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Sample records for based fatigue monitoring

  1. Automatic fatigue monitoring based on real loads. Live demonstration

    International Nuclear Information System (INIS)

    Bergholz, Steffen; Rudolph, Juergen; Bruckmueller, Florian; Heinz, Benedikt; Jouan, Benoit

    2012-01-01

    The fatigue assessment of power plant components based on local fatigue monitoring approaches is an essential part of the integrity concept and modern lifetime management. An integral approach like the AREVA Fatigue Concept (AFC) basically consists of two essential modules: realistic determination of occurring operational thermal loads by means of a high end fatigue monitoring system and related highly qualified fatigue assessment methods and tools. The fatigue monitoring system delivers continuously realistic load data at the fatigue relevant locations. Consequently, realistic operational load sequences are available as input data for all ensuing fatigue analyses. This way, realistic load data are available and qualified fatigue usage factors can be determined. The mode of operation of the fatigue monitoring system will be explained in the framework of a live demonstration by means of the FAMOSi (i = integrated) demonstration wall. The workflow starts with the continuous online measurement of outer wall temperatures transients on a pipe. Visualization is implemented within the FAMOSi viewer software. In a second step, inner wall temperatures are directly calculated. In a third step, the resulting linearly elastic stress history will be calculated as the basis for subsequent code conforming fatigue assessment. Subsequently, the related advanced fatigue assessment methods of the three staged AFC-approach are addressed.

  2. In service monitoring based on fatigue analyses, possibilities and limitations

    International Nuclear Information System (INIS)

    Dittmar, S.; Binder, F.

    2004-01-01

    German LWR reactors are equipped with monitoring systems which are to enable a comparison of real transients with load case catalogues and fatigue catalogues for fatigue analyses. The information accuracy depends on the accuracy of measurements, on the consideration of parameters influencing fatigue (medium, component surface, component size, etc.), and on the accuracy of the load analyses. The contribution attempts a critical evaluation, also inview of the fact that real fatigue damage often are impossible to quantify on the basis of fatigue analyses at a later stage. The effects of the consideration or non-consideration of various influencing factors are discussed, as well as the consequences of the scatter of material characteristics on which the analyses are based. Possible measures to be taken in operational monitoring are derived. (orig.) [de

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

    Science.gov (United States)

    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

  4. SI:FatiguePro 4 Advanced Approach for Fatigue Monitoring

    International Nuclear Information System (INIS)

    Evon, Keith; Gilman, Tim; Carney, Curt

    2012-01-01

    Many nuclear plants are making commitments to implement fatigue monitoring systems in support of license renewal. Current fatigue monitoring systems use the methodology of ASME Code Subarticle NB-3200, which is a design code intended to compute a bounding cumulative usage factor (CUF). The first generation of fatigue monitoring software utilized a simplified, single stress term assumption and classical stress cycle-counting methods that take order into account such as Rainflow or Ordered Overall Range counting. Recently, the NRC has indicated in Regulatory Issue Summary 2008-30 that any fatigue analyses in support of License Renewal should use ASME Code Section III methodologies considering all six stress components. In addition, fatigue calculations for the license renewal term are required to consider the effects of environment. The implementation of a six stress term NB-3200 fatigue calculation to a Boiling Water Reactor (BWR) feedwater nozzle, including environmental effects, is the topic of this paper. Differences in results between the advanced methodology and the simplified methodology are discussed. (author)

  5. FAMOSi: AREVA's new fatigue monitoring system

    International Nuclear Information System (INIS)

    Abib, E.; Heinz, B.

    2015-01-01

    With its local instrumentation, the Fatigue Monitoring System integrated (FAMOSi) is able to detect real thermal loadings like thermal stratification at the primary and secondary piping system. These thermal loadings are the basis for a reliable stress and fatigue evaluation and an essential part for plant lifetime extension programs. FAMOSi uses a fatigue estimation method for an on-line overview about the fatigue status of the plant's components. Detailed fatigue calculations under consideration of environmental assisted fatigue effects were done with the off-line part of the system. This contributes to optimize the operating modes or, to detect malfunctions of components like leaking valves. FAMOSi is used in several power plants in Europe and across the world to reach a better knowledge of plant behavior during start-up, shut-down, spray events or steam generator charging. In some lifetime extension programs, the exchange of heavy components could be avoided due to realistic stress and fatigue calculation based on real thermal loadings. Fatigue monitoring with FAMOSi contributes to cost savings, introduces condition based maintenance and provides a solid basis for life time extension. (authors)

  6. Application of fatigue monitoring system in PWR nuclear power plant

    International Nuclear Information System (INIS)

    Piao Lei

    2014-01-01

    Fatigue failure is one form of equipment failure of nuclear power plant, influencing equipment lifetime and lifetime extension. Fatigue monitoring system can track real thermal transient at fatigue sensitive components, establish a basis for fatigue analyses based on realistic operating loads, identify unexpected operational transients, optimize the plant behavior by improved operating modes, provide supporting data for lifetime management, enhance security of plant and reduce economical loss. Fatigue monitoring system has been applied in many plants and is required to be applied in Generation-III nuclear power plant. It is necessary to develop the fatigue monitoring system with independent intellectual property rights and improve the competitiveness of domestic Generation-III nuclear power technology. (author)

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

    International Nuclear Information System (INIS)

    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

  8. Individual aircraft life monitoring: An engineering approach for fatigue damage evaluation

    Directory of Open Access Journals (Sweden)

    Rui JIAO

    2018-04-01

    Full Text Available Individual aircraft life monitoring is required to ensure safety and economy of aircraft structure, and fatigue damage evaluation based on collected operational data of aircraft is an integral part of it. To improve the accuracy and facilitate the application, this paper proposes an engineering approach to evaluate fatigue damage and predict fatigue life for critical structures in fatigue monitoring. In this approach, traditional nominal stress method is applied to back calculate the S-N curve parameters of the realistic structure details based on full-scale fatigue test data. Then the S-N curve and Miner’s rule are adopted in damage estimation and fatigue life analysis for critical locations under individual load spectra. The relationship between relative small crack length and fatigue life can also be predicted with this approach. Specimens of 7B04-T74 aluminum alloy and TA15M titanium alloy are fatigue tested under two types of load spectra, and there is a good agreement between the experimental results and analysis results. Furthermore, the issue concerning scatter factor in individual aircraft damage estimation is also discussed. Keywords: Fatigue damage, Fatigue monitoring, Fatigue test, Scatter factor, S-N curve

  9. Monitoring and Managing Fatigue in Basketball

    Directory of Open Access Journals (Sweden)

    Toby Edwards

    2018-02-01

    Full Text Available The sport of basketball exposes athletes to frequent high intensity movements including sprinting, jumping, accelerations, decelerations and changes of direction during training and competition which can lead to acute and accumulated chronic fatigue. Fatigue may affect the ability of the athlete to perform over the course of a lengthy season. The ability of practitioners to quantify the workload and subsequent fatigue in basketball athletes in order to monitor and manage fatigue levels may be beneficial in maintaining high levels of performance and preventing unfavorable physical and physiological training adaptations. There is currently limited research quantifying training or competition workload outside of time motion analysis in basketball. In addition, systematic research investigating methods to monitor and manage athlete fatigue in basketball throughout a season is scarce. To effectively optimize and maintain peak training and playing performance throughout a basketball season, potential workload and fatigue monitoring strategies need to be discussed.

  10. Fatigue Monitoring Tool for Airline Operators (FMT

    Directory of Open Access Journals (Sweden)

    Gislason Sigurdur Hrafn

    2017-12-01

    Full Text Available A Fatigue Monitoring Tool (FMT model was constructed for an operational airline in order to manage the fatigue levels of their crews in accordance with Fatigue Risk Management System (FRMS practices. This article describes the implementation of the Fatigue Monitoring Tool model and the airline’s aims to put the recent scientific findings on aviation fatigue into practical use. The model consists of proxy points allotted to various duties and rest periods.

  11. A conductive grating sensor for online quantitative monitoring of fatigue crack

    Science.gov (United States)

    Li, Peiyuan; Cheng, Li; Yan, Xiaojun; Jiao, Shengbo; Li, Yakun

    2018-05-01

    Online quantitative monitoring of crack damage due to fatigue is a critical challenge for structural health monitoring systems assessing structural safety. To achieve online quantitative monitoring of fatigue crack, a novel conductive grating sensor based on the principle of electrical potential difference is proposed. The sensor consists of equidistant grating channels to monitor the fatigue crack length and conductive bars to provide the circuit path. An online crack monitoring system is established to verify the sensor's capability. The experimental results prove that the sensor is suitable for online quantitative monitoring of fatigue crack. A finite element model for the sensor is also developed to optimize the sensitivity of crack monitoring, which is defined by the rate of sensor resistance change caused by the break of the first grating channel. Analysis of the model shows that the sensor sensitivity can be enhanced by reducing the number of grating channels and increasing their resistance and reducing the resistance of the conductive bar.

  12. Fatigue-free PZT-based nanocomposites

    Energy Technology Data Exchange (ETDEWEB)

    Hwang, H J; Sando, M [Nat. Ind. Res. Inst., Nagoya (Japan); Tajima, K [Synergy Ceramics Lab., Fine Ceramics Research Association, Nagoya (Japan); Niihara, K [ISIR, Osaka Univ., Mihogaoka, Ibaraki (Japan)

    1999-03-01

    The goal of this study is to fabricate fatigue-free piezoelectrics-based nanocomposites. Lead zirconate titanate (PZT) and metallic platinum (Pt) were selected as a matrix and secondary phase dispersoid. Fine Pt particles were homogeneously dispersed in the PZT matrix. Fatigue properties of the unpoled PZT-based nanocomposite under electrical cyclic loading were investigated. The electrical-field-induced crack growth was monitored by an optical microscope, and it depended on the number of cycles the sample was subjected to. Resistance to fatigue was significantly enhanced in the nanocomposite. The excellent fatigue behavior of the PZT/Pt nanocomposites may result from the grain boundary strenghtening due to the interaction between the matrix and Pt particles. (orig.) 8 refs.

  13. Fatigue evaluation for Tsing Ma Bridge using structural health monitoring data

    Science.gov (United States)

    Chan, Hung-tin Tommy; Ko, Jan Ming; Li, Zhao-Xia

    2001-08-01

    Fatigue assessment for the Tsing Ma Bridge (TMB) are presented based on the British standard BS5400 and the real-time structural health monitoring data under railway loading. TMB, as an essential portion of transport network for the Hong Kong airport, is the longest suspension bridge in the world carrying both highway and railway traffic. The bridge design has been mainly based on BS5400. A structural health monitoring system - Wind and Structural Health Monitoring System (WASHMS) for TMB has been operated since the bridge commissioning in May 1997. In order to assess the fatigue behavior of TMB under railway loading, strain gauges were installed on the bridge deck to measure the strain-time histories as soon as the bridge is loaded by a standard railway loading due to the service of an actual train. The strain-time history data at the critical members are then used to determine the stress spectrum, of which the rainflow method recommended for railway bridges by BS5400 is applied to count cycles of stress range. Miner's law is employed to evaluate fatigue damage and remaining service life of the bridge. The evaluated results of fatigue damage and remaining service life would help us to well understand about the fatigue design of the bridge and status in fatigue accumulation.

  14. Monitoring driver fatigue using a single-channel electroencephalographic device: A validation study by gaze-based, driving performance, and subjective data.

    Science.gov (United States)

    Morales, José M; Díaz-Piedra, Carolina; Rieiro, Héctor; Roca-González, Joaquín; Romero, Samuel; Catena, Andrés; Fuentes, Luis J; Di Stasi, Leandro L

    2017-12-01

    Driver fatigue can impair performance as much as alcohol does. It is the most important road safety concern, causing thousands of accidents and fatalities every year. Thanks to technological developments, wearable, single-channel EEG devices are now getting considerable attention as fatigue monitors, as they could help drivers to assess their own levels of fatigue and, therefore, prevent the deterioration of performance. However, the few studies that have used single-channel EEG devices to investigate the physiological effects of driver fatigue have had inconsistent results, and the question of whether we can monitor driver fatigue reliably with these EEG devices remains open. Here, we assessed the validity of a single-channel EEG device (TGAM-based chip) to monitor changes in mental state (from alertness to fatigue). Fifteen drivers performed a 2-h simulated driving task while we recorded, simultaneously, their prefrontal brain activity and saccadic velocity. We used saccadic velocity as the reference index of fatigue. We also collected subjective ratings of alertness and fatigue, as well as driving performance. We found that the power spectra of the delta EEG band showed an inverted U-shaped quadratic trend (EEG power spectra increased for the first hour and half, and decreased during the last thirty minutes), while the power spectra of the beta band linearly increased as the driving session progressed. Coherently, saccadic velocity linearly decreased and speeding time increased, suggesting a clear effect of fatigue. Subjective data corroborated these conclusions. Overall, our results suggest that the TGAM-based chip EEG device is able to detect changes in mental state while performing a complex and dynamic everyday task as driving. Copyright © 2017 Elsevier Ltd. All rights reserved.

  15. Keep fatigue usage low for LTO. Benefits of load monitoring and related fatigue evaluations for long term operation

    International Nuclear Information System (INIS)

    Rothenhoefer, H.; Koenig, G.

    2012-01-01

    Design fatigue calculations normally cover a service life of 40 years. Based on design transients with a specified number of cycles the evaluations have to prove that the fatigue usage after 40 years will stay below 1. In 40+ years of operation real loads can differ much from design loads so that premature ageing can occur. For long term operation, monitoring of real loads and detailed fatigue analysis for selected locations can be used to optimize operational modes in order to reduce the loads causing fatigue. As a result fatigue usage can be kept below 1 even for 60+ years. (author)

  16. Automated modal tracking and fatigue assessment of a wind turbine based on continuous dynamic monitoring

    Directory of Open Access Journals (Sweden)

    Oliveira Gustavo

    2015-01-01

    Full Text Available The paper describes the implementation of a dynamic monitoring system at a 2.0 MW onshore wind turbine. The system is composed by two components aiming at the structural integrity and fatigue assessment. The first component enables the continuous tracking of modal characteristics of the wind turbine (natural frequency values, modal damping ratios and mode shapes in order to detect abnormal deviations of these properties, which may be caused by the occurrence of structural damage. On the other hand, the second component allows the estimation of the remaining fatigue lifetime of the structure based on the analysis of the measured cycles of structural vibration.

  17. Reliability analysis of offshore structures using OMA based fatigue stresses

    DEFF Research Database (Denmark)

    Silva Nabuco, Bruna; Aissani, Amina; Glindtvad Tarpø, Marius

    2017-01-01

    focus is on the uncertainty observed on the different stresses used to predict the damage. This uncertainty can be reduced by Modal Based Fatigue Monitoring which is a technique based on continuously measuring of the accelerations in few points of the structure with the use of accelerometers known...... points of the structure, the stress history can be calculated in any arbitrary point of the structure. The accuracy of the estimated actual stress is analyzed by experimental tests on a scale model where the obtained stresses are compared to strain gauges measurements. After evaluating the fatigue...... stresses directly from the operational response of the structure, a reliability analysis is performed in order to estimate the reliability of using Modal Based Fatigue Monitoring for long term fatigue studies....

  18. Real-time Alarm Monitoring System for Detecting Driver Fatigue in Wireless Areas

    Directory of Open Access Journals (Sweden)

    Rongrong Fu

    2017-04-01

    Full Text Available The purpose of this paper was to develop a real-time alarm monitoring system that can detect the fatigue driving state through wireless communication. The drivers’ electroencephalogram (EEG signals were recorded from occipital electrodes. Seven EEG rhythms with different frequency bands as gamma, hbeta, beta, sigma, alpha, theta and delta waves were extracted. They were simultaneously assessed using relative operating characteristic (ROC curves and grey relational analysis to select one as the fatigue feature. The research results showed that the performance of theta wave was the best one. Therefore, theta wave was used as fatigue feature in the following alarm device. The real-time alarm monitoring system based on the result has been developed, once the threshold was settled by using the data of the first ten minutes driving period. The developed system can detect driver fatigue and give alarm to indicate the onset of fatigue automatically.

  19. On-line fatigue monitoring system for reactor pressure vessel

    International Nuclear Information System (INIS)

    Tokunaga, K.; Sakai, A.; Aoki, T.; Ranganath, S.; Stevens, G.L.

    1994-01-01

    A workstation-based, on-line fatigue monitoring system for tracking fatigue usage applied to an operating boiling water reactor (BWR), Tsuruga Unit-1, is described. The system uses the influence function approach and determines component stresses using temperature, pressure, and flow rate data that are made available via signal taps from previously existing plant sensors. Using plant unique influence functions developed specifically for the feedwater nozzle location, the system calculates stresses as a function of time and computed fatigue usage. The analysis method used to compute fatigue usage complies with MITI Code Notification No.501. Fatigue usage results for an entire fuel cycle are presented and compared to assumed design basis events to confirm that actual plant thermal duty is significantly less severe than originally estimated in the design basis stress report. As a result, the system provides the technical basis to more accurately evaluate actual reactor conditions as well as the justification for plant life extension. (author)

  20. Monitoring Low-Cycle Fatigue Material-Degradation by Ultrasonic Methods

    Directory of Open Access Journals (Sweden)

    R. Himawan

    2010-08-01

    Full Text Available Any system consisting of structural material often undergoes fatigue, which is caused by dynamic load cycle. As a structural system, nuclear power plant is very likely to have low-cycle fatigue at many of its components. Taking into account the importance of monitoring low-cycle fatigue on structural components to prevent them from getting failure, the authors have conducted a work to monitor material degradation caused by low-cycle fatigue by using ultrasonic method. An alloy of Cu-40Zn was used as a test specimen. Ultrasonic water immersion procedure was employed in this ultrasonic test. The probe used is a focusing type and has frequency as high as 15 MHz. The specimen area tested is in the middle part divided into 14 points × 23 points. The results, which were frequency spectrums, were analyzed using two parameters: frequency spectrum peak intensity and attenuation function gradient. The analysis indicates that peak intensity increases at the beginning of load cycle and then decreases. Meanwhile, gradient of attenuation function is lower at the beginning of fatigue process, and then consistently gets higher. It concludes that low-fatigue material degradation can be monitored by using ultrasonic method.

  1. International experience feedback on fatigue monitoring systems for nuclear power plants

    International Nuclear Information System (INIS)

    Morilhat, P.

    1997-01-01

    From the very beginning of electro-nuclear programmes the need has become internationally obvious to develop systems aiming at automation and improvement of monitoring of the transients stressing the main mechanical components of nuclear units, by checking the conservativeness of the design no longer from a comparison of causes (temperature and pressure variations) but by directly assessing the results (stresses and linked damage). Prototypes of such systems have appeared since the middle of the 1980's mainly in France, the USA and Germany, and manufacturing them has since continued. Several years of development and on site testing of prototypes of fatigue measuring devices designed by the R and D Direction have enabled contacts with the developers of similar systems to be established and, in some cases, comparisons to be made. The experience accumulated in the use of such systems, both in France and abroad from now on makes a first experience feedback possible. The fatigue measuring device concept is based on a succession of elementary modules which enable the information received from the unit to be processed, first in the form of transient counting (transient meters), then in the form of mechanical diagnosis (fatigue monitoring systems). Among the systems in operation some provide actually only the transient meter part while others link transient meters and fatigue meters (EDF, EPRI and MITSUBISHI systems and some versions of the SIEMENS system). Moreover, numerous systems require, in addition to unit operation instrumentation, specific instrumentation located in monitored areas. The number of devices in operation has not stopped growing since the middle of the 80's to reach 53 systems working in 1996. The biggest developers are EPRI and its consultant Structural Integrity Associates (FatiguePro system), SIEMENS (FAMOS system) and EDF whose gradual implementation of SYSFAC from '96 is going to make its share particularly increase. Technical experience feedback

  2. A Wireless Fatigue Monitoring System Utilizing a Bio-Inspired Tree Ring Data Tracking Technique

    Directory of Open Access Journals (Sweden)

    Shi Bai

    2014-03-01

    Full Text Available Fatigue, a hot scientific research topic for centuries, can trigger sudden failure of critical structures such as aircraft and railway systems, resulting in enormous casualties as well as economic losses. The fatigue life of certain structures is intrinsically random and few monitoring techniques are capable of tracking the full life-cycle fatigue damage. In this paper, a novel in-situ wireless real-time fatigue monitoring system using a bio-inspired tree ring data tracking technique is proposed. The general framework, methodology, and verification of this intelligent system are discussed in details. The rain-flow counting (RFC method is adopted as the core algorithm which quantifies fatigue damages, and Digital Signal Processing (DSP is introduced as the core module for data collection and analysis. Laboratory test results based on strain gauges and polyvinylidene fluoride (PVDF sensors have shown that the developed intelligent system can provide a reliable quick feedback and early warning of fatigue failure. With the merits of low cost, high accuracy and great reliability, the developed wireless fatigue sensing system can be further applied to mechanical engineering, civil infrastructures, transportation systems, aerospace engineering, etc.

  3. A wireless fatigue monitoring system utilizing a bio-inspired tree ring data tracking technique.

    Science.gov (United States)

    Bai, Shi; Li, Xuan; Xie, Zhaohui; Zhou, Zhi; Ou, Jinping

    2014-03-05

    Fatigue, a hot scientific research topic for centuries, can trigger sudden failure of critical structures such as aircraft and railway systems, resulting in enormous casualties as well as economic losses. The fatigue life of certain structures is intrinsically random and few monitoring techniques are capable of tracking the full life-cycle fatigue damage. In this paper, a novel in-situ wireless real-time fatigue monitoring system using a bio-inspired tree ring data tracking technique is proposed. The general framework, methodology, and verification of this intelligent system are discussed in details. The rain-flow counting (RFC) method is adopted as the core algorithm which quantifies fatigue damages, and Digital Signal Processing (DSP) is introduced as the core module for data collection and analysis. Laboratory test results based on strain gauges and polyvinylidene fluoride (PVDF) sensors have shown that the developed intelligent system can provide a reliable quick feedback and early warning of fatigue failure. With the merits of low cost, high accuracy and great reliability, the developed wireless fatigue sensing system can be further applied to mechanical engineering, civil infrastructures, transportation systems, aerospace engineering, etc.

  4. Concept of a new method for fatigue monitoring of nuclear power plant components

    International Nuclear Information System (INIS)

    Zafosnik, M.; Cizelj, L.

    2007-01-01

    Fatigue is one of the well-understood aging mechanisms affecting mechanical components in many industrial facilities including nuclear power plants. Operational experience of nuclear power plants worldwide to date confirmed adequate design of safety related components against fatigue. In some cases however, for example when the plant life extension is envisioned, it may be very useful to monitor the remaining fatigue life of safety related components. Nuclear power plants components are classified into safety classes regarding their importance in mitigating the consequences of hypothetic accidents. Service life of components subjected to fatigue loading can be estimated with Usage Factor uk. A concept of the new method aiming both at monitoring the current state of the component and predicting its remaining lifetime in the life-extension conditions is presented. The method is based on determination of partial Usage Factor of components in which operating transients will be considered and compared to design transients. (author)

  5. Mechanomyography-Based Wearable Monitor of Quasi-Isometric Muscle Fatigue for Motor Neural Prostheses.

    Science.gov (United States)

    Krueger, Eddy; Popović-Maneski, Lana; Nohama, Percy

    2018-02-01

    A motor neural prosthesis based on surface functional electrical stimulation (sFES) can restore functional movement (e.g., standing, walking) in patients with a spinal cord injury (SCI). sFES generates muscle contractions in antigravity muscles and allows balance-assisted standing. This induced standing has several benefits, such as improved cardiovascular function, decreased incidence of urinary infections, reduced joint contractures, and muscle atrophy. The duration of sFES assisted standing is limited due to the quick onset of muscle fatigue. Currently, there is no method available to reliably estimate real-time muscle fatigue during sFES. Simply monitoring the M-wave changes is not suitable due to the high signal disturbances that arise during multi-channel electrical stimulation. Mechanomyography (MMG) is immune to electrical stimulation artifacts and can be used to detect subtle vibrations on the surface of the skin related to activation of the underlying muscle's motor units (MU). The aim of this study was to develop a method for detecting muscle fatigue brought on by sFES. The method was tested in three different heads of the quadriceps muscle in SCI patients during electrically elicited quasi-isometric contraction. Six spinal cord-injured male volunteers, with no voluntary control of the quadriceps muscle participated in the study. Electrical bursts of voltage-controlled monophasic square pulses at frequencies of 1 kHz (50% duty cycle) at 50 Hz (15% duty cycle) were used to generate thigh muscle contractions that controlled the knee joint in the sagittal plane. The pulse amplitudes were set to position the knee joint at a 5° angle from the horizontal plane and when the knee angle dropped to 20° (e.g., the quadriceps were unable to hold the lower leg in the desired position), the test was terminated. Two data segments lasting 10 s each, at the beginning and end of each test, were analyzed. The muscle contraction was assessed by MMG sensors positioned on

  6. Mental fatigue, motivation and action monitoring

    NARCIS (Netherlands)

    Boksem, MAS; Meijman, TF; Lorist, MM

    In this study we examined whether the effects of mental fatigue on behaviour are due to reduced action monitoring as indexed by the error related negativity (Ne/ERN), N2 and contingent negative variation (CNV) event-related potential (ERP) components. Therefore, we had Subjects perform a task, which

  7. On-line fatigue monitoring and probabilistic assessment of margins

    Energy Technology Data Exchange (ETDEWEB)

    Fournier, I. [Electricite de France, 93 - Saint-Denis (France). Direction des Etudes et Recherches; Morilhat, P. [Electricite de France, 93 - Saint-Denis (France). Direction des Etudes et Recherches

    1995-01-01

    An on-line computer-aided system has been developed by Electricite de France, the French utility, for fatigue monitoring of critical locations in the nuclear steam supply system. This tool, called a fatigue meter, includes as input data plant parameters and is based on some conservative assumptions at several steps of the damage assessment (thermal boundary conditions, stress computation,..). In this paper we present recent developments performed towards a better assessment of margins involved in the complete analysis. The methodology is illustrated with an example showing the influence of uncertainty in plant parameters on the final stress computed at a pressurized water reactor 900MW unit pressurizer surge line nozzle. A second example is shown to illustrate the possibility of defining some transient archetypes. ((orig.)).

  8. Monitoring Poisson’s Ratio Degradation of FRP Composites under Fatigue Loading Using Biaxially Embedded FBG Sensors

    Science.gov (United States)

    Akay, Erdem; Yilmaz, Cagatay; Kocaman, Esat S.; Turkmen, Halit S.; Yildiz, Mehmet

    2016-01-01

    The significance of strain measurement is obvious for the analysis of Fiber-Reinforced Polymer (FRP) composites. Conventional strain measurement methods are sufficient for static testing in general. Nevertheless, if the requirements exceed the capabilities of these conventional methods, more sophisticated techniques are necessary to obtain strain data. Fiber Bragg Grating (FBG) sensors have many advantages for strain measurement over conventional ones. Thus, the present paper suggests a novel method for biaxial strain measurement using embedded FBG sensors during the fatigue testing of FRP composites. Poisson’s ratio and its reduction were monitored for each cyclic loading by using embedded FBG sensors for a given specimen and correlated with the fatigue stages determined based on the variations of the applied fatigue loading and temperature due to the autogenous heating to predict an oncoming failure of the continuous fiber-reinforced epoxy matrix composite specimens under fatigue loading. The results show that FBG sensor technology has a remarkable potential for monitoring the evolution of Poisson’s ratio on a cycle-by-cycle basis, which can reliably be used towards tracking the fatigue stages of composite for structural health monitoring purposes. PMID:28773901

  9. Performance Deterioration of Heavy-Haul Railway Bridges under Fatigue Loading Monitored by a Multisensor System

    Directory of Open Access Journals (Sweden)

    Zhiwu Yu

    2018-01-01

    Full Text Available Heavy-haul railway bridges play an increasingly essential role in the transportation in China due to the increasing transport volume. The performance deterioration of the scale models of a typical heavy-haul railway bridge under fatigue loading is monitored in this work, based on a multisensor system including the fiber-reinforced polymer optical fiber Bragg grating and electrical resistance strain gauges, linear variable displacement transducer, and accelerometer. Specifically, by monitoring/observing on the failure mode, fatigue life, load-midspan deflection response, material strain development, and so forth, this work develops an S-N model by comparing the relationship between fatigue life and rebar stress range with that between fatigue life and load level and proposes a damage evolution model considering the coupling of the stiffness degradation and inelastic deformation of specimens. It is found that the fatigue life of specimens is determined by the fatigue life of the rebar at the bottom and it may be lower than 2.0 million cycles with a 30-ton axle weight when environmental factors are taken into account. The predictions of the models agree well with experimental results. Therefore, this work furthers the understanding of the fatigue performance deterioration of the bridges by using a multisensor system.

  10. A Wireless Fatigue Monitoring System Utilizing a Bio-Inspired Tree Ring Data Tracking Technique

    OpenAIRE

    Bai, Shi; Li, Xuan; Xie, Zhaohui; Zhou, Zhi; Ou, Jinping

    2014-01-01

    Fatigue, a hot scientific research topic for centuries, can trigger sudden failure of critical structures such as aircraft and railway systems, resulting in enormous casualties as well as economic losses. The fatigue life of certain structures is intrinsically random and few monitoring techniques are capable of tracking the full life-cycle fatigue damage. In this paper, a novel in-situ wireless real-time fatigue monitoring system using a bio-inspired tree ring data tracking technique is propo...

  11. Mechanomyography versus Electromyography, in monitoring the muscular fatigue

    Directory of Open Access Journals (Sweden)

    Tarata Mihai T

    2003-02-01

    Full Text Available Abstract Background The use of the mechanomyogram (MMG which detects muscular vibrations generated by fused individual fiber twitches has been refined. The study addresses a comparison of the MMG and surface electromyogram (SEMG in monitoring muscle fatigue. Methods The SEMG and MMG were recorded simultaneously from the same territory of motor units in two muscles (Biceps, Brachioradialis of the human (n = 18, during sustained contraction at 25 % MVC (maximal voluntary contraction. Results The RMS (root mean square of the SEMG and MMG increased with advancing fatigue; MF (median frequency of the PSD (power density spectra progressively decreased from the onset of the contraction. These findings (both muscles, all subjects, demonstrate both through the SEMG and MMG a central component of the fatigue. The MF regression slopes of MMG were closer to each other between men and women (Biceps 1.55%; Brachialis 13.2% than were the SEMG MF slopes (Biceps 25.32%; Brachialis 17.72%, which shows a smaller inter-sex variability for the MMG vs. SEMG. Conclusion The study presents another quantitative comparison (MF, RMS of MMG and SEMG, showing that MMG signal can be used for indication of the degree of muscle activation and for monitoring the muscle fatigue when the application of SEMG is not feasible (chronical implants, adverse environments contaminated by electrical noise.

  12. Fatigue Damage Monitoring of a Composite Step Lap Joint Using Distributed Optical Fibre Sensors

    Science.gov (United States)

    Wong, Leslie; Chowdhury, Nabil; Wang, John; Chiu, Wing Kong; Kodikara, Jayantha

    2016-01-01

    Over the past few decades, there has been a considerable interest in the use of distributed optical fibre sensors (DOFS) for structural health monitoring of composite structures. In aerospace-related work, health monitoring of the adhesive joints of composites has become more significant, as they can suffer from cracking and delamination, which can have a significant impact on the integrity of the joint. In this paper, a swept-wavelength interferometry (SWI) based DOFS technique is used to monitor the fatigue in a flush step lap joint composite structure. The presented results will show the potential application of distributed optical fibre sensor for damage detection, as well as monitoring the fatigue crack growth along the bondline of a step lap joint composite structure. The results confirmed that a distributed optical fibre sensor is able to enhance the detection of localised damage in a structure. PMID:28773496

  13. Ultrathin flexible piezoelectric sensors for monitoring eye fatigue

    Science.gov (United States)

    Lü, Chaofeng; Wu, Shuang; Lu, Bingwei; Zhang, Yangyang; Du, Yangkun; Feng, Xue

    2018-02-01

    Eye fatigue is a symptom induced by long-term work of both eyes and brains. Without proper treatment, eye fatigue may incur serious problems. Current studies on detecting eye fatigue mainly focus on computer vision detect technology which can be very unreliable due to occasional bad visual conditions. As a solution, we proposed a wearable conformal in vivo eye fatigue monitoring sensor that contains an array of piezoelectric nanoribbons integrated on an ultrathin flexible substrate. By detecting strains on the skin of eyelid, the sensors may collect information about eye blinking, and, therefore, reveal human’s fatigue state. We first report the design and fabrication of the piezoelectric sensor and experimental characterization of voltage responses of the piezoelectric sensors. Under bending stress, the output voltage curves yield key information about the motion of human eyelid. We also develop a theoretical model to reveal the underlying mechanism of detecting eyelid motion. Both mechanical load test and in vivo test are conducted to convince the working performance of the sensors. With satisfied durability and high sensitivity, this sensor may efficiently detect abnormal eyelid motions, such as overlong closure, high blinking frequency, low closing speed and weak gazing strength, and may hopefully provide feedback for assessing eye fatigue in time so that unexpected situations can be prevented.

  14. Onboard monitoring of fatigue damage rates in the hull girder

    DEFF Research Database (Denmark)

    Nielsen, Ulrik Dam; Jensen, Jørgen Juncher; Pedersen, Preben Terndrup

    2011-01-01

    Most new advanced ships have extensive data collection systems to be used for continuous monitoring of engine and hull performance, for voyage performance evaluation etc. Such systems could be expanded to include also procedures for stress monitoring and for decision support, where the most...... critical wave-induced ship extreme responses and fatigue damage accumulation can be estimated for hypothetical changes in ship course and speed in the automatically estimated wave environment.The aim of this paper is to outline a calculation procedure for fatigue damage rate prediction in hull girders...... taking into account whipping stresses. It is conceptually shown how such a method, which integrates onboard estimation of sea states, can be used to deduce decision support with respect to the accumulated fatigue damage in the hull girder.The paper firstly presents a set of measured full-scale wave...

  15. A novel noncontact electromagnetic field-based sensor for the monitoring of resonant fatigue tests

    International Nuclear Information System (INIS)

    Nam, Si-Byung; Yun, Gun Jin; Binienda, Wieslaw; Carletta, Joan; Kim, Dong-Han

    2011-01-01

    In this paper, a prototype of an electromagnetic field-based (EFB) vibration sensor that uses a novel sensing technique to monitor the resonant fatigue testing of a conductive and/or ferromagnetic target specimen is presented. The distance from the target to a coil within the sensor affects the impedance of the coil. The electronic circuitry for the sensor consists of a relaxation oscillator, an embedded microprocessor module and a high-speed digital-to-analog converter. The impedance of the coil determines the frequency of oscillation of the relaxation oscillator's output, so that vibration of the target causes changes in the oscillation frequency. A timer in the embedded microprocessor module is used to count the oscillations, producing a digital signal that indicates the coil-to-target distance. The digital signal is instantaneously converted to an analog signal to produce the sensor's output. The key technologies proposed include: (1) a novel timer counting method using the input capture functionality and timer of the embedded microprocessor module and (2) significant simplification of the analog electronic circuitry. The performance of the proposed sensor has been verified using AISI 1095 carbon steel and Al6061–T6 aluminum alloy specimens during resonant fatigue tests. The sensor shows a good linearity between displacement amplitudes and output voltages

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

    Science.gov (United States)

    Li, Dongsheng; Cao, Hai

    2012-01-01

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

  17. Assessment of skeletal muscle fatigue of road maintenance workers based on heart rate monitoring and myotonometry

    Directory of Open Access Journals (Sweden)

    Kalkis Henrijs

    2006-07-01

    Full Text Available Abstract Objective This research work is dedicated to occupational health problems caused by ergonomic risks. The research object was road building industry, where workers have to work very intensively, have long work hours, are working in forced/constrained work postures and overstrain during the work specific parts of their bodies. The aim of this study was to evaluate the work heaviness degree and to estimate the muscle fatigue of workers after one week work cycle. The study group consisted of 10 road construction and maintenance workers and 10 pavers aged between 20 and 60 years. Methods Physical load were analyzed by measuring heart rate (HR, work postures (OWAS and perceived exertion (RPE. Assessments of the muscles strain and functional state (tone were carried out using myotonometric (MYO measurements. The reliability of the statistical processing of heart rate monitoring and myotonometry data was determined using correlating analysis. Results This study showed that that road construction and repairing works should be considered as a hard work according to average metabolic energy consumption 8.1 ± 1.5 kcal/min; paving, in its turn, was a moderately hard work according to 7.2 ± 1.1 kcal/min. Several muscle tone levels were identified allowing subdivision of workers into three conditional categories basing on muscle tone and fatigue: I – absolute muscle relaxation and ability to relax; II – a state of equilibrium, when muscles are able to adapt to the work load and are partly able to relax; and III – muscle fatigue and increased tone. It was also found out that the increase of muscle tone and fatigue mainly depend on workers physical preparedness and length of service, and less – on their age. Conclusion We have concluded that a complex ergonomic analysis consisting of heart rate monitoring, assessment of compulsive working postures and myotonometry is appropriate to assess the work heaviness degree and can provide prognosis of

  18. Stress corrosion and corrosion fatigue crack growth monitoring in metals

    International Nuclear Information System (INIS)

    Senadheera, T.; Shipilov, S.A.

    2003-01-01

    Environmentally assisted cracking (including stress corrosion cracking and corrosion fatigue) is one of the major causes for materials failure in a wide variety of industries. It is extremely important to understand the mechanism(s) of environmentally assisted crack propagation in structural materials so as to choose correctly from among the various possibilities-alloying elements, heat treatment of steels, parameters of cathodic protection, and inhibitors-to prevent in-service failures due to stress corrosion cracking and corrosion fatigue. An important step towards understanding the mechanism of environmentally assisted crack propagation is designing a testing machine for crack growth monitoring and that simultaneously provides measurement of electrochemical parameters. In the present paper, a direct current (DC) potential drop method for monitoring crack propagation in metals and a testing machine that uses this method and allows for measuring electrochemical parameters during stress corrosion and corrosion fatigue crack growth are described. (author)

  19. A fatigue monitoring system based on time-domain and frequency-domain analysis of pulse data

    Science.gov (United States)

    Shen, Jiaai

    2018-04-01

    Fatigue is almost a problem that everyone would face, and a psychosis that everyone hates. If we can test people's fatigue condition and remind them of the tiredness, dangers in life, for instance, traffic accidents and sudden death will be effectively reduced, people's fatigued operations will be avoided. And people can be assisted to have access to their own and others' physical condition in time to alternate work with rest. The article develops a wearable bracelet based on FFT Pulse Frequency Spectrum Analysis and IBI's standard deviation and range calculation, according to people's heart rate (BPM) and inter-beat interval (IBI) while being tired and conscious. The hardware part is based on Arduino, pulse rate sensor, and Bluetooth module, and the software part is relied on network micro database and APP. By doing sample experiment to get more accurate standard value to judge tiredness, we prove that we can judge people's fatigue condition based on heart rate (BPM) and inter-beat interval (IBI).

  20. Monitoring for materials fatigue in nuclear power plant

    International Nuclear Information System (INIS)

    Bartonicek, J.; Hienstorfer, W.

    1991-01-01

    The pressurizer surge line in unit 1 of the GKN nuclear power station belongs to the safety-relevant systems that have been monitored since the year 1987. The results of this in-service monitoring period show this component part experiences temperature fluctuations that have not been specified in the design documents of GKN 1. The in-service monitoring revealed both local and global temperature changes in the entire surge line, so that the resulting real stresses affecting the surge line can be derived and incorporated in a realistic fatigue analysis. (orig.) [de

  1. On-line fatigue monitoring and margins probabilistic assessment

    International Nuclear Information System (INIS)

    Fournier, I.; Morilhat, P.

    1993-01-01

    An on-line computer aided system has been developed by Electricite de France, the French utility, for a fatigue monitoring of critical locations in the nuclear steam supply system. This tool, called fatiguemeter, includes as input data only existing plant parameters and is based on some conservative assumptions at several steps of the damage assessment (thermal boundary conditions, stress computation...). This paper presents recent developments performed toward a better assessing of margins involved in the complete analysis. The methodology is enlightened with an example showing the influence of plant parameters incertitude on the final stress computed at a PWR 900 MW unit pressurizer surge line nozzle. (author)

  2. A methodology for on-line fatigue life monitoring of Indian nuclear power plant components

    International Nuclear Information System (INIS)

    Mukhopadhyay, N.K.; Dutta, B.K.; Kushawaha, H.S.

    1992-01-01

    Fatigue is one of the most important aging effects of nuclear power plant components. Information about accumulation of fatigue helps in assessing structural degradation of the components. This assists in-service inspection and maintenance and may also support future life extension program of a plant. In the present report a methodology is being proposed for monitoring on line fatigue life of nuclear power plant components using available plant instrumentations. Major factors affecting fatigue life of a nuclear power plant components are the fluctuations of temperature, pressure and flow rate. Green's function technique is used in on line fatigue monitoring as computation time is much less than finite element method. A code has been developed which computes temperature and stress Green's functions in 2-D and axisymmetric structure by finite element method due to unit change in various fluid parameters. A post processor has also been developed which computes the temperature and stress responses using corresponding Green's functions and actual fluctuation in fluid parameters. In this post processor, the multiple site problem is solved by superimposing single site Green's function technique. It is also shown that Green's function technique is best suited for on line fatigue life monitoring of nuclear power plant components. (author). 6 refs., 43 figs

  3. Investigating real-time monitoring of fatigue indicators of New Zealand forestry workers.

    Science.gov (United States)

    Bowen, Judy; Hinze, Annika; Griffiths, Christopher

    2017-12-27

    The New Zealand forestry industry has one of the highest fatality and injury rates of any industrial sector in the country. Worker fatigue has been identified as one of the main contributing factors. Currently no independent and objective large data source is available that might support an analysis of this, or provide the basis for ongoing monitoring to further investigate. In order to successfully manage fatigue in the forestry workplace, we must identify suitable ways of detecting it. Industry partners are increasingly looking at monitoring solutions (particularly lightweight, wearable technology) that aim to measure worker activities and physiological metrics in order to determine if they are fatigued. In this article we present the results of studies which investigate whether or not such technology can capture meaningful data in a reliable way that is both practical and usable within the forestry domain. Two series of studies were undertaken with in-situ forestry workers using reaction and decision-making times as a measure of potential impairment, while considering activity levels (via step count and heart rate) and job-roles. We present the results of these studies and further provide a comparison of results across different ambient temperatures (winter vs. summer periods). The results of our studies suggest that it may not be possible to identify correlations between workloads (based on both physical and cognitive stresses) and fatigue measures using in-situ measurements as results are highly personalised to individual workers and can be misleading if the wider context is not also taken into consideration. Copyright © 2017 Elsevier Ltd. All rights reserved.

  4. Structural health monitoring of power plant components based on a local temperature measurement concept

    International Nuclear Information System (INIS)

    Rudolph, Juergen; Bergholz, S.; Hilpert, R.; Jouan, B.; Goetz, A.

    2012-01-01

    The fatigue assessment of power plant components based on fatigue monitoring approaches is an essential part of the integrity concept and modern lifetime management. It is comparable to structural health monitoring approaches in other engineering fields. The methods of fatigue evaluation of nuclear power plant components based on realistic thermal load data measured on the plant are addressed. In this context the Fast Fatigue Evaluation (FFE) and Detailed Fatigue Calculation (DFC) of nuclear power plant components are parts of the three staged approach to lifetime assessment and lifetime management of the AREVA Fatigue Concept (AFC). The three stages Simplified Fatigue Estimation (SFE), Fast Fatigue Evaluation (FFE) and Detailed Fatigue Calculation (DFC) are characterized by increasing calculation effort and decreasing degree of conservatism. Their application is case dependent. The quality of the fatigue lifetime assessment essentially depends on one hand on the fatigue model assumptions and on the other hand on the load data as the basic input. In the case of nuclear power plant components thermal transient loading is most fatigue relevant. Usual global fatigue monitoring approaches rely on measured data from plant instrumentation. As an extension, the application of a local fatigue monitoring strategy (to be described in detail within the scope of this paper) paves the way of delivering continuously (nowadays at a frequency of 1 Hz) realistic load data at the fatigue relevant locations. Methods of qualified processing of these data are discussed in detail. Particularly, the processing of arbitrary operational load sequences and the derivation of representative model transients is discussed. This approach related to realistic load-time histories is principally applicable for all fatigue relevant components and ensures a realistic fatigue evaluation. (orig.)

  5. Fatigue Performance of Ti-6Al-4V Additively Manufactured Specimens with Integrated Capillaries of an Embedded Structural Health Monitoring System.

    Science.gov (United States)

    Hinderdael, Michaël; Strantza, Maria; De Baere, Dieter; Devesse, Wim; De Graeve, Iris; Terryn, Herman; Guillaume, Patrick

    2017-08-25

    Additive manufacturing (AM) of metals offers new possibilities for the production of complex structures. Up to now, investigations on the mechanical response of AM metallic parts show a significant spread and unexpected failures cannot be excluded. In this work, we focus on the detection of fatigue cracks through the integration of a Structural Health Monitoring (SHM) system in Ti-6Al-4V specimens. The working principle of the presented system is based on the integration of small capillaries that are capable of detecting fatigue cracks. Four-point bending fatigue tests have been performed on Ti-6Al-4V specimens with integrated capillaries and compared to the reference specimenswithout capillaries. Specimens were produced by conventional subtractive manufacturing of wrought material and AM, using the laser based Directed Energy Deposition (DED) process. In this study, we investigated the effect of the presence of the capillary on the fatigue strength and fatigue initiation location. Finite element (FEM) simulations were performed to validate the experimental test results. The presence of a drilled capillary in the specimens did not alter the fatigue initiation location. However, the laser based DED production process introduced roughness on the capillary surface that altered the fatigue initiation location to the capillary surface. The fatigue performance was greatly reduced when considering a printed capillary. It is concluded that the surface quality of the integrated capillary is of primary importance in order not to influence the structural integrity of the component to be monitored.

  6. Implementation of automated, on-line fatigue monitoring in a boiling water reactor

    International Nuclear Information System (INIS)

    Sakai, Takeshi; Tokunaga, Katsumi; Stevens, G.L.; Ranganath, S.

    1993-01-01

    A workstation-based, on-line fatigue monitoring system for tracking fatigue usage applied to a Japanese operating boiling water reactor (BWR), Tsuruga Unit 1, is described. The system uses the influence function approach and rainflow cycle counting methodology, operates on a workstation computer, and determines component stresses using temperature, pressure, and flow rate data that are made available via signal taps from previously existing plant sensors. Using plant-unique influence functions developed specifically for the feedwater nozzle location, the system calculates stresses as a function of time and computes the fatigue usage. The analysis method used to compute fatigue usage complies with MITI Code Notification number-sign 501. Fatigue values are saved automatically on files at times defined by the user for use at a later time. Of particular note, this paper describes some of the details involved with implementing such a system from the utility perspective. Utility installation details, as well as why such a system was chosen for implementation are presented. Fatigue results for an entire fuel cycle are presented and compared to assumed design basis events to confirm that actual plant thermal duty is significantly less severe than originally estimated in the design basis stress report. Although the system is specifically set up to address fatigue duty for the feedwater nozzle location, a generic shell structure was implemented so that any other components could be added at a future time without software modifications. As a result, the system provides the technical basis to more accurately evaluate actual reactor conditions as well as the justification for plant life extension

  7. Fatigue crack growth monitoring: fracture mechanics and non-destructive testing requirements

    International Nuclear Information System (INIS)

    Williams, S.; Mudge, P.J.

    1982-01-01

    If a fatigue crack is found in a component in service, two options exist if plant integrity is to be maintained: first, the plant can be removed from service and repairs effected or replacements fitted; second, the growth of the crack can be monitored non-destructively until it is either considered to be too large to tolerate, in which case it must be repaired, or until a convenient down time when repair can be effected. The second option has obvious benefits for plant operators, but in such a situation it is essential that errors of the non-destructive estimate of defect size, which will undoubtedly exist, and uncertainties in the fatigue crack growth laws in operation must both be allowed for if a safe extension of service life is to be obtained; i.e. without failure by leakage or fast fracture arising from the fatigue crack. This paper analyses the accuracy required of non-destructive crack measurement techniques to permit the safe monitoring of crack growth by periodic inspection. It then demonstrates that it is possible to achieve adequate crack monitoring using conventional ultrasonic techniques. (author)

  8. Fatigue monitoring desktop guide

    International Nuclear Information System (INIS)

    Woods, K.; Thomas, K.

    2012-01-01

    The development of a program for managing material aging (MMG) in the nuclear industry requires a new and different perspective. The classical method for MMG is cycle counting, which has been shown to have limited success. The classical method has been successful in satisfying the ductile condition per the America Society of Mechanical Engineers' (ASME) design criteria. However, the defined material failure mechanism has transformed from through-wall cracking and leakage (ASME) to crack initiation (NUREG-6909). This transformation is based on current industry experience with material degradation early in plant life and can be attributed to fabrication issues and environment concerns where cycle counting has been unsuccessful. This new perspective provides a different approach to cycle counting that incorporates all of the information about the material conditions. This approach goes beyond the consideration of a static analysis and includes a dynamic assessment of component health, which is required for operating plants. This health definition should consider fabrication, inspections, transient conditions and industry operating experience. In addition, this collection of information can be transparent to a broader audience that may not have a full understanding of the system design or the potential causes of early material degradation. This paper will present the key points that are needed for a successful fatigue monitoring desktop guide. (authors)

  9. A methodology for on line fatigue life monitoring : rainflow cycle counting method

    International Nuclear Information System (INIS)

    Mukhopadhyay, N.K.; Dutta, B.K.; Kushwaha, H.S.

    1992-01-01

    Green's function technique is used in on line fatigue life monitoring to convert plant data to stress versus time data. This technique converts plant data most efficiently to stress versus time data. To compute the fatigue usage factor the actual number of cycles experienced by the component is to be found out from stress versus time data. Using material fatigue properties the fatigue usage factor is to be computed from the number of cycles. Generally the stress response is very irregular in nature. To convert an irregular stress history to stress frequency spectra rainflow cycle counting method is used. This method is proved to be superior to other counting methods and yields best fatigue estimates. A code has been developed which computes the number of cycles experienced by the component from stress time history using rainflow cycle counting method. This postprocessor also computes the accumulated fatigue usage factor from material fatigue properties. The present report describes the development of a code to compute fatigue usage factor using rainflow cycle counting technique and presents a real life case study. (author). 10 refs., 10 figs

  10. Fatigue status assessment for reactor pressure vessel based on actual operational transient

    International Nuclear Information System (INIS)

    Zhu Guangqiang; Liao Changbin; Dai Bing; Gui Chun

    2013-01-01

    Background: Fatigue is an important aging mechanism in RPV and it must be contained to aging management working range. Purpose: In order to ensure the safety operation of nuclear power plants, as extension of RPV service time, it is necessary to assess the fatigue damage caused by actual operation transient. Methods: Based on monitoring data of actual operation during the past eleven years, refer to design transient, the statistic analysis for types and occurrence times of actual transient is carried out, at the same time, every transients are combined as different operation cycles and the temperature field and stress field of typical components are analyzed by FEM. Results: Based on these information, fatigue analysis and assessment are finished, if later-actual transients are similar with the previous transients, the calculation result shows that the ratio between maximum of cumulative usage factors and design calculation value is 0.4967 the design transients is conservative. Conclusions: Fatigue status of RPV could be assessed and traced quickly through fatigue status assessment method in this paper based on actual operational transient and assessment result would be a good reference for RPV aging management. (authors)

  11. Monitoring and Failure Analysis of Corroded Bridge Cables under Fatigue Loading Using Acoustic Emission Sensors

    Directory of Open Access Journals (Sweden)

    Hui Li

    2012-03-01

    Full Text Available Cables play an important role in cable-stayed systems, but are vulnerable to corrosion and fatigue damage. There is a dearth of studies on the fatigue damage evolution of corroded cable. In the present study, the acoustic emission (AE technology is adopted to monitor the fatigue damage evolution process. First, the relationship between stress and strain is determined through a tensile test for corroded and non-corroded steel wires. Results show that the mechanical performance of corroded cables is changed considerably. The AE characteristic parameters for fatigue damage are then established. AE energy cumulative parameters can accurately describe the fatigue damage evolution of corroded cables. The failure modes in each phase as well as the type of acoustic emission source are determined based on the results of scanning electron microscopy. The waveform characteristics, damage types, and frequency distribution of the corroded cable at different damage phases are collected. Finally, the number of broken wires and breakage time of the cables are determined according to the variation in the margin index.

  12. Monitoring and Failure Analysis of Corroded Bridge Cables under Fatigue Loading Using Acoustic Emission Sensors

    Science.gov (United States)

    Li, Dongsheng; Ou, Jinping; Lan, Chengming; Li, Hui

    2012-01-01

    Cables play an important role in cable-stayed systems, but are vulnerable to corrosion and fatigue damage. There is a dearth of studies on the fatigue damage evolution of corroded cable. In the present study, the acoustic emission (AE) technology is adopted to monitor the fatigue damage evolution process. First, the relationship between stress and strain is determined through a tensile test for corroded and non-corroded steel wires. Results show that the mechanical performance of corroded cables is changed considerably. The AE characteristic parameters for fatigue damage are then established. AE energy cumulative parameters can accurately describe the fatigue damage evolution of corroded cables. The failure modes in each phase as well as the type of acoustic emission source are determined based on the results of scanning electron microscopy. The waveform characteristics, damage types, and frequency distribution of the corroded cable at different damage phases are collected. Finally, the number of broken wires and breakage time of the cables are determined according to the variation in the margin index. PMID:22666009

  13. French experience in transient data collection and fatigue monitoring of PWR's nuclear steam supply system

    International Nuclear Information System (INIS)

    Sabaton, M.; Morilhat, P.; Savoldelli, D.; Genette, P.

    1995-10-01

    Electricite de France (EDF), the french national electricity company, is operating 54 standardized pressurizer water reactors. This about 500 reactor-years experience in nuclear stations operation and maintenance area has allowed EDF to develop its own strategy for monitoring of age-related degradations of NPP systems and components relevant for plant safety and reliability. After more than fifteen years of experience in regulatory transient data collection and seven years of successful fatigue monitoring prototypes experimentation, EDF decided to design a new system called SYSFAC (acronym for SYsteme de Surveillance en FAtigue de la Chaudiere) devoted to transient logging and thermal fatigue monitoring of the reactor coolant pressure boundary. The system is fully automatic and directly connected to the on-site data acquisition network without any complementary instrumentation. A functional transient detection module and a mechanical transient detection module are in charge of the general transient data collection. A fatigue monitoring module is aimed towards a precise surveillance of five specific zones particularly sensible to thermal fatigue. After the first step of preliminary studies, the industrial phase of the SYSFAC project is currently going on, with hardware and software tests and implementation. The first SYSFAC system will be delivered to the pilot power plant by the beginning of 1996. The extension to all EDF's nuclear 900 MW is planned after one more year of feedback experience. (authors). 12 refs., 3 figs

  14. Fatigue analysis through automated cycle counting using ThermAND

    International Nuclear Information System (INIS)

    Burton, G.R.; Ding, Y.; Scovil, A.; Yetisir, M.

    2008-01-01

    The potential for fatigue damage due to thermal transients is one of the degradation mechanisms that needs to be managed for plant components. The original design of CANDU stations accounts for projected fatigue usage for specific components over a specified design lifetime. Fatigue design calculations were based on estimates of the number and severity of expected transients for 30 years operation at 80% power. Many CANDU plants are now approaching the end of their design lives and are being considered for extended operation. Industry practice is to have a comprehensive fatigue management program in place for extended operation beyond the original design life. A CANDU-specific framework for fatigue management has recently been developed to identify the options for implementation, and the critical components and locations requiring long-term fatigue monitoring. An essential element of fatigue monitoring is to identify, count and monitor the number of plant transients to ensure that the number assumed in the original design is not exceeded. The number and severity of actual CANDU station thermal transients at key locations in critical systems have been assessed using ThermAND, AECL's health monitor for systems and components, based on archived station operational data. The automated cycle counting has demonstrated that actual transients are generally less numerous than the quantity assumed in the design basis, and are almost always significantly less severe. This paper will discuss the methodology to adapt ThermAND for automated cycle counting of specific system transients, illustrate and test this capability for cycle-based fatigue monitoring using CANDU station data, report the results, and provide data for stress-based fatigue calculations. (author)

  15. Monitoring of surface-fatigue crack propagation in a welded steel angle structure using guided waves and principal component analysis

    Science.gov (United States)

    Lu, Mingyu; Qu, Yongwei; Lu, Ye; Ye, Lin; Zhou, Limin; Su, Zhongqing

    2012-04-01

    An experimental study is reported in this paper demonstrating monitoring of surface-fatigue crack propagation in a welded steel angle structure using Lamb waves generated by an active piezoceramic transducer (PZT) network which was freely surface-mounted for each PZT transducer to serve as either actuator or sensor. The fatigue crack was initiated and propagated in welding zone of a steel angle structure by three-point bending fatigue tests. Instead of directly comparing changes between a series of specific signal segments such as S0 and A0 wave modes scattered from fatigue crack tips, a variety of signal statistical parameters representing five different structural status obtained from marginal spectrum in Hilbert-huang transform (HHT), indicating energy progressive distribution along time period in the frequency domain including all wave modes of one wave signal were employed to classify and distinguish different structural conditions due to fatigue crack initiation and propagation with the combination of using principal component analysis (PCA). Results show that PCA based on marginal spectrum is effective and sensitive for monitoring the growth of fatigue crack although the received signals are extremely complicated due to wave scattered from weld, multi-boundaries, notch and fatigue crack. More importantly, this method indicates good potential for identification of integrity status of complicated structures which cause uncertain wave patterns and ambiguous sensor network arrangement.

  16. Potential drop crack growth monitoring in high temperature biaxial fatigue tests

    International Nuclear Information System (INIS)

    Fitzgerald, B.P.; Krempl, E.

    1993-01-01

    The present work describes a procedure for monitoring crack growth in high temperature, biaxial, low cycle fatigue tests. The reversing DC potential drop equipment monitors smooth, tubular type 304 stainless steel specimens during fatigue testing. Electrical interference from an induction heater is filtered out by an analog filter and by using a long integration time. A Fourier smoothing algorithm and two spline interpolations process the large data set. The experimentally determined electrical potential drop is compared with the theoretical electrostatic potential that is found by solving Laplace's equation for an elliptical crack in a semi-infinite conducting medium. Since agreement between theory and experiment is good, the method can be used to measure crack growth to failure from the threshold of detectability

  17. Generation of data base for on-line fatigue life monitoring of Indian nuclear power plant components: Part I - Generation of Green's functions for end fitting

    International Nuclear Information System (INIS)

    Mukhopadhyay, N.K.; Dutta, B.K.; Kushwaha, H.S.

    1994-01-01

    Green's function technique is the heart of the on- line fatigue monitoring methodology. The plant transients are converted to stress and temperature response using this technique. To implement this methodology in a nuclear power plant, Green's functions are to be generated in advance. For structures of complex geometries, Green's functions are to be stored in a data base to convert on-line, the plant data to temperature/stress response, using a personal computer. End fitting, end shield, pressurizer, steam generator tube sheet are few such components of PHWR where fatigue monitoring is needed. In the present paper, Green's functions are generated for end fitting of a 235 MWe Indian PHWR using finite element method. End fitting has been analysed using both 3-D and 2-D (axisymmetric) finite element models. Temperature and stress Green's functions are generated at few critical locations using the code ABAQUS. (author). 10 refs., 11 figs

  18. Fatigue monitoring desktop guide

    Energy Technology Data Exchange (ETDEWEB)

    Woods, K. [InnoTech Engineering Solutions, LLC (United States); Thomas, K. [Nebraska Public Power District (United States)

    2012-07-01

    The development of a program for managing material aging (MMG) in the nuclear industry requires a new and different perspective. The classical method for MMG is cycle counting, which has been shown to have limited success. The classical method has been successful in satisfying the ductile condition per the America Society of Mechanical Engineers' (ASME) design criteria. However, the defined material failure mechanism has transformed from through-wall cracking and leakage (ASME) to crack initiation (NUREG-6909). This transformation is based on current industry experience with material degradation early in plant life and can be attributed to fabrication issues and environment concerns where cycle counting has been unsuccessful. This new perspective provides a different approach to cycle counting that incorporates all of the information about the material conditions. This approach goes beyond the consideration of a static analysis and includes a dynamic assessment of component health, which is required for operating plants. This health definition should consider fabrication, inspections, transient conditions and industry operating experience. In addition, this collection of information can be transparent to a broader audience that may not have a full understanding of the system design or the potential causes of early material degradation. This paper will present the key points that are needed for a successful fatigue monitoring desktop guide. (authors)

  19. Use of on-line fatigue monitoring of nuclear reactor components as a tool for plant life extension

    International Nuclear Information System (INIS)

    Stevens, G.L.; Ranganath, S.

    1991-01-01

    In this paper the application of an on-line fatigue monitoring system for tracking fatigue usage in operating power plants is described. The system, like several others which have been developed, uses the influence function approach, operates on a microcomputer, and determines component stresses using temperature, pressure, and flow rate data that are typically available from plant computers. Using plant-unique influence functions developed specifically for each component location, the system calculates stresses as a function of time and computes the fatigue usage. Stress values are calculated at time internals defined by the user and the fatigue values are saved on files for use at a later time. The application of the GE Fatigue Monitoring System (GEFMS) to calculate fatigue usage in the feedwater nozzle of a GE boiling Water Reactor is described in this paper

  20. Gearbox Fatigue Load Estimation for Condition Monitoring of Wind Turbines

    DEFF Research Database (Denmark)

    Perisic, Nevena; Pedersen, Bo Juul; Kirkegaard, Poul Henning

    2012-01-01

    control and data acquisition (SCADA) system. Estimated loads can be further used for prediction of remaining operating lifetime of turbine components, detection of high stress level or fault detection. An augmented Kalman filter is chosen as the fatigue load estimator because its characteristics well suit......The focus of the paper is on a design of a fatigue load estimator for predictive condition monitoring systems (CMS) of wind turbines. In order to avoid high-price measurement equipment required for direct load measuring, an indirect approach is suggested using only measurements from supervisory...... for the real time application. This paper presents results of the estimation of the gearbox fatigue load, often called shaft torque, using simulated data of wind turbine. Noise sensitivity of the algorithm is investigated by assuming different levels of measurement noise. Shaft torque estimations are compared...

  1. Factors Associated with Visual Fatigue from Curved Monitor Use: A Prospective Study of Healthy Subjects.

    Directory of Open Access Journals (Sweden)

    Haeng Jin Lee

    Full Text Available To investigate the factors associated with visual fatigue using monitors with various radii of curvature.Twenty normal healthy adults (8 men, 12 women; mean age, 26.2 ± 2.5 years prospectively watched five types of monitors including flat, 4000R, 3000R, 2000R, and 1000R curved monitors for 30 min. An experienced examiner measured the ophthalmological factors including near point of accommodation (NPA, near point of convergence (NPC, refraction, parameters during pupil response at light and saccadic movement just before and after the visual tasks. The questionnaires about subjective ocular symptoms were also investigated just before and after the visual tasks.The NPA increased after the visual tasks with a flat monitor compared with the curved monitors, with the 1000R curved monitor showing the smallest change (p = 0.020. The NPC increased for every monitor after the visual tasks; the largest increase occurred with the flat monitor (p = 0.001. There was no difference in refractive error, pupil response, or saccadic movement in the comparison of before and after the visual tasks. Among the nine factors in the questionnaire, the score of "eye pain" was significantly higher for the flat monitor versus the 1000R curved monitor after the visual tasks (p = 0.034.We identified NPA, NPC, and eye pain as factors associated with visual fatigue. Also, the curvature of the monitor was related to the visual fatigue.

  2. Muscle fatigue evaluation of astronaut upper limb based on sEMG and subjective assessment

    Science.gov (United States)

    Zu, Xiaoqi; Zhou, Qianxiang; Li, Yun

    2012-07-01

    All movements are driven by muscle contraction, and it is easy to cause muscle fatigue. Evaluation of muscle fatigue is a hot topic in the area of astronaut life support training and rehabilitation. If muscle gets into fatigue condition, it may reduce work efficiency and has an impact on psychological performance. Therefore it is necessary to develop an accurate and usable method on muscle fatigue evaluation of astronaut upper limb. In this study, we developed a method based on surface electromyography (sEMG) and subjective assessment (Borg scale) to evaluate local muscle fatigue. Fifteen healthy young male subjects participated in the experiment. They performed isometric muscle contractions of the upper limb. sEMG of the biceps brachii were recorded during the entire process of isotonic muscle contraction and Borg scales of muscle fatigue were collected in certain times. sEMG were divided into several parts, and then mean energy of each parts were calculated by the one-twelfth band octave method. Equations were derived based on the relationship between the mean energy of sEMG and Borg scale. The results showed that cubic curve could describe the degree of local muscle fatigue, and could be used to evaluate and monitor local muscle fatigue during the entire process.

  3. Creep-fatigue monitoring system for header ligaments of fossil power plants

    International Nuclear Information System (INIS)

    Chen, K.L.; Deardorf, A.F.; Copeland, J.F.; Pflasterer, R.; Beckerdite, G.

    1993-01-01

    The cracking of headers (primary and secondary superheater outlet, and reheater outlet headers) at ligament locations is an important issue for fossil power plants. A model for crack initiation and growth has been developed, based on creep-fatigue damage mechanisms. This cracking model is included in a creep-fatigue monitoring system to assess header structural integrity under high temperature operating conditions. The following principal activities are required to achieve this goal: (1) the development of transfer functions and (2) the development of a ligament cracking model. The first task is to develop stress transfer functions to convert measured (monitored) temperatures, pressures and flow rates into stresses to be used to compute damage. Elastic three-dimensional finite element analyses were performed to study transient thermal stress behavior. The sustained pressure stress redistribution due to high temperature creep was studied by nonlinear finite element analyses. The preceding results are used to derive Green's functions and pressure stress gradient transfer functions for monitoring at the juncture of the tube with the header inner surface, and for crack growth at the ligaments. The virtual crack closure method is applied to derive a stress intensity factor K solution for a corner crack at the tube/header juncture. Similarly, using the reference stress method, the steady state creep crack growth parameter C * is derived for a header corner crack. The C * solution for a small corner crack in a header can be inserted directed into the available C t solution, along with K to provide the complete transient creep solution

  4. Fatigue crack growth monitoring in multi-layered structures using guided ultrasonic waves

    International Nuclear Information System (INIS)

    Kostson, E; Fromme, P

    2009-01-01

    This contribution investigates the application of low frequency guided ultrasonic waves for monitoring fatigue crack growth at fastener holes in the 2nd layer of multi-layered plate structures, a common problem in aerospace industry. The model multi-layered structure investigated consists of two aluminum plate-strips adhesively bonded using a structural paste adhesive. Guided ultrasonic waves were excited using multiple piezoelectric discs bonded to the surface of the multi-layered structure. The wave propagation in the tensile specimen was measured using a laser interferometer and compared to numerical simulations. Thickness and width mode shapes of the excited flexural waves were identified from Semi-Analytical Finite Element (SAFE) calculations. Experiments and 3D Finite Element (FE) simulations show a change in the scattered field around fastener holes caused by a defect in the 2nd layer. The amplitude of the guided ultrasonic wave was monitored during fatigue experiments at a single point. The measured changes in the amplitude of the ultrasonic signal due to fatigue crack growth agree well with FE simulations.

  5. An Intelligent Sensor System for Monitoring Fatigue Damage in Welded Steel Components

    Science.gov (United States)

    Fernandes, B.; Gaydecki, P.; Burdekin, F. Michael

    2005-04-01

    A system for monitoring fatigue damage in steel components is described. The sensor, a thin steel sheet with a pre-crack in it, is attached to the component. Its crack length increases by fatigue in service and is recorded using a microcontroller. Measurement is accomplished using conductive tracks in a circuit whose output voltage changes when the crack propagates past a track. Data stored in memory can be remotely downloaded using Bluetooth™ technology to a PC.

  6. An Intelligent Sensor System for Monitoring Fatigue Damage in Welded Steel Components

    International Nuclear Information System (INIS)

    Fernandes, B.; Gaydecki, P.; Burdekin, F. Michael

    2005-01-01

    A system for monitoring fatigue damage in steel components is described. The sensor, a thin steel sheet with a pre-crack in it, is attached to the component. Its crack length increases by fatigue in service and is recorded using a microcontroller. Measurement is accomplished using conductive tracks in a circuit whose output voltage changes when the crack propagates past a track. Data stored in memory can be remotely downloaded using Bluetooth TM technology to a PC

  7. Structural health monitoring in end-of-life prediction for steel bridges subjected to fatigue cracking

    NARCIS (Netherlands)

    Attema, T.; Courage, W.M.G.; Maljaars, J.; Meerveld, H. van; Paulissen, J.H.; Pijpers, R.J.M.; Slobbe, A.T.

    2015-01-01

    This paper presents a monitoring and modelling methodology to assess the current and future conditions of steel bridges subjected to fatigue cracking. Steel bridges are subjected to fatigue cracking as a result of fluctuating stresses caused by the crossing of heavy vehicles. Specifically for

  8. Monitoring fatigue loads on wind turbines using cycle counting data acquisition systems

    Energy Technology Data Exchange (ETDEWEB)

    Soeker, H; Seifert, H [Deutsches Windenergie-Institut (Germany); Fragoulis, A; Vionis, P; Foussekis, D [Center for Renewable Energy Sources (Greece); Dahlberg, J A; Poppen, M [The Aeronautical Research Institue of Sweden (Sweden)

    1996-09-01

    As in any industrial application, the duration of a wind turbine`s life is a key parameter for the evaluation of its economic potential. Assuming a service life of 20 years, components of the turbine have to withstand a number of load cycles of up to 10{sup 8}. Such numbers of load cycles impose high demands on the fatigue characteristics of both, the used materials and the design. Nevertheless, fatigue loading of wind turbine components still remains a parameter of high uncertainty in the design of wind turbines. The specific features of these fatigue loads can be expected to vary with the type of turbine and the site of operation. In order to ensure the reliability of the next generation of larger scale wind turbines improved load assumptions will be of vital importance. Within the scope of the presented research program DEWI, C.R.E.S. and FFA monitored fatigue loads of serial produced wind turbines by means of a monitoring method that uses on-line cycle counting techniques. The blade root bending moments of two pitch controlled, variable speed wind turbines operating in the Hamswehrum wind farm, and also that of a stall controlled, fixed speed wind turbine operating in CRES` complex terrain test site, were measured by DEWI and CRES. In parallel FFA used their database of time series measurements of blade root bending moments on a stall controlled, fixed speed turbine at Alsvik Windfarm in order to derive semi-empirical fatigue load data. The experience gained from application of the on-line measurement technique is discussed with respect to performance, data quality, reliability and cost effectiveness. Investigations on the effects of wind farm and complex terrain operation on the fatigue loads of wind turbine rotor blades are presented. (au)

  9. Self-Calibrating Ultrasonic Methods for In-Situ Monitoring of Fatigue Crack Progression

    International Nuclear Information System (INIS)

    Michaels, J.E.; Mi, B.; Cobb, A.C.; Michaels, T.E.; Stobbe, D.M.

    2005-01-01

    Ultrasonic sensors permanently affixed to aluminum coupons are used to monitor progression of damage during fatigue testing with the long term goal of structural health monitoring for diagnostics and prognostics. Necessary for success are proper design of the ultrasonic testing methods, robust transducer mounting techniques, and real-time signal processing for determining the state of the structure. It is also highly desirable for the overall system to be self-calibrating with built-in diagnostics in order to detect and compensate for sensor degradation or failure. Self-calibrating ultrasonic techniques are applied for monitoring of cracks initiating and propagating from the inaccessible inner diameters of rivet holes where the transducers are mounted on the accessible specimen surface. Angle beam ultrasonic methods are utilized that are suitable for detecting small defects in critical local regions of high stress. Results are presented for aluminum coupons subjected to low cycle fatigue and demonstrate ultrasonic tracking of crack growth

  10. A Muscle Fibre Conduction Velocity Tracking ASIC for Local Fatigue Monitoring.

    Science.gov (United States)

    Koutsos, Ermis; Cretu, Vlad; Georgiou, Pantelis

    2016-12-01

    Electromyography analysis can provide information about a muscle's fatigue state by estimating Muscle Fibre Conduction Velocity (MFCV), a measure of the travelling speed of Motor Unit Action Potentials (MUAPs) in muscle tissue. MFCV better represents the physical manifestations of muscle fatigue, compared to the progressive compression of the myoelectic Power Spectral Density, hence it is more suitable for a muscle fatigue tracking system. This paper presents a novel algorithm for the estimation of MFCV using single threshold bit-stream conversion and a dedicated application-specified integrated circuit (ASIC) for its implementation, suitable for a compact, wearable and easy to use muscle fatigue monitor. The presented ASIC is implemented in a commercially available AMS 0.35 [Formula: see text] CMOS technology and utilizes a bit-stream cross-correlator that estimates the conduction velocity of the myoelectric signal in real time. A test group of 20 subjects was used to evaluate the performance of the developed ASIC, achieving good accuracy with an error of only 3.2% compared to Matlab.

  11. Modal Based Fatigue Monitoring of Steel Structures

    DEFF Research Database (Denmark)

    Graugaard-Jensen, J.; Brincker, Rune; Hjelm, H. P.

    2005-01-01

    In this paper it is shown how the accumulated fatigue in steel structures can be estimated with high accuracy by continuously measuring the accelerations in a few points of the structure. First step is to obtain a good estimate of the mode shapes by performing a natural input modal analysis. The so...... by applying the mode shapes of the calibrated Finite Element model and strains are obtained using the shape functions for the actual elements. The technique has been applied on a model frame structure in the laboratory and on a wind loaded lattice pylon structure. In both cases the estimated stresses has been...

  12. The AREVA integrated and sustainable concept of fatigue design, monitoring and re-assessment; AREVA FATIGUE CONCEPT - ein geschlossenes Konzept zur Verfolgung und Optimierung der auf Ermuedung basierenden Schaedigungseffekte von thermisch und mechanisch beanspruchten Kraftwerksbauteilen

    Energy Technology Data Exchange (ETDEWEB)

    Begholz, Steffen; Rudolph, Juergen [AREVA NP GmbH, Erlangen (Germany)

    2008-07-01

    Prevention of fatigue damage of components is an important topic with respect to safety and availability of a nuclear power plant. The issue of fatigue monitoring should be of primary interest throughout service life. Based on the changing general framework, i.e. planning of new plants with a projected lifetime of 60 years and the lifetime extension of existing plants AREVA is focussing R and D activities on improved detection methods. Primary objective is the realistic determination of the actual usage level of reactor components. The fatigue monitoring is supposed to enhance cost optimization and minimize inspection frequency. Fatigue monitoring should be implemented at the beginning of start-up period since the high loads during this phase introduce a significant contribution to the usage level. AREVA recommends the use of the FAMOS (fatigue monitoring system) for the assessment of the realistic transient loads and the data processing with respect to fatigue evaluation. Every 10 years the actual usage levels should be evaluated in detail according to the standards, based on measured load data. The fatigue evaluation is usually performed using finite element analyses taking into account the transient temperature loads at the component, dependent on the component demands based on elastic or elasto-plastic material behaviour. Potential problematic areas can be identified reliably. Direct measurement of fatigue damage, refined analysis concepts (short crack fracture mechanics, and ratcheting simulation) are supposed to support the concept. [German] Die Vermeidung von Ermuedungsschaeden an Komponenten der nuklearen Kraftwerkstechnik ist ein wichtiges Thema in Hinblick auf die Aufrechterhaltung der Anlagensicherheit sowie auf die Erhoehung der Verfuegbarkeit. Das Thema Ermuedungsueberwachung sollte somit waehrend der gesamten Laufzeit eines Kraftwerkes mit hoher Aufmerksamkeit verfolgt werden. Vor diesem Hintergrund und den sich aendernden Rahmenbedingungen, wie z

  13. Fatigue damage monitoring for basalt fiber reinforced polymer composites using acoustic emission technique

    Science.gov (United States)

    Wang, Wentao; Li, Hui; Qu, Zhi

    2012-04-01

    Basalt fiber reinforced polymer (BFRP) is a structural material with superior mechanical properties. In this study, unidirectional BFRP laminates with 14 layers are made with the hand lay-up method. Then, the acoustic emission technique (AE) combined with the scanning electronic microscope (SEM) technique is employed to monitor the fatigue damage evolution of the BFRP plates in the fatigue loading tests. Time-frequency analysis using the wavelet transform technique is proposed to analyze the received AE signal instead of the peak frequency method. A comparison between AE signals and SEM images indicates that the multi-frequency peaks picked from the time-frequency curves of AE signals reflect the accumulated fatigue damage evolution and fatigue damage patterns. Furthermore, seven damage patterns, that is, matrix cracking, delamination, fiber fracture and their combinations, are identified from the time-frequency curves of the AE signals.

  14. Prediction of Fatigue Crack Growth in Gas Turbine Engine Blades Using Acoustic Emission.

    Science.gov (United States)

    Zhang, Zhiheng; Yang, Guoan; Hu, Kun

    2018-04-25

    Fatigue failure is the main type of failure that occurs in gas turbine engine blades and an online monitoring method for detecting fatigue cracks in blades is urgently needed. Therefore, in this present study, we propose the use of acoustic emission (AE) monitoring for the online identification of the blade status. Experiments on fatigue crack propagation based on the AE monitoring of gas turbine engine blades and TC11 titanium alloy plates were conducted. The relationship between the cumulative AE hits and the fatigue crack length was established, before a method of using the AE parameters to determine the crack propagation stage was proposed. A method for predicting the degree of crack propagation and residual fatigue life based on the AE energy was obtained. The results provide a new method for the online monitoring of cracks in the gas turbine engine blade.

  15. Remote monitoring of fatigue-sensitive details on bridges : [part I and II].

    Science.gov (United States)

    2015-03-01

    Fatigue is one of the most critical problems for steel bridges as well as for any steel structures that needs : to be considered during design and operation. The objectives of this study are to explore monitoring : technologies, and to develop effect...

  16. Measurement of fatigue crack growth rate of reactor structural material in air based on DCPD method

    International Nuclear Information System (INIS)

    Du Donghai; Chen Kai; Yu Lun; Zhang Lefu; Shi Xiuqiang; Xu Xuelian

    2014-01-01

    The principles and details of direct current potential drop (DCPD) in monitoring the crack growth of reactor structural materials was introduced in this paper. Based on this method, the fatigue crack growth rate (CGR) of typical structural materials in nuclear power systems was measured. The effects of applied load, load ratio and loading frequency on the fatigue crack growth rate of reactor structural materials were discussed. The result shows that the fatigue crack growth rate of reactor structural materials depends on the hardness of materials, and the harder the material is, the higher the rate of crack growth is. (authors)

  17. A study on the stress history condensation method for a fatigue monitoring system

    International Nuclear Information System (INIS)

    Ko, Hanok; Jhung, Myungjo; Lee, Kihyoung

    2014-01-01

    Fatigue damage is the one of important aging mechanisms. Time-varying thermal, pressure and mechanical loads produce perturbations of stress cycles primarily at the surface of a component. Stress cycles of sufficient magnitude cause fatigue damage, which can ultimately lead to cracking of the component. According to NUREG-1801, fatigue monitoring systems identify acceptable aging management programs, including programs for fatigue and cyclic operation. In a monitoring system, the rainflow counting method is mainly used as the stress cycle counting method. Before determining the stress cycles using rainflow counting method, stress extremum (or peak/valley) must be identified. Because real stress history contains large numbers of very small cycles, which may be a result of digitization noise, these cycles will slow down the analysis and distort the scaling of graphical displays. As a result, it is found that stress cycles smaller than a threshold value are discarded by using the proposed method. In this paper, an engineering methodology which extracts extremum from the real-time transient data, so-called SEE, has been developed. The proposed method is very simple and so fast because it only uses the difference between the input value and local peak/valley. The stress cycles counted by two methods are compared with those counted by only rainflow counting method and it is found that stress cycles smaller than a threshold value were eliminated

  18. Fatigue data bases in Europe

    International Nuclear Information System (INIS)

    Olivier, R.; Koettgen, V.B.; Seeger, T.; Boller, C.

    1988-01-01

    Based on an inquiry with well-known European fatigue institutions the paper describes existing more or less extensive collections and data bases of S-N and crack growth data, mainly on unwelded and welded steel and aluminium in organizations and countries as follows: CEC, ESA, Federal Republic of Germany, GDR, Italy, Norway, Republic of Ireland, Switzerland, UK. This documentation of the present state is completed by a short survey on available European fatigue standards and design rules, serving as a data base for nominal materials data. Requirements for data base concepts, contents, user interface and data structure are presented in a short overview. (orig./HP)

  19. EMG Processing Based Measures of Fatigue Assessment during Manual Lifting

    Directory of Open Access Journals (Sweden)

    E. F. Shair

    2017-01-01

    Full Text Available Manual lifting is one of the common practices used in the industries to transport or move objects to a desired place. Nowadays, even though mechanized equipment is widely available, manual lifting is still considered as an essential way to perform material handling task. Improper lifting strategies may contribute to musculoskeletal disorders (MSDs, where overexertion contributes as the highest factor. To overcome this problem, electromyography (EMG signal is used to monitor the workers’ muscle condition and to find maximum lifting load, lifting height and number of repetitions that the workers are able to handle before experiencing fatigue to avoid overexertion. Past researchers have introduced several EMG processing techniques and different EMG features that represent fatigue indices in time, frequency, and time-frequency domain. The impact of EMG processing based measures in fatigue assessment during manual lifting are reviewed in this paper. It is believed that this paper will greatly benefit researchers who need a bird’s eye view of the biosignal processing which are currently available, thus determining the best possible techniques for lifting applications.

  20. EMG Processing Based Measures of Fatigue Assessment during Manual Lifting

    Science.gov (United States)

    Marhaban, M. H.; Abdullah, A. R.

    2017-01-01

    Manual lifting is one of the common practices used in the industries to transport or move objects to a desired place. Nowadays, even though mechanized equipment is widely available, manual lifting is still considered as an essential way to perform material handling task. Improper lifting strategies may contribute to musculoskeletal disorders (MSDs), where overexertion contributes as the highest factor. To overcome this problem, electromyography (EMG) signal is used to monitor the workers' muscle condition and to find maximum lifting load, lifting height and number of repetitions that the workers are able to handle before experiencing fatigue to avoid overexertion. Past researchers have introduced several EMG processing techniques and different EMG features that represent fatigue indices in time, frequency, and time-frequency domain. The impact of EMG processing based measures in fatigue assessment during manual lifting are reviewed in this paper. It is believed that this paper will greatly benefit researchers who need a bird's eye view of the biosignal processing which are currently available, thus determining the best possible techniques for lifting applications. PMID:28303251

  1. Evoked EMG-based torque prediction under muscle fatigue in implanted neural stimulation

    Science.gov (United States)

    Hayashibe, Mitsuhiro; Zhang, Qin; Guiraud, David; Fattal, Charles

    2011-10-01

    In patients with complete spinal cord injury, fatigue occurs rapidly and there is no proprioceptive feedback regarding the current muscle condition. Therefore, it is essential to monitor the muscle state and assess the expected muscle response to improve the current FES system toward adaptive force/torque control in the presence of muscle fatigue. Our team implanted neural and epimysial electrodes in a complete paraplegic patient in 1999. We carried out a case study, in the specific case of implanted stimulation, in order to verify the corresponding torque prediction based on stimulus evoked EMG (eEMG) when muscle fatigue is occurring during electrical stimulation. Indeed, in implanted stimulation, the relationship between stimulation parameters and output torques is more stable than external stimulation in which the electrode location strongly affects the quality of the recruitment. Thus, the assumption that changes in the stimulation-torque relationship would be mainly due to muscle fatigue can be made reasonably. The eEMG was proved to be correlated to the generated torque during the continuous stimulation while the frequency of eEMG also decreased during fatigue. The median frequency showed a similar variation trend to the mean absolute value of eEMG. Torque prediction during fatigue-inducing tests was performed based on eEMG in model cross-validation where the model was identified using recruitment test data. The torque prediction, apart from the potentiation period, showed acceptable tracking performances that would enable us to perform adaptive closed-loop control through implanted neural stimulation in the future.

  2. French experience in transient data collection and fatigue monitoring of PWR`s nuclear steam supply system; Experience francaise sur la comptabilisation des transitoires et la surveillance en fatigue des chaudieres REP

    Energy Technology Data Exchange (ETDEWEB)

    Sabaton, M.; Morilhat, P.; Savoldelli, D.; Genette, P.

    1995-10-01

    Electricite de France (EDF), the french national electricity company, is operating 54 standardized pressurizer water reactors. This about 500 reactor-years experience in nuclear stations operation and maintenance area has allowed EDF to develop its own strategy for monitoring of age-related degradations of NPP systems and components relevant for plant safety and reliability. After more than fifteen years of experience in regulatory transient data collection and seven years of successful fatigue monitoring prototypes experimentation, EDF decided to design a new system called SYSFAC (acronym for SYsteme de Surveillance en FAtigue de la Chaudiere) devoted to transient logging and thermal fatigue monitoring of the reactor coolant pressure boundary. The system is fully automatic and directly connected to the on-site data acquisition network without any complementary instrumentation. A functional transient detection module and a mechanical transient detection module are in charge of the general transient data collection. A fatigue monitoring module is aimed towards a precise surveillance of five specific zones particularly sensible to thermal fatigue. After the first step of preliminary studies, the industrial phase of the SYSFAC project is currently going on, with hardware and software tests and implementation. The first SYSFAC system will be delivered to the pilot power plant by the beginning of 1996. The extension to all EDF`s nuclear 900 MW is planned after one more year of feedback experience. (authors). 12 refs., 3 figs.

  3. Comparative study of electromechanical impedance and Lamb wave techniques for fatigue crack detection and monitoring in metallic structures

    Science.gov (United States)

    Lim, Say Ian; Liu, Yu; Soh, Chee Kiong

    2012-04-01

    Fatigue cracks often initiate at the weld toes of welded steel connections. Usually, these cracks cannot be identified by the naked eyes. Existing identification methods like dye-penetration test and alternating current potential drop (ACPD) may be useful for detecting fatigue cracks at the weld toes. To apply these non-destructive evaluation (NDE) techniques, the potential sites have to be accessible during inspection. Therefore, there is a need to explore other detection and monitoring techniques for fatigue cracks especially when their locations are inaccessible or cost of access is uneconomical. Electro-mechanical Impedance (EMI) and Lamb wave techniques are two fast growing techniques in the Structural Health Monitoring (SHM) community. These techniques use piezoelectric ceramics (PZT) for actuation and sensing. Since the monitoring site is only needed to be accessed once for the instrumentation of the transducers, remote monitoring is made possible. The permanent locations of these transducers also translate to having consistent measurement for monitoring. The main focus of this study is to conduct a comparative investigation on the effectiveness and efficiency of the EMI technique and the Lamb wave technique for successful fatigue crack identification and monitoring of welded steel connections using piezoelectric transducers. A laboratory-sized non-load carrying fillet weld specimen is used in this study. The specimen is subjected to cyclic tensile load and data for both techniques are acquired at stipulated intervals. It can be concluded that the EMI technique is sensitive to the crack initiation phase while the Lamb wave technique correlates well with the crack propagation phase.

  4. Active-sensing based damage monitoring of airplane wings under low-temperature and continuous loading condition

    Energy Technology Data Exchange (ETDEWEB)

    Jeon, Jun Young; Jung, Hwee Kwon; Park, Gyu Hae [Dept. of Mechanical Engineering, Chonnam National University, Gwangju (Korea, Republic of); Ha, Jae Seok; Park, Chan Yik [7th R and D Institute, Agency for Denfense Development, Yuseong (Korea, Republic of)

    2016-10-15

    As aircrafts are being operated at high altitude, wing structures experience various fatigue loadings under cryogenic environments. As a result, fatigue damage such as a crack could be develop that could eventually lead to a catastrophic failure. For this reason, fatigue damage monitoring is an important process to ensure efficient maintenance and safety of structures. To implement damage detection in real-world flight environments, a special cooling chamber was built. Inside the chamber, the temperature was maintained at the cryogenic temperature, and harmonic fatigue loading was given to a wing structure. In this study, piezoelectric active-sensing based guided waves were used to detect the fatigue damage. In particular, a beam forming technique was applied to efficiently measure the scattering wave caused by the fatigue damage. The system was used for detection, growth monitoring, and localization of a fatigue crack. In addition, a sensor diagnostic process was also applied to ensure the proper operation of piezoelectric sensors. Several experiments were implemented and the results of the experiments demonstrated that this process could efficiently detect damage in such an extreme environment.

  5. AE characteristic for monitoring of fatigue crack in steel bridge members

    Science.gov (United States)

    Yoon, Dong-Jin; Jung, Juong-Chae; Park, Philip; Lee, Seung-Seok

    2000-06-01

    Acoustic emission technique was employed for the monitoring of crack activity in both steel bridge members and laboratory specimen. Laboratory experiment was carried out to identify AE characteristics of fatigue cracks for compact tension specimen. The relationship between a stress intensity factor and AE signals activity as well as conventional AE parameter analysis was discussed. A field test was also conducted on a railway bridge, which contain several fatigue cracks. Crack activities were investigated while in service with strain measurement. From the results, in the laboratory tests, the features of three parameters such as the length of crack growth, the AE energy, and the cumulative AE events, showed the almost same trend in their increase as the number of fatigue cycle increased. From the comparisons of peak amplitude and AE energy with stress intensity factor, it was verified that the higher stress intensity factors generated AE signals with higher peak amplitude and a large number of AE counts. In the field test, real crack propagation signals were captured and the crack activity was verified in two cases.

  6. Quantification of the Value of Structural Health Monitoring Information for Fatigue Deteriorating Structural Systems

    DEFF Research Database (Denmark)

    Thöns, Sebastian; Schneider, Ronald; Faber, Michael Havbro

    2015-01-01

    This paper addresses the quantification of the value of structural health monitoring (SHM) before its implementation for structural systems on the basis of its Value of Information (VoI). The value of SHM is calculated utilizing the Bayesian pre-posterior decision analysis modelling the structural...... life cycle performance, the integrity management and the structural risks. The relevance and precision of SHM information for the reduction of the structural system risks and the expected cost of the structural integrity management throughout the life cycle constitutes the value of SHM...... and is quantified with this framework. The approach is focused on fatigue deteriorating structural steel systems for which a continuous resistance deterioration formulation is introduced. In a case study, the value of SHM for load monitoring is calculated for a Daniels system subjected to fatigue deterioration...

  7. Crack monitoring method based on Cu coating sensor and electrical potential technique for metal structure

    Directory of Open Access Journals (Sweden)

    Hou Bo

    2015-06-01

    Full Text Available Advanced crack monitoring technique is the cornerstone of aircraft structural health monitoring. To achieve real-time crack monitoring of aircraft metal structures in the course of service, a new crack monitoring method is proposed based on Cu coating sensor and electrical potential difference principle. Firstly, insulation treatment process was used to prepare a dielectric layer on structural substrate, such as an anodizing layer on 2A12-T4 aluminum alloy substrate, and then a Cu coating crack monitoring sensor was deposited on the structure fatigue critical parts by pulsed bias arc ion plating technology. Secondly, the damage consistency of the Cu coating sensor and 2A12-T4 aluminum alloy substrate was investigated by static tensile experiment and fatigue test. The results show that strain values of the coating sensor and the 2A12-T4 aluminum alloy substrate measured by strain gauges are highly coincident in static tensile experiment and the sensor has excellent fatigue damage consistency with the substrate. Thirdly, the fatigue performance discrepancy between samples with the coating sensor and original samples was investigated. The result shows that there is no obvious negative influence on the fatigue performance of the 2A12-T4 aluminum alloy after preparing the Cu coating sensor on its surface. Finally, crack monitoring experiment was carried out with the Cu coating sensor. The experimental results indicate that the sensor is sensitive to crack, and crack origination and propagation can be monitored effectively through analyzing the change of electrical potential values of the coating sensor.

  8. Monitoring training load to understand fatigue in athletes.

    Science.gov (United States)

    Halson, Shona L

    2014-11-01

    Many athletes, coaches, and support staff are taking an increasingly scientific approach to both designing and monitoring training programs. Appropriate load monitoring can aid in determining whether an athlete is adapting to a training program and in minimizing the risk of developing non-functional overreaching, illness, and/or injury. In order to gain an understanding of the training load and its effect on the athlete, a number of potential markers are available for use. However, very few of these markers have strong scientific evidence supporting their use, and there is yet to be a single, definitive marker described in the literature. Research has investigated a number of external load quantifying and monitoring tools, such as power output measuring devices, time-motion analysis, as well as internal load unit measures, including perception of effort, heart rate, blood lactate, and training impulse. Dissociation between external and internal load units may reveal the state of fatigue of an athlete. Other monitoring tools used by high-performance programs include heart rate recovery, neuromuscular function, biochemical/hormonal/immunological assessments, questionnaires and diaries, psychomotor speed, and sleep quality and quantity. The monitoring approach taken with athletes may depend on whether the athlete is engaging in individual or team sport activity; however, the importance of individualization of load monitoring cannot be over emphasized. Detecting meaningful changes with scientific and statistical approaches can provide confidence and certainty when implementing change. Appropriate monitoring of training load can provide important information to athletes and coaches; however, monitoring systems should be intuitive, provide efficient data analysis and interpretation, and enable efficient reporting of simple, yet scientifically valid, feedback.

  9. Fatigue of Ti6Al4V Structural Health Monitoring Systems Produced by Selective Laser Melting

    Directory of Open Access Journals (Sweden)

    Maria Strantza

    2016-02-01

    Full Text Available Selective laser melting (SLM is an additive manufacturing (AM process which is used for producing metallic components. Currently, the integrity of components produced by SLM is in need of improvement due to residual stresses and unknown fracture behavior. Titanium alloys produced by AM are capable candidates for applications in aerospace and industrial fields due to their fracture resistance, fatigue behavior and corrosion resistance. On the other hand, structural health monitoring (SHM system technologies are promising and requested from the industry. SHM systems can monitor the integrity of a structure and during the last decades the research has primarily been influenced by bionic engineering. In that aspect a new philosophy for SHM has been developed: the so-called effective structural health monitoring (eSHM system. The current system uses the design freedom provided by AM. The working principle of the system is based on crack detection by means of a network of capillaries that are integrated in a structure. The main objective of this research is to evaluate the functionality of Ti6Al4V produced by the SLM process in the novel SHM system and to confirm that the eSHM system can successfully detect cracks in SLM components. In this study four-point bending fatigue tests on Ti6Al4V SLM specimens with an integrated SHM system were conducted. Fractographic analysis was performed after the final failure, while finite element simulations were used in order to determine the stress distribution in the capillary region and on the component. It was proven that the SHM system does not influence the crack initiation behavior during fatigue. The results highlight the effectiveness of the eSHM on SLM components, which can potentially be used by industrial and aerospace applications.

  10. Model-Based Load Estimation for Predictive Condition Monitoring of Wind Turbines

    DEFF Research Database (Denmark)

    Perisic, Nevena; Pederen, Bo Juul; Grunnet, Jacob Deleuran

    signal is performed online, and a Load Indicator Signal (LIS) is formulated as a ratio between current estimated accumulated fatigue loads and its expected value based only on a priori knowledge (WTG dynamics and wind climate). LOT initialisation is based on a priori knowledge and can be obtained using...... programme for pre-maintenance actions. The performance of LOT is demonstrated by applying it to one of the most critical WTG components, the gearbox. Model-based load CMS for gearbox requires only standard WTG SCADA data. Direct measuring of gearbox fatigue loads requires high cost and low reliability...... measurement equipment. Thus, LOT can significantly reduce the price of load monitoring....

  11. Fatigue Damage Estimation and Data-based Control for Wind Turbines

    DEFF Research Database (Denmark)

    Barradas Berglind, Jose de Jesus; Wisniewski, Rafal; Soltani, Mohsen

    2015-01-01

    based on hysteresis operators, which can be used in control loops. The authors propose a data-based model predictive control (MPC) strategy that incorporates an online fatigue estimation method through the objective function, where the ultimate goal in mind is to reduce the fatigue damage of the wind......The focus of this work is on fatigue estimation and data-based controller design for wind turbines. The main purpose is to include a model of the fatigue damage of the wind turbine components in the controller design and synthesis process. This study addresses an online fatigue estimation method...... turbine components. The outcome is an adaptive or self-tuning MPC strategy for wind turbine fatigue damage reduction, which relies on parameter identification on previous measurement data. The results of the proposed strategy are compared with a baseline model predictive controller....

  12. Health Monitoring of a Composite Actuator with a PZT Ceramic during Electromechanical Fatigue Loading

    International Nuclear Information System (INIS)

    Woo, Sung Choong; Goo, Nam Seo

    2007-01-01

    This work describes an investigation into the feasibility of using an acoustic emission (AE) technique to evaluate the integrity of a composite actuator with a PZT ceramic under electromechanical cyclic loading. AE characteristics have been analyzed in terms of the behavior of the AE count rate and signal waveform in association with the performance degradation of the composite actuator during the cyclic tests. The results showed that the fatigue cracking of the composite actuator with a PZT ceramic occurred only in the PZT ceramic layer, and that the performance degradation caused by the fatigue damage varied immensely depending on the existence of a protecting composite bottom layer. We confirmed the correlations between the fatigue damage mechanisms and AE signal types for the actuators that exhibited multiple modes of fatigue damage; transgranular micro damage, intergranular fatigue cracking, and breakdown by a short circuiting were related to a burst type signal showing a shortly rising and slowly decaying waveform with a comparably low voltage, a continuous type signal showing a gradual rising and slowly decaying waveform with a very high voltage and a burst and continuous type signal with a high voltage, respectively. Results from the present work showed that the evolution of fatigue damage in the composite actuator with a PZT ceramic can be nondestructively identified via in situ AE monitoring and microscopic observations

  13. Corrosion-fatigue studies of the Zr-based Vitreloy 105 bulk metallic glass

    International Nuclear Information System (INIS)

    Horton Jr, Joe A.; Morrison, M.L.; Buchanan, R.A.; Liaw, Peter K.; Green, B.A.; Wang, G.Y.

    2007-01-01

    The purpose of this study was to characterize the stress-life behavior of the Vitreloy 105 BMG alloy in the four-point bending configuration in a 0.6 M. NaCl electrolyte. At high stress amplitudes, the corrosion-fatigue life was similar to the fatigue lives observed in air. The environment became increasingly detrimental with decreases in stress, and the corrosion-fatigue endurance limit decreased to about 50 MPa, an 88% decrease relative to testing in air. Similar to the tests conducted in air, oxide particles were found on the fracture surfaces but did not appear to significantly affect the corrosion-fatigue lives. However, wear and the resultant corrosion at the outer loading pins resulted in crack initiation in most of the samples. Thus, these results are considered conservative estimates of the corrosion-fatigue behavior of this BMG alloy. Monitoring of the samples and the open-circuit potentials revealed that the onset of significant crack growth occurred at an average of 92% of the total fatigue life. The mechanism of corrosion-fatigue degradation was found to be anodic dissolution

  14. Fatigue assessment of the ITER TF coil case based on JJ1 fatigue tests

    International Nuclear Information System (INIS)

    Hamada, K.; Nakajima, H.; Takano, K.; Kudo, Y.; Tsutsumi, F.; Okuno, K.; Jong, C.

    2005-01-01

    The material of the TF coil case in the ITER requires to withstand cyclic electromagnetic forces applied up to 3 x 10 4 cycles at 4.2 K. A cryogenic stainless steel, JJ1, is used in high stress region of TF coil case. The fatigue characteristics (S-N curve) of JJ1 base metal and welded joint at 4.2 K has been measured. The fatigue strength of base metal and welded joint at 3 x 10 4 cycles are measured as 1032 and 848 MPa, respectively. The design S-N curve is derived from the measured data taking account of the safety factor of 20 for cycle-to-failure and 2 for fatigue strength, and it indicates that an equivalent alternating stress of the case should be kept less than 516 MPa for the base metal and 424 MPa for the welded joint at 3 x 10 4 cycles. It is demonstrated that the TF coil case has enough margins for the cyclic operation. It is also shown the welded joint should be located in low cyclic stress region because a residual stress affects the fatigue life

  15. Construction Worker Fatigue Prediction Model Based on System Dynamic

    OpenAIRE

    Wahyu Adi Tri Joko; Ayu Ratnawinanda Lila

    2017-01-01

    Construction accident can be caused by internal and external factors such as worker fatigue and unsafe project environment. Tight schedule of construction project forcing construction worker to work overtime in long period. This situation leads to worker fatigue. This paper proposes a model to predict construction worker fatigue based on system dynamic (SD). System dynamic is used to represent correlation among internal and external factors and to simulate level of worker fatigue. To validate...

  16. Thermal fatigue evaluation of piping system Tee-connections

    International Nuclear Information System (INIS)

    Metzner, K.J.; Braillard, O.; Faidy, C.; Marcelles, I.; Solin, J.; Stumpfrock, L.

    2004-01-01

    Thermal fatigue is one significant long-term degradation mechanism nuclear power plants (NPP), in particular, as operating plants become older and life time extension activities have been initiated. In general, the common thermal fatigue issues are understood and controlled by plant instrumentation systems. However, incidents in some plants indicate that certain piping system Tees are susceptible to turbulent temperature mixing effects that cannot be adequately monitored by common thermocouple instrumentation. The THERFAT project has been initiated to advance the accuracy and reliability of thermal fatigue load determination in engineering tools and research oriented approaches to outline a science based practical methodology for managing thermal fatigue risks in Tee-connections susceptible to high cyclic thermal fatigue. (orig.)

  17. Damage formation, fatigue behavior and strength properties of ZrO_2-based ceramics

    International Nuclear Information System (INIS)

    Kozulin, A. A.; Kulkov, S. S.; Narikovich, A. S.; Leitsin, V. N.; Kulkov, S. N.

    2016-01-01

    It is suggested that a non-destructive testing technique using a three-dimensional X-ray tomography be applied to detecting internal structural defects and monitoring damage formation in a ceramic composite structure subjected to a bending load. Three-point bending tests are used to investigate the fatigue behavior and mechanical and physical properties of medical-grade ZrO_2-based ceramics. The bending strength and flexural modulus are derived under static conditions at a loading rate of 2 mm/min. The fatigue strength and fatigue limit under dynamic loading are investigated at a frequency of 10 Hz in three stress ranges: 0.91–0.98, 0.8–0.83, and 0.73–0.77 MPa of the static bending strength. The average values of the bending strength and flexural modulus of sintered specimens are 43 MPa and 22 GPa, respectively. The mechanical properties of the ceramics are found to be similar to those of bone tissues. The testing results lead us to conclude that the fatigue limit obtained from 10"5 stress cycles is in the range 33–34 MPa, i.e. it accounts for about 75% of the static bending strength for the test material.

  18. Fatigue crack behaviour in mine excavator

    Energy Technology Data Exchange (ETDEWEB)

    Yin, Y.; Grondin, G.Y.; Elwi, A.E. [Alberta Univ., Edmonton, AB (Canada). Dept. of Civil and Environmental Engineering

    2006-05-15

    Fatigue cracking in excavation equipment represents a significant operating cost for oil sands operators. It is caused by high impact loads, the high frequency of load cycles, and large component sizes found in oil sands processing facilities. Monitoring and repair strategies for fatigue cracks are typically based on vendor specifications and the experience of maintenance personnel. This paper provided details of an optimized crack management program applied to a BE 395B shovel boom. The proposed crack management tool uses a chart to predict the remaining life of a corner crack in the shovel boom. Predictions are based on limited field measurements of operating loads as well as on data obtained from fatigue testing of boom material, and a finite element analysis of the shovel boom. Field and laboratory data are used along with fracture mechanics and finite element modelling to predict crack life. It was concluded that the tool will allow inspectors and planners to schedule repairs based on safe service life. The tool is applicable for any components subjected to fatigue loading. 3 refs., 21 tabs., 64 figs.

  19. ISOTHERMAL AND THERMOMECHANICAL FATIGUE OF A NICKEL-BASE SUPERALLOY

    Directory of Open Access Journals (Sweden)

    Carlos Carvalho Engler-Pinto Júnior

    2014-06-01

    Full Text Available Thermal gradients arising during transient regimes of start-up and shutdown operations produce a complex thermal and mechanical fatigue loading which limits the life of turbine blades and other engine components operating at high temperatures. More accurate and reliable assessment under non-isothermal fatigue becomes therefore mandatory. This paper investigates the nickel base superalloy CM 247LC-DS under isothermal low cycle fatigue (LCF and thermomechanical fatigue (TMF. Test temperatures range from 600°C to 1,000°C. The behavior of the alloy is strongly affected by the temperature variation, especially in the 800°C-1,000°C range. The Ramberg-Osgood equation fits very well the observed isothermal behavior for the whole temperature range. The simplified non-isothermal stress-strain model based on linear plasticity proposed to represent the thermo-mechanical fatigue behavior was able to reproduce the observed behavior for both in-phase and out-of-phase TMF cycling.

  20. Development of a crack monitoring technique for use in a corrosion fatigue study of SA533-B pressure vessel steel

    International Nuclear Information System (INIS)

    Benson, J.M.; Tait, R.B.; Garrett, G.G.

    1981-10-01

    At present there does not exist a realistic crack growth law which will provide a good description of the relationship between the alternating stress intensity factor and the crack growth per cycle of stress. Such a law should be applicable to either the pressurized water reactor environment (PWR) or boiling water reactor environmnt (BWR). This project was formulated with the aim of examining the fatigue crack growth rate of SA533-B steel (a nuclear pressure vessel steel) in the threshold region in a simulated PWR environment. The aim of this report is to develop a crack monitoring technique for use in corrosion fatigue studies. Factors affecting fatigue crack propagation include: frequency, stress range, the effect of irradiation, ageing and environment. The mechanisms of crack propagation that are discussed include: slip dissolution, hydrogen assisted cracking, corrosion potential, and morphology studies. D.C. electrical potential, the compliance technique and the back-faced strain gauge method can be used for crack monitoring. Details are also given on the experimental equipment and programme. The results of the experiment has shown that the potential difference technique for monitoring crack length is a valuable one and is well suited for use in fatigue testing applications

  1. Wireless sleep monitoring headband to identify sleep and track fatigue

    Science.gov (United States)

    Ramasamy, Mouli; Oh, Sechang; Varadan, Vijay K.

    2014-04-01

    Detection of sleepiness and drowsiness in human beings has been a daunting task for both engineering and medical technologies. Accuracy, precision and promptness of detection have always been an issue that has to be dealt by technologists. Commonly, the rudimentary bio potential signals - ECG, EOG, EEG and EMG are used to classify and discriminate sleep from being awake. However, the potential drawbacks may be high false detections, low precision, obtrusiveness, aftermath analysis, etc. To overcome the disadvantages, this paper proposes the design of a wireless and a real time monitoring system to track sleep and detect fatigue. This concept involves the use of EOG and EEG to measure the blink rate and asses the person's condition. In this user friendly and intuitive approach, EOG and EEG signals are obtained by the dry gold wire nano-sensors fabricated on the inner side of a flexible headband. The acquired signals are then electrically transmitted to the data processing and transmission unit, which transmits the processed data to the receiver/monitoring module through WCDMA/GSM communication. This module is equipped with a software program to process, feature extract, analyze, display and store the information. Thereby, immediate detection of a person falling asleep is made feasible and, tracking the sleep cycle continuously provides an insight about the experienced fatigue level. The novel approach of using a wireless, real time, dry sensor on a flexible substrate reduces the obtrusiveness, and techniques adopted in the electronics and software facilitates and substantial increase in efficiency, accuracy and precision.

  2. Fatigue of extracted lead zirconate titanate multilayer actuators under unipolar high field electric cycling

    International Nuclear Information System (INIS)

    Wang, Hong; Lee, Sung-Min; Wang, James L.; Lin, Hua-Tay

    2014-01-01

    Testing of large prototype lead zirconate titanate (PZT) stacks presents substantial technical challenges to electronic testing systems, so an alternative approach that uses subunits extracted from prototypes has been pursued. Extracted 10-layer and 20-layer plate specimens were subjected to an electric cycle test under an electric field of 3.0/0.0 kV/mm, 100 Hz to 10 8 cycles. The effects of measurement field level and stack size (number of PZT layers) on the fatigue responses of piezoelectric and dielectric coefficients were observed. On-line monitoring permitted examination of the fatigue response of the PZT stacks. The fatigue rate (based on on-line monitoring) and the fatigue index (based on the conductance spectrum from impedance measurement or small signal measurement) were developed to quantify the fatigue status of the PZT stacks. The controlling fatigue mechanism was analyzed against the fatigue observations. The data presented can serve as input to design optimization of PZT stacks and to operation optimization in critical applications, such as piezoelectric fuel injectors in heavy-duty diesel engines

  3. Fatigue of extracted lead zirconate titanate multilayer actuators under unipolar high field electric cycling

    Science.gov (United States)

    Wang, Hong; Lee, Sung-Min; Wang, James L.; Lin, Hua-Tay

    2014-12-01

    Testing of large prototype lead zirconate titanate (PZT) stacks presents substantial technical challenges to electronic testing systems, so an alternative approach that uses subunits extracted from prototypes has been pursued. Extracted 10-layer and 20-layer plate specimens were subjected to an electric cycle test under an electric field of 3.0/0.0 kV/mm, 100 Hz to 108 cycles. The effects of measurement field level and stack size (number of PZT layers) on the fatigue responses of piezoelectric and dielectric coefficients were observed. On-line monitoring permitted examination of the fatigue response of the PZT stacks. The fatigue rate (based on on-line monitoring) and the fatigue index (based on the conductance spectrum from impedance measurement or small signal measurement) were developed to quantify the fatigue status of the PZT stacks. The controlling fatigue mechanism was analyzed against the fatigue observations. The data presented can serve as input to design optimization of PZT stacks and to operation optimization in critical applications, such as piezoelectric fuel injectors in heavy-duty diesel engines.

  4. Fatigue of extracted lead zirconate titanate multilayer actuators under unipolar high field electric cycling

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Hong, E-mail: wangh@ornl.gov; Lee, Sung-Min; Wang, James L. [Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States); Lin, Hua-Tay [School of Mechanical and Electronic Engineering, Guangdong University of Technology, Guangzhou, 510006 (China)

    2014-12-21

    Testing of large prototype lead zirconate titanate (PZT) stacks presents substantial technical challenges to electronic testing systems, so an alternative approach that uses subunits extracted from prototypes has been pursued. Extracted 10-layer and 20-layer plate specimens were subjected to an electric cycle test under an electric field of 3.0/0.0 kV/mm, 100 Hz to 10{sup 8} cycles. The effects of measurement field level and stack size (number of PZT layers) on the fatigue responses of piezoelectric and dielectric coefficients were observed. On-line monitoring permitted examination of the fatigue response of the PZT stacks. The fatigue rate (based on on-line monitoring) and the fatigue index (based on the conductance spectrum from impedance measurement or small signal measurement) were developed to quantify the fatigue status of the PZT stacks. The controlling fatigue mechanism was analyzed against the fatigue observations. The data presented can serve as input to design optimization of PZT stacks and to operation optimization in critical applications, such as piezoelectric fuel injectors in heavy-duty diesel engines.

  5. Evaluation of upper limb muscle fatigue based on surface electromyography.

    Science.gov (United States)

    Zhou, Qianxiang; Chen, Yuhong; Ma, Chao; Zheng, Xiaohui

    2011-10-01

    Fatigue is believed to be a major contributory factor to occupational injuries in machine operators. The development of accurate and usable techniques to measure operator fatigue is therefore important. In this study, we used a novel method based on surface electromyography (sEMG) of the biceps brachii and the Borg scale to evaluate local muscle fatigue in the upper limb after isometric muscle action. Thirteen young males performed isometric actions with the upper limb at different force levels. sEMG activities of the biceps brachii were recorded during the actions. Borg scales were used to evaluate the subjective sensation of local fatigue of the biceps brachii after the actions. sEMG activities were analyzed using the one-third band octave method, and an equation to determine the degree of fatigue was derived based on the relationship between the variable and the Borg scale. The results showed that the relationship could be expressed by a conic curve, and could be used to evaluate muscle fatigue during machine operation.

  6. Prediction of residual life of low-cycle fatigue in austenitic stainless steel based on indentation test

    International Nuclear Information System (INIS)

    Yonezu, Akio; Touda, Yuya; Kim, HakGui; Yoneda, Keishi; Sakihara, Masayuki; Minoshima; Kohji

    2011-01-01

    In this study, a method to predict residual life of low-cycle fatigue in austenitic stainless steel (SUS316NG) was proposed based on indentation test. Low-cycle fatigue tests for SUS316NG were first conducted based on uniaxial tensile-compressive loading under the control of true strain range. Applied strain ranges were varied from about 3 to 12%. Their hysteresis loops of stress and strain were monitored during the fatigue tests. Plastic deformation range in hysteresis loop at each cycle could be roughly expressed by bi-linear hardening rule, whose plastic properties involve yield stress and work-hardening coefficient. The cyclic plastic properties were found to be dependent on the number of cycles and applied strain range, due to work-hardening. We experimentally investigated the empirical relationship between the plastic properties and number of cycles for each applied strain range. It is found that the relationship quantitatively predicts the applied strain range and number of cycles, when the plastic properties, or yield stress and work-hardening coefficient were known. Indentation tests were applied to the samples subjected to low cycle fatigue test, in order to quantitatively determine the plastic properties. The estimated properties were assigned to the proposed relationship, yielding the applied strain range and the cycle numbers. The proposed method was applied to the several stainless steel samples subjected to low cycle fatigue tests, suggesting that their residual lives could be reasonably predicted. Our method is thus useful for predicting the residual life of low-cycle fatigue in austenitic stainless steel. (author)

  7. Probabilistic fatigue life prediction methodology for notched components based on simple smooth fatigue tests

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Z. R.; Li, Z. X. [Dept.of Engineering Mechanics, Jiangsu Key Laboratory of Engineering Mechanics, Southeast University, Nanjing (China); Hu, X. T.; Xin, P. P.; Song, Y. D. [State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing (China)

    2017-01-15

    The methodology of probabilistic fatigue life prediction for notched components based on smooth specimens is presented. Weakestlink theory incorporating Walker strain model has been utilized in this approach. The effects of stress ratio and stress gradient have been considered. Weibull distribution and median rank estimator are used to describe fatigue statistics. Fatigue tests under different stress ratios were conducted on smooth and notched specimens of titanium alloy TC-1-1. The proposed procedures were checked against the test data of TC-1-1 notched specimens. Prediction results of 50 % survival rate are all within a factor of two scatter band of the test results.

  8. Construction Worker Fatigue Prediction Model Based on System Dynamic

    Directory of Open Access Journals (Sweden)

    Wahyu Adi Tri Joko

    2017-01-01

    Full Text Available Construction accident can be caused by internal and external factors such as worker fatigue and unsafe project environment. Tight schedule of construction project forcing construction worker to work overtime in long period. This situation leads to worker fatigue. This paper proposes a model to predict construction worker fatigue based on system dynamic (SD. System dynamic is used to represent correlation among internal and external factors and to simulate level of worker fatigue. To validate the model, 93 construction workers whom worked in a high rise building construction projects, were used as case study. The result shows that excessive workload, working elevation and age, are the main factors lead to construction worker fatigue. Simulation result also shows that these factors can increase worker fatigue level to 21.2% times compared to normal condition. Beside predicting worker fatigue level this model can also be used as early warning system to prevent construction worker accident

  9. Monitoring Fatigue Status with HRV Measures in Elite Athletes: An Avenue Beyond RMSSD?

    Science.gov (United States)

    Schmitt, Laurent; Regnard, Jacques; Millet, Grégoire P.

    2015-01-01

    Among the tools proposed to assess the athlete's “fatigue,” the analysis of heart rate variability (HRV) provides an indirect evaluation of the settings of autonomic control of heart activity. HRV analysis is performed through assessment of time-domain indices, the square root of the mean of the sum of the squares of differences between adjacent normal R-R intervals (RMSSD) measured during short (5 min) recordings in supine position upon awakening in the morning and particularly the logarithm of RMSSD (LnRMSSD) has been proposed as the most useful resting HRV indicator. However, if RMSSD can help the practitioner to identify a global “fatigue” level, it does not allow discriminating different types of fatigue. Recent results using spectral HRV analysis highlighted firstly that HRV profiles assessed in supine and standing positions are independent and complementary; and secondly that using these postural profiles allows the clustering of distinct sub-categories of “fatigue.” Since, cardiovascular control settings are different in standing and lying posture, using the HRV figures of both postures to cluster fatigue state embeds information on the dynamics of control responses. Such, HRV spectral analysis appears more sensitive and enlightening than time-domain HRV indices. The wealthier information provided by this spectral analysis should improve the monitoring of the adaptive training-recovery process in athletes. PMID:26635629

  10. Risk Based Optimal Fatigue Testing

    DEFF Research Database (Denmark)

    Sørensen, John Dalsgaard; Faber, M.H.; Kroon, I.B.

    1992-01-01

    Optimal fatigue life testing of materials is considered. Based on minimization of the total expected costs of a mechanical component a strategy is suggested to determine the optimal stress range levels for which additional experiments are to be performed together with an optimal value...

  11. High Frequency Vibration Based Fatigue Testing of Developmental Alloys

    Science.gov (United States)

    Holycross, Casey M.; Srinivasan, Raghavan; George, Tommy J.; Tamirisakandala, Seshacharyulu; Russ, Stephan M.

    Many fatigue test methods have been previously developed to rapidly evaluate fatigue behavior. This increased test speed can come at some expense, since these methods may require non-standard specimen geometry or increased facility and equipment capability. One such method, developed by George et al, involves a base-excited plate specimen driven into a high frequency bending resonant mode. This resonant mode is of sufficient frequency (typically 1200 to 1700 Hertz) to accumulate 107 cycles in a few hours. One of the main limitations of this test method is that fatigue cracking is almost certainly guaranteed to be surface initiated at regions of high stress. This brings into question the validity of the fatigue test results, as compared to more traditional uniaxial, smooth-bar testing, since high stresses are subjecting only a small volume to fatigue damage. This limitation also brings into question the suitability of this method to screen developmental alloys, should their initiation life be governed by subsurface flaws. However, if applicable, the rapid generation of fatigue data using this method would facilitate faster design iterations, identifying more quickly, material and manufacturing process deficiencies. The developmental alloy used in this study was a powder metallurgy boron-modified Ti-6Al-4V, a new alloy currently being considered for gas turbine engine fan blades. Plate specimens were subjected to fully reversed bending fatigue. Results are compared with existing data from commercially available Ti-6Al-4V using both vibration based and more traditional fatigue test methods.

  12. A structural health monitoring fastener for tracking fatigue crack growth in bolted metallic joints

    Science.gov (United States)

    Rakow, Alexi Schroder

    Fatigue cracks initiating at fastener hole locations in metallic components are among the most common form of airframe damage. The fastener hole site has been surveyed as the second leading initiation site for fatigue related accidents of fixed wing aircraft. Current methods for inspecting airframes for these cracks are manual, whereby inspectors rely on non-destructive inspection equipment or hand-held probes to scan over areas of a structure. Use of this equipment often demands disassembly of the vehicle to search appropriate hole locations for cracks, which elevates the complexity and cost of these maintenance inspections. Improved reliability, safety, and reduced cost of such maintenance can be realized by the permanent integration of sensors with a structure to detect this damage. Such an integrated system of sensors would form a structural health monitoring (SHM) system. In this study, an Additive, Interleaved, Multi-layer Electromagnetic (AIME) sensor was developed and integrated with the shank of a fastener to form a SHM Fastener, a new SHM technology targeted at detection of fastener hole cracks. The major advantages of the SHM Fastener are its installation, which does not require joint layer disassembly, its capability to detect inner layer cracks, and its capability to operate in a continuous autonomous mode. Two methods for fabricating the proposed SHM Fastener were studied. The first option consisted of a thin flexible printed circuit film that was bonded around a thin metallic sleeve placed around the fastener shank. The second option consisted of coating sensor materials directly to the shank of a part in an effort to increase the durability of the sensor under severe loading conditions. Both analytical and numerical models were developed to characterize the capability of the sensors and provide a design tool for the sensor layout. A diagnostic technique for crack growth monitoring was developed to complete the SHM system, which consists of the

  13. Fatigue Damage in Wood

    DEFF Research Database (Denmark)

    Clorius, Christian Odin; Pedersen, Martin Bo Uhre; Hoffmeyer, Preben

    1996-01-01

    An investigation of fatigue failure in wood subjected to load cycles in compression parallel to grain is presented. Fatigue failure is found to depend both on the total time under load and on the number of cycles.Recent accelerated fatigue research on wood is reviewed, and a discrepancy between...... to 10 Hz are used. The number of cycles to failure is found to be a poor measure of the fatigue performance of wood. Creep, maximum strain, stiffness and work are monitored throughout the fatigue tests. Accumulated creep is suggested identified with damage and a correlation between stiffness reduction...

  14. Damage formation, fatigue behavior and strength properties of ZrO{sub 2}-based ceramics

    Energy Technology Data Exchange (ETDEWEB)

    Kozulin, A. A., E-mail: kozulyn@ftf.tsu.ru; Kulkov, S. S. [Tomsk State University, Tomsk, 634050 (Russian Federation); Narikovich, A. S.; Leitsin, V. N. [Immanuel Kant Baltic Federal University, Kaliningrad, 236041 (Russian Federation); Kulkov, S. N., E-mail: kulkov@ispms.ru [Tomsk State University, Tomsk, 634050 (Russian Federation); Institute of Strength Physics and Materials Science SB RAS, Tomsk, 634055 (Russian Federation)

    2016-08-02

    It is suggested that a non-destructive testing technique using a three-dimensional X-ray tomography be applied to detecting internal structural defects and monitoring damage formation in a ceramic composite structure subjected to a bending load. Three-point bending tests are used to investigate the fatigue behavior and mechanical and physical properties of medical-grade ZrO{sub 2}-based ceramics. The bending strength and flexural modulus are derived under static conditions at a loading rate of 2 mm/min. The fatigue strength and fatigue limit under dynamic loading are investigated at a frequency of 10 Hz in three stress ranges: 0.91–0.98, 0.8–0.83, and 0.73–0.77 MPa of the static bending strength. The average values of the bending strength and flexural modulus of sintered specimens are 43 MPa and 22 GPa, respectively. The mechanical properties of the ceramics are found to be similar to those of bone tissues. The testing results lead us to conclude that the fatigue limit obtained from 10{sup 5} stress cycles is in the range 33–34 MPa, i.e. it accounts for about 75% of the static bending strength for the test material.

  15. Stress-based fatigue assessment of major component in NPP using modified Green's function approach

    International Nuclear Information System (INIS)

    Ko, Han Ok; Jhung, Myung Jo; Choi, Jae Boong

    2013-01-01

    In this paper, the modified GFA which can consider temperature-dependent material properties is proposed by using a neural network (NN) and weight factor. To verify the modified GFA, thermal stresses by the proposed method are compared with those by FEM. Finally, pros and cons of the new method as well as technical findings from the assessment are discussed to show applicability of them. In this paper, the modified GFA considering temperature-dependent material properties is proposed by using NN and weight factor. To verify the proposed method, thermal stresses by the modified Green's function are compared with those by FEM and the results between two methods show a good agreement. Finally, it is anticipated that more precise fatigue evaluation is performed by using the proposed method. Recently, 434 nuclear reactors are being operated in the world. Among them, about 40% reactors are being operated beyond their design life or will be approaching their life. During the long term operation, various degradation mechanisms are occurred. Fatigue damage caused by alternating operational stresses in terms of temperature or pressure change is the one of important damage mechanisms in the nuclear power plants (NPPs). Although components important to safety were designed to withstand the fatigue damage, cumulative usage factor (CUF) at some locations can exceed the design limit beyond the design life. So, it is necessary to monitor the fatigue damage of major components during the long term operation. Researches on fatigue monitoring system (FMS) have been widely performed. In USA, the FatiguePro was developed by EPRI and was applied to the CE, WEC, B and W and GE type reactors. In Korea, the Kori unit 1 which started commercial operation in 1978 is being operated beyond its design life. At the stage of the license renewal, various plans for degradation mechanisms were established and reviewed. And, in case of fatigue damage, to monitor the fatigue damage of major components

  16. Development of a web-based monitoring system using operation parameters for the main component in nuclear power plants

    Energy Technology Data Exchange (ETDEWEB)

    Son, Dong Chan; An Kang Il; Hong, Suk Young; Lee, Jeong Soo; Lee, Kwang Yeol; Shin, Sun Hee; Lee, Chun Wha; Son, So Hee [Daesang Information Technology Co., Ltd., Seoul (Korea, Republic of)

    2003-03-15

    The frequency of the damage is increasing, which is caused by the fatigue, according to the increase of running of nuclear power plants. So we need to acquire the reliance of design data to estimate the fatigue and damage of major machinery that might happen as time-dependent crack growth characterization. The research is focused on keeping operating record of nuclear power plants about major machinery which consists of a nuclear reactor pressure boarder on each excessive operating condition including normal operating and extraordinary operating by estimating fracture mechanical movements on real time and fatigue about major nuclear power plants machinery, which are acquired the pressure and temperature data. For further details about the scope and contents of R and D are following: development of H/W that is necessary to acquire operating real time data of heating and hydraulic power, selection of a safety variable about major system by each type (the fourth unit), communication protocol development for connecting between CARE system data base server and fatigue monitoring system data base server, development of connecting database for controlling and storing of heating and hydraulic power operating data, real time monitoring system development based on web using JAVA.

  17. Driver fatigue alarm based on eye detection and gaze estimation

    Science.gov (United States)

    Sun, Xinghua; Xu, Lu; Yang, Jingyu

    2007-11-01

    The driver assistant system has attracted much attention as an essential component of intelligent transportation systems. One task of driver assistant system is to prevent the drivers from fatigue. For the fatigue detection it is natural that the information about eyes should be utilized. The driver fatigue can be divided into two types, one is the sleep with eyes close and another is the sleep with eyes open. Considering that the fatigue detection is related with the prior knowledge and probabilistic statistics, the dynamic Bayesian network is used as the analysis tool to perform the reasoning of fatigue. Two kinds of experiments are performed to verify the system effectiveness, one is based on the video got from the laboratory and another is based on the video got from the real driving situation. Ten persons participate in the test and the experimental result is that, in the laboratory all the fatigue events can be detected, and in the practical vehicle the detection ratio is about 85%. Experiments show that in most of situations the proposed system works and the corresponding performance is satisfying.

  18. Areva fatigue concept. Fast fatigue evaluation, a new method for fatigue analysis

    International Nuclear Information System (INIS)

    Heinz, Benedikt; Bergholz, Steffen; Rudolph, Juergen

    2011-01-01

    Within the discussions on the long term operation (LTO) of nuclear power plants the ageing management is on the focus of that analysis. The knowledge of the operational thermal cyclic load data on components of the power plants and their evaluation in the fatigue analysis is a central concern. The changes in fatigue requirements (e.g. the consideration of environmentally assisted fatigue - EAF) recently discussed and LTO efforts are a strong motivation for the identification of margins in the existing fatigue analysis approaches. These margins should be considered within new approaches in order to obtain realistic (or more accurate) analysis results. Of course, these new analysis approaches have to be manageable and efficient. The Areva Fatigue Concept (AFC) offers the comprehensive conceptual basis for the consideration of fatigue on different levels and depths. The combination of data logging and automated fatigue evaluation are important modules of the AFC. Besides the established simplified stress based fatigue estimation Areva develops a further automated fatigue analysis method called Fast Fatigue Evaluation (FFE). This method comprises highly automated stress analyses at the fatigue relevant locations of the component. Hence, a component specific course of stress as a function of time is determined based on FAMOS or similar temperature measurement systems. The subsequent application of the rain flow cycle counting algorithm allows for the determination of the usage factor following the rules of the design code requirements. The new FFE approach constitutes a cycle counting method based on the real stresses in the component, and determined as result a rule-conformity cumulative usage factor. (orig.)

  19. [Analysis of the Muscle Fatigue Based on Band Spectrum Entropy of Multi-channel Surface Electromyography].

    Science.gov (United States)

    Liu, Jian; Zou, Renling; Zhang, Dongheng; Xu, Xiulin; Hu, Xiufang

    2016-06-01

    Exercise-induced muscle fatigue is a phenomenon that the maximum voluntary contraction force or power output of muscle is temporarily reduced due to muscular movement.If the fatigue is not treated properly,it will bring about a severe injury to the human body.With multi-channel collection of lower limb surface electromyography signals,this article analyzes the muscle fatigue by adoption of band spectrum entropy method which combined electromyographic signal spectral analysis and nonlinear dynamics.The experimental result indicated that with the increase of muscle fatigue,muscle signal spectrum began to move to low frequency,the energy concentrated,the system complexity came down,and the band spectrum entropy which reflected the complexity was also reduced.By monitoring the entropy,we can measure the degree of muscle fatigue,and provide an indicator to judge fatigue degree for the sports training and clinical rehabilitation training.

  20. Fatigue life estimation of MD36 and MD523 bogies based on damage accumulation and random fatigue theory

    International Nuclear Information System (INIS)

    Younesian, Davood; Solhmirzaei, Ali; Gachloo, Alireza

    2009-01-01

    Bogies are one of the multifunctional parts of trains which are extremely subjected to random loads. This type of oscillating and random excitation arises from irregularities of the track including rail surface vertical roughness, rail joints, variance in super-elevation, and also wheel imperfections like wheel flats and unbalancy. Since most of the prementioned sources have random nature, a random based theory should be applied for fatigue life estimation of the bogie frame. Two methods of fatigue life estimation are investigated in this paper. The first approach which is being implemented in time domain is based on the damage accumulation (DA) approach. Using Monte-Carlo simulation algorithm, the rail surface roughness is generated. Finite element (FE) model of the bogie is subjected to the generated random excitation in the first approach and the stress time histories are obtained, and consequently the fatigue life is estimated by using the rain-flow algorithm. In the second approach, the fatigue life is estimated in frequency domain. Power spectral density (PSD) of the stress is obtained by using the FE model of the bogie frame and the fatigue life is estimated using Rayleigh technique in random fatigue theory. A comprehensive parametric study is carried out and effects of different parameters like the train speeds and level of the rail surface vertical roughness on the estimated fatigue life are investigated

  1. Fatigue crack propagation: Probabilistic models and experimental evidence

    International Nuclear Information System (INIS)

    Lucia, A.C.; Jovanovic, A.

    1987-01-01

    The central aim of the LWR Primary Circuit Component Life Prediction Project, going on at JRC-Ispra, is to develop and check a 'procedure' (encompassing monitoring and inspection, data collection and analysis, prediction) allowing the quantitatives estimation of the accumulation of structural damage and of the residual lifetime. The ongoing activity matches theoretical development and experimentation, the latter being at present essentially based on a test-rig for room-temperature fatigue cycling of 1:5 scaled models of pressure vessels. During Phase I of fatigue testing of vessel R2, different pieces of information coming from material characterization, non-destructive inspection, continuous monitoring, stress analysis, have been merged and used to infere the future behaviour of the structure. The prediction of residual lifetime (cycles to failure), based on the outcomes of the ultrasonic continuous monitoring and made by means of the COVASTOL code, was in quite good agreement with experimental evidence. (orig./HP)

  2. Multi-purpose fatigue sensor. Part 1. Uniaxial and multiaxial fatigue

    Directory of Open Access Journals (Sweden)

    M.V. Karuskevich

    2016-10-01

    Full Text Available The paper describes the key principles and results of preliminary experiments aimed at the development of new technique for the fatigue life prediction under conditions of biaxial cyclic tension. The foundations of the method were developed early by the numerous tests with monitoring the process of surface deformation relief formation, which is proved to be an indicator of accumulated fatigue damage under uniaxial fatigue. The employed phenomenon was early applied for the development of a family of uniaxial loading fatigue sensors. The formation of strain induced relief has been recently taken into consideration as a part of damage accumulation criteria under biaxial fatigue as well. The home-made testing machine has been designed to implement combined bending and torsion loading that simulates loads experienced by an aircraft wing skin. The experimental evidences on formation and evolution of the deformation relief revealed under conditions of combined loading, supports the proposed concept of biaxial fatigue sensor

  3. Development and Application of a Clinical Microsystem Simulation Methodology for Human Factors-Based Research of Alarm Fatigue.

    Science.gov (United States)

    Kobayashi, Leo; Gosbee, John W; Merck, Derek L

    2017-07-01

    (1) To develop a clinical microsystem simulation methodology for alarm fatigue research with a human factors engineering (HFE) assessment framework and (2) to explore its application to the comparative examination of different approaches to patient monitoring and provider notification. Problems with the design, implementation, and real-world use of patient monitoring systems result in alarm fatigue. A multidisciplinary team is developing an open-source tool kit to promote bedside informatics research and mitigate alarm fatigue. Simulation, HFE, and computer science experts created a novel simulation methodology to study alarm fatigue. Featuring multiple interconnected simulated patient scenarios with scripted timeline, "distractor" patient care tasks, and triggered true and false alarms, the methodology incorporated objective metrics to assess provider and system performance. Developed materials were implemented during institutional review board-approved study sessions that assessed and compared an experimental multiparametric alerting system with a standard monitor telemetry system for subject response, use characteristics, and end-user feedback. A four-patient simulation setup featuring objective metrics for participant task-related performance and response to alarms was developed along with accompanying structured HFE assessment (questionnaire and interview) for monitor systems use testing. Two pilot and four study sessions with individual nurse subjects elicited true alarm and false alarm responses (including diversion from assigned tasks) as well as nonresponses to true alarms. In-simulation observation and subject questionnaires were used to test the experimental system's approach to suppressing false alarms and alerting providers. A novel investigative methodology applied simulation and HFE techniques to replicate and study alarm fatigue in controlled settings for systems assessment and experimental research purposes.

  4. Generic Reliability-Based Inspection Planning for Fatigue Sensitive Details

    DEFF Research Database (Denmark)

    Sørensen, John Dalsgaard; Straub, Daniel; Faber, Michael Havbro

    2005-01-01

    of fatigue sensitive details in fixed offshore steel jacket platforms and FPSO ship structures. Inspection and maintenance activities are planned such that code based requirements to the safety of personnel and environment for the considered structure are fulfilled and at the same time such that the overall......The generic approach for planning of in-service NDT inspections is extended to cover the case where the fatigue load is modified during the design lifetime of the structure. Generic reliability-based inspection planning has been developed as a practical approach to perform inspection planning...... expected costs for design, inspections, repairs and failures are minimized. The method is based on the assumption of “no-finds” of cracks during inspections. Each fatigue sensitive detail is categorized according to their type of details (SN curves), FDF values, RSR values, inspection, repair and failure...

  5. Monitoring mental fatigue in the ageing working population

    NARCIS (Netherlands)

    de Jong, Marlon; Jolij, Jacob; Lorist, Monicque

    2017-01-01

    Mental fatigue, during or after a period of prolonged mental workload, is a common phenomenon in our everyday lives. Mentally fatigued people generally respond more slowly and less accurately to stimuli in their environment, which potentially leads to dangerous situations. The aim of my research is

  6. An Integrated Health Monitoring Method for Structural Fatigue Life Evaluation Using Limited Sensor Data

    Directory of Open Access Journals (Sweden)

    Jingjing He

    2016-11-01

    Full Text Available A general framework for structural fatigue life evaluation under fatigue cyclic loading using limited sensor data is proposed in this paper. First, limited sensor data are measured from various sensors which are preset on the complex structure. Then the strain data at remote spots are used to obtain the strain responses at critical spots by the strain/stress reconstruction method based on empirical mode decomposition (REMD method. All the computations in this paper are directly performed in the time domain. After the local stress responses at critical spots are determined, fatigue life evaluation can be performed for structural health management and risk assessment. Fatigue life evaluation using the reconstructed stresses from remote strain gauge measurement data is also demonstrated with detailed error analysis. Following this, the proposed methodology is demonstrated using a three-dimensional frame structure and a simplified airfoil structure. Finally, several conclusions and future work are drawn based on the proposed study.

  7. Development of a web-based monitoring system using operation parameters for the main component in nuclear power plants

    International Nuclear Information System (INIS)

    Son, Dong Chan; An, Kung Il; Hong, Suk Young; Lee, Jeong Soo; Jung, Duk Jin; Shin, Sun Hee; Son, So Hee

    2004-02-01

    The frequency of the damage is increasing, which is caused by the fatigue, according to the increase of running of nuclear power plants. So we need to acquire the reliance of design data to estimate the fatigue and damage of major machinery that might happen as time-dependent crack growth characterization. The research is focused on keeping operating record of nuclear power plants about major machinery which consists of a nuclear reactor pressure boarder on each excessive operating condition including normal operating and extraordinary operating by estimating fracture mechanical movements on real time and fatigue about major nuclear power plants machinery, which are acquired the pressure and temperature data. For further details about the scope and contents of R and D are following. Development of H/W that is necessary to acquire operating real time data of heating and hydraulic power. Selection of a safety variable about major system by each type (the four NPP, all unit). Communication protocol development for connecting between CARE system data base server and fatigue monitoring system data base server. Development of connecting database for controlling and storing of heating and hydraulic power operating data. Real time monitoring system development based on Web using JAVA

  8. Development of a web-based monitoring system using operation parameters for the main component in nuclear power plants

    Energy Technology Data Exchange (ETDEWEB)

    Son, Dong Chan; An, Kung Il; Hong, Suk Young; Lee, Jeong Soo; Jung, Duk Jin; Shin, Sun Hee; Son, So Hee [Daesang Information Technology Co., Ltd., Seoul (Korea, Republic of)

    2004-02-15

    The frequency of the damage is increasing, which is caused by the fatigue, according to the increase of running of nuclear power plants. So we need to acquire the reliance of design data to estimate the fatigue and damage of major machinery that might happen as time-dependent crack growth characterization. The research is focused on keeping operating record of nuclear power plants about major machinery which consists of a nuclear reactor pressure boarder on each excessive operating condition including normal operating and extraordinary operating by estimating fracture mechanical movements on real time and fatigue about major nuclear power plants machinery, which are acquired the pressure and temperature data. For further details about the scope and contents of R and D are following. Development of H/W that is necessary to acquire operating real time data of heating and hydraulic power. Selection of a safety variable about major system by each type (the four NPP, all unit). Communication protocol development for connecting between CARE system data base server and fatigue monitoring system data base server. Development of connecting database for controlling and storing of heating and hydraulic power operating data. Real time monitoring system development based on Web using JAVA.

  9. Compressive Fatigue in Wood

    DEFF Research Database (Denmark)

    Clorius, Christian Odin; Pedersen, Martin Bo Uhre; Hoffmeyer, Preben

    1999-01-01

    An investigation of fatigue failure in wood subjected to load cycles in compression parallel to grain is presented. Small clear specimens of spruce are taken to failure in square wave formed fatigue loading at a stress excitation level corresponding to 80% of the short term strength. Four...... frequencies ranging from 0.01 Hz to 10 Hz are used. The number of cycles to failure is found to be a poor measure of the fatigue performance of wood. Creep, maximum strain, stiffness and work are monitored throughout the fatigue tests. Accumulated creep is suggested identified with damage and a correlation...

  10. Energy-based fatigue model for shape memory alloys including thermomechanical coupling

    Science.gov (United States)

    Zhang, Yahui; Zhu, Jihong; Moumni, Ziad; Van Herpen, Alain; Zhang, Weihong

    2016-03-01

    This paper is aimed at developing a low cycle fatigue criterion for pseudoelastic shape memory alloys to take into account thermomechanical coupling. To this end, fatigue tests are carried out at different loading rates under strain control at room temperature using NiTi wires. Temperature distribution on the specimen is measured using a high speed thermal camera. Specimens are tested to failure and fatigue lifetimes of specimens are measured. Test results show that the fatigue lifetime is greatly influenced by the loading rate: as the strain rate increases, the fatigue lifetime decreases. Furthermore, it is shown that the fatigue cracks initiate when the stored energy inside the material reaches a critical value. An energy-based fatigue criterion is thus proposed as a function of the irreversible hysteresis energy of the stabilized cycle and the loading rate. Fatigue life is calculated using the proposed model. The experimental and computational results compare well.

  11. Investigation of Effectiveness of Some Vibration-Based Techniques in Early Detection of Real-Time Fatigue Failure in Gears

    Directory of Open Access Journals (Sweden)

    Hasan Ozturk

    2010-01-01

    Full Text Available Bending fatigue crack is a dangerous and insidious mode of failure in gears. As it produces no debris in its early stages, it gives little warning during its progression, and usually results in either immediate loss of serviceability or greatly reduced power transmitting capacity. This paper presents the applications of vibration-based techniques (i.e. conventional time and frequency domain analysis, cepstrum, and continuous wavelet transform to real gear vibrations in the early detection, diagnosis and advancement monitoring of a real tooth fatigue crack and compares their detection and diagnostic capabilities on the basis of experimental results. Gear fatigue damage is achieved under heavy-loading conditions and the gearbox is allowed to run until the gears suffer badly from complete tooth breakage. It has been found that the initiation and progression of fatigue crack cannot be easily detected by conventional time and frequency domain approaches until the fault is significantly developed. On the contrary, the wavelet transform is quite sensitive to any change in gear vibration and reveals fault features earlier than other methods considered.

  12. Evaluation of an energy-based fatigue approach considering mean stress effects

    Energy Technology Data Exchange (ETDEWEB)

    Kabir, S. M. Humayun [Chittagong University of Engineering and Technology, Chittagong (Bangladesh); Yeo, Tae In [University of Ulsan, Ulsan (Korea, Republic of)

    2014-04-15

    In this paper, an attempt is made to extend the total strain energy approach for predicting the fatigue life subjected to mean stress under uniaxial state. The effects of means stress on the fatigue failure of a ferritic stainless steel and high pressure tube steel are studied under strain-controlled low cycle fatigue condition. Based on the fatigue results from different strain ratios, modified total strain energy density approach is proposed to account for the mean stress effects. The proposed damage parameter provides convenient means of evaluating fatigue life with mean stress effects considering the fact that the definitions used for measuring strain energies are the same as in the fully-reversed cycling (R = -1). A good agreement is observed between experimental life and predicted life using proposed approach. Two other mean stress models (Smith-Watson-Topper model and Morrow model) are also used to evaluate the low cycle fatigue data. Based on a simple statistical estimator, the proposed approach is compared with these models and is found realistic.

  13. Evaluation of an energy-based fatigue approach considering mean stress effects

    International Nuclear Information System (INIS)

    Kabir, S. M. Humayun; Yeo, Tae In

    2014-01-01

    In this paper, an attempt is made to extend the total strain energy approach for predicting the fatigue life subjected to mean stress under uniaxial state. The effects of means stress on the fatigue failure of a ferritic stainless steel and high pressure tube steel are studied under strain-controlled low cycle fatigue condition. Based on the fatigue results from different strain ratios, modified total strain energy density approach is proposed to account for the mean stress effects. The proposed damage parameter provides convenient means of evaluating fatigue life with mean stress effects considering the fact that the definitions used for measuring strain energies are the same as in the fully-reversed cycling (R = -1). A good agreement is observed between experimental life and predicted life using proposed approach. Two other mean stress models (Smith-Watson-Topper model and Morrow model) are also used to evaluate the low cycle fatigue data. Based on a simple statistical estimator, the proposed approach is compared with these models and is found realistic.

  14. An Abnormal Increase of Fatigue Life with Dwell Time during Creep-Fatigue Deformation for Directionally Solidified Ni-Based Superalloy DZ445

    Science.gov (United States)

    Ding, Biao; Ren, Weili; Deng, Kang; Li, Haitao; Liang, Yongchun

    2018-03-01

    The paper investigated the creep-fatigue behavior for directionally solidified nickel-based superalloy DZ445 at 900 °C. It is found that the fatigue life shows an abnormal increase when the dwell time exceeds a critical value during creep-fatigue deformation. The area of hysteresis loop and fractograph explain the phenomenon quite well. The shortest life corresponds to the maximal area of hysteresis loop, i. e. the maximum energy to be consumed during the creep-fatigue cycle. The fractographic observation of failed samples further supports the abnormal behavior of fatigue life.

  15. Cement based composites for thin building elements: Fracture and fatigue parameters

    Czech Academy of Sciences Publication Activity Database

    Seitl, Stanislav; Bílek, V.; Keršner, Z.; Veselý, J.

    2010-01-01

    Roč. 2, č. 1 (2010), s. 911-916 E-ISSN 1877-7058. [Fatigue 2010. Praha, 06.06.2010-11.06.2010] R&D Projects: GA ČR GA103/08/0963 Institutional research plan: CEZ:AV0Z20410507 Keywords : Cement-based composites * Fatigue concrete * Wöhler curve * Fibers Subject RIV: JL - Materials Fatigue, Friction Mechanics

  16. Fatigue Evaluation of Recycled Asphalt Mixture Based on Energy-Controlled Mode

    Directory of Open Access Journals (Sweden)

    Tao Ma

    2017-01-01

    Full Text Available The fatigue properties of asphalt mixtures are important inputs for mechanistic-empirical pavement design. To understand the fatigue properties of asphalt mixtures better and to predict the fatigue life of asphalt mixtures more precisely, the energy-controlled test mode was introduced. Based on the implementation theory, the laboratory practice for the energy-controlled mode was realized using a four-point-bending fatigue test with multiple-step loading. In this mode, the fatigue performance of typical AC-20 asphalt specimens with various reclaimed asphalt pavement (RAP contents was tested and evaluated. Results show that the variation regulation of the dissipated energy and accumulative energy is compatible with the loading control principle, which proves the feasibility of the method. In addition, the fatigue life of the asphalt mixture in the energy-controlled mode was between that for the stress-controlled and strain-controlled modes. The specimen with a higher RAP content has a longer fatigue life and better fatigue performance.

  17. Energy-based fatigue model for shape memory alloys including thermomechanical coupling

    International Nuclear Information System (INIS)

    Zhang, Yahui; Zhu, Jihong; Moumni, Ziad; Zhang, Weihong; Van Herpen, Alain

    2016-01-01

    This paper is aimed at developing a low cycle fatigue criterion for pseudoelastic shape memory alloys to take into account thermomechanical coupling. To this end, fatigue tests are carried out at different loading rates under strain control at room temperature using NiTi wires. Temperature distribution on the specimen is measured using a high speed thermal camera. Specimens are tested to failure and fatigue lifetimes of specimens are measured. Test results show that the fatigue lifetime is greatly influenced by the loading rate: as the strain rate increases, the fatigue lifetime decreases. Furthermore, it is shown that the fatigue cracks initiate when the stored energy inside the material reaches a critical value. An energy-based fatigue criterion is thus proposed as a function of the irreversible hysteresis energy of the stabilized cycle and the loading rate. Fatigue life is calculated using the proposed model. The experimental and computational results compare well. (paper)

  18. Effects of mental fatigue on the development of physical fatigue: a neuroergonomic approach.

    Science.gov (United States)

    Mehta, Ranjana K; Parasuraman, Raja

    2014-06-01

    The present study used a neuroergonomic approach to examine the interaction of mental and physical fatigue by assessing prefrontal cortex activation during submaximal fatiguing handgrip exercises. Mental fatigue is known to influence muscle function and motor performance, but its contribution to the development of voluntary physical fatigue is not well understood. A total of 12 participants performed separate physical (control) and physical and mental fatigue (concurrent) conditions at 30% of their maximal handgrip strength until exhaustion. Functional near infrared spectroscopy was employed to measure prefrontal cortex activation, whereas electromyography and joint steadiness were used simultaneously to quantify muscular effort. Compared to the control condition, blood oxygenation in the bilateral prefrontal cortex was significantly lower during submaximal fatiguing contractions associated with mental fatigue at exhaustion, despite comparable muscular responses. The findings suggest that interference in the prefrontal cortex may influence motor output during tasks that require both physical and cognitive processing. A neuroergonomic approach involving simultaneous monitoring of brain and body functions can provide critical information on fatigue development that may be overlooked during traditional fatigue assessments.

  19. Monitoring of fatigue damage in composite lap-joints using guided waves and FBG sensors

    Science.gov (United States)

    Karpenko, Oleksii; Khomenko, Anton; Koricho, Ermias; Haq, Mahmoodul; Udpa, Lalita

    2016-02-01

    Adhesive bonding is being increasingly employed in many applications as it offers possibility of light-weighting and efficient multi-material joining along with reduction in time and cost of manufacturing. However, failure initiation and progression in critical components like joints, specifically in fatigue loading is not well understood, which necessitates reliable NDE and SHM techniques to ensure structural integrity. In this work, concurrent guided wave (GW) and fiber Bragg grating (FBG) sensor measurements were used to monitor fatigue damage in adhesively bonded composite lap-joints. In the present set-up, one FBG sensor was strategically embedded in the adhesive bond-line of a lap-joint, while two other FBGs were bonded on the surface of the adherends. Full spectral responses of FBG sensors were collected and compared at specific intervals of fatigue loading. In parallel, guided waves were actuated and sensed using PZT wafers mounted on the composite adherends. Experimental results demonstrated that time-of-flight (ToF) of the fundamental modes transmitted through the bond-line and spectral response of FBG sensors were sensitive to fatigue loading and damage. Combination of guided wave and FBG measurements provided the desired redundancy and synergy in the data to evaluate the degradation in bond-line properties. Measurements taken in the presence of continuously applied load replicated the in-situ/service conditions. The approach shows promise in understanding the behavior of bonded joints subjected to complex loading.

  20. Effects of human fatigue on speech signals

    Science.gov (United States)

    Stamoulis, Catherine

    2004-05-01

    Cognitive performance may be significantly affected by fatigue. In the case of critical personnel, such as pilots, monitoring human fatigue is essential to ensure safety and success of a given operation. One of the modalities that may be used for this purpose is speech, which is sensitive to respiratory changes and increased muscle tension of vocal cords, induced by fatigue. Age, gender, vocal tract length, physical and emotional state may significantly alter speech intensity, duration, rhythm, and spectral characteristics. In addition to changes in speech rhythm, fatigue may also affect the quality of speech, such as articulation. In a noisy environment, detecting fatigue-related changes in speech signals, particularly subtle changes at the onset of fatigue, may be difficult. Therefore, in a performance-monitoring system, speech parameters which are significantly affected by fatigue need to be identified and extracted from input signals. For this purpose, a series of experiments was performed under slowly varying cognitive load conditions and at different times of the day. The results of the data analysis are presented here.

  1. The relative importance of real-time in-cab and external feedback in managing fatigue in real-world commercial transport operations.

    Science.gov (United States)

    Fitzharris, Michael; Liu, Sara; Stephens, Amanda N; Lenné, Michael G

    2017-05-29

    Real-time driver monitoring systems represent a solution to address key behavioral risks as they occur, particularly distraction and fatigue. The efficacy of these systems in real-world settings is largely unknown. This article has three objectives: (1) to document the incidence and duration of fatigue in real-world commercial truck-driving operations, (2) to determine the reduction, if any, in the incidence of fatigue episodes associated with providing feedback, and (3) to tease apart the relative contribution of in-cab warnings from 24/7 monitoring and feedback to employers. Data collected from a commercially available in-vehicle camera-based driver monitoring system installed in a commercial truck fleet operating in Australia were analyzed. The real-time driver monitoring system makes continuous assessments of driver drowsiness based on eyelid position and other factors. Data were collected in a baseline period where no feedback was provided to drivers. Real-time feedback to drivers then occurred via in-cab auditory and haptic warnings, which were further enhanced by direct feedback by company management when fatigue events were detected by external 24/7 monitors. Fatigue incidence rates and their timing of occurrence across the three time periods were compared. Relative to no feedback being provided to drivers when fatigue events were detected, in-cab warnings resulted in a 66% reduction in fatigue events, with a 95% reduction achieved by the real-time provision of direct feedback in addition to in-cab warnings (p safety culture of the company in terms of how the information is used. Data were analysed on a per-truck trip basis, and the findings are indicative of fatigue events in a large-scale commercial transport fleet. Future research ought to account for individual driver performance, which was not possible with the available data in this retrospective analysis. Evidence that real-time driver monitoring feedback is effective in reducing fatigue events is

  2. Monitoring and managing component fatigue at Point Lepreau Generating Station

    International Nuclear Information System (INIS)

    Stevens, G.L.; Yetisir, M.; Scovil, A.; Slade, J.

    2008-01-01

    Many CANDU plants are now approaching the end of their design lives and are being considered for extended operation beyond their design life. The Canadian Nuclear Safety Commission (CNSC) has asked utilities to address component fatigue issues in plant life extension (PLEX) applications. In particular, environmental effects on fatigue was identified as an issue that needs to be addressed, similar to being addressed for license renewal for U.S. nuclear power plants. To address CNSC concerns, the CANDU Owners Group (COG) has initiated a program to help utilities develop component fatigue management programs for PLEX operation. A summary of a pilot study that was conducted at the Point Lepreau Generating Station (PLGS) is provided below: A plant-specific Recommendation Study provided a comprehensive review of the existing plant-specific systems, cycle counting procedures, and other fatigue-related requirements, and made some general recommendations on how best to implement a fatigue management system for PLEX. The plant-specific study determined that only 10 to 15% of the design transients have been used after 25 effective full power years (EFPY) of operation. Hence, a significant amount of original design margin for fatigue usage margin remains available for PLEX operation. Environmental fatigue considerations in heavy water (D 2 O) were included in the plant-specific assessment. Only warm-up transients were assessed to have dissolved oxygen concentrations that can result in a significant environmental effect for the ferritic steels used in the CANDU primary systems. Due to the low accumulation of transients and the absence of known thermal stratification mechanisms, thermal fatigue is not as significant an issue in CANDU plants as in pressurized water reactor (PWR) and boiling water reactor (BWR) plants. The needs for implementing a comprehensive Fatigue Management Program for PLGS to satisfy PLEX requirements were defined, and specific direction and strategy for

  3. Research on fatigue driving pre-warning system based on multi-information fusion

    Science.gov (United States)

    Zhao, Xuyang; Ye, Wenwu

    2018-05-01

    With the development of science and technology, transportation network has grown faster. But at the same time, the quantity of traffic accidents due to fatigue driving grows faster as well. In the meantime, fatigue driving has been one of the main causes of traffic accidents. Therefore, it is indispensable for us to study the detection of fatigue driving to help to driving safety. There are numerous approaches in discrimination method. Each type of method has its reasonable theoretical basis, but the disadvantages of traditional fatigue driving detection methods have been more and more obvious since we study the traditional physiology and psychological features of fatigue drivers. So we set up a new system based on multi-information fusion and pattern recognition theory. In the paper, the fatigue driving pre-warning system discriminates fatigue by analyzing the characteristic parameters, the parameters derived from the steering wheel angle, the driver's power of gripping and the heart rate. And the data analysis system is established based on fuzzy C-means clustering theory. Finally, KNN classifier is used to establish the relation between feature indexes and fatigue degree. It is verified that the system has the better accuracy, agility and robustness according to our confirmatory experiment.

  4. Fatigue analysis of aluminum drill pipes

    Directory of Open Access Journals (Sweden)

    João Carlos Ribeiro Plácido

    2005-12-01

    Full Text Available An experimental program was performed to investigate the fundamental fatigue mechanisms of aluminum drill pipes. Initially, the fatigue properties were determined through small-scale tests performed in an optic-mechanical fatigue apparatus. Additionally, full-scale fatigue tests were carried out with three aluminum drill pipe specimens under combined loading of cyclic bending and constant axial tension. Finally, a finite element model was developed to simulate the stress field along the aluminum drill pipe during the fatigue tests and to estimate the stress concentration factors inside the tool joints. By this way, it was possible to estimate the stress values in regions not monitored during the fatigue tests.

  5. Feasibility of using a biowatch to monitor GSR as a measure of radiologists' stress and fatigue

    Science.gov (United States)

    Krupinski, Elizabeth A.; MacKinnon, Lea; Reiner, Bruce I.

    2015-03-01

    We have been investigating the impact of fatigue on diagnostic performance of radiologists interpreting medical images. In previous studies we found evidence that eye strain could be objectively measured and that it correlates highly with degradations in diagnostic accuracy as radiologists work long hours. Eye strain however can be difficult to measure in a non-invasive and continuous manner over the work day so we have been investigating other ways to measure physiological stress and fatigue. In this study we evaluated the feasibility of using a commercially available biowatch to measure galvanic skin response (GSR), a well known indicator of stress. 10 radiology residents wore the biowatch for about 8 hours during their normal work day and data were automatically collected at 10 Hz. They completed the Swedish Occupational Fatigue Inventory (SOFI) at the start and finish of the day. GSR values (microsiemens) ranged from 0.14 to 38.27 with an average of 0.50 (0.28 median). Overall GSR tended to be fairly constant as the day progressed, but there were definite spikes indicating higher levels of stress. SOFI scores indicated greater levels of fatigue and stress at the end of the work day. Although further work is needed, GSR measurements obtained via an easy to wear watch may provide a means to monitor stress/fatigue and alert radiologists when to take a break from interpreting images to avoid making errors.

  6. Application of non-destructive impedance-based monitoring technique for cyclic fatigue evaluation of endodontic nickel-titanium rotary instruments.

    Science.gov (United States)

    Chang, Yau-Zen; Liu, Mou-Chuan; Pai, Che-An; Lin, Chun-Li; Yen, Kuang-I

    2011-06-01

    This study investigates the application of non-destructive testing based on the impedance theory in the cyclic fatigue evaluation of endodontic Ni-Ti rotary instruments. Fifty Ni-Ti ProTaper instruments were divided into five groups (n=10 in Groups A to E). Groups A to D were subjected to cyclic fatigue within an artificial canal (Group E was the control group). The mean value of the total life limit (TLL), defined as the instrument being rotated until fracture occurred was found to be 104 s in Group A. Each rotary instrument in Groups B, C and D were rotated until the tested instruments reached 80% (84 s), 60% (62 s) and 40% (42 s) of the TLL. After fatigue testing, each rotary instrument was mounted onto a custom-developed non-destructive testing device to give the tip of the instrument a progressive sideways bend in four mutually perpendicular directions to measure the corresponding impedance value (including the resistance and the reactance). The results indicated that the impedance value showed the same trend as the resistance, implying that the impedance was primarily affected by the resistance. The impedance value for the instruments in the 80% and 60% TLL groups increased by about 6 mΩ (about 7.5%) more than that of the instruments in the intact and 40% TLL groups. The SEM analysis result showed that crack striations were only found at the tip of the thread on the cracked surface of the instrument, consistent with the impedance measurements that found the impedance value of the cracked surface to be significantly different from those in other surfaces. These findings indicate that the impedance value may represent an effective parameter for evaluating the micro-structural status of Ni-Ti rotary instruments subjected to fatigue loading. Copyright © 2010 IPEM. Published by Elsevier Ltd. All rights reserved.

  7. Fatigue approach for addressing environmental effects in fatigue usage calculation

    Energy Technology Data Exchange (ETDEWEB)

    Wilhelm, Paul; Rudolph, Juergen [AREVA GmbH, Erlangen (Germany); Steinmann, Paul [Erlangen-Nuremberg Univ., erlangen (Germany). Chair of Applied Mechanics

    2015-04-15

    Laboratory tests consider simple trapezoidal, triangle, and sinusoidal signals. However, actual plant components are characterized by complex loading patterns and periods of holds. Fatigue tests in water environment show, that the damage from a realistic strain variation or the presence of hold-times within cyclic loading results in an environmental reduction factor (Fen) only half that of a simple waveform. This study proposes a new fatigue approach for addressing environmental effects in fatigue usage calculation for class 1 boiler and pressure vessel reactor components. The currently accepted method of fatigue assessment has been used as a base model and all cycles, which have been comparable with realistic fatigue tests, have been excluded from the code-based fatigue calculation and evaluated directly with the test data. The results presented show that the engineering approach can successfully be integrated in the code-based fatigue assessment. The cumulative usage factor can be reduced considerably.

  8. Fatigue approach for addressing environmental effects in fatigue usage calculation

    International Nuclear Information System (INIS)

    Wilhelm, Paul; Rudolph, Juergen; Steinmann, Paul

    2015-01-01

    Laboratory tests consider simple trapezoidal, triangle, and sinusoidal signals. However, actual plant components are characterized by complex loading patterns and periods of holds. Fatigue tests in water environment show, that the damage from a realistic strain variation or the presence of hold-times within cyclic loading results in an environmental reduction factor (Fen) only half that of a simple waveform. This study proposes a new fatigue approach for addressing environmental effects in fatigue usage calculation for class 1 boiler and pressure vessel reactor components. The currently accepted method of fatigue assessment has been used as a base model and all cycles, which have been comparable with realistic fatigue tests, have been excluded from the code-based fatigue calculation and evaluated directly with the test data. The results presented show that the engineering approach can successfully be integrated in the code-based fatigue assessment. The cumulative usage factor can be reduced considerably.

  9. [Research Progress on the Interaction Effects and Its Neural Mechanisms between Physical Fatigue and Mental Fatigue].

    Science.gov (United States)

    Zhang, Lixin; Zhang, Chuncui; He, Feng; Zhao, Xin; Qi, Hongzhi; Wan, Baikun; Ming, Dong

    2015-10-01

    Fatigue is an exhaustion state caused by prolonged physical work and mental work, which can reduce working efficiency and even cause industrial accidents. Fatigue is a complex concept involving both physiological and psychological factors. Fatigue can cause a decline of concentration and work performance and induce chronic diseases. Prolonged fatigue may endanger life safety. In most of the scenarios, physical and mental workloads co-lead operator into fatigue state. Thus, it is very important to study the interaction influence and its neural mechanisms between physical and mental fatigues. This paper introduces recent progresses on the interaction effects and discusses some research challenges and future development directions. It is believed that mutual influence between physical fatigue and mental fatigue may occur in the central nervous system. Revealing the basal ganglia function and dopamine release may be important to explore the neural mechanisms between physical fatigue and mental fatigue. Future effort is to optimize fatigue models, to evaluate parameters and to explore the neural mechanisms so as to provide scientific basis and theoretical guidance for complex task designs and fatigue monitoring.

  10. Fatigue-free lead zirconate titanate-based capacitors for nonvolatile memories

    International Nuclear Information System (INIS)

    Shannigrahi, S. R.; Jang, Hyun M.

    2001-01-01

    The development of lead zirconate titanate (PZT)-based capacitors has been a long time goal of ferroelectric random access memories (FRAM). However, PZT-based perovskites with common platinum (Pt) electrodes have suffered from a significant reduction of the remanent polarization (P r ) after a certain number of read/write cycles (electrical fatigue). We now report the development of fatigue-free lanthanum-modified PZT capacitors using common Pt electrodes. The capacitors fabricated at 580 o C by applying a PZT seed layer exhibited fatigue-free behavior up to 6.5 x 10 10 switching cycles, a quite stable charge retention profile with time, and comparatively high P r values, all of which assure their suitability for practical FRAM applications. Copyright 2001 American Institute of Physics

  11. Fatigue Load Modeling and Control for Wind Turbines based on Hysteresis Operators

    DEFF Research Database (Denmark)

    Barradas Berglind, Jose de Jesus; Wisniewski, Rafal; Soltani, Mohsen

    2015-01-01

    method based on hysteresis operators, which can be used in control loops. Furthermore, we propose a model predictive control (MPC) strategy that incorporates the online fatigue estimation through the objective function, where the ultimate goal in mind is to reduce the fatigue load of the wind turbine......The focus of this work is on fatigue load modeling and controller design for the wind turbine level. The main purpose is to include a model of the damage effects caused by the fatigue of the wind turbine components in the controller design process. This paper addresses an online fatigue estimation...

  12. Advances in fatigue lifetime predictive techniques; Proceedings of the Symposium, San Francisco, CA, Apr. 24, 1990

    International Nuclear Information System (INIS)

    Mitchell, M.R.; Landgraf, R.W.

    1992-01-01

    Recent progress in the development of methods to predict fatigue performance of materials and structures is reviewed. Attention is given to general approaches to fatigue mechanics, elevated temperature phenomena, spectrum loading, the multiaxial behavior, and applications. Particular attention is given to a fracture-mechanics-based model for cumulative damage assessment, thermo-mechanical fatigue life prediction methods, a probabilistic fracture mechanics approach for structural reliability assessment of space flight systems, a multiaxial fatigue life estimation technique, plasticity and fatigue damage modeling of severely loaded tubing, damage evaluation in composite materials using thermographic stress analysis, and fatigue lifetime monitoring in power plants

  13. Enhancing nuclear power plant safety via on-site mental fatigue management

    Directory of Open Access Journals (Sweden)

    Tsai Ming-Kuan

    2017-01-01

    Full Text Available Nuclear incidents and accidents have occurred at various nuclear power plants. Since some of these incidents and accidents caused by human errors might be preventable, numerous researchers argue that fatigue management for on-site workers is the key, especially for mental fatigue. Thus, this study proposes an approach consisting of two mechanisms. A fatigue monitor could identify the mentally fatigued workers by detecting their brain wave rhythms through a brain-computer interface. For such workers, a fatigue alert would awaken them. If the status of the mentally fatigued workers becomes worse, based on a positioning technique (i.e., wireless networks, this mechanism would alert the nearby workers and managers to deal with this condition. The test results indicate that the proposed approach enhanced the capacity to examine the mentally fatigued workers, ensured the accuracy in locating these workers, and avoided possible nuclear incidents. This study is a useful reference for similar applications in the nuclear industry.

  14. Fatigue Strength Estimation Based on Local Mechanical Properties for Aluminum Alloy FSW Joints

    Directory of Open Access Journals (Sweden)

    Kittima Sillapasa

    2017-02-01

    Full Text Available Overall fatigue strengths and hardness distributions of the aluminum alloy similar and dissimilar friction stir welding (FSW joints were determined. The local fatigue strengths as well as local tensile strengths were also obtained by using small round bar specimens extracted from specific locations, such as the stir zone, heat affected zone, and base metal. It was found from the results that fatigue fracture of the FSW joint plate specimen occurred at the location of the lowest local fatigue strength as well as the lowest hardness, regardless of microstructural evolution. To estimate the fatigue strengths of aluminum alloy FSW joints from the hardness measurements, the relationship between fatigue strength and hardness for aluminum alloys was investigated based on the present experimental results and the available wide range of data from the references. It was found as: σa (R = −1 = 1.68 HV (σa is in MPa and HV has no unit. It was also confirmed that the estimated fatigue strengths were in good agreement with the experimental results for aluminum alloy FSW joints.

  15. Advanced aircraft service life monitoring method via flight-by-flight load spectra

    Science.gov (United States)

    Lee, Hongchul

    This research is an effort to understand current method and to propose an advanced method for Damage Tolerance Analysis (DTA) for the purpose of monitoring the aircraft service life. As one of tasks in the DTA, the current indirect Individual Aircraft Tracking (IAT) method for the F-16C/D Block 32 does not properly represent changes in flight usage severity affecting structural fatigue life. Therefore, an advanced aircraft service life monitoring method based on flight-by-flight load spectra is proposed and recommended for IAT program to track consumed fatigue life as an alternative to the current method which is based on the crack severity index (CSI) value. Damage Tolerance is one of aircraft design philosophies to ensure that aging aircrafts satisfy structural reliability in terms of fatigue failures throughout their service periods. IAT program, one of the most important tasks of DTA, is able to track potential structural crack growth at critical areas in the major airframe structural components of individual aircraft. The F-16C/D aircraft is equipped with a flight data recorder to monitor flight usage and provide the data to support structural load analysis. However, limited memory of flight data recorder allows user to monitor individual aircraft fatigue usage in terms of only the vertical inertia (NzW) data for calculating Crack Severity Index (CSI) value which defines the relative maneuver severity. Current IAT method for the F-16C/D Block 32 based on CSI value calculated from NzW is shown to be not accurate enough to monitor individual aircraft fatigue usage due to several problems. The proposed advanced aircraft service life monitoring method based on flight-by-flight load spectra is recommended as an improved method for the F-16C/D Block 32 aircraft. Flight-by-flight load spectra was generated from downloaded Crash Survival Flight Data Recorder (CSFDR) data by calculating loads for each time hack in selected flight data utilizing loads equations. From

  16. Study on fatigue life evaluation of structural component based on crack growth criterion

    International Nuclear Information System (INIS)

    Shibata, Katsuyuki

    1984-07-01

    As one of the practical application of fracture mechanics, fatigue life evaluation method based on crack growth criterion has been diffusing in various field of technology in order to determine the rational and reliable life of structural components. The fatigue life by this method is evaluated based on the fatigue crack growth analysis from defects, while many problems, such as the influence of residual stress on the crack growth behavior, the effect of overloading, and evaluation method for multiple surface cracks, are not sufficiently solved yet. In this paper, the above problems are treated, and based on some exprimental data some simple mehtods for fatigue life evaluation are proposed regarding the above problems. Verification of the proposed methods are shown in the paper by comparing with some experimental results, and the applicability of the proposed method is also examined by the fatigue test of pipes with cracks in the inner surface. (author)

  17. Assessment of creep-fatigue damage using the UK strain based procedure

    International Nuclear Information System (INIS)

    Bate, S.K.

    1997-01-01

    The UK strain based procedures have been developed for the evaluation of damage in structures, arising from fatigue cycles and creep processes. The fatigue damage is assessed on the basis of modelling crack growth from about one grain depth to an allowable limit which represents an engineering definition of crack formation. Creep damage is based up on the exhaustion of available ductility by creep strain accumulation. The procedures are applicable only when level A and B service conditions apply, as defined in RCC-MR or ASME Code Case N47. The procedures require the components of strain to be evaluated separately, thus they may be used with either full inelastic analysis or simplified methods. To support the development of the UK strain based creep-fatigue procedures an experimental program was undertaken by NNC to study creep-fatigue interaction of structures operating at high temperature. These tests, collectively known as the SALTBATH tests considered solid cylinder and tube-plate specimens, manufactured from Type 316 stainless steel. These specimens were subjected to thermal cycles between 250 deg. C and 600 deg. C. In all the cases the thermal cycle produces tensile residual stresses during dwells at 600 deg. C. One of the tube-plate specimens was used as a benchmark for validating the strain based creep fatigue procedures and subsequently as part of a CEC co-operative study. This benchmark work is described in this paper. A thermal and inelastic stress analysis was carried out using the finite element code ABAQUS. The inelastic behaviour of the material was described using the ORNL constitutive equations. A creep fatigue assessment using the strain based procedures has been compared with an assessment using the RCC-MR inelastic rules. The analyses indicated that both the UK strain based procedures and the RCC-MR rules were conservative, but the conservatism was greater for the RCC-MR rules. (author). 8 refs, 8 figs, 4 tabs

  18. Modeling size effects on fatigue life of a zirconium-based bulk metallic glass under bending

    International Nuclear Information System (INIS)

    Yuan Tao; Wang Gongyao; Feng Qingming; Liaw, Peter K.; Yokoyama, Yoshihiko; Inoue, Akihisa

    2013-01-01

    A size effect on the fatigue-life cycles of a Zr 50 Cu 30 Al 10 Ni 10 (at.%) bulk metallic glass has been observed in the four-point-bending fatigue experiment. Under the same bending-stress condition, large-sized samples tend to exhibit longer fatigue lives than small-sized samples. This size effect on the fatigue life cannot be satisfactorily explained by the flaw-based Weibull theories. Based on the experimental results, this study explores possible approaches to modeling the size effects on the bending-fatigue life of bulk metallic glasses, and proposes two fatigue-life models based on the Weibull distribution. The first model assumes, empirically, log-linear effects of the sample thickness on the Weibull parameters. The second model incorporates the mechanistic knowledge of the fatigue behavior of metallic glasses, and assumes that the shear-band density, instead of the flaw density, has significant influence on the bending fatigue-life cycles. Promising predictive results provide evidence of the potential validity of the models and their assumptions.

  19. Thermography detection on the fatigue damage

    Science.gov (United States)

    Yang, Bing

    It has always been a great temptation in finding new methods to in-situ "watch" the material fatigue-damage processes so that in-time reparations will be possible, and failures or losses can be minimized to the maximum extent. Realizing that temperature patterns may serve as fingerprints for stress-strain behaviors of materials, a state-of-art infrared (IR) thermography camera has been used to "watch" the temperature evolutions of both crystalline and amorphous materials "cycle by cycle" during fatigue experiments in the current research. The two-dimensional (2D) thermography technique records the surface-temperature evolutions of materials. Since all plastic deformations are related to heat dissipations, thermography provides an innovative method to in-situ monitor the heat-evolution processes, including plastic-deformation, mechanical-damage, and phase-transformation characteristics. With the understanding of the temperature evolutions during fatigue, thermography could provide the direct information and evidence of the stress-strain distribution, crack initiation and propagation, shear-band growth, and plastic-zone evolution, which will open up wide applications in studying the structural integrity of engineering components in service. In the current research, theoretical models combining thermodynamics and heat-conduction theory have been developed. Key issues in fatigue, such as in-situ stress-strain states, cyclic softening and hardening observations, and fatigue-life predictions, have been resolved by simply monitoring the specimen-temperature variation during fatigue. Furthermore, in-situ visulizations as well as qualitative and quantitative analyses of fatigue-damage processes, such as Luders-band evolutions, crack propagation, plastic zones, and final fracture, have been performed by thermography. As a method requiring no special sample preparation or surface contact by sensors, thermography provides an innovative and convenient method to in-situ monitor

  20. Fatigue life estimation of a 1D aluminum beam under mode-I loading using the electromechanical impedance technique

    International Nuclear Information System (INIS)

    Lim, Yee Yan; Soh, Chee Kiong

    2011-01-01

    Structures in service are often subjected to fatigue loads. Cracks would develop and lead to failure if left unnoticed after a large number of cyclic loadings. Monitoring the process of fatigue crack propagation as well as estimating the remaining useful life of a structure is thus essential to prevent catastrophe while minimizing earlier-than-required replacement. The advent of smart materials such as piezo-impedance transducers (lead zirconate titanate, PZT) has ushered in a new era of structural health monitoring (SHM) based on non-destructive evaluation (NDE). This paper presents a series of investigative studies to evaluate the feasibility of fatigue crack monitoring and estimation of remaining useful life using the electromechanical impedance (EMI) technique employing a PZT transducer. Experimental tests were conducted to study the ability of the EMI technique in monitoring fatigue crack in 1D lab-sized aluminum beams. The experimental results prove that the EMI technique is very sensitive to fatigue crack propagation. A proof-of-concept semi-analytical damage model for fatigue life estimation has been developed by incorporating the linear elastic fracture mechanics (LEFM) theory into the finite element (FE) model. The prediction of the model matches closely with the experiment, suggesting the possibility of replacing costly experiments in future

  1. Fatigue life estimation of a 1D aluminum beam under mode-I loading using the electromechanical impedance technique

    Science.gov (United States)

    Lim, Yee Yan; Kiong Soh, Chee

    2011-12-01

    Structures in service are often subjected to fatigue loads. Cracks would develop and lead to failure if left unnoticed after a large number of cyclic loadings. Monitoring the process of fatigue crack propagation as well as estimating the remaining useful life of a structure is thus essential to prevent catastrophe while minimizing earlier-than-required replacement. The advent of smart materials such as piezo-impedance transducers (lead zirconate titanate, PZT) has ushered in a new era of structural health monitoring (SHM) based on non-destructive evaluation (NDE). This paper presents a series of investigative studies to evaluate the feasibility of fatigue crack monitoring and estimation of remaining useful life using the electromechanical impedance (EMI) technique employing a PZT transducer. Experimental tests were conducted to study the ability of the EMI technique in monitoring fatigue crack in 1D lab-sized aluminum beams. The experimental results prove that the EMI technique is very sensitive to fatigue crack propagation. A proof-of-concept semi-analytical damage model for fatigue life estimation has been developed by incorporating the linear elastic fracture mechanics (LEFM) theory into the finite element (FE) model. The prediction of the model matches closely with the experiment, suggesting the possibility of replacing costly experiments in future.

  2. Fatigue Life Prediction of High Modulus Asphalt Concrete Based on the Local Stress-Strain Method

    Directory of Open Access Journals (Sweden)

    Mulian Zheng

    2017-03-01

    Full Text Available Previously published studies have proposed fatigue life prediction models for dense graded asphalt pavement based on flexural fatigue test. This study focused on the fatigue life prediction of High Modulus Asphalt Concrete (HMAC pavement using the local strain-stress method and direct tension fatigue test. First, the direct tension fatigue test at various strain levels was conducted on HMAC prism samples cut from plate specimens. Afterwards, their true stress-strain loop curves were obtained and modified to develop the strain-fatigue life equation. Then the nominal strain of HMAC course determined using finite element method was converted into local strain using the Neuber method. Finally, based on the established fatigue equation and converted local strain, a method to predict the pavement fatigue crack initiation life was proposed and the fatigue life of a typical HMAC overlay pavement which runs a risk of bottom-up cracking was predicted and validated. Results show that the proposed method was able to produce satisfactory crack initiation life.

  3. Development of an in situ fatigue sensor.

    Science.gov (United States)

    2011-01-01

    A prototype in situ fatigue sensor has been designed, constructed and evaluated experimentally for its ability to monitor the accumulation of fatigue damage in a cyclically loaded steel structure, e.g., highway bridge. The sensor consists of multiple...

  4. Reduced Electromyographic Fatigue Threshold after Performing a Cognitive Fatiguing Task.

    Science.gov (United States)

    Ferris, Justine R; Tomlinson, Mary A; Ward, Tayler N; Pepin, Marie E; Malek, Moh H

    2018-02-22

    Cognitive fatigue tasks performed prior to exercise may reduce exercise capacity. The electromyographic fatigue threshold (EMGFT) is the highest exercise intensity that can be maintained without significant increase in the EMG amplitude versus time relationship. To date, no studies have examined the effect of cognitive fatigue on the estimation of the EMGFT. The purpose of this study, therefore, was to determine whether or not cognitive fatigue prior to performing exercise reduces the estimated EMGFT. Eight healthy college-aged men were recruited from a university student population and visited the laboratory on multiple occasions. In a randomized order, subjects performed either the cognitive fatigue task (AX Continuous Performance Test; AX-CPT) for 60 min on one visit (experimental condition) or watched a video on trains for 60 min on the other visit (control condition). After each condition, subjects performed the incremental single-leg knee-extensor ergometry test while the EMG amplitude was recorded from the rectus femoris muscle and heart rate was monitored throughout. Thereafter, the EMGFT was calculated for each participant for each visit and compared using paired samples t-test. For exercise outcomes, there were no significant mean differences for maximal power output between the two conditions (control: 51 ± 5 vs. fatigue: 50 ± 3 W), but a significant decrease in EMGFT between the two conditions (control: 31 ± 3 vs. fatigue: 24 ± 2 W; p = 0.013). Moreover, maximal heart rate was significantly different between the two conditions (control: 151 ± 5 vs. fatigue: 132 ± 6; p = 0.027). These results suggest that performing the cognitive fatiguing task reduces the EMGFT with a corresponding reduction in maximal heart rate response.

  5. Design of Fatigue Resistant Heusler-strengthened PdTi-based Shape Memory Alloys for Biomedical Applications

    Science.gov (United States)

    Frankel, Dana J.

    The development of non-surgical transcatheter aortic valve implantation (TAVI) techniques, which utilize collapsible artificial heart valves with shape memory alloy (SMA)-based frames, pushes performance requirements for biomedical SMAs beyond those for well-established vascular stent applications. Fatigue life for these devices must extend into the ultra-high cycle fatigue (UHCF) regime (>600M cycles) with zero probability of failure predicted at applied strain levels. High rates of Ni-hypersensitivity raise biocompatibility concerns, driving the development of low-Ni and Ni-free SMAs. This work focuses on the development of biocompatible, precipitation-strengthened, fatigue-resistant PdTi-based SMAs for biomedical applications. Functional and structural fatigue are both manifestations of cyclic instability resulting in accumulation of slip and eventual structural damage. While functional fatigue is easily experimentally evaluated, structural fatigue is more difficult to measure without the proper equipment. Therefore, in this work a theoretical approach using a model well validated in steels is utilized to investigate structural fatigue behavior in NiTi in the UHCF regime, while low cycle functional fatigue is evaluated in order to monitor the core phenomena of the cyclic instability. Results from fatigue simulations modeling crack nucleation at non-metallic inclusions in commercial NiTi underscore the importance of increasing yield strength for UHCF performance. Controlled precipitation of nanoscale, low-misfit, L21 Heusler aluminides can provide effective strengthening. Phase relations, precipitation kinetics, transformation temperature, transformation strain, cyclic stability, and mechanical properties are characterized in both Ni-free (Pd,Fe)(Ti,Al) and low-Ni high-strength "hybrid" (Pd,Ni)(Ti,Zr,Al) systems. Atom probe tomography is employed to measure phase compositions and particle sizes used to calibrate LSW models for coarsening kinetics and Gibbs

  6. The effects of a home-based arm ergometry exercise programme on physical fitness, fatigue and activity in polio survivors: protocol for a randomised controlled trial

    Directory of Open Access Journals (Sweden)

    Murray Deirdre

    2012-12-01

    Full Text Available Abstract Background Many Polio survivors have reduced mobility, pain and fatigue, which make access to conventional forms of aerobic exercise difficult. Inactivity leads to increased risk of health problems, many of which are prevalent among Polio survivors. Aerobic exercise programmes in Polio survivors should utilise stable muscle groups and should be designed to minimise exacerbation of pain and fatigue. A home-based arm ergometry aerobic exercise programme may represent an affordable and accessible exercise modality, incorporating exercise prescription principles in this group. Methods/design This is a prospective, single blinded, randomised controlled trial. There are two arms; exercise intervention using arm ergometers and control. Polio survivors meeting eligibility criteria will be recruited and randomly allocated to intervention or control groups. Participants allocated to the intervention group will receive a small arm ergometer and a polar heart rate monitor. They will carry out a home-based moderate intensity (50-70% HRMax aerobic exercise programme for eight weeks, following instruction by the treating physiotherapist. Assessments will occur at baseline and after eight weeks and will include tests of physical fitness, activity, energy cost of walking, fatigue and quality of life. Clinically feasible assessment tools including the Six Minute Arm Test, the Physical Activity Scale for People with Physical Disabilities questionnaire, the Physiological Cost Index, Fatigue Severity Scale and the SF-36v2 will be utilised. Discussion The efficacy of a home-based arm ergometry programme in Polio survivors will be examined. No previous trial has examined such a programme using a wide range of outcome measures pertinent to Polio survivors. This study will provide new information on the impact of arm ergometry on physical fitness, activity, body composition, fatigue, pain, muscle strength, and health related quality of life. Also, the study

  7. Maternal fatigue and its relationship to the caregiving environment.

    Science.gov (United States)

    White, Carmel Parker; White, Mark B; Fox, Melissa A

    2009-12-01

    For women with an autoimmune illness, fatigue can be a debilitating symptom that impacts many aspects of their life. There is scant research on maternal fatigue and its impact on the caregiving environment for either well women or women with chronic illnesses. The objective of this study was to examine the role maternal fatigue played in the caregiving environment, specifically in the mother's experience of the daily hassles of parenting, the discipline style she employed, and how she monitored her child's whereabouts. Two-hundred sixty-two mothers participated in this study: 103 mothers with multiple sclerosis (MS), 68 mothers with rheumatoid arthritis (RA), and a comparison group of 91 well mothers. Mothers completed questionnaires assessing their self-reported levels of fatigue, depression, quality and quantity of sleep, parenting daily hassles, discipline styles, and monitoring. After sleep, depression, and number of children were controlled for, fatigue explained additional variance in predicting monitoring for all three groups of mothers. Fatigue was also a significant predictor of parenting daily hassles for both well mothers and mothers with RA, but not for mothers with MS. For mothers with MS, it was the covariates (i.e., the number of children in the family and sleep quality and quantity) that were predictive of parenting daily hassles. Several explanations for mothers with MS not being as influenced by fatigue are discussed.

  8. Real-time driver fatigue detection based on face alignment

    Science.gov (United States)

    Tao, Huanhuan; Zhang, Guiying; Zhao, Yong; Zhou, Yi

    2017-07-01

    The performance and robustness of fatigue detection largely decrease if the driver with glasses. To address this issue, this paper proposes a practical driver fatigue detection method based on face alignment at 3000 FPS algorithm. Firstly, the eye regions of the driver are localized by exploiting 6 landmarks surrounding each eye. Secondly, the HOG features of the extracted eye regions are calculated and put into SVM classifier to recognize the eye state. Finally, the value of PERCLOS is calculated to determine whether the driver is drowsy or not. An alarm will be generated if the eye is closed for a specified period of time. The accuracy and real-time on testing videos with different drivers demonstrate that the proposed algorithm is robust and obtain better accuracy for driver fatigue detection compared with some previous method.

  9. A life evaluation under creep-fatigue-environment interaction of Ni-base wrought alloys

    International Nuclear Information System (INIS)

    Hattori, Hiroshi; Kitagawa, Masaki; Ohtomo, Akira; Itoh, Mitsuyoshi

    1986-01-01

    In order to determine a failure criteria under cyclic loading and affective environment for HTGR systems, a series of strain controlled low-cycle fatigue tests were carried out at HTGR maximum gas temperatures in air, in vacuum and in HTGR helium environments on two nickel-base wrought alloys, namely Inconel 617 and Hastelloy XR. This paper first describes the creep-fatigue-environment properties of these alloys followed by a proposal of an evaluation method of creep-fatigue-environment interaction based on the experimental data to define the more reasonable design criteria, which is a modification of the linear damage summation rule. Second, the creep-fatigue properties of Hastelloy XR at 900 deg C and the result evaluated by this proposed method are shown. This criterion is successfully applied to the life prediction at 900 deg C. In addition, the creep-fatigue properties of Hastelloy XR-II are discussed. (author)

  10. Fatigue behavior of wood-fiber-based tri-axial engineered sandwich composite panels (ESCP)

    Science.gov (United States)

    Jinghao Li; John F. Hunt; Shaoqin Gong; Zhiyong Cai

    2015-01-01

    The static and fatigue bending behavior of wood-fiber-based tri-axial engineered sandwich composite panels (ESCP) has been investigated by four-point bending tests. Fatigue panels and weakened panels (wESCP) with an initial interface defect were manufactured for the fatigue tests. Stress σ vs. number of cycles curves (S-N) were recorded under the different stress...

  11. Reliability-based optimization of maintenance scheduling of mechanical components under fatigue

    Science.gov (United States)

    Beaurepaire, P.; Valdebenito, M.A.; Schuëller, G.I.; Jensen, H.A.

    2012-01-01

    This study presents the optimization of the maintenance scheduling of mechanical components under fatigue loading. The cracks of damaged structures may be detected during non-destructive inspection and subsequently repaired. Fatigue crack initiation and growth show inherent variability, and as well the outcome of inspection activities. The problem is addressed under the framework of reliability based optimization. The initiation and propagation of fatigue cracks are efficiently modeled using cohesive zone elements. The applicability of the method is demonstrated by a numerical example, which involves a plate with two holes subject to alternating stress. PMID:23564979

  12. Low cycle fatigue and creep-fatigue interaction behavior of nickel-base superalloy GH4169 at elevated temperature of 650 °C

    Energy Technology Data Exchange (ETDEWEB)

    Chen, G., E-mail: agang@tju.edu.cn [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Zhang, Y. [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China); Xu, D.K. [Environmental Corrosion Center, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Lin, Y.C. [School of Mechanical and Electrical Engineering, Central South University, Changsha 410083 (China); Chen, X. [School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072 (China)

    2016-02-08

    Total strain-controlled low cycle fatigue (LCF) tests of a nickel based superalloy were performed at 650 °C. Various hold times were introduced at the peak tensile strain to investigate the high-temperature creep-fatigue interaction (CFI) effects under the same temperature. A substantial decrease in fatigue life occurred as the total strain amplitude increased. Moreover, tensile strain holding further reduced fatigue life. The saturation phenomenon of holding effect was found when the holding period reached 120 s. Cyclic softening occurred during the LCF and CFI process and it was related to the total strain amplitude and the holding period. The relationship between life-time and total strain amplitude was obtained by combining Basquin equation and Coffin-Manson equation. The surface and fracture section of the fatigued specimens were observed via scanning electronic microscope (SEM) to determine the failure mechanism.

  13. Study on the effect of prior fatigue and creep-fatigue damage on the fatigue and creep characteristics of 316 FR stainless steel. 2nd report. The effect of prior creep-fatigue damage on the creep and fatigue characteristics

    International Nuclear Information System (INIS)

    Yamauchi, Masafumi; Chuman, Yasuharu; Otani, Tomomi; Takahashi, Yukio

    2001-01-01

    The effect of prior creep-fatigue damage on the creep and the fatigue characteristics was studied to investigate the creep-fatigue life evaluation procedure of 316FR stainless steel. Creep and fatigue tests were conducted at 550degC by using the specimen exposed to prior creep-fatigue cycles at the same temperature and interrupted at 1/4 Nf, 1/2 Nf and 3/4 Nf cycle. The creep and fatigue strength of the pre-damaged material showed monotonic reduction with the prior creep-fatigue damage compared with the virgin material. The creep ductility also showed monotonic reduction with the prior creep-fatigue damage. These results were evaluated by the stress-based Time Fraction Rule and the strain-based Ductility Exhaustion Method. The result showed that the application of the Ductility Exhaustion Method to the creep-fatigue damage evaluation is more promising than the Time Fraction Rule. (author)

  14. A Wireless Sensor Network with Enhanced Power Efficiency and Embedded Strain Cycle Identification for Fatigue Monitoring of Railway Bridges

    OpenAIRE

    Feltrin, Glauco; Popovic, Nemanja; Flouri, Kallirroi; Pietrzak, Piotr

    2016-01-01

    Wireless sensor networks have been shown to be a cost-effective monitoring tool for many applications on civil structures. Strain cycle monitoring for fatigue life assessment of railway bridges, however, is still a challenge since it is data intensive and requires a reliable operation for several weeks or months. In addition, sensing with electrical resistance strain gauges is expensive in terms of energy consumption. The induced reduction of battery lifetime of sensor nodes increases the mai...

  15. Entropy-based Probabilistic Fatigue Damage Prognosis and Algorithmic Performance Comparison

    Data.gov (United States)

    National Aeronautics and Space Administration — In this paper, a maximum entropy-based general framework for probabilistic fatigue damage prognosis is investigated. The proposed methodology is based on an...

  16. Entropy-based probabilistic fatigue damage prognosis and algorithmic performance comparison

    Data.gov (United States)

    National Aeronautics and Space Administration — In this paper, a maximum entropy-based general framework for probabilistic fatigue damage prognosis is investigated. The proposed methodology is based on an...

  17. Development of probabilistic fatigue curve for asphalt concrete based on viscoelastic continuum damage mechanics

    Directory of Open Access Journals (Sweden)

    Himanshu Sharma

    2016-07-01

    Full Text Available Due to its roots in fundamental thermodynamic framework, continuum damage approach is popular for modeling asphalt concrete behavior. Currently used continuum damage models use mixture averaged values for model parameters and assume deterministic damage process. On the other hand, significant scatter is found in fatigue data generated even under extremely controlled laboratory testing conditions. Thus, currently used continuum damage models fail to account the scatter observed in fatigue data. This paper illustrates a novel approach for probabilistic fatigue life prediction based on viscoelastic continuum damage approach. Several specimens were tested for their viscoelastic properties and damage properties under uniaxial mode of loading. The data thus generated were analyzed using viscoelastic continuum damage mechanics principles to predict fatigue life. Weibull (2 parameter, 3 parameter and lognormal distributions were fit to fatigue life predicted using viscoelastic continuum damage approach. It was observed that fatigue damage could be best-described using Weibull distribution when compared to lognormal distribution. Due to its flexibility, 3-parameter Weibull distribution was found to fit better than 2-parameter Weibull distribution. Further, significant differences were found between probabilistic fatigue curves developed in this research and traditional deterministic fatigue curve. The proposed methodology combines advantages of continuum damage mechanics as well as probabilistic approaches. These probabilistic fatigue curves can be conveniently used for reliability based pavement design. Keywords: Probabilistic fatigue curve, Continuum damage mechanics, Weibull distribution, Lognormal distribution

  18. Estimation of fatigue life using electromechanical impedance technique

    Science.gov (United States)

    Lim, Yee Yan; Soh, Chee Kiong

    2010-04-01

    Fatigue induced damage is often progressive and gradual in nature. Structures subjected to large number of fatigue load cycles will encounter the process of progressive crack initiation, propagation and finally fracture. Monitoring of structural health, especially for the critical components, is therefore essential for early detection of potential harmful crack. Recent advent of smart materials such as piezo-impedance transducer adopting the electromechanical impedance (EMI) technique and wave propagation technique are well proven to be effective in incipient damage detection and characterization. Exceptional advantages such as autonomous, real-time and online, remote monitoring may provide a cost-effective alternative to the conventional structural health monitoring (SHM) techniques. In this study, the main focus is to investigate the feasibility of characterizing a propagating fatigue crack in a structure using the EMI technique as well as estimating its remaining fatigue life using the linear elastic fracture mechanics (LEFM) approach. Uniaxial cyclic tensile load is applied on a lab-sized aluminum beam up to failure. Progressive shift in admittance signatures measured by the piezo-impedance transducer (PZT patch) corresponding to increase of loading cycles reflects effectiveness of the EMI technique in tracing the process of fatigue damage progression. With the use of LEFM, prediction of the remaining life of the structure at different cycles of loading is possible.

  19. A Comparison Study of Machine Learning Based Algorithms for Fatigue Crack Growth Calculation.

    Science.gov (United States)

    Wang, Hongxun; Zhang, Weifang; Sun, Fuqiang; Zhang, Wei

    2017-05-18

    The relationships between the fatigue crack growth rate ( d a / d N ) and stress intensity factor range ( Δ K ) are not always linear even in the Paris region. The stress ratio effects on fatigue crack growth rate are diverse in different materials. However, most existing fatigue crack growth models cannot handle these nonlinearities appropriately. The machine learning method provides a flexible approach to the modeling of fatigue crack growth because of its excellent nonlinear approximation and multivariable learning ability. In this paper, a fatigue crack growth calculation method is proposed based on three different machine learning algorithms (MLAs): extreme learning machine (ELM), radial basis function network (RBFN) and genetic algorithms optimized back propagation network (GABP). The MLA based method is validated using testing data of different materials. The three MLAs are compared with each other as well as the classical two-parameter model ( K * approach). The results show that the predictions of MLAs are superior to those of K * approach in accuracy and effectiveness, and the ELM based algorithms show overall the best agreement with the experimental data out of the three MLAs, for its global optimization and extrapolation ability.

  20. Driver Fatigue Detection System Using Electroencephalography Signals Based on Combined Entropy Features

    Directory of Open Access Journals (Sweden)

    Zhendong Mu

    2017-02-01

    Full Text Available Driver fatigue has become one of the major causes of traffic accidents, and is a complicated physiological process. However, there is no effective method to detect driving fatigue. Electroencephalography (EEG signals are complex, unstable, and non-linear; non-linear analysis methods, such as entropy, maybe more appropriate. This study evaluates a combined entropy-based processing method of EEG data to detect driver fatigue. In this paper, 12 subjects were selected to take part in an experiment, obeying driving training in a virtual environment under the instruction of the operator. Four types of enthrones (spectrum entropy, approximate entropy, sample entropy and fuzzy entropy were used to extract features for the purpose of driver fatigue detection. Electrode selection process and a support vector machine (SVM classification algorithm were also proposed. The average recognition accuracy was 98.75%. Retrospective analysis of the EEG showed that the extracted features from electrodes T5, TP7, TP8 and FP1 may yield better performance. SVM classification algorithm using radial basis function as kernel function obtained better results. A combined entropy-based method demonstrates good classification performance for studying driver fatigue detection.

  1. Comparative study of a muscle stiffness sensor and electromyography and mechanomyography under fatigue conditions.

    Science.gov (United States)

    Han, Hyonyoung; Jo, Sungho; Kim, Jung

    2015-07-01

    This paper proposes the feasibility of a stiffness measurement for muscle contraction force estimation under muscle fatigue conditions. Bioelectric signals have been widely studied for the estimation of the contraction force for physical human-robot interactions, but the correlation between the biosignal and actual motion is decreased under fatigue conditions. Muscle stiffness could be a useful contraction force estimator under fatigue conditions because it measures the same physical quantity as the muscle contraction that generates the force. Electromyography (EMG), mechanomyography (MMG), and a piezoelectric resonance-based active muscle stiffness sensor were used to analyze the biceps brachii under isometric muscle fatigue conditions with reference force sensors at the end of the joint. Compared to EMG and MMG, the change in the stiffness signal was smaller (p fatigue condition changed fatigue conditions. This result indicates that the muscle stiffness signal is less sensitive to muscle fatigue than other biosignals. This investigation provides insights into methods of monitoring and compensating for muscle fatigue.

  2. Fatigue Feature Extraction Analysis based on a K-Means Clustering Approach

    Directory of Open Access Journals (Sweden)

    M.F.M. Yunoh

    2015-06-01

    Full Text Available This paper focuses on clustering analysis using a K-means approach for fatigue feature dataset extraction. The aim of this study is to group the dataset as closely as possible (homogeneity for the scattered dataset. Kurtosis, the wavelet-based energy coefficient and fatigue damage are calculated for all segments after the extraction process using wavelet transform. Kurtosis, the wavelet-based energy coefficient and fatigue damage are used as input data for the K-means clustering approach. K-means clustering calculates the average distance of each group from the centroid and gives the objective function values. Based on the results, maximum values of the objective function can be seen in the two centroid clusters, with a value of 11.58. The minimum objective function value is found at 8.06 for five centroid clusters. It can be seen that the objective function with the lowest value for the number of clusters is equal to five; which is therefore the best cluster for the dataset.

  3. [Evaluating fatigue resistance effect of health food by near-infrared tissue oximeter].

    Science.gov (United States)

    Wu, Jian; Ding, Hai-shu; Ye, Da-tian

    2009-09-01

    Currently, chronic fatigue syndrome (CFS) seriously affects people's normal living and work. In the present paper, the physiological parameters, such as tissue oxygenation saturation and heart rate, were used to evaluate the subjects' fatigue degree, and the fatigue resistance capsule and coffee were taken as a measure to adjust the fatigue. Human tissue oxygen saturation (rSO2) can be monitored noninvasively and in real time by near infrared spectroscopy (NIRS) based on spatially-resolved spectroscopy. Aiming at those brainworkers who need to work in an office for a long time; two static experiments were designed to evaluate the fatigue degree of the subjects who either take the fatigue resistance capsules/coffee or not. The rSO2 and heart rate (HR) of the subjects in the experiment group and contrast group were measured respectively for fatigue evaluation. This work particularly analyzed the changes in rSO2 in these two groups. The results show that the rSO2 of subjects in the experiment group evidently increased compared to that in the contrast group when the subjects took the fatigue resistance capsule or coffee, thereby show that the health food can reduce the fatigue to a certain extent.

  4. Green's function method with consideration of temperature dependent material properties for fatigue monitoring of nuclear power plants

    International Nuclear Information System (INIS)

    Koo, Gyeong-Hoi; Kwon, Jong-Jooh; Kim, Wanjae

    2009-01-01

    In this paper, a method to consider temperature dependent material properties when using the Green's function method is proposed by using a numerical weight function approach. This is verified by using detailed finite element analyses for a pressurizer spray nozzle with various assumed thermal transient load cases. From the results, it is found that the temperature dependent material properties can significantly affect the maximum peak stresses and the proposed method can resolve this problem with the weight function approach. Finally, it is concluded that the temperature dependency of the material properties affects the maximum stress ranges for a fatigue evaluation. Therefore, it is necessary to consider this effect to monitor fatigue damage when using a Green's function method for the real operating conditions in a nuclear power plant

  5. A New Multiaxial High-Cycle Fatigue Criterion Based on the Critical Plane for Ductile and Brittle Materials

    Science.gov (United States)

    Wang, Cong; Shang, De-Guang; Wang, Xiao-Wei

    2015-02-01

    An improved high-cycle multiaxial fatigue criterion based on the critical plane was proposed in this paper. The critical plane was defined as the plane of maximum shear stress (MSS) in the proposed multiaxial fatigue criterion, which is different from the traditional critical plane based on the MSS amplitude. The proposed criterion was extended as a fatigue life prediction model that can be applicable for ductile and brittle materials. The fatigue life prediction model based on the proposed high-cycle multiaxial fatigue criterion was validated with experimental results obtained from the test of 7075-T651 aluminum alloy and some references.

  6. Analysis on the factors affecting seafarers fatigue based on European Navigation Inc

    DEFF Research Database (Denmark)

    Zhao, Zhi Wei; Zhu, Yun Qi; Zheng, En Xi

    2017-01-01

    In order to analyze the main factors associated with fatigue and analyze the main factors which contribute to fatigue of different types of seafarers. SPSS software was used to carry out optimal scale multiple regression and variance analysis based on the questionnaire surveys of 454 employees...

  7. Lamb Wave Response of Fatigued Composite Samples

    Science.gov (United States)

    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

  8. Fatigue life prediction of Ni-base thermal solar receiver tubes

    Energy Technology Data Exchange (ETDEWEB)

    Hartrott, Philipp von; Schlesinger, Michael [Fraunhofer-Institut fuer Werkstoffmechanik (IWM), Freiburg im Breisgau (Germany); Uhlig, Ralf; Jedamski, Jens [DLR Deutsches Zentrum fuer Luft- und Raumfahrt e.V., Stuttgart (Germany)

    2010-07-01

    Solar receivers for tower type Solar Thermal Power Plants are subjected to complex thermo-mechanical loads including fast and severe thermo-mechanical cycles. The material temperatures can reach more than 800 C and fall to room temperature very quickly. In order to predict the fatigue life of a receiver design, receiver tubes made of Alloy 625 with a wall thickness of 0.5 mm were tested in isothermal and thermo-cyclic experiments. The number of cycles to failure was in the range of 100 to 100,000. A thermo-mechanical fatigue life prediction model was set up. The model is based on the cyclic deformation of the material and the damage caused by the growth of fatigue micro cracks. The model reasonably predicts the experimental results. (orig.)

  9. A model for life predictions of nickel-base superalloys in high-temperature low cycle fatigue

    Science.gov (United States)

    Romanoski, Glenn R.; Pelloux, Regis M.; Antolovich, Stephen D.

    1988-01-01

    Extensive characterization of low-cycle fatigue damage mechanisms was performed on polycrystalline Rene 80 and IN100 tested in the temperature range from 871 to 1000 C. Low-cycle fatigue life was found to be dominated by propagation of microcracks to a critical size governed by the maximum tensile stress. A model was developed which incorporates a threshold stress for crack extension, a stress-based crack growth expression, and a failure criterion. The mathematical equivalence between this mechanistically based model and the strain-life low-cycle fatigue law was demonstrated using cyclic stress-strain relationships. The model was shown to correlate the high-temperature low-cycle fatigue data of the different nickel-base superalloys considered in this study.

  10. Fatigue crack initiation in nickel-based superalloys studied by microstructure-based FE modeling and scanning electron microscopy

    Directory of Open Access Journals (Sweden)

    Fried M.

    2014-01-01

    Full Text Available In this work stage I crack initiation in polycrystalline nickel-based superalloys is investigated by analyzing anisotropic mechanical properties, local stress concentrations and plastic deformation on the microstructural length scale. The grain structure in the gauge section of fatigue specimens was characterized by EBSD. Based on the measured data, a microstructure-based FE model could be established to simulate the strain and stress distribution in the specimens during the first loading cycle of a fatigue test. The results were in fairly good agreement with experimentally measured local strains. Furthermore, the onset of plastic deformation was predicted by identifying shear stress maxima in the microstructure, presumably leading to activation of slip systems. Measurement of plastic deformation and observation of slip traces in the respective regions of the microstructure confirmed the predicted slip activity. The close relation between micro-plasticity, formation of slip traces and stage I crack initiation was demonstrated by SEM surface analyses of fatigued specimens and an in-situ fatigue test in a large chamber SEM.

  11. High-cycle fatigue behavior of Co-based superalloy 9CrCo at elevated temperatures

    OpenAIRE

    Wan, Aoshuang; Xiong, Junjiang; Lyu, Zhiyang; Li, Kuang; Du, Yisen; Chen, Kejiao; Man, Ziyu

    2016-01-01

    A modified model is developed to characterize and evaluate high-cycle fatigue behavior of Co-based superalloy 9CrCo at elevated temperatures by considering the stress ratio effect. The model is informed by the relationship surface between maximum nominal stress, stress ratio and fatigue life. New formulae are derived to deal with the test data for estimating the parameters of the proposed model. Fatigue tests are performed on Co-based superalloy 9CrCo subjected to constant amplitude loading a...

  12. Multi-metric model-based structural health monitoring

    Science.gov (United States)

    Jo, Hongki; Spencer, B. F.

    2014-04-01

    ABSTRACT The inspection and maintenance of bridges of all types is critical to the public safety and often critical to the economy of a region. Recent advanced sensor technologies provide accurate and easy-to-deploy means for structural health monitoring and, if the critical locations are known a priori, can be monitored by direct measurements. However, for today's complex civil infrastructure, the critical locations are numerous and often difficult to identify. This paper presents an innovative framework for structural monitoring at arbitrary locations on the structure combining computational models and limited physical sensor information. The use of multi-metric measurements is advocated to improve the accuracy of the approach. A numerical example is provided to illustrate the proposed hybrid monitoring framework, particularly focusing on fatigue life assessment of steel structures.

  13. An overview of fatigue

    International Nuclear Information System (INIS)

    Mc Evily, A.J.

    1987-01-01

    Four topics are briefly discussed in this paper: fatigue crack initiation and growth in a nickel-base superalloy single crystal, the environment effect on near-threshold fatigue crack growth behaviour, the role of crack closure in load-interaction effects in fatigue crack growth, and the nature of creep-fatigue interactions, if any, during fatigue crack growth. (Author)

  14. Experiences of Fatigue at Sea

    DEFF Research Database (Denmark)

    Zhao, Zhiwei; Jepsen, Jørgen Riis; Chen, Zhonglong

    2016-01-01

    Fatigue has negative impacts on the general working population as well as on seafarers. In order to study seafarers’ fatigue, a questionnaire-base survey was conducted to gain information about potential risk factors for fatigue and construct indexes indicating fatigue. The study applies T-test t......-test to compare strata of seafarers to analyse work and sleep patterns in global seafaring. Qualitative analysis are also employed to explore the impacts of fatigue on seafarer’s occupational health and safety.......Fatigue has negative impacts on the general working population as well as on seafarers. In order to study seafarers’ fatigue, a questionnaire-base survey was conducted to gain information about potential risk factors for fatigue and construct indexes indicating fatigue. The study applies T...

  15. A wireless body measurement system to study fatigue in multiple sclerosis

    DEFF Research Database (Denmark)

    Yu, Fei; Rabotti, Chiara; Bilberg, Arne

    2012-01-01

    Fatigue is reported as the most common symptom by patients with multiple sclerosis (MS). The physiological and functional parameters related to fatigue in MS patients are currently not well established. A new wearable wireless body measurement system, named Fatigue Monitoring System (FAMOS......), was developed to study fatigue in MS. It can continuously measure electrocardiogram, body-skin temperature, electromyogram and motions of feet. The goal of this study is to test the ability of distinguishing fatigued MS patients from healthy subjects by the use of FAMOS. This paper presents the realization...... of the measurement system including the design of both hardware and dedicated signal processing algorithms. Twenty-six participants including 17 MS patients with fatigue and 9 sex- and age-matched healthy controls were included in the study for continuous 24 h monitoring. The preliminary results show significant...

  16. Monitoring of need for recovery and prolonged fatigue within the working population: Evaluation of reliability and agreement over time.

    Science.gov (United States)

    Hoofs, H; Jansen, N W H; Jansen, M W J; Kant, I J

    2017-01-01

    Need for recovery (NFR) and prolonged fatigue are two important concepts for monitoring short- and long-term outcomes of psychological job demands within employees. For effective monitoring it is, however, important to gain insight in the reproducibility of the instruments that are used. The objective was to assess reproducibility of the NFR scale and Checklist Individual Strength (CIS), measuring NFR and prolonged fatigue respectively, in the working population. Longitudinal data from the Maastricht Cohort Study (MCS) study was used, capturing 12,140 employees from 45 different companies at baseline. A 'working' and 'returning to work' sample was conceived for different intervals; 4-month, 1-year, and 2-year. Reliability, assessed with the interclass correlation, was high within employees with a stable work environment for the NFR scale (0.78) and CIS (0.75). The smallest detectable change, assessing the agreement, was 41.20 for the NFR scale and 31.10 for the CIS. Reliability was satisfactory for both the NFR scale and CIS. The agreement of both scales to detect a changes within employees was, however, less optimal. It is, therefore, suggested that, ideally, both instruments are placed within a broader range of instruments to effectively monitor the outcomes of psychological job demands.

  17. Probability-based assessment and maintenance of welded joints damaged by fatigue

    International Nuclear Information System (INIS)

    Cremona, C.; Lukic, M.

    1998-01-01

    This paper presents a probabilistic reliability assessment procedure for steel components damaged by fatigue. The study combines the structural reliability theory with a maintenance strategy. The fatigue assessment model is based on a modelisation of the fatigue phenomenon issued from the principles of fracture mechanics theory. The safety margin includes the crack growth propagation and allows to treat fatigue damage in a general manner. Damaging cycles and non damaging cycles are distinguished. The sensitivity study of the different parameters shows that some variables can be taken as deterministic. Applications are made on a welded joint 'stiffener/bottom-plate' of a typical steel bridge. The model is then used for taking into account inspection results. Non destructive inspection (NDI) techniques are also used for updating failure probabilities. The results show their ability to be inserted in a maintenance strategy for optimizing the next inspection time. This has led to define cost functions related to the total maintenance cost; this cost is then minimized for determining the optimal next inspection time. An example of welded joint cracked by fatigue highlights the different concepts. The approach presented in the paper is not only restrained to fatigue problems, but can be applied to a wide variety of degrading phenomena. (orig.)

  18. Population based study of fatigue and psychological distress.

    OpenAIRE

    Pawlikowska, T.; Chalder, T.; Hirsch, S. R.; Wallace, P.; Wright, D. J.; Wessely, S. C.

    1994-01-01

    OBJECTIVES--To determine the prevalence of fatigue in the general population and the factors associated with fatigue. DESIGN--Postal survey. SETTING--Six general practices in southern England. SUBJECTS--31,651 men and women aged 18-45 years registered with the practices. MAIN OUTCOME MEASURES--Responses to the 12 item general health questionnaire and a fatigue questionnaire which included self reported measures of duration, severity, and causes of fatigue. RESULTS--15,283 valid questionnaires...

  19. Monitoring of railway bridges in Japan

    Science.gov (United States)

    Abe, Makoto; Komon, Kazuki; Narumoto, Asao; Sugidate, Masao; Mori, Takeshi; Miki, Chitoshi

    2000-06-01

    In Japan, some monitoring systems have been introduced to evaluate conditions of the railway structures. In this work, we introduce the monitoring systems of railway bridges. Here, for example, we show the abstraction of fatigue damage monitoring system. The crack propagation properties of a side notched SUS304 thin sheet, which is affixed to a fatigue test specimen, is studied to develop a fatigue damage monitoring sensor. When cyclic loads are applied to the fatigue specimen, the side notched thin sheet behaves as a displacement controlled condition. The stress intensity factor (Delta) K is expressed by the following equation; (Delta) K equals (Delta) (sigma) (root)GL/2 where GL is the gauge length of the thin sheet. The thin sheet is fatigue pre-cracked, stress- relieved and affixed to a specimen. The results of fatigue crack propagation tests show that the crack propagation rate is dependent on stress range and gauge length, but not on crack length. Under sufficient mean stress conditions, the fatigue crack propagation rate is well expressed by a power low of (Delta) K even at such a low stress range as 20 MPa. Fatigue damage accumulated during a monitoring period can be estimated from crack propagation during the period. The sensitivity of the sensor is controlled through the gauge length of the sensor.

  20. Test Population Selection from Weibull-Based, Monte Carlo Simulations of Fatigue Life

    Science.gov (United States)

    Vlcek, Brian L.; Zaretsky, Erwin V.; Hendricks, Robert C.

    2012-01-01

    Fatigue life is probabilistic and not deterministic. Experimentally establishing the fatigue life of materials, components, and systems is both time consuming and costly. As a result, conclusions regarding fatigue life are often inferred from a statistically insufficient number of physical tests. A proposed methodology for comparing life results as a function of variability due to Weibull parameters, variability between successive trials, and variability due to size of the experimental population is presented. Using Monte Carlo simulation of randomly selected lives from a large Weibull distribution, the variation in the L10 fatigue life of aluminum alloy AL6061 rotating rod fatigue tests was determined as a function of population size. These results were compared to the L10 fatigue lives of small (10 each) populations from AL2024, AL7075 and AL6061. For aluminum alloy AL6061, a simple algebraic relationship was established for the upper and lower L10 fatigue life limits as a function of the number of specimens failed. For most engineering applications where less than 30 percent variability can be tolerated in the maximum and minimum values, at least 30 to 35 test samples are necessary. The variability of test results based on small sample sizes can be greater than actual differences, if any, that exists between materials and can result in erroneous conclusions. The fatigue life of AL2024 is statistically longer than AL6061 and AL7075. However, there is no statistical difference between the fatigue lives of AL6061 and AL7075 even though AL7075 had a fatigue life 30 percent greater than AL6061.

  1. A wireless body measurement system to study fatigue in multiple sclerosis

    NARCIS (Netherlands)

    Yu, F.; Bilberg, A.; Stenager, E.; Rabotti, C.; Zhang, B.; Mischi, M.

    2012-01-01

    Fatigue is reported as the most common symptom by patients with multiple sclerosis (MS). The physiological and functional parameters related to fatigue in MS patients are currently not well established. A new wearable wireless body measurement system, named Fatigue Monitoring System (FAMOS), was

  2. Application of a unified fatigue modelling to some thermomechanical fatigue problems

    International Nuclear Information System (INIS)

    Dang, K. van; Maitournam, H.; Moumni, Z.

    2005-01-01

    Fatigue under thermomechanical loadings is an important topic for nuclear industries. For instance, thermal fatigue cracking is observed in the mixing zones of the nuclear reactor. Classical computations using existing methods based on strain amplitude or fracture mechanics are not sufficiently predictive. In this paper an alternative approach is proposed based on a multiscale modelling thanks to shakedown hypothesis. Examples of predictive results are presented. Finally an application to the RHR problem is discussed. Main ideas of the fatigue modelling: Following an idea of Professor D. Drucker who wrote in 1963 'when applied to the microstructure there is a hope that the concept of endurance limit and shakedown are related, and that fatigue failure can be related to energy dissipated in idealized material when shakedown does not occur.' we have developed a theory of fatigue based on this concept which is different from classical fatigue approaches. Many predictive applications have been already done particularly for the automotive industry. Fatigue resistance of structures undergoing thermomechanical loadings in the high cycle regime as well as in the low cycle regime are calculated using this modelling. However, this fatigue theory is until now rarely used in nuclear engineering. After recalling the main points of the theory, we shall present some relevant applications which were done in different industrial sectors. We shall apply this modelling to the prediction of thermal cracking observed in the mixing zones of RHR. (authors)

  3. Resident fatigue in otolaryngology residents: a Web based survey.

    Science.gov (United States)

    Nida, Andrew M; Googe, Benjamin J; Lewis, Andrea F; May, Warren L

    2016-01-01

    Resident fatigue has become a point of emphasis in medical education and its effects on otolaryngology residents and their patients require further study. The purpose of our study was to evaluate the prevalence and nature of fatigue in otolaryngology residents, evaluate various quality of life measures, and investigate associations of increased fatigue with resident safety. Anonymous survey. Internet based. United States allopathic otolaryngology residents. None. The survey topics included demographics, residency structure, sleep habits and perceived stress. Responses were correlated with a concurrent Epworth Sleep Scale questionnaire to evaluate effects of fatigue on resident training and quality of life. 190 residents responded to the survey with 178 completing the Epworth Sleep Scale questionnaire. Results revealed a mean Epworth Sleep Scale score of 9.9±5.1 with a median of 10.0 indicating a significant number of otolaryngology residents are excessively sleepy. Statistically significant correlations between Epworth Sleep Scale and sex, region, hours of sleep, and work hours were found. Residents taking in-house call had significantly fewer hours of sleep compared to home call (p=0.01). Residents on "head and neck" (typically consisting of a large proportion of head and neck oncologic surgery) rotations tended to have higher Epworth Sleep Scale and had significantly fewer hours of sleep (p=.003) and greater work hours (potolaryngology residents are excessively sleepy. Our data suggest that the effects of fatigue play a role in resident well-being and resident safety. Copyright © 2016 Elsevier Inc. All rights reserved.

  4. Mental Fatigue Monitoring Using a Wearable Transparent Eye Detection System

    Directory of Open Access Journals (Sweden)

    Kota Sampei

    2016-01-01

    Full Text Available We propose mental fatigue measurement using a wearable eye detection system. The system is capable of acquiring movement of the pupil and blinking from the light reflected from the eye. The reflection is detected by dye-sensitized photovoltaic cells. Since these cells are patterned onto the eyeglass and do not require external input power, the system is notable for its lightweight and low power consumption and can be combined with other wearable devices, such as a head mounted display. We performed experiments to correlate information obtained by the eye detection system with the mental fatigue of the user. Since it is quite difficult to evaluate mental fatigue objectively and quantitatively, we assumed that the National Aeronautics and Space Administration Task Load Index (NASA-TLX had a strong correlation with te mental fatigue. While a subject was requested to conduct calculation tasks, the eye detection system collected his/her information that included position, velocity and total movement of the eye, and amount and frequency of blinking. Multiple regression analyses revealed the correlation between NASA-TLX and the information obtained for 3 out of 5 subjects.

  5. Macro and Microscopic Investigation on Fracture Specimen of Alloy 617 Base Metal and Weldment in Low Cycle Fatigue Regime

    International Nuclear Information System (INIS)

    Kim, Seon Jin; Dewa, Rando Tungga; Kim, Won Gon

    2016-01-01

    This paper investigates macro- and microscopic fractography performed on fracture specimens from low cycle fatigue (LCF) testings through an Alloy 617 base metal and weldments. The weldment specimens were taken from gas tungsten arc welding (GTAW) pad of Alloy 617. The aim of the present study is to investigate the macro- and microscopic aspects of the low cycle fatigue fracture mode and mechanism of Alloy 617 base metal and GTAWed weldment specimens. Fully axial total strain controlled fatigue tests were conducted at room temperature with total strain ranges of 0.6, 0.9, 1.2 and 1.5%. Macroscopic fracture surfaces of Alloy 617 base metal specimens showed a flat type normal to the fatigue loading direction, whereas the GTAWed weldment specimens were of a shear/star type. The fracture surfaces of both the base metal and weldment specimens revealed obvious fatigue striations at the crack propagation regime. In addition, the fatigue crack mechanism of the base metal showed a transgranular normal to fatigue loading direction; however, the GTAWed weldment specimens showed a transgranular at approximately 45° to the fatigue loading direction

  6. Macro and Microscopic Investigation on Fracture Specimen of Alloy 617 Base Metal and Weldment in Low Cycle Fatigue Regime

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Seon Jin; Dewa, Rando Tungga [Pukyung National Univ., Busan (Korea, Republic of); Kim, Won Gon [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2016-06-15

    This paper investigates macro- and microscopic fractography performed on fracture specimens from low cycle fatigue (LCF) testings through an Alloy 617 base metal and weldments. The weldment specimens were taken from gas tungsten arc welding (GTAW) pad of Alloy 617. The aim of the present study is to investigate the macro- and microscopic aspects of the low cycle fatigue fracture mode and mechanism of Alloy 617 base metal and GTAWed weldment specimens. Fully axial total strain controlled fatigue tests were conducted at room temperature with total strain ranges of 0.6, 0.9, 1.2 and 1.5%. Macroscopic fracture surfaces of Alloy 617 base metal specimens showed a flat type normal to the fatigue loading direction, whereas the GTAWed weldment specimens were of a shear/star type. The fracture surfaces of both the base metal and weldment specimens revealed obvious fatigue striations at the crack propagation regime. In addition, the fatigue crack mechanism of the base metal showed a transgranular normal to fatigue loading direction; however, the GTAWed weldment specimens showed a transgranular at approximately 45° to the fatigue loading direction.

  7. New fatigue damage analysis of complex engineering components based on FEM

    International Nuclear Information System (INIS)

    Ott, W.

    1987-05-01

    A new type of fatigue damage analysis for multiaxial elastoplastic conditions based on a three-dimensional finite element analysis has been developed. The analysis includes the material model after Mroz. The fatigue life evaluation in the critical areas is based on plastic work at these locations. The proposed damage concept can be applied to arbitrary multiaxial stress-strain paths. For the evaluation of the damage cycles in terms of closed stress-strain hysteresis loops are not required. The damage is determined on the basis of uniaxial material data (stress-strain curve, life to crack iniation curve). (orig./HP) [de

  8. Fatigue and corrosion of a Pd-based bulk metallic glass in various environments

    Energy Technology Data Exchange (ETDEWEB)

    Watanabe, L.Y. [East Los Angeles College, Monterey Park, CA 91754 (United States); Roberts, S.N. [Keck Laboratory of Materials Science, California Institute of Technology, Pasadena, CA 91125 (United States); Baca, N. [Department of Chemistry and Biochemistry, California State University Northridge, Northridge, CA 91330 (United States); Wiest, A. [Naval Surface Warfare Center, Norco, CA (United States); Garrett, S.J. [Department of Chemistry and Biochemistry, California State University Northridge, Northridge, CA 91330 (United States); Conner, R.D., E-mail: rdconner@csun.edu [Department of Manufacturing Systems Engineering and Management, California State University Northridge, 18111 Nordhoff St., Mail Code 8295, Northridge, CA 91330 (United States)

    2013-10-15

    Bulk metallic glasses (BMGs) possess attractive properties for biomedical applications, including high strength, hardness and corrosion resistance, and low elastic modulus. In this study, we conduct rotating beam fatigue tests on Pd{sub 43}Ni{sub 10}Cu{sub 27}P{sub 20} bulk metallic glass in air and Eagle's medium (EM) and measure the corrosive resistance of the alloy by submersion in acidic and basic electrolytes. Fatigue results are compared to those of commonly used biometals in EM. Rotating beam fatigue tests conducted in air and in Eagle's medium show no deterioration in fatigue properties in this potentially corrosive environment out to 10{sup 7} cycles. A specimen size effect is revealed when comparing fatigue results to those of a similar alloy of larger minimum dimensions. Corrosion tests show that the alloy is not affected by highly basic (NaOH) or saline (NaCl) solutions, nor in EM, and is affected by chlorinated acidic solutions (HCl) to a lesser extent than other commonly used biometals. Corrosion in HCl initiates with selective leaching of late transition metals, followed by dissolution of Pd. - Highlights: • Fatigue limit of 600 MPa with no deterioration when exposed to Eagle's medium. • Fatigue shows sample size effect. • Pd-based BMG is unaffected by saline or strong basic solutions. • Pd-based BMG is substantially more resistant to chlorinated acids than CoCrMo, 316 L Stainless, or Ti6Al4V alloys. • Corrosion shows selective leaching of late transition metals, followed by Pd and P.

  9. A New Zealand pilot randomized controlled trial of a web-based interactive self-management programme (MSInvigor8) with and without email support for the treatment of multiple sclerosis fatigue.

    Science.gov (United States)

    van Kessel, Kirsten; Wouldes, Trecia; Moss-Morris, Rona

    2016-05-01

    To pilot and compare the efficacy of an internet-based cognitive behavioural therapy self-management programme with (MSInvigor8-Plus) and without (MSInvigor8-Only) the use of email support in reducing fatigue severity and impact (primary outcomes), and depressed and anxious mood (secondary outcomes). Randomized controlled trial using an independent randomization system built into the website and intention-to-treat analysis. Participants were recruited through the local Multiple Sclerosis Society and hospital neurological services in New Zealand. A total of 39 people (aged 31-63 years), experiencing multiple sclerosis fatigue, able to walk with and without walking aids, were randomized to MSInvigor8-Only (n = 20) or to MSInvigor8-Plus (n = 19). MSInvigor8 is an eight-session programme based on cognitive behaviour therapy principles including psycho-education, self-monitoring, and changing unhelpful activity and thought patterns. Outcome measures included fatigue severity (Chalder Fatigue Scale) and impact (Modified Fatigue Impact Scale), and anxiety and depression (Hospital Anxiety and Depression Scale). Assessments were performed at baseline and at 10 weeks. The MSInvigor8-Plus condition resulted in significantly greater reductions in fatigue severity (F [1,36] = 9.09, p multiple sclerosis in New Zealand. © The Author(s) 2015.

  10. Influence of air and vacuum environment on fatigue behavior of Zr-based bulk metallic glasses

    International Nuclear Information System (INIS)

    Wang, G.Y.; Liaw, P.K.; Yokoyama, Y.; Peter, W.H.; Yang, B.; Freels, M.; Buchanan, R.A.; Liu, C.T.; Brooks, C.R.

    2007-01-01

    High-cycle fatigue (HCF) experiments in air and vacuum at room temperature were conducted on zirconium (Zr)-based bulk-metallic glasses (BMGs): Zr 50 Cu 40 Al 10 , Zr 50 Cu 30 Al 10 Ni 10 , and Zr 50 Cu 37 Al 10 Pd 3 in atomic percent. The fatigue-endurance limit of Zr 50 Cu 37 Al 10 Pd 3 was found to be significantly greater than those of Zr 50 Cu 40 Al 10 and Zr 50 Cu 30 Al 10 Ni 10 , which indicates that the inclusions of Pd and the resulting nano structures improve the fatigue resistances of the Zr-based BMGs. The fatigue lives in vacuum and air were generally found to be comparable

  11. Fatigue in Advanced Cancer Patients: Congruence Between Patients and Their Informal Caregivers About Patients' Fatigue Severity During Cancer Treatment With Palliative Intent and Predictors of Agreement.

    Science.gov (United States)

    Poort, Hanneke; Peters, Marlies E W J; Gielissen, Marieke F M; Verhagen, Constans A H H V M; Bleijenberg, Gijs; van der Graaf, Winette T A; Wearden, Alison J; Knoop, Hans

    2016-09-01

    Informal caregivers (ICs) are increasingly involved in the monitoring of symptoms during advanced cancer patients' treatment with palliative intent. A common but subjective symptom during this extended treatment phase is fatigue. This exploratory longitudinal study aimed to determine agreement between patients and ICs about patients' fatigue severity. In addition, predictors of agreement over time were studied. A sample of 107 patients with advanced cancer (life expectancy ≥ six months) and their ICs completed the subscale fatigue severity of the Checklist Individual Strength based on the patient's status at baseline and six months later. This eight-item subscale has a validated cutoff to determine the presence of clinically relevant levels of fatigue. ICs' own fatigue severity, strain, self-esteem, and relationship satisfaction were examined as predictors of agreement. A total of 107 dyads completed measures at baseline and 69 dyads six months later. At baseline, ICs' significantly overestimated patients' fatigue severity (P congruence about the presence or absence of severe fatigue. On a group level, congruence did not significantly change over time. On a dyad level, there was a tendency to either remain congruent or reach congruence. Next to baseline congruence, ICs' fatigue severity and strain predicted ICs' fatigue ratings (R(2) = 0.22). Most ICs accurately predict presence or absence of clinically relevant levels of patients' fatigue. ICs' own fatigue severity and strain should be taken into account as they influence agreement. Copyright © 2016 American Academy of Hospice and Palliative Medicine. Published by Elsevier Inc. All rights reserved.

  12. Design of a Fatigue Detection System for High-Speed Trains Based on Driver Vigilance Using a Wireless Wearable EEG

    Directory of Open Access Journals (Sweden)

    Xiaoliang Zhang

    2017-03-01

    Full Text Available The vigilance of the driver is important for railway safety, despite not being included in the safety management system (SMS for high-speed train safety. In this paper, a novel fatigue detection system for high-speed train safety based on monitoring train driver vigilance using a wireless wearable electroencephalograph (EEG is presented. This system is designed to detect whether the driver is drowsiness. The proposed system consists of three main parts: (1 a wireless wearable EEG collection; (2 train driver vigilance detection; and (3 early warning device for train driver. In the first part, an 8-channel wireless wearable brain-computer interface (BCI device acquires the locomotive driver’s brain EEG signal comfortably under high-speed train-driving conditions. The recorded data are transmitted to a personal computer (PC via Bluetooth. In the second step, a support vector machine (SVM classification algorithm is implemented to determine the vigilance level using the Fast Fourier transform (FFT to extract the EEG power spectrum density (PSD. In addition, an early warning device begins to work if fatigue is detected. The simulation and test results demonstrate the feasibility of the proposed fatigue detection system for high-speed train safety.

  13. A methodology for strain-based fatigue reliability analysis

    International Nuclear Information System (INIS)

    Zhao, Y.X.

    2000-01-01

    A significant scatter of the cyclic stress-strain (CSS) responses should be noted for a nuclear reactor material, 1Cr18Ni9Ti pipe-weld metal. Existence of the scatter implies that a random cyclic strain applied history will be introduced under any of the loading modes even a deterministic loading history. A non-conservative evaluation might be given in the practice without considering the scatter. A methodology for strain-based fatigue reliability analysis, which has taken into account the scatter, is developed. The responses are approximately modeled by probability-based CSS curves of Ramberg-Osgood relation. The strain-life data are modeled, similarly, by probability-based strain-life curves of Coffin-Manson law. The reliability assessment is constructed by considering interference of the random fatigue strain applied and capacity histories. Probability density functions of the applied and capacity histories are analytically given. The methodology could be conveniently extrapolated to the case of deterministic CSS relation as the existent methods did. Non-conservative evaluation of the deterministic CSS relation and availability of present methodology have been indicated by an analysis of the material test results

  14. Assessment of muscle fatigue using electromygraphm sensing

    Science.gov (United States)

    Helmi, Muhammad Hazimin Bin; Ping, Chew Sue; Ishak, Nur Elliza Binti; Saad, Mohd Alimi Bin Mohd; Mokhtar, Anis Shahida Niza Binti

    2017-08-01

    Muscle fatigue is condition of muscle decline in ability after undergoing any physical activity. Observation of the muscle condition of an athlete during training is crucial to prevent or minimize injury and able to achieve optimum performance in actual competition. The aim of this project is to develop a muscle monitoring system to detect muscle fatigue in swimming athlete. This device is capable to measure muscle stress level of the swimmer and at the same time provide indication of muscle fatigue level to trainer. Electromyography signal was recorded from the muscle movement while practicing the front crawl stroke repetitively. The time domain data was processed to frequency spectra in order to study the effect of muscle fatigue. The results show that the recorded EMG signal is able to sense muscle fatigue.

  15. Model-Based Fatigue Prognosis of Fiber-Reinforced Laminates Exhibiting Concurrent Damage Mechanisms

    Science.gov (United States)

    Corbetta, M.; Sbarufatti, C.; Saxena, A.; Giglio, M.; Goebel, K.

    2016-01-01

    Prognostics of large composite structures is a topic of increasing interest in the field of structural health monitoring for aerospace, civil, and mechanical systems. Along with recent advancements in real-time structural health data acquisition and processing for damage detection and characterization, model-based stochastic methods for life prediction are showing promising results in the literature. Among various model-based approaches, particle-filtering algorithms are particularly capable in coping with uncertainties associated with the process. These include uncertainties about information on the damage extent and the inherent uncertainties of the damage propagation process. Some efforts have shown successful applications of particle filtering-based frameworks for predicting the matrix crack evolution and structural stiffness degradation caused by repetitive fatigue loads. Effects of other damage modes such as delamination, however, are not incorporated in these works. It is well established that delamination and matrix cracks not only co-exist in most laminate structures during the fatigue degradation process but also affect each other's progression. Furthermore, delamination significantly alters the stress-state in the laminates and accelerates the material degradation leading to catastrophic failure. Therefore, the work presented herein proposes a particle filtering-based framework for predicting a structure's remaining useful life with consideration of multiple co-existing damage-mechanisms. The framework uses an energy-based model from the composite modeling literature. The multiple damage-mode model has been shown to suitably estimate the energy release rate of cross-ply laminates as affected by matrix cracks and delamination modes. The model is also able to estimate the reduction in stiffness of the damaged laminate. This information is then used in the algorithms for life prediction capabilities. First, a brief summary of the energy-based damage model

  16. Comparison of algorithms to quantify muscle fatigue in upper limb muscles based on sEMG signals.

    Science.gov (United States)

    Kahl, Lorenz; Hofmann, Ulrich G

    2016-11-01

    This work compared the performance of six different fatigue detection algorithms quantifying muscle fatigue based on electromyographic signals. Surface electromyography (sEMG) was obtained by an experiment from upper arm contractions at three different load levels from twelve volunteers. Fatigue detection algorithms mean frequency (MNF), spectral moments ratio (SMR), the wavelet method WIRM1551, sample entropy (SampEn), fuzzy approximate entropy (fApEn) and recurrence quantification analysis (RQA%DET) were calculated. The resulting fatigue signals were compared considering the disturbances incorporated in fatiguing situations as well as according to the possibility to differentiate the load levels based on the fatigue signals. Furthermore we investigated the influence of the electrode locations on the fatigue detection quality and whether an optimized channel set is reasonable. The results of the MNF, SMR, WIRM1551 and fApEn algorithms fell close together. Due to the small amount of subjects in this study significant differences could not be found. In terms of disturbances the SMR algorithm showed a slight tendency to out-perform the others. Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.

  17. High temperature low cycle fatigue behavior of Ni-base superalloy M963

    International Nuclear Information System (INIS)

    He, L.Z.; Zheng, Q.; Sun, X.F.; Guan, H.R.; Hu, Z.Q.; Tieu, A.K.; Lu, C.; Zhu, H.T.

    2005-01-01

    The cyclic stress-strain response and the low cycle fatigue life behavior of solution treated Ni-base superalloy M963 were studied. Fully reversed strain-controlled tests were performed at temperature range from 700 to 950 deg. C in air at a constant total strain rate. The dislocation characteristics and failed surface observation were evaluated through scanning electron microscopy and transmission electron microscopy, respectively. The alloy exhibited the cyclic hardening, softening, or stable cyclic stress response, which was dependent on the temperature and total strain range. The fracture surface observation revealed that fatigue crack initiation was transgranular and closely related to the total strain range; however, fatigue crack propagation exhibited a strong dependence on testing temperature. The dramatic reduction in fatigue life and intergranular cracking observed at 900 and 950 deg. C were attributed to oxidation

  18. Proposal of fatigue crack growth rate curve in air for nickel-base alloys used in BWR

    International Nuclear Information System (INIS)

    Ogawa, Takuya; Itatani, Masao; Nagase, Hiroshi; Aoike, Satoru; Yoneda, Hideki

    2013-01-01

    When the defects are detected in the nuclear components in Japan, structural integrity assessment should be performed for the technical judgment on continuous service based on the Rules on Fitness-for-Service for Nuclear Power Plants of the Japan Society of Mechanical Engineers Code (JSME FFS Code). Fatigue crack growth analysis is required when the cyclic loading would be applied for the components. Recently, fatigue crack growth rate curve in air environment for Nickel-base alloys weld metal used in BWR was proposed by the authors and it was adopted as a code case of JSME FFS Code to evaluate the embedded flaw. In this study, fatigue crack growth behavior for heat-affected zone (HAZ) of Nickel-base alloys in air was investigated. And a unified fatigue crack growth rate curve in air for HAZ and weld metal of Nickel-base alloys used in BWR was evaluated. As a result, it was found that the curve for weld metal could be applied as a curve for both HAZ and weld metal since moderately conservative assessment of fatigue crack growth rate of HAZ is possible by the curve for weld metal in the Paris region. And the threshold value of stress intensity far range (ΔK th ) is determined to 3.0 MPa√m based on the fatigue crack growth rate of HAZ. (author)

  19. The Vibration Based Fatigue Damage Assessment of Steel and Steel Fiber Reinforced Concrete (SFRC Composite Girder

    Directory of Open Access Journals (Sweden)

    Xu Chen

    2015-01-01

    Full Text Available The steel-concrete composite girder has been usually applied in the bridge and building structures, mostly consisting of concrete slab, steel girder, and shear connector. The current fatigue damage assessment for the composite girder is largely based on the strain values and concrete crack features, which is time consuming and not stable. Hence the vibration-based fatigue damage assessment has been considered in this study. In detail, a steel-steel fiber reinforced concrete (SFRC composite girder was tested. The steel fiber reinforced concrete is usually considered for dealing with the concrete cracks in engineering practice. The composite girder was 3.3m long and 0.45m high. The fatigue load and impact excitation were applied on the specimen sequentially. According to the test results, the concrete crack development and global stiffness degradation during the fatigue test were relatively slow due to the favourable performance of SFRC in tension. But on the other hand, the vibration features varied significantly during the fatigue damage development. Generally, it confirmed the feasibility of executing fatigue damage assessment of composite bridge based on vibration method.

  20. Novel Damage Detection Techniques for Structural Health Monitoring Using a Hybrid Sensor

    Directory of Open Access Journals (Sweden)

    Dengjiang Wang

    2016-01-01

    Full Text Available This study presents a technique for detecting fatigue cracks based on a hybrid sensor monitoring system consisting of a combination of intelligent coating monitoring (ICM and piezoelectric transducer (PZT sensors. An experimental procedure using this hybrid sensor system was designed to monitor the cracks generated by fatigue testing in plate structures. A probability of detection (POD model that quantifies the reliability of damage detection for a specific sensor or the nondestructive testing (NDT method was used to evaluate the weight factor for the ICM and PZT sensors. To estimate the uncertainty of model parameters in this study, the Bayesian method was employed. Realistic data from fatigue testing was used to validate the overall method, and the results show that the novel damage detection technique using a hybrid sensor can quantify fatigue cracks more accurately than results obtained by conventional sensor methods.

  1. Ductile-phase toughening and fatigue crack growth in Nb3Al base alloys

    International Nuclear Information System (INIS)

    Gnanamoorthy, R.; Hanada, S.

    1996-01-01

    Niobium aluminide (Nb 3 Al) base intermetallic compounds exhibit good high-temperature strength and creep properties and potential for applications above 1,200 C provided their inadequately low room-temperature ductility, fracture toughness and fatigue crack growth behavior are improved. Addition of tantalum to Nb 3 Al base materials improves the high-temperature strength significantly and seems to be a potential alloying element. In the present study, room temperature fracture toughness and fatigue crack growth behavior of tantalum alloyed Nb 3 Al base alloy prepared by ingot metallurgy are investigated

  2. Proof of fatigue strength of nuclear components part II: Numerical fatigue analysis for transient stratification loading considering environmental effects

    International Nuclear Information System (INIS)

    Krätschmer, D.; Roos, E.; Schuler, X.; Herter, K.-H.

    2012-01-01

    For the construction, design and operation of nuclear components and systems the appropriate technical codes and standards provide detailed analysis procedures which guarantee a reliable behaviour of the structural components throughout the specified lifetime. Especially for cyclic stress evaluation the different codes and standards provide different fatigue analyses procedures to be performed considering the various mechanical and thermal loading histories and geometric complexities of the components. To consider effects of light water reactor coolant environments, new design curves included in report NUREG/CR-6909 for austenitic stainless steels and for low alloy steels have been presented. For the usage of these new design curves an environmental fatigue correction factor for incorporating environmental effects has to be calculated and used. The application of this environmental correction factor to a fatigue analysis of a nozzle with transient stratification loads, derived by in-service monitoring, has been performed. The results are used to compare with calculated usage factors, based on design curves without taking environmental effects particularly into account. - Highlights: ► We model an nozzle for fatigue analysis und mechanical and thermal loading conditions. ► A simplified as well as a general elastic–plastic fatigue analysis considering environmental effects is performed. ► The influence of different factors calculating the environmental factor F en are shown. ► The presented numerical evaluation methodology allows the consideration of all relevant parameters to assess lifetime.

  3. Effects of Accumulating Work Shifts on Performance-Based Fatigue Using Multiple Strength Measurements in Day and Night Shift Nurses and Aides.

    Science.gov (United States)

    Thompson, Brennan J; Stock, Matt S; Banuelas, Victoria K

    2017-05-01

    Objective This study aimed to examine the effects of accumulating nursing work on maximal and rapid strength characteristics in female nurses and compare these effects in day versus night shift workers. Background Nurses exhibit among the highest nonfatal injury rates of all occupations, which may be a consequence of long, cumulative work shift schedules. Fatigue may accumulate across multiple shifts and lead to performance impairments, which in turn may be linked to injury risks. Method Thirty-seven nurses and aides performed isometric strength-based performance testing of three muscle groups, including the knee extensors, knee flexors, and wrist flexors (hand grip), as well as countermovement jumps, at baseline and following exposure to three 12-hour work shifts in a four-day period. Variables included peak torque (PT) and rate of torque development (RTD) from isometric strength testing and jump height and power output. Results The rigorous work period resulted in significant decreases (-7.2% to -19.2%) in a large majority (8/9) of the isometric strength-based measurements. No differences were noted for the day versus night shift workers except for the RTD at 200 millisecond variable, for which the night shift had greater work-induced decreases than the day shift workers. No changes were observed for jump height or power output. Conclusions A compressed nursing work schedule resulted in decreases in strength-based performance abilities, being indicative of performance fatigue. Application Compressed work schedules involving long shifts lead to functional declines in nurse performance capacities that may pose risks for both the nurse and patient quality of care. Fatigue management plans are needed to monitor and regulate increased levels of fatigue.

  4. Inspection Correlation Study of Ultrasonic-Based In Situ Structural Health Monitoring Monthly Report for December 2014-January 2015

    Science.gov (United States)

    2015-05-01

    fatigue an induced ultrasonic elastic vibration (via piezoelectric transducers [ PZTs ]) propagates through the dogbone specimen. A receiver PZT picks up...inspection of fatigue crack growth in aluminum 7075-T6 dogbone specimens. Acellent Technologies, Inc., is supporting this project through providing...January 2015. 15. SUBJECT TERMS structural health monitoring, probabilistics, fatigue damage, guided waves, Lamb waves 16. SECURITY CLASSIFICATION OF

  5. Surface electromyography based muscle fatigue analysis for stroke patients at different Brunnstrom stages.

    Science.gov (United States)

    Yinjun Tu; Zhe Zhang; Xudong Gu; Qiang Fang

    2016-08-01

    Muscle fatigue analysis has been an important topic in sport and rehabilitation medicine due to its role in muscle performance evaluation and pathology investigation. This paper proposes a surface electromyography (sEMG) based muscle fatigue analysis approach which was specifically designed for stroke rehabilitation applications. 14 stroke patients from 5 different Brunnstrom recovery stage groups were involved in the experiment and features including median frequency and mean power frequency were extracted from the collected sEMG samples for investigation. After signal decomposition, the decline of motor unit firing rate of patients from different groups had also been studied. Statistically significant presence of fatigue had been observed in deltoideus medius and extensor digitorum communis of patients at early recovery stages (P0.01). It had also been discovered that the motor unit firing frequency declines with a range positively correlated to the recovery stage during repetitive movements. Based on the experiment result, it can be verified that as the recovery stage increases, the central nervous system's control ability strengthens and the patient motion becomes more stable and resistive to fatigue.

  6. Impaired cognitive control and reduced cingulate activity during mental fatigue

    NARCIS (Netherlands)

    Lorist, M.M.; Boksem, M.A.S.; Ridderinkhof, K.R.

    2005-01-01

    Neurocognitive mechanisms underlying the effects of mental fatigue are poorly understood. Here, we examined whether error-related brain activity, indexing performance monitoring by the anterior cingulate cortex (ACC), and strategic behavioural adjustments were modulated by mental fatigue, as induced

  7. Impaired cognitive control and reduced cingulate activity during mental fatigue

    NARCIS (Netherlands)

    Lorist, MM; Boksem, MAS; Ridderinkhof, KR

    Neurocognitive mechanisms underlying the effects of mental fatigue are poorly understood. Here, we examined whether error-related brain activity, indexing performance monitoring by the anterior cingulate cortex (ACC), and strategic behavioural adjustments were modulated by mental fatigue, as induced

  8. Fracture strength and fatigue resistance of dental resin-based composites

    NARCIS (Netherlands)

    Keulemans, F.; Palav, P.; Aboushelib, M.M.N.; van Dalen, A.; Kleverlaan, C.J.; Feilzer, A.J.

    2009-01-01

    Objectives: The aim of this study was to evaluate in vitro the influence of fiber-reinforcement on the fracture strength and fatigue resistance of resin-based composites. Methods: One hundred rectangular bar-shaped specimens (2 mm × 2 mm × 25 mm) made of resin-based composite were prepared in a

  9. Effect of test temperature on tensile and fatigue properties of nickel-base heat-resistant alloys

    International Nuclear Information System (INIS)

    Tsuji, Hirokazu; Nakajima, Hajime

    1987-01-01

    A series of tensile and strain controlled low-cycle fatigue tests were conducted at temperatures ranging from RT to 900 0 C on a nickel-base heat-resistant alloy, Hastelloy XR-II, which is one of the candidate alloys for applications in the process heating high-temperature gas-cooled reactor (HTGR). Fatigue tests at room temperature and all tensile tests were conducted in air, while fatigue tests at and above 400 0 C were conducted in the simulated HTGR helium environment. In those tests the effect of test temperature on tensile and fatigue properties was investigated. The ductility minimum point was observed near 600 0 C, while tensile and fatigue strengths decreased with increasing test temperature. The fatigue lives estimated with the method proposed by Manson were compatible with the experimental results under the given conditions. For the specimens fatigued at and above 700 0 C, the percentage of the intergranular fracture mode gradually increased with increasing test temperature. (orig.)

  10. Image-based creep-fatigue damage mechanism investigation of Alloy 617 at 950 °C

    Energy Technology Data Exchange (ETDEWEB)

    Tahir, Fraaz; Dahire, Sonam; Liu, Yongming, E-mail: yongming.liu@asu.edu

    2017-01-02

    Alloy 617 is a primary candidate material to be used in the next generation of nuclear power plants. Structural materials for these plants are expected to undergo creep and fatigue at temperatures as high as 950 °C. This study uses a hybrid-control creep-fatigue loading profile, as opposed to the traditional strain-controlled loading, to generate creep dominated failure. Qualitative and quantitative image analysis through SEM, EDS, and EBSD, is used to show that hybrid control testing is capable of producing creep dominated failure and that time fraction approach is not a valid indicator of creep or fatigue dominated damage. The focus of image analysis is on surface fatigue cracks and internal creep voids. A creep-fatigue damage interaction diagram based on these micro-scale features is plotted. It is shown that the classical time fraction approach suggested by the ASME code does not agree with the experimental findings and has a poor correlation with observed microscale damage features. A new definition of creep damage fraction based on an effective hold time is found to correlate well with the micro-scale image analysis.

  11. Reliability based code calibration of fatigue design criteria of nuclear Class-1 piping

    International Nuclear Information System (INIS)

    Mishra, J.; Balasubramaniyan, V.; Chellapandi, P.

    2016-01-01

    Fatigue design of Class-l piping of NPP is carried out using Section-III of American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel code. The fatigue design criteria of ASME are based on the concept of safety factor, which does not provide means for the management of uncertainties for consistently reliable and economical designs. In this regards, a work is taken up to estimate the implicit reliability level associated with fatigue design criteria of Class-l piping specified by ASME Section III, NB-3650. As ASME fatigue curve is not in the form of analytical expression, the reliability level of pipeline fittings and joints is evaluated using the mean fatigue curve developed by Argonne National Laboratory (ANL). The methodology employed for reliability evaluation is FORM, HORSM and MCS. The limit state function for fatigue damage is found to be sensitive to eight parameters, which are systematically modelled as stochastic variables during reliability estimation. In conclusion a number of important aspects related to reliability of various piping product and joints are discussed. A computational example illustrates the developed procedure for a typical pipeline. (author)

  12. Simulated laparoscopy using a head-mounted display vs traditional video monitor: an assessment of performance and muscle fatigue.

    Science.gov (United States)

    Maithel, S K; Villegas, L; Stylopoulos, N; Dawson, S; Jones, D B

    2005-03-01

    The direction of visual gaze may be an important ergonomic factor that affects operative performance. We designed a study to determine whether a head-mounted display (HMD) worn by the surgeon would improve task performance and/or reduce muscle fatigue during a laparoscopic task when compared to the use of a traditional video monitor display (VMD). Surgical residents (n = 30) were enrolled in the study. A junior group, consisting of 15 postgraduate year (PGY) = 1 subjects with no previous laparoscopic experience, and a senior group, consisting of 15 PGY 4 and PGY 5 subjects with experience, completed a laparoscopic task that was repeated four times using the Computer Enhanced Laparoscopic Training System (CELTS). Groups alternated between using the HMD with the task placed in a downward frontal position and the VMD with the task at a 30 degrees lateral angle. The CELTS module assessed task completion time, depth perception, path length of instruments, response orientation, motion smoothness; the system then generated an overall score. Electromyography (EMG) was used to record sternocleidomastoid muscle activity. Display preference was surveyed. The senior residents performed better than the junior residents overall on all parameters (p < 0.05) except for motion smoothness, where there was no difference. In both groups, the HMD significantly improved motion smoothness when compared to the VMD (p < 0.05). All other parameters were equal. There was less muscle fatigue when using the VMD (p < 0.05). We found that 66% of the junior residents but only 20% of the senior residents preferred the HMD. The CELTS module demonstrated evidence of construct validity by differentiating the performances of junior and senior residents. By aligning the surgeon's visual gaze with the instruments, HMD improved smoothness of motion. Experienced residents preferred the traditional monitor display. Although the VMD produced less muscle fatigue, inexperienced residents preferred the HMD

  13. Competing fatigue failure behaviors of Ni-based superalloy FGH96 at elevated temperature

    Energy Technology Data Exchange (ETDEWEB)

    Miao, Guolei [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Yang, Xiaoguang [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Collaborative Innovation Center of Advanced Aero-engine(CICAAE), Beihang University, Beijing 100191 (China); Shi, Duoqi, E-mail: shdq@buaa.edu.cn [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Collaborative Innovation Center of Advanced Aero-engine(CICAAE), Beihang University, Beijing 100191 (China)

    2016-06-21

    Fatigue experiments were performed on a polycrystalline P/M processed nickel-based superalloy, FGH96 at 600 °C to investigate competing fatigue failure behaviors of the alloy. The experiments were performed at four levels of stress (from high cycle fatigue to low cycle fatigue) at stress ratio of 0.05. There was large variability in fatigue life at both high and low stresses. Scanning electron microscopy (SEM) was used to analyze the failure surfaces. Three types of competing failure modes were observed (surface, sub-surface and internal initiated failures). Crack initiation sites were gradually changed from the surface to the interior with the decreasing of stress level. Roles of microstructures in competing failure mechanism were analyzed. There were six kinds of fatigue crack initiation modes: (1) surface inclusion initiated; (2) surface facet initiated; (3) sub-surface inclusion initiated; (4) sub-surface facet initiated; (5) internal inclusion initiated; (6) internal facet initiated. Inclusions at surface were the life-limiting microstructures at higher stress levels. The probability of occurrence of inclusions initiated is gradually reduced with decreasing of stress level, simultaneously the probability of occurrence of facets initiated is increasing. The existence of the inclusions resulted in large life variability at higher stress levels, while heterogeneity of material caused by random combinations of grains was the main cause of fatigue variability at lower stress levels.

  14. Competing fatigue failure behaviors of Ni-based superalloy FGH96 at elevated temperature

    International Nuclear Information System (INIS)

    Miao, Guolei; Yang, Xiaoguang; Shi, Duoqi

    2016-01-01

    Fatigue experiments were performed on a polycrystalline P/M processed nickel-based superalloy, FGH96 at 600 °C to investigate competing fatigue failure behaviors of the alloy. The experiments were performed at four levels of stress (from high cycle fatigue to low cycle fatigue) at stress ratio of 0.05. There was large variability in fatigue life at both high and low stresses. Scanning electron microscopy (SEM) was used to analyze the failure surfaces. Three types of competing failure modes were observed (surface, sub-surface and internal initiated failures). Crack initiation sites were gradually changed from the surface to the interior with the decreasing of stress level. Roles of microstructures in competing failure mechanism were analyzed. There were six kinds of fatigue crack initiation modes: (1) surface inclusion initiated; (2) surface facet initiated; (3) sub-surface inclusion initiated; (4) sub-surface facet initiated; (5) internal inclusion initiated; (6) internal facet initiated. Inclusions at surface were the life-limiting microstructures at higher stress levels. The probability of occurrence of inclusions initiated is gradually reduced with decreasing of stress level, simultaneously the probability of occurrence of facets initiated is increasing. The existence of the inclusions resulted in large life variability at higher stress levels, while heterogeneity of material caused by random combinations of grains was the main cause of fatigue variability at lower stress levels.

  15. Breast cancer and fatigue: issues for the workplace.

    Science.gov (United States)

    Mock, V

    1998-09-01

    1. Women with breast cancer are at high risk for fatigue as a side effect of treatment with surgery, radiation, and chemotherapy. The risk is compounded by the multiple roles of women who return to work during treatment. 2. The fatigue experience includes a physical component of decreased functional status, an affective component of emotional distress, and a cognitive component of difficulty concentrating. These characteristics of fatigue may present significant challenges for employees. 3. The Family Medical Leave Act provides 12 weeks of unpaid leave to receive medical treatment and/or recover from treatment for breast cancer. 4. The nurse in the workplace can assess and monitor the effects of fatigue and teach employees to manage fatigue through energy conservation, effective use of energy, and health promotion activities to restore energy levels.

  16. Fatigue Assessment of Nickel-Titanium Peripheral Stents: Comparison of Multi-Axial Fatigue Models

    Science.gov (United States)

    Allegretti, Dario; Berti, Francesca; Migliavacca, Francesco; Pennati, Giancarlo; Petrini, Lorenza

    2018-02-01

    Peripheral Nickel-Titanium (NiTi) stents exploit super-elasticity to treat femoropopliteal artery atherosclerosis. The stent is subject to cyclic loads, which may lead to fatigue fracture and treatment failure. The complexity of the loading conditions and device geometry, coupled with the nonlinear material behavior, may induce multi-axial and non-proportional deformation. Finite element analysis can assess the fatigue risk, by comparing the device state of stress with the material fatigue limit. The most suitable fatigue model is not fully understood for NiTi devices, due to its complex thermo-mechanical behavior. This paper assesses the fatigue behavior of NiTi stents through computational models and experimental validation. Four different strain-based models are considered: the von Mises criterion and three critical plane models (Fatemi-Socie, Brown-Miller, and Smith-Watson-Topper models). Two stents, made of the same material with different cell geometries are manufactured, and their fatigue behavior is experimentally characterized. The comparison between experimental and numerical results highlights an overestimation of the failure risk by the von Mises criterion. On the contrary, the selected critical plane models, even if based on different damage mechanisms, give a better fatigue life estimation. Further investigations on crack propagation mechanisms of NiTi stents are required to properly select the most reliable fatigue model.

  17. Fatigue Assessment of Nickel-Titanium Peripheral Stents: Comparison of Multi-Axial Fatigue Models

    Science.gov (United States)

    Allegretti, Dario; Berti, Francesca; Migliavacca, Francesco; Pennati, Giancarlo; Petrini, Lorenza

    2018-03-01

    Peripheral Nickel-Titanium (NiTi) stents exploit super-elasticity to treat femoropopliteal artery atherosclerosis. The stent is subject to cyclic loads, which may lead to fatigue fracture and treatment failure. The complexity of the loading conditions and device geometry, coupled with the nonlinear material behavior, may induce multi-axial and non-proportional deformation. Finite element analysis can assess the fatigue risk, by comparing the device state of stress with the material fatigue limit. The most suitable fatigue model is not fully understood for NiTi devices, due to its complex thermo-mechanical behavior. This paper assesses the fatigue behavior of NiTi stents through computational models and experimental validation. Four different strain-based models are considered: the von Mises criterion and three critical plane models (Fatemi-Socie, Brown-Miller, and Smith-Watson-Topper models). Two stents, made of the same material with different cell geometries are manufactured, and their fatigue behavior is experimentally characterized. The comparison between experimental and numerical results highlights an overestimation of the failure risk by the von Mises criterion. On the contrary, the selected critical plane models, even if based on different damage mechanisms, give a better fatigue life estimation. Further investigations on crack propagation mechanisms of NiTi stents are required to properly select the most reliable fatigue model.

  18. Diffraction-based study of fatigue crack initiation and propagation in aerospace aluminum alloys

    Science.gov (United States)

    Gupta, Vipul K.

    The crack initiation sites and microstructure-sensitive growth of small fatigue cracks are experimentally characterized in two precipitation-hardened aluminum alloys, 7075-T651 and 7050-T7451, stressed in ambient temperature moist-air (warm-humid) and -50°C dry N2 (cold-dry) environmental conditions. Backscattered electron imaging (BSE) and energy dispersive spectroscopy (EDS) of the fracture surfaces showed that Fe-Cu rich constituent particle clusters are the most common initiation sites within both alloys stressed in either environment. The crack growth within each alloy, on average, was observed to be slowed in the cold-dry environment than in the warm-humid environment, but only at longer crack lengths. Although no overwhelming effects of grain boundaries and grain orientations on small-crack growth were observed, crack growth data showed local fluctuations within individual grains. These observations are understood as crack propagation through the underlying substructure at the crack surface and frequent interaction with low/high-angle grain and subgrain boundaries, during cyclic loading, and, are further attributed to periodic changes in crack propagation path and multiple occurrences of crack-branching observed in the current study. SEM-based stereology in combination with electron backscattered diffraction (EBSD) established fatigue crack surface crystallography within the region from ˜1 to 50 mum of crack initiating particle clusters. Fatigue crack facets were parallel to a wide variety of crystallographic planes, with pole orientations distributed broadly across the irreducible stereographic triangle between the {001} and {101}-poles within both warm-humid and cold-dry environments. The results indicate environmentally affected fatigue cracking in both cases, given the similarity between the observed morphology and crystallography with that of a variety of aerospace aluminum alloys cracked in the presence of moist-air. There was no evidence of

  19. Prevalence and impact of severe fatigue in adolescent and young adult cancer patients in comparison with population-based controls.

    Science.gov (United States)

    Poort, Hanneke; Kaal, Suzanne E J; Knoop, Hans; Jansen, Rosemarie; Prins, Judith B; Manten-Horst, Eveliene; Servaes, Petra; Husson, Olga; van der Graaf, Winette T A

    2017-09-01

    The current study determined the prevalence of severe fatigue in adolescent and young adult (AYA) cancer patients (aged 18-35 years at diagnosis) consulting a multidisciplinary AYA team in comparison with gender- and age-matched population-based controls. In addition, impact of severe fatigue on quality of life and correlates of fatigue severity were examined. AYAs with cancer (n = 83) completed questionnaires including the Checklist Individual Strength (CIS-fatigue), Quality of Life (QoL)-Cancer Survivor, Hospital Anxiety and Depression Scale (reflecting psychological distress), and the Cancer Worry Scale (reflecting fear of cancer recurrence or progression). The vast majority of participants had been treated with chemotherapy (87%) and had no active treatment at the time of participation (73.5%). Prevalence of severe fatigue (CIS-fatigue score ≥35) in AYAs with cancer (48%, n = 40/83) was significantly higher in comparison with matched population-based controls (20%, n = 49/249; p fatigued AYAs with cancer reported lower QoL compared to non-severely fatigued AYAs with cancer (p fatigue severity (p fatigue based on a validated cut-off score was highly prevalent in this group of AYAs with cancer. QoL is significantly affected by severe fatigue, stressing the importance of detection and management of this symptom in those patients affected by a life-changing diagnosis of cancer in late adolescence or young adulthood.

  20. Fatigue Load Sensitivity Based Optimal Active Power Dispatch For Wind Farms

    DEFF Research Database (Denmark)

    Zhao, Haoran; Wu, Qiuwei; Huang, Shaojun

    2017-01-01

    This paper proposes an optimal active power dispatch algorithm for wind farms based on Wind Turbine (WT) load sensitivity. The control objectives include tracking power references from the system operator and minimizing fatigue loads experienced by WTs. The sensitivity of WT fatigue loads to power...... sensitivity are derived, which significantly improves the computation efficiency of the local WT controller. The proposed algorithm can be implemented in different active power control schemes. Case studies were conducted with a wind farm under balance control for both low and high wind conditions...

  1. A Fuzzy-Based Fusion Method of Multimodal Sensor-Based Measurements for the Quantitative Evaluation of Eye Fatigue on 3D Displays

    Directory of Open Access Journals (Sweden)

    Jae Won Bang

    2015-05-01

    Full Text Available With the rapid increase of 3-dimensional (3D content, considerable research related to the 3D human factor has been undertaken for quantitatively evaluating visual discomfort, including eye fatigue and dizziness, caused by viewing 3D content. Various modalities such as electroencephalograms (EEGs, biomedical signals, and eye responses have been investigated. However, the majority of the previous research has analyzed each modality separately to measure user eye fatigue. This cannot guarantee the credibility of the resulting eye fatigue evaluations. Therefore, we propose a new method for quantitatively evaluating eye fatigue related to 3D content by combining multimodal measurements. This research is novel for the following four reasons: first, for the evaluation of eye fatigue with high credibility on 3D displays, a fuzzy-based fusion method (FBFM is proposed based on the multimodalities of EEG signals, eye blinking rate (BR, facial temperature (FT, and subjective evaluation (SE; second, to measure a more accurate variation of eye fatigue (before and after watching a 3D display, we obtain the quality scores of EEG signals, eye BR, FT and SE; third, for combining the values of the four modalities we obtain the optimal weights of the EEG signals BR, FT and SE using a fuzzy system based on quality scores; fourth, the quantitative level of the variation of eye fatigue is finally obtained using the weighted sum of the values measured by the four modalities. Experimental results confirm that the effectiveness of the proposed FBFM is greater than other conventional multimodal measurements. Moreover, the credibility of the variations of the eye fatigue using the FBFM before and after watching the 3D display is proven using a t-test and descriptive statistical analysis using effect size.

  2. Fatigue crack growth behavior of a new single crystal nickel-based superalloy (CMSX-4) at 650 C

    International Nuclear Information System (INIS)

    Sengupta, A.; Putatunda, S.K.

    1994-01-01

    CMSX-4 is a recently developed rhenium containing single crystal nickel-based superalloy. This alloy has potential applications in many critical high-temperature applications such as turbine blades, rotors, nuclear reactors, etc. The fatigue crack growth rate and the fatigue threshold data of this material is extremely important for accurate life prediction, as well as failure safe design, at elevated temperatures. In this paper, the fatigue crack growth behavior of CMSX-4 has been studied at 650 C. The investigation also examined the influence of γ' precipitates (size and distribution) on the near-threshold fatigue crack growth rate and the fatigue threshold. The influence of load ratio on the fatigue crack growth rate and the fatigue threshold was also examined. Detailed fractographic studies were carried out to determine the crack growth mechanism in fatigue in the threshold region. Compact tension specimens were prepared from the single crystal nickel-based superalloy CMSX-4 with [001] orientation as the tensile loading axis direction. These specimens were given three different heat treatments to produce three different γ' precipitate sizes and distributions. Fatigue crack growth behavior of these specimens was studied at 650 C in air. The results of the present investigation indicate that the near-threshold fatigue crack growth rate decreases and that the fatigue threshold increases with an increase in the γ' precipitate size at 650 C. The fatigue threshold decreased linearly with an increase in load ratio. Fractographs at 650 C show a stage 2 type of crack growth along {100} type of crystal planes in the threshold region, and along {111} type of crystal planes in the high ΔK region

  3. Application of the strain energy for fatigue life prediction (LCF) of metals by the energy-based criterion

    International Nuclear Information System (INIS)

    Shahram Shahrooi; Ibrahim Henk Metselaar; Zainul Huda; Ghezavati, H.R.

    2009-01-01

    Full text: In this study, the plastic strain energy under multiaxial fatigue condition has been calculated in the cyclic plasticity models by the stress-strain hysteresis loops. Then, using the results of these models, the fatigue lives in energy-based fatigue model is predicted and compared to experimental data. Moreover, a weighting factor on shear plastic work is presented to decrease the life factors in the model fatigue. (author)

  4. Development of sacrificial specimen for fatigue damage prediction of structure (2nd report); Kozobutsu no hiro sonsho yochi no tameno giseishikenhen no kaihatsu ( 2 )

    Energy Technology Data Exchange (ETDEWEB)

    Fujimoto, Y.; Huang, F.; Hada, K.; Sato, A.; Hamada, K.; Iwata, M. [Hiroshima Univ. (Japan)

    1998-12-31

    The study aims at applying the sacrificial specimen developed by the authors of the paper on practical structures, the sacrificial specimens are secured to a smooth specimen and a boxing welded joint, and fatigue tests are performed under varying stress amplitude. The load is cyclic 8 stage block load that has load frequency distribution similar to exponential distribution. Then, a fatigue life prediction of structural element is studied based on monitoring results of the sacrificial specimen. The obtained results are as follows. The sacrificial specimen shows steady fatigue property without occurrence of peeling off or buckling even under varying stress amplitude. A limited accumulated damage value of the sacrificial specimen is obtained under the varying stress amplitude. While arranging the crack growth curve of the varying sacrificial specimen in N/Nf, they show almost the same shape not depending on the life. The prediction method of fatigue life of a structure is described based on monitoring results of the sacrificial specimen. 9 refs., 16 figs., 2 tabs.

  5. Monitoring microstructural evolution of alloy 617 with non-linear acoustics for remaining useful life prediction; multiaxial creep-fatigue and creep-ratcheting

    International Nuclear Information System (INIS)

    Lissenden, Cliff; Hassan, Tasnin; Rangari, Vijaya

    2014-01-01

    The research built upon a prior investigation to develop a unified constitutive model for design-@by-@analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-@fatigue and creep-@ratcheting tests were conducted on the nickel base Alloy 617 at 850 and 950°C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-@controlled cycling, are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-@fatigue and creep-@ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-@fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-@ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched application of the

  6. Nonlinear Fatigue Damage Model Based on the Residual Strength Degradation Law

    Science.gov (United States)

    Yongyi, Gao; Zhixiao, Su

    In this paper, a logarithmic expression to describe the residual strength degradation process is developed in order to fatigue test results for normalized carbon steel. The definition and expression of fatigue damage due to symmetrical stress with a constant amplitude are also given. The expression of fatigue damage can also explain the nonlinear properties of fatigue damage. Furthermore, the fatigue damage of structures under random stress is analyzed, and an iterative formula to describe the fatigue damage process is deduced. Finally, an approximate method for evaluating the fatigue life of structures under repeated random stress blocking is presented through various calculation examples.

  7. Influence of outdoor running fatigue and medial tibial stress syndrome on accelerometer-based loading and stability.

    Science.gov (United States)

    Schütte, Kurt H; Seerden, Stefan; Venter, Rachel; Vanwanseele, Benedicte

    2018-01-01

    Medial tibial stress syndrome (MTSS) is a common overuse running injury with pathomechanics likely to be exaggerated by fatigue. Wearable accelerometry provides a novel alternative to assess biomechanical parameters continuously while running in more ecologically valid settings. The purpose of this study was to determine the influence of outdoor running fatigue and MTSS on both dynamic loading and dynamic stability derived from trunk and tibial accelerometery. Runners with (n=14) and without (n=16) history of MTSS performed an outdoor fatigue run of 3200m. Accelerometer-based measures averaged per lap included dynamic loading of the trunk and tibia (i.e. axial peak positive acceleration, signal power magnitude, and shock attenuation) as well as dynamic trunk stability (i.e. tri-axial root mean square ratio, step and stride regularity, and sample entropy). Regression coefficients from generalised estimating equations were used to evaluate group by fatigue interactions. No evidence could be found for dynamic loading being higher with fatigue in runners with MTSS history (all measures p>0.05). One significant group by running fatigue interaction effect was detected for dynamic stability. Specifically, in MTSS only, decreases mediolateral sample entropy i.e. loss of complexity was associated with running fatigue (prunning state. We suggest that a practical outdoor running fatigue protocol that concurrently captures trunk accelerometry-based movement complexity warrants further prospective investigation as an in-situ screening tool for MTSS individuals. Copyright © 2017 Elsevier B.V. All rights reserved.

  8. A Wireless sEMG Recording System and Its Application to Muscle Fatigue Detection

    Science.gov (United States)

    Chang, Kang-Ming; Liu, Shin-Hong; Wu, Xuan-Han

    2012-01-01

    Surface electromyography (sEMG) is an important measurement for monitoring exercise and fitness. Because if its high sampling frequency requirement, wireless transmission of sEMG data is a challenge. In this article a wireless sEMG measurement system with a sampling frequency of 2 KHz is developed based upon a MSP 430 microcontroller and Bluetooth transmission. Standard isotonic and isometric muscle contraction are clearly represented in the receiving user interface. Muscle fatigue detection is an important application of sEMG. Traditional muscle fatigue is detected from the median frequency of the sEMG power spectrum. The regression slope of the linear regression of median frequency is an important muscle fatigue index. A more negative slope value represents a higher muscle fatigue condition. To test the system performance, muscle fatigue detection was examined by having subjects run on a pedaled-multifunctional elliptical trainer for approximately 30 minutes at three loading levels. Ten subjects underwent a total of 60 exercise sessions to provide the experimental data. Results showed that the regression slope gradually decreases as expected, and there is a significant gender difference. PMID:22368481

  9. Verification of anti-fatigue effect of anserine by angle fatigue indicator based on median frequency changes of electromyograms

    Directory of Open Access Journals (Sweden)

    Hirohisa Kishi

    2013-10-01

    Full Text Available ABSTRACT: Objective: Anserine, which is abundant in avian species and in a wide range of fish such as bonito and tuna, is reported to have anti-fatigue effect. Although chicken soup and bonito soup is traditionally used to recover from physical fatigue, it is generally difficult to verify the effect in humans. This study was to directly demonstrate the anti-fatigue effect of oceanic anserine in humans. Methods: Edible-grade anserine was purified from fish extract with food-grade reagents. Subjects were 17 healthy male volunteers (35.5 ± 5 yr., 75.5 ± 5.0 kg. Each subject performed the isometric exercise tolerance test (ETT on the rectus femoris muscle twice (Ex_1, Ex_2 both for anserine and water conditions on a different day. Median frequency changes (MDF during Functional Foods in Health and Disease 2013; 3(10 389-399 ETTs were calculated and regression curves were calculated over a frequency range of 21-214 Hz. The difference, or angle, between the slopes of Ex_1 and Ex_2 MDF regression curves, which corresponds to the degree of fatigue, was defined as an angle fatigue index and compared between anserine and water intake conditions. Results: MDF decreased during ETTs in most patients and the slopes of regression curves were larger in Ex_2 than in Ex_1. Angle fatigue index for water (control was significantly larger than that for anserine (p<0.01, paired t-test, n=17. The result indicates that anserine have an anti-fatigue effect on skeletal muscle in humans. Conclusions: We proposed the angle fatigue index as a touchstone of the muscle fatigue. The index indicates that anserine is effective to reduce the muscle fatigue in humans.

  10. Human fatigue expression recognition through image-based dynamic multi-information and bimodal deep learning

    Science.gov (United States)

    Zhao, Lei; Wang, Zengcai; Wang, Xiaojin; Qi, Yazhou; Liu, Qing; Zhang, Guoxin

    2016-09-01

    Human fatigue is an important cause of traffic accidents. To improve the safety of transportation, we propose, in this paper, a framework for fatigue expression recognition using image-based facial dynamic multi-information and a bimodal deep neural network. First, the landmark of face region and the texture of eye region, which complement each other in fatigue expression recognition, are extracted from facial image sequences captured by a single camera. Then, two stacked autoencoder neural networks are trained for landmark and texture, respectively. Finally, the two trained neural networks are combined by learning a joint layer on top of them to construct a bimodal deep neural network. The model can be used to extract a unified representation that fuses landmark and texture modalities together and classify fatigue expressions accurately. The proposed system is tested on a human fatigue dataset obtained from an actual driving environment. The experimental results demonstrate that the proposed method performs stably and robustly, and that the average accuracy achieves 96.2%.

  11. Effects of stress concentrations on the fatigue life of a gamma based titanium aluminide

    International Nuclear Information System (INIS)

    Trail, S.J.; Bowen, P.

    1995-01-01

    S-N curves for a gamma based titanium aluminide alloy of composition Ti-47.2Al-2.1Mn-1.9Nb(at.%)+2TiB 2 (wt.%) have been used to define fatigue life. Effects of residual stress, stressed volume, loading ratio, loading mode, elevated temperature and surface roughness have been considered. Residual tensile stresses and micro-cracking are introduced by Electro Discharge Machining and the fatigue life is reduced slightly compared with polished samples. Notched fatigue tests show a significant notch strengthening effect which increases with increasing stress concentration factor. The fracture surfaces of specimens tested at room temperature reveal fully brittle failure mechanisms and no evidence of stable crack growth is observed. The fatigue life appears, therefore, to be determined predominantly by the number of cycles to crack initiation. At the elevated temperature of 830 C, evidence for some stable fatigue crack growth has been found. Probable sites for crack initiation are addressed

  12. Hot-Spot Fatigue and Impact Damage Detection on a Helicopter Tailboom

    Science.gov (United States)

    2011-09-01

    other 14 PZT disks were used as sensors. Among the 28 PZT disks, 16 PZT disks were placed in the two fatigue hot-spot areas to detect cracks initiated...more efficient and effective airframe maintenance, fatigue cracking and impact damage detection technologies were developed and demonstrated on a...SHM system in successfully monitoring fatigue cracks initiated from cyclical loading conditions; detecting, locating and quantifying ballistic

  13. Corrosion fatigue studies on a bulk glassy Zr-based alloy under three-point bending

    Science.gov (United States)

    Grell, Daniel; Wilkin, Yannic; Gostin, Petre F.; Gebert, Annett; Kerscher, Eberhard

    2016-12-01

    Corrosion fatigue (CF) tests were carried out on bulk glassy Zr52.5Cu17.9Al10Ni14.6Ti5 (Vitreloy 105) samples under load-controlled three-point bending conditions with a load ratio of R = 0.1 in 0.01 M Na2SO4 + 0.01 M NaCl electrolyte. During cyclic testing, the bar-shaped specimens were polarized in situ at constant potentials and the current was monitored. Three different anodic potentials within the interval between the pitting potential EP and the repassivation potential ER, and three different load amplitudes were applied. In some cases, in situ microscopic observations revealed the formation of black corrosion products in the vicinity of the crack tip during anodic polarization. Fractographic analysis revealed a clear distinction between two modes of crack growth characterized by smooth dissolution induced regions on the one hand and slim fast fracture areas on the other hand. Both alternating features contributed to a broad striated corrosion fatigue fracture surface. Moreover, further fatigue tests were carried out under free corrosion conditions yielding additional information on crack initiation and crack propagation period by means of the open circuit potential (OCP) changes. Thereby, a slight increase in OCP was detected after rupture of the passive layer due to bare metal exposed to the electrolyte. The electrochemical response increased continuously according to stable crack propagation until fracture occurred. Finally, the fracture surfaces of the corrosion fatigue samples were investigated by energy dispersive X-ray with the objective of analyzing the elemental distribution after anodic dissolution. Interestingly, anodic polarization at a near repassivation potential of -50 mV vs. SCE (Saturated Calomel Electrode, E = 0.241 V vs. SHE, Standard Hydrogen Electrode) led to favorable effects on the fatigue lifetime. In conclusion, all results are conflated to a corrosion fatigue model for bulk glassy Vitreloy 105 under anodic polarization in chloride

  14. Comparison on driving fatigue related hemodynamics activated by auditory and visual stimulus

    Science.gov (United States)

    Deng, Zishan; Gao, Yuan; Li, Ting

    2018-02-01

    As one of the main causes of traffic accidents, driving fatigue deserves researchers' attention and its detection and monitoring during long-term driving require a new technique to realize. Since functional near-infrared spectroscopy (fNIRS) can be applied to detect cerebral hemodynamic responses, we can promisingly expect its application in fatigue level detection. Here, we performed three different kinds of experiments on a driver and recorded his cerebral hemodynamic responses when driving for long hours utilizing our device based on fNIRS. Each experiment lasted for 7 hours and one of the three specific experimental tests, detecting the driver's response to sounds, traffic lights and direction signs respectively, was done every hour. The results showed that visual stimulus was easier to cause fatigue compared with auditory stimulus and visual stimulus induced by traffic lights scenes was easier to cause fatigue compared with visual stimulus induced by direction signs in the first few hours. We also found that fatigue related hemodynamics caused by auditory stimulus increased fastest, then traffic lights scenes, and direction signs scenes slowest. Our study successfully compared audio, visual color, and visual character stimulus in sensitivity to cause driving fatigue, which is meaningful for driving safety management.

  15. Fatigue damage monitoring of structural aluminum alloys

    Directory of Open Access Journals (Sweden)

    С.Р. Ігнатович

    2004-01-01

    Full Text Available  Results of the experiments directed on creation of a new tool method of fatigue damage diagnostics and an estimation of a residual life of aviation designs are presented. It is shown, that the defo rmation relief formed on a surface of cladding  layer of sheets of constructional alloys Д-16АТ, 2024-Т3, 7075-Т6  can be considered as the metal damage indicator  under cyclically repeating loadings.

  16. Analysis of acoustic emission signals of fatigue crack growth and corrosion processes. Investigation of the possibilities for continuous condition monitoring of transport containers by acoustic emission testing

    International Nuclear Information System (INIS)

    Wachsmuth, Janne

    2016-01-01

    Fatigue crack growth and active corrosion processes are the main causes of structural failures of transport products like road tankers, railway tank cars and ships. To prevent those failures, preventive, time-based maintenance is performed. However, preventive inspections are costly and include the risk of not detecting a defect, which could lead to a failure within the next service period. An alternative is the idea of continuous monitoring of the whole structure by means of acoustic emission testing (AT). With AT, defects within the material shall be detected and repaired directly after their appearance. Acoustic emission testing is an online non-destructive testing method. Acoustic emission (AE) arises from changes within the material and is transported by elastic waves through the material. If the AE event generates enough energy, the elastic wave propagates to the boundaries of the component, produces a displacement in the picometre scale and can be detected by a piezoelectric sensor. The sensor produces an electrical signal. From this AE signal, AE features such as the maximum amplitude or the frequency can be extracted. Methods of signal analysis are used to investigate the time and frequency dependency of signal groups. The purpose of the signal analysis is to connect the AE signal with the originating AE source. If predefined damage mechanisms are identified, referencing the damage condition of the structure is possible. Acoustic emission from events of the actual crack propagation process can for example lead to the crack growth rate or the stress intensity factor, both specific values from fracture mechanics. A new development in the domain of acoustic emission testing is the pattern recognition of AE signals. Specific features are extracted from the AE signals to assign them to their damage mechanisms. In this thesis the AE signals from the damage mechanisms corrosion and fatigue crack growth are compared and analysed. The damage mechanisms were

  17. Monitoring of Fatigue Degradation in Austenitic Stainless Steels

    International Nuclear Information System (INIS)

    Kalkhof, D.; Niffenegger, M.; Leber, H.J.

    2004-01-01

    During cyclic loading of austenitic stainless steel, it was observed that microstructural changes occurred; these affect both the mechanical and physical properties of the material. For certain steels, a strain-induced martensite phase transformation was seen. The investigations showed that, for the given material and loading conditions, the volume fraction of martensite depends on the cycle number, temperature and initial material state. It was also found that the martensite content continuously increased with the cycle number. Therefore, the volume fraction of martensite was used as an indication of fatigue usage. It was noted that the temperature dependence of the martensite formation could be described by a Boltzmann function, and that the martensite content decreased with increasing temperature. Two different heats of the austenitic stainless steel X6CrNiTi18-10 (AISI 321, DIN 1.4541) were investigated. It was found that the martensite formation rate was much higher for the cold-worked than for the solution-annealed material. All applied techniques - neutron diffraction and advanced magnetic methods - were successful in detecting the presence of martensite in the differently fatigued specimens. (author)

  18. Reliability Based Calibration of Fatigue Design Guidelines for Ship Structures

    DEFF Research Database (Denmark)

    Folsø, Rasmus; Otto, S.; Parmentier, G.

    2002-01-01

    A simple reliability based framework is applied to calibrate a new set of fatigue design guidelines. This new guideline considers two different approaches for the assessment of both loads, stresses and local stress raising effects, and partial safety factors must be given for any combination...

  19. Probabilistic Fatigue Life Prediction of Bridge Cables Based on Multiscaling and Mesoscopic Fracture Mechanics

    Directory of Open Access Journals (Sweden)

    Zhongxiang Liu

    2016-04-01

    Full Text Available Fatigue fracture of bridge stay-cables is usually a multiscale process as the crack grows from micro-scale to macro-scale. Such a process, however, is highly uncertain. In order to make a rational prediction of the residual life of bridge cables, a probabilistic fatigue approach is proposed, based on a comprehensive vehicle load model, finite element analysis and multiscaling and mesoscopic fracture mechanics. Uncertainties in both material properties and external loads are considered. The proposed method is demonstrated through the fatigue life prediction of cables of the Runyang Cable-Stayed Bridge in China, and it is found that cables along the bridge spans may have significantly different fatigue lives, and due to the variability, some of them may have shorter lives than those as expected from the design.

  20. Cyclic Deformation and Fatigue Behaviors of Alloy 617 Base Metal and Weldments at 900℃ for VHTR Applications

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Seon Jin; Kim, Byung Tak; Dewa, Rando T.; Hwang, Jeong Jun; Kim, Tae Su [Pukyong National Univ., Busan (Korea, Republic of); Kim, Woo Gon; Kim, Eung Seon [KAERI, Daejeon (Korea, Republic of)

    2016-05-15

    An analysis of cyclic deformation can contribute to a deeper understanding of the fatigue fracture mechanisms as well as to improvements in the design and application of VHTR system. However, the studies associated with cyclic deformation and low cycle fatigue (LCF) properties of Alloy 617 have focused mainly on the base metal, with little attention given to the weldments. Totemeier studied on high-temperature creep-fatigue of Alloy 617 base metal and weldments. Current research activities at PKNU and KAERI focus on the study of cyclic deformation and LCF behaviors of Alloy 617 base metal (BM) and weldments (WM) specimens were machined from GTAW buttwelded plates at very high-temperature of 900℃. In this work, the cyclic deformation characteristics and fatigue behaviors of Alloy 617 BM and WM are studied and discussed with respect to LCF. In this paper, cyclic deformation and low cycle fatigue behaviors of Alloy 617 base metal and weldments was evaluated using strain-controlled LCF tests at 900℃for 0.6% total strain range. Results of the current experiments can be concluded; The WM specimen has shown a higher cyclic stress response than the BM specimen. The fatigue life of WM specimen was reduced relative to that of BM specimen.

  1. Fatigue, Work Schedules, and Perceived Performance in Bedside Care Nurses.

    Science.gov (United States)

    Sagherian, Knar; Clinton, Michael E; Abu-Saad Huijer, Huda; Geiger-Brown, Jeanne

    2017-07-01

    Hospital nurses are expected to maintain optimal work performance; yet, fatigue can threaten safe practice and result in unfavorable patient outcomes. This descriptive cross-sectional study explored the association between fatigue, work schedules, and perceived work performance among nurses. The study sample included 77 bedside nurses who were mostly female, single, and between 20 and 29 years of age. The majority worked 8-hour shifts and overtime. Nurses who worked during off days reported significantly higher chronic fatigue compared with those nurses who took time off. Nurses who reported feeling refreshed after sleep had significantly less chronic and acute fatigue and more intershift recovery. Nurses with acute and chronic fatigue perceived poorer physical performance. Also, nurses who reported chronic fatigue perceived they were less alert and less able to concentrate when providing patient care. Less effective communication was also associated with acute and chronic fatigue. In conclusion, fatigue has safety implications for nurses' practice that should be monitored by nursing management.

  2. Fracture resistance and fatigue crack growth characteristics of two Al-Cu-Mg-Zr alloys

    Science.gov (United States)

    Sarkar, Bhaskar; Lisagor, W. B.

    1992-01-01

    The dependence of strength, fracture resistance, and fatigue crack growth rate on the aging conditions of two alloy compositions based on Al-3.7Cu-1.85Mg-0.2Mn is investigated. Mechanical properties were evaluated in two heat treatment conditions and in two orientations (longitudinal and transverse). Compact tension specimens were used to determine fatigue crack growth characteristics and fracture resistance. The aging response was monitored on coupons using hardness measurements determined with a standard Rockwell hardness tester. Fracture resistance is found to increase with increasing yield strength during artificial aging of age-hardenable 2124-Zr alloys processed by powder metallurgy techniques. Fatigue crack growth rate increases with increasing strength. It is argued that these changes are related to deformation modes of the alloys; a homogeneous deformation mode tends to increase fracture resistance and to decrease the resistance to the fatigue crack propagation rate.

  3. Multiaxial fatigue criterion based on parameters from torsion and axial S-N curve

    Directory of Open Access Journals (Sweden)

    M. Margetin

    2016-07-01

    Full Text Available Multiaxial high cycle fatigue is a topic that concerns nearly all industrial domains. In recent years, a great deal of recommendations how to address problems with multiaxial fatigue life time estimation have been made and a huge progress in the field has been achieved. Until now, however, no universal criterion for multiaxial fatigue has been proposed. Addressing this situation, this paper offers a design of a new multiaxial criterion for high cycle fatigue. This criterion is based on critical plane search. Damage parameter consists of a combination of normal and shear stresses on a critical plane (which is a plane with maximal shear stress amplitude. Material parameters used in proposed criterion are obtained from torsion and axial S-N curves. Proposed criterion correctly calculates life time for boundary loading condition (pure torsion and pure axial loading. Application of proposed model is demonstrated on biaxial loading and the results are verified with testing program using specimens made from S355 steel. Fatigue material parameters for proposed criterion and multiple sets of data for different combination of axial and torsional loading have been obtained during the experiment.

  4. Analysis of thermal fatigue events in light water reactors

    Energy Technology Data Exchange (ETDEWEB)

    Okuda, Yasunori [Institute of Nuclear Safety System Inc., Seika, Kyoto (Japan)

    2000-09-01

    Thermal fatigue events, which may cause shutdown of nuclear power stations by wall-through-crack of pipes of RCRB (Reactor Coolant Pressure Boundary), are reported by licensees in foreign countries as well as in Japan. In this paper, thermal fatigue events reported in anomalies reports of light water reactors inside and outside of Japan are investigated. As a result, it is clarified that the thermal fatigue events can be classified in seven patterns by their characteristics, and the trend of the occurrence of the events in PWRs (Pressurized Water Reactors) has stronger co-relation to operation hours than that in BWRs (Boiling Water Reactors). Also, it is concluded that precise identification of locations where thermal fatigue occurs and its monitoring are important to prevent the thermal fatigue events by aging or miss modification. (author)

  5. Uncertainty on Fatigue Damage Accumulation for Composite Materials

    DEFF Research Database (Denmark)

    Toft, Henrik Stensgaard; Sørensen, John Dalsgaard

    2009-01-01

    In the present paper stochastic models for fatigue damage accumulation for composite materials are presented based on public available constant and variable amplitude fatigue tests. The methods used for estimating the SN-curve and accumulated fatigue damage are presented.......In the present paper stochastic models for fatigue damage accumulation for composite materials are presented based on public available constant and variable amplitude fatigue tests. The methods used for estimating the SN-curve and accumulated fatigue damage are presented....

  6. Fatigue Testing of Maglev-Hybrid Box Beam

    Science.gov (United States)

    2009-03-02

    04142009 3. DATES COVERED: (From - To) 23052006-14092008 4. TITLE AND SUBTITLE Fatigue Testing of Maglev -Hybrid Box Beam 5a. CONTRACT NUMBER NA...was previously built under collaboration between Maglev Inc. and Lehigh University. The girder was instrumented with strain gages and LVDT’s to monitor...report March 2,2009 Contract N00014-06-1-0872 Project: Fatigue Testing of Maglev -Hybrid Box Beam Prepared by Dr. J.L. Grenestedt and Dr. R. Sause

  7. Myoelectrical manifestation of fatigue less prominent in patients with cancer related fatigue.

    Directory of Open Access Journals (Sweden)

    Katarzyna Kisiel-Sajewicz

    Full Text Available PURPOSE: A lack of fatigue-related muscle contractile property changes at time of perceived physical exhaustion and greater central than peripheral fatigue detected by twitch interpolation technique have recently been reported in cancer survivors with fatigue symptoms. Based on these observations, it was hypothesized that compared to healthy people, myoelectrical manifestation of fatigue in the performing muscles would be less significant in these individuals while sustaining a prolonged motor task to self-perceived exhaustion (SPE since their central fatigue was more prominent. The purpose of this study was to test this hypothesis by examining electromyographic (EMG signal changes during fatiguing muscle performance. METHODS: Twelve individuals who had advanced solid cancer and cancer-related fatigue (CRF, and 12 age- and gender-matched healthy controls performed a sustained elbow flexion at 30% maximal voluntary contraction till SPE. Amplitude and mean power frequency (MPF of EMG signals of the biceps brachii, brachioradialis, and triceps brachii muscles were evaluated when the individuals experienced minimal, moderate, and severe fatigue. RESULTS: CRF patients perceived physical "exhaustion" significantly sooner than the controls. The myoelectrical manifestation of muscular fatigue assessed by EMG amplitude and MPF was less significant in CRF than controls. The lower MPF even at minimal fatigue stage in CRF may indicate pathophysiologic condition of the muscle. CONCLUSIONS: CRF patients experience less myoelectrical manifestation of muscle fatigue than healthy individuals near the time of SPE. The data suggest that central nervous system fatigue plays a more important role in limiting endurance-type of motor performance in patients with CRF.

  8. Investigation of mental fatigue through EEG signal processing based on nonlinear analysis: Symbolic dynamics

    International Nuclear Information System (INIS)

    Azarnoosh, Mahdi; Motie Nasrabadi, Ali; Mohammadi, Mohammad Reza; Firoozabadi, Mohammad

    2011-01-01

    Highlights: Mental fatigue indices’ variation discussed during simple long-term attentive task. Symbolic dynamics of reaction time and EEG signal determine mental state variation. Nonlinear quantifiers such as entropy can display chaotic behaviors of the brain. Frontal and central lobes of the brain are effective in attention investigations. Mental fatigue causes a reduction in the complexity of the brain’s activity. Abstract: To investigate nonlinear analysis of attention physiological indices this study used a simple repetitive attentive task in four consecutive trials that resulted in mental fatigue. Traditional performance indices, such as reaction time, error responses, and EEG signals, were simultaneously recorded to evaluate differences between the trials. Performance indices analysis demonstrated that a selected task leads to mental fatigue. In addition, the study aimed to find a method to determine mental fatigue based on nonlinear analysis of EEG signals. Symbolic dynamics was selected as a qualitative method used to extract some quantitative qualifiers such as entropy. This method was executed on the reaction time of responses, and EEG signals to distinguish mental states. The results revealed that nonlinear analysis of reaction time, and EEG signals of the frontal and central lobes of the brain could differentiate between attention, and occurrence of mental fatigue in trials. In addition, the trend of entropy variation displayed a reduction in the complexity of mental activity as fatigue occurred.

  9. Usage of Parameterized Fatigue Spectra and Physics-Based Systems Engineering Models for Wind Turbine Component Sizing: Preprint

    Energy Technology Data Exchange (ETDEWEB)

    Parsons, Taylor; Guo, Yi; Veers, Paul; Dykes, Katherine; Damiani, Rick

    2016-01-26

    Software models that use design-level input variables and physics-based engineering analysis for estimating the mass and geometrical properties of components in large-scale machinery can be very useful for analyzing design trade-offs in complex systems. This study uses DriveSE, an OpenMDAO-based drivetrain model that uses stress and deflection criteria to size drivetrain components within a geared, upwind wind turbine. Because a full lifetime fatigue load spectrum can only be defined using computationally-expensive simulations in programs such as FAST, a parameterized fatigue loads spectrum that depends on wind conditions, rotor diameter, and turbine design life has been implemented. The parameterized fatigue spectrum is only used in this paper to demonstrate the proposed fatigue analysis approach. This paper details a three-part investigation of the parameterized approach and a comparison of the DriveSE model with and without fatigue analysis on the main shaft system. It compares loads from three turbines of varying size and determines if and when fatigue governs drivetrain sizing compared to extreme load-driven design. It also investigates the model's sensitivity to shaft material parameters. The intent of this paper is to demonstrate how fatigue considerations in addition to extreme loads can be brought into a system engineering optimization.

  10. Surface electromyography based muscle fatigue detection using high-resolution time-frequency methods and machine learning algorithms.

    Science.gov (United States)

    Karthick, P A; Ghosh, Diptasree Maitra; Ramakrishnan, S

    2018-02-01

    Surface electromyography (sEMG) based muscle fatigue research is widely preferred in sports science and occupational/rehabilitation studies due to its noninvasiveness. However, these signals are complex, multicomponent and highly nonstationary with large inter-subject variations, particularly during dynamic contractions. Hence, time-frequency based machine learning methodologies can improve the design of automated system for these signals. In this work, the analysis based on high-resolution time-frequency methods, namely, Stockwell transform (S-transform), B-distribution (BD) and extended modified B-distribution (EMBD) are proposed to differentiate the dynamic muscle nonfatigue and fatigue conditions. The nonfatigue and fatigue segments of sEMG signals recorded from the biceps brachii of 52 healthy volunteers are preprocessed and subjected to S-transform, BD and EMBD. Twelve features are extracted from each method and prominent features are selected using genetic algorithm (GA) and binary particle swarm optimization (BPSO). Five machine learning algorithms, namely, naïve Bayes, support vector machine (SVM) of polynomial and radial basis kernel, random forest and rotation forests are used for the classification. The results show that all the proposed time-frequency distributions (TFDs) are able to show the nonstationary variations of sEMG signals. Most of the features exhibit statistically significant difference in the muscle fatigue and nonfatigue conditions. The maximum number of features (66%) is reduced by GA and BPSO for EMBD and BD-TFD respectively. The combination of EMBD- polynomial kernel based SVM is found to be most accurate (91% accuracy) in classifying the conditions with the features selected using GA. The proposed methods are found to be capable of handling the nonstationary and multicomponent variations of sEMG signals recorded in dynamic fatiguing contractions. Particularly, the combination of EMBD- polynomial kernel based SVM could be used to

  11. Assessment of Eye Fatigue Caused by 3D Displays Based on Multimodal Measurements

    Science.gov (United States)

    Bang, Jae Won; Heo, Hwan; Choi, Jong-Suk; Park, Kang Ryoung

    2014-01-01

    With the development of 3D displays, user's eye fatigue has been an important issue when viewing these displays. There have been previous studies conducted on eye fatigue related to 3D display use, however, most of these have employed a limited number of modalities for measurements, such as electroencephalograms (EEGs), biomedical signals, and eye responses. In this paper, we propose a new assessment of eye fatigue related to 3D display use based on multimodal measurements. compared to previous works Our research is novel in the following four ways: first, to enhance the accuracy of assessment of eye fatigue, we measure EEG signals, eye blinking rate (BR), facial temperature (FT), and a subjective evaluation (SE) score before and after a user watches a 3D display; second, in order to accurately measure BR in a manner that is convenient for the user, we implement a remote gaze-tracking system using a high speed (mega-pixel) camera that measures eye blinks of both eyes; thirdly, changes in the FT are measured using a remote thermal camera, which can enhance the measurement of eye fatigue, and fourth, we perform various statistical analyses to evaluate the correlation between the EEG signal, eye BR, FT, and the SE score based on the T-test, correlation matrix, and effect size. Results show that the correlation of the SE with other data (FT, BR, and EEG) is the highest, while those of the FT, BR, and EEG with other data are second, third, and fourth highest, respectively. PMID:25192315

  12. Assessment of Eye Fatigue Caused by 3D Displays Based on Multimodal Measurements

    Directory of Open Access Journals (Sweden)

    Jae Won Bang

    2014-09-01

    Full Text Available With the development of 3D displays, user’s eye fatigue has been an important issue when viewing these displays. There have been previous studies conducted on eye fatigue related to 3D display use, however, most of these have employed a limited number of modalities for measurements, such as electroencephalograms (EEGs, biomedical signals, and eye responses. In this paper, we propose a new assessment of eye fatigue related to 3D display use based on multimodal measurements. compared to previous works Our research is novel in the following four ways: first, to enhance the accuracy of assessment of eye fatigue, we measure EEG signals, eye blinking rate (BR, facial temperature (FT, and a subjective evaluation (SE score before and after a user watches a 3D display; second, in order to accurately measure BR in a manner that is convenient for the user, we implement a remote gaze-tracking system using a high speed (mega-pixel camera that measures eye blinks of both eyes; thirdly, changes in the FT are measured using a remote thermal camera, which can enhance the measurement of eye fatigue, and fourth, we perform various statistical analyses to evaluate the correlation between the EEG signal, eye BR, FT, and the SE score based on the T-test, correlation matrix, and effect size. Results show that the correlation of the SE with other data (FT, BR, and EEG is the highest, while those of the FT, BR, and EEG with other data are second, third, and fourth highest, respectively.

  13. Probabilistic Fatigue Life Updating for Railway Bridges Based on Local Inspection and Repair.

    Science.gov (United States)

    Lee, Young-Joo; Kim, Robin E; Suh, Wonho; Park, Kiwon

    2017-04-24

    Railway bridges are exposed to repeated train loads, which may cause fatigue failure. As critical links in a transportation network, railway bridges are expected to survive for a target period of time, but sometimes they fail earlier than expected. To guarantee the target bridge life, bridge maintenance activities such as local inspection and repair should be undertaken properly. However, this is a challenging task because there are various sources of uncertainty associated with aging bridges, train loads, environmental conditions, and maintenance work. Therefore, to perform optimal risk-based maintenance of railway bridges, it is essential to estimate the probabilistic fatigue life of a railway bridge and update the life information based on the results of local inspections and repair. Recently, a system reliability approach was proposed to evaluate the fatigue failure risk of structural systems and update the prior risk information in various inspection scenarios. However, this approach can handle only a constant-amplitude load and has limitations in considering a cyclic load with varying amplitude levels, which is the major loading pattern generated by train traffic. In addition, it is not feasible to update the prior risk information after bridges are repaired. In this research, the system reliability approach is further developed so that it can handle a varying-amplitude load and update the system-level risk of fatigue failure for railway bridges after inspection and repair. The proposed method is applied to a numerical example of an in-service railway bridge, and the effects of inspection and repair on the probabilistic fatigue life are discussed.

  14. Computer based approach to fatigue analysis and design

    International Nuclear Information System (INIS)

    Comstock, T.R.; Bernard, T.; Nieb, J.

    1979-01-01

    An approach is presented which uses a mini-computer based system for data acquisition, analysis and graphic displays relative to fatigue life estimation and design. Procedures are developed for identifying an eliminating damaging events due to overall duty cycle, forced vibration and structural dynamic characteristics. Two case histories, weld failures in heavy vehicles and low cycle fan blade failures, are discussed to illustrate the overall approach. (orig.) 891 RW/orig. 892 RKD [de

  15. Development of a Physically-Based Methodology for Predicting Material Variability in Fatigue Crack Initiation and Growth Response

    National Research Council Canada - National Science Library

    Chan, Kwai

    2004-01-01

    ... of aerospace structural alloys. In this three-year program, physics-based fatigue crack initiation and growth models were developed and integrated into a probabilistic micromechanical code for treating fatigue life variability...

  16. Fatigue Reliability and Calibration of Fatigue Design Factors for Offshore Wind Turbines

    Directory of Open Access Journals (Sweden)

    Sergio Márquez-Domínguez

    2012-06-01

    Full Text Available Consequences of failure of offshore wind turbines (OWTs is in general lower than consequences of failure of, e.g., oil & gas platforms. It is reasonable that lower fatigue design factors can be applied for fatigue design of OWTs when compared to other fixed offshore structures. Calibration of appropriate partial safety factors/Fatigue Design Factors (FDF for steel substructures for OWTs is the scope of this paper. A reliability-based approach is used and a probabilistic model has been developed, where design and limit state equations are established for fatigue failure. The strength and load uncertainties are described by stochastic variables. SN and fracture mechanics approaches are considered for to model the fatigue life. Further, both linear and bi-linear SN-curves are formulated and various approximations are investigated. The acceptable reliability level for fatigue failure of OWTs is discussed and results are presented for calibrated optimal fatigue design factors. Further, the influence of inspections is considered in order to extend and maintain a given target safety level.

  17. Speed limiter integrated fatigue analyzer (SLIFA) for speed and fatigue control on diesel engine truck and bus

    Science.gov (United States)

    Wahyudi, Haris; Pranoto, Hadi; Leman, A. M.; Sebayang, Darwin; Baba, I.

    2017-09-01

    Every second, the number of road traffic deaths is increased globally with millions more sustaining severe injuries and living with long-term adverse health consequences. Jakarta alone in year 2015 had recorded 556 people died due to road accidents, approximately reached 6.231 road accident cases. The identified major contributory factors of such unfortunate events are both driver fatigue and over speeding habit especially related to the driving of truck and bus. This paper presents the idea on how to control the electronic system from input fuel system of injection pump and the combustion chamber engine will control the valve solenoid in injection pump which can lock and fuel will stop for moment, and speed limit can be success, by using sensor heart rate we can input reduce speed limit when fatigue detection driver. Integration process this tool can be relevant when Speed Limiter Integrated Fatigue Analyser (SLIFA) trial in the diesel engine for truck and bus, the result of this research Speed Limiter Integrated Fatigue Analyser (SLIFA) able to control speed of diesel engine for truck and bus almost 30km/h, 60km/h, and until 70 km/h. The installation of the sensor heart rate as the input speed limit SLIFA would work when the driver is detected to be in the fatigue condition. We make Speed Limiter Integrated Fatigue Analyser (SLIFA) for control and monitoring system for diesel engine in truck and bus. Speed Limiter Integrated Fatigue Analyser (SLIFA) system can save the historical of the speed record, fatigue, rpm, and body temperature of the driver.

  18. High-Temperature Creep-Fatigue Behavior of Alloy 617

    Directory of Open Access Journals (Sweden)

    Rando Tungga Dewa

    2018-02-01

    Full Text Available This paper presents the high-temperature creep-fatigue testing of a Ni-based superalloy of Alloy 617 base metal and weldments at 900 °C. Creep-fatigue tests were conducted with fully reversed axial strain control at a total strain range of 0.6%, 1.2%, and 1.5%, and peak tensile hold time of 60, 180, and 300 s. The effects of different constituents on the combined creep-fatigue endurance such as hold time, strain range, and stress relaxation behavior are discussed. Under all creep-fatigue tests, weldments’ creep-fatigue life was less than base metal. In comparison with the low-cycle fatigue condition, the introduction of hold time decreased the cycle number of both base metal and weldments. Creep-fatigue lifetime in the base metal was continually decreased by increasing the tension hold time, except for weldments under longer hold time (>180 s. In all creep-fatigue tests, intergranular brittle cracks near the crack tip and thick oxide scales at the surface were formed, which were linked to the mixed-mode creep and fatigue cracks. Creep-fatigue interaction in the damage-diagram (D-Diagram (i.e., linear damage summation was evaluated from the experimental results. The linear damage summation was found to be suitable for the current limited test conditions, and one can enclose all the data points within the proposed scatter band.

  19. High Sensitive Methods for Health Monitoring of Compressor Blades and Fatigue Detection

    Science.gov (United States)

    Witoś, Mirosław

    2013-01-01

    The diagnostic and research aspects of compressor blade fatigue detection have been elaborated in the paper. The real maintenance and overhaul problems and characteristic of different modes of metal blade fatigue (LCF, HCF, and VHCF) have been presented. The polycrystalline defects and impurities influencing the fatigue, along with their related surface finish techniques, are taken into account. The three experimental methods of structural health assessment are considered. The metal magnetic memory (MMM), experimental modal analysis (EMA) and tip timing (TTM) methods provide information on the damage of diagnosed objects, for example, compressor blades. Early damage symptoms, that is, magnetic and modal properties of material strengthening and weakening phases (change of local dislocation density and grain diameter, increase of structural and magnetic anisotropy), have been described. It has been proven that the shape of resonance characteristic gives abilities to determine if fatigue or a blade crack is concerned. The capabilities of the methods for steel and titanium alloy blades have been illustrated in examples from active and passive experiments. In the conclusion, the MMM, EMA, and TTM have been verified, and the potential for reliable diagnosis of the compressor blades using this method has been confirmed. PMID:24191135

  20. High Sensitive Methods for Health Monitoring of Compressor Blades and Fatigue Detection

    Directory of Open Access Journals (Sweden)

    Mirosław Witoś

    2013-01-01

    Full Text Available The diagnostic and research aspects of compressor blade fatigue detection have been elaborated in the paper. The real maintenance and overhaul problems and characteristic of different modes of metal blade fatigue (LCF, HCF, and VHCF have been presented. The polycrystalline defects and impurities influencing the fatigue, along with their related surface finish techniques, are taken into account. The three experimental methods of structural health assessment are considered. The metal magnetic memory (MMM, experimental modal analysis (EMA and tip timing (TTM methods provide information on the damage of diagnosed objects, for example, compressor blades. Early damage symptoms, that is, magnetic and modal properties of material strengthening and weakening phases (change of local dislocation density and grain diameter, increase of structural and magnetic anisotropy, have been described. It has been proven that the shape of resonance characteristic gives abilities to determine if fatigue or a blade crack is concerned. The capabilities of the methods for steel and titanium alloy blades have been illustrated in examples from active and passive experiments. In the conclusion, the MMM, EMA, and TTM have been verified, and the potential for reliable diagnosis of the compressor blades using this method has been confirmed.

  1. Monitoring crack growth using thermography

    International Nuclear Information System (INIS)

    Djedjiga, Ait Aouita; Abdeldjalil, Ouahabi

    2008-01-01

    The purpose of this work is to present a novel strategy for real-time monitoring crack growth of materials. The process is based on the use of thermal data extracted along the horizontal axis of symmetry of single edge notch tension (SENT) specimens, during fatigue tests. These data are exploited using an implemented program to detect in situ the growth of fatigue crack, with the critical size and propagation speed of the crack. This technique has the advantage to be applicable to a wide range of materials regardless of their electrical conductivity and their surface texture. (authors)

  2. Development and validation of a strain-based Structural Health Monitoring system

    Science.gov (United States)

    Katsikeros, Ch. E.; Labeas, G. N.

    2009-02-01

    An innovative Structural Health Monitoring (SHM) methodology, based on structural strain measurements, which are processed by a back-propagation feed-forward Artificial Neural Network (ANN), is proposed. The demonstration of the SHM methodology and the identification of its capabilities and drawbacks are performed by applying the method in the prediction of fatigue damage states of a typical aircraft cracked lap-joint structure. An ANN of suitable architecture is developed and trained by numerically generated strain data sets, which have been preprocessed by Fast Fourier Transformation (FFT) for the extraction of the Fourier Descriptors (FDs). The Finite Element (FE) substructuring technique is implemented in the stress and strain analysis of the lap-joint structure, due to its efficiency in the calculation of the numerous strain data, which are necessary for the ANN training. The trained network is successfully validated, as it is proven capable to accurately predict crack positions and lengths of a lap-joint structure, which is damaged by fatigue cracks of unknown location and extent. The proposed methodology is applicable to the identification of more complex types of damage or to other critical structural locations, as its basic concept is generic.

  3. A knowledge based system for creep-fatigue assessment

    International Nuclear Information System (INIS)

    Holdsworth, S.R.

    1999-01-01

    A knowledge based system was developed in the BRITE-EURAM C-FAT project to store the material property information necessary to perform complex creep-fatigue assessments and to thereby improve the effectiveness of data retrieval for such purposes. The C-FAT KBS incorporates a multi-level database which is structured to contain not only 'reduced' deformation and fracture test data, but also to enable ready access to the derived parameter constants for the constitutive and model equations used in a range of assessment procedures. The data management scheme is reviewed. The C-FAT KBS also has a dynamic worked example module which allows the sensitivity of predicted lifetimes to material property input data to be evaluated by a number of procedures. Complex cycle creep-fatigue endurance predictions are particularly sensitive to the creep property data used in assessment, and this is demonstrated with reference to the results of a number of large single edge notched bend specimen feature tests performed on a 1CrMoV turbine casting steel at 550 C. (orig.)

  4. Micromechanisms of fracture and fatigue in Ti3Al based and TiAl based intermetallics

    International Nuclear Information System (INIS)

    James, A.W.; Chave, R.A.; Hippsley, C.A.; Bowen, P.

    1993-01-01

    Micromechanisms of fracture and fatigue crack growth resistance in specific Ti 3 Al based and TiAl based intermetallics are reviewed. Effects of test temperature, environment and microstructure on crack growth resistance are considered in detail for several Ti 3 Al and Ti'Al based intermetallic systems under development. The implications of these studies for the structural reliability of these materials is also addressed briefly. (orig.)

  5. High temperature low cycle fatigue behavior of a directionally solidified Ni-base superalloy DZ951

    International Nuclear Information System (INIS)

    Chu Zhaokuang; Yu Jinjiang; Sun Xiaofeng; Guan Hengrong; Hu Zhuangqi

    2008-01-01

    Total strain-controlled low cycle fatigue (LCF) tests were performed at a temperature range from 700 to 900 deg. C in ambient air condition on a directionally solidified Ni-base superalloy DZ951. The fatigue life of DZ951 alloy does not monotonously decrease with increasing temperature, but exhibits a strong dependence on the total strain range. The dislocation characteristics and failed surface observation were evaluated through transmission electron microscopy and scanning electron microscopy. The alloy exhibits cyclic hardening, softening or cyclic stability as a whole, which is dependent on the testing temperature and total strain range. At 700 deg. C, the cyclic plastic deformation process is the main cause of fatigue failure. At 900 deg. C, the failure mostly results from combined fatigue and creep damage under total strain range from 0.6 to 1.2% and the reduction in fatigue life can be taken as the cause of oxidation, creep and cyclic plastic deformation under total strain range of 0.5%

  6. Evaluation of fatigue cracks using nonlinearities of acousto-ultrasonic waves acquired by an active sensor network

    International Nuclear Information System (INIS)

    Zhou, Chao; Hong, Ming; Su, Zhongqing; Wang, Qiang; Cheng, Li

    2013-01-01

    There has been increasing interest in using the nonlinear features of acousto-ultrasonic (AU) waves to detect damage onset (e.g., micro-fatigue cracks) due to their high sensitivity to damage with small dimensions. However, most existing approaches are able to infer the existence of fatigue damage qualitatively, but fail to further ascertain its location and severity. A damage characterization approach, in conjunction with the use of an active piezoelectric sensor network, was established, capable of evaluating fatigue cracks in a quantitative manner (including the co-presence of multiple fatigue cracks, and their individual locations and severities). Fundamental investigations, using both experiment and enhanced finite element analysis dedicated to the simulation of nonlinear AU waves, were carried out to link the accumulation of nonlinearities extracted from high-order AU waves to the characteristic parameters of a fatigue crack. A probability-based diagnostic imaging algorithm was developed, facilitating an intuitive presentation of identification results in images. The approach was verified experimentally by evaluating multi-fatigue cracks near rivet holes of a fatigued aluminum plate, showing satisfactory precision in characterizing real, barely visible fatigue cracks. Compared with existing methods, this approach innovatively (i) uses permanently integrated active sensor networks, conducive to automatic and online health monitoring; (ii) characterizes fatigue cracks at a quantitative level; (iii) allows detection of multiple fatigue cracks; and (iv) visualizes identification results in intuitive images. (paper)

  7. Investigation of bending fatigue-life of aluminum sheets based on rolling direction

    Directory of Open Access Journals (Sweden)

    Raif Sakin

    2018-03-01

    Full Text Available High-cycle fatigue (HCF and low-cycle fatigue (LCF fatigue lives of rolled AA1100 and AA1050 aluminum sheets along different directions were evaluated at room temperature. Four types of samples denoted as longitudinal (L and transverse (T to the rolling direction were compared because the samples along the two typical directions show an obvious anisotropy. A cantilever plane-bending and multi-type fatigue testing machine was specially designed for this purpose. Deflection-controlled fatigue tests were conducted under fully reversed loading. The longest fatigue lives in the LCF region were obtained for AA1050 (L while AA1100 (L samples had the longest fatigue lives in the HCF region. Keywords: AA1100, AA1050, Aluminum sheet, Bending fatigue life, Rolling direction

  8. Fatigue crack shape prediction based on vertex singularity

    Czech Academy of Sciences Publication Activity Database

    Hutař, Pavel; Náhlík, Luboš

    2008-01-01

    Roč. 2, č. 1 (2008), s. 45-52 ISSN 1802-680X R&D Projects: GA ČR GA101/08/1623; GA ČR GP106/06/P239 Institutional research plan: CEZ:AV0Z20410507 Keywords : 3D vertex singularity * crack shape * fatigue crack propagation Subject RIV: JL - Materials Fatigue, Friction Mechanics

  9. Cognitive and Physical Fatigue Tasks Enhance Pain, Cognitive Fatigue and Physical Fatigue in People with Fibromyalgia

    Science.gov (United States)

    Dailey, Dana L; Keffala, Valerie J; Sluka, Kathleen A

    2014-01-01

    Objective Fibromyalgia is a condition characterized by chronic widespread muscle pain and fatigue. The primary objective of this study was to determine if pain, perceived cognitive fatigue, and perceived physical fatigue were enhanced in participants with fibromyalgia compared to healthy controls during a cognitive fatigue task, a physical fatigue task and a dual fatigue task. Methods Twenty four people with fibromyalgia and 33 healthy controls completed pain, fatigue and function measures. A cognitive fatigue task (Controlled Oral Word Association Test) and physical fatigue task (Valpar peg test) were done individually and combined for a dual fatigue task. Resting pain, perceived cognitive fatigue and perceived physical fatigue were assessed during each task using visual analogue scales. Function was assessed with shoulder range of motion and grip. Results People with fibromyalgia had significantly higher increases in pain, cognitive fatigue and physical fatigue when compared to healthy controls after completion of a cognitive fatigue task, a physical fatigue task, or a dual fatigue task (pfatigue tasks, respectively. Conclusions These data show that people with fibromyalgia show larger increases in pain, perceived cognitive fatigue and perceived physical fatigue to both cognitive and physical fatigue tasks compared to healthy controls. The increases in pain and fatigue during cognitive and physical fatigue tasks could influence subject participation in daily activities and rehabilitation. PMID:25074583

  10. A Wireless sEMG Recording System and Its Application to Muscle Fatigue Detection

    Directory of Open Access Journals (Sweden)

    Xuan-Han Wu

    2012-01-01

    Full Text Available Surface electromyography (sEMG is an important measurement for monitoring exercise and fitness. Because if its high sampling frequency requirement, wireless transmission of sEMG data is a challenge. In this article a wireless sEMG measurement system with a sampling frequency of 2 KHz is developed based upon a MSP 430 microcontroller and Bluetooth transmission. Standard isotonic and isometric muscle contraction are clearly represented in the receiving user interface. Muscle fatigue detection is an important application of sEMG. Traditional muscle fatigue is detected from the median frequency of the sEMG power spectrum. The regression slope of the linear regression of median frequency is an important muscle fatigue index. A more negative slope value represents a higher muscle fatigue condition. To test the system performance, muscle fatigue detection was examined by having subjects run on a pedaled-multifunctional elliptical trainer for approximately 30 minutes at three loading levels. Ten subjects underwent a total of 60 exercise sessions to provide the experimental data. Results showed that the regression slope gradually decreases as expected, and there is a significant gender difference.

  11. Monitoring microstructural evolution of alloy 617 with non-linear acoustics for remaining useful life prediction; multiaxial creep-fatigue and creep-ratcheting

    Energy Technology Data Exchange (ETDEWEB)

    Lissenden, Cliff [Pennsylvania State Univ., State College, PA (United States); Hassan, Tasnin [North Carolina State Univ., Raleigh, NC (United States); Rangari, Vijaya [Tuskegee Univ., Tuskegee, AL (United States)

    2014-10-30

    The research built upon a prior investigation to develop a unified constitutive model for design-­by-­analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-­fatigue and creep-­ratcheting tests were conducted on the nickel-­base Alloy 617 at 850 and 950°C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-­controlled cycling, are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-­fatigue and creep-­ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-­fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-­ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched

  12. High-cycle fatigue properties of small-bore socket-welded pipe joint

    International Nuclear Information System (INIS)

    Maekawa, Akira; Noda, Michiyasu; Suzuki, Michiaki

    2009-01-01

    Piping and equipment in nuclear power plants are structures including many welded joints. Reliability of welded joints is one of high-priority issues to improve the safety of nuclear power plants. However, occurrence of fatigue failures in small-bore socket-welded pipe joints by high-cycle vibrations is still reported. In this study, fatigue experiments on a socket-welded joint of austenitic stainless steel pipe was conducted under excitation conditions similar to those in actual plants to investigate vibration characteristics and fatigue strength. It was found that the natural frequency of pipe with socket-welded joint gradually decreased as fatigue damage developed, according to the Miner rule for fatigue life evaluation. The results indicate that the fatigue life of the welded pipe joint could be estimated by monitoring the decreasing ratio of the natural frequency of the pipe. The evaluation of decreasing ratio of the natural frequency in addition to fatigue damage evaluation by the Miner rule could enhance the accuracy of fatigue life evaluation. (author)

  13. Diagnostic and monitoring systems in nuclear power plants

    International Nuclear Information System (INIS)

    Wehling, H.J.; Jax, P.; Streicher, V.

    1987-01-01

    Monitoring systems are important for the availability of nuclear power plants. A survey is given about such systems designed and constructed by the Kraftwerk Union AG Erlangen (Federal Republic of Germany) in order to assure the mechanical integrity of reactor cooling systems. Three monitoring systems based on microprocessors are presented: KUES (acoustic detection of loose parts), SUES (vibration), and FAMOS (fatigue)

  14. On-Road Driver Monitoring System Based on a Solar-Powered In-Vehicle Embedded Platform

    OpenAIRE

    Yen-Lin Chen; Chao-Wei Yu; Zi-Jie Chien; Chin-Hsuan Liu; Hsin-Han Chiang

    2014-01-01

    This study presents an on-road driver monitoring system, which is implemented on a stand-alone in-vehicle embedded system and driven by effective solar cells. The driver monitoring function is performed by an efficient eye detection technique. Through the driver’s eye movements captured from the camera, the attention states of the driver can be determined and any fatigue states can be avoided. This driver monitoring technique is implemented on a low-power embedded in-vehicle platform. Besides...

  15. The Effects of Group Monitoring on Fatigue-Related Einstellung during Mathematical Problem Solving

    Science.gov (United States)

    Frings, Daniel

    2011-01-01

    Fatigue resulting from sleep deficit can lead to decreased performance in a variety of cognitive domains and can result in potentially serious accidents. The present study aimed to test whether fatigue leads to increased Einstellung (low levels of cognitive flexibility) in a series of mathematical problem-solving tasks. Many situations involving…

  16. A Wireless Sensor Network with Enhanced Power Efficiency and Embedded Strain Cycle Identification for Fatigue Monitoring of Railway Bridges

    Directory of Open Access Journals (Sweden)

    Glauco Feltrin

    2016-01-01

    Full Text Available Wireless sensor networks have been shown to be a cost-effective monitoring tool for many applications on civil structures. Strain cycle monitoring for fatigue life assessment of railway bridges, however, is still a challenge since it is data intensive and requires a reliable operation for several weeks or months. In addition, sensing with electrical resistance strain gauges is expensive in terms of energy consumption. The induced reduction of battery lifetime of sensor nodes increases the maintenance costs and reduces the competitiveness of wireless sensor networks. To overcome this drawback, a signal conditioning hardware was designed that is able to significantly reduce the energy consumption. Furthermore, the communication overhead is reduced to a sustainable level by using an embedded data processing algorithm that extracts the strain cycles from the raw data. Finally, a simple software triggering mechanism that identifies events enabled the discrimination of useful measurements from idle data, thus increasing the efficiency of data processing. The wireless monitoring system was tested on a railway bridge for two weeks. The monitoring system demonstrated a good reliability and provided high quality data.

  17. The effect of notches and pits on corrosion fatigue strength

    Science.gov (United States)

    Tatner, Ian

    An investigation has been undertaken to examine the fatigue behaviour of two martensitic steels in air and aggressive environments. The steels studied are, 18% Ni marageing steel and FV520B, the later being a stainless steel turbine blade material and the former being a marageing steel that suffers general corrosion in mild environments. Both steels were heat treated to give similar tensile strength.The design and manufacture of an autoclave allowed push-pull fatigue tests to be conducted in aggressive environments at elevated temperatures.Corrosion potential was monitored using a three electrode cell and was controlled during testing. Base-line fatigue tests were conducted with a range of constant corrosion potentials, using both notched and plain FV520B specimens. In addition fatigue tests with pulsed corrosion potential were performed to asses the effect of transient corrosion conditions on the corrosion fatigue strength. The pulsed tests were designed to simulate service transients in the oxygen content and general chemical hostility in the condensing steam environment during start-up and shut down of the steam turbine.Post test examination of fractured samples was performed using Scanning Electron Microscopy (SEM) and optical microscope techniques. The fractography results were used to quantify microstructural and fracture features of the steels.A model based on the size and geometry of the initial corrosion pitting has been proposed to asses the fatigue life of FV520B in an aggressive environment.The effect of pitting on the corrosion fatigue strength of FV520B has been modelled using linear elastic fracture mechanics (LEFM) type approach. The model has shown a good correlation between predicted fatigue lives with experimental results.The results suggest that the fatigue life is governed by the mechanical stress concentrating effect of the pits rather than the electrochemical damage caused by the environment.Finite Element Analysis (FEA) of the notch allowed

  18. Acoustic Emission Detection and Prediction of Fatigue Crack Propagation in Composite Patch Repairs Using Neural Networks

    International Nuclear Information System (INIS)

    Okafor, A. Chukwujekwu; Singh, Navdeep; Singh, Navrag

    2007-01-01

    An aircraft is subjected to severe structural and aerodynamic loads during its service life. These loads can cause damage or weakening of the structure especially for aging military and civilian aircraft, thereby affecting its load carrying capabilities. Hence composite patch repairs are increasingly used to repair damaged aircraft metallic structures to restore its structural efficiency. This paper presents the results of Acoustic Emission (AE) monitoring of crack propagation in 2024-T3 Clad aluminum panels repaired with adhesively bonded octagonal, single sided boron/epoxy composite patch under tension-tension fatigue loading. Crack propagation gages were used to monitor crack initiation. The identified AE sensor features were used to train neural networks for predicting crack length. The results show that AE events are correlated with crack propagation. AE system was able to detect crack propagation even at high noise condition of 10 Hz loading; that crack propagation signals can be differentiated from matrix cracking signals that take place due to fiber breakage in the composite patch. Three back-propagation cascade feed forward networks were trained to predict crack length based on the number of fatigue cycles, AE event number, and both the Fatigue Cycles and AE events, as inputs respectively. Network using both fatigue cycles and AE event number as inputs to predict crack length gave the best results, followed by Network with fatigue cycles as input, while network with just AE events as input had a greater error

  19. Corrosion strength monitoring of NPP component residual lifetime

    International Nuclear Information System (INIS)

    Denisov, V.G.; Belous, V.N.; Arzhaev, A.I.; Shuvalov, V.A.

    1994-01-01

    Importance of corrosion and fatigue monitoring; types of corrosion determine the NPP equipment life; why automated on-line corrosion and fatigue monitoring is preferable; major stages of lifetime monitoring system development; major groups of sensors for corrosion and strength monitoring system; high temperature on-line monitoring of water chemistry and corrosion; the RBMK-1000 NPP unit automatic water chemistry and corrosion monitoring scheme; examples of pitting, crevice and general corrosion forecast calculations on the basis of corrosion monitoring data; scheme of an experimental facility for water chemistry and corrosion monitoring sensor testing. 2 figs., 4 tabs

  20. Fatigue Reliability of Offshore Wind Turbine Systems

    DEFF Research Database (Denmark)

    Marquez-Dominguez, Sergio; Sørensen, John Dalsgaard

    2012-01-01

    of appropriate partial safety factors / fatigue design factors (FDF) for steel substructures of offshore wind turbines (OWTs). The fatigue life is modeled by the SN approach. Design and limit state equations are established based on the accumulated fatigue damage. The acceptable reliability level for optimal...... fatigue design of OWTs is discussed and results for reliability assessment of typical fatigue critical design of offshore steel support structures are presented....

  1. Fatigue crack detection and identification by the elastic wave propagation method

    Science.gov (United States)

    Stawiarski, Adam; Barski, Marek; Pająk, Piotr

    2017-05-01

    In this paper the elastic wave propagation phenomenon was used to detect the initiation of the fatigue damage in isotropic plate with a circular hole. The safety and reliability of structures mostly depend on the effectiveness of the monitoring methods. The Structural Health Monitoring (SHM) system based on the active pitch-catch measurement technique was proposed. The piezoelectric (PZT) elements was used as an actuators and sensors in the multipoint measuring system. The comparison of the intact and defected structures has been used by damage detection algorithm. One part of the SHM system has been responsible for detection of the fatigue crack initiation. The second part observed the evolution of the damage growth and assess the size of the defect. The numerical results of the wave propagation phenomenon has been used to present the effectiveness and accuracy of the proposed method. The preliminary experimental analysis has been carried out during the tension test of the aluminum plate with a circular hole to determine the efficiency of the measurement technique.

  2. Fatigue Performance Assessment of Composite Arch Bridge Suspenders Based on Actual Vehicle Loads

    Directory of Open Access Journals (Sweden)

    Bin Chen

    2015-01-01

    Full Text Available In the through arch bridges, the suspenders are the key components connecting the arch rib and the bridge deck in the middle, and their safety is an increasing focus in the field of bridge engineering. In this study, various vehicle traffic flow parameters are investigated based on the actual vehicle data acquired from the long-term structural health monitoring system of a composite arch bridge. The representative vehicle types and the probability density functions of several parameters are determined, including the gross vehicle weight, axle weight, time headway, and speed. A finite element model of the bridge structure is constructed to determine the influence line of the cable force for various suspenders. A simulated vehicle flow, generated using the Monte Carlo method, is applied on the influence lines of the target suspender to determine the stress process, and then the stress amplitude spectrum is obtained based on the statistical analysis of the stress process using the rainflow counting method. The fatigue performance levels of various suspenders are analyzed according to the Palmgren-Miner linear cumulative damage theory, which helps to manage the safety of the suspenders.

  3. Crack initiation life in notched Ti-6Al-4V titanium bars under uniaxial and multiaxial fatigue: synthesis based on the averaged strain energy density approach

    Directory of Open Access Journals (Sweden)

    Giovanni Meneghetti

    2017-07-01

    Full Text Available The fatigue behaviour of circumferentially notched specimens made of titanium alloy, Ti-6Al-4V, has been analysed. To investigate the notch effect on the fatigue strength, pure bending, pure torsion and multiaxial bending-torsion fatigue tests have been carried out on specimens characterized by two different root radii, namely 0.1 and 4 mm. Crack nucleation and subsequent propagation have been accurately monitored by using the direct current potential drop (DCPD technique. Based on the results obtained from the potential drop technique, the crack initiation life has been defined in correspondence of a relative potential drop increase V/V0 equal to 1%, and it has been used as failure criterion. Doing so, the effect of extrinsic mechanisms operating during crack propagation phase, such as sliding contact, friction and meshing between fracture surfaces, is expected to be reduced. The experimental fatigue test results have been re-analysed by using the local strain energy density (SED averaged over a structural volume having radius R0 and surrounding the notch tip. Finally, the use of the local strain energy density parameter allowed us to properly correlate the crack initiation life of Ti-6Al-4V notched specimens, despite the different notch geometries and loading conditions involved in the tests

  4. Fatigue crack growth from handling surface anomalies in a nickel based superalloy at high temperature

    Directory of Open Access Journals (Sweden)

    Gourdin Stéphane

    2014-01-01

    Full Text Available Aircraft engine manufacturers have to demonstrate that handling surface anomalies in sensitive areas of discs are not critical for in-service life of a component. Currently, the models used consider anomalies as long cracks propagating from the first cycle, which introduces a certain degree of conservatism when calculating the fatigue life of surface flaws. Preliminary studies have shown that the first stages of crack propagation from surface anomalies are responsible for the conservative results. Thus, the aim of the study is to characterize the crack propagation from typical surface anomalies and to establish a new crack growth model, which can account for the micro-propagation stage. To separate the effects of the geometry of the anomalies and the residual stress state after introduction of the surface flaws, two V-type anomalies are studied: scratches and dents. Different studies have shown that the residual stresses beneath the anomalies seem to control the fatigue life of samples exhibiting scratches and dents. In order to monitor the crack micro-propagation, a direct current potential drop technique, coupled with heat tints is used during fatigue tests at elevated temperature. Thermal treatments releasing the residual stresses are also used to decouple the effect of crack morphology and residual stresses.

  5. Fatigue damage evolution in quasi-unidirectional non-crimp fabric based composite materials for wind turbine blades

    DEFF Research Database (Denmark)

    Mikkelsen, Lars Pilgaard

    scales, the 3D x-ray computer tomography technique is used non-destructive to observe the fatigue damage evolution on the fiber and bundle scale. Those observations are then linked to the larger scales through mechanical testing of representative volumes of the non-crimp fabric bundle structure....... Numerically, those non-crimp fabric bundle structures extracted from the 3D x-ray scans can be used in a multi-scale based finite element models used for understanding the parameters controlling the fatigue damage evolutions. During tensiontension fatigue testing, the damage mechanism is shown...

  6. The Prediction of Fatigue Life Based on Four Point Bending Test

    NARCIS (Netherlands)

    Pramesti, F.P.; Molenaar, A.A.A.; Van de Ven, M.F.C.

    2013-01-01

    To be able to devise optimum strategies for maintenance and rehabilitation, it is essential to formulate an accurate prediction of pavement life and its maintenance needs. One of the pavement life prediction methods is based on the pavement's capability to sustain fatigue. If it were possible to

  7. Influence of dwell times on the thermomechanical fatigue behavior of a directionally solidified Ni-base superalloy

    Czech Academy of Sciences Publication Activity Database

    Guth, S.; Petráš, Roman; Škorík, Viktor; Kruml, Tomáš; Man, Jiří; Lang, K. H.; Polák, Jaroslav

    2015-01-01

    Roč. 80, NOV (2015), s. 426-433 ISSN 0142-1123 R&D Projects: GA MŠk(CZ) EE2.3.30.0063 Institutional support: RVO:68081723 Keywords : Nickel base superalloy * Thermomechanical fatigue * Dwell time * Lifetime behavior * Damage mechanisms Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 2.162, year: 2015

  8. Identification of a Critical Time with Acoustic Emission Monitoring during Static Fatigue Tests on Ceramic Matrix Composites: Towards Lifetime Prediction

    Directory of Open Access Journals (Sweden)

    Nathalie Godin

    2016-02-01

    Full Text Available Non-oxide fiber-reinforced ceramic-matrix composites are promising candidates for some aeronautic applications that require good thermomechanical behavior over long periods of time. This study focuses on the behavior of a SiCf/[Si-B-C] composite with a self-healing matrix at intermediate temperature under air. Static fatigue experiments were performed below 600 °C and a lifetime diagram is presented. Damage is monitored both by strain measurement and acoustic emission during the static fatigue experiments. Two methods of real-time analysis of associated energy release have been developed. They allow for the identification of a characteristic time that was found to be close to 55% of the measured rupture time. This critical time reflects a critical local energy release assessed by the applicability of the Benioff law. This critical aspect is linked to a damage phase where slow crack growth in fibers is prevailing leading to ultimate fracture of the composite.

  9. Fatigue studies of superalloys in Japan

    International Nuclear Information System (INIS)

    Kitagawa, Masaki

    1985-01-01

    In the past 15 years, several national projects were advanced to develop high temperature machinery, such as high temperature gas-cooled reactors, gas turbines and fusion reactors. Before, the studies on the strength of superalloys were rarely carried out, however, by the above research works, superalloys are in rapid progress. Because these machinery are subjected to temperature cycles and vibration stress, the fatigue failure is the main concern in the safety analysis of the components. The purpose of this paper is to summarize the present status of the fatigue research on the alloys for high temperature use in Japan. The superalloys used for gas turbine and HTGR components are listed, and the materials tested were mostly the alloys of nickel base, cobalt base or iron base. In the above national projects, the main purpose was to clarify the high temperature properties including fatigue properties, to develop the method of forecasting the life span and to develop better materials. As the topics about the fatigue research on superalloys, the development of the method for forecasting the life span, the effect of directional solidification, coating and HIP process on the fatigue strength of gas turbine materials, the effect of helium and aging on the fatigue strength of HTGR materials, the fatigue strength of weldment of HTGR materials and others are reported. (Kako, I.)

  10. Evaluation of long-term creep-fatigue life of stainless steel weldment based on a microstructure degradation model

    International Nuclear Information System (INIS)

    Asayama, Tai; Hasebe, Shinichi

    1997-01-01

    This paper describes a newly developed analytical method of evaluation of creep-fatigue strength of stainless weld metals. Based on the observation that creep-fatigue crack initiates adjacent to the interface of sigma-phase/delta-ferrite and matrix, a mechanistic model which allows the evaluation of micro stress/strain concentration adjacent to the interface was developed. Fatigue and creep damage were evaluated using the model which describes the microstructure after exposed to high temperatures for a long time. Thus it was made possible to predict analytically the long-term creep-fatigue life of stainless steel metals whose microstructure is degraded as a result of high temperature service. (author)

  11. Very high cycle fatigue testing of concrete using ultrasonic cycling

    Energy Technology Data Exchange (ETDEWEB)

    Karr, Ulrike; Schuller, Reinhard; Fitzka, Michael; Mayer, Herwig [Univ. of Natural Resources and Life Sciences, Vienna (Austria). Inst. of Physics and Materials Science; Denk, Andreas; Strauss, Alfred [Univ. of Natural Resources and Life Sciences, Vienna (Austria)

    2017-06-01

    The ultrasonic fatigue testing method has been further developed to perform cyclic compression tests with concrete. Cylindrical specimens vibrate in resonance at a frequency of approximately 20 kHz with superimposed compressive static loads. The high testing frequency allows time-saving investigations in the very high cycle fatigue regime. Fatigue tests were carried out on ''Concrete 1'' (compressive strength f{sub c} = 80 MPa) and ''Concrete 2'' (f{sub c} = 107 MPa) under purely compressive loading conditions. Experiments at maximum compressive stresses of 0.44 f{sub c} (Concrete 1) and 0.38 f{sub c} (Concrete 2) delivered specimen failures above 109 cycles, indicating that no fatigue limit exists for concrete below one billion load cycles. Resonance frequency, power required to resonate the specimen and second order harmonics of the vibration are used to monitor fatigue damage in situ. Specimens were scanned by X-ray computed tomography prior to and after testing. Fatigue cracks were produced by ultrasonic cycling in the very high cycle fatigue regime at interfaces of grains as well as in cement. The possibilities as well as limitations of ultrasonic fatigue testing of concrete are discussed.

  12. Strength and fatigue life evaluation of composite laminate with embedded sensors

    Science.gov (United States)

    Rathod, Vivek T.; Hiremath, S. R.; Roy Mahapatra, D.

    2014-04-01

    Prognosis regarding durability of composite structures using various Structural Health Monitoring (SHM) techniques is an important and challenging topic of research. Ultrasonic SHM systems with embedded transducers have potential application here due to their instant monitoring capability, compact packaging potential toward unobtrusiveness and noninvasiveness as compared to non-contact ultrasonic and eddy current techniques which require disassembly of the structure. However, embedded sensors pose a risk to the structure by acting as a flaw thereby reducing life. The present paper focuses on the determination of strength and fatigue life of the composite laminate with embedded film sensors like CNT nanocomposite, PVDF thin films and piezoceramic films. First, the techniques of embedding these sensors in composite laminates is described followed by the determination of static strength and fatigue life at coupon level testing in Universal Testing Machine (UTM). Failure mechanisms of the composite laminate with embedded sensors are studied for static and dynamic loading cases. The coupons are monitored for loading and failure using the embedded sensors. A comparison of the performance of these three types of embedded sensors is made to study their suitability in various applications. These three types of embedded sensors cover a wide variety of applications, and prove to be viable in embedded sensor based SHM of composite structures.

  13. Assessment of muscle fatigue during biking.

    Science.gov (United States)

    Knaflitz, Marco; Molinari, Filippo

    2003-03-01

    The analysis of the surface myoelectric signal recorded while a muscle is performing a sustained contraction is a valuable tool for assessing the progression of localized fatigue. It is well known that the modifications of the spectral content of the myoelectric signal are mainly related to changes in the interstitial fluid pH, which, in turn, affect the membrane excitability of the active muscle fibers. This paper describes the effects of muscle fatigue on the surface myoelectric signal recorded from three thigh and leg muscles during biking, on a population consisting of 22 young healthy volunteers. The purpose of this study was to obtain normative data relative to an exercise protocol mild enough to be applicable, in the future, to pathological subjects as well. Each subject was asked to exercise 30 min on a cycloergometer at a constant velocity and against a constant torque. While subjects were biking, the surface myoelectric signal was recorded from the rectus femoris, the biceps femoris, and the gastrocnemius muscles. In this study, we considered two different aspects of muscle fatigue: first, the localized muscle fatigue as shown by the decrement of the instantaneous frequency of the myoelectric signal during the exercise; second, the modifications of the muscle ON-OFF timing, which could be explained as a strategy for increasing endurance by modifying the role of different muscles during the exercise. The first aspect was studied by obtaining the spectral characteristics of the signals by means of bilinear time-frequency transforms and by applying an original estimator of the instantaneous frequency of stochastic processes based on cross time-frequency transforms. Our results demonstrated that none of the subjects showed significant signs of localized muscle fatigue, since the decrement of the instantaneous frequency during the exercise was always lower than 5% of its initial value. Muscle ON-OFF timing was obtained by applying to the raw myoelectric signal

  14. Implementation of fatigue model for unidirectional laminate based on finite element analysis: theory and practice

    Directory of Open Access Journals (Sweden)

    D. Carrella-Payan

    2016-10-01

    Full Text Available The aim of this study is to deal with the simulation of intralaminar fatigue damage in unidirectional composite under multi-axial and variable amplitude loadings. The variable amplitude and multi-axial loading is accounted for by using the damage hysteresis operator based on Brokate method [6]. The proposed damage model for fatigue is based on stiffness degradation laws from Van Paepegem combined with the ‘damage’ cycle jump approach extended to deal with unidirectional carbon fibres. The parameter identification method is here presented and parameter sensitivities are discussed. The initial static damage of the material is accounted for by using the Ladevèze damage model and the permanent shear strain accumulation based on Van Paepegem’s formulation. This approach is implemented into commercial software (Siemens PLM. The validation case is run on a bending test coupon (with arbitrary stacking sequence and load level in order to minimise the risk of inter-laminar damages. This intra-laminar fatigue damage model combined efficient methods with a low number of tests to identify the parameters of the stiffness degradation law, this overall procedure for fatigue life prediction is demonstrated to be cost efficient at industrial level. This work concludes on the next challenges to be addressed (validation tests, multiple-loadings validation, failure criteria, inter-laminar damages….

  15. Assessment of the crack growth characteristics at the low fatigue limit of a multi-pass welded Ni-based alloy 617

    Energy Technology Data Exchange (ETDEWEB)

    Park, Young Soo; Bae, Dong Ho [Sungkyunkwan University, Suwon (Korea, Republic of)

    2014-04-15

    It has become known that the most effective methodology for green power plant systems is to increase the generating efficiency of steam power plants. Among the materials developed to improve the performance, it is known that the most practical and applicable materials are Ni-based Alloys. However, it is necessary to first guarantee mechanical reliability of the weld for applying these Ni-based Alloys. In this study, firstly, the fatigue strength of multi-pass welded Ni-based Alloy 617 in as-welded and post weld heat-treated conditions were assessed. And then the crack growth characteristics at the low fatigue limit of them were assessed. From the results, fatigue strength of the welds those were post weld heat treated did not show large difference compare to not heat-treated ones. These results mean that the weld of Ni-based Alloy 617 is not influenced remarkably by post weld heat treatment in the metallurgical and mechanical changes. However, it was found that the fatigue crack grew at the low fatigue limit, which was about 48.4% (327 MPa) of the static tensile strength(675.1 MPa) of the weld, and 43.1% of the base material (759.4 MPa).

  16. Fatigue strength reduction factors for welds based on nondestructive examination

    International Nuclear Information System (INIS)

    Hechmer, J.L.; Kuhn, E.J. III

    1999-01-01

    Based on the author's hypothesis that nondestructive examination (NDE) has a major role in predicting the fatigue life of pressure vessels, a project was initiated to develop a defined relationship between NDE and fatigue strength reduction factors (FSRF). Even though a relationship should apply to both base metal and weld metal, the project was limited to weld metal because NDE for base metal is reasonably well established, whereas NDE for weld metal is more variable, depending on application. A matrix of FSRF was developed based on weld type (full penetration, partial penetration, and fillet weld) versus the NDE that is applied. The NDE methods that are included are radiographic testing (RT), ultrasonic testing (UT), magnetic particle testing (MT), dye penetrant testing (PT), and visual testing (VT). The first two methods (RT and UT) are volumetric examinations, and the remaining three are surface examinations. Seven combinations of volumetric and surface examinations were defined; thus, seven levels of FSRF are defined. Following the initial development of the project, a PVRC (Pressure Vessel Research Council) grant was obtained for the purpose of having a broad review. The report (Hechmer, 1998) has been accepted by PVRC. This paper presents the final matrix, the basis for the FSRF, and key definitions for accurate application of the FSRF matrix. A substantial amount of additional information is presented in the PVRC report (Hechmer, 1998)

  17. A New Approach to Fatigue Life Prediction Based on Nucleation and Growth (Preprint)

    National Research Council Canada - National Science Library

    McClung, R. C; Francis, W. L; Hudak, S. J

    2006-01-01

    Prediction of total fatigue life in components is often performed by summing "initiation" and "propagation" life phases, where initiation life is based on stress-life or strain-life methods calibrated...

  18. Gear wear monitoring by modulation signal bispectrum based on motor current signal analysis

    Science.gov (United States)

    Zhang, Ruiliang; Gu, Fengshou; Mansaf, Haram; Wang, Tie; Ball, Andrew D.

    2017-09-01

    Gears are important mechanical components for power transmissions. Tooth wear is one of the most common failure modes, which can present throughout a gear's lifetime. It is significant to accurately monitor gear wear progression in order to take timely predictive maintenances. Motor current signature analysis (MCSA) is an effective and non-intrusive approach which is able to monitor faults from both electrical and mechanical systems. However, little research has been reported in monitoring the gear wear and estimating its severity based on MCSA. This paper presents a novel gear wear monitoring method through a modulation signal bispectrum based motor current signal analysis (MSB-MCSA). For a steady gear transmission, it is inevitable to exist load and speed oscillations due to various errors including wears. These oscillations can induce small modulations in the current signals of the driving motor. MSB is particularly effective in characterising such small modulation signals. Based on these understandings, the monitoring process was implemented based on the current signals from a run-to-failure test of an industrial two stages helical gearbox under a moderate accelerated fatigue process. At the initial operation of the test, MSB analysis results showed that the peak values at the bifrequencies of gear rotations and the power supply can be effective monitoring features for identifying faulty gears and wear severity as they exhibit agreeable changes with gear loads. A monotonically increasing trend established by these features allows a clear indication of the gear wear progression. The dismantle inspection at 477 h of operation, made when one of the monitored features is about 123% higher than its baseline, has found that there are severe scuffing wear marks on a number of tooth surfaces on the driving gear, showing that the gear endures a gradual wear process during its long test operation. Therefore, it is affirmed that the MSB-MSCA approach proposed is reliable

  19. A study on multi-axial fatigue model based on structural stress

    International Nuclear Information System (INIS)

    Kim, Cheol; Kim, Jong Sung; Jin, Tae Eun; Dong, P.

    2004-01-01

    In nuclear components, cyclic loadings that cause complex states of stress are common. Through a reference review, four sources of the multi-axial fatigue data were collected from LBF, University of Illinois, EPRI, and TWI. All these tests were conducted using tube to flange specimens with a circumferential fillet welds. The loading conditions were mostly bending/ torsion combinations, except that TWI used tension/ torsion combinations. None of fatigue correlation parameters have been demonstrated to be satisfactory in correlating the multi-axial fatigue data outside of their own. In this paper, we proposed the characterizing multi-axial fatigue behavior in terms of the structural stress methods by using some of the well-known multi-axial fatigue data available in the references

  20. Experimental study on visual detection for fatigue of fixed-position staff.

    Science.gov (United States)

    Nie, Baisheng; Huang, Xin; Chen, Yang; Li, Anjin; Zhang, Ruming; Huang, Jinxin

    2017-11-01

    Fatigue can lead to decreased work performance and poorer safety and health condition. Fatigue is ubiquitous in production and in life, while the research on it is mainly concentrated in the automotive driving, aircraft piloting and other fields, and it is insufficient to study on the fatigue of fixed-position staff. This paper puts forward a non-contact visual image method, which can monitor the extent of fatigue of fixed-position staff. Fatigue threshold used in judgment is obtained by processing the recorded data of visual images of the experimental subjects when fatiguing and by analyzing eye closure time, percentage of eyelid closure (PERCLOS) value, frequency and number of blinks. The results show that there is significant difference among the four indicators before and after experiment subjects undergo fatigue. The fatigue of experimental subjects is obvious when eye closure time is 3.5 s/min, PERCLOS value 6%, and blink frequency 0.4 times/s. This provides a reference for a wider range of detection of fatigue and a method for avoiding mistakes and accidents. Copyright © 2017 Elsevier Ltd. All rights reserved.

  1. Multidisciplinary health monitoring of a steel bridge deck structure

    NARCIS (Netherlands)

    Pahlavan, P.L.; Pijpers, R.J.M.; Paulissen, J.H.; Hakkesteegt, H.C.; Jansen, T.H.

    2013-01-01

    Fatigue cracks in orthotropic bridge decks are an important cause for the necessary renovation of existing bridges. Parallel utilization of various technologies based on different physical sensing principles can potentially maximize the efficiency of structural health monitoring (SHM) systems for

  2. Direct and indirect measurement of neuromuscular fatigue in Canadian football players.

    Science.gov (United States)

    Clarke, Nick; Farthing, Jonathan P; Lanovaz, Joel L; Krentz, Joel R

    2015-05-01

    This study assessed the effects of a fatiguing game simulation (G-Sim) on the balance of collegiate Canadian football players. The purpose of the study was to evaluate postural control as a potential tool for monitoring neuromuscular fatigue (NMF) in collision-based team sports. Fifteen male Canadian football players were recruited (mean±SD: age 21.8±1.6 years, weight 97.6±14.7 kg). Indirect NMF measures (postural sway and countermovement jump (CMJ)) were performed 24 h before (TBase), immediately before (TPre) and after (TPost), and 24 h (T24) and 48 h after (T48) a Canadian football G-Sim. Peak isometric knee extensor torque of a maximal voluntary contraction (MVC) and electrically evoked tetani at 20 Hz (P20) and 80 Hz (P80) were also recorded as direct NMF measures at TBase, TPre, TPost, and T48. At TPost, we observed significant declines in MVC, P20, and the MVC/P80 ratio (-15.3%, -15.7%, and -12.1%, respectively; n=12) along with reductions in CMJ takeoff velocity and peak power (-6.9% and -6.5%, respectively; n=12) and larger area of the center of pressure trajectory (95.2%; n=10) during a 60-s postural sway task. All variables were no longer different than baseline by T48. Acute neuromuscular impairment in this cohort is likely attributable to alterations in excitation-contraction coupling due to structural damage and central activation failure. Congruency between the direct and indirect measures of NMF suggests monitoring postural sway has the potential to identify both neuromuscular and somatosensory alterations induced by acute game-induced fatigue in collision-based team sports players.

  3. Fatigue evaluation algorithms: Review

    Energy Technology Data Exchange (ETDEWEB)

    Passipoularidis, V.A.; Broendsted, P.

    2009-11-15

    A progressive damage fatigue simulator for variable amplitude loads named FADAS is discussed in this work. FADAS (Fatigue Damage Simulator) performs ply by ply stress analysis using classical lamination theory and implements adequate stiffness discount tactics based on the failure criterion of Puck, to model the degradation caused by failure events in ply level. Residual strength is incorporated as fatigue damage accumulation metric. Once the typical fatigue and static properties of the constitutive ply are determined,the performance of an arbitrary lay-up under uniaxial and/or multiaxial load time series can be simulated. The predictions are validated against fatigue life data both from repeated block tests at a single stress ratio as well as against spectral fatigue using the WISPER, WISPERX and NEW WISPER load sequences on a Glass/Epoxy multidirectional laminate typical of a wind turbine rotor blade construction. Two versions of the algorithm, the one using single-step and the other using incremental application of each load cycle (in case of ply failure) are implemented and compared. Simulation results confirm the ability of the algorithm to take into account load sequence effects. In general, FADAS performs well in predicting life under both spectral and block loading fatigue. (author)

  4. Influence of grain orientation on evolution of surface features in fatigued polycrystalline copper: A comparison of thermal and uniaxial mechanical fatigue results

    International Nuclear Information System (INIS)

    Aicheler, Markus

    2010-01-01

    Surface state plays a major role in the crack nucleation process of pure metals in the High-Cycle-Fatigue (HCF) as well as in the Ultra-High-Cycle-Fatigue (UHCF) regime. Therefore, in studies dealing with HCF or UHCF, special attention is paid to the evolution of surface degradation during fatigue life. The accelerating structures of the future Compact Linear Collider (CLIC) under study at CERN will be submitted to a high number of thermal-mechanical fatigue cycles, arising from Radio Frequency (RF) induced eddy currents, causing local superficial cyclic heating. The number of cycles during the foreseen lifetime of CLIC reaches 2x10 11 . Fatigue may limit the lifetime of CLIC structures. In order to assess the effects of superficial fatigue, specific tests are defined and performed on polycrystalline Oxygen Free Electronic (OFE) grade Copper, a candidate material for the structures. Surface degradation depends on the orientation of near-surface grains. Copper samples thermally fatigued in two different fatigue experiments, pulsed laser and pulsed RF-heating, underwent postmortem Electron Backscattered Diffraction measurements. Samples fatigued by pulsed laser show the same trend in the orientation-fatigue damage behavior as samples fatigued by pulsed RF-heating. It is clearly observed that surface grains, oriented [1 1 1] with respect to the surface, show significantly more damage than surface grains oriented [1 0 0]. Results arising from a third fatigue experiment, the ultrasound (US) swinger, are compared to the results of the mentioned experiments. The US swinger is an uniaxial mechanical fatigue test enabling to apply within several days a total number of cycles representative of the life of the CLIC structures, thanks to a high repetition rate of 24 kHz. For comparison, laser fatigue experiments have much lower repetition rates. The dependence of surface degradation on grain orientation of samples tested by the US swinger was monitored during the fatigue life

  5. Collect Available Creep-Fatigue Data and Study Existing Creep-Fatigue Evaluation Procedures for Grade 91 and Hastelloy XR

    International Nuclear Information System (INIS)

    Asayama, Tai; Tachibana, Yukio

    2007-01-01

    This report describes the results of investigation on Task 5 of DOE/ASME Materials Project based on a contract between ASME Standards Technology, LLC (ASME ST-LLC) and Japan Atomic Energy Agency (JAEA). Task 5 is to collect available creep-fatigue data and study existing creep-fatigue evaluation procedures for Grade 91 steel and Hastelloy XR. Part I of this report is devoted to Grade 91 steel. Existing creep-fatigue data were collected (Appendix A) and analyzed from the viewpoints of establishing a creep-fatigue procedure for VHTR design. A fair amount of creep-fatigue data has been obtained and creep-fatigue phenomena have been clarified to develop design standards mainly for fast breeder reactors. Following this, existing creep-fatigue procedures were studied and it was clarified that the creep-fatigue evaluation procedure of the ASME-NH has a lot of conservatisms and they were analyzed in detail from the viewpoints of the evaluation of creep damage of material. Based on the above studies, suggestions to improve the ASME-NH procedure along with necessary research and development items were presented. Part II of this report is devoted to Hastelloy XR. Existing creep-fatigue data used for development of the high temperature structural design guideline for High Temperature Gas-cooled Reactor (HTGR) were collected. Creep-fatigue evaluation procedure in the design guideline and its application to design of the intermediate heat exchanger (IHX) for High Temperature Engineering Test Reactor (HTTR) was described. Finally, some necessary research and development items in relation to creep-fatigue evaluation for Gen IV and VHTR reactors were presented.

  6. Fatigue-crack propagation response of two nickel-base alloys in a liquid sodium environment

    International Nuclear Information System (INIS)

    Mills, W.J.; James, L.A.

    1979-01-01

    The elevated temperature fatigue-crack propagation response of Inconel 600 and Inconel 718 was characterized within a linear-elastic fracture mechanics framework in air and low-oxygen liquid sodium environments. The crack growth rates of both nickel-base alloys tested in liquid sodium were found to be considerably lower than those obtained in air. This enhanced fatigue resistance in sodium was attributed to the very low oxygen content in the inert sodium environment. Electron fractographic examination of the Inconel 600 and Inconel 718 fatigue fracture surfaces revealed that operative crack growth mechanisms were dependent on the prevailing stress intensity level. Under low growth rate conditions, Inconel 600 and Inconel 718 fracture surfaces exhibited a faceted, crystallographic morphology in both air and sodium environments. In the higher growth rate regime, fatigue striations were observed; however, striations formed in sodium were rather ill-defined. These indistinct striations were attributed to the absence of oxygen in the liquid sodium environment. Striation spacing measurements were found to be in excellent agreement with macroscopic growth rates in both environments

  7. Examining the impact of obesity on individuals with chronic fatigue syndrome.

    Science.gov (United States)

    Flores, Samantha; Brown, Abigail; Adeoye, Samuel; Jason, Leonard A; Evans, Meredyth

    2013-07-01

    Chronic fatigue syndrome (CFS) is a complex disorder affecting multiple body systems. The most commonly used definition of CFS is 6 or more months of fatigue and the presence of at least four of eight minor symptoms. In addition, many health and psychological conditions, including severe obesity-body mass index (BMI) of 40 kg/m(2) or greater-exclude individuals from a diagnosis of CFS. Obesity has been correlated with fatigue, sleep problems, and less satisfaction with general health, functioning, and vitality. The current study investigated weight trends over time in a community-based sample of individuals with CFS and healthy controls. The study further investigated the impact of comorbid weight issues on several health and disability outcomes in a subset of overweight individuals. Overweight and obese individuals with CFS demonstrated poorer functioning than controls who were similarly weighted. One participant was excluded because she had gained weight at a monitoring visit and her BMI was greater than 40 kg/m(2). The implications of these findings for health care workers are discussed. Copyright 2013, SLACK Incorporated.

  8. Mean stress and the exhaustion of fatigue-damage resistance

    Science.gov (United States)

    Berkovits, Avraham

    1989-01-01

    Mean-stress effects on fatigue life are critical in isothermal and thermomechanically loaded materials and composites. Unfortunately, existing mean-stress life-prediction methods do not incorporate physical fatigue damage mechanisms. An objective is to examine the relation between mean-stress induced damage (as measured by acoustic emission) and existing life-prediction methods. Acoustic emission instrumentation has indicated that, as with static yielding, fatigue damage results from dislocation buildup and motion until dislocation saturation is reached, after which void formation and coalescence predominate. Correlation of damage processes with similar mechanisms under monotonic loading led to a reinterpretation of Goodman diagrams for 40 alloys and a modification of Morrow's formulation for life prediction under mean stresses. Further testing, using acoustic emission to monitor dislocation dynamics, can generate data for developing a more general model for fatigue under mean stress.

  9. Damage estimates for European and U.S.sites using the U.S. high-cycle fatigue data base

    Energy Technology Data Exchange (ETDEWEB)

    Sutherland, H J [Wind Energy Technology, Sandia National Lab., Albuquerque, NM (United States)

    1996-09-01

    This paper uses two high-cycle fatigue data bases, one for typical U.S. blade materials and one for European materials, to analyze the service lifetime of a wind turbine blade subjected to the WISPER load spectrum for northern European sites and the WISPER protocol load spectrum for U.S. wind farm sites. The U.S. data base contains over 2200 data points that were obtained using coupon testing procedures. These data are used to construct a Goodman diagram that is suitable for analyzing wind turbine blades. This result is compared to the Goodman diagram derived from the European fatigue data base FACT. The LIFE2 fatigue analysis code for wind turbines is then used to predict the service lifetime of a turbine blade subjected to the two loading histories. The results of this study indicate that the WISPER load spectrum from northern European sites significantly underestimates the WISPER protocol load spectrum from a U.S. wind farm site, i.e., the WISPER load spectrum significantly underestimates the number and magnitude of the loads observed at a U.S. wind farm site. Further, the analysis demonstrate that the European and the U.S. fatigue material data bases are in general agreement for the prediction of tensile failures. However, for compressive failures, the two data bases are significantly different, with the U.S. data base predicting significantly shorter service lifetimes than the European data base. (au) 14 refs.

  10. High-cycle fatigue behavior of Co-based superalloy 9CrCo at elevated temperatures

    Directory of Open Access Journals (Sweden)

    Wan Aoshuang

    2016-10-01

    Full Text Available A modified model is developed to characterize and evaluate high-cycle fatigue behavior of Co-based superalloy 9CrCo at elevated temperatures by considering the stress ratio effect. The model is informed by the relationship surface between maximum nominal stress, stress ratio and fatigue life. New formulae are derived to deal with the test data for estimating the parameters of the proposed model. Fatigue tests are performed on Co-based superalloy 9CrCo subjected to constant amplitude loading at four stress ratios of −1, −0.3, 0.5 and 0.9 in three environments of room temperature (i.e., about 25 °C and elevated temperatures of 530 °C and 620 °C, and the interaction mechanisms between the elevated temperature and stress ratio are deduced and compared with each other from fractographic studies. Finally, the model is applied to experimental data, demonstrating the practical and effective use of the proposed model. It is shown that new model has good correlation with experimental results.

  11. Fatigue Assessment of High Strength Steel Welded Joints Under Bending Loading

    International Nuclear Information System (INIS)

    Lee, Myeong-Woo; Kim, Yun-Jae; Park, Jun-Hyub

    2014-01-01

    In this study, a fatigue assessment method for vehicle suspension systems having welded geometries was established under a bending loading condition. For the fatigue life estimation of the actual product s welded joints made of different steels, bending fatigue tests were performed on welded specimens with a simplified shape for obtaining the moment-fatigue-life plot. Further, geometry modeling of the simplified welded specimens was conducted. Results of finite element analysis were used to obtain the stress-fatigue-life plot. The analysis results were also used to calculate the stress concentration factors for notch-factor-based fatigue life estimation. The test results were compared with results of the general notch-factor-based fatigue life estimation for improving fatigue assessment. As a result, it was concluded that both the welded fatigue tests and the notch-factor-based fatigue life estimation are necessary for accurate fatigue assessment

  12. Lamb Wave Assessment of Fatigue and Thermal Damage in Composites

    Science.gov (United States)

    Seale, Michael D.; Smith, Barry T.; Prosser, W. H.

    2004-01-01

    Among the various techniques available, ultrasonic Lamb waves offer a convenient method of evaluating composite materials. Since the Lamb wave velocity depends on the elastic properties of a structure, an effective tool exists to monitor damage in composites by measuring the velocity of these waves. Lamb wave measurements can propagate over long distances and are sensitive to the desired in-plane elastic properties of the material. This paper describes two studies which monitor fatigue damage and two studies which monitor thermal damage in composites using Lamb waves. In the fatigue studies, the Lamb wave velocity is compared to modulus measurements obtained using strain gage measurements in the first experiment and the velocity is monitored along with the crack density in the second. In the thermal damage studies, one examines samples which were exposed to varying temperatures for a three minute duration and the second includes rapid thermal damage in composites by intense laser beams. In all studies, the Lamb wave velocity is demonstrated to be an excellent method to monitor damage in composites.

  13. Noncontact fatigue crack evaluation using thermoelastic

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ji Min; An, Yun Kyu; Sohn, Hoon [KAIST, Daejeon (Korea, Republic of)

    2012-12-15

    This paper proposes a noncontact thermography technique for fatigue crack evaluation under a cyclic tensile loading. The proposed technique identifies and localizes an invisible fatigue crack without scanning, thus making it possible to instantaneously evaluate an incipient fatigue crack. Based on a thermoelastic theory, a new fatigue crack evaluation algorithm is proposed for the fatigue crack tip localization. The performance of the proposed algorithm is experimentally validated. To achieve this, the cyclic tensile loading is applied to a dog bone shape aluminum specimen using a universal testing machine, and the corresponding thermal responses induced by thermoelastic effects are captured by an infrared camera. The test results confirm that the fatigue crack is well identified and localized by comparing with its microscopic images.

  14. Evaluation of micro fatigue crack growth under equi-biaxial stress by membranous pressure fatigue test

    International Nuclear Information System (INIS)

    Iida, Satoshi; Abe, Shigeki; Nakamura, Takao; Kamaya, Masayuki

    2014-01-01

    For preventing nuclear power plant (NPP) accidents, NPPs are required to ensure system safety in long term safe operation under aging degradation. Now, fatigue accumulation is one of major ageing phenomena and are evaluated to ensure safety by design fatigue curve that are based on the results of uniaxial fatigue tests. On the other hand, thermal stress that occurs in piping of actual components is not uniaxial but equi-biaxial. For accurate evaluation, it is required to conform real circumstance. In this study, membranous pressure fatigue test was conducted to simulated equi-biaxial stress. Crack initiation and crack growth were examined by replica investigation. Calculation result of equivalent stress intensity factor shows crack growth under equi-biaxial stress is faster than under uniaxial stress. It is concluded that equi-biaxial fatigue behavior should be considered in the evaluation of fatigue crack initiation and crack growth. (author)

  15. Study of cumulative fatigue damage detection for used parts with nonlinear output frequency response functions based on NARMAX modelling

    Science.gov (United States)

    Huang, Honglan; Mao, Hanying; Mao, Hanling; Zheng, Weixue; Huang, Zhenfeng; Li, Xinxin; Wang, Xianghong

    2017-12-01

    Cumulative fatigue damage detection for used parts plays a key role in the process of remanufacturing engineering and is related to the service safety of the remanufactured parts. In light of the nonlinear properties of used parts caused by cumulative fatigue damage, the based nonlinear output frequency response functions detection approach offers a breakthrough to solve this key problem. First, a modified PSO-adaptive lasso algorithm is introduced to improve the accuracy of the NARMAX model under impulse hammer excitation, and then, an effective new algorithm is derived to estimate the nonlinear output frequency response functions under rectangular pulse excitation, and a based nonlinear output frequency response functions index is introduced to detect the cumulative fatigue damage in used parts. Then, a novel damage detection approach that integrates the NARMAX model and the rectangular pulse is proposed for nonlinear output frequency response functions identification and cumulative fatigue damage detection of used parts. Finally, experimental studies of fatigued plate specimens and used connecting rod parts are conducted to verify the validity of the novel approach. The obtained results reveal that the new approach can detect cumulative fatigue damages of used parts effectively and efficiently and that the various values of the based nonlinear output frequency response functions index can be used to detect the different fatigue damages or working time. Since the proposed new approach can extract nonlinear properties of systems by only a single excitation of the inspected system, it shows great promise for use in remanufacturing engineering applications.

  16. Importance of fatiguing, overtraining and chronic fatigue in athletes

    Directory of Open Access Journals (Sweden)

    Adam Piesik

    2017-09-01

    Full Text Available Each training that requires achieving a higher heart rate limit and/or increased concentration in time may cause fatigue, considered to be a natural defence mechanism of a body. In the case of excessive fatigue and insufficient time designated for rest and regeneration, an overtraining syndrome (OTS may develop. The main symptom of overtraining is increased fatigue that fails to become reversed in normal conditions of regeneration. Although authors are familiar with the overtraining syndrome and associated symptoms, as of today no diagnostic tool has been developed that may form a basis for a final diagnosis, and the diagnosis itself is frequently based on a subjective assessment of the athlete. Possible causes of the band overtraining syndrome are disorders of sodium, inflammatory processes resulting from physical activity and / or disorders of the autonomic nervous system.

  17. Scanning Electron Microscope Mapping System Developed for Detecting Surface Defects in Fatigue Specimens

    Science.gov (United States)

    Bonacuse, Peter J.; Kantzos, Peter T.

    2002-01-01

    An automated two-degree-of-freedom specimen positioning stage has been developed at the NASA Glenn Research Center to map and monitor defects in fatigue specimens. This system expedites the examination of the entire gauge section of fatigue specimens so that defects can be found using scanning electron microscopy (SEM). Translation and rotation stages are driven by microprocessor-based controllers that are, in turn, interfaced to a computer running custom-designed software. This system is currently being used to find and record the location of ceramic inclusions in powder metallurgy materials. The mapped inclusions are periodically examined during interrupted fatigue experiments. The number of cycles to initiate cracks from these inclusions and the rate of growth of initiated cracks can then be quantified. This information is necessary to quantify the effect of this type of defect on the durability of powder metallurgy materials. This system was developed with support of the Ultra Safe program.

  18. Fatigue Crack Growth Behavior of Nickel-base Superalloy Haynes 282 at 550-750 °C

    Science.gov (United States)

    Rozman, K. A.; Kruzic, J. J.; Hawk, J. A.

    2015-08-01

    The fatigue crack growth rates for nickel-based superalloy Haynes 282 were measured at temperatures of 550, 650, and 750 °C using compact tension specimens with a load ratio of 0.1 and cyclic loading frequencies of 25 Hz and 0.25 Hz. Increasing the temperature from 550 to 750 °C caused the fatigue crack growth rates to increase from ~20 to 60% depending upon the applied stress intensity level. The effect of reducing the applied loading frequency increased the fatigue crack growth rates from ~20 to 70%, also depending upon the applied stress intensity range. The crack path was observed to be transgranular for the temperatures and frequencies used during fatigue crack growth rate testing. At 750 °C, there were some indications of limited intergranular cracking excursions at both loading frequencies; however, the extent of intergranular crack growth was limited and the cause is not understood at this time.

  19. Creep-fatigue behavior of turbine disc of superalloy GH720Li at 650 °C and probabilistic creep-fatigue modeling

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Dianyin [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Collaborative Innovation Center of Advanced Aero-Engine, Beijing 100191 (China); Beijing Key Laboratory of Aero-Engine Structure and Strength, Beijing 100191 (China); Ma, Qihang [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Shang, Lihong [Mining and Materials Engineering, McGill University, Montreal, QC H3A 0C5 (Canada); Gao, Ye [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Wang, Rongqiao, E-mail: wangrq@buaa.edu.cn [School of Energy and Power Engineering, Beihang University, Beijing 100191 (China); Collaborative Innovation Center of Advanced Aero-Engine, Beijing 100191 (China); Beijing Key Laboratory of Aero-Engine Structure and Strength, Beijing 100191 (China)

    2016-07-18

    Creep-fatigue experiments have been conducted in nickel-based superalloy GH720Li at an elevated temperature of 650 °C with a stress ratio of 0.1, based on which, different dwell times at the maximum loading were applied to investigate the effect of dwell time on the creep-fatigue behaviors. The tested specimens were cut from the rim region of an actual turbine disc in the hoop direction. The grain size and precipitates of the GH720Li superalloy were examined through scanning electronic microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) analyses. Experimental data shows creep-fatigue lifetime decreases as the dwell time prolongs. Further, different scattering was observed in the creep-fatigue lifetime at different dwell times. Then a probabilistic model based on the applied mechanical work density (AMWD), with a linear heteroscedastic function that evaluates the non-constant deviation in the creep-fatigue lifetime, was formulated to describe the dependence of creep-fatigue lifetime on the dwell time. Finally, the possible microscopic mechanism of the creep-fatigue behavior has been discussed by SEM with EDS on the fracture surfaces.

  20. Design and simulation of Macro-Fiber composite based serrated microflap for wind turbine blade fatigue load reduction

    Science.gov (United States)

    Sun, Xiao; Dai, Qingli; Bilgen, Onur

    2018-05-01

    A Macro-Fiber Composite (MFC) based active serrated microflap is designed in this research for wind turbine blades. Its fatigue load reduction potential is evaluated in normal operating conditions. The force and displacement output of the MFC-based actuator are simulated using a bimorph beam model. The work done by the aerodynamic, centripetal and gravitational forces acting on the microflap were calculated to determine the required capacity of the MFC-based actuator. MFC-based actuators with a lever mechanical linkage are designed to achieve the required force and displacement to activate the microflap. A feedback control scheme is designed to control the microflap during operation. Through an aerodynamic-aeroelastic time marching simulation with the designed control scheme, the time responses of the wind turbine blades are obtained. The fatigue analysis shows that the serrated microflap can reduce the standard deviation of the blade root flapwise bending moment and the fatigue damage equivalent loads.

  1. Fatigue and damage tolerance scatter models

    Science.gov (United States)

    Raikher, Veniamin L.

    1994-09-01

    Effective Total Fatigue Life and Crack Growth Scatter Models are proposed. The first of them is based on the power form of the Wohler curve, fatigue scatter dependence on mean life value, cycle stress ratio influence on fatigue scatter, and validated description of the mean stress influence on the mean fatigue life. The second uses in addition are fracture mechanics approach, assumption of initial damage existence, and Paris equation. Simple formulas are derived for configurations of models. A preliminary identification of the parameters of the models is fulfilled on the basis of experimental data. Some new and important results for fatigue and crack growth scatter characteristics are obtained.

  2. Monitoring and modeling stress corrosion and corrosion fatigue damage in nuclear reactors

    International Nuclear Information System (INIS)

    Andresen, P.L.; Ford, F.P.; Solomon, H.D.; Taylor, D.F.

    1990-01-01

    Stress corrosion and corrosion fatigue are significant problems in many industries, causing economic penalties from decreased plant availability and component repair or replacement. In nuclear power reactors, environmental cracking occurs in a wide variety of components, including reactor piping and steam generator tubing, bolting materials and pressure vessels. Life assessment for these components is complicated by the belief that cracking is quite irreproducible. Indeed, for conditions which were once viewed as nominally similar, orders of magnitude variability in crack growth rates are observed for stress corrosion and corrosion fatigue of stainless steels and low-alloy steels in 288 degrees C water. This paper shows that design and life prediction approaches are destined to be overly conservative or to risk environmental failure if life is predicted by quantifying only the effects of mechanical parameters and/or simply ignoring or aggregating environmental and material variabilities. Examples include the Nuclear Regulatory Commission (NRC) disposition line for stress-corrosion cracking of stainless steel in boiling water reactor (BWR) water and the American Society of Mechanical Engineers' Section XI lines for corrosion fatigue

  3. Fatigue Life Assessment of Selected Engineering Materials Based on Modified Low-Cycle Fatigue Test

    Directory of Open Access Journals (Sweden)

    Maj M.

    2013-03-01

    Full Text Available In this study, the mechanical tests were carried out on ductile iron of EN-GJS-600-3 grade and on grey cast iron of EN-GJL-250 grade. The fatigue life was evaluated in a modified low-cycle fatigue test (MLCF, which enables the determination of parameters resulting from the Manson-Coffin-Morrow relationship. The qualitative and quantitative metallographic studies conducted by light microscopy on selected samples of ductile iron with spheroidal graphite and grey cast iron with lamellar graphite (showing only small variations in mechanical properties, confirmed also small variations in the geometrical parameters of graphite related with its content and morphological features.

  4. Fatigue Life Assessment of Selected Engineering Materials Based on Modified Low-Cycle Fatigue Test

    Directory of Open Access Journals (Sweden)

    M. Maj

    2013-01-01

    Full Text Available In this study, the mechanical tests were carried out on ductile iron of EN-GJS-600-3 grade and on grey cast iron of EN-GJL-250 grade.The fatigue life was evaluated in a modified low-cycle fatigue test (MLCF, which enables the determination of parameters resulting fromthe Manson-Coffin-Morrow relationship.The qualitative and quantitative metallographic studies conducted by light microscopy on selected samples of ductile iron with spheroidalgraphite and grey cast iron with lamellar graphite (showing only small variations in mechanical properties, confirmed also smallvariations in the geometrical parameters of graphite related with its content and morphological features.

  5. Combined simulation of fatigue crack nucleation and propagation based on a damage indicator

    Directory of Open Access Journals (Sweden)

    M. Springer

    2016-10-01

    Full Text Available Fatigue considerations often distinguish between fatigue crack nucleation and fatigue crack propagation. The current work presents a modeling approach utilizing one Fatigue Damage Indicator to treat both in a unified way. The approach is implemented within the framework of the Finite Element Method. Multiaxial critical plane models with an extended damage accumulation are employed as Fatigue Indicators. Locations of fatigue crack emergence are predicted by these indicators and material degradation is utilized to model local material failure. The cyclic loading is continued on the now degraded structure and the next location prone to material failure is identified and degradation modeled. This way, fatigue crack propagation is represented by an evolving spatial zone of material failure. This propagating damage zone leads to a changing structural response of the pristine structure. By recourse to the Fatigue Damage Indicator a correlation between the number of applied load cycles and the changing structural behavior is established. Finally, the proposed approach is exemplified by cyclic bending experiments in the Low Cycle Fatigue regime

  6. Life Prediction of Low Cycle Fatigue for Ni-base Superalloy GTD111 DS at Elevated Temperature

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Jin Yeol; Yoon, Dong Hyun; Kim, Jae Hoon [Chungnam Nat’l Univ., Daejeon (Korea, Republic of); Bae, Si Yeon; Chang, Sung Yong; Chang, Sung Ho [KEPCO Research Institute, Daejeon (Korea, Republic of)

    2017-08-15

    GTD111 DS of nickel base superalloy has been used for gas turbine blades. In this study, low cycle fatigue test was conducted on the GTD111 DS alloy by setting conditions similar to the real operating environment. The low cycle fatigue tests were conducted at room temperature, 760 °C, 870 °C, and various strain amplitudes. Test results showed that fatigue life decreased with increasing total strain amplitude. Cyclic hardening response was observed at room temperature and 760 °C; however, tests conducted at 870 °C showed cyclic softening response. Stress relaxation was observed at 870 °C because creep effects occurred from holding time. A relationship between fatigue life and total strain range was obtained from the Coffin-Manson method. The fratography using a SEM was carried out at the crack initiation and propagation regions.

  7. Fatigue

    Science.gov (United States)

    ... 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, ...

  8. Probabilistic Analysis for Comparing Fatigue Data Based on Johnson-Weibull Parameters

    Science.gov (United States)

    Vlcek, Brian L.; Hendricks, Robert C.; Zaretsky, Erwin V.

    2013-01-01

    Leonard Johnson published a methodology for establishing the confidence that two populations of data are different. Johnson's methodology is dependent on limited combinations of test parameters (Weibull slope, mean life ratio, and degrees of freedom) and a set of complex mathematical equations. In this report, a simplified algebraic equation for confidence numbers is derived based on the original work of Johnson. The confidence numbers calculated with this equation are compared to those obtained graphically by Johnson. Using the ratios of mean life, the resultant values of confidence numbers at the 99 percent level deviate less than 1 percent from those of Johnson. At a 90 percent confidence level, the calculated values differ between +2 and 4 percent. The simplified equation is used to rank the experimental lives of three aluminum alloys (AL 2024, AL 6061, and AL 7075), each tested at three stress levels in rotating beam fatigue, analyzed using the Johnson- Weibull method, and compared to the ASTM Standard (E739 91) method of comparison. The ASTM Standard did not statistically distinguish between AL 6061 and AL 7075. However, it is possible to rank the fatigue lives of different materials with a reasonable degree of statistical certainty based on combined confidence numbers using the Johnson- Weibull analysis. AL 2024 was found to have the longest fatigue life, followed by AL 7075, and then AL 6061. The ASTM Standard and the Johnson-Weibull analysis result in the same stress-life exponent p for each of the three aluminum alloys at the median, or L(sub 50), lives

  9. Fatigue Life Analysis and Prediction of 316L Stainless Steel Under Low Cycle Fatigue Loading

    Energy Technology Data Exchange (ETDEWEB)

    Oh, Hyeong; Myung, NohJun; Choi, Nak-Sam [Hanyang Univ., Seoul (Korea, Republic of)

    2016-12-15

    In this study, a strain-controlled fatigue test of widely-used 316L stainless steel with excellent corrosion resistance and mechanical properties was conducted, in order to assess its fatigue life. Low cycle fatigue behaviors were analyzed at room temperature, as a function of the strain amplitude and strain ratio. The material was hardened during the initial few cycles, and then was softened during the long post period, until failure occurred. The fatigue life decreased with increasing strain amplitude. Masing behavior in the hysteresis loop was shown under the low strain amplitude, whereas the high strain amplitude caused non-Masing behavior and reduced the mean stress. Low cycle fatigue life prediction based on the cyclic plastic energy dissipation theory, considering Masing and non-Masing effects, showed a good correlation with the experimental results.

  10. Measuring the interactions between different locations in a muscle to monitor localized muscle fatigue.

    Science.gov (United States)

    Bingham, Adrian; Arjunan, Sridhar P; Kumar, Dinesh K

    2017-07-01

    In this study we investigated a technique for estimating the progression of localized muscle fatigue. This technique measures the dependence between motor units using high density surface electromyogram (HD-sEMG) and is based on the Normalized Mutual Information (NMI) measure. The NMI between every pair combination of the electrode array is computed to measure the interactions between electrodes. Participants in the experiment had an array of 64 electrodes (16 by 4) placed over the TA of their dominate leg such that the columns of the array ran parallel with the muscle fibers. The HD-sEMG was recorded whilst the participants maintained an isometric dorsiflexion with their dominate foot until task failure at 40% and 80% of their maximum voluntary contraction (MVC). The interactions between different locations over the muscle were computed using the recorded HD-sEMG signals. The results show that the average interactions between various locations over the TA significantly increased during fatigue at both levels of contraction. This can be attributed to the dependence in the motor units.

  11. Fatigue crack growth studies on a tee junction using ultrasonic non-destructive methods

    International Nuclear Information System (INIS)

    Subramanian, C.V.; Thavasimuthu, M.; Ramesh, A.S.; Jayakumar, T.; Kalyanasundaram, P.; Baldev Raj

    1996-01-01

    Fatigue cracks need to be detected and sized to maintain structural integrity. The significance of cracks detected in service must also be assessed. This paper describes the on-line ultrasonic testing carried out on a Tee joint subjected to fatigue loading. The initiation and growth of the cracks were monitored for every 5,000 cycles up to 40,000 cycles. The study demonstrated the use of ultrasonic testing for fatigue crack growth detection and sizing. (author)

  12. Effect of creep and oxidation on reduced fatigue life of Ni-based alloy 617 at 850 °C

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Xiang, E-mail: chenx@ornl.gov [Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, 104 South Wright Street, Urbana, IL 61801 (United States); Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831 (United States); Yang, Zhiqing [Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831 (United States); Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Sokolov, Mikhail A.; Erdman, Donald L. [Oak Ridge National Laboratory, 1 Bethel Valley Road, Oak Ridge, TN 37831 (United States); Mo, Kun; Stubbins, James F. [Department of Nuclear, Plasma, and Radiological Engineering, University of Illinois at Urbana-Champaign, 104 South Wright Street, Urbana, IL 61801 (United States)

    2014-01-15

    Low cycle fatigue (LCF) and creep–fatigue testing of Ni-based alloy 617 was carried out at 850 °C. Compared with its LCF life, the material’s creep–fatigue life decreases to different extents depending on test conditions. To elucidate the microstructure-fatigue property relationship for alloy 617 and the effect of creep and oxidation on its fatigue life, systematic microstructural investigations were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction (EBSD). In LCF tests, as the total strain range increased, deformations concentrated near high angle grain boundaries (HAGBs). The strain hold period in the creep–fatigue tests introduced additional creep damage to the material, which revealed the detrimental effect of the strain hold time on the material fatigue life in two ways. First, the strain hold time enhanced the localized deformation near HAGBs, resulting in the promotion of intergranular cracking of alloy 617. Second, the strain hold time encouraged grain boundary sliding, which resulted in interior intergranular cracking of the material. Oxidation accelerated the initiation of intergranular cracking in alloy 617. In the crack propagation stage, if oxidation was promoted and the cyclic oxidation damage was greater than the fatigue damage, oxidation-assisted intergranular crack growth resulted in a significant reduction in the material’s fatigue life.

  13. Fatigue and thermal fatigue of Pb-Sn solder joints

    International Nuclear Information System (INIS)

    Frear, D.; Grivas, D.; McCormack, M.; Tribula, D.; Morris, J.W. Jr.

    1987-01-01

    This paper presents a fundamental investigation of the fatigue and thermal fatigue characteristics, with an emphasis on the microstructural development during fatigue, of Sn-Pb solder joints. Fatigue tests were performed in simple shear on both 60Sn-40Pb and 5Sn-95Pb solder joints. Isothermal fatigue tests show increasing fatigue life of 60Sn-40Pb solder joints with decreasing strain and temperature. In contrast, such behavior was not observed in the isothermal fatigue of 5Sn-95Pb solder joints. Thermal fatigue results on 60Sn-40Pb solder cycled between -55 0 C and 125 0 C show that a coarsened region develops in the center of the joint. Both Pb-rich and Sn-rich phases coarsen, and cracks form within these coarsened regions. The failure mode 60Sn-40Pb solder joints in thermal and isothermal fatigue is similar: cracks form intergranularly through the Sn-rich phase or along Sn/Pb interphase boundaries. Extensive cracking is found throughout the 5Sn-95Pb joint for both thermal and isothermal fatigue. In thermal fatigue the 5Sn-95Pb solder joints failed after fewer cycles than 60Sn-40Pb

  14. The effects of moderate fatigue on dynamic balance control and attentional demands

    Directory of Open Access Journals (Sweden)

    Teasdale Normand

    2006-09-01

    Full Text Available Abstract Background During daily activities, the active control of balance often is a task per se (for example, when standing in a moving bus. Other constraints like fatigue can add to the complexity of this balance task. In the present experiment, we examined how moderate fatigue induced by fast walking on a treadmill challenged dynamic balance control. We also examined if the attentional demands for performing the balance task varied with fatigue. Methods Subjects (n = 10 performed simultaneously a dynamic balance control task and a probe reaction time task (RT (serving as an indicator of attentional demands before and after three periods of moderate fatigue (fast walking on a treadmill. For the balance control task, the real-time displacement of the centre of pressure (CP was provided on a monitor placed in front of the subject, at eye level. Subjects were asked to keep their CP within a target (moving box moving upward and downward on the monitor. The tracking performance was measured (time spent outside the moving box and the CP behavior analyzed (mean CP speed and mean frequency of the CP velocity. Results Moderate fatigue led to an immediate decrement of the performance on the balance control task; increase of the percentage of time spent outside the box and increase of the mean CP speed. Across the three fatigue periods, subjects improved their tracking performance and reduced their mean CP speed. This was achieved by increasing their frequency of actions; mean frequency of the CP velocity were higher for the fatigue periods than for the no fatigue periods. Fatigue also induced an increase in the attentional demands suggesting that more cognitive resources had to be allocated to the balance task with than without fatigue. Conclusion Fatigue induced by fast walking had an initial negative impact on the control of balance. Nonetheless, subjects were able to compensate the effect of the moderate fatigue by increasing the frequency of

  15. Online Detection of Driver Fatigue Using Steering Wheel Angles for Real Driving Conditions

    Directory of Open Access Journals (Sweden)

    Zuojin Li

    2017-03-01

    Full Text Available This paper presents a drowsiness on-line detection system for monitoring driver fatigue level under real driving conditions, based on the data of steering wheel angles (SWA collected from sensors mounted on the steering lever. The proposed system firstly extracts approximate entropy (ApEnfeaturesfromfixedslidingwindowsonreal-timesteeringwheelanglestimeseries. Afterthat, this system linearizes the ApEn features series through an adaptive piecewise linear fitting using a given deviation. Then, the detection system calculates the warping distance between the linear features series of the sample data. Finally, this system uses the warping distance to determine the drowsiness state of the driver according to a designed binary decision classifier. The experimental data were collected from 14.68 h driving under real road conditions, including two fatigue levels: “wake” and “drowsy”. The results show that the proposed system is capable of working online with an average 78.01% accuracy, 29.35% false detections of the “awake” state, and 15.15% false detections of the “drowsy” state. The results also confirm that the proposed method based on SWA signal is valuable for applications in preventing traffic accidents caused by driver fatigue.

  16. A New Method to Detect Driver Fatigue Based on EMG and ECG Collected by Portable Non-Contact Sensors

    Directory of Open Access Journals (Sweden)

    Lin Wang

    2017-11-01

    Full Text Available Recently, detection and prediction on driver fatigue have become interest of research worldwide. In the present work, a new method is built to effectively evaluate driver fatigue based on electromyography (EMG and electrocardiogram (ECG collected by portable real-time and non-contact sensors. First, under the non-disturbance condition for driver’s attention, mixed physiological signals (EMG, ECG and artefacts are collected by non-contact sensors located in a cushion on the driver’s seat. EMG and ECG are effectively separated by FastICA, and de-noised by empirical mode decomposition (EMD. Then, three physiological features, complexity of EMG, complexity of ECG, and sample entropy (SampEn of ECG, are extracted and analysed. Principal components are obtained by principal components analysis (PCA and are used as independent variables. Finally, a mathematical model of driver fatigue is built, and the accuracy of the model is up to 91%. Moreover, based on the questionnaire, the calculation results of model are consistent with real fatigue felt by the participants. Therefore, this model can effectively detect driver fatigue.

  17. A short summary on finite element modelling of fatigue crack closure

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Konjengbam Darunkumar [Indian Institute of Technology, Guwahati (India); Parry, Matthew Roger [Airbus Operations Ltd, Bristol(United Kingdom); Sinclair, Ian [University of Southampton, Southampton (United Kingdom)

    2011-12-15

    This paper presents a short summary pertaining to the finite element modelling of fatigue crack closure. Several key issues related to finite element modelling of fatigue crack closure are highlighted: element type, mesh refinement, stabilization of crack closure, crack-tip node release scheme, constitutive model, specimen geometry, stress-states (i.e., plane stress, plane strain), crack closure monitoring. Reviews are presented for both straight and deflected cracks.

  18. Shed a light in fatigue detection with near-infrared spectroscopy during long-lasting driving

    Science.gov (United States)

    Gao, Yuan; Pan, Boan; Li, Kai; Li, Ting

    2016-03-01

    Fatigue driving is one of the leading roles to induce traffic accident and injury, which urgently desires a novel technique to monitor the fatigue level at driving. Functional near infrared spectroscopy (fNIRS) is capable of noninvasive monitoring brain-activities-related hemodynamic responses. Here, we developed a fINRS imager and setup a classic psychological experiment to trigger visual divided attention which varied responding to driving fatigue, and attempted to record the drive-fatigue-level correlated hemodynamic response in the prefrontal cortex. 7 volunteers were recruited to take 7 hours driving and the experimental test was repeated every 1 hour and 8 times in total. The hemodynamic response were extracted and graphed with pseudo image. The analysis on the relationship between the fNIRS-measured hemodynamic response and fatigue level finally displayed that the oxyhemoglobin concentration in one channel of left prefrontal lobe increased with driving duration in significant correlation. And the spatial pattern of hemodynamic response in the prefrontal lobe varied with driving duration as well. The findings indicated the potential of fNIRSmeasured hemodynamic index in some sensitive spot of prefrontal lobe as a driving fatigue indicator and the promising use of fNIRS in traffic safety field.

  19. Low cycle fatigue life of two nickel-base casting alloys in a hydrogen environment

    International Nuclear Information System (INIS)

    Cooper, R.A.

    1976-01-01

    Results of low cycle fatigue tests on alloy Mar-M-246 and Inconel 713 are presented. Based on the limited data, it was concluded that the Mar-M-246 material had a cyclic life in hydrogen that averaged three times higher than the alloy 713LC material for similar strain ranges. The hydrogen environment reduced life for both materials. The life reduction was more than an order of magnitude for the 713LC material. Porosity content of the cast specimens was as expected and was an important factor governing low cycle fatigue life

  20. Research on driver fatigue detection

    Science.gov (United States)

    Zhang, Ting; Chen, Zhong; Ouyang, Chao

    2018-03-01

    Driver fatigue is one of the main causes of frequent traffic accidents. In this case, driver fatigue detection system has very important significance in avoiding traffic accidents. This paper presents a real-time method based on fusion of multiple facial features, including eye closure, yawn and head movement. The eye state is classified as being open or closed by a linear SVM classifier trained using HOG features of the detected eye. The mouth state is determined according to the width-height ratio of the mouth. The head movement is detected by head pitch angle calculated by facial landmark. The driver's fatigue state can be reasoned by the model trained by above features. According to experimental results, drive fatigue detection obtains an excellent performance. It indicates that the developed method is valuable for the application of avoiding traffic accidents caused by driver's fatigue.

  1. Optical Structural Health Monitoring Device

    Science.gov (United States)

    Buckner, Benjamin D.; Markov, Vladimir; Earthman, James C.

    2010-01-01

    This non-destructive, optical fatigue detection and monitoring system relies on a small and unobtrusive light-scattering sensor that is installed on a component at the beginning of its life in order to periodically scan the component in situ. The method involves using a laser beam to scan the surface of the monitored component. The device scans a laser spot over a metal surface to which it is attached. As the laser beam scans the surface, disruptions in the surface cause increases in scattered light intensity. As the disruptions in the surface grow, they will cause the light to scatter more. Over time, the scattering intensities over the scanned line can be compared to detect changes in the metal surface to find cracks, crack precursors, or corrosion. This periodic monitoring of the surface can be used to indicate the degree of fatigue damage on a component and allow one to predict the remaining life and/or incipient mechanical failure of the monitored component. This wireless, compact device can operate for long periods under its own battery power and could one day use harvested power. The prototype device uses the popular open-source TinyOS operating system on an off-the-shelf Mica2 sensor mote, which allows wireless command and control through dynamically reconfigurable multi-node sensor networks. The small size and long life of this device could make it possible for the nodes to be installed and left in place over the course of years, and with wireless communication, data can be extracted from the nodes by operators without physical access to the devices. While a prototype has been demonstrated at the time of this reporting, further work is required in the system s development to take this technology into the field, especially to improve its power management and ruggedness. It should be possible to reduce the size and sensitivity as well. Establishment of better prognostic methods based on these data is also needed. The increase of surface roughness with

  2. Continuum damage mechanics based approach to the fatigue life prediction of cast aluminium alloy with considering the effect of porosity

    Directory of Open Access Journals (Sweden)

    Wang Xiaojia

    2018-01-01

    Full Text Available A damage mechanics based approach is applied for the study of fatigue behaviour of high pressure die cast ADC12 aluminium alloy. A damage coupled elastoplastic constitutive model is presented according to the concept of effective stress and the hypothesis of strain equivalence. An elastic fatigue damage model taking into account the pore-induced stress concentration is developed to investigate fatigue damage evolution of the specimens subjected to cyclic loading. The predicted lives for the specimens with different sizes of pores are consistent with the experimental data. The pore-induced fatigue damage and the variation of fatigue life along with the size of pores are also investigated.

  3. Influence of fatigue time and level on increases in postural sway.

    Science.gov (United States)

    Pline, Kevin M; Madigan, Michael L; Nussbaum, Maury A

    2006-12-15

    The purpose of this study was to investigate the influence of fatigue time and fatigue level on the increases in postural sway during quiet standing. Centre of pressure-based measures of postural sway were collected both before and after fatiguing participants using three different fatigue levels and two different fatigue times. Results showed increasing fatigue time increased sway velocity and sway area, and increasing fatigue level increased sway velocity. Fatigue time effects are important to consider when applying laboratory-based findings to the field given that the fatigue time can differ substantially between the two. Fatigue level effects imply a dose - response relationship between localized muscle fatigue and risk of falling that can have important implications in work/rest cycle scheduling for occupations at risk of injurious falls.

  4. Towards a unified fatigue life prediction method for marine structures

    CERN Document Server

    Cui, Weicheng; Wang, Fang

    2014-01-01

    In order to apply the damage tolerance design philosophy to design marine structures, accurate prediction of fatigue crack growth under service conditions is required. Now, more and more people have realized that only a fatigue life prediction method based on fatigue crack propagation (FCP) theory has the potential to explain various fatigue phenomena observed. In this book, the issues leading towards the development of a unified fatigue life prediction (UFLP) method based on FCP theory are addressed. Based on the philosophy of the UFLP method, the current inconsistency between fatigue design and inspection of marine structures could be resolved. This book presents the state-of-the-art and recent advances, including those by the authors, in fatigue studies. It is designed to lead the future directions and to provide a useful tool in many practical applications. It is intended to address to engineers, naval architects, research staff, professionals and graduates engaged in fatigue prevention design and survey ...

  5. Translating Fatigue to Human Performance

    Science.gov (United States)

    Enoka, Roger M.; Duchateau, Jacques

    2016-01-01

    Despite flourishing interest in the topic of fatigue—as indicated by the many presentations on fatigue at the 2015 annual meeting of the American College of Sports Medicine—surprisingly little is known about its impact on human performance. There are two main reasons for this dilemma: (1) the inability of current terminology to accommodate the scope of the conditions ascribed to fatigue, and (2) a paucity of validated experimental models. In contrast to current practice, a case is made for a unified definition of fatigue to facilitate its management in health and disease. Based on the classic two-domain concept of Mosso, fatigue is defined as a disabling symptom in which physical and cognitive function is limited by interactions between performance fatigability and perceived fatigability. As a symptom, fatigue can only be measured by self-report, quantified as either a trait characteristic or a state variable. One consequence of such a definition is that the word fatigue should not be preceded by an adjective (e.g., central, mental, muscle, peripheral, and supraspinal) to suggest the locus of the changes responsible for an observed level of fatigue. Rather, mechanistic studies should be performed with validated experimental models to identify the changes responsible for the reported fatigue. As indicated by three examples (walking endurance in old adults, time trials by endurance athletes, and fatigue in persons with multiple sclerosis) discussed in the review, however, it has proven challenging to develop valid experimental models of fatigue. The proposed framework provides a foundation to address the many gaps in knowledge of how laboratory measures of fatigue and fatigability impact real-world performance. PMID:27015386

  6. Fatigue Reliability Analysis of Wind Turbine Cast Components

    DEFF Research Database (Denmark)

    Rafsanjani, Hesam Mirzaei; Sørensen, John Dalsgaard; Fæster, Søren

    2017-01-01

    .) and to quantify the relevant uncertainties using available fatigue tests. Illustrative results are presented as obtained by statistical analysis of a large set of fatigue data for casted test components typically used for wind turbines. Furthermore, the SN curves (fatigue life curves based on applied stress......The fatigue life of wind turbine cast components, such as the main shaft in a drivetrain, is generally determined by defects from the casting process. These defects may reduce the fatigue life and they are generally distributed randomly in components. The foundries, cutting facilities and test...... facilities can affect the verification of properties by testing. Hence, it is important to have a tool to identify which foundry, cutting and/or test facility produces components which, based on the relevant uncertainties, have the largest expected fatigue life or, alternatively, have the largest reliability...

  7. Effectiveness of Mindfulness-Based Stress Reduction (MBSR In Stress and Fatigue in Patients with Multiple Sclerosis (MS

    Directory of Open Access Journals (Sweden)

    Ebrahimi Alisaleh

    2016-07-01

    Full Text Available Multiple sclerosis (MS disease can lead to creation of mental and behavioral disorders such as stress and fatigue. Controlling the problems in patients is essential. Hence, this study has considered effectiveness of mindfulnessbased stress reduction in stress and fatigue symptoms in patients with multiple sclerosis (MS.this study is in kind of semi-experimental research in form of pretest posttest pattern with control group. Statistical population of the study consists of all patients with multiple sclerosis referred to Iran MS Association by 2016. Sampling method in this study is available sampling and based on having inclusion criteria. among patients who gained point higher than 21.8 in stress inventory and point higher than 5.1 in fatigue inventory, 30 people are selected as sample randomly and are placed in 2 groups with 15 people in each group. The experimental group was placed under mindfulnessbased stress reduction (MBSR training course including 8 sessions with 2hrs per session. k\\however, no intervention was done in control group. All patients in experimental and control groups fulfilled stress and fatigue inventories before and after intervention. obtained data was analyzed using MANCOVA and in SPSS22 software. obtained results show that there is significant difference between the two groups in terms of stress and fatigue after intervention (p<0.001.according to obtained results, it could be found that treatment method of mindfulness-based stress reduction can help reduction of symptoms of stress and fatigue in patients with MS.

  8. Numerical analysis of rolling contact fatigue crack initiation and fatigue life prediction of the railway crossing

    OpenAIRE

    Xin, L.; Markine, V.L.; Shevtsov, I.

    2015-01-01

    The procedure for analysing rolling contact fatigue crack initiation and fatigue life prediction of the railway turnout crossing is developed. A three-dimensional finite element (FE) model is used to obtain stress and strain results, considering the dynamic effects of wheel-crossing rolling contact. Material model accounting for elastic- plastic isotropic and kinematic hardening effects is adopted. The results from FE analysis are combined with J-S fatigue model that is based on critical plan...

  9. Preparing Safety Cases for Operating Outside Prescriptive Fatigue Risk Management Regulations.

    Science.gov (United States)

    Gander, Philippa; Mangie, Jim; Wu, Lora; van den Berg, Margo; Signal, Leigh; Phillips, Adrienne

    2017-07-01

    Transport operators seeking to operate outside prescriptive fatigue management regulations are typically required to present a safety case justifying how they will manage the associated risk. This paper details a method for constructing a successful safety case. The method includes four elements: 1) scope (prescriptive rules and operations affected); 2) risk assessment; 3) risk mitigation strategies; and 4) monitoring ongoing risk. A successful safety case illustrates this method. It enables landing pilots in 3-pilot crews to choose the second or third in-flight rest break, rather than the regulatory requirement to take the third break. Scope was defined using a month of scheduled flights that would be covered (N = 4151). These were analyzed in the risk assessment using existing literature on factors affecting fatigue to estimate the maximum time awake at top of descent and sleep opportunities in each break. Additionally, limited data collected before the new regulations showed that pilots flying at landing chose the third break on only 6% of flights. A prospective survey comparing subjective reports (N = 280) of sleep in the second vs. third break and fatigue and sleepiness ratings at top of descent confirmed that the third break is not consistently superior. The safety case also summarized established systems for fatigue monitoring, risk assessment and hazard identification, and multiple fatigue mitigation strategies that are in place. Other successful safety cases have used this method. The evidence required depends on the expected level of risk and should evolve as experience with fatigue risk management systems builds.Gander P, Mangie J, Wu L, van den Berg M, Signal L, Phillips A. Preparing safety cases for operating outside prescriptive fatigue risk management regulations. Aerosp Med Hum Perform. 2017; 88(7):688-696.

  10. Fatigue crack growth in welded joints in seawater

    Energy Technology Data Exchange (ETDEWEB)

    Lambert, S.B.

    1988-01-01

    A pipe-to-plate specimen has been developed to study the influence of seawater on the fatigue behaviour of welded tubular joints. DC potential drop techniques have been used to detect fatigue crack initiation, and to monitor the subsequent growth of fatigue cracks. Results for three specimens, tested in air are compared with similar data for tubular and T-plate joints. These comparisons indicate that the pipe/plate is a reasonable model of a tubular joint. Testing was performed on a further six specimens in artificial seawater; two each with free corrosion, optimum cathodic protection, and cathodic overprotection. Fatigue life reduction factors compared with corresponding tests in air were 1.8 and 2.8 for free corrosion, 1.7 and 1.1 with cathodic protection, and 4.2 and 3.3 with cathodic over-protection. These fatigue life reduction factors were comparable to results on T-plate specimens, and were strongly dependent on crack shape development. Linear elastic fracture mechanics techniques appear suitable for the calculation of fatigue crack propagation life. Three approximate solution techniques for crack tip stress intensity factors show reasonable agreement with experimentally derived values. It is recommended that forcing functions be used to model crack aspect ratio development in welded joints. Such forcing functions are influenced by the initial stress distribution and the environment. 207 refs., 192 figs., 22 tabs.

  11. Designing Fatigue Warning Systems: The perspective of professional drivers.

    Science.gov (United States)

    Meng, Fanxing; Li, Shuling; Cao, Lingzhi; Peng, Qijia; Li, Musen; Wang, Chunhui; Zhang, Wei

    2016-03-01

    Professional drivers have been characterized as experiencing heavy fatigue resulting from long driving time in their daily work. This study aimed to explore the potential demand of Fatigue Warning Systems (FWSs) among professional drivers as a means of reducing the danger of fatigue driving and to examine their opinions regarding the design of FWSs. Six focus groups with 35 participants and a questionnaire survey with 600 respondents were conducted among Chinese truck and taxi drivers to collect qualitative and quantitative data concerning the current situation of fatigue driving and opinions regarding the design of FWSs. The results revealed that both truck and taxi drivers had a positive attitude toward FWSs, and they hoped this system could not only monitor and warn them regarding their fatigue but also somewhat relieve their fatigue before they could stop and rest. As for warning signals, participants preferred auditory warnings, as opposed to visual, vibrotactile or electric stimuli. Interestingly, it was proposed that verbal warnings involving the information regarding consequences of fatigue driving or the wishes of drivers' family members would be more effective. Additionally, different warning patterns, including graded, single and continuous warnings, were discussed in the focus group. Finally, the participants proposed many other suggestions, as well as their concerns regarding FWSs, which will provide valuable information for companies who wish to develop FWSs for professional drivers. Copyright © 2015. Published by Elsevier Ltd.

  12. The Nature of Fatigue in Chronic Fatigue Syndrome.

    Science.gov (United States)

    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. © The Author(s) 2015.

  13. Positron lifetime measurements as a non-destructive technique to monitor fatigue damage

    International Nuclear Information System (INIS)

    Byrne, J.G.

    1975-09-01

    In the fatigue cycling of initially hard copper, self consistent positron lifetime and x-ray particle size measurements followed the softening process and revealed a new feature which may be the final development of microvoids before fracture. In the cyclic fatigue of initially soft 4340 steel closely spaced concurrent measurements of these parameters are now in progress. For initially hard 4340 steel fatigue softening was revealed with a large positron lifetime decrease. In hydrogen embrittlement studies positron lifetime was found to be sensitive to hydrogen in an interesting way, i.e., if a specimen is already at its maximum defect density, hydrogen is trapped at some of the defects, reduce their attraction for positrons and hence cause a decrease in positron lifetime; conversely in a soft specimen, hydrogen generates more dislocation length than it can trap at (thus cancelling) hence a positron lifetime increase occurs. In electron irradiated and annealed single crystal copper 4 annealing peaks were seen at 125, 270, 400, and 650 0 K. A clear correlation between decreasing positron lifetime and increasing percent porosity in α alumina was established. This behavior is quite []he opposite to that in metals. (auth)

  14. Individual Patterns in Blood-Borne Indicators of Fatigue-Trait or Chance.

    Science.gov (United States)

    Julian, Ross; Meyer, Tim; Fullagar, Hugh H K; Skorski, Sabrina; Pfeiffer, Mark; Kellmann, Michael; Ferrauti, Alexander; Hecksteden, Anne

    2017-03-01

    Julian, R, Meyer, T, Fullagar, HHK, Skorski, S, Pfeiffer, M, Kellmann, M, Ferrauti, A, and Hecksteden, A. Individual patterns in blood-borne indicators of fatigue-trait or chance. J Strength Cond Res 31(3): 608-619, 2017-Blood-borne markers of fatigue such as creatine kinase (CK) and urea (U) are widely used to fine-tune training recommendations. However, predictive accuracy is low. A possible explanation for this dissatisfactory characteristic is the propensity of athletes to react to different patterns of fatigue indicators (e.g., predominantly muscular [CK] or metabolic [U]). The aim of the present trial was to explore this hypothesis by using repetitive fatigue-recovery cycles. A total of 22 elite junior swimmers and triathletes (18 ± 3 years) were monitored for 9 weeks throughout 2 training phases (low-intensity, high-volume [LIHV] and high-intensity, low-volume [HILV] phases). Blood samples were collected each Monday (recovered) and Friday (fatigued) morning. From measured values of CK, U, free-testosterone (FT), and cortisol (C) as determined in the rested and fatigued state, respectively, Monday-Friday differences (Δ) were calculated and classified by magnitude before calculation of ratios (ΔCK/ΔU and ΔFT/ΔC). Coefficient of variation (CV) was calculated as group-based estimates of reproducibility. Linear mixed modeling was used to differentiate inter- and intraindividual variability. Consistency of patterns was analyzed by comparing with threshold values (1.1 for all weeks). Reproducibility was very low for fatigue-induced changes (CV ≥ 100%) with interindividual variation accounting for 45-60% of overall variability. Case-wise analysis indicated consistent ΔCK/ΔU patterns for 7 individuals in LIHV and 7 in HILV; 5 responded consistently throughout. For ΔFT/ΔC the number of consistent patterns was 2 in LIHV and 3 in HILV. These findings highlight the potential value of an individualized and multivariate approach in the assessment of fatigue.

  15. Performance Demands in Softball Pitching: A Comprehensive Muscle Fatigue Study.

    Science.gov (United States)

    Corben, Jeffrey S; Cerrone, Sara A; Soviero, Julie E; Kwiecien, Susan Y; Nicholas, Stephen J; McHugh, Malachy P

    2015-08-01

    Monitoring pitch count is standard practice in minor league baseball but not in softball because of the perception that fast-pitch softball pitching is a less stressful motion. To examine muscle fatigue after fast-pitch softball performances to provide an assessment of performance demand. Descriptive laboratory study. Bilateral strength measurements (handheld dynamometer) were made on 19 female softball pitchers (mean age [±SD], 15.2 ± 1.2 years) before and after pitching a game (mean number of pitches, 99 ± 21; mean innings pitched, 5 ± 1). A total of 20 tests were performed on the dominant and nondominant sides: forearm (grip, wrist flexion/extension, pronation/supination, elbow flexion/extension), shoulder (flexion, abduction/adduction, external/internal rotation, empty can test), scapula (middle/lower trapezius, rhomboid), and hip (hip flexion/extension, abduction/adduction). Fatigue (percentage strength loss) was categorized based on bilateral versus unilateral presentation using paired t tests: bilateral symmetric (significant on dominant and nondominant and not different between sides), bilateral asymmetric (significant on dominant and nondominant but significantly greater on dominant), unilateral asymmetric (significant on dominant only and significantly greater than nondominant), or unilateral equivocal (significant on dominant only but not different from nondominant). Bilateral symmetric fatigue was evident for all hip (dominant, 19.3%; nondominant, 15.2%) and scapular tests (dominant, 19.2%; nondominant, 19.3%). In general, shoulder tests exhibited bilateral asymmetric fatigue (dominant, 16.9%; nondominant, 11.6%). Forearm tests were more variable, with bilateral symmetric fatigue in the elbow flexors (dominant, 22.5%; nondominant, 19.2%), and wrist flexors (dominant, 21.6%; nondominant, 19.0%), bilateral asymmetric fatigue in the supinators (dominant, 21.8%; nondominant, 15.5%), unilateral asymmetric fatigue in the elbow extensors (dominant, 22

  16. Experimental Study on Fatigue Performance of Foamed Lightweight Soil

    Science.gov (United States)

    Qiu, Youqiang; Yang, Ping; Li, Yongliang; Zhang, Liujun

    2017-12-01

    In order to study fatigue performance of foamed lightweight soil and forecast its fatigue life in the supporting project, on the base of preliminary tests, beam fatigue tests on foamed lightweight soil is conducted by using UTM-100 test system. Based on Weibull distribution and lognormal distribution, using the mathematical statistics method, fatigue equations of foamed lightweight soil are obtained. At the same time, according to the traffic load on real road surface of the supporting project, fatigue life of formed lightweight soil is analyzed and compared with the cumulative equivalent axle loads during the design period of the pavement. The results show that even the fatigue life of foamed lightweight soil has discrete property, the linear relationship between logarithmic fatigue life and stress ratio still performs well. Especially, the fatigue life of Weibull distribution is more close to that derived from the lognormal distribution, in the instance of 50% guarantee ratio. In addition, the results demonstrated that foamed lightweight soil as subgrade filler has good anti-fatigue performance, which can be further adopted by other projects in the similar research domain.

  17. Above-knee prosthesis design based on fatigue life using finite element method and design of experiment.

    Science.gov (United States)

    Phanphet, Suwattanarwong; Dechjarern, Surangsee; Jomjanyong, Sermkiat

    2017-05-01

    The main objective of this work is to improve the standard of the existing design of knee prosthesis developed by Thailand's Prostheses Foundation of Her Royal Highness The Princess Mother. The experimental structural tests, based on the ISO 10328, of the existing design showed that a few components failed due to fatigue under normal cyclic loading below the required number of cycles. The finite element (FE) simulations of structural tests on the knee prosthesis were carried out. Fatigue life predictions of knee component materials were modeled based on the Morrow's approach. The fatigue life prediction based on the FE model result was validated with the corresponding structural test and the results agreed well. The new designs of the failed components were studied using the design of experimental approach and finite element analysis of the ISO 10328 structural test of knee prostheses under two separated loading cases. Under ultimate loading, knee prosthesis peak von Mises stress must be less than the yield strength of knee component's material and the total knee deflection must be lower than 2.5mm. The fatigue life prediction of all knee components must be higher than 3,000,000 cycles under normal cyclic loading. The design parameters are the thickness of joint bars, the diameter of lower connector and the thickness of absorber-stopper. The optimized knee prosthesis design meeting all the requirements was recommended. Experimental ISO 10328 structural test of the fabricated knee prosthesis based on the optimized design confirmed the finite element prediction. Copyright © 2017 IPEM. Published by Elsevier Ltd. All rights reserved.

  18. Time-dependent high-temperature low-cycle fatigue behavior of nickel-base heat-resistant alloys for HTGR

    International Nuclear Information System (INIS)

    Tsuji, Hirokazu; Kondo, Tatsuo

    1988-06-01

    A series of strain controlled low-cycle fatigue tests at 900 deg C in the simulated HTGR helium environment were conducted on Hastelloy X and its modified version, Hastelloy XR in order to examine time-dependent high-temperature low-cycle fatigue behavior. In the tests with the symmetric triangular strain waveform, decreasing the strain rate led to notable reductions in the fatigue life. In the tests with the trapezoidal strain waveform with different holding types, the fatigue life was found to be reduced most effectively in tensile hold-time experiments. Based on the observations of the crack morphology the strain holding in the compressive side was suggested to play the role of suppressing the initiation and the growth of internal cracks or cavities, and to cause crack branching. When the frequency modified fatigue life method and/or the prediction of life by use of the ductility were applied, both the data obtained with the symmetric triangular strain waveform and those with the tensile hold-time experiments lay on the straight line plots. The data, however, obtained with the compressive and/or both hold-time experiments could not be handled satisfactorily by those methods. When the cumulative damage rule was applied, it was found that the reliability of HTGR components was ensured by limiting the creep-fatigue damage fraction within the value of 1. (author)

  19. Out-of-pile fatigue tests on Zircaloy CANDU sheaths

    International Nuclear Information System (INIS)

    Roth, Maria; Ciocanescu, Marin; Gheorghiu, Constantin; Pitigoi, Vasile; Ducu, Catalin; Malinovschi, Viorel

    2005-01-01

    The paper outlines the achievements in the nuclear research field of cooperation on Nuclear Fuel performed as part of the collaboration under the Memorandum of Understanding, settled between Atomic Energy of Canada Limited (AECL) and Institute for Nuclear Research (ICN), The sheath behavior was simulated using out-of-pile fatigue tests, in conditions identical with those met during the operation in power cycling of CANDU reactor, except for irradiation. A special test rig, designed and carried-out at ICN ensured the experimental requirements according to the Canadian testing procedure. The description of the experimental setup and monitoring of testing parameters were also done. The fatigue life time, expressed as number of cycles to rupture (N), was measured as a function of the total strain amplitude (e) induced in the Zircaloy-4 sheath samples. Strain-Life time fatigue dependence (e-N) under low cycle fatigue conditions was also verified using the Coffin-Manson correlation. (authors)

  20. An approach for the fatigue estimation of porous cast iron based on non-destructive testing results

    Directory of Open Access Journals (Sweden)

    Heinrietz André

    2014-06-01

    Full Text Available Big cast iron components made of spheroidal cast iron allow constructing big structures such as stone mills, engine blocks or wind mills with acceptable expenses. Thus, in economically optimized cast processes pores cannot be always prevented in thick walled cast iron components and these components are often rejected because of safety reasons. On the one hand the fatigue performance of high loadable spheroidal cast iron components is reduced significantly by the presence of local porosities which has been pointed out in the past. On the other hand concepts for the fatigue estimation based on fracture mechanics which take the size and localization of the defect into account can lead to erroneous estimations because the defect is modelled as a crack. The challenge of an estimation method is to derive a fatigue life without the necessity to perform component tests. In the contribution an estimation method is presented which is able to determine the fatigue strength of a material volume taking the pores into account. The method can be applied based on data from computer tomographic X-ray (CT or Sampling Phased Array (SPA ultrasonic analyses. The method is presented for three spheroidal cast iron types: ferritic GJS-400-18, ferritic GJS-450-15 with high silicon content and perlitic GJS-700-3.

  1. Risk-Based Operation and Maintenance Using Bayesian Networks

    DEFF Research Database (Denmark)

    Nielsen, Jannie Jessen; Sørensen, John Dalsgaard

    2011-01-01

    This paper describes how risk-based decision making can be used for maintenance planning of components exposed to degradation such as fatigue in offshore wind turbines. In fatigue models, large epistemic uncertainties are usually present. These can be reduced if monitoring results are used to upd...

  2. Fatigue damage assessment under multi-axial non-proportional cyclic loading

    International Nuclear Information System (INIS)

    Mohta, Keshav; Gupta, Suneel K.; Jadhav, P.A.; Bhasin, V.; Vijayan, P.K.

    2016-01-01

    Detailed fatigue analysis is carried out for class I Nuclear Power Plant (NPP) components to rule out the fatigue failure during their design lifetime. ASME Boiler and Pressure Vessel code Section III NB, has provided two schemes for fatigue assessment, one for fixed principal directions (proportional) loading and the other for varying principal directions (non-proportional) loading conditions. Recent literature on multi-axial fatigue tests has revealed lower fatigue lives under nonproportional loading conditions. In an attempt to understand the loading parameter lowering the fatigue life, a finite element based study has been carried out. Here, fatigue damage in a tube has been correlated with the applied axial to shear strain ratio and phase difference between them. The FE analysis has used Chaboche nonlinear kinematic hardening rule to model material's realistic cyclic plastic deformation behavior. The ASME alternating stress intensity (based on linear elastic FEA) and the plastic strain energy dissipation (based on elastic-plastic FEA) have been considered to assess the per cycle fatigue damage. The study has revealed that ASME criteria predicts lower alternating stress intensity (fatigue damage parameter S alt ) for some cases of non-proportional loading than that predicted for corresponding proportional loading case. However, the actual fatigue damage is higher in non-proportional loading than that in corresponding proportional loading case. Further the fatigue damage of an NPP component under realistic multi-axial cyclic loading conditions has been assessed using some popular critical plane based models vis-à-vis ASME Sec. III criteria. (author)

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

    Science.gov (United States)

    Arakere, Nagaraj K.; Swanson, Gregory R.

    2000-01-01

    High Cycle Fatigue (HCF) induced failures in aircraft gas-turbine engines is a pervasive problem affecting a wide range of components and materials. HCF is currently the primary cause of component failures in gas turbine aircraft engines. Turbine blades in high performance aircraft and rocket engines are increasingly being made of single crystal nickel superalloys. Single-crystal Nickel-base superalloys were developed to provide superior creep, stress rupture, melt resistance and thermomechanical fatigue capabilities over polycrystalline alloys previously used in the production of turbine blades and vanes. Currently the most widely used single crystal turbine blade superalloys are PWA 1480/1493 and PWA 1484. These alloys play an important role in commercial, military and space propulsion systems. PWA1493, identical to PWA1480, but with tighter chemical constituent control, is used in the NASA SSME (Space Shuttle Main Engine) alternate turbopump, a liquid hydrogen fueled rocket engine. Objectives for this paper are motivated by the need for developing failure criteria and fatigue life evaluation procedures for high temperature single crystal components, using available fatigue data and finite element modeling of turbine blades. Using the FE (finite element) stress analysis results and the fatigue life relations developed, the effect of variation of primary and secondary crystal orientations on life is determined, at critical blade locations. The most advantageous crystal orientation for a given blade design is determined. Results presented demonstrates that control of secondary and primary crystallographic orientation has the potential to optimize blade design by increasing its resistance to fatigue crack growth without adding additional weight or cost.

  4. Fatigue Crack Propagation Under Variable Amplitude Loading Analyses Based on Plastic Energy Approach

    Directory of Open Access Journals (Sweden)

    Sofiane Maachou

    2014-04-01

    Full Text Available Plasticity effects at the crack tip had been recognized as “motor” of crack propagation, the growth of cracks is related to the existence of a crack tip plastic zone, whose formation and intensification is accompanied by energy dissipation. In the actual state of knowledge fatigue crack propagation is modeled using crack closure concept. The fatigue crack growth behavior under constant amplitude and variable amplitude loading of the aluminum alloy 2024 T351 are analyzed using in terms energy parameters. In the case of VAL (variable amplitude loading tests, the evolution of the hysteretic energy dissipated per block is shown similar with that observed under constant amplitude loading. A linear relationship between the crack growth rate and the hysteretic energy dissipated per block is obtained at high growth rates. For lower growth rates values, the relationship between crack growth rate and hysteretic energy dissipated per block can represented by a power law. In this paper, an analysis of fatigue crack propagation under variable amplitude loading based on energetic approach is proposed.

  5. An Artificial Neural Network-Based Algorithm for Evaluation of Fatigue Crack Propagation Considering Nonlinear Damage Accumulation.

    Science.gov (United States)

    Zhang, Wei; Bao, Zhangmin; Jiang, Shan; He, Jingjing

    2016-06-17

    In the aerospace and aviation sectors, the damage tolerance concept has been applied widely so that the modeling analysis of fatigue crack growth has become more and more significant. Since the process of crack propagation is highly nonlinear and determined by many factors, such as applied stress, plastic zone in the crack tip, length of the crack, etc. , it is difficult to build up a general and flexible explicit function to accurately quantify this complicated relationship. Fortunately, the artificial neural network (ANN) is considered a powerful tool for establishing the nonlinear multivariate projection which shows potential in handling the fatigue crack problem. In this paper, a novel fatigue crack calculation algorithm based on a radial basis function (RBF)-ANN is proposed to study this relationship from the experimental data. In addition, a parameter called the equivalent stress intensity factor is also employed as training data to account for loading interaction effects. The testing data is then placed under constant amplitude loading with different stress ratios or overloads used for model validation. Moreover, the Forman and Wheeler equations are also adopted to compare with our proposed algorithm. The current investigation shows that the ANN-based approach can deliver a better agreement with the experimental data than the other two models, which supports that the RBF-ANN has nontrivial advantages in handling the fatigue crack growth problem. Furthermore, it implies that the proposed algorithm is possibly a sophisticated and promising method to compute fatigue crack growth in terms of loading interaction effects.

  6. Metal magnetic memory technique used to predict the fatigue crack propagation behavior of 0.45%C steel

    Energy Technology Data Exchange (ETDEWEB)

    Chongchong, Li [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China); Lihong, Dong, E-mail: lihong.dong@126.com [National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China); Haidou, Wang [National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China); Guolu, Li [School of Materials Science and Engineering, Hebei University of Technology, Tianjin 300130 (China); Binshi, Xu [National Key Lab for Remanufacturing, Academy of Armored Forces Engineering, Beijing 100072 (China)

    2016-05-01

    Monitoring fatigue crack propagation behavior of ferromagnetic components is very important. In this paper, the tension–tension fatigue tests of center cracked tension (CCT) specimens were carried out; the variation regularity of both tangential and normal components of magnetic signals during fatigue process were investigated. The results showed that the initial abnormal signals which appeared at the notch were reversed after cyclic loading. The abnormal magnetic signals became more significant with the increase of fatigue cycles and reversed again after failure. The characteristic parameters, i.e., the peak value of tangential component, B{sub tp}, and maximum gradient value of normal component, K{sub m}, showed similar variation trends during the fatigue process, which can be divided into three different stages. An approximate linear relationship was found between the characteristic parameters and fatigue crack length 2a. The feasibility of predicting the fatigue crack propagation using the abnormal magnetic signals was discussed. What's more, the variation and distribution of the magnetic signals were also analyzed based on the theory of magnetic charge. - Highlights: • A novel and passive NDT method, i.e. MMMT method, is proposed. • Both tangential and normal components of magnetic signals were investigated. • The prediction of crack propagation by abnormal magnetic signals was discussed. • A linear relationship was found between the parameters and fatigue crack length 2a. • The parameters can be potentially used to evaluate the crack propagation state.

  7. Creep fatigue assessment for EUROFER components

    Energy Technology Data Exchange (ETDEWEB)

    Özkan, Furkan, E-mail: oezkan.furkan@partner.kit.edu; Aktaa, Jarir

    2015-11-15

    Highlights: • Design rules for creep fatigue assessment are developed to EUROFER components. • Creep fatigue assessment tool is developed in FORTRAN code with coupling MAPDL. • Durability of the HCPB-TBM design is discussed under typical fusion reactor loads. - Abstract: Creep-fatigue of test blanket module (TBM) components built from EUROFER is evaluated based on the elastic analysis approach in ASME Boiler Pressure Vessel Code (BPVC). The required allowable number of cycles design fatigue curve and stress-to-rupture curve to estimate the creep-fatigue damage are used from the literature. Local stress, strain and temperature inputs for the analysis of creep-fatigue damage are delivered by the finite element code ANSYS utilizing the Mechanical ANSYS Parametric Design Language (MAPDL). A developed external FORTRAN code used as a post processor is coupled with MAPDL. Influences of different pulse durations (hold-times) and irradiation on creep-fatigue damage for the preliminary design of the Helium Cooled Pebble Bed Test Blanket Module (HCPB-TBM) are discussed for the First Wall component of the TBM box.

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

    Science.gov (United States)

    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.

  9. Roughness Effects on Fretting Fatigue

    Science.gov (United States)

    Yue, Tongyan; Abdel Wahab, Magd

    2017-05-01

    Fretting is a small oscillatory relative motion between two normal loaded contact surfaces. It may cause fretting fatigue, fretting wear and/or fretting corrosion damage depending on various fretting couples and working conditions. Fretting fatigue usually occurs at partial slip condition, and results in catastrophic failure at the stress levels below the fatigue limit of the material. Many parameters may affect fretting behaviour, including the applied normal load and displacement, material properties, roughness of the contact surfaces, frequency, etc. Since fretting damage is undesirable due to contacting, the effect of rough contact surfaces on fretting damage has been studied by many researchers. Experimental method on this topic is usually focusing on rough surface effects by finishing treatment and random rough surface effects in order to increase fretting fatigue life. However, most of numerical models on roughness are based on random surface. This paper reviewed both experimental and numerical methodology on the rough surface effects on fretting fatigue.

  10. Reliability-based fatigue life estimation of shear riveted connections considering dependency of rivet hole failures

    Directory of Open Access Journals (Sweden)

    Leonetti* Davide

    2018-01-01

    Full Text Available Standards and guidelines for the fatigue design of riveted connections make use of a stress range-endurance (S-N curve based on the net section stress range regardless of the number and the position of the rivets. Almost all tests on which S-N curves are based, are performed with a minimum number of rivets. However, the number of rivets in a row is expected to increase the fail-safe behaviour of the connection, whereas the number of rows is supposed to decrease the theoretical stress concentration at the critical locations, and hence these aspects are not considered in the S-N curves. This paper presents a numerical model predicting the fatigue life of riveted connections by performing a system reliability analysis on a double cover plated riveted butt joint. The connection is considered in three geometries, with different number of rivets in a row and different number of rows. The stress state in the connection is evaluated using a finite element model in which the friction coefficient and the clamping force in the rivets are considered in a deterministic manner. The probability of failure is evaluated for the main plate, and fatigue failure is assumed to be originating at the sides of the rivet holes, the critical locations, or hot-spots. The notch stress approach is applied to assess the fatigue life, considered to be a stochastic quantity. Unlike other system reliability models available in the literature, the evaluation of the probability of failure takes into account the stochastic dependence between the failures at each critical location modelled as a parallel system, which means considering the change of the state of stress in the connection when a ligament between two rivets fails. A sensitivity study is performed to evaluate the effect of the pretension in the rivet and the friction coefficient on the fatigue life.

  11. DOProC-based reliability assessment of steel structures exposed to fatigue

    Czech Academy of Sciences Publication Activity Database

    Krejsa, M.; Janas, P.; Krejsa, V.; Kala, Z.; Seitl, Stanislav

    2016-01-01

    Roč. 7, MARCH (2016), s. 228-235 ISSN 2213-0209 Institutional support: RVO:68081723 Keywords : DOProC * Direct Optimized Probabilistic Calculation * Probabilistic methods * FCProbCalc * Fatigue crack Subject RIV: JL - Materials Fatigue, Friction Mechanics

  12. An Analytical Model for Fatigue Life Prediction Based on Fracture Mechanics and Crack Closure

    DEFF Research Database (Denmark)

    Ibsø, Jan Behrend; Agerskov, Henning

    1996-01-01

    test specimens are compared with fatigue life predictions using a fracture mechanics approach. In the calculation of the fatigue life, the influence of the welding residual stresses and crack closure on the fatigue crack growth is considered. A description of the crack closure model for analytical...... of the analytical fatigue lives. Both the analytical and experimental results obtained show that the Miner rule may give quite unconservative predictions of the fatigue life for the types of stochastic loading studied....... determination of the fatigue life is included. Furthermore, the results obtained in studies of the various parameters that have an influence on the fatigue life, are given. A very good agreement between experimental and analytical results is obtained, when the crack closure model is used in determination...

  13. An Analytical Model for Fatigue Life Prediction Based on Fracture Mechanics and Crack Closure

    DEFF Research Database (Denmark)

    Ibsø, Jan Behrend; Agerskov, Henning

    1996-01-01

    test specimens are compared with fatigue life predictions using a fracture mechanics approach. In the calculation of the fatigue life, the influence of the welding residual stresses and crack closure on the fatigue crack growth is considered. A description of the crack closure model for analytical...... determination of the fatigue life is included. Furthermore, the results obtained in studies of the various parameters that have an influence on the fatigue life, are given. A very good agreement between experimental and analytical results is obtained, when the crack closure model is used in determination...... of the analytical fatigue lives. Both the analytical and experimental results obtained show that the Miner rule may give quite unconservative predictions of the fatigue life for the types of stochastic loading studied....

  14. Characteristic of improved fatigue performance for Zr-based bulk metallic glass matrix composites

    International Nuclear Information System (INIS)

    Qiao, J.W.; Huang, E.W.; Wang, G.Y.; Yang, H.J.; Liang, W.; Zhang, Y.; Liaw, P.K.

    2013-01-01

    Zr 58.5 Ti 14.3 Nb 5.2 Cu 6.1 Ni 4.9 Be 11.0 bulk metallic glass matrix composites exhibit improved four-point-bending fatigue endurance with a fatigue limit of 567 MPa, compared to that under the tension–tension fatigue, due to the high-volume-fractioned dendrites, which can effectively blunt the fatigue-induced cracks. Illuminated by high-energy synchrotron X-ray at 200 and 100 K, the corresponding diffraction peaks, such as (110), (200), and (211) shift rightward to small lattice spacings, compared to those at 298 K. However, the peak widths at 100 K and 200 K are almost identical to that of room temperature. Since an identical fatigue specimen was measured under room temperature, 200 K, and 100 K, the invariant of the peak widths reveal the fact of the irreversible microstructure developments induced by fatigue. Even if the fatigue fracture stress is distinguishingly lower than the yielding strength, the deformation of dendrites locally prevails, evidenced by the occurrence of dislocations

  15. Validation of a Smartphone-Based Approach to In Situ Cognitive Fatigue Assessment

    Science.gov (United States)

    Linden, Mark

    2017-01-01

    The most highly correlated results were from the PVT, which showed a positive correlation with those from the prevalidated MFS, measuring 0.342 (Pcognitive tests were entered into a regression model and showed that only reaction time in the PVT was a significant predictor of fatigue (P=.016, F=2.682, 95% CI 9.0-84.2). Higher scores on the MFS were related to increases in reaction time during our mobile variant of the PVT. Conclusions The results show that the PVT mobile cognitive test developed for this study could be used as a valid and reliable method for measuring cognitive fatigue in situ. This test would remove the subjectivity associated with established self-assessment approaches and the need for assessments to be performed in a medical setting. Based on our findings, future work could explore delivering a small set of tests with increased duration to further improve measurement reliability. Moreover, as the smartphone assessment tool can be used as part of everyday life, additional sources of data relating to physiological, psychological, and environmental context could be included within the analysis to improve the nature and precision of the assessment process. PMID:28818818

  16. Validation of a Smartphone-Based Approach to In Situ Cognitive Fatigue Assessment.

    Science.gov (United States)

    Price, Edward; Moore, George; Galway, Leo; Linden, Mark

    2017-08-17

    were from the PVT, which showed a positive correlation with those from the prevalidated MFS, measuring 0.342 (Ptime in the PVT was a significant predictor of fatigue (P=.016, F=2.682, 95% CI 9.0-84.2). Higher scores on the MFS were related to increases in reaction time during our mobile variant of the PVT. The results show that the PVT mobile cognitive test developed for this study could be used as a valid and reliable method for measuring cognitive fatigue in situ. This test would remove the subjectivity associated with established self-assessment approaches and the need for assessments to be performed in a medical setting. Based on our findings, future work could explore delivering a small set of tests with increased duration to further improve measurement reliability. Moreover, as the smartphone assessment tool can be used as part of everyday life, additional sources of data relating to physiological, psychological, and environmental context could be included within the analysis to improve the nature and precision of the assessment process. ©Edward Price, George Moore, Leo Galway, Mark Linden. Originally published in JMIR Mhealth and Uhealth (http://mhealth.jmir.org), 17.08.2017.

  17. Influences of semiconductor morphology on the mechanical fatigue behavior of flexible organic electronics

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Young-Joo; Yeon, Han-Wool; Shin, Hae-A-Seul; Joo, Young-Chang, E-mail: ycjoo@snu.ac.kr [Department of Materials Science and Engineering, Seoul National University, 151-744 Seoul (Korea, Republic of); Uk Lee, Yong; Evans, Louise A. [Center for Process Innovation Limited, Thomas Wright Way, NETPark, Sedgefield, TS21 3FG County Durham (United Kingdom)

    2013-12-09

    The influence of crystalline morphology on the mechanical fatigue of organic semiconductors (OSCs) was investigated using 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) as a crystalline OSC and poly(triarylamine) (PTAA) as an amorphous OSC. During cyclic bending, resistances of the OSCs were monitored using the transmission-line method on a metal-semiconductor-metal structure. The resistance of the TIPS-pentacene increased under fatigue damage in tensile-stress mode, but no such degradation was observed in the PTAA. Both OSCs were stable under compressive bending fatigue. The formation of intergranular cracks at the domain boundaries of the TIPS-pentacene was responsible for the degradation of its electrical properties under tensile bending fatigue.

  18. Prevalence of Fatigue and Associated Factors in a Spinal Cord Injury Population: Data from an Internet-Based and Face-to-Face Surveys.

    Science.gov (United States)

    Cudeiro-Blanco, Javier; Onate-Figuérez, Ana; Soto-León, Vanesa; Avendaño-Coy, Juan; Mordillo-Mateos, Laura; Brocalero-Camacho, Angela; Esclarin-Ruz, Ana; Rotondi, Mario; Aguilar, Juan; Arias, Pablo; Oliviero, Antonio

    2017-08-01

    Fatigue has a profound impact on patients with spinal cord injury (SCI), but only limited treatments are available. The aim of this study was to determine the prevalence of fatigue in SCI and its association with clinical and demographic factors. We used an internet-based survey and a face-to-face interview to estimate the prevalence of fatigue in a SCI population. Fatigue was measured using the Fatigue Severity Scale (FSS). Clinically significant fatigue was defined as FSS scores greater than or equal to four. A total of 253 participants with SCI were included in the study. Clinically significant fatigue was present in one third of our sample. There was no relationship between fatigue and injury level or completeness. We found significant correlations between depression, pain, and level of injury. The relation of fatigue with completeness of injury and spasticity is less clear. Moreover, the online survey and the standard face-to-face interview showed similar results concerning fatigue evaluation. Several factors may contribute to fatigue, however. Future studies should be conducted to clarify which are the most relevant ones and, if possible, to determine which factors are modifiable.

  19. Visual fatigue modeling for stereoscopic video shot based on camera motion

    Science.gov (United States)

    Shi, Guozhong; Sang, Xinzhu; Yu, Xunbo; Liu, Yangdong; Liu, Jing

    2014-11-01

    As three-dimensional television (3-DTV) and 3-D movie become popular, the discomfort of visual feeling limits further applications of 3D display technology. The cause of visual discomfort from stereoscopic video conflicts between accommodation and convergence, excessive binocular parallax, fast motion of objects and so on. Here, a novel method for evaluating visual fatigue is demonstrated. Influence factors including spatial structure, motion scale and comfortable zone are analyzed. According to the human visual system (HVS), people only need to converge their eyes to the specific objects for static cameras and background. Relative motion should be considered for different camera conditions determining different factor coefficients and weights. Compared with the traditional visual fatigue prediction model, a novel visual fatigue predicting model is presented. Visual fatigue degree is predicted using multiple linear regression method combining with the subjective evaluation. Consequently, each factor can reflect the characteristics of the scene, and the total visual fatigue score can be indicated according to the proposed algorithm. Compared with conventional algorithms which ignored the status of the camera, our approach exhibits reliable performance in terms of correlation with subjective test results.

  20. Evidence-Based Guidelines for Fatigue Risk Management in Emergency Medical Services

    Science.gov (United States)

    2018-01-11

    Background: Administrators of Emergency Medical Services (EMS) operations lack guidance on how to mitigate workplace fatigue, which affects greater than half of all EMS personnel. The primary objective of the Fatigue in EMS Project was to create an e...

  1. Perceived Fatigue Interference and Depressed Mood: Comparison of Chronic Fatigue Syndrome/Myalgic Encephalomyelitis Patients with Fatigued Breast Cancer Survivors.

    Science.gov (United States)

    Hall, Daniel L; Antoni, Michael H; Lattie, Emily G; Jutagir, Devika R; Czaja, Sara J; Perdomo, Dolores; Lechner, Suzanne C; Stagl, Jamie M; Bouchard, Laura C; Gudenkauf, Lisa M; Traeger, Lara; Fletcher, MaryAnn; Klimas, Nancy G

    Persistent fatigue and depressive symptoms are both highly prevalent among patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) as well as breast cancer survivors. This study aimed to assess and directly compare perceptions of fatigue as highly interfering in one's daily functioning in both patient populations to better understand their relationships with depressed mood. Participants were 95 female CFS/ME patients and 67 females who were approximately 5 years post-treatment for stage 0-III breast cancer presenting with clinically elevated fatigue severity. Self-report measures were obtained on participants' fatigue-related interference in daily functioning and fatigue severity as well as depressed mood. Hierarchical regression was used to test effects controlling for relevant demographic, psychosocial, and medical covariates. CFS/ME patients endorsed greater depressed mood and fatigue interference than did fatigued breast cancer survivors, p's fatigued breast cancer survivors (β=.18, p =.19). CFS/ME patients reported elevated fatigue symptoms and depression relative to fatigued breast cancer survivors. In the former group, greater depressed mood was highly and significantly associated with greater fatigue-related inference in daily activities. Potential targets for cognitive behavioral interventions are discussed.

  2. The Identification of Fatigue Resistant and Fatigue Susceptible Individuals

    National Research Council Canada - National Science Library

    Harrison, Richard; Chaiken, Scott; Harville, Donald; Fischer, Joseph; Fisher, Dion; Whitmore, Jeff

    2008-01-01

    The present study was designed to target two specific areas regarding fatigue. The primary purpose was to begin investigations into possible genetic markers linked to fatigue resistance and fatigue susceptibility...

  3. Effect of fatigue testing on the properties of Glass-Epoxy composites using the acoustic tool

    Directory of Open Access Journals (Sweden)

    Menail Younès

    2017-01-01

    Full Text Available This study presents the experimental results of the influence of mechanical fatigue on composite material. The plates of Glass fiber with SR 1500 epoxy resin with SD 2505 composite were realized by vacuum molding. Experimental tests were carried out on a standard hydraulic machine INSTRON 8516. The machine is interfaced with a dedicated computer for controlling and data acquisition. The fatigue tests were performed using sinusoidal type of waveform at a displacement control with frequency of 10 Hz. The evolution of Young’s modulus and strain based on fatigue gives us an idea about the resistance of the material. Degradation of mechanical properties was observed, and the results have showed that the Young’s modulus of plates undergo only minor changes. In fact, the residual stiffness and residual strength decrease when the cycle number of fatigue increase (100 to 50000 cycles, indicating that the studied composites have experienced some forms of mechanical damage.The mechanical tests were backed by Acoustic Emission Monitoring (AEM during the load cycle, in order to understand the nature of the failure process in the composites such as fiber breakage, matrix crazing, matrix debonding and delamination etc.

  4. Beyond pain in fibromyalgia: insights into the symptom of fatigue

    Science.gov (United States)

    2013-01-01

    Fatigue is a disabling, multifaceted symptom that is highly prevalent and stubbornly persistent. Although fatigue is a frequent complaint among patients with fibromyalgia, it has not received the same attention as pain. Reasons for this include lack of standardized nomenclature to communicate about fatigue, lack of evidence-based guidelines for fatigue assessment, and a deficiency in effective treatment strategies. Fatigue does not occur in isolation; rather, it is present concurrently in varying severity with other fibromyalgia symptoms such as chronic widespread pain, unrefreshing sleep, anxiety, depression, cognitive difficulties, and so on. Survey-based and preliminary mechanistic studies indicate that multiple symptoms feed into fatigue and it may be associated with a variety of physiological mechanisms. Therefore, fatigue assessment in clinical and research settings must consider this multi-dimensionality. While no clinical trial to date has specifically targeted fatigue, randomized controlled trials, systematic reviews, and meta-analyses indicate that treatment modalities studied in the context of other fibromyalgia symptoms could also improve fatigue. The Outcome Measures in Rheumatology (OMERACT) Fibromyalgia Working Group and the Patient Reported Outcomes Measurement Information System (PROMIS) have been instrumental in propelling the study of fatigue in fibromyalgia to the forefront. The ongoing efforts by PROMIS to develop a brief fibromyalgia-specific fatigue measure for use in clinical and research settings will help define fatigue, allow for better assessment, and advance our understanding of fatigue. PMID:24289848

  5. Contact fatigue of human enamel: Experiments, mechanisms and modeling.

    Science.gov (United States)

    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. Copyright © 2016 Elsevier Ltd. All rights reserved.

  6. Ex-situ X-ray computed tomography data for a non-crimp fabric based glass fibre composite under fatigue loading

    DEFF Research Database (Denmark)

    Jespersen, Kristine Munk; Mikkelsen, Lars Pilgaard

    2017-01-01

    The data published with this article are high resolution X-ray computed tomography (CT) data obtained during an ex-situ fatigue test of a coupon test specimen made from a non-crimp fabric based glass fibre composite similar to those used for wind turbine blades. The fatigue test was interrupted...

  7. Acoustic Techniques for Structural Health Monitoring

    Science.gov (United States)

    Frankenstein, B.; Augustin, J.; Hentschel, D.; Schubert, F.; Köhler, B.; Meyendorf, N.

    2008-02-01

    Future safety and maintenance strategies for industrial components and vehicles are based on combinations of monitoring systems that are permanently attached to or embedded in the structure, and periodic inspections. The latter belongs to conventional nondestructive evaluation (NDE) and can be enhanced or partially replaced by structural health monitoring systems. However, the main benefit of this technology for the future will consist of systems that can be differently designed based on improved safety philosophies, including continuous monitoring. This approach will increase the efficiency of inspection procedures at reduced inspection times. The Fraunhofer IZFP Dresden Branch has developed network nodes, miniaturized transmitter and receiver systems for active and passive acoustical techniques and sensor systems that can be attached to or embedded into components or structures. These systems have been used to demonstrate intelligent sensor networks for the monitoring of aerospace structures, railway systems, wind energy generators, piping system and other components. Material discontinuities and flaws have been detected and monitored during full scale fatigue testing. This paper will discuss opportunities and future trends in nondestructive evaluation and health monitoring based on new sensor principles and advanced microelectronics. It will outline various application examples of monitoring systems based on acoustic techniques and will indicate further needs for research and development.

  8. A novel in situ device based on a bionic piezoelectric actuator to study tensile and fatigue properties of bulk materials.

    Science.gov (United States)

    Wang, Shupeng; Zhang, Zhihui; Ren, Luquan; Zhao, Hongwei; Liang, Yunhong; Zhu, Bing

    2014-06-01

    In this work, a miniaturized device based on a bionic piezoelectric actuator was developed to investigate the static tensile and dynamic fatigue properties of bulk materials. The device mainly consists of a bionic stepping piezoelectric actuator based on wedge block clamping, a pair of grippers, and a set of precise signal test system. Tensile and fatigue examinations share a set of driving system and a set of signal test system. In situ tensile and fatigue examinations under scanning electron microscope or metallographic microscope could be carried out due to the miniaturized dimensions of the device. The structure and working principle of the device were discussed and the effects of output difference between two piezoelectric stacks on the device were theoretically analyzed. The tensile and fatigue examinations on ordinary copper were carried out using this device and its feasibility was verified through the comparison tests with a commercial tensile examination instrument.

  9. Dynamic fatigue on repolarization of lead zirconate-titanate base ceramics with various ferroelectric hardness

    International Nuclear Information System (INIS)

    Gavrilyachenko, V.G.; Semenchev, A.F.; Sklyarova, E.N.; Kuznetsova, E.M.

    2006-01-01

    One studied experimentally changes of the residual polarization in lead zirconate-titanate base ceramics with various ferroelectric hardness under the effect of a strong varying field. The twinning and untwinning of crystallites accompanying repolarization is assumed to be the basic mechanism of propagation of the crystalline structure defects governing the fatigue rates of the ferroelectric-soft ceramics. In ferroelectric-hard ceramics crystallites the stable configurations of mechanical twins, the result of the secondary twinning, are formed when the hysteresis loop is formed. At repolarization in the mentioned structures one observes no motion of the twin boundaries, and the fatigue rates are low ones [ru

  10. Proceeding of 26th domestic symposium on present and future of integrity monitoring technology in nuclear power generation facilities

    International Nuclear Information System (INIS)

    2000-06-01

    As the 26th domestic symposium of Atomic Energy Research Committee, the Japan Welding Engineering Society, the symposium was held titled as 'Current status and future of integrity monitoring techniques in nuclear power facilities'. Six speakers gave lectures titled as 'Maintenance and integrity monitoring in nuclear power plants', 'Present status of fatigue and creep-fatigue monitoring techniques in the US', 'Fatigue monitoring system in Tsuruga-1 nuclear power station', 'Vibration monitoring technique of rotational machine', 'SCC monitoring with electrochemical noise analysis' and Monitoring technique for corrosive environments and crack shape'. (T. Tanaka)

  11. Fatigue testing of wood composites for aerogenerator blades. Pt. 11: Assessment of fatigue damage accumulation using a fatigue modulus approach

    Energy Technology Data Exchange (ETDEWEB)

    Hacker, C L; Ansell, M P [Bath Univ. (United Kingdom)

    1996-12-31

    Stress-strain hysteresis loops have been captured during fatigue tests performed at R=10 (compression-compression) and R=0.1 (tension-tension) on Khaya epoxy wood composites. A fatigue modulus approach, proposed by Hwang and Han in 1989, has been applied to the data and a relationship established between the initial change in fatigue modulus and fatigue life. By following changes in fatigue modulus during the first 100 test cycles it is possible to predict the life of the sample allowing rapid evaluation of the fatigue performance of wood composites. Fatigue modulus values have also been calculated for hysteresis loops captured during complex load - time history tests. Similar trends in change in fatigue modulus suggest that this approach could be used in complex loading conditions to evaluate fatigue damage accumulation and predict fatigue life. (Author)

  12. Perilaku kekuatan fatigue paduan aluminium seri 2014 akibat proses termomekanikal aging

    Directory of Open Access Journals (Sweden)

    Sujita -

    2012-11-01

    Full Text Available Aluminium alloy seri 2014 is material which is often used in industry. Because excellence of mechanic properties. But also have the weakness at properties of strength fatigue. Though fatigue strength is important parameter in desain, especially if application at condition of dinamic loading, so that need the treatment to improve it. Fatigue strength go together the micro structure and mode of failure of failure of effect of stress concentration. Aging treatment ordinary done not yet given the influence which even on the contrary. Inconsistence of fatigue strength alluminium alloy show the phenomenon which must be research instructing at repair of fatigue strength , so that need the advanced treatment in the form of termomechanical aging. The research conducted by using alluminium alloy series 2014 formed by specimen fatigue test of the size diameter 8 mm and long 87 mm relate at standart (ASTM E 513, continued treatment of termomechanical aging, tested the fatigue, and monitoring microstructure of change. By structure micro, the treatmentTMA have the effect which sicnificant to improvement of Alluminium alloy series 2104 fatigue strength. Generally entire process TMA improve of limit fatigue from specimen at condition early of limit fatigue 48.3 N / mm2 (48.3 MPA, mounting to become 50 until MPA, or mount 3.4 % until 44.9%. With the process of termomechanical aging TMA I, happened the increasing of cycle number equal to, 26.3 %, at treatment of TMA II go up equal to 62 % and 89.8% at process of TMA III, at maximal loading (180 Mpa.

  13. A System of Driving Fatigue Detection Based on Machine Vision and Its Application on Smart Device

    Directory of Open Access Journals (Sweden)

    Wanzeng Kong

    2015-01-01

    Full Text Available Driving fatigue is one of the most important factors in traffic accidents. In this paper, we proposed an improved strategy and practical system to detect driving fatigue based on machine vision and Adaboost algorithm. Kinds of face and eye classifiers are well trained by Adaboost algorithm in advance. The proposed strategy firstly detects face efficiently by classifiers of front face and deflected face. Then, candidate region of eye is determined according to geometric distribution of facial organs. Finally, trained classifiers of open eyes and closed eyes are used to detect eyes in the candidate region quickly and accurately. The indexes which consist of PERCLOS and duration of closed-state are extracted in video frames real time. Moreover, the system is transplanted into smart device, that is, smartphone or tablet, due to its own camera and powerful calculation performance. Practical tests demonstrated that the proposed system can detect driver fatigue with real time and high accuracy. As the system has been planted into portable smart device, it could be widely used for driving fatigue detection in daily life.

  14. Postpartum fatigue in the active-duty military woman.

    Science.gov (United States)

    Rychnovsky, Jacqueline D

    2007-01-01

    (a) To describe fatigue levels in military active-duty women, (b) to describe the relationship among selected predictor variables of fatigue, and (c) to examine the relationship between predictor variables, fatigue levels, and performance (as measured by functional status) after childbirth. Based on the Theory of Unpleasant Symptoms, a longitudinal, prospective design. A large military medical facility in the southwest United States. A convenience sample of 109 military active-duty women. Postpartum fatigue. Women were found to be moderately fatigued across time, with no change in fatigue levels from 2 to 6 weeks after delivery. All variables correlated with fatigue during hospitalization and at 2 weeks after delivery, and depression, anxiety, maternal sleep, and functional status correlated with fatigue at 6 weeks after delivery. Regression analyses indicated that maternal anxiety predicted fatigue at 6 weeks after delivery. Over half the women had not regained full functional status when they returned to work, and 40% still displayed symptoms of postpartum depression and anxiety. Military women continue to experiencing postpartum fatigue when they return to the workplace. Future research is needed to examine issues surrounding fatigue and its associated variables during the first year after delivery.

  15. Piezoelectric Bolt Breakers and Bolt Fatigue Testers

    Science.gov (United States)

    Sherrit, Stewart; Badescu, Mircea; Bar-Cohen, Yoseph; Barengoltz, Jack; Heckman, Vanessa

    2008-01-01

    catastrophic misfire. In fatigue-testing applications, devices of the proposed type would offer advantages of compactness and low cost, relative to conventional fatigue- testing apparatuses. In both structural- separation and fatigue-testing applications, bolts to be broken or tested could be instrumented with additional ultrasonic transducers for monitoring of pertinent physical properties and of fatigue failure processes.

  16. Prevalence of fatigue and chronic fatigue syndrome in a primary care practice.

    Science.gov (United States)

    Bates, D W; Schmitt, W; Buchwald, D; Ware, N C; Lee, J; Thoyer, E; Kornish, R J; Komaroff, A L

    1993-12-27

    Our goals were to determine the prevalence of unusual, debilitating fatigue and the frequency with which it was associated with the chronic fatigue syndrome (CFS) or other physical or psychological illness in an outpatient clinic population. We prospectively evaluated a cohort of 1000 consecutive patients in a primary care clinic in an urban, hospital-based general medicine practice. The study protocol included a detailed history, physical examination, and laboratory and psychiatric testing. Five patients who came because of CFS studies were excluded. Of the remaining 995, 323 reported fatigue, and 271 (27%) complained of at least 6 months of unusual fatigue that interfered with their daily lives. Of the 271, self-report or record review revealed a medical or psychiatric condition that could have explained the fatigue in 186 (69%). Thus, 85 (8.5%) of 995 patients had a debilitating fatigue of at least 6 months' duration, without apparent cause. Of these patients, 48 refused further evaluation, and 11 were unavailable for follow-up; 26 completed the protocol. Three of the 26 were hypothyroid, and one had a major psychiatric disorder. Of the remaining 22 patients, three met Centers for Disease Control and Prevention criteria for CFS, four met British criteria, and 10 met the Australian case definition. The point prevalences of CFS were thus 0.3% (95% confidence interval [CI], 0% to 0.6%), 0.4% (95% CI, 0% to 0.8%), and 1.0% (95% CI, 0.4% to 1.6%) using the Centers for Disease Control and Prevention, British, and Australian case definitions, respectively. These estimates were conservative, because they assumed that none of the patients who refused evaluation or were unavailable for follow-up would meet criteria for CFS. While chronic, debilitating fatigue is common in medical outpatients, CFS is relatively uncommon. Prevalence depends substantially on the case definition used.

  17. Fatigue Life Prediction of Package of Suspension Automotive Under Random Vibration Based on Road Roughness

    Directory of Open Access Journals (Sweden)

    Kazem Reza Kashyzadeh

    2015-09-01

    Full Text Available The impact of a suitable suspension system for passenger comfort and vehicle steering is an obvious order and direct impact on the safety of passengers must be considered, to do so different kinds of tests must be exerted, one of these is fatigue testing which is one of the most significant ones. Another issue is the high cost in practical ways, and to cope with this issue various ways must be assessed and analyzed, one of the best and the most efficient ways is modelling and testing in virtual software environments. In the present paper, predict fatigue life of suspension component and package of automotive suspension are the main purposes. First, using MATLAB software, road roughness according to the intercity roads for constant vehicle velocity (100 Km/h has been studied. After that frequency response of components has been analysed, its critical points determined to calculate the fatigue life of the part, and the amount of critical stress obtained based on Von Misses, Tresca and Max Principle criterion for a quarter car model (passive suspension System in 206 Peugeot. Fatigue life of the vehicle components are calculated in terms of kilo-Meters in specialized fatigue software such as 116944, 92638.9, 46388.9 and 191388.9 Km respectively wheel hub, pitman arm, suspension arm and package of suspension. Finally, to prove the given results of the finite element method compared with reported results by other researchers and the results match very well with those.

  18. Perceived Fatigue Interference and Depressed Mood: Comparison of Chronic Fatigue Syndrome/Myalgic Encephalomyelitis Patients with Fatigued Breast Cancer Survivors

    Science.gov (United States)

    Hall, Daniel L.; Antoni, Michael H.; Lattie, Emily G.; Jutagir, Devika R.; Czaja, Sara J.; Perdomo, Dolores; Lechner, Suzanne C.; Stagl, Jamie M.; Bouchard, Laura C.; Gudenkauf, Lisa M.; Traeger, Lara; Fletcher, MaryAnn; Klimas, Nancy G.

    2015-01-01

    Objective Persistent fatigue and depressive symptoms are both highly prevalent among patients with Chronic Fatigue Syndrome/Myalgic Encephalomyelitis (CFS/ME) as well as breast cancer survivors. This study aimed to assess and directly compare perceptions of fatigue as highly interfering in one’s daily functioning in both patient populations to better understand their relationships with depressed mood. Methods Participants were 95 female CFS/ME patients and 67 females who were approximately 5 years post-treatment for stage 0-III breast cancer presenting with clinically elevated fatigue severity. Self-report measures were obtained on participants’ fatigue-related interference in daily functioning and fatigue severity as well as depressed mood. Hierarchical regression was used to test effects controlling for relevant demographic, psychosocial, and medical covariates. Results CFS/ME patients endorsed greater depressed mood and fatigue interference than did fatigued breast cancer survivors, p’sfatigued breast cancer survivors (β=.18, p=.19). Conclusions CFS/ME patients reported elevated fatigue symptoms and depression relative to fatigued breast cancer survivors. In the former group, greater depressed mood was highly and significantly associated with greater fatigue-related inference in daily activities. Potential targets for cognitive behavioral interventions are discussed. PMID:26180660

  19. Effect of the environment on a SG tube fatigue cracking at Fessenheim unit 2

    International Nuclear Information System (INIS)

    Duisabeau, L.; Fargeas, E.; Miloudi, S.; Leduc, A.; Hollner, S.; Thebault, Y.; Legras, L.; Mansour, C.

    2015-01-01

    In 2008, a primary-to-secondary leak was detected at TSP n8 level, on the tube R12C62 of Fessenheim unit 2 SG3. The leak was associated to a high cycle fatigue crack that was confirmed two years after, when the tube was pulled out for destructive examination. It revealed on the one hand a highly oxidized fracture surface and on the other hand, that the fatigue crack was initiated on small IGA (Intergranular Attack) piles located at the OD (Outside Diameter) surface of the alloy 600MA tube. In order to take into account a potential environmental effect on the fatigue limit of alloy 600MA in mechanical calculations implemented to establish the root cause failure analysis, several investigations were conducted to evaluate the environment at the tube/tubesheet interstice. To achieve this goal, a multi-scale analysis has been performed. It includes a global analysis of the corrosion damage of the SG, the SG chemistry monitoring, an evaluation of the pH in confined areas with MulteQ calculations based on hide out returns, as well as oxides characterization on the tube by Transmission Electronic Microscopy. All methods converge to a slightly neutral pH with pollutants such as copper, lead and sulfates leading to the conclusion that the fatigue limit of alloy 600MA has not been reduced by the chemical environment. All these chemical elements are known to affect in a certain extent the corrosion resistance of the alloy 600 in the secondary water. If all these pollutants can be detected during the global monitoring of the plant during operation or outage (blow down, hideout returns, feed water and sludge chemical analysis), transmission electronic microscopy offers a unique technique for better understanding how these pollutants may react in confined area, corroded area or free span oxides in the alloy 600 and thus for a better understanding of the corrosion mechanism of nickel based alloys in the secondary side

  20. High-cycle fatigue of Ni-base superalloy Inconel 713LC

    Czech Academy of Sciences Publication Activity Database

    Kunz, Ludvík; Lukáš, Petr; Konečná, R.

    2010-01-01

    Roč. 32, č. 6 (2010), s. 908-913 ISSN 0142-1123 R&D Projects: GA MPO FT-TA4/023; GA MŠk MEB080812 Institutional research plan: CEZ:AV0Z20410507 Keywords : IN 713LC * High-cycle fatigue * Effect of mean stress * Fractography * Casting defetcts * Extreme value statistics Subject RIV: JL - Materials Fatigue, Friction Mechanics Impact factor: 1.799, year: 2010

  1. Fatigue of wind turbines in the frequency domain

    Energy Technology Data Exchange (ETDEWEB)

    Bishop, N W.M. [Univ. College London (United Kingdom)

    1996-09-01

    Fatigue damage is traditionally determined from time signals of loading, usually in the form of stress or strain. However, there are three design scenarios when a spectral form of loading is more appropriate. In this case the loading is defined in terms of its magnitude at different frequencies in the form of a Power Spectral Density (PSD) plot. First, the measurement engineer recording responses from in-service components or structures may be interested in PSD`s because they are a efficient way of defining a random stress or strain time history. Secondly, the test engineer assessing the reliability of prototypes may be interested in spectral tools because such an approach allows the structural condition of the component to be monitored by continuous inspection of the system transfer function. However, the most important benefit of working with PSD`s is relevant to the structural analysis or designer because of the more sophisticated analysis options with which they can be use. For all three of these design scenarios the fatigue designer is presented with a PSD of stress or strain with which to perform his fatigue calculation. There is therefore a requirement for a reliable, accurate and robust spectral fatigue design tool. Such a tool allows the designer to estimate the rainflow range content and hence content and hence fatigue damage from the PSD. (EG)

  2. Towards a Mobile Assistive Technology for Monitoring and Assessing Cognitive Fatigue in Individuals with Acquired Brain Injury

    OpenAIRE

    Price, Edward; Moore, George; Galway, Leo; Linden, Mark

    2015-01-01

    Those living with an acquired brain injury often have issues with fatigue due to factors resulting from the injury. Cognitive impairments such as lack of memory, concentration and planning have a great impact on an individual’s ability to carry out general everyday tasks, which subsequently has the effect of inducing cognitive fatigue. Moreover, there is difficulty in assessing cognitive fatigue, as there are no real biological markers that can be measured. Rather, it is a very subjective eff...

  3. Energy Dissipation-Based Method for Fatigue Life Prediction of Rock Salt

    Science.gov (United States)

    He, Mingming; Huang, Bingqian; Zhu, Caihui; Chen, Yunsheng; Li, Ning

    2018-05-01

    The fatigue test for rock salt is conducted under different stress amplitudes, loading frequencies, confining pressures and loading rates, from which the evaluation rule of the dissipated energy is revealed and analysed. The evolution of energy dissipation under fatigue loading is divided into three stages: the initial stage, the second stage and the acceleration stage. In the second stage, the energy dissipation per cycle remains stable and shows an exponential relation with the stress amplitude; the failure dissipated energy only depends on the mechanical behaviour of the rock salt and confining pressure, but it is immune to the loading conditions. The energy dissipation of fatigued rock salt is discussed, and a novel model for fatigue life prediction is proposed on the basis of energy dissipation. A simple model for evolution of the accumulative dissipated energy is established. Its prediction results are compared with the test results, and the proposed model is validated.

  4. Fatigue data compilation and evaluation of fatigue on design

    International Nuclear Information System (INIS)

    Nyilas, A.

    1985-05-01

    The aim of this report is a review of the available fatigue data of various materials necessary for the design of large superconducting magnets for fusion. One of the primary objectives of this work is to present a broad outline of the low temperature fatigue data of relevant materials within the scope of available data. Besides the classical fatigue data of materials the fatigue crack propagation measurements are outlined widely. The existing recommendations for the design of cryogenic structures are described. A brief introduction of fracture mechanics as well as a historical background of the development of our present day understanding of fatigue has been done. (orig.) [de

  5. Hull Girder Fatigue Damage Estimations of a Large Container Vessel by Spectral Analysis

    DEFF Research Database (Denmark)

    Andersen, Ingrid Marie Vincent; Jensen, Jørgen Juncher

    2013-01-01

    This paper deals with fatigue damage estimation from the analysis of full-scale stress measurements in the hull of a large container vessel (9,400 TEU) covering several months of operation. For onboard decision support and hull monitoring sys-tems, there is a need for a fast reliable method...... for esti-mation of fatigue damage in the ship hull. The objective of the study is to investigate whether the higher frequency contributions from the hydroelastic responses (springing and whipping) can satisfactory be included in the fatigue damage estimation by only a few parameters derived from the stress...

  6. Basic psychological need experiences, fatigue, and sleep in individuals with unexplained chronic fatigue.

    Science.gov (United States)

    Campbell, Rachel; Tobback, Els; Delesie, Liesbeth; Vogelaers, Dirk; Mariman, An; Vansteenkiste, Maarten

    2017-12-01

    Grounded in self-determination theory, this study tested the hypothesis that the satisfaction and frustration of the psychological needs for autonomy, competence, and relatedness would relate to fatigue and subjective and objective sleep parameters, with stress and negative sleep cognitions playing an explanatory role in these associations. During a stay at a sleep laboratory in Belgium, individuals with unexplained chronic fatigue (N = 160; 78% female) underwent polysomnography and completed a questionnaire at 3 different points in time (i.e., after arrival in the sleep lab, before bedtime, and the following morning) that assessed their need-based experiences and stress during the previous week, fatigue during the preceding day, and sleep-related cognitions and sleep during the previous night. Results indicated that need frustration related to higher stress, which in turn, related to higher evening fatigue. Need frustration also related to poorer subjective sleep quality and shorter sleep duration, as indicated by both subjective and objective shorter total sleep time and subjective (but not objective) longer sleep latency. These associations were accounted for by stress and negative sleep cognitions. These findings suggest that health care professionals working with individuals with unexplained chronic fatigue may consider focusing on basic psychological needs within their therapeutic approach. Copyright © 2017 John Wiley & Sons, Ltd.

  7. Life prediction for high temperature low cycle fatigue of two kinds of titanium alloys based on exponential function

    Science.gov (United States)

    Mu, G. Y.; Mi, X. Z.; Wang, F.

    2018-01-01

    The high temperature low cycle fatigue tests of TC4 titanium alloy and TC11 titanium alloy are carried out under strain controlled. The relationships between cyclic stress-life and strain-life are analyzed. The high temperature low cycle fatigue life prediction model of two kinds of titanium alloys is established by using Manson-Coffin method. The relationship between failure inverse number and plastic strain range presents nonlinear in the double logarithmic coordinates. Manson-Coffin method assumes that they have linear relation. Therefore, there is bound to be a certain prediction error by using the Manson-Coffin method. In order to solve this problem, a new method based on exponential function is proposed. The results show that the fatigue life of the two kinds of titanium alloys can be predicted accurately and effectively by using these two methods. Prediction accuracy is within ±1.83 times scatter zone. The life prediction capability of new methods based on exponential function proves more effective and accurate than Manson-Coffin method for two kinds of titanium alloys. The new method based on exponential function can give better fatigue life prediction results with the smaller standard deviation and scatter zone than Manson-Coffin method. The life prediction results of two methods for TC4 titanium alloy prove better than TC11 titanium alloy.

  8. False Alarms and Overmonitoring: Major Factors in Alarm Fatigue Among Labor Nurses.

    Science.gov (United States)

    Simpson, Kathleen Rice; Lyndon, Audrey

    2018-06-08

    Nurses can be exposed to hundreds of alarms during their shift, contributing to alarm fatigue. The purposes were to explore similarities and differences in perceptions of clinical alarms by labor nurses caring for generally healthy women compared with perceptions of adult intensive care unit (ICU) and neonatal ICU nurses caring for critically ill patients and to seek nurses' suggestions for potential improvements. Nurses were asked via focus groups about the utility of clinical alarms from medical devices. There was consensus that false alarms and too many devices generating alarms contributed to alarm fatigue, and most alarms lacked clinical relevance. Nurses identified certain types of alarms that they responded to immediately, but the vast majority of the alarms did not contribute to their clinical assessment or planned nursing care. Monitoring only those patients who need it and only those physiologic values that are warranted, based on patient condition, may decrease alarm burden.

  9. A population-based study of associations between current posttraumatic stress symptoms and current fatigue.

    Science.gov (United States)

    Lerdal, Anners; Lee, Kathryn A; Rokne, Berit; Knudsen, Øistein; Wahl, Astrid K; Dahl, Alv A

    2010-10-01

    This study explores current experience with posttraumatic stress disorder (PTSD) symptoms and other variables (sociodemographic, mental distress, somatic morbidity, self-rated health, and quality of life [QoL]) in relation to fatigue. A representative sample of the Norwegian population (N = 3,944) was invited to participate in a mailed survey, and 1,857 (47%) returned valid responses on the questionnaire that included the Fatigue Severity Scale and the Posttraumatic Symptom Scale-10. Posttraumatic stress disorder symptoms showed a strong association with fatigue in univariate (β = .41) and multivariate analyses (β = .33). Associations between psychosocial health variables, QoL, and fatigue were confirmed. However, PTSD symptoms showed the strongest association with fatigue in the analyses. Findings need to be replicated in other population samples and in clinical samples with PTSD and fatigue.

  10. Fatigue Crack Growth Mechanisms for Nickel-based Superalloy Haynes 282 at 550-750 °C

    Science.gov (United States)

    Rozman, Kyle A.; Kruzic, Jamie J.; Sears, John S.; Hawk, Jeffrey A.

    2015-10-01

    The fatigue crack growth rates for nickel-based superalloy Haynes 282 were measured at 550, 650, and 750 °C using compact tension specimens with a load ratio of 0.1 and cyclic loading frequencies of 25 and 0.25 Hz. The crack path was observed to be primarily transgranular for all temperatures, and the observed effect of increasing temperature was to increase the fatigue crack growth rates. The activation energy associated with the increasing crack growth rates over these three temperatures was calculated less than 60 kJ/mol, which is significantly lower than typical creep or oxidation mechanisms; therefore, creep and oxidation cannot explain the increase in fatigue crack growth rates. Transmission electron microscopy was done on selected samples removed from the cyclic plastic zone, and a trend of decreasing dislocation density was observed with increasing temperature. Accordingly, the trend of increasing crack growth rates with increasing temperature was attributed to softening associated with thermally assisted cross slip and dislocation annihilation.

  11. Predictors and Trajectories of Morning Fatigue Are Distinct from Evening Fatigue

    Science.gov (United States)

    Wright, Fay; Melkus, Gail D’Eramo; Hammer, Marilyn; Schmidt, Brian L.; Knobf, M. Tish; Paul, Steven M.; Cartwright, Frances; Mastick, Judy; Cooper, Bruce A.; Chen, Lee-May; Melisko, Michelle; Levine, Jon D.; Kober, Kord; Aouizerat, Bradley E.; Miaskowski, Christine

    2015-01-01

    Context Fatigue is the most common symptom in oncology patients during chemotherapy (CTX). Little is known about the predictors of interindividual variability in initial levels and trajectories of morning fatigue severity in these patients. Objectives An evaluation was done to determine which demographic, clinical, and symptom characteristics were associated with initial levels as well as the trajectories of morning fatigue and to compare findings with our companion paper on evening fatigue. Methods A sample of outpatients with breast, gastrointestinal, gynecological, and lung cancer (N=586) completed demographic and symptom questionnaires a total of six times over two cycles of CTX. Fatigue severity was evaluated using the Lee Fatigue Scale. Hierarchical linear modeling (HLM) was used to answer the study objectives. Results A large amount of interindividual variability was found in the morning fatigue trajectories. A piecewise model fit the data best. Patients with higher body mass index (BMI), who did not exercise regularly, with a lower functional status, and who had higher levels of state anxiety, sleep disturbance and depressive symptoms, reported higher levels of morning fatigue at enrollment. Variations in the trajectories of morning fatigue were predicted by the patients’ ethnicity and younger age. Conclusion The modifiable risk factors that were associated with only morning fatigue were BMI, exercise, and state anxiety. Modifiable risk factors that were associated with both morning and evening fatigue included functional status, depressive symptoms, and sleep disturbance. Using this information, clinicians can identify patients at higher risk for more severe morning fatigue and evening fatigue, provide individualized patient education, and tailor interventions to address the modifiable risk factors. PMID:25828559

  12. Work fatigue in urban bus drivers

    Directory of Open Access Journals (Sweden)

    Teresa Makowiec-Dąbrowska

    2015-10-01

    Full Text Available Background: Bus drivers are a special group of professional drivers who are at a very high risk of fatigue. The aim of the study was to examine whether the driver’s subjective assessment of fatigue allows for the determination of its level and identification of its causes. Material and Methods: The study group comprised 45 randomly selected bus drivers (mean age – 43.7±7.9 years, period of employment as drivers – 14.7±8.6 years. Examinations were performed in all subjects four times – before and after work on the “easy” route (outside the city center, small traffic intensity and before and after work on the “difficult” route (city center, heavy traffic. The fatigue test questionnaire, based on the list of symptoms of fatigue prepared by the Japan Research Committee of Fatigue, was used in the study. Results: The rating of fatigue after the work was significantly higher than that before the work. The profile of fatigue after work was not influenced by the type of route, but the assessment of most symptoms of fatigue reached a higher level after the “difficult” routes and the differences were statistically significant for 7 symptoms. Only the ratings of leg fatigue, feeling of heaviness, and the necessity to squint eyes and gaze with effort reached the higher levels after driving the “easy” routes. It has been found that the level of fatigue was significantly correlated with the job characteristics (driving time, the length of the route, number of stops, etc. and with the abundance of food ingested and type of beverage (coffee vs. others drunk prior to driving. Conclusions: The questionnaire used in our study to assess the subjective feeling of fatigue has proved to be a sensitive and useful tool for indicating the level and causes of fatigue. The relationship between the symptoms of fatigue and the characteristics of job and lifestyle shows that actions must be taken by both the employers and employees to prevent fatigue

  13. Equivalence Testing as a Tool for Fatigue Risk Management in Aviation.

    Science.gov (United States)

    Wu, Lora J; Gander, Philippa H; van den Berg, Margo; Signal, T Leigh

    2018-04-01

    Many civilian aviation regulators favor evidence-based strategies that go beyond hours-of-service approaches for managing fatigue risk. Several countries now allow operations to be flown outside of flight and duty hour limitations, provided airlines demonstrate an alternative method of compliance that yields safety levels "at least equivalent to" the prescriptive regulations. Here we discuss equivalence testing in occupational fatigue risk management. We present suggested ratios/margins of practical equivalence when comparing operations inside and outside of prescriptive regulations for two common aviation safety performance indicators: total in-flight sleep duration and psychomotor vigilance task reaction speed. Suggested levels of practical equivalence, based on expertise coupled with evidence from field and laboratory studies, are ≤ 30 min in-flight sleep and ± 15% of reference response speed. Equivalence testing is illustrated in analyses of a within-subjects field study during an out-and-back long-range trip. During both sectors of their trip, 41 pilots were monitored via actigraphy, sleep diary, and top of descent psychomotor vigilance task. Pilots were assigned to take rest breaks in a standard lie-flat bunk on one sector and in a bunk tapered 9 from hip to foot on the other sector. Total in-flight sleep duration (134 ± 53 vs. 135 ± 55 min) and mean reaction speed at top of descent (3.94 ± 0.58 vs. 3.77 ± 0.58) were equivalent after rest in the full vs. tapered bunk. Equivalence testing is a complimentary statistical approach to difference testing when comparing levels of fatigue and performance in occupational settings and can be applied in transportation policy decision making.Wu LJ, Gander PH, van den Berg M, Signal TL. Equivalence testing as a tool for fatigue risk management in aviation. Aerosp Med Hum Perform. 2018; 89(4):383-388.

  14. Current state of low-cycle fatigue research based on multiaxial stress intensity and its challenges. Part 1. Focusing on low-cycle fatigue strength evaluation method of elbow piping subjected to in-plane cyclic bending displacement load

    International Nuclear Information System (INIS)

    Urabe, Yoshio

    2017-01-01

    The R and D of fatigue strength at multiaxial stress intensity is recognized to become extremely important in the future in terms of the elaboration of low-cycle fatigue evaluation of various structures including piping systems and reflection on those standards. This paper focuses on the evaluation method developed by the author, namely cumulative damage rule in consideration of multiaxial stress intensity, and explains the concept and the results of verification and evaluation. It also discusses the engineering problems of the current low cycle fatigue assessment technology that were clarified in the process of developing low-cycle fatigue assessment method based on multiaxial stress intensity. The conservative lifespan and somewhat more conservative actual lifetime of elbow piping can be estimated by the conventional 'revised universal slope method' and 'advanced revised universal slope method.' However, these are empirical rules, and the theoretical basis is not clear. From 'cumulative damage rule in consideration of multiaxial stress intensity,' the author calculated furthermore 'low cycle fatigue evaluation formula based on cumulative damage rule in consideration of multi-axial stress intensity,' and examined it. As a result, an evaluation formula that can reasonably assume the equivalent thermoplastic strain range could be obtained at half of the repeat count as targeted. Furthermore, at the stage where future high precision FEM analysis can be used, direct low-cycle fatigue life curve can be established. (A.O.)

  15. Thermomechanical fatigue life prediction for several solders

    Science.gov (United States)

    Wen, Shengmin

    Since solder connections operate at high homologous temperature, solders are high temperature materials. This feature makes their mechanical behavior and fatigue phenomena unique. Based on experimental findings, a physical damage mechanism is introduced for solders. The mechanism views the damage process as a series of independent local damage events characterized by the failure of individual grains, while the structural damage is the eventual percolation result of such local events. Fine's dislocation energy density concept and Mura's microcrack initiation theory are adopted to derive the fatigue formula for an individual grain. A physical damage metric is introduced to describe the material with damage. A unified creep and plasticity constitutive model is adopted to simulate the mechanical behavior of solders. The model is cast into a continuum damage mechanics framework to simulate material with damage. The model gives good agreement with the experimental results of 96.5Pb-3.5Sn and 96.5Sn-3.5Ag solders under uniaxial strain-controlled cyclic loading. The model is convenient for implementation into commercial computational packages. Also presented is a fatigue theory with its failure criterion for solders based on physical damage mechanism. By introducing grain orientation into the fatigue formula, an m-N curve (m is Schmid factor) at constant loading condition is suggested for fatigue of grains with different orientations. A solder structure is defined as fatigued when the damage metric reaches a critical threshold, since at this threshold the failed grains may form a cluster and percolate through the structure according to percolation theory. Fatigue data of 96.5Pb-3.5Sn solder bulk specimens under various uniaxial tension tests were analyzed. Results show that the theory gives consistent predictions under broad conditions, while inelastic strain theory does not. The theory is anisotropic with no size limitation to its application, which could be suitable for

  16. Fatigue and rupture codified rules comparison

    International Nuclear Information System (INIS)

    Faidy, C.

    2004-01-01

    The European Directive on Pressure Equipment requests risk studies and in particular to assure no risk of fatigue and rupture in operation. The answers to these questions are different in the different existing design codes (EN Standards, ASME III and VIII or RCC-M or CODAP-CODETI codes) and corresponding in operation codes (ASME or RSE-M). Design safety factors, material properties, fabrication, refinement in the analysis methods, monitoring in operation, hydro-proof test level... Around these Codes, different rules are under development. A16 in France, R6 in UK or FITNET at the EC level. This paper is concerned by a comparison between 2 different Codes to analyze the risk of fatigue or rupture of pressure equipments and mainly a comparison between RCC-M Code and EN 13445 standard for pressure vessel. Recommendations for future work will be proposed. (authors)

  17. Multi-cracking in uniaxial and biaxial fatigue of 304L stainless steel

    International Nuclear Information System (INIS)

    Rupil, J.

    2012-01-01

    When a mechanical part is subjected to a repeated mechanical stress, it may be damaged after a number of cycles by several cracks initiation and propagation of a main crack. This is the phenomenon of fatigue damage. The thesis deals specifically with possible damage to some components of nuclear plants due to thermal fatigue. Unlike conventional mechanical fatigue damage where a main crack breaks the part, the thermal fatigue damage usually results in the appearance of a surface crack network. Two aspects are discussed in the thesis. The first is the experimental study of fatigue multiple cracking stage also called multi-cracking. Two mechanical test campaigns with multi-cracking detection by digital image correlation were conducted. These campaigns involve uniaxial and equi-biaxial mechanical loads in tension/compression without mean stress. This work allows to monitor and to observe the evolution of different networks of cracks through mechanical solicitations. The second is the numerical simulation of the phenomenon of fatigue damage. Several types of model are used (stochastic, probabilistic, cohesive finite elements). The experimental results have led to identify a multiple crack initiation law in fatigue which is faced with the numerical results. This comparison shows the relevance of the use of an analytical probabilistic model to find statistical results on the density of cracks that can be initiated with thermal and mechanical fatigue loadings. (author) [fr

  18. Energy Approach-Based Simulation of Structural Materials High-Cycle Fatigue

    Science.gov (United States)

    Balayev, A. F.; Korolev, A. V.; Kochetkov, A. V.; Sklyarova, A. I.; Zakharov, O. V.

    2016-02-01

    The paper describes the mechanism of micro-cracks development in solid structural materials based on the theory of brittle fracture. A probability function of material cracks energy distribution is obtained using a probabilistic approach. The paper states energy conditions for cracks growth at material high-cycle loading. A formula allowing to calculate the amount of energy absorbed during the cracks growth is given. The paper proposes a high- cycle fatigue evaluation criterion allowing to determine the maximum permissible number of solid body loading cycles, at which micro-cracks start growing rapidly up to destruction.

  19. Operating data monitoring and fatigue evaluation systems and findings for boiling water reactors in Japan

    International Nuclear Information System (INIS)

    Maekawa, O.; Kanazawa, Y.; Takahashi, Y.; Tani, M.

    1995-01-01

    The reactor pressure vessel (RPV) is one of the most critical components of a boiling water reactor (BWR) when utilities think about plant life extension (PLEX). Design stress analysis sometimes reports very high fatigue usage factors for such portions of RPVs as stud bolt, feedwater nozzle and support skirt.In order to evaluate design margin and to eliminate excessive conservatism in this design analysis to pave the way for PLEX, Japanese BWR utilities jointly with BWR manufacturers in Japan established a programme (1) to acquire plant operational data on line for specific parameters used in stress analysis, (2) to evaluate margin in the design using measured plant data best estimate boundary conditions for stress analysis, and (3) to establish a simplified fatigue analysis method for BWR RPV.A plant data acquisition system, named OPEDAS, has been developed and installed in Tokyo Electric Power Company's 1100MWe BWR at its Kashiwazaki-Kariwa nuclear power plant. Best estimate stress analysis using measured in-plant data has been carried out and the results show considerable margin in fatigue usage factor over the design. A simplified fatigue analysis method using in-plant data has been developed with the Green's function, although some limitations have been identified for its use. ((orig.))

  20. Asphalt Mixture Fatigue Testing : Influence of Test Type and Specimen Size

    NARCIS (Netherlands)

    Li, N.

    2013-01-01

    Fatigue characterization of an asphalt mixture is commonly estimated by laboratory fatigue tests. Based on the classical fatigue analysis, fatigue lives obtained from different test devices are not comparable even when they are performed at the same test conditions. It is believed that there are two

  1. Are nurses able to assess fatigue, exertion fatigue and types of fatigue in residential home patients?

    NARCIS (Netherlands)

    Tiesinga, L.J.; Dijkstra, Ate; Dassen, T.W.N.; Halfens, R.J.G.; van den Heuvel, W.J.A.

    Although fatigue is recognized as a subjective, generalized, extensive and disabling health care problem with a relatively high prevalence among the chronically ill, there have been no studies to show whether nurses caring for fatigued subjects are able to accurately assess the level of fatigue that

  2. Capturing the post-exertional exacerbation of fatigue following physical and cognitive challenge in patients with chronic fatigue syndrome.

    Science.gov (United States)

    Keech, Andrew; Sandler, Carolina X; Vollmer-Conna, Ute; Cvejic, Erin; Lloyd, Andrew R; Barry, Benjamin K

    2015-12-01

    To design and validate an instrument to capture the characteristic post-exertional exacerbation of fatigue in patients with chronic fatigue syndrome (CFS). Firstly, patients with CFS (N=19) participated in five focus group discussions to jointly explore the nature of fatigue and dynamic changes after activity, and inform development of a self-report instrument - the Fatigue and Energy Scale (FES). The psychometric properties of the FES were then examined in two case-control challenge studies: a physically-demanding challenge (moderate-intensity aerobic exercise; N=10 patients), and a cognitively-demanding challenge (simulated driving; N=11 patients). Finally, ecological validity was evaluated by recording in association with tasks of daily living (N=9). Common descriptors for fatigue included 'exhaustion', 'tiredness', 'drained of energy', 'heaviness in the limbs', and 'foggy in the head'. Based on the qualitative data, fatigue was conceptualised as consisting of 'physical' and 'cognitive' dimensions. Analysis of the psychometric properties of the FES showed good sensitivity to the changing symptoms during a post-exertional exacerbation of fatigue following both physical exercise and driving simulation challenges, as well as tasks of daily living. The 'fatigue' experienced by patients with CFS covers both physical and cognitive components. The FES captured the phenomenon of a post-exertional exacerbation of fatigue commonly reported by patients with CFS. The characteristics of the symptom response to physical and cognitive challenges were similar. Both the FES and the challenge paradigms offer key tools to reliably investigate biological correlates of the dynamic changes in fatigue. Copyright © 2015 Elsevier Inc. All rights reserved.

  3. Compassion Fatigue in Pediatric Nurses.

    Science.gov (United States)

    Berger, Jill; Polivka, Barbara; Smoot, Elizabeth Ann; Owens, Heather

    2015-01-01

    Compassion fatigue in nursing has been shown to impact the quality of patient care and employee satisfaction and engagement. The aims of this study were to determine the prevalence and severity of compassion fatigue among pediatric nurses and variations in prevalence based on respondent demographics using a cross-sectional survey design. Nurses under 40 years of age, with 6-10 years of experience and/or working in a medical-surgical unit had significantly lower compassion satisfaction and higher levels of burnout. Secondary traumatic stress from caring for children with severe illness or injury or end of life was a key contributor to compassion fatigue. Copyright © 2015 Elsevier Inc. All rights reserved.

  4. [Effects of Lifestyle Intervention on Fatigue, Nutritional Status and Quality of Life in Patients with Gynecologic Cancer].

    Science.gov (United States)

    An, Hyunjin; Nho, Ju Hee; Yoo, Sunyoung; Kim, Hyunmin; Nho, Minji; Yoo, Hojeong

    2015-12-01

    The purpose of this study was to examine the effect of lifestyle intervention on the development of fatigue, nutritional status and quality of life of patients with gynecologic cancer. A nonequivalent control group quasi-experimental design was used. Participants were 49 patients with gynecologic cancer. They were assigned to the experiment group (n=24) or the control group (n=25). The lifestyle intervention for this study consisted of physical activity, nutritional education, telephone call counseling, health counseling, monitoring for lifestyle, and affective support based on Cox's Interaction Model of Client Health Behavior and was implemented for six weeks. Significant group differences were found for fatigue (p =.037), nutritional status (p =.034) and social/family well-being (p =.035) in these patients with gynecologic cancer. Results indicate that this lifestyle intervention is effective in lessening fatigue, and improving nutritional status and social/family well-being. Therefore, nurses in hospitals should develop strategies to expand and provide lifestyle interventions for patients with cancer.

  5. Microstructural characterisation and constitutive behaviour of alloy RR1000 under fatigue and creep-fatigue loading conditions

    International Nuclear Information System (INIS)

    Stoecker, C.; Zimmermann, M.; Christ, H.-J.; Zhan, Z.-L.; Cornet, C.; Zhao, L.G.; Hardy, M.C.; Tong, J.

    2009-01-01

    Mechanical behaviour of a nickel-based superalloy, RR1000, has been investigated at 650 deg. C under cyclic and dwell loading conditions. The microstructural characteristics of the alloy have been studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the distribution patterns of the dislocations and slip planes have been compared between samples tested under fatigue and creep-fatigue loading conditions. Constitutive behaviour of the alloy was described by a unified constitutive model, where both cyclic plastic and viscoplastic strains were represented by one inelastic strain. The results show that the precipitation state is very stable at 650 deg. C and only minor differences exist in the dislocation arrangements formed under pure fatigue and combined creep and fatigue conditions. Hence, a unified constitutive model seems to be justified in describing and predicting the constitutive behaviour in both cases.

  6. Are stamina and fatigue polar opposites? A case study.

    Science.gov (United States)

    So, Suzanna; Evans, Meredyth; Jason, Leonard A; Brown, Abigail

    2015-01-01

    Most individuals with Myalgic Encephalomyelitis/chronic fatigue syndrome (ME/CFS) (Carruthers et al., 2003 ), Myalgic Encephalomyelitis (ME) (Carruthers et al., 2011 ), and chronic fatigue syndrome (CFS) (Fukuda et al., 1994 ) indicate that they experience fatigue and sharp decreases in energy levels, which hinder the ability to engage in physical activities (Friedberg & Jason, 1998 ). However, there are some individuals who reduce activity engagement in order to avoid a worsening of symptoms; thus these individuals may endorse lower levels of fatigue. Accordingly, those with low levels of fatigue but low endurance/stamina might be inadvertently excluded from some criteria based on the fatigue requirement. The current study serves as an exploration of the relationship between fatigue and stamina and the effects of these constructs on illness symptomology and their implications for assessment and diagnosis.

  7. Mitigation of Fatigue Loads Using Individual Pitch Control of Wind Turbines Based on FAST

    DEFF Research Database (Denmark)

    Zhang, Yunqian; Chen, Zhe; Cheng, Ming

    2011-01-01

    moments and fatigue. The loading transfer from rotational coordinate system to the fixed coordinate system of the wind turbine is analyzed. In order to make the simulation results more reliable, the wind turbine code FAST is applied to doubly fed induction generator (DFIG) based power system...

  8. Positron lifetime measurements as a non-destructive technique to monitor fatigue damage. Final report, January 1, 1971--June 30, 1978

    International Nuclear Information System (INIS)

    Byrne, J.G.

    1978-06-01

    Positron studies were applied successfully to cyclic fatigue in steel and copper and have shown a capability to nondestructively detect fatigue softening and fatigue hardening. In the case of elastic high cycle fatigue in initially soft steel the fatigue hardening is identified with point defects. For cyclic plastic range, high cycle fatigue cyclic hardening and softening are correlated with changes in dislocation substructure. Positron measurements during the pulse annealing of copper single crystals following electron irradiation at 77 0 K have revealed the formation of multi-vacancy complexes which constitute the precursors of radiation induced voids. Positron studies have been applied to hydrogen embrittlement in 4340 steel and more recently in nickel. The technique can non-destructively detect hydrogen embrittlement and gage its extent. U.S. Patent No. 4064438 was issued on this basis

  9. Fatigue Life Estimation of Medium-Carbon Steel with Different Surface Roughness

    Directory of Open Access Journals (Sweden)

    Changyou Li

    2017-03-01

    Full Text Available Medium-carbon steel is commonly used for the rail, wire ropes, tire cord, cold heading, forging steels, cold finished steel bars, machinable steel and so on. Its fatigue behavior analysis and fatigue life estimation play an important role in the machinery industry. In this paper, the estimation of fatigue life of medium-carbon steel with different surface roughness using established S-N and P-S-N curves is presented. To estimate the fatigue life, the effect of the average surface roughness on the fatigue life of medium-carbon steel has been investigated using 75 fatigue tests in three groups with average surface roughness (Ra: 0.4 μm, 0.8 μm, and 1.6 μm, respectively. S-N curves and P-S-N curves have been established based on the fatigue tests. The fatigue life of medium-carbon steel is then estimated based on Tanaka-Mura crack initiation life model, the crack propagation life model using Paris law, and material constants of the S-N curves. Six more fatigue tests have been conducted to validate the presented fatigue life estimation formulation. The experimental results have shown that the presented model could estimate well the mean fatigue life of medium-carbon steel with different surface roughness.

  10. Scenario based approach to structural damage detection and its value in a risk and reliability perspective

    DEFF Research Database (Denmark)

    Hovgaard, Mads Knude; Hansen, Jannick Balleby; Brincker, Rune

    2013-01-01

    A scenario- and vibration based structural damage detection method is demonstrated though simulation. The method is Finite Element (FE) based. The value of the monitoring is calculated using structural reliability theory. A high cycle fatigue crack propagation model is assumed as the damage mecha......- and without monitoring. Monte Carlo Sampling (MCS) is used to estimate the probabilities and the tower of an onshore NREL 5MW wind turbine is given as a calculation case......A scenario- and vibration based structural damage detection method is demonstrated though simulation. The method is Finite Element (FE) based. The value of the monitoring is calculated using structural reliability theory. A high cycle fatigue crack propagation model is assumed as the damage...

  11. Rate-based structural health monitoring using permanently installed sensors

    Science.gov (United States)

    Corcoran, Joseph

    2017-09-01

    Permanently installed sensors are becoming increasingly ubiquitous, facilitating very frequent in situ measurements and consequently improved monitoring of `trends' in the observed system behaviour. It is proposed that this newly available data may be used to provide prior warning and forecasting of critical events, particularly system failure. Numerous damage mechanisms are examples of positive feedback; they are `self-accelerating' with an increasing rate of damage towards failure. The positive feedback leads to a common time-response behaviour which may be described by an empirical relation allowing prediction of the time to criticality. This study focuses on Structural Health Monitoring of engineering components; failure times are projected well in advance of failure for fatigue, creep crack growth and volumetric creep damage experiments. The proposed methodology provides a widely applicable framework for using newly available near-continuous data from permanently installed sensors to predict time until failure in a range of application areas including engineering, geophysics and medicine.

  12. Evolution of thermal fatigue management of piping in US LWRs

    International Nuclear Information System (INIS)

    McDewitt, M.; Wolfe, K.; McGill, R.

    2015-01-01

    Fatigue usage caused by cyclic changes of thermally stratified reactor coolant in Light Water Reactor (LWR) pressure boundary piping was not an original consideration in US Nuclear Power Plant (NPP) designs. During the mid 1980's, several events involving cracking and leakage due to thermal cycling occurred in reactor coolant system branch piping at both US and International NPPs. In 1988, the US Nuclear Regulatory Commission (US NRC) issued Bulletin 88-08 to alert LWR licensees of the potential for piping failures due to stratified thermal cycling. In response to these events, the US nuclear industry developed initiatives to identify susceptible components and established measures to monitor and prevent future failures. These initiatives have been effective in preventing leakage events, but have also identified fewer defects than expected based on screening model predictions. Improved analytical techniques are being investigated to maintain program effectiveness while minimizing unnecessary non-destructive examinations. This paper discusses the evolution of the US thermal fatigue initiatives, and analytical concepts being evaluated to improve program efficiency. (authors)

  13. Diagnosing and treating Enquiry Based Learning fatigue in Graduate Entry Nursing students.

    Science.gov (United States)

    Stacey, Gemma; Wilson, Claire; Reddy, Helen; Palmer, Chris; Henderson, James; Little, Hannah; Bull, Heather

    2018-01-01

    The use of student directed study approaches such as Enquiry Based Learning (EBL) in the design and implementation of Graduate Entry Nursing Circular is well established. The rational relates to the maximisation of graduate attributes such as motivation to learn, the ability to identify, search and assimilate relevant literature and the desire to take ownership of the direction and pace of learning. Existing alongside this however, is the observation that students remain under confident in the application of knowledge to a clinical context and frustrated with learning approaches which do not appear directly related to improving their competence in this area. We suggest the result of this is a gradual disengagement and dissatisfaction the learning forum amongst students and faculty, which we have defined as EBL fatigue. The symptoms and consequences of EBL fatigue amongst students and faculty are discussed alongside strategies which we suggest may act as preventative measures in reducing the risk of a local epidemic. Copyright © 2017 Elsevier Ltd. All rights reserved.

  14. Fatigue in Advanced Cancer Patients: Congruence Between Patients and Their Informal Caregivers About Patients' Fatigue Severity During Cancer Treatment With Palliative Intent and Predictors of Agreement

    NARCIS (Netherlands)

    Poort, Hanneke; Peters, Marlies E. W. J.; Gielissen, Marieke F. M.; Verhagen, Constans A. H. H. V. M.; Bleijenberg, Gijs; van der Graaf, Winette T. A.; Wearden, Alison J.; Knoop, Hans

    2016-01-01

    Informal caregivers (ICs) are increasingly involved in the monitoring of symptoms during advanced cancer patients' treatment with palliative intent. A common but subjective symptom during this extended treatment phase is fatigue. This exploratory longitudinal study aimed to determine agreement

  15. Fatigue in Advanced Cancer Patients: Congruence Between Patients and Their Informal Caregivers About Patients' Fatigue Severity During Cancer Treatment With Palliative Intent and Predictors of Agreement

    NARCIS (Netherlands)

    Poort, H.; Peters, M.E.W.J.; Gielissen, M.F.M.; Verhagen, C.A.H.H.V.M.; Bleijenberg, G.; Graaf, W.T.A. van der; Wearden, A.J.; Knoop, H.

    2016-01-01

    CONTEXT: Informal caregivers (ICs) are increasingly involved in the monitoring of symptoms during advanced cancer patients' treatment with palliative intent. A common but subjective symptom during this extended treatment phase is fatigue. OBJECTIVES: This exploratory longitudinal study aimed to

  16. Fatigue damage and fracture behavior of tungsten fiber reinforced Zr-based metallic glassy composite

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, H. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Zhang, Z.F. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China)]. E-mail: zhfzhang@imr.ac.cn; Wang, Z.G. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Qiu, K.Q. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Zhang, H.F. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Zang, Q.S. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China); Hu, Z.Q. [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016 (China)

    2006-02-25

    The fatigue life, damage and fracture behavior of tungsten fiber reinforced metallic glass Zr{sub 41.25}Ti{sub 13.75}Ni{sub 10}Cu{sub 12.5}Be{sub 22.5} composites are investigated under cyclic push-pull loading. It is found that the fatigue life of the composite increases with increasing the volume fraction of tungsten fibers. Similar to crystalline metals, the regions of crack initiation, propagation and overload fracture can be discerned on the fracture surface of the specimen. Fatigue crack normally initiates in the metallic glass matrix at the outer surface of the composite specimen and propagates predominantly in the matrix. Different crack front profile around the tungsten fibers and fiber pullout demonstrate that fatigue crack may propagate around the fiber, leading to bridging of the crack faces by the unbroken fiber and hence improved fatigue crack-growth resistance. Locally decreased effective stiffness in the region where fiber distribution is sparse may provide preferential crack path in the composite. A proposed model was exercised to elucidate different tungsten fiber fracture morphologies in the fatigue crack propagation and overload fracture regions in the light of Poisson's ratio effect during fatigue loading.

  17. Fatigue damage and fracture behavior of tungsten fiber reinforced Zr-based metallic glassy composite

    International Nuclear Information System (INIS)

    Zhang, H.; Zhang, Z.F.; Wang, Z.G.; Qiu, K.Q.; Zhang, H.F.; Zang, Q.S.; Hu, Z.Q.

    2006-01-01

    The fatigue life, damage and fracture behavior of tungsten fiber reinforced metallic glass Zr 41.25 Ti 13.75 Ni 10 Cu 12.5 Be 22.5 composites are investigated under cyclic push-pull loading. It is found that the fatigue life of the composite increases with increasing the volume fraction of tungsten fibers. Similar to crystalline metals, the regions of crack initiation, propagation and overload fracture can be discerned on the fracture surface of the specimen. Fatigue crack normally initiates in the metallic glass matrix at the outer surface of the composite specimen and propagates predominantly in the matrix. Different crack front profile around the tungsten fibers and fiber pullout demonstrate that fatigue crack may propagate around the fiber, leading to bridging of the crack faces by the unbroken fiber and hence improved fatigue crack-growth resistance. Locally decreased effective stiffness in the region where fiber distribution is sparse may provide preferential crack path in the composite. A proposed model was exercised to elucidate different tungsten fiber fracture morphologies in the fatigue crack propagation and overload fracture regions in the light of Poisson's ratio effect during fatigue loading

  18. Fatigue proofing: The role of protective behaviours in mediating fatigue-related risk in a defence aviation environment.

    Science.gov (United States)

    Dawson, Drew; Cleggett, Courtney; Thompson, Kirrilly; Thomas, Matthew J W

    2017-02-01

    In the military or emergency services, operational requirements and/or community expectations often preclude formal prescriptive working time arrangements as a practical means of reducing fatigue-related risk. In these environments, workers sometimes employ adaptive or protective behaviours informally to reduce the risk (i.e. likelihood or consequence) associated with a fatigue-related error. These informal behaviours enable employees to reduce risk while continuing to work while fatigued. In this study, we documented the use of informal protective behaviours in a group of defence aviation personnel including flight crews. Semi-structured interviews were conducted to determine whether and which protective behaviours were used to mitigate fatigue-related error. The 18 participants were from aviation-specific trades and included aircrew (pilots and air-crewman) and aviation maintenance personnel (aeronautical engineers and maintenance personnel). Participants identified 147 ways in which they and/or others act to reduce the likelihood or consequence of a fatigue-related error. These formed seven categories of fatigue-reduction strategies. The two most novel categories are discussed in this paper: task-related and behaviour-based strategies. Broadly speaking, these results indicate that fatigued military flight and maintenance crews use protective 'fatigue-proofing' behaviours to reduce the likelihood and/or consequence of fatigue-related error and were aware of the potential benefits. It is also important to note that these behaviours are not typically part of the formal safety management system. Rather, they have evolved spontaneously as part of the culture around protecting team performance under adverse operating conditions. When compared with previous similar studies, aviation personnel were more readily able to understand the idea of fatigue proofing than those from a fire-fighting background. These differences were thought to reflect different cultural

  19. Application of a robust vibration-based non-destructive method for detection of fatigue cracks in structures

    International Nuclear Information System (INIS)

    Razi, Pejman; Esmaeel, Ramadan A; Taheri, Farid

    2011-01-01

    This paper presents the application of a novel vibration-based technique for detecting fatigue cracks in structures. The method utilizes the empirical mode decomposition method (EMD) to establish an effective energy-based damage index. To investigate the feasibility of the method, fatigue cracks of different sizes were introduced in an aluminum beam subjected to a cyclic load under a three-point bending configuration. The vibration signals corresponding to the healthy and the damaged states of the beam were acquired via piezoceramic sensors. The signals were then processed by the proposed methodology to obtain the damage indices. In addition, for the sake of comparison, the frequency and damping analysis were performed on the test specimen. The results of this study concluded with two major observations. Firstly, the method was highly successful in not only predicting the presence of the fatigue crack, but also in quantifying its progression. Secondly, the proposed energy-based damage index was proved to be superior to the frequency-based methods in terms of sensitivity to the damage detection and quantification. As a result, this technique could be regarded as an efficient non-destructive tool, since it is simple, cost-effective and does not rely on analytical modeling of structures. In addition, the capability of the finite element method (FEM) in mimicking the experiments, and hence for consideration as an effective tool for conducting future parametric studies, was also investigated

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

    Science.gov (United States)

    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. Copyright © 2012 Elsevier B.V. All rights reserved.

  1. Fatigue in adults with post-infectious fatigue syndrome: a qualitative content analysis.

    Science.gov (United States)

    Stormorken, Eva; Jason, Leonard A; Kirkevold, Marit

    2015-01-01

    Fatigue is a major problem among individuals with post-infectious fatigue syndrome (PIFS), also known as chronic fatigue syndrome or myalgic encephalomyelitis. It is a complex phenomenon that varies across illnesses. From a nursing perspective, knowledge and understanding of fatigue in this illness is limited. Nurses lack confidence in caring for these patients and devalue their professional role. The aim of this study was to explore in-depth the experiences of fatigue among individuals with PIFS. A detailed description of the phenomenon of fatigue is presented. Increased knowledge would likely contribute to more confident nurses and improved nursing care. A qualitative study with open interviews was employed. In-depth interviews with patients were fully transcribed and underwent a qualitative content analysis. A maximum variation sample of 26 affected adults between 26-59 years old was recruited from a population diagnosed at a fatigue outpatient clinic. The fatigue was a post-exertional, multidimensional, fluctuating phenomenon with varying degrees of severity and several distinct characteristics and was accompanied by concomitant symptoms. Fatigue was perceived to be an all-pervasive complex experience that substantially reduced the ability to function personally or professionally. A range of trigger mechanisms evoked or worsened the fatigue, but the affected were not always aware of what triggered it. There was an excessive increase in fatigue in response to even minor activities. An increase in fatigue resulted in the exacerbation of other concomitant symptoms. The term fatigue does not capture the participants' experiences, which are accompanied by a considerable symptom burden that contributes to the illness experience and the severe disability. Although some aspects of the fatigue experience have been reported previously, more were added in our study, such as the dimension of awakening fatigue and the characteristic beyond time, when time passes unnoticed

  2. Monitoring Knowledge Base (MKB)

    Data.gov (United States)

    U.S. Environmental Protection Agency — The Monitoring Knowledge Base (MKB) is a compilation of emissions measurement and monitoring techniques associated with air pollution control devices, industrial...

  3. Prediction of fretting fatigue behavior under elastic-plastic conditions

    International Nuclear Information System (INIS)

    Shin, Ki Su

    2009-01-01

    Fretting fatigue generally leads to the degradation of the fatigue strength of a material due to cyclic micro-slip between two contacting materials. Fretting fatigue is regarded as an important issue in designing aerospace structures. While many studies have evaluated fretting fatigue behavior under elastic deformation conditions, few have focused on fretting fatigue behavior under elastic-plastic deformation conditions, especially the crack orientation and fatigue life prediction for Ti-6Al-4V. The primary goal of this study was to characterize the fretting fatigue crack initiation behavior in the presence of plasticity. Experimental tests were performed using pad configurations involving elastic-plastic deformations. To calculate stress distributions under elastic-plastic fretting fatigue conditions, FEA was also performed. Several parametric approaches were used to predict fretting fatigue life along with stress distribution resulting from FEA. However, those parameters using surface stresses were unable to establish an equivalence between elastic fretting fatigue data and elastic-plastic fretting fatigue data. Based on this observation, the critical distance methods, which are commonly used in notch analysis, were applied to the fretting fatigue problem. In conclusion, the effective strain range method when used in conjunction with the SMSSR parameter showed a good correlation of data points between the pad configurations involving elastic and elastic plastic deformations

  4. Seafarer fatigue

    DEFF Research Database (Denmark)

    Jepsen, Jørgen Riis; Zhao, Zhiwei; van Leeuwen, Wessel M. A.

    2015-01-01

    Background: The consequences of fatigue for the health and safety of seafarers has caused concern in the industry and among academics, and indicates the importance of further research into risk factors and preventive interventions at sea. This review gives an overview of the key issues relating...... to seafarer fatigue. Materials and methods: A literature study was conducted aiming to collect publications that address risk factors for fatigue, short-term and long-term consequences for health and safety, and options for fatigue mitigation at sea. Due to the limited number of publications that deals...... with seafarers, experiences from other populations sharing the same exposures (e.g. shift work) were also included when appropriate. Results: Work at sea involves multiple risk factors for fatigue, which in addition to acute effects (e.g., impaired cognition, accidents) contributes through autonomic, immunologic...

  5. Fatigue Performance of Fiber Reinforced Concrete

    DEFF Research Database (Denmark)

    Jun, Zhang; Stang, Henrik

    1996-01-01

    The objective of the present study is to obtain basic data of fibre reinforced concrete under fatigue load and to set up a theoretical model based on micromechanics. In this study, the bridging stress in fiber reinforced concrete under cyclic tensile load was investigted in details. The damage...... mechanism of the interface between fiber and matrix was proposed and a rational model given. Finally, the response of a steel fiber reinforced concrete beam under fatigue loading was predicted based on this model and compared with experimental results....

  6. Corrosion fatigue behaviour of ion nitrided AISI 4140 steel

    Energy Technology Data Exchange (ETDEWEB)

    Genel, K. [Sakarya Univ., Adapazari (Turkey). Mech. Eng. Dept.; Demirkol, M.; Guelmez, T. [Faculty of Mechanical Engineering, Istanbul Technical University, Guemuessuyu, 80191, Istanbul (Turkey)

    2000-08-31

    Machine components suffer from corrosion degradation of fatigue characteristics and improvement can be attained by the application of a nitriding treatment, particularly to low alloy steels. In the present study, the effect of ion nitriding on corrosion fatigue performance of AISI 4140 steel has been investigated by conducting a series of rotary bending corrosion fatigue tests at 95 Hz, in 3% NaCl aqueous solution. Hourglass shaped, 4 mm diameter fatigue specimens were ion nitrided at 748 K for 1, 3, 8 and 16 h prior to the tests. It was observed that distinct fatigue limit behaviour of ion nitrided steel in air completely disappeared in corrosive environment besides severe degradation in fatigue characteristics. An improvement reaching to 60% in corrosion fatigue strength can be attained by successive ion nitriding practice based on a fatigue life of 10{sup 7} cycles. An attempt was made to establish an empirical relationship between corrosion fatigue strength and relative case depth, which considers the size of the ion nitrided specimen. It was also determined that a power relationship holds between corrosion fatigue strength and fatigue life of ion nitrided steel. The presence of white layer has resulted in additional improvement in corrosion fatigue resistance, and it was observed that corrosion fatigue cracks were initiated dominantly under the white layer by pit formation mechanism. (orig.)

  7. Corrosion fatigue behaviour of ion nitrided AISI 4140 steel

    International Nuclear Information System (INIS)

    Genel, K.

    2000-01-01

    Machine components suffer from corrosion degradation of fatigue characteristics and improvement can be attained by the application of a nitriding treatment, particularly to low alloy steels. In the present study, the effect of ion nitriding on corrosion fatigue performance of AISI 4140 steel has been investigated by conducting a series of rotary bending corrosion fatigue tests at 95 Hz, in 3% NaCl aqueous solution. Hourglass shaped, 4 mm diameter fatigue specimens were ion nitrided at 748 K for 1, 3, 8 and 16 h prior to the tests. It was observed that distinct fatigue limit behaviour of ion nitrided steel in air completely disappeared in corrosive environment besides severe degradation in fatigue characteristics. An improvement reaching to 60% in corrosion fatigue strength can be attained by successive ion nitriding practice based on a fatigue life of 10 7 cycles. An attempt was made to establish an empirical relationship between corrosion fatigue strength and relative case depth, which considers the size of the ion nitrided specimen. It was also determined that a power relationship holds between corrosion fatigue strength and fatigue life of ion nitrided steel. The presence of white layer has resulted in additional improvement in corrosion fatigue resistance, and it was observed that corrosion fatigue cracks were initiated dominantly under the white layer by pit formation mechanism. (orig.)

  8. Fatigue processes in thermoplastic fibres; Les mecanismes de fatigue dans les fibres thermoplastiques

    Energy Technology Data Exchange (ETDEWEB)

    Herrera Ramirez, J.M.

    2004-09-15

    The present study examines and compares the behaviour of the two types of PA66 fibres and two types of PET fibres under fatigue loading up to failure, and the correlation between the fibres (nano)structures and their structural heterogeneities, with fatigue lifetimes. Several techniques have been used to analyze the materials, such as scanning electron microscopy (SEM), microanalysis (EDS), differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and micro-Raman spectroscopy. A meticulous analysis by scanning electron microscopy of the fracture morphology of fibres broken in tension and in fatigue, as well as a study of the fatigue life, were undertaken. The fatigue process occurs when the cyclic load amplitude is sufficiently large, however a condition for fatigue failure is that the minimum load each cycle must be lower than a threshold stress level. Failure under fatigue conditions leads to distinctive fracture morphologies which are very different from those seen after tensile or creep failure and this allows easy identification of the fatigue process. The fibres have been analyzed in the as received state and after fatigue failure in order to observe the microstructural changes resulting from the fatigue loading. The results will be compared with those obtained for fibres loaded under conditions where the fatigue process was hindered. The role of the microstructure of the fibres in determining fatigue will be discussed in this work and the possibility of improving their resistance to fatigue or eliminating the fatigue process will be discussed. (author)

  9. A literature review on fatigue and creep interaction

    Science.gov (United States)

    Chen, W. C.

    1978-01-01

    Life-time prediction methods, which are based on a number of empirical and phenomenological relationships, are presented. Three aspects are reviewed: effects of testing parameters on high temperature fatigue, life-time prediction, and high temperature fatigue crack growth.

  10. In pile AISI 316L. Low cycle fatigue. Final report

    International Nuclear Information System (INIS)

    Van Nieuwenhove, R.; Moons, F.

    1994-12-01

    In pile testing of the effect of neutron irradiation on the fatigue life of the reference material AISI 316L was performed in the framework of the European fusion technology program. The overall programme, carried out at SCK CEN (Mol,Belgium), exists of two instrumented rigs for low cycle fatigue testing, which were consecutively loaded in the BR-2 reactor during periods Jan (94) June (94) and Aug (94)-Dec(94). In each experiment, two identical samples were loaded by means of a pneumatically driven system. The samples were instrumented with thermocouples, strain gages, linear variable displacement transducers, and activation monitors. The experimental conditions are given. Type of fatigue test: load controlled, symmetric, uniaxial, triangular wave shape; stress range: about 580 MPa; sample shape: hourglass, diameter 3.2 mm, radius 12.5 mm; environment: NaK (peritectic); temperature: 250 C; maximum dpa value up to fracture: 1.7. Two of four samples were broken (one in each experiment) after having experienced 17 419 respectively 11 870 stress cycles. These new data points confirm earlier results from pile fatigue tests: irradiation causes no degradation of fatigue life of AISI 316L steel, at least for the parameters corresponding to these experiments

  11. A Pragmatic Evaluation of the National Cancer Institute Physician Data Query (PDQ)®-Based Brief Counseling on Cancer-Related Fatigue among Patients Undergoing Radiation Therapy

    Science.gov (United States)

    Bauml, Joshua; Xie, Sharon X; Penn, Courtney; Desai, Krupali; Dong, Kimberly W; Bruner, Deborah Watkins; Vapiwala, Neha; Mao, Jun James

    2018-01-01

    Purpose Cancer-Related Fatigue (CRF) negatively affects quality of life among cancer patients. This study seeks to evaluate the outcome and patient receptiveness of a brief counseling program based on National Cancer Institute (NCI) PDQ® information to manage CRF when integrated into Radiation Therapy (RT). Methods We conducted a prospective cohort study among patients undergoing non-palliative RT. Patients with stage I–III tumors and with Karnofsky score 60 or better were given a ten-minute behavioral counseling session during the first two weeks of RT. The Brief Fatigue Inventory (BFI) was administered at baseline/end of RT. Results Of 93 patients enrolled, 89% found the counseling useful and practical. By the end of RT, 59% reported increased exercise, 41.6% sought nutrition counseling, 72.7% prioritized daily activities, 74.4% took daytime naps, and 70.5% talked with other cancer patients. Regarding counseling, patients who had received chemotherapy prior to RT had no change in fatigue (−0.2), those who received RT alone had mild increase in fatigue (0.7, p=0.02), and those who received concurrent chemotherapy experienced a substantial increase in fatigue (3.0 to 5.2, p=0.05). Higher baseline fatigue and receipt of chemotherapy were predictive of worsened fatigue in a multivariate model (both p<0.01). Conclusion Our data suggests that brief behavioral counseling based on NCI guidelines is well accepted by patients showing an uptake in many activities to cope with CRF. Those who receive concurrent chemotherapy and with higher baseline fatigue are at risk for worsening fatigue despite of guideline-based therapy. PMID:29479490

  12. Fatigue crack growth thresholds measurements in structural materials

    International Nuclear Information System (INIS)

    Lindstroem, R.; Lidar, P.; Rosborg, B.

    1999-05-01

    Fatigue crack growth thresholds and da/dN-data at low Δk I -values ( 1/2 ) have been determined for type 304 stainless steel, nickel-base weld metal Alloy 182, nickel-base metal Alloy 600, and low-alloy steel in air at ambient temperature and in high-temperature water and steam. The stainless alloys have been tested in water with 0.2 ppm O 2 at 288 deg C and the low-alloy steel in steam at 286 deg C. The fatigue crack growth threshold was defined as the ΔK I -value resulting in a crack growth rate of 10 -7 mm per cycle. The measured fatigue crack growth thresholds (at frequencies from 0.5 to 20 Hz) are quite similar independent of the material and the environment. A relatively inexpensive and time-saving method for measuring fatigue crack growth thresholds, and fatigue crack growth rates at low ΔK I -values, has been used in the tests. The method is a ΔK I -decreasing test with constant K I Max

  13. The role of central and peripheral muscle fatigue in postcancer fatigue: a randomized controlled trial.

    Science.gov (United States)

    Prinsen, Hetty; van Dijk, Johannes P; Zwarts, Machiel J; Leer, Jan Willem H; Bleijenberg, Gijs; van Laarhoven, Hanneke W M

    2015-02-01

    Postcancer fatigue is a frequently occurring problem, impairing quality of life. Little is known about (neuro)physiological factors determining postcancer fatigue. It may be hypothesized that postcancer fatigue is characterized by low peripheral muscle fatigue and high central muscle fatigue. The aims of this study were to examine whether central and peripheral muscle fatigue differ between fatigued and non-fatigued cancer survivors and to examine the effect of cognitive behavioral therapy (CBT) on peripheral and central muscle fatigue of fatigued cancer survivors in a randomized controlled trial. Sixteen fatigued patients in the intervention group (CBT) and eight fatigued patients in the waiting list group were successfully assessed at baseline and six months later. Baseline measurements of 20 fatigued patients were compared with 20 non-fatigued patients. A twitch interpolation technique and surface electromyography were applied, respectively, during sustained contraction of the biceps brachii muscle. Muscle fiber conduction velocity (MFCV) and central activation failure (CAF) were not significantly different between fatigued and non-fatigued patients. Change scores of MFCV and CAF were not significantly different between patients in the CBT and waiting list groups. Patients in the CBT group reported a significantly larger decrease in fatigue scores than patients in the waiting list group. Postcancer fatigue is neither characterized by abnormally high central muscle fatigue nor by low peripheral muscle fatigue. These findings suggest a difference in the underlying physiological mechanism of postcancer fatigue vs. other fatigue syndromes. Copyright © 2015 American Academy of Hospice and Palliative Medicine. Published by Elsevier Inc. All rights reserved.

  14. The Change of the Seebeck Coefficient Due to Neutron Irradiation and Thermal Fatigue of Nuclear Reactor Pressure Vessel Steel and its Application to the Monitoring of Material Degradation

    International Nuclear Information System (INIS)

    Niffenegger, M.; Reichlin, K.; Kalkhof, D.

    2002-05-01

    The monitoring of material degradation, that might be caused by neutron irradiation and thermal fatigue, is an important topic in lifetime extension of nuclear power plants. We therefore investigated the application of the Seebeck effect for determining material degradation of common reactor pressure vessel steel. The Seebeck coefficient (SC) of several irradiated Charpy specimens made from Japanese JRQ-steel were measured. The specimens suffered a fluence from 0 up to 4.5 x 10 19 neutrons per cm 2 with energies higher than 1 MeV. The measured changes of the SC within this range were about 500 nV, increasing continuously in the range under investigation. Some indications of saturation appeared at fluencies larger than 4.55 x 10 19 neutrons per cm 2 . We obtained a linear dependency between the SC and the temperature shift ΔT 41 of the Charpy-Energy- Temperature curve which is widely used to characterize material embrittlement. Similar measurements were performed on specimens made from the widely used austenitic steel X6CrNiTi18-10 (according to DIN 1.4541) that were fatigued by applying a cyclic strain amplitude of 0.28%. For this kind of fatigue the observed change of SC was somewhat smaller than for the irradiated specimens. Further investigations were made to quantify the size of the gage volume in which the thermoelectric power is generated. It appeared that the information gathered from a Thermo Electric Power (TEP) measurement is very local. To overcome this problem we propose a novel TEP-method using a Thermoelectric Scanning Microscope (TSM). We finally conclude that the change of the SC has a potential for monitoring of material degradation due to neutron irradiation and thermal fatigue, but it has to be taken into account that several influencing parameters could contribute to the TEP in either an additional or extinguishing manner. A disadvantage of the method is the requirement of a clean surface without any oxide layer. A part of this disadvantage can

  15. Jacket Substructure Fatigue Mitigation through Active Control

    DEFF Research Database (Denmark)

    Hanis, Tomas; Natarajan, Anand

    2014-01-01

    to the fatigue design loads on the braces of the jacket. Since large wind turbines of 10MW rating have low rotor speeds (p), the modal frequencies of the sub structures approach 3p at low wind speeds, which leads to a modal coupling and resonance. Therefore an active control system is developed which provides...... sufficient structural damping and consequently a fatigue reduction at the substructure. The resulting reduction in fatigue design loads on the jacket structure based on the active control system is presented....

  16. Cancer-Related Fatigue in Post-Treatment Cancer Survivors: Theory-Based Development of a Web-Based Intervention.

    Science.gov (United States)

    Corbett, Teresa; Walsh, Jane C; Groarke, AnnMarie; Moss-Morris, Rona; Morrissey, Eimear; McGuire, Brian E

    2017-07-04

    Cancer-related fatigue (CrF) is the most common and disruptive symptom experienced by cancer survivors. We aimed to develop a theory-based, interactive Web-based intervention designed to facilitate self-management and enhance coping with CrF following cancer treatment. The aim of our study was to outline the rationale, decision-making processes, methods, and findings which led to the development of a Web-based intervention to be tested in a feasibility trial. This paper outlines the process and method of development of the intervention. An extensive review of the literature and qualitative research was conducted to establish a therapeutic approach for this intervention, based on theory. The psychological principles used in the development process are outlined, and we also clarify hypothesized causal mechanisms. We describe decision-making processes involved in the development of the content of the intervention, input from the target patient group and stakeholders, the design of the website features, and the initial user testing of the website. The cocreation of the intervention with the experts and service users allowed the design team to ensure that an acceptable intervention was developed. This evidence-based Web-based program is the first intervention of its kind based on self-regulation model theory, with the primary aim of targeting the representations of fatigue and enhancing self-management of CrF, specifically. This research sought to integrate psychological theory, existing evidence of effective interventions, empirically derived principles of Web design, and the views of potential users into the systematic planning and design of the intervention of an easy-to-use website for cancer survivors. ©Teresa Corbett, Jane C Walsh, AnnMarie Groarke, Rona Moss-Morris, Eimear Morrissey, Brian E McGuire. Originally published in JMIR Cancer (http://cancer.jmir.org), 04.07.2017.

  17. High cycle fatigue test and regression methods of S-N curve

    International Nuclear Information System (INIS)

    Kim, D. W.; Park, J. Y.; Kim, W. G.; Yoon, J. H.

    2011-11-01

    The fatigue design curve in the ASME Boiler and Pressure Vessel Code Section III are based on the assumption that fatigue life is infinite after 106 cycles. This is because standard fatigue testing equipment prior to the past decades was limited in speed to less than 200 cycles per second. Traditional servo-hydraulic machines work at frequency of 50 Hz. Servo-hydraulic machines working at 1000 Hz have been developed after 1997. This machines allow high frequency and displacement of up to ±0.1 mm and dynamic load of ±20 kN are guaranteed. The frequency of resonant fatigue test machine is 50-250 Hz. Various forced vibration-based system works at 500 Hz or 1.8 kHz. Rotating bending machines allow testing frequency at 0.1-200 Hz. The main advantage of ultrasonic fatigue testing at 20 kHz is performing Although S-N curve is determined by experiment, the fatigue strength corresponding to a given fatigue life should be determined by statistical method considering the scatter of fatigue properties. In this report, the statistical methods for evaluation of fatigue test data is investigated

  18. A gender-based analysis of work patterns, fatigue, and work/life balance among physicians in postgraduate training.

    Science.gov (United States)

    Gander, Philippa; Briar, Celia; Garden, Alexander; Purnell, Heather; Woodward, Alistair

    2010-09-01

    To document fatigue in New Zealand junior doctors in hospital-based clinical training positions and identify work patterns associated with work/life balance difficulties. This workforce has had a duty limitation of 72 hours/week since 1985. The authors chose a gender-based analytical approach because of the increasing proportion of female medical graduates. The authors mailed a confidential questionnaire to all 2,154 eligible junior doctors in 2003. The 1,412 respondents were working > or = 40 hours/week (complete questionnaires from 1,366: response rate: 63%; 49% women). For each participant, the authors calculated a multidimensional fatigue risk score based on sleep and work patterns. Women were more likely to report never/rarely getting enough sleep (P life (odds ratio: 3.83; 95% CI: 2.79-5.28), home life (3.37; 2.43-4.67), personal relationships (2.12; 1.57-2.86), and other commitments (3.06; 2.23-4.19).Qualitative analyses indicated a common desire among men and women for better work/life balance and for part-time work, particularly in relation to parenthood. Limitation of duty hours alone is insufficient to manage fatigue risk and difficulties in maintaining work/life balance. These findings have implications for schedule design, professional training, and workforce planning.

  19. Fatigue failure of sandwich beams with face sheet wrinkle defects

    DEFF Research Database (Denmark)

    Leong, Martin Klitgaard; Hvejsel, C.F.; Thomsen, Ole Thybo

    2012-01-01

    This paper presents experimental fatigue results for GFRP face sheet/balsa core sandwich beams with face sheet wrinkle defects, subjected to fully reversed in-plane fatigue loading. An estimate of the fatigue design limit is presented, based on static test results, finite element analyses and app...

  20. Side Effects: Fatigue

    Science.gov (United States)

    Fatigue is a common side effect of many cancer treatments such as chemotherapy, radiation therapy, immunotherapy, and surgery. Anemia and pain can also cause fatigue. Learn about symptoms and way to manage fatigue.

  1. Fulgide-based WRE holographic materials: influence of the matrix on the fatigue process

    Science.gov (United States)

    Lessard, Roger A.; Lafond, Christophe; Darderian, Geraldine; Gardette, Jean-Luc; Rivaton, Agnes; Bolte, Michele

    2003-12-01

    The reversible reaction that takes place in the writable, readable, erasable (WRE) photosensitive materials involving fulgides (ABERCHROM 540 and 670) was investigated with a photochemical and holographic approach. It appeared that the fatigue of the photosensitive material was strongly dependent on the properties of the matrix used as a support. This was precisely established both by spectroscopic monitoring (λmax, absorbancemax, photo-stationary state) and by following the diffraction efficiency η values. There was a nice correlation between the evolution of the spectral features of C isomer and of the η values all along the WRE cycles. This combined approach was applied to four different supports: PVK, PMMA, PEPC/PS and epoxy RESIN. So for both fulgides: (1) PVK, frequently used in optics, appears as being the worst one. The starting fulgides were destroyed after only a few WRE cycles. This was assigned to the intrinsic photoaging of PVK whose absorption in UV domain is far from negligible and leads to the formation of radical species able to attack the fulgide. (2) Holograms recorded in PMMA and PEPC/PS present similar behavior with a loss of ~10% after 8 cycles. (3) Epoxy RESIN appears to be a very good candidate for these reversible systems; no fatigue was observed after 40 cycles. It has to be attributed to the matrix in which the detrimental rotation process, giving rise to the non photochromic Z isomer, is strongly inhibited.

  2. Hubungan antara Fatigue, Jumlah CD4, dan Kadar Hemoglobin pada Pasien yang Terinfeksi Human Immunodeficiency Virus (HIV

    Directory of Open Access Journals (Sweden)

    Kusman Ibrahim

    2018-01-01

    Full Text Available Keberadaan Human Immunodeficiency Virus (HIV di dalam tubuh secara terus menerus menyebabkan gangguan pada hampir semua sistem tubuh yang berdampak pada munculnya gejala kelelahan (fatigue. Fatigue banyak dilaporkan pada penderita HIV/AIDS dengan prevalensi berkisar antara 20% sampai 60%. Penelitian ini bertujuan menguji hubungan antara fatigue dengan jumlah CD4 dan kadar Hb pada pasien HIV/AIDS. Sebanyak 77 responden direkrut secara purposif di sebuah Klinik Rawat Jalan Rumah Sakit di Kota Bandung. Fatigue diukur menggunakan kuesioner HIV Related Fatigue Score (HRFS. Data yang terkumpul dianalisis menggunakan uji pearson correlation. Hasil penelitian menunjukkan terdapat hubungan yang bermakna antara fatigue dengan jumlah CD4 dalam darah (r = -.289, p< 0.05 dan kadar Hb (r = -.349, p< 0.05. Selain itu, kadar Hb memiliki hubungan yang bermakna dengan jumlah CD4 pada pasien HIV/AIDS (r = .360, p < .01. Hasil penelitian ini mengindikasikan perlunya monitoring kadar CD4 dan Hb secara berkala dan melakukan intervensi untuk mengatasi penurunan Hb dan CD4 sesegera mungkin sehingga dapat mencegah agar fatigue tidak berkelanjutan. Kata kunci: CD4, fatigue, hemoglobin, HIV/AIDS.   The Correlation of Between Fatigue, CD4 Cell Count, and Hemoglobin Level among HIV/AIDS Patients Abstract The existence of Human Immunodeficiency Virus (HIV in the body continuously causes disruption in almost all body systems that impact on the emergence of symptoms of fatigue. Fatigue was widely reported in HIV/AIDS patients with prevalence ranging from 20% to 60%. This study examined the relationship between fatigue and CD4 cell count and hemoglobin levels in HIV/AIDS patients. A total of 77 respondents were recruited purposively in Outpatient Clinic, General Hospital Bandung City. Fatigue was measured using the HIV Related Fatigue Score (HRFS questionnaire. The collected data were analyzed using pearson correlation product moment. The results showed there were significant

  3. Fatigue strength ofcomposite wind turbine blade structures

    DEFF Research Database (Denmark)

    Ardila, Oscar Gerardo Castro

    Wind turbines are normally designed to withstand 20-30 years of life. During this period, the blades, which are the main rotating structures of a wind turbine, are subjected to high fluctuating load conditions as a result of a combination of gravity, inertia, and aeroelastic forces. For this reason......, fatigue is one of the foremost concerns during the design of these structures. However, current standard fatigue methods used for designing wind turbine blades seem not to be completely appropriate for these structures because they are still based on methods developed for metals and not for composite...... materials from which the blades are made. In this sense, the aim of this work is to develop more accurate and reliable fatigue-life prediction models for composite wind turbine blades. In this project, two types of fatigue models are implemented: fatigue-life models and damage mechanics models. In the first...

  4. Interconnect fatigue design for terrestrial photovoltaic modules

    Science.gov (United States)

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

    1982-03-01

    The results of comprehensive investigation of interconnect fatigue that has led to the definition of useful reliability-design and life-prediction algorithms are presented. Experimental data 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--ie., 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.

  5. A randomized controlled trial of qigong exercise on fatigue symptoms, functioning, and telomerase activity in persons with chronic fatigue or chronic fatigue syndrome.

    Science.gov (United States)

    Ho, Rainbow T H; Chan, Jessie S M; Wang, Chong-Wen; Lau, Benson W M; So, Kwok Fai; Yuen, Li Ping; Sham, Jonathan S T; Chan, Cecilia L W

    2012-10-01

    Chronic fatigue is common in the general population. Complementary therapies are often used by patients with chronic fatigue or chronic fatigue syndrome to manage their symptoms. This study aimed to assess the effect of a 4-month qigong intervention program among patients with chronic fatigue or chronic fatigue syndrome. Sixty-four participants were randomly assigned to either an intervention group or a wait list control group. Outcome measures included fatigue symptoms, physical functioning, mental functioning, and telomerase activity. Fatigue symptoms and mental functioning were significantly improved in the qigong group compared to controls. Telomerase activity increased in the qigong group from 0.102 to 0.178 arbitrary units (p chronic fatigue and chronic fatigue syndrome.

  6. Fatigue strength of socket welded pipe joint

    International Nuclear Information System (INIS)

    Iida, K.; Matsuda, F.; Sato, M.; Higuchi, M.; Nakagawa, A.

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