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Sample records for fatigue estimation due

  1. System for estimating fatigue damage

    DOEpatents

    LeMonds, Jeffrey; Guzzo, Judith Ann; Liu, Shaopeng; Dani, Uttara Ashwin

    2017-03-14

    In one aspect, a system for estimating fatigue damage in a riser string is provided. The system includes a plurality of accelerometers which can be deployed along a riser string and a communications link to transmit accelerometer data from the plurality of accelerometers to one or more data processors in real time. With data from a limited number of accelerometers located at sensor locations, the system estimates an optimized current profile along the entire length of the riser including riser locations where no accelerometer is present. The optimized current profile is then used to estimate damage rates to individual riser components and to update a total accumulated damage to individual riser components. The number of sensor locations is small relative to the length of a deepwater riser string, and a riser string several miles long can be reliably monitored along its entire length by fewer than twenty sensor locations.

  2. Changes in bone fatigue resistance due to collagen degradation.

    PubMed

    Wynnyckyj, Chrystia; Willett, Thomas L; Omelon, Sidney; Wang, Jian; Wang, Zhirui; Grynpas, Marc D

    2011-02-01

    Clinical tools for evaluating fracture risk, such as dual energy X-ray absorptiometry (DXA) and quantitative ultrasound (QUS), focus on bone mineral and cannot detect changes in the collagen matrix that affect bone mechanical properties. However, the mechanical response tissue analyzer (MRTA) directly measures a whole bone mechanical property. The aims of our study were to investigate the changes in fatigue resistance after collagen degradation and to determine if clinical tools can detect changes in bone mechanical properties due to fatigue. Male and female emu tibiae were endocortically treated with 1 M KOH for 1-14 days and then either fatigued to failure or fatigued to induce stiffness loss without fracture. Partial fatigue testing caused a decrease in modulus measured by mechanical testing even when not treated with KOH, which was detected by MRTA. At high stresses, only KOH-treated samples had a lower fatigue resistance compared to untreated bones for both sexes. No differences were observed in fatigue behavior at low stresses for all groups. KOH treatment is hypothesized to have changed the collagen structure in situ and adversely affected the bone. Cyclic creep may be an important mechanism in the fast deterioration rate of KOH-treated bones, as creep is the major cause of fatigue failure for bones loaded at high stresses. Therefore, collagen degradation caused by KOH treatment may be responsible for the observed altered fatigue behavior at high stresses, since collagen is responsible for the creep behavior in bone.

  3. Fatigue life estimation procedure for a turbine blade under transient loads

    SciTech Connect

    Vyas, N.S. . Dept. of Mechanical Engineering); Rao, J.S. . Dept. of Mechanical Engineering)

    1994-01-01

    Fatigue analysis and consequent life prediction of turbomachine blading requires the stress load history of the blade. A blade designed for safe operation at particular constant rotor speeds may, however, incur damaging stresses during start-up and shut-down operations. During such operations the blade experiences momentary resonant stresses while passing through the criticals, which may lie in the speed range through which the rotor is accelerated. Fatigue due to these transient influences may accumulate to lead to failure. In this paper a technique for fatigue damage assessment during variable-speed operations is presented. Transient resonant stresses for a blade with nonlinear damping have been determined using a numerical procedure. A fatigue damage assessment procedure is described. The fatigue failure surface is generated on the S-N-mean stress axes and Miner's Rule is employed to estimate the accumulation of fatigue.

  4. Estimating mental fatigue based on electroencephalogram and heart rate variability

    NASA Astrophysics Data System (ADS)

    Zhang, Chong; Yu, Xiaolin

    2010-01-01

    The effects of long term mental arithmetic task on psychology are investigated by subjective self-reporting measures and action performance test. Based on electroencephalogram (EEG) and heart rate variability (HRV), the impacts of prolonged cognitive activity on central nervous system and autonomic nervous system are observed and analyzed. Wavelet packet parameters of EEG and power spectral indices of HRV are combined to estimate the change of mental fatigue. Then wavelet packet parameters of EEG which change significantly are extracted as the features of brain activity in different mental fatigue state, support vector machine (SVM) algorithm is applied to differentiate two mental fatigue states. The experimental results show that long term mental arithmetic task induces the mental fatigue. The wavelet packet parameters of EEG and power spectral indices of HRV are strongly correlated with mental fatigue. The predominant activity of autonomic nervous system of subjects turns to the sympathetic activity from parasympathetic activity after the task. Moreover, the slow waves of EEG increase, the fast waves of EEG and the degree of disorder of brain decrease compared with the pre-task. The SVM algorithm can effectively differentiate two mental fatigue states, which achieves the maximum classification accuracy (91%). The SVM algorithm could be a promising tool for the evaluation of mental fatigue. Fatigue, especially mental fatigue, is a common phenomenon in modern life, is a persistent occupational hazard for professional. Mental fatigue is usually accompanied with a sense of weariness, reduced alertness, and reduced mental performance, which would lead the accidents in life, decrease productivity in workplace and harm the health. Therefore, the evaluation of mental fatigue is important for the occupational risk protection, productivity, and occupational health.

  5. Fatigue life estimates for helicopter loading spectra

    NASA Technical Reports Server (NTRS)

    Khosrovaneh, A. K.; Dowling, N. E.; Berens, A. P.; Gallagher, J. P.

    1989-01-01

    Helicopter loading histories applied to notch metal samples are used as examples, and their fatigue lives are calculated by using a simplified version of the local strain approach. This simplified method has the advantage that it requires knowing the loading history in only the reduced form of ranges and means and number of cycles from the rain-flow cycle counting method. The calculated lives compare favorably with test data.

  6. A real time neural net estimator of fatigue life

    NASA Technical Reports Server (NTRS)

    Troudet, T.; Merrill, W.

    1990-01-01

    A neural net architecture is proposed to estimate, in real-time, the fatigue life of mechanical components, as part of the Intelligent Control System for Reusable Rocket Engines. Arbitrary component loading values were used as input to train a two hidden-layer feedforward neural net to estimate component fatigue damage. The ability of the net to learn, based on a local strain approach, the mapping between load sequence and fatigue damage has been demonstrated for a uniaxial specimen. Because of its demonstrated performance, the neural computation may be extended to complex cases where the loads are biaxial or triaxial, and the geometry of the component is complex (e.g., turbopump blades). The generality of the approach is such that load/damage mappings can be directly extracted from experimental data without requiring any knowledge of the stress/strain profile of the component. In addition, the parallel network architecture allows real-time life calculations even for high frequency vibrations. Owing to its distributed nature, the neural implementation will be robust and reliable, enabling its use in hostile environments such as rocket engines. This neural net estimator of fatigue life is seen as the enabling technology to achieve component life prognosis, and therefore would be an important part of life extending control for reusable rocket engines.

  7. Fatigue life estimation procedure for a turbine blade under transient loads

    SciTech Connect

    Vyas, N.S.; Rao, J.S. Indian Inst. of Technology, New Delhi )

    1992-01-01

    A technique for fatigue damage assessment during variable speed operations is presented. Transient resonant stresses for a blade with nonlinear damping have been determined using a numerical procedure. A fatigue damage assessment procedure is described. The fatigue failure surface is generated on the S-N-mean stress axes, and Miner's rule is employed to estimate the cumulation of fatigue. 16 refs.

  8. Estimation of fatigue damage parameters using guided wave technique

    NASA Astrophysics Data System (ADS)

    Rathod, V. T.; Roy Mahapatra, D.

    2014-03-01

    In the present work we have considered the problem of monitoring a fatigue crack growth in a thin plate specimen. The problem is first solved analytically by modeling the structure with a cyclic plastic zone around the crack. The damaged region is modeled as a visco-elastic zone and other regions are modeled as elastic zones. Using the one-dimensional guided wave model, the reflected and transmitted energies of the guided waves from the fatigue crack and plastic zone are studied. Experimental study of the reflected and transmitted energies is done using guided waves generated and received by piezoelectric wafers. The reflected and transmitted energies are derived at various cycles of fatigue loading till the failure of the structure. Validation of the results from the analytical model is done by comparing the results obtained from the experiments. The reflected and transmitted energy is related to the size of crack size or the magnitude of loading. Using crack size and the nature of loading, a method is proposed to estimate the fatigue life using fracture mechanics approach.

  9. Residual stress relief due to fatigue in tetragonal lead zirconate titanate ceramics

    SciTech Connect

    Hall, D. A.; Mori, T.; Comyn, T. P.; Ringgaard, E.; Wright, J. P.

    2013-07-14

    High energy synchrotron XRD was employed to determine the lattice strain {epsilon}{l_brace}111{r_brace}and diffraction peak intensity ratio R{l_brace}200{r_brace}in tetragonal PZT ceramics, both in the virgin poled state and after a bipolar fatigue experiment. It was shown that the occurrence of microstructural damage during fatigue was accompanied by a reduction in the gradient of the {epsilon}{l_brace}111{r_brace}-cos{sup 2} {psi} plot, indicating a reduction in the level of residual stress due to poling. In contrast, the fraction of oriented 90 Degree-Sign ferroelectric domains, quantified in terms of R{l_brace}200{r_brace}, was not affected significantly by fatigue. The change in residual stress due to fatigue is interpreted in terms of a change in the average elastic stiffness of the polycrystalline matrix due to the presence of inter-granular microcracks.

  10. A real time neural net estimator of fatigue life

    NASA Technical Reports Server (NTRS)

    Troudet, T.; Merrill, W.

    1990-01-01

    A neural network architecture is proposed to estimate, in real-time, the fatigue life of mechanical components, as part of the intelligent Control System for Reusable Rocket Engines. Arbitrary component loading values were used as input to train a two hidden-layer feedforward neural net to estimate component fatigue damage. The ability of the net to learn, based on a local strain approach, the mapping between load sequence and fatigue damage has been demonstrated for a uniaxial specimen. Because of its demonstrated performance, the neural computation may be extended to complex cases where the loads are biaxial or triaxial, and the geometry of the component is complex (e.g., turbopumps blades). The generality of the approach is such that load/damage mappings can be directly extracted from experimental data without requiring any knowledge of the stress/strain profile of the component. In addition, the parallel network architecture allows real-time life calculations even for high-frequency vibrations. Owing to its distributed nature, the neural implementation will be robust and reliable, enabling its use in hostile environments such as rocket engines.

  11. Fatigue Level Estimation of Bill Based on Acoustic Signal Feature by Supervised SOM

    NASA Astrophysics Data System (ADS)

    Teranishi, Masaru; Omatu, Sigeru; Kosaka, Toshihisa

    Fatigued bills have harmful influence on daily operation of Automated Teller Machine(ATM). To make the fatigued bills classification more efficient, development of an automatic fatigued bill classification method is desired. We propose a new method to estimate bending rigidity of bill from acoustic signal feature of banking machines. The estimated bending rigidities are used as continuous fatigue level for classification of fatigued bill. By using the supervised Self-Organizing Map(supervised SOM), we estimate the bending rigidity from only the acoustic energy pattern effectively. The experimental result with real bill samples shows the effectiveness of the proposed method.

  12. Fatigue

    MedlinePlus

    ... to help you find out what's causing your fatigue and recommend ways to relieve it. Fatigue itself is not a disease. Medical problems, treatments, and personal habits can add to fatigue. These include Taking certain medicines, such as antidepressants, ...

  13. The relationship between observed fatigue damage and life estimation models

    NASA Technical Reports Server (NTRS)

    Kurath, Peter; Socie, Darrell F.

    1988-01-01

    Observations of the surface of laboratory specimens subjected to axial and torsional fatigue loadings has resulted in the identification of three damage fatigue phenomena: crack nucleation, shear crack growth, and tensile crack growth. Material, microstructure, state of stress/strain, and loading amplitude all influence which of the three types of fatigue damage occurs during a dominant fatigue life fraction. Fatigue damage maps are employed to summarize the experimental observations. Appropriate bulk stress/strain damage parameters are suggested to model fatigue damage for the dominant fatigue life fraction. Extension of the damage map concept to more complex loadings is presented.

  14. Estimating Viscoelastic Deformation Due to Seasonal Loading

    NASA Technical Reports Server (NTRS)

    Sauber, Jeanne

    2015-01-01

    Scientists have been making summer-­-time geodetic measurements in south central Alaska for decades to estimate the rate at which a continental-­-ocean terrane is accreting to the North American continent. Southern Alaska has big earthquakes every century and large, rapidly changing glaciers. In the last decade, primarily as part of the EarthScope Plate Boundary Observatory project, continuous GPS measurements have recorded the response of sites such as the near-­-coastal geodetic site, AB35 to competing processes: uplift and movement to the northwest due to tectonic forces and the response of the solid Earth to seasonal and longer-­-term changes in the cryosphere (snow and ice) surrounding the site. Which process causes the largest displacements of the site? Figure 1 (Blewitt, Nevada Geodetic Lab, 2015) shows the Northward, Eastward, and Upward motion of AB35 between 2007 and 2015. The site is moving rapidly to the north and west reflecting the tectonic convergence of site toward interior Alaska but there is small wiggle on the North component reflecting seasonal displacements of the site associated with snow loading and unloading. However, the Up component, shows a large seasonal signal due to snow loading in the winter (down) and ice and snow melting in the warmer months (site goes up). Between 2007 and the present, the site position is slowly moving upward, due to tectonic forcing but probably associated with longer-­- term ice melting as well. We are using the CIG finite element modeling (FEM) program Pylith to estimate the surface displacements and stresses associated with seasonal loading changes (top figure and Figure 2 far right) for water year 2012, 2011.8 - 2012.8) and the longer-­-term retreat of the surrounding glaciers.

  15. Structural health monitoring of wind towers: residual fatigue life estimation

    NASA Astrophysics Data System (ADS)

    Benedetti, M.; Fontanari, V.; Battisti, L.

    2013-04-01

    In a recent paper (Benedetti et al 2011 Smart Mater. Struct. 20 055009), the authors investigated the possibility of detecting cracks in critical sites of onshore wind towers using a radial arrangement of strain sensors around the tower periphery in the vicinity of the base welded joint. Specifically, the strain difference between adjacent strain sensors is used as a damage indicator. The number of sensors to be installed is determined by the minimum crack size to be detected, which in turn depends on the expected extreme wind conditions and programmed inspection/repair schedule. In this companion paper, we address these issues by investigating possible strategies for residual fatigue life assessment and management of onshore wind towers once the crack has been detected. For this purpose, fracture mechanics tests are carried out using welded samples to quantify the resistance to fatigue crack growth as well as the elastic-plastic fracture toughness of the welded joint at the tower base. These material strength characteristics are used to estimate (i) the critical crack size for structural integrity on the basis of fracture toughness tests, elastoplastic finite element analyses and loading spectra under extreme wind conditions, (ii) the residual life before structural collapse, applying a frequency-domain method to typical in-service wind actions and wind directionality.

  16. Fatigue

    MedlinePlus

    ... fatigue may be worsened with physical activity or mental stress. It is diagnosed based on the presence of a specific group of symptoms and after all other possible causes of fatigue are ruled out.

  17. Fatigue failure in thin-film polysilicon is due to subcriticalcracking within the oxide layer

    SciTech Connect

    Alsem, D.H.; Muhlstein, C.L.; Stach, E.A.; Ritchie, R.O.

    2005-01-11

    It has been established that microelectromechanical systems (MEMS) created from polycrystalline silicon thin-films are subject to cyclic fatigue. Prior work by the authors has suggested that although bulk silicon is not susceptible to fatigue failure in ambient air, fatigue in micron-scale silicon is a result of a ''reaction-layer'' process, whereby high stresses induce a thickening of the post-release oxide at stress concentrations such as notches, which subsequently undergoes moisture-assisted cracking. However, there exists some controversy regarding the post-release oxide thickness of the samples used in the prior study. In this Letter, we present data from devices from a more recent fabrication run that confirm our prior observations. Additionally, new data from tests in high vacuum show that these devices do not fatigue when oxidation and moisture are suppressed. Each of these observations lends credence to the '''reaction-layer'' mechanism. Recent advances in the design of microelectromechanical systems (MEMS) have increased the demand for more reliable microscale structures. Although silicon is an effective and widely used structural material at the microscale, it is very brittle. Consequently, reliability is a limiting factor for commercial and defense applications. Since the surface to volume ratio of these structural films is very large, classical models for failure modes in bulk materials cannot always be applied. For example, whereas bulk silicon is immune to cyclic fatigue failure thin micron-scale structural films of silicon appear to be highly susceptible. It is clear that at these size scales, surface effects may become dominant in controlling mechanical properties. The main reliability issues for MEMS are stiction, fatigue and wear. Fatigue is important in cases where devices are subjected to a large number of loading cycles with amplitudes below their (single-cycle) fracture stress, which may arise due to vibrations intentionally induced in the

  18. Estimation of uncertainty for fatigue growth rate at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Nyilas, Arman; Weiss, Klaus P.; Urbach, Elisabeth; Marcinek, Dawid J.

    2014-01-01

    Fatigue crack growth rate (FCGR) measurement data for high strength austenitic alloys at cryogenic environment suffer in general from a high degree of data scatter in particular at ΔK regime below 25 MPa√m. Using standard mathematical smoothing techniques forces ultimately a linear relationship at stage II regime (crack propagation rate versus ΔK) in a double log field called Paris law. However, the bandwidth of uncertainty relies somewhat arbitrary upon the researcher's interpretation. The present paper deals with the use of the uncertainty concept on FCGR data as given by GUM (Guidance of Uncertainty in Measurements), which since 1993 is a recommended procedure to avoid subjective estimation of error bands. Within this context, the lack of a true value addresses to evaluate the best estimate by a statistical method using the crack propagation law as a mathematical measurement model equation and identifying all input parameters. Each parameter necessary for the measurement technique was processed using the Gaussian distribution law by partial differentiation of the terms to estimate the sensitivity coefficients. The combined standard uncertainty determined for each term with its computed sensitivity coefficients finally resulted in measurement uncertainty of the FCGR test result. The described procedure of uncertainty has been applied within the framework of ITER on a recent FCGR measurement for high strength and high toughness Type 316LN material tested at 7 K using a standard ASTM proportional compact tension specimen. The determined values of Paris law constants such as C0 and the exponent m as best estimate along with the their uncertainty value may serve a realistic basis for the life expectancy of cyclic loaded members.

  19. Calculation of Local Stress and Fatigue Resistance due to Thermal Stratification on Pressurized Surge Line Pipe

    SciTech Connect

    Bandriyana, B.; Utaja

    2010-06-22

    Thermal stratification introduces thermal shock effect which results in local stress and fatigue problems that must be considered in the design of nuclear power plant components. Local stress and fatigue calculation were performed on the Pressurize Surge Line piping system of the Pressurize Water Reactor of the Nuclear Power Plant. Analysis was done on the operating temperature between 177 to 343 deg. C and the operating pressure of 16 MPa (160 Bar). The stagnant and transient condition with two kinds of stratification model has been evaluated by the two dimensional finite elements method using the ANSYS program. Evaluation of fatigue resistance is developed based on the maximum local stress using the ASME standard Code formula. Maximum stress of 427 MPa occurred at the upper side of the top half of hot fluid pipe stratification model in the transient case condition. The evaluation of the fatigue resistance is performed on 500 operating cycles in the life time of 40 years and giving the usage value of 0,64 which met to the design requirement for class 1 of nuclear component. The out surge transient were the most significant case in the localized effects due to thermal stratification.

  20. Assessment of material degradation due to corrosion-fatigue using a backscattered Rayleigh surface wave.

    PubMed

    Kim, Young H; Song, Sung-Jin; Bae, D H; Kwon, Sung-Duk

    2004-04-01

    Material degradation due to corrosion-fatigue was evaluated nondestructively using backscattered Rayleigh surface wave. A corrosion-fatigue test was carried out for the specimens made of thermo-mechanically controlled process steel in 3.5 wt.% NaCl solution at 25 degrees C. The Backscattering profile, which is the amplitude variation of backscattered ultrasound according to the incident angle, of the specimens were measured in water at room temperature after the corrosion-fatigue test. The velocity of Rayleigh surface wave, determined from the incident angle at which the profile of the backscattered ultrasound became maximum, decreased for the specimen that had the large number of cycles to failure in the corrosion-fatigue test. This fact implies that the corrosion degradation occurred at specimen surface in this specific test is dominantly dependant on the time exposed to corrosion environment. The result observed in the present work demonstrates the high potential of backscattered Rayleigh surface wave as a tool for nondestructive evaluation of corrosion degradation of aged materials.

  1. Metacognitions Are Associated with Subjective Memory Problems in Individuals on Sick Leave due to Chronic Fatigue

    PubMed Central

    Jacobsen, Henrik B.; Aasvik, Julie K.; Borchgrevink, Petter C.; Landrø, Nils I.; Stiles, Tore C.

    2016-01-01

    Background: Subjective cognitive impairments are frequent, but poorly understood in patients with chronic fatigue. We hypothesized that maladaptive metacognitive beliefs at baseline were associated with baseline subjective cognitive impairments, that they predict subjective cognitive impairments at treatment termination, and that a reduction in maladaptive metacognitive beliefs was associated with less subjective cognitive impairments at treatment termination, independent of changes in fatigue, pain, insomnia, depression, and anxiety. Methods: In this non-controlled study, patients (n = 137) on sick leave due to chronic fatigue received a 3.5-week inpatient RTW rehabilitation program. Of these patients 69 (50.4%) was referred with a ICPC-2 diagnosis of chronic fatigue. Patients completed questionnaires about metacognitive beliefs, somatic complaints, psychological complaints, and cognitive impairments before and after treatment. To test the hypotheses we performed paired t-tests of change, as well as seven hierarchical linear regressions. Results: Results showed that baseline maladaptive metacognitive beliefs were significantly associated with subjective cognitive impairments at baseline, controlling for symptoms. Score on baseline metacognitive beliefs did not predict impairments post-treatment. Testing specific maladaptive beliefs, pre-treatment scores on cognitive confidence were associated with subjective cognitive impairments both pre and post-treatment, controlling for symptoms. Post-treatment metacognitive beliefs and post-treatment cognitive confidence were associated with post-treatment subjective cognitive impairments, controlling for pre-treatment impairments and pre-treatment metacognitive beliefs, as well as pre and post-scores on symptom measures. Conclusion: This study reports associations between maladaptive metacognitive beliefs and subjective cognitive impairments in patients with chronic fatigue. Targeting metacognitive beliefs could prove an

  2. A rapid estimation method of structural fatigue analysis for a 17k ton DWT oil tanker

    NASA Astrophysics Data System (ADS)

    Chen, Tuohan; Zheng, Jianli; Bae, Dong-Myung

    2012-06-01

    Fatigue cracks and fatigue damage have been important issues for ships and offshore structures for a long time. However, in the last decade, with the introduction of higher tensile steel in hull structures and increasingly large ship dimensions, the greater attention should be paid to fatigue problems. Most research focuses on how to more easily access the fatigue strength of ships. Also, the major classification societies have already released their fatigue assessment notes. However, due to the complexity of factors influencing fatigue performances, such as wave load and pressure from cargo, the combination of different stress components, stress on concentration of local structure details, means stress, and the corrosive environments, there are different specifications with varying classification societies, leading to the different results from different fatigue assessment methods. This paper established the Det Norske Veritas(DNV) classification notes "fatigue assessment of ship structures" that explains the process of fatigue assessment and simplified methods. Finally, a fatigue analysis was performed by use data of a real ship and the reliability of the result was assessed.

  3. Mechanism and estimation of fatigue crack initiation in austenitic stainless steels in LWR environments.

    SciTech Connect

    Chopra, O. K.; Energy Technology

    2002-08-01

    The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. Figures I-9.1 through I-9.6 of Appendix I to Section III of the Code specify fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Existing fatigue strain-vs.-life ({var_epsilon}-N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. This report provides an overview of fatigue crack initiation in austenitic stainless steels in LWR coolant environments. The existing fatigue {var_epsilon}-N data have been evaluated to establish the effects of key material, loading, and environmental parameters (such as steel type, strain range, strain rate, temperature, dissolved-oxygen level in water, and flow rate) on the fatigue lives of these steels. Statistical models are presented for estimating the fatigue {var_epsilon}-N curves for austenitic stainless steels as a function of the material, loading, and environmental parameters. Two methods for incorporating environmental effects into the ASME Code fatigue evaluations are presented. The influence of reactor environments on the mechanism of fatigue crack initiation in these steels is also discussed.

  4. X-43A Rudder Spindle Fatigue Life Estimate and Testing

    NASA Technical Reports Server (NTRS)

    Glaessgen, Edward H.; Dawicke, David S.; Johnston, William M.; James, Mark A.; Simonsen, Micah; Mason, Brian H.

    2005-01-01

    Fatigue life analyses were performed using a standard strain-life approach and a linear cumulative damage parameter to assess the effect of a single accidental overload on the fatigue life of the Haynes 230 nickel-base superalloy X-43A rudder spindle. Because of a limited amount of information available about the Haynes 230 material, a series of tests were conducted to replicate the overload and in-service conditions for the spindle and corroborate the analysis. Both the analytical and experimental results suggest that the spindle will survive the anticipated flight loads.

  5. FRACTURE MECHANICS APPROACH TO ESTIMATE FATIGUE LIVES OF WELDED LAP-SHEAR SPECIMENS

    SciTech Connect

    Lam, P.; Michigan, J.

    2014-04-25

    A full range of stress intensity factor solutions for a kinked crack is developed as a function of weld width and the sheet thickness. When used with the associated main crack solutions (global stress intensity factors) in terms of the applied load and specimen geometry, the fatigue lives can be estimated for the laser-welded lap-shear specimens. The estimations are in good agreement with the experimental data. A classical solution for an infinitesimal kink is also employed in the approach. However, the life predictions tend to overestimate the actual fatigue lives. The traditional life estimations with the structural stress along with the experimental stress-fatigue life data (S-N curve) are also provided. In this case, the estimations only agree with the experimental data under higher load conditions.

  6. Calculation of Local Stress and Fatigue Resistance due to Thermal Stratification on Pressurized Surge Line Pipe

    NASA Astrophysics Data System (ADS)

    Bandriyana, B.; Utaja

    2010-06-01

    Thermal stratification introduces thermal shock effect which results in local stress and fatique problems that must be considered in the design of nuclear power plant components. Local stress and fatique calculation were performed on the Pressurize Surge Line piping system of the Pressurize Water Reactor of the Nuclear Power Plant. Analysis was done on the operating temperature between 177 to 343° C and the operating pressure of 16 MPa (160 Bar). The stagnant and transient condition with two kinds of stratification model has been evaluated by the two dimensional finite elements method using the ANSYS program. Evaluation of fatigue resistance is developed based on the maximum local stress using the ASME standard Code formula. Maximum stress of 427 MPa occurred at the upper side of the top half of hot fluid pipe stratification model in the transient case condition. The evaluation of the fatigue resistance is performed on 500 operating cycles in the life time of 40 years and giving the usage value of 0,64 which met to the design requirement for class 1 of nuclear component. The out surge transient were the most significant case in the localized effects due to thermal stratification.

  7. Baseline-free estimation of residual fatigue life using a third order acoustic nonlinear parameter.

    PubMed

    Amura, Mikael; Meo, Michele; Amerini, F

    2011-10-01

    Prediction of crack growth and fatigue life estimation of metals using linear/nonlinear acousto-ultrasound methods is an ongoing issue. It is known that by measuring nonlinear parameters, the relative accumulated fatigue damage can be evaluated. However, there is still a need to measure two crack propagation states to assess the absolute residual fatigue life. A procedure based on the measurement of a third-order acoustic nonlinear parameter is presented to assess the residual fatigue life of a metallic component without the need of a baseline. The analytical evaluation of how the cubic nonlinear-parameter evolves during crack propagation is presented by combining the Paris law to the Nazarov-Sutin crack equation. Unlike other developed models, the proposed model assumes a crack surface topology with variable geometrical parameters. Measurements of the cubic nonlinearity parameter on AA2024-T351 specimens demonstrated high sensitivity to crack propagation and excellent agreement with the predicted theoretical behavior. The advantages of using the cubic nonlinearity parameter for fatigue cracks on metals are discussed by comparing the relevant results of a quadratic nonlinear parameter. Then the methodology to estimate crack size and residual fatigue life without the need of a baseline is presented, and advantages and limitations are discussed.

  8. Estimation of Fatigue Damage for an Austenitic Stainless Steel (SUS304) Using Magnetic Methods

    SciTech Connect

    Oka, M.; Yakushiji, T.; Tsuchida, Y.; Enokizono, M.

    2007-03-21

    There are some fatigue damage estimation methods of the austenitic stainless steel that uses the martensitic transformation. For instance, they are the remanent magnetization method, the excitation method, and so on. Those two methods are being researched also in our laboratory now. In the remanent magnetization method, it is well known that the relation between fatigue damage and the remanent magnetization is simple, clear, and reproducible. However, this method has the disadvantage to need a special magnetizer. This method cannot be easily used on the site such as the factory. On the other hand, because the special magnetizer is unnecessary, the excitation method can use easily on the site. The output signal of this method is small. In this paper, two fatigue evaluation methods such as the remanent magnetization method and the excitation method are introduced. In addition, we report on the result of comparing the fatigue evaluation performances of two methods.

  9. Influence of Initial Inclined Surface Crack on Estimated Residual Fatigue Lifetime of Railway Axle

    NASA Astrophysics Data System (ADS)

    Náhlík, Luboš; Pokorný, Pavel; Ševčík, Martin; Hutař, Pavel

    2016-11-01

    Railway axles are subjected to cyclic loading which can lead to fatigue failure. For safe operation of railway axles a damage tolerance approach taking into account a possible defect on railway axle surface is often required. The contribution deals with an estimation of residual fatigue lifetime of railway axle with initial inclined surface crack. 3D numerical model of inclined semi-elliptical surface crack in railway axle was developed and its curved propagation through the axle was simulated by finite element method. Presence of press-fitted wheel in the vicinity of initial crack was taken into account. A typical loading spectrum of railway axle was considered and residual fatigue lifetime was estimated by NASGRO approach. Material properties of typical axle steel EA4T were considered in numerical calculations and lifetime estimation.

  10. Estimation of fatigue and extreme load distributions from limited data with application to wind energy systems.

    SciTech Connect

    Fitzwater, LeRoy M.

    2004-01-01

    An estimate of the distribution of fatigue ranges or extreme loads for wind turbines may be obtained by separating the problem into two uncoupled parts, (1) a turbine specific portion, independent of the site and (2) a site-specific description of environmental variables. We consider contextually appropriate probability models to describe the turbine specific response for extreme loads or fatigue. The site-specific portion is described by a joint probability distribution of a vector of environmental variables, which characterize the wind process at the hub-height of the wind turbine. Several approaches are considered for combining the two portions to obtain an estimate of the extreme load, e.g., 50-year loads or fatigue damage. We assess the efficacy of these models to obtain accurate estimates, including various levels of epistemic uncertainty, of the turbine response.

  11. Measures and Models for Estimating and Predicting Cognitive Fatigue

    NASA Technical Reports Server (NTRS)

    Trejo, Leonard J.; Kochavi, Rebekah; Kubitz, Karla; Montgomery, Leslie D.; Rosipal, Roman; Matthews, Bryan

    2004-01-01

    We analyzed EEG and ERPs in a fatiguing mental task and created statistical models for single subjects. Seventeen subjects (4 F, 18-38 y) viewed 4-digit problems (e.g., 3+5-2+7=15) on a computer, solved the problems, and pressed keys to respond (intertrial interval = 1 s). Subjects performed until either they felt exhausted or three hours had elapsed. Re- and post-task measures of mood (Activation Deactivation Adjective Checklist, Visual Analogue Mood Scale) confirmed that fatigue increased and energy decreased over time. We tested response times (RT); amplitudes of ERP components N1, P2, P300, readiness potentials; and amplitudes of frontal theta and parietal alpha rhythms for change as a function of time. For subjects who completed 3 h (n=9) we analyzed 12 15-min blocks. For subjects who completed at least 1.5 h (n=17), we analyzed the first-, middle-, and last 100 error-free trials. Mean RT rose from 6.7 s to 8.5 s over time. We found no changes in the amplitudes of ERP components. In both analyses, amplitudes of frontal theta and parietal alpha rose by 30% or more over time. We used 30-channel EEG frequency spectra to model the effects of time in single subjects using a kernel partial least squares classifier. We classified 3.5s EEG segments as being from the first 100 or the last 100 trials, using random sub-samples of each class. Test set accuracies ranged from 63.9% to 99.6% correct. Only 2 of 17 subjects had mean accuracies lower than 80%. The results suggest that EEG accurately classifies periods of cognitive fatigue in 90% of subjects.

  12. Assessing Fatigue and Ultimate Load Uncertainty in Floating Offshore Wind Turbines Due to Varying Simulation Length

    SciTech Connect

    Stewart, G.; Lackner, M.; Haid, L.; Matha, D.; Jonkman, J.; Robertson, A.

    2013-07-01

    With the push towards siting wind turbines farther offshore due to higher wind quality and less visibility, floating offshore wind turbines, which can be located in deep water, are becoming an economically attractive option. The International Electrotechnical Commission's (IEC) 61400-3 design standard covers fixed-bottom offshore wind turbines, but there are a number of new research questions that need to be answered to modify these standards so that they are applicable to floating wind turbines. One issue is the appropriate simulation length needed for floating turbines. This paper will discuss the results from a study assessing the impact of simulation length on the ultimate and fatigue loads of the structure, and will address uncertainties associated with changing the simulation length for the analyzed floating platform. Recommendations of required simulation length based on load uncertainty will be made and compared to current simulation length requirements.

  13. Fatigue failure in polysilicon not due to simple stress corrosion cracking.

    PubMed

    Kahn, H; Ballarini, R; Bellante, J J; Heuer, A H

    2002-11-08

    In the absence of a corrosive environment, brittle materials such as silicon should be immune to cyclic fatigue. However, fatigue effects are well known in micrometer-sized polycrystalline silicon (polysilicon) samples tested in air. To investigate the origins of this phenomenon in polysilicon, we developed a fixed-grip fracture mechanics microspecimen but could find no evidence of static stress corrosion cracking. The environmental sensitivity of the fatigue resistance was also investigated under cyclic loading. For low-cycle fatigue, the behavior is independent of the ambient conditions, whether air or vacuum, but is strongly influenced by the ratio of compressive to tensile stresses experienced during each cycle. The fatigue damage most likely originates from contact stresses at processing-related surface asperities; subcritical crack growth then ensues during further cyclic loading. The lower far-field stresses involved in high-cycle fatigue induce reduced levels of fatigue damage. Under these conditions, a corrosive ambient such as laboratory air exacerbates the fatigue process. Without cyclic loading, polysilicon does not undergo stress corrosion cracking.

  14. Excitation, response, and fatigue life estimation methods for the structural design of externally blown flaps

    NASA Technical Reports Server (NTRS)

    Ungar, E. E.; Chandiramani, K. L.; Barger, J. E.

    1972-01-01

    Means for predicting the fluctuating pressures acting on externally blown flap surfaces are developed on the basis of generalizations derived from non-dimensionalized empirical data. Approaches for estimation of the fatigue lives of skin-stringer and honeycomb-core sandwich flap structures are derived from vibration response analyses and panel fatigue data. Approximate expressions for fluctuating pressures, structural response, and fatigue life are combined to reveal the important parametric dependences. The two-dimensional equations of motion of multi-element flap systems are derived in general form, so that they can be specialized readily for any particular system. An introduction is presented of an approach to characterizing the excitation pressures and structural responses which makes use of space-time spectral concepts and promises to provide useful insights, as well as experimental and analytical savings.

  15. Global effect on multi-segment physiological tremors due to localized fatiguing contraction.

    PubMed

    Chen, Yi-Ching; Yang, Jeng-Feng; Hwang, Ing-Shiou

    2012-03-01

    Physiological tremors within a limb are coupled, whereas between-limb tremors are thought to oscillate independently for a healthy subject. This study was undertaken to reinvestigate bilateral tremor relations and intra-limb tremor dynamics for a two-limb task after exhausting a single joint. Fifteen volunteers conducted prolonged tracking with the left (target) shoulder. Neuromuscular functions were monitored before and after the exercise-fatiguing intervention, including tracking displacement, muscle activity of the deltoid, and physiological tremors in the bilateral upper limbs. Localized fatiguing contraction degraded tracking accuracy and movement smoothness, accompanied by an increase in deltoid activation. Segment tremors in the bilateral limbs and inter-limb tremor coherences in 8-12 Hz increased, though coherence peaks in 5-8 Hz waned with fatigue response. Intra-limb tremor relations in the target and non-target limbs were also reorganized with unilateral fatiguing contraction. Tremor coupling in the arm-C7 complexes was enhanced, associated with tremor uncoupling in the forearm-arm and hand-forearm complexes. Tracking error in the pre- fatigue and post-fatigue conditions was predicted by different principal components that had high communalities with tremors of distal and proximal segments of the target limb, respectively. The adaptive changes in tremor dynamics were attributable to fatigue-induced enhancement of common central drive and decline in neural inputs of long-looped reflexes that diverge to contralateral segments.

  16. Wireless Tri-Axial Trunk Accelerometry Detects Deviations in Dynamic Center of Mass Motion Due to Running-Induced Fatigue

    PubMed Central

    2015-01-01

    Small wireless trunk accelerometers have become a popular approach to unobtrusively quantify human locomotion and provide insights into both gait rehabilitation and sports performance. However, limited evidence exists as to which trunk accelerometry measures are suitable for the purpose of detecting movement compensations while running, and specifically in response to fatigue. The aim of this study was therefore to detect deviations in the dynamic center of mass (CoM) motion due to running-induced fatigue using tri-axial trunk accelerometry. Twenty runners aged 18–25 years completed an indoor treadmill running protocol to volitional exhaustion at speeds equivalent to their 3.2 km time trial performance. The following dependent measures were extracted from tri-axial trunk accelerations of 20 running steps before and after the treadmill fatigue protocol: the tri-axial ratio of acceleration root mean square (RMS) to the resultant vector RMS, step and stride regularity (autocorrelation procedure), and sample entropy. Running-induced fatigue increased mediolateral and anteroposterior ratios of acceleration RMS (p < .05), decreased the anteroposterior step regularity (p < .05), and increased the anteroposterior sample entropy (p < .05) of trunk accelerometry patterns. Our findings indicate that treadmill running-induced fatigue might reveal itself in a greater contribution of variability in horizontal plane trunk accelerations, with anteroposterior trunk accelerations that are less regular from step-to-step and are less predictable. It appears that trunk accelerometry parameters can be used to detect deviations in dynamic CoM motion induced by treadmill running fatigue, yet it is unknown how robust or generalizable these parameters are to outdoor running environments. PMID:26517261

  17. Wireless Tri-Axial Trunk Accelerometry Detects Deviations in Dynamic Center of Mass Motion Due to Running-Induced Fatigue.

    PubMed

    Schütte, Kurt H; Maas, Ellen A; Exadaktylos, Vasileios; Berckmans, Daniel; Venter, Rachel E; Vanwanseele, Benedicte

    2015-01-01

    Small wireless trunk accelerometers have become a popular approach to unobtrusively quantify human locomotion and provide insights into both gait rehabilitation and sports performance. However, limited evidence exists as to which trunk accelerometry measures are suitable for the purpose of detecting movement compensations while running, and specifically in response to fatigue. The aim of this study was therefore to detect deviations in the dynamic center of mass (CoM) motion due to running-induced fatigue using tri-axial trunk accelerometry. Twenty runners aged 18-25 years completed an indoor treadmill running protocol to volitional exhaustion at speeds equivalent to their 3.2 km time trial performance. The following dependent measures were extracted from tri-axial trunk accelerations of 20 running steps before and after the treadmill fatigue protocol: the tri-axial ratio of acceleration root mean square (RMS) to the resultant vector RMS, step and stride regularity (autocorrelation procedure), and sample entropy. Running-induced fatigue increased mediolateral and anteroposterior ratios of acceleration RMS (p < .05), decreased the anteroposterior step regularity (p < .05), and increased the anteroposterior sample entropy (p < .05) of trunk accelerometry patterns. Our findings indicate that treadmill running-induced fatigue might reveal itself in a greater contribution of variability in horizontal plane trunk accelerations, with anteroposterior trunk accelerations that are less regular from step-to-step and are less predictable. It appears that trunk accelerometry parameters can be used to detect deviations in dynamic CoM motion induced by treadmill running fatigue, yet it is unknown how robust or generalizable these parameters are to outdoor running environments.

  18. Changes in running pattern due to fatigue and cognitive load in orienteering.

    PubMed

    Millet, Guillaume Y; Divert, Caroline; Banizette, Marion; Morin, Jean-Benoit

    2010-01-01

    The aim of this study was to examine the influence of fatigue on running biomechanics in normal running, in normal running with a cognitive task, and in running while map reading. Nineteen international and less experienced orienteers performed a fatiguing running exercise of duration and intensity similar to a classic distance orienteering race on an instrumented treadmill while performing mental arithmetic, an orienteering simulation, and control running at regular intervals. Two-way repeated-measures analysis of variance did not reveal any significant difference between mental arithmetic and control running for any of the kinematic and kinetic parameters analysed eight times over the fatiguing protocol. However, these parameters were systematically different between the orienteering simulation and the other two conditions (mental arithmetic and control running). The adaptations in orienteering simulation running were significantly more pronounced in the elite group when step frequency, peak vertical ground reaction force, vertical stiffness, and maximal downward displacement of the centre of mass during contact were considered. The effects of fatigue on running biomechanics depended on whether the orienteers read their map or ran normally. It is concluded that adding a cognitive load does not modify running patterns. Therefore, all changes in running pattern observed during the orienteering simulation, particularly in elite orienteers, are the result of adaptations to enable efficient map reading and/or potentially prevent injuries. Finally, running patterns are not affected to the same extent by fatigue when a map reading task is added.

  19. An investigation of fatigue phenomenon in the upper limb muscle due to short duration pulses in an FES system

    NASA Astrophysics Data System (ADS)

    Naeem, Jannatul; Wong Azman, Amelia; Khan, Sheroz; Mohd Mustafah, Yasir

    2013-12-01

    Functional Electrical Stimulation (FES) is a method of artificially stimulating muscles or nerves in order to result in contraction or relaxation of muscles. Many studies have shown that FES system has helped patients to live a better lives especially those who are suffering from physical mobility. Unfortunately, one of the main limitations of an FES system besides of its high cost is largely due to muscle fatigue. Muscle fatigue will affect the training duration which could delay patients' recovery rate. In this paper, we analyzed the occurrence of this fatigue phenomenon in terms of stimulator parameters such as amplitude, frequency, pulse width and pulse shape. The objective of this investigation is to identify other key features of the FES system parameters in order to prolong the training duration among patients. The experiment has been done on a healthy person for the duration of one minute and later the muscles response will be observed. Resultant muscle response is recorded as force using force resistive sensor. The experimental results show muscles will get fatigue at a different rate as the frequency increases. The experiment also shows that the duty cycle is reciprocal to the resultant force.

  20. An electromyographic-based test for estimating neuromuscular fatigue during incremental treadmill running.

    PubMed

    Camic, Clayton L; Kovacs, Attila J; Enquist, Evan A; VanDusseldorp, Trisha A; Hill, Ethan C; Calantoni, Austin M; Yemm, Allison J

    2014-12-01

    The purposes of the present study were two fold: (1) to determine if the model used for estimating the physical working capacity at the fatigue threshold (PWCFT) from electromyographic (EMG) amplitude data during incremental cycle ergometry could be applied to treadmill running to derive a new neuromuscular fatigue threshold for running, and (2) to compare the running velocities associated with the PWCFT, ventilatory threshold (VT), and respiratory compensation point (RCP). Fifteen college-aged subjects (21.5 ± 1.3 y, 68.7 ± 10.5 kg, 175.9 ± 6.7 cm) performed an incremental treadmill test to exhaustion with bipolar surface EMG signals recorded from the vastus lateralis. There were significant (p < 0.05) mean differences in running velocities between the VT (11.3 ± 1.3 km h(-1)) and PWCFT (14.0 ± 2.3 km h(-1)), VT and RCP (14.0 ± 1.8 km h(-1)), but not the PWCFT and RCP. The findings of the present study indicated that the PWCFT model could be applied to a single continuous, incremental treadmill test to estimate the maximal running velocity that can be maintained prior to the onset of neuromuscular fatigue. In addition, these findings suggested that the PWCFT, like the RCP, may be used to differentiate the heavy from severe domains of exercise intensity.

  1. An engineering method for estimating notch-size effect in fatigue tests on steel

    NASA Technical Reports Server (NTRS)

    Kuhn, Paul; Hardrath, Herbert F

    1952-01-01

    Neuber's proposed method of calculating a practical factor of stress concentration for parts containing notches of arbitrary size depends on the knowledge of a "new material constant" which can be established only indirectly. In this paper, the new constant has been evaluated for a large variety of steels from fatigue tests reported in the literature, attention being confined to stresses near the endurance limit. Reasonably satisfactory results were obtained with the assumption that the constant depends only on the tensile strength of the steel. Even in cases where the notches were cracks of which only the depth was known, reasonably satisfactory agreement was found between calculated and experimental factors. It is also shown that the material constant can be used in an empirical formula to estimate the size effect on unnotched specimens tested in bending fatigue.

  2. Self-motion magnitude estimation during linear oscillation - Changes with head orientation and following fatigue

    NASA Technical Reports Server (NTRS)

    Parker, D. E.; Wood, D. L.; Gulledge, W. L.; Goodrich, R. L.

    1979-01-01

    Two types of experiments concerning the estimated magnitude of self-motion during exposure to linear oscillation on a parallel swing are described in this paper. Experiment I examined changes in magnitude estimation as a function of variation of the subject's head orientation, and Experiments II a, II b, and II c assessed changes in magnitude estimation performance following exposure to sustained, 'intense' linear oscillation (fatigue-inducting stimulation). The subjects' performance was summarized employing Stevens' power law R = k x S to the nth, where R is perceived self-motion magnitude, k is a constant, S is amplitude of linear oscillation, and n is an exponent). The results of Experiment I indicated that the exponents, n, for the magnitude estimation functions varied with head orientation and were greatest when the head was oriented 135 deg off the vertical. In Experiments II a-c, the magnitude estimation function exponents were increased following fatigue. Both types of experiments suggest ways in which the vestibular system's contribution to a spatial orientation perceptual system may vary. This variability may be a contributing factor to the development of pilot/astronaut disorientation and may also be implicated in the occurrence of motion sickness.

  3. Rate-dependent impairments in repetitive finger movements in patients with Parkinson's disease are not due to peripheral fatigue.

    PubMed

    Stegemöller, Elizabeth L; Allen, David P; Simuni, Tanya; MacKinnon, Colum D

    2010-09-20

    Performance of repetitive finger movements is an important clinical measure of disease severity in patients with Parkinson's disease (PD) and is associated with a dramatic deterioration in performance at movement rates near 2 Hz and above. The mechanisms contributing to this rate-dependent movement impairment are poorly understood. Since clinical and experimental testing of these movements involve prolonged repetition of movement, a loss of force-generating capacity due to peripheral fatigue may contribute to performance deterioration. This study examined the contribution of peripheral fatigue to the performance of unconstrained index finger flexion movements by measuring maximum voluntary contractions (MVC) immediately before and after repetitive finger movements in patients with PD (both off- and on-medication) and matched control subjects. Movement performance was quantified using finger kinematics, maximum force production, and electromyography (EMG). The principal finding was that peak force and EMG activity during the MVC did not significantly change from the pre- to post-movement task in patients with PD despite the marked deterioration in movement performance of repetitive finger movements. These findings show that the rate-dependent deterioration of repetitive finger movements in PD cannot be explained by a loss of force-generating capacity due to peripheral fatigue, and further suggest that mechanisms contributing to impaired isometric force production in PD are different from those that mediate impaired performance of high-rate repetitive movements.

  4. Changes of the balancing between anode and cathode due to fatigue in commercial lithium-ion cells

    NASA Astrophysics Data System (ADS)

    Kleiner, Karin; Jakes, Peter; Scharner, Sebastian; Liebau, Verena; Ehrenberg, Helmut

    2016-06-01

    The electrode balancing defines the state of charge (SoC) of a lithium-ion cell and is a crucial point considering lifetime and safe operation. The electrode balancing varies during fatigue which results in changes of the individual electrode potentials for fixed (dis-)charge voltages of the full-cell. Therefore the materials are cycled closer or beyond their electrochemical (meta-)stability window. This leads to accelerated degradation reactions or even to safety problems. The origin of the changes in the cell balancing is the limited amount of mobile lithium, which decreases during cycling due to the loss of lithiated active material a), the reduction of accessible lattice sites in the active materials b) and the loss of active lithium outside the electrodes c). In most of the commercial cells a) and b) can be attributed to the cathode, c) occurs due to reactions on the anode surface. Changes in the electrode balancing of three differently fatigued 7 Ah lithium-ion cells are investigated by electrochemical cycling of full- and half-cells, assembled from cell components of the fatigued 7 Ah cells. Based on these results the observed performance drop is assigned to a), b) or c) mentioned above and the capacity losses are quantified.

  5. Dynamic Elbow Flexion Force Estimation Through a Muscle Twitch Model and sEMG in a Fatigue Condition.

    PubMed

    Na, Youngjin; Kim, Jung

    2016-11-14

    We propose a joint force estimation method to compute elbow flexion force using surface electromyogram (sEMG) considering time-varying effects in a fatigue condition. Muscle fatigue is a major cause inducing sEMG changes with respect to time over long periods and repetitive contractions. The proposed method composed the muscle-twitch model representing the force generated by a single spike and the spikes extracted from sEMG. In this study, isometric contractions at six different joint angles (ten subjects) and dynamic contractions with constant velocity (six subjects) were performed under non-fatigue and fatigue conditions. Performance of the proposed method was evaluated and compared with that of previous methods using mean absolute value (MAV). The proposed method achieved average 6.7±2.8 %RMSE for isometric contraction and 15.6±24.7 %RMSE for isokinetic contraction under fatigue condition with more accurate results than the previous methods.

  6. Hydrological model uncertainty due to spatial evapotranspiration estimation methods

    NASA Astrophysics Data System (ADS)

    Yu, Xuan; Lamačová, Anna; Duffy, Christopher; Krám, Pavel; Hruška, Jakub

    2016-05-01

    Evapotranspiration (ET) continues to be a difficult process to estimate in seasonal and long-term water balances in catchment models. Approaches to estimate ET typically use vegetation parameters (e.g., leaf area index [LAI], interception capacity) obtained from field observation, remote sensing data, national or global land cover products, and/or simulated by ecosystem models. In this study we attempt to quantify the uncertainty that spatial evapotranspiration estimation introduces into hydrological simulations when the age of the forest is not precisely known. The Penn State Integrated Hydrologic Model (PIHM) was implemented for the Lysina headwater catchment, located 50°03‧N, 12°40‧E in the western part of the Czech Republic. The spatial forest patterns were digitized from forest age maps made available by the Czech Forest Administration. Two ET methods were implemented in the catchment model: the Biome-BGC forest growth sub-model (1-way coupled to PIHM) and with the fixed-seasonal LAI method. From these two approaches simulation scenarios were developed. We combined the estimated spatial forest age maps and two ET estimation methods to drive PIHM. A set of spatial hydrologic regime and streamflow regime indices were calculated from the modeling results for each method. Intercomparison of the hydrological responses to the spatial vegetation patterns suggested considerable variation in soil moisture and recharge and a small uncertainty in the groundwater table elevation and streamflow. The hydrologic modeling with ET estimated by Biome-BGC generated less uncertainty due to the plant physiology-based method. The implication of this research is that overall hydrologic variability induced by uncertain management practices was reduced by implementing vegetation models in the catchment models.

  7. The use of ultrasonic signals and optical method to estimate the damage of materials after fatigue loading

    NASA Astrophysics Data System (ADS)

    Mishakin, V. V.; Mitenkov, F. M.; Klyushnikov, V. A.; Danilova, N. V.

    2010-12-01

    The influence of fatigue load of steels on parameters of ultrasonic and microplastic characteristics has been studied. A phenomenological theory, which connects process of damage accumulation (before appearance of crack) under fatigue loading with acoustic parameters and microplastic parameters, has been developed. Experimental studies showed that the combination of nondestructive methods of control (acoustical and optical) allows one to estimate the state of materials at an early stage of destruction in both low-cycle and high-cycle areas.

  8. Bilateral Femoral Neck Fatigue Fracture due to Osteomalacia Secondary to Celiac Disease: Report of Three Cases.

    PubMed

    Selek, Ozgur; Memisoglu, Kaya; Selek, Alev

    2015-08-01

    Bilateral non traumatic femoral neck fatigue fracture is a rare condition usually occurring secondary to medical conditions such as pregnancy, pelvic irradiation, corticosteroid exposure, chronic renal failure and osteomalacia. In this report, we present three young female patients with bilateral femoral neck fracture secondary to osteomalacia. The underlying cause of osteomalacia was Celiac disease in all patients. The patients were treated with closed reduction and internal fixation with cannulated lag screws. They were free of pain and full weight bearing was achieved at three months. There were no complications, avascular necrosis and nonunion during the follow up period. In patients with bone pain, non traumatic fractures and muscle weakness, osteomalacia should be kept in mind and proper diagnostic work-up should be performed to identify the underlying cause of osteomalacia such as celiac disease.

  9. Fatigue life estimation procedures for the endurance of a cardiac valve prosthesis: stress/life and damage-tolerant analyses.

    PubMed

    Ritchie, R O; Lubock, P

    1986-05-01

    Projected fatigue life analyses are performed to estimate the endurance of a cardiac valve prosthesis under physiological environmental and mechanical conditions. The analyses are conducted using both the classical stress-strain/life and the fracture mechanics-based damage-tolerant approaches, and provide estimates of expected life in terms of initial flaw sizes which may pre-exist in the metal prior to the valve entering service. The damage-tolerant analysis further is supplemented by consideration of the question of "short cracks," which represents a developing area in metal fatigue research, not commonly applied to data in standard engineering design practice.

  10. Mental fatigue and working memory load estimation: interaction and implications for EEG-based passive BCI.

    PubMed

    Roy, Raphaelle N; Bonnet, Stephane; Charbonnier, Sylvie; Campagne, Aurelie

    2013-01-01

    Current mental state monitoring systems, a.k.a. passive brain-computer interfaces (pBCI), allow one to perform a real-time assessment of an operator's cognitive state. In EEG-based systems, typical measurements for workload level assessment are band power estimates in several frequency bands. Mental fatigue, arising from growing time-on-task (TOT), can significantly affect the distribution of these band power features. However, the impact of mental fatigue on workload (WKL) assessment has not yet been evaluated. With this paper we intend to help fill in this lack of knowledge by analyzing the influence of WKL and TOT on EEG band power features, as well as their interaction and its impact on classification performance. Twenty participants underwent an experiment that modulated both their WKL (low/high) and time spent on the task (short/long). Statistical analyses were performed on the EEG signals, behavioral and subjective data. They revealed opposite changes in alpha power distribution between WKL and TOT conditions, as well as a decrease in WKL level discriminability with increasing TOT in both number of statistical differences in band power and classification performance. Implications for pBCI systems and experimental protocol design are discussed.

  11. Simplified rotor load models and fatigue damage estimates for offshore wind turbines.

    PubMed

    Muskulus, M

    2015-02-28

    The aim of rotor load models is to characterize and generate the thrust loads acting on an offshore wind turbine. Ideally, the rotor simulation can be replaced by time series from a model with a few parameters and state variables only. Such models are used extensively in control system design and, as a potentially new application area, structural optimization of support structures. Different rotor load models are here evaluated for a jacket support structure in terms of fatigue lifetimes of relevant structural variables. All models were found to be lacking in accuracy, with differences of more than 20% in fatigue load estimates. The most accurate models were the use of an effective thrust coefficient determined from a regression analysis of dynamic thrust loads, and a novel stochastic model in state-space form. The stochastic model explicitly models the quasi-periodic components obtained from rotational sampling of turbulent fluctuations. Its state variables follow a mean-reverting Ornstein-Uhlenbeck process. Although promising, more work is needed on how to determine the parameters of the stochastic model and before accurate lifetime predictions can be obtained without comprehensive rotor simulations.

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

    NASA Astrophysics Data System (ADS)

    Fiedler, Brent Alan

    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.

  13. Vortex-induced vibration effect on fatigue life estimate of turbine blades

    NASA Astrophysics Data System (ADS)

    Lau, Y. L.; Leung, R. C. K.; So, R. M. C.

    2007-11-01

    An analysis of a turbine blade fatigue life that includes the physics of fluid-structure interaction on the high cycle fatigue (HCF) life estimate of turbine blades is carried out. The rotor wake excitation is modeled by rows of Karman vortices superimposed on an inviscid uniform flow. The vortex-induced vibration problem is modeled by a linear cascade composed of five turbine blades and the coupled Euler and structural dynamics equations are numerically solved using a time-marching boundary element technique. The analysis can be applied to any blade geometries; it is not limited to the blade geometry considered here. Two major design parameters have been identified; the ratio of blade spacing to blade chord length s/ c of the stator, and the normalized frequency parameter c/ d which is related to the wake passing frequency of the rotor. For a rigid cascade, it is found that aerodynamic resonance prevails at the resonant c/ d values corresponding to an isolated blade while s/ c is responsible for the level of the aerodynamic response. If the central blades were elastic, the parameter s/ c plays a different role in the fluid-structure interaction problem. With a c/ d that could lead to structural resonance for an isolated blade, changing s/ c would stabilize the aerodynamic and structural response of the elastic blade in a cascade. On the contrary, an improper choice of s/ c might turn the elastic blade response into structural resonance even though the oncoming c/ d is non-resonant. The results of the nonlinear effects of c/ d and s/ c could be used together with the Campbell diagram to obtain an improved HCF design of rotor-stator pair.

  14. Estimation of Reduction in Airspace Capacity Due to Convective Weather

    NASA Technical Reports Server (NTRS)

    Sheth, Kapil; Sridhar, Banavar; Namjoshi, Leena

    2006-01-01

    Severe convective weather routinely disrupts normal flow of air traffic in the United States' National Airspace System (NAS). Over the last decade, severe weather has been the most significant cause, accounting for over 70% of air traffic delays in the NAS. Flights incur modification in their nominal routes due to the presence of severe weather, and hence, suffer increased delays. These delays contribute to increased burden on airlines due to extra fuel costs and missed schedules for connecting flights. In this paper, the reduction in air space capacity and the associated air traffic delays due to severe convective weather will be investigated.

  15. Ultrasonic Evaluation of Fatigue Damage

    NASA Astrophysics Data System (ADS)

    Bayer, P.; Singher, L.; Notea, A.

    2004-02-01

    Despite the fact that most engineers and designers are aware of fatigue, many severe breakdowns of industrial plant and machinery still occur due to fatigue. In effect, it's been estimated that fatigue causes at least 80% of the failures in modern engineering components. From an operational point of view, the detection of fatigue damage, preferably at a very early stage, is a critically important consideration in order to prevent possible catastrophic equipment failure and associated losses. This paper describes the investigation involving the use of ultrasonic waves as a potential tool for early detection of fatigue damage. The parameters investigated were the ultrasonic wave velocities (longitudinal and transverse waves) and attenuation coefficient before fatigue damage and after progressive stages of fatigue. Although comparatively small uncertainties were observed, the feasibility of utilizing the velocity of ultrasonic waves as a fatigue monitor was barely substantiated within actual research conditions. However, careful measurements of the ultrasonic attenuation parameter had demonstrated its potential to provide an early assessment of damage during fatigue.

  16. Erasing Errors due to Alignment Ambiguity When Estimating Positive Selection

    PubMed Central

    Redelings, Benjamin

    2014-01-01

    Current estimates of diversifying positive selection rely on first having an accurate multiple sequence alignment. Simulation studies have shown that under biologically plausible conditions, relying on a single estimate of the alignment from commonly used alignment software can lead to unacceptably high false-positive rates in detecting diversifying positive selection. We present a novel statistical method that eliminates excess false positives resulting from alignment error by jointly estimating the degree of positive selection and the alignment under an evolutionary model. Our model treats both substitutions and insertions/deletions as sequence changes on a tree and allows site heterogeneity in the substitution process. We conduct inference starting from unaligned sequence data by integrating over all alignments. This approach naturally accounts for ambiguous alignments without requiring ambiguously aligned sites to be identified and removed prior to analysis. We take a Bayesian approach and conduct inference using Markov chain Monte Carlo to integrate over all alignments on a fixed evolutionary tree topology. We introduce a Bayesian version of the branch-site test and assess the evidence for positive selection using Bayes factors. We compare two models of differing dimensionality using a simple alternative to reversible-jump methods. We also describe a more accurate method of estimating the Bayes factor using Rao-Blackwellization. We then show using simulated data that jointly estimating the alignment and the presence of positive selection solves the problem with excessive false positives from erroneous alignments and has nearly the same power to detect positive selection as when the true alignment is known. We also show that samples taken from the posterior alignment distribution using the software BAli-Phy have substantially lower alignment error compared with MUSCLE, MAFFT, PRANK, and FSA alignments. PMID:24866534

  17. A novel closure based approach for fatigue crack length estimation using the acoustic emission technique in structural health monitoring applications

    NASA Astrophysics Data System (ADS)

    Gagar, Daniel; Foote, Peter; Irving, Philip

    2014-10-01

    Use of Acoustic Emission (AE) for detecting and locating fatigue cracks in metallic structures is widely reported but studies investigating its potential for fatigue crack length estimation are scarce. Crack growth information enables prediction of the remaining useful life of a component using well established fracture mechanics principles. Hence, the prospects of AE for use in structural health monitoring applications would be significantly improved if it could be demonstrated not only as a means of detecting crack growth but also for estimation of crack lengths. A new method for deducing crack length has been developed based on correlations between AE signals generated during fatigue crack growth and corresponding cyclic loads. A model for crack length calculation was derived empirically using AE data generated during fatigue crack growth tests in 2 mm thick SEN aluminium 2014 T6 specimens subject to a tensile stress range of 52 MPa and an R ratio of 0.1. The model was validated using AE data generated independently in separate tests performed with a stress range of 27 MPa. The results showed that predictions of crack lengths over a range of 10 mm to 80 mm can be obtained with the mean of the normalised absolute errors ranging between 0.28 and 0.4. Predictions were also made using existing AE feature-based methods and the results compared to those obtained with the novel approach developed.

  18. High-Throughput Computation and the Applicability of Monte Carlo Integration in Fatigue Load Estimation of Floating Offshore Wind Turbines

    SciTech Connect

    Graf, Peter A.; Stewart, Gordon; Lackner, Matthew; Dykes, Katherine; Veers, Paul

    2016-05-01

    Long-term fatigue loads for floating offshore wind turbines are hard to estimate because they require the evaluation of the integral of a highly nonlinear function over a wide variety of wind and wave conditions. Current design standards involve scanning over a uniform rectangular grid of metocean inputs (e.g., wind speed and direction and wave height and period), which becomes intractable in high dimensions as the number of required evaluations grows exponentially with dimension. Monte Carlo integration offers a potentially efficient alternative because it has theoretical convergence proportional to the inverse of the square root of the number of samples, which is independent of dimension. In this paper, we first report on the integration of the aeroelastic code FAST into NREL's systems engineering tool, WISDEM, and the development of a high-throughput pipeline capable of sampling from arbitrary distributions, running FAST on a large scale, and postprocessing the results into estimates of fatigue loads. Second, we use this tool to run a variety of studies aimed at comparing grid-based and Monte Carlo-based approaches with calculating long-term fatigue loads. We observe that for more than a few dimensions, the Monte Carlo approach can represent a large improvement in computational efficiency, but that as nonlinearity increases, the effectiveness of Monte Carlo is correspondingly reduced. The present work sets the stage for future research focusing on using advanced statistical methods for analysis of wind turbine fatigue as well as extreme loads.

  19. A fracture mechanics approach for estimating fatigue crack initiation in carbon and low-alloy steels in LWR coolant environments

    SciTech Connect

    Park, H. B.; Chopra, O. K.

    2000-04-10

    A fracture mechanics approach for elastic-plastic materials has been used to evaluate the effects of light water reactor (LWR) coolant environments on the fatigue lives of carbon and low-alloy steels. The fatigue life of such steel, defined as the number of cycles required to form an engineering-size crack, i.e., 3-mm deep, is considered to be composed of the growth of (a) microstructurally small cracks and (b) mechanically small cracks. The growth of the latter was characterized in terms of {Delta}J and crack growth rate (da/dN) data in air and LWR environments; in water, the growth rates from long crack tests had to be decreased to match the rates from fatigue S-N data. The growth of microstructurally small cracks was expressed by a modified Hobson relationship in air and by a slip dissolution/oxidation model in water. The crack length for transition from a microstructurally small crack to a mechanically small crack was based on studies on small crack growth. The estimated fatigue S-N curves show good agreement with the experimental data for these steels in air and water environments. At low strain amplitudes, the predicted lives in water can be significantly lower than the experimental values.

  20. Fatigue life estimation for different notched specimens based on the volumetric approach

    NASA Astrophysics Data System (ADS)

    Zehsaz, M.; Hassanifard, S.; Esmaeili, F.

    2010-06-01

    In this paper, the effects of notch radius for different notched specimens has been studied on the values of stress concentration factor, notch strength reduction factor, and fatigue life duration of the specimens. The material which has been selected for this investigation is Al 2024T3 . Volumetric approach has been applied to obtain the values of notch strength reduction factor and results have been compared with those obtained from the Neuber and Peterson methods. Load controlled fatigue tests of mentioned specimens have been conducted on the 250kN servo-hydraulic Zwick/Amsler fatigue testing machine with the frequency of 10Hz. The fatigue lives of the specimens have also been predicted based on the available smooth S-N curve of Al2024-T3 and also the amounts of notch strength reduction factor which have been obtained from volumetric, Neuber and Peterson methods. The values of stress and strain around the notch roots are required to predict the fatigue life of notched specimens, so Ansys finite element code has been used and non-linear analyses have been performed to obtain the stress and strain distributions around the notches. The plastic deformations of the material have been simulated using multi-linear kinematic hardening and cyclic stress-strain relation. The work here shows that the volumetric approach does a very good job for predicting the fatigue life of the notched specimens.

  1. Estimation of the mesoscopic thermoplastic dissipation in High-Cycle Fatigue

    NASA Astrophysics Data System (ADS)

    Charkaluk, Eric; Constantinescu, Andrei

    2006-06-01

    A series of High-Cycle Fatigue (HCF) criteria for polycrystalline materials is based on a multiscale interpretation, proposed initially by Dang Van, in which the principal concepts are a two scales model and a shakedown condition. The purpose of this Note is to extend the study of the different dissipative regimes during cyclic loading within this framework by using a self consistent homogenization scheme in coupled thermoplasticity. It is shown that the Sachs and Lin-Taylor schemes are not able to represent the thermal evolutions observed during fatigue tests. To cite this article: E. Charkaluk, A. Constantinescu, C. R. Mecanique 334 (2006).

  2. Non-destructive estimation of fatigue damage for steel by Barkhausen noise analysis

    SciTech Connect

    Tomita, Yasumitsu; Hashimoto, Kiyoshi; Osawa, Naoki; Inai, Hirohisa

    1993-12-31

    A magnetic Barkhausen noise signals are detected when magnetized domain walls move discontinuously in a ferromagnetic material. This non-uniform motion is sensitive to the microstructures of material which vary continuously with the increase of applied loading cycles. In this paper, the process of fatigue damage accumulation subjected to constant cyclic loading are explored by measuring the Barkhausen noise signal with the progress of loading cycles. The experimental results show the possibility to detect the progress of fatigue damage using the peak Barkhausen noise signal.

  3. Three Dimensional Constraint Effects on the Estimated (Delta)CTOD during the Numerical Simulation of Different Fatigue Threshold Testing Techniques

    NASA Technical Reports Server (NTRS)

    Seshadri, Banavara R.; Smith, Stephen W.

    2007-01-01

    Variation in constraint through the thickness of a specimen effects the cyclic crack-tip-opening displacement (DELTA CTOD). DELTA CTOD is a valuable measure of crack growth behavior, indicating closure development, constraint variations and load history effects. Fatigue loading with a continual load reduction was used to simulate the load history associated with fatigue crack growth threshold measurements. The constraint effect on the estimated DELTA CTOD is studied by carrying out three-dimensional elastic-plastic finite element simulations. The analysis involves numerical simulation of different standard fatigue threshold test schemes to determine how each test scheme affects DELTA CTOD. The American Society for Testing and Materials (ASTM) prescribes standard load reduction procedures for threshold testing using either the constant stress ratio (R) or constant maximum stress intensity (K(sub max)) methods. Different specimen types defined in the standard, namely the compact tension, C(T), and middle cracked tension, M(T), specimens were used in this simulation. The threshold simulations were conducted with different initial K(sub max) values to study its effect on estimated DELTA CTOD. During each simulation, the DELTA CTOD was estimated at every load increment during the load reduction procedure. Previous numerical simulation results indicate that the constant R load reduction method generates a plastic wake resulting in remote crack closure during unloading. Upon reloading, this remote contact location was observed to remain in contact well after the crack tip was fully open. The final region to open is located at the point at which the load reduction was initiated and at the free surface of the specimen. However, simulations carried out using the constant Kmax load reduction procedure did not indicate remote crack closure. Previous analysis results using various starting K(sub max) values and different load reduction rates have indicated DELTA CTOD is

  4. Rate-Dependent Impairments in Repetitive Finger Movements in Patients with Parkinson’s Disease are not Due to Peripheral Fatigue

    PubMed Central

    Stegemöller, Elizabeth L.; Allen, David P.; Simuni, Tanya; MacKinnon, Colum D.

    2010-01-01

    Performance of repetitive finger movements is an important clinical measure of disease severity in patients with Parkinson’s disease (PD) and is associated with a dramatic deterioration in performance at movement rates near 2 Hz and above. The mechanisms contributing to this rate-dependent movement impairment are poorly understood. Since clinical and experimental testing of these movements involve prolonged repetition of movement, a loss of force generating capacity due to peripheral fatigue may contribute to performance deterioration. This study examined the contribution of peripheral fatigue to the performance of unconstrained index finger flexion movements by measuring maximum voluntary contractions (MVC) immediately before and after repetitive finger movements in patients with PD (both off- and on-medication) and matched control subjects. Movement performance was quantified using finger kinematics, maximum force production, and electromyography (EMG). The principal finding was that peak force and EMG activity during the MVC did not significantly change from the pre- to post- movement task in patients with PD despite the marked deterioration in movement performance of repetitive finger movements. These findings show that the rate-dependent deterioration of repetitive finger movements in PD cannot be explained by a loss of force-generating capacity due to peripheral fatigue, and further suggest that mechanisms contributing to impaired isometric force production in PD are different from those that mediate impaired performance of high-rate repetitive movements. PMID:20599591

  5. An approach for developing a national estimate of waterborne disease due to drinking water and a national estimate model application.

    PubMed

    Messner, Michael; Shaw, Susan; Regli, Stig; Rotert, Ken; Blank, Valerie; Soller, Jeff

    2006-01-01

    In this paper, the US Environmental Protection Agency (EPA) presents an approach and a national estimate of drinking water related endemic acute gastrointestinal illness (AGI) that uses information from epidemiologic studies. There have been a limited number of epidemiologic studies that have measured waterborne disease occurrence in the United States. For this analysis, we assume that certain unknown incidence of AGI in each public drinking water system is due to drinking water and that a statistical distribution of the different incidence rates for the population served by each system can be estimated to inform a mean national estimate of AGI illness due to drinking water. Data from public water systems suggest that the incidence rate of AGI due to drinking water may vary by several orders of magnitude. In addition, data from epidemiologic studies show AGI incidence due to drinking water ranging from essentially none (or less than the study detection level) to a rate of 0.26 cases per person-year. Considering these two perspectives collectively, and associated uncertainties, EPA has developed an analytical approach and model for generating a national estimate of annual AGI illness due to drinking water. EPA developed a national estimate of waterborne disease to address, in part, the 1996 Safe Drinking Water Act Amendments. The national estimate uses best available science, but also recognizes gaps in the data to support some of the model assumptions and uncertainties in the estimate. Based on the model presented, EPA estimates a mean incidence of AGI attributable to drinking water of 0.06 cases per year (with a 95% credible interval of 0.02-0.12). The mean estimate represents approximately 8.5% of cases of AGI illness due to all causes among the population served by community water systems. The estimated incidence translates to 16.4 million cases/year among the same population. The estimate illustrates the potential usefulness and challenges of the approach, and

  6. Estimation of Sonic Fatigue by Reduced-Order Finite Element Based Analyses

    NASA Technical Reports Server (NTRS)

    Rizzi, Stephen A.; Przekop, Adam

    2006-01-01

    A computationally efficient, reduced-order method is presented for prediction of sonic fatigue of structures exhibiting geometrically nonlinear response. A procedure to determine the nonlinear modal stiffness using commercial finite element codes allows the coupled nonlinear equations of motion in physical degrees of freedom to be transformed to a smaller coupled system of equations in modal coordinates. The nonlinear modal system is first solved using a computationally light equivalent linearization solution to determine if the structure responds to the applied loading in a nonlinear fashion. If so, a higher fidelity numerical simulation in modal coordinates is undertaken to more accurately determine the nonlinear response. Comparisons of displacement and stress response obtained from the reduced-order analyses are made with results obtained from numerical simulation in physical degrees-of-freedom. Fatigue life predictions from nonlinear modal and physical simulations are made using the rainflow cycle counting method in a linear cumulative damage analysis. Results computed for a simple beam structure under a random acoustic loading demonstrate the effectiveness of the approach and compare favorably with results obtained from the solution in physical degrees-of-freedom.

  7. Damage depth estimation on a fatigue loaded composite structure using thermography and acoustic emission

    NASA Astrophysics Data System (ADS)

    Zalameda, Joseph N.; Winfree, William P.; Horne, Michael R.

    2017-02-01

    Passive thermography and acoustic emission data were obtained on a three stringer panel during periodic fatigue loading. The acoustic emission data were mapped onto thermal data, revealing the cluster of acoustic emission event locations around the thermal signatures of interest. By combining both techniques, progression of damage growth is confirmed and areas of failure are identified. Furthermore, sudden changes in thermally measured damage growth related to a previously measured higher energy acoustic emission event are studied to determine damage depth. A thermal model with a periodic flux heat source is presented to determine the relationship between the damage depth and thermal response. The model results are compared to the measured data. Lastly, the practical application and limitations of this technique are discussed.

  8. Estimation of the maximal voltage induced on an overhead line due to the nearby lightning

    SciTech Connect

    Jankov, V.

    1997-01-01

    Determination of the maximal voltages induced on the overhead power lines by nearby lightning stroke is a complex problem. The scope of this paper is to recognize the parameters that affect the maximal voltages and to present an equation for their estimation. This equation gives an opportunity to calculate the maximal voltage with the reasonable accuracy avoiding complex electromagnetic field calculus. It may be very useful in the estimation of flashover and outage rates due to the nearby strokes.

  9. An estimate of particulates in the vicinity of a Shuttle orbiter due to meteoroid impact

    NASA Technical Reports Server (NTRS)

    Barengoltz, J.

    1978-01-01

    An estimate of the magnitude of released particles in the vicinity of a a Shuttle (STS) Orbiter due to meteoroid impact has been completed. A calculation of the number of particles existing as surface contamination and released by such impacts has been performed. In addition, two estimates of the creation of new particles due to meteoroid cratering (backsplash) have been obtained. In each case, the total number of particles per day as a function of size without regard to velocity, as a function of velocity without regard to size, and as a joint distribution in size and velocity has been calculated.

  10. Probabilistic fatigue methodology and wind turbine reliability

    SciTech Connect

    Lange, C.H.

    1996-05-01

    Wind turbines subjected to highly irregular loadings due to wind, gravity, and gyroscopic effects are especially vulnerable to fatigue damage. The objective of this study is to develop and illustrate methods for the probabilistic analysis and design of fatigue-sensitive wind turbine components. A computer program (CYCLES) that estimates fatigue reliability of structural and mechanical components has been developed. A FORM/SORM analysis is used to compute failure probabilities and importance factors of the random variables. The limit state equation includes uncertainty in environmental loading, gross structural response, and local fatigue properties. Several techniques are shown to better study fatigue loads data. Common one-parameter models, such as the Rayleigh and exponential models are shown to produce dramatically different estimates of load distributions and fatigue damage. Improved fits may be achieved with the two-parameter Weibull model. High b values require better modeling of relatively large stress ranges; this is effectively done by matching at least two moments (Weibull) and better by matching still higher moments. For this purpose, a new, four-moment {open_quotes}generalized Weibull{close_quotes} model is introduced. Load and resistance factor design (LRFD) methodology for design against fatigue is proposed and demonstrated using data from two horizontal-axis wind turbines. To estimate fatigue damage, wind turbine blade loads have been represented by their first three statistical moments across a range of wind conditions. Based on the moments {mu}{sub 1}{hor_ellipsis}{mu}{sub 3}, new {open_quotes}quadratic Weibull{close_quotes} load distribution models are introduced. The fatigue reliability is found to be notably affected by the choice of load distribution model.

  11. Quantifying lost information due to covariance matrix estimation in parameter inference

    NASA Astrophysics Data System (ADS)

    Sellentin, Elena; Heavens, Alan F.

    2017-02-01

    Parameter inference with an estimated covariance matrix systematically loses information due to the remaining uncertainty of the covariance matrix. Here, we quantify this loss of precision and develop a framework to hypothetically restore it, which allows to judge how far away a given analysis is from the ideal case of a known covariance matrix. We point out that it is insufficient to estimate this loss by debiasing the Fisher matrix as previously done, due to a fundamental inequality that describes how biases arise in non-linear functions. We therefore develop direct estimators for parameter credibility contours and the figure of merit, finding that significantly fewer simulations than previously thought are sufficient to reach satisfactory precisions. We apply our results to DES Science Verification weak lensing data, detecting a 10 per cent loss of information that increases their credibility contours. No significant loss of information is found for KiDS. For a Euclid-like survey, with about 10 nuisance parameters we find that 2900 simulations are sufficient to limit the systematically lost information to 1 per cent, with an additional uncertainty of about 2 per cent. Without any nuisance parameters, 1900 simulations are sufficient to only lose 1 per cent of information. We further derive estimators for all quantities needed for forecasting with estimated covariance matrices. Our formalism allows to determine the sweetspot between running sophisticated simulations to reduce the number of nuisance parameters, and running as many fast simulations as possible.

  12. Estimates of the direct and indirect radiative forcing due to tropospheric aerosols: A review

    NASA Astrophysics Data System (ADS)

    Haywood, James; Boucher, Olivier

    2000-11-01

    This paper reviews the many developments in estimates of the direct and indirect global annual mean radiative forcing due to present-day concentrations of anthropogenic tropospheric aerosols since Intergovernmental Panel on Climate Change [1996]. The range of estimates of the global mean direct radiative forcing due to six distinct aerosol types is presented. Additionally, the indirect effect is split into two components corresponding to the radiative forcing due to modification of the radiative properties of clouds (cloud albedo effect) and the effects of anthropogenic aerosols upon the lifetime of clouds (cloud lifetime effect). The radiative forcing for anthropogenic sulphate aerosol ranges from -0.26 to -0.82 W m-2. For fossil fuel black carbon the radiative forcing ranges from +0.16 W m-2 for an external mixture to +0.42 W m-2 for where the black carbon is modeled as internally mixed with sulphate aerosol. For fossil fuel organic carbon the two estimates of the likely weakest limit of the direct radiative forcing are -0.02 and -0.04 W m-2. For biomass-burning sources of black carbon and organic carbon the combined radiative forcing ranges from -0.14 to -0.74 W m-2. Estimates of the radiative forcing due to mineral dust vary widely from +0.09 to -0.46 W m-2; even the sign of the radiative forcing is not well established due to the competing effects of solar and terrestrial radiative forcings. A single study provides a very tentative estimate of the radiative forcing of nitrates to be -0.03 W m-2. Estimates of the cloud albedo indirect radiative forcing range from -0.3 to approximately -1.8 W m-2. Although the cloud lifetime effect is identified as a potentially important climate forcing mechanism, it is difficult to quantify in the context of the present definition of radiative forcing of climate change and current model simulations. This is because its estimation by general circulation models necessarily includes some level of cloud and water vapor feedbacks

  13. The Influence of Roughness on Gear Surface Fatigue

    NASA Technical Reports Server (NTRS)

    Krantz, Timothy

    2005-01-01

    Gear working surfaces are subjected to repeated rolling and sliding contacts, and often designs require loads sufficient to cause eventual fatigue of the surface. This research provides experimental data and analytical tools to further the understanding of the causal relationship of gear surface roughness to surface fatigue. The research included evaluations and developments of statistical tools for gear fatigue data, experimental evaluation of the surface fatigue lives of superfinished gears with a near-mirror quality, and evaluations of the experiments by analytical methods and surface inspections. Alternative statistical methods were evaluated using Monte Carlo studies leading to a final recommendation to describe gear fatigue data using a Weibull distribution, maximum likelihood estimates of shape and scale parameters, and a presumed zero-valued location parameter. A new method was developed for comparing two datasets by extending the current methods of likelihood-ratio based statistics. The surface fatigue lives of superfinished gears were evaluated by carefully controlled experiments, and it is shown conclusively that superfinishing of gears can provide for significantly greater lives relative to ground gears. The measured life improvement was approximately a factor of five. To assist with application of this finding to products, the experimental condition was evaluated. The fatigue life results were expressed in terms of specific film thickness and shown to be consistent with bearing data. Elastohydrodynamic and stress analyses were completed to relate the stress condition to fatigue. Smooth-surface models do not adequately explain the improved fatigue lives. Based on analyses using a rough surface model, it is concluded that the improved fatigue lives of superfinished gears is due to a reduced rate of near-surface micropitting fatigue processes, not due to any reduced rate of spalling (sub-surface) fatigue processes. To complete the evaluations, surface

  14. Estimation of the collective dose in the Portuguese population due to medical procedures in 2010.

    PubMed

    Teles, Pedro; Carmen de Sousa, M; Paulo, Graciano; Santos, Joana; Pascoal, Ana; Cardoso, Gabriela; Lança, Isabel; Matela, Nuno; Janeiro, Luís; Sousa, Patrick; Carvoeiras, Pedro; Parafita, Rui; Santos, Ana Isabel; Simãozinho, Paula; Vaz, Pedro

    2013-05-01

    In a wide range of medical fields, technological advancements have led to an increase in the average collective dose in national populations worldwide. Periodic estimations of the average collective population dose due to medical exposure is, therefore of utmost importance, and is now mandatory in countries within the European Union (article 12 of EURATOM directive 97/43). Presented in this work is a report on the estimation of the collective dose in the Portuguese population due to nuclear medicine diagnostic procedures and the Top 20 diagnostic radiology examinations, which represent the 20 exams that contribute the most to the total collective dose in diagnostic radiology and interventional procedures in Europe. This work involved the collaboration of a multidisciplinary taskforce comprising representatives of all major Portuguese stakeholders (universities, research institutions, public and private healthcare providers, administrative services of the National Healthcare System, scientific and professional associations and private service providers). This allowed us to gather a comprehensive amount of data necessary for a robust estimation of the collective effective dose to the Portuguese population. The methodology used for data collection and dose estimation was based on European Commission recommendations, as this work was performed in the framework of the European wide Dose Datamed II project. This is the first study estimating the collective dose for the population in Portugal, considering such a wide national coverage and range of procedures and consisting of important baseline reference data. The taskforce intends to continue developing periodic collective dose estimations in the future. The estimated annual average effective dose for the Portuguese population was of 0.080±0.017 mSv caput(-1) for nuclear medicine exams and of 0.96±0.68 mSv caput(-1) for the Top 20 diagnostic radiology exams.

  15. Measurement error in mobile source air pollution exposure estimates due to residential mobility during pregnancy.

    PubMed

    Pennington, Audrey Flak; Strickland, Matthew J; Klein, Mitchel; Zhai, Xinxin; Russell, Armistead G; Hansen, Craig; Darrow, Lyndsey A

    2016-12-14

    Prenatal air pollution exposure is frequently estimated using maternal residential location at the time of delivery as a proxy for residence during pregnancy. We describe residential mobility during pregnancy among 19,951 children from the Kaiser Air Pollution and Pediatric Asthma Study, quantify measurement error in spatially resolved estimates of prenatal exposure to mobile source fine particulate matter (PM2.5) due to ignoring this mobility, and simulate the impact of this error on estimates of epidemiologic associations. Two exposure estimates were compared, one calculated using complete residential histories during pregnancy (weighted average based on time spent at each address) and the second calculated using only residence at birth. Estimates were computed using annual averages of primary PM2.5 from traffic emissions modeled using a Research LINE-source dispersion model for near-surface releases (RLINE) at 250 m resolution. In this cohort, 18.6% of children were born to mothers who moved at least once during pregnancy. Mobile source PM2.5 exposure estimates calculated using complete residential histories during pregnancy and only residence at birth were highly correlated (rS>0.9). Simulations indicated that ignoring residential mobility resulted in modest bias of epidemiologic associations toward the null, but varied by maternal characteristics and prenatal exposure windows of interest (ranging from -2% to -10% bias).Journal of Exposure Science and Environmental Epidemiology advance online publication, 14 December 2016; doi:10.1038/jes.2016.66.

  16. Methodology for estimation of time-dependent surface heat flux due to cryogen spray cooling.

    PubMed

    Tunnell, James W; Torres, Jorge H; Anvari, Bahman

    2002-01-01

    Cryogen spray cooling (CSC) is an effective technique to protect the epidermis during cutaneous laser therapies. Spraying a cryogen onto the skin surface creates a time-varying heat flux, effectively cooling the skin during and following the cryogen spurt. In previous studies mathematical models were developed to predict the human skin temperature profiles during the cryogen spraying time. However, no studies have accounted for the additional cooling due to residual cryogen left on the skin surface following the spurt termination. We formulate and solve an inverse heat conduction (IHC) problem to predict the time-varying surface heat flux both during and following a cryogen spurt. The IHC formulation uses measured temperature profiles from within a medium to estimate the surface heat flux. We implement a one-dimensional sequential function specification method (SFSM) to estimate the surface heat flux from internal temperatures measured within an in vitro model in response to a cryogen spurt. Solution accuracy and experimental errors are examined using simulated temperature data. Heat flux following spurt termination appears substantial; however, it is less than that during the spraying time. The estimated time-varying heat flux can subsequently be used in forward heat conduction models to estimate temperature profiles in skin during and following a cryogen spurt and predict appropriate timing for onset of the laser pulse.

  17. Estimating deformation due to soil liquefaction in Urayasu city, Japan using permanent scatterers

    NASA Astrophysics Data System (ADS)

    ElGharbawi, Tamer; Tamura, Masayuki

    2015-11-01

    In Japan, several cities endured severe damage due to soil liquefaction phenomenon, which was developed in association with the massive shaking of the 2011 Tohoku earthquake. Measuring soil liquefaction deformations was not an easy task, mainly because of the total loss of signal coherence in the affected regions. In this paper, we present our approach to estimate the deformations associated with soil liquefaction using interferometric synthetic aperture radar techniques. We use a stack of coseismic interferograms to identify the reliable pixels in the damaged areas using permanent scatterers technique. Then, we estimate and remove the preseismic mean velocity and DEM error components. Finally, we identify the liquefaction deformation component using least squares inversion and spatial phase filtering. We test the performance of the proposed approach using synthetic data, simulating the effects of soil liquefaction. The simulation results show a RMSE of the liquefaction deformation of 5.23 mm. After that, we estimate the deformation associated with soil liquefaction in Urayasu city, Japan, using ALOS-PALSAR data. The proposed approach allows a prompt estimation of the liquefaction deformation by utilizing the SAR images archives with only one postseismic SAR image.

  18. Criteria to estimate the voltage unbalances due to high-speed railway demands

    SciTech Connect

    Chen, T.H. . Dept. of Electrical Engineering and Technology)

    1994-08-01

    This paper has presented simple criteria to estimate the voltage unbalances due to high-speed railway demands that are generally single-phase loads. Feeding traction loads from the public power system may lead to some voltage unbalance on the latter and consequently affect the operation of its energy-supply system and other equipment connected with it. Three transformer connection schemes that are commonly used in power-supply systems for the high-speed railway are discussed and compared. The estimating criteria have been derived and represented by simple formula that can be easily applied to evaluate this voltage unbalance. The results are of value to related engineers and consultants especially during periods of planning and design.

  19. Estimation of organ and effective dose due to Compton backscatter security scans

    SciTech Connect

    Hoppe, Michael E.; Schmidt, Taly Gilat

    2012-06-15

    Purpose: To estimate organ and effective radiation doses due to backscatter security scanners using Monte Carlo simulations and a voxelized phantom set. Methods: Voxelized phantoms of male and female adults and children were used with the GEANT4 toolkit to simulate a backscatter security scan. The backscatter system was modeled based on specifications available in the literature. The simulations modeled a 50 kVp spectrum with 1.0 mm-aluminum-equivalent filtration and a previously measured exposure of approximately 4.6 {mu}R at 30 cm from the source. Photons and secondary interactions were tracked from the source until they reached zero kinetic energy or exited from the simulation's boundaries. The energy deposited in the phantoms' respective organs was tallied and used to calculate total organ dose and total effective dose for frontal, rear, and full scans with subjects located 30 and 75 cm from the source. Results: For a full screen, all phantoms' total effective doses were below the established 0.25 {mu}Sv standard, with an estimated maximum total effective dose of 0.07 {mu}Sv for full screen of a male child. The estimated maximum organ dose due to a full screen was 1.03 {mu}Gy, deposited in the adipose tissue of the male child phantom when located 30 cm from the source. All organ dose estimates had a coefficient of variation of less than 3% for a frontal scan and less than 11% for a rear scan. Conclusions: Backscatter security scanners deposit dose in organs beyond the skin. The effective dose is below recommended standards set by the Health Physics Society (HPS) and the American National Standards Institute (ANSI) assuming the system provides a maximum exposure of approximately 4.6 {mu}R at 30 cm.

  20. Fatigue loading on a 5MW offshore wind turbine due to the combined action of waves and current

    NASA Astrophysics Data System (ADS)

    Peeringa, Johan M.

    2014-06-01

    In the design of an offshore wind turbine the natural frequencies of the structure are of importance. In the design of fixed offshore wind turbine support structures it cannot be avoided that the first eigenmode of the structure lies in the frequency band of wave excitation. This study indicates that wave-current interaction should be taken into account for support structure design load calculations. Wave-current interaction changes the shape of the wave spectrum and the energy content in the wave frequency range of 0.2 - 0.35Hz. This is in the range of natural frequencies fixed offshore wind turbine structures are designed for. The waves are affected by the current in two ways. First there is a frequency shift, Doppler effect, for the fixed observer when the wave travels on a current. Second the shape of the wave is modified in case the wave travels from an area without current into an area with current. Due to wave-current interaction the wave height and wave length change. For waves on an opposing current the wave energy content increases, while for wave on a following current the wave energy content slightly reduces. Simulations of normal production cases between cut-in and cut-out wind speed are performed for a 5MW wind turbine in 20m water depth including waves with 1) a following current, 2) an opposing current and 3) no current present. In case of waves having an opposing current, the 1Hz equivalent fore-aft tower bending moment at the seabed is about 10% higher compared to load cases with waves only.

  1. Flexural fatigue life prediction of closed hat-section using materially nonlinear axial fatigue characteristics

    NASA Technical Reports Server (NTRS)

    Razzaq, Zia

    1989-01-01

    Straight or curved hat-section members are often used as structural stiffeners in aircraft. For instance, they are employed as stiffeners for the dorsal skin as well as in the aerial refueling adjacent area structure in F-106 aircraft. The flanges of the hat-section are connected to the aircraft skin. Thus, the portion of the skin closing the hat-section interacts with the section itself when resisting the stresses due to service loads. The flexural fatigue life of such a closed section is estimated using materially nonlinear axial fatigue characteristics. It should be recognized that when a structural shape is subjected to bending, the fatigue life at the neutral axis is infinity since the normal stresses are zero at that location. Conversely, the fatigue life at the extreme fibers where the normal bending stresses are maximum can be expected to be finite. Thus, different fatigue life estimates can be visualized at various distances from the neural axis. The problem becomes compounded further when significant portions away from the neutral axis are stressed into plastic range. A theoretical analysis of the closed hat-section subjected to flexural cyclic loading is first conducted. The axial fatigue characteristics together with the related axial fatigue life formula and its inverted form given by Manson and Muralidharan are adopted for an aluminum alloy used in aircraft construction. A closed-form expression for predicting the flexural fatigue life is then derived for the closed hat-section including materially nonlinear action. A computer program is written to conduct a study of the variables such as the thicknesses of the hat-section and the skin, and the type of alloy used. The study has provided a fundamental understanding of the flexural fatigue life characteristics of a practical structural component used in aircraft when materially nonlinear action is present.

  2. Direct estimation of entropy loss due to reduced translational and rotational motions upon molecular binding.

    PubMed

    Lu, Benzhuo; Wong, Chung F

    2005-12-05

    The entropic cost due to the loss of translational and rotational (T-R) degree of freedom upon binding has been well recognized for several decades. Tightly bound ligands have higher entropic costs than loosely bound ligands. Quantifying the ligand's residual T-R motions after binding, however, is not an easy task. We describe an approach that uses a reduced Hessian matrix to estimate the contributions due to translational and rotational degrees of freedom to entropy change upon molecular binding. The calculations use a harmonic model for the bound state but only include the T-R degrees of freedom. This approximation significantly speeds up entropy calculations because only 6 x 6 matrices need to be treated, which makes it easier to be used in computer-aided drug design for studying many ligands. The methodological connection with other methods is discussed as well. We tested this approximation by applying it to study the binding of ATP, peptide inhibitor (PKI), and several bound water molecules to protein kinase A (PKA). These ligands span a wide range in size. The model gave reasonable estimates of the residual T-R entropy of bound ligands or water molecules. The residual T-R entropy demonstrated a wide range of values, e.g., 4 to 16 cal/K.mol for the bound water molecules of PKA.

  3. GLODEP2: a computer model for estimating gamma dose due to worldwide fallout of radioactive debris

    SciTech Connect

    Edwards, L.L.; Harvey, T.F.; Peterson, K.R.

    1984-03-01

    The GLODEP2 computer code provides estimates of the surface deposition of worldwide radioactivity and the gamma-ray dose to man from intermediate and long-term fallout. The code is based on empirical models derived primarily from injection-deposition experience gained from the US and USSR nuclear tests in 1958. Under the assumption that a nuclear power facility is destroyed and that its debris behaves in the same manner as the radioactive cloud produced by the nuclear weapon that attached the facility, predictions are made for the gamma does from this source of radioactivity. As a comparison study the gamma dose due to the atmospheric nuclear tests from the period of 1951 to 1962 has been computed. The computed and measured values from Grove, UK and Chiba, Japan agree to within a few percent. The global deposition of radioactivity and resultant gamma dose from a hypothetical strategic nuclear exchange between the US and the USSR is reported. Of the assumed 5300 Mton in the exchange, 2031 Mton of radioactive debris is injected in the atmosphere. The highest estimated average whole body total integrated dose over 50 years (assuming no reduction by sheltering or weathering) is 23 rem in the 30 to 50 degree latitude band. If the attack included a 100 GW(e) nuclear power industry as targets in the US, this dose is increased to 84.6 rem. Hotspots due to rainfall could increase these values by factors of 10 to 50.

  4. Estimation of debris dispersion due to a space vehicle breakup during reentry

    NASA Astrophysics Data System (ADS)

    Reyhanoglu, Mahmut; Alvarado, Juan

    2013-05-01

    This paper studies the problem of the estimation of the extent of the airspace containing falling debris due to a space vehicle breakup. A precise propagation of debris to the ground is not practical for many reasons. There is insufficient knowledge of the initial state vector, ambient wind conditions, and the key parameters including the ballistic coefficients. In addition, propagation of all debris pieces to the ground would require extensive computer time. In this paper, a covariance propagation method is introduced for the estimation of debris dispersion due to a space vehicle breakup. The falling debris is simulated, and the data are analyzed to derive the probability of debris evolution in different altitude layers over time. The concept of positional probability ellipsoids is employed for the visualization of the results. Through a case study, it is shown that while the results of the covariance propagation method are in close agreement with those of the Monte Carlo method, the covariance propagation method is much more computationally efficient than the Monte Carlo method.

  5. Estimating challenge load due to disease outbreaks and other challenges using reproduction records of sows.

    PubMed

    Mathur, P K; Herrero-Medrano, J M; Alexandri, P; Knol, E F; ten Napel, J; Rashidi, H; Mulder, H A

    2014-12-01

    A method was developed and tested to estimate challenge load due to disease outbreaks and other challenges in sows using reproduction records. The method was based on reproduction records from a farm with known disease outbreaks. It was assumed that the reduction in weekly reproductive output within a farm is proportional to the magnitude of the challenge. As the challenge increases beyond certain threshold, it is manifested as an outbreak. The reproduction records were divided into 3 datasets. The first dataset called the Training dataset consisted of 57,135 reproduction records from 10,901 sows from 1 farm in Canada with several outbreaks of porcine reproductive and respiratory syndrome (PRRS). The known disease status of sows was regressed on the traits number born alive, number of losses as a combination of still birth and mummified piglets, and number of weaned piglets. The regression coefficients from this analysis were then used as weighting factors for derivation of an index measure called challenge load indicator. These weighting factors were derived with i) a two-step approach using residuals or year-week solutions estimated from a previous step, and ii) a single-step approach using the trait values directly. Two types of models were used for each approach: a logistic regression model and a general additive model. The estimates of challenge load indicator were then compared based on their ability to detect PRRS outbreaks in a Test dataset consisting of records from 65,826 sows from 15 farms in the Netherlands. These farms differed from the Canadian farm with respect to PRRS virus strains, severity and frequency of outbreaks. The single-step approach using a general additive model was best and detected 14 out of the 15 outbreaks. This approach was then further validated using the third dataset consisting of reproduction records of 831,855 sows in 431 farms located in different countries in Europe and America. A total of 41 out of 48 outbreaks detected

  6. Estimating the loss in expectation of life due to cancer using flexible parametric survival models.

    PubMed

    Andersson, Therese M-L; Dickman, Paul W; Eloranta, Sandra; Lambe, Mats; Lambert, Paul C

    2013-12-30

    A useful summary measure for survival data is the expectation of life, which is calculated by obtaining the area under a survival curve. The loss in expectation of life due to a certain type of cancer is the difference between the expectation of life in the general population and the expectation of life among the cancer patients. This measure is used little in practice as its estimation generally requires extrapolation of both the expected and observed survival. A parametric distribution can be used for extrapolation of the observed survival, but it is difficult to find a distribution that captures the underlying shape of the survival function after the end of follow-up. In this paper, we base our extrapolation on relative survival, because it is more stable and reliable. Relative survival is defined as the observed survival divided by the expected survival, and the mortality analogue is excess mortality. Approaches have been suggested for extrapolation of relative survival within life-table data, by assuming that the excess mortality has reached zero (statistical cure) or has stabilized to a constant. We propose the use of flexible parametric survival models for relative survival, which enables estimating the loss in expectation of life on individual level data by making these assumptions or by extrapolating the estimated linear trend at the end of follow-up. We have evaluated the extrapolation from this model using data on four types of cancer, and the results agree well with observed data.

  7. Estimating random errors due to shot noise in backscatter lidar observations

    NASA Astrophysics Data System (ADS)

    Liu, Zhaoyan; Hunt, William; Vaughan, Mark; Hostetler, Chris; McGill, Matthew; Powell, Kathleen; Winker, David; Hu, Yongxiang

    2006-06-01

    We discuss the estimation of random errors due to shot noise in backscatter lidar observations that use either photomultiplier tube (PMT) or avalanche photodiode (APD) detectors. The statistical characteristics of photodetection are reviewed, and photon count distributions of solar background signals and laser backscatter signals are examined using airborne lidar observations at 532 nm using a photon-counting mode APD. Both distributions appear to be Poisson, indicating that the arrival at the photodetector of photons for these signals is a Poisson stochastic process. For Poisson- distributed signals, a proportional, one-to-one relationship is known to exist between the mean of a distribution and its variance. Although the multiplied photocurrent no longer follows a strict Poisson distribution in analog-mode APD and PMT detectors, the proportionality still exists between the mean and the variance of the multiplied photocurrent. We make use of this relationship by introducing the noise scale factor (NSF), which quantifies the constant of proportionality that exists between the root mean square of the random noise in a measurement and the square root of the mean signal. Using the NSF to estimate random errors in lidar measurements due to shot noise provides a significant advantage over the conventional error estimation techniques, in that with the NSF, uncertainties can be reliably calculated from or for a single data sample. Methods for evaluating the NSF are presented. Algorithms to compute the NSF are developed for the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations lidar and tested using data from the Lidar In-space Technology Experiment.

  8. Estimating random errors due to shot noise in backscatter lidar observations.

    PubMed

    Liu, Zhaoyan; Hunt, William; Vaughan, Mark; Hostetler, Chris; McGill, Matthew; Powell, Kathleen; Winker, David; Hu, Yongxiang

    2006-06-20

    We discuss the estimation of random errors due to shot noise in backscatter lidar observations that use either photomultiplier tube (PMT) or avalanche photodiode (APD) detectors. The statistical characteristics of photodetection are reviewed, and photon count distributions of solar background signals and laser backscatter signals are examined using airborne lidar observations at 532 nm using a photon-counting mode APD. Both distributions appear to be Poisson, indicating that the arrival at the photodetector of photons for these signals is a Poisson stochastic process. For Poisson- distributed signals, a proportional, one-to-one relationship is known to exist between the mean of a distribution and its variance. Although the multiplied photocurrent no longer follows a strict Poisson distribution in analog-mode APD and PMT detectors, the proportionality still exists between the mean and the variance of the multiplied photocurrent. We make use of this relationship by introducing the noise scale factor (NSF), which quantifies the constant of proportionality that exists between the root mean square of the random noise in a measurement and the square root of the mean signal. Using the NSF to estimate random errors in lidar measurements due to shot noise provides a significant advantage over the conventional error estimation techniques, in that with the NSF, uncertainties can be reliably calculated from or for a single data sample. Methods for evaluating the NSF are presented. Algorithms to compute the NSF are developed for the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations lidar and tested using data from the Lidar In-space Technology Experiment.

  9. Estimating Random Errors Due to Shot Noise in Backscatter Lidar Observations

    NASA Technical Reports Server (NTRS)

    Liu, Zhaoyan; Hunt, William; Vaughan, Mark A.; Hostetler, Chris A.; McGill, Matthew J.; Powell, Kathy; Winker, David M.; Hu, Yongxiang

    2006-01-01

    In this paper, we discuss the estimation of random errors due to shot noise in backscatter lidar observations that use either photomultiplier tube (PMT) or avalanche photodiode (APD) detectors. The statistical characteristics of photodetection are reviewed, and photon count distributions of solar background signals and laser backscatter signals are examined using airborne lidar observations at 532 nm using a photon-counting mode APD. Both distributions appear to be Poisson, indicating that the arrival at the photodetector of photons for these signals is a Poisson stochastic process. For Poisson-distributed signals, a proportional, one-to-one relationship is known to exist between the mean of a distribution and its variance. Although the multiplied photocurrent no longer follows a strict Poisson distribution in analog-mode APD and PMT detectors, the proportionality still exists between the mean and the variance of the multiplied photocurrent. We make use of this relationship by introducing the noise scale factor (NSF), which quantifies the constant of proportionality that exists between the root-mean-square of the random noise in a measurement and the square root of the mean signal. Using the NSF to estimate random errors in lidar measurements due to shot noise provides a significant advantage over the conventional error estimation techniques, in that with the NSF uncertainties can be reliably calculated from/for a single data sample. Methods for evaluating the NSF are presented. Algorithms to compute the NSF are developed for the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) lidar and tested using data from the Lidar In-space Technology Experiment (LITE). OCIS Codes:

  10. Estimated crop yield losses due to surface ozone exposure and economic damage in India.

    PubMed

    Debaje, S B

    2014-06-01

    In this study, we estimate yield losses and economic damage of two major crops (winter wheat and rabi rice) due to surface ozone (O3) exposure using hourly O3 concentrations for the period 2002-2007 in India. This study estimates crop yield losses according to two indices of O3 exposure: 7-h seasonal daytime (0900-1600 hours) mean measured O3 concentration (M7) and AOT40 (accumulation exposure of O3 concentration over a threshold of 40 parts per billion by volume during daylight hours (0700-1800 hours), established by field studies. Our results indicate that relative yield loss from 5 to 11% (6-30%) for winter wheat and 3-6% (9-16%) for rabi rice using M7 (AOT40) index of the mean total winter wheat 81 million metric tons (Mt) and rabi rice 12 Mt production per year for the period 2002-2007. The estimated mean crop production loss (CPL) for winter wheat are from 9 to 29 Mt, account for economic cost loss was from 1,222 to 4,091 million US$ annually. Similarly, the mean CPL for rabi rice are from 0.64 to 2.1 Mt, worth 86-276 million US$. Our calculated winter wheat and rabi rice losses agree well with previous results, providing the further evidence that large crop yield losses occurring in India due to current O3 concentration and further elevated O3 concentration in future may pose threat to food security.

  11. Clinical neurophysiology of fatigue.

    PubMed

    Zwarts, M J; Bleijenberg, G; van Engelen, B G M

    2008-01-01

    Fatigue is a multidimensional concept covering both physiological and psychological aspects. Chronic fatigue is a typical symptom of diseases such as cancer, multiple sclerosis (MS), Parkinson's disease (PD) and cerebrovascular disorders but is also presented by people in whom no defined somatic disease has been established. If certain criteria are met, chronic fatigue syndrome can be diagnosed. The 4-item Abbreviated Fatigue Questionnaire allows the extent of the experienced fatigue to be assessed with a high degree of reliability and validity. Physiological fatigue has been well defined and originates in both the peripheral and central nervous system. The condition can be assessed by combining force and surface-EMG measurements (including frequency analyses and muscle-fibre conduction estimations), twitch interpolation, magnetic stimulation of the motor cortex and analysis of changes in the readiness potential. Fatigue is a well-known phenomenon in both central and peripheral neurological disorders. Examples of the former conditions are multiple sclerosis, Parkinson's disease and stroke. Although it seems to be a universal symptom of many brain disorders, the unique characteristics of the concomitant fatigue also point to a specific relationship with several of these syndromes. As regards neuromuscular disorders, fatigue has been reported in patients with post-polio syndrome, myasthenia gravis, Guillain-Barré syndrome, facioscapulohumeral dystrophy, myotonic dystrophy and hereditary motor and sensory neuropathy type-I. More than 60% of all neuromuscular patients suffer from severe fatigue, a prevalence resembling that of patients with MS. Except for several rare myopathies with specific metabolic derangements leading to exercise-induced muscle fatigue, most studies have not identified a prominent peripheral cause for the fatigue in this population. In contrast, the central activation of the diseased neuromuscular system is generally found to be suboptimal. The

  12. Bias in acoustic biomass estimates of Euphausia superba due to diel vertical migration

    NASA Astrophysics Data System (ADS)

    Demer, David A.; Hewitt, Roger P.

    1995-04-01

    The diel vertical migration (DVM) of Antarctic krill ( Euphausia superba) can greatly bias the results of qualitative and quantitative hydroacoustic surveys which are conducted with a down-looking sonar and irrespective of the time of day. To demonstrate and quantify these negative biases on both the estimates of biomass distribution and abundance, a time-depth-density analysis was performed. Data were collected, as part of the United States Antarctic Marine Living Resources Program (AMLR), in the vicinities of Elephant Island, Antarctica, during the austral summers of 1992 and 1993. Five surveys were conducted in 1992; two covered a 105 by 105 n.mi. area centered on Elephant Island, two encompassed a 60 by 35 n.mi. area immediately to the north of the Island, and one covered a 1 n.mi. 2 area centered on a large krill swarm to the west of Seal Island. The 1993 data include repetitions of the two small-area and two large-area surveys. Average krill volume densities were calculated for each hour as well as for three daily periods: day, twilight and night. These data were normalized and presented as a probability of daily average density. With spectral analysis to identify the frequencies of migration, a four-term periodic function was fitted to the probability density function of average daily biomass versus local apparent time. This function was transformed to create a temporal compensation function (TCF) for upwardly adjusting acoustic biomass estimates. The TCF was then applied to the original 1992 survey data; the resulting biomass estimates are an average of 49.5% higher than those calculated disregarding biases due to diel vertical migration. The effect of DVM on the estimates of krill distribution are illustrated by a comparison of compensated and uncompensated density maps of two 1992 surveys. Through this technique, high density kril areas are revealed where uncompensated maps indicated low densities.

  13. A new Tool for Estimating Losses due to Earthquakes: QUAKELOSS2

    NASA Astrophysics Data System (ADS)

    Kaestli, P.; Wyss, M.; Bonjour, C.; Wiemer, S.; Wyss, B. M.

    2007-12-01

    WAPMERR and the Swiss Seismological Service are developing new software for estimating mean damage to buildings, number of injured and number of fatalities due to earthquakes worldwide. The focus for applications is real-time estimates of losses after earthquakes in countries without dense seismograph networks, and results that are easy to digest by relief agencies. Therefore, the standard version of the software addresses losses by settlement, subdivisions of settlements and important pieces of infrastructure. However, a generic design, an open source policy and well defined interfaces will allow the software to work on any gridded or discrete building stock data, to do Monte-Carlo simulations for error assessment and to plug in more elaborate source models than simple point and line sources and thus to compute realistic loss scenarios as well as probabilistic risk maps. It will provide interfaces to SHAKEMAP and PAGER, such that innovations developed for the latter programs may be used in QUAKELOSS2, and vice versa. A client server design will provide a front-end web interface where the user may directly manage servers as well as run the software in one's&pown laboratory. The input-output features and mapping will be designed to allow the user to run QUAKELOSS2 remotely with basic functions, as well as in a laboratory setting including a full-featured GIS setup for additional analysis. In many cases, the input data (earthquake parameters as well as population and building stock data) are poorly known for developing countries. Calibration of loss estimates, using past earthquakes that have caused damage and WAPMERR's experience of four years" estimating losses, will help to produce approximately correct results in countries with strong earthquake activity. A worldwide standard dataset on population and building stock will be provided as open source together with the software. The dataset will be improved successively, based on input from satellite images

  14. Estimating Energy Dissipation Due to Wave Breaking in the Surf Zone Using Infrared Imagery

    NASA Astrophysics Data System (ADS)

    Carini, Roxanne J.

    Wave breaking is the largest forcing mechanism in the surf zone. Therefore, quantifying energy dissipation due to wave breaking is important for improving models that seek to predict nearshore circulation, wave-current interactions, air-sea gas exchange, erosion and accretion of sediment, and storm surge. Wave energy dissipation is difficult to measure with in situ instruments, and even the most reliable estimates are limited to point measurements. Using remote sensing technologies, specifically infrared (IR) imagery, the high spatial and temporal variability of wave breaking may be sampled. Duncan (1981) proposed a model (D81) for dissipation on a wave-by-wave basis, based on wave slope and roller length, the crest-perpendicular length of the aerated region of a breaking wave. The wave roller is composed of active foam, which, in thermal IR images, appears brighter than the surrounding water and the residual foam, the foam left behind in the wake of a breaking wave. Using IR imagery taken during the Surf Zone Optics 2010 experiment at Duck, NC, and exploiting the distinct signature of active foam, a retrieval algorithm was developed to identify and extract breaking wave roller length. Roller length was then used to estimate dissipation rate via the D81 formulation. The D81 dissipation rate estimates compare reasonably to in situ dissipation estimates at a point. When the D81 estimates are compared to the bulk energy flux into the surf zone, it is found that wave breaking dissipates approximately 25-36% of the incoming wave energy. The D81 dissipation rate estimates also agree closely with those from a dissipation parameterization proposed by Janssen and Battjes (2007) (JB07) and commonly applied within larger nearshore circulation models. The JB07 formulation, however, requires additional physical parameters (wave height and water depth) that are often sparsely sampled and are difficult to attain from remote sensing alone. The power of the D81 formulation lies in

  15. Interconnect fatigue design for terrestrial photovoltaic modules

    SciTech Connect

    Mon, G. R.; Moore, D. M.; Ross, Jr., R. G.

    1982-03-01

    Fatigue of solar cell electrical interconnects due to thermal cycling has historically been a major failure mechanism in photovoltaic arrays; the results of a comprehensive investigation of interconnect fatigue that has led to the definition of useful reliability-design and life-prediction algorithms are presented. Experimental data gathered in this study indicate that the classical strain-cycle (fatigue) curve for the interconnect material is a good model of mean interconnect fatigue performance, but it fails to account for the broad statistical scatter, which is critical to reliability prediction. To fill this shortcoming the classical fatigue curve is combined with experimental cumulative interconnect failure rate data to yield statistical fatigue curves (having failure probability as a parameter) which enable: (1) the prediction of cumulative interconnect failures during the design life of an array field; and (2) the unambiguous - i.e., quantitative - interpretation of data from field-service qualification (accelerated thermal cycling) tests. Optimal interconnect cost-reliability design algorithms are derived based on minimizing the cost of energy over the design life of the array field. This procedure yields not only the minimum break-even cost of delivered energy, but also the required degree of interconnect redundancy and an estimate of array power degradation during the design life of the array field. The usefulness of the design algorithms is demonstrated with realistic examples of design optimization, prediction, and service qualification testing.

  16. Estimation of Surface Roughness due to Electrode Erosion in Field-Distortion Gas Switch

    NASA Astrophysics Data System (ADS)

    Liu, Xuandong; Wang, Hu; Li, Xiaoang; Zhang, Qiaogen; Wei, Jin; Qiu, Aici

    2013-08-01

    Field distortion gas switch is one of the crucial elements in a Marx generator, fast linear transformer driver and other pulsed power installations. The performance of the gas switch, which is dramatically affected by the surface roughness due to electrode erosion during the discharge process, directly influences the output parameters, stability and reliability of the pulsed power system. In this paper, an electrode surface roughness (ESR) calculation model has been established based on a great deal of experimental data under operating current. The discharge current waveform, the peak height of the burr, the radius and the depth of etch pits in the electrode erosion region were used to predict the ESR. Also, experimental results indicate that this calculation model can effectively estimate the ESR of the test gas switch.

  17. New perspectives on the damage estimation for buried pipeline systems due to seismic wave propagation

    SciTech Connect

    Pineda Porras, Omar Andrey

    2009-01-01

    Over the past three decades, seismic fragility fonnulations for buried pipeline systems have been developed following two tendencies: the use of earthquake damage scenarios from several pipeline systems to create general pipeline fragility functions; and, the use of damage scenarios from one pipeline system to create specific-system fragility functions. In this paper, the advantages and disadvantages of both tendencies are analyzed and discussed; in addition, a summary of what can be considered the new challenges for developing better pipeline seismic fragility formulations is discussed. The most important conclusion of this paper states that more efforts are needed to improve the estimation of transient ground strain -the main cause of pipeline damage due to seismic wave propagation; with relevant advances in that research field, new and better fragility formulations could be developed.

  18. A statistical method to estimate outflow volume in case of levee breach due to overtopping

    NASA Astrophysics Data System (ADS)

    Brandimarte, Luigia; Martina, Mario; Dottori, Francesco; Mazzoleni, Maurizio

    2015-04-01

    The aim of this study is to propose a statistical method to assess the outflowing water volume through a levee breach, due to overtopping, in case of three different types of grass cover quality. The first step in the proposed methodology is the definition of the reliability function, a the relation between loading and resistance conditions on the levee system, in case of overtopping. Secondly, the fragility curve, which relates the probability of failure with loading condition over the levee system, is estimated having defined the stochastic variables in the reliability function. Thus, different fragility curves are assessed in case of different scenarios of grass cover quality. Then, a levee breach model is implemented and combined with a 1D hydrodynamic model in order to assess the outflow hydrograph given the water level in the main channel and stochastic values of the breach width. Finally, the water volume is estimated as a combination of the probability density function of the breach width and levee failure. The case study is located in the in 98km-braided reach of Po River, Italy, between the cross-sections of Cremona and Borgoforte. The analysis showed how different counter measures, different grass cover quality in this case, can reduce the probability of failure of the levee system. In particular, for a given values of breach width good levee cover qualities can significantly reduce the outflowing water volume, compared to bad cover qualities, inducing a consequent lower flood risk within the flood-prone area.

  19. Estimation of financial burden due to oversupply of medications for chronic diseases.

    PubMed

    Chaiyakunapruk, Nathorn; Thanarungroj, Aekdisak; Cheewasithirungrueng, Nonglak; Srisupha-olarn, Warunee; Nimpitakpong, Piyarat; Dilokthornsakul, Piyameth; Jeanpeerapong, Napawan

    2012-05-01

    Given the potential of financial burden due to oversupply of medications for chronic diseases, this study aims to determine the prevalence of oversupply and to estimate the magnitude of financial loss in Thailand. Electronic patient database in a university-affiliated hospital in Thailand was used. Based on the utilization of top 5 high drug expenditure in 2005, the prevalence and the financial loss of oversupply (medication possession ratio [MPR] >1.00) were estimated. In total, 1893 patients were included in this study. The average age was 65.2 years and the majority were female (56%). The prevalence of oversupply ranged from 23.2% to 62.8%, whereas the annual financial loss ranged from US $4108 to US $10 517. The total amount of loss was US $32 903 or 3.77% of total medication costs. In summary, because of the high prevalence and associated high financial loss, oversupply of medication is a significant financial burden on hospitals and society.

  20. On Assessment and Estimation of Potential Losses due to Land Subsidence in Urban Areas of Indonesia

    NASA Astrophysics Data System (ADS)

    Abidin, Hasanuddin Z.; Andreas, Heri; Gumilar, Irwan; Sidiq, Teguh P.

    2016-04-01

    subsidence have also relation among each other, the accurate quantification of the potential losses caused by land subsidence in urban areas is not an easy task to accomplish. The direct losses can be easier to estimate than the indirect losses. For example, the direct losses due to land subsidence in Bandung was estimated to be at least 180 Million USD; but the indirect losses is still unknown.

  1. Child mortality estimation: methods used to adjust for bias due to AIDS in estimating trends in under-five mortality.

    PubMed

    Walker, Neff; Hill, Kenneth; Zhao, Fengmin

    2012-01-01

    In most low- and middle-income countries, child mortality is estimated from data provided by mothers concerning the survival of their children using methods that assume no correlation between the mortality risks of the mothers and those of their children. This assumption is not valid for populations with generalized HIV epidemics, however, and in this review, we show how the United Nations Inter-agency Group for Child Mortality Estimation (UN IGME) uses a cohort component projection model to correct for AIDS-related biases in the data used to estimate trends in under-five mortality. In this model, births in a given year are identified as occurring to HIV-positive or HIV-negative mothers, the lives of the infants and mothers are projected forward using survivorship probabilities to estimate survivors at the time of a given survey, and the extent to which excess mortality of children goes unreported because of the deaths of HIV-infected mothers prior to the survey is calculated. Estimates from the survey for past periods can then be adjusted for the estimated bias. The extent of the AIDS-related bias depends crucially on the dynamics of the HIV epidemic, on the length of time before the survey that the estimates are made for, and on the underlying non-AIDS child mortality. This simple methodology (which does not take into account the use of effective antiretroviral interventions) gives results qualitatively similar to those of other studies.

  2. Time evolving bed shear stress due the passage of gravity currents estimated with ADVP velocity measurements

    NASA Astrophysics Data System (ADS)

    Zordan, Jessica; Schleiss, Anton J.; Franca, Mário J.

    2016-04-01

    Density or gravity currents are geophysical flows driven by density gradients between two contacting fluids. The physical trigger mechanism of these phenomena lays in the density differences which may be caused by differences in the temperature, dissolved substances or concentration of suspended sediments. Saline density currents are capable to entrain bed sediments inducing signatures in the bottom of sedimentary basins. Herein, saline density currents are reproduced in laboratory over a movable bed. The experimental channel is of the lock-exchange type, it is 7.5 m long and 0.3 m wide, divided into two sections of comparable volumes by a sliding gate. An upstream reach serves as a head tank for the dense mixture; the current propagates through a downstream reach where the main measurements are made. Downstream of the channel a tank exist to absorb the reflection of the current and thus artifacts due to the limited length of the channel. High performance thermoplastic polyurethane simulating fine sediments forms the movable bed. Measures of 3D instantaneous velocities will be made with the use of the non-intrusive technique of the ADV (Acoustic Doppler Current Profiler). With the velocity measurements, the evolution in time of the channel-bed shear stress due the passage of gravity currents is estimated. This is in turn related to the observed erosion and to such parameters determinant for the dynamics of the current as initial density difference, lock length and channel slope. This work was funded by the ITN-Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme FP7-PEOPLE-2013-ITN under REA grant agreement n_607394-SEDITRANS.

  3. Eliminating bias in rainfall estimates from microwave links due to antenna wetting

    NASA Astrophysics Data System (ADS)

    Fencl, Martin; Rieckermann, Jörg; Bareš, Vojtěch

    2014-05-01

    Commercial microwave links (MWLs) are point-to-point radio systems which are widely used in telecommunication systems. They operate at frequencies where the transmitted power is mainly disturbed by precipitation. Thus, signal attenuation from MWLs can be used to estimate path-averaged rain rates, which is conceptually very promising, since MWLs cover about 20 % of surface area. Unfortunately, MWL rainfall estimates are often positively biased due to additional attenuation caused by antenna wetting. To correct MWL observations a posteriori to reduce the wet antenna effect (WAE), both empirically and physically based models have been suggested. However, it is challenging to calibrate these models, because the wet antenna attenuation depends both on the MWL properties (frequency, type of antennas, shielding etc.) and different climatic factors (temperature, due point, wind velocity and direction, etc.). Instead, it seems straight forward to keep antennas dry by shielding them. In this investigation we compare the effectiveness of antenna shielding to model-based corrections to reduce the WAE. The experimental setup, located in Dübendorf-Switzerland, consisted of 1.85-km long commercial dual-polarization microwave link at 38 GHz and 5 optical disdrometers. The MWL was operated without shielding in the period from March to October 2011 and with shielding from October 2011 to July 2012. This unique experimental design made it possible to identify the attenuation due to antenna wetting, which can be computed as the difference between the measured and theoretical attenuation. The theoretical path-averaged attenuation was calculated from the path-averaged drop size distribution. During the unshielded periods, the total bias caused by WAE was 0.74 dB, which was reduced by shielding to 0.39 dB for the horizontal polarization (vertical: reduction from 0.96 dB to 0.44 dB). Interestingly, the model-based correction (Schleiss et al. 2013) was more effective because it reduced

  4. [Estimation of the Power Spectrum of Heart Rate Variability Using Improved Welch Method to Analyze the Degree of Fatigue].

    PubMed

    Xu, Wenhui; Liu, Kaihua; Wang, Liting

    2016-02-01

    Heart rate variability (HRV) is an important point to judge a person's state in modern medicine. This paper is aimed to research a person's fatigue level connected with vagal nerve based on the HRV using the improved Welch method. The process of this method is that it firstly uses a time window function on the signal to be processed, then sets the length of time according to the requirement, and finally makes frequency domain analysis. Compared with classical periodogram method, the variance and consistency of the present method have been improved. We can set time span freely using this method (at present, the time of international standard to measure HRV is 5 minutes). This paper analyses the HRV's characteristics of fatigue crowd based on the database provided by Physio-Net. We therefore draw the conclusion that the accuracy of Welch analyzing HRV combining with appropriate window function has been improved enormously, and when the person changes to fatigue, the vagal activity is diminished and sympathetic activity is raised.

  5. Estimating Indirect Emissions from Land Use Change Due to Biofuels (Invited)

    NASA Astrophysics Data System (ADS)

    Reilly, J. M.

    2010-12-01

    Interest in biofuels as an alternative fuel has led to the realization that they may not be a viable low greenhouse gas alternative, even if process emissions are low, because expansions of land area in biomass crops may lead to forest destruction and hence carbon emissions.(1,2)If the concern was only direct land use effects—changes in carbon stocks on land directly used for biomass—direct measurement would be an option. However, agricultural economists recognize that if biofuels are produced from crops grown on existing cropland the crops previously grown there will likely be replaced by production elsewhere. Given international markets in agricultural products a diversion of land or part of the corn crop in the US for biofuels would result in higher market prices for corn and other crops, and thus spur land conversion almost anywhere around the world. There have now been a number of estimates of the potential land use emissions, and those estimates vary widely and are sensitive to key parameters of both the economic models used in the analysis and the representation of biophysical processes.(3,4,5)Among the important parameters are those that describe the willingness to convert unmanaged land, the ability to intensify production on existing land, the productivity of new land coming to production compared to existing cropland, demand elasticities for agricultural products, and the representation of carbon and nitrogen cycles and storage.(6,7) 1. J. Fargione, J. et al., Science 319, 1235 (2008). 2. T. Searchinger, T et al., Science 319, 1238 (2008) 3. J.M. Melillo, Science, 326: 1397-1399 (2009) 4. M. Wise et al., Science 324, 1183 (2009). 5. W. E. Tyner, et al., Land Use Changes and Consequent CO2 Emissions due to US Corn Ethanol Production: A Comprehensive Analysis, Department of Agricultural Economics, Purdue University (July 2010). 6. T. W. Hertel, The Global Supply and Demand for Agricultural Land in 2050: A Perfect Storm in the Making? AAEA Presidential

  6. Recent wetland land loss due to hurricanes: improved estimates based upon multiple source images

    USGS Publications Warehouse

    Kranenburg, Christine J.; Palaseanu-Lovejoy, Monica; Barras, John A.; Brock, John C.; Wang, Ping; Rosati, Julie D.; Roberts, Tiffany M.

    2011-01-01

    The objective of this study was to provide a moderate resolution 30-m fractional water map of the Chenier Plain for 2003, 2006 and 2009 by using information contained in high-resolution satellite imagery of a subset of the study area. Indices and transforms pertaining to vegetation and water were created using the high-resolution imagery, and a threshold was applied to obtain a categorical land/water map. The high-resolution data was used to train a decision-tree classifier to estimate percent water in a lower resolution (Landsat) image. Two new water indices based on the tasseled cap transformation were proposed for IKONOS imagery in wetland environments and more than 700 input parameter combinations were considered for each Landsat image classified. Final selection and thresholding of the resulting percent water maps involved over 5,000 unambiguous classified random points using corresponding 1-m resolution aerial photographs, and a statistical optimization procedure to determine the threshold at which the maximum Kappa coefficient occurs. Each selected dataset has a Kappa coefficient, percent correctly classified (PCC) water, land and total greater than 90%. An accuracy assessment using 1,000 independent random points was performed. Using the validation points, the PCC values decreased to around 90%. The time series change analysis indicated that due to Hurricane Rita, the study area lost 6.5% of marsh area, and transient changes were less than 3% for either land or water. Hurricane Ike resulted in an additional 8% land loss, although not enough time has passed to discriminate between persistent and transient changes.

  7. A Structural Weight Estimation Program (SWEEP) for Aircraft. Volume 4 - Material Properties, Structure Temperature, Flutter and Fatigue

    DTIC Science & Technology

    1974-06-01

    3 NUMBER OF PAGES -Agfr ^K IS. SECURITY CLASS, (ol Ihl...Section -y I’art 3 - l-’atiguc Module II III INTROlHICnON /VN1) SUMMiY Progr.’un objectives Approacli to l-’atlgue Evaluation Summary of...IHfiwifmMiwK’wwwm^^ r.vimf’r n.r-frtrrriniwwv’w* IVI* m’r>Tr’*’’<’>7’fV"li*W’!l.Jl^!»’-’«’m ■ lyure Title Page Part 3 - Fatigue Module 30

  8. Pedigree error due to extra-pair reproduction substantially biases estimates of inbreeding depression.

    PubMed

    Reid, Jane M; Keller, Lukas F; Marr, Amy B; Nietlisbach, Pirmin; Sardell, Rebecca J; Arcese, Peter

    2014-03-01

    Understanding the evolutionary dynamics of inbreeding and inbreeding depression requires unbiased estimation of inbreeding depression across diverse mating systems. However, studies estimating inbreeding depression often measure inbreeding with error, for example, based on pedigree data derived from observed parental behavior that ignore paternity error stemming from multiple mating. Such paternity error causes error in estimated coefficients of inbreeding (f) and reproductive success and could bias estimates of inbreeding depression. We used complete "apparent" pedigree data compiled from observed parental behavior and analogous "actual" pedigree data comprising genetic parentage to quantify effects of paternity error stemming from extra-pair reproduction on estimates of f, reproductive success, and inbreeding depression in free-living song sparrows (Melospiza melodia). Paternity error caused widespread error in estimates of f and male reproductive success, causing inbreeding depression in male and female annual and lifetime reproductive success and juvenile male survival to be substantially underestimated. Conversely, inbreeding depression in adult male survival tended to be overestimated when paternity error was ignored. Pedigree error stemming from extra-pair reproduction therefore caused substantial and divergent bias in estimates of inbreeding depression that could bias tests of evolutionary theories regarding inbreeding and inbreeding depression and their links to variation in mating system.

  9. Postdialysis fatigue.

    PubMed

    Sklar, A H; Riesenberg, L A; Silber, A K; Ahmed, W; Ali, A

    1996-11-01

    To clarify the demographic and clinicolaboratory features of postdialysis fatigue (PDF), we enrolled 85 patients on maintenance hemodialysis in a cross-sectional study using validated questionnaires and chart review. Forty-three patients complained of fatigue after dialysis. On formal testing using the Kidney Disease Questionnaire, the PDF group had statistically greater severity of fatigue and somatic complaints than the group of patients without subjective fatigue (P = 0.03 and 0.04, respectively). On a scale measuring intensity of fatigue (1 = least to 5 = worst), the PDF group average was 3.4 +/- 1.2. PDF subjects reported that 80% +/- 25% of dialysis treatments were followed by fatigue symptoms. In 28 (65%) of patients, the symptoms started with the first dialysis treatment. They reported needing an average of 4.8 hours of rest or sleep to overcome the fatigue symptoms (range, 0 to 24 hours). There were no significant differences between patients with and without PDF in the following parameters: age; sex; type of renal disease; presence of diabetes mellitus, heart disease (congestive, ischemic), or chronic obstructive lung disease; blood pressure response to dialysis; type or adequacy of dialysis regimen; hematocrit; electrolytes; blood urea nitrogen; creatinine; cholesterol; albumin; parathyroid hormone; ejection fraction; and use of antihistamines, benzodiazepines, and narcotics. In the fatigue group, there was significantly greater use of antihypertensive medications known to have fatigue as a side effect (P = 0.007). Depression was more common in the fatigue group by Beck Depression score (11.6 +/- 8.0 v 7.8 +/- 6.3; P = 0.02). We conclude that (1) postdialysis fatigue is a common, often incapacitating symptom in patients on chronic extracorporeal dialysis; (2) no routinely measured parameter of clinical or dialytic function appears to predict postdialysis fatigue; and (3) depression is highly associated with postdialysis fatigue, but the cause

  10. Fatigue life of laser cut metals

    NASA Technical Reports Server (NTRS)

    Martin, M. R.

    1986-01-01

    Fatigue tests were conducted to determine the actual reduction in fatigue life due to weight removal for balancing by: hand grinding, low power (20 watt) Nd:glass laser, and high power (400 watt) Nd:YAG laser.

  11. Estimation of blood alcohol concentration in deaths due to roadside accidents.

    PubMed

    Arora, Puneet; Chanana, Ashok; Tejpal, Hakumat R

    2013-05-01

    Like any other disease, accidents too are caused by interaction between agent, host, and environment. Human factors include age, (accidents most common between 10 and 24 years), sex, education, medical conditions (heart attack, impaired vision), fatigue, influence of alcohol and other drugs, lack of bodily protection (like helmets, seat belts) and psychosocial factors like lack of experience, impulsiveness, aggressiveness, defective judgment and delay in decisions. Drunken driving is an important risk factor in causing accidents. This study was focused on the status of alcohol consumption in relation with roadside accidents in northern India in the region of Amritsar. The present study was carried out in 100 cases alleged to have died of roadside accident and brought to the mortuary attached to the Department of Forensic Medicine and Toxicology, Government Medical College, Amritsar for autopsy examination. Blood samples were collected from the femoral vein and were tested for the presence of alcohol with steam distillation and titration method using potassium dichromate and sulfuric acid. In the present study, 23% of the fatal driver/pedestrian victims of roadside accidents were found to have consumed alcohol before accident. Most of the victims of road accident were from the age group 21-30 and 31-40 years. Most of the accidents occurred on straight roads instead of bends or intersections, more during daytime and weekends. 57% of the blood alcohol positives were between 100 mg% and 149 mg%. Majority of the victims of roadside accidents were motorcyclists and the striking vehicles were trucks and buses causing head & neck injuries in most of the victims. Death occurred within a few minutes in most of the cases.

  12. Limitation of Ground-based Estimates of Solar Irradiance Due to Atmospheric Variations

    NASA Technical Reports Server (NTRS)

    Wen, Guoyong; Cahalan, Robert F.; Holben, Brent N.

    2003-01-01

    The uncertainty in ground-based estimates of solar irradiance is quantitatively related to the temporal variability of the atmosphere's optical thickness. The upper and lower bounds of the accuracy of estimates using the Langley Plot technique are proportional to the standard deviation of aerosol optical thickness (approx. +/- 13 sigma(delta tau)). The estimates of spectral solar irradiance (SSI) in two Cimel sun photometer channels from the Mauna Loa site of AERONET are compared with satellite observations from SOLSTICE (Solar Stellar Irradiance Comparison Experiment) on UARS (Upper Atmospheric Research Satellite) for almost two years of data. The true solar variations related to the 27-day solar rotation cycle observed from SOLSTICE are about 0.15% at the two sun photometer channels. The variability in ground-based estimates is statistically one order of magnitude larger. Even though about 30% of these estimates from all Level 2.0 Cimel data fall within the 0.4 to approx. 0.5% variation level, ground-based estimates are not able to capture the 27-day solar variation observed from SOLSTICE.

  13. Chronic fatigue and chronic fatigue syndrome: shifting boundaries and attributions.

    PubMed

    Lloyd, A R

    1998-09-28

    The subjective symptom of "fatigue" is one of the most widespread in the general population and is a major source of healthcare utilization. Prolonged fatigue is often associated with neuropsychological and musculoskeletal symptoms that form the basis of several syndromal diagnoses including chronic fatigue syndrome, fibromyalgia, and neurasthenia, and is clearly not simply the result of a lack of force generation from the muscle. Current epidemiologic research in this area relies predominantly on self-report data to document the prevalence and associations of chronic fatigue. Of necessity, this subjective data source gives rise to uncertain diagnostic boundaries and consequent divergent epidemiologic, clinical, and pathophysiologic research findings. This review will highlight the impact of the case definition and ascertainment methods on the varying prevalence estimates of chronic fatigue syndrome and patterns of reported psychological comorbidty. It will also evaluate the evidence for a true postinfective fatigue syndrome.

  14. Risk assessment in diabetes management: how do general practitioners estimate risks due to diabetes?

    PubMed Central

    Häussler, Bertram; Fischer, Gisela C; Meyer, Sibylle; Sturm, Diethard

    2007-01-01

    Objectives To evaluate the ability of general practitioners (GPs) in Germany to estimate the risk of patients with diabetes developing complications. Methods An interview study using a structured questionnaire to estimate risks of four case vignettes having diabetes‐specific complications within the next 10 years, risk reduction and life expectancy potential. A representative random sample of 584 GPs has been drawn, of which 150 could be interviewed. We compared GPs' estimates among each other (intraclass correlation coefficient (ICC) and Cohen's (multirater‐) κ) and with risks for long‐term complications generated by the multifactor disease model “Mellibase”, which is a knowledge‐based support system for medical decision management. Results The risk estimates by GPs varied widely (ICC 0.21 95% CI (0.13 to 0.36)). The average level of potential risk reduction was between 47% and 70%. Compared with Mellibase values, on average, the GPs overestimated the risk threefold. Mean estimates of potential prolongation of life expectancy were close to 10 years for each patient, whereas the Mellibase calculations ranged from 3 to 10 years. Conclusions Overestimation could lead to unnecessary care and waste of resources. PMID:17545348

  15. Fatigue in advanced cancer: a prospective study.

    PubMed

    Hauser, Katherine; Walsh, Declan; Rybicki, Lisa A; Davis, Mellar P; Seyidova-Khoshknabi, Dilara

    2008-01-01

    Fatigue is a common advanced cancer symptom. Clinical features are not well known. The authors surveyed consecutive patients admitted to a palliative medicine program to identify clinical correlates of fatigue. Data collected included age, sex, performance status, primary site, prior chemotherapy/radiation therapy, and blood transfusions. Visual analogue scales assessed fatigue, quality of life, and ability to perform daily activities. Weight change was estimated. Laboratory results including lactate dehydrogenase and hemoglobin were recorded. Fatigue severity was associated with brain metastases, poor performance status, poor quality of life, and reduced ability to perform activities. Prior radiation therapy was associated with less severe fatigue. Age, sex, and hemoglobin level were not associated with fatigue. Fatigue was universal on referral. Brain metastases and poor quality of life independently predicted severity. Hemoglobin level did not predict fatigue. Further studies are necessary to define the clinical features and relationships of fatigue.

  16. Estimated trichloroethene transformation rates due to naturally occurring biodegradation in a fractured-rock aquifer

    USGS Publications Warehouse

    Chapelle, Francis H.; Lacombe, Pierre J.; Bradley, Paul M.

    2012-01-01

    Rates of trichloroethene (TCE) mass transformed by naturally occurring biodegradation processes in a fractured rock aquifer underlying a former Naval Air Warfare Center (NAWC) site in West Trenton, New Jersey, were estimated. The methodology included (1) dividing the site into eight elements of equal size and vertically integrating observed concentrations of two daughter products of TCE biodegradation–cis-dichloroethene (cis-DCE) and chloride–using water chemistry data from a network of 88 observation wells; (2) summing the molar mass of cis-DCE, the first biodegradation product of TCE, to provide a probable underestimate of reductive biodegradation of TCE, (3) summing the molar mass of chloride, the final product of chlorinated ethene degradation, to provide a probable overestimate of overall biodegradation. Finally, lower and higher estimates of aquifer porosities and groundwater residence times were used to estimate a range of overall transformation rates. The highest TCE transformation rates estimated using this procedure for the combined overburden and bedrock aquifers was 945 kg/yr, and the lowest was 37 kg/yr. However, hydrologic considerations suggest that approximately 100 to 500 kg/yr is the probable range for overall TCE transformation rates in this system. Estimated rates of TCE transformation were much higher in shallow overburden sediments (approximately 100 to 500 kg/yr) than in the deeper bedrock aquifer (approximately 20 to 0.15 kg/yr), which reflects the higher porosity and higher contaminant mass present in the overburden. By way of comparison, pump-and-treat operations at the NAWC site are estimated to have removed between 1,073 and 1,565 kg/yr of TCE between 1996 and 2009.

  17. A method for estimating the rolling moment due to spin rate for arbitrary planform wings

    NASA Technical Reports Server (NTRS)

    Poppen, W. A., Jr.

    1985-01-01

    The application of aerodynamic theory for estimating the force and moments acting upon spinning airplanes is of interest. For example, strip theory has been used to generate estimates of the aerodynamic characteristics as a function of spin rate for wing-dominated configurations for angles of attack up to 90 degrees. This work, which had been limited to constant chord wings, is extended here to wings comprised of tapered segments. Comparison of the analytical predictions with rotary balance wind tunnel results shows that large discrepancies remain, particularly for those angles-of-attack greater than 40 degrees.

  18. Estimating How Often Mass Extinctions Due to Impacts Occur on the Earth

    NASA Technical Reports Server (NTRS)

    Buratti, Bonnie J.

    2013-01-01

    This hands-on, inquiry based activity has been taught at JPL's summer workshop "Teachers Touch the Sky" for the past two decades. Students act as mini-investigators as they gather and analyze data to estimate how often an impact large enough to cause a mass extinction occurs on the Earth. Large craters are counted on the Moon, and this number is extrapolated to the size of the Earth. Given the age of the Solar System, the students can then estimate how often large impacts occur on the Earth. This activity is based on an idea by Dr. David Morrison, NASA Ames Research Center.

  19. Probabilistic Fatigue Damage Program (FATIG)

    NASA Technical Reports Server (NTRS)

    Michalopoulos, Constantine

    2012-01-01

    FATIG computes fatigue damage/fatigue life using the stress rms (root mean square) value, the total number of cycles, and S-N curve parameters. The damage is computed by the following methods: (a) traditional method using Miner s rule with stress cycles determined from a Rayleigh distribution up to 3*sigma; and (b) classical fatigue damage formula involving the Gamma function, which is derived from the integral version of Miner's rule. The integration is carried out over all stress amplitudes. This software solves the problem of probabilistic fatigue damage using the integral form of the Palmgren-Miner rule. The software computes fatigue life using an approach involving all stress amplitudes, up to N*sigma, as specified by the user. It can be used in the design of structural components subjected to random dynamic loading, or by any stress analyst with minimal training for fatigue life estimates of structural components.

  20. Dynamic modelling and estimation of the error due to asynchronism in a redundant asynchronous multiprocessor system

    NASA Technical Reports Server (NTRS)

    Huynh, Loc C.; Duval, R. W.

    1986-01-01

    The use of Redundant Asynchronous Multiprocessor System to achieve ultrareliable Fault Tolerant Control Systems shows great promise. The development has been hampered by the inability to determine whether differences in the outputs of redundant CPU's are due to failures or to accrued error built up by slight differences in CPU clock intervals. This study derives an analytical dynamic model of the difference between redundant CPU's due to differences in their clock intervals and uses this model with on-line parameter identification to idenitify the differences in the clock intervals. The ability of this methodology to accurately track errors due to asynchronisity generate an error signal with the effect of asynchronisity removed and this signal may be used to detect and isolate actual system failures.

  1. Estimating mortality, morbidity and disability due to malaria among Africa's non-pregnant population.

    PubMed Central

    Snow, R. W.; Craig, M.; Deichmann, U.; Marsh, K.

    1999-01-01

    The contribution of malaria to morbidity and mortality among people in Africa has been a subject of academic interest, political advocacy, and speculation. National statistics for much of sub-Saharan Africa have proved to be an unreliable source of disease-specific morbidity and mortality data. Credible estimates of disease-specific burdens are required for setting global and national priorities for health in order to rationalize the use of limited resources and lobby for financial support. We have taken an empirical approach to defining the limits of Plasmodium falciparum transmission across the continent and interpolated the distributions of projected populations in 1995. By combining a review of the literature on malaria in Africa and models of acquired functional immunity, we have estimated the age-structured rates of the fatal, morbid and disabling sequelae following exposure to malaria infection under different epidemiological conditions. PMID:10516785

  2. One strategy for estimating the potential soil carbon storage due to CO{sub 2} fertilization

    SciTech Connect

    Harrison, K.G.; Bonani, G.

    1994-06-01

    Soil radiocarbon measurements can be used to estimate soil carbon turnover rates and inventories. A labile component of soil carbon has the potential to respond to perturbations such as CO{sub 2} fertilization, changing climate, and changing land use. Soil carbon has influenced past and present atmospheric CO{sub 2} levels and will influence future levels. A model is used to calculate the amount of additional carbon stored in soil because of CO{sub 2} fertilization.

  3. Estimation of true incidence of polio: overcoming misclassification errors due to stool culture insensitivity.

    PubMed

    Srinivas, V; Puliyel, Jacob M

    2007-08-01

    The diagnosis of polio dependents on culturing the virus in stool samples of children with AFP. Using data obtained under the "Right to Information Act" of instances where only one of the two samples was positive for polio, it was possible to estimate the sensitivity of the system to detect cases of polio. The calculations suggest that there were 1625 (95% CI 1528 to 1725) cases of polio in India in 2006 rather than the 674 reported widely!

  4. Multimodel estimates of premature human mortality due to intercontinental transport of air pollution

    NASA Astrophysics Data System (ADS)

    Liang, C.; Silva, R.; West, J. J.; Sudo, K.; Lund, M. T.; Emmons, L. K.; Takemura, T.; Bian, H.

    2015-12-01

    Numerous modeling studies indicate that emissions from one continent influence air quality over others. Reducing air pollutant emissions from one continent can therefore benefit air quality and health on multiple continents. Here, we estimate the impacts of the intercontinental transport of ozone (O3) and fine particulate matter (PM2.5) on premature human mortality by using an ensemble of global chemical transport models coordinated by the Task Force on Hemispheric Transport of Air Pollution (TF HTAP). We use simulations of 20% reductions of all anthropogenic emissions from 13 regions (North America, Central America, South America, Europe, Northern Africa, Sub-Saharan Africa, Former Soviet Union, Middle East, East Asia, South Asia, South East Asia, Central Asia, and Australia) to calculate their impact on premature mortality within each region and elsewhere in the world. To better understand the impact of potential control strategies, we also analyze premature mortality for global 20% perturbations from five sectors individually: power and industry, ground transport, forest and savannah fires, residential, and others (shipping, aviation, and agriculture). Following previous studies, premature human mortality resulting from each perturbation scenario is calculated using a health impact function based on a log-linear model for O3 and an integrated exposure response model for PM2.5 to estimate relative risk. The spatial distribution of the exposed population (adults aged 25 and over) is obtained from the LandScan 2011 Global Population Dataset. Baseline mortality rates for chronic respiratory disease, ischemic heart disease, cerebrovascular disease, chronic obstructive pulmonary disease, and lung cancer are estimated from the GBD 2010 country-level mortality dataset for the exposed population. Model results are regridded from each model's original grid to a common 0.5°x0.5° grid used to estimate mortality. We perform uncertainty analysis and evaluate the sensitivity

  5. Fatigue in systemic lupus erythematosus.

    PubMed

    Ahn, Grace E; Ramsey-Goldman, Rosalind

    2012-04-01

    Systemic lupus erythematosus is a chronic inflammatory autoimmune disease often characterized by fatigue, with significant effects on physical functioning and wellbeing. The definition, prevalence and factors associated with fatigue, including physical activity, obesity, sleep, depression, anxiety, mood, cognitive dysfunction, vitamin D deficiency/insufficiency, pain, effects of medications and comorbidities, as well as potential therapeutic options of fatigue in the systemic lupus erythematosus population are reviewed. Due to variability in the reliability and validity of various fatigue measures used in clinical studies, clinical trial data have been challenging to interpret. Further investigation into the relationships between these risk factors and fatigue, and improved measures of fatigue, may lead to an improvement in the management of this chronic inflammatory disease.

  6. Creep-Fatigue Interaction Testing

    NASA Technical Reports Server (NTRS)

    Halford, Gary R.

    2001-01-01

    Fatigue fives in metals are nominally time independent below 0.5 T(sub Melt). At higher temperatures, fatigue lives are altered due to time-dependent, thermally activated creep. Conversely, creep rates are altered by super. imposed fatigue loading. Creep and fatigue generally interact synergistically to reduce material lifetime. Their interaction, therefore, is of importance to structural durability of high-temperature structures such as nuclear reactors, reusable rocket engines, gas turbine engines, terrestrial steam turbines, pressure vessel and piping components, casting dies, molds for plastics, and pollution control devices. Safety and lifecycle costs force designers to quantify these interactions. Analytical and experimental approaches to creep-fatigue began in the era following World War II. In this article experimental and life prediction approaches are reviewed for assessing creep-fatigue interactions of metallic materials. Mechanistic models are also discussed briefly.

  7. Estimating the change in asymptotic direction due to secular changes in the geomagnetic field

    NASA Technical Reports Server (NTRS)

    Flueckiger, E. O.; Smart, D. F.; Shea, M. A.; Gentile, L. C.; Bathurat, A. A.

    1985-01-01

    The concept of geomagnetic optics, as described by the asymptotic directions of approach, is extremely useful in the analysis of cosmic radiation data. However, when changes in cutoff occur as a result of evolution in the geomagnetic field, there are corresponding changes in the asymptotic cones of acceptance. A method is introduced of estimating the change in the asymptotic direction of approach for vertically incident cosmic ray particles from a reference set of directions at a specific epoch by considering the change in the geomagnetic cutoff.

  8. Estimated variability of real-ear insertion response (REIR) due to loudspeaker type and placement.

    PubMed

    Stone, Michael A; Moore, Brian C

    2004-05-01

    The real-ear insertion response (REIR) of a hearing aid is estimated as the difference between the aided response and the unaided response in the ear canal. Changes in the position of the loudspeaker relative to the head, between the two measurements, may reduce the accuracy of the estimate. The spatial variability of the sound field at distances close to the loudspeaker is less for a 'flat-panel' loudspeaker than for a conventional cone loudspeaker; the panel might thus lead to a reduced influence of loud-speaker position. To assess this, we measured the real-ear unaided response (REUR) as each of three loudspeakers (two cone type and one panel) was moved in a three-dimensional space centred at either 0 degrees or 45 degrees azimuth, at a distance of 50cm from a KEMAR manikin. Contrary to our expectation, the variability of the REUR was larger for the panel than for the cone loudspeakers The REUR varied less with position for the 0 degrees than for the 45 degrees azimuth. The variability of the REUR decreased with increasing distance of the loudspeaker from KEMAR. We tentatively suggest that loudspeaker-to-client distances of 40-50 cm should be used and that a 0 degrees azimuth is preferable.

  9. Model estimates of sea-level change due to anthropogenic impacts on terrestrial water storage

    NASA Astrophysics Data System (ADS)

    Pokhrel, Yadu N.; Hanasaki, Naota; Yeh, Pat J.-F.; Yamada, Tomohito J.; Kanae, Shinjiro; Oki, Taikan

    2012-06-01

    Global sea level has been rising over the past half century, according to tide-gauge data. Thermal expansion of oceans, melting of glaciers and loss of the ice masses in Greenland and Antarctica are commonly considered as the largest contributors, but these contributions do not entirely explain the observed sea-level rise. Changes in terrestrial water storage are also likely to affect sea level, but comprehensive and reliable estimates of this contribution, particularly through human water use, are scarce. Here, we estimate sea-level change in response to human impacts on terrestrial water storage by using an integrated model that simulates global terrestrial water stocks and flows (exclusive to Greenland and Antarctica) and especially accounts for human activities such as reservoir operation and irrigation. We find that, together, unsustainable groundwater use, artificial reservoir water impoundment, climate-driven changes in terrestrial water storage and the loss of water from closed basins have contributed a sea-level rise of about 0.77mmyr-1 between 1961 and 2003, about 42% of the observed sea-level rise. We note that, of these components, the unsustainable use of groundwater represents the largest contribution.

  10. An Approach for Nonlinear Fatigue Damage Evaluation in Asphalt Pavements

    NASA Astrophysics Data System (ADS)

    Rajbongshi, Pabitra; Thongram, Sonika

    2016-09-01

    Fatigue due to vehicular loads is one of the primary distress mechanisms in asphalt pavements. It happens primarily due to deterioration in asphalt material with load repetitions. Degradation of asphalt material may be evaluated using different parameters. In view of degradation, the incremental damage in a given pavement section would be different for different repetitions, even with same loadings. Therefore, the damage progression becomes nonlinear with repetitions. Accounting such nonlinearity in damage accumulation, and based on different damage evaluation parameters, this paper presents an equivalent approach for fatigue damage evaluation in asphalt pavements. Traditional fatigue equation adopted in mechanistic-empirical pavement design has been used in the present work. Four different criteria, namely number of load repetitions, asphalt stiffness reduction, strain enhancement and fatigue life reduction with repetitions are considered for damage estimation. The proposed approach could estimate same value of nonlinear damage, irrespective of the criteria used. The simplest form of criterion i.e. the number of load repetitions can be used for fatigue performance evaluation. Probabilistically, the damage propagation is also correlated and assessed with the failure probability.

  11. Dynamic strain estimation for fatigue assessment of an offshore monopile wind turbine using filtering and modal expansion algorithms

    NASA Astrophysics Data System (ADS)

    Maes, K.; Iliopoulos, A.; Weijtjens, W.; Devriendt, C.; Lombaert, G.

    2016-08-01

    Offshore wind turbines are exposed to continuous wind and wave excitation. The monitoring of high periodic strains at critical locations is important to assess the remaining lifetime of the structure. At some critical locations below the water level, direct measurements of the strains are not feasible. Response estimation techniques can then be used to estimate the strains from a limited set of response measurements and a system model. This paper compares a Kalman filtering algorithm, a joint input-state estimation algorithm, and a modal expansion algorithm, for the estimation of dynamic strains in the tower of an offshore monopile wind turbine. The algorithms make use of a model of the structure and a limited number of response measurements for the prediction of the strain responses. The strain signals obtained from the response estimation algorithms are compared to the actual measured strains in the tower.

  12. Completeness of the fossil record: Estimating losses due to small body size

    NASA Astrophysics Data System (ADS)

    Cooper, Roger A.; Maxwell, Phillip A.; Crampton, James S.; Beu, Alan G.; Jones, Craig M.; Marshall, Bruce A.

    2006-04-01

    Size bias in the fossil record limits its use for interpreting patterns of past biodiversity and ecological change. Using comparative size frequency distributions of exceptionally good regional records of New Zealand Holocene and Cenozoic Mollusca in museum archive collections, we derive first-order estimates of the magnitude of the bias against small body size and the effect of this bias on completeness of the fossil record. Our database of 3907 fossil species represents an original living pool of 9086 species, from which ˜36% have been removed by size culling, 27% from the smallest size class (<5 mm). In contrast, non-size-related losses compose only 21% of the total. In soft rocks, the loss of small taxa can be reduced by nearly 50% through the employment of exhaustive collection and preparation techniques.

  13. Detection of incoherent joint state due to inaccurate bone motion estimation.

    PubMed

    Schwartz, Cédric; Leboeuf, Fabien; Rémy-Néris, Olivier; Brochard, Sylvain; Lempereur, Mathieu; Burdin, Valérie

    2013-01-01

    In biomechanical modelling and motion analysis, the use of personalised data such as bone geometry would provide more accurate and reliable results. However, there are still a limited number of tools used to measure the evolution of articular interactions. This paper proposes a coherence index to describe the articular status of contact surfaces during motion. The index relies on a robust estimation of the evolution of surfacic interactions between the joint surfaces. The index is first compared to distance maps on simulated motions. It is then used to compare two motion capture protocols (two different localisations of the markers for scapula tracking). The results show that the index detects progressive modifications in the joint and allows distinguishing the two protocols, in accordance with the literature. In the future, the index could, among other things, be used to compare/improve biomechanical models and motion analysis protocols.

  14. Estimating Errors in Satellite Retrievals of Bio-Optical Properties due to Incorrect Aerosol Model Selection

    DTIC Science & Technology

    2011-01-01

    as Martha’s Vineyard or Venice. This is due to a large amount of cloud coverage during the year, as well as the AERONET-OC station being unavailable...can be used to produce a good result for nLw(412) for day 176. This is an instance where the MODIS image has sporadic cloud coverage, as well as haze...1989). [10] Gordon, H. R., Brown, J. W. and Evans, R. H., "Exact Rayleigh scattering calculations for use with the Nimbus -7 Coastal Zone Color

  15. Quantification and Radiological Risk Estimation Due to the Presence of Natural Radionuclides in Maiganga Coal, Nigeria

    PubMed Central

    Kolo, Matthew Tikpangi; Khandaker, Mayeen Uddin; Amin, Yusoff Mohd; Abdullah, Wan Hasiah Binti

    2016-01-01

    Following the increasing demand of coal for power generation, activity concentrations of primordial radionuclides were determined in Nigerian coal using the gamma spectrometric technique with the aim of evaluating the radiological implications of coal utilization and exploitation in the country. Mean activity concentrations of 226Ra, 232Th, and 40K were 8.18±0.3, 6.97±0.3, and 27.38±0.8 Bq kg-1, respectively. These values were compared with those of similar studies reported in literature. The mean estimated radium equivalent activity was 20.26 Bq kg-1 with corresponding average external hazard index of 0.05. Internal hazard index and representative gamma index recorded mean values of 0.08 and 0.14, respectively. These values were lower than their respective precautionary limits set by UNSCEAR. Average excess lifetime cancer risk was calculated to be 0.04×10−3, which was insignificant compared with 0.05 prescribed by ICRP for low level radiation. Pearson correlation matrix showed significant positive relationship between 226Ra and 232Th, and with other estimated hazard parameters. Cumulative mean occupational dose received by coal workers via the three exposure routes was 7.69 ×10−3 mSv y-1, with inhalation pathway accounting for about 98%. All radiological hazard indices evaluated showed values within limits of safety. There is, therefore, no likelihood of any immediate radiological health hazards to coal workers, final users, and the environment from the exploitation and utilization of Maiganga coal. PMID:27348624

  16. Estimation of surface temperature variations due to changes in sky and solar flux with elevation

    NASA Technical Reports Server (NTRS)

    Hummer-Miller, S.

    1981-01-01

    The magnitude of elevation effects due to changes in solar and sky fluxes, on interpretation of single thermal images and composite products such as temperature difference and thermal inertia, are examined. Simple expressions are derived for the diurnal behavior of the two parameters, by fitting field observations in one tropic (Hawaii) and two semi-arid climates (Wyoming and Colorado) (Hummer-Miller, 1981). It is shown that flux variations with elevation can cause changes in the mean diurnal temperature gradient from -4 to -14 degrees C/km, evaluated at 2000 m. Changes in the temperature-difference gradient of 1 to 2 degrees C/km are also produced which is equivalent to an effective thermal-inertia gradient of 100 W s(exp 1/2)/sq m-K-km. An example is presented showing an elevation effect of 12 degrees C on the day and night thermal scenes of a test site in Arizona.

  17. Estimating Orion Heat Shield Failure Due To Ablator Cracking During The EFT-1 Mission

    NASA Technical Reports Server (NTRS)

    Vander Kam, Jeremy C.; Gage, Peter

    2016-01-01

    The Orion EFT-1 heatshield suffered from two major certification challenges: First, the mechanical properties used in design were not evident in the flight hardware and second, the flight article itself cracked during fabrication. The combination of these events motivated the Orion Program to pursue an engineering-level Probabilistic Risk Assessment (PRA) as part of heatshield certification rationale. The PRA provided loss of Mission (LOM) likelihoods considering the probability of a crack occurring during the mission and the likelihood of subsequent structure over-temperature. The methods and input data for the PRA are presented along with a discussion of the test data used to anchor the results. The Orion program accepted an EFT-1 Loss of Vehicle (LOV) risk of 1-in-160,000 due to in-mission Avcoat cracking based on the results of this analysis. Conservatisms in the result, along with future considerations for Exploration Missions (EM) are also addressed.

  18. Estimation of wildfire size and risk changes due to fuels treatments

    USGS Publications Warehouse

    Cochrane, M.A.; Moran, C.J.; Wimberly, M.C.; Baer, A.D.; Finney, M.A.; Beckendorf, K.L.; Eidenshink, J.; Zhu, Z.

    2012-01-01

    Human land use practices, altered climates, and shifting forest and fire management policies have increased the frequency of large wildfires several-fold. Mitigation of potential fire behaviour and fire severity have increasingly been attempted through pre-fire alteration of wildland fuels using mechanical treatments and prescribed fires. Despite annual treatment of more than a million hectares of land, quantitative assessments of the effectiveness of existing fuel treatments at reducing the size of actual wildfires or how they might alter the risk of burning across landscapes are currently lacking. Here, we present a method for estimating spatial probabilities of burning as a function of extant fuels treatments for any wildland fire-affected landscape. We examined the landscape effects of more than 72 000 ha of wildland fuel treatments involved in 14 large wildfires that burned 314 000 ha of forests in nine US states between 2002 and 2010. Fuels treatments altered the probability of fire occurrence both positively and negatively across landscapes, effectively redistributing fire risk by changing surface fire spread rates and reducing the likelihood of crowning behaviour. Trade offs are created between formation of large areas with low probabilities of increased burning and smaller, well-defined regions with reduced fire risk.

  19. Estimation and inference on correlations between biomarkers with repeated measures and left-censoring due to minimum detection levels

    PubMed Central

    Xie, Xianhong; Xue, Xiaonan; Gange, Stephen J.; Strickler, Howard D.; Kim, Mimi Y.

    2013-01-01

    Statistical approaches for estimating and drawing inference on the correlation between two biomarkers which are repeatedly assessed over time and subject to left-censoring due to minimum detection levels are lacking. We propose a linear mixed-effects model and estimate the parameters with the Monte Carlo Expectation Maximization (MCEM) method. Inferences regarding the model parameters and the correlation between the biomarkers are performed by applying Louis’s method and the delta method. Simulation studies were conducted to compare the proposed MCEM method with existing methods including the MLE method, the multiple imputation (MI) method, and two widely used ad hoc approaches: replacing the censored values with the detection limit (DL) or with half of the detection limit (HDL). The results show that the performance of the MCEM with respect to relative bias and coverage probability for the 95% confidence interval is superior to the DL and HDL approaches and exceeds that of the MI method at medium to high levels of censoring, and the standard error estimates from the MCEM method are close to ideal. The MLE method can estimate the parameters accurately; however, a non-positive definite information matrix can occur so that the variances are not estimable. These five methods are illustrated with data from a longitudinal HIV study to estimate and draw inference on the correlation between HIV RNA levels measured in plasma and in cervical secretions at multiple time points. PMID:22714546

  20. Estimate of neutral atoms contribution to the Mercury exosphere due to a new flux of micrometeoroids

    NASA Astrophysics Data System (ADS)

    Borin, Patrizia; Bruno, Marco; Cremonese, Gabriele; Marzari, Francesco

    2010-05-01

    Meteoroid impacts are an important source of neutral atoms in the exosphere of Mercury. Recent papers attribute to impacting particles smaller than 1 cm most of the contribution to exospheric gases. In this work we calculate the vapour and neutral atoms production rates on Mercury, as due to the impacts of micrometeoroids in the size range between 5-100 μm according to the new dynamical model of Borin et al. (2009). The calculations have been performed taking into account two different calibration sources for the meteoroid flux provided by Love and Brownlee (1993) (as for Borin et al., 2009) and by Grun et al. (1985). Moreover, we give different values of the vapour production rates assuming both asteroidal and cometary sources of the dust particles (Wiegert, 2009; Dermott et al., 2002). Following the assumption that the surface of the planet is spatially homogeneous and made up of regolith with anorthositic composition (Cremonese et al., 2005) we provide the production rate for different neutral atoms.

  1. Impacts of individual fish movement patterns on estimates of mortality due to dissolved gas supersaturation in the Columbia River Basin.

    SciTech Connect

    Scheibe, Timothy D.; Richmond, Marshall C.; Fidler, Larry E.

    2002-12-31

    Spatial and temporal distributions of dissolved gases in the Columbia and Snake rivers vary due to many factors including river channel and dam geometries, operational decisions, and natural variations in flow rates. As a result, the dissolved gas exposure histories experienced by migrating juvenile salmonids can vary significantly among individual fish. A discrete, particle-based model of individual fish movements and dissolved gas exposure history has been developed and applied to examine the effects of such variability on estimates of fish mortality. The model, called the Fish Individual-based Numerical Simulator or FINS, is linked to a two-dimensional (vertically-averaged) hydrodynamic simulator that quantifies local water velocity, temperature, and dissolved gas levels as a function of river flow rates and dam operations. Simulated gas exposure histories are then input to biological mortality models to predict the effects of various river configurations on fish injury and mortality due to dissolved gas supersaturation. This model framework provides a critical linkage between hydrodynamic models of the river system and models of biological effects. FINS model parameters were estimated and validated based on observations of individual fish movements collected using radiotelemetry methods during 1997 and 1998. The model was then used to simulate exposure histories under selected operational scenarios. We compare mortality rates estimated using the FINS model approach (incorporating individual behavior and spatial and temporal variability) to those estimated using average exposure times and levels as is done in traditional lumped-parameter model approaches.

  2. Estimated Reduction in Cancer Risk due to PAH Exposures If Source Control Measures during the 2008 Beijing Olympics Were Sustained

    PubMed Central

    Jia, Yuling; Stone, Dave; Wang, Wentao; Schrlau, Jill; Tao, Shu; Massey Simonich, Staci L.

    2011-01-01

    Background The 2008 Beijing Olympic Games provided a unique case study to investigate the effect of source control measures on the reduction in air pollution, and associated inhalation cancer risk, in a Chinese megacity. Objectives We measured 17 carcinogenic polycyclic aromatic hydrocarbons (PAHs) and estimated the lifetime excess inhalation cancer risk during different periods of the Beijing Olympic Games, to assess the effectiveness of source control measures in reducing PAH-induced inhalation cancer risks. Methods PAH concentrations were measured in samples of particulate matter ≤ 2.5 μm in aerodynamic diameter (PM2.5) collected during the Beijing Olympic Games, and the associated inhalation cancer risks were estimated using a point-estimate approach based on relative potency factors. Results We estimated the number of lifetime excess cancer cases due to exposure to the 17 carcinogenic PAHs [12 priority pollutant PAHs and five high-molecular-weight (302 Da) PAHs (MW 302 PAHs)] to range from 6.5 to 518 per million people for the source control period concentrations and from 12.2 to 964 per million people for the nonsource control period concentrations. This would correspond to a 46% reduction in estimated inhalation cancer risk due to source control measures, if these measures were sustained over time. Benzo[b]fluoranthene, dibenz[a,h]anthracene, benzo[a]pyrene, and dibenzo[a,l]pyrene were the most carcinogenic PAH species evaluated. Total excess inhalation cancer risk would be underestimated by 23% if we did not include the five MW 302 PAHs in the risk calculation. Conclusions Source control measures, such as those imposed during the 2008 Beijing Olympics, can significantly reduce the inhalation cancer risk associated with PAH exposure in Chinese megacities similar to Beijing. MW 302 PAHs are a significant contributor to the estimated overall inhalation cancer risk. PMID:21632310

  3. Exposure estimation errors to nitrogen oxides on a population scale due to daytime activity away from home.

    PubMed

    Shafran-Nathan, Rakefet; Yuval; Levy, Ilan; Broday, David M

    2017-02-15

    Accurate estimation of exposure to air pollution is necessary for assessing the impact of air pollution on the public health. Most environmental epidemiology studies assign the home address exposure to the study subjects. Here, we quantify the exposure estimation error at the population scale due to assigning it solely at the residence place. A cohort of most schoolchildren in Israel (~950,000), age 6-18, and a representative cohort of Israeli adults (~380,000), age 24-65, were used. For each subject the home and the work or school addresses were geocoded. Together, these two microenvironments account for the locations at which people are present during most of the weekdays. For each subject, we estimated ambient nitrogen oxide concentrations at the home and work or school addresses using two air quality models: a stationary land use regression model and a dynamic dispersion-like model. On average, accounting for the subjects' work or school address as well as for the daily pollutant variation reduced the estimation error of exposure to ambient NOx/NO2 by 5-10ppb, since daytime concentrations at work/school and at home can differ significantly. These results were consistent regardless which air quality model as used and even for subjects that work or study close to their home. Yet, due to their usually short commute, assigning schoolchildren exposure solely at their residential place seems to be a reasonable estimation. In contrast, since adults commute for longer distances, assigning exposure of adults only at the residential place has a lower correlation with the daily weighted exposure, resulting in larger exposure estimation errors. We show that exposure misclassification can result from not accounting for the subjects' time-location trajectories through the spatiotemporally varying pollutant concentrations field.

  4. Estimating salinity intrusion effects due to climate change on the Lower Savannah River Estuary

    USGS Publications Warehouse

    Conrads, Paul A.; Roehl, Edwin A.; Daamen, Ruby C.; Cook, John B.; Sexton, Charles T.; Tufford, Daniel L.; Carbone, Gregory J.; Dow, Kristin

    2010-01-01

    alternative scenarios of interest. Important freshwater resources are located proximal to the freshwater-saltwater interface of the estuary. The Savannah National Wildlife Refuge is located in the upper portion of the Savannah River Estuary. The tidal freshwater marsh is an essential part of the 28,000-acre refuge and is home to a diverse variety of wildlife and plant communities. Two municipal freshwater intakes are located upstream from the refuge. To evaluate the impact of climate change on salinity intrusion on these resources, inputs of streamflows and mean tidal water levels were modified to incorporate estimated changes in precipitation patterns and sea-level rise appropriate for the Southeastern United States. Changes in mean tidal water levels were changed parametrically for various sea-level rise conditions. Preliminary model results at the U.S. Geological Survey (USGS) Interstate-95 streamgage (station 02198840) for a 7½-year simulation show that historical daily salinity concentrations never exceeded 0.5 practical salinity units (psu). A 1-foot sea-level rise (ft, 30.5 centimeters [cm]) would increase the number of days of salinity concentrations greater than 0.5 psu to 47 days. A 2-ft (61 cm) sea-level rise would increase the number of days to 248.

  5. A revised estimate of the processes contributing to global warming due to climate-carbon feedback

    NASA Astrophysics Data System (ADS)

    Cadule, P.; Bopp, L.; Friedlingstein, P.

    2009-07-01

    Coupled climate-carbon cycle models have shown that anthropogenic climate change has a negative effect on natural carbon sinks i.e., climate change induces a reduction in both land and ocean carbon uptake leading to an additional amount of CO2 in the atmosphere. Friedlingstein et al. (2006) concluded that such supplementary CO2 in the atmosphere would lead to an additional climate warming in 2100. However, as given by Friedlingstein et al. (2006), the role of non-CO2 greenhouse gases (GHGs) and aerosols was neglected both for their direct impact on climate and their indirect impact on the carbon cycle. Besides, the climate models used for IPCC AR4 accounted for the radiative forcing of all GHGs and anthropogenic aerosols but neglected the climate-carbon cycle feedback. In IPCC AR4, Meehl et al. (2007) attempted to reconcile these two methods in order to derive the global warming that would arise from both all anthropogenic forcings and climate-carbon cycle feedback. Here we show that the approach they used is wrong for several reasons. First, as previously done by Friedlingstein et al. (2006), they considered that the warming is proportional to the change in atmospheric CO2 concentration. This assumption leads to consider that the gain in temperature is equal to the gain in CO2. However, because of the non-linearity of the climate response to increased CO2 concentrations, the gain in temperature is lower than the gain in CO2. Second, they assumed that the temperature gains of the climate-carbon cycle feedback generated by CO2, non-CO2 GHGs and aerosols are all equal. We show here that, because of the specific spatial and temporal distribution of the radiative forcing exerted by those external perturbations, the temperature gains are all different. Based on our revised method, we found that, for the SRES A2 scenario, the projected global warming in 2100, due to increases in atmospheric CO2, non-CO2 GHGs and anthropogenic sulphate aerosols, is 2.3-5.6°C. This is

  6. Probabilistic Fatigue: Computational Simulation

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.

    2002-01-01

    Fatigue is a primary consideration in the design of aerospace structures for long term durability and reliability. There are several types of fatigue that must be considered in the design. These include low cycle, high cycle, combined for different cyclic loading conditions - for example, mechanical, thermal, erosion, etc. The traditional approach to evaluate fatigue has been to conduct many tests in the various service-environment conditions that the component will be subjected to in a specific design. This approach is reasonable and robust for that specific design. However, it is time consuming, costly and needs to be repeated for designs in different operating conditions in general. Recent research has demonstrated that fatigue of structural components/structures can be evaluated by computational simulation based on a novel paradigm. Main features in this novel paradigm are progressive telescoping scale mechanics, progressive scale substructuring and progressive structural fracture, encompassed with probabilistic simulation. These generic features of this approach are to probabilistically telescope scale local material point damage all the way up to the structural component and to probabilistically scale decompose structural loads and boundary conditions all the way down to material point. Additional features include a multifactor interaction model that probabilistically describes material properties evolution, any changes due to various cyclic load and other mutually interacting effects. The objective of the proposed paper is to describe this novel paradigm of computational simulation and present typical fatigue results for structural components. Additionally, advantages, versatility and inclusiveness of computational simulation versus testing are discussed. Guidelines for complementing simulated results with strategic testing are outlined. Typical results are shown for computational simulation of fatigue in metallic composite structures to demonstrate the

  7. High Speed Research Program Sonic Fatigue

    NASA Technical Reports Server (NTRS)

    Rizzi, Stephen A. (Technical Monitor); Beier, Theodor H.; Heaton, Paul

    2005-01-01

    The objective of this sonic fatigue summary is to provide major findings and technical results of studies, initiated in 1994, to assess sonic fatigue behavior of structure that is being considered for the High Speed Civil Transport (HSCT). High Speed Research (HSR) program objectives in the area of sonic fatigue were to predict inlet, exhaust and boundary layer acoustic loads; measure high cycle fatigue data for materials developed during the HSR program; develop advanced sonic fatigue calculation methods to reduce required conservatism in airframe designs; develop damping techniques for sonic fatigue reduction where weight effective; develop wing and fuselage sonic fatigue design requirements; and perform sonic fatigue analyses on HSCT structural concepts to provide guidance to design teams. All goals were partially achieved, but none were completed due to the premature conclusion of the HSR program. A summary of major program findings and recommendations for continued effort are included in the report.

  8. Exploring the uncertainty associated with satellite-based estimates of premature mortality due to exposure to fine particulate matter

    NASA Astrophysics Data System (ADS)

    Ford, Bonne; Heald, Colette L.

    2016-03-01

    The negative impacts of fine particulate matter (PM2.5) exposure on human health are a primary motivator for air quality research. However, estimates of the air pollution health burden vary considerably and strongly depend on the data sets and methodology. Satellite observations of aerosol optical depth (AOD) have been widely used to overcome limited coverage from surface monitoring and to assess the global population exposure to PM2.5 and the associated premature mortality. Here we quantify the uncertainty in determining the burden of disease using this approach, discuss different methods and data sets, and explain sources of discrepancies among values in the literature. For this purpose we primarily use the MODIS satellite observations in concert with the GEOS-Chem chemical transport model. We contrast results in the United States and China for the years 2004-2011. Using the Burnett et al. (2014) integrated exposure response function, we estimate that in the United States, exposure to PM2.5 accounts for approximately 2 % of total deaths compared to 14 % in China (using satellite-based exposure), which falls within the range of previous estimates. The difference in estimated mortality burden based solely on a global model vs. that derived from satellite is approximately 14 % for the US and 2 % for China on a nationwide basis, although regionally the differences can be much greater. This difference is overshadowed by the uncertainty in the methodology for deriving PM2.5 burden from satellite observations, which we quantify to be on the order of 20 % due to uncertainties in the AOD-to-surface-PM2.5 relationship, 10 % due to the satellite observational uncertainty, and 30 % or greater uncertainty associated with the application of concentration response functions to estimated exposure.

  9. Exploring the uncertainty associated with satellite-based estimates of premature mortality due to exposure to fine particulate matter

    NASA Astrophysics Data System (ADS)

    Ford, B.; Heald, C. L.

    2015-09-01

    The negative impacts of fine particulate matter (PM2.5) exposure on human health are a primary motivator for air quality research. However, estimates of the air pollution health burden vary considerably and strongly depend on the datasets and methodology. Satellite observations of aerosol optical depth (AOD) have been widely used to overcome limited coverage from surface monitoring and to assess the global population exposure to PM2.5 and the associated premature mortality. Here we quantify the uncertainty in determining the burden of disease using this approach, discuss different methods and datasets, and explain sources of discrepancies among values in the literature. For this purpose we primarily use the MODIS satellite observations in concert with the GEOS-Chem chemical transport model. We contrast results in the United States and China for the years 2004-2011. We estimate that in the United States, exposure to PM2.5 accounts for approximately 4 % of total deaths compared to 22 % in China (using satellite-based exposure), which falls within the range of previous estimates. The difference in estimated mortality burden based solely on a global model vs. that derived from satellite is approximately 9 % for the US and 4 % for China on a nationwide basis, although regionally the differences can be much greater. This difference is overshadowed by the uncertainty in the methodology for deriving PM2.5 burden from satellite observations, which we quantify to be on order of 20 % due to uncertainties in the AOD-to-surface-PM2.5 relationship, 10 % due to the satellite observational uncertainty, and 30 % or greater uncertainty associated with the application of concentration response functions to estimated exposure.

  10. Study on fatigue crack propagation characteristics around welded joint interface in complexed conditions

    NASA Astrophysics Data System (ADS)

    Ota, Akihiko; Suzuki, Naoyuki; Maeda, Yoshio; Mawari, Toshio; Matsuoka, Saburo; Nishijima, Satoshi

    1993-01-01

    Marine structures are often constructed by welding, and they are subject to repeated loading such as waves and mechanical vibrations which can create fatigue cracks and consequently break the structures. Fatigue crack propagation properties of welded joints are studied under random loading in the air, synthetic sea water, and compressive cycling. It was found that the most crucial factor that controls fatigue crack propagation was high tensile residual stress fields of welded joints. This stress constantly kept the cracks open, simplifying fatigue crack propagation, and therefore, the rate of crack propagation could be assessed with high accuracy. In the transverse matching welded joints with cracks in the center, crack closure did not occur due to the tensile residual stress constantly induced at the crack ends in the center of the test samples. Fatigue crack propagation was accelerated both in artificial sea water and in compressive cycling compared to that in the air, and the fatigue lowest values were about half. Serious crack closures occurred in compressive cycling in which dry hours exceeded 45 minutes, and the fatigue crack propagation rate deteriorated remarkably. Mean fatigue crack propagation rate under the random loading is estimated precisely using equivalent stress intensity factor limit.

  11. When the Big One Strikes Again: Estimated Losses due to a Repeat of the 1906 San Francisco Earthquake

    NASA Astrophysics Data System (ADS)

    Kircher, C. A.

    2006-12-01

    The 1906 San Francisco Earthquake, estimated to have a magnitude of 7.9, changed the history of California and indeed the whole nation. The earthquake and the associated fires caused about 3,000 deaths and 524 million in property damage. Much has changed since 1906. What would happen if an earthquake like that of 1906 were to happen today? Here I present results of an ongoing study of building damage and losses likely to occur due to a repeat of the 1906 San Francisco earthquake, using the HAZUS technology. Recent work by Boatwright et al. (2006) provides estimates of spectral response accelerations derived from observations of modified Mercalli intensities (MMI) in the 1906 event. In one scenario we calculate damage and loss estimates using those estimated ground motions. In another we use a method consistent with current seismic provisions of building codes for a magnitude M7.9 event on the San Andreas Fault. Our study region includes 19 counties covering 24,000 square miles, with a population of more than ten million people and about 1.5 trillion of building and contents exposure. The majority of this property and population is within 40 km (25 miles) of the San Andreas Fault. The current population of this Northern California region is about ten times what it was in 1906, and the replacement value of buildings is about 500 times greater. Despite improvements in building codes and construction practices, the growth of the region over the past 100 years causes the range of estimated fatalities, from approximately 800 to about 3,400 depending on time of day and other variables, to be comparable to what it was in 1906. The forecast property loss to buildings ranges from 90 to 120 billion. From 7,000 to 10,000 commercial buildings in the region may be closed due to serious damage; and about 160,000 to 250,000 households may be displaced from damaged residences. Losses due to fire following earthquake, as well as losses to utility and transportation systems, would be

  12. Estimating PM2.5-associated mortality increase in California due to the Volkswagen emission control defeat device

    NASA Astrophysics Data System (ADS)

    Wang, Tianyang; Jerrett, Michael; Sinsheimer, Peter; Zhu, Yifang

    2016-11-01

    The Volkswagen Group of America (VW) was found by the US Environmental Protection Agency (EPA) and the California Air Resources Board (CARB) to have installed "defeat devices" and emit more oxides of nitrogen (NOx) than permitted under current EPA standards. In this paper, we quantify the hidden NOx emissions from this so-called VW scandal and the resulting public health impacts in California. The NOx emissions are calculated based on VW road test data and the CARB Emission Factors (EMFAC) model. Cumulative hidden NOx emissions from 2009 to 2015 were estimated to be over 3500 tons. Adult mortality changes were estimated based on ambient fine particulate matter (PM2.5) change due to secondary nitrate formation and the related concentration-response functions. We estimated that hidden NOx emissions from 2009 to 2015 have resulted in a total of 12 PM2.5-associated adult mortality increases in California. Most of the mortality increase happened in metropolitan areas, due to their high population and vehicle density.

  13. Analysis of Muscle Fatigue Progression using Cyclostationary Property of Surface Electromyography Signals.

    PubMed

    Karthick, P A; Venugopal, G; Ramakrishnan, S

    2016-01-01

    Analysis of neuromuscular fatigue finds various applications ranging from clinical studies to biomechanics. Surface electromyography (sEMG) signals are widely used for these studies due to its non-invasiveness. During cyclic dynamic contractions, these signals are nonstationary and cyclostationary. In recent years, several nonstationary methods have been employed for the muscle fatigue analysis. However, cyclostationary based approach is not well established for the assessment of muscle fatigue. In this work, cyclostationarity associated with the biceps brachii muscle fatigue progression is analyzed using sEMG signals and Spectral Correlation Density (SCD) functions. Signals are recorded from fifty healthy adult volunteers during dynamic contractions under a prescribed protocol. These signals are preprocessed and are divided into three segments, namely, non-fatigue, first muscle discomfort and fatigue zones. Then SCD is estimated using fast Fourier transform accumulation method. Further, Cyclic Frequency Spectral Density (CFSD) is calculated from the SCD spectrum. Two features, namely, cyclic frequency spectral area (CFSA) and cyclic frequency spectral entropy (CFSE) are proposed to study the progression of muscle fatigue. Additionally, degree of cyclostationarity (DCS) is computed to quantify the amount of cyclostationarity present in the signals. Results show that there is a progressive increase in cyclostationary during the progression of muscle fatigue. CFSA shows an increasing trend in muscle fatiguing contraction. However, CFSE shows a decreasing trend. It is observed that when the muscle progresses from non-fatigue to fatigue condition, the mean DCS of fifty subjects increases from 0.016 to 0.99. All the extracted features found to be distinct and statistically significant in the three zones of muscle contraction (p < 0.05). It appears that these SCD features could be useful in the automated analysis of sEMG signals for different neuromuscular conditions.

  14. Chronic Fatigue Syndrome

    MedlinePlus

    Chronic fatigue syndrome (CFS) is a disorder that causes extreme fatigue. This fatigue is not the kind of tired feeling that ... activities. The main symptom of CFS is severe fatigue that lasts for 6 months or more. You ...

  15. Estimation of 210Po and its risk to human beings due to consumption of marine species at Mumbai, India.

    PubMed

    Mishra, S; Bhalke, S; Pandit, G G; Puranik, V D

    2009-07-01

    (210)Po was estimated in the edible muscle and soft tissue of 15 different marine species (fish, crab, prawn and bivalve) collected from Trans-Thane Creek area (Trombay) and Thane. Potential risks associated with consumption of marine organisms due to (210)Po collected from this particular area to human beings were assessed. Estimation of (210)Po was carried out using radiochemical separation and alpha spectrometric technique. The concentration of (210)Po was found to vary from 0.18 to 10.9 Bqkg(-1) wet wt in different biota species and maximum concentrations were observed in bivalves. The variations in (210)Po concentration in different species are mainly due to difference in metabolism and feeding habits. The daily intake and individual dose of (210)Po to human beings through biota consumption was calculated and found to be 31.89 mBqd(-1) and 19.44 microSvyr(-1), respectively. An assessment of the risk on human beings due to consumption of marine organism was undertaken using carcinogenic slope factor for (210)Po. 5th, 50th and 95th percentile of life time risk was calculated to be 9.74E-06, 4.39E-05 and 2.12E-04, respectively.

  16. An estimate by two methods of thyroid absorbed doses due to BRAVO fallout in several northern Marshall Islands

    SciTech Connect

    Musolino, S.V.; Hull, A.P.; Greenhouse, N.A.

    1997-10-01

    Estimates of the thyroid absorbed doses due to fallout originating from the 1 March 1954 BRAVO thermonuclear test on Bikini Atoll have been made for several inhabited locations in the Northern Marshall Islands. Rongelap, Utirik, Rongerik and Ailinginae Atolls were also inhabited on 1 March 1954, where retrospective thyroid absorbed doses have previously been reconstructed. Current estimates are based primarily on external exposure data, which were recorded shortly after each nuclear test in the Castle Series, and secondarily on soil concentrations of {sup 137}Cs in samples collected in 1978 and 1988, along with aerial monitoring done in 1978. External exposures and {sup 137}Cs Soil concentrations were representative of the atmospheric transport and deposition patterns of the entire Castle Series tests and show that the BRAVO test was the major contributor to fallout exposure during the Castle series and other test series which were carried out in the Marshall Islands. These data have been used as surrogates for fission product radioiodines and telluriums in order to estimate the range of thyroid absorbed doses that may have occurred throughout the Marshall Islands. Dosimetry based on these two sets of estimates agreed within a factor of 4 at the locations where BRAVO was the dominant contributor to the total exposure and deposition. Both methods indicate that thyroid absorbed doses in the range of 1 Gy (100 rad) may have been incurred in some of the northern locations, whereas the doses at southern locations did not significantly exceed levels comparable to those from worldwide fallout. The results of these estimates indicate that a systematic medical survey for thyroid disease should be conducted, and that a more definitive dose reconstruction should be made for all the populated atolls and islands in the Northern Marshall Islands beyond Rongelap, Utirik, Rongerik and Ailinginae, which were significantly contaminated by BRAVO fallout. 30 refs., 2 figs., 10 tabs.

  17. An estimate by two methods of thyroid absorbed doses due to BRAVO fallout in several Northern Marshall Islands.

    PubMed

    Musolino, S V; Greenhouse, N A; Hull, A P

    1997-10-01

    Estimates of the thyroid absorbed doses due to fallout originating from the 1 March 1954 BRAVO thermonuclear test on Bikini Atoll have been made for several inhabited locations in the Northern Marshall Islands. Rongelap, Utirik, Rongerik and Ailinginae Atolls were also inhabited on 1 March 1954, where retrospective thyroid absorbed doses have previously been reconstructed. The current estimates are based primarily on external exposure data, which were recorded shortly after each nuclear test in the Castle Series, and secondarily on soil concentrations of 137Cs in samples collected in 1978 and 1988, along with aerial monitoring done in 1978. The external exposures and 137Cs soil concentrations were representative of the atmospheric transport and deposition patterns of the entire Castle Series tests and show that the BRAVO test was the major contributor to fallout exposure during the Castle series and other test series which were carried out in the Marshall Islands. These data have been used as surrogates for fission product radioiodines and telluriums in order to estimate the range of thyroid absorbed doses that may have occurred throughout the Marshall Islands. Dosimetry based on these two sets of estimates agreed within a factor of 4 at the locations where BRAVO was the dominant contributor to the total exposure and deposition. Both methods indicate that thyroid absorbed doses in the range of 1 Gy (100 rad) may have been incurred in some of the northern locations, whereas the doses at southern locations did not significantly exceed levels comparable to those from worldwide fallout. The results of these estimates indicate that a systematic medical survey for thyroid disease should be conducted, and that a more definitive dose reconstruction should be made for all the populated atolls and islands in the Northern Marshall Islands beyond Rongelap, Utirik, Rongerik and Ailinginae, which were significantly contaminated by BRAVO fallout.

  18. Variation in the estimations of ETo and crop water use due to the sensor accuracy of the meteorological variables

    NASA Astrophysics Data System (ADS)

    Moratiel, R.; Martínez-Cob, A.; Latorre, B.

    2013-06-01

    In agricultural ecosystems the use of evapotranspiration (ET) to improve irrigation water management is generally widespread. Commonly, the crop ET (ETc) is estimated by multiplying the reference crop evapotranspiration (ETo) by a crop coefficient (Kc). Accurate estimation of ETo is critical because it is the main factor affecting the calculation of crop water use and water management. The ETo is generally estimated from recorded meteorological variables at reference weather stations. The main objective of this paper was assessing the effect of the uncertainty due to random noise in the sensors used for measurement of meteorological variables on the estimation of ETo, crop ET and net irrigation requirements of grain corn and alfalfa in three irrigation districts of the middle Ebro River basin. Five scenarios were simulated, four of them individually considering each recorded meteorological variable (temperature, relative humidity, solar radiation and wind speed) and a fifth scenario combining together the uncertainty of all sensors. The uncertainty in relative humidity for irrigation districts Riegos del Alto Aragón (RAA) and Bardenas (BAR), and temperature for irrigation district Canal de Aragón y Cataluña (CAC), were the two most important factors affecting the estimation of ETo, corn ET (ETc_corn), alfalfa ET (ETc_alf), net corn irrigation water requirements (IRncorn) and net alfalfa irrigation water requirements (IRnalf). Nevertheless, this effect was never greater than ±0.5% over annual scale time. The wind speed variable (Scenario 3) was the third variable more influential in the fluctuations (±) of evapotranspiration, followed by solar radiation. Considering the accuracy for all sensors over annual scale time, the variation was about ±1% of ETo, ETc_corn, ETc_alf, IRncorn, and IRnalf. The fluctuations of evapotranspiration were higher at shorter time scale. ETo daily fluctuation remained lower than 5 % during the growing season of corn and alfalfa

  19. Estimating statistical isotropy violation in CMB due to non-circular beam and complex scan in minutes

    SciTech Connect

    Pant, Nidhi; Das, Santanu; Mitra, Sanjit; Souradeep, Tarun; Rotti, Aditya E-mail: santanud@iucaa.ernet.in E-mail: sanjit@iucaa.in

    2016-03-01

    Mild, unavoidable deviations from circular-symmetry of instrumental beams along with scan strategy can give rise to measurable Statistical Isotropy (SI) violation in Cosmic Microwave Background (CMB) experiments. If not accounted properly, this spurious signal can complicate the extraction of other SI violation signals (if any) in the data. However, estimation of this effect through exact numerical simulation is computationally intensive and time consuming. A generalized analytical formalism not only provides a quick way of estimating this signal, but also gives a detailed understanding connecting the leading beam anisotropy components to a measurable BipoSH characterisation of SI violation. In this paper, we provide an approximate generic analytical method for estimating the SI violation generated due to a non-circular (NC) beam and arbitrary scan strategy, in terms of the Bipolar Spherical Harmonic (BipoSH) spectra. Our analytical method can predict almost all the features introduced by a NC beam in a complex scan and thus reduces the need for extensive numerical simulation worth tens of thousands of CPU hours into minutes long calculations. As an illustrative example, we use WMAP beams and scanning strategy to demonstrate the easability, usability and efficiency of our method. We test all our analytical results against that from exact numerical simulations.

  20. Estimating Potential Increased Bladder Cancer Risk Due to Increased Bromide Concentrations in Sources of Disinfected Drinking Waters.

    PubMed

    Regli, Stig; Chen, Jimmy; Messner, Michael; Elovitz, Michael S; Letkiewicz, Frank J; Pegram, Rex A; Pepping, T J; Richardson, Susan D; Wright, J Michael

    2015-11-17

    Public water systems are increasingly facing higher bromide levels in their source waters from anthropogenic contamination through coal-fired power plants, conventional oil and gas extraction, textile mills, and hydraulic fracturing. Climate change is likely to exacerbate this in coming years. We estimate bladder cancer risk from potential increased bromide levels in source waters of disinfecting public drinking water systems in the United States. Bladder cancer is the health end point used by the United States Environmental Protection Agency (EPA) in its benefits analysis for regulating disinfection byproducts in drinking water. We use estimated increases in the mass of the four regulated trihalomethanes (THM4) concentrations (due to increased bromide incorporation) as the surrogate disinfection byproduct (DBP) occurrence metric for informing potential bladder cancer risk. We estimate potential increased excess lifetime bladder cancer risk as a function of increased source water bromide levels. Results based on data from 201 drinking water treatment plants indicate that a bromide increase of 50 μg/L could result in a potential increase of between 10(-3) and 10(-4) excess lifetime bladder cancer risk in populations served by roughly 90% of these plants.

  1. Reliability based fatigue design and maintenance procedures

    NASA Technical Reports Server (NTRS)

    Hanagud, S.

    1977-01-01

    A stochastic model has been developed to describe a probability for fatigue process by assuming a varying hazard rate. This stochastic model can be used to obtain the desired probability of a crack of certain length at a given location after a certain number of cycles or time. Quantitative estimation of the developed model was also discussed. Application of the model to develop a procedure for reliability-based cost-effective fail-safe structural design is presented. This design procedure includes the reliability improvement due to inspection and repair. Methods of obtaining optimum inspection and maintenance schemes are treated.

  2. Model parameter estimations from residual gravity anomalies due to simple-shaped sources using Differential Evolution Algorithm

    NASA Astrophysics Data System (ADS)

    Ekinci, Yunus Levent; Balkaya, Çağlayan; Göktürkler, Gökhan; Turan, Seçil

    2016-06-01

    An efficient approach to estimate model parameters from residual gravity data based on differential evolution (DE), a stochastic vector-based metaheuristic algorithm, has been presented. We have showed the applicability and effectiveness of this algorithm on both synthetic and field anomalies. According to our knowledge, this is a first attempt of applying DE for the parameter estimations of residual gravity anomalies due to isolated causative sources embedded in the subsurface. The model parameters dealt with here are the amplitude coefficient (A), the depth and exact origin of causative source (zo and xo, respectively) and the shape factors (q and ƞ). The error energy maps generated for some parameter pairs have successfully revealed the nature of the parameter estimation problem under consideration. Noise-free and noisy synthetic single gravity anomalies have been evaluated with success via DE/best/1/bin, which is a widely used strategy in DE. Additionally some complicated gravity anomalies caused by multiple source bodies have been considered, and the results obtained have showed the efficiency of the algorithm. Then using the strategy applied in synthetic examples some field anomalies observed for various mineral explorations such as a chromite deposit (Camaguey district, Cuba), a manganese deposit (Nagpur, India) and a base metal sulphide deposit (Quebec, Canada) have been considered to estimate the model parameters of the ore bodies. Applications have exhibited that the obtained results such as the depths and shapes of the ore bodies are quite consistent with those published in the literature. Uncertainty in the solutions obtained from DE algorithm has been also investigated by Metropolis-Hastings (M-H) sampling algorithm based on simulated annealing without cooling schedule. Based on the resulting histogram reconstructions of both synthetic and field data examples the algorithm has provided reliable parameter estimations being within the sampling limits of

  3. Hysteresis and Fatigue

    NASA Astrophysics Data System (ADS)

    Erber, T.; Guralnick, S. A.; Michels, S. C.

    1993-06-01

    Fatigue in materials is the result of cumulative damage processes that are usually induced be repeated loading cycles. Since the energy dissipation associated with damage is irreversible, and the loading cycles are accompanied by the evolution of heat, the corresponding relation between stress and strain is not single-valued; but rather exhibits a memory dependence, or hysteresis. Conversely, sustained hysteresis is a necessary condition for fatigue and is related to the rate of damage accumulation. Engineering design and safety standards for estimating fatigue life are based in part on the Manson-Coffin relations between the width of stress-strain hysteresis loops and the number of loading cycles required to produce failure in test pieces. Experimental and theoretical results show that this relation can be extended into a simple phenomenological description of fatigue that directly links total hysteresis energy dissipation, the cumulation of material damage, and the average number of loading cycles leading to failure. Detailed features of the hysteresis can be understood with the help of analogies between the incremental collapse of structures and the inception and organization of damage in materials. In particular, scanning tunneling microscope measurements of the threshold of mechanical irreversibility and acoustic emission patterns may be used to check on the evolution of hysteresis at the microscopic level.

  4. Pilot Fatigue and Circadian Desynchronosis

    NASA Technical Reports Server (NTRS)

    1981-01-01

    Pilot fatigue and circadian desynchronosis, its significance to air transport safety, and research approaches, were examined. There is a need for better data on sleep, activity, and other pertinent factors from pilots flying a variety of demanding schedules. Simulation studies of flight crew performance should be utilized to determine the degree of fatigue induced by demanding schedules and to delineate more precisely the factors responsible for performance decrements in flight and to test solutions proposed to resolve problems induced by fatigue and desynchronosis. It was concluded that there is a safety problem of uncertain magnitude due to transmeridian flying and a potential problem due to fatigue associated with various factors found in air transport operations.

  5. Engineering Aspects of Fatigue Crack Propagation

    DTIC Science & Technology

    1962-01-01

    Estimating Notch-Size Effect in Fatigue Tests on Steel. NACA TN 2805, 1952. - 37 - 19. Landers, Charles B., and Hardrath, Herbert F.: Results of Axial- Load... Charles B., and Howell, F. M.: Axial-Load Fatigue Properties of 24S-T and 75S-T Aluminum Alloy as Determined in Several Laboratories. NACA TR 1190, 1954...Hardrath, Herbert F., Leybold, Herbert A., Landers, Charles B., and Hauschild, Louis W.: Fatigue-Crack Propagation in Aluminum- Alloy Box Beams. NACA

  6. Estimation of ancient organic matter transformation due to thermokarst process at the Bykovsky peninsula on Laptev Sea coast

    NASA Astrophysics Data System (ADS)

    Kholodov, A. L.; Meyer, H.; Schirrmeister, L.; Zolotareva, B.; Nicolsky, D.

    2013-12-01

    Organic carbon stored in frozen Quaternary deposits can potentially be released into the modern biogeochemical cycle due to permafrost degradation. This task takes more and more attention recently including one of the important research questions related to the quality of organic matter (OM) in permafrost. The main method of OM liability estimation is the incubation. But it is impossible to reconstruct in the lab all varieties of natural conditions and real time frames of the organics decay process. Our approach is based on the comparison of quality of OM in (1) initial edoma and (2) taberal deposits (i.e. thawed under the lakes, packed and refrozen after lake drainage). Two pairs of boreholes located at the top of edoma and within adjoining thermokarst depressions had been drilled on Bykovsky Peninsula; northern Siberia near the Lena River delta. Samples taken from permafrost cores were analyzed for TOC, C/N ratio, δ13C and composition of humus. Results show an overall decrease of the carbon pool due to partial decomposition of OM in talik under the lake. Insignificant differences of C/N ratio in original edoma (10.83 in average) and taberal deposits (11.82) point to relatively low stage of decomposition. The average δ13C in edoma is about -24‰, while in taberal deposits δ13C decreases from close to edoma (-24‰) to the bottom of taberal layer to -26‰ in the upper part with exponential trend. This trend can be explained by the increasing duration of organic decomposition within the talik under the lake at the top of the taberal layer in comparison with the bottom due to the process of talik formation. The humic acid content and the humic/fulvic acids ratio have similar patterns. Average content of humus content in edoma is 20% of TOC and ratio of humic and fulvic acids is 1. In taberal deposits content of humus increasing downward from 10 to 20% of TOC and the ratio of humic and fulvic acids is 0.8. The one-dimensional mathematical model of edoma thaw and

  7. Gross margin losses due to Salmonella Dublin infection in Danish dairy cattle herds estimated by simulation modelling.

    PubMed

    Nielsen, T D; Kudahl, A B; Østergaard, S; Nielsen, L R

    2013-08-01

    assumptions about milk yield losses for cows in the resistant or carrier stages had the greatest influence on the estimated GM losses. This was more influential in the poorer management scenarios due to increased number of infected cows. The results can be used to inform dairy farmers of the benefits of preventing introduction and controlling spread of S. Dublin. Furthermore, they can be used in cost-benefit analyses of control actions for S. Dublin both at herd and sector level.

  8. An estimation of the global burden of disease due to skin lesions caused by arsenic in drinking water.

    PubMed

    Fewtrell, Lorna; Fuge, Ron; Kay, David

    2005-06-01

    The global burden of disease due to skin lesions caused by arsenic in drinking water was estimated by combining country-based exposure data with selected exposure-response relationships derived from the literature. Populations were considered to be exposed to elevated arsenic levels if their drinking water contained arsenic concentrations of 50 microg I(-1) or greater. Elevated arsenic concentrations in drinking water result in a significant global burden of disease, even when confining the health outcome to skin lesions. The burden of disease was particularly marked in the World Health Organization (WHO) comparative risk assessment (CRA) 'Sear D' region, which includes Bangladesh, India and Nepal. Unsurprisingly, Bangladesh was the worst affected country with 143 disability adjusted life years (DALYs) per 1,000 population. Although this initial estimate is subject to a large degree of uncertainty, it does represent an important first step in allowing the comparison of the problem relating to elevated arsenic in drinking water to other environmental health outcomes.

  9. Fatigue Characterization of Fire Resistant Syntactic Foam Core Material

    NASA Astrophysics Data System (ADS)

    Hossain, Mohammad Mynul

    established for the three stress states and three types of the failure modes. This equation was used to estimate endurance limit (106 cycles) of the material. Like metallic materials, the compression fatigue life of Eco-Core was found to be dependent on the stress range instead of maximum or mean cyclic stress. Furthermore shear and flexural ultimate failure of the core material was found to be due to a combination of shear and tensile stress.

  10. Helicopter Fatigue Design Guide

    DTIC Science & Technology

    1983-11-01

    de nouveaux materiaux ou technologies accentue I’importance que presente pour les forces de I’O.T.A.N. ce probleme de la maitrise des phenomenes de...fatigue interessant les helicopteres. La commission Structures et Materiaux de I’AGARD a ete conduite a proposer et developper une serie de reflexions...service life for the suspension components due to their vulnerabihty to darnage at high speeds. Spectrum No. 2 led to limitations being applied to

  11. A semi-empirical model for the estimation of maximum horizontal displacement due to liquefaction-induced lateral spreading

    USGS Publications Warehouse

    Faris, Allison T.; Seed, Raymond B.; Kayen, Robert E.; Wu, Jiaer

    2006-01-01

    During the 1906 San Francisco Earthquake, liquefaction-induced lateral spreading and resultant ground displacements damaged bridges, buried utilities, and lifelines, conventional structures, and other developed works. This paper presents an improved engineering tool for the prediction of maximum displacement due to liquefaction-induced lateral spreading. A semi-empirical approach is employed, combining mechanistic understanding and data from laboratory testing with data and lessons from full-scale earthquake field case histories. The principle of strain potential index, based primary on correlation of cyclic simple shear laboratory testing results with in-situ Standard Penetration Test (SPT) results, is used as an index to characterized the deformation potential of soils after they liquefy. A Bayesian probabilistic approach is adopted for development of the final predictive model, in order to take fullest advantage of the data available and to deal with the inherent uncertainties intrinstiic to the back-analyses of field case histories. A case history from the 1906 San Francisco Earthquake is utilized to demonstrate the ability of the resultant semi-empirical model to estimate maximum horizontal displacement due to liquefaction-induced lateral spreading.

  12. Comprehensive chemical characterisation of size-segregated PM10 in Dresden and estimation of changes due to global warming

    NASA Astrophysics Data System (ADS)

    Scheinhardt, Sebastian; Spindler, Gerald; Leise, Silvia; Müller, Konrad; Iinuma, Yoshiteru; Zimmermann, Frank; Matschullat, Jörg; Herrmann, Hartmut

    2013-08-01

    To identify current and future human health risks from urban air pollution, size-segregated particle samples were collected under various seasonal and meteorological conditions in Dresden, Germany. Sampling days were grouped into twelve categories depending on season, air mass origin and temperature. A comprehensive chemical characterisation and mass closure were performed. The particulate matter (PM) mass concentration and composition were shown to be highly dependent on these categories. The highest PM mass concentrations were found on cold winter days, mainly due to compounds of anthropogenic origin. The current annual mean PM mass concentration and composition were calculated using the occurrence frequencies of the categories (weighted mean). Information about future changes of the occurrence frequencies of the categories was deduced from climate models. Assuming that PM concentration and composition within a given category do not change, the annual mean PM mass concentration and composition were calculated for two scenarios (weighted mean, 2071-2100). As a result, it was found that the annual mean PM mass concentration is likely to decrease slightly by 2100, mainly due to a decrease of sulphate and soot mass concentrations. Generally, chemicals originating from anthropogenic emissions (PAHs, trace metals) are estimated to decrease. However, it is concluded that emission reduction measures are still necessary to control urban air quality including PM even if climate change will lead to a certain reduction in PM.

  13. Effects of residual stress and texture on the high-cycle fatigue properties of light metals

    NASA Astrophysics Data System (ADS)

    Jiang, Xiuping

    2007-12-01

    High cycle fatigue tests were conducted on a commercially pure Ti, a forged Ti-6Al-4V alloy, and newly developed high strength AA2026 and AA2099 Al alloys in four-point bend. The effects of surface compressive residual stress and texture on the fatigue properties of these alloys were systematically investigated. The resistance to fatigue crack growth in an alloy was estimated using a simple model that took into account texture and grain structure. The resistance calculations were able to explain the observed behaviors of fatigue crack growth in planar slip materials. Due to strengthening in the surface by enhancement treatment, fatigue cracks were found to be initiated in the subsurface region in the short peened Ti-6Al-4V alloy and sandblasted CP Ti, in contrast to crack initiation on the surface of the untreated samples. When the shot peened Ti-6A1-4V alloy was tested between 25°C and 200°C, the surface compressive residual stress could only be slightly relaxed due to thermal exposure, which did not deteriorate the fatigue strength of the alloy. Similarly, no obvious redistribution of the residual stress was observed when the sandblasted Ti was annealed below 200°C. With increase in the annealing temperature (300°C˜700°C), the compressive residual stresses were significantly relaxed, leading to relatively a lower fatigue strength. In AA2026 & AA2099 Al alloys, crack growth was found to be in a predominantly crystallographic mode in unrecrystallized regions, and a non-crystallographic mode in recrystallized regions. Fatigue cracks were deflected at grain boundaries usually with small twist angles in the unrecrystallized regions, but with large twist angles in the recrystallized regions. The theoretical analysis verified that a large percentage of recrystallized grains could provide strong resistance to fatigue crack growth by producing larger twist angles of crack deflection at their grain boundaries than those of most of the gains in unrecrystallized

  14. Fatigue, Creep-Fatigue, and Thermomechanical Fatigue Life Testing of Alloys

    NASA Technical Reports Server (NTRS)

    Halford, Gary R.; Lerch, Bradley A.; McGaw, Michael A.

    2000-01-01

    low-cycle fatigue testing, wherein some prescribed indication of impending failure due to cracking is adopted. Specific criteria will be described later. As a rule, cracks that develop during testing are not measured nor are the test parameters intentionally altered owing to the presence of cracking.

  15. Low-Cycle Fatigue Life and Fatigue Crack Propagation of Sintered Ag Nanoparticles

    NASA Astrophysics Data System (ADS)

    Shioda, Ryutaro; Kariya, Yoshiharu; Mizumura, Noritsuka; Sasaki, Koji

    2017-02-01

    The low-cycle fatigue life and fatigue crack propagation behavior of sintered silver nanoparticles were investigated using miniature specimens sintered at two different temperatures. The fatigue crack initiation life and fatigue crack propagation rate of sintered Ag nanoparticles were extremely sensitive to changes in the range of inelastic energy density and the cyclic J integral, exhibiting brittle characteristics, in contrast to tin-based lead-free solder alloys. With increasing sintering temperature, the fatigue crack propagation rate decreased. On the other hand, the effect of sintering temperature on the fatigue crack initiation life differed depending on the use of either a smooth specimen (low-cycle fatigue test) or notched specimen (fatigue crack propagation test). For the notched specimens, the probability of grain boundaries around the notch decreased due to increased sintering temperature. Therefore, the fatigue crack initiation life was increased with an increase in sintering temperature in the fatigue crack propagation test. In the smooth specimen, however, the fatigue life decreased with an increase in sintering temperature, as the elastic modulus of the specimen increased with increasing sintering temperature. In the low-cycle fatigue test, the specimen sintered with high internal stress started to develop crack initiation early, causing a decrease in the crack initiation life.

  16. Chronic Fatigue Syndrome (CFS) and Cancer Related Fatigue (CRF): two "fatigue" syndromes with overlapping symptoms and possibly related aetiologies.

    PubMed

    Rovigatti, Ugo

    2012-12-01

    In July 2010, at the Muscle Fatigue Meeting, I presented an overview of Chronic Fatigue Syndrome and Cancer Related Fatigue, emphasizing a critical interpretation of the potential association between Chronic Fatigue Syndrome and Cancer Related Fatigue and a newly discovered retrovirus: Xenotropic Murine Related Virus. Since this association was hotly debated at that time, I suggested at the Meeting that it was wrong and most likely due to the identification of the wrong virus culprit. Today, 20 months after the Meeting, the first part of our prediction has turned out to be correct, as Xenotropic Murine Related Virus was shown to be a laboratory-created artefact. Still, the potential association of fatigue-syndromes with an infection (most likely viral) is sustained by a plethora of evidence and this overview will initially summarize data suggesting prior viral infection(s). The principal hypothesized mechanisms for both peripheral and central Chronic Fatigue Syndrome/Cancer Related Fatigue will be then summarized, also indicating plausible associations and triggering factors. All evidence accrued so far suggests that further research work should be performed in this interesting area and in order to identify an infectious agent for Chronic Fatigue Syndrome/Cancer Related Fatigue. One candidate RNA virus, Micro-Foci inducing Virus, will be described in this overview.

  17. Structural health monitoring and condition based fatigue damage prognosis of complex metallic structures

    NASA Astrophysics Data System (ADS)

    Mohanty, Subhasish

    Current practice in fatigue life prediction is based on assumed initial structural flaws regardless of whether these assumed flaws actually occur in service. Furthermore, the model parameters are often estimated empirically based on previous coupon test results. Small deviations of the initial conditions and model parameters may generate large errors in the expected dynamical behavior of fatigue damage growth. Consequently, a large degree of conservatism is incorporated into structural designs due to these expected uncertainties. The current research in the area of Structural Health Monitoring (SHM) and probabilistic fatigue modeling can help in improved fatigue damage modeling and remaining useful life estimation (RULE) techniques. This thesis discusses an integrated approach of SHM and adaptive prognosis model that not only estimates the current health, but can also forecast the future health and calculate RULE of an aerospace structural component with high level of confidence. The approach does not assume any fixed initial condition and model parameters. This dissertation include the following novel contributions. 1) A Bayesian based off-line Gaussian Process (GP) model is developed, which is the core of the present condition based prognosis approach. 2) Different passive and active SHM approaches are used for on-line damage state estimation. Applications of passive sensing are shown to estimate the time-series fatigue damage states both under constant and random fatigue loading. It is found that there is a good correlation between estimated damage states and optically measured damage states. In addition, applications for both narrow and broadband active sensing approaches are presented to estimate smaller incipient damage. It is demonstrated that the active sensing techniques not only can identify smaller incipient damage but also can quantify fatigue damage during all the three stages (stages I, II, and III) of fatigue life. 3) An integrated on-line SHM and

  18. Estimated crop loss due to coconut mite and financial analysis of controlling the pest using the acaricide abamectin.

    PubMed

    Rezende, Daniela; Melo, José W S; Oliveira, José E M; Gondim, Manoel G C

    2016-07-01

    Reducing the losses caused by Aceria guerreronis Keifer has been an arduous task for farmers. However, there are no detailed studies on losses that simultaneously analyse correlated parameters, and very few studies that address the economic viability of chemical control, the main strategy for managing this pest. In this study the objectives were (1) to estimate the crop loss due to coconut mite and (2) to perform a financial analysis of acaricide application to control the pest. For this, the following parameters were evaluated: number and weight of fruits, liquid albumen volume, and market destination of plants with and without monthly abamectin spraying (three harvests). The costs involved in the chemical control of A. guerreronis were also quantified. Higher A. guerreronis incidence on plants resulted in a 60 % decrease in the mean number of fruits harvested per bunch and a 28 % decrease in liquid albumen volume. Mean fruit weight remained unaffected. The market destination of the harvested fruit was also affected by higher A. guerreronis incidence. Untreated plants, with higher A. guerreronis infestation intensity, produced a lower proportion of fruit intended for fresh market and higher proportions of non-marketable fruit and fruit intended for industrial processing. Despite the costs involved in controlling A. guerreronis, the difference between the profit from the treated site and the untreated site was 18,123.50 Brazilian Real; this value represents 69.1 % higher profit at the treated site.

  19. A multi-feature integration method for fatigue crack detection and crack length estimation in riveted lap joints using Lamb waves

    NASA Astrophysics Data System (ADS)

    He, Jingjing; Guan, Xuefei; Peng, Tishun; Liu, Yongming; Saxena, Abhinav; Celaya, Jose; Goebel, Kai

    2013-10-01

    This paper presents an experimental study of damage detection and quantification in riveted lap joints. Embedded lead zirconate titanate piezoelectric (PZT) ceramic wafer-type sensors are employed to perform in situ non-destructive evaluation (NDE) during fatigue cyclical loading. PZT wafers are used to monitor the wave reflection from the boundaries of the fatigue crack at the edge of bolt joints. The group velocity of the guided wave is calculated to select a proper time window in which the received signal contains the damage information. It is found that the fatigue crack lengths are correlated with three main features of the signal, i.e., correlation coefficient, amplitude change, and phase change. It was also observed that a single feature cannot be used to quantify the damage among different specimens since a considerable variability was observed in the response from different specimens. A multi-feature integration method based on a second-order multivariate regression analysis is proposed for the prediction of fatigue crack lengths using sensor measurements. The model parameters are obtained using training datasets from five specimens. The effectiveness of the proposed methodology is demonstrated using several lap joint specimens from different manufactures and under different loading conditions.

  20. Approach for Estimating Exposures and Incremental Health Effects from Lead Due to Renovation Repair and Painting Activities in Public and Commercial Buildings

    EPA Pesticide Factsheets

    Approach for Estimating Exposures and Incremental Health Effects from Lead Due to Renovation Repair and Painting Activities in Public and Commercial Buildings: links to documents at www.regulations.gov, links to PDFs related to Approach document

  1. [Chronic fatigue syndrome: more than fatigue].

    PubMed

    Royes, Badía; Alvarez, Carballo; Lalinde, Sevillano; Vidal, Llinas; Martín, Alegre

    2010-12-01

    Chronic fatigue syndrome (CFS) is a disease recognized by all international medical organizations and WHO, and is classified under the code G93.3 of the International Classification of Diseases. Its prevalence is estimated around 2.54% being more common in women than in men (8/2) aged between 20 and 40 Is defined as a chronic new description characterized by the presence of subjective feeling of fatigue and exhaustion long disabling of more than 6 months duration that is not relieved by rest. It is a multisystem disorder that often presents a significant number of comorbid phenomena. Not known until specific tests to confirm the diagnosis, nor is there a cure to solve this health problem definitively The strongest evidence is based on the multidisciplinary approach for the symptomatic treatment of pain, sleep disorders, neurocognitive dysfunction, autonomic and control of depression and anxiety. The specific contribution of nursing to care for the person who lives and live with the SFC should be developed primarily in the field of health education and supportive care, support and assistance to help the patient and their relatives are an adaptive response to changes in health.

  2. Hysteresis and fatigue

    SciTech Connect

    Erber, T. ); Guralnick, S.A.; Michels, S.C. )

    1993-06-01

    Energy dissipation associated with damage of materials is irreversible and loading cycles are accompanied by the evolution of heat. The relation between energy dissipation and loading therefore exhibits a memory dependence or hysteresis. Conversely, sustained hysteresis is a necessary condition for fatigue and is related to the rate of damage accumulation. Standards for estimating fatigue life are partially based on the Manson-Coffin relations between the width of stress strain hysteresis loops and the number of loading cycles required to produce failure in test pieces. In the present study, experimental and theoretical results demonstrate that this relation can be extended into a simple phenomenological description of fatigue that directly links total hysteresis energy dissipation, the cumulation of material damage, and the average number of loading cycles leading to failure. Analogies between the incremental collapse of structures and the inception and organization of damage in materials are used to aid understanding of the detailed features of hysteresis. Scanning tunneling microscope measurements of the threshold of mechanical irreversibility and acoustic emission patterns are used to detect the evolution of hysteresis at the microscopic level. 61 refs., 14 figs., 1 tab.

  3. An energy-based approach to estimate seismic attenuation due to wave-induced fluid flow in heterogeneous poroelastic media

    NASA Astrophysics Data System (ADS)

    Solazzi, Santiago G.; Rubino, J. Germán; Müller, Tobias M.; Milani, Marco; Guarracino, Luis; Holliger, Klaus

    2016-11-01

    Wave-induced fluid flow (WIFF) due to the presence of mesoscopic heterogeneities is considered as one of the main seismic attenuation mechanisms in the shallower parts of the Earth's crust. For this reason, several models have been developed to quantify seismic attenuation in the presence of heterogeneities of varying complexity, ranging from periodically layered media to rocks containing fractures and highly irregular distributions of fluid patches. Most of these models are based on Biot's theory of poroelasticity and make use of the assumption that the upscaled counterpart of a heterogeneous poroelastic medium can be represented by a homogeneous viscoelastic solid. Under this dynamic-equivalent viscoelastic medium (DEVM) assumption, attenuation is quantified in terms of the ratio of the imaginary and real parts of a frequency-dependent, complex-valued viscoelastic modulus. Laboratory measurements on fluid-saturated rock samples also rely on this DEVM assumption when inferring attenuation from the phase shift between the applied stress and the resulting strain. However, whether it is correct to use an effective viscoelastic medium to represent the attenuation arising from WIFF at mesoscopic scales in heterogeneous poroelastic media remains largely unexplored. In this work, we present an alternative approach to estimate seismic attenuation due to WIFF. It is fully rooted in the framework of poroelasticity and is based on the quantification of the dissipated power and stored strain energy resulting from numerical oscillatory relaxation tests. We employ this methodology to compare different definitions of the inverse quality factor for a set of pertinent scenarios, including patchy saturation and fractured rocks. This numerical analysis allows us to verify the correctness of the DEVM assumption in the presence of different kinds of heterogeneities. The proposed methodology has the key advantage of providing the local contributions of energy dissipation to the overall

  4. Estimation of the risks of thermal stress due to the microclimate for manual fruit and vegetable harvesters in central Italy.

    PubMed

    Cecchini, M; Colantoni, A; Massantini, R; Monarca, D

    2010-07-01

    Agricultural workers are exposed to various risks, including chemical agents, noise, and many other factors. One of the most characteristic and least known risk factors is constituted by the microclimatic conditions in the different phases of work (in field, in greenhouse, etc). A typical condition is thermal stress due to high temperatures during harvesting operations in open fields or in greenhouses. In Italy, harvesting is carried out for many hours during the day, mainly in the summer, with temperatures often higher than 30 degrees C. According to ISO 7243, these conditions can be considered dangerous for workers' health. The aim of this study is to assess the risks of exposure to microclimatic conditions (heat) for fruit and vegetable harvesters in central Italy by applying methods established by international standards. In order to estimate the risk for workers, the air temperature, radiative temperature, and air speed were measured using instruments in conformity with ISO 7726. Thermodynamic parameters and two more subjective parameters, clothing and the metabolic heat production rate related to the worker's physical activity, were used to calculate the predicted heat strain (PHS) for the exposed workers in conformity with ISO 7933. Environmental and subjective parameters were also measured for greenhouse workers, according to ISO 7243, in order to calculate the wet-bulb globe temperature (WBGT). The results show a slight risk for workers during manual harvesting in the field. On the other hand, the data collected in the greenhouses show that the risk for workers must not be underestimated. The results of the study show that, for manual harvesting work in climates similar to central Italy, it is essential to provide plenty of drinking water and acclimatization for the workers in order to reduce health risks. Moreover, the study emphasizes that the possible health risks for greenhouse workers increase from the month of April through July.

  5. Nursing on empty: compassion fatigue signs, symptoms, and system interventions.

    PubMed

    Harris, Chelsia; Griffin, Mary T Quinn

    2015-01-01

    Few healthcare organizations acknowledge, discuss, or provide interventions for assisting with compassion fatigue. Yet, it is an important concept due to its individual, professional, and financial costs. This article defines compassion fatigue, differentiates it from burnout, and offers system interventions for supporting nurses and reducing compassion fatigue.

  6. Fatigue of Advanced In-Situ Composite Solders

    DTIC Science & Technology

    2007-11-02

    ABSTRACT (Maximum 200 words) " ~~" Solder joints used in surface mount technology experience thermomechanical fatigue due to the mismatches in...solder joint to undergo shear strains. The purpose of this study was to examine and explain the thermomechanical fatigue damage mechanisms of various...types of solder compositions. Shear, creep, low cycle fatigue , and thermomechanical fatigue tests were conducted in this research. The development

  7. Fatigue life extension

    NASA Technical Reports Server (NTRS)

    Matejczyk, D. E.; Lin, J.

    1985-01-01

    Potential fatigue rejuvenation processes were carried out on fatigue-damaged material both with and without observable surface-connected fatigue cracks. The fatigue life of fatigue-damaged MAR-M246(Hf)(DS), a directionally solidified nickel-base superalloy used in turbine airfoils, was extended by reheat treatment. The fatigue life of fatigue-cracked Inconel 718, a wrought nickel-base superalloy used in a wide variety of advanced rocket engine components, was extended by electron-beam welding to close off the surface-connected crack, followed by hot isostatic pressing and reheat treatment.

  8. Quantification of the uncertainty in estimates of climate system properties due to differences in available reconstructions of historical data

    NASA Astrophysics Data System (ADS)

    Forest, C. E.; Libardoni, A.; Sokolov, A. P.

    2013-12-01

    Climate models of intermediate complexity have been used extensively to help determine climate system properties because of their efficiency and ability to easily adjust key climate system components. By comparing model output over a wide range of possible states of the climate with observations, probability distributions for climate system properties can be derived. Observational data for a number of climate variables are available, and in many cases multiple reconstructions are available for the same variable. This study first evaluates how differences in the estimated historical trends of upper-air temperatures translate into uncertainty in estimates of three climate system properties: climate sensitivity, the rate of ocean heat uptake, and net aerosol forcing. These results build upon previous work that explored similar estimates associated with trends in surface temperatures and ocean heat content. Also addressed in this study is quantifying uncertainties in the estimates of the three properties associated with how surface temperature observations are used in the estimation process. Other studies have estimated climate parameters using only global mean surface temperature trends. It is shown here that estimates of all parameters are dependent upon the spatial variation of surface temperature trends. In particular, lower estimates of climate sensitivity are shown to be inconsistent with most observational data sources when using latitude-dependent surface trends. Low climate sensitivity is also shown to lead to inconsistent patterns in ocean heat uptake. These results will be presented in the context of recent investigations using data from previous work by the authors.

  9. Reduction of CO2 Emissions Due to Wind Energy - Methods and Issues in Estimating Operational Emission Reductions

    SciTech Connect

    Holttinen, Hannele; Kiviluoma, Juha; McCann, John; Clancy, Matthew; Millgan, Michael; Pineda, Ivan; Eriksen, Peter Borre; Orths, Antje; Wolfgang, Ove

    2015-10-05

    This paper presents ways of estimating CO2 reductions of wind power using different methodologies. Estimates based on historical data have more pitfalls in methodology than estimates based on dispatch simulations. Taking into account exchange of electricity with neighboring regions is challenging for all methods. Results for CO2 emission reductions are shown from several countries. Wind power will reduce emissions for about 0.3-0.4 MtCO2/MWh when replacing mainly gas and up to 0.7 MtCO2/MWh when replacing mainly coal powered generation. The paper focuses on CO2 emissions from power system operation phase, but long term impacts are shortly discussed.

  10. 75 FR 793 - Damage Tolerance and Fatigue Evaluation of Composite Rotorcraft Structures

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-01-06

    ... amendment would require evaluation of fatigue and residual static strength of composite rotorcraft... static or fatigue loads. The proposal would require consideration of the effects of fatigue damage on... applicant must show that catastrophic failure due to static and fatigue loads, considering the intrinsic...

  11. Anomalous Fatigue Behavior and Fatigue-Induced Grain Growth in Nanocrystalline Nickel Alloys

    NASA Astrophysics Data System (ADS)

    Boyce, Brad L.; Padilla, Henry A.

    2011-07-01

    Fatigue failure due to repetitive loading of metallic devices is a pervasive engineering concern. The present work reveals extraordinary fatigue resistance in nanocrystalline (NC) alloys, which appears to be associated with the small (<100 nm) grain size inhibiting traditional cyclic damage processes. In this study, we examine the fatigue performance of three electrodeposited NC Ni-based metals: Ni, Ni-0.5Mn, and Ni-22Fe (PERMALLOY). When subjected to fatigue stresses at and above the tensile yield strength where conventional coarse-grained (CG) counterparts undergo low-cycle fatigue failure (<104 cycles to failure), these alloys exhibit exceptional fatigue lives (in some cases, >107 cycles to failure). Postmortem examinations show that failed samples contain an aggregate of coarsened grains at the crack initiation site. The experimental data and accompanying microscopy suggest that the NC matrix undergoes abnormal grain growth during cyclic loading, allowing dislocation activity to persist over length scales necessary to initiate a fatigue crack by traditional fatigue mechanisms. Thus, the present observations demonstrate anomalous fatigue behavior in two regards: (1) quantitatively anomalous when considering the extremely high stress levels needed to drive fatigue failure and (2) mechanistically anomalous in light of the grain growth process that appears to be a necessary precursor to crack initiation.

  12. Evaluation of models for estimating changes in fracture permeability due to thermo-mechanical stresses in host rock surrounding a potential repository

    SciTech Connect

    Berge, P A; Blair, S C; Shaffer, R J; Wang, H F

    1997-02-18

    We provide in this report a methodology to estimate bounds on the changes in fracture permeability due to thermal-mechanical processes associated with excavation of drifts and emplacement of waste. This report is the first milestone associated with Task A of the LLNL initiative to evaluate available methods for estimating chamges in fracture permeability surrounding drifts in the Exploratory Studies Facility (ESF) and the potential repository at Yucca Mountain in response to (1) construction-induced stress changes and (2) subsequent thermal pulse effects due to waste emplacement. These results are needed for modeling changes in repository-level moisture movement and seepage.

  13. Cancer risk estimation in Belarussian children due to thyroid irradiation as a consequence of the Chernobyl nuclear accident

    SciTech Connect

    Buglova, E.; Kenigsberg, J.E.; Sergeeva, N.V.

    1996-07-01

    The thyroid doses received by the juvenile population of Belarus following the Chernobyl accident ranged up to about 10 Gy. The thyroid cancer risk estimate recommended in NCRP Report No. 80 was used to predict the number of thyroid cancer cases among children during 1990-1992 in selected Belarussian regions and cities. The results obtained using this risk estimate show an excess of thyroid cancer cases being registered vs. the predicted cases. Thyroid cancer incidence rate among boys under investigation is higher than among girls in the postaccident period. The excess of the observed over the expected incidence in the general juvenile population is caused by the high thyroid cancer incidence rate among boys. These results, which can be considered part of the first stage of a thorough thyroid cancer risk estimation after the Chernobyl accident, demonstrate the critical need to complete these studies in depth. 6 refs., 5 figs., 3 tabs.

  14. The potential for regional-scale bias in top-down CO2 flux estimates due to atmospheric transport errors

    NASA Astrophysics Data System (ADS)

    Miller, S. M.; Fung, I.; Liu, J.; Hayek, M. N.; Andrews, A. E.

    2014-09-01

    Estimates of CO2 fluxes that are based on atmospheric data rely upon a meteorological model to simulate atmospheric CO2 transport. These models provide a quantitative link between surface fluxes of CO2 and atmospheric measurements taken downwind. Therefore, any errors in the meteorological model can propagate into atmospheric CO2 transport and ultimately bias the estimated CO2 fluxes. These errors, however, have traditionally been difficult to characterize. To examine the effects of CO2 transport errors on estimated CO2 fluxes, we use a global meteorological model-data assimilation system known as "CAM-LETKF" to quantify two aspects of the transport errors: error variances (standard deviations) and temporal error correlations. Furthermore, we develop two case studies. In the first case study, we examine the extent to which CO2 transport uncertainties can bias CO2 flux estimates. In particular, we use a common flux estimate known as CarbonTracker to discover the minimum hypothetical bias that can be detected above the CO2 transport uncertainties. In the second case study, we then investigate which meteorological conditions may contribute to month-long biases in modeled atmospheric transport. We estimate 6 hourly CO2 transport uncertainties in the model surface layer that range from 0.15 to 9.6 ppm (standard deviation), depending on location, and we estimate an average error decorrelation time of ∼2.3 days at existing CO2 observation sites. As a consequence of these uncertainties, we find that CarbonTracker CO2 fluxes would need to be biased by at least 29%, on average, before that bias were detectable at existing non-marine atmospheric CO2 observation sites. Furthermore, we find that persistent, bias-type errors in atmospheric transport are associated with consistent low net radiation, low energy boundary layer conditions. The meteorological model is not necessarily more uncertain in these conditions. Rather, the extent to which meteorological uncertainties

  15. Estimation of the radiation dose in man due to 6-(/sup 18/F) fluoro-L-dopa

    SciTech Connect

    Harvey, J.; Firnau, G.; Garnett, E.S.

    1985-08-01

    The radiation dose to the organs of the human body after an intravenous administration of 6-(/sup 18/F) fluoro-L-dopa was estimated using the recommendations of the International Committee on Radiological Protection (ICRP). The bladder wall received the highest dose, and as a consequence the dose to the genitalia was high. The major organs received a dose of 5.66E- 12 to 1.87E- 11 Sv/Bq (20 to 60 mrem/mCi). The effective dose equivalent was estimated at 5.39E- 11 Sv/Bq (200 mrem/mCi).

  16. Peridynamic model for fatigue cracking.

    SciTech Connect

    Silling, Stewart Andrew; Abe Askari

    2014-10-01

    The peridynamic theory is an extension of traditional solid mechanics in which the field equations can be applied on discontinuities, such as growing cracks. This paper proposes a bond damage model within peridynamics to treat the nucleation and growth of cracks due to cyclic loading. Bond damage occurs according to the evolution of a variable called the "remaining life" of each bond that changes over time according to the cyclic strain in the bond. It is shown that the model reproduces the main features of S-N data for typical materials and also reproduces the Paris law for fatigue crack growth. Extensions of the model account for the effects of loading spectrum, fatigue limit, and variable load ratio. A three-dimensional example illustrates the nucleation and growth of a helical fatigue crack in the torsion of an aluminum alloy rod.

  17. Variation in Estimated Ozone-Related Health Impacts of Climate Change due to Modeling Choices and Assumptions

    SciTech Connect

    Post, Ellen S.; Grambsch, A.; Weaver, C. P.; Morefield, Philip; Huang, Jin; Leung, Lai-Yung R.; Nolte, Christopher G.; Adams, P. J.; Liang, Xin-Zhong; Zhu, J.; Mahoney, Hardee

    2012-11-01

    Future climate change may cause air quality degradation via climate-induced changes in meteorology, atmospheric chemistry, and emissions into the air. Few studies have explicitly modeled the potential relationships between climate change, air quality, and human health, and fewer still have investigated the sensitivity of estimates to the underlying modeling choices.

  18. Biases in Estimating Treatment Effects Due to Attrition in Randomized Controlled Trials and Cluster Randomized Controlled Trials: A Simulation Study

    ERIC Educational Resources Information Center

    Dong, Nianbo; Lipsey, Mark W.

    2011-01-01

    Attrition occurs when study participants who were assigned to the treatment and control conditions do not provide outcome data and thus do not contribute to the estimation of the treatment effects. It is very common in experimental studies in education as illustrated, for instance, in a meta-analysis studying "the effects of attrition on baseline…

  19. Multiscale Fatigue Life Prediction for Composite Panels

    NASA Technical Reports Server (NTRS)

    Bednarcyk, Brett A.; Yarrington, Phillip W.; Arnold, Steven M.

    2012-01-01

    Fatigue life prediction capabilities have been incorporated into the HyperSizer Composite Analysis and Structural Sizing Software. The fatigue damage model is introduced at the fiber/matrix constituent scale through HyperSizer s coupling with NASA s MAC/GMC micromechanics software. This enables prediction of the micro scale damage progression throughout stiffened and sandwich panels as a function of cycles leading ultimately to simulated panel failure. The fatigue model implementation uses a cycle jumping technique such that, rather than applying a specified number of additional cycles, a specified local damage increment is specified and the number of additional cycles to reach this damage increment is calculated. In this way, the effect of stress redistribution due to damage-induced stiffness change is captured, but the fatigue simulations remain computationally efficient. The model is compared to experimental fatigue life data for two composite facesheet/foam core sandwich panels, demonstrating very good agreement.

  20. Environmental fatigue in aluminum-lithium alloys

    NASA Technical Reports Server (NTRS)

    Piascik, Robert S.

    1992-01-01

    Aluminum-lithium alloys exhibit similar environmental fatigue crack growth characteristics compared to conventional 2000 series alloys and are more resistant to environmental fatigue compared to 7000 series alloys. The superior fatigue crack growth behavior of Al-Li alloys 2090, 2091, 8090, and 8091 is due to crack closure caused by tortuous crack path morphology and crack surface corrosion products. At high R and reduced closure, chemical environment effects are pronounced resulting in accelerated near threshold da/dN. The beneficial effects of crack closure are minimized for small cracks resulting in rapid growth rates. Limited data suggest that the 'chemically small crack' effect, observed in other alloy system, is not pronounced in Al-Li alloys. Modeling of environmental fatigue in Al-Li-Cu alloys related accelerated fatigue crack growth in moist air and salt water to hydrogen embrittlement.

  1. Measurement of soil contamination by radionuclides due to the Fukushima Dai-ichi Nuclear Power Plant accident and associated estimated cumulative external dose estimation.

    PubMed

    Endo, S; Kimura, S; Takatsuji, T; Nanasawa, K; Imanaka, T; Shizuma, K

    2012-09-01

    Soil sampling was carried out at an early stage of the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident. Samples were taken from areas around FDNPP, at four locations northwest of FDNPP, at four schools and in four cities, including Fukushima City. Radioactive contaminants in soil samples were identified and measured by using a Ge detector and included (129 m)Te, (129)Te, (131)I, (132)Te, (132)I, (134)Cs, (136)Cs, (137)Cs, (140)Ba and (140)La. The highest soil depositions were measured to the northwest of FDNPP. From this soil deposition data, variations in dose rates over time and the cumulative external doses at the locations for 3 months and 1y after deposition were estimated. At locations northwest of FDNPP, the external dose rate at 3 months after deposition was 4.8-98 μSv/h and the cumulative dose for 1 y was 51 to 1.0 × 10(3)mSv; the highest values were at Futaba Yamada. At the four schools, which were used as evacuation shelters, and in the four urban cities, the external dose rate at 3 months after deposition ranged from 0.03 to 3.8μSv/h and the cumulative doses for 1 y ranged from 3 to 40 mSv. The cumulative dose at Fukushima Niihama Park was estimated as the highest in the four cities. The estimated external dose rates and cumulative doses show that careful countermeasures and remediation will be needed as a result of the accident, and detailed measurements of radionuclide deposition densities in soil will be important input data to conduct these activities.

  2. Dose estimation by ESR on tooth enamel from two workers exposed to radiation due to the JCO accident.

    PubMed

    Shiraishi, Kunio; Iwasaki, Midori; Miyazawa, Chyuzo; Yonehara, Hidenori; Matsumoto, Masaki

    2002-09-01

    ESR dosimetry is useful to estimate the external dose for the general population as well as for occupational workers in a nuclear emergency. Three teeth were extracted from two exposed workers (A and B) related to the JCO criticality accident. Tooth enamel was carefully separated from other tooth parts and subjected to ESR dosimetry. Doses equivalent to the gamma-ray dose of 60Co were estimated as follows: for worker A, the buccal and lingual sides of the eighth tooth in the upper right side, 11.8 +/- 3.6 and 12.0 +/- 3.6 Gy, respectively; for worker B, the buccal and lingual sides of the fourth tooth in the upper right side and the fifth tooth in the upper left side, 11.3 +/- 3.4 and 10.8 +/- 3.3 Gy, 11.7 +/- 3.5 and 11.4 +/- 3.4 Gy, respectively. The estimated doses were found to be similar and not dependent on the tooth positions, whether the buccal or lingual sides in each tooth.

  3. Toward a Real-Time Measurement-Based System for Estimation of Helicopter Engine Degradation Due to Compressor Erosion

    NASA Technical Reports Server (NTRS)

    Litt, Jonathan S.; Simo, Donald L.

    2007-01-01

    This paper presents a preliminary demonstration of an automated health assessment tool, capable of real-time on-board operation using existing engine control hardware. The tool allows operators to discern how rapidly individual turboshaft engines are degrading. As the compressor erodes, performance is lost, and with it the ability to generate power. Thus, such a tool would provide an instant assessment of the engine s fitness to perform a mission, and would help to pinpoint any abnormal wear or performance anomalies before they became serious, thereby decreasing uncertainty and enabling improved maintenance scheduling. The research described in the paper utilized test stand data from a T700-GE-401 turboshaft engine that underwent sand-ingestion testing to scale a model-based compressor efficiency degradation estimation algorithm. This algorithm was then applied to real-time Health Usage and Monitoring System (HUMS) data from a T700-GE-701C to track compressor efficiency on-line. The approach uses an optimal estimator called a Kalman filter. The filter is designed to estimate the compressor efficiency using only data from the engine s sensors as input.

  4. Differential Effects of Fatigue on Movement Variability

    PubMed Central

    Cortes, N.; Onate, J.; Morrison, S.

    2014-01-01

    When individuals perform purposeful actions to fatigue, there is typically a general decline in their movement performance. This study was designed to investigate the effects exercise-induced fatigue has on lower limb kinetics and kinematics during a side-step cutting task. In particular, it was of interest to determine what changes could be seen in mean amplitude and all metrics of signal variability with fatigue. The results of the study revealed that post-fatigue there was an overall decrease in absolute force production as reflected by a decline in mean amplitude and variability (SD) of the ground reaction forces (GRFV and GRFML). A decrease in mean and SD of the knee moments were also observed post-exercise. Interestingly, this trend was not mirrored by similar changes in time-dependent properties of these signals. Instead, there was an increase in the SampEn values (reflecting a more variable, irregular signal) for GRF force profiles, knee kinematics and moments following the exercise-induced fatigue. These results illustrate that fatigue can have differential effects on movement variability, resulting in a both an increase and decrease in movement variability, depending on the variable selected. Thus, the impact of fatigue is not simply restricted to a decline in force producing capacity of the system but more importantly it demonstrates that the ability of the person to perform a smooth and controlled action is limited due to fatigue. PMID:24370441

  5. Differential effects of fatigue on movement variability.

    PubMed

    Cortes, N; Onate, J; Morrison, S

    2014-03-01

    When individuals perform purposeful actions to fatigue, there is typically a general decline in their movement performance. This study was designed to investigate the effects exercise-induced fatigue has on lower limb kinetics and kinematics during a side-step cutting task. In particular, it was of interest to determine what changes could be seen in mean amplitude and all metrics of signal variability with fatigue. The results of the study revealed that post-fatigue there was an overall decrease in absolute force production as reflected by a decline in mean amplitude and variability (SD) of the ground reaction forces (GRFV and GRFML). A decrease in mean and SD of the knee moments were also observed post-exercise. Interestingly, this trend was not mirrored by similar changes in time-dependent properties of these signals. Instead, there was an increase in the SampEn values (reflecting a more variable, irregular signal) for GRF force profiles, knee kinematics and moments following the exercise-induced fatigue. These results illustrate that fatigue can have differential effects on movement variability, resulting in a both an increase and decrease in movement variability, depending on the variable selected. Thus, the impact of fatigue is not simply restricted to a decline in force producing capacity of the system but more importantly it demonstrates that the ability of the person to perform a smooth and controlled action is limited due to fatigue.

  6. Radiation dose from MDCT using Monte Carlo simulations: estimating fetal dose due to pulmonary embolism scans accounting for overscan

    NASA Astrophysics Data System (ADS)

    Angel, E.; Wellnitz, C.; Goodsitt, M.; DeMarco, J.; Cagnon, C.; Ghatali, M.; Cody, D.; Stevens, D.; McCollough, C.; Primak, A.; McNitt-Gray, M.

    2007-03-01

    Pregnant women with shortness of breath are increasingly referred for CT Angiography to rule out Pulmonary Embolism (PE). While this exam is typically focused on the lungs, extending scan boundaries and overscan can add to the irradiated volume and have implications on fetal dose. The purpose of this work was to estimate radiation dose to the fetus when various levels of overscan were encountered. Two voxelized models of pregnant patients derived from actual patient anatomy were created based on image data. The models represent an early (< 7 weeks) and late term pregnancy (36 weeks). A previously validated Monte Carlo model of an MDCT scanner was used that takes into account physical details of the scanner. Simulated helical scans used 120 kVp, 4x5 mm beam collimation, pitch 1, and varying beam-off locations (edge of the irradiated volume) were used to represent different protocols plus overscan. Normalized dose (mGy/100mAs) was calculated for each fetus. For the early term and the late term pregnancy models, fetal dose estimates for a standard thoracic PE exam were estimated to be 0.05 and 0.3 mGy/100mAs, respectively, increasing to 9 mGy/100mAs when the beam-off location was extended to encompass the fetus. When performing PE exams to rule out PE in pregnant patients, the beam-off location may have a large effect on fetal dose, especially for late term pregnancies. Careful consideration of ending location of the x-ray beam - and not the end of image data - could result in significant reduction in radiation dose to the fetus.

  7. A survey of fatigue monitoring in the nuclear power industry

    SciTech Connect

    Ware, A.G.

    1991-12-31

    The original design of nuclear power plants addressed fatigue concerns by including calculations of projected fatigue usage for specific components; the calculations were based on estimates of the number and severity of expected transients over the 40-year design life of the plants. In some cases, the transients occurring in the plants are not as severe as was anticipated in the original design analyses, while in other cases events have occurred that were not anticipated in the design basis documents. Field failures caused by fatigue have identified some of those cases. In response, several organizations in the United States and overseas have developed fatigue monitoring programs to more accurately estimate the fatigue usage. One basic approach consists of reconstructing the fatigue usage to date based on the transients recorded in the operating history instead of those projected in the design documents. Another approach includes monitoring the plant instrumentation to determine actual values for parameters such as temperature and pressure and using the measured values in the fatigue usage calculations instead of the values projected in the design documents. The use of existing plant instrumentation to measure temperature, pressure, flow rate, etc., along with the incorporation of conservative assumptions, had generally proven adequate for estimating fatigue usage; however, in some cases additional instrumentation installed for local monitoring can provide a more accurate estimate, especially where thermal stratification is known to occur. Fatigue monitoring can aid in identifying fatigue concerns not anticipated in the original design and for reducing the excessive conservatism in some of the original design calculations so that the fatigue lives of these components can be justified as they age. Fatigue monitoring can also assist efforts to reduce ongoing fatigue usage through design modifications and operating procedure changes.

  8. A survey of fatigue monitoring in the nuclear power industry

    SciTech Connect

    Ware, A.G.

    1991-01-01

    The original design of nuclear power plants addressed fatigue concerns by including calculations of projected fatigue usage for specific components; the calculations were based on estimates of the number and severity of expected transients over the 40-year design life of the plants. In some cases, the transients occurring in the plants are not as severe as was anticipated in the original design analyses, while in other cases events have occurred that were not anticipated in the design basis documents. Field failures caused by fatigue have identified some of those cases. In response, several organizations in the United States and overseas have developed fatigue monitoring programs to more accurately estimate the fatigue usage. One basic approach consists of reconstructing the fatigue usage to date based on the transients recorded in the operating history instead of those projected in the design documents. Another approach includes monitoring the plant instrumentation to determine actual values for parameters such as temperature and pressure and using the measured values in the fatigue usage calculations instead of the values projected in the design documents. The use of existing plant instrumentation to measure temperature, pressure, flow rate, etc., along with the incorporation of conservative assumptions, had generally proven adequate for estimating fatigue usage; however, in some cases additional instrumentation installed for local monitoring can provide a more accurate estimate, especially where thermal stratification is known to occur. Fatigue monitoring can aid in identifying fatigue concerns not anticipated in the original design and for reducing the excessive conservatism in some of the original design calculations so that the fatigue lives of these components can be justified as they age. Fatigue monitoring can also assist efforts to reduce ongoing fatigue usage through design modifications and operating procedure changes.

  9. Estimation of years lived with disability due to noncommunicable diseases and injuries using a population-representative survey.

    PubMed

    Park, Ji In; Jung, Hae Hyuk

    2017-01-01

    The Global Burden of Disease 2010 and the WHO Global Health Estimates of years lived with disability (YLDs) uses disability-weights obtained from lay health-state descriptions, which cannot fully reflect different disease manifestations, according to severity, treatment, and environment. The aim of this study was to provide population-representative YLDs of noncommunicable diseases and injuries using a prevalence-based approach, with the disability weight measured in subjects with specific diseases or injuries. We included a total of 44969 adults, who completed the EQ-5D questionnaire as participation in the Korea National Health and Nutrition Examination Survey 2007-2014. We estimated the prevalence of each of 40 conditions identified from the noncommunicable diseases and injuries in the WHO list. Modified condition-specific disability-weight was determined from the adjusted mean difference of the EQ-5D index between the condition and reference groups. Condition-specific YLDs were calculated as the condition's prevalence multiplied by the condition's disability-weight. All-cause YLDs, estimated as "number of population × (1 - mean score of EQ-5D)" were 2165 thousands in 39044 thousand adults aged ≥20. The combined YLDs for all 40 conditions accounted for 67.6% of all-cause YLDs, and were 1604, 2126, 8749, and 12847 per 100000 young (age 20-59) males, young females, old (age ≥60) males, and old females, respectively. Back pain/osteoarthritis YLDs were exceptionally large (442/40, 864/146, 2037/836, and 4644/3039 per 100000 young males, young females, old males, and old females, respectively). Back pain, osteoarthritis, depression, diabetes, periodontitis, and stroke accounted for 22.3%, 9.1%, 4.6%, 3.3%, 3.2%, and 2.9% of all-cause YLDs, respectively. In conclusion, this estimation of YLDs using prevalence rates and disability-weights measured in a population-representative survey may form the basis for population-level strategies to prevent age

  10. Estimation of Cyclic Error Due to Scattering in the Internal OPD Metrology of the Space Interferometry Mission

    NASA Technical Reports Server (NTRS)

    Tang, Hong; Zhao, Feng

    2005-01-01

    A common-path laser heterodyne interferometer capable of measuring the internal optical path difference (OPD) with accuracy of the order of 10 pm was demonstrated at JPL. To achieve this accuracy, the relative power received by the detector that is contributed by the scattering of light at the optical surfaces should be less than -97 dB. A method has been developed to estimate the cyclic error caused by the scattering of the optical surfaces. The result of the analysis is presented.

  11. Estimation of years lived with disability due to noncommunicable diseases and injuries using a population-representative survey

    PubMed Central

    Park, Ji In

    2017-01-01

    The Global Burden of Disease 2010 and the WHO Global Health Estimates of years lived with disability (YLDs) uses disability-weights obtained from lay health-state descriptions, which cannot fully reflect different disease manifestations, according to severity, treatment, and environment. The aim of this study was to provide population-representative YLDs of noncommunicable diseases and injuries using a prevalence-based approach, with the disability weight measured in subjects with specific diseases or injuries. We included a total of 44969 adults, who completed the EQ-5D questionnaire as participation in the Korea National Health and Nutrition Examination Survey 2007–2014. We estimated the prevalence of each of 40 conditions identified from the noncommunicable diseases and injuries in the WHO list. Modified condition-specific disability-weight was determined from the adjusted mean difference of the EQ-5D index between the condition and reference groups. Condition-specific YLDs were calculated as the condition’s prevalence multiplied by the condition’s disability-weight. All-cause YLDs, estimated as “number of population × (1 − mean score of EQ-5D)” were 2165 thousands in 39044 thousand adults aged ≥20. The combined YLDs for all 40 conditions accounted for 67.6% of all-cause YLDs, and were 1604, 2126, 8749, and 12847 per 100000 young (age 20−59) males, young females, old (age ≥60) males, and old females, respectively. Back pain/osteoarthritis YLDs were exceptionally large (442/40, 864/146, 2037/836, and 4644/3039 per 100000 young males, young females, old males, and old females, respectively). Back pain, osteoarthritis, depression, diabetes, periodontitis, and stroke accounted for 22.3%, 9.1%, 4.6%, 3.3%, 3.2%, and 2.9% of all-cause YLDs, respectively. In conclusion, this estimation of YLDs using prevalence rates and disability-weights measured in a population-representative survey may form the basis for population-level strategies to prevent age

  12. Estimation of the population attributable fraction of road-related injuries due to speeding and passing in Iran

    PubMed Central

    2016-01-01

    OBJECTIVES Speeding and passing are considered to be the main human factors resulting in road traffic injuries (RTIs). This study aimed to estimate the population attributeable fraction (PAF) of speeding and passing in RTIs in rural Iran during 2012. METHODS The contribution of speeding and passing to RTI-related morbidity and mortality was estimated using the PAF method. The prevalence of speeding and passing was obtained from the national traffic police data registry. A logistic regression model was used to measure the association between the above risk factors and RTIs. RESULTS Speeding accounted for 20.96% and 16.61% of rural road-related deaths and injuries, respectively. The corresponding values for passing were 13.50% and 13.44%, respectively. Jointly, the PAF of these factors was 31.63% for road-related deaths and 27.81% for injuries. CONCLUSIONS This study illustrates the importance of controlling speeding and passing as a high-priority aspect of public-health approaches to RTIs in Iran. It is recommended that laws restricting speeding and passing be enforced more strictly. PMID:27608807

  13. Fatigue of composites

    NASA Technical Reports Server (NTRS)

    Salkind, M. J.

    1972-01-01

    The failure mechanisms in the fatigue of composite materials are analyzed in terms of the requirements for designing fatigue-critical composite structures. Fiber reinforced polymers, fiber reinforced metals, fatigue of composite structures, and composite design considerations are discussed. It is concluded that composite materials offer the engineer the opportunity for tailoring stiffness in different directions for designing dynamic components.

  14. Bottom attenuation estimation using sound intensity fluctuations due to mode coupling by nonlinear internal waves in shallow water.

    PubMed

    Grigorev, Valery A; Katsnelson, Boris G; Lynch, James F

    2016-11-01

    Analyses of fluctuations of low frequency signals (300 ± 30 Hz) propagating in shallow water in the presence of nonlinear internal waves (NIWs) in the Shallow Water 2006 experiment are carried out. Signals were received by a vertical line array at a distance of ∼20 km from the source. A NIW train was moving totally inside of the acoustic track, and the angle between the wave front of the NIW and the acoustic track in the horizontal plane was ∼10°. It is shown that the spectrum of the sound intensity fluctuations contains peaks corresponding to the coupling of pairs of propagating modes. Analysis of spectra at different hydrophone depths, and also summed over depth allows the authors to estimate attenuation in the bottom sediments.

  15. Estimating In Vivo Death Rates of Targets due to CD8 T-Cell-Mediated Killing▿ †

    PubMed Central

    Ganusov, Vitaly V.; De Boer, Rob J.

    2008-01-01

    Despite recent advances in immunology, several key parameters determining virus dynamics in infected hosts remain largely unknown. For example, the rate at which specific effector and memory CD8 T cells clear virus-infected cells in vivo is hardly known for any viral infection. We propose a framework to quantify T-cell-mediated killing of infected or peptide-pulsed target cells using the widely used in vivo cytotoxicity assay. We have reanalyzed recently published data on killing of peptide-pulsed splenocytes by cytotoxic T lymphocytes and memory CD8 T cells specific to NP396 and GP276 epitopes of lymphocytic choriomeningitis virus (LCMV) in the mouse spleen. Because there are so many effector CD8 T cells in spleens of mice at the peak of the immune response, NP396- and GP276-pulsed targets are estimated to have very short half-lives of 2 and 14 min, respectively. After the effector numbers have diminished, i.e., in LCMV-immune mice, the half-lives become 48 min and 2.8 h for NP396- and GP276-expressing targets, respectively. Analysis of several alternative models demonstrates that the estimates of half-life times of peptide-pulsed targets are not affected when changes are made in the model assumptions. Our report provides a unifying framework to compare killing efficacies of CD8 T-cell responses specific to different viral and bacterial infections in vivo, which may be used to compare efficacies of various cytotoxic-T-lymphocyte-based vaccines. PMID:18815293

  16. Estimate of the trigger inefficiency due to extra hits in H1 and H2, using clean Chi(2) events

    SciTech Connect

    Mussa, R.; /INFN, Turin /Turin U.

    1992-07-01

    An accurate study of the inefficiency of the trigger selection criterium based on the multiplicity of hits in the two hodoscopes has been done using {chi}{sub 2} events take during the 1991 run, selected requiring that both electron tracks were associated to a Cherenkov hit (so that no multiplicity requirement at trigger level was asked), and a {chi}{sup 2} probability for the kinematic fit bigger than 0.01. In a table it is shown the number of events found for different multiplicities in the two hodoscopes. They have 554/1819 = 30.5 {+-} 1.3% of the events with extra-hits in the two hodoscopes, and they can think of 3 possible sources for this effect: (1) accidental {delta} rays due to the interactions of the beam halo inside or against the walls of the beam pipe give an extra activity on H1 that should be uncorrelated to the hits due to real tracks; (2) {delta} rays at large angles emitted by the electrons interacting with the inner layers of the detector, so that they expect extra-hits close to the real tracks; and (3) the conversion of the {delta} inside the beam pipe and in the inner detectors can give an extra-hit in H2 or H1 and H2: this also doubles the number of sources of {delta} rays, so that a big number of these events have 4 H2 firing.

  17. Ultrasonic absortion in fatigued materials

    NASA Astrophysics Data System (ADS)

    Dugan, S.; Arnold, W.

    2013-01-01

    Non-destructive detection of fatigue damage, allowing an estimate of the residual life-time of components, could contribute to a safe and reliable operation of components and installations. Ultrasonic absorption, i.e. the internal friction, of a material increases with increasing fatigue or creep damage and there are many theories trying to explain the physics behind this phenomenon. Measurement of ultrasonic absorption directly on components could provide information on the degree of damage. A laser ultrasonic method, using laser-generated pulses and optical detection, was applied to study ultrasonic absorption in fatigue specimens of different metals. A characteristic behavior of the ultrasonic absorption coefficient with increasing levels of fatigue damage was found for the titanium alloy Ti-6Al-4V. Another aim of this study was to relate the absorption mechanisms to the behavior of ultrasonic absorption observed in metals with complex microstructure. To achieve this, different ultrasonic absorption mechanisms were analyzed with respect to experimental data. A thermoelastic effect related to the size and elasticity of the microstructure is discussed as the origin of the increased ultrasonic absorption.

  18. Estimation of torque on mechanical heart valves due to magnetic resonance imaging including an estimation of the significance of the Lenz effect using a computational model

    NASA Astrophysics Data System (ADS)

    Robertson, Neil M.; Diaz-Gomez, Manuel; Condon, Barrie

    2000-12-01

    Mitral and aortic valve replacement is a procedure which is common in cardiac surgery. Some of these replacement valves are mechanical and contain moving metal parts. Should the patient in whom such a valve has been implanted be involved in magnetic resonance imaging, there is a possible dangerous interaction between the moving metal parts and the static magnetic field due to the Lenz effect. Mathematical models of two relatively common forms of single-leaflet valves have been derived and the magnitude of the torque which opposes the motion of the valve leaflet has been calculated for a valve disc of solid metal. In addition, a differential model of a ring-strengthener valve type has been considered to determine the likely significance of the Lenz effect in the context of the human heart. For common magnetic field strengths at present, i.e. 1 to 2 T, the effect is not particularly significant. However, there is a marked increase in back pressure as static magnetic field strength increases. There are concerns that, since field strengths in the range 3 to 4 T are increasingly being used, the Lenz effect could become significant. At 5 to 10 T the malfunction of the mechanical heart valve could cause the heart to behave as though it is diseased. For unhealthy or old patients this could possibly prove fatal.

  19. 210Po and 210Pb Activity Concentrations in Cigarettes Produced in Vietnam and Their Estimated Dose Contribution Due to Smoking

    NASA Astrophysics Data System (ADS)

    Tran, Thuy-Ngan N.; Le, Cong-Hao; Chau, Van-Tao

    Smoking cigarettes contributes significantly to the increase of radiation in human body because 210Po and 210Pb exist relatively high in tobacco leaves. Therefore, these two radioisotopes in eighteen of the most frequently sold cigarette brands produced in Vietnam were examined in this study. 210Po was determined by alpha spectroscopy using a passivated implanted planar silicon (PIPS) detector after a procedure including radiochemical separation and spontaneous deposition of polonium on a copper disc (the deposition efficiency of 210Po on a copper disc was approximately 94%). Sequentially, 210Pb was determined through the ingrowth of 210Po after storing the sample solutions for approximately six months. The activity concentrations of 210Po in cigarettes ranged from 13.8 to 82.6 mBq/cigarette (the mean value was 26.4 mBq/cigarette) and the activity concentrations of 210Pb in cigarettes ranged from 13.9 to 78.8 mBq/cigarette (the mean value was 25.8 mBq/cigarette). The annual committed effective dose for smokers who smoke one pack per day was also estimated to be 295.4 µSv/year (223.0 µSv/year and 72.4 µSv/year from 210Po and 210Pb, respectively). These indicated that smoking increased the risk of developing lung cancer was approximately 60 times greater for smokers than for non-smokers.

  20. Estimation of the carbon monoxide emissions due to Sandia National Laboratories commuter and on-base traffic for conformity determination

    SciTech Connect

    McClellan, Y.; Royer, R.

    1996-09-01

    This report describes the analysis and conclusion of an investigation of the carbon monoxide emissions resulting from Sandia National Laboratories and Department of Energy (DOE) commuter and on-base traffic for the Clean Air Act (CAA) Conformity Determination. Albuquerque/Bernalillo County was classified as a nonattainment area by the Environmental Protection Agency. Nonattainment area is an area which is shown by monitored data or which is calculated by air quality modeling to exceed any National Ambient Air Quality Standard (NAAQS) for the pollutant. Albuquerque/Bernalillo County exceeds the NAAQS for carbon monoxide and ozone. The Conformity Determination was needed to complete the CAA Title V Permitting process for SNL and the DOE. The analysis used the EPA approved MOBILE5a Carbon Monoxide (CO) emissions modeling program. This analysis will provide a baseline for mobile sources to allow Sandia to estimate any future activity and how that activity will impact CO emissions. The General Conformity Rule (AQCR 43) requires that operations which will increase CO emissions in nonattaimnent or maintenance areas such as Bernalillo County undergo conformity analyses to determine whether or not they will impact ambient air quality in the area.

  1. Natural radioactivity in groundwater and estimates of committed effective dose due to water ingestion in the state of Chihuahua (Mexico).

    PubMed

    Villalba, L; Montero-Cabrera, M E; Manjón-Collado, G; Colmenero-Sujo, L; Rentería-Villalobos, M; Cano-Jiménez, A; Rodríguez-Pineda, A; Dávila-Rangel, I; Quirino-Torres, L; Herrera-Peraza, E F

    2006-01-01

    The activity concentration of 222Rn, 226Ra and total uranium in groundwater samples collected from wells distributed throughout the state of Chihuahua has been measured. The values obtained of total uranium activity concentration in groundwater throughout the state run from <0.03 up to 1.34 Bq l-1. Generally, radium activity concentration was <0.16 Bq l-1, with some exceptions; in spring water of San Diego de Alcalá, in contrast, the value reached approximately 5.3 Bq l-1. Radon activity concentration obtained throughout the state was from 1.0 to 39.8 Bq l-1. A linear correlation between uranium and radon dissolved in groundwater of individual wells was observed near Chihuahua City. Committed effective dose estimates for reference individuals were performed, with results as high as 134 microSv for infants in Aldama city. In Aldama and Chihuahua cities the average and many individual wells showed activity concentration values of uranium exceeding the Mexican norm of drinking water quality.

  2. SIMPLE estimate of the free energy change due to aliphatic mutations: superior predictions based on first principles.

    PubMed

    Bueno, Marta; Camacho, Carlos J; Sancho, Javier

    2007-09-01

    The bioinformatics revolution of the last decade has been instrumental in the development of empirical potentials to quantitatively estimate protein interactions for modeling and design. Although computationally efficient, these potentials hide most of the relevant thermodynamics in 5-to-40 parameters that are fitted against a large experimental database. Here, we revisit this longstanding problem and show that a careful consideration of the change in hydrophobicity, electrostatics, and configurational entropy between the folded and unfolded state of aliphatic point mutations predicts 20-30% less false positives and yields more accurate predictions than any published empirical energy function. This significant improvement is achieved with essentially no free parameters, validating past theoretical and experimental efforts to understand the thermodynamics of protein folding. Our first principle analysis strongly suggests that both the solute-solute van der Waals interactions in the folded state and the electrostatics free energy change of exposed aliphatic mutations are almost completely compensated by similar interactions operating in the unfolded ensemble. Not surprisingly, the problem of properly accounting for the solvent contribution to the free energy of polar and charged group mutations, as well as of mutations that disrupt the protein backbone remains open.

  3. Fatigue handbook: Offshore steel structures

    SciTech Connect

    Almarnaess, A.

    1985-01-01

    The contents of this book are: Overview of Offshore Steel Structures; Loads on Ocean Structures; Fracture Mechanics As a Tool in Fatigue Analysis; Basic Fatigue Properties of Welded Joints; Significance of Defects; Improving the Fatigue Strength of Welded Joints; Effects of Marine Environment and Cathodic Protection on Fatigue of Structural Steels Fatigue of Tubular Joints; Unstable Fracture; Fatigue Life Calculations; and Fatigue in Building Codes Background and Applications.

  4. Indoor inhalation dose estimates due to radon and thoron in some areas of South-Western Punjab, India.

    PubMed

    Kumar, Sanjeev; Singh, Surinder; Bajwa, Bikramjit Singh; Singh, Bhupinder; Sabharwal, Arvind D; Eappen, K P

    2012-08-01

    LR-115 (type II)-based radon-thoron discriminating twin-chamber dosemeters have been used for estimating radon ((222)Rn) and thoron ((220)Rn) concentrations in dwellings of south-western Punjab, India. The present study region has shown pronounced cases of cancer incidents in the public [Thakur, Rao, Rajwanshi, Parwana and Kumar (Epidemiological study of high cancer among rural agricultural community of Punjab in Northern India. Int J Environ Res Public Health 2008; 5(5):399-407) and Kumar et al. (Risk assessment for natural uranium in subsurface water of Punjab state, India. Hum Ecol Risk Assess 2011;17:381-93)]. Radon being a carcinogen has been monitored in some dwellings selected randomly in the study area. Results show that the values of radon ((222)Rn)  varied from 21 to 79 Bq m(-3), with a geometric mean of 45 Bq m(-3) [geometric standard deviation (GSD 1.39)], and those of thoron ((220)Rn)  from minimum detection level to 58 Bq m(-3) with a geometric mean of 19 Bq m(-3) (GSD 1.88). Bare card data are used for computing the progeny concentration by deriving the equilibrium factor (F) using a root finding method [Mayya, Eappen and Nambi (Methodology for mixed field inhalation dosimetry in monazite areas using a twin-cup dosemeter with three track detectors. Radiat Prot Dosim 1998;77(3):177-84)]. Inhalation doses have been calculated and compared using UNSCEAR equilibrium factors and by using the calculated F-values. The results show satisfactory comparison between the values.

  5. German experiences in local fatigue monitoring

    SciTech Connect

    Abib, E.; Bergholz, S.; Rudolph, J.

    2012-07-01

    The ageing management of nuclear power plants (NPP) has gained an increasing importance in the last years. The reasons are mainly due to the international context of extending period of plants operation. Moreover, new scientific discoveries, such as the corrosive influence of the medium on the fatigue process (environmentally assisted fatigue - EAF) play an important role and influence the code development (ASME, EAF code cases). The fatigue damage process takes a central position in ageing mechanisms of components. It must be ensured through appropriate evidence that facilities are being operated under allowable boundary conditions. In the design phase of NPP, fatigue analyses are still based on theoretical considerations and empirical values, which are summarized in the design transient catalogue, necessary for licensing. These analyses aim at proving the admissibility of the loads in terms of stress and fatigue usage. These analyses will also provide the fatigue-relevant positions in the NPP and give a basis for future design improvements and optimization of operating modes. The design transients are in practice conservatively correlated with the real transients occurring during operation. Uncertainties reveal very conservative assumptions regarding forecast temperatures, temperature gradients and frequencies of events. During operation of the plant, it has to be recurrently proved, that the plant is being operated under designed boundary conditions. Moreover, operating signals are constantly acquired to enable a fatigue evaluation. For example, in Germany fatigue evaluation is based on decades of experience and regulatory requirements. The rule KTA 3201.4 [1] establishes the rules for qualified fatigue monitoring. The rule DIN 25475-3 [2] on fatigue monitoring systems is available in draft version. Experience shows that some significant differences occur between the design transients and the real occurred transients during plant operation. The reasons for it

  6. Offshore wind turbine foundation monitoring, extrapolating fatigue measurements from fleet leaders to the entire wind farm

    NASA Astrophysics Data System (ADS)

    Weijtens, Wout; Noppe, Nymfa; Verbelen, Tim; Iliopoulos, Alexandros; Devriendt, Christof

    2016-09-01

    The present contribution is part of the ongoing development of a fatigue assessment strategy driven purely on in-situ measurements on operational wind turbines. The primary objective is to estimate the remaining life time of existing wind farms and individual turbines by instrumenting part of the farm with a load monitoring setup. This load monitoring setup allows to measure interface loads and local stress histories. This contribution will briefly discuss how these load measurements can be translated into fatigue assessment of the instrumented turbine. However, due to different conditions at the wind farm, such as turbulence, differences in water depth and foundation design this turbine will not be fully representable for all turbines in the farm. In this paper we will use the load measurements on two offshore wind turbines in the Northwind offshore wind farm to discuss fatigue progression in an operational wind farm. By calculating the damage equivalent loads on the two turbines the fatigue progression is quantified for every 10 minute interval and can be analyzed against turbulence and site conditions. In future work these results will be used to predict the fatigue life progression in the entire farm.

  7. Contribution of Hamstring Fatigue to Quadriceps Inhibition Following Lumbar Extension Exercise

    PubMed Central

    Hart, Joseph M.; Kerrigan, D. Casey; Fritz, Julie M.; Saliba, Ethan N.; Gansneder, Bruce; Ingersoll, Christopher D.

    2006-01-01

    The purpose of this study was to determine the contribution of hamstrings and quadriceps fatigue to quadriceps inhibition following lumbar extension exercise. Regression models were calculated consisting of the outcome variable: quadriceps inhibition and predictor variables: change in EMG median frequency in the quadriceps and hamstrings during lumbar fatiguing exercise. Twenty-five subjects with a history of low back pain were matched by gender, height and mass to 25 healthy controls. Subjects performed two sets of fatiguing isometric lumbar extension exercise until mild (set 1) and moderate (set 2) fatigue of the lumbar paraspinals. Quadriceps and hamstring EMG median frequency were measured while subjects performed fatiguing exercise. A burst of electrical stimuli was superimposed while subjects performed an isometric maximal quadriceps contraction to estimate quadriceps inhibition after each exercise set. Results indicate the change in hamstring median frequency explained variance in quadriceps inhibition following the exercise sets in the history of low back pain group only. Change in quadriceps median frequency explained variance in quadriceps inhibition following the first exercise set in the control group only. In conclusion, persons with a history of low back pain whose quadriceps become inhibited following lumbar paraspinal exercise may be adapting to the fatigue by using their hamstring muscles more than controls. Key Points A neuromuscular relationship between the lumbar paraspinals and quadriceps while performing lumbar extension exercise may be influenced by hamstring muscle fatigue. QI following lumbar extension exercise in persons with a history of LBP group may involve significant contribution from the hamstring muscle group. More hamstring muscle contribution may be a necessary adaptation in the history of LBP group due to weaker and more fatigable lumbar extensors. PMID:24198683

  8. Future Estimation of Convenience Living Facilities Withdrawal due to Population Decline all Over Japan from 2010 TO 2040 - Focus on Supermarkets, Convenience Stores and Drugstores

    NASA Astrophysics Data System (ADS)

    Nishimoto, Yuka; Akiyama, Yuki; Shibasaki, Ryosuke

    2016-06-01

    Population explosion is considered to be one of the most crucial problems in the world. However, in Japan, the opposite problem: population decline has become serious now. Japanese population is estimated to decrease by twenty millions in 2040. This negative situation will cause to increase areas where many residents cannot make a daily living all over Japan because many convenience living facilities such as supermarkets, convenience stores and drugstores will be difficult to maintain their market area population due to future population decline. In our research, we used point data of convenience living facilities developed by address geocoding of digital telephone directory and point data of future population projection developed by distribution of Japanese official population projection data proportionally among the building volume of digital residential map, which can monitor building volumes all over Japan. In conclusion, we estimated that various convenience living facilities in Japan will shrink and close by population decline in near future. In particular, it is cleared that approximately 14.7% of supermarkets will be possible to withdraw all over Japan by 2040. In addition, it is cleared that over 40% of supermarkets in some countryside prefectures will be possible to withdraw by 2040. Thus, we estimated future distributions of convenience living facilities that cannot maintain their market area population due to future population decline. Moreover, we estimated the number of people that they will become inconvenience in buying fresh foods.

  9. Estimation of landslides activities evolution due to land-use and climate change in a Pyrenean valley

    NASA Astrophysics Data System (ADS)

    Vandromme, Rosalie; Bernardie, Séverine; Houet, Thomas; Grémont, Marine; Grandjean, Gilles; Thiery, Yannick

    2016-04-01

    Global changes would have impacts worldwide, but their effects should be even more exacerbated in areas particularly vulnerable. Mountainous areas are among these vulnerable territories. Ecological systems are often at a fragile equilibrium, socio-economical activities are often climate-dependent and climate-driven natural hazards can be a major threat for human activities. In order to estimate the capacity of such mountainous valleys to face global changes (climate, but also climate- and human- induced land-use changes), it is necessary to be able to evaluate the evolution of the different threats. The present work shows a method to evaluate the influences of the evolution of both vegetation cover and climate on landslides activities over a whole valley until 2100, to propose adequate solutions for current and future forestry management. Firstly, the assessment of future land use is addressed through the construction of four prospective socio-economic scenarios up to 2050 and 2100, which are then spatially validated and modeled with LUCC models. Secondly, the climate change inputs of the project correspond to 2 scenarios of emission of greenhouse gases. The used simulations available on the portal DRIAS (http://www.drias-climat.fr) were performed with the GHG emissions scenarios (RCP: Representative concentration pathways, according to the standards defined by the GIEC) RCP 4.5 and RCP 8.5. The impact of land use and climate change is then addressed through the use of these scenarios into hazards computations. For that we use a large-scale slope stability assessment tool ALICE which combines a mechanical stability model (using finite slope analysis), a vegetation module which interfere with the first model, to take into account the effects of vegetation on the mechanical soil properties (cohesion and over-load), and an hydrogeological model. All these elements are interfaced within a GIS-based solution. In that way, future changes in temperature, precipitation and

  10. Organ-specific radiation-induced cancer risk estimates due to radiotherapy for benign pigmented villonodular synovitis

    NASA Astrophysics Data System (ADS)

    Mazonakis, Michalis; Tzedakis, Antonis; Lyraraki, Efrossyni; Damilakis, John

    2016-09-01

    Pigmented villonodular synovitis (PVNS) is a benign disease affecting synovial membranes of young and middle-aged adults. The aggressive treatment of this disorder often involves external-beam irradiation. This study was motivated by the lack of data relating to the radiation exposure of healthy tissues and radiotherapy-induced cancer risk. Monte Carlo methodology was employed to simulate a patient’s irradiation for PVNS in the knee and hip joints with a 6 MV photon beam. The average radiation dose received by twenty-two out-of-field critical organs of the human body was calculated. These calculations were combined with the appropriate organ-, age- and gender-specific risk coefficients of the BEIR-VII model to estimate the lifetime probability of cancer development. The risk for carcinogenesis to colon, which was partly included in the treatment fields used for hip irradiation, was determined with a non-linear mechanistic model and differential dose-volume histograms obtained by CT-based 3D radiotherapy planning. Risk assessments were compared with the nominal lifetime intrinsic risk (LIR) values. Knee irradiation to 36 Gy resulted in out-of-field organ doses of 0.2-24.6 mGy. The corresponding range from hip radiotherapy was 1.2-455.1 mGy whereas the organ equivalent dose for the colon was up to 654.9 mGy. The organ-specific cancer risks from knee irradiation for PVNS were found to be inconsequential since they were at least 161.5 times lower than the LIRs irrespective of the patient’s age and gender. The bladder and colon cancer risk from radiotherapy in the hip joint was up to 3.2 and 6.6 times smaller than the LIR, respectively. These cancer risks may slightly elevate the nominal incidence rates and they should not be ignored during the patient’s treatment planning and follow-up. The probabilities for developing any other solid tumor were more than 20 times lower than the LIRs and, therefore, they may be considered as small.

  11. The scale-of-choice effect and how estimates of assortative mating in the wild can be biased due to heterogeneous samples.

    PubMed

    Rolán-Alvarez, Emilio; Carvajal-Rodríguez, Antonio; de Coo, Alicia; Cortés, Beatriz; Estévez, Daniel; Ferreira, Mar; González, Rubén; Briscoe, Adriana D

    2015-07-01

    The mode in which sexual organisms choose mates is a key evolutionary process, as it can have a profound impact on fitness and speciation. One way to study mate choice in the wild is by measuring trait correlation between mates. Positive assortative mating is inferred when individuals of a mating pair display traits that are more similar than those expected under random mating while negative assortative mating is the opposite. A recent review of 1134 trait correlations found that positive estimates of assortative mating were more frequent and larger in magnitude than negative estimates. Here, we describe the scale-of-choice effect (SCE), which occurs when mate choice exists at a smaller scale than that of the investigator's sampling, while simultaneously the trait is heterogeneously distributed at the true scale-of-choice. We demonstrate the SCE by Monte Carlo simulations and estimate it in two organisms showing positive (Littorina saxatilis) and negative (L. fabalis) assortative mating. Our results show that both positive and negative estimates are biased by the SCE by different magnitudes, typically toward positive values. Therefore, the low frequency of negative assortative mating observed in the literature may be due to the SCE's impact on correlation estimates, which demands new experimental evaluation.

  12. Continuous fatigue crack monitoring of bridges: Long-Term Electrochemical Fatigue Sensor (LTEFS)

    NASA Astrophysics Data System (ADS)

    Moshier, Monty A.; Nelson, Levi; Brinkerhoff, Ryan; Miceli, Marybeth

    2016-04-01

    Fatigue cracks in steel bridges degrade the load-carrying capacity of these structures. Fatigue damage accumulation caused by the repetitive loading of everyday truck traffic can cause small fatigue cracks initiate. Understanding the growth of these fatigue cracks is critical to the safety and reliability of our transportation infrastructure. However, modeling fatigue in bridges is difficult due to the nature of the loading and variations in connection integrity. When fatigue cracks reach critical lengths failures occur causing partial or full closures, emergency repairs, and even full structural failure. Given the aging US highway and the trend towards asset management and life extension, the need for reliable, cost effective sensors and monitoring technologies to alert bridge owners when fatigue cracks are growing is higher than ever. In this study, an innovative Long-Term Electrochemical Fatigue Sensor (LTEFS) has been developed and introduced to meet the growing NDT marketplace demand for sensors that have the ability to continuously monitor fatigue cracks. The performance of the LTEFS has been studied in the laboratory and in the field. Data was collected using machined specimens with different lengths of naturally initiated fatigue cracks, applied stress levels, applied stress ratios, and for both sinusoidal and real-life bridge spectrum type loading. The laboratory data was evaluated and used to develop an empirically based algorithm used for crack detection. Additionally, beta-tests on a real bridge structure has been completed. These studies have conclusively demonstrated that LTEFS holds great potential for long-term monitoring of fatigue cracks in steel structures

  13. Chronic fatigue syndrome: aetiology, diagnosis and treatment

    PubMed Central

    Avellaneda Fernández, Alfredo; Pérez Martín, Álvaro; Izquierdo Martínez, Maravillas; Arruti Bustillo, Mar; Barbado Hernández, Francisco Javier; de la Cruz Labrado, Javier; Díaz-Delgado Peñas, Rafael; Gutiérrez Rivas, Eduardo; Palacín Delgado, Cecilia; Rivera Redondo, Javier; Ramón Giménez, José Ramón

    2009-01-01

    Chronic fatigue syndrome is characterised by intense fatigue, with duration of over six months and associated to other related symptoms. The latter include asthenia and easily induced tiredness that is not recovered after a night's sleep. The fatigue becomes so severe that it forces a 50% reduction in daily activities. Given its unknown aetiology, different hypotheses have been considered to explain the origin of the condition (from immunological disorders to the presence of post-traumatic oxidative stress), although there are no conclusive diagnostic tests. Diagnosis is established through the exclusion of other diseases causing fatigue. This syndrome is rare in childhood and adolescence, although the fatigue symptom per se is quite common in paediatric patients. Currently, no curative treatment exists for patients with chronic fatigue syndrome. The therapeutic approach to this syndrome requires a combination of different therapeutic modalities. The specific characteristics of the symptomatology of patients with chronic fatigue require a rapid adaptation of the educational, healthcare and social systems to prevent the problems derived from current systems. Such patients require multidisciplinary management due to the multiple and different issues affecting them. This document was realized by one of the Interdisciplinary Work Groups from the Institute for Rare Diseases, and its aim is to point out the main social and care needs for people affected with Chronic Fatigue Syndrome. For this, it includes not only the view of representatives for different scientific societies, but also the patient associations view, because they know the true history of their social and sanitary needs. In an interdisciplinary approach, this work also reviews the principal scientific, medical, socio-sanitary and psychological aspects of Chronic Fatigue Syndrome. PMID:19857242

  14. Fatigue and hysteresis modeling of ferroelectric materials

    NASA Astrophysics Data System (ADS)

    Yoo, In. K.; Desu, Seshu B.

    1993-10-01

    Due to their nonlinear properties, ferroelectric materials are ideal candidates for smart materials. Degradation properties such as low voltage breakdown, fatigue, and aging have been major problems in commercial applications of these materials. Such degradations affect the lifetime of ferroelectric materials. Therefore, it is important to understand degradation for reliability improvement. In this article, recent studies on fatigue and hysteresis of ferroelectric ceramics such as Lead Zirconate Titanate (PZT) thin films is reviewed. A new fatigue model is discussed in detail which is based on effective one-directional movement of defects by internal field difference, defect entrapment at the ferroelectrics-electrode interface, and resultant polarization loss at the interface. A fatigue equation derived from this model is presented. Fatigue parameters such as initial polarization, piling constant, and decay constant are defined from the fatigue equation and voltage and temperature dependence of fatigue parameters are discussed. The jump distance of defect calculated from voltage dependence of the decay constant is close to the lattice constant of ferroelectric materials, which implies that oxygen or lead vacancies migrate either parallel or antiparallel to the polarization direction. From the temperature dependence of the decay constant, it is shown that the activation energy for domain wall movement plays an important role in fatigue. The hysteresis model of ferroelectrics is shown using polarization reversal. The hysteresis loop is made by four polarization stages: nucleation, growth, merging, and shrinkage of domains. The hysteresis equation confirms that dielectric viscosity controls hysteresis properties, and temperature dependence of the coefficient of dielectric viscosity is also discussed in conjunction with fatigue mechanism.

  15. Cancer-related fatigue.

    PubMed

    Visovsky, Constance; Schneider, Susan M

    2003-01-01

    Approximately 1.3 million people in the United States will be diagnosed with cancer in 2003 and millions of other individuals are already living with the disease. Fatigue continues to be the most prevalent and disruptive symptom of cancer and its treatment regimens. Fatigue was the most frequent and distressing cancer-related symptom occurring in women with lung cancer, two times greater than the next symptom, pain, and remains one of the most common symptoms in newly diagnosed lung cancer patients at any stage of the disease. There are many causes of cancer-related fatigue including preexisting conditions, physical and psychological symptoms caused by cancer, and the consequences of cancer treatment. High levels of fatigue decrease quality of life, physical functional status, and symptom management. This article presents an evidenced-base review of cancer-related fatigue, strategies for the management of cancer-related fatigue, and recommendations for clinical practice.

  16. Fatigue of cellular materials

    SciTech Connect

    Huang, J.S.; Lin, J.Y.

    1996-01-01

    The fatigue of cellular materials is analyzed using dimensional arguments. When the first unbroken cell wall ahead of the macrocrack tip fails after some cycles of loading, the macrocrack advances one cell diameter, giving the macrocrack growth rate of cellular materials. Paris law for microcrack propagation, Basquin law for high cycle fatigue and Coffin-Manson law for low cycle fatigue are employed in calculating the number of cycles to failure of the first unbroken cell wall ahead of the macrocrack tip. It is found that fatigue of cellular materials depends on cyclic stress intensity range, cell size, relative density and the fatigue parameters of the solid from which they are made. Theoretical modelling of fatigue of foams is compared to data in polymer foams; agreement is good.

  17. Accelerated Fatigue Test Rationale,

    DTIC Science & Technology

    1980-03-01

    stress cycles. The high cycle fatigue (i.e. elastic stress-strain) typically extends beyond 104 cycles. The Coffin - Manson low cycle fatigue expression...g "Engineering strain is usually more convenient to use than "true" strain. The Coffin - Manson can be modified 12J to give -1/B .- Cu (2 Nf) (21...Mowbray Ci03 has shown that this relationship also reduces to the Coffin - Manson low cycle fatigue expression. An important aspect of the Dowling and

  18. The fatigue strength of riveted joints and lugs

    NASA Technical Reports Server (NTRS)

    Schijve, J

    1956-01-01

    This report deals with a number of tests on riveted joints and lugs for the primary purpose of comparing the several types of riveted joints and to study the effect of various factors on the fatigue strength of lugs. A check was made to ascertain whether or not an estimate of the fatigue life at a certain loading could be made from the dimensions of the joint and the fatigue data of the unnotched materials. Recommendations are made on the proportioning of joints to obtain better fatigue behavior.

  19. Fatigue behaviour of composites

    NASA Astrophysics Data System (ADS)

    Hartwig, G.; Hübner, R.; Knaak, S.; Pannkoke, C.

    An important design parameter for cyclically loaded structures (e.g. transport vessels) is the fatigue endurance limit. The cryogenic fatigue behaviour with different types of fibres and matrices has been investigated. The main emphasis it put on the behaviour of fibre dominated properties. It is surprising that the fatigue strength even of unidirectional fibre composites is strongly influenced by the matrix type. This will be discussed for carbon fibre composites with thermoplastic and duroplastic matrices under tensile and shear loading. For crossplies (with non-woven fabrics) the interaction between laminates controls the fatigue behaviour. The interaction depends on the matrix type and is different for tensile and shear loading.

  20. Fatigue crack growth in an aluminum alloy-fractographic study

    NASA Astrophysics Data System (ADS)

    Salam, I.; Muhammad, W.; Ejaz, N.

    2016-08-01

    A two-fold approach was adopted to understand the fatigue crack growth process in an Aluminum alloy; fatigue crack growth test of samples and analysis of fractured surfaces. Fatigue crack growth tests were conducted on middle tension M(T) samples prepared from an Aluminum alloy cylinder. The tests were conducted under constant amplitude loading at R ratio 0.1. The stress applied was from 20,30 and 40 per cent of the yield stress of the material. The fatigue crack growth data was recorded. After fatigue testing, the samples were subjected to detailed scanning electron microscopic (SEM) analysis. The resulting fracture surfaces were subjected to qualitative and quantitative fractographic examinations. Quantitative fracture analysis included an estimation of crack growth rate (CGR) in different regions. The effect of the microstructural features on fatigue crack growth was examined. It was observed that in stage II (crack growth region), the failure mode changes from intergranular to transgranular as the stress level increases. In the region of intergranular failure the localized brittle failure was observed and fatigue striations are difficult to reveal. However, in the region of transgranular failure the crack path is independent of the microstructural features. In this region, localized ductile failure mode was observed and well defined fatigue striations were present in the wake of fatigue crack. The effect of interaction of growing fatigue crack with microstructural features was not substantial. The final fracture (stage III) was ductile in all the cases.

  1. A Nonlinear Reduced Order Method for Prediction of Acoustic Fatigue

    NASA Technical Reports Server (NTRS)

    Przekop, Adam; Rizzi, Stephen A.

    2006-01-01

    The goal of this investigation is to assess the quality of high-cycle-fatigue life estimation via a reduced order method, for structures undergoing geometrically nonlinear random vibrations. Modal reduction is performed with several different suites of basis functions. After numerically solving the reduced order system equations of motion, the physical displacement time history is obtained by an inverse transformation and stresses are recovered. Stress ranges obtained through the rainflow counting procedure are used in a linear damage accumulation method to yield fatigue estimates. Fatigue life estimates obtained using various basis functions in the reduced order method are compared with those obtained from numerical simulation in physical degrees-of-freedom.

  2. Errors in the estimation of approximate entropy and other recurrence-plot-derived indices due to the finite resolution of RR time series.

    PubMed

    García-González, Miguel A; Fernández-Chimeno, Mireya; Ramos-Castro, Juan

    2009-02-01

    An analysis of the errors due to the finite resolution of RR time series in the estimation of the approximate entropy (ApEn) is described. The quantification errors in the discrete RR time series produce considerable errors in the ApEn estimation (bias and variance) when the signal variability or the sampling frequency is low. Similar errors can be found in indices related to the quantification of recurrence plots. An easy way to calculate a figure of merit [the signal to resolution of the neighborhood ratio (SRN)] is proposed in order to predict when the bias in the indices could be high. When SRN is close to an integer value n, the bias is higher than when near n - 1/2 or n + 1/2. Moreover, if SRN is close to an integer value, the lower this value, the greater the bias is.

  3. Modeling and Simulation for Estimating the Influence of Renal Dysfunction on the Hypouricemic Effect of Febuxostat in Hyperuricemic Patients Due to Overproduction or Underexcretion of Uric Acid.

    PubMed

    Hirai, Toshinori; Kimura, Toshimi; Echizen, Hirotoshi

    2016-01-01

    Whether renal dysfunction influences the hypouricemic effect of febuxostat, a xanthine oxidase (XO) inhibitor, in patients with hyperuricemia due to overproduction or underexcretion of uric acid (UA) remains unclear. We aimed to address this question with a modeling and simulation approach. The pharmacokinetics (PK) of febuxostat were analyzed using data from the literature. A kinetic model of UA was retrieved from a previous human study. Renal UA clearance was estimated as a function of creatinine clearance (CLcr) but non-renal UA clearance was assumed constant. A reversible inhibition model for bovine XO was adopted. Integrating these kinetic formulas, we developed a PK-pharmacodynamic (PK-PD) model for estimating the time course of the hypouricemic effect of febuxostat as a function of baseline UA level, febuxostat dose, treatment duration, body weight, and CLcr. Using the Monte Carlo simulation method, we examined the performance of the model by comparing predicted UA levels with those reported in the literature. We also modified the models for application to hyperuricemia due to UA overproduction or underexcretion. Thirty-nine data sets comprising 735 volunteers or patients were retrieved from the literature. A good correlation was observed between the hypouricemic effects of febuxostat estimated by our PK-PD model and those reported in the articles (observed) (r=0.89, p<0.001). The hypouricemic effect was estimated to be augmented in patients with renal dysfunction irrespective of the etiology of hyperuricemia. While validation in clinical studies is needed, the modeling and simulation approach may be useful for individualizing febuxostat doses in patients with various clinical characteristics.

  4. A Taxonomy of Fatigue Concepts and Their Relation to Hearing Loss.

    PubMed

    Hornsby, Benjamin W Y; Naylor, Graham; Bess, Fred H

    2016-01-01

    Fatigue is common in individuals with a variety of chronic health conditions and can have significant negative effects on quality of life. Although limited in scope, recent work suggests persons with hearing loss may be at increased risk for fatigue, in part due to effortful listening that is exacerbated by their hearing impairment. However, the mechanisms responsible for hearing loss-related fatigue, and the efficacy of audiologic interventions for reducing fatigue, remain unclear. To improve our understanding of hearing loss-related fatigue, as a field it is important to develop a common conceptual understanding of this construct. In this article, the broader fatigue literature is reviewed to identify and describe core constructs, consequences, and methods for assessing fatigue and related constructs. Finally, the current knowledge linking hearing loss and fatigue is described and may be summarized as follows: Hearing impairment may increase the risk of subjective fatigue and vigor deficits; adults with hearing loss require more time to recover from fatigue after work and have more work absences; sustained, effortful, listening can be fatiguing; optimal methods for eliciting and measuring fatigue in persons with hearing loss remain unclear and may vary with listening condition; and amplification may minimize decrements in cognitive processing speed during sustained effortful listening. Future research is needed to develop reliable measurement methods to quantify hearing loss-related fatigue, explore factors responsible for modulating fatigue in people with hearing loss, and identify and evaluate potential interventions for reducing hearing loss-related fatigue.

  5. The Effects of Hot Corrosion Pits on the Fatigue Resistance of a Disk Superalloy

    NASA Technical Reports Server (NTRS)

    Gabb, Timothy P.; Telesman, Jack; Hazel, Brian; Mourer, David P.

    2009-01-01

    The effects of hot corrosion pits on low cycle fatigue life and failure modes of the disk superalloy ME3 were investigated. Low cycle fatigue specimens were subjected to hot corrosion exposures producing pits, then tested at low and high temperatures. Fatigue lives and failure initiation points were compared to those of specimens without corrosion pits. Several tests were interrupted to estimate the fraction of fatigue life that fatigue cracks initiated at pits. Corrosion pits significantly reduced fatigue life by 60 to 98 percent. Fatigue cracks initiated at a very small fraction of life for high temperature tests, but initiated at higher fractions in tests at low temperature. Critical pit sizes required to promote fatigue cracking were estimated, based on measurements of pits initiating cracks on fracture surfaces.

  6. Dynamic Fatigue of ULE Glass

    NASA Technical Reports Server (NTRS)

    Tucker, Dennis S.; Nettles, Alan T.; Brantley, Lott W. (Technical Monitor)

    2001-01-01

    Ultra Low Expansion (ULE) glass is used in a number of applications which require a low thermal expansion coefficient. One such application is telescope mirror elements. An allowable stress can be calculated for this material based upon modulus of rupture data; however, this does not take into account the problem of delayed failure. Delayed failure, due to stress corrosion can significantly shorten the lifetime of a glass article. Knowledge of the factors governing the rate of subcritical flaw growth in a given environment enables the development of relations between lifetime, applied stress and failure probability for the material under study. Dynamic fatigue is one method of obtaining the necessary information to develop these relationships. In this study, the dynamic fatigue method was used to construct time-to-failure diagrams for both 230/270 ground and optically polished samples. The grinding and polishing process reduces the surface flaw size and subsurface damage, and relieves residual stress by removing materials with successively smaller grinding media. This resulted in an increase in the strength of the optic during the grinding and polishing sequence. There was also an increase in the lifetime due to grinding and polishing. It was found that using the fatigue parameters determined from the 230/270 grit surface are not significantly different from the optically polished values. Although the lower bound of the polished samples is more conservative, neither time-to-failure curves lie beyond the upper or lower bound of the confidence limits. Therefore, designers preferring conservative limits could use samples without residual stress present (polished samples) to determine the fatigue parameters and inert Weibull parameters from samples with the service condition surface, to determine time-to-failure of the optical element.

  7. High temperature tension-compression fatigue behavior of a tungsten copper composite

    NASA Technical Reports Server (NTRS)

    Verrilli, Michael J.; Gabb, Timothy P.

    1990-01-01

    The high temperature fatigue of a (O)12 tungsten fiber reinforced copper matrix composite was investigated. Specimens having fiber volume percentages of 10 and 36 were fatigued under fully-reversed, strain-controlled conditions at both 260 and 560 C. The fatigue life was found to be independent of fiber volume fraction because fatigue damage preferentially occurred in the matrix. Also, the composite fatigue lives were shorter at 560 C as compared to 260 C due to changes in mode of matrix failure. On a total strain basis, the fatigue life of the composite at 560 C was the same as the life of unreinforced copper, indicating that the presence of the fibers did not degrade the fatigue resistance of the copper matrix in this composite system. Comparison of strain-controlled fatigue data to previously-generated load-controlled data revealed that the strain-controlled fatigue lives were longer because of mean strain and mean stress effects.

  8. Experimental estimation of tungsten impurity sputtering due to Type I ELMs in JET-ITER-like wall using pedestal electron cyclotron emission and target Langmuir probe measurements

    NASA Astrophysics Data System (ADS)

    Guillemaut, C.; Jardin, A.; Horacek, J.; Borodkina, I.; Autricque, A.; Arnoux, G.; Boom, J.; Brezinsek, S.; Coenen, J. W.; De La Luna, E.; Devaux, S.; Eich, T.; Harting, D.; Kirschner, A.; Lipschultz, B.; Matthews, G. F.; Meigs, A.; Moulton, D.; O'Mullane, M.; Stamp, M.; contributors, JET

    2016-02-01

    The ITER baseline scenario, with 500 MW of DT fusion power and Q = 10, will rely on a Type I ELMy H-mode and will be achieved with a tungsten (W) divertor. W atoms sputtered from divertor targets during mitigated ELMs are expected to be the dominant source in ITER. W impurity concentration in the plasma core can dramatically degrade its performance and lead to potentially damaging disruptions. Understanding the physics of the target W source due to sputtering during ELMs and inter-ELMs is important and can be helped by experimental measurements with improved precision. It has been established that the ELMy target ion impact energy has a simple linear dependence with the pedestal electron temperature measured by Electron Cyclotron Emission (ECE). It has also been shown that Langmuir Probes (LP) ion flux measurements are reliable during ELMs due to the surprisingly low electron temperature. Therefore, in this paper, LP and ECE measurements in JET-ITER-Like-Wall (ILW) unseeded Type I ELMy H-mode experiments have been used to estimate the W sputtering flux from divertor targets in ELM and inter-ELM conditions. Comparison with similar estimates using W I spectroscopy measurements shows a reasonable agreement for the ELM and inter-ELM W source. The main advantage of the method involving LP measurements is the very high time resolution of the diagnostic (˜10 μs) allowing very precise description of the W sputtering source during ELMs.

  9. Aerodynamic Heating and Fatigue

    NASA Technical Reports Server (NTRS)

    Kroll, Wilhelmina D.

    1959-01-01

    A review of the physical condition's under which future airplanes will operate has been made and the necessity for considering fatigue in the design has been established. A survey of the literature shows what phases of elevated-temperature fatigue have been investigated. Other studies that would yield data of particular interest to the designer of aircraft structures are indicated.

  10. Fracture and fatigue in osteocytes.

    PubMed

    Mulargia, Simone; Dooley, Clodagh; Cristofolini, Luca; Taylor, David

    2014-11-01

    Fatigue is a common mode of mechanical failure which occurs when a material is subjected to repeated cycles at a strain level less than that needed for monotonic fracture. Fatigue has been observed and measured in many different materials but, until recently, not in cells. We devised a novel experiment which allowed us to create both monotonic failure and fatigue in the cellular processes of osteocytes within samples of bone (Dooley et al., European Cells and Materials 2014). In the present paper, we describe the results of further experiments and a computer simulation, which has allowed us to estimate the strain history of each sample tested and thus present, for the first time, strain/life data for cells. Failure occurred during the first cycle at strains of 0.1-0.2; at lower strains failure occurred after a number of cycles which depended inversely on the applied strain range. Scatter in the strain/life data was reduced when we allowed for the effects of mean stress using the Smith-Watson-Topper parameter. We confirmed that aspects of our experimental method (the types of microcrack used and the testing of fresh versus frozen samples) did not affect the results. Such information is useful because many cell types, including the cellular processes of osteocytes, experience cyclic strain in vivo.

  11. Estimates of Nitrogen, Phosphorus, Biochemical Oxygen Demand, and Fecal Coliforms Entering the Environment Due to Inadequate Sanitation Treatment Technologies in 108 Low and Middle Income Countries.

    PubMed

    Fuhrmeister, Erica R; Schwab, Kellogg J; Julian, Timothy R

    2015-10-06

    Understanding the excretion and treatment of human waste (feces and urine) in low and middle income countries (LMICs) is necessary to design appropriate waste management strategies. However, excretion and treatment are often difficult to quantify due to decentralization of excreta management. We address this gap by developing a mechanistic, stochastic model to characterize phosphorus, nitrogen, biochemical oxygen demand (BOD), and fecal coliform pollution from human excreta for 108 LMICs. The model estimates excretion and treatment given three scenarios: (1) use of existing sanitation systems, (2) use of World Health Organization-defined "improved sanitation", and (3) use of best available technologies. Our model estimates that more than 10(9) kg/yr each of phosphorus, nitrogen and BOD are produced. Of this, 22(19-27)%, 11(7-15)%, 17(10-23)%, and 35 (23-47)% (mean and 95% range) BOD, nitrogen, phosphorus, and fecal coliforms, respectively, are removed by existing sanitation systems. Our model estimates that upgrading to "improved sanitation" increases mean removal slightly to between 17 and 53%. Under the best available technology scenario, only approximately 60-80% of pollutants are treated. To reduce impact of nutrient and microbial pollution on human and environmental health, improvements in both access to adequate sanitation and sanitation treatment efficiency are needed.

  12. Elevated temperature biaxial fatigue

    NASA Technical Reports Server (NTRS)

    Jordan, E. H.

    1984-01-01

    A three year experimental program for studying elevated temperature biaxial fatigue of a nickel based alloy Hastelloy-X has been completed. A new high temperature fatigue test facility with unique capabilities has been developed. Effort was directed toward understanding multiaxial fatigue and correlating the experimental data to the existing theories of fatigue failure. The difficult task of predicting fatigue lives for non-proportional loading was used as an ultimate test for various life prediction methods being considered. The primary means of reaching improved undertanding were through several critical non-proportional loading experiments. It was discovered that the cracking mode switched from primarily cracking on the maximum shear planes at room temperature to cracking on the maximum normal strain planes at 649 C.

  13. Fatigue in soccer: a brief review.

    PubMed

    Mohr, Magni; Krustrup, Peter; Bangsbo, Jens

    2005-06-01

    This review describes when fatigue may develop during soccer games and the potential physiological mechanisms that cause fatigue in soccer. According to time-motion analyses and performance measures during match-play, fatigue or reduced performance seems to occur at three different stages in the game: (1) after short-term intense periods in both halves; (2) in the initial phase of the second half; and (3) towards the end of the game. Temporary fatigue after periods of intense exercise in the game does not appear to be linked directly to muscle glycogen concentration, lactate accumulation, acidity or the breakdown of creatine phosphate. Instead, it may be related to disturbances in muscle ion homeostasis and an impaired excitation of the sarcolemma. Soccer players' ability to perform maximally is inhibited in the initial phase of the second half, which may be due to lower muscle temperatures compared with the end of the first half. Thus, when players perform low-intensity activities in the interval between the two halves, both muscle temperature and performance are preserved. Several studies have shown that fatigue sets in towards the end of a game, which may be caused by low glycogen concentrations in a considerable number of individual muscle fibres. In a hot and humid environment, dehydration and a reduced cerebral function may also contribute to the deterioration in performance. In conclusion, fatigue or impaired performance in soccer occurs during various phases in a game, and different physiological mechanisms appear to operate in different periods of a game.

  14. Fatigue associated with prolonged graded running.

    PubMed

    Giandolini, Marlene; Vernillo, Gianluca; Samozino, Pierre; Horvais, Nicolas; Edwards, W Brent; Morin, Jean-Benoît; Millet, Guillaume Y

    2016-10-01

    Scientific experiments on running mainly consider level running. However, the magnitude and etiology of fatigue depend on the exercise under consideration, particularly the predominant type of contraction, which differs between level, uphill, and downhill running. The purpose of this review is to comprehensively summarize the neurophysiological and biomechanical changes due to fatigue in graded running. When comparing prolonged hilly running (i.e., a combination of uphill and downhill running) to level running, it is found that (1) the general shape of the neuromuscular fatigue-exercise duration curve as well as the etiology of fatigue in knee extensor and plantar flexor muscles are similar and (2) the biomechanical consequences are also relatively comparable, suggesting that duration rather than elevation changes affects neuromuscular function and running patterns. However, 'pure' uphill or downhill running has several fatigue-related intrinsic features compared with the level running. Downhill running induces severe lower limb tissue damage, indirectly evidenced by massive increases in plasma creatine kinase/myoglobin concentration or inflammatory markers. In addition, low-frequency fatigue (i.e., excitation-contraction coupling failure) is systematically observed after downhill running, although it has also been found in high-intensity uphill running for different reasons. Indeed, low-frequency fatigue in downhill running is attributed to mechanical stress at the interface sarcoplasmic reticulum/T-tubule, while the inorganic phosphate accumulation probably plays a central role in intense uphill running. Other fatigue-related specificities of graded running such as strategies to minimize the deleterious effects of downhill running on muscle function, the difference of energy cost versus heat storage or muscle activity changes in downhill, level, and uphill running are also discussed.

  15. Fatigue countermeasures in aviation.

    PubMed

    Caldwell, John A; Mallis, Melissa M; Caldwell, J Lynn; Paul, Michel A; Miller, James C; Neri, David F

    2009-01-01

    Pilot fatigue is a significant problem in modern aviation operations, largely because of the unpredictable work hours, long duty periods, circadian disruptions, and insufficient sleep that are commonplace in both civilian and military flight operations. The full impact of fatigue is often underappreciated, but many of its deleterious effects have long been known. Compared to people who are well-rested, people who are sleep deprived think and move more slowly, make more mistakes, and have memory difficulties. These negative effects may and do lead to aviation errors and accidents. In the 1930s, flight time limitations, suggested layover durations, and aircrew sleep recommendations were developed in an attempt to mitigate aircrew fatigue. Unfortunately, there have been few changes to aircrew scheduling provisions and flight time limitations since the time they were first introduced, despite evidence that updates are needed. Although the scientific understanding of fatigue, sleep, shift work, and circadian physiology has advanced significantly over the past several decades, current regulations and industry practices have in large part failed to adequately incorporate the new knowledge. Thus, the problem of pilot fatigue has steadily increased along with fatigue-related concerns over air safety. Accident statistics, reports from pilots themselves, and operational flight studies all show that fatigue is a growing concern within aviation operations. This position paper reviews the relevant scientific literature, summarizes applicable U.S. civilian and military flight regulations, evaluates various in-flight and pre-/postflight fatigue countermeasures, and describes emerging technologies for detecting and countering fatigue. Following the discussion of each major issue, position statements address ways to deal with fatigue in specific contexts with the goal of using current scientific knowledge to update policy and provide tools and techniques for improving air safety.

  16. Fatigue, fracture, and life prediction criteria for composite materials in magnets

    SciTech Connect

    Wong, F.M.G.

    1990-06-01

    An explosively-bonded copper/Inconel 718/copper laminate conductor was proposed to withstand the severe face compression stresses in the central core of the Alcator C-MOD tokamak toroidal field (TF) magnet. Due to the severe duty of the TF magnet, it is critical that an accurate estimate of useful life be determined. As part of the effort to formulate an appropriate life prediction, fatigue crack growth experiments were performed on the laminate as well as its components. Metallographic evaluation of the laminate interface revealed many shear bands in the Inconel 718. Shear bands and shear band cracks were produced in the Inconel 718 as a result of the explosion bonding process. These shear bands were shown to have a detrimental effect on the crack growth behavior of the laminate, by significantly reducing the load carrying capability of the reinforcement layer and providing for easy crack propagation paths. Fatigue crack growth rate was found not only to be dependent on temperature but also on orientation. Fatigue cracks grew faster in directions which contained shear bands in the plane of the propagating crack. Fractography showed crack advancement by fatigue cracking in the Inconel 718 and ductile tearing of the copper at the interface. However, further away from the interfaces, the copper exhibited fatigue striations indicating that cracks were now propagating by fatigue. Laminate life prediction results showed a strong dependence on shear band orientation, and exhibited little variation between room temperature and 77{degree}K. Predicted life of this laminate was lower when the crack propagation was along a shear band than when crack propagation was across the shear bands. Shear bands appear to have a dominating effect on crack growth behavior.

  17. Multimodal tissue imaging: using coregistered optical tomography data to estimate tissue autofluorescence intensity change due to scattering and absorption by neoplastic epithelial cells.

    PubMed

    Pahlevaninezhad, Hamid; Cecic, Ivana; Lee, Anthony M D; Kyle, Alastair H; Lam, Stephen; MacAulay, Calum; Lane, Pierre M

    2013-10-01

    Autofluorescence (AF) imaging provides valuable information about the structural and chemical states of tissue that can be used for early cancer detection. Optical scattering and absorption of excitation and emission light by the epithelium can significantly affect observed tissue AF intensity. Determining the effect of epithelial attenuation on the AF intensity could lead to a more accurate interpretation of AF intensity. We propose to use optical coherence tomography coregistered with AF imaging to characterize the AF attenuation due to the epithelium. We present imaging results from three vital tissue models, each consisting of a three-dimensional tissue culture grown from one of three epithelial cell lines (HCT116, OVCAR8, and MCF7) and immobilized on a fluorescence substrate. The AF loss profiles in the tissue layer show two different regimes, each approximately linearly decreasing with thickness. For thin cell cultures (<300 μm), the AF signal changes as AF(t)/AF(0)=1-1.3t (t is the thickness in millimeter). For thick cell cultures (>400 μm), the AF loss profiles have different intercepts but similar slopes. The data presented here can be used to estimate AF loss due to a change in the epithelial layer thickness and potentially to reduce AF bronchoscopy false positives due to inflammation and non-neoplastic epithelial thickening.

  18. Maintenance of genetic variation in human personality: testing evolutionary models by estimating heritability due to common causal variants and investigating the effect of distant inbreeding.

    PubMed

    Verweij, Karin J H; Yang, Jian; Lahti, Jari; Veijola, Juha; Hintsanen, Mirka; Pulkki-Råback, Laura; Heinonen, Kati; Pouta, Anneli; Pesonen, Anu-Katriina; Widen, Elisabeth; Taanila, Anja; Isohanni, Matti; Miettunen, Jouko; Palotie, Aarno; Penke, Lars; Service, Susan K; Heath, Andrew C; Montgomery, Grant W; Raitakari, Olli; Kähönen, Mika; Viikari, Jorma; Räikkönen, Katri; Eriksson, Johan G; Keltikangas-Järvinen, Liisa; Lehtimäki, Terho; Martin, Nicholas G; Järvelin, Marjo-Riitta; Visscher, Peter M; Keller, Matthew C; Zietsch, Brendan P

    2012-10-01

    Personality traits are basic dimensions of behavioral variation, and twin, family, and adoption studies show that around 30% of the between-individual variation is due to genetic variation. There is rapidly growing interest in understanding the evolutionary basis of this genetic variation. Several evolutionary mechanisms could explain how genetic variation is maintained in traits, and each of these makes predictions in terms of the relative contribution of rare and common genetic variants to personality variation, the magnitude of nonadditive genetic influences, and whether personality is affected by inbreeding. Using genome-wide single nucleotide polymorphism (SNP) data from > 8000 individuals, we estimated that little variation in the Cloninger personality dimensions (7.2% on average) is due to the combined effect of common, additive genetic variants across the genome, suggesting that most heritable variation in personality is due to rare variant effects and/or a combination of dominance and epistasis. Furthermore, higher levels of inbreeding were associated with less socially desirable personality trait levels in three of the four personality dimensions. These findings are consistent with genetic variation in personality traits having been maintained by mutation-selection balance.

  19. Interpolated twitches in fatiguing single mouse muscle fibres: implications for the assessment of central fatigue.

    PubMed

    Place, Nicolas; Yamada, Takashi; Bruton, Joseph D; Westerblad, Håkan

    2008-06-01

    An electrically evoked twitch during a maximal voluntary contraction (twitch interpolation) is frequently used to assess central fatigue. In this study we used intact single muscle fibres to determine if intramuscular mechanisms could affect the force increase with the twitch interpolation technique. Intact single fibres from flexor digitorum brevis of NMRI mice were dissected and mounted in a chamber equipped with a force transducer. Free myoplasmic [Ca2+] ([Ca2+](i)) was measured with the fluorescent Ca2+ indicator indo-1. Seven fibres were fatigued with repeated 70 Hz tetani until 40% initial force with an interpolated pulse evoked every fifth tetanus. Results showed that the force generated by the interpolated twitch increased throughout fatigue, being 9 +/- 1% of tetanic force at the start and 19 +/- 1% at the end (P < 0.001). This was not due to a larger increase in [Ca2+](i) induced by the interpolated twitch during fatigue but rather to the fact that the force-[Ca2+](i) relationship is sigmoidal and fibres entered a steeper part of the relationship during fatigue. In another set of experiments, we observed that repeated tetani evoked at 150 Hz resulted in more rapid fatigue development than at 70 Hz and there was a decrease in force ('sag') during contractions, which was not observed at 70 Hz. In conclusion, the extent of central fatigue is difficult to assess and it may be overestimated when using the twitch interpolation technique.

  20. Effect of heat treatment on fatigue resistance of spring steel 60Si2CrVAT

    NASA Astrophysics Data System (ADS)

    Shiyong, Liu; Deyi, Liu; Shicheng, Liu

    2010-07-01

    Fatigue resistance of heat-treated spring steel 60Si2CrVAT due to three-point bending with step growth in the load is studied. The microstructure of the steel and fatigue fracture surfaces are analyzed by the method of scanning electron microscopy. The possibilities of raising the fatigue resistance of springs used in high-speed freight bogies are considered.

  1. 14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Metallic damage tolerance and fatigue... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue... evaluation of the strength, detail design, and fabrication must show that catastrophic failure due to...

  2. 14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 14 Aeronautics and Space 1 2014-01-01 2014-01-01 false Metallic damage tolerance and fatigue... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue... evaluation of the strength, detail design, and fabrication must show that catastrophic failure due to...

  3. 14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Metallic damage tolerance and fatigue... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue... evaluation of the strength, detail design, and fabrication must show that catastrophic failure due to...

  4. 14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 14 Aeronautics and Space 1 2012-01-01 2012-01-01 false Metallic damage tolerance and fatigue... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue... evaluation of the strength, detail design, and fabrication must show that catastrophic failure due to...

  5. 14 CFR 23.574 - Metallic damage tolerance and fatigue evaluation of commuter category airplanes.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 14 Aeronautics and Space 1 2013-01-01 2013-01-01 false Metallic damage tolerance and fatigue... COMMUTER CATEGORY AIRPLANES Structure Fatigue Evaluation § 23.574 Metallic damage tolerance and fatigue... evaluation of the strength, detail design, and fabrication must show that catastrophic failure due to...

  6. Jumplike fatigue crack growth in compressor blades

    NASA Astrophysics Data System (ADS)

    Limar', L. V.; Demina, Yu. A.; Botvina, L. R.

    2014-04-01

    It is shown that power relations between the two main fractographic characteristics of fracture surfaces forming during jumplike fatigue crack growth, namely, the crack depth and the corresponding crack front length, can be used to estimate the fracture stress during vibration tests of the compressor blades of an aviation gas turbine engine, which are made of VT3-1 titanium alloy.

  7. Altered resting brain connectivity in persistent cancer related fatigue.

    PubMed

    Hampson, Johnson P; Zick, Suzanna M; Khabir, Tohfa; Wright, Benjamin D; Harris, Richard E

    2015-01-01

    There is an estimated 3 million women in the US living as breast cancer survivors and persistent cancer related fatigue (PCRF) disrupts the lives of an estimated 30% of these women. PCRF is associated with decreased quality of life, decreased sleep quality, impaired cognition and depression. The mechanisms of cancer related fatigue are not well understood; however, preliminary findings indicate dysfunctional activity in the brain as a potential factor. Here we investigate the relationship between PCRF on intrinsic resting state connectivity in this population. Twenty-three age matched breast cancer survivors (15 fatigued and 8 non-fatigued) who completed all cancer-related treatments at least 12 weeks prior to the study, were recruited to undergo functional connectivity magnetic resonance imaging (fcMRI). Intrinsic resting state networks were examined with both seed based and independent component analysis methods. Comparisons of brain connectivity patterns between groups as well as correlations with self-reported fatigue symptoms were performed. Fatigued patients displayed greater left inferior parietal lobule to superior frontal gyrus connectivity as compared to non-fatigued patients (P < 0.05 FDR corrected). This enhanced connectivity was associated with increased physical fatigue (P = 0.04, r = 0.52) and poor sleep quality (P = 0.04, r = 0.52) in the fatigued group. In contrast greater connectivity in the non-fatigued group was found between the right precuneus to the periaqueductal gray as well as the left IPL to subgenual cortex (P < 0.05 FDR corrected). Mental fatigue scores were associated with greater default mode network (DMN) connectivity to the superior frontal gyrus (P = 0.05 FDR corrected) among fatigued subjects (r = 0.82) and less connectivity in the non-fatigued group (r = -0.88). These findings indicate that there is enhanced intrinsic DMN connectivity to the frontal gyrus in breast cancer survivors with persistent fatigue. As

  8. Altered resting brain connectivity in persistent cancer related fatigue

    PubMed Central

    Hampson, Johnson P.; Zick, Suzanna M.; Khabir, Tohfa; Wright, Benjamin D.; Harris, Richard E.

    2015-01-01

    There is an estimated 3 million women in the US living as breast cancer survivors and persistent cancer related fatigue (PCRF) disrupts the lives of an estimated 30% of these women. PCRF is associated with decreased quality of life, decreased sleep quality, impaired cognition and depression. The mechanisms of cancer related fatigue are not well understood; however, preliminary findings indicate dysfunctional activity in the brain as a potential factor. Here we investigate the relationship between PCRF on intrinsic resting state connectivity in this population. Twenty-three age matched breast cancer survivors (15 fatigued and 8 non-fatigued) who completed all cancer-related treatments at least 12 weeks prior to the study, were recruited to undergo functional connectivity magnetic resonance imaging (fcMRI). Intrinsic resting state networks were examined with both seed based and independent component analysis methods. Comparisons of brain connectivity patterns between groups as well as correlations with self-reported fatigue symptoms were performed. Fatigued patients displayed greater left inferior parietal lobule to superior frontal gyrus connectivity as compared to non-fatigued patients (P < 0.05 FDR corrected). This enhanced connectivity was associated with increased physical fatigue (P = 0.04, r = 0.52) and poor sleep quality (P = 0.04, r = 0.52) in the fatigued group. In contrast greater connectivity in the non-fatigued group was found between the right precuneus to the periaqueductal gray as well as the left IPL to subgenual cortex (P < 0.05 FDR corrected). Mental fatigue scores were associated with greater default mode network (DMN) connectivity to the superior frontal gyrus (P = 0.05 FDR corrected) among fatigued subjects (r = 0.82) and less connectivity in the non-fatigued group (r = −0.88). These findings indicate that there is enhanced intrinsic DMN connectivity to the frontal gyrus in breast cancer survivors with persistent fatigue. As

  9. SU-E-J-164: Estimation of DVH Variation for PTV Due to Interfraction Organ Motion in Prostate VMAT Using Gaussian Error Function

    SciTech Connect

    Lewis, C; Jiang, R; Chow, J

    2015-06-15

    Purpose: We developed a method to predict the change of DVH for PTV due to interfraction organ motion in prostate VMAT without repeating the CT scan and treatment planning. The method is based on a pre-calculated patient database with DVH curves of PTV modelled by the Gaussian error function (GEF). Methods: For a group of 30 patients with different prostate sizes, their VMAT plans were recalculated by shifting their PTVs 1 cm with 10 increments in the anterior-posterior, left-right and superior-inferior directions. The DVH curve of PTV in each replan was then fitted by the GEF to determine parameters describing the shape of curve. Information of parameters, varying with the DVH change due to prostate motion for different prostate sizes, was analyzed and stored in a database of a program written by MATLAB. Results: To predict a new DVH for PTV due to prostate interfraction motion, prostate size and shift distance with direction were input to the program. Parameters modelling the DVH for PTV were determined based on the pre-calculated patient dataset. From the new parameters, DVH curves of PTVs with and without considering the prostate motion were plotted for comparison. The program was verified with different prostate cases involving interfraction prostate shifts and replans. Conclusion: Variation of DVH for PTV in prostate VMAT can be predicted using a pre-calculated patient database with DVH curve fitting. The computing time is fast because CT rescan and replan are not required. This quick DVH estimation can help radiation staff to determine if the changed PTV coverage due to prostate shift is tolerable in the treatment. However, it should be noted that the program can only consider prostate interfraction motions along three axes, and is restricted to prostate VMAT plan using the same plan script in the treatment planning system.

  10. Mechanisms of peripheral fatigue.

    PubMed

    Kirkendall, D T

    1990-08-01

    Fatigue can be defined as the failure to maintain an expected power output. This is often an antecedent to some sports-related injury. It is important for those involved in physical performance to be familiar with the variety of mechanisms which can lead to fatigue. All too often, a single factor is described as the cause of fatigue when actually fatigue may be a combination of factors that contribute to the sequence of events that results in decreased performance. It may be suggested that every step in the chain of events that leads to voluntary contraction of skeletal muscle could be a culprit in fatigue. Peripheral sites and processes include the motor neuron, neuromuscular junction, sarcolemmal membrane, excitation-contraction coupling, accumulation of metabolites, or depletion of fuels. Physical training is frequently designed to delay the onset of fatigue. The actual mechanism(s) add to the specificity concept, that is, a "specificity of fatigue". To the performer, the end result is the same, the inability to maintain his or her expected level of performance or power output.

  11. Elevated temperature biaxial fatigue

    NASA Technical Reports Server (NTRS)

    Jordan, E. H.

    1985-01-01

    A 3 year experimental program for studying elevated temperature biaxial fatigue of a nickel based alloy Hastelloy-X has been completed. A new high temperature fatigue test facility with unique capabilities has been developed. Effort was directed toward understanding multiaxial fatigue and correlating the experimental data to the existing theories of fatigue failure. The difficult task of predicting fatigue lives for nonproportional loading was used as an ultimate test for various life prediction methods being considered. The primary means of reaching improved understanding were through several critical nonproportional loading experiments. The direction of cracking observed on failed specimens was also recorded and used to guide the development of the theory. Cyclic deformation responses were permanently recorded digitally during each test. It was discovered that the cracking mode switched from primarily cracking on the maximum shear planes at room temperature to cracking on the maximum normal strain planes at 649 C. In contrast to some other metals, loading path in nonproportional loading had little effect on fatigue lives. Strain rate had a small effect on fatigue lives at 649 C. Of the various correlating parameters the modified plastic work and octahedral shear stress were the most successful.

  12. A new method for estimation of TEC from GNSS receivers during multiple cycle slips and data loss due to ionospheric irregularities

    NASA Astrophysics Data System (ADS)

    Dashora, Nirvikar

    2012-07-01

    Estimation of total electron content (TEC) is a must to utilize the GNSS signal for ionospheric research. The estimation of absolute ionospheric TEC from raw GNSS data itself is a lengthy and complex task and requires knowledge of sophisticated computer programming skills, satellite orbital geometry and many other aspects like GNSS signal structure, satellite and receiver specific information etc. Not many software are available that automatize the complex task of cycle slip detection and correction. The estimation of satellite and receiver biases is one more step left before getting true TEC. In equatorial and low latitudes, where the nighttime ionospheric irregularities are oft-occurring phenomena, estimation of TEC becomes a challenge. This is because, during TEC depletions and scintillations, the loss of lock in the receiver results either in data loss or sharp gradients in the recorded delays; more often for phase than code. Raw data in form of accumulated phase in radians and total code-range in meters show random occurrences of multiple cycle slips and data loss of several minutes in the data file. Thus, such phase and code data has to be corrected first before processing it to obtain TEC. Almost all available software/algorithms suggest flagging such data for no further use. Hence, TEC cannot be estimated during multiple cycle slip events within few minutes from raw GPS data. But, for ionospheric research the time of occurrence, evolution and drift of depletions are very useful. This paper details a complete new software for pre-processing the raw RINEX (receiver independent exchange format) data and retrieval of TEC using code and carrier-phase measurements from an stand alone dual frequency GPS receiver. We use modified and new sets of algorithms a GNSS receiver. It is significant to note that we are able to retrieves almost all the the corrupted TEC data points due to random multiple cycle slip events which are oft-occurring phenomena during ESF in

  13. Too generous to a fault? Is reliable earthquake safety a lost art? Errors in expected human losses due to incorrect seismic hazard estimates

    NASA Astrophysics Data System (ADS)

    Bela, James

    2014-11-01

    "One is well advised, when traveling to a new territory, to take a good map and then to check the map with the actual territory during the journey." In just such a reality check, Global Seismic Hazard Assessment Program (GSHAP) maps (prepared using PSHA) portrayed a "low seismic hazard," which was then also assumed to be the "risk to which the populations were exposed." But time-after-time-after-time the actual earthquakes that occurred were not only "surprises" (many times larger than those implied on the maps), but they were often near the maximum potential size (Maximum Credible Earthquake or MCE) that geologically could occur. Given these "errors in expected human losses due to incorrect seismic hazard estimates" revealed globally in these past performances of the GSHAP maps (> 700,000 deaths 2001-2011), we need to ask not only: "Is reliable earthquake safety a lost art?" but also: "Who and what were the `Raiders of the Lost Art?' "

  14. Nondestructive characterization of fatigue damage with thermography

    NASA Astrophysics Data System (ADS)

    Roesner, Henrik; Sathish, Shamachary; Meyendorf, Norbert

    2001-08-01

    A thermal imaging NDE method has been developed for nondestructive characterization of early stages of fatigue damage. The method is based on evaluation of the thermal effects induced in a material by a short-term mechanical loading. The mechanical loading causes in addition to thermoelastic temperature change, an increase due to heat dissipation that depends upon the microstructure of the material in a characteristic manner. The origin of this heat dissipation is the mechanical damping process. Utilizing the initial temperature rise due to a short-term mechanical loading, the dissipated energy per cycle was evaluated as a thermal parameter. This new thermal NDE parameter allows a quantitative characterization of the mechanical hysteresis, without the need for calibration to eliminate influences of thermal boundary conditions. The measurement of the thermal NDE parameters has been performed on Ti-6Al-4V dog-bone specimens, fatigued in low cycle fatigue (LCF) as well as in high cycle fatigue (HCF) experiments. Characteristic dependence of the NDE parameters on the already accumulated fatigue damage has been observed. The advantage of the thermal method is the applicability to components under service conditions because of simplicity, rapid measurements (a few seconds) and the ability of locally resolved evaluations.

  15. Thermomechanical Multiaxial Fatigue Testing Capability Developed

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Structural components in aeronautical gas turbine engines typically experience multiaxial states of stress under nonisothermal conditions. To estimate the durability of the various components in the engine, one must characterize the cyclic deformation and fatigue behavior of the materials used under thermal and complex mechanical loading conditions. To this end, a testing protocol and associated test control software were developed at the NASA Lewis Research Center for thermomechanical axial-torsional fatigue tests. These tests are to be performed on thin-walled, tubular specimens fabricated from the cobalt-based superalloy Haynes 188. The software is written in C and runs on an MS-DOS based microcomputer.

  16. Estimation of extreme sea levels along the Bangladesh coast due to storm surge and sea level rise using EEMD and EVA

    NASA Astrophysics Data System (ADS)

    Lee, Han Soo

    2013-09-01

    Extreme sea levels due to storm surge and future sea level rise (SLR) in the year 2050 are estimated using ensemble empirical mode decomposition (EEMD) and extreme value analysis (EVA) based on long-term sea level records from Hiron Point (HP) on the coast of western Bangladesh. EEMD is an adaptive method that can detrend the nonlinear trend and separate the tidal motions from the original sea level records to reconstruct storm surge levels at HP. The reconstructed storm surge levels are then applied to EVA to obtain the extreme storm surges in the target return periods at a 95% confidence interval (CI). The 30, 50, and 100 year return levels at HP obtained by EVA are 1.59, 1.66, and 1.75 m. The SLR trend obtained from EEMD is 4.46 mm/yr over April 1990 to March 2009, which is larger than the recent altimetry-based global rate of 3.3 ± 0.4 mm/yr over the period from 1993 to 2007. The resulting SLR in 2050 is estimated as 0.34 m. Therefore, the extreme sea level in 2050 due to SLR and the storm surge at a 100 year return level would be 2.09 m (95% CI from 1.91 to 2.48 m). The SLR depends not only on changes in the mass and volume of sea water but also on other factors, such as local subsidence, river discharge, sediment and the effects of vegetation. The residual nonlinear trend of SLR obtained from EEMD can be regarded as an adaptive sea level after considering those factors and their nonlinearity.

  17. Fatigue 󈨛. Volume 2,

    DTIC Science & Technology

    1987-06-01

    fatigue cracks grown in a nominally elastic field. EXPERIMENTAL DETAILS A low alloy steel (QIN) with a composition closely similar to HY80 , i.e. 2.5...Prediction of Steel Cords - A. PRAKASH, 645 G.A. COSTELLO, R.M. SHEMENSKI AND D.K. KIM Effect of Hold Time on Fatigue of Lead Rich 655 PbSn Solder...S. VAYNMAN, M.E. FINE AND D.A. JEANNOTTE On Cleavage in Fatigue for Rail Steels - 667 ZHU DONG, CAI QIGONG and YAO HENG Influence of Cleavage on

  18. Utility of birefringence changes due to collagen thermal denaturation rate process analysis: vessel wall temperature estimation for new short term heating balloon angioplasty

    NASA Astrophysics Data System (ADS)

    Kaneko, Kenji; Shimazaki, Natsumi; Gotoh, Maya; Nakatani, Eriko; Arai, Tsunenori

    2007-02-01

    Our photo thermal reaction heating architecture balloon realizes less than 10 s short term heating that can soften vessel wall collagen without damaging surrounding tissue thermally. New thermal balloon angioplasty, photo-thermo dynamic balloon angioplasty (PTDBA) has experimentally shown sufficient opening with 2 atm low pressure dilation and prevention of chronic phase restenosis and acute phase thrombus in vivo. Even though PTDBA has high therapeutic potential, the most efficient heating condition is still under study, because relationship of treatment and thermal dose to vessel wall is not clarified yet. To study and set the most efficient heating condition, we have been working on establishment of temperature history estimation method from our previous experimental results. Heating target of PTDBA, collagen, thermally denatures following rate process. Denaturation is able to be quantified with measured collagen birefringence value. To express the denaturation with equation of rate process, the following ex vivo experiments were performed. Porcine extracted carotid artery was soaked in two different temperature saline baths to enforce constant temperature heating. Higher temperature bath was set to 40 to 80 degree Celsius and soaking duration was 5 to 40 s. Samples were observed by a polarizing microscope and a scanning electron microscope. The birefringence was measured by polarizing microscopic system using Brace-Koehler compensator 1/30 wavelength. The measured birefringence showed temperature dependency and quite fit with the rate process equation. We think vessel wall temperature is able to be estimated using the birefringence changes due to thermal denaturation.

  19. Effect of Extended CT Perfusion Acquisition Time on Ischemic Core and Penumbra Volume Estimation in Patients with Acute Ischemic Stroke due to a Large Vessel Occlusion

    PubMed Central

    Borst, Jordi; Marquering, Henk A.; Beenen, Ludo F. M.; Berkhemer, Olvert A.; Dankbaar, Jan Willem; Riordan, Alan J.; Majoie, Charles B. L. M.

    2015-01-01

    Background and Purpose It has been suggested that CT Perfusion acquisition times <60 seconds are too short to capture the complete in and out-wash of contrast in the tissue, resulting in incomplete time attenuation curves. Yet, these short acquisitions times are not uncommon in clinical practice. The purpose of this study was to investigate the occurrence of time attenuation curve truncation in 48 seconds CT Perfusion acquisition and to quantify its effect on ischemic core and penumbra estimation in patients with acute ischemic stroke due to a proximal intracranial arterial occlusion of the anterior circulation. Materials and Methods We analyzed CT Perfusion data with 48 seconds and extended acquisition times, assuring full time attenuation curves, of 36 patients. Time attenuation curves were classified as complete or truncated. Ischemic core and penumbra volumes resulting from both data sets were compared by median paired differences and interquartile ranges. Controlled experiments were performed using a digital CT Perfusion phantom to investigate the effect of time attenuation curve truncation on ischemic core and penumbra estimation. Results In 48 seconds acquisition data, truncation was observed in 24 (67%) cases for the time attenuation curves in the ischemic core, in 2 cases for the arterial input function and in 5 cases for the venous output function. Analysis of extended data resulted in smaller ischemic cores and larger penumbras with a median difference of 13.2 (IQR: 4.3–26.0)ml (P<0.001) and; 12.4 (IQR: 4.1–25.7)ml (P<0.001), respectively. The phantom data showed increasing ischemic core overestimation with increasing tissue time attenuation curve truncation. Conclusions Truncation is common in patients with large vessel occlusion and results in repartitioning of the area of hypoperfusion into larger ischemic core and smaller penumbra estimations. Phantom experiments confirmed that truncation results in overestimation of the ischemic core. PMID

  20. Nondestructive Evaluation of Metal Fatigue.

    DTIC Science & Technology

    1977-02-01

    Magnetic perturbation signatures and Barkhausen noise results have been obtained from an AISI 4340 steel fatigue specimen stress-cycled at 180ksi...vicinity of the fatigue crack. Barkhausen noise signals were obtained on a grid pattern in the vicinity of several fatigue cracks with a Barkhausen ...fatigue specimens are being fabricated for magnetic perturbation and Barkhausen noise analysis measurements. Fatigue cracks in Ti-6Al-4V specimens were investigated with the electric current injection technique.

  1. Statistical optimisation techniques in fatigue signal editing problem

    SciTech Connect

    Nopiah, Z. M.; Osman, M. H.; Baharin, N.; Abdullah, S.

    2015-02-03

    Success in fatigue signal editing is determined by the level of length reduction without compromising statistical constraints. A great reduction rate can be achieved by removing small amplitude cycles from the recorded signal. The long recorded signal sometimes renders the cycle-to-cycle editing process daunting. This has encouraged researchers to focus on the segment-based approach. This paper discusses joint application of the Running Damage Extraction (RDE) technique and single constrained Genetic Algorithm (GA) in fatigue signal editing optimisation.. In the first section, the RDE technique is used to restructure and summarise the fatigue strain. This technique combines the overlapping window and fatigue strain-life models. It is designed to identify and isolate the fatigue events that exist in the variable amplitude strain data into different segments whereby the retention of statistical parameters and the vibration energy are considered. In the second section, the fatigue data editing problem is formulated as a constrained single optimisation problem that can be solved using GA method. The GA produces the shortest edited fatigue signal by selecting appropriate segments from a pool of labelling segments. Challenges arise due to constraints on the segment selection by deviation level over three signal properties, namely cumulative fatigue damage, root mean square and kurtosis values. Experimental results over several case studies show that the idea of solving fatigue signal editing within a framework of optimisation is effective and automatic, and that the GA is robust for constrained segment selection.

  2. The power induced effects module: A FORTRAN code which estimates lift increments due to power induced effects for V/STOL flight

    NASA Technical Reports Server (NTRS)

    Sandlin, Doral R.; Howard, Kipp E.

    1991-01-01

    A user friendly FORTRAN code that can be used for preliminary design of V/STOL aircraft is described. The program estimates lift increments, due to power induced effects, encountered by aircraft in V/STOL flight. These lift increments are calculated using empirical relations developed from wind tunnel tests and are due to suckdown, fountain, ground vortex, jet wake, and the reaction control system. The code can be used as a preliminary design tool along with NASA Ames' Aircraft Synthesis design code or as a stand-alone program for V/STOL aircraft designers. The Power Induced Effects (PIE) module was validated using experimental data and data computed from lift increment routines. Results are presented for many flat plate models along with the McDonnell Aircraft Company's MFVT (mixed flow vectored thrust) V/STOL preliminary design and a 15 percent scale model of the YAV-8B Harrier V/STOL aircraft. Trends and magnitudes of lift increments versus aircraft height above the ground were predicted well by the PIE module. The code also provided good predictions of the magnitudes of lift increments versus aircraft forward velocity. More experimental results are needed to determine how well the code predicts lift increments as they vary with jet deflection angle and angle of attack. The FORTRAN code is provided in the appendix.

  3. Chronic Fatigue Syndrome

    MedlinePlus

    ... Do you recommend that I also see a mental health provider? Don't hesitate to ask other questions ... for evidence of some of the top suspects. Mental health issues. Fatigue is also a symptom of a ...

  4. Chronic Fatigue Syndrome

    MedlinePlus

    ... of fatigue. Think "alternative." Acupuncture, reiki, massage, stretching, yoga, and t'ai chi seem to help many ... not beginning therapy — and therapies like the stress-management techniques and graded exercise previously mentioned have been ...

  5. Micromechanics of Fatigue.

    DTIC Science & Technology

    1992-06-01

    recalled. Application of the derived tools to Apha-Two- Titanium Aluminide Aliov is made with a first series of strain controlled fatigue tests the locally...accumulation, and, multiaxial fatigue. In section 6, application is performed on the Alpha-Two- Titanium Alum:Aide Alloy.With a first serie of strain controlled ...tests needed for the identification of the model are described in the following figures. Test n’l is a classical tensile test strain controlled 1 = 0

  6. Fracture and Fatigue

    DTIC Science & Technology

    1988-04-01

    fracture. The main additional categories of crack growth are elastic-plastic crack growth, fatigue crack growth, and crack growth as affected by...FRACTURE AND FATIGUE R. 0. RITCHIE W. W. GERBERICH J. H. UNDERWOOD DTIC AM ELECTE JUL 1 11988 APRIL 1988 FH US ARMY ARMAMENT RESEARCH, DEVELOPMENT AND...other authorized documents. N The use of trade name(s) and/or manufacturer (s) does not constitute an official indorsement or approval. DESTRUCTION NOTICE

  7. Regional distribution of fatiguing illnesses in the United States: a pilot study.

    PubMed

    Bierl, Cynthia; Nisenbaum, Rosane; Hoaglin, David C; Randall, Bonnie; Jones, Ann-Britt; Unger, Elizabeth R; Reeves, William C

    2004-02-04

    BACKGROUND: Chronic fatigue syndrome (CFS) is a debilitating illness with no known cause or effective therapy. Population-based epidemiologic data on CFS prevalence are critical to put CFS in a realistic context for public health officials and others responsible for allocating resources. METHODS: We conducted a pilot random-digit-dialing survey to estimate the prevalence of fatiguing illnesses in different geographic regions and in urban and rural populations of the United States. This report focuses on 884 of 7,317 respondents 18 to 69 years old. Fatigued (440) and randomly selected non-fatigued (444) respondents completed telephone questionnaires concerning fatigue, other symptoms, and medical history. RESULTS: We estimated 12,186 per 100,000 persons 18 to 69 years of age suffered from fatigue lasting for at least 6 months (chronic fatigue), and 1,197 per 100,000 described an illness that, though lacking clinical evaluation, met criteria for CFS (CFS-like). Chronic fatigue and CFS-like illness were more common in rural than in urban populations, although the differences were not significant. The prevalence of these fatiguing illnesses did not differ meaningfully among the four regions surveyed, and no significant geographic trends were observed. CONCLUSIONS: This investigation estimated that nearly 2.2 million American adults suffer from CFS-like illness. The study also suggested the need to focus future investigations of fatigue on populations with lower incomes and less education. There was no evidence for regional differences in the occurrence of fatiguing illnesses.

  8. Fatigue and multiple sclerosis.

    PubMed

    Béthoux, F

    2006-07-01

    Even if the definition and pathophysiology of fatigue in multiple sclerosis (MS) are still debated, and despite the scarcity of objective markers correlated with the subjective sensation of fatigue, a review of the literature shows the importance of its detection and management, and allows one to propose therapeutic strategies. Fatigue is not only the most frequently reported symptom in MS, but also a frequent source of activity and participation limitations, psychological distress, and impairment of quality of life. Its management, which must be initiated early, is based on a comprehensive evaluation of its characteristics and consequences (sometimes with the use of scales such as the Fatigue Severity Scale and the Modified Fatigue Impact Scale), and on the identification of many potential contributing factors (psychological disorders, sleep disturbances, pain, infections and other comorbidities, medications, and deconditioning). Rehabilitative interventions are essential to the treatment of fatigue. Beyond the traditional energy conservation strategies and cooling techniques, several randomized controlled studies have demonstrated the positive impact of aerobic exercise. Medications are partially beneficial, and with the exception of amantadine, their efficacy has not been confirmed by randomized double-blind trials.

  9. BIOMARKERS for CHRONIC FATIGUE

    PubMed Central

    Broderick, Gordon; Fletcher, Mary Ann

    2012-01-01

    Fatigue that persists for 6 months or more is termed chronic fatigue. Chronic fatigue (CF) in combination with a minimum of 4 of 8 symptoms and the absence of diseases that could explain these symptoms, constitute the case definition for chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME). Inflammation, immune system activation, autonomic dysfunction, impaired functioning in the hypothalamic-pituitary-adrenal axis, and neuroendocrine dysregulation have all been suggested as root causes of fatigue. The identification of objective markers consistently associated with CFS/ME is an important goal in relation to diagnosis and treatment, as the current case definitions are based entirely on physical signs and symptoms. This review is focused on the recent literature related to biomarkers for fatigue associated with CFS/ME and, for comparison, those associated with other diseases. These markers are distributed across several of the body’s core regulatory systems. A complex construct of symptoms emerges from alterations and/or dysfunctions in the nervous, endocrine and immune systems. We propose that new insight will depend on our ability to develop and deploy an integrative profiling of CFS/ME pathogenesis at the molecular level. Until such a molecular signature is obtained efforts to develop effective treatments will continue to be severely limited. PMID:22732129

  10. Life Estimation of Hip Joint Prosthesis

    NASA Astrophysics Data System (ADS)

    Desai, C.; Hirani, H.; Chawla, A.

    2014-11-01

    Hip joint is one of the largest weight-bearing structures in the human body. In the event of a failure of the natural hip joint, it is replaced with an artificial hip joint, known as hip joint prosthesis. The design of hip joint prosthesis must be such so as to resist fatigue failure of hip joint stem as well as bone cement, and minimize wear caused by sliding present between its head and socket. In the present paper an attempt is made to consider both fatigue and wear effects simultaneously in estimating functional-life of the hip joint prosthesis. The finite element modeling of hip joint prosthesis using HyperMesh™ (version 9) has been reported. The static analysis (load due to the dead weight of the body) and dynamic analysis (load due to walking cycle) have been described. Fatigue life is estimated by using the S-N curve of individual materials. To account for progressive wear of hip joint prosthesis, Archard's wear law, modifications in socket geometry and dynamic analysis have been used in a sequential manner. Using such sequential programming reduction in peak stress has been observed with increase in wear. Finally life is estimated on the basis of socket wear.

  11. Statistical summaries of fatigue data for design purposes

    NASA Technical Reports Server (NTRS)

    Wirsching, P. H.

    1983-01-01

    Two methods are discussed for constructing a design curve on the safe side of fatigue data. Both the tolerance interval and equivalent prediction interval (EPI) concepts provide such a curve while accounting for both the distribution of the estimators in small samples and the data scatter. The EPI is also useful as a mechanism for providing necessary statistics on S-N data for a full reliability analysis which includes uncertainty in all fatigue design factors. Examples of statistical analyses of the general strain life relationship are presented. The tolerance limit and EPI techniques for defining a design curve are demonstrated. Examples usng WASPALOY B and RQC-100 data demonstrate that a reliability model could be constructed by considering the fatigue strength and fatigue ductility coefficients as two independent random variables. A technique given for establishing the fatigue strength for high cycle lives relies on an extrapolation technique and also accounts for "runners." A reliability model or design value can be specified.

  12. Fatigue in Parkinson's disease: report from a mutidisciplinary symposium

    PubMed Central

    Friedman, Joseph H; Beck, James C; Chou, Kelvin L; Clark, Gracia; Fagundes, Christopher P; Goetz, Christopher G; Herlofson, Karen; Kluger, Benzi; Krupp, Lauren B; Lang, Anthony E; Lou, Jao-Shin; Marsh, Laura; Newbould, Anne; Weintraub, Daniel

    2016-01-01

    Fatigue is a severe problem for many people living with Parkinson's disease (PD). Best estimates suggest that more than 50% of patients experience this debilitating symptom. Little is known about its etiology or treatment, making the understanding of fatigue a true unmet need. As part of the Parkinson's Disease Foundation Community Choice Research Program, patients, caregivers, and scientists attended a symposium on fatigue on 16 and 17 October 2014. We present a summary of that meeting, reviewing what is known about the diagnosis and treatment of fatigue, its physiology, and what we might learn from multiple sclerosis (MS), depression, and cancer—disorders in which fatigue figures prominently too. We conclude with focused recommendations to enhance our understanding and treatment of this prominent problem in PD. PMID:27239558

  13. Effect of Crystal Orientation on Fatigue Failure of Single Crystal Nickel Base Turbine Blade Superalloys

    NASA Technical Reports Server (NTRS)

    Arakere, N. K.; Swanson, G.

    2002-01-01

    High cycle fatigue (HCF) induced failures in aircraft gas turbine and rocket engine turbopump blades is a pervasive problem. Single crystal nickel turbine blades are being utilized in rocket engine turbopumps and jet engines throughout industry because of their superior creep, stress rupture, melt resistance, and thermomechanical fatigue capabilities over polycrystalline alloys. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493, PWA 1484, RENE' N-5 and CMSX-4. These alloys play an important role in commercial, military and space propulsion systems. Single crystal materials have highly orthotropic properties making the position of the crystal lattice relative to the part geometry a significant factor in the overall analysis. The failure modes of single crystal turbine blades are complicated to predict due to the material orthotropy and variations in crystal orientations. Fatigue life estimation of single crystal turbine blades represents an important aspect of durability assessment. It is therefore of practical interest to develop effective fatigue failure criteria for single crystal nickel alloys and to investigate the effects of variation of primary and secondary crystal orientation on fatigue life. A fatigue failure criterion based on the maximum shear stress amplitude /Delta(sub tau)(sub max))] on the 24 octahedral and 6 cube slip systems, is presented for single crystal nickel superalloys (FCC crystal). This criterion reduces the scatter in uniaxial LCF test data considerably for PWA 1493 at 1200 F in air. Additionally, single crystal turbine blades used in the alternate advanced high-pressure fuel turbopump (AHPFTP/AT) are modeled using a large-scale three-dimensional finite element model. This finite element model is capable of accounting for material orthotrophy and variation in primary and secondary crystal orientation. Effects of variation in crystal orientation on blade stress response are studied based on 297

  14. FEA Based Tool Life Quantity Estimation of Hot Forging Dies Under Cyclic Thermo-Mechanical Loads

    NASA Astrophysics Data System (ADS)

    Behrens, B.-A.; Bouguecha, A.; Schäfer, F.; Hadifi, T.

    2011-01-01

    Hot forging dies are exposed during service to a combination of cyclic thermo-mechanical, tribological and chemical loads. Besides abrasive and adhesive wear on the die surface, fatigue crack initiation with subsequent fracture is one of the most frequent causes of failure. In order to extend the tool life, the finite element analysis (FEA) may serve as a means for process design and process optimisation. So far the FEA based estimation of the production cycles until initial cracking is limited as tool material behaviour due to repeated loading is not captured with the required accuracy. Material models which are able to account for cyclic effects are not verified for the fatigue life predictions of forging dies. Furthermore fatigue properties from strain controlled fatigue tests of relevant hot work steels are to date not available to allow for a close-to-reality fatigue life prediction. Two industrial forging processes, where clear fatigue crack initiation has been observed are considered for a fatigue analysis. For this purpose the relevant tool components are modelled with elasto-plastic material behaviour. The predicted sites, where crack initiation occurs, agree with the ones observed on the real die component.

  15. An attempt to estimate the economic value of the loss of human life due to landslide and flood events in Italy

    NASA Astrophysics Data System (ADS)

    Salvati, Paola; Bianchi, Cinzia; Hussin, Haydar; Guzzetti, Fausto

    2013-04-01

    Landslide and flood events in Italy cause wide and severe damage to buildings and infrastructure, and are frequently involved in the loss of human life. The cost estimates of past natural disasters generally refer to the amount of public money used for the restoration of the direct damage, and most commonly do not account for all disaster impacts. Other cost components, including indirect losses, are difficult to quantify and, among these, the cost of human lives. The value of specific human life can be identified with the value of a statistical life (VLS), defined as the value that an individual places on a marginal change in their likelihood of death This is different from the value of an actual life. Based on information of fatal car accidents in Italy, we evaluate the cost that society suffers for the loss of life due to landslide and flood events. Using a catalogue of fatal landslide and flood events, for which information about gender and age of the fatalities is known, we determine the cost that society suffers for the loss of their life. For the purpose, we calculate the economic value in terms of the total income that the working-age population involved in the fatal events would have earned over the course of their life. For the computation, we use the pro-capita income calculated as the ratio between the GDP and the population value in Italy for each year, since 1980. Problems occur for children and retired people that we decided not to include in our estimates.

  16. Creep-fatigue interaction in aircraft gas turbine components by simulation and testing at scaled temperatures

    NASA Astrophysics Data System (ADS)

    Sabour, Mohammad Hossein

    Advanced gas turbine engines, which use hot section airfoil cooling, present a wide range of design problems. The frequencies of applied loads and the natural frequencies of the blade also are important since they have significant effects on failure of the component due to fatigue phenomenon. Due to high temperature environment the thermal creep and fatigue are quite severe. One-dimensional creep model, using ANSYS has been formulated in order to predict the creep life of a gas turbine engine blade. Innovative mathematical models for the prediction of the operating life of aircraft components, specifically gas turbine blades, which are subjected to creep-fatigue at high temperatures, are proposed. The components are modeled by FEM, mathematically, and using similitude principles. Three models have been suggested and evaluated numerically and experimentally. Using FEM method for natural frequencies causes phenomena such as curve veering which is studied in more detail. The simulation studies on the life-limiting modes of failure, as well as estimating the expected lifetime of the blade, using the proposed models have been carried out. Although the scale model approach has been used for quite some time, the thermal scaling has been used in this study for the first time. The only thermal studies in literature using scaling for structures is by NASA in which materials of both the prototype and the model are the same, but in the present study materials also are different. The finite element method is employed to model the structure. Because of stress redistribution due to the creep process, it is necessary to include a full inelastic creep step in the finite element formulation. Otherwise over-conservative creep life predictions will be estimated if only the initial elastic stresses are considered. The experimental investigations are carried out in order to validate the models. The main contributions in the thesis are: (1) Using similitude theory for life prediction of

  17. Some aspects of thermomechanical fatigue of AISI 304L stainless steel; Part 1: Creep-fatigue damage

    SciTech Connect

    Zauter, R. ); Christ, H.J. . Inst. of Materials Technology); Mughrabi, H. . Inst. for Materials Science)

    1994-02-01

    Thermomechanical fatigue (TMF) tests on the austenitic stainless steel AISI 304L have been conducted under true' plastic-strain control in vacuum. This report considers the damage occurring during TMF loading. It is shown how the temperature interval and the phasing (in phase, out-of-phase) determine the mechanical response and the lifetime of the specimens. If creep-fatigue interaction takes place during in-phase cycling, the damage occurs inside the material, leading creep-induced damage, and no lifetime reduction occurs, even if the material is exposed periodically to temperature in the creep regime. A formula is proposed which allows prediction of the failure mode, depending on whether creep-fatigue damage occurs or not. At a given strain rate, the formula is able to estimate the temperature of transition between pure fatigue and creep-fatigue damage.

  18. Improving Fatigue Performance of AHSS Welds

    SciTech Connect

    Feng, Zhili; Yu, Xinghua; Erdman, III, Donald L.; Wang, Yanli; Kelly, Steve; Hou, Wenkao; Yan, Benda; Wang, Zhifeng; Yu, Zhenzhen; Liu, Stephen

    2015-03-01

    Reported herein is technical progress on a U.S. Department of Energy CRADA project with industry cost-share aimed at developing the technical basis and demonstrate the viability of innovative in-situ weld residual stresses mitigation technology that can substantially improve the weld fatigue performance and durability of auto-body structures. The developed technology would be costeffective and practical in high-volume vehicle production environment. Enhancing weld fatigue performance would address a critical technology gap that impedes the widespread use of advanced high-strength steels (AHSS) and other lightweight materials for auto body structure light-weighting. This means that the automotive industry can take full advantage of the AHSS in strength, durability and crashworthiness without the concern of the relatively weak weld fatigue performance. The project comprises both technological innovations in weld residual stress mitigation and due-diligence residual stress measurement and fatigue performance evaluation. Two approaches were investigated. The first one was the use of low temperature phase transformation (LTPT) weld filler wire, and the second focused on novel thermo-mechanical stress management technique. Both technical approaches have resulted in considerable improvement in fatigue lives of welded joints made of high-strength steels. Synchrotron diffraction measurement confirmed the reduction of high tensile weld residual stresses by the two weld residual stress mitigation techniques.

  19. Influence of Fatigue in Neuromuscular Control of Spinal Stability

    PubMed Central

    Granata, Kevin P.; Slota, Greg P.; Wilson, Sara E.

    2006-01-01

    Lifting-induced fatigue may influence neuromuscular control of spinal stability. Stability is primarily controlled by muscle recruitment, active muscle stiffness, and reflex response. Fatigue has been observed to affect each of these neuromuscular parameters and may therefore affect spinal stability. A biomechanical model of spinal stability was implemented to evaluate the effects of fatigue on spinal stability. The model included a 6-degree-of-freedom representation of the spine controlled by 12 deformable muscles from which muscle recruitment was determined to simultaneously achieve equilibrium and stability. Fatigue-induced reduction in active muscle stiffness necessitated increased antagonistic cocontraction to maintain stability resulting in increased spinal compression with fatigue. Fatigueinduced reduction in force-generating capacity limited the feasible set of muscle recruitment patterns, thereby restricting the estimated stability of the spine. Electromyographic and trunk kinematics from 21 healthy participants were recorded during sudden-load trials in fatigued and unfatigued states. Empirical data supported the model predictions, demonstrating increased antagonistic cocontraction during fatigued exertions. Results suggest that biomechanical factors including spinal load and stability should be considered when performing ergonomic assessments of fatiguing lifting tasks. Potential applications of this research include a biomechanical tool for the design of administrative ergonomic controls in manual materials handling industries. PMID:15151156

  20. Prediction of residual fatigue life using nonlinear ultrasound

    NASA Astrophysics Data System (ADS)

    Amura, Mikael; Meo, Michele

    2012-04-01

    Prediction of fatigue life of components during service is an on-going and unsolved challenge for the NDT and structural health monitoring community. It has been demonstrated by a number of researchers that nonlinear guided waves or the acoustic nonlinear signature of fatigued cracked material provides clear signs of the progressive fatigue damage in the material, unlike linear guided waves. However, even with nonlinear acoustic-ultrasound methods there is a necessity to compare the current nonlinear feature to a previously measured cracked material state to assess the absolute residual fatigue life. In this paper, a new procedure based on the measurement of the second-order acoustic nonlinearity is presented which is able to assess the fatigue life of a metallic component without the need of a baseline. The Nazarov-Sutin crack nonlinearity equation and the Paris law are combined in order to obtain an analytical solution able to evaluate the theoretical second-order quadratic nonlinear parameters as a function of the crack growth and fatigue life that evolve during cyclic loading in metals. The model makes the assumption that the crack surface topology has variable geometrical parameters. The method was tested on aluminum alloy specimens AA2024-T351, containing fatigue fracture of different sizes, and excellent correlation was obtained between the theoretical and measured second-order nonlinear parameter. Then, it was demonstrated clearly that by measuring the nonlinear parameters it is possible to estimate crack size and fatigue life. Finally, advantages and limitations of the procedure are discussed.

  1. Experimental studies on physical deterioration and electrical fatigue behavior in ferroelectric polymers

    NASA Astrophysics Data System (ADS)

    He, Xiangtong

    Ferroelectric materials are widely used in various electronic applications based upon their excellent electrical bi-stabilities and dielectric performance in response to the applied electric field. They have been utilized to make nonvolatile electronic memories by exploiting the hysteretic behavior and high energy density capacitors in regard to the high capability of electrical energy storage. One critical issue is that the ferroelectrics are required to endure a large number of electrical cycles. A large body of scientific efforts has been devoted to high fatigue failure resistance of ferroelectric-based electronic devices. Fatigue failure of ferroelectric materials still needs to be solved. It is the objective of this work to explore the intrinsic origin of fatigue failure mechanisms. In this study, it was found that electric-field-induced stress relaxation in α-phase poly(vinylidene fluoride) (PVDF) films can be well described by using the Kohlraush function groups, also known as the stretched exponential relaxation function. The electric strength of the dielectric is strongly dependent on its elastic properties due to the electromechanical coupling effect. Our fitting result of the stretched exponent is in accordance with a Weibull cumulative distribution function. This indicates that the elastic properties of insulating polymers are crucial to the capability of electrical energy storage. In ferroelectric materials, the electromechanical coupling may be indicative of the microscopic origin of polarization fatigue. Further experiments were focused on the polarization fatigue in semi-crystalline poly(vinylidene fluoride trifluoroethylene) [P(VDF-TrFE)] copolymers films, whose ferroelectric response is superior to PVDF homopolymer films. Fatigue resistance of normal virgin P(VDF-TrFE) films was compared to that of P(VDF-TrFE) films modulated by using magnetic field. It was shown that normal P(VDF-TrFE) films exhibit a higher fatigue resistance. The artificially

  2. Understanding and Counteracting Fatigue in Flight Crews

    NASA Technical Reports Server (NTRS)

    Mallis, Melissa; Neri, David; Rosekind, Mark; Gander, Philippa; Caldwell, John; Graeber, Curtis

    2007-01-01

    The materials included in the collection of documents describe the research of the NASA Ames Fatigue Countermeasures Group (FCG), which examines the extent to which fatigue, sleep loss, and circadian disruption affect flight-crew performance. The group was formed in 1980 in response to a Congressional request to examine a possible safety problem of uncertain magnitude due to transmeridian flying and a potential problem due to fatigue in association with various factors found in air-transport operations and was originally called the Fatigue/Jet Lag Program. The goals of the FCG are: (1) the development and evaluation of strategies for mitigating the effects of sleepiness and circadian disruption on pilot performance levels; (2) the identification and evaluation of objective approaches for the prediction of alertness changes in flight crews; and (3) the transfer and application of research results to the operational field via classes, workshops, and safety briefings. Some of the countermeasure approaches that have been identified to be scientifically valid and operationally relevant are brief naps (less than 40 min) in the cockpit seat and 7-min activity breaks, which include postural changes and ambulation. Although a video-based alertness monitor based on slow eyelid closure shows promise in other operational environments, research by the FCG has demonstrated that in its current form at the time of this reporting, it is not feasible to implement it in the cockpit. Efforts also focus on documenting the impact of untreated fatigue on various types of flight operations. For example, the FCG recently completed a major investigation into the effects of ultra-long-range flights (20 continuous hours in duration) on the alertness and performance of pilots in order to establish a baseline set of parameters against which the effectiveness of new ultra-long-range fatigue remedies can be judged.

  3. Recovery from supraspinal fatigue is slowed in old adults after fatiguing maximal isometric contractions.

    PubMed

    Hunter, Sandra K; Todd, Gabrielle; Butler, Jane E; Gandevia, Simon C; Taylor, Janet L

    2008-10-01

    This study compared the contribution of supraspinal fatigue to muscle fatigue in old and young adults. Transcranial magnetic stimulation (TMS) of motor cortex was used to assess voluntary activation during maximal voluntary contractions (MVCs) of elbow flexor muscles in 17 young adults (25.5 +/- 3.6 yr; mean +/- SD) and 7 old adults (73.0 +/- 3.3 yr). Subjects performed a fatigue task involving six sustained MVCs (22-s duration, separated by 10 s). Young adults exhibited greater reductions in maximal voluntary torque (67 +/- 15% of baseline) than the old (37 +/- 6%; P < 0.001). Increments in torque (superimposed twitch) generated by TMS during sustained MVCs increased for the young and old (P < 0.001) but were larger for the old adults at the start of the sustained contractions and during recovery (P < 0.05). Voluntary activation was less for the old adults at the start of some sustained contractions and during recovery (P = 0.02). Motor-evoked potential area increased similarly with age during the fatiguing task but was greater for the old adults than young during recovery. Silent period duration lengthened less for the old adults during the fatigue task. At the end of the fatiguing task, peak relaxation rate of muscle fibers had declined more in the young than the old adults. The greater endurance with age is largely due to a difference in mechanisms located within the muscle. However, recovery from the fatiguing exercise is impaired for old adults because of greater supraspinal fatigue than in the young.

  4. Estimation of annual effective dose due to natural radioactive elements in ingestion of foodstuffs in tin mining area of Jos-Plateau, Nigeria.

    PubMed

    Jibiri, N N; Farai, I P; Alausa, S K

    2007-01-01

    Soils and food crops from a former tin mining location in a high background radiation area on the Jos-Plateau, Nigeria were collected and analyzed by gamma spectrometry to measure their contents of 40K, 238U and 232Th. As well as collecting samples, in situ dose rates on farms were measured using a precalibrated survey meter. Activity concentrations determined in food crops were compared with the local food derivatives or diets to investigate the possible removal or addition of radionuclides during food preparation by cooking or other means. Potassium-40 was found to contribute the highest activity in all the food products. The activity concentration of 40K, 238U and 232Th in local prepared diets ranged between 60 and 494 Bq kg-1, between BDL and 48 Bq kg-1 and between BDL and 17 Bq kg-1, respectively. The internal effective dose to individuals from the consumption of the food types was estimated on the basis of the measured radionuclide contents in the food crops. It ranged between 0.2 microSv y-1 (beans) and 2164 microSv y-1 (yam) while the annual external gamma effective dose in the farms due to soil radioactivity ranged between 228 microSv and 4065 microSv.

  5. Estimation of Effective Transmission Loss Due to Subtropical Hydrometeor Scatters using a 3D Rain Cell Model for Centimeter and Millimeter Wave Applications

    NASA Astrophysics Data System (ADS)

    Ojo, J. S.; Owolawi, P. A.

    2014-12-01

    The problem of hydrometeor scattering on microwave radio communication down links continues to be of interest as the number of the ground and earth space terminals continually grows The interference resulting from the hydrometeor scattering usually leads to the reduction in the signal-to-noise ratio ( SNR) at the affected terminal and at worst can even end up in total link outage. In this paper, an attempt has been made to compute the effective transmission loss due to subtropical hydrometeors on vertically polarized signals in Earth-satellite propagation paths in the Ku, Ka and V band frequencies based on the modified Capsoni 3D rain cell model. The 3D rain cell model has been adopted and modified using the subtropical log-normal distributions of raindrop sizes and introducing the equivalent path length through rain in the estimation of the attenuation instead of the usual specific attenuation in order to account for the attenuation of both wanted and unwanted paths to the receiver. The co-channels, interference at the same frequency is very prone to the higher amount of unwanted signal at the elevation considered. The importance of joint transmission is also considered.

  6. Ratcheting fatigue behavior of Zircaloy-2 at room temperature

    NASA Astrophysics Data System (ADS)

    Rajpurohit, R. S.; Sudhakar Rao, G.; Chattopadhyay, K.; Santhi Srinivas, N. C.; Singh, Vakil

    2016-08-01

    Nuclear core components of zirconium alloys experience asymmetric stress or strain cycling during service which leads to plastic strain accumulation and drastic reduction in fatigue life as well as dimensional instability of the component. Variables like loading rate, mean stress, and stress amplitude affect the influence of asymmetric loading. In the present investigation asymmetric stress controlled fatigue tests were conducted with mean stress from 80 to 150 MPa, stress amplitude from 270 to 340 MPa and stress rate from 30 to 750 MPa/s to study the process of plastic strain accumulation and its effect on fatigue life of Zircaloy-2 at room temperature. It was observed that with increase in mean stress and stress amplitude accumulation of ratcheting strain was increased and fatigue life was reduced. However, increase in stress rate led to improvement in fatigue life due to less accumulation of ratcheting strain.

  7. Fatigue Crack Growth Monitoring Using Rayleigh-Like Waves

    NASA Astrophysics Data System (ADS)

    Masserey, B.; Fromme, P.

    2010-02-01

    A common problem in aircraft maintenance is the development of fatigue cracks at fasteners due to stress concentration. The use of Rayleigh-like waves for the monitoring of fatigue crack growth at a fastener hole in tensile, aluminum specimens is investigated. Rayleigh-like waves can propagate along the structure and have good sensitivity for the detection of small defects. They are excited in the specimen during fatigue experiments using standard wedge transducers and measured using laser interferometry. Fatigue crack growth during cyclic loading is monitored optically and the changes in the ultrasonic signal caused by crack growth are quantified. The laser measurements show a good sensitivity for the early detection of fatigue damage.

  8. On high-cycle fatigue of 316L stents.

    PubMed

    Barrera, Olga; Makradi, Ahmed; Abbadi, Mohammed; Azaouzi, Mohamed; Belouettar, Salim

    2014-01-01

    This paper deals with fatigue life prediction of 316L stainless steel cardiac stents. Stents are biomedical devices used to reopen narrowed vessels. Fatigue life is dominated by the cyclic loading due to the systolic and diastolic pressure and the design against premature mechanical failure is of extreme importance. Here, a life assessment approach based on the Dang Van high cycle fatigue criterion and on finite element analysis is applied to explore the fatigue reliability of 316L stents subjected to multiaxial fatigue loading. A finite element analysis of the stent vessel subjected to cyclic pressure is performed to carry out fluctuating stresses and strain at some critical elements of the stent where cracks or complete fracture may occur. The obtained results show that the loading path of the analysed stent subjected to a pulsatile load pressure is located in the safe region concerning infinite lifetime.

  9. Literature survey on oxidations and fatigue lives at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Liu, H. W.; Oshida, Y.

    1984-01-01

    Nickel-base superalloys are the most complex and the most widely used for high temperature applications such as aircraft engine components. The desirable properties of nickel-base superalloys at high temperatures are tensile strength, thermomechanical fatigue resistance, low thermal expansion, as well as oxidation resistance. At elevated temperature, fatigue cracks are often initiated by grain boundary oxidation, and fatigue cracks often propagate along grain boundaries, where the oxidation rate is higher. Oxidation takes place at the interface between metal and gas. Properties of the metal substrate, the gaseous environment, as well as the oxides formed all interact to make the oxidation behavior of nickel-base superalloys extremely complicated. The important topics include general oxidation, selective oxidation, internal oxidation, grain boundary oxidation, multilayer oxide structure, accelerated oxidation under stress, stress-generation during oxidation, composition and substrate microstructural changes due to prolonged oxidation, fatigue crack initiation at oxidized grain boundaries and the oxidation accelerated fatigue crack propagation along grain boundaries.

  10. Acoustic fatigue life prediction for nonlinear structures with multiple resonant modes

    NASA Astrophysics Data System (ADS)

    Miles, R. N.

    1992-03-01

    This report documents an effort to develop practical and accurate methods for estimating the fatigue lives of complex aerospace structures subjected to intense random excitations. The emphasis of the current program is to construct analytical schemes for performing fatigue life estimates for structures that exhibit nonlinear vibration behavior and that have numerous resonant modes contributing to the response.

  11. Acoustic fatigue life prediction for nonlinear structures with multiple resonant modes

    NASA Technical Reports Server (NTRS)

    Miles, R. N.

    1992-01-01

    This report documents an effort to develop practical and accurate methods for estimating the fatigue lives of complex aerospace structures subjected to intense random excitations. The emphasis of the current program is to construct analytical schemes for performing fatigue life estimates for structures that exhibit nonlinear vibration behavior and that have numerous resonant modes contributing to the response.

  12. Prestraining and Its Influence on Subsequent Fatigue Life

    NASA Technical Reports Server (NTRS)

    Halford, Gary R.; Mcgaw, Michael A.; Kalluri, Sreeramesh

    1995-01-01

    An experimental program was conducted to study the damaging effects of tensile and compressive prestrains on the fatigue life of nickel-base, Inconel 718 superalloy at room temperature. To establish baseline fatigue behavior, virgin specimens with a solid uniform gage section were fatigued to failure under fully-reversed strain-control. Additional specimens were prestrained to 2 percent, 5 percent, and 10 percent (engineering strains) in the tensile direction and to 2 percent (engineering strain) in the compressive direction under stroke-control, and were subsequently fatigued to failure under fully-reversed strain-control. Experimental results are compared with estimates of remaining fatigue lives (after prestraining) using three life prediction approaches: (1) the Linear Damage Rule; (2) the Linear Strain and Life Fraction Rule; and (3) the nonlinear Damage Curve Approach. The Smith-Watson-Topper parameter was used to estimate fatigue lives in the presence of mean stresses. Among the cumulative damage rules investigated, best remaining fatigue life predictions were obtained with the nonlinear Damage Curve Approach.

  13. Thermal fatigue of beryllium

    SciTech Connect

    Deksnis, E.; Ciric, D.; Falter, H.

    1995-09-01

    Thermal fatigue life of S65c beryllium castellated to a geometry 6 x 6 x (8-10)mm deep has been tested for steady heat fluxes of 3 MW/m{sup 2} to 5 MW/m{sup 2} and under pulsed heat fluxes (10-20 MW/m{sup 2}) for which the time averaged heat flux is 5 MW/m{sup 2}. These tests were carried out in the JET neutral beam test facility A test sequence with peak surface temperatures {le} 600{degrees}C produced no visible fatigue cracks. In the second series of tests, with T{sub max} {le} 750{degrees}C evidence for fatigue appeared after a minimum of 1350 stress cycles. These fatigue data are discussed in view of the observed lack of thermal fatigue in JET plasma operations with beryllium PFC. JET experience with S65b and S65c is reviewed; recent operations with {Phi} = 25 MW/m{sup 2} and sustained melting/resolidification are also presented. The need for a failure criterion for finite element analyses of Be PFC lifetimes is discussed.

  14. Mean stress effects in biaxial fatigue of Inconel 718

    SciTech Connect

    Socie, D.F.; Shield, T.W.

    1984-07-01

    Biaxial fatigue tests were conducted on Inconel 718 thin-walled tubular specimens to quantify the effect of mean stress. The specimens were loaded in combined tension and torsion in strain control at room temperature. Fatigue lives ranged from 3000 to 15,000 cycles depending on the mean stress. These data were correlated with a parameter based on the maximum plastic shear strain amplitude, normal strain amplitude and mean normal stress on the plane of maximum shear strain amplitude. This parameter was combined with the Coffin-Manson equation for estimating fatigue lives. Observations of the cracking behavior show that mean stress affects the rate of crack growth and distribution of cracks.

  15. Effect of electrostimulation training-detraining on neuromuscular fatigue mechanisms.

    PubMed

    Jubeau, Marc; Zory, Raphaël; Gondin, Julien; Martin, Alain; Maffiuletti, Nicola A

    2007-08-31

    The aim of this study was to evaluate the effects of neuromuscular electrical stimulation (NMES) training and subsequent detraining on neuromuscular fatigue mechanisms. Ten young healthy men completed one NMES fatigue protocol before and after a NMES training program of 4 weeks and again after 4 weeks of detraining. Muscle fatigue (maximal voluntary torque loss), central fatigue (activation failure), and peripheral fatigue (transmission failure and contractile failure) of the plantar flexor muscles were assessed by using a series of electrically evoked and voluntary contractions with concomitant electromyographic and torque recordings. At baseline, maximal voluntary torque decreased significantly with fatigue (P<0.001), due to both activation and transmission failure. After detraining, maximal voluntary torque loss was significantly reduced (P<0.05). In the same way, the relative decrease in muscle activation after training and detraining was significantly lower compared to baseline values (P<0.05). Short-term NMES training-detraining of the plantar flexor muscles significantly reduced the muscle fatigue associated to one single NMES exercise session. This was mainly attributable to a reduction in activation failure, i.e., lower central fatigue, probably as a result of subject's accommodation to pain and discomfort during NMES.

  16. Methylphenidate for Fatigue in Ambulatory Men with Prostate Cancer

    PubMed Central

    Roth, Andrew J.; Nelson, Christian; Rosenfeld, Barry; Scher, Howard; Slovin, Susan; Morris, Michael; Arauz, Gabrielle; Breitbart, William

    2013-01-01

    Purpose Fatigue is a highly prevalent and clinically significant symptom of advanced prostate cancer. To date, however, there are no published controlled trials of interventions for fatigue in men with prostate cancer. Method This six-week, randomized, double-blind, placebo-controlled design, evaluated the efficacy of methylphenidate to treat fatigue in prostate cancer patients. Inclusion criteria included men with advanced prostate cancer and the presence of moderate to severe fatigue. Patients with major depression, hypothyroidism, uncontrolled hypertension, arrhythmia or anemia were excluded. Fatigue levels, blood pressure, pulse and other safety concerns were monitored regularly. Results Thirty-two subjects were randomized to methylphenidate (N=16) or placebo (N=16). Brief Fatigue Inventory (BFI) total scores significantly decreased for both groups, however the methylphenidate group, as compared to placebo, reported greater decrease on BFI severity scores (p=.03) and a trend toward greater decrease on BFI total scores (p=.07). A significantly greater number of subjects in the methylphenidate group vs. the placebo group demonstrated clinically significant improvement in fatigue on total BFI scores (7/10 vs. 3/13) and BFI severity scores (8/10 vs. 3/13). Importantly, six subjects in the methylphenidate group discontinued due to increased blood pressure or tachycardia. There were no serious adverse events. Conclusions Methylphenidate is effective in treating fatigue in men with prostate cancer; however, oncologists need to monitor for possible pulse and blood pressure elevations. PMID:20665492

  17. Estimation of excess mortality due to long-term exposure to PM2.5 in Japan using a high-resolution model for present and future scenarios

    NASA Astrophysics Data System (ADS)

    Goto, Daisuke; Ueda, Kayo; Ng, Chris Fook Sheng; Takami, Akinori; Ariga, Toshinori; Matsuhashi, Keisuke; Nakajima, Teruyuki

    2016-09-01

    Particulate matter with a diameter of less than 2.5 μm, known as PM2.5, can affect human health, especially in elderly people. Because of the imminent aging of society in the near future in most developed countries, the human health impacts of PM2.5 must be evaluated. In this study, we used a global-to-regional atmospheric transport model to simulate PM2.5 in Japan with a high-resolution stretched grid system (∼10 km for the high-resolution model, HRM) for the present (the 2000) and the future (the 2030, as proposed by the Representative Concentrations Pathway 4.5, RCP4.5). We also used the same model with a low-resolution uniform grid system (∼100 km for the low-resolution model, LRM). These calculations were conducted by nudging meteorological fields obtained from an atmosphere-ocean coupled model and providing emission inventories used in the coupled model. After correcting for bias, we calculated the excess mortality due to long-term exposure to PM2.5 among the elderly (over 65 years old) based on different minimum PM2.5 concentration (MINPM) levels to account for uncertainty using the simulated PM2.5 distributions to express the health effect as a concentration-response function. As a result, we estimated the excess mortality for all of Japan to be 31,300 (95% confidence intervals: 20,700 to 42,600) people in 2000 and 28,600 (95% confidence intervals: 19,000 to 38,700) people in 2030 using the HRM with a MINPM of 5.8 μg/m3. In contrast, the LRM resulted in underestimates of approximately 30% (for PM2.5 concentrations in the 2000 and 2030), approximately 60% (excess mortality in the 2000) and approximately 90% (excess mortality in 2030) compared to the HRM results. We also found that the uncertainty in the MINPM value, especially for low PM2.5 concentrations in the future (2030) can cause large variability in the estimates, ranging from 0 (MINPM of 15 μg/m3 in both HRM and LRM) to 95,000 (MINPM of 0 μg/m3 in HRM) people.

  18. An indentation fatigue strength law

    NASA Astrophysics Data System (ADS)

    Xu, Baoxing; Yonezu, Akio; Chen, Xi

    2010-05-01

    Indentation fatigue, where a cyclic load is applied on the sample via an indenter, emerges as an alternative approach for measuring the fatigue properties of materials. We have carried out indentation fatigue tests on a poly(vinyl chloride) (PVC) bulk material, as well as on TiN and NiP films/coatings deposited on SUS304 steel substrates, and demonstrate that a simple power-law relationship can be established between the indentation load amplitude and number of cycles to failure. Such a law is very similar to the conventional fatigue strength law obtained from uniaxial tests. The agreement between the fatigue stress exponents obtained by uniaxial and indentation fatigue tests suggests the potential applicability of the indentation fatigue technique for extracting the fatigue properties of materials.

  19. Low-cycle thermal fatigue

    NASA Technical Reports Server (NTRS)

    Halford, G. R.

    1986-01-01

    A state-of-the-art review is presented of the field of thermal fatigue. Following a brief historical review, the concept is developed that thermal fatigue can be viewed as processes of unbalanced deformation and cracking. The unbalances refer to dissimilar mechanisms occurring in opposing halves of thermal fatigue loading and unloading cycles. Extensive data summaries are presented and results are interpreted in terms of the unbalanced processes involved. Both crack initiation and crack propagation results are summarized. Testing techniques are reviewed, and considerable discussion is given to a technique for thermal fatigue simulation, known as the bithermal fatigue test. Attention is given to the use of isothermal life prediction methods for the prediction of thermal fatigue lives. Shortcomings of isothermally-based life prediction methods are pointed out. Several examples of analyses and thermal fatigue life predictions of high technology structural components are presented. Finally, numerous dos and don'ts relative to design against thermal fatigue are presented.

  20. Chronic Fatigue Syndrome (CFS): Symptoms

    MedlinePlus

    ... please visit this page: About CDC.gov . Chronic Fatigue Syndrome (CFS) Share Compartir Symptoms On this Page ... Symptoms What's the Clinical Course of CFS? Chronic fatigue syndrome can be misdiagnosed or overlooked because its ...

  1. Notched Fatigue Behavior of PEEK

    PubMed Central

    Murphy, JE; Brinkman, JG; Kurtz, SM; Rimnac, CM

    2013-01-01

    Poly(ether-ether-ketone) (PEEK) has been used as a load bearing orthopaedic implant material with clinical success. All of the orthopaedic applications contain stress concentrations (notches) in their design; however, little work has been done to examine the fatigue behavior of PEEK in the presence of a notch. This work examines both stress-life (SN) fatigue behavior and the fracture behavior of unfilled PEEK under tension tension loading in circumferentially grooved round bar specimens with different elastic stress concentration factors. It was found that the majority of the loading was elastic in nature, and that there was only a small portion on the lifetime where there was a detectable change in structural behavior prior to gross fracture. Fractographic analysis via SEM further elucidated the potential fracture micromechanisms. Additional analysis was conducted to estimate the percent of the lifetime spent in crack initiation vs propagation, and it was found that the specimens spent the majority of the time in the crack initiation phase. PMID:20864160

  2. Fatigue and fracture overview

    NASA Technical Reports Server (NTRS)

    Halford, Gary R.

    1986-01-01

    The accomplishments achieved under the isotropic creep-fatigue crack initiation life prediction program are summarized. A sizeable creep-fatigue crack initiation data base was generated on the nickel-base superalloy, B-1900. Companion constitutive modeling programs have also generated extensive data bases on the same heat of material. The crack initiation results have formed the basis of a new approach to creep-fatigue life prediction. The term Cyclic Damage Accumulation (CDA) was coined for the method, which was evaluated under isothermal, uniaxial conditions. Stringent laboratory verification experiments were used to test the accuracy of the method. Considering the quite limited material property data needed to evaluate the constants in the approach, the prediction accuracy is acceptable. At the expense of the larger data base required, Lewis developed total strain- strainrange partitioning method (TS-SRP) is capable of a higher degree of accuracy.

  3. Fatigue and Barkhausen effect

    NASA Astrophysics Data System (ADS)

    Tong, Wei

    Piezomagnetism designates a change in the magnetization of materials induced by mechanical actions such as tension or compression. The type of Barkhausen effect that occurs in this work consists of sudden, discontinuous jumps in a material's magnetization that appear in response to smooth (continuous) stress variations. A series of strain controlled fatigue tests with an alternating sinusoidal waveform were carried out to study the relationship between the endurance limit and the Barkhausen effect. Results of fatigue tests on steel specimens exhibiting Barkhausen pulses at various stages are reported and a threshold-crossing analysis is applied to the test results. These studies show that when the fatigue limit is approached, the Barkhausen pulses become, in general, more intense in amplitude and quantity than at other stress levels. A hypothetical mechanism is proposed that relates the intensity of the Barkhausen response to the inception of micro-cracking and rearrangements of the mechanical lattice at the microscopic level.

  4. Estimating Parallax Error Due to Orbital Motion for HST/WFC3 Spatial Scan Observations of 19 Long-period Classical Cepheids

    NASA Astrophysics Data System (ADS)

    Anderson, Richard I.; Casertano, Stefano; Riess, Adam G.

    2017-01-01

    We employ the Hubble Space Telescope's Wide Field Camera 3 (HST/WFC3) in spatial scanning mode to measure 30 - 40μas parallax of 19 classical Cepheids in the Milky Way with the aim of improving the calibration of the cosmic distance scale (Riess et al. 2014; Casertano et al. 2016). The measured parallaxes are an order of magnitude more precise than parallaxes from the first Gaia data release and thus furthermore provide important cross-checks for Gaia data processing.Here we present our work aimed at estimating the parallax error due to orbital motion caused by undetected companion stars (Anderson et al. 2016). We have secured more than 1600 high-precision radial velocity (RV) measurements of the 19 long-period (Ppuls > 9d) Cepheids in our sample using ground-based telescopes on both hemispheres to investigate the presence of spectroscopic companions. We model the RV variability together with orbital motion using a grid of input orbital periods, Porb. We determine upper limits on the (unsigned) projected parallax error induced by hypothetical companions using the orbital configuration upper limits determined by modeling RV data. We thus show that our HST/WFC3 parallax measurements are subject to an error of less than 2% in parallax (i.e., typically less than ±7μas) for 16 stars in the sample, and < 4% for two Cepheids with fewer RV observations. For YZ Carinae, however, we correct the previously published orbital solution and show that the astrometric model must take into account orbital motion to avoid significant (approx. ±100μas) parallax error.We have further investigated long-timescale (Porb > 10yr) orbital motion using literature data and RV templates based on our new data. We thus discover new evidence for RV signals due to long-term orbital motion for 4 Cepheids and critically assess putative evidence for spectroscopic binarity previously reported based on data of much lesser quality. We caution that astrometric measurements of binaries with Porb on

  5. Fatigue and fatigue crack growth processes in hard tissues: The importance of age and surface integrity

    NASA Astrophysics Data System (ADS)

    Majd, Hessam

    With the progressive increase in partially and fully dentate seniors, fracture has become an increasingly common form of restored tooth failure. Dentin undergoes progressive changes in microstructure with patient age, and studies are now suggesting that there is a reduction in fatigue strength and fatigue crack growth resistance of this tissue. This dissertation explores aging of dentin, the influence of flaws that are introduced during restorative processes on the fatigue properties of dentin, and proposes models for characterizing the damage initiation and growth process during fatigue of dentin. Results from this investigation show that the fatigue crack growth properties (Paris Law parameters (C, m) andDeltaKth) of human dentin undergo the most significant changes at a patient age of 42 years. Based on the fatigue crack growth responses, three age groups were established including young (age≤33), aged (34≤age ≤49) and old (50≤age) patients for further analysis. There were significant differences in the initiation and growth behavior between the tissues of patients from the three age groups. With regards to the influence of restorative processes, there was no influence on the quasi-static responses of dentin. However, the endurance limit of dentin treated with the dental burs (28 MPa) and abrasive air jet (35 MPa) were approximately 36% and 20% lower than that of the control (44 MPa), respectively. Both cutting processes caused a significant reduction (p≤0.0001) in fatigue strength. An accumulative damage model was developed to characterize fatigue of the control and bur treated dentin as well as provide a model for fatigue life prediction. The damage models were derived as a function of number of loading cycles (N), and ratio of applied stress to ultimate strength (r). The developed models provide estimations for the initial state of damage, the state of damage during the life, as well as the damage accumulation rate for cyclic loading of dentin

  6. The Effect of Osteoporosis Treatments on Fatigue Properties of Cortical Bone Tissue.

    PubMed

    Brock, Garry R; Chen, Julia T; Ingraffea, Anthony R; MacLeay, Jennifer; Pluhar, G Elizabeth; Boskey, Adele L; van der Meulen, Marjolein C H

    2015-06-01

    Bisphosphonates are commonly prescribed for treatment of osteoporosis. Long-term use of bisphosphonates has been correlated to atypical femoral fractures (AFF). AFFs arise from fatigue damage to bone tissue that cannot be repaired due to pharmacologic treatments. Despite fatigue being the primary damage mechanism of AFFs, the effects of osteoporosis treatments on fatigue properties of cortical bone are unknown. To examine if fatigue-life differences occur in bone tissue after different pharmacologic treatments for osteoporosis, we tested bone tissue from the femurs of sheep given a metabolic acidosis diet to induce osteoporosis, followed by treatment with a selective estrogen reception modulator (raloxifene), a bisphosphonate (alendronate or zoledronate), or parathyroid hormone (teriparatide, PTH). Beams of cortical bone tissue were created and tested in four-point bending fatigue to failure. Tissues treated with alendronate had reduced fatigue life and less modulus loss at failure compared to other treatments, while tissue treated with PTH had a prolonged fatigue life. No loss of fatigue life occurred with zoledronate treatment despite its greater binding affinity and potency compared to alendronate. Tissue mineralization measured by microCT did not explain the differences seen in fatigue behavior. Increased fatigue life with PTH suggests that current treatment methods for AFF could have beneficial effects for restoring fatigue life. These results indicate that fatigue life differs with each type of osteoporosis treatment.

  7. The Effect of Structural Quality on Fatigue Life in 319 Aluminum Alloy Castings

    NASA Astrophysics Data System (ADS)

    Özdeş, Hüseyin; Tiryakioğlu, Murat

    2016-12-01

    Tensile and fatigue life data for 319 aluminum alloy from seventeen datasets reported in four independent studies from the literature have been reanalyzed. Analysis of fatigue life data involved mean stress correction for different R ratios used in fatigue testing, inclusion of survival (runout) data along with failure data, as well as volumetric correction for Weibull distributions for different specimen sizes used in these studies. Tensile data have been transformed into the structural quality index, Q T, which is used as a measure of the structural quality of castings. A distinct relationship has been observed between the expected fatigue life and mean quality index. Moreover, fatigue strengths at 104 and 106 cycles have been found increase with quality index, providing further evidence about the relationship observed between structural quality and fatigue performance. Empirical equations between Basquin parameters and structural quality index have been developed. The use of the comprehensive methodology to estimate fatigue life is demonstrated with an example.

  8. The Effect of Structural Quality on Fatigue Life in 319 Aluminum Alloy Castings

    NASA Astrophysics Data System (ADS)

    Özdeş, Hüseyin; Tiryakioğlu, Murat

    2017-02-01

    Tensile and fatigue life data for 319 aluminum alloy from seventeen datasets reported in four independent studies from the literature have been reanalyzed. Analysis of fatigue life data involved mean stress correction for different R ratios used in fatigue testing, inclusion of survival (runout) data along with failure data, as well as volumetric correction for Weibull distributions for different specimen sizes used in these studies. Tensile data have been transformed into the structural quality index, Q T, which is used as a measure of the structural quality of castings. A distinct relationship has been observed between the expected fatigue life and mean quality index. Moreover, fatigue strengths at 104 and 106 cycles have been found increase with quality index, providing further evidence about the relationship observed between structural quality and fatigue performance. Empirical equations between Basquin parameters and structural quality index have been developed. The use of the comprehensive methodology to estimate fatigue life is demonstrated with an example.

  9. Fatigue Damage Accumulation Under Quasi-Random Loading of Composite Airframe Elements

    NASA Astrophysics Data System (ADS)

    Strizhius, V.

    2016-09-01

    To perform engineering estimations of the fatigue life of quasi-randomly loaded layered composites, with geometric concentrators, representing the longitudinal elements of composite wing of a transport airplane, a special rule of fatigue damage accumulation is suggested. The main propositions of the method for calculating the fatigue life of these elements by using this rule are formulated. The examples of estimations presented show a good agreement between analytical results and experimental data. A number of important conclusions about the effect of different levels of cyclic loading and "GAG" cycles of different flight types of the quasi-random "TWIST" program on the total fatigue life are made.

  10. Influence of axle-wheel interface on ultrasonic testing of fatigue cracks in wheelset.

    PubMed

    Makino, Kazunari; Biwa, Shiro

    2013-01-01

    For the ultrasonic testing at the wheel seat of railway axles, quantitative investigation of the reflection and transmission phenomena at the axle-wheel interface is important. This paper describes the influence of the axle-wheel interface on the ultrasonic testing of a fatigue crack in a wheelset by applying the spring interface model. The normal and tangential stiffnesses were identified experimentally for an as-manufactured wheelset at the normal incidence, and the reflection coefficient for the shear-wave oblique incidence was calculated. A parametric study was performed to clarify the influence of these interfacial stiffnesses on the incident-angle dependence of the reflection coefficient. The calculated reflection coefficient at the incident angle of 45° qualitatively explained the relative echo-height decrease due to the presence of a wheel observed experimentally for a wheelset in fatigue loading by rotating bending. The quantitative difference between the experimental and calculated results was considered to be due to the reduction of the effective interference of shrink fit by the wear at the axle-wheel interface during the fatigue loading as well as by the applied bending moment. For the estimated relative echo-height decrease to agree with the experimental results, the interfacial stiffnesses were found to be smaller than the values identified for the as-manufactured wheelset by a factor of 0.5-0.7.

  11. The effects of temperature on the mechanical performance in fatigued single muscle fibers of the frog induced by twitch and tetanus.

    PubMed

    Inamura, N; Fujisige, A; Miyake, S; Ono, A; Tsuchiya, T

    2000-02-01

    Muscle fatigue induced by consecutive twitches or tetani was studied in single skeletal muscle fibers of the frog, Rana japonica. The fatigue by twitch appeared sooner after the start of stimulation at lower temperatures (2-5 degrees C) than at higher ones (15-20 degrees C), while the fatigue by tetanus appeared sooner at higher temperatures. When a twitch-fatigued fiber was bathed in a solution with caffeine (15 mM), the contracture force was much higher than the fatigued force, while in tetanus fatigue, the force by caffeine was not different from the fatigued force. The length-force relation in fatigued fibers was compared with that in pre-fatigue at low and high temperatures. It was noticed that the ascending limb of the length-force curve in fatigued fibers by twitch was lower than that in pre-fatigue at the low temperatures; namely, the fatigue by twitch was more marked in shorter muscle length, while no marked change in the length-force relation was detected in the tetanus fatigue at the low and high temperatures. The maximum shortening velocity, measured by the slack test, decreased in both types of fatigue. These results suggest that the fatigue by twitch may be mainly due to the failure of activation of the contractile system, while in the fatigue by tetanus, the rate of the interaction between actin and myosin may be impaired due to the change in intracellular chemical environment.

  12. The Nature of Fatigue in Chronic Fatigue Syndrome.

    PubMed

    Olson, Karin; Zimka, Oksana; Stein, Eleanor

    2015-10-01

    In this article, we report the findings of our study on the nature of fatigue in patients diagnosed with chronic fatigue syndrome. Using ethnoscience as a design, we conducted a series of unstructured interviews and card sorts to learn more about how people with chronic fatigue syndrome describe fatigue. Participants (N = 14) described three distinct domains: tiredness, fatigue, and exhaustion. Most participants experienced tiredness prior to diagnosis, fatigue during daily life, and exhaustion after overexertion. We also discuss participants' ability to adapt to a variety of stressors and prevent shifts to exhaustion, and relate our findings to stress theory and other current research. Primary strategies that promoted adaptation to stressors included pacing and extended rest periods. These findings can aid health care professionals in detecting impending shifts between tiredness, fatigue, and exhaustion and in improving adaptive strategies, thereby improving quality of life.

  13. Aggravation of fatigue by steroid therapy in terminally ill patients with cancer.

    PubMed

    Matsuo, Naoki; Yomiya, Kinomi

    2014-05-01

    Steroids are commonly used for fatigue relief in terminally ill cancer patients. However, steroid-induced adverse effects including depression, myopathy, and hyperglycemia may contribute to fatigue. We report our experiences with aggravation of fatigue with steroid use in three cases. Case 1 was a 65-year-old man with advanced gastric cancer. He was started on betamethasone (2 mg/d) for fatigue, but the fatigue worsened due to steroid-induced depression. Discontinuation of steroids and initiation of an antidepressant ameliorated the fatigue. Case 2 was a 68-year-old man with advanced lung cancer. He complained of fatigue. Betamethasone (1 mg/d) was started and alleviated the fatigue. However, when the betamethasone dose was increased to 2 mg/d, the fatigue, with muscle weakness and myalgia, worsened due to steroid-induced myopathy. We therefore switched from betamethasone (2 mg/d) to prednisolone (10 mg /d). The fatigue resolved and the patient returned to his previous condition. Case 3 was a 73-year-old man with recurrent bile duct cancer. He also had diabetes mellitus. He developed fatigue, anorexia and fever. We started betamethasone (1.5 mg/d) for these symptoms, but the fatigue and anorexia worsened due to steroid-induced hyperglycemia. Blood glucose rose to 532 mg/dL. Therefore, insulin therapy was started, and the dose of betamethasone was reduced to 0.5 mg/d. His glucose level decreased to less than 320 mg/dL and he recovered from the fatigue while achieving moderate oral intake. In conclusion, the possibility of steroid-induced secondary fatigue in terminally ill cancer patients should be taken into consideration.

  14. Static and Fatigue Analysis of Wind Turbine Blades Subject to Cold Weather Conditions Using Finite Element Analysis

    NASA Astrophysics Data System (ADS)

    Lillo Gallardo, Patricio Andres

    Canada has aggressive targets for introducing wind energy across the country, but also faces challenges in achieving these goals due to the harsh Canadian climate. One issue which has received little attention in other countries not experiencing these extremes is the behaviour of composite blades in winter conditions. The scope of the work presented is to analyze the static stresses and fatigue response in cold climates using finite element models of the blade. The work opens with a quantification of the extremes of cold experienced in candidate Canadian wind turbine deployment locations. The thesis then narrows its focus to a consideration of the stresses in the root of the composite blades, specifically two common blade-hub connection methods: embedded root carrots and T-bolts. Finite element models of the root are proposed to properly simulate boundary conditions, applied loading and thermal stresses for a 1.5 MW wind turbine. It is shown that the blade root is strongly affected by the thermal stresses caused by the mismatch and orthotrophy of the coefficients of thermal expansion of the blade root constituents. Fatigue analysis of a blade is then presented using temperature dependent material properties including estimated fatigue coefficients.It was found that the natural frequencies of a 1.5 MW wind turbine blade are not significantly altered at cold temperatures. Additionally, cold temperatures slightly increase stresses in the composite blade skin when the blade is loaded, due to an increase in stiffness. Cold temperatures also lead to higher cyclic flapwise bending moments acting on the blade. However, this increase was found not to affect the lifetime fatigue damage. Finally, it was found that the cold climate as seen in Canada improves the fatigue strength of the saturated composite materials used in the blade. The predicted fatigue damage of the triaxial fabric and the spar cap layers in cold climates was therefore predicted to be half that of the

  15. Some aspects of thermomechanical fatigue of AISI 304L stainless steel: Part I. creep- fatigue damage

    NASA Astrophysics Data System (ADS)

    Zauter, R.; Christ, H. J.; Mughrabi, H.

    1994-02-01

    Thermomechanical fatigue (TMF) tests on the austenitic stainless steel AISI 304L have been conducted under “true≓ plastic-strain control in vacuum. This report considers the damage oc-curring during TMF loading. It is shown how the temperature interval and the phasing (in-phase, out-of-phase) determine the mechanical response and the lifetime of the specimens. If creep-fatigue interaction takes place during in-phase cycling, the damage occurs inside the ma-terial, leading to intergranular cracks which reduce the lifetime considerably. Out-of-phase cy-cling inhibits creep-induced damage, and no lifetime reduction occurs, even if the material is exposed periodically to temperatures in the creep regime. A formula is proposed which allows prediction of the failure mode, depending on whether creep-fatigue damage occurs or not. At a given strain rate, the formula is able to estimate the temperature of transition between pure fatigue and creep-fatigue damage.

  16. Probabilistic fatigue life prediction of metallic and composite materials

    NASA Astrophysics Data System (ADS)

    Xiang, Yibing

    Fatigue is one of the most common failure modes for engineering structures, such as aircrafts, rotorcrafts and aviation transports. Both metallic materials and composite materials are widely used and affected by fatigue damage. Huge uncertainties arise from material properties, measurement noise, imperfect models, future anticipated loads and environmental conditions. These uncertainties are critical issues for accurate remaining useful life (RUL) prediction for engineering structures in service. Probabilistic fatigue prognosis considering various uncertainties is of great importance for structural safety. The objective of this study is to develop probabilistic fatigue life prediction models for metallic materials and composite materials. A fatigue model based on crack growth analysis and equivalent initial flaw size concept is proposed for metallic materials. Following this, the developed model is extended to include structural geometry effects (notch effect), environmental effects (corroded specimens) and manufacturing effects (shot peening effects). Due to the inhomogeneity and anisotropy, the fatigue model suitable for metallic materials cannot be directly applied to composite materials. A composite fatigue model life prediction is proposed based on a mixed-mode delamination growth model and a stiffness degradation law. After the development of deterministic fatigue models of metallic and composite materials, a general probabilistic life prediction methodology is developed. The proposed methodology combines an efficient Inverse First-Order Reliability Method (IFORM) for the uncertainty propogation in fatigue life prediction. An equivalent stresstransformation has been developed to enhance the computational efficiency under realistic random amplitude loading. A systematical reliability-based maintenance optimization framework is proposed for fatigue risk management and mitigation of engineering structures.

  17. Convicted of fatigued driving: who, why and how?

    PubMed

    Radun, Igor; Radun, Jenni E

    2009-07-01

    Fatigue is a major cause of road traffic accidents. However, due to the blurred concept of fatigue and the lack of reliable testing devices (cf. the breath analyzer for alcohol levels), it is extremely difficult to incorporate fatigue in operationalized terms into either traffic or criminal law. Even though the Finnish Road Traffic Act explicitly forbids driving while tired, it is done only on a general level among other factors (sickness, etc.) that impair a driver's fitness to drive (Article 63). The present study was done to investigate the circumstances of fatigue driving offenses. From the Finnish Vehicle Administration driver record database we extracted all drivers (N=768) punished under Article 63 from 2004-2005. Of these drivers, 90.4% committed a fatigue-related traffic offense. Accidents, predominantly single vehicle, were the most common (92.5%) consequence of fatigued driving. Although fatigue-related accidents are thought to be serious, our data shows that most of the accidents (81.6%) did not involve personal injuries. Almost every twentieth driver was punished because his vehicle was drifting on the road. The presence of alcohol or drugs was noted in 13% of the cases. Only 3.1% of the punished drivers officially denied being tired or falling asleep. Young men (< or =35 yrs) represented 50% of all punished drivers. Time of day and seasonal effects were clear in this data. This study shows that even without a reliable fatigue detector and unambiguous criteria for recognizing the contribution of fatigue to accident causation, Finnish police and the courts punish a significant number of drivers every year on the basis of fatigue.

  18. Muscle Deoxygenation Causes Muscle Fatigue

    NASA Technical Reports Server (NTRS)

    Murthy, G.; Hargens, A. R.; Lehman, S.; Rempel, D.

    1999-01-01

    Muscle fatigue is a common musculoskeletal disorder in the work place, and may be a harbinger for more disabling cumulative trauma disorders. Although the cause of fatigue is multifactorial, reduced blood flow and muscle oxygenation may be the primary factor in causing muscle fatigue during low intensity muscle exertion. Muscle fatigue is defined as a reduction in muscle force production, and also occurs among astronauts who are subjected to postural constraints while performing lengthy, repetitive tasks. The objectives of this research are to: 1) develop an objective tool to study the role of decreased muscle oxygenation on muscle force production, and 2) to evaluate muscle fatigue during prolonged glovebox work.

  19. FATIGUE OF DENTAL CERAMICS

    PubMed Central

    Zhang, Yu; Sailer, Irena; Lawn, Brian R

    2013-01-01

    Objectives Clinical data on survival rates reveal that all-ceramic dental prostheses are susceptible to fracture from repetitive occlusal loading. The objective of this review is to examine the underlying mechanisms of fatigue in current and future dental ceramics. Data/sources The nature of various fatigue modes is elucidated using fracture test data on ceramic layer specimens from the dental and biomechanics literature. Conclusions Failure modes can change over a lifetime, depending on restoration geometry, loading conditions and material properties. Modes that operate in single-cycle loading may be dominated by alternative modes in multi-cycle loading. While post-mortem examination of failed prostheses can determine the sources of certain fractures, the evolution of these fractures en route to failure remains poorly understood. Whereas it is commonly held that loss of load-bearing capacity of dental ceramics in repetitive loading is attributable to chemically-assisted 'slow crack growth' in the presence of water, we demonstrate the existence of more deleterious fatigue mechanisms, mechanical rather than chemical in nature. Neglecting to account for mechanical fatigue can lead to gross overestimates in predicted survival rates. Clinical significance Strategies for prolonging the clinical lifetimes of ceramic restorations are proposed based on a crack-containment philosophy. PMID:24135295

  20. Incompatibility and Mental Fatigue

    ERIC Educational Resources Information Center

    Herzog, Thomas R.; Hayes, Lauren J.; Applin, Rebecca C.; Weatherly, Anna M.

    2011-01-01

    A straightforward prediction from attention restoration theory is that the level of incompatibility in a person's life should be positively correlated with that person's level of mental (or directed attention) fatigue. The authors tested this prediction by developing a new self-report measure of incompatibility in which they attempted to isolate…

  1. Probabilistic fatigue life prediction using ultrasonic inspection data considering equivalent initial flaw size uncertainty

    NASA Astrophysics Data System (ADS)

    Guan, X.; Zhang, J.; Kadau, K.; Zhou, S. K.

    2013-01-01

    This study presents a systematical method for probabilistic fatigue life prediction using ultrasonic inspection data. A probabilistic model to correlate the ultrasonic inspection reported size and the actual size is proposed based on historical data of rotor flaw sizing. Both of the reported size and the actual size are quantified in terms of the equivalent reflector diameter. The equivalent initial flaw size (EIFS) is then calculated based on the actual size for fatigue propagation analysis. All major uncertainties, such as EIFS uncertainty, fatigue crack growth model parameter uncertainty, and experimental data measurement uncertainty are explicitly included in the fatigue life prediction. Bayesian parameter estimation is used to estimate fatigue crack growth model parameters and measurement uncertainties using a limited number of fatigue testing data points. The overall procedure is demonstrated using a Cr-Mo-V rotor segment with ultrasonic inspection data. Interpretations of the probabilistic prediction results are given.

  2. Monte carlo estimates of uncertainties in predictions by a photochemical grid model (UAM-IV) due to uncertainties in input variables

    NASA Astrophysics Data System (ADS)

    Hanna, Steven R.; Chang, Joseph C.; Fernau, Mark E.

    Because photochemical grid models such as UAM-IV are being used to make policy decisions concerning emissions controls, it is important to know (1) the uncertainties in the model predictions due to the combined effects of uncertainties in the full set of input variables, and (2) the individual input parameters whose variations have the greatest effect on variations in model predictions. A preliminary Monte Carloun certainty analysis system has been developed and the methodology has been demonstrated using anapplication of the standard U.S. regulatory model, UAM-IV, to the 230 km by 290 km New York City domain for the 6-8 July 1988 ozone episode. As a first step, ten modeling experts were asked to estimate the typical uncertainties of 109 UAM-IV input parameters, including 23 variables related to emissions, boundary conditions, and meteorological conditions; and 86 variables related to chemical rate constants. For many of the model inputs, the assumed range of uncertainty was about plus or minus 30% of a normal mid-range value, and, in most cases, the distributions were assumed to have a log-normal shape. The regulatory agency's "base run" application of UAM-IV to this ozone episode was used to define the mid-range or median values of all input parameters. 50 Monte Carlo UAM-IV runs were then carried out by simple random sampling of each of the 109 input parameters from the assumed distributions. The 50 predicted values of peak hourly averaged ozone concentrations anywhere on the geographic domain for the episode were found to follow a log-normal distribution and exhibit a variability from 176 to 331 ppb. The locations of the 50 predicted ozone peaks varied from 100 km upwind (southwest) of New York City to 150 km down wind (northeast) of the city. Variability in the input parameter known as the anthropogenic volatile organic compound (VOC) area source emissions had the most influence on the variations in the 50 predicted peak ozone concentrations.

  3. Estimating errors in cloud amount and cloud optical thickness due to limited spatial sampling using a satellite imager as a proxy for nadir-view sensors

    NASA Astrophysics Data System (ADS)

    Liu, Yinghui

    2015-07-01

    Cloud climatologies from space-based active sensors have been used in climate and other studies without their uncertainties specified. This study quantifies the errors in monthly mean cloud amount and optical thickness due to the limited spatial sampling of space-based active sensors. Nadir-view observations from a satellite imager, the Moderate Resolution Imaging Spectroradiometer (MODIS), serve as a proxy for those active sensors and observations within 10° of the sensor's nadir view serve as truth for data from 2003 to 2013 in the Arctic. June-July monthly mean cloud amount and liquid water and ice cloud optical thickness from MODIS for both observations are calculated and compared. Results show that errors increase with decreasing sample numbers for monthly means in cloud amount and cloud optical thickness. The root-mean-square error of monthly mean cloud amount from nadir-view observations increases with lower latitudes, with 0.7% (1.4%) at 80°N and 4.2% (11.2%) at 60°N using data from 2003 to 2013 (from 2012). For a 100 km resolution Equal-Area Scalable Earth Grid (EASE-Grid) cell of 1000 sample numbers, the absolute differences in these two monthly mean cloud amounts are less than 6.5% (9.0%, 11.5%) with an 80 (90, 95)%chance; such differences decrease to 4.0% (5.0%, 6.5%) with 5000 sample numbers. For a 100 km resolution EASE-Grid of 1000 sample numbers, the absolute differences in these two monthly mean cloud optical thicknesses are less than 2.7 (3.8) with a 90% chance for liquid water cloud (ice cloud); such differences decrease to 1.3 (1.0) for 5000 sample numbers. The uncertainties in monthly mean cloud amount and optical thickness estimated in this study may provide useful information for applying cloud climatologies from active sensors in climate studies and suggest the need for future spaceborne active sensors with a wide swath.

  4. Fatigue Properties and Morphology of Fatigue Fracture of Bulk Metallic Glass

    NASA Astrophysics Data System (ADS)

    Zhao, X. Y.; Chen, Z. H.; Wang, H. P.; Zhan, J.

    2016-11-01

    Changes in the amorphous structure and fatigue resistance of Zr57.5Cu27.3Al8.5Ni6.7 bulk metallic glass are studied. A copper-rich phase produced by cyclic stresses is discovered. This phase observed on the fracture surface may hinder crack propagation. The specimens after fatigue failure have a V shape (do not break into two completely) due to the high density of shear bands and multiple branching of the shear bands in the strained region.

  5. Fatigue failure of an open cell and a closed cell aluminium alloy foam

    SciTech Connect

    Harte, A.M.; Fleck, N.A.; Ashby, M.F. . Engineering Dept.)

    1999-06-22

    The tension-tension and compression-compression cyclic properties are measured for an open cell Duocel foam of composition Al 6101-T6, and a closed cell Alporas foam of composition Al-5Ca-3Ti (wt%). the Duocel foam has a relatively uniform microstructure, and undergoes homogeneous straining in both monotonic and fatigue tests. In contrast, the Alporas foam is more irregular in microstructure, and exhibits crush-band formation at random locations under uniaxial compression; in compression-compression fatigue, a single crush band forms and broadens with additional fatigue cycles. Progressive shortening of the specimen in compression-compression fatigue, and progressive lengthening in tension-tension fatigue are due to a combination of low cycle fatigue failure and cyclic ratchetting. S-N fatigue curves are presented for the onset of progressive shortening in the compression tests, and material separation in the tension tests; it is envisaged that such curves will be of practical use in design.

  6. An exploration of the utility of mathematical modeling predicting fatigue from sleep/wake history and circadian phase applied in accident analysis and prevention: the crash of Comair Flight 5191.

    PubMed

    Pruchnicki, Shawn A; Wu, Lora J; Belenky, Gregory

    2011-05-01

    On 27 August 2006 at 0606 eastern daylight time (EDT) at Bluegrass Airport in Lexington, KY (LEX), the flight crew of Comair Flight 5191 inadvertently attempted to take off from a general aviation runway too short for their aircraft. The aircraft crashed killing 49 of the 50 people on board. To better understand this accident and to aid in preventing similar accidents, we applied mathematical modeling predicting fatigue-related degradation in performance for the Air Traffic Controller on-duty at the time of the crash. To provide the necessary input to the model, we attempted to estimate circadian phase and sleep/wake histories for the Captain, First Officer, and Air Traffic Controller. We were able to estimate with confidence the circadian phase for each. We were able to estimate with confidence the sleep/wake history for the Air Traffic Controller, but unable to do this for the Captain and First Officer. Using the sleep/wake history estimates for the Air Traffic Controller as input, the mathematical modeling predicted moderate fatigue-related performance degradation at the time of the crash. This prediction was supported by the presence of what appeared to be fatigue-related behaviors in the Air Traffic Controller during the 30 min prior to and in the minutes after the crash. Our modeling results do not definitively establish fatigue in the Air Traffic Controller as a cause of the accident, rather they suggest that had he been less fatigued he might have detected Comair Flight 5191's lining up on the wrong runway. We were not able to perform a similar analysis for the Captain and First Officer because we were not able to estimate with confidence their sleep/wake histories. Our estimates of sleep/wake history and circadian rhythm phase for the Air Traffic Controller might generalize to other air traffic controllers and to flight crew operating in the early morning hours at LEX. Relative to other times of day, the modeling results suggest an elevated risk of fatigue

  7. Noninvasive fatigue fracture model of the rat ulna.

    PubMed

    Tami, A E; Nasser, P; Schaffler, M B; Knothe Tate, M L

    2003-11-01

    Fatigue damage occurs in response to repeated cyclic loading and has been observed in situ in cortical bone of humans and other animals. When microcracks accumulate and coalesce, failure ensues and is referred to as fatigue fracture. Experimental study of fatigue fracture healing is inherently difficult due to the lack of noninvasive models. In this study, we hypothesized that repeated cyclic loading of the rat ulna results in a fatigue fracture. The aim of the study was to develop a noninvasive long bone fatigue fracture model that induces failure through accumulation and coalescence of microdamage and replicates the morphology of a clinical fracture. Using modified end-load bending, right ulnae of adult Sprague-Dawley rats were cyclically loaded in vivo to fatigue failure based on increased bone compliance, which reflects changes in bone stiffness due to microdamage. Preterminal tracer studies with 0.8% Procion Red solution were conducted according to protocols described previously to evaluate perfusion of the vasculature as well as the lacunocanalicular system at different time points during healing. Eighteen of the 20 animals loaded sustained a fatigue fracture of the medial ulna, i.e. through the compressive cortex. In all cases, the fracture was closed and non-displaced. No disruption to the periosteum or intramedullary vasculature was observed. The loading regime did not produce soft tissue trauma; in addition, no haematoma was observed in association with application of load. Healing proceeded via proliferative woven bone formation, followed by consolidation within 42 days postfracture. In sum, a noninvasive long bone fatigue fracture model was developed that lends itself for the study of internal remodeling of periosteal woven bone during fracture healing and has obvious applications for the study of fatigue fracture etiology.

  8. Fatigue properties of Graphene interconnects on flexible substrates

    NASA Astrophysics Data System (ADS)

    Paradee, Gary

    This thesis represents the first determination of the fatigue behavior of Graphene as interconnect material electronic components on flexible substrates. The potential application of this interconnect material is for displays on flexible substrates where fatigue resistance is required due to the stress placed on the interconnect during mechanical bending. As the display is cyclically deformed (fatigued) during normal operation, cracks in the interconnect layer initiate and propagate leading to the lineout failure condition. The major contribution of this work is to show that Graphene is a superior interconnect material to the present state of the art Indium Tin Oxide (ITO) due to its electrical, optical and mechanical properties. The experimental approach in this thesis is based on Graphene samples which were fabricated on Silicon Nitrite (Si3N4)/Polyethylene Naphthalate (PEN) substrates. For comparison, both patterned and uniform ITO films ITO films on Si3N4/PEN were fabricated. The results of the in-depth characterization of Graphene are reported and based on Atomic Force Microscopy (AFM), Raman Spectroscopy and Scanning Electron Microscopy (SEM) are reported. The fatigue characteristics of ITO were determined at stress amplitudes ranging from 2000 MPa to 400 MPa up to 5000 cycles. The fatigue characteristics of Graphene were determined at stress amplitudes ranging from 80 GPa to 40 GPa up to 5000 cycles. The fatigue S-N curves were determined and showed that Graphene's endurance limit is 40 GPa. Beyond the endurance limit, there is no observable high cycle or low cycle fatigue indication for Graphene on a flexible substrate such as PEN. The microstructural analysis by SEM and AFM did not reveal normal fatigue crack growth and propagation. This thesis presents the first comprehensive behavior of Graphene in a bending fatigue stress environment present in numerous flexible electronic applications. The design and stress environments for safe operation has been

  9. Acoustic Nonlinearity in Polycrystalline Nickel from Fatigue-Generated Microstructures

    SciTech Connect

    Cantrell, John H.

    2005-04-09

    An analytical model of the nonlinear interaction of ultrasonic waves with dislocation substructures formed during the fatigue of wavy slip metals is presented. The model is applied to the calculation of the acoustic nonlinearity parameters {beta} of polycrystalline nickel for increasingly higher levels of fatigue from the virgin state. The values calculated for stress-controlled loading at 345 MPa predict a monotonic increase in {beta} of more than 390 percent as a function of percent life to fracture due to substructural evolution.

  10. Quantifying fatigue risk in model-based fatigue risk management.

    PubMed

    Rangan, Suresh; Van Dongen, Hans P A

    2013-02-01

    The question of what is a maximally acceptable level of fatigue risk is hotly debated in model-based fatigue risk management in commercial aviation and other transportation modes. A quantitative approach to addressing this issue, referred to by the Federal Aviation Administration with regard to its final rule for commercial aviation "Flightcrew Member Duty and Rest Requirements," is to compare predictions from a mathematical fatigue model against a fatigue threshold. While this accounts for duty time spent at elevated fatigue risk, it does not account for the degree of fatigue risk and may, therefore, result in misleading schedule assessments. We propose an alternative approach based on the first-order approximation that fatigue risk is proportional to both the duty time spent below the fatigue threshold and the distance of the fatigue predictions to the threshold--that is, the area under the curve (AUC). The AUC approach is straightforward to implement for schedule assessments in commercial aviation and also provides a useful fatigue metric for evaluating thousands of scheduling options in industrial schedule optimization tools.

  11. Fatigue damage evolution study with non-destructive magnetic properties measurement method using scanning SQUID microscopy

    NASA Astrophysics Data System (ADS)

    Lee, Tae-Kyu

    The fatigue process can be precisely defined in the crack propagation stage, where the fatigue damage can be evaluated by observed cracks and where an increase of the dislocation density occurs at the first 10% of the fatigue life. But for the stages between dislocation saturation and prior to nucleation, no definition can be given due to the relative difficulty in quantifying the damage. Especially, detecting a high-cycle fatigue damage is a particularly important yet an unsolved problem in non-destructive testing. There are no reliable techniques to measure the progress of fatigue in the intermediate fatigue regime, the second stage of fatigue, where the overall dislocation density is approximately constant and the microstructural changes are subtle include about 80% of the fatigue life in high-cycle fatigue. In this study, a non-destructive evaluation method is established by continuously measuring the magnetic properties, which interact with the developing fatigue damage during cyclic loading. Dislocations and microcracks which are initiated during the fatigue act as pinning sites which impede the motion of magnetic domain walls under the applied magnetic field, thereby influencing the bulk magnetic properties. The remanence field of various fatigued steel specimens are detected using a scanning microscope based on a high transition temperature Superconducting Quantum Interference Device (SQUID). The results show the development of localized peaks in remanent magnetization prior to the formation of visible fatigue cracks. Even in the second stage of fatigue, where the macroscopic state of the sample is relatively constant, the results show that a scanning SQUID microscope is capable of detecting regions of fatigue damage both on surface and in sub-surface regions.

  12. Analysis of muscle fatigue in helicopter pilots.

    PubMed

    Balasubramanian, Venkatesh; Dutt, Ashwani; Rai, Shobhit

    2011-11-01

    Helicopter pilots espouse ergonomically unfavourable postures and endure vibration which result in low back pain. The objective of this study was to investigate the effects of a helicopter flight on pilots back and shoulder muscles using surface Electromyography (sEMG) analysis. This study also correlates low back pain symptoms from Rehabilitation Bioengineering Group Pain Scale (RBGPS) questionnaire with muscle fatigue rates obtained. RBGPS was administered on 20 Coast Guard helicopter pilots. sEMG was acquired before and after flight from erector spinae and trapezius muscles in 8 of these 20 pilots. Statistical analysis of time and frequency domain parameters indicated significant fatigue in right trapezius muscle due to flying. Muscle fatigue correlated with average duration of flight (r² = 0.913), total service as pilot (r² = 0.825), pain (r² = 0.463) and total flying hours (r² = 0.507). However, muscle fatigue weakly correlated with Body Mass Index (BMI) (r² = 0.000144) and age (r² = 0.033).

  13. Fatigue properties of shuttle thermal protection system

    NASA Technical Reports Server (NTRS)

    Sawyer, J. W.; Cooper, P. A.

    1980-01-01

    Static and cyclic load tests were conducted to determine the static and fatigue strength of the RIS tile/SIP thermal protection system used on the orbiter of the space shuttle. The material systems investigated include the densified and undensified LI-900 tile system on the .40 cm thick SIP and the densified and undensified LI-2200 tile system on the .23 cm (.090 inch) thick SIP. The tests were conducted at room temperature with a fully reversed uniform cyclic loading at 1 Hertz. Cyclic loading causes a relatively large reduction in the stress level that each of the SIP/tile systems can withstand for a small number of cycles. For example, the average static strength of the .40 cm thick SIP/LI-900 tile system is reduced from 86 kPa to 62 kPa for a thousand cycles. Although the .23 cm thick SIP/LI-2200 tile system has a higher static strength, similar reductions in the fatigue strength are noted. Densifying the faying surface of the RSI tile changes the failure mode from the SIP/tile interface to the parent RSI or the SIP and thus greatly increases the static strength of the system. Fatigue failure for the densified tile system, however, occurs due to complete separation or excessive elongation of the SIP and the fatigue strength is only slightly greater than that for the undensified tile system.

  14. Probabilistic Material Strength Degradation Model for Inconel 718 Components Subjected to High Temperature, Mechanical Fatigue, Creep and Thermal Fatigue Effects

    NASA Technical Reports Server (NTRS)

    Bast, Callie Corinne Scheidt

    1994-01-01

    This thesis presents the on-going development of methodology for a probabilistic material strength degradation model. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes four effects that typically reduce lifetime strength: high temperature, mechanical fatigue, creep, and thermal fatigue. Statistical analysis was conducted on experimental Inconel 718 data obtained from the open literature. This analysis provided regression parameters for use as the model's empirical material constants, thus calibrating the model specifically for Inconel 718. Model calibration was carried out for four variables, namely, high temperature, mechanical fatigue, creep, and thermal fatigue. Methodology to estimate standard deviations of these material constants for input into the probabilistic material strength model was developed. Using the current version of PROMISS, entitled PROMISS93, a sensitivity study for the combined effects of mechanical fatigue, creep, and thermal fatigue was performed. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing a combination of mechanical fatigue and high temperature effects by model to the combination by experiment were conducted. Thus, for Inconel 718, the basic model assumption of independence between effects was evaluated. Results from this limited verification study strongly supported this assumption.

  15. Fatigue Life Prediction of Steel Bridges for Extreme Loading Using a New Damage Indicator

    NASA Astrophysics Data System (ADS)

    Karunananda, Pallaha Athawudagedara Kamal; Ohga, Mitao; Dissanayake, Punchi Bandage Ranjith; Siriwardane, Siriwardane Arachchilage Sudath Chaminda

    High cycle fatigue (HCF) damage caused by normal traffic loading is one of the major modes of failures in steel bridges. During bridge service life, there are extreme loading situations such as typhoons, earthquakes which cause higher amplitude loading than normal traffic loading. Due to this reason, critical members could undergo overstress cycles in the plastic range. Therefore, such members are subjected to low cycle fatigue (LCF) during these situations while subjecting to HCF in serviceable condition. Bridges, which are not seriously damaged, generally continue to be functioned after these extreme loading situations and fatigue life estimation is required to ensure their safety. Therefore, this paper presents a new damage indicator based fatigue model to predict life of steel bridges due to combined effect of extreme and normal traffic loadings. It consists of a modified strain life curve and a strain based damage indicator. Both the strain life curve and the damage indicator are newly proposed in the study. Modified strain life curve consists of Coffin Manson relation in the LCF regime and a new strain life curve in the HCF regime. Damage variable is based on von Mises equivalent strain and modified by factors to consider effects of loading non proportionality and loading path in multiaxial stress state. The new damage indicator can capture the loading sequence effect. The proposed model is verified with experimental test results of combined HCF and LCF of three materials; S304L stainless steel, Haynes 188 (a Cobolt superalloy) and S45C steel obtained from the literature. The verification of experimental results confirms the validity of the proposed model.

  16. Increased Incidence of Fatigue in Patients with Primary Immunodeficiency Disorders: Prevalence and Associations Within the US Immunodeficiency Network Registry

    PubMed Central

    Guffey, Danielle; Minard, Charles G.; Orange, Jordan S.

    2017-01-01

    Introduction Patients with primary immunodeficiency (PID) often report fatigue, yet this symptom has not been studied in PID. Fatigue affects 6–7.5% of healthy adults. The goal of this study is to estimate the prevalence of fatigue in patients with PID and investigate its associated factors. Methods We analyzed 2537 PID patients registered in USIDNET to determine responses to the field “fatigue” in the core registry form. Demographics, immune phenotypes, and comorbid conditions were compared between fatigued and non-fatigued patients to identify relevant associations and potential drivers. A focused analysis was performed for patients with predominantly antibody deficiency disorders (PADs). Results Fatigue was reported in 25.9%(95% CI 23.7–28.3) of PAD patients, compared to 6.4% (95% CI 4.9–8.2) of non-PAD. Patients with common variable immunodeficiency (CVID) had the highest prevalence of fatigue (p < 0.001) among all PID diagnoses. Other factors that were associated with a higher rate of fatigue among PAD patients included female sex, higher BMI, depression, bronchiectasis, and autoimmunity. Additionally, fatigued PAD patients had lower absolute lymphocyte, CD3, CD4, and CD8 counts compared to non-fatigued patients. Conclusion Our findings suggest that fatigue is overrepresented in PAD patients. Prospective studies to estimate prevalence, risk factors, and fatigue etiology in PID are warranted, so therapeutic interventions can be considered. PMID:28124237

  17. Fatigue strength of tubular structural elements at bending vibrations. Communication 2: TSE fatigue strength at programmed load variation

    NASA Astrophysics Data System (ADS)

    Gerasimchuk, O. N.; Gorodetskij, S. S.; Gryaznov, B. A.; Nalimov, Yu. S.

    1994-04-01

    Programs of a block loading with a prescribed and random alternation of stress amplitudes, simulating service load spectra, are presented. The results of fatigue testing of straight and bent tubular structural elements are given. A conclusion is drawn that low fatigue strength of VNS25 steel bent TSEs is due to an unfavorable technological inheritance of the tube bending and deplanation of the section during the test.

  18. On the Notch Effect in Low Temperature Carburized Stainless Steel under Fatigue

    NASA Astrophysics Data System (ADS)

    Minak, G.

    2010-06-01

    The present paper describes the fatigue behaviour of carburized notched AISI 316 austenitic stainless steel specimens. Rotary four point bending fatigue tests have been performed using carburized smooth specimens with two different values of surface rugosity and notched specimen with two different stress concentration factors Kt, of 3.55 and 6.50 and the effects of carburizing on fatigue strength and notch sensitivity were discussed. Results show a general improvement of the fatigue life due to the treatment for all the series with an apparent notch sensitivity lower than one in the case of blunt notches due to secondary effects that were singled out.

  19. Factors in the fatigue of heavy vehicle drivers.

    PubMed

    Perttula, Pia; Ojala, Tarja; Kuosma, Eeva

    2011-04-01

    This study assessed work-related and driver-related factors in fatigue among Finnish heavy vehicle drivers. 683 professional drivers responded to a questionnaire, 27.8% of whom reported often feeling fatigue during their work shifts. Of the respondents, 27.5% reported having momentarily fallen asleep at the wheel while driving during the past year. Almost half (46.8%) of the fatigued drivers estimated the reasons for momentarily falling asleep were work-related. Long working shifts and short sleeps significantly increased the risk of momentarily falling asleep at the wheel. The risk of fatigue was the highest for the drivers who were unable to choose the time of their breaks.

  20. Monitoring of fatigue crack under complex environment using guided waves

    NASA Astrophysics Data System (ADS)

    Tang, Jianfei; Yan, Gang; Xu, Xiwu

    2011-11-01

    This paper presents an experimental study on monitoring of fatigue crack under complex environment using guided waves. An experimental set-up consisting of an electrical oven, a MTS testing machine and a monitoring system is established to perform the study. First, the combined effects of temperature, load and vibration on the propagation of guided waves in metallic structure is studied. Then, a statistical approach is proposed to detect fatigue crack under these combined effects. Damage feature is extracted after the guided wave signals are processed by Fourier transform. A Monte Carlo procedure is employed to estimate the probability density functions of the feature before and after cracking, respectively. By comparing the probability density functions, the probability of existence of fatigue crack is determined. Experimental study on a fatigue coupon under combined effects of temperature, load and vibration is conducted to demonstrate the effectiveness of the proposed method.

  1. Monitoring of fatigue crack under complex environment using guided waves

    NASA Astrophysics Data System (ADS)

    Tang, Jianfei; Yan, Gang; Xu, Xiwu

    2012-04-01

    This paper presents an experimental study on monitoring of fatigue crack under complex environment using guided waves. An experimental set-up consisting of an electrical oven, a MTS testing machine and a monitoring system is established to perform the study. First, the combined effects of temperature, load and vibration on the propagation of guided waves in metallic structure is studied. Then, a statistical approach is proposed to detect fatigue crack under these combined effects. Damage feature is extracted after the guided wave signals are processed by Fourier transform. A Monte Carlo procedure is employed to estimate the probability density functions of the feature before and after cracking, respectively. By comparing the probability density functions, the probability of existence of fatigue crack is determined. Experimental study on a fatigue coupon under combined effects of temperature, load and vibration is conducted to demonstrate the effectiveness of the proposed method.

  2. Study of fatigue behavior of longitudinal welded pipes

    NASA Astrophysics Data System (ADS)

    Simion, P.; Dia, V.; Istrate, B.; Hrituleac, G.; Hrituleac, I.; Munteanu, C.

    2016-08-01

    During transport and storage of the various fluids, welded pipes are subjected to cyclic loading due to pressure fluctuations that often exceed the prescribed values for normal operation. These cyclic loading can significantly reduce the life of the pipes; as a result the design should be based on the fatigue strength not only on static resistance. In general the fatigue strength of pipes is dependent by strength, pipe geometry and surface quality. In case of the electric longitudinal welded pipes, the fatigue strength is significantly limited by concentration of residual stress and the size of existing defects in the weld seam. This paper presents the fatigue behaviour of the electric welded pipes by high frequency, under conditions that simulate real operating conditions pipes. Fatigue testing was performed on welded pipes made of micro alloyed carbon steels. Some of these pipes were previously subjected to a heat treatment of normalization, in order to also determine the influence of heat treatment on the fatigue strength of welded pipes. To determine and correlate the different factors affecting the fatigue strength, welded pipes were also subjected to various tests: tensile tests, impact tests, measurement of micro hardness, microstructural analysis by optical microscopy and scanning electron microscopy.

  3. Postural stability in altered and unaltered sensory environments following fatiguing exercise of lower extremity joints.

    PubMed

    Dickin, D C; Doan, J B

    2008-12-01

    Investigations of postural recovery following controlled external perturbations have provided models for healthy and pathological balance behavior. Less work, however, has investigated postural responses related to internal perturbations of the balance system. In this study, lower extremity joint (knee, or ankle) and overall fatigue of the dominant leg provided the internal perturbations to the balance system. Postural sway was examined during unilateral dominant leg standing before and immediately following fatiguing exercise, as well as at 10, 20, and 30 min post-fatigue activity. Sway was measured in both firm and sway-referenced support surface (external perturbation) conditions. Both joint-localized fatigue and overall fatigue were found to induce impairments in postural control, which were further exacerbated by external postural perturbations. Follow-up pairwise comparisons indicated that these impairments persisted at 10 and 30 min post-fatigue. No differences in postural sway were found between fatigue locations or across any interactions between sway and fatigue location. The results indicated that muscular fatigue imposed a prolonged internal perturbation to postural control, regardless of any individual or combined joint fatigue localization. This global effect, combined with the prolonged impairment in postural response, provides support for critical contributions from a central mechanism to postural deficits due to fatigue.

  4. Reduced Order Methods for Prediction of Thermal-Acoustic Fatigue

    NASA Technical Reports Server (NTRS)

    Przekop, A.; Rizzi, S. A.

    2004-01-01

    The goal of this investigation is to assess the quality of high-cycle-fatigue life estimation via a reduced order method, for structures undergoing random nonlinear vibrations in a presence of thermal loading. Modal reduction is performed with several different suites of basis functions. After numerically solving the reduced order system equations of motion, the physical displacement time history is obtained by an inverse transformation and stresses are recovered. Stress ranges obtained through the rainflow counting procedure are used in a linear damage accumulation method to yield fatigue estimates. Fatigue life estimates obtained using various basis functions in the reduced order method are compared with those obtained from numerical simulation in physical degrees-of-freedom.

  5. Fatigue crack monitoring with coupled piezoelectric film acoustic emission sensors

    NASA Astrophysics Data System (ADS)

    Zhou, Changjiang

    Fatigue-induced cracking is a commonly seen problem in civil infrastructures reaching their original design life. A number of high-profile accidents have been reported in the past that involved fatigue damage in structures. Such incidences often happen without prior warnings due to lack of proper crack monitoring technique. In order to detect and monitor the fatigue crack, acoustic emission (AE) technique, has been receiving growing interests recently. AE can provide continuous and real-time monitoring data on damage progression in structures. Piezoelectric film AE sensor measures stress-wave induced strain in ultrasonic frequency range and its feasibility for AE signal monitoring has been demonstrated recently. However, extensive work in AE monitoring system development based on piezoelectric film AE sensor and sensor characterization on full-scale structures with fatigue cracks, have not been done. A lack of theoretical formulations for understanding the AE signals also hinders the use of piezoelectric film AE sensors. Additionally, crack detection and source localization with AE signals is a very important area yet to be explored for this new type of AE sensor. This dissertation presents the results of both analytical and experimental study on the signal characteristics of surface stress-wave induced AE strain signals measured by piezoelectric film AE sensors in near-field and an AE source localization method based on sensor couple theory. Based on moment tensor theory, generalized expression for AE strain signal is formulated. A special case involving the response of piezoelectric film AE sensor to surface load is also studied, which could potentially be used for sensor calibration of this type of sensor. A new concept of sensor couple theory based AE source localization technique is proposed and validated with both simulated and experimental data from fatigue test and field monitoring. Two series of fatigue tests were conducted to perform fatigue crack

  6. Estimation of indirect genetic effects in group-housed mink (Neovison vison) should account for systematic interactions either due to kin or sex.

    PubMed

    Alemu, S W; Berg, P; Janss, L; Bijma, P

    2016-02-01

    Social interactions among individuals are abundant, both in wild and in domestic populations. With social interactions, the genes of an individual may affect the trait values of other individuals, a phenomenon known as indirect genetic effects (IGEs). IGEs can be estimated using linear mixed models. Most IGE models assume that individuals interact equally to all group mates irrespective of relatedness. Kin selection theory, however, predicts that an individual will interact differently with family members versus non-family members. Here, we investigate kin- and sex-specific non-genetic social interactions in group-housed mink. Furthermore, we investigated whether systematic non-genetic interactions between kin or individuals of the same sex influence the estimates of genetic parameters. As a second objective, we clarify the relationship between estimates of the traditional IGE model and a family-based IGE model proposed in a previous study. Our results indicate that male siblings in mink show different non-genetic interactions than female siblings in mink and that this may impact the estimation of genetic parameters. Moreover, we have shown how estimates from a family-based IGE model can be translated to the ordinary direct-indirect model and vice versa. We find no evidence for genetic differences in interactions among related versus unrelated mink.

  7. Fatigue Assessment: Subjective Peer-to-Peer Fatigue Scoring (Reprint)

    DTIC Science & Technology

    2013-10-01

    basis for sleepiness and fatigue, as well as potential performance defi cits associ- ated with fatigued states. There are many biomathematical models ...in current use with most fundamentally infl uenced by the two or three-process model ( 7 , 9 , 12 ). Yet models are subject to many limitations...7 ). Thus, models have potential to be of great value, but also lack many independent variables that may be im- portant in fatigue and related

  8. Ultrasonic characterization of fatigue crack closure

    SciTech Connect

    Thompson, R.B.; Buck, O.; Rehbein, D.K.

    1991-01-01

    The characterization of fatigue crack closure is an important objective because of its influence on fatigue crack propagation, particularly under conditions of variable amplitude loading. This paper describes a nontraditional technique for characterizing closure, in which ultrasonic scattering measurements are used to obtain estimates of the number density and size of asperities bridging the crack faces, with subsequent estimates of the crack tip shielding being based on those geometrical parameters. The paper first reviews the experimental configuration and the basic elasto-dynamic theory underlying the technique. It then presents recent results obtained in studies of the influence of block overloads and load shedding on the growth of fatigue cracks in aluminum alloys. In both cases, the change in the closure state after the overload can be unambiguously seen even in the raw data. Moreover, data analysis suggests that it may be possible to predict when the crack will reinitiate based on more subtle changes in the ultrasonically inferred closure state. In the case of load shedding, a massive closure region is observed, whose characteristics appear consistent with the notion that threshold phenomena can be explained in terms of crack closure. 20 refs., 10 figs.

  9. [Childhood chronic fatigue syndrome].

    PubMed

    Miike, Teruhisa

    2007-06-01

    Chronic fatigue syndrome in childhood and adolescents(CCFS) is a complex and debilitation with severe morbidity and confusion. It is common condition with up to 3-5% of children and adolescents showing strange fatigue and confusion for more than 30 days. In this condition, four major symptoms are important: sleep disorders, easy fatigability, disturbed learning and memorization and immunological problems. Routine laboratory studies are similar to adult CFS, although abnormalities can be seen on serum pyruvic acid level, OGTT pattern, deep body temperature rhythm, hormonal secretion rhythm, and cerebral blood flow. For a diagnosis of CCFS, a research group supported by Japanese ministry of health, labor and welfare developed CCFS case definition on 2004. Treatment focused to correct disrupted circadian rhythms and supply of energy.

  10. Probabilistic Mesomechanical Fatigue Model

    NASA Technical Reports Server (NTRS)

    Tryon, Robert G.

    1997-01-01

    A probabilistic mesomechanical fatigue life model is proposed to link the microstructural material heterogeneities to the statistical scatter in the macrostructural response. The macrostructure is modeled as an ensemble of microelements. Cracks nucleation within the microelements and grow from the microelements to final fracture. Variations of the microelement properties are defined using statistical parameters. A micromechanical slip band decohesion model is used to determine the crack nucleation life and size. A crack tip opening displacement model is used to determine the small crack growth life and size. Paris law is used to determine the long crack growth life. The models are combined in a Monte Carlo simulation to determine the statistical distribution of total fatigue life for the macrostructure. The modeled response is compared to trends in experimental observations from the literature.

  11. Integration of measurements with atmospheric dispersion models: Source term estimation for dispersal of (239)Pu due to non-nuclear detonation of high explosive

    NASA Astrophysics Data System (ADS)

    Edwards, L. L.; Harvey, T. F.; Freis, R. P.; Pitovranov, S. E.; Chernokozhin, E. V.

    1992-10-01

    The accuracy associated with assessing the environmental consequences of an accidental release of radioactivity is highly dependent on our knowledge of the source term characteristics and, in the case when the radioactivity is condensed on particles, the particle size distribution, all of which are generally poorly known. This paper reports on the development of a numerical technique that integrates the radiological measurements with atmospheric dispersion modeling. This results in a more accurate particle-size distribution and particle injection height estimation when compared with measurements of high explosive dispersal of (239)Pu. The estimation model is based on a non-linear least squares regression scheme coupled with the ARAC three-dimensional atmospheric dispersion models. The viability of the approach is evaluated by estimation of ADPIC model input parameters such as the ADPIC particle size mean aerodynamic diameter, the geometric standard deviation, and largest size. Additionally we estimate an optimal 'coupling coefficient' between the particles and an explosive cloud rise model. The experimental data are taken from the Clean Slate 1 field experiment conducted during 1963 at the Tonopah Test Range in Nevada. The regression technique optimizes the agreement between the measured and model predicted concentrations of (239)Pu by varying the model input parameters within their respective ranges of uncertainties. The technique generally estimated the measured concentrations within a factor of 1.5, with the worst estimate being within a factor of 5, very good in view of the complexity of the concentration measurements, the uncertainties associated with the meteorological data, and the limitations of the models. The best fit also suggest a smaller mean diameter and a smaller geometric standard deviation on the particle size as well as a slightly weaker particle to cloud coupling than previously reported.

  12. On the relationship between time-series studies, dynamic population studies, and estimating loss of life due to short-term exposure to environmental risks.

    PubMed

    Burnett, Richard T; Dewanji, Anup; Dominici, Francesca; Goldberg, Mark S; Cohen, Aaron; Krewski, Daniel

    2003-07-01

    There is a growing concern that short-term exposure to combustion-related air pollution is associated with increased risk of death. This finding is based largely on time-series studies that estimate associations between daily variations in ambient air pollution concentrations and in the number of nonaccidental deaths within a community. Because these results are not based on cohort or dynamic population designs, where individuals are followed in time, it has been suggested that estimates of effect from these time-series studies cannot be used to determine the amount of life lost because of short-term exposures. We show that results from time-series studies are equivalent to estimates obtained from a dynamic population when each individual's survival experience can be summarized as the daily number of deaths. This occurs when the following conditions are satisfied: a) the environmental covariates vary in time and not between individuals; b) on any given day, the probability of death is small; c) on any given day and after adjusting for known risk factors for mortality such age, sex, smoking habits, and environmental exposures, each subject of the at-risk population has the same probability of death; d) environmental covariates have a common effect on mortality of all members of at-risk population; and e) the averages of individual risk factors, such as smoking habits, over the at-risk population vary smoothly with time. Under these conditions, the association between temporal variation in the environmental covariates and the survival experience of members of the dynamic population can be estimated by regressing the daily number of deaths on the daily value of the environmental covariates, as is done in time-series mortality studies. Issues in extrapolating risk estimates based on time-series studies in one population to estimate the amount of life lost in another population are also discussed.

  13. Chronic Fatigue Syndrome

    PubMed Central

    Leyton, Edward; Pross, Hugh

    1992-01-01

    To determine the effect of certain herbal and homeopathic preparations on symptoms, lymphocyte markers, and cytotoxic function of the lymphocytes in patients with chronic fatigue syndrome, we studied six outpatients diagnosed with the disease by their family physicians. Patients were given herbal and homeopathic preparations after a 3-week symptom-recording period. After treatment, symptoms were again recorded. Blood samples were taken before and after treatment. None of the values showed any significant change after treatment. PMID:21221272

  14. [Fatigue and anemia].

    PubMed

    Ivanova, K; Zeller, A

    2009-12-02

    We herein report on an 80-year old male patient with a history of muscle weakness, fatigue and weight loss since several months. Because of a pathologic synacthen test in combination with decreased levels of ACTH, we diagnosed a secondary chronic adrenal insufficiency. Because of a normochromic, normocytic, and hypo-proliferative anemia, bone marrow puncture was performed, showing an anemia of chronic disease. We initiated hydrocortisone and anemia and patients' symptoms were fully reconstituted.

  15. Aerodynamic-thermomechanic coupling and creep-fatigue damage prediction. Part B: Thermomechanic investigation

    SciTech Connect

    Bruchet, P.

    1995-12-31

    The purpose of this paper is creep-fatigue damage prediction during the cold start-up of a 250 MW steam turbine high pressure rotor. Calculations were performed taking into account aerodynamic and thermal effects. Aerodynamic effects were obtained from a calculation of the bucket root and diaphragm packing leakage flow performed with the finite elements code N3S (see Part A : Aerodynamic investigation). Then, thermomechanical calculations were undertaken with the finite elements mechanical code ASTER and with the thermal boundary conditions previously obtained. These calculations pointed out plastified zones in the first two stages of the HP rotor. Consequently, it was necessary to estimate the thermal fatigue life reduction due to the start-up as well as the creep damage. These calculations were performed using frequency dependent Manson-Coffin curves for fatigue damage and Larson-Miller curves for creep damage. The start-up influence on the rotor residual life was particularly studied and interesting results are available.

  16. Changes in muscle strength, relaxation rate and fatiguability during the human menstrual cycle.

    PubMed Central

    Sarwar, R; Niclos, B B; Rutherford, O M

    1996-01-01

    1. The effect of the different phases of the menstrual cycle on skeletal muscle strength, contractile properties and fatiguability was investigated in ten young, healthy females. Results were compared with a similar group on the combined (non-phasic) oral contraceptive pill (OC). Cycle phases were divided into the early and mid-follicular, mid-cycle (ovulatory) and mid- and late luteal. Cycle phases were estimated from the first day of the menstrual bleed. 2. Subjects were studied weekly through two complete cycles. Measurements included quadriceps and handgrip maximum voluntary isometric force and the relaxation times, force-frequency relationship and fatigue index of the quadriceps during percutaneous stimulation at a range of frequencies from 1 to 100 Hz. 3. In the women not taking the OC there was a significant increase of about 11% in quadriceps and handgrip strength at mid-cycle compared with both the follicular and luteal phases. Accompanying the increases in strength there was a significant slowing of relaxation and increase in fatiguability at mid-cycle. No changes in any parameter were found in the women taking the OC. 4. The changes in muscle function at mid-cycle may be due to the increase in oestrogen that occurs prior to ovulation. PMID:8735711

  17. Applications of infrared thermography for nondestructive testing of fatigue cracks in steel bridges

    NASA Astrophysics Data System (ADS)

    Sakagami, Takahide; Izumi, Yui; Kobayashi, Yoshihiro; Mizokami, Yoshiaki; Kawabata, Sunao

    2014-05-01

    In recent years, fatigue crack propagations in aged steel bridge which may lead to catastrophic structural failures have become a serious problem. For large-scale steel structures such as orthotropic steel decks in highway bridges, nondestructive inspection of deteriorations and fatigue damages are indispensable for securing their safety and for estimating their remaining strength. As conventional NDT techniques for steel bridges, visual testing, magnetic particle testing and ultrasonic testing have been commonly employed. However, these techniques are time- and labor- consuming techniques, because special equipment is required for inspection, such as scaffolding or a truck mount aerial work platform. In this paper, a new thermography NDT technique, which is based on temperature gap appeared on the surface of structural members due to thermal insulation effect of the crack, is developed for detection of fatigue cracks. The practicability of the developed technique is demonstrated by the field experiments for highway steel bridges in service. Detectable crack size and factors such as measurement time, season or spatial resolution which influence crack detectability are investigated.

  18. Fatigue syndrome in sarcoidosis.

    PubMed

    Górski, Witold; Piotrowski, Wojciech J

    2016-01-01

    Sarcoidosis is an inflammatory disease of unknown etiology. Most commonly it results in the formation of non-caseating granulomas in intrathoracic lymph nodes and lung parenchyma, but the clinical course and picture may be complicated by extrapulmonary involvement and many non-respiratory signs and symptoms which are directly related to the disease. In addition, sarcoidosis patients may suffer from a plethora of symptoms of uncertain or unknown origin. Fatigue is one of these symptoms, and according to some authors it is reported by the majority of patients with active sarcoidosis, but also by a smaller proportion of patients with inactive sarcoidosis, or even with complete clinical and radiological remission. Therefore the term fatigue syndrome is frequently used to name this clinical problem. The definition of fatigue syndrome in sarcoidosis is imprecise and the syndrome is usually recognized by use of validated questionnaires. In this review the uptodate knowledge in this field was presented and different challenges connected with this syndrome were described.

  19. Effect of fatigue on single-leg hop landing biomechanics.

    PubMed

    Orishimo, Karl F; Kremenic, Ian J

    2006-11-01

    The objective of this study was to measure adaptations in landing strategy during single-leg hops following thigh muscle fatigue. Kinetic, kinematic, and electromyographic data were recorded as thirteen healthy male subjects performed a single-leg hop in both the unfatigued and fatigued states. To sufficiently fatigue the thigh muscles, subjects performed at least two sets of 50 step-ups. Fatigue was assessed by measuring horizontal hopping ability following the protocol. Joint motion and loading, as well as muscle activation patterns, were compared between fatigued and unfatigued conditions. Fatigue significantly increased knee motion (p = 0.012) and shifted the ankle into a more dorsiflexed position (p = 0.029). Hip flexion was also reduced following fatigue (p = 0.042). Peak extension moment tended to decrease at the knee and increase at the ankle and hip (p = 0.014). Ankle plantar flexion moment at the time of peak total support moment increased from 0.8 (N x m)/kg (SD, 0.6 [N x m]/kg) to 1.5 (N x m)/kg (SD, 0.8 [N x m]/kg) (p = 0.006). Decreased knee moment and increased knee flexion during landings following fatigue indicated that the control of knee motion was compromised despite increased activation of the vastus medialis, vastus lateralis, and rectus femoris (p = 0.014, p = 0.014, and p = 0.017, respectively). Performance at the ankle increased to compensate for weakness in the knee musculature and to maintain lower extremity stability during landing. Investigating the biomechanical adaptations that occur in healthy subjects as a result of muscle fatigue may give insight into the compensatory mechanisms and loading patterns occurring in patients with knee pathology. Changes in single-leg hop landing performance could be used to demonstrate functional improvement in patients due to training or physical therapy.

  20. Fracture mechanics and corrosion fatigue.

    NASA Technical Reports Server (NTRS)

    Mcevily, A. J.; Wei, R. P.

    1972-01-01

    Review of the current state-of-the-art in fracture mechanics, particularly in relation to the study of problems in environment-enhanced fatigue crack growth. The usefulness of this approach in developing understanding of the mechanisms for environmental embrittlement and its engineering utility are discussed. After a brief review of the evolution of the fracture mechanics approach and the study of environmental effects on the fatigue behavior of materials, a study is made of the response of materials to fatigue and corrosion fatigue, the modeling of the mechanisms of the fatigue process is considered, and the application of knowledge of fatigue crack growth to the prediction of the high cycle life of unnotched specimens is illustrated.

  1. Lamb Wave Response of Fatigued Composite Samples

    NASA Technical Reports Server (NTRS)

    Seale, Michael; Smith, Barry T.; Prosser, William H.; Masters, John E.

    1994-01-01

    Composite materials are being more widely used today by aerospace, automotive, sports equipment, and a number of other commercial industries because of their advantages over conventional metals. Composites have a high strength-to-weight ratio and can be constructed to meet specific design needs. Composite structures are already in use in secondary parts of the Douglas MD-11 and are planned to be used in the new MD-12X. Plans also exist for their use in primary and secondary structures on the Boeing 777. Douglas proposed MD-XX may also incorporate composite materials into primary structures such as the wings and tail. Use of composites in these structures offers weight savings, corrosion resistance, and improved aerodynamics. Additionally, composites have been used to repair cracks in many B-1Bs where traditional repair techniques were not very effective. Plans have also been made to reinforce all of the remaining B-1s with composite materials. Verification of the structural integrity of composite components is needed to insure safe operation of these aerospace vehicles. One aspect of the use of these composites is their response to fatigue. To track this progression of fatigue in aerospace structures, a convenient method to nondestructively monitor this damage needs to be developed. Traditional NDE techniques used on metals are not easily adaptable to composites due to the inhomogeneous and anisotropic nature of these materials. Finding an effective means of nondestructively monitoring fatigue damage is extremely important to the safety and reliability of such structures. Lamb waves offer one method of evaluating these composite materials. As a material is fatigued, the modulus degrades. Since the Lamb wave velocity can be related to the modulus of the material, an effective tool can be developed to monitor fatigue damage in composites by measuring the velocity of these waves. In this work, preliminary studies have been conducted which monitor fatigue damage in

  2. New fast least-squares algorithm for estimating the best-fitting parameters due to simple geometric-structures from gravity anomalies

    PubMed Central

    Essa, Khalid S.

    2013-01-01

    A new fast least-squares method is developed to estimate the shape factor (q-parameter) of a buried structure using normalized residual anomalies obtained from gravity data. The problem of shape factor estimation is transformed into a problem of finding a solution of a non-linear equation of the form f(q) = 0 by defining the anomaly value at the origin and at different points on the profile (N-value). Procedures are also formulated to estimate the depth (z-parameter) and the amplitude coefficient (A-parameter) of the buried structure. The method is simple and rapid for estimating parameters that produced gravity anomalies. This technique is used for a class of geometrically simple anomalous bodies, including the semi-infinite vertical cylinder, the infinitely long horizontal cylinder, and the sphere. The technique is tested and verified on theoretical models with and without random errors. It is also successfully applied to real data sets from Senegal and India, and the inverted-parameters are in good agreement with the known actual values. PMID:25685472

  3. World Health Organization Estimates of the Relative Contributions of Food to the Burden of Disease Due to Selected Foodborne Hazards: A Structured Expert Elicitation

    PubMed Central

    Hald, Tine; Aspinall, Willy; Devleesschauwer, Brecht; Cooke, Roger; Corrigan, Tim; Havelaar, Arie H.; Gibb, Herman J.; Torgerson, Paul R.; Kirk, Martyn D.; Angulo, Fred J.; Lake, Robin J.; Speybroeck, Niko; Hoffmann, Sandra

    2016-01-01

    Background The Foodborne Disease Burden Epidemiology Reference Group (FERG) was established in 2007 by the World Health Organization (WHO) to estimate the global burden of foodborne diseases (FBDs). This estimation is complicated because most of the hazards causing FBD are not transmitted solely by food; most have several potential exposure routes consisting of transmission from animals, by humans, and via environmental routes including water. This paper describes an expert elicitation study conducted by the FERG Source Attribution Task Force to estimate the relative contribution of food to the global burden of diseases commonly transmitted through the consumption of food. Methods and Findings We applied structured expert judgment using Cooke’s Classical Model to obtain estimates for 14 subregions for the relative contributions of different transmission pathways for eleven diarrheal diseases, seven other infectious diseases and one chemical (lead). Experts were identified through international networks followed by social network sampling. Final selection of experts was based on their experience including international working experience. Enrolled experts were scored on their ability to judge uncertainty accurately and informatively using a series of subject-matter specific ‘seed’ questions whose answers are unknown to the experts at the time they are interviewed. Trained facilitators elicited the 5th, and 50th and 95th percentile responses to seed questions through telephone interviews. Cooke’s Classical Model uses responses to the seed questions to weigh and aggregate expert responses. After this interview, the experts were asked to provide 5th, 50th, and 95th percentile estimates for the ‘target’ questions regarding disease transmission routes. A total of 72 experts were enrolled in the study. Ten panels were global, meaning that the experts should provide estimates for all 14 subregions, whereas the nine panels were subregional, with experts

  4. Origin of Human Losses due to the Emilia Romagna, Italy, M5.9 Earthquake of 20 May 2012 and their Estimate in Real Time

    NASA Astrophysics Data System (ADS)

    Wyss, M.

    2012-12-01

    Estimating human losses within less than an hour worldwide requires assumptions and simplifications. Earthquake for which losses are accurately recorded after the event provide clues concerning the influence of error sources. If final observations and real time estimates differ significantly, data and methods to calculate losses may be modified or calibrated. In the case of the earthquake in the Emilia Romagna region with M5.9 on May 20th, the real time epicenter estimates of the GFZ and the USGS differed from the ultimate location by the INGV by 6 and 9 km, respectively. Fatalities estimated within an hour of the earthquake by the loss estimating tool QLARM, based on these two epicenters, numbered 20 and 31, whereas 7 were reported in the end, and 12 would have been calculated if the ultimate epicenter released by INGV had been used. These four numbers being small, do not differ statistically. Thus, the epicenter errors in this case did not appreciably influence the results. The QUEST team of INGV has reported intensities with I ≥ 5 at 40 locations with accuracies of 0.5 units and QLARM estimated I > 4.5 at 224 locations. The differences between the observed and calculated values at the 23 common locations show that the calculation in the 17 instances with significant differences were too high on average by one unit. By assuming higher than average attenuation within standard bounds for worldwide loss estimates, the calculated intensities model the observed ones better: For 57% of the locations, the difference was not significant; for the others, the calculated intensities were still somewhat higher than the observed ones. Using a generic attenuation law with higher than average attenuation, but not tailored to the region, the number of estimated fatalities becomes 12 compared to 7 reported ones. Thus, attenuation in this case decreased the discrepancy between observed and reported death by approximately a factor of two. The source of the fatalities is

  5. Application of Weakest Link Probabilistic Framework for Fatigue Notch Factor to Aero Engine Materials

    DTIC Science & Technology

    2014-08-25

    Inlet Air Filtration Systems," Gas Machinery Research Council, no. 1, 2010. [13] Robert Anthony Kupkovits, " THERMOMECHANICAL FATIGUE BEHAVIOR OF THE...and Neu R W , " Thermomechanical fatigue behavior of a directionally solidified Ni-base superallloy," Journal of engineering materials and...engine due to its high strength and good creep, fatigue , and corrosion resistance at high temperature. The microstructure features of these alloys

  6. Fatigue behavior of unirradiated V-5Cr-5Ti

    SciTech Connect

    Gieseke, B.G.; Stevens, C.O.; Grossbeck, M.L.

    1995-04-01

    The objective of this research is to determine the low cycle fatigue behavior of V-5Cr-5Ti alloys for a range of temperatures and the extent of environmental effects at ambient temperatures. The results of in-vacuum low cycle fatigue tests are presented for unirradiated V-5Cr-5Ti tested at room temperature, 240, and 400{degree}C. A comparison of the fatigue data generated in rough and high vacuums shows that a pronounced environmental degradation of the fatiuge properties exists in this alloy at room temperature. Fatigue life was reduced by as much as 84%. Cyclic stress range data and SEM observations suggest that this reduction is due to a combination of increases in rates of crack initiation and subsequent growth. The relative contribution of each difference is dependent upon the strain range.

  7. Static and dynamic fatigue properties of carbon ligament prosthesis.

    PubMed

    Błazewicz, S; Wajler, C; Chłopek, J

    1996-10-01

    The aim of the present paper was to characterize the static and dynamic mechanical properties of carbon braids used in medicine as prostheses of ligaments and tendons. A computing system (PC software) was used to register and analyze the data of mechanical tests. Tensile static tests (creep testing) were utilized to determine the failure-free value of static force. Fatigue dynamic properties of carbon braids in tensile-tensile cyclic tests including the effect of simulated body conditions were analyzed. The braids were immersed in isotonic solution at 37 degrees C. Fatigue life was markedly lowered in air in comparison with simulated body conditions. For a given value of maximum cyclic force, decreasing the minimum/maximum force ratio decreased the number of cycles to failure. The mechanical approach of fatigue behavior based on approximately maximum fatigue force and number of cycles to failure by analytical expression was given. Energy dissipation due to the hysteresis loop was considered.

  8. Gear Fatigue Diagnostics and Prognostics

    DTIC Science & Technology

    2013-01-01

    one for single gear tooth fatigue, and one for gear-on-gear dynamometer-based tester ) we have been collecting crack initiation and crack propagation...fatigue tester ); and torque, angular speed, vibration, temperature, and crack-propagation (gear-on-gear dynamometer-based tester ). The main outcome...Description The test consists of two set of tests on a dynamometer and one set of test on the fatigue tester and some additional activities. Fig

  9. Bending fatigue tests on SiC-Al tapes under alternating stress at room temperature

    NASA Technical Reports Server (NTRS)

    Herzog, J. A.

    1981-01-01

    The development of a testing method for fatigue tests on SiC-Al tapes containing a small amount of SiC filaments under alternating stress is reported. The fatigue strength curves resulting for this composite are discussed. They permit an estimate of its behavior under continuous stress and in combination with various other matrices, especially metal matrices.

  10. Fatigue life variability and reliability analysis of a wind turbine blade

    NASA Astrophysics Data System (ADS)

    Veers, P. S.; Sutherland, H. J.; Ashwill, T. D.

    Wind turbines must withstand harsh environments that induce many stress cycles into their components. A numerical analysis package is used to illustrate the sobering variability in predicted fatigue life with relatively small changes in inputs. The variability of the input parameters is modeled to obtain estimates of the fatigue reliability of the turbine blades.

  11. Determinants of fatigue and stress

    PubMed Central

    2011-01-01

    Background Fatigue can be triggered by previous perceived stress which may lead to impairment of performance and function. The purpose of the study was to investigate the relationship between fatigue and perceived stress. Method Health determinants including sociodemographic factors for associations between fatigue and perceived stress in the general population (N = 2,483) are outlined. Fatigue and stress were assessed with the Chalder Fatigue Scale (CFS) and the Perceived Stress Questionnaire (PSQ). Results Within the general population, 25.9% of male and 34.5% of female respondents reported moderate fatigue during the last six months; 9.7% of subjects reported substantial fatigue lasting six months or longer. An adjusted regression analysis (R2corr = .28, p < .001) showed that fatigue is highest associated with perceived stress and self-perceived health status. The following factors were correlated with increased rates of fatigue and perceived stress: female gender, divorce/separation, low social class and poor health status. Conclusion We conclude that the two conditions overlap most in terms of socio-economic status and self-perceived health status. PMID:21774803

  12. Mode II fatigue crack propagation.

    NASA Technical Reports Server (NTRS)

    Roberts, R.; Kibler, J. J.

    1971-01-01

    Fatigue crack propagation rates were obtained for 2024-T3 bare aluminum plates subjected to in-plane, mode I, extensional loads and transverse, mode II, bending loads. These results were compared to the results of Iida and Kobayashi for in-plane mode I-mode II extensional loads. The engineering significance of mode I-mode II fatigue crack growth is considered in view of the present results. A fatigue crack growth equation for handling mode I-mode II fatigue crack growth rates from existing mode I data is also discussed.

  13. Recovery of PdiTwitch following the induction of diaphragm fatigue in normal subjects.

    PubMed

    Travaline, J M; Sudarshan, S; Criner, G J

    1997-11-01

    Low frequency diaphragm fatigue (LFF) may play a major role in the pathogenesis of ventilatory failure; however, recovery from LFF is not well studied. We measured transdiaphragmatic twitch pressure (PdiT) at FRC (using a reduction of PdiT as an index of LFF) and maximum transdiaphragmatic pressure (Pdimax) before and after the induction of diaphragm fatigue in seven normal subjects, age 31 +/- 3 yr (mean +/- SD). Fatigue was induced by breathing through an inspiratory resistive load. PdiT produced by bilateral transcutaneous supramaximal electrophrenic stimulation was measured at baseline, 15, 30 min, 1, 2, 3, 4 h, and then 1 to 3 times between hour 20-25 post-fatigue. Pdimax estimated by twitch occlusion was measured at baseline, 30 min, 2-3, and 20-25 h post-fatigue. Pre-fatigue values (mean +/- SE) were: PdiT 23.6 +/- 2.5 cm H2O. The mean +/- SD time to fatigue was 25.3 +/- 12.3 min. Post-fatigue PdiT was reduced to 50%, and by 3 h was 72% of the initial value; 100% by 25 h. Pdimax was reduced to 75% post-fatigue, but recovered to 87% by 3 h, and 100% by 25 h. We concluded that recovery of PdiT and Pdimax in normal subjects starts to occur within the first few hours following diaphragm fatigue, and is complete by 25 h.

  14. Cardiovascular, muscular and perceptual contributions to physical fatigue in prevalent kidney transplant recipients.

    PubMed

    Chan, Winnie; Jones, David; Bosch, Jos A; McPhee, Jamie; Crabtree, Nicola; McTernan, Philip G; Kaur, Okdeep; Inston, Nicholas; Moore, Sue; McClean, Andrew; Harper, Lorraine; Phillips, Anna C; Borrows, Richard

    2016-03-01

    Physical fatigue is debilitating and common among kidney transplant recipients (KTRs). This study investigated the mechanistic aetiology of physical fatigue in this setting through examinations of muscle mass, muscular and cardiovascular function, and perceived exertion. The incidence of physical fatigue, its association with quality of life (QoL), and the predictors of perceived exertion, were evaluated. This single-centre observational cross-sectional study enrolled 55 KTRs. Muscle mass was quantified using dual-energy x-ray absorptiometry. Muscular function was assessed by jumping mechanography. Cardiovascular function (maximal oxygen consumption and oxygen pulse) was estimated during submaximal exercise testing, with perceived exertion determined using age-adjusted Borg scale-ratings. Physical fatigue was measured using Multi-Dimensional Fatigue Inventory-20. QoL was assessed using Medical Outcomes Study Short Form-36. Demographic, clinical, nutritional, psychosocial and behavioural predictors of perceived exertion were assessed. Of clinical importance, increased perceived exertion was the only independent predictor of physical fatigue (P = 0.001), with no association found between physical fatigue and muscular or cardiovascular parameters. Physical fatigue occurred in 22% of KTRs, and negatively impacted on QoL (P < 0.001). Predictors of heightened perception included anxiety (P < 0.05) and mental fatigue (P < 0.05). Perception is a key determinant of physical fatigue in KTRs, paving the way for future interventions.

  15. Linking asphalt binder fatigue to asphalt mixture fatigue performance using viscoelastic continuum damage modeling

    NASA Astrophysics Data System (ADS)

    Safaei, Farinaz; Castorena, Cassie; Kim, Y. Richard

    2016-08-01

    Fatigue cracking is a major form of distress in asphalt pavements. Asphalt binder is the weakest asphalt concrete constituent and, thus, plays a critical role in determining the fatigue resistance of pavements. Therefore, the ability to characterize and model the inherent fatigue performance of an asphalt binder is a necessary first step to design mixtures and pavements that are not susceptible to premature fatigue failure. The simplified viscoelastic continuum damage (S-VECD) model has been used successfully by researchers to predict the damage evolution in asphalt mixtures for various traffic and climatic conditions using limited uniaxial test data. In this study, the S-VECD model, developed for asphalt mixtures, is adapted for asphalt binders tested under cyclic torsion in a dynamic shear rheometer. Derivation of the model framework is presented. The model is verified by producing damage characteristic curves that are both temperature- and loading history-independent based on time sweep tests, given that the effects of plasticity and adhesion loss on the material behavior are minimal. The applicability of the S-VECD model to the accelerated loading that is inherent of the linear amplitude sweep test is demonstrated, which reveals reasonable performance predictions, but with some loss in accuracy compared to time sweep tests due to the confounding effects of nonlinearity imposed by the high strain amplitudes included in the test. The asphalt binder S-VECD model is validated through comparisons to asphalt mixture S-VECD model results derived from cyclic direct tension tests and Accelerated Loading Facility performance tests. The results demonstrate good agreement between the asphalt binder and mixture test results and pavement performance, indicating that the developed model framework is able to capture the asphalt binder's contribution to mixture fatigue and pavement fatigue cracking performance.

  16. Modeling of fatigue life of materials and structures under low-cycle loading

    NASA Astrophysics Data System (ADS)

    Volkov, I. A.; Korotkikh, Yu. G.

    2014-05-01

    A damaged medium model (DMM) consisting of three interconnected components (relations determining the cyclic elastoplastic behavior of the material, kinetic damage accumulation equations, and the strength criterion for the damaged material) was developed to estimate the stress strain state and the fatigue life of important engineering objects. The fatigue life of a strip with a cut under cyclic loading was estimated to obtain qualitative and quantitative estimates of the DMM constitutive relations under low-cycle loading. It was shown that the considered version of the constitutive relations reliably describes the main effects of elastoplastic deformation and the fatigue life processes of materials and structures.

  17. Cryogenic fatigue data developed for Inconel 718

    NASA Technical Reports Server (NTRS)

    Schmidt, E. H.

    1967-01-01

    Data were obtained on the cryogenic fatigue properties of Inconel 718 bar using axial loading and rotating beam fatigue tests. Results also disclosed the fatigue properties of Inconel 718 sheet materials.

  18. An EEG-Based Fatigue Detection and Mitigation System.

    PubMed

    Huang, Kuan-Chih; Huang, Teng-Yi; Chuang, Chun-Hsiang; King, Jung-Tai; Wang, Yu-Kai; Lin, Chin-Teng; Jung, Tzyy-Ping

    2016-06-01

    Research has indicated that fatigue is a critical factor in cognitive lapses because it negatively affects an individual's internal state, which is then manifested physiologically. This study explores neurophysiological changes, measured by electroencephalogram (EEG), due to fatigue. This study further demonstrates the feasibility of an online closed-loop EEG-based fatigue detection and mitigation system that detects physiological change and can thereby prevent fatigue-related cognitive lapses. More importantly, this work compares the efficacy of fatigue detection and mitigation between the EEG-based and a nonEEG-based random method. Twelve healthy subjects participated in a sustained-attention driving experiment. Each participant's EEG signal was monitored continuously and a warning was delivered in real-time to participants once the EEG signature of fatigue was detected. Study results indicate suppression of the alpha- and theta-power of an occipital component and improved behavioral performance following a warning signal; these findings are in line with those in previous studies. However, study results also showed reduced warning efficacy (i.e. increased response times (RTs) to lane deviations) accompanied by increased alpha-power due to the fluctuation of warnings over time. Furthermore, a comparison of EEG-based and nonEEG-based random approaches clearly demonstrated the necessity of adaptive fatigue-mitigation systems, based on a subject's cognitive level, to deliver warnings. Analytical results clearly demonstrate and validate the efficacy of this online closed-loop EEG-based fatigue detection and mitigation mechanism to identify cognitive lapses that may lead to catastrophic incidents in countless operational environments.

  19. Fatigue-induced changes of impedance and performance in target tracking.

    PubMed

    Selen, L P J; Beek, P J; van Dieën, J H

    2007-07-01

    Kinematic variability is caused, in part, by force fluctuations. It has been shown empirically and numerically that the effects of force fluctuations on kinematics can be suppressed by increasing joint impedance. Given that force variability increases with muscular fatigue, we hypothesized that joint impedance would increase with fatigue to retain a prescribed accuracy level. To test this hypothesis, subjects tracked a target by elbow flexion and extension both with fatigued and unfatigued elbow flexor and extensor muscles. Joint impedance was estimated from controlled perturbations to the elbow. Contrary to the hypothesis, elbow impedance decreased, whereas performance, expressed as the time-on-target, was unaffected by fatigue. Further analysis of the data revealed that subjects changed their control strategy with increasing fatigue. Although their overall kinematic variability increased, task performance was retained by staying closer to the center of the target when fatigued. In conclusion, the present study reveals a limitation of impedance modulation in the control of movement variability.

  20. Nondestructive evaluation of fatigue damage on low-alloy steel by magnetic technique

    SciTech Connect

    Hirasawa, T.; Komura, I.; Chujow, N.

    1994-12-31

    In the nuclear power plant, fatigue damage is one of the most significant degradation behavior which is expected that the structural components is received during long term operation. In order to estimate the plant life and to ensure the reliability of the plants, nondestructive detection and evaluation of fatigue damage of the components are a key technology. Magneto mechanical acoustic emission (MAE) method was applied to the evaluation of fatigue damage of reactor pressure vessel steel. Several MAE parameters which were obtained from the signal processing and waveform analysis on fatigue specimens, were measured and investigated as a function of cumulative fatigue damage factor. Consequently, these MAE parameters were compared to the results by X-ray diffraction technique, hardness testing and microstructural observation. The usefulness of MAE method as the nondestructive evaluation technique of fatigue damage was discussed.

  1. Recovery of central and peripheral neuromuscular fatigue after exercise.

    PubMed

    Carroll, Timothy John; Taylor, Janet L; Gandevia, Simon C

    2016-12-08

    Sustained physical exercise leads to a reduced capacity to produce voluntary force that typically outlasts the exercise bout. This "fatigue" can be due both to impaired muscle function, termed "peripheral fatigue", and a reduction in the capacity of the central nervous system to activate muscles, termed "central fatigue". In this mini-review we consider the factors that determine the recovery of voluntary force generating capacity after various types of exercise. After brief, high-intensity exercise there is typically a rapid restitution of force that is due to recovery of central fatigue (typically within 2min) and aspects of peripheral fatigue associated with excitation-contraction coupling and re-perfusion of muscles (typically within 3-5 min). Complete recovery of muscle function may be incomplete for some hours, however, due to prolonged impairment in intracellular Ca(2+) release or sensitivity. After low-intensity exercise of long duration, voluntary force typically shows rapid, partial, recovery within the first few minutes, due largely to recovery of the central, neural component. However, this ability to voluntarily activate muscles may not recover completely within 30 minutes after exercise. Recovery of peripheral fatigue contributes comparatively little to the fast initial force restitution, and is typically incomplete for at least 20-30 minutes. Work remains to identify what factors underlie the prolonged central fatigue that usually accompanies long-duration single joint and locomotor exercise, and to document how the time-course of neuromuscular recovery is affected by exercise intensity and duration in locomotor exercise. Such information could be useful to enhance rehabilitation and sports performance.

  2. Experimental study of crack initiation and propagation in high- and gigacycle fatigue in titanium alloys

    SciTech Connect

    Bannikov, Mikhail E-mail: oborin@icmm.ru Oborin, Vladimir E-mail: oborin@icmm.ru Naimark, Oleg E-mail: oborin@icmm.ru

    2014-11-14

    Fatigue (high- and gigacycle) crack initiation and its propagation in titanium alloys with coarse and fine grain structure are studied by fractography analysis of fracture surface. Fractured specimens were analyzed by interferometer microscope and SEM to improve methods of monitoring of damage accumulation during fatigue test and to verify the models for fatigue crack kinetics. Fatigue strength was estimated for high cycle fatigue regime using the Luong method [1] by “in-situ” infrared scanning of the sample surface for the step-wise loading history for different grain size metals. Fine grain alloys demonstrated higher fatigue resistance for both high cycle fatigue and gigacycle fatigue regimes. Fracture surface analysis for plane and cylindrical samples was carried out using optical and electronic microscopy method. High resolution profilometry (interferometer-profiler New View 5010) data of fracture surface roughness allowed us to estimate scale invariance (the Hurst exponent) and to establish the existence of two characteristic areas of damage localization (different values of the Hurst exponent). Area 1 with diameter ∼300 μm has the pronounced roughness and is associated with damage localization hotspot. Area 2 shows less amplitude roughness, occupies the rest fracture surface and considered as the trace of the fatigue crack path corresponding to the Paris kinetics.

  3. Elevated temperature axial and torsional fatigue behavior of Haynes 188

    NASA Technical Reports Server (NTRS)

    Bonacuse, Peter J.; Kalluri, Sreeramesh

    1992-01-01

    The results of high-temperature axial and torsional low-cycle fatigue experiments performed on Haynes 188, a wrought cobalt-base superalloy, are reported. Fatigue tests were performed at 760 C in air on thin-walled tubular specimens at various ranges under strain control. Data are also presented for coefficient of thermal expansion, elastic modulus, and shear modulus at various temperatures from room to 1000 C, and monotonic and cyclic stress-strain curves in tension and in shear at 760 C. The data set is used to evaluate several multiaxial fatigue life models (most were originally developed for room temperature multiaxial life prediction) including von Mises equivalent strain range (ASME boiler and pressure vessel code), Manson-Halford, Modified Multiaxiality Factor (proposed here), Modified Smith-Watson-Topper, and Fatemi-Socie-Kurath. At von Mises equivalent strain ranges (the torsional strain range divided by the square root of 3, taking the Poisson's ratio to be 0.5), torsionally strained specimens lasted, on average, factors of 2 to 3 times longer than axially strained specimens. The Modified Multiaxiality Factor approach shows promise as a useful method of estimating torsional fatigue life from axial fatigue data at high temperatures. Several difficulties arose with the specimen geometry and extensometry used in these experiments. Cracking at extensometer probe indentations was a problem at smaller strain ranges. Also, as the largest axial and torsional strain range fatigue tests neared completion, a small amount of specimen buckling was observed.

  4. Assessment of Low Cycle Fatigue Behavior of Powder Metallurgy Alloy U720

    NASA Technical Reports Server (NTRS)

    Gabb, Tomothy P.; Bonacuse, Peter J.; Ghosn, Louis J.; Sweeney, Joseph W.; Chatterjee, Amit; Green, Kenneth A.

    2000-01-01

    The fatigue lives of modem powder metallurgy disk alloys are influenced by variabilities in alloy microstructure and mechanical properties. These properties can vary as functions of variables the different steps of materials/component processing: powder atomization, consolidation, extrusion, forging, heat treating, and machining. It is important to understand the relationship between the statistical variations in life and these variables, as well as the change in life distribution due to changes in fatigue loading conditions. The objective of this study was to investigate these relationships in a nickel-base disk superalloy, U720, produced using powder metallurgy processing. Multiple strain-controlled fatigue tests were performed at 538 C (1000 F) at limited sets of test conditions. Analyses were performed to: (1) assess variations of microstructure, mechanical properties, and LCF failure initiation sites as functions of disk processing and loading conditions; and (2) compare mean and minimum fatigue life predictions using different approaches for modeling the data from assorted test conditions. Significant variations in life were observed as functions of the disk processing variables evaluated. However, the lives of all specimens could still be combined and modeled together. The failure initiation sites for tests performed at a strain ratio R(sub epsilon) = epsilon(sub min)/epsilon(sub max) of 0 were different from those in tests at a strain ratio of -1. An approach could still be applied to account for the differences in mean and maximum stresses and strains. This allowed the data in tests of various conditions to be combined for more robust statistical estimates of mean and minimum lives.

  5. Laser etching causing fatigue fracture at the neck-shoulder junction of an uncemented femoral stem: A case report.

    PubMed

    Jang, Bob; Kanawati, Andrew; Brazil, Declan; Bruce, Warwick

    2013-01-01

    Fatigue fracture of a femoral component in total hip arthroplasty is a rare occurrence but well documented in the literature. It is understood that proximal loosing of a femoral stem with a well fixed stem distally will result in cantilever bending and eventual fatigue fracture of the stem. Other factors which may potentiate a fatigue fracture are material design, implant positioning, and patient characteristics. More recently, laser etching on the femoral neck of an implant has resulted in fatigue fracture. We report a case of a fatigue fracture at the neck-shoulder junction in a well fixed, uncemented, femoral component due to laser etching in the region of high tensile stress.

  6. Fatigue behavior of porous biomaterials manufactured using selective laser melting.

    PubMed

    Yavari, S Amin; Wauthle, R; van der Stok, J; Riemslag, A C; Janssen, M; Mulier, M; Kruth, J P; Schrooten, J; Weinans, H; Zadpoor, A A

    2013-12-01

    Porous titanium alloys are considered promising bone-mimicking biomaterials. Additive manufacturing techniques such as selective laser melting allow for manufacturing of porous titanium structures with a precise design of micro-architecture. The mechanical properties of selective laser melted porous titanium alloys with different designs of micro-architecture have been already studied and are shown to be in the range of mechanical properties of bone. However, the fatigue behavior of this biomaterial is not yet well understood. We studied the fatigue behavior of porous structures made of Ti6Al4V ELI powder using selective laser melting. Four different porous structures were manufactured with porosities between 68 and 84% and the fatigue S-N curves of these four porous structures were determined. The three-stage mechanism of fatigue failure of these porous structures is described and studied in detail. It was found that the absolute S-N curves of these four porous structures are very different. In general, given the same absolute stress level, the fatigue life is much shorter for more porous structures. However, the normalized fatigue S-N curves of these four structures were found to be very similar. A power law was fitted to all data points of the normalized S-N curves. It is shown that the measured data points conform to the fitted power law very well, R(2)=0.94. This power law may therefore help in estimating the fatigue life of porous structures for which no fatigue test data is available. It is also observed that the normalized endurance limit of all tested porous structures (<0.2) is lower than that of corresponding solid material (c.a. 0.4).

  7. Analysis of Crew Fatigue in AIA Guantanamo Bay Aviation Accident

    NASA Technical Reports Server (NTRS)

    Rosekind, Mark R.; Gregory, Kevin B.; Miller, Donna L.; Co, Elizabeth L.; Lebacqz, J. Victor; Statler, Irving C. (Technical Monitor)

    1994-01-01

    Flight operations can engender fatigue, which can affect flight crew performance, vigilance, and mood. The National Transportation Safety Board (NTSB) requested the NASA Fatigue Countermeasures Program to analyze crew fatigue factors in an aviation accident that occurred at Guantanamo Bay, Cuba. There are specific fatigue factors that can be considered in such investigations: cumulative sleep loss, continuous hours of wakefulness prior to the incident or accident, and the time of day at which the accident occurred. Data from the NTSB Human Performance Investigator's Factual Report, the Operations Group Chairman's Factual Report, and the Flight 808 Crew Statements were analyzed, using conservative estimates and averages to reconcile discrepancies among the sources. Analysis of these data determined the following: the entire crew displayed cumulative sleep loss, operated during an extended period of continuous wakefulness, and obtained sleep at times in opposition to the circadian disposition for sleep, and that the accident occurred in the afternoon window of physiological sleepiness. In addition to these findings, evidence that fatigue affected performance was suggested by the cockpit voice recorder (CVR) transcript as well as in the captain's testimony. Examples from the CVR showed degraded decision-making skills, fixation, and slowed responses, all of which can be affected by fatigue; also, the captain testified to feeling "lethargic and indifferent" just prior to the accident. Therefore, the sleep/wake history data supports the hypothesis that fatigue was a factor that affected crewmembers' performance. Furthermore, the examples from the CVR and the captain's testimony support the hypothesis that the fatigue had an impact on specific actions involved in the occurrence of the accident.

  8. Simulation of ionomer membrane fatigue under mechanical and hygrothermal loading conditions

    NASA Astrophysics Data System (ADS)

    Khorasany, Ramin M. H.; Kjeang, Erik; Wang, G. G.; Rajapakse, R. K. N. D.

    2015-04-01

    Understanding the fatigue lifetime of common perfluorosulfonic acid (PFSA) ionomer membranes under fluctuating hygrothermal conditions is essential for the development of durable fuel cell technologies. For this purpose, a finite element based fatigue lifetime prediction model is developed based on an elastic-plastic constitutive model combined with a Smith-Watson-Topper (SWT) fatigue formulation. The model is validated against previously reported experimental results for a membrane under cyclic mechanical loadings. The validated model is then utilized to investigate the membrane fatigue lifetime in ex-situ applications under cyclic humidity and temperature conditions. The simulations suggest that the membrane fatigue lifetime is shorter under fluctuating humidity loadings than for temperature loadings. Additionally, the membrane fatigue lifetime is found to be more sensitive to the amplitude of the strain oscillations than to the mean strain under hygrothermal cycling. Most notably, the model predicts that simultaneous humidity and temperature cycling can exacerbate the fatigue process and reduce the fatigue lifetime by several orders of magnitude compared to isolated humidity or temperature cycling. The combination of measured mechanical fatigue data and the present numerical model provides a useful toolkit for analysis of membrane fatigue due to hygrothermal variations, which can be costly and time-consuming when addressed experimentally.

  9. On the importance of considering porosity when simulating the fatigue of bone cement.

    PubMed

    Jeffers, Jonathan R T; Browne, Martin; Roques, Anne; Taylor, Mark

    2005-08-01

    Fatigue cracking in the cement mantle of total hip replacement has been identified as a possible cause of implant loosening. Retrieval studies and in vitro tests have found porosity in the cement may facilitate fatigue cracking of the mantle. The fatigue process has been simulated computationally using a finite element/continuum damage mechanics (FE/CDM) method and used as a preclinical testing tool, but has not considered the effects of porosity. In this study, experimental tensile and four-point bend fatigue tests were performed. The tensile fatigue S-N data were used to drive the computational simulation (FE/CDM) of fatigue in finite element models of the tensile and four-point bend specimens. Porosity was simulated in the finite element models according to the theory of elasticity and using Monte Carlo methods. The computational fatigue simulations generated variability in the fatigue life at any given stress level, due to each model having a unique porosity distribution. The fracture site also varied between specimens. Experimental validation was achieved for four-point bend loading, but only when porosity was included. This demonstrates that the computational simulation of fatigue, driven by uniaxial S-N data can be used to simulate nonuniaxial loadcases. Further simulations of bone cement fatigue should include porosity to better represent the realities of experimental models.

  10. Fatigue damage prognosis of internal delamination in composite plates under cyclic compression loadings using affine arithmetic as uncertainty propagation tool

    NASA Astrophysics Data System (ADS)

    Gbaguidi, Audrey J.-M.

    Structural health monitoring (SHM) has become indispensable for reducing maintenance costs and increasing the in-service capacity of a structure. The increased use of lightweight composite materials in aircraft structures drastically increased the effects of fatigue induced damage on their critical structural components and thus the necessity to predict the remaining life of those components. Damage prognosis, one of the least investigated fields in SHM, uses the current damage state of the system to forecast its future performance by estimating the expected loading environments. A successful damage prediction model requires the integration of technologies in areas like measurements, materials science, mechanics of materials, and probability theories, but most importantly the quantification of uncertainty in all these areas. In this study, Affine Arithmetic is used as a method for incorporating the uncertainties due to the material properties into the fatigue life prognosis of composite plates subjected to cyclic compressive loadings. When loadings are compressive in nature, the composite plates undergo repeated buckling-unloading of the delaminated layer which induces mixed modes I and II states of stress at the tip of the delamination in the plates. The Kardomateas model-based prediction law is used to predict the growth of the delamination, while the integration of the effects of the uncertainties for modes I and II coefficients in the fatigue life prediction model is handled using Affine arithmetic. The Mode I and Mode II interlaminar fracture toughness and fatigue characterization of the composite plates are first experimentally studied to obtain the material coefficients and fracture toughness, respectively. Next, these obtained coefficients are used in the Kardomateas law to predict the delamination lengths in the composite plates while using Affine Arithmetic to handle their uncertainties. At last, the fatigue characterization of the composite plates during

  11. Fatigue and fracture: Overview

    NASA Technical Reports Server (NTRS)

    Halford, G. R.

    1984-01-01

    A brief overview of the status of the fatigue and fracture programs is given. The programs involve the development of appropriate analytic material behavior models for cyclic stress-strain-temperature-time/cyclic crack initiation, and cyclic crack propagation. The underlying thrust of these programs is the development and verification of workable engineering methods for the calculation, in advance of service, of the local cyclic stress-strain response at the critical life governing location in hot section compounds, and the resultant crack initiation and crack growth lifetimes.

  12. Fatigue 󈨛. Volume 3,

    DTIC Science & Technology

    1987-06-01

    Figure 5 appears to be composed of fibrils or crazes which have been torn in the fracture process. There is little of this rough fibrous material on the...their work on the role of crazes in the fatigue of polycarbonate. They suggested that the smooth area evident at the edge of an untreated sample is a...remnant of a single craze which first formed during cyclic loading at a point of high local surface stress. Under cyclic loading, this craze grew, as

  13. Reversal bending fatigue testing

    DOEpatents

    Wang, Jy-An John; Wang, Hong; Tan, Ting

    2014-10-21

    Embodiments for apparatuses for testing reversal bending fatigue in an elongated beam are disclosed. Embodiments are configured to be coupled to first and second end portions of the beam and to apply a bending moment to the beam and create a pure bending condition in an intermediate portion of the beam. Embodiments are further configured to cyclically alternate the direction of the bending moment applied to the beam such that the intermediate portion of the beam cyclically bends in opposite directions in a pure bending condition.

  14. Regional distribution of fatiguing illnesses in the United States: a pilot study

    PubMed Central

    Bierl, Cynthia; Nisenbaum, Rosane; Hoaglin, David C; Randall, Bonnie; Jones, Ann-Britt; Unger, Elizabeth R; Reeves, William C

    2004-01-01

    Background Chronic fatigue syndrome (CFS) is a debilitating illness with no known cause or effective therapy. Population-based epidemiologic data on CFS prevalence are critical to put CFS in a realistic context for public health officials and others responsible for allocating resources. Methods We conducted a pilot random-digit-dialing survey to estimate the prevalence of fatiguing illnesses in different geographic regions and in urban and rural populations of the United States. This report focuses on 884 of 7,317 respondents 18 to 69 years old. Fatigued (440) and randomly selected non-fatigued (444) respondents completed telephone questionnaires concerning fatigue, other symptoms, and medical history. Results We estimated 12,186 per 100,000 persons 18 to 69 years of age suffered from fatigue lasting for at least 6 months (chronic fatigue), and 1,197 per 100,000 described an illness that, though lacking clinical evaluation, met criteria for CFS (CFS-like). Chronic fatigue and CFS-like illness were more common in rural than in urban populations, although the differences were not significant. The prevalence of these fatiguing illnesses did not differ meaningfully among the four regions surveyed, and no significant geographic trends were observed. Conclusions This investigation estimated that nearly 2.2 million American adults suffer from CFS-like illness. The study also suggested the need to focus future investigations of fatigue on populations with lower incomes and less education. There was no evidence for regional differences in the occurrence of fatiguing illnesses. PMID:14761250

  15. Uncertainty Analysis in Fatigue Life Prediction of Gas Turbine Blades Using Bayesian Inference

    NASA Astrophysics Data System (ADS)

    Li, Yan-Feng; Zhu, Shun-Peng; Li, Jing; Peng, Weiwen; Huang, Hong-Zhong

    2015-12-01

    This paper investigates Bayesian model selection for fatigue life estimation of gas turbine blades considering model uncertainty and parameter uncertainty. Fatigue life estimation of gas turbine blades is a critical issue for the operation and health management of modern aircraft engines. Since lots of life prediction models have been presented to predict the fatigue life of gas turbine blades, model uncertainty and model selection among these models have consequently become an important issue in the lifecycle management of turbine blades. In this paper, fatigue life estimation is carried out by considering model uncertainty and parameter uncertainty simultaneously. It is formulated as the joint posterior distribution of a fatigue life prediction model and its model parameters using Bayesian inference method. Bayes factor is incorporated to implement the model selection with the quantified model uncertainty. Markov Chain Monte Carlo method is used to facilitate the calculation. A pictorial framework and a step-by-step procedure of the Bayesian inference method for fatigue life estimation considering model uncertainty are presented. Fatigue life estimation of a gas turbine blade is implemented to demonstrate the proposed method.

  16. Improving turbine blade fatigue life

    NASA Technical Reports Server (NTRS)

    Buddenbohm, H. W.

    1988-01-01

    Turbine airfoil design, materials, and cooling system management are variables which, when optimized, can contribute to longer turbine component lives. These advancements have been identified as redesign techniques to improve the turbine fatigue life of the SSME High Pressure Fuel Turbopump. This paper discusses the general program approach toward improving turbine fatigue life.

  17. Caffeine to Sustain Operational Fatigue

    DTIC Science & Technology

    2000-03-01

    It Caffeine is the most widely used psychostimulant and provided data about the most commonly used may be useful in operational fatigue-coping...palpitation, psychomotor agitation. Caffeine candy 05 withdrawal may cause headache, fatigue, anxiety, soda 04 insomnia, nausea, performance impainnents. snuff

  18. High cycle fatigue of weld repaired cast Ti-6AI-4V

    NASA Astrophysics Data System (ADS)

    Hunter, G. B.; Hodi, F. S.; Eagar, T. W.

    1982-09-01

    In order to determine the effects of weld repair on fatigue life of titanium-6Al-4V castings, a series of specimens was exposed to variations in heat treatment, weld procedure, HIP cycle, cooling rate, and surface finish. The results indicate that weld repair is not detrimental to HCF properties as fatigue cracks were located primarily in the base metal. Fine surface finish and large colony size are the primary variables improving the fatigue life. The fusion zone resisted fatigue crack initiation due to a basketweave morphology and thin grain boundary alpha. Multipass welds were shown not to affect fatigue life when compared with single pass welds. A secondary HIP treatment was not detrimental to fatigue properties, but was found to be unnecessary.

  19. Fatigue monitoring in Nuclear Power Plants

    SciTech Connect

    Ware, A.G.; Shah, V.N.

    1995-04-01

    This paper summarizes fatigue monitoring methods and surveys their application in the nuclear power industry. The paper is based on a review of the technical literature. Two main reasons for fatigue monitoring are more frequent occurrence of some transients than that assumed in the fatigue design analysis and the discovery of stressors that were not included in the fatigue design analysis but may cause significant fatigue damage at some locations. One fatigue monitoring method involves use of plant operating data and procedures to update the fatigue usage. Another method involves monitoring of plant operating parameters using existing, or if needed, supplementary plant instrumentation for online computation of fatigue usage. Use of fatigue monitoring has better defined the operational transients. Most operational transients have been found less severe and fewer in numbers than anticipated in the design fatigue analysis. Use of fatigue monitoring has assisted in quantifying newly discovered stressors and has helped in detecting the presence of thermal stratification of unsuspected locations.

  20. Propagating of uncertainties due to human-induced surface-heterogeneities in regional estimation of energy and mass exchange from flux aggregation

    NASA Astrophysics Data System (ADS)

    Siqueira, M. B.

    2013-05-01

    Agriculture and forestry practices have added a multitude of vegetation heterogeneity scales to the landscape. The effects of the human induced heterogeneity, such as multi-crop agriculture and selective logging, on regional estimates of gas exchange from remote sensing platforms can now be added to the list of major problems that must be confronted by the ecohydrology communities. The last decade provided perhaps the most rapid advances given developments in satellite remote sensing products and computational methods. Recent studies on sub-pixel heterogeneity effects on pixel-averaged fluxes using a two-source (soil + vegetation) energy balance model over semi-arid landscapes have concluded that sub-pixel variability could lead to significantly biased results when compared to true turbulent energy fluxes. Moreover, these studies have shown that errors in outputs from flux models driven by remotely sensed surface properties would be dependent on the distribution and the magnitude of the sub-pixel spatial variability. In addition, it has been demonstrated that the discrepancy is not only associated with the spatial variability level but also a function of the wind speed (i.e. the turbulent state of the atmosphere), suggesting that a formal analysis of turbulence on scalar transport is the logical step to increase confidence in subpixel flux estimates under these circumstances. Computational-fluid-mechanic studies point towards the importance of sub-pixel spatial heterogeneity on regional flux estimates, suggesting that they are sensitive to the scale of the land surface heterogeneity. These studies primarily considered the effects of small-scale (sub-grid) heterogeneity on pixel-scale energy budgets. However, the emergent theme remains the same - large uncertainties are associated with fluxes derived from spatially averaged surface properties. To advance in this topic, the heterogeneity should be confronted with two dynamic-length-scale, namely, the convective scale

  1. Estimate of sulfur, arsenic, mercury, fluorine emissions due to spontaneous combustion of coal gangue: An important part of Chinese emission inventories.

    PubMed

    Wang, Shaobin; Luo, Kunli; Wang, Xing; Sun, Yuzhuang

    2016-02-01

    A rough estimate of the annual amount of sulfur, arsenic, mercury and fluoride emission from spontaneous combustion of coal gangue in China was determined. The weighted mean concentrations of S, As, Hg, and F in coal gangue are 1.01%, 7.98, 0.18, and 365.54 mg/kg, respectively. Amounts of S, As, Hg, and F emissions from coal gangue spontaneous combustion show approximately 1.13 Mt, and 246, 45, and 63,298 tons in 2013, respectively. The atmospheric release amount of sulfur from coal gangue is more than one tenth of this from coal combustion, and the amounts of As, Hg, and F are close to or even exceed those from coal combustion. China's coal gangue production growth from 1992 to 2013 show an obvious growth since 2002. It may indicate that Chinese coal gangue has become a potential source of air pollution, which should be included in emission inventories.

  2. Fatigue life prediction modeling for turbine hot section materials

    NASA Technical Reports Server (NTRS)

    Halford, G. R.; Meyer, T. G.; Nelson, R. S.; Nissley, D. M.; Swanson, G. A.

    1988-01-01

    A major objective of the fatigue and fracture efforts under the Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline and highly anisotropic single crystal alloys were addressed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxiality of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) and the Total Strain Version of Strainrange Partitioning (TS-SRP) for nominally isotropic materials, and the Tensile Hysteretic Energy Model for anisotropic superalloys. A fatigue model is being developed based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex nonlinear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model was derived. The models are described and discussed.

  3. Fatigue life prediction modeling for turbine hot section materials

    NASA Technical Reports Server (NTRS)

    Halford, G. R.; Meyer, T. G.; Nelson, R. S.; Nissley, D. M.; Swanson, G. A.

    1989-01-01

    A major objective of the fatigue and fracture efforts under the NASA Hot Section Technology (HOST) program was to significantly improve the analytic life prediction tools used by the aeronautical gas turbine engine industry. This was achieved in the areas of high-temperature thermal and mechanical fatigue of bare and coated high-temperature superalloys. The cyclic crack initiation and propagation resistance of nominally isotropic polycrystalline and highly anisotropic single crystal alloys were addressed. Life prediction modeling efforts were devoted to creep-fatigue interaction, oxidation, coatings interactions, multiaxiality of stress-strain states, mean stress effects, cumulative damage, and thermomechanical fatigue. The fatigue crack initiation life models developed to date include the Cyclic Damage Accumulation (CDA) and the Total Strain Version of Strainrange Partitioning (TS-SRP) for nominally isotropic materials, and the Tensile Hysteretic Energy Model for anisotropic superalloys. A fatigue model is being developed based upon the concepts of Path-Independent Integrals (PII) for describing cyclic crack growth under complex nonlinear response at the crack tip due to thermomechanical loading conditions. A micromechanistic oxidation crack extension model was derived. The models are described and discussed.

  4. Fatigue characterization of advanced carbon-carbon composites

    NASA Technical Reports Server (NTRS)

    Mahfuz, Hassan; Das, Partha S.; Jeelani, Shaik; Baker, Dean M.; Johnson, Sigured A.

    1992-01-01

    Response of quasi-isotropic laminates of SiC coated Carbon-Carbon (C/C) composites under flexural fatigue are investigated at room temperature. Virgin as well as mission cycled specimens are tested to study the effects of thermal and pressure cycling on the fatigue performance of C/C. Tests were conducted in three point bending with a stress ratio of 0.2 and frequency of 1 Hz. Fatigue strength of C/C has been found to be considerably high - approximately above 85 percent of the ultimate flexural strength. The fatigue strength appears to be decreasing with the increase in the number of mission cycling of the specimens. This lower strength with the mission cycled specimens is attributed to the loss of interfacial bond strength due to thermal and pressure cycling of the material. C/C is also found to be highly sensitive to the applied stress level during cyclic loading, and this sensitivity is observed to increase with the mission cycling. Weibull characterization on the fatigue data has been performed, and the wide scatter in the Weibull distribution is discussed. Fractured as well as untested specimens were C-scanned, and the progressive damage growth during fatigue is presented.

  5. Contact fatigue of human enamel: Experiments, mechanisms and modeling.

    PubMed

    Gao, S S; An, B B; Yahyazadehfar, M; Zhang, D; Arola, D D

    2016-07-01

    Cyclic contact between natural tooth structure and engineered ceramics is increasingly common. Fatigue of the enamel due to cyclic contact is rarely considered. The objectives of this investigation were to evaluate the fatigue behavior of human enamel by cyclic contact, and to assess the extent of damage over clinically relevant conditions. Cyclic contact experiments were conducted using the crowns of caries-free molars obtained from young donors. The cuspal locations were polished flat and subjected to cyclic contact with a spherical indenter of alumina at 2Hz. The progression of damage was monitored through the evolution in contact displacement, changes in the contact hysteresis and characteristics of the fracture pattern. The contact fatigue life diagram exhibited a decrease in cycles to failure with increasing cyclic load magnitude. Two distinct trends were identified, which corresponded to the development and propagation of a combination of cylindrical and radial cracks. Under contact loads of less than 400N, enamel rod decussation resisted the growth of subsurface cracks. However, at greater loads the damage progressed rapidly and accelerated fatigue failure. Overall, cyclic contact between ceramic appliances and natural tooth structure causes fatigue of the enamel. The extent of damage is dependent on the magnitude of cyclic stress and the ability of the decussation to arrest the fatigue damage.

  6. Estimating change in cardiovascular disease and diabetes burdens due to dietary and metabolic factors in Korea 1998–2011: a comparative risk assessment analysis

    PubMed Central

    Cho, Yoonsu; Cudhea, Frederick; Park, Ju-Hyun; Lee, Jong-Tae; Mozaffarian, Dariush; Singh, Gitanjali

    2016-01-01

    Objectives Over the past 10 years, the burden of chronic diseases in Korea has increased. However, there are currently no quantitative estimates of how changes in diet and metabolic factors have contributed to these shifting burdens. This study aims to evaluate the contributions of dietary and metabolic risk factors to death from cardiometabolic diseases (CMDs) such as cardiovascular conditions, strokes and diabetes in Korea, and to estimate how these contributions have changed over the past 10 years (1998–2011). Design and methods We used data on 6 dietary and 4 metabolic risk factors by sex, age and year from the Korea National Health and Nutrition Examination Survey. The relative risks for the effects of the risk factors on CMD mortality were obtained from meta-analyses. The population-attributable fraction attributable to the risk factors was calculated by using a comparative risk assessment approach across sex and age strata (males and females, age groups 25–34, 35–44, 45–54, 55–64, 65–74 and 75+ years) from 1998 to 2011. Results The results showed that a suboptimal diet and high blood pressure were the main risk factors for CMD mortality in Korea. High blood pressure accounted for 127 096 (95% uncertainty interval (UI): 121 907 to 132 218) deaths from CMD. Among the individual dietary risk factors, a high intake of sodium (42 387 deaths; 95% UI: 42 387 to 65 094) and a low intake of fruit (50 244 deaths; 95% UI: 40 981 to 59 178) and whole grains (54 248 deaths; 95% UI: 47 020 to 61 343) were responsible for the highest number of CMD deaths in Korea. Conclusions Indicating the relative importance of risk factors in Korea, the results suggest that metabolic and dietary risk factors were major contributors to CMD mortality. PMID:28003293

  7. Classifying lower extremity muscle fatigue during walking using machine learning and inertial sensors.

    PubMed

    Zhang, Jian; Lockhart, Thurmon E; Soangra, Rahul

    2014-03-01

    Fatigue in lower extremity musculature is associated with decline in postural stability, motor performance and alters normal walking patterns in human subjects. Automated recognition of lower extremity muscle fatigue condition may be advantageous in early detection of fall and injury risks. Supervised machine learning methods such as support vector machines (SVMs) have been previously used for classifying healthy and pathological gait patterns and also for separating old and young gait patterns. In this study we explore the classification potential of SVM in recognition of gait patterns utilizing an inertial measurement unit associated with lower extremity muscular fatigue. Both kinematic and kinetic gait patterns of 17 participants (29 ± 11 years) were recorded and analyzed in normal and fatigued state of walking. Lower extremities were fatigued by performance of a squatting exercise until the participants reached 60% of their baseline maximal voluntary exertion level. Feature selection methods were used to classify fatigue and no-fatigue conditions based on temporal and frequency information of the signals. Additionally, influences of three different kernel schemes (i.e., linear, polynomial, and radial basis function) were investigated for SVM classification. The results indicated that lower extremity muscle fatigue condition influenced gait and loading responses. In terms of the SVM classification results, an accuracy of 96% was reached in distinguishing the two gait patterns (fatigue and no-fatigue) within the same subject using the kinematic, time and frequency domain features. It is also found that linear kernel and RBF kernel were equally good to identify intra-individual fatigue characteristics. These results suggest that intra-subject fatigue classification using gait patterns from an inertial sensor holds considerable potential in identifying "at-risk" gait due to muscle fatigue.

  8. Understanding postoperative fatigue.

    PubMed

    Rose, E A; King, T C

    1978-07-01

    Performance characteristics of the central nervous, cardiovascular, respiratory and muscular systems in man postoperatively have received little investigative attention, despite the well known syndrome of postoperative fatigue. The impairmen in perception and psychomotor skills that has been shown to result from caloric restriction, bedrest, sedation and sleep deprivation suggests that a similar deficit may occur after surgical procedures. After a simple elective surgical procedure, maximal oxygen uptake decreases and the adaptability of heart rate to submaximal workloads is impaired. Similar deleterious effects on cardiorespiratory performance have been documented with starvation and bedrest; an understanding of cardiorespiratory performance postoperatively awaits further investigation. Maximal muscular force of contraction is also impaired by caloric restriction and bedrest, suggesting that similar effects may be seen in the postoperative state, although this has not been studied. A better understanding of the syndrome of postoperative fatigue could be achieved by a descriptive analysis of physiologic performance postoperatively. Such descriptive data could form the basis for objective evaluation of therapeutic measures intended to improve performance, such as nutritional supplementation and pharmacologic intervention. The observation that exercise with the patient in the supine position may decrease the impairment in maximal aerobic power otherwise expected in immobilized patients suggests that controlled exercise therapy may be of value in reducing physiologic impairment postoperatively.

  9. Bearing fatigue investigation 3

    NASA Technical Reports Server (NTRS)

    Nahm, A. H.; Bamberger, E. N.; Signer, H. R.

    1982-01-01

    The operating characteristics of large diameter rolling-element bearings in the ultra high speed regimes expected in advanced turbine engines for high performance aircraft were investigated. A high temperature lubricant, DuPont Krytox 143 AC, was evaluated at bearing speeds to 3 million DN. Compared to the results of earlier, similar tests using a MIL-L-23699 (Type II) lubricant, bearings lubricated with the high density Krytox fluid showed significantly higher power requirements. Additionally, short bearing lives were observed when this fluid was used with AISI M50 bearings in an air atmosphere. The primary mode of failure was corrosion initiated surface distress (fatigue) on the raceways. The potential of a case-carburized bearing to sustain a combination of high-tangential and hertzian stresses without experiencing race fracture was also investigated. Limited full scale bearing tests of a 120 mm bore ball bearing at a speed of 25,000 rpm (3 million DN) indicated that a carburized material could sustain spalling fatigue without subsequent propagation to fracture. Planned life tests of the carburized material had to be aborted, however, because of apparent processing-induced material defects.

  10. Soil carbon sequestration due to post-Soviet cropland abandonment: estimates from a large-scale soil organic carbon field inventory.

    PubMed

    Wertebach, Tim-Martin; Hölzel, Norbert; Kämpf, Immo; Yurtaev, Andrey; Tupitsin, Sergey; Kiehl, Kathrin; Kamp, Johannes; Kleinebecker, Till

    2017-02-04

    The break-up of the Soviet Union in 1991 triggered cropland abandonment on a continental scale, which in turn led to carbon accumulation on abandoned land across Eurasia. Previous studies have estimated carbon accumulation rates across Russia based on large-scale modelling. Studies that assess carbon sequestration on abandoned land based on robust field sampling are rare. We investigated soil organic carbon (SOC) stocks using a randomized sampling design along a climatic gradient from forest steppe to Sub-Taiga in Western Siberia (Tyumen Province). In total, SOC contents were sampled on 470 plots across different soil and land-use types. The effect of land use on changes in SOC stock was evaluated, and carbon sequestration rates were calculated for different age stages of abandoned cropland. While land-use type had an effect on carbon accumulation in the topsoil (0-5 cm), no independent land-use effects were found for deeper SOC stocks. Topsoil carbon stocks of grasslands and forests were significantly higher than those of soils managed for crops and under abandoned cropland. SOC increased significantly with time since abandonment. The average carbon sequestration rate for soils of abandoned cropland was 0.66 Mg C ha(-1)  yr(-1) (1-20 years old, 0-5 cm soil depth), which is at the lower end of published estimates for Russia and Siberia. There was a tendency towards SOC saturation on abandoned land as sequestration rates were much higher for recently abandoned (1-10 years old, 1.04 Mg C ha(-1)  yr(-1) ) compared to earlier abandoned crop fields (11-20 years old, 0.26 Mg C ha(-1)  yr(-1) ). Our study confirms the global significance of abandoned cropland in Russia for carbon sequestration. Our findings also suggest that robust regional surveys based on a large number of samples advance model-based continent-wide SOC prediction.

  11. Dental Implants Fatigue as a Possible Failure of Implantologic Treatment: The Importance of Randomness in Fatigue Behaviour

    PubMed Central

    Prados-Privado, María; Prados-Frutos, Juan Carlos; Manchón, Ángel; Rojo, Rosa; Felice, Pietro; Bea, José Antonio

    2015-01-01

    Objective. To show how random variables concern fatigue behaviour by a probabilistic finite element method. Methods. Uncertainties on material properties due to the existence of defects that cause material elastic constant are not the same in the whole dental implant the dimensions of the structural element and load history have a decisive influence on the fatigue process and therefore on the life of a dental implant. In order to measure these uncertainties, we used a method based on Markoff chains, Bogdanoff and Kozin cumulative damage model, and probabilistic finite elements method. Results. The results have been obtained by conventional and probabilistic methods. Mathematical models obtained the same result regarding fatigue life; however, the probabilistic model obtained a greater mean life but with more information because of the cumulative probability function. Conclusions. The present paper introduces an improved procedure to study fatigue behaviour in order to know statistics of the fatigue life (mean and variance) and its probability of failure (fatigue life versus probability of failure). PMID:26583137

  12. Fatigue and corrosion fatigue of beryllium-copper spring materials

    SciTech Connect

    Bagheri, R.; Miller, G.A. )

    1993-03-01

    Fine gage, 0.006-in. d(0.15-mm) thick, beryllium-copper (Be-Cu) spring materials with tensile strength in the range of 70 to 145 ksi were subjected to cyclic loading in air and salt water environments. Plain and notched (center hole) hour glass specimens were subjected to sinusoidal loading with R = (minimum/maximum) stress = 0.1 at cyclic frequencies of 50 Hz in air and 1 Hz in salt water. Fatigue life was typically from 10[sup 4] to 10[sup 6] cycles with crack initiation as the dominant fatigue process. The excellence fatigue performance of Be-Cu alloys in salt water is well-known, however, current findings demonstrate 10 to 37% reduction in fatigue strength of unnotched specimens in this environment for a life of 3 x 10[sup 5] cycles. This strength degradation is attributed to the use of a lower cyclic frequency for present than for previous tests, i.e., 1 versus about 20 Hz. There was no effect of salt water on crack initiation in notched specimens. The ratios of the fatigue strengths, namely (cold-rolled/annealed) and (aged/annealed), for plain and notched specimens tested in air, decreased from 2 to about 1.4 as fatigue life increased from 10[sup 4] to 10[sup 6] cycles. This effect is attributed to cyclic hardening of the annealed material. The fatigue stress concentration factor, K[sub f] = (plain/notched) fatigue strength, increased by about 30% as fatigue cycles increased from 10[sup 4] to 10[sup 6]. The ranking of K[sub f] values of the various material conditions from highest to lowest was: cold-rolled, aged, and annealed.

  13. Subjective but Not Actigraphy-Defined Sleep Predicts Next-Day Fatigue in Chronic Fatigue Syndrome: A Prospective Daily Diary Study

    PubMed Central

    Russell, Charlotte; Wearden, Alison J.; Fairclough, Gillian; Emsley, Richard A.; Kyle, Simon D.

    2016-01-01

    Study Objectives: This study aimed to (1) examine the relationship between subjective and actigraphy-defined sleep, and next-day fatigue in chronic fatigue syndrome (CFS); and (2) investigate the potential mediating role of negative mood on this relationship. We also sought to examine the effect of presleep arousal on perceptions of sleep. Methods: Twenty-seven adults meeting the Oxford criteria for CFS and self-identifying as experiencing sleep difficulties were recruited to take part in a prospective daily diary study, enabling symptom capture in real time over a 6-day period. A paper diary was used to record nightly subjective sleep and presleep arousal. Mood and fatigue symptoms were rated four times each day. Actigraphy was employed to provide objective estimations of sleep duration and continuity. Results: Multilevel modelling revealed that subjective sleep variables, namely sleep quality, efficiency, and perceiving sleep to be unrefreshing, predicted following-day fatigue levels, with poorer subjective sleep related to increased fatigue. Lower subjective sleep efficiency and perceiving sleep as unrefreshing predicted reduced variance in fatigue across the following day. Negative mood on waking partially mediated these relationships. Increased presleep cognitive and somatic arousal predicted self-reported poor sleep. Actigraphy-defined sleep, however, was not found to predict following-day fatigue. Conclusions: For the first time we show that nightly subjective sleep predicts next-day fatigue in CFS and identify important factors driving this relationship. Our data suggest that sleep specific interventions, targeting presleep arousal, perceptions of sleep and negative mood on waking, may improve fatigue in CFS. Citation: Russell C, Wearden AJ, Fairclough G, Emsley RA, Kyle SD. Subjective but not actigraphy-defined sleep predicts next-day fatigue in chronic fatigue syndrome: a prospective daily diary study. SLEEP 2016;39(4):937–944. PMID:26715232

  14. Calculation of the false alarm in pure frequency detection due to zero crossings of a narrow-band process - The possibility of estimating its autocorrelation envelope

    NASA Astrophysics Data System (ADS)

    Hay, J.

    Consideration is given to problems of pure frequency detection in the magnetic recording of acoustic noise in the presence of zero crossings by sinusoidal reference waves and narrow-band random processes. The principle of the partial detection of a sine wave based on isochronous zero crossings near a given coherent sequence threshold is reviewed, and a track detection criterion is introduced. A model of the signal detection process is then presented based on a probabilistic description of zero crossings which permits the definition of the normalized duration of a coherent sequence of zero crossings, and the model is validated in an experimental study of a narrow band process centered at 3240 Hz. The probability of the simultaneous detection of two channels is also calculated. The application of the model to parasitic detection in a two-frequency code is considered. Attention is then given to the relation between the isochronism of the coherent sequences of zero crossings and spectral sharpness, and a means for the direct estimation of the autocorrelation envelope of the narrowband noise process is derived.

  15. Absorbed Dose Rate Due to Intake of Natural Radionuclides by Tilapia Fish (Tilapia nilotica,Linnaeus, 1758) Estimated Near Uranium Mining at Caetite, Bahia, Brazil

    SciTech Connect

    Pereira, Wagner de S; Kelecom, Alphonse

    2008-08-07

    The uranium mining at Caetite (Uranium Concentrate Unit--URA) is in its operational phase. Aiming to estimate the radiological environmental impact of the URA, a monitoring program is underway. In order to preserve the biota of the deleterious effects from radiation and to act in a pro-active way as expected from a licensing body, the present work aims to use an environmental protection methodology based on the calculation of absorbed dose rate in biota. Thus, selected target organism was the Tilapia fish (Tilapia nilotica, Linnaeus, 1758) and the radionuclides were: uranium (U-238), thorium (Th-232), radium (Ra-226 and Ra-228) and lead (Pb-210). As, in Brazil there are no radiation exposure limits adopted for biota the value proposed by the Department of Energy (DOE) of the United States of 3.5x10{sup 3} {mu}Gy y{sup -1} has been used. The derived absorbed dose rate calculated for Tilapia was 2.51x10{sup 0} {mu}Gy y{sup -1}, that is less than 0.1% of the dose limit established by DOE. The critical radionuclide was Ra-226, with 56% of the absorbed dose rate, followed by U-238 with 34% and Th-232 with 9%. This value of 0.1% of the limit allows to state that, in the operational conditions analyzed, natural radionuclides do not represent a radiological problem to biota.

  16. Concentration of 3H in ground water and estimation of committed effective dose due to ground water ingestion in some places in the Maharashtra state, India.

    PubMed

    Reddy, P J; Bhade, S P D; Kolekar, R V; Singh, Rajvir; Pradeepkumar, K S

    2014-01-01

    The measurement of tritium in environmental samples requires highest possible sensitivity. In the present study, the authors have optimised the counting window for the analysis of (3)H in environmental samples using the recently installed Ultra Low Level Quantulus 1220 Liquid Scintillation Counting at BARC to improve the detection limit of the system. The optimised counting window corresponding to the highest figure of merit of 883.8 was found to be 20-162 channels. Different brands of packaged drinking waters were analysed to select a blank that would define the system background. The minimum detectable activity (MDA) achieved was 1.5 Bq l(-1) for a total counting time of 500 min. The concentration of tritium in well and bore well water samples collected from the villages of Pune, villages located at 1.8 km from Tarapur Atomic Power Station, Kolhapur and Ratnagiri, was analysed. The activity concentration ranged from 0.55 to 3.66 Bq l(-1). The associated age-dependant dose from water ingestion in the study area was estimated. The effective committed dose recorded for different age classes is negligible compared with World Health Organization and US Environmental Protection Agency dose guidelines.

  17. Estimation of the SAR in the human head and body due to radiofrequency radiation exposure from handheld mobile phones with hands-free accessories.

    PubMed

    Bit-Babik, G; Chou, C K; Faraone, A; Gessner, A; Kanda, M; Balzano, Q

    2003-04-01

    It was reported by others that hands-free accessories increase the absorption of RF energy in a human head compared to a handset alone. The results of this study show that the opposite is observed when proper dosimetric methods are employed. It is pointed out that for correct estimation of the exposure level it is necessary to use appropriate physical and experimental models and measurement instrumentation, following internationally recommended standards. The human phantoms used for measurements involving the hands-free accessories should include the torso; i.e., measurements should not be performed on the head phantom alone. This has a significant impact on the results because the RF energy coupled into the leads of hands-free accessories is strongly attenuated by the body. Numerical simulations using the Finite-Difference Time-Domain (FDTD) method and experimental measurements with a miniature electric-field probe are in good agreement and show a decrease, not an increase, in RF energy exposure in the human head from hands-free accessories.

  18. Development of the electrochemical fatigue sensor for evaluating fatigue damage

    SciTech Connect

    Li, Y.F.; Wang, J.; Wang, M.Z.; DeLuccia, J.; Laird, C.

    1999-07-01

    The Electrochemical Fatigue Sensor (EFS) is a device which operates by an electrochemical-mechanical interaction and which can sense the type and extent of fatigue damage both before and after crack initiation. It was initially explored through studies on soft metals. Here the authors report efforts to determine the ability of the device to read damage in hardened commercial alloys: 7075 aluminum alloy, 4130 steel and Ti-6Al-4V. They also demonstrate that the device, which uses an electrolytic medium, does not degrade the fatigue properties if care is used in electrolyte selection.

  19. Complementary and alternative medical therapy utilization by people with chronic fatiguing illnesses in the United States

    PubMed Central

    Jones, James F; Maloney, Elizabeth M; Boneva, Roumiana S; Jones, Ann-Britt; Reeves, William C

    2007-01-01

    Background Chronic fatiguing illnesses, including chronic fatigue syndrome (CFS), pose a diagnostic and therapeutic challenge. Previous clinical reports addressed the utilization of health care provided to patients with CFS by a variety of practitioners with other than allopathic training, but did not examine the spectrum of complementary and alternative medicine (CAM) therapies used. This study was designed to measure CAM therapy use by persons with fatiguing illnesses in the United States population. Methods During a random-digit dialing survey to estimate the prevalence of CFS-like illness in urban and rural populations from different geographic regions of the United States, we queried the utilization of CAM including manipulation or body-based therapies, alternative medical systems, mind-body, biologically-based, and energy modalities. Results Four hundred forty fatigued and 444 non-fatigued persons from 2,728 households completed screening. Fatigued subjects included 53 persons with prolonged fatigue, 338 with chronic fatigue, and 49 with CFS-like illness. Mind-body therapy (primarily personal prayer and prayer by others) was the most frequently used CAM across all groups. Among women, there was a significant trend of increasing overall CAM use across all subgroups (p-trend = 0.003). All categories of CAM use were associated with significantly poorer physical health scores, and all but one (alternative medicine systems) were associated with significantly poorer mental health scores. People with CFS-like illness were significantly more likely to use body-based therapy (chiropractic and massage) than non-fatigued participants (OR = 2.52, CI = 1.32, 4.82). Use of body-based therapies increased significantly in a linear trend across subgroups of non-fatigued, prolonged fatigued, chronic fatigued, and CFS-like subjects (p-trend = 0.002). People with chronic fatigue were also significantly more likely to use body-based therapy (OR = 1.52, CI = 1.07, 2.16) and mind

  20. Thermomechanical Fatigue of LEAD-97 - TIN-3

    NASA Astrophysics Data System (ADS)

    Lawson, Lawrence Richard

    The thermomechanical fatigue properties of 96.5 wt.% Pb 3.5 wt% Sn alloy were studied at temperatures ranging from 15^circC to 100 ^circC. Cycling was performed at various periods ranging from 184 to 1040 seconds. Hold times at peak tensile strain of up to 419 seconds were introduced. Triangular waveforms for strain control and temperature were employed and the effects of varying the relative phase of these were studied. As a part of fatigue testing, measurements of crack length per unit area and depth of penetration were made. In addition to these fatigue tests, additional measurements of the production and recovery of excess lattice vacancy concentration due to straining and measurements of grain boundary sliding were also performed. Strong thermomechanical and phase effects were seen. The number of cycles to failure was seen to be smaller, when the peak temperature of the temperature cycle coincided with the peak tensile strain, than in an isothermal test under the same conditions except at the peak temperature of the thermal cycle. The number of cycles to failure was larger, when the lowest temperature of the thermal cycle coincided with the peak tensile strain, than in an isothermal test under the same conditions except at the maximum temperature of the thermal cycle and, where measured, at the minimum temperature of the thermal cycle as well. Also, unusual dependence of the number of cycles to failure on frequency was observed. These and other results were modeled using a vacancy -impurity complex model. Oxygen was chosen as the principal impurity since fatigue tests were conducted in air. Treating the complexes thermodynamically as if they were a chemical compound, the theoretical dependence of the number of cycles to failure on oxygen partial pressure was explored.

  1. Remote sensing applications for estimating changes on crop evapotranspiration of the most water intensive crops, due to climate change in Cyprus

    NASA Astrophysics Data System (ADS)

    Papadavid, G.; Neocleous, D.; Stylianou, A.; Markou, M.; Kountios, G.; Hadjimitsis, D.

    2016-08-01

    Water allocation to crops, and especially to the most water intensive ones, has always been of great importance in agricultural process. Deficit or excess water irrigation quantities could create either crop health related problems or water over-consumption situation which lead to stored water reduction and toxic material depletion to deeper ground layers, respectively. In this context, and under the current conditions, where Cyprus is facing effects of climate changes, purpose of this study is basically to estimate the needed crop water requirements of the past (1995-2004) and the corresponding ones of the present (2005-2015) in order to test if there were any significant changes regarding the crop water requirements of the most water intensive trees in Cyprus. Mediterranean region has been identified as the region that will suffer the most from climate change. Thus the paper refers to effects of climate changes on crop evapotranspiration (ETc) using remotely sensed data from Landsat TM/ ETM+ / OLI employing a sound methodology used worldwide, the Surface Energy Balance Algorithm for Land (SEBAL). Though the general feeling is that of changes on climate will consequently affect ETc, the results have indicated that there is no significant effect of climate change on crop evapotranspiration, despite the fact that some climatic factors have changed. Applying Student's T-test, the mean values for the most water intensive trees in Cyprus of the 1994-2004 decade have shown no statistical difference from the mean values of 2005-2015 decade's for all the cases, concluding that the climate change taking place the last decades in Cyprus have either not affected the crop evapotranspiration or the crops have manage to adapt into the new environmental conditions through time.

  2. Determining The Electromyographic Fatigue Threshold Following a Single Visit Exercise Test.

    PubMed

    Galen, Sujay S; Guffey, Darren R; Coburn, Jared W; Malek, Moh H

    2015-07-27

    Theoretically, the electromyographic (EMG) fatigue threshold is the exercise intensity an individual can maintain indefinitely without the need to recruit more motor units which is associated with an increase in the EMG amplitude. Although different protocols have been used to estimate the EMG fatigue threshold they require multiple visits which are impractical for a clinical setting. Here, we present a protocol for estimating the EMG fatigue threshold for cycle ergometry which requires a single visit. This protocol is simple, convenient, and completed within 15-20 min, therefore, has the potential to be translated into a tool that clinicians can use in exercise prescription.

  3. Monte Carlo estimation of radiation dose in organs of female and male adult phantoms due to FDG-F18 absorbed in the lungs

    NASA Astrophysics Data System (ADS)

    Belinato, Walmir; Santos, William S.; Silva, Rogério M. V.; Souza, Divanizia N.

    2014-03-01

    The determination of dose conversion factors (S values) for the radionuclide fluorodeoxyglucose (18F-FDG) absorbed in the lungs during a positron emission tomography (PET) procedure was calculated using the Monte Carlo method (MCNPX version 2.7.0). For the obtained dose conversion factors of interest, it was considered a uniform absorption of radiopharmaceutical by the lung of a healthy adult human. The spectrum of fluorine was introduced in the input data file for the simulation. The simulation took place in two adult phantoms of both sexes, based on polygon mesh surfaces called FASH and MASH with anatomy and posture according to ICRP 89. The S values for the 22 internal organs/tissues, chosen from ICRP No. 110, for the FASH and MASH phantoms were compared with the results obtained from a MIRD V phantoms called ADAM and EVA used by the Committee on Medical Internal Radiation Dose (MIRD). We observed variation of more than 100% in S values due to structural anatomical differences in the internal organs of the MASH and FASH phantoms compared to the mathematical phantom.

  4. Fatigue management in the workplace

    PubMed Central

    Sadeghniiat-Haghighi, Khosro; Yazdi, Zohreh

    2015-01-01

    Workers’ fatigue is a significant problem in modern industry, largely because of high demand jobs, long duty periods, disruption of circadian rhythms, and accumulative sleep debt that are common in many industries. Fatigue is the end result of integration of multiple factors such as time awake, time of day, and workload. Then, the full understanding of circadian biologic clock, dynamics of transient and cumulative sleep loss, and recovery is required for effective management of workplace fatigue. It can be more investigated in a new field of sleep medicine called occupational sleep medicine. Occupational sleep medicine is concerned with maintaining best productivity and safety in the industrial settings. The fatigue risk management system (FRMS) is a comprehensive approach that is based on applying scientific evidence of sleep knowledge to manage workers fatigue. It is developing rapidly in the highly safety demand jobs; especially truck drivers, pilots, and power plant workers. The objective of this review is to explain about fatigue in the workplace with emphasis on its association work performance and errors/accidents. Also, we discussed about different methods of fatigue measurement and management. PMID:26257477

  5. Fatigue management in the workplace.

    PubMed

    Sadeghniiat-Haghighi, Khosro; Yazdi, Zohreh

    2015-01-01

    Workers' fatigue is a significant problem in modern industry, largely because of high demand jobs, long duty periods, disruption of circadian rhythms, and accumulative sleep debt that are common in many industries. Fatigue is the end result of integration of multiple factors such as time awake, time of day, and workload. Then, the full understanding of circadian biologic clock, dynamics of transient and cumulative sleep loss, and recovery is required for effective management of workplace fatigue. It can be more investigated in a new field of sleep medicine called occupational sleep medicine. Occupational sleep medicine is concerned with maintaining best productivity and safety in the industrial settings. The fatigue risk management system (FRMS) is a comprehensive approach that is based on applying scientific evidence of sleep knowledge to manage workers fatigue. It is developing rapidly in the highly safety demand jobs; especially truck drivers, pilots, and power plant workers. The objective of this review is to explain about fatigue in the workplace with emphasis on its association work performance and errors/accidents. Also, we discussed about different methods of fatigue measurement and management.

  6. Effects of LWR coolant environments on fatigue design curves of carbon and low-alloy steels

    SciTech Connect

    Chopra, O.K.; Shack, W.J.

    1998-03-01

    The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. Figures I-9.1 through I-9.6 of Appendix I to Section III of the code specify fatigue design curves for structural materials. While effects of reactor coolant environments are not explicitly addressed by the design curves, test data indicate that the Code fatigue curves may not always be adequate in coolant environments. This report summarizes work performed by Argonne National Laboratory on fatigue of carbon and low-alloy steels in light water reactor (LWR) environments. The existing fatigue S-N data have been evaluated to establish the effects of various material and loading variables such as steel type, dissolved oxygen level, strain range, strain rate, temperature, orientation, and sulfur content on the fatigue life of these steels. Statistical models have been developed for estimating the fatigue S-N curves as a function of material, loading, and environmental variables. The results have been used to estimate the probability of fatigue cracking of reactor components. The different methods for incorporating the effects of LWR coolant environments on the ASME Code fatigue design curves are presented.

  7. The fatigue behavior of composite laminates under various mean stresses

    NASA Technical Reports Server (NTRS)

    Rotem, A.

    1991-01-01

    A method is developed for predicting the S-N curve of a composite laminate which is subjected to an arbitrary stress ratio, R (minimum stress/maximum stress). The method is based on the measuring of the S-N behavior of two distinct cases, tension-tension and compression-compression fatigue loadings. Using these parameters, expressions are formulated that estimate the fatigue behavior under any stress ratio loading. Experimental results from the testing of graphite/epoxy laminates, with various structures, are compared with the predictions and show good agreement.

  8. Atlas of fatigue curves

    SciTech Connect

    Boyer, H.E.

    1986-01-01

    This Atlas was developed to serve engineers who are looking for fatigue data on a particular metal or alloy. Having these curves compiled in a single book will also facilitate the computerization of the involved data. It is pointed out that plans are under way to make the data in this book available in ASCII files for analysis by computer programs. S-N curves which typify effects of major variables are considered along with low-carbon steels, medium-carbon steels, alloy steels, HSLA steels, high-strength alloy steels, heat-resisting steels, stainless steels, maraging steels, cast irons, and heat-resisting alloys. Attention is also given to aluminum alloys, copper alloys, magnesium alloys, molybdenum, tin alloys, titanium and titanium alloys, zirconium, steel castings, closed-die forgings, powder metallurgy parts, composites, effects of surface treatments, and test results for component parts.

  9. New creep-fatigue damage model based on the frequency modified strain range method

    SciTech Connect

    Kim, Y.J.; Seok, C.S.; Park, J.J.

    1996-12-01

    For mechanical systems operating at high temperature, damage due to the interaction effect of creep and fatigue plays an important role. The objective of this paper is to propose a modified creep-fatigue damage model which separately analyzes the pure creep damage due to the hold time and the creep-fatigue interaction damage during the startup and the shutdown period. The creep damage was calculated by the general creep damage equation and the creep-fatigue interaction damage was calculated by the modified equation which is based on the frequency modified strain range method with strain rate term. In order to verify the proposed model, a series of high temperature low cycle fatigue tests were performed. The test specimens were made from Inconel-718 superalloy and the test parameters were wave form and hold time. A good agreement between the predicted lives based on the proposed model and experimentally obtained ones was obtained.

  10. Fractographic analysis of initiation and growth of fatigue cracks at rivet holes

    NASA Astrophysics Data System (ADS)

    Pelloux, R.; Warren, A.; O'Grady, J.

    A series of fatigue tests were performed on riveted panels of clad 2024-T3 without epoxy bonds. Fatigue crack initiation occurred at the apex of the rivet hole chamfers. Transgranular fatigue crack growth by ductile striation formation occurred through the sheet. The fracture features at low, medium and high growth rates were examined with the SEM. Microscopic crack propagation rates as measured by fatigue striation spacings correlate with macroscopic crack growth rates observed. The fatigue crack growth rate is fairly constant over a length of 6 mm (0.25 in.) from the edge of the rivet hole, due to the fact that the stress intensity range is approximately constant in this region. Transition to fast fracture and unstable crack propagation is readily identified due to marked yielding of the cladding material.

  11. Rolling Contact Fatigue of Ceramics

    SciTech Connect

    Wereszczak, Andrew A; Wang, W.; Wang, Y.; Hadfield, M.; Kanematsu, W.; Kirkland, Timothy Philip; Jadaan, Osama M.

    2006-09-01

    High hardness, low coefficient of thermal expansion and high temperature capability are properties also suited to rolling element materials. Silicon nitride (Si{sub 3}N{sub 4}) has been found to have a good combination of properties suitable for these applications. However, much is still not known about rolling contact fatigue (RCF) behavior, which is fundamental information to assess the lifetime of the material. Additionally, there are several test techniques that are employed internationally whose measured RCF performances are often irreconcilable. Due to the lack of such information, some concern for the reliability of ceramic bearings still remains. This report surveys a variety of topics pertaining to RCF. Surface defects (cracks) in Si{sub 3}N{sub 4} and their propagation during RCF are discussed. Five methods to measure RCF are then briefly overviewed. Spalling, delamination, and rolling contact wear are discussed. Lastly, methods to destructively (e.g., C-sphere flexure strength testing) and non-destructively identify potential RCF-limiting flaws in Si{sub 3}N{sub 4} balls are described.

  12. Effect of an amorphous titania nanotubes coating on the fatigue and corrosion behaviors of the biomedical Ti-6Al-4V and Ti-6Al-7Nb alloys.

    PubMed

    Campanelli, Leonardo Contri; Bortolan, Carolina Catanio; da Silva, Paulo Sergio Carvalho Pereira; Bolfarini, Claudemiro; Oliveira, Nilson Tadeu Camarinho

    2017-01-01

    An array of self-organized TiO2 nanotubes with an amorphous structure was produced on the biomedical Ti-6Al-4V and Ti-6Al-7Nb alloys, and the resulting fatigue and corrosion behaviors were studied. The electrochemical response of the nanotubular oxide surfaces was investigated in Ringer physiological solution through potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The absence of transpassivation in the chloride-containing solution, in addition to the micron-scale values of the passivation current density, indicated the excellent corrosion behavior of the coating and the satisfactory protection against the creation of potential stress concentrators in the surface. Axial fatigue tests were performed in physiological solution on polished and coated conditions, with characterization of the treated surfaces by scanning electron microscopy before and after the tests. The surface modification was not deleterious to the fatigue response of both alloys mainly due to the nano-scale dimension of the nanotubes layer. An estimation based on fracture mechanics revealed that a circumferential crack in the range of 5μm depth would be necessary to affect the fatigue performance, which is far from the thickness of the studied coating, although no cracks were actually observed in the oxide surfaces after the tests.

  13. High cycle fatigue and fracture behaviour of a hot isostatically pressed nickel-based superalloy

    NASA Astrophysics Data System (ADS)

    Qiu, Chunlei; Wu, Xinhua

    2014-01-01

    Powder of a nickel-based superalloy, RR1000, has been hot isostatically pressed (HIPped) at a supersolvus temperature and post-HIP heat treated to produce different microstructures. Microstructures were investigated using a scanning electron microscope together with an energy dispersive X-ray spectrometer and a wave-length dispersive X-ray spectrometer. High cycle four-point bending fatigue and tension-tension fatigue tests have been performed on the fabricated samples. It was found that HIPped and aged samples showed the best four-point bending fatigue limit while HIPped and solution-treated and aged samples had the lowest fatigue limit. The four-point bending fatigue crack initiations all occurred from the sample surfaces either at the sites of inclusion clusters or by cleavage through large grains on the surfaces. The tension-tension fatigue crack initiation occurred mainly due to large hafnia inclusion clusters, with lower fatigue lives for samples where inclusions were closer to the surface. Crack initiation at the compact Al2O3 inclusion cluster led to a much higher fatigue life than found when cracks were initiated by large hafnia inclusion clusters. The tension-tension fatigue limits were shown to decrease with increased testing temperature (from room temperature to 700 °C).

  14. Low-Cycle Fatigue Behavior of Die-Cast Mg Alloys AZ91 and AM60

    NASA Astrophysics Data System (ADS)

    Rettberg, Luke H.; Jordon, J. Brian; Horstemeyer, Mark F.; Jones, J. Wayne

    2012-07-01

    The influence of microstructure and artificial aging response (T6) on the low-cycle fatigue behavior of super vacuum die-cast (SVDC) AZ91 and AM60 has been investigated. Fatigue lifetimes were determined from the total strain-controlled fatigue tests for strain amplitudes of 0.2 pct, 0.4 pct, 0.6 pct, 0.8 pct, and 1.0 pct under fully reversed loading at a frequency of 5 Hz. Cyclic stress-strain behavior was determined using an incremental step test (IST) and compared with the more traditional constant amplitude test. Two locations in a prototype casting were investigated to examine the role of microstructure and porosity on fatigue behavior. At all total strain amplitudes microstructure refinement had a negligible impact on fatigue life because of significant levels of porosity. AM60 showed an improvement in fatigue life at higher strain amplitudes when compared with AZ91 because of higher ductility. T6 heat treatment had no impact on fatigue life. Cyclic stress-strain behavior obtained via the incremental step test varied from constant amplitude test results due to load history effects. The constant amplitude test is believed to be the more accurate test method. In general, larger initiation pores led to shorter fatigue life. The fatigue life of AZ91 was more sensitive to initiation pore size and pore location than AM60 at the lowest tested strain amplitude of 0.2 pct. Fatigue crack paths did not favor any specific phase, interdentritic structure or eutectic structure. A multistage fatigue (MSF) model showed good correlation to the experimental strain-life results. The MSF model reinforced the dominant role of inclusion (pore) size on the scatter in fatigue life.

  15. Neuromuscular Fatigue During 200 M Breaststroke

    PubMed Central

    Conceição, Ana; Silva, António J.; Barbosa, Tiago; Karsai, István; Louro, Hugo

    2014-01-01

    The aims of this study were: i) to analyze activation patterns of four upper limb muscles (duration of the active and non-active phase) in each lap of 200m breaststroke, ii) quantify neuromuscular fatigue, with kinematics and physiologic assessment. Surface electromyogram was collected for the biceps brachii, deltoid anterior, pectoralis major and triceps brachii of nine male swimmers performing a maximal 200m breaststroke trial. Swimming speed, SL, SR, SI decreased from the 1st to the 3rd lap. SR increased on the 4th lap (35.91 ± 2.99 stroke·min-1). Peak blood lactate was 13.02 ± 1.72 mmol·l-1 three minutes after the maximal trial. The EMG average rectified value (ARV) increased at the end of the race for all selected muscles, but the deltoid anterior and pectoralis major in the 1st lap and for biceps brachii, deltoid anterior and triceps brachii in the 4th lap. The mean frequency of the power spectral density (MNF) decreased at the 4th lap for all muscles. These findings suggest the occurrence of fatigue at the beginning of the 2nd lap in the 200m breaststroke trial, characterized by changes in kinematic parameters and selective changes in upper limb muscle action. There was a trend towards a non-linear fatigue state. Key Points Fatigue in the upper limbs occurs in different way as it described by 100m swimming events. Neuromuscular fatigue was estimated by analyzing the physiological changes (high blood lactate concentrations), biomechanical changes in the swimming stroke characteristics (decreased in swimming velocity), and by the changes in the EMG amplitude and frequency parameters at the end of the swimming bout. The amplitude signal of EMG provided by the ARV demonstrated an increase at the end with the respect to the beginning for all muscles under study, excepted for the muscle deltoid anterior. The mean frequency (MNF) in our study decrease at the end of the swimming in the 4th lap relative to the 1st lap for all muscles under observation, along the

  16. Fatigue Management Strategies for the Stratospheric Observatory for Infrared Astronomy

    NASA Technical Reports Server (NTRS)

    Bendrick, Gregg

    2012-01-01

    Operation of the Stratospheric Observatory for Infrared Astronomy entails a great deal of night-time work, with the potential for both acute and chronic sleep loss, as well as circadian rhythm dysynchrony. Such fatigue can result in performance decrements, with an increased risk of operator error. The NASA Dryden Flight Research Center manages this fatigue risk by means of a layered approach, to include: 1) Education and Training 2) Work Schedule Scoring 3) Obtained Sleep Metrics 4) Workplace and Operational Mitigations and 5) Incident or Accident Investigation. Specifically, quantitative estimation of the work schedule score, as well as the obtained sleep metric, allows Supervisors and Managers to better manage the risk of fatigue within the context of mission requirements.

  17. Fatigue case study and loading spectra for wind turbines

    NASA Astrophysics Data System (ADS)

    Sutherland, H. J.

    The paper discusses two aspects of Sandia's Wind Energy Program. The first section of the paper presents a case study of fatigue in wind turbines. This case study was prepared for the American Society of Testing Material's (ASTM) Standard Technical Publication (STP) on fatigue education. Using the LIFE2 code, the student is lead through the process of cumulative damage summation for wind turbines and typical data are used to demonstrate the range of life estimates that will result from typical parameter variations. The second section summarizes the results from a workshop held by Sandia and the National Renewable Energy Laboratory (NREL) to discuss fatigue life prediction methodologies. This section summarizes the workshop discussions on the use of statistical modeling to deduce the shape and magnitude of the low-probability-of-occurrence, high-stress tail of the load distribution on a wind turbine during normal operation.

  18. Muscular fatigue detection using sEMG in dynamic contractions.

    PubMed

    Bueno, Diana R; Lizano, J M; Montano, L

    2015-08-01

    In this work we have studied different indicators of muscle fatigue from the electrical signal produced by the muscles when contract (sEMG or EMG: surface electromyography): Mean Frequency of the power spectrum (MNF), Median Frequency (Fmed), Dimitrov Spectral Index (FInsm5), Root Mean Square (RMS), and Zerocrossing (ZC). The most reliable features are selected to develop a detection algorithm that estimates muscle fatigue. The approach used in the algorithm is probabilistic and is based on the technique of Gaussian Mixture Model (GMM). The system is divided into two stages: training and validation. During training, the algorithm learns the distribution of data regarding fatigue evolution; after that, the algorithm is validated with data that have not been used to train. Therefore, two experimental sessions have been performed with 6 healthy subjects for biceps.

  19. Coping with cancer - managing fatigue

    MedlinePlus

    ... cause fatigue. Simply having cancer can drain your energy: Some cancers release proteins called cytokines that can ... tumors can change the way your body uses energy and leave you feeling tired. Many cancer treatments ...

  20. Fatigue of internal combustion engines

    NASA Technical Reports Server (NTRS)

    Dumanois, P

    1924-01-01

    The above conditions enable the employment of a criterion of general fatigue which simultaneously takes account of both mechanical and thermal conditions, for the sake of comparing any projected engine with engines of the same type already in use.

  1. Chronic Fatigue Syndrome (For Parents)

    MedlinePlus

    ... help reduce symptoms of fatigue. acupuncture, massage, stretching, yoga, and tai chi, which have been helpful for ... that antidepressant medications can help ease the symptoms. Pain medications and anti-inflammatory drugs, such as ibuprofen, ...

  2. Resolving the frustration of fatigue.

    PubMed

    Harpham, W S

    1999-01-01

    Fatigue is a ubiquitous side effect of many cancer therapies. Nevertheless, after treatment is complete, many survivors continue to feel a profound tiredness that affects almost all aspects of life. Even after recovery, patients are often frustrated by their continuing need for extra rest. In this deeply personal, first-person account, a physician relates the various ways that cancer-related fatigue can affect family dynamics, job responsibilities, social interactions, finances, and intimacy. Clinicians can help by searching for treatable medical conditions, but also by taking cancer-related fatigue, and the frustrations it causes, seriously. Patients should be reassured that the fatigue they feel is real, and that by learning personal energy conservation, they should be able to improve their abilities to function, to socialize, to interact with others, and ultimately to adjust to a "new normal" baseline.

  3. Multiaxial plasticity and fatigue life prediction in coiled tubing

    SciTech Connect

    Tipton, S.M.

    1996-12-31

    Coiled tubing is being used increasingly in the oil well drilling and servicing industry. Continuous steel tubing of structural dimensions (up to 89 mm or 3.5 in. in diameter) is wound onto a large-diameter reel for repeated deployment into and out of a well bore. The bending strain range associated with each wrap-unwrap cycle can exceed 3% with lives well below 100 cycles. During constant internal pressure fatigue testing, tubing has been observed to grow in diameter by as much as 30%. This paper describes an analytical model to predict the fatigue behavior of coiled tubing subjected to variable pressure service conditions. The approach utilizes standard low-cycle fatigue data but requires additional experimental results from constant pressure fatigue testing. The algorithm is based on estimates of biaxial ratcheting from an incremental plasticity model using a hybrid associated flow rule, a modified kinematic hardening rule with multiple von Mises yield surfaces, and a specialized limit surface concept. An empirical damage parameter was formulated based on constant pressure fatigue data using mean and fluctuating von Mises equivalent strain components occurring throughout the life of a section of tubing. This parameters is used with the Palmgren-Miner definition of cumulative damage to track damage that is accumulating nonlinearly under constant or variable pressure histories. Modifications to standard incremental plasticity components and implementation assumptions used to apply the model are presented and discussed. The predictive capability of the model is demonstrated relative to data generated under constant and variable pressure histories.

  4. Fretting fatigue of anisotropic materials at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Haradanahalli, Murthy N.

    The purpose of this research is to develop an experimental procedure to characterize the contact between blade and disk in aircraft turbo-machinery and to develop a model to predict the life of components based on contact conditions. An experimental setup has been developed to conduct fretting fatigue tests at 610°C. Fretting fatigue lives are characterized for the contacting pair of IN100 and single crystal nickel subjected to a range of loading conditions. A well characterized set of experiments has been conducted to obtain the friction coefficient in the slip zone. Material principal axes and the crystallographic plane of fracture were determined. A robust quasi-analytical approach, based on solution to singular integral equations, has been used to analyze the contact stresses. Different multi-axial fatigue parameters have been investigated for their ability to predict the initiation life of the specimens, after applying a stressed area correction factor using weakest link approach. Multiaxial fatigue parameters also predicted crack nucleation at the edge of contact, consistent with observations of the fractured specimens. Crack propagation lives were evaluated using conventional fracture mechanics, after making certain assumptions to simplify the problem. Total life was estimated as the sum of nucleation life and propagation life. These predicted lives were compared with experimentally observed failure lives. The quality of the comparison provides confidence in the notion that conventional life prediction tools can be used to assess fretting fatigue at elevated temperatures.

  5. Creep fatigue life prediction for engine hot section materials (isotropic)

    NASA Technical Reports Server (NTRS)

    Moreno, Vito; Nissley, David; Lin, Li-Sen Jim

    1985-01-01

    The first two years of a two-phase program aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components are discussed. In Phase 1 (baseline) effort, low cycle fatigue (LCF) models, using a data base generated for a cast nickel base gas turbine hot section alloy (B1900+Hf), were evaluated for their ability to predict the crack initiation life for relevant creep-fatigue loading conditions and to define data required for determination of model constants. The variables included strain range and rate, mean strain, strain hold times and temperature. None of the models predicted all of the life trends within reasonable data requirements. A Cycle Damage Accumulation (CDA) was therefore developed which follows an exhaustion of material ductility approach. Material ductility is estimated based on observed similarities of deformation structure between fatigue, tensile and creep tests. The cycle damage function is based on total strain range, maximum stress and stress amplitude and includes both time independent and time dependent components. The CDA model accurately predicts all of the trends in creep-fatigue life with loading conditions. In addition, all of the CDA model constants are determinable from rapid cycle, fully reversed fatigue tests and monotonic tensile and/or creep data.

  6. Elevated temperature axial and torsional fatigue behavior of Haynes 188

    NASA Technical Reports Server (NTRS)

    Bonacuse, Peter J.; Kalluri, Sreeramesh

    1995-01-01

    The results are reported for high-temperature axial and torsional low-cycle fatigue experiments performed at 760 C in air on thin-walled tubular specimens of Haynes 188, a wrought cobalt-based superalloy. Data are also presented for mean coefficient of thermal expansion, elastic modulus, and shear modulus at various temperatures from room to 1000 C, and monotonic and cyclic stress-strain curves in tension and in shear at 760 C. This data set is used to evaluate several multiaxial fatigue life models (most were originally developed for room temperature multiaxial life prediction) including von Mises equivalent strain range (ASME Boiler and Pressure Code), Manson-Halford, modified multiaxiality factor (proposed in this paper), modified Smith-Watson-Topper, and Fatemi-Socie-Kurath. At von Mises equivalent strain ranges (the torsional strain range divided by the square root of 3, taking the Poisson's ratio to be 0.5), torsionally strained specimens lasted, on average, factors of 2 to 3 times longer than axially strained specimens. The modified multiaxiality factor approach shows promise as a useful method of estimating torsional fatigue life from axial fatigue data at high temperatures. Several difficulties arose with the specimen geometry and extensometry used in these experiments. Cracking at extensometer probe indentations was a problem at smaller strain ranges. Also, as the largest axial and torsional strain range fatigue tests neared completion, a small amount of specimen buckling was observed.

  7. A study of crack closure in fatigue

    NASA Technical Reports Server (NTRS)

    Shih, T. T.; Wei, R. P.

    1973-01-01

    Crack closure phenomenon in fatigue was studied by using a Ti-6Al-4V titanium alloy. The occurrence of crack closure was directly measured by an electrical-potential method, and indirectly by load-strain measurement. The experimental results showed that the onset of crack closure depends on both the stress ratio, and the maximum stress intensity factor. No crack closure was observed for stress ratio, greater than 0.3 in this alloy. A two-dimensional elastic model was used to explain the behavior of the recorded load-strain curves. Closure force was estimated by using this model. Yield level stress was found near the crack tip. Based on this estimated closure force, the crack opening displacement was calculated. This result showed that onset of crack closure detected by electrical-potential measurement and crack-opening-displacement measurement is the same. The implications of crack closure on fatigue crack are considered. The experimental results show that crack closure cannot fully account for the effect of stress ratio, on crack growth, and that it cannot be regarded as the sole cause for delay.

  8. Microstructure-sensitive extreme value probabilities of fatigue in advanced engineering alloys

    NASA Astrophysics Data System (ADS)

    Przybyla, Craig P.

    A novel microstructure-sensitive extreme value probabilistic framework is introduced to evaluate material performance/variability for damage evolution processes (e.g., fatigue, fracture, creep). This framework employs newly developed extreme value marked correlation functions (EVMCF) to identify the coupled microstructure attributes (e.g., phase/grain size, grain orientation, grain misorientation) that have the greatest statistical relevance to the extreme value response variables (e.g., stress, elastic/plastic strain) that describe the damage evolution processes of interest. This is an improvement on previous approaches that account for distributed extreme value response variables that describe the damage evolution process of interest based only on the extreme value distributions of a single microstructure attribute; previous approaches have given no consideration of how coupled microstructure attributes affect the distributions of extreme value response. This framework also utilizes computational modeling techniques to identify correlations between microstructure attributes that significantly raise or lower the magnitudes of the damage response variables of interest through the simulation of multiple statistical volume elements (SVE). Each SVE for a given response is constructed to be a statistical sample of the entire microstructure ensemble (i.e., bulk material); therefore, the response of interest in each SVE is not expected to be the same. This is in contrast to computational simulation of a single representative volume element (RVE), which often is untenably large for response variables dependent on the extreme value microstructure attributes. This framework has been demonstrated in the context of characterizing microstructure-sensitive high cycle fatigue (HCF) variability due to the processes of fatigue crack formation (nucleation and microstructurally small crack growth) in polycrystalline metallic alloys. Specifically, the framework is exercised to

  9. Fatigue and the criminal law.

    PubMed

    Jones, Christopher B; Dorrian, Jillian; Rajaratnam, Shanthakumar M W

    2005-01-01

    Fatigue is an increasingly recognised risk factor for transportation accidents. In light of this, there is the question of whether driving whilst fatigued should be a criminal offence. This paper discusses the current legal position, including the problems of voluntary conduct and self awareness. Three models for reform are proposed. The manner in which scientific research can inform legal consideration and future directions for research are discussed.

  10. Fatigue behavior and encrustation characteristics of nanocrystalline metals

    NASA Astrophysics Data System (ADS)

    Lai, Li-Chung

    The nanocrstalline (NC) metals have been reported to have high mechanical performance owing to it's small grain interior and a large volume fraction of grain boundary (GB) atoms. Small grain leads to the forbidden dislocation activities in grain interior while GB activities become dominant due to a higher volume fraction of GB atoms. Regarding the fatigue response to nanocrstalline metals, it has been reported that decreasing grain led to both significantly improvement on the fatigue-endurance limit and deleterious effect on the resistance to subcritical fatigue crack propagation. The increases endurance limit has been attributed to the greater resistance to fatigue crack initiation at near-surface regions. On the other hand, the less resistance to fatigue crack growth were resulted from less tortuous fatigue crack profiles supported by the deflection/closure theory. However, it has never been studied the influence of proceeding and pre-existing defects on the fatigue performance considering the difference response of NC structure from than coarse grain (CG) structure. In the present work, the influence of electrical discharge machining (EDM) and surface defects on the fatigue behavior of both conventional cold-rolled CG and electro-deposited (ED) NC Ni were investigated. The experimental results revealed considerable influence by EDM on the fatigue strength of NC Ni, while it has little or no affect on that for CG Ni. Specifically, EDM led to a 50 to 75% reduction in fatigue strength for NC Ni despite a relatively small depth of EDM affected material (˜ 1% of width). Rationale for this effect can be attributed to grain growth, microcracks, and a higher sulfur content at the GBs in the EDM affected zone. In addition, the pre-existing surface defects that appear to be due to impurity segregation near the electro-deposition substrate significantly reduced the fatigue resistance of ED NC Ni. In order to understand the fatigued behavior in NC Ni, crack tip grain

  11. Effect of cyclic high loading rates on the fatigue strength of aluminum-based composites

    NASA Astrophysics Data System (ADS)

    Calderon Arteaga, Hermes Eskander

    The study of fatigue under high loading rates is of great interest in the complete characterization of a new series of composites with Al-Cu-Mg matrix reinforced with AlB2 dispersoids. Homogeneous and functionally graded composites were prepared via gravity and centrifugal casting, respectively. Through centrifugal casting a gradual variation of the volume fraction of reinforcing particles along the cross section was obtained. In specific fabrication conditions, even complete segregation of the reinforcement particles was achieved. Charpy impact tests as well as hardness tests were conducted to assess the composite strength as a function of the weight percent of boron. The tensile properties of gravity cast samples were obtained. Then for both casting conditions, simple edge-notched bend SE(B) specimens were tested under fatigue conditions (three-point bending). The results from impact and hardness tests allowed identifying an interaction between the Mg dissolved in the matrix and the diborides. This interaction, which has never been reported before, was responsible for the strength reduction observed. It was assumed that a substitutional diffusion of Al by Mg atoms in the hp3 structure of diboride was causing the strength reduction, and three approaches were developed to estimate the amount of Mg depleted from the matrix by the diborides during the composite processing. Gravity cast samples were more sensitive to monotonic damage due to fatigue loads where compared with functionally-graded composites. Contrary to the centrifugal cast samples, gravity samples were also affected by the loading rate. The Mg-AlB2 interaction was also responsible for the reduction in the fatigue resistance as the weight percent of boron increased in both types of composites; regression models were obtained to predict the crack growth curve slope change as function of the boron level. The particle distribution showed to affect the crack growth behavior of the FGMs, decreasing the

  12. A Novel Method for the Prediction of Critical Inclusion Size Leading to Fatigue Failure

    NASA Astrophysics Data System (ADS)

    Saberifar, S.; Mashreghi, A. R.

    2012-06-01

    The fatigue behavior of two commercial 30MnVS6 steels with similar microstructure and mechanical properties containing inclusions of different sizes were studied in the 107 cycles fatigue regime. The scanning electron microscopy (SEM) investigations of the fracture surfaces revealed that the nonmetallic inclusions are the main sources of fatigue crack initiation. Calculated according to the Murakami's model, the stress intensity factors were found to be suitable for the assessment of fatigue behavior. In this article, a new method is proposed for the prediction of the critical inclusion size, using Murakami's model. According to this method, a critical stress intensity factor was determined for the estimation of the critical inclusion size causing the fatigue failure.

  13. Unstimulated cortisol secretory activity in everyday life and its relationship with fatigue and chronic fatigue syndrome: a systematic review and subset meta-analysis.

    PubMed

    Powell, Daniel J H; Liossi, Christina; Moss-Morris, Rona; Schlotz, Wolff

    2013-11-01

    The hypothalamic-pituitary-adrenal (HPA) axis is a psychoneuroendocrine regulator of the stress response and immune system, and dysfunctions have been associated with outcomes in several physical health conditions. Its end product, cortisol, is relevant to fatigue due to its role in energy metabolism. The systematic review examined the relationship between different markers of unstimulated salivary cortisol activity in everyday life in chronic fatigue syndrome (CFS) and fatigue assessed in other clinical and general populations. Search terms for the review related to salivary cortisol assessments, everyday life contexts, and fatigue. All eligible studies (n=19) were reviewed narratively in terms of associations between fatigue and assessed cortisol markers, including the cortisol awakening response (CAR), circadian profile (CP) output, and diurnal cortisol slope (DCS). Subset meta-analyses were conducted of case-control CFS studies examining group differences in three cortisol outcomes: CAR output; CAR increase; and CP output. Meta-analyses revealed an attenuation of the CAR increase within CFS compared to controls (d=-.34) but no statistically significant differences between groups for other markers. In the narrative review, total cortisol output (CAR or CP) was rarely associated with fatigue in any population; CAR increase and DCS were most relevant. Outcomes reflecting within-day change in cortisol levels (CAR increase; DCS) may be the most relevant to fatigue experience, and future research in this area should report at least one such marker. Results should be considered with caution due to heterogeneity in one meta-analysis and the small number of studies.

  14. Fatigue after Stroke: The Patient's Perspective.

    PubMed

    Barbour, Victoria Louise; Mead, Gillian Elizabeth

    2012-01-01

    Background. Fatigue after stroke is common and distressing to patients. Aims. Our aims were to explore patients' perceptions of post-stroke fatigue, including the causes of fatigue and the factors that alleviate fatigue, in a mixed methods study. Results. We interviewed 15 patients who had had a stroke and were inpatients on stroke rehabilitation wards. A substantial proportion of patients reported that their fatigue started at the time of their stroke. Various different factors were reported to improve fatigue, including exercise, good sleep, rehabilitation and rest. Fatigue influences patients' sense of "control" after their stroke. Conclusion. Our results are consistent with the possibility that poststroke fatigue might be triggered by factors that occur at the time of the stroke (e.g., the stroke lesion itself, or admission to hospital) and then exacerbated by poor sleep and boredom. These factors should be considered when developing complex interventions to improve post-stroke fatigue.

  15. Assessment of fatigue in cancer patients.

    PubMed

    Jacobsen, Paul B

    2004-01-01

    Increased recognition of the problem of fatigue in cancer patients can be attributed, in part, to the development of measures that have provided researchers with the tools necessary for quantifying and characterizing fatigue and exploring its etiology and treatment. Although a consensus regarding the definition of fatigue is lacking, there is general agreement that it is a subjective and multidimensional phenomenon whose assessment requires the use of self-report methods. Consistent with this view, several multidimensional measures of fatigue have been developed and validated for use with cancer patients. These measures differ considerably in their format and content and, as with the definition of fatigue, there is no consensus at the present time regarding the dimensional structure of fatigue. In addition to measuring fatigue on a continuum along one or more dimensions, it may also be possible to assess a clinical syndrome of cancer-related fatigue. Criteria for assessing fatigue in this manner have been proposed and are currently undergoing evaluation. Despite the progress that has been made, there are several important unresolved issues in the assessment of fatigue in cancer patients. These include how to distinguish fatigue from depression, how to use self-reports of fatigue in clinical decision-making, how to capture temporal changes in fatigue, and how best to address the continuing lack of consensus regarding the conceptualization and measurement of fatigue.

  16. Assessment of failure of cemented polyethylene acetabular component due to bone remodeling: A finite element study.

    PubMed

    Ghosh, Rajesh

    2016-09-01

    The aim of the study is to determine failure of the cemented polyethylene acetabular component, which might occur due to excessive bone resorption, cement-bone interface debonding and fatigue failure of the cement mantle. Three-dimensional finite element models of intact and implanted pelvic bone were developed and bone remodeling algorithm was implemented for present analysis. Soderberg fatigue failure diagram was used for fatigue assessment of the cement mantle. Hoffman failure criterion was considered for prediction of cement-bone interface debonding. Results indicate fatigue failure of the cement mantle and implant-bone interface debonding might not occur due to bone remodeling.

  17. Feasibility of detecting fatigue damage in composites with coda waves

    NASA Astrophysics Data System (ADS)

    Livings, Richard; Dayal, Vinay; Barnard, Dan

    2015-03-01

    Coda waves are the late arriving portion of bulk or guided waves, and are the result of scattering of the waves due to heterogeneities in the material. Since these waves interact with a region multiple times, the effect of otherwise undetectable changes in material and/or stress state accumulates and becomes detectable. This work examines the feasibility of detecting incipient fatigue damage in CFRP sample with coda wave analysis. Specimens are subjected to low cycle fatigue in a four-point bend set-up. Ultrasonic measurements are periodically taken perpendicular to the direction of loading during the fatiguing process after removing all loads. Detection and reception sensitivity of coda waves in composites are studied. Also studied are the effects of the coupling between the transducer and sample for a reliable and repeatable measurement.

  18. [Sleep patterns and fatigue of nursing students who work].

    PubMed

    Ferreira, Luciane Ruiz Carmona; de Martino, Milva Maria Figueiredo

    2012-10-01

    It has been observed there is currently a growing interest in developing research regarding the sleep patterns of workers who must wake up very early or who work nights. Therefore, the objective of this study was to identify the levels of fatigue and the sleep patterns of nursing students who study during the day and work at night. Participants were thirty students who completed the Epworth Sleepiness Scale and Sleep Journal for thirty days. It was found that sleep duration was longer among men compared to women on days off work, and when on vacation from school compared to the regular school period. Participants showed high levels of fatigue and sleepiness, characterized by the incidence of excessive daytime sleepiness. In conclusion, night workers who endure sleep deprivation have additional wake hours due to studying, thus causing high levels of fatigue, which may harm their performance at school and at work.

  19. Automatic Fatigue Detection of Drivers through Yawning Analysis

    NASA Astrophysics Data System (ADS)

    Azim, Tayyaba; Jaffar, M. Arfan; Ramzan, M.; Mirza, Anwar M.

    This paper presents a non-intrusive fatigue detection system based on the video analysis of drivers. The focus of the paper is on how to detect yawning which is an important cue for determining driver's fatigue. Initially, the face is located through Viola-Jones face detection method in a video frame. Then, a mouth window is extracted from the face region, in which lips are searched through spatial fuzzy c-means (s-FCM) clustering. The degree of mouth openness is extracted on the basis of mouth features, to determine driver's yawning state. If the yawning state of the driver persists for several consecutive frames, the system concludes that the driver is non-vigilant due to fatigue and is thus warned through an alarm. The system reinitializes when occlusion or misdetection occurs. Experiments were carried out using real data, recorded in day and night lighting conditions, and with users belonging to different race and gender.

  20. Postpartum early discharge: impact on maternal fatigue and functional ability.

    PubMed

    Smith-Hanrahan, C; Deblois, D

    1995-02-01

    The purpose of this study was to determine the impact of a postpartum early discharge program, with home follow-up by hospital nursing staff, on the maternal fatigue and functional ability of low-risk mothers with healthy neonates. A quasi-experimental design was used. Subjects were randomly assigned to one of two groups receiving the early-discharge program (hospital stay less than 60 hours plus home follow-up by hospital-based nurses; n = 35) or traditional hospital care (hospital stay more than 60 hours and no home follow-up by hospital staff; n = 17). A third group emerged from those originally assigned to traditional care but later transferred to early discharge due to bed shortages (n = 29). The Rhoten Fatigue Scale and the Inventory of Functional Status After Childbirth were used to collect the data at discharge and 1 and 6 weeks postpartum period. No significant differences between groups were found, suggesting that early discharge with adequate home follow-up does not affect the low-risk mother's fatigue and functional ability to any significantly greater extent than traditional care. It was also noted that, regardless of type of care, the proportion of subjects reporting severe fatigue was relatively large (25%, 31%, and 19% at discharge, 1 and 6 weeks postpartum period), highlighting the need for further study of maternal fatigue in the postpartum period.

  1. Fatigue-Resistance Enhancements by Glass-Forming Metallic Films

    SciTech Connect

    Liu, F. X.; Liaw, Peter K; Jiang, W. H.; Chiang, C L; Gao, Yanfei; Guan, Y F; Chu, J. P.; Rack, P. D.

    2007-01-01

    Zr-based glass-forming metallic films were coated on a 316L stainless steel and a Ni-based alloy by the magnetron-sputter deposition. Four-point-bending fatigue tests were conducted on those coated materials with the film surface on the tensile side. Results showed that the fatigue life and fatigue-endurance limit of the materials could be considerably improved, and the enhancements vary with the maximum applied stress and the substrate material. Fractographs showed that the film remained well adhered to the substrate even after the severe plastic deformation. Surface-roughness measurements indicated the improvement of the surface finishes due to the deposition of the glass-forming film. Nanoindentation test results suggested that the thin film exhibited both high yield strength and good ductility. The reduction of the surface roughness, good adhesion between the film and the substrate, and the excellent strength and ductility of the glass-forming metallic film are the major factors for the fatigue-resistance enhancements of the coated material. A micromechanical model is developed to illustrate the mechanisms of fatigue-resistance enhancements through the interaction between the amorphous film and the substrate slip bands.

  2. Experimental investigation of fatigue in a cantilever energy harvesting beam

    NASA Astrophysics Data System (ADS)

    Avvari, Panduranga Vittal; Yang, Yaowen; Liu, Peiwen; Soh, Chee Kiong

    2015-03-01

    Over the last decade, cantilever energy harvesters gained immense popularity owing to the simplicity of the design and piezoelectric energy harvesting (PEH) using the cantilever design has undergone considerable evolution. The major drawback of a vibrating cantilever beam is its vulnerability to fatigue over a period of time. This article brings forth an experimental investigation into the phenomenon of fatigue of a PEH cantilever beam. As there has been very little literature reported in this area, an effort has been made to scrutinize the damage due to fatigue in a linear vibrating cantilever PEH beam consisting of an aluminum substrate with a piezoelectric macro-fiber composite (MFC) patch attached near the root of the beam and a tip mass attached to the beam. The beam was subjected to transverse vibrations and the behavior of the open circuit voltage was recorded with passing time. Moreover, electro-mechanical admittance readings were obtained periodically using the same MFC patch as a Structural health monitoring (SHM) sensor to assess the health of the PEH beam. The results show that with passing time the PEH beam underwent fatigue in both the substrate and MFC, which is observed in a complimentary trend in the voltage and admittance readings. The claim is further supported using the variation of root mean square deviation (RMSD) of the real part of admittance (conductance) readings. Thus, this study concludes that the fatigue issue should be addressed in the design of PEH for long term vibration energy harvesting.

  3. Computational simulation of acoustic fatigue for hot composite structures

    NASA Technical Reports Server (NTRS)

    Singhal, Surendra N.; Murthy, Pappu L. N.; Chamis, Christos C.; Nagpal, Vinod K.; Sutjahjo, Edhi

    1991-01-01

    Predictive methods/computer codes for the computational simulation of acoustic fatigue resistance of hot composite structures subjected to acoustic excitation emanating from an adjacent vibrating component are discussed. Select codes developed over the past two decades at the NASA Lewis Research Center are used. The codes include computation of acoustic noise generated from a vibrating component, degradation in material properties of a composite laminate at use temperature, dynamic response of acoustically excited hot multilayered composite structure, degradation in the first ply strength of the excited structure due to acoustic loading, and acoustic fatigue resistance of the excited structure, including the propulsion environment. Effects of the laminate lay-up and environment on the acoustic fatigue life are evaluated. The results show that, by keeping the angled plies on the outer surface of the laminate, a substantial increase in the acoustic fatigue life is obtained. The effect of environment (temperature and moisture) is to relieve the residual stresses leading to an increase in the acoustic fatigue life of the excited panel.

  4. Probabilistic Simulation for Combined Cycle Fatigue in Composites

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.

    2010-01-01

    A methodology to compute probabilistic fatigue life of polymer matrix laminated composites has been developed and demonstrated. Matrix degradation effects caused by long term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress dependent multifactor interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/- 45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical cyclic loads and low thermal cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical cyclic loads and high thermal cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

  5. Exercise and Fatigue in Adolescent and Young Adult Survivors of Hodgkin Lymphoma: A Report from the Children's Oncology Group.

    PubMed

    Macpherson, Catherine Fiona; Hooke, Mary C; Friedman, Debra L; Campbell, Kristin; Withycombe, Janice; Schwartz, Cindy L; Kelly, Kara; Meza, Jane

    2015-09-01

    Fatigue is a significant problem for adolescent and young adult (AYA) Hodgkin lymphoma (HL) survivors. The relationship between exercise and fatigue is complex. This study explored the trajectory of and the relationship between exercise and fatigue over 36 months post-therapy in a cohort of 103 AYA-aged HL survivors treated on Children's Oncology Group (COG) study AHOD0031. Descriptive statistics and generalized estimating equations were used in this secondary data analysis. Exercise and fatigue improved over time but were unrelated; amount of exercise at end of therapy predicted amount of exercise at 12 (p = 0.02) and 36 (p = 0.0008) months post-therapy.

  6. Effect of material heat treatment on fatigue crack initiation in austenitic stainless steels in LWR environments.

    SciTech Connect

    Chopra, O. K.; Alexandreanu, B.; Shack, W. J.; Energy Technology

    2005-07-31

    The ASME Boiler and Pressure Vessel Code provides rules for the design of Class 1 components of nuclear power plants. Figures I-9.1 through I-9.6 of Appendix I to Section III of the Code specify design curves for applicable structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. The existing fatigue strain-vs.-life ({var_epsilon}-N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping steels. Under certain environmental and loading conditions, fatigue lives of austenitic stainless steels (SSs) can be a factor of 20 lower in water than in air. This report presents experimental data on the effect of heat treatment on fatigue crack initiation in austenitic Type 304 SS in LWR coolant environments. A detailed metallographic examination of fatigue test specimens was performed to characterize the crack morphology and fracture morphology. The key material, loading, and environmental parameters and their effect on the fatigue life of these steels are also described. Statistical models are presented for estimating the fatigue {var_epsilon}-N curves for austenitic SSs as a function of material, loading, and environmental parameters. Two methods for incorporating the effects of LWR coolant environments into the ASME Code fatigue evaluations are presented.

  7. Damage mechanics characterization on fatigue behavior of a solder joint material

    SciTech Connect

    Chow, C.L.; Yang, F.; Fang, H.E.

    1998-08-01

    This paper presents the first part of a comprehensive mechanics approach capable of predicting the integrity and reliability of solder joint material under fatigue loading without viscoplastic damage considerations. A separate report will be made to present a comprehensive damage model describing life prediction of the solder material under thermomechanical fatigue loading. The method is based on a theory of damage mechanics which makes possible a macroscopic description of the successive material deterioration caused by the presence of microcracks/voids in engineering materials. A damage mechanics model based on the thermodynamic theory of irreversible processes with internal state variables is proposed and used to provide a unified approach in characterizing the cyclic behavior of a typical solder material. With the introduction of a damage effect tensor, the constitutive equations are derived to enable the formulation of a fatigue damage dissipative potential function and a fatigue damage criterion. The fatigue evolution is subsequently developed based on the hypothesis that the overall damage is induced by the accumulation of fatigue and plastic damage. This damage mechanics approach offers a systematic and versatile means that is effective in modeling the entire process of material failure ranging from damage initiation and propagation leading eventually to macro-crack initiation and growth. As the model takes into account the load history effect and the interaction between plasticity damage and fatigue damage, with the aid of a modified general purpose finite element program, the method can readily be applied to estimate the fatigue life of solder joints under different loading conditions.

  8. A study on the influence of microstructure on small fatigue cracks

    NASA Astrophysics Data System (ADS)

    Castelluccio, Gustavo M.

    In spite of its significance in industrial applications, the prediction of the influence of microstructure on the early stages of crack formation and growth in engineering alloys remains underdeveloped. The formation and early growth of fatigue cracks in the high cycle fatigue regime lasts for much of the fatigue life, and it is strongly influenced by microstructural features such as grain size, twins and morphological and crystallographic texture. However, most fatigue models do not predict the in uence of the microstructure on early stages of crack formation, or they employ parameters that should be calibrated with experimental data from specimens with microstructures of interest. These post facto strategies are adequate to characterize materials, but they are not fully appropriate to aid in the design of fatigue-resistant engineering alloys. This thesis considers finite element computational models that explicitly render the microstructure of selected FCC metallic systems and introduces a fatigue methodology that estimates transgranular and intergranular fatigue growth for microstructurally small cracks. The driving forces for both failure modes are assessed by means of fatigue indicators, which are used along with life correlations to estimate the fatigue life. Furthermore, cracks with meandering paths are modeled by considering crack growth on a grain-by-grain basis with a damage model embedded analytically to account for stress and strain redistribution as the cracks extend. The methodology is implemented using a crystal plasticity constitutive model calibrated for studying the effect of microstructure on early fatigue life of a powder processed Ni-base RR1000 superalloy at elevated temperature under high cycle fatigue conditions. This alloy is employed for aircraft turbine engine disks, which undergo a thermomechanical production process to produce a controlled bimodal grain size distribution. The prediction of the fatigue life for this complex

  9. Review of the margins for ASME code fatigue design curve - effects of surface roughness and material variability.

    SciTech Connect

    Chopra, O. K.; Shack, W. J.; Energy Technology

    2003-10-03

    The ASME Boiler and Pressure Vessel Code provides rules for the construction of nuclear power plant components. The Code specifies fatigue design curves for structural materials. However, the effects of light water reactor (LWR) coolant environments are not explicitly addressed by the Code design curves. Existing fatigue strain-vs.-life ({var_epsilon}-N) data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of pressure vessel and piping ste