These are representative sample records from Science.gov related to your search topic.
For comprehensive and current results, perform a real-time search at Science.gov.
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

Failure mechanisms in MEMS.  

SciTech Connect

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

Walraven, Jeremy Allen

2003-07-01

5

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

6

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

2014-11-01

7

Targeted disruption of Tbc1d20 with zinc-finger nucleases causes cataracts and testicular abnormalities in mice.  

PubMed

BackgroundLoss-of-function mutations in TBC1D20 cause Warburg Micro syndrome 4 (WARBM4), which is an autosomal recessive syndromic disorder characterized by eye, brain, and genital abnormalities. Blind sterile (bs) mice carry a Tbc1d20-null mutation and exhibit cataracts and testicular phenotypes similar to those observed in WARBM4 patients. In addition to TBC1D20, mutations in RAB3GAP1, RAB3GAP2 and RAB18 cause WARBM1-3 respectively. However, regardless of which gene harbors the causative mutation, all individuals affected with WARBM exhibit indistinguishable clinical presentations. In contrast, bs, Rab3gap1 -/- , and Rab18 -/- mice exhibit distinct phenotypes; this phenotypic variability of WARBM mice was previously attributed to potential compensatory mechanisms. Rab3gap1 -/- and Rab18 -/- mice were genetically engineered using standard approaches, whereas the Tbc1d20 mutation in the bs mice arose spontaneously. There is the possibility that another unidentified mutation within the bs linkage disequilibrium may be contributing to the bs phenotypes and thus contributing to the phenotypic variability in WARBM mice. The goal of this study was to establish the phenotypic consequences in mice caused by the disruption of the Tbc1d20 gene.ResultsThe zinc finger nuclease (ZFN) mediated genomic editing generated a Tbc1d20 c.[418_426del] deletion encoding a putative TBC1D20-ZFN protein with an in-frame p.[H140_Y143del] deletion within the highly conserved TBC domain. The evaluation of Tbc1d20 ZFN/ZFN eyes identified severe cataracts and thickened pupillary sphincter muscle. Tbc1d20 ZFN/ZFN males are infertile and the analysis of the seminiferous tubules identified disrupted acrosomal development. The compound heterozygote Tbc1d20 ZFN/bs mice, generated from an allelic bs/+ X Tbc1d20 ZFN/+ cross, exhibited cataracts and aberrant acrosomal development indicating a failure to complement.ConclusionsOur findings show that the disruption of Tbc1d20 in mice results in cataracts and aberrant acrosomal formation, thus establishing bs and Tbc1d20 ZFN/ZFN as allelic variants. Although the WARBM molecular disease etiology remains unclear, both the bs and Tbc1d20 ZFN/ZFN mice are excellent model organisms for future studies to establish TBC1D20-mediated molecular and cellular functions. PMID:25476608

Park, Anna; Liegel, Ryan P; Ronchetti, Adam; Ebert, Allison D; Geurts, Aron; Sidjanin, Duska J

2014-12-01

8

Mechanisms of thermal barrier coating degradation and failure  

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

9

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

10

Failure mechanisms in fibrous scaffolds.  

PubMed

Polymeric fibrous scaffolds have been considered as replacements for load-bearing soft tissues, because of their ability to mimic the microstructure of natural tissues. Poor toughness of fibrous materials results in failure, which is an issue of importance to both engineering and medical practice. The toughness of fibrous materials depends on the ability of the microstructure to develop toughening mechanisms. However, such toughening mechanisms are still not well understood, because the detailed evolution at the microscopic level is difficult to visualize. A novel and simple method was developed, namely, a sample-taping technique, to examine the detailed failure mechanisms of fibrous microstructures. This technique was compared with in situ fracture testing by scanning electron microscopy. Examination of three types of fibrous networks showed that two different failure modes occurred in fibrous scaffolds. For brittle cracking in gelatin electrospun scaffolds, the random network morphology around the crack tip remained during crack propagation. For ductile failure in polycaprolactone electrospun scaffolds and nonwoven fabrics, the random network deformed via fiber rearrangement, and a large number of fiber bundles formed across the region in front of the notch tip. These fiber bundles not only accommodated mechanical strain, but also resisted crack propagation and thus toughened the fibrous scaffolds. Such understanding provides insight for the production of fibrous materials with enhanced toughness. PMID:23470550

Koh, C T; Strange, D G T; Tonsomboon, K; Oyen, M L

2013-07-01

11

Effect of Coating Process Condition on High-Temperature Oxidation and Mechanical Failure Behavior for Plasma Sprayed Thermal Barrier Coating Systems  

NASA Astrophysics Data System (ADS)

In order to clarify the thermal and/or mechanical failure behavior of the plasma sprayed thermal barrier coating (TBC) system in connection with their coating characteristics depending on the coating process condition, two kinds of the failure analytical tests were conducted for TBC systems processed under different conditions. One was the high-temperature oxidation test, which was conducted at 1100°C under both the isothermal and thermal cycle conditions. The other was the in-situ observation of mechanical failure behavior, which was conducted under the static loadings at ambient temperature; as the most fundamental aspect, by means of an optical microscopy. It was found that the thermal and mechanical failure behavior of TBC system depends strongly on the top-coat (TC)/bond-coat (BC) interfacial condition, the reheat-treatment (RHT) after spraying and so on. For the TBC system with vacuum plasma sprayed (VPS) BC as well as for that with atmospheric plasma sprayed (APS) BC, in particular, the RHT at an appropriate temperature in Ar atmosphere was found to be effective for improving the oxidation property. For the TBC system with APS-BC, however, it was impossible to prevent the crack growth into the BC interior under the tensile loading in spite of conducting the RHT, since the microdefects such as oxides within the APS-BC tend to provide an easy crack propagation path. Furthermore, it was clarified that the smoothening process on the BC surface is able to prevent perfectly the occurrence of the wart-like oxide during oxidation, but at the same time increases also the risk of the TC spalling under the mechanical loading.

Takahashi, Satoru; Yoshiba, Masayuki; Harada, Yoshio

12

Failure mechanism models for brittle fracture  

Microsoft Academic Search

This tutorial illustrates designs where brittle fracture can endanger system performance, thereby acting as an overstress failure mechanism. Analytic (physics-of-failure) methods, based on continuum fracture-mechanisms rather than on molecular micro-mechanics, are presented to design against such failures. The associated stress-analysis techniques and material characterizations have matured appreciably over the past 40 years and are routinely used in aerospace, automotive, and

Abhijit Dasgupta; Jun Ming Hu

1992-01-01

13

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

14

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

15

The lustering of TBC-2  

NASA Astrophysics Data System (ADS)

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

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

1995-05-01

16

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

17

Field failure mechanisms for photovoltaic modules  

NASA Technical Reports Server (NTRS)

Beginning in 1976, Department of Energy field centers have installed and monitored a number of field tests and application experiments using current state-of-the-art photovoltaic modules. On-site observations of module physical and electrical degradation, together with in-depth laboratory analysis of failed modules, permits an overall assessment of the nature and causes of early field failures. Data on failure rates are presented, and key failure mechanisms are analyzed with respect to origin, effect, and prospects for correction. It is concluded that all failure modes identified to date are avoidable or controllable through sound design and production practices.

Dumas, L. N.; Shumka, A.

1981-01-01

18

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

19

Compression failure mechanisms in unidirectional composites  

NASA Technical Reports Server (NTRS)

Compression failure mechanisms in unidirectional composites were examined. Possible failure modes of constituent materials are summarized and analytical models for fiber microbuckling are reviewed from a unified viewpoint. Due to deficiencies in available models, a failure model based on nonlinear properties and initial fiber curvature is proposed. The effect of constituent properties on composite compression behavior was experimentally investigated using two different graphite fibers and four different epoxy resins. The predominant microscopic scale failure mode was found to be shear crippling. In a soft resin, shear crippling was in the form of buckling of fibers on a microscopic scale. However, stiff resins failure was characterized by the formation of a kink band. For unidirectional laminates, compressive strength, and compressive modulus to a less extent, were found to increase with increasing magnitude of resin modulus. The change in compressive strength with resin modulus was predicted using the proposed nonlinear model.

Hahn, H. T.; Williams, J. G.

1984-01-01

20

Failure mechanisms in wire ropes  

Microsoft Academic Search

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

C. R. Chaplin

1995-01-01

21

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

22

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

23

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

24

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

25

Mechanical support for postcardiotomy heart failure.  

PubMed

Cardiac failure remains a life-threatening complication for certain patients undergoing intracardiac repair. Despite improvements in surgical techniques, methods of myocardial protection, and postoperative care, patients are frequently at risk to develop postoperative low output syndrome. Approximately 1% of cardiac surgical patients cannot be weaned from extracorporeal circulation in spite of adequate volume loading, the use of inotropic support, and initiation of intraaortic balloon pumping. In these cases, ventricular assist devices (VAD) can mechanically aid the failing heart and reverse the low output state. The concept of mechanical support for the failing left ventricle was first proposed by Clauss et al. in 1961. By 1968, Kantrowitz and associates had developed and refined the first intraaortic balloon pump (IABP). Through the efforts of Moulopolous and others, this device evolved into the present-day intraaortic balloon pump (IABP). Clinical evidence for the efficacy of left ventricular assist devices (LVAD) remained questionable until 1980, when the National Heart, Blood and Lung Institute evaluated short-term LVADs by comparing various types of mechanical aids. This report focused attention primarily on the failing left ventricle (LV). As the use of inotropic support, intraaortic balloon pumping, and LVADs improved, a small group of patients emerged who could not be separated from extracorporeal circulation due to a failing right ventricle. The failing right ventricle emerged as a unique clinical entity similar to postcardiotomy left ventricular failure that also benefited from mechanical cardiac assistance. Current therapy at major centers incorporating mechanical assist devices is based on the premise that the low output state will allow the failing heart to recover from a reversible injury. The frequent occurrence of postcardiotomy ischemia may be due to several factors such as poor myocardial protection, overdistension of the LV, emboli, coronary spasm or technical problems. Whatever the etiology, the end product of cardiac failure is a demand for oxygen consumption that cannot be met, thus leading to cardiac demise. PMID:2980017

Campbell, C D; Tolitano, D J; Weber, K T; Statler, P M; Replogle, R L

1988-09-01

26

Mechanisms of failure of modular prostheses.  

PubMed

The expectations of wear and longevity of total hip components are based in large part on Charnley's early work. The evolution of the total hip from the one-piece, all-polyethylene acetabular component and fixed-head femoral component to the myriad of parts that comprise many of today's total hip designs has brought with it an array of potential mechanisms for failure that were not present in the earlier design. The risk/benefit ratio of these new designs may need to be reevaluated based on the additional mechanisms for failure that they provide. One hundred eleven acetabular hip prostheses and 139 femoral prostheses, all of modular configuration, retrieved by surgeons in the field, and sent for histologic examination, were analyzed for this study. A number of component characteristics were found to be correlated to early failure. These included acetabular designs with thin polyethylene bearings, poor fixation of the polyethylene to the metal shell, and geometries that permitted a moment to be applied to the bearing insert, tending to cause it to rotate in the metal shell. Modular femoral components were observed to be susceptible to corrosion, with titanium-alloy stems mated to cast cobalt-alloy heads at greatest risk attributable to a galvanic effect. All modular connections of femoral and acetabular components are at risk for disassociation and fretting; therefore, clever design and precision machining are necessary to produce prostheses in which the benefits of modularity exceed the risks. PMID:1446428

Collier, J P; Mayor, M B; Jensen, R E; Surprenant, V A; Surprenant, H P; McNamar, J L; Belec, L

1992-12-01

27

Implantation failure: molecular mechanisms and clinical treatment  

PubMed Central

BACKGROUND Implantation is a complex initial step in the establishment of a successful pregnancy. Although embryo quality is an important determinant of implantation, temporally coordinated differentiation of endometrial cells to attain uterine receptivity and a synchronized dialog between maternal and embryonic tissues are crucial. The exact mechanism of implantation failure is still poorly understood. METHODS This review summarizes the current knowledge about the proposed mechanisms of implantation failure in gynecological diseases, the evaluation of endometrial receptivity and the treatment methods to improve implantation. RESULTS The absence or suppression of molecules essential for endometrial receptivity results in decreased implantation rates in animal models and gynecological diseases, including endometriosis, hydrosalpinx, leiomyoma and polycystic ovarian syndrome. The mechanisms are diverse and include abnormal cytokine and hormonal signaling as well as epigenetic alterations. CONCLUSIONS Optimizing endometrial receptivity in fertility treatment will improve success rates. Evaluation of implantation markers may help to predict pregnancy outcome and detect occult implantation deficiency. Treating the underlying gynecological disease with medical or surgical interventions is the optimal current therapy. Manipulating the expression of key endometrial genes with gene or stem cell-based therapies may some day be used to further improve implantation rates. PMID:20729534

Cakmak, Hakan; Taylor, Hugh S.

2011-01-01

28

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

29

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

30

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

31

Cyclic Failure Mechanisms of Thermal and Environmental Barrier Coating Systems Under Thermal Gradient Test Conditions  

NASA Technical Reports Server (NTRS)

Plasma-sprayed ZrO2-8wt%Y2O3 and mullite+BSAS/Si multilayer thermal and environmental barrier coating (TBC-EBC) systems on SiC/SiC ceramic matrix composite (CMC) substrates were thermally cyclic tested under high thermal gradients using a laser high-heat-flux rig in conjunction with furnace exposure in water-vapor environments. Coating sintering and interface damage were assessed by monitoring the real-time thermal conductivity changes during the laser heat-flux tests and by examining the microstructural changes after exposure. Sintering kinetics of the coating systems were also independently characterized using a dilatometer. It was found that the coating failure involved both the time-temperature dependent sintering and the cycle frequency dependent cyclic fatigue processes. The water vapor environments not only facilitated the initial coating conductivity increases due to enhanced sintering and interface reaction, but also promoted later conductivity reductions due to the accelerated coating cracking and delamination. The failure mechanisms of the coating systems are also discussed based on the cyclic test results and are correlated to the sintering and thermal stress behavior under the thermal gradient test conditions.

Zhu, Dongming; Lee, Kang N.; Miller, Robert A.

2002-01-01

32

Cytoplasmic retention of a nucleocytoplasmic protein TBC1D3 by microtubule network is required for enhanced EGFR signaling.  

PubMed

The hominoid oncogene TBC1D3 enhances epidermal growth factor receptor (EGFR) signaling and induces cell transformation. However, little is known regarding its spatio-temporal regulation and mechanism of tumorigenesis. In the current study, we identified the microtubule subunit ?-tubulin as a potential interaction partner for TBC1D3 using affinity purification combined with mass spectrometry analysis. The interaction between TBC1D3 and ?-tubulin was confirmed by co-immunoprecipitation. Using the same method, we also revealed that TBC1D3 co-precipitated with endogenous ?-tubulin, another subunit of the microtubule. In agreement with these results, microtubule cosedimentation assays showed that TBC1D3 associated with the microtubule network. The ?-tubulin-interacting site of TBC1D3 was mapped to amino acids 286?353 near the C-terminus of the TBC domain. Deletion mutation within these amino acids was shown to abolish the interaction of TBC1D3 with ?-tubulin. Interestingly, the deletion mutation caused a complete loss of TBC1D3 from the cytoplasmic filamentous and punctate structures, and TBC1D3 instead appeared in the nucleus. Consistent with this, wild-type TBC1D3 exhibited the same nucleocytoplasmic distribution in cells treated with the microtubule depolymerizing agent nocodazole, suggesting that the microtubule network associates with and retains TBC1D3 in the cytoplasm. We further found that deficiency in ?-tubulin-interacting resulted in TBC1D3's inability to inhibit c-Cbl recruitment and EGFR ubiquitination, ultimately leading to dysregulation of EGFR degradation and signaling. Taken together, these studies indicate a novel model by which the microtubule network regulates EGFR stability and signaling through tubulin dimer/oligomer interaction with the nucleocytoplasmic protein TBC1D3. PMID:24714105

He, Ze; Tian, Tian; Guo, Dan; Wu, Huijuan; Chen, Yang; Zhang, Yongchen; Wan, Qing; Zhao, Huzi; Wang, Congyang; Shen, Hongjing; Zhao, Lei; Bu, Xiaodong; Wan, Meiling; Shen, Chuanlu

2014-01-01

33

Assessment of Cyclic Lifetime of NiCoCrAlY/ZrO2-Based EB-PVD TBC Systems via Reactive Element Enrichment in the Mixed Zone of the TGO Scale  

NASA Astrophysics Data System (ADS)

The chemical composition of the alumina-zirconia mixed zone (MZ) of an electron beam physical vapor deposited thermal barrier coating (EB-PVD TBC) system is affected by service conditions and by the interdiffusion of elements from the substrate alloy below and the zirconia top coat. Three NiCoCrAlY bond-coated Ni-base substrates with YPSZ or CeSZ EB-PVD TBCs were subjected to a cyclic furnace oxidation test (FCT) at 1373 K (1100 °C) in order to provide experimental evidence of a link between chemistry of the MZ, the substrate alloy, the ceramic top coat, and the time in the FCT. Energy dispersive spectroscopy of the MZ revealed preferred accumulation of Cr, Zr, Y, and Ce. The concentration of the reactive elements (RE = Ce + Y + Zr) was related to the respective average lifetimes of the TBC systems at 1373 K (1100 °C). The RE content in the MZ turned out to be a life-limiting parameter for YPSZ and CeSZ TBC systems which can be utilized to predict their relative lifetimes on the individual substrates. Conversely, the TBC failure mechanisms of YPSZ and CeSZ TBC systems are dissimilar.

Fritscher, Klaus; Braue, Wolfgang; Schulz, Uwe

2013-05-01

34

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

35

Failure mechanisms of load-sharing complex systems  

NASA Astrophysics Data System (ADS)

We investigate the failure mechanisms of load-sharing complex systems. The system is composed of multiple nodes or components whose failures are determined based on the interaction of their respective strengths and loads (or capacity and demand, respectively) as well as the ability of a component to share its load with its neighbors when needed. We focus on two distinct mechanisms to model the interaction between components' strengths and loads. The failure mechanisms of these two models demonstrate temporal scaling phenomena, phase transitions, and multiple distinct failure modes excited by extremal dynamics. For critical ranges of parameters the models demonstrate power-law and exponential failure patterns. We identify the similarities and differences between the two mechanisms and the implications of our results for the failure mechanisms of complex systems in the real world.

Siddique, Shahnewaz; Volovoi, Vitali

2014-01-01

36

Mesh convergence differences based on failure mechanisms  

SciTech Connect

Material properties affect the deformation and failure modes in structural parts. When performing finite element analyses to compare response for different materials, different levels of mesh discretization may be necessary for each analyses because the failure mode changes, even through the part geometry and loading remain the same. Take, for example, strain localization, a material dependent phenomenon. When localization occurs, the mesh needs to be much finer to capture the steep strain gradients in the region of localization than in a case where localization does not occur. Although this requirement is almost intuitive once stated, it is often not used in practice because the effects are less pronounced when failure is not present, and also because failure modes are difficult to anticipate. The lack of availability of constitutive models for failure prediction is also a contributing factor. This paper describes a recent study regarding the effect of mesh refinement on failure prediction in a part modeled with two different materials.

Pilat, K.R. [Cornell Univ., Ithaca, NY (United States); Revelli, V.D. [Sandia National Labs., Livermore, CA (United States)

1994-04-01

37

TBC1D1 reduces palmitate oxidation by inhibiting ?-HAD activity in skeletal muscle.  

PubMed

In skeletal muscle the Rab-GTPase-activating protein TBC1D1 has been implicated in the regulation of fatty acid oxidation by an unknown mechanism. We determined whether TBC1D1 altered fatty acid utilization via changes in protein-mediated fatty acid transport and/or selected enzymes regulating mitochondrial fatty acid oxidation. We also determined the effects of TBC1D1 on glucose transport and oxidation. Electrotransfection of mouse soleus muscles with TBC1D1 cDNA increased TBC1D1 protein after 2 wk (P<0.05), without altering its paralog AS160. TBC1D1 overexpression decreased basal palmitate oxidation (-22%) while blunting 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR)-stimulated palmitate oxidation (-18%). There was a tendency to increase fatty acid esterification (+10 nmol·g(-1)·60 min(-1), P=0.07), which reflected the reduction in fatty acid oxidation (-12 nmol·g(-1)·60 min(-1)). Concomitantly, basal (+21%) and AICAR-stimulated glucose oxidation (+8%) were increased in TBC1D1-transfected muscles relative to their respective controls (P<0.05), independent of changes in GLUT4 and glucose transport. The reductions in TBC1D1-mediated fatty acid oxidation could not be attributed to changes in the transporter FAT/CD36, muscle mitochondrial content, CPT1 expression or the expression and phosphorylation of AS160, acetyl-CoA carboxylase, or AMPK. However, TBC1D1 overexpression reduced ?-HAD enzyme activity (-18%, P<0.05). In conclusion, TBC1D1-mediated reduction of muscle fatty acid oxidation appears to occur via inhibition of ?-HAD activity. PMID:25163918

Maher, A C; McFarlan, J; Lally, J; Snook, L A; Bonen, A

2014-11-01

38

Field failure mechanisms for photovoltaic modules  

Microsoft Academic Search

Beginning in 1976, Department of Energy field centers have installed and monitored a number of field tests and application experiments using current state-of-the-art photovoltaic modules. On-site observations of module physical and electrical degradation, together with in-depth laboratory analysis of failed modules, permits an overall assessment of the nature and causes of early field failures. Data on failure rates are presented,

L. N. Dumas; A. Shumka

1981-01-01

39

Failure mechanisms for compacted uranium oxide fuel cores  

SciTech Connect

Tension, compression, and shear tests were performed on test specimens of aluminum-clad, compacted powder fuel cores to determine failure mechanisms of the core material. The core, which consists of 70% uranium oxide in an aluminum matrix, frequently fails during post-extrusion drawing. Tests were conducted to various strain levels up to failure of the core. Sections were made of tested specimens to microscopically study initiation of failure. Two failure modes wee observed. Tensile failure mode is initiated by prior tensile failure of uranium oxide particles with the separation path strongly influenced by the arrangement of particles. Delamination mode consists of the separation of laminae formed during extrusion of tubes. Separation proceeds from fine cracks formed parallel to the laminae. Tensile failure mode was experienced in tension and shear tests. Delamination mode was produced in compression tests.

Berghaus, D.G.; Peacock, H.B.

1980-01-01

40

Mechanisms of antibiotic neurotoxicity in renal failure.  

PubMed

Neurological complications of antibiotics are relatively common in renal failure. Central nervous system neurotoxicity due to penicillin and beta-lactam antibiotics is best documented with fewer accounts of ototoxicity, peripheral nerve toxicity and neuromuscular blockade. In the context of risk stratification, the goal of this review is to explore the mosaic of factors in renal impairment that may contribute to susceptibility to antibiotic neurotoxicity. Improved knowledge of the pathogenesis of these formidable adverse events among the renal failure subjects should help prevent antibiotic neurotoxicity in the future. PMID:15164960

Chow, Kai Ming; Szeto, Cheuk Chun; Hui, Andrew Che-Fai; Li, Philip Kam-Tao

2004-03-01

41

PVD TBC experience on GE aircraft engines  

NASA Technical Reports Server (NTRS)

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

Maricocchi, Antonio; Bartz, Andi; Wortman, David

1995-01-01

42

Mechanisms of antibiotic neurotoxicity in renal failure  

Microsoft Academic Search

Neurological complications of antibiotics are relatively common in renal failure. Central nervous system neurotoxicity due to penicillin and ?-lactam antibiotics is best documented with fewer accounts of ototoxicity, peripheral nerve toxicity and neuromuscular blockade. In the context of risk stratification, the goal of this review is to explore the mosaic of factors in renal impairment that may contribute to susceptibility

Kai Ming Chow; Cheuk Chun Szeto; Andrew Che-Fai Hui; Philip Kam-Tao Li

2004-01-01

43

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

44

Mechanical failure and glass transition in metallic glasses  

SciTech Connect

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

Egami, Takeshi [ORNL

2011-01-01

45

THERMO-MECHANICAL SIMULATIONS OF DUCTILE FAILURE BY MESHFREE METHOD  

E-print Network

is proposed to incorporate reproducing kernel particle method (RPKM) with rate dependent Johnson-Cook model mechanics tool to model adiabatic shear band and spall fracture, which are the main mechanisms of failure program. His main interest lies in Multiscale Modeling, Advanced Computational Mechanics, and Structural

Ponce, V. Miguel

46

Failure mechanisms of platinum aluminide bond coat/electron beam-physical vapor deposited thermal barrier coatings  

NASA Astrophysics Data System (ADS)

Thermal barrier coatings (TBCs) allow operation of structural components, such as turbine blades and vanes in industrial and aircraft gas engines, at temperatures close to the substrate melting temperatures. They consist of four different layers; a high strength creep-resistant nickel-based superalloy substrate, an oxidation resistant bond coat (BC), a low thermal conductivity ceramic topcoat and a thermally grown oxide (TGO), that is predominantly alpha-Al 2O3, that forms between the BC and the TBC. Compressive stresses (3--5 GPa) that are generated in the thin TGO (0.25--8 mum) due to the mismatch in thermal coefficient of expansion between the TGO and BC play a critical role in the failure of these coatings. In this study, the failure mechanisms of a commercial yttria-stabilized zirconia (7YSZ) electron beam-physical vapor deposited (EB-PVD) coating on platinum aluminide (beta-(Ni,Pt)Al) bond coat have been identified. Two distinct mechanisms have been found responsible for the observed damage initiation and progression at the TGO/bond coat interface. The first mechanism leads to localized debonding at TGO/bond coat interface due to increased out-of-plane tensile stress, along bond coat features that manifest themselves as ridges. The second mechanism causes cavity formation at the TGO/bond coat interface, driven by cyclic plasticity of the bond coat. It has been found that the debonding at the TGO/bond coat interface due to the first mechanism is solely life determining. The final failure occurs by crack extension along either the TGO/bond coat interface or the TGO/YSZ interface or a combination of both, leading to large scale buckling. Based on these mechanisms, it is demonstrated that the bond coat grain size and the aspect ratio of the ridges have a profound influence on spallation lives of the coating. The removal of these ridges by fine polishing prior to TBC deposition led to a four-fold improvement in life. The failure mechanism identified for the improved coatings indicates absence of both the mechanisms that were responsible for damage initiation and progression and hence the final spallation was very different, accounting for the life improvement. The change in compressive residual stress in the TGO layer reflects the damage progression in the TGO layer. To this end, the TGO stresses were measured non-destructively as function of thermal cycles using the novel photoluminescence piezospectroscopy (PLPS) technique. The compressive stresses were found to increase in the first few cycles, (up to 10 cycles) and gradually decrease with increasing number of cycles, up to failure. The standard deviation of the measured stress, indicative of the damage evolution, is found to significantly increase just before the failure of the coating. The sensitivity of the TGO stress to the peak temperature amplitude is also established. Application of the PLPS technique was demonstrated for the first time, both on plasma-sprayed and EB-PVD thermal barrier coated turbine-blades.

Vaidyanathan, Krishnakumar

47

PVD TBC experience on GE aircraft engines  

NASA Technical Reports Server (NTRS)

The higher performance levels of modern gas turbine engines present significant challenges in the reliability of materials in the turbine. The increased engine temperatures required to achieve the higher performance levels reduce the strength of the materials used in the turbine sections of the engine. Various forms of Thermal Barrier Coatings (TBC's) have been used for many years to increase the reliability of gas turbine engine components. Recent experience with the Physical Vapor Deposition (PVD) process using ceramic material has demonstrated success in extending the service life of turbine blades and nozzles. Engine test results of turbine components with a 125 micrometer (0.005 in) PVD TBC have demonstrated component operating temperatures of 56-83 C (100-150 F) lower than uncoated components. Engine testing has also revealed the TBC is susceptible to high angle particle impact damage. Sand particles and other engine debris impact the TBC surface at the leading edge of airfoils and fracture the PVD columns. As the impacting continues the TBC erodes away in local areas. Analysis of the eroded areas has shown a slight increase in temperature over a fully coated area, however, a significant temperature reduction was realized over an airfoil without any TBC.

Bartz, A.; Mariocchi, A.; Wortman, D. J.

1995-01-01

48

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

49

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

50

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

51

MICRO-MECHANISMS OF COMPRESSION FAILURE Sia Nemat Nasser  

E-print Network

. These materials find varied applications based on their mechanical properties. SiC, Al2O3 and TiB2 find extensive micro-mechanisms of dynamic brittle failure in compression are examined over a broad range of recent advances in novel experimental techniques to study the dynamic behavior of brittle materials

Nemat-Nasser, Sia

52

Analysis of failure mechanism and stress influence on cylinder  

Microsoft Academic Search

Cylinder, which converts pressure of compressed gas into mechanical energy, is one of main pneumatic actuators in electromechan ical products. With application of cylinder becoming broader and broader, the demand on high reliability of cylinder gets more and more urgent. In order to improve the reliability of cylinder, it must be made clear the failure mechanism of it beforehand. This

Juan Chen; Xiaoye Qi; Bohong Liu; Deyi Wang

2011-01-01

53

Damage mechanics of electromigration induced failure  

Microsoft Academic Search

Electromigration is a major road block in the pursuit of nanoelectronics and next generation power electronics. The current density in the state-of-the-art microelectronics solder joints is about 103A\\/cm2. In the next generation nanoelectronics solder joints this current density is expected to increase by an order of magnitude, at least. In this paper, a new damage mechanics formulation is implemented in

Cemal Basaran; Minghui Lin

2008-01-01

54

Rockfall failure mechanisms in Yosemite Valley, California (USA)  

NASA Astrophysics Data System (ADS)

Rockfall hazard is especially high in Yosemite Valley, with tens of rockfalls inventoried every year. A rockfall on 5 October 2013 from Ahwiyah Point consisted of a volume of 740 cubic meters and occurred within the perimeter of a larger event on 28 March 2009 that released 25'400 cubic meters of rock (Zimmer et al., 2012). In both events (2009 and 2013), the initial rockfall volumes dislodged a second one approximately equivalent in size by impacting the cliff below the source area during the fall. Rock fragments of up to several cubic meters were deposited on the talus slope, damaging a heavily used and recently reconstructed hiking path. We performed extensive mapping of structural features for several cliffs of Yosemite Valley to improve the assessment of the most susceptible rockfall areas. In particular we mapped and characterized the main brittle structures, the exfoliation joints and the failure mechanisms of the past rockfalls. Several failure mechanisms exist in Yosemite including the propagation of brittle structures that may lead to tensile, planar sliding, wedge sliding or toppling failures. Frequently, topographically-parallel exfoliation joints and topographically-oblique discontinuities coexist, resulting in complex failures. We also developed a methodology to examine how the distribution of joints within the cliff faces of Yosemite Valley affects overall stability with respect to the identified failure mechanisms. For these analyses, we used terrestrial laser scanning (TLS) to collect high resolution point clouds of the vertical and overhanging rock faces throughout the Valley. This provided the necessary 3D data to identify the main joint sets, perform spacing and trace length measurements, and calculate volumes of previous and potential rockfalls. We integrated this information with stability calculations to identify the likely failure mechanisms for each area of cliff and to obtain the number of potential failures per square meter of cliff face. The areas of a cliff with the highest number of potential failures per cliff surface are considered to be the most susceptible to rockfalls. We then compared these areas to field observations displaying the most visually unstable compartments by considering the following factors: 1) the compartment's degree of isolation due to bounding fractures, 2) the existence of basal steep, sliding prone discontinuities, 3) the opening of cracks, 4) the persistence of cracks, 5) the existence of overhangs, 6) the surrounding rockfall activity, 7) the water seepage along the limiting cracks, 8) the proximity to very fractured layers, 9) the proximity to geologic limits. Our preliminary results show a link between the type of failure mechanism, the persistence of discontinuities and the volume of analyzed rockfalls. Generally, planar or wedge sliding isolate larger unstable compartments compared to tensile failures along exfoliation joints.

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

2014-05-01

55

PVD TBC experience on GE aircraft engines  

NASA Astrophysics Data System (ADS)

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

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

1997-06-01

56

Failure analysis of deployment mechanism of a satellite solar array  

Microsoft Academic Search

The reliability issue of a solar array deployment mechanism was analyzed with FMECA and FTA. The main failure modes, their effects and criticalities were illustrated. A fault tree was built. Both qualitative analysis and the quantitative analysis of the fault tree were performed. The probability of the top event, the structural importance and the critical importance coefficients of different basic

Yi Yang; Shaoze Yan; Liyang Xie; Jianing Wu

2011-01-01

57

PmTBC1D20, a Rab GTPase-activating protein from the black tiger shrimp, Penaeus monodon, is involved in white spot syndrome virus infection.  

PubMed

TBC (TRE2/BUB2/CDC16) domain proteins contain an ? 200-amino-acid motif and function as Rab GTPase-activating proteins that are required for regulating the activity of Rab proteins, and so, in turn, endocytic membrane trafficking in cells. TBC domain family member 20 (TBC1D20) has recently been reported to mediate Hepatitis C virus replication. Herein, PmTBC1D20 identified from the black tiger shrimp, Penaeus monodon, was characterized and evaluated for its role in white spot syndrome virus (WSSV) infection. The full-length cDNA sequence of PmTBC1D20 contains 2003 bp with a predicted 1443 bp open reading frame encoding a deduced 480 amino acid protein. Its transcript levels were significantly up-regulated at 24 and 48 h by ? 2.3- and 2.1-fold, respectively, after systemic infection with WSSV. In addition, depletion of PmTBC1D20 transcript in shrimps by double stranded RNA interference led to a decrease in the level of transcripts of three WSSV genes (VP28, ie1 and wsv477). This suggests the importance of PmTBC1D20 in WSSV infection. This is the first report of TBC1D20 in a crustacean and reveals the possible mechanism used by WSSV to modulate the activity of the host protein, PmTBC1D20, for its benefit in viral trafficking and replication. PMID:24076066

Yingvilasprasert, Wanchart; Supungul, Premruethai; Tassanakajon, Anchalee

2014-02-01

58

Register of experts for information on mechanics of structural failure  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

59

Migratory gold resistive shorts - Chemical aspects of a failure mechanism  

NASA Technical Reports Server (NTRS)

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

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

1975-01-01

60

Deformation and failure mechanisms in metal matrix composites  

NASA Technical Reports Server (NTRS)

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

Newaz, G.; Majumdar, B. S.

1991-01-01

61

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

62

Analysis of Mechanical Failure of Polymer Microneedles by Axial Force  

PubMed Central

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

Park, Jung-Hwan; Prausnitz, Mark R.

2010-01-01

63

Register of experts for information on mechanics of structural failure  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

64

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

65

GaN-ON-Si Failure Mechanisms and Reliability Improvements  

Microsoft Academic Search

The degradation of 36mm AlGaN\\/GaN HFETs-on-Si under DC stress conditions has been studied on a large number of nominally identical devices that were chosen randomly across a production process. A common and primary degradation phenomenon was observed in the devices. A combination of electrical and physical analysis was used to identify a possible failure mechanism related to the Ni\\/Au Schottky

S. Singhal; J. C. Roberts; P. Rajagopal; T. Li; A. W. Hanson; R. Therrien; J. W. Johnson; I. C. Kizilyalli; K. J. Linthicum

2006-01-01

66

The failure mode analysis of motion mechanism for airbus A320 flap  

Microsoft Academic Search

Flap plays an important role in the process of the plane flying, once the flap failure may cause serious flight accidents. Based on FMEA of the A320 flap, this article summarizes the main failure modes of motion mechanism for A320 flaps, and analyzes the failure mechanism from the point view of design, tooling, use and maintenance. According to the failure

Fei Xiang; Weimin Cui; Yunlong Zhong

2011-01-01

67

The Hominoid-specific Oncogene TBC1D3 Activates Ras and Modulates Epidermal Growth Factor Receptor Signaling and Trafficking*S?  

PubMed Central

Hominoid- and human-specific genes may have evolved to modulate signaling pathways of a higher order of complexity. TBC1D3 is a hominoid-specific oncogene encoded by a cluster of eight paralogs on chromosome 17. Initial work indicates that TBC1D3 is widely expressed in human tissues (Hodzic, D., Kong, C., Wainszelbaum, M. J., Charron, A. J., Su, X., and Stahl, P. D. (2006) Genomics 88,731 -73616863688). In this study, we show that TBC1D3 expression has a powerful effect on cell proliferation that is further enhanced by epidermal growth factor (EGF) in both human and mouse cell lines. EGF activation of the Erk and protein kinase B/Akt pathways is enhanced, both in amplitude and duration, by TBC1D3 expression, whereas RNA interference silencing of TBC1D3 suppresses the activation. Light microscopy and Western blot experiments demonstrate that increased signaling in response to EGF is coupled with a significant delay in EGF receptor (EGFR) trafficking and degradation, which significantly extends the life span of EGFR. Moreover, TBC1D3 suppresses polyubiquitination of the EGFR and the recruitment of c-Cbl. Using the Ras binding domain of Raf1 to monitor GTP-Ras we show that TBC1D3 expression enhances Ras activation in quiescent cells, which is further increased by EGF treatment. We speculate that TBC1D3 may alter Ras GTP loading. We conclude that the expression of TBC1D3 generates a delay in EGFR degradation, a decrease in ubiquitination, and a failure to recruit adapter proteins that ultimately dysregulate EGFR signal transduction and enhance cell proliferation. Altered growth factor receptor trafficking and GTP-Ras turnover may be sites where recently evolved genes such as TBC1D3 selectively modulate signaling in hominoids and humans. PMID:18319245

Wainszelbaum, Marisa J.; Charron, Audra J.; Kong, Chen; Kirkpatrick, Donald S.; Srikanth, Priya; Barbieri, M. Alejandro; Gygi, Steven P.; Stahl, Philip D.

2008-01-01

68

Bibliography of information on mechanics of structural failure  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

69

Methods of failure and reliability assessment for mechanical heart pumps.  

PubMed

Artificial blood pumps are today's most promising bridge-to-recovery (BTR), bridge-to-transplant (BTT), and destination therapy solutions for patients suffering from intractable congestive heart failure (CHF). Due to an increased need for effective, reliable, and safe long-term artificial blood pumps, each new design must undergo failure and reliability testing, an important step prior to approval from the United States Food and Drug Administration (FDA), for clinical testing and commercial use. The FDA has established no specific standards or protocols for these testing procedures and there are only limited recommendations provided by the scientific community when testing an overall blood pump system and individual system components. Product development of any medical device must follow a systematic and logical approach. As the most critical aspects of the design phase, failure and reliability assessments aid in the successful evaluation and preparation of medical devices prior to clinical application. The extent of testing, associated costs, and lengthy time durations to execute these experiments justify the need for an early evaluation of failure and reliability. During the design stages of blood pump development, a failure modes and effects analysis (FMEA) should be completed to provide a concise evaluation of the occurrence and frequency of failures and their effects on the overall support system. Following this analysis, testing of any pump typically involves four sequential processes: performance and reliability testing in simple hydraulic or mock circulatory loops, acute and chronic animal experiments, human error analysis, and ultimately, clinical testing. This article presents recommendations for failure and reliability testing based on the National Institutes of Health (NIH), Society for Thoracic Surgeons (STS) and American Society for Artificial Internal Organs (ASAIO), American National Standards Institute (ANSI), the Association for Advancement of Medical Instrumentation (AAMI), and the Bethesda Conference. It further discusses studies that evaluate the failure, reliability, and safety of artificial blood pumps including in vitro and in vivo testing. A descriptive summary of mechanical and human error studies and methods of artificial blood pumps is detailed. PMID:15644079

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

2005-01-01

70

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

SciTech Connect

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

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

1997-10-01

71

Mechanical failure classification for spherical roller bearing ofhydraulic injection molding machine using DWT-SVM  

Microsoft Academic Search

This paper presents a combined discrete wavelet transform (DWT) and support vector machine (SVM) technique for mechanical failure classification of spherical roller bearing application in high performance hydraulic injection molding machine. The proposed technique consists of preprocessing the mechanical failure vibration signal samples using Db2 discrete wavelet transform at the fourth level of decomposition of vibration signal for mechanical failure

Guang-ming Xian

2010-01-01

72

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

73

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.

74

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

75

MECHANICAL FAILURE DIAGNOSIS IN AUTOMOTIVE AIR CONDITIONING SYSTEMS THROUGH THERMAL MEASUREMENTS  

Microsoft Academic Search

The present paper describes a simulation model for the operation of an automotive air conditioning system subjected to typical mechanical failures. A review identified the most common mechanical failures in automotive A\\/C systems. Simple mathematical models of two of the most common of these failures were developed and introduced in a simulation model of the vapor compression cycle. Simulated components

Sergio Libanio Campos; José Luiz Fernandes; José Alberto Reis Parise

76

The role of microstructure and phase distribution in the failure mechanisms and life prediction model for PSZ coatings  

NASA Technical Reports Server (NTRS)

Partially Stabilized Zirconia (PSZ) may become widely used for Thermal Barrier Coatings (TBC). Failure of these coatings can occur due to thermal fatigue in oxidizing atmospheres. The failure is due to the strains that develop due to thermal gradients, differences in thermal expansion coefficients, and oxidation of the bond coating. The role of microstructure and the cubic, tetragonal, and monoclinic phase distribution in the strain development and subsequent failure will be discussed. An X-ray diffraction technique for accurate determination of the fraction of each phase in PSZ will be applied to understanding the phase transformations and strain development. These results will be discussed in terms of developing a model for life prediction in PSZ coatings during thermal cycling.

Sisson, R. D., Jr.; Sone, Ichiro; Biederman, R. R.

1985-01-01

77

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

78

08853010/$25.00 TBC IEEE 1IEEE TransaCTIons on UlTrasonICs, FErroElECTrICs, and FrEqUEnCy ConTrol, vol. TBC, no. TBC, TBC TBC  

E-print Network

0885­3010/$25.00 © TBC IEEE 1IEEE TransaCTIons on UlTrasonICs, FErroElECTrICs, and FrEqUEnCy Con, density, and spatial organization ranging from tightly clustered to nearly regular to mimic a broad range distribution models used in ultrason- ics literature. section IV describes the pool of synthetic Us data

Clark, James J.

79

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

80

Mechanisms of renal hyporesponsiveness to ANP in heart failure.  

PubMed

The atrial natriuretic peptide (ANP) plays an important role in chronic heart failure (CHF), delaying the progression of the disease. However, despite high ANP levels, natriuresis falls when CHF progresses from a compensated to a decompensated state, suggesting emergence of renal resistance to ANP. Several mechanisms have been proposed to explain renal hyporesponsiveness, including decreased renal ANP availability, down-regulation of natriuretic peptide receptors and altered ANP intracellular transduction signal. It has been demonstrated that the activity of neutral endopeptidase (NEP) is increased in CHF, and that its inhibition enhances renal cGMP production and renal sodium excretion. In vitro as well as in vivo studies have provided strong evidence of an increased degradation of intracellular cGMP by phosphodiesterase in CHF. In experimental models, ANP-dependent natriuresis is improved by phosphodiesterase inhibitors, which may arise as new therapeutic agents in CHF. Sodium-retaining systems likely contribute to renal hyporesponsiveness to ANP through different mechanisms. Among these systems, the renin-angiotensin-aldosterone system has received particular attention, as angiotensin II and ANP have renal actions at the same sites and inhibition of angiotensin-converting enzyme and angiotensin-receptor blockade improve ANP hyporesponsiveness. Less is known about the interactions between the sympathetic nervous system, endothelin or vasopressin and ANP, which may also blunt ANP-induced natriuresis. To summarize, renal hyporesponsiveness to ANP is probably multifactorial. New treatments designed to restore renal ANP efficiency should limit sodium retention in CHF patients and thus delay the progression to overt heart failure. PMID:12925036

Charloux, A; Piquard, F; Doutreleau, S; Brandenberger, G; Geny, B

2003-09-01

81

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

Microsoft Academic Search

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

Alexander N. Guz

2009-01-01

82

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.

83

Abstract: Transactions and recoverable memories are pow-erful mechanisms for handling failures and manipulating  

E-print Network

[Chen96]. Combined with an uninterruptible power supply, Rio provides persistent memory to applications]. Transactions are acclaimed widely as a powerful mechanism for handling failures. Transactions simplify pro

Chen, Peter M.

84

Accelerated life testing design based on wear failure mechanism for pneumatic cylinders  

Microsoft Academic Search

The piston and piston pole sealing ring are the weak units as well as leakage sources which easily result in the cylinders failure. The primary criterion for determining test acceleration factors is that the failure mode or failure mechanism should not change or be different from that expected from a non-accelerated test. Working temperature, frequency and motion velocity are chosen

Juan Chen; Qiang Wu; Guochang Bai; Jungong Ma; Zhanlin Wang

2009-01-01

85

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

86

Degradation of a TBC with HVOF-CoNiCrAlY Bond Coat  

NASA Astrophysics Data System (ADS)

Thermal barrier coatings (TBCs) provide both thermal insulation and oxidation and corrosion protection to the substrate metal, and their durability is influenced by delamination near the interface between the ceramic topcoat and the metallic bond coat, where a layer of thermally grown oxide (TGO) forms during service exposure. In the present work, the degradation process of a TBC with an air-plasma-spray ZrO2-8 wt.%Y2O3 topcoat and a high-velocity oxy-fuel CoNiCrAlY bond coat was studied, in terms of TGO growth kinetics and aluminum depletion in the bond coat, as well as cracking behavior. The results show that the TGO growth kinetics can be described by a transient oxidation stage with ?3 = k 1 t followed by a steady-state oxidation stage with ?2 = c + k 2 t. Significant aluminum depletion was observed in the bond coat after extended thermal exposure; however, chemical failure of the bond coat did not occur even after the aluminum content near the TGO/CoNiCrAlY interface decreased to 4.5 at.%. A power-law relationship between the maximum crack length in the TBC and the TGO thickness was observed, which may serve as the basis for TBC life prediction.

Chen, Weijie R.

2014-06-01

87

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

88

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

89

Experimental investigation of the tensile properties and failure mechanisms of three-dimensional woven composites.  

E-print Network

??This PhD thesis presents an experimental investigation into the tensile properties, strengthening mechanics and failure mechanisms of three-dimensional (3D) woven composites with through-the-thickness (z-binder) reinforcement.… (more)

Rudov-Clark, S

2007-01-01

90

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-armor weldments, the overall ballistic performance of the armor is controlled by the ballistic limits of its weld

Grujicic, Mica

91

77 FR 34457 - Pipeline Safety: Mechanical Fitting Failure Reports  

Federal Register 2010, 2011, 2012, 2013

...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

92

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

PubMed

Burns are responsible for significant mortality and morbidity worldwide and are among the most devastating of all injuries, with outcomes spanning the spectrum from physical impairments and disabilities to emotional and mental consequences. Management of burns and their sequelae even in well-equipped, modern burn units of advanced affluent societies remains demanding and extremely costly. Undoubtedly, in most low and middle income countries (LMICs) with limited resources and inaccessibility to sophisticated skills and technologies, the same standard of care is obviously not possible. Unfortunately, over 90% of fatal fire-related burns occur in developing or LMICs with South-East Asia alone accounting for over half of these fire-related deaths. If burn prevention is an essential part of any integrated burn management protocol anywhere, focusing on burn prevention in LMICs rather than treatment cannot be over-emphasized where it remains the major and probably the only available way of reducing the current state of morbidity and mortality. Like other injury mechanisms, the prevention of burns requires adequate knowledge of the epidemiological characteristics and associated risk factors, it is hence important to define clearly, the social, cultural and economic factors, which contribute to burn causation. While much has been accomplished in the areas of primary and secondary prevention of fires and burns in many developed or high-income countries (HICs) such as the United States due to sustained research on the epidemiology and risk factors, the same cannot be said for many LMICs. Many health authorities, agencies, corporations and even medical personnel in LMICs consider injury prevention to have a much lower priority than disease prevention for understandable reasons. Consequently, burns prevention programmes fail to receive the government funding that they deserve. Prevention programmes need to be executed with patience, persistence, and precision, targeting high-risk groups. Depending on the population of the country, burns prevention could be a national programme. This can ensure sufficient funds are available and lead to proper coordination of district, regional, and tertiary care centres. It could also provide for compulsory reporting of all burn admissions to a central registry, and these data could be used to evaluate strategies and prevention programmes that should be directed at behavioural and environmental changes which can be easily adopted into lifestyle. Particularly in LMICs, the emphasis in burn prevention should be by advocating change from harmful cultural practices. This needs to be done with care and sensitivity. The present review is a summary of what has already been accomplished in terms of burn prevention highlighting some of the successes but above all the numerous pitfalls and failures. Recognizing these failures is the first step towards development of more effective burn prevention strategies particularly in LMICs in which burn injury remains endemic and associated with a high mortality rate. Burn prevention is not easy, but easy or not, we have no options; burns must be prevented. PMID:18926639

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

2009-03-01

93

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

PubMed

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

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

2014-09-15

94

Register of specialized sources for information on mechanics of structural failure  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

95

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

96

Groundwater seepage mechanisms of streambank erosion and failure  

Technology Transfer Automated Retrieval System (TEKTRAN)

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

97

Failure mechanism of winding insulations in inverter-fed motors  

Microsoft Academic Search

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

Weijun Yin

1997-01-01

98

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

Federal Register 2010, 2011, 2012, 2013

...is not to be listed as a ``Material or Weld'' cause but as ``Other.'' The commenters...Report Form. The phrase ``material, weld or joint failure (including compression...replaced with the phrase ``Material or Welds.'' Section 192.1009 What must an...

2011-02-01

99

Failure Mechanisms in PMMA\\/ATH Acrylic Casting Dispersion  

Microsoft Academic Search

Acrylic casting dispersion is used to fabricate particulate composites such as poly-methyl methacrylate (PMMA) filled with a fine dispersion alumina trihydrate (ATH). This composite is subjected to severe temperature variations during in-service conditions, giving rise to high thermal stresses which lead to failure by cracking. The influence of the interfacial bond strength between a particle and the matrix on the

Shihua Nie; Cemal Basaran; Clyde S. Hutchins; Hale Ergun

100

Lock-up failure of a four-bar linkage deployment mechanism  

NASA Technical Reports Server (NTRS)

A successful failure investigation of a four-bar linkage deployment mechanism has been performed. Possible failure causes such as the mismatch of material coefficient of thermal expansion (CTE), excessive hinge friction, limit switch interference, and thermal gradient induced resistive preload were investigated and are discussed. The final conclusions and corrective actions taken are described. Finally, valuable lessons learned during the investigation are discussed.

Zinn, Michael

1993-01-01

101

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

102

Materials failure mechanisms of hybrid ball bearings with silicon nitride balls  

Microsoft Academic Search

A modified Shell four-ball apparatus was used to determine failure mechanisms and estimate time to failure of hybrid ball bearings using silicon nitride and zirconia balls. The machine was set up to hold a hybrid bearing containing three ceramic balls, instead of the usual 14 in order to increase contact pressure. Five kinds of silicon nitride ceramics, which differed in

K. Thoma; L. Rohr; H. Rehmann; S. Roos; J. Michler

2004-01-01

103

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

104

Failure criteria used in a probabilistic fracture mechanics code  

SciTech Connect

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

Lo, T.Y.

1985-01-01

105

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

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

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

108

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

109

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

110

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

PubMed

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

2013-05-01

111

[Nutritional management of intestinal failure and potential stimulation mechanisms].  

PubMed

Severe forms of intestinal failure represent one of the most complex pathologies to manage, in both children and adults. In adults, the most common causes are chronic intestinal pseudo-obstruction and severe short bowel syndrome following large intestinal resections, particularly due to massive mesenteric ischemic, within the context of cardiopathies occurring with atrial fibrillation. The essential management after stabilizing the patient consists in nutritional support, either by parenteral or enteral routes, with tolerance to oral diet being the final goal of intestinal adaptation in these pathologies. Surgery may be indicated in some cases to increase the absorptive surface area. Parenteral nutrition is an essential support measure that sometimes has to be maintained for long time, even forever, except for technique-related complications or unfavorable clinical course that would lead to extreme surgical alternatives such as intestinal transplantation. Hormonal therapy with trophism-stimulating factors opens new alternatives that are already being tried in humans. PMID:17679297

Pérez de la Cruz, A J; Moreno-Torres Herrera, R; Pérez Roca, C

2007-05-01

112

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

NASA Technical Reports Server (NTRS)

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

Chamis, C. C.

1976-01-01

113

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

PubMed Central

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

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

2014-01-01

114

Stress analysis of slope failure using the Discrete Element Method: Mechanical controls on landslide sizes  

NASA Astrophysics Data System (ADS)

We carry out numerical simulations using the Discrete Element Method (DEM) to understand the controls and mechanisms of slope failure and resulting landslide size distribution. Our modeled 2D slopes are constructed of numerous spheres simulating mechanically homogeneous material with friction and cohesion. This approach enables us to simulate earth-like materials and behaviors, as discontinuities and heterogeneities can develop and propagate as the material undergoes yield and failure. Appealingly, the material properties and rheologies can evolve over time, and can be tracked in detail throughout the simulated process. Our initial results demonstrate that landslide size and failure mode are strongly dependent upon the Factor of Safety (FS), defined as the ratio of resisting stresses to driving stresses. When material strength is low (FS<< 1), landslides encompass the entire slope height. With increasing material strength, the landslides encompass decreasing proportions of the lower slopes, until they vanish close to stabilization of the slope at FS=1. As natural landslides commonly encompass large portions of failing slopes, we argue that they occur under conditions of FS< 1, at least by the completion of the failure process. Therefore in reality, slope failure occurs as a dynamic process in which failure initiates at FS~1, but FS decreases as a fracture surface propagates with loss of cohesion, resulting in larger landslides than would be predicted for FS=1. To examine the mechanical causes of slope failure in more detail, we probed the stress field in a modeled slope throughout the initial failure process, within the framework of critical state soil mechanics. We are able to constrain the yield surface and failure conditions (i.e., critical state line) of the slope material in the 3D differential stress - mean stress - porosity space, and to map stress paths of individual material elements within this domain. Failure initiates at the slope-foot, where slope material loses cohesion and disintegrates. The failure surface propagates upwards at about 100 m/sec, forming a discrete sliding plane that separates the disintegrated and intact materials. The propagation of the failure surface is detected as a reduction in mean stress as the landslide undergoes tensile failure and disintegration. This stress evolution is well-resolved in plots of progressive changes in the normalized strength ratio (i.e., differential stress/mean stress) for the failing slope. Initial failure occurs at a high normalized strength ratios, consistent with brittle failure (along the Hvorslev surface), whereupon the strength ratio decreases toward the critical state line, consistent with post-failure weakening to reach residual strength of the rock. Significant downward slope movement occurs only after the failure surface and associated drop in the normalized strength ratio has reached the top of the slope. Our approach demonstrates the utility of mapping out the evolving stress conditions in the critical state mechanics framework to better predict the complex evolution of deforming slopes, thereby obtaining clearer insights into the mechanisms that constrain landslide failure modes, geometries, and resulting size distributions.

Katz, O.; Morgan, J. K.; Dugan, B.

2009-12-01

115

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

116

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

117

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

118

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

119

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 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, Brandon; Staab, Lucas; Culberson, Michael; Pellicciotti, Joseph

2014-01-01

120

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

Microsoft Academic Search

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

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

1978-01-01

121

Renalase Deficiency in Heart Failure Model of Rats---A Potential Mechanism Underlying Circulating Norepinephrine Accumulation  

Microsoft Academic Search

BackgroundSympathetic overactivity and catecholamine accumulation are important characteristic findings in heart failure, which contribute to its pathophysiology. Here, we identify a potential mechanism underlying norepinephrine accumulation in a rat model of heart failure.Methodology\\/Principal FindingsInitially, we constructed a rat model of unilateral renal artery stenosis (n = 16) and found that the expression of renalase, a previously identified secreted amine oxidase,

Rong Gu; Wen Lu; Jun Xie; Jian Bai; Biao Xu; Annarosa Leri

2011-01-01

122

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

123

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

124

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

125

Mechanisms of the beneficial effects of beta-adrenoceptor antagonists in congestive heart failure  

PubMed Central

Many clinical studies have documented favourable effects (reduced morbidity and mortality) of beta-adrenoceptor (?-AR) antagonists, such as carvedilol, metoprolol, propranolol, atenolol and bisoprolol, in congestive heart failure. These agents attenuate the effects of sympathetic activation during the development of heart failure, prevent ventricular remodelling and improve cardiac function. Because ?-AR blockers are known to exert negative inotropic action, the mechanisms responsible for their beneficial effects in heart failure have been a subject of debate. While attenuation of changes in ?-AR cyclic AMP-mediated signal transduction in heart failure is considered to be responsible for the beneficial effects of ?-AR antagonists, other mechanisms such as the effects of these agents on subcellular remodelling, oxidative stress, apoptosis and defect in calcium handling, are equally important in preventing cardiac alterations in the failing heart. Moreover, ?-AR antagonists are not a homogeneous group of drugs because they differ in their pharmacokinetics and pharmacodynamics, in addition to the selective and nonselective nature of their actions on ?-AR. Various ?-AR blocking agents have been shown to possess different ancillary properties and produce effects that are independent of ?-AR. In fact, different ?-AR antagonists have been observed to lower the elevated levels of plasma catecholamines in heart failure. Thus, the beneficial effects of ?-AR antagonists are not only elicited through their interaction with mediated ?-AR signal transduction sites in the myocardium, but other mechanisms may also contribute to their favourable actions in heart failure. PMID:21264074

Rehsia, Navneet S; Dhalla, Naranjan S

2010-01-01

126

Application of damage mechanics to ice failure in compression  

Microsoft Academic Search

In this work some principles of viscoelastic theory as applicable to ice are reviewed. A multiaxial ice model, incorporating nonlinear damage, is presented based on the Burgers viscoelastic body with nonlinear dashpots in both the Kelvin and the Maxwell units. This mechanical ice model is found to be very efficient and accurate, especially for short loading periods. It includes the

J. Xiao; I. J. Jordaan

1996-01-01

127

Immune mechanisms in acetaminophen-induced acute liver failure  

PubMed Central

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.

Krenkel, Oliver; Mossanen, Jana C.

2014-01-01

128

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

PubMed

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

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

2014-11-24

129

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

PubMed

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

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

2014-10-27

130

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

131

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

132

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

133

Dynamic Mechanical Behavior and Failure Mechanism of Polymer Composites Embedded with Tetraneedle-Shaped ZnO Whiskers  

NASA Astrophysics Data System (ADS)

Quasi-static and dynamic mechanical properties of glass-fiber reinforced polymer composites embedded with and without tetraneedle-shaped ZnO whiskers (T-ZnOw) in two loading directions are investigated by a split Hopkinson pressure bar. The stress-strain curves, ultimate strength, failure strain and elastic modulus are obtained and the failure mechanism of the composites is investigated by a high-speed camera and a scanning electron microscope. Strain rate effects on the mechanical behavior are discussed and the corresponding models are derived by fitting the experimental data. The experimental results show that the composites with T-ZnOw under dynamic loading have multiple failure modes and better mechanical properties. Finally, the strengthening and toughening mechanisms of T-ZnOw are analyzed. It is shown that T-ZnOw can improve mechanical properties of the composites, and can make the composites have some new features. The present results provide a reliable basis for advanced composite design and manufacture, and have broad applications in the field of aerospace.

Rong, Ji-Li; Wang, Dan; Wang, Xi; Li, Jian; Xu, Tian-Fu; Lu, Ming-Ming; Cao, Mao-Sheng

2013-01-01

134

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

135

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

136

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

Microsoft Academic Search

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

Johan Liu; Katrin Gustafsson; Zonghe Lai; Changhai Li

1997-01-01

137

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

Microsoft Academic Search

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

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

1989-01-01

138

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

139

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

140

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

141

The ESD failure mechanism of ultra-HV 700V LDMOS  

Microsoft Academic Search

A new kind of ESD failure mechanism is found in the UHV 700V LDNMOS during the HBM ESD zapping event. The device is damaged by its own charges and board stored charges, not damaged by the HBM stress current. The device junction capacitor and test-board capacitor store the charges from the ESD tester before the avalanche breakdown occurring. After the

Jian-Hsing Lee; Tzu-Cheng Kao; Chien-Liang Chan; Jin-Lian Su; Hung-Der Su; Kuo-Cheng Chang

2011-01-01

142

Failure strain and mechanical property data for the Type IIIA waste tank liners  

SciTech Connect

The SRS Waste Tanks at the Savannah River Site to be employed in the In-Tank Precipitation (ITP) process are undergoing a structural evaluation in order to define their response to a hypothetical deflagration accident. This report provides mechanical property data to support the structural analyses, and characterizes the impact of mechanical property variability and materials degradation on the failure strain of the primary liner.

Thomas, J.K.

1992-06-01

143

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

144

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

145

GaAs FET failure mechanisms due to high humidity and ionic contamination  

NASA Astrophysics Data System (ADS)

Various types of GaAs FET structures have been tested under temperature cycling from -10 to 100 C at 95% RH in the presence of ionic contamination, with and without bias. Devices which exhibited excessive leakage currents were failure analyzed and the results correlated with the electrical degradation. It is found that Al-gate FETs in both hermetic and nonhermetic configurations typically fail by a gate-source short. The failure mechanisms were Al corrosion, metallic ion migration via electrolytic paths, and Au-Al phase formation. Devices with Au/refractory gates are found to be less susceptible to failure in hostile environment; even in nonhermetic configuration, these devices did not exhibit catastrophic gate shortening.

Anderson, W. T., Jr.; Christou, A.

1980-08-01

146

Tip cooling effect and failure mechanism of field-emitting carbon nanotubes.  

PubMed

The cooling effect accompanying field electron emission has been considered for a single carbon nanotube (CNT) used as a field emission (FE) electron source. An improved model for the failure mechanism of field emitting CNTs has been proposed and validated. Our model predicts a maximum temperature (T-max) located at an interior point rather than the tip of the CNTs, and the failure of the CNT emitters tends to take place at the T-max point, inducing a segment by segment breakdown process. A combination of Joule heating and electrostatic force effect is proposed responsible for initiating the failure of the field emitting CNT and validated by in situ FE observation. PMID:17212441

Wei, Wei; Liu, Yang; Wei, Yang; Jiang, Kaili; Peng, Lian-Mao; Fan, Shoushan

2007-01-01

147

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

PubMed Central

BACKGROUND—The rate of failure of non-invasive mechanical ventilation (NIMV) in patients with chronic obstructive pulmonary disease (COPD) with acute respiratory insufficiency ranges from 5% to 40%. Most of the studies report an incidence of "late failure" (after >48 hours of NIMV) of about 10-20%. The recognition of this subset of patients is critical because prolonged application of NIMV may unduly delay the time of intubation.?METHODS—In this multicentre study the primary aims were to assess the rate of "late NIMV failure" and possible associated predictive factors; secondary aims of the study were evaluation of the best ventilatory strategy in this subset of patients and their outcomes in and out of hospital. The study was performed in two respiratory intensive care units (ICUs) on patients with COPD admitted with an episode of hypercapnic respiratory failure (mean (SD) pH 7.23(0.07), PaCO2 85.3 (15.8) mm Hg).?RESULTS—One hundred and thirty seven patients initially responded to NIMV in terms of objective (arterial blood gas tensions) and subjective improvement. After 8.4 (2.8) days of NIMV 31 patients (23%; 95% confidence interval (CI) 18 to 33) experienced a new episode of acute respiratory failure while still ventilated. The occurrence of "late NIMV failure" was significantly associated with functional limitations (ADL scale) before admission to the respiratory ICU, the presence of medical complications (particularly hyperglycaemia), and a lower pH on admission. Depending on their willingness or not to be intubated, the patients received invasive ventilation (n=19) or "more aggressive" (more hours/day) NIMV (n=12). Eleven (92%) of those in this latter subgroup died while in the respiratory ICU compared with 10 (53%) of the patients receiving invasive ventilation. The overall 90 day mortality was 21% and, after discharge from hospital, was similar in the "late NIMV failure" group and in patients who did not experience a second episode of acute respiratory failure.?CONCLUSIONS—The chance of COPD patients with acute respiratory failure having a second episode of acute respiratory failure after an initial (first 48 hours) successful response to NIMV is about 20%. This event is more likely to occur in patients with more severe functional and clinical disease who have more complications at the time of admission to the ICU. These patients have a very poor in-hospital prognosis, especially if NIMV is continued rather than prompt initiation of invasive ventilation.?? PMID:10992532

Moretti, M.; Cilione, C.; Tampieri, A.; Fracchia, C.; Marchioni, A.; Nava, S.

2000-01-01

148

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

149

Examination of cadmium safety rod thermal test specimens and failure mechanism evaluation  

SciTech Connect

The reactor safety rods may be subjected to high temperatures due to gamma heating after the core coolant level has dropped during the ECS phase of a hypothetical LOCA event. Accordingly, an experimental cadmium safety rod testing subtask was established as part of a task to address the response of reactor core components to this accident. Companion reports describe the experiments and a structural evaluation (finite element analysis) of the safety rod. This report deals primarily with the examination of the test specimens, evaluation of possible failure mechanisms, and confirmatory separate effects experiments. It is concluded that the failures observed in the cadmium safety rod thermal tests which occurred at low temperature (T < 600{degrees}C) with slow thermal ramp rates (slow cladding strain rates) resulted from localized dissolution of the stainless steel cladding by the cadmium/aluminum solution and subsequent ductility exhaustion and rupture. The slow thermal ramp rate is believed to be the root cause for the failures; specifically, the slow ramp rate led to localized cladding shear deformation which ruptured the protective oxide film on the cladding inner surface and allowed dissolution to initiate. The test results and proposed failure mechanism support the conclusion that the rods would not fail below 500{degrees}C even at slow ramp rates. The safety rod thermal test specimen failures which occurred at high temperature (T > 800{degrees}C) with fast thermal ramp rates are concluded to be mechanical in nature without significant environmental degradation. Based on these tests, tasks were initiated to design and manufacture B{sub 4}C safety rods to replace the cadmium safety rods. The B{sub 4}C safety rods have been manufactured at this time and it is currently planned to charge them to the reactor in the near future. 60 refs.

Thomas, J.K.; Peacock, H.B.; Iyer, N.C.

1992-01-01

150

Fatigue of the resin-enamel bonded interface and the mechanisms of failure.  

PubMed

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 oth 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 predominantly 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

2013-05-01

151

Tbc1d15-17 regulates synaptic development at the Drosophila neuromuscular junction.  

PubMed

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 intracellular 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

2013-08-01

152

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

NASA Astrophysics Data System (ADS)

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

Kidd, Theresa Hiromi

153

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

154

Investigation of failure mechanism and modification for film-lubricated precise angular-contact ball bearing  

Microsoft Academic Search

This paper describes an experimental investigation into the performance and lubrication failure mechanism of precise angular-contact ball bearings treated with MoS2-sputtered film, etc. As an important executive component of various spacecrafts, there are some strict requirements on the lubrication performance of angular-contact ball bearing, but the related experimental data are rare to see in literatures. In this experiment, the lubrication

Wang Chengbiao; Yu Xiang; Weng Lijun; Yu Deyang

2005-01-01

155

Sealing Mechanism and Failure Analysis of Automotive Engine Crankshaft Oil Seal  

Microsoft Academic Search

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

Aifang Yan; Qingping Yan

2012-01-01

156

Bibliography of information on mechanics of structural failure (hydrogen embrittlement, protective coatings, composite materials, NDE)  

NASA Technical Reports Server (NTRS)

This bibliography is comprised of approximately 1,600 reference citations related to four problem areas in the mechanics of failure in aerospace structures. The bibliography represents a search of the literature published in the period 1962-1976, the effort being largely limited to documents published in the United States. Listings are subdivided into the four problem areas: Hydrogen Embrittlement; Protective Coatings; Composite Materials; and Nondestructive Evaluation. An author index is included.

Carpenter, J. L., Jr.

1976-01-01

157

Mechanical heart valves: Changes in patient survival and valve failure rates  

Microsoft Academic Search

The effect of patient related variables and mechanical heart valve substitutes on survival and valve failure rates was studied\\u000a in 2,778 patients operated between 1966 and 1986. Of these 48.2% were operated without cardioplegic protection (phase I) and\\u000a 51.8% thereafter (phase II). Mitral vlave replacement (MVR) was performed in 1,257 patients (phase I: 51.58%, phase II: 48.42%);\\u000a aortic valve replacement

T. K. Kaul; J. L. Mercer; D. R. Ramsdale

1992-01-01

158

Properties and failure mechanisms of z-pinned laminates in monotonic and cyclic tension  

Microsoft Academic Search

The effects of through-thickness reinforcement of carbon\\/epoxy laminates with thin pins on the in-plane tensile properties, tensile fatigue life and failure mechanisms are investigated. Tensile studies in the 0° fibre direction are performed on unidirectional and quasi-isotropic laminates reinforced with different volume contents and sizes of fibrous composite z-pins. Microstructural analysis reveals that z-pinning causes several types of damage, including

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

2006-01-01

159

Failure mechanisms of a whisker-reinforced ceramic tool when machining nickel-based alloys  

Microsoft Academic Search

Cutting behavior and failure mechanisms of the SiC-whisker-reinforced Al2O3 ceramic cutting tool JX-1 in turning nickel-based alloys have been investigated in comparison with those of other kinds of ceramic and carbide tools. The resistance to depth-of-cut notch wear of the JX-1 has been found to be greater than that of other Al2O3-based ceramic tools because of the toughening effect of

Zhao Jun; Deng Jianxin; Zhang Jianhua; Ai Xing

1997-01-01

160

Reliability characterizations and failure mechanism of ultra-thin oxides for MOS devices  

Microsoft Academic Search

The aggressive scaling of smaller\\/faster logic and memory devices demands accurate reliability characterization and knowledge of the failure mechanisms of ultra-thin (<30 A) silicon dioxide (SiO 2) layers in the gates of metal-oxide semiconductor (MOS) structures. The increased occurrence of soft breakdown in ultra-thin oxide films necessitates the development of more sophisticated techniques to detect breakdown. One such technique is

Bin Wang

2001-01-01

161

Renalase Deficiency in Heart Failure Model of Rats—A Potential Mechanism Underlying Circulating Norepinephrine Accumulation  

PubMed Central

Background Sympathetic overactivity and catecholamine accumulation are important characteristic findings in heart failure, which contribute to its pathophysiology. Here, we identify a potential mechanism underlying norepinephrine accumulation in a rat model of heart failure. Methodology/Principal Findings Initially, we constructed a rat model of unilateral renal artery stenosis (n?=?16) and found that the expression of renalase, a previously identified secreted amine oxidase, was markedly reduced in the ischemic compared to the non-ischemic kidney (protein: 0.295±0.085 versus 0.765±0.171, p<0.05). Subsequently, we utilized an isolated perfused rat kidney model to demonstrate that the clearance rate of norepinephrine decreased with reduction of perfusion flow. On the basis of these findings, we hypothesized the reduced renal blood supply which occurs in heart failure would result in impaired synthesis of renalase by the kidney and consequently reduced degradation of circulating norepinephrine. To verify this, we used a rat model of infarction-induced heart failure (n?=?12 per group). In these rats, the flow velocity of renal artery, when measured at four weeks, is obviously lower in the operation group. Renal expression of renalase was reduced (protein: 0.476±0.043 for control, 0.248±0.029 for operation versus 0.636±0.151 for sham-operation) and this was associated with an increase in circulating norepinephrine (0.168±0.016 ng/mL for control, 0.203±0.019 ng/mL for operation versus 0.138±0.008 ng/mL for sham-operation). Conclusions/Significance Renalase expression is influenced by renal blood flow and impaired synthesis of renalase by the kidney may represent a potential mechanism underlying circulating norepinephrine accumulation in heart failure. PMID:21297953

Gu, Rong; Lu, Wen; Xie, Jun; Bai, Jian; Xu, Biao

2011-01-01

162

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

163

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

164

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

165

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

166

International Journal of Rock Mechanics & Mining Sciences 41 (2004) 6987 Numerical analysis of initiation and progressive failure in natural  

E-print Network

International Journal of Rock Mechanics & Mining Sciences 41 (2004) 69­87 Numerical analysis of initiation and progressive failure in natural rock slopes--the 1991 Randa rockslide E. Eberhardta, *, D of progressive failure and the numerical modelling of rock mass strength degradation in natural rock slopes using

167

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

168

Finite Element Analyses of Failure Mechanisms and Structure-Property Relationships in Microtruss Materials  

NASA Astrophysics Data System (ADS)

Microtruss materials are assemblies of struts or columns arranged periodically in space. The majority of past research efforts have focused on the key issue of microtruss architectural optimization. By contrast, this study focuses on the internal material structure at the level of the individual struts. Microstructural, geometrical, and material design techniques are used to improve their mechanical properties. The finite element method is used to verify and create predictive analytical models, explain the dependence of strut properties on geometry, material properties and failure mechanisms, and extend the strut design analysis into suggestions for the improvement of fabrication methods. Three strut design methods are considered. First, microstructural design is performed by considering the influence of strut geometry on the strain energy imparted during stretch bending. By using the perforation geometry to modify the location and magnitude of this strain energy, microtruss materials with lower density and higher strength can be fabricated. Second, structural sleeves of aluminum oxide and electrodeposited nanocrystalline nickel are used to reinforce architecturally optimized aluminum alloy microtruss assemblies, creating hybrid materials with high weight-specific strength. The mechanical properties are controlled by the interaction between material and mechanical failure; this interaction is studied through finite element analyses and a proposed analytical relationship to provide suggestions for further improvements. Finally, hollow cylindrical struts are fabricated from electrodeposited nanocrystalline nickel. The high strength to weight ratio achieved in these struts is due to the microstructural and cross-sectional efficiency of the material.

Bele, Eral

169

Failure mechanisms and lifetime prediction methodology for polybutylene pipe in water distribution system  

NASA Astrophysics Data System (ADS)

Polybutylene (PB) is a semicrystalline thermoplastics. It has been widely used in potable water distribution piping system. However, field practice shows that failure occurs much earlier than the expected service lifetime. What are the causes and how to appropriately evaluate its lifetime motivate this study. In this thesis, three parts of work have been done. First is the understanding of PB, which includes material thermo and mechanical characterization, aging phenomena and notch sensitivity. The second part analyzes the applicability of the existing lifetime testing method for PB. It is shown that PB is an anomaly in terms of the temperature-lifetime relation because of the fracture mechanism transition across the testing temperature range. The third part is the development of the methodology of lifetime prediction for PB pipe. The fracture process of PB pipe consists of three stages, i.e., crack initiation, slow crack growth (SCG) and crack instability. The practical lifetime of PB pipe is primarily determined by the duration of the first two stages. The mechanism of crack initiation and the quantitative estimation of the time to crack initiation are studied by employing environment stress cracking technique. A fatigue slow crack growth testing method has been developed and applied in the study of SCG. By using Paris-Erdogan equation, a model is constructed to evaluate the time for SCG. As a result, the total lifetime is determined. Through this work, the failure mechanisms of PB pipe has been analyzed and the lifetime prediction methodology has been developed.

Niu, Xiqun

170

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

NASA Astrophysics Data System (ADS)

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

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

2013-05-01

171

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

Microsoft Academic Search

In order to improve the hot corrosion resistance of conventional YSZ TBC system, the overlay of AlâOâ coating was deposited on the TBC by EB-PVD techniques. Hot corrosion tests were carried out on the TBC with and without AlâOâ coating in molten salts mixtures (NaâSOâ + 5%VâOâ) at 950 C for 10h. The microstructures of TBC and overlay before and

Scott X. Mao

2002-01-01

172

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

173

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

NASA Technical Reports Server (NTRS)

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

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

1981-01-01

174

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

175

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

Microsoft Academic Search

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

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

1995-01-01

176

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

177

Failure analysis of radio frequency (rf) micro-electro-mechanical systems (MEMS)  

NASA Astrophysics Data System (ADS)

MEMS are rapidly emerging as critical components in the telecommunications industry. This enabling technology is currently being implemented in a variety of product and engineering applications. MEMS are currently being used as optical switches to reroute light, tunable filters, and mechanical resonators. Radio frequency (RF) MEMS must be compatible with current Gallium Arsenide (GaAs) microwave integrated circuit (MMIC) processing technologies for maximum integration levels. The RF MEMS switch discussed in this paper was fabricated using various layers of polyimide, silicon oxynitride (SiON), gold, and aluminum monolithically fabricated on a GaAs substrate. Fig. 1 shows a metal contacting series switch. This switch consists of gold signal lines (transmission lines), and contact metallization. SiON was deposited to form the fixed-fixed beam, and aluminum was deposited to form the top actuation electrode. To ensure product performance and reliability, RF MEMS switches are tested at both the wafer and package levels. Various processing irregularities may pass the visual inspection but fail electrical testing. This paper will focus on the failure mechanisms found in the first generation of RF MEMS developed at Sandia National Laboratories. Various tools and techniques such as scanning electron microscopy (SEM), resistive contrast imaging (RCI), focused ion beam (FIB), and thermally-induced voltage alteration (TIVA) have been employed to diagnose the failure mechanisms. The analysis performed using these tools and techniques led to corrective actions implemented in the next generation of RF MEMS metal contacting series switches.

Walraven, Jeremy A.; Cole, Edward I., Jr.; Sloan, Lynn R.; Hietala, Susan L.; Tigges, Chris P.; Dyck, Christopher W.

2001-10-01

178

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

179

Development Testing and Subsequent Failure Investigation of a Spring Strut Mechanism  

NASA Technical Reports Server (NTRS)

Commodities are transferred between the Multi-Purpose Crew Vehicle (MPCV) crew module (CM) and service module (SM) via an external umbilical that is driven apart with spring-loaded struts after the structural connection is severed. The spring struts must operate correctly for the modules to separate safely. There was no vibration testing of strut development units scoped in the MPCV Program Plan; therefore, any design problems discovered as a result of vibration testing would not have been found until the component qualification. The NASA Engineering and Safety Center (NESC) and Lockheed Martin (LM) performed random vibration testing on a single spring strut development unit to assess its ability to withstand qualification level random vibration environments. Failure of the strut while exposed to random vibration resulted in a follow-on failure investigation, design changes, and additional development tests. This paper focuses on the results of the failure investigations including identified lessons learned and best practices to aid in future design iterations of the spring strut and to help other mechanism developers avoid similar pitfalls.

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

2014-01-01

180

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

181

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

182

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

183

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

184

Accurate in vitro identification of fracture onset in bones: failure mechanism of the proximal human femur.  

PubMed

Bone fractures have extensively been investigated, especially for the proximal femur. While failure load can easily be recorded, and the fracture surface is readily accessible, identification of the point of fracture initiation is difficult. Accurate location of fracture initiation is extremely important to understand the multi-scale determinants of bone fracture. In this study, a recently developed technique based on electro-conductive lines was applied to the proximal femoral metaphysis to elucidate the fracture mechanism. Eight cadaveric femurs were prepared with 15-20 electro-conductive lines (crack-grid) covering the proximal region. The crack-grid was connected to a dedicated data-logger that monitored electrical continuity of each line at 700 kHz. High-speed videos (12,000 frames/s, 0.1-0.2 mm pixel size) of the destructive tests were acquired. Most crack-grid-lines failed in a time-span of 0.08-0.50 ms, which was comparable to that identified in the high-speed videos, and consistent with previous video recordings. However, on all specimens 1-3 crack-grid-lines failed significantly earlier (2-200 ms) than the majority of the crack-grid-lines. The first crack-grid-line to fail was always the closest one to the point of fracture initiation identified in the high-speed videos (superior-lateral neck region). Then the crack propagated simultaneously, at comparable velocity on the anterior and posterior sides of the neck. Such a failure pattern has never been observed before, as spatial resolution of the high-speed videos prevented from observing the initial opening of a crack. This mechanism (fracture onset, time-lag, followed by catastrophic failure) can be explained with a transfer of load to the internal trabecular structure caused by the initial fracture of the thin cortical shell. This study proves the suitability of the crack-grid method to investigate bone fractures associated to tensile stress. The crack-grid method enables significantly faster sampling than high-speed cameras. The present findings elucidate some aspects of the failure mechanism of the proximal human femoral metaphysis. PMID:23218142

Juszczyk, Mateusz Maria; Cristofolini, Luca; Salvà, Marco; Zani, Lorenzo; Schileo, Enrico; Viceconti, Marco

2013-01-01

185

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

186

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

187

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

188

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

2014-10-18

189

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

190

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

191

Failure of fluid-saturated granular materials: a unified approach to capture diffuse and localized instability mechanisms  

NASA Astrophysics Data System (ADS)

Granular materials are susceptible to a wide variety of failure and deformation mechanisms, especially because of their interaction with the pore fluids and the surrounding environment. An adequate modeling of their mechanical response is therefore essential for understanding a number of geological processes, such as the onset of rapid landslides, hillslope denudation and sediment transport, or even the mechanics of fault gauges. Depending on the type of material, the groundwater conditions and the surrounding kinematic constraints, both diffuse and localized mechanisms are possible, and these may occur under either drained or undrained conditions. In the geomechanics literature, failure modes are usually explained and modeled with the tools of continuum mechanics, such as the mathematical theory of plasticity. Due to the complexity of granular material behavior, however, most classical models for frictional strength are unable to capture the variety of instability mechanisms observed for such class of geomaterials (e.g., liquefaction, shear banding, etc.). Sophisticated strain-hardening plasticity models are therefore required for numerical modeling purposes, thus making the evaluation of critical failure conditions less straightforward than in perfect plasticity theories. Here we propose a mathematical strategy that can be adapted to any elastoplastic model and allows the onset of failure in elastoplastic geomaterials to be expressed in a more general manner. More specifically, our theory expresses the failure conditions as a function of local kinematics and solid-fluid interactions. The stability criterion used in this study is based on the so-called stability modulus, a scalar index of failure that was formulated by linking the physical concept controllability to the mathematical notion of plastic admissibility upon an incremental loading path [Buscarnera et al, 2011]. In this contribution, different loading constraints are considered, accounting for the possible occurrence of diffuse and localized failure mechanisms. While the mathematical strategy to calculate the failure indices is discussed in a general manner, a particular application is presented, focused on the simulation of the mechanical response of loose, saturated sands. Failure mechanisms are simulated under axisymmetric, plane-strain and simple shear conditions. For each of these cases, the indices are used to infer whether a failure mode is more likely to occur in a localized or homogeneous manner. At this reference, the role of drainage conditions is specifically explored. The results of numerical analyses are compared to data from classical experiments available in the literature. Finally, the theory is used to explain the mechanisms of failure that may have provoked a series of underwater flow failures in the shallow sand veneers located along the banks of the Jamuna River, in Bangladesh [Hight et al, 1998] The analyses conducted in this work elucidate the remarkable dependence of geomaterial stability on both kinematic conditions and pore-fluid constraints. In particular, the links between generalized failure mechanisms and the onset of landslides has been elucidated through numerical simulations. The results obtained by our analyses therefore provide a simple and consistent strategy to unify the mathematical description of the material instabilities that are involved in a variety of failure mechanisms of geological settings. Buscarnera G., Dattola G., Di Prisco C. (2011) " Controllability, uniqueness and existence of the incremental response: A mathematical criterion for elastoplastic constitutive laws", International Journal of Solids and Structures, 48 (13), pp. 1867-1878. Hight, D. W., Georgiannou, V. N., Martin, P. L., and Mundegar, A. K. (1998) "Flow slides in micaceous sand." Problematic soils, Yanagisawa, E., Moroto, N., and Mitachi, T., eds., Baklema, Rotterdam, Sendai, Japan, pp. 945-958.

Mihalache, Constance; Buscarnera, Giuseppe

2013-04-01

192

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

193

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

194

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

195

Evaluating the berkovitz method to predict fatigue loads in mechanical failure investigations  

NASA Astrophysics Data System (ADS)

This article evaluates a proposed analytical-experimental methodology by which the fatigue load levels leading to failure of structural components is inferred. The so-called Berkovitz method is recognized to depend fundamentally on a 1:1 relationship of micro- and macroscopic crack propagation rates. Compact tensile specimens of a high-strength aluminum alloy were fatigue tested at room temperature according to ASTM-E647, in plane-stress and plane-strain conditions, respectively. Unloading elastic compliance and low-magnification visual techniques monitored crack propagation rates. Topographical survey of fractured surfaces was carried out in a scanning electron microscope to measure striation spacing at constant-? K locations. By inputting these values in the Berkovitz model, the load spectrum applied during the fatigue testing could be derived. Research results have shown that, if correctly and carefully used, the assessed procedure provides accurate estimation of fatigue loads, so constituting a powerful tool during failure analysis of mechanical components operating in constant amplitude loading conditions.

Ruckert, C. O. F. T.; Tarpani, J. R.; Milan, M. T.; Bose Filho, W. W.; Spinelli, D.

2006-12-01

196

ME3738 protects from concanavalin A-induced liver failure via an IL-6-dependent mechanism.  

PubMed

ME3738 is a new compound that attenuates liver disease in several models of acute and chronic liver inflammation. We used the concanavalin A (Con A) model to elucidate the molecular mechanisms of ME3738 to block liver cell damage. Pretreatment of BALB/c mice with ME3738 prior to Con A injection resulted in a significant reduction in liver injury. The protective effect of ME3738 prior to Con A injection was associated with a reduction in IL-6 serum levels and NF-kappaB DNA binding in liver nuclear extracts. However, STAT3 DNA binding was induced via ME3738 prior to Con A injection. Further analysis showed that ME3738 induces IL-6 serum levels and activates STAT3 DNA binding and target gene transcription. The relevance of this finding was assessed in IL-6(-/-) mice. In these animals, ME3738 induced no increase in IL-6 serum expression, and activation of IL-6-dependent pathways was not found. In addition, ME3738 did not protect IL-6(-/-) animals from Con A-induced liver failure, while IL-6 injection was still effective. Therefore, we demonstrate that ME3738 triggers IL-6 expression, which activates pathways that are relevant to protect from Con A-induced liver failure. PMID:12884300

Klein, Christian; Wüstefeld, Torsten; Heinrich, Peter C; Streetz, Konrad L; Manns, Michael P; Trautwein, Christian

2003-08-01

197

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

198

Studies on the mechanism of non-oliguric experimental acute renal failure.  

PubMed Central

Although acute renal failure, caused either by renal ischemia or nephrotoxic agents, is usually characterized by oliguria, a severe fall in glomerular filtration rate, and a fall in renal blood flow, some patients and experimental models display a non-oliguric pattern of renal injury. The present study was designed to evaluate the mechanism of preservation of high urinary flow rate under this condition. Following the administration of the aminoglycoside gentamicin to rats for five days, a decrease in concentrating ability was demonstrated, caused by impaired vasopressin-mediated water transport. Further treatment resulted in a fall in Cin to 15 percent of control, although RBF was reduced to only 67 percent of control, and urine flow rate rose above control levels. Induction of acute and renal failure with dichromate was associated with variable high or low urinary flow rates according to pre-injury intake of sodium. Urine volume correlated directly with cortical blood flow. These data suggest that the non-oliguric pattern of acute renal injury is caused by preservation of cortical perfusion in the setting of severe tubular injury. PMID:7324506

Appel, G. B.; Siegel, N. J.; Appel, A. S.; Hayslett, J. P.

1981-01-01

199

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

200

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

201

Structural analysis of SiC Schottky diodes failure mechanism under current overload  

NASA Astrophysics Data System (ADS)

1.2 kV-10 A tungsten Schottky diodes (W-SBD) have been aged and tested at limit under current overload (surge current pulses) to determine their structural weakest spots. All devices showed no ageing at 40 A amplitudes and a surge current capability higher than 60 A. Infrared lock-in measurements have located the weakest spots on the surface of failed chips and allowed us to non-invasively infer their origin: Schottky barrier modification by metal contact change. After, a focused ion beam coupled with scanning electron microscope has been used to analyse the physical signature at these locations. These inspections have revealed that the destruction mechanism responsible for their failure was the electromigration and thermomigration of tungsten into aluminum, locally modifying the electrical behaviour of the Schottky barrier (loss of blocking capability).

León, J.; Berthou, M.; Perpiñà, X.; Banu, V.; Montserrat, J.; Vellvehi, M.; Godignon, P.; Jordà, X.

2014-02-01

202

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

NASA Astrophysics Data System (ADS)

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

Roach, Michael David

203

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

PubMed

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

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

2014-11-24

204

Nontraumatic fracture of the femoral condylar prosthesis in a total knee arthroplasty leading to mechanical failure.  

PubMed

This paper reports a case of fatigue fracture of the femoral component in a cruciate-retaining cemented total knee arthroplasty (TKA). A 64-year-old man had undergone a primary TKA for osteoarthritis 10 years previously at another institution using the PFC-Sigma prosthesis. The patient recovered fully and was back to his regular activities. He presented with a history of sudden onset pain and locking of the left knee since the preceding three months. There was no history of trauma, and the patient was mobilizing with difficulty using crutches. Radiographs revealed fracture of the posterior condyle of the femoral prosthesis. Revision surgery was performed as an elective procedure revealing the broken prosthesis. The TC3RP-PFC revision prosthesis was used with a medial parapatellar approach. The patient recovered fully without any squeal. Mechanical failure of the knee arthroplasty prosthesis is rare, and nontraumatic fracture of the femoral metallic component has not been reported before. PMID:24587928

Swamy, Girish N; Quah, Conal; Bagouri, Elmunzar; Badhe, Nitin P

2014-01-01

205

Nontraumatic Fracture of the Femoral Condylar Prosthesis in a Total Knee Arthroplasty Leading to Mechanical Failure  

PubMed Central

This paper reports a case of fatigue fracture of the femoral component in a cruciate-retaining cemented total knee arthroplasty (TKA). A 64-year-old man had undergone a primary TKA for osteoarthritis 10 years previously at another institution using the PFC-Sigma prosthesis. The patient recovered fully and was back to his regular activities. He presented with a history of sudden onset pain and locking of the left knee since the preceding three months. There was no history of trauma, and the patient was mobilizing with difficulty using crutches. Radiographs revealed fracture of the posterior condyle of the femoral prosthesis. Revision surgery was performed as an elective procedure revealing the broken prosthesis. The TC3RP-PFC revision prosthesis was used with a medial parapatellar approach. The patient recovered fully without any squeal. Mechanical failure of the knee arthroplasty prosthesis is rare, and nontraumatic fracture of the femoral metallic component has not been reported before. PMID:24587928

Swamy, Girish N.; Quah, Conal; Bagouri, Elmunzar; Badhe, Nitin P.

2014-01-01

206

Nonlinear elastic behavior and failure mechanism of polyhedral graphite particles undergoing uniaxial compression  

NASA Astrophysics Data System (ADS)

Load-displacement responses and ultimate strength of polyhedral graphite particles (PGPs) undergoing in situ nano-compression at ambient temperature have been studied. The dynamic responses of PGPs to uniaxial loads exhibit a typical nonlinear elastic behavior for graphitic nanomaterials. Based on the analysis of stress-strain relationship, the intrinsic strength is slightly larger than actual ultimate strength, indicating the mechanical properties influenced by the initial defects in PGPs. For a given case, compressive Young's modulus E and third-order elastic modulus D achieve to 12.8 GPa and -13.9 GPa, respectively. Weibull probability analysis confirmed its broad range of structural defects inside PGPs and mechanical properties are sensitive to initial defects. The values of ultimate strength of tested PGPs with diameter of 150-400 nm fall within 2-4.5 GPa, which are in the range between shear elastic modulus C44 of turbo-g (minimum) and C44 of hex-g (maximum) in the literature. The deformation and failure mechanisms are discussed and rationalized in terms of structural factors and elastic moduli of perfect graphite crystals.

Li, B.; Zhang, P.; Fu, Q. Q.; Li, X. F.; Zhao, X.; Song, X. L.

2014-08-01

207

The Mechanisms and Countermeasures of Failure in Low-Voltage Electronic Watt-Hour-Meters Caused by Lightning  

NASA Astrophysics Data System (ADS)

Experimental study was carried out for classified a mechanism of failure of low-voltage electronic Watt-Hour Meters. As the results, the mechanism of failure of electronic meters is clarified into two patterns. One is due to the magnetic field generated by lightning current passing through the inside of an electronic meter. The other is due to the blow out of electric wire caused by lightning current flowing into the power supply circuit for processing unit. For these failure mechanisms, following counter measures were clarified. One is that a magnetic shielding measure using a metallic plate covering the processing unit was effective for reducing the magnetic field. The other measure is that a relocation of the ZnO device in the electronic meter was effective for reducing the lightning current flowing into the power supply circuit.

Asakawa, Akira; Hurukawa, Seiji; Takahashi, Akihisa; Ishimoto, Kazuyuki

208

Silencing of TBC1D15 promotes RhoA activation and membrane blebbing.  

PubMed

Membrane blebs are round-shaped dynamic membrane protrusions that occur under many physiological conditions. Membrane bleb production is primarily controlled by actin cytoskeletal rearrangements mediated by RhoA. Tre2-Bub2-Cdc16 (TBC) domain-containing proteins are negative regulators of the Rab family of small GTPases and contain a highly conserved TBC domain. In this report, we show that the expression of TBC1D15 is associated with the activity of RhoA and the production of membrane blebs. Depletion of TBC1D15 induced activation of RhoA and membrane blebbing, which was abolished by the addition of an inhibitor for RhoA signaling. In addition, we show that TBC1D15 is required for the accumulation of RhoA at the equatorial cortex for the ingression of the cytokinetic furrow during cytokinesis. Our results demonstrate a novel role for TBC1D15 in the regulation of RhoA during membrane blebbing and cytokinesis. PMID:24337944

Takahara, Yuko; Maeda, Masao; Hasegawa, Hitoki; Ito, Satoko; Hyodo, Toshinori; Asano, Eri; Takahashi, Masahide; Hamaguchi, Michinari; Senga, Takeshi

2014-04-01

209

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

210

Mechanical behavior and failure micromechanisms of Al/Al2O3 composites under cyclic deformation  

NASA Astrophysics Data System (ADS)

The mechanical behavior under fully reversed cyclic deformation was determined through the incremental step method for two Al alloys reinforced with 15 vol pct A12O3 particulates in the naturally aged and peak-aged conditions. The composites exhibited cyclic strain hardening in all cases, but the hardening was more pronounced in the naturally aged condition. This behavior was reflected by the stress-strain curves in monotonie tension and in fatigue, and the cyclic strain-hardening coefficient was about twice the monotonie one for both materials and tempers. The tensile and cyclic strengths of the materials were very similar, and the dominant failure mechanism under both loading conditions was paniculate fracture, which was very localized around the fracture region in fatigue, but was spread along the specimen length in monotonie tension. In addition, a few A12O3 particulates were broken in compression during cyclic deformation. The final fracture micromechanism was the growth and coalescence of voids in the matrix from broken ceramic particulates. This last stage in the fracture process was fast and started when a critical volume fraction of broken reinforcements (between 30 and 45 pct) was reached in a given section of the specimen.

Poza, P.; Llorca, J.

1995-12-01

211

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

212

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

213

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

PubMed Central

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

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

2012-01-01

214

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

Microsoft Academic Search

In order to improve the hot corrosion resistance of conventional YSZ TBC system, a dense and continues overlay of AlâOâ coating of about 25 μm 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 AlâOâ coating in molten salts mixtures

Scott X. Mao

2002-01-01

215

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

216

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

217

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

218

A Study of the Failure Mechanism of Planar Non-Persistent Open Joints Using PFC2D  

NASA Astrophysics Data System (ADS)

Particle flow code 2D (PFC2D) was adopted to simulate the shear behavior of rocklike material samples containing planar non-persistent joints. Direct shear loading was conducted to investigate the effect of joint separation on the failure behavior of rock bridges. Initially calibration of PFC was undertaken with respect to the data obtained from experimental laboratory tests to ensure the conformity of the simulated numerical models response. Furthermore, validation of the simulated models were cross checked with the results of direct shear tests performed on non-persistent jointed physical models. Through numerical direct shear tests, the failure process was visually observed, and the failure patterns were found reasonably similar to the experimentally observed trends. The discrete element simulations demonstrated that the macro-scale shear zone resulted from the progressive failure of the tension-induced micro-cracks. The failure pattern was mostly influenced by joint separation, while the shear strength was linked to the failure pattern and failure mechanism. Furthermore, it was observed that the failure zone is relatively narrow and has a symmetrical pattern when rock bridges occupy a low percentage of the total shear surface. This may be due to the high stress interactions between the subsequent joints separated by a rock bridge. In contrast, when rock bridges are occupying sufficient area prohibiting the stress interactions to occur then the rupture of surface is more complex and turns into a shear zone. This zone was observed to be relatively thick with an unsymmetrical pattern. The shear strength of rock bridges is reduced by increasing the joint length as a result of increasing both the stress concentration at tip of the joints and the stress interaction between the joints.

Ghazvinian, A.; Sarfarazi, V.; Schubert, W.; Blumel, M.

2012-09-01

219

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

220

Characterization and Electrochemical Mechanism for Bromide-Containing Conductive Anodic Filament (CAF) Failure  

NASA Astrophysics Data System (ADS)

Conductive anodic filament (CAF) is a failure mode in printed wiring boards (PWBs) that occurs under temperature-humidity-bias (T-H-B) conditions. The filament, which is copper containing, grows subsurface from the anode to the cathode along the epoxy-glass fiber interface. In this study, hole-to-hole test coupons were processed using two thermal excursions for a high-bromide-containing (~15 wt.%) hot air soldering leveling (HASL) fluid. The coupons were then exposed to accelerated temperature, humidity, and bias conditions of 85°C, 85% relative humidity (RH), and 200 V bias, respectively, for 28 days. The aged coupons were then cross-sectioned, and scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) revealed that, in addition to bromide CAF, a copper-bromide-containing compound was present in the polymer matrix. The bromide-containing CAF was characterized using transmission electron microscopy (TEM) to be Cu2(OH)3Br. In addition, the copper-containing compound formed in the polymer matrix was characterized using x-ray photoelectron spectroscopy (XPS) to be CuBr. An electrochemical mechanism for the formation of bromide-containing CAF has been proposed based on the XPS data. It has been shown using Fourier-transform infrared (FTIR) spectroscopy that the polyol constituent from the flux diffuses into the board during soldering. Ion chromatography was used to show that bromide ions from the flux also diffuse into the board material during soldering.

Caputo, Antonio; Turbini, Laura J.; Perovic, Doug D.

2011-09-01

221

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

222

Mechanical characterization of liver capsule through uniaxial quasi-static tensile tests until failure.  

PubMed

Accidentology data showed that liver is often injured in car crashes; three types of injuries occur: hematoma, laceration and vessel failure. This paper focuses on surface laceration, which involves liver capsule and hepatic parenchyma. Liver capsule behavior has been studied but its failure properties are still unclear, particularly on a local point of view. In the present study, tensile quasi-static tests are run on parenchyma and capsule samples until failure to characterize capsule failure. Normalized load as well as failure properties-ultimate load per width unit and ultimate strain-are determined. Digital image correlation is used to measure the full local strain field on the capsule. Mean values of failure characteristics for hepatic capsule are 47+/-29% for the ultimate local strain and 0.3+/-0.3 N/mm for the ultimate load per width unit. A comparison between human and porcine tissues is conducted based on Mann-Whitney statistical test; it reveals that capsule characteristics are close between these two species; however, freezing preservation significantly affects porcine capsule failure properties. Therefore using porcine instead of human tissue to determine failure characteristics of liver capsule seems satisfactory only on fresh tissues. PMID:20394930

Brunon, A; Bruyère-Garnier, K; Coret, M

2010-08-10

223

Mechanical characterization of liver capsule through uniaxial quasi-static tensile tests until failure  

Microsoft Academic Search

Accidentology data showed that liver is often injured in car crashes; three types of injuries occur: hematoma, laceration and vessel failure. This paper focuses on surface laceration, which involves liver capsule and hepatic parenchyma. Liver capsule behavior has been studied but its failure properties are still unclear, particularly on a local point of view. In the present study, tensile quasi-static

A. Brunon; K. Bruyère-Garnier; M. Coret

2010-01-01

224

Investigation of failure mechanisms in high-power microwave transmission windows  

Microsoft Academic Search

Thermal runaway and window failure restrict the power output of high power (˜1 MW), long pulse length (˜10 sec) gyrotrons used for plasma heating in magnetic confinement fusion experiments. Chemical vapor deposition diamond is used as window material due to its low loss tangent and high thermal conductivity, but still suffers from occasional, unpredictable failure. With the use of a

Herman L. Bosman

2004-01-01

225

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

226

Platelet aggregation measurement for assessment of hemostasis failure mechanisms in patients with gastroduodenal ulcer bleeding  

PubMed Central

Background The purpose of this study was to identify factors associated with the risk of unsustainable hemostasis in patients with gastric and duodenal ulcer bleeding by in vitro assessment of platelet reactivity using artificial neural networks. Methods Patients with gastroduodenal ulcers complicated by bleeding were studied. Platelet aggregation was measured using aggregometry with adenosine diphosphate 5 ?M, epinephrine 2.5 ?M, 5-hydroxytryptophan 10 ?M, collagen 1 ?M, and thrombin 0.06 NIH Unit/mL as agonists. Multiple logistic regression was used to evaluate the independent relationship between demographic, clinical, endoscopic, and laboratory data and in vitro assessment of platelet reactivity and local parameters of hemostasis in patients with ulcer bleeding. Results Analysis of platelet aggregation in patients with gastroduodenal ulcer bleeding allowed the variability of platelet response to different agonists used in effective concentration which induces 50% platelet aggregation (EC50) to be established. The relationship between platelet aggregation and the spatial-temporal characteristics of ulcers complicated by bleeding was demonstrated. Adrenoreactivity of platelets was associated with time elapsed since the start of ulcer bleeding and degree of hemorrhage. The lowest platelet response to collagen and thrombin was detected in patients with active bleeding (P < 0.001) and unsustainable recent bleeding (P < 0.01). Decreased adenosine diphosphate-induced platelet aggregation in patients with ulcer bleeding was correlated with the platelet response to thrombin (r = 0.714, P < 0.001) and collagen (r = 0.584, P < 0.01). Conclusion Estimation of platelet reactivity in vitro indicates the key mechanisms of failure of hemostasis in patients with ulcer bleeding. In addition to gender, an important determinant of unsustainable hemostasis was a decreased platelet response to thrombin and adenosine diphosphate. PMID:23950655

Barinov, Edward; Sulaieva, Oksana; Lyakch, Yuriy; Guryanov, Vitaliy; Kondratenko, Petr; Radenko, Yevgeniy

2013-01-01

227

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

228

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

Microsoft Academic Search

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

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

2010-01-01

229

The behavior of the micro-mechanical cement-bone interface affects the cement failure in total hip replacement  

PubMed Central

In the current study, the effects of different ways to implement the complex micro-mechanical behavior of the cement-bone interface on the fatigue failure of the cement mantle was investigated. In an FEA-model of a cemented hip reconstruction the cement-bone interface was modeled and numerically implemented in four different ways: (I) as infinitely stiff, (II) as infinitely strong with a constant stiffness, (III) a mixed-mode failure response with failure in tension and shear, and (IV) realistic mixed mode behavior obtained from micro FEA-models. Case II, III and IV were analyzed using data from a stiff and a compliant micro-FEA model and their effects on cement failure were analyzed. The data used for Case IV was derived from experimental specimens that were tested previously. Although the total number of cement cracks was low for all cases, the compliant Case II resulted in twice as many cracks as Case I. All cases caused similar stress distributions at the interface. In all cases, the interface did not display interfacial softening; all stayed the elastic zone. Fatigue failure of the cement mantle resulted in a more favorable stress distribution at the cement-bone interface in terms of less tension and lower shear tractions. We conclude that immediate cement-bone interface failure is not likely to occur, but its local compliancy does affect the formation of cement cracks. This means that at a macro-level the cement-bone interface should be modeled as a compliant layer. However, implementation of interfacial post-yield softening does seem to be necessary. PMID:21036358

Waanders, Daan; Janssen, Dennis; Mann, Kenneth A.; Verdonschot, Nico

2010-01-01

230

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

231

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

232

Mechanisms of degradation and failure in a plasma deposited thermal barrier coating  

NASA Technical Reports Server (NTRS)

Failure of a two layer plasma deposited thermal barrier coating is caused by cyclic thermal exposure and occurs by spallation of the outer ceramic layer. Spallation life is quantitatively predictable, based on the severity of cyclic thermal exposure. This paper describes and attempts to explain unusual constitutive behavior observed in the insulative ceramic coating layer, and presents details of the ceramic cracking damage accumulation process which is responsible for spallation failure. Comments also are offered to rationalize the previously documented influence of interfacial oxidation on ceramic damage accumulation and spallation life.

Demasi-Marcin, Jeanine T.; Sheffler, Keith D.; Bose, Sudhangshu

1989-01-01

233

Special Education Management System Project Document. 3. Santa Cruz TBC Procedures.  

ERIC Educational Resources Information Center

Presented in chart form with accompanying booklet is the Task Base Composite (TBC), part of the Santa Cruz Special Education Management System Project, which lists 700 staff tasks to aid in the administrative determination of personnel needs, deployment, and program costs. Listed tasks are either "Learner Line" (tasks directly involving or…

Santa Cruz County Superintendent of Schools, CA.

234

TB & TBC Series System Newport Corporation warrants this product to be free of defects in material  

E-print Network

TB & TBC Series System OPERATOR'S MANUAL #12;ii Warranty Newport Corporation warrants this product at Newport's option. To exercise this warranty, write or call your local Newport representative or contact Newport headquarters in Irvine, California. You will be given prompt assistance and return instructions

Kleinfeld, David

235

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

236

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...

237

Root-soil mechanical interactions during pullout and failure of root bundles  

Microsoft Academic Search

Roots play a major role in reinforcing and stabilizing steep hillslopes. Most studies in slope stability implement root reinforcement as an apparent cohesion by upscaling the behavior of static individual roots. Recent studies, however, have shown that much better predictions of slope stability can be made if the progressive failure of bundles of roots are considered. The characteristics of progressive

M. Schwarz; D. Cohen; D. Or

2010-01-01

238

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

239

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...

240

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

Microsoft Academic Search

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 (¹³¹I) to 13 normal dogs, 3 autotransplanted (denervated) dogs, 5 dogs with left ventricular failure, and 5 dogs

Mark A. Rabinovitch; Colin P. Rose; Jean L. Rouleau; Claude Chartrand; Donald M. Wieland; Luigi Lepanto; Francine Legault; Samy Suissa; Leonard Rosenthall; John H. Burgess

1987-01-01

241

Investigation of Mechanisms of Blade Failure of Forged Hastalloy B and Cast Stellite 21 Turbine Blades in Turbojet Engine  

NASA Technical Reports Server (NTRS)

An investigation was conducted to study the mechanisms of blade failure of forged Hastelloy B and cast Stellite 21. The blades were mounted in a 16-25-6 alloy rotor and subjected to 20-minute cycles consisting of 15 minutes at rated speed and approximately 5 minutes at idle. The first failures of the Hastelloy B and Stellite 21 blades were probably the result of excessive vibratory stresses and occurred after 14.25 and 16.75 hours, respectively. After 28.75 hours of operation, all but 3 of the original 25 Hastelloy B blades had either failed or contained stress-rupture-type cracks and four of the original 27 Stellite 21 blades contained stress-rupture-type cracks.

Yaker, C; Robards, C F; Garrett, F B

1951-01-01

242

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

243

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

244

Mechanism of electromigration failure in Al thin film interconnects containing Sc  

SciTech Connect

In order to understand the role of Sc on electromigration (EM) failure, Al interconnects with 0.1 and 0.3 wt.% Sc sere tested as a function of post-pattern annealing time. In response to the evolution of the line structure, the statistics of lifetime evolved. While the addition of Sc greatly reduces the rate of evolution of the failure statistics because the grain growth rate decreases, the MTF variation was found to be very similar to that of pure Al. These observations seem to show that Sc has little influence on the kinetics of Al EM; however, it has some influence on the EM resistance of the line since it is an efficient grain refiner. Unlike Cu in Al, Sc does not seem to migrate, which may explain its lack of influence on the kinetics of Al EM.

Kim, Choong-un; Kang, S.H.; Morris, J.W. Jr. [Lawrence Berkeley Lab., CA (United States); Genin, F.Y. [Lawrence Livermore National Lab., CA (United States)

1995-05-01

245

Seismic Passive Earth Pressure Behind Non Vertical Wall with Composite Failure Mechanism: Pseudo-Dynamic Approach  

Microsoft Academic Search

This note shows a study on the seismic passive earth pressure behind a non-vertical cantilever retaining wall using pseudo-dynamic\\u000a approach. A composite failure surface comprising of an arc of the logarithmic spiral near the wall and a straight line in\\u000a the planar shear zone near the ground, has been considered behind the retaining wall. The effects of soil friction angle,

Priyanka Ghosh; Sreevalsa Kolathayar

2011-01-01

246

Stochastic and systematic patterning failure mechanisms for contact-holes in EUV lithography: Part 2  

NASA Astrophysics Data System (ADS)

Patterning uncertainty in EUV lithography arises from each lithographic component: the source, the photomask, the optical system, and the photoresist. All contribute to line roughness and contact disuniformity. In extreme cases, feature variability can result in patterning failures such as line microbridging or random missing contact holes. Historically, redundant contact holes (or vias) were placed to overcome the effects of a missing contact. Due to the aggressive CD shrink of feature size, the use of redundant contacts has been progressively decreased. For some types of devices, almost every contact of the billions found on the chip must be electrically active in order for the device to function. In such scenario, lithographic printing failures may cause catastrophic loss of yield, considering that closed contacts can hardly be corrected by smoothing techniques or etching. In this paper, the minimum contact CD which prints without failure - the contact hole printability limit - is studied for 54nm and 44nm pitch dense arrays. We find that the same resist may show dramatically different printability limits depending upon sizing dose and illumination conditions. This analysis will be implemented to estimate, through simulation-assisted experiments, the required exposure dose and aerial image to safely print sub-30nm contact holes.

Vaglio Pret, Alessandro; De Bisschop, Peter; Smith, Mark D.; Biafore, John J.

2014-03-01

247

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

248

Failure mechanisms of LiNi0.5Mn1.5O4 electrode at elevated temperature  

NASA Astrophysics Data System (ADS)

Failure mechanisms involved in the high-voltage LiNi0.5Mn1.5O4 electrode are studied at an elevated temperature (60 °C). At ambient temperature (25 °C), this oxygen-deficient spinel-structured electrode shows a reasonable cycle performance, but a rapid capacity decay after 40 cycles at 60 °C. An increase of electrode polarization and formation of electrically isolated active material, both of which become prominent from the 40th cycle, suggest that the electrode failure is mainly caused by the breakdown of electrically conductive network that is made between the active material, carbon and current collector in the composite electrode. The post-mortem electron microscope study reveals a crack formation at the electrode layer/aluminum current collector interface as well as inside the composite electrode layer, which can account for the electrode polarization and electrical isolation. The failure can, however, be mitigated by increasing the load of conductive carbon or polymeric binder, and also by using an etched aluminum foil as the current collector. All these countermeasures seem to be beneficial to reinforce the electrically conductive network.

Yoon, Taeho; Park, Sangjin; Mun, Junyoung; Ryu, Ji Heon; Choi, Wonchang; Kang, Yoon-Sok; Park, Jin-Hwan; Oh, Seung M.

2012-10-01

249

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

250

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

251

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

252

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

253

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

254

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

255

Effects of Creep and Cyclic Loading on the Mechanical Properties and Failure of Human Achilles Tendons  

E-print Network

, Stanford, CA (Received 9 September 2002; accepted 18 February 2003) Abstract--The Achilles tendon is one understood. This study examines the ex vivo mechanical behavior of excised human Achilles tendons to elucidate the relationships between mechanical loading and Achilles tendon injury. Eighteen tendons

Stanford University

256

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

257

Molecular dynamics simulations of mechanical failure in polymorphic arrangements of amyloid fibrils containing structural defects  

PubMed Central

Summary We examine how the different steric packing arrangements found in amyloid fibril polymorphs can modulate their mechanical properties using steered molecular dynamics simulations. Our calculations demonstrate that for fibrils containing structural defects, their ability to resist force in a particular direction can be dominated by both the number and molecular details of the defects that are present. The simulations thereby suggest a hierarchy of factors that govern the mechanical resilience of fibrils, and illustrate the general principles that must be considered when quantifying the mechanical properties of amyloid fibres containing defects. PMID:23946911

Ndlovu, Hlengisizwe; Ashcroft, Alison E; Radford, Sheena E

2013-01-01

258

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

PubMed

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. PMID:19098354

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

2009-01-21

259

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

260

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

Microsoft Academic Search

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

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

261

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

NASA Astrophysics Data System (ADS)

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

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

1992-05-01

262

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

263

Therapeutic CDK4/6 inhibition in breast cancer: key mechanisms of response and failure.  

PubMed

A hallmark of cancer is the deregulation of cell-cycle machinery, ultimately facilitating aberrant proliferation that fuels tumorigenesis and disease progression. Particularly, in breast cancers, cyclin D1 has a crucial role in the development of disease. Recently, a highly specific inhibitor of CDK4/6 activity (PD-0332991) has been developed that may have efficacy in the treatment of breast cancer. To interrogate the utility of PD-0332991 in treating breast cancers, therapeutic response was evaluated on a panel of breast cancer cell lines. These analyses showed that the chronic loss of Rb is specifically associated with evolution to a CDK4/6-independent state and, ultimately, resistance to PD-0332991. However, to interrogate the functional consequence of Rb directly, knockdown experiments were performed in models that represent immortalized mammary epithelia and multiple subtypes of breast cancer. These studies showed a highly specific role for Rb in mediating the response to CDK4/6 inhibition that was dependent on transcriptional repression manifest through E2F, and the ability to attenuate CDK2 activity. Acquired resistance to PD-03322991 was specifically associated with attenuation of CDK2 inhibitors, indicating that redundancy in CDK functions represents a determinant of therapeutic failure. Despite these caveats, in specific models, PD-0332991 was a particularly effective therapy, which induced Rb-dependent cytostasis. Combined, these findings indicate the critical importance of fully understanding cell-cycle regulatory pathways in directing the utilization of CDK inhibitors in the clinic. PMID:20473330

Dean, J L; Thangavel, C; McClendon, A K; Reed, C A; Knudsen, E S

2010-07-15

264

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.

265

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

266

Kidney Failure  

MedlinePLUS

... Details» www.kidneyfund.org > Kidney Disease > Kidney Failure Kidney Failure Kidney failure is when your kidneys stop ... are the tests for kidney failure? How is kidney failure (ESRD) different from chronic kidney disease (CKD)? ...

267

Fatigue failure kinetics and structural changes in lead-free interconnects due to mechanical and thermal cycling  

NASA Astrophysics Data System (ADS)

Environmental and human health concerns drove European parliament to mandate the Reduction of Hazardous Substances (RoHS) for electronics. This was enacted in July 2006 and has practically eliminated lead in solder interconnects. There is concern in the electronics packaging community because modern lead-free solder is rich in tin. Presently, near-eutectic tin-silver-copper solders are favored by industry. These solders are stiffer than the lead-tin near-eutectic alloys, have a higher melting temperature, fewer slip systems, and form intermetallic compounds (IMC) with Cu, Ni and Ag, each of which tend to have a negative effect on lifetime. In order to design more reliable interconnects, the experimental observation of cracking mechanisms is necessary for the correct application of existing theories. The goal of this research is to observe the failure modes resulting from mode II strain and to determine the damage mechanisms which describe fatigue failures in 95.5 Sn- 4.0 Ag - 0.5 Cu wt% (SAC405) lead-free solder interconnects. In this work the initiation sites and crack paths were characterized for SAC405 ball-grid array (BGA) interconnects with electroless-nickel immersion-gold (ENIG) pad-finish. The interconnects were arranged in a perimeter array and tested in fully assembled packages. Evaluation methods included monotonic and displacement controlled mechanical shear fatigue tests, and temperature cycling. The specimens were characterized using metallogaphy, including optical and electron microscopy as well as energy dispersive spectroscopy (EDS) and precise real-time electrical resistance structural health monitoring (SHM). In mechanical shear fatigue tests, strain was applied by the substrates, simulating dissimilar coefficients of thermal expansion (CTE) between the board and chip-carrier. This type of strain caused cracks to initiate in the soft Sn-rich solder and grow near the interface between the solder and intermetallic compounds (IMC). The growth near the interface was found to be caused by dislocation pile-ups at the IMC when the plastic zone ahead of the crack tip reached this interface. In temperature cycling testing, strains arose within the interconnect due to CTE mismatch between the solder and IMC. The substrates had matched CTE for all specimens in this research. Because of this, all the temperature cycling cracks were observed at interfaces, generally between the solder and IMC. Additionally, real-time electrical resistance may be a useful non-destructive evaluation (NDE) tool for the empirical observation of fatigue cracking in ball-grid arrays (BGA) during both mechanical and temperature cycling tests.

Fiedler, Brent Alan

268

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

269

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

270

Nicorandil ameliorates mitochondrial dysfunction in doxorubicin-induced heart failure in rats: possible mechanism of cardioprotection.  

PubMed

Despite of its known cardiotoxicity, doxorubicin is still a highly effective anti-neoplastic agent in the treatment of several cancers. In the present study, the cardioprotective effect of nicorandil was investigated on hemodynamic alterations and mitochondrial dysfunction induced by cumulative administration of doxorubicin in rats. Doxorubicin was injected i.p. over 2 weeks to obtain a cumulative dose of 18 mg/kg. Nicorandil (3 mg/kg/day) was given orally with or without doxorubicin treatment. Heart rate and aortic blood flow were recorded 24 h after receiving the last dose of doxorubicin. Rats were then sacrificed and hearts were rapidly excised for estimation of caspase-3 activity, phosphocreatine and adenine nucleotides contents in addition to cytochrome c, Bcl2, Bax and caspase 3 expression. Moreover, mitochondrial oxidative phosphorylation capacity, creatine kinase activity and oxidative stress markers were measured together with the examination of DNA fragmentation and ultrastructural changes. Nicorandil was effective in alleviating the decrement of heart rate and aortic blood flow and the state of mitochondrial oxidative stress induced by doxorubicin cardiotoxicity. Nicorandil also preserved phosphocreatine and adenine nucleotides contents by restoring mitochondrial oxidative phosphorylation capacity and creatine kinase activity. Moreover, nicorandil provided a significant cardioprotection via inhibition of apoptotic signaling pathway, DNA fragmentation and mitochondrial ultrastructural changes. Interestingly, nicorandil did not interfere with cytotoxic effect of doxorubicin against the growth of solid Ehrlich carcinoma. In conclusion, nicorandil was effective against the development of doxorubicin-induced heart failure in rats as indicated by improvement of hemodynamic perturbations, mitochondrial dysfunction and ultrastructural changes without affecting its antitumor activity. PMID:23872193

Ahmed, Lamiaa A; El-Maraghy, Shohda A

2013-11-01

271

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

272

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

273

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

274

Mechanism of Stent Failure in a Patient with Fibromuscular Dysplasia following Renal Artery Stenting.  

PubMed

Endovascular techniques used in the management of renal artery stenosis (RAS) have unique complications, to include stent facture, thrombosis, aneurysm formation, migration, and in-stent restenosis. Described here is an unusual complication of renal artery obstruction and recurrent hypertension without progressive loss of renal function, secondary to intermittent arterial kinking with respiratory and cardiac motion in a patient with fibromuscular dysplasia. This mechanical complication has implication not only in successful endovascular treatment of RAS, but raises questions regarding the alterations in dynamic motion with the cardio-respiratory cycle in stented visceral arteries in other vascular pathologies requiring renal artery stenting (i.e., juxtarenal or pararenal aortic aneurysms). PMID:25192822

Wang, Lin C; Scott, Daniel J; Clemens, Michael S; Hislop, Sean J; Arthurs, Zachary M

2015-01-01

275

Monitoring of temperature fatigue failure mechanism for polyvinyl alcohol fiber concrete using acoustic emission sensors.  

PubMed

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

276

The mechanism of decrease in dynamic mitral regurgitation during heart failure treatment: importance of reduction in the regurgitant orifice size  

Microsoft Academic Search

Objectives. The purpose of this study was to quantify and characterize the regurgitant flow pattern and regurgitant orifice area in patients undergoing therapy for severe heart failure using contemporary echocardiographic techniques.Background. Mitral regurgitation may be dynamic in patients with heart failure and ultimately correlate with outcome in a group of patients.Methods. Fourteen patients with severe heart failure felt to require

Luis B. Rosario; Lynne W. Stevenson; Scott D. Solomon; Richard T. Lee; Sharon C. Reimold

1998-01-01

277

Shear failure mechanism in granite inferred from multi-scale brittle structures  

NASA Astrophysics Data System (ADS)

The brittle structures of a Hercynian granite (La Borne, French Massif Central) observed at several scales, from regional to microscopic, are presented and interpreted on mechanical terms. Emphasis is placed on strike slip faults, joints, and cracks related to incipient shear fracturing during horizontal compression. Three compressive tectonic phases have been identified according to their brittle structures and characterised by the burial depth at the time of their generation. The two first phases (H1, H2) are Hercynian and occurred while the granite was deeply buried (˜5 to 3 km depth) whereas the last phase (P) is Pyrenean and occurred at very low depth. The geometric organizations of cracks, joints and faults are clearly similar at various scales from about 10 ?m to several m. These field observations are strong arguments for the occurrence of shear structures at microscopic to macroscopic scales during tectonic events. Following this inference, it is proposed that, at least in the case of Hercynian phases, cracks, joints and macroscopic strike slip faults have been generated by the same mechanical process under high overburden weight. Therefore, incipient fractures seem to be generated as shearing structures and to evolve by coalescence with neighbouring ones with the same direction.

Raynaud, Suzanne; Vasseur, Guy

2014-09-01

278

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

279

Physical Mechanisms of Failure, Ultralow Partial Pressure Lubrication, and the Reservoir Effect in MEMS  

NASA Astrophysics Data System (ADS)

The aim of this work is to examine the effectiveness of self-assembled monolayer (SAM) coatings as long term lubrication coatings in microsystems, to examine the failure regimes of SAM coated devices, to examine the role of mobility in adsorbed lubricating films, and to examine evolution of the coefficient of friction of devices surrounded by ultralow partial pressures of alcohols up to saturation. Finally the role of self assembled monlayers in vapor phase lubrication is examined. Self-assembled monolayers are ubiquitous in fabrication of free-standing microdevices because of their ability to prevent release related and dormancy related stiction. However their ability to lubricate under sliding and normal contact conditions is not well documented. It can be shown that the energy dissipated per unit area in one sliding cycle due to friction is significant under general loading conditions. Therefore from an energy dissipated standpoint the bond energies of the silane molecules should not be enough to withstand even a short number of cycles. An extension of this is the energy imparted to the surface through a normal loading cycle through a loss of kinetic energy. It can also be shown that this is enough to break the silicon oxygen bonds however this is over a longer time scale than in sliding. Also there is an open question on the role of mobile and non-mobile adsorbed species on friction. Is the mobility of a molecule/layer on a surface an indicator of the effectiveness of the lubrication potential of the layer? Do submonolayer coverages of alcohols "lock-up" to contacting surfaces by disrupting non-corrogated potentials? Is there a distinct lowering of frictional forces at the formation of a monolayer? Controlled adsorption of mobile and non-mobile species on rubbing contacts is necessary to elucidate this physical relationship. To accomplish this one must take into account that friction measurements are highly scale dependant. Therefore to ensure the accuracy of measurements relating to microsystem contact conditions experiments must be conducted on actual microdevices. In the work presented here I have used microelectromechanical system (MEMS) tribometers to measure the friction and adhesive forces of SAM coated surfaces over the coarse of many sliding cycles as well as normal contacting cycles. It is shown that robustly adhered monolayer coatings degrade extremely rapidly and there is a direct correlation between the respective energies dissipated both in sliding and normal contacting cycles and the time it takes for the layers to degrade. Also it is shown that devices fail in two main modes: one where wear of the devices in the form of dislocation of polysilicon grains leads to a low/adhesion high wear regime and another where high adhesive forces are developed and the devices fail with little to no wear. In the studies of ultra low partial pressure lubrication of devices a clear correlation between lubricant mobility to device lubrication is observed even in the presence of a vapor, which should in principle be able to replenish removed lubricant in between sliding cycles. We show that ultralow partial pressures nominally corresponding to submonolayer coverages of ethanol and pentanol show a distinct decrease in coefficient of friction and lubricate MEMS microcontacts however this is only loosely correlated to their effectiveness as lubricants. Pentanol was only shown to lubricate at the point at which it becomes mobile on the surface where as ethanol is mobile at all times and lubricates effectively at very low partial pressures. Trifluoroethanol is not mobile at any portion of its isotherm and does not effectively lubricate the contacts. We also show the ability of the surrounding SAM to act as a lubricant reservoir when vapors of ethanol are removed. The correlation of lubricant mobility to lubrication can be used to predict the effectiveness to new lubricants as well as allow for the tailoring of lubricants to specific applications.

Hook, David Adam

280

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

PubMed Central

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

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

2010-01-01

281

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

282

Bilateral patellar component shear failure of highly cross-linked polyethylene components: report of a case and laboratory analysis of failure mechanisms.  

PubMed

A case of bilateral patellar component failure due to fatigue fracture of the all-polyethylene fixation pegs in a highly cross-linked ultra-high-molecular-weight polyethylene design is presented. To recreate this failure mode, a novel test method was developed to investigate the effects of peg orientation and cement technique on patella fatigue strength under cyclic compression and shear loading. Patellar peg orientation had a minor effect on shear strength, whereas lack of cement in the backside patellar groove had a substantial effect. The shear fatigue strength exceeded in vivo force estimates when the patellar groove was fully cemented. The test results and retrieval analysis suggest that high activity level and inadequate cement fixation of the patellar component may contribute to all-polyethylene patellar component peg fractures. PMID:21978565

Stulberg, Bernard N; Wright, Timothy M; Stoller, Alex P; Mimnaugh, Kimberly L; Mason, James J

2012-05-01

283

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

284

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

285

Early G2/M checkpoint failure as a molecular mechanism underlying etoposide-induced chromosomal aberrations  

PubMed Central

Topoisomerase II (Topo II) inhibitors are cell cycle–specific DNA-damaging agents and often correlate with secondary leukemia with chromosomal translocations involving the mixed-lineage leukemia/myeloid lymphoid leukemia (MLL) gene on chromosome 11 band q23 (11q23). In spite of the clinical importance, the molecular mechanism for this chromosomal translocation has yet to be elucidated. In this study, we employed 2-color FISH and detected intracellular chromosomal translocations induced by etoposide treatment. Cells such as ataxia-telangiectasia mutated–deficient fibroblasts and U2OS cells, in which the early G2/M checkpoint after treatment with low concentrations of etoposide has been lost, executed mitosis with etoposide-induced DNA double-strand breaks, and 2-color FISH signals located on either side of the MLL gene were segregated in the postmitotic G1 phase. Long-term culture of cells that had executed mitosis under etoposide treatment showed frequent structural abnormalities of chromosome 11. These findings provide convincing evidence for Topo II inhibitor–induced 11q23 translocation. Our study also suggests an important role of the early G2/M checkpoint in preventing fixation of chromosomal abnormalities and reveals environmental and genetic risk factors for the development of chromosome 11 translocations, namely, low concentrations of Topo II inhibitors and dysfunctional early G2/M checkpoint control. PMID:16357944

Nakada, Shinichiro; Katsuki, Yoko; Imoto, Issei; Yokoyama, Tetsuji; Nagasawa, Masayuki; Inazawa, Johji; Mizutani, Shuki

2006-01-01

286

Origin and mechanisms of heart failure in hypertensive patients: left ventricular remodelling in hypertensive heart disease.  

PubMed

This review-editorial proposes a biological explanation for most of the physiological characteristics of the hypertrophied chronically overloaded heart. Various growth signals, including mechanical, hormonal and paracrine factors, appear now to be involved in the induction of myocyte hypertrophy and/or phenotypic modifications. A majority of the modifications in passive myocardial compliance are due to an enhanced collagen density, and the diminution of the atrial contribution to ventricular filling is certainly a consequence of an isomyosin change in this particular tissue. The systolic dysfunction reflects, in fact, one of the most essential parts of the adaptational process, the slowing of Vmax. In humans, this diminution is a consequence of a rather complex change in the expression of various genes coding for proteins responsible for myoplasmic calcium transient. Arrhythmogenicity, a well-known detrimental property of the hypertrophied heart, reflects the fragility of calcium homeostasis in this type of cell, and this fragility is likely to be a direct consequence of membrane protein rearrangement. PMID:8281969

Dubus, I; Samuel, J L; Swynghedauw, B

1993-11-01

287

Stability and mechanism of failure of The Barrier, southwest British Columbia  

NASA Astrophysics Data System (ADS)

The Barrier is a steep, 250 m-high escarpment of dacite in Garibaldi Provincial Park, British Columbia. The lava flow comprises four lobes, two of which (Lobes 3 and 4) came into contact with the late Pleistocene Cordilleran ice sheet. Lobe 3 was the source of a major landslide in 1855-1856 and a smaller event in 1977. This thesis investigates potential mechanisms responsible for landslides from The Barrier. Methods that I applied include magnetic surveys to determine the three-dimensional character of lava flows forming The Barrier, long-range photogrammetry to map the structure of the escarpment in digital terrain models, field mapping, distinct element modelling, and passive seismic landslide monitoring. Of particular importance to the stability of The Barrier are ice-contact structures in the volcanic rocks, which provide clues about emplacement environments. Results show that The Barrier should be considered potentially unstable and that past instability is intimately linked to structures produced by emplacement of the lavas against glacier ice. My work also provides new geophysical and geomechanical data for The Barrier. Keywords: The Barrier; landslide; rock fall; Garibaldi Provincial Park; Pleistocene; magnetic survey; photogrammetry; survey; UDEC; geophysics; modelling; distinct element code; Voronoi; tessellation; ice-contact volcanism.

Schon, Peter

288

Damage and failure mechanisms of continuous glass fiber reinforced polyphenylene sulfide  

NASA Technical Reports Server (NTRS)

The damage that accompanies flexural deformation of a unidirectional glass fiber composite of polyphenylene sulfide was examined by AE and SEM. These complementary techniques were used to identify damage mechanisms at the microscale and correlate them with the macroscopic stress state in four-point bending. The flexural stress-strain curve was nominally linear to about 1.0 percent strain, but the onset of damage detectable by AE occurred at 0.3 percent strain. Two peaks in the AE amplitude distribution were observed at 35 dB and 60 dB. Low-amplitude events were detected along the entire length of the specimen, and correlation with direct observations of damage made by deforming the composite on the SEM stage suggested that these events arose from matrix cracking and fiber debonding concentrated at flaws on the composite. High amplitude events occurred primarily in the region of highest flexural stress between the inner loading points. They were attributed to fracture of glass fibers on the tension side and surface damage on the compressive side.

Chen, F.; Hiltner, A.; Baer, E.

1992-01-01

289

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 thermal barrier coatings (TBCs), culminating in the water drop failure test. Both phenomena are discussed in terms of moisture effects on bulk alumina and bulk aluminides. A mechanism is proposed based on hydrogen embrittlement and is supported by a cathodic hydrogen charging experiment. Hydroxylation of aluminum from the alloy interface appears to be the relevant basic reaction.

Smialek, James L.

2008-01-01

290

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

291

Mechanisms of high-temperature fatigue failure in alloy 800H  

NASA Astrophysics Data System (ADS)

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 × 10-3 s-1 and slow-slow (S-S): 4 × 10-5 s-1) and asymmetrical ramp rates (fast-slow (F-S): 4 × 10-3 s-1 / 4 × 10-5 s-1 and slow-fast (S-F): 4 × 10-5 / 4 × 10-3 s-1) 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 > S-S > F-S > 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.

Rao, K. Bhanu Sankara; Schuster, H.; Halford, G. R.

1996-04-01

292

Numerical investigations of failure in EB-PVD thermal barrier coating systems  

NASA Astrophysics Data System (ADS)

Thermal barrier coating (TBC) systems are used in high temperature applications in turbine engines. TBCs are applied on superalloy substrates and are multilayered coatings comprised of a metallic bond coat, a thermally grown oxide (TGO) and a ceramic top coat. They provide thermal protection for the superalloy substrate and are considered to hold the greatest potential for increased operating temperatures. Failure of the TBC system most commonly occurs as a result of large scale buckling and spallation. The buckling is a consequence of many small-scale delaminations that arise in the top coat above local imperfections in the TGO, and durability of the TBC system is governed by a sequence of crack nucleation, propagation and coalescence. The numerical investigations that are employed in this dissertation are used to determine the stress development near the imperfections and are based on microstructural observations and measured material properties of TBC test buttons supplied by GE Aircraft Engines. The test buttons were subject to thermal cycling at GE and cycled to different percentages of TBC life. Numerical simulations of two different types of TBC tests are used to show that the top coat out-of-plane stress increases with a decrease of the substrate radius of curvature and a decrease in the heating rate. An inherent scaling parameter in the TBC system is identified and used to demonstrate that the stress developed in the top coat is governed by the evolution of an imperfection in the TGO. The effect of a martensitic phase transformation in the bond coat, related to a change in bond coat chemistry, is shown to significantly increase the top coat out-of-plane tensile stress. Finally, a subsurface crack is simulated in the top coat and used to determine the influence of the bond coat on failure of the TBC system. While the bond coat inelastic properties are the most important factors in determining the extent of the crack opening displacement, the bond coat martensitic phase transformation governs when the crack propagates. The crack propagates during heat-up when the martensitic phase transformation is included, and it propagates during cool-down when the transformation is not included.

Glynn, Michael L.

293

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

PubMed

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

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

2014-01-01

294

Heart Failure  

MedlinePLUS

... page from the NHLBI on Twitter. What Is Heart Failure? Heart failure is a condition in which the ... underway for Heart Failure, visit www.clinicaltrials.gov . Heart Failure in the News April 9, 2014 Drug does ...

295

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

296

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

297

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

298

Development of a ReaxFF Reactive Force Field for Ettringite and Study of its Mechanical Failure Modes from Reactive Dynamics  

E-print Network

Development of a ReaxFF Reactive Force Field for Ettringite and Study of its Mechanical Failure developed a first-principles-based ReaxFF reactive force field for Ca/Al/H/O/S. Here, we report on the development of this ReaxFF force field and on its validation and application using reactive molecular dynamics

Goddard III, William A.

299

Associations of insulin resistance and type 2 diabetes to heart failure: Epidemiology, potential mechanisms, and clinical perspectives  

Microsoft Academic Search

Heart failure, a common condition in most industrialized nations, is disabling and deadly. Type 2 diabetes, recognized as\\u000a a risk factor for incident heart failure more than three decades ago, consistently has been associated with a twofold to threefold\\u000a increased risk of heart failure and type 2 diabetes often coexist, and several studies have shown that type 2 diabetes in

Erik Ingelsson

2008-01-01

300

Complementary regulation of TBC1D1 and AS160 by growth factors, insulin and AMPK activators.  

PubMed

AS160 (Akt substrate of 160 kDa) and TBC1D1 are related RabGAPs (Rab GTPase-activating proteins) implicated in regulating the trafficking of GLUT4 (glucose transporter 4) storage vesicles to the cell surface. All animal species examined contain TBC1D1, whereas AS160 evolved with the vertebrates. TBC1D1 has two clusters of phosphorylated residues, either side of the second PTB (phosphotyrosine-binding domain). Each cluster contains a 14-3-3-binding site. When AMPK (AMP-activated protein kinase) is activated in HEK (human embryonic kidney)-293 cells, 14-3-3s bind primarily to pSer237 (where pSer is phosphorylated serine) in TBC1D1, whereas 14-3-3 binding depends primarily on pThr596 (where pThr is phosphorylated threonine) in cells stimulated with IGF-1 (insulin-like growth factor 1), EGF (epidermal growth factor) and PMA; and both pSer237 and pThr596 contribute to 14-3-3 binding in cells stimulated with forskolin. In HEK-293 cells, LY294002 inhibits phosphorylation of Thr596 of TBC1D1, and promotes phosphorylation of AMPK and Ser237 of TBC1D1. In vitro phosphorylation experiments indicated regulatory interactions among phosphorylated sites, for example phosphorylation of Ser235 prevents subsequent phosphorylation of Ser237. In rat L6 myotubes, endogenous TBC1D1 is strongly phosphorylated on Ser237 and binds to 14-3-3s in response to the AMPK activators AICAR (5-aminoimidazole-4-carboxamide-1-b-D-ribofuranoside), phenformin and A-769662, whereas insulin promotes phosphorylation of Thr596 but not 14-3-3 binding. In contrast, AS160 is phosphorylated on its 14-3-3-binding sites (Ser341 and Thr642) and binds to 14-3-3s in response to insulin, but not A-769662, in L6 cells. These findings suggest that TBC1D1 and AS160 may have complementary roles in regulating vesicle trafficking in response to insulin and AMPK-activating stimuli in skeletal muscle. PMID:17995453

Chen, Shuai; Murphy, Jane; Toth, Rachel; Campbell, David G; Morrice, Nick A; Mackintosh, Carol

2008-01-15

301

TBC1D13 IS A RAB35 SPECIFIC GAP THAT PLAYS AN IMPORTANT ROLE IN GLUT4 TRAFFICKING IN ADIPOCYTES  

PubMed Central

Insulin stimulates glucose transport in adipocytes by triggering translocation of GLUT4 glucose transporters to the plasma membrane (PM) and several Rabs including Rab10 have been implicated in this process. To delineate the molecular regulation of this pathway, we conducted a TBC/RabGAP overexpression screen in adipocytes. This identified TBC1D13 as a potent inhibitor of insulin-stimulated GLUT4 translocation without affecting other trafficking pathways. To determine the potential Rab substrate for TBC1D13 we conducted a yeast two-hybrid screen and found that the GTP bound forms of Rabs 1 and 10 specifically interacted with TBC1D13 but not with eight other TBC proteins. Surprisingly, a comprehensive in vitro> screen for TBC1D13 GAP activity revealed Rab35 but not Rab10 as a specific substrate. TBC1D13 also displayed in vivo GAP activity towards Rab35. Overexpression of constitutively active Rab35 but not constitutively active Rab10 reversed the block in insulin-stimulated GLUT4 translocation observed with TBC1D13 overexpression. These studies implicate an important role for Rab35 in insulin-stimulated GLUT4 translocation in adipocytes. PMID:22762500

Davey, Jonathan R; Humphrey, Sean J; Junutula, Jagath R; Mishra, Ashwini K; Lambright, David G; James, David E; Stöckli, Jacqueline

2012-01-01

302

TBC1D13 is a RAB35 specific GAP that plays an important role in GLUT4 trafficking in adipocytes.  

PubMed

Insulin stimulates glucose transport in adipocytes by triggering translocation of GLUT4 glucose transporters to the plasma membrane (PM) and several Rabs including Rab10 have been implicated in this process. To delineate the molecular regulation of this pathway, we conducted a TBC/RabGAP overexpression screen in adipocytes. This identified TBC1D13 as a potent inhibitor of insulin-stimulated GLUT4 translocation without affecting other trafficking pathways. To determine the potential Rab substrate for TBC1D13 we conducted a yeast two-hybrid screen and found that the GTP bound forms of Rabs 1 and 10 specifically interacted with TBC1D13 but not with eight other TBC proteins. Surprisingly, a comprehensive in vitro screen for TBC1D13 GAP activity revealed Rab35 but not Rab10 as a specific substrate. TBC1D13 also displayed in vivo GAP activity towards Rab35. Overexpression of constitutively active Rab35 but not constitutively active Rab10 reversed the block in insulin-stimulated GLUT4 translocation observed with TBC1D13 overexpression. These studies implicate an important role for Rab35 in insulin-stimulated GLUT4 translocation in adipocytes. PMID:22762500

Davey, Jonathan R; Humphrey, Sean J; Junutula, Jagath R; Mishra, Ashwini K; Lambright, David G; James, David E; Stöckli, Jacqueline

2012-10-01

303

Characterization of Tbc2, a nucleus-encoded factor specifically required for translation of the chloroplast psbC mRNA in Chlamydomonas reinhardtii  

PubMed Central

Genetic analysis has revealed that the three nucleus-encoded factors Tbc1, Tbc2, and Tbc3 are involved in the translation of the chloroplast psbC mRNA of the eukaryotic green alga Chlamydomonas reinhardtii. In this study we report the isolation and phenotypic characterization of two new tbc2 mutant alleles and their use for cloning and characterizing the Tbc2 gene by genomic complementation. TBC2 encodes a protein of 1,115 residues containing nine copies of a novel degenerate 38–40 amino acid repeat with a quasiconserved PPPEW motif near its COOH-terminal end. The middle part of the Tbc2 protein displays partial amino acid sequence identity with Crp1, a protein from Zea mays that is implicated in the processing and translation of the chloroplast petA and petD RNAs. The Tbc2 protein is enriched in chloroplast stromal subfractions and is associated with a 400-kD protein complex that appears to play a role in the translation of specifically the psbC mRNA. PMID:12045185

Auchincloss, Andrea H.; Zerges, William; Perron, Karl; Girard-Bascou, Jacqueline; Rochaix, Jean-David

2002-01-01

304

Obesity and natriuretic peptides, BNP and NT-proBNP: mechanisms and diagnostic implications for heart failure.  

PubMed

Many advances have been made in the diagnosis and management of heart failure (HF) in recent years. Cardiac biomarkers are an essential tool for clinicians: point of care B-type natriuretic peptide (BNP) and its N-terminal counterpart (NT-proBNP) levels help distinguish cardiac from non-cardiac causes of dyspnea and are also useful in the prognosis and monitoring of the efficacy of therapy. One of the major limitations of HF biomarkers is in obese patients where the relationship between BNP and NT-proBNP levels and myocardial stiffness is complex. Recent data suggest an inverse relationship between BNP and NT-proBNP levels and body mass index. Given the ever-increasing prevalence of obesity world-wide, it is important to understand the benefits and limitations of HF biomarkers in this population. This review will explore the biology, physiology, and pathophysiology of these peptides and the cardiac endocrine paradox in HF. We also examine the clinical evidence, mechanisms, and plausible biological explanations for the discord between BNP levels and HF in obese patients. PMID:25156856

Madamanchi, Chaitanya; Alhosaini, Hassan; Sumida, Arihiro; Runge, Marschall S

2014-10-20

305

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

306

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

307

Key condenser failure mechanisms  

SciTech Connect

Eight practical lessons highlight many of the factors that can influence condenser tube corrosion at coal-fired utilities and the effects contaminant in-leakage can have on steam generating units. 1 ref., 4 figs.

Buecker, B.

2009-04-15

308

Structural and Population-Based Evaluations of TBC1D1 p.Arg125Trp  

PubMed Central

Obesity is now a leading cause of preventable death in the industrialised world. Understanding its genetic influences can enhance insight into molecular pathogenesis and potential therapeutic targets. A non-synonymous polymorphism (rs35859249, p.Arg125Trp) in the N-terminal TBC1D1 phosphotyrosine-binding (PTB) domain has shown a replicated association with familial obesity in women. We investigated these findings in the Avon Longitudinal Study of Parents and Children (ALSPAC), a large European birth cohort of mothers and offspring, and by generating a predicted model of the structure of this domain. Structural prediction involved the use of three separate algorithms; Robetta, HHpred/MODELLER and I-TASSER. We used the transmission disequilibrium test (TDT) to investigate familial association in the ALSPAC study cohort (N?=?2,292 mother-offspring pairs). Linear regression models were used to examine the association of genotype with mean measurements of adiposity (Body Mass Index (BMI), waist circumference and Dual-energy X-ray absorptiometry (DXA) assessed fat mass), and logistic regression was used to examine the association with odds of obesity. Modelling showed that the R125W mutation occurs in a location of the TBC1D1 PTB domain that is predicted to have a function in a putative protein:protein interaction. We did not detect an association between R125W and BMI (mean per allele difference 0.27 kg/m2 (95% Confidence Interval: 0.00, 0.53) P?=?0.05) or obesity (odds ratio 1.01 (95% Confidence Interval: 0.77, 1.31, P?=?0.96) in offspring after adjusting for multiple comparisons. Furthermore, there was no evidence to suggest that there was familial association between R125W and obesity (?2?=?0.06, P?=?0.80). Our analysis suggests that R125W in TBC1D1 plays a role in the binding of an effector protein, but we find no evidence that the R125W variant is related to mean BMI or odds of obesity in a general population sample. PMID:23667688

Richardson, Tom G.; Thomas, Elaine C.; Sessions, Richard B.; Lawlor, Debbie A.; Tavaré, Jeremy M.; Day, Ian N. M.

2013-01-01

309

Cobalt-alloy implant debris induce HIF-1? hypoxia associated responses: a mechanism for metal-specific orthopedic implant failure.  

PubMed

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

310

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

311

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

312

Numerical Modeling of Thermal-Mechanical Niche Formation and Block Failure on Herschel Island, Yukon Territory, Canada.  

NASA Astrophysics Data System (ADS)

Wave action is the critical variable influencing coastal erosion rates in Arctic environments. Melting of interstitial ice and/or massive ice results in the addition of fine-grained sediment to the swash zone. This sediment is then held in suspension and transported along the coast by longshore currents. Removal of the insulating layer of unfrozen material exposes frozen cliff sediments directly to wave action, increasing the rate of thaw. Development of a thermoerosional niche proceeds until either (a) the storm abates and direct heat conduction to the coastal sediment stops, or (b) the overburden pressure exceeds the shear stress of the material, in which case a cohesive block of frozen sediment will fall directly onto the beach. In the case of (b), mechanical erosion of the cliff sediments will cease until the block material has been fully eroded and transported away, allowing the waves to again interact directly with the cliff sediments. A numerical model originally proposed by Kobayashi et al. (1999) was further developed to simulate the horizontal retreat associated with thermoerosional niche formation and block failure on Herschel Island during the annual 3-4 month ice-free period extending from mid-June to late September. The model was parameterized using data obtained from oblique aerial photographs, video footage and existing geomorphological data. Herschel Island was classified into three distinct categories based on cliff height, cliff angle, and ice content. Low frequency, high-magnitude storm events generate several metres of coastal backwasting in a very short time. Values for storm frequency and storm surge were modified from the existing model to reflect the 30-year mean. Results were compared with measured rates of coastal retreat in each distinct category for the previous 30 years. A high level of correlation is demonstrated between model results and existing data. A climate change factor was then introduced, predicting an increase in storm frequency and storm surge height.

Turner, J. D.; Pollard, W. H.

2004-05-01

313

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

314

Enhanced Characteristics of HVOF-sprayed MCrAlY Bond Coats for TBC Applications  

NASA Astrophysics Data System (ADS)

This study is focused on the variation of the microstructures of different CoNiCrAlY bond coats sprayed by the high-velocity oxy-fuel (HVOF) process for thermal barrier coating (TBC) applications. Three different size fractions of the CoNiCrAlY bond coat powder have been considered for this investigation: AMDRY 9951 (5-37 ?m), AMDRY 9954 (11-62 ?m), and AMDRY 995C (45-75 ?m). The influence of HVOF process parameters and process conditions have been studied in detail to achieve quality bond coats in terms of low porosity level, low oxygen content, and high surface roughness. The results have been promising and have shown that dense bond coats with low porosity can be achieved by HVOF spraying through the appropriate selection of powder size and process parameters. Importantly, HVOF bond coats appear to be competitive to VPS bond coats in terms of its oxygen content and high surface roughness.

Rajasekaran, B.; Mauer, G.; Vaßen, R.

2011-12-01

315

Heart Failure  

MedlinePLUS

... Pressure High Blood Pressure Tools & Resources Stroke More Heart Failure Sign Up for Our Heart-Health E-news ... with brochures and downloadable patient information sheets. Downloadable Heart Failure Resources What is Heart Failure? (PDF) How Can ...

316

Respiratory Failure  

MedlinePLUS

... the air sacs. This process is called gas exchange. In respiratory failure, gas exchange is impaired. Respiratory failure can be acute (short ... oxygen—into your airways and then your lungs. Rate This Content: Next >> December 19, 2011 Respiratory Failure ...

317

Effect of ENIG deposition on the failure mechanisms of thermomechanically loaded lead-free 2nd level interconnections in LTCC\\/PWB assemblies  

Microsoft Academic Search

Purpose – The purpose of this paper is to investigate the effect of electroless NiAu (ENIG) deposition on the failure mechanisms and characteristic lifetimes of three different non-collapsible lead-free 2nd level interconnections in low-temperature co-fired ceramic (LTCC)\\/printed wiring board (PWB) assemblies. Design\\/methodology\\/approach – Five LTCC module\\/PWB assemblies were fabricated and exposed to a temperature cycling test over a ?40 to

O. Nousiainen; T. Kangasvieri; K. Kautio; R. Rautioaho; J. Vähäkangas

2010-01-01

318

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

319

Failure Assessment  

NASA Technical Reports Server (NTRS)

Three questions to which software developers want accurate, precise answers are "How can the software system fail?", "mat bad things will happen if the software fails?t', and "How many failures will the software experience?". Numerous techniques have been devised to answer these questions; three of the best known are: 1) Software Fault Tree Analysis (SFTA) 2) Software Failure Modes, Effects, and Criticality Analysis (SFMECA 3) Software Fault/Failure Modeling. SFTA and SFMECA have been successfully used to analyze the flight software for a number of robotic planetary exploration missions, including Galileo, Cassini, and Deep Space 1. Given the increasing interest in reusing software components from mission to mission, one of us has developed techniques for reusing the corresponding portions of the SFTA and SFMECA, reducing the effort required to conduct these analyses. SFTA has also been shown to be effective in analyzing the security aspects of software systems; intrusion mechanisms and effects can easily be modeled using these techniques. The Bi- Directional Safety Analysis (BDSA) method combines a forward search (similar to SFMECA) from potential failure modes to their effects, with a backward search (similar to SFTA) from feasible hazards to the contributing causes of each hazard. BDSA offers an efficient way to identify latent failures. Recent work has extended BDSA to product-line applications such as flight-instrumentation displays and developed tool support for the reuse of the failure-analysis artifacts within a product line. BDSA has also been streamlined to support those projects having tight cost and/or schedule constraints for their failure analysis efforts. We discuss lessons learned from practice, describe available tools, and identi@ some future directions for the topic. A substantial amount of research has been devoted to estimating the number of failures that a software system will experience during test and operations, as well as the number of faults that have been inserted into that system during its development. One of us has found that the amount of structural change to a system during its development is strongly related to the number of faults inserted into it. Using techniques requiring no additional effort on the part of the development organization, the required measurements of structural evolution can be easily obtained from a development effort's configuration management system and readily transformed into an estimate of fault content. So far, structure-fault relationships have been identified for source code; current work seeks to examine artifacts available earlier in the lifecycle to determine if similar relationships between structure and fault content can be found. In particular, relationships between requirements change requests and the number of faults inserted into the implemented system would provide a significant improvement in our ability to control software quality during the early development phases.

Lutz, Robyn; Nikora, Allen

2005-01-01

320

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

321

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

322

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

323

Crystal structure of a Chlamydomonas reinhardtii flagellar RabGAP TBC-domain at 1.8 Å resolution.  

PubMed

Rab GTPases play a crucial role in the regulation of many intracellular membrane trafficking pathways including endocytosis and ciliogenesis. Rab GTPase activating proteins (RabGAPs) increase the GTP hydrolysis rate of Rab GTPases and turn them into guanine nucleotide diphosphate (GDP) bound inactive form. Here, we determined the crystal structure of the putative catalytic domain of a RabGAP (which we name CrfRabGAP) that is found in the flagellar proteome of the unicellular green alga Chlamydomonas reinhardtii. BLAST searches revealed potential human orthologues of CrfRabGAP as TBC1D3 and TBC1D26. Sequence and structural comparison with other canonical RabGAPs revealed that the CrfRabGAP does not contain the canonical catalytic residues required for the activation of Rab GTPases. The function of noncanonical RabGAPs-like CrfRabGAP might be to serve as Rab effectors rather than activators. PMID:24810373

Bhogaraju, Sagar; Lorentzen, Esben

2014-09-01

324

Multidisciplinary analysis of the operational temperature increase of turbine blades in combustion engines by application of the ceramic thermal barrier coatings (TBC)  

Microsoft Academic Search

The improvement of the temperature resistance of the aircraft engine elements can be obtained by application of a single ceramic thermal barrier coating (TBC) (e.g. Noda [1]) or several composite layers (e.g. Sadowski [2]). Engine elements protected by TBC can work safely in elevated temperature range above 1000°C. Continuous endeavour to increase thermal resistance of engine the elements requires, apart

T. Sadowski; P. Golewski

2011-01-01

325

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

326

No evidence that manual closure of the bronchial stump has a lower failure rate than mechanical stapler closure following anatomical lung resection.  

PubMed

A best evidence topic in cardiothoracic surgery was written according to a structured protocol. The question addressed was whether manual closure of the bronchial stump is safer with lower failure rates than mechanical closure using a stapling device following anatomical lung resection. One hundred and twenty-nine papers were identified using the search below. Eight papers presented the best evidence to answer the clinical question as they included sufficient number of patients to reach conclusions regarding the issues of interest for this review. Complications, complication rates and operation time were included in the assessment. The author, journal, date and country of publication, patient group studied, study type, relevant outcomes, results and study weaknesses of the papers are tabulated. When looking at manual vs mechanical staples, it was noted that stapler failure can occur in around 4% of cases. The rate of bronchopleural fistula (BPF) development varied more in patients who underwent manual closure (1.5-12.5%) than in patients who underwent mechanical closure (1-5.7%). Although most of the studies reviewed showed no statistical differences between manual and mechanical closure in terms of BPF development, one study, however, showed that manual closure was significantly associated with lower numbers of postoperative BPF, while another study showed that mechanical closure is significantly associated with lower incidence of BPF. When looking at the role of the learning curve and training opportunities, it seems that the surgeon's inexperience when using mechanical staples can contribute to BPF development. A surgeon's experience can play a major role in the prevention of BPF development in patients having manual closure. Manual closure can provide a cheap and reliable technique when compared with costs incurred from using staplers, it is applicable in all situations and can be taught to surgeons in training with an acceptable risk. However, there is a lack of evidence to suggest that manual closure is better than mechanical stapler closure following anatomical lung resection. PMID:24351508

Zakkar, Mustafa; Kanagasabay, Robin; Hunt, Ian

2014-04-01

327

Detection of SNPs in the TBC1D1 gene and their association with carcass traits in chicken.  

PubMed

TBC1D1 plays an important role in numerous fundamental physiological processes including muscle metabolism, regulation of whole body energy homeostasis and lipid metabolism. The objective of the present study was to identify single nucleotide polymorphisms (SNPs) in chicken TBC1D1 using 128 Erlang mountainous chickens and to determine if these SNPs are associated with carcass traits. The approach consisted of sequencing TBC1D1 using a panel of DNA from different individuals, revealing twenty-two SNPs. Among these SNPs, two polymorphisms (g.69307744C>T and g.69307608T>G) of block 1, four polymorphisms (g.69322320C>T, g.69322314G>A, g.69317290A>G and g.69317276T>C) of block 2 and four polymorphisms of block 3 (g.69349746G>A, g.69349736C>G, g.69349727C>T and g.69349694C>T) exhibited a high degree of linkage disequilibrium in all test populations. An association analysis was performed between the twenty-two SNPs and seven performance traits. SNPs g.69307744C>T, g.69340192G>A and g.69355665T>C were demonstrated to have a strong effect on liveweight (BW), carcass weight (CW), semi-eviscerated weight (SEW) and eviscerated weight (EW) and g.69340070C>T polymorphism was related to BW, SEW and BMW in chicken populations. However, for the other SNPs, there were no significant correlations between different genotypes and carcass traits. Meanwhile, haplotype CT-TG of block 1 and combined genotype AG-TT-AC-CT of block 3 were significantly associated with BW, CW, SEW and EW. Overall, our results provide evidence that polymorphisms in TBC1D1 are associated with carcass traits and would be a useful candidate gene in selection programs for improving carcass traits. PMID:24979340

Wang, Yan; Xu, Heng-Yong; Gilbert, Elizabeth R; Peng, Xing; Zhao, Xiao-Ling; Liu, Yi-Ping; Zhu, Qing

2014-09-01

328

The adaptor protein APPL2 inhibits insulin-stimulated glucose uptake by interacting with TBC1D1 in skeletal muscle.  

PubMed

Insulin stimulates glucose uptake by promoting the trafficking of GLUT4 to the plasma membrane in muscle cells, and impairment of this insulin action contributes to hyperglycemia in type 2 diabetes. The adaptor protein APPL1 potentiates insulin-stimulated Akt activation and downstream actions. However, the physiological functions of APPL2, a close homolog of APPL1, in regulating glucose metabolism remain elusive. We show that insulin-evoked plasma membrane recruitment of GLUT4 and glucose uptake are impaired by APPL2 overexpression but enhanced by APPL2 knockdown. Likewise, conditional deletion of APPL2 in skeletal muscles enhances insulin sensitivity, leading to an improvement in glucose tolerance. We identified the Rab-GTPase-activating protein TBC1D1 as an interacting partner of APPL2. Insulin stimulates TBC1D1 phosphorylation on serine 235, leading to enhanced interaction with the BAR domain of APPL2, which in turn suppresses insulin-evoked TBC1D1 phosphorylation on threonine 596 in cultured myotubes and skeletal muscle. Substitution of serine 235 with alanine diminishes APPL2-mediated inhibition on insulin-dependent TBC1D1 phosphorylation on threonine 596 and the suppressive effects of TBC1D1 on insulin-induced glucose uptake and GLUT4 translocation to the plasma membrane in cultured myotubes. Therefore, the APPL2-TBC1D1 interaction is a key step to fine tune insulin-stimulated glucose uptake by regulating the membrane recruitment of GLUT4 in skeletal muscle. PMID:24879834

Cheng, Kenneth K Y; Zhu, Weidong; Chen, Bin; Wang, Yu; Wu, Donghai; Sweeney, Gary; Wang, Baile; Lam, Karen S L; Xu, Aimin

2014-11-01

329

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

7596 Materials Science and Engineering A, 2011, 528(1-2): p. 7596­ 7605 High strain rate comprising hollow particles dispersed in a matrix material. Available studies on high strain rate compressive, the high strain rate failure occurs by crack propagation in the direction of compression. Compressive

Gupta, Nikhil

330

Light water reactor lower head failure analysis  

Microsoft Academic Search

This document presents the results from a US Nuclear Regulatory Commission-sponsored research program to investigate the mode and timing of vessel lower head failure. Major objectives of the analysis were to identify plausible failure mechanisms and to develop a method for determining which failure mode would occur first in different light water reactor designs and accident conditions. Failure mechanisms, such

J. L. Rempe; S. A. Chavez; G. L. Thinnes

1993-01-01

331

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' ...

332

Experimental aspects and mechanical modeling paradigms for the prediction of degradation and failure in nanocomposite materials subjected to fatigue loading conditions  

NASA Astrophysics Data System (ADS)

The objective of the current research was to contribute to the area of mechanics of composite polymeric materials. This objective was reached by establishing a quantitative assessment of the fatigue strength and evolution of mechanical property changes during fatigue loading of nanocomposite fibers and films. Both experimental testing and mathematical modeling were used to gain a fundamental understanding of the fatigue behavior and material changes that occurred during fatigue loading. In addition, the objective of the study was to gain a qualitative and fundamental understanding of the failure mechanisms that occurred between the nanoagent and matrix in nanocomposite fibers. This objective was accomplished by examining scanning electron microscopy (SEM) fractographs. The results of this research can be used to better understand the behavior of nanocomposite materials in applications where degradation due to fatigue and instability of the composite under loading conditions may be a concern. These applications are typically encountered in automotive, aerospace, and civil engineering applications where fatigue and/or fracture are primary factors that contribute to failure.

Averett, Rodney D.

2008-10-01

333

Dynamic failure in brittle solids  

SciTech Connect

Failure of brittle solids within the extremes of the shock loading environment is not well understood. Recent shock-wave data on compression shear failure and tensile spall failure for selected high-strength ceramics are presented and used to examine the mechanisms of dynamic failure. Energy-based theories are used to bound the measured strength properties. A new concept of failure waves in brittle solids is explored in light of the kinetic processes of high-rate fracture. Classical failure criteria are compared with the present base of dynamic strength data on ceramics.

Grady, D.E.

1994-04-01

334

[Results of singular valve replacement with a mechanical prosthesis or bioprosthesis in valve diseases with advanced myocardial failure].  

PubMed

Surgery may prolong survival in some patients in advanced cardiac failure due to valvular heart disease refractory to digitalo-diuretic and vasodilator therapy. The operative risk is high and myocardial dysfunction after surgery is also a problem. However, in some cases, surprising improvement is observed. An analysis of the principal publications in the literature on the natural history of valvular heart disease and the results of surgery in the last ten years show that: In chronic aortic valve disease complicated by congestive heart failure, the natural prognosis does not exceed 2 to 3 years in either aortic stenosis or regurgitation. On the other hand, prosthetic valve replacement is associated with a 57% 4 years survival in aortic regurgitation, and a 70% 5 years survival in aortic stenosis, but with an operative mortality of 20 to 27%. Surgery is even more valuable in acute aortic regurgitation due to endocarditis, leading to a 60% 2 years survival compared to only 6% with medical therapy alone. In chronic mitral valve disease with advanced cardiac failure, the natural prognosis does not exceed 4.5 years in mitral regurgitation, 8 years in mitral stenosis and an intermediate period in mixed mitral valve disease. On the other hand, prosthetic valve replacement with an operative risk of 21 to 26% is associated with a life expectancy of 56 to 60% at 5 years, and 46% at 10 years, operative mortality included. The surgical results depend on good myocardial protection and intensive pre-, per- and post-operative care using positive inotropic agents, vasodilators and, when necessary, intra aortic balloon pumping.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:6439158

Bensaid, J; Christides, C; Virot, P; Doumeix, J J; Blanc, P

1984-11-01

335

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

336

Mechanisms of gut barrier failure in the pathogenesis of necrotizing enterocolitis: Toll-like receptors throw the switch.  

PubMed

Necrotizing enterocolitis (NEC) is the leading cause of death from gastrointestinal causes in premature infants, and its overall survival has not improved in the past three decades. While the precise cause of NEC remains incompletely understood, we and others have shown that a major predisposing factor in the development and propagation of NEC is a breakdown of the intestinal barrier which leads to bacterial translocation and systemic sepsis. In seeking to identify the causes involved, we and others have also determined that activation of the receptor for bacterial endotoxin, namely toll-like receptor 4 (TLR4), is required for the development of intestinal barrier failure leading to NEC. We have also shown that the premature infant is endowed with strategies that can either limit or promote the extent of TLR4 signaling within the gut, which together determine the relative propensity with which NEC develops. In this review, we highlight the evidence for TLR4 signaling in the pathogenesis of NEC through a survey of its effects on gut barrier failure. We identify how TLR4 regulation within the gut can explain the unique susceptibility of the premature infant to the development of NEC, and highlight how strategies to limit the degree of TLR4 signaling can serve as novel therapeutic approaches for this devastating disease. PMID:23611610

Hackam, David J; Good, Misty; Sodhi, Chhinder P

2013-05-01

337

Microstructure and failure mechanism in As-deposited, vacuum plasma-sprayed Ti-6Al-4V alloy  

NASA Astrophysics Data System (ADS)

The microstructure, phase composition, and chemical composition of vacuum plasma-sprayed Ti-6Al-4V alloys were examined in detail using a variety of techniques, including x-ray diffraction, x-ray photoelectron spectroscopy, and transmission electron microscopy. The observed chemistry and structure were related to the conditions under which the deposit was formed and the phase equilibria in the Ti alloy system. The porosity of the deposit was in the range of 3 to 5%. A slight decrease in the Al content and a slight increase in the amount of oxygen and hydrogen was found relative to the starting powder. Within individual splats, a columnar solidification structure can be seen. However, the as-deposited material is ?90% ?? martensite that is present in the form of fine lathes on the order of 500 nm in width surrounded by residual ?-phase. This herringbone structure obscures to some extent the preexisting columnar structure of the as-solidified ?-phase. The material fails at low elongations (˜1%) when tested in tension, with a macroscopic stress-strain curve, which appears to be quite brittle. Examination of the fracture surface, however, reveals a ductile failure mode within individual splats, which is consistent with the structure described above. Sections perpendicular to the fracture surface show that failure occurs at the weak splat boundaries through the development and growth of voids between splats.

Salimijazi, H. R.; Coyle, T. W.; Mostaghimi, J.; Leblanc, L.

2005-06-01

338

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

339

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

340

Effect of oxygen on the mechanical properties and character of failure of powder steel 40N3M  

Microsoft Academic Search

An examination was made of the origin of the different forms of oxygen, since it requires individual detailed study, and the effect of oxygen on the mechanical properties of steel 40N3M was investigated as a function of its overall content in this steel. It is shown that oxygen sprayed and deformed steels lowers the mechanical properties even when its content

T. P. Moskvina; A. P. Gulyaev

1988-01-01

341

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

342

An automated dynamic fracture procedure and a continuum damage mechanics based model for finite element simulations of delamination failure in laminated composites  

NASA Astrophysics Data System (ADS)

An active field of research that has developed due to the increasing use of computational techniques like finite element simulations for analysis of highly complex structural mechanics problems and the increasing use of composite laminates in varied industries such as aerospace, automotive, bio-medical, etc. is the development of numerical models to capture the behavior of composite materials. One of the big challenges not yet overcome convincingly in this field is the modeling of delamination failure which is one of the primary modes of damage in composite laminates. Hence, the primary aim of this work is to develop two numerical models for finite element simulations of delamination failure in composite laminates and implement them in the explicit finite element software DYNA3D/LS-DYNA. Dynamic fracture mechanics is an example of a complex structural analysis problem for which finite element simulations seem to be the only possible way to extract detailed information on sophisticated physical quantities of the crack-tip at any instant of time along a highly transient history of fracture. However, general purpose, commercial finite element software which have capabilities to do fracture analyses are still limited in their use to stationary cracks and crack propagation along trajectories known a priori. Therefore, an automated dynamic fracture procedure capable of simulating dynamic propagation of through-thickness cracks in arbitrary directions in linear, isotropic materials without user-intervention is first developed and implemented in DYNA3D for its default 8-node solid (brick) element. Dynamic energy release rate and stress intensity factors are computed in the model using integral expressions particularly well-suited for the finite element method. Energy approach is used to check for crack propagation and the maximum circumferential stress criterion is used to determine the direction of crack growth. Since the re-meshing strategy used to model crack growth explicitly in the model induces spurious high-frequency oscillations in the finite element results after crack initiation, a "gradual nodal release" procedure is implemented as part of the model to overcome this problem. Also, an in-built contact algorithm of DYNA3D is modified to adapt it to the remeshing strategy to maintain proper contact conditions at newly added elements. Finally, the model is suitably modified for simulating delamination failure in laminated composites and used to predict delamination resistance characteristics which are important considerations for effective use of composite structures. Continuum damage mechanics is a popular approach for modeling the in-plane failure modes in composites. However, its applicability to modeling delamination has not been sufficiently analyzed yet. Hence, as the second part of this dissertation work, a new material model is developed for unidirectional polymer matrix composites in which this approach is used to predict delamination failure and used to perform a qualitative study of the damage mechanics approach to modeling delamination. The new material model is developed using micro-mechanics and accounts for the strain-rate dependent behavior of polymer matrix composites. It is implemented for three different element formulations with different transverse shear strain assumptions and the effect of these assumptions on the delamination prediction using this approach is analyzed.

Aminjikarai Vedagiri, Srinivasa Babu

343

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

344

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

345

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

346

Effect of noninvasive mechanical ventilation in elderly patients with hypercapnic acute-on-chronic respiratory failure and a do-not-intubate order  

PubMed Central

Noninvasive mechanical ventilation (NIMV) is effective in the treatment of patients with acute respiratory failure (ARF). It proved to reduce the need of endotracheal intubation (ETI), the incidence of ETI-associated pneumonia, and mortality compared to nonventilated patients. A particular aspect concerns the outcome of NIMV in patients referring to an emergency room (ER) for ARF, and with a do-not-intubate (DNI) status due to advanced age or critical conditions. The aim of our study is to assess the outcome of NIMV in a group of elderly patients with acute hypercapnic ARF who had a DNI status. An overall number of 62 subjects (30 males, 32 females, mean age 81 ± 4.8 years, range 79–91 years) referred to our semi-intensive respiratory department were enrolled in the study. The underlying diseases were severe chronic obstructive pulmonary disease (COPD) in 50/62 subjects, restrictive thoracic disorders in 7/62 subjects, and multiorgan failure in 5/62 subjects. Fifty-four/62 patients were successfully treated with NIMV while 2/62 did not respond to NIMV and were therefore submitted to ETI (one survived). Among NIMV-treated patients, death occurred in 6 patients after a mean of 9.9 days; the overall rate of NIMV failure was 12.9%. Negative prognostic factors for NIMV response proved to be: an older age, a low Glasgow Coma Score, a high APACHE score at admission, a high PaCO2 after 12 hours and a low pH both after 1 and 12 hours of NIMV. We conclude that elderly patients with acute hypercapnic ARF with a DNI status can be successfully treated by NIMV. PMID:19281095

Scarpazza, Paolo; Incorvaia, Cristoforo; di Franco, Giuseppe; Raschi, Stefania; Usai, Pierfranco; Bernareggi, Monica; Bonacina, Cristiano; Melacini, Chiara; Vanni, Silvia; Bencini, Serena; Pravettoni, Chiara; Di Cara, Giuseppe; Yacoub, Mona-Rita; Galeazzo, Gian; Riario-Sforza; Guffanti, Enrico; Casali, Walter

2008-01-01

347

Exploratory Investigation of Failure Mechanisms in Transition Regions between Solid Laminates and X-cor(registered tm) Truss Sandwich  

NASA Technical Reports Server (NTRS)

Small sub-component specimens consisting of solid laminates at the ends that transition to X-cor(R) truss sandwich in the center, were tested in a combination of three point bending, uni-axial tension, and combined tension and bending. The failure process in the transition region was documented for each loading using digital video and high-resolution cameras. For the 3-point bending tests, most of the deformation occurred in the solid laminate regions on either end of the specimen. Some pin debonding from the skin of the X-cor(R) truss sandwich was observed in the transition region and was accompanied by audible "pings" throughout the loading. Tension loaded specimens failed in the sandwich skin in the middle of the gage length, accompanied by separation of the sandwich core from the back skin and by delamination between the top skin and bottom skin at the transition region. The pinging associated with pin debonding occurred as the load was increased. However, the frequency of the pinging exceeded any visual observations of pin debonding in the video of the transition region. For specimens tested in combined tension and bending, the greatest amount of pinging occurred during initial application of the axial load. High-resolution images in the transition region indicated that the pinging corresponded to pins debonding and buckling due to the through-thickness Poisson contraction of the specimen. This buckling continued to a much smaller extent as the transverse load was applied.

OBrien, T. Kevin; Paris, Isabelle L.

2004-01-01

348

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

349

International Journal of Rock Mechanics & Mining Sciences 46, 11151123. Modelling and back-analysing failures in steep limestone cliffs  

E-print Network

International Journal of Rock Mechanics & Mining Sciences 46, 1115­1123. 1 Modelling and back author: D. Hantz (Didier.Hantz@ujf-grenoble.fr) March 2009 Abstract The observation of 12 rock fall scars in steep limestone cliffs has shown that the fallen masses were stable as a result of relatively small rock

Paris-Sud XI, Université de

350

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

351

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

352

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

353

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

PubMed

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

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

2014-01-01

354

Reliability evaluation and failure analysis for high voltage ceramic capacitor  

Microsoft Academic Search

This paper presents a result of failure analysis and reliability evaluation for high voltage ceramic capacitors. The failure modes and failure mechanisms were studied in two ways in order to estimate component life and failure rate. The causes of failure mechanisms for zero resistance phenomena under withstanding voltage test in high voltage ceramic capacitors molded by epoxy resin were studied

Jin-Woo Kim; Seung-Hun Shin; Dong-Su Ryu; Seog-Weon Chang

2001-01-01

355

Failure mechanisms of 3-D woven SiC/SiC composites under tensile and flexural loading at room and elevated temperatures  

NASA Technical Reports Server (NTRS)

Nicalon silicon carbide 3D yarn with silicon carbide matrix composites made through a chemical vapor infiltration (CVI) process were investigated under tensile and flexural loading at 23, 1200 and 1550 C in air. The effectiveness of a chemical vapor deposition (CVD) SiC surface coating was also evaluated in severe oxidizing environment. Acoustic emission sensors and in situ optical microscopy were used at room temperature to monitor the failure mechanisms. It is shown that the level of tensile stress at which nonlinear behavior begins is not drastically reduced at 1200 and 1550 C when composites were protected by a SiC surface coating. Extensive fiber pull-out was observed only in the 1550 C specimen. Similar behaviors were also found in flexural specimens.

Chulya, Abhisak; Gyekenyesi, John Z.; Gyekenyesi, John P.

1992-01-01

356

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

357

Fatigue Strength and Failure Mechanisms of Nitrided Small Parts of a 30CrMoV9 Steel  

Microsoft Academic Search

An investigation of nitriding effect on fatigue behavior of small-size specimens of a 30CrMoV9 (?SN 15330) nitriding steel heat treated to high strength was carried out, and fatigue damage mechanisms were evaluated. Circular cross-section specimens either smooth or notched, with the diameter approximately 2 mm in gauge section were used. Axial fatigue tests were carried out at constant load amplitude, loading

Ivo ?erný; Dagmar Mikulová; Ivan Fürbacher

2011-01-01

358

Implantation of a mechanical valve in a previously implanted mitral bioprosthetic orifice in a patient with mitral bioprosthetic failure.  

PubMed

Complete removal of a previously implanted dysfunctional mitral bioprosthesis could result in extensive damage. Therefore, a 66-year-old female patient with a deteriorated mitral bioprosthesis had leaflet excision, and a "new" mechanical valve was sewn onto the previously implanted bioprosthetic sewing cuff. On postoperative echocardiography, the implanted valve had good hemodynamic performance with no paravalvular leakage. The patient's clinical condition improved after surgery. PMID:17491353

Tsutsumi, Koji; Anzai, Tomohiro; Takahashi, Ryuichi

2007-04-01

359

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

360

Regulation of exosome secretion by Rab35 and its GTPase-activating proteins TBC1D10A–C  

PubMed Central

Oligodendrocytes secrete vesicles into the extracellular space, where they might play a role in neuron–glia communication. These exosomes are small vesicles with a diameter of 50–100 nm that are formed within multivesicular bodies and are released after fusion with the plasma membrane. The intracellular pathways that generate exosomes are poorly defined. Because Rab family guanosine triphosphatases (GTPases) together with their regulators are important membrane trafficking organizers, we investigated which Rab GTPase-activating proteins interfere with exosome release. We find that TBC1D10A–C regulate exosome secretion in a catalytic activity–dependent manner. We show that Rab35 is the target of TBC1D10A–C and that the inhibition of Rab35 function leads to intracellular accumulation of endosomal vesicles and impairs exosome secretion. Rab35 localizes to the surface of oligodendroglia in a GTP-dependent manner, where it increases the density of vesicles, suggesting a function in docking or tethering. These findings provide a basis for understanding the biogenesis and function of exosomes in the central nervous system. PMID:20404108

Hsu, Chieh; Morohashi, Yuichi; Yoshimura, Shin-ichiro; Manrique-Hoyos, Natalia; Jung, SangYong; Lauterbach, Marcel A.; Bakhti, Mostafa; Grønborg, Mads; Möbius, Wiebke; Rhee, JeongSeop; Barr, Francis A.

2010-01-01

361

PNL-SA-22914 Presented at the 48th Meeting of the Mechanical Failures Prevention Group (MFPG 48) 19-21 April 1994 in Wakefield, MA  

E-print Network

a real-time operational assessment, nor can it be readily modified to predict failures (perform), it is incapable of predicting failures. The current diagnostic process depends upon humans to integrate

362

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 ...

363

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

364

Total liquid ventilation provides superior respiratory support to conventional mechanical ventilation in a large animal model of severe respiratory failure.  

PubMed

Total liquid ventilation (TLV) has the potential to provide respiratory support superior to conventional mechanical ventilation (CMV) in the acute respiratory distress syndrome (ARDS). However, laboratory studies are limited to trials in small animals for no longer than 4 hours. The objective of this study was to compare TLV and CMV in a large animal model of ARDS for 24 hours. Ten sheep weighing 53 ± 4 (SD) kg were anesthetized and ventilated with 100% oxygen. Oleic acid was injected into the pulmonary circulation until PaO2:FiO2 ? 60 mm Hg, followed by transition to a protective CMV protocol (n = 5) or TLV (n = 5) for 24 hours. Pathophysiology was recorded, and the lungs were harvested for histological analysis. Animals treated with CMV became progressively hypoxic and hypercarbic despite maximum ventilatory support. Sheep treated with TLV maintained normal blood gases with statistically greater PO2 (p < 10(-9)) and lower PCO2 (p < 10(-3)) than the CMV group. Survival at 24 hours in the TLV and CMV groups were 100% and 40%, respectively (p < 0.05). Thus, TLV provided gas exchange superior to CMV in this laboratory model of severe ARDS. PMID:21084968

Pohlmann, Joshua R; Brant, David O; Daul, Morgan A; Reoma, Junewai L; Kim, Anne C; Osterholzer, Kathryn R; Johnson, Kent J; Bartlett, Robert H; Cook, Keith E; Hirschl, Ronald B

2011-01-01

365

Anti-CD95-induced lethality requires radioresistant Fcgamma RII+ cells. A novel mechanism for fulminant hepatic failure.  

PubMed

The Jo2 anti-mouse CD95 monoclonal antibody induces lethality in mice characterized by hepatocyte death and liver hemorrhage. Mice bearing a defect in Fas expression or in the Fas-mediated apoptotic pathway are resistant to Jo2. Here we show that FcgammaRII knockout mice or mice with monoclonal antibody-blocked FcgammaRII are also resistant to Jo2. The critical FcgammaRII(+) cells are radioresistant and could not be reconstituted with splenic cells. Death of sinusoidal lining cells and destruction of sinusoids were observed, consistent with the characteristic liver hemorrhage and the selective FcgammaRII expression in sinusoidal lining cells but not hepatocytes. Hemorrhage developed coincident with hepatocyte death and the sharp rise of serum alanine aminotransferase and alanine aminotransferase. Invariably, moribund mice showed severe liver hemorrhage and destruction of sinusoids. The data demonstrate a novel mechanism by which the destruction of liver sinusoids, induced by the Jo2-mediated co-engagement of Fas and FcgammaRII, leads to severe hemorrhage and lethal fulminant hepatitis. PMID:12477718

Jodo, Satoshi; Kung, John T; Xiao, Sheng; Chan, Derek V; Kobayashi, Seiichi; Tateno, Masatoshi; Lafyatis, Robert; Ju, Shyr-Te

2003-02-28

366

The TBC1D15 Oncoprotein Controls Stem Cell Self-Renewal through Destabilization of the Numb-p53 Complex  

PubMed Central

Stem cell populations are maintained through self-renewing divisions in which one daughter cell commits to a specific fate while the other retains the multipotent characteristics of its parent. The p53 tumor suppressor, in conjunction with its interacting partner protein Numb, preserves this asymmetry and functions as a vital barrier against the unchecked expansion of tumor stem cell pools; however, little is known about the biological control of the Numb-p53 interaction. We show here that Numb and p53 are the constituents of a high molecular mass complex, which is disintegrated upon activation of aPKC?, a Numb kinase. Using large-scale affinity purification and tandem mass spectrometry, we identify TBC1D15 as a Numb-associated protein and demonstrate that its amino-terminal domain disengages p53 from Numb, triggering p53 proteolysis and promoting self-renewal and pluripotency. Cellular levels of TBC1D15 are diminished upon acute nutrient deprivation through autophagy-mediated degradation, indicating that TBC1D15 serves as a conduit through which cellular metabolic status is linked to self-renewal. The profound deregulation of TBC1D15 expression exhibited in a diverse array of patient tumors underscores its proposed function as an oncoprotein. PMID:23468968

Feldman, Douglas E.; Chen, Chialin; Punj, Vasu; Machida, Keigo

2013-01-01

367

Aerospace Engineering Failure course website  

NSDL National Science Digital Library

This website provides a selection of learning materials from a laboratory-based undergraduate engineering course on structural and material failure. PDFs of lecture topics as well as lab handouts are provided. Topics include advanced fatigue and fracture mechanics, statistical failure analysis, structural health monitoring, non-destructive evaluation (NDE) and others.

Jr., David L.; Lestari, Wahyu

2012-01-01

368

Materials Failure Case Studies  

NSDL National Science Digital Library

This website offers innovative course materials for teaching engineering design and analysis through failure case studies, supporting the integration of research in forensic engineering into undergraduate education. The site includes an introduction to the overall project and a bibliography as well as typical civil engineering and engineering mechanics courses, with over 50 case studies currently listed. This web site is a companion to the book Beyond Failure: Forensic Case Studies for Civil Engineers, Delatte, Norbert J., ASCE Press. The site is a living document that will supplement the book with web links, additional information, and supplemental illustrations. At this time, not all of the cases have been filled in yet.

Delatte, Norbert J., Jr.

2008-12-12

369

Influence of Thermal Cycle Frequency on the TGO Growth and Cracking Behaviors of an APS-TBC  

NASA Astrophysics Data System (ADS)

The durability of thermal barrier coatings (TBCs) is controlled by fracture near the interface between the ceramic topcoat and the metallic bond coat, where a layer of thermally grown oxide (TGO) forms during service exposure. In the present work, the influence of thermal cycle frequency on the oxidation performance, in terms of TGO growth and cracking behavior, of an air-plasma-sprayed (APS) Co-32Ni-21Cr-8Al-0.5Y (wt.%) bond coat was studied. The results show that while TGO growth exhibited an initial parabolic growth behavior followed by an accelerated growth stage, higher cycle frequency resulted in a faster TGO growth and a higher crack propagation rate. It is found that a power-law relationship exists between the maximum crack length and the TGO thickness, which is independent of the cycle frequency. This relationship may warrant a TBC life prediction methodology based on the maximum crack length criterion.

Chen, W. R.; Wu, X.; Dudzinski, D.

2012-12-01

370

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

NASA Astrophysics Data System (ADS)

Modern aero engine turbine blades made of nickel-based superalloys are covered by thermal barrier coatings (TBC) for thermal and oxidation protection. A new generation of TBCs consist of a bond coat (thin layer of MCrAlY, where M may be Ni, Co, Fe) followed by a ceramic top coat of RE2Zr2O7 (RE - rare earth element). In this paper we present the possibility of the electron backscatter diffraction (EBSD) method for characterisation of the microstructure and crystallographic orientation of a new TBC consisting of a Gd2Zr2O7 top coat and a NiFeCrAlY bond coat after long thermal exposure (1100 °C, 500 h). During thermal exposure, a thermally grown oxide (TGO) layer forms at the bond coat/top coat interface. The TGO is mainly composed of Al2O3. But, there is a possible reaction between Gd2Zr2O7 and Al2O3, leading to Gd-Al-O phases. Phase composition plays an important role in controlling the stress evolution, TGO deformation and crack propagation. Application of SEM-EDS-EBSD techniques allows direct characterisation of the chemical composition, phase composition and crystallographic orientation in the ceramic top coat and TGO layers. This paper presents the possibilities of using the EBSD method for phase identification (Gd2Zr2O7, spinel Ni(Al,Cr)2O4, GdAlO3 and other phases) and orientation analysis of grains in the TGO layer.

Chmiela, B.; Soza?ska, M.; Moskal, G.

2012-03-01

371

Transfusion-independent ?0-thalassemia after bone marrow transplantation failure: proposed involvement of high parental HbF and an epigenetic mechanism  

PubMed Central

Currently, bone marrow transplantation is the only curative treatment for ?-thalassemia and sickle cell disease. In rare cases, sustained and full fetal hemoglobin production was observed in patients after failure of bone marrow transplantation. This rendered the patients transfusion-free, despite genetic disease and transplant rejection. The mechanisms underlying this phenomenon remain unexplored. We have studied a trio (father-mother-child) in which the affected child became transfusion-independent after rejection of an allogeneic bone marrow graft. Remarkably, we found that his non-thalassemic mother also expressed unusually high levels of ?-globin. High HbF in one of the parents may therefore be of prognostic value in these rare cases. Genotyping of the HBB locus and the HbF quantitative trait loci HBS1L-MYB, KLF1 and BCL11A, and protein expression analysis of KLF1 and BCL11A, failed to explain the increased HbF levels, indicating that an as yet unidentified HbF modifier locus may be involved. We hypothesize that epigenetic events brought about by the transplantation procedure allow therapeutic levels of HbF expression in the child. Potential implications of our observations for reactivation of ?-globin expression and interpretation of the French globin gene therapy case are discussed. PMID:25232502

Paciaroni, Katia; Lucarelli, Guido; Martelli, Fabrizio; Migliaccio, Anna Rita; von Lindern, Marieke; Borg, Joseph; Gillemans, Nynke; van Dijk, Thamar B; Philipsen, Sjaak

2014-01-01

372

Heart Failure  

MedlinePLUS

... of breath Common causes of heart failure are coronary artery disease, high blood pressure and diabetes. It is more common in people who are 65 years old or older, African Americans, people who are ... treatments fail. NIH: National Heart, Lung, and Blood Institute

373

TOXICOLOGICAL MECHANISMS OF IMPLEMENTATION FAILURE  

EPA Science Inventory

Implantation in mammals requires the successful completion of a series of integrated phenomena, including uterine preparation, synchronized embryo transport, embryonic attachment, uterine transformation, placental development, and the requisite hormonal milieu to support each ste...

374

School Failure  

Microsoft Academic Search

School failure is an important worldwide issue, leading to underemployment (unemployment or job dissatisfaction) and a lower\\u000a quality of life. The overall dropout rate in the United States is 10–25%, depending on how it is reckoned. But it is common\\u000a for the most struggling high schools to lose 25–50% of their students between 9th and 12th grade, and on any

Peter W. Dowrick; Natalie Crespo

375

Influence of stratigraphic factors on the failure mechanisms of sinkholes related to man-made underground caves at Cutrofiano (South-Eastern Italy)  

NASA Astrophysics Data System (ADS)

An increasing number of areas in southern Italy are being interested by sinkholes related to the presence of man-made cavities, with underground quarries representing the more problematic typology of anthropogenic caves in terms of instability. The case of Cutrofiano (Apulia, SE Italy) is here presented as a representative case study. This territory is well known for the underground quarrying activity of soft calcarenitic rocks that caused in the last decades widespread phenomena of subsidence at the surface, with extensive damage and problems to the main communication routes in the area. A very complex and intricate network of subterranean galleries is present underground, for a total development on the order of several tens of kilometres. The Gravina Calcarenite Formation, that is the object of the underground quarries, consists of whitish calcarenite with an upper greenish clayey-sandy interval rich in fossils. This formation is overlain by grey sandy clays (Subapennine Clays) grading upward to fossil-rich sands (Brindisi Sands). In recent years, clay mining has been resumed at the ground surface, following the opening of a cement factory, and resulting in the realization of wide open-pit quarries. The local sedimentary sequence is closed by terraced calcarenite deposits, that holds a phreatic groundwater body. The results of detailed geological, geomorphological and geomechanical surveys, supported by laboratory tests, show that in the Cutrofiano area the thickness of the stratigraphical succession, the depth of the underground galleries, the structural conditions of the rock mass, and the failure mechanisms observed within the quarries are variable. The geological model reconstructed represents the base for the implementation of numerical simulations, which are aimed at defining the eventual mechanisms of rock failure, up to the formation of the sinkhole. Local changes in the stratigraphy are very common in the area, due to the overall slight attitude of the strata, dipping toward the SW, and to lateral variations in the geological succession. Thus, at least two different geological settings may be recognized: the first is typical of those areas closest to the town, where the calcarenite rock mass is at low depth, and appears to be covered by very thin deposits; in such a situation, the underground quarries develop at depths ranging from 7 to 10 meters below the ground surface. The second setting, which typically characterizes the sectors a few kilometres farther south, shows, on the other hand, the presence of thick cover of the clay-sandy intervals, and has the galleries of underground quarries located at depth variable from 15 to 45 m. Starting from these different situations, two-dimensional numerical analyses have been developed by using the finite element method to investigate the stress-strain evolution of the rock mass surrounding the galleries due to long-term degradation of the rock properties induced by weathering and water infiltration. The results obtained from the numerical simulations point out a quite different behaviour between the two geological settings, since the presence of the significant clay layer overlying the calcarenite substratum affects the geometry of the subsidence cone, and, consequently, the real extent of the likely sinkholes at the surface. These outcomes are of great importance to highlight the need to use detailed, site-specific, data in order to perform numerical modelling, and warn about the common habit of extending a small number of borehole data, tens of hundreds of meters apart, over large areas. Especially when carried out to define vulnerability and/or risk of specific elements at risk, the researches should be performed having available on-site data, or, alternatively, the end users should be properly warned in the use of the outcomes from the study.

Lollino, Piernicola; Margiotta, Stefano; Parise, Mario

2013-04-01

376

IFN-? induces aberrant CD49b+ NK cell recruitment through regulating CX3CL1: a novel mechanism by which IFN-? provokes pregnancy failure  

PubMed Central

Interferon-? (IFN-?), a pleiotropic lymphokine, has important regulatory effects on many cell types. Although IFN-? is essential for the initiation of uterine vascular modifications and maintenance of decidual integrity, IFN-? administration can also cause pregnancy failure in many species. However, little is known about the effector mechanisms involved. In this study, using an IFN-?-induced abortion mouse model, we reported that no Dolichos biflorus agglutinin lectin-positive uterine natural killer (uNK) cells were observed in the uteri from IFN-?-induced abortion mice. By contrast, the percentage of CD3?CD49b+ NK cells in the uterus and blood from a foetal resorption group was significantly higher than that of the control group. Similarly, significantly upregulated expression of CD49b (a pan-NK cell marker), CX3CL1 and CX3CR1 (CX3CL1 receptor) was detected in the uteri of IFN-?-induced abortion mice. Using isolated uterine stromal cells, we showed that upregulated expression of CX3CL1 by IFN-? was dependent on a Janus family kinase 2-signal transducers and activators of transcription 1 (JAK2-STAT1) pathway. We further demonstrated the chemotactic activity of CX3CL1 in uterine stromal cell conditioned medium on primary splenic NK cells. Finally, we observed increased recruitment of CD49b+ NK cells into the endometrium after exogenous CX3CL1 administration. Collectively, our findings indicate that IFN-? can significantly increase uterine CX3CL1 expression via activation of the JAK2-STAT1 pathway, thus inducing CD49b+ NK cell uterine homing, and eventually provoke foetal loss. Thus, we provide a new line of evidence correlating the deleterious effects of IFN-? on pregnancy with the aberrant regulation of CX3CL1 and CD49b+ NK cells. PMID:25375377

Li, Z-Y; Chao, H-H; Liu, H-Y; Song, Z-H; Li, L-L; Zhang, Y-J; Yang, Y; Peng, J-P

2014-01-01

377

Pt-modified Ni aluminides, MCrAlY-base multilayer coatings and TBC systems fabricated by Spark Plasma Sintering for the protection of Ni-base superalloys  

Microsoft Academic Search

Pt-modified Ni aluminides and MCrAlY coatings (where M=Ni and\\/or Co) are widely used on turbine blades and vanes for protection against oxidation and corrosion and as bond coatings in thermal barrier coating (TBC) systems. The present work shows the ability of a new fabrication technique, the Spark Plasma Sintering, to develop rapidly new coating compositions and microstructures. This technique allows

Daniel Monceau; Djar Oquab; Claude Estournes; Mathieu Boidot; Serge Selezneff; Yannick Thebault; Yannick Cadoret

2009-01-01

378

The anti-inflammatory effects of a selectin ligand mimetic, TBC1269, are not a result of competitive inhibition of leukocyte rolling in vivo  

Microsoft Academic Search

Selectins and their ligands support leu- kocyte rolling, facilitating the subsequent firm ad- hesion and migration that occur during inflamma- tion. TBC-1269 (Bimosiamose), a structural mi- metic of natural selectin ligands, inhibits P-, E-, and L-selectin in vitro, has anti-inflammatory ef- fects in vivo, and recently underwent phase II clin- ical trials for childhood asthma and psoriasis. We studied whether

Anne E. R. Hicks; Kate B. Abbitt; Paul Dodd; Victoria C. Ridger; Paul G. Hellewell; Keith E. Norman

2004-01-01

379

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

380

Affinity between TBC1D4 (AS160) phosphotyrosine-binding domain and insulin-regulated aminopeptidase cytoplasmic domain measured by isothermal titration calorimetry.  

PubMed

Uptake of circulating glucose into the cells happens via the insulin- mediated signalling pathway, which translocates the glucose transporter 4 (GLUT4) vesicles from the intracellular compartment to the plasma membrane. Rab?GTPases are involved in this vesicle trafficking, where Rab?GTPase-activating proteins (RabGAP) enhance the GTP to GDP hydrolysis. TBC1D4 (AS160) and TBC1D1 are functional RabGAPs in the adipocytes and the skeletonal myocytes, respectively. These proteins contain two phosphotyrosine-binding domains (PTBs) at the amino-terminus of the catalytic RabGAP domain. The second PTB has been shown to interact with the cytoplasmic region of the insulin-regulated aminopeptidase (IRAP) of the GLUT4 vesicle. In this study, we quantitatively measured the ??M affinity (KD) between TBC1D4 PTB and IRAP using isothermal titration calorimetry, and further showed that IRAP residues 1-49 are the major region mediating this interaction. We also demonstrated that the IRAP residues 1-15 are necessary but not sufficient for the PTB interaction. PMID:22732222

Park, SangYoun; Kim, Keon Young; Kim, Sunmin; Yu, Young Seok

2012-06-01

381

Failure modes in surface micromachined microelectromechanical actuators  

SciTech Connect

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

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

1998-03-01

382

Peyronie's disease and erectile failure  

SciTech Connect

A total of 20 patients with Peyronie's disease, including 15 with erectile failure and 5 with normal potency, underwent evaluation with dynamic xenon washout and infusion cavernosography. Abnormal drainage from the cavernous body was found in 13 of the 15 patients with erectile failure and in none of the 5 potent patients, indicating that this condition seems to be the underlying pathological mechanism leading to erectile impotence in patients with Peyronie's disease.

Metz, P.; Ebbehoj, J.; Uhrenholdt, A.; Wagner, G.

1983-12-01

383

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

384

Progressive Failure Analysis Methodology for Laminated Composite Structures  

NASA Technical Reports Server (NTRS)

A progressive failure analysis method has been developed for predicting the failure of laminated composite structures under geometrically nonlinear deformations. The progressive failure analysis uses C(exp 1) shell elements based on classical lamination theory to calculate the in-plane stresses. Several failure criteria, including the maximum strain criterion, Hashin's criterion, and Christensen's criterion, are used to predict the failure mechanisms and several options are available to degrade the material properties after failures. The progressive failure analysis method is implemented in the COMET finite element analysis code and can predict the damage and response of laminated composite structures from initial loading to final failure. The different failure criteria and material degradation methods are compared and assessed by performing analyses of several laminated composite structures. Results from the progressive failure method indicate good correlation with the existing test data except in structural applications where interlaminar stresses are important which may cause failure mechanisms such as debonding or delaminations.

Sleight, David W.

1999-01-01

385

Light water reactor lower head failure analysis  

SciTech Connect

This document presents the results from a US Nuclear Regulatory Commission-sponsored research program to investigate the mode and timing of vessel lower head failure. Major objectives of the analysis were to identify plausible failure mechanisms and to develop a method for determining which failure mode would occur first in different light water reactor designs and accident conditions. Failure mechanisms, such as tube ejection, tube rupture, global vessel failure, and localized vessel creep rupture, were studied. Newly developed models and existing models were applied to predict which failure mechanism would occur first in various severe accident scenarios. So that a broader range of conditions could be considered simultaneously, calculations relied heavily on models with closed-form or simplified numerical solution techniques. Finite element techniques-were employed for analytical model verification and examining more detailed phenomena. High-temperature creep and tensile data were obtained for predicting vessel and penetration structural response.

Rempe, J.L.; Chavez, S.A.; Thinnes, G.L. [EG and G Idaho, Inc., Idaho Falls, ID (United States)] [and others

1993-10-01

386

ABSTRACT.--A removal experiment was conducted to measure how much and by what mechanisms brood parasitic Brown-headed Cowbirds (Molothrus ater) cause nest failures in a  

E-print Network

Sparrow (Melospiza melodia). When numbers of female cowbirds were reduced experimentally, nest failures y por qué me- canismos Molothrus ater ocasiona fracasos de nidificación en Melospiza melodia, una frecuencia de fracasos de nidificación a un tercio de los niveles del grupo control de M. melodia durante los

Zanette, Liana

387

Cardiac Mechanics and Ventricular Twist by Three-Dimensional Strain Analysis in Relation to B-Type Natriuretic Peptide as a Clinical Prognosticator for Heart Failure Patients  

PubMed Central

Background Three dimensional (3D) echocardiography-derived measurements of myocardial deformation and twist have recently advanced as novel clinical tools. However, with the exception of left ventricular ejection fraction and mass quantifications in hypertension and heart failure populations, the prognostic value of such imaging techniques remains largely unexplored. Methods We studied 200 subjects (mean age: 60.2±16 years, 54% female, female n?=?107) with known hypertension (n?=?51), diastolic heart failure (n?=?61), or systolic heart failure (n?=?30), recruited from heart failure outpatient clinics. Fifty-eight healthy volunteers were used as a control group. All participants underwent 3D-based myocardial deformation and twist analysis (Artida, Toshiba Medical Systems, Tokyo, Japan). We further investigated associations between these measures and brain natriuretic peptide levels and clinical outcomes. Results The global 3D strain measurements of the healthy, hypertension, diastolic heart failure, and systolic heart failure groups were 28.03%, 24.43%, 19.70%, and 11.95%, respectively (all p<0.001). Global twist measurements were estimated to be 9.49°, 9.77°, 8.32°, and 4.56°, respectively. We observed significant differences regarding 3D-derived longitudinal, radial, and global 3D strains between the different disease categories (p<0.05), even when age, gender, BMI and heart rate were matched. In addition, 3D-derived longitudinal, circumferential, and 3D strains were all highly correlated with brain natriuretic peptide levels (p<0.001). At a mean 567.7 days follow-up (25th–75th IQR: 197–909 days), poorer 3D-derived longitudinal, radial, and global 3D strain measurements remained independently associated with a higher risk of cardiovascular related death or hospitalization due to heart failure, after adjusting for age, gender, and left ventricular ejection fraction (all p<0.05). Conclusions 3D-based strain analysis may be a feasible and useful diagnostic tool for discriminating the extent of myocardial dysfunction. Furthermore, it is able to provide a prognostic value beyond traditional echocardiographic parameters in terms of ejection fraction. PMID:25545637

Chang, Sheng-Nan; Lai, Yau-Huei; Yen, Chih-Hsuan; Tsai, Chia-Ti; Lin, Jou-Wei; Bulwer, Bernard E.; Hung, Ta-Chuan; Hou, Charles Jia-Yin; Kuo, Jen-Yuan; Hung, Chung-Lieh; Hwang, Juey-Jen; Yeh, Hung-I

2014-01-01

388

A new plasticity and failure model for ballistic application  

Microsoft Academic Search

Ballistic phenomena give rise to a plethora of failure modes that compete. Johnson–Cook (JC) plasticity and failure models have been extremely successful because, while being conceptually simple, they capture the essence of the operative mechanics and they provide reasonably good predictions for ballistic limits. Nevertheless, the Johnson–Cook models, due to their isotropic flow and failure surface, cannot reproduce certain failure

Sidney Chocron; Borja Erice; Charles E. Anderson

2011-01-01

389

Evaluation of TBC-coated {beta}-NiAl substrates without a bond coat  

SciTech Connect

{beta}-NiAl substrates with various alloy additions and oxide dispersions were coated with Y{sub 2}O{sub 3}-stabilized ZrO{sub 2} using electron beam-physical vapor deposition. Cyclic oxidation experiments (1000-1200 C) were conducted to study effect of substrate dopants such as Y and Zr on coating lifetime without the intermediate metallic bond coat layer used in conventional thermal barrier coatings. Oxidation kinetics and Al{sub 2}O{sub 3} scale microstructures were compared to those for uncoated substrates. Degradation of substrate-alumina interface by void formation was the primary mechanism leading to coating spallation. Coating lifetime was correlated to alumina scale adhesion on unocated substrates.

Pint, B.A. [Oak Ridge National Lab., TN (United States); Nagaraj, B.A.; Rosenzweig, M.A. [General Electric Co., Cincinnati, OH (United States). Aircraft Engines

1996-04-01

390

High-Speed Solder Ball Shear and Pull Tests vs. Board Level Mechanical Drop Tests: Correlation of Failure Mode and Loading Speed  

Microsoft Academic Search

This study compares high-speed bondtesting (shear and pull) with board level drop testing (BLDT) of BGA packages using Sn4.0%Ag0.5%Cu solder balls and either an ENIG or OSP package substrate surface finish. High-speed shear and pull testing were carried out at various speeds; failure modes were recorded, together with force and fracture energy data. In addition, detailed microscopic analysis (SEM and

Fubin Song; S. W. R. Lee; K. Newman; B. Sykes; S. Clark

2007-01-01

391

Investigation of heat transfer in zirconium potassium perchlorate at low temperature: A study of the failure mechanism of the NASA standard initiator  

NASA Technical Reports Server (NTRS)

The objective of this work was to study the reasons for the failure of pyrotechnic initiators at very low temperatures (10 to 100 K). A two-dimensional model of the NASA standard initiator was constructed to model heat transfer from the electrically heated stainless steel bridgewire to the zirconium potassium perchlorate explosive charge and the alumina charge cup. Temperature dependent properties were used in the model to simulate initiator performance over a wide range of initial temperatures (10 to 500 K). A search of the thermophysical property data base showed that pure alumina has a very high thermal conductivity at low temperatures. It had been assumed to act as a thermal insulator in all previous analyses. Rapid heat transfer from the bridgewire to the alumina at low initial temperatures was shown to cause failure of the initiators if the wire did not also make good contact with the zirconium potassium perchlorate charge. The mode is able to reproduce the results of the tests that had been conducted to investigate the cause for failure. It also provides an explanation for previously puzzling results and suggests simple design changes that will increase reliability at very low initial temperatures.

Varghese, Philip L.

1989-01-01

392

Acute kidney failure  

MedlinePLUS

Kidney failure; Renal failure; Renal failure - acute; ARF; Kidney injury - acute ... There are many possible causes of kidney damage. They include: ... cholesterol (cholesterol emboli) Decreased blood flow due to very ...

393

Living with Heart Failure  

MedlinePLUS

... page from the NHLBI on Twitter. Living With Heart Failure Currently, heart failure has no cure. You'll ... avoid harmful side effects. Take Steps To Prevent Heart Failure From Getting Worse Certain actions can worsen your ...

394

Influence of "Island-Like" Oxides in the Bond-Coat on the Stress and Failure Patterns of the Thermal-Barrier Coatings Fabricated by Atmospheric Plasma Spraying During Long-Term High Temperature Oxidation  

NASA Astrophysics Data System (ADS)

Thermal-barrier coatings (TBCs) are very important ceramic-coating materials due to their excellent performance at high temperature. The inner zone of the bond-coat is often easily endured oxidized (internal oxidation) in the process of thermal spraying and the long-time exposure to the high temperature, and the "island-like" oxides can be formed. Especially, when the bond-coat was fabricated by atmospheric plasma spraying (APS), this trend is more evident. In this paper, the stress distribution around the thermally grown oxide (TGO) has been calculated by the finite element method when the "island-like" oxides have been considered. The simulation results indicate that the maximum tensile stress and compressive stress existed in the TGO, and the existence of the "island-like" oxides will further decrease the maximum tensile stress level in the TGO. While the "island-like" oxides in the bond-coat will decrease the effective thickness of the TGO at the metallic layer/ceramic layer interface due to the oxidation of the metallic elements in the bond-coat. The crack propagation equation has been established and the failure mechanism of the TBC due to the formation and growth of the TGO has also been discussed in detail. The lifetime of the TBCs which have experienced high temperature oxidation has been predicted and the theoretical results agreed well with the experimental data.

Wang, L.; Zhao, Y. X.; Zhong, X. H.; Tao, S. Y.; Zhang, W.; Wang, Y.

2014-02-01

395

Failure Analysis at the Kennedy Space Center  

NASA Technical Reports Server (NTRS)

History has shown that failures occur in every engineering endeavor, and what we learn from those failures contributes to the knowledge base to safely complete future missions. The necessity of failure analysis is at its apex at the end of one aged program (i.e. Shuttle) and at the beginning of a new and untested program (i.e. Constellation). The information that we gain through failure analysis corrects the deficiencies in the current vehicle to make the next generation of vehicles more efficient and safe.