ATP resulting in necrosis. In contrast, maintenance of ATP stores is required for the execution of apoptosis. Recent data suggest that necrosis resulting from severe liver damage is associated with poor outcome of ALF patients. Discrimination between apoptosis and necrosis might be therefore useful for the identification of ALF patients requiring liver transplantation. Identification of the molecular cell death mechanisms remains an important issue not only for early prediction of ALF outcome, but also for therapeutic interventions. In view of the pleiotropic functions of critical mediators of cell death and tissue regeneration, a particular challenge will be to reduce hepatocellular death without inhibiting the regenerative capacity of the liver. Here, we review the molecular mechanisms of hepatocyte injury and the pathways leading to apoptosis and necrosis, which might represent potential diagnostic and therapeutic targets in ALF. PMID:22485095

Bantel, Heike; Schulze-Osthoff, Klaus

2012-01-01

72

Failure of Standard Quantum Mechanics for the Description of Compound Quantum Entities  

E-print Network

Failure of Standard Quantum Mechanics for the Description of Compound Quantum Entities Diederik that proves that two separated quantum entities cannot be described by means of standard quantum mechanics of this result indicates a failure of standard quantum mechanics, and not just some peculiar shortcoming due

Aerts, Diederik

73

Von Mises Failure Criterion in Mechanics of Materials: How to Efficiently Use it Under Interval  

E-print Network

, the resulting irreversible damage start weakening the mechanical construction can lead to a failure in the longVon Mises Failure Criterion in Mechanics of Materials: How to Efficiently Use it Under Interval@utep.edu, t ampownuk@utep.edu, :j:olgak@utep.edu, *sstarks@utep.edu Abstract-One of the main objective of mechanics

Pownuk, Andrzej

74

The use of fracture mechanics in failure analysis in the offshore diamond mining industry  

Microsoft Academic Search

This paper considers two major failures of offshore diamond mining equipment, which should not have occurred had both fracture mechanics aspects and materials behaviour been more fully understood. The two case studies include (a) failure of a wire rope swivel, and (b) failure of a load cell (used for monitoring rope load). In case (a) the swivel shank had failed

R. B. Tait; C. Emslie

2005-01-01

75

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

SciTech Connect

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.

Scott X. Mao

2002-08-31

76

Failure Modes and Mechanisms in Gray Cast Iron Pipes  

Microsoft Academic Search

Failures in cast iron water mains are more complex and diverse than is widely understood in the industry. This paper discusses the modes and causes of pipe failures that have been encountered during a three year investigation by the National Research Council Canada. In addition to corrosion, manufacturing defects, human error and unexpected levels of pipe loading all play a

J. M. Makar; R. Desnoyers; S. E. McDonald

77

Non-destructive microwave evaluation of TBC delamination induced by acute angle laser drilling  

NASA Astrophysics Data System (ADS)

Laser drilling has been applied to the production of cooling holes of various size and angles in the modern aerospace gas turbine components such as turbine blades, nozzle guide vanes, combustion chambers and afterburner. These parts are usually made of heat resistant nickel superalloys. The superalloy substrate is coated with yttria-stabilized zirconia thermal barrier coatings (TBCs) to protect them from reaching excessive temperatures in hot engine environments. Drilling the parts at acute angles to the surface is complicated because (i) multiple layers are being drilled through, (ii) the melt ejection and heat flow patterns around the hole are non-symmetrical and (iii) the drilling distance is greater than when drilling normal to the surface. In a previous investigation by the authors, delamination of TBC was addressed as a main problem of angled drilling and mechanisms involved were discussed. Characterization of delamination cracks was normally performed via metallographic techniques. It involves sectioning the samples using an abrasive cutting machine, grinding with successively finer silicon carbide paper up to the centre of the hole and polishing to allow optical microscopic analysis of the cracks. However, clamping and sectioning process of thermal-spray-coated workpieces can introduce cracks in brittle coatings due to the drag of the cut-off wheels. Hence, it is not possible to decide if the delamination is caused as a result of post-process sectioning or laser drilling. In this paper, a microwave non-destructive testing (NDT) technique is employed to evaluate the integrity of TBC after acute angle laser drilling. An Agilent 8510 XF network analyser operating over the frequency range of 45 MHz to 110 GHz was used to measure the amplitude and phase variations of scattered waves. The results significantly indicated the existence of delamination of 1-1.5 mm long at the TBC/substrate interface on the leading edge part of an acute-angled hole laser drilled using a 400 W Nd:YAG laser.

Sezer, H. K.; Li, Lin; Wu, Z.; Anderson, B.; Williams, P.

2007-01-01

78

Correlation between the failure mechanism and dark currents of high power photodetectors  

Microsoft Academic Search

We experimentally investigate the role of dark current on the failure mechanism of high power photodiodes. A theoretical model built to fit the experimental data indicates that the effective barrier height and the dark current are the fundamental parameters in the failure mechanism

M. S. Islam; A. Nespola; M. Yeahia; M. C. Wu; D. L. Sivco; A. Y. Cho

2000-01-01

79

77 FR 34457 - Pipeline Safety: Mechanical Fitting Failure Reports  

Federal Register 2010, 2011, 2012, 2013, 2014

...Outside Force Damage,'' ``Material or Welds/Fusions,'' ``Equipment...fitting. One option is ``Material or Welds/Fusions'' with a subcategory of...failure data under the ``Material or Welds/Fusions'' leak cause category...

2012-06-11

80

Neuroinflammation in acute liver failure: mechanisms and novel therapeutic targets.  

PubMed

It is increasingly evident that neuroinflammatory mechanisms are implicated in the pathogenesis of the central nervous system (CNS) complications (intracranial hypertension, brain herniation) of acute liver failure (ALF). Neuroinflammation in ALF is characterized by microglial activation and arterio-venous difference studies as well as studies of gene expression confirm local brain production and release of proinflammatory cytokines including TNF-? and the interleukins IL-1? and IL-6. Although the precise nature of the glial cell responsible for brain cytokine synthesis is not yet established, evidence to date supports a role for both astrocytes and microglia. The neuroinflammatory response in ALF progresses in parallel with the progression of hepatic encephalopathy (HE) and with the severity of brain edema (astrocyte swelling). Mechanisms responsible for the relaying of signals from the failing liver to the brain include transduction of systemic proinflammatory signals as well as the effects of increased brain lactate leading to increased release of cytokines from both astrocytes and microglia. There is evidence in support of a synergistic effect of proinflammatory cytokines and ammonia in the pathogenesis of HE and brain edema in ALF. Therapeutic implications of the findings of a neuroinflammatory response in ALF are multiple. Removal of both ammonia and proinflammatory cytokines is possible using antibiotics or albumen dialysis. Mild hypothermia reduces brain ammonia transfer, brain lactate production, microglial activation and proinflammatory cytokine production resulting in reduced brain edema and intracranial pressure in ALF. N-Acetylcysteine acts as both an antioxidant and anti-inflammatory agent at both peripheral and central sites of action independently resulting in slowing of HE progression and prevention of brain edema. Novel treatments that directly target the neuroinflammatory response in ALF include the use of etanercept, a TNF-? neutralizing molecule and minocycline, an agent with potent inhibitory actions on microglial activation that are independent of its antimicrobial properties; both agents have been shown to be effective in reducing neuroinflammation and in preventing the CNS complications of ALF. Translation of these findings to the clinic has the potential to provide rational targeted approaches to the prevention and treatment of these complications in the near future. PMID:21864609

Butterworth, Roger F

2011-11-01

81

Percutaneous mechanical devices in the management of decompensated heart failure.  

PubMed

Heart failure is the only cardiovascular disease diagnosis increasing in prevalence in the United States. A number of drugs have been shown to reduce morbidity and mortality in patients with chronic heart failure. Despite these advances, the frequency of hospitalization for heart failure has continued to increase, and clinical trial data are lacking in demonstrable benefit of drug therapy for patients hospitalized with acute, decompensated heart failure. A number of percutaneous devices have been developed and are in various stages of investigation and use to improve symptoms and clinical outcomes in patients hospitalized with heart failure. These include "add-on" devices, such as continuous aortic flow augmentation and ultrafiltration devices, and "rescue" devices to be used in patients who are rapidly deteriorating despite medical therapy. In addition to the intra-aortic balloon pump, newer approaches include percutaneous ventricular assist devices that are available for short-term use to stabilize patients until recovery can occur or as "bridges" to longer-term assist or cardiac transplantation. In the coming years, expanded clinical investigation is likely to explore the potential for devices to normalize underlying cardiac function and thereby improve long-term clinical outcomes. PMID:17386185

Mather, Paul J; Konstam, Marvin A

2007-03-01

82

Prediction of Mechanical Shaft Failures Due to Pulsating Torques of Variable-Frequency Drives  

Microsoft Academic Search

Mechanical damage of rotating shafts has been reported for several years from various high-power applications. This paper shows that the variable frequency drive incorporated in a rotating shaft is one of the main root causes of mechanical-shaft failures. Simple analytical relationships show that the frequencies of the motor air-gap torque have a more significant impact on the mechanical-shaft failure than

Joseph Song-Manguelle; Stefan Schröder; Tobias Geyer; Gabriel Ekemb; Jean-Maurice Nyobe-Yome

2010-01-01

83

Characterization of Alumina Interfaces in TBC Systems  

SciTech Connect

Interfacial segregants in thermally grown {alpha}-Al{sub 2}O{sub 3} scales formed during high temperature exposure of thermal barrier coating systems reflect the oxygen-active dopants present in the bond coating and substrate, such as Y and Hf. These dopants diffuse outward and segregate to the substrate-alumina interface and the alumina grain boundaries. Related studies suggest that these segregants affect the growth and mechanical properties of the alumina-scale; however, the characterization of segregation in alumina formed on coated superalloy systems has been limited. Segregation examples evaluated using analytical transmission electron microscopy are given from traditional Pt-modified aluminide coatings and newer Pt diffusion coatings. Model systems are used to illustrate that grain boundary segregants on the columnar alumina boundaries are not because of the reverse diffusion of cations from the Y{sub 2}O{sub 3}-stabilized ZrO{sub 2} top coating, and that interstitial elements in the substrate likely affect the outward flux of cation dopants. The dynamic nature of this segregation and oxygen-potential gradient-driven diffusion is discussed in light of observations of substrate dopant and interstitial contents affecting coating performance.

Pint, Bruce A [ORNL; More, Karren Leslie [ORNL

2009-01-01

84

A review of mechanisms and models for dynamic failure, strength, and fragmentation  

NASA Astrophysics Data System (ADS)

Modeling of catastrophic disruption requires understanding the processes of dynamic failure and fragmentation. This paper summarizes current mechanisms and models for dynamic failure, strength, and fragmentation, reviewing these from a mechanics perspective and with an emphasis on making links to the developing advances in these areas in the engineering and computational mechanics communities. We describe dynamic failure processes, examine size and rate effects, articulate the scaling concepts that arise naturally from these processes, and examine the influences of these processes on effective strength and fragmentation.

Ramesh, K. T.; Hogan, James D.; Kimberley, Jamie; Stickle, Angela

2015-03-01

85

Investigating compression failure mechanisms in composite laminates with a transient fiberglass-epoxy birefringent material  

NASA Technical Reports Server (NTRS)

An experimental study is reported in which a nondestructive technique involving the use of a transparent fiberglass-epoxy composite birefringent material has been used to investigate compression failure mechanisms in graphite-epoxy laminates. It is shown that the birefringency and transparency of the fiberglass-epoxy material permits regions of high stress to be located and the mechanisms of local failure propagation to be identified within the laminate. The material may also be useful for studying stress fields and for identifying failure initiation and propagation mechanisms in a wide variety of composite-structure problems.

Shuart, M. J.; Williams, J. G.

1984-01-01

86

Failure mechanism of epoxy polymer: transition from ductile to brittle failure  

Microsoft Academic Search

The failure processes of an epoxy polymer (Epicote 21506) were studied by using a high speed camera evolving over a range of strain rates from 0.0001s-1 to 668s-1. The front surface of the specimen was monitored by the high speed camera to capture the deformation and cracking processes. A split Hopkinson pressure bar (SHPB) was utilized to examine the dynamic

Wei Wu; Guowei Ma

2009-01-01

87

On the Mechanism of Failure of Particulate Rigid Disks  

Microsoft Academic Search

The sliding system used with particulate rigid disks, involving a ceramic head sliding against a disk coated with iron oxide particles in a resin iv unusual in a number of ways. Perhaps the most striking is that, in use, there is for a long time no measurable wear, but once damage is initiated failure is rapid. To investigate this type

Ernest Rabinowicz; Farid Kaymaram

1991-01-01

88

Reverse remodeling in heart failure—mechanisms and therapeutic opportunities  

Microsoft Academic Search

Heart failure (HF) involves changes in cardiac structure, myocardial composition, myocyte deformation, and multiple biochemical and molecular alterations that impact heart function and reserve capacity. Collectively, these changes have been referred to as 'cardiac remodeling'. Understanding the components of this process with the goal of stopping or reversing its progression has become a major objective. This concept is often termed

Norimichi Koitabashi; David A. Kass

2011-01-01

89

Wear as a product failure mechanism – Overview and case studies  

Microsoft Academic Search

Tribology is the technology of interactive surfaces in relative motion, incorporating the science of friction, lubrication and wear. The subject is a recognised and researched area in its own right, being of interest to both the academic and engineering community. However, the attention of the forensic (or failure) investigator will often focus on one area, that of any resultant wear

Colin R. Gagg; Peter R. Lewis

2007-01-01

90

Failure mechanisms and design considerations for fault tolerant aerospace drives  

Microsoft Academic Search

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.

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

2010-01-01

91

Fabrication of TBC-armored rocket combustion chambers by EB-PVD methods and TLP assembling  

Microsoft Academic Search

A thermal barrier coating (TBC) system for rocket chambers made of Cu-based high strength alloys has been developed in a pilot project in line with EB-PVD (electron-beam physical vapor deposition) technology aiming at TBC application on Cu-based walls of real rocket combustion chambers. The TBC system consists of a metallic bond coating compatible with Cu-based material and an yttria partially

Uwe Schulz; Klaus Fritscher; Manfred Peters; Dirk Greuel; Oskar Haidn

2005-01-01

92

Contraction regulates site-specific phosphorylation of TBC1D1 in skeletal muscle.  

PubMed

TBC1D1 (tre-2/USP6, BUB2, cdc16 domain family member 1) is a Rab-GAP (GTPase-activating protein) that is highly expressed in skeletal muscle, but little is known about TBC1D1 regulation and function. We studied TBC1D1 phosphorylation on three predicted AMPK (AMP-activated protein kinase) phosphorylation sites (Ser231, Ser660 and Ser700) and one predicted Akt phosphorylation site (Thr590) in control mice, AMPK?2 inactive transgenic mice (AMPK?2i TG) and Akt2-knockout mice (Akt2 KO). Muscle contraction significantly increased TBC1D1 phosphorylation on Ser231 and Ser660, tended to increase Ser700 phosphorylation, but had no effect on Thr590. AICAR (5-aminoimidazole-4-carboxyamide ribonucleoside) also increased phosphorylation on Ser231, Ser660 and Ser700, but not Thr590, whereas insulin only increased Thr590 phosphorylation. Basal and contraction-stimulated TBC1D1 Ser231, Ser660 and Ser700 phosphorylation were greatly reduced in AMPK?2i TG mice, although contraction still elicited a small increase in phosphorylation. Akt2 KO mice had blunted insulin-stimulated TBC1D1 Thr590 phosphorylation. Contraction-stimulated TBC1D1 Ser231 and Ser660 phosphorylation were normal in high-fat-fed mice. Glucose uptake in vivo was significantly decreased in tibialis anterior muscles overexpressing TBC1D1 mutated on four predicted AMPK phosphorylation sites. In conclusion, contraction causes site-specific phosphorylation of TBC1D1 in skeletal muscle, and TBC1D1 phosphorylation on AMPK sites regulates contraction-stimulated glucose uptake. AMPK and Akt regulate TBC1D1 phosphorylation, but there must be additional upstream kinases that mediate TBC1D1 phosphorylation in skeletal muscle. PMID:20701589

Vichaiwong, Kanokwan; Purohit, Suneet; An, Ding; Toyoda, Taro; Jessen, Niels; Hirshman, Michael F; Goodyear, Laurie J

2010-10-15

93

Mechanics-based statistics of failure risk of quasibrittle structures and size effect  

E-print Network

of F is necessarily Gaussian, or normal (except in far-left tails); and (ii) perfectly brittle failures the problem, including its scaling aspect, for the broad and increasingly important class of quasi- brittleMechanics-based statistics of failure risk of quasibrittle structures and size effect on safety

94

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

E-print Network

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

Fortin, Jérôme

95

Investigation of thermally induced failure mechanisms in integrated spiral planar power passives  

Microsoft Academic Search

Research on the development of electromagnetically integrated passive structures have, in recent years, led to a number of technological improvements such as improved constructional technology. The reliability and physics of failure of these structures have in contrast received little attention. In this paper, the main thermally induced failure mechanisms are investigated experimentally for an integrated LC structure as representative of

J. T. Strydom; J. D. van Wyk

2002-01-01

96

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

Microsoft Academic Search

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

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

1984-01-01

97

Reverse remodeling of the extracellular matrix in heart failure after left ventricular mechanical support  

Microsoft Academic Search

This thesis describes a study of the changes in the extracellular matrix (ECM) of the myocardium, in patients with end stage heart failure and during mechanical support (Left Ventricular Assist Device support, LVAD) of the left ventricle. The changes during LVAD support may lead to recovery of the heart. Chapter 1 is a general introduction about heart failure, heart transplantation,

A. H. Bruggink

2008-01-01

98

Tbc1d15-17 Regulates Synaptic Development at the Drosophila Neuromuscular Junction  

PubMed Central

Members of the Tre-2/Bub2/Cdc16 (TBC) family of proteins are believed to function as GTPase-activating proteins (GAPs) for Rab GTPases, which play pivotal roles in intra-cellular membrane trafficking. Although membrane trafficking is fundamental to neuronal morphogenesis and function, the roles of TBC-family Rab GAPs have been poorly characterized in the nervous system. In this paper, we provide genetic evidence that Tbc1d15-17, the Drosophila homolog of mammalian Rab7-GAP TBC1d15, is required for normal presynaptic growth and postsynaptic organization at the neuromuscular junction (NMJ). A loss-of-function mutation in tbc1d15-17 or its presynaptic knockdown leads to an increase in synaptic bouton number and NMJ length. tbc1d15-17 mutants are also defective in the distribution of the postsynaptic scaffold Discs-large (Dlg) and in the level of the postsynaptic glutamate subunit GluRIIA. These postsynaptic phenotypes are recapitulated by postsynaptic knockdown of Tbc1d15-17. We also show that presynaptic overexpression of a constitutively active Rab7 mutant in a wild-type background causes a synaptic overgrowth phenotype resembling that of tbc1d15-17 mutants, while a dominant-negative form of Rab7 has the opposite effect. Together, our findings establish a novel role for Tbc1d15-17 and its potential substrate Rab7 in regulating synaptic development. PMID:23812537

Lee, Min-Jung; Jang, Sooyeon; Nahm, Minyeop; Yoon, Jin-Ho; Lee, Seungbok

2013-01-01

99

A study of the failure mechanism of chlorine anodes  

SciTech Connect

Thin coating RuO{sub 2}{minus}TiO{sub 2} electrodes, which mimic the DSA anodes, have been prepared and tested for their activity toward the chlorine evolution reaction and subjected to life time testing. Rutherford Backscattering Spectrometry has been used concurrently with electrochemical measurements to analyze changes in the ruthenium content of the coating. The decrease in electrode activity is found to be closely related to a decrease in Ru content, and the measured profiles indicate that the loss takes place across the thin coating. Failure is observed for electrodes with a Ru content below a critical concentration, but there is no evidence for the build up of a pure TiO{sub 2} layer. AFM imaging of an anode after failure sustained the hypothesis of loss of material.

Vallet, C.E.; Zuhr, R.A. [Oak Ridge National Lab., TN (United States); Tilak, B.V.; Chen, C.P. [Occidental Chemical Corp., Grand Island, NY (United States)

1995-12-31

100

Statins stimulate atherosclerosis and heart failure: pharmacological mechanisms.  

PubMed

In contrast to the current belief that cholesterol reduction with statins decreases atherosclerosis, we present a perspective that statins may be causative in coronary artery calcification and can function as mitochondrial toxins that impair muscle function in the heart and blood vessels through the depletion of coenzyme Q10 and 'heme A', and thereby ATP generation. Statins inhibit the synthesis of vitamin K2, the cofactor for matrix Gla-protein activation, which in turn protects arteries from calcification. Statins inhibit the biosynthesis of selenium containing proteins, one of which is glutathione peroxidase serving to suppress peroxidative stress. An impairment of selenoprotein biosynthesis may be a factor in congestive heart failure, reminiscent of the dilated cardiomyopathies seen with selenium deficiency. Thus, the epidemic of heart failure and atherosclerosis that plagues the modern world may paradoxically be aggravated by the pervasive use of statin drugs. We propose that current statin treatment guidelines be critically reevaluated. PMID:25655639

Okuyama, Harumi; Langsjoen, Peter H; Hamazaki, Tomohito; Ogushi, Yoichi; Hama, Rokuro; Kobayashi, Tetsuyuki; Uchino, Hajime

2015-03-01

101

Mechanisms of bioprosthetic heart valve failure: Fatigue causes collagen denaturation and glycosaminoglycan loss  

E-print Network

Mechanisms of bioprosthetic heart valve failure: Fatigue causes collagen denaturation heart valve (BPHV) degeneration, characterized by extracellular matrix deterioration, remod- eling; FTIR spectroscopy; in vitro ac- celerated fatigue; bioprosthetic heart valve degeneration

Zand, Robert

102

A Failure Detection and Handling Mechanism for the SR Distributed Programming Language  

E-print Network

, the server becomes an orphan. If a node containing a server crashes, or a network partition prevents of a failure detection and handling mechanism is to locate orphans and failed invoca­ tions and to assist

California at Davis, University of

103

Mechanical support in acute and chronic heart failure  

Microsoft Academic Search

Heart failure (HF) is the leading cause of hospital admissions in the United States in people over the age of 65 years. Major\\u000a advancements in the medical therapy of HF, combined with automatic implantable cardioverterdefibrillators and cardiac resynchronization\\u000a therapy, have substantially reduced the mortality and morbidity of chronic HF, but mortality remains high, and the availability\\u000a of donor hearts for

Andreas Brieke; Joseph Cleveland Jr; JoAnn Lindenfeld

2008-01-01

104

Method of Testing and Predicting Failures of Electronic Mechanical Systems  

NASA Technical Reports Server (NTRS)

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

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

1996-01-01

105

Diastolic dysfunction and diastolic heart failure: Mechanisms and epidemiology  

Microsoft Academic Search

Studies have demonstrated that diastolic dysfunction is frequently present in asymptomatic community-based individuals, especially\\u000a in the elderly with hypertension, coronary artery disease, and diabetes. The presence of diastolic dysfunction is a predictor\\u000a for the development of heart failure (HF) and confers a higher risk of mortality. These findings have raised the question\\u000a of whether treating preclinical diastolic dysfunction will be

Anita Deswal

2005-01-01

106

Laboratory and 3-D-distinct element analysis of failure mechanism of slope under external surcharge  

NASA Astrophysics Data System (ADS)

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 details. There are however increasing interest on the consequences after the initiation of failure which 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 details 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 laboratory model test in the present research. A more refined study about the development of failure, microcosmic failure mechanism and the post-failure mechanism of slope 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.

Li, N.; Cheng, Y. M.

2014-09-01

107

Mechanics of dual-mode dilative failure in subaqueous sediment deposits  

NASA Astrophysics Data System (ADS)

We introduce dual-mode dilative failure with flume experiments. Dual-mode dilative failure combines slow and steady release of sediments by breaching with periodic sliding, which rapidly releases an internally coherent wedge of sediments. It occurs in dilative sandy deposits. This periodic slope failure results from cyclic evolution of the excess pore pressure in the deposit. Sliding generates large, transient, negative excess pore pressure that strengthens the deposit and allows breaching to occur. During breaching, negative excess pore pressure dissipates, the deposit weakens, and ultimately sliding occurs once again. We show that the sliding frequency is proportional to the coefficient of consolidation. We find that thicker deposits are more susceptible to dual-mode dilative failure. Discovery of dual-mode dilative failure provides a new mechanism to consider when interpreting the sedimentary deposits linked to submarine slope failures.

You, Yao; Flemings, Peter; Mohrig, David

2014-07-01

108

Nano-mechanics modelling of deformation and failure behaviours at asphalt–aggregate interfaces  

Microsoft Academic Search

The nano-mechanics method has recently emerged as a powerful computational approach to model from nano to macro microstructure deformation and failure behaviours in materials. This paper reviews the advances of nano-mechanics modelling method. Then it introduces the recent advances of our research on the molecular origin of deformation and failure processes of asphalt–aggregate interfaces. This research includes studies of bulk

Yang Lu; Linbing Wang

2011-01-01

109

Rupture failure and mechanical strength of the electrode wire used in wire EDM  

Microsoft Academic Search

In the application of wire EDM, wire rupture is very troublesome and impedes further increase of cutting speed. Instead of the spark characteristics or the temperature distribution, the rupture mechanism and the mechanical strength of the wire are the focus of this investigation. Wire rupture is a mechanical failure in essence, although the process heat has significant influence on the

Y. F. Luo

1999-01-01

110

Failure mechanisms in laminated carbon/carbon composites under biaxial compression  

SciTech Connect

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.

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

111

Accelerated Thermal Cycling and Failure Mechanisms for BGA and CSP Assemblies  

NASA Technical Reports Server (NTRS)

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

Ghaffarian, Reza

2000-01-01

112

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

SciTech Connect

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.

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

1995-12-31

113

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

SciTech Connect

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.

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

1995-09-01

114

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

SciTech Connect

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 2000s{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. {copyright} {ital 1996 American Institute of Physics.}

Richards Thissell, W.; Zurek, A.K. [Materials Research and Processing Science, MS: G755, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Addessio, F. [Materials Research and Processing Science, MS: G755, Fluid Dynamics, MS: B216, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

1996-05-01

115

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

NASA Technical Reports Server (NTRS)

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.

Clements, L. L.

1981-01-01

116

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

NASA Astrophysics Data System (ADS)

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.

Anoop Krishnan, N. M.; Ghosh, Debraj

2014-07-01

117

Lubrication and failure mechanisms of graphite fluoride films  

NASA Technical Reports Server (NTRS)

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

Fusaro, R. L.

1978-01-01

118

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

E-print Network

service, therefore require large deformability of device components (e.g., metal interconnects). ThinTHEORETICAL & APPLIED MECHANICS LETTERS 1, 041002 (2011) Competing failure mechanisms of thin metal online 10 July 2011) Abstract The ductility of thin metal films on polymer substrates reported in recent

Li, Teng

119

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

120

The Rab-GTPase-activating protein TBC1D1 regulates skeletal muscle glucose metabolism.  

PubMed

The Rab-GTPase-activating protein TBC1D1 has emerged as a novel candidate involved in metabolic regulation. Our aim was to determine whether TBC1D1 is involved in insulin as well as energy-sensing signals controlling skeletal muscle metabolism. TBC1D1-deficient congenic B6.SJL-Nob1.10 (Nob1.10(SJL)) and wild-type littermates were studied. Glucose and insulin tolerance, glucose utilization, hepatic glucose production, and tissue-specific insulin-mediated glucose uptake were determined. The effect of insulin, AICAR, or contraction on glucose transport was studied in isolated skeletal muscle. Glucose and insulin tolerance tests were normal in TBC1D1-deficient Nob1.10(SJL) mice, yet the 4-h-fasted insulin concentration was increased. Insulin-stimulated peripheral glucose utilization during a euglycemic hyperinsulinemic clamp was similar between genotypes, whereas the suppression of hepatic glucose production was increased in TBC1D1-deficient mice. In isolated extensor digitorum longus (EDL) but not soleus muscle, glucose transport in response to insulin, AICAR, or contraction was impaired by TBC1D1 deficiency. The reduction in glucose transport in EDL muscle from TBC1D1-deficient Nob1.10(SJL) mice may be explained partly by a 50% reduction in GLUT4 protein, since proximal signaling at the level of Akt, AMPK, and acetyl-CoA carboxylase (ACC) was unaltered. Paradoxically, in vivo insulin-stimulated 2-deoxyglucose uptake was increased in EDL and tibialis anterior muscle from TBC1D1-deficient mice. In conclusion, TBC1D1 plays a role in regulation of glucose metabolism in skeletal muscle. Moreover, functional TBC1D1 is required for AICAR- or contraction-induced metabolic responses, implicating a role in energy-sensing signals. PMID:22693207

Szekeres, Ferenc; Chadt, Alexandra; Tom, Robby Z; Deshmukh, Atul S; Chibalin, Alexander V; Björnholm, Marie; Al-Hasani, Hadi; Zierath, Juleen R

2012-08-15

121

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

SciTech Connect

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)

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

122

Failure mechanisms of laminates transversely loaded by bolt push-through  

NASA Technical Reports Server (NTRS)

Stiffened composite panels proposed for fuselage and wing design utilize a variety of stiffener-to-skin attachment concepts including mechanical fasteners. The attachment concept is an important factor influencing the panel's strength and can govern its performance following local damage. Mechanical fasteners can be an effective method for preventing stiffener-skin separation. One potential failure mode for bolted panels occurs when the bolts pull through the stiffener attachment flange or skin. The resulting loss of support by the skin to the stiffener and by the stiffener to the skin can result in local buckling and subsequent panel collapse. The characteristic failure modes associated with bolt push-through failure are described and the results of a parametric study of the effects that different material systems, boundary conditions, and laminates have on the forces and displacements required to cause damage and bolt pushthrough failure are presented.

Waters, W. A., Jr.; Williams, J. G.

1985-01-01

123

Mechanical and electrical failure of thin films bonded to solid substrates  

Microsoft Academic Search

Solid thin films bonded to substrates are found in a variety of important technological device applications. Often these films are under large stress and can fail dramatically and irreversibly. However, a detailed understanding of the mechanical failure mechanisms relevant to thin films under stress has, despite obvious technological importance, not been achieved. If, instead of being-subjected to large stresses, the

Kevin Mahlon Crosby

1997-01-01

124

Dynamic Failure of a Lamina Meshwork in Cell Nuclei under Extreme Mechanical Deformation  

E-print Network

Dynamic Failure of a Lamina Meshwork in Cell Nuclei under Extreme Mechanical Deformation Zhao Qin protein meshwork at the inner nuclear membrane. It confers mechanical strength to the cell's nucleus and also sustains the overall structural integrity of the cell. The rupture of nuclear lamina is involved

Buehler, Markus J.

125

Development Testing and Subsequent Failure Investigation of a Spring Strut Mechanism  

NASA Technical Reports Server (NTRS)

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

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

2014-01-01

126

Investigation of failure mechanisms in integrated vacuum circuits  

NASA Technical Reports Server (NTRS)

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.

Rosengreen, A.

1972-01-01

127

Respiratory failure and mechanical ventilation: Pathophysiology and methods of promoting weaning  

Microsoft Academic Search

Respiratory failure may be manifested either by impaired gas exchange or by impaired ventilatory function. The latter results\\u000a in more severe problems in weaning patients from mechanical ventilation. Ventilatory failure may result from inadequate respiratory\\u000a drive, excessive respiratory workload, inadequate respiratory muscle endurance, or a combination of these factors.\\u000a \\u000a Simple bedside tests of ventilatory function are useful for evaluating the

Jill P. Karpel; Thomas K. Aldrich

1986-01-01

128

Role of Cytokines in the Mechanism of Action of Amlodipine: The PRAISE Heart Failure Trial  

Microsoft Academic Search

Objectives. We sought to determine whether the beneficial effects of amlodipine in heart failure may be mediated by a reduction in tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6) levels. We postulated that TNF-alpha and IL-6 levels may also have predictive value in patients with congestive heart failure (CHF).Background. The molecular mechanism for progression of CHF may involve cytokine overexpression. The

Emile R Mohler; Leif C Sorensen; Jalal K Ghali; Douglas D Schocken; Park W Willis; John A Bowers; Anne B Cropp; Milton L Pressler

1997-01-01

129

Failure of thick, low density air plasma sprayed thermal barrier coatings  

NASA Astrophysics Data System (ADS)

This research was directed at developing fundamental understandings of the variables that influence the performance of air plasma sprayed (APS) yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBC). Focus was placed on understanding how and why each variable influenced the performance of the TBC system along with how the individual variables interacted with one another. It includes research on the effect of surface roughness of NiCoCrAlY bond coats deposited by argon-shrouded plasma spraying, the interdiffusion behavior of bond coats coupled to commercial superalloys, and the microstructural and compositional control of APS topcoats to maximize the coating thicknesses that can be applied without spallation. The specimens used for this research were prepared by Praxair Surface Technologies and have been evaluated using cyclic oxidation and thermal shock tests. TBC performance was sensitive to bond coat roughness with the rougher bond coats having improved cyclic performance than the smoother bond coats. The explanation being the rough bond coat surface hindered the propagation of the delamination cracks. The failure mechanisms of the APS coatings were found to depend on a combination of the topcoat thickness, topcoat microstructure and the coefficient of thermal expansion (CTE) mismatch between the superalloy and topcoat. Thinner topcoats tended to fail at the topcoat/TGO interface due to bond coat oxidation whereas thicker topcoats failed within the topcoat due to the strain energy release rate of the thicker coating exceeding the fracture strength of the topcoat. Properties of free-standing high and conventional purity YSZ topcoats of both a lowdensity (LD) and dense-vertically fissure (DVF) microstructures were evaluated. The densification rate and phase evolution were sensitive to the YSZ purity and the starting microstructure. Increasing the impurity content resulted in enhanced sintering and phase decomposition rates, with the exception of the conventional-purity DVF which exhibited a density decrease during sintering. A combination of the DVF and LD topcoat microstructures (dual TBC) resulted in significant increase in cyclic durability. A 1275 mum thick dual TBC coating was found to have a comparable furnace cyclic life to that of a 100 im LD TBC.

Helminiak, Michael Aaron

130

An autonomous recovery mechanism against optical distribution network failures in EPON  

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

131

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

PubMed Central

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

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

2014-01-01

132

A model of continuum damage mechanics for fatigue failure  

Microsoft Academic Search

This paper describes the development of a generalized model of continuum damage mechanics for fatigue fracture. With the introduction of a new damage effect tensor, the necessary constitutive equations of elasticity and plasticity coupled with damage are for the first instance derived. This is followed by the formulations of fatigue damage dissipative potential function and a fatigue damage criterion which

C. L. Chow; Y. Wei

1991-01-01

133

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

SciTech Connect

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.

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

2009-04-01

134

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

NASA Astrophysics Data System (ADS)

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 steels obtained from scanning electron microscopy (SEM) are used as representative volume elements (RVEs) in the finite element calculations. Ductile failure of the RVE is predicted as plastic strain localization during the deformation process. Systematic computations are conducted on the RVE to quantitatively evaluate the influence of the martensite mechanical properties and volume fraction on the macroscopic mechanical properties of DP steels. These properties include the ultimate tensile strength (UTS), ultimate ductility, and failure modes. The computational results show that, as the strength and volume fraction of the martensite phase increase, the UTS of DP steels increases, but the UTS strain and failure strain decrease. In addition, 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. The methodology and data presented in this article can be used to tailor DP steel design for its intended purposes and desired properties.

Choi, K. S.; Liu, W. N.; Sun, X.; Khaleel, M. A.

2009-04-01

135

Toward Optimum Scale and TBC Adhesion on Single Crystal Superalloys  

NASA Technical Reports Server (NTRS)

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.

Smialek, James L.

1998-01-01

136

Immune mechanisms in acetaminophen-induced acute liver failure.  

PubMed

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

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

2014-12-01

137

Disruption of AMPKalpha1 signaling prevents AICAR-induced inhibition of AS160/TBC1D4 phosphorylation and glucose uptake in primary rat adipocytes.  

PubMed

The aim of this study was to investigate the molecular mechanisms by which AMP-kinase (AMPK) activation inhibits basal and insulin-stimulated glucose uptake in primary adipocytes. Rat epididymal adipocytes were exposed to 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR) for 1 h. Subsequently, basal and insulin-stimulated glucose uptake and the phosphorylation of AMPK, acetyl-CoA carboxylase, Akt, and the Akt substrate of 160 kDa (AS160/TBC1D4) were determined. In order to investigate whether these effects of AICAR were mediated by AMPK activation, these parameters were also assessed in adipocytes either expressing LacZ (control) or a kinase-dead AMPKalpha1 mutant. AICAR increased AMPK activation without affecting basal and insulin-stimulated Akt1/2 phosphorylation on Thr(308) and Ser(473) residues. However, AMPK activation suppressed the phosphorylation of AS160/TBC1D4 and its interaction with the 14-3-3 signal transduction-regulatory protein, which was accompanied by significant reductions in plasma membrane glucose transporter 4 content and glucose uptake under basal and insulin-stimulated conditions. Phosphorylation of Akt substrates glycogen synthase kinase 3alpha and -beta were unaltered by AICAR, indicating that the AMPK-regulatory effects were specific to the AS160/TBC1D4 signaling pathway. Expression of the kinase-dead AMPKalpha1 mutant fully prevented the suppression of AS160/TBC1D4 phosphorylation, plasma membrane glucose transporter 4 content, and the inhibitory effect of AICAR-induced AMPK activation on basal and insulin-stimulated glucose uptake. This study is the first to provide evidence that disruption of AMPKalpha1 signaling prevents the suppressive effects of AMPK activation on AS160/TBC1D4 phosphorylation and glucose uptake, indicating that insulin-signaling steps that are common to white adipose tissue and skeletal muscle regulation of glucose uptake are distinctly affected by AMPK activation. PMID:20501641

Gaidhu, Mandeep P; Perry, Robert L S; Noor, Fawad; Ceddia, Rolando B

2010-07-01

138

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

SciTech Connect

25 {micro}m and a 2 {micro}m thick Al{sub 2}O{sub 3} overlay were deposited by HVOF thermal spray and by sol-gel coating method, respectively, onto to the surface of YSZ coating. Indenter test was employed to investigate the spalling of YSZ with and without Al{sub 2}O{sub 3} overlay after hot corrosion. The results showed that 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. Thick Al{sub 2}O{sub 3} overlay will increase compressive stress and failure in TBC. During next reporting time, Al{sub 2}O{sub 3} overlay will be deposited on the YSZ surface by the composite-sol-gel route (CSG). Hot corrosion tests will be carried out on the TBC.

Scott X. Mao

2005-01-31

139

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

NASA Technical Reports Server (NTRS)

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).

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

2006-01-01

140

Failure mechanism of Hedstroem endodontic files in vivo.  

PubMed

Intracanal fracture of endodontic Hedstroem files (H-files) jeopardizes the outcome of endodontic therapy. The aim of this study was to evaluate the fracture mechanism of H-files after multiple in vivo uses. Five each of size #20 and #25 ISO H-files fractured during clinical use were collected from different dental clinics. Four fractured files of each size and three unused files of each corresponding size were embedded in a resin along their longitudinal axis and after metallographic grinding and polishing studied under an incident light microscope. One specimen in the fractured group was investigated under a scanning electron microscope. Light microscopy results showed that unused files were free of structural defects (cracks, pores, etc.), whereas fractured files demonstrated the presence of many cracks mostly located at the flute depth region. Secondary cracks were identified beyond the fracture plane of fractured files both with a light microscope and a scanning electron microscope. Experimental results demonstrated that fatigue is closely associated with the fracture mechanism of H-files (#20, #25) under clinical conditions. PMID:12067133

Zinelis, Spiros; Margelos, John

2002-06-01

141

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

142

Noninvasive Positive Pressure Ventilation or Conventional Mechanical Ventilation for Neonatal Continuous Positive Airway Pressure Failure  

PubMed Central

Background: The aim of this study was to assess the success rate of nasal intermittent positive pressure ventilation (NIPPV) for treatment of continuous positive airway pressure (CPAP) failure and prevention of conventional ventilation (CV) in preterm neonates. Methods: Since November 2012 to April 2013, a total number of 55 consecutive newborns with gestational ages of 26-35 weeks who had CPAP failure were randomly assigned to one of the two groups. The NIPPV group received NIPPV with the initial peak inspiratory pressure (PIP) of 16-20 cmH2O and frequency of 40-60 breaths/min. The CV group received PIP of 12-20 cmH2O and frequency of 40-60 breaths/min. Results: About 74% of newborns who received NIPPV for management of CPAP failure responded to NIPPV and did not need intubation and mechanical ventilation. Newborns with lower postnatal age at entry to the study and lower 5 min Apgar score more likely had NIPPV failure. In addition, treatment failure was higher in newborns who needed more frequent doses of surfactant. Duration of oxygen therapy was 9.28 days in CV group and 7.77 days in NIPPV group (P = 0.050). Length of hospital stay in CV group and NIPPV groups were 48.7 and 41.7 days, respectively (P = 0.097). Conclusions: NIPPV could decrease the need for intubation and mechanical ventilation in preterm infants with CPAP failure. PMID:25489454

Badiee, Zohreh; Nekooie, Babak; Mohammadizadeh, Majid

2014-01-01

143

A study of failure in bonded lap joints using fracture mechanics  

NASA Astrophysics Data System (ADS)

Although adhesively bonded lap joint has already been widely applied in structures, the strength prediction of the joint is still a challenge. Among many parameters which affect the failure load of the lap joint, the adhesive layer thickness is a very important one. In this study, fracture mechanics is used to analyze the failure mechanism of the lap joint and evaluate the thickness effect on strength of the lap joint. Generally, the adhesive material is softer than the substrates and the crack in the adhesive layer is constrained by the rigid boundaries. The stress field is changed due to the effect of the rigid boundaries. For linear elastic material, the K-Dominance zone is highly reduced and the traditional constant stress intensity factor prediction over-predicts the failure load of the specimens. Constant effective fracture toughness is proposed for better strength prediction by considering of the non-singular stress term ahead of the crack tip. For elastic-plastic material, CTOA is proven to be insensitive to the constraining of the rigid boundaries and can be used as the failure criterion for fracture analysis. Both experimental and FEA simulation show that constant CTOA criterion well predicts the adhesive thickness effect on strength of the DCB specimens for mode I fracture failure. The failure initiation mode of single lap joint is analyzed and the constant CTOA criterion is also proven to be capable to prediction the strength of single lap joint.

Qian, Haiyang

144

Identification of fundamental deformation and failure mechanisms in armor ceramics  

NASA Astrophysics Data System (ADS)

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.

Muller, Andrea Marie

145

Effect of Bond Coat Materials on Thermal Fatigue Failure of EB-PVD Thermal Barrier Coatings  

NASA Astrophysics Data System (ADS)

Effect of MCrAlY bond coat alloy systems on thermal fatigue failure of thermal barrier coatings (TBCs) was investigated, where the TBC specimen consisted of Ni-based superalloy IN738LC substrate, bond coat, and 8 wt.% Y2O3-stabilized ZrO2 (YSZ) top coat. The top coat was fabricated by EB-PVD method with 250 ?m in thickness. Three kinds of MCrAlY alloys were studied as the bond coat material. Employing the originally developed test equipment, thermal fatigue tests were carried out, by applying thermal cycles between 400 and 950°C in air. Special attention was paid not only to the failure life of the TBC specimen, but also the underlying failure mechanisms. The experimental results clearly demonstrated that the effect of MCrAlY bond coat alloys on the thermal fatigue life was very significant. Some discussions were made on the experimental results based on the measurements of mechanical and metallurgical properties of the bond coat alloys: i.e., elastic stiffness, thermal expansion coefficient and high temperature oxidation resistance.

Yamagishi, Satoshi; Okazaki, Masakazu; Sakaguchi, Motoki; Matsubara, Hideaki

146

Investigating Deformation and Failure Mechanisms in Nanoscale Multilayer Metallic Composites  

SciTech Connect

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.

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

2014-10-22

147

Acoustic emission classification for failure prediction due to mechanical fatigue  

NASA Astrophysics Data System (ADS)

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

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

2000-06-01

148

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

SciTech Connect

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

Kim, Choongun

1993-04-01

149

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

NASA Astrophysics Data System (ADS)

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

Buscarnera, G.

2013-12-01

150

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

SciTech Connect

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.

Scott X. Mao

2003-03-10

151

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

NASA Technical Reports Server (NTRS)

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.

Liu, David Donhang; Sampson, Michael J.

2012-01-01

152

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

NASA Technical Reports Server (NTRS)

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.

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

1973-01-01

153

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

E-print Network

of Philosophy Material Science and Engineering Mark R. O'Masta May 2014 #12;APPROVAL SHEET The dissertation for the School of Engineering and Applied Science: James H. Aylor, Dean School of Engineering and Applied ScienceMechanisms of Dynamic Deformation and Failure in Ultra- High Molecular Weight Polyethylene Fiber

Wadley, Haydn

154

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

Microsoft Academic Search

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

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

2008-01-01

155

Continuum damage mechanics analyses of type IV creep failure in ferritic steel crossweld specimens  

Microsoft Academic Search

A major high temperature failure mechanism for weldments in ferritic steel steam pipework is circumferential creep cracking within the region of the heat affected zone, adjacent to the parent material, that experiences the lowest temperatures during the welding process. This is commonly known as type IV cracking. In recent years a number of experimental studies have investigated the occurrence of

I. J Perrin; D. R Hayhurst

1999-01-01

156

Probabilistic investigation of failure mechanisms o f coastal flood defence structures  

Microsoft Academic Search

This paper aims at a probabilistic investigation of various possible failure mechanisms which are often experienced by coastal flood defenc e structures under the impact of sea loads. The factors that affect structure performance are usual ly diverse. In order to undertake an effective assessment of the overall reliability of the coasta l flood defence it is essential to have

J. K. Vrijling

2007-01-01

157

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

NASA Technical Reports Server (NTRS)

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

Fusaro, R. L.

1978-01-01

158

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

NASA Technical Reports Server (NTRS)

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

Fusaro, R. L.

1981-01-01

159

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

NASA Technical Reports Server (NTRS)

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

Fusaro, R. L.

1980-01-01

160

Numerical investigations on the fatigue failure of forging tools due to thermo-mechanical cyclic loading  

Microsoft Academic Search

During service hot forging dies are exposed to a combination of cyclic thermo-mechanical, tribological and chemical loads.\\u000a Besides abrasive and adhesive wear on the die surface, fatigue crack initiation with subsequent fracture is one of the most\\u000a frequent cause of failure. Fatigue cracks in forging dies are caused by local elasto-plastic strains due to cyclic mechanical\\u000a and thermal loads. Aiming

B.-A. Behrens; A. Bouguecha; H. W. Raedt; M. Sc. T. Hadifi

2010-01-01

161

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

NASA Technical Reports Server (NTRS)

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

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

1995-01-01

162

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

NASA Astrophysics Data System (ADS)

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.

Sarva, Sai Sushilkumar

163

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

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

164

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

NASA Technical Reports Server (NTRS)

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

Lathrop, J. W.

1983-01-01

165

Influence of bone volume fraction and architecture on computed large-deformation failure mechanisms in human trabecular bone  

Microsoft Academic Search

Large-deformation bending and buckling have long been proposed as failure mechanisms by which the strength of trabecular bone can be affected disproportionately to changes in bone density, and thus may represent an important aspect of bone quality. We sought here to quantify the contribution of large-deformation failure mechanisms on strength, to determine the dependence of these effects on bone volume

Grant Bevill; Senthil K. Eswaran; Atul Gupta; Panayiotis Papadopoulos; Tony M. Keaveny

2006-01-01

166

Charpy impact properties and failure mechanism of 3D MWK composites at room and cryogenic temperatures  

NASA Astrophysics Data System (ADS)

The charpy impact experiments on the 3D MWK (Multi-axial warp knitted) composites with four different fiber architectures are performed at room (20 °C) and liquid nitrogen temperatures (as low as -196 °C). Macro-Fracture morphology and SEM micrographs are examined to understand the impact deformation and failure mechanism. The results show that the impact properties decrease significantly with the increase of the fiber ply angle at both room and liquid nitrogen temperatures. Meanwhile, the impact energy at liquid nitrogen temperature has been improved significantly than that at room temperature. Moreover, the fiber architecture has remarkable effect on the impact damage and failure patterns of composites at room and liquid nitrogen temperatures. At liquid nitrogen temperature, the matrix solidification and the interfacial adhesion capacity increase greatly, which effectively hinders the stress wave propagation. However, more micro-cracks appear and the brittle failure feature becomes more obvious.

Li, Dian-sen; Jiang, Nan; Zhao, Chuang-qi; Jiang, Lei; Tan, Yi

2014-07-01

167

Large-scale statistical analysis of early failures in Cu electromigration, Part I: Dominating mechanisms  

NASA Astrophysics Data System (ADS)

With continuing scaling of Cu-based metallization, the electromigration (EM) failure risk has remained one of the most important reliability concerns for advanced process technologies. The main factors requiring attention are the activation energy related to the dominating diffusion mechanism, the current exponent as well as the median lifetimes and lognormal standard deviation values of experimentally acquired failure time distributions. In general, the origin and scaling behavior of these parameters are relatively well understood. However, the observation of strong bimodality for the electron up-flow direction in dual-inlaid Cu interconnects has added complexity. The failure voids can occur both within the via ("early" mode) or within the trench ("late" mode). Over the last few years, bimodality has been reported also in down-flow EM, leading to very short lifetimes due to small, slit-shaped voids under vias. These voids, requiring only a very limited amount of mass movement, are generally causing concerns with respect to long-term, reliable chip operation at elevated temperatures. For a more thorough investigation of the aforementioned early failure phenomena, specific test structures were designed based on the Wheatstone Bridge (WSB) technique. The use of these structures enabled an increase in the tested sample size past 800 000 for the 90 nm technology node, allowing a direct analysis of EM failure mechanisms at the single-digit ppm regime. Results indicate that down-flow EM can exhibit bimodality at very small percentage levels, not readily identifiable with standard testing methods. The activation energy for the down-flow early failure mechanism was determined to be 0.83±0.01 eV. Within the small error bounds of this large-scale statistical experiment, this value is deemed to be significantly lower than the usually reported activation energy of 0.90 eV for EM-induced diffusion along Cu/SiCN interfaces. Due to the advantages of the WSB technique, we were also able to expand the experimental temperature range down to 150 °C, coming quite close to typical operating conditions up to 125 °C. As a result of the lowered activation energy, we conclude that the down-flow early failure mode may control the chip lifetime at operating conditions. This publication contains the first part of our large-scale statistical analysis of early failures in Cu EM. In the second part of this study, we will discuss the EM scaling behavior across 90, 65, and 45 nm technologies. In addition, short-length effects will be evaluated using our large-scale, statistical approach. Utilizing the advantages of the WSB technique, the total sample size will be increased past 1.2 million.

Hauschildt, Meike; Gall, Martin; Hernandez, Richard

2010-07-01

168

Friction Stir Weld Failure Mechanisms in Aluminum-Armor Structures Under Ballistic Impact Loading Conditions  

NASA Astrophysics Data System (ADS)

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.

Grujicic, M.; Pandurangan, B.; Arakere, A.; Yen, C.-F.; Cheeseman, B. A.

2013-01-01

169

Analysis of seismic disaster failure mechanism and dam-break simulation of high arch dam  

NASA Astrophysics Data System (ADS)

Based on a Chinese national high arch dam located in a meizoseismal region, a nonlinear numerical analysis model of the damage and failure process of a dam-foundation system is established by employing a 3-D deformable distinct element code (3DEC) and its re-development functions. The proposed analysis model considers the dam-foundation-reservoir coupling effect, influence of nonlinear contact in the opening and closing of the dam seam surface and abutment rock joints during strong earthquakes, and radiation damping of far field energy dissipation according to the actual workability state of an arch dam. A safety assessment method and safety evaluation criteria is developed to better understand the arch dam system disaster process from local damage to ultimate failure. The dynamic characteristics, disaster mechanism, limit bearing capacity and the entire failure process of a high arch dam under a strong earthquake are then analyzed. Further, the seismic safety of the arch dam is evaluated according to the proposed evaluation criteria and safety assessment method. As a result, some useful conclusions are obtained for some aspects of the disaster mechanism and failure process of an arch dam. The analysis method and conclusions may be useful in engineering practice.

Zhang, Jingkui; Zhang, Liaojun

2014-06-01

170

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

PubMed Central

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

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

2013-01-01

171

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

NASA Astrophysics Data System (ADS)

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.

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

2014-08-01

172

A new failure mechanism for clayey-soil foundation beds of structures  

Microsoft Academic Search

A new failure mechanism of beds formed from compressible clayey soils exposes the essence of a concept - the bearing capacity\\u000a of the foundation beds of structures and its interrelation with the development of settlements. It is proposed to distinguish\\u000a four states of a foundation bed with increasing external vertical load in lieu of the three deformation phases known from

A. A. Grigoryan

2009-01-01

173

Failure mechanisms in wood joints bonded with urea-formaldehyde adhesives  

Microsoft Academic Search

Wood joints bonded with urea-formaldehyde (UF) are weakened by cyclic swelling and shrinking. To study the failure mechanisms\\u000a in UF-bonded joints, specimens were bonded with unmodified, modified (amine), or phenol formaldehyde adhesive and subjected\\u000a to accelerated aging. Modification of the adhesive properties increased the cleavage fracture toughness and shear strength\\u000a of bonded joints and improved the resistance of joints to

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

1994-01-01

174

Analysis of failure modes and mechanisms in thermally actuated micromachined relays for harsh environments space applications  

Microsoft Academic Search

This paper reports test results on electrical characteristics, evaluation of design, failure modes, and reliability of thermally actuated, commercially available micromachined relays. The selected parts have been characterized over a wide range of temperatures (from -100°C to +180°C) and varying load conditions (voltages from 10 V to 70 V, and currents from 5 mA to 200 mA). Mechanical integrity of

Alexander Teverovsky; Ashok Sharma

2003-01-01

175

Creep failure of a simply supported beam through a uniaxial Continuum Damage Mechanics model  

Microsoft Academic Search

Summary  Creep failure of elastic-damageable beams is investigated using a simple Continuum Damage Mechanics model. A single-degree-of-freedom\\u000a system is first studied for the bending problem of the visco-damage spring. The strong analogy between the behavior of such\\u000a a system and the one of an imperfection sensitive viscoelastic column, with specific references to the buckling of columns\\u000a is shown. In particular, the

N. Challamel; C. Lanos; C. Casandjian

2007-01-01

176

IMPERMEABLE THIN Al{sub 2}O{sub 3} OVERLAY FOR TBC PROTECTION FROM SULFATE AND VANADATE ATTACK IN GAS TURBINES  

SciTech Connect

To improve the hot corrosion resistance of YSZ thermal barrier coatings, a 25 {micro}m thick Al{sub 2}O{sub 3} overlay were deposited by HVOF thermal spray, respectively, onto to the surface of YSZ coating. In the next reporting period, we will measure or calculate the residue stress within Al{sub 2}O{sub 3} overlay and YSZ coating to study the mechanism of effect of Al{sub 2}O{sub 3} overlay on spalling of YSZ coating. However, due to the thermal expansion mismatch between YSZ coating and Al{sub 2}O{sub 3} overlay, such surface modification using Al{sub 2}O{sub 3} overlay might deteriorate strain tolerance of the TBC. In the present work, in order to investigate the effect of Al{sub 2}O{sub 3} overlay on residual stress developed in the samples during cooling after hot corrosion at high temperature, Finite Element method (FEM) was employed to determine the detailed stress states in the test specimens after cooling. The results showed that there is no high stress concentration at the interface between the YSZ and the bond coat for TBCs system without Al{sub 2}O{sub 3} overlay. On the other hand, the maximum compressive stress with a value of approximately, -330 MPa occurred within the Al{sub 2}O{sub 3} overlay. The maximum tensile stress in YSZ coat near the Al{sub 2}O{sub 3} overlay is in the range of 10-133 MPa. The maximum compressive stress of approximately -160 MPa occurred near the YSZ-bond coat interface. X axis stress play a dominant role in influencing the coating failure and spalling. In the next reporting period, we will study the thickness of Al{sub 2}O{sub 3} overlay on hot corrosion resistance and spalling of YSZ coating.

Scott X. Mao

2004-03-31

177

Damage mechanisms and failure modes of cortical bone under components of physiological loading.  

PubMed

Fatigue damage development in cortical bone was investigated in vitro under different mechanical components of physiological loading including tension, compression, and torsion. During each test, stress and strain data were collected continuously to monitor and statistically determine the occurrence of the primary, secondary, and tertiary stages associated with fatigue and/or creep failure of bone. The resultant microdamage and failure modes were identified by histological and fractographic analysis, respectively. The tensile group demonstrated Mode I cracking and the three classic stages of fatigue and creep suggesting a low crack initiation threshold, steady crack propagation and final failure by coalescence of microcracks. In contrast, the compressive group displayed Mode II cracking and a two-stage fatigue behavior with limited creep suggesting a high crack initiation threshold followed by a sudden fracture. The torsion group also displayed a two-stage fatigue profile but demonstrated extensive damage from mixed mode (Modes II and III) microcracking and predominant time-dependent damage. Thus, fatigue behavior of bone was found to be uniquely related to the individual mechanical components of physiological loading and the latter determined the specific damage mechanisms associated with fatigue fracture. PMID:16140189

George, W T; Vashishth, D

2005-09-01

178

Relationship Between Pre-failure and Post-failure Mechanical Properties of Rock Material of Different Origin  

NASA Astrophysics Data System (ADS)

Under compression, gathering data related to the post-failure part of the stress-strain curve requires stiff servo-controlled testing systems. In unconfined conditions, data related to the post-peak region of the intact rock parameters are not common as pre-peak and peak state parameters of stress-strain behavior. For problems involving rock in the failed state around structures, proper choice of plastic constitutive laws and post-failure parameters is important for the modeling of the failed state. The aim is to relate commonly used intact rock parameters of pre-failure (tangent modulus E i and secant modulus E s) and peak strength ( ? ci) states to parameters of the post-failure state under unconfined compression. Post-failure parameters are the drop modulus ( D pf), representing the slope of the falling portion in brittle state, residual strength ( ? cr), and dilatancy angle ( ?°). Complete stress-strain curves were generated for various intact rock of different origin. Seventy-three post-failure tests were conducted. Samples included in the testing program were chosen to represent rocks of different origin. Specimens of granite, rhyodacite, dunite, quartzite series, glauberite, argillite, marl, and lignite were used in the tests. The results from the pre-failure and peak state testing parts were processed and compared to the post-failure stress-strain parameters. For the estimation of post-failure parameters in terms of the pre-peak and peak states, the functional relations were assessed. It was found that the drop modulus D pf increases with rock strength ? ci, following a power function with an approximate power of two. With an exponential trend, the D pf/ E s ratio increases with decreasing E i/ ? ci ratio. Relations estimating the residual strength and dilatancy from the pre-peak and peak state parameters are in logarithmic and exponential functional forms, respectively.

Tutluo?lu, Levent; Öge, ?brahim Ferid; Karpuz, Celal

2015-01-01

179

Failure mechanisms of polycrystalline diamond compact drill bits in geothermal environments  

SciTech Connect

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.

Hoover, E.R.; Pope, L.E.

1981-09-01

180

How heterogeneity in the shear dilation of a deposit controls the mechanics of breaching slope failure  

NASA Astrophysics Data System (ADS)

Breaching is a type of retrogressive submarine slope failure associated with pore pressure drops in both space and time, and this drop strengthens the failing deposit. Breaching is characterized by a near-vertical failure surface that retreats with a relatively constant velocity, on the order of a millimeter per second. Breaching is controlled by interactions between shear-dilation-generated pore pressure drops and pore pressure dissipation through intergranular fluid flow. Laboratory measurements show that shear dilation in a deposit increases with increasing effective stress ratio between the major principal effective stress and the minor principal effective stress as well as decreasing confining stress. We present a two-dimensional numerical model that indicates how effective stress ratio and confining stress produce spatially varying dilation, affecting the mechanics of breaching. Experimental results show that dilation in a breaching deposit increases with proximity to the failure surface. As a result, the maximum magnitude of pore pressure drop is very close to the failure surface. The numerical model confirms that the sediment release is dominated by pore pressure dissipation through intergranular fluid flow in the horizontal direction. This allows the erosion rate to be treated as a constant in the vertical direction. Numerical model results also show that because dilation decreases with increasing vertical depth, the deposit becomes less stable with depth, suggesting a potential upper limit for the thickness of the deposit undergoing breaching.

You, Yao; Flemings, Peter; Mohrig, David; Germaine, John

2014-11-01

181

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

PubMed Central

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

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

182

Failure modes of plasma-sprayed thermal barrier coatings  

NASA Astrophysics Data System (ADS)

Conventional plasma-sprayed thermal barrier coatings (TBCs) are known to fail by spallation of the yttria-stabilized zirconia (YSZ) topcoat exposing the underlying metal to high temperatures. Failure takes place by crack propagation in the YSZ just above the YSZ/thermally grown oxide (TGO) interface. Compressive stress in the TGO due to thermal expansion coefficient mismatch and oxidation is believed to play a key role in the failure. However, non-destructive measurement of the compressive stress in the TGO has been challenging due to the overlying ceramic top layer. In this study, TBC samples coated to current industrial specifications were thermally cycled to various fractions of their life to determine the failure mechanisms. The technique of Cr3+ piezospectroscopy was successfully applied to the plasma-sprayed samples for the first time in an effort to measure compressive stress in the TGO through the ceramic top layer. In addition, a new nano-grained plasma-sprayed TBC was studied in order to develop a next generation TBC with enhanced properties. Results from observations on cross-sections and spalled surfaces have identified two competing failure mechanisms for TBCs: (1) cracking along asperity tips at the TGO/bond coat interface, and (2) cracking in the ceramic between the asperity tips. TGO residual compressive stress was found to increase in the first 1 to 10 cycles and then decrease with increasing number of cycles. The standard deviation of the stress measurement, which is a measure of damage accumulation in the TGO layer, was found to increase at higher numbers of cycles. Measurement of compressive stress in the TGO using Cr3+ piezo-spectroscopy was limited to YSZ thicknesses of <50 mum due to an impurity present in the YSZ layer. When no impurity was present the limiting thickness was <170 mum due to scattering by microstructural defects such as solute, porosity, and most importantly splat boundaries. A new nano-grained TBC was fabricated with a resulting microstructure that contained no splat boundaries or microcracking. The coating had a high porosity, 22 vol%, and strain relieving vertical microcracks. When compared to conventional plasma-sprayed TBCs, the nano-grained TBCs have a similar cyclic lifetime and failure mechanism but a lower compressive stress in the TGO. Since thermal conductivity is a key physical property of interest in TBCs, a fundamental study was performed to understand the effects of grain boundaries and porosity on the thermal conductivity of YSZ. To that end, monolithic YSZ samples were manufactured using the fugitive sphere method to create tailored porosity utilizing polymer spheres. The grain boundaries were found to have little effect on the thermal conductivity while the porosity was found to have a small effect in the size range studied (5mum--15mum).

Schlichting, Kevin Walter

183

Failure mechanism of shear-wall dominant multi-story buildings  

USGS Publications Warehouse

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.

Yuksel, S.B.; Kalkan, E.

2008-01-01

184

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

Microsoft Academic Search

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

Theodoros Vassilakopoulos; Spyros Zakynthinos; Charis Roussos

2005-01-01

185

Lubrication and failure mechanisms of molybdenum disulfide films. 1: Effect of atmosphere  

NASA Technical Reports Server (NTRS)

Friction, wear, and wear lives of rubbed molybdenum disulfide (MoS2 films applied to sanded 440C HT steel surfaces were evaluated in moist air, dry air, and dry argon. Optical microscope observations were made as a function of sliding distance to determine the effect of moisture and oxygen on the lubricating and failure mechanisms of MoS2 films. In general, the lubrication process consisted of the formation of a thin, metallic colored, coalesced film of MoS2 that flowed between the surfaces in relative motion. In air, failure was due to the transformation of the metallic colored, coalesced films to a black, powdery material. Water in the air appeared to accelerate the transformation rate. In argon, no transformation of MoS2 was observed with the microscope, but cracking and spalling of the coalesced film occurred and resulted in the gradual depletion of the film.

Fusaro, R. L.

1978-01-01

186

On the mechanism of wetting failure during fluid displacement along a moving substrate  

NASA Astrophysics Data System (ADS)

This work investigates the onset of wetting failure for displacement of Newtonian fluids in parallel channels. A hydrodynamic model is developed for planar geometries where an advancing fluid displaces a receding fluid along a moving substrate. The model is evaluated with three distinct approaches: (i) the low-speed asymptotic theory of Cox [J. Fluid Mech. 168, 169-194 (1986)], (ii) a one-dimensional (1D) lubrication approach, and (iii) a two-dimensional (2D) flow model solved with the Galerkin finite element method (FEM). Approaches (ii) and (iii) predict the onset of wetting failure at a critical capillary number Cacrit, which coincides with a turning point in the steady-state solution family for a given set of system parameters. The 1D model fails to accurately describe interface shapes near the three-phase contact line when air is the receding fluid, producing large errors in estimates of Cacrit for these systems. Analysis of the 2D flow solution reveals that strong pressure gradients are needed to pump the receding fluid away from the contact line. A mechanism is proposed in which wetting failure results when capillary forces can no longer support the pressure gradients necessary to steadily displace the receding fluid. The effects of viscosity ratio, substrate wettability, and fluid inertia are then investigated through comparisons of Cacrit values and characteristics of the interface shape. Surprisingly, the low-speed asymptotic theory (i) matches trends computed from (iii) throughout the entire investigated parameter space. Furthermore, predictions of Cacrit from the 2D flow model compare favorably to values measured in experimental air-entrainment studies, supporting the proposed wetting-failure mechanism.

Vandre, E.; Carvalho, M. S.; Kumar, S.

2013-10-01

187

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

E-print Network

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. The increase of spatial correlation FBM for a local load sharing, results in a transition from ductile-like failure characteristics into brittle-like failure. The study identified a global failure criterion based on macroscopic properties (external load and cumulative damage) which is independent of spatial correlation or load redistribution rules. This invariant metric could be applied for early warning of a class of geophysical ruptures.

Jerome Faillettaz; Dani Or

2013-10-22

188

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

An alternative mechanism of pile failure in liquefiable deposits during earthquakes S. BHATTACHARYA*, S. P. G. MADABHUSHI and M. D. BOLTON This paper proposes an alternative mechanism of pile failure in liquefiable deposits during earthquakes. This failure mechanism, based on pile buckling, is formulated by back

Bolton, Malcolm

189

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

DOEpatents

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.

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

190

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

NASA Astrophysics Data System (ADS)

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.

Li, N.; Cheng, Y. M.

2015-01-01

191

A Rab-GAP TBC Domain Protein Binds Hepatitis C Virus NS5A and Mediates Viral Replication?  

PubMed Central

Hepatitis C virus (HCV) is an important cause of liver disease worldwide. Current therapies are inadequate for most patients. Using a two-hybrid screen, we isolated a novel cellular binding partner interacting with the N terminus of HCV nonstructural protein NS5A. This partner contains a TBC Rab-GAP (GTPase-activating protein) homology domain found in all known Rab-activating proteins. As the first described interaction between such a Rab-GAP and a viral protein, this finding suggests a new mechanism whereby viruses may subvert host cell machinery for mediating the endocytosis, trafficking, and sorting of their own proteins. Moreover, depleting the expression of this partner severely impairs HCV RNA replication with no obvious effect on cell viability. These results suggest that pharmacologic disruption of this NS5A-interacting partner can be contemplated as a potential new antiviral strategy against a pathogen affecting nearly 3% of the world's population. PMID:17686842

Sklan, Ella H.; Staschke, Kirk; Oakes, Tina M.; Elazar, Menashe; Winters, Mark; Aroeti, Benjamin; Danieli, Tsafi; Glenn, Jeffrey S.

2007-01-01

192

Frequency-dependent failure mechanisms of nanocrystalline gold interconnect lines under general alternating current  

NASA Astrophysics Data System (ADS)

Thermal fatigue failure of metallization interconnect lines subjected to alternating currents (AC) is becoming a severe threat to the long-term reliability of micro/nanodevices with increasing electrical current density/power. Here, thermal fatigue failure behaviors and damage mechanisms of nanocrystalline Au interconnect lines on the silicon glass substrate have been investigated by applying general alternating currents (the pure alternating current coupled with a direct current (DC) component) with different frequencies ranging from 0.05 Hz to 5 kHz. We observed both thermal fatigue damages caused by Joule heating-induced cyclic strain/stress and electromigration (EM) damages caused by the DC component. Besides, the damage formation showed a strong electrically-thermally-mechanically coupled effect and frequency dependence. At lower frequencies, thermal fatigue damages were dominant and the main damage forms were grain coarsening with grain boundary (GB) cracking/voiding and grain thinning. At higher frequencies, EM damages took over and the main damage forms were GB cracking/voiding of smaller grains and hillocks. Furthermore, the healing effect of the reversing current was considered to elucidate damage mechanisms of the nanocrystalline Au lines generated by the general AC. Lastly, a modified model was proposed to predict the lifetime of the nanocrystalline metal interconnect lines, i.e., that was a competing drift velocity-based approach based on the threshold time required for reverse diffusion/healing to occur.

Luo, X. M.; Zhang, B.; Zhang, G. P.

2014-09-01

193

Failure Predictions for VHTR Core Components using a Probabilistic Contiuum Damage Mechanics Model  

SciTech Connect

The proposed work addresses the key research need for the development of constitutive models and overall failure models for graphite and high temperature structural materials, with the long-term goal being to maximize the design life of the Next Generation Nuclear Plant (NGNP). To this end, the capability of a Continuum Damage Mechanics (CDM) model, which has been used successfully for modeling fracture of virgin graphite, will be extended as a predictive and design tool for the core components of the very high- temperature reactor (VHTR). Specifically, irradiation and environmental effects pertinent to the VHTR will be incorporated into the model to allow fracture of graphite and ceramic components under in-reactor conditions to be modeled explicitly using the finite element method. The model uses a combined stress-based and fracture mechanics-based failure criterion, so it can simulate both the initiation and propagation of cracks. Modern imaging techniques, such as x-ray computed tomography and digital image correlation, will be used during material testing to help define the baseline material damage parameters. Monte Carlo analysis will be performed to address inherent variations in material properties, the aim being to reduce the arbitrariness and uncertainties associated with the current statistical approach. The results can potentially contribute to the current development of American Society of Mechanical Engineers (ASME) codes for the design and construction of VHTR core components.

Fok, Alex

2013-10-30

194

Failure mechanisms of nano-silicon anodes upon cycling: an electrode porosity evolution model.  

PubMed

With a specific capacity of 3600 mA h g(-1), silicon is a promising anode active material for Li-ion batteries (LIBs). However, because of the huge volume changes undergone by Si particles upon (de)alloying with lithium, Si electrodes suffer from rapid capacity fading. A deep understanding of the associated failure mechanisms is necessary to improve these electrochemical performances. To reach this goal, we investigate here nano-Si based electrodes by several characterization techniques. Thanks to all these techniques, many aspects, such as the behaviour of the active material or the solid electrolyte interphase (SEI) and the lithiation mechanisms, are studied upon cycling. A clear picture of the failure mechanisms of nano-Si based electrodes is provided. In particular, by combining Hg analyses, SEM observations of electrode cross-sections, and EIS measurements, we follow the evolution of the porosity within the electrode. For the first time, our results clearly show a real dynamic of the pore size distribution: the first cycles lead to the formation of a micrometric porosity which is not present initially. During the following cycles, these large pores are progressively filled up with SEI products which form continuously at the Si particle surface. Thus, from the 50th cycle, Li(+) ion diffusion is dramatically hindered leading to a strongly heterogeneous lithiation of the electrode and a rapid capacity fading. PMID:25010355

Radvanyi, Etienne; Porcher, Willy; De Vito, Eric; Montani, Alexandre; Franger, Sylvain; Jouanneau Si Larbi, Séverine

2014-08-28

195

User-defined Material Model for Thermo-mechanical Progressive Failure Analysis  

NASA Technical Reports Server (NTRS)

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.

Knight, Norman F., Jr.

2008-01-01

196

Modeling the Deformation-Failure Mechanisms of Thin Hollow Glass Microspheres  

NASA Astrophysics Data System (ADS)

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.

Garza-Cruz, Tryana V.; Nakagawa, Masami

2009-06-01

197

On the failure load and mechanism of polycrystalline graphene by nanoindentation  

PubMed Central

Nanoindentation has been recently used to measure the mechanical properties of polycrystalline graphene. However, the measured failure loads are found to be scattered widely and vary from lab to lab. We perform molecular dynamics simulations of nanoindentation on polycrystalline graphene at different sites including grain center, grain boundary (GB), GB triple junction, and holes. Depending on the relative position between the indenter tip and defects, significant scattering in failure load is observed. This scattering is found to arise from a combination of the non-uniform stress state, varied and weakened strengths of different defects, and the relative location between the indenter tip and the defects in polycrystalline graphene. Consequently, the failure behavior of polycrystalline graphene by nanoindentation is critically dependent on the indentation site, and is thus distinct from uniaxial tensile loading. Our work highlights the importance of the interaction between the indentation tip and defects, and the need to explicitly consider the defect characteristics at and near the indentation site in polycrystalline graphene during nanoindentation. PMID:25500732

Sha, Z. D.; Wan, Q.; Pei, Q. X.; Quek, S. S.; Liu, Z. S.; Zhang, Y. W.; Shenoy, V. B.

2014-01-01

198

On the failure load and mechanism of polycrystalline graphene by nanoindentation  

NASA Astrophysics Data System (ADS)

Nanoindentation has been recently used to measure the mechanical properties of polycrystalline graphene. However, the measured failure loads are found to be scattered widely and vary from lab to lab. We perform molecular dynamics simulations of nanoindentation on polycrystalline graphene at different sites including grain center, grain boundary (GB), GB triple junction, and holes. Depending on the relative position between the indenter tip and defects, significant scattering in failure load is observed. This scattering is found to arise from a combination of the non-uniform stress state, varied and weakened strengths of different defects, and the relative location between the indenter tip and the defects in polycrystalline graphene. Consequently, the failure behavior of polycrystalline graphene by nanoindentation is critically dependent on the indentation site, and is thus distinct from uniaxial tensile loading. Our work highlights the importance of the interaction between the indentation tip and defects, and the need to explicitly consider the defect characteristics at and near the indentation site in polycrystalline graphene during nanoindentation.

Sha, Z. D.; Wan, Q.; Pei, Q. X.; Quek, S. S.; Liu, Z. S.; Zhang, Y. W.; Shenoy, V. B.

2014-12-01

199

On the failure load and mechanism of polycrystalline graphene by nanoindentation.  

PubMed

Nanoindentation has been recently used to measure the mechanical properties of polycrystalline graphene. However, the measured failure loads are found to be scattered widely and vary from lab to lab. We perform molecular dynamics simulations of nanoindentation on polycrystalline graphene at different sites including grain center, grain boundary (GB), GB triple junction, and holes. Depending on the relative position between the indenter tip and defects, significant scattering in failure load is observed. This scattering is found to arise from a combination of the non-uniform stress state, varied and weakened strengths of different defects, and the relative location between the indenter tip and the defects in polycrystalline graphene. Consequently, the failure behavior of polycrystalline graphene by nanoindentation is critically dependent on the indentation site, and is thus distinct from uniaxial tensile loading. Our work highlights the importance of the interaction between the indentation tip and defects, and the need to explicitly consider the defect characteristics at and near the indentation site in polycrystalline graphene during nanoindentation. PMID:25500732

Sha, Z D; Wan, Q; Pei, Q X; Quek, S S; Liu, Z S; Zhang, Y W; Shenoy, V B

2014-01-01

200

DEFORMATION AND FRACTURE OF POORLY CONSOLIDATED MEDIA - Borehole Failure Mechanisms in High-Porosity Sandstone  

SciTech Connect

We investigated failure mechanisms around boreholes and the formation of borehole breakouts in high-porosity sandstone, with particular interest to grain-scale micromechanics of failure leading to the hitherto unrecognized fracture-like borehole breakouts and apparent compaction band formation in poorly consolidated granular materials. We also looked at a variety of drilling-related factors that contribute to the type, size and shape of borehole breakouts. The objective was to assess their effect on the ability to establish correlations between breakout geometry and in situ stress magnitudes, as well as on borehole stability prediction, and hydrocarbon/water extraction in general. We identified two classes of medium to high porosity (12-30%) sandstones, arkosic, consisting of 50-70% quartz and 15 to 50% feldspar, and quartz-rich sandstones, in which quartz grain contents varied from 90 to 100%. In arkose sandstones critical far-field stress magnitudes induced compressive failure around boreholes in the form of V-shaped (dog-eared) breakouts, the result of dilatant intra-and trans-granular microcracking subparallel to both the maximum horizontal far-field stress and to the borehole wall. On the other hand, boreholes in quartz-rich sandstones failed by developing fracture-like breakouts. These are long and very narrow (several grain diameters) tabular failure zones perpendicular to the maximum stress. Evidence provided mainly by SEM observations suggests a failure process initiated by localized grain-bond loosening along the least horizontal far-field stress springline, the packing of these grains into a lower porosity compaction band resembling those discovered in Navajo and Aztec sandstones, and the emptying of the loosened grains by the circulating drilling fluid starting from the borehole wall. Although the immediate several grain layers at the breakout tip often contain some cracked or even crushed grains, the failure mechanism enabled by the formation of the compaction band is largely non-dilatant, a major departure from the dilatant mechanism observed in Tablerock sandstone. The experimental results suggest that unlike our previous assertion, the strength of grain bonding and the mineral composition, rather than the porosity, are major factors in the formation of compaction bands and the ensuing fracture-like breakouts. Some breakout dimensions in all rocks were correlatable to the far-field principal stresses, and could potentially be used (in conjunction with other information) as indicators of their magnitudes. However, we found that several factors can significantly influence breakout geometry. Larger boreholes and increased drilling-fluid flow rates produce longer fracture-like breakouts, suggesting that breakouts in field-scale wellbores could reach considerable lengths. On the other hand, increased drilling-fluid weight and increased drill-bit penetration rate resulted in a decrease in breakout length. These results indicate that breakout growth can be controlled to some degree by manipulating drilling variables. Realizing how drilling variables impact borehole breakout formation is important in understanding the process by which breakouts form and their potential use as indicators of the far-field in situ stress magnitudes and as sources of sand production. As our research indicates, the final breakout size and mechanism of formation can be a function of several variables and conditions, meaning there is still much to be understood about this phenomenon.

Bezalel c. Haimson

2005-06-10

201

Discovery of TBC1D1 as an insulin-, AICAR-, and contraction-stimulated signaling nexus in mouse skeletal muscle.  

PubMed

The Akt substrate of 160 kDa (AS160) is phosphorylated on Akt substrate (PAS) motifs in response to insulin and contraction in skeletal muscle, regulating glucose uptake. Here we discovered a dissociation between AS160 protein expression and apparent AS160 PAS phosphorylation among soleus, tibialis anterior, and extensor digitorum longus muscles. Immunodepletion of AS160 in tibialis anterior muscle lysates resulted in minimal depletion of the PAS band at 160 kDa, suggesting the presence of an additional PAS immunoreactive protein. By immunoprecipitation and mass spectrometry, we identified this protein as the AS160 paralog TBC1D1, an obesity candidate gene regulating GLUT4 translocation in adipocytes. TBC1D1 expression was severalfold higher in skeletal muscles compared with all other tissues and was the dominant protein detected by the anti-PAS antibody at 160 kDa in tibialis anterior and extensor digitorum longus but not soleus muscles. In vivo stimulation by insulin, contraction, and the AMP-activated protein kinase (AMPK) activator AICAR increased TBC1D1 PAS phosphorylation. Using mass spectrometry on TBC1D1 from mouse skeletal muscle, we identified several novel phosphorylation sites on TBC1D1 and found the majority were consensus or near consensus sites for AMPK. Semiquantitative analysis of spectra suggested that AICAR caused greater overall phosphorylation of TBC1D1 sites compared with insulin. Purified Akt and AMPK phosphorylated TBC1D1 in vitro, and AMPK, but not Akt, reduced TBC1D1 electrophoretic mobility. TBC1D1 is a major PAS immunoreactive protein in skeletal muscle that is phosphorylated in vivo by insulin, AICAR, and contraction. Both Akt and AMPK phosphorylate TBC1D1, but AMPK may be the more robust regulator. PMID:18276596

Taylor, Eric B; An, Ding; Kramer, Henning F; Yu, Haiyan; Fujii, Nobuharu L; Roeckl, Katja S C; Bowles, Nicole; Hirshman, Michael F; Xie, Jianxin; Feener, Edward P; Goodyear, Laurie J

2008-04-11

202

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

NASA Astrophysics Data System (ADS)

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.

Sakamoto, Haruo; Hanai, Masahiro

203

Epidemiology of noninvasive mechanical ventilation in acute respiratory failure - a retrospective population-based study  

PubMed Central

Background Noninvasive mechanical ventilation (NIV) is a front-line therapy for the management of acute respiratory failure (ARF) in the intensive care units. However, the data on factors and outcomes associated with the use of NIV in ARF patients is lacking. Therefore, we aimed to determine the utilization of NIV for ARF in a population-based study. Methods We conducted a populated-based retrospective cohort study, where in all consecutively admitted adults (?18?years) with ARF from Olmsted County, Rochester, MN, at the Mayo Clinic medical and surgical ICUs, during 2006 were included. Patients without research authorization or on chronic NIV use for sleep apnea were excluded. Results Out of 1461 Olmsted County adult residents admitted to the ICUs in 2006, 364 patients developed ARF, of which 146 patients were initiated on NIV. The median age in years was 75 (interquartile range, 60–84), 48% females and 88.7% Caucasians. Eighteen patients (12%) were on Continuous Positive Airway Pressure (CPAP) mode and 128 (88%) were on noninvasive intermittent positive-pressure ventilation (NIPPV) mode. Forty-six (10%) ARF patients were put on NIV for palliative strategy to alleviate dyspnea. Seventy-six ARF patients without treatment limitation were given a trial of NIV and 49 patients succeeded, while 27 had to be intubated. Mortality was similar between the patients initially supported with NIV versus invasive mechanical ventilation (33% vs 22%, P=0.289). In the multivariate analysis, the development of acute respiratory distress syndrome (ARDS) and higher APACHE III scores were associated with the failure of initial NIV treatment. Conclusions Our results have important implications for a future planning of NIV in a suburban US community with high access to critical care services. The higher APACHE III scores and the development of ARDS are associated with the failure of initial NIV treatment. PMID:23570601

2013-01-01

204

A procedure for combining acoustically induced and mechanically induced loads (first passage failure design criterion)  

NASA Technical Reports Server (NTRS)

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.

Crowe, D. R.; Henricks, W.

1983-01-01

205

Mechanisms and Clinical Consequences of Untreated Central Sleep Apnea in Heart Failure  

PubMed Central

Central sleep apnea (CSA) is a highly prevalent, though often unrecognized, comorbidity in patients with heart failure (HF). Data from HF population studies suggest that it may present in 30% to 50% of HF patients. CSA is recognized as an important contributor to the progression of HF and to HF-related morbidity and mortality. Over the past 2 decades, an expanding body of research has begun to shed light on the pathophysiologic mechanisms of CSA. Armed with this growing knowledge base, the sleep, respiratory, and cardiovascular research communities have been working to identify ways to treat CSA in HF with the ultimate goal of improving patient quality of life and clinical outcomes. In this paper, we examine the current state of knowledge about the mechanisms of CSA in HF and review emerging therapies for this disorder. PMID:25572513

Costanzo, Maria Rosa; Khayat, Rami; Ponikowski, Piotr; Augostini, Ralph; Stellbrink, Christoph; Mianulli, Marcus; Abraham, William T.

2015-01-01

206

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

NASA Astrophysics Data System (ADS)

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.

Liu, C.; Thompson, D. G.

2015-01-01

207

Heart failure with preserved ejection fraction: mechanisms, clinical features, and therapies.  

PubMed

The clinical syndrome comprising heart failure (HF) symptoms but with a left ventricular ejection fraction (EF) that is not diminished, eg, HF with preserved EF, is increasingly the predominant form of HF in the developed world, and soon to reach epidemic proportions. It remains among the most challenging of clinical syndromes for the practicing clinician and scientist alike, with a multitude of proposed mechanisms involving the heart and other organs and complex interplay with common comorbidities. Importantly, its morbidity and mortality are on par with HF with reduced EF, and as the list of failed treatments continues to grow, HF with preserved EF clearly represents a major unmet medical need. The field is greatly in need of a more unified approach to its definition and view of the syndrome that engages integrative and reserve pathophysiology beyond that related to the heart alone. We need to reflect on prior treatment failures and the message this is providing, and redirect our approaches likely with a paradigm shift in how the disease is viewed. Success will require interactions between clinicians, translational researchers, and basic physiologists. Here, we review recent translational and clinical research into HF with preserved EF and give perspectives on its evolving demographics and epidemiology, the role of multiorgan deficiencies, potential mechanisms that involve the heart and other organs, clinical trials, and future directions. PMID:24951759

Sharma, Kavita; Kass, David A

2014-06-20

208

Development, Testing, and Failure Mechanisms of a Replicative Ice Phase Change Material Heat Exchanger  

NASA Technical Reports Server (NTRS)

Phase change materials (PCM) may be useful for thermal control systems that involve cyclical heat loads or cyclical thermal environments such as Low Earth Orbit (LEO) and Low Lunar Orbit (LLO). Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. One advantage that PCM's have over evaporators in this scenario is that they do not use a consumable. Wax PCM units have been baselined for the Orion thermal control system and also provide risk mitigation for the Altair Lander. However, the use of water as a PCM has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. An ice PCM heat exchanger that replicates the thermal energy storage capacity of an existing wax PCM unit was fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion are investigated. This paper presents the results to date of this investigation. Nomenclature

Leimkuehler, Thomas O.; Hansen, Scott; Stephan, Ryan A.

2010-01-01

209

Testing and Failure Mechanisms of Ice Phase Change Material Heat Exchangers  

NASA Technical Reports Server (NTRS)

Phase change materials (PCM) may be useful for thermal control systems that involve cyclical heat loads or cyclical thermal environments such as specific spacecraft orientations in Low Earth Orbit (LEO) and low beta angle Low Lunar Orbit (LLO). Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. One advantage that PCM s have over evaporators in this scenario is that they do not use a consumable. The use of water as a PCM rather than the more traditional paraffin wax has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. A number of ice PCM heat exchangers were fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion were investigated. This paper presents the results of testing that occurred from March through September of 2010 and builds on testing that occurred during the previous year.

Leimkuehler, Thomas O.; Stephan, Ryan A.; Hawkins-Reynolds, Ebony

2011-01-01

210

Development, Testing, and Failure Mechanisms of a Replicative Ice Phase Change Material Heat Exchanger  

NASA Technical Reports Server (NTRS)

Phase change materials (PCM) may be useful for thermal control systems that involve cyclical heat loads or cyclical thermal environments such as Low Earth Orbit (LEO) and Low Lunar Orbit (LLO). Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. One advantage that PCM s have over evaporators in this scenario is that they do not use a consumable. Wax PCM units have been baselined for the Orion thermal control system and also provide risk mitigation for the Altair Lander. However, the use of water as a PCM has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. An ice PCM heat exchanger that replicates the thermal energy storage capacity of an existing wax PCM unit was fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion are investigated. This paper presents the results to date of this investigation.

Leimkuehler, Thomas O.; Hansen, Scott; Stephan, Ryan A.

2009-01-01

211

Testing and Failure Mechanisms of Ice Phase Change Material Heat Exchangers  

NASA Technical Reports Server (NTRS)

Phase change materials (PCM) may be useful for thermal control systems that involve cyclical heat loads or cyclical thermal environments such as Low Earth Orbit (LEO) and Low Lunar Orbit (LLO). Thermal energy can be stored in the PCM during peak heat loads or in adverse thermal environments. The stored thermal energy can then be released later during minimum heat loads or in more favorable thermal environments. One advantage that PCM s have over evaporators in this scenario is that they do not use a consumable. The use of water as a PCM rather than the more traditional paraffin wax has the potential for significant mass reduction since the latent heat of formation of water is approximately 70% greater than that of wax. One of the potential drawbacks of using ice as a PCM is its potential to rupture its container as water expands upon freezing. In order to develop a space qualified ice PCM heat exchanger, failure mechanisms must first be understood. Therefore, a methodical experimental investigation has been undertaken to demonstrate and document specific failure mechanisms due to ice expansion in the PCM. A number of ice PCM heat exchangers were fabricated and tested. Additionally, methods for controlling void location in order to reduce the risk of damage due to ice expansion were investigated. This paper presents the results of testing that occurred from March through September of 2010 and builds on testing that occurred during the previous year.

Leimkuehler, Thomas O.; Stephan, Ryan A.; Hawkins-Reynolds, Ebony

2010-01-01

212

Central mechanisms for exercise training-induced reduction in sympatho-excitation in chronic heart failure.  

PubMed

The control of sympathetic outflow in the chronic heart failure (CHF) state is markedly abnormal. Patients with heart failure present with increased plasma norepinephrine and increased sympathetic nerve activity. The mechanism for this sympatho-excitation is multiple and varied. Both depression in negative feedback sensory control mechanisms and augmentation of excitatory reflexes contribute to this sympatho-excitation. These include the arterial baroreflex, cardiac reflexes, arterial chemoreflexes and cardiac sympathetic afferent reflexes. In addition, abnormalities in central signaling in autonomic pathways have been implicated in the sympatho-excitatory process in CHF. These mechanisms include increases in central Angiotensin II and the Type 1 receptor, increased in reactive oxygen stress, upregulation in glutamate signaling and NR1 (N-methyl-D-aspartate subtype 1) receptors and others. Exercise training in the CHF state has been shown to reduce sympathetic outflow and result in increased survival and reduced cardiac events. Exercise training has been shown to reduce central Angiotensin II signaling including the Type 1 receptor and reduce oxidative stress by lowering the expression of many of the subunits of NADPH oxidase. In addition, there are profound effects on the central generation of nitric oxide and nitric oxide synthase in sympatho-regulatory areas of the brain. Recent studies have pointed to the balance between Angiotensin Converting Enzyme (ACE) and ACE2, translating into Angiotensin II and Angiotensin 1-7 as important regulators of sympathetic outflow. These enzymes appear to be normalized following exercise training in CHF. Understanding the precise molecular mechanisms by which exercise training is sympatho-inhibitory will uncover new targets for therapy. PMID:25458427

Haack, Karla K V; Zucker, Irving H

2015-03-01

213

Cortical and Spinal Mechanisms of Task Failure of Sustained Submaximal Fatiguing Contractions  

PubMed Central

In this and the subsequent companion paper, results are presented that collectively seek to delineate the contribution that supraspinal circuits have in determining the time to task failure (TTF) of sustained submaximal contractions. The purpose of this study was to compare adjustments in supraspinal and spinal excitability taken concurrently throughout the performance of two different fatigue tasks with identical mechanical demands but different TTF (i.e., force-matching and position-matching tasks). On separate visits, ten healthy volunteers performed the force-matching or position-matching task at 15% of maximum strength with the elbow flexors to task failure. Single-pulse transcranial magnetic stimulation (TMS), paired-pulse TMS, paired cortico-cervicomedullary stimulation, and brachial plexus electrical stimulation were delivered in a 6-stimuli sequence at baseline and every 2–3 minutes throughout fatigue-task performance. Contrary to expectations, the force-matching task TTF was 42% shorter (17.5±7.9 min) than the position-matching task (26.9±15.11 min; p<0.01); however, both tasks caused the same amount of muscle fatigue (p?=?0.59). There were no task-specific differences for the total amount or rate of change in the neurophysiologic outcome variables over time (p>0.05). Therefore, failure occurred after a similar mean decline in motorneuron excitability developed (p<0.02, ES?=?0.35–0.52) coupled with a similar mean increase in measures of corticospinal excitability (p<0.03, ES?=?0.30–0.41). Additionally, the amount of intracortical inhibition decreased (p<0.03, ES?=?0.32) and the amount of intracortical facilitation (p>0.10) and an index of upstream excitation of the motor cortex remained constant (p>0.40). Together, these results suggest that as fatigue develops prior to task failure, the increase in corticospinal excitability observed in relationship to the decrease in spinal excitability results from a combination of decreasing intracortical inhibition with constant levels of intracortical facilitation and upstream excitability that together eventually fail to provide the input to the motor cortex necessary for descending drive to overcome the spinal cord resistance, thereby contributing to task failure. PMID:24667484

Williams, Petra S.; Hoffman, Richard L.; Clark, Brian C.

2014-01-01

214

Effects of mechanical layering on magmatic reservoir failure and magma propagation within the Venusian lithosphere  

NASA Astrophysics Data System (ADS)

Failure of magmatic reservoirs and propagation of magmas is controlled in part by the state of stress within the lithosphere. Such stresses are induced by a range of loadings (e.g., gravitational, magmatic and tectonic). In addition, the response of the lithosphere to these loadings depends on its physical properties. Magmatic reservoirs on planetary bodies have been studied using homogeneous lithosphere mainly composed of crustal material. However, planetary lithospheres may include substantial fractions of mantle material, with greater stiffness and density than those typical of crust. The mechanics of a heterogeneous lithosphere may influence the failure of a magmatic reservoir and the propagation of the magma. To explore this scenario, we created two-layered axisymmetric elastic models made of mantle and crustal components using the COMSOL Multiphysics finite element package, in which a stiffer and denser mantle is underlying a softer and lighter crust. A spherical reservoir was created at the contact between the two layers. In these models, we analyzed the magmatic reservoir stability, the amount of overpressure needed to reach failure and the type of resulting intrusions within the two-layered lithosphere for three distinct environments: 1- lithostatic; 2- upward flexure due to a rising mantle plume; and 3- downward flexure due to a basaltic shield volcano. The results show that in most cases, magmatic reservoirs fail below the mantle-crust contact. The resulting failure is driven by the in-plane stress tangential to the chamber, favoring lateral sill injections. In the flexure cases, magma chambers may become unstable (i.e., require no additional overpressure to fail) depending on the crust/mantle ratio. In some cases, we observed that the magma chambers failure can be driven by the (out-of-plane) hoop stress favoring radial dike intrusions. The stability of magmatic reservoirs and the type and orientation of magmatic intrusions on Venus are influenced by the state of stress and heterogeneities within the lithosphere. Using our result, we can infer the potential crust/mantle ratios of the Venusian lithosphere in a particular tectonic environment in order to sustain stable and viable magmatic reservoirs and generate radial dikes as observed on the surface of Venus.

Le Corvec, N.; McGovern, P. J.

2013-12-01

215

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

PubMed Central

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

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

2015-01-01

216

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

PubMed

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

Zhang, Ren-Hui; Wang, Li-Ping; Lu, Zhi-Bin

2015-01-01

217

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

SciTech Connect

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.

S Park; W Jin; S Shoelson

2011-12-31

218

Failure analysis of porcupine quills under axial compression reveals their mechanical response during buckling.  

PubMed

Porcupine quills are natural structures formed by a thin walled conical shell and an inner foam core. Axial compression tests, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR) were all used to compare the characteristics and mechanical properties of porcupine quills with and without core. The failure mechanisms that occur during buckling were analyzed by scanning electron microscopy (SEM), and it was found that delamination buckling is mostly responsible for the decrease in the measured buckling stress of the quills with regard to predicted theoretical values. Our analysis also confirmed that the foam core works as an energy dissipater improving the mechanical response of an empty cylindrical shell, retarding the onset of buckling as well as producing a step wise decrease in force after buckling, instead of an instantaneous decrease in force typical for specimens without core. Cell collapse and cell densification in the inner foam core were identified as the key mechanisms that allow for energy absorption during buckling. PMID:25123434

Torres, Fernando G; Troncoso, Omar P; Diaz, John; Arce, Diego

2014-11-01

219

Analysis of the thermo-mechanical fatigue response of metal matrix composite laminates with interfacial normal and shear failure  

SciTech Connect

In this study, an analysis of the thermo-mechanical fatigue (TMF) behavior of titanium-based metal matrix composites (MMCs) is accomplished by employing a modified method of cells micromechanics model coupled with a fiber/matrix interfacial failure scheme and the Bodner-Partom unified constitutive theory. Interfacial failure is based on a probabilistic failure criterion which considers the equivalent interfacial compliance to be a function of the interfacial stress. In this approach, the effects of both normal and shear failure of the interface have been included. MMC laminates with angle-ply and quasi-isotropic layups are analyzed for monotonic, cyclic, and thermo-mechanical fatigue loads, and where it is appropriate, comparisons with experimental data are made.

Robertson, D.D.; Mall, S. [Air Force Inst. of Tech., Wright-Patterson AFB, OH (United States). Dept. of Aeronautics and Astronautics

1996-12-31

220

Simulation of localization failure with strain-gradient-enhanced damage mechanics  

NASA Astrophysics Data System (ADS)

Strain gradient implies an important characteristic in localized damage deformation, which can be observed in the softening state of brittle materials, and strain gradients constitute the basic behaviours of localization failure area of the materials. The most important point in strain gradient is its damaging function including an internal length scale, which can be used to express the scale effects of mechanical responses of brittle rock mass. By extending the strain gradient theory and introducing an intrinsic material length scale into the constitutive law, the authors develop an isotropic damage model as well as a micro-crack-based anisotropic damage model for rock-like materials in this paper. The proposed models were used to simulate the damage localization under uniaxial tension and plain strain compression, respectively. The simulated results well illustrated the potential of these models in dealing with the well-known mesh-sensitivity problem in FEM. In the computation, elements with C1 continuity have been implemented to incorporate the proposed models for failure localization. When regular rectangle elements are encountered, the coupling between finite difference method (FDM) and conventional finite element method (FEM) is used to avoid large modification to the existing FEM code, and to obtain relatively higher efficiency and reasonably good accuracy. Application of the anisotropic model to the 3D-non-linear FEM analysis of Ertan arch dam has been conducted and the results of its numerical simulation coincide well with those from the failure behaviours obtained by Ertan geophysical model test. In this paper, new applications of gradient theories and models for a feasible approach to simulate localized damage in brittle materials are presented.

Zhou, Weiyuan; Zhao, Jidong; Liu, Yuangao; Yang, Qiang

2002-07-01

221

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

NASA Astrophysics Data System (ADS)

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.

Lollino, Piernicola; Mezzina, Giuseppe; Cotecchia, Federica

2014-05-01

222

Microstructural studies on failure mechanisms in thermo-mechanical fatigue of repaired DS R80 and IN 738 Superalloys  

NASA Astrophysics Data System (ADS)

Directionally solidified Rene 80 (DS R80) and polycrystalline Inconel 738(IN 738) Superalloys were tested in thermo-mechanical fatigue (TMF) over the temperature range of 500-900°C and plastic strain range from 0.1 to 0.8% using a DSI Gleeble thermal simulator. Thermo-mechanical testing was carried out on the parent material (baseline) in the conventional solution treated and aged condition (STA), as well as gas tungsten arc welded (GTAW) with an IN-738 filler, followed by solution treatment and ageing. Comparison of the baseline alloy microstructure with that of the welded and heat treated alloy showed that varying crack initiation mechanisms, notably oxidation by stress assisted grain boundary oxidation, grain boundary MC carbides fatigue crack initiation, fatigue crack initiation from sample surfaces, crack initiation from weld defects and creep deformation were operating, leading to different “weakest link” and failure initiation points. The observations from this study show that the repaired samples had extra crack initiation sites not present in the baseline, which accounted for their occasional poor fatigue life. These defects include lack of fusion between the weld and the base metal, fusion zone cracking, and heat affected zone microfissures.

Abrokwah, Emmanuel Otchere

223

Failure modes and wear mechanisms of M35 high-speed steel drills when machining inconel 901  

Microsoft Academic Search

High-Speed Steel drills (M35) with different drill-point geometries were used to machine a nickel base, Inconel 901, superalloy at various combinations of cutting speed and feed in order to assess their overall performance and to identify their failure modes as well as the wear mechanisms responsible for drill failure. Test results show a general reduction in drill performance at higher

E. O. Ezugwu; C. J. Lai

1995-01-01

224

Conventional knockout of Tbc1d1 in mice impairs insulin- and AICAR-stimulated glucose uptake in skeletal muscle.  

PubMed

In the obesity-resistant SJL mouse strain, we previously identified a naturally occurring loss-of-function mutation in the gene for Tbc1d1. Characterization of recombinant inbred mice that carried the Tbc1d1(SJL) allele on a C57BL/6J background indicated that loss of TBC1D1 protects from obesity, presumably by increasing the use of fat as energy source. To provide direct functional evidence for an involvement of TBC1D1 in energy substrate metabolism, we generated and characterized conventional Tbc1d1 knockout mice. TBC1D1-deficient mice showed moderately reduced body weight, decreased respiratory quotient, and an elevated resting metabolic rate. Ex vivo analysis of intact isolated skeletal muscle revealed a severe impairment in insulin- and AICAR-stimulated glucose uptake in glycolytic extensor digitorum longus muscle and a substantially increased rate of fatty acid oxidation in oxidative soleus muscle. Our results provide direct evidence that TBC1D1 plays a major role in glucose and lipid utilization, and energy substrate preference in skeletal muscle. PMID:23892475

Dokas, Janine; Chadt, Alexandra; Nolden, Tobias; Himmelbauer, Heinz; Zierath, Juleen R; Joost, Hans-Georg; Al-Hasani, Hadi

2013-10-01

225

Mechanisms of force failure during repetitive maximal efforts in a human upper airway muscle.  

PubMed

The upper airway respiratory muscles play an important role in the regulation of airway resistance, but surprisingly little is known about their contractile properties and endurance performance. We developed a technique that allows measurement of force and the electromyogram (EMG) of human nasal dilator muscles (NDMs). Endurance performance was quantified by measuring NDM "flaring" force and EMG activity as healthy human subjects performed 10 s maximal voluntary contractions (MVCs), separated by 10 s rest, until the area under the force curve fell to 50% MVC (the time limit of the fatigue task, Tlim), which was reached in 34.2 +/- 3.1 contractions (685.0 +/- 62.3 s). EMG activity was unchanged except at Tlim, where it averaged 78.7 +/- 3.6% of pretest activity (P < 0.01). M-wave amplitude did not change, suggesting that neuromuscular propagation was not impaired. MVC force increased to 80% of the pretest level within 10 min of recovery but twitch force failed to recover, suggesting low-frequency fatigue. The data suggest that a failure of the nervous system to excite muscle could explain at most only a small fraction of the NDM force loss during an intermittent fatigue task, and then only at Tlim. Thus, the majority of the force failure during this task is due to impairment of mechanisms that reside within the muscle fibers. PMID:12115954

DelloRusso, Christiana; Khurana, Nilam; Rankin, Lucinda; Sullivan, Jenna; Fregosi, Ralph F

2002-07-01

226

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

PubMed

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

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

2006-06-20

227

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

PubMed Central

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

Bažant, Zden?k P.; Pang, Sze-Dai

2006-01-01

228

Failure mechanics in low-velocity impacts on thin composite plates  

NASA Technical Reports Server (NTRS)

Eight-ply quasi-isotropic composite plates of Thornel 300 graphite in Narmco 5208 epoxy resin (T300/5208) were tested to establish the degree of equivalence between low-velocity impact and static testing. Both the deformation and failure mechanics under impact were representable by static indentation tests. Under low-velocity impacts such as tool drops, the dominant deformation mode of the plates was the first, or static, mode. Higher modes are excited on contact, but they decay significantly by the time the first-mode load reaches a maximum. The delamination patterns were observed by X-ray analysis. The areas of maximum delamination patterns were observed by X-ray analysis. The areas of maximum delamination coincided with the areas of highest peel stresses. The extent of delamination was similar for static and impact tests. Fiber failure damage was established by tensile tests on small fiber bundles obtained by deplying test specimens. The onset of fiber damage was in internal plies near the lower surface of the plates. The distribution and amount of fiber damage was similar fo impact and static tests.

Elber, W.

1983-01-01

229

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

PubMed Central

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

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

230

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

PubMed

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 Mg(2+) (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 Mg(2+) 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

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

2014-11-15

231

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

NASA Technical Reports Server (NTRS)

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

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

2008-01-01

232

[Non-invasive mechanical ventilation in the treatment of acute heart failure].  

PubMed

When acute heart failure progresses and there is acute cardiogenic pulmonary edema, routine therapeutic measures should be accompanied by other measures that help to correct oxygenation of the patient. The final and most drastic step is mechanical ventilation. Non-invasive ventilation has been developed in the last few years as a method that attempts to improve oxygenation without the need for intubation, thus, in theory, reducing morbidity and mortality in these patients. The present article describes the controversies surrounding the results of this technique and discusses its indications. The article also discusses how to start non-invasive ventilation in patients with acute pulmonary edema from a practical point of view. PMID:24930085

Alfonso Megido, Joaquín; González Franco, Alvaro

2014-03-01

233

Finite Element Modeling of the Different Failure Mechanisms of a Plasma Sprayed Thermal Barrier Coatings System  

NASA Astrophysics Data System (ADS)

A new finite element model is used to investigate catastrophic failures of a thermal barrier coatings system due to crack propagation along the interfaces between the ceramic top-coat, thermally grown oxide, and bond-coat layers, as well as between the lamellas structure of the ceramic layer. The thermo-mechanical model is designed to take into account a non-homogenous temperature distribution and the effects of the residual stresses generated during the coating process. Crack propagation is simulated using the contact tool "Debond" present in the ABAQUS finite element code. Simulations are performed with a geometry corresponding to similar or dissimilar amplitudes of asperity, and for different thicknesses of the oxide layer. The numerical results have shown that crack evolution depends crucially on the ratio of the loading rate caused by growth and swelling of the oxide layer and also on the interface roughness obtained during the spraying of coatings.

Ranjbar-Far, M.; Absi, J.; Mariaux, G.

2012-12-01

234

A mechanics framework for a progressive failure methodology for laminated composites  

NASA Technical Reports Server (NTRS)

A laminate strength and life prediction methodology has been postulated for laminated composites which accounts for the progressive development of microstructural damage to structural failure. A damage dependent constitutive model predicts the stress redistribution in an average sense that accompanies damage development in laminates. Each mode of microstructural damage is represented by a second-order tensor valued internal state variable which is a strain like quantity. The mechanics framework together with the global-local strategy for predicting laminate strength and life is presented in the paper. The kinematic effects of damage are represented by effective engineering moduli in the global analysis and the results of the global analysis provide the boundary conditions for the local ply level stress analysis. Damage evolution laws are based on experimental results.

Harris, Charles E.; Allen, David H.; Lo, David C.

1989-01-01

235

The unsteady nature of sea cliff retreat due to mechanical abrasion, failure and comminution feedbacks  

NASA Astrophysics Data System (ADS)

Sea cliff retreat is often linked to large waves, heavy precipitation and seismic events, but the specific operative mechanics have not been well constrained. In particular, what is the role of mechanical abrasion by beach sediments in cliff/platform evolution and how does it relate to the episodic nature of cliff retreat observed at certain locations? Here we present a simple, numerical model of sea cliff retreat that incorporates mechanical abrasion of a basal notch, threshold-controlled failure of the cantilevered block, and a feedback mechanism wherein retreat is dependent on the rate of sediment comminution within the surf zone. Using shore platform and cliff characteristics found in two coastal settings (the central California coast and the English North Sea coast), the model produces retreat rates comparable to those observed via field measurements. The highest retreat rates coincide with the steepest shore platforms and increasing wave height. Steeper platforms promote wave access to the cliff toe and, correspondingly, the receding cliff face produces additional accommodation space for the platform beach, preserving the erosive efficacy of the beach sediments. When exposed to energetic wave forcing, the slope of the inner platform segment controls retreat rates for concave platforms, whereas the slope of the outer platform segment exerts greater control for convex platforms. Platform beaches approached a long-term dynamic equilibrium on the concave profiles, leading to more consistent and steady retreat. Platform beaches were ephemeral on convex profiles, mirroring observed sand wave (Ord) migration on the Holderness coast, UK. These findings agree with previous field observations and support mechanical abrasion as a viable cause of temporal heterogeneity in cliff retreat rate for both coastlines.

Kline, Shaun W.; Adams, Peter N.; Limber, Patrick W.

2014-08-01

236

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

E-print Network

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 ...

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

2011-01-01

237

Failure assessment diagrams for cracks in welds with mismatched mechanical properties  

SciTech Connect

The case of a crack located in a weld with a mismatch in mechanical properties from the surrounding base material is addressed. It is shown that both over- and under-matching of yield stress and differences in hardening behavior between the weld and base materials can be treated by defining an equivalent stress-strain curve. This curve depends on geometry, crack size and the mechanical properties of both the weld and base materials. Having defined an equivalent stress-strain curve, a failure assessment curve is constructed using the method of R6 Option 2. Validation for the approach has been addressed by comparison with finite-element results for center-cracked plates, three point bend specimens and cylindrical geometries. A selection of the results for cylindrical geometries is given. An important input to the definition of the equivalent stress-strain curve is the limit load of the mismatched geometry and this is discussed. Conventional assessment methods based on the use of the tensile properties of the weaker material in the weld are also discussed.

Lei, Y. [East China Univ. of Science and Technology, Shanghai (China); Ainsworth, R.A. [Nuclear Electric plc, Barnwood (United Kingdom)

1996-12-01

238

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

NASA Astrophysics Data System (ADS)

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.

Chen, Ying

239

Metaiodobenzylguanidine (/sup 131/I) scintigraphy detects impaired myocardial sympathetic neuronal transport function of canine mechanical-overload heart failure  

SciTech Connect

In heart failure secondary to chronic mechanical overload, cardiac sympathetic neurons demonstrate depressed catecholamine synthetic and transport function. To assess the potential of sympathetic neuronal imaging for detection of depressed transport function, serial scintigrams were acquired after the intravenous administration of metaiodobenzylguanidine (/sup 131/I) to 13 normal dogs, 3 autotransplanted (denervated) dogs, 5 dogs with left ventricular failure, and 5 dogs with compensated left ventricular hypertrophy due to a surgical arteriovenous shunt. Nine dogs were killed at 14 hours postinjection for determination of metaiodobenzylguanidine (/sup 131/I) and endogenous norepinephrine content in left atrium, left ventricle, liver, and spleen. By 4 hours postinjection, autotransplanted dogs had a 39% reduction in mean left ventricular tracer accumulation, reflecting an absent intraneuronal tracer pool. Failure dogs demonstrated an accelerated early mean left ventricular tracer efflux rate (26.0%/hour versus 13.7%/hour in normals), reflecting a disproportionately increased extraneuronal tracer pool. They also showed reduced late left ventricular and left atrial concentrations of tracer, consistent with a reduced intraneuronal tracer pool. By contrast, compensated hypertrophy dogs demonstrated a normal early mean left ventricular tracer efflux rate (16.4%/hour) and essentially normal late left ventricular and left atrial concentrations of tracer. Metaiodobenzylguanidine (/sup 131/I) scintigraphic findings reflect the integrity of the cardiac sympathetic neuronal transport system in canine mechanical-overload heart failure. Metaiodobenzylguanidine (/sup 123/I) scintigraphy should be explored as a means of early detection of mechanical-overload heart failure in patients.

Rabinovitch, M.A.; Rose, C.P.; Rouleau, J.L.; Chartrand, C.; Wieland, D.M.; Lepanto, L.; Legault, F.; Suissa, S.; Rosenthall, L.; Burgess, J.H.

1987-12-01

240

Optical performance of the TBC-2 solar collector before and after the 1993 mirror lustering  

SciTech Connect

In 1993, the mirror facets of one of Sandia`s point-focusing solar collectors, the Test Bed Concentrator {number_sign}2 (TBC-2), were reconditioned. The concentrator`s optical performance was evaluated before and after this operation. This report summarizes and compares the results of these tests. The tests demonstrated that the concentrator`s total power and peak flux were increased while the overall flux distribution in the focal plane remained qualitatively the same.

Houser, R.; Strachan, J. [Sandia National Labs., Albuquerque, NM (United States). Solar Thermal Test Dept.

1995-02-01

241

Functional and physical competition between phospholamban and its mutants provides insight into the molecular mechanism of gene therapy for heart failure  

E-print Network

into the molecular mechanism of gene therapy for heart failure Elizabeth L. Lockamy, Razvan L. Cornea, Christine B of S16E-based gene therapy in animal models of heart failure, and establish a powerful platform for designing and testing more effective PLBM targeted for gene therapy of heart failure in humans. Ó 2011

Thomas, David D.

242

Effect of Hf Additions to Pt Aluminide Bond Coats on EB-PVD TBC Life  

NASA Technical Reports Server (NTRS)

Small Hf additions were incorporated into a Pt aluminide coating during chemical vapor deposition (CVD) on single crystal RENE N5 substrates. Standard yttria-stabilized zirconia top coats were subsequently deposited onto the coated substrates by electron beam-physical vapor deposition (EB-PVD). The coated substrates underwent accelerated thermal cycle testing in a furnace at a temperature in excess of 1121 C (2050 F) (45 minute hot exposure, 15 minute cool to approximately 121 C (250 F)) until the thermal barrier coating (TBC) failed by spallation. Incorporating Hf in the bond coat increased the TBC life by slightly more than three times that of a baseline coating without added Hf. Scanning electron microscopy of the spalled surfaces indicated that the presence of the Hf increased the adherence of the thermally grown alumina to the Pt aluminide bond coat. The presence of oxide pegs growing into the coating from the thermally grown alumina may also partially account for the improved TBC life by creating a near-surface layer with a graded coefficient of thermal expansion.

Nesbitt, James; Nagaraj, Ben; Williams, Jeffrey

2000-01-01

243

Effect of Superalloy Substrate and Bond Coating on TBC Lifetime  

SciTech Connect

Several different single-crystal superalloys were coated with different bond coatings to study the effect of composition on the cyclic oxidation lifetime of an yttria-stabilized zirconia (YSZ) top coating deposited by electron beam physical vapor deposition from a commercial source. Three different superalloys were coated with a 7 {micro}m Pt layer that was diffused into the surface prior to YSZ deposition. One of the superalloys, N5, was coated with a low activity, Pt-modified aluminide coating and Pt-diffusion coatings with 3 and 7 {micro}m of Pt. Three coatings of each type were furnace cycled to failure in 1 h cycles at 1150 C to assess average coating lifetime. The 7 {micro}m Pt diffusion coating on N5 had an average YSZ coating lifetime >50% higher than a Pt-modified aluminide coating on N5. Without a YSZ coating, the Pt-modified aluminide coating on N5 showed the typical surface deformation during cycling, however, the deformation was greatly reduced when constrained by the YSZ coating. The 3 {micro}m Pt diffusion coating had a similar average lifetime as the Pt-modified aluminide coating but a much wider scatter. The Pt diffusion bond coating on superalloy X4 containing Ti exhibited the shortest YSZ coating lifetime, this alloy-coating combination also showed the worst alumina scale adhesion without a YSZ coating. The third generation superalloy N6 exhibited the longest coating lifetime with a 7 {micro}m Pt diffusion coating.

Pint, Bruce A [ORNL; Haynes, James A [ORNL; Zhang, Ying [Tennessee Technological University

2010-01-01

244

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

Microsoft Academic Search

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

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

1996-01-01

245

Investigating compression failure mechanisms in composite laminates with a transparent fiberglass-epoxy birefringent materials  

NASA Technical Reports Server (NTRS)

The response and failure of a + or - 45s class laminate was studied by transparent fiberglass epoxy composite birefringent material. The birefringency property allows the laminate stress distribution to be observed during the test and also after the test if permanent residual stresses occur. The location of initial laminate failure and of the subsequent failure propagation are observed through its transparency characteristics. Experimental results are presented.

Shuart, M. J.; Williams, J. G.

1984-01-01

246

Advanced composites: Design and application. Proceedings of the meeting of the Mechanical Failures Prevention Group  

NASA Technical Reports Server (NTRS)

The design and application of advanced composites is discussed with emphasis on aerospace, aircraft, automotive, marine, and industrial applications. Failure modes in advanced composites are also discussed.

Shives, T. R.; Willard, W. A.

1979-01-01

247

Embryo malposition as a potential mechanism for mercury-induced hatching failure in bird eggs  

USGS Publications Warehouse

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.

Herring, G.; Ackerman, J.T.; Eagles-Smith, C. A.

2010-01-01

248

Embryo malposition as a potential mechanism for mercury-induced hatching failure in bird eggs.  

PubMed

We examined the prevalence of embryo malpositions and deformities in relation to total mercury (THg) and selenium (Se) concentrations in American avocet (Recurvirostra americana), black-necked stilt (Himantopus mexicanus), and Forster's tern (Sterna forsteri) eggs in San Francisco Bay (CA, USA) during 2005 to 2007. Overall, 11% of embryos were malpositioned in eggs > or =18 d of age (n = 282) and 2% of embryos were deformed in eggs > or =13 d of age (n = 470). Considering only those eggs that failed to hatch (n = 62), malpositions occurred in 24% of eggs > or =18 d of age and deformities occurred in 7% of eggs > or =13 d of age. The probability of an embryo being malpositioned increased with egg THg concentrations in Forster's terns, but not in avocets or stilts. The probability of embryo deformity was not related to egg THg concentrations in any species. Using a reduced dataset with both Se and THg concentrations measured in eggs (n = 87), we found no interaction between Se and THg on the probability of an embryo being malpositioned or deformed. Results of the present study indicate that embryo malpositions were prevalent in waterbird eggs that failed to hatch and the likelihood of an embryo being malpositioned increased with egg THg concentrations in Forster's terns. We hypothesize that malpositioning of avian embryos may be one reason for mercury-related hatching failure that occurs late in incubation, but further research is needed to elucidate this potential mechanism. PMID:20821633

Herring, Garth; Ackerman, Joshua T; Eagles-Smith, Collin A

2010-08-01

249

Mechanisms of failure of coatings used in flue gas desulfurization systems  

SciTech Connect

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

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

1986-05-01

250

Impact of left ventricular diastolic function on left atrial mechanics in systolic heart failure.  

PubMed

The relation between left atrial (LA) mechanics and left ventricular (LV) diastolic function and adverse cardiovascular events are not well established in chronic systolic heart failure (HF). In 108 patients, we performed comprehensive echocardiography with an assessment of LA global longitudinal strain (LA?) by Velocity Vector Imaging. We also performed complete diastolic examinations including mitral inflow, pulmonary vein flow, and tissue Doppler. Death, cardiac transplantation, and HF hospitalization were tracked for 5 years. In our study cohort (age 57 ± 15 years, LV ejection fraction 25 ± 6%), mean global LA negative (?negative), positive (?positive), and total ? (?total) were -6.8 ± 4.4%, 7.7 ± 5.7%, and 14.5 ± 8.2%, respectively. All LA? indexes correlated with individual indexes of LV diastolic dysfunction, including mitral flow early (E) to late diastolic velocity ratio (p <0.05 for all), mitral deceleration time (p <0.01 for all), E to early diastolic velocity of the septal mitral annulus (e') ratio (p <0.05 for all), pulmonary vein flow systolic to diastolic velocity ratio (p <0.001 for all), and maximal LA volume index (p <0.01 for all). All LA? indexes increased across diastolic stage (p <0.001 for all). In multivariate logistic regression analysis, LA?negative and LA?total were associated with the presence of LV diastolic dysfunction grade III even after adjustment for E/e' septal and LA volume index. In Cox proportional hazards analysis, lower magnitude LA?negative predicted long-term adverse clinical events. In conclusion, more impaired LA mechanics are associated with more severe diastolic dysfunction and predict long-term adverse events in patients with chronic systolic HF. PMID:23764244

Motoki, Hirohiko; Borowski, Allen G; Shrestha, Kevin; Troughton, Richard W; Martin, Maureen G; Tang, W H Wilson; Klein, Allan L

2013-09-15

251

Probing the Failure Mechanism of SnO2 Nanowires for Sodium-ion Batteries  

SciTech Connect

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.

Gu, Meng; Kushima, Akihiro; Shao, Yuyan; Zhang, Jiguang; Liu, Jun; Browning, Nigel D.; Li, Ju; Wang, Chong M.

2013-09-30

252

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

PubMed Central

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

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

2013-01-01

253

The analysis and mechanism study of test in the splitting failure of surrounding rock masses of underground caverns  

NASA Astrophysics Data System (ADS)

The underground caverns that locate in high geostress are being excavated. The surrounding rock masses are prone to appear longitudinal splitting cracks and lead to brittle craze even failure, like rockburst etc, and endanger the safety of engineering. The test of brittle rock and simulation analysis are carried out to study the extension process of splitting cracks and the phenomena of split failure are obtained. The mechanism and conditions are discussed according to the special project phenomena. The results can supply some significant guidance to design and construction of similar engineering.

Li, Xiaojing; Zhu, Weishen; Li, Yong; Xin, Xiaoli; Zhang, Qianbing

2008-11-01

254

International Journal of Crashworthiness, 2012, 17(3): p. 327-336 Mechanical Properties and Failure Mechanisms of Closed-Cell PVC Foams  

E-print Network

and Failure Mechanisms of Closed-Cell PVC Foams Michele Colloca, Gleb Dorogokupets, Nikhil Gupta1 , Maurizio chloride (PVC) foams with varying densities is conducted under tension, compression, and impact loading. Experimental results on four classes of high performance PVC foams show that the elastic modulus, strength

Gupta, Nikhil

255

Does the Mean Arterial Pressure Influence Mortality Rate in Patients with Acute Hypoxemic Respiratory Failure under Mechanical Ventilation?  

PubMed Central

Background In sepsis patients, target mean arterial pressures (MAPs) greater than 65 mm Hg are recommended. However, there is no such recommendation for patients receiving mechanical ventilation. We aimed to evaluate the influence of MAP over the first 24 hours after intensive care unit (ICU) admission on the mortality rate at 60 days post-admission in patients showing acute hypoxemic respiratory failure under mechanical ventilation. Methods This prospective, multicenter study included 22 ICUs and compared the mortality and clinical outcomes in patients showing acute hypoxemic respiratory failure with high (75-90 mm Hg) and low (65-74.9 mm Hg) MAPs over the first 24 hours of admission to the ICU. Results Of the 844 patients with acute hypoxemic respiratory failure, 338 had a sustained MAP of 65-90 mm Hg over the first 24 hours of admission to the ICU. At 60 days, the mortality rates in the low (26.2%) and high (24.5%) MAP groups were not significantly different. The ICU days, hospital days, and 60-day mortality rate did not differ between the groups. Conclusion In the first 24 hours of ICU admission, MAP range between 65 and 90 mm Hg in patients with acute hypoxemic respiratory failure under mechanical ventilation may not cause significantly differences in 60-day mortality. PMID:25861341

Gjonbrataj, Juarda; Kim, Hyun Jung; Jung, Hye In

2015-01-01

256

Mechanical failure of prosthetic human implants: A 10-year experience with aortic stent graft devices  

Microsoft Academic Search

Objective: The first endovascular stent graft was implanted to treat an abdominal aortic aneurysm more than a decade ago. This technique has evolved dramatically with the growing understanding of metallurgic and fabric sciences and improved device designs. However the potential for stent graft material failure remains. This investigation describes the incidence of material failure, potential modes of device fatigue, and

Tikva S. Jacobs; Jamie Won; Edwin C. Gravereaux; Peter L. Faries; Nicholas Morrissey; Victoria J. Teodorescu; Larry H. Hollier; Michael L. Marin

2003-01-01

257

PATHOPHYSIOLOGICAL MECHANISMS AND DRUGS LEADING TO DECREASE IN RENAL FUNCTION IN CONGESTIVE HEART FAILURE  

Microsoft Academic Search

Summary. Literature review shows that elevated serum creatinine (or diminished creatinine clearance) is frequent in patients with heart failure (40%) and prognostically bad as it indicates an independently manifold increased mortality. In addition, even renal function worsening during hospitalization (increase in serum creatinine by approximately 30 micromol\\/L or higher) is not a rare finding (every 4 patients with heart failure)

Goran P. Kora?evi?

2005-01-01

258

Thermo-mechanical forcing of deformation and progressive failure in large rock slope instabilities  

NASA Astrophysics Data System (ADS)

Thermo-elastic rock slope deformation is often considered to be of relatively minor importance and limited to shallow depths subject to seasonal warming and cooling. Here we demonstrate how thermo-mechanical (TM) effects can drive rock slope deformation at greater depths below the annual thermal active layer. We present 2D numerical models of a simplified slope subject to annual surface temperature cycles. Results show that near-surface thermo-elastic stresses can propagate to depths of 100 m and more as a result of topography and elasticity of the rock mass. Such stress changes can induce shear dislocation along discontinuities, which has both a reversible component controlled by compliance, and provided that the stress state is sufficiently close to the strength limit, an irreversible component (i.e. slip). Induced slip increments are followed by stress redistribution resulting in propagation of slip fronts. Thus, deformation and progressive rock slope failure can be driven solely by TM forcing. The net TM effect acts as a meso-scale fatigue process involving incremental discontinuity slip and hysteresis driven by periodic loading. We apply the model to explore TM effects in the case of the current rock slope instability above the village Randa in Switzerland. There, the uppermost part of an 800 m high cliff of gneissic rocks formed after two catastrophic slope failures in 1991 remains unstable. The unstable mass of about 6 million m3 currently moves at rates up to 30 mm/yr. Deformation monitoring at the surface and in boreholes has revealed an intriguing seasonal trend: an abrupt increase of displacement rate occurs in early winter during cooling of the near-surface rock mass, while a subsequent displacement rate decrease occurs each year after snowmelt as the rock begins to warm. This seasonal trend was measured at different depths down to 68 m, where temperatures remain constant throughout the year. Site-specific numerical models, which reproduce the internal structure and kinematics of the present-day instability, were able to simulate the correct order of magnitude of observed displacement rates and seasonal amplitudes simply by including TM forcing.

Gischig, V. S.; Moore, J. R.; Evans, K. F.; Amann, F.; Loew, S.

2011-12-01

259

Study of the breakdown failure mechanisms for power AlGaN/GaN HEMTs implemented using a RF compatible process  

E-print Network

Study of the breakdown failure mechanisms for power AlGaN/GaN HEMTs implemented using a RF failure mechanisms for a family of power AlGaN/GaN HEMTs were studied. These devices were fabricated using semiconduc- tors for high power electronic applications [1­3]. AlGaN/GaN HEM- Ts have received much attention

Ng, Wai Tung

260

Mutations in TBC1D24, a gene associated with epilepsy, also cause nonsyndromic deafness DFNB86.  

PubMed

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

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

261

Modelling river bank erosion processes and mass failure mechanisms using 2-D depth averaged numerical model  

NASA Astrophysics Data System (ADS)

Bank erosion is a key process that may cause a large number of economic and environmental problems (e.g. land loss, damage to structures and aquatic habitat). Stream bank erosion (toe erosion and mass failure) represents an important form of channel morphology changes and a significant source of sediment. With the advances made in computational techniques, two-dimensional (2-D) numerical models have become valuable tools for investigating flow and sediment transport in open channels at large temporal and spatial scales. However, the implementation of mass failure process in 2D numerical models is still a challenging task. In this paper, a simple, innovative algorithm is implemented in the Telemac-Mascaret modeling platform to handle bank failure: failure occurs whether the actual slope of one given bed element is higher than the internal friction angle. The unstable bed elements are rotated around an appropriate axis, ensuring mass conservation. Mass failure of a bank due to slope instability is applied at the end of each sediment transport evolution iteration, once the bed evolution due to bed load (and/or suspended load) has been computed, but before the global sediment mass balance is verified. This bank failure algorithm is successfully tested using two laboratory experimental cases. Then, bank failure in a 1:40 scale physical model of the Rhine River composed of non-uniform material is simulated. The main features of the bank erosion and failure are correctly reproduced in the numerical simulations, namely the mass wasting at the bank toe, followed by failure at the bank head, and subsequent transport of the mobilised material in an aggradation front. Volumes of eroded material obtained are of the same order of magnitude as the volumes measured during the laboratory tests.

Die Moran, Andres; El kadi Abderrezzak, Kamal; Tassi, Pablo; Herouvet, Jean-Michel

2014-05-01

262

Gender related alterations of ?-adrenoceptor mechanisms in heart failure due to arteriovenous fistula.  

PubMed

This study was undertaken to determine gender related changes in different components of ?-adrenoceptor (?-AR) system in response to arteriovenous fistula (AV-shunt), which is known to produce heart failure due to volume overload. AV-shunt was induced in male and female rats for 16 weeks by the needle technique; ovariectomized (OVX) rats treated with or without estrogen were also used. Although AV-shunt for 16 weeks produced cardiac hypertrophy in both sexes, male animals showed cardiac dysfunction whereas cardiac performance was maintained in females. Both ?(1) -AR and ?(2) -AR protein content and mRNA levels were decreased in male and increased in female hearts post-AV-shunt. The basal adenylyl cyclase (AC) activity was lower in the female heart; however, AC protein content and the increase in epinephrine (EPi)-stimulated AC activity were greater in the female AV-shunt group as compared to males. While AC V/VI and ?-arrestin 2 mRNA levels were decreased in males, mRNA level for GRK2 was increased in females post-AV-shunt. In contrast to intact females, AV-shunt OVX animals showed depressed cardiac function, decreased ?(1) -AR, ?(2) -AR, and AC protein content, as well as reduced EPi-stimulated AC activity. Treatment of OVX rats with 17-? estradiol attenuated the AV-shunt induced changes in ?-AR and AC protein content as well as cardiac dysfunction. These results reveal that ?-AR signal transduction system in response to AV-shunt is downregulated in males and upregulated in females. Furthermore, estrogen appears to play an important role in the upregulation of ?-AR mechanisms and the maintenance of cardiac function in AV-shunt females. PMID:22015551

Dent, Melissa R; Tappia, Paramjit S; Dhalla, Naranjan S

2012-08-01

263

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

SciTech Connect

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.

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

2013-09-30

264

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

SciTech Connect

To improve the hot corrosion resistance of YSZ thermal barrier coatings, a 25 {micro}m and a 2 {micro}m thick Al{sub 2}O{sub 3} overlay were deposited by HVOF thermal spray and by sol-gel coating method, respectively, onto to the surface of YSZ coating. Indenter test was employed to investigate the spalling of YSZ with and without Al{sub 2}O{sub 3} overlay after hot corrosion. The results showed that 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. In the next reporting period, we will measure or calculate the residue stress within Al{sub 2}O{sub 3} overlay and YSZ coating to study the mechanism of effect of Al{sub 2}O{sub 3} overlay on spalling of YSZ coating.

Scott X. Mao

2003-12-16

265

Molecular mechanisms of cardiomyogenesis and the prospects for cardiomyocyte regeneration in cardiac failure  

Microsoft Academic Search

The review briefs the current state of research in molecular biological and cell aspects of cardiac development and the prospects\\u000a of applying the corresponding results to treating heart failure by cardiomyocyte regeneration in damaged myocardium.

V. P. Shirinsky; A. Yu. Khapchaev; O. V. Stepanova

2008-01-01

266

Mechanics of progressive failures leading to rapid shallow landslides using the fiber bundle model  

NASA Astrophysics Data System (ADS)

Shallow landslides are often sudden events caused by the rapid failure of a slip surface. Yet, such global failure is the culmination of a series of steps that begin with the initiation and growth of local cracks and failure planes that, with increased load eventually coalesce to form a continuous surface. The dynamics of such failure events is controlled, in part, by the rate of soil weakening during water infiltration and by distribution of tree roots that span across these failure zones. Conventional approaches rely on static limit-equilibrium analysis to compute the ratio of soil resistive strength to gravitational driving forces (factor of safety) to determine slope stability, often ignoring dynamics leading to failure as well as heterogeneities associated with land cover, subsurface material properties, hydrologic pathways, and presence of biological elements such as roots. Casting the problem in terms of stable or unstable slope does not describe the progressive formation of cracks in heterogeneous soils or the failure of roots that stretch across tension cracks or basal shear planes. Here we use the fiber bundle model (FBM) to describe soil and root failure focusing on landslide initiation. The FBM consists of a bundle of parallel, elastic-brittle fibers of identical length and stiffness stretched quasi-statically between two plates. Heterogeneity is introduced by fibers having finite threshold strength drawn randomly from a probability density function. Step-loading of the bundle causes weak fibers to break and load redistribution (either global or local) among surviving fibers can trigger secondary, tertiary, and so on, failures, a process known as an avalanche. We illustrate the potential utility of the FBM for two cases: (1) modeling of lateral root reinforcement where fibers represent roots of different sizes and strengths, and (2) modeling of progressive weakening of soils by water infiltration where fibers are analogs of bonds between soil aggregates whose strength distribution evolves with changes in water content. The main advantages of the fiber bundle model is its ability to account for progressive failure and heterogeneities of soils on slopes, to describe the complex rheological behavior of soils and soil elements such as roots using simple basic blocks (the fibers) whose properties can be directly related to the properties of the materials, and to represent physical processes of failure in soils and roots.

Cohen, Denis; Schwarz, Massimiliano; Or, Dani

2010-05-01

267

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

SciTech Connect

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.

Scott X. Mao

2002-08-31

268

HMG-CoA reductase inhibitors in chronic heart failure: potential mechanisms of benefit and risk.  

PubMed

HMG-CoA reductase inhibitors (statins) have been shown to reduce mortality and cardiovascular morbidity in patients with hyperlipidaemia and those with coronary artery disease. However, evidence for statin treatment in patients with chronic heart failure (CHF) remains a subject of debate. Patients with heart failure were generally excluded in the existing trials and a different patient population with a distinct pattern of morbidity and treatment was studied. In addition, no safety data are available for statins in patients with heart failure, where there are potential concerns about coenzyme Q10 depletion and excessive low-density lipoprotein reduction. This review summarises the clinical and preclinical evidence for potential beneficial effects of statins in CHF. In experimental systems, statins have been shown to improve cardiac function through antioxidative and anti-inflammatory action. Statins improve endothelial function, may reduce neurohormonal activation, and stimulate endothelial progenitor cells. Some of these effects occur independently of cholesterol lowering and can be explained by inhibition of isoprenylation of signal transducing proteins of the family of Rho guanosine triphosphatases. Two ongoing controlled randomised trials (CORONA [Controlled Rosuvastatin Multinational Study in Heart Failure] and GISSI-HF [Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto Miocardico--Heart Failure]) will help us to assess whether the described beneficial effects of statins in heart failure outweigh the potential negative effects and translate into the reduction of clinical endpoints. PMID:16451090

Laufs, Ulrich; Custodis, Florian; Böhm, Michael

2006-01-01

269

Evaluation of SRV pipe-failure rates via probabilistic mechanical design  

SciTech Connect

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 amount of overlap of the probabilistic stress and strength distribution of the pipe is used as a measure of failure probability. If these distributions are known, the probability of failure can be computed in a straightforward manner. To obtain the distribution of stresses experienced in an SRV line during a transient, the values measured during SRV actuation in the early stages of operation of the Mark II plant at Caorso, Italy were used. Assuming normally distributed variables, stress and strength distributions were found: the stress distribution from the values measured in the Caorso plant, the strength distributions from the results of material testing found in the literature. A failure probability for a newly installed SRV pipe was calculated and estimates were made of the effects of fatigue and corrosion on this value.

Lehner, J.R.; Economos, C.

1983-01-01

270

Microstructure-property relationships of SiC fibre-reinforced magnesium aluminosilicates—II. Mechanical properties and failure characteristics  

Microsoft Academic Search

Interfacial frictional shear stresses, flexural properties and failure mechanisms are reported for two magnesium aluminosilicates unidirectionally reinforced with Nicalon SiC fibres. Composites A and B were hot-pressed at 1500 and 920°C, respectively. High values of interfacial frictional shear stresses inferred from Marshall's analysis of the micro-indentation technique could be attributed in part to the presence of compressive radial stresses at

A. Kumar; K. M. Knowles

1996-01-01

271

Continuum damage mechanics based modeling progressive failure of woven-fabric composite laminate under low velocity impact  

Microsoft Academic Search

A continuum damage mechanics (CDM) meso-model was derived for both intraply and interply progressive failure behaviors of\\u000a a 2D woven-fabric composite laminate under a transversely low velocity impact. An in-plane anisotropic damage constitutive\\u000a model of a 2D woven composite ply was derived based on CDM within a thermodynamic framework, an elastic constitutive model\\u000a with damage for the fibre directions and

Zhi-gang Hu; Yan Zhang

2010-01-01

272

Lowside driver's failure mechanism in a class-D amplifier under short circuit test and a robust driver device  

Microsoft Academic Search

The failure mechanism in a class-D audio amplifier under short-circuit test is analyzed. The damage, always in the low-side driver, is due to high current induced thermal run-away, which occurs during the shutdown after the over-current is detected. However, this high current doesn't come from the over-current itself since the current is limited to below that the transistor in the

Jian-Hsing Lee; J. R. Shih; Tong-Chern Ong; K. Wu

2010-01-01

273

Effects of service condition on rolling contact fatigue failure mechanism and lifetime of thermal spray coatings—A review  

NASA Astrophysics Data System (ADS)

The service condition determines the Rolling Contact Fatigue(RCF) failure mechanism and lifetime under ascertain material structure integrity parameter of thermal spray coating. The available literature on the RCF testing of thermal spray coatings under various condition services is considerable; it is generally difficult to synthesize all of the result to obtain a comprehensive understanding of the parameters which has a great effect on a thermal spray coating's resistance of RCF. The effects of service conditions(lubrication states, contact stresses, revolve speed, and slip ratio) on the changing of thermal spray coatings' contact fatigue lifetime is introduced systematically. The effects of different service condition on RCF failure mechanism of thermal spray coating from the change of material structure integrity are also summarized. Moreover, In order to enhance the RCF performance, the parameter optimal design formula of service condition and material structure integrity is proposed based on the effect of service condition on thermal spray coatings' contact fatigue lifetime and RCF failure mechanism. The shortage of available literature and the forecast focus in future researches are discussed based on available research. The explicit result of RCF lifetime law and parameter optimal design formula in term of lubrication states, contact stresses, revolve speed, and slip ratio, is significant to improve the RCF performance on the engineering application.

Cui, Huawei; Cui, Xiufang; Wang, Haidou; Xing, Zhiguo; Jin, Guo

2015-01-01

274

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

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

Laizhu Jiang; Hannu Hänninen; Jukka Paro; Veijo Kauppinen

1996-01-01

275

Market failure in the pharmaceutical industry and how it can be overcome: the CureShare mechanism.  

PubMed

Allowing patients to take part in the initial investment for the development of cures for their illnesses can, under certain conditions, lead to the development of drugs that would have otherwise not been developed and to a dramatic welfare increase. We theoretically analyze these conditions. The suggested patient investment mechanism, which we call CureShare, does not involve any philanthropy or government subsidies. It is simply a way to overcome market failure. Based on empirical data, we estimate that applying this mechanism may save thousands of lives annually and may dramatically improve the quality of many others. PMID:23417217

Levy, Moshe; Rizansky, Adi

2014-03-01

276

Three-Dimensional Numerical Investigations of the Failure Mechanism of a Rock Disc with a Central or Eccentric Hole  

NASA Astrophysics Data System (ADS)

The diametrical compression of a circular disc (Brazilian test) or cylinder with a small eccentric hole is a simple but important test to determine the tensile strength of rocks. This paper studies the failure mechanism of circular disc with an eccentric hole by a 3D numerical model (RFPA3D). A feature of the code RFPA3D is that it can numerically simulate the evolution of cracks in three-dimensional space, as well as the heterogeneity of the rock mass. First, numerically simulated Brazilian tests are compared with experimental results. Special attention is given to the effect of the thickness to radius ratio on the failure modes and the peak stress of specimens. The effects of the compressive strength to tensile strength ratio ( C/T), the loading arc angle (2 ?), and the homogeneity index ( m) are also studied in the numerical simulations. Secondly, the failure process of a rock disc with a central hole is studied. The effects of the ratio of the internal hole radius ( r) to the radius of the rock disc ( R) on the failure mode and the peak stress are investigated. Thirdly, the influence of the vertical and horizontal eccentricity of an internal hole on the initiation and propagation of cracks inside a specimen are simulated. The effect of the radius of the eccentric hole and the homogeneity index ( m) are also investigated.

Wang, S. Y.; Sloan, S. W.; Tang, C. A.

2014-11-01

277

Failure mechanisms in wood joints bonded with urea-formaldehyde adhesives  

Microsoft Academic Search

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

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

1994-01-01

278

A damage-based numerical analysis of brittle rocks failure mechanism  

Microsoft Academic Search

The dominant causes of irreversible rock deformations are damage process and plastic flow. Most of the existing elastic–plastic models employed in the analysis and design of rock structures only consider the plastic flow and ignore the full damage process. The common plastic models used to simulate the rock failure, does not model the rock realistically and often the important issues

H. Molladavoodi; A. Mortazavi

2011-01-01

279

MITIGATION OF SCC AND CORROSION FATIGUE FAILURES IN 300M LANDING GEAR STEEL USING MECHANICAL SUPPRESSION  

Microsoft Academic Search

300M steel is widely used in landing gear because of its unique combination of ultrahigh strength with high fracture toughness. However, 300M is vulnerable to both corrosion fatigue and stress corrosion cracking (SCC) failures with catastrophic consequences for aircraft landing gear. Plating and shot peening surface treatments currently used to extend life are only partly effective. A surface treatment is

Paul S. Prevéy; N. Jayaraman; Neal Ontko; Michael Shepard; Robert Ware; Jack Coate

280

Full-Field Strain Methods for Investigating Failure Mechanisms in Triaxial Braided Composites  

NASA Technical Reports Server (NTRS)

Recent advancements in braiding technology have led to commercially viable manufacturing approaches for making large structures with complex shape out of triaxial braided composite materials. 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 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. This report presents some new techniques that have been developed to investigate local deformation and failure using digital image correlation techniques. 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 correlations were made between these local failures and global composite deformation and strength.

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

2008-01-01

281

Seepage and piping: Solitary and integrated mechanisms of streambank erosion and failure  

Technology Transfer Automated Retrieval System (TEKTRAN)

Recent work has shown that a majority of the sediment entering streams and rivers now comes from streambanks. We lack the understanding of the processes controlling streambank failure to be able to predict how erosion control methods will work for all conditions. Research underway at Oklahoma State...

282

Cerebral Blood Flow in Acute Liver Failure: A Finding in Search of a Mechanism  

Microsoft Academic Search

In the last few years, several abnormalities of cerebral blood flow (CBF), namely loss of cerebral autoregulation, altered reactivity to carbon dioxide, and development of cerebral hyperemia, have been described in patients as well as experimental models of acute liver failure (ALF) and\\/or hyperammonemia. The development of cerebral hyperemia seems particularly relevant to the pathogenesis of brain edema in ALF.

Javier Vaquero; Chuhan Chung; Andres T. Blei

2004-01-01

283

Mechanisms of heart failure with well preserved ejection fraction in dogs following limited coronary microembolization  

Microsoft Academic Search

Objective: It has been suggested that in some settings, heart failure (HF) may occur with normal ejection fraction (EF) as a consequence of undetected systolic dysfunction. However, others have argued that this can only occur in the presence of diastolic dysfunction. We therefore sought to determine the contribution of diastolic dysfunction in an animal model of HF with normal EF.

Kun-Lun Hea; Marc Dicksteinb; Hani N. Sabbahc; Geng-Hua Yid; Anguo Gud; Mathew Maurerd; Chi-Ming Weie; Jie Wangd; Daniel Burkhoff

284

Slope Failure Mechanisms Due to Seepage: Three-Dimensional Soil Block Experiments  

Technology Transfer Automated Retrieval System (TEKTRAN)

Seepage erosion has been suggested to potentially play an important role in streambank failure and gully formation. However, although seepage erosion has three-dimensional characteristics, two-dimensional lysimeters were used in previous research to analyze for the hydraulic and geotechnical control...

285

A method for intermediate strain rate compression testing and study of compressive failure mechanism of Mg-Al-Zn alloy  

NASA Astrophysics Data System (ADS)

Obtaining meaningful information from the test results is a challenge in the split-Hopkinson pressure bar (SHPB) test method if the specimen does not fail during the test. Although SHPB method is now widely used for high strain rate testing, this limitation has made it difficult to use it for characterization of materials in the intermediate strain rate range (typically 10-1000 s-1). In the present work, a method is developed to characterize materials in the intermediate strain rate range using SHPB setup. In this method, the specimen is repeatedly tested under compression at a given strain rate until failure is achieved. The stress-strain graphs obtained from each test cycle are used to plot the master stress-strain graph for that strain rate. This method is used to study the strain rate dependence of compressive response of a Mg-Al-Zn alloy in the intermediate strain rate range. A remarkable difference is observed in the failure mechanism of the alloy under quasi-static and intermediate strain rate compression. Matrix cracking is the main failure mechanism under quasi-static compression, whereas shattering of intermetallic precipitates, along with plastic deformation of the matrix, is discovered to become prominent as the strain rate is increased.

Gupta, Nikhil; Luong, Dung D.; Rohatgi, Pradeep K.

2011-05-01

286

Small-scale mechanical characterization of viscoelastic adhesive systems  

NASA Astrophysics Data System (ADS)

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.

Shean, T. A. V.

287

Failure Morphologies of Cyclically Oxidized ZrO2-Based Thermal Barrier Coatings  

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

288

Beyond the measurement of QRS complex toward mechanical dyssynchrony: cardiac resynchronisation therapy in heart failure patients with a normal QRS duration  

PubMed Central

Mechanical systolic dyssynchrony exists in many patients with heart failure, irrespective of QRS duration, and so more patients may derive benefit from cardiac resynchronisation therapy than previously considered PMID:15084530

Auricchio, A; Yu, C M

2004-01-01

289

Verapamil Reverses Glucose Intolerance in Preexisting Chronic Renal Failure: Studies on Mechanisms  

Microsoft Academic Search

Glucose-induced insulin secretion is impaired in chronic renal failure (CRF), and this abnormality is due to the elevation of cytosolic calcium [Ca2+]i and other derangements in pancreatic islet metabolism. Verapamil given to rats from day 1 of CRF prevented the rise in [Ca2+]i of islets and the impairment in insulin secretion. However, it is not known whether verapamil can reverse

Prasert Thanakitcharu; George Z. Fadda; Suha M. Hajjar; Edi Levi; Olivera Stojceva-Taneva; Shaul G. Massry

1992-01-01

290

Drug Insight: statins for nonischemic heart failure—evidence and potential mechanisms  

Microsoft Academic Search

While 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors, also known as statins, have a well-established in role in the treatment and prevention of ischemic coronary artery disease, their utility in the setting of heart failure (HF) and left ventricular (LV) dysfunction remains under investigation. Although a reduction in LDL is the major effect of statin therapy, pleiotropic effects have been demonstrated, which could

Antonio Abbate; Valentin Fuster; George W Vetrovec; Michael J Lipinski

2007-01-01

291

From solids to fluidized soils: diffuse failure mechanisms in geostructures with applications to fast catastrophic landslides  

Microsoft Academic Search

Geomaterials are mixtures of solids with voids which are filled by fluids such as air and water. Due to the strong coupling\\u000a between phases, pore pressures can be generated if loading is applied fast enough. In the case of loose metastable materials,\\u000a unstable behavior and catastrophic failure can happen. An important case is that of fast catastrophic landslides with large

M. Pastor; D. Manzanal; J. A. Fernández Merodo; P. Mira; T. Blanc; V. Drempetic; B. Haddad; M. Sánchez

2010-01-01

292

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

Microsoft Academic Search

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

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

2009-01-01

293

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

NASA Astrophysics Data System (ADS)

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.

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

2010-06-01

294

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

NASA Technical Reports Server (NTRS)

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.

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

2008-01-01

295

Impact failure analysis of re-circulating mechanism in ball screw  

Microsoft Academic Search

A ball screw driven mechanism is a major component in high-speed\\/high-precision transmitting systems. In such a mechanism, the return tube has been designed to provide the path for a steel ball rolling in screw grooves. As the driven shaft in the mechanism operates at high rotating speed, forces caused by the impact activity between the steel ball and return tube

Jui-Pin Hung; James Shih-Shyn Wu; Jerry Y. Chiu

2004-01-01

296

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

NASA Technical Reports Server (NTRS)

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.

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

2002-01-01

297

Microstructure, joint strength and failure mechanisms of SnPb and Pb-free solders in BGA packages  

Microsoft Academic Search

The microstructure, joint strength and failure mechanisms of SnPbAg, SnAg and SnAgCu solders on Cu\\/Ni\\/Au BGA pad metallization were investigated after multiple reflows or high temperature aging. In the SnPbAg system, a two-layer structure, i.e., Ni3Sn4 and (Au, Ni)Sn4, was formed at the solder-substrate metallization interface after aging at 125, 150, and 175°C. However, such structure was not present in

Ming Li; K. Y. Lee; D. R. Olsen; William T. Chen; B. T. C. Tan; S. Mhaisalkar

2002-01-01

298

Relationship between Early Inflammatory Response and Clinical Evolution of the Severe Multiorgan Failure in Mechanical Circulatory Support-Treated Patients  

PubMed Central

Background. The mechanical circulatory support (MCS) is an effective treatment in critically ill patients with end-stage heart failure (ESHF) that, however, may cause a severe multiorgan failure syndrome (MOFS) in these subjects. The impact of altered inflammatory response, associated to MOFS, on clinical evolution of MCS postimplantation patients has not been yet clarified. Methods. Circulating cytokines, adhesion molecules, and a marker of monocyte activation (neopterin) were determined in 53?MCS-treated patients, at preimplant and until 2 weeks. MOFS was evaluated by total sequential organ failure assessment score (tSOFA). Results. During MCS treatment, 32 patients experienced moderate MOFS (tSOFA?

Campolo, Jonica; Botta, Luca; Parolini, Marina; Milazzo, Filippo; Nonini, Sandra; Martinelli, Luigi; Paino, Roberto; Marraccini, Paolo

2014-01-01

299

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

NASA Astrophysics Data System (ADS)

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.

Okubo, C. H.

2013-12-01

300

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

NASA Astrophysics Data System (ADS)

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).

Reyer, D.; Philipp, S. L.

2013-12-01

301

Formation Mechanism of Type IV Failure in High Cr Ferritic Heat-Resistant Steel-Welded Joint  

NASA Astrophysics Data System (ADS)

The mechanism of type IV failure has been investigated by using a conventional 9Cr ferritic heat-resistant steel Gr.92. In order to clarify the main cause of type IV failure, different heat treatments were performed on the base metal in order to change the prior austenite grain (PAG) size and precipitate distribution after applying the heat-affected zone (HAZ) simulated thermal cycle at the peak temperature of around A c3 ( A c3 HAZ thermal cycle) and postweld heat treatment (PWHT). The microstructural evolution during the A c3 HAZ thermal cycle and PWHT was investigated by means of scanning electron microscope (SEM), electron backscatter diffraction (EBSD), electron probe microanalysis (EPMA), and transmission electron microscope (TEM). It was found that M23C6 carbides were scarcely precipitated at the newly formed fine PAG, block, and lath boundaries in A c3 HAZ-simulated Gr.92, because the carbide forming elements such as Cr and C were segregated at the former PAG and block boundaries of the base metal. On the other hand, if all the boundaries were covered by sufficient M23C6 carbides by homogenization of the alloying elements prior to applying the HAZ thermal cycle, the creep strength was much improved even if the fine PAG was formed. From these results, it is concluded that fine-grained microstructure cannot account for the occurrence of type IV failure, and it only has a small effect during long-term creep. The most important factor is the precipitate formation behavior at various boundaries. Without sufficient boundary strengthening by precipitates, the microstructure of A c3 HAZ undergoes severe changes even during PWHT and causes premature failure during creep.

Liu, Y.; Tsukamoto, S.; Shirane, T.; Abe, F.

2013-10-01

302

Transition in Failure Mechanism Under Cyclic Creep in 316LN Austenitic Stainless Steel  

NASA Astrophysics Data System (ADS)

Cyclic creep behavior of a type 316LN austenitic stainless steel was investigated in the temperature range from 823 K to 923 K (550 °C to 650 °C). A transition from fatigue-dominated to creep-dominated failure mode was observed with an increase in the mean stress. The threshold value of mean stress for the transition was seen to be a strong function of the test temperature. Occurrence of dynamic strain aging proved beneficial owing to a substantial reduction in the strain accumulation during cyclic loading.

Sarkar, Aritra; Nagesha, A.; Parameswaran, P.; Sandhya, R.; Mathew, M. D.

2014-06-01

303

Hygrothermal effects on the mechanical behaviour of graphite fibre-reinforced epoxy laminates beyond initial failure  

NASA Technical Reports Server (NTRS)

The critical load levels and associated cracking beyond which a multidirectional laminate can be considered as structurally failed has been determined by loading graphite fiber-reinforced epoxy laminates to different strain levels up to ultimate failure. Transverse matrix cracking was monitored by acoustic and optical methods. The residual stiffness and strength parallel and perpendicular to the cracks were determined and related to the environmental/loading history. Within the range of experimental conditions studied, it is concluded that the transverse cracking process does not have a crucial effect on the structural performance of multidirectional composite laminates.

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

1986-01-01

304

FAILURE MECHANISM OF RAILWAY EMBANKMENT DUE TO INUNDATION FLOW CAUSED BY HEAVY RAINFALL  

NASA Astrophysics Data System (ADS)

Railway and road embankments on a flood plain affect the propagation of inundation flow. In inundation simulation, the embankment in the flooded area is treated as the solid wall that inundation flow is able to overflow. However, the embankment involves the potential to be damaged during a severe flood event, and the breakage of the embankments causes not only physical damage but also a reduction of transportation function. In this study, the damage to the embankment of the Kishin line during the flood event in August 2009 is analyzed. The topographic and hydraulic conditions of the embankment failure are discussed.

Tsubaki, Ryota; Kawahara, Yoshihisa; Sayama, Takahiro; Fujita, Ichiro

305

Specific features of electronic structures and optical susceptibilities of g-BC3 and t-BC3 phases.  

PubMed

Details of comparison for some specific features of electronic structures and optical susceptibilities of g-BC3 and t-BC3 phases are provided. Calculations show that the g-BC3 phase is a narrow band gap semiconductor constructed from the ABAB stacking sequence. Whereas t-BC3 is a metallic phase constructed by a sandwich-like metal-insulator lattice from an alternately stacking sequence of metallic CBC and insulating CCC blocks. The two phases possess only two types of bonds (B-C and C-C). The density of states at the Fermi level N(EF) of the t-BC3 phase is determined by the overlapping of B-2p and C-2p empty orbitals of the CBC block with C-2p empty orbitals of the CCC block, and the shape of the Fermi surface originated from these empty orbitals. The B atoms cause a small perturbation on the C-ring's structure and hence to the charge density distribution. The linear optical properties of the two phases confirm the existence of the lossless regions and the considerable anisotropy. The second harmonic generation of the t-BC3 phase shows that ?(?) is the dominant component of about 3.9 pm V(-1) at the static limit and 5.8 pm V(-1) at ? = 1064 nm, which suggests that the t-BC3 phase could be considered as a promising nonlinear optical material in comparison with the well known KTiOPO4 nonlinear optical single crystal. PMID:25721411

Reshak, A H

2015-03-11

306

On the initiation of shear faults during brittle compressive failure: A new mechanism  

NASA Astrophysics Data System (ADS)

Brittle materials loaded under compression generally fail by shear faulting. This paper addresses the initiation of the fault. It presents direct observational evidence from ice, which is used as a model material for rock, and shows that wing cracking and "splay cracking" are important processes in the localization of deformation, both prior to and during fault initiation. Wing cracks develop at the tips of sliding intergranular cracks and tend to align with the maximum principal stress. Splay cracks emanate from one side of the sliding parent crack. The theme of the paper is that the splay cracks play the dominant role in triggering the fault. The central idea is that the slender columns between the splay cracks are more likely to buckle and fail than are the columns between adjacent wing cracks because they do not have two fixed ends; instead, the end stemming from the inclined parent crack is free. A moment is then applied by frictional sliding of the parent inclined crack, and this causes the fixed-free columns to break at a much lower stress than the fixed-fixed columns. Columns created near a free surface are more likely to fail than those created elsewhere, and this explains the observation that shear localization tends to initiate near free surfaces. A first-order calculation shows that the failure stress of the splay-created columns is of the same order of magnitude as the terminal failure stress.

Schulson, Erland M.; Iliescu, Daniel; Renshaw, Carl E.

1999-01-01

307

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

PubMed

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

Oshima, Yasushi; Fetto, Joseph F

2015-01-01

308

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

Microsoft Academic Search

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

Abdelwahed Barkaoui; Awad Bettamer; Ridha Hambli

2011-01-01

309

Design evaluation of shock induced failure mechanisms of MEMS by correlation of numerical and experimental results  

Microsoft Academic Search

The paper presents a novel approach improve MEMS reliability even during new devices. Firstly, the shock i mechanisms of breakage and stiction are test structures. The obtained results in ter rated loads are compared to acting loads mechanical shock, which are calculated impact model. The model is based superposition approach and can be app designs. It accounts for impacts at

M. Naumann; D. Lin; J. Mehner; A. McNeil; T. F. Miller

2011-01-01

310

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

Microsoft Academic Search

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

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

2010-01-01

311

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

NASA Technical Reports Server (NTRS)

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.

Lathrop, J. W.

1984-01-01

312

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

SciTech Connect

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.

Scott X. Mao

2005-10-30

313

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

NASA Astrophysics Data System (ADS)

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.

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

2009-01-01

314

Mechanism of alteration of sodium potassium pump of erythrocytes from patients with chronic renal failure.  

PubMed Central

We examined intracellular electrolytes, K influx, and [3H]ouabain-binding capacity of erythrocytes from 32 normal subjects and 45 patients with end-stage renal failure on dialysis, including 16 with high intracellular Na (mean 17.3 +/- 3.9 mmol/liter cell water). The [3H]ouabain-binding capacity of erythrocytes with high cell Na was markedly reduced as compared with that of erythrocytes from normal subjects (274 +/- 52 vs. 455 +/- 59 sites/cell, P less than 0.001). The mean serum creatinine was higher in the uremic group with high cell Na. There was a significant linear correlation between intracellular Na and [3H]ouabain-binding in both normal and uremic subjects. Cross-incubation of normal cells with uremic plasma for 24 h failed to reduce [3H]ouabain-binding capacity of normal cells. In spite of a substantial increase in cell Na, K pump influx was not higher in uremic erythrocytes with high cell Na. When intracellular Na was altered with nystatin (cell Na equal to 120 mmol/liter cell water in both groups), K pump influx was proportional to the number of Na-K pump sites so that the ion turnover rate per pump site was similar in the two groups. Uremic plasma failed to depress K pump influx of normal erythrocytes. The passive net influx of Na in uremic cells with high intracellular Na was not different from that observed in erythrocytes from normal subjects. When erythrocytes were separated by age on Percoll density gradients, the number of Na-K pump sites of the youngest uremic cells was significantly lower than that of the youngest normal cells, suggesting that decreased synthesis of Na-K pump sites, rather than accelerated loss of Na-K pump sites during aging, was responsible for the decrease in [3H]ouabain-binding capacity of erythrocytes from uremic subjects. Taken together, these findings suggest that a decrease in the number of Na-K pump sites plays a major role in the abnormality of Na-K pump of erythrocytes from patients with chronic renal failure. PMID:6094614

Cheng, J T; Kahn, T; Kaji, D M

1984-01-01

315

Effects of direct mechanical ventricular assistance on regional myocardial function in an animal model of acute heart failure.  

PubMed

Direct mechanical ventricular assistance (DMVA) improves hemodynamics in failing hearts without complications associated with a blood/device interface. Epicardial Doppler displacement transducers provide exact measurements of tissue displacement and regional myocardial function (RMF). An in vivo porcine model of acute heart failure was used to examine the effects of DMVA on RMF, which have not been reported before. In 8 anesthetized pigs cardiac output (CO), left ventricular pressure (LVP), aortic blood pressure (BP), systolic contractility (dp/dt max), and systolic wall thickening fraction (WT%) were measured. A multichamber pump system (IMPS) surrounding the left ventricle was implanted and the measurements were repeated. Then acute heart failure was induced by beta-blockade, resulting in a decline of all measured parameters to more than 30% compared to baseline values. In the further course of the experiment, repeated measurements were taken at several intervals with and without DMVA by the implanted device. The IMPS implantation caused no significant hemodynamic changes. Under conditions of acute heart failure DMVA improved LVP (46 +/- 7 to 81 +/- 9 mm Hg), dp/dt max (532 +/- 207 to 744 +/- 361 mm Hg/s), CO (1.5 +/- 0.1 to 1.9 +/- 0.5 L/min) and WT% (19 +/- 7% to 32 +/- 8%). Left ventricular myocardium not directly assisted by external pressure application showed improved regional myocardial function during DMVA. We conclude that DMVA is capable of improving hemodynamics due to extrinsic compression. It also enhances the remaining myocardial function of the failing heart, which might lead to myocardial recovery. These synergistic effects are considered responsible for the high efficiency shown by the IMPS in previous investigations. PMID:12662213

Kaczmarek, Ingo; Feindt, Peter; Boeken, Udo; Guerler, Semih; Gams, Emmeran

2003-03-01

316

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

SciTech Connect

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.

Dennis H. LeMieux

2005-10-01

317

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

SciTech Connect

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.

Dennis H. LeMieux

2003-07-01

318

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

SciTech Connect

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.

Dennis H. LeMieux

2003-10-01

319

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

SciTech Connect

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.

Dennis H. LeMieux

2004-10-01

320

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

SciTech Connect

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.

Dennis H. LeMieux

2002-04-01

321

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

SciTech Connect

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.

Dennis H. LeMieux

2005-04-01

322

Celiprolol, A Vasodilatory Blocker, Inhibits Pressure Overload-Induced Cardiac Hypertrophy and Prevents the Transition to Heart Failure via Nitric Oxide-Dependent Mechanisms in Mice  

Microsoft Academic Search

Background—The blockade of-adrenergic receptors reduces both mortality and morbidity in patients with chronic heart failure, but the cellular mechanism remains unclear. Celiprolol, a selective 1-blocker, was reported to stimulate the expression of endothelial NO synthase (eNOS) in the heart, and NO levels have been demonstrated to be related to myocardial hypertrophy and heart failure. Thus, we aimed to clarify whether

Yulin Liao; Masanori Asakura; Seiji Takashima; Akiko Ogai; Yoshihiro Asano; Yasunori Shintani; Tetsuo Minamino; Hiroshi Asanuma; Shoji Sanada; Jiyoong Kim; Soichiro Kitamura; Hitonobu Tomoike; Masatsugu Hori; Masafumi Kitakaze

323

A new failure mechanism on analog I\\/O cell under ND-mode ESD stress in deep-submicron CMOS technology  

Microsoft Academic Search

A new ESD failure mechanism has been found in the analog pins with pure-diode protection scheme during ND-mode ESD stress. The failure is caused by the parasitic npn interaction between ESD protection diode and guard ring structure. The parasitic npn bipolar, which was constructed between the N+\\/PW diode and the N+\\/NW guard ring, provides the discharging path between the I\\/O

Shih-Hung Chen; Ming-Dou Ker; Che-Hao Chuang

2005-01-01

324

Causes, mechanisms, and rates of failing of Mark II fuel elements (failures 39, 40, and 41)  

Microsoft Academic Search

It is concluded from radiometallurgy investigations that the three n-reactor Mark II driver elements (numbers 39, 40, and 41) have failed by cause of very localized and severe overheating of the inner cladding and that localized corrosion has been the mechanism by which the cladding has failed and coolant has been admitted. The fundamental cause resulted from impaired heat transfer

Guay

1968-01-01

325

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

E-print Network

­nearly per- fect plastic manner (i.e., vanishing strain hardening), with its flow stress approaching 2 GPa as strain hardening and strain rate hardening) are dimin- ished, and the destabilizing mechanisms (such) or tungsten heavy alloys (WHA) to make high-density kinetic energy anti-armor penetrators requires

Wei, Qiuming

326

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

E-print Network

@rtweng.com & schultz@mines.unr.edu) 2 Now at: RTW Professional Engineers and Consultants, Inc., 825 Railroad St., Elko in the large relief exposures (up to 8 km) of basaltic wall rock and soft interior layered deposits (ILDs mechanisms of six landslides in central Valles Marineris, where exposures of interior layered deposits (ILDs

327

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

E-print Network

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

Lutchen, Kenneth

328

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

ERIC Educational Resources Information Center

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…

Poder, Kaire; Lauri, Triin

2014-01-01

329

Effect of heart failure on the mechanism of exercise-induced augmentation of mitral valve flow.  

PubMed

The exercise response of left ventricular (LV) filling dynamics may be altered by congestive heart failure (CHF). Accordingly, we studied 18 conscious dogs, instrumented to measure micromanometer LV and left atrial (LA) pressures and determine LV volume from three dimensions. CHF was produced by 4-5 weeks of right ventricular rapid pacing. Before CHF, exercise (5.5-8.5 mph for 8-15 minutes) increased the maximum rate of LV filling (dV/dtmax) (197 +/- 37 versus 297 +/- 56 ml/sec [mean +/- SD], p < 0.05) in response to an increase in the maximum early diastolic LA to LV pressure gradient (5.8 +/- 2.0 versus 9.8 +/- 1.9 mm Hg, p < 0.05) produced by a fall in minimum LV pressure (1.0 +/- 2.9 versus -3.9 +/- 3.1 mm Hg, p < 0.01), whereas mean LA pressure was unchanged (6.4 +/- 3.1 versus 6.4 +/- 4.2 mm Hg, p = NS). The time constant of LV relaxation was shortened (28.1 +/- 3.2 versus 21.0 +/- 4.2 msec, p < 0.05). After CHF, dV/dtmax (141 +/- 51 versus 200 +/- 59 ml/sec, p < 0.05) and the maximum LA to LV pressure gradient (6.0 +/- 1.1 versus 11.1 +/- 2.7 mm Hg, p < 0.05) continued to increase with exercise (3-5.0 mph for 4-8 minutes). However, the time constant of LV relaxation was prolonged (35.6 +/- 4.8 versus 38.9 +/- 5.5 msec, p < 0.05), and minimum LV pressure (15.1 +/- 5.6 versus 17.6 +/- 5.9 mm Hg, p < 0.05) and mean LA pressure increased (22.6 +/- 7.2 versus 29.1 +/- 7.3 mm Hg, p < 0.05). These altered effects of exercise on LV diastolic filling dynamics persisted when heart rate and wall stress during exercise before and after CHF were matched by varying the level of exercise. We conclude that, during normal exercise, mitral valve flow is augmented by a fall of early diastolic LV pressure without a rise in LA pressure. After CHF, early diastolic LV pressure does not fall but increases during exercise. Thus, the increase in the early diastolic LA to LV pressure gradient and the rate of mitral valve flow results from an increase in LA pressure during exercise after CHF. This study suggests that the failure of the enhancement of LV relaxation and an increase in early diastolic LV pressure with exercise after CHF may contribute to exercise intolerance in CHF. PMID:8095187

Cheng, C P; Noda, T; Nozawa, T; Little, W C

1993-04-01

330

Microstructure and hydrogen induced failure mechanisms in iron-nickel weldments  

NASA Astrophysics Data System (ADS)

A recent series of inexplicable catastrophic failures of specific subsea dissimilar metal Fe-Ni butter welds has illuminated a fundamental lack of understanding of both the microstructure created along the fusion line as well as its impact on the hydrogen susceptibility of these interfaces. In order to remedy this, the present work compares and contrasts the microstructure and hydrogen-induced fracture morphology of AISI 8630-IN 625 and F22-IN 625 dissimilar metal weld interfaces as a function of post-weld heat treatment duration. A variety of techniques were used to study details of both the microstructure and fracture morphology including optical microscopy, scanning electron microscopy, secondary ion mass spectrometry, transmission electron microscopy, electron backscatter diffraction, and energy dispersive x-ray spectroscopy. For both systems, the microstructure along the weld interface consisted of a coarse grain heat-affected zone in the Fe-base metal followed by discontinuous martensitic partially-mixed zones and a continuous partially-mixed zone on the Ni-side of the fusion line. Within the partially mixed zone on the Ni-side there exists a 200 nm-wide transition zone within a 20 mum-wide planar solidification region followed by a cellular dendritic region with Nb-Mo rich carbides decorating the dendrite boundaries. The size, area fraction and composition of the discontinuous PMZ were determined to be controlled by uneven mixing in the liquid weld pool influenced by convection currents produced from the welding procedure. The virgin martensitic microstructure produced in these regions is formed as consequence of a both the local composition and the post-weld heat treatment. The local higher Ni content results in these regions being retransformed into austenite during the post-weld heat treatment and then virgin martensite while cooling to room temperature. Although there were differences in the volume of the discontinuous partially mixed-zones, the major difference in the weld metal interfaces was the presence of M 7C3 precipitates in the planar solidification region. The formation of these precipitates, which were found in what was previously referred to as the "featureless-zone," were determined to be dependent on the carbon content of the Fe-base metal and the duration of the post-weld heat treatment. A high density of these ordered 100 nm-long by 10 nm-wide needle-like precipitates were found in the AISI 8630-IN 625 weldment in the 10 hour post-weld heat treatment condition while only the initial stages of their nucleation were evident in the F22-IN 625 15 hour post-weld heat treatment specimen. The study of the fractured specimens revealed that the M7C 3 carbides play a key role in the susceptibility to hydrogen embrittlement of the Fe-Ni butter weldments. The fractures initially nucleate along the isolated Fe-base metal -- discontinuous partially mixed zone interfaces. The M7C3 carbides accumulate hydrogen and then provide a low energy fracture path between the discontinuous partially mixed zones leading to catastrophic failure. The result is a fracture morphology that alternates between flat regions produced by fracture along the discontinuous partially mixed zones and cleavage-like fracture regions produced by fracture along the ordered carbide matrix interfaces.

Fenske, Jamey Alan

331

Severe acute respiratory failure secondary to acute fibrinous and organizing pneumonia requiring mechanical ventilation: a case report and literature review.  

PubMed

A 27-year-old woman was admitted to our ICU with acute hypoxemic respiratory failure and criteria for ARDS. Despite an F(IO(2)) of 1.0 and a lung protective strategy, the patient died on day 15 without any improvement. The relatives gave consent for post-mortem analysis. The histopathologic study of the lung showed findings typical of an acute fibrinous and organizing pneumonia. Apropos of this case we performed a PubMed search. We found 13 articles, including a total of 29 patients. Acute fibrinous and organizing pneumonia is an unusual cause of acute lung injury. The diagnostic criterion is histopathologic. There is little information regarding the pathophysiology of this illness. Important questions remain regarding this disease, including predisposing factors and management. Patients who require mechanical ventilation have poor outcomes. PMID:22348347

López-Cuenca, Sonia; Morales-García, Silvia; Martín-Hita, Ana; Frutos-Vivar, Fernando; Fernández-Segoviano, Pilar; Esteban, Andrés

2012-08-01

332

Mechanical approach in the management of advanced acute and chronic heart failure: the state of the art.  

PubMed

Despite the progress in medical therapy, advanced heart failure (AHF) remains a global epidemic with high morbidity and mortality. Novel cardiac support strategies such as pharmacologic agents, mechanical circulatory support (MCS), and cell- or matrix-based therapies are promising for these patients. The indications, types, and timing of MCS implantation depend to a large extent on the presentation, clinical status of the patient, underlying etiology, and long-term prospects. The presence or absence of end-organ damage has a significant impact on prognosis following MCS initiation. Although many patients with acute AHF may have end-organ damage, their prospect of recovery, once appropriate therapy is instituted, is better than for patients who had AHF for longer periods of time. We consider the multidisciplinary approaches used for the management of AHF and the novel cardiac support strategies (eg, MCS). Appropriate selection of patient, device, time, and end point is essential for better outcomes. PMID:24569513

El-Menyar, Ayman; Carr, Cornelia; AlKhulaifi, Abdulaziz

2015-02-01

333

Strain Shielding from Mechanically Activated Covalent Bond Formation during Nanoindentation of Graphene Delays the Onset of Failure.  

PubMed

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

Kumar, Sandeep; Parks, David M

2015-03-11

334

Failure mode analysis and a mechanism for hot-ductility improvement in the Nb-microalloyed steel  

NASA Astrophysics Data System (ADS)

Loss of hot ductility at the straightening stage of the continuous casting of high-strength low-alloy steel is attributed to different microalloying elements, in particular, Nb. However, such elements are essential for the desired mechanical characteristics of the final product. Since the chemistry cannot be altered to alleviate the problem, thermomechanical processing was studied in order to improve the hot ductility. Two Nb-microalloyed steels, one also containing B, were examined. The thermal history occurring in the continuous casting process was taken into account as well. First, it was noticed that the steel with B has a higher hot ductility than the other after being subjected to in-situ melting followed by the thermal schedule. Grain boundary sliding was recognized as the failure mechanism. Then, the effect of deformation applied in the vicinity of the ?? ? transformation, while the thermal schedule was being executed, was investigated. Such deformation appeared to improve the hot ductility remarkably. Finally, the mechanism of such improvement in the hot ductility was elaborated.

Zarandi, Faramarz; Yue, Steven

2004-12-01

335

Impact failure mechanisms in alumina tiles on finite thickness support and the effect of confinement  

Microsoft Academic Search

The quasi-static and the dynamic damage mechanisms in alumina tiles backed by finite thickness support plates and subjected to a variety of boundary conditions were investigated. The tile\\/plate assemblies were impacted by NATO 0.3cal. armor piercing (AP) rounds with hardened and sharpened steel core. The alumina tile samples were 50×50mm2 area, their thicknesses ranging from 3 to 12mm. The backup

Dov Sherman

2000-01-01

336

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

SciTech Connect

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.

JI Young Chang

2001-05-31

337

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

Microsoft Academic Search

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

JI Young Chang

2001-01-01

338

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

PubMed Central

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

Li, Dongsheng; Cao, Hai

2012-01-01

339

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

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

340

Failure of feedback as a putative common mechanism of spreading depolarizations in migraine and stroke  

NASA Astrophysics Data System (ADS)

The stability of cortical function depends critically on proper regulation. Under conditions of migraine and stroke a breakdown of transmembrane chemical gradients can spread through cortical tissue. A concomitant component of this emergent spatio-temporal pattern is a depolarization of cells detected as slow voltage variations. The propagation velocity of ˜3mm/min indicates a contribution of diffusion. We propose a mechanism for spreading depolarizations (SD) that rests upon a nonlocal or noninstantaneous feedback in a reaction-diffusion system. Depending upon the characteristic space and time scales of the feedback, the propagation of cortical SD can be suppressed by shifting the bifurcation line, which separates the parameter regime of pulse propagation from the regime where a local disturbance dies out. The optimization of this feedback is elaborated for different control schemes and ranges of control parameters.

Dahlem, Markus A.; Schneider, Felix M.; Schöll, Eckehard

2008-06-01

341

Compression strength failure mechanisms in unidirectional composite laminates containing a hole  

NASA Technical Reports Server (NTRS)

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.

Johnson, Eric R.

1993-01-01

342

A new failure mechanism in thin film by collaborative fracture and delamination: interacting duos of cracks  

E-print Network

When a thin film moderately adherent to a substrate is subjected to residual stress, the cooperation between fracture and delamination leads to unusual fracture patterns such as spirals, alleys of crescents and various types of strips, all characterized by a robust characteristic length scale. We focus on the propagation of a duo of cracks: two fractures in the film connected by a delamination front and progressively detaching a strip. We show experimentally that the system selects an equilibrium width on the order of 25 times the thickness of the coating and independent of both fracture and adhesion energies. We investigate numerically the selection of the width and the condition for propagation by considering Griffith's criterion and the principle of local symmetry. In addition, we propose a simplified model based on maximum of energy release rate, which provides insights of the physical mechanisms leading to these regular patterns, and predicts the effect of material properties on the selected with of the detaching strip.

Joel Marthelot; Jose Bico; Francisco Melo; Benoit Roman

2014-12-02

343

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

NASA Astrophysics Data System (ADS)

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.

Parise, M.; Lollino, P.

2011-11-01

344

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

SciTech Connect

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.

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

345

Inventory of landslides in southern Illinois near the New Madrid Seismic Zone and the possible failure mechanism at three sites  

SciTech Connect

A total of 221 landslides was inventoried along a 200-kilometer reach of the Ohio and the Mississippi Rivers from Olmsted to Chester, IL using Side-Looking Airborne Radar imagery, vertical, stereoscopic, black and white aerial photography at various scales, and low altitude, oblique color and color infrared photography. Features observed on aerial photographs were used to classify landslides into three types (rock/debris fall, block slide, and rotational/translational slide) at three levels of confidence: certain, probable, or possible. Some landslides combined two or more types at a single site. Only a few of the landslides showed evidence of repeated activity; most are ancient landforms. Most of the landslides were developed in the loess, alluvium, colluvium, and weak clay layers of the Chesterian Series or in the Porter's Creek Clay and McNairy Formation. Failure of three representative landslides was modeled under static (aseismic) and dynamic (seismic) situations using three different sliding mechanisms. Both the pseudo-static method and a simplified method of the Newmark displacement analysis were used to determine the stability of the slope under earthquake conditions. The three representative landslides selected for detailed slope stability analysis were the Ford Hill, Jones Ridge, and Olmsted landslides. The Ford Hill and Jones Ridge landslides have similar slope geometries. Their modes of failure were recognized as a translational block slide on a weak clay layer. The Olmsted landslide is a complex of several rotational slides of different ages and a mega block slide on weak clay layers. The stability analyses of these three landslides suggest that they would not have occurred under aseismic conditions. However, under earthquake loadings similar to those generated by the 1811-12 earthquakes, most of the slopes could have experienced large displacements leading to landslide initiation.

Su, Wen June (Illinois State Geological Survey, Champaign, IL (United States). Engineering Geology Section)

1992-01-01

346

Mechanical failure characterization of optical components caused by laser induced damage initiated at contaminants  

SciTech Connect

The goal of this research is to quantify by numerical techniques the effects of surface and subsurface absorbing defects on damage initiation and growth in high power laser optical components. The defects include laser absorbing spots (e.g., surface particulate contamination) and surface damage regions (e.g., micro-cracks and voids) which are present due to environmental exposure and fabrication processes. This report focuses on three sources of contamination that can cause damage to optical components: (1) Front surface particle contamination, (2) Back surface particle contamination, and (3) Subsurface particle contamination. The DYNA2D (non-linear structural mechanics) code was used to model the growth of damage in the glass substrate. The damage in the nominally transparent glass substrate as a result of front surface particle contamination was found to be dependent on the magnitude of the resultant pressure pulse applied to the particle and the initial area of contact between the particle and glass substrate. The pressures generated from a back surface particle being blown off the surface provided sufficient loading to severely damage (crack) the glass substrate. A subsurface Ceria dioxide particle showed a strong surface interaction that influenced the formation and direction of the damage (cracking) that ultimately resulted in the blow-out of the damaged material leaving a relatively clean crater in the glass. Crater shape and size was determined. Since fused silica is the most transparent, and therefore laser damage resistant, of the optical materials, it is used for the most at-risk optical elements. The present studies are for a fused silica substrate. Some oxides such as Ceria are transparent in the infrared and visible, but absorbing in the UV part of the spectrum. Because ICF lasers like NIF use frequency tripling, effects of such oxides must be included.

Faux, D. R., LLNL

1997-12-01

347

Mechanisms of High-Temperature Fatigue Failure in Alloy 800H  

NASA Technical Reports Server (NTRS)

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.

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

1996-01-01

348

Heart Failure  

MedlinePLUS

... Pressure High Blood Pressure Tools & Resources Stroke More Heart Failure Prevention & Treatment of Heart Failure Pause Previous Banner ... you agree to the Terms and Conditions Downloadable Heart Failure Resources What is Heart Failure? (PDF) How Can ...

349

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

PNL-SA-22914 Presented at the 48th Meeting of the Mechanical Failures Prevention Group (MFPG 48) 19 Stratford, CT 06497 February 10, 1994 Abstract: The US Army Ordnance Center & School and Pacific Northwest of developing a real time prognostics capability. #12;PNL-SA-22914 Presented at the 48th Meeting

350

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

NASA Astrophysics Data System (ADS)

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.

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

2012-10-01

351

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

PubMed Central

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

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

352

Identification of a novel phosphorylation site on TBC1D4 regulated by AMP-activated protein kinase in skeletal muscle.  

PubMed

TBC1D4 (also known as AS160) regulates glucose transporter 4 (GLUT4) translocation and glucose uptake in adipocytes and skeletal muscle. Its mode of action involves phosphorylation of serine (S)/threonine (T) residues by upstream kinases resulting in inactivation of Rab-GTPase-activating protein (Rab-GAP) activity leading to GLUT4 mobilization. The majority of known phosphorylation sites on TBC1D4 lie within the Akt consensus motif and are phosphorylated by insulin stimulation. However, the 5'-AMP-activated protein kinase (AMPK) and other kinases may also phosphorylate TBC1D4, and therefore we hypothesized the presence of additional phosphorylation sites. Mouse skeletal muscles were contracted or stimulated with 5-aminoimidazole-4-carboxamide-1-beta-d-ribofuranoside (AICAR), and muscle lysates were subjected to mass spectrometry analyses resulting in identification of novel putative phosphorylation sites on TBC1D4. The surrounding amino acid sequence predicted that S711 would be recognized by AMPK. Using a phosphospecific antibody against S711, we found that AICAR and contraction increased S711 phosphorylation in mouse skeletal muscle, and this increase was abolished in muscle-specific AMPKalpha2 kinase-dead transgenic mice. Exercise in human vastus lateralis muscle also increased TBC1D4 S711 phosphorylation. Recombinant AMPK, but not Akt1, Akt2, or PKCzeta, phosphorylated purified muscle TBC1D4 on S711 in vitro. Interestingly, S711 was also phosphorylated in response to insulin in an Akt2- and rapamycin-independent, but a wortmannin-sensitive, manner, suggesting this site is regulated by one or more additional upstream kinases. Despite increased S711 phosphorylation with AICAR, contraction, and insulin, mutation of S711 to alanine did not alter glucose uptake in response to these stimuli. S711 is a novel TBC1D4 phosphorylation site regulated by AMPK in skeletal muscle. PMID:19923418

Treebak, Jonas T; Taylor, Eric B; Witczak, Carol A; An, Ding; Toyoda, Taro; Koh, Ho-Jin; Xie, Jianxin; Feener, Edward P; Wojtaszewski, Jørgen F P; Hirshman, Michael F; Goodyear, Laurie J

2010-02-01

353

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

SciTech Connect

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.

Kelkar, Sharad [Los Alamos National Laboratory

2011-01-01

354

Material property evaluation of thick thermal barrier coating systems  

Microsoft Academic Search

Coating system optimization is a critical step in the design and development of plasma-sprayed thermal barrier coatings (TBC's) for diesel engines. The author reports on physical and mechanical property measurements and bench screening tests performed to evaluate the candidate TBC systems. Additional understanding of the material behavior and failure mechanisms of thick TBC's gained from the property measurements and bench

R. C. Brink

1989-01-01

355

IMPERMEABLE THIN Al{sub 2}O{sub 3} OVERLAY FOR TBC PROTECTION FROM SULFATE AND VANADATE ATTACK IN GAS TURBINES  

SciTech Connect

To improve the hot corrosion resistance of YSZ thermal barrier coatings, a 25 {micro}m and a 2 {micro}m thick Al{sub 2}O{sub 3} overlay were deposited by HVOF thermal spray and by sol-gel coating method, respectively, onto to the surface of YSZ coating. Indenter test was employed to investigate the spalling of YSZ with and without Al{sub 2}O{sub 3} overlay after hot corrosion. The results showed that 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. In the next reporting period, we will measure or calculate the residue stress within Al{sub 2}O{sub 3} overlay and YSZ coating to study the mechanism of effect of Al{sub 2}O{sub 3} overlay on spalling of YSZ coating.

Scott X. Mao

2003-12-16

356

ANew Failure Mechanism on Analog I\\/O Cell under ND-Mode ESD Stress in Deep-Submicron CMOS Technology  

Microsoft Academic Search

Abstract Anew,ESD failure mechanism ,has been found ,in the analog,pins ,with ,pure-diode ,protection ,scheme ,during ND-mode ESD stress. The failure is caused,by the,parasitic npn interaction between,ESD protection diode and guard ring structure. The parasitic npn bipolar, which was constructed between the N+\\/PW diode and the N+\\/NW guard ring, provides,the discharging ,path between ,the I\\/O pad ,to the grounded,VDD under the

Shih-hung Chen; Ming-dou Ker; Che-hao Chuang

357

Metallization failures  

NASA Technical Reports Server (NTRS)

Metallization-related failure mechanisms were shown to be a major cause of integrated circuit failures under accelerated stress conditions, as well as in actual use under field operation. The integrated circuit industry is aware of the problem and is attempting to solve it in one of two ways: (1) better understanding of the aluminum system, which is the most widely used metallization material for silicon integrated circuits both as a single level and multilevel metallization, or (2) evaluating alternative metal systems. Aluminum metallization offers many advantages, but also has limitations particularly at elevated temperatures and high current densities. As an alternative, multilayer systems of the general form, silicon device-metal-inorganic insulator-metal, are being considered to produce large scale integrated arrays. The merits and restrictions of metallization systems in current usage and systems under development are defined.

Beatty, R.

1971-01-01

358

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

NASA Technical Reports Server (NTRS)

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.

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

1981-01-01

359

Differences in Mechanisms of Failure, Intraoperative Findings, and Surgical Characteristics Between Single- and Multiple-Revision ACL Reconstructions  

PubMed Central

Background The factors that lead to patients failing multiple anterior cruciate ligament (ACL) reconstructions are not well understood. Hypothesis Multiple-revision ACL reconstruction will have different characteristics than first-time revision in terms of previous and current graft selection, mode of failure, chondral/meniscal injuries, and surgical charactieristics. Study Design Case-control study; Level of evidence, 3. Methods A prospective multicenter ACL revision database was utilized for the time period from March 2006 to June 2011. Patients were divided into those who underwent a single-revision ACL reconstruction and those who underwent multiple-revision ACL reconstructions. The primary outcome variable was Marx activity level. Primary data analyses between the groups included a comparison of graft type, perceived mechanism of failure, associated injury (meniscus, ligament, and cartilage), reconstruction type, and tunnel position. Data were compared by analysis of variance with a post hoc Tukey test. Results A total of 1200 patients (58% men; median age, 26 years) were enrolled, with 1049 (87%) patients having a primary revision and 151 (13%) patients having a second or subsequent revision. Marx activity levels were significantly higher (9.77) in the primary-revision group than in those patients with multiple revisions (6.74). The most common cause of reruptures was a traumatic, noncontact ACL graft injury in 55% of primary-revision patients; 25% of patients had a nontraumatic, gradual-onset recurrent injury, and 11% had a traumatic, contact injury. In the multiple-revision group, a nontraumatic, gradual-onset injury was the most common cause of recurrence (47%), followed by traumatic noncontact (35%) and nontraumatic sudden onset (11%) (P < .01 between groups). Chondral injuries in the medial compartment were significantly more common in the multiple-revision group than in the single-revision group, as were chondral injuries in the patellofemoral compartment. Conclusion Patients with multiple-revision ACL reconstructions had lower activity levels, were more likely to have chondral injuries in the medial and patellofemoral compartments, and had a high rate of a nontraumatic, recurrent injury of their graft. PMID:23698386

Chen, James L.; Allen, Christina R.; Stephens, Thomas E.; Haas, Amanda K.; Huston, Laura J.; Wright, Rick W.; Feeley, Brian T.

2013-01-01

360

Effect of Bond Coat Materials on Thermal Fatigue Failure of EB-PVD Thermal Barrier Coatings  

Microsoft Academic Search

Effect of MCrAlY bond coat alloy systems on thermal fatigue failure of thermal barrier coatings (TBCs) was investigated, where the TBC specimen consisted of Ni-based superalloy IN738LC substrate, bond coat, and 8 wt.% Y2O3-stabilized ZrO2 (YSZ) top coat. The top coat was fabricated by EB-PVD method with 250 mum in thickness. Three kinds of MCrAlY alloys were studied as the

Satoshi Yamagishi; Masakazu Okazaki; Motoki Sakaguchi; Hideaki Matsubara

2008-01-01

361

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

SciTech Connect

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.

Scott X. Mao

2002-11-30

362

Levels of flame retardants HBCD, TBBPA and TBC in surface soils from an industrialized region of East China.  

PubMed

Hexabromocyclododecanes (HBCDs) and tetrabromobisphenol A (TBBPA) are of increasing concern because of their potential environmental persistence, bioaccumulation and toxicity. Tris-(2,3-dibromopropyl)isocyanurate (TBC) is another brominated flame retardant (BFR) which has recently been found in the environment and begun to attract attention. The objective of this study is to determine the concentration of these three BFRs in surface soil samples collected from a heavily industrialized and urbanized region in East China. Levels of ?HBCDs ranged from below detection limits (0.020 ng g(-1)) to 102.6 ng g(-1) on a dry weight basis (dw) with a median level of 15.8 ng g(-1) dw. For TBBPA, the concentration ranged from below detection limits (0.025 ng g(-1)) to 78.6 ng g(-1) dw with a median level of 9.17 ng g(-1) dw. TBC was found at relatively lower concentrations ranging from below detection limits (0.024 ng g(-1)) to 16.4 ng g(-1) dw with a median level of 0.95 ng g(-1) dw. The concentrations of these three BFRs are significantly positively correlated, indicating a common source. Variable BFRs levels were found in different types of soils, with significantly higher concentrations observed at waste dumping sites and industrial areas. The diastereoisomer profiles of HBCDs in most of the soil samples differed from those of the commercial products. The mass inventories of HBCDs, TBBPA and TBC in this region gave preliminarily estimates of 6.68, 2.67 and 0.85 kg, respectively. Therefore, the ubiquitous contamination of soils by these BFRs may well reflect their widespread usage in the study area. PMID:24599331

Tang, Jianfeng; Feng, Jiayong; Li, Xinhu; Li, Gang

2014-05-01

363

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

PubMed Central

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

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

2013-01-01

364

Strain accumulation controls failure of a plate boundary zone: Linking deformation of the Central Andes and lithosphere mechanics  

NASA Astrophysics Data System (ADS)

We make use of observations on orogenic strain accumulation and deformation partitioning in the Central Andes to explore the backarc strength evolution at the lithospheric scale. In plan view, the Altiplano-Puna plateaux experienced rapid initial increase of surface area undergoing active deformation during the Cenozoic. Beyond the maximum lateral extent reached around 10-15 Ma (40-50% of entire proto-Andes undergoing deformation) at 10-20% total strain, rapid localization initiated at the eastern flank of the Altiplano (Inter- and Subandean thrust belt) but not at the Puna latitude. Localization was associated with a significant increase in bulk shortening rate. Average fault slip rates equally increased by an order of magnitude following a protracted period of stable average rates. Estimates of strength evolution based on force balance calculations and critical wedge analysis suggest significant backarc weakening driving this change after the Middle Miocene. Strain accumulation led to localization and weakening with development of a detachment propagating through crust and upper mantle. We find that lithosphere-scale failure resulting from strain weakening beyond a critical strain threshold (c. 20%) and fault coalescence with formation of a weak detachment in shales (effective coefficient of friction < 0.1) plays a key role in the evolution of the Andes. Strain-related lithosphere weakening appears to dominate over the impact of external forcing mechanisms, such as variations of plate convergence, mantle-assisted processes, or erosion. Comparison of these orogen-scale observations with experimental rock rheology indicates substantial similarity of deformation behavior with similar weakening thresholds across a wide range of scales.

Oncken, O.; Boutelier, D.; Dresen, G.; Schemmann, K.

2012-12-01

365

Assessment of the BD MGIT TBc Identification Test for the Detection of Mycobacterium tuberculosis Complex in a Network of Mycobacteriology Laboratories  

PubMed Central

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

Ramos, Jorge; Couto, Isabel; Narciso, Inácio; Coelho, Elizabeth; Viegas, Sofia

2014-01-01

366

Heart Failure  

MedlinePLUS

... page from the NHLBI on Twitter. What Is Heart Failure? Heart failure is a condition in which the heart can' ... force. Some people have both problems. The term "heart failure" doesn't mean that your heart has stopped ...

367

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 ...

368

Performance of the MGIT TBc identification test and meta-analysis of MPT64 assays for identification of the Mycobacterium tuberculosis complex in liquid culture.  

PubMed

Rapid MPT64-based immunochromatographic tests (MPT64 ICTs) have been developed to detect Mycobacterium tuberculosis complex (MTBC) in culture. We demonstrated the noninferiority of one commercial MTP64 ICT, the MGIT TBc identification (TBcID) test, to GenoType line probe assays for MTBC identification in positive MGIT cultures. Meta-analysis of MPT64 ICT performance for identification of MTBC in liquid culture confirmed similar very high sensitivities and specificities for all three commercial MPT64 assays for which sufficient data were available. PMID:21998426

Brent, Andrew J; Mugo, Daisy; Musyimi, Robert; Mutiso, Agnes; Morpeth, Susan; Levin, Michael; Scott, J Anthony G

2011-12-01

369

N-Acetylcysteine attenuates cerebral complications of non-acetaminophen-induced acute liver failure in mice: antioxidant and anti-inflammatory mechanisms  

Microsoft Academic Search

N-acetylcysteine (NAC) is an effective antidote to treat acetaminophen (APAP)-induced acute liver failure (ALF). NAC is hepatoprotective\\u000a and prevents the neurological complications of ALF, namely hepatic encephalopathy and brain edema. The protective effect of\\u000a NAC and its mechanisms of action in ALF due to other toxins, however, are still controversial. In the present study, we investigated\\u000a the effects of NAC

Chantal Bémeur; Javier Vaquero; Paul Desjardins; Roger F. Butterworth

2010-01-01

370

Observations and analyses of failure mechanisms in thermal barrier systems with two phase bond coats based on NiCoCrAlY  

Microsoft Academic Search

The failure mechanisms operative in a thermal barrier system with a NiCoCrAlY bond coat are ascertained by examining test specimens subjected to thermal cycling in a burner rig. The findings are augmented by observations made on an actual turbine blade. The morphology and microstructure of the thermally grown oxide (TGO) have been characterized: emphasizing heterogeneities, especially “pegs”, and the TGO

T Xu; S Faulhaber; C Mercer; M Maloney; A Evans

2004-01-01

371

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)

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.

Okayasu, Mitsuhiro; Takeuchi, Shuhei; Ohfuji, Hiroaki

2014-11-01

372

Effect of non-invasive mechanical ventilation on sleep and nocturnal ventilation in patients with chronic respiratory failure  

PubMed Central

BACKGROUND—Chronic respiratory failure (CRF) is associated with nocturnal hypoventilation. Due to the interaction of sleep and breathing, sleep quality is reduced during nocturnal hypoventilation. Non-invasive mechanical ventilation (NMV), usually performed overnight, relieves symptoms of hypoventilation and improves daytime blood gas tensions in patients with CRF. The time course of the long term effect of NMV on sleep and breathing during both spontaneous ventilation (withdrawing the intervention) and NMV was investigated in patients with CRF due to thoracic restriction.?METHODS—Fifteen consecutive patients (13 women) of mean (SD) age 57.9 (12.0) years with CRF due to thoracic restriction were included in the study. During the one year observation period four polysomnographic studies were performed: three during spontaneous breathing without NMV—before initiation of NMV (T0) and after withdrawing NMV for one night at six months (T6) and 12 months (T12-)—and the fourth during NMV after 12 months (T12+). Daytime blood gas tensions and lung function were also measured.?RESULTS—Spontaneous ventilation (in terms of mean oxygen saturation) progressively improved (from T0 to T12-) during both REM sleep (24.8%, 95% CI 12.9 to 36.9) and NREM sleep (21.5%, 95% CI 12.4to 30.6). Sleep quality during spontaneous ventilation also improved in terms of increased total sleep time (26.8%, 95% CI 11.6 to 42.0) and sleep efficiency (17.5%, 95% CI 5.4 to 29.6) and decreased awakenings (54.0%, 95% CI 70.3 to 37.7). Accordingly, REM and NREM sleep stages 3 and 4 significantly improved. However, the most significant improvements in both nocturnal ventilation and sleep quality were seen during NMV at 12months.?CONCLUSIONS—After long term NMV both spontaneous ventilation during sleep and sleep quality in patients with CRF due to thoracic restriction showed evidence of progressive improvement compared with baseline after withdrawal of NMV for a single night at six and 12 months. However, the greatest improvements in nocturnal ventilation and sleep were achieved during NMV at 12months.?? PMID:10722771

Schonhofer, B.; Kohler, D.

2000-01-01

373

Electro-thermally induced structural failure actuator (ETISFA) for implantable controlled drug delivery devices based on micro-electro-mechanical-systems.  

PubMed

A new electro-thermally induced structural failure actuator (ETISFA) is introduced as an activation mechanism for on demand controlled drug delivery from a Micro-Electro-Mechanical-System (MEMS). The device architecture is based on a reservoir that is sealed by a silicon nitride membrane. The release mechanism consists of an electrical fuse constructed on the membrane. Activation causes thermal shock of the suspended membrane allowing the drugs inside of the reservoir to diffuse out into the region of interest. The effects of fuse width and thickness were explored by observing the extent to which the membrane was ruptured and the required energy input. Device design and optimization simulations of the opening mechanism are presented, as well as experimental data showing optimal energy consumption per fuse geometry. In vitro release experiments demonstrated repeatable release curves of mannitol-C(14) that precisely follow ideal first order release kinetics. Thermally induced structural failure was demonstrated as a feasible activation mechanism that holds great promise for controlled release in biomedical microdevices. PMID:20820485

Elman, N M; Masi, B C; Cima, M J; Langer, R

2010-10-21

374

Hypertension in renal failure  

Microsoft Academic Search

Hypertension is a common component of the morbidity associated with renal failure. The mechanisms that contribute to high blood pressure are reviewed in this section. Also covered are therapies to reduce hypertension, the treatment goals of those therapies, and the outcomes of antihypertensive therapy on kidney function in patients with renal failure. Various antihypertensive agents are specifically addressed, and a

Michael Cirigliano

1998-01-01

375

The kinetic and mechanical aspects of hydrogen-induced failure in metals. Ph.D. Thesis, 1971  

NASA Technical Reports Server (NTRS)

Premature hydrogen-induced failure observed to occur in many metal systems involves three stages of fracture: (1) crack initiation, (2) stable slow crack growth, and (3) unstable rapid crack growth. The presence of hydrogen at some critical location on the metal surface or within the metal lattice was shown to influence one or both of the first two stages of brittle fracture but has a negligible effect on the unstable rapid crack growth stage. The relative influence of the applied parameters of time, temperature, etc., on the propensity of a metal to exhibit hydrogen induced premature failure was investigated.

Nelson, H. G.

1972-01-01

376

Core valve implant failure in the presence of mechanical mitral prosthesis: Importance of assessing left ventricular outflow tract.  

PubMed

Transcatheter aortic valve replacement in the presence of a mitral prosthetic valve is a technically challenging endeavor. The presence of a mitral prosthesis can alter the geometry of the landing zone for the device. A multi slice computerized tomography with comprehensive review of left ventricular outflow tract and aortic root in its entirety is critical for preventing implant failure. Technical expedients to treat implant failure involve understanding of the device as well its relationship with the mitral prosthesis. © 2014 Wiley Periodicals, Inc. PMID:24403211

Sarkar, Kunal; Speciale, Giulio; Ussia, Gian Paolo

2015-04-01

377

Acute severe cardiac failure complicating myocardial infarction. Experience with 100 patients referred for consideration of mechanical left ventricular assistance  

Microsoft Academic Search

One hundred patients were referred with suspected acute cardiac failure following acute myocardial infarction. The diagnosis was confirmed in 72: 31 of these patients underwent elective medical treatment, with 2 survivors (6%); 41 were accepted for counter pulsation, but 9 died before this could be initiated and another 2 died shortly after vain attempts to pass the balloon catheter were

M F ORourke; V P Chang; H M Windsor; M X Shanahan; J B Hickie; J J Morgan; J F Gunning; A W Seldon; G V Hall; G Michell; D Goldfarb; D G Harrision

1975-01-01

378

Research on the failure process and mechanism of soil slope in seasonal frozen regions based on numerical simulation  

Microsoft Academic Search

In seasonal frozen regions, shallow landslide hazards in soil slopes usually happen, which pose a serious threat to road safety operations. The direct influence factor of soil slope failure is the shear strength of the soil between the freezing and thawing surface. Continuum explicit finite difference method (FDM) is applied in the research, and the thawing process of soil slope

Qi Ge; He Wu; Ya-feng Gong; Jia-ping Zhang

2011-01-01

379

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

PubMed Central

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

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

2014-01-01

380

Mechanical properties and oxidation resistance of plasma-sprayed multilayered Al 2O 3\\/ZrO 2 thermal barrier coatings  

Microsoft Academic Search

Coupled with functionally graded materials (FGM) concept, Al2O3 was proposed as a potential candidate as an interlayer to improve the oxidation resistance of thermal barrier coating (TBC) system due to its low oxygen diffusivity. Plasma spray process was utilized to produce Al2O3\\/ZrO2 functionally graded thermal barrier coating (FG-TBC). This article discusses physical and mechanical properties, thermal behavior, and high-temperature oxidation

Andi M. Limarga; Sujanto Widjaja; Tick Hon Yip

2005-01-01

381

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

PubMed Central

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

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

2013-01-01

382

Respiratory Failure  

MedlinePLUS

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

383

Kidney Failure  

MedlinePLUS

... at Risk? Professional Education Advocacy Donate Kidney Disease Chronic Kidney Disease Kidney-Friendly Diet & Foods for CKD Polycystic Kidney Disease Kidney Failure End Stage Renal Disease Complication: Anemia Complication: Bone Disease Kidney Failure Treatment Kidney Problems ...

384

Oxidative stress and heart failure  

Microsoft Academic Search

Various abnormalities have been implicated in the transition of hypertrophy to heart failure but the exact mechanism is still unknown. Thus heart failure subsequent to hypertrophy remains a major clinical problem. Recently, oxidative stress has been suggested to play a critical role in the pathogenesis of heart failure. Here we describe antioxidant changes as well as their significance during hypertrophy

Neelam Singh; Arvinder K. Dhalla; Charita Seneviratne; Pawan K. Singal

1995-01-01

385

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 ...

386

The use of failure mode and effects analysis to construct an effective disposal and prevention mechanism for infectious hospital waste  

SciTech Connect

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.

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

387

The use of failure mode and effects analysis to construct an effective disposal and prevention mechanism for infectious hospital waste.  

PubMed

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

Ho, Chao Chung; Liao, Ching-Jong

2011-12-01

388

Acute Lung Failure  

PubMed Central

Lung failure is the most common organ failure seen in the intensive care unit. The pathogenesis of acute respiratory failure (ARF) can be classified as (1) neuromuscular in origin, (2) secondary to acute and chronic obstructive airway diseases, (3) alveolar processes such as cardiogenic and noncardiogenic pulmonary edema and pneumonia, and (4) vascular diseases such as acute or chronic pulmonary embolism. This article reviews the more common causes of ARF from each group, including the pathological mechanisms and the principles of critical care management, focusing on the supportive, specific, and adjunctive therapies for each condition. PMID:21989697

Mac Sweeney, Rob; McAuley, Daniel F.; Matthay, Michael A.

2013-01-01

389

Failure of Viral Shells  

NASA Astrophysics Data System (ADS)

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.

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

390

Regulated Inositol?Requiring Protein 1?Dependent Decay as a Mechanism of Corin RNA and Protein Deficiency in Advanced Human Systolic Heart Failure  

PubMed Central

Background The compensatory actions of the endogenous natriuretic peptide system require adequate processing of natriuretic peptide pro?hormones into biologically active, carboxyl?terminal fragments. Natriuretic peptide pro?peptide processing is accomplished by corin, a transmembrane serine protease expressed by cardiomyocytes. Brain natriuretic peptide (BNP) processing is inadequate in advanced heart failure and is independently associated with adverse outcomes; however, the molecular mechanisms causing impaired BNP processing are not understood. We hypothesized that the development of endoplasmic reticulum stress in cardiomyocytes in advanced heart failure triggers inositol?requiring protein 1 (IRE1)?dependent corin mRNA decay, which would favor a molecular substrate favoring impaired natriuretic peptide pro?peptide processing. Methods and Results Two independent samples of hearts obtained from patients with advanced heart failure at transplant demonstrated that corin RNA was reduced as Atrial natriuretic peptide (ANP)/BNP RNA increased. Increases in spliced X?box protein 1, a marker for IRE1?endoribonuclease activity, were associated with decreased corin RNA. Moreover, ?50% of the hearts demonstrated significant reductions in corin RNA and protein as compared to the nonfailing control sample. In vitro experiments demonstrated that induction of endoplasmic reticulum stress in cultured cardiomyocytes with thapsigargin activated IRE1's endoribonuclease activity and time?dependent reductions in corin mRNA. In HL?1 cells, overexpression of IRE1 activated IRE1 endoribonuclease activity and caused corin mRNA decay, whereas IRE1?RNA interference with shRNA attenuated corin mRNA decay after induction of endoplasmic reticulum stress with thapsigargin. Pre?treatment of cells with Actinomycin D to inhibit transcription did not alter the magnitude or time course of thapsigargin?induced corin mRNA decline, supporting the hypothesis that this was the result of IRE1?mediated corin mRNA degradation. Conclusions These data support the hypothesis that endoplasmic reticulum stress?mediated, IRE1?dependent targeted corin mRNA decay is a mechanism leading to corin mRNA resulting in corresponding corin protein deficiency may contribute to the pathophysiology of impaired natriuretic peptide pro?hormone processing in humans processing in humans with advanced systolic heart failure. PMID:25516437

Lee, Rebecca; Xu, Bin; Rame, J. Eduardo; Felkin, Leanne E.; Barton, Paul; Dries, Daniel L.

2014-01-01

391

Investigation of deformation and failure mechanisms in woven and nonwoven fabrics under quasi-static loading conditions  

E-print Network

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 ...

Jearanaisilawong, Petch, 1979-

2004-01-01

392

A coupled numerical and experimental study on thermo-mechanical fatigue failure in SnAgCu solder joints  

Microsoft Academic Search

In ball grid array (BGA) packages, solder balls are exposed to cyclic thermo-mechanical strains arising from the thermal mismatch between package components. Since fatigue cracks in solder balls are observed generally at the chip side junction, dedicated fatigue experiments are conducted using eutectic SnAgCu- Ni\\/Au specimens in order to mechanically characterize the bonding interface. Sn based solders are prone to

M. Erinc; P. J. G. Schreurs; M. G. D. Geers

2007-01-01

393

Inhibition of adhesion of human neutrophils and eosinophils to P-selectin by the sialyl Lewis x antagonist TBC1269: Preferential activity against neutrophil adhesion in vitro  

Microsoft Academic Search

Background: Leukocyte rolling on vascular endothelium is mediated by selectins and their carbohydrate-containing counterligands. The tetrasaccharide sialyl Lewisx (sLex) binds to all 3 selectins, so compounds that mimic sLex are potential antagonists. Objective: Our purpose was to examine the ability of the sLex mimetic TBC1269 to inhibit binding of human neutrophils and eosinophils to P-selectin. Methods: Expression of the primary

Kelly L. Davenpeck; Kurt L. Berens; Richard A. F. Dixon; Brian Dupre; Bruce S. Bochner

2000-01-01

394

Effect of Interfacial Roughness of Bond Coat on the Residual Adhesion Strength of a Plasma Sprayed TBC System after Thermal Cycle Fatigue  

NASA Astrophysics Data System (ADS)

The effect of the bond coat on residual adhesion strength after thermal cycle fatigue was investigated in plasma-sprayed thermal barrier coatings (TBC). This study used CoNiCrAlY powder with two different particle sizes for spraying bond coat material to examine the effect of interface roughness between the bond coat and top coat. In addition, the bond coat was sprayed on either by a high velocity oxy-fuel (HVOF) or a low pressure plasma spray (LPPS). The residual adhesion strength of the TBC top coat was evaluated as a function of the number of thermal cycles by the modified 4-point bending test. In addition, SEM observations of thermal fatigue cracking morphologies and measurements of the residual stress in the ceramic top coat were carried out. The experimental results indicated that, after thermal cycle fatigue, microcracks were generated in the ceramic top coat; however, they were moderated in a rough interface TBC compared to a smooth interface TBC. In addition, the bond coat sprayed by the HVOF method showed a higher resistance to microcracking than the coat sprayed using the LPPS. Residual stress in the ceramic top coat is almost zero at 0 thermal cycles. After thermal cycle fatigue, it becomes compressional stress; however, it is independent of the bond coat. There was little difference in the adhesion strength by bond coat in as-sprayed conditions. On the other hand, the specimen with a rough interface exhibited higher residual adhesion strength after thermal cycle fatigue compared with the specimens with a relatively smooth interface. In addition, if the bond coat is sprayed by HVOF, the residual adhesion strength increases. It was revealed that the difference in residual adhesion strength by bond coat is related to the distribution morphology of thermal fatigue microcracks.

Yamazaki, Yasuhiro; Fukanuma, Hirotaka; Ohno, Naoyuki

395

Excess F-actin mechanically impedes mitosis leading to cytokinesis failure in X-linked neutropenia by exceeding Aurora B kinase error correction capacity  

PubMed Central

The constitutively active mutant of the Wiskott-Aldrich Syndrome protein (CA-WASp) is the cause of X-linked neutropenia and is linked with genomic instability and myelodysplasia. CA-WASp generates abnormally high levels of cytoplasmic F-actin through dysregulated activation of the Arp2/3 complex leading to defects in cell division. As WASp has no reported role in cell division, we hypothesized that alteration of cell mechanics due to increased F-actin may indirectly disrupt dynamic events during mitosis. Inhibition of the Arp2/3 complex revealed that excess cytoplasmic F-actin caused increased cellular viscosity, slowed all phases of mitosis, and perturbed mitotic mechanics. Comparison of chromosome velocity to the cytoplasmic viscosity revealed that cells compensated for increased viscosity by up-regulating force applied to chromosomes and increased the density of microtubules at kinetochores. Mitotic abnormalities were due to overload of the aurora signalling pathway as subcritical inhibition of Aurora in CA-WASp cells caused increased cytokinesis failure, while overexpression reduced defects. These findings demonstrate that changes in cell mechanics can cause significant mitotic abnormalities leading to genomic instability, and highlights the importance of mechanical sensors such as Aurora B in maintaining the fidelity of haematopoietic cell division. PMID:22972986

Moulding, D.A.; Moeendarbary, E.; Valon, L.; Record, J.; Charras, G.T.; Thrasher, A.J.

2015-01-01

396

Excess F-actin mechanically impedes mitosis leading to cytokinesis failure in X-linked neutropenia by exceeding Aurora B kinase error correction capacity.  

PubMed

The constitutively active mutant of the Wiskott-Aldrich Syndrome protein (CA-WASp) is the cause of X-linked neutropenia and is linked with genomic instability and myelodysplasia. CA-WASp generates abnormally high levels of cytoplasmic F-actin through dysregulated activation of the Arp2/3 complex leading to defects in cell division. As WASp has no reported role in cell division, we hypothesized that alteration of cell mechanics because of increased F-actin may indirectly disrupt dynamic events during mitosis. Inhibition of the Arp2/3 complex revealed that excess cytoplasmic F-actin caused increased cellular viscosity, slowed all phases of mitosis, and perturbed mitotic mechanics. Comparison of chromosome velocity to the cytoplasmic viscosity revealed that cells compensated for increased viscosity by up-regulating force applied to chromosomes and increased the density of microtubules at kinetochores. Mitotic abnormalities were because of overload of the aurora signaling pathway as subcritical inhibition of Aurora in CA-WASp cells caused increased cytokinesis failure, while overexpression reduced defects. These findings demonstrate that changes in cell mechanics can cause significant mitotic abnormalities leading to genomic instability, and highlight the importance of mechanical sensors such as Aurora B in maintaining the fidelity of hematopoietic cell division. PMID:22972986

Moulding, Dale A; Moeendarbary, Emad; Valon, Leo; Record, Julien; Charras, Guillaume T; Thrasher, Adrian J

2012-11-01

397

Materials Science and Engineering A, 2011, 528(1-2): p. 7596 7605 High strain rate compressive response ofsyntactic foams: trends in mechanical properties and failure mechanisms  

E-print Network

, carbon, or polymer microballoons [8, 9] and fly ash cenospheres [10]. Enclosing porosity inside thin and Vasanth Chakravarthy Shunmugasamy Composite Materials and Mechanics Laboratory Department of Mechanical, Fax: 1-718-260 3532, Email: ngupta@poly.edu Abstract Syntactic foams are composite materials

Gupta, Nikhil

398

Saturn component failure rate and failure rate modifiers  

NASA Technical Reports Server (NTRS)

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.

1971-01-01

399

The dual role of fission yeast Tbc1/cofactor C orchestrates microtubule homeostasis in tubulin folding and acts as a GAP for GTPase Alp41/Arl2.  

PubMed

Supplying the appropriate amount of correctly folded ?/?-tubulin heterodimers is critical for microtubule dynamics. Formation of assembly-competent heterodimers is remarkably elaborate at the molecular level, in which the ?- and ?-tubulins are separately processed in a chaperone-dependent manner. This sequential step is performed by the tubulin-folding cofactor pathway, comprising a specific set of regulatory proteins: cofactors A-E. We identified the fission yeast cofactor: the orthologue of cofactor C, Tbc1. In addition to its roles in tubulin folding, Tbc1 acts as a GAP in regulating Alp41/Arl2, a highly conserved small GTPase. Of interest, the expression of GDP- or GTP-bound Alp41 showed the identical microtubule loss phenotype, suggesting that continuous cycling between these forms is important for its functions. In addition, we found that Alp41 interacts with Alp1(D), the orthologue of cofactor D, specifically when in the GDP-bound form. Intriguingly, Alp1(D) colocalizes with microtubules when in excess, eventually leading to depolymerization, which is sequestered by co-overproducing GDP-bound Alp41. We present a model of the final stages of the tubulin cofactor pathway that includes a dual role for both Tbc1 and Alp1(D) in opposing regulation of the microtubule. PMID:23576550

Mori, Risa; Toda, Takashi

2013-06-01

400

The dual role of fission yeast Tbc1/cofactor C orchestrates microtubule homeostasis in tubulin folding and acts as a GAP for GTPase Alp41/Arl2  

PubMed Central

Supplying the appropriate amount of correctly folded ?/?-tubulin heterodimers is critical for microtubule dynamics. Formation of assembly-competent heterodimers is remarkably elaborate at the molecular level, in which the ?- and ?-tubulins are separately processed in a chaperone-dependent manner. This sequential step is performed by the tubulin-folding cofactor pathway, comprising a specific set of regulatory proteins: cofactors A–E. We identified the fission yeast cofactor: the orthologue of cofactor C, Tbc1. In addition to its roles in tubulin folding, Tbc1 acts as a GAP in regulating Alp41/Arl2, a highly conserved small GTPase. Of interest, the expression of GDP- or GTP-bound Alp41 showed the identical microtubule loss phenotype, suggesting that continuous cycling between these forms is important for its functions. In addition, we found that Alp41 interacts with Alp1D, the orthologue of cofactor D, specifically when in the GDP-bound form. Intriguingly, Alp1D colocalizes with microtubules when in excess, eventually leading to depolymerization, which is sequestered by co-overproducing GDP-bound Alp41. We present a model of the final stages of the tubulin cofactor pathway that includes a dual role for both Tbc1 and Alp1D in opposing regulation of the microtubule. PMID:23576550

Mori, Risa; Toda, Takashi

2013-01-01

401

Protective mechanisms of acacetin against D-galactosamine and lipopolysaccharide-induced fulminant hepatic failure in mice.  

PubMed

This study examined the hepatoprotective effects of acacetin (1), a flavonoid isolated from Agastache rugosa, against d-galactosamine (GalN) and lipopolysaccharide (LPS)-induced fulminant hepatic failure. Mice were given an intraperitoneal injection of 1 (25, 50, and 100 mg/kg), or the vehicle alone (5% dimethyl sulfoxide-saline), 1 h before GalN (800 mg/kg)/LPS (40 ?g/kg) treatment and sacrificed at 6 h after GalN/LPS injection. GalN/LPS markedly increased mortality and serum aminotransferase activity, and these increases were attenuated by 1. GalN/LPS increased serum tumor necrosis factor-? (TNF-?) and interleukin-6 (IL-6) levels, while 1 attenuated TNF-? levels and further increased IL-6 levels. GalN/LPS increased protein expression of toll-like receptor 4, phosphorylation of extracellular signal-related kinase, and p38 and c-Jun N-terminal kinase and increased nuclear protein expression of nuclear factor ?B; these increases were attenuated by 1. GalN/LPS increased Atg5 and Atg7 protein expressions, and these increases were augmented by 1. GalN/LPS activated autophagic flux as indicated by decreased microtubule-associated protein 1 light chain 3-II and sequestosome1/p62 protein expression. This activation was enhanced by 1. These findings suggest that 1 protects against GalN/LPS-induced liver injury by suppressing TLR4 signaling and enhancing autophagic flux. PMID:25382719

Cho, Hong-Ik; Park, Jin-Hyun; Choi, Hyo-Sun; Kwak, Jong Hwan; Lee, Dong-Ung; Lee, Sang Kook; Lee, Sun-Mee

2014-11-26

402

Ceramic High Performance Material. Lightweighted Mirrors and Stable Structures for Large Adaptive Optics (TBC)  

NASA Astrophysics Data System (ADS)

BOOSTEC recent developments on Silicon Carbide material manufacturing permit to create new design for large adaptive optics and stable structures. High level thermomechanical performances are fully qualified for spatial components and can be transferred to ground applications. To reach new AO requirements for resonnance frequencies, thermal dissipation, mechanical resistance and stability and to apply on very large size mirrors, frames and structures, BOOSTEC proposes additionnal manufacturing capacities. Presentation of recent progress on ceramic parts implementations.

Chaillot, Stéphane

2011-09-01

403

Biomechanical modeling and morphology analysis indicates plaque rupture due to mechanical failure unlikely in atherosclerosis-prone mice  

PubMed Central

Spontaneous plaque rupture in mouse models of atherosclerosis is controversial, although numerous studies have discussed so-called “vulnerable plaque” phenotypes in mice. We compared the morphology and biomechanics of two acute and one chronic murine model of atherosclerosis to human coronaries of the thin-cap fibroatheroma (TCFA) phenotype. Our acute models were apolipoprotein E-deficient (ApoE?/?) and LDL receptor-deficient (LDLr?/?) mice, both fed a high-fat diet for 8 wk with simultaneous infusion of angiotensin II (ANG II), and our chronic mouse model was the apolipoprotein E-deficient strain fed a regular chow diet for 1 yr. We found that the mouse plaques from all three models exhibited significant morphological differences from human TCFA plaques, including the plaque burden, plaque thickness, eccentricity, and amount of the vessel wall covered by lesion as well as significant differences in the relative composition of plaques. These morphological differences suggested that the distribution of solid mechanical stresses in the walls may differ as well. Using a finite-element analysis computational solid mechanics model, we computed the relative distribution of stresses in the walls of murine and human plaques and found that although human TCFA plaques have the highest stresses in the thin fibrous cap, murine lesions do not have such stress distributions. Instead, local maxima of stresses were on the media and adventitia, away from the plaque. Our results suggest that if plaque rupture is possible in mice, it may be driven by a different mechanism than mechanics. PMID:23203971

Campbell, Ian C.; Weiss, Daiana; Suever, Jonathan D.; Virmani, Renu; Veneziani, Alessandro; Vito, Raymond P.; Oshinski, John N.

2013-01-01

404

Biomechanical modeling and morphology analysis indicates plaque rupture due to mechanical failure unlikely in atherosclerosis-prone mice.  

PubMed

Spontaneous plaque rupture in mouse models of atherosclerosis is controversial, although numerous studies have discussed so-called "vulnerable plaque" phenotypes in mice. We compared the morphology and biomechanics of two acute and one chronic murine model of atherosclerosis to human coronaries of the thin-cap fibroatheroma (TCFA) phenotype. Our acute models were apolipoprotein E-deficient (ApoE(-/-)) and LDL receptor-deficient (LDLr(-/-)) mice, both fed a high-fat diet for 8 wk with simultaneous infusion of angiotensin II (ANG II), and our chronic mouse model was the apolipoprotein E-deficient strain fed a regular chow diet for 1 yr. We found that the mouse plaques from all three models exhibited significant morphological differences from human TCFA plaques, including the plaque burden, plaque thickness, eccentricity, and amount of the vessel wall covered by lesion as well as significant differences in the relative composition of plaques. These morphological differences suggested that the distribution of solid mechanical stresses in the walls may differ as well. Using a finite-element analysis computational solid mechanics model, we computed the relative distribution of stresses in the walls of murine and human plaques and found that although human TCFA plaques have the highest stresses in the thin fibrous cap, murine lesions do not have such stress distributions. Instead, local maxima of stresses were on the media and adventitia, away from the plaque. Our results suggest that if plaque rupture is possible in mice, it may be driven by a different mechanism than mechanics. PMID:23203971

Campbell, Ian C; Weiss, Daiana; Suever, Jonathan D; Virmani, Renu; Veneziani, Alessandro; Vito, Raymond P; Oshinski, John N; Taylor, W Robert

2013-02-01

405

Electrophysiological Remodeling in Heart Failure  

PubMed Central

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

Wang, Yanggan; Hill, Joseph A.

2010-01-01

406

Postmortem and insitu TEM methods to study the mechanism of failure in controlled-morphology high-impact polystrene resin  

SciTech Connect

Advanced Styrenic resins are being developed throughout the industry to bridge the properties gap between traditional HIPS (High Impact Polystyrene) and ABS (Acrylonitrile-Butadiene-Styrene copolymers) resins. These new resins have an unprecedented balance of high gloss and high impact energies. Dow Chemical`s contribution to this area is based on a unique combination of rubber morphologies including labyrinth, onion skin, and core-shelf rubber particles. This new resin, referred as a controlled morphology resin (CMR), was investigated to determine the toughening mechanism of this unique rubber morphology. This poster will summarize the initial studies of these resins using the double-notch four-point bend test of Su and Yee, tensile stage electron microscopy, and Poisson Ratio analysis of the fracture mechanism.

Cieslinski, R.C.; Dineen, M.T.; Hahnfeld, J.L. [Dow Chemical Company, Midland, MI (United States)

1996-12-31

407

Failure mode analysis and a mechanism for hot-ductility improvement in the Nb-microalloyed steel  

Microsoft Academic Search

Loss of hot ductility at the straightening stage of the continuous casting of high-strength low-alloy steel is attributed\\u000a to different microalloying elements, in particular, Nb. However, such elements are essential for the desired mechanical characteristics\\u000a of the final product. Since the chemistry cannot be altered to alleviate the problem, thermomechanical processing was studied\\u000a in order to improve the hot ductility.

Faramarz Zarandi; Steven Yue

2004-01-01

408

Ballistic-Failure Mechanisms in Gas Metal Arc Welds of Mil A46100 Armor-Grade Steel: A Computational Investigation  

NASA Astrophysics Data System (ADS)

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.

Grujicic, M.; Snipes, J. S.; Galgalikar, R.; Ramaswami, S.; Yavari, R.; Yen, C.-F.; Cheeseman, B. A.

2014-09-01

409

Heart Failure  

MedlinePLUS

... report any unexplained changes to your doctor. Other Organizations ... What is the likely cause of my congestive heart failure? How serious is my condition? How will my life change now that we know I have heart ...

410

Heart Failure  

MedlinePLUS

... this? Submit What's this? Submit Button Related CDC Web Sites Heart Disease Stroke High Blood Pressure Salt ... and empower Americans to make heart-healthy choices. Web Sites with More Information About Heart Failure For ...

411

Thermomechanical Fatigue Damage/Failure Mechanisms in SCS-6/Timetal 21S [0/90](Sub S) Composite  

NASA Technical Reports Server (NTRS)

The thermomechanical fatigue (TMF) deformation, damage, and life behaviors of SCS6/Timetal 21S (0/90)s were investigated under zero-tension conditions. In-phase (IP) and out-of-phase (OP) loadings were investigated with a temperature cycle from 150 to 650 deg C. An advanced TMF test technique was used to quantify mechanically damage progression. The technique incorporated explicit measurements of the macroscopic (1) isothermal static moduli at the temperature extremes of the TMF cycle and (2) coefficient of thermal expansion (CTE) as functions of the TMF cycles. The importance of thermal property degradation and its relevance to accurate post-test data analysis and interpretation is briefly addressed. Extensive fractography and metallography were conducted on specimens from failed and interrupted tests to characterize the extent of damage at the microstructure level. Fatigue life results indicated trends analogous to those established for similar unidirectional(0) reinforced titanium matrix composite systems. High stress IP and mid to low stress OP loading conditions were life-limiting in comparison to maximum temperature isothermal conditions. Dominant damage mechanisms changed with cycle type. Damage resulting from IP TMF conditions produced measurable decreases in static moduli but only minimal changes in the CTE. Metallography on interrupted and failed specimens revealed extensive (0) fiber cracking with sparse matrix damage. No surface initiated matrix cracks were present. Comparable OP TMF conditions initiated environment enhanced surface cracking and matrix cracking initiated at (90) fiber/matrix (F/M) interfaces. Notable static moduli and CTE degradations were measured. Fractography and metallography revealed that the transverse cracks originating from the surface and (90) F/M interfaces tended to converge and coalesce at the (0) fibers.

Castelli, Michael G.

1994-01-01

412

Combining mechanical and chemical effects in the deformation and failure of a cylindrical electrode particle in a Li-ion battery  

E-print Network

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.

Jeevanjyoti Chakraborty; Colin P. Please; Alain Goriely; S. Jonathan Chapman

2014-07-31

413