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Sample records for modeling combat fatigue

  1. Recognising and combating compassion fatigue in nursing.

    Science.gov (United States)

    Mendes, Aysha

    In this monthly column, Aysha Mendes explores the reasons why nurses may feel compassion fatigue and ways NHS organisations and nurses themselves can engage in activities that will help them renew their emotional energy.

  2. Cumulative fatigue damage models

    Science.gov (United States)

    Mcgaw, Michael A.

    1988-01-01

    The problem of calculating expected component life under fatigue loading conditions is complicated by the fact that component loading histories contain, in many cases, cyclic loads of widely varying amplitudes. In such a case a cumulative damage model is required, in addition to a fatigue damage criterion, or life relationship, in order to compute the expected fatigue life. The traditional cumulative damage model used in design is the linear damage rule. This model, while being simple to use, can yield grossly unconservative results under certain loading conditions. Research at the NASA Lewis Research Center has led to the development of a nonlinear cumulative damage model, named the double damage curve approach (DDCA), that has greatly improved predictive capability. This model, which considers the life (or loading) level dependence of damage evolution, was applied successfully to two polycrystalline materials, 316 stainless steel and Haynes 188. The cumulative fatigue behavior of the PWA 1480 single-crystal material is currently being measured to determine the applicability of the DDCA for this material.

  3. Combating compassion fatigue: an exemplar of an approach to nursing renewal.

    Science.gov (United States)

    Romano, Jean; Trotta, Rebecca; Rich, Victoria L

    2013-01-01

    Compassion fatigue is a phenomenon commonly experienced by nurses. The cumulative emotional burden of caring for critically ill patients and their families, coupled with the increasing complexity of the health care practice environment, significantly drives the experience of compassion fatigue. Compassion fatigue can negatively impact nurses' physical and emotional well-being. If left unaddressed, compassion fatigue can lead to burnout among nurses. Burnout has been correlated to increased patient mortality, increased infection rates, and decreased patient satisfaction. In addition, it causes nurses to leave the nursing profession. Opportunities for nursing renewal, coupled with a leadership culture that values renewal practices, could combat the negative effects of compassion fatigue. A Center for Nursing Renewal was created at the Hospital of the University of Pennsylvania in Philadelphia, Pennsylvania, to provide a variety of renewal opportunities for nurses. This center is supported by a nursing culture that recognizes the ill effects of compassion fatigue and promotes wellness and renewal practices among nurses.

  4. Fatigue modelling for gas nitriding

    Directory of Open Access Journals (Sweden)

    H. Weil

    2016-10-01

    Full Text Available The present study aims to develop an algorithm able to predict the fatigue lifetime of nitrided steels. Linear multi-axial fatigue criteria are used to take into account the gradients of mechanical properties provided by the nitriding process. Simulations on rotating bending fatigue specimens are made in order to test the nitrided surfaces. The fatigue model is applied to the cyclic loading of a gear from a simulation using the finite element software Ansys. Results show the positive contributions of nitriding on the fatigue strength

  5. Medical Movies on the Web Debuts with Gene Kelly's "Combat Fatigue Irritability" 1945 Film | NIH MedlinePlus the ...

    Science.gov (United States)

    ... National Library of Medicine (NLM) is a World War II U.S. Navy training film directed by and starring Gene Kelly, who was then a rising Hollywood star. Combat Fatigue Irritability is a historically significant, yet ...

  6. Nonlinear cumulative damage model for multiaxial fatigue

    Institute of Scientific and Technical Information of China (English)

    SHANG De-guang; SUN Guo-qin; DENG Jing; YAN Chu-liang

    2006-01-01

    On the basis of the continuum fatigue damage theory,a nonlinear uniaxial fatigue cumulative damage model is first proposed.In order to describe multiaxial fatigue damage characteristics,a nonlinear multiaxial fatigue cumulative damage model is developed based on the critical plane approach,The proposed model can consider the multiaxial fatigue limit,mean hydrostatic pressure and the unseparated characteristic for the damage variables and loading parameters.The recurrence formula of fatigue damage model was derived under multilevel loading,which is used to predict multiaxial fatigue life.The results showed that the proposed nonlinear multiaxial fatigue cumulative damage model is better than Miner's rule.

  7. Combat modeling with partial differential equations

    Energy Technology Data Exchange (ETDEWEB)

    Protopopescu, V.; Santoro, R.T.; Dockery, J.; Cox, R.L.; Barnes, J.M.

    1987-11-01

    A new analytic model based on coupled nonlinear partial differential equations is proposed to describe the temporal and spatial evolution of opposing forces in combat. Analytic descriptions of combat have been developed previously using relatively simpler models based on ordinary differential equations (.e.g, Lanchester's equations of combat) that capture only the global temporal variation of the forces, but not their spatial movement (advance, retreat, flanking maneuver, etc.). The rationale for analytic models and, particularly, the motivation for the present model are reviewed. A detailed description of this model in terms of the mathematical equations together with the possible and plausible military interpretation are presented. Numerical solutions of the nonlinear differential equation model for a large variety of parameters (battlefield length, initial force ratios, initial spatial distribution of forces, boundary conditions, type of interaction, etc.) are implemented. The computational methods and computer programs are described and the results are given in tabular and graphic form. Where possible, the results are compared with the predictions given by the traditional Lanchester equations. Finally, a PC program is described that uses data downloaded from the mainframe computer for rapid analysis of the various combat scenarios. 11 refs., 10 figs., 5 tabs.

  8. Peridynamic model for fatigue cracking.

    Energy Technology Data Exchange (ETDEWEB)

    Silling, Stewart Andrew; Abe Askari (Boeing)

    2014-10-01

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

  9. Modelling combat strategies in fungal mycelia.

    Science.gov (United States)

    Boswell, Graeme P

    2012-07-07

    Fungal mycelia have a well-established role in nutrient cycling and are widely used as agents in biological control and in the remediation of polluted landscapes. Competition and combat between different fungal communities is common in these contexts and its outcome impacts on local biodiversity and the success of such biotechnological applications. In this investigation a mathematical model representing mycelia as a system of partial differential equations is used to simulate combat between two fungal colonies growing into a nutrient-free domain. The resultant equations are integrated numerically and the model simulates well-established outcomes of combat between fungal communities. The outcome of pairwise combat is shown to depend on numerous factors including the suppression of advancing hyphae in rivals, the degradation of a rival's established biomass and the utilization and redistribution of available nutrient resources. It is demonstrated how non-transitive hierarchies in fungal communities can be established through switching mechanisms, mirroring observations reported in experimental studies, and how specialized defensive structures can emerge through changes in the redistribution of internal resources.

  10. Human performance modeling for system of systems analytics: combat performance-shaping factors.

    Energy Technology Data Exchange (ETDEWEB)

    Lawton, Craig R.; Miller, Dwight Peter

    2006-01-01

    The US military has identified Human Performance Modeling (HPM) as a significant requirement and challenge of future systems modeling and analysis initiatives. To support this goal, Sandia National Laboratories (SNL) has undertaken a program of HPM as an integral augmentation to its system-of-system (SoS) analytics capabilities. The previous effort, reported in SAND2005-6569, evaluated the effects of soldier cognitive fatigue on SoS performance. The current effort began with a very broad survey of any performance-shaping factors (PSFs) that also might affect soldiers performance in combat situations. The work included consideration of three different approaches to cognition modeling and how appropriate they would be for application to SoS analytics. This bulk of this report categorizes 47 PSFs into three groups (internal, external, and task-related) and provides brief descriptions of how each affects combat performance, according to the literature. The PSFs were then assembled into a matrix with 22 representative military tasks and assigned one of four levels of estimated negative impact on task performance, based on the literature. Blank versions of the matrix were then sent to two ex-military subject-matter experts to be filled out based on their personal experiences. Data analysis was performed to identify the consensus most influential PSFs. Results indicate that combat-related injury, cognitive fatigue, inadequate training, physical fatigue, thirst, stress, poor perceptual processing, and presence of chemical agents are among the PSFs with the most negative impact on combat performance.

  11. Combat Simulation Modeling in Naval Special Warfare Mission Planning.

    Science.gov (United States)

    1995-12-01

    This thesis explores the potential role of combat simulation modeling in the Naval Special Warfare mission planning cycle. It discusses methods for...at the tactical level. The thesis concludes by discussing additional applications of combat simulation modeling within the Naval Special Warfare community and makes recommendations for its effective and efficient implementation.

  12. MODELS OF FATIGUE LIFE CURVES IN FATIGUE LIFE CALCULATIONS OF MACHINE ELEMENTS – EXAMPLES OF RESEARCH

    Directory of Open Access Journals (Sweden)

    Grzegorz SZALA

    2014-03-01

    Full Text Available In the paper there was attempted to analyse models of fatigue life curves possible to apply in calculations of fatigue life of machine elements. The analysis was limited to fatigue life curves in stress approach enabling cyclic stresses from the range of low cycle fatigue (LCF, high cycle fatigue (HCF, fatigue limit (FL and giga cycle fatigue (GCF appearing in the loading spectrum at the same time. Chosen models of the analysed fatigue live curves will be illustrated with test results of steel and aluminium alloys.

  13. Common Mathematical Model of Fatigue Characteristics

    Directory of Open Access Journals (Sweden)

    Z. Maléř

    2004-01-01

    Full Text Available This paper presents a new common mathematical model which is able to describe fatigue characteristics in the whole necessary range by one equation only:log N = A(R + B(R ∙ log Sawhere A(R = AR2 + BR + C and B(R = DR2 + AR + F.This model was verified by five sets of fatigue data taken from the literature and by our own three additional original fatigue sets. The fatigue data usually described the region of N 104 to 3 x 106 and stress ratio of R = -2 to 0.5. In all these cases the proposed model described fatigue results with small scatter. Studying this model, following knowledge was obtained:– the parameter ”stress ratio R” was a good physical characteristic– the proposed model provided a good description of the eight collections of fatigue test results by one equation only– the scatter of the results through the whole scope is only a little greater than that round the individual S/N curve– using this model while testing may reduce the number of test samples and shorten the test time– as the proposed model represents a common form of the S/N curve, it may be used for processing uniform objective fatigue life results, which may enable mutual comparison of fatigue characteristics.

  14. Mixed martial arts induces significant fatigue and muscle damage up to 24 hours post-combat.

    Science.gov (United States)

    Ghoul, Nihel; Tabben, Montassar; Miarka, Bianca; Tourny, Claire; Chamari, Karim; Coquart, Jeremy

    2017-06-22

    This study investigates the physiological/physical responses to a simulated mixed martial arts (MMA) competition over 24 hr. Twelve fighters performed a simulated MMA competition, consisting of three 5-min MMA matches. Physiological/physical data were assessed before (Trest), directly after round 1 (Trd1), round 2 (Trd2) and round 3 (Trd3), and then 30-min (Trecovery30min) and/or 24-hr (Trecovery24h) post-competition. Heart rate (HR), rating of perceived exertion (RPE) and blood lactate concentration ([La]) were assessed at Trest, Trd1, Trd2 and Trd3. Biological data were collected at Trest, Trd3, Trecovery30min and Trecovery24h. Physical tests were performed at Trest, Trecovery30min and Trecovery24h. HR, RPE and [La] were high during competition. Leukocytes, hemoglobin, total protein and glycemia were increased at Trd3 compared with all other time points (p<0.05). Cortisol was increased at Trd3 compared with Trest and Trecovery24h (p<0.05). Testosterone was higher at Trd3 and Trecovery30min than Trest (p<0.001). Higher values of uric acid were noted during recovery periods (p<0.001). Lactate dehydrogenase was lower at Trest compared with Trd3, Trecovery30min and Trecovery24h (p<0.05). Countermovement jump was higher at Trest than Trecovery30min (p=0.020). Consequently, MMA is a high-intensity intermittent combat sport that induces significant fatigue and muscle damage, both of which are still present 24-hr post-competition.

  15. Human Muscle Fatigue Model in Dynamic Motions

    CERN Document Server

    Ma, Ruina; Bennis, Fouad; Ma, Liang

    2012-01-01

    Human muscle fatigue is considered to be one of the main reasons for Musculoskeletal Disorder (MSD). Recent models have been introduced to define muscle fatigue for static postures. However, the main drawbacks of these models are that the dynamic effect of the human and the external load are not taken into account. In this paper, each human joint is assumed to be controlled by two muscle groups to generate motions such as push/pull. The joint torques are computed using Lagrange's formulation to evaluate the dynamic factors of the muscle fatigue model. An experiment is defined to validate this assumption and the result for one person confirms its feasibility. The evaluation of this model can predict the fatigue and MSD risk in industry production quickly.

  16. Eagle II: A prototype for multi-resolution combat modeling

    Energy Technology Data Exchange (ETDEWEB)

    Powell, D.R.; Hutchinson, J.L.

    1993-02-01

    Eagle 11 is a prototype analytic model derived from the integration of the low resolution Eagle model with the high resolution SIMNET model. This integration promises a new capability to allow for a more effective examination of proposed or existing combat systems that could not be easily evaluated using either Eagle or SIMNET alone. In essence, Eagle II becomes a multi-resolution combat model in which simulated combat units can exhibit both high and low fidelity behavior at different times during model execution. This capability allows a unit to behave in a highly manner only when required, thereby reducing the overall computational and manpower requirements for a given study. In this framework, the SIMNET portion enables a highly credible assessment of the performance of individual combat systems under consideration, encompassing both engineering performance and crew capabilities. However, when the assessment being conducted goes beyond system performance and extends to questions of force structure balance and sustainment, then SISMNET results can be used to ``calibrate`` the Eagle attrition process appropriate to the study at hand. Advancing technologies, changes in the world-wide threat, requirements for flexible response, declining defense budgets, and down-sizing of military forces motivate the development of manpower-efficient, low-cost, responsive tools for combat development studies. Eagle and SIMNET both serve as credible and useful tools. The integration of these two models promises enhanced capabilities to examine the broader, deeper, more complex battlefield of the future with higher fidelity, greater responsiveness and low overall cost.

  17. Pilot's visual attention allocation modeling under fatigue.

    Science.gov (United States)

    Wu, Xu; Wanyan, Xiaoru; Zhuang, Damin

    2015-01-01

    Human factors involved with visual attention mechanism and fatigue are critical causes of modern aviation accidents. To investigate the connection between attention and flight fatigue, a mathematical model of pilot's visual attention allocation was established based on information processing channels. Multi-task condition and current psychophysical state were taken into account as well. Sixteen participants were recruited to perform a long-term dual-task in a Boeing 737-800 flight simulator. The primary task was an envelope flight task and the secondary was an unusual attitude (UA) recovery task. Reaction time of the secondary task was recorded as a behavior performance index, while heart rate and respiration rate were measured as physiological indices as well as fixation distribution as attention allocation index. The experiment results showed a significant affect of experiment time that indicated the occurrence and influence of fatigue. Eye movement tracking also revealed good agreement with the predictable model and hence verified its effectiveness. Moreover, applicability of the model was validated under flight fatigue and multiple tasks condition. The current study provided a quantitative connection between pilot's visual attention allocation and flight fatigue, which was verified in the ergonomics experiment.

  18. Fatigue modeling of materials with complex microstructures

    DEFF Research Database (Denmark)

    Qing, Hai; Mishnaevsky, Leon

    2011-01-01

    A new approach and method of the analysis of microstructure-lifetime relationships of materials with complex structures is presented. The micromechanical multiscale computational analysis of damage evolution in materials with complex hierarchical microstructures is combined with the phenomenologi......A new approach and method of the analysis of microstructure-lifetime relationships of materials with complex structures is presented. The micromechanical multiscale computational analysis of damage evolution in materials with complex hierarchical microstructures is combined...... with the phenomenological model of fatigue damage growth. As a result, the fatigue lifetime of materials with complex structures can be determined as a function of the parameters of their structures. As an example, the fatigue lifetimes of wood modeled as a cellular material with multilayered, fiber reinforced walls were...

  19. A Survey of Combat Models for Use in CARF (Combat Active Replacement Factor) Value Generation

    Science.gov (United States)

    1985-03-01

    requirements for the degree of MASTER OF SCIENCE IN CPERATIONS RESEARCH from the NAVAL POSTGRADUATE SCHOOL darch 1985 Author: tv Approved by :... - n Z ...GENERATION OF A WARTIME ACTIVE REPLACEMENT FACTOR (WARF) 65 A. THE PREPROCESSER ................. 66 B. THE COMBAT SAMPLE GEERATOR (COSAGE) MODEL 66 C. THE...en -T,, , -T T L T 17, V 7777% T -T T K 97 7 Ř 7 T W 71 T 7 - Z W.; ., . 7. , II. THE CARF GENERA7ION SYSTEM TODAY The previous and current CARF

  20. A predictive fatigue life model for anodized 7050 aluminium alloy

    OpenAIRE

    Chaussumier, Michel; Mabru, Catherine; Shahzad, Majid; Chieragatti, Rémy; Rezaï-Aria, Farhad

    2013-01-01

    International audience; The objective of this study is to predict fatigue life of anodized 7050 aluminum alloy specimens. In the case of anodized 7050-T7451 alloy, fractographic observations of fatigue tested specimens showed that pickling pits were the predominant sites for crack nucleation and subsequent failure. It has been shown that fatigue failure was favored by the presence of multiple cracks. From these experimental results, a fatigue life predictive model has been developed including...

  1. A Predictive Model for Massive Transfusion in Combat Casualty Patients

    Science.gov (United States)

    2008-02-01

    A Predictive Model for Massive Transfusion in Combat Casualty Patients Daniel F . McLaughlin, MD, Sarah E. Niles, MD, MPH, Jose Salinas, PhD, Jeremy G...Silver Springs, Maryland. Address for reprints: Daniel F . McLaughlin, MD, United States Insti- tute of Surgical Research, 3400 Rawley E. Chambers...see that here? Thank you again for an excellent study, which I believe should alter practice for many of us. Dr. Daniel F . McLaughlin (US Army

  2. A Verification and Analysis of the USAF/DoD Fatigue Model and Fatigue Management Technology

    Science.gov (United States)

    2005-11-01

    We Nap: Evolution, Chronobiology, and Functions of Polyphasic and Ultrashort Sleep . Stampi, C. (ed) Birkhduser, Boston. Defense Acquisition...Windows® soffivare application of the Sleep , Activity, Fatigue, and Task Effectiveness (SAFTE) applied model. The application, the Fatigue Avoidance...Scheduling Tool (FASTTM) was re-engineered as a clone from the SAFTE specification. The verification considered nine sleep /wake schedules that were

  3. Effective turbulence models and fatigue reliability in wind farms

    DEFF Research Database (Denmark)

    Sørensen, John Dalsgaard; Frandsen, Sten Tronæs; Tarp-Johansen, N.J.

    2008-01-01

    intensity in wakes behind wind turbines can imply a significant reduction in the fatigue lifetime of wind turbines placed in wakes. Ill this paper the design code model ill the wind turbine code [IEC 61400-1, Wind turbine generator systems - Part 1: Safety requirements. 2005] is evaluated from...... a probabilistic point of view, including the importance of modeling the SN-curve by a bi-linear model. Fatigue models relevant for welded, cast steel and fiber reinforced details are considered. Further, the influence on the fatigue reliability is investigated from modeling the fatigue response by a stochastic...

  4. A Dynamic Distribution Model for Combat Logistics

    Science.gov (United States)

    1999-11-23

    develop a heuristic algorithm for a similar problem, only capacity expansion can occur in any amount (modeled with continuous variables) while in...and Rutenberg (1977) solve it with a heuristic algorithm . Our problem is also related to the dynamic facility location problem. This problem seeks to

  5. A dynamic distribution model for combat logistics

    OpenAIRE

    Gue, Kevin R.

    1999-01-01

    New warfare doctrine for the U.S. Marine Corps emphasizes small, highly mobile forces supported from the sea, rather than from large, land based supply points. The goal of logistics planners is to support these forces with as little inventory on land as possible. We show how to configure the land based distribution system over time to support a given battle plan with minimum inventory. Logistics planners could use the model to support tactical or operational decision making.

  6. Graphics development of DCOR: Deterministic combat model of Oak Ridge

    Energy Technology Data Exchange (ETDEWEB)

    Hunt, G. [Georgia Inst. of Tech., Atlanta, GA (United States); Azmy, Y.Y. [Oak Ridge National Lab., TN (United States)

    1992-10-01

    DCOR is a user-friendly computer implementation of a deterministic combat model developed at ORNL. To make the interpretation of the results more intuitive, a conversion of the numerical solution to a graphic animation sequence of battle evolution is desirable. DCOR uses a coarse computational spatial mesh superimposed on the battlefield. This research is aimed at developing robust methods for computing the position of the combative units over the continuum (and also pixeled) battlefield, from DCOR`s discrete-variable solution representing the density of each force type evaluated at gridpoints. Three main problems have been identified and solutions have been devised and implemented in a new visualization module of DCOR. First, there is the problem of distributing the total number of objects, each representing a combative unit of each force type, among the gridpoints at each time level of the animation. This problem is solved by distributing, for each force type, the total number of combative units, one by one, to the gridpoint with the largest calculated number of units. Second, there is the problem of distributing the number of units assigned to each computational gridpoint over the battlefield area attributed to that point. This problem is solved by distributing the units within that area by taking into account the influence of surrounding gridpoints using linear interpolation. Finally, time interpolated solutions must be generated to produce a sufficient number of frames to create a smooth animation sequence. Currently, enough frames may be generated either by direct computation via the PDE solver or by using linear programming techniques to linearly interpolate intermediate frames between calculated frames.

  7. Graphics development of DCOR: Deterministic combat model of Oak Ridge. [Deterministic Combat model of Oak Ridge (DCOR)

    Energy Technology Data Exchange (ETDEWEB)

    Hunt, G. (Georgia Inst. of Tech., Atlanta, GA (United States)); Azmy, Y.Y. (Oak Ridge National Lab., TN (United States))

    1992-10-01

    DCOR is a user-friendly computer implementation of a deterministic combat model developed at ORNL. To make the interpretation of the results more intuitive, a conversion of the numerical solution to a graphic animation sequence of battle evolution is desirable. DCOR uses a coarse computational spatial mesh superimposed on the battlefield. This research is aimed at developing robust methods for computing the position of the combative units over the continuum (and also pixeled) battlefield, from DCOR's discrete-variable solution representing the density of each force type evaluated at gridpoints. Three main problems have been identified and solutions have been devised and implemented in a new visualization module of DCOR. First, there is the problem of distributing the total number of objects, each representing a combative unit of each force type, among the gridpoints at each time level of the animation. This problem is solved by distributing, for each force type, the total number of combative units, one by one, to the gridpoint with the largest calculated number of units. Second, there is the problem of distributing the number of units assigned to each computational gridpoint over the battlefield area attributed to that point. This problem is solved by distributing the units within that area by taking into account the influence of surrounding gridpoints using linear interpolation. Finally, time interpolated solutions must be generated to produce a sufficient number of frames to create a smooth animation sequence. Currently, enough frames may be generated either by direct computation via the PDE solver or by using linear programming techniques to linearly interpolate intermediate frames between calculated frames.

  8. Bayesian inference model for fatigue life of laminated composites

    DEFF Research Database (Denmark)

    Dimitrov, Nikolay Krasimirov; Kiureghian, Armen Der; Berggreen, Christian

    2016-01-01

    A probabilistic model for estimating the fatigue life of laminated composite plates is developed. The model is based on lamina-level input data, making it possible to predict fatigue properties for a wide range of laminate configurations. Model parameters are estimated by Bayesian inference...

  9. Stochastic modeling of thermal fatigue crack growth

    CERN Document Server

    Radu, Vasile

    2015-01-01

    The book describes a systematic stochastic modeling approach for assessing thermal-fatigue crack-growth in mixing tees, based on the power spectral density of temperature fluctuation at the inner pipe surface. It shows the development of a frequency-temperature response function in the framework of single-input, single-output (SISO) methodology from random noise/signal theory under sinusoidal input. The frequency response of stress intensity factor (SIF) is obtained by a polynomial fitting procedure of thermal stress profiles at various instants of time. The method, which takes into account the variability of material properties, and has been implemented in a real-world application, estimates the probabilities of failure by considering a limit state function and Monte Carlo analysis, which are based on the proposed stochastic model. Written in a comprehensive and accessible style, this book presents a new and effective method for assessing thermal fatigue crack, and it is intended as a concise and practice-or...

  10. Can an intercultural education model combat discrimination and xenophobia?

    Directory of Open Access Journals (Sweden)

    Moisès Esteban Guitart

    2010-03-01

    Full Text Available In this article we present a qualitative study conducted with six indigenous and six mestizos from Intercultural University of Chiapas. The aim of the study is to exemplify the mutual perception between different ethno-linguistic groups, as well as the possible change occurred after the admission to the University. That is, opinions about the other group after and before entering the University. We conclude that a higher education intercultural model can promote mutual understanding and relationship between indigenous and mestizos and thus combat prejudices and stereotypes.     

  11. Comparison of multiaxial fatigue damage models under variable amplitude loading

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Hong; Shang, De Guang; Tian, Yu Jie [Beijing Univ. of Technology, Beijing (China); Liu, Jian Zhong [Beijing Institute of Aeronautical Materials, Beijing (China)

    2012-11-15

    Based on the cycle counting method of Wang and Brown and on the linear accumulation damage rule of Miner, four multiaxial fatigue damage models without any weight factors proposed by Pan et al., Varvani Farahani, Shang and Wang, and Shang et al. are used to compute fatigue damage. The procedure is evaluated using the low cycle fatigue experimental data of 7050 T7451 aluminum alloy and En15R steel under tension/torsion variable amplitude loading. The results reveal that the procedure is convenient for engineering design and application, and that the four multiaxial fatigue damage models provide good life estimates.

  12. Physical and Model Uncertainty for Fatigue Design of Composite Material

    DEFF Research Database (Denmark)

    Toft, Henrik Stensgaard; Sørensen, John Dalsgaard

    The main aim of the present report is to establish stochastic models for the uncertainties related to fatigue design of composite materials. The uncertainties considered are the physical uncertainty related to the static and fatigue strength and the model uncertainty related to Miners rule...

  13. Ignoring the Innocent: Non-combatants in Urban Operations and in Military Models and Simulations

    Science.gov (United States)

    2006-01-01

    of non- combatants. Increasing the number of non-combatants and introducing more realistic non-combatant behavior would add realism to military...discussed, Schelling (1978) uses ABM to _________________ 41 New Line Cinema , Lord of the Rings: the Two Towers Extended DVD, 2003. See the feature on...effectiveness of a certain weapon system may have a high degree of visual realism but still make for a poor model if there are significant oversights

  14. Linking asphalt binder fatigue to asphalt mixture fatigue performance using viscoelastic continuum damage modeling

    Science.gov (United States)

    Safaei, Farinaz; Castorena, Cassie; Kim, Y. Richard

    2016-08-01

    Fatigue cracking is a major form of distress in asphalt pavements. Asphalt binder is the weakest asphalt concrete constituent and, thus, plays a critical role in determining the fatigue resistance of pavements. Therefore, the ability to characterize and model the inherent fatigue performance of an asphalt binder is a necessary first step to design mixtures and pavements that are not susceptible to premature fatigue failure. The simplified viscoelastic continuum damage (S-VECD) model has been used successfully by researchers to predict the damage evolution in asphalt mixtures for various traffic and climatic conditions using limited uniaxial test data. In this study, the S-VECD model, developed for asphalt mixtures, is adapted for asphalt binders tested under cyclic torsion in a dynamic shear rheometer. Derivation of the model framework is presented. The model is verified by producing damage characteristic curves that are both temperature- and loading history-independent based on time sweep tests, given that the effects of plasticity and adhesion loss on the material behavior are minimal. The applicability of the S-VECD model to the accelerated loading that is inherent of the linear amplitude sweep test is demonstrated, which reveals reasonable performance predictions, but with some loss in accuracy compared to time sweep tests due to the confounding effects of nonlinearity imposed by the high strain amplitudes included in the test. The asphalt binder S-VECD model is validated through comparisons to asphalt mixture S-VECD model results derived from cyclic direct tension tests and Accelerated Loading Facility performance tests. The results demonstrate good agreement between the asphalt binder and mixture test results and pavement performance, indicating that the developed model framework is able to capture the asphalt binder's contribution to mixture fatigue and pavement fatigue cracking performance.

  15. Computational stress and damage modelling for rolling contact fatigue

    DEFF Research Database (Denmark)

    Cerullo, Michele

    Rolling contact fatigue in radial roller bearings is studied by means of a 2D plane strain nite element program. The Dang Van multiaxial fatigue criterion is firstly used, in a macroscopic study modeling the bearing raceway, to investigate the region where fatigue cracks are more likely to nucleate....... A Hertzian and an elastohydrodynamic lubricated pressure distribution are applied on the bearing raceway to model the contact between the roller and the ring, and the results are compared in light of the Dang Van criterion. The beneficial effects of a hardening treatment of the ring surface...

  16. Combating Combination of Hypertension and Diabetes in Different Rat Models

    Directory of Open Access Journals (Sweden)

    Talma Rosenthal

    2010-03-01

    Full Text Available Rat experimental models are used extensively for studying physiological mechanisms and treatments of hypertension and diabetes co-existence. Each one of these conditions is a major risk factor for cardiovascular disease (CVD, and the combination of the two conditions is a potent enhancer of CVD. Five major animal models that advanced our understanding of the mechanisms and therapeutic approaches in humans are discussed in this review: Zucker, Goto-Kakizaki, SHROB, SHR/NDmcr-cp and Cohen Rosenthal diabetic hypertensive (CRDH rats. The use of various drugs, such as angiotensin-converting enzyme (ACE inhibitors (ACEIs, various angiotensin receptor blockers (ARBs, and calcium channel blockers (CCBs, to combat the effects of concomitant pathologies on the combination of diabetes and hypertension, as well as the non-pharmacological approach are reviewed in detail for each rat model. Results from experiments on these models indicate that classical factors contributing to the pathology of hypertension and diabetes combination—Including hypertension, hyperglycemia, hyperinsulinemia and hyperlipidemia—can now be treated, although these treatments do not completely prevent renal complications. Animal studies have focused on several mechanisms involved in hypertension/diabetes that remain to be translated into clinical medicine, including hypoxia, oxidative stress, and advanced glycation. Several target molecules have been identified that need to be incorporated into a treatment modality. The challenge continues to be the identification and interpretation of the clinical evidence from the animal models and their application to human treatment.

  17. Probabilistic models for creep-fatigue in a steel alloy

    Science.gov (United States)

    Ibisoglu, Fatmagul

    In high temperature components subjected to long term cyclic operation, simultaneous creep and fatigue damage occur. A new methodology for creep-fatigue life assessment has been adopted without the need to separate creep and fatigue damage or expended life. Probabilistic models, described by hold times in tension and total strain range at temperature, have been derived based on the creep rupture behavior of a steel alloy. These models have been validated with the observed creep-fatigue life of the material with a scatter band close to a factor of 2. Uncertainties of the creep-fatigue model parameters have been estimated with WinBUGS which is an open source Bayesian analysis software tool that uses Markov Chain Monte Carlo method to fit statistical models. Secondly, creep deformation in stress relaxation data has been analyzed. Well performing creep equations have been validated with the observed data. The creep model with the highest goodness of fit among the validated models has been used to estimate probability of exceedance at 0.6% strain level for the steel alloy.

  18. Force-time course parameters and force fatigue model during an intermittent fatigue protocol in motorcycle race riders.

    Science.gov (United States)

    Marina, M; Rios, M; Torrado, P; Busquets, A; Angulo-Barroso, R

    2015-06-01

    Fatigue in forearm muscles may be critical for motorcycle riders in relation to performance and forearm disorders. Force-time course parameters were examined to better characterize the reduction in the maximal force generating capacity (MVC) during an intermittent fatigue protocol (IFP) specifically designed for motorcycle riders. Also, a mathematical force fatigue model is proposed. Forty motorcyclists (aged 27.6 ± 6.8 years) performed an IFP that simulated the braking gesture and posture of a rider. Fatigue was confirmed by a 40% decrement of the normalized MVC in comparison with basal value. Contraction time increased in comparison with basal condition (P ≤ 0.034). Relaxation kinetics presented two phases: (a) a pre-fatigue phase where half relaxation time (HRTraw ) and normalized (HRTnor ) decreased (P ≤ 0.013) while relaxation rate (RRraw ) remained unchanged; and (b) a fatiguing phase where HRTraw , HRTnor increased and RRraw decreased (P ≤ 0.047). Normalized RRraw (RRnor ) declined progressively (P ≤ 0.016). The proposed nonlinear force fatigue model confirmed a satisfactory adjustment (R(2)  = 0.977 ± 0.018). This mathematical expression derived three patterns of force fatigue: three-phase, exponential and linear, representing 70%, 13%, and 17% of the participants, respectively. Overall, these results provided further support to force fatigue theoretical and applied proposals.

  19. Bayesian inference and model comparison for metallic fatigue data

    KAUST Repository

    Babuška, Ivo

    2016-02-23

    In this work, we present a statistical treatment of stress-life (S-N) data drawn from a collection of records of fatigue experiments that were performed on 75S-T6 aluminum alloys. Our main objective is to predict the fatigue life of materials by providing a systematic approach to model calibration, model selection and model ranking with reference to S-N data. To this purpose, we consider fatigue-limit models and random fatigue-limit models that are specially designed to allow the treatment of the run-outs (right-censored data). We first fit the models to the data by maximum likelihood methods and estimate the quantiles of the life distribution of the alloy specimen. To assess the robustness of the estimation of the quantile functions, we obtain bootstrap confidence bands by stratified resampling with respect to the cycle ratio. We then compare and rank the models by classical measures of fit based on information criteria. We also consider a Bayesian approach that provides, under the prior distribution of the model parameters selected by the user, their simulation-based posterior distributions. We implement and apply Bayesian model comparison methods, such as Bayes factor ranking and predictive information criteria based on cross-validation techniques under various a priori scenarios.

  20. Probabilistic Material Strength Degradation Model for Inconel 718 Components Subjected to High Temperature, Mechanical Fatigue, Creep and Thermal Fatigue Effects

    Science.gov (United States)

    Bast, Callie Corinne Scheidt

    1994-01-01

    This thesis presents the on-going development of methodology for a probabilistic material strength degradation model. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes four effects that typically reduce lifetime strength: high temperature, mechanical fatigue, creep, and thermal fatigue. Statistical analysis was conducted on experimental Inconel 718 data obtained from the open literature. This analysis provided regression parameters for use as the model's empirical material constants, thus calibrating the model specifically for Inconel 718. Model calibration was carried out for four variables, namely, high temperature, mechanical fatigue, creep, and thermal fatigue. Methodology to estimate standard deviations of these material constants for input into the probabilistic material strength model was developed. Using the current version of PROMISS, entitled PROMISS93, a sensitivity study for the combined effects of mechanical fatigue, creep, and thermal fatigue was performed. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing a combination of mechanical fatigue and high temperature effects by model to the combination by experiment were conducted. Thus, for Inconel 718, the basic model assumption of independence between effects was evaluated. Results from this limited verification study strongly supported this assumption.

  1. From the combat medic to the forward surgical team: the Madigan model for improving trauma readiness of brigade combat teams fighting the Global War on Terror.

    Science.gov (United States)

    Sohn, Vance Y; Miller, Joseph P; Koeller, Craig A; Gibson, Steven O; Azarow, Kenneth S; Myers, Jerome B; Beekley, Alec C; Sebesta, James A; Christensen, Jon B; Rush, Robert M

    2007-03-01

    Medics assigned to combat units have a notable paucity of trauma experience. Our goal was to provide intense trauma refresher training for the conventional combat medic to better prepare them for combat casualty care in the War on Terror. Our Tactical Combat Casualty Care Course (TC3) consisted of the following five phases: (1) One and one-half-day didactic session; (2) Half-day simulation portion with interactive human surgical simulators for anatomical correlation of procedures and team building; (3) Half-day of case presentations and triage scenarios from Iraq/Afghanistan and associated skills stations; (4) Half-day live tissue lab where procedures were performed on live anesthetized animals in a controlled environment; and (5) One-day field phase where live anesthetized animals and surgical simulators were combined in a real-time, field-training event to simulate realistic combat injuries, evacuation problems, and mass casualty scenarios. Data collection consisted of surveys, pre- and posttests, and after-action comments. A total of 1317 personnel participated in TC3 from October 2003 through May 2005. Over the overlapping study period from December 2004 to April 2005, 327 soldiers participated in the formal five-phase course. Three hundred four (94%) students were combat medics who were preparing for combat operations in Iraq or Afghanistan. Of those completing the training, 97% indicated their confidence and ability to treat combat casualties were markedly improved. Moreover, of those 140 medics who took the course and deployed to Iraq for 1 year, 99% indicated that the principles taught in the TC3 course helped with battlefield management of injured casualties during their deployment. The hybrid training model is an effective method for training medical personnel to deal with modern battle injuries. This course increases the knowledge and confidence of combat medics deploying and fighting the Global War on Terrorism.

  2. Bayesian inference and model comparison for metallic fatigue data

    KAUST Repository

    Babuska, Ivo

    2016-01-06

    In this work, we present a statistical treatment of stress-life (S-N) data drawn from a collection of records of fatigue experiments that were performed on 75S-T6 aluminum alloys. Our main objective is to predict the fatigue life of materials by providing a systematic approach to model calibration, model selection and model ranking with reference to S-N data. To this purpose, we consider fatigue-limit models and random fatigue-limit models that are specially designed to allow the treatment of the run-outs (right-censored data). We first fit the models to the data by maximum likelihood methods and estimate the quantiles of the life distribution of the alloy specimen. We then compare and rank the models by classical measures of fit based on information criteria. We also consider a Bayesian approach that provides, under the prior distribution of the model parameters selected by the user, their simulation-based posterior distributions.

  3. Probabilistic Model for Fatigue Crack Growth in Welded Bridge Details

    DEFF Research Database (Denmark)

    Toft, Henrik Stensgaard; Sørensen, John Dalsgaard; Yalamas, Thierry

    2013-01-01

    In the present paper a probabilistic model for fatigue crack growth in welded steel details in road bridges is presented. The probabilistic model takes the influence of bending stresses in the joints into account. The bending stresses can either be introduced by e.g. misalignment or redistributio...

  4. Fatigue Reliability and Effective Turbulence Models in Wind Farms

    DEFF Research Database (Denmark)

    Sørensen, John Dalsgaard; Frandsen, S.; Tarp-Johansen, N.J.

    2007-01-01

    behind wind turbines can imply a significant reduction in the fatigue lifetime of wind turbines placed in wakes. In this paper the design code model in the wind turbine code IEC 61400-1 (2005) is evaluated from a probabilistic point of view, including the importance of modeling the SN-curve by linear...

  5. Extension of recovery time from fatigue by repeated rest with short-term sleep during continuous fatigue load: Development of chronic fatigue model.

    Science.gov (United States)

    Kanzaki, Akinori; Okauchi, Takashi; Hu, Di; Shingaki, Tomotaka; Katayama, Yumiko; Koyama, Hidenori; Watanabe, Yasuyoshi; Cui, Yilong

    2016-05-01

    Homeostasis is known to be involved in maintaining the optimal internal environment, helping to achieve the best performance of biological functions. At the same time, a deviation from optimal conditions often attenuates the performance of biological functions, and such restricted performance could be considered as individual fatigue, including physical and mental fatigue. The present study seeks to develop an animal model of chronic or subacute fatigue in which the recovery time is extended through the gradual disruption of homeostasis. We show that repeated short-term rest periods with certain lengths of sleep during continuous fatigue loading extend recovery from spontaneous nighttime activity but not physical performance in comparison with a continuous fatigue-loading procedure. Furthermore, the immobility time in a forced swimming test was extended by repeated short-term rests. These results suggest that repeated short-term rest with certain lengths of sleep during continuous fatigue loading is able to extend the recovery from mental fatigue but not from physical fatigue and that this effect might occur via the disruption of a homeostatic mechanism that is involved in restoring the optimal internal environment.

  6. The Quantified Judgement Model and Historic Ground Combat

    Science.gov (United States)

    1988-09-01

    GEOGRAPHIC REGION NUMBER OF INCIDENTS Atlantic Community 572 Middle East 159 Asia 102 East Europe 8 Latin America 282 Africa 37 Figure 2. Distribution of...FORCE BLUE FORCE S 1500 500 OE 1.0 2.5 Q 2.0 1.5 The Combat Power Ratios are: P(r) 1500x 1.0x 2.0 -1.6 Pfb) - 500x 2.5 x 1.5 and PIb ) _ 500 x 250 x 150

  7. Beyond compassion fatigue: the transactional model of physician compassion.

    Science.gov (United States)

    Fernando, Antonio T; Consedine, Nathan S

    2014-08-01

    Physician compassion is expected by both patients and the medical profession and is central to effective clinical practice. Yet, despite the centrality of compassion to medical practice, most compassion-related research has focused on compassion fatigue, a specific type of burnout among health providers. Although such research has highlighted the phenomenon among clinicians, the focus on compassion fatigue has neglected the study of compassion itself. In this article, we present the Transactional Model of Physician Compassion. After briefly critiquing the utility of the compassion fatigue concept, we offer a view in which physician compassion stems from the dynamic but interrelated influences of physician, patient and family, clinical situation, and environmental factors. Illuminating the specific aspects of physicians' intrapersonal, interpersonal, clinical, and professional functioning that may interfere with or enhance compassion allows for targeted interventions to promote compassion in both education and practice as well as to reduce the barriers that impede it.

  8. A subregional model for delamination prediction of rubber composite under fatigue loading

    Institute of Scientific and Technical Information of China (English)

    TIAN Zhen-hui; TAN Hui-feng

    2005-01-01

    Results from fatigue experiments of cross-laminated steel cord-rubber composites (SCRC) indicate that fatigue damage life can be categorized into three regimes. In terms of fatigue modes, a subregional fatigue model is developed to describe the damages evolution of SCRC under fatigue loads. Firstly, finite element analysis is introduced to determine interply stress distribution of the specimen. Then, based on the experimental fatigue data, subregional models are introduced to simulate relations between maximum strain, effective stiffness,delamination shear stress and fatigue cycles. Relations between crack density, delamination length growth rate,macro crack density and cycles are modeled by two semi-empirical models. A reasonable prediction result was achieved by the current model, where model parameters can be determined by basic outputs of fatigue testing.

  9. Hybrid reliability model for fatigue reliability analysis of steel bridges

    Institute of Scientific and Technical Information of China (English)

    曹珊珊; 雷俊卿

    2016-01-01

    A kind of hybrid reliability model is presented to solve the fatigue reliability problems of steel bridges. The cumulative damage model is one kind of the models used in fatigue reliability analysis. The parameter characteristics of the model can be described as probabilistic and interval. The two-stage hybrid reliability model is given with a theoretical foundation and a solving algorithm to solve the hybrid reliability problems. The theoretical foundation is established by the consistency relationships of interval reliability model and probability reliability model with normally distributed variables in theory. The solving process is combined with the definition of interval reliability index and the probabilistic algorithm. With the consideration of the parameter characteristics of theS−N curve, the cumulative damage model with hybrid variables is given based on the standards from different countries. Lastly, a case of steel structure in the Neville Island Bridge is analyzed to verify the applicability of the hybrid reliability model in fatigue reliability analysis based on the AASHTO.

  10. A model for high-cycle fatigue crack propagation

    Energy Technology Data Exchange (ETDEWEB)

    Balbi, Marcela Angela [Rosario National Univ. (Argentina); National Council of Scientific Research and Technology (CONICET) (Argentina)

    2017-02-01

    This paper deals with the prediction of high-cycle fatigue behavior for four different materials (7075-T6 alloy, Ti-6Al-4 V alloy, JIS S10C steel and 0.4 wt.-% C steel) using Chapetti's approach to estimate the fatigue crack propagation curve. In the first part of the paper, a single integral equation for studying the entire propagation process is determined using the recent results of Santus and Taylor, which consider a double regime of propagation (short and long cracks) characterized by the model of El Haddad. The second part of the paper includes a comparison of the crack propagation behavior model proposed by Navarro and de los Rios with the one mentioned in the first half of this work. The results allow us to conclude that the approach presented in this paper is a good and valid estimation of high-cycle fatigue crack propagation using a single equation to describe the entire fatigue crack regime.

  11. A Small-Unit Amphibious Operation Combat Model.

    Science.gov (United States)

    1983-03-01

    ASIC LANC COMBAT ALGC--ITHYM C REAL*8 CSEEOl p EIL T S LF~TTS tP15J C0OMMON IGFPI/ IP9CIR(6W IEC %C(61,.𔃾VTOIR(16I,X(6I Y(61,SPD(61COMMCON /C.RP2/ TA...EVIST.GE.ZT) CO~ IC 2C IF( EVIST.LE.Z,- SIZE7) :ETURN VIS= CZT -EVIST I/SUET IF(VIS.LTAIlSFk7I, VS F!T=VIS RE! UP ,i 10 IF(PTS.L7.ZOI FETURN 20 VI!FRT=C.C

  12. Probabilistic Modeling of Fatigue Damage Accumulation for Reliability Prediction

    Directory of Open Access Journals (Sweden)

    Vijay Rathod

    2011-01-01

    Full Text Available A methodology for probabilistic modeling of fatigue damage accumulation for single stress level and multistress level loading is proposed in this paper. The methodology uses linear damage accumulation model of Palmgren-Miner, a probabilistic S-N curve, and an approach for a one-to-one transformation of probability density functions to achieve the objective. The damage accumulation is modeled as a nonstationary process as both the expected damage accumulation and its variability change with time. The proposed methodology is then used for reliability prediction under single stress level and multistress level loading, utilizing dynamic statistical model of cumulative fatigue damage. The reliability prediction under both types of loading is demonstrated with examples.

  13. Phenomena and computational models of non-proportional fatigue of materials

    CERN Document Server

    Skibicki, Dariusz

    2014-01-01

    This book gives an overview on the fatigue of materials under non-proportional loads. It presents the rich spectrum of phenomena and treats various computational models to mathematically describe the non-proportional fatigue of materials.

  14. Research on system-of-systems combat simulation model formal specification and representation

    Institute of Scientific and Technical Information of China (English)

    Liu Chen

    2006-01-01

    To makesystem-of-systems combat simulation models easy to be developed and reused, simulation model formal specification and representation are researched. According to the view of system-of-systems combat simulation, and based on DEVS, the simulation model's fundamental formalisms are explored. It includes entity model, system-of-systems model and experiment model. It also presents rigorous formal specification. XML data exchange standard is combined to design the XML based language, SCSL, to support simulation model representation. The corresponding relationship between SCSL and simulation model formalism is discussed and the syntax and semantics of elements in SCSL are detailed. Based on simulation model formal specification, the abstract simulation algorithm is given and SCSL virtual machine, which is capable of automatically interpreting and executing simulation model represented by SCSL, is designed. Finally an application case is presented, which can show the validation of the theory and verification of SCSL.

  15. 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

    Fatigue in steel structures subjected to stochastic loading is studied. Of special interest is the problem of fatigue damage accumulation and in this connection, a comparison between experimental results and results obtained using fracture mechanics. Fatigue test results obtained for welded plate...... 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...

  16. Fatigue Life Analysis of Rolling Bearings Based on Quasistatic Modeling

    Directory of Open Access Journals (Sweden)

    Wei Guo

    2015-01-01

    Full Text Available Rolling bearings are widely used in aeroengine, machine tool spindles, locomotive wheelset, and so forth. Rolling bearings are usually the weakest components that influence the remaining life of the whole machine. In this paper, a fatigue life prediction method is proposed based on quasistatic modeling of rolling bearings. With consideration of radial centrifugal expansion and thermal deformations on the geometric displacement in the bearings, the Jones’ bearing model is updated, which can predict the contact angle, deformation, and load between rolling elements and bearing raceways more accurately. Based on Hertz contact theory and contact mechanics, the contact stress field between rolling elements and raceways is calculated. A coupling model of fatigue life and damage for rolling bearings is given and verified through accelerated life test. Afterwards, the variation of bearing life is investigated under different working conditions, that is, axial load, radial load, and rotational speed. The results suggested that the working condition had a great influence on fatigue life of bearing parts and the order in which the damage appears on bearing parts.

  17. Development of a Generic Creep-Fatigue Life Prediction Model

    Science.gov (United States)

    Goswami, Tarun

    2002-01-01

    The objective of this research proposal is to further compile creep-fatigue data of steel alloys and superalloys used in military aircraft engines and/or rocket engines and to develop a statistical multivariate equation. The newly derived model will be a probabilistic fit to all the data compiled from various sources. Attempts will be made to procure the creep-fatigue data from NASA Glenn Research Center and other sources to further develop life prediction models for specific alloy groups. In a previous effort [1-3], a bank of creep-fatigue data has been compiled and tabulated under a range of known test parameters. These test parameters are called independent variables, namely; total strain range, strain rate, hold time, and temperature. The present research attempts to use these variables to develop a multivariate equation, which will be a probabilistic equation fitting a large database. The data predicted by the new model will be analyzed using the normal distribution fits, the closer the predicted lives are with the experimental lives (normal line 1 to 1 fit) the better the prediction. This will be evaluated in terms of a coefficient of correlation, R 2 as well. A multivariate equation developed earlier [3] has the following form, where S, R, T, and H have specific meaning discussed later.

  18. Validating and Verifying Biomathematical Models of Human Fatigue

    Science.gov (United States)

    Martinez, Siera Brooke; Quintero, Luis Ortiz; Flynn-Evans, Erin

    2015-01-01

    Airline pilots experience acute and chronic sleep deprivation, sleep inertia, and circadian desynchrony due to the need to schedule flight operations around the clock. This sleep loss and circadian desynchrony gives rise to cognitive impairments, reduced vigilance and inconsistent performance. Several biomathematical models, based principally on patterns observed in circadian rhythms and homeostatic drive, have been developed to predict a pilots levels of fatigue or alertness. These models allow for the Federal Aviation Administration (FAA) and commercial airlines to make decisions about pilot capabilities and flight schedules. Although these models have been validated in a laboratory setting, they have not been thoroughly tested in operational environments where uncontrolled factors, such as environmental sleep disrupters, caffeine use and napping, may impact actual pilot alertness and performance. We will compare the predictions of three prominent biomathematical fatigue models (McCauley Model, Harvard Model, and the privately-sold SAFTE-FAST Model) to actual measures of alertness and performance. We collected sleep logs, movement and light recordings, psychomotor vigilance task (PVT), and urinary melatonin (a marker of circadian phase) from 44 pilots in a short-haul commercial airline over one month. We will statistically compare with the model predictions to lapses on the PVT and circadian phase. We will calculate the sensitivity and specificity of each model prediction under different scheduling conditions. Our findings will aid operational decision-makers in determining the reliability of each model under real-world scheduling situations.

  19. 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

    Fatigue in steel structures subjected to stochastic loading is studied. Of special interest is the problem of fatigue damage accumulation and in this connection, a comparison between experimental results and results obtained using fracture mechanics. Fatigue test results obtained for welded plate...... 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....

  20. Comparison of two multiaxial fatigue models applied to dental implants

    Directory of Open Access Journals (Sweden)

    JM. Ayllon

    2015-07-01

    Full Text Available This paper presents two multiaxial fatigue life prediction models applied to a commercial dental implant. One model is called Variable Initiation Length Model and takes into account both the crack initiation and propagation phases. The second model combines the Theory of Critical Distance with a critical plane damage model to characterise the initiation and initial propagation of micro/meso cracks in the material. This paper discusses which material properties are necessary for the implementation of these models and how to obtain them in the laboratory from simple test specimens. It also describes the FE models developed for the stress/strain and stress intensity factor characterisation in the implant. The results of applying both life prediction models are compared with experimental results arising from the application of ISO-14801 standard to a commercial dental implant.

  1. Modeling Quasi-Static and Fatigue-Driven Delamination Migration

    Science.gov (United States)

    De Carvalho, N. V.; Ratcliffe, J. G.; Chen, B. Y.; Pinho, S. T.; Baiz, P. M.; Tay, T. E.

    2014-01-01

    An approach was proposed and assessed for the high-fidelity modeling of progressive damage and failure in composite materials. It combines the Floating Node Method (FNM) and the Virtual Crack Closure Technique (VCCT) to represent multiple interacting failure mechanisms in a mesh-independent fashion. Delamination, matrix cracking, and migration were captured failure and migration criteria based on fracture mechanics. Quasi-static and fatigue loading were modeled within the same overall framework. The methodology proposed was illustrated by simulating the delamination migration test, showing good agreement with the available experimental data.

  2. Human performance modeling for system of systems analytics :soldier fatigue.

    Energy Technology Data Exchange (ETDEWEB)

    Lawton, Craig R.; Campbell, James E.; Miller, Dwight Peter

    2005-10-01

    The military has identified Human Performance Modeling (HPM) as a significant requirement and challenge of future systems modeling and analysis initiatives as can be seen in the Department of Defense's (DoD) Defense Modeling and Simulation Office's (DMSO) Master Plan (DoD 5000.59-P 1995). To this goal, the military is currently spending millions of dollars on programs devoted to HPM in various military contexts. Examples include the Human Performance Modeling Integration (HPMI) program within the Air Force Research Laboratory, which focuses on integrating HPMs with constructive models of systems (e.g. cockpit simulations) and the Navy's Human Performance Center (HPC) established in September 2003. Nearly all of these initiatives focus on the interface between humans and a single system. This is insufficient in the era of highly complex network centric SoS. This report presents research and development in the area of HPM in a system-of-systems (SoS). Specifically, this report addresses modeling soldier fatigue and the potential impacts soldier fatigue can have on SoS performance.

  3. Combat-Related Heterotopic Ossification: Development of Animal Models for Identifying Mechanisms and Testing Therapeutics

    Science.gov (United States)

    2016-03-01

    etiology, treatment, and prevention is the absence of a reliable and reproducible small animal model that can be used to characterize combat‐related HO...contamination and subsequent wound colonization may be a key risk factor. Using a small animal model of blast-related extremity injury involving a...to the systemic and perhaps local antimicrobial therapies geared towards decreasing bioburden in combat wounds. 6 Using our blast-related HO

  4. [Research on Mental Fatigue Detecting Method Based on Sleep Deprivation Models].

    Science.gov (United States)

    Wang, Xiaolu; Gao, Xiang; Xu, Minpeng; Qi, Hongzhi; Wang, Xuemin; Ming, Dong; Zhou, Peng

    2015-06-01

    Mental fatigue is an important factor of human health and safety. It is important to achieve dynamic mental fatigue detection by using electroencephalogram (EEG) signals for fatigue prevention and job performance improvement. We in our study induced subjects' mental fatigue with 30 h sleep deprivation (SD) in the experiment. We extracted EEG features, including relative power, power ratio, center of gravity frequency (CGF), and basic relative power ratio. Then we built mental fatigue prediction model by using regression analysis. And we conducted lead optimization for prediction model. Result showed that R2 of prediction model could reach to 0.932. After lead optimization, 4 leads were used to build prediction model, in which R' could reach to 0.811. It can meet the daily applicatioi accuracy of mental fatigue prediction.

  5. Measures and Models for Estimating and Predicting Cognitive Fatigue

    Science.gov (United States)

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

    2004-01-01

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

  6. A Model of the Fatigue Life Distribution of Composite Laminates Based on Their Static Strength Distribution

    Institute of Scientific and Technical Information of China (English)

    Wu Fuqiang; Yao Weixing

    2008-01-01

    The reasons of the static strength dispersion and the fatigue life dispersion of composite laminates are analyzed in this article.It is concluded that the inner original defects,which derived from the manufacturing process of composite laminates,are the common and major reason of causing the random distributions of the static strength and the fatigue life.And there is a correlative relation between the two distributions.With the study of statistical relationship between the fatigue loading and the fatigue life in the uniform confidence level and the same survival rate S-N curves of material,the relationship between the static strength distribution and the fatigue life distribution through a material S-N curve model has been obtained.And then the model which is used to describe the distributions of fatigue life of composites,based on their distributions of static strength,is set up.This model reasonably reflects the effects of the inner original defects on the static strength dispersion and on the fatigue life dispersion of composite laminates.The experimental data of three kinds of composite laminates are employed to verify this model,and the results show that this model can predict the random distributions of fatigue life for composites under any fatigue loads fairly well.

  7. Comparative Study of Fatigue Damage Models Using Different Number of Classes Combined with the Rainflow Method

    Directory of Open Access Journals (Sweden)

    S. Zengah

    2013-06-01

    Full Text Available Fatigue damage increases with applied load cycles in a cumulative manner. Fatigue damage models play a key role in life prediction of components and structures subjected to random loading. The aim of this paper is the examination of the performance of the “Damaged Stress Model”, proposed and validated, against other fatigue models under random loading before and after reconstruction of the load histories. To achieve this objective, some linear and nonlinear models proposed for fatigue life estimation and a batch of specimens made of 6082T6 aluminum alloy is subjected to random loading. The damage was cumulated by Miner’s rule, Damaged Stress Model (DSM, Henry model and Unified Theory (UT and random cycles were counted with a rain-flow algorithm. Experimental data on high-cycle fatigue by complex loading histories with different mean and amplitude stress values are analyzed for life calculation and model predictions are compared.

  8. Probabilistic Modelling of Fatigue Life of Composite Laminates Using Bayesian Inference

    DEFF Research Database (Denmark)

    Dimitrov, Nikolay Krasimirov; Kiureghian, Armen Der

    2014-01-01

    A probabilistic model for estimating the fatigue life of laminated composite plates subjected to constant-amplitude or variable-amplitude loading is developed. The model is based on lamina-level input data, making it possible to predict fatigue properties for a wide range of laminate configuratio...

  9. A Cumulative Damage Reliability Model on the Basis of Contact Fatigue of the Rolling Bearing

    Institute of Scientific and Technical Information of China (English)

    HUANG Li

    2006-01-01

    A cumulative damage reliability model of contact fatigue of the rolling bearing is more identical with the actual conditions. It is put forward on the basis of contact fatigue life probability distribution of the rolling bearing that obey Weibull distribution and rest on the Miner cumulative damage theory. Finally a case is given to predict the reliability of bearing roller by using these models.

  10. SPARTAN II: An Instructional High Resolution Land Combat Model

    Science.gov (United States)

    1993-03-01

    White Sands Missile Range, New Mexico (14: C1,J4). TRAC uses these two models for doctrinal and force-structure evaluation and for training and education...8217 COMMON SHARED soldato, evento , ptgto, tgtreco, bluecount, & redcount, activeblue, activered, timetostop ’obs observer ID ’time = current simulation time

  11. Experiments in Error Propagation within Hierarchal Combat Models

    Science.gov (United States)

    2015-09-01

    and variances of Blue MTTK, Red MTTK, and P[Blue Wins] by Experimental Design are statistically different (Wackerly, Mendenhall III and Schaeffer...2008). Although the data is not normally distributed, the t-test is robust to non-normality (Wackerly, Mendenhall III and Schaeffer 2008). There is...this is handled by transforming the predicted values with a natural logarithm (Wackerly, Mendenhall III and Schaeffer 2008). The model considers

  12. Fatigue reliability based on residual strength model with hybrid uncertain parameters

    Institute of Scientific and Technical Information of China (English)

    Jun Wang; Zhi-Ping Qiu

    2012-01-01

    The aim of this paper is to evaluate the fatigue reliability with hybrid uncertain parameters based on a residual strength model.By solving the non-probabilistic setbased reliability problem and analyzing the reliability with randomness,the fatigue reliability with hybrid parameters can be obtained.The presented hybrid model can adequately consider all uncertainties affecting the fatigue reliability with hybrid uncertain parameters.A comparison among the presented hybrid model,non-probabilistic set-theoretic model and the conventional random model is made through two typical numerical examples.The results show that the presented hybrid model,which can ensure structural security,is effective and practical.

  13. Dust Plume Modeling at Fort Bliss: Move-Out Operations, Combat Training and Wind Erosion

    Energy Technology Data Exchange (ETDEWEB)

    Chapman, Elaine G.; Rishel, Jeremy P.; Rutz, Frederick C.; Seiple, Timothy E.; Newsom, Rob K.; Allwine, K Jerry

    2006-09-29

    The potential for air-quality impacts from heavy mechanized vehicles operating in the training ranges and on the unpaved main supply routes at Fort Bliss was investigated. This report details efforts by the staff of Pacific Northwest National Laboratory for the Fort Bliss Directorate of Environment in this investigation. Dust emission and dispersion from typical activities, including move outs and combat training, occurring on the installation were simulated using the atmospheric modeling system DUSTRAN. Major assumptions associated with designing specific modeling scenarios are summarized, and results from the simulations are presented.

  14. Hybrid Model for Early Onset Prediction of Driver Fatigue with Observable Cues

    Directory of Open Access Journals (Sweden)

    Mingheng Zhang

    2014-01-01

    Full Text Available This paper presents a hybrid model for early onset prediction of driver fatigue, which is the major reason of severe traffic accidents. The proposed method divides the prediction problem into three stages, that is, SVM-based model for predicting the early onset driver fatigue state, GA-based model for optimizing the parameters in the SVM, and PCA-based model for reducing the dimensionality of the complex features datasets. The model and algorithm are illustrated with driving experiment data and comparison results also show that the hybrid method can generally provide a better performance for driver fatigue state prediction.

  15. Experimental Investigation and Stochastic Modelling of the Fatigue Behaviour of Welded Steel Joints

    DEFF Research Database (Denmark)

    Lassen, Tom

    The present report describes the fatigue behaviour of surface cracks in welded steel joints. Emphasis is laid on fracture mechanics modelling and the stochastic nature of the fatigue process. Various sources which may contribute to the observed scatter in time to crack initiation and time spent...

  16. 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...

  17. Fatigue of Chinese railway employees and its influential factors: Structural equation modelling.

    Science.gov (United States)

    Tsao, Liuxing; Chang, Jing; Ma, Liang

    2017-07-01

    Fatigue is an identifiable and preventable cause of accidents in transport operations. Regarding the railway sector, incident logs and simulation studies show that employee fatigue leads to lack of alertness, impaired performance, and occurrence of incidents. China has one of the largest rail systems in the world, and Chinese railway employees work under high fatigue risks; therefore, it is important to assess their fatigue level and find the major factors leading to fatigue. We designed a questionnaire that uses Multidimensional Fatigue Instrument (MFI-20), NASA-TLX and subjective rating of work overtime feelings to assess employee fatigue. The contribution of each influential factor of fatigue was analysed using structural equation modelling. In total, 297 employees from the rail maintenance department and 227 employees from the locomotive department returned valid responses. The average scores and standard deviations for the five subscales of MFI-20, namely General Fatigue, Physical Fatigue, Reduced Activity, Reduced Motivation, and Mental Fatigue, were 2.9 (0.8), 2.8 (0.8), 2.5 (0.8), 2.5 (0.7), and 2.4 (0.8) among the rail maintenance employees and 3.5 (0.8), 3.5 (0.7), 3.3 (0.7), 3.0 (0.6), and 3.1 (0.7), respectively, among the locomotive employees. The fatigue of the locomotive employees was influenced by feelings related to working overtime (standardized r = 0.22) and workload (standardized r = 0.27). The work overtime control and physical working environment significantly influenced subjective feelings (standardized r = -0.25 and 0.47, respectively), while improper work/rest rhythms and an adverse physical working environment significantly increased the workload (standardized r = 0.48 and 0.33, respectively). Copyright © 2017 Elsevier Ltd. All rights reserved.

  18. Depression, Fatigue, and Pre-Sleep Arousal: A Mediation Model

    Science.gov (United States)

    Karlson, Cynthia W.; Stevens, Natalie R.; Olson, Christy A.; Hamilton, Nancy A.

    2010-01-01

    Fatigue is a common and debilitating symptom of clinical depression; however, the causes are not well understood. The present study was designed to test the hypotheses that subjective sleep, objective sleep, and arousal in the pre-sleep state would mediate the relationship between depression status and fatigue. Sleep, pre-sleep arousal, and…

  19. Probabilistic Fatigue Model for Reinforced Concrete Onshore Wind Turbine Foundations

    DEFF Research Database (Denmark)

    Marquez-Dominguez, Sergio; Sørensen, John Dalsgaard

    2013-01-01

    Reinforced Concrete Slab Foundation (RCSF) is the most common onshore wind turbine foundation type installed by the wind industry around the world. Fatigue cracks in a RCSF are an important issue to be considered by the designers. Causes and consequences of the cracks due to fatigue damage in RCSFs...

  20. Probabilistic Fatigue Model for Reinforced Concrete Onshore Wind Turbine Foundations

    DEFF Research Database (Denmark)

    Marquez-Dominguez, Sergio; Sørensen, John Dalsgaard

    2013-01-01

    Reinforced Concrete Slab Foundation (RCSF) is the most common onshore wind turbine foundation type installed by the wind industry around the world. Fatigue cracks in a RCSF are an important issue to be considered by the designers. Causes and consequences of the cracks due to fatigue damage in RCSFs...

  1. Models of initiation fatigue crack paths proposed by Macha

    Directory of Open Access Journals (Sweden)

    Z. Marciniak

    2015-10-01

    Full Text Available Professor E. Macha devoted his academic life to solving the problems connected with random multiaxial fatigue in components of machines and structures. In his studies he formulated stress, strain and energy criteria related to critical plane concept. He also proposed several methods to determine critical plane position. In particular, he formulated and verified weight functions applied in order to determine critical plane position. The variance method constituted another significant contribution to the development of methods for determining critical plane position. Apart from these criteria, Macha was exploring energy approach in fatigue of materials and the development of fatigue cracks. He has also observed that strain characteristics multiplied by stress amplitude determined at specimen half-life are applied to estimate fatigue life using energy criteria. However, for cyclically instable materials, stress amplitude value may differ a lot; therefore he proposed the method to determine energy fatigue characteristics directly from experimental research.

  2. Fatigue Behavior of Plain Concrete Under Biaxial Compression:Experiments and Theoretical Model

    Institute of Scientific and Technical Information of China (English)

    朱劲松; 宋玉普; 曹伟

    2003-01-01

    The effects of different lateral confinement stress on the fatigue behavior of and cumulative damage to plain concrete are investigated experimentally. Eighty 100 mm×100 mm×100 mm specimens of ordinary strength concrete are tested under constant- or variable-amplitude fatigue loading and lateral confinement pressure in two orthogonal directions. A fatigue equation is developed by modifying the classical Aas-Jakobsen S-N equation for taking into account the effect of the confined stress on fatigue strength of plain concrete. The results of variable-amplitude fatigue tests indicate that the linear damage theory proposed by Palmgren and Miner is unreasonable in the biaxial stress state. A nonlinear cumulative damage model that could model the effects of the magnitude and sequence of variable-amplitude fatigue loading and lateral confinement pressure is proposed on the basis of the evolution laws of the residual strains in the longitudinal direction during fatigue tests. The residual fatigue life predicted by this model is found to be in good agreement with the results of the experimental research.

  3. A Modified Fatigue Damage Model for High-Cycle Fatigue Life Prediction

    Directory of Open Access Journals (Sweden)

    Meng Wang

    2016-01-01

    Full Text Available Based on the assumption of quasibrittle failure under high-cycle fatigue for the metal material, the damage constitutive equation and the modified damage evolution equation are obtained with continuum damage mechanics. Then, finite element method (FEM is used to describe the failure process of metal material. The increment of specimen’s life and damage state can be researched using damage mechanics-FEM. Finally, the lifetime of the specimen is got at the given stress level. The damage mechanics-FEM is inserted into ABAQUS with subroutine USDFLD and the Python language is used to simulate the fatigue process of titanium alloy specimens. The simulation results have a good agreement with the testing results under constant amplitude loading, which proves the accuracy of the method.

  4. A new muscle fatigue and recovery model and its ergonomics application in human simulation

    CERN Document Server

    Ma, Liang; Bennis, Fouad; Zhang, Wei; Guillaume, François; 10.1080/17452759.2010.504056

    2010-01-01

    Although automatic techniques have been employed in manufacturing industries to increase productivity and efficiency, there are still lots of manual handling jobs, especially for assembly and maintenance jobs. In these jobs, musculoskeletal disorders (MSDs) are one of the major health problems due to overload and cumulative physical fatigue. With combination of conventional posture analysis techniques, digital human modelling and simulation (DHM) techniques have been developed and commercialized to evaluate the potential physical exposures. However, those ergonomics analysis tools are mainly based on posture analysis techniques, and until now there is still no fatigue index available in the commercial software to evaluate the physical fatigue easily and quickly. In this paper, a new muscle fatigue and recovery model is proposed and extended to evaluate joint fatigue level in manual handling jobs. A special application case is described and analyzed by digital human simulation technique.

  5. The representation of inflammatory signals in the brain - a model for subjective fatigue in multiple sclerosis.

    Science.gov (United States)

    Hanken, Katrin; Eling, Paul; Hildebrandt, Helmut

    2014-01-01

    In multiple sclerosis (MS) patients, fatigue is rated as one of the most common and disabling symptoms. However, the pathophysiology underlying this fatigue is not yet clear. Several lines of evidence suggest that immunological factors, such as elevated levels of pro-inflammatory cytokines, may contribute to subjective fatigue in MS patients. Pro-inflammatory cytokines represent primary mediators of immune-to-brain-communication, modulating changes in the neurophysiology of the central nervous system. Recently, we proposed a model arguing that fatigue in MS patients is a subjective feeling, which is related to inflammation. Moreover, it implies that fatigue can be measured behaviorally only by applying specific cognitive tasks related to alertness and vigilance. In the present review, we focus on the subjective feeling of MS-related fatigue. We examine the hypothesis that the subjective feeling of MS-related fatigue may be a variant of inflammation-induced sickness behavior, resulting from cytokine-mediated activity changes within brain areas involved in interoception and homeostasis including the insula, the anterior cingulate, and the hypothalamus. We first present studies demonstrating a relationship between pro-inflammatory cytokines and subjective fatigue in healthy individuals, in people with inflammatory disorders, and particularly in MS patients. Subsequently, we discuss studies analyzing the impact of anti-inflammatory treatment on fatigue. In the next part of this review, we present studies on the transmission and neural representation of inflammatory signals, with a special focus on possible neural concomitants of inflammation-induced fatigue. We also present two of our studies on the relationship between local gray and white matter atrophy and fatigue in MS patients. Finally, we discuss some implications of our findings and future perspectives.

  6. Modeling the effects of control systems of wind turbine fatigue life

    Energy Technology Data Exchange (ETDEWEB)

    Pierce, K.G.; Laino, D.J. [Univ. of Utah, Salt Lake City, UT (United States)

    1996-12-31

    In this study we look at the effect on fatigue life of two types of control systems. First, we investigate the Micon 65, an upwind, three bladed turbine with a simple yaw control system. Results indicate that increased fatigue damage to the blade root can be attributed to continuous operation at significant yaw error allowed by the control system. Next, we model a two-bladed teetered rotor turbine using three different control systems to adjust flap deflections. The first two limit peak power output, the third limits peak power and cyclic power output over the entire range of operation. Results for simulations conducted both with and without active control are compared to determine how active control affects fatigue life. Improvement in fatigue lifetimes were seen for all control schemes, with increasing fatigue lifetime corresponding to increased flap deflection activity. 13 refs., 6 figs., 2 tabs.

  7. Fatigue Load Estimation through a Simple Stochastic Model

    Directory of Open Access Journals (Sweden)

    Pedro G. Lind

    2014-12-01

    Full Text Available We propose a procedure to estimate the fatigue loads on wind turbines, based on a recent framework used for reconstructing data series of stochastic properties measured at wind turbines. Through a standard fatigue analysis, we show that it is possible to accurately estimate fatigue loads in any wind turbine within one wind park, using only the load measurements at one single turbine and the set of wind speed measurements. Our framework consists of deriving a stochastic differential equation that describes the evolution of the torque at one wind turbine driven by the wind speed. The stochastic equation is derived directly from the measurements and is afterwards used for predicting the fatigue loads for neighboring turbines. Such a framework could be used to mitigate the financial efforts usually necessary for placing measurement devices in all wind turbines within one wind farm. Finally, we also discuss the limitations and possible improvements of the proposed procedure.

  8. Fatigue Loads Estimation Through a Simple Stochastic Model

    CERN Document Server

    Lind, Pedro G; Peinke, Joachim

    2014-01-01

    We propose a procedure to estimate the fatigue loads on wind turbines, based in a recent framework used for reconstructing data series of stochastic properties measured at wind turbines. Through a standard fatigue analysis, we show that it is possible to accurately estimate fatigue loads in any wind turbine within one wind park, using only the load measurements at one single turbine and the set of wind speed measurements. Our framework consists of deriving a stochastic differential equation that describes the evolution of the torque at one wind turbine driven by the wind speed. The stochastic equation is derived directly from the measurements and is afterwards used for predicting the fatigue loads at neighboring turbines. Such a framework could be used to mitigate the financial efforts usually necessary for placing measurement devices in all wind turbines within one wind farm. Finally, we also discuss the limitations and possible improvements of the proposed procedure.

  9. Fatigue assessment of an existing steel bridge by finite element modelling and field measurements

    Science.gov (United States)

    Kwad, J.; Alencar, G.; Correia, J.; Jesus, A.; Calçada, R.; Kripakaran, P.

    2017-05-01

    The evaluation of fatigue life of structural details in metallic bridges is a major challenge for bridge engineers. A reliable and cost-effective approach is essential to ensure appropriate maintenance and management of these structures. Typically, local stresses predicted by a finite element model of the bridge are employed to assess the fatigue life of fatigue-prone details. This paper illustrates an approach for fatigue assessment based on measured data for a connection in an old bascule steel bridge located in Exeter (UK). A finite element model is first developed from the design information. The finite element model of the bridge is calibrated using measured responses from an ambient vibration test. The stress time histories are calculated through dynamic analysis of the updated finite element model. Stress cycles are computed through the rainflow counting algorithm, and the fatigue prone details are evaluated using the standard SN curves approach and the Miner’s rule. Results show that the proposed approach can estimate the fatigue damage of a fatigue prone detail in a structure using measured strain data.

  10. Fatigue Modeling via Mammalian Auditory System for Prediction of Noise Induced Hearing Loss.

    Science.gov (United States)

    Sun, Pengfei; Qin, Jun; Campbell, Kathleen

    2015-01-01

    Noise induced hearing loss (NIHL) remains as a severe health problem worldwide. Existing noise metrics and modeling for evaluation of NIHL are limited on prediction of gradually developing NIHL (GDHL) caused by high-level occupational noise. In this study, we proposed two auditory fatigue based models, including equal velocity level (EVL) and complex velocity level (CVL), which combine the high-cycle fatigue theory with the mammalian auditory model, to predict GDHL. The mammalian auditory model is introduced by combining the transfer function of the external-middle ear and the triple-path nonlinear (TRNL) filter to obtain velocities of basilar membrane (BM) in cochlea. The high-cycle fatigue theory is based on the assumption that GDHL can be considered as a process of long-cycle mechanical fatigue failure of organ of Corti. Furthermore, a series of chinchilla experimental data are used to validate the effectiveness of the proposed fatigue models. The regression analysis results show that both proposed fatigue models have high corrections with four hearing loss indices. It indicates that the proposed models can accurately predict hearing loss in chinchilla. Results suggest that the CVL model is more accurate compared to the EVL model on prediction of the auditory risk of exposure to hazardous occupational noise.

  11. Fatigue Modeling via Mammalian Auditory System for Prediction of Noise Induced Hearing Loss

    Directory of Open Access Journals (Sweden)

    Pengfei Sun

    2015-01-01

    Full Text Available Noise induced hearing loss (NIHL remains as a severe health problem worldwide. Existing noise metrics and modeling for evaluation of NIHL are limited on prediction of gradually developing NIHL (GDHL caused by high-level occupational noise. In this study, we proposed two auditory fatigue based models, including equal velocity level (EVL and complex velocity level (CVL, which combine the high-cycle fatigue theory with the mammalian auditory model, to predict GDHL. The mammalian auditory model is introduced by combining the transfer function of the external-middle ear and the triple-path nonlinear (TRNL filter to obtain velocities of basilar membrane (BM in cochlea. The high-cycle fatigue theory is based on the assumption that GDHL can be considered as a process of long-cycle mechanical fatigue failure of organ of Corti. Furthermore, a series of chinchilla experimental data are used to validate the effectiveness of the proposed fatigue models. The regression analysis results show that both proposed fatigue models have high corrections with four hearing loss indices. It indicates that the proposed models can accurately predict hearing loss in chinchilla. Results suggest that the CVL model is more accurate compared to the EVL model on prediction of the auditory risk of exposure to hazardous occupational noise.

  12. Torsional fatigue model for limitorque type SMB/SB/SBD actuators for motor-operated valves

    Energy Technology Data Exchange (ETDEWEB)

    Somogyi, D.; Alvarez, P.D.; Kalsi, M.S. [Kalsi Engineering, Inc., Sugar Land, TX (United States)

    1996-12-01

    Kalsi Engineering, Inc. has recently developed a computer program to predict the torsional fatigue life of Limitorque Type SMB/SB/SBD actuators for motor-operated valves under given loading levels, including those that exceed the ratings. The development effort was an outgrowth of the {open_quote}Thrust Rating Increase{close_quote} test program. The fatigue model computes all pertinent stress components and their variations as a function of the loading ramp. The cumulative damage and fatigue life due to stress cycling is computed by use of a modification of Miner`s rule. Model predictions were validated against actual cyclic loading test results.

  13. Mathematical Model of Load Pass and Prediction of Fatigue Life on Bolt Threads with Reduced Lead

    Science.gov (United States)

    Asayama, Yukiteru

    A mathematical model is proposed in order to elucidate the mechanism that the fatigue strength of external threads increases by reducing the lead on a thread system such as a bolt and nut. The model is constructed from the concept that a local strain proportional to the reducing degree of the lead, although the local strain is at first produced in the bolt thread farthest from the bearing surface of the nut, is induced in each thread root with an increase of applied load. The fatigue life predicted from the mathematical model shows good agreement with the experimental fatigue life of cadmium-plated external threads with the reduced lead on the material having strength as high as 1270MPa. The model can provide useful suggestions for the design of fasteners for aerospace, which are required to satisfy severe requirements of fatigue strengths and dimensions.

  14. Factors related to fatigue; priority of interventions to reduce or eliminate fatigue and the exploration of a multidisciplinary research model for further study of fatigue

    NARCIS (Netherlands)

    Tiesinga, LJ; Dassen, TWN; Halfens, RJG; van den Heuvel, WJA

    1999-01-01

    A growing interest in the health problem presented by fatigue, both in clinical practice and research, coupled with a decreasing number of reported studies on fatigue in the last decade, make an updated and systematic review of factors related to fatigue necessary. A search of the literature, compri

  15. Multiaxial fatigue modeling for Nitinol shape memory alloys under in-phase loading.

    Science.gov (United States)

    Mahtabi, M J; Shamsaei, Nima

    2015-03-01

    The realistic loading condition for many components is multiaxial arising from multidirectional loading or geometry complexities. In this study, some multiaxial stress-based classical and critical plane fatigue models are briefly reviewed and their application for martensitic Nitinol under torsion and in-phase axial-torsion loading is evaluated. These models include von Mises equivalent stress, Tresca, Findley, McDiarmid, and a proposed stress-based Fatemi-Socie-type model. As the fatigue cracks appear to be on the maximum shear plane for the martensitic Nitinol, all the models examined here consider the shear stress as the primary damage parameter. Among all the models considered in this study, the proposed Fatemi-Socie-type model provides a better prediction for fatigue lives when compared to torsion and in-phase multiaxial fatigue experimental data from literature. Analyses indicate that critical plane approaches are more appropriate for multiaxial fatigue prediction of Nitinol alloys, at least in martensitic phase. Finally, recommendations are made to calibrate more reliable multiaxial fatigue models for Nitinol. Copyright © 2015 Elsevier Ltd. All rights reserved.

  16. Insilico modeling of Wolbachia and its potentials in combating mosquito borne diseases Chikungunya and Dengue

    Directory of Open Access Journals (Sweden)

    N.M.Guruprasad

    2013-09-01

    Full Text Available Mosquito borne diseases are major health burden both in tropical and subtropical regions. The enormous use of insecticides to control mosquitoes causes biomagnification of chemicals in environment and mosquitoes have developed resistance to insecticides. The inefficiency of insecticides to combat mosquitoes prompted researchers to develop efficient alternative methods. Wolbachia endosymbiont is a one of efficient new approach to control mosquitoes. Wolbachia strain invade mosquitoes biology by reducing host lifespan, phenotype and inhibit virus replication. In the present study, insilico modeling and docking of Wolbachia and human pathogens Chikungunya (CHIK and Dengue (DEN virus was done. Docking is the method to find the binding affinity of protein and ligand complex molecules for finding potential inhibitor. Using Hex, we obtained energy total (e-total values in kcal/mol for all docked complex. In the contest of overall analyzing the docking E-total values of docked complexes reveals that WSP-B has show strong binding affinity than WSP-A to both DEN and CHIK. Based on obtained result, we suggest WSP-B has potential inhibitor for both DEN and CHIK virus. Further, biophysical characterization of Wolbachia will help to develop a drug to combat CHIK and DEN viruses.

  17. Creep-Fatigue Damage Investigation and Modeling of Alloy 617 at High Temperatures

    Science.gov (United States)

    Tahir, Fraaz

    imaging analysis showed that the microstructural damage features (cracks and voids) are correlated with a new mechanical driving force parameter. The results from this image-based damage analysis were used to develop a phenomenological life-prediction methodology called the effective time fraction approach. Finally, the constitutive creep-fatigue response of the material at 950°C was modeled using a unified viscoplastic model coupled with a damage accumulation model. The simulation results were used to validate an energy-based constitutive life-prediction model, as a mechanistic model for potential component and structure level creep-fatigue analysis.

  18. Shakedown based model for high-cycle fatigue of shape memory alloys

    Science.gov (United States)

    Gu, Xiaojun; Moumni, Ziad; Zaki, Wael; Zhang, Weihong

    2016-11-01

    The paper presents a high-cycle fatigue criterion for shape memory alloys (SMAs) based on shakedown analysis. The analysis accounts for phase transformation as well as reorientation of martensite variants as possible sources of fatigue damage. In the case of high-cycle fatigue, once the structure has reached an asymptotic state, damage is assumed to become confined at the mesoscopic scale, or the scale of the grain, with no discernable inelasticity at the macroscopic scale. Using a multiscale approach, a high-cycle fatigue criterion analogous to the Dang Van model (Dang Van 1973) for elastoplastic metals is derived for SMAs obeying the Zaki-Moumni model for SMAs (Zaki and Moumni 2007a). For these alloys, a safe domain is established in stress deviator space, consisting of a hypercylinder with axis parallel to the direction of martensite orientation at the mesoscopic scale. Safety with regard to high-cycle fatigue, upon elastic shakedown, is conditioned by the persistence of the macroscopic stress path at every material point within the hypercylinder, whose size depends on the volume fraction of martensite. The proposed criterion computes a fatigue factor at each material point, indicating its degree of safeness with respect to high cycle fatigue.

  19. Fatigue Modeling for Superelastic NiTi Considering Cyclic Deformation and Load Ratio Effects

    Science.gov (United States)

    Mahtabi, Mohammad J.; Shamsaei, Nima

    2017-08-01

    A cumulative energy-based damage model, called total fatigue toughness, is proposed for fatigue life prediction of superelastic NiTi alloys with various deformation responses (i.e., transformation stresses), which also accounts for the effects of mean strain and stress. Mechanical response of superelastic NiTi is highly sensitive to chemical composition, material processing, as well as operating temperature; therefore, significantly different deformation responses may be obtained for seemingly identical NiTi specimens. In this paper, a fatigue damage parameter is proposed that can be used for fatigue life prediction of superelastic NiTi alloys with different mechanical properties such as loading and unloading transformation stresses, modulus of elasticity, and austenite-to-martensite start and finish strains. Moreover, the model is capable of capturing the effects of tensile mean strain and stress on the fatigue behavior. Fatigue life predictions using the proposed damage parameter for specimens with different cyclic stress responses, tested at various strain ratios (R ɛ = ɛ min /ɛ max) are shown to be in very good agreement with the experimentally observed fatigue lives.

  20. Fatigue characterization of a crankshaft steel: Use and interaction of new models

    Directory of Open Access Journals (Sweden)

    Sergio Blasón

    2016-01-01

    Full Text Available The peculiar geometrical shape and working conditions of crankshafts make fatigue becoming responsible for most of the failure cases in such components. Therefore, improvement of crankshaft performance requires enhancing its fatigue life. In this work, the fatigue behavior of a D38MSV5S steel, used for crankshafts in compact vehicles, is investigated according to two traditional ways of analysis, namely the stress based and the fracture mechanics based approaches, though using advanced design models: On the one side, a probabilistic Weibull regression S-N model is assessed for experimental results obtained from fatigue resonance tests. On the other side, the crack growth rate curve is calculated from crack growth tests, carried out on SENB specimens, using a normalizing procedure. Specific Matlab programs are developed to facilitate the evaluation process. The information gained from both models will contribute to provide a probabilistic interpretation to the Kitagawa-Takahashi diagram.

  1. Stages of decompensation in combat-related posttraumatic stress disorder: a new conceptual model.

    Science.gov (United States)

    Wang, S; Wilson, J P; Mason, J W

    1996-01-01

    This conceptual article presents a model of severe, chronic combat-related PTSD based on several years of longitudinal clinical observations of Vietnam veterans. The model describes a repeating cycle of decompensation that profoundly disrupts the veteran's life. There appear to be "stages" of decompensation that can be described clinically and may be distinct physiologically. The stages describe a wide range of functioning, from adaptive to totally dysfunctional PTSD core symptoms, as well as several other dimensions of clinical functioning, such as affect regulation, defenses, ego states, interactions with the environment, capacity for self-destruction/suicide and capacity for attachment and insight are described for each stage. Clinical and research implications are discussed.

  2. Probabilistic Material Strength Degradation Model for Inconel 718 Components Subjected to High Temperature, High-Cycle and Low-Cycle Mechanical Fatigue, Creep and Thermal Fatigue Effects

    Science.gov (United States)

    Bast, Callie C.; Boyce, Lola

    1995-01-01

    The development of methodology for a probabilistic material strength degradation is described. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes five effects that typically reduce lifetime strength: high temperature, high-cycle mechanical fatigue, low-cycle mechanical fatigue, creep and thermal fatigue. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing predictions of high-cycle mechanical fatigue and high temperature effects with experiments are presented. Results from this limited verification study strongly supported that material degradation can be represented by randomized multifactor interaction models.

  3. Modeling of fatigue life of materials and structures under low-cycle loading

    Science.gov (United States)

    Volkov, I. A.; Korotkikh, Yu. G.

    2014-05-01

    A damaged medium model (DMM) consisting of three interconnected components (relations determining the cyclic elastoplastic behavior of the material, kinetic damage accumulation equations, and the strength criterion for the damaged material) was developed to estimate the stress strain state and the fatigue life of important engineering objects. The fatigue life of a strip with a cut under cyclic loading was estimated to obtain qualitative and quantitative estimates of the DMM constitutive relations under low-cycle loading. It was shown that the considered version of the constitutive relations reliably describes the main effects of elastoplastic deformation and the fatigue life processes of materials and structures.

  4. Joint Interagency Task Forces; the Right Model to Combat Transnational Organized Crime

    Science.gov (United States)

    2015-05-18

    South/Central Asia focused on terrorism, piracy , infectious disease, WMD development. 67 In the article, “Death of a Combatant Command,” the authors...administration/eop/nsc/transnational-crime/definition; Internet ; Accessed March 20, 2015. 2 Ibid. 3 The White House Office of the Press Secretary...strategy-combat- transnational-organized-crime; Internet ; Accessed March 20, 2015. 4 Gerald A. Boston, "The United States Military’s Role in Combating

  5. TAC BRAWLER - An application of engagement simulation modeling to simulator visual system display requirements for air combat maneuvering

    Science.gov (United States)

    Kerchner, R. M.; Hughes, R. G.; Lee, A.

    1984-01-01

    The TAC BRAWLER air combat simulation models both the acquisition and use of visual information by the pilot. It was used to provide the designers of manned simulators for air-to-air combat with information regarding the training implications of display system resolution, inherent target contrast, field of view, and transport delay. Various display designs were simulated, and the resulting quantitative and qualitative differences in engagements were considered indicators of possible mistraining. Display resolution was found to alter combats primarily through its effect on detection ranges; the 'pixel averaging' contrast management technique was shown to largely compensate for this problem. Transport delay significantly degrades pilot tracking ability, but the training impact of the effect is unclear.

  6. A model of rotationally-sampled wind turbulence for predicting fatigue loads in wind turbines

    Science.gov (United States)

    Spera, David A.

    1995-01-01

    Empirical equations are presented with which to model rotationally-sampled (R-S) turbulence for input to structural-dynamic computer codes and the calculation of wind turbine fatigue loads. These equations are derived from R-S turbulence data which were measured at the vertical-plane array in Clayton, New Mexico. For validation, the equations are applied to the calculation of cyclic flapwise blade loads for the NASA/DOE Mod-2 2.5-MW experimental HAWT's (horizontal-axis wind turbines), and the results compared to measured cyclic loads. Good correlation is achieved, indicating that the R-S turbulence model developed in this study contains the characteristics of the wind which produce many of the fatigue loads sustained by wind turbines. Empirical factors are included which permit the prediction of load levels at specified percentiles of occurrence, which is required for the generation of fatigue load spectra and the prediction of the fatigue lifetime of structures.

  7. STRATIFIED MODEL FOR ESTIMATING FATIGUE CRACK GROWTH RATE OF METALLIC MATERIALS

    Institute of Scientific and Technical Information of China (English)

    YANG Yong-yu; LIU Xin-wei; YANG Fan

    2005-01-01

    The curve of relationship between fatigue crack growth rate and the stress strength factor amplitude represented an important fatigue property in designing of damage tolerance limits and predicting life of metallic component parts. In order to have a morereasonable use of testing data, samples from population were stratified suggested by the stratified random sample model (SRAM). The data in each stratum corresponded to the same experiment conditions. A suitable weight was assigned to each stratified sample according to the actual working states of the pressure vessel, so that the estimation of fatigue crack growth rate equation was more accurate for practice. An empirical study shows that the SRAM estimation by using fatigue crack growth rate data from different stoves is obviously better than the estimation from simple random sample model.

  8. Modelling probabilistic fatigue crack propagation rates for a mild structural steel

    Directory of Open Access Journals (Sweden)

    J.A.F.O. Correia

    2015-01-01

    Full Text Available A class of fatigue crack growth models based on elastic–plastic stress–strain histories at the crack tip region and local strain-life damage models have been proposed in literature. The fatigue crack growth is regarded as a process of continuous crack initializations over successive elementary material blocks, which may be governed by smooth strain-life damage data. Some approaches account for the residual stresses developing at the crack tip in the actual crack driving force assessment, allowing mean stresses and loading sequential effects to be modelled. An extension of the fatigue crack propagation model originally proposed by Noroozi et al. (2005 to derive probabilistic fatigue crack propagation data is proposed, in particular concerning the derivation of probabilistic da/dN-ΔK-R fields. The elastic-plastic stresses at the vicinity of the crack tip, computed using simplified formulae, are compared with the stresses computed using an elasticplastic finite element analyses for specimens considered in the experimental program proposed to derive the fatigue crack propagation data. Using probabilistic strain-life data available for the S355 structural mild steel, probabilistic crack propagation fields are generated, for several stress ratios, and compared with experimental fatigue crack propagation data. A satisfactory agreement between the predicted probabilistic fields and experimental data is observed.

  9. Prediction Model for Fatigue Stiffness Decay of Concrete Beam Based on Neural Network

    Institute of Scientific and Technical Information of China (English)

    王海超; 何世钦; 贡金鑫

    2003-01-01

    With the method of neural network, the processes of fatigue stiffness decreasing and deflection increasing of reinforced concrete beams under cyclic loading were simulated. The simulating system was built with the given experimental data. The prediction model of neural network structure and the corresponding parameters were obtained. The precision and results were satisfied and could be used to investigate the fatigue properties of reinforced concrete beams in complex environment and under repeating loads.

  10. A joint fatigue - creep deterioration model for masonry with acoustic emission based damage assessment

    OpenAIRE

    Tomor, Adrienn K.; Verstrynge, Els

    2013-01-01

    The paper investigates the long-term fatigue and creep deterioration processes in historical brick masonry. Based on two independent laboratory test series, the relationship between stress level and life expectancy was considered for fatigue and creep loading in the form of SN type models. The process of deterioration was investigated with the help of acoustic emission technique to identify stages and characteristics of the damage accumulation process. Based on the test data and acoustic emis...

  11. A Multiaxial Low Cycle Fatigue Life Prediction Model for Both Proportional and Non-proportional Loading Conditions

    Science.gov (United States)

    Paul, Surajit Kumar

    2014-09-01

    This paper has presented a life prediction model in the field of multiaxial low-cycle fatigue. The proposed model is generally applied for constant amplitude multiaxial proportional and non-proportional loading. Depending upon applied strain path the equivalent strain varies within a cycle. Equivalent average strain amplitude is considered as fatigue damage parameter in the proposed model. The model has requirement of only two material constants and no other tuning parameters. The model is examined by the proportional and non-proportional low-cycle fatigue life experimental data for eight different types of materials. The model is successfully correlated with multiaxial fatigue lives of eight different materials.

  12. Effects of memantine, an N-methyl-D-aspartate receptor antagonist, on fatigue and neuronal brain damage in a rat model of combined (physical and mental) fatigue.

    Science.gov (United States)

    Morimoto, Yasuo; Zhang, Qian; Adachi, Koji

    2012-01-01

    Most of the fatigue in everyday life is a combination of physical and mental fatigue. Recently, an animal model of combined fatigue was designed by housing rats in a cage filled with water. We have previously hypothesized that mental fatigue is caused partly by neuronal brain damage through the activation of N-methyl-D-aspartate (NMDA) receptors by quinolinic acid (QUIN), a metabolite of tryptophan (TRP). Therefore, we investigated whether the same mechanism also participates in combined fatigue. Rats were housed for 5 d under water-immersed conditions, and the extent of fatigue was evaluated by a weight-loaded forced swimming test. The swimming time of the water-immersed group was shorter than that of the control group, indicating that rats were fatigued by water-immersion. However, unexpectedly, the blood and brain levels of QUIN in the water-immersed group were lower than those of the control group. QUIN levels in both the blood and brains of a food-restricted nonimmersed group, where body weight was matched with the water-immersed group, were also decreased, suggesting that decreased QUIN in the water-immersed group originated from a reduced intake of TRP-containing food. On the other hand, hippocampal neuronal damage was shown in the water-immersed group, similar to that seen in other fatigue models where QUIN increased. Memantine, an NMDA receptor antagonist, inhibited not only the reduction in swimming times but also the neuronal damage induced by water-immersion. These results suggest that neuronal brain damage by an endogenous NMDA receptor agonist other than QUIN participates in combined fatigue by water immersion.

  13. Applicability of WaveWatch-III wave model to fatigue assessment of offshore floating structures

    Science.gov (United States)

    Zou, Tao; Kaminski, Miroslaw Lech

    2016-09-01

    In design and operation of floating offshore structures, one has to avoid fatigue failures caused by action of ocean waves. The aim of this paper is to investigate the applicability of WaveWatch-III wave model to fatigue assessment of offshore floating structures. The applicability was investigated for Bluewaters' FPSO (Floating Production, Storage and Offloading) which had been turret moored at Sable field for half a decade. The waves were predicted as sea-state time series consisting of one wind sea and one swell. The predicted waves were compared with wave data obtained from ERA-interim and buoy measurements. Furthermore, the fatigue calculations were also carried out for main deck and side shell locations. It has been concluded that predicted fatigue damages of main deck using WaveWatch-III are in a very good agreement regardless of differences in predicted wind waves and swells caused by differences in wave system partitioning. When compared to buoy measurements, the model underestimates fatigue damages of side shell by approximately 30 %. The reason for that has been found in wider directional spreading of actual waves. The WaveWatch-III wave model has been found suitable for the fatigue assessment. However, more attention should be paid on relative wave directionality, wave system partitioning and uncertainty analysis in further development.

  14. Numerical fatigue life assessment of cardiovascular stents: A two-scale plasticity-damage model

    Science.gov (United States)

    Santos, H. A. F. A.; Auricchio, F.; Conti, M.

    2013-07-01

    Cardiovascular disease has become a major global health care problem in the last decades. To tackle this problem, the use of cardiovascular stents has been considered a promising and effective approach. Numerical simulations to evaluate the in vivo behavior of stents are becoming more and more important to assess potential failures. As the material failure of a stent device has been often associated with fatigue issues, numerical approaches for fatigue life assessment of stents have gained special interest in the engineering community. Numerical fatigue life predictions can be used to modify the design and prevent failure without making and testing numerous physical devices, thus preventing from undesired fatigue failures. We present a numerical fatigue life model for the analysis of cardiovascular balloon-expandable stainless steel stents that can hopefully provide useful information either to be used for product improvement or for clinicians to make life-saving decisions. This model incorporates a two-scale continuum damage mechanics model and the so-called Soderberg fatigue failure criterion. We provide numerical results for both Palmaz-Schatz and Cypher stent designs and demonstrate that a good agreement is found between the numerical and the available experimental results.

  15. Survey on damage mechanics models for fatigue life prediction

    NARCIS (Netherlands)

    Silitonga, S.; Maljaars, J.; Soetens, F.; Snijder, H.H.

    2013-01-01

    Engineering methods to predict the fatigue life of structures have been available since the beginning of the 20th century. However, a practical problem arises from complex loading conditions and a significant concern is the accuracy of the methods under variable amplitude loading. This paper provide

  16. 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.

  17. Development of a probabilistic model for the prediction of fatigue life in the very high cycle fatigue (VHCF range based on inclusion population

    Directory of Open Access Journals (Sweden)

    Kolyshkin A.

    2014-06-01

    Full Text Available The VHCF behaviour of metallic materials containing microstructural defects such as non-metallic inclusions is determined by the size and distribution of the damage dominating defects. In the present paper, the size and location of about 60.000 inclusions measured on the longitudinal and transversal cross sections of AISI 304 sheet form a database for the probabilistic determination of failure-relevant inclusion distribution in fatigue specimens and their corresponding fatigue lifes. By applying the method of Murakami et al. the biggest measured inclusions were used in order to predict the size of failure-relevant inclusions in the fatigue specimens. The location of the crack initiating inclusions was defined based on the modeled inclusion population and the stress distribution in the fatigue specimen, using the probabilistic Monte Carlo framework. Reasonable agreement was obtained between modeling and experimental results.

  18. Modeling of Fatigue Crack Propagation in Aluminum Alloys Using an Energy Based Approach

    Directory of Open Access Journals (Sweden)

    F. Khelil

    2013-08-01

    Full Text Available Materials fatigue is a particularly serious and unsafe kind of material destruction. Investigations of the fatigue crack growth rate and fatigue life constitute very important and complex problems in mechanics. The understanding of the cracking mechanisms, taking into account various factors such as the load pattern, the strain rate, the stress ratio, etc., is of a first need. In this work an energy approach of the Fatigue Crack Growth (FCG was proposed. This approach is based on the numerical determination of the plastic zone by introducing a novel form of plastic radius. The experimental results conducted on two aluminum alloys of types 2024-T351 and 7075-T7351 were exploited to validate the developed numerical model. A good agreement has been found between the two types of results.

  19. A new Cumulative Damage Model for Fatigue Life Prediction under Shot Peening Treatment

    Directory of Open Access Journals (Sweden)

    Abdul-Jabar H. Ali

    2015-07-01

    Full Text Available In this paper, fatigue damage accumulation were studied using many methods i.e.Corton-Dalon (CD,Corton-Dalon-Marsh(CDM, new non-linear model and experimental method. The prediction of fatigue lifetimes based on the two classical methods, Corton-Dalon (CDandCorton-Dalon-Marsh (CDM, are uneconomic and non-conservative respectively. However satisfactory predictions were obtained by applying the proposed non-linear model (present model for medium carbon steel compared with experimental work. Many shortcomings of the two classical methods are related to their inability to take into account the surface treatment effect as shot peening. It is clear that the new model shows that a much better and conservative prediction of fatigue life in comparison with CD and CDM methods. The prediction of the present model gave slightly below the experimental data while the CDM gave overestimate prediction and CD showed strongly underestimates the life of specimens.

  20. Application of a Multi-Objective Network Model to a Combat Simulation Game: The Drive on Metz Case Study

    Science.gov (United States)

    2014-03-27

    VBA ) macros to set up the scenario. The assumptions required to implement the model are listed in Section 1.4.3 and are again summarized here: 1. One... model could be increased by reworking the VBA code to be more efficient or using a more advanced programming language or technique. Efficiency can also...APPLICATION OF A MULTI-OBJECTIVE NETWORK MODEL TO A COMBAT SIMULATION GAME: “THE DRIVE ON METZ” CASE STUDY THESIS Timothy D. Frawley, Captain, USAF

  1. Crack Closure Effects on Fatigue Crack Propagation Rates: Application of a Proposed Theoretical Model

    Directory of Open Access Journals (Sweden)

    José A. F. O. Correia

    2016-01-01

    Full Text Available Structural design taking into account fatigue damage requires a thorough knowledge of the behaviour of materials. In addition to the monotonic behaviour of the materials, it is also important to assess their cyclic response and fatigue crack propagation behaviour under constant and variable amplitude loading. Materials whenever subjected to fatigue cracking may exhibit mean stress effects as well as crack closure effects. In this paper, a theoretical model based on the same initial assumptions of the analytical models proposed by Hudak and Davidson and Ellyin is proposed to estimate the influence of the crack closure effects. This proposal based further on Walker’s propagation law was applied to the P355NL1 steel using an inverse analysis (back-extrapolation of experimental fatigue crack propagation results. Based on this proposed model it is possible to estimate the crack opening stress intensity factor, Kop, the relationship between U=ΔKeff/ΔK quantity and the stress intensity factor, the crack length, and the stress ratio. This allows the evaluation of the influence of the crack closure effects for different stress ratio levels, in the fatigue crack propagation rates. Finally, a good agreement is found between the proposed theoretical model and the analytical models presented in the literature.

  2. Fatigue analysis of piezoelectric microdevice based on a continuum damage model

    Directory of Open Access Journals (Sweden)

    Xianqiao Wang

    2013-09-01

    Full Text Available The utilization of piezoelectric materials in MEMS devices under harsh environments has gained affordable appreciations due to its unique mechanical and electrical material properties. However, the reliability of MEMS devices triggered by fatigue damage remains elusive and needs to be further explored. Here, we present a continuum constitutive model for piezoelectric materials containing a substantive amount of randomly dispersed microcracks. The constitutive equation of the piezoelectric materials with microcracks is formulated via Helmholtz free energy by combining the Kachanvo damage evolution law and the Chaboche fatigue damage development to express the fatigue damage growth. A case of the fatigue damage analysis of the piezoelectric microplate with transverse matrix cracks in the status of plane stress is presented by adopting the von Karman’s plate theory. With numerical schemes employed, the effect of cyclic impulsive loadings and electrical loadings on the fatigue damage and fatigue life prediction of a piezoelectric microplate is investigated and discussed. The findings provide valuable insights into the fundamental mechanism of reliability in piezoelectric MEMS devices due to cyclic loadings, thereby offering new ways to exploit and fabricate the piezoelectric-based MEMS devices suitable for harsh conditions.

  3. Fatigue and Model Analysis of the CNC Cylindrical Grinder

    Directory of Open Access Journals (Sweden)

    Lin Jui-Chang

    2016-01-01

    Full Text Available The purpose of this study is to lower deviation of workpiece by meeting high stability and rigidity to prevent the resonance in producing procedure of the CNC universal cylindrical grinding machine. Using finite element analysis software ABAQUS in grinder machine tools for numerical simulation of several analyses for the following: structural rigidity analysis, optimized design, vibration frequency analysis and fatigue damage analysis. This work aims on state of the transmission of outer diameter spindle to proceed in stress and fatigue life analysis by FE-SAFE Subroutine. The max values of equivalent stress and average amount of displacement in structural rigidity analysis are 0.67(Mpa and 0.92(µm. Optimization design effectively reducing extreme value of stress, the largest decline of about 5.43%. Modal analysis compared with the experimental, the average error percentage was less than 10% of parts. The whole structure error does not exceed 3%. The fatigue life of approximately 1,193,988 times, estimates into real life time can use more than sixty years, from the viewpoint of structural strength, spindle has a good high breaking strength is designed to be safe.

  4. Coupling damage and reliability model of low-cycle fatigue and high energy impact based on the local stress-strain approach

    Institute of Scientific and Technical Information of China (English)

    Chen Hongxia; Chen Yunxia; Yang Zhou

    2014-01-01

    Fatigue induced products generally bear fatigue loads accompanied by impact processes, which reduces their reliable life rapidly. This paper introduces a reliability assessment model based on a local stress-strain approach considering both low-cycle fatigue and high energy impact loads. Two coupling relationships between fatigue and impact are given with effects of an impact process on fatigue damage and effects of fatigue damage on impact performance. The analysis of the former modifies the fatigue parameters and the Manson-Coffin equation for fatigue life based on material theories. On the other hand, the latter proposes the coupling variables and the difference of fracture toughness caused by accumulative fatigue damage. To form an overall reliability model including both fatigue failure and impact failure, a competing risk model is developed. A case study of an actuator cylinder is given to validate this method.

  5. Evaluation of Fatigue Crack Growth and Fracture Properties of Cryogenic Model Materials

    Science.gov (United States)

    Newman, John A.; Forth, Scott C.; Everett, Richard A., Jr.; Newman, James C., Jr.; Kimmel, William M.

    2002-01-01

    The criteria used to prevent failure of wind-tunnel models and support hardware were revised as part of a project to enhance the capabilities of cryogenic wind tunnel testing at NASA Langley Research Center. Specifically, damage-tolerance fatigue life prediction methods are now required for critical components, and material selection criteria are more general and based on laboratory test data. The suitability of two candidate model alloys (AerMet 100 and C-250 steel) was investigated by obtaining the fatigue crack growth and fracture data required for a damage-tolerance fatigue life analysis. Finally, an example is presented to illustrate the newly implemented damage tolerance analyses required of wind-tunnel model system components.

  6. Probabilistic Fatigue Life Prediction of Turbine Disc Considering Model Parameter Uncertainty

    Science.gov (United States)

    He, Liping; Yu, Le; Zhu, Shun-Peng; Ding, Liangliang; Huang, Hong-Zhong

    2016-06-01

    Aiming to improve the predictive ability of Walker model for fatigue life prediction and taking the turbine disc alloy GH4133 as the application example, this paper investigates a new approach for probabilistic fatigue life prediction when considering parameter uncertainty inherent in the life prediction model. Firstly, experimental data are used to update the model parameters using Bayes' theorem, so as to obtain the posterior probability distribution functions of two parameters of the Walker model, as well to achieve the probabilistic life prediction model for turbine disc. During the updating process, Markov Chain Monte Carlo (MCMC) technique is used to generate samples of the given distribution and estimating the parameters distinctly. After that, the turbine disc life is predicted using the probabilistic Walker model based on Monte Carlo simulation technique. The experimental results indicate that: (1) after using the small sample test data obtained from turbine disc, parameter uncertainty of the Walker model can be quantified and the corresponding probabilistic model for fatigue life prediction can be established using Bayes' theorem; (2) there exists obvious dispersion of life data for turbine disc when predicting fatigue life in practical engineering application.

  7. Fatigue Analysis of Steel Catenary Risers Based on a Plasticity Model

    Institute of Scientific and Technical Information of China (English)

    Yongqiang Dong; LipingSun

    2015-01-01

    The most critical issue in the steel catenary riser design is to evaluate the fatigue damage in the touchdown zone accurately. Appropriate modeling of the riser-soil resistance in the touchdown zone can lead to significant cost reduction by optimizing design. This paper presents a plasticity model that can be applied to numerically simulate riser-soil interaction and evaluate dynamic responses and the fatigue damage of a steel catenary riser in the touchdown zone. Utilizing the model, numerous riser-soil elements are attached to the steel catenary riser finite elements, in which each simulates local foundation restraint along the riser touchdown zone. The riser-soil interaction plasticity model accounts for the behavior within an allowable combined loading surface. The model will be represented in this paper, allowing simple numerical implementation. More importantly, it can be incorporated within the structural analysis of a steel catenary riser with the finite element method. The applicability of the model is interpreted theoretically and the results are shown through application to an offshore 8.625″ steel catenary riser example. The fatigue analysis results of the liner elastic riser-soil model are also shown. According to the comparison results of the two models, the fatigue life analysis results of the plasticity framework are reasonable and the horizontal effects of the riser-soil interaction can be included.

  8. Fatigue analysis of steel catenary risers based on a plasticity model

    Science.gov (United States)

    Dong, Yongqiang; Sun, Liping

    2015-03-01

    The most critical issue in the steel catenary riser design is to evaluate the fatigue damage in the touchdown zone accurately. Appropriate modeling of the riser-soil resistance in the touchdown zone can lead to significant cost reduction by optimizing design. This paper presents a plasticity model that can be applied to numerically simulate riser-soil interaction and evaluate dynamic responses and the fatigue damage of a steel catenary riser in the touchdown zone. Utilizing the model, numerous riser-soil elements are attached to the steel catenary riser finite elements, in which each simulates local foundation restraint along the riser touchdown zone. The riser-soil interaction plasticity model accounts for the behavior within an allowable combined loading surface. The model will be represented in this paper, allowing simple numerical implementation. More importantly, it can be incorporated within the structural analysis of a steel catenary riser with the finite element method. The applicability of the model is interpreted theoretically and the results are shown through application to an offshore 8.625″ steel catenary riser example. The fatigue analysis results of the liner elastic riser-soil model are also shown. According to the comparison results of the two models, the fatigue life analysis results of the plasticity framework are reasonable and the horizontal effects of the riser-soil interaction can be included.

  9. Creep-fatigue modelling in structural steels using empirical and constitutive creep methods implemented in a strip-yield model

    Science.gov (United States)

    Andrews, Benjamin J.

    The phenomena of creep and fatigue have each been thoroughly studied. More recently, attempts have been made to predict the damage evolution in engineering materials due to combined creep and fatigue loading, but these formulations have been strictly empirical and have not been used successfully outside of a narrow set of conditions. This work proposes a new creep-fatigue crack growth model based on constitutive creep equations (adjusted to experimental data) and Paris law fatigue crack growth. Predictions from this model are compared to experimental data in two steels: modified 9Cr-1Mo steel and AISI 316L stainless steel. Modified 9Cr-1Mo steel is a high-strength steel used in the construction of pressure vessels and piping for nuclear and conventional power plants, especially for high temperature applications. Creep-fatigue and pure creep experimental data from the literature are compared to model predictions, and they show good agreement. Material constants for the constitutive creep model are obtained for AISI 316L stainless steel, an alloy steel widely used for temperature and corrosion resistance for such components as exhaust manifolds, furnace parts, heat exchangers and jet engine parts. Model predictions are compared to pure creep experimental data, with satisfactory results. Assumptions and constraints inherent in the implementation of the present model are examined. They include: spatial discretization, similitude, plane stress constraint and linear elasticity. It is shown that the implementation of the present model had a non-trivial impact on the model solutions in 316L stainless steel, especially the spatial discretization. Based on these studies, the following conclusions are drawn: 1. The constitutive creep model consistently performs better than the Nikbin, Smith and Webster (NSW) model for predicting creep and creep-fatigue crack extension. 2. Given a database of uniaxial creep test data, a constitutive material model such as the one developed for

  10. Evaluation of creep-fatigue life-prediction models for the solar central receiver

    Science.gov (United States)

    Hyzak, J. M.; Hughes, D. A.

    1981-09-01

    The applicability of several creep fatigue models to life prediction of boiler tubes in a solar central receiver (SCR) was evaluated. The SCR boiler tubes will experience compressive strain dwell loading with hold times up to 6 to 8 hours at temperatures where time dependent deformation will occur. The evaluation criteria include the ability of the model to account for mean stress effects and to be practical in the long life, small strain range regime. A correlation between maximum tensile stress and fatigue life is presented. Using this correlation, compressive dwell behavior is predicted based on continuous cycling data. The limits of this predictive scheme are addressed.

  11. Simplified Model for Evaluation of VIV-induced Fatigue Damage of Deepwater Marine Risers

    Institute of Scientific and Technical Information of China (English)

    XUE Hong-xiang; TANG Wen-yong; ZHANG Sheng-kun

    2009-01-01

    A simplified empirical model for fatigue analysis of deepwater marine risers due to vortex-induced vibration (VIV) in non-uniform current is presented. A simplified modal vibration equation is employed according to the characteristics of deepwater top tensioned risers. The response amplitude of each mode is determined by a balance between the energy feeding into the riser over the lock-in regions and the energy dissipated by the fluid damping over the remainder based on the data from self-excited oscillation and forced oscillation experiments of rigid cylinders. Multi-modal VIV fatigue loading is obtained by the square root of the sum of squares approach.Compared with previous works, this model can take fully account of the main intrinsic natures of VIV for low mass ratio structures on lock-in regions, added mass and nonlinear fluid damping. In addition, a closed form solution of fatigue damage is presented for the case of a riser with uniform mass and cross-section oscillating in a uniform flow. Fatigue analysis of a typical deepwater riser operating in Gulf of Mexico and West Africa shows that the current velocity profiles affect the riser's fatigue life significantly and the most dangerous locations of the riser are also pointed out.

  12. Microtexture Analysis and Modeling of Ambient Fatigue and Creep-Fatigue Damages in Ti-6Al-4V Alloy

    Science.gov (United States)

    Kumar, Jalaj; Singh, A. K.; Raman, S. Ganesh Sundara; Kumar, Vikas

    2017-02-01

    In the present investigation, microtexture analysis using electron back-scattered diffraction technique has been performed to study fatigue- and creep-fatigue damages and associated deformation structures in Ti-6Al-4V alloy. Special emphasis has been given to low-angle grain boundary configuration and its possible application as a damage indicator. Damage is mostly present in the form of voids as investigated through scanning electron microscopy. Stored deformation energies have been evaluated for the strain-controlled fatigue-, the stress-controlled fatigue-, and the creep-fatigue-tested samples. Stored deformation energies have also been analyzed vis-à-vis total damage energies to quantify the contribution of damages to various samples. A relation between the stored deformation energy and the applied strain amplitude has been proposed in this study.

  13. Combat Model Based on Complex Network%基于复杂网络的作战体系模型

    Institute of Scientific and Technical Information of China (English)

    董印权; 陈春鹏

    2013-01-01

    Aiming at the fragility of complex network,the method founding combat model was proposed based on the complex network theory using Agent technology and OODA (Observe-Orient-Decide-Act)process to meet the antagonistic effect requirement.Using bottom-up method,the model could be extended repeatedly.The combat model has some attributes,e.g.Agent,hierarchical,nesting,and redundancy of vertexes and edges,helping to antagonistic effect of campaign.Using several characteristic parameters,the combat model was analyzed by simulation showing that the combat model is not only robust,but also less fragility,which can meet the antagonistic effect requirement during campaign.%针对复杂网络的脆弱性问题,面向作战体系的对抗性需求,基于复杂网络理论,利用Agent技术和OODA(观察、判断、决策、行动)作战过程,提出了作战体系模型的杓建方法.采用自底向上方法,该模型可以通过迭代扩充模型的层次,具有Agent属性、层次性、嵌套性、节点和边的冗余性等作战体系用于对抗的属性.对特征参数的仿真试验结果表明,该作战体系模型不仅具有较好的鲁棒性,而且对脆弱性也有明显的改善,能够较好的满足指挥体系在作战中的对抗需求.

  14. Sensitivity Analysis of Fatigue Crack Growth Model for API Steels in Gaseous Hydrogen

    Science.gov (United States)

    Amaro, Robert L; Rustagi, Neha; Drexler, Elizabeth S; Slifka, Andrew J

    2014-01-01

    A model to predict fatigue crack growth of API pipeline steels in high pressure gaseous hydrogen has been developed and is presented elsewhere. The model currently has several parameters that must be calibrated for each pipeline steel of interest. This work provides a sensitivity analysis of the model parameters in order to provide (a) insight to the underlying mathematical and mechanistic aspects of the model, and (b) guidance for model calibration of other API steels. PMID:26601024

  15. Sensitivity Analysis of Fatigue Crack Growth Model for API Steels in Gaseous Hydrogen.

    Science.gov (United States)

    Amaro, Robert L; Rustagi, Neha; Drexler, Elizabeth S; Slifka, Andrew J

    2014-01-01

    A model to predict fatigue crack growth of API pipeline steels in high pressure gaseous hydrogen has been developed and is presented elsewhere. The model currently has several parameters that must be calibrated for each pipeline steel of interest. This work provides a sensitivity analysis of the model parameters in order to provide (a) insight to the underlying mathematical and mechanistic aspects of the model, and (b) guidance for model calibration of other API steels.

  16. Modeling Creep-Fatigue-Environment Interactions in Steam Turbine Rotor Materials for Advanced Ultra-supercritical Coal Power Plants

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Chen [General Electric Global Research, Niskayuna, NY (United States)

    2014-04-01

    The goal of this project is to model creep-fatigue-environment interactions in steam turbine rotor materials for advanced ultra-supercritical (A-USC) coal power Alloy 282 plants, to develop and demonstrate computational algorithms for alloy property predictions, and to determine and model key mechanisms that contribute to the damages caused by creep-fatigue-environment interactions.

  17. SHM-Based Probabilistic Fatigue Life Prediction for Bridges Based on FE Model Updating.

    Science.gov (United States)

    Lee, Young-Joo; Cho, Soojin

    2016-03-02

    Fatigue life prediction for a bridge should be based on the current condition of the bridge, and various sources of uncertainty, such as material properties, anticipated vehicle loads and environmental conditions, make the prediction very challenging. This paper presents a new approach for probabilistic fatigue life prediction for bridges using finite element (FE) model updating based on structural health monitoring (SHM) data. Recently, various types of SHM systems have been used to monitor and evaluate the long-term structural performance of bridges. For example, SHM data can be used to estimate the degradation of an in-service bridge, which makes it possible to update the initial FE model. The proposed method consists of three steps: (1) identifying the modal properties of a bridge, such as mode shapes and natural frequencies, based on the ambient vibration under passing vehicles; (2) updating the structural parameters of an initial FE model using the identified modal properties; and (3) predicting the probabilistic fatigue life using the updated FE model. The proposed method is demonstrated by application to a numerical model of a bridge, and the impact of FE model updating on the bridge fatigue life is discussed.

  18. Double-sigmoid model for fitting fatigue profiles in mouse fast- and slow-twitch muscle.

    Science.gov (United States)

    Cairns, S P; Robinson, D M; Loiselle, D S

    2008-07-01

    We present a curve-fitting approach that permits quantitative comparisons of fatigue profiles obtained with different stimulation protocols in isolated slow-twitch soleus and fast-twitch extensor digitorum longus (EDL) muscles of mice. Profiles from our usual stimulation protocol (125 Hz for 500 ms, evoked once every second for 100-300 s) could be fitted by single-term functions (sigmoids or exponentials) but not by a double exponential. A clearly superior fit, as confirmed by the Akaiki Information Criterion, was achieved using a double-sigmoid function. Fitting accuracy was exceptional; mean square errors were typically 0.9995. The first sigmoid (early fatigue) involved approximately 10% decline of isometric force to an intermediate plateau in both muscle types; the second sigmoid (late fatigue) involved a reduction of force to a final plateau, the decline being 83% of initial force in EDL and 63% of initial force in soleus. The maximal slope of each sigmoid was seven- to eightfold greater in EDL than in soleus. The general applicability of the model was tested by fitting profiles with a severe force loss arising from repeated tetanic stimulation evoked at different frequencies or rest periods, or with excitation via nerve terminals in soleus. Late fatigue, which was absent at 30 Hz, occurred earlier and to a greater extent at 125 than 50 Hz. The model captured small changes in rate of late fatigue for nerve terminal versus sarcolemmal stimulation. We conclude that a double-sigmoid expression is a useful and accurate model to characterize fatigue in isolated muscle preparations.

  19. Modeling Delamination in Postbuckled Composite Structures Under Static and Fatigue Loads

    Science.gov (United States)

    Bisagni, Chiara; Brambilla, Pietro; Bavila, Carlos G.

    2013-01-01

    The ability of the Abaqus progressive Virtual Crack Closure Technique (VCCT) to model delamination in composite structures was investigated for static, postbuckling, and fatigue loads. Preliminary evaluations were performed using simple Double Cantilever Beam (DCB) and Mixed-Mode Bending (MMB) specimens. The nodal release sequences that describe the propagation of the delamination front were investigated. The effect of using a sudden or a gradual nodal release was evaluated by considering meshes aligned with the crack front as well as misaligned meshes. Fatigue simulations were then performed using the Direct Cyclic Fatigue (DCF) algorithm. It was found that in specimens such as the DCB, which are characterized by a nearly linear response and a pure fracture mode, the algorithm correctly predicts the Paris Law rate of propagation. However, the Abaqus DCF algorithm does not consider different fatigue propagation laws in different fracture modes. Finally, skin/stiffener debonding was studied in an aircraft fuselage subcomponent in which debonding occurs deep into post-buckling deformation. VCCT was shown to be a robust tool for estimating the onset propagation. However, difficulties were found with the ability of the current implementation of the Abaqus progressive VCCT to predict delamination propagation within structures subjected to postbuckling deformations or fatigue loads.

  20. Contact fatigue response of porcelain-veneered alumina model systems.

    Science.gov (United States)

    Stappert, Christian F J; Baldassarri, Marta; Zhang, Yu; Stappert, Dina; Thompson, Van P

    2012-02-01

    Fatigue damage modes and reliability of hand-veneered (HV) and over-pressed (OP) aluminum-oxide layer structures were compared. Influence of luting cement thickness on mechanical performance was investigated. Sixty-four aluminum-oxide plates (10 × 10 × 0.5 mm) were veneered with hand built-up or pressed porcelain (0.7 mm) and adhesively luted (50- or 150-μm cement thickness) to water-aged composite resin blocks (12 × 12 × 4 mm). Single-load-to-failure and fatigue tests were performed with a spherical tungsten carbide indenter (d = 6.25 mm) applied in the center of the veneer layer. Specimens were inspected with polarized-reflected-light and scanning electron microscopy. Use-level probability Weibull curves were plotted with two-sided 90% confidence bounds, and reliability at 75,000 cycles and 250 N load was calculated. For all specimens but two OP with 50-μm cement thickness, failure was characterized by flexural radial cracks initiating at the bottom surface of the alumina core and propagating into the veneering porcelain before cone cracks could extend to the porcelain/alumina interface. HV specimens showed higher reliability compared to OP. Those with 50-μm cement thickness were more reliable relative to their 150-μm counterparts (HV_50 μm: 95% (0.99/0.67); HV_150 μm: 55% (0.92/0.01); OP_50 μm: 69% (0.84/0.48); OP_150 μm: 15% (0.53/0.004)). Similar failure modes were observed in HV and OP specimens. Radial cracks developing in the core and spreading into the veneer are suggested to cause bulk fracture, which is the characteristic failure mode for alumina core crowns. However, the highest resistance to fatigue loading was found for the HV specimens with thin cement thickness, while the lowest occurred for the OP with thick cement layer.

  1. The Fracture Mechanical Markov Chain Fatigue Model Compared with Empirical Data

    DEFF Research Database (Denmark)

    Gansted, L.; Brincker, Rune; Hansen, Lars Pilegaard

    The applicability of the FMF-model (Fracture Mechanical Markov Chain Fatigue Model) introduced in Gansted, L., R. Brincker and L. Pilegaard Hansen (1991) is tested by simulations and compared with empirical data. Two sets of data have been used, the Virkler data (aluminium alloy) and data...... that the FMF-model gives adequate description of the empirical data using model parameters characteristic of the material....

  2. Bi-variable damage model for fatigue life prediction of metal components

    Institute of Scientific and Technical Information of China (English)

    Miao Zhang; Qing-Chun Meng; Xing Zhang; Wei-Ping Hu

    2011-01-01

    Based on the theory of continuum damage mechanics, a bi-variable damage mechanics model is developed, which, according to thermodynamics, is accessible to derivation of damage driving force, damage evolution equation and damage evolution criteria. Furthermore, damage evolution equations of time rate are established by the generalized Drucker's postulate. The damage evolution equation of cycle rate is obtained by integrating the time damage evolution equations, and the fatigue life prediction method for smooth specimens under repeated loading with constant strain amplitude is constructed. Likewise, for notched specimens under the repeated loading with constant strain amplitude, the fatigue life prediction method is obtained on the ground of the theory of conservative integral in damage mechanics. Thus, the material parameters in the damage evolution equation can be obtained by reference to the fatigue test results of standard specimens with stress concentration factor equal to 1, 2 and 3.

  3. Fatigue design of a cellular phone folder using regression model-based multi-objective optimization

    Science.gov (United States)

    Kim, Young Gyun; Lee, Jongsoo

    2016-08-01

    In a folding cellular phone, the folding device is repeatedly opened and closed by the user, which eventually results in fatigue damage, particularly to the front of the folder. Hence, it is important to improve the safety and endurance of the folder while also reducing its weight. This article presents an optimal design for the folder front that maximizes its fatigue endurance while minimizing its thickness. Design data for analysis and optimization were obtained experimentally using a test jig. Multi-objective optimization was carried out using a nonlinear regression model. Three regression methods were employed: back-propagation neural networks, logistic regression and support vector machines. The AdaBoost ensemble technique was also used to improve the approximation. Two-objective Pareto-optimal solutions were identified using the non-dominated sorting genetic algorithm (NSGA-II). Finally, a numerically optimized solution was validated against experimental product data, in terms of both fatigue endurance and thickness index.

  4. A Critical Plane-energy Model for Multiaxial Fatigue Life Prediction of Homogeneous and Heterogeneous Materials

    Science.gov (United States)

    Wei, Haoyang

    A new critical plane-energy model is proposed in this thesis for multiaxial fatigue life prediction of homogeneous and heterogeneous materials. Brief review of existing methods, especially on the critical plane-based and energy-based methods, are given first. Special focus is on one critical plane approach which has been shown to work for both brittle and ductile metals. The key idea is to automatically change the critical plane orientation with respect to different materials and stress states. One potential drawback of the developed model is that it needs an empirical calibration parameter for non-proportional multiaxial loadings since only the strain terms are used and the out-of-phase hardening cannot be considered. The energy-based model using the critical plane concept is proposed with help of the Mroz-Garud hardening rule to explicitly include the effect of non-proportional hardening under fatigue cyclic loadings. Thus, the empirical calibration for non-proportional loading is not needed since the out-of-phase hardening is naturally included in the stress calculation. The model predictions are compared with experimental data from open literature and it is shown the proposed model can work for both proportional and non-proportional loadings without the empirical calibration. Next, the model is extended for the fatigue analysis of heterogeneous materials integrating with finite element method. Fatigue crack initiation of representative volume of heterogeneous materials is analyzed using the developed critical plane-energy model and special focus is on the microstructure effect on the multiaxial fatigue life predictions. Several conclusions and future work is drawn based on the proposed study.

  5. New model of propagation rates of long crack due to structure fatigue

    Institute of Scientific and Technical Information of China (English)

    Jian-tao LIU; Ping-an DU; Ming-jing HUANG; Qing ZHOU

    2009-01-01

    By comparison of the characteristics of existing models for long fatigue crack propagation rates,a new model,called the generalized passivation-lancet model for long fatigue crack propagation rates (GPLFCPR),and a general formula for characterizing the process of crack growth rates are proposed based on the passivation-lancet theory.The GPLFCPR model overcomes disadvantages of the existing models and can describe the rules of the entire fatiguc crack growth process from the cracking threshold to the critical fracturing point effectively with explicit physical meaning. It also reflects the influence of material characteristics,such as strength parameters,fracture parameters and heat treatment. Experimental results obtained by testing LZ50 steel,AlZnMgCu0.5,0.5Cr0.5Mo0.25V steel,etc.,show good consistency with the new model. The GPLFCPR model is valuable in theoretical research and practical applications.

  6. Health-aware Model Predictive Control of Wind Turbines using Fatigue Prognosis

    DEFF Research Database (Denmark)

    Sardi, Hector Eloy Sanchez; Escobet, Teressa; Puig, Vicenc;

    2015-01-01

    management module with the control provides a mechanism for the wind turbine to operate safely and optimize the trade-off between components life and energy production. The research presented in this paper explores the integration of model predictive control (MPC) with fatigue-based prognosis approach...

  7. Multistage Fatigue Modeling of Cast A356-T6 and A380-F Aluminum Alloys

    Science.gov (United States)

    Xue, Y.; Burton, C. L.; Horstemeyer, M. F.; McDowell, D. L.; Berry, J. T.

    2007-08-01

    This article presents a microstructure-based multistage fatigue (MSF) model extended from the model developed by McDowell et al.[1,2] to an A380-F aluminum alloy to consider microstructure-property relations of descending order, signifying deleterious effects of defects/discontinuities: (1) pores or oxides greater than 100 μm, (2) pores or oxides greater than 50 μm near the free surface, (3) a high porosity region with an area greater than 200 μm, and (4) oxide film of an area greater than 10,000 μm2. These microconstituents, inclusions, or discontinuities represent different casting features that may dominate fatigue life at stages of fatigue damage evolutions. The incubation life is estimated using a modified Coffin Mansion law at the microscale based on the microplasticity at the discontinuity. The microstructurally small crack (MSC) and physically small crack (PSC) growth was modeled using the crack tip displacement as the driving force, which is affected by the porosity and dendrite cell size (DCS). When the fatigue damage evolves to several DCSs, cracks behave as long cracks with growth subject to the effective stress intensity factor in linear elastic fracture mechanics. Based on an understanding of the microstructures of A380-F and A356-T6 aluminum alloys, an engineering treatment of the MSF model was introduced for A380-F aluminum alloys by tailoring a few model parameters based on the mechanical properties of the alloy. The MSF model is used to predict the upper and lower bounds of the experimental fatigue strain life and stress life of the two cast aluminum alloys.

  8. The stretch-shortening cycle : a model to study naturally occurring neuromuscular fatigue.

    Science.gov (United States)

    Nicol, Caroline; Avela, Janne; Komi, Paavo V

    2006-01-01

    Neuromuscular fatigue has traditionally been examined using isolated forms of either isometric, concentric or eccentric actions. However, none of these actions are naturally occurring in human (or animal) ground locomotion. The basic muscle function is defined as the stretch-shortening cycle (SSC), where the preactivated muscle is first stretched (eccentric action) and then followed by the shortening (concentric) action. As the SSC taxes the skeletal muscles very strongly mechanically, its influence on the reflex activation becomes apparent and very different from the isolated forms of muscle actions mentioned above. The ground contact phases of running, jumping and hopping etc. are examples of the SSC for leg extensor muscles; similar phases can also be found for the upper-body activities. Consequently, it is normal and expected that the fatigue phenomena should be explored during SSC activities. The fatigue responses of repeated SSC actions are very versatile and complex because the fatigue does not depend only on the metabolic loading, which is reportedly different among muscle actions. The complexity of SSC fatigue is well reflected by the recovery patterns of many neuromechanical parameters. The basic pattern of SSC fatigue response (e.g. when using the complete exhaustion model of hopping or jumping) is the bimodality showing an immediate reduction in performance during exercise, quick recovery within 1-2 hours, followed by a secondary reduction, which may often show the lowest values on the second day post-exercise when the symptoms of muscle soreness/damage are also greatest. The full recovery may take 4-8 days depending on the parameter and on the severity of exercise. Each subject may have their own time-dependent bimodality curve. Based on the reviewed literature, it is recommended that the fatigue protocol is 'completely' exhaustive to reduce the important influence of inter-subject variability in the fatigue responses. The bimodality concept is

  9. 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….

  10. Damage and failure modeling of lotus-type porous material subjected to low-cycle fatigue

    Directory of Open Access Journals (Sweden)

    J. Kramberger

    2016-01-01

    Full Text Available The investigation of low-cycle fatigue behaviour of lotus-type porous material is presented in this paper. Porous materials exhibit some unique features which are useful for a number of various applications. This paper evaluates a numerical approach for determining of damage initiation and evolution of lotus-type porous material with computational simulations, where the considered computational models have different pore topology patterns. The low-cycle fatigue analysis was performed by using a damage evolution law. The damage state was calculated and updated based on the inelastic hysteresis energy for stabilized cycle. Degradation of the elastic stifness was modeled using scalar damage variable. In order to examine crack propagation path finite elements with severe damage were deleted and removed from the mesh during simulation. The direct cyclic analysis capability in Abaqus/Standard was used for low-cycle fatigue analysis to obtain the stabilized response of a model subjected to the periodic loading. The computational results show a qualitative understanding of pores topology influence on low-cycle fatigue under transversal loading conditions in relation to pore orientation.

  11. Discussion of "Simplified Model of Low Cycle Fatigue for RC Frames"

    OpenAIRE

    1999-01-01

    To model strength degradation due to low cycle fatigue, at least three different approaches can be considered. One possibility is based on the formulation of a new free energy function and damage energy release rate, as was proposed by Ju(1989). The second approach uses the notion of bounding surface introduced in cyclic plasticity by Dafalias and Popov (1975). From this concept, some models have been proposed to quantify damage in concrete or RC (Suaris et al. 1990). The model proposed by...

  12. A New Modelling of Crack Propagation with Fatigue-Creep-Oxidation Interaction under Non Isothermal Loading

    Science.gov (United States)

    2003-02-01

    propagation of metallic materials at high temperature such as Ni-base superalloy for turbine discs . The strong requirements in design procedures have led to the...This paper deals with the extension of a crack growth model to high temperature complex loading and application to turbine disc . The proposed model is...which comprises fatigue with or without hold times and special sequence tests representative to the disc in service. The crack growth model is built up

  13. Risk factors and visual fatigue of baggage X-ray security screeners: a structural equation modelling analysis.

    Science.gov (United States)

    Yu, Rui-Feng; Yang, Lin-Dong; Wu, Xin

    2016-06-03

    This study identified the risk factors influencing visual fatigue in baggage X-ray security screeners and estimated the strength of correlations between those factors and visual fatigue using structural equation modelling approach. Two hundred and five X-ray security screeners participated in a questionnaire survey. The result showed that satisfaction with the VDT's physical features and the work environment conditions were negatively correlated with the intensity of visual fatigue, whereas job stress and job burnout had direct positive influences. The path coefficient between the image quality of VDT and visual fatigue was not significant. The total effects of job burnout, job stress, the VDT's physical features and the work environment conditions on visual fatigue were 0.471, 0.469, -0.268 and -0.251 respectively. These findings indicated that both extrinsic factors relating to VDT and workplace environment and psychological factors including job burnout and job stress should be considered in the workplace design and work organisation of security screening tasks to reduce screeners' visual fatigue. Practitioner Summary: This study identified the risk factors influencing visual fatigue in baggage X-ray security screeners and estimated the strength of correlations between those factors and visual fatigue. The findings were of great importance to the workplace design and the work organisation of security screening tasks to reduce screeners' visual fatigue.

  14. Isothermal fatigue behavior and damage modeling of a high temperature woven PMC[Polymer Matrix Composite

    Energy Technology Data Exchange (ETDEWEB)

    Gyekenyesi, A.L.

    2000-01-01

    This study focuses on the fully reversed fatigue behavior exhibited by a carbon fiber/polyimide resin woven laminate at room and elevated temperatures. Nondestructive video edge view microscopy and destructive sectioning techniques were used to study the microscopic damage mechanisms that evolved. The elastic stiffness was monitored and recorded throughout the fatigue life of the coupon. In addition, residual compressive strength tests were conducted on fatigue coupons with various degrees of damage as quantified by stiffness reduction. Experimental results indicated that the monotonic tensile properties were only minimally influenced by temperature, while the monotonic compressive and fully reversed fatigue properties displayed greater reductions due to the elevated temperature. The stiffness degradation as a function of cycles, consisted of three stages; a short-lived high degradation period, a constant degradation rate segment covering the majority of the life, and a final stage demonstrating an increasing rate of degradation up to failure. Concerning the residual compressive strength tests at room and elevated temperatures, the elevated temperature coupons appeared much more sensitive to damage. At elevated temperatures, coupons experienced a much larger loss in compressive strength when compared to room temperature coupons with equivalent damage. The fatigue damage accumulation law proposed for the model incorporates a scalar representation for damage, but admits a multiaxial, anisotropic evolutionary law. The model predicts the current damage (as quantified by residual stiffness) and remnant life of a composite that has undergone a known load at temperature. The damage/life model is dependent on the applied multiaxial stress state as well as temperature. Comparisons between the model and data showed good predictive capabilities concerning stiffness degradation and cycles to failure.

  15. Computational Modeling to Predict Fatigue Behavior of NiTi Stents: What Do We Need?

    Directory of Open Access Journals (Sweden)

    Elena Dordoni

    2015-05-01

    Full Text Available NiTi (nickel-titanium stents are nowadays commonly used for the percutaneous treatment of peripheral arterial disease. However, their effectiveness is still debated in the clinical field. In fact a peculiar cyclic biomechanical environment is created before and after stent implantation, with the risk of device fatigue failure. An accurate study of the device fatigue behavior is of primary importance to ensure a successful stenting procedure. Regulatory authorities recognize the possibility of performing computational analyses instead of experimental tests for the assessment of medical devices. However, confidence in numerical methods is only possible after verification and validation of the models used. For the case of NiTi stents, mechanical properties are strongly dependent on the device dimensions and the whole treatments undergone during manufacturing process. Hence, special attention should be paid to the accuracy of the description of the device geometry and the material properties implementation into the numerical code, as well as to the definition of the fatigue limit. In this paper, a path for setting up an effective numerical model for NiTi stent fatigue assessment is proposed and the results of its application in a specific case study are illustrated.

  16. Substrate Creep on The Fatigue Life of A Model Dental Multilayer Structure

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, J; Huang, M; Niu, X; soboyejo, W

    2006-10-09

    In this paper, we investigated the effects of substrate creep on the fatigue behavior of a model dental multilayer structure, in which a top glass layer was bonded to a polycarbonate substrate through a dental adhesive. The top glass layers were ground using 120 grit or 600 grit sand papers before bonding to create different sub-surface crack sizes and morphologies. The multilayer structures were tested under cyclic Hertzian contact loading to study crack growth and obtain fatigue life curves. The experiment results showed that the fatigue lives of the multilayer structures were impaired by increasing crack sizes in the sub-surfaces. They were also significantly reduced by the substrate creep when tested at relatively low load levels i.e. P{sub m} < 60 N (Pm is the maximum magnitude of cyclic load). But at relatively high load levels i.e. P{sub m} > 65 N, slow crack growth (SCG) was the major failure mechanisms. A modeling study was then carried out to explore the possible failure mechanisms over a range of load levels. It is found that fatigue life at relatively low load levels can be better estimated by considering the substrate creep effect (SCE).

  17. Incorporation of caffeine into a quantitative model of fatigue and sleep.

    Science.gov (United States)

    Puckeridge, M; Fulcher, B D; Phillips, A J K; Robinson, P A

    2011-03-21

    A recent physiologically based model of human sleep is extended to incorporate the effects of caffeine on sleep-wake timing and fatigue. The model includes the sleep-active neurons of the hypothalamic ventrolateral preoptic area (VLPO), the wake-active monoaminergic brainstem populations (MA), their interactions with cholinergic/orexinergic (ACh/Orx) input to MA, and circadian and homeostatic drives. We model two effects of caffeine on the brain due to competitive antagonism of adenosine (Ad): (i) a reduction in the homeostatic drive and (ii) an increase in cholinergic activity. By comparing the model output to experimental data, constraints are determined on the parameters that describe the action of caffeine on the brain. In accord with experiment, the ranges of these parameters imply significant variability in caffeine sensitivity between individuals, with caffeine's effectiveness in reducing fatigue being highly dependent on an individual's tolerance, and past caffeine and sleep history. Although there are wide individual differences in caffeine sensitivity and thus in parameter values, once the model is calibrated for an individual it can be used to make quantitative predictions for that individual. A number of applications of the model are examined, using exemplar parameter values, including: (i) quantitative estimation of the sleep loss and the delay to sleep onset after taking caffeine for various doses and times; (ii) an analysis of the system's stable states showing that the wake state during sleep deprivation is stabilized after taking caffeine; and (iii) comparing model output successfully to experimental values of subjective fatigue reported in a total sleep deprivation study examining the reduction of fatigue with caffeine. This model provides a framework for quantitatively assessing optimal strategies for using caffeine, on an individual basis, to maintain performance during sleep deprivation.

  18. Flight Attendant Work/Rest Patterns, Alertness, and Performance Assessment: Field Validation of Biomathematical Fatigue Modeling

    Science.gov (United States)

    2012-09-01

    Speed (R2=0.539, p<.05), and Lapses (R2=0.901, p<.001). Despite inherent technical limitations and issues of inter -individual variability, these...Aviation Safety Authority [ CASA ], 2010; also see Spencer and Robertson, 2007). mEThOd All human subjects procedures involved in this project were...to the various fatigue-producing inputs accounted for by any given model ( CASA , 2010; Van Dongen, Bender & Dinges 2012). Most model predictions

  19. Evaluation of Creep-Fatigue Damage Based on Simplified Model Test Approach

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Yanli [ORNL; Li, Tianlei [ORNL; Sham, Sam [ORNL; Jetter, Robert I [Consultant

    2013-01-01

    Current methods used in the ASME Code, Subsection NH for the evaluation of creep-fatigue damage are based on the separation of elevated temperature cyclic damage into two parts, creep damage and fatigue damage. This presents difficulties in both evaluation of test data and determination of cyclic damage in design. To avoid these difficulties, an alternative approach was identified, called the Simplified Model Test or SMT approach based on the use of creep-fatigue hold time test data from test specimens with elastic follow-up conservatively designed to bound the response of general structural components of interest. A key feature of the methodology is the use of the results of elastic analysis directly in design evaluation similar to current methods in the ASME Code, Subsection NB. Although originally developed for current material included in Subsection NH, recent interest in the application of Alloy 617 for components operating at very high temperatures has caused renewed interest in the SMT approach because it provides an alternative to the proposed restriction on the use of current Subsection NH simplified methods at very high temperatures. A comprehensive review and assessment of five representative simplified methods for creep-fatigue damage evaluation is presented in Asayama [1]. In this review the SMT methodology was identified as the best long term approach but the need for test data precluded its near term implementation. Asayama and Jetter [2] is a summary of the more comprehensive report by Asayama [1] with a summary of the SMT approach presented by Jetter [3].

  20. The representation of inflammatory signals in the brain – a model for subjective fatigue in multiple sclerosis

    Directory of Open Access Journals (Sweden)

    Katrin eHanken

    2014-12-01

    Full Text Available In multiple sclerosis (MS patients, fatigue is rated as one of the most common and disabling symptoms. However, the pathophysiology underlying this fatigue is not yet clear. Several lines of evidence suggest that immunological factors, such as elevated levels of proinflammatory cytokines, may contribute to subjective fatigue in MS patients. Proinflammatory cytokines represent primary mediators of immune-to-brain-communication, modulating changes in the neurophysiology of the central nervous system. Recently, we proposed a model arguing that fatigue in MS patients is a subjective feeling which is related to inflammation. Moreover, it implies that fatigue can be measured behaviorally only by applying specific cognitive tasks related to alertness and vigilance. In the present review we focus on the subjective feeling of MS-related fatigue. We examine the hypothesis that the subjective feeling of MS-related fatigue may be a variant of inflammation-induced sickness behavior, resulting from cytokine-mediated activity changes within brain areas involved in interoception and homeostasis including the insula, the anterior cingulate and the hypothalamus. We first present studies demonstrating a relationship between proinflammatory cytokines and subjective fatigue in healthy individuals, in people with inflammatory disorders, and particularly in MS patients. Subsequently, we discuss studies analyzing the impact of anti-inflammatory treatment on fatigue. In the next part of this review we present studies on the transmission and neural representation of inflammatory signals, with a special focus on possible neural concomitants of inflammation-induced fatigue. We also present two of our studies on the relationship between local gray and white matter atrophy and fatigue in MS patients. Finally, we discuss some implications of our findings and future perspectives.

  1. The Representation of Inflammatory Signals in the Brain – A Model for Subjective Fatigue in Multiple Sclerosis

    Science.gov (United States)

    Hanken, Katrin; Eling, Paul; Hildebrandt, Helmut

    2014-01-01

    In multiple sclerosis (MS) patients, fatigue is rated as one of the most common and disabling symptoms. However, the pathophysiology underlying this fatigue is not yet clear. Several lines of evidence suggest that immunological factors, such as elevated levels of pro-inflammatory cytokines, may contribute to subjective fatigue in MS patients. Pro-inflammatory cytokines represent primary mediators of immune-to-brain-communication, modulating changes in the neurophysiology of the central nervous system. Recently, we proposed a model arguing that fatigue in MS patients is a subjective feeling, which is related to inflammation. Moreover, it implies that fatigue can be measured behaviorally only by applying specific cognitive tasks related to alertness and vigilance. In the present review, we focus on the subjective feeling of MS-related fatigue. We examine the hypothesis that the subjective feeling of MS-related fatigue may be a variant of inflammation-induced sickness behavior, resulting from cytokine-mediated activity changes within brain areas involved in interoception and homeostasis including the insula, the anterior cingulate, and the hypothalamus. We first present studies demonstrating a relationship between pro-inflammatory cytokines and subjective fatigue in healthy individuals, in people with inflammatory disorders, and particularly in MS patients. Subsequently, we discuss studies analyzing the impact of anti-inflammatory treatment on fatigue. In the next part of this review, we present studies on the transmission and neural representation of inflammatory signals, with a special focus on possible neural concomitants of inflammation-induced fatigue. We also present two of our studies on the relationship between local gray and white matter atrophy and fatigue in MS patients. Finally, we discuss some implications of our findings and future perspectives. PMID:25566171

  2. A Simulation Method for High-Cycle Fatigue-Driven Delamination using a Cohesive Zone Model

    DEFF Research Database (Denmark)

    Bak, Brian Lau Verndal; Turon, A.; Lindgaard, Esben;

    2016-01-01

    on parameter fitting of any kind. The method has been implemented as a zero-thickness eight-node interface element for Abaqus and as a spring element for a simple finite element model in MATLAB. The method has been validated in simulations of mode I, mode II, and mixed-mode crack loading for both self......A novel computational method for simulating fatigue-driven mixed-mode delamination cracks in laminated structures under cyclic loading is presented. The proposed fatigue method is based on linking a cohesive zone model for quasi-static crack growth and a Paris' law-like model described......-similar and non-self-similar crack propagation. The method produces highly accurate results compared with currently available methods and is capable of simulating general mixed-mode non-self-similar crack growth problems....

  3. Modelling of ultrasonic impact treatment (UIT of welded joints and its effect on fatigue strength

    Directory of Open Access Journals (Sweden)

    K.L. Yuan

    2015-10-01

    Full Text Available Ultrasonic impact treatment (UIT is a remarkable post-weld technique applying mechanical impacts in combination with ultrasound into the welded joints. In the present work, a 3D simulation method including welding simulation, numerical modelling of UIT-process and an evaluation of fatigue crack growth has been developed. In the FE model, the actual treatment conditions and local mechanical characteristics due to acoustic softening are set as input parameters. The plastic deformation and compressive stress layer are found to be more pronounced when acoustic softening takes place. The predicted internal residual stress distributions of welded joint before and after UIT are compared with experimental results, showing a fairly good agreement with each other. Finally, simulated results of fatigue crack growth in various residual stress fields are well compared with test results, so that the proposed model may provide an effective tool to simulate UIT-process in engineering structures.

  4. Can neuromuscular fatigue explain running strategies and performance in ultra-marathons?: the flush model.

    Science.gov (United States)

    Millet, Guillaume Y

    2011-06-01

    While the industrialized world adopts a largely sedentary lifestyle, ultra-marathon running races have become increasingly popular in the last few years in many countries. The ability to run long distances is also considered to have played a role in human evolution. This makes the issue of ultra-long distance physiology important. In the ability to run multiples of 10 km (up to 1000 km in one stage), fatigue resistance is critical. Fatigue is generally defined as strength loss (i.e. a decrease in maximal voluntary contraction [MVC]), which is known to be dependent on the type of exercise. Critical task variables include the intensity and duration of the activity, both of which are very specific to ultra-endurance sports. They also include the muscle groups involved and the type of muscle contraction, two variables that depend on the sport under consideration. The first part of this article focuses on the central and peripheral causes of the alterations to neuromuscular function that occur in ultra-marathon running. Neuromuscular function evaluation requires measurements of MVCs and maximal electrical/magnetic stimulations; these provide an insight into the factors in the CNS and the muscles implicated in fatigue. However, such measurements do not necessarily predict how muscle function may influence ultra-endurance running and whether this has an effect on speed regulation during a real competition (i.e. when pacing strategies are involved). In other words, the nature of the relationship between fatigue as measured using maximal contractions/stimulation and submaximal performance limitation/regulation is questionable. To investigate this issue, we are suggesting a holistic model in the second part of this article. This model can be applied to all endurance activities, but is specifically adapted to ultra-endurance running: the flush model. This model has the following four components: (i) the ball-cock (or buoy), which can be compared with the rate of perceived

  5. A Continuum Damage Mechanics Model for the Static and Cyclic Fatigue of Cellular Composites

    Science.gov (United States)

    Huber, Otto

    2017-01-01

    The fatigue behavior of a cellular composite with an epoxy matrix and glass foam granules is analyzed and modeled by means of continuum damage mechanics. The investigated cellular composite is a particular type of composite foam, and is very similar to syntactic foams. In contrast to conventional syntactic foams constituted by hollow spherical particles (balloons), cellular glass, mineral, or metal place holders are combined with the matrix material (metal or polymer) in the case of cellular composites. A microstructural investigation of the damage behavior is performed using scanning electron microscopy. For the modeling of the fatigue behavior, the damage is separated into pure static and pure cyclic damage and described in terms of the stiffness loss of the material using damage models for cyclic and creep damage. Both models incorporate nonlinear accumulation and interaction of damage. A cycle jumping procedure is developed, which allows for a fast and accurate calculation of the damage evolution for constant load frequencies. The damage model is applied to examine the mean stress effect for cyclic fatigue and to investigate the frequency effect and the influence of the signal form in the case of static and cyclic damage interaction. The calculated lifetimes are in very good agreement with experimental results. PMID:28809806

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

    Science.gov (United States)

    Na, Youngjin; Kim, Jung

    2016-11-14

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

  7. Fatigue behaviour FEM modeling of deep groove ball bearing mounted in automotive alternator submitted to variable loading

    Directory of Open Access Journals (Sweden)

    Azianou Ayao. E.

    2014-06-01

    Full Text Available Ball bearings subsurface materials are subjected to rolling contact fatigue with multiaxial stress state during loading cycle. The complex operating conditions of automotive bearings are different from classic operating conditions their fatigue crack initiation predicted by standards can be seen underestimated. This work presents a numerical approach of ball bearings to evaluate its fatigue behaviour in order to predict the life. A preliminary study has been done to evaluate the load distribution in the bearings. The results are integrated in a numerical dynamic model to study the bearing material rolling fatigue behaviour in constant and variable loading cases. By using fatigue criteria and damage laws, the analysis of stress state in bearing material leads to life prediction or the number of cycles before crack initiations. These results are compared to current standard methods used for ball bearing life prediction.

  8. 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.

  9. Comparison of Combat Gauze and TraumaStat in Two Severe Groin Injury Models

    Science.gov (United States)

    2011-07-01

    Lidocaine (1 %-2%) was spread on the artery to maximize dilation of the vessel. Any proximal side branches from the artery were ligated to avoid...level rating scale. These actions , application, and removal presented no difficulty for either test dressing. DISCUSSION Combat Gauze and...consistent with lower TMS performance. Mechanism of action of these dressings may be asso- ciated with their absorption and clotting abilities, which were

  10. Fatigue and Serviceability Limit State Model Basis for Assessment of Offshore Wind Energy Converters

    DEFF Research Database (Denmark)

    Thons, S.; Faber, M. H.; Rücker, W.

    2012-01-01

    This paper develops the models for the structural performance of the loading and probabilistic characterization for the fatigue and the serviceability limit states for the support structure of offshore wind energy converters. These models and a sensitivity study are part of a risk based assessment...... al. ("Ultimate Limit State Model Basis for Assessment of Offshore Wind Energy Con-verters," ASME J. Offshore Mech. Arct. Eng.), the model basis for the assessment is completed. The process of establishing and analyzing such a model basis contributes to a detailed understanding of the deterministic...

  11. Effect of fibre arrangement on the multiaxial fatigue of fibrous composites: a micromechanical computational model

    Directory of Open Access Journals (Sweden)

    Roberto Brighenti

    2015-10-01

    Full Text Available Structural components made of fibre-reinforced materials are frequently used in engineering applications. Fibre-reinforced composites are multiphase materials, and complex mechanical phenomena take place at limit conditions but also during normal service situations, especially under fatigue loading, causing a progressive deterioration and damage. Under repeated loading, the degradation mainly occurs in the matrix material and at the fibre-matrix interface, and such a degradation has to be quantified for design structural assessment purposes. To this end, damage mechanics and fracture mechanics theories can be suitably applied to examine such a problem. Damage concepts can be applied to the matrix mechanical characteristics and, by adopting a 3-D mixed mode fracture description of the fibre-matrix detachment, fatigue fracture mechanics concepts can be used to determine the progressive fibre debonding responsible for the loss of load bearing capacity of the reinforcing phase. In the present paper, a micromechanical model is used to evaluate the unixial or multiaxial fatigue behaviour of structures with equi-oriented or randomly distributed fibres. The spatial fibre arrangement is taken into account through a statistical description of their orientation angles for which a Gaussian-like distribution is assumed, whereas the mechanical effect of the fibres on the composite is accounted for by a homogenization approach aimed at obtaining the macroscopic elastic constants of the material. The composite material behaves as an isotropic one for randomly distributed fibres, while it is transversally isotropic for unidirectional fibres. The fibre arrangement in the structural component influences the fatigue life with respect to the biaxiality ratio for multiaxial constant amplitude fatigue loading. One representative parametric example is discussed.

  12. Wind turbine fatigue damage evaluation based on a linear model and a spectral method

    DEFF Research Database (Denmark)

    Tibaldi, Carlo; Henriksen, Lars Christian; Hansen, Morten Hartvig;

    2015-01-01

    to power spectral densities of wind turbine sensor responses to turbulent wind. In this paper, the model is validated both in time domain and frequency domain with a nonlinear aeroservoelastic model. The approach is compared quantitatively against fatigue damage obtained from the power spectra of time...... different wind speeds above rated and load dependency on the number of turbulence seeds used for their evaluation. For the full-range normal operation, the maximum difference between the two frequency domain-based estimates of the tower base lateral fatigue moments is 36%, whereas the differences...... for the other sensors are less than 15%. For the load variation evaluation, the maximum difference of the tower base longitudinal bending moment variation is 22%. Such large difference occurs only when the change in controller tuning has a low effect on the loads. Furthermore, results show that loads evaluated...

  13. Microstructurally based thermomechanical fatigue lifetime model of solder joints for electronic applications

    Energy Technology Data Exchange (ETDEWEB)

    Frear, D.R.; Rashid, M.M.; Burchett, S.N.

    1993-07-01

    We present a new methodology for predicting the fatigue life of solder joints for electronics applications. This approach involves integration of experimental and computational techniques. The first stage involves correlating the manufacturing and processing parameters with the starting microstructure of the solder joint. The second stage involves a series of experiments that characterize the evolution of the microstructure during thermal cycling. The third stage consists of a computer modeling and simulation effort that utilizes the starting microstructure and experimental data to produce a reliability prediction of the solder joint. This approach is an improvement over current methodologies because it incorporates the microstructure and properties of the solder directly into the model and allows these properties to evolve as the microstructure changes during fatigue.

  14. Littoral Combat Ship Crew Scheduling

    Science.gov (United States)

    2015-03-01

    package DON Department of the Navy F&R Fix and Relax GAMS General Algebraic Modeling System LCS Littoral Combat Ship LCSRON Littoral Combat Ship...but that can be acceptable depending on the scheduler needs. F&R produces superior long-term schedules when compared to a similar-length RH schedule...LEFT BLANK 29 IV. MODEL IMPLEMENTATION LCSS is implemented with the General Algebraic Modeling System (GAMS) using the GAMS/CPLEX (GAMS, 2014

  15. Low Cycle Fatigue Behaviour of DP Steels: Micromechanical Modelling vs. Validation

    Directory of Open Access Journals (Sweden)

    Ghazal Moeini

    2017-07-01

    Full Text Available This study aims to simulate the stabilised stress-strain hysteresis loop of dual phase (DP steel using micromechanical modelling. For this purpose, the investigation was conducted both experimentally and numerically. In the experimental part, the microstructure characterisation, monotonic tensile tests and low cycle fatigue tests were performed. In the numerical part, the representative volume element (RVE was employed to study the effect of the DP steel microstructure of the low cycle fatigue behavior of DP steel. A dislocation-density based model was utilised to identify the tensile behavior of ferrite and martensite. Then, by establishing a correlation between the monotonic and cyclic behavior of ferrite and martensite phases, the cyclic deformation properties of single phases were estimated. Accordingly, Chaboche kinematic hardening parameters were identified from the predicted cyclic curve of individual phases in DP steel. Finally, the predicted hysteresis loop from low cycle fatigue modelling was in very good agreement with the experimental one. The stabilised hysteresis loop of DP steel can be successfully predicted using the developed approach.

  16. On simulating sustained isometric muscle fatigue: a phenomenological model considering different fiber metabolisms.

    Science.gov (United States)

    Grasa, J; Sierra, M; Muñoz, M J; Soteras, F; Osta, R; Calvo, B; Miana-Mena, F J

    2014-11-01

    The present study shows a new computational FEM technique to simulate the evolution of the mechanical response of 3D muscle models subjected to fatigue. In an attempt to obtain very realistic models, parameters needed to adjust the mathematical formulation were obtained from in vivo experimental tests. The fatigue contractile properties of three different rat muscles (Tibialis Anterior, Extensor Digitorium Longus and Soleus) subjected to sustained maximal isometric contraction were determined. Experiments were conducted on three groups [Formula: see text] of male Wistar rats [Formula: see text] using a protocol previously developed by the authors for short tetanic contractions. The muscles were subjected to an electrical stimulus to achieve tetanic contraction during 10 s. The parameters obtained for each muscle were incorporated into a finite strain formulation for simulating active and passive behavior of muscles with different fiber metabolisms. The results show the potential of the model to predict muscle fatigue under high-frequency stimulation and the 3D distribution of mechanical variables such as stresses and strains.

  17. Why Does Military Combat Experience Adversely Affect Marital Relations?

    Science.gov (United States)

    Gimbel, Cynthia; Booth, Alan

    1994-01-01

    Describes investigation of ways in which combat decreases marital quality and stability. Results support three models: (1) factors propelling men into combat also make them poor marriage material; (2) combat causes problems that increase marital adversity; and (3) combat intensifies premilitary stress and antisocial behavior which then negatively…

  18. Fatigue-crack-initiation numerical modelling of a Ni-base powder metallurgy alloy

    Institute of Scientific and Technical Information of China (English)

    2012-01-01

    A simplified three-dimensional numerical model was presented to simulate the micro-crack nucleation and growth to some predefined dimension(approximately 0.38 mm) on the throat surface of a Ni-base powder metallurgy(PM) specimen.The numerical simulation of micro-crack initiation was based on the Tanaka-Mura micro-crack initiation models,where individual grains of the mesoscopic model were simulated using the Voronoi tessellation.Four improvements were made in the model.(1) Considering crack initiation along with 12 principal slip systems on octahedral slip planes of face centered cubic(FCC) crystal in three-dimensional(3-D) models.(2) Considering the effect of secondary phase precipitate due to impinging slip and dislocation pileup.(3) The Tanaka-Mura theory of fatigue-crack-initiation from notches was applied to simulate the crack initiation from another crack tip.(4) The coalescence of random initiated micro-cracks was simulated once they intersected with each other and a macro-crack was finally formed.The calculated results were in good agreement with the experimental data which verified the rationality of the simulation model.The applicability of the proposed model for treating fatigue-crack-initiation life in engineering structures was preliminarily achieved.%A simplified three-dimensional numerical model was presented to simulate the micro-crack nucleation and growth to some predefined dimension(approximately 0.38 mm) on the throat surface of a Ni-base powder metallurgy(PM) specimen.The numerical simulation of micro-crack initiation was based on the Tanaka-Mura micro-crack initiation models,where individual grains of the mesoscopic model were simulated using the Voronoi tessellation.Four improvements were made in the model.(1) Considering crack initiation along with 12 principal slip systems on octahedral slip planes of face centered cubic(FCC) crystal in three-dimensional(3-D) models.(2) Considering the effect of secondary phase

  19. 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.

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

    Science.gov (United States)

    Muskulus, M

    2015-02-28

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

  1. Chronic fatigue syndrome, fibromyalgia, and related illnesses: a clinical model of assessment and intervention.

    Science.gov (United States)

    Friedberg, Fred

    2010-06-01

    A clinically informative behavioral literature on chronic fatigue syndrome (CFS) and fibromyalgia (FM) has emerged over the past decade. The purpose of this article is to (a) define these conditions and their less severe counterparts, i.e., unexplained chronic fatigue (UCF) and chronic widespread pain; (b) briefly review the behavioral theory and intervention literature on CFS and FM; and (c) describe a user-friendly clinical model of assessment and intervention for these illnesses. The assessments described will facilitate understanding of the somewhat unusual and puzzling somatic presentations that characterize these patients. Using an individualized cognitive-behavioral approach the mental health clinician can offer significant help to these often stigmatized and medically underserved patients. (c) 2010 Wiley Periodicals, Inc.

  2. Modeling of thermo-mechanical fatigue and damage in shape memory alloy axial actuators

    Science.gov (United States)

    Wheeler, Robert W.; Hartl, Darren J.; Chemisky, Yves; Lagoudas, Dimitris C.

    2015-04-01

    The aerospace, automotive, and energy industries have seen the potential benefits of using shape memory alloys (SMAs) as solid state actuators. Thus far, however, these actuators are generally limited to non-critical components or over-designed due to a lack of understanding regarding how SMAs undergo thermomechanical or actuation fatigue and the inability to accurately predict failure in an actuator during use. The purpose of this study was to characterize the actuation fatigue response of Nickel-Titanium-Hafnium (NiTiHf) axial actuators and, in turn, use this characterization to predict failure and monitor damage in dogbone actuators undergoing various thermomechanical loading paths. Calibration data was collected from constant load, full cycle tests ranging from 200-600MPa. Subsequently, actuator lifetimes were predicted for four additional loading paths. These loading paths consisted of linearly varying load with full transformation (300-500MPa) and step loads which transition from zero stress to 300-400MPa at various martensitic volume fractions. Thermal cycling was achieved via resistive heating and convective cooling and was controlled via a state machine developed in LabVIEW. A previously developed fatigue damage model, which is formulated such that the damage accumulation rate is general in terms of its dependence on current and local stress and actuation strain states, was utilized. This form allows the model to be utilized for specimens undergoing complex loading paths. Agreement between experiments and simulations is discussed.

  3. Mechanism-Based Modeling for Low Cycle Fatigue of Cast Austenitic Steel

    Science.gov (United States)

    Wu, Xijia; Quan, Guangchun; Sloss, Clayton

    2017-09-01

    A mechanism-based approach—the integrated creep-fatigue theory (ICFT)—is used to model low cycle fatigue behavior of 1.4848 cast austenitic steel over the temperature range from room temperature (RT) to 1173 K (900 °C) and the strain rate range from of 2 × 10-4 to 2 × 10-2 s-1. The ICFT formulates the material's constitutive equation based on the physical strain decomposition into mechanism strains, and the associated damage accumulation consisting of crack nucleation and propagation in coalescence with internally distributed damage. At room temperature, the material behavior is controlled by plasticity, resulting in a rate-independent and cyclically stable behavior. The material exhibits significant cyclic hardening at intermediate temperatures, 673 K to 873 K (400 °C to 600 °C), with negative strain rate sensitivity, due to dynamic strain aging. At high temperatures >1073 K (800 °C), time-dependent deformation is manifested with positive rate sensitivity as commonly seen in metallic materials at high temperature. The ICFT quantitatively delineates the contribution of each mechanism in damage accumulation, and predicts the fatigue life as a result of synergistic interaction of the above identified mechanisms. The model descriptions agree well with the experimental and fractographic observations.

  4. Mechanism-Based Modeling for Low Cycle Fatigue of Cast Austenitic Steel

    Science.gov (United States)

    Wu, Xijia; Quan, Guangchun; Sloss, Clayton

    2017-06-01

    A mechanism-based approach—the integrated creep-fatigue theory (ICFT)—is used to model low cycle fatigue behavior of 1.4848 cast austenitic steel over the temperature range from room temperature (RT) to 1173 K (900 °C) and the strain rate range from of 2 × 10-4 to 2 × 10-2 s-1. The ICFT formulates the material's constitutive equation based on the physical strain decomposition into mechanism strains, and the associated damage accumulation consisting of crack nucleation and propagation in coalescence with internally distributed damage. At room temperature, the material behavior is controlled by plasticity, resulting in a rate-independent and cyclically stable behavior. The material exhibits significant cyclic hardening at intermediate temperatures, 673 K to 873 K (400 °C to 600 °C), with negative strain rate sensitivity, due to dynamic strain aging. At high temperatures >1073 K (800 °C), time-dependent deformation is manifested with positive rate sensitivity as commonly seen in metallic materials at high temperature. The ICFT quantitatively delineates the contribution of each mechanism in damage accumulation, and predicts the fatigue life as a result of synergistic interaction of the above identified mechanisms. The model descriptions agree well with the experimental and fractographic observations.

  5. Modelling and laboratory studies on the adhesion fatigue performance for thin-film asphalt and aggregate system.

    Science.gov (United States)

    Wang, Dongsheng; Yi, Junyan; Feng, Decheng

    2014-01-01

    Adhesion between asphalt and aggregate plays an important role in the performance of asphalt mixtures. A low-frequency adhesion fatigue test was proposed in this paper to study the effect of environment on the asphalt-aggregate adhesion system. The stress-based fatigue model had been utilized to describe the fatigue behavior of thin-film asphalt and aggregate system. The factors influencing the adhesion fatigue performance were also investigated. Experiment results show that asphalt has more important effect on the adhesion performance comparing with aggregate. Basalt, which is regarded as hydrophobic aggregates with low silica content, has better adhesion performance to asphalt binder when compared with granite. The effects of aging on the adhesion fatigue performance are different for PG64-22 and rubber asphalt. Long-term aging is found to reduce the adhesion fatigue lives for rubber asphalt and aggregate system, while the effect of long-term aging for aggregate and PG64-22 binder system is positive. Generally the increased stress amplitude and test temperature could induce greater damage and lead to less fatigue lives for adhesion test system.

  6. Growth of inclined fatigue cracks using the biaxial CJP model

    Directory of Open Access Journals (Sweden)

    G. Laboviciute

    2015-07-01

    Full Text Available The CJP model of crack tip stresses is a modified version of the Williams crack tip stress field which takes account of simplified stress distributions that arise from the presence of a zone of plastic deformation associated with the crack flanks and crack tip, and that act on the elastic field responsible for driving crack growth. The elastic stress field responsible for crack growth is therefore controlled by the applied loading and by the induced boundary stresses at the interface with the plastic zone. This meso-scale model of crack tip stresses leads to a modified set of crack tip stress intensity factors that include the resultant influence of plastic wake-induced crack tip shielding, and which therefore have the potential to help resolve some longstanding controversies associated with plasticity-induced closure. A full-field approach has now been developed for stress using photoelasticity and also for displacement using digital image correlation. This paper considers the characterisation of crack growth rate data with the biaxial CJP model, using compact tension specimens that contain inclined cracks at the notch tip with initial angles of 30°, 45° and 60° to the horizontal axis. Significant experimental difficulties are experienced in growing cracks in a biaxial field under uniaxial tensile loading, as the natural tendency of the crack is to turn so that it becomes perpendicular to the maximum principal stress direction. However, crack angle is not an issue in the CJP model which calculates the stress field parallel with, and perpendicular to, the crack plane. These stress components can be rotated into directions comparable with the usual KI and KII directions and used to calculate stress intensity parameters that should be directly comparable with the standard stress intensity formulations. Another difficulty arises, however, in finding published expressions for KI and KII for CT specimens with curved or kinked cracks. The CJP model

  7. Bayesian Model on Fatigue Crack Growth Rate of Type 304 Stainless Steel

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Sanhae; Yoon, Jae Young; Hwang, Il Soon [Nuclear Materials Laboratory, Seoul National University, Seoul (Korea, Republic of)

    2015-10-15

    The fatigue crack growth rate curve is typically estimated by deterministic methods in accordance with the ASME Boiler and Pressure Vessel Code Sec. XI. The reliability of nuclear materials must also consider the environmental effect. This can be overcome by probabilistic methods that estimate the degradation of materials. In this study, fatigue tests were carried out on Type 304 stainless steel (STS 304) to obtain a fatigue crack growth rate curve and Paris' law constants. Tests were conducted on a constant load and a constant delta K, respectively. The unknown constants of Paris' law were updated probabilistically by Bayesian inference and the method can be used for the probabilistic structural integrity assessment of other nuclear materials. In this paper, Paris' law constants including C and m for Type 304 stainless steel were determined by probabilistic approach with Bayesian Inference. The Bayesian update process is limited in accuracy, because this method should assume initial data distribution. If we select an appropriate distribution, this updating method is powerful enough to get data results considering the environment and materials. Until now, remaining lives of NPPs are estimated by deterministic methods using a priori model to finally assess structural integrity. Bayesian approach can utilize in-service inspection data derived from aged properties.

  8. Application of an interface failure model to predict fatigue crack growth in an implanted metallic femoral stem.

    Science.gov (United States)

    Chen, J; Browne, M; Taylor, M; Gregson, P J

    2004-03-01

    A novel computational modelling technique has been developed for the prediction of crack growth in load bearing orthopaedic alloys subjected to fatigue loading. Elastic-plastic fracture mechanics has been used to define a three-dimensional fracture model, which explicitly models the opening, sliding and tearing process. This model consists of 3D nonlinear spring elements implemented in conjunction with a brittle material failure function, which is defined by the fracture energy for each nonlinear spring element. Thus, the fracture energy criterion is implicit in the brittle material failure function to search for crack initiation and crack development automatically. A degradation function is employed to reduce interfacial fracture properties corresponding to the number of cycles; thus fatigue lifetime can be predicted. Unlike other failure modelling methods, this model predicts the failure load, crack path and residual stiffness directly without assuming any pre-flaw condition. As an example, fatigue of a cobalt based alloy (CoCrMo) femoral stem is simulated. Experimental fatigue data was obtained from four point bending tests. The finite element model simulated a fully embedded implant with a constant point load. Comparison between the model and mechanical test results showed good agreement in fatigue crack growth rate.

  9. Abductive networks applied to electronic combat

    Science.gov (United States)

    Montgomery, Gerard J.; Hess, Paul; Hwang, Jong S.

    1990-08-01

    A practical approach to dealing with combinatorial decision problems and uncertainties associated with electronic combat through the use of networks of high-level functional elements called abductive networks is presented. It describes the application of the Abductory Induction Mechanism (AIMTM) a supervised inductive learning tool for synthesizing polynomial abductive networks to the electronic combat problem domain. From databases of historical expert-generated or simulated combat engagements AIM can often induce compact and robust network models for making effective real-time electronic combat decisions despite significant uncertainties or a combinatorial explosion of possible situations. The feasibility of applying abductive networks to realize advanced combat decision aiding capabilities was demonstrated by applying AIM to a set of electronic combat simulations. The networks synthesized by AIM generated accurate assessments of the intent lethality and overall risk associated with a variety of simulated threats and produced reasonable estimates of the expected effectiveness of a group of electronic countermeasures for a large number of simulated combat scenarios. This paper presents the application of abductive networks to electronic combat summarizes the results of experiments performed using AIM discusses the benefits and limitations of applying abductive networks to electronic combat and indicates why abductive networks can often result in capabilities not attainable using alternative approaches. 1. ELECTRONIC COMBAT. UNCERTAINTY. AND MACHINE LEARNING Electronic combat has become an essential part of the ability to make war and has become increasingly complex since

  10. Combating illiteracy

    Science.gov (United States)

    A science course for nonscientists at Columbia University's Columbia College that was created in 1981 as an experiment to combat “the national crisis of scientific illiteracy” has received major new foundation support and has achieved a permanent place in the college's curriculum.The course, The Theory and Practice of Science, has received a $240,000 grant from the Andrew W. Mellon Foundation, according to Robert E. Pollack, college dean, professor of biological sciences, and originator of the course. The grant will be used for the preparation and publication in 1985 of a textbook, titled The Scientific Experience, which will permit the course to be taught at other schools around the country.

  11. Modelling the Strength and Fatigue Life of a Unidirectional Fibrous Composite by Using Daniels' Sequence and Markov Chains

    Science.gov (United States)

    Paramonov, Yu.; Cimanis, V.; Varickis, S.; Kleinhofs, M.

    2013-11-01

    A review of the previous works of the authors dedicated to the use of Daniels' sequence (DS) for analyzing the relation between the distribution of the static strength of components of a unidirectional fibrous composite (UFC) and the distribution of its fatigue life is presented. A generalization of the DS which can be used to analyze the association of distribution of the static strength of composite components with distribution of the static strength of the UFC itself is given. In analyzing the fatigue life of a UFC, unlike in Daniels' model, the loading rate and randomness of the number of still workable components in the weak microvolume in which the destruction process takes place are taken into account. By analyzing the fatigue life, it is possible to explain the existence of the random fatigue strength and to calculate the maximum load at which the probability of absence of fatigue failure is great enough when the number of cycles of fatigue loading tends to infinity. Numerical examples of processing of experimental data are presented, and estimates for parameters of the corresponding nonlinear regression model, which can be interpreted as the strength parameters of UFC, are obtained.

  12. Analytical modeling of contact acoustic nonlinearity of guided waves and its application to evaluating severity of fatigue damage

    Science.gov (United States)

    Wang, Kai; Su, Zhongqing

    2016-04-01

    Targeting quantitative estimate of fatigue damage, a dedicated analytical model was developed based on the modal decomposition method and the variational principle. The model well interprets the contact acoustic nonlinearity induced by a "breathing" crack in a two-dimensional scenario, and the nonlinear characteristics of guided ultrasonic waves (GUWs) (e.g., reflection, transmission, mode conversion and high-order generation) when GUWs traversing the crack. Based on the model, a second-order reflection index was defined. Using the index, a fatigue damage evaluation framework was established, showing demonstrated capacity of estimating the severity of fatigue damage in a quantitative manner. The approach, in principle, does not entail a benchmarking process against baseline signals pre-acquired from pristine counterparts. The results obtained using the analytical modeling were compared with those from finite element simulation, showing good coincidence. Limitations of the model were also discussed.

  13. Multi-Axial Damage Index and Accumulation Model for Predicting Fatigue Life of CMC Materials Project

    Data.gov (United States)

    National Aeronautics and Space Administration — The fatigue life of CMCs must be well characterized for the safe and reliable use of these materials as integrated TPS components. Existing fatigue life prediction...

  14. Fatigue life assessment of cardiovascular balloon-expandable stents: a two-scale plasticity-damage model approach.

    Science.gov (United States)

    Argente dos Santos, H A F; Auricchio, F; Conti, M

    2012-11-01

    Cardiovascular disease has become a major global health care problem in the present decade. To tackle this problem, the use of cardiovascular stents has been considered a promising and effective approach. Numerical simulations to evaluate the in vivo behavior of stents are becoming more and more important to assess potential failures. As the material failure of a stent device has been often associated with fatigue issues, as a result of the high number of cyclic loads these devices are subjected to in vivo, numerical approaches for fatigue life assessment of stents has gained special interest in the engineering community. Numerical fatigue predictions can be used to modify the design and prevent failure, without making and testing numerous physical devices, thus preventing from undesired fatigue failures. This work presents a fatigue life numerical method for the analysis of cardiovascular balloon-expandable stainless steel stents. The method is based on a two-scale continuum damage mechanics model in which both plasticity and damage mechanisms are assumed to take place at a scale smaller than the scale of the representative volume element. The fatigue failure criterion is based on the Soderberg relation. The method is applied to the fatigue life assessment of both PalmazShatz and Cypher stent designs. Validation of the method is performed through comparison of the obtained numerical results with some experimental results available for the PalmazShatz stent design. The present study gives also possible directions for future research developments in the framework of the numerical fatigue life assessment of real balloon-expandable stents.

  15. Determining early markers of disease using Raman spectroscopy in a rat combat-trauma model of heterotopic ossification

    Science.gov (United States)

    Cilwa, Katherine E.; Qureshi, Ammar T.; Forsberg, Jonathan A.; Davis, Thomas A.; Crane, Nicole J.

    2016-02-01

    Traumatic heterotopic ossification (HO) is the pathological formation of bone in soft tissue and is a debilitating sequela following acute trauma involving blast-related extremity musculoskeletal injuries, severe burns, spinal cord injury, and traumatic brain injury. Over 60% of combat related injuries and severe burns develop HO; often resulting in reduced mobility, chronic pain, ulceration, tissue entrapment, and reduced ambulation. Detection and prognosis is limited by current clinical imaging modalities (computed tomography, radiography, and ultrasound). This study identifies Raman spectral signatures corresponding to histological changes in a combat-trauma induced rat HO model at early time points prior to radiographic evidence of HO. HO was induced in Sprague-Dawley rats via blast over pressure injury, mid-femoral fracture, soft tissue crush injury, and limb amputation through the zone of injury. Rats were euthanized, and amputated limbs were formalin fixed and embedded in paraffin; 10 μm sections were placed on gold slides, and paraffin was chemically removed. Tissues from sham-treated animals served as controls. Tissue maps consisting of Raman spectra were generated using a Raman microprobe system with an 80-90 μm spot size and 785 nm excitation in regions exhibiting histological evidence of early HO development according to adjacent HE sections. Factors were extracted from mapping data using Band-Target Entropy Minimization algorithms. Areas of early HO were highlighted by a Raman factor indicative of the presence of collagen. Identification of collagen as an early marker of HO prior to radiographic detection in a clinically relevant animal model serves to inform future clinical work.

  16. Mechanisms and Modelling of Environment-Dependent Fatigue Crack Growth in a Nickel Based Superalloy

    Science.gov (United States)

    1991-12-12

    depends on the strain range, Pilling-Bedworth Ratio (PBR) and current crack length. If • oxygen penetration becomes more significant, Marshall [61...1978 [611 P. Marshall , "The Influence of Environment on Fatigue and Creep/Fatigue," in Fatigue at High Temperature, International Spring Meeting... Jhon arid W. Volker, Plenum Press, New York, NY, 1983, pp.377-390 (78] S. D. Antolovich and E. Rosa, "Low Cycle Fatigue of Rene 77 at Elevated

  17. Physiological models to understand exercise fatigue and the adaptations that predict or enhance athletic performance.

    Science.gov (United States)

    Noakes, T D

    2000-06-01

    A popular concept in the exercise sciences holds that fatigue develops during exercise of moderate to high intensity, when the capacity of the cardiorespiratory system to provide oxygen to the exercising muscles falls behind their demand inducing "anaerobic" metabolism. But this cardiovascular/anaerobic model is unsatisfactory because (i) a more rigorous analysis indicates that the first organ to be affected by anaerobiosis during maximal exercise would likely be the heart, not the skeletal muscles. This probability was fully appreciated by the pioneering exercise physiologists, A. V Hill, A. Bock and D. B. Dill, but has been systematically ignored by modern exercise physiologists; (ii) no study has yet definitely established the presence of either anaerobiosis, hypoxia or ischaemia in skeletal muscle during maximal exercise; (iii) the model is unable to explain why exercise terminates in a variety of conditions including prolonged exercise, exercise in the heat and at altitude, and in those with chronic diseases of the heart and lungs, without any evidence for skeletal muscle anaerobiosis, hypoxia or ischaemia, and before there is full activation of the total skeletal muscle mass, and (iv) cardiovascular and other measures believed to relate to skeletal muscle anaerobiosis, including the maximum oxygen consumption (VO2 max) and the "anaerobic threshold", are indifferent predictors of exercise capacity in athletes with similar abilities. This review considers four additional models that need to be considered when factors limiting either short duration, maximal or prolonged submaximal exercise are evaluated. These additional models are: (i) the energy supply/energy depletion model; (ii) the muscle power/muscle recruitment model; (iii) the biomechanical model and (iv) the psychological model. By reviewing features of these models, this review provides a broad overview of the physiological, metabolic and biomechanical factors that may limit exercise performance under

  18. Micromechanics Fatigue Damage Analysis Modeling for Fabric Reinforced Ceramic Matrix Composites

    Science.gov (United States)

    Min, J. B.; Xue, D.; Shi, Y.

    2013-01-01

    A micromechanics analysis modeling method was developed to analyze the damage progression and fatigue failure of fabric reinforced composite structures, especially for the brittle ceramic matrix material composites. A repeating unit cell concept of fabric reinforced composites was used to represent the global composite structure. The thermal and mechanical properties of the repeating unit cell were considered as the same as those of the global composite structure. The three-phase micromechanics, the shear-lag, and the continuum fracture mechanics models were integrated with a statistical model in the repeating unit cell to predict the progressive damages and fatigue life of the composite structures. The global structure failure was defined as the loss of loading capability of the repeating unit cell, which depends on the stiffness reduction due to material slice failures and nonlinear material properties in the repeating unit cell. The present methodology is demonstrated with the analysis results evaluated through the experimental test performed with carbon fiber reinforced silicon carbide matrix plain weave composite specimens.

  19. Numerical Modeling of the Surface Fatigue Crack Propagation Including the Closure Effect

    Science.gov (United States)

    Guchinsky, Ruslan; Petinov, Sergei

    2016-01-01

    Presently modeling of surface fatigue crack growth for residual life assessment of structural elements is almost entirely based on application of the Linear Elastic Fracture Mechanics (LEFM). Generally, it is assumed that the crack front does not essentially change its shape, although it is not always confirmed by experiment. Furthermore, LEFM approach cannot be applied when the stress singularity vanishes due to material plasticity, one of the leading factors associated with the material degradation and fracture. Also, evaluation of stress intensity factors meets difficulties associated with changes in the stress state along the crack front circumference. An approach proposed for simulation the evolution of surface cracks based on application of the Strain-life criterion for fatigue failure and of the finite element modeling of damage accumulation. It takes into account the crack closure effect, the nonlinear behavior of damage accumulation and material compliance increasing due to the damage advance. The damage accumulation technique was applied to model the semi-elliptical crack growth from the initial defect in the steel compact specimen. The results of simulation are in good agreement with the published experimental data.

  20. Towards smart prosthetic hand: Adaptive probability based skeletan muscle fatigue model.

    Science.gov (United States)

    Kumar, Parmod; Sebastian, Anish; Potluri, Chandrasekhar; Urfer, Alex; Naidu, D; Schoen, Marco P

    2010-01-01

    Skeletal muscle force can be estimated using surface electromyographic (sEMG) signals. Usually, the surface location for the sensors is near the respective muscle motor unit points. Skeletal muscles generate a spatial EMG signal, which causes cross talk between different sEMG signal sensors. In this study, an array of three sEMG sensors is used to capture the information of muscle dynamics in terms of sEMG signals. The recorded sEMG signals are filtered utilizing optimized nonlinear Half-Gaussian Bayesian filters parameters, and the muscle force signal using a Chebyshev type-II filter. The filter optimization is accomplished using Genetic Algorithms. Three discrete time state-space muscle fatigue models are obtained using system identification and modal transformation for three sets of sensors for single motor unit. The outputs of these three muscle fatigue models are fused with a probabilistic Kullback Information Criterion (KIC) for model selection. The final fused output is estimated with an adaptive probability of KIC, which provides improved force estimates.

  1. 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

  2. Fatigue Damage Mechanical Model of the Envelope Material for Stratospheric Airships

    Science.gov (United States)

    Meng, Junhui; Qu, Zhipeng; Zhu, Weiyu; Lv, Mingyun

    2017-08-01

    As a major part of the stratospheric airship structure, the envelope material is used to contain lifting gas and keep the aerodynamic configuration. The main force on the envelope material comes from differential pressure between inside and outside the structure, which is cyclic stress because of the alternative temperature. Three different damage modes of the envelope material, including fracture damage of fabric yarns, cracking damage of resin matrix and functional membrane are investigated in this paper. A theoretical model to predict fatigue life of the envelope material under cycle load is developed base on the damage evolution properties of the material. The results indicates that the theoretical model can well predict the fatigue life. In addition, it can be seen from the results that the fracture of fabric yarns is the main damage modes for the material with off-axial angle of 0°and 90°, while the cracking damage of resin and functional membrane is the main damage modes for the material with other off-axial angles.

  3. Modeling of fatigue crack induced nonlinear ultrasonics using a highly parallelized explicit local interaction simulation approach

    Science.gov (United States)

    Shen, Yanfeng; Cesnik, Carlos E. S.

    2016-04-01

    This paper presents a parallelized modeling technique for the efficient simulation of nonlinear ultrasonics introduced by the wave interaction with fatigue cracks. The elastodynamic wave equations with contact effects are formulated using an explicit Local Interaction Simulation Approach (LISA). The LISA formulation is extended to capture the contact-impact phenomena during the wave damage interaction based on the penalty method. A Coulomb friction model is integrated into the computation procedure to capture the stick-slip contact shear motion. The LISA procedure is coded using the Compute Unified Device Architecture (CUDA), which enables the highly parallelized supercomputing on powerful graphic cards. Both the explicit contact formulation and the parallel feature facilitates LISA's superb computational efficiency over the conventional finite element method (FEM). The theoretical formulations based on the penalty method is introduced and a guideline for the proper choice of the contact stiffness is given. The convergence behavior of the solution under various contact stiffness values is examined. A numerical benchmark problem is used to investigate the new LISA formulation and results are compared with a conventional contact finite element solution. Various nonlinear ultrasonic phenomena are successfully captured using this contact LISA formulation, including the generation of nonlinear higher harmonic responses. Nonlinear mode conversion of guided waves at fatigue cracks is also studied.

  4. A Novel Creep-Fatigue Life Prediction Model for P92 Steel on the Basis of Cyclic Strain Energy Density

    Science.gov (United States)

    Ji, Dongmei; Ren, Jianxing; Zhang, Lai-Chang

    2016-09-01

    A novel creep-fatigue life prediction model was deduced based on an expression of the strain energy density in this study. In order to obtain the expression of the strain energy density, the load-controlled creep-fatigue (CF) tests of P92 steel at 873 K were carried out. Cyclic strain of P92 steel under CF load was divided into elastic strain, applying and unloading plastic strain, creep strain, and anelastic strain. Analysis of cyclic strain indicates that the damage process of P92 steel under CF load consists of three stages, similar to pure creep. According to the characteristics of the strains above, an expression was defined to describe the strain energy density for each cycle. The strain energy density at stable stage is inversely proportional to the total strain energy density dissipated by P92 steel. However, the total strain energy densities under different test conditions are proportional to the fatigue life. Therefore, the expression of the strain energy density at stable stage was chosen to predict the fatigue life. The CF experimental data on P92 steel were employed to verify the rationality of the novel model. The model obtained from the load-controlled CF test of P92 steel with short holding time could predict the fatigue life of P92 steel with long holding time.

  5. Comparison between SSF and Critical-Plane models to predict fatigue lives under multiaxial proportional load histories

    Directory of Open Access Journals (Sweden)

    Manuel de Freitas

    2016-10-01

    Full Text Available Materials can be classified as shear or tensile sensitive, depending on the main fatigue microcrack initiation process under multiaxial loadings. The nature of the initiating microcrack can be evaluated from a stress scale factor (SSF, which usually multiplies the hydrostatic or the normal stress term from the adopted multiaxial fatigue damage parameter. Low SSF values are associated with a shear-sensitive material, while a large SSF indicates that a tensile-based multiaxial fatigue damage model should be used instead. For tension-torsion histories, a recent published approach combines the shear and normal stress amplitudes using a SSF polynomial function that depends on the stress amplitude ratio (SAR between the shear and the normal components. Alternatively, critical-plane models calculate damage on the plane where damage is maximized, adopting a SSF value that is assumed constant for a given material, sometimes varying with the fatigue life (in cycles, but not with the SAR, the stress amplitude level, or the loading path shape. In this work, in-phase proportional tension-torsion tests in 42CrMo4 steel specimens for several values of the SAR are presented. The SSF approach is then compared with critical-plane models, based on their predicted fatigue lives and the observed values for these tension-torsion histories

  6. A Novel Creep-Fatigue Life Prediction Model for P92 Steel on the Basis of Cyclic Strain Energy Density

    Science.gov (United States)

    Ji, Dongmei; Ren, Jianxing; Zhang, Lai-Chang

    2016-11-01

    A novel creep-fatigue life prediction model was deduced based on an expression of the strain energy density in this study. In order to obtain the expression of the strain energy density, the load-controlled creep-fatigue (CF) tests of P92 steel at 873 K were carried out. Cyclic strain of P92 steel under CF load was divided into elastic strain, applying and unloading plastic strain, creep strain, and anelastic strain. Analysis of cyclic strain indicates that the damage process of P92 steel under CF load consists of three stages, similar to pure creep. According to the characteristics of the strains above, an expression was defined to describe the strain energy density for each cycle. The strain energy density at stable stage is inversely proportional to the total strain energy density dissipated by P92 steel. However, the total strain energy densities under different test conditions are proportional to the fatigue life. Therefore, the expression of the strain energy density at stable stage was chosen to predict the fatigue life. The CF experimental data on P92 steel were employed to verify the rationality of the novel model. The model obtained from the load-controlled CF test of P92 steel with short holding time could predict the fatigue life of P92 steel with long holding time.

  7. Aircraft Combat Survivability Estimation and Synthetic Tradeoff Methods

    Institute of Scientific and Technical Information of China (English)

    LI Shu-lin; LI Shou-an; LI Wei-ji; LI Dong-xia; FENG Feng

    2005-01-01

    A new concept is proposed that susceptibility, vulnerability, reliability, maintainability and supportability should be essential factors of aircraft combat survivability. A weight coefficient method and a synthetic method are proposed to estimate aircraft combat survivability based on the essential factors. Considering that it takes cost to enhance aircraft combat survivability, a synthetic tradeoff model between aircraft combat survivability and life cycle cost is built. The aircraft combat survivability estimation methods and synthetic tradeoff with a life cycle cost model will be helpful for aircraft combat survivability design and enhancement.

  8. Study of creep-fatigue behavior in a 1000 MW rotor using a phenomenological lifetime model

    Energy Technology Data Exchange (ETDEWEB)

    Zhao, Nailong; Wang, Weizhe; Jiang, Jishen; Liu, Yingzheng [School of Mechanical Engineering, Shanghai (China)

    2017-02-15

    In this study, the phenomenological lifetime model was applied to part of an ultra-supercritical steam turbine rotor model to predict its lifetime as a post processing of the finite element method. To validate the accuracy and adaptation of the post processing program, stress strain hysteresis loops of a cylinderal model under service-like load cycle conditions in cycle N = 1 and 300 were constructed, and the comparison of the results with experimental data on the same cylinderal specimen showed them to be satisfactory. The temperature and von Mises stress distributions of the rotor during a startup-running-shutdown-natural cool process were numerically studied using ABAQUS and the damage caused by the interaction of creep and fatigue was subsequently computed and discussed. It was found that the maximum damage appeared at the inlet notch zone, with the blade groove areas and the front notch areas also suffering a large damage amplitude.

  9. PROBABILISTIC MODELS FOR LONG FATIGUE CRACK GROWTH RATES OF LZ50 AXLE STEEL

    Institute of Scientific and Technical Information of China (English)

    ZHAO Yong-xiang; HE Chao-ming; YANG Bing; HUANG Yu-zhong; GAO Qing; WU Ping-bo

    2005-01-01

    Experimental study is performed on the probabilistic models for the long fatigue crack growth rates (da/dN) of LZ50 axle steel. An equation for crack growth rate was derived to consider the trend of stress intensity factor range going down to the threshold and the average stress effect. The probabilistic models were presented on the equation. They consist of the probabilistic da/dN-△K relations, the confidence-based da/dN-△K relations, and the probabilistic- and confidence-based da/dN-△K relations.Efforts were made respectively to characterize the effects of probabilistic assessments due to the scattering regularity of test data, the number of sampling, and both of them.These relations can provide wide selections for practice. Analysis on the test data of LZ50 steel indicates that the present models are available and feasible.

  10. Summary of the key features of seven biomathematical models of human fatigue and performance

    Science.gov (United States)

    Mallis, Melissa M.; Mejdal, Sig; Nguyen, Tammy T.; Dinges, David F.

    2004-01-01

    BACKGROUND: Biomathematical models that quantify the effects of circadian and sleep/wake processes on the regulation of alertness and performance have been developed in an effort to predict the magnitude and timing of fatigue-related responses in a variety of contexts (e.g., transmeridian travel, sustained operations, shift work). This paper summarizes key features of seven biomathematical models reviewed as part of the Fatigue and Performance Modeling Workshop held in Seattle, WA, on June 13-14, 2002. The Workshop was jointly sponsored by the National Aeronautics and Space Administration, U.S. Department of Defense, U.S. Army Medical Research and Materiel Command, Office of Naval Research, Air Force Office of Scientific Research, and U.S. Department of Transportation. METHODS: An invitation was sent to developers of seven biomathematical models that were commonly cited in scientific literature and/or supported by government funding. On acceptance of the invitation to attend the Workshop, developers were asked to complete a survey of the goals, capabilities, inputs, and outputs of their biomathematical models of alertness and performance. Data from the completed surveys were summarized and juxtaposed to provide a framework for comparing features of the seven models. RESULTS: Survey responses revealed that models varied greatly relative to their reported goals and capabilities. While all modelers reported that circadian factors were key components of their capabilities, they differed markedly with regard to the roles of sleep and work times as input factors for prediction: four of the seven models had work time as their sole input variable(s), while the other three models relied on various aspects of sleep timing for model input. Models also differed relative to outputs: five sought to predict results from laboratory experiments, field, and operational data, while two models were developed without regard to predicting laboratory experimental results. All modelers

  11. Job stress, fatigue, and job dissatisfaction in Dutch lorry drivers: towards an occupation specific model of job demands and control

    OpenAIRE

    de Croon, E.M.; Blonk, R. W. B.; de Zwart, B.C.H.; Frings-Dresen, M.H.W.; Broersen, J.P.J.

    2002-01-01

    Objectives: Building on Karasek's model of job demands and control (JD-C model), this study examined the effects of job control, quantitative workload, and two occupation specific job demands (physical demands and supervisor demands) on fatigue and job dissatisfaction in Dutch lorry drivers.

  12. Numerical simulation of fatigue crack growth rate and crack retardation due to an overload using a cohesive zone model

    NARCIS (Netherlands)

    Silitonga, S.; Maljaars, J.; Soetens, F.; Snijder, H.H.

    2014-01-01

    In this work, a numerical method is pursued based on a cohesive zone model (CZM). The method is aimed at simulating fatigue crack growth as well as crack growth retardation due to an overload. In this cohesive zone model, the degradation of the material strength is represented by a variation of the

  13. Modelling of pavement materials on steel decks using the five-point bending test: Thermo mechanical evolution and fatigue damage

    Science.gov (United States)

    Arnaud, L.; Houel, A.

    2010-06-01

    This paper deals with the modelling of wearing courses on steel orthotropic decks such as the Millau viaduct in France. This is of great importance when dealing with durability: due to the softness of such a support, the pavement is subjected to considerable strains that may generate top-down cracks in the layer at right angles of the orthotropic plate stiffeners and shear cracks at the interface between pavement and steel. Therefore, a five-point bending fatigue test was developed and improved since 2003 at the ENTPE laboratory, to test different asphalt concrete mixes. This study aims at modelling the mechanical behavior of the wearing course throughout the fatigue test by a finite element method (Comsol Multiphysics software). Each material - steel, sealing sheet, asphalt concrete layer - is considered and modelled. The modelling of asphalt concrete is complex since it is a heterogeneous material, a viscoelastic medium and it thermosensitive. The actual characteristics of the asphalt concrete (thermo physical parameter and viscoelastic complex modulus) are determined experimentally on cylindrical cores. Moreover, a damage law based on Miner's damage is included in the model. The modelling of the fatigue test leads to encouraging results. Finally, results from the model are compared to the experimental data obtained from the five-point bending fatigue test device. The experimental data are very consistent with the numerical simulation.

  14. Evaluation of protective effect of Aegle marmelos Corr. in an animal model of chronic fatigue syndrome

    Directory of Open Access Journals (Sweden)

    Vanphawng Lalremruta

    2012-01-01

    Full Text Available Objective: To evaluate ethanolic extract of leaves of Aegle marmelos in an experimental animal model of chronic fatigue syndrome for potential therapeutic benefit. Materials and Methods: Age/weight-matched female Wistar albino rats were grouped into five groups. (Group I- V (n = 8. Group I served as naïve control and II served as stress control. Except for group I animals, other group animals were subjected to forced swimming every day for 15 minutes to induce a state of chronic fatigue and simultaneously treated with ethanolic extract of Aegle marmelos (EEAM 150 and 250 mg/kg b.w. and Imipramine (20 mg.kg b.w., respectively. Duration of immobility, anxiety level and locomotor activity were assessed on day 1, 7, 14 and 21 followed by biochemical estimation of oxidative biomarkers at the end of the study. Results: Treatment with EEAM (150 and 250 mg/kg b.w. resulted in a statistically significant and dose dependent reduction (P <0.001 in the duration of immobility, reduction in anxiety and increase in locomotor activity. Dose dependent and significant reduction in LPO level and increase in CAT and SOD was observed in extract treated animals. Conclusion: The results are suggestive of potential protective effect of A. marmelos against experimentally induced CFS.

  15. FATIGUE GROWTH MODELING OF MIXED-MODE CRACK IN PLANE ELASTIC MEDIA

    Institute of Scientific and Technical Information of China (English)

    Yan Xiangqiao

    2005-01-01

    This paper presents an extension of a displacement discontinuity method with cracktip elements (a boundary element method) proposed by the author for fatigue crack growth analysis in plane elastic media under mixed-mode conditions. The boundary element method consists of the non-singular displacement discontinuity elements presented by Crouch and Starfield and the crack-tip displacement discontinuity elements due to the author. In the boundary element implementation the left or right crack-tip element is placed locally at the corresponding left or right crack tip on top of the non-singular displacement discontinuity elements that cover the entire crack surface and the other boundaries. Crack growth is simulated with an incremental crack extension analysis based on the maximum circumferential stress criterion. In the numerical simulation, for each increment of crack extension, remeshing of existing boundaries is not required because of an intrinsic feature of the numerical approach. Crack growth is modeled by adding new boundary elements on the incremental crack extension to the previous crack boundaries. At the same time, the element characteristics of some related elements are adjusted according to the manner in which the boundary element method is implemented. As an example, the fatigue growth process of cracks emanating from a circular hole in a plane elastic plate is simulated using the numerical simulation approach.

  16. Third metacarpal condylar fatigue fractures in equine athletes occur within previously modelled subchondral bone.

    Science.gov (United States)

    Whitton, R Christopher; Trope, Gareth D; Ghasem-Zadeh, Ali; Anderson, Garry A; Parkin, Timothy D H; Mackie, Eleanor J; Seeman, Ego

    2010-10-01

    Bone modelling and remodelling reduce the risk of fatigue fractures; the former by adapting bone to its loading circumstances, the latter by replacing fatigued bone. Remodelling transiently increases porosity because of the normal delay in onset of the formation phase of the remodelling sequence. Protracted intense loading suppresses remodelling leaving modelling as the only means of maintaining bone strength. We therefore hypothesized that race horses with fatigue fractures of the distal third metacarpal bone (MC3) will have reduced porosity associated with suppressed remodelling while continued adaptive modelling will result in higher volume fraction (BV/TV) at this site. Using high resolution peripheral quantitative computed tomography (HR-pQCT), we measured the distal aspect of the MC3 obtained at postmortem from 13 thoroughbred race horses with condylar fractures of the MC3 (cases), 8 horses without fractures (training controls), 14 horses with a fracture at another site (fractured controls) and 9 horses resting from training (resting controls). Porosity of the subchondral bone of MC3 was lower in cases than resting controls (12±1.4% vs. 18±1.6%, P=0.017) although areas of focal porosity were observed adjacent to fractures in 6/13 horses. BV/TV of the distal metacarpal epiphysis tended to be higher in horses with condylar fractures (0.79±0.015) than training controls (0.74±0.019, P=0.070), but also higher in controls with a fracture elsewhere (0.79±0.014) than the training controls (0.74±0.019, P=0.040). BV/TV was higher in horses over three years of age than those aged two or three years (0.79±0.01 vs. 0.74±0.01, P=0.016). All metacarpal condylar fractures occurred within focal areas of high BV/TV. We infer that intense training in equine athletes suppresses remodelling of third metacarpal subchondral bone limiting damage repair while modelling increases regional bone volume in an attempt to minimise local stresses but may fail to offset bone

  17. 综合作战实力建设优化模型研究%Research on the Optimization Model of Integrated Combat Power Construction

    Institute of Scientific and Technical Information of China (English)

    严建钢; 杨士锋; 陈钰宁

    2014-01-01

    本文根据战争(战斗)的风险与收益共存准则、作战理论以及现代资产投资组合理论( Portfolio理论),提出了综合作战实力建设优化的概念,并建立了综合作战实力建设优化模型,解决了在有限的资源情况下进行战争(战斗)各种力量建设的最优投资比例,使有限的资源发挥最大的效益。%In this paper , according to the principle of the war ( combat ) benefits and risks that coexist , operational theory and modern assets portfolio theory ( portfolio theory ) , we put forward the war ( combat ) force construction optimization concept , and the establishment of a war ( combat ) force construction optimization model , solve the limited resources in optimal investment proportion of various wars (combat)construction,and make limited natural resources produce the biggest beneficial result .

  18. Cyclic stress-strain behaviour under thermomechanical fatigue conditions - Modeling by means of an enhanced multi-component model

    Energy Technology Data Exchange (ETDEWEB)

    Christ, H J [Institut fuer Werkstofftechnik, Universitaet Siegen, D-57068 Siegen (Germany); Bauer, V, E-mail: hans-juergen.christ@uni-siegen.d [Wieland Werke AG, Graf-Arco Str. 36, D-89072 Ulm (Germany)

    2010-07-01

    The cyclic stress-strain behaviour of metals and alloys in cyclic saturation can reasonably be described by means of simple multi-component models, such as the model based on a parallel arrangement of elastic-perfectly plastic elements, which was originally proposed by Masing already in 1923. This model concept was applied to thermomechanical fatigue loading of two metallic engineering materials which were found to be rather oppositional with respect to cyclic plastic deformation. One material is an austenitic stainless steel of type AISI304L which shows dynamic strain aging (DSA) and serves as an example for a rather ductile alloy. A dislocation arrangement was found after TMF testing deviating characteristically from the corresponding isothermal microstructures. The second material is a third-generation near-gamma TiAl alloy which is characterized by a very pronounced ductile-to-brittle transition (DBT) within the temperature range of TMF cycling. Isothermal fatigue testing at temperatures below the DBT temperature leads to cyclic hardening, while cyclic softening was found to occur above DBT. The combined effect under TMF leads to a continuously developing mean stress. The experimental observations regarding isothermal and non-isothermal stress-strain behaviour and the correlation to the underlying microstructural processes was used to further develop the TMF multi-composite model in order to accurately predict the TMF stress-strain response by taking the alloy-specific features into account.

  19. 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...... is observed between stiffness reduction and accumulated creep. A failure model based on the total work during the fatigue life is rejected, and a modified work model based on elastic, viscous and non-recovered viscoelastic work is experimentally supported, and an explanation at a microstructural level...

  20. System-Level Heat Transfer Analysis, Thermal- Mechanical Cyclic Stress Analysis, and Environmental Fatigue Modeling of a Two-Loop Pressurized Water Reactor. A Preliminary Study

    Energy Technology Data Exchange (ETDEWEB)

    Mohanty, Subhasish [Argonne National Lab. (ANL), Argonne, IL (United States); Soppet, William [Argonne National Lab. (ANL), Argonne, IL (United States); Majumdar, Saurin [Argonne National Lab. (ANL), Argonne, IL (United States); Natesan, Ken [Argonne National Lab. (ANL), Argonne, IL (United States)

    2015-01-03

    This report provides an update on an assessment of environmentally assisted fatigue for light water reactor components under extended service conditions. This report is a deliverable in April 2015 under the work package for environmentally assisted fatigue under DOE's Light Water Reactor Sustainability program. In this report, updates are discussed related to a system level preliminary finite element model of a two-loop pressurized water reactor (PWR). Based on this model, system-level heat transfer analysis and subsequent thermal-mechanical stress analysis were performed for typical design-basis thermal-mechanical fatigue cycles. The in-air fatigue lives of components, such as the hot and cold legs, were estimated on the basis of stress analysis results, ASME in-air fatigue life estimation criteria, and fatigue design curves. Furthermore, environmental correction factors and associated PWR environment fatigue lives for the hot and cold legs were estimated by using estimated stress and strain histories and the approach described in NUREG-6909. The discussed models and results are very preliminary. Further advancement of the discussed model is required for more accurate life prediction of reactor components. This report only presents the work related to finite element modelling activities. However, in between multiple tensile and fatigue tests were conducted. The related experimental results will be presented in the year-end report.

  1. Alarm fatigue: a roadmap for mitigating the cacophony of beeps.

    Science.gov (United States)

    Purbaugh, Thomas

    2014-01-01

    The phenomenon known as alarm fatigue is the direct result of excessive alarms in hospitals. This article highlights the effects of alarm fatigue and reviews current clinical recommendations and guidelines to raise nurse awareness and provide tools to combat the problem.

  2. Experimental Modeling and Optimization of Fatigue Life and Hardness of Carbon Steel CK35 under Dynamic Buckling

    Directory of Open Access Journals (Sweden)

    Ahmed Naif Al-Khazraji

    2014-12-01

    Full Text Available The aim of this paper is to model and optimize the fatigue life and hardness of medium carbon steel CK35 subjected to dynamic buckling. Different ranges of shot peening time (STP and critical points of slenderness ratio which is between the long and intermediate columns, as input factors, were used to obtain their influences on the fatigue life and hardness, as main responses. Experimental measurements of shot peening time and buckling were taken and analyzed using (DESIGN EXPERT 8 experimental design software which was used for modeling and optimization purposes. Mathematical models of responses were obtained and analyzed by ANOVA variance to verify the adequacy of the models. The resultant quadratic models were obtained. A good agreement was found between the results of these models and optimization with the experimental ones with confidence level of 95 %.

  3. Historical approaches to post-combat disorders.

    Science.gov (United States)

    Jones, Edgar

    2006-04-29

    Almost every major war in the last century involving western nations has seen combatants diagnosed with a form of post-combat disorder. Some took a psychological form (exhaustion, combat fatigue, combat stress reaction and post-traumatic stress disorder), while others were characterized by medically unexplained symptoms (soldier's heart, effort syndrome, shell shock, non-ulcer dyspepsia, effects of Agent Orange and Gulf War Syndrome). Although many of these disorders have common symptoms, the explanations attached to them showed considerable diversity often reflected in the labels themselves. These causal hypotheses ranged from the effects of climate, compressive forces released by shell explosions, side effects of vaccinations, changes in diet, toxic effects of organophosphates, oil-well fires or depleted-uranium munitions. Military history suggests that these disorders, which coexisted in the civilian population, reflected popular health fears and emerged in the gaps left by the advance of medical science. While the current Iraq conflict has yet to produce a syndrome typified by medically unexplained symptoms, it is unlikely that we have seen the last of post-combat disorders as past experience suggests that they have the capacity to catch both military planners and doctors by surprise.

  4. The representation of inflammatory signals in the brain: A model for subjective fatigue in multiple sclerosis

    NARCIS (Netherlands)

    Hanken, K.; Eling, P.A.T.M.; Hildebrandt, H.

    2014-01-01

    In multiple sclerosis (MS) patients, fatigue is rated as one of the most common and disabling symptoms. However, the pathophysiology underlying this fatigue is not yet clear. Several lines of evidence suggest that immunological factors, such as elevated levels of pro-inflammatory cytokines, may

  5. Implementation of creep-fatigue model into finite-element code to assess cooled turbine blade.

    CSIR Research Space (South Africa)

    Dedekind, MO

    1994-01-01

    Full Text Available Turbine blades which are designed with airfoil cooling are subject to thermo-mechanical fatigue as well as creep damage. These problems arise due to thermal cycling and high operating temperatures in service. An implementation of fatigue and creep...

  6. Can the social model explain all of disability experience? Perspectives of persons with chronic fatigue syndrome.

    Science.gov (United States)

    Taylor, Renee R

    2005-01-01

    The social model of disability has had a major influence on the academic field of disability studies and on contemporary understandings of the causes and experience of disability. The purpose of this study was to examine the adequacy of the social model for explaining the disability experience of persons with chronic fatigue syndrome (CFS). This qualitative study examined the experiences of 47 adults with CFS participating in a research project that aimed to evaluate a participant-designed rehabilitation program. Data were aggregated from focus group interviews, open-ended questionnaires, progress notes, and from a program evaluation questionnaire. Data analysis was based on a grounded theory approach and used triangulation of multiple data sources and member checks to assure dependability of findings. Four themes emerged from the analysis: (1) minimization and mistrust of the disability; (2) negative experiences of impairment; (3) lack of identification with the disability community; and (4) the focus on advocacy as a quest for legitimacy. These themes varied in the extent to which they conformed to the principles set forth by the social model. Although the social model has important contributions to lend to occupational therapy practice, it is important to recognize that it may not capture the full reality of disability. In particular, the social model has serious limitations in describing the disability experience of individuals with disabilities who do not have visibly obvious disabilities and whose impairments do not conform to the traditional viewpoint of disability.

  7. A limit-cycle model of leg movements in cross-country skiing and its adjustments with fatigue.

    Science.gov (United States)

    Cignetti, F; Schena, F; Mottet, D; Rouard, A

    2010-08-01

    Using dynamical modeling tools, the aim of the study was to establish a minimal model reproducing leg movements in cross-country skiing, and to evaluate the eventual adjustments of this model with fatigue. The participants (N=8) skied on a treadmill at 90% of their maximal oxygen consumption, up to exhaustion, using the diagonal stride technique. Qualitative analysis of leg kinematics portrayed in phase planes, Hooke planes, and velocity profiles suggested the inclusion in the model of a linear stiffness and an asymmetric van der Pol-type nonlinear damping. Quantitative analysis revealed that this model reproduced the observed kinematics patterns of the leg with adequacy, accounting for 87% of the variance. A rising influence of the stiffness term and a dropping influence of the damping terms were also evidenced with fatigue. The meaning of these changes was discussed in the framework of motor control.

  8. Time and frequency domain models for multiaxial fatigue life estimation under random loading

    Directory of Open Access Journals (Sweden)

    Andrea Carpinteri

    2015-07-01

    Full Text Available Engineering structures and components are often subjected to random fatigue loading produced, for example, by wind turbulences, marine waves and vibrations. The methods available in the literature for fatigue assessment under random loading are formulated in time domain or, alternatively, in frequency domain. The former methods require the knowledge of the loading time history, and a large number of experimental tests/numerical simulations is needed to obtain statistically reliable results. The latter methods are generally more advantageous with respect to the time domain ones, allowing a rapid fatigue damage evaluation. In the present paper, a multiaxial criterion formulated in the frequency-domain is presented to estimate the fatigue lives of smooth metallic structures subjected to combined bending and torsion random loading. A comparison in terms of fatigue life prediction by employing a time domain methods, previously proposed by the authors, is also performed.

  9. Environmental fatigue of an Al-Li-Cu alloy. Part 3: Modeling of crack tip hydrogen damage

    Science.gov (United States)

    Piascik, Robert S.; Gangloff, Richard P.

    1992-01-01

    Environmental fatigue crack propagation rates and microscopic damage modes in Al-Li-Cu alloy 2090 (Parts 1 and 2) are described by a crack tip process zone model based on hydrogen embrittlement. Da/dN sub ENV equates to discontinuous crack advance over a distance, delta a, determined by dislocation transport of dissolved hydrogen at plastic strains above a critical value; and to the number of load cycles, delta N, required to hydrogenate process zone trap sites that fracture according to a local hydrogen concentration-tensile stress criterion. Transgranular (100) cracking occurs for process zones smaller than the subgrain size, and due to lattice decohesion or hydride formation. Intersubgranular cracking dominates when the process zone encompasses one or more subgrains so that dislocation transport provides hydrogen to strong boundary trapping sites. Multi-sloped log da/dN-log delta K behavior is produced by process zone plastic strain-hydrogen-microstructure interactions, and is determined by the DK dependent rates and proportions of each parallel cracking mode. Absolute values of the exponents and the preexponential coefficients are not predictable; however, fractographic measurements theta sub i coupled with fatigue crack propagation data for alloy 2090 established that the process zone model correctly describes fatigue crack propagation kinetics. Crack surface films hinder hydrogen uptake and reduce da/dN and alter the proportions of each fatigue crack propagation mode.

  10. Modeling and fatigue assessment of weld start-end locations based on the effective notch stress approach

    Energy Technology Data Exchange (ETDEWEB)

    Malikoutsakis, M. [Aristotle University of Thessaloniki, Faculty of Mechanical Engineering, Laboratory of Machine Elements Machine Design, 54124 Thessaloniki (Greece); Savaidis, G.

    2011-04-15

    The present paper contains a methodology for modeling and life assessment of fatigue loaded welded components providing distinct weld start and end locations. The proposed methodology follows the IIW recommendation regarding modeling and finite element meshing of weld toe and root by means of an effective notch radius and uses the corresponding Woehler curve (FAT class) to assess the durability. Geometrical singularities and, therewith, numerical discontinuities, can be overcome especially when 3D weld root problems are treated. The fatigue life assessment is performed on the basis of normal stresses acting at the failure-critical weld toe and root locations. Comprehensive experimental database containing stress and fatigue life results derived from motor truck's hypoid rear axles providing complex 3D welds subject to vertical, longitudinal, and torsional loading is used to verify the calculation accuracy of the proposed methodology. The agreement between experimentally determined and calculated fatigue results is satisfactory. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. A Study of Simulation Effectiveness in Modeling Heavy Combined Arms Combat in Urban Environments

    Science.gov (United States)

    2007-05-01

    appearance of reality (the suspension of disbelief ) equals reality for training effect. 8. Treatment of Vehicles and Aircraft 1. Hulks (Creation...small units, the suspension of disbelief presented by the models in OFP/VBS1 works as effectively as the more precise models presented by JCATS

  12. Anything, Anywhere, Any Time: Combat Cargo in the Korean War

    Science.gov (United States)

    2000-01-01

    end all scenes for most any man, even a military man. . . . 20 Ten thousand pictures could not convey the composite sensations to the viewer...significantly the smell—a horrible, pungent combination of blood on filthy combat fatigues, unwashed bodies, spent gunpower, and vehicle exhaust fumes—all

  13. Models of Information Aggregation Pertaining to Combat Identification: A Review of the Literature (Modele du Regroupement de L’information Concernant L’identification au Combat: Une Analyse Documentaire)

    Science.gov (United States)

    2007-04-01

    REGROUPEMENT DE L’INFORMATION CONCERNANT L’IDENTIFICATION AU COMBAT : UNE ANALYSE DOCUMENTAIRE . by: Julie Famewo, Michael Matthews and Tab...papers/paper490. pdf . Kraemer, C., Noth, M, & Weber, M. (2006). Information aggregation with costly information and random ordering: Experimental

  14. QUICK ASSESSMENT METHODOLOGY FOR RELIABILITY OF SOLDER JOINTS IN BALL GRID ARRAY (BGA) ASSEMBLY——PART Ⅰ: CREEP CONSTITUTIVE RELATION AND FATIGUE MODEL

    Institute of Scientific and Technical Information of China (English)

    史训清; 王志平; John HL Pang; 张学仁; 聂景旭

    2002-01-01

    In this study, a new unified creep constitutive relation and a modified energy-based fatigue model have been established respectively to describe the creep flow and predict the fatigue life of Sn-Pb solders. It is found that the relation successfully elucidates the creep mechanism related to current constitutive relations.The model can be used to describe the temperature and frequency dependent low cycle fatigue behavior of the solder. The relation and the model are further employed in part Ⅱ to develop the numerical simulation approach for the long-term reliability assessment of the plastic ball grid array (BGA) assembly.

  15. A Comprehensive Action Model to Combat Drug Abuse in High School

    Science.gov (United States)

    Petrillo, Robert F.

    1970-01-01

    Emphasized in the model are: creation and adoption of new Board policies and procedures to deal with the drug abuser, crash Emergency Room" program of drug education for grades 4 through 12, inservice education of staff, lowkey parent education, increased employment of paraprofessional supervisory personnel, and community acceptance of and…

  16. Simulation of Delamination Propagation in Composites Under High-Cycle Fatigue by Means of Cohesive-Zone Models

    Science.gov (United States)

    Turon, Albert; Costa, Josep; Camanho, Pedro P.; Davila, Carlos G.

    2006-01-01

    A damage model for the simulation of delamination propagation under high-cycle fatigue loading is proposed. The basis for the formulation is a cohesive law that links fracture and damage mechanics to establish the evolution of the damage variable in terms of the crack growth rate dA/dN. The damage state is obtained as a function of the loading conditions as well as the experimentally-determined coefficients of the Paris Law crack propagation rates for the material. It is shown that by using the constitutive fatigue damage model in a structural analysis, experimental results can be reproduced without the need of additional model-specific curve-fitting parameters.

  17. Integrating Operational Energy Implications into System-Level Combat Effects Modeling: Assessing the Combat Effectiveness and Fuel Use of ABCT 2020 and Current ABCT

    Science.gov (United States)

    2015-01-01

    Endy M. Daehner, John Matsumura, Thomas J. Herbert , Jeremy R. Kurz, Keith Walters Integrating Operational Energy Implications into System-Level... George Guthridge, and Megan Corso for their clear guid- ance and assistance throughout the study. We also received valuable information and insights from...helped with processing modeling and simulation outputs. Laura Novacic and Donna Mead provided invaluable administrative assistance and help with

  18. development of modelling characteristics of training activity in single combats (in terms of boxing

    Directory of Open Access Journals (Sweden)

    Gaskov A. V.

    2010-02-01

    Full Text Available Approach of the systems of creation of model descriptions of sportsmen is presented. The integral estimations of different sides of preparedness are developed (technical, tactical, psychical, general and special physical. They allow in the structure of preparedness of boxers in number to characterize a level, determine strong and weak links. Studied and analysed more than ten precontest stages. The stages ended with successful appearance of boxers on the competitions of the Russian and international scale.

  19. A Capability-Based, Meta-Model Approach to Combatant Ship Design

    Science.gov (United States)

    2011-03-01

    horizontal, parallel to a Compass Course of 090° to keep the trigonometry used in the motion model simple, however as long the box is kept a true...make a course correction. Some of these include greater government-contractor collaboration, inventive contracting initiatives, and extensive... course . However, the computations required to simulate this are complex and it is likely they will unduly slow the simulation down, so the more

  20. Look Again: An Investigation of False Positive Detections in Combat Models

    Science.gov (United States)

    2008-06-01

    those states (Macmillan & Creelman , 1991). Denoted by d’, sensitivity is scaled between zero and one, with an infallible observer having a d’ equal to...Macmillan & Creelman , 1991), and is also scaled between zero and one. Varying either the observer’s sensitivity or bias, or both, changes his...Graphics Based Target Detection Model, Master of Science, Naval Postgraduate School, September. Macmillan, N. A., & Creelman , C. D., 1991, Detection Theory

  1. Modeling and Assessment of Alternative Cooling Methods of the Combat Operation Center

    Science.gov (United States)

    2012-12-01

    LEFT BLANK 61 LIST OF REFERENCES Aziz, M. H., Nie, O. C., Yam, J. C. M., & Wei, L. C. (2003). TCO reduction. Retrieved from IEEE Xplore website...content&Itemid=345 Kochut, A. (2009, September 21–23). Power and performance modeling of virtualized desktop systems. Retrieved from IEEE Xplore ...August 1–3). Does low-power design imply energy efficiency for data centers? Retrieved from IEEE Xplore website: http

  2. 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.

  3. Extreme Environment Damage Index and Accumulation Model for CMC Laminate Fatigue Life Prediction Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Materials Research & Design (MR&D) is proposing in the SBIR Phase II an effort to develop a tool for predicting the fatigue life of C/SiC composite...

  4. Adapting the Dynamic Allocation of Fires and Sensors (DAFS) Model for Use in Maritime Combat Analysis

    Science.gov (United States)

    2008-03-01

    modeled with each system regressed separately. 61 Term Estimate Std Error ChiSquare Prob>ChiSq Intercept[0] 1.37219214 1.954061 0.49 0.4825...the nature of the scenario. Term Estimate Std Error ChiSquare Prob>ChiSq Intercept[0] -0.3810495 0.7347278 0.27 0.6040 100mm 0.36501304 0.3889876...regard to the victory conditions. Term Estimate Std Error ChiSquare Prob>ChiSq Intercept[0] 0.62150508 1.4619724 0.18 0.6708 KLC-1 -0.0815833

  5. Addressing Occupational Fatigue in Nurses: A Risk Management Model for Nurse Executives.

    Science.gov (United States)

    Steege, Linsey M; Pinekenstein, Barbara

    2016-04-01

    Addressing occupational fatigue in nursing work systems and mitigating associated risks to nurses require strategic management and high-level decision making as well as daily management through operational and tactical actions. Nurse executives are well positioned to lead implementation of a proposed multilevel fatigue risk management system that includes monitoring and decision-support tools to support a culture of safety and nurse well-being.

  6. Genetic design of pigs as experimental models in the combat between chronic diseases and healthy aging

    DEFF Research Database (Denmark)

    Bolund, Lars

    2012-01-01

    pigs. We can also produce clones of pigs, some disease prone and some fluorescing, to perform experiments in regenerative medicine where the fate of healthy fluorescent cells can be followed in the, basically identical, disease prone animals. It is also our hope that our pig models can contribute...... with and without intervention. The genome of different pig breeds have been sequenced, revealing that the pig is genetically more similar to man than conventional laboratory animals - in agreement with the similarities in organ development, physiology and metabolism. Genetically designed minipigs (Göttingen...... and Yucatan) are obtained by genetic engineering of somatic cells and animal cloning by somatic cell nuclear transfer. Primary minipig fibroblasts are genetically modified in culture by transposon-based transgenesis and/or homologous recombination with AAV-transduced constructs. The designed pig cells...

  7. Assessment of the service life of structural steels by using degradation models with allowance for fatigue and creep of the material

    Science.gov (United States)

    Volkov, I. A.; Egunov, V. V.; Igumnov, L. A.; Kazakov, D. A.; Korotkikh, Yu. G.; Mitenkov, F. M.

    2015-11-01

    A mathematical model is developed within the framework of equations of damaged medium mechanics to describe the processes of viscoplastic straining and damage accumulation in structural steels with allowance for fatigue and creep of the material. A model of damage summation due to interaction of low-cycle fatigue and creep of the material is proposed. Material parameters and scalar functions of equations of mechanics of damaged media are determined. Viscoplastic straining and fatigue-induced damage accumulation in 08Kh18N10T and 12Kh18N9 are studied numerically, and the data obtained are compared with available results of physical experiments.

  8. Finite Element Modeling of Material Fatigue and Cracking Problems for Steam Power System HP Devices Exposed to Thermal Shocks

    Directory of Open Access Journals (Sweden)

    Pawlicki Jakub

    2016-09-01

    Full Text Available The paper presents a detailed analysis of the material damaging process due to low-cycle fatigue and subsequent crack growth under thermal shocks and high pressure. Finite Element Method (FEM model of a high pressure (HP by-pass valve body and a steam turbine rotor shaft (used in a coal power plant is presented. The main damaging factor in both cases is fatigue due to cycles of rapid temperature changes. The crack initiation, occurring at a relatively low number of load cycles, depends on alternating or alternating-incremental changes in plastic strains. The crack propagation is determined by the classic fracture mechanics, based on finite element models and the most dangerous case of brittle fracture. This example shows the adaptation of the structure to work in the ultimate conditions of high pressure, thermal shocks and cracking.

  9. Simulation Methods for High-Cycle Fatigue-Driven Delamination using Cohesive Zone Models - Fundamental Behavior and Benchmark Studies

    DEFF Research Database (Denmark)

    Bak, Brian Lau Verndal; Lindgaard, Esben; Turon, A.;

    2015-01-01

    A novel computational method for simulating fatigue-driven delamination cracks in composite laminated structures under cyclic loading based on a cohesive zone model [2] and new benchmark studies with four other comparable methods [3-6] are presented. The benchmark studies describe and compare...... the traction-separation response in the cohesive zone and the transition phase from quasistatic to fatigue loading for each method. Furthermore, the accuracy of the predicted crack growth rate is studied and compared for each method. It is shown that the method described in [2] is significantly more accurate...... than the other methods [3-6]. Finally, studies are presented of the dependency and sensitivity to the change in different quasi-static material parameters and model specific fitting parameters. It is shown that all the methods except [2] rely on different parameters which are not possible to determine...

  10. Combating unmeasured confounding in cross-sectional studies: evaluating instrumental-variable and Heckman selection models.

    Science.gov (United States)

    DeMaris, Alfred

    2014-09-01

    Unmeasured confounding is the principal threat to unbiased estimation of treatment "effects" (i.e., regression parameters for binary regressors) in nonexperimental research. It refers to unmeasured characteristics of individuals that lead them both to be in a particular "treatment" category and to register higher or lower values than others on a response variable. In this article, I introduce readers to 2 econometric techniques designed to control the problem, with a particular emphasis on the Heckman selection model (HSM). Both techniques can be used with only cross-sectional data. Using a Monte Carlo experiment, I compare the performance of instrumental-variable regression (IVR) and HSM to that of ordinary least squares (OLS) under conditions with treatment and unmeasured confounding both present and absent. I find HSM generally to outperform IVR with respect to mean-square-error of treatment estimates, as well as power for detecting either a treatment effect or unobserved confounding. However, both HSM and IVR require a large sample to be fully effective. The use of HSM and IVR in tandem with OLS to untangle unobserved confounding bias in cross-sectional data is further demonstrated with an empirical application. Using data from the 2006-2010 General Social Survey (National Opinion Research Center, 2014), I examine the association between being married and subjective well-being.

  11. 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)

  12. Factors associated with intern fatigue.

    Science.gov (United States)

    Friesen, Lindsay D; Vidyarthi, Arpana R; Baron, Robert B; Katz, Patricia P

    2008-12-01

    Prior data suggest that fatigue adversely affects patient safety and resident well-being. ACGME duty hour limitations were intended, in part, to reduce resident fatigue, but the factors that affect intern fatigue are unknown. To identify factors associated with intern fatigue following implementation of duty hour limitations. Cross-sectional confidential survey of validated questions related to fatigue, sleep, and stress, as well as author-developed teamwork questions. Interns in cognitive specialties at the University of California, San Francisco. Univariate statistics characterized the distribution of responses. Pearson correlations elucidated bivariate relationships between fatigue and other variables. Multivariate linear regression models identified factors independently associated with fatigue, sleep, and stress. Of 111 eligible interns, 66 responded (59%). In a regression analysis including gender, hours worked in the previous week, sleep quality, perceived stress, and teamwork, only poorer quality of sleep and greater perceived stress were significantly associated with fatigue (p 80 h was not significantly associated with perceived stress, quality of sleep, or fatigue. Simply decreasing the number of duty hours may be insufficient to reduce intern fatigue. Residency programs may need to incorporate programmatic changes to reduce stress, improve sleep quality, and foster teamwork in order to decrease intern fatigue and its deleterious consequences.

  13. Effects of Exercise on Behavior and Peripheral Blood Lymphocyte Apoptosis in a Rat Model of Chronic Fatigue Syndrome

    Institute of Scientific and Technical Information of China (English)

    邹军; 苑建齐; 吕爽; 屠嘉衡

    2010-01-01

    This study examined the effects of exercise on behavior and peripheral blood leukocyte apoptosis in a rat model of chronic fatigue syndrome(CFS).Thirty-six healthy male Sprague-Dawley rats were equally randomized into 3 groups:the control group,CFS model group and the exercise group in terms of body weight.A total of 25 rats entered the final statistical analysis due to 11 deaths during the study.CFS model was established by subjecting the rats in CFS model group and exercise group to electric shock,chronic...

  14. How should a bio-mathematical model be used within a fatigue risk management system to determine whether or not a working time arrangement is safe?

    Science.gov (United States)

    Dawson, Drew; Darwent, David; Roach, Gregory D

    2017-02-01

    Bio-mathematical models that predict fatigue and/or sleepiness have proved a useful adjunct in the management of what has been typically referred to as fatigue-related risk. Codifying what constitutes appropriate use of these models will be increasingly important over the next decade. Current guidelines for determining a safe working time arrangement based on model outputs generally use a single upper threshold and are, arguably, over-simplistic. These guidelines fail to incorporate explicitly essential aspects of the risk assessment process - namely, the inherent uncertainty and variability in human sleep-wake behavior; the non-linear relationship between fatigue, task performance and safety outcomes; the consequence of a fatigue-related error and its influence on overall risk; and the impact of risk mitigation or controls in reducing the likelihood or consequence of a fatigue-related error. As industry and regulatory bodies increasingly move toward performance-based approaches to safety management, any fatigue risk management system that includes a bio-mathematical model should specify what exactly is measured by the model, and how the model can be used in the context of a safety management system approach. This will require significant dialog between the various parties with an interest in bio-mathematical models, i.e. developers, vendors, end-users, and regulators.

  15. Evaluation of Fatigue Life Reliability of Steering Knuckle Using Pearson Parametric Distribution Model

    Directory of Open Access Journals (Sweden)

    E. A. Azrulhisham

    2010-01-01

    Full Text Available Steering module is a part of automotive suspension system which provides a means for an accurate vehicle placement and stability control. Components such as steering knuckle are subjected to fatigue failures due to cyclic loads arising from various driving conditions. This paper intends to give a description of a method used in the fatigue life reliability evaluation of the knuckle used in a passenger car steering system. An accurate representation of Belgian pave service loads in terms of response-time history signal was obtained from accredited test track using road load data acquisition. The acquired service load data was replicated on durability test rig and the SN method was used to estimate the fatigue life. A Pearson system was developed to evaluate the predicted fatigue life reliability by considering the variations in material properties. Considering random loads experiences by the steering knuckle, it is found that shortest life appears to be in the vertical load direction with the lowest fatigue life reliability between 14000–16000 cycles. Taking into account the inconsistency of the material properties, the proposed method is capable of providing the probability of failure of mass-produced parts.

  16. Fatigue Evaluation Algorithms: Review

    DEFF Research Database (Denmark)

    Passipoularidis, Vaggelis; Brøndsted, Povl

    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...... 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...

  17. Fatigue Strain and Damage Analysis of Concrete in Reinforced Concrete Beams under Constant Amplitude Fatigue Loading

    Directory of Open Access Journals (Sweden)

    Fangping Liu

    2016-01-01

    Full Text Available Concrete fatigue strain evolution plays a very important role in the evaluation of the material properties of concrete. To study fatigue strain and fatigue damage of concrete in reinforced concrete beams under constant amplitude bending fatigue loading, constant amplitude bending fatigue experiments with reinforced concrete beams with rectangular sections were first carried out in the laboratory. Then, by analyzing the shortcomings and limitations of existing fatigue strain evolution equations, the level-S nonlinear evolution model of fatigue strain was constructed, and the physical meaning of the parameters was discussed. Finally, the evolution of fatigue strain and fatigue damage of concrete in the compression zone of the experimental beam was analyzed based on the level-S nonlinear evolution model. The results show that, initially, fatigue strain grows rapidly. In the middle stages, fatigue strain is nearly a linear change. Because the experimental data for the third stage are relatively scarce, the evolution of the strain therefore degenerated into two phases. The model has strong adaptability and high accuracy and can reflect the evolution of fatigue strain. The fatigue damage evolution expression based on fatigue strain shows that fatigue strain and fatigue damage have similar variations, and, with the same load cycles, the greater the load level, the larger the damage, in line with the general rules of damage.

  18. Carbon nanotube reinforced hybrid composites: Computational modeling of environmental fatigue and usability for wind blades

    DEFF Research Database (Denmark)

    Dai, Gaoming; Mishnaevsky, Leon

    2015-01-01

    The potential of advanced carbon/glass hybrid reinforced composites with secondary carbon nanotube reinforcement for wind energy applications is investigated here with the use of computational experiments. Fatigue behavior of hybrid as well as glass and carbon fiber reinforced composites...... with the secondary CNT reinforcements (especially, aligned tubes) present superior fatigue performances than those without reinforcements, also under combined environmental and cyclic mechanical loading. This effect is stronger for carbon composites, than for hybrid and glass composites....... automatically using the Python based code. 3D computational studies of environment and fatigue analyses of multiscale composites with secondary nano-scale reinforcement in different material phases and different CNTs arrangements are carried out systematically in this paper. It was demonstrated that composites...

  19. Modeling time-dependent corrosion fatigue crack propagation in 7000 series aluminum alloys

    Science.gov (United States)

    Mason, Mark E.; Gangloff, Richard P.

    1994-01-01

    Stress corrosion cracking and corrosion fatigue experiments were conducted with the susceptible S-L orientation of AA7075-T651, immersed in acidified and inhibited NaCl solution, to provide a basis for incorporating environmental effects into fatigue crack propagation life prediction codes such as NASA FLAGRO. This environment enhances da/dN by five to ten-fold compared to fatigue in moist air. Time-based crack growth rates from quasi-static load experiments are an order of magnitude too small for accurate linear superposition prediction of da/dN for loading frequencies above 0.001 Hz. Alternate methods of establishing da/dt, based on rising-load or ripple-load-enhanced crack tip strain rate, do not increase da/dt and do not improve linear superposition. Corrosion fatigue is characterized by two regimes of frequency dependence; da/dN is proportional to f(exp -1) below 0.001 Hz and to F(exp 0) to F(exp -0.1) for higher frequencies. Da/dN increases mildly both with increasing hold-time at K(sub max) and with increasing rise-time for a range of loading waveforms. The mild time-dependence is due to cycle-time-dependent corrosion fatigue growth. This behavior is identical for S-L nd L-T crack orientations. The frequency response of environmental fatigue in several 7000 series alloys is variable and depends on undefined compositional or microstructural variables. Speculative explanations are based on the effect of Mg on occluded crack chemistry and embritting hydrogen uptake, or on variable hydrogen diffusion in the crack tip process zone. Cracking in the 7075/NaCl system is adequately described for life prediction by linear superposition for prolonged load-cycle periods, and by a time-dependent upper bound relationship between da/dN and delta K for moderate loading times.

  20. 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....

  1. Exfoliation Corrosion and Pitting Corrosion and Their Role in Fatigue Predictive Modeling: State-of-the-Art Review

    Directory of Open Access Journals (Sweden)

    David W. Hoeppner

    2012-01-01

    Full Text Available Intergranular attack (IG and exfoliation corrosion (EC have a detrimental impact on the structural integrity of aircraft structures of all types. Understanding the mechanisms and methods for dealing with these processes and with corrosion in general has been and is critical to the safety of critical components of aircraft. Discussion of cases where IG attack and exfoliation caused issues in structural integrity in aircraft in operational fleets is presented herein along with a much more detailed presentation of the issues involved in dealing with corrosion of aircraft. Issues of corrosion and fatigue related to the structural integrity of aging aircraft are introduced herein. Mechanisms of pitting nucleation are discussed which include adsorption-induced, ion migration-penetration, and chemicomechanical film breakdown theories. In addition, pitting corrosion (PC fatigue models are presented as well as a critical assessment of their application to aircraft structures and materials. Finally environmental effects on short crack behavior of materials are discussed, and a compilation of definitions related to corrosion and fatigue are presented.

  2. MODELING ENERGY EXPENDITURE AND OXYGEN CONSUMPTION IN HUMAN EXPOSURE MODELS: ACCOUNTING FOR FATIGUE AND EPOC

    Science.gov (United States)

    Human exposure and dose models often require a quantification of oxygen consumption for a simulated individual. Oxygen consumption is dependent on the modeled Individual's physical activity level as described in an activity diary. Activity level is quantified via standardized val...

  3. MODELING ENERGY EXPENDITURE AND OXYGEN CONSUMPTION IN HUMAN EXPOSURE MODELS: ACCOUNTING FOR FATIGUE AND EPOC

    Science.gov (United States)

    Human exposure and dose models often require a quantification of oxygen consumption for a simulated individual. Oxygen consumption is dependent on the modeled Individual's physical activity level as described in an activity diary. Activity level is quantified via standardized val...

  4. Fatigue Analysis and Life Prediction of Dumpers with Cumulative Fatigue Damage Approach

    Institute of Scientific and Technical Information of China (English)

    LI Shouju; LIU Yingxi; SUN Huiling

    2004-01-01

    A fatigue damage model is developed for evaluating accumulative fatigue damage of dumpers. The loading spectrums acted on dumpers are created according to measured strain data in field. The finite element analysis is carried out for assessing stress distribution and strength characteristics of dumpers. Fatigue damage indexes and service life are calculated by a modified Palmgren-Miner rule. The investigation shows that fatigue notch factor has a significant influence on the calculation of fatigue damage of dumpers.

  5. Impact of Higher Fidelity Models on Simulation of Active Aerodynamic Load Control For Fatigue Damage Reduction

    NARCIS (Netherlands)

    Resor, B.; Wilson, D.; Berg, D.; Berg, J.; Barlas, T.; Van Wingerden, J.W.; Van Kuik, G.A.M.

    2010-01-01

    Active aerodynamic load control of wind turbine blades is being investigated by the wind energy research community and shows great promise, especially for reduction of turbine fatigue damage in blades and nearby components. For much of this work, full system aeroelastic codes have been used to simul

  6. Computer simulation on fatigue behavior of cemented hip prostheses: a physiological model.

    Science.gov (United States)

    Hung, Jui-Pin; Chen, Jian-Horng; Chiang, Hsiu-Lu; Wu, James Shih-Shyn

    2004-11-01

    This paper is concerned with the investigation on the fatigue failure of implant fixation by numerical approaches. A computer algorithm based on finite element analysis and continuum damage mechanics was proposed to quantify the fatigue damage rate of cement mantle under physiological conditions. In examining the interfacial debonding effect, the interface elements were introduced at cement-stem interfaces and calibrated with the increase of loading cycles. Current results reveal that the major sites for failure initiation are in the proximal anterior-medial regions and at the distal prosthesis tip, which clearly demonstrate the same failure scenario as observed in clinical studies. Such fatigue failures not only result in the corruption of cement-stem interfaces, but also greatly affect the cement stress distribution and the damage rate in subsequent loading cycles. Another significant result is that the predicted damage rate increases steadily with gait cycles. This trend in damage development is consistent with the findings obtained from fatigue tests available in literature. It is anticipated that presented methodology can serve as a pre-clinical validation of cemented hip prostheses.

  7. Impact of Higher Fidelity Models on Simulation of Active Aerodynamic Load Control For Fatigue Damage Reduction

    NARCIS (Netherlands)

    Resor, B.; Wilson, D.; Berg, D.; Berg, J.; Barlas, T.; Van Wingerden, J.W.; Van Kuik, G.A.M.

    2010-01-01

    Active aerodynamic load control of wind turbine blades is being investigated by the wind energy research community and shows great promise, especially for reduction of turbine fatigue damage in blades and nearby components. For much of this work, full system aeroelastic codes have been used to

  8. A fatigue crack initiation model incorporating discrete dislocation plasticity and surface roughness

    NARCIS (Netherlands)

    Brinckmann, Steffen; Van der Giessen, Erik

    2007-01-01

    Although a thorough understanding of fatigue crack initiation is lacking, experiments have shown that the evolution of distinct dislocation distributions and surface roughness are key ingredients. In the present study we introduce a computational framework that ties together dislocation dynamics, th

  9. Numerical simulation of stable fatigue crack growth rate using a cohesive zone model

    NARCIS (Netherlands)

    Silitonga, S.; Maljaars, J.; Soetens, F.; Snijder, H.H.

    2012-01-01

    Predicting the remaining fatigue life of a structure with crack(s) is generally conducted by the fracture mechanics method. This method is aimed at predicting the crack growth and final fracture due to fluctuating loads. The crack growth curve required for these calculations is constructed on the ba

  10. A model for the training effects in swimming demonstrates a strong relationship between parasympathetic activity, performance and index of fatigue.

    Directory of Open Access Journals (Sweden)

    Sébastien Chalencon

    Full Text Available Competitive swimming as a physical activity results in changes to the activity level of the autonomic nervous system (ANS. However, the precise relationship between ANS activity, fatigue and sports performance remains contentious. To address this problem and build a model to support a consistent relationship, data were gathered from national and regional swimmers during two 30 consecutive-week training periods. Nocturnal ANS activity was measured weekly and quantified through wavelet transform analysis of the recorded heart rate variability. Performance was then measured through a subsequent morning 400 meters freestyle time-trial. A model was proposed where indices of fatigue were computed using Banister's two antagonistic component model of fatigue and adaptation applied to both the ANS activity and the performance. This demonstrated that a logarithmic relationship existed between performance and ANS activity for each subject. There was a high degree of model fit between the measured and calculated performance (R(2=0.84±0.14,p<0.01 and the measured and calculated High Frequency (HF power of the ANS activity (R(2=0.79±0.07, p<0.01. During the taper periods, improvements in measured performance and measured HF were strongly related. In the model, variations in performance were related to significant reductions in the level of 'Negative Influences' rather than increases in 'Positive Influences'. Furthermore, the delay needed to return to the initial performance level was highly correlated to the delay required to return to the initial HF power level (p<0.01. The delay required to reach peak performance was highly correlated to the delay required to reach the maximal level of HF power (p=0.02. Building the ANS/performance identity of a subject, including the time to peak HF, may help predict the maximal performance that could be obtained at a given time.

  11. Atomistic modeling of nanowires, small-scale fatigue damage in cast magnesium, and materials for MEMS

    Energy Technology Data Exchange (ETDEWEB)

    Dunn, Martin L. [Univ. of Colorado, Boulder, CO (United States); Talmage, Mellisa J. [Univ. of Colorado, Boulder, CO (United States); McDowell, David L. [Georgia Inst. of Technology, Atlanta, GA (United States); West, Neil [Univ. of Colorado, Boulder, CO (United States); Gullett, Philip Michael [Mississippi State Univ., Mississippi State, MS (United States); Miller, David C. [Univ. of Colorado, Boulder, CO (United States); Spark, Kevin [Univ. of Colorado, Boulder, CO (United States); Diao, Jiankuai [Univ. of Colorado, Boulder, CO (United States); Horstemeyer, Mark F. [Mississippi State Univ., Mississippi State, MS (United States); Zimmerman, Jonathan A. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Gall, K. [Georgia Inst. of Technology, Atlanta, GA (United States)

    2006-10-01

    titled 'Atomistic Modeling of Nanowires, Small-scale Fatigue Damage in Cast Magnesium, and Materials for MEMS'. This project supported a strategic partnership between Sandia National Laboratories and the University of Colorado at Boulder by providing funding for the lead author, Ken Gall, and his students, while he was a member of the University of Colorado faculty.

  12. Complex network models reveal correlations among network metrics, exercise intensity and role of body changes in the fatigue process

    Science.gov (United States)

    Pereira, Vanessa Helena; Gama, Maria Carolina Traina; Sousa, Filipe Antônio Barros; Lewis, Theodore Gyle; Gobatto, Claudio Alexandre; Manchado-Gobatto, Fúlvia Barros

    2015-05-01

    The aims of the present study were analyze the fatigue process at distinct intensity efforts and to investigate its occurrence as interactions at distinct body changes during exercise, using complex network models. For this, participants were submitted to four different running intensities until exhaustion, accomplished in a non-motorized treadmill using a tethered system. The intensities were selected according to critical power model. Mechanical (force, peak power, mean power, velocity and work) and physiological related parameters (heart rate, blood lactate, time until peak blood lactate concentration (lactate time), lean mass, anaerobic and aerobic capacities) and IPAQ score were obtained during exercises and it was used to construction of four complex network models. Such models have both, theoretical and mathematical value, and enables us to perceive new insights that go beyond conventional analysis. From these, we ranked the influences of each node at the fatigue process. Our results shows that nodes, links and network metrics are sensibility according to increase of efforts intensities, been the velocity a key factor to exercise maintenance at models/intensities 1 and 2 (higher time efforts) and force and power at models 3 and 4, highlighting mechanical variables in the exhaustion occurrence and even training prescription applications.

  13. Study on sand particles creep model and open pit mine landslide mechanism caused by sand fatigue liquefaction

    Science.gov (United States)

    Du, Dong-Ning; Wang, Lai-Gui; Zhang, Xiang-Dong; Zhang, Shu-Kun

    2017-06-01

    The sand particles in the sand - rock composite slope of the open pit mine occurs creep deformation and fatigue liquefaction under the action of vehicle load vibration and hydraulic gradient, which causes landslide geological disasters and it destroys the surface environment. To reveal the mechanism, a mechanics model based on the model considering the soil structural change with a new “plastic hinge” element is developed, to improve its constitutive and creep curve equations. Data from sand creep experiments are used to identify the parameters in the model and to validate the model. The results show that the mechanical model can describe the rotation progress between the sand particles, disclose the negative acceleration creep deformation stage during the third phase, and require fewer parameters while maintaining accuracy. It provides a new creep model considering rotation to analyze sand creep mechanism, which provides a theoretical basis for revealing the open pit mine landslide mechanism induced by creep deformation and fatigue liquefaction of sandy soil.

  14. Complex network models reveal correlations among network metrics, exercise intensity and role of body changes in the fatigue process.

    Science.gov (United States)

    Pereira, Vanessa Helena; Gama, Maria Carolina Traina; Sousa, Filipe Antônio Barros; Lewis, Theodore Gyle; Gobatto, Claudio Alexandre; Manchado-Gobatto, Fúlvia Barros

    2015-05-21

    The aims of the present study were analyze the fatigue process at distinct intensity efforts and to investigate its occurrence as interactions at distinct body changes during exercise, using complex network models. For this, participants were submitted to four different running intensities until exhaustion, accomplished in a non-motorized treadmill using a tethered system. The intensities were selected according to critical power model. Mechanical (force, peak power, mean power, velocity and work) and physiological related parameters (heart rate, blood lactate, time until peak blood lactate concentration (lactate time), lean mass, anaerobic and aerobic capacities) and IPAQ score were obtained during exercises and it was used to construction of four complex network models. Such models have both, theoretical and mathematical value, and enables us to perceive new insights that go beyond conventional analysis. From these, we ranked the influences of each node at the fatigue process. Our results shows that nodes, links and network metrics are sensibility according to increase of efforts intensities, been the velocity a key factor to exercise maintenance at models/intensities 1 and 2 (higher time efforts) and force and power at models 3 and 4, highlighting mechanical variables in the exhaustion occurrence and even training prescription applications.

  15. Fatigue (PDQ)

    Science.gov (United States)

    ... of daily living . Better quality of life . More satisfaction with life. A greater sense of well-being. ... and decrease fatigue. The importance of eating enough food and drinking enough fluids. Physical therapy for patients ...

  16. An improved thermal network model of the IGBT module for wind power converters considering the effects of base plate solder fatigue

    Science.gov (United States)

    Li, H.; Hu, Y. G.; Liu, S. Q.; Li, Y.; Liao, X. L.; Liu, Z. X.

    2016-08-01

    This study presents an improved thermal network model of the IGBT module that considers the effects of base plate solder fatigue on the junction temperature of the said module used in wind power converters. First, the coupling thermal structure 3D finite element model of the IGBT module is established based on the structure and material parameters of the module used in the wind power converters of a doubly fed induction generator. The junction temperature of the module is also investigated at different thermal desquamating degrees of the base plate solder. Second, the thermal resistance parameters are determined at different desquamating degrees, and the improved thermal network model that considers the effects of base plate solder fatigue is established. Finally, the two results of the calculation of the junction temperature are compared in different fatigue stages through the improved thermal network model and the 3D finite element model, which testify to the effectiveness of the improved thermal network model.

  17. 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.

  18. Neural mechanisms of mental fatigue.

    Science.gov (United States)

    Ishii, Akira; Tanaka, Masaaki; Watanabe, Yasuyoshi

    2014-01-01

    Fatigue is defined as a decline in the ability and efficiency of mental and/or physical activities that is caused by excessive mental and/or physical activities. Fatigue can be classified as physical or mental. Mental fatigue manifests as potentially impaired cognitive function and is one of the most significant causes of accidents in modern society. Recently, it has been shown that the neural mechanisms of mental fatigue related to cognitive task performance are more complex than previously thought and that mental fatigue is not caused only by impaired activity in task-related brain regions. There is accumulating evidence supporting the existence of mental facilitation and inhibition systems. These systems are involved in the neural mechanisms of mental fatigue, modulating the activity of task-related brain regions to regulate cognitive task performance. In this review, we propose a new conceptual model: the dual regulation system of mental fatigue. This model contributes to our understanding of the neural mechanisms of mental fatigue and the regulatory mechanisms of cognitive task performance in the presence of mental fatigue.

  19. Modelling the fatigue behaviour of a stratified glass-epoxy composite: theoretical and experimental aspects; Modelisation du comportement en fatigue d`un composite stratifie verre-epoxyde: aspects theoriques et experimentaux

    Energy Technology Data Exchange (ETDEWEB)

    Verdiere, N.; Suri, C. [Laboratoire de mecanique appliquee, 25 - Besancon (France)

    1996-01-01

    Composite materials are used in the manufacture of water transport pipework for use in PWR`s. Estimation of their life expectancy relies on long and costly tests (ASTM D2992B standard). It would be extremely advantageous to have another method relying only on short laboratory tests which could be based on a mechanical behaviour and damage model. For several years, the Laboratoire de Mecanique Appliquee de Besancon has been developing a mechanical behaviour model for composite material tubes for different types of multiaxial stresses. However, this model does not take into account the fatigue behaviour. We therefore needed to find out how this type of stress could be incorporated into the model. To this end, research was undertaken in the form of a thesis (by E. Joseph) both to perfect the multiaxial fatigue stress testing machines and to take into account this type of behaviour in the mechanical model. This study covered glass fibre/epoxy resin composite material tubes and allowed their behaviour to be modelled. An important part of the work concerned the instrumentation and adaptation of test machines which hitherto did not exist so that the research could be carried out. For each of the stress axes (traction, internal pressure without vacuum effect ({Sigma}{sup zz}=0) and internal pressure with vacuum effect ({Sigma}{sup zz}=1/2{Sigma}{sup {theta}{theta}})), instantaneous behaviour was studied. Three stress levels and frequency values were used to define the fatigue behaviour. (authors). 23 refs., 41 figs., 5 tabs.

  20. A damage-coupled multi-axial time-dependent low cycle fatigue failure model for SS304 stainless steel at high temperature

    Institute of Scientific and Technical Information of China (English)

    Yujie LIU; Qing GAO; Guozheng KANG

    2011-01-01

    Based on the time-dependent strain cyclic characteristics and fatigue behaviors of SS304 stainless steel under multi-axial cyclic loading at 700℃, and in the frameof unified visoco-plastic cyclic constitutive model and continuum damage mechanics theory, the damage-coupled multi-axial time-dependent constitutive model and fatigue failure model were proposed. In the model, the evolution equation of damage was introduced in and the time-dependent effects, e.g. holding time, loading rate, were taken into account. The model was applied to the simulation of whole-life cyclic deformation behaviors and prediction of LCF life for SS304 stainless steel in multiaxial time-dependent low cycle fatigue tests. It is shown that the simulated results agree well with experimental ones.

  1. Modelling of pavement materials on steel decks using the fivepoint bending test: thermo mechanical evolution and fatigue damage

    OpenAIRE

    Arnaud, Laurent; Houel, Adrien

    2010-01-01

    This paper deals with the modelling of wearing courses on steel orthotropic decks such as the Millau viaduct in France. This is of great importance when dealing with durability: due to the softness of such a support, the pavement is subjected to considerable strains that may generate top-down cracks in the layer at right angles of the orthotropic plate stiffeners and shear cracks at the interface between pavement and steel. Therefore, a five-point bending fatigue test was developed and improv...

  2. Respuesta orgánica en una simulación de combate Organic response to a combat simulation

    Directory of Open Access Journals (Sweden)

    V.J. Clemente Suárez

    2012-06-01

    Full Text Available Antecedentes y objetivos: El análisis de la respuesta orgánica durante el combate es un campo de estudio poco tratado en la bibliografía específica, por ello se planteo como objetivo de este trabajo el analizar el efecto de una simulación de combate en el organismo de los combatientes. Material y Métodos: Se analizó el umbral de frecuencia crítica de fusión (UFCF como medio de detectar fatiga del sistema nervioso central (SNC, fuerza explosiva de piernas, fuerza isométrica, lactato sanguíneo y percepción subjetiva de esfuerzo en 20 combatientes antes y después de realizar una simulación de combate. Resultados: Después de la simulación los sujetos mostraron un aumento significativo (pBackground and Objectives: Analysis of organic response in combat is a bit field of study specifically studied in specific literature, for this reason the objective of this work is to analyze the effect of a combat simulation in the organism of soldiers. Material and Methods: We analyzed the critical flicker fusion frequency (CFFF as a means of detecting fatigue of central nervous system (CNS, leg explosive strength, isometric strength, blood lactate and rating of perceived exertion in 20 soldiers before and after performing a combat simulation. Results: After combat simulation, soldiers showed a significant increase (p<0,05 in lactate levels (2,57±0,62 mmol/l vs. 4,92±2,18 mmol/l and isometric strength and a decrease in legs explosive strength. CFFF values decreased, showing signs of fatigue of CNS. Conclusions: Combat simulation was highly stressful, showing signs of fatigue of the CNS, are carried out in anaerobic conditions, despite the low speed o execution, and the subjective perception of effort does not correspond to the organic response obtained. These data could use to adapting current training systems for current missions in combat zones.

  3. Carbon nanotube reinforced hybrid composites: Computational modeling of environmental fatigue and usability for wind blades

    DEFF Research Database (Denmark)

    Dai, Gaoming; Mishnaevsky, Leon

    2015-01-01

    The potential of advanced carbon/glass hybrid reinforced composites with secondary carbon nanotube reinforcement for wind energy applications is investigated here with the use of computational experiments. Fatigue behavior of hybrid as well as glass and carbon fiber reinforced composites...... with and without secondary CNT reinforcement is simulated using multiscale 3D unit cells. The materials behavior under both mechanical cyclic loading and combined mechanical and environmental loading (with phase properties degraded due to the moisture effects) is studied. The multiscale unit cells are generated...... with the secondary CNT reinforcements (especially, aligned tubes) present superior fatigue performances than those without reinforcements, also under combined environmental and cyclic mechanical loading. This effect is stronger for carbon composites, than for hybrid and glass composites....

  4. [Auditory fatigue].

    Science.gov (United States)

    Sanjuán Juaristi, Julio; Sanjuán Martínez-Conde, Mar

    2015-01-01

    Given the relevance of possible hearing losses due to sound overloads and the short list of references of objective procedures for their study, we provide a technique that gives precise data about the audiometric profile and recruitment factor. Our objectives were to determine peripheral fatigue, through the cochlear microphonic response to sound pressure overload stimuli, as well as to measure recovery time, establishing parameters for differentiation with regard to current psychoacoustic and clinical studies. We used specific instruments for the study of cochlear microphonic response, plus a function generator that provided us with stimuli of different intensities and harmonic components. In Wistar rats, we first measured the normal microphonic response and then the effect of auditory fatigue on it. Using a 60dB pure tone acoustic stimulation, we obtained a microphonic response at 20dB. We then caused fatigue with 100dB of the same frequency, reaching a loss of approximately 11dB after 15minutes; after that, the deterioration slowed and did not exceed 15dB. By means of complex random tone maskers or white noise, no fatigue was caused to the sensory receptors, not even at levels of 100dB and over an hour of overstimulation. No fatigue was observed in terms of sensory receptors. Deterioration of peripheral perception through intense overstimulation may be due to biochemical changes of desensitisation due to exhaustion. Auditory fatigue in subjective clinical trials presumably affects supracochlear sections. The auditory fatigue tests found are not in line with those obtained subjectively in clinical and psychoacoustic trials. Copyright © 2013 Elsevier España, S.L.U. y Sociedad Española de Otorrinolaringología y Patología Cérvico-Facial. All rights reserved.

  5. HIGH TEMPERATURE TIME DEPENDENT UNIAXIAL AND MULTIAXIAL FATIGUE DAMAGE MODEL%高温时间相关单多轴疲劳损伤模型

    Institute of Scientific and Technical Information of China (English)

    孙国芹; 尚德广; 李承山

    2009-01-01

    针对高温疲劳中蠕变和氧化因素的影响,提出高温循环加载下时间相关疲劳损伤模型.根据材料高温疲劳微观观察和疲劳过程,充分考虑拉压应变率和循环周期不同而造成的不同损伤,提出高温影响折算时间的计算方法.结合损伤理论和高温对疲劳损伤的影响,把无保载时间的高温疲劳损伤分为纯疲劳损伤、时间相关损伤和交互损伤,损伤模型经高温2.25Cr-1Mo钢单多轴疲劳试验验证,结果表明,误差在两个因子之内.%Time dependent fatigue damage model under cyclic loading was proposed by considering the effect of creep and oxidation at high temperature on the fatigue damage. The high temperature fatigue damage without holding time was divided into pure fatigue damage, damage caused by the time dependent factors and interactive damage to combine effect of high temperature to fatigue damage with the damage rule. The converting time influenced by high temperature was proposed according to tension-compression strain rate and different cycle period based on the SEM(scanning electron microscope) observation of the fatigue rupture surface and fatigue process. The results for 2.25Cr-1Mo steel tests under uniaxial and multiaxial high temperature fatigue showed an error within a factor of two.

  6. Chronic Fatigue Syndrome

    Science.gov (United States)

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

  7. Fatigue Analysis of Large-scale Wind turbine

    Directory of Open Access Journals (Sweden)

    Zhu Yongli

    2017-01-01

    Full Text Available The paper does research on top flange fatigue damage of large-scale wind turbine generator. It establishes finite element model of top flange connection system with finite element analysis software MSC. Marc/Mentat, analyzes its fatigue strain, implements load simulation of flange fatigue working condition with Bladed software, acquires flange fatigue load spectrum with rain-flow counting method, finally, it realizes fatigue analysis of top flange with fatigue analysis software MSC. Fatigue and Palmgren-Miner linear cumulative damage theory. The analysis result indicates that its result provides new thinking for flange fatigue analysis of large-scale wind turbine generator, and possesses some practical engineering value.

  8. Fatigue Reliability of Offshore Wind Turbine Systems

    DEFF Research Database (Denmark)

    Marquez-Dominguez, Sergio; Sørensen, John Dalsgaard

    2012-01-01

    Optimization of the design of offshore wind turbine substructures with respect to fatigue loads is an important issue in offshore wind energy. A stochastic model is developed for assessing the fatigue failure reliability. This model can be used for direct probabilistic design and for calibration...... 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...

  9. Crack propagation monitoring in a full-scale aircraft fatigue test based on guided wave-Gaussian mixture model

    Science.gov (United States)

    Qiu, Lei; Yuan, Shenfang; Bao, Qiao; Mei, Hanfei; Ren, Yuanqiang

    2016-05-01

    For aerospace application of structural health monitoring (SHM) technology, the problem of reliable damage monitoring under time-varying conditions must be addressed and the SHM technology has to be fully validated on real aircraft structures under realistic load conditions on ground before it can reach the status of flight test. In this paper, the guided wave (GW) based SHM method is applied to a full-scale aircraft fatigue test which is one of the most similar test status to the flight test. To deal with the time-varying problem, a GW-Gaussian mixture model (GW-GMM) is proposed. The probability characteristic of GW features, which is introduced by time-varying conditions is modeled by GW-GMM. The weak cumulative variation trend of the crack propagation, which is mixed in time-varying influence can be tracked by the GW-GMM migration during on-line damage monitoring process. A best match based Kullback-Leibler divergence is proposed to measure the GW-GMM migration degree to reveal the crack propagation. The method is validated in the full-scale aircraft fatigue test. The validation results indicate that the reliable crack propagation monitoring of the left landing gear spar and the right wing panel under realistic load conditions are achieved.

  10. Effect of linear and non-linear blade modelling techniques on simulated fatigue and extreme loads using Bladed

    Science.gov (United States)

    Beardsell, Alec; Collier, William; Han, Tao

    2016-09-01

    There is a trend in the wind industry towards ever larger and more flexible turbine blades. Blade tip deflections in modern blades now commonly exceed 10% of blade length. Historically, the dynamic response of wind turbine blades has been analysed using linear models of blade deflection which include the assumption of small deflections. For modern flexible blades, this assumption is becoming less valid. In order to continue to simulate dynamic turbine performance accurately, routine use of non-linear models of blade deflection may be required. This can be achieved by representing the blade as a connected series of individual flexible linear bodies - referred to in this paper as the multi-part approach. In this paper, Bladed is used to compare load predictions using single-part and multi-part blade models for several turbines. The study examines the impact on fatigue and extreme loads and blade deflection through reduced sets of load calculations based on IEC 61400-1 ed. 3. Damage equivalent load changes of up to 16% and extreme load changes of up to 29% are observed at some turbine load locations. It is found that there is no general pattern in the loading differences observed between single-part and multi-part blade models. Rather, changes in fatigue and extreme loads with a multi-part blade model depend on the characteristics of the individual turbine and blade. Key underlying causes of damage equivalent load change are identified as differences in edgewise- torsional coupling between the multi-part and single-part models, and increased edgewise rotor mode damping in the multi-part model. Similarly, a causal link is identified between torsional blade dynamics and changes in ultimate load results.

  11. 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...

  12. Long-chain n-3 DHA reduces the extent of skeletal muscle fatigue in the rat in vivo hindlimb model.

    Science.gov (United States)

    Peoples, Gregory E; McLennan, Peter L

    2014-03-28

    Dietary fish oil modifies skeletal muscle membrane fatty acid composition and oxygen efficiency similar to changes in the myocardium. Oxygen efficiency is a key determinant of sustained force in mammalian skeletal muscle. Therefore, in the present study, we tested the effects of a fish-oil diet on skeletal muscle fatigue under the stress of contraction using the rat in vivo autologous perfused hindlimb model. For 8 weeks, male Wistar rats were fed a diet rich in saturated fat (SF), a diet rich in n-6 PUFA or a diet rich in long-chain (LC) n-3 PUFA DHA derived from fish oil. In anaesthetised, mechanically ventilated rats, with their hindlimbs perfused with arterial blood at a constant flow, the gastrocnemius-plantaris-soleus muscle bundle was stimulated via sciatic nerve (2 Hz, 6-12 V, 0·05 ms) to contract repetitively for 30 min. Rats fed the n-3 PUFA diet developed higher maximum twitch tension than those fed the SF and n-6 PUFA diets (PDHA into skeletal muscle membranes increases the efficiency of oxygen use over a range of contractile force and this is expressed as a higher sustained force and prolonged time to fatigue.

  13. Fatigue Minimization Work Shift Scheduling for Air Traffic Controllers

    Directory of Open Access Journals (Sweden)

    Ta-Chung Wang

    2013-05-01

    Full Text Available It is common for Air Traffic Controllers to control air traffic during the night and to experience fatigue. Although fatigue is not the direct cause of aviation accidents, 21 percent of accidents are fatigue-related. Therefore countries and companies have tried to regulate work hours to avoid extreme fatigue, thus decreasing human error resulting from fatigue. However, these regulations may not reflect that actual fatigue variation and fatigue levels can be decreased still more by scheduling appropriately. This paper focuses on optimal work shift scheduling to reduce air traffic controller fatigue. First, a mathematical model is established to describe fatigue levels. The objective function is to reduce the fatigue peak produced by work shifts as much as possible. Various constraints, such as holidays and manpower requirements are considered. The optimization problem is then solved using integer programming. We take a sample schedule and draw conclusions by comparing our results with the original fatigue levels.

  14. Influence of K{sub max} and r on fatigue crack growth - A 3D-model

    Energy Technology Data Exchange (ETDEWEB)

    Gudladt, Hans-Joachim [Institut fuer Werkstoffkunde, Universitaet der Bundeswehr Muenchen, Neubiberg (Germany); Steinbock, Johanna [Lehrstuhl fuer Werkstoffkunde und Werkstoffmechanik, Technische Universitaet Muenchen, Garching (Germany)

    2010-04-15

    To study the influence of the stress intensity factor and the R-ratio on the fatigue crack growth rate different kind of crack propagation experiment have been carried out on the steels X5CrNi18-10 and C45E. The experiments show that both parameters the maximum stress intensity K{sub max} and the R-ratio affect the crack growth rate. Consequently, the authors developed a 3D-model, which describes the dependence of da/dN on K{sub max} and the R-ratio. Discussing the experiments, special attention has been paid to the threshold behavior of the investigated materials. Finally, a new model to describe the influence of the R-ratio on the threshold K{sub max,th} for R-ratios from -{infinity} to 1 is presented. (Abstract Copyright [2010], Wiley Periodicals, Inc.)

  15. Chronic fatigue syndrome: Harvey and Wessely's (biopsychosocial model versus a bio(psychosocial model based on inflammatory and oxidative and nitrosative stress pathways

    Directory of Open Access Journals (Sweden)

    Twisk Frank NM

    2010-06-01

    Full Text Available Abstract Background In a recently published paper, Harvey and Wessely put forward a 'biopsychosocial' explanatory model for myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS, which is proposed to be applicable to (chronic fatigue even when apparent medical causes are present. Methods Here, we review the model proposed by Harvey and Wessely, which is the rationale for behaviourally oriented interventions, such as cognitive behaviour therapy (CBT and graded exercise therapy (GET, and compare this model with a biological model, in which inflammatory, immune, oxidative and nitrosative (IO&NS pathways are key elements. Discussion Although human and animal studies have established that the pathophysiology of ME/CFS includes IO&NS pathways, these abnormalities are not included in the model proposed by Harvey and Wessely. Activation of IO&NS pathways is known to induce fatigue and somatic (F&S symptoms and can be induced or maintained by viral and bacterial infections, physical and psychosocial stressors, or organic disorders such as (autoimmune disorders. Studies have shown that ME/CFS and major depression are both clinical manifestations of shared IO&NS pathways, and that both disorders can be discriminated by specific symptoms and unshared or differentiating pathways. Interventions with CBT/GET are potentially harmful for many patients with ME/CFS, since the underlying pathophysiological abnormalities may be intensified by physical stressors. Conclusions In contrast to Harvey and Wessely's (biopsychosocial model for ME/CFS a bio(psychosocial model based upon IO&NS abnormalities is likely more appropriate to this complex disorder. In clinical practice, we suggest physicians should also explore the IO&NS pathophysiology by applying laboratory tests that examine the pathways involved.

  16. A Study on the Topology Model of Combat Systems Based on Complex Networks%基于复杂网络理论的作战系统结构拓扑模型研究

    Institute of Scientific and Technical Information of China (English)

    齐紫微

    2013-01-01

    基于复杂网络理论,分析了信息化作战系统网络结构,构建了传统作战系统和信息化作战系统拓扑模型的生成算法,并通过对传统作战系统和信息化作战系统结构拓扑模型度量性质的比较,说明了信息化战争下的作战系统结构特点,为进一步研究网络化战争提供了良好的模型基础.%Based on Complex Networks,the network structure of the informational war is analyzed;a generating algorithm of the topology model on the traditional combat systems and the informational combat is constructed;and by comparing the metric properties of the topology models under traditional and informational combat systems,the characteristics of the combat systems for the informational war are elaborated.These provide a better model basis for further research in cyber warfare.

  17. 基于兰彻斯特混合律的反恐数学模型研究%Research on Models of Forecasting Anti-terrorist Combat Based on Lanchester Equation

    Institute of Scientific and Technical Information of China (English)

    李浩; 吴帅; 王公宝

    2012-01-01

    针对影响反恐作战效能的主要因素,基于兰彻斯特理论初步建立了用于预测反恐作战胜负的数学模型,并结合算例对模型进行了分析及应用。本模型能够很好地反映实际情况,具有较好的实用性,而且简单易行,容易推广。%Under the circumstances of considering the main factors of the effectiveness of anti-terrorist combat,a mathematical model on the basis of basic ideas of Lanchester equation was built to forecast anti-terrorist combat.The paper analyzed the mathematical model with an example of anti-terrorist combat.The results indicate that the model is effective and simple in forecasting anti-terrorist combat.

  18. Research of Cooperation Model of Combat Planning Based on Petri-net%基于Petri网的作战计划制定协作模型研究

    Institute of Scientific and Technical Information of China (English)

    刘兴林; 陈行军; 孙光明

    2011-01-01

    Cooperation model is one of primary technique in multiple platform combat planning system designing. Several typical cooperation models of conflict progress is proposed in this paper, by Petri-net simulation method, the cooperation model that can solve the conflict problems is designed and validated. The conclusion is that cooperation model cannot resolve all conflict problems, to solve the problems of cooperation planning using cooperation model and profession model is an effective method.%协作模型是设计多平台作战计划制定系统的关键技术之一,文章提出了协作过程冲突的几种典型模式,利用Petri网的过程仿真方法,设计并验证了解决冲突的协作模型,认为协作模型不能解决所有冲突问题,在协作模型与业务模型中分别处理协作制定的冲突问题是系统设计的有效方法.

  19. 2011 Combat Vehicles Conference

    Science.gov (United States)

    2011-10-26

    Capability-Platform (JBC-P) • Light-weight Crew-served Weapons • Joint Capability Release ( JCR ) • Combat Vehicle Improvements Mr. Scott Davis PEO...WIN-T INC 3 JTRS CREW V2 Relocation/V3 CS 11-12 OoC ( JCR ) BFT II VRC 103 & 104 CS 13-14 MSS Duke TI OSRVT (Rover 6) Nett

  20. MODELING AND FATIGUE ANALYSIS OF AUTOMOTIVE WHEEL RIM WITH DIFFERENT MATERIALS

    Directory of Open Access Journals (Sweden)

    MERIGE PHANI SRUJAN

    2016-08-01

    Full Text Available In the design of automobile, the industry is exploringpolymericmaterial in order to obtain reduction of weight withoutsignificantdecrease in vehicle quality and reliability. Fuel consumption of the vehicle is directly proportional to the weight of the wheel rim. Thusin this project a standard wheel of four wheeler ischosenand analyzed by applying loads and using different materials .AluminumAlloy,Magnesium Alloy, PEEK,PEEK with 20% Glassfiber, PEEK with 30% GlassFiber are the materials chosen.The whole design is made by using SOLIDWORKS as per original equipment manufacturer(OEM’Srequirement. Analysis has been carried out using ANSYS todetermine deformation and fatigue life of the wheel. The whole analysisisdonebymeansofsoftwarethereforeresultandobservationsaretrustworthy and met ourexpectation.

  1. A new model of low cycle fatigue crack growth rate%一种新型的低周疲劳裂纹扩展速率模型

    Institute of Scientific and Technical Information of China (English)

    吴晓松; 陈荐; 何建军; 任延杰; 高鹏

    2011-01-01

    The plastic strain at crack tip of low cycle fatigue and the strain distribution on the cyclic plasticity zone of crack tip obey the HRR theoretical solution approximately were analyzed in this paper. A new low cycle fatigue crack growth mathematical model is derived by the combination of these mechanisms which include the crack tip sharpen, the passivation rev crack and crack interaction mechanics and the Ramberg-Osgood's circulation stressstrain curve and the Coffin-Manson's fatigue life curve. The experimental data of low cycle fatigue crack growth rate which belongs to the 30CrlMolV and St-4340 are contrasted. The comparison result shows that the low cycle fatigue crack growth rate model adopted in this paper is able to predict reasonably the low cycle fatigue crack growth rate of the materials used.%基于低周疲劳裂纹扩展机制,假设裂纹尖端循环塑性区内应变分布服从HRR理论解,利用裂纹尖端锐化、钝化启裂低周疲劳裂纹扩展机制,结合Ramberg-Osgood循环应力应变曲线和Manson-Coffin疲劳寿命曲线等断裂力学理论,推导出一种新的低周疲劳裂纹扩展速率数学模型.与30Cr1Mo1V和St-4340的低周疲劳裂纹扩展速率试验数据进行对比,结果表明该低周疲劳裂纹扩展速率模型能够较好地预测材料的低周疲劳裂纹扩展速率.

  2. Corrosion Fatigue

    Science.gov (United States)

    1981-10-01

    the applied protection systems, (2) crevices for moisture entrapment, (3) galvanic couples when steel or titanium fasteners are used, and (4) fatigue...Activ Material Structure Exposed Normal Environment* Unexposed Atmosphere Aluminum alloys Steel 1.25 2.0 4.0 Titanium " Magnesium " (4.0) (8.0) (10.0...APPRNDIX - Chromic Acid Anodizing The surface treatment consists in the following process : D egreasing with trichlorethylene vapor, * Pickling , Composition

  3. 潜艇作战系统的服务描述与建模方法研究%Research on Military Information Service Description and Modeling Methods of Submarine Combat System

    Institute of Scientific and Technical Information of China (English)

    胡习霜

    2013-01-01

    在军事信息服务定义的基础上,针对军事信息服务的语义化、动态化等特性,提出一种潜艇作战系统的服务描述和建模方法.其中服务描述采用基本描述、功能描述和非功能描述相结合的方法;建模方法采用扩展的本体定义元模型,增强了军事信息服务的语义性和动态性.最后将所提方法应用到面向服务的潜艇作战系统中,为开展潜艇作战系统服务化研究提供参考.%Service enable combat system and combat system based on SOA is the development trend of submarine combat system in the future. Firstly, the concept of military information service is introduced then the service description and modeling methods are proposed aiming at the dynamic and semantic character of the military information service. The service description contains the basic description, function description and the non-function description. The modeling method is the extended Ontology Definition MetaModel which can describe the dynamic and semantic character of the military information service properly. Finally, the submarine combat system based on SOA is constructed based on the proposed methods. All of these lay the foundation down for the research of the service enable submarine combat system.

  4. Modeling of creep-fatigue interaction of zirconium {alpha} under cyclic loading at 200 C; Modelisation du comportement et de l`endommagement en fatigue-fluage du zirconium {alpha} a 200C

    Energy Technology Data Exchange (ETDEWEB)

    Vogel, C.

    1996-04-01

    The present work deals with mechanical behaviour of zirconium alpha at 200 deg. C and crack initiation prediction methods, particularly when loading conditions lead to interaction of fatigue and creep phenomena. A classical approach used to study interaction between cyclic effects and constant loading effects does not give easy understanding of experimental results. Therefore, a new approach has been developed, which allow to determine a number of cycles for crack initiation for complex structures under large loading conditions. To study influence of fatigue and creep interaction on crack initiation, a model was chosen, using a scalar variable, giving representation of the material deterioration state. The model uses a non linear cumulating effect between the damage corresponding to cyclic loads and the damage correlated to time influence. The model belongs to uncoupled approaches between damage and behaviour, which is described here by a two inelastic deformations model. This mechanical behaviour model is chosen because it allows distinction between a plastic and a viscous part in inelastic flow. Cyclic damage is function of stress amplitude and mean stress. For the peculiar sensitivity of the material to creep, a special parameter bas been defined to be critical toward creep damage. It is the kinematic term associated to state variables describing this type of hardening in the viscous mechanism. (author).

  5. 基于DEVS的作战指挥行为建模研究%Study on Combat Commanding Behavior Modeling Based on DEVS

    Institute of Scientific and Technical Information of China (English)

    李京; 王子明; 李冬

    2014-01-01

    针对传统计算机兵力生成(computer generated force,CGF)建模所使用的经典人工智能编程语言存在的不足,提出一种基于离散事件系统(discrete event system specification,DEVS)的作战指挥行为建模方法。从DEVS原子模型和耦合的DEVS模型对DEVS做规范介绍,统一、规范描述指挥主体的生理和心理因素如何影响作战指挥行为,建立一种包含评估模块、压力模块和行为模块的作战指挥行为模型。结果表明:该模型能很好地将指挥主体的压力和自身生理状况融入到作战指挥行为中,能较为合理地反映出在紧张对抗环境中指挥主体的实际指挥行为。%Aiming at the shortcoming of typical artificial intelligence programming language for traditional computer generated force (CGF) modeling, put forward a new modeling method of combat commanding behavior based on discrete event system specification (DEVS). From DEVS atomic model and coupling DEVS model, make a standard introduction for DEVS, and also make an unified and standard description about how the physiological and psychological factors of commander make an influence on commanding behavior, establish a commanding behavior model which including evaluation model, pressure model and behavior model. The results show that the model can combine the commander pressure and physiological state with commanding behavior, and it can reflect reasonably the commanding behavior under the circumstance full of nervousness and confrontation.

  6. Mechanisms underlying fatigue: a voxel-based morphometric study of chronic fatigue syndrome

    Directory of Open Access Journals (Sweden)

    Watanabe Yasuyoshi

    2004-10-01

    Full Text Available Abstract Background Fatigue is a crucial sensation that triggers rest, yet its underlying neuronal mechanisms remain unclear. Intense long-term fatigue is a symptom of chronic fatigue syndrome, which is used as a model to study the mechanisms underlying fatigue. Methods Using magnetic resonance imaging, we conducted voxel-based morphometry of 16 patients and 49 age-matched healthy control subjects. Results We found that patients with chronic fatigue syndrome had reduced gray-matter volume in the bilateral prefrontal cortex. Within these areas, the volume reduction in the right prefrontal cortex paralleled the severity of the fatigue of the subjects. Conclusion These results are consistent with previous reports of an abnormal distribution of acetyl-L-carnitine uptake, which is one of the biochemical markers of chronic fatigue syndrome, in the prefrontal cortex. Thus, the prefrontal cortex might be an important element of the neural system that regulates sensations of fatigue.

  7. Human Behavior and Performance as Essential Ingredients in Realistic Modeling of Combat - MORIMOC II. Proceedings of the Military Operations Research Society Mini-Symposium Held in Alexandria, Virginia on 22-24 February 1989. Volume 2

    Science.gov (United States)

    1989-05-01

    analyze combat in terms of numbers, he suggested somewhat contemptuously, is "kind of war by algebra ." Among other things, he wrote: "... the impulse... Rotman and Kowalczyk have shown that the Center for Night Vision and Electro- Optics (CNVEO) search model, currently the mainstay target acquisition...January 1989. 2. Institute for Defense Analysis, Extending the CNVO Search Model to the Multi-Target Environment, by S.R. Rotman and M.L. Kowakczyk, 12

  8. A Study of the Protective Effect of Triticum aestivum L. in an Experimental Animal Model of Chronic Fatigue Syndrome

    Directory of Open Access Journals (Sweden)

    Mukundam Borah

    2014-01-01

    Full Text Available Background: Oxidative stress plays a major role in the pathogenesis of chronic fatigue syndrome (CFS. Keeping in view the proven antioxidant activity of Triticum aestivum L., this study has been undertaken to explore the potential therapeutic benefit of this plant in the treatment of CFS. Objective: To study the protective effect of the ethanolic extract of the leaves of Triticum aestivum (EETA in an experimental mice model of CFS. Materials and Methods: Five groups of albino mice (20-25 g were selected for the study, with five animals in each group. Group A served as the naïve control and Group B served as the stressed control. Groups C and D received EETA (100 mg/kg and 200 mg/kg b.w.. Group E received imipramine (20 mg/kg b.w.. Except for Group A, mice in each group were forced to swim 6 min each for 7 days to induce a state of chronic fatigue. Duration of immobility was measured on every alternate day. After 7 days, various behavioral tests (mirror chamber and elevated plus maize test for anxiety, open field test for locomotor activity and biochemical estimations (malondialdehyde [MDA] and catalase activity in mice brain were performed. Results: Forced swimming in the stressed group resulted in a significant increase in immobility period, decrease in locomotor activity and elevated anxiety level. The brain homogenate showed significantly increased MDA and decreased catalase levels. The extract-treated groups showed significantly (P < 0.05 improved locomotor activity, decreased anxiety level, elevated catalase levels and reduction of MDA. Conclusion: The study confirms the protective effects of EETA in CFS.

  9. Neuromuscular strain as a contributor to cognitive and other symptoms in Chronic Fatigue Syndrome: Hypothesis and conceptual model.

    Directory of Open Access Journals (Sweden)

    Peter C. Rowe

    2013-05-01

    Full Text Available Individuals with chronic fatigue syndrome (CFS have heightened sensitivity and increased symptoms following various physiologic challenges, such as orthostatic stress, physical exercise, and cognitive challenges. Similar heightened sensitivity to the same stressors in fibromyalgia (FM has led investigators to propose that these findings reflect a state of central sensitivity. A large body of evidence supports the concept of central sensitivity in FM. A more modest literature provides partial support for this model in CFS, particularly with regard to pain. Nonetheless, fatigue and cognitive dysfunction have not been explained by the central sensitivity data thus far. Peripheral factors have attracted attention recently as contributors to central sensitivity. Work by Brieg, Sunderland, and others has emphasized the ability of the nervous system to undergo accommodative changes in length in response to the range of limb and trunk movements carried out during daily activity. If that ability to elongate is impaired—due to movement restrictions in tissues adjacent to nerves, or due to swelling or adhesions within the nerve itself—the result is an increase in mechanical tension within the nerve. This adverse neural tension, also termed neurodynamic dysfunction, is thought to contribute to pain and other symptoms through a variety of mechanisms. These include mechanical sensitization and altered nociceptive signaling, altered proprioception, adverse patterns of muscle recruitment and force of muscle contraction, reduced intra-neural blood flow, and release of inflammatory neuropeptides. Because it is not possible to differentiate completely between adverse neural tension and strain in muscles, fascia, and other soft tissues, we use the more general term neuromuscular strain. In our clinical work, we have found that neuromuscular restrictions are common in CFS, and that many symptoms of CFS can be reproduced by selectively adding neuromuscular strain

  10. Neuromuscular strain as a contributor to cognitive and other symptoms in chronic fatigue syndrome: hypothesis and conceptual model.

    Science.gov (United States)

    Rowe, Peter C; Fontaine, Kevin R; Violand, Richard L

    2013-01-01

    Individuals with chronic fatigue syndrome (CFS) have heightened sensitivity and increased symptoms following various physiologic challenges, such as orthostatic stress, physical exercise, and cognitive challenges. Similar heightened sensitivity to the same stressors in fibromyalgia (FM) has led investigators to propose that these findings reflect a state of central sensitivity. A large body of evidence supports the concept of central sensitivity in FM. A more modest literature provides partial support for this model in CFS, particularly with regard to pain. Nonetheless, fatigue and cognitive dysfunction have not been explained by the central sensitivity data thus far. Peripheral factors have attracted attention recently as contributors to central sensitivity. Work by Brieg, Sunderland, and others has emphasized the ability of the nervous system to undergo accommodative changes in length in response to the range of limb and trunk movements carried out during daily activity. If that ability to elongate is impaired-due to movement restrictions in tissues adjacent to nerves, or due to swelling or adhesions within the nerve itself-the result is an increase in mechanical tension within the nerve. This adverse neural tension, also termed neurodynamic dysfunction, is thought to contribute to pain and other symptoms through a variety of mechanisms. These include mechanical sensitization and altered nociceptive signaling, altered proprioception, adverse patterns of muscle recruitment and force of muscle contraction, reduced intra-neural blood flow, and release of inflammatory neuropeptides. Because it is not possible to differentiate completely between adverse neural tension and strain in muscles, fascia, and other soft tissues, we use the more general term "neuromuscular strain." In our clinical work, we have found that neuromuscular restrictions are common in CFS, and that many symptoms of CFS can be reproduced by selectively adding neuromuscular strain during the

  11. Gear fatigue damage for a 500 kW wind turbine exposed to increasing turbulence using a flexible multibody model

    Directory of Open Access Journals (Sweden)

    Martin Felix Jørgensen

    2014-04-01

    Full Text Available This paper investigates gear tooth fatigue damage in a 500 kW wind turbine using FLEX5 and own multibody code. FLEX5 provides the physical wind field, rotor and generator torque and the multibody code is used for obtaining gear tooth reaction forces in the planetary gearbox. Different turbulence levels are considered and the accumulated fatigue damage levels are compared. An example where the turbulence/fatigue sensitivity could be important, is in the middle of a big wind farm. Interior wind turbines in large wind farms will always operate in the wake of other wind turbines, causing increased turbulence and therefore increased fatigue damage levels. This article contributes to a better understanding of gear fatigue damage when turbulence is increased (e.g. in the center of large wind farms or at places where turbulence is pronounced.

  12. 3D-FE Modeling of 316 SS under Strain-Controlled Fatigue Loading and CFD Simulation of PWR Surge Line

    Energy Technology Data Exchange (ETDEWEB)

    Mohanty, Subhasish [Argonne National Lab. (ANL), Argonne, IL (United States); Barua, Bipul [Argonne National Lab. (ANL), Argonne, IL (United States); Listwan, Joseph [Argonne National Lab. (ANL), Argonne, IL (United States); Majumdar, Saurin [Argonne National Lab. (ANL), Argonne, IL (United States); Natesan, Ken [Argonne National Lab. (ANL), Argonne, IL (United States)

    2017-03-01

    In financial year 2017, we are focusing on developing a mechanistic fatigue model of surge line pipes for pressurized water reactors (PWRs). To that end, we plan to perform the following tasks: (1) conduct stress- and strain-controlled fatigue testing of surge-line base metal such as 316 stainless steel (SS) under constant, variable, and random fatigue loading, (2) develop cyclic plasticity material models of 316 SS, (3) develop one-dimensional (1D) analytical or closed-form model to validate the material models and to understand the mechanics associated with 316 SS cyclic hardening and/or softening, (4) develop three-dimensional (3D) finite element (FE) models with implementation of evolutionary cyclic plasticity, and (5) develop computational fluid dynamics (CFD) model for thermal stratification, thermal-mechanical stress, and fatigue of example reactor components, such as a PWR surge line under plant heat-up, cool-down, and normal operation with/without grid-load-following. This semi-annual progress report presents the work completed on the above tasks for a 316 SS laboratory-scale specimen subjected to strain-controlled cyclic loading with constant, variable, and random amplitude. This is the first time that the accurate 3D-FE modeling of the specimen for its entire fatigue life, including the hardening and softening behavior, has been achieved. We anticipate that this work will pave the way for the development of a fully mechanistic-computer model that can be used for fatigue evaluation of safety-critical metallic components, which are traditionally evaluated by heavy reliance on time-consuming and costly test-based approaches. This basic research will not only help the nuclear reactor industry for fatigue evaluation of reactor components in a cost effective and less time-consuming way, but will also help other safety-related industries, such as aerospace, which is heavily dependent on test-based approaches, where a single full-scale fatigue test can cost

  13. Music and Combat Motivation

    Science.gov (United States)

    2015-04-01

    1   AIR COMMAND AND STAFF COLLEGE AIR UNIVERSITY MUSIC AND COMBAT MOTIVATION by Sally C. Maddocks, Major, USAF Master of...accordance with Air Force Instruction 51-303, it is not copyrighted, but is the property of the United States government.  3   Music has the power...are many historical examples from which to draw evidence of the impact of music on fielded forces. One must study not only the historical events, but

  14. MANAGING FATIGUE IN SPORTS

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    @@ Fatigue is a multifactorial process. Depletion of energy sources, including adenosine triphosphate (ATP), phosphocreatine (PCr), plus carbohydrates (CHO) like muscle glycogen and blood glucose can contribute to fatigue.

  15. Experimental and three-dimensional finite element investigation of fatigue

    Science.gov (United States)

    Bomidi, John A. R.

    Materials often fail at cyclic loads that are lower than their ultimate strength or even their yield strength due to progressive internal material degradation; commonly known as fatigue. Moreover, there is a wide scatter in observed fatigue lives of mechanical components operating under identical loading conditions. The randomness of fatigue failure is considered to be linked to basic microstructural effects such as random microstructure topology and the initiation/growth of cracks along inter/transgranular planes. Several modeling approaches have been previously presented ranging from 2D discrete element to 3D Finite Element methods with explicit representation of microstructure topology and continuum damage mechanics to capture dispersion in rolling contact fatigue life and fatigue spalling. There is, however, a need to compare the modeling approach with experimental fatigue test conditions in order to verify and as required enhance the modeling approach to capture observed fatigue failure. This dissertation presents experimental test results and three-dimensional modeling approach that capture fatigue failure. The three-dimensional modeling approach is enhanced according to the experimental observations to consider inter/trans granular failure, different modes of fatigue initiation and propagation and finally for considering effect of plasticity in fatigue of rolling contacts. The following phenomena have been investigated: (1) Fatigue of microbeams: (a )Results of fatigue life and failure from 3D modeling of intergranular fatigue in microbeams are compared with experimental observations reported in literature (2) Tensile fatigue of thin sheets: (a) A test rig with a new grip and alignment system is developed to address the challenges associated with thin sheet testing and conduct fatigue experiments. (b) The 3D fatigue model is enhanced to capture the dominant transgranular fatigue observed in the experiments. The observed and modeled fatigue life and failure

  16. Théorie à Gradient: Models de Comportement et Critères de Fatigue; Application en Micromécanique

    OpenAIRE

    2013-01-01

    145 pages including appendices.; In the present thesis, two new classes of phenomenological models in the framework of the continuum thermodynamics and gradient theory are proposed. The first one is standard gradient constitutive model used to deal with the mechanical problems at micro-scale, and the other concerns gradient fatigue criteria for the problems at small scale. Using these, some common effects which are not captured yet in the classical mechanics but become significant at sufficie...

  17. Concept development of "compassion fatigue" in clinical nurses: Application of Schwartz-Barcott and Kim's hybrid model

    Directory of Open Access Journals (Sweden)

    Mahdieh Sabery

    2017-06-01

    Full Text Available Compassion fatigue is not a new concept in nursing; yet, it is not well known and there is no fixed clear definition of the term. The ambiguity surrounding how to define compassion fatigue has challenged its measurement and evaluation. Thus, any attempt to determine attributes of this underdeveloped concept and studying it in a new socio-cultural context requires concept development. The purpose of this study is to clarify the concept of compassion fatigue through concept development and to produce a vivid and tentative definition of this concept in clinical practice. Concept development was conducted using a three-step hybrid concept analysis including theoretical, fieldwork, and final analysis phases according to Schwartz-Barcott and Kim's method. We reviewed and analyzed 48 articles that met the inclusion criteria. Following, the first author conducted 13 interviews with clinical nurses followed by an inductive content analysis. Finally, a comprehensive definition of compassion fatigue in nurses was attained. Compassion fatigue in nurses can be explained as a cumulative and progressive process of absorption of the patient’s pain and suffering formed from the sympathetic and caring interactions with the patients and their families. The physical, emotional, intellectual, spiritual, social, and organizational consequences of compassion fatigue are so extensive that they threaten the existential integrity of the nurse. Context-based variables (culture, family, and community such as personality features like devotion behaviors and commitment towards the patient, exposure to multiple stressors, organizational challenges, and lack of self-care are factors associated with an increased risk of compassion fatigue. Concept development of compassion fatigue is the first step in the protection of nurses against the destructive consequences of compassion fatigue and to improve quality of care.

  18. 基于不完全信息空战的火力分配建模与应用%Research on Weapon-Target Assignment Modeling and Application Based on Incomplete Information Air Combat

    Institute of Scientific and Technical Information of China (English)

    隋永华; 郭雷; 俞利新; 王海晏

    2012-01-01

    To solve the problem of weapon-target assignment in an incomplete information air combat, the common weapon-target assignment model is analized, the defect of which is pointed out, and an improved weapon-target assignment model is built. The computation method of the key arguments of the model is proposed according to the character of incomplete information air combat. The improved mode can work efficiently based on the limited papameters obtained easily in the condition of incomplete information. Finally,the efficiency of the model is validated through a typical air combat example.%为了解决不完全信息空战中的火力分配问题,分析了常规空战火力分配模型,指出了其中的不足,建立了一种改进的火力分配模型.针对不完全信息空战特点,给出了其中关键参数的确定方法.该改进模型可有效利用战机在不完全信息条件下容易获取的有限参数进行火力分配,具有很强的实用性.最后通过典型应用实例验证了模型的有效性.

  19. [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.

  20. PMMA-hydroxyapatite composite material retards fatigue failure of augmented bone compared to augmentation with plain PMMA: in vivo study using a sheep model.

    Science.gov (United States)

    Arabmotlagh, Mohammad; Bachmaier, Samuel; Geiger, Florian; Rauschmann, Michael

    2014-11-01

    Polymethylmethacrylate (PMMA) is the most commonly used void filler for augmentation of osteoporotic vertebral fracture, but the differing mechanical features of PMMA and osteoporotic bone result in overload and failure of adjacent bone. The aim of this study was to compare fatigue failure of bone after augmentation with PMMA-nanocrystalline hydroxyapatite (HA) composite material or with plain PMMA in a sheep model. After characterization of the mechanical properties of a composite material consisting of PMMA and defined amounts (10, 20, and 30% volume fraction) of HA, the composite material with 30% volume fraction HA was implanted in one distal femur of sheep; plain PMMA was implanted in the other femur. Native non-augmented bone served as control. Three and 6 months after implantation, the augmented bone samples were exposed to cyclic loading and the evolution of damage was investigated. The fatigue life was highest for the ovine native bone and lowest for bone-PMMA specimens. Bone-composite specimens showed significantly higher fatigue life than the respective bone-PMMA specimens in both 3- and 6-month follow-up groups. These results suggest that modification of mechanical properties of PMMA by addition of HA to approximate those of cancellous bone retards fatigue failure of the surrounding bone compared to augmented bone with plain PMMA.

  1. Gear fatigue damage for a 500 kW wind turbine exposed to increasing turbulence using a flexible multibody model

    DEFF Research Database (Denmark)

    Jørgensen, Martin Felix; Pedersen, Niels Leergaard; Sørensen, Jens Nørkær

    2014-01-01

    This paper investigates gear tooth fatigue damage in a 500 kW wind turbine using FLEX5 and own multibody code. FLEX5 provides the physical wind eld, rotor and generator torque and the multibody code is used for obtaining gear tooth reaction forces in the planetary gearbox. Dierent turbulence levels...... and therefore increased fatigue damage levels. This article contributes to a better understanding of gear fatigue damage when turbulence is increased (e.g. in the center of large wind farms or at places where turbulence is pronounced)....

  2. A Geometric Approach to Modeling Microstructurally Small Fatigue Crack Formation. 2; Simulation and Prediction of Crack Nucleation in AA 7075-T651

    Science.gov (United States)

    Hochhalter, Jake D.; Littlewood, David J.; Christ, Robert J., Jr.; Veilleux, M. G.; Bozek, J. E.; Ingraffea, A. R.; Maniatty, Antionette M.

    2010-01-01

    The objective of this paper is to develop further a framework for computationally modeling microstructurally small fatigue crack growth in AA 7075-T651 [1]. The focus is on the nucleation event, when a crack extends from within a second-phase particle into a surrounding grain, since this has been observed to be an initiating mechanism for fatigue crack growth in this alloy. It is hypothesized that nucleation can be predicted by computing a non-local nucleation metric near the crack front. The hypothesis is tested by employing a combination of experimentation and nite element modeling in which various slip-based and energy-based nucleation metrics are tested for validity, where each metric is derived from a continuum crystal plasticity formulation. To investigate each metric, a non-local procedure is developed for the calculation of nucleation metrics in the neighborhood of a crack front. Initially, an idealized baseline model consisting of a single grain containing a semi-ellipsoidal surface particle is studied to investigate the dependence of each nucleation metric on lattice orientation, number of load cycles, and non-local regularization method. This is followed by a comparison of experimental observations and computational results for microstructural models constructed by replicating the observed microstructural geometry near second-phase particles in fatigue specimens. It is found that orientation strongly influences the direction of slip localization and, as a result, in uences the nucleation mechanism. Also, the baseline models, replication models, and past experimental observation consistently suggest that a set of particular grain orientations is most likely to nucleate fatigue cracks. It is found that a continuum crystal plasticity model and a non-local nucleation metric can be used to predict the nucleation event in AA 7075-T651. However, nucleation metric threshold values that correspond to various nucleation governing mechanisms must be calibrated.

  3. Fatigue Analysis of a Mono-Tower Platform

    DEFF Research Database (Denmark)

    Kirkegaard, Poul Henning; Sørensen, John Dalsgaard; Brincker, Rune

    In this paper, a fatigue reliability analysis of a Mono-tower platform is presented. The failure mode, fatigue failure in the butt welds, is investigated with two different models. The one with the fatigue strength expressed through SN relations, the other with the fatigue strength expressed thro...... of the natural period, damping ratio, current, stress Spectrum and parameters describing the fatigue strength. Further, soil damping is shown to be significant for the Mono-tower.......In this paper, a fatigue reliability analysis of a Mono-tower platform is presented. The failure mode, fatigue failure in the butt welds, is investigated with two different models. The one with the fatigue strength expressed through SN relations, the other with the fatigue strength expressed...

  4. Fatigue Reliability Analysis of a Mono-Tower Platform

    DEFF Research Database (Denmark)

    Kirkegaard, Poul Henning; Sørensen, John Dalsgaard; Brincker, Rune

    1991-01-01

    In this paper, a fatigue reliability analysis of a Mono-tower platform is presented. The failure mode, fatigue failure in the butt welds, is investigated with two different models. The one with the fatigue strength expressed through SN relations, the other with the fatigue strength expressed thro...... of the natural period, damping ratio, current, stress spectrum and parameters describing the fatigue strength. Further, soil damping is shown to be significant for the Mono-tower.......In this paper, a fatigue reliability analysis of a Mono-tower platform is presented. The failure mode, fatigue failure in the butt welds, is investigated with two different models. The one with the fatigue strength expressed through SN relations, the other with the fatigue strength expressed...

  5. Trajectories of fatigue in family caregivers of patients undergoing radiation therapy for prostate cancer.

    Science.gov (United States)

    Fletcher, Barbara A Swore; Schumacher, Karen L; Dodd, Marylin; Paul, Steven M; Cooper, Bruce A; Lee, Kathryn; West, Claudia; Aouizerat, Bradley E; Swift, Patrick S; Wara, William; Miaskowski, Christine

    2009-04-01

    Predictors of and trajectories for evening and morning fatigue were evaluated in family caregivers of oncology patients using hierarchical linear modeling. Evening fatigue trajectory fit a quadratic model. Predictors included baseline sleep disturbances in family caregivers and baseline evening fatigue in patients. Morning fatigue trajectory fit a linear model. Predictors were baseline trait anxiety, levels of perceived family support, and baseline morning fatigue in patients. Findings suggest considerable inter-individual variability in the trajectories of evening and morning fatigue. Evaluating family caregivers for sleep disturbance, anxiety, and poor family support, as well as high levels of patient fatigue, could identify those family caregivers at highest risk for sustained fatigue trajectories.

  6. "Shell Shock": An Entity that Predated Combat-related Posttraumatic Stress Disorder

    Directory of Open Access Journals (Sweden)

    Ragul Ganesh

    2015-01-01

    Full Text Available In the last century, numerous soldiers had been diagnosed with various post combat disorders. The terminology that has been utilized to describe such patients include combat fatigue, combat stress reaction, soldier′s heart, effort syndrome, non-ulcer dyspepsia, effects of agent orange and gulf war syndrome. The initial description of such post combat disorder was probably ′shell shock′ which came into vogue during the World War I. The soldiers, undergoing unyielding artillery bombardment, in the trenches suffered persistent symptoms of headache, behavioural changes and memory impairment, and was designated at the time as ′shell shock′. Myers and Mott, independently studied numerous soldiers to elucidate the features and aetiology of the entity. An attempt was made to restrict the usage of the term, but the psychological distress of the soldiers persisted to be addressed in some manner or the other, culminating in the genesis of Post Traumatic Stress Disorder.

  7. Fatigue life extension

    Science.gov (United States)

    Matejczyk, D. E.; Lin, J.

    1985-01-01

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

  8. A Low Order Model for Analyzing effects of Blade Fatigue Load Control

    DEFF Research Database (Denmark)

    Kallesøe, Bjarne Skovmose

    2006-01-01

    , and torsional blade oscillations, and rotor speed). The aerodynamics is described by a model of unsteady aerodynamic. The equations of motion are derived in nonlinear and linear form. The linear equations of motion are used for stability analysis and control design. The nonlinear equations of motion are used...... for time simulations to evaluate control performance. The stability analysis shows that the model is capable of predicting classical flutter, and stall-induced vibrations. The results from the stability analysis are compared with known results, showing good agreement. The model is used to compare......A new low order mathematical model is introduced to analyse blade dynamics and blade load reducing control strategies for wind turbines. The model consists of a typical wing section model combined with a rotor speed model, leading to four structural degrees of freedom (flapwise, edgewise...

  9. Probabilistic Fatigue Damage Prognosis Using a Surrogate Model Trained Via 3D Finite Element Analysis

    Science.gov (United States)

    Leser, Patrick E.; Hochhalter, Jacob D.; Newman, John A.; Leser, William P.; Warner, James E.; Wawrzynek, Paul A.; Yuan, Fuh-Gwo

    2015-01-01

    Utilizing inverse uncertainty quantification techniques, structural health monitoring can be integrated with damage progression models to form probabilistic predictions of a structure's remaining useful life. However, damage evolution in realistic structures is physically complex. Accurately representing this behavior requires high-fidelity models which are typically computationally prohibitive. In the present work, a high-fidelity finite element model is represented by a surrogate model, reducing computation times. The new approach is used with damage diagnosis data to form a probabilistic prediction of remaining useful life for a test specimen under mixed-mode conditions.

  10. A conceptual framework for interpretation of MMC fatigue

    Energy Technology Data Exchange (ETDEWEB)

    Talreja, R. [Georgia Inst. of Tech., Atlanta (United States). School of Aerospace Engineering

    1995-09-01

    A previously developed conceptual framework for interpretation of fatigue of polymer matrix composites (PMCs) is revisited for the purpose of the interpretation of fatigue in metal matrix composites (MMCs). With appropriate modifications, the basic features in the mechanisms based fatigue life diagrams of PMCs are found to hold for MMCs as well. Fatigue data for different MMC systems are examined with the interpretative framework and some observed trends are clarified. Approaches to fatigue life modeling are discussed for the different regions of behavior interpreted by the fatigue life diagram concept. (orig.)

  11. Nonpharmacologic approach to fatigue in patients with cancer.

    Science.gov (United States)

    Pachman, Deirdre R; Price, Katharine A; Carey, Elise C

    2014-01-01

    Cancer-related fatigue is a common yet underappreciated problem with a significant impact on functional ability and quality of life. Practice guidelines mandate that all cancer patients and survivors be screened for cancer-related fatigue (CRF) at regular intervals. Comorbidities that could contribute to fatigue should be treated, and patients with moderate to severe fatigue should undergo a comprehensive evaluation. Nonpharmacologic interventions are important tools to combat CRF and should be incorporated into routine practice. Physical activity, educational interventions, and cognitive-behavioral therapy have the most supportive data and can be recommended to patients with confidence. From a practical standpoint, general education on CRF is something that most care providers can readily offer patients as part of routine care. Other interventions that appear promising but are as yet lacking convincing evidence include mindfulness-based stress reduction, yoga, and acupuncture. Reiki, Qigong, hypnosis, and music therapy may be worthy of further investigation.

  12. A finite element model on effects of impact load and cavitation on fatigue crack propagation in mechanical bileaflet aortic heart valve.

    Science.gov (United States)

    Mohammadi, H; Klassen, R J; Wan, W-K

    2008-10-01

    Pyrolytic carbon mechanical heart valves (MHVs) are widely used to replace dysfunctional and failed heart valves. As the human heart beats around 40 million times per year, fatigue is the prime mechanism of mechanical failure. In this study, a finite element approach is implemented to develop a model for fatigue analysis of MHVs due to the impact force between the leaflet and the stent and cavitation in the aortic position. A two-step method to predict crack propagation in the leaflets of MHVs has been developed. Stress intensity factors (SIFs) are computed at a small initiated crack located on the leaflet edge (the worst case) using the boundary element method (BEM). Static analysis of the crack is performed to analyse the stress distribution around the front crack zone when the crack is opened; this is followed by a dynamic crack analysis to consider crack propagation using the finite element approach. Two factors are taken into account in the calculation of the SIFs: first, the effect of microjet formation due to cavitation in the vicinity of leaflets, resulting in water hammer pressure; second, the effect of the impact force between the leaflet and the stent of the MHVs, both in the closing phase. The critical initial crack length, the SIFs, the water hammer pressure, and the maximum jet velocity due to cavitation have been calculated. With an initial crack length of 35 microm, the fatigue life of the heart valve is greater than 60 years (i.e. about 2.2 x 10(9) cycles) and, with an initial crack length of 170 microm, the fatigue life of the heart valve would be around 2.5 years (i.e. about 9.1 x 10(7) cycles). For an initial crack length greater than 170 microm, there is catastrophic failure and fatigue cracking no longer occurs. A finite element model of fatigue analysis using Patran command language (PCL custom code) in MSC software can be used to evaluate the useful lifespan of MHVs. Similar methodologies can be extended to other medical devices under cyclic

  13. Predictive Models to Estimate Probabilities of Injuries and Adverse Performance Outcomes in U.S. Army Basic Combat Training

    Science.gov (United States)

    2014-03-01

    Height (inches) was measured in stocking feet using a stadiometer (Seca, Hamburg , Germany). Body mass (lbs) was measured in stocking feet, ACU pants...undergarments and t-shirts using a digital scale (Seca model 770, Hamburg , Germany). 7 APFT Data Collection The 1-1-1 initial physical fitness test...physical damage to the. body as a result of an energy exchange .14 Recruit attrition was defined as failure to successfully complete a cycle of

  14. Combating hooliganism in the Netherlands. An evaluation of measures to combat hooliganism with longitudinal registration data

    NARCIS (Netherlands)

    Schaap, D.P.; Postma, M; Jansen, L.; Tolsma, J.

    2014-01-01

    Football hooliganism is an undesirable but widespread phenomenon. In this contribution, a range of measures to combat hooliganism in the Netherlands is evaluated. We use (logistic) multi-level models to analyze data on hooliganism from the Dutch Football Vandalism Information Office covering 3431

  15. Combating hooliganism in the Netherlands: An evaluation of measures to combat hooliganism with longitudinal registration data

    NARCIS (Netherlands)

    Schaap, D.P.; Postma, M; Jansen, L.; Tolsma, J.

    2014-01-01

    Football hooliganism is an undesirable but widespread phenomenon. In this contribution, a range of measures to combat hooliganism in the Netherlands is evaluated. We use (logistic) multi-level models to analyze data on hooliganism from the Dutch Football Vandalism Information Office covering 3431

  16. ¿Puede un modelo educativo intercultural combatir la discriminación y la xenofobia? Can an intercultural education model combat discrimination and xenophobia?

    Directory of Open Access Journals (Sweden)

    Moisès Esteban Guitart

    2010-03-01

    Full Text Available El objetivo que nos proponemos en el siguiente texto es ofrecer una reflexión, desde la psicología cultural, perspectiva teórica desde la que hablamos, alrededor de la interculturalidad como práctica institucionalizada y, por lo tanto, creadora de significados y relaciones. Para ello se exploran algunas producciones narrativas de estudiantes indígenas y mestizos de la Universidad Intercultural de Chiapas (UNICH alrededor de la discriminación y de su experiencia, antes y después, de participar en dicho escenario sociocultural. Realizamos doce entrevistas en profundidad (historias de vida a seis mestizos y seis indígenas de dicha universidad. Según el análisis de los significados que emergen en las entrevistas exploradas, interpretamos concluyendo que el contexto de relaciones que se da en la UNICH fomenta la conciliación de los puntos de vista tradicionalmente enfrentados entre indígenas y mestizos a través de la apropiación de un discurso intercultural. In this article we present a qualitative study conducted with six indigenous and six mestizos from Intercultural University of Chiapas. The aim of the study is to exemplify the mutual perception between different ethno-linguistic groups, as well as the possible change occurred after the admission to the University. That is, opinions about the other group after and before entering the University. We conclude that a higher education intercultural model can promote mutual understanding and relationship between indigenous and mestizos and thus combat prejudices and stereotypes.

     

     

     

     

     

  17. Fatigue in Rheumatoid Arthritis.

    Science.gov (United States)

    Katz, Patricia

    2017-05-01

    The purpose of this study was to review the current information on fatigue in rheumatoid arthritis (RA). Severe fatigue is common among individuals with RA and has a significant impact on quality of life (QOL). RA-related factors (e.g., inflammation, pain) are associated with greater fatigue, but other factors, such as obesity, physical inactivity, sleep disturbance, and depression, explain the majority of variation in fatigue. Medications targeting RA have little effect on fatigue. Instead, the most effective interventions seem to address non-RA-specific factors such as physical inactivity or use cognitive behavioral approaches. No recommendations have been made for tools to measure fatigue in RA, leading to potential difficulty comparing studies. Although fatigue has great impact on patients' QOL, effective interventions that are feasible for broad dissemination remain elusive. Additional multi-faceted research is needed to identify modifiable sources of fatigue. Such research would be enhanced by harmonization of fatigue measurement across studies.

  18. A Research on the Generating Model of Combat Capabilities of Fire Force%现代化消防铁军核心战斗力生成模式研究

    Institute of Scientific and Technical Information of China (English)

    姜自清; 张源

    2012-01-01

    The modernized fire force plays an important part in maintaining the social and economic stability and development. To construct modernized fire force and enhance the combat capability is a daunting and pressing task that fire forces now are faced. This paper summarizes the challenges that fire forces face under the new situation, analyses the constituent elements of combat capabilities of fire force, and discusses generating model of combat capabilities of fire force.%现代化消防铁军是维护我国经济社会发展稳定的重要保障力量,打造一支现代化消防铁军,提升其核心战斗力是当前消防部队面临的一项艰巨而又迫切的任务。分析现代化消防铁军核心战斗力的构成要素,探讨现代化消防铁军核心战斗力的生成模式。

  19. Modelling the Effects of Surface Residual Stresses on Fatigue Behavior of PM Disk Alloys Project

    Data.gov (United States)

    National Aeronautics and Space Administration — A finite element based model will be developed and validated to capture the evolution of residual stresses and cold work at machined features of compressor and...

  20. Cost effectiveness of strategies to combat breast, cervical, and colorectal cancer in sub-Saharan Africa and South East Asia: mathematical modelling study.

    NARCIS (Netherlands)

    G.M. Ginsberg (Gary); J.A. Lauer (Jeremy); S.G. Zelle (Sten); S.A. Baeten (Stefan); R.M.P.M. Baltussen (Rob)

    2012-01-01

    textabstractTo determine the costs and health effects of interventions to combat breast, cervical, and colorectal cancers in order to guide resource allocation decisions in developing countries. Two World Health Organization sub-regions of the world: countries in sub-Saharan Africa with very high ad

  1. Cost effectiveness of strategies to combat breast, cervical, and colorectal cancer in sub-Saharan Africa and South East Asia: mathematical modelling study.

    NARCIS (Netherlands)

    Ginsberg, G.M.; Lauer, J.A.; Zelle, S.; Baeten, S.; Baltussen, R.M.

    2012-01-01

    OBJECTIVE: To determine the costs and health effects of interventions to combat breast, cervical, and colorectal cancers in order to guide resource allocation decisions in developing countries. SETTING: Two World Health Organization sub-regions of the world: countries in sub-Saharan Africa with very

  2. Statistical modelling of compression and fatigue damage of unidirectional fiber reinforced composites

    DEFF Research Database (Denmark)

    Mishnaevsky, Leon; Brøndsted, Povl

    2009-01-01

    A statistical computational model of strength and damage of unidirectional carbon fiber reinforced composites under compressive and cyclic compressive loading is presented in this paper. The model is developed on the basis of the Budiansky–Fleck fiber kinking condition, continuum damage mechanics...... concept and the Monte-Carlo method. The effects of fiber misalignment variability, fiber clustering, load sharing rules on the damage in composite are studied numerically. It is demonstrated that the clustering of fibers has a negative effect of the damage resistance of a composite. Further, the static...

  3. Research progress of exercise-induced fatigue

    Directory of Open Access Journals (Sweden)

    Peng-yi DAI

    2016-12-01

    Full Text Available Exercise-induced fatigue is a comprehensive response to a variety of physiological and biochemical changes in the body, and can affect people's quality of life to different extents. If no timely recovery after occurrence of fatigue, accumulated gradually, it can lead to "burnout", a "overtraining syndrome", "chronic fatigue syndrome", etc., which will cause endocrine disturbance, immune suppression, even physical illness. Exercise-induced fatigue becomes an important factor endangering human health. In recent years, many experts and scholars at home and abroad are committed to the research of exercise-induced fatigue, and have put forward a variety of hypothesis to explain the cause of exercise-induced fatigue. They expect to find out the methods for preventing and eliminating exercise-induced fatigue. This article discusses mainly the pathogenesis, model building, elimination/ relief, etc. of exercise-induced fatigue to point out the research achievements of exercise-induced fatigue and its existing problems. DOI: 10.11855/j.issn.0577-7402.2016.11.14

  4. An Evaluation of Four Current Models to Predict the Creep-Fatigue Interaction in Rene 95

    Science.gov (United States)

    1979-06-01

    life of AISI 304 stainless steel, whose life was degraded by waveshapes in which more time was spent under a tensile strain hold than under a...Air Force Flight Dynamics Laboratory, Wright-Patterson AFB, OH, 1970), pp. 301 -311. 13. H. L. Bernstein, "An Evaluation of Four Models for the Creep

  5. Systemically administered AAV9-sTRAIL combats invasive glioblastoma in a patient-derived orthotopic xenograft model

    Directory of Open Access Journals (Sweden)

    Matheus HW Crommentuijn

    2016-01-01

    Full Text Available Adeno-associated virus (AAV vectors expressing tumoricidal genes injected directly into brain tumors have shown some promise, however, invasive tumor cells are relatively unaffected. Systemic injection of AAV9 vectors provides widespread delivery to the brain and potentially the tumor/microenvironment. Here we assessed AAV9 for potential glioblastoma therapy using two different promoters driving the expression of the secreted anti-cancer agent sTRAIL as a transgene model; the ubiquitously active chicken β-actin (CBA promoter and the neuron-specific enolase (NSE promoter to restrict expression in brain. Intravenous injection of AAV9 vectors encoding a bioluminescent reporter showed similar distribution patterns, although the NSE promoter yielded 100-fold lower expression in the abdomen (liver, with the brain-to-liver expression ratio remaining the same. The main cell types targeted by the CBA promoter were astrocytes, neurons and endothelial cells, while expression by NSE promoter mostly occurred in neurons. Intravenous administration of either AAV9-CBA-sTRAIL or AAV9-NSE-sTRAIL vectors to mice bearing intracranial patient-derived glioblastoma xenografts led to a slower tumor growth and significantly increased survival, with the CBA promoter having higher efficacy. To our knowledge, this is the first report showing the potential of systemic injection of AAV9 vector encoding a therapeutic gene for the treatment of brain tumors.

  6. A low cycle fatigue model for low carbon manganese steel including the effect of dynamic strain aging

    Energy Technology Data Exchange (ETDEWEB)

    Huang, Zhi Yong, E-mail: huangzy@scu.edu.cn [Sichuan University, School of Aeronautics and Astronautics, No.29 Jiuyanqiao Wangjiang Road, Chengdu 610064 (China); Wagner, Danièle [Université Paris Ouest Nanterre La Défense (France); Wang, Qing Yuan; Khan, Muhammad Kashif [Sichuan University, School of Aeronautics and Astronautics, No.29 Jiuyanqiao Wangjiang Road, Chengdu 610064 (China); Chaboche, Jean–Louis [ONERA, DMSM, 29 avenue de la Division Lecerc, F-92320, Chatillon (France)

    2016-01-27

    Carbon–manganese steel A48 (French standards) is used in steam generator pipes of the nuclear power plant where it is subjected to the cyclic thermal load. The Dynamic Strain Aging (DSA) influences the mechanical behavior of the steel in low cycle fatigue (LCF) at favorable temperature and strain rate. The peak stress of A48 steel experiences hardening–softening–hardening (HSH) evolution at 200 °C and 0.4% s{sup −1} strain rate in fatigue loading. In this study, isotropic and kinematic hardening rules with DSA effect have been modified. The HSH evolution of cyclic stress associated with cumulative plastic deformation has also been estimated.

  7. 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

  8. Beneficial Effect of Brewers' Yeast Extract on Daily Activity in a Murine Model of Chronic Fatigue Syndrome

    Directory of Open Access Journals (Sweden)

    Takashi Takahashi

    2006-01-01

    Full Text Available The aim of this study was to assess the effect of Brewers' yeast extract (BYE on daily activity in a mouse model of chronic fatigue syndrome (CFS. CFS was induced by repeated injection of Brucella abortus (BA antigen every 2 weeks. BYE was orally administered to mice in a dose of 2 g per kg per day for 2 weeks before injecting BA and for 4 weeks thereafter. We evaluated daily running activity in mice receiving BYE as compared with that in untreated mice. Weekly variation of body weight (BW and survival in both groups was monitored during the observation period. Spleen weight (SW, SW/BW ratio, percent splenic follicular area and expression levels of interferon-γ (IFN-γ and interleukin-10 (IL-10 mRNA in spleen were determined in both groups at the time of sacrifice. The daily activity during 2 weeks after the second BA injection was significantly higher in the treated group than in the control. There was no difference in BW between both groups through the experimental course. Two mice in the control died 2 and 7 days after the second injection, whereas no mice in the treated group died. Significantly decreased SW and SW/BW ratio were observed in the treated mice together with elevation of splenic follicular area. There were suppressed IFN-γ and IL-10 mRNA levels in spleens from the treated mice. Our results suggest that BYE might have a protective effect on the marked reduction in activity following repeated BA injection via normalization of host immune responses.

  9. Beneficial effect of brewers' yeast extract on daily activity in a murine model of chronic fatigue syndrome.

    Science.gov (United States)

    Takahashi, Takashi; Yu, Fei; Zhu, Shi-Jie; Moriya, Junji; Sumino, Hiroyuki; Morimoto, Shigeto; Yamaguchi, Nobuo; Kanda, Tsugiyasu

    2006-03-01

    The aim of this study was to assess the effect of Brewers' yeast extract (BYE) on daily activity in a mouse model of chronic fatigue syndrome (CFS). CFS was induced by repeated injection of Brucella abortus (BA) antigen every 2 weeks. BYE was orally administered to mice in a dose of 2 g per kg per day for 2 weeks before injecting BA and for 4 weeks thereafter. We evaluated daily running activity in mice receiving BYE as compared with that in untreated mice. Weekly variation of body weight (BW) and survival in both groups was monitored during the observation period. Spleen weight (SW), SW/BW ratio, percent splenic follicular area and expression levels of interferon-gamma (IFN-gamma) and interleukin-10 (IL-10) mRNA in spleen were determined in both groups at the time of sacrifice. The daily activity during 2 weeks after the second BA injection was significantly higher in the treated group than in the control. There was no difference in BW between both groups through the experimental course. Two mice in the control died 2 and 7 days after the second injection, whereas no mice in the treated group died. Significantly decreased SW and SW/BW ratio were observed in the treated mice together with elevation of splenic follicular area. There were suppressed IFN-gamma and IL-10 mRNA levels in spleens from the treated mice. Our results suggest that BYE might have a protective effect on the marked reduction in activity following repeated BA injection via normalization of host immune responses.

  10. Decay in chest compression quality due to fatigue is rare during prolonged advanced life support in a manikin model

    Directory of Open Access Journals (Sweden)

    Bjørshol Conrad A

    2011-08-01

    Full Text Available Abstract Background The aim of this study was to measure chest compression decay during simulated advanced life support (ALS in a cardiac arrest manikin model. Methods 19 paramedic teams, each consisting of three paramedics, performed ALS for 12 minutes with the same paramedic providing all chest compressions. The patient was a resuscitation manikin found in ventricular fibrillation (VF. The first shock terminated the VF and the patient remained in pulseless electrical activity (PEA throughout the scenario. Average chest compression depth and rate was measured each minute for 12 minutes and divided into three groups based on chest compression quality; good (compression depth ≥ 40 mm, compression rate 100-120/minute for each minute of CPR, bad (initial compression depth 120/minute or decay (change from good to bad during the 12 minutes. Changes in no-flow ratio (NFR, defined as the time without chest compressions divided by the total time of the ALS scenario over time was also measured. Results Based on compression depth, 5 (26%, 9 (47% and 5 (26% were good, bad and with decay, respectively. Only one paramedic experienced decay within the first two minutes. Based on compression rate, 6 (32%, 6 (32% and 7 (37% were good, bad and with decay, respectively. NFR was 22% in both the 1-3 and 4-6 minute periods, respectively, but decreased to 14% in the 7-9 minute period (P = 0.002 and to 10% in the 10-12 minute period (P Conclusions In this simulated cardiac arrest manikin study, only half of the providers achieved guideline recommended compression depth during prolonged ALS. Large inter-individual differences in chest compression quality were already present from the initiation of CPR. Chest compression decay and thereby fatigue within the first two minutes was rare.

  11. Modeling Fatigue Damage Onset and Progression in Composites Using an Element-Based Virtual Crack Closure Technique Combined With the Floating Node Method

    Science.gov (United States)

    De Carvalho, Nelson V.; Krueger, Ronald

    2016-01-01

    A new methodology is proposed to model the onset and propagation of matrix cracks and delaminations in carbon-epoxy composites subject to fatigue loading. An extended interface element, based on the Floating Node Method, is developed to represent delaminations and matrix cracks explicitly in a mesh independent fashion. Crack propagation is determined using an element-based Virtual Crack Closure Technique approach to determine mixed-mode energy release rates, and the Paris-Law relationship to obtain crack growth rate. Crack onset is determined using a stressbased onset criterion coupled with a stress vs. cycle curve and Palmgren-Miner rule to account for fatigue damage accumulation. The approach is implemented in Abaqus/Standard® via the user subroutine functionality. Verification exercises are performed to assess the accuracy and correct implementation of the approach. Finally, it was demonstrated that this approach captured the differences in failure morphology in fatigue for two laminates of identical stiffness, but with layups containing ?deg plies that were either stacked in a single group, or distributed through the laminate thickness.

  12. Research on sand pile model of cumulative fatigue damage%沙堆疲劳损伤累积模型的研究

    Institute of Scientific and Technical Information of China (English)

    温洁明; 陈国军; 陈家权; 吴燕瑞; 赵政飞

    2011-01-01

    由于材料具有循环硬化与软化、循环蠕变与松弛等特性,导致其在变幅循环应力作用下的疲劳损伤与加载顺序密切相关.国内外研究者提出了许多损伤累积模型,但有些模型未明确地阐述加载顺序的影响.通过分析影响疲劳损伤的重要因素,提出伴随损伤、视在损伤和耦合损伤新概念,结合模糊理论定量计算由耦合效应引起的耦合损伤,建立了一个能考虑加载顺序对疲劳损伤累积影响的沙堆疲劳损伤累积模型.选取16Mn和316L不锈钢材料的试验数据进行疲劳寿命预测,分析结果表明,所建立的模型能适用于不同加载顺序下的疲劳损伤累积计算,L-H和H-L两种加载顺序下疲劳寿命的预测结果与试验结果吻合良好,其寿命预测误差分散带基本在2倍因子内,预测精度高,便于工程应用.%The fatigue damage under variable amplitude cyclic stress is closely related with the loading sequence because of the cyclic hardening and softening cyclic creep and relaxation, and other characteristics of materials. Many domestic and foreign researchers have proposed models of damage accumulation, but some models are not explicitly described effect of the loading sequence.Therefore, new concepts of the adjoining damage, apparent damage and coupled damage were proposed by analyzing key factors affecting fatigue damage. Coupled damage produced by coupled effect was calculated quantitatively with the fuzzy theory. The sand pile model of cumulative fatigue damage is built by taking into account the effects of fatigue damage accumulation of loading sequence.Fatigue lives of 16Mn and 316L stainless steel were predicted and compared with test data. The results showed that the model can be applied to different loading sequence for calculating accumulative fatigue damage. Predicted results of fatigue life under two sequences of L-H and H-L were in good agreement with experimental ones. Scatter band of predicted

  13. Thermal Acoustic Fatigue Apparatus

    Data.gov (United States)

    Federal Laboratory Consortium — The Thermal Acoustic Fatigue Apparatus (TAFA) is a progressive wave tube test facility that is used to test structures for dynamic response and sonic fatigue due to...

  14. Insomnia and Fatigue

    Science.gov (United States)

    ... Styles Common Yoga Poses Special Situations Yoga and Lymphedema Risk Yoga and Metastatic Breast Cancer Side Effects ... Insomnia and Fatigue Treatment for Insomnia and Fatigue Lymphedema Lymphedema Risk Treating Lymphedema Menopausal Symptoms Mouth Sores ...

  15. Tensile and Fatigue Testing and Material Hardening Model Development for 508 LAS Base Metal and 316 SS Similar Metal Weld under In-air and PWR Primary Loop Water Conditions

    Energy Technology Data Exchange (ETDEWEB)

    Mohanty, Subhasish [Argonne National Lab. (ANL), Argonne, IL (United States); Soppet, William [Argonne National Lab. (ANL), Argonne, IL (United States); Majumdar, Saurin [Argonne National Lab. (ANL), Argonne, IL (United States); Natesan, Ken [Argonne National Lab. (ANL), Argonne, IL (United States)

    2015-09-01

    This report provides an update on an assessment of environmentally assisted fatigue for light water reactor components under extended service conditions. This report is a deliverable in September 2015 under the work package for environmentally assisted fatigue under DOE’s Light Water Reactor Sustainability program. In an April 2015 report we presented a baseline mechanistic finite element model of a two-loop pressurized water reactor (PWR) for systemlevel heat transfer analysis and subsequent thermal-mechanical stress analysis and fatigue life estimation under reactor thermal-mechanical cycles. In the present report, we provide tensile and fatigue test data for 508 low-alloy steel (LAS) base metal, 508 LAS heat-affected zone metal in 508 LAS–316 stainless steel (SS) dissimilar metal welds, and 316 SS-316 SS similar metal welds. The test was conducted under different conditions such as in air at room temperature, in air at 300 oC, and under PWR primary loop water conditions. Data are provided on materials properties related to time-independent tensile tests and time-dependent cyclic tests, such as elastic modulus, elastic and offset strain yield limit stress, and linear and nonlinear kinematic hardening model parameters. The overall objective of this report is to provide guidance to estimate tensile/fatigue hardening parameters from test data. Also, the material models and parameters reported here can directly be used in commercially available finite element codes for fatigue and ratcheting evaluation of reactor components under in-air and PWR water conditions.

  16. Empirical modelling of the dynamic response of fatigue during intermittent submaximal contractions of human forearm and calf muscles.

    Science.gov (United States)

    Green, Simon; Stefanovic, Brad; Warman, Joel; Askew, Christopher D

    2015-02-01

    Maximum force (Fmax) declines during intermittent submaximal contractions, but the linearity of this fatigue response and number of underlying phases is not clear. Healthy men were studied during two experiments (n=10 each). Experiment 1 involved single bouts of intermittent forearm contractions (50% Fmax) to failure using both limbs assigned as Armcontrol or Armtraining. Experiment 2 involved five bouts of intermittent calf contractions (60% Fmax) to failure using the same limb where data from the longest single trial (Calfsingle) or averaged across five bouts (Calfaveraged) were analysed. Fmax was assessed at 25-30s intervals during exercise and fitted to ten mono- and biphasic functions consisting of linear and/or nonlinear terms. For each fatigue response, the function which provided the best fit was determined on statistical grounds. Biphasic functions provided the majority of best fits during Armcontrol (9/10), Armtraining (10/10), Calfsingle (7/10) and Calfaveraged (9/10). For each condition, linear functions provided the best fit in 4-5 out of 10 responses. Two biphasic functions differentiated only by their first term (linear versus exponential) provided the best fit for 29/40 fatigue responses. These outcomes suggest that fatigue during intermittent contractions exhibits a biphasic response characterised by nonlinear and linear behaviour.

  17. Using agility to combat cyber attacks.

    Science.gov (United States)

    Anderson, Kerry

    2017-06-01

    Some incident response practitioners feel that they have been locked in a battle with cyber criminals since the popular adoption of the internet. Initially, organisations made great inroads in preventing and containing cyber attacks. In the last few years, however, cyber criminals have become adept at eluding defence security technologies and rapidly modifying their exploit strategies for financial or political gains. Similar to changes in military combat tactics, cyber criminals utilise distributed attack cells, real-time communications, and rapidly mutating exploits to minimise the potential for detection. Cyber criminals have changed their attack paradigm. This paper describes a new incident response paradigm aimed at combating the new model of cyber attacks with an emphasis on agility to increase the organisation's ability to respond rapidly to these new challenges.

  18. Combating trafficking: the Swiss approach

    Directory of Open Access Journals (Sweden)

    Sebastian Rauber

    2006-05-01

    Full Text Available Switzerland is committed to combating and preventingtrafficking in human beings. Effective policy implementationin a federal structure depends on networking,effective information exchange and development ofrobust cooperation mechanisms.

  19. Advanced Capabilities for Combat Medics

    National Research Council Canada - National Science Library

    Convertino, Victor A; Cooke, William H; Salinas, Jose; Holcomb, John B

    2004-01-01

    The US Army Institute of Surgical Research (USAISR) has the lead for directing the Research Program Area for Advanced Triage Capabilities for Combat Medics in the Medical Research and Materiel Command (MRMC...

  20. Optimal Fatigue Testing

    DEFF Research Database (Denmark)

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

    1993-01-01

    This paper considers the reassessment of the reliability of tubular joints subjected to fatigue load. The reassessment is considered in two parts namely the task of utilizing new experimental data on fatigue life to update the reliability of the tubular joint ant the task of planning new fatigue ...

  1. Evidence of Combat in Triceratops

    OpenAIRE

    Andrew A Farke; Wolff, Ewan D. S.; Tanke, Darren H.

    2009-01-01

    BACKGROUND: The horns and frill of Triceratops and other ceratopsids (horned dinosaurs) are interpreted variously as display structures or as weapons against conspecifics and predators. Lesions (in the form of periosteal reactive bone, healing fractures, and alleged punctures) on Triceratops skulls have been used as anecdotal support of intraspecific combat similar to that in modern horned and antlered animals. If ceratopsids with different cranial morphologies used their horns in such combat...

  2. O combate ao escorpionismo

    Directory of Open Access Journals (Sweden)

    Octavio de Magalhães

    1946-09-01

    Full Text Available O outor estuda os processos de combate aos acidentes pelas picadas dos escorpiões, visando: a Profilaxia e b Terapêutica. Refere-se à luta nos campos e nas cidades e aqui, dentro e fora dos domicílios. Assinala os diferentes métodos para o combate a êsses artrópodos peçonhentos. Fala na luta direta, indireta, na vacinação pelo anaveneno, na propaganda pela educação racional da população contra o perigo dos acidentes. Refere-se à "cata" dos escorpiões, à luta química, ao emprêgo de animais escorpiófagos, á feitura de casas e jardins anti-escorpiões. Na primeira parte do presente trabalho o autor trata da luta química pelo d. D. T. contra os tityus bahiensis e serrulatus, concluindo que êste corpo químico é um poderoso elemento de luta contra êstes escorpiões. Na segunda parte do trabalho, o autor trata da terapêutica dos acidentes. Mostra a necessidade do emprêgo convenientemente da única terapêutica racional e eficaz contra a intoxicação escorpiônica: a soroterapia específica. Assinala a necessidade da injeção de doses maciças de um sôro de alta valência, preparado em bovídeos, para evitar o mais possível o choque anafilático, no menor tempo possível após as picadas. Aconselha o empêgo de anaveneno escorpiônico, para vacinação principalmente de crianças de baixa idade, nos lugares fortemente infestados pelos escorpiões (principalmente Tityus serrulatus, maximé quando no local não houver sôro anti-escorpiônico específico, como meio preventivo contra a gravidade das intoxicações. Cita finalmente os trabalhos recentes de Grasset, Shaasfsma e Hodgson, na África do Sul, que confirmam muitas idéias do autor e mostram a unidade universal do síndromo escorpiônico descrito no Brasil.

  3. Application of the Janus Combat Model for analysis of alternatives : a study of the operational effectiveness of the common missile as compared to the Hellfire

    OpenAIRE

    2002-01-01

    Approved for public release; distribution is unlimited By 2010, 100 percent of the existing stockpile of Hellfire and TOW 2A/2B missiles will reach their design shelf life. The stock of Hellfire missiles available to support Army air-to-ground combat will be depleted by 2015. Of particular interest to the Aviation community is the Comanche first unit equipped (FUE) in 2009, which will be significantly impacted by the scarcity and condition of this primary weapon. This research employs the ...

  4. Rethinking Posse Comitatus: The Use of Military Force in Combating Urban Crime Using British Royal Marines in Northern Ireland as a Model

    Science.gov (United States)

    1996-01-01

    leaders of two rival black gangs , the Bloods and the Cryps, met to establish an unprecedented truce so that they could focus their efforts jointly against...percent of all homicides in Los Angeles County.56 In Los Angeles the Crips and the Bloods have an estimated 70,000 members with franchises in most...criminal behavior portend increased demands for assistance from the military to combat gang wars, drug wars and other violent crimes. Recommendation

  5. Fatigue Damage Accumulation of Steel/rubber Composite

    Institute of Scientific and Technical Information of China (English)

    Zhenhui TIAN; Huifeng TAN; Xingwen DU

    2006-01-01

    The fatigue damage accumulation of [±20°] laminated steel cord reinforced rubber composite under T-T loading was studied. Results indicate that the increase in the cyclic maximum strain exhibits three-stage tendency in the process of fatigue. The macroscopic fatigue damage initiates from the ends of steel cords in the form of cylindrical crack. Damage propagates along with the increase in crack numbers, the cord/matrix interface debonding and the growth of interply cracks. By using the dynamic creep as parameter, a linear fatigue damage accumulation model was established. This model can be used under dual loading conditions to estimate the residual fatigue life of the specimen.

  6. Mixed-mode fatigue fracture of adhesive joints in harsh environments and nonlinear viscoelastic modeling of the adhesive

    Science.gov (United States)

    Arzoumanidis, Alexis Gerasimos

    A four point bend, mixed-mode, reinforced, cracked lap shear specimen experimentally simulated adhesive joints between load bearing composite parts in automotive components. The experiments accounted for fatigue, solvent and temperature effects on a swirled glass fiber composite adherend/urethane adhesive system. Crack length measurements based on compliance facilitated determination of da/dN curves. A digital image processing technique was also utilized to monitor crack growth from in situ images of the side of the specimen. Linear elastic fracture mechanics and finite elements were used to determine energy release rate and mode-mix as a function of crack length for this specimen. Experiments were conducted in air and in a salt water bath at 10, 26 and 90°C. Joints tested in the solvent were fully saturated. In air, both increasing and decreasing temperature relative to 26°C accelerated crack growth rates. In salt water, crack growth rates increased with increasing temperature. Threshold energy release rate is shown to be the most appropriate design criteria for joints of this system. In addition, path of the crack is discussed and fracture surfaces are examined on three length scales. Three linear viscoelastic properties were measured for the neat urethane adhesive. Dynamic tensile compliance (D*) was found using a novel extensometer and results were considerably more accurate and precise than standard DMTA testing. Dynamic shear compliance (J*) was determined using an Arcan specimen. Dynamic Poisson's ratio (nu*) was extracted from strain gage data analyzed to include gage reinforcement. Experiments spanned three frequency decades and isothermal data was shifted by time-temperature superposition to create master curves spanning thirty decades. Master curves were fit to time domain Prony series. Shear compliance inferred from D* and nu* compared well with measured J*, forming a basis for finding the complete time dependent material property matrix for this

  7. Probabilistic fatigue methodology and wind turbine reliability

    Energy Technology Data Exchange (ETDEWEB)

    Lange, C.H. [Stanford Univ., CA (United States)

    1996-05-01

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

  8. Cumulative creep fatigue damage in 316 stainless steel

    Science.gov (United States)

    Mcgaw, Michael A.

    1989-01-01

    The cumulative creep-fatigue damage behavior of 316 stainless steel at 1500 F was experimentally established for the two-level loading cases of fatigue followed by fatigue, creep fatigue followed by fatigue, and fatigue followed by creep fatigue. The two-level loadings were conducted such that the lower life (high strain) cycling was applied first for a controlled number of cycles and the higher life (low strain) cycling was conducted as the second level to failure. The target life levels in this study were 100 cycles to failure for both the fatigue and creep-fatigue lowlife loading, 5000 cycles to failure for the higher life fatigue loading and 10,000 cycles to failure for the higher life creep-fatigue loading. The failed specimens are being examined both fractographically and metallographically to ascertain the nature of the damaging mechanisms that produced failure. Models of creep-fatigue damage accumulation are being evaluated and knowledge of the various damaging mechanisms is necessary to ensure that predictive capability is instilled in the final failure model.

  9. Damage identity in fatigue assessment of structures

    Directory of Open Access Journals (Sweden)

    S.V. Petinov

    2016-04-01

    Full Text Available The modified strain criterion-based method for fatigue assessment of structures is discussed. The damage is estimated based on the specified parameters of the criterion and the damage summation procedure by employing the finite-element method. With a reasonably fine mesh of the finiteelement model of the ‘critical location’ structure, the condition of the identity of damage in the material of the test specimen and the structure is provided and, respectively, the effect of uncertainty on the fatigue life assessment of the structure is reduced. The implementation of this version of the method is using the example of the fatigue life evaluation of a ship hull and superstructure detail at expansion joint. For comparison, the fatigue life of the detail is estimated using the standard S-N approach. The results are in approximate agreement; however, reducing the computational uncertainties with the help of the deformation criterion shows more physically reasonable fatigue properties of the detail.

  10. 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...... failure explanation under fatigue and static load conditions is observed. In the present study 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 between stiffness reduction...

  11. Time Domain Modeling and Analysis of Dynamic Gear Contact Force in a Wind Turbine Gearbox with Respect to Fatigue Assessment

    Directory of Open Access Journals (Sweden)

    Torgeir Moan

    2012-11-01

    Full Text Available The gearbox is one of the most expensive components of the wind turbine system. In order to refine the design and hence increase the long-term reliability, there has been increasing interest in utilizing time domain simulations in the prediction of gearbox design loads. In this study, three problems in time domain based gear contact fatigue analysis under dynamic conditions are discussed: (1 the torque reversal problem under low wind speed conditions, (2 statistical uncertainty effects due to time domain simulations and (3 simplified long term contact fatigue analysis of the gear tooth under dynamic conditions. Several recommendations to deal with these issues are proposed based on analyses of the National Renewable Energy Laboratory’s 750 kW land-based Gearbox Reliability Collaborative wind turbine.

  12. Modeling Cyclic Fatigue Hysteresis Loops of 2D Woven Ceramic Matrix Composites at Elevated Temperatures in Steam

    Directory of Open Access Journals (Sweden)

    Longbiao Li

    2016-05-01

    Full Text Available In this paper, the cyclic fatigue hysteresis loops of 2D woven SiC/SiC ceramic matrix composites (CMCs at elevated temperatures in steam have been investigated. The interface slip between fibers and the matrix existing in matrix cracking modes 3 and 5, in which matrix cracking and interface debonding occurred in longitudinal yarns, is considered as the major reason for hysteresis loops of 2D woven CMCs. The hysteresis loops of 2D SiC/SiC composites corresponding to different peak stresses, test conditions, and loading frequencies have been predicted using the present analysis. The damage parameter, i.e., the proportion of matrix cracking mode 3 in the entire matrix cracking modes of the composite, and the hysteresis dissipated energy increase with increasing fatigue peak stress. With increasing cycle number, the interface shear stress in the longitudinal yarns decreases, leading to transition of interface slip types of matrix cracking modes 3 and 5.

  13. Towards Whole Body Fatigue Assessment of Human Movement: A Fatigue-Tracking System Based on Combined sEMG and Accelerometer Signals

    Directory of Open Access Journals (Sweden)

    Haiwei Dong

    2014-01-01

    Full Text Available This paper proposes a method to assess the overall fatigue of human body movement. First of all, according to previous research regarding localized muscular fatigue, a linear relation is assumed between the mean frequency and the muscular working time when the muscle is experiencing fatigue. This assumption is verified with a rigorous statistical analysis. Based on this proven linearity, localized muscular fatigue is simplified as a linear model. Furthermore, localized muscular fatigue is considered a dynamic process and, hence, the localized fatigue levels are tracked by updating the parameters with the most current surface electromyogram (sEMG measurements. Finally, an overall fatigue level is computed by fusing localized muscular fatigue levels. The developed fatigue-tracking system is evaluated with two fatigue experiments (in which 10 male subjects and seven female subjects participated, including holding self-weight (dip start position training and lifting weight with one arm (arm curl training.

  14. Experimental and Finite Element Modeling of Near-Threshold Fatigue Crack Growth for the K-Decreasing Test Method

    Science.gov (United States)

    Smith, Stephen W.; Seshadri, Banavara R.; Newman, John A.

    2015-01-01

    The experimental methods to determine near-threshold fatigue crack growth rate data are prescribed in ASTM standard E647. To produce near-threshold data at a constant stress ratio (R), the applied stress-intensity factor (K) is decreased as the crack grows based on a specified K-gradient. Consequently, as the fatigue crack growth rate threshold is approached and the crack tip opening displacement decreases, remote crack wake contact may occur due to the plastically deformed crack wake surfaces and shield the growing crack tip resulting in a reduced crack tip driving force and non-representative crack growth rate data. If such data are used to life a component, the evaluation could yield highly non-conservative predictions. Although this anomalous behavior has been shown to be affected by K-gradient, starting K level, residual stresses, environmental assisted cracking, specimen geometry, and material type, the specifications within the standard to avoid this effect are limited to a maximum fatigue crack growth rate and a suggestion for the K-gradient value. This paper provides parallel experimental and computational simulations for the K-decreasing method for two materials (an aluminum alloy, AA 2024-T3 and a titanium alloy, Ti 6-2-2-2-2) to aid in establishing clear understanding of appropriate testing requirements. These simulations investigate the effect of K-gradient, the maximum value of stress-intensity factor applied, and material type. A material independent term is developed to guide in the selection of appropriate test conditions for most engineering alloys. With the use of such a term, near-threshold fatigue crack growth rate tests can be performed at accelerated rates, near-threshold data can be acquired in days instead of weeks without having to establish testing criteria through trial and error, and these data can be acquired for most engineering materials, even those that are produced in relatively small product forms.

  15. Numerical modeling of hydrogen diffusion in structural steels under cathodic overprotection and its effects on fatigue crack propagation

    Energy Technology Data Exchange (ETDEWEB)

    Silva Diniz, D.; Almeida Silva, A. [Federal University of Campina Grande, Campina Grande-PB (Brazil); Andrade Barbosa, J.M. [Federal University of Pernambuco, Recife-PE (Brazil); Palma Carrasco, J.

    2012-05-15

    This paper presents a numerical simulation of the effect of hydrogen atomic diffusion on fatigue crack propagation on structural steels. The simulation was performed with a specimen type CT of API 5CT P110 steel, loaded in the tensile opening mode, in plane strain state and under the effects of a cyclic mechanical load and the hydrogen concentration at the crack tip. As hydrogen source, a cathodic protection system was considered, commonly used in subsea pipelines. The equations of evolution of variables at the crack tip form a non-linear system of ordinary differential equations that was solved by means of the 4th order Runge-Kutta method. The solid-solid diffusion through the lattice ahead of the crack tip was simulated using the finite difference method. The simulations results show that under these conditions, the fatigue crack evolution process is enhanced by the hydrogen presence in the material, and that the start time of the crack propagation decreases as its concentration increases. These results show good correlation and consistency with macroscopic observations, providing a better understanding of hydrogen embrittlement in fatigue crack propagation processes in structural steels. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  16. Needs and Concerns of Male Combat Veterans with Mild Traumatic Brain Injury

    Science.gov (United States)

    2013-01-01

    fatigue and/ or insomnia, and tinnitus ) and emotions and behaviors (anger, fear, and depression ). These symptoms are directly related to the...mirror those of other disorders such as post- traumatic stress disorder (PTSD), depression , anxiety disorder, and adjustment disorder, all of which can...applicable to Veterans with mTBI, there may be addi- tional needs and concerns specifically related to combat, such as PTSD, depressive symptoms, anxiety

  17. Empirical Analysis of Operation Iraqi Freedom Combat Mortality Using the Navy-Marine Corps Combat Trauma Registry Expeditionary Medical Encounter Database for Applications to Tactical Medical Logistics Modeling and Simulation

    Science.gov (United States)

    2009-05-15

    Methods to more accurately forecast medical needs and effectively meet those needs are constantly being developed to support service-related modeling and...Self Non-Accident Sports/Recreation Training Unknown Other: N/A Glasgow Coma Scale (Circle each) Eye Opening Verbal...Methods to more accurately forecast medical needs, for example by tactical medical logistics modeling and simulation, are constantly being developed

  18. Study on combat effectiveness of air defense missile weapon system based on queuing theory

    Science.gov (United States)

    Zhao, Z. Q.; Hao, J. X.; Li, L. J.

    2017-01-01

    Queuing Theory is a method to analyze the combat effectiveness of air defense missile weapon system. The model of service probability based on the queuing theory was constructed, and applied to analyzing the combat effectiveness of "Sidewinder" and "Tor-M1" air defense missile weapon system. Finally aimed at different targets densities, the combat effectiveness of different combat units of two types' defense missile weapon system is calculated. This method can be used to analyze the usefulness of air defense missile weapon system.

  19. A pilot study of the use of kaolin-impregnated gauze (Combat Gauze) for packing high-grade hepatic injuries in a hypothermic coagulopathic swine model.

    Science.gov (United States)

    Sena, Matthew J; Douglas, Geoffrey; Gerlach, Travis; Grayson, J Kevin; Pichakron, Kullada O; Zierold, Dustin

    2013-08-01

    Severe hepatic injuries may be highly lethal, and perihepatic packing remains the mainstay of treatment. This is not always successful, particularly in the setting of hypothermia and coagulopathy. Kaolin-impregnated Combat Gauze (CG) is an effective hemostatic dressing used primarily to treat external wounds. The objective of this study was to determine the ability of CG to control severe hemorrhage in hypothermic, coagulopathic swine with a high-grade hepatic injury. Anesthetized animals underwent splenectomy and were cooled to 32°C while undergoing a 60% exchange transfusion with Hextend. A grade V liver injury was created in the left middle hepatic lobe. Animals were allowed to freely bleed for 30 s and then randomized to treatment with CG or plain gauze laparotomy pads (PG) applied to the injury site. Animals were then resuscitated with warmed Hextend. There was no difference between groups in preinjury hemodynamic or laboratory values. Animals packed with CG had less blood loss when compared with standard packing (CG = 25 mL/kg versus PG = 58 mL/kg, P = 0.05). There was a trend towards lower hetastarch resuscitation requirements in the CG group (CG = 7 mL/kg versus PG = 44 mL/kg, P = 0.06) but no statistically significant difference in mortality (CG = 13% versus PG = 50%, P = 0.11). Histology of the injury sites revealed more adherent clot in the CG group, but no inflammation, tissue necrosis, or residual material. In pigs with severe hepatic injury, Combat Gauze reduced blood loss and resuscitation requirements when compared with plain laparotomy pads. Combat Gauze may be safe and effective for use on severe liver injuries. Published by Elsevier Inc.

  20. Multiaxial fatigue low cycle fatigue testing

    Science.gov (United States)

    Zamrik, S. Y.

    1985-01-01

    Multiaxial testing methods are reviewed. Advantages and disadvantages of each type test is discussed. Significant multiaxial data available in the literature is analyzed. The yield theories are compared for multiaxial fatigue analysis.

  1. Fatigue and cardiorespiratory function following abdominal surgery.

    Science.gov (United States)

    Christensen, T; Bendix, T; Kehlet, H

    1982-07-01

    Subjective feelings of fatigue were assessed before operation and 10, 20 and 30 days after uncomplicated elective abdominal surgery in 16 otherwise healthy patients, using a constructed fatigue scale model. In addition, all patients had an orthostatic stress test performed at the same times. Six of the patients also underwent a bicycle ergometer test measuring heart rate and oxygen consumption. Subjective feelings of fatigue were increased (P less than 0.01) at all three postoperative observations, and only 5 of 16 patients returned to their preoperative level. The increased subjective feeling of fatigue correlated positively (RS = 0.53, P less than 0.001) with the increased pulse rate seen during orthostatic stress after operation. Heart rate was about 5 per cent higher (n.s.) after operation when bicycling at the same work loads, while oxygen consumption decreased by about 2 per cent (P less than 0.01) at all three postoperative bicycle tests. It is concluded that even electric uncomplicated abdominal surgery is followed by a pronounced feeling of fatigue, which may persist 1 month after surgery in about one-third of patients. The fatigue scale model seems applicable for future studies on the pathogenesis and treatment of the postoperative fatigue syndrome.

  2. Fatigue crack propagation analysis of plaque rupture.

    Science.gov (United States)

    Pei, Xuan; Wu, Baijian; Li, Zhi-Yong

    2013-10-01

    Rupture of atheromatous plaque is the major cause of stroke or heart attack. Considering that the cardiovascular system is a classic fatigue environment, plaque rupture was treated as a chronic fatigue crack growth process in this study. Fracture mechanics theory was introduced to describe the stress status at the crack tip and Paris' law was used to calculate the crack growth rate. The effect of anatomical variation of an idealized plaque cross-section model was investigated. The crack initiation was considered to be either at the maximum circumferential stress location or at any other possible locations around the lumen. Although the crack automatically initialized at the maximum circumferential stress location usually propagated faster than others, it was not necessarily the most critical location where the fatigue life reached its minimum. We found that the fatigue life was minimum for cracks initialized in the following three regions: the midcap zone, the shoulder zone, and the backside zone. The anatomical variation has a significant influence on the fatigue life. Either a decrease in cap thickness or an increase in lipid pool size resulted in a significant decrease in fatigue life. Comparing to the previously used stress analysis, this fatigue model provides some possible explanations of plaque rupture at a low stress level in a pulsatile cardiovascular environment, and the method proposed here may be useful for further investigation of the mechanism of plaque rupture based on in vivo patient data.

  3. Low-cycle fatigue of surgical cements

    Directory of Open Access Journals (Sweden)

    A. Balin

    2007-01-01

    Full Text Available Purpose: In case when surgical cement is used to fix endoprostheses of joints the fatigue character of mechanicalinterraction in the cement seems to be a significant importance. The paper suggests to adapt the research methodof low cycle fatigue for modelling the loads on surgical cements in an artificial hip joint. Surgical cements havealso been modified in order to improve their functional properties.Design/methodology/approach: Low cycle fatigue tests were conducted on samples made from Palamedcement without an addition and on samples modified with glassy carbon and titanium. The tests were conductedon a servohydraulic fatigue testing machine, MTS-810, with displacement control.Findings: Fatigue tests proved viscoelastic character of all the tested materials. During the fatigue tests, thephenomenon of stress cyclic relaxation was observed.Research limitations/implications: Modelling the loadings of cement in endoprostheses of joints with the lowcycle fatigue method takes into account all high value stresses, while cement is being used for endoprosthesesfor many years in the conditions of random stress and deformation courses. Therefore the obtained stress anddeformation values are bigger than those which would have been obtained in real conditions in the same time.Practical implications: The low cycle fatigue tests carried out showed how important is the factor of timefor the behavior of surgical cement in the conditions of changeable loadings. This fact is essential to assessits usability for endoprosthesoplasty of joints, specially of a hip joint. Post deformation return which is acharacteristic feature for material viscoelasticity enables its regeneration conditioning expected durability ofendoprosthesis of joints.Originality/value: Low cycle fatigue testing method for modelling of loads on surgical cement in artificial hipjoint enables to carry out the tests in a shorter period of time.

  4. COMBATING PIRACY: THE INDONESIAN CASE

    Directory of Open Access Journals (Sweden)

    Melda Kamil Ariadno

    2013-08-01

    Full Text Available Piracy at sea has been a threat to international navigation ever since the sea traverse by ships from west to east and north to south. Threat to international trade has resulted to various efforts in combating piracy regionally as well as internationally. International law has differentiated between piracy and sea-armed robbery, while the first requires regional or international cooperation due to universal jurisdiction, the second will directly fall under the jurisdiction of coastal state. Strait of Malacca has been used by international navigation and very fragile to the threat of piracy or even appropriately called as sea armed robbery since most of the time happened in the part of Indonesian territorial sea. Various efforts to combat piracy have been carried out by Indonesia including to cooperate with Malaysia and Singapore. This article discuss about piracy at sea, its legal definition and effort to combat piracy.

  5. Experimental characterization of fatigue crack tip processes

    Science.gov (United States)

    Lankford, J.; Leverant, G. R.

    1985-01-01

    Many analytical models have been proposed to describe the physical processes attendant to a fatigue crack tip, as well as the rate at which fatigue cracks grow. By applying advanced experimental methods (such as electron channeling, stereoimaging, and in-situ cyclic loading in an SEM) to a broad range of structural materials, it has been shown that it is possible to critically assess the physical assumptions incorporated into the models. Refinements in existing models and the development of new ones have resulted. New insights into materials' behavior are providing guidelines for improving the fatigue resistance of structural alloys. In the near future, even more advanced experimental methods, such as high temperature SEM stages and small angle neutron scattering, will be available to study creep/fatigue interactions in metals and ceramics.

  6. Neurologic Health in Combat Sports.

    Science.gov (United States)

    Seifert, Tad

    2017-08-01

    Neurologic injuries of both an acute and chronic nature have been reported in the literature for various combat sport styles; however, reports of the incidence and prevalence of these injury types vary greatly. Combat sports clinicians must continue to strive for the development, implementation, and enforcement of uniform minimum requirements for brain safety. These health care providers must also seize on the honor to provide this oft-underserved population with the health care advocacy they very much deserve, but often do not receive. Copyright © 2017 Elsevier Inc. All rights reserved.

  7. CPR PRO® device reduces rescuer fatigue during continuous chest compression cardiopulmonary resuscitation: a randomized crossover trial using a manikin model.

    Science.gov (United States)

    Kovic, Ivor; Lulic, Dinka; Lulic, Ileana

    2013-10-01

    The performance of high-quality chest compressions with minimal interruptions is one of the most important elements of the "Chain of Survival." To evaluate the impact of a novel CPR PRO(®) (CPRO) device for manual chest compression on rescuer fatigue, pain, and cardiopulmonary resuscitation (CPR) quality. Randomized crossover trial of 24 health care professionals performing continuous chest compression CPR for 10 min with a CPRO device and conventional manual CPR (MCPR). Data about chest compressions were recorded using a manikin. Rescuers' physiologic signs were recorded before and after each session, and heart rate (HR) data were tracked continuously. Fatigue was assessed with ratings of perceived exertion, and pain questionnaire. All subjects completed 10 min of CPR with both methods. Significantly more rest breaks were taken during MCPR sessions (1.7 ± 2 vs. 0.21 ± 0.72). Subjects' perceived exertion was higher after MCPR, as well as the average (120.7 ± 16.8 vs. 110.8 ± 17.6) and maximal HR (134.3 ± 18.5 vs. 123.42 ± 16.5) during testing. Subjects reported more pain in the hands, especially the wrist, after performing MCPR. Average depth of compressions was higher with the CPRO device (4.6 ± 7.0 vs. 4.3 ± 7.9) and declined more slowly over time. Other CPR quality parameters, such as the correct position and complete release of pressure, were also better for CPRO CPR. CPRO device reduces rescuer fatigue and pain during continuous chest compression CPR, which results in a higher quality of CPR in a simulation setting. Copyright © 2013 Elsevier Inc. All rights reserved.

  8. The central governor model of exercise regulation teaches us precious little about the nature of mental fatigue and self-control failure

    Directory of Open Access Journals (Sweden)

    Michael eInzlicht

    2016-05-01

    Full Text Available Self-control is considered broadly important for many domains of life. One of its unfortunate features, however, is that it tends to wane over time, with little agreement about why this is the case. Recently, there has been a push to address this problem by looking to the literature in exercise physiology, specifically the work on the central governor model of physical fatigue. Trying to explain how and why mental performance wanes over time, the central governor model suggests that exertion is throttled by some central nervous system mechanism that receives information about energetic bodily needs and motivational drives to regulate exertion and, ultimately, to prevent homeostatic breakdown, chiefly energy depletion. While we admire the spirit of integration and the attempt to shed light on an important topic in psychology, our concern is that the central governor model is very controversial in exercise physiologists, with increasing calls to abandon it altogether, making it a poor fit for psychology. Our concerns are threefold. First, while we agree that preservation of bodily homeostasis makes for an elegant ultimate account, the fact that such important homeostatic concerns can be regularly overturned with even slight incentives (e.g., a smile renders the ultimate account impotent and points to other ultimate functions for fatigue. Second, despite the central governor being thought to take as input information about the metabolic needs of the body, there is no credible evidence that mental effort actually consumes inordinate amounts of energy that are not already circulating in the brain. Third, recent modifications of the model make the central governor appear like an all-knowing homunculus and unfalsifiable in principle, thus contributing very little to our understanding of why people tend to disengage from effortful tasks over time. We note that the latest models in exercise physiology have actually borrowed concepts and models from

  9. Compassion fatigue in nurses.

    Science.gov (United States)

    Yoder, Elizabeth A

    2010-11-01

    Compassion fatigue, trigger situations, and coping strategies were investigated in hospital and home care nurses. The Professional Quality of Life Scale measured compassion fatigue, compassion satisfaction, and burnout. Narrative questions elicited trigger situations and coping strategies. Compassion fatigue scores were significantly different between nurses who worked 8- or 12-hour shifts. Fifteen percent of the participants had scores indicating risk of the compassion fatigue. There were significant differences in compassion satisfaction, depending on the unit worked and time as a nurse. The most common category of trigger situations was caring for the patient. Work-related and personal coping strategies were identified. Copyright © 2010 Elsevier Inc. All rights reserved.

  10. Myth vs. Fact: Adrenal Fatigue

    Science.gov (United States)

    ... unlikely to cover the costs. What is the theory behind adrenal fatigue? Supporters of adrenal fatigue believe ... by producing hormones like cortisol. According to the theory of adrenal fatigue, when people are faced with ...

  11. Chronic Fatigue Syndrome (CFS): Symptoms

    Science.gov (United States)

    ... CDC.gov . Chronic Fatigue Syndrome (CFS) Share Compartir Symptoms On this Page Primary Symptoms Other Symptoms What's ... a doctor distinguish CFS from other illnesses. Primary Symptoms As the name chronic fatigue syndrome suggests , fatigue ...

  12. Integrated physical training in combat sports

    Directory of Open Access Journals (Sweden)

    Raquel Hernández García

    2011-03-01

    Full Text Available AbstractThis paper aims to define the concepts of embedded training (EI and integrated fitness (PFI and the importance of these concepts have in training in combat sports. And define a set of guidelines and examples of PFI in the combat sport of judo.Key words: integrated training, integrated physical training, combat sports, judo

  13. Combat Injury Coding: A Review and Reconfiguration

    Science.gov (United States)

    2013-01-01

    characterize combat anatomic injury, and the Military Functional Incapacity Scale (MFIS), which indicates immediate tactical functional impairment, were...Combat Injury Scale and Military Functional Incapacity Scale were developed, tested and validated by teams of civilian and tri-service military expertise...characterizes the unique injuries encountered in combat, es- pecially those caused by explosions, and its derivative, the Military Functional Incapacity

  14. Damage Model of Interaction Between Fatigue and Creep for Asphalt Mixture%沥青混合料疲劳-蠕变交互作用损伤模型

    Institute of Scientific and Technical Information of China (English)

    朱洪洲; 严恒; 唐伯明

    2011-01-01

    In order to study fatigue performance of asphalt mixture under cyclic loading and describe combined action process of fatigue-creep damage effect,considering the dynamic character of asphalt mixture and using the elementary theory of viscoelastic damage mechanics,complex modulus was used to define damage variable based on strain equivalence hypothesis.By analyzing the damage evolution rules of asphalt mixture under cyclic loading and using fatigue-creep coupling damage theory,the damage evolution equations of asphalt mixture under fatigue-creep damage effect were built.The damage evolution and fatigue life prediction model of considering the effects of stress and temperature was derived.Results show that the proposed damage model of satisfying thermodynamic laws and physical requirement is proved.Fatigue failure of asphalt mixture is caused by fatigue-creep damage effect.The proposed fatigue model can be better used to predict the fatigue life of asphalt mixture under different temperatures and stresses.%为了研究沥青混合料在重复荷载作用下的疲劳特性并描述疲劳-蠕变损伤效应共同作用的过程,考虑沥青混合料具有的动态性质,从粘弹性损伤力学基本理论出发,基于应变等效假设,采用复数模量定义了损伤变量。通过分析沥青混合料在周期荷载作用下的损伤变化规律,运用疲劳-蠕变耦合损伤理论,建立了疲劳-蠕变损伤效应共同作用时的损伤演化方程,提出了体现温度及应力影响的损伤模型和疲劳寿命预测模型,并对损伤模型进行了分析。研究结果表明:构建的损伤模型满足热力学准则和物理条件;沥青混合料疲劳失效是由疲劳-蠕变损伤效应共同影响所致;利用提

  15. 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

  16. Comparison of Three Fatigue Crack Growth Rate Models%3种疲劳裂纹扩展速率模型比较

    Institute of Scientific and Technical Information of China (English)

    张杰; 马永亮

    2012-01-01

    Paris模型、Walker模型和Forman模型是常用的3种疲劳裂纹扩展速率模型,为比较3种模型在不同应力比下,拟合疲劳裂纹稳定扩展阶段速率的异同,采用标准紧凑拉伸试样进行疲劳裂纹扩展速率试验,由试验数据拟合得到3种模型公式的参数,并进行对比分析.结果表明,3种模型拟合精度均随应力比增大逐渐降低;对于单一应力比下的疲劳裂纹扩展,3种模型均具有较好的精度,但对于不同应力比下的疲劳裂纹扩展,Walker模型的拟合结果随应力比增大略有失真;而Forman模型的拟合结果随应力比增大有较大失真.%Paris law, Walker law and Forman law are three kinds of widely used fatigue crack growth rate models. The fatigue crack growth tests were designed in order to get the similarities and differences between three models. The tests were performed for several compact tension (CT) specimens made of high strength steel under different stress ratios, and the parameters of the three models were obtained by test data. The results of the comparison show that the fitting accuracy of the three models decreases as stress ratio increases; the fitting accuracy of the three models is good under the same stress ratio, but Walker law has slight distortion and Forman law has large distortion as stress ratio increases.

  17. Decentralisation and Combating Educational Exclusion.

    Science.gov (United States)

    van Langen, Annemarie; Dekkers, Hetty

    2001-01-01

    Describes Dutch policies to combat educational disadvantage arising from economic, social, and cultural factors by funding efforts at the local level. Compares Dutch efforts to success factors and obstacles encountered in similar initiatives in the United States, England and Wales, and Australia, where public education and local authority have…

  18. New Russian Combat Small Boats

    Directory of Open Access Journals (Sweden)

    Aleksandr F. Mitrofanov

    2016-12-01

    Full Text Available The article presents an overview of small combat boats. The author provides a description and gives an analysis of the characteristics of the boat "Raptor", boat "BK-16", boat "Strizh-4-1 DSh", and assault boat "BK-10".

  19. Combating corruption in global health.

    Science.gov (United States)

    Mackey, Tim K; Kohler, Jillian; Lewis, Maureen; Vian, Taryn

    2017-08-09

    Corruption is a critical challenge to global health efforts, and combating it requires international action, advocacy, and research. Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

  20. Evidence of combat in triceratops.

    Directory of Open Access Journals (Sweden)

    Andrew A Farke

    Full Text Available BACKGROUND: The horns and frill of Triceratops and other ceratopsids (horned dinosaurs are interpreted variously as display structures or as weapons against conspecifics and predators. Lesions (in the form of periosteal reactive bone, healing fractures, and alleged punctures on Triceratops skulls have been used as anecdotal support of intraspecific combat similar to that in modern horned and antlered animals. If ceratopsids with different cranial morphologies used their horns in such combat, this should be reflected in the rates of lesion occurrence across the skull. METHODOLOGY/PRINCIPAL FINDINGS: We used a G-test of independence to compare incidence rates of lesions in Triceratops (which possesses two large brow horns and a smaller nasal horn and the related ceratopsid Centrosaurus (with a large nasal horn and small brow horns, for the nasal, jugal, squamosal, and parietal bones of the skull. The two taxa differ significantly in the occurrence of lesions on the squamosal bone of the frill (P = 0.002, but not in other cranial bones (P > 0.20. CONCLUSIONS/SIGNIFICANCE: This pattern is consistent with Triceratops using its horns in combat and the frill being adapted as a protective structure for this taxon. Lower pathology rates in Centrosaurus may indicate visual rather than physical use of cranial ornamentation in this genus, or a form of combat focused on the body rather than the head.

  1. A Direct Interception Missile Assignment Model in Firepower Planning of Double-Layer Anti-Missile Combat%直接分配到弹的双层反导火力规划模型

    Institute of Scientific and Technical Information of China (English)

    李龙跃; 刘付显; 杨国哲; 赵麟锋

    2014-01-01

    Firepower application is one of the core problem in anti-missile power construction,Firepower Planning of double-layer anti-missile combat in terminal phase is a Nondeterministic polynomial hard Mod-eling question.We analysis the problem,when to assign the interception missiles to the targets and give the model assumptions;Then we establish the direct interception missile assignment model in firepower planning of double-layer anti-missile combat This model break the research which targets only can be as-signed to the weapon system or fire units in the past,assigned the interception missiles to ballistic missiles one by one,it's a new idea about firepower planning.%反导作战火力运用是反导力量建设的核心内容之一,末段双层反导火力规划是一个复杂的不确定多约束条件优化问题,对火力规划进行了问题分析、弹-目分配时机分析和模型假设;分2个阶段建立了直接分配到弹的末段双层反导火力规划模型,模型重点考虑拦截目标与拦截弹杀伤时间窗口的对应关系,建立起武器系统拦截弹与来袭目标的弹-目对应分配关系,提供一种新的、快速的双层反导火力规划方法。

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

    DEFF Research Database (Denmark)

    Dominguez, Sergio Marquez; Sørensen, John Dalsgaard

    2012-01-01

    Consequences of failure of offshore wind turbines (OWTs) are 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...... 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....... 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...

  3. Framework for Dynamic Evaluation of Muscle Fatigue in Manual Handling Work

    CERN Document Server

    Ma, Liang; Chablat, Damien; Zhang, Wei

    2008-01-01

    Muscle fatigue is defined as the point at which the muscle is no longer able to sustain the required force or work output level. The overexertion of muscle force and muscle fatigue can induce acute pain and chronic pain in human body. When muscle fatigue is accumulated, the functional disability can be resulted as musculoskeletal disorders (MSD). There are several posture exposure analysis methods useful for rating the MSD risks, but they are mainly based on static postures. Even in some fatigue evaluation methods, muscle fatigue evaluation is only available for static postures, but not suitable for dynamic working process. Meanwhile, some existing muscle fatigue models based on physiological models cannot be easily used in industrial ergonomic evaluations. The external dynamic load is definitely the most important factor resulting muscle fatigue, thus we propose a new fatigue model under a framework for evaluating fatigue in dynamic working processes. Under this framework, virtual reality system is taken to ...

  4. 低周疲劳过程损伤变量的复合分析法和三阶段损伤演化模型%Combination Analyzing Method to Characterize Damage Variable and Three Stage Model of Fatigue Damage in Low-cycle Fatigue

    Institute of Scientific and Technical Information of China (English)

    吴健栋; 蔡志鹏; 汤之南; 李克俭; 王梁; 潘际銮; 霍鑫; 许晓进

    2015-01-01

    采用疲劳损伤力学的方法分析NiCrMoV钢核电汽轮机低压焊接转子1︰1模拟件接头低周疲劳过程,针对损伤变量表征方法中的弹性模量法和应力幅值法应用的局限性,并考虑循环前期循环软化造成的材料的损伤,提出适用于循环软化材料的低周疲劳全过程损伤变量表征的复合分析法,提高了疲劳过程各阶段材料损伤测量的准确性;提出低周疲劳损伤过程的三阶段损伤模型,将焊接接头的疲劳损伤过程分为应力松弛、微空洞和微裂纹的萌生和扩展以及宏观裂纹的萌生和扩展三个阶段,并用于分析焊接接头的低周疲劳损伤过程.试验结果表明,在NiCrMoV 钢汽轮机低压焊接转子接头的低周疲劳损伤过程分析中,采用复合分析法表征损伤变量较弹性模量法和应力幅值法更为合理,且三阶段疲劳损伤模型能很好地反映疲劳损伤过程.%The fatigue damage mechanics is used to analyze the low-cycle fatigue process of 1︰1 simulated sample of NiCrMoV steel nuclear turbine LP welded rotor. A combination analyzing method(CAM) is presented for the limitations of elastic modulus method(EM) and stress amplitude method(SAM) on the definition of fatigue damage variable, which considers material damage during cyclic softening and applies to low-cycle fatigue of cyclic softening materials and improves the accuracy of damage measurement of fatigue process. A new fatigue damage model—three stage model of fatigue damage(TSM-FD) is also proposed to analyze the low-cycle fatigue process of welded joint, which divides fatigue process of welded joint into three stages, as stress relaxation, initiation and propagation of micro hole and crack and initiation and propagation of macro crack. The results show that, in low-cycle fatigue analysis of NiCrMoV steel nuclear turbine LP welded rotor, CAM is more reasonable than EM and SAM to characterize damage variable, and TSM-FD can well describe the

  5. CORROSION FATIGUE OF NUCLEAR-GRADE STAINLESS STEEL IN HIGH TEMPERATURE WATER AND ITS ENVIRONMENTAL FATIGUE DESIGN MODEL%核级不锈钢高温水腐蚀疲劳机制及环境疲劳设计模型

    Institute of Scientific and Technical Information of China (English)

    吴欣强; 徐松; 韩恩厚; 柯伟

    2011-01-01

    通过模拟核电高温高压循环水腐蚀疲劳实验,研究了国产核级不锈钢的环境疲劳损伤行为与失效机制;评价了影响不锈钢高温高压水疲劳寿命的环境和载荷等因素,建立了一个植入环境损伤效应的疲劳设计模型,给出了便于工程应用的核级不锈钢的环境疲劳设计曲线.%The high safety of light water reactor nuclear power plants (NPPs) requires very strict design standard and service property of pressure boundary components materials. The service degradation and life assessment of the components materials primarily depend on the understanding of environmentally assisted failure mechanism, accumulation of service property data and construction of evaluation models. Currently domestic NPPs are relying on foreign design, operation and life assessment standards. However, recent experimental data indicate that even the ASME design fatigue code may be deficient in safety margin under certain conditions of loading and environment. In the present work, based on the corrosion fatigue tests in simulated NPPs' high temperature pressurized water, the corrosion fatigue behavior and environmentally assisted failure mechanism of domestic nuclear-grade stainless steel have been investigated. The factors affecting fatigue life of nuclear grade stainless steel in high temperature water were evaluated. A design fatigue model was constructed by taking environmental degradation effects into account and the corresponding design curves were given for the convenience of engineering applications.

  6. Examining fatigue in COPD

    DEFF Research Database (Denmark)

    Al-Shair, Khaled; Muellerova, Hana; Yorke, Janelle

    2012-01-01

    ABSTRACT: INTRODUCTION: Fatigue is a disruptive symptom that inhibits normal functional performance of COPD patients in daily activities. The availability of a short, simple, reliable and valid scale would improve assessment of the characteristics and influence of fatigue in COPD. METHODS......: At baseline, 2107 COPD patients from the ECLIPSE cohort completed the Functional Assessment of Chronic Illness Therapy Fatigue (FACIT-F) scale. We used well-structured classic method, the principal components analysis (PCA) and Rasch analysis for structurally examining the 13-item FACIT-F. RESULTS: Four items...... were less able to capture fatigue characteristics in COPD and were deleted. PCA was applied to the remaining 9 items of the modified FACIT-F and resulted in three interpretable dimensions: i) general (5 items); ii) functional ability (2 items); and iii) psychosocial fatigue (2 items). The modified...

  7. Biaxial Fatigue Cracking from Notch

    Science.gov (United States)

    2013-03-04

    Leevers (reference 11) noticed that the variation in  from 0 to 2 has little effect on the da/dN in PVC ( polyvinyl - chloride ), but reduces the da/dN...under biaxial rotating and bending. Ahmad (reference 2) formulated a model for the biaxial fatigue crack growth in aggressive environment, outlined by...1962, Vol. 90, pp. 238-239. 20. ASM Handbook , Vol. 12 Fractography: 1992, p. 430, 438. 21. Metals Handbook , Vol. 9 Fractography and Atlas of

  8. Mechanical Behavior and Fatigue Studies of Rubber Components Used in Tracked Vehicles

    Science.gov (United States)

    2010-08-17

    relaxation as the cycles evolve. Fatigue Modeling A MultiStage Fatigue (MSF) model developed in [3] has been applied to many types of aluminum ...McDowell, K. Gall, M.F. Horstemeyer and J. Fan. “Microstructure-based Fatigue Modeling of Cast A356 - T6 Alloy.” Engineering Fracture Mechanics, vol. 70

  9. LIFE PREDICTION APPROACH FOR RANDOM MULTIAXIAL FATIGUE

    Institute of Scientific and Technical Information of China (English)

    Wang Lei; Wang Dejun

    2005-01-01

    According to the concept of critical plane, a life prediction approach for random multiaxial fatigue is presented. First, the critical plane under the multiaxial random loading is determined based on the concept of the weight-averaged maximum shear strain direction. Then the shear and normal strain histories on the determined critical plane are calculated and taken as the subject of multiaxial load simplifying and multiaxial cycle counting. Furthermore, a multiaxial fatigue life prediction model including the parameters resulted from multiaxial cycle counting is presented and applied to calculating the fatigue damage generated from each cycle. Finally, the cumulative damage is added up using Miner's linear rule, and the fatigue prediction life is given. The experiments under multiaxial loading blocks are used for the verification of the proposed method. The prediction has a good correction with the experimental results.

  10. A Pilot Project Demonstrating that Combat Medics Can Safely Administer Parenteral Medications in the Emergency Department.

    Science.gov (United States)

    Schauer, Steven G; Cunningham, Cord W; Fisher, Andrew D; DeLorenzo, Robert A

    2017-08-15

    Introduction Select units in the military have improved combat medic training by integrating their functions into routine clinical care activities with measurable improvements in battlefield care. This level of integration is currently limited to special operations units. It is unknown if regular Army units and combat medics can emulate these successes. The goal of this project was to determine whether US Army combat medics can be integrated into routine emergency department (ED) clinical care, specifically medication administration. Project Design This was a quality assurance project that monitored training of combat medics to administer parenteral medications and to ensure patient safety. Combat medics were provided training that included direct supervision during medication administration. Once proficiency was demonstrated, combat medics would prepare the medications under direct supervision, followed by indirect supervision during administration. As part of the quality assurance and safety processes, combat medics were required to document all medication administrations, supervising provider, and unexpected adverse events. Additional quality assurance follow-up occurred via complete chart review by the project lead. Data During the project period, the combat medics administered the following medications: ketamine (n=13), morphine (n=8), ketorolac (n=7), fentanyl (n=5), ondansetron (n=4), and other (n=6). No adverse events or patient safety events were reported by the combat medics or discovered during the quality assurance process. In this limited case series, combat medics safely administered parenteral medications under indirect provider supervision. Future research is needed to further develop this training model for both the military and civilian setting. Schauer SG , Cunningham C W, Fisher AD , DeLorenzo RA . A pilot project demonstrating that combat medics can safely administer parenteral medications in the emergency department.

  11. Rezultati modeliranja borbenog manevra napada aviona na zemaljski cilj iz oštrog obrušavanja / The results of combat attack maneuver modelling on ground target using aircraft steep diving

    Directory of Open Access Journals (Sweden)

    Nikola Pekić

    2005-11-01

    Full Text Available U ovom radu prikazani su rezultati matematičkog modeliranja kretanja aviona u borbenom manevru pri napadu na zemaljski cilj iz oštrog obrušavanja. Kretanje aviona razmatrano je kao kretanje materijalne tačke u prostoru. Takođe, prikazane su prednosti aviona sa otklonom vektora potiska i njegove primene u manevru u odnosu na avion sa klasičnom pogonskom grupom i klasičnim aerodinamičkim upravljačkim površinama. / This paper presents the results of mathematical modeling of aircraft movement in combat maneuver during attack on ground target using steep diving. Aircraft movement is considered as movement of a material point in space. Also, the advantages of aircraft with thrust vector deflection and its applications during maneuver when compared to the aircraft with classical engines and classical aerodynamic controls.

  12. Thermal emission in fatigue described by power laws

    Directory of Open Access Journals (Sweden)

    Gallinatti A.E.

    2010-06-01

    Full Text Available In the present work, a theoretical model proposed by the literature and focused on the relationship between microplasticizations thermal behaviour and fatigue scatter is analysed and applied to fatigue test results of standard and notched steel specimens. The same experimental data are subjected to the TCM (Two Curves Method thermographic elaboration technique, in order to quickly evaluate fatigue limit values. TCM method has been modified, aiming at interpolating thermal data referred to the region of loads upper than fatigue limit with a non linear regression law having the same mathematical structure of the theoretical model equations (power laws.

  13. Mental health status of Sri Lanka Navy personnel three years after end of combat operations: a follow up study.

    Directory of Open Access Journals (Sweden)

    Raveen Hanwella

    Full Text Available The main aim of this study was to assess the mental health status of the Navy Special Forces and regular forces three and a half years after the end of combat operations in mid 2009, and compare it with the findings in 2009. This cross sectional study was carried out in the Sri Lanka Navy (SLN, three and a half years after the end of combat operations. Representative samples of SLN Special Forces and regular forces deployed in combat areas were selected using simple random sampling. Only personnel who had served continuously in combat areas during the one year period prior to the end of combat operations were included in the study. The sample consisted of 220 Special Forces and 275 regular forces personnel. Compared to regular forces a significantly higher number of Special Forces personnel had experienced potentially traumatic events. Compared to the period immediately after end of combat operations, in the Special Forces, prevalence of psychological distress and fatigue showed a marginal increase while hazardous drinking and multiple physical symptoms showed a marginal decrease. In the regular forces, the prevalence of psychological distress, fatigue and multiple somatic symptoms declined and prevalence of hazardous drinking increased from 16.5% to 25.7%. During the same period prevalence of smoking doubled in both Special Forces and regular forces. Prevalence of PTSD reduced from 1.9% in Special Forces to 0.9% and in the regular forces from 2.07% to 1.1%. Three and a half years after the end of combat operations mental health problems have declined among SLN regular forces while there was no significant change among Special Forces. Hazardous drinking among regular forces and smoking among both Special Forces and regular forces have increased.

  14. Memory for Fatigue in Chronic Fatigue Syndrome: Relationships to Fatigue Variability, Catastrophizing, and Negative Affect

    Science.gov (United States)

    Sohl, Stephanie J.; Friedberg, Fred

    2008-01-01

    Fatigue in chronic fatigue syndrome (CFS) is usually assessed with retrospective measures rather than real-time momentary symptom assessments. In this study, the authors hypothesized that in participants with CFS, discrepancies between recalled and momentary fatigue would be related to catastrophizing, anxiety, and depression and to variability of momentary fatigue. They also expected that catastrophizing, anxiety, and depression would be associated with momentary fatigue. The authors asked 53 adults with CFS to carry electronic diaries for 3 weeks and record their experiences of momentary fatigue. The authors assessed participants' fatigue recall with weekly ratings and administered questionnaires for catastrophizing, depression, and anxiety. Recall discrepancy was significantly related to the variability of momentary fatigue. In addition, catastrophizing, depression, and momentary fatigue were all significantly related to recall discrepancy. Catastrophizing, depression, anxiety, and momentary negative affect were all significantly associated with momentary fatigue. The findings suggest that momentary fatigue in patients with CFS is related to modifiable psychological factors. PMID:18400687

  15. Modeling and Simulation of Combat Systems Paralysis Based on Complex Network%基于复杂网络作战体系破击的建模与仿真

    Institute of Scientific and Technical Information of China (English)

    王长春; 陈俊良; 陈超

    2012-01-01

    在分析体系破击作战机理的基础上,根据从物质世界到观念世界的抽象过程,提出了基于复杂网络的体系破击仿真分析框架,并建立了考虑信息因子和破击能力的作战体系破击新模型。最后通过仿真实验,得到了一些结论:(1)一定条件下,体系破击的能力比攻击信息更加重要;(2)只有在一定的破击能力下,作战体系才对随机攻击表现出鲁棒性,对蓄意攻击表现出脆弱性。%The operation mechanism of systems paralysis was firstly analyzed. A simulation and analysis frame was established based on the abstraction from the physical system to concept system. A new complex network model was built, in which attack capability and information factor were considered. Finally, the new model was verified and some conclusions were got by simulation: (1) On some conditions, attack capability is more important than information factor; (2) Only on the condition of enough attack capability, a small fraction of nodes randomly can prevent a combat systems network from collapsing and a small fraction of nodes preferentially can destroy a combat systems network.

  16. Research on Conceptual Modeling of U.S. Kinetic Energy Anti-Satellite Combat System Based on UML%基于UML的美军动能反卫作战系统概念建模

    Institute of Scientific and Technical Information of China (English)

    郝琳; 毕义明; 王桐

    2016-01-01

    In this paper,the conceptual model of the U.S. Kinetic Energy Anti-Satellit combat system is discussed by utilizing UML. Aiming at the operational tasks of combat system,main behaviour of system are identified firstly,then function requirement is defined with the use-case diagram. Secondly,all of the entities are identified with class diagram and relationship analysed. Finally, dynamic Interactive in different phase are displayed by sequence diagram. This description of conceptual model is normative,and can be provide good foundation for Development of Simulation System.%针对美军动能反卫作战系统,利用UML方法,对其作战仿真概念建模进行了初步的探讨。针对作战系统的反卫作战任务,首先识别系统的主要行为,利用用例图定义系统的功能需求;其次利用类图标识系统用例模型中的所有实体,并分析这些实体的关联关系;最后,采用顺序图展示对象在系统执行过程中不同阶段的动态交互。这样建立的概念模型描述规范,为下一步仿真系统的开发奠定了良好知识表示基础。

  17. Fatigue in knee and hip osteoarthritis: the role of pain and physical function.

    Science.gov (United States)

    Snijders, Gijs F; van den Ende, Cornelia H M; Fransen, Jaap; van Riel, Piet L C M; Stukstette, Mirelle J P M; Defoort, Koen C; Arts-Sanders, Marianne A; van den Hoogen, Frank H J; den Broeder, Alfons A

    2011-10-01

    It is suggested that serious levels of fatigue are present in nearly half of patients with OA. However, it is unclear which dimensions of fatigue are involved, if fatigue is related to pain and physical function, and if fatigue is influenced by therapy. The aims of this study were to measure levels of different dimensions of fatigue before and after evidenced-based conservative treatment and to investigate the association between fatigue and pain and physical function in patients with knee or hip OA. In this observational cohort study, levels of different dimensions of fatigue were measured in knee and/or hip OA patients before and after 12 weeks of conservative treatment. Cross-sectional and longitudinal relations between (change in) fatigue dimensions and (change in) pain or physical function were studied using association models, controlling for predefined possible confounders. A total of 231 patients was included, with 47% experiencing severe fatigue. A small decrease in levels of fatigue was seen after standardized treatment. The level of fatigue severity was cross-sectionally and longitudinally associated with physical function, whereas the level of physical fatigue was cross-sectionally and longitudinally associated with pain and physical function. No confounders were identified. Important levels of fatigue are common in knee and hip OA patients. After evidence-based tailored conservative treatment targeted to improve pain and physical function, a small decrease in fatigue levels was found. Reduction in levels of different fatigue dimensions were related to the change in physical function and pain.

  18. 一种新的低周疲劳损伤累积模型及试验验证%New Low Cycle Fatigue Damage Accumulation Model and Experimental Results

    Institute of Scientific and Technical Information of China (English)

    张磊; 杨自春; 曹跃云

    2011-01-01

    基于连续介质损伤力学理论,依据疲劳损伤的加载参数与损伤变量之间的不可分割性等特点,建立了一种新的低周疲劳损伤累积模型。经过对00Cr17Ni14Mo2钢和2.25Cr1Mo钢的低周疲劳试验数据的分析,得到了相应的疲劳损伤累积模型。将该模型与不同的损伤累积模型相比较,结果表明:该累积模型的计算结果与试验结果能更好地一致,能更真实地反映损伤的非线性累积过程。该累积模型考虑了损伤和应变的耦合作用以及平均应力、疲劳极限对其的影响,且物理意义明确,具有一定的实用价值。%Based on the theory of continuum damage mechanics,a new low cycle fatigue damage model was established,which combined the unseparable characteristics of the damage variables and loading parameters.Through the analysis of test data of the low cycle fatigue damage of steel 00Cr17Ni14Mo2 and 2.25Cr1Mo,the fatigue damage evolution equations under different plastic strain amplitudes were acquired,which are in good agreement with the experimental results.While the constants of new low cycle fatigue damage model were obtained by fitting,two fatigue damage evolution equations of steel 00Cr17Ni14Mo2 and 2.25Cr1Mo were given respectively.And comparing with several fatigue damage accumulation models,the results show that except linear damage accumulation model,the rest of the models could reflect the nonlinear damage accumulation process of material.The new model established herein accords the experimental results best,which truly reflects the nonlinear damage accumulation process,and takes the coupling of damage and strain,fatigue limit,mean pressure into consideration.Therefore,the new damage model has a clear physical meaning and practical value.

  19. Fatigue Management (La Gestion de la Fatigue)

    Science.gov (United States)

    1991-12-01

    Management Pre’face Etant donne la tenidance de plus en plus marque ~e vets le maintien en service des aironefs au-delak des dates lintites...transport aircraft designed prototype sade its first flight one year about 20 years ago; from the fatigue point later. The results of the flight testing

  20. 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...

  1. Prolonged unexplained fatigue in paediatrics

    NARCIS (Netherlands)

    Bakker, R.J.

    2010-01-01

    Prolonged Unexplained Fatigue in Paediatrics. Fatigue, as the result of mental or physical exertion, will disappear after rest, drinks and food. Fatigue as a symptom of illness will recover with the recovering of the illness. But when fatigue is ongoing for a long time, and not the result of exertio

  2. 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...

  3. Forecasting method of fatigue life test data for metal materials

    Institute of Scientific and Technical Information of China (English)

    张怀亮; 邱显焱; 谭冠军

    2001-01-01

    GM(1, 1) model of grey system theory is used to forecast fatigue life test data for metal materials. The method can reduce test time and save test cost, and reliability indexes of metal materials can be obtained quickly. The results of an example show that grey system theory has a high precision for forecasting fatigue life test data for metal materials. A valuable method is put forward, which can effectively reduce the fatigue life test time for metal materials.

  4. 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.

  5. Detecting and combating malicious email

    CERN Document Server

    Ryan, Julie JCH

    2014-01-01

    Malicious email is, simply put, email with a malicious purpose. The malicious purpose could be fraud, theft, espionage, or malware injection. The processes by which email execute the malicious activity vary widely, from fully manual (e.g. human-directed) to fully automated. One example of a malicious email is one that contains an attachment which the recipient is directed to open. When the attachment is opened, malicious software is installed on the recipient's computer. Because malicious email can vary so broadly in form and function, automated detection is only marginally helpful. The education of all users to detect potential malicious email is important to containing the threat and limiting the damage. It is increasingly necessary for all email users to understand how to recognize and combat malicious email. Detecting and Combating Malicious Email describes the different types of malicious email, shows how to differentiate malicious email from benign email, and suggest protective strategies for both perso...

  6. Lessons Learned: Employment and Tactical Use of The Combat Medic During Stability Support Operations.

    Science.gov (United States)

    Eldred, Michael S

    2016-01-01

    It is the intent of this article to define the strategy by which Combat Medics have been employed in contemporary stability operations and counterinsurgency conflicts. This article describes the advances in training based on Tactical Combat Casualty Care and how training evolved into an evidence-based model. Training platforms evolved with shifts in mission requirements, new technology, improved medical techniques, and changing protocols. The last portion of this article details recommendations in doctrine, materiel, and training that could enable optimal sustainment standards while retaining operational capability across a wide variety of combat and peace operations. Lessons learned and changes adapted for Medics that are addressed: (1) advances in training and employment of the Combat Medic necessitated by tactics and strategy of current conflicts, (2) Combat Medic regulatory requirements and centralized, just-in-time training, and (3) changes in sustainment training driven by certification requirements and use of medical simulation training centers.

  7. Computed tomographic imaging of subchondral fatigue cracks in the distal end of the third metacarpal bone in the thoroughbred racehorse can predict crack micromotion in an ex-vivo model.

    Directory of Open Access Journals (Sweden)

    Marie-Soleil Dubois

    Full Text Available Articular stress fracture arising from the distal end of the third metacarpal bone (MC3 is a common serious injury in Thoroughbred racehorses. Currently, there is no method for predicting fracture risk clinically. We describe an ex-vivo biomechanical model in which we measured subchondral crack micromotion under compressive loading that modeled high speed running. Using this model, we determined the relationship between subchondral crack dimensions measured using computed tomography (CT and crack micromotion. Thoracic limbs from 40 Thoroughbred racehorses that had sustained a catastrophic injury were studied. Limbs were radiographed and examined using CT. Parasagittal subchondral fatigue crack dimensions were measured on CT images using image analysis software. MC3 bones with fatigue cracks were tested using five cycles of compressive loading at -7,500N (38 condyles, 18 horses. Crack motion was recorded using an extensometer. Mechanical testing was validated using bones with 3 mm and 5 mm deep parasagittal subchondral slots that modeled naturally occurring fatigue cracks. After testing, subchondral crack density was determined histologically. Creation of parasagittal subchondral slots induced significant micromotion during loading (p<0.001. In our biomechanical model, we found a significant positive correlation between extensometer micromotion and parasagittal crack area derived from reconstructed CT images (SR = 0.32, p<0.05. Correlations with transverse and frontal plane crack lengths were not significant. Histologic fatigue damage was not significantly correlated with crack dimensions determined by CT or extensometer micromotion. Bones with parasagittal crack area measurements above 30 mm2 may have a high risk of crack propagation and condylar fracture in vivo because of crack micromotion. In conclusion, our results suggest that CT could be used to quantify subchondral fatigue crack dimensions in racing Thoroughbred horses in-vivo to

  8. Enhancing Brigade Combat Team Adaptability

    Science.gov (United States)

    2010-06-11

    participation and support of my unnamed heroes , the leaders of the Brigade Combat Team that provided such rich insight into the phenomenon of organizational... Archetype ” ARFORGEN (Short Deployment Cycles) OIF/OEF Low number of BCTs (Growing Action) (Slowing Action)(Condition) Key Terms -Trust -Confidence...Behavior – Climate - Trust Adapted from Peter Senge’s (2006) “Limits to Growth Archetype ” Key Terms -Trust -Confidence -Competence -Opportunity

  9. Metabolic Factors in Fatigue

    Institute of Scientific and Technical Information of China (English)

    Mark Hargreaves

    2006-01-01

    Increased non-oxidative and oxidative ATP production via metabolic pathways in skeletal muscle is essential for the maintenance of force and power production during exercise. However, substrate depletion and accumulation of metabolic byproducts are potential causes of fatigue. Reduced PCr availability can limit power production during sprint exercise, whereas carbohydrate depletion is a major limitation to endurance performance. During sprint exercise increased Pi and H+ may contribute to fatigue, and during prolonged strenuous exercise, the accumulation of NH3, reactive oxygen species, and heat can limit performance. Appropriate training programs and nutritional interventions are potential strategies to enhance fatigue resistance and exercise performance.

  10. Fatigue 󈨛. Volume 2,

    Science.gov (United States)

    1987-06-01

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

  11. Combats escènics

    Directory of Open Access Journals (Sweden)

    Pawel Rouba Billowicz

    2016-04-01

    Full Text Available “Combats Escènics” és un treball que tracta sobre la interpretació artística de la violència d’artistes de l’espectacle per tal de divertir el públic i emetre un missatge humanista mitjançant una coreografia ritual. En aquest estudi es presenta una classificació del combat escènic des del doble vessant agonista/antagonista, es realitza un passeig històric de la representació artística del combat a través de les diferents etapes i de les diverses cultures, s’aborda la preparació escènica de l’actor i del coreògraf, i s’entreveuen les perspectives de futur d’aquesta modalitat artística. Estudi realitzat per Pawel Rouba Billewicz (Inowroclaw, Polònia, 1939 - Barcelona, 2007, director, coreògraf, actor, mestre d’armes, mestre del gest i de la pantomima i professor de l’INEF de Catalunya. Aquest article, editorialment inèdit, es publica postmortem per Apunts. Educació Física i Esports com a homenatge i reconeixement de l’autor per la seva extraordinària i polivalent aportació al camp de l’art i l’Activitat Física i l’Esport.

  12. Managing fatigue: It really is about sleep.

    Science.gov (United States)

    Darwent, David; Dawson, Drew; Paterson, Jessica L; Roach, Gregory D; Ferguson, Sally A

    2015-09-01

    Biomathematical models of fatigue can assist organisations to estimate the fatigue consequences of a roster before operations commence. These estimates do not account for the diversity of sleep behaviours exhibited by employees. The purpose of this study was to develop sleep transfer functions describing the likely distributions of sleep around fatigue level estimates produced by a commercial biomathematical model of fatigue. Participants included 347 (18 females, 329 males) train drivers working commercial railway operations in Australia. They provided detailed information about their sleep behaviours using sleep diaries and wrist activity monitors. On average, drivers slept for 7.7 (±1.7)h in the 24h before work and 15.1 (±2.5)h in the 48h before work. The amount of sleep obtained by drivers before shifts differed only marginally across morning, afternoon and night shifts. Shifts were also classified into one of seven ranked categories using estimated fatigue level scores. Higher fatigue score categories were associated with significant reductions in the amount of sleep obtained before shifts, but there was substantial within-category variation. The study findings demonstrate that biomathematical models of fatigue have utility for designing round-the-clock rosters that provide sufficient sleep opportunities for the average employee. Robust variability in the amount of sleep obtained by drivers indicate that models are relatively poor tools for ensuring that all employees obtain sufficient sleep. These findings demonstrate the importance of developing approaches for managing the sleep behaviour of individual employees. Copyright © 2015 Elsevier Ltd. All rights reserved.

  13. Understanding Muscle Dysfunction in Chronic Fatigue Syndrome

    Directory of Open Access Journals (Sweden)

    Gina Rutherford

    2016-01-01

    Full Text Available Introduction. Chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME is a debilitating disorder of unknown aetiology, characterised by severe disabling fatigue in the absence of alternative diagnosis. Historically, there has been a tendency to draw psychological explanations for the origin of fatigue; however, this model is at odds with findings that fatigue and accompanying symptoms may be explained by central and peripheral pathophysiological mechanisms, including effects of the immune, oxidative, mitochondrial, and neuronal pathways. For example, patient descriptions of their fatigue regularly cite difficulty in maintaining muscle activity due to perceived lack of energy. This narrative review examined the literature for evidence of biochemical dysfunction in CFS/ME at the skeletal muscle level. Methods. Literature was examined following searches of PUB MED, MEDLINE, and Google Scholar, using key words such as CFS/ME, immune, autoimmune, mitochondria, muscle, and acidosis. Results. Studies show evidence for skeletal muscle biochemical abnormality in CFS/ME patients, particularly in relation to bioenergetic dysfunction. Discussion. Bioenergetic muscle dysfunction is evident in CFS/ME, with a tendency towards an overutilisation of the lactate dehydrogenase pathway following low-level exercise, in addition to slowed acid clearance after exercise. Potentially, these abnormalities may lead to the perception of severe fatigue in CFS/ME.

  14. Understanding Muscle Dysfunction in Chronic Fatigue Syndrome.

    Science.gov (United States)

    Rutherford, Gina; Manning, Philip; Newton, Julia L

    2016-01-01

    Introduction. Chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME) is a debilitating disorder of unknown aetiology, characterised by severe disabling fatigue in the absence of alternative diagnosis. Historically, there has been a tendency to draw psychological explanations for the origin of fatigue; however, this model is at odds with findings that fatigue and accompanying symptoms may be explained by central and peripheral pathophysiological mechanisms, including effects of the immune, oxidative, mitochondrial, and neuronal pathways. For example, patient descriptions of their fatigue regularly cite difficulty in maintaining muscle activity due to perceived lack of energy. This narrative review examined the literature for evidence of biochemical dysfunction in CFS/ME at the skeletal muscle level. Methods. Literature was examined following searches of PUB MED, MEDLINE, and Google Scholar, using key words such as CFS/ME, immune, autoimmune, mitochondria, muscle, and acidosis. Results. Studies show evidence for skeletal muscle biochemical abnormality in CFS/ME patients, particularly in relation to bioenergetic dysfunction. Discussion. Bioenergetic muscle dysfunction is evident in CFS/ME, with a tendency towards an overutilisation of the lactate dehydrogenase pathway following low-level exercise, in addition to slowed acid clearance after exercise. Potentially, these abnormalities may lead to the perception of severe fatigue in CFS/ME.

  15. Effect of ageing on fatigue properties of asphalt

    Institute of Scientific and Technical Information of China (English)

    王佶; 庞凌; 吴少鹏; 刘全涛; 陈筝

    2008-01-01

    The fatigue properties of asphalts were investigated after various laboratory simulation ageing tests and outdoor natural exposure ultraviolet radiation ageing,by dynamic shear rheometer(DSR) time sweep fatigue test in constant strain model and a new type of specimen which was introduced to avoid the problem of adhesion failure between rotor and asphalt binder.The results show that outdoor natural exposure ageing(NEA) causes the decrease of retained fatigue life distinctly,and photodegradation caused by outdoor NEA of 1 250 μm thin films asphalt for three months,is found to be severer than pressure ageing vessel(PAV) with respects to retained fatigue life.The effect of photodegradation increases as the time of outdoor NEA increases.DSR time sweep fatigue test in constant strain indicates that the aged styrene-butadiene-styrene(SBS) modified asphalt still displays better fatigue properties than the corresponding base asphalt after ageing.

  16. Bending Fatigue of Carburized Steel at Very Long Lives

    Science.gov (United States)

    Nelson, D. V.; Long, Z.

    2016-01-01

    The bending fatigue behavior of two carburized steels is investigated for lives between approximately 105 and 108 cycles. Cracks are observed to start at sub-surface inclusions and develop features on fracture surfaces resembling "fish eyes" in appearance. This type of sub-surface cracking tends to govern fatigue strength at long lives. Previous studies of "fish eye" fatigue in carburized steel have been relatively few and have mainly considered failures originating at depths beneath a carburized case, where compressive residual stresses are minimal and hardness values approach those in the core. This study provides fatigue data for cracks originating within cases at various depths where compressive residual stresses are substantial and hardness is much higher than in the core. Fatigue strength is predicted by a simple model, accounting for the influence of residual stresses and hardness values at the different depths at which cracks started. Predictions of fatigue strength are compared with data generated in this study.

  17. A Numerical Modelling Approach for Time-Dependent Deformation of Hot Forming Tools under the Creep-Fatigue Regime

    Directory of Open Access Journals (Sweden)

    B. Reggiani

    2016-01-01

    Full Text Available The present study was aimed at predicting the time-dependent deformation of tools used in hot forming applications subjected to the creep-fatigue regime. An excessive accumulated plastic deformation is configured as one of the three main causes of premature failure of tools in these critical applications and it is accumulated cycle by cycle without evident marks leading to noncompliant products. With the aim of predicting this accumulated deformation, a novel procedure was developed, presented, and applied to the extrusion process as an example. A time-hardening primary creep law was used and novel regression equations for the law’s coefficients were developed to account not only for the induced stress-temperature state but also for the dwell-time value, which is determined by the selected set of process parameters and die design. The procedure was validated against experimental data both on a small-scale extrusion die at different stress, temperature, load states, and for different geometries and on an industrial extrusion die which was discarded due to the excessive plastic deformation after 64 cycles. A numerical-experimental good agreement was achieved.

  18. Hyperthermia and fatigue

    DEFF Research Database (Denmark)

    Nybo, Lars

    2008-01-01

    of the cardiovascular function, which eventually reduces arterial oxygen delivery to the exercising muscles. Accordingly, aerobic energy turnover is impaired and anaerobic metabolism provokes peripheral fatigue. In contrast, metabolic disturbances of muscle homeostasis are less important during prolonged exercise......The present review addresses mechanisms of importance for hyperthermia-induced fatigue during short intense activities and prolonged exercise in the heat. Inferior performance during physical activities with intensities that elicit maximal oxygen uptake is to a large extent related to perturbation...... of the dopaminergic system, but may primarily relate to inhibitory signals from the hypothalamus arising secondary to an increase in brain temperature. Fatigue is an integrated phenomenon, and psychological factors, including the anticipation of fatigue, should not be neglected and the interaction between central...

  19. Fatigue in soccer

    DEFF Research Database (Denmark)

    Mohr, Magni; Krustrup, Peter; Bangsbo, Jens

    2005-01-01

    This review describes when fatigue may develop during soccer games and the potential physiological mechanisms that cause fatigue in soccer. According to time?-?motion analyses and performance measures during match-play, fatigue or reduced performance seems to occur at three different stages......, acidity or the breakdown of creatine phosphate. Instead, it may be related to disturbances in muscle ion homeostasis and an impaired excitation of the sarcolemma. Soccer players' ability to perform maximally is inhibited in the initial phase of the second half, which may be due to lower muscle...... concentrations in a considerable number of individual muscle fibres. In a hot and humid environment, dehydration and a reduced cerebral function may also contribute to the deterioration in performance. In conclusion, fatigue or impaired performance in soccer occurs during various phases in a game, and different...

  20. 基于面部视觉特征的精神疲劳可拓辨识模型%Mental Fatigue Recognition Extension Model Based on Facial Visual Cues

    Institute of Scientific and Technical Information of China (English)

    陈云华; 余永权; 张灵; 丁伍洋

    2013-01-01

    在基于面部视觉特征的精神疲劳辨识中,被测者的生活、工作负担和睡眠质量等背景信息对于准确辨识疲劳具有非常重要的作用,但却无法直接从面部视频中获取.为此,以可拓学的理论和思想方法为基础,结合经典数学的一些方法和现有的计算机视觉技术,提出并构建了一种全新的精神疲劳可拓辨识模型.该模型基于矛盾转化的思想,将无法直接从面部视频中获取到的背景信息转化为与之相关联的可以直接从面部视频中获取到的面部疲态的计算,并融合现有的面部疲劳特征进行精神疲劳辨识.实验结果验证了该模型的有效性.%The background information,such as life burden,work load and sleep quality, plays a very important role in mental fatigue recognition based on facial visual cues, however, they cannot be directly extracted from facial video. Based on the theory, ideals and methods of extenics,combined with some classic mathematical methods and existing computer vision technology, this paper proposed a new mental fatigue extension recognition model. Based on the idea of contradictions transformation, the background information which cannot be directly extracted from the facial video is translated into the corresponding facial fatigue appearance in the model,and the facial fatigue appearance can be directly extracted from the facial video. And this model also proposes a fusion approach for existing facial fatigue visual cues and facial fatigue appearance to recognize mental fatigue. The experimental results verify the validity of the model.

  1. Probabilistic Model of Fatigue Damage in Steel Box-girder Bridge Subject to Stochastic Vehicle Loads%随机车载下钢箱梁桥疲劳损伤概率模型

    Institute of Scientific and Technical Information of China (English)

    罗媛; 颜东煌; 鲁乃唯; 汪勤用

    2016-01-01

    将具有确定性参数的典型疲劳车辆模型改进为随机疲劳车流模型,采用小样本车辆轴重与等效疲劳应力数据拟合响应面的方法解决了车流作用下桥梁有限元应力时程分析耗时过长的问题.提出钢箱梁顶板-U肋疲劳损伤概率建模方法,最后将疲劳损伤概率模型应用于可靠度评估领域,揭示了车流参数对结构疲劳可靠指标的影响规律.研究结果表明:行车道重载车辆的较高占有率是导致其顶板-U肋疲劳可靠指标远低于超车道的重要原因;车辆轴重的增长致使钢箱梁疲劳可靠指标迅速降低,车重年线性增长系数由0增长至1%时,行车道顶板-U肋处100 a的疲劳可靠指标由3.42下降至0.72.随机疲劳车流模型与疲劳损伤概率模型具有一定的应用前景.%The typical fatigue truck model with deterministic parameters is developed to be a stochastic vehicle flow model. The time-consuming problem of bridge finite element analysis under traffic flow loads is solved by using a response surface method to approximate the function between vehicle axle weight of a few training data and equivalent fatigue stresses. A probabilistic fatigue damage modeling method applies to rib-to-deck details of steel box-girder bridges is presented. Finally, the fatigue damage model is applied to the reliability assessment, and the influence of traffic flow parameters on structural fatigue reliability is revealed. The numerical result indicates that (1) the higher occupancy rate of heavy vehicle flow in the slow lane is the main reason for the decrease of the fatigue reliability of corresponding rib-to-deck details compared with the fast lane;(2) the increase of the vehicle axle weight causes a rapid decrease of the fatigue reliability index of the steel box girders, when the annual linear growth factor increases from 0 to 1%, the fatigue reliability index of rib-to-deck detail in the slow lane decreases from 3. 42 to 0. 72 . There is

  2. 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....

  3. Compassion Fatigue: An Application of the Concept to Informal Caregivers of Family Members with Dementia

    OpenAIRE

    2011-01-01

    Introduction. Compassion fatigue is a concept used with increasing frequency in the nursing literature. The objective of this paper is to identify common themes across the literature and to apply these themes, and an existing model of compassion fatigue, to informal caregivers for family members with dementia. Findings. Caregivers for family members with dementia may be at risk for developing compassion fatigue. The model of compassion fatigue provides an informative framework for understandi...

  4. On the evolution and comparison of multiaxial fatigue criteria

    Directory of Open Access Journals (Sweden)

    B. Kenmeugne

    2012-02-01

    Full Text Available This paper opens up with the definition of some fatigue criteria for multiaxial cyclic loading. This introduces the problem of the prevalence of random multiaxial loading in the service environment ofmechanical components. Following this introduction, a survey of fatigue criteria found in the literature is presented. A comparative analysis of some fatigue models is also presented. This analysis suggests that the selection of a fatigue criterion be based on whether or not the principal directions of stress tensors are mobile or invariable with time.

  5. Mental fatigue impairs emotion regulation.

    Science.gov (United States)

    Grillon, Christian; Quispe-Escudero, David; Mathur, Ambika; Ernst, Monique

    2015-06-01

    Because healthy physical and mental functioning depends on the ability to regulate emotions, it is important to identify moderators of such regulations. Whether mental fatigue, subsequent to the depletion of cognitive resources, impairs explicit emotion regulation to negative stimuli is currently unknown. This study explored this possibility. In a within-subject design over 2 separate sessions, healthy individuals performed easy (control session) or difficult (depletion session) cognitive tasks. Subsequently, they were presented with neutral and negative pictures, with instructions to either maintain or regulate (i.e., reduce) the emotions evoked by the pictures. Emotional reactivity was probed with the startle reflex. The negative pictures evoked a similar aversive state in the control and depletion sessions as measured by startle potentiation. However, subjects were able to down-regulate their aversive state only in the control session, not in the depletion session. These results indicate that mental fatigue following performance of cognitive tasks impairs emotion regulation without affecting emotional reactivity. These findings suggest that mental fatigue needs to be incorporated into models of emotion regulation.

  6. Fatigue Crack Topography.

    Science.gov (United States)

    1984-01-01

    evaluating ciack initiation time and crack propagation, prgram I was used for performing the major fatigue test with the aircraft structure. In...advantage to begin with the end of the fracture, this is especially so in the case of the quantitative evaluation of striations. The overload fracture...Select the Measuring Line for Quantitative Evaluation Actually, the fatigue fracture should be inspected completely from the point of origin to the

  7. The Recognition Of Fatigue

    DEFF Research Database (Denmark)

    Elsass, Peter; Jensen, Bodil; Mørup, Rikke;

    2007-01-01

    Elsass P., Jensen B., Morup R., Thogersen M.H. (2007). The Recognition Of Fatigue: A qualitative study of life-stories from rehabilitation clients. International Journal of Psychosocial Rehabilitation. 11 (2), 75-87......Elsass P., Jensen B., Morup R., Thogersen M.H. (2007). The Recognition Of Fatigue: A qualitative study of life-stories from rehabilitation clients. International Journal of Psychosocial Rehabilitation. 11 (2), 75-87...

  8. Barriers to Combating Human Trafficking in Colombia

    Science.gov (United States)

    2015-03-01

    COMBATING HUMAN TRAFFICKING IN COLOMBIA by Daniel Joseph Wilcox March 2015 Thesis Advisor: Rodrigo Nieto-Gómez Second Reader: Maiah Jaskoski...Master ’s Thesis 4. TITLE AND SUBTITLE BARRIERS TO COMBATING HUMAN TRAFFICKING IN COLOMBIA 6. AUTHOR(S) Daniel Joseph Wilcox 7. PERFORMING...maximum 200 words) 12b. DISTRIBUTION CODE Despite intema.tional and domestic policies and programs intended to combat human trafficking , Colombia

  9. Driver Fatigue Features Extraction

    Directory of Open Access Journals (Sweden)

    Gengtian Niu

    2014-01-01

    Full Text Available Driver fatigue is the main cause of traffic accidents. How to extract the effective features of fatigue is important for recognition accuracy and traffic safety. To solve the problem, this paper proposes a new method of driver fatigue features extraction based on the facial image sequence. In this method, first, each facial image in the sequence is divided into nonoverlapping blocks of the same size, and Gabor wavelets are employed to extract multiscale and multiorientation features. Then the mean value and standard deviation of each block’s features are calculated, respectively. Considering the facial performance of human fatigue is a dynamic process that developed over time, each block’s features are analyzed in the sequence. Finally, Adaboost algorithm is applied to select the most discriminating fatigue features. The proposed method was tested on a self-built database which includes a wide range of human subjects of different genders, poses, and illuminations in real-life fatigue conditions. Experimental results show the effectiveness of the proposed method.

  10. Compassion Fatigue: An Application of the Concept to Informal Caregivers of Family Members with Dementia

    Directory of Open Access Journals (Sweden)

    Jennifer R. Day

    2011-01-01

    Full Text Available Introduction. Compassion fatigue is a concept used with increasing frequency in the nursing literature. The objective of this paper is to identify common themes across the literature and to apply these themes, and an existing model of compassion fatigue, to informal caregivers for family members with dementia. Findings. Caregivers for family members with dementia may be at risk for developing compassion fatigue. The model of compassion fatigue provides an informative framework for understanding compassion fatigue in the informal caregiver population. Limitations of the model when applied to this population were identified as traumatic memories and the emotional relationship between parent and child, suggesting areas for future research. Conclusions. Research is needed to better understand the impact of compassion fatigue on informal caregivers through qualitative interviews, to identify informal caregivers at risk for compassion fatigue, and to provide an empirical basis for developing nursing interventions for caregivers experiencing compassion fatigue.

  11. Compassion fatigue: an application of the concept to informal caregivers of family members with dementia.

    Science.gov (United States)

    Day, Jennifer R; Anderson, Ruth A

    2011-01-01

    Introduction. Compassion fatigue is a concept used with increasing frequency in the nursing literature. The objective of this paper is to identify common themes across the literature and to apply these themes, and an existing model of compassion fatigue, to informal caregivers for family members with dementia. Findings. Caregivers for family members with dementia may be at risk for developing compassion fatigue. The model of compassion fatigue provides an informative framework for understanding compassion fatigue in the informal caregiver population. Limitations of the model when applied to this population were identified as traumatic memories and the emotional relationship between parent and child, suggesting areas for future research. Conclusions. Research is needed to better understand the impact of compassion fatigue on informal caregivers through qualitative interviews, to identify informal caregivers at risk for compassion fatigue, and to provide an empirical basis for developing nursing interventions for caregivers experiencing compassion fatigue.

  12. Real-Time Assessment of Fatigue in Patients With Multiple Sclerosis: How Does It Relate to Commonly Used Self-Report Fatigue Questionnaires?

    Science.gov (United States)

    Heine, Martin; van den Akker, Lizanne Eva; Blikman, Lyan; Hoekstra, Trynke; van Munster, Erik; Verschuren, Olaf; Visser-Meily, Anne; Kwakkel, Gert

    2016-11-01

    (1) To assess real-time patterns of fatigue; (2) to assess the association between a real-time fatigue score and 3 commonly used questionnaires (Checklist Individual Strength [CIS] fatigue subscale, Modified Fatigue Impact Scale (MFIS), and Fatigue Severity Scale [FSS]); and (3) to establish factors that confound the association between the real-time fatigue score and the conventional fatigue questionnaires in patients with multiple sclerosis (MS). Cross-sectional study. MS-specialized outpatient facility. Ambulant patients with MS (N=165) experiencing severe self-reported fatigue. Not applicable. A real-time fatigue score was assessed by sending participants 4 text messages on a particular day (How fatigued do you feel at this moment?; score range, 0-10). Latent class growth mixed modeling was used to determine diurnal patterns of fatigue. Regression analyses were used to assess the association between the mean real-time fatigue score and the CIS fatigue subscale, MFIS, and FSS. Significant associations were tested for candidate confounders (eg, disease severity, work status, sleepiness). Four significantly different fatigue profiles were identified by the real-time fatigue score, namely a stable high (n=79), increasing (n=57), stable low (n=16), and decreasing (n=13). The conventional questionnaires correlated poorly (rquestionnaires, ranging from 15.4% to 35%. Perceived fatigue showed 4 different diurnal patterns in patients with MS. Severity of sleepiness is an important confounder to take into account in the assessment of fatigue. Copyright © 2016 American Congress of Rehabilitation Medicine. Published by Elsevier Inc. All rights reserved.

  13. Biopsychosocial determinants of physical and mental fatigue in patients with spondyloarthropathy.

    Science.gov (United States)

    Da Costa, Deborah; Zummer, Michel; Fitzcharles, Mary-Ann

    2011-04-01

    The objectives of this study are to characterize fatigue in patients with spondyloarthropathy (SpA) using a multidimensional assessment and to delineate contributors to dimensions of fatigue. Fatigue in 125 participants with SpA was assessed using the Multidimensional Fatigue Inventory (MFI-20). Participants completed standardized questionnaires assessing sleep quality, depressed mood, perceived stress, social support, leisure time physical activity, functional capacity, and disease activity. Hierarchical multiple regressions were computed to identify contributors to physical and mental fatigue. Patients scored high on all five MFI-20 fatigue dimensions, with general fatigue and physical fatigue having the highest scores. A hierarchical multiple regression showed that worse functional capacity, greater perceived stress, more depressed mood and less participation in leisure time physical activity contributed to higher physical fatigue scores. The results of the second model found depressed mood to be the strongest determinant of mental fatigue, followed by poorer sleep quality and younger age. These findings indicate that fatigue in SpA is a multidimensional experience, with physical and mental aspects likely having different etiologies. A number of variables potentially amenable to treatment were found to be associated with physical and mental fatigue. A multidimensional assessment of fatigue in SpA is needed to tailor and optimize interventions aimed at alleviating fatigue.

  14. 疲劳裂纹扩展的非平衡统计模型%Nonequilibrium Statistical Modeling of Fatigue Crack Growth Behaviour

    Institute of Scientific and Technical Information of China (English)

    胡海云; 邢修三

    2001-01-01

    In order to study the influence of microstructural texture on the growth of short fatigue cracks in metals, the nonequilibrium statistical theory of fatigue fracture correlating a microscopic mechanism with the macroscopic properties is modified to take into consideration the microstructural features of a material, thereby allowing a rationalisation of the experimental data of short fatigue crack growth and long fatigue crack growth. The nonequilibrium statistical theory thus developed relates the growth of cracks with a dislocation mechanism to simulate short fatigue crack growth with the long fatigue crack growth behaviour and predicts the fatigue crack growth rates throughout the fatigue lifetime. The results is finally compared with that of other fatigue theories.%为了研究金属中微观结构对疲劳短裂纹扩展性能的影响,在宏观与微观相结合的疲劳断裂非平衡统计理论中,考虑了材料微观结构因素,从而能够合理地解释有关疲劳短裂纹及长裂纹的实验结果.建立的非平衡统计理论模型把位错机理同裂纹扩展联系起来进行模拟,得到了包括疲劳短裂纹及长裂纹的整个金属疲劳寿命内的普适裂纹扩展速率公式,并和他人的理论结果进行了比较.

  15. Fatigue Reliability of Casted Wind Turbine Components Due to Defects

    DEFF Research Database (Denmark)

    Rafsanjani, Hesam Mirzaei; Sørensen, John Dalsgaard

    2015-01-01

    and their influence on the fatigue strength of the components. The fatigue life is dependent on the number, type, location and size of the defects in the component and is therefore quite uncertain and needs to be described by stochastic models. In this paper, the Poisson distribution for modeling of defects...... of component are considered and the surface and sub-surface defects categorized. Furthermore, a model to estimate the probability of failure by fatigue due to the defects is proposed. This model is used to estimate the failure location of component and it is compared to models of defect distributions...

  16. Detecting Intelligent Agent Behavior with Environment Abstraction in Complex Air Combat Systems

    Science.gov (United States)

    2013-01-01

    by concept explorations, “wh optimizations of the models co y at multiple levels, the onceptual framework also 12, 13]. Starting from the tual...l with the modeling layer – where we have in frameworks as well as dynamic system forma Finally, the pragmatic level includes use of ON A: Approved...levels N (EA) rm and the DIS nal capabilities, on in a combat he entire combat formation to the orm level. The frastructure) are m2DIS API as

  17. Numerical Studies of Low Cycle Fatigue in Forward Extrusion Dies

    DEFF Research Database (Denmark)

    Pedersen, Thomas Ø

    2000-01-01

    Forward extrusion dies typically fail due to transverse fatigue cracks or wear. Fatigue cracks are initiated in regions where the material is subjected to repeated plastic deformations, e.g. the transition radius in a forward extrusion die, in the present work, a material model capable of describ...

  18. Partial Safety Factors for Fatigue Design of Wind Turbine Blades

    DEFF Research Database (Denmark)

    Toft, Henrik Stensgaard; Sørensen, John Dalsgaard

    2010-01-01

    In the present paper calibration of partial safety factors for fatigue design of wind turbine blades is considered. The stochastic models for the physical uncertainties on the material properties are based on constant amplitude fatigue tests and the uncertainty on Miners rule for linear damage...

  19. Optimal Repellent Usage to Combat Dengue Fever.

    Science.gov (United States)

    Dorsett, Chasity; Oh, Hyunju; Paulemond, Marie Laura; Rychtář, Jan

    2016-05-01

    Dengue fever is one of the most important vector-borne diseases. It is transmitted by Aedes Stegomyia aegypti, and one of the most effective strategies to combat the disease is the reduction of exposure to bites of these mosquitoes. In this paper, we present a game-theoretical model in which individuals choose their own level of protection against mosquito bites in order to maximize their own benefits, effectively balancing the cost of protection and the risk of contracting the dengue fever. We find that even when the usage of protection is strictly voluntary, as soon as the cost of protection is about 10,000 times less than the cost of contracting dengue fever, the optimal level of protection will be within 5 % of the level needed for herd immunity.

  20. Statistical optimisation techniques in fatigue signal editing problem

    Energy Technology Data Exchange (ETDEWEB)

    Nopiah, Z. M.; Osman, M. H. [Fundamental Engineering Studies Unit Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 UKM (Malaysia); Baharin, N.; Abdullah, S. [Department of Mechanical and Materials Engineering Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, 43600 UKM (Malaysia)

    2015-02-03

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

  1. Target distribution in cooperative combat based on Bayesian optimization algorithm

    Institute of Scientific and Technical Information of China (English)

    Shi Zhifu; Zhang An; Wang Anli

    2006-01-01

    Target distribution in cooperative combat is a difficult and emphases. We build up the optimization model according to the rule of fire distribution. We have researched on the optimization model with BOA. The BOA can estimate the joint probability distribution of the variables with Bayesian network, and the new candidate solutions also can be generated by the joint distribution. The simulation example verified that the method could be used to solve the complex question, the operation was quickly and the solution was best.

  2. A criterion for high-cycle fatigue life and fatigue limit prediction in biaxial loading conditions

    Institute of Scientific and Technical Information of China (English)

    ukasz Pejkowski; Dariusz Skibicki

    2016-01-01

    This paper presents a criterion for high-cycle fatigue life and fatigue strength estimation under periodic proportional and non-proportional cyclic loading. The cri-terion is based on the mean and maximum values of the second invariant of the stress deviator. Important elements of the criterion are: function of the non-proportionality of fatigue loading and the materials parameter that expresses the materials sensitivity to non-proportional loading. The methods for the materials parameters determination uses three S–N curves: tension–compression, torsion, and any non-proportional loading proposed. The criterion has been verified using experimental data, and the results are included in the paper. These results should be considered as promis-ing. The paper also includes a proposal for multiaxial fatigue models classification due to the approach for the non-proportionality of loading.

  3. Thermal fatigue of beryllium

    Energy Technology Data Exchange (ETDEWEB)

    Deksnis, E.; Ciric, D.; Falter, H. [JET Joint undertaking, Abingdon (United Kingdom)] [and others

    1995-09-01

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

  4. STRESS-STRAIN FINITE ELEMENT ANALYSIS AND FATIGUE LIFE PREDICTION FOR BOLTED CONNECTIONS

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    A cyclic plasticity model is used into finite element (FE) method to obtain the details of elastic-plastic stress-strain in the bolts under cyclic axial loading. Two criteria in multiaxial fatigue are employed to predict fatigue lives of bolts. The predicted fatigue lives are in favorable agreement with the experimental results for machined bolts.

  5. Tactical/Combat Engines Cetane Window Evaluation

    Science.gov (United States)

    2013-01-31

    custom diesel fuels typically used in Homogeneous Charge Coupled Ignition ( HCCI ) research engines . These fuels are characterized by a very heavy...UNCLASSIFIED TACTICAL/COMBAT ENGINES CETANE WINDOW EVALUATION INTERIM REPORT TFLRF No. 436 by Gregory A. Hansen, Douglas Yost...report when no longer needed. Do not return it to the originator. UNCLASSIFIED UNCLASSIFIED TACTICAL/COMBAT ENGINES CETANE WINDOW

  6. Suicide attempts in U.S. Army combat arms, special forces and combat medics.

    Science.gov (United States)

    Ursano, Robert J; Kessler, Ronald C; Naifeh, James A; Mash, Holly Herberman; Fullerton, Carol S; Ng, Tsz Hin Hinz; Aliaga, Pablo A; Wynn, Gary H; Dinh, Hieu M; McCarroll, James E; Sampson, Nancy A; Kao, Tzu-Cheg; Schoenbaum, Michael; Heeringa, Steven G; Stein, Murray B

    2017-05-25

    The U.S. Army suicide attempt rate increased sharply during the wars in Iraq and Afghanistan. Risk may vary according to occupation, which significantly influences the stressors that soldiers experience. Using administrative data from the Army Study to Assess Risk and Resilience in Servicemembers (Army STARRS), we identified person-month records for all active duty Regular Army enlisted soldiers who had a medically documented suicide attempt from 2004 through 2009 (n = 9650) and an equal-probability sample of control person-months (n = 153,528). Logistic regression analyses examined the association of combat occupation (combat arms [CA], special forces [SF], combat medic [CM]) with suicide attempt, adjusting for socio-demographics, service-related characteristics, and prior mental health diagnosis. In adjusted models, the odds of attempting suicide were higher in CA (OR = 1.2 [95% CI: 1.1-1.2]) and CM (OR = 1.4 [95% CI: 1.3-1.5]), but lower in SF (OR = 0.3 [95% CI: 0.2-0.5]) compared to all other occupations. CA and CM had higher odds of suicide attempt than other occupations if never deployed (ORs = 1.1-1.5) or previously deployed (ORs = 1.2-1.3), but not when currently deployed. Occupation was associated with suicide attempt in the first ten years of service, but not beyond. In the first year of service, primarily a time of training, CM had higher odds of suicide attempt than both CA (OR = 1.4 [95% CI: 1.2-1.6]) and other occupations (OR = 1.5 [95% CI: 1.3-1.7]). Discrete-time hazard functions revealed that these occupations had distinct patterns of monthly risk during the first year of service. Military occupation can inform the understanding suicide attempt risk among soldiers.

  7. Combat ready clamp medic technique.

    Science.gov (United States)

    Tovmassian, Robert V; Kragh, John F; Dubick, Michael A; Baer, David G; Blackbourne, Lorne H

    2012-01-01

    Junctional hemorrhage control device use on the battlefield might be lifesaving, but little experience is reported. The purpose of the present case report is to detail prehospital use of the Combat Ready Clamp (called the CRoC by its users, Combat Medical Systems, Fayetteville, NC; Instructions for Use, 2010) in casualty care in order to increase awareness of junctional hemorrhage control. The CRoC was used to control difficult inguinal bleeding on the battlefield for an Afghani man with a hindquarter traumatic amputation. The device promptly controlled exsanguination from a critical injury when placed during rotary-wing casualty evacuation. The flight medic applied the device in 90 seconds. The device performed well without complications to control bleeding. The CRoC, a new junctional hemorrhage control device, was used as indicated on the battlefield with mechanical and physiologic success and without device problems. By controlling difficult inguinal bleeding resulting from battlefield trauma, the device facilitated casualty stabilization and delivery to a surgical facility. The device facilitated the ability of a new flight medic to focus his expertise on a critically injured battlefield casualty with demonstrable success. 2012.

  8. A Life Prediction Model for Low Cycle Fatigue Based on Continuum Damage Mechanics%一种基于连续损伤力学的低周疲劳寿命预测模型

    Institute of Scientific and Technical Information of China (English)

    陈凌; 张贤明; 欧阳平

    2015-01-01

    According to the basic conservation law of continuous media and continuum damage me-chanics,the decrease of effective bearing area caused by the material fatigue damage could be expressed as a function of mean strain.The low cycle fatigue damage evolution of the micro crack stage and the fatigue crack stage were analyzed.And then,a model for the life prediction of low cycle fatigue was es-tablished.Through low cycle fatigue experiments with smooth specimens of 31 6L steel at 420℃ under stress control,the damage evolution were described and the fatigue life prediction was carried out by the method mentioned above.Results show that the micro crack stage is the main stage of low cycle fatigue life consumption of material.And compared with the experimental data,it is found that the predicted results which are obtained by the sampling data of different life periods are in good agree-ment with the experimental ones.%基于连续介质基本守恒定律和连续损伤力学,可将材料疲劳损伤造成的有效承载面积减小表示为平均应变的函数,在此基础上,按微裂纹阶段和疲劳裂纹阶段对材料低周疲劳的损伤演化进行了分析,并建立了一种低周疲劳寿命预测模型。对316L 钢光滑试样进行420℃环境下应力控制的低周疲劳试验,采用上述方法进行损伤描述和寿命预测。结果表明微裂纹阶段是材料低周疲劳寿命消耗的主要阶段,采用各寿命段采样数据获得的寿命预测结果与试验结果较符合。

  9. 地面无人作战系统机械臂运动学建模与仿真%Establishment and Simulation Study on Kinematics Model of Unmanned Ground Combat Vehicle Robot Manipulators

    Institute of Scientific and Technical Information of China (English)

    席雷平; 陈自力; 田庆民

    2012-01-01

    The correlative problem of robotic manipulators kinematics model is discussed for Unmanned Ground Combat Vehicle in this paper. Considering the structure of robotic manipulators, the kinematics model is established with D-H method. Based on it,the forward and inverse kinematics equations are solved. Then,simulation and verification is performed by Robotics Toolbox of Matlab software for the structure and kinematics analysis. The results show that this method is correct and feasible.%以某地面无人作战系统中的机械臂为研究对象,探讨其运动学模型建立中的相关问题.结合该机械臂的结构特点,利用D-H方法建立其相应的运动学模型,并在该基础上求解机械臂的正、逆运动学方程.最后在Matlab环境下,借助Robotics Toolbox工具箱对该机械臂的结构和运动学问题进行验证和仿真.仿真结果表明:该设计方法是正确可行的.

  10. Trajectories of Evening Fatigue in Oncology Outpatients Receiving Chemotherapy

    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 a distressing, persistent sense of physical tiredness that is not proportional to a person’s recent activity. Fatigue impacts patients’ treatment decisions and can limit their self-care activities. While significant interindividual variability in fatigue severity has been noted, little is known about predictors of interindividual variability in initial levels and trajectories of evening fatigue severity in oncology patients receiving chemotherapy (CTX). Objectives To determine whether demographic, clinical, and symptom characteristics were associated with initial levels as well as the trajectories of 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 evening fatigue trajectories. A piecewise model fit the data best. Patients who were White, diagnosed with breast, gynecological, or lung cancer, and who had more years of education, child care responsibilities, lower functional status, and higher levels of sleep disturbance and depression reported higher levels of evening fatigue at enrollment. Conclusion This study identified both non-modifiable (e.g., ethnicity) and modifiable (e.g., child care responsibilities, depressive symptoms, sleep disturbance) risk factors for more severe evening fatigue. Using this information, clinicians can identify patients at higher risk for more severe evening fatigue, provide individualized patient education, and tailor interventions to address the modifiable risk factors. PMID:25828560

  11. Effects of Pilates exercises on sensory interaction, postural control and fatigue in patients with multiple sclerosis.

    Science.gov (United States)

    Soysal Tomruk, Melda; Uz, Muhammed Zahid; Kara, Bilge; İdiman, Egemen

    2016-05-01

    Decreased postural control, sensory integration deficits and fatigue are important problems that cause functional impairments in patients with multiple sclerosis (pwMS). To examine the effect of modified clinical Pilates exercises on sensory interaction and balance, postural control and fatigue in pwMS. Eleven patients with multiple sclerosis and 12 healthy matched controls were recruited in this study. Limits of stability and postural stability tests were used to evaluate postural control by Biodex Balance System and sensory interaction assessed. Fatigue was assessed by Modified Fatigue Impact Scale. Pilates exercises were applied two times a week for 10 weeks and measurements were repeated to pwMS after exercise training. Postural control and fatigue (except psychosocial parameter) of pwMS were significantly worser than healthy controls (pPilates training (ppilates exercises (p>0.05). Ten-week Pilates training is effective to improve sensory interaction and to decrease fatigue. Pilates exercises can be applied safely in ambulatory pwMS for enhance sensory interaction and balance and combat fatigue. More investigations are needed. Copyright © 2016 Elsevier B.V. All rights reserved.

  12. Crack nucleation using combined crystal plasticity modelling, high-resolution digital image correlation and high-resolution electron backscatter diffraction in a superalloy containing non-metallic inclusions under fatigue.

    Science.gov (United States)

    Zhang, Tiantian; Jiang, Jun; Britton, Ben; Shollock, Barbara; Dunne, Fionn

    2016-05-01

    A crystal plasticity finite-element model, which explicitly and directly represents the complex microstructures of a non-metallic agglomerate inclusion within polycrystal nickel alloy, has been developed to study the mechanistic basis of fatigue crack nucleation. The methodology is to use the crystal plasticity model in conjunction with direct measurement at the microscale using high (angular) resolution-electron backscatter diffraction (HR-EBSD) and high (spatial) resolution-digital image correlation (HR-DIC) strain measurement techniques. Experimentally, this sample has been subjected to heat treatment leading to the establishment of residual (elastic) strains local to the agglomerate and subsequently loaded under conditions of low cyclic fatigue. The full thermal and mechanical loading history was reproduced within the model. HR-EBSD and HR-DIC elastic and total strain measurements demonstrate qualitative and quantitative agreement with crystal plasticity results. Crack nucleation by interfacial decohesion at the nickel matrix/agglomerate inclusion boundaries is observed experimentally, and systematic modelling studies enable the mechanistic basis of the nucleation to be established. A number of fatigue crack nucleation indicators are also assessed against the experimental results. Decohesion was found to be driven by interface tensile normal stress alone, and the interfacial strength was determined to be in the range of 1270-1480 MPa.

  13. Fatigue life prediction in composites

    CSIR Research Space (South Africa)

    Huston, RJ

    1994-01-01

    Full Text Available as the modulus is measured accurately. Its main disadvantage is that it can be applied only to constant amplitude fatigue loadings. REFERENCES 1. Mandell, J. F., Huang, D. D. & McGarry, F. J., Tensile fatigue performance...

  14. Fatigue Reliability Assessment of Correlated Welded Web-frame Joints

    Institute of Scientific and Technical Information of China (English)

    W. Huang; Y. Garbatov; C. Guedes Soares

    2014-01-01

    The objective of this work is to analyze the fatigue reliability of complex welded structures composed of multiple web-frame joints, accounting for correlation effects. A three-dimensional finite element model using the 20-node solid elements is generated. A linear elastic finite element analysis was performed, hotspot stresses in a web-frame joint were analyzed and fatigue damage was quantified employing the S-N approach. The statistical descriptors of the fatigue life of a non-correlated web-frame joint containing several critical hotspots were estimated. The fatigue reliability of a web-frame joint wasmodeled as a series system of correlated components using the Ditlevsen bounds. The fatigue reliability of the entire welded structure with multiple web-frame joints, modeled as a parallel system of non-correlated web-frame joints was also calculated.

  15. Fatigue Behavior for Composite Laminates with Circular Hole

    Institute of Scientific and Technical Information of China (English)

    Qi Hongyu; Wen Weidong; Sun Lianwen

    2004-01-01

    Based on the fatigue model of exponential function and WN criterion of static strength for the composite material laminates with a circular hole, the stress correct factorβ is presented. In order to gain the factorβ, the fatigue experiments of laminates with holes in different diameters and the same ratio of width and diameter. The fatigue behavior is usually accompanied with extensive damages. Those damages can affect composite materials in their strength and stiffness. The new model based on damage theory and strain equivalent hypothesis meets engineering requirement.T300/KH304, which is recently studied, is a high capability composite material. The fatigue analysis and tests of laminates with a hole in diameter of 5 mm are carried under difference stress levels. The simple, prompt and practical method was provided for the predication of fatigue life of composite material plate with a circular hole.

  16. Fatigue design 1998

    Energy Technology Data Exchange (ETDEWEB)

    Marquis, G.; Solin, J. [eds.] [VTT Manufacturing Technology, Espoo (Finland)

    1998-12-31

    These preprints contain the presentations to be delivered at the Fatigue Design 1998 symposium held on May 26-29, 1998 in Espoo. Fatigue Design 1998 is the tenth in a series of VTT symposia addressing the challenge of fatigue of materials, components and structures. Previous international events were in 1992 and 1995. The key theme of the current meeting is `RELIABILITY`. The two volumes (VTT symposium 181-182) represent 56 contributions by authors representing 26 countries. Emphasis has been given to application oriented research topics that report new technologies, new uses of existing methods and case studies. The objective of the symposium is to bring together researchers and engineers to share experiences and new innovations in designing reliable components to resist alternating loads. (orig.)

  17. Fatigue crack initiation for Al-Zn-Mg alloy welded joint

    Institute of Scientific and Technical Information of China (English)

    Liang ZHANG; Xuesong LIU; Linsen WANG; Ping WANG; Hongyuan FANG

    2012-01-01

    To investigate fatigue crack initiation characteristics of A1-Zn-Mg alloy welded joint,notched specimens were used in fatigue test for the base metal,welding bead and heat affected zone (HAZ).The fatigue fracture surface near the fatigue crack initiation site was observed by scanning electron microscope (SEM).The results show that the differences of fatigue crack initiation life among base metal,welding bead and HAZ are not obvious.Inhomogeneity in microstructure and mechanical performance of HAZ influences the fatigue crack initiation life.The ratio of fatigue crack initiation life (Ni) to fatigue failure life (Nf) for the base metal,welding bead and HAZ of A7N01 aluminium alloy welded joint are 26.32%,40.21% and 60.67%,respectively.Fatigue crack initiation life can be predicted using a uniform model.Observation of fatigue fracture surfaces shows that for the welding bead a fatigue crack initiates from the smooth surface due to the welding process,the blowhole in HAZ causes fatigue crack and the crushed second phase particles play an important role in fatigue crack initiation for the base metal.

  18. Fatigue in primary biliary cirrhosis

    OpenAIRE

    Cauch-Dudek, K; Abbey, S; Stewart, D; Heathcote, E

    1998-01-01

    Background—Fatigue is a frequent and debilitating symptom in patients with primary biliary cirrhosis (PBC). 
Aims—To study fatigue in relation to sleep, depression, and liver disease severity. 
Methods—Patients with PBC completed validated self report questionnaires measuring fatigue, sleep quality, depression, and functional capacity. Verbally reported fatigue and observer rated measure of depression and ursodeoxycholic acid (UDCA) use were recorded. Liver biochemistry and ...

  19. Fatigue Crack Extension Model of Aluminium Alloy with Prior Corrosion Damage Based on Localised Corrosion Damage%基于局部腐蚀损伤的铝合金预腐蚀疲劳裂纹扩展模型

    Institute of Scientific and Technical Information of China (English)

    孔光明; 李旭东; 穆志韬

    2014-01-01

    目的:建立铝合金预腐蚀疲劳裂纹扩展模型。方法采用表征局部环境腐蚀损伤影响程度的参数孔蚀率对腐蚀疲劳裂纹扩展速率进行修正。结果修正后的腐蚀铝合金试件的疲劳裂纹扩展速率与试验结果吻合程度良好。结论修正后的铝合金预腐蚀疲劳裂纹扩展速率模型合理有效,试验数据和预测模型可为海军飞机结构的损伤容限设计提供参考。%Objective To establish a modified model for pre-corrosion fatigue crack growth rate of aluminum alloy. Methods Considering that the local damage around the crack tip was more reasonable for accelerating crack growth rate in corrosive environment, the pitting rate, which was a parameter characterizing the influence of corrosion in local environ-ment, was used to correct the corrosion fatigue crack growth rate. Results The experimental results were in good agreement with predictions of the amended fatigue crack growth rate model for corroded aluminum alloy specimens. Conclusion The corrected aluminum alloy pre-corrosion fatigue crack growth rate model was reasonable and effective, and the test data and the prediction model could provide a reference for the damage tolerance design of navy aircraft structure.

  20. Randomized controlled trial of the Valencia model of waking hypnosis plus CBT for pain, fatigue, and sleep management in patients with cancer and cancer survivors.

    Science.gov (United States)

    Mendoza, M E; Capafons, A; Gralow, J R; Syrjala, K L; Suárez-Rodríguez, J M; Fann, J R; Jensen, M P

    2016-07-28

    This study evaluated the efficacy of an intervention combining the Valencia model of waking hypnosis with cognitive-behavioral therapy (VMWH-CBT) in managing cancer-related pain, fatigue, and sleep problems in individuals with active cancer or who were post-treatment survivors. We hypothesized that four sessions of VMWH-CBT would result in greater improvement in participants' symptoms than four sessions of an education control intervention. Additionally, we examined the effects on several secondary outcome domains that are associated with increases in these symptoms (depression, pain interference, pain catastrophizing, and cancer treatment distress). The study design was a randomized controlled crossover clinical trial comparing the VMWH-CBT intervention with education control. Participants (N = 44) received four sessions of both treatments, in a counterbalanced order (n = 22 per order condition). Participants were 89% female (N = 39) with mean age of 61 years (SD = 12.2). They reported significantly greater improvement after receiving the active treatment relative to the control condition in all the outcome measures. Treatment gains were maintained at 3-month follow-up. This study supports the beneficial effects of the VMWH-CBT intervention relative to a control condition and that treatment gains remain stable. VMWH-CBT-trained clinicians should be accessible for managing symptoms both during and after cancer treatment, though the findings need to be replicated in larger samples of cancer survivors. Copyright © 2016 John Wiley & Sons, Ltd.

  1. Probabilistic prediction of fatigue damage based on linear fracture mechanics

    Directory of Open Access Journals (Sweden)

    M. Krejsa

    2017-01-01

    Full Text Available Paper describes in detail and gives example of the probabilistic assessment of a steel structural element subject to fatigue load, particular attention being paid to cracks from the edge and those from surface. Fatigue crack damage depends on a number of stress range cycles. Three sizes are important for the characteristics of the propagation of fatigue cracks - the initial size, detectable size and acceptable size. The theoretical model of fatigue crack progression in paper is based on a linear fracture mechanics. When determining the required degree of reliability, it is possible to specify the time of the first inspection of the construction which will focus on the fatigue damage. Using a conditional probability, times for subsequent inspections can be determined. For probabilistic calculation of fatigue crack progression was used the original and new probabilistic methods - the Direct Optimized Probabilistic Calculation (“DOProC”, which is based on optimized numerical integration. The algorithm of the probabilistic calculation was applied in the FCProbCalc code (“Fatigue Crack Probabilistic Calculation”, using which is possible to carry out the probabilistic modelling of propagation of fatigue cracks in a user friendly environment very effectively.

  2. Fatigue failure analysis of pin-loaded lugs

    Directory of Open Access Journals (Sweden)

    Slobodanka Boljanović

    2016-01-01

    Full Text Available In the present paper, mathematical models are proposed in order to analyze the strength of pinloaded lugs with semi-elliptical crack and through-the-thickness crack. The crack growth investigation of considered crack configurations tackles the fatigue life evaluation and the crack path simulation of semi-elliptical crack. The residual strength is estimated by applying the two-parameter driving force model. The numerical and analytical approaches are employed for the stress intensity factor calculation. Experimental fatigue crack growth data are used in order to verify efficiency of the developed models. A good correlation between fatigue crack growth estimations and experimental observations is obtained.

  3. Compassion fatigue in military healthcare teams.

    Science.gov (United States)

    Owen, Regina Peterson; Wanzer, Linda

    2014-02-01

    Since the onset of the Iraq war and Afghanistan conflicts, military healthcare teams have had increasing exposure to the traumatic effects of caring for wounded warriors, leading to a phenomenon termed compassion fatigue. The purpose of this integrative review was to develop a proposed definition for compassion fatigue in support of these teams. There is no current standardized formal definition, and this lack of clarity can inhibit intervention. Seven main themes evolved from the literature review and were integrated with the core elements of the Bandura Social Cognitive Theory Model as the first step in developing a uniformed definition.

  4. Computer Simulations of the Fatigue Crack Propagation

    Directory of Open Access Journals (Sweden)

    A. Materna

    2000-01-01

    Full Text Available The following hypothesis for design of structures based on the damage tolerance philosophy is laid down: the perpendicular fatigue crack growth rate v in a certain point of a curved crack front is given by the local value of stress intensity factor per unit of nominal stress K' and the local triaxiality T which describes the constraint. The relationship v = f (K', T is supposed to be typical for a given loading spectrum and material. Such relationship for a 2024 Al alloy and the flight-simulation spectrum was derived from the fatigue test of the rectangular panel with the central hole and used for three-dimensional simulation of the corner fatigue crack propagation in the model of the wing spar flangeplate. Finite element and boundary element methods were used for these computations. The results of the simulation are in good agreement with the experiment.

  5. On the applicability of multi-surface, two-surface and non-linear kinematic hardening models in multiaxial fatigue

    Directory of Open Access Journals (Sweden)

    M.A. Meggiolaro

    2015-07-01

    Full Text Available In this work, a comparison between NLK and Mróz-Garud’s multi-surface formulations is presented. A unified common notation is introduced to describe the involved equations, showing that the Mróz-Garud model can be regarded as a particular case of the NLK formulation. It is also shown that the classic two-surface model, which is an unconventional simplified plasticity model based on the translation of only two surfaces, can also be represented using this formulation. Such common notation allows a direct quantitative comparison among multi-surface, two-surface, and NLK hardening models.

  6. Evaluation of combat service support logistics concepts for supplying a USMC Regimental Task Force

    OpenAIRE

    2001-01-01

    One of the primary responsibilities of a Marine Corps Combat Service Support Element (CSSE) is to provide water, fuel, and ammunition requirements for the primary task forces and other Marine Expeditionary Force (MEF) elements. This thesis evaluates existing and proposed concepts on how to best use the CSSE resources of a Force Service Support Group to transport supplies to Regimental Combat Teams over constrained networks with time constraints. A model was developed that optimizes the use of...

  7. A qualitative analysis of future air combat with 'fire and forget' missiles

    Science.gov (United States)

    Shinar, J.; Davidovitz, A.

    1987-01-01

    A set of previous examples have demonstrated that the two-target game formulation is adequate for modeling air-to-air combat between two aggressively motivated fighter aircraft. The present paper describes such an engagement between two aircraft of different speed but equipped with the same 'fire and forget' type guided missiles. The results of the analysis suggest a new concept of air combat tactics for future scenarios.

  8. The patient experience of fatigue in motor neurone disease

    Directory of Open Access Journals (Sweden)

    Chris J Gibbons

    2013-10-01

    Full Text Available Aims This paper is a qualitative investigation that aims to investigate the lived experience of fatigue in patients with motor neurone disease – a progressive and fatal neurological condition. Background Fatigue is a disabling symptom in motor neurone disease (MND that affects a large number of patients. However, the term ‘fatigue’ is in itself imprecise, as it remains a phenomenon without a widely accepted medical definition. This study sought to investigate the phenomenon of fatigue from the perspective of the MND patient. Methods Ten patients with MND participated in semi-structured recorded interviews at a regional neuroscience centre in Liverpool, U.K. Transcripts analysis was broadly informed by the principles of interpretative phenomenological analysis (IPA. Findings Fatigue was unanimously explained to be disabling and progressive phenomenon. Participants described two forms of fatigue: whole-body tiredness, or use-dependent reversible muscle weakness related to exertion of limb and bulbar muscles. Both weakness and whole-body tiredness could be experienced simultaneously, and patients used the terms ‘fatigue’ and ‘tiredness’ interchangeably. Alongside descriptions of fatigue themes of Adaptation, Motivation, Avoidance, Frustration and Stress were revealed. Fatigue could be defined as reversible motor weakness and whole-body tiredness that was predominantly brought on by muscular exertion and was partially relieved by rest.Conclusion The results of this study support a multi-dimensional model of fatigue for patients with MND. Fatigue appears to be experienced and explained in two ways, both as an inability to sustain motor function and as a pervasive tiredness. Fatigue was only partially relieved by rest and tended to worsen throughout the day. It is crucial that MND care practitioners and researchers appreciate the semantic dichotomy within fatigue.

  9. Analysis of Two-Parameter (△K and Kmax) Fatigue Crack Propagation Models%包含△K和Kmax二参数的疲劳裂纹扩展模型

    Institute of Scientific and Technical Information of China (English)

    钱怡; 崔维成

    2011-01-01

    除了材料自身特性和环境因素外,疲劳裂纹扩展的方式取决于裂纹尖端附近的应力场.而该应力场由外加应力和残余应力组成,受到引起循环塑性区的应力强度因子变化幅度△K和产生单调塑性区的最大应力强度因子Kmax的共同影响.因此,驱动裂纹扩展的外部驱动力应该是△K和Kmax.通过比较Vasudevan和Sadananda,Kuiawski、张嘉振等人提出的3种典型的二参数疲劳裂纹扩展模型的特点,提出了一个兼顾内、外应力,适合变幅载荷下疲劳裂纹扩展的新模型.%The fatigue crack growth is dominated by stress field around the crack-tip except for the material characteristics and the effect of environment. The stress around the crack-tip is the superimposition of the residual stress and the externally applied stress, which are affected by maximum stress intensity factor, Kmax, and stress intensity factor range, △K. The former can be associated with the monotonic plastic zone, while the latter with the cyclic plastic zone. Therefore, the fatigue crack driving force should include two parameters △K and Kmax. After comparing three kinds of fatigue crack growth rate models, which were derived by Vasudevan and Sadananda, Kujawski, and Zhang, a new fatigue crack growth rate model is proposed. The model can deal with the variable amplitude loading cases, and will take into account the residual stress and the externally applied stress.

  10. Traumatic andropause after combat injury.

    Science.gov (United States)

    Jones, Gareth Huw; Kirkman-Brown, Jackson; Sharma, Davendra Murray; Bowley, Douglas

    2015-08-28

    In association with lower extremity amputation, complex genitourinary injuries have emerged as a specific challenge in modern military trauma surgery. Testicular injury or loss has profound implications for the recovering serviceman, in terms of hormone production and future fertility. The initial focus of treatment for patients with traumatic testicular loss is haemostasis, resuscitation and management of concurrent life-threatening injuries. Multiple reoperations are commonly required to control infection in combat wounds; in a review of 300 major lower extremity amputations, 53% of limbs required revisional surgery, with infection the commonest indication. Atypical infections, such as invasive fungal organisms, can also complicate military wounding. We report the case of a severely wounded serviceman with complete traumatic andropause, whose symptomatic temperature swings were initially mistaken for signs of occult sepsis.

  11. Simulation model of fatigue crack opening/closing phenomena for predicting RPG load under arbitrary stress distribution field

    Energy Technology Data Exchange (ETDEWEB)

    Toyosada, M.; Niwa, T. [Kyushu Univ., Fukuoka (Japan)

    1995-12-31

    In this paper, Newman`s calculation model is modified to solve his neglected effect of the change of stress distribution ahead of a crack, and to leave elastic plastic materials along the crack surface because of the compatibility of Dugdale model. In addition to above treatment, the authors introduce plastic shrinkage at an immediate generation of new crack surfaces due to emancipation of internal force with the magnitude of yield stress level during unloading process in the model. Moreover, the model is expanded to arbitrary stress distribution field. By using the model, RPG load is simulated for a center notched specimen under constant amplitude loading with various stress ratios and decreased maximum load while keeping minimum load.

  12. Polarization Fatigue in Ferroelectric Thin Films

    Institute of Scientific and Technical Information of China (English)

    王忆; K.H.WONG; 吴文彬

    2002-01-01

    The fatigue problem in ferroelectric thin films is investigated based on the switched charge per unit area versus switching cycles. The temperature, dielectric permittivity, voltage bias, frequency and defect valence dependent switching polarization properties are calculated quantitatively with an extended Dawber-Scott model. The results are in agreement with the recent experiments.

  13. Exploring Chronic Fatigue Syndrome in Adolescents

    NARCIS (Netherlands)

    Putte, E.M. van de

    2006-01-01

    The research for this thesis has been conducted in three consecutive studies: Fatigue in Teenagers-I (FIT-I) in 2002, FIT-II in 2004 and FIT-III in 2006. In each FIT-study different research questions were formulated on the basis of the biopsychosocial model. The three FIT-studies resulted in the ch

  14. Enhancements to the Animated Tutor for Air Combat Simulation

    Science.gov (United States)

    1993-03-01

    1979 (30:11). Ada is named in honor of Augusta Ada Byron, Countess of Lovelace , who is reported to have been the first programmer (29:44). The first...Introduction. .. .. .. .. .... .... .... .... ......... 2-1 2.2 War Games .. .. .. .. .... .... .... .... ........... 2-1 2.3 History of Ada ...2-2 2.4 Ada Structures. .. .. .. .... .... .... .... ......... 2-3 2.5 Ada in Combat Modeling, Wargaming and Simulations 2-5 2.6

  15. Blended Training for Combat Medics

    Science.gov (United States)

    Fowlkes, Jennifer; Dickinson, Sandra; Lazarus, Todd

    2010-01-01

    Bleeding from extremity wounds is the number one cause of preventable death on the battlefield and current research stresses the importance of training in preparing every Soldier to use tourniquets. HapMed is designed to provide tourniquet application training to combat medics and Soldiers using a blended training solution encompassing information, demonstration, practice, and feedback. The system combines an instrumented manikin arm, PDA, and computer. The manikin arm provides several training options including stand-alone, hands-on skills training in which soldiers can experience the actual torque required to staunch bleeding from an extremity wound and be timed on tourniquet application. This is more realistic than using a block of wood to act as a limb, which is often how training is conducted today. Combining the manikin arm with the PDA allows instructors to provide scenario based training. In a classroom or field setting, an instructor can specify wound variables such as location, casualty size, and whether the wound is a tough bleed. The PDA also allows more detailed feedback to be provided. Finally, combining the manikin arm with game-based technologies, the third component, provides opportunities to build knowledge and to practice battlefield decision making. Not only do soldiers learn how to apply a tourniquet, but when to apply a tourniquet in combat. The purpose of the paper is to describe the learning science underlying the design of HapMed, illustrate the training system and ways it is being expanded to encompass other critical life-saving tasks, and report on feedback received from instructors and trainees at military training and simulation centers.

  16. Caffeine, fatigue, and cognition

    NARCIS (Netherlands)

    Lorist, M.M.; Tops, M.

    2003-01-01

    Effects of caffeine and fatigue are discussed with special attention to adenosine-dopamine interactions. Effects of caffeine on human cognition are diverse. Behavioural measurements indicate a general improvement in the efficiency of information processing after caffeine, while the EEG data support

  17. FATIGUE OF DENTAL CERAMICS

    Science.gov (United States)

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

    2013-01-01

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

  18. Incompatibility and Mental Fatigue

    Science.gov (United States)

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

    2011-01-01

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

  19. Caffeine, fatigue, and cognition

    NARCIS (Netherlands)

    Lorist, M.M.; Tops, M.

    2003-01-01

    Effects of caffeine and fatigue are discussed with special attention to adenosine-dopamine interactions. Effects of caffeine on human cognition are diverse. Behavioural measurements indicate a general improvement in the efficiency of information processing after caffeine, while the EEG data support

  20. Fatigue of dental ceramics.

    Science.gov (United States)

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

    2013-12-01

    Clinical data on survival rates reveal that all-ceramic dental prostheses are susceptible to fracture from repetitive occlusal loading. The objective of this review is to examine the underlying mechanisms of fatigue in current and future dental ceramics. The nature of various fatigue modes is elucidated using fracture test data on ceramic layer specimens from the dental and biomechanics literature. Failure modes can change over a lifetime, depending on restoration geometry, loading conditions and material properties. Modes that operate in single-cycle loading may be dominated by alternative modes in multi-cycle loading. While post-mortem examination of failed prostheses can determine the sources of certain fractures, the evolution of these fractures en route to failure remains poorly understood. Whereas it is commonly held that loss of load-bearing capacity of dental ceramics in repetitive loading is attributable to chemically assisted 'slow crack growth' in the presence of water, we demonstrate the existence of more deleterious fatigue mechanisms, mechanical rather than chemical in nature. Neglecting to account for mechanical fatigue can lead to gross overestimates in predicted survival rates. Strategies for prolonging the clinical lifetimes of ceramic restorations are proposed based on a crack-containment philosophy. Copyright © 2013 Elsevier Ltd. All rights reserved.